XANES study of hydrogen incorporation in a Pd-capped Nb thin film

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ruckman, M.W.; Reisfeld, G.; Jisrawi, N.M.

X-ray absorption near-edge structure (XANES) measurements were used to probe the H-charging-induced electronic structure changes of a 2400 {Angstrom} Nb film capped with Pd. These results are discussed in terms of {ital ab initio} linear augmented plane-wave (LAPW) band-structure calculations for this material. The Pd-L{sub 3}-edge XANES clearly manifested the spectral (Pd-d state related) changes expected for Pd-hydride formation, a white line feature degradation, and the appearance of a Pd-H antibonding feature at 6 eV above the threshold. The Nb-L{sub 2,3} edge changes with H charging show a distinct enhancement of the white line strength; a feature 6 eV abovemore » the edges, associated with Nb-H antibonding states in analogy with the Pd results; the suppression of a threshold-onset feature of Nb metal; and a shift of the centrum of the white line feature towards the threshold. Comparison of the Nb sphere projection of the d{sub 3/2} component of the LAPW density of states (DOS) to the Nb-L{sub 2}-edge spectra yields good basic agreement with the observed spectral changes. In particular, the substantial theoretical reduction in the DOS at, and just above, the Fermi energy (E{sub f}) is directly related to the near threshold Nb-L{sub 2,3} spectral changes. The more modest white line enhancement in the theoretical DOS is noted and discussed. Nb-K-edge XANES are also discussed in terms of the Nb-site p-state projected LAPW DOS. This last comparison indicates a p-state reduction near E{sub f} upon H charging of the Nb. {copyright} {ital 1998} {ital The American Physical Society}« less

PROCEEDINGS ON SYNCHROTRON RADIATION: Transfer characterization of sulfur from coal-burning emission to plant leaves by PIXE and XANES

NASA Astrophysics Data System (ADS)

Bao, Liang-Man; Zhang, Gui-Lin; Zhang, Yuan-Xim; Li, Yan; Lin, Jun; Liu, Wei; Cao, Qing-Chen; Zhao, Yi-Dong; Ma, Chen-Yan; Han, Yong

2009-11-01

The impact of coal-burning emission on sulfur in camphor leaves was investigated using Proton Induced X-ray Emission (PIXE) and synchrotron radiation technique X-ray Absorption Near-Edge Structure (XANES) spectroscopy. The PIXE results show that the sulfur concentrations in the leaves collected at the polluted site are significantly higher than those in controls. The Sulfur XANES spectra show the presence of organic (disulfides, thiols, thioethers, sulfonates and sulfoxides) and inorganic sulfur (sulfates) in the leaves. The inorganic sulfur in the leaves of camphor tree polluted by coal combustion is 15% more than that of the control site. The results suggest that the long-term coal-burning pollution resulted in an enhanced content of the total sulfur and sulfate in the leaves, and the uptake of sulfur by leaves had exceeded the metabolic requirement of plants and the excess of sulfur was stored as SO2-4. It can monitor the sulfur pollution in atmosphere.

Magnesium K-edge XANES spectroscopy of geological standards.

PubMed

Yoshimura, Toshihiro; Tamenori, Yusuke; Iwasaki, Nozomu; Hasegawa, Hiroshi; Suzuki, Atsushi; Kawahata, Hodaka

2013-09-01

Magnesium K-edge X-ray absorption near-edge structure (XANES) spectra have been investigated to develop a systematic understanding of a suite of Mg-bearing geological materials such as silicate and carbonate minerals, sediments, rocks and chemical reagents. For the model compounds the Mg XANES was found to vary widely between compounds and to provide a fingerprint for the form of Mg involved in geologic materials. The energy positions and resonance features obtained from these spectra can be used to specify the dominant molecular host site of Mg, thus shedding light on Mg partitioning and isotope fractionation in geologic materials and providing a valuable complement to existing knowledge of Mg geochemistry.

Sulfur K-edge XANES analysis of natural and synthetic basaltic glasses: Implications for S speciation and S content as function of oxygen fugacity

NASA Astrophysics Data System (ADS)

Jugo, Pedro J.; Wilke, Max; Botcharnikov, Roman E.

2010-05-01

XANES analyses at the sulfur K-edge were used to determine the oxidation state of S in natural and synthetic basaltic glasses and to constrain the fO2 conditions for the transition from sulfide (S2-) to sulfate (S6+) in silicate melts. XANES spectra of basaltic samples from the Galapagos spreading center, the Juan de Fuca ridge and the Lau Basin showed a dominant broad peak at 2476.8 eV, similar to the spectra obtained from synthetic sulfide-saturated basalts and pyrrhotite. An additional sharp peak at 2469.8 eV, similar to that of crystalline sulfides, was present in synthetic glasses quenched from hydrous melts but absent in anhydrous glasses and may indicate differences in sulfide species with hydration or presence of minute sulfide inclusions exsolved during quenching. The XANES spectra of a basalt from the 1991 eruption of Mount Pinatubo, Philippines, and absarokitic basalts from the Cascades Range, Oregon, U.S.A., showed a sharp peak at 2482.8 eV, characteristic of synthetic sulfate-saturated basaltic glasses and crystalline sulfate-bearing minerals such as haüyne. Basaltic samples from the Lamont Seamount, the early submarine phase of Kilauea volcano and the Loihi Seamount showed unequivocal evidence of the coexistence of S2- and S6+ species, emphasizing the relevance of S6+ to these systems. XANES spectra of basaltic glasses synthesized in internally-heated pressure vessels and equilibrated at fO2 ranging from FMQ-1.7 to FMQ+2.7 showed systematic changes in the features related to S2- and S6+ with changes in fO2. No significant features related to sulfite (S4+) species were observed. These results were used to construct a function that allows estimates of S6+/ΣS from XANES data. Theoretical considerations and comparison of compiled S6+/ΣS data obtained by SKα shifts estimated with electron probe microanalysis (EPMA) and S6+/ΣS obtained from XANES spectra show that data obtained from EPMA measurements underestimate S6+/ΣS in samples that are sulfate

Sulfur K-edge XANES analysis of natural and synthetic basaltic glasses: Implications for S speciation and S content as function of oxygen fugacity

NASA Astrophysics Data System (ADS)

Jugo, Pedro J.; Wilke, Max; Botcharnikov, Roman E.

2010-10-01

XANES analyses at the sulfur K-edge were used to determine the oxidation state of S species in natural and synthetic basaltic glasses and to constrain the fO 2 conditions for the transition from sulfide (S 2-) to sulfate (S 6+) in silicate melts. XANES spectra of basaltic samples from the Galapagos spreading center, the Juan de Fuca ridge and the Lau Basin showed a dominant broad peak at 2476.8 eV, similar to the spectra obtained from synthetic sulfide-saturated basalts and pyrrhotite. An additional sharp peak at 2469.8 eV, similar to that of crystalline sulfides, was present in synthetic glasses quenched from hydrous melts but absent in anhydrous glasses and may indicate differences in sulfide species with hydration or presence of minute sulfide inclusions exsolved during quenching. The XANES spectra of a basalt from the 1991 eruption of Mount Pinatubo, Philippines, and absarokitic basalts from the Cascades Range, Oregon, USA, showed a sharp peak at 2482.8 eV, characteristic of synthetic sulfate-saturated basaltic glasses and crystalline sulfate-bearing minerals such as hauyne. Basaltic samples from the Lamont Seamount, the early submarine phase of Kilauea volcano and the Loihi Seamount showed unequivocal evidence of the coexistence of S 2- and S 6+ species, emphasizing the relevance of S 6+ to these systems. XANES spectra of basaltic glasses synthesized in internally-heated pressure vessels and equilibrated at fO 2 ranging from FMQ - 1.4 to FMQ + 2.7 showed systematic changes in the features related to S 2- and S 6+ with changes in fO 2. No significant features related to sulfite (S 4+) species were observed. These results were used to construct a function that allows estimates of S 6+/ΣS from XANES data. Comparison of S 6+/ΣS data obtained by S Kα shifts measured with electron probe microanalysis (EPMA), S 6+/ΣS obtained from XANES spectra, and theoretical considerations show that data obtained from EPMA measurements underestimate S 6+/ΣS in samples that

XANES mapping of organic sulfate in three scleractinian coral skeletons

NASA Astrophysics Data System (ADS)

Cuif, Jean-Pierre; Dauphin, Yannicke; Doucet, Jean; Salome, Murielle; Susini, Jean

2003-01-01

The presence and localization of organic sulfate within coral skeletons are studied by using X-ray absorption near edge structure spectroscopy (XANES) fluorescence. XANES spectra are recorded from four reference sulfur-bearing organic molecules: three amino acids (H-S-C bonds in cysteine; C-S-C bonds in methionine; one disulfide bond C-S-S-C bonds in cystine) and a sulfated sugar (C-SO 4 bonds in chondroitin sulfate). Spectral responses of three coral skeletons show that the sulfated form is extremely dominant in coral aragonite, and practically exclusive within both centres of calcification and the surrounding fibrous tissues of coral septa. Mapping of S-sulfate concentrations in centres and fibres gives us direct evidence of high concentration of organic sulfate in centres of calcification. Additionally, a banding pattern of S-sulfate is visible in fibrous part of the coral septa, evidencing a biochemical zonation that corresponds to the step-by-step growth of fibres.

Polarized XANES Monitors Femtosecond Structural Evolution of Photoexcited Vitamin B 12

DOE PAGES

Miller, Nicholas A.; Deb, Aniruddha; Alonso-Mori, Roberto; ...

2017-01-30

Ultrafast, polarization-selective time-resolved X-ray absorption near-edge structure (XANES) was used to characterize the photochemistry of vitamin B 12, cyanocobalamin (CNCbl), in solution. Cobalamins are important biological cofactors involved in methyl transfer, radical rearrangement, and light-activated gene regulation, while also holding promise as light-activated agents for spatiotemporal controlled delivery of therapeutics. We introduce polarized femtosecond XANES, combined with UV–visible spectroscopy, to reveal sequential structural evolution of CNCbl in the excited electronic state. Femtosecond polarized XANES provides the crucial structural dynamics link between computed potential energy surfaces and optical transient absorption spectroscopy. Polarization selectivity can be used to uniquely identify electronic contributionsmore » and structural changes, even in isotropic samples when well-defined electronic transitions are excited. Our XANES measurements reveal that the structural changes upon photoexcitation occur mainly in the axial direction, where elongation of the axial Co–CN bond and Co–N Im bond on a 110 fs time scale is followed by corrin ring relaxation on a 260 fs time scale. In conclusion, these observations expose features of the potential energy surfaces controlling cobalamin reactivity and deactivation.« less

Polarized XANES Monitors Femtosecond Structural Evolution of Photoexcited Vitamin B 12

DOE Office of Scientific and Technical Information (OSTI.GOV)

Miller, Nicholas A.; Deb, Aniruddha; Alonso-Mori, Roberto

Ultrafast, polarization-selective time-resolved X-ray absorption near-edge structure (XANES) was used to characterize the photochemistry of vitamin B 12, cyanocobalamin (CNCbl), in solution. Cobalamins are important biological cofactors involved in methyl transfer, radical rearrangement, and light-activated gene regulation, while also holding promise as light-activated agents for spatiotemporal controlled delivery of therapeutics. We introduce polarized femtosecond XANES, combined with UV–visible spectroscopy, to reveal sequential structural evolution of CNCbl in the excited electronic state. Femtosecond polarized XANES provides the crucial structural dynamics link between computed potential energy surfaces and optical transient absorption spectroscopy. Polarization selectivity can be used to uniquely identify electronic contributionsmore » and structural changes, even in isotropic samples when well-defined electronic transitions are excited. Our XANES measurements reveal that the structural changes upon photoexcitation occur mainly in the axial direction, where elongation of the axial Co–CN bond and Co–N Im bond on a 110 fs time scale is followed by corrin ring relaxation on a 260 fs time scale. In conclusion, these observations expose features of the potential energy surfaces controlling cobalamin reactivity and deactivation.« less

Structural investigations of Pu{sup III} phosphate by X-ray diffraction, MAS-NMR and XANES spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Popa, Karin; Raison, Philippe E., E-mail: philippe.raison@ec.europa.eu; Martel, Laura

2015-10-15

PuPO{sub 4} was prepared by a solid state reaction method and its crystal structure at room temperature was solved by powder X-ray diffraction combined with Rietveld refinement. High resolution XANES measurements confirm the +III valence state of plutonium, in agreement with valence bond derivation. The presence of the americium (as β{sup −} decay product of plutonium) in the +III oxidation state was determined based on XANES spectroscopy. High resolution solid state {sup 31}P NMR agrees with the XANES results and the presence of a solid-solution. - Graphical abstract: A full structural analysis of PuPO{sub 4} based on Rietveld analysis ofmore » room temperature X-ray diffraction data, XANES and MAS NMR measurements was performed. - Highlights: • The crystal structure of PuPO{sub 4} monazite is solved. • In PuPO{sub 4} plutonium is strictly trivalent. • The presence of a minute amount of Am{sup III} is highlighted. • We propose PuPO{sub 4} as a potential reference material for spectroscopic and microscopic studies.« less

Combined In-Situ XRD and In-Situ XANES Studies on the Reduction Behavior of a Rhenium Promoted Cobalt Catalyst

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kumar, Nitin; Payzant, E Andrew; Jothimurugesan, K

2011-01-01

A 10% Co 4% Re/(2% Zr/SiO2) catalyst was prepared by co-impregnation using a silica support modified by 2% Zr. The catalyst was characterized by temperature programmed reduction (TPR), in situ XRD and in situ XANES analysis where it was simultaneously exposed to H2 using a temperature programmed ramp. The results showed the two step reduction of large crystalline Co3O4 with CoO as an intermediate. TPR results showed that the reduction of highly dispersed Co3O4 was facilitated by reduced rhenium by a H2-spillover mechanism. In situ XRD results showed the presence of both, Co-hcp and Co-fcc phases in the reduced catalystmore » at 400 C. However, the Co-hcp phase was more abundant, which is thought to be the more active phase as compared to the Co-fcc phase for CO hydrogenation. CO hydrogenation at 270 C and 5 bar pressure produces no detectable change in the phases during the time of experiment. In situ XANES results showed a decrease in the metallic cobalt in the presence of H2/CO, which can be attributed due to oxidation of the catalyst by reaction under these conditions.« less

New insights into the role of Mn and Fe in coloring origin of blue decorations of blue-and-white porcelains by XANES spectroscopy

NASA Astrophysics Data System (ADS)

Zhu, Jian; Luo, Wugan; Chen, Dongliang; Xu, Wei; Ming, Chaofang; Wang, Changsui; Wang, Lihua

2013-04-01

Blue and white porcelain is one of the most valuable ancient ceramics varieties in ancient China. It is well known for its beautiful blue decorations. However, the origin of its blue color has not been very clear till now. In this research, two blue and white porcelains from Jingdezhen, Jiangxi province were selected and Mn and Fe K-edge XANES spectra were recorded from blue decorations with or without transparent glaze. Results showed that Mn K-edge XANES features were almost identical between different samples while that of iron changed. The above findings indicated the positive role of iron in the variation of blue decorations. As for manganese, although more system researches were need, its negative role on the variations of the tone of blue decorations was obtained. On the other hand, the paper also revealed the XAFS results will be affect by the glaze layer above the pigment. These findings provided us more information to understand the coloring origin of blue decorations of blue-and-white porcelain by means of XANES spectroscopy.

XANES study of Fe-implanted strontium titanate

NASA Astrophysics Data System (ADS)

Lobacheva, O.; Goncharova, L. V.; Chavarha, M.; Sham, T. K.

2014-03-01

Properties of strontium titanate SrTiO3 (STO) depend to a great extent on the substitutional dopants and defects of crystal structure. The ion beam implantation method was used for doping STO (001) crystals with Fe at different doses. Implanted samples were then annealed at 350°C in oxygen to induce recrystallization and remove oxygen vacancies produced during ion implantation process. The effect of Fe doping and post-implantation annealing was studied by X-ray Absorption Near Edge Spectroscopy (XANES) method and Superconducting Quantum Interference Device (SQUID). XANES allowed to monitor the change in structure of STO crystals and in the local environment of Fe following the implantation and annealing steps. SQUID measurements revealed correlation between magnetic moment and Fe implantation dose. Ferromagnetic hysteresis was observed on selected Fe-implanted STO at 5 K. The observed magnetic properties can be correlated with the several Fe oxide phases in addition to the presence of O/Ti vacancies.

Local Environment Sensitivity of the Cu K-Edge XANES Features in Cu-SSZ-13: Analysis from First-Principles.

PubMed

Zhang, Renqin; McEwen, Jean-Sabin

2018-05-22

Cu K-edge X-ray absorption near-edge spectra (XANES) have been widely used to study the properties of Cu-SSZ-13. In this Letter, the sensitivity of the XANES features to the local environment for a Cu + cation with a linear configuration and a Cu 2+ cation with a square-linear configuration in Cu-SSZ-13 is reported. When a Cu + cation is bonded to H 2 O or NH 3 in a linear configuration, the XANES has a strong peak at around 8983 eV. The intensity of this peak decreases as the linear configuration is broken. As for the Cu 2+ cations in a square-planar configuration with a coordination number of 4, two peaks at around 8986 and 8993 eV are found. An intensity decrease for both peaks at around 8986 and 8993 eV is found in an NH 3 _4_Z 2 Cu model as the N-Cu-N angle changes from 180 to 100°. We correlate these features to the variation of the 4p state by PDOS analysis. In addition, the feature peaks for both the Cu + cation and Cu 2+ cation do not show a dependence on the Cu-N bond length. We further show that the feature peaks also change when the coordination number of the Cu cation is varied, while these feature peaks are independent of the zeolite topology. These findings help elucidate the experimental XANES features at an atomic and an electronic level.

Oxidation of shallow conduit magma: Insight from μ-XANES analysis on volcanic ash particle

NASA Astrophysics Data System (ADS)

Miwa, T.; Ishibashi, H.; Iguchi, M.

2014-12-01

Redox state of magma is important to understand dynamics of volcanic eruptions because magma properties such as composition of degassed volatiles, stability field of minerals, and rheology of magma depend on redox state. To evaluate redox state of magma, Fe3+/ΣFe ratio [= Fe3+/( Fe3++ Fe2+)] of volcanic glass has been measured non-destructively by Fe-K edge μ-XANES (micro X-ray Absorption Near Edge Structure) spectroscopy (e.g., Cottrell and Kelly, 2011). We performed textural, compositional, and Fe-K edge μ-XANES analyses on volcanic ash to infer oxidation process of magma at shallow conduit during eruption at Bromo Volcano, Indonesia. The volcanic ash particles were collected in 24th March 2011 by real-time sampling from ongoing activity. The activity was characterized by strombolian eruption showing magma head ascended to near the ground surface. The ash sample contains two type of volcanic glasses named as Brown and Black glasses (BrG and BlG), based on their color. Textual analysis shows microlite crystallinities are same in the two type of glasses, ranging from 0 to 3 vol.%. EPMA analyses show that all of the glasses have almost identical andesitic composition with SiO2 = 60 wt.%. In contrast, Fe-K edge μ-XANES spectra with the analytical method by Ishibashi et al. (in prep) demonstrate that BrG (Fe3+/ΣFe = 0.20-0.26) is more oxidized than BlG (Fe3+/ΣFe = 0.32-0.60). From combination of the glass composition, the measured Fe3+/ΣFe ratio and 1060 degree C of temperature (Kress and Carmichael, 1991), the oxygen fugacities are estimated to be NNO and NNO+4 for BrG and BlG, respectively. The volcanic glasses preserve syn-eruptive physicochemical conditions by rapid quenching due to their small size ranging from 125 to 250 μm. Our results demonstrate that BrG and BlG magmas are textually and chemically identical but their redox conditions are different at the eruption. The oxidation of magma can be caused by following two processes; 1) diffusive transport

First-Principles Fe L 2,3 -Edge and O K-Edge XANES and XMCD Spectra for Iron Oxides

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sassi, Michel; Pearce, Carolyn I.; Bagus, Paul S.

X-ray absorption near-edge structure (XANES) and X-ray magnetic circular dichroism (XMCD) spectroscopies are tools in widespread use for providing detailed local atomic structure, oxidation state, and magnetic structure information for materials and organometallic complexes. The analysis of these spectra for transition-metal L-edges is routinely performed on the basis of ligand-field multiplet theory because one- and two-particle mean-field ab initio methods typically cannot describe the multiplet structure. Here we show that multireference configuration interaction (MRCI) calculations can satisfactorily reproduce measured XANES spectra for a range of complex iron oxide materials including hematite and magnetite. MRCI Fe L2,3-edge XANES and XMCD spectramore » of Fe(II)O6, Fe(III)O6, and Fe(III)O4 in magnetite are found to be in very good qualitative agreement with experiment and multiplet calculations. Point-charge embedding and small distortions of the first-shell oxygen ligands have only small effects. Oxygen K-edge XANES/XMCD spectra for magnetite investigated by a real-space Green’s function approach complete the very good qualitative agreement with experiment. Material-specific differences in local coordination and site symmetry are well reproduced, making the approach useful for assigning spectral features to specific oxidation states and coordination environments.« less

Ag XANES data of biosolids

EPA Pesticide Factsheets

The dataset contains energy and absorption data for XANES spectra indicated in Figure 1 of the manuscript.This dataset is associated with the following publication:Donner, E., K. Scheckel , R. Sekine, R. Popelka-Filcoff, J. Bennett, G. Brunetti, R. Naidu, S. McGrath, and E. Lombi. Non-labile silver species in biosolids remain stable throughout 50 years of weathering and ageing.. D.O. Carpenter, and E.Y. Zeng ENVIRONMENTAL POLLUTION. Elsevier Science Ltd, New York, NY, USA, 205: 78-86, (2015).

XANES analyses of silicon crystalline irradiated by nitrogen/oxygen ions.

PubMed

Yoshida, T; Hara, T; Li, T; Yoshida, H; Tanabe, T

2001-03-01

X-ray absorption techniques have been applied to the characterization of 5 keV nitrogen / oxygen ions implanted silicon samples. The depth selective measurement of XANES by recording in PEY mode and the quantitative analysis by superposition of XANES spectra were carried out to elucidate the depth profile of implanted ions. It has been revealed that the silicon nitride phase were formed in silicon after prolonged N+ irradiation and it extended over the deep part of the damaged region from the surface. On the other hand, for the O+ irradiation, silicon dioxide phase were produced only in the shallow part of the damaged region, i.e., the silicon dioxide phase likely broke off during the irradiation.

Speciation Mapping of Environmental Samples Using XANES Imaging

EPA Science Inventory

Fast X-ray detectors with large solid angles and high dynamic ranges open the door to XANES imaging, in which millions of spectra are collected to image the speciation of metals at micrometre resolution, over areas up to several square centimetres. This paper explores how such mu...

XANES and EXAFS study of Au-substituted YBa2Cu3O(7-delta)

NASA Technical Reports Server (NTRS)

Ruckman, Mark W.; Hepp, Aloysius F.

1990-01-01

The near-edge structure (XANES) of the Au L3 and Cu K edges of YBa2Au(0.3)Cu(2.7)O(7-delta) was studied. X ray diffraction suggests that Au goes on the Cu(1) site and XANES shows that this has little effect on the oxidation state of the remaining copper. The gold L3 edge develops a white line feature whose position lies between that of trivalent gold oxide (Au2O3) and monovalent potassium gold cyanide (KAu(CN)2) and whose intensity relative to the edge step is smaller than in the two reference compounds. The L3 EXAFS for Au in the superconductor resembles that of Au2O3. However, differences in the envelope of the Fourier filtered component for the first shell suggest that the local structure of the Au in the superconductor is not equivalent to Au2O3.

In situ TPR XANES study of the partial oxidation of methane using a Ni-substituted hexaaluminate catalyst

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kugler, E.L.; Gardner, T.H.; Campos, Andrew

2008-04-01

Metallic Ni formation near the mirror cation site, Ba in this study, is believed to cause the partial oxidation activity observed in Ni-substituted hexaaluminate catalysts. The BaNi1.0Al11.6O19-d catalyst was prepared by coprecipitation with nitrate salt precursors; following the coprecipitation procedure, the catalyst was calcined at 1400°C to create the hexaaluminate structure. TPR XANES in fluorescence was used to probe the local structure of the BaNi1.0Al11.6O19-d catalyst to determine whether metallic nickel forms at different temperatures: 825°C, 875°C, 925°C. The XANES results indicate that the Ni in the hexaaluminate catalyst only reduces if the temperature is maintained at 925°C. Once themore » metallic state is formed, the oxidation state is stable; even in the POX environment. Future work using a theoretical approach to the XANES data using FEFF 8.4 gives information on the interactions between Ni and Ba, which will be used to further optimize the catalyst.« less

Diamond xenolith and matrix organic matter in the Sutter's Mill meteorite measured by C-XANES

NASA Astrophysics Data System (ADS)

Kebukawa, Yoko; Zolensky, Michael E.; Kilcoyne, A. L. David; Rahman, Zia; Jenniskens, Peter; Cody, George D.

2014-11-01

The Sutter's Mill (SM) meteorite fell in El Dorado County, California, on April 22, 2012. This meteorite is a regolith breccia composed of CM chondrite material and at least one xenolithic phase: oldhamite. The meteorite studied here, SM2 (subsample 5), was one of three meteorites collected before it rained extensively on the debris site, thus preserving the original asteroid regolith mineralogy. Two relatively large (10 μm sized) possible diamond grains were observed in SM2-5 surrounded by fine-grained matrix. In the present work, we analyzed a focused ion beam (FIB) milled thin section that transected a region containing these two potential diamond grains as well as the surrounding fine-grained matrix employing carbon and nitrogen X-ray absorption near-edge structure (C-XANES and N-XANES) spectroscopy using a scanning transmission X-ray microscope (STXM) (Beamline 5.3.2 at the Advanced Light Source, Lawrence Berkeley National Laboratory). The STXM analysis revealed that the matrix of SM2-5 contains C-rich grains, possibly organic nanoglobules. A single carbonate grain was also detected. The C-XANES spectrum of the matrix is similar to that of insoluble organic matter (IOM) found in other CM chondrites. However, no significant nitrogen-bearing functional groups were observed with N-XANES. One of the possible diamond grains contains a Ca-bearing inclusion that is not carbonate. C-XANES features of the diamond-edges suggest that the diamond might have formed by the CVD process, or in a high-temperature and -pressure environment in the interior of a much larger parent body.

Reduced chromium in olivine grains from lunar basalt 15555 - X-ray Absorption Near Edge Structure (XANES)

NASA Technical Reports Server (NTRS)

Sutton, S. R.; Jones, K. W.; Gordon, B.; Rivers, M. L.; Bajt, S.; Smith, J. V.

1993-01-01

The oxidation state of Cr in 200-micron regions within individual lunar olivine and pyroxene grains from lunar basalt 15555 was inferred using X-ray Absorption Near Edge Structure (XANES). Reference materials had previously been studied by optical absorption spectroscopy and included Cr-bearing borosilicate glasses synthesized under controlled oxygen fugacity and Cr-doped olivines. The energy dependence of XANES spectral features defined by these reference materials indicated that Cr is predominantly divalent in the lunar olivine and trivalent in the pyroxene. These results, coupled with the apparent f(02)-independence of partitioning coefficients for Cr into olivine, imply that the source magma was dominated by divalent Cr at the time of olivine crystallization.

Surface complexation and precipitate geometry for aqueous Zn(II) sorption on ferrihydrite: II. XANES analysis and simulation

USGS Publications Warehouse

Waychunas, G.A.; Fuller, C.C.; Davis, J.A.; Rehr, J.J.

2003-01-01

X-ray absorption near-edge spectroscopy (XANES) analysis of sorption complexes has the advantages of high sensitivity (10- to 20-fold greater than extended X-ray absorption fine structure [EXAFS] analysis) and relative ease and speed of data collection (because of the short k-space range). It is thus a potentially powerful tool for characterization of environmentally significant surface complexes and precipitates at very low surface coverages. However, quantitative analysis has been limited largely to "fingerprint" comparison with model spectra because of the difficulty of obtaining accurate multiple-scattering amplitudes for small clusters with high confidence. In the present work, calculations of the XANES for 50- to 200-atom clusters of structure from Zn model compounds using the full multiple-scattering code Feff 8.0 accurately replicate experimental spectra and display features characteristic of specific first-neighbor anion coordination geometry and second-neighbor cation geometry and number. Analogous calculations of the XANES for small molecular clusters indicative of precipitation and sorption geometries for aqueous Zn on ferrihydrite, and suggested by EXAFS analysis, are in good agreement with observed spectral trends with sample composition, with Zn-oxygen coordination and with changes in second-neighbor cation coordination as a function of sorption coverage. Empirical analysis of experimental XANES features further verifies the validity of the calculations. The findings agree well with a complete EXAFS analysis previously reported for the same sample set, namely, that octahedrally coordinated aqueous Zn2+ species sorb as a tetrahedral complex on ferrihydrite with varying local geometry depending on sorption density. At significantly higher densities but below those at which Zn hydroxide is expected to precipitate, a mainly octahedral coordinated Zn2+ precipitate is observed. An analysis of the multiple scattering paths contributing to the XANES

Chemical species of sulfur in prostate cancer cells studied by XANES spectroscopy

NASA Astrophysics Data System (ADS)

Czapla, Joanna; Kwiatek, Wojciech M.; Lekki, Janusz; Dulińska-Litewka, Joanna; Steininger, Ralph; Göttlicher, Jörg

2013-12-01

The role of sulfur in prostate cancer progression may be significant for understanding the process of carcinogenesis. This work, based on X-ray Absorption Near Edge Structure (XANES) spectroscopy, is focused on determination of sulfur chemical species occurring in prostate cancer cell lines. The experimental material consisted of four commercially available cell lines: three from metastasized prostate cancer (PC3, LNCaP, and DU145) and one, used as a control, from the non-tumourigenic peripheral zone of the prostate (PZ-HPV-7). The experiment was performed at the SUL-X beamline of the synchrotron radiation source ANKA, Karlsruhe (Germany). The K-edge XANES spectra of sulfur were analyzed by deconvolution in order to establish sulfur species that occur in prostate cancer cells and to find out whether there are any differences in their content between various cell lines. Experimental spectra were fitted in two ways: with two Gaussian peaks and one arctangent step function, and additionally by a Linear Combination Fit with spectra of reference compounds in order to obtain quantitative chemical information. All fitting procedures were performed with the Athena code (Ravel and Newville, 2005) and the results of deconvolution were used to determine the fraction of each sulfur form. The results of data analysis showed that cell lines from different metastasis had different ratio of reduced to oxidized sulfur species. The LCF analysis demonstrated that the highest content of GSH, one of the most important sulfur-bearing compounds in cells, was observed in DU145 cells. These findings may confirm the hypothesis of changes in redox balance in case of cancer initiation and progression.

Polarized XANES and EXAFS spectroscopic investigation into copper(II) complexes on vermiculite

NASA Astrophysics Data System (ADS)

Furnare, Luca J.; Vailionis, Arturas; Strawn, Daniel G.

2005-11-01

Interaction of heavy metals with clay minerals can dominate solid-solution reactions in soil, controlling the fate of the metals in the environment. In this study we used powdered and polarized extended X-ray absorption fine structure (EXAFS) spectroscopy and X-ray absorption near edge spectroscopy (XANES) to investigate Cu sorbed on Llano vermiculite and compare the results to reported Cu sorption mechanism on Wyoming (WY) smectite and reduced South African (SA) vermiculite. Analysis of the Cu K-edge spectra revealed that Cu sorbed on Llano vermiculite at high ionic strength ( I) has the greatest degree of covalent bond character, followed by Cu sorbed on montmorillonite at high I, and Cu sorbed on reduced SA vermiculite at high I. Cu sorbed on clay minerals at low I has the least covalent character. EXAFS data from Cu sorbed Ca- and K-equilibrated Llano vermiculites showed the presence of a second-shell Al, Si, or Mg backscatterer at 3.02 Å. This distance is consistent with Cu sorbing via a corner-sharing monodentate or bidentate bond. Polarized XANES and EXAFS results revealed that the angle between the Cu atom and the mineral sorption sites is 68° with respect to the [001] direction. From the bond angle and the persistence of the second-shell backscatterer when the interlayer is collapsed (K-equilibration), we conclude that Cu adsorption on the Llano vermiculite is not occurring in the interlayer but rather Cu is adsorbing onto the edges of the vermiculite. Results from this research provide evidence that Cu forms inner-sphere and outer-sphere complexes on clay minerals, and does not form the vast multinuclear surface precipitates that have been observed for Co, Zn, and Ni.

Synchrotron WAXS and XANES studies of silica (SiO2) powders synthesized from Indonesian natural sands

NASA Astrophysics Data System (ADS)

Muchlis, Khairanissa; Aini Fauziyah, Nur; Soontaranon, Siriwat; Limpirat, Wanwisa; Pratapa, Suminar

2017-01-01

In this study, we have investigated polymorphic silica (SiO2) powders using, Wide Angle X-ray Scattering (WAXS) and X-Ray Absorption Near Edge Spectroscopy (XANES), laboratory X-Ray Diffraction (XRD) instruments. The WAXS and XANES spectra were collected using synchrotron radiation at Synchrotron Light Research Institute (SLRI), Nakhon Ratchasima, Thailand. The silica powders were obtained by processing silica sand from Tanah Laut, South Kalimantan, Indonesia. Purification process of silica sand was done by magnetic separation and immersion with HCl. The purification step was needed to reduce impurity or undesirable non Si elements. Three polymorphs of silica were produced, i.e. amorphous phase (A), quartz (B), and cristobalite (C). WAXS profile for each phase was presented in terms of intensity vs. 2θ prior to analyses. Both XRD (λCuKα=1.54056 Å) and WAXS (λ=1.09 Å) patttern show that (1) A sample contains no crystallites, (2) B sample is monophasic, contains only quartz, and (3) C sample contains cristobalite and trydimite. XRD quantitative analysis using Rietica gave 98,8 wt% cristobalite, while the associated WAXS data provided 98.7 wt% cristobalite. Si K-edge XANES spectra were measured at energy range 1840 to 1920 eV. Qualitatively, the pre-edge and edge features for all phases are similar, but their main peaks in the post-edge region are different.

Local structure in LaMnO3 and CaMnO3 perovskites: A quantitative structural refinement of Mn K -edge XANES data

NASA Astrophysics Data System (ADS)

Monesi, C.; Meneghini, C.; Bardelli, F.; Benfatto, M.; Mobilio, S.; Manju, U.; Sarma, D. D.

2005-11-01

Hole-doped perovskites such as La1-xCaxMnO3 present special magnetic and magnetotransport properties, and it is commonly accepted that the local atomic structure around Mn ions plays a crucial role in determining these peculiar features. Therefore experimental techniques directly probing the local atomic structure, like x-ray absorption spectroscopy (XAS), have been widely exploited to deeply understand the physics of these compounds. Quantitative XAS analysis usually concerns the extended region [extended x-ray absorption fine structure (EXAFS)] of the absorption spectra. The near-edge region [x-ray absorption near-edge spectroscopy (XANES)] of XAS spectra can provide detailed complementary information on the electronic structure and local atomic topology around the absorber. However, the complexity of the XANES analysis usually prevents a quantitative understanding of the data. This work exploits the recently developed MXAN code to achieve a quantitative structural refinement of the Mn K -edge XANES of LaMnO3 and CaMnO3 compounds; they are the end compounds of the doped manganite series LaxCa1-xMnO3 . The results derived from the EXAFS and XANES analyses are in good agreement, demonstrating that a quantitative picture of the local structure can be obtained from XANES in these crystalline compounds. Moreover, the quantitative XANES analysis provides topological information not directly achievable from EXAFS data analysis. This work demonstrates that combining the analysis of extended and near-edge regions of Mn K -edge XAS spectra could provide a complete and accurate description of Mn local atomic environment in these compounds.

Ab-initio Calculation of the XANES of Lithium Phosphates and LiFePO4

NASA Astrophysics Data System (ADS)

Yiu, Y. M.; Yang, Songlan; Wang, Dongniu; Sun, Xueliang; Sham, T. K.

2013-04-01

Lithium iron phosphate has been regarded as a promising cathode material for the next generation lithium ion batteries due to its high specific capacity, superior thermal and cyclic stability [1]. In this study, the XANES (X-ray Absorption Near Edge Structure) spectra of lithium iron phosphate and lithium phosphates of various compositions at the Li K, P L3,2, Fe M3,2 and O K-edges have been simulated self-consistently using ab-initio calculations based on multiple scattering theory (the FEFF9 code) and DFT (Density Functional Theory, the Wien2k code). The lithium phosphates under investigation include LiFePO4, γ-Li3PO4, Li4P2O7 and LiPO3. The calculated spectra are compared to the experimental XANES recorded in total electron yield (TEY) and fluorescence yield (FLY). This work was carried out to assess the XANES of possible phases presented in LiFePO4 based Li ion battery applications [2].

Antimony leaching and chemical species analyses in an industrial solid waste: Surface and bulk speciation using ToF-SIMS and XANES.

PubMed

Kappen, P; Ferrando-Miguel, G; Reichman, S M; Innes, L; Welter, E; Pigram, P J

2017-05-05

The surface chemistry and bulk chemical speciation of solid industrial wastes containing 8wt-% antimony (Sb) were investigated using synchrotron X-ray Absorption Near Edge Structure (XANES) and Time-of-Flight Ion Secondary Mass Spectrometry (ToF-SIMS). Leaching experiments were conducted in order to better understand the behavior of Sb in waste streams and to inform regulatory management of antimony-containing wastes. The experiments also demonstrate how a combination of XANES and ToF-SIMS adds value to the field of waste investigations. Leaching treatments (acid and base) were performed at a synchrotron over 24h time periods. Surface analyses of the wastes before leaching showed the presence of Sb associated with S and O. Bulk analyses revealed Sb to be present, primarily, as trivalent sulfide species. Both acid and base leaching did not change the antimony speciation on the solid. Leaching transferred about 1% of the total Sb into solution where Sb was found to be present as Sb(V). XANES data showed similarities between leachate and FeSbO 4 . During base leaching, the Sb content in solution gradually increased over time, and potential desorption mechanisms are discussed. Copyright © 2017 Elsevier B.V. All rights reserved.

Microanalysis of iron oxidation state in iron oxides using X Ray Absorption Near Edge Structure (XANES)

NASA Technical Reports Server (NTRS)

Sutton, S. R.; Delaney, J.; Bajt, S.; Rivers, M. L.; Smith, J. V.

1993-01-01

An exploratory application of x ray absorption near edge structure (XANES) analysis using the synchrotron x ray microprobe was undertaken to obtain Fe XANES spectra on individual sub-millimeter grains in conventional polished sections. The experiments concentrated on determinations of Fe valence in a suite of iron oxide minerals for which independent estimates of the iron speciation could be made by electron microprobe analysis and x ray diffraction.

Chromium in urban sediment particulates: an integrated micro-chemical and XANES study

NASA Astrophysics Data System (ADS)

Taylor, Kevin; Byrne, Patrick; Hudson-Edwards, Karen

2015-04-01

Chromium is generally common within the urban sediment cascade as a result of abundant industrial and transport-related sources. The risks that Cr-bearing particles pose to ecosystems and humans depend on the solid phase chemical speciation of Cr in the particles. In this study, we use bulk chemical digests, sequential chemical extraction analysis, electron microscopy, electron microprobe and microfocus XANES analysis to describe the solid-phase speciation of Cr in urban particulate matter from both aquatic sediment and road dust sediment (RDS) in Manchester, UK. Cr-bearing grains within RDS are predominantly iron oxide grains, commonly of goethite or haematite mineralogy, but Cr-bearing silicate glass grains are also present. Iron oxide glass grains most likely have sorbed Cr, and derive from the rusting of Cr-steel particles from vehicles. Electron microprobe analysis indicates concentrations of Cr up to 3200 μg/g in these grains, and XANES analysis indicates that Cr(III) is the dominant oxidation state, with some trace amounts of Cr(VI). Cr-bearing grains within aquatic sediments are dominated by alumino-silicate glass grains derived from industrial waste. These grains contain Cr-rich areas with up to 19% Cr2O3 and XANES analysis indicates that Cr is present as Cr(III). The dominance of Cr(III) in these urban particulate grains suggests limited bioavailability or toxicity. However, the presence within two markedly different grain types (iron oxides and silicate glasses) indicates that the long-term geochemical behaviour and environmental risk of RDS and the aquatic sediments studied are likely to be quite different. These findings highlight the importance of understanding sources of metal contaminants in urban environments and the geochemical processes that affect their transfer through the urban sediment cascade and the wider river basin.

Monitoring morphology and hydrogen coverage of nanometric Pt/γ-Al2 O3 particles by in situ HERFD-XANES and quantum simulations.

PubMed

Gorczyca, Agnes; Moizan, Virginie; Chizallet, Celine; Proux, Olivier; Del Net, William; Lahera, Eric; Hazemann, Jean-Louis; Raybaud, Pascal; Joly, Yves

2014-11-10

Platinum nanoclusters highly dispersed on γ-alumina are widely used as heterogeneous catalysts. To understand the chemical interplay between the Pt nanoparticles, the support, and the reductive atmosphere, we performed X-ray absorption near edge structure (XANES) in situ experiments recorded in high energy resolution fluorescence detection (HERFD) mode. Spectra are assigned by comparison with simulated XANES spectra on models obtained by molecular dynamics (DFT-MD). We propose platinum cluster morphologies and quantify the hydrogen coverages compatible with XANES spectra recorded at variable hydrogen pressures and temperatures. Using cutting-edge methodologies to assign XANES spectra, this work gives unequalled atomic insights into the characterization of supported nanoclusters. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Borosilicate glass structure: An investigation of high resolution B K-edge XANES

NASA Astrophysics Data System (ADS)

Dong, S.; Henderson, G. S.; Galoisy, L.; Calas, G.

2009-05-01

The Alkali-borosilicate glasses in the systems Na2O-B2O3-SiO2 and K2O- B2O3-SiO2 have been prepared by melting/quenching in air and studied using synchrotron radiation B K-edge XANES to estimate the evolution of boron coordination as a function of composition. The ratio of alkali/B2O3 (R) and SiO2/B2O3 (K) in the glasses are respectively between 0.5 to 2.0 and 0.5 to 7.0. The edge features of trigonal B ([3]B) and tetrahedral B ([4]B) in B K-edge XANES spectra have been interpreted carefully from B standards such as (B2O3 and BPO4), as well as, a wide range of borate minerals. We find that the proportion of tetrahedral B in glass is increasing as a function of both R and K, similar to previous studies. Contributions of the [3]B and [4]B features to the B K-edge XANES is complex with 6-7 individual transitions contributing to the overall spectral envelope. Many of these transitions are common to both B coordination states making extraction of quantitative [4]B numbers difficult. However, we can calculate the proportion of tetrahedral B accurately by appropriate curve- fitting.

Vanadium K Xanes Studies of EET79001 Impact-Melt Glasses Revisited

NASA Technical Reports Server (NTRS)

Sutton, S. R.; Rao, M. N.; Nyquist, L. E.; Ross, D. K.

2016-01-01

Some impact-melt glasses in shergottites are rich in Martian atmospheric noble gases and sulfur suggesting a possible association with regolith-derived secondary mineral assemblages in the shocked samples. Previously, we studied two glasses, # 506 (Lith C in Lith A) and # 507 (Lith C in Lith B) from EET79001 [1,2] and suggested that sulfur initially existed as sulfate in the glass precursor materials and, on shock-melting of the precursors, the sulfate was reduced to sulfides in the shock glasses. To examine the validity of this hypothesis, we used V K microXANES techniques to measure the valence states of vanadium in the Lith C glasses from Lith A and Lith B in EET79001 [3] to complement and com-pare with previous analogous measurements on,78 glass (Lith C in Lith A) [4,5]. We reported the preliminary results in [3]. Vanadium is ideal for addressing the redox issue because it has multiple valence states and is a well-studied element. Vanadium in basalts exists mostly as V(sup 3+), V(sup 4+) and V(sup 5+) in terrestrial samples, mainly as V(sup 3+) with minor V(sup 2+) and minor V(sup 4+) in lunar samples and as roughly equal mixtures of V(sup 3+) and V(sup 4+) in Martian meteorites. In this report, we discuss the application of the V K XANES results to decipher the nature of shock reduction occurring in the silicate glasses during the impact process.

Structure, Bonding, and Stability of Mercury Complexes with Thiolate and Thioether Ligands from High-Resolution XANES Spectroscopy and First-Principles Calculations.

PubMed

Manceau, Alain; Lemouchi, Cyprien; Rovezzi, Mauro; Lanson, Martine; Glatzel, Pieter; Nagy, Kathryn L; Gautier-Luneau, Isabelle; Joly, Yves; Enescu, Mironel

2015-12-21

We present results obtained from high energy-resolution L3-edge XANES spectroscopy and first-principles calculations for the structure, bonding, and stability of mercury(II) complexes with thiolate and thioether ligands in crystalline compounds, aqueous solution, and macromolecular natural organic matter (NOM). Core-to-valence XANES features that vary in intensity differentiate with unprecedented sensitivity the number and identity of Hg ligands and the geometry of the ligand environment. Post-Hartree-Fock XANES calculations, coupled with natural population analysis, performed on MP2-optimized Hg[(SR)2···(RSR)n] complexes show that the shape, position, and number of electronic transitions observed at high energy-resolution are directly correlated to the Hg and S (l,m)-projected empty densities of states and occupations of the hybridized Hg 6s and 5d valence orbitals. Linear two-coordination, the most common coordination geometry in mercury chemistry, yields a sharp 2p to 6s + 5d electronic transition. This transition varies in intensity for Hg bonded to thiol groups in macromolecular NOM. The intensity variation is explained by contributions from next-nearest, low-charge, thioether-type RSR ligands at 3.0-3.3 Å from Hg. Thus, Hg in NOM has two strong bonds to thiol S and k additional weak Hg···S contacts, or 2 + k coordination. The calculated stabilization energy is -5 kcal/mol per RSR ligand. Detection of distant ligands beyond the first coordination shell requires precise measurement of, and comparison to, spectra of reference compounds as well as accurate calculation of spectra for representative molecular models. The combined experimental and theoretical approaches described here for Hg can be applied to other closed-shell atoms, such as Ag(I) and Au(I). To facilitate further calculation of XANES spectra, experimental data, a new crystallographic structure of a key mercury thioether complex, Cartesian coordinates of the computed models, and examples of

Sulfur K-edge XANES and acid volatile sulfide analyses of changes in chemical speciation of S and Fe during sequential extraction of trace metals in anoxic sludge from biogas reactors.

PubMed

Shakeri Yekta, Sepehr; Gustavsson, Jenny; Svensson, Bo H; Skyllberg, Ulf

2012-01-30

The effect of sequential extraction of trace metals on sulfur (S) speciation in anoxic sludge samples from two lab-scale biogas reactors augmented with Fe was investigated. Analyses of sulfur K-edge X-ray absorption near edge structure (S XANES) spectroscopy and acid volatile sulfide (AVS) were conducted on the residues from each step of the sequential extraction. The S speciation in sludge samples after AVS analysis was also determined by S XANES. Sulfur was mainly present as FeS (≈ 60% of total S) and reduced organic S (≈ 30% of total S), such as organic sulfide and thiol groups, in the anoxic solid phase. Sulfur XANES and AVS analyses showed that during first step of the extraction procedure (the removal of exchangeable cations), a part of the FeS fraction corresponding to 20% of total S was transformed to zero-valent S, whereas Fe was not released into the solution during this transformation. After the last extraction step (organic/sulfide fraction) a secondary Fe phase was formed. The change in chemical speciation of S and Fe occurring during sequential extraction procedure suggests indirect effects on trace metals associated to the FeS fraction that may lead to incorrect results. Furthermore, by S XANES it was verified that the AVS analysis effectively removed the FeS fraction. The present results identified critical limitations for the application of sequential extraction for trace metal speciation analysis outside the framework for which the methods were developed. Copyright © 2011 Elsevier B.V. All rights reserved.

Ca L2,3-edge XANES and Sr K-edge EXAFS study of hydroxyapatite and fossil bone apatite.

PubMed

Zougrou, I M; Katsikini, M; Brzhezinskaya, M; Pinakidou, F; Papadopoulou, L; Tsoukala, E; Paloura, E C

2016-08-01

Upon burial, the organic and inorganic components of hard tissues such as bone, teeth, and tusks are subjected to various alterations as a result of interactions with the chemical milieu of soil, groundwater, and presence of microorganisms. In this study, simulation of the Ca L 2,3-edge X-ray absorption near edge structure (XANES) spectrum of hydroxyapatite, using the CTM4XAS code, reveals that the different symmetry of the two nonequivalent Ca(1) and Ca(2) sites in the unit cell gives rise to specific spectral features. Moreover, Ca L 2,3-edge XANES spectroscopy is applied in order to assess variations in fossil bone apatite crystallinity due to heavy bacterial alteration and catastrophic mineral dissolution, compared to well-preserved fossil apatite, fresh bone, and geologic apatite reference samples. Fossilization-induced chemical alterations are investigated by means of Ca L 2,3-edge XANES and scanning electron microscopy (SEM) and are related to histological evaluation using optical microscopy images. Finally, the variations in the bonding environment of Sr and its preference for substitution in the Ca(1) or Ca(2) sites upon increasing the Sr/Ca ratio is assessed by Sr K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy.

Ca L2,3-edge XANES and Sr K-edge EXAFS study of hydroxyapatite and fossil bone apatite

NASA Astrophysics Data System (ADS)

Zougrou, I. M.; Katsikini, M.; Brzhezinskaya, M.; Pinakidou, F.; Papadopoulou, L.; Tsoukala, E.; Paloura, E. C.

2016-08-01

Upon burial, the organic and inorganic components of hard tissues such as bone, teeth, and tusks are subjected to various alterations as a result of interactions with the chemical milieu of soil, groundwater, and presence of microorganisms. In this study, simulation of the Ca L 2,3-edge X-ray absorption near edge structure (XANES) spectrum of hydroxyapatite, using the CTM4XAS code, reveals that the different symmetry of the two nonequivalent Ca(1) and Ca(2) sites in the unit cell gives rise to specific spectral features. Moreover, Ca L 2,3-edge XANES spectroscopy is applied in order to assess variations in fossil bone apatite crystallinity due to heavy bacterial alteration and catastrophic mineral dissolution, compared to well-preserved fossil apatite, fresh bone, and geologic apatite reference samples. Fossilization-induced chemical alterations are investigated by means of Ca L 2,3-edge XANES and scanning electron microscopy (SEM) and are related to histological evaluation using optical microscopy images. Finally, the variations in the bonding environment of Sr and its preference for substitution in the Ca(1) or Ca(2) sites upon increasing the Sr/Ca ratio is assessed by Sr K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy.

Ce(III) and Ce(IV) (re)distribution and fractionation in a laterite profile from Madagascar: Insights from in situ XANES spectroscopy at the Ce LIII-edge

NASA Astrophysics Data System (ADS)

Janots, Emilie; Bernier, Felix; Brunet, Fabrice; Muñoz, Manuel; Trcera, Nicolas; Berger, Alfons; Lanson, Martine

2015-03-01

The distribution of trivalent and tetravalent cerium, Ce(III) and Ce(IV) respectively, in a lateritic profile from Madagascar, has been characterized by X-ray-absorption near-edge structure (XANES) spectroscopy at the Ce LIII-edge on the LUCIA beamline (SOLEIL synchrotron, France). XANES spectra were acquired on bulk-rock samples as well as on specific lateritic minerals or polymineral zones (in-situ measurements) of the tonalite bedrock and the three overlying weathered horizons (C-, B- and A-horizons). Geochemically, the bedrock, and the A- and C-horizons show similar rare earth element content (REE = 363-405 mg/kg). They also display the same positive Ce-anomaly (CeCN/Ce∗ = 1.12-1.45), which is therefore likely to be inherited from the bedrock. In the B-horizon, the higher REE content (REE = 2194 mg/kg) and the larger Ce-anomaly (CeCN/Ce∗ = 4.26) are consistent with an accumulation zone caused by the evaporation of groundwater during the dry season. There is a good agreement between the Ce(III)/Cetotal ratio (XCe(III)) deduced from the positive Ce-anomaly (bulk-rock geochemical data) and that derived from XANES spectroscopy on the same bulk-rock samples (BR-XCe(III)-XANES) in the bedrock, and the C- and B-horizons. In the A-horizon, XANES measurements on bulk rock and minerals revealed a higher BR-XCe(III)-XANES (up to 100%) compared to the XCe(III) deduced from geochemical data (XCe(III) = 79%). The preservation of a positive Ce-anomaly in the A-horizon suggests that the Ce mobilization and redistribution during weathering occurred with no significant Ce fractionation from other trivalent REE. Remarkably, the only investigated sample where cerianite is observed belongs to the B-horizon. Within this horizon, Ce oxidation state varies depending on the microstructural position (porosity, cracks, clay-rich groundmass). The highest Ce(IV) concentrations are measured in cerianite (and aluminophosphates) localized in pores at the vicinity of Mn-rich domains (XCe(III)-XANES

Identification of Martian Regolith Sulfur Components in Shergottites Using Sulfur K Xanes and Fe/S Ratios

NASA Technical Reports Server (NTRS)

Sutton, S. R.; Ross, D. K.; Rao, M. N.; Nyquist, L. E.

2014-01-01

Based on isotopic anomalies in Kr and Sm, Sr-isotopes, S-isotopes, XANES results on S-speciation, Fe/S ratios in sulfide immiscible melts [5], and major element correlations with S determined in impact glasses in EET79001 Lith A & Lith B and Tissint, we have provided very strong evidence for the occurrence of a Martian regolith component in some impact melt glasses in shergottites. Using REE measurements by LA-ICP-MS in shergottite impact glasses, Barrat and co-workers have recently reported conflicting conclusions about the occurrence of Martian regolith components: (a) Positive evidence was reported for a Tissint impact melt, but (b) Negative evidence for impact melt in EET79001 and another impact melt in Tissint. Here, we address some specific issues related to sulfur speciation and their relevance to identifying Martian regolith components in impact glasses in EET79001 and Tissint using sulfur K XANES and Fe/S ratios in sulfide immiscible melts. XANES and FE-SEM measurements in approx. 5 micron size individual sulfur blebs in EET79001 and Tissint glasses are carried out by us using sub-micron size beams, whereas Barrat and coworkers used approx. 90 micron size laser spots for LA- ICP-MS to determine REE abundances in bulk samples of the impact melt glasses. We contend that Martian regolith components in some shergottite impact glasses are present locally, and that studying impact melts in various shergottites can give evidence both for and against regolith components because of sample heterogeneity.

The interaction of copper ions with Staphylococcus aureus, Pseudomonas aeruginosa, and Escherichia coli: an X-ray absorption near-edge structure (XANES) spectroscopy study.

PubMed

Zanzen, Ulrike; Bovenkamp-Langlois, Lisa; Klysubun, Wantana; Hormes, Josef; Prange, Alexander

2018-04-01

The antimicrobial properties of copper ions have been known for a long time. However, the exact mechanism of action of the transition metal on microorganisms has long been unclear. X-ray absorption near-edge structure (XANES) spectroscopy at the Cu K edge allows the determination of copper speciation in Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa that have been treated with Cu(II) and Cu(I) solutions. The death/inactivation of the bacteria was observed using plate counting and light microscopy. The Cu K-XANES spectra of the two Gram-negative bacteria are different than those of the Gram-positive strain. The results clearly show that the Cu + -S bond contributes to the antibacterial activity of copper, as in the case of silver. The detailed evaluation of the differentiated absorption spectra shows that Cu + (not Cu 2+ ) is the dominant ion that binds to the bacteria. Because Cu + is not the most common copper ion, copper is not as effective an antibacterial agent as silver, whose common valency is actually + 1. Any reaction of copper with phosphorus from the bacteria can be excluded after the evaluation of the absorption spectra.

XANES and EXAFS investigation of uranium incorporation on nZVI in the presence of phosphate.

PubMed

Qiu, Muqing; Wang, Min; Zhao, Qingzhou; Hu, Baowei; Zhu, Yuling

2018-06-01

Effect of phosphate on the reduction of U(VI) on nZVI was determined by batch, XPS, XANES and EXAFS techniques. The batch experiments showed that nZVI was quite effective for the removal of uranium under the anaerobic conditions, whereas the addition of phosphate enhanced uranium removal over wide pH range. At low pH, the reduction of U(VI) to U(IV) significantly decreased with increasing phosphate concentration by XPS and XANES analysis. According to EXAFS analysis, the occurrence of UU shell at 10 mg/L phosphate and pH 4.0 was similar to that of U (IV) O 2 (s), whereas the UP and UFe shells were observed at 50 mg/L phosphate, revealing that reductive co-precipitate (U (IV) O 2 (s)) and precipitation of uranyl-phosphate were observed at low and high phosphate, respectively. The findings are crucial for the prediction of the effect of phosphate on the speciation and binding of uranium by nZVI at low pH, which is significant in controlling the mobility of U(VI) in contaminated environments. Copyright © 2018 Elsevier Ltd. All rights reserved.

µ-XANES AND µ-XRF INVESTIGATIONS OF METAL BINDING MECHANISMS IN BIOSOLIDS

EPA Science Inventory

Micro-X-ray fluorescence (µ-XRF) microprobe analysis and micro-X-ray absorption near edge spectroscopy (µ-XANES) were employed to identify Fe and Mn phases and their association with selected toxic elements in two biosolids (limed composted and Nu-Earth) containing low ...

Linear Combination Fitting (LCF)-XANES analysis of As speciation in selected mine-impacted materials

EPA Pesticide Factsheets

This table provides sample identification labels and classification of sample type (tailings, calcinated, grey slime). For each sample, total arsenic and iron concentrations determined by acid digestion and ICP analysis are provided along with arsenic in-vitro bioaccessibility (As IVBA) values to estimate arsenic risk. Lastly, the table provides linear combination fitting results from synchrotron XANES analysis showing the distribution of arsenic speciation phases present in each sample along with fitting error (R-factor).This dataset is associated with the following publication:Ollson, C., E. Smith, K. Scheckel, A. Betts, and A. Juhasz. Assessment of arsenic speciation and bioaccessibility in mine-impacted materials. Diana Aga, Wonyong Choi, Andrew Daugulis, Gianluca Li Puma, Gerasimos Lyberatos, and Joo Hwa Tay JOURNAL OF HAZARDOUS MATERIALS. Elsevier Science Ltd, New York, NY, USA, 313: 130-137, (2016).

XANES, EXAFS and Kbeta spectroscopic studies of the oxygen-evolving complex in Photosystem II

DOE Office of Scientific and Technical Information (OSTI.GOV)

Robblee, John Henry

A key question for the understanding of photosynthetic water oxidation is whether the four oxidizing equivalents necessary to oxidize water to dioxygen are accumulated on the four Mn ions of the oxygen evolving complex (OEC), or whether some ligand-centered oxidations take place before the formation and release of dioxygen during the S 3 → [S 4] → S 0 transition. Progress in instrumentation and flash sample preparation allowed us to apply Mn Kβ X-ray emission spectroscopy (Kb XES) to this problem for the first time. The Kβ XES results, in combination with Mn X-ray absorption near-edge structure (XANES) and electronmore » paramagnetic resonance (EPR) data obtained from the same set of samples, show that the S 2 → S 3 transition, in contrast to the S 0 → S 1 and S 1 → S 2 transitions, does not involve a Mn-centered oxidation. This is rationalized by manganese μ-oxo bridge radical formation during the S 2 → S 3 transition. Using extended X-ray absorption fine structure (EXAFS) spectroscopy, the local environment of the Mn atoms in the S 0 state has been structurally characterized. These results show that the Mn-Mn distance in one of the di-μ-oxo-bridged Mn-Mn moieties increases from 2.7 Å in the S 1} state to 2.85 Å in the S 0 state. Furthermore, evidence is presented that shows three di-μ-oxo binuclear Mn 2 clusters may be present in the OEC, which is contrary to the widely held theory that two such clusters are present in the OEC. The EPR properties of the S 0 state have been investigated and a characteristic ''multiline'' signal in the S 0 state has been discovered in the presence of methanol. This provides the first direct confirmation that the native S 0 state is paramagnetic. In addition, this signal was simulated using parameters derived from three possible oxidation states of Mn in the S 0 state. The dichroic nature of X-rays from synchrotron radiation and single-crystal Mn complexes have been exploited to selectively probe Mn-ligand bonds

XANES evidence for sulphur speciation in Mn-, Ni- and W-bearing silicate melts

NASA Astrophysics Data System (ADS)

Evans, K. A.; O'Neill, H. St. C.; Mavrogenes, J. A.; Keller, N. S.; Jang, L.-Y.; Lee, J.-F.

2009-11-01

spectra of the component element monosulphides. Mn-, W- and Ni-XANES and EXAFS for synthetic glasses without sulphide exsolution did not show any sensitivity to the presence of sulphur, which is unsurprising as S:O ratios were sufficiently low that metals would be mostly co-ordinated by O. Mn EXAFS spectra were consistent with divalent Mn in 5 co-ordinated Mn-O melt species. W spectra were consistent with tetrahedrally co-ordinated hexavalent W, most likely in scheelite-like melt species, and Ni spectra were consistent with [4] co-ordinated divalent Ni. These results indicate lower co-ordinations for both W and Ni than those inferred by some previous workers. Cation co-ordination may reflect the proportion of non-bridging oxygens, which is lower in the Ca-rich and Al-poor samples investigated here than for previous studies.

Mercury speciation on three European mining districts by XANES techniques

NASA Astrophysics Data System (ADS)

Esbri, J. M.; Garcia-Noguero, E. M.; Guerrero, B.; Kocman, D.; Bernaus, A.; Gaona, X.; Higueras, P.; Alvarez, R.; Loredo, J.; Horvat, M.; Ávila, M.

2009-04-01

The mobility, bioavailability and toxicity of mercury in the environment depend on the chemical species in which is present in soil, sediments, water or air. In this work we used synchrotron radiation to determine mercury species in geological samples of three mercury mining districts: Almadén (Spain), Idria (Slovenia) and Asturias (Spain). The aim of this study was to find differences on mobility and bioavailability of mercury on three mining districts with different type of mineralization. For this porpoises we selected samples of ore, calcines, soils and stream sediments from the three sites, completely characterized by the Almadén School of Mines, Josef Stefan Institute of Ljubljana and Oviedo School of Mines. Speciation of mercury was carried out on Synchrotron Laboratories of Hamburg (HASYLAB) by XANES techniques. Spectra of pure compounds [HgCl2, HgSO4, HgO, CH3HgCl, Hg2Cl2 (calomel), HgSred (cinnabar), HgSblack (metacinnabar), Hg2NCl0.5(SO4)0.3(MoO4)0.1(CO3)0.1(H2O) (mosesite), Hg3S2Cl2 (corderoite), Hg3(SO4)O2 (schuetteite) y Hg2ClO (terlinguaite)] were obtained on transmittance mode. The number and type of the compounds required to reconstruct experimental spectra for each sample was obtained by PCA analysis and linear fitting of minimum quadratics of the pure compounds spectra. This offers a semiquantitative approach to the mineralogical constitution of each analyzed sample. The results put forward differences on the efficiency of roasting furnaces from the three studied sites, evidenced by the presence of metacinnabar on the less efficient (Almadén and Asturias) and absence on the most efficient (Idria). For the three studied sites, sulfide species (cinnabar and metacinnabar) were largely more abundant than soluble species (chlorides and sulfates). On the other hand, recent results on the mobility of both Hg and As on the target sites will be presented. These results correlate with the related chemical species found by XANES techniques.

Organometallic model complexes elucidate the active gallium species in alkane dehydrogenation catalysts based on ligand effects in Ga K-edge XANES

DOE PAGES

Getsoian, Andrew "Bean"; Das, Ujjal; Camacho-Bunquin, Jeffrey; ...

2016-06-13

Gallium-modified zeolites are known catalysts for the dehydrogenation of alkanes, reactivity that finds industrial application in the aromatization of light alkanes by Ga-ZSM5. While the role of gallium cations in alkane activation is well known, the oxidation state and coordination environment of gallium under reaction conditions has been the subject of debate. Edge shifts in Ga K-edge XANES spectra acquired under reaction conditions have long been interpreted as evidence for reduction of Ga(III) to Ga(I). However, a change in oxidation state is not the only factor that can give rise to a change in the XANES spectrum. In order tomore » better understand the XANES spectra of working catalysts, we have synthesized a series of molecular model compounds and grafted surface organometallic Ga species and compared their XANES spectra to those of gallium-based catalysts acquired under reducing conditions. We demonstrate that changes in the identity and number of gallium nearest neighbors can give rise to changes in XANES spectra similar to those attributed in literature to changes in oxidation state. Specifically, spectral features previously attributed to Ga(I) may be equally well interpreted as evidence for low-coordinate Ga(III) alkyl or hydride species. Furthermore, these findings apply both to gallium-impregnated zeolite catalysts and to silica-supported single site gallium catalysts, the latter of which is found to be active and selective for dehydrogenation of propane and hydrogenation of propylene.« less

2D XANES-XEOL mapping: observation of enhanced band gap emission from ZnO nanowire arrays

NASA Astrophysics Data System (ADS)

Wang, Zhiqiang; Guo, Xiaoxuan; Sham, Tsun-Kong

2014-05-01

Using 2D XANES-XEOL spectroscopy, it is found that the band gap emission of ZnO nanowire arrays is substantially enhanced i.e. that the intensity ratio between the band gap and defect emissions increases by more than an order of magnitude when the excitation energy is scanned across the O K-edge. Possible mechanisms are discussed.Using 2D XANES-XEOL spectroscopy, it is found that the band gap emission of ZnO nanowire arrays is substantially enhanced i.e. that the intensity ratio between the band gap and defect emissions increases by more than an order of magnitude when the excitation energy is scanned across the O K-edge. Possible mechanisms are discussed. Electronic supplementary information (ESI) available: XEOL spectra with different excitation energies. X-ray attenuation length vs. photon energy. Details of surface defects in ZnO NWs. The second O K-edge and Zn L-edge 2D XANES-XEOL maps. Comparison of the first and second TEY at O K-edge and Zn L-edge scans, respectively. Raman spectra of the ZnO NWs with different IBGE/IDE ratios. See DOI: 10.1039/c4nr01049c

Silicon K-edge XANES spectra of silicate minerals

NASA Astrophysics Data System (ADS)

Li, Dien; Bancroft, G. M.; Fleet, M. E.; Feng, X. H.

1995-03-01

Silicon K-edge x-ray absorption near-edge structure (XANES) spectra of a selection of silicate and aluminosilicate minerals have been measured using synchrotron radiation (SR). The spectra are qualitatively interpreted based on MO calculation of the tetrahedral SiO{4/4-}cluster. The Si K-edge generally shifts to higher energy with increased polymerization of silicates by about 1.3 eV, but with considerable overlap for silicates of different polymerization types. The substitution of Al for Si shifts the Si K-edge to lower energy. The chemical shift of Si K-edge is also sensitive to cations in more distant atom shells; for example, the Si K-edge shifts to lower energy with the substitution of Al for Mg in octahedral sites. The shifts of the Si K-edge show weak correlation with average Si-O bond distance (dSi-O), Si-O bond valence (sSi-O) and distortion of SiO4 tetrahedra, due to the crystal structure complexity of silicate minerals and multiple factors effecting the x-ray absorption processes.

EXAFS and XANES investigation of the ETS-10 microporous titanosilicate.

PubMed

Prestipino, C; Solari, P L; Lamberti, C

2005-07-14

In this work, we report state-of-the-art analysis of both Ti K-edge high-resolution XANES and EXAFS data collected on the ETS-10 molecular sieve at the GILDA BM8 beamline of the ESRF facility. The interatomic distances and the angles obtained in our EXAFS study are in fair agreement with the single-crystal XRD data of Wang and Jacobson (Chem. Commun. 1999, 973) and with the recent ab initio periodic study of Damin et al. (J. Phys. Chem. B 2004, 108, 1328) Differently from previous EXAFS work (J. Phys. Chem. 1996, 100, 449), our study supports a model of ETS-10 where the Ti atoms are bonded with two equivalent axial oxygen atoms. This model is also able to reproduce the edge and the post-edge region of the XANES spectrum. Conversely, the weak but well-defined pre-edge peak at 4971.3 eV can be explained only by assuming that a fraction of Ti atoms are in a local geometry similar to that of the pentacoordinated Ti sites in the ETS-4 structure. These Ti atoms in ETS-10 should be the terminal of the -Ti-O-Ti-O-Ti- chains, of which the actual number is strongly increased by the high crystal defectivity (Ti vacancies).

A XANES Study of Sulfur Speciation and Reactivity in Cokes for Anodes Used in Aluminum Production

NASA Astrophysics Data System (ADS)

Jahrsengene, Gøril; Wells, Hannah C.; Rørvik, Stein; Ratvik, Arne Petter; Haverkamp, Richard G.; Svensson, Ann Mari

2018-03-01

Availability of anode raw materials in the growing aluminum industry results in a wider range of petroleum cokes being used to produce carbon anodes. The boundary between anode grade cokes and what previously was considered non-anode grades are no longer as distinct as before, leading to introduction of cokes with higher sulfur and higher trace metal impurity content in anode manufacturing. In this work, the chemical nature of sulfur in five industrial cokes, ranging from 1.42 to 5.54 wt pct S, was investigated with K-edge XANES, while the reactivity of the cokes towards CO2 was measured by a standard mass loss test. XANES identified most of the sulfur as organic sulfur compounds. In addition, a significant amount is identified (16 to 53 pct) as S-S bound sulfur. A strong inverse correlation is observed between CO2-reactivity and S-S bound sulfur in the cokes, indicating that the reduction in reactivity is more dependent on the amount of this type of sulfur compound rather than the total amount of sulfur or the amount of organic sulfur.

A XANES Study of Sulfur Speciation and Reactivity in Cokes for Anodes Used in Aluminum Production

NASA Astrophysics Data System (ADS)

Jahrsengene, Gøril; Wells, Hannah C.; Rørvik, Stein; Ratvik, Arne Petter; Haverkamp, Richard G.; Svensson, Ann Mari

2018-06-01

Availability of anode raw materials in the growing aluminum industry results in a wider range of petroleum cokes being used to produce carbon anodes. The boundary between anode grade cokes and what previously was considered non-anode grades are no longer as distinct as before, leading to introduction of cokes with higher sulfur and higher trace metal impurity content in anode manufacturing. In this work, the chemical nature of sulfur in five industrial cokes, ranging from 1.42 to 5.54 wt pct S, was investigated with K-edge XANES, while the reactivity of the cokes towards CO2 was measured by a standard mass loss test. XANES identified most of the sulfur as organic sulfur compounds. In addition, a significant amount is identified (16 to 53 pct) as S-S bound sulfur. A strong inverse correlation is observed between CO2-reactivity and S-S bound sulfur in the cokes, indicating that the reduction in reactivity is more dependent on the amount of this type of sulfur compound rather than the total amount of sulfur or the amount of organic sulfur.

Localization and Speciation of Arsenic in Soil and Desert Plant Parkinsonia florida using μXRF and μXANES

PubMed Central

Castillo-Michel, Hiram; Hernandez-Viezcas, Jose; Dokken, Kenneth M.; Marcus, Matthew A.; Peralta-Videa, Jose R.; Gardea-Torresdey, Jorge L.

2011-01-01

Parkinsonia florida is a plant species native to the semi-desert regions of North America. The cultivation characteristics of this shrub/tree suggest that it could be used for phytoremediation purposes in semiarid regions. This work describes, through the use of synchrotron μXRF and μXANES techniques and ICP-OES, the arsenic (As) accumulation and distribution in P. florida plants grown in two soils spiked with As at 20 mg kg-1. Plants grown in a sandy soil accumulated at least twice more As in the roots compared to plants grown in a loamy soil. The lower As accumulation in plants grown in the loamy soil corresponded to a lower concentration of As in the water soluble fraction (WSF) of this soil. LC-ICP-MS speciation analysis showed only As(V) in the WSF from all treatments. In contrast, linear combination XANES speciation analysis from the root tissues showed As mainly present in the reduced As(III) form. Moreover, a fraction of the reduced As was found coordinating to S in a form consistent with As-Cys3. The percentage of As coordinated to sulfur was smaller for plants grown in the loamy soil when compared to the sandy soil. PMID:21842861

Localization and speciation of arsenic in soil and desert plant Parkinsonia florida using μXRF and μXANES.

PubMed

Castillo-Michel, Hiram; Hernandez-Viezcas, Jose; Dokken, Kenneth M; Marcus, Matthew A; Peralta-Videa, Jose R; Gardea-Torresdey, Jorge L

2011-09-15

Parkinsonia florida is a plant species native to the semidesert regions of North America. The cultivation characteristics of this shrub/tree suggest that it could be used for phytoremediation purposes in semiarid regions. This work describes, through the use of synchrotron μXRF and μXANES techniques and ICP-OES, the arsenic (As) accumulation and distribution in P. florida plants grown in two soils spiked with As at 20 mg kg(-1). Plants grown in a sandy soil accumulated at least twice more As in the roots compared to plants grown in a loamy soil. The lower As accumulation in plants grown in the loamy soil corresponded to a lower concentration of As in the water-soluble fraction (WSF) of this soil. LC-ICP-MS speciation analysis showed only As(V) in the WSF from all treatments. In contrast, linear combination XANES speciation analysis from the root tissues showed As mainly present in the reduced As(III) form. Moreover, a fraction of the reduced As was found coordinating to S in a form consistent with As-Cys(3). The percentage of As coordinated to sulfur was smaller for plants grown in the loamy soil when compared to the sandy soil.

EXAFS and XANES investigation of (Li, Ni) codoped ZnO thin films grown by pulsed laser deposition.

PubMed

Mino, Lorenzo; Gianolio, Diego; Bardelli, Fabrizio; Prestipino, Carmelo; Senthil Kumar, E; Bellarmine, F; Ramanjaneyulu, M; Lamberti, Carlo; Ramachandra Rao, M S

2013-09-25

Ni doped, Li doped and (Li, Ni) codoped ZnO thin films were successfully grown using a pulsed laser deposition technique. Undoped and doped ZnO thin films were investigated using extended x-ray absorption fine structure (EXAFS) and x-ray absorption near edge spectroscopy (XANES). Preliminary investigations on the Zn K-edge of the undoped and doped ZnO thin films revealed that doping has not influenced the average Zn-Zn bond length and Debye-Waller factor. This shows that both Ni and Li doping do not appreciably affect the average local environment of Zn. All the doped ZnO thin films exhibited more than 50% of substitutional Ni, with a maximum of 77% for 2% Ni and 2% Li doped ZnO thin film. The contribution of Ni metal to the EXAFS signal clearly reveals the presence of Ni clusters. The Ni-Ni distance in the Ni(0) nanoclusters, which are formed in the film, is shorter with respect to the reference Ni metal foil and the Debye-Waller factor is higher. Both facts perfectly reflect what is expected for metal nanoparticles. At the highest doping concentration (5%), the presence of Li favors the growth of a secondary NiO phase. Indeed, 2% Ni and 5% Li doped ZnO thin film shows %Nisub = 75 ± 11, %Nimet = 10 ± 8, %NiO = 15 ± 8. XANES studies further confirm that the substitutional Ni is more than 50% in all the samples. These results explain the observed magnetic properties.

Characterization of Sulfur Compounds in Coffee Beans by Sulfur K-XANES Spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lichtenberg, H.; Hormes, J.; Institute of Physics, University of Bonn, Nussallee 12, 53115 Bonn

2007-02-02

In this 'feasibility study' the influence of roasting on the sulfur speciation in Mexican coffee beans was investigated by sulfur K-XANES Spectroscopy. Spectra of green and slightly roasted beans could be fitted to a linear combination of 'standard' reference spectra for biological samples, whereas longer roasting obviously involves formation of additional sulfur compounds in considerable amounts.

Olivine-melt relationships and syneruptive redox variations in the 1959 eruption of Kīlauea Volcano as revealed by XANES

NASA Astrophysics Data System (ADS)

Helz, R. T.; Cottrell, E.; Brounce, M. N.; Kelley, K. A.

2017-03-01

and (2) the melts originally had Fe+ 3/FeT ≥ 0.175, consistent with oxygen fugacity (fO2) at least 0.4 log units above the fayalite-magnetite-quartz (FMQ) buffer at 1 atm and magmatic temperature of 1200 °C. The second process is interaction between the melts and atmospheric oxygen, which results in higher Fe+ 3/FeT ratios. Detailed μ-XANES traverses show gradients in Fe+ 3/FeT of 0.145 to 0.628 over distances of 100-150 μm in thin, visibly reddened matrix glass bordering some scoriae, presumably caused by contact with air. This process was extremely rapid, giving insight into how fast the Fe+ 3/FeT ratio can change in response to changes in external conditions.

XANES analysis of dried and calcined bones.

PubMed

Rajendran, Jayapradhi; Gialanella, Stefano; Aswath, Pranesh B

2013-10-01

The structure of dried and calcined bones from chicken, bovine, deer, pig, sheep and chamois was examined using X-ray Absorption Near Edge Structure (XANES) spectroscopy. The oxygen K-edge absorption edge indicates that the surface of dried bone has a larger proportion of carbonate than the interior that is made up of phosphates. The phosphorus L and K edge clearly indicate that pyrophosphates, α-tricalcium phosphate (α-TCP) and hydrogen phosphates of Ca do not exist in either the dried bone or calcined bone and phosphorus exists as either β-tricalcium phosphate (β-TCP) or hydroxyapatite, both in the dried and calcined conditions. The Ca K-edge analysis indicates that β-TCP is the likely form of phosphate in both the dried and calcined conditions. Copyright © 2013 Elsevier B.V. All rights reserved.

XPS and XANES studies of biomimetic composites based on B-type nano-hydroxyapatite

NASA Astrophysics Data System (ADS)

Goloshchapov, D. L.; Gushchin, M. S.; Kashkarov, V. M.; Seredin, P. V.; Ippolitov, Y. A.; Khmelevsky, N. O.; Aksenenko, A. Yu.

2018-06-01

The paper presents an investigation of the local atomic structure of nanocrystalline carbonate-substituted hydroxyapatite (CHAP) contained in biomimetic composites - analogues of intact human tooth tissues. Using the XPS technique, the presence of impurity Mg and F atoms and structurally bound carbon in CHAP, at the concentrations typical of apatite enamel and dentine was determined. The XANES method was used to study the changes occurring in P L2,3 spectra of biocomposites with CHAP, depending on the percentage of the amino acid matrix. The appearance of maxima in the spectra of XANES P L2,3 near 135.7 eV for the samples with the composition of amino acid complex/hydroxyapatite - 5/95, 25/75 and the splitting of a broad peak of 146.9 eV in the spectrum of a biocomposite with a composition of 40/60 indicates at the interaction of molecular complex of amino acids with atomic environment of phosphorus. This fact can be used in the fundamental medicine for synthesizing of new biomaterials in dentistry.

Reference spectra of important adsorbed organic and inorganic phosphate binding forms for soil P speciation using synchrotron-based K-edge XANES spectroscopy.

PubMed

Prietzel, Jörg; Harrington, Gertraud; Häusler, Werner; Heister, Katja; Werner, Florian; Klysubun, Wantana

2016-03-01

Direct speciation of soil phosphorus (P) by linear combination fitting (LCF) of P K-edge XANES spectra requires a standard set of spectra representing all major P species supposed to be present in the investigated soil. Here, available spectra of free- and cation-bound inositol hexakisphosphate (IHP), representing organic P, and of Fe, Al and Ca phosphate minerals are supplemented with spectra of adsorbed P binding forms. First, various soil constituents assumed to be potentially relevant for P sorption were compared with respect to their retention efficiency for orthophosphate and IHP at P levels typical for soils. Then, P K-edge XANES spectra for orthophosphate and IHP retained by the most relevant constituents were acquired. The spectra were compared with each other as well as with spectra of Ca, Al or Fe orthophosphate and IHP precipitates. Orthophosphate and IHP were retained particularly efficiently by ferrihydrite, boehmite, Al-saturated montmorillonite and Al-saturated soil organic matter (SOM), but far less efficiently by hematite, Ca-saturated montmorillonite and Ca-saturated SOM. P retention by dolomite was negligible. Calcite retained a large portion of the applied IHP, but no orthophosphate. The respective P K-edge XANES spectra of orthophosphate and IHP adsorbed to ferrihydrite, boehmite, Al-saturated montmorillonite and Al-saturated SOM differ from each other. They also are different from the spectra of amorphous FePO4, amorphous or crystalline AlPO4, Ca phosphates and free IHP. Inclusion of reference spectra of orthophosphate as well as IHP adsorbed to P-retaining soil minerals in addition to spectra of free or cation-bound IHP, AlPO4, FePO4 and Ca phosphate minerals in linear combination fitting exercises results in improved fit quality and a more realistic soil P speciation. A standard set of P K-edge XANES spectra of the most relevant adsorbed P binding forms in soils is presented.

Synchrotron Micro-XANES Measurements of Vanadium Oxidation State in Glasses as a Function of Oxygen Fugacity: Experimental Calibration of Data Relevant to Partition Coefficient Determination

NASA Technical Reports Server (NTRS)

Delaney, J. S.; Sutton, S. R.; Newville, M.; Jones, J. H.; Hanson, B.; Dyar, M. D.; Schreiber, H.

2000-01-01

Oxidation state microanalyses for V in glass have been made by calibrating XANES spectral features with optical spectroscopic measurements. The oxidation state change with fugacity of O2 will strongly influence partitioning results.

In situ S-K XANES study of polymer electrolyte fuel cells: changes in the chemical states of sulfonic groups depending on humidity.

PubMed

Isegawa, Kazuhisa; Nagami, Tetsuo; Jomori, Shinji; Yoshida, Masaaki; Kondoh, Hiroshi

2016-09-14

Changes in the chemical states of sulfonic groups of Nafion in polymer electrolyte fuel cells (PEFCs) under gas-flowing conditions were studied using in situ S-K XANES spectroscopy. The applied potential to the electrodes and the humidity of the cell were changed under flowing H 2 gas in the anode and He gas in the cathode. While the potential shows no significant effect on the S-K XANES spectra, the humidity is found to induce reversible changes in the spectra. Comparison of the spectral changes with simulations based on the density functional theory calculations indicates that the humidity influences the chemical state of the sulfonic group; under wet conditions the sulfonic group is in the form of a sulfonate ion. By drying treatment the sulfonate ion binds to hydrogen and becomes sulfonic acid. Furthermore, a small fraction of the sulfonic acid irreversibly decomposes to atomic sulfur. The peak energy of the atomic sulfur suggests that the generated atomic sulfur is adsorbed on the Pt catalyst surfaces.

In Situ XANES of U and Th in Silicate Liquids at High Pressure and Temperature

NASA Astrophysics Data System (ADS)

Mallmann, G.; Wykes, J.; Berry, A.; O'Neill, H. S.; Cline, C. J., II; Turner, S.; Rushmer, T. A.

2016-12-01

Although the chemical environments of elements in silicate melts at specific conditions of temperature, pressure and oxygen fugacity (fO2) are often inferred from measurements after quenching the melts to glasses, it is widely recognized that changes may occur during the quenching process, making measurements in situ at high pressure and temperature highly desirable. A case of importance in geochemistry is the speciation of uranium in silicate melts as a function of pressure. Evidence from mineral-melt partitioning and XANES (X-ray Absorption Near-Edge Structure) spectroscopy of glasses suggests that U5+ may be stable at low pressures in the Earth's crust (along with U4+ or U6+, depending on fO2) where basaltic liquids crystallize, but not in the Earth's upper mantle where peridotite partially melts to produce such liquids. To test these observations we recorded in situ transmission U and Th L3-edge XANES spectra of U and Th-doped silicate liquids at 1.6 GPa and 1350°C using the D-DIA apparatus at the X-ray Absorption Spectroscopy Beamline of the Australian Synchrotron. Data for thorium, which occurs exclusively as a tetravalent cation under terrestrial fO2 conditions, were collected as a `control' to monitor for changes in coordination. The cell assembly consisted of a boron-epoxy cube as pressure medium, alumina sleeve and cylindrical graphite heater. The starting mix, a powdered synthetic average MORB silicate glass doped with 2 wt.% of U and Th, was loaded into San Carlos olivine capsules along with solid oxygen buffers (either Re-ReO2 or Ru-RuO2) in a sandwich arrangement. The capsule was then placed inside the graphite heater and insulated with crushable MgO powder. Temperature was monitored using a type D thermocouple. U and Th L3-edge XANES spectra were recorded throughout the heating/compression cycle and then after quenching. Our preliminary assessment indicates that the U-XANES spectra recorded for the liquid in situ at high pressure and temperature and

Olivine-melt relationships and syneruptive redox variations in the 1959 eruption of Kīlauea Volcano as revealed by XANES

USGS Publications Warehouse

Helz, Rosalind L.; Cottrell, Elizabeth; Brounce, Maryjo N.; Kelley, Katherine A.

2017-01-01

degassing during the eruption and (2) the melts originally had Fe+ 3/FeT ≥ 0.175, consistent with oxygen fugacity (fO2) at least 0.4 log units above the fayalite-magnetite-quartz (FMQ) buffer at 1 atm and magmatic temperature of 1200 °C.The second process is interaction between the melts and atmospheric oxygen, which results in higher Fe+ 3/FeT ratios. Detailed μ-XANES traverses show gradients in Fe+ 3/FeT of 0.145 to 0.628 over distances of 100–150 μm in thin, visibly reddened matrix glass bordering some scoriae, presumably caused by contact with air. This process was extremely rapid, giving insight into how fast the Fe+ 3/FeT ratio can change in response to changes in external conditions.

Using X-ray Microscopy and Hg L3 XANES to study Hg Binding in the Rhizosphere of Spartina Cordgrass

PubMed Central

Patty, Cynthia; Barnett, Brandy; Mooney, Bridget; Kahn, Amanda; Levy, Silvio; Liu, Yijin; Pianetta, Piero; Andrews, Joy C

2009-01-01

San Francisco Bay has been contaminated historically by mercury from mine tailings as well as contemporary industrial sources. Native Spartina foliosa and non-native S. alterniflora-hybrid cordgrasses are dominant florae within the SF Bay estuary environment. Understanding mercury uptake and transformations in these plants will help to characterize the significance of their roles in mercury biogeochemical cycling in the estuarine environment. Methylated mercury can be biomagnified up the food web, resulting in levels in sport fish up to one million times greater than in surrounding waters and resulting in advisories to limit fish intake. Understanding the uptake and methylation of mercury in the plant rhizosphere can yield insight into ways to manage mercury contamination. The transmission x-ray microscope on beamline 6-2 at the Stanford Synchrotron Radiation Lightsource (SSRL) was used to obtain absorption contrast images and 3D tomography of Spartina foliosa roots that were exposed to 1 ppm Hg (as HgCl2) hydroponically for one week. Absorption contrast images of micron-sized roots from S. foliosa revealed dark particles, and dark channels within the root, due to Hg absorption. 3D tomography showed that the particles are on the root surface, and slices from the tomographic reconstruction revealed that the particles are hollow, consistent with microorganisms with a thin layer of Hg on the surface. Hg L3 XANES of ground-up plant roots and Hg L3 micro-XANES from microprobe analysis of micron-sized roots (60–120 microns in size) revealed three main types of speciation in both Spartina species: Hg-S ligation in a form similar to Hg(II) cysteine, Hg-S bonding as in cinnabar and metacinnabar, and methylmercury-carboxyl bonding in a form similar to methylmercury acetate. These results are interpreted within the context of obtaining a “snapshot” of mercury methylation in progress. PMID:19848152

Using X-ray microscopy and Hg L3 XANES to study Hg binding in the rhizosphere of Spartina cordgrass.

PubMed

Patty, Cynthia; Barnett, Brandy; Mooney, Bridget; Kahn, Amanda; Levy, Silvio; Liu, Yijin; Pianetta, Piero; Andrews, Joy C

2009-10-01

San Francisco Bay has been contaminated historically by mercury from mine tailings as well as contemporary industrial sources. Native Spartina foliosa and non-native S. alterniflora-hybrid cordgrasses are dominant florae within the SF Bay estuary environment. Understanding mercury uptake and transformations in these plants will help to characterize the significance of their roles in mercury biogeochemical cycling in the estuarine environment. Methylated mercury can be biomagnified up the food web, resulting in levels in sport fish up to 1 million times greater than in surrounding waters and resulting in advisories to limit fish intake. Understanding the uptake and methylation of mercury in the plant rhizosphere can yield insight into ways to manage mercury contamination. The transmission X-ray microscope on beamline 6-2 at the Stanford Synchrotron Radiation Lightsource (SSRL) was used to obtain absorption contrast images and 3D tomography of Spartina foliosa roots that were exposed to 1 ppm Hg (as HgCl2) hydroponically for 1 week. Absorption contrast images of micrometer-sized roots from S. foliosa revealed dark particles, and dark channels within the root, due to Hg absorption. 3D tomography showed that the particles are on the root surface, and slices from the tomographic reconstruction revealed that the particles are hollow, consistent with microorganisms with a thin layer of Hg on the surface. Hg L3 XANES of ground-up plant roots and Hg L3 micro-XANES from microprobe analysis of micrometer-sized roots (60-120 microm in size) revealed three main types of speciation in both Spartina species: Hg-S ligation in a form similar to Hg(II) cysteine, Hg-S bonding as in cinnabar and metacinnabar, and methylmercury-carboxyl bonding in a form similar to methylmercury acetate. These results are interpreted within the context of obtaining a "snapshot" of mercury methylation in progress.

Olivine-melt relationships and syneruptive redox variations in the 1959 eruption of K$$\\bar{i}$$lauea Volcano as revealed by XANES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Helz, R. T.; Cottrell, E.; Brounce, M. N.

The 1959 summit eruption of Kmore » $$\\bar{i}$$lauea Volcano exhibited high lava fountains of gas-rich, primitive magma, containing olivine + chromian spinel in highly vesicular brown glass. Microprobe analysis of these samples shows that euhedral rims on olivine phenocrysts, in direct contact with glass, vary significantly in forsterite (Fo) content, at constant major-element melt composition, as do unzoned groundmass olivine crystals. Ferric/total iron (Fe+ 3/FeT)ratios for matrix and interstitial glasses, plus olivine-hosted glass inclusions in eight 1959 scoria samples have been determined by micro X-ray absorption near-edge structure spectroscopy (μ-XANES). These data show that much of the variation in Fo content reflects variation in oxidation state of iron in the melt, which varies with sulfur concentration in the glass and (locally) with proximity to scoria edges in contact with air. Data for 24 olivine-melt pairs in the better-equilibrated samples from later in the eruption show KD averaging 0.280 ± 0.03 for the exchange of Fe and Mg between olivine and melt, somewhat displaced from the value of 0.30 ± 0.03 given by Roeder and Emslie (1970). This may reflect the low SiO2 content of the 1959 magmas, which is lower than that in most K$$\\bar{i}$$lauea tholeiites. More broadly, we show the potential of μ-XANES and electron microprobe to revisit and refine the value of KD in natural systems.« less

Analysis of the detailed configuration of hydrated lanthanoid(III) ions in aqueous solution and crystalline salts by using K- and L(3)-edge XANES spectroscopy.

PubMed

D'Angelo, Paola; Zitolo, Andrea; Migliorati, Valentina; Persson, Ingmar

2010-01-11

The structural properties of the hydrated lanthanoid(III) ions in aqueous solution and in the isostructural trifluoromethanesulfonate salts have been investigated by a quantitative analysis of the X-ray absorption near-edge structure (XANES) spectra at the K- and L(3)-edges. The XANES analysis has provided a clear description of the variation of lanthanoid(III) hydration properties across the series. It was found that all of the lanthanoid(III) hydration complexes retain a tricapped trigonal prism (TTP) geometry, and along the series two of the capping water molecules become less and less strongly bound, before finally, on average, one of them leaves the hydration cluster. This gives rise to an eight-coordinated distorted bicapped trigonal prism with two different Ln--O capping distances for the smallest lanthanoid(III) ions. This systematic study has shown that for lanthanoid compounds more accurate structural information is obtained from the analysis of the L(3)-edge than from K-edge XANES data. Moreover, whereas the second hydration shells provide a detectable contribution to the L(3)-edge XANES spectra of the lighter lanthanoid ions, the K-edge spectra are insensitive to the more distant coordination spheres.

PREFACE: Proceedings of the First International Workshop on the Theoretical Calculation of ELNES and XANES (TEX2008) (Nagoya, Japan, 2-4 July 2008) Proceedings of the First International Workshop on the Theoretical Calculation of ELNES and XANES (TEX2008) (Nagoya, Japan, 2-4 July 2008)

NASA Astrophysics Data System (ADS)

Tanaka, Isao; Mizoguchi, Teruyasu; Yamamoto, Tomoyuki

2009-03-01

Both electron energy loss near edge structure (ELNES) spectroscopy and x-ray absorption near edge structure (XANES) spectroscopy provide information on the local structural and chemical environments of selected elements of interest. Recent technological progress in scanning transmission electron microscopy has enabled ELNES measurements with atomic column spatial resolution. Very dilute concentrations (nanograms per milliliter or ppb level) of dopants can be observed using third-generation synchrotron facilities when x-ray fluorescence is measured with highly efficient detectors. With such technical developments, ELNES and XANES have become established as essential tools in a large number of fields of natural science, including condensed matter physics, chemistry, mineralogy and materials science. In addition to these developments in experimental methodology, notable progress in reproducing spectra using theoretical methods has recently been made. Using first-principles methods, one can analyze and interpret spectra without reference to experiment. This is quite important since we are often interested in the analysis of exotic materials or specific atoms located at lattice discontinuities such as surfaces and interfaces, where appropriate experimental data are difficult to obtain. Using the structures predicted by reliable first-principles calculations, one can calculate theoretical ELNES and XANES spectra without too much difficulty even in such cases. Despite the fact that ELNES and XANES probe the same phenomenon—essentially the electric dipole transition from a core orbital to an unoccupied band—there have not been many opportunities for researchers in the two areas to meet and discuss. Theoretical calculations of ELNES spectra have been mainly confined to the electron microscopy community. On the other hand, the theory of XANES has been developed principally by researchers in the x-ray community. Publications describing the methods have been written more

The Valence of Iron in CM Chondrite Serpentine as Measured by Synchrotron Xanes

NASA Technical Reports Server (NTRS)

Mikouchi, T.; Zolensky, Michael E.; Satake, W.; Le, L.

2012-01-01

Fe-bearing phyllosilicates are the dominant product of aqueous alteration in carbonaceous chondrites, and serpentine is the most abundant phyllosilicate in CM2 chondrites that are the most abundant carbonaceous chondrite. Browning et al. predicted that Fe(3+)/(sum of Fe) ratios of serpentine in CM chondrites should change with progressive alteration. They proposed that progressive CM alteration is best monitored by evaluating the progress of Si and Fe3+ substitutions that necessarily attend the transition from end-member cronstedtite to serpentine. Their proposed Mineralogic Alteration Index, 2-(Fe(3+)/(2-Si)), was intended to highlight and utilize the relevant ex-change information in the stoichiometric phyllosilicate formulas based upon the coupled substitution of 2(Fe(3+), Al) = Si + (Mg, Fe(2+)...) in serpentine. The value of this ratio increases as alteration proceeds. We always wanted to directly test Browning s pre-diction through actual measurements of the Fe3+ con-tent of serpentine at the micron scale appropriate to EPMA analyses (Zega et al. have measured it at much finer scale), and this test can now be made using Synchrotron Radiation X-ray Absorption Near-Edge Structure (SR-XANES). Thus, we have recently begun investigation with CMs that span a large portion of the range of observed aqueous alteration, and we first analyzed Murray, Nogoya, and ALH84029 by SR-XANES. However, we did not find clear correlation between Fe3+/(sum of Fe) ratios of serpentine and their alteration degrees. We thus analyzed serpentine in three more CMs and here report their Fe3+/(sum of Fe) ratios in comparison with our previous results.

Interaction of Nanostructured Calcium Silicate Hydrate with Ibuprofen Drug Molecules: X-ray Absorption Near Edge Structure (XANES) Study at the Ca, Si and O K-edge

NASA Astrophysics Data System (ADS)

Guo, X. X.; Sham, T. K.; Zhu, Y. J.; Hu, Y. F.

2013-04-01

Mesoporous calcium silicate hydrate (CSH) nanostructure has been proven to be bioactive and biocompatible, and has a bright future in the application of bone treatment among other applications. X-ray absorption near edge structure (XANES) is a powerful tool for the study of the interactions of calcium silicate hydrates with drug molecules because it is element specific and it probes the unoccupied electronic states. Herein, we report the use of the calcium, silicon and oxygen K-edge XANES spectroscopy to identify how drug molecules interact with different groups in calcium silicate hydrate mesoporous nano-carriers with different morphologies. Significant changes are observed in XANES spectra after drug loading into the calcium silicate hydrate system, especially at the Si and O K-edge. The implications of these findings are discussed.

Change in Localizations of Arsenic in Rice Grains After Cooking with High Arsenic Waters - µXRF and XANES studies

NASA Astrophysics Data System (ADS)

Datta, S.; Ryan, B.; Kumar, N.; Bortz, T.; Bolen, Z. T.

2016-12-01

Threats of Arsenic (As) through food uptake, via consumption of rice, is a potential pathway that presents a concern not only for the millions of inhabitants who reside in river valleys and irrigate their soil with contaminated water, but the global rice market as well. This study focuses on high As rice from India and Bangladesh grown in such soils, and the effect of boiling rice with As-contaminated water in preparation for dietary intake. Husked and unhusked rice grains were boiled with >500 µg/L As-bearing water from the field to simulate local cooking methods. The resulting cooked water was analyzed using iCAP low limit detection via ICP-MS to understand the changes in dissolved elemental concentrations before and after cooking, and HPLC was introduced to measure for changes in As speciation in the waters. Using spectroscopic methods such as µXRF mapping associated with µXANES, distribution/localization and speciation changes of As in rice grains were identified. Further, with Linear Combination Fitting (LCF) of XANES spectra utilizing relevant reference compounds (As-S, AsIII, AsV, MMA and DMA), organic and inorganic As species were able to be mapped within rice grains. The results for uncooked/raw grains showed that predominantly As-S combined with AsIII and AsV accounted for 90% of speciation in most samples, localized in areas such as the outer aleurone layer. When analyzing cooked rice grains, the speciation appears to be an unidentified As species while the best LCF shows between 63-93% of As as MMA. Arsenic was found less localized throughout the cooked grains but rather heterogeneously distributed when compared to the uncooked/raw samples. The analyses of boiled/cooked water resulted in a significant decrease in dissolved As post-cooking (90%), but a subsequent increase in elements such as K, La, Li, Mo, Na, Ni, and Zr was observed; As-V was shown to be the main in-As species in the cooked water. The impact that this study portrays is consuming rice

XANES Spectroscopic Analysis of Phosphorus Speciation in Alum-Amended Poultry Litter

DOE Office of Scientific and Technical Information (OSTI.GOV)

Seiter,J.; Staats-Borda, K.; Ginder-Vogel, M.

2008-01-01

Aluminum sulfate (alum; Al2(SO4)3{center_dot}14H2O) is used as a chemical treatment of poultry litter to reduce the solubility and release of phosphate, thereby minimizing the impacts on adjacent aquatic ecosystems when poultry litter is land applied as a crop fertilizer. The objective of this study was to determine, through the use of X-ray absorption near edge structure (XANES) spectroscopy and sequential extraction, how alum amendments alter P distribution and solid-state speciation within the poultry litter system. Our results indicate that traditional sequential fractionation procedures may not account for variability in P speciation in heterogeneous animal manures. Analysis shows that NaOH-extracted Pmore » in alum amended litters is predominantly organic ({approx}80%), whereas in the control samples, >60% of NaOH-extracted P was inorganic P. Linear least squares fitting (LLSF) analysis of spectra collected of sequentially extracted litters showed that the P is present in inorganic (P sorbed on Al oxides, calcium phosphates) and organic forms (phytic acid, polyphosphates, and monoesters) in alum- and non-alum-amended poultry litter. When determining land application rates of poultry litter, all of these compounds must be considered, especially organic P. Results of the sequential extractions in conjunction with LLSF suggest that no P species is completely removed by a single extractant. Rather, there is a continuum of removal as extractant strength increases. Overall, alum-amended litters exhibited higher proportions of Al-bound P species and phytic acid, whereas untreated samples contained Ca-P minerals and organic P compounds. This study provides in situ information about P speciation in the poultry litter solid and about P availability in alum- and non-alum-treated poultry litter that will dictate P losses to ground and surface water systems.« less

A New Look at the Structural and Magnetic Properties of Potassium Neptunate K2NpO4 Combining XRD, XANES Spectroscopy, and Low-Temperature Heat Capacity.

PubMed

Smith, Anna L; Colineau, Eric; Griveau, Jean-Christophe; Popa, Karin; Kauric, Guilhem; Martin, Philippe; Scheinost, Andreas C; Cheetham, Anthony K; Konings, Rudy J M

2017-05-15

The physicochemical properties of the potassium neptunate K 2 NpO 4 have been investigated in this work using X-ray diffraction, X-ray absorption near edge structure (XANES) spectroscopy at the Np-L 3 edge, and low-temperature heat capacity measurements. A Rietveld refinement of the crystal structure is reported for the first time. The Np(VI) valence state has been confirmed by the XANES data, and the absorption edge threshold of the XANES spectrum has been correlated to the Mössbauer isomer shift value reported in the literature. The standard entropy and heat capacity of K 2 NpO 4 have been derived at 298.15 K from the low-temperature heat capacity data. The latter suggest the existence of a magnetic ordering transition around 25.9 K, most probably of the ferromagnetic type.

Sulfur and iron speciation in gas-rich impact-melt glasses from basaltic shergottites determined by microXANES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sutton, S.R.; Rao, M.N.; Nyquist, L.E.

2008-04-28

Sulfur and iron K XANES measurements were made on GRIM glasses from EET 79001. Iron is in the ferrous state. Sulfur speciation is predominately sulfide coordination but is Fe coordinated in Lith B and, most likely, Ca coordinated in Lith A. Sulfur is abundantly present as sulfate near Martian surface based on chemical and mineralogical investigations on soils and rocks in Viking, Pathfinder and MER missions. Jarosite is identified by Moessbauer studies on rocks at Meridian and Gusev, whereas MgSO{sub 4} is deduced from MgO-SO{sub 3} correlations in Pathfinder MER and Viking soils. Other sulfate minerals such as gypsum andmore » alunogen/S-rich aluminosilicates and halides are detected only in martian meteorites such as shergottites and nakhlites using SEM/FE-SEM and EMPA techniques. Because sulfur has the capacity to occur in multiple valence states, determination of sulfur speciation (sulfide/sulfate) in secondary mineral assemblages in soils and rocks near Mars surface may help us understand whether the fluid-rock interactions occurred under oxidizing or reducing conditions. On Earth, volcanic rocks contain measurable quantities of sulfur present as both sulfide and sulfate. Carroll and Rutherford showed that oxidized forms of sulfur may comprise a significant fraction of total dissolved sulfur, if the oxidation state is higher than {approx}2 log fO{sub 2} units relative to the QFM buffer. Terrestrial samples containing sulfates up to {approx}25% in fresh basalts from the Galapagos Rift on one hand and high sulfide contents present in oceanic basalts on the other indicate that the relative abundance of sulfide and sulfate varies depending on the oxygen fugacity of the system. Basaltic shergottites (bulk) such as Shergotty, EET79001 and Zagami usually contain small amounts of sulfur ({approx}0.5%) as pyrrhotite. But, in isolated glass pockets containing secondary salts (known as GRIM glasses) in these meteorites, sulfur is present in high abundance ({approx}1

Micro-XANES Determination Fe Speciation in Natural Basalts at Mantle-Relevant fO2

NASA Astrophysics Data System (ADS)

Fischer, R.; Cottrell, E.; Lanzirotti, A.; Kelley, K. A.

2007-12-01

We demonstrate that the oxidation state of iron (Fe3+/ΣFe) can be determined with a precision of ±0.02 (10% relative) on natural basalt glasses at mantle-relevant fO2 using Fe K-edge X-ray absorption near edge structure (XANES) spectroscopy. This is equivalent to ±0.25 log unit resolution relative to the QFM buffer. Precise determination of the oxidation state over this narrow range (Fe3+/ΣFe=0.06-0.30) and at low fO2 (down to QFM-2) relies on appropriate standards, high spectral resolution, and highly reproducible methods for extracting the pre-edge centroid position. We equilibrated natural tholeiite powder in a CO/CO2 gas mixing furnace at 1350°C from QFM-3 to QFM+2 to create six glasses of known Fe3+/ΣFe, independently determined by Mössbauer spectroscopy. XANES spectra were collected at station X26A at NSLS, Brookhaven Natl. Lab, in fluorescence mode (9 element Ge array detector) using both Si(111) and Si(311) monochromators. Generally, the energy position of the 1s→3d (pre-edge) transition centroid is the most sensitive monitor of Fe oxidation state using XANES. For the mixture of Fe oxidation states in these glasses and the resulting coordination geometries, the pre-edge spectra are best defined by two multiple 3d crystal field transitions. The Si(311) monochromator, with higher energy resolution, substantially improved spectral resolution for the 1s→3d transition. Dwell times of 5s at 0.1eV intervals across the pre-edge region yielded spectra with the 1s→3d transition peaks clearly resolved. The pre-edge centroid position is highly sensitive to the background subtraction and peak fitting procedures. Differences in fitting models result in small but significant differences in the calculated peak area of each pre-edge multiplet, and the relative contribution of each peak to the calculated centroid. We assessed several schemes and obtained robust centroid positions by simultaneously fitting the background with a damped harmonic oscillator (DHO

Progressive Oxidation of Pyrite in Five Bituminous Coal Samples: An As XANES and 57Fe Mossbauer Spectroscopic Study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kolker,A.; Huggins, F.

2007-01-01

Naturally occurring pyrite commonly contains minor substituted metals and metalloids (As, Se, Hg, Cu, Ni, etc.) that can be released to the environment as a result of its weathering. Arsenic, often the most abundant minor constituent in pyrite, is a sensitive monitor of progressive pyrite oxidation in coal. To test the effect of pyrite composition and environmental parameters on the rate and extent of pyrite oxidation in coal, splits of five bituminous coal samples having differing amounts of pyrite and extents of As substitution in the pyrite, were exposed to a range of simulated weathering conditions over a period ofmore » 17 months. Samples investigated include a Springfield coal from Indiana (whole coal pyritic S = 2.13 wt.%; As in pyrite = detection limit (d.l.) to 0.06 wt.%), two Pittsburgh coal samples from West Virginia (pyritic S = 1.32-1.58 wt.%; As in pyrite = d.l. to 0.34 wt.%), and two samples from the Warrior Basin, Alabama (pyritic S = 0.26-0.27 wt.%; As in pyrite = d.l. to 2.72 wt.%). Samples were collected from active mine faces, and expected differences in the concentration of As in pyrite were confirmed by electron microprobe analysis. Experimental weathering conditions in test chambers were maintained as follows: (1) dry Ar atmosphere; (2) dry O{sub 2} atmosphere; (3) room atmosphere (relative humidity {approx}20-60%); and (4) room atmosphere with samples wetted periodically with double-distilled water. Sample splits were removed after one month, nine months, and 17 months to monitor the extent of As and Fe oxidation using As X-ray absorption near-edge structure (XANES) spectroscopy and {sup 57}Fe Mossbauer spectroscopy, respectively. Arsenic XANES spectroscopy shows progressive oxidation of pyritic As to arsenate, with wetted samples showing the most rapid oxidation. {sup 57}Fe Mossbauer spectroscopy also shows a much greater proportion of Fe{sup 3+} forms (jarosite, Fe{sup 3+} sulfate, FeOOH) for samples stored under wet conditions, but much

Optimized Finite Difference Method for the Full-Potential XANES Simulations: Application to Molecular Adsorption Geometries in MOFs and Metal-Ligand Intersystem Crossing Transients.

PubMed

Guda, Sergey A; Guda, Alexander A; Soldatov, Mikhail A; Lomachenko, Kirill A; Bugaev, Aram L; Lamberti, Carlo; Gawelda, Wojciech; Bressler, Christian; Smolentsev, Grigory; Soldatov, Alexander V; Joly, Yves

2015-09-08

Accurate modeling of the X-ray absorption near-edge spectra (XANES) is required to unravel the local structure of metal sites in complex systems and their structural changes upon chemical or light stimuli. Two relevant examples are reported here concerning the following: (i) the effect of molecular adsorption on 3d metals hosted inside metal-organic frameworks and (ii) light induced dynamics of spin crossover in metal-organic complexes. In both cases, the amount of structural models for simulation can reach a hundred, depending on the number of structural parameters. Thus, the choice of an accurate but computationally demanding finite difference method for the ab initio X-ray absorption simulations severely restricts the range of molecular systems that can be analyzed by personal computers. Employing the FDMNES code [Phys. Rev. B, 2001, 63, 125120] we show that this problem can be handled if a proper diagonalization scheme is applied. Due to the use of dedicated solvers for sparse matrices, the calculation time was reduced by more than 1 order of magnitude compared to the standard Gaussian method, while the amount of required RAM was halved. Ni K-edge XANES simulations performed by the accelerated version of the code allowed analyzing the coordination geometry of CO and NO on the Ni active sites in CPO-27-Ni MOF. The Ni-CO configuration was found to be linear, while Ni-NO was bent by almost 90°. Modeling of the Fe K-edge XANES of photoexcited aqueous [Fe(bpy)3](2+) with a 100 ps delay we identified the Fe-N distance elongation and bipyridine rotation upon transition from the initial low-spin to the final high-spin state. Subsequently, the X-ray absorption spectrum for the intermediate triplet state with expected 100 fs lifetime was theoretically predicted.

Speciation of sulfur in humic and fulvic acids using X-ray absorption near-edge structure (XANES) spectroscopy

NASA Astrophysics Data System (ADS)

Morra, Matthew J.; Fendorf, Scott E.; Brown, Paul D.

1997-02-01

Sulfur species in soils and sediments have previously been determined indirectly using destructive techniques. A direct and more accurate method for S speciation would improve our understanding of S biogeochemistry. X-ray absorption near edge structure (XANES) spectroscopy was performed on purified humic and fulvic acids from terrestrial and aquatic environments. This methodology allows direct determination of S species using the relationship that exists with the energy required for core electron transitions and in some cases, correlation with additional spectral features. Soil, peat, and aquatic humic acids were dominated by sulfonates with an oxidation state of +5, but also contained ester-bonded sulfates with an oxidation state of +6. Leonardite humic acid contained ester-bonded sulfate and an unidentified S compound with an oxidation state of +4.0. In contrast, high-valent S in soil, peat, and aquatic fulvic acids was exclusively in the form of sulfonic acids. Reduced S species were also present in both humic and fulvic acids. XANES is a valuable method for the speciation of S in humic materials and of potential use in S speciation of unfractionated soils.

Fe K-Edge X-ray absorption near-edge spectroscopy (XANES) and X-ray diffraction (XRD) analyses of LiFePO4 and its base materials

NASA Astrophysics Data System (ADS)

Latif, C.; Negara, V. S. I.; Wongtepa, W.; Thamatkeng, P.; Zainuri, M.; Pratapa, S.

2018-03-01

XANES analysis has been performed with the aim of knowing the Fe oxidation state in a synthesized LiFePO4 and its base materials. XANES measurements were performed at SLRI on energy around Fe K-edge. An XRD analysis has also been performed with the aim of knowing the phase composition, lattice parameters and crystallite size of the LiFePO4 as well as the base materials. From the XRD analysis, it was found that the dominating phase in the iron sand sample was Fe3O4 and the only phase found after calcination was LiFePO4. The latter phase exhibited crystallite size of 100 nm and lattice parameters a = 10.169916 Å, b = 5.919674 Å, c = 4.627893 Å. Qualitative analysis of XANES data revealed that the oxidation number of Fe in the sample before calcination was greater than that after calcination and Fe in the natural iron sand, indicated by the E0 values of 7129.2 eV, 7120.6 eV and 7124.4 eV respectively.

Existence of Fe{sup 4+} ions in Co{sub 2.25}Fe{sub 0.75}O{sub 4} spinel ferrite confirmed from SXRD and XANES spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Panda, Manas Ranjan, E-mail: manasranjan056@gmail.com; Bhowmik, R. N.; Sinha, A. K.

2015-06-24

The Co{sub 2.25}Fe{sub 0.75}O{sub 4} ferrite composition has been prepared by chemical co-precipitation route. The as-prepared sample after annealing at 900°C in air formed single phase cubic spinel structure. Synchrotron X-ray diffraction and X-ray absorption near edge structure (XANES) measurements were used to study charge states of the cations in octahedral and tetrahedral sites of the cubic spinel structure. Raman spectra indicated normal cubic spinel structure. XANES data suggested the existence of Fe{sup 4+} ions in the spinel structure.

Correlated NanoSIMS, TEM, and XANES Studies of Presolar Grains

NASA Astrophysics Data System (ADS)

Groopman, Evan Edward

The objective of this thesis is to describe the correlated study of individual presolar grains via Nano-scale Secondary Ion Mass Spectrometry (NanoSIMS), Transmission Electron Microscopy (TEM), and Scanning Transmission X-ray Microscopy (STXM) utilizing X-ray Absorption Near Edge Structure (XANES), with a focus on connecting these correlated laboratory studies to astrophysical phenomena. The correlated isotopic, chemical, and microstructural studies of individual presolar grains provide the most detailed description of their formation environments, and help to inform astrophysical models and observations of stellar objects. As a part of this thesis I have developed and improved upon laboratory techniques for micromanipulating presolar grains and embedding them in resin for ultramicrotomy after NanoSIMS analyses and prior to TEM characterization. The new methods have yielded a 100% success rate and allow for the specific correlation of microstructural and isotopic properties of individual grains. Knowing these properties allows for inferences to be made regarding the condensation sequences and the origins of the stellar material that condensed to form these grains. NanoSIMS studies of ultramicrotomed sections of presolar graphite grains have revealed complex isotopic heterogeneities that appear to be primary products of the grains' formation environments and not secondary processing during the grains' lifetimes. Correlated excesses in 15N and 18O were identified as being carried by TiC subgrains within presolar graphite grains from supernovae (SNe). These spatially-correlated isotopic anomalies pinpoint the origin of the material that formed these grains: the inner He/C zone. Complex microstructures and isotopic heterogeneities also provide evidence for mixing in globular SN ejecta, which is corroborated by models and telescopic observations. In addition to these significant isotopic discoveries, I have also observed the first reported nanocrystalline core

STXM-XANES Analysis of Organic Matter in Dark Clasts and Halite Crystals in Zag and Monahans Meteorites

NASA Technical Reports Server (NTRS)

Kebukawa, Y.; Zolensky, M. E.; Fries, M.; Nakato, A.; Kilcoyne, A. L. D.; Takeichi, Y.; Suga, H.; Miyamoto, C.; Rahman, Z.; Kobayashi, K.;

Direct determination of oxidation state of gold deposits in metal-reducing bacterium Shewanella algae using X-ray absorption near-edge structure spectroscopy (XANES).

PubMed

Konishi, Yasuhiro; Tsukiyama, Takeshi; Saitoh, Norizoh; Nomura, Toshiyuki; Nagamine, Shinsuke; Takahashi, Yoshio; Uruga, Tomoya

2007-06-01

X-ray absorption near-edge structure spectroscopy (XANES) was successfully employed to determine the gold valence in the metal-reducing bacterium Shewanella algae after exposure to a 1 mM aqueous HAuCl4 solution for 10-120 min. XANES spectra revealed the oxidation state of gold in the bacterial cells to be Au(0) without any contribution from Au(III), demonstrating that S. algae cells can reduce AuCl4- ions to elemental gold. Transmission electron microscopy (TEM) and energy dispersive X-ray (EDX) analysis confirmed that gold nanoparticles 5-15 nm in size were deposited in the periplasmic space of the bacterial cells; a preferable, cell surface location for the easy recovery of biogenic nanoparticles.

Use of X-ray absorption near edge structure (XANES) to identify physisorption and chemisorption of phosphate onto ferrihydrite-modified diatomite.

PubMed

Xiong, Wenhui; Peng, Jian; Hu, Yongfeng

2012-02-15

This paper presents a novel technique integrating bulk-sensitive and surface-sensitive XANES methods to distinguish between physisorption and chemisorption for phosphate adsorption onto ferrihydrite-modified diatomite (FHMD). XANES P K-edge, L-edge, and Fe M-edge spectra were obtained for reference samples (K(2)HPO(4) and FePO(4)·2H(2)O) and test samples (phosphate adsorbed onto FHMD (FHMD-Ps) and Si-containing ferrihydrite (FHYD-Ps)). A resolvable pre-edge peak in the P K-edge spectra of FHMD-Ps and FHYD-Ps provided direct evidence for the formation of P-O-Fe(III) coordination and the occurrence of chemisorption. The resemblance between the P L-edge spectra of K(2)HPO(4) and FHMD-Ps and the marked difference between the spectra of FHMD-Ps and FePO(4)·2H(2)O indicated the intact existence of the adsorbate and the adsorbent. The similarity between Fe M-edge spectra of FHMD and FHMD-Ps and the difference between the spectra of FHMD-Ps and FePO(4)·2H(2)O confirmed the findings from P L-edge analyses. Therefore, chemisorption and physisorption coexisted during phosphate adsorption onto FHMD. Phosphate chemisorption occurred in the deeper zone of FHMD (from 50 nm to 5 μm); whereas physisorption occurred in the zone of FHMD shallower than 50 nm since the probing depth of XANES P K-edge method is 5 μm and that of P L-edge and Fe M-edge methods is 50 nm. Copyright © 2011 Elsevier Inc. All rights reserved.

Sequestration of Tellurium From Seawater by Ferromanganese Crusts: A XANES/EXAFS Perspective

NASA Astrophysics Data System (ADS)

Hein, J. R.; Bargar, J.; Koschinsky, A.; Dunham, R.; Halliday, A. N.

2007-12-01

Marine iron-oxyhydroxide/manganese-oxide crusts (Fe-Mn crusts) provide the richest known source of tellurium (Te). Te averages about 50 ppm in Fe-Mn crusts distributed globally, with concentrations locally up to 210 ppm. The sorption of Te onto Fe-Mn crusts likely controls the dominant redox species and concentration of Te in the global ocean (Hein et al., 2003). However, little is known about the mechanisms by which Te is sequestered by Fe-Mn crusts and Fe-Mn colloids in the water column, and then stabilized in the Fe/Mn oxyhydroxide/oxide framework. Two primary hypotheses are being tested: (a) Te(IV) is initially the predominant adsorbed species, which is subsequently oxidized on the Fe-oxyhydroxide and/or Mn oxide phases in natural systems and in sorption experiments. (b) Once oxidized, Te(VI) remains tightly bound to the Fe phase in Fe-Mn crusts as adsorbed surface complexes. These hypotheses are being examined by using the Stanford Synchrotron Radiation Laboratory's (SSRL) synchrotron-based XANES (x-ray absorption near-edge structure) spectroscopy to assess Te oxidation state in natural samples and samples in which Te(IV) and Te(VI) were sorbed onto synthetic and natural FeOOH and Mn oxides. EXAFS (extended x-ray absorption fine structure) spectroscopy is being used to resolve the local molecular-scale structure around Te in these same samples. Data have thus far been obtained for six Fe-Mn crusts from a variety of geographic locations and water depths of occurrence, with differing chemical compositions; and two model compounds, Te(IV) sorbed on FeOOH and Te(IV) sorbed on MnO2. XANES data show that for all six Fe-Mn crust samples, 85 to 100 percent of the Te occurs as Te(VI). For the model compounds, about 65 percent of the Te(IV) sorbed onto the MnO2 had oxidized to Te(VI) by the time (one week) the sample was analyzed, whereas Te sorbed onto FeOOH remained at about 100 percent Te(IV). The most striking result from the EXAFS data is that all spectra for the

The darkening of zinc yellow: XANES speciation of chromium in artist;s paints after light and chemical exposures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zanella, Luciana; Casadio, Francesca; Gray, Kimberly A.

2012-03-14

The color darkening of selected brushstrokes of the masterpiece A Sunday on La Grande Jatte - 1884 (by Georges Seurat) has been attributed to the alteration of the chromate pigment zinc yellow. The pigment originally displays a bright greenish-yellow color but may undergo, after aging, darkening to a dull, ocher tone. We used XANES to probe the oxidation state of Cr on paint reconstructions, and show that color changes are associated with the reduction of Cr(VI) to Cr(III). Paint mixtures containing the pigment and linseed oil to mimic mixtures used in La Grande Jatte were subjected to artificial aging inmore » the presence of light, SO{sub 2}, and variable air humidity - 50 and 90% relative humidity. High relative humidity led to the largest degree of Cr(VI) reduction whereas low relative humidity promoted light-induced alterations. These results are corroborated by visible reflectance measurements on the same laboratory samples and contribute to a better understanding of the chemical reactivity of chromate pigments, which are present in many historical works of art.« less

First Ti-XANES analyses of refractory inclusions from Murchison

DOE Office of Scientific and Technical Information (OSTI.GOV)

Simon, S.B.; Sutton, S.R.; Grossman, L.

2009-03-23

Ti valence in refractory phases is an important recorder of redox conditions in the early solar nebula. We report the valence of Ti in pyroxene, spinel and hibonite in spinel-hibonite and spinel-pyroxene inclusions and in a coarse hibonite grain. A system of solar composition is so reducing that Ti{sup 3+} and Ti{sup 4+} can coexist, making the valence of Ti a valuable indicator of f{sub O2} conditions during formation of nebular materials. The Ti{sup 3+}/Ti{sup 4+} ratios observed in the Ti-rich phases fassaite and rhoenite in coarse-grained refractory inclusions from CV3 chondrites have been shown to be quantitatively consistent withmore » formation in a gas of solar composition (log f{sub O2} = IW-6.8), but these are the only objects in chondrites for which this is the case. Here, we report the valence of Ti in various phases in refractory inclusions from the Murchison CM2 chondrite. The second-highest temperature, major-element-bearing phase predicted to condense from a gas of solar composition, hibonite (ideally CaAl{sub 12}O{sub 19}), can contain significant amounts of Ti, but the hibonite structure can have oxygen vacancies, so calculation of Ti valence from stoichiometry of electron probe analyses is not recommended for hibonite. To date, the only reported measurement of Ti valence in meteoritic hibonite was done by electron spin resonance, on coarse crystals from a Murchison hibonite-perovskite-melilite inclusion. Spinel and most of the pyroxene in CM inclusions contain too little Ti for derivation of Ti{sup 3+}/Ti{sup 4+} ratios from electron probe analyses. X-ray absorption near edge spectroscopy (XANES), however, allows determination of Ti valence in relatively Ti-poor phases. In the present work, we apply synchrotron microXANES to a large hibonite grain from Murchison and to spinel-hibonite (sp-hib) and spinel-pyroxene (sp-pyx) inclusions from Murchison, refractory materials whose Ti{sup 3+}/Ti{sup 4+} ratios have not been previously measured

Alternative difference analysis scheme combining R-space EXAFS fit with global optimization XANES fit for X-ray transient absorption spectroscopy.

PubMed

Zhan, Fei; Tao, Ye; Zhao, Haifeng

2017-07-01

Time-resolved X-ray absorption spectroscopy (TR-XAS), based on the laser-pump/X-ray-probe method, is powerful in capturing the change of the geometrical and electronic structure of the absorbing atom upon excitation. TR-XAS data analysis is generally performed on the laser-on minus laser-off difference spectrum. Here, a new analysis scheme is presented for the TR-XAS difference fitting in both the extended X-ray absorption fine-structure (EXAFS) and the X-ray absorption near-edge structure (XANES) regions. R-space EXAFS difference fitting could quickly provide the main quantitative structure change of the first shell. The XANES fitting part introduces a global non-derivative optimization algorithm and optimizes the local structure change in a flexible way where both the core XAS calculation package and the search method in the fitting shell are changeable. The scheme was applied to the TR-XAS difference analysis of Fe(phen) 3 spin crossover complex and yielded reliable distance change and excitation population.

Combining µXANES and µXRD mapping to analyse the heterogeneity in calcium carbonate granules excreted by the earthworm Lumbricus terrestris

PubMed Central

Brinza, Loredana; Schofield, Paul F.; Hodson, Mark E.; Weller, Sophie; Ignatyev, Konstantin; Geraki, Kalotina; Quinn, Paul D.; Mosselmans, J. Frederick W.

2014-01-01

The use of fluorescence full spectral micro-X-ray absorption near-edge structure (µXANES) mapping is becoming more widespread in the hard energy regime. This experimental method using the Ca K-edge combined with micro-X-ray diffraction (µXRD) mapping of the same sample has been enabled on beamline I18 at Diamond Light Source. This combined approach has been used to probe both long- and short-range order in calcium carbonate granules produced by the earthworm Lumbricus terrestris. In granules produced by earthworms cultured in a control artificial soil, calcite and vaterite are observed in the granules. However, granules produced by earthworms cultivated in the same artificial soil amended with 500 p.p.m. Mg also contain an aragonite. The two techniques, µXRD and µXANES, probe different sample volumes but there is good agreement in the phase maps produced. PMID:24365942

Triple point fcc-hcp-liquid in the Fe phase diagram determined by in-situ XANES diagnostic and post-mortem XRD and FIB-SEM analysis.

NASA Astrophysics Data System (ADS)

Morard, G.; Boccato, S.; Rosa, A. D.; Anzellini, S.; Miozzi Ferrini, F.; Laura, H.; Garbarino, G.; Harmand, M.; Guyot, F. J.; Boulard, E.; Kantor, I.; Irifune, T.; Torchio, R.

2017-12-01

Iron is the main constituent of planetary cores. Studying its phase diagram under high pressure is necessary to constrain properties of planetary interiors, and to model key parameters such as the generation of magnetic field. Though, strong controversy on the melting curve of pure Fe still remains. Recently, Aquilanti et al, (PNAS, 2015) reported a Fe melting curved based on XANES measurements which is in open disagreement with previous X-ray diffraction results (Anzellini et al, Science, 2013). Discrepancies in the melting temperature exceed several hundred degrees close to Mbar pressures, which may be related to differences in temperature measurement techniques, melting diagnostics, or to chemical reactions of the sample with the surrounding medium. We therefore performed new in situ high P/T XANES experiments on pure Fe (up to 115 GPa and 4000 K) at the ESRF beamline ID24, combining the energy dispersive absorption set up with laser heated diamond anvil cells. X-ray diffraction maps were collected from all recovered samples in order to identify and characterize laser-heated spots. The XANES melting criterion was further cross checked by analyzing the recovered sample textures using FIB cutting techniques and SEM imaging. We found systematically that low melting temperatures are related to the presence of Fe3C, implying that in those cases chemical reactions occurred during heating resulting in carbon contamination from the diamonds. These low melting points fall onto the melting line reported by Aquilanti et al, (2015). Uncontaminated points are in agreement with the melting curve of Anzellini et al, (2013) within their uncertainties. Moreover, this data set allowed us to refine the location of the triple point in the Fe phase diagram at 105 (±10) GPa and 3600 (±200) K, which may imply a small kink in the melting curve around this point. This refined Fe phase diagram could be then used to compute thermodynamic models for planetary cores.

Fischer–Tropsch Synthesis: XANES Spectra of Potassium in Promoted Precipitated Iron Catalysts as a Function of Time On-stream

DOE PAGES

Jacobs, Gary; Pendyala, Venkat Ramana Rao; Martinelli, Michela; ...

2017-06-06

XANES K-edge spectra of potassium promoter in precipitated Fe catalysts were acquired following activation by carburization in CO and as a function of time on-stream during the course of a Fischer–Tropsch synthesis run for a 100Fe:2K catalyst by withdrawing catalysts, sealed in wax product, for analysis. CO-activated and end-of-run spectra of the catalyst were also obtained for a 100Fe:5K catalyst. Peaks representing electronic transitions and multiple scattering were observed and resembled reference spectra for potassium carbonate or potassium formate. The shift in the multiple scattering peak to higher energy was consistent with sintering of potassium promoter during the course ofmore » the reaction test. The catalyst, however, retained its carbidic state, as demonstrated by XANES and EXAFS spectra at the iron K-edge, suggesting that sintering of potassium did not adversely affect the carburization rate, which is important for preventing iron carbides from oxidizing. This method serves as a starting point for developing better understanding of the chemical state and changes in structure occurring with alkali promoter.« less

Comparison of Nickel XANES Spectra and Elemental Maps from a Ureilite, a LL3.8 Ordinary Chondrite, Two Carbonaceous Chondrites and Two Large Cluster IDPs

NASA Technical Reports Server (NTRS)

Wirick, S.; Flynn, G. J.; Sutton, S.; Zolensky, M. E.

2014-01-01

Nickel in the extraterrestrial world is commonly found in both Fe-Ni sulfide and Fe-Ni met-al forms [1] and in the pure metal state in the interior of iron meteorites where it is not easily oxidized. Ni is also found in olivine, pyroxene and glasses and in some melts the partitioning of Ni between the olivines and glass is controlled by the amount of S in the melt [2]. Its most common valence state is Ni(2+) but Ni also occurs as Ni(0), Ni(+), and Ni(3+) and rarely as Ni(2-), Ni(1-) and Ni(4+) [3]. It's valence state in olivines is Ni(2+) in octa-hedral coordination on the M1 site and rarely on the M2 site.[4]. The chemical sensitivity of X-ray absorp-tion near-edge structure (XANES) spectroscopy is well established and can be used to determine not only va-lence states but also coordination sites [5]. We report here Ni XANES spectroscopy and elemental maps collected from 2 carbonaceous chondrites, 2 large clus-ter IDPs, 1 ureilite and 1 LL3 orginary chondrite.Using XANES it may be possible to find a common trait in the large cluster IDPs that will also be found in mete-orite samples.

Alternative difference analysis scheme combining R -space EXAFS fit with global optimization XANES fit for X-ray transient absorption spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhan, Fei; Tao, Ye; Zhao, Haifeng

Time-resolved X-ray absorption spectroscopy (TR-XAS), based on the laser-pump/X-ray-probe method, is powerful in capturing the change of the geometrical and electronic structure of the absorbing atom upon excitation. TR-XAS data analysis is generally performed on the laser-on minus laser-off difference spectrum. Here, a new analysis scheme is presented for the TR-XAS difference fitting in both the extended X-ray absorption fine-structure (EXAFS) and the X-ray absorption near-edge structure (XANES) regions.R-space EXAFS difference fitting could quickly provide the main quantitative structure change of the first shell. The XANES fitting part introduces a global non-derivative optimization algorithm and optimizes the local structure changemore » in a flexible way where both the core XAS calculation package and the search method in the fitting shell are changeable. The scheme was applied to the TR-XAS difference analysis of Fe(phen) 3spin crossover complex and yielded reliable distance change and excitation population.« less

Manganese speciation in Diplodon chilensis patagonicus shells: a XANES study

NASA Astrophysics Data System (ADS)

Soldati, A. L.; Vicente-Vilas, V.; Goettlicher, J.; Jacob, D. E.

2009-04-01

century, resolving the environmental signal annually and even seasonally (Soldati et al., 2008b). High resolution trace elemental analysis by LA-ICPMS and EPMA in the shells show that elements like Mg and Mn are related to the seasonal pattern and can be enriched along the organic-rich annual shell growth lines. Thus, these elements could possibly be bound organically instead of occupying a defined site in the crystal lattice of the calcium carbonate phase. LA-ICP-MS results show that Mn concentrations in these Diplodon shells range between 1000-300 g/g and 100-10 g/g and that the areas of enrichment are in the micrometer range. Raman and XRD measurements at high spatial resolution failed in recognizing whether the Mn is in carbonate solid solution or not. Therefore, speciation techniques like X-ray absorption fine structure (XAFS) spectroscopy with a high lateral resolution are required to address this question. Prior to XAFS spectroscopy the samples were mapped with the intensity of the Mn Kα fluorescence emission line in order to locate the Mn rich areas of interest. Because of the Mn concentrations in the sub % range the XAFS spectra at the positions of interest have been recorded in fluorescence mode using a 7 element Si(Li) detector. This study focuses on the near edge (XANES: X-ray absorption near edge structure) part of the spectra. For data evaluation, XANES spectra of reference substances were additionally measured in order to get first hints to Mn valence and bonding. As standards were used Mn and Mn rich carbonates, Mn oxides with Mn in different oxidation states, and Mn in organic compounds (Mn-porphyrin and Mn-acetate). The XAFS measurements have been carried out at the SUL-X beamline of the synchrotron radiation source ANKA of the Forschungszentrum Karlsruhe. Data evaluation is ongoing. References MEIBOM, A., CUIF, J.P., HOULBREQUE, F., MOSTEFAOUI, S., DAUPHIN, Y., MEIBOM; K.L. & DUNBAR, R. (2008). Compositional variations at ultra-structure length scales

In situ XANES and EXAFS Analysis of Redox Active Fe Center Ionic Liquids

DOE PAGES

Apblett, Christopher A.; Stewart, David M.; Fryer, Robert T.; ...

2015-10-23

We apply in situ X-Ray Absorption Near Edge Spectroscopy (XANES) and Extended X-Ray Absorption Fine Structure (EXAFS) techniques to a metal center ionic liquid undergoing oxidation and reduction in a three electrode spectroscopic cell. Furthermore, the determination of the extent of reduction under negative bias on the working electrode and the extent of oxidation are determined after pulse voltammetry to quiescence. While the ionic liquid undergoes full oxidation, it undergoes only partial reduction, likely due to transport issues on the timescale of the experiment. Nearest neighbor Fe-O distances in the fully oxidized state match well to expected values for similarlymore » coordinated solids, but reduction does not result in an extension of the Fe-O bond length, as would be expected from comparisons to the solid phase. Instead, little change in bond length is observed. Finally, we suggest that this may be due to a more complex interaction between the monodentate ligands of the metal center anion and the surrounding charge cloud, rather than straightforward electrostatics between the metal center and the nearest neighbor grouping.« less

HgL(3) XANES Study of Mercury Methylation in Shredded Eichhornia Crassipes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rajan, M.; Darrow, J.; Hua, M.

2009-05-21

Eichhornia crassipes (water hyacinth) is a non-native plant found in abundance in the Sacramento-San Joaquin River Delta (hereafter called Delta). This species has become a problem, clogging waterways and wetlands. Water hyacinth are also known to accumulate mercury. Recent attempts to curb its proliferation have included shredding with specialized boats. The purpose of this research is to better understand the ability of water hyacinth to phytoremediate mercury and to determine the effect of shredding and anoxic conditions on mercury speciation in plant tissue. In the field assessment, total mercury levels in sediment from the Dow Wetlands in the Delta weremore » found to be 0.273 {+-} 0.070 ppm Hg, and levels in hyacinth roots and shoots from this site were 1.17 {+-} 0.08 ppm and 1.03 {+-} 0.52 ppm, respectively, indicating bioaccumulation of mercury. Plant samples collected at this site were also grown in nutrient solution with 1 ppm HgCl{sub 2} under (1) aerobic conditions, (2) anaerobic conditions, and (3) with shredded plant material only. The greatest accumulation was found in the roots of whole plants. Plants grown in these conditions were also analyzed at Stanford Synchrotron Radiation Laboratory using Hg L{sub 3} X-ray Absorption Near Edge Spectroscopy (XANES), a method to examine speciation that is element-specific and noninvasive. Least-squares fitting of the XANES data to methylated and inorganic mercury(II) model compounds revealed that in plants grown live and aerobically, 5 {+-} 3% of the mercury was in the form of methylmercury, in a form similar to methylmercury cysteine. This percentage increased to 16 {+-} 4% in live plants grown anaerobically and to 22 {+-} 6% in shredded anaerobic plants. We conclude that shredding of the hyacinth plants and, in fact, subjection of plants to anaerobic conditions (e.g., as in normal decay, or in crowded growth conditions) increases mercury methylation. Mechanical removal of the entire plant is significantly

Roles of Pt and BaO in the Sulfation of Pt/BaO/Al2O3 Lean NOx Trap Materials: Sulfur K-edge XANES and Pt LIII XAFS Studies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, Do Heui; Kwak, Ja Hun; Szanyi, Janos

2008-02-28

The roles of barium oxide and platinum during the sulfation of Pt-BaO/Al2O3 lean NOx trap catalysts were investigated by S K edge XANES (X-ray absorption near-edge spectroscopy) and Pt LIII XAFS (X-ray absorption fine structure). All of the samples studied (Al2O3, BaO/Al2O3, Pt/Al2O3 and Pt-BaO/Al2O3) were pre-sulfated prior to the X-ray absorption measurements. It was found that barium oxide itself has the ability to directly form barium sulfate even in the absence of Pt and gas phase oxygen. In the platinum-containing samples, the presence of Pt-O species plays an important role in the formation of sulfate species. Even if bariummore » and aluminum sites are available for SO2 to form sulfate, for the case of the BaO(8)/Al2O3 sample, where the barium coverage is about 0.26 ML, S XANES spectroscopy results show that barium sulfates are preferentially produced over aluminum sulfates . When oxygen is absent from the gas phase, the sulfation route that involves Pt-O is eliminated after the initially present Pt-O species are completely consumed. In this case, formation of sulfates is suppressed unless barium oxide is also present. Pt LIII XAFS results show that the first coordination sphere around the Pt atoms in the Pt particles is dependent upon the redox nature of the gas mixture used during the sulfation process. Sulfation under reducing environments (e.g. SO2+H2) leads to formation of Pt-S bonds, while oxidizing conditions (e.g. SO2+O2) continue to show the presence of Pt-O bonds. In addition, the former condition was found to give rise to a higher degree of Pt sintering than the latter one. This result explains why samples sulfated under reducing conditions had lower NOx uptakes than those sulfated under oxidizing conditions. Therefore, our results provide needed information for the development of optimum practical operation conditions (e.g. sulfation or desulfation) for lean NOx trap catalysts that minimize deactivation by sulfur.« less

Roles of Pt and BaO in the Sulfation of Pt/BaO/Al2O3 Lean NOx Trap Materials: Sulfur K-edge XANES and Pt Llll XAFS Studies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim,D.; Kwak, J.; Szanyi, J.

2008-01-01

The roles of barium oxide and platinum during the sulfation of Pt-BaO/Al2O3 lean NOx trap catalysts were investigated by S K edge XANES (X-ray absorption near-edge spectroscopy) and Pt LIII XAFS (X-ray absorption fine structure). All of the samples studied [Al2O3, BaO(x; x = 8 or 20 wt %)/Al2O3, Pt(2.5 wt %)/Al2O3, and Pt(2 wt %)-BaO(x; x = 8 or 20 wt %)/Al2O3] were pre-sulfated prior to the X-ray absorption measurements. It was found that barium oxide itself has the ability to directly form barium sulfate even in the absence of Pt and gas-phase oxygen. In the platinum-containing samples, themore » presence of Pt-O species plays an important role in the formation of sulfate species. For the case of the BaO(8)/Al2O3 sample, where the barium coverage is about 0.26 ML, both baria and alumina phases are available for sulfation. S XANES results show that barium sulfates are formed preferentially over aluminum sulfates. When oxygen is absent from the gas phase, the sulfation route that involves Pt-O is eliminated after the initially present Pt-O species are completely consumed. In this case, formation of sulfates is suppressed unless barium oxide is also present. Pt LIII XAFS results show that the first coordination sphere around the Pt atoms in the Pt particles is dependent upon the gas mixture used during the sulfation process. Sulfation under reducing environments (e.g., SO2/H2) leads to formation of Pt-S bonds, while oxidizing conditions (e.g., SO2/O2) continue to show the presence of Pt-O bonds. In addition, a reducing environment was found to cause Pt sintering in greater extent than an oxidizing one. This result explains why samples sulfated under reducing conditions had lower NOx uptakes than those sulfated under oxidizing conditions. Therefore, our results provide needed information for the development of optimum practical operation conditions (e.g., sulfation or desulfation) for lean NOx trap catalysts that minimize deactivation by sulfur.« less

Structure of assemblies of metal nanowires in mesoporous alumina membranes studied by EXAFS, XANES, X-ray diffraction and SAXS.

PubMed

Benfield, Robert E; Grandjean, Didier; Dore, John C; Esfahanian, Hamid; Wu, Zhonghua; Kröll, Michael; Geerkens, Marcus; Schmid, Günter

2004-01-01

Mesoporous alumina membranes ("anodic aluminium oxide", or "AAO") are made by anodic oxidation of aluminium metal. These membranes contain hexagonal arrays of parallel non-intersecting cylindrical pores perpendicular to the membrane surface. By varying the anodisation voltage, the pore diameters are controllable within the range 5-250 nm. We have used AAO membranes as templates for the electrochemical deposition of metals within the pores to produce nanowires. These represent assemblies of one-dimensional quantum wires with prospective applications in electronic, optoelectronic and magnetic devices. Detailed characterisation of the structures of these nanowire assemblies on a variety of length scales is essential to understand their physical properties and evaluate their possible applications. We have used EXAFS, XANES, WAXS, high energy X-ray diffraction and SAXS to study their structure and bonding. In this paper we report the results of our studies of four different nanowire systems supported in AAO membranes. These are the ferromagnetic metals iron and cobalt, the superconducting metal tin, and the semiconductor gallium nitride. Iron nanowires in pores of diameter over the range 12 nm-72 nm are structurally very similar to bcc bulk iron. They have a strong preferred orientation within the alumina pores. Their XANES shows significant differences from that of bulk iron, showing that the electronic structure of the iron nanowires depends systematically on their diameter. Cobalt nanowires are composed of a mixture of hcp and fcc phases, but the ratio of the two phases does not depend in a simple way on the pore diameter or preparation conditions. In bulk cobalt, the fcc beta-phase is normally stable only at high temperatures. Strong preferred orientation of the c-axis in the pores was found. Tin nanowires in alumina membranes with pores diameters between 12 nm and 72 nm have a tetragonal beta-structure at ambient temperature and also at 80 K. Magnetic

Tetrahedrally Coordinated Fe3+ in Silicate Glasses: A Mossbauer, Iron K-edge XANES and Raman Spectroscopies Study

NASA Astrophysics Data System (ADS)

Cochain, B.; Neuville, D. R.; McCammon, C.; Henderson, G. S.; de Ligny, D.; Pinet, O.; Richet, P.

2009-05-01

In natural or industrial glasses, iron is the most abundant transition metal. A good knowledge of its redox equilibrium is important to better understand the chemical and structural evolution of magmas (crystallization, viscosity), and also to optimize vitrification processes and properties of iron-bearing glasses. To study the role of iron in silicate glasses and melts, we have used in a consistent manner the Mössbauer, iron K-edge XANES and Raman spectroscopies to investigate several series of silicate glasses as a function of redox state. The samples were selected to cover a wide composition range and to investigate the interactions of iron with two network forming cations, namely, Al3+ and B3+. The glasses investigated were synthesized at high temperature under various conditions of oxygen fugacity to achieve different redox ratios for each composition. Therefore, the iron redox state was varied from the most oxidized to the most reduced. Iron redox ratios were first determined by wet chemical analysis and in some cases by room temperature Mossbauer spectroscopy. This experimental method was also used to determine the local structure of iron of some of the investigated glasses. These results where compared to iron K-edge XANES/EXAFS spectroscopy results, which lead to the iron redox state and indicate that Fe2+ is in octahedral coordination whereas Fe3+ is in tetrahedral coordination. In addition, Raman spectroscopy gave us information on the network polymerization of glasses. Clearly changes in Raman spectra are visible with the evolution of iron redox ratio. For a given composition, we observed systematically, in the 800-1200 cm-1 envelope, which is sensitive to the environment of tetrahedrally coordinated cations, the growth of a band with the iron content and the oxidation state of the sample. The peak area of this band, which we attribute to vibrational modes involving tetrahedrally coordinated Fe3+, increases with the oxidation of the sample. This

Distribution and oxidation state of copper in the cell walls of treated wood examined by synchrotron based XANES and XFM

Treesearch

Samuel L. Zelinka; Grant T. Kirker; Joseph E. Jakes; Leandro Passarini; Barry Lai

2016-01-01

Recently, synchrotron based X-ray fluorescence microscopy (XFM) and X-ray absorption near edge spectroscopy (XANES) were used to examine the metal fastener corrosion in copper-treated wood. XFM is able to map the copper concentration in the wood with a spatial resolution of 0.5 µm and is able to quantify the copper concentration to within 0.05 µg cm-3...

Microanalysis (micro-XRF, micro-XANES, and micro-XRD) of a tertiary sediment using microfocused synchrotron radiation.

PubMed

Denecke, Melissa A; Somogyi, Andrea; Janssens, Koen; Simon, Rolf; Dardenne, Kathy; Noseck, Ulrich

2007-06-01

Micro-focused synchrotron radiation techniques to investigate actinide elements in geological samples are becoming an increasingly used tool in nuclear waste disposal research. In this article, results using mu-focus techniques are presented from a bore core section of a U-rich tertiary sediment collected from Ruprechtov, Czech Republic, a natural analog to nuclear waste repository scenarios in deep geological formations. Different methods are applied to obtain various, complementary information. Elemental and element chemical state distributions are obtained from micro-XRF measurements, oxidation states of As determined from micro-XANES, and the crystalline structure of selected regions are studied by means of micro-XRD. We find that preparation of the thin section created an As oxidation state artifact; it apparently changed the As valence in some regions of the sample. Results support our previously proposed hypothesis of the mechanism for U-enrichment in the sediment. AsFeS coating on framboid Fe nodules in the sediment reduced mobile groundwater-dissolved U(VI) to less-soluble U(IV), thereby immobilizing the uranium in the sediment.

EXAFS and XANES analysis of oxides at the nanoscale.

PubMed

Kuzmin, Alexei; Chaboy, Jesús

2014-11-01

Worldwide research activity at the nanoscale is triggering the appearance of new, and frequently surprising, materials properties in which the increasing importance of surface and interface effects plays a fundamental role. This opens further possibilities in the development of new multifunctional materials with tuned physical properties that do not arise together at the bulk scale. Unfortunately, the standard methods currently available for solving the atomic structure of bulk crystals fail for nanomaterials due to nanoscale effects (very small crystallite sizes, large surface-to-volume ratio, near-surface relaxation, local lattice distortions etc.). As a consequence, a critical reexamination of the available local-structure characterization methods is needed. This work discusses the real possibilities and limits of X-ray absorption spectroscopy (XAS) analysis at the nanoscale. To this end, the present state of the art for the interpretation of extended X-ray absorption fine structure (EXAFS) is described, including an advanced approach based on the use of classical molecular dynamics and its application to nickel oxide nanoparticles. The limits and possibilities of X-ray absorption near-edge spectroscopy (XANES) to determine several effects associated with the nanocrystalline nature of materials are discussed in connection with the development of ZnO-based dilute magnetic semiconductors (DMSs) and iron oxide nanoparticles.

Mn K-Edge XANES and Kβ XES Studies of Two Mn–Oxo Binuclear Complexes: Investigation of Three Different Oxidation States Relevant to the Oxygen-Evolving Complex of Photosystem II

PubMed Central

Visser, Hendrik; Anxolabéhère-Mallart, Elodie; Bergmann, Uwe; Glatzel, Pieter; Robblee, John H.; Cramer, Stephen P.; Girerd, Jean-Jacques; Sauer, Kenneth; Klein, Melvin P.; Yachandra, Vittal K.

2014-01-01

Two structurally homologous Mn compounds in different oxidation states were studied to investigate the relative influence of oxidation state and ligand environment on Mn K-edge X-ray absorption near-edge structure (XANES) and Mn Kβ X-ray emission spectroscopy (Kβ XES). The two manganese compounds are the di-μ-oxo compound [L′2MnIIIO2MnIVL′2](ClO4)3, where L′ is 1,10-phenanthroline (Cooper, S. R.; Calvin, M. J. Am. Chem. Soc. 1977, 99, 6623–6630) and the linear mono-μ-oxo compound [LMnIIIOMnIIIL](ClO4)2, where L− is the monoanionic N,N-bis(2-pyridylmethyl)-N′-salicylidene-1,2-diaminoethane ligand (Horner, O.; Anxolabéhère-Mallart, E.; Charlot, M. F.; Tchertanov, L.; Guilhem, J.; Mattioli, T. A.; Boussac, A.; Girerd, J.-J. Inorg. Chem. 1999, 38, 1222–1232). Preparative bulk electrolysis in acetonitrile was used to obtain higher oxidation states of the compounds: the MnIVMnIV species for the di-μ-oxo compound and the MnIIIMnIV and MnIVMnIV species for the mono-μ-oxo compound. IR, UV/vis, EPR, and EXAFS spectra were used to determine the purity and integrity of the various sample solutions. The Mn K-edge XANES spectra shift to higher energy upon oxidation when the ligand environment remains similar. However, shifts in energy are also observed when only the ligand environment is altered. This is achieved by comparing the di-μ-oxo and linear mono-μ-oxo Mn–Mn moieties in equivalent oxidation states, which represent major structural changes. The magnitude of an energy shift due to major changes in ligand environment can be as large as that of an oxidation-state change. Therefore, care must be exercised when correlating the Mn K-edge energies to manganese oxidation states without taking into account the nature of the ligand environment and the overall structure of the compound. In contrast to Mn K-edge XANES, Kβ XES spectra show less dependence on ligand environment. The Kβ1,3 peak energies are comparable for the di-μ-oxo and mono

Reduced As Components in Highly Oxidized Environments: Evidence from Full Spectral XANES Imaging using the Maia Massively Parallel Detector

DOE Office of Scientific and Technical Information (OSTI.GOV)

Etschmann, B.; Ryan, C; Brugger, J

2010-01-01

Synchrotron X-ray fluorescence (SXRF) and X-ray absorption spectroscopy (XAS) have become standard tools to measure element concentration, distribution at micrometer- to nanometer-scale, and speciation (e.g., nature of host phase; oxidation state) in inhomogeneous geomaterials. The new Maia X-ray detector system provides a quantum leap for the method in terms of data acquisition rate. It is now possible to rapidly collect fully quantitative maps of the distribution of major and trace elements at micrometer spatial resolution over areas as large as 1 x 5 cm{sup 2}. Fast data acquisition rates also open the way to X-ray absorption near-edge structure (XANES) imaging,more » in which spectroscopic information is available at each pixel in the map. These capabilities are critical for studying inhomogeneous Earth materials. Using a 96-element prototype Maia detector, we imaged thin sections of an oxidized pisolitic regolith (2 x 4.5 mm{sup 2} at 2.5 x 2.5 {micro}m{sup 2} pixel size) and a metamorphosed, sedimentary exhalative Mn-Fe ore (3.3 x 4 mm{sup 2} at 1.25 x 5 {micro}m{sup 2}). In both cases, As K-edge XANES imaging reveals localized occurrence of reduced As in parts of these oxidized samples, which would have been difficult to recognize using traditional approaches.« less

X-ray absorption spectroscopy: EXAFS (Extended X-ray Absorption Fine Structure) and XANES (X-ray Absorption Near Edge Structure)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alp, E.E.; Mini, S.M.; Ramanathan, M.

1990-04-01

The x-ray absorption spectroscopy (XAS) had been an essential tool to gather spectroscopic information about atomic energy level structure in the early decades of this century. It has also played an important role in the discovery and systematization of rare-earth elements. The discovery of synchrotron radiation in 1952, and later the availability of broadly tunable synchrotron based x-ray sources have revitalized this technique since the 1970's. The correct interpretation of the oscillatory structure in the x-ray absorption cross-section above the absorption edge by Sayers et. al. has transformed XAS from a spectroscopic tool to a structural technique. EXAFS (Extended X-raymore » Absorption Fine Structure) yields information about the interatomic distances, near neighbor coordination numbers, and lattice dynamics. An excellent description of the principles and data analysis techniques of EXAFS is given by Teo. XANES (X-ray Absorption Near Edge Structure), on the other hand, gives information about the valence state, energy bandwidth and bond angles. Today, there are about 50 experimental stations in various synchrotrons around the world dedicated to collecting x-ray absorption data from the bulk and surfaces of solids and liquids. In this chapter, we will give the basic principles of XAS, explain the information content of essentially two different aspects of the absorption process leading to EXAFS and XANES, and discuss the source and samples limitations.« less

Fischer-Tropsch Synthesis: XANES Investigation of Hydrogen Chloride Poisoned Iron and Cobalt-Based Catalysts at the K-Edges of Cl, Fe, and Co

DOE PAGES

Pendyala, Venkat Ramana Rao; Jacobs, Gary; Ma, Wenping; ...

2016-07-23

The effect of co-fed hydrogen chloride (HCl) in syngas on the performance of iron and cobalt-based Fischer-Tropsch (FT) catalysts was investigated in our earlier studies [ACS Catal. 5 (2015) 3124-3136 and DOE final report 2011; Catal. Lett. 144 (2014) 1127-1133]. For an iron catalyst, lower HCl concentrations (< 2.0 ppmw of HCl)) in syngas did not significantly affect the activity, whereas rapid deactivation occurred at higher concentrations (~20 ppmw). With cobalt catalysts, even low concentrations of HCl (100 ppbw) caused catalyst deactivation, and the deactivation rate increased with increasing HCl concentration in the syngas. The deactivation of the catalysts ismore » explained by the chloride being adsorbed on the catalyst surface to (1) block the active sites and/or (2) electronically modify the sites. In this study, XANES spectroscopy was employed to investigate HCl poisoning mechanism on the iron and cobalt catalysts. Cl K-edge normalized XANES results indicate that Cl is indeed present on the catalyst following HCl poisoning and exhibits a structure similar to the family of compounds MCl; two main peaks are formed, with the second peak consisting of a main peak and a higher energy shoulder. At the Co K and Fe K edges, the white line was observed to be slightly increased relative to the same catalyst under clean conditions. There is then the additional possibility that Cl adsorption may act in part to intercept electron density from the FT metallic function (e.g.,cobalt or iron carbide). If so, this would result in less back-donation and therefore hinder the scission of molecules such as CO.« less

How water molecules affect the catalytic activity of hydrolases--a XANES study of the local structures of peptide deformylase.

PubMed

Cui, Peixin; Wang, Yu; Chu, Wangsheng; Guo, Xiaoyun; Yang, Feifei; Yu, Meijuan; Zhao, Haifeng; Dong, Yuhui; Xie, Yaning; Gong, Weimin; Wu, Ziyu

2014-12-12

Peptide deformylase (PDF) is a prokaryotic enzyme that catalyzes the deformylation of nascent peptides generated during protein synthesis and water molecules play a key role in these hydrolases. Using X-ray absorption near edge spectroscopy (XANES) and ab initio calculations we accurately probe the local atomic environment of the metal ion binding in the active site of PDF at different pH values and with different metal ions. This new approach is an effective way to monitor existing correlations among functions and structural changes. We show for the first time that the enzymatic activity depends on pH values and metal ions via the bond length of the nearest coordinating water (Wat1) to the metal ion. Combining experimental and theoretical data we may claim that PDF exhibits an enhanced enzymatic activity only when the distance of the Wat1 molecule with the metal ion falls in the limited range from 2.15 to 2.55 Å.

XANES: observation of quantum confinement in the conduction band of colloidal PbS quantum dots

NASA Astrophysics Data System (ADS)

Demchenko, I. N.; Chernyshova, M.; He, X.; Minikayev, R.; Syryanyy, Y.; Derkachova, A.; Derkachov, G.; Stolte, W. C.; Piskorska-Hommel, E.; Reszka, A.; Liang, H.

2013-04-01

The presented investigations aimed at development of inexpensive method for synthesized materials suitable for utilization of solar energy. This important issue was addressed by focusing, mainly, on electronic local structure studies with supporting x-ray diffraction (XRD) and transmission electron microscopy (TEM) analysis of colloidal galena nano-particles (NPs) and quantum dots (QDs) synthesized using wet chemistry under microwave irradiation. Performed x-ray absorption near edge structure (XANES) analysis revealed an evidence of quantum confinement for the sample with QDs, where the bottom of the conduction band was shifted to higher energy. The QDs were found to be passivated with oxides at the surface. Existence of sulfate/sulfite and thiosulfate species in pure PbS and QDs, respectively, was identified.

The origin of luminescence from di[4-(4-diphenylaminophenyl)phenyl]sulfone (DAPSF), a blue light emitter: an X-ray excited optical luminescence (XEOL) and X-ray absorption near edge structure (XANES) study.

PubMed

Zhang, Duo; Zhang, Hui; Zhang, Xiaohong; Sham, Tsun-Kong; Hu, Yongfeng; Sun, Xuhui

2016-03-07

The electronic structure and optical properties of di[4-(4-diphenylaminophenyl)phenyl]sulfone (denoted as DAPSF), a highly efficient fluorophor, have been investigated using X-ray excited optical luminescence (XEOL) and X-ray absorption near edge structure (XANES) spectroscopy at excitation energies across the C, N, O K-edges and the sulfur K-edge. The results indicate that the blue luminescence is mainly related to the sulfur functional group.

From lapis lazuli to ultramarine blue: investigating Cennino Cennini’s recipe using sulfur K-edge XANES

DOE PAGES

Ganio, Monica; Pouyet, Emeline S.; Webb, Samuel M.; ...

2017-09-22

As one of the most desired and expensive artists’ materials throughout history, there has long been interest in studying natural lapis lazuli. The traditional method of extracting the blue component, lazurite, from lapis lazuli, as outlined in Cennini’s Il Libro dell’Arte, involves a lengthy purification process: (1) finely grind the rock; (2) mix with pine rosin, gum mastic, and beeswax; (3) massage in water to collect the lazurite. Repeating the process produces several grades of the pigment, typically referred to as ultramarine blue. Here, we investigate the sulfur environment within the aluminosilicate framework of lazurite during its extraction from lapismore » lazuli. The sulfur XANES fingerprint from samples taken at the different stages in Cennini’s extraction method were examined. All spectra contain a strong absorption peak at 2483 eV, attributable to sulfate present in the lazurite structure. However, intensity variations appear in the broad envelope of peaks between 2470 and 2475 eV and the pre-peak at 2469.1 eV, indicating a variation in the content of trisulfur (S 3 –˙) radicals. By studying the effect of each step of Cennini’s process, this study elucidates the changes occurring during the extraction and the variability within different grades of the precious coloring material. The increasing application of XANES to the study of artist’s materials and works of art motivated extending the research to assess the possibility of X-ray induced damage. Direct comparison of micro-focused and unfocused beam experiments suggests an increase of the S 3 –˙ radicals with prolonged exposure. Furthermore, analysis indicates that induced damage follows first-order kinetics, providing a first assessment on the acceptable amount of radiation exposure to define the optimal acquisition parameters to allow safe analyses of lapis lazuli and ultramarine pigments.« less

From lapis lazuli to ultramarine blue: investigating Cennino Cennini’s recipe using sulfur K-edge XANES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ganio, Monica; Pouyet, Emeline S.; Webb, Samuel M.

As one of the most desired and expensive artists’ materials throughout history, there has long been interest in studying natural lapis lazuli. The traditional method of extracting the blue component, lazurite, from lapis lazuli, as outlined in Cennini’s Il Libro dell’Arte, involves a lengthy purification process: (1) finely grind the rock; (2) mix with pine rosin, gum mastic, and beeswax; (3) massage in water to collect the lazurite. Repeating the process produces several grades of the pigment, typically referred to as ultramarine blue. Here, we investigate the sulfur environment within the aluminosilicate framework of lazurite during its extraction from lapismore » lazuli. The sulfur XANES fingerprint from samples taken at the different stages in Cennini’s extraction method were examined. All spectra contain a strong absorption peak at 2483 eV, attributable to sulfate present in the lazurite structure. However, intensity variations appear in the broad envelope of peaks between 2470 and 2475 eV and the pre-peak at 2469.1 eV, indicating a variation in the content of trisulfur (S 3 –˙) radicals. By studying the effect of each step of Cennini’s process, this study elucidates the changes occurring during the extraction and the variability within different grades of the precious coloring material. The increasing application of XANES to the study of artist’s materials and works of art motivated extending the research to assess the possibility of X-ray induced damage. Direct comparison of micro-focused and unfocused beam experiments suggests an increase of the S 3 –˙ radicals with prolonged exposure. Furthermore, analysis indicates that induced damage follows first-order kinetics, providing a first assessment on the acceptable amount of radiation exposure to define the optimal acquisition parameters to allow safe analyses of lapis lazuli and ultramarine pigments.« less

EXAFS/XANES studies of plutonium-loaded sodalite/glass waste forms

NASA Astrophysics Data System (ADS)

Richmann, Michael K.; Reed, Donald T.; Kropf, A. Jeremy; Aase, Scott B.; Lewis, Michele A.

2001-09-01

A sodalite/glass ceramic waste form is being developed to immobilize highly radioactive nuclear wastes in chloride form, as part of an electrochemical cleanup process. Two types of simulated waste forms were studied: where the plutonium was alone in an LiCl/KCl matrix and where simulated fission-product elements were added representative of the electrometallurgical treatment process used to recover uranium from spent nuclear fuel also containing plutonium and a variety of fission products. Extended X-ray absorption fine structure spectroscopy (EXAFS) and X-ray absorption near-edge spectroscopy (XANES) studies were performed to determine the location, oxidation state, and particle size of the plutonium within these waste form samples. Plutonium was found to segregate as plutonium(IV) oxide with a crystallite size of at least 4.8 nm in the non-fission-element case and 1.3 nm with fission elements present. No plutonium was observed within the sodalite in the waste form made from the plutonium-loaded LiCl/KCl eutectic salt. Up to 35% of the plutonium in the waste form made from the plutonium-loaded simulated fission-product salt may be segregated with a heavy-element nearest neighbor other than plutonium or occluded internally within the sodalite lattice.

Ionic gold in calcrete revealed by LA-ICP-MS, SXRF and XANES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lintern, Melvyn J.; Hough, Robert M.; Ryan, Chris G.

2009-04-02

Highly anomalous Au concentrations in calcrete were discovered in 1987 at the Bounty Gold Deposit, Western Australia. A strong correlation was noted between the Ca, Mg, Sr and Au in soil profiles which have not only attracted the interest of mineral explorers but also chemists, soil scientists, metallurgists and climatologists. Gold has been considered an inert element and so its strong association with the alkaline earth group of relatively mobile elements is both remarkable and intriguing. Despite widespread interest, there have been few published papers on the Au-calcrete phenomenon. Here, we present work conducted on calcareous soil samples from abovemore » the Bounty mineralization in Western Australia, prior to mining. Using SXRF (synchrotron X-ray fluorescence) and XANES (micro-X-ray absorption near-edge structure), we have shown for the first time the distribution of Au in calcrete and that it occurs in both particulate and ionic form. Much of the ionic Au associated with Br is found in a root tubule. The observations are consistent with an evapotranspiration model for the formation of Au in the calcrete; Au has been mobilized then precipitated as vadose water has been removed from the soil by trees and shrubs. While the association between Au and Ca is very strong in bulk sample analyses down the soil profile, other detailed analyses on sub-samples using wet chemical, LA-ICP-MS (laser ablation inductively coupled mass spectrometry) and SXRF techniques show that it is not apparent at the sub-millimeter scale. This suggests that the Au and Ca are behaving similarly but independently and they do not (at the {micro}m scale) co-precipitate with carbonate minerals. These results corroborate other studies that suggest biotic influences can affect the mobilization and distribution of Au in surficial materials. Water-extractable Au in calcrete has been reported previously and the ionic Au described in this study likely represents that soluble component. The

Probing Selenium-Ion Distributions and Changes in Redox-State at Biofilm/Mineral Interfaces by Coupling Long-period X-ray Standing Wave and XANES Measurements

NASA Astrophysics Data System (ADS)

Templeton, A. S.; Trainor, T. P.; Spormann, A. M.; Brown, G. E.

2002-12-01

due to a lower affinity for binding to the mineral surface. XANES spectra show that rapid reduction of selenate by B. cepacia to Se(IV) and Se(0) species subsequently results in a vertical segregation of Se species at the B. cepacia/alpha-Al2O3 interface. Elemental Se accumulates within the biofilm with the Se(VI), whereas selenite intermediates preferentially sorb to the underlying oxide surface.

Btu accounting: Showing results

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nelson, K.E.

1994-10-01

In the preceding article in this series last month, the author showed how to calculate the energy consumed to make a pound of product. To realize a payoff, however, the results must be presented in graphs or tables that clearly display what has happened. They must call attention to plant performance and ultimately lead to more efficient use of energy. Energy-consumption reporting is particularly valuable when viewed over a period of time. The author recommend compiling data annually and maintaining a ten-year performance history. Four cases are considered: individual plant performance; site performance for sites having more than one plant;more » company performance, for companies having more than one site; and performance based on product, for identical or similar products made at different plants or sites. Of these, individual plant performance is inherently the most useful. It also serves as the best basis for site, company and product performance reports. A key element in energy accounting is the relating of all energy consumption to a common basis. As developed last month in Part 1 in this series, the author chose Btu[sub meth] (i.e., Btu of methane equivalent, expressed as its higher heating value) for this purpose. It represents the amount of methane that would be needed to replace (in the case of fuels) or generate (in the case of steam and power) the energy being used.« less

Composition-driven Cu-speciation and reducibility in Cu-CHA zeolite catalysts: a multivariate XAS/FTIR approach to complexity† †Electronic supplementary information (ESI) available: Sample description and synthesis details, experimental setup for in situ XAS and FTIR spectroscopy, details on the MCR-ALS method, details on DFT-assisted XANES simulations, details on the determination of N pure by PCA, MCR-ALS results for downsized and upsized component spaces, additional information to support the assignment of theoretical XANES curves, details on EXAFS analysis, details on IR spectral deconvolution. See DOI: 10.1039/c7sc02266b Click here for additional data file.

PubMed Central

Martini, A.; Lomachenko, K. A.; Pankin, I. A.; Negri, C.; Berlier, G.; Beato, P.; Falsig, H.; Bordiga, S.; Lamberti, C.

2017-01-01

The small pore Cu-CHA zeolite is attracting increasing attention as a versatile platform to design novel single-site catalysts for deNOx applications and for the direct conversion of methane to methanol. Understanding at the atomic scale how the catalyst composition influences the Cu-species formed during thermal activation is a key step to unveil the relevant composition–activity relationships. Herein, we explore by in situ XAS the impact of Cu-CHA catalyst composition on temperature-dependent Cu-speciation and reducibility. Advanced multivariate analysis of in situ XANES in combination with DFT-assisted simulation of XANES spectra and multi-component EXAFS fits as well as in situ FTIR spectroscopy of adsorbed N2 allow us to obtain unprecedented quantitative structural information on the complex dynamics during the speciation of Cu-sites inside the framework of the CHA zeolite. PMID:29147509

X-Ray Absorption Near-Edge Structure (XANES) Spectroscopy Study of the Interaction of Silver Ions with Staphylococcus aureus, Listeria monocytogenes, and Escherichia coli

PubMed Central

Zanzen, Ulrike; Krishna, Katla Sai; Hormes, Josef

2013-01-01

Silver ions are widely used as antibacterial agents, but the basic molecular mechanism of this effect is still poorly understood. X-ray absorption near-edge structure (XANES) spectroscopy at the Ag LIII, S K, and P K edges reveals the chemical forms of silver in Staphylococcus aureus and Escherichia coli (Ag+ treated). The Ag LIII-edge XANES spectra of the bacteria are all slightly different and very different from the spectra of silver ions (silver nitrate and silver acetate), which confirms that a reaction occurs. Death or inactivation of bacteria was observed by plate counting and light microscopy. Silver bonding to sulfhydryl groups (Ag-S) in cysteine and Ag-N or Ag-O bonding in histidine, alanine, and dl-aspartic acid was detected by using synthesized silver-amino acids. Significantly lower silver-cysteine content, coupled with higher silver-histidine content, in Gram-positive S. aureus and Listeria monocytogenes cells indicates that the peptidoglycan multilayer could be buffering the biocidal effect of silver on Gram-positive bacteria, at least in part. Bonding of silver to phosphate groups was not detected. Interaction with DNA or proteins can occur through Ag-N bonding. The formation of silver-cysteine can be confirmed for both bacterial cell types, which supports the hypothesis that enzyme-catalyzed reactions and the electron transport chain within the cell are disrupted. PMID:23934494

SORPTION OF ARSENATE AND ARSENITE ON RUO2 X H2O: ANALYSIS OF SORBED PHASE OXIDATION STATE BY XANES IN ADVANCED PHOTON SOURCE ACTIVITY REPORT 2002

EPA Science Inventory

The sorption reactions of arsenate (As(V)) and arsenite (As(III)) on RuO₂ x H₂O were examined by X-ray Absorption Near Edge Spectroscopy (XANES) to elucidate the solid state speciation of sorbed As. At all pH values studied (pH 4-8), RuO₂ x H

Reactions of SO 2 on hydrated cement particle system for atmospheric pollution reduction: A DRIFTS and XANES study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ramakrishnan, Girish; Wu, Qiyuan; Moon, Juhyuk

An investigation of the adsorptive property of hydrated cement particle system for sulfur dioxide (SO2) removal was conducted. In situ and ex situ experiments using Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) and X-ray Absorption Near Edge Spectroscopy (XANES) characterization techniques were employed to identify surface species formed during the exposure to SO2. Oxidation of SO2 to sulfate and sulfite species observed during these experiments indicated dominant reaction pathways for SO2 reaction with concrete constituents, such as calcium hydroxide, which were also moderated by adsorption on porous surfaces of crushed aggregates. The impact of variable composition of concrete on itsmore » adsorption capacity and reaction mechanisms was also proposed in this work.« less

Chemical Heterogeneity of a Large Cluster IDP: Clues to its Formation History Using X-ray Fluorescence Mapping and XANES Spectroscopy

NASA Technical Reports Server (NTRS)

Wirick, S.; Flynn, G. J.; Sutton, S.; Zolensky, M. E.

2013-01-01

Chondritic porous IDPs may be among the most primitive objects found in our solar system [1]. They consist of many micron to submicron minerals, glasses and carbonaceous matter [2,3,4,5,6,7] with > 10(exp 4) grains in a 10 micron cluster [8]. Speculation on the environment where these fine grained, porous IDPs formed varies with possible sources being presolar dusty plasma clouds, protostellar condensation, solar asteroids or comets [4,6,9]. Also, fine grained dust forms in our solar system today [10,11]. Isotopic anomalies in some particles in IDPs suggest an interstellar source[4,7,12]. IDPs contain relic particles left from the dusty plasma that existed before the protostellar disk formed and other grains in the IDPs formed later after the cold dense nebula cloud collapsed to form our protostar and other grains formed more recently. Fe and CR XANES spectroscopy is used here to investigate the oxygen environment in a large (>50 10 micron or larger sub-units) IDP. Conclusions: Analyzing large (>50 10 micron or larger sub-units) CP IDPs gives one a view on the environments where these fine dust grains formed which is different from that found by only analyzing the small, 10 micron IDPs. As with cluster IDP L2008#5 [3], L2009R2 cluster #13 appears to be an aggregate of grains that sample a diversity of solar and perhaps presolar environments. Sub-micron, grain by grain measurement of trace element contents and elemental oxidation states determined by XANES spectroscopy offers the possibility of understanding the environments in which these grains formed when compared to standard spectra. By comparing thermodynamic modeling of condensates with analytical data an understanding of transport mechanisms operating in the early solar system may be attained.

XANES and Mg isotopic analyses of spinels in Ca-Al-rich inclusions: Evidence for formation under oxidizing conditions

NASA Astrophysics Data System (ADS)

Paque, J. M.; Sutton, S. R.; Simon, S. B.; Beckett, J. R.; Burnett, D. S.; Grossman, L.; Yurimoto, H.; Itoh, S.; Connolly, H. C.

2013-10-01

Ti valence measurements in MgAl2O4 spinel from calcium-aluminum-rich inclusions (CAIs) by X-ray absorption near-edge structure (XANES) spectroscopy show that many spinels have predominantly tetravalent Ti, regardless of host phases. The average spinel in Allende type B1 inclusion TS34 has 87% Ti+4. Most spinels in fluffy type A (FTA) inclusions also have high Ti valence. In contrast, the rims of some spinels in TS34 and spinel grain cores in two Vigarano type B inclusions have larger amounts of trivalent titanium. Spinels from TS34 have approximately equal amounts of divalent and trivalent vanadium. Based on experiments conducted on CAI-like compositions over a range of redox conditions, both clinopyroxene and spinel should be Ti+3-rich if they equilibrated with CAI liquids under near-solar oxygen fugacities. In igneous inclusions, the seeming paradox of high-valence spinels coexisting with low-valence clinopyroxene can be explained either by transient oxidizing conditions accompanying low-pressure evaporation or by equilibration of spinel with relict Ti+4-rich phases (e.g., perovskite) prior to or during melting. Ion probe analyses of large spinel grains in TS34 show that they are enriched in heavy Mg, with an average Δ25Mg of 4.25 ± 0.028‰, consistent with formation of the spinel from an evaporating liquid. Δ25Mg shows small, but significant, variation, both within individual spinels and between spinel and adjacent melilite hosts. The Δ25Mg data are most simply explained by the low-pressure evaporation model, but this model has difficulty explaining the high Ti+4 concentrations in spinel.

Solid-phase cadmium speciation in soil using L3-edge XANES spectroscopy with partial least-squares regression.

PubMed

Siebers, Nina; Kruse, Jens; Eckhardt, Kai-Uwe; Hu, Yongfeng; Leinweber, Peter

2012-07-01

Cadmium (Cd) has a high toxicity and resolving its speciation in soil is challenging but essential for estimating the environmental risk. In this study partial least-square (PLS) regression was tested for its capability to deconvolute Cd L(3)-edge X-ray absorption near-edge structure (XANES) spectra of multi-compound mixtures. For this, a library of Cd reference compound spectra and a spectrum of a soil sample were acquired. A good coefficient of determination (R(2)) of Cd compounds in mixtures was obtained for the PLS model using binary and ternary mixtures of various Cd reference compounds proving the validity of this approach. In order to describe complex systems like soil, multi-compound mixtures of a variety of Cd compounds must be included in the PLS model. The obtained PLS regression model was then applied to a highly Cd-contaminated soil revealing Cd(3)(PO(4))(2) (36.1%), Cd(NO(3))(2)·4H(2)O (24.5%), Cd(OH)(2) (21.7%), CdCO(3) (17.1%) and CdCl(2) (0.4%). These preliminary results proved that PLS regression is a promising approach for a direct determination of Cd speciation in the solid phase of a soil sample.

Micro-XANES Measurements on Experimental Spinels and the Oxidation State of Vanadium in Spinel-Melt Pairs

NASA Technical Reports Server (NTRS)

Righter, K.; Sutton, S.R.; Newville, M.

2004-01-01

Spinel can be a significant host phase for V as well as other transition metals such as Ni and Co. However, vanadium has multiple oxidation states V(2+), V(3+), V(4+) or V(5+) at oxygen fugacities relevant to natural systems. We do know that D(V) spinel/melt is correlated with V and TiO2 content and fO2, but the uncertainty of the oxidation state under the range of natural conditions has made elusive a thorough understanding of D(V) spinel/melt. For example, V(3+) is likely to be stable in spinels, based on exchange with Al in experiments in the CaO-MgO-Al2O3-SiO2 system. On the other hand, it has been argued that V(4+) will be stable across the range of natural oxygen fugacities in nature. In order to gain a better understanding of D(V) spinel/melt we have equilibrated spinel-melt pairs at controlled oxygen fugacities, between HM to NNO, where V is present in the spinel at natural levels (approx. 300 ppm V). These spinel-melt pairs were analyzed using micro-XANES at the Advanced Photon Source at Argonne National Laboratory. The new results will be used together with spinel compositional data (Ti, V content) and oxygen fugacity, to unravel the effects of these variables on D(V) spinel/melt.

Vanadium, sulfur, and iron valences in melt inclusions as a window into magmatic processes: A case study at Nyamuragira volcano, Africa

NASA Astrophysics Data System (ADS)

Head, Elisabet; Lanzirotti, Antonio; Newville, Matthew; Sutton, Stephen

2018-04-01

This study describes microscale sulfur (S), vanadium (V), and iron (Fe) K-edge X-ray absorption near edge structure (μ-XANES) spectroscopy measurements on olivine-hosted melt inclusions (MI) preserved in tephras (1986 and 2006) and lavas (1938 and 1948) erupted from Nyamuragira volcano (D.R. Congo, Africa). The S, V, and Fe spectroscopic data are used to constrain the evolution of oxygen fugacity (fO2) and sulfur speciation for the entrapped melts. Melt inclusions from lavas show evidence of post-entrapment crystallization and were thus reheated prior to μ-XANES analysis. The MI from tephra show no evidence of post-entrapment crystallization and were, therefore, not reheated. Sulfur, V, and Fe μ-XANES results from 1938, 1948, and 2006 eruptive materials are all similar within analytical uncertainty and provide similar average calculated melt fO2's based on XANES oxybarometry. However, olivine-hosted MI from the 1986 tephras yield significantly different S, V, and Fe XANES spectra when compared to MI from the other eruptions, with disagreement between calculated fO2's from the three valence state oxybarometers beyond the uncertainty of the calibration models. Their V μ-XANES spectra are also significantly more ordered and yield more reduced average V valence. The S μ-XANES spectra display a significantly more intense low-energy spectral resonance, which indicates differences in Fe-S bonding character, and greater variability in their measured sulfate content. These V and S spectroscopic features are best explained by crystallization of sub-micrometer magnetite and sulfide crystallites within the 1986 inclusions. The sensitivity of XANES spectroscopy to short-range order allows these crystallites to be recognized even though they are not easily detected by imaging analysis. This shows that V and S μ-XANES are potentially highly sensitive tools for identifying the presence of volumetrically minor amounts of spinel and sulfide within inclusions extracted from

Rapid reduction of MORB glass in piston cylinder experiments with graphite capsule - a XANES study

NASA Astrophysics Data System (ADS)

Ni, P.; Zhang, Y.; Fiege, A.; Newville, M.; Lanzirotti, A.

2017-12-01

Graphite capsules have been widely used in high-pressure, high-temperature experiments to prevent iron loss from iron-bearing samples. One common uncertainty with this experimental setup is the oxygen fugacity (fO2) inside the capsule imposed by the presence of graphite. As Holloway et al. (1992) pointed out, the use of graphite capsule places an upper limit on the fO2 in the experiment to be below CCO (graphite-CO-CO2 buffer). More recently, Medard et al. (2015) estimated the fO2 for their experiments using Pt-graphite or graphite-only capsules to be CCO-0.8. Despite the improved understanding on the fO2 using graphite capsule, the mechanism and kinetics of fO2 control in graphite capsule is still poorly understood. Such knowledge is especially important to understand whether equilibrium fO2 is reached in the sample when short experiment durations are needed (e.g. for kinetic experiments). In this study, MORB glasses after olivine dissolution (Chen and Zhang 2008) and plagioclase dissolution (Yu et al. 2016) experiments at 0.5 GPa and 1300 ºC with durations ranging from 10 s to 30 min are analyzed by XANES to obtain Fe3+/Fetotal profiles from their contact with the graphite capsule. The results show rapid Fe reduction away from the graphite-melt interface, causing a decrease of Fe3+/Fetotal from 12% to 3%. In a duration of 30 min, the 1200-µm-thick and 2000-µm-diameter basaltic glass reached near equilibrium in its iron oxidation state, with Fe3+/Fetotal ranging from 3% to 4% throughout the run product. The equilibrium Fe3+/Fetotal ratio corresponds to an fO2 of CCO-1.4, which is within error compared to the result in Medard et al. (2015). Even in the shortest experiment with an effective duration of only 10 s, a 60 µm long reduction profile was detected. Such a rapid fO2 change can be explained by rapid H2 diffusion in melt and its reaction with ferric iron: H2+Fe2O3=2FeO+H2O, which is also supported by the H2O concentration profiles measured along the

Combination of first-principles molecular dynamics and XANES simulations for LiCoO2-electrolyte interfacial reactions in a lithium-ion battery

NASA Astrophysics Data System (ADS)

Tamura, Tomoyuki; Kohyama, Masanori; Ogata, Shuji

2017-07-01

We performed a first-principles molecular dynamics (FPMD) simulation of the interfacial reactions between a LiCoO2 electrode and a liquid ethylene carbonate (EC) electrolyte. For configurations during the FPMD simulation, we also performed first-principles Co K-edge x-ray absorption near-edge structure (XANES) simulations, which can properly reproduce the bulk and surface spectra of LiCoO2. We observed strong absorption of an EC molecule on the LiCoO2 {110} surface, involving ring opening of the molecule, bond formation between oxygen atoms in the molecule and surface Co ions, and emission of one surface Li ion, while all the surface Co ions remain Co3 +. The surface Co ions having the bond with an oxygen atom in the molecule showed remarkable changes in simulated K-edge spectra which are similar to those of the in situ observation under electrolyte soaking [D. Takamatsu et al., Angew. Chem., Int. Ed. 51, 11597 (2012), 10.1002/anie.201203910]. Thus, the local environmental changes of surface Co ions due to the reactions with an EC molecule can explain the experimental spectrum changes.

Coordination chemistry of titanium (IV) in silicate glasses and melts: IV. XANES studies of synthetic and natural volcanic glasses and tektites at ambient temperature and pressure

NASA Astrophysics Data System (ADS)

Farges, François; Brown, Gordon E.

1997-05-01

The coordination environment of Ti(IV) in seven natural and synthetic glasses of basaltic, trachytic, rhyolitic composition as well as four tektites has been studied using high-resolution Ti K-edge x-ray absorption near edge structure (XANES) spectroscopy at ambient temperature and pressure. Pre-edge features of Ti K-edge XANES spectra for these glasses suggest that [5]Ti is the dominant Ti coordination in all volcanic glasses. However, in the less polymerized glasses studied (basaltic and trachytic), [6]Ti is also important (30-50% of the total Ti) but [4]Ti was not detected. In contrast, [4]Ti is important in the most polymerized glasses (rhyolites and tektites) (from 30 to 60% of the total Ti depending on NBO/T) with [6]Ti below the detection level (≈10 at%). The local structure around Ti in the natural volcanic glasses is similar to that observed in compositionally similar synthetic silicate glasses and also in Ti-bearing silicate glass and melts with simpler compositions. The presence of F, Cl, and H 2O does not appear to affect the coordination of Ti, based on Ti K-edge XANES measurements of natural glasses bearing these volatile components. In contrast, the presence of nonbridging oxygens (produced by network modifiers) favors [5]Ti in these glass/melts. In parallel, [4]Ti is important when nonbridging oxygens are at small concentrations (NBO/T < 0.1). [6]Ti is detected (i.e., when present >10% of the total Ti) when alkaline-earths are dominant over alkalis, in agreement with bond-valence predictions for Ti-bearing silicate glass/melts below TiO 2 saturation. The abundance of [5]Ti in these silicate glasses (and presumably their melts) is in sharp contrast with the rarity of this Ti coordination state in common rock-forming minerals. Titanium cannot readily enter the structure of most rock-forming minerals, because it is present dominantly as titanyl-bearing ( [5]TiO) units in most natural magmas. In contrast, [6]Ti and [4]Ti (present, respectively, in

Following the movement of Cu ions in a SSZ-13 zeolite during dehydration, reduction and adsorption: a combined in situ TP-XRD, XANES/DRIFTS study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kwak, Ja Hun; Varga, Tamas; Peden, Charles HF

2014-05-05

Cu-SSZ-13 has been shown to possess high activity and superior N2 formation selectivity in the selective catalytic reduction of NOx under oxygen rich conditions. Here, a combination of synchrotron-based (XRD and XANES) and vibrational (DRIFTS) spectroscopy tools have been used to follow the changes in the location and coordination environment of copper ions in a Cu-SSZ-13 zeolite during calcinations, reduction with CO, and adsorption of CO and H2O. XANES spectra collected during these procedures provides critical information not only on the variation in the oxidation state of the copper species in the zeolite structure, but also on the changes inmore » the coordination environment around these ions as they interact with the framework, and with different adsorbates (H2O and CO). Time-resolved XRD data indicate the movement of copper ions and the consequent variation of the unit cell parameters during dehydration. DRIFT spectra provide information about the adsorbed species present in the zeolite, as well as the oxidation states of and coordination environment around the copper ions. A careful analysis of the asymmetric T-O-T vibrations of the CHA framework perturbed by copper ions in different coordination environments proved to be especially informative. The results of this study will aid the identification of the location, coordination and oxidation states of copper ions obtained during in operando catalytic studies. Financial support was provided by the US Department of Energy (DOE), Office of Energy Efficiency and Renewable Energy, Vehicle Technologies Program. Part of this work (sample preparation) was performed in the Environmental Molecular Sciences Laboratory (EMSL) at Pacific Northwest National Laboratory (PNNL). The EMSL is a national scientific user facility supported by the US DOE, Office of Biological and Environmental Research. PNNL is a multi-program national laboratory operated for the US DOE by Battelle. All of the spectroscopy work reported here

Experimental and theoretical studies of dipole and quadrupole contributions to the vanadium K-edge XANES for VOPO4.2H2O xerogel

NASA Astrophysics Data System (ADS)

Poumellec, B.; Kraizman, V.; Aifa, Y.; Cortès, R.; Novakovich, A.; Vedrinskii, R.

1998-09-01

Angular dependence of the vanadium K-edge x-ray appearance near-edge structure (XANES) for the VOPO4.2H2O xerogel is thoroughly studied both experimentally and theoretically. The main attention is paid to the pre-edge fine structure (PEFS) of the spectra which was shown earlier to be a useful tool for the atomic short order investigations. Good quantitative agreement between theory and experiment obtained for both dipole and quadrupole contributions to the spectra proves validity of the calculation method developed and enables us to ascertain the nature of all the features in the PEFS's. The p-d mixture effect due to distortion of the central coordination octahedron and the quadrupole transitions are proved to be the only mechanisms responsible for the PEFS formation in the case considered. We show that in order to achieve quantitative agreement between experimental and theoretical spectra, it is necessary to include the effect of atomic vibrations, which makes the forbidden transitions to molecular orbitals of the central octahedron (MOCO's) dipole allowed, and to take into account deviation of the crystal layers from the substrate plane, which is not a single crystal but a texture.

Magnetite Crisis in Miniature: Vanadium, Sulfur, and Iron Valence State Measurements in Melt Inclusions from Nyamuragira Volcano (D.R. Congo, Africa)

NASA Astrophysics Data System (ADS)

Head, E.; Lanzirotti, A.; Sutton, S.; Newville, M.

2017-12-01

Sulfur (S), vanadium (V), and iron (Fe) K-edge micro-X-ray absorption near edge structure (micro-XANES) spectroscopy of melt inclusions (MI) from Nyamuragira volcano (D.R. Congo, Africa) shows that diffusive loss of H from olivine-hosted melt inclusions may lead to crystallization of submicron magnetite and sulfide crystallites that are imperceptible petrographically or via electron microscopy. Micro-XANES was used to constrain the evolution of oxygen fugacity (fO2) and sulfur speciation for MI preserved in Nyamuragira tephra (1986 and 2006) and lava (1938 and 1948). The S, V, and Fe valence state oxybarometry for 1938, 1948, and 2006 MI are all consistent with equilibration at FMQ-1, and sulfur in MI from these three eruptions are sulfide-dominated (< 9% sulfate). However, Fe and V micro-XANES data for 1986 MI appear to be more reduced by 1-2 log units, while S micro-XANES data indicate more variable sulfate content. The 1986 results are best explained by diffusive loss of H from the entrapped melt. Submicron magnetite forms as Fe oxidizes in the melt in response to the loss of H, and V strongly partitions into these magnetite nanolites due to its compatibility. The nanolites are consistently analyzed within the beam volume and, thus, the measured V XANES appears more ordered. Magnetite crystallization from the melt also triggers precipitation of crystalline FeS phases within the inclusion, leading to a more ordered S XANES spectra as well. This may suggest a different magma storage history for the 1986 eruption compared to the others. Results demonstrate that coupled S, V, and Fe micro-XANES analysis of alkalic MI can provide accurate measures of the fO2 of entrapped melts, and that S and V micro-XANES spectroscopy are potentially highly sensitive tools for identifying diffusive water loss in olivine-hosted MIs.

A X-Ray Absorption Study of Transition Metal Oxides

NASA Astrophysics Data System (ADS)

Bunker, Grant Byrd

This work is an experimental and theoretical study of the x-ray absorption near-edge structure of selected 3d transition metal compounds. The goal is to understand the physical mechanisms of XANES, using the competing multiple scattering (MS) and single scattering formalisms of Durham et al, and of Muller and Schaich, respectively. Careful experimental measurements of the K edge absorption of Mn oxides and KMnO(,4) at 300(DEGREES)K, 140(DEGREES)K and 80(DEGREES)K were made. These materials were chosen because they exhibit a variety of structures and oxidation states. Computer simulations of the XANES using the formalisms above were also performed. The experimental results show that atoms beyond the first coordination shell significantly affect the XANES near and above the edge; in particular the temperature dependent XANES and the "white line" in MnO establish this. We conclude that XANES, like EXAFS, is primarily sensitive to geometrical structure, except within about 1 Rydberg of the Fermi level. Two types of MS are distinguished: type 1 (forward scattering) is important in both XANES and EXAFS regions; type 2 (large angle scattering) is important only at and below the edge. MS of the photoelectron among the first shell Oxygen atoms in KMnO(,4) is observed experimentally, and found to become negligible above (DBLTURN) 1 Rydberg past the edge. The sharp features in XANES are primarily due to scattering from distant atoms, rather than localized states, except below the edge. This is supported by the observation that (alpha)-Mn(,2)O(,3) and Mn(,3)O(,4) spectra are nearly identical; their structures are the same, but the average oxidation states are different. We find the bond length strongly affects the edge position and the intensity of the 3d absorption in tetrahedrally coordinated transition metals. Other new results are the first shell EXAFS amplitude in MnO shows an anomalous energy dependence, which apparently cannot be explained by current theory. A new

13. DETAIL VIEW OF BUTTRESS 4 SHOWING THE RESULTS OF ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

13. DETAIL VIEW OF BUTTRESS 4 SHOWING THE RESULTS OF POOR CONSTRUCTION WORK. THOUGH NOT A SERIOUS STRUCTURAL DEFICIENCY, THE 'HONEYCOMB' TEXTURE OF THE CONCRETE SURFACE WAS THE RESULT OF INADEQUATE TAMPING AT THE TIME OF THE INITIAL 'POUR'. - Hume Lake Dam, Sequioa National Forest, Hume, Fresno County, CA

14. DETAIL VIEW OF BUTTRESS 4 SHOWING THE RESULTS OF ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

14. DETAIL VIEW OF BUTTRESS 4 SHOWING THE RESULTS OF INADEQUATE TAMPING. THE SIZE OF THE GRANITE AGGREGATE USED IN THE DAMS CONCRETE IS CLEARLY SHOWN. - Hume Lake Dam, Sequioa National Forest, Hume, Fresno County, CA

Chemical forms of sulfur in geological and archeological asphaltenes from Middle East, France, and Spain determined by sulfur K- and L-edge X-ray absorption near-edge structure spectroscopy

NASA Astrophysics Data System (ADS)

Sarret, Géraldine; Connan, Jacques; Kasrai, Masoud; Bancroft, G. Michael; Charrié-Duhaut, Armelle; Lemoine, Sylvie; Adam, Pierre; Albrecht, Pierre; Eybert-Bérard, Laurent

1999-11-01

Asphaltene samples extracted from archeological and geological bitumens from the Middle East, France, and Spain were studied by sulfur K- and L-edge X-ray absorption near-edge structure (XANES) spectroscopy in combination with isotopic analyses (δ 13C and δD). Within each series, the samples were genetically related by their δ 13C values. The gross and elemental composition and the δD values were used to characterize the weathering state of the samples. Sulfur K- and L-edge XANES results show that in all the samples, dibenzothiophenes are the dominant forms of sulfur. In the least oxidized asphaltenes, minor species include disulfides, alkyl and aryl sulfides, and sulfoxides. With increasing alteration the proportion of oxidized sulfur (sulfoxides, sulfones, sulfonates and sulfates) increases, whereas the disulfide and sulfide content decreases. This evolution is observed in all the series, regardless of the origin of the asphaltenes. This work illustrates the advantages of XANES spectroscopy as a selective probe for determining sulfur speciation in natural samples. It also shows that S K- and L-edge XANES spectroscopy are complementary for identifying the oxidized and reduced forms of sulfur, respectively.

D-DIA High Pressure Facility at the Australian Synchrotron: First Results

NASA Astrophysics Data System (ADS)

Rushmer, T. A.; Wykes, J.

2016-12-01

The recent acquisition of a D-DIA type cubic multi-anvil apparatus for use at the Australian Synchrotron provides exciting opportunities for conducting a wide range of in situ experiments at high pressure and temperature. The MQ-AS D-DIA apparatus was designed as a mobile system capable of moving between beamlines. The apparatus was installed at the XAS beamline in May, 2016 and experiments performed since then include 1) a proof-of-concept in situ U and Th L3-edge XANES study of MORB liquid; 2) a proof-of-concept falling sphere viscometry of silicate liquid; and 3) room temperature transmission XANES in the high pressure assembly at energies as low as the Ga K-edge and as high as Sb K-edge. The MQ-AS D-DIA apparatus comprises a 350 ton ram in a four post press frame. The press is installed on a positioning table with motorised X-Y-Z-θ axes capable of positioning accuracy of <10 microns. The Rockland Research D-DIA module is equipped with 4 mm and 6 mm TEL anvils, capable of producing maximum sample pressure of 6 GPa. Stepper motors drive the main and differential ram hydraulic pressure generators in a control loop closed by pressure transducers. Samples are heated by graphite resistance furnaces driven by a Eurotherm 3504 PID controller driving a 5 V 200 A step down transformer via a phase angle power controller. Temperature is monitored via a thermocouple and power by true RMS voltage and current transducers. The XAS beamline at the Australian Synchrotron comprises a 1.9 T 40 pole wiggler, a bendable collimating mirror, a Si(111) / Si(311) DCM and a toroidal focussing mirror. Accessible energies are 5-34 keV with photon fluxes of 108-1012 photons/sec at the sample. Here we present an overview of our recent results. More detailed results of the in situ U and Th L3-edge XANES study are presented by Mallmann et al. (this meeting). In situ imaging and XRD experiments with the D-DIA apparatus on the AS Imaging and Medical Beamline are planned for the coming year.

Direct determination of europium valence state by XANES in extraterrestrial merrillite: Implications for REE crystal chemistry and martian magmatism

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shearer, C.K.; Papike, J.J.; Burger, P.V.

2012-03-15

The relative proportion of divalent and trivalent Eu has proven to be a useful tool for estimating f{sub O{sub 2}} in various magmatic systems. However, in most cases, direct determination of the Eu valence state has not been made. In this study, direct determination of Eu valence by XANES and REE abundance in merrillite provide insights into the crystal chemistry of these phosphates and their ability to record conditions of magmatism. Merrillite strongly prefers Eu{sup 3+} to Eu{sup 2+}, with the average valence state of Eu ranging between 2.9 and 3 over approximately six orders of magnitude in f{sub O{submore » 2}}. The dramatic shift in the REE patterns of merrillite in martian basaltic magmas, from highly LREE-depleted to LREE-enriched, parallels many other trace element and isotopic variations and reflects the sources for these magmas. The behavior of REE in the merrillite directly reflects the relationship between the eightfold-coordinated Ca1 site and adjacent sixfold Na and tetrahedral P sites that enables charge balancing through coupled substitutions.« less

Nanoparticulate mackinawite formation; a stopped and continuous flow XANES and EXAFS investigation

NASA Astrophysics Data System (ADS)

Butler, I. B.; Bell, A. M.; Charnock, J. M.; Rickard, D.; Vaughan, D. J.; Oldroyd, A.

2009-12-01

The sequestration of sulfur and iron within sedimentary iron sulfides, and ultimately as pyrite, is a major sink in global biogeochemical cycles of those elements and has impacts on global carbon and oxygen cycles. The formation of the metastable black iron (II) monosulfide mackinawite is a key process because mackinawite forms in aqueous solutions where the Fe(II) and S(-II) IAP exceeds mackinawite’s Ksp. Mackinawite is the first formed iron sulfide phase, a consequence of Ostwald’s step rule and is a reactant phase during the formation of thermodynamically stable sedimentary iron sulfide minerals such as pyrite. The reaction of dissolved Fe(II) and sulfide is extremely fast and reactions in the environmentally significant near-neutral pH range tend to completion in <1 second. We have combined stopped and continuous flow techniques with X-ray absorption spectroscopy to evaluate the products of the fast precipitation kinetics of mackinawite over millisecond timescales. EXAFS spectra and data collected during flow experiments were compared with those from a well characterised freeze-dried nanoparticulate mackinawite standard and with published data. Published work has used Rietveld crystal structure refinement to determine bond distances of 2.2558 and 2.5976Å for Fe-S and Fe-Fe respectively. In our experiments Fe K edge XANES is consistent with tetrahedrally coordinated Fe in the precipitated sulfide phase. EXAFS data show that local Fe-S and Fe-Fe coordination and interatomic distances (Fe-S = 2.24Å; Fe-Fe = 2.57Å) are consistent with those determined for the standard mackinawite and published data. The coordination and spacing are developed in the precipitated phase after <10ms reaction at pH5, and considerably faster in experiments at near neutral to alkaline pH. No evidence for phases structurally intermediate between hexaqua Fe(II) and precipitated mackinawite was observed. Aqueous FeS° cluster complexes previously identified as intermediates during

Gun Shows and Gun Violence: Fatally Flawed Study Yields Misleading Results

PubMed Central

Hemenway, David; Webster, Daniel; Pierce, Glenn; Braga, Anthony A.

2010-01-01

A widely publicized but unpublished study of the relationship between gun shows and gun violence is being cited in debates about the regulation of gun shows and gun commerce. We believe the study is fatally flawed. A working paper entitled “The Effect of Gun Shows on Gun-Related Deaths: Evidence from California and Texas” outlined this study, which found no association between gun shows and gun-related deaths. We believe the study reflects a limited understanding of gun shows and gun markets and is not statistically powered to detect even an implausibly large effect of gun shows on gun violence. In addition, the research contains serious ascertainment and classification errors, produces results that are sensitive to minor specification changes in key variables and in some cases have no face validity, and is contradicted by 1 of its own authors’ prior research. The study should not be used as evidence in formulating gun policy. PMID:20724672

Gun shows and gun violence: fatally flawed study yields misleading results.

PubMed

Wintemute, Garen J; Hemenway, David; Webster, Daniel; Pierce, Glenn; Braga, Anthony A

2010-10-01

A widely publicized but unpublished study of the relationship between gun shows and gun violence is being cited in debates about the regulation of gun shows and gun commerce. We believe the study is fatally flawed. A working paper entitled "The Effect of Gun Shows on Gun-Related Deaths: Evidence from California and Texas" outlined this study, which found no association between gun shows and gun-related deaths. We believe the study reflects a limited understanding of gun shows and gun markets and is not statistically powered to detect even an implausibly large effect of gun shows on gun violence. In addition, the research contains serious ascertainment and classification errors, produces results that are sensitive to minor specification changes in key variables and in some cases have no face validity, and is contradicted by 1 of its own authors' prior research. The study should not be used as evidence in formulating gun policy.

Study of the Warm Dense Matter with XANES spectroscopy - Applications to planetary interiors

NASA Astrophysics Data System (ADS)

Denoeud, Adrien

With the recent discovery of many exoplanets, modelling the interior of these celestial bodies is becoming a fascinating scientific challenge. In this context, it is crucial to accurately know the equations of state and the macroscopic and microscopic physical properties of their constituent materials in the Warm Dense Matter regime (WDM). Moreover, planetary models rely almost exclusively on physical properties obtained using first principles simulations based on density functional theory (DFT) predictions. It is thus of paramount importance to validate the basic underlying mechanisms occurring for key planetary constituents (metallization, dissociation, structural modifications, phase transitions, etc....) as pressure and temperature both increase. In this work, we were interested in two materials that can be mainly found in the Earth-like planets: silica, or SiO2, as a model compound of the silicates that constitute the major part of their mantles, and iron, which is found in abundance in their cores. These two materials were compressed and brought to the WDM regime by using strong shock created by laser pulses during various experiments performed on the LULI2000 (Palaiseau, France) and the JLF (Livermore, US) laser facilities and on the LCLS XFEL (Stanford, US). In order to penetrate this dense matter and to have access to its both ionic and electronic structures, we have probed silica and iron with time-resolved X-ray Absorption Near Edge Structure (XANES). In parallel with these experiments, we performed quantum molecular dynamics simulations based on DFT at conditions representative of the region investigated experimentally so as to extract the interesting physical processes and comprehend the limits of the implemented models. In particular, these works allowed us to highlight the metallization processes of silica in temperature and the structural changes of its liquid in density, as well as to more constrain the melting curve of iron at very high pressures.

High-Iron Biosolids Compost-Induced Changes in Lead and Arsenic Speciation and Bioaccessibility in Co-contaminated Soils

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brown, Sally L; Clausen, Ingrid; Chappell, Mark A

2012-10-23

The safety of urban farming has been questioned due to the potential for contamination in urban soils. A laboratory incubation, a field trial, and a second laboratory incubation were conducted to test the ability of high-Fe biosolids–based composts to reduce the bioaccessibility of soil Pb and As in situ. Lead and As bioaccessibility were evaluated using an in vitro assay. Changes in Pb, As, and Fe speciation were determined on select samples after the second laboratory incubation using μ–X-ray fluorescence mapping followed by μ–X-ray absorption near-edge structure (XANES). A compost with Fe added to wastewater treatment residuals (Fe WTR compost)more » added to soils at 100 g kg -1 decreased Pb bioaccessibility in both laboratory incubations. Mixed results were observed for As. Composts tested in the field trial (Fe added as Fe powder or FeCl 2) did not reduce bioaccessible Pb, and limited reductions were observed in bioaccessible As. These composts had no effect on Pb bioaccessibility during the second laboratory incubation. Bulk XANES showed association of Pb with sulfates and carbonates in the control soil. μ-XANES for three points in the Fe WTR amended soil showed Pb present as Fe-sorbed Pb (88 and 100% of two points) and pyromorphite (12 and 53% of two points). Bulk XANES of the Fe WTR compost showed 97% of total Fe present as Fe 3+. The results of this study indicate that addition of high-Fe biosolids compost is an effective means to reduce Pb accessibility only for certain types of Fe-rich materials.« less

XPS and Ag L3-edge XANES characterization of silver and silver-gold sulfoselenides

NASA Astrophysics Data System (ADS)

Mikhlin, Yuri L.; Pal'yanova, Galina A.; Tomashevich, Yevgeny V.; Vishnyakova, Elena A.; Vorobyev, Sergey A.; Kokh, Konstantin A.

2018-05-01

Gold and silver sulfoselenides are of interest as materials with high ionic conductivity and promising magnetoresistive, thermoelectric, optical, and other physico-chemical properties, which are strongly dependent on composition and structure. Here, we applied X-ray photoelectron spectroscopy and Ag L3 X-ray absorption near-edge structure (XANES) to study the electronic structures of low-temperature compounds and solid solutions Ag2SxSe1-x (0 < x < 1), AgAuS, and Ag3AuSxSe2-x (x = 0, 1, 2). Upon substitution of Se with S, a steady increase in the positive charge at Ag(I) sites and only minor changes in the local charge at chalcogen atoms were found from the photoelectron Ag 3d, S 2p, Se 3d, and Ag M4,5VV Auger spectra. The intensity of the Ag L3-edge peak, which is known to correlate with hole counts in the Ag 4d shell having a formal d10 configuration, was enhanced by 20-25% from Ag2Se to Ag2S and from Ag3AuSe2 to Ag3AuS2. The effect of gold is more pronounced, and the number of Ag d holes and the negative charge of S and Se notably decreased for Au-containing compounds; in particular, the Ag L3-edge peak is about 35% lower for AgAuS relative to Ag2S. At the same time, the Au 4f binding energy and, therefore, charge at Au(I) sites increase with increasing S content due to the transfer of electron density from Au to Ag atoms. It was concluded that the effects mainly originate from shortening of the metal-chalcogen and especially the Ausbnd Ag interatomic distances in substances having similar coordination geometry.

Ab initio X-ray absorption modeling of Cu-SAPO-34: Characterization of Cu exchange sites under different conditions

DOE PAGES

Zhang, Renqin; Helling, Kathy; McEwen, Jean-Sabin

2016-03-29

Copper-exchanged SAPO-34 (Cu-SAPO-34) provides excellent catalytic activity and hydrothermal sta-bility in the selective catalytic reduction (SCR) of NOxby using NH3as a reductant. Here, we find that the6-membered ring (6MR) site is the most energetically favorable for a Cu+ion while the 8-memberedring (8MR) sites are less favorable by about 0.5 eV with respect to the 6MR site in Cu-SAPO-34. Uponadsorption of molecular species (H2O, O, OH, O2), the energy differences between Cu in the 8MR and 6MRsites decreases and almost disappears. Further, a thermodynamic phase diagram study shows that a Cu+ion bound to a single H2O molecule is the most stablemore » species at low oxygen potential values while aCu2+ion bound to 2 OH species is more stable when the oxygen chemical potential is sufficiently high. Bycomparing Cu K-edge XANES between Cu-SSZ-13 and Cu-SAPO-34 with Cu in different oxidation states,we conclude that it is difficult to differentiate the simulated XANES of Cu in these structures at a givenoxidation state. By studying the Cu K-edge XANES of several favorable structures in Cu-SAPO-34 in thepresence of adspecies, the simulated XANES results capture the real trend of the edge shift with oxidationstate and gives new insights into the experimentally determined XANES of Cu-SAPO-34 obtained understandard SCR conditions.« less

XANES study of elemental mercury oxidation over RuO 2/TiO 2 and selective catalytic reduction catalysts for mercury emissions control

DOE PAGES

Liu, Zhouyang; Li, Can; Sriram, Vishnu; ...

2016-07-25

Linear combination fitting of the X-ray Absorption Near Edge Spectroscopy (XANES) was used to quantify oxidized mercury species over RuO 2/TiO 2 and Selective Catalytic Reduction (SCR) catalysts under different simulated flue gas conditions. Halogen gases play a major role in mercury oxidation. In the absence of halogen gas, elemental mercury can react with sulfur that is contained in both the RuO2/TiO2 and SCR catalysts to form HgS and HgSO 4. In the presence of HCl or HBr gas, HgCl 2 or HgBr 2 is the main oxidized mercury species. When both HCl and HBr gases are present, HgBr2 ismore » the preferred oxidation product and no HgCl 2 can be found. The formation of HgO and HgS cannot be neglected with or without halogen gas. Other simulated flue gas components such as NO, NH 3, SO 2 and CO 2 do not have significant effect on oxidized mercury speciation when halogen gas is present.« less

Retention Mechanisms of Citric Acid in Ternary Kaolinite-Fe(III)-Citrate Acid Systems Using Fe K-edge EXAFS and L3,2-edge XANES Spectroscopy

PubMed Central

Yang, Jianjun; Wang, Jian; Pan, Weinan; Regier, Tom; Hu, Yongfeng; Rumpel, Cornelia; Bolan, Nanthi; Sparks, Donald

2016-01-01

Organic carbon (OC) stability in tropical soils is strongly interlinked with multivalent cation interaction and mineral association. Low molecular weight organic acids (LMWOAs) represent the readily biodegradable OC. Therefore, investigating retention mechanisms of LMWOAs in mineral-cation-LMWOAs systems is critical to understanding soil C cycling. Given the general acidic conditions and dominance of kaolinite in tropical soils, we investigated the retention mechanisms of citric acid (CA) in kaolinite-Fe(III)-CA systems with various Fe/CA molar ratios at pH ~3.5 using Fe K-edge EXAFS and L3,2-edge XANES techniques. With Fe/CA molar ratios >2, the formed ferrihydrite mainly contributed to CA retention through adsorption and/or coprecipitation. With Fe/CA molar ratios from 2 to 0.5, ternary complexation of CA to kaolinite via a five-coordinated Fe(III) bridge retained higher CA than ferrihydrite-induced adsorption and/or coprecipitation. With Fe/CA molar ratios ≤0.5, kaolinite-Fe(III)-citrate complexation preferentially occurred, but less CA was retained than via outer-sphere kaolinite-CA complexation. This study highlighted the significant impact of varied Fe/CA molar ratios on CA retention mechanisms in kaolinite-Fe(III)-CA systems under acidic conditions, and clearly showed the important contribution of Fe-bridged ternary complexation on CA retention. These findings will enhance our understanding of the dynamics of CA and other LMWOAs in tropical soils. PMID:27212680

Retention mechanisms of citric acid in ternary kaolinite-Fe(III)-citrate acid systems using Fe K-edge EXAFS and L 3,2-edge XANES spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Jianjun; Wang, Jian; Pan, Weinan

Organic carbon (OC) stability in tropical soils is strongly interlinked with multivalent cation interaction and mineral association. Low molecular weight organic acids (LMWOAs) represent the readily biodegradable OC. Therefore, investigating retention mechanisms of LMWOAs in mineral-cation-LMWOAs systems is critical to understanding soil C cycling. Given the general acidic conditions and dominance of kaolinite in tropical soils, we investigated the retention mechanisms of citric acid (CA) in kaolinite-Fe(III)-CA systems with various Fe/CA molar ratios at pH ~3.5 using Fe K-edge EXAFS and L- 3,2-edge XANES techniques. With Fe/CA molar ratios >2, the formed ferrihydrite mainly contributed to CA retention through adsorptionmore » and/or coprecipitation. With Fe/CA molar ratios from 2 to 0.5, ternary complexation of CA to kaolinite via a five-coordinated Fe(III) bridge retained higher CA than ferrihydrite-induced adsorption and/or coprecipitation. With Fe/CA molar ratios ≤ 0.5, kaolinite-Fe(III)-citrate complexation preferentially occurred, but less CA was retained than via outer-sphere kaolinite-CA complexation. This study highlighted the significant impact of varied Fe/CA molar ratios on CA retention mechanisms in kaolinite-Fe(III)-CA systems under acidic conditions, and clearly showed the important contribution of Fe-bridged ternary complexation on CA retention. In conclusion, these findings will enhance our understanding of the dynamics of CA and other LMWOAs in tropical soils.« less

Retention mechanisms of citric acid in ternary kaolinite-Fe(III)-citrate acid systems using Fe K-edge EXAFS and L 3,2-edge XANES spectroscopy

DOE PAGES

Yang, Jianjun; Wang, Jian; Pan, Weinan; ...

2016-05-23

Organic carbon (OC) stability in tropical soils is strongly interlinked with multivalent cation interaction and mineral association. Low molecular weight organic acids (LMWOAs) represent the readily biodegradable OC. Therefore, investigating retention mechanisms of LMWOAs in mineral-cation-LMWOAs systems is critical to understanding soil C cycling. Given the general acidic conditions and dominance of kaolinite in tropical soils, we investigated the retention mechanisms of citric acid (CA) in kaolinite-Fe(III)-CA systems with various Fe/CA molar ratios at pH ~3.5 using Fe K-edge EXAFS and L- 3,2-edge XANES techniques. With Fe/CA molar ratios >2, the formed ferrihydrite mainly contributed to CA retention through adsorptionmore » and/or coprecipitation. With Fe/CA molar ratios from 2 to 0.5, ternary complexation of CA to kaolinite via a five-coordinated Fe(III) bridge retained higher CA than ferrihydrite-induced adsorption and/or coprecipitation. With Fe/CA molar ratios ≤ 0.5, kaolinite-Fe(III)-citrate complexation preferentially occurred, but less CA was retained than via outer-sphere kaolinite-CA complexation. This study highlighted the significant impact of varied Fe/CA molar ratios on CA retention mechanisms in kaolinite-Fe(III)-CA systems under acidic conditions, and clearly showed the important contribution of Fe-bridged ternary complexation on CA retention. In conclusion, these findings will enhance our understanding of the dynamics of CA and other LMWOAs in tropical soils.« less

XAS Characterization of the Zn Site of Non-structural Protein 3 (NS3) from Hepatitis C Virus

NASA Astrophysics Data System (ADS)

Ascone, I.; Nobili, G.; Benfatto, M.; Congiu-Castellano, A.

2007-02-01

XANES spectra of non structural protein 3 (NS3) have been calculated using 4 Zn coordination models from three crystallographic structures in the Protein Data Base (PDB): 1DY9, subunit B, 1CU1 subunit A and B, and 1JXP subunit B. Results indicate that XANES is an appropriate tool to distinguish among them. Experimental XANES spectra have been simulated refining crystallographic data. The model obtained by XAS is compared with the PDB models.

Full-Field Calcium K-Edge X-ray Absorption Near-Edge Structure Spectroscopy on Cortical Bone at the Micron-Scale: Polarization Effects Reveal Mineral Orientation.

PubMed

Hesse, Bernhard; Salome, Murielle; Castillo-Michel, Hiram; Cotte, Marine; Fayard, Barbara; Sahle, Christoph J; De Nolf, Wout; Hradilova, Jana; Masic, Admir; Kanngießer, Birgit; Bohner, Marc; Varga, Peter; Raum, Kay; Schrof, Susanne

2016-04-05

Here, we show results on X-ray absorption near edge structure spectroscopy in both transmission and X-ray fluorescence full-field mode (FF-XANES) at the calcium K-edge on human bone tissue in healthy and diseased conditions and for different tissue maturation stages. We observe that the dominating spectral differences originating from different tissue regions, which are well pronounced in the white line and postedge structures are associated with polarization effects. These polarization effects dominate the spectral variance and must be well understood and modeled before analyzing the very subtle spectral variations related to the bone tissue variations itself. However, these modulations in the fine structure of the spectra can potentially be of high interest to quantify orientations of the apatite crystals in highly structured tissue matrices such as bone. Due to the extremely short wavelengths of X-rays, FF-XANES overcomes the limited spatial resolution of other optical and spectroscopic techniques exploiting visible light. Since the field of view in FF-XANES is rather large the acquisition times for analyzing the same region are short compared to, for example, X-ray diffraction techniques. Our results on the angular absorption dependence were verified by both site-matched polarized Raman spectroscopy, which has been shown to be sensitive to the orientation of bone building blocks and by mathematical simulations of the angular absorbance dependence. As an outlook we further demonstrate the polarization based assessment of calcium-containing crystal orientation and specification of calcium in a beta-tricalcium phosphate (β-Ca3(PO4)2 scaffold implanted into ovine bone. Regarding the use of XANES to assess chemical properties of Ca in human bone tissue our data suggest that neither the anatomical site (tibia vs jaw) nor pathology (healthy vs necrotic jaw bone tissue) affected the averaged spectral shape of the XANES spectra.

Testing Delays Resulting in Increased Identification Accuracy in Line-Ups and Show-Ups.

ERIC Educational Resources Information Center

Dekle, Dawn J.

1997-01-01

Investigated time delays (immediate, two-three days, one week) between viewing a staged theft and attempting an eyewitness identification. Compared lineups to one-person showups in a laboratory analogue involving 412 subjects. Results show that across all time delays, participants maintained a higher identification accuracy with the showup…

An x-ray absorption spectroscopy study of Ni-Mn-Ga shape memory alloys.

PubMed

Sathe, V G; Dubey, Aditi; Banik, Soma; Barman, S R; Olivi, L

2013-01-30

The austenite to martensite phase transition in Ni-Mn-Ga ferromagnetic shape memory alloys was studied by extended x-ray absorption fine structure (EXAFS) and x-ray absorption near-edge structure (XANES) spectroscopy. The spectra at all the three elements', namely, Mn, Ga and Ni, K-edges in several Ni-Mn-Ga samples (with both Ni and Mn excess) were analyzed at room temperature and low temperatures. The EXAFS analysis suggested a displacement of Mn and Ga atoms in opposite direction with respect to the Ni atoms when the compound transforms from the austenite phase to the martensite phase. The first coordination distances around the Mn and Ga atoms remained undisturbed on transition, while the second and subsequent shells showed dramatic changes indicating the presence of a modulated structure. The Mn rich compounds showed the presence of antisite disorder of Mn and Ga. The XANES results showed remarkable changes in the unoccupied partial density of states corresponding to Mn and Ni, while the electronic structure of Ga remained unperturbed across the martensite transition. The post-edge features in the Mn K-edge XANES spectra changed from a double peak like structure to a flat peak like structure upon phase transition. The study establishes strong correlation between the crystal structure and the unoccupied electronic structure in these shape memory alloys.

Electrochemically-Induced Redox Reactions in Basalt at High Pressure and Temperature: An Iron and Vanadium K-edge XANES Study

NASA Astrophysics Data System (ADS)

Kavner, A.; Walker, D.; Newville, M.; Sutton, S. R.

2005-12-01

An applied electric field across a silicate sample at high pressures and temperatures in a piston cylinder apparatus can generate a wide range of oxidation states of polyvalent cations within a single experiment. If two or more polyvalent cations are included, this technique can be used to cross-calibrate oxybarometers within a single experiment. The redox state of Fe and V within a partially melted basaltic silicate was manipulated in situ in a piston-cylinder experiment with a DC power supply providing a source and sink of electrons to the sample. A 1V electrical potential differential was applied across vanadium-doped and Fe-bearing synthetic basalt samples for 24 hrs. at 20 kbar and 1400°C in a specially-designed piston cylinder sample assembly. Three experiments were performed: a control sample with no applied voltage, one with bottom cathode and top anode, and a third with top cathode and bottom anode. Synchrotron-based x-ray absorption near edge structure (XANES) spectroscopy was used to provide spot analysis of iron and vanadium oxidation states with 5μm x 5μm spatial resolution throughout the recovered samples. Systematic spatial changes of increasing oxidation states of V and Fe were observed approaching the anode. The differences in oxidation states were mapped to a corresponding local effective oxygen fugacity by comparison and extension of a calibration of vanadium oxidation states as a function of controlled oxygen fugacity from a previous study (Sutton et al., 2005, GCA, vol. 69, pp. 2333-2348). The vanadium mapping indicates that a 1V potential drop across the sample induces effective oxygen fugacity perturbations in excess of ten orders of magnitude. The presence of both Fe and V within the same sample provides a wide range of oxygen fugacity cross-calibration in these recovered samples. A relationship between oxygen fugacity and electrochemical driving force is derived. The experimental results are in good agreement with the derived

Pressure induced coordination change of Al in silicate melts from Al K edge XANES of high pressure NaAlSi2O6-NaAlSi3O8 glasses

NASA Astrophysics Data System (ADS)

Li, Dien; Secco, R. A.; Bancroft, G. M.; Fleet, M. E.

Aluminum K-edge XANES spectra of high pressure and high temperature (4.4 GPa and 1575°C) glasses along the NaAlSi2O6 (Jd)-NaAlSi3O8 (Ab) join are reported using synchrotron radiation, and shown to provide direct experimental evidence for the pressure-induced coordination change of Al. Five- and six-fold coordinated Al (5Al and 6Al), characterized by Al K-edge positions at 1567.8 and 1568.7 eV, respectively, first appear in glass of composition Jd60Ab40 and increase in proportion progressively with increasing Jd content. The end-member jadeite glass contains about 6% of each of 5Al and 6Al. The present direct measurements confirm literature suggestions for the important role of Al in controlling viscosity and diffusion in mantle melts.

Comparison Analysis of Coal Biodesulfurization and Coal's Pyrite Bioleaching with Acidithiobacillus ferrooxidans

PubMed Central

Hong, Fen-Fen; He, Huan; Liu, Jin-Yan; Tao, Xiu-Xiang; Zheng, Lei; Zhao, Yi-Dong

2013-01-01

Acidithiobacillus ferrooxidans (A. ferrooxidans) was applied in coal biodesulfurization and coal's pyrite bioleaching. The result showed that A. ferrooxidans had significantly promoted the biodesulfurization of coal and bioleaching of coal's pyrite. After 16 days of processing, the total sulfur removal rate of coal was 50.6%, and among them the removal of pyritic sulfur was up to 69.9%. On the contrary, after 12 days of processing, the coal's pyrite bioleaching rate was 72.0%. SEM micrographs showed that the major pyrite forms in coal were massive and veinlets. It seems that the bacteria took priority to remove the massive pyrite. The sulfur relative contents analysis from XANES showed that the elemental sulfur (28.32%) and jarosite (18.99%) were accumulated in the biotreated residual coal. However, XRD and XANES spectra of residual pyrite indicated that the sulfur components were mainly composed of pyrite (49.34%) and elemental sulfur (50.72%) but no other sulfur contents were detected. Based on the present results, we speculated that the pyrite forms in coal might affect sulfur biooxidation process. PMID:24288464

Speciation and distribution of copper in a mining soil using multiple synchrotron-based bulk and microscopic techniques.

PubMed

Yang, Jianjun; Liu, Jin; Dynes, James J; Peak, Derek; Regier, Tom; Wang, Jian; Zhu, Shenhai; Shi, Jiyan; Tse, John S

2014-02-01

Molecular-level understanding of soil Cu speciation and distribution assists in management of Cu contamination in mining sites. In this study, one soil sample, collected from a mining site contaminated since 1950s, was characterized complementarily by multiple synchrotron-based bulk and spatially resolved techniques for the speciation and distribution of Cu as well as other related elements (Fe, Ca, Mn, K, Al, and Si). Bulk X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy revealed that soil Cu was predominantly associated with Fe oxides instead of soil organic matter. This agreed with the closest association of Cu to Fe by microscopic X-ray fluorescence (U-XRF) and scanning transmission X-ray microscopy (STXM) nanoanalysis, along with the non-occurrence of photoreduction of soil Cu(II) by quick Cu L3,2-edge XANES spectroscopy (Q-XANES) which often occurs when Cu organic complexes are present. Furthermore, bulk-EXAFS and STXM-coupled Fe L3,2-edge nano-XANES analysis revealed soil Cu adsorbed primarily to Fe(III) oxides by inner-sphere complexation. Additionally, Cu K-edge μ-XANES, L3,2-edge bulk-XANES, and successive Q-XANES results identified the presence of Cu2S rather than radiation-damage artifacts dominant in certain microsites of the mining soil. This study demonstrates the great benefits in use of multiple combined synchrotron-based techniques for comprehensive understanding of Cu speciation in heterogeneous soil matrix, which facilitates our prediction of Cu reactivity and environmental fate in the mining site.

Arsenic speciation in biological samples using XAS and mixed oxidation state calibration standards of inorganic arsenic.

PubMed

Parsons, J G; Lopez, M L; Castillo-Michel, H; Peralta-Videa, J R; Gardea-Torresdey, J L

2009-08-01

The speciation of elements without pre-edge features preformed with X-ray absorption near edge structure (XANES) can lead to problems when the energy difference between two species is small. The speciation of arsenic (As) in plant samples was investigated using the mixtures As2S3/As2O5, As2S3/As2O3, or As2O3/As2O5. The data showed that the energy separation (eV) between As2O5 and As2S3 was 5.8, between As2O3 and As2O5 was 3.6, and between As2S3 and As2O3 was 2.1. From the intensity of the white-line feature and the concentration of As species, calibration curves showing a limit of detection of approximately 10% were generated. In addition, an error of +/-10% was determined for the linear combination-XANES (LC-XANES) fitting technique. The difference between the LC-XANES fittings and calculations from the calibration curves was <10%. The data also showed that the speciation of As in a sample can be determined using EXAFS (extended X-ray absorption fine structure). Finally, it was also shown that both EXAFS and XANES of the sample should be examined to determine the true speciation of an element. Even though there is a difference of 2 eV between As(III) bound to O and As(III) bound to S, in the EXAFS region the As(III)-S and As(III)-O ligands are clearly visible. However, distinction between the As(III)-O and As(V)-O ligands in the EXAFS spectra was not clearly visible in this study.

The Development of Molybdenum Speciation as a Paleoredox Tool

NASA Astrophysics Data System (ADS)

Rodley, J.; Peacock, C.; Mosselmans, J. F. W.; Poulton, S.

2017-12-01

The redox state of the oceans has changed throughout geological time and an understanding of these changes is essential to elucidate links between ocean chemistry, climate and life. Due to its abundance in seawater and redox-sensitive nature, molybdenum has enormous potential as a paleoredox proxy. Although a significant amount of research has been done on molybdenum in ancient and modern sediments in terms of its concentrations and isotopic ratios there remains a limited understanding of the drawdown mechanisms of molybdenum under different redox conditions restricting its use in identifying a range of redox states. In order to address these uncertainties, we have developed a novel sequential extraction technique to examine molybdenum concentrations in six sediment fractions from modern samples that represent oxic, nitrogenous, ferruginous and euxinic environments. In addition we use µ-XRF and µ-XANES synchrotron spectroscopy to examine the molybdenum speciation within these fractions and environments. To interpret our µ-XANES data we have developed an extensive library of molybdenum XANES standards that represent molybdenum sequestration by the sediment fractions identified from the sequential extraction. To further verify our synchrotron results we developed a series of µ-XANES micro-column experiments to examine preferential uptake pathways of molybdenum to different sediment phases under a euxinic water column. The initial data from both the sequential extraction and µ-XANES methods indicate that molybdenum is not limited to a single burial pathway in any of the redox environments. We find that each of the redox environments can be characterised by a limited set of molybdenum phase associations, with molybdenum adsorption to pyrite likely the dominant burial pathway. These findings agree with existing research for molybdenum speciation in euxinic environments suggesting that both pyrite and sulphidised organic matter act as important molybdenum sinks. Our

Electronic Structures and Optical Properties of α-Al2O3Nanowires

NASA Astrophysics Data System (ADS)

Wang, Zhiqiang; Li, Chunlei; Liu, Lijia; Sham, Tsun-Kong

2013-04-01

The electronic structure and optical properties of α-Al2O3 nanowires (NWs) have been investigated using X-ray absorption near-edge structures (XANES) and X-ray excited optical luminescence (XEOL). The XANES were recorded in total electron yield (TEY) and total fluorescence yield (TFY) across the K- and L3,2-edges of aluminium and the K-edge of oxygen. The results indicate that the NWs are of a core/shell structure with a single-crystalline core and an amorphous shell. The XEOL spectra of the NWs show an intense peak at 404 nm, which comes from the F centre located in the amorphous shell of the NWs. The implication of these findings and the sensitivity of XEOL for defect detection are discussed.

Ti K-edge EXAFS and XANES study on tektites from different strewnfields

NASA Astrophysics Data System (ADS)

Wang, L.; Furuta, T.; Okube, M.; Yoshiasa, A.

2011-12-01

The concentration and local structure of each element may have various kinds of information about the asteroid impact and mass extinction. Farges and Brown have discussed about the Ti local structure by XANES, and concluded that Ti in tektite occupies 4-coordinated site. EXAFS can be analyzed to give precise information about the distance from Ti to near neighbors. The XAFS measurement of Ti local structure was preformed at the beamline 9C of the Photon Factory in KEK, Tsukuba, Japan. The specimens of tektites are from different strewnfields, they are: indochinite, bediasite, hainanite, philippinite, australite and moldavite. Sample for comparison are Libya desert glass and suevite. The k3χ(k) function was transformed into the radial structure function (RSF) for Ti K-edge of six tektites. The RSF for the Ti atom in indochinite and bediasite are similar; hainanite, australite and philippinite are similar; and moldavite is discriminated from others. It indicates that they have the same local atomic environmental around the Ti atoms and extended structure respectively. Coordination numbers and radial structure function are determined by EXAFS analyses (Table 1). We classified the tektites in three types: in indochinite and bediasite, Ti occupies 4-coordinated tetrahedral site and Ti-O distances are 1.84-1.81 Å; in hainanite, australite and philippinite, Ti occupies 5-coordinated trigonal bi-pyramidal or tetragonal pyramidal site and Ti-O distances are 1.92-1.87 Å; in moldavite, Ti occupies the 6-coordinated octahedral site and Ti-O distance is 2.00-1.96 Å. Formation of tektites is related to the impact process. It is generally recognized that tektites were formed under higher temperature and high pressure. But through this study, local structures of Ti are differing in three strewnfields and even different locations of the same strewnfield. What caused the various local structures will be another topic of tektite studies. Local structure of Ti may be changed in

Temperature dependence of pre-edge features in Ti K-edge XANES spectra for ATiO₃ (A = Ca and Sr), A₂TiO₄ (A = Mg and Fe), TiO₂ rutile and TiO₂ anatase.

PubMed

Hiratoko, Tatsuya; Yoshiasa, Akira; Nakatani, Tomotaka; Okube, Maki; Nakatsuka, Akihiko; Sugiyama, Kazumasa

2013-07-01

XANES (X-ray absorption near-edge structure) spectra of the Ti K-edges of ATiO3 (A = Ca and Sr), A2TiO4 (A = Mg and Fe), TiO2 rutile and TiO2 anatase were measured in the temperature range 20-900 K. Ti atoms for all samples were located in TiO6 octahedral sites. The absorption intensity invariant point (AIIP) was found to be between the pre-edge and post-edge. After the AIIP, amplitudes damped due to Debye-Waller factor effects with temperature. Amplitudes in the pre-edge region increased with temperature normally by thermal vibration. Use of the AIIP peak intensity as a standard point enables a quantitative comparison of the intensity of the pre-edge peaks in various titanium compounds over a wide temperature range.

Studies on absorption coefficient near edge of multi elements

NASA Astrophysics Data System (ADS)

Eisa, M. H.; Shen, H.; Yao, H. Y.; Mi, Y.; Zhou, Z. Y.; Hu, T. D.; Xie, Y. N.

2005-12-01

X-ray absorption near edge structure (XANES) was used to study the near edge mass-absorption coefficients of seven elements, such as, Ti, V, Fe, Co, Ni, Cu and Zn. It is well known that, on the near edge absorption of element, when incident X-ray a few eV change can make the absorption coefficient an order magnitude alteration. So that, there are only a few points mass-absorption coefficient at the near edge absorption and that always average value in published table. Our results showed a wide range of data, the total measured data of mass-absorption coefficient of the seven elements was about 505. The investigation confirmed that XANES is useful technique for multi-element absorption coefficient measurement. Details of experimental methods and results are given and discussed. The experimental work has been performed at Beijing Synchrotron Radiation Facility. The measured values were compared with the published data. Good agreement between experimental results and published data is obtained.

Determining the Oxygen Fugacity of Lunar Pyroclastic Glasses Using Vanadium Valence - An Update

NASA Technical Reports Server (NTRS)

Karner, J. M.; Sutton, S. R.; Papike, J. J.; Shearer, C. K.; Jones, J. H.; Newville, M.

2004-01-01

We have been developing an oxygen barometer based on the valence state of V (V(2+), V(3+), V(4+), and V(5+)) in solar system basaltic glasses. The V valence is determined by synchrotron micro x-ray absorption near edge structure (XANES), which uses x-ray absorption associated with core-electronic transitions (absorption edges) to reveal a pre-edge peak whose intensity is directly proportional to the valence state of an element. XANES has advantages over other techniques that determine elemental valence because measurements can be made non-destructively in air and in situ on conventional thin sections at a micrometer spatial resolution with elemental sensitivities of approx. 100 ppm. Recent results show that fO2 values derived from the V valence technique are consistent with fO2 estimates determined by other techniques for materials that crystallized above the IW buffer. The fO2's determined by V valence (IW-3.8 to IW-2) for the lunar pyroclastic glasses, however, are on the order of 1 to 2.8 log units below previous estimates. Furthermore, the calculated fO2's decrease with increasing TiO2 contents from the A17 VLT to the A17 Orange glasses. In order to investigate these results further, we have synthesized lunar green and orange glasses and examined them by XANES.

Study of distorted octahedral structure in 3d transition metal complexes using XAFS

NASA Astrophysics Data System (ADS)

Gaur, A.; Nitin Nair, N.; Shrivastava, B. D.; Das, B. K.; Chakrabortty, Monideepa; Jha, S. N.; Bhattacharyya, D.

2018-01-01

Distortion in octahedral structure of 3d transition metal complexes (Mn, Fe, Co, Ni, Cu, Zn) has been studied using XAFS showing divergent nature of Cu complex. EXAFS analysis showed elongated metal-oxygen bonds for Cu complex leading to more distorted structure. Derivative XANES spectrum at Cu K-edge exhibits splitting of main edge which is correlated to elongated Cu-O bond length. Using these coordination geometry around metal centers, theoretical XANES spectra have been generated and features observed have been correlated to the corresponding metals p-DOS. It has been shown that distorted octahedral field in Cu complex is responsible for splitting of p-DOS.

Synchrotron-based P K-edge XANES spectroscopy reveals rapid changes of phosphorus speciation in the topsoil of two glacier foreland chronosequences

NASA Astrophysics Data System (ADS)

Prietzel, Jörg; Dümig, Alexander; Wu, Yanhong; Zhou, Jun; Klysubun, Wantana

2013-05-01

Phosphorus (P) is a crucial element for life on Earth, and the bioavailability of P in terrestrial ecosystems, which is dependent on the soil P stock and its speciation, may limit ecosystem productivity and succession. In our study, for the first time a direct speciation of soil P in two glacier foreland chronosequences has been conducted using synchrotron-based X-ray Absorption Near-Edge Structure (XANES) spectroscopy. The chronosequences are located in the forefields of Hailuogou Glacier (Gongga Shan, China) and Damma Glacier (Swiss Alps). The age since deglaciation of the investigated soils ranges from 0 to 120 years at Hailuogou, and from 15 to >700 years at Damma. Differences in climate conditions (cooler at Damma, in contrast to Hailuogou precluding the establishment of forest in advanced ecosystem succession stages) and in the chemical composition of the parent material result in different soil contents of total P and Fe/Al oxyhydroxides, which are much smaller at Damma than at Hailuogou. Nevertheless, both chronosequences show similar trends of their topsoil P status with increasing soil age. Our study reveals a rapid change of topsoil P speciation in glacier retreat areas already during initial stages of pedogenesis: Initially dominating bedrock-derived apatite-P and Al-bound P is depleted; Fe-bound P and particularly organically-bound P is accumulated. Organic P strongly dominates in the topsoil of the mature soils outside the proglacial area of Damma Glacier (age 700-3000 years), and already 50 years after deglacation in the topsoil of the retreat area of Hailuogou Glacier. A key factor for the change in topsoil P speciation is the establishment of vegetation, resulting in soil organic matter (SOM) accumulation as well as accelerated soil acidification and apatite dissolution by organic acids, which are produced by SOM-degrading micro-organisms, mykorrhiza fungi, and plant roots. Particularly the succession of grassland to forest seems to accelerate the

Integrated experimental and theoretical approach for the structural characterization of Hg2+ aqueous solutions

NASA Astrophysics Data System (ADS)

D'Angelo, Paola; Migliorati, Valentina; Mancini, Giordano; Barone, Vincenzo; Chillemi, Giovanni

2008-02-01

The structural and dynamic properties of the solvated Hg2+ ion in aqueous solution have been investigated by a combined experimental-theoretical approach employing x-ray absorption spectroscopy and molecular dynamics (MD) simulations. This method allows one to perform a quantitative analysis of the x-ray absorption near-edge structure (XANES) spectra of ionic solutions using a proper description of the thermal and structural fluctuations. XANES spectra have been computed starting from the MD trajectory, without carrying out any minimization in the structural parameter space. The XANES experimental data are accurately reproduced by a first-shell heptacoordinated cluster only if the second hydration shell is included in the calculations. These results confirm at the same time the existence of a sevenfold first hydration shell for the Hg2+ ion in aqueous solution and the reliability of the potentials used in the MD simulations. The combination of MD and XANES is found to be very helpful to get important new insights into the quantitative estimation of structural properties of disordered systems.

Determination of Arsenic Poisoning and Metabolism in Hair by Synchrotron Radiation: The Case of Phar Lap

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kempson, Ivan M.; Henry, Dermot A.; U. South Australia)

2010-08-26

Fresh physical evidence about the demise of the racehorse Phar Lap (see photograph) has been gathered from the study of mane hair samples by synchrotron radiation analysis with high resolution X-ray fluorescence (XRF) and X-ray absorption near edge structure (XANES) analyses. The results are indicative of arsenic ingestion and metabolism, and show that the racing champion died from arsenic poisoning.

Noninvasive Synchrotron-Based X-ray Raman Scattering Discriminates Carbonaceous Compounds in Ancient and Historical Materials [ In situ synchrotron-based X-Ray Raman scattering discriminates carbonaceous compounds in ancient and historical materials

DOE PAGES

Gueriau, Pierre; Rueff, Jean -Pascal; Bernard, Sylvain; ...

2017-09-13

Carbon compounds are ubiquitous and occur in a diversity of chemical forms in many systems including ancient and historic materials ranging from cultural heritage to paleontology. Determining their speciation cannot only provide unique information on their origin but may also elucidate degradation processes. Synchrotron-based X-ray absorption near-edge structure (XANES) spectroscopy at the carbon K-edge (280–350 eV) is a very powerful method to probe carbon speciation. However, the short penetration depth of soft X-rays imposes stringent constraints on sample type, preparation, and analytical environment. A hard X-ray probe such as X-ray Raman scattering (XRS) can overcome many of these difficulties. Heremore » we report the use of XRS at ~6 keV incident energy to collect carbon K-edge XANES data and probe the speciation of organic carbon in several specimens relevant to cultural heritage and natural history. This methodology enables the measurement to be done in a nondestructive way, in air, and provides information that is not compromised by surface contamination by ensuring that the dominant signal contribution is from the bulk of the probed material. Using the backscattering geometry at large photon momentum transfer maximizes the XRS signal at the given X-ray energy and enhances nondipole contributions compared to conventional XANES, thereby augmenting the speciation sensitivity. The capabilities and limitations of the technique are discussed. As a result, we show that despite its small cross section, for a range of systems the XRS method can provide satisfactory signals at realistic experimental conditions. XRS constitutes a powerful complement to FT-IR, Raman, and conventional XANES spectroscopy, overcoming some of the limitations of these techniques.« less

Fe-bearing Olenite with Tetrahedrally Coordinated Al from an Abyssal Pegmatite at Kutna Hora, Czech Republic: Structure, Crystal Chemistry, Optical and XANES Spectra

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cempirek,J.; Novak, M.; Ertl, A.

2006-01-01

The pale blue rim of olenite on a black crystal of olenite-schorl tourmaline from an abyssal pegmatite at the locality Kuklik, near Kutna Hora, Czech Republic, has been chemically and structurally characterized. The optimized formula, calculated using chemical and structural data, is {sup X}(Na{sub 0.54}Ca{sub 0.14}K{sub 0.01}{D'Alembertian}{sub 0.31}){sup Y}(Al{sub 2.15}Fe{sup 2+}{sub 0.06}Ti{sup 4+}{sub 0.01}) {sup Z}(Al{sub 5.90}Mg{sub 0.10}) {sup T}(Si{sub 5.60}Al{sub 0.40})B{sub 3}O{sub 27} {sup V}[(OH){sub 2.49}O{sub 0.51}] {sup W}(O{sub 0.99}F{sub 0.01}), with {alpha} 15.8838(3), c 7.1056(2) {angstrom} and R = 0.017. The relatively short bond-length, 1.992 {angstrom}, confirms the high content of Al at the Y site ({approx}2.1more » atoms per formula unit, apfu). It is similar to that of olenite from the type locality, though the olenite from Kuklik contains significant amounts of Fe at the Y site, and significant amounts of {sup [4]}Al ({approx}0.4 apfu) instead of {sup [4]}B in the T site. This finding is supported by results of the structure determination, which show an enlarged bond-length of {approx}1.626 {angstrom}. This sample of olenite shows that nonstoichiometric content of Si does not always imply {sup [4]}B in aluminous tourmaline. No H could be found at the O1 site by refinement, and the spherical distribution of electron density in the difference-Fourier map around the O1 site supports the conclusion that this site is only or mainly occupied by O and not by OH. On a bond-angle distortion ({sigma}{sub oct}{sup 2} of the ZO{sub 6} octahedron) - distance diagram, the olenite from Kuklik lies between compositions containing 3 (OH) at the V site, and natural buergerite, which contains 0.3 (OH) and 2.7 O at the V site (O3 site). The (OH) content with {approx}2.5 (OH) pfu, which was calculated for a charge-balanced formula, is in a good agreement with these findings and with the integrated intensity of the OH overtones in the 7000

Evaluating the electronic structure of formal Ln II ions in Ln II(C 5H 4SiMe 3) 3 1– using XANES spectroscopy and DFT calculations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fieser, Megan E.; Ferrier, Maryline Ghislaine; Su, Jing

Here, the isolation of [K(2.2.2-cryptand)][Ln(C 5H 4SiMe 3) 3], formally containing LnII, for all lanthanides (excluding Pm) was surprising given that +2 oxidation states are typically regarded as inaccessible for most 4f-elements. Herein, X-ray absorption near-edge spectroscopy (XANES), ground-state density functional theory (DFT), and transition dipole moment calculations are used to investigate the possibility that Ln(C 5H 4SiMe 3) 3 1– (Ln = Pr, Nd, Sm, Gd, Tb, Dy, Y, Ho, Er, Tm, Yb and Lu) compounds represented molecular Ln II complexes. Results from the ground-state DFT calculations were supported by additional calculations that utilized complete-active-space multi-configuration approach with second-ordermore » perturbation theoretical correction (CASPT2). Through comparisons with standards, Ln(C 5H 4SiMe 3) 3 1– (Ln = Sm, Tm, Yb, Lu, Y) are determined to contain 4f 6 5d 0 (Sm II), 4f 13 5d 0 (Tm II), 4f 14 5d 0 (Yb II), 4f 14 5d 1 (Lu II), and 4d 1 (Y II) electronic configurations. Additionally, our results suggest that Ln(C 5H 4SiMe 3) 3 1– (Ln = Pr, Nd, Gd, Tb, Dy, Ho, and Er) also contain Ln II ions, but with 4f n 5d 1 configurations (not 4f n +1 5d 0). In these 4f n 5d 1 complexes, the C 3h-symmetric ligand environment provides a highly shielded 5d-orbital of a' symmetry that made the 4f n 5d 1 electronic configurations lower in energy than the more typical 4f n+1 5d 0 configuration.« less

Evaluating the electronic structure of formal Ln II ions in Ln II(C 5H 4SiMe 3) 3 1– using XANES spectroscopy and DFT calculations

DOE PAGES

Fieser, Megan E.; Ferrier, Maryline Ghislaine; Su, Jing; ...

2017-06-30

Here, the isolation of [K(2.2.2-cryptand)][Ln(C 5H 4SiMe 3) 3], formally containing LnII, for all lanthanides (excluding Pm) was surprising given that +2 oxidation states are typically regarded as inaccessible for most 4f-elements. Herein, X-ray absorption near-edge spectroscopy (XANES), ground-state density functional theory (DFT), and transition dipole moment calculations are used to investigate the possibility that Ln(C 5H 4SiMe 3) 3 1– (Ln = Pr, Nd, Sm, Gd, Tb, Dy, Y, Ho, Er, Tm, Yb and Lu) compounds represented molecular Ln II complexes. Results from the ground-state DFT calculations were supported by additional calculations that utilized complete-active-space multi-configuration approach with second-ordermore » perturbation theoretical correction (CASPT2). Through comparisons with standards, Ln(C 5H 4SiMe 3) 3 1– (Ln = Sm, Tm, Yb, Lu, Y) are determined to contain 4f 6 5d 0 (Sm II), 4f 13 5d 0 (Tm II), 4f 14 5d 0 (Yb II), 4f 14 5d 1 (Lu II), and 4d 1 (Y II) electronic configurations. Additionally, our results suggest that Ln(C 5H 4SiMe 3) 3 1– (Ln = Pr, Nd, Gd, Tb, Dy, Ho, and Er) also contain Ln II ions, but with 4f n 5d 1 configurations (not 4f n +1 5d 0). In these 4f n 5d 1 complexes, the C 3h-symmetric ligand environment provides a highly shielded 5d-orbital of a' symmetry that made the 4f n 5d 1 electronic configurations lower in energy than the more typical 4f n+1 5d 0 configuration.« less

Aluminium X-ray absorption Near Edge Structure in model compounds and Earth's surface minerals

NASA Astrophysics Data System (ADS)

Ildefonse, P.; Cabaret, D.; Sainctavit, P.; Calas, G.; Flank, A.-M.; Lagarde, P.

Aluminium K-edge X-ray absorption near edge spectra (XANES) of a suite of silicate and oxides minerals consist of electronic excitations occurring in the edge region, and multiple scattering resonances at higher energies. The main XANES feature for four-fold Al is at around 2 eV lower energy than the main XANES feature for six-fold Al. This provides a useful probe for coordination numbers in clay minerals, gels, glasses or material with unknown Al-coordination number. Six-fold aluminium yields a large variety of XANES features which can be correlated with octahedral point symmetry, number of aluminium sites and distribution of Al-O distances. These three parameters may act together, and the quantitative interpretation of XANES spectra is difficult. For a low point symmetry (1), variations are mainly related to the number of Al sites and distribution of Al-O distances: pyrophyllite, one Al site, is clearly distinguished from kaolinite and gibbsite presenting two Al sites. For a given number of Al-site (1), variations are controlled by changes in point symmetry, the number of XANES features being increased as point symmetry decreases. For a given point symmetry (1) and a given number of Al site (1), variations are related to second nearest neighbours (gibbsite versus kaolinite). The amplitude of the XANES feature at about 1566 eV is a useful probe for the assessment of AlIV/Altotal ratios in 2/1 phyllosilicates. Al-K XANES has been performed on synthetic Al-bearing goethites which cannot be studied by 27Al NMR. At low Al content, Al-K XANES is very different from that of α-AlOOH but at the highest level, XANES spectrum tends to that of diaspore. Al-K XAS is thus a promising tool for the structural study of poorly ordered materials such as clay minerals and natural alumino-silicate gels together with Al-subsituted Fe-oxyhydroxides.

The characterization of Cr secondary oxide phases in ZnO films studied by X-ray spectroscopy and photoemission spectroscopy

NASA Astrophysics Data System (ADS)

Chiou, J. W.; Chang, S. Y.; Huang, W. H.; Chen, Y. T.; Hsu, C. W.; Hu, Y. M.; Chen, J. M.; Chen, C.-H.; Kumar, K.; Guo, J.-H.

2011-03-01

X-ray absorption near-edge structure (XANES), X-ray emission spectroscopy (XES), and X-ray photoemission spectroscopy (XPS) were used to characterize the Cr secondary oxide phases in ZnO films that had been prepared using a co-sputtering method. Analysis of the Cr L3,2-edge XANES spectra reveals that the intensity of white-line features decreases subtly as the sputtering power increases, indicating that the occupation of Cr 3 d orbitals increases with Cr concentration in (Zn, Cr)O films. The O K-edge spectra show that the intensity of XANES features of (Zn, Cr)O films is lower than those of ZnO film, suggesting enhanced occupation of O 2 p-derived states through O 2 p-Cr 3 d hybridization. The XES and XPS spectra indicate that the line shapes in the valence band of (Zn, Cr)O films are quite different from those of ZnO and that the Cr 2O 3 phase dominates the spinel structure of (Zn, Cr)O films increasingly as the Cr sputtering power is increased. Over all results suggest that the non-ferromagnetic behavior of (Zn, Cr)O films can be attributed to the dominant presence of Cr 2O 3, whereas the bulk comprise phase segregations of Cr 2O 3 and/or ZnCr 2O 4, which results them the most stable TM-doped ZnO material against etching.

Mobility of rare earth elements in mine drainage: Influence of iron oxides, carbonates, and phosphates.

PubMed

Edahbi, Mohamed; Plante, Benoît; Benzaazoua, Mostafa; Ward, Matthew; Pelletier, Mia

2018-05-01

The geochemical behavior of rare earth elements (REE) was investigated using weathering cells. The influence of sorption and precipitation on dissolved REE mobility and fractionation is evaluated using synthetic iron-oxides, carbonates, and phosphates. Sorption cell tests are conducted on the main lithologies of the expected waste rocks from the Montviel deposit. The sorbed materials are characterized using a scanning electron microscope (SEM) equipped with a microanalysis system (energy dispersive spectroscopy EDS) (SEM-EDS), X-ray diffraction (XRD), and X-ray absorption near edge structure (XANES) in order to understand the effect of the synthetic minerals on REE mobility. The results confirm that sorption and precipitation control the mobility and fractionation of REE. The main sorbent phases are the carbonates, phosphates (present as accessory minerals in the Montviel waste rocks), and iron oxides (main secondary minerals generated upon weathering of the Montviel lithologies). The XANES results show that REE are present as trivalent species after weathering. Thermodynamic equilibrium calculations results using Visual Minteq suggest that REE could precipitate as secondary phosphates (REEPO 4 ). Copyright © 2018 Elsevier Ltd. All rights reserved.

Surface modification study of borate materials from B K-edge X-ray absorption spectroscopy

NASA Astrophysics Data System (ADS)

Kasrai, Masoud; Fleet, Michael E.; Muthupari, Swaminathan; Li, D.; Bancroft, G. M.

The B K-edge X-ray absorption near-edge structure (XANES) spectra of two borates with tetrahedrally-coordinated B [[4]B; natural danburite (CaB2Si2O8) and synthetic boron phosphate (BPO4)] have been recorded in total electron yield (TEY) and fluorescence yield (FY) modes to investigate the surface and bulk structure of these materials. The TEY XANES measurement shows that danburite is susceptible to surface damage involving conversion of [4]B sites to [3]B sites by reaction with moisture and/or mechanical abrasion (grinding, polishing, etc.). The bulk of the mineral is essentially unaffected. Commercial boron phosphate powder exhibits more extensive surface and bulk damage, which increases with air exposure but is recovered on heating at 650°C. In contrast to ELNES, the XANES technique is not affected by beam damage and when collected in the FY mode is capable of yielding meaningful information on the coordination and intermediate-range structure of B in borate and borosilicate materials.

Cobalamin Concentrations in Fetal Liver Show Gender Differences: A Result from Using a High-Pressure Liquid Chromatography-Inductively Coupled Plasma Mass Spectrometry as an Ultratrace Cobalt Speciation Method.

PubMed

Bosle, Janine; Goetz, Sven; Raab, Andrea; Krupp, Eva M; Scheckel, Kirk G; Lombi, Enzo; Meharg, Andrew A; Fowler, Paul A; Feldmann, Jörg

2016-12-20

Maternal diet and lifestyle choices may affect placental transfer of cobalamin (Cbl) to the fetus. Fetal liver concentration of Cbl reflects nutritional status with regards to vitamin B12, but at these low concentration current Cbl measurement methods lack robustness. An analytical method based on enzymatic extraction with subsequent reversed-phase-high-pressure liquid chromatography (RP-HPLC) separation and parallel ICPMS and electrospray ionization (ESI)-Orbitrap-MS to determine specifically Cbl species in liver samples of only 10-50 mg was developed using 14 pig livers. Subsequently 55 human fetal livers were analyzed. HPLC-ICPMS analysis for cobalt (Co) and Cbl gave detection limits of 0.18 ng/g and 0.88 ng/g d.m. in liver samples, respectively, with a recovery of >95%. Total Co (Co t ) concentration did not reflect the amount of Cbl or vitamin B12 in the liver. Cbl bound Co contributes only 45 ± 15% to Co t . XRF mapping and μXANES analysis confirmed the occurrence of non-Cbl cobalt in pig liver hot spots indicating particular Co. No correlations of total cobalt nor Cbl with fetal weight or weeks of gestation were found for the human fetal livers. Although no gender difference could be identified for total Co concentration, female livers were significantly higher in Cbl concentration (24.1 ± 7.8 ng/g) than those from male fetuses (19.8 ± 7.1 ng/g) (p = 0.04). This HPLC-ICPMS method was able to quantify total Co t and Cbl in fetus liver, and it was sensitive and precise enough to identify this gender difference.

The speciation of soluble sulphur compounds in bacterial culture fluids by X-ray absorption near edge structure spectroscopy.

PubMed

Franz, Bettina; Lichtenberg, Henning; Hormes, Josef; Dahl, Christiane; Prange, Alexander

2009-11-01

Over the last decade X-ray absorption near edge structure (XANES) spectroscopy has been used in an increasing number of microbiological studies. In addition to other applications it has served as a valuable tool for the investigation of the sulphur globules deposited intra- or extracellularly by certain photo- and chemotrophic sulphur-oxidizing (Sox) bacteria. For XANES measurements, these deposits can easily be concentrated by filtration or sedimentation through centrifugation. However, during oxidative metabolism of reduced sulphur compounds, such as sulphide or thiosulphate, sulphur deposits are not the only intermediates formed. Soluble intermediates such as sulphite may also be produced and released into the medium. In this study, we explored the potential of XANES spectroscopy for the detection and speciation of sulphur compounds in culture supernatants of the phototrophic purple sulphur bacterium Allochromatium vinosum. More specifically, we investigated A. vinosum DeltasoxY, a strain with an in frame deletion of the soxY gene. This gene encodes an essential component of the thiosulphate-oxidizing Sox enzyme complex. Improved sample preparation techniques developed for the DeltasoxY strain allowed for the first time not only the qualitative but also the quantitative analysis of bacterial culture supernatants by XANES spectroscopy. The results thus obtained verified and supplemented conventional HPLC analysis of soluble sulphur compounds. Sulphite and also oxidized organic sulphur compounds were shown by XANES spectroscopy to be present, some of which were not seen when standard HPLC protocols were used.

Correlation of the oxidation state of cerium in sol-gel glasses as a function of thermal treatment via optical spectroscopy and XANES studies.

PubMed

Assefa, Zerihun; Haire, R G; Caulder, D L; Shuh, D K

2004-07-01

Sol-gel glass matrices containing lanthanides have numerous technological applications and their formation involves several chemical facets. In the case of cerium, its ability to exist in two different oxidation states or in mixed valence state provides additional complexities for the sol-gel process. The oxidation state of cerium present during different facets of preparation of sol-gel glasses, and also as a function of the starting oxidation state of cerium added, were studied both by optical spectroscopy and X-ray absorption near-edge structures (XANES). The findings acquired by each approach were compared. The primary focus was on the redox chemistries associated with sample preparation, gelation, and thermal treatment. When Ce3+ is introduced into the starting sols, the trivalent state normally prevails in the wet and room temperature-dried gels. Heating in air at >100 degrees C can generate a light yellow coloration with partial oxidation to the tetravalent state. Above 200 degrees C and up to approximately 1000 degrees C, cerium is oxidized to its tetravalent state. In contrast, when tetravalent cerium is introduced into the sol, both the wet and room temperature-dried gels lose the yellow-brown color of the initial ceric ammonium nitrate solution. When the sol-gel is heated to 110 degrees C it turns yellowish as the cerium tends to be re-oxidized. The yellow color is believed to represent the effect of oxidation and oligomerization of the cerium-silanol units in the matrix. The luminescence properties are also affected by these changes, the details of which are reported herein.

Effects of strain relaxation in Pr 0.67Sr 0.33MnO 3 films probed by polarization dependent X-ray absorption near edge structure

DOE PAGES

zhang, Bangmin; Chen, Jingsheng; Venkatesan, T.; ...

2016-01-28

In this study, the Mn K edge X-ray absorption near edge structure (XANES) of Pr 0.67Sr 0.33MnO 3 films with different thicknesses on (001) LaAlO 3 substrate were measured, and the effects of strain relaxation on film properties were investigated. The films experienced in-plane compressive strain and out-of-plane tensile strain. Strain relaxation evolved with the film thickness. In the polarization dependent XANES measurements, the in-plane (parallel) and out-of-plane (perpendicular) XANES spectrocopies were anisotropic with different absorption energy E r. The resonance energy Er along two directions shifted towards each other with increasing film thickness. Based on the X-ray diffraction results,more » it was suggested that the strain relaxation weakened the difference of the local environment and probability of electronic charge transfer (between Mn 3d and O 2p orbitals) along the in-plane and out-of-plane directions, which was responsible for the change of E r. XANES is a useful tool to probe the electronic structures, of which the effects on magnetic properties with the strain relaxation was also been studied.« less

Dehydration of the Uranyl Peroxide Studtite, [UO 2(η 2-O 2)(H 2O) 2]·2H 2O, Affords a Drastic Change in the Electronic Structure: A Combined X-ray Spectroscopic and Theoretical Analysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vitova, Tonya; Pidchenko, Ivan; Biswas, Saptarshi

The dehydration of studtite, [UO 2(2-O 2)(H 2O)2]·2H 2O, to metastudtite, [UO 2(2-O 2)(H 2O) 2], uranyl peroxide minerals that are major oxidative alteration phases of UO2 under conditions of geological storage, has been studied using X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy. XPS of the U 4f region shows small but significant differences between studtite and metastudtite, with the 4f binding energy of studtite the highest reported for a uranyl mineral studied by this technique. Further information on the changes in the electronic structure was elucidated using U M4-edge High Energy Resolution XANES (HR-XANES) spectroscopy, which directly probesmore » f-orbital states. The transition from the 3d to the 5f* orbital is sensitive to variations of the U=Oaxial bond length and to changes in the bond covalency. We report evidences that the covalence in the uranyl fragment decreases upon dehydration. Photoluminescence spectroscopy at near liquid helium temperatures reveals significant spectral differences between the two materials, correlating with the X-ray spectroscopy results. A theoretical investigation has been conducted on the structures of both studtite and metastudtite and benchmarked to the HR-XANES spectra. These illustrate the sensitivity of the 3d to the 5f * transition towards U=Oaxial bond variation.« less

Acid-Sulfate-Weathering Activity in Shergottite Sites on Mars Recorded in Grim Glasses

NASA Technical Reports Server (NTRS)

Rao, M. N.; Nyquist, L. E.; Ross, K.; Sutton, S. R.; Schwandt, C. S.

2011-01-01

Based on mass spectrometric studies of sulfur species in Shergotty and EET79001, [1] and [2] showed that sulfates and sulfides occur in different proportions in shergottites. Sulfur speciation studies in gas-rich impact-melt (GRIM) glasses in EET79001 by the XANES method [3] showed that S K-XANES spectra in GRIM glasses from Lith A indicate that S is associated with Ca and Al presumably as sulfides/sulfates whereas the XANES spectra of amorphous sulfide globules in GRIM glasses from Lith B indicate that S is associated with Fe as FeS. In these amorphous iron sulfide globules, [4] found no Ni using FE-SEM and suggested that the globules resulting from immiscible sulfide melt may not be related to the igneous iron sulfides having approximately 1-3% Ni. Furthermore, in the amorphous iron sulfides from 507 GRIM glass, [5] determined delta(sup 34)S values ranging from +3.5%o to -3.1%o using Nano-SIMS. These values plot between the delta(sup 34)S value of +5.25%o determined in the sulfate fraction in Shergotty [6] at one extreme and the value of -1.7%o obtained for igneous sulfides in EET79001 and Shergotty [7] at the other. These results suggest that the amorphous Fe-S globules likely originated by shock reduction of secondary iron sulfate phases occurring in the regolith precursor materials during impact [7]. Sulfates in the regolith materials near the basaltic shergottite sites on Mars owe their origin to surficial acid-sulfate interactions. We examine the nature of these reactions by studying the composition of the end products in altered regolith materials. For the parent material composition, we use that of the host shergottite material in which the impact glasses are situated.

A structural study of bone changes in knee osteoarthritis by synchrotron-based X-ray fluorescence and X-ray absorption spectroscopy techniques

NASA Astrophysics Data System (ADS)

Sindhupakorn, Bura; Thienpratharn, Suwittaya; Kidkhunthod, Pinit

2017-10-01

Osteoarthritis (OA) is characterized by degeneration of articular cartilage and thickening of subchondral bone. The present study investigated the changing of biochemical components of cartilage and bone compared between normal and OA people. Using Synchrotron-based X-ray fluorescence (SR-XRF) and X-ray absorption spectroscopy (XAS) techniquesincluding X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) were employed for the bone changes in kneeosteoarthritisstudies. The bone samples were collected from various osteoarthritis patients with both male and female in the ages range between 20 and 74 years old. SR-XRF results excited at 4240 eV for Ca elements show a majority three main groups, based on their XRF intensities, 20-36 years, 40-60 years and over 70 years, respectively. By employing XAS techniques, XANES features can be used to clearly explain in term of electronic transitions occurring in bone samples which are affected from osteoarthritis symptoms. Moreover, a structural change around Ca ions in bone samples is obviously obtained by EXAFS results indicating an increase of Ca-amorphous phase when the ages increase.

Supervised Machine-Learning-Based Determination of Three-Dimensional Structure of Metallic Nanoparticles

DOE PAGES

Timoshenko, Janis; Lu, Deyu; Lin, Yuewei; ...

2017-09-29

Tracking the structure of heterogeneous catalysts under operando conditions remains a challenge due to the paucity of experimental techniques that can provide atomic-level information for catalytic metal species. Here we report on the use of X-ray absorption near edge structure (XANES) spectroscopy and supervised machine learning (SML) for refining the three-dimensional geometry of metal catalysts. SML is used to unravel the hidden relationship between the XANES features and catalyst geometry. To train our SML method, we rely on ab-initio XANES simulations. Our approach allows one to solve the structure of a metal catalyst from its experimental XANES, as demonstrated heremore » by reconstructing the average size, shape and morphology of well-defined platinum nanoparticles. This method is applicable to the determination of the nanoparticle structure in operando studies and can be generalized to other nanoscale systems. In conclusion, it also allows on-the-fly XANES analysis, and is a promising approach for high-throughput and time-dependent studies.« less

Supervised Machine-Learning-Based Determination of Three-Dimensional Structure of Metallic Nanoparticles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Timoshenko, Janis; Lu, Deyu; Lin, Yuewei

Tracking the structure of heterogeneous catalysts under operando conditions remains a challenge due to the paucity of experimental techniques that can provide atomic-level information for catalytic metal species. Here we report on the use of X-ray absorption near edge structure (XANES) spectroscopy and supervised machine learning (SML) for refining the three-dimensional geometry of metal catalysts. SML is used to unravel the hidden relationship between the XANES features and catalyst geometry. To train our SML method, we rely on ab-initio XANES simulations. Our approach allows one to solve the structure of a metal catalyst from its experimental XANES, as demonstrated heremore » by reconstructing the average size, shape and morphology of well-defined platinum nanoparticles. This method is applicable to the determination of the nanoparticle structure in operando studies and can be generalized to other nanoscale systems. In conclusion, it also allows on-the-fly XANES analysis, and is a promising approach for high-throughput and time-dependent studies.« less

Investigation of the nanoscale two-component ZnS-ZnO heterostructures by means of HR-TEM and X-ray based analysis

NASA Astrophysics Data System (ADS)

Pankin, I. A.; Polozhentsev, O. E.; Soldatov, M. A.; Bugaev, A. L.; Tsaturyan, A.; Lomachenko, K. A.; Guda, A. A.; Budnyk, A. P.; Lamberti, C.; Soldatov, A. V.

2018-06-01

This article is devoted to the spectroscopic characterization of ZnS-ZnO nanoscale heterostructures synthesized by the microwave-assisted solvothermal method. The synthesized samples were investigated by means of X-ray powder diffraction (XRPD), high energy resolution fluorescence detected X-ray absorption near-edge-structure (HERFD-XANES) spectroscopy, valence-to-core X-ray emission spectroscopy (VtC-XES) and high resolution transmission electron microscopy (HR-TEM) as well as energy dispersive X-ray spectroscopy (EDX). The average crystallite size estimated by the broadening of XRPD peaks increases from 2.7 nm to 3.7 nm in the temperature range from 100 °C to 150 °C. HR-TEM images show that nanoparticles are arranged in aggregates with the 60-200 nm size. Theoretical estimation shows that the systems synthesized at higher temperatures more prone to the agglomeration. The full profile Reitveld analysis of XRPD data reveals the formation of hexagonal zinc sulfide structure, whereas electron diffraction data reveal also the formation of cubic zinc sulfide and claim the polymorphous character of the system. High energy resolution Zn K-edge XANES data unambiguously demonstrate the presence of a certain amount of the zinc oxide which is likely to have an amorphous structure and could not be detected by XRPD. Qualitative analysis of XANES data allows deriving ZnS/ZnO ratio as a function of synthesis temperature. EDX analysis depicts homogeneous distribution of ZnS and amorphous ZnO phases across the conglomerates. A complementary element-selective valence to core X-ray emission spectroscopy evidences formation of two-component system and confirms estimations of ZnS/ZnO fractions obtained by linear combination fit of XANES data.

The coordination of sulfur in synthetic and biogenic Mg calcites: The red coral case

NASA Astrophysics Data System (ADS)

Perrin, J.; Rivard, C.; Vielzeuf, D.; Laporte, D.; Fonquernie, C.; Ricolleau, A.; Cotte, M.; Floquet, N.

2017-01-01

Sulfur has been recognized in biogenic calcites for a long time. However, its structural position is matter of debate. For some authors, sulfur is a marker of the organic matrix while it is part of the calcite structure itself for others. To better understand the place of sulfur in calcite, sulfated magnesian calcites (S-MgCalcite) have been synthetized at high pressure and temperature and studied by μ-XANES spectroscopy. S-MgCalcite XANES spectra show two different types of sulfur: sulfate (SO42-) as a predominant species and a small contribution of sulfite (SO32-), both substituting for carbonate ions in the calcite structure. To address the question of the position of sulfur in biogenic calcites, the oxidation states of sulfur in the skeleton and organic tissues of Corallium rubrum have been investigated by micro X-ray fluorescence (μ-XRF) and sulfur K-edge micro X-ray absorption near edge structure (μ-XANES) spectroscopy at the European Synchrotron Radiation Facility (ESRF, Grenoble, France) on beamline ID21. In the skeleton, sulfur is mainly present as oxidized sulfur SO42- (+VI), plus a weak sulfite contribution. XANES spectra indicate that sulfur is inorganically incorporated as sulfur structurally substituted to carbonate ions (SSS). Although an organic matrix is present in the red coral skeleton, reduced organic sulfur could not be detected by μ-XANES spectroscopy in the skeleton probably due to low organic/inorganic sulfur ratio. In the organic tissues surrounding the skeleton, several sulfur oxidation states have been detected including disulfide (S-S), thioether (R-S-CH3), sulfoxide (SO2), sulfonate (SO2O-) and sulfate (SO42-). The unexpected occurrence of inorganic sulfate within the organic tissues suggests the presence of pre-organized organic/inorganic complexes in the circulatory system of the red coral, precursors to biomineralization ahead of the growth front.

Observation of high-spin mixed oxidation state of cobalt in ceramic Co3TeO6

NASA Astrophysics Data System (ADS)

Singh, Harishchandra; Ghosh, Haranath; Chandrasekhar Rao, T. V.; Sinha, A. K.; Rajput, Parasmani

2014-12-01

We report coexistence of high spin Co3+ and Co2+ in ceramic Co3TeO6 using X-ray Absorption Near Edge Structure (XANES), DC magnetization, and first principles ab-initio calculations. The main absorption line of cobalt Co K-edge XANES spectra, along with a linear combination fit, led us to estimate relative concentration of Co2+ and Co3+as 60:40. The pre edge feature of XANES spectrum shows crystal field splitting of ˜1.26 eV between eg and t2g states, suggesting a mixture of high spin states of both Co2+ and Co3+. Temperature dependent high field DC magnetization measurements reveal dominant antiferromagnetic order with two Neel temperatures (TN1 ˜ 29 K and TN2 ˜ 18 K), consistent with single crystal study. A larger effective magnetic moment is observed in comparison to that reported for single crystal (which contains only Co2+), supports our inference that Co3+ exists in high spin state. Furthermore, we show that both Co2+ and Co3+ being in high spin states constitute a favorable ground state through first principles ab-initio calculations, where Rietveld refined synchrotron X-ray diffraction data are used as input.

A Study of Ziegler–Natta Propylene Polymerization Catalysts by Spectroscopic Methods

PubMed Central

Tkachenko, Olga P.; Kucherov, Alexey V.; Kustov, Leonid M.; Virkkunen, Ville; Leinonen, Timo; Denifl, Peter

2017-01-01

Ziegler–Natta polymerization catalysts were characterized by a complex of surface- and bulk-sensitive methods (DRIFTS, XPS, ESR, and XAS = XANES + EXAFS). A diffuse-reflectance Fourier-transform IR spectroscopy (DRIFTS) study showed the presence of strong Lewis acid sites in different concentrations and absence of strong basic sites in the polymerization catalysts. X-ray photoelectron spectroscopy (XPS), electron-spin resonance (ESR), and (X-ray absorption near-edge structure (XANES) analysis revealed the presence of Ti4+, Ti3+, Ti2+, and Ti1+ species in the surface layers and in the bulk of catalysts. The samples under study differ drastically in terms of the number of ESR-visible paramagnetic sites. The EXAFS study shows the presence of a Cl atom as a nearest neighbor of the absorbing Ti atom. PMID:28772850

Investigation of arsenic species in tailings and windblown dust from a gold mining area.

PubMed

Ono, F B; Tappero, R; Sparks, D; Guilherme, L R G

2016-01-01

Research has shown the presence of high levels of arsenic (up to 2666 mg As kg(-1)) in tailings from a gold mining area of Brazil. This is an important point of attention, generating concerns about impacts on human health. Yet, a recent study showed that As bioaccessibility in the same area was very low (<4.4%). Thus, determination of the direct solid-phase speciation of As in the mine tailings and windblown dust is needed to explain this low bioaccessibility. Mine samples were collected from four subareas and windblown dust from eight sites. Synchrotron-based bulk-X-ray absorption near-edge structure (bulk-XANES) spectroscopy, micro-X-ray absorption near-edge structure (μ-XANES), and μ-X-ray fluorescence (μ-SXRF) spectroscopy were applied to determine As speciation. Bulk-XANES spectra indicated that As occurs as the As(V) oxidation state. Micro-XANES and μ-SXRF analyses revealed that As was also present as arsenopyrite (FeAsS) and its weathering products, but mostly it was As(V) as poorly crystalline ferric arsenate. This supports the findings of low bioaccessible As and highlights the importance of Fe oxides in immobilizing As in the terrestrial environment. All air particulate samples exhibited As-rich particles (up to 313 mg As kg(-1)). The air particulates exhibited solid-phase As species very similar to those found in the mine samples, which indicates that As in the windblown dust is not easily available.

Influence of point defects on the near edge structure of hexagonal boron nitride

NASA Astrophysics Data System (ADS)

McDougall, Nicholas L.; Partridge, Jim G.; Nicholls, Rebecca J.; Russo, Salvy P.; McCulloch, Dougal G.

2017-10-01

Hexagonal boron nitride (hBN) is a wide-band-gap semiconductor with applications including gate insulation layers in graphene transistors, far-ultraviolet light emitting devices and as hydrogen storage media. Due to its complex microstructure, defects in hBN are challenging to identify. Here, we combine x-ray absorption near edge structure (XANES) spectroscopy with ab initio theoretical modeling to identify energetically favorable defects. Following annealing of hBN samples in vacuum and oxygen, the B and N K edges exhibited angular-dependent peak modifications consistent with in-plane defects. Theoretical calculations showed that the energetically favorable defects all produce signature features in XANES. Comparing these calculations with experiments, the principle defects were attributed to substitutional oxygen at the nitrogen site, substitutional carbon at the boron site, and hydrogen passivated boron vacancies. Hydrogen passivation of defects was found to significantly affect the formation energies, electronic states, and XANES. In the B K edge, multiple peaks above the major 1 s to π* peak occur as a result of these defects and the hydrogen passivated boron vacancy produces the frequently observed doublet in the 1 s to σ* transition. While the N K edge is less sensitive to defects, features attributable to substitutional C at the B site were observed. This defect was also calculated to have mid-gap states in its band structure that may be responsible for the 4.1-eV ultraviolet emission frequently observed from this material.

Forensic analysis of tire rubbers based on their sulfur chemical states.

PubMed

Funatsuki, Atsushi; Shiota, Kenji; Takaoka, Masaki; Tamenori, Yusuke

2015-05-01

The chemical states of sulfur in 11 tires were analyzed using X-ray absorption near-edge structure (XANES) in order to discriminate between various tire rubbers. All tires had peaks around 2471.5 and 2480.5eV, and the shapes and heights of these peaks differed among tires, suggesting that the sulfur chemical state could be used for discrimination between tire rubbers. Based on t-tests on the results of XANES, 43 of 55 combinations were different at a significance level of 5%. Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.

Layer speciation and electronic structure investigation of freestanding hexagonal boron nitride nanosheets

NASA Astrophysics Data System (ADS)

WangEqual Contribution To This Work., Jian; Wang, Zhiqiang; Cho, Hyunjin; Kim, Myung Jong; Sham, T. K.; Sun, Xuhui

2015-01-01

Chemical imaging, thickness mapping, layer speciation and polarization dependence have been performed on single and multilayered (up to three layers and trilayered nanosheets overlapping to form 6 and 9 layers) hexagonal boron nitride (hBN) nanosheets by scanning transmission X-ray microscopy. Spatially-resolved XANES directly from freestanding regions of different layers has been extracted and compared with sample normal and 30° tilted configurations. Notably a double feature σ* excitonic state and a stable high energy σ* state were observed at the boron site in addition to the intense π* excitonic state. The boron projected σ* DOS, especially the first σ* exciton, is sensitive to surface modification, particularly in the single layered hBN nanosheet which shows more significant detectable contaminants and defects such as tri-coordinated boron/nitrogen oxide. The nitrogen site has shown very weak or no excitonic character. The distinct excitonic effect on boron and nitrogen was interpreted to the partly ionic state of hBN. Bulk XANES of hBN nanosheets was also measured to confirm the spectro-microscopic STXM result. Finally, the unoccupied electronic structures of hBN and graphene were compared.Chemical imaging, thickness mapping, layer speciation and polarization dependence have been performed on single and multilayered (up to three layers and trilayered nanosheets overlapping to form 6 and 9 layers) hexagonal boron nitride (hBN) nanosheets by scanning transmission X-ray microscopy. Spatially-resolved XANES directly from freestanding regions of different layers has been extracted and compared with sample normal and 30° tilted configurations. Notably a double feature σ* excitonic state and a stable high energy σ* state were observed at the boron site in addition to the intense π* excitonic state. The boron projected σ* DOS, especially the first σ* exciton, is sensitive to surface modification, particularly in the single layered hBN nanosheet which

[Effect of Long-Term Fertilization on Organic Nitrogen Functional Groups in Black Soil as Revealed by Synchrotron-Based X-Ray Absorption Near-Edge Structure Spectroscopy].

PubMed

Li, Hui; Gao, Qiang; Wang, Shuai; Zhu, Ping; Zhang, Jin-jing; Zhao, Yi-dong

2015-07-01

Nitrogen (N) is a common limiting nutrient in crop production. The N content of soil has been used as an important soil fertility index. Organic N is the major form of N in soil. In most agricultural surface soils, more than 90% of total N occurs in organic forms. Therefore, understanding the compositional characteristics of soil organic N functional groups can provide the scientific basis for formulating the reasonable farmland management strategies. Synchrotron radiation soft X-ray absorption near-edge structure (N K-edge XANES) spectroscopy is the most powerful tool to characterize in situ organic N functional groups compositions in soil. However, to our most knowledge, no studies have been conducted to examine the organic N functional groups compositions of soil using N K-edge XANES spectroscopy under long-term fertilization practices. Based on a long-term field experiment (started in 1990) in a black soil (Gongzhuling, Northeast China), we investigated the differences in organic N functional groups compositions in bulk soil and clay-size soil fraction among fertilization patterns using synchrotron-based N K- edge XANES spectroscopy. Composite soil samples (0-20 cm) were collected in 2008. The present study included six treatments: farmland fallow (FALL), no-fertilization control (CK), chemical nitrogen, phosphorus, and potassium fertilization (NPK), NPK in combination with organic manure (NPKM), 1.5 times of NPKM (1.5 NPKM), and NPK in combination with maize straw (NPKS). The results showed that N K-edge XANES spectra of all the treatments under study exhibited characteristic absorption peaks in the ranges of 401.2-401.6 and 402.7-403.1 eV, which were assigned as amides/amine-N and pyrrole-N, respectively. These characteristic absorption peaks were more obvious in clay-size soil fraction than in bulk soil. The results obtained from the semi-quantitative analysis of N K-edge XANES spectra indicated that the relative proportion of amides/amine-N was the highest

Direct deconvolution of two-state pump-probe X-ray absorption spectra and the structural changes in a 100 ps transient of Ni(II)-tetramesitylporphyrin.

PubMed

Della-Longa, S; Chen, L X; Frank, P; Hayakawa, K; Hatada, K; Benfatto, M

2009-05-04

Full multiple scattering (FMS) Minuit XANES (MXAN) has been combined with laser pump-probe K-edge X-ray absorption spectroscopy (XAS) to determine the structure of photoexcited Ni(II)tetramesitylporphyrin, Ni(II)TMP, in dilute toluene solution. It is shown that an excellent simulation of the XANES spectrum is obtained, excluding the lowest-energy bound-state transitions. In ground-state Ni(II)TMP, the first-shell and second-shell distances are, respectively, d(Ni-N) = (1.93 +/- 0.02) A and d(Ni-C) = (2.94 +/- 0.03) A, in agreement with a previous EXAFS result. The time-resolved XANES difference spectrum was obtained (1) from the spectra of Ni(II)TMP in its photoexcited T(1) state and its ground state, S(0). The XANES difference spectrum has been analyzed to obtain both the structure and the fraction of the T(1) state. If the T(1) fraction is kept fixed at the value (0.37 +/- 0.10) determined by optical transient spectroscopy, a 0.07 A elongation of the Ni-N and Ni-C distances [d(Ni-N) and d(Ni-C)] is found, in agreement with the EXAFS result. However, an evaluation of both the distance elongation and the T(1) fraction can also be obtained using XANES data only. According to experimental evidence, and MXAN simulations, the T(1) fraction is (0.60 +/- 0.15) with d(Ni-N) = (1.98 +/- 0.03) A (0.05 A elongation). The overall uncertainty of these results depends on the statistical correlation between the distances and T(1) fraction, and the chemical shift of the ionization energy because of subtle changes of metal charge between the T(1) and S(0) states. The T(1) excited-state structure results, independently obtained without the excited-state fraction from optical transient spectroscopy, are still in agreement with previous EXAFS investigations. Thus, full multiple scattering theory applied through the MXAN formalism can be used to provide structural information, not only on the ground-state molecules but also on very short-lived excited states through differential

MICROSCANNING XRF, XANES, AND XRD STUDIES OF THEDECORATED SURFACE OF ROMAN TERRA SIGILLATA CERAMICS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mirguet, C.; Sciau, P.; Goudeau, P.

Different microscanning synchrotron techniques were used to better understand the elaboration process and origins of Terra Sigillata potteries from the Roman period. A mixture Gallic slip sample cross-section showing red and yellow colors was studied. The small (micron) size of the X-ray beam available at Stanford Synchrotron Radiation Laboratory (SSRL) and Advanced Light Source (ALS) synchrotron sources, coupled with the use of a sample scanning stage allowed us to spatially resolve the distribution of the constitutive mineral phases related to the chemical composition. Results show that red color is a result of iron-rich hematite crystals and the yellow part ismore » a result of the presence of Ti-rich rutile-type phase (brookite). Volcanic-type clay is at the origin of these marble Terra Sigillata.« less

ICE CHEMISTRY ON OUTER SOLAR SYSTEM BODIES: ELECTRON RADIOLYSIS OF N{sub 2}-, CH{sub 4}-, AND CO-CONTAINING ICES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Materese, Christopher K.; Cruikshank, Dale P.; Sandford, Scott A.

Radiation processing of the surface ices of outer Solar System bodies may be an important process for the production of complex chemical species. The refractory materials resulting from radiation processing of known ices are thought to impart to them a red or brown color, as perceived in the visible spectral region. In this work, we analyzed the refractory materials produced from the 1.2-keV electron bombardment of low-temperature N{sub 2}-, CH{sub 4}-, and CO-containing ices (100:1:1), which simulates the radiation from the secondary electrons produced by cosmic ray bombardment of the surface ices of Pluto. Despite starting with extremely simple icesmore » dominated by N{sub 2}, electron irradiation processing results in the production of refractory material with complex oxygen- and nitrogen-bearing organic molecules. These refractory materials were studied at room temperature using multiple analytical techniques including Fourier-transform infrared spectroscopy, X-ray absorption near-edge structure (XANES) spectroscopy, and gas chromatography coupled with mass spectrometry (GC-MS). Infrared spectra of the refractory material suggest the presence of alcohols, carboxylic acids, ketones, aldehydes, amines, and nitriles. XANES spectra of the material indicate the presence of carboxyl groups, amides, urea, and nitriles, and are thus consistent with the IR data. Atomic abundance ratios for the bulk composition of these residues from XANES analysis show that the organic residues are extremely N-rich, having ratios of N/C ∼ 0.9 and O/C ∼ 0.2. Finally, GC-MS data reveal that the residues contain urea as well as numerous carboxylic acids, some of which are of interest for prebiotic and biological chemistries.« less

Ice Chemistry on Outer Solar System Bodies: Electron Radiolysis of N2-, CH4-, and CO-Containing Ices

NASA Astrophysics Data System (ADS)

Materese, Christopher K.; Cruikshank, Dale P.; Sandford, Scott A.; Imanaka, Hiroshi; Nuevo, Michel

2015-10-01

Radiation processing of the surface ices of outer Solar System bodies may be an important process for the production of complex chemical species. The refractory materials resulting from radiation processing of known ices are thought to impart to them a red or brown color, as perceived in the visible spectral region. In this work, we analyzed the refractory materials produced from the 1.2-keV electron bombardment of low-temperature N2-, CH4-, and CO-containing ices (100:1:1), which simulates the radiation from the secondary electrons produced by cosmic ray bombardment of the surface ices of Pluto. Despite starting with extremely simple ices dominated by N2, electron irradiation processing results in the production of refractory material with complex oxygen- and nitrogen-bearing organic molecules. These refractory materials were studied at room temperature using multiple analytical techniques including Fourier-transform infrared spectroscopy, X-ray absorption near-edge structure (XANES) spectroscopy, and gas chromatography coupled with mass spectrometry (GC-MS). Infrared spectra of the refractory material suggest the presence of alcohols, carboxylic acids, ketones, aldehydes, amines, and nitriles. XANES spectra of the material indicate the presence of carboxyl groups, amides, urea, and nitriles, and are thus consistent with the IR data. Atomic abundance ratios for the bulk composition of these residues from XANES analysis show that the organic residues are extremely N-rich, having ratios of N/C ∼ 0.9 and O/C ∼ 0.2. Finally, GC-MS data reveal that the residues contain urea as well as numerous carboxylic acids, some of which are of interest for prebiotic and biological chemistries.

Phosphorous Speciation in WTR-treated Biosolids Using XANES

NASA Astrophysics Data System (ADS)

Zhang, T. Q.; Huff, D.; Lin, Z.-Q.

2009-04-01

The concept of co-application of biosolids and drinking water treatment residues (DWTRs) represents an environmentally sustainable and economically sound strategy for the management of municipal solid wastes. This study demonstrated the effectiveness of reducing water-soluble P in biosolids-amended agricultural soil by the addition of DWTRs. Results showed that total P in soil leachate was significantly reduced during the initial 42-days of a 200-day greenhouse study when biosolids (50 g kg-1) were applied along with DWTRs (40 g kg-1). Particulate P was the dominant fraction of P in the soil leachate, which decreases with increasing DWTR application rate. The application of DWTRs does not significantly decrease the growth and yield of wheat (Triticum aestivum L.). The primary P chemical composition in biosolids include cupper phytate [Cu(IP6)6], barium phytate [Ba6IP6], and cupper phosphate [Cu3(PO4)2]. The addition of DWTRs to biosolids alternated the P speciation, and the P speciation change became significant with increasing the incubation time of the mixture of biosolids and DWTRs. The chemical component of Cu3(PO4)2 became non significant (<5%) with the addition of DWTRs. During the 14-day incubation time period, the proportion of P that was adsorbed on amorphous Fe(OH)3 increased substantially from 8 to 46% and Ba6IP6 increased steadily from 30 to 50%, while the proportion of Cu(IP6)6 decreased significantly from 53 to 5%. The amorphous Fe(OH)3-adsorbed P and Ba6IP6 formed the dominant P chemical components in the mixture of biosolids and DWTRs.

XAS study of TiO2-based nanomaterials

NASA Astrophysics Data System (ADS)

Schneider, K.; Zajac, D.; Sikora, M.; Kapusta, Cz.; Michalow-Mauke, K.; Graule, Th.; Rekas, M.

2015-07-01

X-Ray Absorption Spectroscopy studies of the W (0-1 at% W) and Mo-doped TiO2 (0-1 at% Mo) nanoparticle specimens at the K edges of titanium and molybdenum as well as at the L2 L3 edges of tungsten are presented. The materials were prepared with Flame Spray Synthesis process by oxidation of metal-organic precursors. The Ti:K edge spectra in the XANES range show pre-edge and post-edge features characteristic for anatase. A decrease of the amplitude of the EXAFS function with doping is observed and attributed to a softening of the crystal lattice. The Mo EXAFS functions show a considerable decrease of the second-neighbour-shell peak with increasing Mo content, which is attributed to an increased number of cation vacancies. For tungsten a less pronounced effect is observed. The Mo and W XANES spectra do not show noticeable changes with doping level, which indicates their unchanged oxidation states.

X-ray absorption studies of chlorine valence and local environments in borosilicate waste glasses

NASA Astrophysics Data System (ADS)

McKeown, David A.; Gan, Hao; Pegg, Ian L.; Stolte, W. C.; Demchenko, I. N.

2011-01-01

Chlorine (Cl) is a constituent of certain types of nuclear wastes and its presence can affect the physical and chemical properties of silicate melts and glasses developed for the immobilization of such wastes. Cl K-edge X-ray absorption spectra (XAS) were collected and analyzed to characterize the unknown Cl environments in borosilicate waste glass formulations, ranging in Cl-content from 0.23 to 0.94 wt.%. Both X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) data for the glasses show trends dependent on calcium (Ca) content. Near-edge data for the Ca-rich glasses are most similar to the Cl XANES of CaCl 2, where Cl - is coordinated to three Ca atoms, while the XANES for the Ca-poor glasses are more similar to the mineral davyne, where Cl is most commonly coordinated to two Ca in one site, as well as Cl and oxygen nearest-neighbors in other sites. With increasing Ca content in the glass, Cl XANES for the glasses approach that for CaCl 2, indicating more Ca nearest-neighbors around Cl. Reliable structural information obtained from the EXAFS data for the glasses is limited, however, to Cl sbnd Cl, Cl sbnd O, and Cl sbnd Na distances; Cl sbnd Ca contributions could not be fit to the glass data, due to the narrow k-space range available for analysis. Structural models that best fit the glass EXAFS data include Cl sbnd Cl, Cl sbnd O, and Cl sbnd Na correlations, where Cl sbnd O and Cl sbnd Na distances decrease by approximately 0.16 Å as glass Ca content increases. XAS for the glasses indicates Cl - is found in multiple sites where most Cl-sites have Ca neighbors, with oxygen, and possibly, Na second-nearest neighbors. EXAFS analyses suggest that Cl sbnd Cl environments may also exist in the glasses in minor amounts. These results are generally consistent with earlier findings for silicate glasses, where Cl - was associated with Ca 2+ and Na + in network modifier sites.

Site-selective XAFS spectroscopy tuned to surface active sites of Cu/ZnO and Cr/SiO2 catalysts.

PubMed

Izumi, Y; Nagamori, H; Kiyotaki, F; Minato, T

2001-03-01

XAFS (X-ray absorption fine structure) spectra were measured by using the fluorescence spectrometer for the emitted X-ray from sample. The chemical shifts between Cu0 and Cu1 and between CrIII and CrVI were evaluated. Tuning the fluorescence spectrometer to each energy, the Cu0 and CuI site-selective XANES for Cu/ZnO catalyst were measured. The first one was similar to the XANES of Cu metal and the second one was the 5 : 5 average of XANES for CuI sites + Cu metal. The population ratio of copper site of the Cu/ZnO catalyst was found to be Cu metal: Cu2O : CuI atomically dispersed on surface = 70(+/-23) : 22(+/-14) : 8(+/-5). Site-selective XANES for CrIII site of Cr/SiO2 catalyst was also studied.

The oxidation state of Fe in MORB glasses and the oxygen fugacity of the upper mantle

NASA Astrophysics Data System (ADS)

Cottrell, Elizabeth; Kelley, Katherine A.

2011-05-01

Micro-analytical determination of Fe3+/∑Fe ratios in mid-ocean ridge basalt (MORB) glasses using micro X-ray absorption near edge structure (μ-XANES) spectroscopy reveals a substantially more oxidized upper mantle than determined by previous studies. Here, we show that global MORBs yield average Fe3+/∑Fe ratios of 0.16 ± 0.01 (n = 103), which trace back to primary MORB melts equilibrated at the conditions of the quartz-fayalite-magnetite (QFM) buffer. Our results necessitate an upward revision of the Fe3+/∑Fe ratios of MORBs, mantle oxygen fugacity, and the ferric iron content of the mantle relative to previous wet chemical determinations. We show that only 0.01 (absolute, or < 10%) of the difference between Fe3+/∑Fe ratios determined by micro-colorimety and XANES can be attributed to the Mössbauer-based XANES calibration. The difference must instead derive from a bias between micro-colorimetry performed on experimental vs. natural basalts. Co-variations of Fe3+/∑Fe ratios in global MORB with indices of low-pressure fractional crystallization are consistent with Fe3+ behaving incompatibly in shallow MORB magma chambers. MORB Fe3+/∑Fe ratios do not, however, vary with indices of the extent of mantle melting (e.g., Na2O(8)) or water concentration. We offer two hypotheses to explain these observations: The bulk partition coefficient of Fe3+ may be higher during peridotite melting than previously thought, and may vary with temperature, or redox exchange between sulfide and sulfate species could buffer mantle melting at ~ QFM. Both explanations, in combination with the measured MORB Fe3+/∑Fe ratios, point to a fertile MORB source with greater than 0.3 wt.% Fe2O3.

Crystal structure and electronic states of Co and Gd ions in a Gd0.4Sr0.6CoO2.85 single crystal

NASA Astrophysics Data System (ADS)

Platunov, M. S.; Dudnikov, V. A.; Orlov, Yu. S.; Kazak, N. V.; Solovyov, L. A.; Zubavichus, Ya. V.; Veligzhanin, A. A.; Dorovatovskii, P. V.; Vereshchagin, S. N.; Shaykhutdinov, K. A.; Ovchinnikov, S. G.

2016-02-01

X-ray diffraction and X-ray absorption near edge structure (XANES) spectra have been measured at the Co K-edge and Gd L 3-edge in GdCoO3 and Gd0.4Sr0.6CoO2.85 cobaltites. The effect of Sr substitution on the crystal structure and electronic and magnetic states of Co3+ ions in a Gd0.4Sr0.6CoO2.85 single crystal has been analyzed. The XANES measurements at the Co K-edge have not showed a noticeable shift of the absorption edge with an increase in the concentration of Sr. This indicates that the effective valence of cobalt does not change. An increase in the intensity of absorption at the Gd L 3-edge is due to an increase in the degree of hybridization of the Gd(5 d) and O(2 p) states. The effect of hole doping on the magnetic properties results in the appearance of the ferromagnetic component and in a significant increase in the magnetic moment.

Evolution of Eu valence and superconductivity in layered Eu0.5La0.5FBiS2 -xSex system

NASA Astrophysics Data System (ADS)

Mizuguchi, Y.; Paris, E.; Wakita, T.; Jinno, G.; Puri, A.; Terashima, K.; Joseph, B.; Miura, O.; Yokoya, T.; Saini, N. L.

2017-02-01

We have studied the effect of Se substitution on Eu valence in a layered Eu0.5La0.5FBiS2 -xSex superconductor using a combined analysis of x-ray absorption near-edge structure (XANES) and x-ray photoelectron spectroscopy (XPS) measurements. Eu L3-edge XANES spectra reveal that Eu is in the mixed valence state with coexisting Eu2 + and Eu3 +. The average Eu valence decreases sharply from ˜2.3 for x =0.0 to ˜2.1 for x =0.4 . Consistently, Eu 3 d XPS shows a clear decrease in the average valence by Se substitution. Bi 4 f XPS indicates that effective charge carriers in the BiCh2 (Ch = S, Se) layers are slightly increased by Se substitution. On the basis of the present results it has been discussed that the metallic character induced by Se substitution in Eu0.5La0.5FBiS2 -xSex is likely to be due to increased in-plane orbital overlap driven by reduced in-plane disorder that affects the carrier mobility.

Problems with the thermogravimetric determination of oxygen stoichiometries in pure and rare-earth substituted La2RuO5

NASA Astrophysics Data System (ADS)

Riegg, S.; Müller, T.; Ebbinghaus, S. G.

2013-06-01

The oxygen stoichiometries of pure and rare-earth substituted La2RuO5 have been investigated by thermogravimetry (TG) in reducing atmosphere. Assuming that the observed total weight loss is caused by the reduction of Ru4+ to Ru-metal, remarkable oxygen deficiencies were calculated. These would correspond to ruthenium oxidation states significantly lower than the ones experimentally observed by XANES. To explain this discrepancy we investigated the reduction products by X-ray absorption spectroscopy (XAS). EXAFS measurements at the Ru-K edge revealed the presence of an X-ray amorphous ruthenium oxide, indicating an incomplete reduction. The apparent oxygen deficiencies obtained for pure and rare-earth substituted samples correlate with the amount of remaining ruthenium oxide. The presence of a ruthenium oxide species was furthermore verified by Ru-LIII XANES investigations. Our results show that the determination of oxygen contents by thermogravimetry might fail even for the easily reducable nobel metal oxides and therefore has to be applied with caution if the reaction products cannot be identified unambiguously.

Specimen charging in X-ray absorption spectroscopy: correction of total electron yield data from stabilized zirconia in the energy range 250-915 eV.

PubMed

Vlachos, Dimitrios; Craven, Alan J; McComb, David W

2005-03-01

The effects of specimen charging on X-ray absorption spectroscopy using total electron yield have been investigated using powder samples of zirconia stabilized by a range of oxides. The stabilized zirconia powder was mixed with graphite to minimize the charging but significant modifications of the intensities of features in the X-ray absorption near-edge fine structure (XANES) still occurred. The time dependence of the charging was measured experimentally using a time scan, and an algorithm was developed to use this measured time dependence to correct the effects of the charging. The algorithm assumes that the system approaches the equilibrium state by an exponential decay. The corrected XANES show improved agreement with the electron energy-loss near-edge fine structure obtained from the same samples.

Long-Term Trial Results Show No Mortality Benefit from Annual Prostate Cancer Screening

Cancer.gov

Thirteen year follow-up data from the Prostate, Lung, Colorectal and Ovarian (PLCO) cancer screening trial show higher incidence but similar mortality among men screened annually with the prostate-specific antigen (PSA) test and digital rectal examination

Low Z elements (Mg, Al, and Si) K-edge X-ray absorption spectroscopy in minerals and disordered systems

NASA Astrophysics Data System (ADS)

Ildefonse, Ph.; Calas, G.; Flank, A. M.; Lagarde, P.

1995-05-01

Soft X-ray absorption near edge spectroscopy (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy have been performed at the Mg-, Al- and Si-K edges in order to establish the ability of this spectroscopy to derive structural information in disordered solids such as glasses and gels. Mg- and Al-K XANES are good structural probes to determine the coordination state of these elements in important minerals, glasses and gels. In a CaOsbnd MgOsbnd 2SiO2 glass Mg XANES spectra differ from that found in the crystalline equivalent, with a significant shift of the edge maxima to lower energy, consistent with a CN lower than 6. Mg-EXAFS on the same sample are in agreement and indicate the presence of 5-coordinated Mg with Mgsbnd O distances of 2.01Å. In aluminosilicate gels, Alsbnd K XANES has been used to investigate the [4]Al/Altotal ratios. These ratios increase as the Al/Si ratios decrease. Aluminosilicate and ferric-silicate gels were studied by using Sisbnd K edge XANES. XANES spectra differ significantly among the samples studied. Aluminosilicate gels with Al/Si= 1 present a different Al and Si local environment from that known in clay minerals with the same Al/Si ratio. The gel-to-mineral transformation thus implies a dissolution-recrystallization mechanism. On the contrary, ferric-silicate gel presents a Si local environment close to that found in nontronite which may be formed by a long range ordering of the initial gels.

Solid state synthesis of layered sodium manganese oxide for sodium-ion battery by in-situ high energy X-ray diffraction and X-ray absorption near edge spectroscopy [Solid state synthesis of layered sodium manganese oxide for sodium-ion battery by in-situ HEXRD and XANES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ma, Tianyuan; Xu, Gui -Liang; Zeng, Xiaoqiao

In situ high energy X-ray diffraction (HEXRD) and in situ X-ray absorption near edge spectroscopy (XANES) were carried out to understand the soild state synthesis of Na xMnO 2, with particular interest on the synthesis of P2 type Na 2/3MnO 2. It was found that there were multi intermediate phases formed before NaMnO 2 appeared at about 600 °C. And the final product after cooling process is a combination of O'3 NaMnO 2 with P2 Na 2/3MnO 2. A P2 type Na 2/3MnO 2 was synthesized at reduced temperature (600 °C). The influence of Na 2CO 3 impurity on themore » electrochemical performance of P2 Na 2/3MnO 2 was thoroughly investigated in our work. It was found that the content of Na 2CO 3 can be reduced by optimizing Na 2CO 3/MnCO 3 ratio during the solid state reaction or other post treatment such as washing with water. Lastly, we expected our results could provide a good guide for future development of high performance cathode materials for sodium-ion batteries.« less

Solid state synthesis of layered sodium manganese oxide for sodium-ion battery by in-situ high energy X-ray diffraction and X-ray absorption near edge spectroscopy [Solid state synthesis of layered sodium manganese oxide for sodium-ion battery by in-situ HEXRD and XANES

DOE PAGES

Ma, Tianyuan; Xu, Gui -Liang; Zeng, Xiaoqiao; ...

2016-12-07

In situ high energy X-ray diffraction (HEXRD) and in situ X-ray absorption near edge spectroscopy (XANES) were carried out to understand the soild state synthesis of Na xMnO 2, with particular interest on the synthesis of P2 type Na 2/3MnO 2. It was found that there were multi intermediate phases formed before NaMnO 2 appeared at about 600 °C. And the final product after cooling process is a combination of O'3 NaMnO 2 with P2 Na 2/3MnO 2. A P2 type Na 2/3MnO 2 was synthesized at reduced temperature (600 °C). The influence of Na 2CO 3 impurity on themore » electrochemical performance of P2 Na 2/3MnO 2 was thoroughly investigated in our work. It was found that the content of Na 2CO 3 can be reduced by optimizing Na 2CO 3/MnCO 3 ratio during the solid state reaction or other post treatment such as washing with water. Lastly, we expected our results could provide a good guide for future development of high performance cathode materials for sodium-ion batteries.« less

Atomistic simulation and XAS investigation of Mn induced defects in Bi{sub 12}TiO{sub 20}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rezende, Marcos V dos S.; Santos, Denise J.; Jackson, Robert A.

2016-06-15

This work reports an investigation of the valence and site occupancy of Mn dopants in Bi{sub 12}TiO{sub 20} (BTO: Mn) host using X-ray Absorption (XAS) and atomistic simulation techniques based on energy minimisation. X-ray Absorption Near Edge Structure (XANES) at the Mn K-edges gave typical results for Mn ions with mixed valences of 3+ and 4+. Extended X-ray Absorption Fine Structure (EXAFS) results indicated that Mn ions are probably substituted at Ti sites. Atomistic simulation was performed assuming the incorporation of Mn{sup 2+}, Mn{sup 3+} and Mn{sup 4+} ions at either Bi{sup 3+} or Ti{sup 4+} sites, and the resultsmore » were compared to XANES and EXAFS measurements. Electrical conductivity for pure and doped samples was used to evaluate the consistency of the proposed model. - Graphical abstract: The structure of Bi{sub 12}TiO{sub 20} (BTO). Display Omitted - Highlights: • Pure and Mn-doped Bi{sub 12}TiO{sub 20} samples were studied by experimental techniques combined with atomistic simulation. • Good agreement between experimental and simulation results was obtained. • XANES results suggest a mixture of 3+ and 4+ valences for Mn, occupying the Ti4+ site in both cases. • Charge compensation by holes is most energetically favoured, explaining the enhancement observed in AC dark conductivity.« less

Investigation of the stability of glass-ceramic composites containing CeTi 2 O 6 and CaZrTi 2 O 7 after ion implantation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Paknahad, Elham; Grosvenor, Andrew P.

Glass-ceramic composite materials have been investigated for nuclear waste sequestration applications due to their ability to incorporate large amounts of radioactive waste elements. A key property that needs to be understood when developing nuclear waste sequestration materials is how the structure of the material responds to radioactive decay of nuclear waste elements, which can be simulated by high energy ion implantation. Borosilicate glass-ceramic composites containing brannerite-type (CeTi2O6) or zirconolite-type (CaZrTi2O7) oxides were synthesized at different annealing temperatures and investigated after being implanted with high-energy Au ions to mimic radiation induced structural damage. Backscattered electron (BSE) images were collected to investigatemore » the interaction of the brannerite crystallites with the glass matrix before and after implantation and showed that the morphology of the crystallites in the composite materials were not affected by radiation damage. Surface sensitive Ti K-edge glancing angle XANES spectra collected from the implanted composite materials showed that the structures of the CeTi2O6 and CaZrTi2O7 ceramics were damaged as a result of implantation; however, analysis of Si L2,3-edge XANES spectra indicated that the glass matrix was not affected by ion implantation.« less

Investigation of the stability of glass-ceramic composites containing CeTi2O6 and CaZrTi2O7 after ion implantation

NASA Astrophysics Data System (ADS)

Paknahad, Elham; Grosvenor, Andrew P.

2017-12-01

Glass-ceramic composite materials have been investigated for nuclear waste sequestration applications due to their ability to incorporate large amounts of radioactive waste elements. A key property that needs to be understood when developing nuclear waste sequestration materials is how the structure of the material responds to radioactive decay of nuclear waste elements, which can be simulated by high energy ion implantation. Borosilicate glass-ceramic composites containing brannerite-type (CeTi2O6) or zirconolite-type (CaZrTi2O7) oxides were synthesized at different annealing temperatures and investigated after being implanted with high-energy Au ions to mimic radiation induced structural damage. Backscattered electron (BSE) images were collected to investigate the interaction of the brannerite crystallites with the glass matrix before and after implantation and showed that the morphology of the crystallites in the composite materials were not affected by radiation damage. Surface sensitive Ti K-edge glancing angle XANES spectra collected from the implanted composite materials showed that the structures of the CeTi2O6 and CaZrTi2O7 ceramics were damaged as a result of implantation; however, analysis of Si L2,3-edge XANES spectra indicated that the glass matrix was not affected by ion implantation.

Radiation damages during synchrotron X-ray micro-analyses of Prussian blue and zinc white historic paintings: detection, mitigation and integration

NASA Astrophysics Data System (ADS)

Gervais, Claire; Thoury, Mathieu; Réguer, Solenn; Gueriau, Pierre; Mass, Jennifer

2015-11-01

High-flux synchrotron techniques allow microspectroscopic analyses of artworks that were not feasible even a few years ago, allowing for a more detailed characterization of their constituent materials and a better understanding of their chemistry. However, interaction between high-flux photons and matter at the sub-microscale can generate damages which are not visually detectable. We show here different methodologies allowing to evidence the damages induced by microscopic X-ray absorption near-edge structure spectroscopy analysis (μXANES) at the Fe and Zn K-edges of a painting dating from the turn of the twentieth century containing Prussian blue and zinc white. No significant degradation of the pigments was noticed, in agreement with the excellent condition of the painting. However, synchrotron radiation damages occurred at several levels, from chemical changes of the binder, modification of crystal defects in zinc oxide, to Prussian blue photoreduction. They could be identified by using both the μXANES signal during analysis and with photoluminescence imaging in the deep ultraviolet and visible ranges after analysis. We show that recording accurately damaged areas is a key step to prevent misinterpretation of results during future re-examination of the sample. We conclude by proposing good practices that could help in integrating radiation damage avoidance into the analytical pathway.

Conventional physical therapy and physical therapy based on reflex stimulation showed similar results in children with myelomeningocele.

PubMed

Aizawa, Carolina Y P; Morales, Mariana P; Lundberg, Carolina; Moura, Maria Clara D Soares de; Pinto, Fernando C G; Voos, Mariana C; Hasue, Renata H

2017-03-01

We aimed to investigate whether infants with myelomeningocele would improve their motor ability and functional independence after ten sessions of physical therapy and compare the outcomes of conventional physical therapy (CPT) to a physical therapy program based on reflex stimulation (RPT). Twelve children were allocated to CPT (n = 6, age 18.3 months) or RPT (n = 6, age 18.2 months). The RPT involved proprioceptive neuromuscular facilitation. Children were assessed with the Gross Motor Function Measure and the Pediatric Evaluation of Disability Inventory before and after treatment. Mann-Whitney tests compared the improvement on the two scales of CPT versus RPT and the Wilcoxon test compared CPT to RPT (before vs. after treatment). Possible correlations between the two scales were tested with Spearman correlation coefficients. Both groups showed improvement on self-care and mobility domains of both scales. There were no differences between the groups, before, or after intervention. The CPT and RPT showed similar results after ten weeks of treatment.

Origin of luminescence from ZnO/CdS core/shell nanowire arrays

NASA Astrophysics Data System (ADS)

Wang, Zhiqiang; Wang, Jian; Sham, Tsun-Kong; Yang, Shaoguang

2014-07-01

Chemical imaging, electronic structure and optical properties of ZnO/CdS nano-composites have been investigated using scanning transmission X-ray microscopy (STXM), X-ray absorption near-edge structure (XANES) and X-ray excited optical luminescence (XEOL) spectroscopy. STXM and XANES results confirm that the as-prepared product is ZnO/CdS core/shell nanowires (NWs), and further indicate that ZnS was formed on the surface of ZnO NWs as the interface between ZnO and CdS. The XEOL from ZnO/CdS NW arrays exhibits one weak ultraviolet (UV) emission at 375 nm, one strong green emission at 512 nm, and two broad infrared (IR) emissions at 750 and 900 nm. Combining XANES and XEOL, it is concluded that the UV luminescence is the near band gap emission (BGE) of ZnO; the green luminescence comes from both the BGE of CdS and defect emission (DE, zinc vacancies) of ZnO; the IR luminescence is attributed to the DE (bulk defect related to the S site) of CdS; ZnS contributes little to the luminescence of the ZnO/CdS NW arrays. Interestingly, the BGE and DE from oxygen vacancies of ZnO in the ZnO/CdS nano-composites are almost entirely quenched, while DE from zinc vacancies changes little.Chemical imaging, electronic structure and optical properties of ZnO/CdS nano-composites have been investigated using scanning transmission X-ray microscopy (STXM), X-ray absorption near-edge structure (XANES) and X-ray excited optical luminescence (XEOL) spectroscopy. STXM and XANES results confirm that the as-prepared product is ZnO/CdS core/shell nanowires (NWs), and further indicate that ZnS was formed on the surface of ZnO NWs as the interface between ZnO and CdS. The XEOL from ZnO/CdS NW arrays exhibits one weak ultraviolet (UV) emission at 375 nm, one strong green emission at 512 nm, and two broad infrared (IR) emissions at 750 and 900 nm. Combining XANES and XEOL, it is concluded that the UV luminescence is the near band gap emission (BGE) of ZnO; the green luminescence comes from both the

First X-Ray absorption spectroscopy results on Aeolian dust archived in Antarctica and Alpine firn cores

NASA Astrophysics Data System (ADS)

Marcelli, A.; Maggi, V.; Cibin, G.; Sala, M.; Marino, F.; Delmonte, B.

2006-12-01

. Samples for Total Reflection XAS measurements were prepared just for this kind of measurements by depositing the insoluble mineral dust on clean Si wafer substrates. In addition, the XANES spectra show clear differences, corresponding to different samples mineral iron hosts, demonstrating that with this fully non-distructive technique, new information about the dust mineralogy at very low concentration can be performed. The analysis is then complementary to other well established techniques like XRD and PIXE.

Mechanism study of sulfur fertilization mediating copper translocation and biotransformation in rice (Oryza sativa L.) plants.

PubMed

Sun, Lijuan; Yang, Jianjun; Fang, Huaxiang; Xu, Chen; Peng, Cheng; Huang, Haomin; Lu, Lingli; Duan, Dechao; Zhang, Xiangzhi; Shi, Jiyan

2017-07-01

Metabolism of sulfur (S) is suggested to be an important factor for the homeostasis and detoxification of Cu in plants. We investigated the effects of S fertilizers (S 0 , Na 2 SO 4 ) on Cu translocation and biotransformation in rice plants by using multiple synchrotron-based techniques. Fertilization of S increased the biomass and yield of rice plants, as well as the translocation factor of Cu from root to shoot and shoot to grain, resulting in enhanced Cu in grain. Sulfur K-edge X-ray near edge structure (XANES) analysis showed that fertilization of S increased the concentration of glutathione in different rice tissues, especially in rice stem and leaf. Copper K-edge XANES results indicated that a much higher proportion of Cu (I) species existed in rice grain than husk and leaf, which was further confirmed by soft X-ray scanning transmission microscopy results. Sulfur increased the proportion of Cu (I) species in rice grain, husk and leaf, suggesting the inducing of Cu (II) reduction in rice tissues by S fertilization. These results suggested that fertilization of S in paddy soils increased the accumulation of Cu in rice grain, possibly due to the reduction of Cu (II) to Cu (I) by enhancing glutathione synthesis and increasing the translocation of Cu from shoot to grain. Copyright © 2017 Elsevier Ltd. All rights reserved.

Identification of F impurities in F-doped ZnO by synchrotron X-ray absorption near edge structures

NASA Astrophysics Data System (ADS)

Na-Phattalung, Sutassana; Limpijumnong, Sukit; Min, Chul-Hee; Cho, Deok-Yong; Lee, Seung-Ran; Char, Kookrin; Yu, Jaejun

2018-04-01

Synchrotron X-ray absorption near edge structure (XANES) measurements of F K-edge in conjunction with first-principles calculations are used to identify the local structure of the fluorine (F) atom in F-doped ZnO. The ZnO film was grown by pulsed laser deposition with an Nd:YAG laser, and an oxyfluoridation method was used to introduce F ions into the ZnO films. The measured XANES spectrum of the sample was compared against the first-principles XANES calculations based on various models for local atomic structures surrounding F atoms. The observed spectral features are attributed to ZnF2 and FO defects in wurtzite bulk ZnO.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Unuigbe, David M.; Harting, Margit; Jonah, Emmanuel O.

The presence of native oxide on the surface of silicon nanoparticles is known to inhibit charge transport on the surfaces. Scanning electron microscopy (SEM) studies reveal that the particles in the printed silicon network have a wide range of sizes and shapes. High-resolution transmission electron microscopy reveals that the particle surfaces have mainly the (111)- and (100)-oriented planes which stabilizes against further oxidation of the particles. X-ray absorption spectroscopy (XANES) and X-ray photoelectron spectroscopy (XPS) measurements at the O 1s-edge have been utilized to study the oxidation and local atomic structure of printed layers of silicon nanoparticles which were milledmore » for different times. XANES results reveal the presence of the +4 (SiO 2) oxidation state which tends towards the +2 (SiO) state for higher milling times. Si 2pXPS results indicate that the surfaces of the silicon nanoparticles in the printed layers are only partially oxidized and that all three sub-oxide, +1 (Si 2O), +2 (SiO) and +3 (Si 2O 3), states are present. The analysis of the change in the sub-oxide peaks of the silicon nanoparticles shows the dominance of the +4 state only for lower milling times.« less

Investigation of nanoparticulate silicon as printed layers using scanning electron microscopy, transmission electron microscopy, X-ray absorption spectroscopy and X-ray photoelectron spectroscopy

DOE PAGES

Unuigbe, David M.; Harting, Margit; Jonah, Emmanuel O.; ...

2017-08-21

The presence of native oxide on the surface of silicon nanoparticles is known to inhibit charge transport on the surfaces. Scanning electron microscopy (SEM) studies reveal that the particles in the printed silicon network have a wide range of sizes and shapes. High-resolution transmission electron microscopy reveals that the particle surfaces have mainly the (111)- and (100)-oriented planes which stabilizes against further oxidation of the particles. X-ray absorption spectroscopy (XANES) and X-ray photoelectron spectroscopy (XPS) measurements at the O 1s-edge have been utilized to study the oxidation and local atomic structure of printed layers of silicon nanoparticles which were milledmore » for different times. XANES results reveal the presence of the +4 (SiO 2) oxidation state which tends towards the +2 (SiO) state for higher milling times. Si 2pXPS results indicate that the surfaces of the silicon nanoparticles in the printed layers are only partially oxidized and that all three sub-oxide, +1 (Si 2O), +2 (SiO) and +3 (Si 2O 3), states are present. The analysis of the change in the sub-oxide peaks of the silicon nanoparticles shows the dominance of the +4 state only for lower milling times.« less

Biosorption of Cr(VI) by coconut coir: spectroscopic investigation on the reaction mechanism of Cr(VI) with lignocellulosic material.

PubMed

Shen, Ying-Shuian; Wang, Shan-Li; Huang, Shiuh-Tsuen; Tzou, Yu-Min; Huang, Jang-Hung

2010-07-15

In this study, the removal mechanism of Cr(VI) from water by coconut coir (CC) was investigated using X-ray photoelectron spectroscopy (XPS), Cr K-edge X-ray absorption near edge structure (XANES) and FTIR spectroscopy. The results showed that, upon reaction with CC at pH 3, Cr(VI) was reduced to Cr(III), which was either bound to CC or released back into solution. As revealed by the FTIR spectra of CC before and after reacting with Cr(VI), the phenolic methoxyl and hydroxyl groups of lignin in CC are the dominant drivers of Cr(VI) reduction, giving rise to carbonyl and carboxyl groups on CC. These functional groups can subsequently provide binding sites for Cr(III) resulting from Cr(VI) reduction. In conjunction with forming complexes with carbonyl and carboxyl groups, the formation of Cr(III) hydroxide precipitate could also readily occur as revealed by the linear combination fitting of the Cr K-edge XANES spectrum using a set of reference compounds. The phenolic groups in lignin are responsible for initiating Cr(VI) reduction, so lignocellulosic materials containing a higher amount of phenolic groups are expected to be more effective scavengers for removal of Cr(VI) from the environment. 2010 Elsevier B.V. All rights reserved.

Results From Mars Show Electrostatic Charging of the Mars Pathfinder Sojourner Rover

NASA Technical Reports Server (NTRS)

Kolecki, Joseph C.; Siebert, Mark W.

1998-01-01

Indirect evidence (dust accumulation) has been obtained indicating that the Mars Pathfinder rover, Sojourner, experienced electrostatic charging on Mars. Lander camera images of the Sojourner rover provide distinctive evidence of dust accumulation on rover wheels during traverses, turns, and crabbing maneuvers. The sol 22 (22nd Martian "day" after Pathfinder landed) end-of-day image clearly shows fine red dust concentrated around the wheel edges with additional accumulation in the wheel hubs. A sol 41 image of the rover near the rock "Wedge" (see the next image) shows a more uniform coating of dust on the wheel drive surfaces with accumulation in the hubs similar to that in the previous image. In the sol 41 image, note particularly the loss of black-white contrast on the Wheel Abrasion Experiment strips (center wheel). This loss of contrast was also seen when dust accumulated on test wheels in the laboratory. We believe that this accumulation occurred because the Martian surface dust consists of clay-sized particles, similar to those detected by Viking, which have become electrically charged. By adhering to the wheels, the charged dust carries a net nonzero charge to the rover, raising its electrical potential relative to its surroundings. Similar charging behavior was routinely observed in an experimental facility at the NASA Lewis Research Center, where a Sojourner wheel was driven in a simulated Martian surface environment. There, as the wheel moved and accumulated dust (see the following image), electrical potentials in excess of 100 V (relative to the chamber ground) were detected by a capacitively coupled electrostatic probe located 4 mm from the wheel surface. The measured wheel capacitance was approximately 80 picofarads (pF), and the calculated charge, 8 x 10(exp -9) coulombs (C). Voltage differences of 100 V and greater are believed sufficient to produce Paschen electrical discharge in the Martian atmosphere. With an accumulated net charge of 8 x 10(exp

Transformation of Strontium during formation of biogenic calcium carbonate

NASA Astrophysics Data System (ADS)

Ohnuki, T.; Kozai, N.; Sakamoto, F.; Yamashita, M.; Horiieke, T.; Utsunomiya, S.

2016-12-01

Some amounts of radionuclides contaminated water containing 90Sr generated in the Fukushima Daiichi Nuclear Power Plant were leaked to sea water in the port. One of the possible method to eliminate 90Sr is co-precipitated with biogenic carbonates minerals (CCM). Specific bacteria are known to form biogenic CCM in groundwater. In the present study, we have screened specific bacterium to form CCM in saline water, and studied transformation of Sr during biogenic CCM. A marine microbe of strain TK2d, which is screened from Tokyo bay to form CCM in saline solution, was grown in the medium solution contained urea and Sr. The concentratuion of Sr2+ in the solution was monitored by ICP-OES (ICP-OES; 720 Agilent Technologies, Inc., USA) during the formation of biogenic CCM. The precipitates were analyzed by SEM, TEM, and XAFS. When 1.0 mM Sr was dissolved in the medium solution, the concentration of Sr decreased up to 0.02 mM within 10 days, indicating that most of Sr in the solution was eliminated within 10 days. SEM and TEM analyses showed that needle shaped CCM containing Ca and Sr were formed. The CCM was not single crystalline, but poly-crystalline of calcite and aragonite. The elemental mapping showed that Sr was present at the same position of Ca, indicating that Sr was coprecipitated with Ca. The XANES analysis of Sr in the precipitates showed that the XANES spectrum was not the same as that of Sr coprecipitated with an abiotic Ca carbonates. Linear combination fitting of XANES spectra by those of SrCl2 and SrCO3 showed that both Sr2+ and SrCO3 were present in CCM. Longer contact time resulted in higher content of SrCO3, indicating that Sr was incorporated gradually with time into CCM structure. Thus, Sr was changed its chemical species from adsorbed one to the incorporated one in biogenic CCM in saline solution. This work was partially supported by a research grant from the Japan Science and Technology Agency, Japan (research grant No. 260502).

Nb K-edge x-ray absorption investigation of the pressure induced amorphization in A-site deficient double perovskite La1/3NbO3.

PubMed

Marini, C; Noked, O; Kantor, I; Joseph, B; Mathon, O; Shuker, R; Kennedy, B J; Pascarelli, S; Sterer, E

2016-02-03

Nb K-edge x-ray absorption spectroscopy is utilized to investigate the changes in the local structure of the A-site deficient double perovskite La1/3NbO3 which undergoes a pressure induced irreversible amorphization. EXAFS results show that with increasing pressure up to 7.5 GPa, the average Nb-O bond distance decreases in agreement with the expected compression and tilting of the NbO6 octahedra. On the contrary, above 7.5 GPa, the average Nb-O bond distance show a tendency to increase. Significant changes in the Nb K-edge XANES spectrum with evident low energy shift of the pre-peak and the absorption edge is found to happen in La1/3NbO3 above 6.3 GPa. These changes evidence a gradual reduction of the Nb cations from Nb(5+) towards Nb(4+) above 6.3 GPa. Such a valence change accompanied by the elongation of the average Nb-O bond distances in the octahedra, introduces repulsion forces between non-bonding adjacent oxygen anions in the unoccupied A-sites. Above a critical pressure, the Nb reduction mechanism can no longer be sustained by the changing local structure and amorphization occurs, apparently due to the build-up of local strain. EXAFS and XANES results indicate two distinct pressure regimes having different local and electronic response in the La1/3NbO3 system before the occurence of the pressure induced amorphization at  ∼14.5 GPa.

Analysis of electronic structure of amorphous InGaZnO/SiO{sub 2} interface by angle-resolved X-ray photoelectron spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ueoka, Y.; Ishikawa, Y.; Maejima, N.

2013-10-28

The electronic structures of amorphous indium gallium zinc oxide (a-IGZO) on a SiO{sub 2} layers before and after annealing were observed by constant final state X-ray photoelectron spectroscopy (CFS-XPS) and X-ray adsorption near-edge structure spectroscopy (XANES). From the results of angle-resolved CFS-XPS, the change in the electronic state was clearly observed in the a-IGZO bulk rather than in the a-IGZO/SiO{sub 2} interface. This suggests that the electronic structures of the a-IGZO bulk strongly affected the thin-film transistor characteristics. The results of XANES indicated an increase in the number of tail states upon atmospheric annealing (AT). We consider that the increasemore » in the number of tail states decreased the channel mobility of AT samples.« less

The Oxidation State of Tungsten in Iron Bearing and Iron Free Silicate Glasses: Results from W L-Edge Xanes Measurements

NASA Technical Reports Server (NTRS)

Danielson, Lisa R.; Righter, K.; Sutton S.; Newville, M.; Le, L.

2007-01-01

Tungsten is important in constraining core formation of the Earth because this element is a moderately siderophile element (depleted approx. 10 relative to chondrites) and, as a member of the Hf-W isotopic system, it is useful in constraining the timing of core formation. A number of previous experimental studies have been carried out to determine the silicate solubility and metal-silicate partitioning behavior of W, including its concomitant oxidation state. However, results of previous studies (figure 1) are inconsistent on whether W occurs as W(4+) or W(6+).

Effect of Zn doping on the magneto-caloric effect and critical constants of Mott insulator MnV{sub 2}O{sub 4}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shahi, Prashant; Kumar, A.; Shukla, K. K.

2014-09-15

X-ray absorption near edge spectra (XANES) and magnetization of Zn doped MnV{sub 2}O{sub 4} have been measured and from the magnetic measurement the critical exponents and magnetocaloric effect have been estimated. The XANES study indicates that Zn doping does not change the valence states in Mn and V. It has been shown that the obtained values of critical exponents β, γ and δ do not belong to universal class and the values are in between the 3D Heisenberg model and the mean field interaction model. The magnetization data follow the scaling equation and collapse into two branches indicating that themore » calculated critical exponents and critical temperature are unambiguous and intrinsic to the system. All the samples show large magneto-caloric effect. The second peak in magneto-caloric curve of Mn{sub 0.95}Zn{sub 0.05}V{sub 2}O{sub 4} is due to the strong coupling between orbital and spin degrees of freedom. But 10% Zn doping reduces the residual spins on the V-V pairs resulting the decrease of coupling between orbital and spin degrees of freedom.« less

Selenium speciation in seleniferous agricultural soils under different cropping systems using sequential extraction and X-ray absorption spectroscopy.

PubMed

Qin, Hai-Bo; Zhu, Jian-Ming; Lin, Zhi-Qing; Xu, Wen-Po; Tan, De-Can; Zheng, Li-Rong; Takahashi, Yoshio

2017-06-01

Selenium (Se) speciation in soil is critically important for understanding the solubility, mobility, bioavailability, and toxicity of Se in the environment. In this study, Se fractionation and chemical speciation in agricultural soils from seleniferous areas were investigated using the elaborate sequential extraction and X-ray absorption near-edge structure (XANES) spectroscopy. The speciation results quantified by XANES technique generally agreed with those obtained by sequential extraction, and the combination of both approaches can reliably characterize Se speciation in soils. Results showed that dominant organic Se (56-81% of the total Se) and lesser Se(IV) (19-44%) were observed in seleniferous agricultural soils. A significant decrease in the proportion of organic Se to the total Se was found in different types of soil, i.e., paddy soil (81%) > uncultivated soil (69-73%) > upland soil (56-63%), while that of Se(IV) presented an inverse tendency. This suggests that Se speciation in agricultural soils can be significantly influenced by different cropping systems. Organic Se in seleniferous agricultural soils was probably derived from plant litter, which provides a significant insight for phytoremediation in Se-laden ecosystems and biofortification in Se-deficient areas. Furthermore, elevated organic Se in soils could result in higher Se accumulation in crops and further potential chronic Se toxicity to local residents in seleniferous areas. Copyright © 2017 Elsevier Ltd. All rights reserved.

MAX: Multiplatform Applications for XAFS

NASA Astrophysics Data System (ADS)

Alain, Michalowicz; Jacques, Moscovici; Diane, Muller-Bouvet; Karine, Provost

2009-11-01

MAX is a new EXAFS and XANES analysis package, replacing our old "EXAFS pour le Mac" software suite. The major improvement is the ability to work with strictly the same code, compiled at once for Microsoft Windows, Apple MacOSX and LINUX systems, justifying the title "Multiplatform Applications for XAFS". It is organized as four modules: ABSORBIX (X-ray absorbance and fluorescence self-absorption calculations), CHEROKEE (EXAFS and XANES data treatment), ROUNDMIDNIGHT (EXAFS modeling and fit) and CRYSTALFFREV (from crystal structures and molecular modeling to FEFF EXAFS and XANES theoretical calculations). Most features developed in "EXAFS pour le Mac" are still available, but with much improvements in the user's interface, data treatment algorithms and new functionalities.

Comb-Push Ultrasound Shear Elastography of Breast Masses: Initial Results Show Promise

PubMed Central

Song, Pengfei; Fazzio, Robert T.; Pruthi, Sandhya; Whaley, Dana H.; Chen, Shigao; Fatemi, Mostafa

2015-01-01

Purpose or Objective To evaluate the performance of Comb-push Ultrasound Shear Elastography (CUSE) for classification of breast masses. Materials and Methods CUSE is an ultrasound-based quantitative two-dimensional shear wave elasticity imaging technique, which utilizes multiple laterally distributed acoustic radiation force (ARF) beams to simultaneously excite the tissue and induce shear waves. Female patients who were categorized as having suspicious breast masses underwent CUSE evaluations prior to biopsy. An elasticity estimate within the breast mass was obtained from the CUSE shear wave speed map. Elasticity estimates of various types of benign and malignant masses were compared with biopsy results. Results Fifty-four female patients with suspicious breast masses from our ongoing study are presented. Our cohort included 31 malignant and 23 benign breast masses. Our results indicate that the mean shear wave speed was significantly higher in malignant masses (6 ± 1.58 m/s) in comparison to benign masses (3.65 ± 1.36 m/s). Therefore, the stiffness of the mass quantified by the Young’s modulus is significantly higher in malignant masses. According to the receiver operating characteristic curve (ROC), the optimal cut-off value of 83 kPa yields 87.10% sensitivity, 82.61% specificity, and 0.88 for the area under the curve (AUC). Conclusion CUSE has the potential for clinical utility as a quantitative diagnostic imaging tool adjunct to B-mode ultrasound for differentiation of malignant and benign breast masses. PMID:25774978

The effect of site geometry, Ti content and Ti oxidation state on the Ti K-edge XANES spectrum of synthetic hibonite

NASA Astrophysics Data System (ADS)

Doyle, P. M.; Berry, A. J.; Schofield, P. F.; Mosselmans, J. F. W.

2016-08-01

The Al-rich oxide hibonite (CaAl12O19) is modeled to be the second mineral to condense from a gas of solar composition and is found within calcium-aluminum-rich inclusions and the matrix of chondritic meteorites. Both Ti3+ and Ti4+ are reported in meteoritic hibonite, so hibonite has been proposed as a single mineral oxybarometer that could be used to elucidate conditions within the first 0.2 Myrs of the Solar System. Synthetic hibonites with Ti3+/(Ti3+ + Ti4+) (hereafter Ti3+/ΣTi) ranging between 0 and 1 were prepared as matrix-matched standards for meteoritic hibonite. The largest yield of both Ti-free and Ti-bearing hibonite at ∼1300 and ∼1400 °C was obtained by a single sinter under reducing conditions. In situ micro-beam Ti K-edge X-ray absorption near edge structure (XANES) spectra were recorded from the synthetic hibonites, as well as from terrestrial hibonite. Spectral features in the post-crest region were shown to correlate with the Ti4+ content. Furthermore, Ti4+ on the M2 trigonal bipyramidal and the adjoining M4 octahedral sites appears to cause variability in the post-crest region as a function of orientation. For this suite of synthetic hibonites it was observed that the pre-edge peak region is not influenced by orientation, but is controlled by Ti3+/ΣTi, site geometry and/or Ti concentration. In particular, the pre-edge peak intensities reflect Ti coordination environment and distortion of the M4 octahedral site. Therefore, although pre-edge peak intensities have previously been used to determine Ti3+/ΣTi in meteoritic minerals, we excluded use of the pre-edge peak intensities for quantifying Ti valence states in hibonite. The energy of the absorption edge at a normalized intensity of 0.8 (E0.8) and the energy of the minimum between the pre-edge region and the absorption edge (Em1) were found to vary systematically with Ti3+/ΣTi. Ti3+/ΣTi in hibonite as a function of Em1 was modeled by a quadratic function that may be used to quantify Ti3

Near-edge study of gold-substituted YBa2Cu3O(7-delta)

NASA Technical Reports Server (NTRS)

Ruckman, Mark W.; Hepp, Aloysius F.

1991-01-01

The valence of Cu and Au in YBa2Au0.3Cu2.7O7-delta was investigated using X-ray absorption near edge structure (XANES). X-ray and neutron diffraction studies indicate that Au goes on the Cu(1) site and Cu K-edge XANES shows that this has little effect on the oxidation state of the remaining copper. The Au L3 edge develops a white line feature whose position lies between that of trivalent gold oxide and monovalent potassium gold cyanide, and whose height relative to the edge step is smaller than in the two reference compounds. The appearance of the Au L3 edge suggests that fewer Au 3d states are involved in forming the Au-O bond in YBa2Au0.3Cu2.7O7-delta than in trivalent gold oxide.

Near-edge study of gold-substituted YBa2Cu3O(7-delta)

NASA Technical Reports Server (NTRS)

Ruckman, Mark W.; Hepp, Aloysius F.

1991-01-01

The valence of Cu and Au in YBa2Au0.3Cu2.7O7-delta was investigated using x-ray absorption near edge structure (XANES). X-ray and neutron diffraction studies indicate that Au goes on the Cu(1) site and Cu K-edge XANES shows that this has little effect on the oxidation state of the remaining copper. The Au L3 edge develops a white line feature whose position lies between that of trivalent gold oxide and monovalent potassium gold cyanide, and whose height relative to the edge step is smaller than in the two reference compounds. The appearance of the Au L3 edge suggests that fewer Au 3d states are involved in forming the Au-O bond in YBa2Au0.3Cu2.7O7-delta than in trivalent gold oxide.

Multi-edge X-ray absorption spectroscopy study of road dust samples from a traffic area of Venice using stoichiometric and environmental references

NASA Astrophysics Data System (ADS)

Valotto, Gabrio; Cattaruzza, Elti; Bardelli, Fabrizio

2017-02-01

The appropriate selection of representative pure compounds to be used as reference is a crucial step for successful analysis of X-ray absorption near edge spectroscopy (XANES) data, and it is often not a trivial task. This is particularly true when complex environmental matrices are investigated, being their elemental speciation a priori unknown. In this paper, an investigation on the speciation of Cu, Zn, and Sb based on the use of conventional (stoichiometric compounds) and non-conventional (environmental samples or relevant certified materials) references is explored. This method can be useful in when the effectiveness of XANES analysis is limited because of the difficulty in obtaining a set of references sufficiently representative of the investigated samples. Road dust samples collected along the bridge connecting Venice to the mainland were used to show the potentialities and the limits of this approach.

Elemental and Molecular Segregation in Oil Paintings due to Lead Soap Degradation.

PubMed

Chen-Wiegart, Yu-Chen Karen; Catalano, Jaclyn; Williams, Garth J; Murphy, Anna; Yao, Yao; Zumbulyadis, Nicholas; Centeno, Silvia A; Dybowski, Cecil; Thieme, Juergen

2017-09-14

The formation of Pb, Zn, and Cu carboxylates (soaps) has caused visible deterioration in hundreds of oil paintings dating from the 15th century to the present. Through transport phenomena not yet understood, free fatty acids in the oil binding medium migrate through the paint and react with pigments containing heavy metals to form soaps. To investigate the complex correlation among the elemental segregation, types of chemical compounds formed, and possible mechanisms of the reactions, a paint sample cross-section from a 15th century oil painting was examined by synchrotron X-ray techniques. X-ray fluorescence (XRF) microscopy, quantified with elemental correlation density distribution, showed Pb and Sn segregation in the soap-affected areas. X-ray absorption near edge structure (XANES) around the Pb-L3 absorption edge showed that Pb pigments and Pb soaps can be distinguished while micro-XANES gave further information on the chemical heterogeneity in the paint film. The advantages and limitations of these synchrotron-based techniques are discussed and compared to those of methods routinely used to analyze paint samples. The results presented set the stage for improving the information extracted from samples removed from works of art and for correlating observations in model paint samples to those in the naturally aged samples, to shed light onto the mechanism of soap formation.

Elemental and Molecular Segregation in Oil Paintings due to Lead Soap Degradation

DOE PAGES

Chen-Wiegart, Yu-chen Karen; Catalano, Jaclyn; Williams, Garth J.; ...

2017-09-14

The formation of Pb, Zn, and Cu carboxylates (soaps) has caused visible deterioration in hundreds of oil paintings dating from the 15th century to the present. Through transport phenomena not yet understood, free fatty acids in the oil binding medium migrate through the paint and react with pigments containing heavy metals to form soaps. To investigate the complex correlation among the elemental segregation, types of chemical compounds formed, and possible mechanisms of the reactions, a paint sample cross-section from a 15th century oil painting was examined by synchrotron X-ray techniques. X-ray fluorescence (XRF) microscopy, quantified with elemental correlation density distribution,more » showed Pb and Sn segregation in the soap-affected areas. X-ray absorption near edge structure (XANES) around the Pb-L3 absorption edge showed that Pb pigments and Pb soaps can be distinguished while micro-XANES gave further information on the chemical heterogeneity in the paint film. The advantages and limitations of these synchrotron-based techniques are discussed and compared to those of methods routinely used to analyze paint samples. The results presented set the stage for improving the information extracted from samples removed from works of art and for correlating observations in model paint samples to those in the naturally aged samples, to shed light onto the mechanism of soap formation.« less

Elemental and Molecular Segregation in Oil Paintings due to Lead Soap Degradation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen-Wiegart, Yu-chen Karen; Catalano, Jaclyn; Williams, Garth J.

The formation of Pb, Zn, and Cu carboxylates (soaps) has caused visible deterioration in hundreds of oil paintings dating from the 15th century to the present. Through transport phenomena not yet understood, free fatty acids in the oil binding medium migrate through the paint and react with pigments containing heavy metals to form soaps. To investigate the complex correlation among the elemental segregation, types of chemical compounds formed, and possible mechanisms of the reactions, a paint sample cross-section from a 15th century oil painting was examined by synchrotron X-ray techniques. X-ray fluorescence (XRF) microscopy, quantified with elemental correlation density distribution,more » showed Pb and Sn segregation in the soap-affected areas. X-ray absorption near edge structure (XANES) around the Pb-L3 absorption edge showed that Pb pigments and Pb soaps can be distinguished while micro-XANES gave further information on the chemical heterogeneity in the paint film. The advantages and limitations of these synchrotron-based techniques are discussed and compared to those of methods routinely used to analyze paint samples. The results presented set the stage for improving the information extracted from samples removed from works of art and for correlating observations in model paint samples to those in the naturally aged samples, to shed light onto the mechanism of soap formation.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Getsoian, Andrew "Bean"; Das, Ujjal; Camacho-Bunquin, Jeffrey

Gallium-modified zeolites are known catalysts for the dehydrogenation of alkanes, reactivity that finds industrial application in the aromatization of light alkanes by Ga-ZSM5. While the role of gallium cations in alkane activation is well known, the oxidation state and coordination environment of gallium under reaction conditions has been the subject of debate. Edge shifts in Ga K-edge XANES spectra acquired under reaction conditions have long been interpreted as evidence for reduction of Ga(III) to Ga(I). However, a change in oxidation state is not the only factor that can give rise to a change in the XANES spectrum. In order tomore » better understand the XANES spectra of working catalysts, we have synthesized a series of molecular model compounds and grafted surface organometallic Ga species and compared their XANES spectra to those of gallium-based catalysts acquired under reducing conditions. We demonstrate that changes in the identity and number of gallium nearest neighbors can give rise to changes in XANES spectra similar to those attributed in literature to changes in oxidation state. Specifically, spectral features previously attributed to Ga(I) may be equally well interpreted as evidence for low-coordinate Ga(III) alkyl or hydride species. Furthermore, these findings apply both to gallium-impregnated zeolite catalysts and to silica-supported single site gallium catalysts, the latter of which is found to be active and selective for dehydrogenation of propane and hydrogenation of propylene.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Getsoian, Andrew “Bean”; Das, Ujjal; Camacho-Bunquin, Jeffrey

Gallium-modified zeolites are known catalysts for the dehydrogenation of alkanes, reactivity that finds industrial application in the aromatization of light alkanes by Ga-ZSM5. While the role of gallium cations in alkane activation is well known, the oxidation state and coordination environment of gallium under reaction conditions has been the subject of debate. Edge shifts in Ga K-edge XANES spectra acquired under reaction conditions have long been interpreted as evidence for reduction of Ga(III) to Ga(I). However, a change in oxidation state is not the only factor that can give rise to a change in the XANES spectrum. In order tomore » better understand the XANES spectra of working catalysts, we have synthesized a series of molecular model compounds and grafted surface organometallic Ga species and compared their XANES spectra to those of gallium-based catalysts acquired under reducing conditions. We demonstrate that changes in the identity and number of gallium nearest neighbors can give rise to changes in XANES spectra similar to those attributed in literature to changes in oxidation state. Specifically, spectral features previously attributed to Ga(I) may be equally well interpreted as evidence for low-coordinate Ga(III) alkyl or hydride species. These findings apply both to gallium-impregnated zeolite catalysts and to silica-supported single site gallium catalysts, the latter of which is found to be active and selective for dehydrogenation of propane and hydrogenation of propylene.« less

Can we trust mass spectrometry for determination of arsenic peptides in plants: comparison of LC-ICP-MS and LC-ES-MS/ICP-MS with XANES/EXAFS in analysis of Thunbergia alata.

PubMed

Bluemlein, Katharina; Raab, Andrea; Meharg, Andrew A; Charnock, John M; Feldmann, Jörg

2008-04-01

The weakest step in the analytical procedure for speciation analysis is extraction from a biological material into an aqueous solution which undergoes HPLC separation and then simultaneous online detection by elemental and molecular mass spectrometry (ICP-MS/ES-MS). This paper describes a study to determine the speciation of arsenic and, in particular, the arsenite phytochelatin complexes in the root from an ornamental garden plant Thunbergia alata exposed to 1 mg As L(-1) as arsenate. The approach of formic acid extraction followed by HPLC-ES-MS/ICP-MS identified different As(III)-PC complexes in the extract of this plant and made their quantification via sulfur (m/z 32) and arsenic (m/z 75) possible. Although sulfur sensitivity could be significantly increased when xenon was used as collision gas in ICP-qMS, or when HR-ICP-MS was used in medium resolution, the As:S ratio gave misleading results in the identification of As(III)-PC complexes due to the relatively low resolution of the chromatography system in relation to the variety of As-peptides in plants. Hence only the parallel use of ES-MS/ICP-MS was able to prove the occurrence of such arsenite phytochelatin complexes. Between 55 and 64% of the arsenic was bound to the sulfur of peptides mainly as As(III)(PC(2))(2), As(III)(PC(3)) and As(III)(PC(4)). XANES (X-ray absorption near-edge spectroscopy) measurement, using the freshly exposed plant root directly, confirmed that most of the arsenic is trivalent and binds to S of peptides (53% As-S) while 38% occurred as arsenite and only 9% unchanged as arsenate. EXAFS data confirmed that As-S and As-O bonds occur in the plants. This study confirms, for the first time, that As-peptides can be extracted by formic acid and chromatographically separated on a reversed-phase column without significant decomposition or de-novo synthesis during the extraction step.

The Effect of Thermal Reduction on the Photoluminescence and Electronic Structures of Graphene Oxides

PubMed Central

Chuang, C.-H.; Wang, Y.-F.; Shao, Y.-C.; Yeh, Y.-C.; Wang, D.-Y.; Chen, C.-W.; Chiou, J. W.; Ray, Sekhar C.; Pong, W. F.; Zhang, L.; Zhu, J. F.; Guo, J. H.

2014-01-01

Electronic structures of graphene oxide (GO) and hydro-thermally reduced graphene oxides (rGOs) processed at low temperatures (120–180°C) were studied using X-ray absorption near-edge structure (XANES), X-ray emission spectroscopy (XES) and resonant inelastic X-ray scattering (RIXS). C K-edge XANES spectra of rGOs reveal that thermal reduction restores C = C sp2 bonds and removes some of the oxygen and hydroxyl groups of GO, which initiates the evolution of carbonaceous species. The combination of C K-edge XANES and Kα XES spectra shows that the overlapping π and π* orbitals in rGOs and GO are similar to that of highly ordered pyrolytic graphite (HOPG), which has no band-gap. C Kα RIXS spectra provide evidence that thermal reduction changes the density of states (DOSs) that is generated in the π-region and/or in the gap between the π and π* levels of the GO and rGOs. Two-dimensional C Kα RIXS mapping of the heavy reduction of rGOs further confirms that the residual oxygen and/or oxygen-containing functional groups modify the π and σ features, which are dispersed by the photon excitation energy. The dispersion behavior near the K point is approximately linear and differs from the parabolic-like dispersion observed in HOPG. PMID:24717290

The effect of thermal reduction on the photoluminescence and electronic structures of graphene oxides.

PubMed

Chuang, C-H; Wang, Y-F; Shao, Y-C; Yeh, Y-C; Wang, D-Y; Chen, C-W; Chiou, J W; Ray, Sekhar C; Pong, W F; Zhang, L; Zhu, J F; Guo, J H

2014-04-10

Electronic structures of graphene oxide (GO) and hydro-thermally reduced graphene oxides (rGOs) processed at low temperatures (120-180°C) were studied using X-ray absorption near-edge structure (XANES), X-ray emission spectroscopy (XES) and resonant inelastic X-ray scattering (RIXS). C K-edge XANES spectra of rGOs reveal that thermal reduction restores C = C sp(2) bonds and removes some of the oxygen and hydroxyl groups of GO, which initiates the evolution of carbonaceous species. The combination of C K-edge XANES and Kα XES spectra shows that the overlapping π and π* orbitals in rGOs and GO are similar to that of highly ordered pyrolytic graphite (HOPG), which has no band-gap. C Kα RIXS spectra provide evidence that thermal reduction changes the density of states (DOSs) that is generated in the π-region and/or in the gap between the π and π* levels of the GO and rGOs. Two-dimensional C Kα RIXS mapping of the heavy reduction of rGOs further confirms that the residual oxygen and/or oxygen-containing functional groups modify the π and σ features, which are dispersed by the photon excitation energy. The dispersion behavior near the K point is approximately linear and differs from the parabolic-like dispersion observed in HOPG.

Speciation of Mg in biogenic calcium carbonates

NASA Astrophysics Data System (ADS)

Farges, F.; Meibom, A.; Flank, A.-M.; Lagarde, P.; Janousch, M.; Stolarski, J.

2009-11-01

A selection of marine biominerals, mostly aragonitic coral skeletons were probed at the Mg K-edge by XANES spectroscopy coupled to μXRF methods and compared to an extensive set of relevant model compounds (silicates, carbonates, oxides and organic). Extensive methodologies are required to better describe the speciation of Mg in those minerals. A combination of ab-initio XANES calculations for defective clusters around Mg in aragonite together with wavelets analyzes of the XANES region are required to robustly interpret the spectra. When using those methodologies, the speciation of Mg ranges from a magnesite-type environment in some scleractinian corals to an organic-type environment. In all environments, the Mg-domains probed appear to be less than 1 nm in size.

Selenium Accumulation, Distribution, and Speciation in Spineless Prickly Pear Cactus: A Drought- and Salt-Tolerant, Selenium-Enriched Nutraceutical Fruit Crop for Biofortified Foods1[OA

PubMed Central

Bañuelos, Gary S.; Fakra, Sirine C.; Walse, Spencer S.; Marcus, Matthew A.; Yang, Soo In; Pickering, Ingrid J.; Pilon-Smits, Elizabeth A.H.; Freeman, John L.

2011-01-01

The organ-specific accumulation, spatial distribution, and chemical speciation of selenium (Se) were previously unknown for any species of cactus. We investigated Se in Opuntia ficus-indica using inductively coupled plasma mass spectrometry, microfocused x-ray fluorescence elemental and chemical mapping (μXRF), Se K-edge x-ray absorption near-edge structure (XANES) spectroscopy, and liquid chromatography-mass spectrometry (LC-MS). μXRF showed Se concentrated inside small conic, vestigial leaves (cladode tips), the cladode vasculature, and the seed embryos. Se K-edge XANES demonstrated that approximately 96% of total Se in cladode, fruit juice, fruit pulp, and seed is carbon-Se-carbon (C-Se-C). Micro and bulk XANES analysis showed that cladode tips contained both selenate and C-Se-C forms. Inductively coupled plasma mass spectrometry quantification of Se in high-performance liquid chromatography fractions followed by LC-MS structural identification showed selenocystathionine-to-selenomethionine (SeMet) ratios of 75:25, 71:29, and 32:68, respectively in cladode, fruit, and seed. Enzymatic digestions and subsequent analysis confirmed that Se was mainly present in a “free” nonproteinaceous form inside cladode and fruit, while in the seed, Se was incorporated into proteins associated with lipids. μXRF chemical mapping illuminated the specific location of Se reduction and assimilation from selenate accumulated in the cladode tips into the two LC-MS-identified C-Se-C forms before they were transported into the cladode mesophyll. We conclude that Opuntia is a secondary Se-accumulating plant whose fruit and cladode contain mostly free selenocystathionine and SeMet, while seeds contain mainly SeMet in protein. When eaten, the organic Se forms in Opuntia fruit, cladode, and seed may improve health, increase Se mineral nutrition, and help prevent multiple human cancers. PMID:21059825

Selenium Accumulation, Distribution, and Speciation in Spineless Prickly Pear Cactus: A Drought- and Salt-Tolerant, Selenium-Enriched Nutraceutical Fruit Crop for Biofortified Foods

DOE Office of Scientific and Technical Information (OSTI.GOV)

Banuelos, Gary S.; Fakra, Sirine C.; Walse, Spencer S.

The organ-specific accumulation, spatial distribution, and chemical speciation of selenium (Se) were previously unknown for any species of cactus. We investigated Se in Opuntia ficus-indica using inductively coupled plasma mass spectrometry, microfocused x-ray fluorescence elemental and chemical mapping ({micro}XRF), Se K-edge x-ray absorption near-edge structure (XANES) spectroscopy, and liquid chromatography-mass spectrometry (LC-MS). {micro}XRF showed Se concentrated inside small conic, vestigial leaves (cladode tips), the cladode vasculature, and the seed embryos. Se K-edge XANES demonstrated that approximately 96% of total Se in cladode, fruit juice, fruit pulp, and seed is carbon-Se-carbon (C-Se-C). Micro and bulk XANES analysis showed that cladode tipsmore » contained both selenate and C-Se-C forms. Inductively coupled plasma mass spectrometry quantification of Se in high-performance liquid chromatography fractions followed by LC-MS structural identification showed selenocystathionine-to-selenomethionine (SeMet) ratios of 75:25, 71:29, and 32:68, respectively in cladode, fruit, and seed. Enzymatic digestions and subsequent analysis confirmed that Se was mainly present in a 'free' nonproteinaceous form inside cladode and fruit, while in the seed, Se was incorporated into proteins associated with lipids. {micro}XRF chemical mapping illuminated the specific location of Se reduction and assimilation from selenate accumulated in the cladode tips into the two LC-MS-identified C-Se-C forms before they were transported into the cladode mesophyll. We conclude that Opuntia is a secondary Se-accumulating plant whose fruit and cladode contain mostly free selenocystathionine and SeMet, while seeds contain mainly SeMet in protein. When eaten, the organic Se forms in Opuntia fruit, cladode, and seed may improve health, increase Se mineral nutrition, and help prevent multiple human cancers.« less

Structural evolution of fluorinated graphene upon molten-alkali treatment probed by X-ray absorption near-edge structure spectroscopy

NASA Astrophysics Data System (ADS)

Liang, Xianqing; Pan, Deyou; Lao, Ming; Liang, Shuiying; Huang, Dan; Zhou, Wenzheng; Guo, Jin

2017-05-01

The structural evolution of fluorinated graphene (FG) nanosheets upon molten-alkali treatment has been systematically investigated utilizing X-ray absorption near-edge structure (XANES) spectroscopy. It is found that the hydroxyl groups can progressively displace fluorine atoms to form covalent bonds to the graphene sheets under designed molten-alkali condition. The XANES spectra also reveal the formation of epoxide groups through intramolecular dehydration of neighbouring hydroxyl groups after substitution reaction. At high alkali-FG weight ratio, the restoration of the π-conjugated structure in graphene sheets can be observed due to the gradual decomposition of epoxide groups. Our experimental results indicate that the surface chemistry and electronic structure of hydroxyl-functionalized FG (HFG) can be readily tuned by varying the ratio of reactants.

Specific features of the atomic structure of metallic layers of multilayered (CoFeZr/SiO2)32 and (CoFeZr/ a-Si)40 nanostructures with different interlayers

NASA Astrophysics Data System (ADS)

Domashevskaya, E. P.; Guda, A. A.; Chernyshev, A. V.; Sitnikov, V. G.

2017-02-01

Multilayered nanostructures (MN) were prepared by ion-beam successive sputtering from two targets, one of which was a metallic Co45Fe45Zr10 alloy plate and another target was a quartz (SiO2) or silicon plate on the surface of a rotating glass-ceramic substrate in an argon atmosphere. The Co and Fe K edges X-ray absorption fine structure of XANES in the (CoFeZr/SiO2)32 sample with oxide interlayers was similar to XANES of metallic Fe foil. This indicated the existence in metallic layers of multilayered CoFeZr nanocrystals with a local environment similar to the atomic environment in solid solutions on the base of bcc Fe structure, which is also confirmed by XRD data. XANES near the Co and Fe K edges absorption in another multilayered nanostructure with silicon interlayers (CoFeZr/ a-Si)40 differs from XANES of MN with dielectric SiO2 interlayer, which demonstrates a dominant influence of the Fe-Si and Co-Si bonds in the local environment of 3 d Co and Fe metals when they form CoFeSi-type silicide phases in thinner bilayers of this MN.

Application toward Confocal Full-Field Microscopic X-ray Absorption Near Edge Structure Spectroscopy.

PubMed

Tack, Pieter; Vekemans, Bart; Laforce, Brecht; Rudloff-Grund, Jennifer; Hernández, Willinton Y; Garrevoet, Jan; Falkenberg, Gerald; Brenker, Frank; Van Der Voort, Pascal; Vincze, Laszlo

2017-02-07

Using X-ray absorption near edge structure (XANES) spectroscopy, information on the local chemical structure and oxidation state of an element of interest can be acquired. Conventionally, this information can be obtained in a spatially resolved manner by scanning a sample through a focused X-ray beam. Recently, full-field methods have been developed to obtain direct 2D chemical state information by imaging a large sample area. These methods are usually in transmission mode, thus restricting the use to thin and transmitting samples. Here, a fluorescence method is displayed using an energy-dispersive pnCCD detector, the SLcam, characterized by measurement times far superior to what is generally applicable. Additionally, this method operates in confocal mode, thus providing direct 3D spatially resolved chemical state information from a selected subvolume of a sample, without the need of rotating a sample. The method is applied to two samples: a gold-supported magnesia catalyst (Au/MgO) and a natural diamond containing Fe-rich inclusions. Both samples provide XANES spectra that can be overlapped with reference XANES spectra, allowing this method to be used for fingerprinting and linear combination analysis of known XANES reference compounds.

Comb-push ultrasound shear elastography of breast masses: initial results show promise.

PubMed

Denis, Max; Mehrmohammadi, Mohammad; Song, Pengfei; Meixner, Duane D; Fazzio, Robert T; Pruthi, Sandhya; Whaley, Dana H; Chen, Shigao; Fatemi, Mostafa; Alizad, Azra

2015-01-01

To evaluate the performance of Comb-push Ultrasound Shear Elastography (CUSE) for classification of breast masses. CUSE is an ultrasound-based quantitative two-dimensional shear wave elasticity imaging technique, which utilizes multiple laterally distributed acoustic radiation force (ARF) beams to simultaneously excite the tissue and induce shear waves. Female patients who were categorized as having suspicious breast masses underwent CUSE evaluations prior to biopsy. An elasticity estimate within the breast mass was obtained from the CUSE shear wave speed map. Elasticity estimates of various types of benign and malignant masses were compared with biopsy results. Fifty-four female patients with suspicious breast masses from our ongoing study are presented. Our cohort included 31 malignant and 23 benign breast masses. Our results indicate that the mean shear wave speed was significantly higher in malignant masses (6 ± 1.58 m/s) in comparison to benign masses (3.65 ± 1.36 m/s). Therefore, the stiffness of the mass quantified by the Young's modulus is significantly higher in malignant masses. According to the receiver operating characteristic curve (ROC), the optimal cut-off value of 83 kPa yields 87.10% sensitivity, 82.61% specificity, and 0.88 for the area under the curve (AUC). CUSE has the potential for clinical utility as a quantitative diagnostic imaging tool adjunct to B-mode ultrasound for differentiation of malignant and benign breast masses.

Probing defect emissions in bulk, micro- and nano-sized α-Al2O3 via X-ray excited optical luminescence

NASA Astrophysics Data System (ADS)

Wang, Zhiqiang; Li, Chunlei; Liu, Lijia; Sham, Tsun-Kong

2013-02-01

The electronic structure and optical properties of bulk, micro-sized, and nano-sized α-Al2O3 (wafer, microparticles (MPs), nanowires (NWs), and nanotubes (NTs)) have been investigated using X-ray absorption near-edge structures (XANES) and X-ray excited optical luminescence (XEOL). XANES results show that the wafer, MPs, and NTs have characteristic features of α-Al2O3. The NWs have a core/shell structure with a single crystalline α-Al2O3 core surrounded by an amorphous shell, which is consistent with transmission electron microscopy result. It is found that some Al3+ in the shell and core/shell interface of the NWs as well as the surface of the NTs were reduced to Al2+ or Al1+ during the growth process. XEOL results show that the wafer and MPs have a broad emission at 325 nm and a sharp emission at 694 nm, which are attributed to F+ center and Cr3+ impurities, respectively. The NWs exhibit an intense emission at 404 nm that comes from F center, while the NTs show relatively weak luminescence at 325, 433, and 694 nm, which are attributed to F+ center, F center, and Cr3+ impurities, respectively. The O K-edge XEOL confirms that the emissions of α-Al2O3 in the range of 250-550 nm are related to the oxygen site. Furthermore, on the basis of XEOL and photoluminescence yield, the strong luminescence of the NWs (404 nm) is related to the Al2+ or Al1+ in the shell and core/shell interface, while the luminescence of the NTs at 325 and 433 nm are related to the bulk and the Al2+ or Al1+ on the surface, respectively.

Arsenic mobilization in spent nZVI waste residue: Effect of Pantoea sp. IMH.

PubMed

Ye, Li; Liu, Wenjing; Shi, Qiantao; Jing, Chuanyong

2017-11-01

Nanoscale zero-valent iron (nZVI) is an effective arsenic (As) scavenger. However, spent nZVI may pose a higher environmental risk than our initial thought in the presence of As-reducing bacteria. Therefore, our motivation was to explore the As redox transformation and release in spent nZVI waste residue in contact with Pantoea sp. IMH, an arsC gene container adopting the As detoxification pathway. Our incubation results showed that IMH preferentially reduce soluble As(V), not solid-bound As(V), and was innocent in elevating total dissolved As concentrations. μ-XRF and As μ-XANES spectra clearly revealed the heterogeneity and complexity of the inoculated and control samples. Nevertheless, the surface As local coordination was not affected by the presence of IMH as evidenced by similar As-Fe atomic distance (3.32-3.36 Å) and coordination number (1.9) in control and inoculated samples. The Fe XANES results suggested that magnetite in nZVI residue was partly transformed to ferrihydrite, and the IMH activity slowed down the nZVI aging process. IMH distorted Fe local coordination without change its As adsorption capacity as suggested by Mössbauer spectroscopy. Arsenic retention is not inevitably enhanced by in situ formed secondary Fe minerals, but depends on the relative As affinity between the primary and secondary iron minerals. Copyright © 2017 Elsevier Ltd. All rights reserved.

Enhanced Air Stability in REPb3 (RE = Rare Earths) by Dimensional Reduction Mediated Valence Transition.

PubMed

Subbarao, Udumula; Sarkar, Sumanta; Jana, Rajkumar; Bera, Sourav S; Peter, Sebastian C

2016-06-06

We conceptually selected the compounds REPb3 (RE = Eu, Yb), which are unstable in air, and converted them to the stable materials in ambient conditions by the chemical processes of "nanoparticle formation" and "dimensional reduction". The nanoparticles and the bulk counterparts were synthesized by the solvothermal and high-frequency induction furnace heating methods, respectively. The reduction of the particle size led to the valence transition of the rare earth atom, which was monitored through magnetic susceptibility and X-ray absorption near edge spectroscopy (XANES) measurements. The stability was checked by X-ray diffraction and thermogravimetric analysis over a period of seven months in oxygen and argon atmospheres and confirmed by XANES. The nanoparticles showed outstanding stability toward aerial oxidation over a period of seven months compared to the bulk counterpart, as the latter one is more prone to the oxidation within a few days.

Multi-edge X-ray absorption spectroscopy study of road dust samples from a traffic area of Venice using stoichiometric and environmental references.

PubMed

Valotto, Gabrio; Cattaruzza, Elti; Bardelli, Fabrizio

2017-02-15

The appropriate selection of representative pure compounds to be used as reference is a crucial step for successful analysis of X-ray absorption near edge spectroscopy (XANES) data, and it is often not a trivial task. This is particularly true when complex environmental matrices are investigated, being their elemental speciation a priori unknown. In this paper, an investigation on the speciation of Cu, Zn, and Sb based on the use of conventional (stoichiometric compounds) and non-conventional (environmental samples or relevant certified materials) references is explored. This method can be useful in when the effectiveness of XANES analysis is limited because of the difficulty in obtaining a set of references sufficiently representative of the investigated samples. Road dust samples collected along the bridge connecting Venice to the mainland were used to show the potentialities and the limits of this approach. Copyright © 2016 Elsevier B.V. All rights reserved.

Local structural variation with oxygen fugacity in Fe 2SiO 4+x fayalitic iron silicate melts

DOE PAGES

Alderman, O.L.G.; Lazareva, L.; Wilding, M. C.; ...

2017-01-07

Here, the structure of molten Fe 2SiO 4+x has been studied using both high-energy X-ray diffraction and Fe K-edge X-ray absorption near-edge structure (XANES) spectroscopy, combined with aerodynamic levitation and laser beam heating. A wide range of Fe 3+ contents were accessed by varying the levitation and atmospheric gas composition. Diffraction measurements were made in the temperature ( T) and oxygen partial pressure ranges 1624(21) < T < 2183(94) K (uncertainties in parentheses) and –5.6(3) < ΔFMQ < +2.8(5) log units (relative to the Fayalite-Magnetite-Quartz buffer). Iron K-edge XANES measurements covered the ranges 1557(33) < T < 1994(36) K andmore » –2.1(3) < ΔFMQ < +4.4(3) log units. Fe 3+ contents, x = Fe 3+/ΣFe, estimated directly from the pre-edge peaks of the XANES spectra varied between 0.15(1) and 0.40(2). While these agree in some cases with semi-empirical models, notable discrepancies are discussed in the context of the redox kinetics and the limitations in both the models and in the calibrations used to derive oxidation state from XANES spectra. XANES pre-edge peak areas imply average Fe–O coordination numbers, n FeO, close to 5 for all Fe 3+/ΣFe. Diffraction measurements yielded values of 4.4(2) < n FeO < 4.7(1). There is limited evidence for a linear trend n FeO(x) = 4.46(3) + 0.4(1)x. Asymmetric Fe–O bond length distributions peak at around 1.96 Å and have a shoulder arising from longer interatomic distances. Mean r FeO lie close to 2.06 Å, consistent with n FeO close to 5. These observations suggest that Fe 2+ is less efficient at stabilizing tetrahedral Fe 3+ compared to large monovalent alkali cations. Comparison of in-situ XANES estimates of Fe 3+/ΣFe in the melts to those of the quenched solids obtained from XANES as well as Mössbauer spectroscopy indicate rapid oxidation during cooling, enabled by stirring of the melt by the levitation gas flow. As such, the oxidation state of hot komatiitic and other highly fluid melts

Local structural variation with oxygen fugacity in Fe2SiO4+x fayalitic iron silicate melts

NASA Astrophysics Data System (ADS)

Alderman, O. L. G.; Lazareva, L.; Wilding, M. C.; Benmore, C. J.; Heald, S. M.; Johnson, C. E.; Johnson, J. A.; Hah, H.-Y.; Sendelbach, S.; Tamalonis, A.; Skinner, L. B.; Parise, J. B.; Weber, J. K. R.

2017-04-01

The structure of molten Fe2SiO4+x has been studied using both high-energy X-ray diffraction and Fe K-edge X-ray absorption near-edge structure (XANES) spectroscopy, combined with aerodynamic levitation and laser beam heating. A wide range of Fe3+ contents were accessed by varying the levitation and atmospheric gas composition. Diffraction measurements were made in the temperature (T) and oxygen partial pressure ranges 1624(21) < T < 2183(94) K (uncertainties in parentheses) and -5.6(3) < ΔFMQ < +2.8(5) log units (relative to the Fayalite-Magnetite-Quartz buffer). Iron K-edge XANES measurements covered the ranges 1557(33) < T < 1994(36) K and -2.1(3) < ΔFMQ < +4.4(3) log units. Fe3+ contents, x = Fe3+/ΣFe, estimated directly from the pre-edge peaks of the XANES spectra varied between 0.15(1) and 0.40(2). While these agree in some cases with semi-empirical models, notable discrepancies are discussed in the context of the redox kinetics and the limitations in both the models and in the calibrations used to derive oxidation state from XANES spectra. XANES pre-edge peak areas imply average Fe-O coordination numbers, nFeO, close to 5 for all Fe3+/ΣFe. Diffraction measurements yielded values of 4.4(2) < nFeO < 4.7(1). There is limited evidence for a linear trend nFeO(x) = 4.46(3) + 0.4(1)x. Asymmetric Fe-O bond length distributions peak at around 1.96 Å and have a shoulder arising from longer interatomic distances. Mean rFeO lie close to 2.06 Å, consistent with nFeO close to 5. These observations suggest that Fe2+ is less efficient at stabilizing tetrahedral Fe3+ compared to large monovalent alkali cations. Comparison of in-situ XANES estimates of Fe3+/ΣFe in the melts to those of the quenched solids obtained from XANES as well as Mössbauer spectroscopy indicate rapid oxidation during cooling, enabled by stirring of the melt by the levitation gas flow. As such, the oxidation state of hot komatiitic and other highly fluid melts may not be retained, even during

Communication: X-ray excited optical luminescence from TbCl3 at the giant resonance of terbium

NASA Astrophysics Data System (ADS)

Heigl, F.; Jürgensen, A.; Zhou, X.-T.; Hu, Y.-F.; Zuin, L.; Sham, T. K.

2013-02-01

We have studied the optical recombination channels of TbCl3 using x-ray excited optical luminescence at the N4,5 absorption edge of Tb (giant resonance) in both the energy and time domain. The luminescence exhibits a relatively fast 5D3, and a slow 5D4 decay channel in the blue and green, respectively. The rather short lifetime of the 5D3 state indicates that the decay is mainly driven by Tb-Tb ion interaction via non-radiative energy transfer (cross-relaxation). At the giant resonance the X-ray Absorption Near Edge Structure (XANES) recorded using partial photoluminescence yield is inverted. In the pre-edge region the contrast of the spectral feature is significantly better in optical XANES than in total electron yield. Changes in the intensity of 5D3-7F5 (544 nm) and 5D4-7F6 (382 nm) optical transitions as the excitation energy is tuned across the giant resonance are also noted. The results provide detailed insight into the dynamics of the optical recombination channels and an alternative method to obtain high sensitivity, high energy resolution XANES at the giant resonance of light emitting rare-earth materials.

XAFS studies of nickel and sulfur speciation in residual oil fly-ash particulate matters (ROFA PM).

PubMed

Pattanaik, Sidhartha; Huggins, Frank E; Huffman, Gerald P; Linak, William P; Miller, C Andrew

2007-02-15

XAFS spectroscopy has been employed to evaluate the effect of fuel compositions and combustion conditions on the amount, form, and distribution of sulfur and nickel in size-fractionated ROFA PM. Analysis of S K-edge XANES establish that sulfate is abundant in all PM. However, depending upon the combustion conditions, lesser amounts of thiophenic sulfur, metal sulfide, and elemental sulfur may also be observed. Least-squares fitting of Ni K-edge XANES reveals that most of the nickel in PM is present as bioavailable NiSO4.nH2O. The insoluble Ni mainly exists as a minor species, as nickel ferrite in PM2.5 (PM < 2.5 microm) and nickel sulfide, Ni(x)SY(y) in PM2.5+ (PM > 2.5 microm). The Ni K-edge XANES results are in agreement with the EXAFS data. Such detailed speciation of Ni and S in PM is needed for determining their mobility, bioavailability, and reactivity, and hence, their role in PM toxicity. This information is also important for understanding the mechanism of PM formation, developing effective remediation measures, and providing criteria for identification of potential emission sources. Transition metals complexing with sulfur is ubiquitous in nature. Therefore, this information on metal sulfur complex can be critical to a large body of environmental literature.

Correlation between bonding structure and microstructure in fullerenelike carbon nitride thin films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gago, R.; Abendroth, B.; Moeller, W.

2005-03-15

The bonding structure of highly ordered fullerenelike (FL) carbon nitride (CN{sub x}) thin films has been assessed by x-ray absorption near-edge spectroscopy (XANES). Samples with different degrees of FL character have been analyzed to discern spectral signatures related to the FL microstructure. The XANES spectra of FL-CN{sub x} films resemble that of graphitic CN{sub x}, evidencing the sp{sup 2} hybridization of both C and N atoms. The FL structure is achieved with the promotion of N in threefold positions over pyridinelike and cyanidelike bonding environments. In addition, the relative {pi}{sup *}/{sigma}* XANES intensity ratio at the C(1s) edge is independentmore » of the FL character, while it decreases {approx}40% at the N(1s) edge with the formation of FL arrangements. This result indicates that there is no appreciable introduction of C-sp{sup 3} hybrids with the development of FL structures and, additionally, that a different spatial localization of {pi} electrons at C and N sites takes place in curved graphitic structures. The latter has implications for the elastic properties of graphene sheets and could, as such, explain the outstanding elastic properties of FL-CN{sub x}.« less

Study of Eu{sup 3+} → Eu{sup 2+} reduction in BaAl{sub 2}O{sub 4}:Eu prepared in different gas atmospheres

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rezende, Marcos V. dos S., E-mail: mvsrezende@gmail.com; Valerio, Mário E.G.; Jackson, Robert A.

2015-01-15

Highlights: • The effect of different gas atmospheres on the Eu reduction process was studied. • The Eu reduction was monitored analyzing XANES region at the Eu L{sub III}-edge. • Hydrogen reducing agent are the most appropriate gas for Eu{sup 2+} stabilization. • Only a part of the Eu ions can be stabilized in the divalent state. • A model of Eu reduction process is proposed. - Abstract: The effect of different gas atmospheres such as H{sub 2}(g), synthetic air, carbon monoxide (CO) and nitrogen (N{sub 2}) on the Eu{sup 3+} → Eu{sup 2+} reduction process during the synthesis ofmore » Eu-doped BaAl{sub 2}O{sub 4} was studied using synchrotron radiation. The Eu{sup 3+} → Eu{sup 2+} reduction was monitored analyzing XANES region when the sample are excited at the Eu L{sub III}-edge. The results show that the hydrogen reducing agent are the most appropriate gas for Eu{sup 2+} stabilization in BaAl{sub 2}O{sub 4} and that only a part of the Eu ions can be stabilized in the divalent state. A model of Eu reduction process, based on the incorporation of charge compensation defects, is proposed.« less

Selenium inhibits the phytotoxicity of mercury in garlic (Allium sativum).

PubMed

Zhao, Jiating; Gao, Yuxi; Li, Yu-Feng; Hu, Yi; Peng, Xiaomin; Dong, Yuanxing; Li, Bai; Chen, Chunying; Chai, Zhifang

2013-08-01

To investigate the influence of selenium on mercury phytotoxicity, the levels of selenium and mercury were analyzed with inductively coupled plasma-mass spectrometry (ICP-MS) in garlic tissues upon exposure to different dosages of inorganic mercury (Hg(2+)) and selenite (SeO3(2-)) or selenate (SeO4(2-)). The distributions of selenium and mercury were examined with micro-synchrotron radiation X-ray fluorescence (μ-SRXRF), and the mercury speciation was investigated with micro-X-ray absorption near edge structure (μ-XANES). The results show that Se at higher exposure levels (>1mg/L of SeO3(2-) or SeO4(2-)) would significantly inhibit the absorption and transportation of Hg when Hg(2+) levels are higher than 1mg/L in culture media. SeO3(2-) and SeO4(2-) were found to be equally effective in reducing Hg accumulation in garlic. The inhibition of Hg uptake by Se correlates well with the influence of Se on Hg phytotoxicity as indicated by the growth inhibition factor. Elemental imaging using μ-SRXRF also shows that Se could inhibit the accumulation and translocation of Hg in garlic. μ-XANES analysis shows that Hg is mainly present in the forms of Hg-S bonding as Hg(GSH)2 and Hg(Met)2. Se exposure elicited decrease of Hg-S bonding in the form of Hg(GSH)2, together with Se-mediated alteration of Hg absorption, transportation and accumulation, may account for attenuated Hg phytotoxicity by Se in garlic. Copyright © 2013 Elsevier Inc. All rights reserved.

A re-assessment of the oxidation state of iron in MORB glasses

NASA Astrophysics Data System (ADS)

Berry, Andrew J.; Stewart, Glen A.; O'Neill, Hugh St. C.; Mallmann, Guilherme; Mosselmans, J. Fred W.

2018-02-01

The oxidation state of Fe, Fe/+3 ΣFe (where ΣFe =Fe2+ +Fe3+), in glass samples of mid-ocean ridge basalt (MORB), from a wide range of localities, was determined by XANES spectroscopy to be 0.10(2) (n = 42). This value is lower than that reported previously by XANES, 0.16 (1) (n = 103), but consistent with the most recent value determined by redox titrations, 0.11 (2) (n = 104), all for similar sets of samples. We attribute the anomalously high XANES value of 0.16 to a calibration error resulting from the interpretation of Mössbauer spectra and the resulting Fe/+3 ΣFe values of the standards. Our alternative interpretation removes the problem of resolving Fe/+3 ΣFe values <∼0.1 in basaltic glasses, produces isomer shift and quadrupole splitting values for Fe3+ that are independent of Fe3+/ΣFe (as is the case for Fe2+), and gives Fe/+3 ΣFe values that are consistent with the thermodynamically expected dependence on oxygen fugacity (fO2). Fe/+3Fe2+ is related to fO2 for our synthetic MORB composition by the temperature independent expression ΔQFM = 4 log ⁡ (Fe3+ /Fe2+) + 4.23 (5), where ΔQFM is the fO2 in log units relative to the quartz-fayalite-magnetite buffer. The average fO2 of natural MORB was estimated to be QFM+0.1.

Theory and X-ray Absorption Spectroscopy for Aluminum Coordination Complexes – Al K-Edge Studies of Charge and Bonding in (BDI)Al, (BDI)AlR2, and (BDI)AlX2 Complexes.

PubMed

Altman, Alison B; Pemmaraju, C D; Camp, Clément; Arnold, John; Minasian, Stefan G; Prendergast, David; Shuh, David K; Tyliszczak, Tolek

2015-08-19

Polarized aluminum K-edge X-ray absorption near edge structure (XANES) spectroscopy and first-principles calculations were used to probe electronic structure in a series of (BDI)Al, (BDI)AlX2, and (BDI)AlR2 coordination compounds (X = F, Cl, I; R = H, Me; BDI = 2,6-diisopropylphenyl-β-diketiminate). Spectral interpretations were guided by examination of the calculated transition energies and polarization-dependent oscillator strengths, which agreed well with the XANES spectroscopy measurements. Pre-edge features were assigned to transitions associated with the Al 3p orbitals involved in metal-ligand bonding. Qualitative trends in Al 1s core energy and valence orbital occupation were established through a systematic comparison of excited states derived from Al 3p orbitals with similar symmetries in a molecular orbital framework. These trends suggested that the higher transition energies observed for (BDI)AlX2 systems with more electronegative X(1-) ligands could be ascribed to a decrease in electron density around the aluminum atom, which causes an increase in the attractive potential of the Al nucleus and concomitant increase in the binding energy of the Al 1s core orbitals. For (BDI)Al and (BDI)AlH2 the experimental Al K-edge XANES spectra and spectra calculated using the eXcited electron and Core-Hole (XCH) approach had nearly identical energies for transitions to final state orbitals of similar composition and symmetry. These results implied that the charge distributions about the aluminum atoms in (BDI)Al and (BDI)AlH2 are similar relative to the (BDI)AlX2 and (BDI)AlMe2 compounds, despite having different formal oxidation states of +1 and +3, respectively. However, (BDI)Al was unique in that it exhibited a low-energy feature that was attributed to transitions into a low-lying p-orbital of b1 symmetry that is localized on Al and orthogonal to the (BDI)Al plane. The presence of this low-energy unoccupied molecular orbital on electron-rich (BDI)Al distinguishes

Direct Synthesis of Novel and Reactive Sulfide-modified Nano Iron through Nanoparticle Seeding for Improved Cadmium-Contaminated Water Treatment

PubMed Central

Su, Yiming; Adeleye, Adeyemi S.; Huang, Yuxiong; Zhou, Xuefei; Keller, Arturo A.; Zhang, Yalei

2016-01-01

Magnetic sulfide-modified nanoscale zerovalent iron (S-nZVI) is of great technical and scientific interest because of its promising application in groundwater remediation, although its synthesis is still a challenge. We develop a new nanoparticle seeding method to obtain a novel and reactive nanohybrid, which contains an Fe(0) core covered by a highly sulfidized layer under high extent of sulfidation. Syntheses monitoring experiments show that seeding accelerates the reduction rate from Fe2+ to Fe0 by 19%. X-ray adsorption near edge structure (XANES) spectroscopy and extended X-ray absorption fine structure analyses demonstrate the hexahedral Fe-Fe bond (2.45 and 2.83 Å) formation through breaking down of the 1.99 Å Fe-O bond both in crystalline and amorphous iron oxide. The XANES analysis also shows 24.2% (wt%) of FeS with bond length of 2.4 Å in final nanohybrid. Both X-ray diffraction and Mössbauer analyses further confirm that increased nanoparticle seeding results in formation of more Fe0 crystals. Nano-SiO2 seeding brings down the size of single Fe0 grain from 32.4 nm to 18.7 nm, enhances final Fe0 content from 5.9% to 55.6%, and increases magnetization from 4.7 to 65.5 emu/g. The synthesized nanohybrid has high cadmium removal capacity and holds promising prospects for treatment of metal-contaminated water. PMID:27095387

Direct Synthesis of Novel and Reactive Sulfide-modified Nano Iron through Nanoparticle Seeding for Improved Cadmium-Contaminated Water Treatment

NASA Astrophysics Data System (ADS)

Su, Yiming; Adeleye, Adeyemi S.; Huang, Yuxiong; Zhou, Xuefei; Keller, Arturo A.; Zhang, Yalei

2016-04-01

Magnetic sulfide-modified nanoscale zerovalent iron (S-nZVI) is of great technical and scientific interest because of its promising application in groundwater remediation, although its synthesis is still a challenge. We develop a new nanoparticle seeding method to obtain a novel and reactive nanohybrid, which contains an Fe(0) core covered by a highly sulfidized layer under high extent of sulfidation. Syntheses monitoring experiments show that seeding accelerates the reduction rate from Fe2+ to Fe0 by 19%. X-ray adsorption near edge structure (XANES) spectroscopy and extended X-ray absorption fine structure analyses demonstrate the hexahedral Fe-Fe bond (2.45 and 2.83 Å) formation through breaking down of the 1.99 Å Fe-O bond both in crystalline and amorphous iron oxide. The XANES analysis also shows 24.2% (wt%) of FeS with bond length of 2.4 Å in final nanohybrid. Both X-ray diffraction and Mössbauer analyses further confirm that increased nanoparticle seeding results in formation of more Fe0 crystals. Nano-SiO2 seeding brings down the size of single Fe0 grain from 32.4 nm to 18.7 nm, enhances final Fe0 content from 5.9% to 55.6%, and increases magnetization from 4.7 to 65.5 emu/g. The synthesized nanohybrid has high cadmium removal capacity and holds promising prospects for treatment of metal-contaminated water.

The Physics of Equestrian Show Jumping

NASA Astrophysics Data System (ADS)

Stinner, Art

2014-04-01

This article discusses the kinematics and dynamics of equestrian show jumping. For some time I have attended a series of show jumping events at Spruce Meadows, an international equestrian center near Calgary, Alberta, often referred to as the "Wimbledon of equestrian jumping." I have always had a desire to write an article such as this one, but when I searched the Internet for information and looked at YouTube presentations, I could only find simplistic references to Newton's laws and the conservation of mechanical energy principle. Nowhere could I find detailed calculations. On the other hand, there were several biomechanical articles with empirical reports of the results of kinetic and dynamic investigations of show jumping using high-speed digital cameras and force plates. They summarize their results in tables that give information about the motion of a horse jumping over high fences (1.40 m) and the magnitudes of the forces encountered when landing. However, they do not describe the physics of these results.

Selenium speciation in phosphate mine soils and evaluation of a sequential extraction procedure using XAFS.

PubMed

Favorito, Jessica E; Luxton, Todd P; Eick, Matthew J; Grossl, Paul R

2017-10-01

Selenium is a trace element found in western US soils, where ingestion of Se-accumulating plants has resulted in livestock fatalities. Therefore, a reliable understanding of Se speciation and bioavailability is critical for effective mitigation. Sequential extraction procedures (SEP) are often employed to examine Se phases and speciation in contaminated soils but may be limited by experimental conditions. We examined the validity of a SEP using X-ray absorption spectroscopy (XAS) for both whole and a sequence of extracted soils. The sequence included removal of soluble, PO 4 -extractable, carbonate, amorphous Fe-oxide, crystalline Fe-oxide, organic, and residual Se forms. For whole soils, XANES analyses indicated Se(0) and Se(-II) predominated, with lower amounts of Se(IV) present, related to carbonates and Fe-oxides. Oxidized Se species were more elevated and residual/elemental Se was lower than previous SEP results from ICP-AES suggested. For soils from the SEP sequence, XANES results indicated only partial recovery of carbonate, Fe-oxide and organic Se. This suggests Se was incompletely removed during designated extractions, possibly due to lack of mineral solubilization or reagent specificity. Selenium fractions associated with Fe-oxides were reduced in amount or removed after using hydroxylamine HCl for most soils examined. XANES results indicate partial dissolution of solid-phases may occur during extraction processes. This study demonstrates why precautions should be taken to improve the validity of SEPs. Mineralogical and chemical characterizations should be completed prior to SEP implementation to identify extractable phases or mineral components that may influence extraction effectiveness. Sequential extraction procedures can be appropriately tailored for reliable quantification of speciation in contaminated soils. Copyright © 2017 Elsevier Ltd. All rights reserved.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Favorito, Jessica E.; Luxton, Todd P.; Eick, Matthew J.

Selenium is a trace element found in western US soils, where ingestion of Se-accumulating plants has resulted in livestock fatalities. Therefore, a reliable understanding of Se speciation and bioavailability is critical for effective mitigation. Sequential extraction procedures (SEP) are often employed to examine Se phases and speciation in contaminated soils but may be limited by experimental conditions. We examined the validity of a SEP using X-ray absorption spectroscopy (XAS) for both whole and a sequence of extracted soils. The sequence included removal of soluble, PO4-extractable, carbonate, amorphous Fe-oxide, crystalline Fe-oxide, organic, and residual Se forms. For whole soils, XANES analysesmore » indicated Se(0) and Se(-II) predominated, with lower amounts of Se(IV) present, related to carbonates and Fe-oxides. Oxidized Se species were more elevated and residual/elemental Se was lower than previous SEP results from ICP-AES suggested. For soils from the SEP sequence, XANES results indicated only partial recovery of carbonate, Fe-oxide and organic Se. This suggests Se was incompletely removed during designated extractions, possibly due to lack of mineral solubilization or reagent specificity. Selenium fractions associated with Fe-oxides were reduced in amount or removed after using hydroxylamine HCl for most soils examined. XANES results indicate partial dissolution of solid-phases may occur during extraction processes. This study demonstrates why precautions should be taken to improve the validity of SEPs. Mineralogical and chemical characterizations should be completed prior to SEP implementation to identify extractable phases or mineral components that may influence extraction effectiveness. Sequential extraction procedures can be appropriately tailored for reliable quantification of speciation in contaminated soils.« less

Structure and phase formation behavior and dielectric and magnetic properties of lead iron tantalate-lead zirconate titanate multiferroic ceramics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wongmaneerung, R., E-mail: re_nok@yahoo.com; Tipakontitikul, R.; Jantaratana, P.

2016-03-15

Highlights: • The multiferroic ceramics consisted of PFT and PZT. • Crystal structure changed from cubic to mixedcubic and tetragonal with increasing PZT content. • Dielectric showed the samples underwent a typical relaxor ferroelectric behavior. • Magnetic properties showed very interesting behavior with square saturated magnetic hysteresis loops. - Abstract: Multiferroic (1 − x)Pb(Fe{sub 0.5}Ta{sub 0.5})O{sub 3}–xPb(Zr{sub 0.53}Ti{sub 0.47})O{sub 3} (or PFT–PZT) ceramics were synthesized by solid-state reaction method. The crystal structure and phase formation of the ceramics were examined by X-ray diffraction (XRD). The local structure surrounding Fe and Ti absorbing atoms was investigated by synchrotron X-ray Absorption Near-Edgemore » Structure (XANES) measurement. Dielectric properties were studied as a function of frequency and temperature using a LCR meter. A vibrating sample magnetometer (VSM) was used to determine the magnetic hysteresis loops. XRD study indicated that the crystal structure of the sample changed from pure cubic to mixed cubic and tetragonal with increasing PZT content. XANES measurements showed that the local structure surrounding Fe and Ti ions was similar. Dielectric study showed that the samples underwent a typical relaxor ferroelectric behavior while the magnetic properties showed very interesting behavior with square saturated magnetic hysteresis loops.« less

Estimating the number of pure chemical components in a mixture by X-ray absorption spectroscopy.

PubMed

Manceau, Alain; Marcus, Matthew; Lenoir, Thomas

2014-09-01

Principal component analysis (PCA) is a multivariate data analysis approach commonly used in X-ray absorption spectroscopy to estimate the number of pure compounds in multicomponent mixtures. This approach seeks to describe a large number of multicomponent spectra as weighted sums of a smaller number of component spectra. These component spectra are in turn considered to be linear combinations of the spectra from the actual species present in the system from which the experimental spectra were taken. The dimension of the experimental dataset is given by the number of meaningful abstract components, as estimated by the cascade or variance of the eigenvalues (EVs), the factor indicator function (IND), or the F-test on reduced EVs. It is shown on synthetic and real spectral mixtures that the performance of the IND and F-test critically depends on the amount of noise in the data, and may result in considerable underestimation or overestimation of the number of components even for a signal-to-noise (s/n) ratio of the order of 80 (σ = 20) in a XANES dataset. For a given s/n ratio, the accuracy of the component recovery from a random mixture depends on the size of the dataset and number of components, which is not known in advance, and deteriorates for larger datasets because the analysis picks up more noise components. The scree plot of the EVs for the components yields one or two values close to the significant number of components, but the result can be ambiguous and its uncertainty is unknown. A new estimator, NSS-stat, which includes the experimental error to XANES data analysis, is introduced and tested. It is shown that NSS-stat produces superior results compared with the three traditional forms of PCA-based component-number estimation. A graphical user-friendly interface for the calculation of EVs, IND, F-test and NSS-stat from a XANES dataset has been developed under LabVIEW for Windows and is supplied in the supporting information. Its possible application to

Ca 3d unoccupied states in Bi2Sr2CaCu2O8 investigated by Ca L2,3 x-ray-absorption near-edge structure

NASA Astrophysics Data System (ADS)

Borg, A.; King, P. L.; Pianetta, P.; Lindau, I.; Mitzi, D. B.; Kapitulnik, A.; Soldatov, A. V.; della Longa, S.; Bianconi, A.

1992-10-01

The high-resolution Ca L2,3 x-ray-absorption near-edge-structure (XANES) spectrum of a Bi2Sr2CaCu2O8 single crystal has been measured by use of a magnetic-projection x-ray microscope probing a surface area of 200×200 μm2. The Ca L2,3 XANES spectrum is analyzed by performing a multiple-scattering XANES calculation in real space and comparing the results with the spectrum of CaF2. Good agreement between the calculated and experimental crystal-field splitting Δf of the Ca 3d final states is found and the splitting is shown to be smaller by 0.5 eV than in the initial state. The Ca 3d partial density of states is found to be close to the Fermi level in the initial state. The Ca-O(in plane) distance is shown to be a critical parameter associated with the shift of the Ca 3d states relative to the Fermi level; in particular, we have studied the effect of the out-of-plane dimpling mode of the in-plane oxygen atoms O(in plane) that will move the Ca 3d states on or off the Fermi level. This mode can therefore play a role in modulating the charge transfer between the two CuO2 planes separated by the Ca ions.

Formation of Environmentally Persistent Free Radical (EPFR) in Iron(III) Cation-Exchanged Smectite Clay

PubMed Central

Nwosu, Ugwumsinachi G.; Roy, Amitava; dela Cruz, Albert Leo N.; Dellinger, Barry; Cook, Robert

2016-01-01

Environmentally persistent free radicals (EPFRs) have been found at a number of Superfund sites, with EPFRs being formed via a proposed redox process at ambient environmental conditions. The possibility of such a redox process taking place at ambient environmental conditions is studied utilizing a surrogate soil system of phenol and iron(III)-exchanged calcium montmorillonite clay, Fe(III)CaM. Sorption of phenol by the Fe(III)CaM is demonstrated by Fourier-transformed infra-red (FT-IR) spectroscopy, as evidenced by the peaks between 1345 cm−1 and 1595 cm−1, and at lower frequencies between 694 cm−1 and 806 cm−1, as well as X-ray diffraction (XRD) spectroscopy, as shown by an increase in interlayer spacing within Fe(III)CaM. The formation and characterization of the EPFRs is determined by electron paramagnetic resonance (EPR) spectroscopy, showing phenoxyl-type radical with a g-factor of 2.0034 and ΔHp-p of 6.1 G at an average concentration of 7.5 × 1017 spins/g. EPFRs lifetime data are indicative of oxygen and water molecules being responsible for EPFR decay. The change in the oxidation state of the iron redox center is studied by X-ray absorption near-edge structure (XANES) spectroscopy, showing that 23% of the Fe(III) is reduced to Fe(II). X-ray photoemission spectroscopy (XPS) results confirm the XANES results. These findings, when combined with the EPFR concentration data, demonstrate that the stoichiometry of the EPFR formation under the conditions of this study is 1.5 × 10−2 spins/Fe(II) atom. PMID:26647158

Formation of environmentally persistent free radical (EPFR) in iron(III) cation-exchanged smectite clay.

PubMed

Nwosu, Ugwumsinachi G; Roy, Amitava; dela Cruz, Albert Leo N; Dellinger, Barry; Cook, Robert

2016-01-01

Environmentally persistent free radicals (EPFRs) have been found at a number of Superfund sites, with EPFRs being formed via a proposed redox process at ambient environmental conditions. The possibility of such a redox process taking place at ambient environmental conditions is studied utilizing a surrogate soil system of phenol and iron(III)-exchanged calcium montmorillonite clay, Fe(III)CaM. Sorption of phenol by the Fe(III)CaM is demonstrated by Fourier-transformed infra-red (FT-IR) spectroscopy, as evidenced by the peaks between 1345 cm(-1) and 1595 cm(-1), and at lower frequencies between 694 cm(-1) and 806 cm(-1), as well as X-ray diffraction (XRD) spectroscopy, as shown by an increase in interlayer spacing within Fe(III)CaM. The formation and characterization of the EPFRs is determined by electron paramagnetic resonance (EPR) spectroscopy, showing phenoxyl-type radical with a g-factor of 2.0034 and ΔHP-P of 6.1 G at an average concentration of 7.5 × 10(17) spins per g. EPFRs lifetime data are indicative of oxygen and water molecules being responsible for EPFR decay. The change in the oxidation state of the iron redox center is studied by X-ray absorption near-edge structure (XANES) spectroscopy, showing that 23% of the Fe(III) is reduced to Fe(II). X-ray photoemission spectroscopy (XPS) results confirm the XANES results. These findings, when combined with the EPFR concentration data, demonstrate that the stoichiometry of the EPFR formation under the conditions of this study is 1.5 × 10(-2) spins per Fe(II) atom.

Nitrogen K-edge x-ray absorption near edge structure of pyrimidine-containing nucleotides in aqueous solution

NASA Astrophysics Data System (ADS)

Shimada, Hiroyuki; Minami, Hirotake; Okuizumi, Naoto; Sakuma, Ichiro; Ukai, Masatoshi; Fujii, Kentaro; Yokoya, Akinari; Fukuda, Yoshihiro; Saitoh, Yuji

2015-05-01

X-ray absorption near edge structure (XANES) was measured at energies around the N K-edge of the pyrimidine-containing nucleotides, cytidine 5'-monophosphate (CMP), 2'-deoxythymidine 5'-monophosphate (dTMP), and uridine 5'-monophosphate (UMP), in aqueous solutions and in dried films under various pH conditions. The features of resonant excitations below the N K-edge in the XANES spectra for CMP, dTMP, and UMP changed depending on the pH of the solutions. The spectral change thus observed is systematically explained by the chemical shift of the core-levels of N atoms in the nucleobase moieties caused by structural changes due to protonation or deprotonation at different proton concentrations. This interpretation is supported by the results of theoretical calculations using density functional theory for the corresponding nucleobases in the neutral and protonated or deprotonated forms.

4d Electronic structure analysis of ruthenium in the perovskite oxides by Ru K- and L-edge XAS.

PubMed

Kim, J Y; Hwang, S H; Kim, S J; Demazeau, G; Choy, J H; Shimada, H

2001-03-01

The 4d electronic structure of ruthenium in the perovskite oxides, La2MRuIVO6 (M = Zn, Mg, and Li) and Ba2YRuVO6, has been investigated by the Ru K-and L-edge XANES and EXAFS analyses. Such X-ray absorption spectroscopic results clarify that the RuIV (d4) and RuV (d3) ions are stabilized in nearly regular Oh site. Comparing the Ru L-edge XANES spectra of perovskites containing isovalent ruthenium, it has been found that the t2g state is mainly influenced by A site cation, whereas the eg is mainly affected by neighboring B site cation. The experimental EXAFS spectra in the range of R < or = approximately 4.5 A are well reproduced by ab-initio calculation based on crystallographic data, which supports the long-range structure presented by Rietveld refinement.

Atomistic nucleation sites of Pt nanoparticles on N-doped carbon nanotubes.

PubMed

Sun, Chia-Liang; Pao, Chih-Wen; Tsai, Huang-Ming; Chiou, Jau-Wern; Ray, Sekhar C; Wang, Houng-Wei; Hayashi, Michitoshi; Chen, Li-Chyong; Lin, Hong-Ji; Lee, Jyh-Fu; Chang, Li; Tsai, Min-Hsiung; Chen, Kuei-Hsien; Pong, Way-Faung

2013-08-07

The atomistic nucleation sites of Pt nanoparticles (Pt NPs) on N-doped carbon nanotubes (N-CNTs) were investigated using C and N K-edge and Pt L3-edge X-ray absorption near-edge structure (XANES)/extended X-ray absorption fine structure (EXAFS) spectroscopy. Transmission electron microscopy and XANES/EXAFS results revealed that the self-organized Pt NPs on N-CNTs are uniformly distributed because of the relatively high binding energies of the adsorbed Pt atoms at the imperfect sites. During the atomistic nucleation process of Pt NPs on N-CNTs, stable Pt-C and Pt-N bonds are presumably formed, and charge transfer occurs at the surface/interface of the N-CNTs. The findings in this study were consistent with density functional theory calculations performed using cluster models for the undoped, substitutional-N-doped and pyridine-like-N-doped CNTs.

Sulfur Speciation in Biochars by Very High Resolution Benchtop Kα X-ray Emission Spectroscopy.

PubMed

Holden, William M; Seidler, Gerald T; Cheah, Singfoong

2018-05-30

The analytical chemistry of sulfur-containing materials poses substantial technical challenges, especially due to the limitations of 33 S NMR and the time-intensive preparations required for wet-chemistry analyses. A number of prior studies have found that synchrotron-based X-ray absorption near edge structure (XANES) measurements can give detailed speciation of sulfur chemistry in such cases. However, due to the obvious access limitations, synchrotron XANES of sulfur cannot be part of routine analytical practice across the chemical sciences community. Here, in a study of the sulfur chemistry in biochars, we compare and contrast the chemical inferences available from synchrotron XANES with that given by benchtop, extremely high resolution wavelength-dispersive X-ray fluorescence (WD-XRF) spectroscopy, also often called X-ray emission spectroscopy (XES). While the XANES spectra have higher total information content, often giving differentiation between different moieties having the same oxidation state, the lower sensitivity of the S Kα XES to coordination and local structure provides pragmatic benefit for the more limited goal of quantifying the S oxidation state distribution. Within that constrained metric, we find good agreement between the two methods. As the sulfur concentrations were as low as 150 ppm, these measurements provide proof-of-principle for characterization of the sulfur chemistry of biochars and potential applications to other areas such as soils, batteries, catalysts, and fossil fuels and their combustion products.

Ab initio modeling of nonequilibrium electron-ion dynamics of iron in the warm dense matter regime

NASA Astrophysics Data System (ADS)

Ogitsu, T.; Fernandez-Pañella, A.; Hamel, S.; Correa, A. A.; Prendergast, D.; Pemmaraju, C. D.; Ping, Y.

2018-06-01

The spatiotemporal electron and ion relaxation dynamics of iron induced by femtosecond laser pulses was studied using a one-dimensional two-temperature model (1D-TTM) where electron and ion temperature-dependent thermophysical parameters such as specific heat (C ), electron-phonon coupling (G ), and thermal conductivity (K ) were calculated with ab initio density-functional-theory (DFT) simulations. Based on the simulated time evolutions of electron and ion temperature distributions [Te(x ,t ) and Ti(x ,t ) ], the time evolution of x-ray absorption near-edge spectroscopy (XANES) was calculated and compared with experimental results reported by Fernandez-Pañella et al., where the slope of XANES spectrum at the onset of absorption (s ) was used due to its excellent sensitivity to the electron temperature. Our results indicate that the ion temperature dependence on G and C , which is largely neglected in the past studies, is very important for studying the nonequilibrium electron-ion relaxation dynamics of iron in warm dense matter (WDM) conditions. It is also shown that the 1 /s behavior becomes very sensitive to the thermal gradient profile, in other words, to the values of K in a TTM simulation, for target thickness of about two to four times the mean free path of conduction electrons. Our approach based on 1D-TTM and XANES simulations can be used to determine the optimal combination of target geometry and laser fluence for a given target material, which will enable us to tightly constrain the thermophysical parameters under electron-ion nonequilibrium WDM conditions.

Structure and magnetic properties of Fe-doped ZnO prepared by the sol-gel method.

PubMed

Liu, Huilian; Yang, Jinghai; Zhang, Yongjun; Yang, Lili; Wei, Maobin; Ding, Xue

2009-04-08

Zn(0.97)Fe(0.03)O nanoparticles were synthesized by the sol-gel method. X-ray diffraction (XRD) and transmission electron microscope (TEM) analysis revealed that the samples had pure ZnO wurtzite structure and Fe ions were well incorporated into the ZnO crystal lattice. X-ray photoelectron spectroscopy (XPS) showed that both Fe(2+) and Fe(3+) existed in Zn(0.97)Fe(0.03)O. The result of x-ray absorption near-edge structure (XANES) further testified that Fe ions took the place of Zn sites in our samples. Magnetic measurements indicated that Zn(0.97)Fe(0.03)O was ferromagnetic at room temperature.

Sorption of Cr(III) and Cr(VI) to High and Low Pressure Synthetic Nano-Magnetite (Fe3O4)Particles

PubMed Central

Parsons, Jason G.; Hernandez, Jeffrey; Gonzalez, Christina M.; Gardea-Torresdey, J. L.

2014-01-01

The binding of Cr(III) and Cr(VI) to synthetic nano-magnetie particles synthesized under open vessel conditions and a microwave assisted hydrothermal synthesis techniques was investigated. Batch studies showed that the binding of both the Cr(III) and Cr(VI) bound to the nano-materials in a pH dependent manner. The Cr(III) maximized at binding at pH 4 and 100% binding. Similarly, the Cr(VI) ions showed a maximum binding of 100% at pH 4. The data from the time dependency studies showed for the most part the majority of the binding occurred within the first 5 minutes of contact with the nanomaterial and remained constant thereafter. In addition, the effects of the possible interferences were investigated which showed some effects on the binding of both Cr(III) and Cr(VI). However, the interferences never completely eliminated the chromium binding. Isotherm studies conducted at room temperature showed the microwave synthesized nanomaterials had a binding capacity of 1208 ± 43.9 mg/g and 555 ± 10.5 mg/g for Cr(VI) and Cr(III), respectively. However, the microwave assisted synthesized nanomaterials had capacities of 1705 ± 14.5 and 555± 10.5 mg/g for Cr(VI) and Cr(III), respectively. XANES studies showed the Cr(VI) was reduced to Cr(III), and the Cr(III) remained as Cr(III). In addition, the XANES studies indicated that the chromium remained coordinated in an octahedral arrangement of oxygen atoms. PMID:25097452

Recent results of synchrotron radiation induced total reflection X-ray fluorescence analysis at HASYLAB, beamline L

NASA Astrophysics Data System (ADS)

Streli, C.; Pepponi, G.; Wobrauschek, P.; Jokubonis, C.; Falkenberg, G.; Záray, G.; Broekaert, J.; Fittschen, U.; Peschel, B.

2006-11-01

At the Hamburger Synchrotronstrahlungslabor (HASYLAB), Beamline L, a vacuum chamber for synchrotron radiation-induced total reflection X-ray fluorescence analysis, is now available which can easily be installed using the adjustment components for microanalysis present at this beamline. The detector is now in the final version of a Vortex silicon drift detector with 50-mm 2 active area from Radiant Detector Technologies. With the Ni/C multilayer monochromator set to 17 keV extrapolated detection limits of 8 fg were obtained using the 50-mm 2 silicon drift detector with 1000 s live time on a sample containing 100 pg of Ni. Various applications are presented, especially of samples which are available in very small amounts: As synchrotron radiation-induced total reflection X-ray fluorescence analysis is much more sensitive than tube-excited total reflection X-ray fluorescence analysis, the sampling time of aerosol samples can be diminished, resulting in a more precise time resolution of atmospheric events. Aerosols, directly sampled on Si reflectors in an impactor were investigated. A further application was the determination of contamination elements in a slurry of high-purity Al 2O 3. No digestion is required; the sample is pipetted and dried before analysis. A comparison with laboratory total reflection X-ray fluorescence analysis showed the higher sensitivity of synchrotron radiation-induced total reflection X-ray fluorescence analysis, more contamination elements could be detected. Using the Si-111 crystal monochromator also available at beamline L, XANES measurements to determine the chemical state were performed. This is only possible with lower sensitivity as the flux transmitted by the crystal monochromator is about a factor of 100 lower than that transmitted by the multilayer monochromator. Preliminary results of X-ray absorption near-edge structure measurements for As in xylem sap from cucumber plants fed with As(III) and As(V) are reported. Detection limits

AMS 14C analysis of teeth from archaeological sites showing anomalous esr dating results

NASA Astrophysics Data System (ADS)

Grün, Rainer; Abeyratne, Mohan; Head, John; Tuniz, Claudio; Hedges, Robert E. M.

We have carried out AMS radiocarbon analysis on two groups of samples: the first one gave reasonable ESR age estimates and the second one yielded serious age underestinations. All samples were supposedly older than 35 ka, the oldest being around 160 ka. Two pretreatment techniques were used for radiocarbon dating: acid evolution and thermal release. Heating to 600, 750 and 900°C combined with total de-gassing at these temperatures was chosen to obtain age estimates on the organic fraction, secondary carbonates and original carbonate present in the hydroxyapatite mineral phase, respectively. All radiocarbon results present serious age underestimations. The secondary carbonate fraction gives almost modern results indicating an extremely rapid exchange of this component. Owing to this very rapid carbonate exchange it is not likely that the ESR signals used for dating are associated with the secondary carbonates. One tooth from Tabun with independent age estimates of >150 ka was further investigated by the Oxford AMS laboratory, yielding an age estimate of 1930±100 BP on the residual collagen from dentine and 18,000±160 BP on the carbonate component of the enamel bioapatite. We did not, however, find an explanation of why some samples give serious ESR underestimatioils whilst many others provide reasonable results.

X-ray absorption near edge structure/electron energy loss near edge structure calculation using the supercell orthogonalized linear combination of atomic orbitals method

NASA Astrophysics Data System (ADS)

Ching, Wai-Yim; Rulis, Paul

2009-03-01

Over the last eight years, a large number of x-ray absorption near edge structure (XANES) and/or electron energy loss near edge structure (ELNES) spectroscopic calculations for complex oxides and nitrides have been performed using the supercell-OLCAO (orthogonalized linear combination of atomic orbitals) method, obtaining results in very good agreement with experiments. The method takes into account the core-hole effect and includes the dipole matrix elements calculated from ab initio wavefunctions. In this paper, we describe the method in considerable detail, emphasizing the special advantages of this method for large complex systems. Selected results are reviewed and several hitherto unpublished results are also presented. These include the Y K edge of Y ions segregated to the core of a Σ31 grain boundary in alumina, O K edges of water molecules, C K edges in different types of single walled carbon nanotubes, and the Co K edge in the cyanocobalamin (vitamin B12) molecule. On the basis of these results, it is argued that the interpretation of specific features of the calculated XANES/ELNES edges is not simple for complex material systems because of the delocalized nature of the conduction band states. The long-standing notion of the 'fingerprinting' technique for spectral interpretation of experimental data is not tenable. A better approach is to fully characterize the structure under study, using either crystalline data or accurate ab initio modeling. Comparison between calculated XANES/ELNES spectra and available measurements enables us to ascertain the validity of the modeled structure. For complex crystals or structures, it is necessary to use the weighted sum of the spectra from structurally nonequivalent sites for comparison with the measured data. Future application of the supercell-OLCAO method to complex biomolecular systems is also discussed.

Arsenic Speciation in Plankton Organisms from Contaminated Lakes: Transformations at the Base of the Freshwater Food Chain

DOE Office of Scientific and Technical Information (OSTI.GOV)

Caumette, Guilhem; Koch, Iris; Estrada, Esteban

2012-02-06

The two complementary techniques high performance liquid chromatography-inductively coupled plasma-mass spectrometry (HPLC-ICP-MS) and X-ray absorption near edge structure (XANES) analysis were used to assess arsenic speciation in freshwater phytoplankton and zooplankton collected from arsenic-contaminated lakes in Yellowknife (Northwest Territories, Canada). Arsenic concentrations in lake water ranged from 7 {micro}g L{sup -1} in a noncontaminated lake to 250 {micro}g L{sup -1} in mine-contaminated lakes, which resulted in arsenic concentrations ranging from 7 to 340 mg kg{sup -1} d.w. in zooplankton organisms (Cyclops sp.) and from 154 to 894 mg kg{sup -1} d.w. in phytoplankton. The main arsenic compounds identified by HPLC-ICP-MSmore » in all plankton were inorganic arsenic (from 38% to 98% of total arsenic). No other arsenic compounds were found in phytoplankton, but zooplankton organisms showed the presence of organoarsenic compounds, the most common being the sulfate arsenosugar, up to 47% of total arsenic, with traces of phosphate sugar, glycerol sugar, methylarsonate (MMA), and dimethylarsinate (DMA). In the uncontaminated Grace Lake, zooplankton also contained arsenobetaine (AB). XANES characterization of arsenic in the whole plankton samples showed AsV-O as the only arsenic compound in phytoplankton, and AsIII-S and AsV-O compounds as the two major inorganic arsenic species in zooplankton. The proportion of organoarsenicals and inorganic arsenic in zooplankton depends upon the arsenic concentration in lakes and shows the impact of arsenic contamination: zooplankton from uncontaminated lake has higher proportions of organoarsenic compounds and contains arsenobetaine, while zooplankton from contaminated area contains mostly inorganic arsenic.« less

Tuning Ni-catalyzed CO 2 hydrogenation selectivity via Ni-ceria support interactions and Ni-Fe bimetallic formation

DOE PAGES

Winter, Lea R.; Gomez, Elaine; Yan, Binhang; ...

2017-10-16

CO 2 hydrogenation over Fe-modified Ni/CeO 2 catalysts was investigated in a batch reactor using time-resolved in situ FTIR spectroscopy. Low loading of Ni/CeO 2 was associated with high selectivity to CO over CH 4, while higher Ni loading improved CO 2 hydrogenation activity with a reduced CO selectivity. X-ray absorption near-edge structure (XANES) analysis revealed Ni to be metallic for all catalysts including the CO-selective low loading 0.5% Ni catalyst, suggesting that the selectivity trend is due to structural rather than oxidation state effects. The loading amount of 1.5% Ni was selected for co-impregnation with Fe, based on themore » significant shift in product selectivity towards CH 4 for that loading amount, in order to shift the selectivity towards CO while maintaining high activity. Temperature programmed reduction (TPR) results indicated bimetallic interactions between Ni and Fe, and XANES analysis showed that about 70% of Fe in the bimetallic catalysts was oxidized. The Ni-Fe catalysts demonstrated improved selectivity towards CO without significantly compromising activity, coupling the high activity of Ni catalysts and the high CO selectivity of Fe. The general trends in Ni loading and bimetallic modification should guide efforts to develop non-precious metal catalysts for the selective production of CO by CO 2 hydrogenation.« less

Inhibition of phosphorus sorption on calcite by dairy manure-sourced DOC.

PubMed

Weyers, Eva; Strawn, Daniel G; Peak, Derek; Baker, Leslie L

2017-10-01

In confined animal feeding operations, such as dairies, manure is amended to soils at high rates leading to increases in P and organic matter in the soils. Phosphorus reacts with soil-Ca to form Ca-P minerals, which controls P availability for leaching and transport through the watershed. In this research, the effects of manure sourced dissolved organic matter (DOM) on P sorption on calcite were measured at different reaction times and concentrations. Reactions were monitored in 1% and 10% manure-to-water extract solutions spiked with P. When manure-DOM was present, a significant reduction in P sorption occurred (2-90% absolute decrease) compared to samples without manure-DOM. The greatest decrease occurred in the samples reacted in the 10% manure solution. XANES spectroscopic analysis showed that at 1% manure solution, a Ca-P phase similar to hydroxyapatite formed. In the calcite samples reacted in the 10% manure solution, K-edge XANES spectroscopy revealed that P occurred as a Ca-Mg-P phase instead of the less soluble hydroxyapatite-like phase. Results from this study suggest that in manure-amended calcareous soils, increased DOM from manure will decrease P sorption capacity and increase the overall P concentration in solution, which will increase the mobility of P and subsequently pose greater risks for impairment of surface water quality. Copyright © 2017 Elsevier Ltd. All rights reserved.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Winter, Lea R.; Gomez, Elaine; Yan, Binhang

CO 2 hydrogenation over Fe-modified Ni/CeO 2 catalysts was investigated in a batch reactor using time-resolved in situ FTIR spectroscopy. Low loading of Ni/CeO 2 was associated with high selectivity to CO over CH 4, while higher Ni loading improved CO 2 hydrogenation activity with a reduced CO selectivity. X-ray absorption near-edge structure (XANES) analysis revealed Ni to be metallic for all catalysts including the CO-selective low loading 0.5% Ni catalyst, suggesting that the selectivity trend is due to structural rather than oxidation state effects. The loading amount of 1.5% Ni was selected for co-impregnation with Fe, based on themore » significant shift in product selectivity towards CH 4 for that loading amount, in order to shift the selectivity towards CO while maintaining high activity. Temperature programmed reduction (TPR) results indicated bimetallic interactions between Ni and Fe, and XANES analysis showed that about 70% of Fe in the bimetallic catalysts was oxidized. The Ni-Fe catalysts demonstrated improved selectivity towards CO without significantly compromising activity, coupling the high activity of Ni catalysts and the high CO selectivity of Fe. The general trends in Ni loading and bimetallic modification should guide efforts to develop non-precious metal catalysts for the selective production of CO by CO 2 hydrogenation.« less

Nitrogen K-edge x-ray absorption near edge structure of pyrimidine-containing nucleotides in aqueous solution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shimada, Hiroyuki, E-mail: hshimada@cc.tuat.ac.jp; Minami, Hirotake; Okuizumi, Naoto

2015-05-07

X-ray absorption near edge structure (XANES) was measured at energies around the N K-edge of the pyrimidine-containing nucleotides, cytidine 5′-monophosphate (CMP), 2′-deoxythymidine 5′-monophosphate (dTMP), and uridine 5′-monophosphate (UMP), in aqueous solutions and in dried films under various pH conditions. The features of resonant excitations below the N K-edge in the XANES spectra for CMP, dTMP, and UMP changed depending on the pH of the solutions. The spectral change thus observed is systematically explained by the chemical shift of the core-levels of N atoms in the nucleobase moieties caused by structural changes due to protonation or deprotonation at different proton concentrations.more » This interpretation is supported by the results of theoretical calculations using density functional theory for the corresponding nucleobases in the neutral and protonated or deprotonated forms.« less

Physical properties of superbulky lanthanide metallocenes: synthesis and extraordinary luminescence of [Eu(II)(Cp(BIG))2] (Cp(BIG) = (4-nBu-C6H4)5-cyclopentadienyl).

PubMed

Harder, Sjoerd; Naglav, Dominik; Ruspic, Christian; Wickleder, Claudia; Adlung, Matthias; Hermes, Wilfried; Eul, Matthias; Pöttgen, Rainer; Rego, Daniel B; Poineau, Frederic; Czerwinski, Kenneth R; Herber, Rolfe H; Nowik, Israel

2013-09-09

The superbulky deca-aryleuropocene [Eu(Cp(BIG))2], Cp(BIG) = (4-nBu-C6H4)5-cyclopentadienyl, was prepared by reaction of [Eu(dmat)2(thf)2], DMAT = 2-Me2N-α-Me3Si-benzyl, with two equivalents of Cp(BIG)H. Recrystallizyation from cold hexane gave the product with a surprisingly bright and efficient orange emission (45% quantum yield). The crystal structure is isomorphic to those of [M(Cp(BIG))2] (M = Sm, Yb, Ca, Ba) and shows the typical distortions that arise from Cp(BIG)⋅⋅⋅Cp(BIG) attraction as well as excessively large displacement parameter for the heavy Eu atom (U(eq) = 0.075). In order to gain information on the true oxidation state of the central metal in superbulky metallocenes [M(Cp(BIG))2] (M = Sm, Eu, Yb), several physical analyses have been applied. Temperature-dependent magnetic susceptibility data of [Yb(Cp(BIG))2] show diamagnetism, indicating stable divalent ytterbium. Temperature-dependent (151)Eu Mössbauer effect spectroscopic examination of [Eu(Cp(BIG))2] was examined over the temperature range 93-215 K and the hyperfine and dynamical properties of the Eu(II) species are discussed in detail. The mean square amplitude of vibration of the Eu atom as a function of temperature was determined and compared to the value extracted from the single-crystal X-ray data at 203 K. The large difference in these two values was ascribed to the presence of static disorder and/or the presence of low-frequency torsional and librational modes in [Eu(Cp(BIG))2]. X-ray absorbance near edge spectroscopy (XANES) showed that all three [Ln(Cp(BIG))2] (Ln = Sm, Eu, Yb) compounds are divalent. The XANES white-line spectra are at 8.3, 7.3, and 7.8 eV, for Sm, Eu, and Yb, respectively, lower than the Ln2O3 standards. No XANES temperature dependence was found from room temperature to 100 K. XANES also showed that the [Ln(Cp(BIG))2] complexes had less trivalent impurity than a [EuI2(thf)x] standard. The complex [Eu(Cp(BIG))2] shows already at room temperature

Effects of X-ray irradiation on the Eu3+ → Eu2+ conversion in CaAl2O4 phosphors

NASA Astrophysics Data System (ADS)

Gomes, Manassés A.; Carvalho, Jéssica C.; Andrade, Adriano B.; Rezende, Marcos V.; Macedo, Zélia S.; Valerio, Mário E. G.

2018-01-01

This paper reports structural and luminescence properties of Eu-doped CaAl2O4 produced by an alternative sol-gel method using coconut water. Results of differential thermal analysis (DTA), thermogravimetric analysis (TGA), and X-ray diffraction (XRD) allowed us to identify the best synthesis conditions for sample preparation. Simultaneous measurements of X-ray absorption spectroscopy (XAS) and X-ray excited optical luminescence (XEOL) were also performed in the X-ray energy range of the Eu LIII edge. Results from photoluminescence (PL) showed only the characteristic Eu3+ emission. However, radioluminescence emission spectra from Eu-doped CaAl2O4 shows a process of conversion of Eu3+ to Eu2+, which is induced by X-ray irradiation and is dependent on the radiation dose energy. X-ray absorption near edge structure (XANES) measurements corroborate Eu reduction due to irradiation, showing that only the Eu3+ ion is present in stable form in the CaAl2O4.

Sulfur Speciation in Biochars by Very High Resolution Benchtop Ka X-Ray Emission Spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cheah, Singfoong; Holden, William M.; Seidler, Gerald T.

The analytical chemistry of sulfur-containing materials poses substantial technical challenges, especially due to the limitations of 33S NMR and the time-intensive preparations required for wet-chemistry analyses. A number of prior studies have found that synchrotron-based X-ray absorption near edge structure (XANES) measurements can give detailed speciation of sulfur chemistry in such cases. However, due to the obvious access limitations, synchrotron XANES of sulfur cannot be part of routine analytical practice across the chemical sciences community. Here, in a study of the sulfur chemistry in biochars, we compare and contrast the chemical inferences available from synchrotron XANES with that given bymore » benchtop, extremely high resolution wavelength-dispersive X-ray fluorescence (WD-XRF) spectroscopy, also often called X-ray emission spectroscopy (XES). While the XANES spectra have higher total information content, often giving differentiation between different moieties having the same oxidation state, the lower sensitivity of the S Ka XES to coordination and local structure provides pragmatic benefit for the more limited goal of quantifying the S oxidation state distribution. Within that constrained metric, we find good agreement between the two methods. As the sulfur concentrations were as low as 150 ppm, these measurements provide proof-of-principle for characterization of the sulfur chemistry of biochars and potential applications to other areas such as soils, batteries, catalysts, and fossil fuels and their combustion products.« less

Near-edge X-ray absorption spectra for metallic Cu and Mn

NASA Astrophysics Data System (ADS)

Greaves, G. N.; Durham, P. J.; Diakun, G.; Quinn, P.

1981-11-01

The measurement of X-ray absorption fine structure of metals- both in the extended region (EXAFS) as well as in the near edge region (XANES)-has been widely discussed (see refs 1-6 for Cu and refs 7-9 for Mn). The recent availability of intense X-ray fluxes from storage rings has usually been exploited for EXAFS leaving the XANES often with poorer resolution than earlier work performed on conventional sources (for example, compare the near edge structure for copper in ref. 1 with refs 3 or 6). In addition, whilst the theory and analysis of EXAFS is relatively well-established2,10, a theory for the strong scattering regime near to the absorption edge has only recently been developed11. We report here the first high resolution XANES spectra for Cu and Mn which were performed at the SRS storage ring at Daresbury. Although both metals have close-packed structures consisting of atoms of similar size their local atomic structure is different in detail. Significant differences are found in their respective XANES reflecting the senstivity of this region of the X-ray absorption fine structure to the local atomic structure. Spectra for the two metals have been analysed using the new multiple scattering formalism. This is a real space calculation and unlike a conventional band structure approach it does not require structural periodicity but works from the local arrangement of atoms.

Electronic State of Sodium trans-[Tetrachloridobis(1H-indazole)ruthenate(III)] (NKP-1339) in Tumor, Liver and Kidney Tissue of a SW480-bearing Mouse

NASA Astrophysics Data System (ADS)

Blazevic, Amir; Hummer, Alfred A.; Heffeter, Petra; Berger, Walter; Filipits, Martin; Cibin, Giannantonio; Keppler, Bernhard K.; Rompel, Annette

2017-01-01

Ruthenium complexes are promising candidates for anticancer agents, especially NKP-1339 (sodium trans-[tetrachloridobis(1H-indazole)ruthenate(III)]), which is on the edge to clinical applications. The anticancer mechanism seems to be tightly linked to the redox chemistry but despite progress in human clinical trials the in vivo Ru oxidation state and the coordination of Ru remains unclear. The Ru-based anticancer drug NKP-1339 was studied applying XANES (Cl K- and Ru L2,3-edges) in tumor, kidney and liver tissue of a SW480 bearing mouse. Based on coordination charge and 3D XANES plots containing a series of model compounds as well as pre-edge analysis of the ligand Cl K-edge it is suggested that NKP-1339 remains in its +III oxidation state after 24 hours and at least one of the four chlorido ligands remain covalently bound to the Ru ion showing a biotransformation from RuIIIN2Cl4 to RuIIIClx(N/O)6-x (X = 1 or 2).

Electronic State of Sodium trans-[Tetrachloridobis(1H-indazole)ruthenate(III)] (NKP-1339) in Tumor, Liver and Kidney Tissue of a SW480-bearing Mouse

PubMed Central

Blazevic, Amir; Hummer, Alfred A.; Heffeter, Petra; Berger, Walter; Filipits, Martin; Cibin, Giannantonio; Keppler, Bernhard K.; Rompel, Annette

2017-01-01

Ruthenium complexes are promising candidates for anticancer agents, especially NKP-1339 (sodium trans-[tetrachloridobis(1H-indazole)ruthenate(III)]), which is on the edge to clinical applications. The anticancer mechanism seems to be tightly linked to the redox chemistry but despite progress in human clinical trials the in vivo Ru oxidation state and the coordination of Ru remains unclear. The Ru-based anticancer drug NKP-1339 was studied applying XANES (Cl K- and Ru L2,3-edges) in tumor, kidney and liver tissue of a SW480 bearing mouse. Based on coordination charge and 3D XANES plots containing a series of model compounds as well as pre-edge analysis of the ligand Cl K-edge it is suggested that NKP-1339 remains in its +III oxidation state after 24 hours and at least one of the four chlorido ligands remain covalently bound to the Ru ion showing a biotransformation from RuIIIN2Cl4 to RuIIIClx(N/O)6−x (X = 1 or 2). PMID:28112202

10. INTERIOR VIEW SHOWING MOUNTINGS FROM TUNING DEVICE. VIEW SHOWS ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

10. INTERIOR VIEW SHOWING MOUNTINGS FROM TUNING DEVICE. VIEW SHOWS COPPER SHEETING ON WALLS. - Chollas Heights Naval Radio Transmitting Facility, Helix House, 6410 Zero Road, San Diego, San Diego County, CA

Lead speciation in indoor dust: a case study to assess old paint contribution in a Canadian urban house

DOE Office of Scientific and Technical Information (OSTI.GOV)

Beauchemin, Suzanne; MacLean, Lachlan C.W.; Rasmussen, Pat E.

Residents in older homes may experience increased lead (Pb) exposures due to release of lead from interior paints manufactured in past decades, especially pre-1960s. The objective of the study was to determine the speciation of Pb in settled dust from an urban home built during WWII. X-ray absorption near-edge structure (XANES) and micro-X-ray diffraction (XRD) analyses were performed on samples of paint (380-2,920 mg Pb kg{sup -1}) and dust (200-1,000 mg Pb kg{sup -1}) collected prior to renovation. All dust samples exhibited a Pb XANES signature similar to that of Pb found in paint. Bulk XANES and micro-XRD identified Pbmore » species commonly found as white paint pigments (Pb oxide, Pb sulfate, and Pb carbonate) as well as rutile, a titanium-based pigment, in the <150 {micro}m house dust samples. In the dust fraction <36 {micro}m, half of the Pb was associated with the Fe-oxyhydroxides, suggesting additional contribution of outdoor sources to Pb in the finer dust. These results confirm that old paints still contribute to Pb in the settled dust for this 65-year-old home. The Pb speciation also provided a clearer understanding of the Pb bioaccessibility: Pb carbonate > Pb oxide > Pb sulfate. This study underscores the importance of taking precautions to minimize exposures to Pb in house dust, especially in homes where old paint is exposed due to renovations or deterioration of painted surfaces.« less

Lead Speciation in Indoor Dust: A Case Study to Assess Old Paint Contribution in a Canadian Urban House

DOE Office of Scientific and Technical Information (OSTI.GOV)

S Beauchemin; L MacLean; P Rasmussen

Residents in older homes may experience increased lead (Pb) exposures due to release of lead from interior paints manufactured in past decades, especially pre-1960s. The objective of the study was to determine the speciation of Pb in settled dust from an urban home built during WWII. X-ray absorption near-edge structure (XANES) and micro-X-ray diffraction (XRD) analyses were performed on samples of paint (380-2,920 mg Pb kg{sup -1}) and dust (200-1,000 mg Pb kg{sup -1}) collected prior to renovation. All dust samples exhibited a Pb XANES signature similar to that of Pb found in paint. Bulk XANES and micro-XRD identified Pbmore » species commonly found as white paint pigments (Pb oxide, Pb sulfate, and Pb carbonate) as well as rutile, a titanium-based pigment, in the <150 m house dust samples. In the dust fraction <36 {mu}m, half of the Pb was associated with the Fe-oxyhydroxides, suggesting additional contribution of outdoor sources to Pb in the finer dust. These results confirm that old paints still contribute to Pb in the settled dust for this 65-year-old home. The Pb speciation also provided a clearer understanding of the Pb bioaccessibility: Pb carbonate > Pb oxide > Pb sulfate. This study underscores the importance of taking precautions to minimize exposures to Pb in house dust, especially in homes where old paint is exposed due to renovations or deterioration of painted surfaces.« less

The effect of nitrogen incorporation on the bonding structure of hydrogenated carbon nitride films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Camero, M.; Buijnsters, J. G.; Gomez-Aleixandre, C.

2007-03-15

This work describes the composition and bonding structure of hydrogenated carbon nitride (a-CN{sub x}:H) films synthesized by electron cyclotron resonance chemical vapor deposition using as precursor gases argon, methane, and nitrogen. The composition of the films was derived from Rutherford backscattering and elastic recoil detection analysis and the bonding structure was examined by infrared (IR) spectroscopy and x-ray absorption near edge spectroscopy (XANES). By varying the nitrogen to methane ratio in the applied gas mixture, polymeric a-CN{sub x}:H films with N/C contents varying from 0.06 to 0.49 were obtained. Remarkably, the H content of the films ({approx}40 at. %) wasmore » rather unaffected by the nitrogenation process. The different bonding states as detected in the measured XANES C(1s) and N(1s) spectra have been correlated with those of a large number of reference samples. The XANES and IR spectroscopy results indicate that N atoms are efficiently incorporated into the amorphous carbon network and can be found in different bonding environments, such as pyridinelike, graphitelike, nitrilelike, and amino groups. The nitrogenation of the films results in the formation of N-H bonding environments at the cost of C-H structures. Also, the insertion of N induces a higher fraction of double bonds in the structure at the expense of the linear polymerlike chains, hence resulting in a more cross-linked solid. The formation of double bonds takes place through complex C=N structures and not by formation of graphitic aromatic rings. Also, the mechanical and tribological properties (hardness, friction, and wear) of the films have been studied as a function of the nitrogen content. Despite the major modifications in the bonding structure with nitrogen uptake, no significant changes in these properties are observed.« less

Sulfide-driven arsenic mobilization from arsenopyrite and black shale pyrite

USGS Publications Warehouse

Zhu, W.; Young, L.Y.; Yee, N.; Serfes, M.; Rhine, E.D.; Reinfelder, J.R.

2008-01-01

We examined the hypothesis that sulfide drives arsenic mobilization from pyritic black shale by a sulfide-arsenide exchange and oxidation reaction in which sulfide replaces arsenic in arsenopyrite forming pyrite, and arsenide (As-1) is concurrently oxidized to soluble arsenite (As+3). This hypothesis was tested in a series of sulfide-arsenide exchange experiments with arsenopyrite (FeAsS), homogenized black shale from the Newark Basin (Lockatong formation), and pyrite isolated from Newark Basin black shale incubated under oxic (21% O2), hypoxic (2% O2, 98% N2), and anoxic (5% H2, 95% N2) conditions. The oxidation state of arsenic in Newark Basin black shale pyrite was determined using X-ray absorption-near edge structure spectroscopy (XANES). Incubation results show that sulfide (1 mM initial concentration) increases arsenic mobilization to the dissolved phase from all three solids under oxic and hypoxic, but not anoxic conditions. Indeed under oxic and hypoxic conditions, the presence of sulfide resulted in the mobilization in 48 h of 13-16 times more arsenic from arsenopyrite and 6-11 times more arsenic from isolated black shale pyrite than in sulfide-free controls. XANES results show that arsenic in Newark Basin black shale pyrite has the same oxidation state as that in FeAsS (-1) and thus extend the sulfide-arsenide exchange mechanism of arsenic mobilization to sedimentary rock, black shale pyrite. Biologically active incubations of whole black shale and its resident microorganisms under sulfate reducing conditions resulted in sevenfold higher mobilization of soluble arsenic than sterile controls. Taken together, our results indicate that sulfide-driven arsenic mobilization would be most important under conditions of redox disequilibrium, such as when sulfate-reducing bacteria release sulfide into oxic groundwater, and that microbial sulfide production is expected to enhance arsenic mobilization in sedimentary rock aquifers with major pyrite-bearing, black

Oxidation States of Grim Glasses in EET79001 Based on Vanadium Valence

NASA Technical Reports Server (NTRS)

Sutton, S. R.; Rao, M. N.; Nyquist, L. E.

2010-01-01

Gas-rich impact-melt (GRIM) glasses in SNC meteorites are very rich in Martian atmospheric noble gases and sulfur suggesting a possible occurrence of regolith-derived secondary mineral assemblages in these samples. Previously, we have studied two GRIM glasses, 506 and 507, from EET79001 Lith A and Lith B, respectively, for elemental abundances and spatial distribution of sulfur using EMPA (WDS) and FE-SEM (EDS) techniques and for sulfur-speciation using K-edge XANES techniques. These elemental and FE-SEM micro-graph data at several locations in the GRIM glasses from Shergotty (DBS), Zagami 994 and EET79001, Lith B showed that FeO and SO3 are positively correlated (SO3 represents a mixture of sulfide and sulfate). FE-SEM (EDS) study revealed that the sulfur-rich pockets in these glasses contain numerous micron-sized iron-sulfide (Fe-S) globules sequestered throughout the volume. However, in some areas (though less frequently), we detected significant Fe-S-O signals suggesting the occurrence of iron sulfate. These GRIM glasses were studied by K-edge microXANES techniques for sulfur speciation in association with iron in sulfur-rich areas. In both samples, we found the sulfur speciation dominated by sulfide with minor oxidized sulfur mixed in with various proportions. The abundance of oxidized sulfur was greater in 506 than in 507. Based on these results, we hypothesize that sulfur initially existed as sulfate in the glass precursor materials and, on shock-impact melting of the precursor materials producing these glasses, the oxidized sulfur was reduced to predominately sulfide. In order to further test this hypothesis, we have used microXANES to measure the valence states of vanadium in GRIM glasses from Lith A and Lith B to complement and compare with previous analogous measurements on Lith C (note: 506 and 507 contain the largest amounts of martian atmospheric gases but the gas-contents in Lith C measured by are unknown). Vanadium is ideal for addressing this re

Structural changes correlated with magnetic spin state isomorphism in the S 2 state of the Mn 4CaO 5 cluster in the oxygen-evolving complex of photosystem II

DOE PAGES

Chatterjee, Ruchira; Han, Guangye; Kern, Jan; ...

2016-05-09

The Mn 4CaO 5 cluster in photosystem II catalyzes the four-electron redox reaction of water oxidation in natural photosynthesis. This catalytic reaction cycles through four intermediate states (S i, i = 0 to 4), involving changes in the redox state of the four Mn atoms in the cluster. Recent studies suggest the presence and importance of isomorphous structures within the same redox/intermediate S-state. It is highly likely that geometric and electronic structural flexibility play a role in the catalytic mechanism. Among the catalytic intermediates that have been identified experimentally thus far, there is clear evidence of such isomorphism in themore » S2 state, with a high-spin (5/2) (HS) and a low spin (1/2) (LS) form, identified and characterized by their distinct electron paramagnetic resonance (EPR spectroscopy) signals. We studied these two S2 isomers with Mn extended X-ray absorption fine structure (EXAFS) and absorption and emission spectroscopy (XANES/XES) to characterize the structural and electronic structural properties. The geometric and electronic structure of the HS and LS S2 states are different as determined using Mn EXAFS and XANES/XES, respectively. The Mn K-edge XANES and XES for the HS form are different from the LS and indicate a slightly lower positive charge on the Mn atoms compared to the LS form. Based on the EXAFS results which are clearly different, we propose possible structural differences between the two spin states. As a result, such structural and magnetic redox-isomers if present at room temperature, will likely play a role in the mechanism for water-exchange/oxidation in photosynthesis.« less

Effects of sulfation level on the desulfation behavior of pre-sulfated Pt BaO/Al2O3 lean NOx trap catalysts: a combined H2 Temperature-Programmed Reaction, in-situ sulfur K-edge X-ray Absorption Near-Edge Spectroscopy, X-ray Photoelectron Spectroscopy, and Time-Resolved X-ray Diffraction Study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, Do Heui; Szanyi, Janos; Kwak, Ja Hun

2009-04-03

Desulfation by hydrogen of pre-sulfated Pt(2wt%) BaO(20wt%)/Al2O3 with various sulfur loading (S/Ba = 0.12, 0.31 and 0.62) were investigated by combining H2 temperature programmed reaction (TPRX), x-ray photoelectron spectroscopy (XPS), in-situ sulfur K-edge x-ray absorption near-edge spectroscopy (XANES), and synchrotron time-resolved x-ray diffraction (TR-XRD) techniques. We find that the amount of H2S desorbed during the desulfation in the H2 TPRX experiments is not proportional to the amount of initial sulfur loading. The results of both in-situ sulfur K-edge XANES and TR-XRD show that at low sulfur loadings, sulfates were transformed to a BaS phase and remained in the catalyst, rathermore » than being removed as H2S. On the other hand, when the deposited sulfur level exceeded a certain threshold (at least S/Ba = 0.31) sulfates were reduced to form H2S, and the relative amount of the residual sulfide species in the catalyst was much less than at low sulfur loading. Unlike samples with high sulfur loading (e.g., S/Ba = 0.62), H2O did not promote the desulfation for the sample with S/Ba of 0.12, implying that the formed BaS species originating from the reduction of sulfates at low sulfur loading are more stable to hydrolysis. The results of this combined spectroscopy investigation provide clear evidence to show that sulfates at low sulfur loadings are less likely to be removed as H2S and have a greater tendency to be transformed to BaS on the material, leading to the conclusion that desulfation behavior of Pt BaO/Al2O3 lean NOx trap catalysts is markedly dependent on the sulfation levels.« less

Effects of Sulfation Level on the Desulfation Behavior of Presulfated Pt-BaO/Al2O3 Lean

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, D.; Szanyi, J; Kwak, J

2009-01-01

Desulfation by hydrogen of presulfated Pt (2 wt %)-BaO(20 wt %)/Al2O3 with various sulfur loading (S/Ba = 0.12, 0.31, and 0.62) were investigated by combining H2 temperature programmed reaction (TPRX), X-ray photoelectron spectroscopy (XPS), in situ sulfur K-edge X-ray absorption near-edge spectroscopy (XANES), and synchrotron time-resolved X-ray diffraction (TR-XRD) techniques. We find that the amount of H2S desorbed during the desulfation in the H2 TPRX experiments is not proportional to the amount of initial sulfur loading. The results of both in situ sulfur K-edge XANES and TR-XRD show that at low sulfur loadings, sulfates were transformed to a BaS phasemore » and remained in the catalyst rather than being removed as H2S. On the other hand, when the deposited sulfur level exceeded a certain threshold (at least S/Ba = 0.31) sulfates were reduced to form H2S, and the relative amount of the residual sulfide species in the catalyst was much less than at low sulfur loading. Unlike samples with high sulfur loading (e.g., S/Ba = 0.62), H2O did not promote the desulfation for the sample with S/Ba of 0.12, implying that the formed BaS species originating from the reduction of sulfates at low sulfur loading are more stable to hydrolysis. The results of this combined spectroscopy investigation provide clear evidence to show that sulfates at low sulfur loadings are less likely to be removed as H2S and have a greater tendency to be transformed to BaS on the material, leading to the conclusion that desulfation behavior of Pt-BaO/Al2O3 lean NOx trap catalysts is markedly dependent on the sulfation levels.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pacold, J. I.; Altman, A. B.; Donald, S B

Materials of interest for nuclear forensic science are often highly heterogeneous, containing complex mixtures of actinide compounds in a wide variety of matrices. Scanning transmission X-ray microscopy (STXM) is ideally suited to study such materials, as it can be used to chemically image specimens by acquiring X-ray absorption near-edge spectroscopy (XANES) data with 25 nm spatial resolution. In particular, STXM in the soft X-ray synchrotron radiation regime (approximately 120 – 2000 eV) can collect spectroscopic information from the actinides and light elements in a single experiment. Thus, STXM combines the chemical sensitivity of X-ray absorption spectroscopy with high spatial resolutionmore » in a single non-destructive characterization method. This report describes the application of STXM to a broad range of nuclear materials. Where possible, the spectroscopic images obtained by STXM are compared with information derived from other analytical methods, and used to make inferences about the process history of each material. STXM measurements can yield information including the morphology of a sample, “elemental maps” showing the spatial distribution of major chemical constituents, and XANES spectra from localized regions of a sample, which may show spatial variations in chemical composition.« less

Preparation of γ-LiV2O5 from polyoxovanadate cluster Li7[V15O36(CO3)] as a high-performance cathode material and its reaction mechanism revealed by operando XAFS

NASA Astrophysics Data System (ADS)

Wang, Heng; Isobe, Jin; Shimizu, Takeshi; Matsumura, Daiju; Ina, Toshiaki; Yoshikawa, Hirofumi

2017-08-01

γ-phase LiV2O5, which shows superior electrochemical performance as cathode material in Li-ion batteries, was prepared by annealing the polyoxovanadate cluster Li7 [V15O36(CO3)]. The reaction mechanism was studied using operando X-ray absorption fine structure (XAFS), powder X-ray diffraction (PXRD), and X-ray photoelectron spectroscopy (XPS) analyses. The X-ray absorption near edge structure (XANES) and XPS results reveal that γ-LiV2O5 undergoes two-electron redox reaction per V2O5 pyramid unit, resulting in a large reversible capacity of 260 Ah/kg. The extended X-ray absorption fine structure (EXAFS) and PXRD analyses also suggest that the V-V distance slightly increases, due to the reduction of V5+ to V4+ during Li ion intercalation as the material structure is maintained. As a result, γ-LixV2O5 shows highly reversible electrochemical reaction with x = 0.1-1.9.

Pressure-induced amorphization and collapse of magnetic order in the type-I clathrate Eu8Ga16Ge30

NASA Astrophysics Data System (ADS)

Mardegan, J. R. L.; Fabbris, G.; Veiga, L. S. I.; Adriano, C.; Avila, M. A.; Haskel, D.; Giles, C.

2013-10-01

We investigate the low temperature structural and electronic properties of the type-I clathrate Eu8Ga16Ge30 under pressure using x-ray powder diffraction (XRD), x-ray absorption near-edge structure (XANES), and x-ray magnetic circular dichroism (XMCD) techniques. The XRD measurements reveal a transition to an amorphous phase above 18 GPa. Unlike previous reports on other clathrate compounds, no volume collapse is observed prior to the crystalline-amorphous phase transition which takes place when the unit cell volume is reduced to 81% of its ambient pressure value. Fits of the pressure-dependent relative volume to a Murnaghan equation of state yield a bulk modulus B0=65±3 GPa and a pressure derivative B0'=3.3±0.5. The Eu L2-edge XMCD data shows quenching of the magnetic order at a pressure coincident with the crystalline-amorphous phase transition. This information along with the persistence of an Eu2+ valence state observed in the XANES spectra up to the highest pressure point (22 GPa) indicates that the suppression of XMCD intensity is due to the loss of long range magnetic order. When compared with other clathrates, the results point to the importance of guest ion-cage interactions in determining the mechanical stability of the framework structure and the critical pressure for amorphization. Finally, the crystalline structure is not found to recover after pressure release, resulting in an amorphous material that is at least metastable at ambient pressure and temperature.

28. MAP SHOWING LOCATION OF ARVFS FACILITY AS BUILT. SHOWS ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

28. MAP SHOWING LOCATION OF ARVFS FACILITY AS BUILT. SHOWS LINCOLN BOULEVARD, BIG LOST RIVER, AND NAVAL REACTORS FACILITY. F.C. TORKELSON DRAWING NUMBER 842-ARVFS-101-2. DATED OCTOBER 12, 1965. INEL INDEX CODE NUMBER: 075 0101 851 151969. - Idaho National Engineering Laboratory, Advanced Reentry Vehicle Fusing System, Scoville, Butte County, ID

Photo-oxidative doping in π-conjugated zig-zag chain of carbon atoms with sulfur-functional group

NASA Astrophysics Data System (ADS)

Ikeura-Sekiguchi, Hiromi; Sekiguchi, Tetsuhiro

2017-12-01

Photo-oxidative doping processes were studied for the trans-polyacetylene backbone with the -SCH3 side group as a chemically representative of the precisely controlled S-functionalized zig-zag graphene nanoribbon edge. Sulfur K-edge X-ray absorption near edge structure (XANES) spectroscopy indicates that photochemical reaction of S-CH3 with atmospheric O2 forms selectively oxidized products such as -S(O)CH3 and -SO3- bound to the polyacetylene (PA) backbone. Using the correlation between the oxidation states of sulfur and the XANES peak positions, the partial charge distribution of CH3Sδ+-PAδ- has been estimated. Such positively charged sulfur atoms can attract higher electronegative oxygen atoms and expect to enhance the photooxidization capabilities. The formation of the -SO3- side group is evidently responsible for hole doping into the PA backbone. The results can provide some strategy for area-selective and controllable doping processes of atomic-scale molecular systems with the assistance of UV light.

Investigating the Geochemical Model for Molybdenum Mineralization in the JEB Tailings Management Facility at McClean Lake, Saskatchewan: An X-ray Absorption Spectroscopy Study.

PubMed

Blanchard, Peter E R; Hayes, John R; Grosvenor, Andrew P; Rowson, John; Hughes, Kebbi; Brown, Caitlin

2015-06-02

The geochemical model for Mo mineralization in the JEB Tailings Management Facility (JEB TMF), operated by AREVA Resources Canada at McClean Lake, Saskatchewan, was investigated using X-ray Absorption Near-Edge Spectroscopy (XANES), an elemental-specific technique that is sensitive to low elemental concentrations. Twenty five samples collected during the 2013 sampling campaign from various locations and depths in the TMF were analyzed by XANES. Mo K-edge XANES analysis indicated that the tailings consisted primarily of Mo(6+) species: powellite (CaMoO4), ferrimolybdite (Fe2(MoO4)3·8H2O), and molybdate adsorbed on ferrihydrite (Fe(OH)3 - MoO4). A minor concentration of a Mo(4+) species in the form of molybdenite (MoS2) was also present. Changes in the Mo mineralization over time were inferred by comparing the relative amounts of the Mo species in the tailings to the independently measured aqueous Mo pore water concentration. It was found that ferrimolybdite and molybdate adsorbed on ferrihydrite initially dissolves in the TMF and precipitates as powellite.

Sulbutiamine shows promising results in reducing fatigue in patients with multiple sclerosis.

PubMed

Sevim, Serhan; Kaleağası, Hakan; Taşdelen, Bahar

2017-08-01

Fatigue is the most frequent and often debilitating symptom for patients with multiple sclerosis (MS). There are no available effective therapies for fatigue associated with MS, and it is unclear whether a successful therapy of MS leads to clinical improvement. Sulbutiamine is a lipophilic compound that crosses the blood-brain barrier more readily than thiamine and increases the levels of thiamine and thiamine phosphate esters in the brain. Whereas several clinical trials have demonstrated the beneficial effects of sulbutiamine in patients with asthenia, there have been no reports on the effects of sulbutiamine on fatigue in patients with MS. Our study was designed to evaluate the short-term effects of sulbutiamine on fatigue in patients with MS. Patients were included if fatigue was one of their three predominant symptoms. They were required to have a total score on the Fatigue Impact Scale (FIS) of >20, and on the Beck Depression Inventory of <17, and no relapse in the last 3 months prior to onset of the study. Patients were advised to receive 400mg orally of sulbutiamine once daily for two months. The outcome of the study was in the changes of FIS. Twenty-six patients with MS (18 females and 8 males) were selected. The patients were 18-57 years of age (mean:37,2). The average score of Expanded Disability Status Scale (EDSS) of the patients was 2,71. A significant number of the subjects who were on some kind of disease modifying treatment (DMT) demonstrated obvious improvement in their total FIS scores, whereas none of the subjects who were not on any DMT improved (13/23 vs. 0/5). The average fatigue score was 77 (SD:30,5) at the baseline and 60,5 (SD:29,7) on Day 60, respectively. Sulbutiamine intake resulted in a significant reduction on the total score of FIS and on all three subscales assessing physical, cognitive, and psychosocial functioning (all p-values < 0,01). There were no serious adverse events. Sulbutiamin appears to be effective in treating fatigue

Arsenic sorption to nanoparticulate mackinawite (FeS): An examination of phosphate competition.

PubMed

Niazi, Nabeel Khan; Burton, Edward D

2016-11-01

Nanoparticulate mackinawite (FeS) can be an important host-phase for arsenic (As) in sulfidic, subsurface environments. Although not previously investigated, phosphate (PO 4 3- ) may compete with As for available sorption sites on FeS, thereby enhancing As mobility in FeS-bearing soils, sediments and groundwater systems. In this study, we examine the effect of PO 4 3- on sorption of arsenate (As(V)) and arsenite (As(III)) to nanoparticulate FeS at pH 6, 7 and 9. Results show that PO 4 3- (at 0.01-1.0 mM P) did not significantly affect sorption of either As(V) or As(III) to nanoparticulate FeS at initial aqueous As concentrations ranging from 0.01 to 1.0 mM. At pH 9 and 7, sorption of both As(III) and As(V) to nanoparticulate FeS was similar, with distribution coefficient (K d ) values spanning 0.76-15 L g -1 (which corresponds to removal of 87-98% of initial aqueous As(III) and As(V) concentrations). Conversely, at pH 6, the sorption of As(III) was characterized by substantially higher K d values (6.3-93.4 L g -1 ) than those for As(V) (K d  = 0.21-0.96 L g -1 ). Arsenic K-edge X-ray absorption near edge structure (XANES) spectroscopy indicated that up to 52% of the added As(V) was reduced to As(III) in As(V) sorption experiments, as well as the formation of minor amounts of an As 2 S 3 -like species. In As(III) sorption experiments, XANES spectroscopy also demonstrated the formation of an As 2 S 3 -like species and the partial oxidation of As(III) to As(V) (despite the strictly O 2 -free experimental conditions). Overall, the XANES data indicate that As sorption to nanoparticulate FeS involves several redox transformations and various sorbed species, which display a complex dependency on pH and As loading but that are not influenced by the co-occurrence of PO 4 3- . This study shows that nanoparticulate FeS can help to immobilize As(III) and As(V) in sulfidic subsurface environments where As co-exists with PO 4 3- . Copyright © 2016 Elsevier Ltd. All

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, H. L.; Hirschmann, M. M.; Cottrell, E.

Experiments establishing the effect of pressure on the Fe 3+/ΣFe ratio of andesitic silicate melts buffered by coexisting Ru and RuO 2 were performed from 100 kPa to 7 GPa and 1400–1750 °C. Fe 3+/ΣFe ratios were determined by room temperature Mössbauer spectroscopy, but corrected for the effects of recoilless fraction. Fe 3+/ΣFe ratios in quenched glasses decrease with increasing pressure consistent with previous results between 100 kPa and 3 GPa (O’Neill et al., 2006), but show only small pressure effects above 5 GPa. Ratios also decrease with increasing temperature. Mössbauer hyperfine parameters indicate mean coordination of Fe 3+ ionsmore » of ~5 in glasses, with no dependence on the pressure from which the glasses were quenched, but show an increase with pressure in mean coordination of Fe 2+ ions, from ~5 to ~6. XANES spectra on these glasses show variations in pre-edge intensities and centroid positions that are systematic with Fe 3+/ΣFe, but are displaced from those established from otherwise identical andesitic glasses quenched at 100 kPa (Zhang et al., 2016). These systematics permit construction of a new XANES calibration curve relating pre-edge sub-peak intensities to Fe 3+/ΣFe applicable to high pressure glasses. Consistent with interpretations of the Mössbauer hyperfine parameters, XANES pre-edge peak features in high pressure glasses are owing chiefly to the effects of pressure on the coordination of Fe 2+ ions from ~5.5 to ~6, with negligible effects evident for Fe 3+ ions. We use the new data to construct a thermodynamic model relating the effects of oxygen fugacity and pressure on Fe 3+/ΣFe. We apply this model to calculate variations in oxygen fugacity in isochemical (constant Fe 3+/ΣFe) columns of magma representative of magma oceans, in which fO2 is fixed at the base by equilibration with molten Fe. These calculations indicate that oxygen fugacities at the surface of shallow magma oceans are more reduced than at depth. For

Multiscale correlations of iron phases and heavy metals in technogenic magnetic particles from contaminated soils.

PubMed

Yu, Xiuling; Lu, Shenggao

2016-12-01

Technogenic magnetic particles (TMPs) are carriers of heavy metals and organic contaminants, which derived from anthropogenic activities. However, little information on the relationship between heavy metals and TMP carrier phases at the micrometer scale is available. This study determined the distribution and association of heavy metals and magnetic phases in TMPs in three contaminated soils at the micrometer scale using micro-X-ray fluorescence (μ-XRF) and micro-X-ray absorption near-edge structure (μ-XANES) spectroscopy. Multiscale correlations of heavy metals in TMPs were elucidated using wavelet transform analysis. μ-XRF mapping showed that Fe was enriched and closely correlated with Co, Cr, and Pb in TMPs from steel industrial areas. Fluorescence mapping and wavelet analysis showed that ferroalloy was a major magnetic signature and heavy metal carrier in TMPs, because most heavy metals were highly associated with ferroalloy at all size scales. Multiscale analysis revealed that heavy metals in the TMPs were from multiple sources. Iron K-edge μ-XANES spectra revealed that metallic iron, ferroalloy, and magnetite were the main iron magnetic phases in the TMPs. The relative percentage of these magnetic phases depended on their emission sources. Heatmap analysis revealed that Co, Pb, Cu, Cr, and Ni were mainly derived from ferroalloy particles, while As was derived from both ferroalloy and metallic iron phases. Our results indicated the scale-dependent correlations of magnetic phases and heavy metals in TMPs. The combination of synchrotron based X-ray microprobe techniques and multiscale analysis provides a powerful tool for identifying the magnetic phases from different sources and quantifying the association of iron phases and heavy metals at micrometer scale. Copyright © 2016 Elsevier Ltd. All rights reserved.

Ligand-tailored single-site silica supported titanium catalysts: Synthesis, characterization and towards cyanosilylation reaction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, Wei; Li, Yani; Yu, Bo

2015-01-15

A successive anchoring of Ti(NMe{sub 2}){sub 4}, cyclopentadiene and a O-donor ligand, 1-hydroxyethylbenzene (PEA), 1,1′-bi-2-naphthol (Binol) or 2,3-dihydroxybutanedioic acid diethyl ester (Tartrate), on silica was conducted by SOMC strategy in moderate conditions. The silica, monitored by in-situ Fourier transform infrared spectroscopy (in-situ FT-IR), was pretreated at different temperatures (200, 500 and 800 °C). The ligand tailored silica-supported titanium complexes were characterized by in-situ FT-IR, {sup 13}C CP MAS-NMR, X-ray photoelectron spectroscopy (XPS), X-ray absorption near edge structure (XANES) and elemental analysis in detail, verifying that the surface titanium species are single sited. The catalytic activity of the ligand tailored single-sitemore » silica supported titanium complexes was evaluated by a cyanosilylation of benzaldehyde. The results showed that the catalytic activity is dependent strongly on the dehydroxylation temperatures of silica and the configuration of the ligands. - Graphical abstract: The ligand-tailored silica supported “single site” titanium complexes were synthesized by SOMC strategy and fully characterized. Their catalytic activity were evaluated by benzaldehyde silylcyanation. - Highlights: • Single-site silica supported Ti active species was prepared by SOMC technique. • O-donor ligand tailored Ti surface species was synthesized. • The surface species was characterized by XPS, {sup 13}C CP-MAS NMR, XANES etc. • Catalytic activity of the Ti active species in silylcyanation reaction was evaluated.« less

Understanding of sub-band gap absorption of femtosecond-laser sulfur hyperdoped silicon using synchrotron-based techniques

PubMed Central

Limaye, Mukta V.; Chen, S. C.; Lee, C. Y.; Chen, L. Y.; Singh, Shashi B.; Shao, Y. C.; Wang, Y. F.; Hsieh, S. H.; Hsueh, H. C.; Chiou, J. W.; Chen, C. H.; Jang, L. Y.; Cheng, C. L.; Pong, W. F.; Hu, Y. F.

2015-01-01

The correlation between sub-band gap absorption and the chemical states and electronic and atomic structures of S-hyperdoped Si have been extensively studied, using synchrotron-based x-ray photoelectron spectroscopy (XPS), x-ray absorption near-edge spectroscopy (XANES), extended x-ray absorption fine structure (EXAFS), valence-band photoemission spectroscopy (VB-PES) and first-principles calculation. S 2p XPS spectra reveal that the S-hyperdoped Si with the greatest (~87%) sub-band gap absorption contains the highest concentration of S2− (monosulfide) species. Annealing S-hyperdoped Si reduces the sub-band gap absorptance and the concentration of S2− species, but significantly increases the concentration of larger S clusters [polysulfides (Sn2−, n > 2)]. The Si K-edge XANES spectra show that S hyperdoping in Si increases (decreased) the occupied (unoccupied) electronic density of states at/above the conduction-band-minimum. VB-PES spectra evidently reveal that the S-dopants not only form an impurity band deep within the band gap, giving rise to the sub-band gap absorption, but also cause the insulator-to-metal transition in S-hyperdoped Si samples. Based on the experimental results and the calculations by density functional theory, the chemical state of the S species and the formation of the S-dopant states in the band gap of Si are critical in determining the sub-band gap absorptance of hyperdoped Si samples. PMID:26098075

Uranium fate in Hanford sediment altered by simulated acid waste solutions

DOE PAGES

Gartman, Brandy N.; Qafoku, Nikolla P.; Szecsody, James E.; ...

2015-07-31

Many aspects of U(VI) behavior in sediments that are previously exposed to acidic waste fluids for sufficiently long times to induce significant changes in pH and other physical, mineralogical and chemical properties, are not well documented in the literature. For this reason, we conducted a series of macroscopic batch experiments combined with a variety of bulk characterization studies (Mössbauer and laser spectroscopy), micro-scale inspections (µ-XRF), and molecular scale interrogations (XANES) with the objectives to: i) determine the extent of U(VI) partitioning to Hanford sediments previously exposed to acidic waste simulants (pH = 2 and pH = 5) and under neutralmore » conditions (pH = 8) at varying background solution concentrations (i.e., NaNO 3); ii) determine micron-scale solid phase associated U valence state and phase identity; and iii) provide information for a plausible conceptual model of U(VI) attenuation under waste plume acidic conditions. The results of the batch experiments showed that the acid pre-treated sediment had high affinity for aqueous U(VI), which was removed from solution via two pH dependent and apparently different mechanisms (adsorption at pH = 2 and precipitation at pH = 5). The micro-scale inspections and XANES analyses confirmed that high concentration areas were rich mainly in U(VI), demonstrating that most of the added U(VI) was not reduced to U(IV). The laser spectroscopy data showed that uranyl phosphates {e.g. metaautunite [Ca(UO 2) 2(PO 4) 2•10-12H 2O] and phosphuranylite [KCa(H 3O) 3(UO 2) 7(PO 4) 4O 4•8(H 2O)]} were present in the sediments. They also showed clear differences between the U bearing phases in the experiments conducted in the presence or absence of air. As a result, the data generated from these experiments will help in a better understanding of the reactions and processes that have a significant effect and/or control U mobility.« less

Comparative investigation of N donor ligand-lanthanide complexes from the metal and ligand point of view

NASA Astrophysics Data System (ADS)

Prüßmann, T.; Denecke, M. A.; Geist, A.; Rothe, J.; Lindqvist-Reis, P.; Löble, M.; Breher, F.; Batchelor, D. R.; Apostolidis, C.; Walter, O.; Caliebe, W.; Kvashnina, K.; Jorissen, K.; Kas, J. J.; Rehr, J. J.; Vitova, T.

2013-04-01

N-donor ligands such as n-Pr-BTP (2,6-bis(5,6-dipropyl-1,2,4-triazin-3-yl)pyridine) studied here preferentially bind An(III) over Ln(III) in liquid-liquid separation of trivalent ac-tinides from spent nuclear fuel. The chemical and physical processes responsible for this selectivity are not yet well understood. We present systematic comparative near-edge X-ray absorption structure (XANES) spectroscopy investigations at the Gd L3 edge of [GdBTP3](NO3)3, [Gd(BTP)3](OTf)3, Gd(NO3)3, Gd(OTf)3 and N K edge of [Gd(BTP)3](NO3)3, Gd(NO3)3 complexes. The pre-edge absorption resonance in Gd L3 edge high-energy resolution X-ray absorption near edge structure spectra (HR-XANES) is explained as arising from 2p3/2 → 4f/5d electronic transitions by calculations with the FEFF9.5 code. Experimental evidence is found for higher electronic density on Gd in [Gd(BTP)3](NO3)3 and [Gd(BTP)3](OTf)3 compared to Gd in Gd(NO3)3 and Gd(OTf)3, and on N in [Gd(BTP)3](NO3)3 compared to n-Pr-BTP. The origin of the pre-edge structure in the N K edge XANES is explained by density functional theory (DFT) with the ORCA code. Results at the N K edge suggest a change in ligand orbital occupancies and mixing upon complexation but further work is necessary to interpret observed spectral variations.

Chemical and structural order in silicon oxynitrides by methods of surface physics

NASA Astrophysics Data System (ADS)

Finster, J.; Heeg, J.; Klinkenberg, E.-D.

A large number of thin amorphous layers of SiO xN y and several (crystalline) reference compounds (SiO 2, Si 3N 4, Si 2N 2O) are studied. Although XANES and SEXAFS are well sulted to derive structural and chemical order, for these compounds many problems remain to be solved. We show how core level spectra (XPS, AES) can be used to gain such information (e.g. random bonding structure, N coordination, oxidation behaviour).

In situ XAFS and micro-XAFS studies on LiNi 0.8Co 0.15Al 0.05O 2 cathode material for lithium-ion batteries

NASA Astrophysics Data System (ADS)

Nonaka, T.; Okuda, C.; Seno, Y.; Nakano, H.; Koumoto, K.; Ukyo, Y.

We have applied in situ X-ray absorption fine structure (XAFS) and in situ micro-XAFS techniques to study LiNi 0.8Co 0.15Al 0.05O 2 cathode materials in Li-ion coin cells that show various levels of capacity fading: fresh cell, cycle tested cell and aging tested cell. The change in the oxidation state and local structure of Ni and Co during charge has been investigated. Ni and Co K-edge X-ray absorption near edge structure (XANES) show that the Ni oxidation state is converted from Ni 3+ to Ni 4+ upon charging, whereas the Co oxidation state hardly changes. Ni K-edge extended X-ray absorption fine structure (EXAFS) reveals that the Jahn-Teller distorted NiO 6 octahedron turns into the symmetric octahedron upon charging, which is consistent with the change in the Ni oxidation state. Ni K-edge micro-XANES show that the oxidation of Ni proceeds homogeneously in a grain of LiNi 0.8Co 0.15Al 0.05O 2 within the special resolution of ∼2 μm, and proceeds independently of the grain size. All the behaviors of Ni and Co observed in these experiments for the fresh cell remain unchanged after the capacity fade is induced by cycle tests or aging tests, which demonstrates the considerable stability of the LiNi 0.8Co 0.15Al 0.05O 2 cathode material.

Highly efficient Cu-decorated iron oxide nanocatalyst for low pressure CO 2 conversion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Halder, Avik; Kilianová, Martina; Yang, Bing

We report a nanoparticulate iron oxide based catalyst for CO2 conversion with high efficiency at low pressures and on the effect of the presence of copper on the catalyst's restructuring and its catalytic performance. In situ X-ray scattering reveals the restructuring of the catalyst at the nanometer scale. In situ X-ray absorption near edge structure (XANES) shows the evolution of the composition and oxidation state of the iron and copper components under reaction conditions along with the promotional effect of copper on the chemical transformation of the iron component. X-ray diffraction (XRD), XANES and Raman spectroscopy proved that the startingmore » nano catalyst is composed of iron oxides differing in chemical nature (alpha-Fe2O3, Fe3O4, FeO(OH)) and dimensionality, while the catalyst after CO2 conversion was identified as a mixture of alpha-Fe, Fe3C, and traces of Fe5C2. The significant increase of the rate CO2 is turned over in the presence of copper nanoparticles indicates that Cu nanoparticles activate hydrogen, which after spilling over to the neighbouring iron sites, facilitate a more efficient conversion of carbon dioxide.« less

Observation of the origin of d0 magnetism in ZnO nanostructures using X-ray-based microscopic and spectroscopic techniques

NASA Astrophysics Data System (ADS)

Singh, Shashi B.; Wang, Yu-Fu; Shao, Yu-Cheng; Lai, Hsuan-Yu; Hsieh, Shang-Hsien; Limaye, Mukta V.; Chuang, Chen-Hao; Hsueh, Hung-Chung; Wang, Hsaiotsu; Chiou, Jau-Wern; Tsai, Hung-Ming; Pao, Chih-Wen; Chen, Chia-Hao; Lin, Hong-Ji; Lee, Jyh-Fu; Wu, Chun-Te; Wu, Jih-Jen; Pong, Way-Faung; Ohigashi, Takuji; Kosugi, Nobuhiro; Wang, Jian; Zhou, Jigang; Regier, Tom; Sham, Tsun-Kong

2014-07-01

Efforts have been made to elucidate the origin of d0 magnetism in ZnO nanocactuses (NCs) and nanowires (NWs) using X-ray-based microscopic and spectroscopic techniques. The photoluminescence and O K-edge and Zn L3,2-edge X-ray-excited optical luminescence spectra showed that ZnO NCs contain more defects than NWs do and that in ZnO NCs, more defects are present at the O sites than at the Zn sites. Specifically, the results of O K-edge scanning transmission X-ray microscopy (STXM) and the corresponding X-ray-absorption near-edge structure (XANES) spectroscopy demonstrated that the impurity (non-stoichiometric) region in ZnO NCs contains a greater defect population than the thick region. The intensity of O K-edge STXM-XANES in the impurity region is more predominant in ZnO NCs than in NWs. The increase in the unoccupied (occupied) density of states at/above (at/below) the conduction-band minimum (valence-band maximum) or the Fermi level is related to the population of defects at the O sites, as revealed by comparing the ZnO NCs to the NWs. The results of O K-edge and Zn L3,2-edge X-ray magnetic circular dichroism demonstrated that the origin of magnetization is attributable to the O 2p orbitals rather than the Zn d orbitals. Further, the local density approximation (LDA) + U verified that vacancies in the form of dangling or unpaired 2p states (due to Zn vacancies) induced a significant local spin moment in the nearest-neighboring O atoms to the defect center, which was determined from the uneven local spin density by analyzing the partial density of states of O 2p in ZnO.Efforts have been made to elucidate the origin of d0 magnetism in ZnO nanocactuses (NCs) and nanowires (NWs) using X-ray-based microscopic and spectroscopic techniques. The photoluminescence and O K-edge and Zn L3,2-edge X-ray-excited optical luminescence spectra showed that ZnO NCs contain more defects than NWs do and that in ZnO NCs, more defects are present at the O sites than at the Zn sites

Speciation and Elemental Mapping of Metal Containing Aerosols

NASA Astrophysics Data System (ADS)

Fraund, M. W.; Moffet, R.; Harder, T.; Williams, G.; Chen-Wiegart, Y. C. K.; Laskin, A.; Gilles, M. K.; Schoonen, M. A.; Thieme, J.

2017-12-01

Transition metals play a key roles in biogeochemical processes and health effects of aerosols. The Submicron Resolution X-ray (SRX) beamline at the second National Synchrotron Light Source (NSLS-II) can be used to obtain spatially resolved elemental composition using X-ray fluorescence (XRF) as well as element specific molecular information through X-ray absorption near edge structure (XANES) spectroscopy. Here, XANES spectroscopy was used to identify the oxidation state of iron-rich particles collected from the Cape Hedo Observatory on the island of Okinawa, Japan which is subject to aerosols from both biogenic (Gobi desert) and anthropogenic sources (e.g. Beijing and Shanghai). This data was compared with standards to help classify the minerology and source of these aerosol particles with regards to their potential solubility and bioavailability. In another application of the XRF/XANES measurements from NSLS-II, Pb rich particles from Mexico City were probed for distribution and speciation of Pb. Prior study has indicated that elevated concentrations of Pb occur in an industrialized section of northern Mexico City. It has been established that Pb and Zn are internally mixed in atmospheric aerosol and that Zn primarily exists as ZnCl2 and Zn(NO3)2. Based on these observations, it is hypothesized that Pb also exists as PbCl2 and Pb(NO3)­2. In this study it is shown that X-ray absorption near edge structure (XANES) spectroscopy at the Pb L-edge supports Pb being present as PbCl2 and Pb(NO3)2. Submicron resolution X-ray fluorescence mapping is also used to provide complimentary information on the collocation of other high-Z elements.

Nitrogen incorporation in carbon nitride films produced by direct and dual ion-beam sputtering

DOE Office of Scientific and Technical Information (OSTI.GOV)

Abrasonis, G.; Gago, R.; Jimenez, I.

2005-10-01

Carbon (C) and carbon nitride (CN{sub x}) films were grown on Si(100) substrates by direct ion-beam sputtering (IBS) of a carbon target at different substrate temperatures (room temperature-450 deg. C) and Ar/N{sub 2} sputtering gas mixtures. Additionally, the effect of concurrent nitrogen-ion assistance during the growth of CN{sub x} films by IBS was also investigated. The samples were analyzed by elastic recoil detection analysis (ERDA) and x-ray absorption near-edge spectroscopy (XANES). The ERDA results showed that significant nitrogen amount (up to 20 at. %) was incorporated in the films, without any other nitrogen source but the N{sub 2}-containing sputtering gas.more » The nitrogen concentration is proportional to the N{sub 2} content in the sputtering beam and no saturation limit is reached under the present working conditions. The film areal density derived from ERDA revealed a decrease in the amount of deposited material at increasing growth temperature, with a correlation between the C and N losses. The XANES results indicate that N atoms are efficiently incorporated into the carbon network and can be found in different bonding environments, such as pyridinelike, nitrilelike, graphitelike, and embedded N{sub 2} molecules. The contribution of molecular and pyridinelike nitrogen decreases when the temperature increases while the contribution of the nitrilelike nitrogen increases. The concurrent nitrogen ion assistance resulted in the significant increase of the nitrogen content in the film but it induced a further reduction of the deposited material. Additionally, the assisting ions inhibited the formation of the nitrilelike configurations while promoting nitrogen environments in graphitelike positions. The nitrogen incorporation and release mechanisms are discussed in terms of film growth precursors, ion bombardment effects, and chemical sputtering.« less

Characterization of local atomic structure in Co/Zn based ZIFs by XAFS

NASA Astrophysics Data System (ADS)

Podkovyrina, Yulia; Butova, Vera; Bulanova, Elena; Budnyk, Andriy; Kremennaya, Maria; Soldatov, Alexander; Lamberti, Carlo

2018-03-01

The local atomic structure in bimetallic Co/Zn zeolitic imidazolate frameworks (ZIFs) was studied using X-ray Absorption Fine Structure (XAFS) spectroscopy and theoretical calculations. The experimental Co K-edge and Zn K-edge XANES (X-ray Absorption Near Edge Structure) spectra of Zn1-xCoxC8H10N4 samples (x = 0.05, 0.25, 0.75) synthesized by microwave synthesis were compared with the data for the ZIF-67 (x=1) and ZIF-8 (x=0). Theoretical XANES spectra for the bimetallic ZIFs were calculated. It was shown that in bimetallic ZIFs the Co and Zn atoms have the similar local environment.

Electronic structure of transition metal-cysteine complexes from X-ray absorption spectroscopy.

PubMed

Leung, Bonnie O; Jalilehvand, Farideh; Szilagyi, Robert K

2008-04-17

The electronic structures of HgII, NiII, CrIII, and MoV complexes with cysteine were investigated by sulfur K-edge X-ray absorption near-edge structure (XANES) spectroscopy and density functional theory. The covalency in the metal-sulfur bond was determined by analyzing the intensities of the electric-dipole allowed pre-edge features appearing in the XANES spectra below the ionization threshold. Because of the well-defined structures of the selected cysteine complexes, the current work provides a reference set for further sulfur K-edge XAS studies of bioinorganic active sites with transition metal-sulfur bonds from cysteine residues as well as more complex coordination compounds with thiolate ligands.

Depth distribution of secondary phases in kesterite Cu 2ZnSnS 4 by angle-resolved X-ray absorption spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Just, J.; Lützenkirchen-Hecht, D.; Müller, O.

The depth distribution of secondary phases in the solar cell absorber material Cu 2ZnSnS 4 (CZTS) is quantitatively investigated using X-ray Absorption Near Edge Structure (XANES) analysis at the K-edge of sulfur at varying incidence angles. Varying information depths from several nanometers up to the full thickness is achieved. A quantitative profile of the phase distribution is obtained by a self-consistent fit of a multilayer model to the XANES spectra for different angles. Single step co-evaporated CZTS thin-films are found to exhibit zinc and copper sulfide secondary phases preferentially at the front or back interfaces of the film.

Depth distribution of secondary phases in kesterite Cu 2ZnSnS 4 by angle-resolved X-ray absorption spectroscopy

DOE PAGES

Just, J.; Lützenkirchen-Hecht, D.; Müller, O.; ...

2017-12-12

The depth distribution of secondary phases in the solar cell absorber material Cu 2ZnSnS 4 (CZTS) is quantitatively investigated using X-ray Absorption Near Edge Structure (XANES) analysis at the K-edge of sulfur at varying incidence angles. Varying information depths from several nanometers up to the full thickness is achieved. A quantitative profile of the phase distribution is obtained by a self-consistent fit of a multilayer model to the XANES spectra for different angles. Single step co-evaporated CZTS thin-films are found to exhibit zinc and copper sulfide secondary phases preferentially at the front or back interfaces of the film.

The Material Properties of CsSnBr3 and CsBr:Sn-1% and Their Potential as Scintillator Detector Material

DTIC Science & Technology

2010-03-01

Iodide or Cesium Iodide are the benchmarks for ease of use and quick identification of isotope species. This research aims to explore Cesium Bromide doped...oxidation states of 3+, 4+, 5+ and 6+ were used to identify the Pu pollution in the Rocky Flats area. The identification of the Pu4+ oxidation state...point was causing the normalization of the spectra to be much higher than what it should be. The XANES structures lineup showing the Sn in the CsSnBr3

The Great Cometary Show

NASA Astrophysics Data System (ADS)

2007-01-01

The ESO Very Large Telescope Interferometer, which allows astronomers to scrutinise objects with a precision equivalent to that of a 130-m telescope, is proving itself an unequalled success every day. One of the latest instruments installed, AMBER, has led to a flurry of scientific results, an anthology of which is being published this week as special features in the research journal Astronomy & Astrophysics. ESO PR Photo 06a/07 ESO PR Photo 06a/07 The AMBER Instrument "With its unique capabilities, the VLT Interferometer (VLTI) has created itself a niche in which it provide answers to many astronomical questions, from the shape of stars, to discs around stars, to the surroundings of the supermassive black holes in active galaxies," says Jorge Melnick (ESO), the VLT Project Scientist. The VLTI has led to 55 scientific papers already and is in fact producing more than half of the interferometric results worldwide. "With the capability of AMBER to combine up to three of the 8.2-m VLT Unit Telescopes, we can really achieve what nobody else can do," added Fabien Malbet, from the LAOG (France) and the AMBER Project Scientist. Eleven articles will appear this week in Astronomy & Astrophysics' special AMBER section. Three of them describe the unique instrument, while the other eight reveal completely new results about the early and late stages in the life of stars. ESO PR Photo 06b/07 ESO PR Photo 06b/07 The Inner Winds of Eta Carinae The first results presented in this issue cover various fields of stellar and circumstellar physics. Two papers deal with very young solar-like stars, offering new information about the geometry of the surrounding discs and associated outflowing winds. Other articles are devoted to the study of hot active stars of particular interest: Alpha Arae, Kappa Canis Majoris, and CPD -57o2874. They provide new, precise information about their rotating gas envelopes. An important new result concerns the enigmatic object Eta Carinae. Using AMBER with

Chemical Behavior of Sulfur in Minerals and Silicate Glasses Studied Using Inner Shell Spectroscopy

NASA Astrophysics Data System (ADS)

Alonso Mori, R.; Paris, E.; Glatzel, P.; Giuli, G.; Scaillet, B.

2008-12-01

effective charge around the sulfur atom based on the Mulliken population analysis generated by DFT calculations, and then successfully correlated with the observed experimental shifts. In order to check these results using a theoretical framework other than DFT, we also performed calculations using a multiple scattering approach (FEFF8.4). X-ray absorption and emission spectroscopy has been applied to three series of peralkaline rhyolitic obsidians each with different alkali/alumina ratios ((Na2O + K2O)/Al2O3). The occurrence of sulfur was accurately determined by using the energy shift of the S Ka emission lines to make a quantitative analysis. We observe that we can follow the evolution of sulfur as a function of controlled formation conditions with respect to pressure, temperature or oxygen fugacity, and determine whether it is present as sulfate or sulfide. XANES and Kb emission lines also yield detailed information on the local chemistry and structure, and thus help us to understand the geochemical role of S in these systems.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mammen, Nisha; Spanu, Leonardo; Tyo, Eric C.

Having the ability to tune the oxidation state of Cu nanoparticles is essential for their utility as catalysts. The degree of oxidation that maximizes product yield and selectivity is known to vary, depending on the particular reaction. Using first principles calculations and XANES measurements, we show that for subnanometer sizes in the gas phase, smaller Cu clusters are more resistant to oxidation. However, this trend is reversed upon deposition on an alumina support. We are able to explain this result in terms of strong cluster-support interactions, which differ significantly for the oxidized and elemental clusters. The stable cluster phases alsomore » feature novel oxygen stoichiometries. Our results suggest that one can tune the degree of oxidation of Cu catalysts by optimizing not just their size, but also the support they are deposited on.« less

"The Show"

ERIC Educational Resources Information Center

Gehring, John

2004-01-01

For the past 16 years, the blue-collar city of Huntington, West Virginia, has rolled out the red carpet to welcome young wrestlers and their families as old friends. They have come to town chasing the same dream for a spot in what many of them call "The Show". For three days, under the lights of an arena packed with 5,000 fans, the…

NASA Radar Images Show Continued Deformation from Mexico Quake

NASA Image and Video Library

2010-08-04

This image shows a UAVSAR interferogram swath overlaid atop a Google Earth image. New NASA airborne radar images show the continuing deformation in Earth surface resulting from the magnitude 7.2 temblor in Baja California on April 4, 2010.

Influence of oxygen on growth of carbon thin films

NASA Astrophysics Data System (ADS)

Kumar, Prabhat; Gupta, Mukul; Phase, D. M.; Stahn, Jochen

2018-04-01

In this work we studied the influence of oxygen gas on growth of carbon thin films in a magnetron sputtering process. X-ray absorption spectroscopy (XAS), x-ray and neutron reflectivity techniques were used to probe carbon thin films deposited with and without oxygen at room temperature. XAS in particularly x-ray absorption near edge spectroscopy (XANES) is powerful technique to identify the nature of hybridization of carbon atoms with other elements. In a XANES pattern, presence of C=O and C-O bonds is generally observed in spite of the fact that oxygen has not been deliberately included in the growth process. In order to confirm the presence of such features, we introduced a small amount of oxygen at 1% during the growth of carbon thin films. Though such additions do not affect the number density as observed by x-ray and neutron reflectivity, they severally affect the C K-edge spectra as evidenced by an enhancement in carbon-oxygen hybridization. Observed results are helpful in analyzing the C K-edge spectra more confidently.

The role of the 5f valence orbitals of early actinides in chemical bonding

PubMed Central

Vitova, T.; Pidchenko, I.; Fellhauer, D.; Bagus, P. S.; Joly, Y.; Pruessmann, T.; Bahl, S.; Gonzalez-Robles, E.; Rothe, J.; Altmaier, M.; Denecke, M. A.; Geckeis, H.

2017-01-01

One of the long standing debates in actinide chemistry is the level of localization and participation of the actinide 5f valence orbitals in covalent bonds across the actinide series. Here we illuminate the role of the 5f valence orbitals of uranium, neptunium and plutonium in chemical bonding using advanced spectroscopies: actinide M4,5 HR-XANES and 3d4f RIXS. Results reveal that the 5f orbitals are active in the chemical bonding for uranium and neptunium, shown by significant variations in the level of their localization evidenced in the spectra. In contrast, the 5f orbitals of plutonium appear localized and surprisingly insensitive to different bonding environments. We envisage that this report of using relative energy differences between the 5fδ/ϕ and 5fπ*/5fσ* orbitals as a qualitative measure of overlap-driven actinyl bond covalency will spark activity, and extend to numerous applications of RIXS and HR-XANES to gain new insights into the electronic structures of the actinide elements. PMID:28681848

The role of the 5f valence orbitals of early actinides in chemical bonding

NASA Astrophysics Data System (ADS)

Vitova, T.; Pidchenko, I.; Fellhauer, D.; Bagus, P. S.; Joly, Y.; Pruessmann, T.; Bahl, S.; Gonzalez-Robles, E.; Rothe, J.; Altmaier, M.; Denecke, M. A.; Geckeis, H.

2017-07-01

One of the long standing debates in actinide chemistry is the level of localization and participation of the actinide 5f valence orbitals in covalent bonds across the actinide series. Here we illuminate the role of the 5f valence orbitals of uranium, neptunium and plutonium in chemical bonding using advanced spectroscopies: actinide M4,5 HR-XANES and 3d4f RIXS. Results reveal that the 5f orbitals are active in the chemical bonding for uranium and neptunium, shown by significant variations in the level of their localization evidenced in the spectra. In contrast, the 5f orbitals of plutonium appear localized and surprisingly insensitive to different bonding environments. We envisage that this report of using relative energy differences between the 5fδ/φ and 5fπ*/5fσ* orbitals as a qualitative measure of overlap-driven actinyl bond covalency will spark activity, and extend to numerous applications of RIXS and HR-XANES to gain new insights into the electronic structures of the actinide elements.

Low toxic maghemite nanoparticles for theranostic applications

PubMed Central

Zolotukhin, Peter V; Belanova, Anna A; Soldatov, Mikhail A; Lastovina, Tatiana A; Kubrin, Stanislav P; Nikolsky, Anatoliy V; Mirmikova, Lidia I

2017-01-01

Background Iron oxide nanoparticles have numerous and versatile biological properties, ranging from direct and immediate biochemical effects to prolonged influences on tissues. Most applications have strict requirements with respect to the chemical and physical properties of such agents. Therefore, developing rational design methods of synthesis of iron oxide nanoparticles remains of vital importance in nanobiomedicine. Methods Low toxic superparamagnetic iron oxide nanoparticles (SPIONs) for theranostic applications in oncology having spherical shape and maghemite structure were produced using the fast microwave synthesis technique and were fully characterized by several complementary methods (transmission electron microscopy [TEM], X-ray diffraction [XRD], dynamic light scattering [DLS], X-ray photoelectron spectroscopy [XPS], X-ray absorption near edge structure [XANES], Mossbauer spectroscopy, and HeLa cells toxicity testing). Results TEM showed that the majority of the obtained nanoparticles were almost spherical and did not exceed 20 nm in diameter. The averaged DLS hydrodynamic size was found to be ~33 nm, while that of nanocrystallites estimated by XRD waŝ16 nm. Both XRD and XPS studies evidenced the maghemite (γ-Fe2O3) atomic and electronic structure of the synthesized nanoparticles. The XANES data analysis demonstrated the structure of the nanoparticles being similar to that of macroscopic maghemite. The Mossbauer spectroscopy revealed the γ-Fe2O3 phase of the nanoparticles and vibration magnetometry study showed that reactive oxygen species in HeLa cells are generated both in the cytoplasm and the nucleus. Conclusion Quasispherical Fe3+ SPIONs having the maghemite structure with the average size of 16 nm obtained by using the fast microwave synthesis technique are expected to be of great value for theranostic applications in oncology and multimodal anticancer therapy. PMID:28919740

Mineralogical controls on antimony and arsenic mobility during tetrahedrite-tennantite weathering at historic mine sites Špania Dolina-Piesky and Lubietová-Svätodušná, Slovakia

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bor,; #269; inová rAdková, AnežkA

The legacy of copper (Cu) mining at Špania Dolina-Piesky and Lubietová-Svätodušná (central Slovakia) is waste rock and soil, surface waters, and groundwaters contaminated with antimony (Sb), arsenic (As), Cu, and other metals. Copper ore is hosted in chalcopyrite (CuFeS2) and sulfosalt solid-solution tetrahedrite-tennantite {Cu6[Cu4(Fe,Zn)2]Sb4S13–Cu6[Cu4(Fe,Zn)2]As4S13} that show wide-spread oxidation characteristic by olive-green color secondary minerals. Tetrahedrite-tennantite can be a significant source of As and Sb contamination. Synchrotron-based μ-XRD, μ-XRF, and μ-XANES combined with electron microprobe analyses have been used to determine the mineralogy, chemical composition, element distribution, and Sb speciation in tetrahedrite-tennantite oxidation products in waste rock. Our results show thatmore » the mobility of Sb is limited by the formation of oxidation products such as tripuhyite and roméite group mineral containing 36.54 wt% Sb for samples where the primary mineral chemical composition is close to tetrahedrite end-member. Antimony K-edge μ-XANES spectra of these oxidation products indicate that the predominant Sb oxidation state is 5+. Arsenic and Cu are also hosted by amorphous phases containing 6.23 wt% Sb on average and these are intergrown with tripuhyite and roméite. Antimony in this environment is not very mobile, meaning it is not easily released from solid phases to water, especially compared to As, Cu, and S. For samples where the primary sulfosalt is close to tennantite composition, the oxidation products associated with tennantite relicts contain 2.43 wt% Sb and are amorphous. The variable solubility of the secondary minerals that have been identified is expected to influence mobility of Sb and As in near-surface environment.« less

Structural Changes Correlated with Magnetic Spin State Isomorphism in the S2 State of the Mn4CaO5 Cluster in the Oxygen-Evolving Complex of Photosystem II

PubMed Central

Chatterjee, Ruchira; Han, Guangye; Kern, Jan; Gul, Sheraz; Fuller, Franklin D.; Garachtchenko, Anna; Young, Iris; Weng, Tsu-Chien; Nordlund, Dennis; Alonso-Mori, Roberto; Bergmann, Uwe; Sokaras, Dimosthenis; Hatakeyama, Makoto; Yachandra, Vittal K.; Yano, Junko

2016-01-01

The Mn4CaO5 cluster in Photosystem II catalyzes the four-electron redox reaction of water oxidation in natural photosynthesis. This catalytic reaction cycles through four intermediate states (Si, i = 0 to 4), involving changes in the redox state of the four Mn atoms in the cluster. Recent studies suggest the presence and importance of isomorphous structures within the same redox/intermediate S-state. It is highly likely that geometric and electronic structural flexibility play a role in the catalytic mechanism. Among the catalytic intermediates that have been identified experimentally thus far, there is clear evidence of such isomorphism in the S2 state, with a high-spin (5/2) (HS) and a low spin (1/2) (LS) form, identified and characterized by their distinct electron paramagnetic resonance (EPR spectroscopy) signals. We studied these two S2 isomers with Mn extended X-ray absorption fine structure (EXAFS) and absorption and emission spectroscopy (XANES/XES) to characterize the structural and electronic structural properties. The geometric and electronic structure of the HS and LS S2 states are different as determined using Mn EXAFS and XANES/XES, respectively. The Mn K-edge XANES and XES for the HS form are different from the LS and indicate a slightly lower positive charge on the Mn atoms compared to the LS form. Based on the EXAFS results which are clearly different, we propose possible structural differences between the two spin states. Such structural and magnetic redox-isomers if present at room temperature, will likely play a role in the mechanism for water-exchange/oxidation in photosynthesis. PMID:28044099

Physics Reality Show

NASA Astrophysics Data System (ADS)

Erukhimova, Tatiana

The attention span of K-12 students is very short; they are used to digesting information in short snippets through social media and TV. To get the students interested in physics, we created the Physics Reality Show: a series of staged short videos with duration no longer than a few minutes. Each video explains and illustrates one physics concept or law through a fast-paced sequence of physics demonstrations and experiments. The cast consists entirely of physics undergraduate students with artistic abilities and substantial experience in showing physics demonstrations at current outreach events run by the department: Physics Shows and Physics & Engineering Festival. Undergraduate students are of almost the same age as their high-school audience. They are in the best position to connect with kids and convey their fascination with physics. The PI and other faculty members who are involved in the outreach advise and coach the cast. They help students in staging the episodes and choosing the most exciting and relevant demonstrations. Supported by the APS mini-outreach Grant.

Manganese(IV) Oxide Production by Acremonium sp. Strain KR21-2 and Extracellular Mn(II) Oxidase Activity

PubMed Central

Miyata, Naoyuki; Tani, Yukinori; Maruo, Kanako; Tsuno, Hiroshi; Sakata, Masahiro; Iwahori, Keisuke

2006-01-01

Ascomycetes that can deposit Mn(III, IV) oxides are widespread in aquatic and soil environments, yet the mechanism(s) involved in Mn oxide deposition remains unclear. A Mn(II)-oxidizing ascomycete, Acremonium sp. strain KR21-2, produced a Mn oxide phase with filamentous nanostructures. X-ray absorption near-edge structure (XANES) spectroscopy showed that the Mn phase was primarily Mn(IV). We purified to homogeneity a laccase-like enzyme with Mn(II) oxidase activity from cultures of strain KR21-2. The purified enzyme oxidized Mn(II) to yield suspended Mn particles; XANES spectra indicated that Mn(II) had been converted to Mn(IV). The pH optimum for Mn(II) oxidation was 7.0, and the apparent half-saturation constant was 0.20 mM. The enzyme oxidized ABTS [2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid)] (pH optimum, 5.5; Km, 1.2 mM) and contained two copper atoms per molecule. Moreover, the N-terminal amino acid sequence (residues 3 to 25) was 61% identical with the corresponding sequence of an Acremonium polyphenol oxidase and 57% identical with that of a Myrothecium bilirubin oxidase. These results provide the first evidence that a fungal multicopper oxidase can convert Mn(II) to Mn(IV) oxide. The present study reinforces the notion of the contribution of multicopper oxidase to microbially mediated precipitation of Mn oxides and suggests that Acremonium sp. strain KR21-2 is a good model for understanding the oxidation of Mn in diverse ascomycetes. PMID:17021194

[Distribution and speciation of Pb in Arabidopsis thaliana shoot and rhizosphere soil by in situ synchrotron radiation micro X-ray fluorescence and X-ray absorption near edge structure].

PubMed

Shen, Ya-Ting

2014-03-01

In order to investigate plant reacting mechanism with heavy metal stress in organ and tissue level, synchrotron radiation micro X-ray fluorescence (micro-SRXRF) was used to determine element distribution characteristics of K, Ca, Mn, Fe, Cu, Zn, Pb in an Arabidopsis thaliana seedling grown in tailing dam soil taken from a lead-zinc mine exploration area. The results showed a regular distribution characters of K, Ca, Fe, Cu and Zn, while Pb appeared not only in root, but also in a leaf bud which was beyond previously understanding that Pb mainly appeared in plant root. Pb competed with Mn in the distribution of the whole seedling. Pb may cause the increase of oxidative stress in root and leaf bud, and restrict Mn absorption and utilization which explained the phenomenon of seedling death in this tailing damp soil. Speciation of Pb in Arabidopsis thaliana and tailing damp rhizosphere soil were also presented after using PbL3 micro X-ray absorption near edge structure (micro-XANES). By comparison of PbL3 XANES peak shape and peak position between standard samples and rhizosphere soil sample, it was demonstrated that the tailing damp soil was mainly formed by amorphous forms like PbO (64.2%), Pb (OH)2 (28.8%) and Pb3O4 (6.3%) rather than mineral or organic Pb speciations. The low plant bioavailability of Pb demonstrated a further research focusing on Pb absorption and speciation conversion is needed, especially the role of dissolve organic matter in soil which may enhance Pb bioavailability.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yung, M. M.; Cheah, S.; Kuhn, J. N.

The production of biofuels can proceed via a biomass gasification to produce syngas, which can then undergo catalytic conditioning and reforming reactions prior to being sent to a fuel synthesis reactor. Catalysts used for biomass conditioning are plagued by short lifetimes which are a result of, among other things, poisoning. Syngas produced from biomass gasification may contain between 30-300 ppm H2S, depending on the feedstock and gasification conditions, and H2S is a key catalyst poison. In order to overcome catalyst poisoning, either an H2S-tolerant catalyst or an efficient regeneration protocol should be employed. In this study, sulfur K-edge X-ray absorptionmore » near edge spectroscopy (XANES) was used to monitor sulfur species on spent catalyst samples and the transformation of these species from sulfides to sulfates during steam and air regeneration on a Ni/Mg/K/Al2O3 catalyst used to condition biomass-derived syngas. Additionally, nickel K-edge EXAFS and XANES are used to examine the state of nickel species on the catalysts. Post-reaction samples showed the presence of sulfides on the H2S-poisoned nickel catalyst and although some gaseous sulfur species were observed to leave the catalyst bed during regeneration, sulfur remained on the catalyst and a transformation from sulfides to sulfates was observed. The subsequent H2 reduction led to a partial reduction of sulfates back to sulfides. A proposed reaction sequence is presented and recommended regeneration strategies are discussed.« less

Interface structure in nanoscale multilayers near continuous-to-discontinuous regime

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pradhan, P. C.; Majhi, A.; Nayak, M., E-mail: mnayak@rrcat.gov.in

2016-07-28

Interfacial atomic diffusion, reaction, and formation of microstructure in nanoscale level are investigated in W/B{sub 4}C multilayer (ML) system as functions of thickness in ultrathin limit. Hard x-ray reflectivity (XRR) and x-ray diffuse scattering in conjunction with x-ray absorption near edge spectroscopy (XANES) in soft x-ray and hard x-ray regimes and depth profiling x-ray photoelectron spectroscopy (XPS) have been used to precisely evaluate detailed interfacial structure by systematically varying the individual layer thickness from continuous-to-discontinuous regime. It is observed that the interfacial morphology undergoes an unexpected significant modification as the layer thickness varies from continuous-to-discontinuous regime. The interfacial atomic diffusionmore » increases, the physical density of W layer decreases and that of B{sub 4}C layer increases, and further more interestingly the in-plane correlation length decreases substantially as the layer thickness varies from continuous-to-discontinuous regime. This is corroborated using combined XRR and x-ray diffused scattering analysis. XANES and XPS results show formation of more and more tungsten compounds at the interfaces as the layer thickness decreases below the percolation threshold due to increase in the contact area between the elements. The formation of compound enhances to minimize certain degree of disorder at the interfaces in the discontinuous region that enables to maintain the periodic structure in ML. The degree of interfacial atomic diffusion, interlayer interaction, and microstructure is correlated as a function of layer thickness during early stage of film growth.« less

Probing the organic-mineral interface at the molecular level in model biominerals.

PubMed

Metzler, Rebecca A; Kim, Il Won; Delak, Katya; Evans, John Spencer; Zhou, Dong; Beniash, Elia; Wilt, Fred; Abrecht, Mike; Chiou, Jau-Wern; Guo, Jinghua; Coppersmith, Susan N; Gilbert, P U P A

2008-03-18

It is widely known that macromolecules, such as proteins, can control the nucleation and growth of inorganic solids in biomineralizing organisms. However, what is not known are the complementary molecular interactions, organization, and rearrangements that occur when proteins interact with inorganic solids during the formation of biominerals. The organic-mineral interface (OMI) is expected to be the site for these phenomena, and is therefore extraordinarily interesting to investigate. In this report, we employ X-ray absorption near edge (XANES) spectromicroscopy to investigate the electronic structure of both calcium carbonate mineral crystals and polypeptides, and detect changing bonds at the OMI during crystal growth in the presence of polypeptides. We acquired XANES spectra from calcium carbonate crystals grown in the presence of three mollusk nacre-associated polypeptides (AP7N, AP24N, n16N) and in the presence of a sea urchin spicule matrix protein, LSM34. All these model biominerals gave similar results, including the disruption of CO bonds in calcite and enhancement of the peaks associated with C-H bonds and C-O bonds in peptides, indicating ordering of the amino acid side chains in the mineral-associated polypeptides and carboxylate binding. This is the first evidence of the mutual effect of calcite on peptide chain and peptide chain on calcite during biomineralization. We also show that these changes do not occur when Asp and Glu are replaced in the n16N sequence with Asn and Gln, respectively, demonstrating that carboxyl groups in Asp and Glu do participate in polypeptide-mineral molecular associations.

The inhibition of Pb(IV) oxide formation in chlorinated water by orthophosphate.

PubMed

Lytle, Darren A; Schock, Michael R; Scheckel, Kirk

2009-09-01

Historically, understanding lead solubility and its control in drinking water has been based on Pb(II) chemistry. Unfortunately, there is very little information available regarding the nature of Pb(IV) oxides in finished drinking water and water distribution systems, and the conditions under which they persist. The objective of this research was to explore the impact of orthophosphate on the realistic pathways that lead to the formation of Pb(IV) oxides in chlorinated water. The results of XRD and XANES analysis showed that, in the absence of orthophosphate (DIC = 10 mg C/L, 24 degrees C, pH 7.75-8.1, 3 mg Cl2/L goal), Pb(IV) oxides formed with time following a transformation from the Pb(II) mineral hydrocerussite. Under the same experimental conditions, orthophosphate dosing inhibited the formation of Pb(IV) oxides. The Pb(II) mineral hydroxypyromorphite, Pb5(PO4)3OH, was the only mineral phase identified during the entire study of over 600 days, although the presence of some chloropyromorphite, Pb5(PO4)3Cl, could not be ruled out The conclusions were further supported by SEM, TEM, and XANES analysis of lead colloids, and lead precipitation experiments conducted in the absence of free chlorine. The findings provide an important explanation for the absence of Pb(IV) oxides in some water systems that have used, or currently use, orthophosphate for corrosion control when otherwise, based on disinfection practices and water quality, its presence would be anticipated, as well as why the conversion from free chlorine to chloramines was not observed to increase lead release.

Chlorine in coal and its relationship with boiler corrosion. Technical report, 1 March--31 May 1994

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chou, M.I.M.; Lytle, J.M.; Ruch, R.R.

1994-09-01

Limited literature and use history data have suggested that some high-chlorine Illinois coals do not cause boiler corrosion while extensive data developed by the British correlate corrosion with chlorine content and other parameters related to the coal and boiler. The differences in corrosivity in coals may be due to the coal properties, to blending of coals, or to the boiler parameters in which they were burned. The goals of this study focus on coal properties. In this quarter, both destructive temperature-programmed Thermogravimetry with Fourier transform infrared (TGA-FTIR) and non-destructive X-ray absorption near-edge structure (XANES) techniques were used to examine themore » forms and the evolution characteristics of chlorine in coals. The TGA-FTIR results indicate that under oxidation condition, both British and Illinois coals release hydrogen chloride gas. Illinois coals release the gas at high temperature with maximum evolution temperature ranged between 210 and 280 C. The XANES results indicate that chlorine in coal exists in ionic forms including a solid salt form. The solid NaCl salt form, however, is observed only in some of the British coals and none of the Illinois coals. These results combined with TGA-FTIR results suggest that the chlorine ions in Illinois coals are different from the chlorine ions in British coals.« less

Effects of Sulfation Level on the Desulfation Behavior of Presulfated Pt-BaO/Al2O3 Lean NOx Trap Catalysts: A Combined H2 Temperature-Programmed Reaction, in Situ Sulfur K-Edge X-ray Absorption Near-Edge Spectroscopy, X-ray Photoelectron Spectroscopy, and Time-Resolved X-ray Diffraction Study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, D.H.; Hanson, J.; Szanyi, J.

2009-04-30

Desulfation by hydrogen of presulfated Pt (2 wt %)-BaO(20 wt %)/Al{sub 2}O{sub 3} with various sulfur loading (S/Ba = 0.12, 0.31, and 0.62) were investigated by combining H{sub 2} temperature programmed reaction (TPRX), X-ray photoelectron spectroscopy (XPS), in situ sulfur K-edge X-ray absorption near-edge spectroscopy (XANES), and synchrotron time-resolved X-ray diffraction (TR-XRD) techniques. We find that the amount of H{sub 2}S desorbed during the desulfation in the H{sub 2} TPRX experiments is not proportional to the amount of initial sulfur loading. The results of both in situ sulfur K-edge XANES and TR-XRD show that at low sulfur loadings, sulfates weremore » transformed to a BaS phase and remained in the catalyst rather than being removed as H{sub 2}S. On the other hand, when the deposited sulfur level exceeded a certain threshold (at least S/Ba = 0.31) sulfates were reduced to form H{sub 2}S, and the relative amount of the residual sulfide species in the catalyst was much less than at low sulfur loading. Unlike samples with high sulfur loading (e.g., S/Ba = 0.62), H{sub 2}O did not promote the desulfation for the sample with S/Ba of 0.12, implying that the formed BaS species originating from the reduction of sulfates at low sulfur loading are more stable to hydrolysis. The results of this combined spectroscopy investigation provide clear evidence to show that sulfates at low sulfur loadings are less likely to be removed as H{sub 2}S and have a greater tendency to be transformed to BaS on the material, leading to the conclusion that desulfation behavior of Pt-BaO/Al{sub 2}O{sub 3} lean NO{sub x} trap catalysts is markedly dependent on the sulfation levels.« less

A multi-technique approach to assess chemical speciation of phosphate in soils

NASA Astrophysics Data System (ADS)

Belchior Abdala, Dalton; Rodrigues, Marcos; Herrera, Wilfrand; Pavinato, Paulo Sergio

2017-04-01

different P pools considered in the fractionation protocol, (ii) two synchrotron-based X-ray absorption spectroscopic techniques, XANES and EXAFS, for chemical characterization of the P forms and mineralogy of Fe-(hydr)oxides present in a sample, and (iii) Scanning Electron Microscopy and Energy-Dispersive spectroscopy, SEM/EDS, to provide complimentary information to corroborate and aid in the interpretation of our P XANES data. It was shown that the combination of techniques can assist us not only in the determination of the P chemical species present in a given material, but also to better understand the complex and dynamic processes to which P is subjected in soils. The association of spectroscopy (XANES and EXAFS) and microscopy (SEM/EDS) with wet chemistry data in this study was key to shift our understanding of the relationship between P and other soil mineral components from a macroscopic into a microscopic one. This represents a strong driving force to integrate the results of multi-analytical techniques into a more complete understanding of the systems under study. In addition, we provide a library of reference spectra for P K-edge XANES containing P sorbed to single and binary mixtures of mineral analogues intended to assist in the identification of P sorbed species commonly found in soils and sediments. Key-words: P K-edge XANES, Fe K-edge EXAFS, sequential chemical fractionation, soil phosphorus

Direct Determination of the Intracellular Oxidation State of Plutonium

PubMed Central

Gorman-Lewis, Drew; Aryal, Baikuntha P.; Paunesku, Tatjana; Vogt, Stefan; Lai, Barry; Woloschak, Gayle E.; Jensen, Mark P.

2013-01-01

Microprobe X-ray absorption near edge structure (μ-XANES) measurements were used to determine directly, for the first time, the oxidation state of intracellular plutonium in individual 0.1 μm2 areas within single rat pheochromocytoma cells (PC12). The living cells were incubated in vitro for 3 hours in the presence of Pu added to the media in different oxidation states (Pu(III), Pu(IV), and Pu(VI)) and in different chemical forms. Regardless of the initial oxidation state or chemical form of Pu presented to the cells, the XANES spectra of the intracellular Pu deposits was always consistent with tetravalent Pu even though the intracellular milieu is generally reducing. PMID:21755934

Electronic structure of nickel silicide in subhalf-micron lines and blanket films: An x-ray absorption fine structures study at the Ni and Si L3,2 edge

NASA Astrophysics Data System (ADS)

Naftel, S. J.; Coulthard, I.; Sham, T. K.; Xu, D.-X.; Erickson, L.; Das, S. R.

1999-05-01

We report a Ni and Si L3,2-edge x-ray absorption near edge structures (XANES) study of nickel-silicon interaction in submicron (0.15 and 0.2 μm) lines on a n-Si(100) wafer as well as a series of well characterized Ni-Si blanket films. XANES measurements recorded in both total electron yield and soft x-ray fluorescence yield indicate that under the selected silicidation conditions, the more desirable low resistivity phase, NiSi, is indeed the dominant phase in the subhalf-micron lines although the formation of this phase is less complete as the line becomes narrower and this is accompanied by a Ni rich surface.

Applications of Hard X-ray Full-Field Transmission X-ray Microscopy at SSRL

NASA Astrophysics Data System (ADS)

Liu, Y.; Andrews, J. C.; Meirer, F.; Mehta, A.; Gil, S. Carrasco; Sciau, P.; Mester, Z.; Pianetta, P.

2011-09-01

State-of-the-art hard x-ray full-field transmission x-ray microscopy (TXM) at beamline 6-2C of Stanford Synchrotron Radiation Lightsource has been applied to various research fields including biological, environmental, and material studies. With the capability of imaging a 32-micron field-of-view at 30-nm resolution using both absorption mode and Zernike phase contrast, the 3D morphology of yeast cells grown in gold-rich media was investigated. Quantitative evaluation of the absorption coefficient was performed for mercury nanoparticles in alfalfa roots exposed to mercury. Combining XANES and TXM, we also performed XANES-imaging on an ancient pottery sample from the Roman pottery workshop at LaGraufesenque (Aveyron).

Dynamic study of sub-micro sized LiFePO4 cathodes by in-situ tender X-ray absorption near edge structure

NASA Astrophysics Data System (ADS)

Wang, Dongniu; Wang, Huixin; Yang, Jinli; Zhou, Jigang; Hu, Yongfeng; Xiao, Qunfeng; Fang, Haitao; Sham, Tsun-Kong

2016-01-01

Olivine-type phosphates (LiMPO4, M = Fe, Mn, Co) are promising cathode materials for lithium-ion batteries that are generally accepted to follow first order equilibrium phase transformations. Herein, the phase transformation dynamics of sub-micro sized LiFePO4 particles with limited rate capability at a low current density of 0.14 C was investigated. An in-situ X-ray Absorption Near Edge Structure (XANES) measurement was conducted at the Fe and P K-edge for the dynamic studies upon lithiation and delithiation. Fe K-edge XANES spectra demonstrate that not only lithium-rich intermediate phase LixFePO4 (x = 0.6-0.75), but also lithium-poor intermediate phase LiyFePO4 (y = 0.1-0.25) exist during the charge and discharge, respectively. Furthermore, during charge and discharge, a fluctuation of the FePO4 and LiFePO4 fractions obtained by liner combination fitting around the imaginary phase fractions followed Faraday's law and the equilibrium first-order two-phase transformation versus reaction time is present, respectively. The charging and discharging process has a reversible phase transformation dynamics with symmetric structural evolution routes. P K-edge XANES spectra reveal an enrichment of PF6-1 anions at the surface of the electrode during charging.

Using X-ray absorption to probe sulfur oxidation states in complex molecules

NASA Astrophysics Data System (ADS)

Vairavamurthy, A.

1998-10-01

X-ray absorption near-edge structure (XANES) spectroscopy offers an important non-destructive tool for determining oxidation states and for characterizing chemical speciation. The technique was used to experimentally verify the oxidation states of sulfur in different types of complex molecules because there are irregularities and uncertainties in assigning the values traditionally. The usual practice of determining oxidation states involves using a set of conventional rules. The oxidation state is an important control in the chemical speciation of sulfur, ranging from -2 to +6 in its different compounds. Experimental oxidation-state values for various types of sulfur compounds, using their XANES peak-energy positions, were assigned from a scale in which elemental sulfur and sulfate are designated as 0 and +6, respectively. Because these XANES-based values differed considerably from conventionally determined oxidation states for most sulfur compounds, a new term 'oxidation index' was coined to describe them. The experimental values were closer to those conventional values obtained by assigning shared electrons to the more electronegative atoms than to those based on other customary rules for assigning them. Because the oxidation index is distinct and characteristic for each different type of sulfur functionality, it becomes an important parameter for characterizing sulfur species, and for experimentally verifying uncertain oxidation states.

"The Cosby Show": The View from the Black Middle Class.

ERIC Educational Resources Information Center

Inniss, Leslie B.; Feagin, Joe R.

1995-01-01

Examines the black middle-class response to "The Cosby Show." The study asked about the portrayal of blacks in the media, but did not specifically ask about "The Cosby Show." Results from 100 respondents revealed two significant aspects: that the show renders black problems as irrelevant and that it fosters hope and optimism…

The Reduction of Cr(VI) to Cr(III) by Natural Fe-Bearing Minerals: A Synchrotron XAS Study

NASA Astrophysics Data System (ADS)

Xu, H.; Guo, X.; Ding, M.; Migdissov, A. A.; Boukhalfa, H.; Sun, C.; Roback, R. C.; Reimus, P. W.; Katzman, D.

2017-12-01

Cr(VI) in the form of CrO42- is a pollutant species in groundwater and soils that can pose health and environmental problems. Cr(VI) associated with use as a corrosion inhibitor at a power plant from 1956-1972 is present in a deep groundwater aquifer at Los Alamos National Laboratory. A potential remediation strategy for the Cr contamination is reduction of Cr(VI) to Cr(III) via the acceptance of electrons from naturally occurring or induced Fe(II) occurring in Fe-bearing minerals. In this work, using synchrotron-based X-ray techniques, we investigated the Cr reduction behavior by Fe-bearing minerals from outcrop and core samples representative of the contaminated portion of the aquifer. Samples were exposed to solutions with a range of known Cr (VI) concentrations. XANES and EXAFS spectra showed that all the Cr(VI) had been reduced to Cr(III), and micro XRF mapping revealed close correlation of Cr and Fe distribution, implying that Fe(II) in minerals reduced Cr(VI) in the solution. Similar behavior was observed from in-situ XANES measurements on Cr reduction and adsorption by mineral separates from the rock samples in Cr(VI)-bearing solutions. In addition, to obtain reference parameters for interpreting the data of natural samples, we collected Cr and Fe EXAFS spectra of Cr(III)-Fe(III) hydroxide solid solutions, which show progressive changes in the local structure around Cr and Fe over the whole series.

Archeological Applications of XAFS: Prehistorical Paintings And Medieval Glasses

DOE Office of Scientific and Technical Information (OSTI.GOV)

Farges, F.; Chalmin, E.; Vignaud, C.

2006-10-27

High-resolution manganese and iron K-edges XANES spectra were collected on several samples of archeological interest: prehistorical paintings and medieval glasses. XANES spectra were collected at the ID21 facility (ESRF, Grenoble, France) using a micro-beam device and at the 11-2 beamline (SSRL, Stanford, USA) using a submillimetric beam. The medieval glasses studied are from gothic glass windows from Normandy (XIVth century). The aim of this study is to help understand the chemical durability of these materials, exposed to weathering since the XIVth century. They are used as analogues of weathered glasses used to dump metallic wastes. These glasses show surficial enrichmentmore » in manganese, due to its oxidation from II (glass) to III/IV (surface), which precipitates as amorphous oxy-hydroxides. Similarly, iron is oxidized on the surface and forms ferrihydrite-type aggregates. The prehistorical paintings are from Lascaux and Ekain (Basque country). We choose in that study the black ones, rich in manganese to search for potential evidences of some 'savoir-faire' that the Paleolithic men could have used to realize their paint in rock art, as shown earlier for Fe-bearing pigments. A large number of highly valuable samples, micrometric scaled, were extracted from these frescoes and show large variation in the mineralogical nature of the black pigments used, from an amorphous psilomelane-type to a well-crystallized pyrolusite. Correlation with the crystals morphology helps understanding the know-how of these early artists.« less

Targeted Therapy Larotrectinib Shows Promise in Early Trials

Cancer.gov

The drug larotrectinib shrank tumors in patients with 13 different cancer types, results from three small clinical trials show. The drug, which targets tumors with TRK fusions, was effective in children and adults, this Cancer Currents post explains.

Selenium inhibits the phytotoxicity of mercury in garlic (Allium sativum)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhao, Jiating; Gao, Yuxi, E-mail: gaoyx@ihep.ac.cn; Li, Yu-Feng

2013-08-15

To investigate the influence of selenium on mercury phytotoxicity, the levels of selenium and mercury were analyzed with inductively coupled plasma-mass spectrometry (ICP-MS) in garlic tissues upon exposure to different dosages of inorganic mercury (Hg{sup 2+}) and selenite (SeO{sub 3}{sup 2−}) or selenate (SeO{sub 4}{sup 2−}). The distributions of selenium and mercury were examined with micro-synchrotron radiation X-ray fluorescence (μ-SRXRF), and the mercury speciation was investigated with micro-X-ray absorption near edge structure (μ-XANES). The results show that Se at higher exposure levels (>1 mg/L of SeO{sub 3}{sup 2−} or SeO{sub 4}{sup 2−}) would significantly inhibit the absorption and transportation ofmore » Hg when Hg{sup 2+} levels are higher than 1 mg/L in culture media. SeO{sub 3}{sup 2−} and SeO{sub 4}{sup 2−} were found to be equally effective in reducing Hg accumulation in garlic. The inhibition of Hg uptake by Se correlates well with the influence of Se on Hg phytotoxicity as indicated by the growth inhibition factor. Elemental imaging using μ-SRXRF also shows that Se could inhibit the accumulation and translocation of Hg in garlic. μ-XANES analysis shows that Hg is mainly present in the forms of Hg–S bonding as Hg(GSH){sub 2} and Hg(Met){sub 2}. Se exposure elicited decrease of Hg–S bonding in the form of Hg(GSH){sub 2}, together with Se-mediated alteration of Hg absorption, transportation and accumulation, may account for attenuated Hg phytotoxicity by Se in garlic. -- Highlights: ► Hg phytotoxicity can be mitigated by Se supplement in garlic growth. ► Se can inhibit the accumulation and transportation of Hg in garlic tissues. ► Localization and speciation of Hg in garlic can be modified by Se.« less

Characterization of yellow and colorless decorative glasses from the Temple of the Emerald Buddha, Bangkok, Thailand

NASA Astrophysics Data System (ADS)

Klysubun, Wantana; Ravel, Bruce; Klysubun, Prapong; Sombunchoo, Panidtha; Deenan, Weeraya

2013-06-01

Yellow and colorless ancient glasses, which were once used to decorate the Temple of the Emerald Buddha, Bangkok, Thailand, around 150 years ago, are studied to unravel the long-lost glass-making recipes and manufacturing techniques. Analyses of chemical compositions, using synchrotron x-ray fluorescence (SRXRF), indicate that the Thai ancient glasses are soda lime silica glasses (60 % SiO2; 10 % Na2O; 10 % CaO) bearing lead oxide between 2-16 %. Iron (1.5-9.4 % Fe2O3) and manganese (1.7 % MnO) are present in larger abundance than the other 3 d transition metals detected (0.04-0.2 %). K-edge x-ray absorption near edge spectroscopy (XANES) and extended x-ray absorption fine structure spectroscopy (EXAFS) provide conclusive evidence on the oxidation states of Fe being 3+ and Mn being 2+ and on short-length tetrahedral structures around the cations. This suggests that iron is used as a yellow colorant with manganese as a decolorant. L 3-edge XANES results reveal the oxidation states of lead as 2+. The results from this work provide information crucial for replicating these decorative glasses for the future restoration of the Temple of the Emerald Buddha.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reynolds, Emily; Kennedy, Brendan J.; Avdeev, Maxim

A combination of S-XRD and NPD demonstrate the structure of Ba{sub 2}Y{sub 0.879}UO{sub 6+x} to be monoclinic in space group I2/m. That the U is hexavalent is evident from the U L{sub 2}-edge XANES measurements. This appears to be a rare example of a double perovskite containing vacancies at the octahedral B-sites and interstitial oxygen defects, which combine to stabilise hexavalent U and appears to be a consequence of the preparation of the sample in air. The Y vacancies, coupled with anion disorder, results in a distortion of the BO{sub 6} octahedra. - Graphical abstract: The structure of Ba{sub 2}Y{submore » 0.879}UO{sub 6+x} is shown to be a rare example of a double perovskite containing vacancies at the octahedral B-sites and interstitial oxygen defects. - Highlights: • Structure of Ba{sub 2}Y{sub 0.879}UO{sub 6+x} refined. • U L-edge XANES demonstrates the U is hexavalent. • Rare example of a perovskite containing vacancies at the octahedral B-site. • Y vacancies result in a distortion of the BO{sub 6} octahedra.« less

Arsenic speciation in sinter mineralization from a hydrothermal channel of El Tatio geothermal field, Chile

NASA Astrophysics Data System (ADS)

Alsina, Marco A.; Zanella, Luciana; Hoel, Cathleen; Pizarro, Gonzalo E.; Gaillard, Jean-François; Pasten, Pablo A.

2014-10-01

El Tatio geothermal field is the principal natural source of arsenic for the Loa River, the main surface water resource in the hyper-arid Atacama Desert (Antofagasta Region, Northern Chile). Prior investigations by bulk X-ray absorption spectroscopy have identified hydrous ferric oxides as the principal arsenic-containing phase in sinter material from El Tatio, suggesting sorption as the main mechanism for arsenic scavenging by the solid phases of these hot spring environments. Here we examine siliceous sinter material sampled from a hydrothermal channel using synchrotron based X-ray micro-probe techniques, including As and Fe Kα X-ray fluorescence (μ-XRF), As K-edge X-ray absorption near edge structure (μ-XANES), and X-ray diffraction (μ-XRD). Least-squares linear fitting of μ-XANES spectra shows that arsenic is predominantly present as arsenate sorbed on hydrous ferric oxides (63% molar proportion), but we also identify nodular arsenide micro-mineralizations (37% molar proportion) similar to loellingite (FeAs2), not previously detected during bulk-scale analysis of the sinter material. Presence of arsenide mineralizations indicates development of anoxic environments on the surface of the siliceous sinter, and suggests a more complex biogeochemistry for arsenic than previously observed for circum-neutral pH brine hot spring environments.

X-ray physico-chemical imaging during activation of cobalt-based Fischer-Tropsch synthesis catalysts

NASA Astrophysics Data System (ADS)

Beale, Andrew M.; Jacques, Simon D. M.; Di Michiel, Marco; Mosselmans, J. Frederick W.; Price, Stephen W. T.; Senecal, Pierre; Vamvakeros, Antonios; Paterson, James

2017-11-01

The imaging of catalysts and other functional materials under reaction conditions has advanced significantly in recent years. The combination of the computed tomography (CT) approach with methods such as X-ray diffraction (XRD), X-ray fluorescence (XRF) and X-ray absorption near-edge spectroscopy (XANES) now enables local chemical and physical state information to be extracted from within the interiors of intact materials which are, by accident or design, inhomogeneous. In this work, we follow the phase evolution during the initial reduction step(s) to form Co metal, for Co-containing particles employed as Fischer-Tropsch synthesis (FTS) catalysts; firstly, working at small length scales (approx. micrometre spatial resolution), a combination of sample size and density allows for transmission of comparatively low energy signals enabling the recording of `multimodal' tomography, i.e. simultaneous XRF-CT, XANES-CT and XRD-CT. Subsequently, we show high-energy XRD-CT can be employed to reveal extent of reduction and uniformity of crystallite size on millimetre-sized TiO2 trilobes. In both studies, the CoO phase is seen to persist or else evolve under particular operating conditions and we speculate as to why this is observed. This article is part of a discussion meeting issue 'Providing sustainable catalytic solutions for a rapidly changing world'.

Synchrotron-based XAS on structure investigation of La0.99-xSrx(Na, K, Ba)0.01MnO3 nanoparticles: Evidence of magnetic properties

NASA Astrophysics Data System (ADS)

Daengsakul, Sujittra; Saengplot, Saowalak; Kidkhunthod, Pinit; Pimsawat, Adulphan; Maensiri, Santi

2018-04-01

This work presents the structural study of La0.99-xSrx(Na, K, Ba)0.01MnO3 or LSAM nanoparticles synthesized using thermal-hydro decomposition method where A denotes Na, K, Sr and Ba, respectively. The effect of ionic radii size of A dopants or rA from the substitution of A for La and Sr on the MnO6 octrahedral structure, where the average size of the cations occupying in A-site or 〈rA〉 is fixed at ∼ 1.24 Å, is focused. The LSAM nanoparticles are carefully studied using X-ray diffraction (XRD) including Rietveld refinement and X-ray Absorption Spectroscopy (XAS) including X-ray Absorption Near edge Structure (XANES) and X-ray Absorption Fine Structure (EXAFS). The Rietveld refinement shows all nano-powder samples have rhombohedral structure. By XANES technique we found that the effect of A substitutions at A-site causes a slight change of mean oxidation state of Mn between 3.54 and 3.60. Furthermore, the structural distortion of MnO6 octrahedral in samples is analysed and obtained from EXAFS. The observed trend of ferromagnetism for all LSAM samples can be clearly explained by evidences of A-site doping, structural distortion around Mn atoms and mixing Mn3+/Mn4+ valence states.

Birnessite catalysis of the Maillard Reaction: Its significance in natural humification

NASA Astrophysics Data System (ADS)

Jokic, A.; Frenkel, A. I.; Vairavamurthy, M. A.; Huang, P. M.

Although mineral colloids are known to play a significant role in transforming organic matter in soils and sediments, there still are many gaps in our understanding of the mechanisms of organic-mineral interactions. In this study, we investigated the role of a major oxide-mineral birnessite (a form of Mn(IV) oxide) in catalyzing the condensation reaction between sugars and amino acids, the Maillard reaction, for forming humic substances. The Maillard reaction is perceived to be a major pathway in natural humification. Using a suite of spectroscopic methods (including ESR, XANES, EXAFS and 13C NMR), our results show that Mn(IV) oxide markedly accelerates the Maillard reaction between glucose and glycine at ranges of temperatures and pH typical of natural environments. These results demonstrate the importance of manganese oxide catalysis in the Maillard reaction, and its significance in the natural abiotic formation of humic substances.

Children with autism show specific handwriting impairments

PubMed Central

Fuentes, Christina T.; Mostofsky, Stewart H.; Bastian, Amy J.

2009-01-01

Background: Handwriting skills, which are crucial for success in school, communication, and building children’s self-esteem, have been observed to be poor in individuals with autism. Little information exists on the handwriting of children with autism, without delineation of specific features that can contribute to impairments. As a result, the specific aspects of handwriting in which individuals with autism demonstrate difficulty remain unknown. Methods: A case-control study of handwriting samples from children with and without autism spectrum disorders (ASD) was performed using the Minnesota Handwriting Assessment. Samples were scored on an individual letter basis in 5 categories: legibility, form, alignment, size, and spacing. Subjects were also tested on the Wechsler Intelligence Scale for Children–IV and the Physical and Neurological Examination for Subtle (Motor) Signs. Results: We found that children with ASD do indeed show overall worse performance on a handwriting task than do age- and intelligence-matched controls. More specifically, children with ASD show worse quality of forming letters but do not show differences in their ability to correctly size, align, and space their letters. Within the ASD group, motor skills were significantly predictive of handwriting performance, whereas age, gender, IQ, and visuospatial abilities were not. Conclusions: We addressed how different elements of handwriting contribute to impairments observed in children with autism. Our results suggest that training targeting letter formation, in combination with general training of fine motor control, may be the best direction for improving handwriting performance in children with autism. GLOSSARY ADI-R = Autism Diagnostic Interview–Revised; ADOS-G = Autism Diagnostic Observation Schedule–Generic; ASD = autism spectrum disorders; DICA-IV = Diagnostic Interview for Children and Adolescents, 4th edition; DSM-IV = Diagnostic and Statistical Manual of Mental Disorders, 4th

Structural Transformations in High-Capacity Li 2 Cu 0.5 Ni 0.5 O 2 Cathodes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ruther, Rose E.; Samuthira Pandian, Amaresh; Yan, Pengfei

2017-03-21

Cathode materials that can cycle > 1 Li+ per transition metal are of substantial interest to increase the overall energy density of lithium-ion batteries. Li2Cu0.5Ni0.5O2 has a very high theoretical capacity of ~ 500 mAh/g assuming both Li+ are cycled reversibly. The Cu2+/3+ and Ni2+/3+/4+ redox couples are also at high voltage, which could further boost the energy density of this system. Despite such promise, Li2Cu0.5Ni0.5O2 undergoes irreversible phase changes during charge (delithiation) that result in large first-cycle irreversible loss and poor long-term cycling stability. Oxygen is evolved before the Cu2+/3+ or Ni3+/4+ transitions are accessed. In this contribution, XRD,more » TEM, and TXM-XANES are used to follow the chemical and structural changes that occur in Li2Cu0.5Ni0.5O2 during electrochemical cycling. Li2Cu0.5Ni0.5O2 is a solid solution of orthorhombic Li2CuO2 and Li2NiO2, but the structural changes more closely mimic the Li2NiO2 endmember. Li2Cu0.5Ni0.5O2 loses long-range order during charge, but TEM analysis provides clear evidence for particle exfoliation and the transformation from orthorhombic to a partially layered structure. Linear combination fitting and principal component analysis of TXM-XANES are used to map the different phases that emerge during cycling ex situ and in situ. Significant changes in the XANES at the Cu and Ni K-edges correlate with the onset of oxygen evolution.« less

Structural transformations in high-capacity Li 2Cu 0.5Ni 0.5O 2 cathodes

DOE PAGES

Ruther, Rose E.; Pandian, Amaresh Samuthira; Yan, Pengfei; ...

2017-03-09

Cathode materials that can cycle >1 Li + per transition metal are of substantial interest for increasing the overall energy density of lithium-ion batteries. Li 2Cu 0.5Ni 0.5O 2 has a very high theoretical capacity of ~500 mAh/g assuming both Li+ ions are cycled reversibly. The Cu 2+/3+ and Ni 2+/3+/4+ redox couples are also at high voltage, which could further boost the energy density of this system. Despite such promise, Li 2Cu 0.5Ni 0.5O 2 undergoes irreversible phase changes during charge (delithiation) that result in large first-cycle irreversible loss and poor long-term cycling stability. Oxygen evolves before the Cumore » 2+/3+ or Ni 3+/4+ transitions are accessed. In this contribution, X-ray diffraction, transmission electron microscopy (TEM), and transmission X-ray microscopy combined with X-ray absorption near edge structure (TXM–XANES) are used to follow the chemical and structural changes that occur in Li 2Cu 0.5Ni 0.5O 2 during electrochemical cycling. Li 2Cu 0.5Ni 0.5O 2 is a solid solution of orthorhombic Li2CuO2 and Li2NiO2, but the structural changes more closely mimic the changes that the Li 2NiO 2 endmember undergoes. Li 2Cu 0.5Ni 0.5O 2 loses long-range order during charge, but TEM analysis provides clear evidence of particle exfoliation and the transformation from orthorhombic to a partially layered structure. Linear combination fitting and principal component analysis of TXM–XANES are used to map the different phases that emerge during cycling ex situ and in situ. Lastly, significant changes in the XANES at the Cu and Ni K-edges correlate with the onset of oxygen evolution.« less

Spectromicroscopy of boron in human glioblastomas following administration of Na2B12H11SH.

PubMed

Gilbert, B; Perfetti, L; Fauchoux, O; Redondo, J; Baudat, P A; Andres, R; Neumann, M; Steen, S; Gabel, D; Mercanti, D; Ciotti, M T; Perfetti, P; Margaritondo, G; De Stasio, G

2000-07-01

Boron neutron capture therapy (BNCT) is an experimental, binary treatment for brain cancer which requires as the first step that tumor tissue is targeted with a boron-10 containing compound. Subsequent exposure to a thermal neutron flux results in destructive, short range nuclear reaction within 10 microm of the boron compound. The success of the therapy requires than the BNCT agents be well localized in tumor, rather than healthy tissue. The MEPHISTO spectromicroscope, which performs microchemical analysis by x-ray absorption near edge structure (XANES) spectroscopy from microscopic areas, has been used to study the distribution of trace quantities of boron in human brain cancer tissues surgically removed from patients first administered with the compound Na2B12H11SH (BSH). The interpretation of XANES spectra is complicated by interference from physiologically present sulfur and phosphorus, which contribute structure in the same energy range as boron. We addressed this problem with the present extensive set of spectra from S, B, and P in relevant compounds. We demonstrate that a linear combination of sulfate, phosphate and BSH XANES can be used to reproduce the spectra acquired on boron-treated human brain tumor tissues. We analyzed human glioblastoma tissue from two patients administered and one not administered with BSH. As well as weak signals attributed to BSH, x-ray absorption spectra acquired from tissue samples detected boron in a reduced chemical state with respect to boron in BSH. This chemical state was characterized by a sharp absorption peak at 188.3 eV. Complementary studies on BSH reference samples were not able to reproduce this chemical state of boron, indicating that it is not an artifact produced during sample preparation or x-ray exposure. These data demonstrate that the chemical state of BSH may be altered by in vivo metabolism.

Na-Ion Intercalation and Charge Storage Mechanism in 2D Vanadium Carbide

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bak, Seong-Min; Qiao, Ruimin; Yang, Wanli

Two-dimensional vanadium carbide MXene containing surface functional groups (denoted as V2CTx, where Tx are surface functional groups) was synthesized and studied as anode material for Na-ion batteries. V2CTx anode exhibits reversible charge storage with good cycling stability and high rate capability through electrochemical test. The charge storage mechanism of V2CTx material during Na+ intercalation/deintercalation and the redox reaction of vanadium were studied using a combination of synchrotron based X-ray diffraction (XRD), hard X-ray absorption near edge spectroscopy (XANES) and soft X-ray absorption spectroscopy (sXAS). Experimental evidence of a major contribution of redox reaction of vanadium to the charge storage andmore » the reversible capacity of V2CTx during sodiation/desodiation process have been provided through V K-edge XANES and V L2,3-edge sXAS results. A correlation between the CO32- content and Na+ intercalation/deintercalation states in the V2CTx electrode observed from C and O K-edge in sXAS results imply that some additional charge storage reactions may take place between the Na+-intercalated V2CTx and the carbonate based non-aqueous electrolyte. The results of this study will provide valuable information for the further studies on V2CTx as anode material for Na-ion batteries and capacitors.« less

Pilot evaluation of a media literacy program for tobacco prevention targeting early adolescents shows mixed results.

PubMed

Kaestle, Christine E; Chen, Yvonnes; Estabrooks, Paul A; Zoellner, Jamie; Bigby, Brandon

2013-01-01

The purpose of this pilot study was to assess the impact of media literacy for tobacco prevention for youth delivered through a community site. A randomized pretest-posttest evaluation design with matched-contact treatment and control conditions. The pilot study was delivered through the YMCA in a lower-income suburban and rural area of Southwest Virginia, a region long tied, both economically and culturally, to the tobacco industry. Children ages 8 to 14 (76% white, 58% female) participated in the study (n = 38). The intervention was an antismoking media literacy program (five 1-hour lessons) compared with a matched-contact creative writing control program. General media literacy, three domains of tobacco-specific media literacy ("authors and audiences," "messages and meanings," and "representation and reality"), tobacco attitudes, and future expectations were assessed. Multiple regression modeling assessed the impact of the intervention, controlling for pretest measures, age, and sex. General media literacy and tobacco-specific "authors and audiences" media literacy improved significantly for treatment compared with control (p < .05); results for other tobacco-specific media literacy measures and for tobacco attitudes were not significant. Future expectations of smoking increased significantly for treatment participants ages 10 and younger (p < .05). Mixed results indicated that improvements in media literacy are accompanied by an increase in future expectations to smoke for younger children.

Distributing and Showing Farmer Learning Videos in Bangladesh

ERIC Educational Resources Information Center

Bentley, Jeffery W.; Van Mele, Paul; Harun-ar-Rashid, Md.; Krupnik, Timothy J.

2016-01-01

Purpose: To describe the results of showing farmer learning videos through different types of volunteers. Design/Methodology/Approach: Semi-structured interviews with volunteers from different occupational groups in Bangladesh, and a phone survey with 227 respondents. Findings: Each occupational group acted differently. Shop keepers, tillage…

X-ray absorption studies of gamma irradiated Nd doped phosphate glass

NASA Astrophysics Data System (ADS)

Rai, V. N.; Rajput, Parasmani; Jha, S. N.; Bhattacharyya, D.

2015-06-01

This paper presents the X-ray absorption near edge structure (XANES) studies of Nd doped phosphate glasses before and after gamma irradiation. The intensity and location of LIII edge white line peak of Nd changes depending on its concentration as well as on the ratio of O/Nd in the glass matrix. The decrease in the peak intensity of white line after gamma irradiation indicates towards reduction of Nd3+ to Nd2+ in the glass matrix, which increases with an increase in the doses of gamma irradiation. Similarity in the XANES spectra of Nd doped phosphate glasses and Nd2O3 suggests that coordination geometry around Nd3+ in glass samples may be identical to that of Nd2O3.

Children of Low Socioeconomic Status Show Accelerated Linear Growth in Early Childhood; Results from the Generation R Study

PubMed Central

Silva, Lindsay M.; van Rossem, Lenie; Jansen, Pauline W.; Hokken-Koelega, Anita C. S.; Moll, Henriëtte A.; Hofman, Albert; Mackenbach, Johan P.; Jaddoe, Vincent W. V.; Raat, Hein

2012-01-01

Objectives People of low socioeconomic status are shorter than those of high socioeconomic status. The first two years of life being critical for height development, we hypothesized that a low socioeconomic status is associated with a slower linear growth in early childhood. We studied maternal educational level (high, mid-high, mid-low, and low) as a measure of socioeconomic status and its association with repeatedly measured height in children aged 0–2 years, and also examined to what extent known determinants of postnatal growth contribute to this association. Methods This study was based on data from 2972 mothers with a Dutch ethnicity, and their children participating in The Generation R Study, a population-based cohort study in Rotterdam, the Netherlands (participation rate 61%). All children were born between April 2002 and January 2006. Height was measured at 2 months (mid-90% range 1.0–3.9), 6 months (mid-90% range 5.6–11.4), 14 months (mid-90% range 13.7–17.9) and 25 months of age (mid-90% range 23.6–29.6). Results At 2 months, children in the lowest educational subgroup were shorter than those in the highest (difference: −0.87 cm; 95% CI: −1.16, −0.58). Between 1 and 18 months, they grew faster than their counterparts. By 14 months, children in the lowest educational subgroup were taller than those in the highest (difference at 14 months: 0.40 cm; 95% CI: 0.08,0.72). Adjustment for other determinants of postnatal growth did not explain the taller height. On the contrary, the differences became even larger (difference at 14 months: 0.61 cm; 95% CI: 0.26,0.95; and at 25 months: 1.00 cm; 95% CI: 0.57,1.43) Conclusions Compared with children of high socioeconomic status, those of low socioeconomic status show an accelerated linear growth until the18th month of life, leading to an overcompensation of their initial height deficit. The long-term consequences of these findings remain unclear and require further study. PMID:22649522

Probing the Electronic Structure of - and Electron-Doped High-Temperature Superconductors with Photoemission and X-Ray Absorption Spectroscopies

NASA Astrophysics Data System (ADS)

Lederman, Eli R.

1990-01-01

The electronic structures of hole- and electron -doped high temperature superconductors have been probed using x-ray absorption near-edge spectroscopy (XANES) and photoelectron emission spectroscopy (PES). These measurements have been performed on RBa_2Cu _3O_{rm 7-y} , La_{rm 2-x}Sr _{rm x}CuO _4 and Ln_{rm 2 -x}Ce_{rm x} CuO_{rm 4} for R = Y, Eu and Ln = Nd, Pr and Sm. The parameters x and y have been varied to include a range of hole and electron carrier densities and the undoped parent compounds. Previous XANES and PES results have indicated that unoccupied states of O 2p character can be associated with the carriers in the materials RBa_2 Cu_3O_{ rm 7-y} and La_{ rm 2-x}Sr_{rm x}CuO_4 and that the density of holes increases with O and Sr content, respectively. Conduction was hole-based in all known high-T_{ rm c} cuprates until the recent discovery of superconductivity in Ln_{rm 2-x}Ce_{rm x} CuO_4. Hall coefficient measurements have suggested that the carriers in this system are electrons added with Ce doping. It has been anticipated that these electron-doped materials will provide an important test for models of high temperature superconductivity. PES measurements are presented that show significant Cu 3d character in the valence band of these electron-based materials, but that the Cu^{2+} /Cu^{1+} ratio is unchanged by the level of Ce doping, indicating that doped electrons are itinerant rather than highly correlated. Resonant photoemission from the valence band indicates the presence of unoccupied O 2p states, but these holes are less abundant than in the hole-doped materials. Measurements of XANES at the O 1s edge suggest that unoccupied states of O 2p character in the electron -doped materials are not related to conduction in a simple way. The density of these holes is shown to decrease upon Ce doping and the process of reduction, despite the fact that both are necessary of superconductivity. Furthermore, whereas the O 2p holes are at E_{rm F} in the

X-Ray absorption spectroscopy quantitative analysis of biomimetic copper(II) complexes with tridentate nitrogen ligands mimicking the tris(imidazole) array of protein centres.

PubMed

Borghi, Elena; Casella, Luigi

2010-02-21

In this study copper(ii) complexes with the tridentate nitrogen ligand bis[2-(1-methylbenzimidazol-2-yl)ethyl]amine (2-BB) are considered as model compounds for the Cu-tris(imidazole) array found in several copper proteins. 2-BB chelates copper(ii) forming two six-membered rings and the complexes contain methanol, nitrite, azide and water as ancillary ligands; both the coordination numbers and stereochemistries differ in these complexes. Their key structural features were investigated by using full multiple-scattering theoretical analysis of the copper K-edge X-ray absorption spectrum with the MXAN code. We showed that using cluster sizes large enough to include all atoms of the ligand, the analysis of the XANES region can give both a structural model of the metal centre and map the structure of the 2-BB complexes. Complex [Cu(2-BB)(N(3))](+) provided a critical test through the comparison of the XANES simulation results with crystallographic data, thus permitting the extension of the method to the complex [Cu(2-BB)(H(2)O)(n)](+) (n = 1 or 2), for which crystallographic data are not available but is expected to bear a five-coordinated Cu(3N)(2O) core (n = 2). The structural data of [Cu(2-BB)(MeOH)(ClO(4))](+) and [Cu(2-BB)(NO(2))](+), both with a Cu(3N)(2O) core but with a different stereochemistry, were used as the starting parameters for two independent simulations of the XANES region of the [Cu(2-BB)(H(2)O)(2)](+) cation. The two structural models generated by simulation converge towards a structure for the aqua-cation with a lower coordination number. New calculations, where four-coordinated Cu(3N)(O) cores were considered as the starting structures, validated that the structure of the aqua-complex in the powder state has a copper(ii) centre with a four-coordinated Cu(3N)(O) core and a molecular formula [Cu(2-BB)(H(2)O)](ClO(4)).(H(2)O). A water solvation molecule, presumed to be disordered from the simulations with the two Cu(3N)(2O) cores, is present. The

The photodegradation of cadmium yellow paints in Henri Matisse's Le Bonheur de vivre (1905-1906)

NASA Astrophysics Data System (ADS)

Mass, Jennifer L.; Opila, Robert; Buckley, Barbara; Cotte, Marine; Church, Jonathan; Mehta, Apurva

2013-04-01

Evidence for the alteration of the yellow paints in Henri Matisse's Le Bonheur de vivre (1905-1906, The Barnes Foundation) has been observed since the 1990s. The changes in this iconic work of Matisse's Fauvist period include lightening, darkening, and flaking of the yellow paints. Handheld X-ray fluorescence (XRF) and multispectral imaging surveys reveal that the degradation is confined to cadmium yellow (CdS) paints. The discoloration of cadmium yellow paints in Impressionist, Post-Impressionist and early modernist work from the 1880s through the 1920s has been ascribed to the photo-oxidative degradation of CdS. Preliminary investigations of the degraded yellow paints in this work involved Cd LIII-edge X-ray Absorption Near Edge Spectroscopy (XANES) at the Stanford Synchrotron Radiation Light Source (SSRL Menlo Park, California) and Scanning Electron Microscopy-energy dispersive X-ray analysis (SEM-EDS) at the Winterthur Museum Scientific Research and Analysis Laboratory. To determine if the visual changes in the paints did in fact indicate photo-oxidative degradation and if different chemistries could be observed for the lightened versus darkened regions, synchrotron radiation-micro Fourier Transform InfraRed (SR-μFTIR) spectroscopy, X-ray Fluorescence (SR-μXRF) mapping and micro X-ray Absorption Near Edge Spectroscopy (μXANES) mapping at the Cd LIII-edge of the altered paint cross-sections were carried out at the European synchrotron radiation facility (ESRF, Grenoble, France) beamline ID-21. The goal is to elucidate the discoloration mechanisms observed in the paint using elemental and speciation mapping. The μXANES mapping and SR-FTIR imaging showed a substantial enrichment of CdCO3 in the off-white surface crust of the faded/discolored CdS paint. This suggests that the CdCO3 is present as an insoluble photodegradation product rather than solely a paint filler or starting reagent. Additionally, oxalates and sulfates were found to be concentrated at the

Talk Show Science.

ERIC Educational Resources Information Center

Moore, Mitzi Ruth

1992-01-01

Proposes having students perform skits in which they play the roles of the science concepts they are trying to understand. Provides the dialog for a skit in which hot and cold gas molecules are interviewed on a talk show to study how these properties affect wind, rain, and other weather phenomena. (MDH)

Microbial reduction of uranium (VI) by Bacillus sp. dwc-2: A macroscopic and spectroscopic study.

PubMed

Li, Xiaolong; Ding, Congcong; Liao, Jiali; Du, Liang; Sun, Qun; Yang, Jijun; Yang, Yuanyou; Zhang, Dong; Tang, Jun; Liu, Ning

2017-03-01

The microbial reduction of U(VI) by Bacillus sp. dwc-2, isolated from soil in Southwest China, was explored using transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and X-ray absorption near edge spectroscopy (XANES). Our studies indicated that approximately 16.0% of U(VI) at an initial concentration of 100mg/L uranium nitrate could be reduced by Bacillus sp. dwc-2 at pH8.2 under anaerobic conditions at room temperature. Additionally, natural organic matter (NOM) played an important role in enhancing the bioreduction of U(VI) by Bacillus sp. dwc-2. XPS results demonstrated that the uranium presented mixed valence states (U(VI) and U(IV)) after bioreduction, which was subsequently confirmed by XANES. Furthermore, the TEM and high resolution transmission electron microscopy (HRTEM) analysis suggested that the reduced uranium was bioaccumulated mainly within the cell and as a crystalline structure on the cell wall. These observations implied that the reduction of uranium may have a significant effect on its fate in the soil environment in which these bacterial strains occur. Copyright © 2016. Published by Elsevier B.V.

Relating electronic and geometric structure of atomic layer deposited BaTiO 3 to its electrical properties

DOE PAGES

Torgersen, Jan; Acharya, Shinjita; Dadlani, Anup Lal; ...

2016-03-24

Atomic layer deposition allows the fabrication of BaTiO 3 (BTO) ultrathin films with tunable dielectric properties, which is a promising material for electronic and optical technology. Industrial applicability necessitates a better understanding of their atomic structure and corresponding properties. Through the use of element-specific X-ray absorption near edge structure (XANES) analysis, O K-edge of BTO as a function of cation composition and underlying substrate (RuO 2 and SiO 2) is revealed. By employing density functional theory and multiple scattering simulations, we analyze the distortions in BTO’s bonding environment captured by the XANES spectra. The spectral weight shifts to lower energymore » with increasing Ti content and provides an atomic scale (microscopic) explanation for the increase in leakage current density. Differences in film morphologies in the first few layers near substrate–film interfaces reveal BTO’s homogeneous growth on RuO 2 and its distorted growth on SiO 2. As a result, this work links structural changes to BTO thin-film properties and provides insight necessary for optimizing future BTO and other ternary metal oxide-based thin-film devices.« less

Damage and annealing recovery of boron-implanted ultra-shallow junction: The correlation between beam current and surface configuration

NASA Astrophysics Data System (ADS)

Chang, Feng-Ming; Wu, Zong-Zhe; Lin, Yen-Fu; Kao, Li-Chi; Wu, Cheng-Ta; JangJian, Shiu-Ko; Chen, Yuan-Nian; Lo, Kuang Yao

2018-03-01

The condition of the beam current in the implantation process is a key issue in the damage rate and structural evolution in the sequent annealing process, especially for ultra-shallow layers. In this work, we develop a compensative optical method combined with UV Raman, X-ray photoelectron spectroscopy (XPS), and X-ray absorption near edge spectroscopy (XANES) to inspect the influence of the beam current in the implantation process. The optima condition of the beam current in the implantation process is determined by higher effective Si-B bond portion in UV Raman spectra and less the peak of B-B bond in XPS spectra which is caused by B cluster defects. Results of XANES indicate that the B oxide layer is formed on the surface of the ultra-shallow junction. The defects in the ultra-shallow junction after annealing are analyzed by novel optical analyses, which cannot be inspected by a traditional thermal wave and resistance measurement. This work exhibits the structural variation of the ultra-shallow junction via a variant beam current and provides a valuable metrology in examining the chemical states and the effective activation in the implantation technology.

X-ray absorption near-edge structure micro-spectroscopy study of vanadium speciation in Phycomyces blakesleeanus mycelium.

PubMed

Žižić, Milan; Dučić, Tanja; Grolimund, Daniel; Bajuk-Bogdanović, Danica; Nikolic, Miroslav; Stanić, Marina; Križak, Strahinja; Zakrzewska, Joanna

2015-09-01

Vanadium speciation in the fungus Phycomyces blakesleeanus was examined by X-ray absorption near-edge structure (XANES) spectroscopy, enabling assessment of oxidation states and related molecular symmetries of this transition element in the fungus. The exposure of P. blakesleeanus to two physiologically important vanadium species (V(5+) and V(4+)) resulted in the accumulation of this metal in central compartments of 24 h old mycelia, most probably in vacuoles. Tetrahedral V(5+), octahedral V(4+), and proposed intracellular complexes of V(5+) were detected simultaneously after addition of a physiologically relevant concentration of V(5+) to the mycelium. A substantial fraction of the externally added V(4+) remained mostly in its original form. However, observable variations in the pre-edge-peak intensities in the XANES spectra indicated intracellular complexation and corresponding changes in the molecular coordination symmetry. Vanadate complexation was confirmed by (51)V NMR and Raman spectroscopy, and potential binding compounds including cell-wall constituents (chitosan and/or chitin), (poly)phosphates, DNA, and proteins are proposed. The evidenced vanadate complexation and reduction could also explain the resistance of P. blakesleeanus to high extracellular concentrations of vanadium.

Phase Changes of Monosulfoaluminate in NaCl Aqueous Solution

DOE PAGES

Yoon, Seyoon; Ha, Juyoung; Chae, Sejung Rosie; ...

2016-05-21

Monosulfoaluminate (Ca 4Al 2(SO 4)(OH) 12∙6H 2O) plays an important role in anion binding in Portland cement by exchanging its original interlayer ions (SO 4 2- and OH -) with chloride ions. In this study, scanning transmission X-ray microscope (STXM), X-ray absorption near edge structure (XANES) spectroscopy, and X-ray diffraction (XRD) were used to investigate the phase change of monosulfoaluminate due to its interaction with chloride ions. Pure monosulfoaluminate was synthesized and its powder samples were suspended in 0, 0.1, 1, 3, and 5 M NaCl solutions for seven days. At low chloride concentrations, a partial dissolution of monosulfoaluminate formedmore » ettringite, while, with increasing chloride content, the dissolution process was suppressed. As the NaCl concentration increased, the dominant mechanism of the phase change became ion exchange, resulting in direct phase transformation from monosulfoaluminate to Kuzel’s salt or Friedel’s salt. The phase assemblages of the NaCl-reacted samples were explored using thermodynamic calculations and least-square linear combination (LC) fitting of measured XANES spectra. A comprehensive description of the phase change and its dominant mechanism are discussed.« less

X-ray absorption spectroscopic studies on gold nanoparticles in mesoporous and microporous materials.

PubMed

Akolekar, Deepak B; Foran, Garry; Bhargava, Suresh K

2004-05-01

Au L(3)-edge X-ray absorption spectroscopic measurements were carried out over a series of mesoporous and microporous materials containing gold nanoparticles to investigate the effects of the host matrix and preparation methods on the properties of gold nanoparticles. The materials of structure type MCM-41, ZSM-5, SAPO-18 and LSX with varying framework composition containing low concentrations of gold nanoparticles were prepared and characterized. In these materials the size of the gold nanoparticles varied in the range approximately 1 to 4 nm. A series of gold nanoparticles within different mesoporous and microporous materials have been investigated using X-ray absorption fine structure (XANES, EXAFS) and other techniques. Information such as atomic distances, bonding and neighbouring environment obtained from XAFS measurements was useful in elucidating the nature and structure of gold nanoparticles on these catalytic materials. The influence of the high-temperature (823, 1113, 1273 K) treatment on gold nanoparticles inside the mesoporous matrix was investigated using the XAFS technique. The XAFS and XANES results confirm various characteristics of gold nanoparticles in these materials suitable for catalysis, fabrication of nanodevices and other applications.

Obesity in show cats.

PubMed

Corbee, R J

2014-12-01

Obesity is an important disease with a high prevalence in cats. Because obesity is related to several other diseases, it is important to identify the population at risk. Several risk factors for obesity have been described in the literature. A higher incidence of obesity in certain cat breeds has been suggested. The aim of this study was to determine whether obesity occurs more often in certain breeds. The second aim was to relate the increased prevalence of obesity in certain breeds to the official standards of that breed. To this end, 268 cats of 22 different breeds investigated by determining their body condition score (BCS) on a nine-point scale by inspection and palpation, at two different cat shows. Overall, 45.5% of the show cats had a BCS > 5, and 4.5% of the show cats had a BCS > 7. There were significant differences between breeds, which could be related to the breed standards. Most overweight and obese cats were in the neutered group. It warrants firm discussions with breeders and cat show judges to come to different interpretations of the standards in order to prevent overweight conditions in certain breeds from being the standard of beauty. Neutering predisposes for obesity and requires early nutritional intervention to prevent obese conditions. Journal of Animal Physiology and Animal Nutrition © 2014 Blackwell Verlag GmbH.

Solvation structure of the halides from x-ray absorption spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Antalek, Matthew; Hedman, Britt; Sarangi, Ritimukta, E-mail: ritis@slac.stanford.edu

2016-07-28

Three-dimensional models for the aqueous solvation structures of chloride, bromide, and iodide are reported. K-edge extended X-ray absorption fine structure (EXAFS) and Minuit X-ray absorption near edge (MXAN) analyses found well-defined single shell solvation spheres for bromide and iodide. However, dissolved chloride proved structurally distinct, with two solvation shells needed to explain its strikingly different X-ray absorption near edge structure (XANES) spectrum. Final solvation models were as follows: iodide, 8 water molecules at 3.60 ± 0.13 Å and bromide, 8 water molecules at 3.40 ± 0.14 Å, while chloride solvation included 7 water molecules at 3.15 ± 0.10 Å, andmore » a second shell of 7 water molecules at 4.14 ± 0.30 Å. Each of the three derived solvation shells is approximately uniformly disposed about the halides, with no global asymmetry. Time-dependent density functional theory calculations simulating the chloride XANES spectra following from alternative solvation spheres revealed surprising sensitivity of the electronic state to 6-, 7-, or 8-coordination, implying a strongly bounded phase space for the correct structure during an MXAN fit. MXAN analysis further showed that the asymmetric solvation predicted from molecular dynamics simulations using halide polarization can play no significant part in bulk solvation. Classical molecular dynamics used to explore chloride solvation found a 7-water solvation shell at 3.12 (−0.04/+0.3) Å, supporting the experimental result. These experiments provide the first fully three-dimensional structures presenting to atomic resolution the aqueous solvation spheres of the larger halide ions.« less

The Inhibition of Pb(IV) Oxide Formation in Chlorinated Water by Orthophosphate

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lytle, Darren A.; Schock, Michael R.; Scheckel, Kirk

2009-10-05

Historically, understanding lead solubility and its control in drinking water has been based on Pb(II) chemistry. Unfortunately, there is very little information available regarding the nature of Pb(IV) oxides in finished drinking water and water distribution systems, and the conditions under which they persist. The objective of this research was to explore the impact of orthophosphate on the realistic pathways that lead to the formation of Pb(IV) oxides in chlorinated water. The results of XRD and XANES analysis showed that, in the absence of orthophosphate (DIC = 10 mg C/L, 24 C, pH 7.75-8.1, 3 mg Cl{sub 2}/L goal), Pb(IV)more » oxides formed with time following a transformation from the Pb(II) mineral hydrocerussite. Under the same experimental conditions, orthophosphate dosing inhibited the formation of Pb(IV) oxides. The Pb(II) mineral hydroxypyromorphite, Pb{sub 5}(PO{sub 4}){sub 3}OH, was the only mineral phase identified during the entire study of over 600 days, although the presence of some chloropyromorphite, Pb{sub 5}(PO{sub 4}){sub 3}Cl, could not be ruled out. The conclusions were further supported by SEM, TEM, and XANES analysis of lead colloids, and lead precipitation experiments conducted in the absence of free chlorine. The findings provide an important explanation for the absence of Pb(IV) oxides in some water systems that have used, or currently use, orthophosphate for corrosion control when otherwise, based on disinfection practices and water quality, its presence would be anticipated, as well as why the conversion from free chlorine to chloramines was not observed to increase lead release.« less

Showing and Telling Farming: Agricultural Shows and Re-Imaging British Agriculture

ERIC Educational Resources Information Center

Holloway, Lewis

2004-01-01

Some actors in the ''mainstream'' agricultural sector are beginning to engage in strategies of influencing public perceptions of farming, responding to public anxieties over industrialised agriculture and to a supposed separation of non-farming publics from food production. This paper focuses on agricultural shows as sites and events central to…

Investigation of the Structural Stability of Ion-Implanted Gd 2Ti 2-xSn xO 7 Pyrochlore-Type Oxides by Glancing Angle X-ray Absorption Spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aluri, Esther Rani; Hayes, John R.; Walker, James D.S.

2016-03-24

Rare-earth titanate and stannate pyrochlore-type oxides have been investigated in the past for the sequestration of nuclear waste elements because of their resistance to radiation-induced structural damage. In order to enhance this property, it is necessary to understand the effect of radioactive decay of the incorporated actinide elements on the local chemical environment. In this study, Gd 2Ti 2–xSn xO 7 materials have been implanted with Au– ions to simulate radiation-induced structural damage. Glancing angle X-ray absorption near-edge spectroscopy (GA-XANES), glancing angle X-ray absorption fine structure (GA-EXAFS) analysis, and powder X-ray diffraction have been used to investigate changes in themore » local coordination environment of the metal atoms in the damaged surface layer. Examination of GA-XANES/EXAFS spectra from the implanted Gd 2Ti 2–xSn xO 7 materials collected at various glancing angles allowed for an investigation of how the local coordination environment around the absorbing atoms changed at different depths in the damaged surface layer. This study has shown the usefulness of GA-XANES to the examination of ion-implanted materials and has suggested that Gd 2Ti 2–xSn xO 7 becomes more susceptible to ion-beam-induced structural damage with increasing Sn concentration.« less

Structural reconstruction of the catalytic center of LiPDF through multiple scattering calculation with MXAN

NASA Astrophysics Data System (ADS)

Guo, Xiaoyun; Chu, Wangsheng; Ma, Sixuan; Gong, Weimin; Benfatto, Maurizio; Hu, Tiandou; Xie, Yaning; Wu, ZiYu

2006-11-01

Peptide deformylase (PDF, EC 3.5.1.27) is essential for the normal growth of eubacterium but not for mammalians. Recently, PDF has been studied as a target for new antibiotics. In this paper, X-ray absorption spectroscopy was employed to determine the local structure around the zinc ion of PDF from Leptospira Interrogans in dry powder, because it is very difficult to obtain the crystallized sample of LiPDF. We performed X-ray absorption near edge structure (XANES) calculation and reconstructed successfully the local geometry of the active center, and the results from calculations show that a water molecule (Wat1) has moved towards the zinc ion and lies in the distance range to coordinate with the zinc ion weakly. In addition, the sensitivity of theoretical spectra to the different ligand bodies was evaluated in terms of goodness-of-fit.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mukerjee, S.; McBreen, J.; Srinivasan, S.

Electrocatalysis for the oxygen reduction reaction (ORR) on five binary Pt alloy electrocatalysts (PtCr/C, PtMn/C, PtFe/C, PtCo/C and PtNi/C) supported on carbon have been investigated. The electrochemical characteristics for ORR in a proton conducting fuel cell environment has been correlated with the electronic and structural parameters determined under in situ conditions using XANES and EXAFS technique respectively. Results indicate that all the alloys possess higher Pt 5d band vacancies as compared to Pt/C. There is also evidence of lattice contraction in the alloys (supported by XRD results). Further, the Pt/C shows increase in Pt 5 d band vacancies during potentialmore » transitions from 0.54 to 0.84 V vs. RHE, which has been ration@ on the basis of OH type adsorption. In contrast to this, the alloys do not exhibit such an enhancement. Detailed EXAFS analysis supports the presence of OH species on Pt/C and its relative absence in the alloys. Correlation of the electrochemical results with bond distances and d-band vacancies show a volcano type behavior with the PtCr/C on top of the curve.« less

Micron to Mine: Synchrotron Science for Mineral Exploration, Production, and Remediation

NASA Astrophysics Data System (ADS)

Banerjee, N.; Van Loon, L.; Flynn, T.

2017-12-01

Synchrotron science for mineral exploration, production, and remediation studies is a powerful tool that provides industry with relevant micron to macro geochemical information. Synchrotron micro X-ray fluorescence (SR-µXRF) offers a direct, high-resolution, rapid, and cost-effective chemical analysis while preserving the context of the sample by mapping ore minerals with ppm detection limits. Speciation of trace and deleterious elements can then be probed using X-ray absorption near-edge structure (XANES) spectroscopy. Large-scale (tens of cm) µXRF mapping and XANES analysis of samples collected at various mine locations have been undertaken to address questions regarding mineralization history to develop novel trace element exploration vectors. This information provides integral insights into trace element associations with ore minerals, local redox conditions responsible for mineralization, and mineralizing mechanisms. Gold is commonly intimately associated with sulfide mineralization (e.g., pyrite, arsenopyrite, etc.) and is present both as inclusions and filling fractures in sulfide grains. Gold may also occur as nanoparticles and/or in the sulfide mineral crystal lattice, known as "invisible gold". Understanding the nature and distribution of invisible gold in ore is integral to processing efficiency. The high flux and energy of a synchrotron light source allows for the detection of invisible gold by µXRF, and can probe its nature (metallic Au0 vs. lattice bound Au1+) using XANES spectroscopy. The long-term containment and management of arsenic is necessary to protect the health of both humans and the environment. Understanding the relationship of arsenic mineralization to gold deposits can lead to more sophisticated planning for mineral processing and the eventual storage of gangue materials. µXANES spectroscopy is an excellent tool for determining arsenic speciation within the context of the sample. Mineral phases such as arsenopyrite, scorodite, and

Classroom Assessments of 6000 Teachers: What Do the Results Show about the Effectiveness of Teaching and Learning?

ERIC Educational Resources Information Center

Hill, Flo H.; And Others

This paper presents the results of a series of summary analyses of descriptive statistics concerning 5,720 Louisiana teachers who were assessed with the System for Teaching and Learning Assessment and Review (STAR)--a comprehensive on-the-job statewide teacher assessment system--during the second pilot year (1989-90). Data were collected by about…

Learning from a dive show in an aquarium setting

NASA Astrophysics Data System (ADS)

Walsh, Lori M.

A study was conducted at an aquarium next to a theme park to understand information recalled from two versions of shows viewed at the largest display. The goal of this research was to determine if learning was enhanced by having a diver in water as the treatment group. This project focused on the knowledge recalled about shark and ray feeding adaptations, the information recalled about the mentioned conservation message about sustainable seafood and the potential of the two shows to make memorable experiences. During the project, 30 adult participants from each group were given a survey with five open-ended questions. Results suggest that the diver might distract from biological content information, or that the diver is such a novel element that it interferes with recall. While guests seemed to recall information about rays and sharks, the amount of information was not substantial. It appears that the diver does not affect content messaging but does impact whether guests attend to Seafood Watch messaging. The diver may have been so novel that the treatment group could not attend to the conservation message that was delivered, regardless of topic, or the control group recalled the message because the guests were not distracted by the diver or feeding. The absence of a diver seems to allow the guests to better attend to what is happening outside of the tank. While adding a diver increases photo opportunities and may bring guests to a show, the results seem to indicate that it does not significantly increase recall. The results of this study show that guests in a theme park setting can recall information from an educational program. Guests may not enter this hybrid aquarium with the intention of learning, but recall, one of the components in learning, does occur.

Reaction of YBa2Cu3O(7-beta) with Gold, Silver, Bismuth and Lead: Substitution Chemistry and Composite Fabrication

NASA Technical Reports Server (NTRS)

Hepp, Aloysius F.; Gaier, James R.

1993-01-01

The reaction of YBa2Cu3O(7-beta) with Au, Ag, Bi, and Ph ions or metal is described. Three types of materials were produced: a well-defined series of homogeneous superconductors was obtained for Au ion substitution with little effect on T(sub c); attempted Ag and Bi ion substitution resulted in multi-phase samples with slightly enhanced T(sub c); finally, attempts to produce superconducting metal/superconducting ceramic composites with Pb and Bi powders resulted in multi-phase samples with drastically diminished superconducting properties. For Au- substituted superconductors, YBa2(Cu(l-x)Au(x))3O(7-beta), a substitution series (x = 0 - 0.1) has been synthesized. For x = 0.1 there was no change in the a and b lattice parameters (a = 3.826 A and b = 3.889 A) but a 0.06 A c axis expansion to 11.75 A was observed. The valence of Cu and Au in YBa2Au(0.3)Cu(2.7)O(7-beta) was investigated using X-ray Absorption Near-Edge Structure (XANES). X-ray studies indicate that Au goes into the Cu(l) site and Cu K edge XANES shows that this has little effect on the oxidation state of the remaining copper. A small effect on T(sub c) is observed (T(sub c) = 89 K for x = 0.10). Ag and Bi addition results in a rise in T(sub c) and a decrease in (delta)T(sub c) at low levels (x = 0.10 Ag, T(sub c) = 94 K and (delta)T(sub c) = 0.5 K; x = 0.02 Bi, T(sub c) = 94 K and (delta)T(sub c) = 1K) relative to typical values for YBa2Cu3O(7-beta) (T(sub c) = 91 K, (delta)T(sub c) = 2 K). Attempts at fabrication of Pb- and Pb(1-x)Bi(x)-superconductor composites are described. Cold pressing followed by low temperature (200 C) sintering resulted in a composite which excluded flux below 90 K but did not show zero electrical resistance until the metal (alloy) superconducting transition. X-ray diffraction showed the presence of pervoskite and metal. Processing at moderate (450 C) or high (950 C) temperatures resulted in oxygen-depleted pervoskite and/or metal oxides. These materials displayed greatly

Correlating the degree of metal–promoter interaction to ethanol selectivity over MnRh/CNTs CO hydrogenation catalysts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Jingjing; Guo, Zhao; Childers, David

2014-05-01

Multi-walled carbon nanotubes (MCNTs) were used as a support for Rh-based catalysts for high pressure (20 bar) CO hydrogenation. 3 wt% Rh/CNTs catalysts were loaded with 1 wt% and 2 wt% Mn promoter, respectively, in order to study the effect of metal–promoter interactions for ethanol synthesis. Both STEM and EXAFS results showed ≈1 nm Rh particles in promoted as well as the unpromoted catalysts, STEM and EELS results verified the enhanced metal–promoter interaction when the amount of Mn promoter increased from 1 wt% to 2 wt%. The enhancement in the degree of metal–promoter interaction leads to an increase in themore » ethanol selectivity. Moreover, due to the nature of CNTs (low Z number), the Mn–Rh interactions could be observed at atomic resolution during the STEM–EELS characterization, and the promoter phase is confirmed as Mn(II) oxide by XANES and EELS.« less

Investigating the local structure of B-site cations in (1-x)BaTiO3-xBiScO3 and (1-x)PbTiO3-xBiScO3 using X-ray absorption spectroscopy

NASA Astrophysics Data System (ADS)

Blanchard, Peter E. R.; Grosvenor, Andrew P.

2018-05-01

The structural properties of (1-x)BaTiO3-xBiScO3 and (1-x)PbTiO3-xBiScO3 were investigated using powder X-ray diffraction and X-ray absorption spectroscopy. Diffraction measurements confirmed that substituting small amounts of BiScO3 into BaTiO3 initially stabilizes a cubic phase at x = 0.2 before impurity phases begin to form at x = 0.5. BiScO3 substitution also resulted in noticeable changes in the local coordination environment of Ti4+. X-ray absorption near-edge spectroscopy (XANES) analysis showed that replacing Ti4+ with Sc3+ results in an increase in the off-centre displacement of Ti4+ cations. Surprisingly, BiScO3 substitution has no effect on the displacement of the Ti4+ cation in the (1-x)PbTiO3-xBiScO3 solid solution.

Ferrate (IV) as a Possible Oxidant on the Martian Surface

NASA Astrophysics Data System (ADS)

Tsapin, Alexandre; Goldfeld, M. G.; McDonald, G. D.; Nealson, K. H.; Mohnke, J.; Moskovitz, B.; Solheid, P.; Kemner, K. H.; Orlandini, K.

Viking experiments showed that Martian soil has a very strong oxidant, which could be responsible for the results of experiments performed on Viking landers. These experiments were designed specifically to detect life on Mars. The nature of that oxidant was not determined during Viking mission. Later several groups tried to reconstruct Viking experiments and find out the nature of Martian oxidant. None of these attempts were completely successful. The general perception was that there are several chemically different oxidants on Martian surface. In this study we suggested that potassium ferrate K_2FeO_4 can be Martian oxidant responsible at least partially for the results of experiments on Viking landers. We characterized liquid and powder preparation of Fe (VI) with EPR, optical spectroscopy, Mossbauer spectroscopy, and by Fe-XANES. All properties of our preparations of (FeVI) are consistent with the proposal role of that compound as a strong oxidant on Martian surface.

Microanalysis of iron oxidation states in earth and planetary materials

NASA Astrophysics Data System (ADS)

Bajt, S.; Sutton, S. R.; Delaney, J. S.

1995-02-01

Initial studies have been made on quantifying Fe oxidation states in different iron-bearing minerals using K-edge XANES. The energy of a weak pre-edge peak in the XANES spectrum due to 1s-3d electron transition was used to quantify ferric/ferrous ratios with microprobe spatial resolution. The estimated accuracy of the technique was +/- 10% in terms of Fe3+/((Fe2+ + Fe3+)). The detection limit was ~ 100 ppm with a synchrotron beam of ~ 100 μm in diameter. The pre-edge peak energy in well-characterized samples with known Fe oxidation states was found to be a linear function of the ferric/(ferrous) ratio. The technique was applied to altered magnetics (ideally Fe3O4), and various silicates and oxides from meteorites.

Elucidating the Nature of the Excited State of a Heteroleptic Copper Photosensitizer by using Time-Resolved X-ray Absorption Spectroscopy.

PubMed

Moonshiram, Dooshaye; Garrido-Barros, Pablo; Gimbert-Suriñach, Carolina; Picón, Antonio; Liu, Cunming; Zhang, Xiaoyi; Karnahl, Michael; Llobet, Antoni

2018-04-25

We report the light-induced electronic and geometric changes taking place within a heteroleptic Cu I photosensitizer, namely [(xant)Cu(Me 2 phenPh 2 )]PF 6 (xant=xantphos, Me 2 phenPh 2 =bathocuproine), by time-resolved X-ray absorption spectroscopy in the ps-μs time regime. Time-resolved X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) analysis enabled the elucidation of the electronic and structural configuration of the copper center in the excited state as well as its decay dynamics in different solvent conditions with and without triethylamine acting as a sacrificial electron donor. A three-fold decrease in the decay lifetime of the excited state is observed in the presence of triethylamine, showing the feasibility of the reductive quenching pathway in the latter case. A prominent pre-edge feature is observed in the XANES spectrum of the excited state upon metal to charge ligand transfer transition, showing an increased hybridization of the 3d states with the ligand p orbitals in the tetrahedron around the Cu center. EXAFS and density functional theory illustrate a significant shortening of the Cu-N and an elongation of the Cu-P bonds together with a decrease in the torsional angle between the xantphos and bathocuproine ligand. This study provides mechanistic time-resolved understanding for the development of improved heteroleptic Cu I photosensitizers, which can be used for the light-driven production of hydrogen from water. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Bone apatite composition of necrotic trabecular bone in the femoral head of immature piglets.

PubMed

Aruwajoye, Olumide O; Kim, Harry K W; Aswath, Pranesh B

2015-04-01

Ischemic osteonecrosis of the femoral head (IOFH) can lead to excessive resorption of the trabecular bone and collapse of the femoral head as a structure. A well-known mineral component to trabecular bone is hydroxyapatite, which can be present in many forms due to ionic substitution, thus altering chemical composition. Unfortunately, very little is known about the chemical changes to bone apatite following IOFH. We hypothesized that the apatite composition changes in necrotic bone possibly contribute to increased osteoclast resorption and structural collapse of the femoral head. The purpose of this study was to assess the macroscopic and local phosphate composition of actively resorbed necrotic trabecular bone to isolate differences between areas of increased osteoclast resorption and normal bone formation. A piglet model of IOFH was used. Scanning electron microscopy (SEM), histology, X-ray absorbance near edge structure (XANES), and Raman spectroscopy were performed on femoral heads to characterize normal and necrotic trabecular bone. Backscattered SEM, micro-computed tomography and histology showed deformity and active resorption of necrotic bone compared to normal. XANES and Raman spectroscopy obtained from actively resorbed necrotic bone and normal bone showed increased carbonate-to-phosphate content in the necrotic bone. The changes in the apatite composition due to carbonate substitution may play a role in the increased resorption of necrotic bone due to its increase in solubility. Indeed, a better understanding of the apatite composition of necrotic bone could shed light on osteoclast activity and potentially improve therapeutic treatments that target excessive resorption of bone.

Radar Shows Evidence of Seas

NASA Image and Video Library

2007-03-13

This movie, comprised of several detailed images taken by Cassini radar instrument, shows bodies of liquid near Titan north pole. These images show that many of the features commonly associated with lakes on Earth

Evidence for an unorthodox firing sequence employed by the Berlin Painter. Deciphering ancient ceramic firing conditions through high-resolution material characterization and replication

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cianchetta, I.; Trentelman, K.; Maish, J.

XANES spectroscopy was used to complement the results previously obtained with Raman spectroscopy by the same group to determine the firing conditions used in the production of a single vessel painted by the Berlin Painter in the 5th century B.C. The vessel, part of the collection of the J. Paul Getty Museum, presents a complicated layered architecture of black and red gloss, with different stratigraphies present on the interior and exterior surfaces. The study of two samples, one each from the interior and exterior surface of the vessel, was performed with the complementary analytical techniques of X-ray nano- and micro-spectroscopymore » (X-ray fluorescence spectroscopy (XRF) and full-field transmission X-ray micro-spectroscopy (FF-XANES) across the Fe K edge), and supported by a replication study. The replicates, made in a laboratory furnace providing complete control over the firing temperature and oxygen partial pressure, provided a paradigm for the comparison of the mineralogical phases observed in the ancient samples, which led to a deeper understanding of the firing conditions necessary for the production of the Berlin Painter's vessel. Our results confirm the necessity of multiple firings and painting applications to obtain the Berlin Painter's architecture and provide a further example of the multiplicity of techniques and practices employed by the potters of the Kerameikos in ancient Athens.« less

Effect of iron oxide reductive dissolution on the transformation and immobilization of arsenic in soils: New insights from X-ray photoelectron and X-ray absorption spectroscopy.

PubMed

Fan, Jian-Xin; Wang, Yu-Jun; Liu, Cun; Wang, Li-Hua; Yang, Ke; Zhou, Dong-Mei; Li, Wei; Sparks, Donald L

2014-08-30

The geochemical behavior and speciation of arsenic (As) in paddy soils is strongly controlled by soil redox conditions and the sequestration by soil iron oxyhydroxides. Hence, the effects of iron oxide reductive dissolution on the adsorption, transformation and precipitation of As(III) and As(V) in soils were investigated using batch experiments and synchrotron based techniques to gain a deeper understanding at both macroscopic and microscopic scales. The results of batch sorption experiments revealed that the sorption capacity of As(V) on anoxic soil was much higher than that on control soil. Synchrotron based X-ray fluorescence (μ-XRF) mapping studies indicated that As was heterogeneously distributed and was mainly associated with iron in the soil. X-ray absorption near edge structure (XANES), micro-X-ray absorption near edge structure (μ-XANES) and X-ray photoelectron spectroscopy (XPS) analyses revealed that the primary speciation of As in the soil is As(V). These results further suggested that, when As(V) was introduced into the anoxic soil, the rapid coprecipitation of As(V) with ferric/ferrous ion prevented its reduction to As(III), and was the main mechanism controlling the immobilization of As. This research could improve the current understanding of soil As chemistry in paddy and wetland soils. Copyright © 2014 Elsevier B.V. All rights reserved.

Evidence for an unorthodox firing sequence employed by the Berlin Painter. Deciphering ancient ceramic firing conditions through high-resolution material characterization and replication

DOE PAGES

Cianchetta, I.; Trentelman, K.; Maish, J.; ...

2014-12-10

XANES spectroscopy was used to complement the results previously obtained with Raman spectroscopy by the same group to determine the firing conditions used in the production of a single vessel painted by the Berlin Painter in the 5th century B.C. The vessel, part of the collection of the J. Paul Getty Museum, presents a complicated layered architecture of black and red gloss, with different stratigraphies present on the interior and exterior surfaces. The study of two samples, one each from the interior and exterior surface of the vessel, was performed with the complementary analytical techniques of X-ray nano- and micro-spectroscopymore » (X-ray fluorescence spectroscopy (XRF) and full-field transmission X-ray micro-spectroscopy (FF-XANES) across the Fe K edge), and supported by a replication study. The replicates, made in a laboratory furnace providing complete control over the firing temperature and oxygen partial pressure, provided a paradigm for the comparison of the mineralogical phases observed in the ancient samples, which led to a deeper understanding of the firing conditions necessary for the production of the Berlin Painter's vessel. Our results confirm the necessity of multiple firings and painting applications to obtain the Berlin Painter's architecture and provide a further example of the multiplicity of techniques and practices employed by the potters of the Kerameikos in ancient Athens.« less

Cacodylic acid for precommercial thinning in mixed-conifer stands shows erratic results.

Treesearch

William W. Oliver

1970-01-01

In a small-scale test, a silvicide consisting of cacodylic acid was injected during the growing season at dosages recommended by the manufacturer. The treatment did not thin adequately two of three mixed-conifer stands. Ponderosa pine and lower crown classes seemed more susceptible to the silvicide than Douglas-fir and upper crown classes. No flashback was recognized....

Analysis of organic grain coatings in primitive interplanetary dust particles: Implications for the origin of Solar System organic matter

NASA Astrophysics Data System (ADS)

Flynn, George

Analysis of organic grain coatings in primitive interplanetary dust particles: Implications for the origin of Solar System organic matter Chondritic, porous interplanetary dust particles (CP IDPs), the most primitive samples of extraterrestrial material available for laboratory analysis [1], are unequilibrated aggregates of mostly submicron, anhydrous grains of a diverse mineralogy. They contain organic matter not produced by parent body aqueous processing [2], some carrying H and N isotopic anomalies consistent with molecular cloud or outer Solar System material [3]. Scanning Transmission X-Ray Microscope (STXM) imaging at the C K-edge shows the individual grains in 10 micron aggregate CP IDPs are coated by a layer of carbonaceous material 100 nm thick. This structure implies a three-step formation sequence. First, individual grains condensed from the cooling nebular gas. Then complex, refractory organic molecules covered the surfaces of the grains either by deposition, formation in-situ, or a combination of both processes. Finally, the grains collided and stuck together forming the first dust-size material in the Solar System. Ultramicrotome sections, 70 to 100 nm thick were cut from several CP IDPs, embedded in elemental S to avoid exposure to C-based embedding media. X-ray Absorption Near Edge Structure (XANES) spectra were derived from image stacks obtained using a STXM. "Cluster analysis" was used to compare the C-XANES spectra from each of the pixels in an image stack and identify pixels exhibiting similar spectra. When applied to a CP IDP, cluster analysis identifies most carbonaceous grain coatings in a particle as having similar C-XANES spectra. Two processes are commonly suggested in the literature for production of organic grain coatings. The similarity in thickness and C-XANES spectra of the coatings on different minerals in the same IDP indicates the first, mineral specific catalysis, was not the process that produced these organic rims. Our results

A high-voltage rechargeable magnesium-sodium hybrid battery

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Yifei; An, Qinyou; Cheng, Yingwen

2017-04-01

Growing global demand of safe and low-cost energy storage technology triggers strong interests in novel battery concepts beyond state-of-art Li-ion batteries. Here we report a high-voltage rechargeable Mg–Na hybrid battery featuring dendrite-free deposition of Mg anode and Na-intercalation cathode as a low-cost and safe alternative to Li-ion batteries for large-scale energy storage. A prototype device using a Na3V2(PO4)3 cathode, a Mg anode, and a Mg–Na dual salt electrolyte exhibits the highest voltage (2.60 V vs. Mg) and best rate performance (86% capacity retention at 10C rate) among reported hybrid batteries. Synchrotron radiation-based X-ray absorption near edge structure (XANES), atomic-pair distributionmore » function (PDF), and high-resolution X-ray diffraction (HRXRD) studies reveal the chemical environment and structural change of Na3V2(PO4)3 cathode during the Na ion insertion/deinsertion process. XANES study shows a clear reversible shift of vanadium K-edge and HRXRD and PDF studies reveal a reversible two-phase transformation and V–O bond length change during cycling. The energy density of the hybrid cell could be further improved by developing electrolytes with a higher salt concentration and wider electrochemical window. This work represents a significant step forward for practical safe and low-cost hybrid batteries.« less

Nanoscale morphological and chemical changes of high voltage lithium-manganese rich NMC composite cathodes with cycling.

PubMed

Yang, Feifei; Liu, Yijin; Martha, Surendra K; Wu, Ziyu; Andrews, Joy C; Ice, Gene E; Pianetta, Piero; Nanda, Jagjit

2014-08-13

Understanding the evolution of chemical composition and morphology of battery materials during electrochemical cycling is fundamental to extending battery cycle life and ensuring safety. This is particularly true for the much debated high energy density (high voltage) lithium-manganese rich cathode material of composition Li(1 + x)M(1 - x)O2 (M = Mn, Co, Ni). In this study we combine full-field transmission X-ray microscopy (TXM) with X-ray absorption near edge structure (XANES) to spatially resolve changes in chemical phase, oxidation state, and morphology within a high voltage cathode having nominal composition Li1.2Mn0.525Ni0.175Co0.1O2. Nanoscale microscopy with chemical/elemental sensitivity provides direct quantitative visualization of the cathode, and insights into failure. Single-pixel (∼ 30 nm) TXM XANES revealed changes in Mn chemistry with cycling, possibly to a spinel conformation and likely including some Mn(II), starting at the particle surface and proceeding inward. Morphological analysis of the particles revealed, with high resolution and statistical sampling, that the majority of particles adopted nonspherical shapes after 200 cycles. Multiple-energy tomography showed a more homogeneous association of transition metals in the pristine particle, which segregate significantly with cycling. Depletion of transition metals at the cathode surface occurs after just one cycle, likely driven by electrochemical reactions at the surface.

Nanoscale Morphological and Chemical Changes of High Voltage Lithium–Manganese Rich NMC Composite Cathodes with Cycling

PubMed Central

2015-01-01

Understanding the evolution of chemical composition and morphology of battery materials during electrochemical cycling is fundamental to extending battery cycle life and ensuring safety. This is particularly true for the much debated high energy density (high voltage) lithium–manganese rich cathode material of composition Li1 + xM1 – xO2 (M = Mn, Co, Ni). In this study we combine full-field transmission X-ray microscopy (TXM) with X-ray absorption near edge structure (XANES) to spatially resolve changes in chemical phase, oxidation state, and morphology within a high voltage cathode having nominal composition Li1.2Mn0.525Ni0.175Co0.1O2. Nanoscale microscopy with chemical/elemental sensitivity provides direct quantitative visualization of the cathode, and insights into failure. Single-pixel (∼30 nm) TXM XANES revealed changes in Mn chemistry with cycling, possibly to a spinel conformation and likely including some Mn(II), starting at the particle surface and proceeding inward. Morphological analysis of the particles revealed, with high resolution and statistical sampling, that the majority of particles adopted nonspherical shapes after 200 cycles. Multiple-energy tomography showed a more homogeneous association of transition metals in the pristine particle, which segregate significantly with cycling. Depletion of transition metals at the cathode surface occurs after just one cycle, likely driven by electrochemical reactions at the surface. PMID:25054780

Coordinated Analyses of Mineral-organic Matter Associations in Interplanetary Dust Particles

NASA Technical Reports Server (NTRS)

Nakamura-Messenger, K.; Herzog, G. F.; Smith, T.; Keller, L. P.; Flynn, G. J.; Khodja, H.; Taylor, S.; Wirick, S.; Messenger, S.

2012-01-01

Little is known about the timing and processes involved in the incorporation of organic matter with inorganic materials in early Solar System bodies. Recently, X-ray absorption near-edge spectroscopy (XANES) studies showed carbon-rich rims surrounding individual mineral grains in anhydrous IDPs [1,2]. These carbonaceous rims are believed to have formed prior to parent body formation and likely served to bond mineral grains during accretion into larger aggregates. We are exploring the nature of these carbonaceous rims through coordinated analyses of their chemistry, mineralogy, spectroscopy and isotopic characteristics. Here we report our preliminary mineralogical observations.

Na-Ion Intercalation and Charge Storage Mechanism in Two-Dimensional Vanadium Carbide

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bak, Seong -Min; Qiao, Ruimin; Yang, W.

We synthesized two-dimensional vanadium carbide MXene containing surface functional groups (denoted as V 2CT x, where T x are surface functional groups) and studied as anode material for Na-ion batteries. V 2CT x anode exhibits reversible charge storage with good cycling stability and high rate capability through electrochemical test. Furthermore, the charge storage mechanism of V 2CT x material during Na + intercalation/deintercalation and the redox reaction of vanadium were studied using a combination of synchrotron based X-ray diffraction (XRD), hard X-ray absorption near edge spectroscopy (XANES) and soft X-ray absorption spectroscopy (sXAS). Experimental evidence of a major contribution ofmore » redox reaction of vanadium to the charge storage and the reversible capacity of V 2CT x during sodiation/desodiation process have been provided through V K-edge XANES and V L2,3-edge sXAS results. A correlation between the CO 3 2- content and Na + intercalation/deintercalation states in the V 2CT x electrode observed from C and O K-edge in sXAS results imply that some additional charge storage reactions may take place between the Na +-intercalated V 2CT x and the carbonate based non-aqueous electrolyte. Our results of this study will provide valuable information for the further studies on V 2CT x as anode material for Na-ion batteries and capacitors.« less

Complete transformation of ZnO and CuO nanoparticles in culture medium and lymphocyte cells during toxicity testing.

PubMed

Ivask, Angela; Scheckel, Kirk G; Kapruwan, Pankaj; Stone, Vicki; Yin, Hong; Voelcker, Nicolas H; Lombi, Enzo

2017-03-01

Here, we present evidence on complete transformation of ZnO and CuO nanoparticles, which are among the most heavily studied metal oxide particles, during 24 h in vitro toxicological testing with human T-lymphocytes. Synchrotron radiation-based X-ray absorption near edge structure (XANES) spectroscopy results revealed that Zn speciation profiles of 30 nm and 80 nm ZnO nanoparticles, and ZnSO 4 - exposed cells were almost identical with the prevailing species being Zn-cysteine. This suggests that ZnO nanoparticles are rapidly transformed during a standard in vitro toxicological assay, and are sequestered intracellularly, analogously to soluble Zn. Complete transformation of ZnO in the test conditions was further supported by almost identical Zn spectra in medium to which ZnO nanoparticles or ZnSO 4 was added. Likewise, Cu XANES spectra for CuO and CuSO 4 -exposed cells and cell culture media were similar. These results together with our observation on similar toxicological profiles of ZnO and soluble Zn, and CuO and soluble Cu, underline the importance of dissolution and subsequent transformation of ZnO and CuO nanoparticles during toxicological testing and provide evidence that the nano-specific effect of ZnO and CuO nanoparticles is negligible in this system. We strongly suggest to account for this aspect when interpreting the toxicological results of ZnO and CuO nanoparticles.

Na-Ion Intercalation and Charge Storage Mechanism in Two-Dimensional Vanadium Carbide

DOE PAGES

Bak, Seong -Min; Qiao, Ruimin; Yang, W.; ...

2017-07-14

We synthesized two-dimensional vanadium carbide MXene containing surface functional groups (denoted as V 2CT x, where T x are surface functional groups) and studied as anode material for Na-ion batteries. V 2CT x anode exhibits reversible charge storage with good cycling stability and high rate capability through electrochemical test. Furthermore, the charge storage mechanism of V 2CT x material during Na + intercalation/deintercalation and the redox reaction of vanadium were studied using a combination of synchrotron based X-ray diffraction (XRD), hard X-ray absorption near edge spectroscopy (XANES) and soft X-ray absorption spectroscopy (sXAS). Experimental evidence of a major contribution ofmore » redox reaction of vanadium to the charge storage and the reversible capacity of V 2CT x during sodiation/desodiation process have been provided through V K-edge XANES and V L2,3-edge sXAS results. A correlation between the CO 3 2- content and Na + intercalation/deintercalation states in the V 2CT x electrode observed from C and O K-edge in sXAS results imply that some additional charge storage reactions may take place between the Na +-intercalated V 2CT x and the carbonate based non-aqueous electrolyte. Our results of this study will provide valuable information for the further studies on V 2CT x as anode material for Na-ion batteries and capacitors.« less

Chromium-removal processes during groundwater remediation by a zerovalent iron permeable reactive barrier.

PubMed

Wilkin, Richard T; Su, Chunming; Ford, Robert G; Paul, Cynthia J

2005-06-15

Solid-phase associations of chromium were examined in core materials collected from a full-scale, zerovalent iron permeable reactive barrier (PRB) at the U.S. Coast Guard Support Center located near Elizabeth City, NC. The PRB was installed in 1996 to treat groundwater contaminated with hexavalent chromium. After eight years of operation, the PRB remains effective at reducing concentrations of Cr from average values >1500 microg L(-1) in groundwater hydraulically upgradient of the PRB to values <1 microg L(-1) in groundwater within and hydraulically downgradient of the PRB. Chromium removal from groundwater occurs at the leading edge of the PRB and also within the aquifer immediately upgradient of the PRB. These regions also witness the greatest amount of secondary mineral formation due to steep geochemical gradients that result from the corrosion of zerovalent iron. X-ray absorption near-edge structure (XANES) spectroscopy indicated that chromium is predominantly in the trivalent oxidation state, confirming that reductive processes are responsible for Cr sequestration. XANES spectra and microscopy results suggest that Cr is, in part, associated with iron sulfide grains formed as a consequence of microbially mediated sulfate reduction in and around the PRB. Results of this study provide evidence that secondary iron-bearing mineral products may enhance the capacity of zerovalent iron systems to remediate Cr in groundwater, either through redox reactions at the mineral-water interface or by the release of Fe(II) to solution via mineral dissolution and/or metal corrosion.

Complete transformation of ZnO and CuO nanoparticles in ...

EPA Pesticide Factsheets

Here, we present evidence on complete transformation of ZnO and CuO nanoparticles, which are among the most heavily studied metal oxide particles, during 24 h in vitro toxicological testing with human T-lymphocytes. Synchrotron radiation-based X-ray absorption near edge structure (XANES) spectroscopy results revealed that Zn speciation profiles of 30 nm and 80 nm ZnO nanoparticles, and ZnSO4- exposed cells were almost identical with the prevailing species being Zn-cysteine. This suggests that ZnO nanoparticles are rapidly transformed during a standard in vitro toxicological assay, and are sequestered intracellularly, analogously to soluble Zn. Complete transformation of ZnO in the test conditions was further supported by almost identical Zn spectra in medium to which ZnO nanoparticles or ZnSO4 was added. Likewise, Cu XANES spectra for CuO and CuSO4-exposed cells and cell culture media were similar. These results together with our observation on similar toxicological profiles of ZnO and soluble Zn, and CuO and soluble Cu, underline the importance of dissolution and subsequent transformation of ZnO and CuO nanoparticles during toxicological testing and provide evidence that the nano-specific effect of ZnO and CuO nanoparticulates is negligible in this system. We strongly suggest to account for this aspect when interpreting the toxicological results of ZnO and CuO nanoparticles. Although a number of studies have discussed the transformation of nanoparticles during

Girls Not Boys Show Gender-Connotation Encoding from Print.

ERIC Educational Resources Information Center

Perez, Susan M.; Kee, Daniel W.

2000-01-01

Investigated possible gender differences in third grade students' encoding of gender-connotation from words using the release from proactive interference method to measure gender-connotation encoding. Students were presented with stimulus word triads in print. Results showed reliable proactive interference buildup and release for…

DYZ1 arrays show sequence variation between the monozygotic males

PubMed Central

2014-01-01

Background Monozygotic twins (MZT) are an important resource for genetical studies in the context of normal and diseased genomes. In the present study we used DYZ1, a satellite fraction present in the form of tandem arrays on the long arm of the human Y chromosome, as a tool to uncover sequence variations between the monozygotic males. Results We detected copy number variation, frequent insertions and deletions within the sequences of DYZ1 arrays amongst all the three sets of twins used in the present study. MZT1b showed loss of 35 bp compared to that in 1a, whereas 2a showed loss of 31 bp compared to that in 2b. Similarly, 3b showed 10 bp insertion compared to that in 3a. MZT1a germline DNA showed loss of 5 bp and 1b blood DNA showed loss of 26 bp compared to that of 1a blood and 1b germline DNA, respectively. Of the 69 restriction sites detected in DYZ1 arrays, MboII, BsrI, TspEI and TaqI enzymes showed frequent loss and or gain amongst all the 3 pairs studied. MZT1 pair showed loss/gain of VspI, BsrDI, AgsI, PleI, TspDTI, TspEI, TfiI and TaqI restriction sites in both blood and germline DNA. All the three sets of MZT showed differences in the number of DYZ1 copies. FISH signals reflected somatic mosaicism of the DYZ1 copies across the cells. Conclusions DYZ1 showed both sequence and copy number variation between the MZT males. Sequence variation was also noticed between germline and blood DNA samples of the same individual as we observed at least in one set of sample. The result suggests that DYZ1 faithfully records all the genetical changes occurring after the twining which may be ascribed to the environmental factors. PMID:24495361

Children's Understanding of Showing Off.

ERIC Educational Resources Information Center

Bennett, Mark; Yeeles, Caroline

1990-01-01

Interviews 46 British children, ages 8 to 11, to test their understanding of showing off. Confirms prediction that younger childrens' understanding of motivation for showing off is based on psychological determinants and that 11-year-olds' understanding focuses on interpersonal determinants. Also discusses children's understanding of emotional…

Tuning the Selectivity of Single-Site Supported Metal Catalysts with Ionic Liquids

DOE PAGES

Babucci, Melike; Fang, Chia -Yu; Hoffman, Adam S.; ...

2017-09-11

1,3-Dialkylimidazolium ionic liquid coatings act as electron donors, increasing the selectivity for partial hydrogenation of 1,3-butadiene catalyzed by iridium complexes supported on high-surface-area γ-Al 2O 3. High-energy-resolution fluorescence detection X-ray absorption near-edge structure (HERFD XANES) measurements quantify the electron donation and are correlated with the catalytic activity and selectivity. Furthermore, the results demonstrate broad opportunities to tune electronic environments and catalytic properties of atomically dispersed supported metal catalysts.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Babucci, Melike; Fang, Chia -Yu; Hoffman, Adam S.

1,3-Dialkylimidazolium ionic liquid coatings act as electron donors, increasing the selectivity for partial hydrogenation of 1,3-butadiene catalyzed by iridium complexes supported on high-surface-area γ-Al 2O 3. High-energy-resolution fluorescence detection X-ray absorption near-edge structure (HERFD XANES) measurements quantify the electron donation and are correlated with the catalytic activity and selectivity. Furthermore, the results demonstrate broad opportunities to tune electronic environments and catalytic properties of atomically dispersed supported metal catalysts.

Planning a Successful Tech Show

ERIC Educational Resources Information Center

Nikirk, Martin

2011-01-01

Tech shows are a great way to introduce prospective students, parents, and local business and industry to a technology and engineering or career and technical education program. In addition to showcasing instructional programs, a tech show allows students to demonstrate their professionalism and skills, practice public presentations, and interact…

Hey Teacher, Your Personality's Showing!

ERIC Educational Resources Information Center

Paulsen, James R.

1977-01-01

A study of 30 fourth, fifth, and sixth grade teachers and 300 of their students showed that a teacher's age, sex, and years of experience did not relate to students' mathematics achievement, but that more effective teachers showed greater "freedom from defensive behavior" than did less effective teachers. (DT)

A Holographic Road Show.

ERIC Educational Resources Information Center

Kirkpatrick, Larry D.; Rugheimer, Mac

1979-01-01

Describes the viewing sessions and the holograms of a holographic road show. The traveling exhibits, believed to stimulate interest in physics, include a wide variety of holograms and demonstrate several physical principles. (GA)

Retention and chemical speciation of uranium in an oxidized wetland sediment from the Savannah River Site.

PubMed

Li, Dien; Seaman, John C; Chang, Hyun-Shik; Jaffe, Peter R; Koster van Groos, Paul; Jiang, De-Tong; Chen, Ning; Lin, Jinru; Arthur, Zachary; Pan, Yuanming; Scheckel, Kirk G; Newville, Matthew; Lanzirotti, Antonio; Kaplan, Daniel I

2014-05-01

Uranium speciation and retention mechanisms onto Savannah River Site (SRS) wetland sediments was studied using batch (ad)sorption experiments, sequential extraction, U L3-edge X-ray absorption near-edge structure (XANES) spectroscopy, fluorescence mapping and μ-XANES. Under oxidized conditions, U was highly retained by the SRS wetland sediments. In contrast to other similar but much lower natural organic matter (NOM) sediments, significant sorption of U onto the SRS sediments was observed at pH < 4 and pH > 8. Sequential extraction indicated that the U species were primarily associated with the acid soluble fraction (weak acetic acid extractable) and organic fraction (Na-pyrophosphate extractable). Uranium L3-edge XANES spectra of the U-bound sediments were nearly identical to that of uranyl acetate. Based on fluorescence mapping, U and Fe distributions in the sediment were poorly correlated, U was distributed throughout the sample and did not appear as isolated U mineral phases. The primary oxidation state of U in these oxidized sediments was U(VI), and there was little evidence that the high sorptive capacity of the sediments could be ascribed to abiotic or biotic reduction to the less soluble U(IV) species or to secondary mineral formation. Collectively, this study suggests that U may be strongly bound to wetland sediments, not only under reducing conditions by reductive precipitation, but also under oxidizing conditions through NOM-uranium bonding. Published by Elsevier Ltd.

Fate of zinc in an electroplating sludge during electrokinetic treatments.

PubMed

Liu, Shou-Heng; Wang, H Paul

2008-08-01

Chemical structure of zinc in the electrokinetic treatments of an electroplating sludge has been studied by in situ extended X-ray absorption fine structural (EXAFS) and X-ray absorption near edge structural (XANES) spectroscopies in the present work. The least-square fitted XANES spectra indicate that the main zinc compounds in the sludge were ZnCO(3) (75%), ZnOSiO(2) (17%) and Zn(OH)(2) (7%). Zinc in the sludge possessed a Zn-O bond distance of 2.07 A with a coordination number (CN) of 5. In the second shells, the bond distance of Zn-(O)-Si was 3.05 A (CN=2). An increase of Zn-(O)-Si (0.05 A) with a decrease of its CN (from 5 to <1) was found in the early stage of the electrokinetic treatment. Prolong the electrokinetic treatment time to 180 min, about 34% of Zn(II) was dissolved into the aqueous phase and about 68% of Zn(II) in the sludge (or 23% of total zinc) was migrated to the cathode under the electric field (5 V cm(-1)). The dissolution and electromigration rates of Zn(II) in the sludge were 1.0 and 0.6 mmol h(-1)g(-1) sludge, respectively during the electrokinetic treatment. This work also exemplifies the utilization of in situ EXAFS and XANES for revealing speciation and possible reaction pathways during the course of zinc recycling from the sludge by electrokinetic treatments.

Development of Tc(IV)-Incorporated Fe Minerals to Enhance 99Tc Retention in Glass Waste Form

DOE Office of Scientific and Technical Information (OSTI.GOV)

Um, Wooyong; Luksic, Steven A.; Wang, Guohui

Iron minerals have been considered to be good hosts for Tc immobilization because the Tc(IV) ion substitutes for Fe(III) in the crystal structure of the Fe oxide due to similarities in (1) cation size [Tc(IV) = 78.5 pm ; Fe(III) = 69 or 78.5 pm], (2) metal-oxygen interatomic distance (Tc—O = 0.199 nm, Fe—O = 0.203 nm), (3) number of coordinating oxygen atoms (both 6-fold coordinated), and (4) the redox potential (Eh=ca. +20 mV at pH = 7) for a redox couple between Tc(VII)/Tc(IV) and Fe(III)/Fe(II). Magnetite, maghemite, and trevorite are iron oxide minerals and all belong to spinel mineralmore » group. Laboratory testing shows that Tc can be removed from aqueous waste solutions by a process of Tc reduction from Tc(VII) to Tc(IV) followed by co-precipitation with iron oxide minerals during recrystallization of Fe(OH)2(s) used as an initial solid precursor. X-ray absorption near edge structure (XANES) spectroscopy confirmed that Tc was in the +4 oxidation state in final Tc-Fe minerals. The Tc-incorporated Fe minerals were also tested for Tc retention in glass melts at different temperatures between 600 – 1,000 oC in a furnace. After being cooled in air, the solid glass specimens collected at different temperatures were analyzed for Tc oxidation state using XANES and Tc retention using liquid scintillation counting (LSC). Even though Tc(IV) started to reoxidize at 600 oC, Tc retention in the final glass specimen prepared with Tc-incorporated Fe mineral even at high temperatures was at least two times higher than glass prepared with KTcO4 salt. Higher Tc retention in glass is considered to result from limited and delayed Tc volatilization process due to Fe mineral encapsulation for Tc. Therefore, the results showing the presence of Tc(IV) in the Fe mineral structure indicate strong possibility to enhance Tc retention in borosilicate glass as well as to reduce the remediation costs at the Hanford Site.« less

Fat stigmatization in television shows and movies: a content analysis.

PubMed

Himes, Susan M; Thompson, J Kevin

2007-03-01

To examine the phenomenon of fat stigmatization messages presented in television shows and movies, a content analysis was used to quantify and categorize fat-specific commentary and humor. Fat stigmatization vignettes were identified using a targeted sampling procedure, and 135 scenes were excised from movies and television shows. The material was coded by trained raters. Reliability indices were uniformly high for the seven categories (percentage agreement ranged from 0.90 to 0.98; kappas ranged from 0.66 to 0.94). Results indicated that fat stigmatization commentary and fat humor were often verbal, directed toward another person, and often presented directly in the presence of the overweight target. Results also indicated that male characters were three times more likely to engage in fat stigmatization commentary or fat humor than female characters. To our knowledge, these findings provide the first information regarding the specific gender, age, and types of fat stigmatization that occur frequently in movies and television shows. The stimuli should prove useful in future research examining the role of individual difference factors (e.g., BMI) in the reaction to viewing such vignettes.

Effect of aluminum on the local structure of silicon in zeolites as studied by Si K edge X-ray absorption near-edge fine structure: spectra simulation with a non-muffin tin atomic background.

PubMed

Bugaev, Lusegen A; Bokhoven, Jeroen A van; Khrapko, Valerii V

2009-04-09

Experimental Si K edge X-ray absorption near-edge fine structure (XANES) of zeolite faujasite, mordenite, and beta are interpreted by means of the FEFF8 code, replacing the theoretical atomic background mu(0) by a background that was extracted from an experimental spectrum. To some extent, this diminished the effect of the inaccuracy introduced by the MT potential and accounted for the intrinsic loss of photoelectrons. The agreement of the theoretical and experimental spectra at energies above the white lines enabled us to identify structural distortion around silicon, which occurs with increasing aluminum content. The Si K edge XANES spectra are very sensitive to slight distortions in the silicon coordination. Placing an aluminum atom on a nearest neighboring T site causes a distortion in the silicon tetrahedron, shortening one of the silicon-oxygen bonds relative to the other three.

In Situ X-ray Absorption Near-Edge Structure Spectroscopy of ZnO Nanowire Growth During Chemical Bath Deposition

DOE Office of Scientific and Technical Information (OSTI.GOV)

McPeak, Kevin M.; Becker, Matthew A.; Britton, Nathan G.

2010-12-03

Chemical bath deposition (CBD) offers a simple and inexpensive route to deposit semiconductor nanostructures, but lack of fundamental understanding and control of the underlying chemistry has limited its versatility. Here we report the first use of in situ X-ray absorption spectroscopy during CBD, enabling detailed investigation of both reaction mechanisms and kinetics of ZnO nanowire growth from zinc nitrate and hexamethylenetetramine (HMTA) precursors. Time-resolved X-ray absorption near-edge structure (XANES) spectra were used to quantify Zn(II) speciation in both solution and solid phases. ZnO crystallizes directly from [Zn(H{sub 2}O){sub 6}]{sup 2+} without long-lived intermediates. Using ZnO nanowire deposition as an example,more » this study establishes in situ XANES spectroscopy as an excellent quantitative tool to understand CBD of nanomaterials.« less

Acetate- and thiol-capped monodisperse ruthenium nanoparticles: XPS, XAS, and HRTEM studies.

PubMed

Chakroune, Nassira; Viau, Guillaume; Ammar, Souad; Poul, Laurence; Veautier, Delphine; Chehimi, Mohamed M; Mangeney, Claire; Villain, Françoise; Fiévet, Fernand

2005-07-19

Monodisperse ruthenium nanoparticles were prepared by reduction of RuCl3 in 1,2-propanediol. The mean particle size was controlled by appropriate choice of the reduction temperature and the acetate ion concentration. Colloidal solutions in toluene were obtained by coating the metal particles with dodecanethiol. High-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and X-ray absorption spectroscopy (XANES and EXAFS for the Ru K-absorption edge) were performed on particles of two different diameters, 2 and 4 nm, and in different environments, polyol/acetate or thiol. For particles stored in polyol/acetate XPS studies revealed superficial oxidation limited to one monolayer and a surface coating containing mostly acetate ions. Analysis of the EXAFS spectra showed both oxygen and ruthenium atoms around the ruthenium atoms with a Ru-Ru coordination number N smaller than the bulk value, as expected for fine particles. In the case of 2 nm acetate-capped particles N is consistent with particles made up of a metallic core and an oxidized monolayer. For 2 nm thiol-coated particles, a Ru-S bond was evidenced by XPS and XAS. For the 4 nm particles XANES and XPS studies showed that most of the ruthenium atoms are in the zerovalent state. Nevertheless, in both cases, when capped with thiol, the Ru-Ru coordination number inferred from EXAFS is much smaller than for particles of the same size stored in polyol. This is attributed to a structural disorganization of the particles by thiol chemisorption. HRTEM studies confirm the marked dependence of the structural properties of the ruthenium particles on their chemical environment; they show the acetate-coated particles to be single crystals, whereas the thiol-coated particles appear to be polycrystalline.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Farges, F.; Rossano, S.; Wilke, M.

A large number (67) of silicate glasses containing variable amounts of iron oxide were studied by high-resolution XANES spectroscopy at the Fe K-edge to determine an accurate method to derive redox information from pre-edge features. The glass compositions studied mimic geological magmas, ranging from basaltic to rhyolitic, dry and hydrous, with variable quench rates. The studied glasses also include more chemically simple calco-sodic silicate glass compositions. The Fe contents range from 30 wt.% to less than 2000 ppm. For most of the series of composition studied, the pre-edge information varies linearly with redox, even under high-resolution conditions. The average coordinationmore » of Fe(II) is often similar to its Fe(III) counterpart except in highly polymerized glasses because of the strong influence exerted by the tetrahedral framework on iron's sites. Natural volcanic glasses (from various volcanoes around the world) show similar variations. The average coordination of Fe(II) is often comprised between 4.5 and 5. Fe(III) shows larger variations in coordination (4 to 6, depending on composition). Bond valence models are proposed to predict the average coordination of Fe based on composition. Molecular dynamics simulations (Born-Mayer-Huggins) potentials were carried out on some compositions to estimate the magnitude of disorder effects (both static and thermal) in the XAFS analysis. XANES calculations based on the MD simulations and FEFF 8.2 show large variations in the local structures around Fe. Also, 5-coordinated Fe(III) is found to be an important moiety in ferrisilicate glasses. For Fe(II), discrepancies between glass and melt are larger and are related to its greater structural relaxation at T{sub g}. Also, a strong destructive interference between network formers and modifiers explain the relatively weak intensity of the next-nearest neighbors contributions in the experimental spectra.« less

Application of x-ray absorption fine structure (XAFS) to local-order analysis in Fe-Cr maghemite-like materials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Montero-Cabrera, M. E., E-mail: elena.montero@cimav.edu.mx; Fuentes-Cobas, L. E.; Macías-Ríos, E.

2015-07-23

The maghemite-like oxide system γ-Fe{sub 2-x}Cr{sub x}O{sub 3} (x=0.75, 1 and 1.25) was studied by X-ray absorption fine structure (XAFS) and by synchrotron radiation X-ray diffraction (XRD). Measurements were performed at the Stanford Synchrotron Radiation Lightsource at room temperature, at beamlines 2-1, 2-3 and 4-3. High-resolution XRD patterns were processed by means of the Rietveld method. In cases of atoms being neighbors in the Periodic Table, the order/disorder degree of the considered solutions is indiscernible by “normal” (absence of “anomalous scattering”) diffraction experiments. Thus, maghemite-like materials were investigated by XAFS in both Fe and Cr K-edges to clarify, via short-rangemore » structure characterization, the local ordering of the investigated system. Athena and Artemis graphic user interfaces for IFEFFIT and FEFF8.4 codes were employed for XAFS spectra interpretation. Pre-edge decomposition and theoretical modeling of X-ray absorption near edge structure (XANES) transitions were performed. By analysis of the Cr K-edge XANES, it has been confirmed that Cr is located in an octahedral environment. Fitting of the extended X-ray absorption fine structure (EXAFS) spectra was performed under the consideration that the central atom of Fe is allowed to occupy octa- and tetrahedral positions, while Cr occupies only octahedral ones. Coordination number of neighboring atoms, interatomic distances and their quadratic deviation average were determined for x=1, by fitting simultaneously the EXAFS spectra of both Fe and Cr K-edges. The results of fitting the experimental spectra with theoretical standards showed that the cation vacancies tend to follow a regular pattern within the structure of the iron-chromium maghemite (FeCrO{sub 3})« less

Study by NOAA and Partners Shows Some Gulf Dolphins Severely Ill | NOAA

Science.gov Websites

Publications Press Releases Story Archive Home Study by NOAA and Partners Shows Some Gulf Dolphins Severely Ill Study by NOAA and Partners Shows Some Gulf Dolphins Severely Ill Aug 2011: Veterinarians collect samples of 2011, preliminary results show that many of the dolphins in the study are underweight, anemic

Speciation and distribution of arsenic and localization of nutrients in rice grains

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lombi, E.; Scheckel, K.G.; Pallon, J.

2012-09-05

Arsenic (As) contamination of rice grains and the generally low concentration of micronutrients in rice have been recognized as a major concern for human health. Here, we investigated the speciation and localization of As and the distribution of (micro)nutrients in rice grains because these are key factors controlling bioavailability of nutrients and contaminants. Bulk total and speciation analyses using high-pressure liquid chromatography (HPLC)-inductively coupled plasma mass spectrometry (ICP-MS) and X-ray absorption near-edge spectroscopy (XANES) was complemented by spatially resolved microspectroscopic techniques ({mu}-XANES, {mu}-X-ray fluorescence ({mu}-XRF) and particle induced X-ray emission (PIXE)) to investigate both speciation and distribution of As andmore » localization of nutrients in situ. The distribution of As and micronutrients varied between the various parts of the grains (husk, bran and endosperm) and was characterized by element-specific distribution patterns. The speciation of As in bran and endosperm was dominated by As(III)-thiol complexes. The results indicate that the translocation from the maternal to filial tissues may be a bottleneck for As accumulation in the grain. Strong similarities between the distribution of iron (Fe), manganese (Mn) and phosphorus (P) and between zinc (Zn) and sulphur (S) may be indicative of complexation mechanisms in rice grains.« less

Imaging Catalytic Activation of CO 2 on Cu 2O (110): A First-Principles Study

DOE PAGES

Li, Liang; Zhang, Rui; Vinson, John; ...

2018-03-05

Balancing global energy needs against increasing greenhouse gas emissions requires new methods for efficient CO 2 reduction. While photoreduction of CO 2 is a viable approach for fuel generation, the rational design of photocatalysts hinges on precise characterization of the surface catalytic reactions. Cu 2O is a promising next-generation photocatalyst, but the atomic-scale description of the interaction between CO 2 and the Cu 2O surface is largely unknown, and detailed experimental measurements are lacking. In this study, density-functional-theory (DFT) calculations have been performed to identify the Cu 2O (110) surface stoichiometry that favors CO 2 reduction. To facilitate interpretation ofmore » scanning tunneling microscopy (STM) and X-ray absorption near-edge structures (XANES) measurements, which are useful for characterizing catalytic reactions, we present simulations based on DFT-derived surface morphologies with various adsorbate types. STM and XANES simulations were performed using the Tersoff Hamann approximation and Bethe-Salpeter equation (BSE) approach, respectively. The results provide guidance for observation of CO 2 reduction reaction on, and rational surface engineering of, Cu 2O (110). In conclusion, they also demonstrate the effectiveness of computational image and spectroscopy modeling as a predictive tool for surface catalysis characterization.« less

Insight into the Capacity Fading Mechanism of Amorphous Se 2 S 5 Confined in Micro/Mesoporous Carbon Matrix in Ether-Based Electrolytes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, Gui-Liang; Ma, Tianyuan; Sun, Cheng-Jun

2016-04-13

In contrast to the stable cycle performance of space confined Se-based cathodes for lithium batteries in carbonate-based electrolytes, their common capacity fading in ether-based electrolytes has been paid less attention and not yet well-addressed so far. In this work, the lithiation/delithiation of amorphous Se2S5 confined in micro/mesoporous carbon (Se2S5/MPC) cathode was investigated by in situ X-ray near edge absorption spectroscopy (XANES) and theoretical calculations. The Se2S5/MPC composite was synthesized by a modified vaporization-condensation method to ensure a good encapsulation of Se2S5 into the pores of MPC host. In situ XANES results illustrated that the lithiation/delithiation reversibility of Se component wasmore » gradually decreased in ether-based electrolytes, leading to an aggravated formation of long-chain polyselenides during cycling and further capacity decay. Moreover, ab initio calculations revealed that the binding energy of polyselenides (Li2Sen) with carbon host is in an order of Li2Se6 > Li2Se4 > Li2Se. The insights into the failure mechanism of Se-based cathode gain in this work are expected to serve as a guide for future design on high performance Se-based cathodes.« less

Characterization by 27Al NMR, X-ray absorption spectroscopy, and density functional theory techniques of the species responsible for benzene hydrogenation in Y zeolite-supported carburized molybdenum catalysts.

PubMed

Rocha, Angela S; da Silva, Victor Teixeira; Eon, Jean G; de Menezes, Sônia M C; Faro, Arnaldo C; Rocha, Alexandre B

2006-08-17

Carburized molybdenum catalysts supported on a dealuminated NaH-Y zeolite were prepared by carburization under a 20% methane in hydrogen flow of two precursors obtained by adsorption of molybdenum hexacarbonyl, one containing 5 wt % and the other 10 wt % Mo, and a third one was prepared by impregnation with aqueous ammonium heptamolybdate, containing 5 wt % Mo. The three catalysts displayed very distinct behaviors in the benzene hydrogenation reaction at atmospheric pressure and 363 K. By using XANES spectroscopy at the molybdenum L edge, EXAFS and XANES spectroscopy at the molybdenum K edge, and 27Al solid-state NMR spectroscopy, it was shown that different carburized molybdenum species exist in each sample. In the catalyst containing 10 wt % Mo, formation of molybdenum carbide nanoparticles was observed, with an estimated diameter of 1.8 nm. In the catalyst containing 5 wt % Mo and prepared by carburization of adsorbed molybdenum hexacarbonyl, formation of molybdenum oxycarbide dimers is proposed. In the latter case, density functional theory calculations have led to a dimer structure which is compatible with EXAFS results. In the catalyst prepared by impregnation with ammonium heptamolybdate solution followed by carburization, the molybdenum seems to interact with extraframework alumina to produce highly disordered mixed molybdenum-aluminum oxycarbides.

Imaging Catalytic Activation of CO 2 on Cu 2O (110): A First-Principles Study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Liang; Zhang, Rui; Vinson, John

Balancing global energy needs against increasing greenhouse gas emissions requires new methods for efficient CO 2 reduction. While photoreduction of CO 2 is a viable approach for fuel generation, the rational design of photocatalysts hinges on precise characterization of the surface catalytic reactions. Cu 2O is a promising next-generation photocatalyst, but the atomic-scale description of the interaction between CO 2 and the Cu 2O surface is largely unknown, and detailed experimental measurements are lacking. In this study, density-functional-theory (DFT) calculations have been performed to identify the Cu 2O (110) surface stoichiometry that favors CO 2 reduction. To facilitate interpretation ofmore » scanning tunneling microscopy (STM) and X-ray absorption near-edge structures (XANES) measurements, which are useful for characterizing catalytic reactions, we present simulations based on DFT-derived surface morphologies with various adsorbate types. STM and XANES simulations were performed using the Tersoff Hamann approximation and Bethe-Salpeter equation (BSE) approach, respectively. The results provide guidance for observation of CO 2 reduction reaction on, and rational surface engineering of, Cu 2O (110). In conclusion, they also demonstrate the effectiveness of computational image and spectroscopy modeling as a predictive tool for surface catalysis characterization.« less

Papers from U.S. Department of Energy Science Undergraduate Laboratory Internship Program (SULI) 2010

DOE Office of Scientific and Technical Information (OSTI.GOV)

Not Available

2011-06-22

The solvation sphere of halides in water has been investigated using a combination of extended x-ray absorption fine structure (EXAFS) and x-ray absorption near-edge structure (XANES) analysis techniques. The results have indicated that I{sup -} and Br{sup -} both have an asymmetric, 8 water molecule primary solvation spheres. These spheres are identical, with the Br{sup -} sphere about .3 {angstrom} smaller than the I{sup -} sphere. This study utilized near-edge analysis to supplement EXAFS analysis which suffers from signal dampening/broadening due to thermal noise. This paper has reported on the solvation first sphere of I{sup -} and Br{sup -} inmore » water. Using EXAFS and XANES analysis, strong models which describe the geometric configuration of water molecules coordinated to a central anion have been developed. The combination of these techniques has provided us with a more substantiated argument than relying solely on one or the other. An important finding of this study is that the size of the anion plays a smaller role than previously assumed in determining the number of coordinating water molecules. Further experimental and theoretical investigation is required to understand why the size of the anion plays a minor role in determining the number of water molecules bound.« less

Pulse studies to decipher the role of surface morphology in CuO/CeO₂ nanocatalysts for the water gas shift reaction

DOE PAGES

Rodriguez, Jose A.; Zhao, Fuzhen; Liu, Zongyuan; ...

2015-01-23

The water-gas shift reaction (WGS, CO + H₂O → CO₂) was studied over CuO/CeO₂ catalysts with two different ceria particle morphohologies, in the form of nanospheres (ns) and nanocubes (nc). To understand the strong dependence of the WGS reaction activity on the ceria nanoshapes, pulses of CO (without and with water vapor) were employed during in situ X-ray diffraction (XRD) and X-ray absoprtion near edge structure (XANES) measurements done to characterize the catalysts. The results showed that CuO/CeO₂ (ns) exhibited a substantially better activity than CuO/CeO₂ (nc). The higher activity was associated with the unique properties of CuO/CeO₂ (ns), suchmore » as the easier reduction of highly dispersed CuO to metallic Cu, the stability of metallic Cu and a larger concentration Ce³⁺ in CeO₂ (ns).« less

XAFS study of copper(II) complexes with square planar and square pyramidal coordination geometries

NASA Astrophysics Data System (ADS)

Gaur, A.; Klysubun, W.; Nitin Nair, N.; Shrivastava, B. D.; Prasad, J.; Srivastava, K.

2016-08-01

X-ray absorption fine structure of six Cu(II) complexes, Cu2(Clna)4 2H2O (1), Cu2(ac)4 2H2O (2), Cu2(phac)4 (pyz) (3), Cu2(bpy)2(na)2 H2O (ClO4) (4), Cu2(teen)4(OH)2(ClO4)2 (5) and Cu2(tmen)4(OH)2(ClO4)2 (6) (where ac, phac, pyz, bpy, na, teen, tmen = acetate, phenyl acetate, pyrazole, bipyridine, nicotinic acid, tetraethyethylenediamine, tetramethylethylenediamine, respectively), which were supposed to have square pyramidal and square planar coordination geometries have been investigated. The differences observed in the X-ray absorption near edge structure (XANES) features of the standard compounds having four, five and six coordination geometry points towards presence of square planar and square pyramidal geometry around Cu centre in the studied complexes. The presence of intense pre-edge feature in the spectra of four complexes, 1-4, indicates square pyramidal coordination. Another important XANES feature, present in complexes 5 and 6, is prominent shoulder in the rising part of edge whose intensity decreases in the presence of axial ligands and thus indicates four coordination in these complexes. Ab initio calculations were carried out for square planar and square pyramidal Cu centres to observe the variation of 4p density of states in the presence and absence of axial ligands. To determine the number and distance of scattering atoms around Cu centre in the complexes, EXAFS analysis has been done using the paths obtained from Cu(II) oxide model and an axial Cu-O path from model of a square pyramidal complex. The results obtained from EXAFS analysis have been reported which confirmed the inference drawn from XANES features. Thus, it has been shown that these paths from model of a standard compound can be used to determine the structural parameters for complexes having unknown structure.

Finite difference method accelerated with sparse solvers for structural analysis of the metal-organic complexes

NASA Astrophysics Data System (ADS)

Guda, A. A.; Guda, S. A.; Soldatov, M. A.; Lomachenko, K. A.; Bugaev, A. L.; Lamberti, C.; Gawelda, W.; Bressler, C.; Smolentsev, G.; Soldatov, A. V.; Joly, Y.

2016-05-01

Finite difference method (FDM) implemented in the FDMNES software [Phys. Rev. B, 2001, 63, 125120] was revised. Thorough analysis shows, that the calculated diagonal in the FDM matrix consists of about 96% zero elements. Thus a sparse solver would be more suitable for the problem instead of traditional Gaussian elimination for the diagonal neighbourhood. We have tried several iterative sparse solvers and the direct one MUMPS solver with METIS ordering turned out to be the best. Compared to the Gaussian solver present method is up to 40 times faster and allows XANES simulations for complex systems already on personal computers. We show applicability of the software for metal-organic [Fe(bpy)3]2+ complex both for low spin and high spin states populated after laser excitation.

THE DISTRIBUTION, SOLID-PHASE SPECIATION, AND DESORPTION/DISSOLUTION OF AS IN IRON-BASED DRINKING WATER TREATMENT MEDIA 1

EPA Science Inventory

Arsenic concentrations (Total Recoverable As by EPA Method 3051, soluble, Toxicity Characteristic Leaching Procedure extractable) and solid-phase speciation (by X-ray Absorption Near-Edge Spectroscopy-XANES) were assessed as a function of depth through Fe-media beds for two comme...

THE DISTRIBUTION, SOLID-PHASE SPECIATION, AND DESORPTION/DISSOLUTION OF AS IN IRON-BASED DRINKING WATER TREATMENT MEDIA - JOURNAL

EPA Science Inventory

Arsenic concentrations (Total Recoverable As by EPA Method 3051, soluble, Toxicity Characteristic Leaching Procedure extractable) and solid-phase speciation (by X-ray Absorption Near-Edge Spectroscopy-XANES) were assessed as a function of depth through Fe-media beds for two comme...

Skills in minimally invasive and open surgery show limited transferability to robotic surgery: results from a prospective study.

PubMed

Kowalewski, Karl-Friedrich; Schmidt, Mona W; Proctor, Tanja; Pohl, Moritz; Wennberg, Erica; Karadza, Emir; Romero, Philipp; Kenngott, Hannes G; Müller-Stich, Beat P; Nickel, Felix

2018-04-01

There is limited evidence on the transferability of conventional laparoscopic and open surgical skills to robotic-assisted surgery. The primary aim of this study was to evaluate the transferability of expertise in conventional laparoscopy and open surgery to robotic-assisted surgery using the da Vinci Skills Simulator (dVSS). Secondary aims included evaluating the influence of individual participants' characteristics. Participants performed four tasks on the dVSS: Peg Board 1 (PB), Pick and Place (PP), Thread the Rings (TR), and Suture Sponge 1 (SS). Participants were classified into three groups (Novice, Intermediate, Experts) according to experience in laparoscopic and open surgery. All tasks were performed twice except for SS. Performance was assessed using the built-in scoring system. 37 medical students and 25 surgeons participated. Experts did not perform significantly better than less experienced participants on the dVSS. Specifically, with regard to laparoscopic experience, total simulator scores were: Novices 68.2 ± 28.8; Intermediates 65.1 ± 31.2; Experts 65.1 ± 30.0; p = 0.611. Regarding open surgical experience, scores were: Novices 68.6 ± 28.7; Intermediates 68.2 ± 30.8; Experts 63.2 ± 30.3; p = 0.305. Although there were some significant differences among groups for single parameters in specific tasks, there was no constant superiority of one group. Laparoscopic and open surgical Novices improved significantly in overall score and time for all three tasks (p < 0.05). Laparoscopic intermediates improved only in PP time (4.64 ± 3.42; p = 0.006), open Intermediates in PB score (11.98 ± 13.01; p = 0.025), and open Experts in PP score (6.69 ± 11.48; p = 0.048). Laparoscopic experts showed no improvement. Participants with gaming experience had better overall scores than non-gamers when comparing all second attempts (Gamer 83.62 ± 7.57; Non-Gamer 76.31 ± 12.78; p = 0.008) as

The environmental consequences of the oil shale utilization in Jordan: The effect of combustion processes

NASA Astrophysics Data System (ADS)

El-Hasan, Tayel

2015-04-01

The geochemical analysis of the upper Cretaceous organic rich oil shale of El-Lajjoun revealed that it contains considerable concentrations of trace element when compared to the average world shale. The aim of this study was to deduce the effect of various combustion processes on the geochemical and mineralogical characteristics of the produced ashes.The oil shale powder samples were burned under Aerobic Combustion Process (ACP) at 700˚C, 850˚C and 1000˚C respectively, beside the anaerobic (pyrolysis) combustion process (PCP) at 600, 650, 700, 750 and 800˚C respectively.The ashes produced from the (ACP) caused almost all major oxides contents to increase with increasing burning temperature, particularly SiO2 and CaO were nearly doubled at temperature 1000 ˚C. Moreover, trace elements showed the same trend where ashes at higher temperatures (i.e. 1000 ˚C) have doubled its contents of trace elements such as Cr, Ni, Zn, Cu and U. This was reflected through enrichment of calcite and quartz beside the anhydrite as the main mineral phases in the ACP ashes. As for the PCP ash show similar trend but relatively with lower concentrations as evident from its lowerEnrichment Factor (EF) values. This might be due to the higher organic matter remained in the PCP ashes compared with ACP ashes. However, PCP is more likely associated with toxic Cd and Asgasses as evident from their lowerconcentrations in the ashes.Moreover, recent results using the synchrotron-based XANES technique confirm that toxic elements are found in higher oxidation state due to ACP. The investigation was concerned on As and Cr. Thechromium in the original shales was in the form of Cr (III) and then it was converted to Cr(VI) in the ashes due of the ACP. Similarly, As (III) the XANES results showed that it was converted into As(V) too. These findingsare alarming and should be taken seriously. Because elements with higher oxidation states became more mobile, thus they can easily leached from the ash

Bonobos (Pan paniscus) show an attentional bias toward conspecifics’ emotions

PubMed Central

Kret, Mariska E.; Jaasma, Linda; Bionda, Thomas; Wijnen, Jasper G.

2016-01-01

In social animals, the fast detection of group members’ emotional expressions promotes swift and adequate responses, which is crucial for the maintenance of social bonds and ultimately for group survival. The dot-probe task is a well-established paradigm in psychology, measuring emotional attention through reaction times. Humans tend to be biased toward emotional images, especially when the emotion is of a threatening nature. Bonobos have rich, social emotional lives and are known for their soft and friendly character. In the present study, we investigated (i) whether bonobos, similar to humans, have an attentional bias toward emotional scenes compared with conspecifics showing a neutral expression, and (ii) which emotional behaviors attract their attention the most. As predicted, results consistently showed that bonobos’ attention was biased toward the location of the emotional versus neutral scene. Interestingly, their attention was grabbed most by images showing conspecifics such as sexual behavior, yawning, or grooming, and not as much—as is often observed in humans—by signs of distress or aggression. The results suggest that protective and affiliative behaviors are pivotal in bonobo society and therefore attract immediate attention in this species. PMID:26976586

Bonobos (Pan paniscus) show an attentional bias toward conspecifics' emotions.

PubMed

Kret, Mariska E; Jaasma, Linda; Bionda, Thomas; Wijnen, Jasper G

2016-04-05

In social animals, the fast detection of group members' emotional expressions promotes swift and adequate responses, which is crucial for the maintenance of social bonds and ultimately for group survival. The dot-probe task is a well-established paradigm in psychology, measuring emotional attention through reaction times. Humans tend to be biased toward emotional images, especially when the emotion is of a threatening nature. Bonobos have rich, social emotional lives and are known for their soft and friendly character. In the present study, we investigated (i) whether bonobos, similar to humans, have an attentional bias toward emotional scenes compared with conspecifics showing a neutral expression, and (ii) which emotional behaviors attract their attention the most. As predicted, results consistently showed that bonobos' attention was biased toward the location of the emotional versus neutral scene. Interestingly, their attention was grabbed most by images showing conspecifics such as sexual behavior, yawning, or grooming, and not as much-as is often observed in humans-by signs of distress or aggression. The results suggest that protective and affiliative behaviors are pivotal in bonobo society and therefore attract immediate attention in this species.

Experimental research on showing automatic disappearance pen handwriting based on spectral imaging technology

NASA Astrophysics Data System (ADS)

Su, Yi; Xu, Lei; Liu, Ningning; Huang, Wei; Xu, Xiaojing

2016-10-01

Purpose to find an efficient, non-destructive examining method for showing the disappearing words after writing with automatic disappearance pen. Method Using the imaging spectrometer to show the potential disappearance words on paper surface according to different properties of reflection absorbed by various substances in different bands. Results the disappeared words by using different disappearance pens to write on the same paper or the same disappearance pen to write on different papers, both can get good show results through the use of the spectral imaging examining methods. Conclusion Spectral imaging technology can show the disappearing words after writing by using the automatic disappearance pen.

Honored Teacher Shows Commitment.

ERIC Educational Resources Information Center

Ratte, Kathy

1987-01-01

Part of the acceptance speech of the 1985 National Council for the Social Studies Teacher of the Year, this article describes the censorship experience of this honored social studies teacher. The incident involved the showing of a videotape version of the feature film entitled "The Seduction of Joe Tynan." (JDH)

Low toxic maghemite nanoparticles for theranostic applications.

PubMed

Kuchma, Elena A; Zolotukhin, Peter V; Belanova, Anna A; Soldatov, Mikhail A; Lastovina, Tatiana A; Kubrin, Stanislav P; Nikolsky, Anatoliy V; Mirmikova, Lidia I; Soldatov, Alexander V

2017-01-01

Iron oxide nanoparticles have numerous and versatile biological properties, ranging from direct and immediate biochemical effects to prolonged influences on tissues. Most applications have strict requirements with respect to the chemical and physical properties of such agents. Therefore, developing rational design methods of synthesis of iron oxide nanoparticles remains of vital importance in nanobiomedicine. Low toxic superparamagnetic iron oxide nanoparticles (SPIONs) for theranostic applications in oncology having spherical shape and maghemite structure were produced using the fast microwave synthesis technique and were fully characterized by several complementary methods (transmission electron microscopy [TEM], X-ray diffraction [XRD], dynamic light scattering [DLS], X-ray photoelectron spectroscopy [XPS], X-ray absorption near edge structure [XANES], Mossbauer spectroscopy, and HeLa cells toxicity testing). TEM showed that the majority of the obtained nanoparticles were almost spherical and did not exceed 20 nm in diameter. The averaged DLS hydrodynamic size was found to be ~33 nm, while that of nanocrystallites estimated by XRD waŝ16 nm. Both XRD and XPS studies evidenced the maghemite (γ-Fe 2 O 3 ) atomic and electronic structure of the synthesized nanoparticles. The XANES data analysis demonstrated the structure of the nanoparticles being similar to that of macroscopic maghemite. The Mossbauer spectroscopy revealed the γ-Fe 2 O 3 phase of the nanoparticles and vibration magnetometry study showed that reactive oxygen species in HeLa cells are generated both in the cytoplasm and the nucleus. Quasispherical Fe 3+ SPIONs having the maghemite structure with the average size of 16 nm obtained by using the fast microwave synthesis technique are expected to be of great value for theranostic applications in oncology and multimodal anticancer therapy.

Speciation And Uptake of Arsenic Accumulated By Corn Seedlings Using XAS And DRC-ICP-MS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Parsons, J.G.; Martinez-Martinez, A.; Peralta-Videa, J.R.

ICP-MS was used to investigate the uptake of As(III) and As(V) from hydroponics growth media by corn seedlings. It was found that arsenic uptake by the plant roots for the arsenic(V) and arsenic(III) treatments were 95 and 112 ppm, respectively. However, in the shoots of the arsenic (V) treatments had 18 ppm whereas arsenic(III) treatments had 12 ppm. XANES studies showed that As for both treatments arsenic was present as a mixture of an As(III) sulfur complex and an As(V) oxygen complex. The XANES data was corroborated by the EXAFS studies showing the presence of both oxygen and sulfur ligandsmore » coordinated to the arsenic. Iron concentrations were found to increase by 4 fold in the As(V) contaminated growth media and 7 fold in the As(III) treatment compared to the control iron concentration of 500 ppm. Whereas, the total iron concentration in the shoots was found to decrease by approximately the same amount for both treatments from 360 ppm in the control to approximately 125 ppm in both arsenic treatments. Phosphorus concentrations were found to decrease in both the roots and shoots compared to the control plants. The total sulfur in the roots was found to increase in the arsenic(III) and arsenic(V) treatments to 560 ppm and 800 ppm, respectively, compared to the control plants 358 ppm. In addition, the total sulfur in shoots of the plants was found to remain relatively constant at approximately 1080 ppm. The potassium concentrations in the plants were found to increase in the roots and decrease in the shoots.« less

Best in show but not best shape: a photographic assessment of show dog body condition.

PubMed

Such, Z R; German, A J

2015-08-01

Previous studies suggest that owners often wrongly perceive overweight dogs to be in normal condition. The body shape of dogs attending shows might influence owners' perceptions, with online images of overweight show winners having a negative effect. This was an observational in silico study of canine body condition. 14 obese-prone breeds and 14 matched non-obese-probe breeds were first selected, and one operator then used an online search engine to identify 40 images, per breed, of dogs that had appeared at a major national UK show (Crufts). After images were anonymised and coded, a second observer subjectively assessed body condition, in a single sitting, using a previously validated method. Of 1120 photographs initially identified, 960 were suitable for assessing body condition, with all unsuitable images being from longhaired breeds. None of the dogs (0 per cent) were underweight, 708 (74 per cent) were in ideal condition and 252 (26 per cent) were overweight. Pugs, basset hounds and Labrador retrievers were most likely to be overweight, while standard poodles, Rhodesian ridgebacks, Hungarian vizslas and Dobermanns were least likely to be overweight. Given the proportion of show dogs from some breeds that are overweight, breed standards should be redefined to be consistent with a dog in optimal body condition. British Veterinary Association.

Lemurs and macaques show similar numerical sensitivity.

PubMed

Jones, Sarah M; Pearson, John; DeWind, Nicholas K; Paulsen, David; Tenekedjieva, Ana-Maria; Brannon, Elizabeth M

2014-05-01

We investigated the precision of the approximate number system (ANS) in three lemur species (Lemur catta, Eulemur mongoz, and Eulemur macaco flavifrons), one Old World monkey species (Macaca mulatta) and humans (Homo sapiens). In Experiment 1, four individuals of each nonhuman primate species were trained to select the numerically larger of two visual arrays on a touchscreen. We estimated numerical acuity by modeling Weber fractions (w) and found quantitatively equivalent performance among all four nonhuman primate species. In Experiment 2, we tested adult humans in a similar procedure, and they outperformed the four nonhuman species but showed qualitatively similar performance. These results indicate that the ANS is conserved over the primate order.

Amnesic patients show superior generalization in category learning.

PubMed

O'Connell, Garret; Myers, Catherine E; Hopkins, Ramona O; McLaren, R P; Gluck, Mark A; Wills, Andy J

2016-11-01

Generalization is the application of existing knowledge to novel situations. Questions remain about the precise role of the hippocampus in this facet of learning, but a connectionist model by Gluck and Myers (1993) predicts that generalization should be enhanced following hippocampal damage. In a two-category learning task, a group of amnesic patients (n = 9) learned the training items to a similar level of accuracy as matched controls (n = 9). Both groups then classified new items at various levels of distortion. The amnesic group showed significantly more accurate generalization to high-distortion novel items, a difference also present compared to a larger group of unmatched controls (n = 33). The model prediction of a broadening of generalization gradients in amnesia, at least for items near category boundaries, was supported by the results. Our study shows for the first time that amnesia can sometimes improve generalization. (PsycINFO Database Record (c) 2016 APA, all rights reserved).

Obesity in show dogs.

PubMed

Corbee, R J

2013-10-01

Obesity is an important disease with a growing incidence. Because obesity is related to several other diseases, and decreases life span, it is important to identify the population at risk. Several risk factors for obesity have been described in the literature. A higher incidence of obesity in certain breeds is often suggested. The aim of this study was to determine whether obesity occurs more often in certain breeds. The second aim was to relate the increased prevalence of obesity in certain breeds to the official standards of that breed. To this end, we investigated 1379 dogs of 128 different breeds by determining their body condition score (BCS). Overall, 18.6% of the show dogs had a BCS >5, and 1.1% of the show dogs had a BCS>7. There were significant differences between breeds, which could be correlated to the breed standards. It warrants firm discussions with breeders and judges in order to come to different interpretations of the standards to prevent overweight conditions from being the standard of beauty. © 2012 Blackwell Verlag GmbH.

Nickel distribution and isotopic fractionation in a Brazilian lateritic regolith: Coupling Ni isotopes and Ni K-edge XANES

NASA Astrophysics Data System (ADS)

Ratié, G.; Garnier, J.; Calmels, D.; Vantelon, D.; Guimarães, E.; Monvoisin, G.; Nouet, J.; Ponzevera, E.; Quantin, C.

2018-06-01

Ultramafic (UM) rocks are known to be nickel (Ni) rich and to weather quickly, which makes them a good candidate to look at the Ni isotope systematics during weathering processes at the Earth's surface. The present study aims at identifying the Ni solid speciation and discussing the weathering processes that produce Ni isotope fractionation in two deep laterite profiles under tropical conditions (Barro Alto, Goiás State, Brazil). While phyllosilicates and to a lower extent goethite are the main Ni-bearing phases in the saprolitic part of the profile, iron (Fe) oxides dominate the Ni budget in the lateritic unit. Nickel isotopic composition (δ60Ni values) has been measured in each unit of the regolith, i.e., rock, saprock, saprolite and laterite (n = 52). δ60Ni varies widely within the two laterite profiles, from -0.10 ± 0.05‰ to 1.43 ± 0.05‰, showing that significant Ni isotope fractionation occurs during the weathering of UM rocks. Overall, our results show that during weathering, the solid phase is depleted in heavy Ni isotopes due to the preferential sorption and incorporation of light Ni isotopes into Fe oxides; the same mechanisms likely apply to the incorporation of Ni into phyllosilicates (type 2:1). However, an isotopically heavy Ni pool is observed in the solid phase at the bottom of the saprolitic unit. This feature can be explained by two hypotheses that are not mutually exclusive: (i) a depletion in light Ni isotopes during the first stage of weathering due to the preferential dissolution of light Ni-containing minerals, and (ii) the sorption or incorporation of isotopically heavy Ni carried by percolating waters (groundwater samples have δ60Ni of 2.20 and 2.27‰), that were enriched in heavy Ni isotopes due to successive weathering processes in the overlying soil and laterite units.

Female Emotional Eaters Show Abnormalities in Consummatory and Anticipatory Food Reward

PubMed Central

Bohon, Cara; Stice, Eric; Spoor, Sonja

2009-01-01

Objective To test the hypothesis that emotional eaters show greater neural activation in response to food intake and anticipated food intake than nonemotional eaters and whether these differences are amplified during a negative versus neutral mood state. Method Female emotional eaters and nonemotional eaters (N = 21) underwent functional magnetic resonance imaging (fMRI) during receipt and anticipated receipt of chocolate milkshake and a tasteless control solution while in a negative and neutral mood. Results Emotional eaters showed greater activation in the parahippocampal gyrus and anterior cingulate (ACC) in response to anticipated receipt of milkshake and greater activation in the pallidum, thalamus, and ACC in response to receipt of milkshake during a negative relative to a neutral mood. In contrast, nonemotional eaters showed decreased activation in reward regions during a negative versus a neutral mood. Discussion Results suggest that emotional eating is related to increased anticipatory and consummatory food reward, but only during negative mood. PMID:19040270

Stage a Water Show

ERIC Educational Resources Information Center

Frasier, Debra

2008-01-01

In the author's book titled "The Incredible Water Show," the characters from "Miss Alaineus: A Vocabulary Disaster" used an ocean of information to stage an inventive performance about the water cycle. In this article, the author relates how she turned the story into hands-on science teaching for real-life fifth-grade students. The author also…

Molecular Analysis of Mixed Endometrial Carcinomas Shows Clonality in Most Cases.

PubMed

Köbel, Martin; Meng, Bo; Hoang, Lien N; Almadani, Noorah; Li, Xiaodong; Soslow, Robert A; Gilks, C Blake; Lee, Cheng-Han

2016-02-01

Mixed endometrial carcinoma refers to a tumor that comprises 2 or more distinct histotypes. We studied 18 mixed-type endometrial carcinomas-11 mixed serous and low-grade endometrioid carcinomas (SC/EC), 5 mixed clear cell and low-grade ECs (CCC/EC), and 2 mixed CCC and SCs (CCC/SC), using targeted next-generation sequencing and immunohistochemistry to compare the molecular profiles of the different histotypes present in each case. In 16 of 18 cases there was molecular evidence that both components shared a clonal origin. Eight cases (6 EC/SC, 1 EC/CCC, and 1 SC/CCC) showed an SC molecular profile that was the same in both components. Five cases (3 CCC/EC and 2 SC/EC) showed a shared endometrioid molecular profile and identical mismatch-repair protein deficiency in both components. A single SC/EC case harbored the same POLE exonuclease domain mutation in both components. One SC/CCC and 1 EC/CCC case showed both shared and unique molecular features in the 2 histotype components, suggesting early molecular divergence from a common clonal origin. In 2 cases, there were no shared molecular features, and these appear to be biologically unrelated synchronous tumors. Overall, these results show that the different histologic components in mixed endometrial carcinomas typically share the same molecular aberrations. Mixed endometrial carcinomas most commonly occur through morphologic mimicry, whereby tumors with serous-type molecular profile show morphologic features of EC or CCC, or through underlying deficiency in DNA nucleotide repair, with resulting rapid accrual of mutations and intratumoral phenotypic heterogeneity. Less commonly, mixed endometrial carcinomas are the result of early molecular divergence from a common progenitor clone or are synchronous biologically unrelated tumors (collision tumors).

Molecular analysis of mixed endometrial carcinomas shows clonality in most cases

PubMed Central

Hoang, Lien N.; Almadani, Noorah; Li, Xiaodong; Soslow, Robert A; Gilks, C. Blake; Lee, Cheng-Han

2016-01-01

Mixed endometrial carcinoma refers to a tumor that is comprised of two or more distinct histotypes. We studied 18 mixed-type endometrial carcinomas - 11 mixed serous and low-grade endometrioid carcinomas (SC/EC), 5 mixed clear cell and low-grade endometrioid carcinomas (CCC/EC), and 2 mixed clear cell and serous carcinoma (CCC/SC), using targeted next generation sequencing and immunohistochemistry to compare the molecular profiles of the different histotypes present in each case. In 16 of 18 cases there was molecular evidence that both components shared a clonal origin. Eight cases (6 EC/SC, 1 EC/CCC and 1 SC/CCC) showed a serous carcinoma molecular profile that was the same in both components. Five cases (3 CCC/EC and 2 SC/EC) showed a shared endometrioid molecular profile and identical mismatch repair protein (MMR) deficiency in both components. A single SC/EC case harbored the same POLE exonuclease domain mutation in both components. One SC/CCC and one EC/CCC case showed both shared and unique molecular features in the two histotype components, suggesting early molecular divergence from a common clonal origin. In two cases, there were no shared molecular features and these appear to be biologically unrelated synchronous tumors. Overall, these results show that the different histologic components in mixed endometrial carcinomas typically share the same molecular aberrations. Mixed endometrial carcinomas most commonly occur through morphological mimicry, whereby tumors with serous-type molecular profile show morphological features of endometrioid or clear cell carcinoma, or through underlying deficiency in DNA nucleotide repair, with resulting rapid accrual of mutations and intratumoral phenotypic heterogeneity. Less commonly, mixed endometrial carcinomas are the result of early molecular divergence from a common progenitor clone or are synchronous biologically unrelated tumors (collision tumors). PMID:26492180

Detection of uranium and chemical state analysis of individual radioactive microparticles emitted from the Fukushima nuclear accident using multiple synchrotron radiation X-ray analyses.

PubMed

Abe, Yoshinari; Iizawa, Yushin; Terada, Yasuko; Adachi, Kouji; Igarashi, Yasuhito; Nakai, Izumi

2014-09-02

Synchrotron radiation (SR) X-ray microbeam analyses revealed the detailed chemical nature of radioactive aerosol microparticles emitted during the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, resulting in better understanding of what occurred in the plant during the early stages of the accident. Three spherical microparticles (∼2 μm, diameter) containing radioactive Cs were found in aerosol samples collected on March 14th and 15th, 2011, in Tsukuba, 172 km southwest of the FDNPP. SR-μ-X-ray fluorescence analysis detected the following 10 heavy elements in all three particles: Fe, Zn, Rb, Zr, Mo, Sn, Sb, Te, Cs, and Ba. In addition, U was found for the first time in two of the particles, further confirmed by U L-edge X-ray absorption near-edge structure (XANES) spectra, implying that U fuel and its fission products were contained in these particles along with radioactive Cs. These results strongly suggest that the FDNPP was damaged sufficiently to emit U fuel and fission products outside the containment vessel as aerosol particles. SR-μ-XANES spectra of Fe, Zn, Mo, and Sn K-edges for the individual particles revealed that they were present at high oxidation states, i.e., Fe(3+), Zn(2+), Mo(6+), and Sn(4+) in the glass matrix, confirmed by SR-μ-X-ray diffraction analysis. These radioactive materials in a glassy state may remain in the environment longer than those emitted as water-soluble radioactive Cs aerosol particles.

Mercury speciation in piscivorous fish from mining-impacted reservoirs

USGS Publications Warehouse

Kuwabara, J.S.; Arai, Y.; Topping, B.R.; Pickering, I.J.; George, G.N.

2007-01-01

Guadalupe Reservoir (GUA), California, and Lahontan Reservoir (LAH), Nevada, U.S. are both affected either directly or indirectly by the legacy of gold and silver mining in the Sierra Nevada during the nineteenth century. Analysis of total mercury in fish from these lentic systems consistently indicate elevated concentrations (>1 ??g??g-1 wet weight; hereinafter, all concentrations are reported as wet weight unless indicated otherwise) well above the U.S. Environmenal Protection Agency's human consumption advisory level for fish (<0.3 ??g??g-1). Replicate X-ray absorption near edge structure (XANES) analyses on largemouth bass and hybrid striped bass from GUA and LAH were performed to determine predominant chemical species of mercury accumulated by these high-trophic-level piscivores that are exposed to elevated mercury through trophic transfer in mining-impacted lentic systems. Despite distinct differences in mercury source, the proximity of the source, and concentrations of complexing ligands, results of XANES analysis clearly indicated that mercury accumulated in these individual fish from the two reservoirs were dominated by methylmercury cysteine complexes. These findings are consistent with results from commercial fish species inhabiting marine environments which are presumed to include differing mercury sources (e.g., atmospheric, hydrothermal, or benthic). The dominance of methylmercury cysteine complexes in muscle tissues of fish obtained from such contrasting environments and exposure conditions suggests that a generic toxicological model for the consumption of fish could be applicable over a wide range of ecologic settings. ?? 2007 American Chemical Society.

Development of analytical procedures for the determination of hexavalent chromium in corrosion prevention coatings used in the automotive industry.

PubMed

Séby, F; Castetbon, A; Ortega, R; Guimon, C; Niveau, F; Barrois-Oudin, N; Garraud, H; Donard, O F X

2008-05-01

The European directive 2000/53/EC limits the use of Cr(VI) in vehicle manufacturing. Although a maximum of 2 g of Cr(VI) was authorised per vehicle for corrosion prevention coatings of key components, since July 2007 its use has been prohibited except for some particular applications. Therefore, the objective of this work was to develop direct analytical procedures for Cr(VI) determination in the different steel coatings used for screws. Instead of working directly with screws, the optimisation of the procedures was carried out with metallic plates homogeneously coated to improve the data comparability. Extraction of Cr(VI) from the metallic parts was performed by sonication. Two extraction solutions were tested: a direct water extraction solution used in standard protocols and an ammonium/ammonia buffer solution at pH 8.9. The extracts were further analysed for Cr speciation by high-performance liquid chromatography (HPLC) inductively coupled plasma (ICP) atomic emission spectrometry or HPLC ICP mass spectrometry depending on the concentration level. When possible, the coatings were also directly analysed by solid speciation techniques (X-ray photoelectron spectroscopy, XPS, and X-ray absorption near-edge structure, XANES) for validation of the results. Very good results between the different analytical approaches were obtained for the sample of coating made up of a heated paint containing Zn, Al and Cr when using the extracting buffer solution at pH 8.9. After a repeated four-step extraction procedure on the same portion test, taking into account the depth of the surface layer reached, good agreement with XPS and XANES results was obtained. In contrast, for the coatings composed of an alkaline Zn layer where Cr(VI) and Cr(III) are deposited, only the extraction procedure using water allowed the detection of Cr(VI). To elucidate the Cr(VI) reduction during extraction at pH 8.9, the reactivity of Cr(VI) towards different species of Zn generally present in the

Phase transitions in biogenic amorphous calcium carbonate.

PubMed

Gong, Yutao U T; Killian, Christopher E; Olson, Ian C; Appathurai, Narayana P; Amasino, Audra L; Martin, Michael C; Holt, Liam J; Wilt, Fred H; Gilbert, P U P A

2012-04-17

Crystalline biominerals do not resemble faceted crystals. Current explanations for this property involve formation via amorphous phases. Using X-ray absorption near-edge structure (XANES) spectroscopy and photoelectron emission microscopy (PEEM), here we examine forming spicules in embryos of Strongylocentrotus purpuratus sea urchins, and observe a sequence of three mineral phases: hydrated amorphous calcium carbonate (ACC · H(2)O) → dehydrated amorphous calcium carbonate (ACC) → calcite. Unexpectedly, we find ACC · H(2)O-rich nanoparticles that persist after the surrounding mineral has dehydrated and crystallized. Protein matrix components occluded within the mineral must inhibit ACC · H(2)O dehydration. We devised an in vitro, also using XANES-PEEM, assay to identify spicule proteins that may play a role in stabilizing various mineral phases, and found that the most abundant occluded matrix protein in the sea urchin spicules, SM50, stabilizes ACC · H(2)O in vitro.

Spatial Heterodyne Observation of Water (SHOW) from a high altitude aircraft

NASA Astrophysics Data System (ADS)

Bourassa, A. E.; Langille, J.; Solheim, B.; Degenstein, D. A.; Letros, D.; Lloyd, N. D.; Loewen, P.

2017-12-01

The Spatial Heterodyne Observations of Water instrument (SHOW) is limb-sounding satellite prototype that is being developed in collaboration between the University of Saskatchewan, York University, the Canadian Space Agency and ABB. The SHOW instrument combines a field-widened SHS with an imaging system to observe limb-scattered sunlight in a vibrational band of water (1363 nm - 1366 nm). Currently, the instrument has been optimized for deployment on NASA's ER-2 aircraft. Flying at an altitude of 70, 000 ft the ER-2 configuration and SHOW viewing geometry provides high spatial resolution (< 500 m) limb-measurements of water vapor in the Upper troposphere and lower stratosphere region. During an observation campaign from July 15 - July 22, the SHOW instrument performed 10 hours of observations from the ER-2. This paper describes the SHOW measurement technique and presents the preliminary analysis and results from these flights. These observations are used to validate the SHOW measurement technique and demonstrate the sampling capabilities of the instrument.

Effects of Mineral Compositions on Matrix Diffusion and Sorption of 75Se(IV) in Granite.

PubMed

Yang, Xiaoyu; Ge, Xiangkun; He, Jiangang; Wang, Chunli; Qi, Liye; Wang, Xiangyun; Liu, Chunli

2018-02-06

Exploring the migration behaviors of selenium in granite is critical for the safe disposal of radioactive waste. The matrix diffusion and sorption of 75 Se(IV) (analogue for 79 Se) in granite were systematically studied to set reliable parameters in this work. Through-diffusion and batch sorption experiments were conduct with four types of Beishan granite. The magnitudes of the obtained apparent diffusion coefficient (D a ) values are of the following order: monzogranite > granodiorite-2 > granodiorite-1, which is opposite to the sequence of the K d values obtained from both the diffusion model and batch sorption experiments. The EPMA results of the granitic flakes showed that there was no obvious enrichment of Se(IV) on quartz, microcline and albite. Only biotite showed a weak affinity for Se(IV). Macroscopic sorption behaviors of Se(IV) on the four types of granite were identical with the sequence of the granitic biotite contents. Quantitative fitting results were also provided. XPS and XANES spectroscopy data revealed that bidentate inner-sphere complexes were formed between Se(IV) and Fe(III). Our results indicate that biotite can be representative of the Se(IV) sorption in complex mineral assemblages such as granite, and the biotite contents are critically important to evaluate Se(IV) transport in granite.

A high pressure La K-edge X-ray absorption fine structure spectroscopy investigation of La1/3NbO3

NASA Astrophysics Data System (ADS)

Marini, C.; Joseph, B.; Noked, O.; Shuker, R.; Kennedy, B. J.; Mathon, O.; Pascarelli, S.; Sterer, E.

2018-01-01

La K-edge X-ray absorption spectroscopy has been used to elucidate the changes in the local electronic and lattice structure that occur in the A-site deficient double perovskite La?NbO? up to 6 GPa. The pressure evolution of the oxygen dodecahedrum around the A-site has been examined. XANES (X-ray absorption near edge structure) data show modifications ascribed to the increase of bands overlapping as a consequence of the bond distance contraction, which has been directly probed by EXAFS (extended x-ray absorption fine structure) spectra. The La-O Debye Waller factors (DWFs) tend to increase whereas the La-Nb bond DWFs show only a tendency to decrease indicating the robustness of the crystal lattice structure, even in presence of the oxygen disordering. This permits the system to reverse back to its original conditions in this pressure range as evident from the measurements upon pressure release. The present results have been interpreted in the light of charge transfer related to the two-step reduction mechanism acting at the Nb site (with niobium ions passing from Nb? to Nb?) which also results in the elongation of the Nb-O bond distances in the octahedra, in agreement with the Nb K-edge results reported earlier.

Research project shows importance of pre-employment hearing testing.

PubMed

Karlovich, R S

1992-02-01

Forty employees received pure-tone baseline hearing tests at the time they began employment as LSM operators for the U.S. Postal Services; the workplace eight-hour average sound level (TWA) was 85 dBA. Nineteen operators from the original group had their hearing retested three years later. None of the retested subjects showed large or systematic changes in hearing sensitivity over the three-year period. For the audiometric frequencies most susceptible to noise exposure (3000, 4000, 6000 Hz), only 5 percent of the operators showed a bilateral change in threshold greater than 5 dB at any frequency, and none of them showed more than a 10 dB threshold change in both ears. None of the operators displayed a Standard Threshold Shift as described by OSHA. The data further suggested that many workers began their LSM work assignment with a pre-existing hearing loss and, based upon audiometric and history information, the impairment probably resulted from prior occupational and/or nonoccupational noise exposure. The importance of hearing-conservation programs for employees is emphasized.

Speciation and Distribution of Phosphorus in a Fertilized Soil: A Synchrotron-Based Investigation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lombi, E.; Scheckel, K.G.; Armstrong, R.D.

2008-06-09

Phosphorus availability is often a limiting factor for crop production around the world. The efficiency of P fertilizers in calcareous soils is limited by reactions that decrease P availability; however, fluid fertilizers have recently been shown, in highly calcareous soils of southern Australia, to be more efficient for crop (wheat [Triticum aestivum L.]) P nutrition than granular products. To elucidate the mechanisms responsible for this differential response, an isotopic dilution technique (E value) coupled with a synchrotron-based spectroscopic investigation were used to assess the reaction products of a granular (monoammonium phosphate, MAP) and a fluid P (technical-grade monoammonium phosphate, TG-MAP)more » fertilizer in a highly calcareous soil. The isotopic exchangeability of P from the fluid fertilizer, measured with the E-value technique, was higher than that of the granular product. The spatially resolved spectroscopic investigation, performed using nano x-ray fluorescence and nano x-ray absorption near-edge structure (n-XANES), showed that P is heterogeneously distributed in soil and that, at least in this highly calcareous soil, it is invariably associated with Ca rather than Fe at the nanoscale. 'Bulk' XANES spectroscopy revealed that, in the soil surrounding fertilizer granules, P precipitation in the form of octacalcium phosphate and apatite-like compounds is the dominant mechanism responsible for decreases in P exchangeability. This process was less prominent when the fluid P fertilizer was applied to the soil.« less

A high-voltage rechargeable magnesium-sodium hybrid battery

DOE PAGES

Li, Yifei; An, Qinyou; Cheng, Yingwen; ...

2017-02-13

There is a growing global demand for safe and low-cost energy storage technology which triggers strong interests in novel battery concepts beyond state-of-art Li-ion batteries. We report a high-voltage rechargeable Mg–Na hybrid battery featuring dendrite-free deposition of Mg anode and Na-intercalation cathode as a low-cost and safe alternative to Li-ion batteries for large-scale energy storage. A prototype device using a Na 3V 2(PO 4) 3 cathode, a Mg anode, and a Mg–Na dual salt electrolyte exhibits the highest voltage (2.60 V vs. Mg) and best rate performance (86% capacity retention at 10 C rate) among reported hybrid batteries. Synchrotron radiation-basedmore » X-ray absorption near edge structure (XANES), atomic-pair distribution function (PDF), and high-resolution X-ray diffraction (HRXRD) studies reveal the chemical environment and structural change of Na 3V 2(PO 4) 3 cathode during the Na ion insertion/deinsertion process. XANES study shows a clear reversible shift of vanadium K-edge and HRXRD and PDF studies reveal a reversible two-phase transformation and V–O bond length change during cycling. The energy density of the hybrid cell could be further improved by developing electrolytes with a higher salt concentration and wider electrochemical window. Our work represents a significant step forward for practical safe and low-cost hybrid batteries.« less

Adenoma Detection Rate: I Will Show You Mine if You Show Me Yours

PubMed Central

Oliveira Ferreira, Alexandre; Fidalgo, Catarina; Palmela, Carolina; Costa Santos, Maria Pia; Torres, Joana; Nunes, Joana; Loureiro, Rui; Ferreira, Rosa; Barjas, Elídio; Glória, Luísa; Santos, António Alberto; Cravo, Marília

2017-01-01

Background Colorectal cancer (CRC) is the first cause of cancer-related mortality in Portugal. CRC screening reduces disease-specific mortality. Colonoscopy is currently the preferred method for screening as it may contribute to the reduction of CRC incidence. This beneficial effect is strongly associated with the adenoma detection rate (ADR). Aim Our aim was to evaluate the quality of colonoscopy at our unit by measuring the currently accepted quality parameters and publish them as benchmarking indicators. Methods From 5,860 colonoscopies, 654 screening procedures (with and without previous fecal occult blood testing) were analyzed. Results The mean age of the patients was 66.4 ± 7.8 years, and the gender distribution was 1:1. The overall ADR was 36% (95% confidence interval [CI] 32–39), the mean number of adenomas per colonoscopy was 0.66 (95% CI 0.56–0.77), and the sessile serrate lesion detection rate was 1% (95% CI 0–2). The bowel preparation was rated as adequate in 496 (76%) patients. The adjusted cecal intubation rate (CIR) was 93.7% (95% CI 91.7–95.8). Most colonoscopies were performed under monitored anesthesia care (53%), and 35% were unsedated. The use of sedation (propofol or midazolam based) was associated with a higher CIR with an odds ratio of 3.60 (95% CI 2.02–6.40, p < 0.001). Conclusion Our data show an above-standard ADR. The frequency of poor bowel preparation and the low sessile serrated lesion detection rate were acknowledged, and actions were implemented to improve both indicators. Quality auditing in colonoscopy should be compulsory, and while many units may do so internally, this is the first national report from a high-throughput endoscopy unit. PMID:28848785

Tracking the Chemical Transformations at the Brønsted Acid Site upon Water-Induced Deprotonation in a Zeolite Pore

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vjunov, Aleksei; Wang, Meng; Govind, Niranjan

We report the structural changes induced by Brønsted acidic site deprotonation in a zeolite with MFI structure as a function of temperature up to 430°C using in situ Al K-edge X-ray absorption fine structure spectroscopy (XAFS). At ambient conditions, the protons are present as hydrated hydronium ions (H3O+(H2O)n) that are ion-paired to the anionic, Al tetrahedral (T) site. At elevated temperatures, loss of water molecules hydrating the hydronium ions leads to an unstable free hydronium ion that disso-ciates to form the hydroxylated T-site. The formation of this (-O3)-Al-(OH-) species leads to the elongation of one of the four Al-O bondsmore » and causes significant distortion of the tetrahedral symmetry about the Al atom. This distortion leads to the appearance of new pre-edge features in the Al K-edge X-ray absorption near edge structure (XANES) spectra. The pre-edge peak assignment is confirmed by time-dependent density functional theory calculation of the XANES spectrum. The XANES spectra are also sensitive to solutes or solvent that are in proximity to the T-site. A second structural transition occurs at about the same temperature, namely the conversion of a minor fraction of extra-framework octahedral Al present in the sample at ambient conditions to a tetrahedral species through the de-coordination of H2O-ligands. Both IR spectroscopy and thermogravimetric analysis (TGA) are further used to confirm the overall chemical transformation of the T-site.« less

Bilateral femoral neck fractures resulting from pregnancy-associated osteoporosis showed bone marrow edema on magnetic resonance imaging.

PubMed

Kasahara, Kyoko; Kita, Nobuyuki; Kawasaki, Taku; Morisaki, Shinsuke; Yomo, Hiroko; Murakami, Takashi

2017-06-01

Femoral neck fractures resulting from pregnancy-associated osteoporosis is a rare condition. Herein, we report an undoubted case of pregnancy-associated osteoporosis in a 38-year-old primiparous patient with pre-existing anorexia nervosa who suffered bilateral femoral neck fractures in the third trimester and early post-partum period. Magnetic resonance imaging revealed femoral neck fractures as well as diffuse marrow edema involving both femoral heads, which are considered under ordinary circumstances as characteristic imaging findings of transient osteoporosis of the hip. Based on our experience, we propose that pregnancy-associated osteoporosis might be present in femoral neck fractures attributed to transient osteoporosis of the hip in pregnancy. Conversely, bone status should be carefully and accurately estimated in cases of potential transient osteoporosis of the hip in pregnancy to reduce future fracture risk. © 2017 The Authors Journal of Obstetrics and Gynaecology Research published by John Wiley & Sons Australia, Ltd on behalf of Japan Society of Obstetrics and Gynecology.

Revealing the Influence of Silver in Ni-Ag Catalysts on the Selectivity of Higher Olefin Synthesis from Stearic Acid

NASA Astrophysics Data System (ADS)

Danyushevsky, V. Ya.; Murzin, V. Yu.; Kuznetsov, P. S.; Shamsiev, R. S.; Katsman, E. A.; Khramov, E. V.; Zubavichus, Y. V.; Berenblyum, A. S.

2018-01-01

Results on the conversion of stearic acid to olefins over Ni-Ag/γ-Al2O3 catalysts are presented. XANES and EXAFS experiments in situ and DFT calculations were applied to reveal the structure of active sites therein. It is shown that the introduction of Ag to Ni catalysts leads to an increase in the olefin yield. After a reduction in hydrogen (350°C, 3 h) alumina-supported nanoparticles of nickel sulfides and metallic Ag are formed. The role of metal hydrides formed during the reaction is extensively discussed.

Children with autism spectrum disorder show reduced adaptation to number

PubMed Central

Turi, Marco; Burr, David C.; Igliozzi, Roberta; Aagten-Murphy, David; Muratori, Filippo; Pellicano, Elizabeth

2015-01-01

Autism is known to be associated with major perceptual atypicalities. We have recently proposed a general model to account for these atypicalities in Bayesian terms, suggesting that autistic individuals underuse predictive information or priors. We tested this idea by measuring adaptation to numerosity stimuli in children diagnosed with autism spectrum disorder (ASD). After exposure to large numbers of items, stimuli with fewer items appear to be less numerous (and vice versa). We found that children with ASD adapted much less to numerosity than typically developing children, although their precision for numerosity discrimination was similar to that of the typical group. This result reinforces recent findings showing reduced adaptation to facial identity in ASD and goes on to show that reduced adaptation is not unique to faces (social stimuli with special significance in autism), but occurs more generally, for both parietal and temporal functions, probably reflecting inefficiencies in the adaptive interpretation of sensory signals. These results provide strong support for the Bayesian theories of autism. PMID:26056294

Mullite and Mullite Ceramics

DTIC Science & Technology

1994-01-01

possible. The here reported measurements were carried out with synchrotron radiation from the electron storage ring ELSA of the Bonn University. All...Physikalisches Institut der Universitdt Bonn , Bonn , Germany Measurements of X-ray absorption spectra near the absorption edge of a selected element (XANES