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Sample records for hydrogen adsorbate structures

  1. Hydrogen molecule on lithium adsorbed graphene: A DFT study

    NASA Astrophysics Data System (ADS)

    Kaur, Gagandeep; Gupta, Shuchi; Gaganpreet, Dharamvir, Keya

    2016-05-01

    Electronic structure calculations for the adsorption of molecular hydrogen on lithium (Li) decorated and pristine graphene have been studied systematically using SIESTA code [1] within the framework of the first-principle DFT under the Perdew-Burke-Ernzerhof (PBE) form of the generalized gradient approximation (GGA)[2], including spin polarization. The energy of adsorption of hydrogen molecule on graphene is always enhanced by the presence of co-adsorbed lithium. The most efficient adsorption configuration is when H2 is lying parallel to lithium adsorbed graphene which is in contrast to its adsorption on pristine graphene (PG) where it prefers perpendicular orientation.

  2. Hydrogen adsorption of ruthenium: Isosteres of solubility of adsorbed hydrogen

    SciTech Connect

    Zaginaichenko, S.Y.; Matysina, Z.A.; Schur, D.V.; Pishuk, V.K.

    1998-12-31

    The theoretical investigation of solubility isosteres of adsorbed hydrogen has been performed for free face (0001) of crystals with hexagonal close-packed lattice A3 of Mg type. The face free energy has been calculated and its dependence on temperature, pressure, hydrogen concentration and character of hydrogen atoms distribution over surface interstitial sites of different type has been defined. The equations of thermodynamic equilibrium and solubility of adsorbed hydrogen have been defined. The plots of isosteres in the region of phase transition from isotropic to anisotropic state have been constructed and it has been established that in anisotropic state the order in distribution of hydrogen atoms over interstitial sites of different type must become apparent. Comparison of the theoretical isosteres with experimental for ruthenium has been carried out, the isotropic-anisotropic state transition can stipulate a stepwise and break-like change in isosteres.

  3. Structure and properties of water film adsorbed on mica surfaces

    NASA Astrophysics Data System (ADS)

    Zhao, Gutian; Tan, Qiyan; Xiang, Li; Cai, Di; Zeng, Hongbo; Yi, Hong; Ni, Zhonghua; Chen, Yunfei

    2015-09-01

    The structure profiles and physical properties of the adsorbed water film on a mica surface under conditions with different degrees of relative humidity are investigated by a surface force apparatus. The first layer of the adsorbed water film shows ice-like properties, including a lattice constant similar with ice crystal, a high bearing capacity that can support normal pressure as high as 4 MPa, a creep behavior under the action of even a small normal load, and a character of hydrogen bond. Adjacent to the first layer of the adsorbed water film, the water molecules in the outer layer are liquid-like that can flow freely under the action of external loads. Experimental results demonstrate that the adsorbed water layer makes the mica surface change from hydrophilic to weak hydrophobic. The weak hydrophobic surface may induce the latter adsorbed water molecules to form water islands on a mica sheet.

  4. High-performances carbonaceous adsorbents for hydrogen storage

    NASA Astrophysics Data System (ADS)

    Zhao, Weigang; Fierro, Vanessa; Aylon, E.; Izquierdo, M. T.; Celzard, Alain

    2013-03-01

    Activated carbons (ACs) with controlled microporosity have been prepared and their H2 storage performances have been tested in a gravimetric device. Such adsorbents are natural Chinese anthracites chemically activated with alkaline hydroxides, NaOH or KOH. Outstanding total storage capacities of hydrogen, as high as 6.6wt.% equivalent to excess capacity of 6.2 wt.%, have been obtained at 4MPa for some of these adsorbents. These values of hydrogen adsorption are among the best, if not the highest, ever published so far in the open literature. They are well above those of some commercial materials, e.g. Maxsorb-3, considered as a reference of high-performance adsorbent for hydrogen adsorption. Such exceptional storage capacities may be ascribed to a higher volume of micropores (< 2nm).

  5. Hydrogen storage on palladium adsorbed graphene: A density functional theory study

    NASA Astrophysics Data System (ADS)

    Pantha, Nurapati; Khaniya, Asim; Adhikari, Narayan Prasad

    2015-07-01

    We have performed density functional theory (DFT)-based first-principles calculations to study the stability, geometrical structures, and electronic properties of a single palladium (Pd) atom adsorbed graphene with reference to pristine graphene. The study also covers the adsorption properties of molecular hydrogen/s on the most stable Pd-graphene geometry by taking into account London dispersion forces in addition to the standard DFT calculations in the Quantum ESPRESSO package. From the analysis of estimated values of binding energy of Pd on different occupation sites (i.e., bridge, hollow, and top) of graphene supercells, the bridge site is found to be the most favorable one with the magnitudes of 1.114, 1.426, and 1.433 eV in 2×2, 3×3, and 4×4 supercells, respectively. The study of the electronic properties of Pd adsorbed graphene shows a bandgap of 45 meV, which can account for the breaking of the symmetry of the graphene structure. Regarding the gaseous (hydrogen) adsorption on Pd-adatom graphene, we checked the increasing number of molecular hydrogens (H2) from one to seven on the 3×3 supercell, and found that the adsorption energy per H2 decreases on increasing hydrogen concentration and lies within the range of 0.998-0.151 eV.

  6. Application of Henry's Law for Binding Energies of Adsorbed Hydrogen

    NASA Astrophysics Data System (ADS)

    Gillespie, Andrew; Dohnke, Elmar; Stalla, David; Sweany, Mark; Pfeifer, Peter

    2015-03-01

    The method of isosteres is the simplest method used to calculate the differential enthalpy of adsorption. However, it is incredibly sensitive to the choice of model and respective fitting parameters. For a set of isotherms measured on a specific sample, most models converge upon a similar value at high coverage, but are inconsistent in the low pressure regime. In this talk, we investigate the application of various models for localized and mobile adsorption at low pressures in order to obtain binding energy of hydrogen to the adsorbent surface. Henry's Law analysis of the Langmuir Model of adsorption yield binding energies in excellent agreement with those obtained from the Clausius Clapeyron relation. Work supported by DOE-EERE, Award No. DE-FG36-08GO18142.

  7. Hydrogen storage on high-surface-area carbon monoliths for Adsorb hydrogen Gas Vehicle

    NASA Astrophysics Data System (ADS)

    Soo, Yuchoong; Pfeifer, Peter

    2014-03-01

    Carbon briquetting can increase hydrogen volumetric storage capacity by reducing the useless void volume resulting in a better packing density. It is a robust and efficient space-filling form for an adsorbed hydrogen gas vehicle storage tank. To optimize hydrogen storage capacity, we studied three fabrication process parameters: carbon-to-binder ratio, compaction temperature, and pyrolysis atmosphere. We found that carbon-to-binder ratio and pyrolysis atmosphere have influences on gravimetric excess adsorption. Compaction temperature has large influences on gravimetric and volumetric storage capacity. We have been able to optimize these parameters for high hydrogen storage. All monolith uptakes (up to 260 bar) were measured by a custom-built, volumetric, reservoir-type instrument.

  8. Removal of hydrogen sulfide at ambient conditions on cadmium/GO-based composite adsorbents.

    PubMed

    Florent, Marc; Wallace, Rajiv; Bandosz, Teresa J

    2015-06-15

    Cadmium-based materials with various hydroxide to carbonate ratios and their composites with graphite oxide were synthesized by a fast and simple precipitation procedure and then used as H2S adsorbents at ambient conditions in the dark or upon a visible light exposure. The structural properties and chemical features of the adsorbents were analyzed before and after hydrogen sulfide adsorption. The results showed that the high ratio of hydroxide to carbonate led to an improved H2S adsorption capacity. In moist conditions cadmium hydroxide was the best adsorbent. Moreover, it showed photoactive properties. While the incorporation of a graphene-based phase slightly decreased the extent of the improvement in the H2S adsorption capacity in moist conditions caused by photoactivity, its presence in the composites enhanced the performance in dry conditions. This was linked to photoactivity of CdS that can split H2S resulting in the formation of water in the system. The graphene-based phase enhanced the electron transfer and delayed the recombination of photoinduced charges. Carbonate-based materials showed a very good adsorption capacity in dark conditions in the presence of moisture. Upon the light exposure, CdS likely photocatalyzes the reduction of carbonate ions to formates/formaldehydes. Their deposition on the surface limits the number of sites available to H2S adsorption. PMID:25792480

  9. Interaction between adsorbed hydrogen and potassium on a carbon nanocone containing material as studied by photoemission

    SciTech Connect

    Yu, Xiaofeng; Raaen, Steinar

    2015-09-14

    Hydrogen adsorption on a potassium doped carbon nanocone containing material was studied by photoelectron spectroscopy and work function measurement. The valence band spectra indicate that there is charge transfer from potassium to carbon. Upon deposition on carbon potassium is in its ionic state for lower doping and shows both ionic and metallic behavior at higher doping. Adsorption of hydrogen facilitates diffusion of potassium on the carbon material as seen by changes in the K{sub 2p} core level spectrum. Variations in the measured sample work function indicate that hydrogen initially adsorb on the K dopants and subsequently adsorb on the carbon cone containing material.

  10. Towards 9 weight percent, reversible, room temperature hydrogen adsorbents: Hydrogen saturated organometallic bucky balls

    NASA Astrophysics Data System (ADS)

    Zhao, Yufeng

    2005-03-01

    A new concept for high-capacity hydrogen absorbents is introduced by first-principles calculations. Transition metal (TM) atoms bound to fullerenes are proposed as a medium for high density, room temperature, ambient pressure storage of hydrogen. TMs bind to C60 or C48B12 by charge transfer interactions to produce stable organometallic bucky balls (OBBs) and bind to multiple dihydrogen molecules through the so-called Kubas interaction [1]. A particular scandium OBB can bind as many as eleven hydrogen atoms per TM, ten of which are bound in the form of dihydrogen molecular ligands that can be adsorbed and desorbed reversibly. In this case, the calculated binding energy is around 0.3 eV/H2, which is ideal for use on-board vehicles. The theoretical maximum retrievable H2 storage density is about 9 weight percent. This work was supported by the U.S. DOE EERE, BES/MS, and BES/CS under contract No. DEAC36-99GO10337. [1] G.J. Kubas, J. Organometallic Chem. 635, 37 (2001).

  11. Heat capacity of quantum adsorbates: Hydrogen and helium on evaporated gold films

    SciTech Connect

    Birmingham, J.T. |

    1996-06-01

    The author has constructed an apparatus to make specific heat measurements of quantum gases adsorbed on metallic films at temperatures between 0.3 and 4 K. He has used this apparatus to study quench-condensed hydrogen films between 4 and 923 layers thick with J = 1 concentrations between 0.28 and 0.75 deposited on an evaporated gold surface. He has observed that the orientational ordering of the J = 1 molecules depends on the substrate temperature during deposition of the hydrogen film. He has inferred that the density of the films condensed at the lowest temperatures is 25% higher than in bulk H{sub 2} crystals and have observed that the structure of those films is affected by annealing at 3.4 K. The author has measured the J = 1 to J = 0 conversion rate to be comparable to that of the bulk for thick films; however, he found evidence that the gold surface catalyzes conversion in the first two to four layers. He has also used this apparatus to study films of {sup 4}He less than one layer thick adsorbed on an evaporated gold surface. He shows that the phase diagram of the system is similar to that for {sup 4}He/graphite although not as rich in structure, and the phase boundaries occur at different coverages and temperatures. At coverages below about half a layer and at sufficiently high temperatures, the {sup 4}He behaves like a two-dimensional noninteracting Bose gas. At lower temperatures and higher coverages, liquidlike and solidlike behavior is observed. The Appendix shows measurements of the far-infrared absorptivity of the high-{Tc} superconductor La{sub 1.87}Sr{sub 0.13}CuO{sub 4}.

  12. Electronic structure of benzene adsorbed on Ni and Cu surfaces

    SciTech Connect

    Weinelt, M.; Nilsson, A.; Wassdahl, N.

    1997-04-01

    Benzene has for a long time served as a prototype adsorption system of large molecules. It adsorbs with the molecular plane parallel to the surface. The bonding of benzene to a transition metal is typically viewed to involve the {pi} system. Benzene adsorbs weakly on Cu and strongly on Ni. It is interesting to study how the adsorption strength is reflected in the electronic structure of the adsorbate-substrate complex. The authors have used X-ray Emission (XE) and X-ray Absorption (XA) spectroscopies to selectively study the electronic states localized on the adsorbed benzene molecule. Using XES the occupied states can be studies and with XAS the unoccupied states. The authors have used beamline 8.0 and the Swedish endstation equipped with a grazing incidence x-ray spectrometer and a partial yield absorption detector. The resolution in the XES and XAS were 0.5 eV and 0.05 eV, respectively.

  13. Electrochemical desorption of hydrogen atoms adsorbed on liquid gallium

    SciTech Connect

    Krivenko, A.G.; Vekin, A.B.; Benderskii, V.A.

    1987-12-01

    Laser-pulse electron photoemission was used to measure absolute values of the rate constants, W/sub 3/, of electrochemical desorption (ECD) of hydrogen atoms from liquid gallium. The W/sub 3/ were shown to be a linear function of hydrogen concentration, in accord with the fact that both hydrogen ions and water molecules are involved in desorption. The components of W/sub 3/ arising from the two reaction channels are exponential functions of electrode potential, and in their order of magnitude (approx. 10/sup 8/ liter/mole x sec and approx. 10/sup 6/ sec/sup -1/) are close to the corresponding constants for mercury and bismuth. In the desorption involving hydrogen ions, the H/D isotope effect decreases from 5 to 3 as the overpotential is raised from 0.75 to 1.15 V. It was suggested that isotope effects which are higher than those found for Hg and Bi electrodes arise from longer proton tunneling distance.

  14. Structural characterization of adsorbed helical and beta-sheet peptides

    NASA Astrophysics Data System (ADS)

    Samuel, Newton Thangadurai

    Adsorbed peptides on surfaces have potential applications in the fields of biomaterials, tissue engineering, peptide microarrays and nanobiotechnology. The surface region, the "biomolecular interface" between a material and the biological environment, plays a crucial role in these applications. As a result, characterization of adsorbed peptide structure, especially with respect to identity, concentration, spatial distribution, conformation and orientation, is important. The present research employs NEXAFS (near-edge X-ray absorption fine structure spectroscopy) and SFG (sum frequency generation spectroscopy) to provide information about the adsorbed peptide structure. Soft X-ray NEXAFS is a synchrotron-based technique which typically utilizes polarized X-rays to interrogate surfaces under ultra-high vacuum conditions. SFG is a non-linear optical technique which utilizes a combination of a fixed visible and a tunable infrared laser beams to generate a surface-vibrational spectrum of surface species. SFG has the added advantage of being able to directly analyze the surface-structure at the solid-liquid interface. The main goals of the present research were twofold: characterize the structure of adsorbed peptides (1) ex situ using soft X-ray NEXAFS, and (2) in situ using non-linear laser spectroscopy (SFG). Achieving the former goal involved first developing a comprehensive characterization of the carbon, nitrogen and oxygen k-edge NEXAFS spectra for amino acids, and then using a series of helical and beta-sheet peptides to demonstrate the sensitivity of polarization-dependent NEXAFS to secondary structure of adsorbed peptides. Characterizing the structure of adsorbed peptides in situ using SFG involved developing a model system to probe the solid-liquid interface in situ; demonstrating the ability to probe the molecular interactions and adsorbed secondary structure; following the time-dependent ordering of the adsorbed peptides; and establishing the ability to obtain

  15. Rotational Spectromicroscopy: Imaging the Orbital Interaction between Molecular Hydrogen and an Adsorbed Molecule.

    PubMed

    Li, Shaowei; Yuan, Dingwang; Yu, Arthur; Czap, Gregory; Wu, Ruqian; Ho, W

    2015-05-22

    A hydrogen molecule can diffuse freely on the surface and be trapped above an adsorbed molecule within the junction of a scanning tunneling microscope. The trapped dihydrogen exhibits the properties of a free rotor. Here we show that the intermolecular interaction between dihydrogen and Mg-porphyrin (MgP) can be visualized by imaging j=0 to 2 rotational excitation of dihydrogen. The interaction leads to a weakened H-H bond and modest electron donation from the dihydrogen to the lowest unoccupied molecular orbital of MgP, a process similarly observed for the interaction between dihydrogen and an adsorbed Au atom. PMID:26047242

  16. Rotational Spectromicroscopy: Imaging the Orbital Interaction between Molecular Hydrogen and an Adsorbed Molecule

    NASA Astrophysics Data System (ADS)

    Li, Shaowei; Yuan, Dingwang; Yu, Arthur; Czap, Gregory; Wu, Ruqian; Ho, W.

    2015-05-01

    A hydrogen molecule can diffuse freely on the surface and be trapped above an adsorbed molecule within the junction of a scanning tunneling microscope. The trapped dihydrogen exhibits the properties of a free rotor. Here we show that the intermolecular interaction between dihydrogen and Mg-porphyrin (MgP) can be visualized by imaging j =0 to 2 rotational excitation of dihydrogen. The interaction leads to a weakened H-H bond and modest electron donation from the dihydrogen to the lowest unoccupied molecular orbital of MgP, a process similarly observed for the interaction between dihydrogen and an adsorbed Au atom.

  17. Probing the effects of 2D confinement on hydrogen dynamics in water and ice adsorbed in graphene oxide sponges.

    PubMed

    Romanelli, Giovanni; Senesi, Roberto; Zhang, Xuan; Loh, Kian Ping; Andreani, Carla

    2015-12-21

    We studied the single particle dynamics of water and ice adsorbed in graphene oxide (GO) sponges at T = 293 K and T = 20 K. We used Deep Inelastic Neutron Scattering (DINS) at the ISIS neutron and muon spallation source to derive the hydrogen mean kinetic energy, 〈EK〉, and momentum distribution, n(p). The goal of this work was to study the hydrogen dynamics under 2D confinement and the potential energy surface, fingerprinting the hydrogen interaction with the layered structure of the GO sponge. The observed scattering is interpreted within the framework of the impulse approximation. Samples of both water and ice adsorbed in GO show n(p) functions with almost harmonic and anisotropic line shapes and 〈EK〉 values in excess of the values found at the corresponding temperatures in the bulk. The hydrogen dynamics are discussed in the context of the interaction between the interfacial water and ice and the confining hydrophilic surface of the GO sponge. PMID:26556604

  18. Spectral evidence for hydrogen-induced reversible segregation of CO adsorbed on titania-supported rhodium.

    PubMed

    Panayotov, D; Mihaylov, M; Nihtianova, D; Spassov, T; Hadjiivanov, K

    2014-07-14

    The reduction of a 1.3% Rh/TiO2 sample with carbon monoxide leads to the formation of uniform Rh nanoparticles with a mean diameter of dp ≈ 2.2 nm. Adsorption of CO on the reduced Rh/TiO2 produces linear and bridged carbonyls bound to metallic Rh(0) sites and only a few geminal dicarbonyls of Rh(I). The ν(CO) of linear Rh(0)-CO complexes is strongly coverage dependent: it is observed at 2078 cm(-1) at full coverage and at ca. 2025 cm(-1) at approximated zero coverage. At low coverage, this shift is mainly caused by a dipole-dipole interaction between the adsorbed CO molecules while at high coverage, the chemical shift also becomes important. Hydrogen hardly affects the CO adlayer at high CO coverages. However, on a partially CO-covered surface (θCO ≈ 0.5), the adsorption of H2 at increasing pressure leads to a gradual shift in the band of linear Rh(0)-CO from 2041 to 2062 cm(-1). Subsequent evacuation almost restores the original spectrum, demonstrating the reversibility of the hydrogen effect. Through the use of (12)CO + (13)CO isotopic mixtures, it is established that the addition of hydrogen to the CO-Rh/TiO2 system leads to an increase in the dynamic interaction between the adsorbed CO molecules. This evidences an increase in the density of the adsorbed CO molecules and indicates segregation of the CO and hydrogen adlayers. When CO is adsorbed on a hydrogen-precovered surface, the carbonyl band maximum is practically coverage independent and is observed at 2175-2173 cm(-1). These results are explained by a model according to which CO successively occupies different rhodium nanoparticles. PMID:24866330

  19. Decontamination of adsorbed chemical warfare agents on activated carbon using hydrogen peroxide solutions.

    PubMed

    Osovsky, Ruth; Kaplan, Doron; Nir, Ido; Rotter, Hadar; Elisha, Shmuel; Columbus, Ishay

    2014-09-16

    Mild treatment with hydrogen peroxide solutions (3-30%) efficiently decomposes adsorbed chemical warfare agents (CWAs) on microporous activated carbons used in protective garments and air filters. Better than 95% decomposition of adsorbed sulfur mustard (HD), sarin, and VX was achieved at ambient temperatures within 1-24 h, depending on the H2O2 concentration. HD was oxidized to the nontoxic HD-sulfoxide. The nerve agents were perhydrolyzed to the respective nontoxic methylphosphonic acids. The relative rapidity of the oxidation and perhydrolysis under these conditions is attributed to the microenvironment of the micropores. Apparently, the reactions are favored due to basic sites on the carbon surface. Our findings suggest a potential environmentally friendly route for decontamination of adsorbed CWAs, using H2O2 without the need of cosolvents or activators. PMID:25133545

  20. Interactions between Adsorbed Hydrogenated Soy Phosphatidylcholine (HSPC) Vesicles at Physiologically High Pressures and Salt Concentrations

    PubMed Central

    Goldberg, Ronit; Schroeder, Avi; Barenholz, Yechezkel; Klein, Jacob

    2011-01-01

    Using a surface force balance, we measured normal and shear interactions as a function of surface separation between layers of hydrogenated soy phosphatidylcholine (HSPC) small unilamellar vesicles (SUVs) adsorbed from dispersion at physiologically high salt concentrations (0.15 M NaNO3). Cryo-scanning electron microscopy shows that each surface is coated by a close-packed HSPC-SUV layer with an overlayer of liposomes on top. A clear attractive interaction between the liposome layers is seen upon approach and separation, followed by a steric repulsion upon further compression. The shear forces reveal low friction coefficients (μ = 0.008–0.0006) up to contact pressures of at least 6 MPa, comparable to those observed in the major joints. The spread in μ-values may be qualitatively accounted for by different local liposome structure at different contact points, suggesting that the intrinsic friction of the HSPC-SUV layers at this salt concentration is closer to the lower limit (μ = ∼0.0006). This low friction is attributed to the hydration lubrication mechanism arising from rubbing of the hydrated phosphocholine-headgroup layers exposed at the outer surface of each liposome, and provides support for the conjecture that phospholipids may play a significant role in biological lubrication. PMID:21575574

  1. Adsorbate structures and catalytic reactions studied in the torrpressure range by scanning tunneling microscopy

    SciTech Connect

    Hwang, Kevin Shao-Lin

    2003-05-23

    High-pressure, high-temperature scanning tunneling microscopy (HPHTSTM) was used to study adsorbate structures and reactions on single crystal model catalytic systems. Studies of the automobile catalytic converter reaction [CO + NO {yields} 1/2 N{sub 2} + CO{sub 2}] on Rh(111) and ethylene hydrogenation [C{sub 2}H{sub 4} + H{sub 2} {yields} C{sub 2}H{sub 6}] on Rh(111) and Pt(111) elucidated information on adsorbate structures in equilibrium with high-pressure gas and the relationship of atomic and molecular mobility to chemistry. STM studies of NO on Rh(111) showed that adsorbed NO forms two high-pressure structures, with the phase transformation from the (2 x 2) structure to the (3 x 3) structure occurring at 0.03 Torr. The (3 x 3) structure only exists when the surface is in equilibrium with the gas phase. The heat of adsorption of this new structure was determined by measuring the pressures and temperatures at which both (2 x 2) and (3 x 3) structures coexisted. The energy barrier between the two structures was calculated by observing the time necessary for the phase transformation to take place. High-pressure STM studies of the coadsorption of CO and NO on Rh(111) showed that CO and NO form a mixed (2 x 2) structure at low NO partial pressures. By comparing surface and gas compositions, the adsorption energy difference between topsite CO and NO was calculated. Occasionally there is exchange between top-site CO and NO, for which we have described a mechanism for. At high NO partial pressures, NO segregates into islands, where the phase transformation to the (3 x 3) structure occurs. The reaction of CO and NO on Rh(111) was monitored by mass spectrometry (MS) and HPHTSTM. From MS studies the apparent activation energy of the catalytic converter reaction was calculated and compared to theory. STM showed that under high-temperature reaction conditions, surface metal atoms become mobile. Ethylene hydrogenation and its poisoning by CO was also studied by STM on Rh

  2. Structure of Inert Gases Adsorbed in MCM-41

    NASA Astrophysics Data System (ADS)

    Evans, Dylan; Sokol, Paul

    One-dimensional quantum liquids of 3He or 4He have generated recent interest for investigation in the Luttinger liquid model. Unfortunately, current studies lack a clear demonstration of definitively one-dimensional behavior. We propose using the templated, porous material, MCM-41, as a host for an atomic Luttinger liquid. In general, the pores of MCM-41 are too wide to provide a strictly one-dimensional environment, so we investigate preplating these pores with inert gases to effectively reduce their diameter. We present the results of studies of the structure of inert gases in MCM-41. Nitrogen sorption isotherms were used to characterize the sample. Then, using inert gases as adsorbates, we determined the minimum effective pore diameter that can be achieved in our sample before capillary condensation takes over. X-ray powder diffraction (XRD) was performed on the ideally preplated sample to investigate the structure of the adsorbates in the nanopores. The XRD measurements are compared to simulations of core-shell cylinder model scattering, and the validity of the model is assessed. The prospects for creating a definitively one-dimensional channel for the application of studying the structure and dynamics of helium confined in one dimension are discussed. This work was supported by the National Science Foundation under Grant DGE-1069091.

  3. Chemical and structural characterization of copper adsorbed on mosses (Bryophyta).

    PubMed

    González, Aridane G; Jimenez-Villacorta, Felix; Beike, Anna K; Reski, Ralf; Adamo, Paola; Pokrovsky, Oleg S

    2016-05-01

    The adsorption of copper on passive biomonitors (devitalized mosses Hypnum sp., Sphagnum denticulatum, Pseudoscleropodium purum and Brachythecium rutabulum) was studied under different experimental conditions such as a function of pH and Cu concentration in solution. Cu assimilation by living Physcomitrella patents was also investigated. Molecular structure of surface adsorbed and incorporated Cu was studied by X-ray Absorption Spectroscopy (XAS). Devitalized mosses exhibited the universal adsorption pattern of Cu as a function of pH, with a total binding sites number 0.05-0.06 mmolg(dry)(-1) and a maximal adsorption capacity of 0.93-1.25 mmolg(dry)(-1) for these devitalized species. The Extended X-ray Absorption Fine Structure (EXAFS) fit of the first neighbor demonstrated that for all studied mosses there are ∼4.5 O/N atoms around Cu at ∼1.95 Å likely in a pseudo-square geometry. The X-ray Absorption Near Edge Structure (XANES) analysis demonstrated that Cu(II)-cellulose (representing carboxylate groups) and Cu(II)-phosphate are the main moss surface binding moieties, and the percentage of these sites varies as a function of solution pH. P. patens exposed during one month to Cu(2+) yielded ∼20% of Cu(I) in the form of Cu-S(CN) complexes, suggesting metabolically-controlled reduction of adsorbed and assimilated Cu(2+). PMID:26852210

  4. Organic silicon compounds anf hydrogen sulfide removal from biogas by mineral and adsorbent

    NASA Astrophysics Data System (ADS)

    Choi, J.

    2015-12-01

    Biogas utilized for energy production needs to be free from organic silicon compounds and hydrogen sulfide , as their burning has damaging effects on utilities and humans; organic silicon compounds and hydrogen sulfide can be found in biogas produced from biomass wastes, due to their massive industrial use in synthetic product,such as cosmetics, detergents and paints.Siloxanes and hydrogen sulfide removal from biogas can be carried out by various methods (Ajhar et al., 2010); aim of the present work is to find a single practical andeconomic way to drastically and simultaneously reduce both hydrogen sulfide and the siloxanes concentration to less than 1 ppm. Some commercial activated carbons previously selected (Monteleoneet al., 2011) as being effective in hydrogen sulfide up taking have been tested in an adsorption measurement apparatus, by flowing both hydrogen sulphide and volatile siloxane (Decamethycyclopentasiloxane or D5) in a nitrogen stream,typically 25-300 ppm D5 over N2, through an clay minerals, Fe oxides and Silica; the adsorption process was analyzed by varying some experimental parameters (concentration, grain size, bed height). The best silica shows an adsorption capacity of 0.2 g D5 per gram of silica. The next thermo gravimetric analysis (TGA) confirms the capacity data obtained experimentally by the breakthrough curve tests.The capacity results depend on D5 and hydrogen sulphide concentrations. A regenerative silica process is then carried out byheating the silica bed up to 200 ° C and flushing out the adsorbed D5 and hydrogen sulphide samples in a nitrogen stream in athree step heating procedure up to 200 ° C. The adsorption capacity is observed to degrade after cyclingthe samples through several adsorption-desorption cycles.

  5. Measurement of Fatigue Crack Growth Relationships in Hydrogen Gas for Pressure Swing Adsorber Vessel Steels

    SciTech Connect

    Somerday, Brian P.; Barney, Monica

    2014-12-04

    We measured the hydrogen-assisted fatigue crack growth rates (da/dN) for SA516 Grade 70 steel as a function of stress-intensity factor range (ΔK) and load-cycle frequency to provide life-prediction data relevant to pressure swing adsorber (PSA) vessels. For ΔK values up to 18.5 MPa m1/2, the baseline da/dN versus ΔK relationship measured at 1Hz in 2.8 MPa hydrogen gas represents an upper bound with respect to crack growth rates measured at lower frequency. However, at higher ΔK values, we found that the baseline da/dN data had to be corrected to account for modestly higher crack growth rates at the lower frequencies relevant to PSA vessel operation.

  6. Measurement of Fatigue Crack Growth Relationships in Hydrogen Gas for Pressure Swing Adsorber Vessel Steels

    DOE PAGESBeta

    Somerday, Brian P.; Barney, Monica

    2014-12-04

    We measured the hydrogen-assisted fatigue crack growth rates (da/dN) for SA516 Grade 70 steel as a function of stress-intensity factor range (ΔK) and load-cycle frequency to provide life-prediction data relevant to pressure swing adsorber (PSA) vessels. For ΔK values up to 18.5 MPa m1/2, the baseline da/dN versus ΔK relationship measured at 1Hz in 2.8 MPa hydrogen gas represents an upper bound with respect to crack growth rates measured at lower frequency. However, at higher ΔK values, we found that the baseline da/dN data had to be corrected to account for modestly higher crack growth rates at the lower frequenciesmore » relevant to PSA vessel operation.« less

  7. Hydrogen embrittlement of structural steels.

    SciTech Connect

    Somerday, Brian P.

    2010-06-01

    Carbon-manganese steels are candidates for the structural materials in hydrogen gas pipelines, however it is well known that these steels are susceptible to hydrogen embrittlement. Decades of research and industrial experience have established that hydrogen embrittlement compromises the structural integrity of steel components. This experience has also helped identify the failure modes that can operate in hydrogen containment structures. As a result, there are tangible ideas for managing hydrogen embrittement in steels and quantifying safety margins for steel hydrogen containment structures. For example, fatigue crack growth aided by hydrogen embrittlement is a key failure mode for steel hydrogen containment structures subjected to pressure cycling. Applying appropriate structural integrity models coupled with measurement of relevant material properties allows quantification of safety margins against fatigue crack growth in hydrogen containment structures. Furthermore, application of these structural integrity models is aided by the development of micromechanics models, which provide important insights such as the hydrogen distribution near defects in steel structures. The principal objective of this project is to enable application of structural integrity models to steel hydrogen pipelines. The new American Society of Mechanical Engineers (ASME) B31.12 design code for hydrogen pipelines includes a fracture mechanics-based design option, which requires material property inputs such as the threshold for rapid cracking and fatigue crack growth rate under cyclic loading. Thus, one focus of this project is to measure the rapid-cracking thresholds and fatigue crack growth rates of line pipe steels in high-pressure hydrogen gas. These properties must be measured for the base materials but more importantly for the welds, which are likely to be most vulnerable to hydrogen embrittlement. The measured properties can be evaluated by predicting the performance of the pipeline

  8. Separation of Rebaudiana A from Steviol glycoside using a polymeric adsorbent with multi-hydrogen bonding in a non-aqueous system.

    PubMed

    Ba, Jing; Zhang, Na; Yao, Lijuan; Ma, Ning; Wang, Chunhong

    2014-11-15

    Rebaudioside A (RA) and stevioside (SS) are the primary effective glycoside components in Stevia Rebaudiana. The RA glycoside is sweeter, and it tastes similarly to sucrose. Because extracts with a high RA content can be used as natural sweeteners for food additives approved by the FAO and FDA, RA should generate high market demand. In this study, an efficient method for separating RA was established based on the synergistic multi-hydrogen bonding interaction between a polymeric adsorbent and the RA glycoside. To overcome the destruction of the hydrophobic affinity required for the selective adsorption of RA, an innovative non-aqueous environment was established for adsorption and separation. To this end, an initial polymeric adsorbent composed of a glycidyl methacrylate and trimethylolpropane trimethacrylate (GMA-co-TMPTMA) copolymer matrix was synthesized, and polyethylene polyamine was employed as a functional reagent designed to react with the epoxy group on GME-co-TMPTMA to form a highly selective macroporous adsorbent. The effects of the different functional reagents and the solvent polarity on the adsorption selectivity for RA and SS, respectively, were investigated. Matching the structure of the polyethylene polyamine and sugar ligand on the glycoside molecule was essential in ensuring that the maximum synergistic interaction between adsorbent and adsorbate would be achieved. Moreover, the hydrogen-bonding force was observed to increase when the polarity of the adsorption solvent decreased. Therefore, among the synthesized macroporous polymeric adsorbents, the GTN4 adsorbent-bonding tetraethylenepentamine functional group provided the best separation in an n-butyl alcohol solution. Under the optimized gradient elution conditions, RA and SS can be effectively separated, and the contents of RA and SS increased from 33.5% and 51.5% in the initial crude extract to 95.4% and 78.2% after separation, respectively. Compared to conventional methods, the adsorption

  9. First-principles vdW-DF study on the enhanced hydrogen storage capacity of Pt-adsorbed graphene.

    PubMed

    Khosravi, Azadeh; Fereidoon, Abdolhosein; Ahangari, Morteza Ghorbanzadeh; Ganji, Masoud Darvish; Emami, Seyede Negar

    2014-05-01

    Ab initio vdW calculations with the DFT level of theory were used to investigate hydrogen (H₂) adsorption on Pt-adsorbed graphene (Pt-graphene). We have explored the most energetically favorable sites for single Pt atom adsorption on the graphene surface. The interaction of H₂ with the energetically favorable Pt-graphene system was then investigated. We found that H₂ physisorbs on pristine graphene with a binding energy of -0.05 eV, while the binding energy is enhanced to -1.98 eV when H₂ binds Pt-adsorbed graphene. We also found that up to four H₂ molecules can be adsorbed on the Pt-graphene system with a -0.74 eV/H₂ binding energy. The effect of graphene layer stretching on the Pt-graphene capacity/ability for hydrogen adsorption was evaluated. Our results show that the number of H₂ molecules adsorbed on the Pt-graphene surface rises to six molecules with a binding energy of approximately -0.29 eV/H₂. Our first-principles results reveal that the Young's modulus was slightly decreased for Pt adsorption on the graphene layer. The first-principles calculated Young's modulus for the H₂-adsorbed Pt-graphene system demonstrates that hydrogen adsorption can dramatically increase the Young's modulus of such systems. As a result, hydrogen adsorption on the Pt-graphene system might enhance the substrate strength. PMID:24777315

  10. Hydrogen adsorbed at N-polar InN: Significant changes in the surface electronic properties

    NASA Astrophysics Data System (ADS)

    Eisenhardt, A.; Krischok, S.; Himmerlich, M.

    2015-06-01

    The interaction of atomic hydrogen and ammonia with as-grown N-polar InN surfaces is investigated using in situ photoelectron spectroscopy. Changes in the surface electronic properties, including the band alignment and work function, as well as the chemical bonding states of the substrate and adsorbates are characterized. Ammonia molecules are dissociating at the InN surface, resulting in adsorption of hydrogen species. Consequently, the considerable changes of the chemical and electronic properties of the InN surface during ammonia interaction are almost identical to those found for adsorption of atomic hydrogen. In both cases, hydrogen atoms preferentially bond to surface nitrogen atoms, resulting in the disappearance of the nitrogen dangling-bond-related occupied surface state close to the valence band edge at ˜1.6 eV binding energy and the formation of new occupied electron states at the conduction band edge. Furthermore, a decrease in work function during adsorption from 4.7 to 3.7-3.8 eV, as well as an increase in the surface downward band bending by 0.3 eV, confirm that hydrogen is acting as electron donor at InN surfaces and therefore has to be considered as one main reason for the surface electron accumulation observed at N-polar InN samples exposed to ambient conditions, for example as the dissociation product of molecules. The measured formation and occupation of electronic states above the conduction band minimum occur in conjunction with the observed increase in surface electron concentration and underline the relationship between the energy position of occupied electron states and surface band alignment for InN as a small-band-gap semiconductor.

  11. Correlation effects in photoemission from adsorbates: Hydrogen on narrow-band metals

    NASA Astrophysics Data System (ADS)

    Rubio, J.; Refolio, M. C.; López Sancho, M. P.; López Sancho, J. M.

    1988-08-01

    This paper deals with photoemission from a one-level atom adsorbed on a metal surface within the context of Anderson's Hamiltonian. The occupied part of the adsorbate density of states (DOS) is calculated by means of a many-electron approach that incorporates the following ingredients: (1) A neat separation between final-state interactions and initial (ground-state) effects. (2) The method (a Lehmann-type representation) leans heavily on the resolvent operator, R(z)=(z-H)-1, which is obtained by expressing Dyson's equation in terms of the (N-1)-electron states (configurations) that diagonalize the hopping-free part of Anderson's Hamiltonian, thereby including the atomic correlation (U) in a nonperturbative way while expanding in powers of the hopping parameter (V). (3) By using blocking methods, the matrix elements of R are grouped into equivalent 4×4 matrix blocks, with residual interactions, which are then put in correspondence with the sites of a rectangular lattice, thereby making the problem isomorphic to that of finding a noninteracting one-electron Green's function in the Wannier representation. (4) Renormalized perturbation theory, along with a series of convolution theorems due to Hugenholtz and Van Hove, allows one to develop a self-consistency equation that automatically takes into account an infinite number of configurations. The resulting DOS is compared with photoemission spectra from hydrogen adsorbed on tungsten (half-filled metal band) and nickel (almost full). Correlation effects turn out to produce peaks at the appropriate energies, so that an unusually good agreement is found despite the featureless, semielliptical DOS adopted for the metal. Only gross features of this quantity, such as width, center, and occupation of the band, seem to matter in a photoemission calculation.

  12. Structural, energetic, and electronic properties of hydrogenated titanium clusters.

    PubMed

    Dhilip Kumar, T J; Tarakeshwar, P; Balakrishnan, N

    2008-05-21

    Hydrogen undergoes dissociative chemisorption on small titanium clusters. How the electronic structure of the cluster changes as a function of the number of adsorbed hydrogen atoms is an important issue in nanocatalysis and hydrogen storage. In this paper, a detailed theoretical investigation of the structural, energetic, and electronic properties of the icosahedral Ti13 cluster is presented as a function of the number of adsorbed hydrogen atoms. The results show that hydrogen loaded Ti13H20 and Ti13H30 clusters are exceptionally stable and are characterized by hydrogen multicenter bonds. In Ti13H20, the dissociated hydrogen atoms are bound to each of the 20 triangular faces of Ti13, while in Ti13H30, they are bound to the 30 Ti-Ti edges of Ti13. Consequently, the chemisorption and desorption energies of the Ti13H20 (1.93 eV, 3.10 eV) are higher than that of Ti13H30 (1.13 eV, 1.95 eV). While increased hydrogen adsorption leads to an elongation of the Ti-Ti bonds, there is a concomitant increase in the electrostatic interaction between the dissociated hydrogen atoms and the Ti13 cluster. This enhanced interaction results from the participation of the subsurface titanium atom at higher hydrogen concentrations. Illustrative results of hydrogen saturation on the larger icosahedral Ti55 cluster are also discussed. The importance of these results on hydrogen saturated titanium clusters in elucidating the mechanism of hydrogen adsorption and desorption in titanium doped complex metal hydrides is discussed. PMID:18500893

  13. Spin-polarized hydrogen adsorbed on the surface of superfluid {sup 4}He

    SciTech Connect

    Marín, J. M.; Boronat, J.; Markić, L. Vranješ

    2013-12-14

    The experimental realization of a thin layer of spin-polarized hydrogen H↓ adsorbed on top of the surface of superfluid {sup 4}He provides one of the best examples of a stable, nearly two-dimensional (2D) quantum Bose gas. We report a theoretical study of this system using quantum Monte Carlo methods in the limit of zero temperature. Using the full Hamiltonian of the system, composed of a superfluid {sup 4}He slab and the adsorbed H↓ layer, we calculate the main properties of its ground state using accurate models for the pair interatomic potentials. Comparing the results for the layer with the ones obtained for a strictly 2D setup, we analyze the departure from the 2D character when the density increases. Only when the coverage is rather small the use of a purely 2D model is justified. The condensate fraction of the layer is significantly larger than in 2D at the same surface density, being as large as 60% at the largest coverage studied.

  14. Revisiting the inelastic electron tunneling spectroscopy of single hydrogen atom adsorbed on the Cu(100) surface

    NASA Astrophysics Data System (ADS)

    Jiang, Zhuoling; Wang, Hao; Sanvito, Stefano; Hou, Shimin

    2015-12-01

    Inelastic electron tunneling spectroscopy (IETS) of a single hydrogen atom on the Cu(100) surface in a scanning tunneling microscopy (STM) configuration has been investigated by employing the non-equilibrium Green's function formalism combined with density functional theory. The electron-vibration interaction is treated at the level of lowest order expansion. Our calculations show that the single peak observed in the previous STM-IETS experiments is dominated by the perpendicular mode of the adsorbed H atom, while the parallel one only makes a negligible contribution even when the STM tip is laterally displaced from the top position of the H atom. This propensity of the IETS is deeply rooted in the symmetry of the vibrational modes and the characteristics of the conduction channel of the Cu-H-Cu tunneling junction, which is mainly composed of the 4s and 4pz atomic orbitals of the Cu apex atom and the 1s orbital of the adsorbed H atom. These findings are helpful for deepening our understanding of the propensity rules for IETS and promoting IETS as a more popular spectroscopic tool for molecular devices.

  15. Revisiting the inelastic electron tunneling spectroscopy of single hydrogen atom adsorbed on the Cu(100) surface

    SciTech Connect

    Jiang, Zhuoling; Wang, Hao; Sanvito, Stefano; Hou, Shimin

    2015-12-21

    Inelastic electron tunneling spectroscopy (IETS) of a single hydrogen atom on the Cu(100) surface in a scanning tunneling microscopy (STM) configuration has been investigated by employing the non-equilibrium Green’s function formalism combined with density functional theory. The electron-vibration interaction is treated at the level of lowest order expansion. Our calculations show that the single peak observed in the previous STM-IETS experiments is dominated by the perpendicular mode of the adsorbed H atom, while the parallel one only makes a negligible contribution even when the STM tip is laterally displaced from the top position of the H atom. This propensity of the IETS is deeply rooted in the symmetry of the vibrational modes and the characteristics of the conduction channel of the Cu-H-Cu tunneling junction, which is mainly composed of the 4s and 4p{sub z} atomic orbitals of the Cu apex atom and the 1s orbital of the adsorbed H atom. These findings are helpful for deepening our understanding of the propensity rules for IETS and promoting IETS as a more popular spectroscopic tool for molecular devices.

  16. Zero-point vibration of hydrogen adsorbed on Si and Pt surfaces.

    PubMed

    Fukutani, K; Itoh, A; Wilde, M; Matsumoto, M

    2002-03-18

    Hydrogen atoms adsorbed on Si(111) and Pt(111) were investigated by nuclear reaction analysis (NRA) using 1H(15N,alphagamma)12C. From measurements of the NRA spectrum at normal and tilted ion incidences the zero-point vibrational energies of H on Si(111) in the perpendicular and parallel directions were found to be 123.4+/-4.6 and 44.6+/-6.2 meV, respectively, which are consistent with harmonic potentials. The zero-point energies obtained for Pt(111)-H were 80.8+/-3.9 and 62.1+/-6.0 meV for perpendicular and parallel directions, respectively. These results indicate that the stretching mode is harmonic, while the bending mode is strongly anharmonic. PMID:11909413

  17. Correlation of adsorption isotherms of hydrogen isotopes on mordenite adsorbents using reactive vacancy solution theory

    SciTech Connect

    Munakata, K.; Nakamura, A.; Kawamura, Y.

    2015-03-15

    The authors have applied the isotherm equations derived from the reactive vacancy solution theory (RVST) to correlation of experimental and highly non-ideal adsorption isotherms of hydrogen and deuterium on a mordenite adsorbent, and have examined the ability of the isotherm equations to match this correlation. Several isotherm equations such as Langmuir, Freundlich, Toth, Vacancy Solution Theory and so forth were also tested, but they did not work. For the Langmuir-Freundlich equation tests have indicated that its 'ability to correlate' of the adsorption isotherms is not satisfactory. For the multi-site Langmuir-Freundlich (MSLF) equation the correlation of the isotherms appears to be somewhat improved but remains unsatisfactory. The results show that the isotherm equations derived from RVST can better correlate the experimental isotherms.

  18. Structure formation in adsorbed overlayers comprising functional cross-shaped molecules: A Monte Carlo study

    NASA Astrophysics Data System (ADS)

    Kasperski, Adam; Nieckarz, Damian; Szabelski, Paweł

    2015-11-01

    Surface confined self-assembly of functional star-shaped organic molecules is a promising method to create nanoporous networks with tailorable structure and functions. In this work we use the Monte Carlo simulation method to demonstrate how the morphology of these supramolecular assemblies can be tuned by manipulating intrinsic parameters of the building blocks and modified by the presence of co-adsorbed metal atoms. To that purpose we study the 2D self-assembly of planar cruciform molecules modeled as collections of interconnected segments, some of which were activated to represent discrete interaction centers. We consider a few exemplary adsorbed systems in which the molecules with different size, aspect ratio and intramolecular distribution of active centers form superstructures stabilized by short-range segment-segment interactions or by metal-segment interactions. These two situations correspond to supramolecular assemblies sustained by, for example, hydrogen bonding and metal-organic ligand coordination, respectively. The simulated results show that proper encoding of intramolecular interactions into the cruciform building bricks allows for directing the self-assembly towards largely diversified structures ranging from nanoclusters to porous grids. The obtained findings can facilitate designing and optimization of molecular networks comprising cross-shaped units including functionalized porphyrins and phthalocyanines and they can be helpful in preliminary selection of these building blocks.

  19. Chiral modification of platinum: ab initio study of the effect of hydrogen coadsorption on stability and geometry of adsorbed cinchona alkaloids.

    PubMed

    Hahn, Konstanze R; Seitsonen, Ari P; Baiker, Alfons

    2015-11-01

    The cinchona alkaloids cinchonidine and cinchonine belong to the most efficient chiral modifiers for the noble metal-catalyzed enantioselective hydrogenation of C=O and C=C bonds. Under reaction conditions these modifiers are coadsorbed on the noble metal surface with hydrogen. Using density functional theory, we studied the effect of coadsorbed hydrogen on the adsorption mode of cinchonidine and cinchonine on a Pt(111) surface at different hydrogen coverages. The theoretical study indicates that the presence of coadsorbed hydrogen affects both the adsorption geometry as well as the stability of the adsorbed cinchona alkaloids. At all hydrogen coverages the cinchona alkaloids are found to be adsorbed via anchoring of the quinoline moiety. In the absence of hydrogen as well as at low hydrogen coverage the quinoline moiety adsorbs nearly parallel to the surface, whereas at higher hydrogen coverage it becomes tilted. Higher hydrogen coverage as well as partial hydrogenation of the quinoline part of the cinchona alkaloid and hydrogen transfer to the C[double bond, length as m-dash]C double bond at 10, 11 position of the quinuclidine moiety destabilize the adsorbed cinchona alkaloid, whereas hydrogen transfer to the nitrogen atom of the quinoline and the quinuclidine moiety stabilizes the adsorbed molecule. The stability as well as the adsorption geometry of the cinchona alkaloids are affected by the coadsorbed hydrogen and are proposed to influence the efficiency of the enantiodifferentiating ability of the chirally modified platinum surface. PMID:26426825

  20. Geometric and electronic structures of potassium-adsorbed rubrene complexes

    SciTech Connect

    Li, Tsung-Lung; Lu, Wen-Cai

    2015-06-28

    The geometric and electronic structures of potassium-adsorbed rubrene complexes are studied in this article. It is found that the potassium-rubrene (K{sub 1}RUB) complexes inherit the main symmetry characteristics from their pristine counterparts and are thus classified into D{sub 2}- and C{sub 2h}-like complexes according to the relative orientations of the four phenyl side groups. The geometric structures of K{sub 1}RUB are governed by two general effects on the total energy: Deformation of the carbon frame of the pristine rubrene increases the total energy, while proximity of the potassium ion to the phenyl ligands decreases the energy. Under these general rules, the structures of D{sub 2}- and C{sub 2h}-like K{sub 1}RUB, however, exhibit their respective peculiarities. These peculiarities can be illustrated by their energy profiles of equilibrium structures. For the potassium adsorption-sites, the D{sub 2}-like complexes show minimum-energy basins, whereas the C{sub 2h}-like ones have single-point minimum-energies. If the potassium atom ever has the energy to diffuse from the minimum-energy site, the potassium diffusion path on the D{sub 2}-like complexes is most likely along the backbone in contrast to the C{sub 2h}-like ones. Although the electronic structures of the minimum-energy structures of D{sub 2}- and C{sub 2h}-like K{sub 1}RUB are very alike, decompositions of their total spectra reveal insights into the electronic structures. First, the spectral shapes are mainly determined by the facts that, in comparison with the backbone carbons, the phenyl carbons have more uniform chemical environments and far less contributions to the electronic structures around the valence-band edge. Second, the electron dissociated from the potassium atom mainly remains on the backbone and has little effects on the electronic structures of the phenyl groups. Third, the two phenyls on the same side of the backbone as the potassium atom have more similar chemical environments

  1. Geometric and electronic structures of potassium-adsorbed rubrene complexes

    NASA Astrophysics Data System (ADS)

    Li, Tsung-Lung; Lu, Wen-Cai

    2015-06-01

    The geometric and electronic structures of potassium-adsorbed rubrene complexes are studied in this article. It is found that the potassium-rubrene (K1RUB) complexes inherit the main symmetry characteristics from their pristine counterparts and are thus classified into D2- and C2h-like complexes according to the relative orientations of the four phenyl side groups. The geometric structures of K1RUB are governed by two general effects on the total energy: Deformation of the carbon frame of the pristine rubrene increases the total energy, while proximity of the potassium ion to the phenyl ligands decreases the energy. Under these general rules, the structures of D2- and C2h-like K1RUB, however, exhibit their respective peculiarities. These peculiarities can be illustrated by their energy profiles of equilibrium structures. For the potassium adsorption-sites, the D2-like complexes show minimum-energy basins, whereas the C2h-like ones have single-point minimum-energies. If the potassium atom ever has the energy to diffuse from the minimum-energy site, the potassium diffusion path on the D2-like complexes is most likely along the backbone in contrast to the C2h-like ones. Although the electronic structures of the minimum-energy structures of D2- and C2h-like K1RUB are very alike, decompositions of their total spectra reveal insights into the electronic structures. First, the spectral shapes are mainly determined by the facts that, in comparison with the backbone carbons, the phenyl carbons have more uniform chemical environments and far less contributions to the electronic structures around the valence-band edge. Second, the electron dissociated from the potassium atom mainly remains on the backbone and has little effects on the electronic structures of the phenyl groups. Third, the two phenyls on the same side of the backbone as the potassium atom have more similar chemical environments than the other two on the opposite side, which leads to the largely enhanced

  2. Structure of Non-Equilibrium Adsorbed Polymer Layers

    NASA Astrophysics Data System (ADS)

    O'Shaughnessy, Ben; Vavylonis, Dimitrios

    2004-03-01

    Equilibrium polymer adsorption has been widely studied theoretically. Many experiments however implicate strong non-equilibrium effects for monomer sticking energies somewhat larger than kT, the most common case. The structure and slow dynamics in these layers is not understood. We analyze theoretically non-equilibrium layers from dilute solutions in the limit of irreversible monomer adsorption. We find the density profile ˜ z-4/3 and loop distribution ˜ s-11/5 of the resulting layer are no different to equilibrium. However, single chain statistics are radically different: the layer consists of a flat inner portion of fully collapsed chains plus an outer part whose chains make only fN surface contacts where N is chain length. The contact fractions f follow a broad distribution, P(f) ˜ f-4/5, consistent with experiment [H. M. Schneider et al, Langmuir 12, 994 (1996)], and the lateral size R of adsorbed chains is of order the bulk coil size, R ˜ N^3/5. For equilibrium layers, by contrast, P has a unique peak at a value of f of order unity, while R ˜ N^1/2 is significantly less. The relaxation of a non-equilibrium layer towards equilibrium thus entails chain shrinkage and tighter binding. We speculate that the observed decrease of bulk-layer chain exchange rates with increasing aging reflects these internal layer dynamics.

  3. Quantitative analysis of desorption and decomposition kinetics of formic acid on Cu(111): The importance of hydrogen bonding between adsorbed species

    SciTech Connect

    Shiozawa, Yuichiro; Koitaya, Takanori; Mukai, Kozo; Yoshimoto, Shinya; Yoshinobu, Jun

    2015-12-21

    Quantitative analysis of desorption and decomposition kinetics of formic acid (HCOOH) on Cu(111) was performed by temperature programmed desorption (TPD), X-ray photoelectron spectroscopy, and time-resolved infrared reflection absorption spectroscopy. The activation energy for desorption is estimated to be 53–75 kJ/mol by the threshold TPD method as a function of coverage. Vibrational spectra of the first layer HCOOH at 155.3 K show that adsorbed molecules form a polymeric structure via the hydrogen bonding network. Adsorbed HCOOH molecules are dissociated gradually into monodentate formate species. The activation energy for the dissociation into monodentate formate species is estimated to be 65.0 kJ/mol at a submonolayer coverage (0.26 molecules/surface Cu atom). The hydrogen bonding between adsorbed HCOOH species plays an important role in the stabilization of HCOOH on Cu(111). The monodentate formate species are stabilized at higher coverages, because of the lack of vacant sites for the bidentate formation.

  4. Quantitative analysis of desorption and decomposition kinetics of formic acid on Cu(111): The importance of hydrogen bonding between adsorbed species

    NASA Astrophysics Data System (ADS)

    Shiozawa, Yuichiro; Koitaya, Takanori; Mukai, Kozo; Yoshimoto, Shinya; Yoshinobu, Jun

    2015-12-01

    Quantitative analysis of desorption and decomposition kinetics of formic acid (HCOOH) on Cu(111) was performed by temperature programmed desorption (TPD), X-ray photoelectron spectroscopy, and time-resolved infrared reflection absorption spectroscopy. The activation energy for desorption is estimated to be 53-75 kJ/mol by the threshold TPD method as a function of coverage. Vibrational spectra of the first layer HCOOH at 155.3 K show that adsorbed molecules form a polymeric structure via the hydrogen bonding network. Adsorbed HCOOH molecules are dissociated gradually into monodentate formate species. The activation energy for the dissociation into monodentate formate species is estimated to be 65.0 kJ/mol at a submonolayer coverage (0.26 molecules/surface Cu atom). The hydrogen bonding between adsorbed HCOOH species plays an important role in the stabilization of HCOOH on Cu(111). The monodentate formate species are stabilized at higher coverages, because of the lack of vacant sites for the bidentate formation.

  5. Structure of collagen adsorbed on a model implant surface resolved by polarization modulation infrared reflection-absorption spectroscopy.

    PubMed

    Brand, Izabella; Habecker, Florian; Ahlers, Michael; Klüner, Thorsten

    2015-03-01

    The polarization modulation infrared reflection-absorption spectra of collagen adsorbed on a titania surface and quantum chemical calculations are used to describe components of the amide I mode to the protein structure at a sub-molecular level. In this study, imino acid rich and poor fragments, representing the entire collagen molecule, are taken into account. The amide I mode of the collagen triple helix is composed of three absorption bands which involve: (i) (∼1690cm(-1)) the CO stretching modes at unhydrated groups, (ii) (1655-1673cm(-1)) the CO stretching at carbonyl groups at imino acids and glycine forming intramolecular hydrogen bonds with H atoms at both NH2 and, unusual for proteins, CH2 groups at glycine at a neighbouring chain and (iii) (∼1640cm(-1)) the CO stretching at carbonyl groups forming hydrogen bonds between two, often charged, amino acids as well as hydrogen bonds to water along the entire helix. The IR spectrum of films prepared from diluted solutions (c<50μgml(-1)) corresponds to solution spectra indicating that native collagen molecules interact with water adsorbed on the titania surface. In films prepared from solutions (c⩾50μgml(-1)) collagen multilayers are formed. The amide I mode is blue-shifted by 18cm(-1), indicating that intramolecular hydrogen bonds at imino acid rich fragments are weakened. Simultaneous red-shift of the amide A mode implies that the strength of hydrogen bonds at the imino acid poor fragments increases. Theoretically predicted distortion of the collagen structure upon adsorption on the titania surface is experimentally confirmed. PMID:25498816

  6. Study of the conformational change of adsorbed proteins on biomaterial surfaces using hydrogen-deuterium exchange with mass spectroscopy.

    PubMed

    Kim, Jinku

    2016-05-01

    There is no doubt that protein adsorption plays a crucial role in determining biocompatibility of biomaterials. Despite the information of the identity and composition of blood plasma/serum proteins adsorbed on surfaces of biomaterials to understand which proteins are involved in blood/biomaterial interactions, it still does not provide information about the conformations and orientations of adsorbed protein, which are very important in determining biological responses to biomaterials. Therefore, our laboratory has developed an experimental technology to probe protein conformations on materials that is applicable to mixtures of proteins. Herein, the new application of hydrogen/deuterium (H/D) exchange combined with mass spectrometry was applied to determine conformational changes of adsorbed proteins at biomaterial surfaces. The results suggest that there may be a significant conformational change in adsorbed proteins at 'low' bulk concentrations that leads to a large change in the kinetics of H/D exchange as compared to 'high' bulk concentrations. This technique may eventually be useful for the study of the kinetics of protein conformational changes. PMID:26896658

  7. Adsorbate modification of the structural, electronic, and magnetic properties of ferromagnetic fcc {110} surfaces

    NASA Astrophysics Data System (ADS)

    Gunn, D. S. D.; Jenkins, Stephen J.

    2011-03-01

    We identify trends in structural, electronic, and magnetic modifications that occur on ferromagnetic {110} surfaces upon varying either the substrate material or the adsorbate species. First, we have modeled the adsorption of several first-row p-block elements on the surface of fcc Co{110} at two coverages [0.5 and 1.0 monolayer (ML)]. All adsorbates were found to expand the distance between the first and second substrate layers and to contract the distance between the second and third layers. The energetic location of a characteristic trough in the density-of-d-states difference plot correlates with the direction of the adsorbate magnetic coupling to the surface, and a trend of antiferromagnetic to ferromagnetic coupling to the surface was observed across the elements from boron to fluorine. A high fluorine adatom coverage (1.0 ML) was found to enhance the surface spin magnetic moment by 11%. Second, we also calculate and contrast adsorption of 0.5 and 1.0 ML of carbon, nitrogen, and oxygen adatoms on fcc iron, cobalt, and nickel {110} surfaces and compare the structural, electronic, and magnetic properties of these systems. Carbon and nitrogen are found to couple antiferromagnetically, and oxygen ferromagnetically, to all surfaces. It was found that antiferromagnetically coupled adsorbates retained their largest spin moment values on iron, whereas ferromagnetically coupled adsorbates possessed their lowest moments on this surface. The strongly localized influence of these adsorbates is clearly illustrated in partial density-of-states plots for the surface atoms.

  8. Eley-Rideal surface chemistry: Direct reactivity of gas phase atomic hydrogen with adsorbed species

    SciTech Connect

    Weinberg, W.H.

    1996-10-01

    Selected examples of Eley-Rideal surface chemistry are presented in order to review this field. Reactions on Ru(100) only are considered. The specific examples employed are: (i) hydrogenation of oxygen atoms, (ii) hydrogenation of CO, (iii) formation of dihydrogen, and (iv) hydrogenation of formate. 80 refs., 8 figs.

  9. Hydrocarbon dissociation on palladium studied with a hydrogen sensitive Pd-metal-oxide-semiconductor structure

    NASA Astrophysics Data System (ADS)

    Dannetun, H.; Lundström, I.; Petersson, L.-G.

    1988-01-01

    The polycrystalline Pd surface of a hydrogen sensitive palladium-silicon dioxide-silicon [Pd-MOS (metal-oxide-semiconductor)] structure has been exposed to small unsaturated hydrocarbons in the temperature range 300-500 K. Apart from the hydrogen response of the Pd-MOS structure also work function (ΔΦ) and electron energy-loss studies were performed. At 500 K the hydrocarbons dissociate completely upon adsorption and produce a surface with atomically adsorbed carbon. The Pd-MOS structure can be used to observe both the dehydrogenation of the hydrocarbon molecules and the process of carbon adsorbing on the palladium surface. The sticking coefficient at this temperature for all hydrocarbons is close to unity. Furthermore, the hydrogen sensitivity of the structure is not drastically reduced by the adsorbed carbon. If the hydrocarbon adsorption is performed at 300 K there is still, at least on the initially clean surface, a large dehydrogenation. The dissociation is, however, not at all complete and there are considerable amounts of hydrocarbon species adsorbed for each gas. The induced work function shifts due to the different hydrocarbons vary from -1.0 to -1.7 eV. The hydrogen sensitivity of the Pd-MOS structure is reduced for growing hydrocarbon coverages and disappears completely for work function shifts of -1.7 eV.

  10. Structural investigations of adsorbed films of Methyl Halides on Boron Nitride

    NASA Astrophysics Data System (ADS)

    Sprung, Michael; Freitag, Andrea; Hanson, Jonathan; Larese, John

    2000-03-01

    The Methyl Halides are a group of molecules whose properties of thin adsorbed films on Graphite have been well characterized. Boron Nitride forms a hexagonal structure with a slightly larger (about 2% ) unit cell than Graphite. The study of thin films of Methyl Halides (CH_3R, R=Cl, Br and I) on Boron Nitride is motivated by the hope to gain a better understanding of adsorbate-substrate interaction. High resolution adsorption isotherms and x-ray powder diffraction have been used to investigate the monolayer structures of CH_3R adsorbed on Boron Nitride. The experiments were carried out at the Beamline X7B of the NSLS. The gases were dosed onto the sample with an automated gas handling system, and a Mar345 image plate detector was used to collect the data. The measurements were performed in a temperature range between 50 and 175 K. All three adsorbates form a solid monolayer structure on Boron Nitride at low temperature. The structure of Methyl Chloride and Methyl Bromide is very similar to the high-density structure of CH_3Cl on Graphite. This is surprising for CH_3Br because it forms a different structure on Graphite. Methyl Iodide forms similar structures on both substrates.

  11. Scanning electrochemical microscopy: surface interrogation of adsorbed hydrogen and the open circuit catalytic decomposition of formic acid at platinum.

    PubMed

    Rodríguez-López, Joaquín; Bard, Allen J

    2010-04-14

    The surface interrogation mode of scanning electrochemical microscopy (SECM) is extended to the in situ quantification of adsorbed hydrogen, H(ads), at polycrystalline platinum. The methodology consists of the production, at an interrogator electrode, of an oxidized species that is able to react with H(ads) on the Pt surface and report the amounts of this adsorbate through the SECM feedback response. The technique is validated by comparison to the electrochemical underpotential deposition (UPD) of hydrogen on Pt. We include an evaluation of electrochemical mediators for their use as oxidizing reporters for adsorbed species at platinum; a notable finding is the ability of tetramethyl-p-phenylenediamine (TMPD) to oxidize (interrogate) H(ads) on Pt at low pH (0.5 M H(2)SO(4) or 1 M HClO(4)) and with minimal background effects. As a case study, the decomposition of formic acid (HCOOH) in acidic media at open circuit on Pt was investigated. Our results suggest that formic acid decomposes at the surface of unbiased Pt through a dehydrogenation route to yield H(ads) at the Pt surface. The amount of H(ads) depended on the open circuit potential (OCP) of the Pt electrode at the time of interrogation; at a fixed concentration of HCOOH, a more negative OCP yielded larger amounts of H(ads) until reaching a coulomb limiting coverage close to 1 UPD monolayer of H(ads). The introduction of oxygen into the cell shifted the OCP to more positive potentials and reduced the quantified H(ads); furthermore, the system was shown to be chemically reversible, as several interrogations could be run consecutively and reproducibly regardless of the path taken to reach a given OCP. PMID:20225806

  12. Hydrogen uptake in vanadium first wall structures

    SciTech Connect

    Simonen, E.P.; Jones, R.H.

    1996-04-01

    Evaluation of hydrogen sources and transport are needed to assess the mechanical integrity of V structures. Two sources include implantation and transmutation. The proposed coatings for the DEMO and ITER first wall strongly influence retention of hydrogen isotopes. Upper limit calculations of hydrogen inventory were based on recycling to the plasma and an impermeable coolant-side coating. Hydrogen isotope concentrations in V approaching 1,000 appm may be activated.

  13. Evaluation of Hydrogen Isotope Exchange Methodology on Adsorbents for Tritium Removal

    SciTech Connect

    Morgan, Gregg A.; Xiao, S. Xin

    2015-03-06

    The Savannah River National Laboratory has demonstrated a potential process that can be used to remove tritium from tritiated water using Pt-catalyzed molecular sieves. The process is an elemental isotope exchange process in which H2 (when flowed through the molecular sieves) will exchange with the adsorbed water, D2O, leaving H2O adsorbed on the molecular sieves. Various formulations of catalyzed molecular sieve material were prepared using two different techniques, Pt-implantation and Pt-ion exchange. This technology has been demonstrated for a protium (H) and deuterium (D) system, but can also be used for the removal of tritium from contaminated water (T2O, HTO, and DTO) using D2 (or H2)

  14. Evaluation of hydrogen isotope exchange methodology on adsorbents for tritium removal

    SciTech Connect

    Morgan, G.A.; Xin Xiao, S.

    2015-03-15

    The Savannah River National Laboratory has demonstrated a potential process that can be used to remove tritium from tritiated water using Pt-catalyzed molecular sieves. The process is an elemental isotope exchange process in which H{sub 2} (when flowed through the molecular sieves) will exchange with the adsorbed water, D{sub 2}O, leaving H{sub 2}O adsorbed on the molecular sieves. Various formulations of catalyzed molecular sieve material were prepared using two different techniques, Pt-implantation and Pt-ion exchange. This technology has been demonstrated for a protium (H) and deuterium (D) system, but can also be used for the removal of tritium from contaminated water (T{sub 2}O, HTO, and DTO) using D{sub 2} (or H{sub 2}). (authors)

  15. Evaluation of Hydrogen Isotope Exchange Methodology on Adsorbents for Tritium Removal

    DOE PAGESBeta

    Morgan, Gregg A.; Xiao, S. Xin

    2015-03-06

    The Savannah River National Laboratory has demonstrated a potential process that can be used to remove tritium from tritiated water using Pt-catalyzed molecular sieves. The process is an elemental isotope exchange process in which H2 (when flowed through the molecular sieves) will exchange with the adsorbed water, D2O, leaving H2O adsorbed on the molecular sieves. Various formulations of catalyzed molecular sieve material were prepared using two different techniques, Pt-implantation and Pt-ion exchange. This technology has been demonstrated for a protium (H) and deuterium (D) system, but can also be used for the removal of tritium from contaminated water (T2O, HTO,more » and DTO) using D2 (or H2)« less

  16. In situ laser Raman spectra of iron phthalocyanine adsorbed on copper and gold electrodes. [Electronic structure

    SciTech Connect

    Melendres, C.A.; Rios, C.B.; Feng, X.; McMasters, R.

    1983-01-01

    Raman spectra of iron phthalocyanine (FePc) and its tetrasulfonated derivative (FeTSPc) adsorbed on copper and gold electrodes have been observed in situ in 0.05 M H/sub 2/SO/sub 4/ solution. Results confirm the authors previous finding on the coordination of FePc to water molecules to solution. Evidence suggests that the iron phthalocyanines are probably oriented with their planes parallel to the electrode surface even in immersed electrodes. A decrease in intensity and broadening of some vibrational bands are observed on increasing cathodic polarization; these are attributed to a lifting of the degeneracy of the vibrational modes due to a change in symmetry of the adsorbed molecules brought about by polarization induced by the double-layer field. The effect of carbon on the Raman spectra is discussed. The iron phthalocyanines appear to be stable at potentials close to hydrogen evolution in the absence of oxygen. 18 references, 8 figures.

  17. Infrared spectroscopy of water clusters co-adsorbed with hydrogen molecules on a sodium chloride film

    NASA Astrophysics Data System (ADS)

    Yamakawa, Koichiro; Fukutani, Katsuyuki

    2016-06-01

    Hydrogen gas containing a trace of water vapor was dosed on a vacuum-evaporated sodium chloride film at 13 K, and water clusters formed on the substrate were investigated by infrared absorption spectroscopy. Absorption bands due to (H2O)n clusters with n = 3-6 and an induced absorption band due to hydrogen were clearly observed. With increasing gas dosage, the intensities of the cluster bands increased linearly while the intensity of the hydrogen band was constant. This suggests that the water clusters were formed in two-dimensional matrices of hydrogen. We found that the water clusters did exist on the surface upon heating even after the hydrogen molecules had desorbed. A further rise of the substrate temperature up to 27 K yielded the formation of larger clusters, (H2O)n with n > 6 . We also discuss the origins of the two bands of the trimer in terms of pseudorotation and a metastable isomer.

  18. Interlocking order parameter fluctuations in structural transitions between adsorbed polymer phases.

    PubMed

    Martins, Paulo H L; Bachmann, Michael

    2016-01-21

    By means of contact-density chain-growth simulations of a simple coarse-grained lattice model for a polymer grafted at a solid homogeneous substrate, we investigate the complementary behavior of the numbers of surface-monomer and monomer-monomer contacts under various solvent and thermal conditions. This pair of contact numbers represents an appropriate set of order parameters that enables the distinct discrimination of significantly different compact phases of polymer adsorption. Depending on the transition scenario, these order parameters can interlock in perfect cooperation. The analysis helps understand the transitions from compact filmlike adsorbed polymer conformations into layered morphologies and dissolved adsorbed structures, respectively, in more detail. PMID:26690091

  19. Structure and Dynamics of Proteins Adsorbed to Biomaterial Interfaces

    SciTech Connect

    Drobny, Gary P.; Long, Joanna R.; Shaw, Wendy J.; Cotten, Myriam L.; Stayton, Partick S.

    2002-10-31

    Biomineralization, defined as the organized deposition of inorganic materials in the cellular or extracellular matrix, may be as simple a process as the formation of an iron oxide crystal in the vesicle of a magnetobacterium, or as complex a process as the formation of the intricate calcium carbonate and calcium phosphate structures found in marine coccoliths, invertebrate shells, vertebrate skeletons and teeth. The phenomenon of Biomineralization has attracted a great deal of attention recently from the materials science community, which seeks to understand the way in which inorganic biological composites are synthesized and processed in nature.

  20. Solution- and Adsorbed-State Structural Ensembles Predicted for the Statherin-Hydroxyapatite System

    PubMed Central

    Masica, David L.; Gray, Jeffrey J.

    2009-01-01

    Abstract We have developed a multiscale structure prediction technique to study solution- and adsorbed-state ensembles of biomineralization proteins. The algorithm employs a Metropolis Monte Carlo-plus-minimization strategy that varies all torsional and rigid-body protein degrees of freedom. We applied the technique to fold statherin, starting from a fully extended peptide chain in solution, in the presence of hydroxyapatite (HAp) (001), (010), and (100) monoclinic crystals. Blind (unbiased) predictions capture experimentally observed macroscopic and high-resolution structural features and show minimal statherin structural change upon adsorption. The dominant structural difference between solution and adsorbed states is an experimentally observed folding event in statherin's helical binding domain. Whereas predicted statherin conformers vary slightly at three different HAp crystal faces, geometric and chemical similarities of the surfaces allow structurally promiscuous binding. Finally, we compare blind predictions with those obtained from simulation biased to satisfy all previously published solid-state NMR (ssNMR) distance and angle measurements (acquired from HAp-adsorbed statherin). Atomic clashes in these structures suggest a plausible, alternative interpretation of some ssNMR measurements as intermolecular rather than intramolecular. This work demonstrates that a combination of ssNMR and structure prediction could effectively determine high-resolution protein structures at biomineral interfaces. PMID:19383454

  1. Theoretical study of the dynamics of atomic hydrogen adsorbed on graphene multilayers

    NASA Astrophysics Data System (ADS)

    Moaied, Mohammed; Moreno, J. A.; Caturla, M. J.; Ynduráin, Félix; Palacios, J. J.

    2015-04-01

    We present a theoretical study of the dynamics of H atoms adsorbed on graphene bilayers with Bernal stacking. First, through extensive density functional theory calculations, including van der Waals interactions, we obtain the activation barriers involved in the desorption and migration processes of a single H atom. These barriers, along with attempt rates and the energetics of H pairs, are used as input parameters in kinetic Monte Carlo simulations to study the time evolution of an initial random distribution of adsorbed H atoms. The simulations reveal that, at room temperature, H atoms occupy only one sublattice before they completely desorb or form clusters. This sublattice selectivity in the distribution of H atoms may last for sufficiently long periods of time upon lowering the temperature down to 0 ∘C . The final fate of the H atoms, namely, desorption or cluster formation, depends on the actual relative values of the activation barriers which can be tuned by doping. In some cases, a sublattice selectivity can be obtained for periods of time experimentally relevant even at room temperature. This result shows the possibility for observation and applications of the ferromagnetic state associated with such distribution.

  2. Formation of 1D adsorbed water structures on CaO(001)

    NASA Astrophysics Data System (ADS)

    Zhao, Xunhua; Bhattacharya, Saswata; Ghiringhelli, Luca M.; Levchenko, Sergey V.; Scheffler, Matthias

    2015-03-01

    Understanding the interaction of water with oxide surfaces is of fundamental importance for basic and engineering sciences. Recently, a spontaneous formation of one-dimensional (1D) adsorbed water structures have been observed on CaO(001). Interestingly, at other alkaline earth metal oxides, in particular MgO(001) and SrO(001), such structures have not been found experimentally. We calculate the relative stability of adsorbed water structures on the three oxides using density-functional theory combined with the ab initio atomistic thermodynamics. Low-energy structures at different coverages are obtained with a first-principles genetic algorithm. Finite-temperature vibrational spectra are calculated using ab initio molecular dynamics. We find a range of (T, p) conditions where 1D structures are thermodynamically stable on CaO(001). The orientation and vibrational spectra of the 1D structures are in agreement with the experiments. The formation of the 1D structures is found to be actuated by a symmetry breaking in the adsorbed water tetramer, as well as by a balance between water-water and water-substrate interactions, determined by the lattice constant of the oxide.

  3. Hydrogen bonded structures in organic amine oxalates

    NASA Astrophysics Data System (ADS)

    Vaidhyanathan, R.; Natarajan, S.; Rao, C. N. R.

    2002-05-01

    Oxalates of n-propylamine, n-butylamine, ethylenediamine, 1,4-butanediamine, piperazine, guanidine and 1,4-diazabicyclo[2,2,2]octane (DABCO) have been synthesized and characterized by single crystal X-ray diffraction and other techniques. The amine oxalates show different types of hydrogen bonded networks, linear hydrogen bonded chains characterizing the oxalates of the first five amines. Guanidinium oxalate has a sheet like structure while DABCO oxalate has dimeric hydrogen bonded rings. Hydrogen bonded structures of these oxalates are discussed in detail, besides relating their thermal stability to the strengths of the networks.

  4. Persistent hydrogen bonding in polymorphic crystal structures.

    PubMed

    Galek, Peter T A; Fábián, László; Allen, Frank H

    2009-02-01

    The significance of hydrogen bonding and its variability in polymorphic crystal structures is explored using new automated structural analysis methods. The concept of a chemically equivalent hydrogen bond is defined, which may be identified in pairs of structures, revealing those types of bonds that may persist, or not, in moving from one polymorphic form to another. Their frequency and nature are investigated in 882 polymorphic structures from the Cambridge Structural Database. A new method to compare conformations of equivalent molecules is introduced and applied to derive distinct subsets of conformational and packing polymorphs. The roles of chemical functionality and hydrogen-bond geometry in persistent interactions are systematically explored. Detailed structural comparisons reveal a large majority of persistent hydrogen bonds that are energetically crucial to structural stability. PMID:19155561

  5. Molecular Association and Structure of Hydrogen Peroxide.

    ERIC Educational Resources Information Center

    Giguere, Paul A.

    1983-01-01

    The statement is sometimes made in textbooks that liquid hydrogen peroxide is more strongly associated than water, evidenced by its higher boiling point and greater heat of vaporization. Discusses these and an additional factor (the nearly double molecular mass of the peroxide), focusing on hydrogen bonds and structure of the molecule. (JN)

  6. Ab initio study of 3d, 4d, and 5d transition metal adatoms and dimers adsorbed on hydrogen-passivated zigzag graphene nanoribbons

    NASA Astrophysics Data System (ADS)

    Longo, R. C.; Carrete, J.; Gallego, L. J.

    2011-06-01

    We performed extensive density-functional calculations of the structural, electronic, and magnetic properties of systems comprising one or two adatoms of Fe, Co, Ni, Ru, Rh, Pd, or Pt adsorbed on a hydrogen-passivated zigzag graphene nanoribbon (GNR). In all cases, the most stable structure featured the adatom(s) at positions near one of the edges of the GNR. However, whereas in the most stable structures of the single-adatom systems Ni/GNR, Ru/GNR, Rh/GNR, and Pd/GNR the adatom was located above a bay of the zigzag edge, Fe/GNR and Co/GNR were found to be most stable when the adatoms were at a first-row hole site, while the two configurations were nearly equienergetic for Pt/GNR. Similarly, whereas the most stable structures of the two-adatom systems Ni2/GNR, Ru2/GNR, Rh2/GNR, and Pd2/GNR had the adatoms above two neighboring edge bays, Co2/GNR and Pt2/GNR were most stable with the adatoms stacked in a double-decker configuration above a single edge bay, and Fe2/GNR with the adatoms stacked at a single first-row hole site. Adatom adsorption involved strong hybridization between the metal d states and the GNR states, and adsorption at sites near a GNR edge generally reduced the average magnetic moment of carbon atoms at that edge to near zero, though in some cases—notably two Co2/GNR configurations—it led to the GNR edges having non-negligible magnetic moments of the same sign even though at the start of the optimization the metal atoms were nonmagnetic and the GNR edges had opposite signs (the preferred configuration of the pristine GNR). The electronic character of GNRs with adsorbed transition metal atoms or dimers depended on the species and concentration of the adsorbate and on the adsorption site(s), different stable or near-stable systems exhibiting semiconducting, zero-gap semiconducting, metallic, or half-metallic behavior.

  7. Hydrogen structures in heavily hydrogenated crystalline and amorphous silicon

    SciTech Connect

    Jackson, W.G.; Franz, A.; Chabal, Y.; Weldon, M.K.; Jin, H.C.; Abelson, J.R.

    1998-12-31

    The hydrogen binding energy distribution and IR spectra of hydrogen platelets in c-Si have been measured and compared to H in other forms of silicon including hydrogenated polycrystalline and amorphous Si. The binding distribution for platelet containing samples, determined using H evolution, exhibits two peaks: a bulk peak at 1.8--1.9 eV below the transport barrier, and a second possibly surface related peak 1.8--1.9 eV below the surface evolution barrier. The bulk peak grows at 250 C and is consistent with calculated energies for platelet structures. The same two evolution peaks are found in hydrogenated polycrystalline Si and amorphous silicon. The IR spectra for heavily hydrogenated c-Si are dominated by the stretching modes at 2076 and 2128 cm{sup {minus}1}. Most surprisingly there appears to be a strong mode at 856 cm{sup {minus}1} which is associated with a deformation mode of SiH{sub 3}. Even more surprising, this SiH{sub 3} 856 cm{sup {minus}1} mode remains until 550 C indicating that the SiH{sub 3} containing structures are rather stable.

  8. Differential Pair Distribution Function Study of the Structure of Arsenate Adsorbed on Nanocrystalline [gamma]-Alumina

    SciTech Connect

    Li, Wei; Harrington, Richard; Tang, Yuanzhi; Kubicki, James D.; Aryanpour, Masoud; Reeder, Richard J.; Parise, John B.; Phillips, Brian L.

    2012-03-15

    Structural information is important for understanding surface adsorption mechanisms of contaminants on metal (hydr)oxides. In this work, a novel technique was employed to study the interfacial structure of arsenate oxyanions adsorbed on {gamma}-alumina nanoparticles, namely, differential pair distribution function (d-PDF) analysis of synchrotron X-ray total scattering. The d-PDF is the difference of properly normalized PDFs obtained for samples with and without arsenate adsorbed, otherwise identically prepared. The real space pattern contains information on atomic pair correlations between adsorbed arsenate and the atoms on {gamma}-alumina surface (Al, O, etc.). PDF results on the arsenate adsorption sample on {gamma}-alumina prepared at 1 mM As concentration and pH 5 revealed two peaks at 1.66 {angstrom} and 3.09 {angstrom}, corresponding to As-O and As-Al atomic pair correlations. This observation is consistent with those measured by extended X-ray absorption fine structure (EXAFS) spectroscopy, which suggests a first shell of As-O at 1.69 {+-} 0.01 {angstrom} with a coordination number of 4 and a second shell of As-Al at 3.13 {+-} 0.04 {angstrom} with a coordination number of 2. These results are in agreement with a bidentate binuclear coordination environment to the octahedral Al of {gamma}-alumina as predicted by density functional theory (DFT) calculation.

  9. Untangleing the effects of chain rigidity on the structure and dynamics of strongly adsorbed polymer melts

    SciTech Connect

    Carrillo, Jan-Michael Y.; Cheng, Shiwang; Kumar, Rajeev; Goswami, Monojoy; Sokolov, Alexei P; Sumpter, Bobby G.

    2015-06-11

    Here, we present a detailed analysis of coarse-grained molecular dynamics simulations of semiflexible polymer melts in contact with a strongly adsorbing substrate. We have characterized the segments in the interfacial layer by counting the number of trains, loops, tails and unadsorbed segments. For more rigid chains, a tail and an adsorbed segment (a train) dominate while loops are more prevalent in more flexible chains. The tails exhibit a non-uniformly stretched conformation akin to the polydispersed pseudobrush envisioned by Guiselin. To probe the dynamics of the segments we computed the layer z-resolved intermediate coherent collective dynamics structure factor, S(q, t, z), mean-square displacement of segments, and the 2nd Legendre polynomial of the time-autocorrelation of unit bond vectors, 2[ni(t,z)•ni(0,z)]>. Our results show that segmental dynamics is slower for stiffer chains and there is a strong correlation between the structure and dynamics in the interfacial layer. There is no glassy layer, and the slowing down in dynamics of stiffer chains in the adsorbed region can be attributed to the densification and the more persistent layering of segments.

  10. Untangleing the effects of chain rigidity on the structure and dynamics of strongly adsorbed polymer melts

    DOE PAGESBeta

    Carrillo, Jan-Michael Y.; Cheng, Shiwang; Kumar, Rajeev; Goswami, Monojoy; Sokolov, Alexei P; Sumpter, Bobby G.

    2015-06-11

    Here, we present a detailed analysis of coarse-grained molecular dynamics simulations of semiflexible polymer melts in contact with a strongly adsorbing substrate. We have characterized the segments in the interfacial layer by counting the number of trains, loops, tails and unadsorbed segments. For more rigid chains, a tail and an adsorbed segment (a train) dominate while loops are more prevalent in more flexible chains. The tails exhibit a non-uniformly stretched conformation akin to the polydispersed pseudobrush envisioned by Guiselin. To probe the dynamics of the segments we computed the layer z-resolved intermediate coherent collective dynamics structure factor, S(q, t, z),more » mean-square displacement of segments, and the 2nd Legendre polynomial of the time-autocorrelation of unit bond vectors, 2[ni(t,z)•ni(0,z)]>. Our results show that segmental dynamics is slower for stiffer chains and there is a strong correlation between the structure and dynamics in the interfacial layer. There is no glassy layer, and the slowing down in dynamics of stiffer chains in the adsorbed region can be attributed to the densification and the more persistent layering of segments.« less

  11. Effect of fly ash addition on the removal of hydrogen sulfide from biogas and air on sewage sludge-based composite adsorbents.

    PubMed

    Seredych, Mykola; Strydom, Christien; Bandosz, Teresa J

    2008-01-01

    Desulfurization adsorbents were prepared from the mixtures of various compositions of New York City sewage sludge and fly ashes from SASOL, South Africa, by pyrolysis at 950 degrees C. The resulting materials were used as adsorbents of hydrogen sulfide from simulated dry digester gas mixture or moist air. The adsorbents before and after H(2)S removal were characterized using adsorption of nitrogen, elemental analysis, pH measurements, XRF, XRD, and thermal analysis. It was found that the addition of fly ash decreases the desulfurization capacity in comparison with the sewage sludge-based materials. The extent of this decrease depends on the type of ash, its content and the composition of challenging gas. Although the presence of CO(2) deactivates some adsorption sites to various degrees depending on the sample composition, the addition of ashes has a more detrimental effect when the adsorbents are used to remove hydrogen sulfide from air. This is likely the result of hydrophobicity of ashes since the H(2)S removal capacity was found to be strongly dependent on the reactivity towards water/water adsorption. On the other hand, the addition of ashes strongly decreases the porosity of materials where sulfur, as a product of hydrogen sulfide oxidation, can be stored. PMID:17935967

  12. Changes in the quaternary structure of amelogenin when adsorbed onto surfaces

    SciTech Connect

    Tarasevich, Barbara J.; Lea, Alan S.; Bernt, William; Engelhard, Mark H.; Shaw, Wendy J.

    2009-02-02

    The amelogenin protein is involved in the formation of highly controlled and anisotropic hydroxyapatite crystals in tooth enamel. Amelogenin is unique in that it self assembles to form supramolecular quaternary structures called “nanospheres,” spherical aggregates of amelogenin monomers typically 20-60 nm in diameter. Although nanospheres have been observed in solution, the quaternary structure of amelogenin adsorbed onto surfaces is not well known. A better understanding of the surface structure is of great importance, however, because the function of amelogenin depends on it. We report studies of the adsorption of amelogenin onto self-assembled monolayers (SAMs) containing COOH and CH3 end group functionality as well as single crystal fluoroapatite (FAP), a biologically relevant surface. The supramolecular structures of the protein in solution as determined by dynamic light scattering (DLS) were compared with the supramolecular structures of the protein physisorbed onto surfaces as studied by atomic force microscopy (AFM). We found that although our solutions contained only nanospheres of narrow size distribution, smaller structures such as monomers and dimers were observed onto both hydrophilic and hydrophobic surfaces. This suggests that amelogenin can adsorb onto surfaces as small structures that peel away or “shed” from the nanospheres that are present in solution.

  13. Second-harmonic generation in boron nitride nanotubes adsorbed with molecular hydrogen

    NASA Astrophysics Data System (ADS)

    Vazquez-Nava, Raul; Salazar-Aparicio, Ramses; Arzate, Norberto; Mendoza, Bernardo

    2014-03-01

    We present ab initio calculations for second harmonic response of single wall zigzag pristine and with molecular hydrogen adsorption boron nitride nanotubes. These calculations were performed with density functional theory within the local-density approximation (LDA) and the application of the GW approximation to calculate the band gap GW correction. A length-guage formalism for calculating the nonlinear optical response with the correct implementation of the scissor correction was used to obtain the nonlinear susceptibility χ (2)(- 2 ω ω , ω) of zigzag BN nanotubes. We found that contrary to that reported in the literature, the (5,0) and (9,0) boron nitride nannotubes have a non vanishing SHG response. We also found that SHG is not a suitable thecnique to monitor the physisorption of H2 molecules on the external surface of BN nanotubes. This work was partially supported by CONACYT-México, grants 153930.

  14. Molecular hydrogen adsorbed on benzene: Insights from a quantum Monte Carlo study.

    PubMed

    Beaudet, Todd D; Casula, Michele; Kim, Jeongnim; Sorella, Sandro; Martin, Richard M

    2008-10-28

    We present a quantum Monte Carlo study of the hydrogen-benzene system where binding is very weak. We demonstrate that the binding is well described at both variational Monte Carlo (VMC) and diffusion Monte Carlo (DMC) levels by a Jastrow correlated single determinant geminal wave function with an optimized compact basis set that includes diffuse orbitals. Agreement between VMC and fixed-node DMC binding energies is found to be within 0.18 mhartree, suggesting that the calculations are well converged with respect to the basis. Essentially the same binding is also found in independent DMC calculations using a different trial wave function of a more conventional Slater-Jastrow form, supporting our conclusion that the binding energy is accurate and includes all effects of correlation. We compare with previous calculations, and we discuss the physical mechanisms of the interaction, the role of diffuse basis functions, and the charge redistribution in the bond. PMID:19045302

  15. Density-functional investigation of the geometric and electronic structure of ethylene oxide adsorbed on Si(100)

    NASA Astrophysics Data System (ADS)

    Wang, Lu; Li, Qing-Fang; Yang, Cui-Hong; Wei, Yue-Ling; Zhu, Xing-Feng; Rao, Wei-Feng

    2016-05-01

    The geometric and electronic structures of the ethylene oxide (EO) molecule adsorbed on Si(100)-(2 × 1) surface were investigated by using the density-functional theory calculations. All possible adsorbed structures were considered and it was found that only four adsorption structures are stable. The calculations of the formation energy revealed the most stable conformation and demonstrated that the nature of Si-O bond significantly affects the stability of adsorption systems. The analysis of corresponding electronic structures showed that two adsorbed structures are still semiconductor compounds but the other two are not. In particular, the EO after adsorbing was found to be connected via a ring-opening reaction where the molecule forms a five-membered ring together with the surface of dimer silicon atoms, and the produced five-membered ring is almost perpendicular to the silicon surface.

  16. Platinum nanoparticle during electrochemical hydrogen evolution: Adsorbate distribution, active reaction species, and size effect

    DOE PAGESBeta

    Tan, Teck L.; Wang, Lin -Lin; Zhang, Jia; Johnson, Duane D.; Bai, Kewu

    2015-03-02

    For small Pt nanoparticles (NPs), catalytic activity is, as observed, adversely affected by size in the 1–3 nm range. We elucidate, via first-principles-based thermodynamics, the operation H* distribution and cyclic voltammetry (CV) during the hydrogen evolution reaction (HER) across the electrochemical potential, including the underpotential region (U ≤ 0) that is difficult to assess in experiment. We consider multiple adsorption sites on a 1 nm Pt NP model and show that the characteristic CV peaks from different H* species correspond well to experiment. We next quantify the activity contribution from each H* species to explain the adverse effect of size.more » From the resolved CV peaks at the standard hydrogen electrode potential (U = 0), we first deduce that the active species for the HER are the partially covered (100)-facet bridge sites and the (111)-facet hollow sites. Upon evaluation of the reaction barriers at operation H* distribution and microkinetic modeling of the exchange current, we find that the nearest-neighbor (100)-facet bridge site pairs have the lowest activation energy and contribute to ~75% of the NP activity. Edge bridge sites (fully covered by H*) per se are not active; however, they react with neighboring (100)-facet H* to account for ~18% of the activity, whereas (111)-facet hollow sites contribute little. As a result, extrapolating the relative contributions to larger NPs in which the ratio of facet-to-edge sites increases, we show that the adverse size effect of Pt NP HER activity kicks in for sizes below 2 nm.« less

  17. Platinum nanoparticle during electrochemical hydrogen evolution: Adsorbate distribution, active reaction species, and size effect

    SciTech Connect

    Tan, Teck L.; Wang, Lin -Lin; Zhang, Jia; Johnson, Duane D.; Bai, Kewu

    2015-03-02

    For small Pt nanoparticles (NPs), catalytic activity is, as observed, adversely affected by size in the 1–3 nm range. We elucidate, via first-principles-based thermodynamics, the operation H* distribution and cyclic voltammetry (CV) during the hydrogen evolution reaction (HER) across the electrochemical potential, including the underpotential region (U ≤ 0) that is difficult to assess in experiment. We consider multiple adsorption sites on a 1 nm Pt NP model and show that the characteristic CV peaks from different H* species correspond well to experiment. We next quantify the activity contribution from each H* species to explain the adverse effect of size. From the resolved CV peaks at the standard hydrogen electrode potential (U = 0), we first deduce that the active species for the HER are the partially covered (100)-facet bridge sites and the (111)-facet hollow sites. Upon evaluation of the reaction barriers at operation H* distribution and microkinetic modeling of the exchange current, we find that the nearest-neighbor (100)-facet bridge site pairs have the lowest activation energy and contribute to ~75% of the NP activity. Edge bridge sites (fully covered by H*) per se are not active; however, they react with neighboring (100)-facet H* to account for ~18% of the activity, whereas (111)-facet hollow sites contribute little. As a result, extrapolating the relative contributions to larger NPs in which the ratio of facet-to-edge sites increases, we show that the adverse size effect of Pt NP HER activity kicks in for sizes below 2 nm.

  18. Synthesis of adsorbents with dendronic structures for protein hydrophobic interaction chromatography.

    PubMed

    Mata-Gómez, Marco A; Yaman, Sena; Valencia-Gallegos, Jesus A; Tari, Canan; Rito-Palomares, Marco; González-Valdez, José

    2016-04-22

    Here, we introduced a new technology based on the incorporation of dendrons-branched chemical structures-onto supports for synthesis of HIC adsorbents. In doing so we studied the synthesis and performance of these novel HIC dendron-based adsorbents. The adsorbents were synthesized in a facile two-step reaction. First, Sepharose 4FF (R) was chemically modified with polyester dendrons of different branching degrees i.e. third (G3) or fifth (G5) generations. Then, butyl-end valeric acid ligands were coupled to dendrons via ester bond formation. UV-vis spectrophotometry and FTIR analyses of the modified resins confirmed the presence of the dendrons and their ligands on them. Inclusion of dendrons allowed the increment of ligand density, 82.5 ± 11 and 175.6 ± 5.7 μmol ligand/mL resin for RG3 and RG5, respectively. Static adsorption capacity of modified resins was found to be ∼ 60 mg BSA/mL resin. Interestingly, dynamic binding capacity was higher at high flow rates, 62.5 ± 0.8 and 58.0 ± 0.5mg/mL for RG3 and RG5, respectively. RG3 was able to separate lipase, β-lactoglobulin and α-chymotrypsin selectively as well as fractionating of a whole proteome from yeast. This innovative technology will improve the existing HIC resin synthesis methods. It will also allow the reduction of the amount of adsorbent used in a chromatographic procedure and thus permit the use of smaller columns resulting in faster processes. Furthermore, this method could potentially be considered as a green technology since both, dendrons and ligands, are formed by ester bonds that are more biodegradable allowing the disposal of used resin waste in a more ecofriendly manner when compared to other exiting resins. PMID:27018188

  19. First principles DFT investigation of yttrium-decorated boron-nitride nanotube: Electronic structure and hydrogen storage

    SciTech Connect

    Jain, Richa Naja; Chakraborty, Brahmananda; Ramaniah, Lavanya M.

    2015-06-24

    The electronic structure and hydrogen storage capability of Yttrium-doped BNNTs has been theoretically investigated using first principles density functional theory (DFT). Yttrium atom prefers the hollow site in the center of the hexagonal ring with a binding energy of 0.8048eV. Decorating by Y makes the system half-metallic and magnetic with a magnetic moment of 1.0µ{sub B}. Y decorated Boron-Nitride (8,0) nanotube can adsorb up to five hydrogen molecules whose average binding energy is computed as 0.5044eV. All the hydrogen molecules are adsorbed with an average desorption temperature of 644.708 K. Taking that the Y atoms can be placed only in alternate hexagons, the implied wt% comes out to be 5.31%, a relatively acceptable value for hydrogen storage materials. Thus, this system can serve as potential hydrogen storage medium.

  20. First principles DFT investigation of yttrium-decorated boron-nitride nanotube: Electronic structure and hydrogen storage

    NASA Astrophysics Data System (ADS)

    Jain, Richa Naja; Chakraborty, Brahmananda; Ramaniah, Lavanya M.

    2015-06-01

    The electronic structure and hydrogen storage capability of Yttrium-doped BNNTs has been theoretically investigated using first principles density functional theory (DFT). Yttrium atom prefers the hollow site in the center of the hexagonal ring with a binding energy of 0.8048eV. Decorating by Y makes the system half-metallic and magnetic with a magnetic moment of 1.0µB. Y decorated Boron-Nitride (8,0) nanotube can adsorb up to five hydrogen molecules whose average binding energy is computed as 0.5044eV. All the hydrogen molecules are adsorbed with an average desorption temperature of 644.708 K. Taking that the Y atoms can be placed only in alternate hexagons, the implied wt% comes out to be 5.31%, a relatively acceptable value for hydrogen storage materials. Thus, this system can serve as potential hydrogen storage medium.

  1. Hydrogen passivation of silicon nanowire structures

    NASA Astrophysics Data System (ADS)

    Aouida, S.; Benabderrahmane Zaghouani, R.; Bachtouli, N.; Bessais, B.

    2016-05-01

    In this work, we focus on hydrogen passivation of silicon nanowire structures (SiNWs) obtained by metal assisted chemical etching (MACE) intended to be used in silicon-based solar cells. SiNWs present high surface defects density causing the minority carrier lifetime reduction. Our results show that hydrogen passivation of SiNWs ameliorates minority carrier lifetime by reducing the dangling bonds and then the surface recombination velocity. This enhancement is limited by SiNWs distribution.

  2. First principles DFT investigation of yttrium-doped graphene: Electronic structure and hydrogen storage

    SciTech Connect

    Desnavi, Sameerah; Chakraborty, Brahmananda; Ramaniah, Lavanya M.

    2014-04-24

    The electronic structure and hydrogen storage capability of Yttrium-doped grapheme has been theoretically investigated using first principles density functional theory (DFT). Yttrium atom prefers the hollow site of the hexagonal ring with a binding energy of 1.40 eV. Doping by Y makes the system metallic and magnetic with a magnetic moment of 2.11 μ{sub B}. Y decorated graphene can adsorb up to four hydrogen molecules with an average binding energy of 0.415 eV. All the hydrogen atoms are physisorbed with an average desorption temperature of 530.44 K. The Y atoms can be placed only in alternate hexagons, which imply a wt% of 6.17, close to the DoE criterion for hydrogen storage materials. Thus, this system is potential hydrogen storage medium with 100% recycling capability.

  3. Adsorbed and near surface structure of ionic liquids at a solid interface.

    PubMed

    Segura, Juan José; Elbourne, Aaron; Wanless, Erica J; Warr, Gregory G; Voïtchovsky, Kislon; Atkin, Rob

    2013-03-01

    The structure of solid-ionic liquid (IL) interfaces has been characterised with unprecedented clarity by employing a range of atomic force microscopy (AFM) imaging techniques and tip pressures appropriate for the system under study. Soft contact and amplitude-modulation (AM) AFM imaging have been used to elucidate the lateral structure of ILs adsorbed onto mica, and in the near surface ion layers. Data is presented for ethylammonium nitrate (EAN) and 1-ethyl-3-methylimidazolium bis(trifluoro-methylsulfonyl)imide (EMIm TFSI). Whereas EAN is a protic IL that forms a nanostructured sponge phase in the bulk, EMIm TFSI is aprotic and has weak (or absent) bulk association structure. Comparison of results obtained for the two liquids elucidates how the strength of bulk liquid morphology effects lateral organisation at the surface, and any effect of IL class, i.e. protic versus aprotic. Imaging reveals EAN self assembles at the solid surface in a worm-like morphology, whereas EMIm cations adsorb in a more isolated fashion, but still in rows templated by the mica surface. To the authors' knowledge, the wormlike structures present at the EAN-mica interface are the smallest self-assembled aggregates ever imaged on a solid surface. PMID:23361257

  4. Neutron Reflectometry Studies of the Adsorbed Structure of the Amelogenin, LRAP

    SciTech Connect

    Tarasevich, Barbara J.; Perez-Salas, Ursula; Masica, David L.; Philo, John; Krueger, Susan; Majkrzak, Charles F.; Gray, Jeffrey J.; Shaw, Wendy J.

    2013-03-21

    Amelogenins make up over 90 percent of the protein present during enamel formation and have been demonstrated to be critical in proper enamel development, but the mechanism governing this control is not well understood. Leucine-rich amelogenin peptide (LRAP) is a 59-residue splice variant of amelogenin and contains the charged regions from the full protein thought to control crystal regulation. In this work, we utilized neutron reflectivity (NR) to investigate the structure and orientation of LRAP adsorbed from solutions onto molecularly smooth COOH-terminated self-assembled monolayers (SAMs) surfaces. Sedimentation velocity experiments revealed that LRAP is primarily a monomer in saturated calcium phosphate (SCP) solutions (0.15 M NaCl) at pH 7.4. LRAP adsorbed as ~33 Å thick layers at ~70% coverage as determined by NR. Rosetta simulations of the dimensions of LRAP in solution (37 Å diameter) indicate that the NR determined z dimension is consistent with an LRAP monomer. Sedimentation velocity experiments and Rosetta simulation show that the LRAP monomer has an extended, asymmetric shape in solution. The NR data suggests that the protein is not completely extended on the surface, having some degree of structure away from the surface. A protein orientation with the C-terminal and inner N-terminal region (~8-24)) located near the surface is consistent with the higher scattering length density (SLD) and higher protein hydration found near the surface by NR. This work presents new information on the tertiary and quaternary structure of LRAP in solution and adsorbed onto surfaces. It also presents further evidence that the monomeric species may be an important functional form of amelogenin proteins.

  5. Neutron Reflectometry Studies of the Adsorbed Structure of the Amelogenin, LRAP

    PubMed Central

    Tarasevich, Barbara J.; Perez-Salas, Ursula; Masica, David L.; Philo, John; Kienzle, Paul; Krueger, Susan; Majkrzak, Charles F.; Gray, Jeffrey L.; Shaw, Wendy J.

    2013-01-01

    Amelogenins make up over 90 percent of the protein present during enamel formation and have been demonstrated to be critical in proper enamel development, but the mechanism governing this control is not well understood. Leucine-rich amelogenin peptide (LRAP) is a 59-residue splice variant of amelogenin and contains the charged regions from the full protein thought to control crystal regulation. In this work, we utilized neutron reflectivity (NR) to investigate the structure and orientation of LRAP adsorbed from solutions onto molecularly smooth COOH-terminated self-assembled monolayers (SAMs) surfaces. Sedimentation velocity (SV) experiments revealed that LRAP is primarily a monomer in saturated calcium phosphate (SCP) solutions (0.15 M NaCl) at pH 7.4. LRAP adsorbed as ~32 Å thick layers at ~70% coverage as determined by NR. Rosetta simulations of the dimensions of LRAP in solution (37 Å diameter) indicate that the NR determined z dimension is consistent with an LRAP monomer. SV experiments and Rosetta simulation show that the LRAP monomer has an extended, asymmetric shape in solution. The NR data suggests that the protein is not completely extended on the surface, having some degree of structure away from the surface. A protein orientation with the C-terminal and inner N-terminal region (residues ~8–24) located near the surface is consistent with the higher scattering length density (SLD) found near the surface by NR. This work presents new information on the tertiary and quaternary structure of LRAP in solution and adsorbed onto surfaces. It also presents further evidence that the monomeric species may be an important functional form of amelogenin proteins. PMID:23477285

  6. LEED structure analysis of Sb adsorbed Si(0 0 1) surface

    NASA Astrophysics Data System (ADS)

    Mitsui, T.; Hongo, S.; Urano, T.

    2001-06-01

    Sb adsorbed Si(0 0 1) surfaces have been investigated by LEED and AES. After a few monolayer (ML) deposition at room temperature, the LEED patterns of 1×1, 2×1 and c(4×4) have been observed successively as elevating the annealing temperature. Two structures (1×1 and 2×1) were examined by LEED I- V curve analysis. The genetic algorithm (GA) was operated to search a global optimum structure. For the 1×1 structure, a good R-factor value of 0.22 was obtained for the model in which topmost 1 ML Sb atoms sit on the Si atoms of fourth substrate layer. For the 2×1 structure, two cases of 1 ML and a half ML Sb coverage was examined, and an Sb dimer model with 1 ML coverage gave a better R-factor value.

  7. Structure and Reactivity of Alkyl Ethers Adsorbed on CeO(2)(111) Model Catalysts

    SciTech Connect

    Calaza, Florencia C; Chen, Tsung-Liang; Mullins, David R; Overbury, Steven {Steve} H

    2011-01-01

    The effect of surface hydroxyls on the adsorption of ether on ceria was explored. Adsorption of dimethyl ether (DME) and diethyl ether (DEE) on oxidized and reduced CeO{sub 2}(111) films was studied and compared with Ru(0001) using RAIRS and sXPS within a UHV environment. On Ru(0001) the ethers adsorb weakly with the molecular plane close to parallel to the surface plane. On the ceria films, the adsorption of the ethers was stronger than on the metal surface, presumably due to stronger interaction of the ether oxygen lone pair electrons with a cerium cation. This interaction causes the ethers to tilt away from the surface plane compared to the Ru(0001) surface. No pronounced differences were found between oxidized (CeO{sub 2}) and reduced (CeOx) films. The adsorption of the ethers was found to be perturbed by the presence of OH groups on hydroxylated CeOx. In the case of DEE, the geometry of adsorption resembles that found on Ru, and in the case of dimethyl ether DME is in between that one found on clean CeOx and the metal surface. Decomposition of the DEE was observed on the OH/CeOx surface following high DEE exposure at 300 K and higher temperatures. Ethoxides and acetates were identified as adsorbed species on the surface by means of RAIRS and ethoxides and formates by s-XPS. No decomposition of dimethyl ether was observed on the OH/CeOx at these higher temperatures, implying that the dissociation of the C-O bond from ethers requires the presence of {beta}-hydrogen.

  8. Structure and Reactivity of Alkyl Ethers Adsorbed on CeO2(111) Model Catalysts

    SciTech Connect

    F Calaza; T Chen; D Mullins; S Overbury

    2011-12-31

    The effect of surface hydroxyls on the adsorption of ether on ceria was explored. Adsorption of dimethyl ether (DME) and diethyl ether (DEE) on oxidized and reduced CeO{sub 2}(111) films was studied and compared with Ru(0001) using RAIRS and sXPS within a UHV environment. On Ru(0001) the ethers adsorb weakly with the molecular plane close to parallel to the surface plane. On the ceria films, the adsorption of the ethers was stronger than on the metal surface, presumably due to stronger interaction of the ether oxygen lone pair electrons with a cerium cation. This interaction causes the ethers to tilt away from the surface plane compared to the Ru(0001) surface. No pronounced differences were found between oxidized (CeO{sub 2}) and reduced (CeOx) films. The adsorption of the ethers was found to be perturbed by the presence of OH groups on hydroxylated CeOx. In the case of DEE, the geometry of adsorption resembles that found on Ru, and in the case of dimethyl ether DME is in between that one found on clean CeOx and the metal surface. Decomposition of the DEE was observed on the OH/CeOx surface following high DEE exposure at 300 K and higher temperatures. Ethoxides and acetates were identified as adsorbed species on the surface by means of RAIRS and ethoxides and formates by s-XPS. No decomposition of dimethyl ether was observed on the OH/CeOx at these higher temperatures, implying that the dissociation of the C-O bond from ethers requires the presence of {beta}-hydrogen.

  9. Temperature-induced ordering of metal/adsorbate structures at electrochemical interfaces.

    SciTech Connect

    Lucas, C. A.; Thompson, P.; Cormack, M.; Brownrigg, A.; Fowler, B.; Strmcnik, D.; Stamenkovic, V.; Greeley, J.; Menzel, A.; You, H.; Markovic, N. M.; Univ. Liverpool; Paul Scherrer Inst.

    2009-01-01

    The influence of temperature changes in water-based electrolytes on the atomic structure at the electrochemical interface has been studied using in situ surface X-ray scattering (SXS) in combination with cyclic voltammetry. Results are presented for the potential-dependent surface reconstruction of Au(100), the adsorption and ordering of bromide anions on the Au(100) surface, and the adsorption and oxidation of CO on Pt(111) in pure HClO{sub 4} and in the presence of anions. These systems represent a range of structural phenomena, namely metal surface restructuring and ordering transitions in both nonreactive spectator species and reactive adsorbate layers. The key effect of temperature appears to be in controlling the kinetics of the surface reactions that involve oxygenated species, such as hydroxyl adsorption and oxide formation. The results indicate that temperature effects should be considered in the determination of structure-function relationships in many important electrochemical systems.

  10. Temperature-induced ordering of metal/adsorbate structures at electrochemical interfaces.

    PubMed

    Lucas, Christopher A; Thompson, Paul; Cormack, Michael; Brownrigg, Alexander; Fowler, Ben; Strmcnik, Dusan; Stamenkovic, Vojislav; Greeley, Jeff; Menzel, Andreas; You, Hoydoo; Marković, Nenad M

    2009-06-10

    The influence of temperature changes in water-based electrolytes on the atomic structure at the electrochemical interface has been studied using in situ surface X-ray scattering (SXS) in combination with cyclic voltammetry. Results are presented for the potential-dependent surface reconstruction of Au(100), the adsorption and ordering of bromide anions on the Au(100) surface, and the adsorption and oxidation of CO on Pt(111) in pure HClO(4) and in the presence of anions. These systems represent a range of structural phenomena, namely metal surface restructuring and ordering transitions in both nonreactive spectator species and reactive adsorbate layers. The key effect of temperature appears to be in controlling the kinetics of the surface reactions that involve oxygenated species, such as hydroxyl adsorption and oxide formation. The results indicate that temperature effects should be considered in the determination of structure-function relationships in many important electrochemical systems. PMID:19489644

  11. Hydrogen-hydrogen intermolecular structure of polyethylene in the melt

    NASA Astrophysics Data System (ADS)

    Londono, J. D.; Annis, B. K.; Habenschuss, A.; Smith, G. D.; Borodin, O.; Tso, C.; Hsieh, E. T.; Soper, A. K.

    1999-05-01

    Three polyethylene samples, which differed in their degree of deuteration, were studied in neutron diffraction isotopic substitution (NDIS) experiments at 428 K. These results were complemented at small wavevectors by small angle neutron measurements. The intermolecular hydrogen-hydrogen (HH) structure function, hHH(Q), was obtained without recourse to intramolecular structure models, as demonstrated in a prior report. The PE experimental results are compared to computer simulation results for the alkanes C100 at 509 K and C44 at 350, 400, and 450 K. The small temperature dependence of the HH intermolecular radial distribution functions, gHH(r) for C44 indicates that the differences observed between the PE, C100, and C44 (450 K) results are, for the most part, not due to just temperature differences. It is shown that the string model, an analytic result from an integral equation theory of polymers (PRISM), can account approximately for the overall shape of the gHH(r) functions, and that this overall shape is dependent on the radius of gyration of the molecule. Further analysis shows that there are two other contributions to gHH(r), both of which are independent of chain length to first order. The first is due to chain-chain packing, and the second is due to local HH intermolecular correlations. These results are significant because they demonstrate that hHH(Q) is a useful function for studying intermolecular polymer structure, which has been shown to underpin phase behavior in polyolefin blends.

  12. Path integral Monte Carlo simulations of H2 adsorbed to lithium-doped benzene: A model for hydrogen storage materials.

    PubMed

    Lindoy, Lachlan P; Kolmann, Stephen J; D'Arcy, Jordan H; Crittenden, Deborah L; Jordan, Meredith J T

    2015-11-21

    Finite temperature quantum and anharmonic effects are studied in H2-Li(+)-benzene, a model hydrogen storage material, using path integral Monte Carlo (PIMC) simulations on an interpolated potential energy surface refined over the eight intermolecular degrees of freedom based upon M05-2X/6-311+G(2df,p) density functional theory calculations. Rigid-body PIMC simulations are performed at temperatures ranging from 77 K to 150 K, producing both quantum and classical probability density histograms describing the adsorbed H2. Quantum effects broaden the histograms with respect to their classical analogues and increase the expectation values of the radial and angular polar coordinates describing the location of the center-of-mass of the H2 molecule. The rigid-body PIMC simulations also provide estimates of the change in internal energy, ΔUads, and enthalpy, ΔHads, for H2 adsorption onto Li(+)-benzene, as a function of temperature. These estimates indicate that quantum effects are important even at room temperature and classical results should be interpreted with caution. Our results also show that anharmonicity is more important in the calculation of U and H than coupling-coupling between the intermolecular degrees of freedom becomes less important as temperature increases whereas anharmonicity becomes more important. The most anharmonic motions in H2-Li(+)-benzene are the "helicopter" and "ferris wheel" H2 rotations. Treating these motions as one-dimensional free and hindered rotors, respectively, provides simple corrections to standard harmonic oscillator, rigid rotor thermochemical expressions for internal energy and enthalpy that encapsulate the majority of the anharmonicity. At 150 K, our best rigid-body PIMC estimates for ΔUads and ΔHads are -13.3 ± 0.1 and -14.5 ± 0.1 kJ mol(-1), respectively. PMID:26590532

  13. Edge states and local electronic structure around an adsorbed impurity in a topological superconductor

    NASA Astrophysics Data System (ADS)

    Tai, Yuan-Yen; Choi, Hongchul; Ahmed, Towfiq; Ting, C. S.; Zhu, Jian-Xin

    2015-11-01

    Recently, topological superconducting states have attracted much interest. In this paper, we consider a topological superconductor with Z2 topological mirror order [Y.-Y. Tai et al., Phys. Rev. B 91, 041111(R) (2015), 10.1103/PhysRevB.91.041111] and s±-wave superconducting pairing symmetry, within a two-orbital model originally designed for iron-based superconductivity [Y.-Y. Tai et al., Europhys. Lett. 103, 67001 (2013), 10.1209/0295-5075/103/67001]. We predict the existence of gapless edge states. We also study the local electronic structure around an adsorbed interstitial magnetic impurity in the system, and find the existence of low-energy in-gap bound states even with a weak spin polarization on the impurity. We also discuss the relevance of our results to a recent scanning tunneling microscopy experiment on a Fe(Te,Se) compound with an adsorbed Fe impurity [J.-X. Yin et al., Nat. Phys. 11, 543 (2015), 10.1038/nphys3371], for which our density functional calculations show the Fe impurity is spin polarized.

  14. Influence of structural fluctuations on lifetimes of adsorbate states at hybrid organic-semiconductor interfaces

    NASA Astrophysics Data System (ADS)

    Müller, M.; Sánchez-Portal, D.; Lin, H.; Fratesi, G.; Brivio, G. P.; Selloni, A.

    On the road towards a more realistic description of charge transfer processes at hybrid organic-semiconductor interfaces for photovoltaic applications we extend our first-principles scheme for the extraction of elastic linewidths to include the effects of structural fluctuations. Based on snapshots obtained from Car-Parinello molecular dynamics simulations at room temperature, we set up geometries in which dye molecules at interfaces are attached to a semi-infinite TiO2 substrate. The elastic linewidths are computed using a Green's function method. This effectively introduces the coupling to a continuum of states in the substrate. In particular we investigate catechol and isonicotinic acid on rutile(110) and anatase(101) at the level of semi-local density functional theory. We perform multiple calculations of linewidths and peak-positions associated with the adsorbate's frontier orbitals for different geometric configurations to obtain a time-averaged analysis of such physical properties. We compare the results from the considered systems to understand the effects of dynamics onto interfacial charge transfer and systematically assess the dependence of the extracted elastic lifetimes on the relative alignment between adsorbate and substrate states. This project has received funding from the European Union Seventh Framework Programme under Grant Agreement No. 607323 [THINFACE].

  15. X-ray standing wave investigation of the surface structure of selenite anions adsorbed on calcite.

    SciTech Connect

    Cheng, L.; Lyman, P. F.; Sturchio, N. C.; Bedzyk, M. J.; Northwestern Univ.

    1997-01-01

    The adsorption of selenite ions (SeO{sup 2-}{sub 3}) from a dilute aqueous solution onto a freshly-cleaved calcite (10 {ovr 1} 4) surface was studied with the X-ray standing wave (XSW) technique. The complex ion SeO{sup 2-}{sub 3} is found to selectively adsorb at the CO{sup 2-}{sub 3} site via ionic exchange, forming a two-dimensional solid-solution of the form Ca(SeO{sub 3}){sub x}(CO{sub 3}){sub 1-x} at the interface. The calcite (10 {ovr 1} 4), (0006) and (11 {ovr 2} 0) Bragg reflections were used to triangulate the Se position with respect to the calcite lattice. The local surface structure at the SeO{sup 2-}{sub 3} adsorbate site, derived from the XSW results, is consistent with a model in which the base of the SeO{sup 2-}{sub 3} trigonal pyramid aligns with (and replaces) the CO{sup 2-}{sub 3} equilateral triangular group. The SeO{sup 2-}{sub 3} adsorption saturated at a coverage of 0.02 monolayers. Under identical chemical conditions, selenate (SeO{sup 2-}{sub 4}) adsorption was inhibited.

  16. Pre-adsorbed type-I collagen structure-dependent changes in osteoblastic phenotype

    SciTech Connect

    Hanagata, Nobutaka . E-mail: HANAGATA.Nobutaka@nims.go.jp; Takemura, Taro; Monkawa, Akira; Ikoma, Toshiyuki; Tanaka, Junzo

    2006-06-16

    Type-I collagen is the most abundant extracellular matrix in bones and modulates various functions of osteoblasts. We prepared two different structures of type-I collagen on tissue culture grade polystylene (TCPS) surfaces, one is feltwork structure of filamentous molecules from acid solutions (ACs) and the other is network structure of fibrils from neutral solutions (NCs), to examine effects of the structures on the maturation process of osteoblast-like cells. No significant differences of cell proliferation were observed between TCPS and ACs, but NCs delayed the proliferation. In initial cell attachment, the cells on ACs had tense lamellipodia with sharp tips, while those on NCs had loose lamellipodia. No detectable differences in levels of expressed integrin {alpha}{sub 2}- and {alpha}{sub 5}-subunits were observed between the structures. Although the matrix mineralization in NCs was also delayed in comparison with TCPS and ACs, fully mineralized levels in NCs were the same as those of TCPS and ACs. In addition, although we examined the effects of densities of pre-adsorbed collagen molecules on osteoblast maturation, the effects were less serious than those of the structures. This study suggests that the structures of collagen affect proliferation and mineralization of osteoblast-like cells.

  17. Novel Hydrogen Hydrate Structures under Pressure

    NASA Astrophysics Data System (ADS)

    Qian, Guang-Rui; Lyakhov, Andriy O.; Zhu, Qiang; Oganov, Artem R.; Dong, Xiao

    2014-07-01

    Gas hydrates are systems of prime importance. In particular, hydrogen hydrates are potential materials of icy satellites and comets, and may be used for hydrogen storage. We explore the H2O-H2 system at pressures in the range 0-100 GPa with ab initio variable-composition evolutionary simulations. According to our calculation and previous experiments, the H2O-H2 system undergoes a series of transformations with pressure, and adopts the known open-network clathrate structures (sII, C0), dense ``filled ice'' structures (C1, C2) and two novel hydrate phases. One of these is based on the hexagonal ice framework and has the same H2O:H2 ratio (2:1) as the C0 phase at low pressures and similar enthalpy (we name this phase Ih-C0). The other newly predicted hydrate phase has a 1:2 H2O:H2 ratio and structure based on cubic ice. This phase (which we name C3) is predicted to be thermodynamically stable above 38 GPa when including van der Waals interactions and zero-point vibrational energy, and explains previously mysterious experimental X-ray diffraction and Raman measurements. This is the hydrogen-richest hydrate and this phase has a remarkable gravimetric density (18 wt.%) of easily extractable hydrogen.

  18. Novel hydrogen hydrate structures under pressure.

    PubMed

    Qian, Guang-Rui; Lyakhov, Andriy O; Zhu, Qiang; Oganov, Artem R; Dong, Xiao

    2014-01-01

    Gas hydrates are systems of prime importance. In particular, hydrogen hydrates are potential materials of icy satellites and comets, and may be used for hydrogen storage. We explore the H₂O-H₂ system at pressures in the range 0-100 GPa with ab initio variable-composition evolutionary simulations. According to our calculation and previous experiments, the H₂O-H₂ system undergoes a series of transformations with pressure, and adopts the known open-network clathrate structures (sII, C₀), dense "filled ice" structures (C₁, C₂) and two novel hydrate phases. One of these is based on the hexagonal ice framework and has the same H₂O:H₂ ratio (2:1) as the C₀ phase at low pressures and similar enthalpy (we name this phase Ih-C₀). The other newly predicted hydrate phase has a 1:2 H₂O:H₂ ratio and structure based on cubic ice. This phase (which we name C₃) is predicted to be thermodynamically stable above 38 GPa when including van der Waals interactions and zero-point vibrational energy, and explains previously mysterious experimental X-ray diffraction and Raman measurements. This is the hydrogen-richest hydrate and this phase has a remarkable gravimetric density (18 wt.%) of easily extractable hydrogen. PMID:25001502

  19. Potential structural material problems in a hydrogen energy system

    NASA Technical Reports Server (NTRS)

    Gray, H. R.; Nelson, H. G.; Johnson, R. E.; Mcpherson, W. B.; Howard, F. S.; Swisher, J. H.

    1976-01-01

    Potential structural material problems that may be encountered in the three components of a hydrogen energy system - production, transmission/storage, and utilization - have been identified. Hydrogen embrittlement, corrosion, oxidation, and erosion may occur during the production of hydrogen. Hydrogen embrittlement is of major concern during both transmission and utilization of hydrogen. Specific materials research and development programs necessary to support a hydrogen energy system are described. An awareness of probable shortages of strategic materials has been maintained in these suggested programs.

  20. Potential structural material problems in a hydrogen energy system

    NASA Technical Reports Server (NTRS)

    Gray, H. R.; Nelson, H. G.; Johnson, R. E.; Mcpherson, B.; Howard, F. S.; Swisher, J. H.

    1975-01-01

    Potential structural material problems that may be encountered in the three components of a hydrogen energy system - production, transmission/storage, and utilization - were identified. Hydrogen embrittlement, corrosion, oxidation, and erosion may occur during the production of hydrogen. Hydrogen embrittlement is of major concern during both transmission and utilization of hydrogen. Specific materials research and development programs necessary to support a hydrogen energy system are described.

  1. Coordination structure of adsorbed Zn(II) at Water-TiO2 interfaces

    SciTech Connect

    He, G.; Pan, G.; Zhang, M.; Waychunas, G.A.

    2011-01-15

    The local structure of aqueous metal ions on solid surfaces is central to understanding many chemical and biological processes in soil and aquatic environments. Here, the local coordination structure of hydrated Zn(II) at water-TiO{sub 2} interfaces was identified by extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES) spectroscopy combined with density functional theory (DFT) calculations. A nonintegral coordination number of average {approx}4.5 O atoms around a central Zn atom was obtained by EXAFS analysis. DFT calculations indicated that this coordination structure was consistent with the mixture of 4-coordinated bidentate binuclear (BB) and 5-coordinated bidentate mononuclear (BM) metastable equilibrium adsorption (MEA) states. The BB complex has 4-coordinated Zn, while the monodentate mononuclear (MM) complex has 6-coordinated Zn, and a 5-coordinated adsorbed Zn was found in the BM adsorption mode. DFT calculated energies showed that the lower-coordinated BB and BM modes were thermodynamically more favorable than the higher-coordinated MM MEA state. The experimentally observed XANES fingerprinting provided additional direct spectral evidence of 4- and 5-coordinated Zn-O modes. The overall spectral and computational evidence indicated that Zn(II) can occur in 4-, 5-, and 6-oxygen coordinated sites in different MEA states due to steric hindrance effects, and the coexistence of different MEA states formed the multiple coordination environments.

  2. Structure and composition of clean and hydrogen covered MoRe surfaces

    NASA Astrophysics Data System (ADS)

    Hammer, L.; Meyer, S.; Rath, C.

    1995-04-01

    The clean and hydrogen covered (100) and (110) faces of Mo(0.75)Re(0.23) alloy single crystals show 1x1 structures. By means of LEED structure analyses we have determined the interlayer distances as well as the layer concentrations down to the sixth layer. While the clean (110) surface turns out to be nearly bulklike terminated, the clean (100) face is found to exhibit both an extended oscillatory layer relaxation and composition profile. Hydrogen adsorption at low temperatures does not alter the composition profile and removes the small remaining relaxation for the (110) surface. In case of the (100) face a substantial reduction of the relaxation is observed for the outermost layer distances as well, while deeper layer relaxations are preserved indicating a strong coupling off relaxation and composition profiles. Hydrogen is found to adsorb in quasi-threefold coordinated sites for the (110) and bridge sites for the (100) face.

  3. LEED crystallography studies of the structure of clean and adsorbate-covered Ir, Pt and Rh crystal surfaces

    SciTech Connect

    Koestner, R.J.

    1982-08-01

    There have only been a few Low Energy Electron Diffraction (LEED) intensity analyses carried out to determine the structure of molecules adsorbed on metal surfaces; most surface crystallography studies concentrated on the structure of clean unreconstructed or atomic adsorbate-covered transition metal faces. The few molecular adsorption systems already investigated by dynamical LEED are CO on Ni(100), Cu(100) and Pd(100) as well as C/sub 2/H/sub 2/ and C/sub 2/H/sub 4/ adsorbed on Pt(111). The emphasis of this thesis research has been to extend the applicability of LEED crystallography to the more complicated unit cells found in molecular overlayers on transition metals or in there constructed surfaces of clean transition metals.

  4. Impact of temperature and electrical potentials on the stability and structure of collagen adsorbed on the gold electrode

    NASA Astrophysics Data System (ADS)

    Meiners, Frank; Ahlers, Michael; Brand, Izabella; Wittstock, Gunther

    2015-01-01

    The morphology and structure of collagen type I adsorbed on gold electrodes were studied as a function of electrode potential and temperature by means of capacitance measurements, polarization modulation infrared reflection-absorption spectroscopy and scanning force microscopy at temperatures of 37 °C, 43 °C and 50 °C. The selected temperatures corresponded to the normal body temperature, temperature of denaturation of collagen molecules and denaturation of collagen fibrils, respectively. Independently of the solution temperature, collagen was adsorbed on gold electrodes in the potential range - 0.7 V < E < 0.4 V vs. Ag/AgCl, where the protein film was very stable. Fragments of collagen molecules made a direct contact to the gold surface and water was present in the film. Protein molecules were oriented preferentially with their long axis towards the gold surface. Collagen molecules in the adsorbed state preserved their native triple helical structure even at temperatures corresponding to collagen denaturation in aqueous solutions. Application of E < - 0.75 V vs. Ag/AgCl leads to the swelling of the protein film by water and desorption from the electrode surface. IR spectra provided no evidence of the thermal denaturation of adsorbed collagen molecules. A temperature increase to 50 °C leads to a distortion of the collagen film. The processes of aggregation and fibrilization were preferred over thermal denaturation for collagen adsorbed on the electrode surface and exposed to changing potentials.

  5. Redetermination of piperidinium hydrogen sulfide structure

    NASA Technical Reports Server (NTRS)

    Andras, Maria T.; Hepp, Aloysius F.; Fanwick, Phillip E.; Duraj, Stan A.; Gordon, Edward M.

    1994-01-01

    The presence of adventitious water in a reaction between dicyclopentamethylene thiuram-disulfide (C5H10NCS2)(sub 2) and a picoline solution of tricyclopentadienyl indium(III) (C5H5)(sub 3). It resulted in the formation of piperidinium hydrogen sulfide (C5H13NS). The piperidinium hydrogen sulfide produced in this way was unambiguously characterized by X-ray crystallography. The structure determination showed that the piperidinium hydrogen sulfide crystal (MW = 119.23 g/mol) has an orthorhombic (Pbcm) unit cell whose parameters are: a = 9.818(2), b = 7.3720(1), c = 9.754(1) A, V = 706.0(3) A(exp 3), Z=4. D(sub chi) = 1.122 g cm(exp -3), Mo K(alpha) (lamda = 0.71073), mu= 3.36 cm(exp -1), F(000) = 264.0, T =293 K, R = 0.036 for 343 reflections with F(sub O)(sup 2) greater than 3 sigma (F(sub O)(sup 2)) and 65 variables. The compound consists of (C5H10NH2)(+) cations and (SH)(-) anions with both species residing on crystallographic mirror planes. N-H -- S hydrogen bonding contributes to the interconnection of neighboring piperidinium components of the compound.

  6. Separation of the attractive and repulsive contributions to the adsorbate-adsorbate interactions of polar adsorbates on Si(100)

    NASA Astrophysics Data System (ADS)

    Lin, Ying-Hsiu; Jeng, Horng-Tay; Lin, Deng-Sung

    2015-11-01

    Dissociative adsorption of H2O, NH3, CH3OH and CH3NH2 polar molecules on the Si(100) surface results in a 1:1 mixture of two adsorbates (H and multi-atomic fragment A = OH, NH2, CH3O, CH3NH, respectively) on the surface. By using density functional theory (DFT) calculations, the adsorption geometry, the total energies and the charge densities for various possible ordered structures of the mixed adsorbate layer have been found. Analyzing the systematic trends in the total energies unveils concurrently the nearest-neighbor interactions ENN and the next nearest-neighbor interactions ENNN between two polar adsorbates A. In going from small to large polar adsorbates, ENN's exhibit an attractive-to-repulsive crossover behavior, indicating that they include competing attractive and repulsive contributions. Exploration of the charge density distributions allows the estimation of the degree of charge overlapping between immediately neighboring A's, the resulting contribution of the steric repulsions, and that of the attractive interactions to the corresponding ENN's. The attractive contributions to nearest neighboring adsorbate-adsorbate interactions between the polar adsorbates under study are shown to result from hydrogen bonds or dipole-dipole interactions.

  7. Electrochemical reduction of oxygen and hydrogen peroxide catalyzed by a surface copper(II)-2,4,6-tris(2-piridil)-1,3,5-triazine complex adsorbed on a graphite electrode

    NASA Astrophysics Data System (ADS)

    Dias, Vera L. N.; Fernandes, Elizabeth N.; da Silva, Leila M. S.; Marques, Edmar P.; Zhang, Jiujun; Marques, Aldaléa L. Brandes

    A graphite electrode irreversibly adsorbed by 2,4,6-tris(2-piridil)-1,3,5-triazine (abbreviated as TPT) was examined by cyclic voltammetry. The adsorbed TPT exhibited two irreversible reduction waves in the potential range of -0.7 and -1.0 V (versus SCE). Upon strong adsorption, TPT can serve as a coordination ligand for copper ions to form a surface complex. Its three adjacent nitrogen positions provide strong affinity to the metal ions and bond copper(II) to an electrode surface. A 1:1 coordination between Cu(II) or Cu(I) and the TPT ligand to form [Cu(II)(TPT)] 2+ or [Cu(I)(TPT)] + is the predominant process, evidenced by spectrophotometry, surface cyclic voltammetry, and coordinated structural feasibility of Cu(II)/Cu(I)-TPT complexes. The predominant copper(II)-TPT surface complex shows a reversible redox wave, which is identified as one-electron process of [Cu(II)(TPT)] 2+ ↔ [Cu(I)(TPT)] +. The electrode adsorbed by [Cu(II)(TPT)] 2+ complex showed electrocatalytic activity towards oxygen and/or hydrogen peroxide reductions. The catalyzed reduction of oxygen and hydrogen peroxide were identified as four-electron and two-electron process to form water. It is suggested that the possible electrocatalytic reductions were due to an inner-sphere mechanism, which involved a coordination between substrate (O 2 or H 2O 2) and [Cu(I)(TPT)] +. The reduction kinetics were also investigated by a rotating disk electrode method.

  8. Analysis of structure and orientation of adsorbed polymers in solution subject to a dynamic shear stress

    SciTech Connect

    Smith, G.; Baker, S.; Toprakcioglu, C.

    1996-09-01

    This is the final report of a three-year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). Polymer-based separation techniques rely on the ability of a binding portion of the polymer to interact with a specific molecule in a solution flowing past the polymer. The location of the binding site within or out of the entangled polymer chains is thus crucial to the effectiveness of these methods. For this reason, the details of flow induced deformation of the polymer chains is important in such applications as exclusion chromatography, waste water treatment, ultrafiltration, enhanced oil recovery and microbial adhesion. Few techniques exist to examine the structure and orientation of polymeric materials, and even fewer to examine systems in a dynamic fluid flow. The goal of this project was to understand the molecular structure and orientation of adsorbed polymers with and without active binding ligands as a function of solvent shear rate, solvent power, polymer molecular weight, surface polymer coverage and heterogeneity of the surface polymer chains by neutron reflectometry in a newly designed shear cell. Geometrical effects on binding of molecules in the flow was also studied subject to the same parameters.

  9. Di- and triethanolamine grafted kaolinites of different structural order as adsorbents of heavy metals.

    PubMed

    Koteja, Anna; Matusik, Jakub

    2015-10-01

    Efficient sorbents based on widely available clay minerals are of particular value in the field of pollution control. The research shows mineral-based sorbents formed through organic modification of two kaolinites differing in structural order. Their structure and texture was characterized by XRD, FTIR, DTA/TG, CHN, XPS and N2 adsorption/desorption methods. The obtained materials were tested as adsorbents of Cd(II), Zn(II), Pb(II) and Cu(II) in equilibrium and kinetic experiments. Moreover, the sorption mechanisms were subjected to investigation. The synthesis procedure involved interlayer grafting of kaolinites with diethanolamine (DEA) and triethanolamine (TEA). The organo-kaolinites showed resistance to hydrolysis and temperature up to ∼300 °C. The adsorption improvement was observed for the modified materials, particular the DEA derivatives and materials based on the poorly ordered kaolinite. The XPS analyses of elements local environment coupled with binding strength tests enabled to confirm the immobilization mechanisms. The pure kaolinites removed metal ions through either the ion-exchange or the surface complexation, exclusively on the external surfaces. In turn, the grafted materials additionally immobilized ions in the interlayer space which was expanded. The ions were attracted by the grafted DEA or TEA, which are N and O-donors and readily form complexes with metals, particularly with the Cu(II). PMID:26057107

  10. Binding energies and electronic structures of adsorbed titanium chains on carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Yang, Chih-Kai; Zhao, Jijun; Lu, Jianping

    2002-03-01

    Our calculations based on first principles have shown that titanium is much favored energetically over gold and aluminum to form a continuous chain on a variety of single-wall carbon nanotubes (SWNT). Results from two zigzag nanotubes, (10,0) and (14,0), and two armchairs, (6,6) and (8,8), indicate that binding energy for a Ti-adsorbed SWNT is generally six to seven eV per unit cell larger than a Au or Al-adsorbed SWNT. Furthermore, the adsorbed Ti chain generates additional states in the band gaps of the two semi-conducting zigzag nanotubes, transforming them into metals.

  11. Band structure of hydrogenated silicene on Ag(111): Evidence for half-silicane

    NASA Astrophysics Data System (ADS)

    Wang, W.; Olovsson, W.; Uhrberg, R. I. G.

    2016-02-01

    In the case of graphene, hydrogenation removes the conductivity due to the bands forming the Dirac cone by opening up a band gap. This type of chemical functionalization is of the utmost importance for electronic applications. As predicted by theoretical studies, a similar change in the band structure is expected for silicene, the closest analog to graphene. We here report a study of the atomic and electronic structures of hydrogenated silicene with hydrogen on one side, the so-called half-silicane. The ("2 √{3 }×2 √{3 } ") phase of silicene on Ag(111) was used in this Rapid Communication since it can be formed homogeneously across the entire surface of the Ag substrate. Low-energy electron diffraction and scanning tunneling microscopy data clearly show that hydrogenation changes the structure of silicene on Ag(111) resulting in a (1 × 1) periodicity with respect to the silicene lattice. The hydrogenated silicene also exhibits a quasiregular (2 √{3 }×2 √{3 } )-like arrangement of vacancies. Angle-resolved photoelectron spectroscopy revealed two dispersive bands which can be unambiguously assigned to half-silicane. The common top of these bands is located at ˜0.9 eV below the Fermi level. We find that the experimental bands are closely reproduced by the theoretical band structure of free-standing silicene with H adsorbed on the upper hexagonal sublattice.

  12. Phosphate adsorption on aluminum-impregnated mesoporous silicates: surface structure and behavior of adsorbents.

    PubMed

    Shin, Eun Woo; Han, James S; Jang, Min; Min, Soo-Hong; Park, Jae Kwang; Rowell, Roger M

    2004-02-01

    Phosphorus from excess fertilizers and detergents ends up washing into lakes, creeks, and rivers. This overabundance of phosphorus causes excessive aquatic plant and algae growth and depletes the dissolved oxygen supply in the water. In this study, aluminum-impregnated mesoporous adsorbents were tested for their ability to remove phosphate from water. The surface structure of the materials was investigated with X-ray diffraction (XRD), a N2 adsorption-desorption technique, Fourier transform-infrared (FT-IR), and X-ray photoelectron spectroscopy (XPS) to understand the effect of surface properties on the adsorption behavior of phosphate. The mesoporous materials were loaded with Al components by reaction with surface silanol groups. In the adsorption test, the Al-impregnated mesoporous materials showed fast adsorption kinetics as well as high adsorption capacities, compared with activated alumina. The uniform mesopores of the Al-impregnated mesoporous materials caused the diffusion rate in the adsorption process to increase, which in turn caused the fast adsorption kinetics. High phosphate adsorption capacities of the Al-impregnated mesoporous materials were attributed to not only the increase of surface hydroxyl density on Al oxide due to well-dispersed impregnation of Al components but also the decrease in stoichiometry of surface hydroxyl ions to phosphate by the formation of monodentate surface complexes. PMID:14968882

  13. Dephenolization of stored olive-mill wastewater, using four different adsorbing matrices to attain a low-cost feedstock for hydrogen photo-production.

    PubMed

    Padovani, Giulia; Pintucci, Cristina; Carlozzi, Pietro

    2013-06-01

    This investigation deals with the conversion of olive-mill wastewater (OMW) into several feedstocks suitable for hydrogen photo-production. The goal was reached by means of two sequential steps: (i) a pre-treatment process of stored-OMW for the removal of polyphenols, which made it possible to obtain several effluents, and (ii) a photo-fermentative process for hydrogen production by means of Rhodopseudomonas palustris sp. Four different adsorbent matrices (Azolla, granular active carbon, resin, and zeolite) were used to dephenolize stored-OMW. The four liquid fractions attained by using the above process created the same number of effluents, and these were diluted with water and then used for hydrogen photo-production. The maximum hydrogen production rate (14.31 mL/L/h) was attained with the photo-fermenter containing 25% of the effluent, which came from the pre-treatment of stored-OMW using granular active carbon. Using the carbon effluent as feedstock, the greatest light conversion efficiency of 2.29% was achieved. PMID:23612177

  14. A surface extended X-ray absorption fine structure study of tellurium adsorbed onto Si(100)

    NASA Astrophysics Data System (ADS)

    Burgess, S. R.; Cowie, B. C. C.; Wilks, S. P.; Dunstan, P. R.; Dunscombe, C. J.; Williams, R. H.

    1996-09-01

    The adsorption of tellurium on Si(100) has been studied using surface extended X-ray adsorption fine structure (SEXAFS) and X-ray standing wave spectroscopy (XSW). This particular system is of interest due to its potential applicability in the surfactant aided growth of CdHgTeCdTeSi(100) based infra-red detectors. The Te/Si(100) structure was generated by depositing a thick layer (˜ 100 Å) of CdTe onto a clean Si (2 × 1) double domain surface, and annealing the sample to 350°C. This resulted is a ˜ 1 ML Te terminated surface where the (2 × 1) reconstruction was lost in favour of a (1 × 1) symmetry. X-ray absorption of the Te L 3 edge ( E = 4341 eV), with a photon energy range of 4440-4700 eV, was probed using a total yield detection scheme. The SEXAFS results indicated that the Te atoms sat in 2-fold bridge sites directly above a fourth layer Si atom. The corresponding bond length was measured to be 2.52 ± 0.05 Å. The XSW measurements of the (400) reflection gave a coherent position of 1.63 ± 0.03 Å and a coherent fraction of 0.65. This is consistent with the breaking of the SiSi dimers and thus could be an example of the phenomena of adsorbate-induced dereconstruction of the surface. These results are compared with those of Bennet et al. who examined a similar system using soft X-ray photoemission (SXPS) and the STM study of Yoshikawa et al.

  15. Geometries and electronic structures of the hydrogenated diamond (100) surface upon exposure to active ions: A first principles study

    NASA Astrophysics Data System (ADS)

    Liu, Feng-Bin; Li, Jing-Lin; Chen, Wen-Bin; Cui, Yan; Jiao, Zhi-Wei; Yan, Hong-Juan; Qu, Min; Di, Jie-Jian

    2016-02-01

    To elucidate the effects of physisorbed active ions on the geometries and electronic structures of hydrogenated diamond films, models of HCO 3 - , H3O+, and OH- ions physisorbed on hydrogenated diamond (100) surfaces were constructed. Density functional theory was used to calculate the geometries, adsorption energies, and partial density of states. The results showed that the geometries of the hydrogenated diamond (100) surfaces all changed to different degrees after ion adsorption. Among them, the H3O+ ion affected the geometry of the hydrogenated diamond (100) surfaces the most. This is well consistent with the results of the calculated adsorption energies, which indicated that a strong electrostatic attraction occurs between the hydrogenated diamond (100) surface and H3O+ ions. In addition, electrons transfer significantly from the hydrogenated diamond (100) surface to the adsorbed H3O+ ion, which induces a downward shift in the HOMO and LUMO energy levels of the H3O+ ion. However, for active ions like OH- and HCO 3 - , no dramatic change appears for the electronic structures of the adsorbed ions.

  16. Hydrogen embrittlement of structural alloys. A technology survey

    NASA Technical Reports Server (NTRS)

    Carpenter, J. L., Jr.; Stuhrke, W. F.

    1976-01-01

    Technical abstracts for about 90 significant documents relating to hydrogen embrittlement of structural metals and alloys are reviewed. Particular note was taken of documents regarding hydrogen effects in rocket propulsion, aircraft propulsion and hydrogen energy systems, including storage and transfer systems.

  17. Fundamental characteristics of synthetic adsorbents intended for industrial chromatographic separations.

    PubMed

    Adachi, Tadashi; Isobe, Eiji

    2004-05-14

    With the aim of obtaining comprehensive information on the selection of synthetic adsorbents for industrial applications, effect of pore and chemical structure of industrial-grade synthetic adsorbents on adsorption capacity of several pharmaceutical compounds was investigated. For relatively low molecular mass compounds, such as cephalexin, berberine chloride and tetracycline hydrochloride, surface area per unit volume of polystyrenic adsorbents dominated the equilibrium adsorption capacity. On the contrary, effect of pore size of the polystyrenic adsorbents on the equilibrium adsorption capacity was observed for relatively high molecular mass compounds, such as rifampicin, Vitamin B12 and insulin. Polystyrenic adsorbent with high surface area and small pore size showed small adsorption capacity for relatively high molecular mass compounds, whereas polystyrenic adsorbent with relatively small surface area but with large pore size showed large adsorption capacity. Effect of chemical structure on the equilibrium adsorption capacity of several pharmaceutical compounds was also studied among polystyrenic, modified polystyrenic and polymethacrylic adsorbents. The modified polystyrenic adsorbent showed larger adsorption capacity for all compounds tested in this study due to enhanced hydrophobicity. The polymethacrylic adsorbent possessed high adsorption capacity for rifampicin and insulin, but it showed lower adsorption capacity for the other compounds studied. This result may be attributed to hydrogen bonding playing major role for the adsorption of compounds on polymethacrylic adsorbent. Furthermore, column adsorption experiments were operated to estimate the effect of pore characteristics of the polystyrenic adsorbents on dynamic adsorption behavior, and it is found that both surface area and pore size of the polystyrenic adsorbents significantly affect the dynamic adsorption capacity as well as flow rate. PMID:15139411

  18. Modeling the construction of polymeric adsorbent media: effects of counter-ions on ligand immobilization and pore structure.

    PubMed

    Riccardi, Enrico; Wang, Jee-Ching; Liapis, Athanasios I

    2014-02-28

    Molecular dynamics modeling and simulations are employed to study the effects of counter-ions on the dynamic spatial density distribution and total loading of immobilized ligands as well as on the pore structure of the resultant ion exchange chromatography adsorbent media. The results show that the porous adsorbent media formed by polymeric chain molecules involve transport mechanisms and steric resistances which cause the charged ligands and counter-ions not to follow stoichiometric distributions so that (i) a gradient in the local nonelectroneutrality occurs, (ii) non-uniform spatial density distributions of immobilized ligands and counter-ions are formed, and (iii) clouds of counter-ions outside the porous structure could be formed. The magnitude of these counter-ion effects depends on several characteristics associated with the size, structure, and valence of the counter-ions. Small spherical counter-ions with large valence encounter the least resistance to enter a porous structure and their effects result in the formation of small gradients in the local nonelectroneutrality, higher ligand loadings, and more uniform spatial density distributions of immobilized ligands, while the formation of exterior counter-ion clouds by these types of counter-ions is minimized. Counter-ions with lower valence charges, significantly larger sizes, and elongated shapes, encounter substantially greater steric resistances in entering a porous structure and lead to the formation of larger gradients in the local nonelectroneutrality, lower ligand loadings, and less uniform spatial density distributions of immobilized ligands, as well as substantial in size exterior counter-ion clouds. The effects of lower counter-ion valence on pore structure, local nonelectroneutrality, spatial ligand density distribution, and exterior counter-ion cloud formation are further enhanced by the increased size and structure of the counter-ion. Thus, the design, construction, and functionality of

  19. Modeling the construction of polymeric adsorbent media: Effects of counter-ions on ligand immobilization and pore structure

    NASA Astrophysics Data System (ADS)

    Riccardi, Enrico; Wang, Jee-Ching; Liapis, Athanasios I.

    2014-02-01

    Molecular dynamics modeling and simulations are employed to study the effects of counter-ions on the dynamic spatial density distribution and total loading of immobilized ligands as well as on the pore structure of the resultant ion exchange chromatography adsorbent media. The results show that the porous adsorbent media formed by polymeric chain molecules involve transport mechanisms and steric resistances which cause the charged ligands and counter-ions not to follow stoichiometric distributions so that (i) a gradient in the local nonelectroneutrality occurs, (ii) non-uniform spatial density distributions of immobilized ligands and counter-ions are formed, and (iii) clouds of counter-ions outside the porous structure could be formed. The magnitude of these counter-ion effects depends on several characteristics associated with the size, structure, and valence of the counter-ions. Small spherical counter-ions with large valence encounter the least resistance to enter a porous structure and their effects result in the formation of small gradients in the local nonelectroneutrality, higher ligand loadings, and more uniform spatial density distributions of immobilized ligands, while the formation of exterior counter-ion clouds by these types of counter-ions is minimized. Counter-ions with lower valence charges, significantly larger sizes, and elongated shapes, encounter substantially greater steric resistances in entering a porous structure and lead to the formation of larger gradients in the local nonelectroneutrality, lower ligand loadings, and less uniform spatial density distributions of immobilized ligands, as well as substantial in size exterior counter-ion clouds. The effects of lower counter-ion valence on pore structure, local nonelectroneutrality, spatial ligand density distribution, and exterior counter-ion cloud formation are further enhanced by the increased size and structure of the counter-ion. Thus, the design, construction, and functionality of

  20. The role of adsorbed hydrogen species in the dehydrogenation and hydrocracking of saturated hydrocarbons on supported metal catalysts

    NASA Astrophysics Data System (ADS)

    Babenkova, L. V.; Naidina, I. N.

    1994-07-01

    The role of certain hydrogen absorption complexes in the dehydrogenation and hydrocracking of hydrocarbons on low-percentage one-component, (Pt, Pd/Al2O3) and bimetallic (Pd-Co, Pd-Ce, Pt-Co, Pt-Sn/Al2O3) catalysts is discussed. It is shown that the combination of metals in reduced forms and forms oxidised to different extents on the catalyst surfaces is responsible for their high capacity for the chemisorption of hydrogen, the wide range of its energetic inhomogeneity, and the high activity of the catalysts in the conversion of saturated hydrocarbons. Catalysts containing on the surface mainly sites for the type Hδ- chemisorption are the most active in the dehydrogenation of hydrocarbons, whereas specimens chemisorbing hydrogen mainly in the Hδ+ form are the most active in the hydrockracking of hydrocarbons. It is concluded that the strongly bound atomic hydrogen Hδ+ plays a dual role, since it not only participates directly in the dehydrogenation reaction but also promotes the reduction of the electron-deficient surface centres, which optimises the number of centres for the activation of C-H bonds. The bibliography includes 75 references.

  1. Rate inhibition of steam gasification of adsorbed hydrogen. Technical progress report, October 1, 1994--December 31, 1994

    SciTech Connect

    Miller, D.J.

    1995-04-01

    Work during the fifth quarter of the grant period has involved both gasification experiments in steam and hydrogen and continued development of the reaction apparatus and analytical methods. Most of the latter work has focused on mass spectrometric analysis of the effluent gases to obtain better response factors and to reduce background signals resulting from impurities in the reacting gas stream.

  2. Structure and Properties of Tactic Hydrogenated Polynorbornenes

    NASA Astrophysics Data System (ADS)

    Burns, Adam B.; Register, Richard A.

    Tacticity is one of the most important structural parameters for determining the physical properties of a polymer. A high degree of steroregularity typically promotes crystallization, with different tacticities giving rise to differences in crystal structure, melting point, and degree of crystallinity. In polynorbornene (PN) made by ring-opening metathesis polymerization (ROMP), tacticity is determined by the relative configuration of the nonplanar cyclopentylene rings enchained in the backbone. Traditional ROMP initiators yield atactic polymers (aPN); however, recent advances in catalyst design have produced both isotactic and syndiotactic PN. Newly reported cis,isotactic- and cis,syndiotactic-PNs were catalytically hydrogenated (abbreviated ihPN and shPN, respectively) without altering the tacticity. The thermal and structural characteristics of ihPN and shPN were studied by differential scanning calorimetry (DSC) and wide-angle x-ray scattering (WAXS) and compared to that of ahPN. Remarkably, all three polymers are semicrystalline, each with a distinct crystal structure. ihPN has a nominal melting point of 165 C, more than 20 C above that of ahPN. WAXS patterns of melt-drawn fibers of ihPN show few strong reflections indicative of either a highly symmetric unit cell or poor long-range order. ihPN fibers also exhibit a crystal-crystal transition near 130 C, which is not fully reversible on subsequent cooling. On the other hand, shPN has a nominal melting point some 15 C below that of ahPN, and shPN fibers show no evidence of polymorphism.

  3. Electronic structure study on 2D hydrogenated Icosagens nitride nanosheets

    NASA Astrophysics Data System (ADS)

    Ramesh, S.; Marutheeswaran, S.; Ramaclus, Jerald V.; Paul, Dolon Chapa

    2014-12-01

    Metal nitride nanosheets has attracted remarkable importance in surface catalysis due to its characteristic ionic nature. In this paper, using density functional theory, we investigate geometric stability and electronic properties of hydrogenated Icosagen nitride nanosheets. Binding energy of the sheets reveals hydrogenation is providing more stability. Band structure of the hydrogenated sheets is found to be n-type semiconductor. Partial density of states shows metals (B, Al, Ga and In) and its hydrogens dominating in the Fermi region. Mulliken charge analysis indications that hydrogenated nanosheets are partially hydridic surface nature except boron nitride.

  4. Adsorbent and adsorbent bed for materials capture and separation processes

    SciTech Connect

    Liu, Wei

    2011-01-25

    A method device and material for performing adsorption wherein a fluid mixture is passed through a channel in a structured adsorbent bed having a solid adsorbent comprised of adsorbent particles having a general diameter less than 100 um, loaded in a porous support matrix defining at least one straight flow channel. The adsorbent bed is configured to allow passage of a fluid through said channel and diffusion of a target material into said adsorbent under a pressure gradient driving force. The targeted molecular species in the fluid mixture diffuses across the porous support retaining layer, contacts the adsorbent, and adsorbs on the adsorbent, while the remaining species in the fluid mixture flows out of the channel.

  5. Adlayer structure dependent ultrafast desorption dynamics in carbon monoxide adsorbed on Pd (111).

    PubMed

    Hong, Sung-Young; Xu, Pan; Camillone, Nina R; White, Michael G; Camillone, Nicholas

    2016-07-01

    We report our ultrafast photoinduced desorption investigation of the coverage dependence of substrate-adsorbate energy transfer in carbon monoxide adlayers on the (111) surface of palladium. As the CO coverage is increased, the adsorption site population shifts from all threefold hollows (up to 0.33 ML), to bridge and near bridge (>0.5 to 0.6 ML) and finally to mixed threefold hollow plus top site (at saturation at 0.75 ML). We show that between 0.24 and 0.75 ML this progression of binding site motifs is accompanied by two remarkable features in the ultrafast photoinduced desorption of the adsorbates: (i) the desorption probability increases roughly two orders magnitude, and (ii) the adsorbate-substrate energy transfer rate observed in two-pulse correlation experiments varies nonmonotonically, having a minimum at intermediate coverages. Simulations using a phenomenological model to describe the adsorbate-substrate energy transfer in terms of frictional coupling indicate that these features are consistent with an adsorption-site dependent electron-mediated energy coupling strength, ηel, that decreases with binding site in the order: three-fold hollow > bridge and near bridge > top site. This weakening of ηel largely counterbalances the decrease in the desorption activation energy that accompanies this progression of adsorption site motifs, moderating what would otherwise be a rise of several orders of magnitude in the desorption probability. Within this framework, the observed energy transfer rate enhancement at saturation coverage is due to interadsorbate energy transfer from the copopulation of molecules bound in three-fold hollows to their top-site neighbors. PMID:27394118

  6. Adlayer structure dependent ultrafast desorption dynamics in carbon monoxide adsorbed on Pd (111)

    NASA Astrophysics Data System (ADS)

    Hong, Sung-Young; Xu, Pan; Camillone, Nina R.; White, Michael G.; Camillone, Nicholas

    2016-07-01

    We report our ultrafast photoinduced desorption investigation of the coverage dependence of substrate-adsorbate energy transfer in carbon monoxide adlayers on the (111) surface of palladium. As the CO coverage is increased, the adsorption site population shifts from all threefold hollows (up to 0.33 ML), to bridge and near bridge (>0.5 to 0.6 ML) and finally to mixed threefold hollow plus top site (at saturation at 0.75 ML). We show that between 0.24 and 0.75 ML this progression of binding site motifs is accompanied by two remarkable features in the ultrafast photoinduced desorption of the adsorbates: (i) the desorption probability increases roughly two orders magnitude, and (ii) the adsorbate-substrate energy transfer rate observed in two-pulse correlation experiments varies nonmonotonically, having a minimum at intermediate coverages. Simulations using a phenomenological model to describe the adsorbate-substrate energy transfer in terms of frictional coupling indicate that these features are consistent with an adsorption-site dependent electron-mediated energy coupling strength, ηel, that decreases with binding site in the order: three-fold hollow > bridge and near bridge > top site. This weakening of ηel largely counterbalances the decrease in the desorption activation energy that accompanies this progression of adsorption site motifs, moderating what would otherwise be a rise of several orders of magnitude in the desorption probability. Within this framework, the observed energy transfer rate enhancement at saturation coverage is due to interadsorbate energy transfer from the copopulation of molecules bound in three-fold hollows to their top-site neighbors.

  7. Stability, structural and electronic properties of benzene molecule adsorbed on free standing Au layer

    NASA Astrophysics Data System (ADS)

    Katoch, Neha; Kapoor, Pooja; Sharma, Munish; Kumar, Ashok; Ahluwalia, P. K.

    2016-05-01

    We report stability and electronic properties of benzene molecule adsorbed on the Au atomic layer within the framework of density function theory (DFT). Horizontal configuration of benzene on the top site of Au monolayer prefers energetically over other studied configurations. On the adsorption of benzene, the ballistic conductance of Au monolayer is found to decrease from 4G0 to 2G0 suggesting its applications for the fabrications of organic sensor devices based on the Au atomic layers.

  8. The effect of grain boundaries and adsorbates on the electrical properties of hydrogenated ultra nano crystalline diamond.

    SciTech Connect

    Gan, L.; Bolker, A.; Saguy, C.; Kalish, R.; Tan, D. L.; Tay, B. K.; Gruen, D.; Bruno, P.; Materials Science Division; Technion Haifa; Nanyang Technological Univ.

    2009-02-26

    The results of a comprehensive study on the temperature dependence of the electrical properties of hydrogenated and air exposed undoped UNCD layers following heating/cooling cycles are presented. The results clearly show that, in contrast to hydrogenated and air exposed single crystal type IIa diamond, which exhibits a clear highly conductive p-type surface layer, the electrical properties of hydrogen and H{sub 2}O exposure of UNCD are determined by the properties of the entire layer. The changes in the electrical conductivity of UNCD as a result of heating are governed by two different processes: (i) Loss of water from the external surface that takes place at about 150 C. This process is reversible, reviving the electrical properties upon exposure to humidity, just like in single crystalline diamond.(ii) Modification of the inter-grain material, which occurs at higher temperatures possibly due to H diffusion and passivation of some dangling bonds in the inter-grain material. This increases the resistivity in an irreversible manner. The conduction mechanism in the inter-grain material is characterized by variable range hopping in band tails thus indirectly proving that the material between the grains is some kind of amorphous carbon.

  9. Electronic structure and binding geometry of tetraphenylporphyrin-derived molecules adsorbed on metal and metal oxide surfaces

    NASA Astrophysics Data System (ADS)

    Coh, Senia

    Tetraphenylporphyrin (TPP)-derived molecules have been studied extensively as efficient photosensitizers when chemisorbed on the metal oxide substrates in dye-sensitized solar cells. Still, many fundamental electronic properties of the dye/oxide interface are not understood and need careful consideration. In this thesis we present a comprehensive study of the electronic structure, energy level alignment and the adsorption geometry of the TPP-derived dye molecules adsorbed on TiO2(110), ZnO(1120) and Ag(100) single crystal surfaces using ultra-high vacuum (UHV) based surface sensitive techniques. The alignment of the molecular energy levels with respect to the TiO 2 and ZnO band edges for all TPP-derived molecules we studied was found to be insensitive to either the nature of the functional groups located on the phenyl rings, presence of zinc as a central metal ion and different binding geometry of the molecules. Binding geometry, molecule-molecule interaction and the aggregation effects in the adsorbed layer, that were observed in the UV-visible spectra of the molecules adsorbed on ZnO substrate were not observed in the ultraviolet photoemission (UPS) and inverse photoemission (IPS) spectra of the occupied and unoccupied molecular states. Using near edge X-ray absorption fine structure (NEXAFS) and scanning tunneling microscopy (STM), binding geometry of the two representative TPP-derivatives was directly determined to be upright, with the porphyrin ring under large angle with respect to the surface for the p-ZnTCPP molecules and with the porphyrin ring parallel to the surface for the m-ZnTCPP molecules. We observe that the energies and the energy level alignment of the ZnTPP molecular levels measured in UPS and IPS depend on the substrate on which the molecules are adsorbed (Ag(100) or TiO2(110) single crystal surfaces). The differences are attributed to different charge screening properties of these two materials. Image charges created in the substrates during

  10. Electronic excited states as a probe of surface adsorbate structure and dynamics in liquid xenon

    SciTech Connect

    Peterson, E.S.

    1992-08-01

    A combination of second harmonic generation (SHG) and a simple dipole-dipole interaction model is presented as a new technique for determining adsorbate geometries on surfaces. The polarization dependence of SHG is used to define possible geometries of the adsorbate about the surface normal. Absorption band shifts using geometry constraints imposed by SHG data are derived for a dimer constructed from two arbitrarily placed monomers on the surface using the dipole-dipole interaction potential. These formulae can be used to determine the orientation of the two monomers relative to each other. A simplified version of this formalism is used to interpret absorption band shifts for rhodamine B adsorbed on fused silica. A brief history of the exciton is given with particular detail to Xe. Data are presented for transient absorption at RT in liquid xenon on the picosecond time scale. These are observations of both tunneling through the barrier that separates the free and trapped exciton states and the subsequent trapping of the exciton. In high densities both of these processes are found to occur within 2 to 6 picoseconds in agreement with theories of Kmiecik and Schreiber and of Martin. A threshold density is observed that separates relaxation via single binary collisions and relaxation that proceeds via Martin's resonant energy transfer hopping mechanism.

  11. Electronic excited states as a probe of surface adsorbate structure and dynamics in liquid xenon

    SciTech Connect

    Peterson, E.S.

    1992-08-01

    A combination of second harmonic generation (SHG) and a simple dipole-dipole interaction model is presented as a new technique for determining adsorbate geometries on surfaces. The polarization dependence of SHG is used to define possible geometries of the adsorbate about the surface normal. Absorption band shifts using geometry constraints imposed by SHG data are derived for a dimer constructed from two arbitrarily placed monomers on the surface using the dipole-dipole interaction potential. These formulae can be used to determine the orientation of the two monomers relative to each other. A simplified version of this formalism is used to interpret absorption band shifts for rhodamine B adsorbed on fused silica. A brief history of the exciton is given with particular detail to Xe. Data are presented for transient absorption at RT in liquid xenon on the picosecond time scale. These are observations of both tunneling through the barrier that separates the free and trapped exciton states and the subsequent trapping of the exciton. In high densities both of these processes are found to occur within 2 to 6 picoseconds in agreement with theories of Kmiecik and Schreiber and of Martin. A threshold density is observed that separates relaxation via single binary collisions and relaxation that proceeds via Martin`s resonant energy transfer hopping mechanism.

  12. Structure analysis and photochemistry of adsorbates on platinum and palladium surfaces. [1,2-dichloroethene

    SciTech Connect

    Grassian, V.H.

    1987-05-01

    The vibrational spectra of benzene and toluene adsorbed on Pd(111) indicates at 180K these molecules weakly bond to the surface. The adsorption of benzene and toluene on Pt(111) is much stronger as indicated by large frequency shifts from gas phase values. Pyridine adsorption on both Pt(111) and Pd(111) was studied as a function of temperature. At room temperature pyridine decomposes on the surface to form an ..cap alpha..-pyridyl fragment (NC/sub 5/H/sub 4/) on Pt(111), whereas the molecule remains intact on Pd(111). The electron energy loss spectra of pyridine adsorbed on these surfaces is compared to the ir spectra of two osmium cluster compounds: Os/sub 3/(CO)/sub 11/(NC/sub 5/H/sub 5/), a pyridine complex, and HOs/sub 3/(CO)/sub 10/(NC/sub 5/H/sub 4/), a pyridyl complex. The stronger interaction of these molecules to the platinum surface is a consequence of the stronger bonding of the 5d orbitals as compared to the 4d orbitals. The uv photochemistry of 2-butene and 1,2-dichloroethene when adsorbed on Pt and Pd surfaces was also studied.

  13. Surface Structure and Chemical Switching of Thioctic Acid Adsorbed on Au(111) as Observed Using Near-Edge X-ray Absorption Fine Structure

    SciTech Connect

    Meulenberg, R W; van Buuren, T; Vance, A L; Terminello, L J; Willey, T M; Bostedt, C; Fadley, C S

    2004-01-06

    Thioctic acid (alpha-lipoic acid) is a molecule with a large disulfide-containing base, a short alkyl-chain with four CH{sub 2} units, and a carboxyl termination. Self-assembled monolayer (SAM) films of thioctic acid adsorbed on Au(111) have been investigated with near-edge x-ray absorption fine structure (NEXAFS) spectroscopy and x-ray photoelectron spectroscopy (XPS) to determine film quality, bonding and morphology. Using standard preparation protocols for SAMs, that is, dissolving thioctic acid in ethanol and exposing gold to the solution, results in poor films. These films are highly disordered, contain a mixture of carboxyl and carboxylate terminations, have more than monolayer coverage, and exhibit unbound disulfide. Conversely, forming films by dissolving 1 mmol thioctic acid into 5% acetic acid in ethanol (as previously reported with carboxyl-terminated alkyl-thiols) forms ordered monolayers with small amounts of unbound sulfur. NEXAFS indicates tilted over endgroups with the carboxyl group normal on average 38{sup o} from the surface normal. Slight dichroism in other features indicates alkyl chains statistically more upright than prostrate on the surface. Reflection-absorption Fourier transform infrared (RA-FTIR) spectra indicate hydrogen bonding between neighboring molecules. In such well-formed monolayers, a stark reorientation occurs upon deprotonation of the endgroup by rinsing in a KOH solution. The carboxylate plane normal is now about 66{sup o} from sample normal, a much more upright orientation. Data indicate this reorientation may also cause a more upright orientation to the alkyl portion of the molecules.

  14. Influence of surface charge on the rate, extent, and structure of adsorbed Bovine Serum Albumin to gold electrodes.

    PubMed

    Beykal, Burcu; Herzberg, Moshe; Oren, Yoram; Mauter, Meagan S

    2015-12-15

    The objective of this work is to investigate the rate, extent, and structure of amphoteric proteins with charged solid surfaces over a range of applied potentials and surface charges. We use Electrochemical Quartz Crystal Microbalance with Dissipation Monitoring (E-QCM-D) to investigate the adsorption of amphoteric Bovine Serum Albumin (BSA) to a gold electrode while systematically varying the surface charge on the adsorbate and adsorbent by manipulating pH and applied potential, respectively. We also perform cyclic voltammetry-E-QCM-D on an adsorbed layer of BSA to elucidate conformational changes in response to varied applied potentials. We confirm previous results demonstrating that increasing magnitude of applied potential on the gold electrode is positively correlated with increasing mass adsorption when the protein and the surface are oppositely charged. On the other hand, we find that the rate of BSA adsorption is not governed by simple electrostatics, but instead depends on solution pH, an observation not well documented in the literature. Cyclic voltammetry with simultaneous E-QCM-D measurements suggest that BSA protein undergoes a conformational change as the surface potential varies. PMID:26348658

  15. Adsorbent phosphates

    NASA Technical Reports Server (NTRS)

    Watanabe, S.

    1983-01-01

    An adsorbent which uses as its primary ingredient phosphoric acid salts of zirconium or titanium is presented. Production methods are discussed and several examples are detailed. Measurements of separating characteristics of some gases using the salts are given.

  16. Adsorption of hydrogen sulfide onto activated carbon fibers: effect of pore structure and surface chemistry.

    PubMed

    Feng, Wenguo; Kwon, Seokjoon; Borguet, Eric; Vidic, Radisav

    2005-12-15

    To understand the nature of H2S adsorption onto carbon surfaces under dry and anoxic conditions, the effects of carbon pore structure and surface chemistry were studied using activated carbon fibers (ACFs) with different pore structures and surface areas. Surface pretreatments, including oxidation and heattreatment, were conducted before adsorption/desorption tests in a fixed-bed reactor. Raw ACFs with higher surface area showed greater adsorption and retention of sulfur, and heat treatment further enhanced adsorption and retention of sulfur. The retained amount of hydrogen sulfide correlated well with the amount of basic functional groups on the carbon surface, while the desorbed amount reflected the effect of pore structure. Temperature-programmed desorption (TPD) and thermal gravimetric analysis (TGA) showed that the retained sulfurous compounds were strongly bonded to the carbon surface. In addition, surface chemistry of the sorbent might determine the predominant form of adsorbate on the surface. PMID:16475362

  17. Li adsorption, hydrogen storage and dissociation using monolayer MoS2: an ab initio random structure searching approach.

    PubMed

    Putungan, Darwin Barayang; Lin, Shi-Hsin; Wei, Ching-Ming; Kuo, Jer-Lai

    2015-05-01

    Utilizing ab initio random structure searching, we investigated Li adsorption on MoS2 and hydrogen molecules on Li-decorated MoS2. In contrast to graphene, Li can be adsorbed on both sides of MoS2, with even stronger binding than on the single side. We found that high coverages of Li can be attained without Li clustering, which is essential for hydrogen storage and Li ion batteries. Moreover, regarding battery applications, Li diffusion was also found to be easy. The fully-lithiated MoS2 can then adsorb H2 with 4.4 wt%. Interestingly, our calculations revealed that hydrogen molecules can be dissociated at high Li coverage with a minimal energy barrier. We further showed that the dissociated hydrogen atom can readily diffuse on the surface, thus keeping the reaction site active. We therefore propose that Li-MoS2 could be an inexpensive alternative catalyst to noble metals in hydrogen dissociation reactions. PMID:25849099

  18. Quantum chemical investigation on the role of Li adsorbed on anatase (101) surface nano-materials on the storage of molecular hydrogen.

    PubMed

    Srinivasadesikan, V; Raghunath, P; Lin, M C

    2015-06-01

    Lithiation of TiO2 has been shown to enhance the storage of hydrogen up to 5.6 wt% (Hu et al. J Am Chem Soc 128:11740-11741, 2006). The mechanism for the process is still unknown. In this work we have carried out a study on the adsorption and diffusion of Li atoms on the surface and migration into subsurface layers of anatase (101) by periodic density functional theory calculations implementing on-site Coulomb interactions (DFT+U). The model consists of 24 [TiO2] units with 11.097 × 7.655 Å(2) surface area. Adsorption energies have been calculated for different Li atoms (1-14) on the surface. A maximum of 13 Li atoms can be accommodated on the surface at two bridged O, Ti-O, and Ti atom adsorption sites, with 83 kcal mol(-1) adsorption energy for a single Li atom adsorbed between two bridged O atoms from where it can migrate into the subsurface layer with 27 kcal mol(-1) energy barrier. The predicted adsorption energies for H2 on the lithiated TiO2 (101) surface with 1-10 Li atoms revealed that the highest adsorption energies occurred on 1-Li, 5-Li, and 9-Li surfaces with 3.5, 4.4, and 7.6 kcal mol(-1), respectively. The values decrease rapidly with additional H2 co-adsorbed on the lithiated surfaces; the maximum H2 adsorption on the 9Li-TiO2(a) surface was estimated to be only 0.32 wt% under 100 atm H2 pressure at 77 K. The result of Bader charge analysis indicated that the reduction of Ti occurred depending on the Li atoms covered on the TiO2 surface. PMID:25966674

  19. Hydrogen in magnesium palladium thin layer structures

    NASA Astrophysics Data System (ADS)

    Kruijtzer, G. L.

    2008-02-01

    In this thesis, the study of hydrogen storage, absorption and desorption in magnesium layers is described. The magnesium layers have a thickness of 50-500 nm and are covered by a palladium layer which acts as a hydrogen dissociation/association catalyst. The study was preformed under ultra high vacuum conditions to avoid oxygen contamination. The main analysis techniques were RBS, ERD and TDS.

  20. Origin of the periodic structure in the conductance curve of gold nanojunctions in hydrogen environment

    NASA Astrophysics Data System (ADS)

    Jiang, Zhuoling; Wang, Hao; Sanvito, Stefano; Hou, Shimin

    2016-03-01

    The evolution of the atomic structure and the vibrational and electronic transport properties of gold atomic junctions incorporating molecular and atomic hydrogen upon elongation have been investigated with the nonequilibrium Green's function formalism combined with density functional theory. Our calculations show that for the case of gold junctions doped with a single H2 molecule the low-bias conductance drops rapidly with the electrodes' separation, while it remains almost constant if a single H atom replaces the molecule. In contrast, when one considers two H atoms adsorbed on a gold monatomic chain forming an Au-H-Au-H-Au double-bridge structure, the low-bias conductance increases first and then shows a plateau upon stretching the junction, in perfect agreement with experiments on gold nanocontacts in hydrogen environment. Furthermore, also the distribution of the calculated vibrational energies of the two H atoms is consistent with the experimental result in the low-conductance region, demonstrating clear evidence that hydrogen molecules can dissociate on stretched gold monatomic chains. These findings are helpful to improve our understanding of the structure-property relation of gold nanocontacts and also provide a new prospect for gold nanowires being used as chemical sensors and catalysts.

  1. Structure and energetics of hydrogen-bonded networks of methanol on close packed transition metal surfaces

    NASA Astrophysics Data System (ADS)

    Murphy, Colin J.; Carrasco, Javier; Lawton, Timothy J.; Liriano, Melissa L.; Baber, Ashleigh E.; Lewis, Emily A.; Michaelides, Angelos; Sykes, E. Charles H.

    2014-07-01

    Methanol is a versatile chemical feedstock, fuel source, and energy storage material. Many reactions involving methanol are catalyzed by transition metal surfaces, on which hydrogen-bonded methanol overlayers form. As with water, the structure of these overlayers is expected to depend on a delicate balance of hydrogen bonding and adsorbate-substrate bonding. In contrast to water, however, relatively little is known about the structures methanol overlayers form and how these vary from one substrate to another. To address this issue, herein we analyze the hydrogen bonded networks that methanol forms as a function of coverage on three catalytically important surfaces, Au(111), Cu(111), and Pt(111), using a combination of scanning tunneling microscopy and density functional theory. We investigate the effect of intermolecular interactions, surface coverage, and adsorption energies on molecular assembly and compare the results to more widely studied water networks on the same surfaces. Two main factors are shown to direct the structure of methanol on the surfaces studied: the surface coverage and the competition between the methanol-methanol and methanol-surface interactions. Additionally, we report a new chiral form of buckled hexamer formed by surface bound methanol that maximizes the interactions between methanol monomers by sacrificing interactions with the surface. These results serve as a direct comparison of interaction strength, assembly, and chirality of methanol networks on Au(111), Cu(111), and Pt(111) which are catalytically relevant for methanol oxidation, steam reforming, and direct methanol fuel cells.

  2. Reversible Hydrogen Storage Materials – Structure, Chemistry, and Electronic Structure

    SciTech Connect

    Robertson, Ian M.; Johnson, Duane D.

    2014-06-21

    To understand the processes involved in the uptake and release of hydrogen from candidate light-weight metal hydride storage systems, a combination of materials characterization techniques and first principle calculation methods have been employed. In addition to conventional microstructural characterization in the transmission electron microscope, which provides projected information about the through thickness microstructure, electron tomography methods were employed to determine the three-dimensional spatial distribution of catalyst species for select systems both before and after dehydrogenation. Catalyst species identification as well as compositional analysis of the storage material before and after hydrogen charging and discharging was performed using a combination of energy dispersive spectroscopy, EDS, and electron energy loss spectroscopy, EELS. The characterization effort was coupled with first-principles, electronic-structure and thermodynamic techniques to predict and assess meta-stable and stable phases, reaction pathways, and thermodynamic and kinetic barriers. Systems studied included:NaAlH4, CaH2/CaB6 and Ca(BH4)2, MgH2/MgB2, Ni-Catalyzed Magnesium Hydride, TiH2-Catalyzed Magnesium Hydride, LiBH4, Aluminum-based systems and Aluminum

  3. Angular Resolved X-Ray Absorption Near Edge Structure Investigation of Adsorbed Alkanethiol Monolayers on III-V(110) Surfaces

    NASA Astrophysics Data System (ADS)

    Chassé, T.; Zerulla, D.; Hallmeier, K. H.

    The structure of alkanethiol monolayers on III-V(110) surfaces was studied by analyzing the X-ray absorption near edge structure (XANES) of the carbon K edge. Pronounced absorption maxima were observed for special orientations of the polarization vector of the radiation as revealed from angular-dependent measurements, suggesting a rather well-defined molecular axis of the alkyl chains. From quantitative evaluations of these angular dependences the chains were found to be tilted from the normal towards the [001] direction of the (110) surfaces by 34° and 15° in the case of hexadecanethiol (HDT) adsorption on InP and GaP, respectively. The similarities as well as the differences in tilt angles between the substrates are dicussed in terms of constraints imposed by the surface structure and lattice constants as well as the space requirements of the van der Waals spheres of the adsorbed thiols. A unique feature observed on these monolayers is the nearly complete alignment of the alkyl chains with respect to the azimuthal orientation. We suggest that this adsorbate system represents the case of a single domain orientation within the organic monolayer.

  4. Structural changes and intermolecular interactions of filled ice Ic structure for hydrogen hydrate under high pressure

    NASA Astrophysics Data System (ADS)

    Machida, S.; Hirai, H.; Kawamura, T.; Yamamoto, Y.; Yagi, T.

    2010-03-01

    High-pressure experiments of hydrogen hydrate were performed using a diamond anvil cell under conditions of 0.1-44.2 GPa and at room temperature. Also, high pressure Raman studies of solid hydrogen were performed in the pressure range of 0.1-43.7 GPa. X-ray diffractometry (XRD) for hydrogen hydrate revealed that a known high-pressure structure, filled ice Ic structure, of hydrogen hydrate transformed to a new high-pressure structure at approximately 35-40 GPa. A comparison of the Raman spectroscopy of a vibron for hydrogen molecules between hydrogen hydrate and solid hydrogen revealed that the extraction of hydrogen molecules from hydrogen hydrate occurred above 20 GPa. Also, the Raman spectra of a roton revealed that the rotation of hydrogen molecules in hydrogen hydrate was suppressed at around 20 GPa and that the rotation recovered under higher pressure. These results indicated that remarkable intermolecular interactions in hydrogen hydrate between neighboring hydrogen molecules and between guest hydrogen molecules and host water molecules might occur. These intermolecular interactions could produce the stability of hydrogen hydrate.

  5. Structure of 4-methylpyridinium Hydrogen Sulfide

    NASA Technical Reports Server (NTRS)

    Andras, Maria T.; Hepp, Aloysius F.; Fanwick, Phillip E.; Martuch, Robert A.; Duraj, Stan A.; Gordon, Edward M.

    1994-01-01

    4-Methylpyridinium hydrogen sulfide, (C6H7NH)HS, M(sub r) = 127.21, consists of C6H7NH(+) cations and HS(-) anions. Z = 2 for the crystal with monoclinic space group Cm (#8), dimensions of a = 8.679(2) A, b = 7.964(1) A, and c = 4.860(2) A, an angle beta of 101.10(2) degrees, and a volume of V = 329.6(3) A(exp 3). R = 0.039 and R(sub w) = 0.048 for 385 reflections with F(sub o)(exp 2) greater than 3 sigma(F(sub o)(exp 2)) and 59 variables. Both the C6H7NH(+) cation and the HS(-) anion lie on crystallographic mirror planes with the N,S, two carbon atoms, and two hydrogen atoms positioned in the planes. The hydrogen atom of the HS(-) anion was not located.

  6. First-principle study of the electronic structure and magnetism of lithium-adsorbed 3d transition-metal phthalocyanines

    NASA Astrophysics Data System (ADS)

    Wang, M.; Hu, Y.; Zhang, Z.; Li, Y.; Zhou, T.; Ren, J.

    2016-02-01

    Based on density functional theory (DFT) calculations, the electronic structures and magnetic properties of 3d transition-metal phthalocyanine (TMPc, TM = Ti, V, Cr, Mn, Fe, Co, Ni and Cu), as well as Li-adsorbed phthalocyanines have been studied. The results show that the pristine TMPcs all have a good D4h symmetry. When there is one Li atom adsorbed on TMPcs directly over (LiTMPc-α) or slantly above (LiTMPc-β) the TM atoms, the geometries and electronic structures will be changed. For LiTMPc-α systems, the central TM atoms will deviate from the molecular plane and the molecules exhibit good C4v symmetry. LiTMPc-β systems are more stable than LiTMPc-α systems but it do not possess D4h and C4v symmetries. The total and local magnetic moments and the charge transfer are also presented. Finally, by using the orbit mixing and splitting theory under D4h and C4v symmetry, we get the ordering of the energy levels of the central TM atoms.

  7. The structure of PMDA-PDA polyimide monolayers adsorbed on gold surfaces

    NASA Astrophysics Data System (ADS)

    Keil, M.; Paggel, J. J.; Schedel-Niedrig, Th.; Yokoyama, S.; Sotobayashi, H.; Bradshaw, A. M.

    1995-11-01

    Monolayers of the rod-like PMDA-PDA polyimide adsorbed on flame-annealed polycrystalline gold films have been studied with scanning tunnelling microscopy (STM) and X-ray absorption spectroscopy. The polyimide layer was deposited using the Langmuir-Blodgett preparation technique of Imai and Kakimoto. STM measurements in air showed that the polyimide chains were aligned along the <211> directions of the {111}-oriented single crystal regions of the surface. Although {111}-oriented areas were barely identifiable in the corresponding UHV experiments, aligned polymer chains were also observed over large areas of the surface. X-ray absorption measurements on the latter samples at the nitrogen K-edge showed a preferential orientation of the aromatic ring planes.

  8. Anomalous fast dynamics of adsorbate overlayers near an incommensurate structural transition.

    PubMed

    Granato, Enzo; Ying, S C; Elder, K R; Ala-Nissila, T

    2013-09-20

    We investigate the dynamics of a compressively strained adsorbed layer on a periodic substrate via a simple two-dimensional model that admits striped and hexagonal incommensurate phases. We show that the mass transport is superfast near the striped-hexagonal phase boundary and in the hexagonal phase. For an initial step profile separating a bare substrate region (or "hole") from the rest of a striped incommensurate phase, the superfast domain wall dynamics leads to a bifurcation of the initial step profile into two interfaces or profiles propagating in opposite directions with a hexagonal phase in between. This yields a theoretical understanding of the recent experiments for the Pb/Si(111) system. PMID:24093278

  9. Nanoporous Gyroid-Structured Epoxy from Block Copolymer Templates for High Protein Adsorbability.

    PubMed

    Wang, Xin-Bo; Lin, Tze-Chung; Hsueh, Han-Yu; Lin, Shih-Chieh; He, Xiao-Dong; Ho, Rong-Ming

    2016-06-28

    Nanoporous epoxy with gyroid texture is fabricated by using a nanoporous polymer with gyroid-forming nanochannels as a template for polymerization of epoxy. The nanoporous polymer template is obtained from the self-assembly of degradable block copolymer, polystyrene-b-poly(l-lactide) (PS-PLLA), followed by hydrolysis of PLLA blocks. Templated polymerization can be conducted under ambient conditions to create well-defined, bicontinuous epoxy networks in a PS matrix. By taking advantage of multistep curing of epoxy, well-ordered robust nanoporous epoxy can be obtained after removal of PS template, giving robust porous materials. The through-hole nanoporous epoxy in the film state can be used as a coated layer to enhance the adsorbability for both lysozyme and bovine serum albumin. PMID:27245380

  10. Exploring the interfacial structure of protein adsorbates and the kinetics of protein adsorption: an in situ high-energy X-ray reflectivity study.

    PubMed

    Evers, Florian; Shokuie, Kaveh; Paulus, Michael; Sternemann, Christian; Czeslik, Claus; Tolan, Metin

    2008-09-16

    The high energy X-ray reflectivity technique has been applied to study the interfacial structure of protein adsorbates and protein adsorption kinetics in situ. For this purpose, the adsorption of lysozyme at the hydrophilic silica-water interface has been chosen as a model system. The structure of adsorbed lysozyme layers was probed for various aqueous solution conditions. The effect of solution pH and lysozyme concentration on the interfacial structure was measured. Monolayer formation was observed for all cases except for the highest concentration. The adsorbed protein layers consist of adsorbed lysozyme molecules with side-on or end-on orientation. By means of time-dependent X-ray reflectivity scans, the time-evolution of adsorbed proteins was monitored as well. The results of this study demonstrate the capabilities of in situ X-ray reflectivity experiments on protein adsorbates. The great advantages of this method are the broad wave vector range available and the high time resolution. PMID:18715021

  11. Influence of molecular structure and adsorbent properties on sorption of organic compounds to a temperature series of wood chars.

    PubMed

    Lattao, Charisma; Cao, Xiaoyan; Mao, Jingdong; Schmidt-Rohr, Klaus; Pignatello, Joseph J

    2014-05-01

    Chars from wildfires and soil amendments (biochars) are strong adsorbents that can impact the fate of organic compounds in soil, yet the effects of solute and adsorbent properties on sorption are poorly understood. We studied sorption of benzene, naphthalene, and 1,4-dinitrobenzene from water to a series of wood chars made anaerobically at different heat treatment temperatures (HTT) from 300 to 700 °C, and to graphite as a nonporous, unfunctionalized reference adsorbent. Peak suppression in the NMR spectrum by sorption of the paramagnetic relaxation probe TEMPO indicated that only a small fraction of char C atoms lie near sorption sites. Sorption intensity for all solutes maximized with the 500 °C char, but failed to trend regularly with N2 or CO2 surface area, micropore volume, mesopore volume, H/C ratio, O/C ratio, aromatic fused ring size, or HTT. A model relating sorption intensity to a weighted sum of microporosity and mesoporosity was more successful. Sorption isotherm linearity declined progressively with carbonization of the char. Application of a thermodynamic model incorporating solvent-water and char-graphite partition coefficients permitted for the first time quantification of steric (size exclusion in pores) and π-π electron donor-acceptor (EDA) free energy contributions, relative to benzene. Steric hindrance for naphthalene increases exponentially from 9 to 16 kJ/mol (∼ 1.6-2.9 log units of sorption coefficient) with the fraction of porosity in small micropores. π-π EDA interactions of dinitrobenzene contribute -17 to -19 kJ/mol (3-3.4 log units of sorption coefficient) to sorption on graphite, but less on chars. π-π EDA interaction of naphthalene on graphite is small (-2 to 2 kJ/mol). The results show that sorption is a complex function of char properties and solute molecular structure, and not very predictable on the basis of readily determined char properties. PMID:24758543

  12. The structures and dynamics of atomic and molecular adsorbates on metal surfaces by scanning tunneling microscopy and low energy electron diffraction

    SciTech Connect

    Yoon, Hyungsuk Alexander

    1996-12-01

    Studies of surface structure and dynamics of atoms and molecules on metal surfaces are presented. My research has focused on understanding the nature of adsorbate-adsorbate and adsorbate-substrate interactions through surface studies of coverage dependency and coadsorption using both scanning tunneling microscopy (STM) and low energy electron diffraction (LEED). The effect of adsorbate coverage on the surface structures of sulfur on Pt(111) and Rh(111) was examined. On Pt(111), sulfur forms p(2x2) at 0.25 ML of sulfur, which transforms into a more compressed ({radical}3x{radical}3)R30{degrees} at 0.33 ML. On both structures, it was found that sulfur adsorbs only in fcc sites. When the coverage of sulfur exceeds 0.33 ML, it formed more complex c({radical}3x7)rect structure with 3 sulfur atoms per unit cell. In this structure, two different adsorption sites for sulfur atoms were observed - two on fcc sites and one on hcp site within the unit cell.

  13. Benzene derivatives adsorbed to the Ag(111) surface: Binding sites and electronic structure

    SciTech Connect

    Miller, Daniel P.; Tymińska, Nina; Zurek, Eva; Simpson, Scott

    2015-03-14

    Dispersion corrected Density Functional Theory calculations were employed to study the adsorption of benzenes derivatized with functional groups encompassing a large region of the activated/deactivated spectrum to the Ag(111) surface. Benzenes substituted with weak activating or deactivating groups, such as methyl and fluoro, do not have a strong preference for adsorbing to a particular site on the substrate, with the corrugations in the potential energy surface being similar to those of benzene. Strong activating (N(CH{sub 3}){sub 2}) and deactivating (NO{sub 2}) groups, on the other hand, possess a distinct site preference. The nitrogen in the former prefers to lie above a silver atom (top site), but in the latter a hollow hexagonal-closed-packed (H{sub hcp}) site of the Ag(111) surface is favored instead. Benzenes derivatized with classic activating groups donate electron density from their highest occupied molecular orbital to the surface, and those functionalized with deactivating groups withdraw electron density from the surface into orbitals that are unoccupied in the gas phase. For benzenes functionalized with two substituents, the groups that are strongly activating or deactivating control the site preference and the other groups assume sites that are, to a large degree, dictated by their positions on the benzene ring. The relative stabilities of the ortho, meta, and para positional isomers of disubstituted benzenes can, in some cases, be modified by adsorption to the surface.

  14. Ground-State Structures of Atomic Metallic Hydrogen

    NASA Astrophysics Data System (ADS)

    McMahon, Jeffrey M.; Ceperley, David M.

    2011-04-01

    Ab initio random structure searching using density functional theory is used to determine the ground-state structures of atomic metallic hydrogen from 500 GPa to 5 TPa. Including proton zero-point motion within the harmonic approximation, we estimate that molecular hydrogen dissociates into a monatomic body-centered tetragonal structure near 500 GPa (rs=1.23) that remains stable to 1 TPa (rs=1.11). At higher pressures, hydrogen stabilizes in an …ABCABC… planar structure that is similar to the ground state of lithium, but with a different stacking sequence. With increasing pressure, this structure compresses to the face-centered cubic lattice near 3.5 TPa (rs=0.92).

  15. Structural sensitivity studies of ethylene hydrogenation on platinum and rhodium surfaces

    SciTech Connect

    Quinlan, M.A. |

    1996-01-01

    The catalytic hydrogenation of ethylene and hydrogen on the well characterized surfaces of the noble metals platinum and rhodium has been studied for the purposes of determining the relative activity of these two substrates as well as the degree of structure sensitivity. The Pt(111) and the Rh(755) single crystal surfaces,as well as Pt and Rh foils, were employed as substrates to study the effect of surface step structure on reactivity. In addition, vibrational spectroscopy studies were performed for ethylene adsorption on the stepped Rh(755) surface. The catalytic reaction were obtained using a combined ultrahigh vacuum chamber coupled with an atmospheric pressure reaction chamber that functioned as a batch reactor. Samples could be prepared using standard surface science techniques and characterized for surface composition and geometry using Auger Electron Spectroscopy and Low Energy Electron Diffraction. A comparison of the reactivity of Rh(111) with the results from this study on Rh(755) allows a direct determination of the effect of step structure on ethylene hydrogenation activity. Structure sensitivity is expected to exhibit orders of magnitude differences in rate as surface orientation is varied. In this case, no significant differences were found, confirming the structure insensitivity of this reaction over this metal. The turnover frequency of the Rh(111) surface, 5 {times} 10{sup 1} s{sup {minus}1}, is in relatively good agreement with the turnover frequency of 9 {times} 10{sup 1} s{sup {minus}1} measured for the Rh(755) surface. Rate measurements made on the Pt(111) surface and the Pt foil are in excellent agreement, both measuring 3 {times} 10{sup 2} s{sup minus}1. Likewise, it is concluded that no strong structure sensitivity for the platinum surfaces exists. High Resolution Electron Energy Loss Spectroscopy studies of adsorbed ethylene on the Rh(755) surface compare favorably with the ethylidyne spectra obtained on the Rh(111) and Rh(100) surfaces.

  16. Development of hydrogen resistant structural alloy NASA-23

    NASA Technical Reports Server (NTRS)

    Bhat, B. N.; Mcpherson, W. B.; Kuruvilla, A. K.; Chen, P. S.; Panda, B.

    1993-01-01

    Hydrogen-resistant alloy NASA-23 was developed specifically as a structural alloy for application in liquid propulsion systems that use hydrogen fuel. NASA-23 was designed to be similar to Alloy 718 in strength, ductility, and corrosion resistance, but with superior resistance to hydrogen environment embrittlement. The alloy is readily processed; it can be both hot and cold worked and is castable and weldable. A material property data base is being generated for both cast and wrought NASA-23. This paper will present the status of alloy development and discuss potential applications in propulsion systems.

  17. Adsorption isotherms and structure of cationic surfactants adsorbed on mineral oxide surfaces prepared by atomic layer deposition.

    PubMed

    Wangchareansak, Thipvaree; Craig, Vincent S J; Notley, Shannon M

    2013-12-01

    The adsorption isotherms and aggregate structures of adsorbed surfactants on smooth thin-film surfaces of mineral oxides have been studied by optical reflectometry and atomic force microscopy (AFM). Films of the mineral oxides of titania, alumina, hafnia, and zirconia were produced by atomic layer deposition (ALD) with low roughness. We find that the surface strongly influences the admicelle organization on the surface. At high concentrations (2 × cmc) of cetyltrimethylammonium bromide (CTAB), the surfactant aggregates on a titania surface exhibit a flattened admicelle structure with an average repeat distance of 8.0 ± 1.0 nm whereas aggregates on alumina substrates exhibit a larger admicelle with an average separation distance of 10.5 ± 1.0 nm. A wormlike admicelle structure with an average separation distance of 7.0 ± 1.0 nm can be observed on zirconia substrates whereas a bilayered aggregate structure on hafnia substrates was observed. The change in the surface aggregate structure can be related to an increase in the critical packing parameter through a reduction in the effective headgroup area of the surfactant. The templating strength of the surfaces are found to be hafnia > alumina > zirconia > titania. Weakly templating surfaces are expected to have superior biocompatibility. PMID:24224944

  18. Structural and orientation effects on electronic energy transfer between silicon quantum dots with dopants and with silver adsorbates

    SciTech Connect

    Vinson, N.; Freitag, H.; Micha, D. A.

    2014-06-28

    Starting from the atomic structure of silicon quantum dots (QDs), and utilizing ab initio electronic structure calculations within the Förster resonance energy transfer (FRET) treatment, a model has been developed to characterize electronic excitation energy transfer between QDs. Electronic energy transfer rates, K{sub EET}, between selected identical pairs of crystalline silicon quantum dots systems, either bare, doped with Al or P, or adsorbed with Ag and Ag{sub 3}, have been calculated and analyzed to extend previous work on light absorption by QDs. The effects of their size and relative orientation on energy transfer rates for each system have also been considered. Using time-dependent density functional theory and the hybrid functional HSE06, the FRET treatment was employed to model electronic energy transfer rates within the dipole-dipole interaction approximation. Calculations with adsorbed Ag show that: (a) addition of Ag increases rates up to 100 times, (b) addition of Ag{sub 3} increases rates up to 1000 times, (c) collinear alignment of permanent dipoles increases transfer rates by an order of magnitude compared to parallel orientation, and (d) smaller QD-size increases transfer due to greater electronic orbitals overlap. Calculations with dopants show that: (a) p-type and n-type dopants enhance energy transfer up to two orders of magnitude, (b) surface-doping with P and center-doping with Al show the greatest rates, and (c) K{sub EET} is largest for collinear permanent dipoles when the dopant is on the outer surface and for parallel permanent dipoles when the dopant is inside the QD.

  19. Study of hydrogenated silicene: The initialization model of hydrogenation on planar, low buckled and high buckled structures of silicene

    SciTech Connect

    Syaputra, Marhamni Wella, Sasfan Arman; Wungu, Triati Dewi Kencana; Purqon, Acep; Suprijadi

    2015-09-30

    We study the hydrogenation structures possessed by silicene i.e. planar (PL), low buckled (LB) and high buckled (HB). On those structures we found the hydrogenation process occurs with some particular notes. Hydrogen stable position on the silicene surface is determined by its initial configuration. We only considered the fully hydrogenated case with the formula unit (SiH){sub n} for all of these structures. Physical and electronic structure shift after the process are compared with hydrogenated graphene. Moreover, we observed a chemical process in the presence of hydrogen on the PL structure by nudged elastic band (NEB) which illustrates how hydrogen has a significant impact to the force barrier of the PL that changing it from its original structure.

  20. Conformational changes of α-lactalbumin adsorbed at oil-water interfaces: interplay between protein structure and emulsion stability.

    PubMed

    Zhai, Jiali; Hoffmann, Søren V; Day, Li; Lee, Tzong-Hsien; Augustin, Mary Ann; Aguilar, Marie-Isabel; Wooster, Tim J

    2012-02-01

    The conformation and structural dimensions of α-lactalbumin (α-La) both in solution and adsorbed at oil-water interfaces of emulsions were investigated using synchrotron radiation circular dichroism (SRCD) spectroscopy, front-face tryptophan fluorescence (FFTF) spectroscopy, and dual polarization interferometry (DPI). The near-UV SRCD and the FFTF results demonstrated that the hydrophobic environment of the aromatic residues located in the hydrophobic core of native α-La was significantly altered upon adsorption, indicating the unfolding of the hydrophobic core of α-La upon adsorption. The far-UV SRCD results showed that adsorption of α-La at oil-water interfaces created a new non-native secondary structure that was more stable to thermally induced conformational changes. Specifically, the α-helical conformation increased from 29.9% in solution to 45.8% at the tricaprylin-water interface and to 58.5% at the hexadecane-water interface. However, the β-sheet structure decreased from 18.0% in solution to less than 10% at both oil-water interfaces. The DPI study showed that adsorption of α-La to a hydrophobic C18-water surface caused a change in the dimensions of α-La from the native globule-like shape (2.5-3.7 nm) to a compact/dense layer approximately 1.1 nm thick. Analysis of the colloidal stability of α-La stabilized emulsions showed that these emulsions were physically stable against droplet flocculation at elevated temperatures both in the absence and in the presence of 120 mM NaCl. In the absence of salt, the thermal stability of emulsions was due to the strong electrostatic repulsion provided by the adsorbed α-La layer, which was formed after the adsorption and structural rearrangement. In the presence of salt, although the electrostatic repulsion was reduced via electrostatic screening, heating did not induce strong and permanent droplet flocculation. The thermal stability of α-La stabilized emulsions in the presence of salt is a combined effect of

  1. Zero-Temperature Structures of Atomic Metallic Hydrogen

    NASA Astrophysics Data System (ADS)

    McMahon, Jeffrey; Ceperley, David

    2011-03-01

    Since the first prediction of an atomic metallic phase of hydrogen by Wigner and Huntington over 75 years ago, there have been many theoretical efforts aimed at determining the crystal structures of the zero-temperature phases. We present results from ab initio random structure searching with density functional theory performed to determine the ground state structures from 500 GPa to 5 TPa. We estimate that molecular hydrogen dissociates into a monatomic body-centered tetragonal structure near 500 GPa (rs = 1.225), which then remains stable to 2.5 TPa (rs = 0.969). At higher pressures, hydrogen stabilizes in an . . . ABCABC . . . planar structure that is remarkably similar to the ground state of lithium, which compresses to the face-centered cubic lattice beyond 5 TPa (rs < 0.86). Our results provide a complete ab initio description of the atomic metallic crystal structures of hydrogen, resolving one of the most fundamental and long outstanding issues concerning the structures of the elements.

  2. Carbon-Oxygen Hydrogen Bonding in Biological Structure and Function

    PubMed Central

    Horowitz, Scott; Trievel, Raymond C.

    2012-01-01

    Carbon-oxygen (CH···O) hydrogen bonding represents an unusual category of molecular interactions first documented in biological structures over 4 decades ago. Although CH···O hydrogen bonding has remained generally underappreciated in the biochemical literature, studies over the last 15 years have begun to yield direct evidence of these interactions in biological systems. In this minireview, we provide a historical context of biological CH···O hydrogen bonding and summarize some major advancements from experimental studies over the past several years that have elucidated the importance, prevalence, and functions of these interactions. In particular, we examine the impact of CH···O bonds on protein and nucleic acid structure, molecular recognition, and enzyme catalysis and conclude by exploring overarching themes and unresolved questions regarding unconventional interactions in biomolecular structure. PMID:23048026

  3. Effect of the internal motions of an adsorbate on the characteristics of adsorption for structurally heterogenous surfaces of slit-like pores

    NASA Astrophysics Data System (ADS)

    Tovbin, Yu. K.; Zaitseva, E. S.; Rabinovich, A. B.

    2016-01-01

    The effect of internal motions of an adsorbate on the local characteristics of adsorption and layering phase diagrams are studied for structurally heterogeneous surfaces of slit-like pores. A molecular model describing adsorbate distributions inside slit-like pores, which is based on discrete distribution functions (lattice gas model), is used for the calculation. Molecular distributions are calculated by the Lennard-Jones potential (12-6) in a quasi-chemical approximation reflecting the effects of direct correlations of interacting particles and for the combined interaction of an adsorbate with walls in the average potential approximation (9-3) and the short-range Lennard-Jones potential for structurally heterogeneous surface areas. The conclusion is made that internal motions reflect the vibrational motion of molecules within a modified quasi-dimer model and a displacement of the adsorbate during its translational motion inside cells. It was found that the taking into account of internal motions decreases the critical temperature of adsorbate layering in slit-like pores.

  4. Auroral zone effects on hydrogen geocorona structure and variability

    NASA Technical Reports Server (NTRS)

    Moore, T. E.; Biddle, A. P.; Waite, J. H., Jr.; Killeen, T. L.

    1985-01-01

    The effect of diurnal and magnetospheric modulations on the structure of the hydrogen geocorona is analyzed on the basis of recent observations. Particular attention is given to the enhancement of neutral escape by plasma effects, including the recently observed phenomenon of low-altitude ion acceleration. It is found that, while significant fluxes of neutral H should be produced by transverse ion acceleration in the auroral zone, the process is probably insufficient to account for the observed polar depletion of hydrogen atoms. Analysis of recent exospheric temperature measurements from the Dynamics Explorer-2 satellite suggest that neutral heating in and near the high latitude cusp may be the major contributor to depleted atomic hydrogen densities at high latitudes. Altitude profiles of the production rates for escaping neutral hydrogen atoms during periods of maximum, minimum, and typical solar activity are provided.

  5. Structure and friction of stearic acid and oleic acid films adsorbed on iron oxide surfaces in squalane.

    PubMed

    Doig, Michael; Warrens, Chris P; Camp, Philip J

    2014-01-14

    The structure and friction of fatty acid surfactant films adsorbed on iron oxide surfaces lubricated by squalane are examined using large-scale molecular dynamics simulations. The structures of stearic acid and oleic acid films under static and shear conditions, and at various surface coverages, are described in detail, and the effects of unsaturation in the tail group are highlighted. At high surface coverage, the measured properties of stearic acid and oleic acid films are seen to be very similar. At low and intermediate surface coverages, the presence of a double bond, as in oleic acid, is seen to give rise to less penetration of lubricant in to the surfactant film and less layering of the lubricant near to the film. The kinetic friction coefficient is measured as a function of shear rate within the hydrodynamic (high shear rate) lubrication regime. Lubricant penetration and layering are observed to be correlated with friction coefficient. The friction coefficient with oleic acid depends only weakly on surface coverage, while stearic acid admits more lubricant penetration, and its friction coefficient increases significantly with decreasing surface coverage. Connections between film structure and friction are discussed. PMID:24364665

  6. Advanced fabrication techniques for hydrogen-cooled engine structures

    NASA Technical Reports Server (NTRS)

    Buchmann, O. A.; Arefian, V. V.; Warren, H. A.; Vuigner, A. A.; Pohlman, M. J.

    1985-01-01

    Described is a program for development of coolant passage geometries, material systems, and joining processes that will produce long-life hydrogen-cooled structures for scramjet applications. Tests were performed to establish basic material properties, and samples constructed and evaluated to substantiate fabrication processes and inspection techniques. Results of the study show that the basic goal of increasing the life of hydrogen-cooled structures two orders of magnitude relative to that of the Hypersonic Research Engine can be reached with available means. Estimated life is 19000 cycles for the channels and 16000 cycles for pin-fin coolant passage configurations using Nickel 201. Additional research is required to establish the fatigue characteristics of dissimilar-metal coolant passages (Nickel 201/Inconel 718) and to investigate the embrittling effects of the hydrogen coolant.

  7. Rapid visualization of hydrogen positions in neutron protein crystallography structures

    SciTech Connect

    Blakeley, Matthew P.; Meilleur, Flora; Myles, Dean A A; Weiss, Kevin L; Munshi, Parthapratim; Shang-Lin, Chung

    2012-01-01

    Neutron crystallography is a powerful technique to visualize experimentally the position of light atoms, including hydrogen and its isotope deuterium. Over the last several years, structural biologists have shown an increasing interest for the technique as it uniquely complements X-ray crystallographic data by revealing the position of hydrogen/deuterium atoms in macromolecules. With this regained interest, access to macromolecule neutron crystallography beam lines is becoming a limiting step. In this report we show that rapid data collection could be a valuable alternative to long data collection time when appropriate. Comparison of perdeuterated Rubredoxin structures refined against neutron data sets collected over hours and up to five days shows that rapid neutron data collection in just 14 hours is sufficient to provide the position of 262 hydrogen positions atoms without ambiguity.

  8. The stability and electronic structure of lithium adsorbed in triplet form of (5.0) carbon nanotubes and (5.0) boron nitrogen nanotubes: Density functional theory studies

    NASA Astrophysics Data System (ADS)

    Li, Ke Jing; Shao, Qing Yi; Zhang, Juan; Yao, Xin Hua

    2016-07-01

    Using density functional theory (DFT), we have investigated the stability and electronic structure of lithium (Li) adsorbed in triplet form of (5.0) carbon nanotubes (CNTs) and (5.0) boron nitrogen nanotubes (BNNTs). We have mainly found that three (5.0) tubes are covalently connected. The triplet form is an energetically stable semiconductor. Li atom can be chemically adsorbed in the triplet form of nanotubes (NTs). Meanwhile, upon the adsorption of Li, the triplet form convert into metal. Hence, the triplet form can improve reactivity and sensitivity of NTs to Li significantly.

  9. First-Principles Electronic Structure Calculations of N2H4 Adsorbed on Single-Wall Carbon Nanotubes

    NASA Astrophysics Data System (ADS)

    Yu, M.; Tian, W. Q.; Jayanthi, C. S.; Wu, S. Y.

    2008-03-01

    Recent experiments conducted by Desai et al. [1] reveal that single-wall carbon nanotube (SWCNT) networks exposed to N2H4 vapor at various pressures exhibit considerable drop in resistance with respect to the pristine sample. Experimental findings reveal: (i) n-type behavior for the adsorption of N2H4/SWCNT, and (ii) the binding of N2H4 on SWCNT as chemisorption. In the present work, we have performed first-principles electronic structure calculations [2] for the N2H4 adsorbed on the (14, 0) SWCNT, where several orientations for the N2H4 molecule were considered. Calculations for the combined system were performed using 3 unit cells with the DFT/GGA and ultra soft pseudo-potentials. Our calculations reveal: (i) the binding of N2H4 on SWCNT as physisorption, and (ii) the electronic structure of SWCNT to be practically unaltered by the adsorption of N2H4, suggesting that there will not be a dramatic drop in resistance for N2H4/SWCNT. This is in disagreement with the experimental findings. To further understand the experimental observations, we will discuss mechanisms that may alter the binding nature of N2H4 on SWCNT. [1] S. Desai, G. Sumanasekera, et al. (APS, March 2008). [2] G. Kresse and J. Furthmuller, Phys. Rev. B 54, 11169 (1996).

  10. Band structure and charge doping effects of the potassium-adsorbed FeSe /SrTiO3 system

    NASA Astrophysics Data System (ADS)

    Zheng, Fawei; Wang, Li-Li; Xue, Qi-Kun; Zhang, Ping

    2016-02-01

    We theoretically study, through combining the density functional theory and an unfolding technique, the electronic band structure and the charge doping effects for the deposition of potassium on multilayer FeSe films grown on SrTiO3 (001) surface. These results form a theoretical baseline for further detailed studies of low-temperature electronic properties and their multiway quantum engineering of FeSe thin films. We explain the Fermi-surface topology observed in experiment and formulate the amount of doped electrons as a function of atomic K coverage. We show that the atomic K deposition efficiently dopes electrons to the top layer of FeSe. Both checkerboard- and pair-checkerboard-antiferromagnetic (AFM) FeSe layers show electron pockets at the M point and no Fermi pocket at the Γ point with moderate atomic K coverage. The electron transfer from the K adsorbate to the FeSe film introduces a strong electric field, which leads to a double-Weyl-cone structure at the M point in the Brillouin zone of checkerboard-AFM FeSe. We demonstrate that with experimentally accessible heavy-electron doping, an electronlike Fermi pocket will emerge at the Γ point, which should manifest itself in modulating the high-temperature superconductivity of FeSe thin films.

  11. High-resolution electron-energy-loss spectroscopy and photoelectron-diffraction studies of the geometric structure of adsorbates on single-crystal metal surfaces

    SciTech Connect

    Rosenblatt, D.H.

    1982-11-01

    Two techniques which have made important contributions to the understanding of surface phenomena are high resolution electron energy loss spectroscopy (EELS) and photoelectron diffraction (PD). EELS is capable of directly measuring the vibrational modes of clean and adsorbate covered metal surfaces. In this work, the design, construction, and performance of a new EELS spectrometer are described. These results are discussed in terms of possible structures of the O-Cu(001) system. Recommendations for improvements in this EELS spectrometer and guidelines for future spectrometers are given. PD experiments provide accurate quantitative information about the geometry of atoms and molecules adsorbed on metal surfaces. The technique has advantages when used to study disordered overlayers, molecular overlayers, multiple site systems, and adsorbates which are weak electron scatterers. Four experiments were carried out which exploit these advantages.

  12. Path integral Monte Carlo simulations of H{sub 2} adsorbed to lithium-doped benzene: A model for hydrogen storage materials

    SciTech Connect

    Lindoy, Lachlan P.; Kolmann, Stephen J.; D’Arcy, Jordan H.; Jordan, Meredith J. T.; Crittenden, Deborah L.

    2015-11-21

    Finite temperature quantum and anharmonic effects are studied in H{sub 2}–Li{sup +}-benzene, a model hydrogen storage material, using path integral Monte Carlo (PIMC) simulations on an interpolated potential energy surface refined over the eight intermolecular degrees of freedom based upon M05-2X/6-311+G(2df,p) density functional theory calculations. Rigid-body PIMC simulations are performed at temperatures ranging from 77 K to 150 K, producing both quantum and classical probability density histograms describing the adsorbed H{sub 2}. Quantum effects broaden the histograms with respect to their classical analogues and increase the expectation values of the radial and angular polar coordinates describing the location of the center-of-mass of the H{sub 2} molecule. The rigid-body PIMC simulations also provide estimates of the change in internal energy, ΔU{sub ads}, and enthalpy, ΔH{sub ads}, for H{sub 2} adsorption onto Li{sup +}-benzene, as a function of temperature. These estimates indicate that quantum effects are important even at room temperature and classical results should be interpreted with caution. Our results also show that anharmonicity is more important in the calculation of U and H than coupling—coupling between the intermolecular degrees of freedom becomes less important as temperature increases whereas anharmonicity becomes more important. The most anharmonic motions in H{sub 2}–Li{sup +}-benzene are the “helicopter” and “ferris wheel” H{sub 2} rotations. Treating these motions as one-dimensional free and hindered rotors, respectively, provides simple corrections to standard harmonic oscillator, rigid rotor thermochemical expressions for internal energy and enthalpy that encapsulate the majority of the anharmonicity. At 150 K, our best rigid-body PIMC estimates for ΔU{sub ads} and ΔH{sub ads} are −13.3 ± 0.1 and −14.5 ± 0.1 kJ mol{sup −1}, respectively.

  13. Thermal and structural tests of a hydrogen cooled panel

    NASA Technical Reports Server (NTRS)

    Richard, C. E.; Duncan, J. D.; Gellersen, E. W.; Demogenes, C.

    1972-01-01

    An experimental evaluation of the thermal and structural performance of a hydrogen-cooled panel is presented. The panel, which was of brazed Inconel 625 and Inconel 718 construction, was designed for a heat flux of 100 BTU per second-foot squared and an external surface pressure of 100 psi.

  14. The diammoniate of diborane: Crystal structure and hydrogen release

    SciTech Connect

    Bowden, Mark E.; Heldebrant, David J.; Karkamkar, Abhijeet J.; Proffen, Thomas E.; Schenter, Gregory K.; Autrey, Thomas

    2010-10-12

    [(NH3)2BH2]+[BH4]- is formed from the room temperature decomposition of NH4+BH4-, via a NH3BH3 intermediate. Its crystal structure has been determined and contains disordered BH4- ions in 2 distinct sites. Hydrogen release is similar to that from NH3BH3 but with faster kinetics.

  15. Thick-Film Carbon Dioxide Sensor via Anodic Adsorbate Stripping Technique and Its Structural Dependence

    PubMed Central

    Photinon, Kanokorn; Wang, Shih-Han; Liu, Chung-Chiun

    2009-01-01

    A three-electrode based CO2 sensor was fabricated using thick-film technology. The performance of this sensor was further enhanced by incorporating platinum nanoparticles onto the working electrode surface. An eight-fold increase in the signal output was obtained from the electrode with the platinum nanoparticles. The sensing output was linearly related to the CO2 presented. Stability measurements demonstrated that the decline of the active surface area and the sensitivity of the sensor were 8% and 13%, respectively, over a two week period of time. The sensor response appeared to be a structural dependence of the crystallographic orientation of platinum electrode. PMID:22399993

  16. Electronic structure of uracil-like nucleobases adsorbed on Si(001): uracil, thymine and 5-fluorouracil

    NASA Astrophysics Data System (ADS)

    Molteni, Elena; Onida, Giovanni; Cappellini, Giancarlo

    2016-04-01

    We study the electronic properties of the Si(001):Uracil, Si(001):Thymine, and Si(001):5-Fluorouracil systems, focusing on the Si dimer-bridging configuration with adsorption governed by carbonyl groups. While the overall structural and electronic properties are similar, with small differences due to chemical substitutions, much larger effects on the surface band dispersion and bandgap show up as a function of the molecular orientation with respect to the surface. An off-normal orientation of the molecular planes is favored, showing larger bandgap and lower total energy than the upright position. We also analyze the localization of gap-edge occupied and unoccupied surface states. Supplementary material in the form of one pdf file available from the Journal web page at http://dx.doi.org/10.1140/epjb/e2016-70011-1

  17. Underpotential deposition of Cu on Pt(001): Interface structure and the influence of adsorbed bromide

    NASA Astrophysics Data System (ADS)

    Lucas, C. A.; Markovic, N. M.; Ross, P. N.

    1998-05-01

    Using in situ x-ray diffraction, we studied the underpotential deposition (UPD) of copper onto a Pt(001) electrode both in pure perchloric acid and in the presence of bromide anions. In pure perchloric acid, the Cu is deposited in pseudomorphic p(1×1) islands. In the presence of bromide anions, the strong Pt-Br interaction significantly broadens the potential range of Cu UPD. We propose that Br remains in the interface region throughout the UPD process, at first in a disordered Cu-Br phase and then, at more negative potential, forming a c(2×2) closed-packed monolayer on top of the completed p(1×1) Cu monolayer. The structures are compared to those found during Cu UPD onto Pt(111), and explained in terms of the metal-halide interactions and the Pt surface atomic geometry.

  18. Electronic Structures of Clusters of Hydrogen Vacancies on Graphene

    PubMed Central

    Wu, Bi-Ru; Yang, Chih-Kai

    2015-01-01

    Hydrogen vacancies in graphane are products of incomplete hydrogenation of graphene. The missing H atoms can alter the electronic structure of graphane and therefore tune the electronic, magnetic, and optical properties of the composite. We systematically studied a variety of well-separated clusters of hydrogen vacancies in graphane, including the geometrical shapes of triangles, parallelograms, hexagons, and rectangles, by first-principles density functional calculation. The results indicate that energy levels caused by the missing H are generated in the broad band gap of pure graphane. All triangular clusters of H vacancies are magnetic, the larger the triangle the higher the magnetic moment. The defect levels introduced by the missing H in triangular and parallelogram clusters are spin-polarized and can find application in optical transition. Parallelograms and open-ended rectangles are antiferromagnetic and can be used for nanoscale registration of digital information. PMID:26468677

  19. Density functional studies of small Au clusters adsorbed on α-FeOOH: Structural and electronic properties

    NASA Astrophysics Data System (ADS)

    Fortunato, Leandro F.; Zubieta, Carolina E.; Fuente, Silvia A.; Belelli, Patricia G.; Ferullo, Ricardo M.

    2016-11-01

    We report a density functional theory (DFT) investigation on the interaction of tiny Aun (n = 1-5) clusters with the bare and hydroxylated (110) surfaces of goethite (α-FeOOH). Both adsorption and atom-by-atom nucleation processes were modeled. The adsorption is shown to be strong on the bare surface and takes place preferentially through the interaction of Au atoms with unsaturated surface oxygen anions, accompanied with an electronic charge transfer from the metal to the support. Au3, Au4 and Au5 planar structures resulted to be particularly stable due to polarization effects; indeed, Coulombic repulsion between basal Au atoms and surface oxygen anions promotes the displacement of the electronic density toward terminal Au atoms producing a Au+δ(basal)/Au-δ(terminal) polarization. On the hydroxylated surface, Au clusters adsorb more weakly with respect to the bare surface, mainly through monocoordinated surface hydroxyl groups and tricoordinated oxygen ions. Concerning the nucleation mechanism, while on the hydroxylated surface the nucleation energy is governed by the spin of the interacting systems, on the bare surface polarization effects seems to play a predominant role.

  20. Predicted novel hydrogen hydrate structures under pressure from first principles

    NASA Astrophysics Data System (ADS)

    Qian, Guangrui; Lyakhov, Andriy; Zhu, Qiang; Oganov, Artem; Dong, Xiao

    2014-03-01

    Gas hydrates are systems of prime importance. In particular, hydrogen hydrates are potential materials of icy satellites and comets, and may be used for hydrogen storage. We explore the H2O-H2 system at pressures in the range 0 ~ 100 GPa with ab initio variable-composition evolutionary simulations. According to our calculation and previous experiments, the H2O-H2 system undergoes a series of transformations with pressure, and adopts the known open-network clathrate structures (sII, C0), dense ``filled ice'' structures (C1, C2) and two novel hydrogen hydrate phases. One of these structures is based on the hexagonal ice framework and has the same H2O:H2 ratio (2:1) as the C0 phase at low pressures and similar enthalpy (we name this phase Ih-C0). The other newly predicted hydrate phase has a 1:2 H2O:H2 ratio and structure based on cubic ice. This phase (which we name C3) is predicted to be thermodynamically stable above 38 GPa when including van der Waals interactions and zero-point vibrational energy. This is the hydrogen-richest hydrate and this phase has the highest gravimetric densities (18 wt.%) of extractable hydrogen among all known materials. We thank the DARPA (Grants No. W31P4Q1310005 and No. W31P4Q1210008), National Science Founda- tion (EAR-1114313, DMR-1231586), AFOSR (FA9550- 13-C-0037), DOE (DE-AC02-98CH10886), CRDF Global (UKE2-7034-KV-11) for financial support. We thank Purdue University Teragrid for providing computational resources and technical support for this work (Charge No.: TG-DMR110058).

  1. Influence of ionic strength changes on the structure of pre-adsorbed salivary films. A response of a natural multi-component layer.

    PubMed

    Macakova, Lubica; Yakubov, Gleb E; Plunkett, Mark A; Stokes, Jason R

    2010-05-01

    Salivary films coating oral surfaces are critically important for oral health. This study focuses on determining the underlying nature of this adsorbed film and how it responds to departures from physiological conditions due to changes in ionic strength. Under physiological conditions, it is found that pre-adsorbed in vitro salivary film on hydrophobic surfaces is present as a highly hydrated viscoelastic layer. We follow the evolution of this film in terms of its effective thickness, hydration and viscoelastic properties, as well as adsorbed mass of proteins, using complementary surface characterisation methods: a Surface Plasmon Resonance (SPR) and a Quartz Crystal Microbalance with Dissipation Monitoring (QCM-D). Our results support a heterogeneous model for the structure of the salivary film with an inner dense anchoring layer and an outer highly extended hydrated layer. Further swelling of the film was observed upon decreasing the salt concentration down to 1mM NaCl. However, upon exposure to deionised water, a collapse of the film occurs that was associated with the loss of water contained within the adsorbed layer. We suggest that the collapse in deionised water is driven by an onset of electrostatic attraction between different parts of the multi-component salivary film. It is anticipated that such changes could also occur when the oral cavity is exposed to food, beverage, oral care and pharmaceutical formulations where drastic changes to the structural integrity of the film is likely to have implications on oral health, sensory perception and product performance. PMID:20133111

  2. Structural changes of filled ice Ic structure for hydrogen hydrate under high pressure.

    PubMed

    Machida, Shin-ichi; Hirai, Hisako; Kawamura, Taro; Yamamoto, Yoshitaka; Yagi, Takehiko

    2008-12-14

    High-pressure experiments of hydrogen hydrate, filled ice Ic structure, were performed using a diamond-anvil cell in the pressure range of 0.1-80.3 GPa at room temperature. In situ x-ray diffractometry (XRD) revealed that structural changes took place at approximately 35-40 and 55-60 GPa, and that the high-pressure phase of hydrogen hydrate survived up to at least 80.3 GPa. Raman spectroscopy showed that the changes in vibrational mode for the hydrogen molecules in hydrogen hydrate occurred at around 40 and 60 GPa, and these results were consistent with those of the XRD. At about 40 GPa, the intermolecular distance of host water molecules consisting the framework attained the critical distance of symmetrization of the hydrogen bond for water molecules, which suggested that symmetrization of the hydrogen bond occurred at around 40 GPa. The symmetrization might introduce some structural change in the filled ice Ic structure. In addition, the existence of the high-pressure phase above 55-60 GPa implies that a denser structure than that of filled ice Ic may exist in hydrogen hydrate. PMID:19071926

  3. Hydrogenated graphene and hydrogenated silicene: computational insights.

    PubMed

    Nguyen, Manh-Thuong; Phong, Pham Nam; Tuyen, Nguyen Duc

    2015-06-01

    Density functional calculations are performed to study the energetic, structural, and electronic properties of graphene and silicene functionalized with hydrogen. Our calculations predict that H atoms bind much more strongly to silicene than to graphene. The adsorbed H atoms tend to cooperatively stabilize each other leading to a two-dimensional nucleation and growth mechanism. The different structural and electronic modifications induced by H in fully functionalized graphene and silicene (known as graphane and silicane) are also explained. Finally, the electronic properties of defective graphane with multiple hydrogen vacancies are investigated. Engineering the vacancies in graphane offers a way to modify the electronic properties of this material. PMID:25820304

  4. Influence of Subsurface Hydrogen on the Structural Properties of Graphene Templates Grown on Ru(0001)

    NASA Astrophysics Data System (ADS)

    Grady, Maxwell; Diaconescu, Bogdan; Valovcin, Darren; Hagelberg, Frank; Pohl, Karsten

    2014-03-01

    Graphene has aroused tremendous interest due to its remarkable electronic and mechanical properties. Graphene's optical properties and conductance make it an ideal candidate for use in nanoelectronic devices and organic photoelectric devices. We will present a STM/LEED/DFT study of the single layer graphene on Ru(0001) system grown via a novel growth mechanism that co-adsorbs atomic hydrogen and carbon vapor to the ruthenium surface while simultaneously segregating carbon from the crystal bulk to the surface. Structural studies show a wide array of moire superlattices sizes ranging from 0.9 to 3.0 nm. DFT calculations help explain the appearance of these graphene reconstructions driven by the H presence at the Ru interface. A LEED I(V) study guided by DFT calculations will accompany the STM investigation to provide insight into the graphene layer thickness. The structural polymorphism displayed by this system is of interest for the study of directed self-assembly. Control over moire superstructure size can aid in future work using graphene as a nanotemplate for self-assembled growth of nanoelectronic and organic photovoltaic devices based on pentacenes and fullerenes. Finally the impact of the structural changes on the electronic properties of the system will be studied. Supported by NSF NSEC-425826 and DMR-1006863.

  5. Enhanced Photovoltaic Properties of Potassium-Adsorbed Titania Nanotubes

    SciTech Connect

    Richter, C.; Jaye, C; Fischer, D; Lewis, L; Willey, R; Menon, L

    2009-01-01

    It is demonstrated that vertically-aligned titania nanotube planar arrays fabricated by electrochemical anodization using standard potassium-containing electrolytes invariably contain a significant amount of surface-adsorbed potassium ions, hitherto undetected, that affect the titania photoelectrochemical or PEC performance. Synchrotron-based near edge X-ray absorption fine structure (NEXAFS) spectroscopy reveals the strong ionic nature of surface potassium-titania bonds that alters the PEC performance over that of pure titania nanotubes through reduction of the external electrical bias needed to produce hydrogen at maximum efficiency. This result implies that the external electrical energy input required per liter of solar hydrogen produced with potassium-adsorbed titania nanotubes may be reduced. Tailoring the potassium content may thus be an alternative means to fine-tune the photoelectrochemical response of TiO2 nanotube-based PEC electrodes.

  6. Facile Isolation of Adsorbent-Free Long and Highly-Pure Chirality-Selected Semiconducting Single-Walled Carbon Nanotubes Using A Hydrogen-bonding Supramolecular Polymer

    PubMed Central

    Toshimitsu, Fumiyuki; Nakashima, Naotoshi

    2015-01-01

    The ideal form of semiconducting-single-walled carbon nanotubes (sem-SWNTs) for science and technology is long, defect-free, chirality pure and chemically pure isolated narrow diameter tubes. While various techniques to solubilize and purify sem-SWNTs have been developed, many of them targeted only the chiral- or chemically-purity while sacrificing the sem-SWNT intrinsic structural identities by applying strong ultra-sonication and/or chemical modifications. Toward the ultimate purification of the sem-SWNTs, here we report a mild-conditioned extraction of the sem-SWNTs using removable supramolecular hydrogen-bonding polymers (HBPs) that are composed of dicarboxylic- or diaminopyridyl-fluorenes with ~70%-(8,6)SWNT selective extraction. Replacing conventional strong sonication techniques by a simple shaking using HPBs was found to provide long sem-SWNTs (>2.0 μm) with a very high D/G ratio, which was determined by atomic force microscopy observations. The HBPs were readily removed from the nanotube surfaces by an outer stimulus, such as a change in the solvent polarities, to provide chemically pure (8,6)-enriched sem-SWNTs. We also describe molecular mechanics calculations to propose possible structures for the HBP-wrapped sem-SWNTs, furthermore, the mechanism of the chiral selectivity for the sorted sem-SWNTs is well explained by the relationship between the molecular surface area and mass of the HBP/SWNT composites. PMID:26658356

  7. Facile Isolation of Adsorbent-Free Long and Highly-Pure Chirality-Selected Semiconducting Single-Walled Carbon Nanotubes Using A Hydrogen-bonding Supramolecular Polymer

    NASA Astrophysics Data System (ADS)

    Toshimitsu, Fumiyuki; Nakashima, Naotoshi

    2015-12-01

    The ideal form of semiconducting-single-walled carbon nanotubes (sem-SWNTs) for science and technology is long, defect-free, chirality pure and chemically pure isolated narrow diameter tubes. While various techniques to solubilize and purify sem-SWNTs have been developed, many of them targeted only the chiral- or chemically-purity while sacrificing the sem-SWNT intrinsic structural identities by applying strong ultra-sonication and/or chemical modifications. Toward the ultimate purification of the sem-SWNTs, here we report a mild-conditioned extraction of the sem-SWNTs using removable supramolecular hydrogen-bonding polymers (HBPs) that are composed of dicarboxylic- or diaminopyridyl-fluorenes with ~70%-(8,6)SWNT selective extraction. Replacing conventional strong sonication techniques by a simple shaking using HPBs was found to provide long sem-SWNTs (>2.0 μm) with a very high D/G ratio, which was determined by atomic force microscopy observations. The HBPs were readily removed from the nanotube surfaces by an outer stimulus, such as a change in the solvent polarities, to provide chemically pure (8,6)-enriched sem-SWNTs. We also describe molecular mechanics calculations to propose possible structures for the HBP-wrapped sem-SWNTs, furthermore, the mechanism of the chiral selectivity for the sorted sem-SWNTs is well explained by the relationship between the molecular surface area and mass of the HBP/SWNT composites.

  8. Facile Isolation of Adsorbent-Free Long and Highly-Pure Chirality-Selected Semiconducting Single-Walled Carbon Nanotubes Using A Hydrogen-bonding Supramolecular Polymer.

    PubMed

    Toshimitsu, Fumiyuki; Nakashima, Naotoshi

    2015-01-01

    The ideal form of semiconducting-single-walled carbon nanotubes (sem-SWNTs) for science and technology is long, defect-free, chirality pure and chemically pure isolated narrow diameter tubes. While various techniques to solubilize and purify sem-SWNTs have been developed, many of them targeted only the chiral- or chemically-purity while sacrificing the sem-SWNT intrinsic structural identities by applying strong ultra-sonication and/or chemical modifications. Toward the ultimate purification of the sem-SWNTs, here we report a mild-conditioned extraction of the sem-SWNTs using removable supramolecular hydrogen-bonding polymers (HBPs) that are composed of dicarboxylic- or diaminopyridyl-fluorenes with ~70%-(8,6)SWNT selective extraction. Replacing conventional strong sonication techniques by a simple shaking using HPBs was found to provide long sem-SWNTs (>2.0 μm) with a very high D/G ratio, which was determined by atomic force microscopy observations. The HBPs were readily removed from the nanotube surfaces by an outer stimulus, such as a change in the solvent polarities, to provide chemically pure (8,6)-enriched sem-SWNTs. We also describe molecular mechanics calculations to propose possible structures for the HBP-wrapped sem-SWNTs, furthermore, the mechanism of the chiral selectivity for the sorted sem-SWNTs is well explained by the relationship between the molecular surface area and mass of the HBP/SWNT composites. PMID:26658356

  9. Structure and hydrogen bonding in ortho-hydroxy Ketimines

    NASA Astrophysics Data System (ADS)

    Filarowski, A.; Koll, A.; Głowiak, T.

    2003-01-01

    Two ortho-hydroxy Ketimines (2,2'-dihydroxybenzophenone- N-methyl-imine ( 1) and 2,2'-dihydroxy-4-methoxy-benzophenone- N-methyl-imine ( 2)) were synthesized with the hydrogen atom replaced in the azomethine group by the ortho-hydroxyphenyl substituent. The crystal structures were determined, which contain two types of hydrogen bonds; the intra-molecular O⋯N ( d(ON)=2.540 Å, d(ON)=2.502 Å for compound 1, d(ON)=2.559 Å for compound 2, and intermolecular O⋯O ( d(OO)=2.632 Å, d(OO)=2.582 Å for compound 1 and d(OO)=2.581 Å for compound 2. FT-IR spectra of compounds 1 and 2 in solid state as function of temperature were recorded. Relation between the intra-molecular and intermolecular hydrogen bonds was discussed. Influence of methoxy group substituted in phenol ring on the hydrogen bond properties has been investigated.

  10. Lightweight Intermetallics with Laves Structures as Potential Hydrogen Storage Materials

    NASA Astrophysics Data System (ADS)

    Billet, Beau Austin

    Hydrogen storage was identified by the US Department of Energy as a "grand challenge" for the implementation of hydrogen-powered fuel cell vehicles for reduced CO2 emissions from transportation vehicles. None of the hydrogen storage options currently developed can satisfy the high gravimetric, volumetric and system design requirements. Intermetallic compounds with Laves structures in the formula of AB2 have long been known to store hydrogen in their interstitial sites to serve as reversible hydrogen storage materials (A and B are metallic elements). They have the potential to be hydrided to a maximum of ~ AB2H6 due to the impeding H-H interactions at neighboring interstitial sites. To achieve the highest weight percent of hydrogen storage in AB2H6, the lowest combined atomic weight of AB2 is required. The CaLi2 compound is the lightest known Laves phase, but it could not maintain its Laves structure when it was hydrided. Existing work of Akiba's group showed that a ternary Laves phase CaLi1.8Mg0.2 could be hydrided to form a hydrogenated Laves phase, but the absorbed hydrogen could not be released for reversible storage. Substitutions (Ca,X)Li1.8Mg0.2 are explored in the present study to see whether heavier elements [X = Sr, Ba and Ce] in small quantities can make the lightweight Laves compounds reversibly store hydrogen. Induction melting was successful in obtaining the desired Laves phases. The base system, CaLi1.8Mg0.2, formed a single phase, consistent with the literature result. Both Ca0.9Ba0.1Li 1.8Mg0.2 and Ca0.9Ce0.1Li1.8Mg 0.2 also formed a single-phase C14 Laves, whereas both Ca0.9Sr 0.1Li1.8Mg0.2 and Ca0.8Sr0.2Li 1.8Mg0.2 formed two seperature Laves phases with the same crystal structure, indicating a phase separation. The Ca0.8Ba 0.2Li1.8Mg0.2 composition completely lost the Laves-phase structure, forming CaLi2, CaMg2, BaLi 4 and Ca. All compounds tested at temperatures from 25 °C to 150 °C show the characteristic "plateau" behavior in the pressure

  11. Hydrogenation induced structure and property changes in GdGa

    NASA Astrophysics Data System (ADS)

    Nedumkandathil, Reji; Kranak, Verina F.; Johansson, Robert; Ångström, Jonas; Balmes, Oliver; Andersson, Mikael S.; Nordblad, Per; Scheicher, Ralph H.; Sahlberg, Martin; Häussermann, Ulrich

    2016-07-01

    Hydrides GdGaHx were obtained by exposing the Zintl phase GdGa with the CrB structure to a hydrogen atmosphere at pressures from 1.5 to 50 bar and temperatures from 50 to 500 °C. Structural analysis by powder X-ray diffraction suggests that conditions with hydrogen pressures in a range between 15 and 50 bar and temperatures below 500 °C afford a uniform hydride phase with the NdGaH1.66 structure (Cmcm, a=3.9867(7) Å, b=12.024(2) Å, c=4.1009(6) Å) which hosts H in two distinct positions, H1 and H2. H1 is coordinated in a tetrahedral fashion by Gd atoms, whereas H2 atoms are inserted between Ga atoms. The assignment of the NdGaH1.66 structure is corroborated by first principles DFT calculations. Modeling of phase and structure stability as a function of composition resulted in excellent agreement with experimental lattice parameters when x=1.66 and revealed the presence of five-atom moieties Ga-H2-Ga-H2-Ga in GdGaH1.66. From in situ powder X-ray diffraction using synchrotron radiation it was established that hydrogenation at temperatures above 200 °C affords a hydride with x≈1.3, which is stable up to 500 °C, and that additional H absorption, yielding GdGaH1.66, takes place at lower temperatures. Consequently, GdGaH1.66 desorbs H above T=200 °C. Without the presence of hydrogen, hydrides GdGaHx decompose at temperatures above 300 °C into GdH2 and an unidentified Gd-Ga intermetallics. Thus the hydrogenation of GdGa is not reversible. From magnetic measurements the Curie-Weiss constant and effective magnetic moment of GdGaH1.66 were obtained. The former indicates antiferromagnetic interactions, the latter attains a value of ~8 μB which is typical for compounds containing Gd3+ions.

  12. Morphology and structure of photosensitive dye J-aggregates adsorbed on AgBr microcrystals grown in gelatin.

    PubMed

    Saijo, H; Shiojiri, M

    1998-07-15

    Though the cyanine dye J-aggregates carry the role to sense the exposing light in the silver halide photographic system, little research on the morphology of the aggregates in adsorption has been made with modern surface analytical methods. In this paper, we describe the size, epitaxy, multi-layered array formation, nucleation and preferential adsorption, and irregular distribution of population between particles and the segregation on a particle, of J-aggregates adsorbed on AgBr grown in gelatin. We employed cathodoluminescence microscopy, low energy high resolution scanning electron microscopy, and atomic force microscopy. Dye molecules aggregate together near the surface of AgBr and adsorb on the surface. The growth of adsorbed aggregates is controlled by the diffusion of dye molecules from the surrounding solution. The population of J-aggregates adsorbed on an AgBr particle varies from almost none to full coverage. Each aggregate is about (20-30) x (30-50) nm in size and is 2.1 nm thick for thiacarbocyanine with sodium ion, 1.04 nm for thiacarbocyanine with tosyl ion, and 0.5 nm for an oxacarbocyanine. The aggregates connect their longer edges to each other to form arrays, and the arrays build up multi-layered stacks. The arrays align parallel and segregate to form terraces. The longer edges of J-aggregates align along [210] on AgBr (100) or [632] on AgBr (111). PMID:9728883

  13. Vibrational Studies of Adsorbate-Induced Reconstruction on Molybdenum Surfaces.

    NASA Astrophysics Data System (ADS)

    Lopinski, Gregory Peter

    Adsorbate-induced rearrangement of the substrate structure strongly modifies the adsorbate-substrate and adsorbate-adsorbate interactions, leading to the complex behavior observed in many chemisorption systems. In this thesis the H/Mo(211), O/Mo(211) and Na/Mo(100) systems have been studied using high resolution electron energy loss spectroscopy (HREELS) to observe vibrations of the adsorbed atoms. The vibrational data is correlated with observations of the long-range order probed by LEED as well as the work function changes induced by adsorption. Adsorbate -induced substrate reconstruction plays an important role in all three of these systems. Studies of the coadsorption systems O+H/Mo(211) and Na+O/Mo(100) indicate how these effects can influence interactions between adsorbates. For H/Mo(211), above 1ML a (1 x 1) to (1 x 2) transition is observed and attributed to modification of the substrate periodicity. Below 1ML, H atoms are bridge bonded and induce local distortions of the substrate. The transition to the (1 x 2) phase involves the ordering of these displacements and occupation of three-fold sites partially populated by conversion of the bridge bonded species. This conversion accounts for the sawtooth-like coverage dependence of the work function. The structural model proposed for this system is also supported by the desorption parameters and partial molar entropy extracted from adsorption isobars. Oxygen adsorption on Mo(211) involves the occupation of multiple binding sites, with both the long-range order and the local geometry of the adsorbate phases strongly temperature dependent. Coadsorption of low coverages of oxygen and hydrogen leads to segregation of the two adsorbates which can be understood in terms of a substrate-mediated repulsive interaction between O and H. For Na/Mo(100), the frequency of the Na-Mo symmetric stretch mode does not shift with coverage although the mode intensity is strongly coverage dependent. The absence of a frequency shift

  14. Hydrogen adsorption on functionalized nanoporous activated carbons.

    PubMed

    Zhao, X B; Xiao, B; Fletcher, A J; Thomas, K M

    2005-05-12

    There is considerable interest in hydrogen adsorption on carbon nanotubes and porous carbons as a method of storage for transport and related energy applications. This investigation has involved a systematic investigation of the role of functional groups and porous structure characteristics in determining the hydrogen adsorption characteristics of porous carbons. Suites of carbons were prepared with a wide range of nitrogen and oxygen contents and types of functional groups to investigate their effect on hydrogen adsorption. The porous structures of the carbons were characterized by nitrogen (77 K) and carbon dioxide (273 K) adsorption methods. Hydrogen adsorption isotherms were studied at 77 K and pressure up to 100 kPa. All the isotherms were Type I in the IUPAC classification scheme. Hydrogen isobars indicated that the adsorption of hydrogen is very temperature dependent with little or no hydrogen adsorption above 195 K. The isosteric enthalpies of adsorption at zero surface coverage were obtained using a virial equation, while the values at various surface coverages were obtained from the van't Hoff isochore. The values were in the range 3.9-5.2 kJ mol(-1) for the carbons studied. The thermodynamics of the adsorption process are discussed in relation to temperature limitations for hydrogen storage applications. The maximum amounts of hydrogen adsorbed correlated with the micropore volume obtained from extrapolation of the Dubinin-Radushkevich equation for carbon dioxide adsorption. Functional groups have a small detrimental effect on hydrogen adsorption, and this is related to decreased adsorbate-adsorbent and increased adsorbate-adsorbate interactions. PMID:16852056

  15. Structure sensitive adsorption of hydrogen on ruthenium and ruthenium-silver catalysts supported on silica

    SciTech Connect

    Kumar, N.

    1999-02-12

    Supported metal catalysts typically consist of particles with sizes less than 10 nm, and because of the small crystallite size, low coordination number sites (edges and corners) represent a significant fraction of all surface sites. Furthermore, it has been demonstrated that adsorption rates can be much greater at these low coordination sites than on basal plane sites. What has not been generally appreciated, however, is that preferential adsorption at edge and corner sites may explain the mechanism by which a promoter, or the addition of a second metal to form a bimetallic, can alter the selectivity and rate of reaction. For example, the measurements of hydrogen adsorption onto supported Ru-Ag catalysts show marked decreases in the amount of hydrogen adsorbed relative to the amount adsorbed on Ru catalysts. Although it is known that Ag does not dissociatively adsorb hydrogen, this decrease cannot be explained by a simple one-to-one site blocking mechanism unless Ag preferentially populates edges and corners, thereby reducing the number of Ru edge sites. Indeed, Monte Carlo simulations of Ru-Group IB metal catalysts predict that Group IB metal atoms preferentially populate corner and edge sites of ruthenium crystals. This evidence, taken together, suggests that adsorption occurs preferentially at Ru corner and edge sites, which act as portals onto basal planes. A model based on this portal theory for hydrogen adsorption onto supported ruthenium bimetallic catalysts has been developed using a rate equation approach. Specifically, the model accounts for the following features: (1) preferential adsorption through portals, (2) basal plane site-energy multiplicity, and (3) hydrogen spillover onto the support. A comparison of model predictions with experiment is presented for different concentration of Ag in Ru-Ag catalysts. The portal model of hydrogen adsorption can explain the observed decreased in the amount of hydrogen adsorbed on Ru-Ag catalysts. The model can be

  16. Structure and Reactions of Carbon and Hydrogen on Ru(0001): A Scanning Tunneling Microscopy Study

    SciTech Connect

    Shimizu, Tomoko K.; Mugarza, Aitor; Cerda, Jorge; Salmeron, Miquel

    2008-09-09

    The interaction between carbon and hydrogen atoms on a Ru(0001) surface was studied using scanning tunneling microscopy (STM), Density Functional Theory (DFT) and STM image calculations. Formation of CH species by reaction between adsorbed H and C was observed to occur readily at 100 K. When the coverage of H increased new complexes of the form CH+nH (n = 1, 2 and 3) were observed. These complexes, never observed before, might be precursors for further hydrogenation reactions. DFT analysis reveals that a considerable energy barrier exists for the CH+H {yields} CH{sub 2} reaction.

  17. Intramolecular Hydrogen Bonding in Benzoxazines: When Structural Design Becomes Functional.

    PubMed

    Froimowicz, Pablo; Zhang, Kan; Ishida, Hatsuo

    2016-02-18

    The future evolution of benzoxazines and polybenzoxazines as advanced molecular, structural, functional, engineering, and newly commercial materials depends to a great extent on a deeper and more fundamental understanding at the molecular level. In this contribution, the field of benzoxazines is briefly introduced along with a more detailed review of ortho-amide-functional benzoxazines, which are the main subjects of this article. Provided in this article are the detailed and solid scientific evidences of intramolecular five-membered-ring hydrogen bonding, which is supposed to be responsible for the unique and characteristic features exhibited by this ever-growing family of ortho-functionalized benzoxazines. One-dimensional (1D) (1)H NMR spectroscopy was used to study various concentrations of benzoxazines in various solvents with different hydrogen-bonding capability and at various temperatures to investigate in detail the nature of hydrogen bonding in both ortho-amide-functionalized benzoxazine and its para counterpart. These materials were further investigated by two-dimensional (2D) (1)H-(1)H nuclear Overhauser effect spectroscopy (NOESY) to verify and support the conclusions derived during the 1D (1)H NMR experiments. Only highly purified single-crystal benzoxazine samples have been used for this study to avoid additional interactions caused by any impurities. PMID:26797690

  18. Hydrogen bonding, structure, and dynamics of benzonitrile-water

    NASA Astrophysics Data System (ADS)

    Melandri, Sonia; Consalvo, Daniela; Caminati, Walther; Favero, Paolo G.

    1999-09-01

    Rotational transitions with high quantum numbers J and K of the 1:1 complex of benzonitrile with H2O and D2O have been investigated in the frequency range 60-78 GHz with the free jet absorption microwave technique to get detailed information on the unusual hydrogen bond and on the dynamics of the large amplitude motions of the water moiety. With respect to previous microwave studies [V. Storm, D. Consalvo, and H. Dreizler, Z. Naturforsch. A 52, 293 (1997); R. M. Helm, H.-P. Vogel, H. J. Neusser, V. Storm, D. Consalvo, and H. Dreizler, 52, 655 (1997); V. Storm, H. Dreizler, and D. Consalvo, Chem. Phys. 239, 109 (1998)] the position of the water oxygen has been confirmed and the planar configuration of the complex has been determined. The distance of the oxygen atom to the ortho hydrogen is 2.48 Å, the angle to the ortho C-H bond is 144° and the angle between the free hydrogen atom of water with the same C-H bond is 164°. A coupled analysis of the 0+ and 0- states observed for the normal species was performed and the experimental data were reproduced by a flexible model which allowed the determination of the barrier to internal rotation of water [V2=287(20) cm-1] and the structural relaxation associated with the dynamic process.

  19. Comparison of adsorbents for H2S and D4 removal for biogas conversion in a solid oxide fuel cell.

    PubMed

    Sigot, Léa; Ducom, Gaëlle; Benadda, Belkacem; Labouré, Claire

    2016-01-01

    Biogas contains trace compounds detrimental for solid oxide fuel cell (SOFC) application, especially sulphur-containing compounds and volatile organic silicon compounds (VOSiCs). It is therefore necessary to remove these impurities from the biogas for fuelling an SOFC. In this paper, dynamic lab-scale adsorption tests were performed on synthetic polluted gas to evaluate the performance of a polishing treatment to remove hydrogen sulphide (H2S - sulphur compound) and octamethylcyclotetrasiloxane (D4 - VOSiC). Three kinds of adsorbents were tested: an activated carbon, a silica gel (SG) and a zeolite (Z). Z proved to be the best adsorbent for H2S removal, with an adsorbed quantity higher than [Formula: see text] at the SOFC tolerance limit. However, as concerns D4 removal, SG was the most efficient adsorbent, with an adsorbed quantity of about 184 mgD4/gSG at the SOFC tolerance limit. These results could not be explained by structural characteristics of the adsorbents, but they were partly explained by chemical interactions between the adsorbate and the adsorbent. In these experiments, internal diffusion was the controlling step, Knudsen diffusion being predominant to molecular diffusion. As Z was also a good adsorbent for D4 removal, competition phenomena were investigated with Z for the simultaneous removal of H2S and D4. It was shown that H2S retention was dramatically decreased in the presence of D4, probably due to D4 polymerization resulting in pore blocking. PMID:26183696

  20. Electronic structure of hydrogenated diamond: Microscopical insight into surface conductivity

    NASA Astrophysics Data System (ADS)

    Iacobucci, S.; Alippi, Paola; Calvani, P.; Girolami, M.; Offi, F.; Petaccia, L.; Trucchi, D. M.

    2016-07-01

    We have correlated the surface conductivity of hydrogen-terminated diamond to the electronic structure in the Fermi region. Significant density of electronic states (DOS) in proximity of the Fermi edge has been measured by photoelectron spectroscopy (PES) on surfaces exposed to air, corresponding to a p -type electric conductive regime, while upon annealing a depletion of the DOS has been achieved, resembling the diamond insulating state. The surface and subsurface electronic structure has been determined, exploiting the different probing depths of PES applied in a photon energy range between 7 and 31 eV. Ab initio density functional calculations including surface charge depletion and band-bending effects favorably compare with electronic states measured by angular-resolved photoelectron spectroscopy. Such states are organized in the energy-momentum space in a twofold structure: one, bulk-derived, band disperses in the Γ -X direction with an average hole effective mass of (0.43 ±0.02 ) m0 , where m0 is the bare electron mass; a second flatter band, with an effective mass of (2.2 ±0.9 ) m0 , proves that a hole gas confined in the topmost layers is responsible for the conductivity of the (2 ×1 ) hydrogen-terminated diamond (100 ) surface.

  1. Molecular-dynamics study of structure II hydrogen clathrates.

    PubMed

    Alavi, Saman; Ripmeester, J A; Klug, D D

    2005-07-01

    Molecular-dynamics simulations are used to study the stability of structure II hydrogen clathrates with different H2 guest occupancies. Simulations are done at pressures of 2.5 kbars and 1.013 bars and for temperatures ranging from 100 to 250 K. For a structure II unit cell with 136 water molecules, H2 guest molecule occupancies of 0-64 are studied with uniform occupancies among each type of cage. The simulations show that at 100 K and 2.5 kbars, the most stable configurations have single occupancy in the small cages and quadruple occupancy in the large cages. The optimum occupancy for the large cages decreases as the temperature is raised. Double occupancy in the small cages increases the energy of the structures and causes tetragonal distortion in the unit cell. The spatial distribution of the hydrogen guest molecules in the cages is determined by studying the guest-water and guest-guest radial distribution functions at various temperatures. PMID:16050759

  2. Light-induced metastable structural changes in hydrogenated amorphous silicon

    SciTech Connect

    Fritzsche, H.

    1996-09-01

    Light-induced defects (LID) in hydrogenated amorphous silicon (a-Si:H) and its alloys limit the ultimate efficiency of solar panels made with these materials. This paper reviews a variety of attempts to find the origin of and to eliminate the processes that give rise to LIDs. These attempts include novel deposition processes and the reduction of impurities. Material improvements achieved over the past decade are associated more with the material`s microstructure than with eliminating LIDs. We conclude that metastable LIDs are a natural by-product of structural changes which are generally associated with non-radiative electron-hole recombination in amorphous semiconductors.

  3. Quasiparticle excitations of adsorbates on doped graphene

    NASA Astrophysics Data System (ADS)

    Lischner, Johannes; Wickenburg, Sebastian; Wong, Dillon; Karrasch, Christoph; Wang, Yang; Lu, Jiong; Omrani, Arash A.; Brar, Victor; Tsai, Hsin-Zon; Wu, Qiong; Corsetti, Fabiano; Mostofi, Arash; Kawakami, Roland K.; Moore, Joel; Zettl, Alex; Louie, Steven G.; Crommie, Mike

    Adsorbed atoms and molecules can modify the electronic structure of graphene, but in turn it is also possible to control the properties of adsorbates via the graphene substrate. In my talk, I will discuss the electronic structure of F4-TCNQ molecules on doped graphene and present a first-principles based theory of quasiparticle excitations that captures the interplay of doping-dependent image charge interactions between substrate and adsorbate and electron-electron interaction effects on the molecule. The resulting doping-dependent quasiparticle energies will be compared to experimental scanning tunnelling spectra. Finally, I will also discuss the effects of charged adsorbates on the electronic structure of doped graphene.

  4. Enhanced hydrogenation activity and diastereomeric interactions of methyl pyruvate co-adsorbed with R-1-(1-naphthyl)ethylamine on Pd(111)

    NASA Astrophysics Data System (ADS)

    Mahapatra, Mausumi; Burkholder, Luke; Garvey, Michael; Bai, Yun; Saldin, Dilano K.; Tysoe, Wilfred T.

    2016-08-01

    Unmodified racemic sites on heterogeneous chiral catalysts reduce their overall enantioselectivity, but this effect is mitigated in the Orito reaction (methyl pyruvate (MP) hydrogenation to methyl lactate) by an increased hydrogenation reactivity. Here, this effect is explored on a R-1-(1-naphthyl)ethylamine (NEA)-modified Pd(111) model catalyst where temperature-programmed desorption experiments reveal that NEA accelerates the rates of both MP hydrogenation and H/D exchange. NEA+MP docking complexes are imaged using scanning tunnelling microscopy supplemented by density functional theory calculations to allow the most stable docking complexes to be identified. The results show that diastereomeric interactions between NEA and MP occur predominantly by binding of the C=C of the enol tautomer of MP to the surface, while simultaneously optimizing C=O....H2N hydrogen-bonding interactions. The combination of chiral-NEA driven diastereomeric docking with a tautomeric preference enhances the hydrogenation activity since C=C bonds hydrogenate more easily than C=O bonds thus providing a rationale for the catalytic observations.

  5. Enhanced hydrogenation activity and diastereomeric interactions of methyl pyruvate co-adsorbed with R-1-(1-naphthyl)ethylamine on Pd(111).

    PubMed

    Mahapatra, Mausumi; Burkholder, Luke; Garvey, Michael; Bai, Yun; Saldin, Dilano K; Tysoe, Wilfred T

    2016-01-01

    Unmodified racemic sites on heterogeneous chiral catalysts reduce their overall enantioselectivity, but this effect is mitigated in the Orito reaction (methyl pyruvate (MP) hydrogenation to methyl lactate) by an increased hydrogenation reactivity. Here, this effect is explored on a R-1-(1-naphthyl)ethylamine (NEA)-modified Pd(111) model catalyst where temperature-programmed desorption experiments reveal that NEA accelerates the rates of both MP hydrogenation and H/D exchange. NEA+MP docking complexes are imaged using scanning tunnelling microscopy supplemented by density functional theory calculations to allow the most stable docking complexes to be identified. The results show that diastereomeric interactions between NEA and MP occur predominantly by binding of the C=C of the enol tautomer of MP to the surface, while simultaneously optimizing C=O····H2N hydrogen-bonding interactions. The combination of chiral-NEA driven diastereomeric docking with a tautomeric preference enhances the hydrogenation activity since C=C bonds hydrogenate more easily than C=O bonds thus providing a rationale for the catalytic observations. PMID:27488075

  6. Enhanced hydrogenation activity and diastereomeric interactions of methyl pyruvate co-adsorbed with R-1-(1-naphthyl)ethylamine on Pd(111)

    PubMed Central

    Mahapatra, Mausumi; Burkholder, Luke; Garvey, Michael; Bai, Yun; Saldin, Dilano K.; Tysoe, Wilfred T.

    2016-01-01

    Unmodified racemic sites on heterogeneous chiral catalysts reduce their overall enantioselectivity, but this effect is mitigated in the Orito reaction (methyl pyruvate (MP) hydrogenation to methyl lactate) by an increased hydrogenation reactivity. Here, this effect is explored on a R-1-(1-naphthyl)ethylamine (NEA)-modified Pd(111) model catalyst where temperature-programmed desorption experiments reveal that NEA accelerates the rates of both MP hydrogenation and H/D exchange. NEA+MP docking complexes are imaged using scanning tunnelling microscopy supplemented by density functional theory calculations to allow the most stable docking complexes to be identified. The results show that diastereomeric interactions between NEA and MP occur predominantly by binding of the C=C of the enol tautomer of MP to the surface, while simultaneously optimizing C=O····H2N hydrogen-bonding interactions. The combination of chiral-NEA driven diastereomeric docking with a tautomeric preference enhances the hydrogenation activity since C=C bonds hydrogenate more easily than C=O bonds thus providing a rationale for the catalytic observations. PMID:27488075

  7. First-Principles Study of Electronic Structure and Hydrogen Adsorption of 3d Transition Metal Exposed Paddle Wheel Frameworks

    SciTech Connect

    Bak, J. H.; Le, V. D.; Kang, J.; Wei, S. H.; Kim, Y. H.

    2012-04-05

    Open-site paddle wheels, comprised of two transition metals bridged with four carboxylate ions, have been widely used for constructing metal-organic frameworks with large surface area and high binding energy sites. Using first-principles density functional theory calculations, we have investigated atomic and electronic structures of various 3d transition metal paddle wheels before and after metal exposure and their hydrogen adsorption properties at open metal sites. Notably, the hydrogen adsorption is impeded by covalent metal-metal bonds in early transition metal paddle wheels from Sc to Cr and by the strong ferromagnetic coupling of diatomic Mn and Fe in the paddle wheel configurations. A significantly enhanced H{sub 2} adsorption is predicted in the nonmagnetic Co{sub 2} and Zn{sub 2} paddle wheel with the binding energy of {approx}0.2 eV per H{sub 2}. We also propose the use of two-dimensional Co{sub 2} and Zn{sub 2} paddle wheel frameworks that could have strongly adsorbed dihydrogen up to 1.35 wt % for noncryogenic hydrogen storage applications.

  8. Extra adsorption and adsorbate superlattice formation in metal-organic frameworks

    NASA Astrophysics Data System (ADS)

    Sung Cho, Hae; Deng, Hexiang; Miyasaka, Keiichi; Dong, Zhiyue; Cho, Minhyung; Neimark, Alexander V.; Ku Kang, Jeung; Yaghi, Omar M.; Terasaki, Osamu

    2015-11-01

    Metal-organic frameworks (MOFs) have a high internal surface area and widely tunable composition, which make them useful for applications involving adsorption, such as hydrogen, methane or carbon dioxide storage. The selectivity and uptake capacity of the adsorption process are determined by interactions involving the adsorbates and their porous host materials. But, although the interactions of adsorbate molecules with the internal MOF surface and also amongst themselves within individual pores have been extensively studied, adsorbate-adsorbate interactions across pore walls have not been explored. Here we show that local strain in the MOF, induced by pore filling, can give rise to collective and long-range adsorbate-adsorbate interactions and the formation of adsorbate superlattices that extend beyond an original MOF unit cell. Specifically, we use in situ small-angle X-ray scattering to track and map the distribution and ordering of adsorbate molecules in five members of the mesoporous MOF-74 series along entire adsorption-desorption isotherms. We find in all cases that the capillary condensation that fills the pores gives rise to the formation of ‘extra adsorption domains’—that is, domains spanning several neighbouring pores, which have a higher adsorbate density than non-domain pores. In the case of one MOF, IRMOF-74-V-hex, these domains form a superlattice structure that is difficult to reconcile with the prevailing view of pore-filling as a stochastic process. The visualization of the adsorption process provided by our data, with clear evidence for initial adsorbate aggregation in distinct domains and ordering before an even distribution is finally reached, should help to improve our understanding of this process and may thereby improve our ability to exploit it practically.

  9. Structure, vibrations, and hydrogen bond parameters of dibenzotetraaza[14]annulene

    NASA Astrophysics Data System (ADS)

    Gawinkowski, S.; Eilmes, J.; Waluk, J.

    2010-07-01

    Geometry and vibrational structure of dibenzo[ b, i][1,4,8,11]tetraaza[14]annulene (TAA) have been studied using infrared and Raman spectroscopy combined with quantum-chemical calculations. The assignments were proposed for 106 out of the total of 108 TAA vibrations, based on comparison of the theoretical predictions with the experimental data obtained for the parent molecule and its isotopomer in which the NH protons were replaced by deuterons. Reassignments were suggesteded for the NH stretching and out-of-plane vibrations. The values of the parameters of the intramolecular NH⋯N hydrogen bonds were analysed in comparison with the corresponding data for porphyrin and porphycene, molecules with the same structural motif, a cavity composed of four nitrogen atoms and two inner protons. Both experiment and calculations suggest that the molecule of TAA is not planar and is present in a trans tautomeric form, with the protons located on the opposite nitrogen atoms.

  10. The structure of deuterated benzene films adsorbed on the graphite (0001) basal plane: what happens below and above the monolayer coverage?

    PubMed

    Bahn, Emanuel; Hedgeland, Holly; Jardine, Andrew P; Henry, Paul F; Hansen, Thomas C; Fouquet, Peter

    2014-10-28

    An exact description of the interactions in aromatic carbon systems is a key condition for the design of carbon based nanomaterials. In this paper we investigate the binding and adsorbate structure of the simplest prototype system in this class - the single aromatic ring molecule benzene on graphite. We have collected neutron diffraction data of the ordered phase of deuterated benzene, C6D6, adsorbed on the graphite (0001) basal plane surface. We examined relative coverages from 0.15 up to 1.3 monolayers (ML) in a temperature range of 80 to 250 K. The results confirm the flat lying commensurate (√7 × √7)R19.1° monolayer with lattice constants a = b = 6.5 Å at coverages of less than 1 ML. For this structure we observe a progressive melting well below the desorption temperature. At higher coverages we do neither observe an ordered second layer nor a densification of the structure by upright tilting of first layer molecules, as generally assumed up to now. Instead, we see the formation of clusters with a bulk crystalline structure for coverages only weakly exceeding 1 ML. PMID:25209023

  11. Sum frequency generation vibrational spectroscopy studies of adsorbates on Pt(111): Studies of CO at high pressures and temperatures, coadsorbed with olefins and its role as a poison in ethylene hydrogenation

    SciTech Connect

    Kung, Kyle Yi

    2000-12-31

    High pressure high temperature CO adsorption and coadsorption with ethylene and propylene on Pt(111) was monitored in situ with infrared-visible sum frequency generation (SFG). At high pressures and high temperatures, CO dissociates on a Pt(111) surface to form carbon. At 400 torr CO pressure and 673K, CO modifies the Pt(111) surface through a carbonyl intermediate, and dissociates to leave carbon on the surface. SFG was used to follow the CO peak evolution from monolayer adsorption in ultra high vacuum (UHV) to 400 torr CO pressure. At this high pressure, a temperature dependence study from room temperature to 823K was carried out. Auger electron spectroscopy was used to identify carbon on the surface CO coadsorption with ethylene and CO coadsorption with propylene studies were carried out with 2-IR 1-visible SFG. With this setup, two spectral ranges covering the C-H stretch range and the CO stretch range can be monitored simultaneously. The coadsorption study with ethylene reveals that after 5L ethylene exposure on a Pt(111) surface to form ethylidyne , CO at high pressures cannot completely displace the ethylidyne from the surface. Instead, CO first adsorbs on defect sites at low pressures and then competes with ethylidyne for terrace sites at high pressures. Propylene coadsorption with CO at similar conditions shows that propylidyne undergoes conformation changes with increased CO pressure and at 1 torr, is absent from the Pt(111) surface. Experiments on CO poisoning of ethylene hydrogenation was carried by 2-IR 1-visible SFG. At 1 torr CO,10 torr ethylene and 100 torr hydrogen, CO was found to block active sites necessary for ethylene hydrogenation, Above 425K, CO desorbs from the surface to allow ethylene hydrogenation to occur. The gas phase species were monitored by gas chromatography.

  12. Catalase-like activity studies of the manganese(II) adsorbed zeolites

    NASA Astrophysics Data System (ADS)

    Ćiçek, Ekrem; Dede, Bülent

    2013-12-01

    Preparation of manganese(II) adsorbed on zeolite 3A, 4A, 5A. AW-300, ammonium Y zeolite, organophilic, molecular sieve and catalase-like enzyme activity of manganese(II) adsorbed zeolites are reported herein. Firstly zeolites are activated at 873 K for two hours before contact manganese(II) ions. In order to observe amount of adsorption, filtration process applied for the solution. The pure zeolites and manganese(II) adsorbed zeolites were analysed by FT-IR. As a result according to the FT-IR spectra, the incorporation of manganese(II) cation into the zeolite structure causes changes in the spectra. These changes are expected particularly in the pseudolattice bands connected with the presence of alumino and silicooxygen tetrahedral rings in the zeolite structure. Furthermore, the catalytic activities of the Mn(II) adsorbed zeolites for the disproportionation of hydrogen peroxide were investigated in the presence of imidazole. The Mn(II) adsorbed zeolites display efficiency in the disproportion reactions of hydrogen peroxide, producing water and dioxygen in catalase-like activity.

  13. The investigation of hydrogenation influence on structure changes of zirconium with nickel layer

    NASA Astrophysics Data System (ADS)

    Kudiiarov, V. N.; Bordulev, Yu S.; Laptev, R. S.; Pushilina, N. S.; Kashkarov, E. B.; Syrtanov, M. S.

    2016-06-01

    The results of experimental investigation of hydrogenation influence on structure changes of zirconium alloy (Zr-1%Nb) with thin nickel layer have presented in this work. Nickel layer was formed by magnetron sputter deposition. Hydrogenation was carried out at gas atmosphere at constant temperature. Different hydrogen concentrations were obtained by varying time of hydrogenation. Defect and phase structure was studied by means of X-ray diffraction, glow discharge optical emission spectroscopy, positron lifetime and Doppler broadening spectroscopies. New experimental data about the evolution of the positron annihilation parameters depending on hydrogen concentration in Zr-1Nb alloy with nickel layer was obtained.

  14. Phase Space Structures Explain Hydrogen Atom Roaming in Formaldehyde Decomposition.

    PubMed

    Mauguière, Frédéric A L; Collins, Peter; Kramer, Zeb C; Carpenter, Barry K; Ezra, Gregory S; Farantos, Stavros C; Wiggins, Stephen

    2015-10-15

    We re-examine the prototypical roaming reaction--hydrogen atom roaming in formaldehyde decomposition--from a phase space perspective. Specifically, we address the question "why do trajectories roam, rather than dissociate through the radical channel?" We describe and compute the phase space structures that define and control all possible reactive events for this reaction, as well as provide a dynamically exact description of the roaming region in phase space. Using these phase space constructs, we show that in the roaming region, there is an unstable periodic orbit whose stable and unstable manifolds define a conduit that both encompasses all roaming trajectories exiting the formaldehyde well and shepherds them toward the H2···CO well. PMID:26499774

  15. The structure of carbon monoxide adsorbed on the NaCl(100) surface—A combined LEED and DFT-D/vdW-DF study

    SciTech Connect

    Vogt, Jochen; Vogt, Birgit

    2014-12-07

    The structure of the first layer CO adsorbed on NaCl(100) is investigated experimentally by means of quantitative low-energy electron diffraction at 25 K, and theoretically by means of density functional theory. Consistent with earlier helium atom diffraction results, the monolayer structure has p(2×1) symmetry with a glide-plane along the longer axis of the unit cell. The structure analysis confirms the binding of CO via the carbon end to the NaCl(100) surface. The vertical distance of carbon above Na{sup +} is 2.58 ± 0.08 Å, in good agreement with geometry optimizations based on dispersion-corrected density functional theory, and 0.15 Å lower than predicted in calculations based on the nonlocal van der Waals density functional.

  16. The structure of carbon monoxide adsorbed on the NaCl(100) surface—a combined LEED and DFT-D/vdW-DF study.

    PubMed

    Vogt, Jochen; Vogt, Birgit

    2014-12-01

    The structure of the first layer CO adsorbed on NaCl(100) is investigated experimentally by means of quantitative low-energy electron diffraction at 25 K, and theoretically by means of density functional theory. Consistent with earlier helium atom diffraction results, the monolayer structure has p(2×1) symmetry with a glide-plane along the longer axis of the unit cell. The structure analysis confirms the binding of CO via the carbon end to the NaCl(100) surface. The vertical distance of carbon above Na(+) is 2.58 ± 0.08 Å, in good agreement with geometry optimizations based on dispersion-corrected density functional theory, and 0.15 Å lower than predicted in calculations based on the nonlocal van der Waals density functional. PMID:25481162

  17. Progress in our understanding of structure bonding and reactivity of metal surfaces and adsorbed monolayers at the molecular level: A 25 year perspective

    NASA Astrophysics Data System (ADS)

    Somorjai, G. A.

    1995-12-01

    Over fifty techniques have been developed during the past 25 years that permit molecular level investigation of structure and bonding of the surface monolayer. Among them, low-energy electron diffraction surface crystallography and vibrational spectroscopies using photons and electrons have contributed the lion's share of quantitative experimental data. (Most of these investigations have utilized small area (~1 cm 2) external surfaces, although microporous large internal surface area samples were also scrutinized.) From these studies, the physical picture of the surface which emerges is one of a separate phase with distinct structure, composition, and bonding that is distinguishable from the solid bulk. The new surface phenomena which were discovered include clean surface reconstruction, adsorbate-induced restructuring, ordering and reactivity of surface defects (steps and kinks), cluster-like bonding, the large mobility of adsorbates, and the coadsorption bond. Techniques were also developed that permit in situ molecular level study of surfaces during reactions at high pressures and temperatures with good time resolution (10 -12-10 -3 sec). Molecular surface science has had a great impact in major applications involving surface phenomena-selective adsorption, heterogeneous catalysis, coatings, microelectronics, electrochemistry, and tribology-and spawned new surface technologies. The demands of these applications focus attention on the behavior of the buried interface, both solid-liquid and solid-solid.

  18. Study on Pt-structured anodic alumina catalysts for catalytic combustion of toluene: Effects of competitive adsorbents and competitive impregnation methods

    NASA Astrophysics Data System (ADS)

    Zhang, Qi; Luan, Hongjuan; Li, Tao; Wu, Yongqiang; Ni, Yanhui

    2016-01-01

    Novel competitive impregnation methods were used to prepare high dispersion Pt-structured anodic alumina catalysts. It is found that competitive adsorbents owning different acidity result in different Pt loading amount and also exert great effects on Pt distribution, particle size and redox ability. The suitable adsorption ability of lactic acid led to its best activity for catalytic combustion of toluene. Co-competitive and pre-competitive impregnation methods were also compared and the mechanisms of two competitive methods were proposed. Co-competitive impregnation made Pt distribute more uniformly through pore channels and resulted in better catalytic activity, because of the weaker spatial constraint effect of lactic acid. Furthermore, the optimized Pt-structured anodic alumina catalyst also showed a good chlorine-resistance under moisture atmosphere, because water could promote the reaction of dichloromethane (DCM) transformation and clean chloride by-products to release more active sites.

  19. Protein structural dynamics at the gas/water interface examined by hydrogen exchange mass spectrometry.

    PubMed

    Xiao, Yiming; Konermann, Lars

    2015-08-01

    Gas/water interfaces (such as air bubbles or foam) are detrimental to the stability of proteins, often causing aggregation. This represents a potential problem for industrial processes, for example, the production and handling of protein drugs. Proteins possess surfactant-like properties, resulting in a high affinity for gas/water interfaces. The tendency of previously buried nonpolar residues to maximize contact with the gas phase can cause significant structural distortion. Most earlier studies in this area employed spectroscopic tools that could only provide limited information. Here we use hydrogen/deuterium exchange (HDX) mass spectrometry (MS) for probing the conformational dynamics of the model protein myoglobin (Mb) in the presence of N(2) bubbles. HDX/MS relies on the principle that unfolded and/or highly dynamic regions undergo faster deuteration than tightly folded segments. In bubble-free solution Mb displays EX2 behavior, reflecting the occurrence of short-lived excursions to partially unfolded conformers. A dramatically different behavior is seen in the presence of N(2) bubbles; EX2 dynamics still take place, but in addition the protein shows EX1 behavior. The latter results from interconversion of the native state with conformers that are globally unfolded and long-lived. These unfolded species likely correspond to Mb that is adsorbed to the surface of gas bubbles. N(2) sparging also induces aggregation. To explain the observed behavior we propose a simple model, that is, "semi-unfolded" ↔ "native" ↔ "globally unfolded" → "aggregated". This model quantitatively reproduces the experimentally observed kinetics. To the best of our knowledge, the current study marks the first exploration of surface denaturation phenomena by HDX/MS. PMID:25761782

  20. Protein structural dynamics at the gas/water interface examined by hydrogen exchange mass spectrometry

    PubMed Central

    Xiao, Yiming; Konermann, Lars

    2015-01-01

    Gas/water interfaces (such as air bubbles or foam) are detrimental to the stability of proteins, often causing aggregation. This represents a potential problem for industrial processes, for example, the production and handling of protein drugs. Proteins possess surfactant-like properties, resulting in a high affinity for gas/water interfaces. The tendency of previously buried nonpolar residues to maximize contact with the gas phase can cause significant structural distortion. Most earlier studies in this area employed spectroscopic tools that could only provide limited information. Here we use hydrogen/deuterium exchange (HDX) mass spectrometry (MS) for probing the conformational dynamics of the model protein myoglobin (Mb) in the presence of N2 bubbles. HDX/MS relies on the principle that unfolded and/or highly dynamic regions undergo faster deuteration than tightly folded segments. In bubble-free solution Mb displays EX2 behavior, reflecting the occurrence of short-lived excursions to partially unfolded conformers. A dramatically different behavior is seen in the presence of N2 bubbles; EX2 dynamics still take place, but in addition the protein shows EX1 behavior. The latter results from interconversion of the native state with conformers that are globally unfolded and long-lived. These unfolded species likely correspond to Mb that is adsorbed to the surface of gas bubbles. N2 sparging also induces aggregation. To explain the observed behavior we propose a simple model, that is, “semi-unfolded” ↔ “native” ↔ “globally unfolded” → “aggregated”. This model quantitatively reproduces the experimentally observed kinetics. To the best of our knowledge, the current study marks the first exploration of surface denaturation phenomena by HDX/MS. PMID:25761782

  1. Micro-structured femtosecond laser assisted FBG hydrogen sensor.

    PubMed

    Karanja, Joseph Muna; Dai, Yutang; Zhou, Xian; Liu, Bin; Yang, Minghong

    2015-11-30

    We discuss hydrogen sensors based on fiber Bragg gratings (FBGs) micro-machined by femtosecond laser to form microgrooves and sputtered with Pd/Ag composite film. The atomic ratio of the two metals is controlled at Pd:Ag = 3:1. At room temperature, the hydrogen sensitivity of the sensor probe micro-machined by 75 mW laser power and sputtered with 520 nm of Pd/Ag film is 16.5 pm/%H. Comparably, the standard FBG hydrogen sensitivity becomes 2.5 pm/%H towards the same 4% hydrogen concentration. At an ambient temperature of 35°C, the processed sensor head has a dramatic rise in hydrogen sensitivity. Besides, the sensor shows good response and repeatability during hydrogen concentration test. PMID:26698733

  2. Structure, hydrogen bonding and thermal expansion of ammonium carbonate monohydrate.

    PubMed

    Fortes, A Dominic; Wood, Ian G; Alfè, Dario; Hernández, Eduardo R; Gutmann, Matthias J; Sparkes, Hazel A

    2014-12-01

    We have determined the crystal structure of ammonium carbonate monohydrate, (NH4)2CO3·H2O, using Laue single-crystal diffraction methods with pulsed neutron radiation. The crystal is orthorhombic, space group Pnma (Z = 4), with unit-cell dimensions a = 12.047 (3), b = 4.453 (1), c = 11.023 (3) Å and V = 591.3 (3) Å(3) [ρcalc = 1281.8 (7) kg m(-3)] at 10 K. The single-crystal data collected at 10 and 100 K are complemented by X-ray powder diffraction data measured from 245 to 273 K, Raman spectra measured from 80 to 263 K and an athermal zero-pressure calculation of the electronic structure and phonon spectrum carried out using density functional theory (DFT). We find no evidence of a phase transition between 10 and 273 K; above 273 K, however, the title compound transforms first to ammonium sesquicarbonate monohydrate and subsequently to ammonium bicarbonate. The crystallographic and spectroscopic data and the calculations reveal a quite strongly hydrogen-bonded structure (EHB ≃ 30-40 kJ mol(-1)), on the basis of H...O bond lengths and the topology of the electron density at the bond critical points, in which there is no free rotation of the ammonium cation at any temperature. The barrier to free rotation of the ammonium ions is estimated from the observed librational frequency to be ∼ 36 kJ mol(-1). The c-axis exhibits negative thermal expansion, but the thermal expansion behaviour of the a and b axes is ormal. PMID:25449618

  3. Structure, hydrogen bonding and thermal expansion of ammonium carbonate monohydrate

    PubMed Central

    Fortes, A. Dominic; Wood, Ian G.; Alfè, Dario; Hernández, Eduardo R.; Gutmann, Matthias J.; Sparkes, Hazel A.

    2014-01-01

    We have determined the crystal structure of ammonium carbonate monohydrate, (NH4)2CO3·H2O, using Laue single-crystal diffraction methods with pulsed neutron radiation. The crystal is orthorhombic, space group Pnma (Z = 4), with unit-cell dimensions a = 12.047 (3), b = 4.453 (1), c = 11.023 (3) Å and V = 591.3 (3) Å3 [ρcalc = 1281.8 (7) kg m−3] at 10 K. The single-crystal data collected at 10 and 100 K are complemented by X-ray powder diffraction data measured from 245 to 273 K, Raman spectra measured from 80 to 263 K and an athermal zero-pressure calculation of the electronic structure and phonon spectrum carried out using density functional theory (DFT). We find no evidence of a phase transition between 10 and 273 K; above 273 K, however, the title compound transforms first to ammonium sesquicarbonate monohydrate and subsequently to ammonium bicarbonate. The crystallographic and spectroscopic data and the calculations reveal a quite strongly hydrogen-bonded structure (E HB ≃ 30–40 kJ mol−1), on the basis of H⋯O bond lengths and the topology of the electron density at the bond critical points, in which there is no free rotation of the ammonium cation at any temperature. The barrier to free rotation of the ammonium ions is estimated from the observed librational frequency to be ∼ 36 kJ mol−1. The c-axis exhibits negative thermal expansion, but the thermal expansion behaviour of the a and b axes is ormal. PMID:25449618

  4. Structure and hydrogen bonding in plasma deposited polymorphous silicon thin films

    NASA Astrophysics Data System (ADS)

    Lebib, S.; Cabarrocas, P. Roca I.

    2004-04-01

    We present a detailed study of the structure and hydrogen bonding in silicon thin films ranging from amorphous to microcrystalline. We emphasize the results for hydrogenated polymorphous silicon films obtained under plasma conditions close to powder formation where silicon clusters and nanocrystals contribute to growth. Fourier Transform Infra-Red (FTIR) spectroscopy, Raman spectroscopy, X-Ray-Diffraction (XRD), and hydrogen evolution measurements are performed to characterize the hydrogen bonding and the structure of the films in their as-deposited state and after isochronal annealing at increasing temperature in the range of 300 to 600 °C. While Raman spectroscopy and XRD give an average information on the structure of the films, without clear evidence of the presence of crystallites in the polymorphous films, infrared spectroscopy and hydrogen evolution measurements which probe the local hydrogen related structure are shown to be perfectly adapted to characterize polymorphous silicon films. In particular, IR spectroscopy measurements, reveal the presence of a stretching band at 2030 cm^{-1}, associated with a peak at 873 cm^{-1} in the bending region and a downward shift in the Si-H wagging mode from 640 cm^{-1} to 622 cm^{-1}. We attribute the 2030 cm^{-1} mode to the presence of hydrogen bonded at the surface of the plasma produced silicon clusters and nanocrystals. This assignment is supported by hydrogen evolution measurements in which a sharp low-temperature hydrogen evolution peak appears at around 420 °C followed by up to five peaks at higher temperatures. This particular hydrogen bonding in polymorphous silicon films is also supported by isochronal annealing studies which show that the bands at 2030 cm^{-1} and 873 cm^{-1} vanish at annealing temperatures corresponding to the low temperature hydrogen evolution peak. Based on these results and their correlation with the hydrogen-related material structure, we propose a picture for the structure of

  5. States of water adsorbed on perindopril crystals

    NASA Astrophysics Data System (ADS)

    Stepanov, V. A.; Khmelevskaya, V. S.; Bogdanov, N. Yu.; Gorchakov, K. A.

    2011-10-01

    The relationship between the structural state of adsorbed water, the crystal structure of the substances, and the solubility of the perindopril salt C19H32N2O5 · C4H11N in water was studied by IR spectroscopy and X-ray diffractometry. The high-frequency shift of the stretching vibrations of adsorbed water and the solubility depend on the crystal structure of the drug substance. A reversible chemical reaction occurred between the adsorbed water and the perindopril salt.

  6. Nanohole Structuring for Improved Performance of Hydrogenated Amorphous Silicon Photovoltaics.

    PubMed

    Johlin, Eric; Al-Obeidi, Ahmed; Nogay, Gizem; Stuckelberger, Michael; Buonassisi, Tonio; Grossman, Jeffrey C

    2016-06-22

    While low hole mobilities limit the current collection and efficiency of hydrogenated amorphous silicon (a-Si:H) photovoltaic devices, attempts to improve mobility of the material directly have stagnated. Herein, we explore a method of utilizing nanostructuring of a-Si:H devices to allow for improved hole collection in thick absorber layers. This is achieved by etching an array of 150 nm diameter holes into intrinsic a-Si:H and then coating the structured material with p-type a-Si:H and a conformal zinc oxide transparent conducting layer. The inclusion of these nanoholes yields relative power conversion efficiency (PCE) increases of ∼45%, from 7.2 to 10.4% PCE for small area devices. Comparisons of optical properties, time-of-flight mobility measurements, and internal quantum efficiency spectra indicate this efficiency is indeed likely occurring from an improved collection pathway provided by the nanostructuring of the devices. Finally, we estimate that through modest optimizations of the design and fabrication, PCEs of beyond 13% should be obtainable for similar devices. PMID:27227369

  7. Sulfates of organic diamines: hydrogen-bonded structures and properties

    NASA Astrophysics Data System (ADS)

    Jayaraman, K.; Choudhury, A.; Rao, C. N. R.

    2002-03-01

    In order to investigate the supramolecular hydrogen-bonded networks and other structural features exhibited by compounds containing an organic cation and an inorganic anion, sulfates of the organic diamines, ethylenediamine ( I), 1,3-diaminopropane ( II), piperazine ( III), and 1,4-diazabicyclo[2.2.2]octane (DABCO) ( IV) have been prepared investigated by X-ray crystallography. While II, III, and IV crystallize in the centrosymmetric space group, Pbca, P2 1/n, Pbcn, respectively, I crystallizes in the non-centrosymmetric space group, P4 1 exhibiting chirality and weak NLO properties. I- IV exhibit different types of supramolecular H-bonded networks involving the organic cation and the SO 2-4 anion. The nature and strength of the H-bonding network vary from one compound to another, with the strongest network found in piperazinium sulfate, III, and the weakest in II. While in III, water molecules form part of the H-bonded network, they are present as guest molecules in the channels of IV. Thermal stability of the compounds as well as the infrared spectra reflect the stabilities of these H-bonded solids.

  8. High temperature carbon dioxide capture on nano-structured MgO-Al2O3 and CaO-Al2O3 adsorbents: an experimental and theoretical study.

    PubMed

    Bang, Yongju; Han, Seung Ju; Kwon, Soonchul; Hiremath, Vishwanath; Song, In Kyu; Seo, Jeong Gil

    2014-11-01

    Nano-structured alkaline-earth metal oxide adsorbents (denoted as MgO-Al2O3 and CaO-Al2O3) were prepared by an epoxide-driven one-pot sol-gel method, and they were applied to the dynamic and static CO2 adsorption. For comparison, a nano-structured aluminum oxide adsorbent (denoted as Al2O3) was also prepared by a similar method. MgO-Al2O3 adsorbent exhibited a well-developed mesopore structure through the formation of MgAl2O4 spinel phase, whereas CaO-Al2O3 adsorbent was composed of nano-sized CaO and CaAl2O4, resulting in a pore plugging. It was revealed that total basicity increased in the order of Al2O3 (0.11 mmol-CO2/g) < MgO-Al2O3 (0.37 mmol-CO2/g) < CaO-Al2O3, (1.21 mmol-CO2/g), which is in concurrent with adsorption energy obtained from DFT calculations. However, it was found that both basicity and base strength of the adsorbents played an important role in determining the CO2 adsorptive performance at different operating temperature. Among the adsorbents tested, MgO-Al2O3, which mostly retained medium basic sites, exhibited a best CO2 adsorptive performance at 200 degrees C. Furthermore, the experimental results are well supported by theoretical estimation, suggesting a useful design method of adsorbents for facile and regenerative adsorption in the applications of CO2 capture. PMID:25958558

  9. Hollow-fiber-based adsorbers for gas separation by pressure-swing adsorption

    SciTech Connect

    Feng, X.; Pan, C.Y.; McMinis, C.W.; Ivory, J.; Ghosh, D.

    1998-07-01

    Hollow-fiber-based adsorbers for gas separation by pressure-swing adsorption (PSA) was studied experimentally. The high efficiency of hollow-fiber-based adsorbers for gas separation was illustrated by hydrogen separation using fine-powder-activated carbon and molecular sieve as adsorbents. The adsorption equilibrium and dynamics of the hollow-fiber adsorbers were determined. The pressure drop of the gas flowing through the adsorbers was also examined. The adsorbers were tested for hydrogen separation from nitrogen, carbon dioxide, and a multicomponent gas mixture simulating ammonia synthesis purge gas. The PSA systems using the hollow-fiber adsorbers were very effective for hydrogen purification. The high separation efficiency is derived from the fast mass-transfer rate and low pressure drop, two key features of hollow-fiber-based adsorbers.

  10. Dependence of hydrogen permeabilities of isotropic graphites on the pore structure

    NASA Astrophysics Data System (ADS)

    Yamawaki, M.; Yamaguchi, K.; Suzuki, Y.; Tanaka, S.

    1991-03-01

    The permeation behavior of molecular hydrogen through isotropic graphites is investigated. The observed dependences of the permeation rate on pressure, specimen thickness, temperature and molecular weight suggest that hydrogen permeates by molecular flow, probably through open pores. A simple pore structure model is developed and is compared with the experimental results. It is revealed that hydrogen permeation through isotropic graphites depends not only on the pore size or the porosity, but also on the pore size distribution and tortuosity.

  11. Intramolecular hydrogen bonding and calixarene-like structures in p-cresol/formaldehyde resins

    NASA Astrophysics Data System (ADS)

    Opaprakasit, P.; Scaroni, A.; Painter, P.

    2001-08-01

    The nature of the strong hydrogen bonds found in p-cresol/formaldehyde (PCF) resins, compared to ordinary phenolic compounds, is studied. The evidence from FTIR spectroscopy indicates that this strong interaction is due to intramolecular hydrogen bonding from "calixarene-like" structures. The formation of this structure in PCF is enabled by its "linear" (all- ortho-linkage) structure, which is not present in branched resins. Additionally, a transition is observed at around 175 to 200°C where the intramolecular hydrogen bonded structure is lost. This structure cannot be recovered upon cooling or annealing due to restrictions on conformational rotations that are coupled to a new pattern of intermolecular hydrogen bonding. However, the structure is reformed by dissolving the resin in solution and casting new films.

  12. CO2 Hydrogenation to Formic Acid on Ni(111)

    SciTech Connect

    Peng, Guowen; Sibener, S. J.; Schatz, George C.; Ceyer, Sylvia T.; Mavrikakis, Manos

    2011-12-26

    Periodic, self-consistent, density functional theory (DFT) calculations are employed to study CO2 hydrogenation on Ni(111). CO2 hydrogenation with H adsorbed on the surface and with H absorbed in the subsurface is investigated systematically, and the respective microscopic reaction mechanisms are elucidated. We show that on Ni(111) CO2 hydrogenation to formate intermediate is more favorable than to carboxyl intermediate. The hydrogenation to formate goes through the unidentate structure that rapidly transforms into the bidentate structure. Further hydrogenation from formate to formic acid is energetically more difficult than formate formation. Formation of adsorbed formic acid from adsorbed CO2 and surface hydrogen is an endothermic reaction. Because subsurface H in Ni(111) is substantially less stable compared to surface H, its reaction with adsorbed CO2 to adsorbed formic acid is an exothermic one. Finally, our results may have significant implications for the synthesis of liquid fuels from CO2 and for catalytic hydrogenation reactions in general.

  13. Analyzing and Tracking Burning Structures in Lean Premixed Hydrogen Flames

    SciTech Connect

    Bremer, Peer-Timo; Weber, Gunther; Pascucci, Valerio; Day, Marc; Bell, John

    2009-06-01

    This paper presents topology-based methods to robustly extract, analyze, and track features defined as subsets of isosurfaces. First, we demonstrate how features identified by thresholding isosurfaces can be defined in terms of the Morse complex. Second, we present a specialized hierarchy that encodes the feature segmentation independent of the threshold while still providing a flexible multi-resolution representation. Third, for a given parameter selection we create detailed tracking graphs representing the complete evolution of all features in a combustion simulation over several hundred time steps. Finally, we discuss a user interface that correlates the tracking information with interactive rendering of the segmented isosurfaces enabling an in-depth analysis of the temporal behavior. We demonstrate our approach by analyzing three numerical simulations of lean hydrogen flames subject to different levels of turbulence. Due to their unstable nature, lean flames burn in cells separated by locally extinguished regions. The number, area, and evolution over time of these cells provide important insights into the impact of turbulence on the combustion process. Utilizing the hierarchy we can perform an extensive parameter study without re-processing the data for each set of parameters. The resulting statistics enable scientist to select appropriate parameters and provide insight into the sensitivity of the results wrt. to the choice of parameters. Our method allows for the first time to quantitatively correlate the turbulence of the burning process with the distribution of burning regions, properly segmented and selected. In particular, our analysis shows that counter-intuitively stronger turbulence leads to larger cell structures, which burn more intensely than expected. This behavior suggests that flames could be stabilized under much leaner conditions than previously anticipated.

  14. Adsorptive capacity and evolution of the pore structure of alumina on reaction with gaseous hydrogen fluoride.

    PubMed

    McIntosh, Grant J; Agbenyegah, Gordon E K; Hyland, Margaret M; Metson, James B

    2015-05-19

    Brunauer-Emmet-Teller (BET) specific surface areas are generally used to gauge the propensity of uptake on adsorbents, with less attention paid to kinetic considerations. We explore the importance of such parameters by modeling the pore size distributions of smelter grade aluminas following HF adsorption, an industrially important process in gas cleaning at aluminum smelters. The pore size distributions of industrially fluorinated aluminas, and those contacted with HF in controlled laboratory trials, are reconstructed from the pore structure of the untreated materials when filtered through different models of adsorption. These studies demonstrate the presence of three distinct families of pores: those with uninhibited HF uptake, kinetically limited porosity, and pores that are surface blocked after negligible scrubbing. The surface areas of the inaccessible and blocked pores will overinflate estimates of the adsorption capacity of the adsorbate. We also demonstrate, contrary to conventional understanding, that porosity changes are attributed not to monolayer uptake but more reasonably to pore length attenuation. The model assumes nothing specific regarding the Al2O3-HF system and is therefore likely general to adsorbate/adsorbent phenomena. PMID:25913681

  15. Ultrafast conversions between hydrogen bonded structures in liquid water observed by femtosecond x-ray spectroscopy

    SciTech Connect

    Wen, Haidan; Huse, Nils; Schoenlein, Robert W.; Lindenberg, Aaron M.

    2010-05-01

    We present the first femtosecond soft x-ray spectroscopy in liquids, enabling the observation of changes in hydrogen bond structures in water via core-hole excitation. The oxygen K-edge of vibrationally excited water is probed with femtosecond soft x-ray pulses, exploiting the relation between different water structures and distinct x-ray spectral features. After excitation of the intramolecular OH stretching vibration, characteristic x-ray absorption changes monitor the conversion of strongly hydrogen-bonded water structures to more disordered structures with weaker hydrogen-bonding described by a single subpicosecond time constant. The latter describes the thermalization time of vibrational excitations and defines the characteristic maximum rate with which nonequilibrium populations of more strongly hydrogen-bonded water structures convert to less-bonded ones. On short time scales, the relaxation of vibrational excitations leads to a transient high-pressure state and a transient absorption spectrum different from that of statically heated water.

  16. Toward quantitative STM: Scanning tunneling microscopy study of structure and dynamics of adsorbates on transition metal surfaces

    SciTech Connect

    Dunphy, J.C.

    1995-05-01

    STM was applied to chemisorbed S layers on Re(000l) and Mo(100) surfaces. As function of coverage on both these surfaces, S orders into several different overlayer structures, which have been studied by dynamic LEED. STM images of all these structures were obtained. Approximate location of S atoms in the structures was determined by inspecting the images, especially the regions containing defects. Results are in agreement with LEED except for the p(2{times}l) overlayer of sulfur on Mo(100). The STM images were compared to calculations made with Electron Scattering Quantum Chemistry (ESQC) theory. Variation of contrast in experimental images is explained as a result of changes in STM tip termination structure. STM image contrast is a result of changes in the interference between different paths for the tunneling electrons. The simplest structure on the Mo(100) surface was used as a model for developing and testing a method of quantitative structure determination with the STM. Experimental STM images acquired under a range of tunneling conditions were compared to theoretical calculations of the images as a function of surface structure to determine the structure which best fit. Results matched within approximately 0.1 Angstroms a LEED structural determination. At lower S coverage, diffusion of S atoms over the Re(0001) surface and the lateral interaction between these atoms were investigated by application of a new image analysis technique. The interaction between the S and a coadsorbed CO layer was also studied, and CO was found to induce compression of the S overlayer. A similar result was found for Au deposited on the sulfur covered Mo(100) surface. The interaction between steps on the Mo surface was found to be influenced by S adsorption and this observation was interpreted with the theory of equilibrium crystal shape. Design of an STM instrument which operates at cryogenic and variable sample temperatures, and its future applications, are described.

  17. Structural investigations of hydrogenated epitaxial graphene grown on 4H-SiC (0001)

    SciTech Connect

    Tokarczyk, M.; Kowalski, G. Stępniewski, R.; Możdżonek, M.; Strupiński, W.; Ciepielewski, P.; Borysiuk, J.

    2013-12-09

    Structural investigations of hydrogenated epitaxial graphene grown on SiC(0001) are presented. It is shown that hydrogen plays a dual role. In addition to contributing to the well-known removal of the buffer layer, it goes between the graphene planes, resulting in an increase of the interlayer spacing to 3.6 Å–3.8 Å. It is explained by the intercalation of molecular hydrogen between carbon planes, which is followed by H{sub 2} dissociation, resulting in negatively charged hydrogen atoms trapped between the graphene layers, with some addition of covalent bonding to carbon atoms. Negatively charged hydrogen may be responsible for p-doping observed in hydrogenated multilayer graphene.

  18. Sequential desorption energy of hydrogen from nickel clusters

    SciTech Connect

    Deepika,; Kumar, Rakesh; R, Kamal Raj.; Kumar, T. J. Dhilip

    2015-06-24

    We report reversible Hydrogen adsorption on Nickel clusters, which act as a catalyst for solid state storage of Hydrogen on a substrate. First-principles technique is employed to investigate the maximum number of chemically adsorbed Hydrogen molecules on Nickel cluster. We observe a maximum of four Hydrogen molecules adsorbed per Nickel atom, but the average Hydrogen molecules adsorbed per Nickel atom decrease with cluster size. The dissociative chemisorption energy per Hydrogen molecule and sequential desorption energy per Hydrogen atom on Nickel cluster is found to decrease with number of adsorbed Hydrogen molecules, which on optimization may help in economical storage and regeneration of Hydrogen as a clean energy carrier.

  19. Structural properties and magic structures in hydrogenated finite and infinite silicon nanowires

    NASA Astrophysics Data System (ADS)

    Zdetsis, A. D.; Koukaras, E. N.; Garoufalis, C. S.

    2007-11-01

    Unusual effects such as bending and "canting," related with the stability, have been identified by ab initio real-space calculations for hydrogenated silicon nanowires. We have examined in detail the electronic and structural properties of finite and infinite nanowires as a function of length (and width) and have developed stability and bending rules, demonstrating that "magic" wires do not bend. Reconstructed 2×1 nanowires are practically as stable as the magic ones. Our calculations are in good agreement with the experimental data of Ma et al. [Science 299, 1874 (2003).].

  20. CRYOGENIC ADSORPTION OF HYDROGEN ISOTOPES OVER NANO-STRUCTURED MATERIALS

    SciTech Connect

    Xiao, S.; Heung, L.

    2010-10-07

    Porous materials such as zeolites, activated carbon, silica gels, alumina and a number of industrial catalysts are compared and ranked for hydrogen and deuterium adsorption at liquid nitrogen temperature. All samples show higher D{sub 2} adsorption than that of H{sub 2}, in which a HY sample has the greatest isotopic effect while 13X has the highest hydrogen uptake capacity. Material's moisture content has significant impact to its hydrogen uptake. A material without adequate drying could result in complete loss of its adsorption capacity. Even though some materials present higher H{sub 2} adsorption capacity at full pressure, their adsorption at low vapor pressure may not be as good as others. Adsorption capacity in a dynamic system is much less than in a static system. A sharp desorption is also expected in case of temperature upset.

  1. Computer simulation of hydrogen permeability of structural materials through protective coating defect

    NASA Astrophysics Data System (ADS)

    Kostikova, E. K.; Zaika, Yu V.

    2015-12-01

    In the context of problems of hydrogen and thermonuclear power engineering intensive research of the hydrogen isotopes properties is being conducted. Mathematical models help to specify physical-chemical ideas about the interaction of hydrogen isotopes with structural materials, to estimate the limiting factors and to significantly reduce the expenses of experimental research by means of numerical simulation for different parameters and experimental conditions (including extreme ones). Classical diffusion models are often insufficient. The paper is devoted to the models and numerical solution of the boundary-value problems of hydrogen permeability taking into account nonlinear sorption-desorption dynamics on the surface. Algorithms based on difference approximations. The results of computer simulation of the hydrogen flux from a structural material sample are presented.

  2. Characterization of pore structure of a strong anion-exchange membrane adsorbent under different buffer and salt concentration conditions.

    PubMed

    Tatárová, Ivana; Fáber, René; Denoyel, Renaud; Polakovic, Milan

    2009-02-01

    The quantitative characterization of pore structure of Sartobind Q, a strongly basic membrane anion exchanger that is formed by cross-linked cellulose support and a hydrogel layer on its pore surface, was made combining the results obtained by several experimental techniques: liquid impregnation, batch size-exclusion, inverse size-exclusion chromatography, and permeability. Mercury intrusion and nitrogen sorption porosimetry were carried out for a dry cellulose support membrane in order to get additional information for building a model of the bimodal pore structure. The model incorporated the distribution of the total pore volume between transport and gel-layer pores and the partitioning of solutes of different molecular weights was expressed through the cylindrical pore model for the transport pores and random plane model for the gel layer. The effect of composition of liquid phase on the pore structure was investigated in redistilled water, phosphate and Tris-HCl buffers containing up to 1M NaCl. Evident differences in the bimodal pore structure were observed here when both the specific volume and size of the hydrogel layer pores significantly decreased with the ionic strength of liquid phase. PMID:19117574

  3. Adsorption mechanism of ester phosphate on baryum titanate in organic medium. Preliminary results on the structure of the adsorbed layer

    NASA Astrophysics Data System (ADS)

    Le Bars, N.; Tinet, D.; Faugère, A. M.; van Damme, H.; Levitz, P.

    1991-05-01

    The purpose of this work is to evidence the adsorption mechanism and the structure of commercial phosphate ester surfactant stabilized BaTiO3 in organic suspension, and to relate these characteristics to rheological behaviour. Binders and plasticizers are omitted to reduce the number of system components. Firstly adsorption isotherm were determined by inductively coupled argon plasma technique and interpretated based on transmission electron microscopy and ^{31}P nuclear magnetic resonance studies. Preliminary rheological measurements were then performed and related to suspension structure. Structure of the adsorption layer is critically discussed. L'objectif de cette étude est la compréhension du mécanisme d'adsorption d'agents dispersants phosphatés dans des suspensions organiques de BaTiO3, ainsi que la caractérisation de la structure, et du comportement rhéologique de ces suspensions. Liants et plastifiants ne sont pas utilisés, afin de réduire le nombre de composants dans le système. Dans un premier temps, l'isotherme d'adsorption est établie par dosage en émission plasma, puis interprétée sur la base de résultats de Microscopie Eloctronique à Transmission, et de spectroscopie par Résonance Magnétique Nucléaire du ^{31}P. Des mesures rhéologiques préliminaires sont effectuées pour caractériser la structure des suspensions.

  4. Formation of ordered gas-solid structures via solidification in metal-hydrogen systems

    SciTech Connect

    Shapovalov, V.I. |

    1998-12-31

    This work contains theoretical discussions concerning the large amount of previously published experimental data related to gas eutectic transformations in metal-hydrogen systems. Theories of pore nucleation and growth in these gas-solid materials will be presented and related to observed morphologies and structures. This work is intended to be helpful to theorists that work with metal-hydrogen systems, and experimentalists engaged in manufacturing technology development of these ordered gas-solid structures.

  5. Nickel-hydrogen. [metal hydrides, electrochemical corrosion, and structural design

    NASA Technical Reports Server (NTRS)

    Mchenry, E. J.

    1977-01-01

    Because of the disintegration of LaNi5 as the lattice expands on absorbing hydrogen, a nickel hydrogen cell similar to a nickel cadmium cell was designed. The positive electrode is wrapped in a microporous separator and the leads are insulated. A negative conducting grid is inserted and welded to the top of the can into an open ended container which is then turned upside down and filled so that LiNa5 powder occupies all the space not used by the rest of the components. The bottom of the can is then welded on. A fill tube is located either on the bottom or on the top of the can. When welded shut, the cell is put into a pressure bomb and the lanthanum nickel is activated at about 1,000 pounds of hydrogen. Electrolytes are added to the cell as well as whatever amount of hydrogen precharge desired, and the cell is sealed. Advantages and disadvantages of the cell are discussed.

  6. Effects of hydroxylated γ-Al2O3 support and H adsorbate on the Geometry and Electronic Structure of Pt Nanoparticles

    NASA Astrophysics Data System (ADS)

    Shafai, Ghazal; Hong, Sampyo; Rahman, Talat S.

    2015-03-01

    We have studied the effects of hydroxylated γ-Al2O3(110) support and H adsorbate on the geometry and electronic structures of Ptx (n =22,44) nanoparticles (NP) using DFT. We find that Pt22 interacts more strongly with a less hydrated support, while Pt44 more with a hydroxylated one. We also find a structural transition of the Pt22 (and not Pt44) from a biplanar to a 3D-like shape as a function of hydroxilation. H induces a much larger shift in the unoccupied d-band center than does the support. Also, these shifts are well correlated with metal-support interaction. The increased hydroxylation on γ-Al2O3(110) causes weaker metal-support interaction. As a result, the d-band width of a Pt NP decreases causing the center of the unoccupied d band to shift to lower energy (red shift). In the light of these results, we will discuss the features of XANES spectra obtained for γ-Al2O3(110) supported Pt nanoparticles. Work supported in part by NSF under Grant CHE-1310327.

  7. Quantitative structure-property relationships on photolysis of PCDD/Fs adsorbed to spruce (Picea abies (L.) Karst.) needle surfaces under sunlight irradiation.

    PubMed

    Niu, Junfeng; Huang, Liping; Chen, Jingwen; Yu, Gang; Schramm, Karl-Werner

    2005-02-01

    By partial least squares (PLS) regression, quantitative structure-property relationship (QSPR) models were developed for photolysis half-life (t1/2) of PCDD/Fs and PAHs sorbed to spruce (Picea abies (L.) Karst.) needle surfaces and irradiated by sunlight. Quantum chemical descriptors computed by PM3 Hamiltonian were used predictor variables. PLS analysis for the PCDDs and PAHs respectively resulted in no correlation by our statistical methods. The cross-validated Qcum2 value for the optimal QSPR model of PCDFs is 0.722, indicating a good predictive ability for logt1/2 of PCDFs adsorbed to spruce needle surfaces. The QSPR results show that the number of chlorine atoms bonded to the parent structure and (E(LUMO)-E(HOMO))2 has a dominant effect on t1/2 values of PCDFs. Increasing the number of chlorine atoms and (E(LUMO)-E(HOMO))2 values leads to increase of logt1/2 values of PCDFs. PMID:15639263

  8. Analysis of structural changes in active site of luciferase adsorbed on nanofabricated hydrophilic Si surface by molecular-dynamics simulations

    SciTech Connect

    Nishiyama, Katsuhiko; Hoshino, Tadatsugu

    2007-05-21

    Interactions between luciferase and a nanofabricated hydrophilic Si surface were explored by molecular-dynamics simulations. The structural changes in the active-site residues, the residues affecting the luciferin binding, and the residues affecting the bioluminescence color were smaller on the nanofabricated hydrophilic Si surface than on both a hydrophobic Si surface and a hydrophilic Si surface. The nanofabrication and wet-treatment techniques are expected to prevent the decrease in activity of luciferase on the Si surface.

  9. Structural instability of the diamond C(111) surface induced by hydrogen chemisorption

    NASA Astrophysics Data System (ADS)

    Su, C.; Lin, J.-C.

    1998-12-01

    The low energy electron diffraction technique was used to study the hydrogen chemisorption induced structural instability on the diamond C(111) surface. From the quantitative analysis of diffraction spots intensity on the as-dosed, partially desorbed, and annealed hydrogenated C(111) surfaces, the correlation between the (1×1)↔(2×1) phase transformation, hydrogen coverage, and surface temperature is shown. Thermal treatment with partial hydrogen desorption on the fully hydrogenated C(111) surface induces a (1×1)-(2×1) reconstruction with the observable half-order spots intensity (I1/2) emerging only after heating the substrate to 1270 K. Conversely, thermal annealing of the partially hydrogenated C(111) surface without desorbing H causes the size shrinking of the (2×1) domains as well as the relaxation of the hydrogenated domains. The temperature effect of I1/2 summarized from both thermal studies reveals that the (2×1) domain instability originated from the relaxation of the hydrogenated domains at elevated temperatures. In addition, the H chemisorption behavior on C(111) at different surface temperatures suggests that the terrace edges could be the preferential sites for the initial H adsorption and the growth of the hydrogenated domains might predominantly start from the terrace boundaries at a surface temperature as low as 125 K. The present study also allows us to tentatively propose that there might exist a low-temperature chemisorption state in addition to the hydrogenated metastable state as suggested by the sum-frequency generation spectroscopy and theoretical studies. A possible mechanism for the hydrogen chemisorption induced structural transformation is also discussed.

  10. Hydrogen-bonds structure in poly(2-hydroxyethyl methacrylate) studied by temperature-dependent infrared spectroscopy

    PubMed Central

    Morita, Shigeaki

    2014-01-01

    Hydrogen-bonds structure in poly(2-hydroxyethyl methacrylate) (PHEMA) were investigated by means of temperature-dependent infrared (IR) spectroscopy. Spectral variations involved with the OH…OH and C=O…HO types of hydrogen-bonds were found around the glass transition temperature of 80°C. Hydrogen-bonds among the hydroxyl groups gradually dissociate with increasing temperature. In contrast, discontinuous variation in the carbonyl bands was observed around the glass transition temperature. An association of the C=O…HO type of hydrogen-bond with increasing temperature above the glass transition temperature was revealed. These were concluded from the present study that hydrogen-bonds among the hydroxyl groups in each side chain terminal suppress the main chain mobility in the polymer matrix below the glass transition temperature, while the dissociation of the OH…OH type of hydrogen-bonds induces the association of the C=O…HO type of hydrogen-bond. As a result, the mobility of the main chain is induced by the change in hydrogen-bonds structure at the glass transition temperature. PMID:24790979