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Sample records for hydrogen adsorbate structures

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

    SciTech Connect

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

    2016-05-06

    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 H{sub 2} is lying parallel to lithium adsorbed graphene which is in contrast to its adsorption on pristine graphene (PG) where it prefers perpendicular orientation.

  2. Thermodynamics and structure of hydrogen, methane, argon, oxygen, and carbon dioxide adsorbed on single-wall carbon nanotube bundles

    NASA Astrophysics Data System (ADS)

    Bienfait, M.; Zeppenfeld, P.; Dupont-Pavlovsky, N.; Muris, M.; Johnson, M. R.; Wilson, T.; Depies, M.; Vilches, O. E.

    2004-07-01

    Adsorption isotherms, isosteric heats of adsorption, and neutron diffraction measurements of hydrogen, methane, argon, oxygen, and carbon dioxide adsorbed on single-wall carbon nanotube bundles show that all species, except CO2 , condense first on high-energy binding sites, such as the grooves and the widest interstitial channels, and then on the outer rounded surface of the bundles. As for CO2 , only one set of adsorption sites is observed, which is attributed mainly to the grooves. The diffraction results further reveal that the average packing of the bundles is not changed upon adsorption and that no significant overall bundle dilation is observed on our sample. Molecular dynamic simulations confirm and complete our interpretation.

  3. Structures and vibrational frequency shifts of argon(n)hydrogen chloride clusters and vibrations of carbon monoxide adsorbed on copper(100) surface

    NASA Astrophysics Data System (ADS)

    Bahel, Atul

    1999-07-01

    The ability to vary the number of atoms or molecules in a cluster enables us to observe how its various structural and dynamical properties evolve with size, from those typical of isolated gas phase molecules towards the bulk limit. In an effort to understand the vibrational frequency shifts of hydrogen chloride solvated by argon atoms, a three-step methodology was implemented. First, Monte Carlo simulated annealing followed by a direct minimization using Newton-Raphson (NR) steps was employed to search the optimum geometries of ArnHCl (n = 1-12) clusters. In the second step, 5D quantum bound state calculations were performed to compute zero point energies of a cluster for HCl in the vibrational state of 0 and 1. Finally, the vibrational frequency shift of HCl in the cluster was calculated by taking the difference between two zero point energies. Our calculations show that the convergence of HCl vibrational shift to its matrix value is slow. It requires at least 5 solvation shells before it reaches within 1 cm- 1 and 8 solvation shells are needed for HCl to reach the vibrational shift of 15 cm-1 equal to its experimentally observed matrix value. During the course of this dissertation, we also studied adsorption of the CO molecule on Cu surface. The vibrational motions of adsorbed atoms and molecules play important roles in their chemistry and photochemistry. For adsorbates on metal surfaces, the most extensive experimental studies have been done on the vibrations of CO chemisorbed on Cu(100). However, theoretically it still remains a challenging task. To accurately compute the vibrations of CO adsorbed on Cu(100) surface, we improved 5D and implemented 6D quantum bound state discrete variable representation with successive diagonalization and truncation technique. A realistic many-body potential of Tully et al. [J. Vac. Sci. Technol. A 11, 1914 (1993)] was used for these calculations. Our 6D calculated value for the doubly degenerate CO translation is 27.3 cm- 1

  4. Structure of water adsorbed on a single graphene sheet

    NASA Astrophysics Data System (ADS)

    Gordillo, M. C.; Martí, J.

    2008-08-01

    We present the result of molecular-dynamics simulations of water adsorbed on top of a single graphene layer at temperatures between 25 and 50°C . The analysis of the energy per particle and the density profiles indicate that the behavior of the adsorbed liquid is similar to the case of multiple graphene layers (graphite) with the only difference being the values of configurational energy. Other structural properties, such as stability ranges, hydrogen bond distributions, and molecular orientations are also presented.

  5. High-capacity hydrogen storage in Al-adsorbed graphene

    NASA Astrophysics Data System (ADS)

    Ao, Z. M.; Peeters, F. M.

    2010-05-01

    A high-capacity hydrogen storage medium—Al-adsorbed graphene—is proposed based on density-functional theory calculations. We find that a graphene layer with Al adsorbed on both sides can store hydrogen up to 13.79wt% with average adsorption energy -0.193eV/H2 . Its hydrogen storage capacity is in excess of 6wt% , surpassing U. S. Department of Energy (DOE’s) target. Based on the binding-energy criterion and molecular-dynamics calculations, we find that hydrogen storage can be recycled at near ambient conditions. This high-capacity hydrogen storage is due to the adsorbed Al atoms that act as bridges to link the electron clouds of the H2 molecules and the graphene layer. As a consequence, a two-layer arrangement of H2 molecules is formed on each side of the Al-adsorbed graphene layer. The H2 concentration in the hydrogen storage medium can be measured by the change in the conductivity of the graphene layer.

  6. 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).

  7. Second virial coefficient of helium adsorbed on liquid hydrogen

    SciTech Connect

    Paine, C.G.; Seidel, G.M. )

    1994-08-01

    The nonlinear dependence of the surface energy of liquid hydrogen as a function of the density of helium gas in equilibrium with the liquid surface has been used to determine the second virial coefficient of the two-dimensional gas of helium atoms adsorbed on the surface. The surface energy of both liquid hydrogen and liquid deuterium has been measured in the presence of [sup 4]He and [sup 3]He. The experimental results are in rough agreement with theoretical prediction.

  8. Electrochemical hydrogenation of a homogeneous nickel complex to form a surface adsorbed hydrogen-evolving species.

    PubMed

    Martin, Daniel J; McCarthy, Brian D; Donley, Carrie L; Dempsey, Jillian L

    2015-03-28

    A Ni(II) complex degrades electrochemically in the presence of acid in acetonitrile to form an electrode adsorbed film that catalytically evolves hydrogen. Comparison with a similar compound permitted investigation of the degradation mechanism.

  9. Interaction of Pd electron states with adsorbed hydrogen

    NASA Astrophysics Data System (ADS)

    Solov'ev, S. M.; Pettenkofer, C.; Pronin, I. I.; Potekhina, N. D.; Petrov, V. N.

    2013-02-01

    Investigations of electrons excited into image states (IS) of Pd clusters and their interaction with adsorbed hydrogen using photoelectron (PE) spectroscopy with synchrotron radiation is presented. Pd clusters were deposited on pyrolytic graphite surfaces which were used as inert substrates. PE spectra measured for Pd clusters at low photon energies show additional peaks at energies of ~ 4.7 and 5.25 eV that corresponds to Pd image states at energies EIS - Evac ≈ - 0.75 ± 0.1 eV and EIS - Evac ≈ - 0.2 ± 0.1 eV. After hydrogen adsorption on graphite with Pd clusters the H-induced features: positive peaks at energy - 2 eV, - 3.5 eV, - 7 eV and a small negative peak at - 4.6 eV, were observed in the valence band spectra of Pd below EF. While the peaks at - 3.5 eV and - 2 eV are the result of the formation of H-induced states in the SBZ the - 7 eV peak is due to strong interaction of Pd clusters with hydrogen producing a H―Pd bonding adsorbate state. It is proposed that a charge transfer from IS2 to Pd-H bond dominates over the H- anion neutralization via transfer of excess charge from H- to IS1.

  10. Infrared overtone spectroscopy of adsorbed hydrogen in MOF-5

    NASA Astrophysics Data System (ADS)

    FitzGerald, Stephen A.; Nelson, Jocienne N.; Gilmour, Elizabeth; Rowsell, Jesse L. C.

    2015-01-01

    Overtone spectroscopy is used to observe the rovibrational spectra of the hydrogen isotopologues H2, HD, and D2 adsorbed in the metal-organic framework known as MOF-5. It is shown that the overtone spectrum facilitates the identification of hydrogen modes which are obscured in the fundamental region by the presence of MOF-5 features. Further, the overtone spectrum of H2 at the primary adsorption site is greatly enhanced relative to other sites, and thus ambiguities about feature assignment can be avoided. The frequency (wavenumber) of the overtone modes are in good agreement with a Buckingham perturbative model while the relative intensity of the Q2 (0) pure vibrational mode is found to be anomalously large, most likely arising through mode coupling to the MOF-5 framework.

  11. Phase diagram of hydrogen adsorbed on Ni(111)

    NASA Astrophysics Data System (ADS)

    Nagai, Kiyoshi; Ohno, Yuichi; Nakamura, Takashi

    1984-08-01

    The phase diagram for the H/Ni(111) system is calculated by treating a lattice gas on a honeycomb lattice through the position-space renormalization-group theory with prefacing transformation. The following interparticle interactions are considered: (A) nearest-neighbor exclusion, second-neighbor repulsion, and third-neighbor attraction, which was previously proposed by Domany et al.; (B) nearest-neighbor exclusion, second- and third-neighbor repulsions, and further-neighbor interactions up to the sixth-neighbor one. When the interaction parameters involved are suitably adjusted, both the interactions (A) and (B) lead to the phase diagrams in good agreement with the experimental one by Christmann et al. The change of the isosteric heat of hydrogen adsorption with the adsorbed amount is also calculated. The result obtained from interaction (B) is consistent with experiment, whereas that from interaction (A) is not.

  12. [Interactions between proteins and cation exchange adsorbents analyzed by NMR and hydrogen/deuterium exchange technique].

    PubMed

    Wang, Kang; Hao, Dongxia; Qi, Shuting; Ma, Guanghui

    2014-09-01

    In silico acquirement of the accurate residue details of protein on chromatographic media is a bottleneck in protein chromatography separation and purification. Here we developed a novel approach by coupling with H/D exchange and nuclear magnetic resonance to observe hen egg white lysozyme (HEWL) unfolding behavior adsorbed on cation exchange media (SP Sepharose FF). Analysis of 1D 1H-NMR shows that protein unfolding accelerated H/D exchange rate, leading to more loss of signal of amide hydrogen owing to exposure of residues and the more unfolding of protein. Analysis of two-dimensional hydrogen-hydrogen total correlation spectroscopy shows that lysozyme lost more signals and experienced great unfolding during its adsorption on media surface. However, for several distinct fragments, the protection degrees varied, the adsorbed lysozyme lost more signal intensity and was less protected at disorder structures (coil, bend, and turn), but was comparatively more protected against exchange at secondary structure domains (α-helix, β-sheet). Finally, the binding site was determined by electrostatic calculations using computer simulation methods in conjunction with hydrogen deuterium labeled protein and NMR. This study would help deeply understand the microscopic mechanism of protein chromatography and guide the purposely design of chromatographic process and media. Moreover, it also provide an effective tool to study the protein and biomaterials interaction in other applications.

  13. Dimeric configurations of atomic hydrogen adsorbed on a monolayer hexagonal boron nitride

    NASA Astrophysics Data System (ADS)

    Shi, Jianzhang; Hao, Ruirui; Ji, Linan; Feng, Shujian; Sun, Tianye

    2017-10-01

    Atomic hydrogen adsorbed on the two-dimensional monolayer hexagonal boron nitride is systematically discussed based on dispersion-corrected density function theory (DFT-D). Main emphasis has been placed on aggregation states of two hydrogen atoms, including equal or ectopic adsorption with single side, and double-sided adsorption. The hydrogen atoms are chemisorbed on the top of boron sites, while they are physisorbed on the top of nitrogen or honeycomb sites. Furthermore, two adsorbed hydrogen atoms are most likely to keep close to form meta-TB dimer with single side. Besides, a possible stabilizing mechanism related to the adsorbed performance is investigated.

  14. Isotope tracer study of hydrogen spillover on carbon-based adsorbents for hydrogen storage.

    PubMed

    Lachawiec, Anthony J; Yang, Ralph T

    2008-06-17

    A composite material comprising platinum nanoparticles supported on molecular sieve templated carbon was synthesized and found to adsorb 1.35 wt % hydrogen at 298 K and 100 atm. The isosteric heat of adsorption for the material at low coverage was approximately 14 kJ/mol, and it approached a value of 10.6 kJ/mol as coverage increased for pressures at and above 1 atm. The increase in capacity is attributed to spillover, which is observed with the use of isotopic tracer TPD. IRMOF-8 bridged to Pt/C, a material known to exhibit hydrogen spillover at room temperature, was also studied with the hydrogen-deuterium scrambling reaction for comparison. The isotherms were reversible. For desorption, sequential doses of H2 and D2 at room temperature and subsequent TPD yield product distributions that are strong indicators of the surface diffusion controlled reverse spillover process.

  15. Increasing the density of adsorbed hydrogen with coordinatively unsaturated metal centers in metal-organic frameworks.

    PubMed

    Liu, Yun; Kabbour, Houria; Brown, Craig M; Neumann, Dan A; Ahn, Channing C

    2008-05-06

    Storing molecular hydrogen in porous media is one of the promising avenues for mobile hydrogen storage. In order to achieve technologically relevant levels of gravimetric density, the density of adsorbed H2 must be increased beyond levels attained for typical high surface area carbons. Here, we demonstrate a strong correlation between exposed and coordinatively unsaturated metal centers and enhanced hydrogen surface density in many framework structures. We show that the MOF-74 framework structure with open Zn(2+) sites displays the highest surface density for physisorbed hydrogen in framework structures. Isotherm and neutron scattering methods are used to elucidate the strength of the guest-host interactions and atomic-scale bonding of hydrogen in this material. As a metric with which to compare adsorption density with other materials, we define a surface packing density and model the strength of the H(2-)surface interaction required to decrease the H(2)-H(2) distance and to estimate the largest possible surface packing density based on surface physisorption methods.

  16. Studies on the Structural Transformation of Pt Clusters with Adsorbed Hydrogen on α-Al2O3(0001) Using Multiple Scattering Approach to Pt L3-edge Polarized X-Ray Absorption Near Edge Structure Spectra for the Pt Cluster

    NASA Astrophysics Data System (ADS)

    Ohtani, Kunihiro

    1998-03-01

    The X-ray absorption near edge structure (XANES) or the Extended X-ray absorption fine structure (EXAFS) study with polarization dependence is useful for determining the structures of the metal clusters. We have calculated Pt L3-edge XANES spectra for various structures of Pt clusters with adsorbed hydrogen, such as the one-layer-thick raft, and the hemispherical and spherical structures on α-Al2O3(0001), using the full multiple scattering approach. Comparison of the calculated results with the experimental results have yielded important information. With an increase in the spherically symmetric character of Pt clusters, the influence of Pt-support interaction on the XANES spectra decreases, that is, the hydrogen-Pt interaction plays a dominant role in such cases. We expect that Pt clusters with the one-layer-thick raft, or hemispherical structures are on the top site of surface oxygen atoms.

  17. Effects due to adsorbed atoms upon angular and energy distributions of surface produced negative hydrogen ions

    NASA Astrophysics Data System (ADS)

    Wada, M.; Bacal, M.; Kasuya, T.; Kato, S.; Kenmotsu, T.; Sasao, M.

    2013-02-01

    Exposure to Cs added hydrogen discharge makes surface of plasma grid of a negative hydrogen ion source covered with Cs and hydrogen. A Monte-Carlo particle simulation code ACAT was run to evaluate the effects due to adsorbed Cs and H atoms upon the angular and energy distributions of H atoms leaving the surface. Accumulation of H atoms on the surface reduces particle reflection coefficients and the mean energy of backscattered H atoms. Angular distributions of H atoms reflected from the hydrogen covered surface tend to be under-cosine at lower energies. Desorption of adsorbed H atoms is more efficient for hydrogen positive ions than for Cs positive ions at lower incident energy. At higher energy more than 100 eV, Cs ions desorb adsorbed H atoms more efficiently than hydrogen ions.

  18. Structure and catalytic behavior of myoglobin adsorbed onto nanosized hydrotalcites.

    PubMed

    Bellezza, Francesca; Cipiciani, Antonio; Latterini, Loredana; Posati, Tamara; Sassi, Paola

    2009-09-15

    The adsorption of myoglobin (Mb) onto nanosized nickel aluminum hydrotalcite (NiAl-HTlc) surface was studied, and the structural properties of the resulting protein layer were analyzed by using FT-IR, Raman, and fluorescence spectroscopies. Upon adsorption onto the nanoparticle surface, the protein molecules maintained their secondary structure, while the tertiary structure was altered. The fluorescence spectra and anisotropy values of adsorbed Mb revealed that the emitting amino acid residues are affected by different microenvironments when compared to the native protein behavior. Moreover, the decrease of fluorescence decay times of tryptophan indicated the occurrence of interactions among the fluorophores and the constituents of the nanoparticles, such as the metal cations, which can take place when conformational changes of Mb occur. Raman spectra indicated that the interaction of Mb molecules with NiAl-HTlc nanoparticles modified the porphyrin core, changing the spin state of the heme iron from high spin (HS) to low spin (LS). The enzymatic activity of the nanostructured biocomposite was evaluated in the oxidation of 2-methoxyphenol by hydrogen peroxide and discussed on the basis of structural properties of adsorbed myoglobin.

  19. Sewage sludge-derived materials as efficient adsorbents for removal of hydrogen sulfide.

    PubMed

    Bagreev, A; Bashkova, S; Locke, D C; Bandosz, T J

    2001-04-01

    Sewage sludge-derived materials were used as adsorbents of hydrogen sulfide from moist air. The adsorbent obtained by carbonization at 950 degrees C has a capacity twice of that of coconut-shell-based activated carbon. The capacity of the sludge-derived materials increases with increasing carbonization temperature. It is likelythatduring carbonization at 950 degrees C a mineral-like phase is formed that consists of such catalytically active metals as iron, zinc, and copper. The results obtained demonstrate that the presence of iron oxide significantly increases the capacity of commercial carbon and activated alumina. The sludge-derived adsorbents are efficient for hydrogen sulfide removal until the pore entrances are blocked with sulfur as the product of oxidation reaction. For materials in which the catalytic effect is predominant, hydrogen sulfide is adsorbed until all pores are filled with sulfur. There is also indication that chemisorption plays a significant role in the removal of hydrogen sulfide from moist air.

  20. Properties of SBA-15 modified by iron nanoparticles as potential hydrogen adsorbents and sensors

    NASA Astrophysics Data System (ADS)

    Bouazizi, N.; Ouargli, R.; Nousir, S.; Slama, R. Ben; Azzouz, A.

    2015-02-01

    SBA-15-Fe was synthesized via the incorporation of Fe0 nanoparticles (Fe(0)-Nps) in the mesoporous channels. Electron microscopy and X-ray diffraction showed that dispersion of fine iron NPs occurs mainly inside the channels of SBA-15, producing a slight structure compaction. This was accompanied by a significant improvement of both the affinity towards hydrogen and electrical conductivity, as supported by hydrogen adsorption tests and impedance measurements. CO2 thermal programmed desorption measurements revealed an attenuation of the acid character of the solid surface. This was explained in terms of strong iron interaction with the lattice oxygen atoms that reduces the SiO-H bond polarity. The close vicinity of fine Fe(0)-Nps combined with the large pore size of SBA-15 appear to contribute to a synergistic improvement of the electrical conductivity. The results reported herein open new prospects for SBA-15 as potential adsorbents for hydrogen storage and carriers for hydrogen sensors. The use of iron in lieu of noble metals for designing such materials is a novelty, because such applications of iron-loaded silica have not been envisaged so far due to the high reactivity of iron towards air and water. The development of such technologies, if any, should address this issue.

  1. 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.

  2. Hydrogen storage using carbon adsorbents: past, present and future

    NASA Astrophysics Data System (ADS)

    Dillon, A. C.; Heben, M. J.

    2001-03-01

    Interest in hydrogen as a fuel has grown dramatically since 1990, and many advances in hydrogen production and utilization technologies have been made. However, hydrogen storage technologies must be significantly advanced if a hydrogen based energy system, particularly in the transportation sector, is to be established. Hydrogen can be made available on-board vehicles in containers of compressed or liquefied H2, in metal hydrides, via chemical storage or by gas-on-solid adsorption. Although each method possesses desirable characteristics, no approach satisfies all of the efficiency, size, weight, cost and safety requirements for transportation or utility use. Gas-on-solid adsorption is an inherently safe and potentially high energy density hydrogen storage method that could be extremely energy efficient. Consequently, the hydrogen storage properties of high surface area ``activated'' carbons have been extensively studied. However, activated carbons are ineffective in storing hydrogen because only a small fraction of the pores in the typically wide pore-size distribution are small enough to interact strongly with hydrogen molecules at room temperatures and moderate pressures. Recently, many new carbon nanostructured absorbents have been produced including graphite nanofibers and carbon multi-wall and single-wall nanotubes. The following review provides a brief history of the hydrogen adsorption studies on activated carbons and comments on the recent experimental and theoretical investigations of the hydrogen adsorption properties of the new nanostructured carbon materials.

  3. 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}.

  4. Structures of multidomain proteins adsorbed on hydrophobic interaction chromatography surfaces.

    PubMed

    Gospodarek, Adrian M; Sun, Weitong; O'Connell, John P; Fernandez, Erik J

    2014-12-05

    In hydrophobic interaction chromatography (HIC), interactions between buried hydrophobic residues and HIC surfaces can cause conformational changes that interfere with separations and cause yield losses. This paper extends our previous investigations of protein unfolding in HIC chromatography by identifying protein structures on HIC surfaces under denaturing conditions and relating them to solution behavior. The thermal unfolding of three model multidomain proteins on three HIC surfaces of differing hydrophobicities was investigated with hydrogen exchange mass spectrometry (HXMS). The data were analyzed to obtain unfolding rates and Gibbs free energies for unfolding of adsorbed proteins. The melting temperatures of the proteins were lowered, but by different amounts, on the different surfaces. In addition, the structures of the proteins on the chromatographic surfaces were similar to the partially unfolded structures produced in the absence of a surface by temperature as well as by chemical denaturants. Finally, it was found that patterns of residue exposure to solvent on different surfaces at different temperatures can be largely superimposed. These findings suggest that protein unfolding on various HIC surfaces might be quantitatively related to protein unfolding in solution and that details of surface unfolding behavior might be generalized.

  5. Nano-sized Adsorbate Structure Formation in Anisotropic Multilayer System

    NASA Astrophysics Data System (ADS)

    Kharchenko, Vasyl O.; Kharchenko, Dmitrii O.; Yanovsky, Vladimir V.

    2017-05-01

    In this article, we study dynamics of adsorbate island formation in a model plasma-condensate system numerically. We derive the generalized reaction-diffusion model for adsorptive multilayer system by taking into account anisotropy in transfer of adatoms between neighbor layers induced by electric field. It will be found that with an increase in the electric field strength, a structural transformation from nano-holes inside adsorbate matrix toward separated nano-sized adsorbate islands on a substrate is realized. Dynamics of adsorbate island sizes and corresponding distributions are analyzed in detail. This study provides an insight into details of self-organization of adatoms into nano-sized adsorbate islands in anisotropic multilayer plasma-condensate systems.

  6. Repeatable Hydrogen Storage using Nano-structured Graphite Materials

    NASA Astrophysics Data System (ADS)

    Kajiura, Hisashi; Kadono, Koji; Tsutsui, Shigemitsu; Murakami, Yousuke

    2004-03-01

    Repeatable hydrogen adsorption and desorption with nano-structured graphite material (NSG) was confirmed using a high-accuracy volumetric measuring apparatus at room temperature [1]. The NSG was prepared from commercially obtained graphite powder with a purity of 99.997% (GoodFellow Cambridge Ltd.) using a mechanical milling process at a pressure of 2.0 x 10-4 Pa. The untreated graphite adsorbed 0.02wt% of hydrogen, while 0.20 - 0.25wt% of hydrogen can be repeatedly adsorbed by the NSG. Measurements of the hydrogen adsorption rate at constant pressure and pore-size distribution suggest that the hydrogen molecules are adsorbed through a diffusion process into pores with a diameter less than 1 nm. [1] H.Kajiura et al., APL82(2003)1929.

  7. Development of porous structured polyvinyl alcohol/zeolite/carbon composites as adsorbent

    NASA Astrophysics Data System (ADS)

    Laksmono, J. A.; Sudibandriyo, M.; Saputra, A. H.; Haryono, A.

    2017-05-01

    Adsorption is a separation process that has higher energy efficiency than others. Analyzing the nature of the adsorbate and the selection of suitable adsorbent are key success in adsorption. The performance of the adsorbent can be modified either physically or chemically to obtain the efficiency and effectiveness of the adsorption, this can be facilitated by using a composite adsorbent. In this study, we have conducted the preparation process of a polyvinyl alcohol (PVA)/zeolite/carbon composites. The resulting adsorbent composites are dedicated for ethanol - water dehydration proposes. The composites were prepared using cross-linked polymerization method followed by supercritical fluid extraction (SFE) to obtain the porous structured upon drying process. The characterization of the functional groups and morphology were performed by using Fourier Transform Infra-Red (FTIR) and Scanning Electron Microscopy (SEM), respectively. The FTIR analysis showed that composite prepared by SFE method formed hydrogen bonding confirmed by the appearance of peaks at 2950 - 3000 cm-1 compared to composite without SFE method, whereas, the results of SEM study showed the formation of three layered structures. On basis of the obtained results, it can be shown that PVA/zeolite/carbon has high potential to be develop further as an adsorbent composite.

  8. Helium and Hydrogen Adsorbed on Spheres and Cylinders

    NASA Astrophysics Data System (ADS)

    Hernández, E. S.; Szybisz, L.

    2014-07-01

    We examine the metastable and unstable regimes of condensation of superfluid helium and parahydrogen on spheres and cylinders at finite temperatures, employing finite range density functionals. The goal is to compare calculations of sizes and spreads of films at the onset of metastability and of instability with the predictions of a simple phenomenological model that contemplates the curvature of the substrate. We have focused on two cases, helium on nanospheres and nanocylinders of different materials, and hydrogen on fullerenes. We are able to locate the onset of metastability and of spinodal instability in the adsorption isotherms of every sample and to extract the width of the condensed fluid. It is shown that the predictions of the so-called simple model agree surprisingly well with the more elaborate calculations.

  9. 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.

  10. 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.

  11. Hydrogen Embrittlement of Structural Steels

    SciTech Connect

    Somerday, Brian P.; San Marchi, Christopher W

    2014-08-01

    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 embrittlement in steels and quantifying safety margins for steel hydrogen containment structures. For example, fatigue crack growth aided by hydrogen embrittlement is a well-established failure mode for steel hydrogen containment structures subjected to pressure cycling. This pressure cycling represents one of the key differences in operating conditions between current hydrogen pipelines and those anticipated in a hydrogen delivery infrastructure. Applying structural integrity models in design codes coupled with measurement of relevant material properties allows quantification of the reliability/integrity of steel hydrogen pipelines subjected to pressure cycling. Furthermore, application of these structural integrity models is aided by the development of physics-based predictive models, which provide important insights such as the effects of microstructure on hydrogen-assisted fatigue crack growth. Successful implementation of these structural integrity and physics-based models enhances confidence in the design codes and enables decisions about materials selection and operating conditions for reliable and efficient steel hydrogen pipelines.

  12. Crystalline structures of alkylamide monolayers adsorbed on the surface of graphite.

    PubMed

    Bhinde, Tej; Clarke, Stuart M; Phillips, Tamsin K; Arnold, Thomas; Parker, Julia E

    2010-06-01

    Synchrotron X-ray and neutron diffraction have been used to determine the two-dimensional crystalline structures of alkylamides adsorbed on graphite at submonolayer coverage. The calculated structures show that the plane of the carbon backbone of the amide molecules is parallel to the graphite substrate. The molecules form hydrogen-bonded dimers, and adjacent dimers form additional hydrogen bonds yielding extended chains. By presenting data from a number of members of the homologous series, we have identified that these chains pack in different arrangements depending on the number of carbons in the amide molecule. The amide monolayers are found to be very stable relative to other closely related alkyl species, a feature which is attributed to the extensive hydrogen bonding present in these systems. The characteristics of the hydrogen bonds have been determined and are found to be in close agreement with those present in the bulk materials.

  13. Efficient hydrogen sulfide adsorbents obtained by pyrolysis of sewage sludge derived fertilizer modified with spent mineral oil.

    PubMed

    Bagreev, Andrey; Bandosz, Teresa J

    2004-01-01

    Terrene, sewage sludge derived granulated fertilizer, was impregnated with spent mineral oil and then pyrolyzed at 600, 800, and 950 degrees C. Materials obtained were characterized from the point of view of the pore structure and surface chemistry. Then the H2S breakthrough capacitywas measured using a lab designed test. The results showed that the new adsorbents over perform by 30% materials obtained by simple thermal treatment of Terrene and by 230% virgin coconut shell based activated carbon. The surface reaction products were evaluated using thermal analysis. On the surface of new adsorbents hydrogen sulfide is oxidized mainly to elemental sulfur which is then deposited within the pore system. The breakthrough occurs when all small pores available to promote catalytic oxidation (caused by the inorganic sludge component) are filled with sulfur. An increase in pyrolysis temperature leads to an improvement in the performance of materials as hydrogen sulfide adsorbents. This is caused likely by changes in an inorganic phase and inorganic/carbonaceous phase interactions during pyrolysis.

  14. 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.

  15. Renormalization-group approach for para-hydrogen adsorbed on exfoliated graphite

    NASA Astrophysics Data System (ADS)

    Mello, E. V. L.; Carneiro, G. M.

    1986-04-01

    Heat-capacity measurements of para-hydrogen adsorbed on graphite were performed recently and revealed an interesting phase diagram similar to 4He. We report a renormalization-group study based on a three-state Potts model with vacancies which approximates the experimental situation. The resulting global phase diagram is in a three parameter space of pair-interaction constants and chemical potential as studied by Berker, Ostlund and Putnam. The Lennard-Jones or other effective potential between the para-H 2 adsorbed molecules determines the subspace relevant to this adsorbate. A method to calculate thermodynamic densities is discussed and the resulting temperature versus density diagram agrees well with the experiment.

  16. Surface atomic relaxation and magnetism on hydrogen-adsorbed Fe(110) surfaces from first principles

    NASA Astrophysics Data System (ADS)

    Chohan, Urslaan K.; Jimenez-Melero, Enrique; Koehler, Sven P. K.

    2016-11-01

    We have computed adsorption energies, vibrational frequencies, surface relaxation and buckling for hydrogen adsorbed on a body-centred-cubic Fe(110) surface as a function of the degree of H coverage. This adsorption system is important in a variety of technological processes such as the hydrogen embrittlement in ferritic steels, which motivated this work, and the Haber-Bosch process. We employed spin-polarised density functional theory to optimise geometries of a six-layer Fe slab, followed by frozen mode finite displacement phonon calculations to compute Fe-H vibrational frequencies. We have found that the quasi-threefold (3f) site is the most stable adsorption site, with adsorption energies of ∼3.0 eV/H for all coverages studied. The long-bridge (lb) site, which is close in energy to the 3f site, is actually a transition state leading to the stable 3f site. The calculated harmonic vibrational frequencies collectively span from 730 to 1220 cm-1, for a range of coverages. The increased first-to-second layer spacing in the presence of adsorbed hydrogen, and the pronounced buckling observed in the Fe surface layer, may facilitate the diffusion of hydrogen atoms into the bulk, and therefore impact the early stages of hydrogen embrittlement in steels.

  17. Interactions between adsorbed hydrogenated soy phosphatidylcholine (HSPC) vesicles at physiologically high pressures and salt concentrations.

    PubMed

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

    2011-05-18

    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.

  18. Structure of adsorbed organometallic rhodium: model single atom catalysts.

    PubMed

    Bennett, R A; McCavish, N D; Basham, M; Dhanak, V R; Newton, M A

    2007-02-02

    We have determined the structure of a complex rhodium carbonyl chloride [Rh(CO)2Cl] molecule adsorbed on the TiO2(110) surface by the normal incidence x-ray standing wave technique. The data show that the technique is applicable to reducible oxide systems and that the dominant adsorbed species is undissociated with Rh binding atop bridging oxygen and to the Cl found close to the fivefold coordinated Ti ions in the surface. A minority geminal dicarbonyl species, where Rh-Cl bond scission has occurred, is found bridging the bridging oxygen ions forming a high-symmetry site.

  19. A Comprehensive Study of Hydrogen Adsorbing to Amorphous Water ice: Defining Adsorption in Classical Molecular Dynamics

    NASA Astrophysics Data System (ADS)

    Dupuy, John L.; Lewis, Steven P.; Stancil, P. C.

    2016-11-01

    Gas-grain and gas-phase reactions dominate the formation of molecules in the interstellar medium (ISM). Gas-grain reactions require a substrate (e.g., a dust or ice grain) on which the reaction is able to occur. The formation of molecular hydrogen (H2) in the ISM is the prototypical example of a gas-grain reaction. In these reactions, an atom of hydrogen will strike a surface, stick to it, and diffuse across it. When it encounters another adsorbed hydrogen atom, the two can react to form molecular hydrogen and then be ejected from the surface by the energy released in the reaction. We perform in-depth classical molecular dynamics simulations of hydrogen atoms interacting with an amorphous water-ice surface. This study focuses on the first step in the formation process; the sticking of the hydrogen atom to the substrate. We find that careful attention must be paid in dealing with the ambiguities in defining a sticking event. The technical definition of a sticking event will affect the computed sticking probabilities and coefficients. Here, using our new definition of a sticking event, we report sticking probabilities and sticking coefficients for nine different incident kinetic energies of hydrogen atoms [5-400 K] across seven different temperatures of dust grains [10-70 K]. We find that probabilities and coefficients vary both as a function of grain temperature and incident kinetic energy over the range of 0.99-0.22.

  20. HYDROGEN GENERATION FROM PLASMATRON REFORMERS: A PROMISING TECHNOLOGY FOR NOX ADSORBER REGENERATION AND OTHER AUTOMOTIVE APPLICATIONS

    SciTech Connect

    Bromberg, L.; Crane, S; Rabinovich, A.; Kong, Y; Cohn, D; Heywood, J; Alexeev, N.; Samokhin, A.

    2003-08-24

    Plasmatron reformers are being developed at MIT and ArvinMeritor [1]. In these reformers a special low power electrical discharge is used to promote partial oxidation conversion of hydrocarbon fuels into hydrogen and CO. The partial oxidation reaction of this very fuel rich mixture is difficult to initiate. The plasmatron provides continuous enhanced volume initiation. To minimize electrode erosion and electrical power requirements, a low current, high voltage discharge with wide area electrodes is used. The reformers operate at or slightly above atmospheric pressure. Plasmatron reformers provide the advantages of rapid startup and transient response; efficient conversion of the fuel to hydrogen rich gas; compact size; relaxation or elimination of reformer catalyst requirements; and capability to process difficult to reform fuels, such as diesel and bio-oils. These advantages facilitate use of onboard hydrogen-generation technology for diesel exhaust after-treatment. Plasma-enhanced reformer technology can provide substantial conversion even without the use of a catalyst. Recent progress includes a substantial decrease in electrical power consumption (to about 200 W), increased flow rate (above 1 g/s of diesel fuel corresponding to approximately 40 kW of chemical energy), soot suppression and improvements in other operational features.. Plasmatron reformer technology has been evaluated for regeneration of NOx adsorber after-treatment systems. At ArvinMeritor tests were performed on a dual-leg NOx adsorber system using a Cummins 8.3L diesel engine both in a test cell and on a vehicle. A NOx adsorber system was tested using the plasmatron reformer as a regenerator and without the reformer i.e., with straight diesel fuel based regeneration as the baseline case. The plasmatron reformer was shown to improve NOx regeneration significantly compared to the baseline diesel case. The net result of these initial tests was a significant decrease in fuel penalty, roughly 50% at

  1. Quantum dynamics of hydrogen interacting with single-walled carbon nanotubes: multiple H-atom adsorbates.

    PubMed

    McAfee, Jason L; Poirier, Bill

    2011-02-21

    In a previous paper [J. L. McAfee and B. Poirier, J. Chem. Phys. 130, 064701 (2009)], using spin-polarized density functional theory (DFT), the authors reported a binding energy of 0.755 eV, for a single hydrogen atom adsorbed on a pristine (unrelaxed) (5,5) single-walled carbon nanotube (SWNT) substrate. A full three-dimensional (3D) potential energy surface (PES) for the SWNT-H system was also developed, and used in a quantum dynamics calculation to compute all rovibrational bound states, and associated equatorial and longitudinal adsorbate migration rates. A highly pronounced preference for the latter migration pathway at ambient temperatures was observed. In this work, we extend the aforementioned study to include multiple H-atom adsorbates. Extensive DFT calculations are performed, in order to ascertain the most relevant dynamical pathways. For two adsorbates, the SWNT-H-H system is found to exhibit highly site-specific binding, as well as long-range correlation and pronounced binding energy enhancement. The latter effect is even more pronounced in the full-hydrogenation limit, increasing the per-adsorbate binding energy to 2.6 eV. To study migration dynamics, a single-hole model is developed, for which the binding energy drops to 2.11 eV. A global 3D PES is developed for the hole migration model, using 40 radial × 18 cylindrical ab initio geometries, fit to a Fourier basis with radially dependent expansion coefficients (rms error 4.9 meV). As compared with the single-adsorbate case, the hole migration PES does not exhibit separate chemisorption and physisorption wells. The barrier to longitudinal migration is also found to be much lower. Quantum dynamics calculations for all rovibrational states are then performed (using a mixed spectral basis/phase-space optimized discrete variable representation), and used to compute longitudinal migration rates. Ramifications for the use of SWNTs as potential hydrogen storage materials are discussed.

  2. Structure and dynamics of highly adsorbed semiflexible polymer melts

    NASA Astrophysics Data System (ADS)

    Carrillo, Jan-Michael; Cheng, Shiwang; Kumar, Rajeev; Goswami, Monojoy; Sokolov, Alexie; Sumpter, Bobby

    2015-03-01

    We present a detailed analysis of coarse-grained molecular dynamics simulations of melts of semi-flexible polymer chains in the presence of an adsorbing substrate. For polymer chains located far from the substrate the chain conformations follow the worm-like chain model, in contrast to the reflected Gaussian conformation near the substrate. This is demonstrated in the chain center-of-mass distribution normal to the substrate and the probability of a polymer chain ends to be the closest to the substrate. Both quantities agree with Silberberg's derivation for an ideal chain in the presence of a reflecting wall. We characterized the adsorbed chains and counted the number of loops and tails. For stiff chains, a tail and an adsorbed segment dominate the chain conformation of the adsorbed layer. Also, the mean-square end-to-end distance normal to the substrate is proportional to the normal component of the mean-square end-to-end distance of the tails. The tails do not follow the worm-like chain model and exhibit a stretched conformation. This picture for the adsorbed layer is akin to the ``polydisperse pseudobrush'' envisioned by Guiselin. We probe the dynamics of the segments by calculating the layer (z-)resolved intermediate coherent collective dynamics structure factor, S(q,t,z), for q values equivalent to the bond length. The segment dynamics is slower for stiffer chains. In the adsorbed layer, dynamics is slowed down and can be described by two relaxation times. Department of Energy, Office of Science DE-AC05-00OR227.

  3. 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

  4. Removal of hydrogen sulfide using palygorskite in a fixed bed adsorber.

    PubMed

    Higuchi, T; Zhang, Q; Sekine, M; Imai, T; Yamamoto, K

    2012-01-01

    This work describes the use of a novel palygorskite, a type of magnesium aluminium silicate clay possessing a high specific surface area and pore surface activity, as a low cost and highly efficient adsorbent for hydrogen sulfide (H(2)S) removal. Adsorption of H(2)S on palygorskite pretreated with acid or base was investigated in a fixed bed adsorber. The samples after base pretreatment had better dynamic adsorption performances than raw material and samples pretreated with acid. The H(2)S adsorption capacity decreased with an increase in inlet H(2)S concentration. This can be interpreted by the fact that H(2)S adsorption on the surface of palygorskite is chemisorption. The adsorption capacity increased from 25 to 50 °C, then decreased from 50 to 100 °C, which indicates that chemisorption took place and its better reaction temperature was around 50 °C.

  5. Structural damages in adsorbed vaccines affected by freezing.

    PubMed

    Kurzątkowski, Wiesław; Kartoğlu, Ümit; Staniszewska, Monika; Górska, Paulina; Krause, Aleksandra; Wysocki, Mirosław Jan

    2013-03-01

    This study was planned to evaluate structural damages in adsorbed vaccines affected by freezing using scanning electron microscopy and X-ray analysis of the elements. Randomly selected 42 vials of eight different types of WHO pre-qualified adsorbed freeze-sensitive vaccines from 10 manufacturers were included in the study. Vaccines were kept at 5 °C. Selected numbers of vials from each type were then exposed to -25 °C for 24 h periods. All samples were evaluated for their structure using scanning electron microscopy, X-ray analysis of the elements and precipitation time. Scanning electron microscopy of vaccines affected by freezing showed either smooth or rough surfaced conglomerates associated with phosphate content of the precipitate. These vaccines precipitated 2-15 times faster compared to non-frozen samples. Non-frozen samples showed uniform flocculent structure either dense or dispersed. X-ray analysis of precipitates in frozen samples confirmed that the precipitate is mainly aluminium clutters. Scanning electron microscopy confirmed that the lattice structure of bonds between adsorbent and the antigen is broken and aluminium forms conglomerates that grow in size and weight. The precipitation time of vaccines affected by freezing is 4.5 times faster on average compared to non-frozen samples. These facts form the basis of the "shake test".

  6. 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.

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

    SciTech Connect

    Hwang, Kevin Shao-Lin

    2003-01-01

    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 → 1/2 N2 + CO2] on Rh(111) and ethylene hydrogenation [C2H4 + H2 → C2H6] 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

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

    DOE PAGES

    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

  9. 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.

  10. Hydrogen bonding with adsorbent during storage governs drug dissolution from solid-dispersion granules.

    PubMed

    Gupta, Manish K; Tseng, Yin-Chao; Goldman, David; Bogner, Robin H

    2002-11-01

    To investigate changes in drug dissolution on storage of ternary solid-dispersion granules containing poorly water-soluble drugs. Hot-melt granulation was used to prepare ternary solid-dispersion granules in which the drug was dispersed in a carrier and coated onto an adsorbent. Seven drugs including four carboxylic acid-containing drugs (BAY 12-9566, naproxen, ketoprofen, and indomethacin). a hydroxyl-containing drug (testosterone), an amide-containing drug (phenacetin), and a drug with no proton-donating group (progesterone) were studied. Gelucire 50/13 and polyethylene glycol (PEG) 8000 were used as dispersion carriers whereas Neusilin US2 (magnesium aluminosilicate) was used as the surface adsorbent. Two competing mechanisms have been proposed to explain the complex changes observed in drug dissolution upon storage of solid dispersion granules. Conversion of the crystalline drug to the amorphous hydrogen bonded (to Neusilin) state seems to increase dissolution, whereas, the phenomenon of Ostwald ripening can be used to explain the decrease in drug dissolution upon storage. The solubility of the drug in Gelucire is a crucial factor in determining the predominant mechanism by governing the flux toward the surface of Neusilin. The mobility for this phenomenon was provided by the existence of the eutectic mixture in the molten liquid state during storage. A competitive balance between hydrogen bonding of the drugs with Neusilin and Ostwald ripening determines drug dissolution from solid-dispersion granules upon storage.

  11. Structure of CO2 adsorbed on the KCl(100) surface.

    PubMed

    Traeger, Franziska; Hadnadjev, Milica; Vogt, Jochen; Weiss, Helmut

    2011-06-30

    The structure and dynamics of the adsorbate CO(2)/KCl(100) from a diluted phase to a saturated monolayer have been investigated with He atom scattering (HAS), low-energy electron diffraction (LEED), and polarization dependent infrared spectroscopy (PIRS). Two adsorbate phases with different CO(2) coverage have been found. The low-coverage phase is disordered at temperatures near 80 K and becomes at least partially ordered at lower temperatures, characterized by a (2√2×√2)R45° diffraction pattern. The saturated 2D phase has a high long-range order and exhibits (6√2×√2)R45° symmetry. Its isosteric heat of adsorption is 26 ± 4 kJ mol(-1). According to PIRS, the molecules are oriented nearly parallel to the surface, the average tilt angle in the saturated monolayer phase is 10° with respect to the surface plane. For both phases, structure models are proposed by means of potential calculations. For the saturated monolayer phase, a striped herringbone structure with 12 inequivalent molecules is deduced. The simulation of infrared spectra based on the proposed structures and the vibrational exciton approach gives reasonable agreement between experimental and simulated infrared spectra.

  12. 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.

  13. 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

    2016-05-05

    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+).

  14. 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.

  15. Evaluating topologically diverse metal–organic frameworks for cryo-adsorbed hydrogen storage

    SciTech Connect

    Gómez-Gualdrón, Diego A.; Colón, Yamil J.; Zhang, Xu; Wang, Timothy C.; Chen, Yu-Sheng; Hupp, Joseph T.; Yildirim, Taner; Farha, Omar K.; Zhang, Jian; Snurr, Randall Q.

    2016-01-01

    Metal–organic frameworks (MOFs) are porous materials synthesized by combining inorganic and organic molecular building blocks into crystalline networks of distinct topologies. Due to the combinatorial possibilities, there are millions of possible MOF structures. Aiming to exploit their exceptional tunability, surface areas and pore volumes, researchers have investigated MOFs for storage of gaseous fuels such as hydrogen for over a decade, but a suitable MOF to store hydrogen at ambient conditions has not yet been found. Here, we sought to rapidly determine the viability of using MOFs for hydrogen storage at recently proposed, cryogenic operating conditions. We constructed a large and structurally diverse set of 13 512 potential MOF structures based on 41 different topologies and used molecular simulation to determine MOF hydrogen deliverable capacities between 100 bar/77 K and 5 bar/160 K. The highest volumetric deliverable capacity was 57 g L-1 of MOF, which surpasses the 37 g L-1 of tank of the incumbent technology (compressing hydrogen to 700 bar at ambient temperature). To validate our in silico MOF construction method, we synthesized a new isoreticular family of MOFs (she-MOF-x series) based on the she topology, which is extremely rare among MOFs. To validate our hydrogen storage predictions, we activated and measured hydrogen adsorption on she-MOF-1 and NU-1103. The latter MOF showed outstanding stability and a good combination of volumetric and gravimetric performance, presenting 43.2 g L-1 of MOF and 12.6 wt% volumetric and gravimetric deliverable capacities, respectively.

  16. Location of hydrogen adsorbed on Rh(111) studied by low-energy electron diffraction and nuclear reaction analysis

    SciTech Connect

    Fukuoka, Masayuki; Okada, Michio; Matsumoto, Masuaki; Ogura, Shouhei; Fukutani, Katsuyuki; Kasai, Toshio

    2007-06-15

    The structures of clean and hydrogen-adsorbed Rh(111) surfaces were investigated by dynamical low-energy electron-diffraction (LEED) analysis. Exposure of D{sub 2} induced no additional LEED patterns except for (1x1). Surface-layer relaxation occurs vertically on both clean and D-saturated surfaces. On the clean surface, the interlayer distance between the first and second layers (d{sub 12}) is smaller by 1.2({+-}0.6)% than the corresponding bulk distance of 2.194 A. On the other hand, the contraction of d{sub 12} is removed on the D-saturated surface. Detailed LEED analysis demonstrates that the D atoms are adsorbed on the fcc threefold hollow sites. The absolute saturation coverage of H on Rh(111) was determined to be 0.84 ML by nuclear reaction analysis (NRA). Moreover, the zero-point vibrational energy of H was derived from the analysis of the NRA resonance profile, which is discussed in comparison with the results of high-resolution electron-energy-loss spectroscopy.

  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. 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.

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

    PubMed

    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 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.

  20. 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.

  1. 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

    2015-11-07

    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.

  2. STM observation of the chemical reaction of atomic hydrogen on the N-adsorbed Cu(001) surface

    NASA Astrophysics Data System (ADS)

    Hattori, Takuma; Yamada, Masamichi; Komori, Fumio

    2017-01-01

    Chemical reaction of atomic hydrogen with the N-adsorbed Cu(001) surfaces was investigated at room temperature by scanning tunnel microscopy. At the low exposure of atomic hydrogen, it reacted with the N atoms and turned to be the NH species on the surface. The reaction rate is proportional to the amount of the unreacted N atoms. By increasing the exposure of atomic hydrogen from this condition, the amount of nitrogen species on the surface decreased. This is attributed to the formation of ammonia and its desorption from the surface. The NH species on the surface turn to NH3 through the surface NH2 species by atomic hydrogen. Coexistence of the clean Cu surface enhances the rate of ammonia formation owing to atomic hydrogen migrating on the clean surface.

  3. 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.

  4. Modeling and testing of cryo-adsorbent hydrogen storage tanks with improved thermal isolation

    NASA Astrophysics Data System (ADS)

    Raymond, Alexander William; Reiter, Joseph

    2012-06-01

    One storage concept for hydrogen-fueled vehicles is physical adsorption of hydrogen at cryogenic temperatures (nominally 80 K). During long idle periods, parasitic heat transfer from the environment induces desorption to the tank void volume. This desorption increases tank pressure such that it must be vented. To reduce the amount of fuel lost to venting, parasitic heating is minimized using multi-layer vacuum insulation and thermally isolating structures. A model is developed to predict the amount of conduction through structural supports and hydrogen lines, radiation through multi-layer insulation, and rarified gas conduction in the vacuum jacket of a tank sized for adsorption storage. The model reveals that conduction through structural supports is significant for cases of interest. Thus, two structural support architectures are compared: one utilizing G-10 CR composite and another involving KevlarTM cable. The structural members are sized to support comparable inertial loadings; the overall parasitic heat transfer is found to be as much as 38 percent less for the KevlarTM design. A lumped-parameter tank simulation is used to relate parasitic heat transfer to dormancy time and venting rate. The results of thermal testing of a sub-scale tank simulator are compared with model predictions.

  5. Structural transitions between epitaxially ordered phases in adsorbed submonolayers

    NASA Astrophysics Data System (ADS)

    Ostlund, S.; Berker, A. N.

    1980-06-01

    The global phase diagram of a triangular lattice-gas model for submonolayers adsorbed epitaxially on basal graphite is studied using a position-space renormalization method. This model has nearest-neighbor exclusion, and accomodates dominant third-neighbor interaction. Each cell of 12 sites is mapped onto a single local degree of freedom with a single-triplet-quadruplet structure. The lattice gas, with up to 20th-neighbor interactions, is thereby transformed into a nearest-neighbor model, which is then analyzed by a Migdal-Kadanoff renormalization transformation. At low temperatures, as coverage is increased from zero, gas, 2 × 2 solid, and 3×3 solid phases can be encountered, separated by first-order transitions. These solids undergo first-or higher-order transitions into fluid phases as temperature is increased at given density. Triple points, multicritical points, and/or critical end-points occur for various relative strengths of interactions. For certain plausible potentials, the 2 × 2 solid occurs at finite temperature, but not at zero temperature. Distinct liquid and gas phases, with a solid-liquid-gas triple point, are found in some cases. Contact is made with the phase diagram of methane physisorbed on basal graphite, suggesting that the effective hard-core radius of methane is increased by adsorption. A phase diagram very similar to that exhibited by oxygen chemisorbed on nickel (111), with both 2 × 2 and 3×3 structures, is also obtained.

  6. Low density specific heat measurements of para-hydrogen adsorbed on exfoliated graphite

    NASA Astrophysics Data System (ADS)

    Chaves, F. A. B.; Cortez, M. E. B. P.; Rapp, R. E.; Lerner, E.

    1985-02-01

    Heat-capacity measurements of para-hydrogen adsorbed on bare graphite foam for coverages below about the ( 3× 3) R30° configuration between 0.0126 and 0.0622 Å -2 were made as a function of temperature in the range of 5 to 25 K using a quasiadiabatic method. From the data a phase diagram is suggested having three distinct regions: a pure ( 3× RCD>3)R30° ; phase, a coexistence region between ( 3× 3)R30° and fluid and a pure fluid region. A tricritical point seems to exist at TTC ⋍ 12.4 K and nTC ⋍ 0.039 Å-2. The critical exponent α = 0.37 ± 0.03 was calculated which, within our experimental measurements, is the theoretical 3-state Potts value of {1}/{3}. Considering the adatoms behaving as localized Einstein oscillators, for the 0.0636 Å -2 density, an average Einstein temperature of 54.4 ± 4.9 K was obtained. Our results are compared with data obtained by other authors.

  7. 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.

  8. The desorption and reactivity of butanol adsorbed on lithium iron phosphate (LISICON) activated in a hydrogen plasma

    NASA Astrophysics Data System (ADS)

    Pylinina, A. I.; Mikhalenko, I. I.; Yagodovskaya, T. V.; Yagodovskii, V. D.

    2010-12-01

    The reactivity and desorption of butanol-2 adsorbed on Li3Fe2(PO4)3 not subjected and subjected to treatment in a glow discharge hydrogen plasma were studied under flow conditions with a gas chromatographic analysis of products. X-ray photoelectron spectroscopy data showed that the number of phosphate groups on the surface of the phosphate was two times larger than the stoichiometric number and increased after plasma chemical treatment. The strength of butanol-phosphate bonds also increased, and the selectivity of alcohol decomposition with the formation of an olefin (dehydration) and ketone (dehydrogenation) changed. After plasma treatment, dehydrogenation centers were deactivated. The selectivities of alcohol transformations in the adsorbed state and under vapor phase conditions were different. Ketone was formed from adsorbed alcohol because the activation energies of dehydrogenation were equal for the two reaction variants.

  9. 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

  10. 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

  11. The effect of pre-adsorbed atoms on the reactivity of methanol- d4 on Ru(0 0 1): Comparison between hydrogen and oxygen

    NASA Astrophysics Data System (ADS)

    Barros, Ricardo B.; Garcia, Ana Rosa; Ilharco, Laura M.

    2006-06-01

    The influence of pre-adsorbed H and O on the adsorption and decomposition of methanol- d4 on Ru(0 0 1) surfaces is analysed by RAIRS. It is shown that the reactivity of CD 3OD at 90 K is not determined by the nature of the modifying atom nor by the structure of the pre-adsorbed layer: a low dose of CD 3OD (0.1 L) undergoes O-D bond breaking, yielding CD 3O-, both on Ru(0 0 1)-H (0.5 ⩽ θH < 1 ML) and on Ru(0 0 1)-O (0.25 ⩽ θO ⩽ 0.6 ML) surfaces. At 90 K, methoxide- d3 acquires a tilted configuration on all these surfaces, despite the fact that oxygen forms ordered phases whereas hydrogen (adsorbed at this temperature) does not. A fraction of the methoxide- d3 undergoes C-D bond breaking at 110 K on all the modified surfaces, in a lower extent than on clean Ru(0 0 1). The stabilizing effect is more pronounced on the O modified layers, and is coverage dependent. The chemical nature of the pre-adsorbed atom is determinant of the unreacted methoxide geometry, as only oxygen is capable of inducing a reorientation of this species towards C 3v local symmetry. Confirmation of the adsorption geometries, both at 90 and 110 K, was obtained from the RAIR spectra of the selectively labelled CHD 2OH, adsorbed on the same surfaces. The long-range repulsive interactions between the pre-adsorbed atom and the final decomposition product at 130 K (carbon monoxide) are more evident on the denser O layer (0.6 ML), since this species does not remain on the surface. No partially hydrogenated intermediates were detected on the H modified surfaces, suggesting that, in case exchange reactions occur, they yield only gaseous products. On the contrary, direct evidence for the participation of pre-adsorbed O was supplied by the detection of deuterated formate (DCOO) for θO = 0.6 ML.

  12. Theoretical estimation of the vibrational perturbation of the molecular properties of hydrogen adsorbed within a zeolite A framework

    NASA Astrophysics Data System (ADS)

    Larin, A. V.; Jousse, F.; Leherte, L.; Vercauteren, D. P.

    1997-08-01

    An iterative numerical procedure is proposed to evaluate the variation of the dependence versus the internuclear distance of several molecular properties (polarizabilities, multipole moments) of hydrogen adsorbed within zeolite A. Dealing with a method which includes only the vibrational perturbation, it is shown that the dependence on internuclear distance of the properties of H 2 does not change upon adsorption in NaA as compared to the gas.

  13. The crystalline structures of carboxylic acid monolayers adsorbed on graphite.

    PubMed

    Bickerstaffe, A K; Cheah, N P; Clarke, S M; Parker, J E; Perdigon, A; Messe, L; Inaba, A

    2006-03-23

    X-ray and neutron diffraction have been used to investigate the formation of solid crystalline monolayers of all of the linear carboxylic acids from C(6) to C(14) at submonolayer coverage and from C(8) to C(14) at multilayer coverages, and to characterize their structures. X-rays and neutrons highlight different aspects of the monolayer structures, and their combination is therefore important in structural determination. For all of the acids with an odd number of carbon atoms, the unit cell is rectangular of plane group pgg containing four molecules. The members of the homologous series with an even number of carbon atoms have an oblique unit cell with two molecules per unit cell and plane group p2. This odd-even variation in crystal structure provides an explanation for the odd-even variation observed in monolayer melting points and mixing behavior. In all cases, the molecules are arranged in strongly hydrogen-bonded dimers with their extended axes parallel to the surface and the plane of the carbon skeleton essentially parallel to the graphite surface. The monolayer crystal structures have unit cell dimensions similar to certain close-packed planes of the bulk crystals, but the molecular arrangements are different. There is a 1-3% compression on increasing the coverage over a monolayer.

  14. A theoretical study of the interaction of hydrogen and oxygen with palladium or gold adsorbed on pyridine-like nitrogen-doped graphene.

    PubMed

    Rangel, Eduardo; Magana, Luis Fernando; Sansores, Luis Enrique

    2014-12-15

    The interaction of H2 and O2 molecules in the presence of nitrogen-doped graphene decorated with either a palladium or gold atom was investigated by using density functional theory. It was found that two hydrogen molecules were adsorbed on the palladium atom. The interaction of these adsorbed hydrogen molecules with two oxygen molecules generates two hydrogen peroxide molecules first through a Eley-Rideal mechanism and then through a Langmuir-Hinshelwood mechanism. The barrier energies for this reaction were small; therefore, we expect that this process may occur spontaneously at room temperature. In the case of gold, a single hydrogen molecule is adsorbed and dissociated on the metal atom. The interaction of the dissociated hydrogen molecule on the surface with one oxygen molecule generates a water molecule. The competitive adsorption between oxygen and hydrogen molecules slightly favors oxygen adsorption. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  15. Mass transport of adsorbates near a discontinuous structural phase transition

    NASA Astrophysics Data System (ADS)

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

    2016-12-01

    We study the mass transport dynamics of an adsorbed layer near a discontinuous incommensurate striped-honeycomb phase transition via numerical simulations of a coarse-grained model focusing on the motion of domain walls rather than individual atoms. Following an initial step profile created in the incommensurate striped phase, an intermediate hexagonal incommensurate phase nucleates and grows, leading to a bifurcation into two sharp profiles propagating in opposite directions as opposed to broad profiles induced by atomic diffusive motion. Our results are in agreement with recent numerical simulations of a microscopic model as well as experimental observations for the Pb/Si(111) adsorbate system.

  16. 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. Copyright © 2016 Elsevier B.V. All rights reserved.

  17. 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

    2015-03-05

    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.

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

    NASA Astrophysics Data System (ADS)

    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) (∼1690 cm-1) the Cdbnd O stretching modes at unhydrated groups, (ii) (1655-1673 cm-1) the Cdbnd O 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) (∼1640 cm-1) the Cdbnd O 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 < 50 μg ml-1) corresponds to solution spectra indicating that native collagen molecules interact with water adsorbed on the titania surface. In films prepared from solutions (c ⩾ 50 μg ml-1) collagen multilayers are formed. The amide I mode is blue-shifted by 18 cm-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.

  19. The structural and electronic properties of metal atoms adsorbed on graphene

    NASA Astrophysics Data System (ADS)

    Liu, Wenjiang; Zhang, Cheng; Deng, Mingsen; Cai, Shaohong

    2017-09-01

    Based on density functional theory (DFT), we studied the structural and electronic properties of seven different metal atoms adsorbed on graphene (M + graphene). The geometries, adsorption energies, density of states (DOS), band structures, electronic dipole moment, magnetic moment and work function (WF) of M + graphene were calculated. The adsorption energies ΔE indicated that Li, Na, K, Ca and Fe adsorbed on graphene were tending to form stable structures. However, diffusion would occur on Cu and Ag adsorbed on graphene. In addition, the electronic structure near the Fermi level of graphene was significantly affected by Fe (Cu and Ag), compared with Li (Na, K and Ca). The electronic dipole moment and magnetic moment of M + graphene were sensitive to the adsorbed metal atoms. Moreover, we found electropositive (electronegative) adsorption can decrease (increase) the WF of the surface. Specially, the WF of Ag + graphene and Fe + graphene would increase because surface dipole moment make a contribution to electron.

  20. 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.

  1. Hydrogen Bonding Controls the Dynamics of Catechol Adsorbed on a TiO2(110) Surface

    NASA Astrophysics Data System (ADS)

    Diebold, Ulrike; Li, Shao-Chun; Chu, Li-Na; Gong, Xue-Qing

    2011-03-01

    Direct studies of how organic molecules diffuse on metal oxide surfaces can provide insights into catalysis and molecular assembly processes. We studied individual catechol molecules, C6 H4 (OH)2 , on a rutile Ti O2 (110) surface with scanning tunnelingmicroscopy. Surface hydroxyls enhanced the diffusivity of adsorbed catecholates. The capture and release of a proton caused individual molecules to switch between mobile and immobile states within a measurement period of minutes. Density functional theory calculations showed that the transfer of hydrogen from surface hydroxyls to the molecule and its interaction with surface hydroxyls substantially lowered the activation barrier for rotational motion across the surface. Hydrogen bonding can play an essential role in the initial stages of the dynamics of molecular assembly.

  2. 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.

  3. FTIR spectroscopy and thermodynamics of hydrogen adsorbed in a cross-linked polymer.

    PubMed

    Spoto, Giuseppe; Vitillo, Jenny G; Cocina, Donato; Damin, Alessandro; Bonino, Francesca; Zecchina, Adriano

    2007-09-28

    The adsorption of H(2) in a cross-linked poly(styrene-co-divinylbenzene) (St-DVB) microporous polymer (BET surface area 920 m(2) g(-1)) is studied by volumetric and gravimetric methods, FTIR spectroscopy at variable temperature (300-14 K) and ab initio calculations. At 77 K the polymer reversibly stores up to 1.3 mass% H(2) at a pressure of 1 bar and 1.8 mass% at 10 bar. The adsorption process involves the specific interaction of H(2) with the structural phenyl rings through weak dispersive forces. The interacting molecules become IR active and give rise to vibrational and rotational-vibrational manifestations which are affected by the temperature, the contact time and the H(2) equilibrium pressure. The spectra of the H(2)/St-DVB system reported here represent the first IR evidence of the adsorption of hydrogen on unsaturated molecules. The adsorption enthalpy is evaluated by the VTIR (variable temperature IR spectroscopy) method (C. Otero Areán et al., Phys. Chem. Chem. Phys., 2007, DOI: 10.1039/b615535a) and compared with the results of ab initio calculations for the H(2)/benzene interaction and with literature data.

  4. Quantification of the Influence of Protein-Protein Interactions on Adsorbed Protein Structure and Bioactivity

    PubMed Central

    Wei, Yang; Thyparambil, Aby A.; Latour, Robert A.

    2013-01-01

    While protein-surface interactions have been widely studied, relatively little is understood at this time regarding how protein-surface interaction effects are influenced by protein-protein interactions and how these effects combine with the internal stability of a protein to influence its adsorbed-state structure and bioactivity. The objectives of this study were to develop a method to study these combined effects under widely varying protein-protein interaction conditions using hen egg-white lysozyme (HEWL) adsorbed on silica glass, poly(methyl methacrylate), and polyethylene as our model systems. In order to vary protein-protein interaction effects over a wide range, HEWL was first adsorbed to each surface type under widely varying protein solution concentrations for 2 h to saturate the surface, followed by immersion in pure buffer solution for 15 h to equilibrate the adsorbed protein layers in the absence of additionally adsorbing protein. Periodic measurements were made at selected time points of the areal density of the adsorbed protein layer as an indicator of the level of protein-protein interaction effects within the layer, and these values were then correlated with measurements of the adsorbed protein’s secondary structure and bioactivity. The results from these studies indicate that protein-protein interaction effects help stabilize the structure of HEWL adsorbed on silica glass, have little influence on the structural behavior of HEWL on HDPE, and actually serve to destabilize HEWL’s structure on PMMA. The bioactivity of HEWL on silica glass and HDPE was found to decrease in direct proportion to the degree of adsorption-induce protein unfolding. A direct correlation between bioactivity and the conformational state of adsorbed HEWL was less apparent on PMMA, thus suggesting that other factors influenced HEWL’s bioactivity on this surface, such as the accessibility of HEWL’s bioactive site being blocked by neighboring proteins or the surface

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

    DOE PAGES

    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

  6. 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)

  7. 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)

  8. Local structure and distribution of remaining elements inside extraction chromatography adsorbents

    NASA Astrophysics Data System (ADS)

    Watanabe, Sou; Sano, Yuichi; Shiwaku, Hideaki; Yaita, Tsuyoshi; Ohno, Simpei; Arai, Tsuyoshi; Matsuura, Haruaki; Koka, Masashi; Satoh, Takahiro

    2017-08-01

    A new adsorbent of the extraction chromatography technology impregnating CMPO and HDEHP extractants for minor actinide recovery process was prepared and fundamental performance were evaluated by batch-wise adsorption/elution experiments, EXAFS analysis and PIXE-CT analysis. Selective minor actinides recovery from the adsorbent charging minor actinides and lanthanides was revealed to be possible owing to synergistic extraction of lanthanides by CMPO and HDEHP. Discharging the residual lanthanides is essential for repeated use of the adsorbent, and ammonium acetate solution was proposed as an appropriate eluent although the elution ratio is not large enough. In order to enhance the elution performance of the lanthanides, improvements in structure of the adsorbent as well as in the eluent were shown to be important.

  9. Influence of the intramolecular potential of adsorbed hydrogen on frequency shift calculations

    NASA Astrophysics Data System (ADS)

    Larin, Alexander V.

    1995-01-01

    The influence of the choice of the intramolecular potential on the resulting frequency shift of the fundamental vibrational transition in the dihydrogen molecule adsorbed on zeolite NaA is estimated. It is shown that an improved Morse potential and the potential calculated by Kołtsos and Wolniewicz lead to the same frequency shift value. Application of the Buckingham method for the frequency shift calculation to this case is discussed.

  10. 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)

  11. 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)

  12. Electronic structures of hydrogenated Si(001) surfaces

    NASA Astrophysics Data System (ADS)

    Lee, Seung Mi; Lee, Young Hee

    1996-02-01

    We have studied the electronic structure of clean and hydrogenated Si(001) surfaces via the empirical tight-binding total energy scheme. In the clean Si(001) surface, several reconstructed structures such as symmetric (2 × 1), buckled (2 × 1), p(2 × 2), and are studied. We find that higher-orderings such as the c(4 × 2) and p(2 × 2) are energetically favorable configurations. The electr density of states of these structures are also provided and compared with experimental results. In the hydrogenated Si(001) surface, there are three stable structures: monohydride, dihydride, and a (3 × 1) phase upon hydrogen coverage. We suggest that the electronic density of states can provide a way to distinguish the respective structures by several characteristic hydrogen-related peaks. These are further compared with experimental results.

  13. The Structure and Properties of Carbon Fiber Based Adsorbent Monoliths

    SciTech Connect

    Burchell, T.; Judkins, R.R.; Rogers, M.R.; Shaw, W.S.

    1998-11-06

    Carbon fiber monoliths manufactured by a novel slurry molding process from isotropic pitch-derived fibers are being developed at ORNL for gas separation and storage applications [1]. Low density (p = 0.2 - 0,3 g/cm3) monoliths have been successfully demonstrated to have an acceptable pressure drop for gas separation applications and are currently being developed for C02/CH4 separations, whereas monoliths with densities in the range p = 0.4 - 0.6 g/cm3 have been "shown to have natural gas storage capacities of >100 VIV at 500 psi pressure and room temperature. Thermal conductivity, as a function of temperature, was measured using the LASER flash, thermal- pulse method. Another approach to minimizing the temperature gradients that develop in a storage bed is to increase the thermal conductivity of the adsorbent carbon. To this end, we have developed hybrid monoliths that contain small fractions of mesophase pitch- derived carbon fibers. Our hybrid monoliths exhibit thermal conductivities in the range 0.2-0.9 W/m.K depending on the blend and density of the monolith. In comparison, a packed bed of granular carbon at comparable density would have a thermal conductivity of approximately 0.1 W/m.K [ 1 ]. The thermal conductivities of several of the hybrid The improved thermal conductivity of our monoliths is attributed to the bonding between the fibers and the incorporation of high thermal conductivity, mesophase pitch-derived carbon fibers. These features are visible in the SEM micrograph in Fig. 4.

  14. Quantitative adsorbate structure determination for quasicrystals using x-ray standing waves.

    PubMed

    Diehl, R D; Li, H I; Su, S Y; Mayer, A; Stanisha, N A; Ledieu, J; Lovelock, K R J; Jones, Robert G; Deyko, A; Wearing, L H; McGrath, R; Chaudhuri, A; Woodruff, D P

    2014-09-05

    The quantitative structure determination of adsorbed species on quasicrystal surfaces has so far appeared to present insurmountable problems. The normal incidence standing x-ray wave field technique offers a simple solution, without extensive data sets or large computations. Its application to quasicrystals raises several conceptual difficulties that are related to the phase problem in x-ray diffraction. We demonstrate their solution for the case of Si atoms adsorbed on the decagonal Co-rich modification of the Al-Co-Ni quasicrystal to determine the local structure, comprising 6-atom clusters in particular hollow sites.

  15. Quantitative Adsorbate Structure Determination for Quasicrystals Using X-Ray Standing Waves

    NASA Astrophysics Data System (ADS)

    Diehl, R. D.; Li, H. I.; Su, S. Y.; Mayer, A.; Stanisha, N. A.; Ledieu, J.; Lovelock, K. R. J.; Jones, Robert G.; Deyko, A.; Wearing, L. H.; McGrath, R.; Chaudhuri, A.; Woodruff, D. P.

    2014-09-01

    The quantitative structure determination of adsorbed species on quasicrystal surfaces has so far appeared to present insurmountable problems. The normal incidence standing x-ray wave field technique offers a simple solution, without extensive data sets or large computations. Its application to quasicrystals raises several conceptual difficulties that are related to the phase problem in x-ray diffraction. We demonstrate their solution for the case of Si atoms adsorbed on the decagonal Co-rich modification of the Al-Co-Ni quasicrystal to determine the local structure, comprising 6-atom clusters in particular hollow sites.

  16. 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.

  17. Structure and dynamics of water adsorbed in carbon nanotubes : a joint neutron scattering and molecular-dynamics study.

    SciTech Connect

    de Souza, N. R.; Kolesnikov, A. I.; Loong, C.-K.; Moravsky, A. P.; Loutfy, R. O.; Burnham, C. J.; Intense Pulsed Neutron Source; MER Corp.; Univ. of Utah

    2004-01-01

    The advent of nanocarbons, from single- and multiple-walled nanotubes to nanohorns, avails model studies of confined molecules on the nanoscale. Water encapsulated inside the quasi-one-dimensional channels of these materials is expected to exhibit anomalous behavior due to the unique geometry of nanotubes and the weak interaction between the water molecules and the carbon atoms. We have employed neutron small-to-wide angle diffraction, quasielastic and inelastic scattering in conjunction with molecular-dynamics simulations to characterize the structures and dynamics of water adsorbed in open-ended single- and double-walled nanotubes over a wide range of spatial and temporal scales. We find that a square-ice sheet wrapped next to the inner nanotube wall and a water chain in the interior are the key structural elements of nanotube-confined water/ice. This configuration results in a hydrogen-bond connectivity that markedly differs from that in bulk water. This significantly softened hydrogen-bond network manifests in strong energy shifts of the observed and simulated inter- and intra-molecular vibrations. The very large mean-square displacement of hydrogen atoms observed experimentally and the strong anharmonicity inferred from simulations explain the fluid-like behavior at temperatures far below the freezing point of normal water.

  18. Structure of a peptide adsorbed on graphene and graphite.

    PubMed

    Katoch, Jyoti; Kim, Sang Nyon; Kuang, Zhifeng; Farmer, Barry L; Naik, Rajesh R; Tatulian, Suren A; Ishigami, Masa

    2012-05-09

    Noncovalent functionalization of graphene using peptides is a promising method for producing novel sensors with high sensitivity and selectivity. Here we perform atomic force microscopy, Raman spectroscopy, infrared spectroscopy, and molecular dynamics simulations to investigate peptide-binding behavior to graphene and graphite. We studied a dodecamer peptide identified with phage display to possess affinity for graphite. Optical spectroscopy reveals that the peptide forms secondary structures both in powder form and in an aqueous medium. The dominant structure in the powder form is α-helix, which undergoes a transition to a distorted helical structure in aqueous solution. The peptide forms a complex reticular structure upon adsorption on graphene and graphite, having a helical conformation different from α-helix due to its interaction with the surface. Our observation is consistent with our molecular dynamics calculations, and our study paves the way for rational functionalization of graphene using biomolecules with defined structures and, therefore, functionalities.

  19. On the possible mechanism of the W(001) surface reconstruction with adsorbed hydrogen

    NASA Astrophysics Data System (ADS)

    Egorushkin, V. E.; Savushkin, E. V.

    1990-12-01

    The reconstruction of the (001) face of tungsten is treated as a Jahn-Teller transition connected with two narrow surface electronic bands along the Γ M lines. The surface periodic lattice distortion is found to be accompanied by the occurence of the hydrogen ordering in an adlayer with the result that the reconstruction temperature raises.

  20. Lithium boride sheet and nanotubes: structure and hydrogen storage.

    PubMed

    Zhang, Hong; Wang, Jing; Tian, Zhi-Xue; Liu, Ying

    2015-06-07

    A new class of Li-B sheets, along with the related nanotubes, with a Li2B5 primitive cell has been designed using first-principles density functional theory. The dynamical stability of the proposed structures was confirmed by calculation of the soft phonon modes, and the calculated electronic structures show that all are metallic. The application of both the sheets and nanotubes for hydrogen storage has been investigated and it has been found that both of them can adsorb two H2 molecules around each Li atom, with an average binding energy of 0.152-0.194 eV per H2, leading to a gravimetric density of 10.6 wt%.

  1. 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.

  2. 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.

  3. HREELS studies of formamide on Pt(111): hydrogen bonding interactions between adsorbates

    NASA Astrophysics Data System (ADS)

    Flores, Cynthia R.; Gao, Quanyin; Hemminger, John C.

    1990-12-01

    The adsorption properties of formamide, HCONH 2, on Pt(111) have been studied using high-resolution electron energy loss spectroscopy (HREELS). At low dosages, dissociative adsorption of formamide at 170 K results in the formation of coadsorbed NH 3 and CO. The onset of molecular adsorption occurs just prior to formation of a monolayer. At saturation monolayer coverages, hydrogen-bonding interactions between the chemisorbed molecules result in red-shifting of the ν(NH 2) vibrational frequency from the gas phase value of 3570 to 3307 cm -1. The linewidths of the ν s(NH 2) and ν a(NH 2) modes are broadened into a singular peak due to enhanced coupling with NH 2 modes of lower frequency. In the case of HCOND 2, the ν s(ND 2) and ν a(ND 2) peaks are distinctly resolved. Upon heating multilayer coverages of formamide, the hydrogen-bonding interactions lead to autocatalytic desorption of formamide at 223 K.

  4. Role of Structure and Glycosylation of Adsorbed Protein Films in Biolubrication

    PubMed Central

    Veeregowda, Deepak H.; Busscher, Henk J.; Vissink, Arjan; Jager, Derk-Jan; Sharma, Prashant K.; van der Mei, Henny C.

    2012-01-01

    Water forms the basis of lubrication in the human body, but is unable to provide sufficient lubrication without additives. The importance of biolubrication becomes evident upon aging and disease, particularly under conditions that affect secretion or composition of body fluids. Insufficient biolubrication, may impede proper speech, mastication and swallowing, underlie excessive friction and wear of articulating cartilage surfaces in hips and knees, cause vaginal dryness, and result in dry, irritated eyes. Currently, our understanding of biolubrication is insufficient to design effective therapeutics to restore biolubrication. Aim of this study was to establish the role of structure and glycosylation of adsorbed protein films in biolubrication, taking the oral cavity as a model and making use of its dynamics with daily perturbations due to different glandular secretions, speech, drinking and eating, and tooth brushing. Using different surface analytical techniques (a quartz crystal microbalance with dissipation monitoring, colloidal probe atomic force microscopy, contact angle measurements and X-ray photo-electron spectroscopy), we demonstrated that adsorbed salivary conditioning films in vitro are more lubricious when their hydrophilicity and degree of glycosylation increase, meanwhile decreasing their structural softness. High-molecular-weight, glycosylated proteins adsorbing in loops and trains, are described as necessary scaffolds impeding removal of water during loading of articulating surfaces. Comparing in vitro and in vivo water contact angles measured intra-orally, these findings were extrapolated to the in vivo situation. Accordingly, lubricating properties of teeth, as perceived in 20 volunteers comprising of equal numbers of male and female subjects, could be related with structural softness and glycosylation of adsorbed protein films on tooth surfaces. Summarizing, biolubrication is due to a combination of structure and glycosylation of adsorbed protein

  5. 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.

  6. Molecular weight distribution effects on the structure of strongly adsorbed polymers by Monte Carlo simulation

    NASA Astrophysics Data System (ADS)

    Kuppa, Vikram K.

    2012-06-01

    Monte Carlo simulations are reported to study the structure of polymers adsorbed from solution onto strongly attractive, perfectly smooth substrates. Six systems spanning a range of molecular weight distributions are investigated with a coarse-grained united atom model for freely rotating chains. By employing a global replica exchange algorithm and topology altering Monte Carlo moves, a range of monomer-surface attraction from weak (0.27kT) to strong (4kT) is simultaneously explored. Thus for the first time ever, equilibrium polymer adsorption on highly attractive surfaces is studied, with all adsorbed molecules displaying similar properties and statistics. The architecture of the adsorbed layers, including density profiles, bond orientation order parameters, radii of gyration, and distribution of the adsorbed chain fractions, is shown to be highly dependent on the polydispersity of the polymer phase. The homology of polymer chains, and the ergodicity of states explored by the molecules is in contrast to the metastable, kinetically constrained paradigm of irreversible adsorption. The structure of more monodisperse systems is qualitatively similar to experimental results and theoretical predictions, but result from very different chain conformations and statistics. The polydispersity-dependent behavior is explained in the context of the competition between polymers to make contact with the surface.

  7. 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.

  8. 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.

  9. Tunability of the Adsorbate Binding on Bimetallic Alloy Nanoparticles for the Optimization of Catalytic Hydrogenation.

    PubMed

    Luo, Long; Duan, Zhiyao; Li, Hao; Kim, Joohoon; Henkelman, Graeme; Crooks, Richard M

    2017-04-07

    In this paper, we show that PtAu and PdAu random alloy dendrimer-encapsulated nanoparticles with an average size of ∼1.6 nm have different catalytic activity trends for allyl alcohol hydrogenation. Specifically, PtAu nanoparticles exhibit a linear increase in activity with increasing Pt content, whereas PdAu dendrimer-encapsulated nanoparticles show a maximum activity at a Pd content of ∼60%. Both experimental and theoretical results suggest that this contrasting behavior is caused by differences in the strength of H binding on the PtAu and PdAu alloy surfaces. The results have significant implications for predicting the catalytic performance of bimetallic nanoparticles on the basis of density functional theory calculations.

  10. DFT and TB study of the geometry of hydrogen adsorbed on graphynes

    NASA Astrophysics Data System (ADS)

    Lee, Hunpyo; Koo, Jahyun; Capone, Massimo; Kwon, Yongkyung; Lee, Hoonkyung

    2014-09-01

    Using density-functional calculations (DFT) and a tight-binding model, we investigate the origin of distinct favorable geometries which depend on the type of graphyne used. The change in the H geometry is described in terms of the tuning of the hopping between sp2-bonded C atoms and sp-bonded C atoms hybridized with the H atoms. We find that the different preferred geometry for each type of graphyne is associated with the electronic effects due to different symmetries rather than a steric effect minimizing the repulsive interaction between the H atoms. The band gaps are significantly tuned as the hopping varies, except in α-graphyne, in agreement with the result of our previous DFT study (Koo J et al 2013 J. Phys. Chem. C 117 11960). Our model can be used to describe the geometry and electronic properties of hydrogenated graphynes.

  11. Reactions of hydrogen atoms with acetone monolayers adsorbed on graphite monolayer covered Pt(111) surfaces

    NASA Astrophysics Data System (ADS)

    Dinger, A.; Lutterloh, C.; Biener, J.; Küppers, J.

    1999-08-01

    Acetone monolayers were prepared on C covered Pt(111) surfaces and exposed to gaseous H(D) atoms at 90 K. Reaction products were investigated with HREELS and TDS methods. Two major reaction pathways were identified: (1) transformation of acetone to isopropanol via two consecutive hydrogenation steps; (2) H abstraction from acetone methyl groups with subsequent rehydrogenation of the methylene group. Since two-fold H abstraction from the isopropanol product restores the acetone surface reactant, an equilibrium between acetone and isopropanol is established on the surface. This equilibrium is perturbed by side reactions in which propane, propene and water are formed, e.g. via OH abstraction from isopropanol. The cross-sections of the H induced reactions of a few tenths of an angstrom squared are compatible with the operation of an Eley-Rideal mechanism.

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

    DOE PAGES

    Tan, Teck L.; Wang, Lin -Lin; Zhang, Jia; ...

    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

  13. 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.

  14. Hot-atom versus Eley-Rideal dynamics in hydrogen recombination on Ni(100). I. The single-adsorbate case.

    PubMed

    Martinazzo, R; Assoni, S; Marinoni, G; Tantardini, G F

    2004-05-08

    We compare the efficiency of the Eley-Rideal (ER) reaction with the formation of hot-atom (HA) species in the simplest case, i.e., the scattering of a projectile off a single adsorbate, considering the Hydrogen and Hydrogen-on-Ni(100) system. We use classical mechanics and the accurate embedded diatomics-in-molecules potential to study the collision system over a wide range of collision energies (0.10-1.50 eV), both with a rigid and a nonrigid Ni substrate and for impact on the occupied and neighboring empty cells. In the rigid model metastable and truly bound hot-atoms occur and we find that the cross section for the formation of bound hot-atoms is considerably higher than that for the ER reaction over the whole range of collision energies examined. Metastable hot-atoms form because of the inefficient energy transfer to the adsorbate and have lifetimes of the order 0.1-0.7 ps, depending on the collision energy. When considering the effects of lattice vibrations we find, on average, a consistent energy transfer to the substrate, say 0.1-0.2 eV, which forced us to devise a two-step dynamical model to get rid of the problems associated with the use of periodic boundary conditions. Results for long-lived HA formation due to scattering on the occupied cell at a surface temperature of 120 K agree well with those of the rigid model, suggesting that in the above process the substrate plays only a secondary role and further calculations at surface temperatures of 50 and 300 K are in line with these findings. However, considerably high cross sections for formation of long-lived hot-atoms result also from scattering off the neighboring cells where the energy transfer to the lattice cannot be neglected. Metastable hot-atoms are reduced in number and have usually lifetimes shorter than those of the rigid-model, say less than 0.3 ps. In addition, ER cross sections are only slightly affected by the lattice motion and show a little temperature dependence. Finally, we find also

  15. 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.

  16. Capturing the Local Adsorption Structures of Carbon Dioxide in Polyamine-Impregnated Mesoporous Silica Adsorbents.

    PubMed

    Huang, Shing-Jong; Hung, Chin-Te; Zheng, Anmin; Lin, Jen-Shan; Yang, Chun-Fei; Chang, Yu-Chi; Deng, Feng; Liu, Shang-Bin

    2014-09-18

    Interactions between amines and carbon dioxide (CO2) are essential to amine-functionalized solid adsorbents for carbon capture, and an in-depth knowledge of these interactions is crucial to adsorbent design and fabrication as well as adsorption/desorption processes. The local structures of CO2 adsorbed on a tetraethylenepentamine-impregnated mesoporous silica SBA-15 were investigated by solid-state (13)C{(14)N} S-RESPDOR MAS NMR technique and theoretical DFT calculations. Two types of adsorption species, namely, secondary and tertiary carbamates as well as distant ammonium groups were identified together with their relative concentrations and relevant (14)N quadrupolar parameters. Moreover, a dipolar coupling of 716 Hz was derived, corresponding to a (13)C-(14)N internuclear distance of 1.45 Å. These experimental data are in excellent agreement with results obtained from DFT calculations, revealing that the distribution of surface primary and secondary amines readily dictates the CO2 adsorption/desorption properties of the adsorbent.

  17. Structure and chemical composition of layers adsorbed at interfaces with champagne.

    PubMed

    Aguié-Béghin, V; Adriaensen, Y; Péron, N; Valade, M; Rouxhet, P; Douillard, R

    2009-11-11

    The structure and the chemical composition of the layer adsorbed at interfaces involving champagne have been investigated using native champagne, as well as ultrafiltrate (UFch) and ultraconcentrate (UCch) obtained by ultrafiltration with a 10(4) nominal molar mass cutoff. The layer adsorbed at the air/liquid interface was examined by surface tension and ellipsometry kinetic measurements. Brewster angle microscopy demonstrated that the layer formed on polystyrene by adsorption or drop evaporation was heterogeneous, with a domain structure presenting similarities with the layer adsorbed at the air/liquid interface. The surface chemical composition of polystyrene with the adlayer was determined by X-ray photoelectron spectroscopy (XPS). The contribution of champagne constituents varied according to the liquid (native, UFch, and UCch) and to the procedure of adlayer formation (evaporation, adsorption, and adsorption + rinsing). However, their chemical composition was not significantly influenced either by ultrafiltration or by the procedure of deposition on polystyrene. Modeling this composition in terms of classes of model compounds gave approximately 35% (w/w) of proteins and 65% (w/w) of polysaccharides. In the adlayer, the carboxyl groups or esters represent about 18% of carbon due to nonpolypeptidic compounds, indicating the presence of either uronic acids in the complex structure of pectic polysaccharides or of polyphenolic esters. This structural and chemical information and its relationship with the experimental procedures indicate that proteins alone cannot be used as a realistic model for the macromolecules forming the adsorption layer of champagne. Polysaccharides, the other major macromolecular components of champagne wine, are assembled with proteins at the interfaces, in agreement with the heterogeneous character of the adsorbed layer at interfaces.

  18. Controlling the Electronic Structure of Graphene Using Surface-adsorbate Interactions

    DTIC Science & Technology

    2015-07-21

    between nonhybridized states at the K point. Here we use alkali - metal adsorbate to reduce and even eliminate this energy gap, and also identify a new...cone after intercalation [12,17]. However, studies of alkali - metal intercalants have resulted *piotr.matyba@jila.colorado.edu in severe...studies, are not understood. We note that adsorption of alkali metals on top of graphene inducen doping and was used to control the electronic structure

  19. Self-consistent structure of metallic hydrogen

    NASA Technical Reports Server (NTRS)

    Straus, D. M.; Ashcroft, N. W.

    1977-01-01

    A calculation is presented of the total energy of metallic hydrogen for a family of face-centered tetragonal lattices carried out within the self-consistent phonon approximation. The energy of proton motion is large and proper inclusion of proton dynamics alters the structural dependence of the total energy, causing isotropic lattices to become favored. For the dynamic lattice the structural dependence of terms of third and higher order in the electron-proton interaction is greatly reduced from static lattice equivalents.

  20. 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.

  1. The quantum dynamics of interfacial hydrogen: Path integral maximum entropy calculation of adsorbate vibrational line shapes for the H/Ni(111) system

    NASA Astrophysics Data System (ADS)

    Kim, Dongsup; Doll, J. D.; Gubernatis, J. E.

    1997-01-01

    Vibrational line shapes for a hydrogen atom on an embedded atom model (EAM) of the Ni(111) surface are extracted from path integral Monte Carlo data. Maximum entropy methods are utilized to stabilize this inversion. Our results indicate that anharmonic effects are significant, particularly for vibrational motion parallel to the surface. Unlike their normal mode analogs, calculated quantum line shapes for the EAM potential predict the correct ordering of vibrational features corresponding to parallel and perpendicular adsorbate motion.

  2. Structure and Redox Properties of 5-Amino-3-nitro-1H-1,2,4-triazole (ANTA) Adsorbed on a Silica Surface: A DFT M05 Computational Study.

    PubMed

    Sviatenko, Liudmyla K; Gorb, Leonid; Hill, Frances C; Leszczynska, Danuta; Leszczynski, Jerzy

    2015-07-23

    A cluster approximation was applied at the M05/tzvp level to model an adsorption of 5-amino-3-nitro-1H-1,2,4-triazole (ANTA) on the (001) surface of α-quartz. Structures of the obtained ANTA-silica complexes confirm a nearly parallel orientation of the nitro compound toward the surface. The atoms in molecules (AIM) method was applied to analyze binding between ANTA and the silica surface. Attachment or loss of an electron was found to lead to a significant deviation from coplanarity in the complexes and to a strengthening of a hydrogen bonding. Redox properties of the adsorbed ANTA were compared with those of gas-phase and hydrated species by calculation of the ionization potential, electron affinity, oxidation and reduction Gibbs free energies, and oxidation and reduction potentials. It was shown that the adsorbed ANTA has a lower ability to undergo redox transformations as compared to that of the hydrated one.

  3. Structure, Dynamics, and Thermodynamics of Small Molecules Adsorbed in Zeolite Micropores: Simulation and Statistical Mechanics.

    NASA Astrophysics Data System (ADS)

    van Tassel, Paul Robert

    1993-01-01

    This thesis describes a fully detailed molecular simulation and modeling effort aimed at understanding the fundamentals of adsorption and diffusion of small molecules in zeolite micropores. The primary emphasis is on determining the relationship between the structure and chemistry of the zeolite adsorbent and the structure, dynamics, and thermodynamics of the adsorbed phase. Further emphasis is on developing simple, predictive models of zeolite adsorption and diffusion. We begin by presenting a Monte Carlo simulation of single component adsorption of xenon, methane, and argon in zeolite NaA. The form of the adsorbate density distribution indicates the presence of discrete adsorption sites which arrange in polyhedra whose geometry depends on the number and position of zeolite framework ions. Isotherm plateaus are attributed to either (i) a low energy adsorbate configuration or (ii) the saturation of polyhedral sites. Viewing the adsorbed phase as an ordered arrangement differs from the conventional delocalized model, yet it helps explain certain experimental observations. Next, a study of binary mixtures of small molecules in zeolite NaA using the Monte Carlo method is presented. The mixing in the pore is determined to be highly nonideal by comparison to a simple pore volume filling model. Strong selectivity for a more polarizable molecule (xenon) is observed only at low pore loading. At higher pore loading, a smaller, less polarizable molecule (argon) adsorbs selectively at a significantly lower pressure than predicted by the model. This enhanced selectivity is due to the ability of the smaller molecule to pack more efficiently inside of the pore. Finally, we present two simple lattice models whose forms are arrived at following careful consideration of simulation results. The first describes the adsorption of small molecules in a zeolite. A polyhedral lattice is postulated whose neighboring sites interact energetically and entropically. The second model describes

  4. 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.

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

    DOE PAGES

    Carrillo, Jan-Michael Y.; Cheng, Shiwang; Kumar, Rajeev; ...

    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

  6. Structure of an adsorbed dimyristoylphosphatidylcholine bilayer measured with specular reflection of neutrons.

    PubMed Central

    Johnson, S J; Bayerl, T M; McDermott, D C; Adam, G W; Rennie, A R; Thomas, R K; Sackmann, E

    1991-01-01

    Using specular reflection of neutrons, we investigate for the first time the structure of a single dimyristoylphosphatidylcholine bilayer adsorbed to a planar quartz surface in an aqueous environment. We demonstrate that the bilayer is strongly adsorbed to the quartz surface and is stable to phase state changes as well as exchange of the bulk aqueous phase. Our results show that the main phase transition is between the L alpha phase and the metastable L beta'* phase, with formation of the P beta' ripple phase prevented by lateral stress on the adsorbed bilayer. By performing contrast variation experiments, we are able to elucidate substantial detail in the interfacial structure. We measure a bilayer thickness of 43.0 +/- 1.5 A in the L alpha phase (T = 31 degrees C) and 46.0 +/- 1.5 A in the L beta'* phase (T = 20 degrees C). The polar head group is 8.0 +/- 1.5 A thick in the L alpha phase. The water layer between the quartz and bilayer is 30 +/- 10 A for the lipid in both the L alpha and L'* phase. Our results agree well with those previously reported from experiments using lipid vesicles and monolayers, thus establishing the feasibility of our experimental methods. PMID:2009353

  7. Structure study of oxygen-adsorbed Ni(111) surface by high energy ion scattering

    NASA Astrophysics Data System (ADS)

    Narusawa, T.; Gibson, W. M.; Törnqvist, E.

    1982-01-01

    Surface atomic structures of clean, oxygen-adsorbed, and oxidized (111) nickel have been studied quantitatively by using MeV ion scattering in combination with AES and MEED. We show that; the clean (111) nickel surface has the bulk-like structure with reconstruction or relaxation less than 0.02 Å, the surface thermal vibration amplitude is enhanced by ~20% compared to the bulk value, adsorbed oxygen results in surface lattice expansion by ~0.15 Å which is closely correlated to the p(2 × 2) or (√3 × √3) R30° superstructure, and oxidation at room temperature saturates at a stage which incorporates ~ 3 monolayers of nickel in a stoichiometric amorphous film of NiO whereas at temperatures higher than ~200° C thicker oxide films are produced. Our study indicates that each oxygen atom adsorbed on the Ni(111) surface interacts with and relaxes three nearest neighbor nickel atoms, and after saturation of the relaxation, oxidation of three monolayers takes place abruptly after which the oxide layer on the surface apparently blocks further reaction.

  8. Structure study of oxygen-adsorbed Ni(111) surface by high energy for scattering

    NASA Astrophysics Data System (ADS)

    Narusawa, T.; Gibson, W. M.; Toerngrist, E.

    1981-11-01

    Surface atomic structures of clean, oxygen-adsorbed, and oxidized (111) nickel have been studied quantitatively by using MeV ion scattering in combination with AES and MEED. We show that; the clean (111) nickel surface has the bulk-like structure with reconstruction or relaxation less than 0.02 A, the surface thermal vibration amplitude is enhanced by approx. 20% compared to the bulk value, adsorbed oxygen results in surface lattice expansion by approx. 0.15 A which is closely correlated to the p(2x2) or (sq root 3 times sq root 3)R30 degrees superstructure, and oxidation at room temperature saturates at a stage which incorporates approx. 3 monolayers of nickel in a stoichiometric amorphous film of NiO whereas at temperatures higher than approx. 200 C thicker oxide films are produced. Our study indicates that each oxygen atom adsorbed on the Ni(111) surface interacts with and relaxes three nearest neighbor nickel atoms, and after saturation of the relaxation, oxidation of three monolayers takes place abruptly after which the oxide layer on the surface apparently blocks further reaction.

  9. Adsorbate-induced modification of electronic band structure of epitaxial Bi(111) films

    NASA Astrophysics Data System (ADS)

    Matetskiy, A. V.; Bondarenko, L. V.; Tupchaya, A. Y.; Gruznev, D. V.; Eremeev, S. V.; Zotov, A. V.; Saranin, A. A.

    2017-06-01

    Changes of the electronic band structure of Bi(111) films on Si(111) induced by Cs and Sn adsorption have been studied using angle-resolved photoemission spectroscopy and density functional theory calculations. It has been found that small amounts of Cs when it presents at the surface in a form of the adatom gas leads to shifting of the surface and quantum well states to the higher binding energies due to the electron donation from adsorbate to the Bi film. In contrast, adsorbed Sn dissolves into the Bi film bulk upon heating and acts as an acceptor dopant, that results in shifting of the surface and quantum well states upward to the lower binding energies. These results pave the way to manipulate with the Bi thin film electron band structure allowing to achieve a certain type of conductivity (electron or hole) with a single spin channel at the Fermi level making the adsorbate-modified Bi a reliable base for prospective spintronics applications.

  10. The effect of gold nanoparticle structure on the conformation and function of adsorbed proteins

    NASA Astrophysics Data System (ADS)

    Gagner, Jennifer E.

    Many applications of nanobiomaterials rely on or are enhanced by specific, protein-mediated interactions with biological systems. These interactions can be engineered by chemically modifying the surface of the material to affect protein adsorption, or by altering the topography of the nanoscale surface. The attachment or adsorption of proteins onto materials can greatly affect the structure and subsequent function of those proteins, giving rise to unpredictable and potentially undesirable effects. Thus, it is essential to develop a detailed understanding of how nanostructured surface characteristics, such as atomic-scale topography, surface energy, and chemical structure may affect protein adsorption, structure, function, and stability. The presented work on gold nanoparticles (AuNP) in the forms of spheres (AuNS), rods (AuNR), cubes (AuNC) and octahedra (AuNO) will elucidate the effect of nanoparticle morphology on adsorbed model proteins lysozyme (Lyz) and α-chymotrypsin (ChT). It has been found that nanoparticle morphology does affect the structure of adsorbed proteins as well as the extent of the surface coverage; however, the final form of the nano-bio conjugate is protein specific. Lyz conjugates underwent loss of structure and rapid aggregation regardless of AuNP morphology; however, ChT conjugates exhibited no structure loss when immobilized on AuNS, and a significant, loading specific structure loss when adsorbed on AuNR. Further work will be presented on efforts to determine the role of crystal structure, surface energy, and ligand chemistry on adsorbed proteins. Wet chemical methods are used to synthesize AuNC with f100g facets and AuNO with f111g facets. Nanoparticles are characterized through electron microscopy, X-ray and electron diffraction, X-ray photoelectron spectroscopy and inductively coupled plasma mass spectroscopy. Protein conjugation and changes in protein structure are monitored through a variety of physical and spectroscopic techniques

  11. 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.

  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. Octahedral palladium nanoparticles as excellent hosts for electrochemically adsorbed and absorbed hydrogen.

    PubMed

    Zalineeva, Anna; Baranton, Stève; Coutanceau, Christophe; Jerkiewicz, Gregory

    2017-02-01

    We report new results for electrochemical H adsorption on and absorption in octahedral palladium nanoparticles (Pd-NPs) with an average tip-to-tip size of 7.8 nm and a narrow size distribution. They reveal a very high H loading of 0.90 that cannot be achieved using bulk Pd materials or larger NPs; this behavior is assigned to a combination of two factors: their small size and face morphology. Temperature-dependent cyclic voltammetry (CV) studies in the range of 296 to 333 K reveal unique features that are attributed to electrochemical H adsorption, H absorption, and H2 generation. The CV features are used to prepare H adsorption and absorption isotherms that are then used in thermodynamic data analysis. Modeling of the experimental results demonstrates that, upon H adsorption and absorption, Pd-NPs develop a core-shell-skin structure, each with its unique H loading. The electrochemical results obtained for octahedral Pd-NPs are compared to analogous data obtained for cubic Pd-NPs with a similar size as well as for larger cubic Pd-NPs and bulk materials under gas-phase conditions.

  14. Octahedral palladium nanoparticles as excellent hosts for electrochemically adsorbed and absorbed hydrogen

    PubMed Central

    Zalineeva, Anna; Baranton, Stève; Coutanceau, Christophe; Jerkiewicz, Gregory

    2017-01-01

    We report new results for electrochemical H adsorption on and absorption in octahedral palladium nanoparticles (Pd-NPs) with an average tip-to-tip size of 7.8 nm and a narrow size distribution. They reveal a very high H loading of 0.90 that cannot be achieved using bulk Pd materials or larger NPs; this behavior is assigned to a combination of two factors: their small size and face morphology. Temperature-dependent cyclic voltammetry (CV) studies in the range of 296 to 333 K reveal unique features that are attributed to electrochemical H adsorption, H absorption, and H2 generation. The CV features are used to prepare H adsorption and absorption isotherms that are then used in thermodynamic data analysis. Modeling of the experimental results demonstrates that, upon H adsorption and absorption, Pd-NPs develop a core-shell-skin structure, each with its unique H loading. The electrochemical results obtained for octahedral Pd-NPs are compared to analogous data obtained for cubic Pd-NPs with a similar size as well as for larger cubic Pd-NPs and bulk materials under gas-phase conditions. PMID:28168217

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

    NASA Astrophysics Data System (ADS)

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

    2015-11-01

    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.

  16. Hydrogen adsorbed in a metal organic framework-5: coupled translation-rotation eigenstates from quantum five-dimensional calculations.

    PubMed

    Matanović, Ivana; Belof, Jonathan L; Space, Brian; Sillar, Kaido; Sauer, Joachim; Eckert, Juergen; Bačić, Zlatko

    2012-07-07

    We report rigorous quantum five-dimensional (5D) calculations of the coupled translation-rotation (T-R) eigenstates of a H(2) molecule adsorbed in metal organic framework-5 (MOF-5), a prototypical nanoporous material, which was treated as rigid. The anisotropic interactions between H(2) and MOF-5 were represented by the analytical 5D intermolecular potential energy surface (PES) used previously in the simulations of the thermodynamics of hydrogen sorption in this system [Belof et al., J. Phys. Chem. C 113, 9316 (2009)]. The global and local minima on this 5D PES correspond to all of the known binding sites of H(2) in MOF-5, three of which, α-, β-, and γ-sites are located on the inorganic cluster node of the framework, while two of them, the δ- and ε-sites, are on the phenylene link. In addition, 2D rotational PESs were calculated ab initio for each of these binding sites, keeping the center of mass of H(2) fixed at the respective equilibrium geometries; purely rotational energy levels of H(2) on these 2D PESs were computed by means of quantum 2D calculations. On the 5D PES, the three adjacent γ-sites lie just 1.1 meV above the minimum-energy α-site, and are separated from it by a very low barrier. These features allow extensive wave function delocalization of even the lowest translationally excited T-R eigenstates over the α- and γ-sites, presenting significant challenges for both the quantum bound-state calculations and the analysis of the results. Detailed comparison is made with the available experimental data.

  17. Hydrogen adsorbed in a metal organic framework-5: Coupled translation-rotation eigenstates from quantum five-dimensional calculations

    NASA Astrophysics Data System (ADS)

    Matanović, Ivana; Belof, Jonathan L.; Space, Brian; Sillar, Kaido; Sauer, Joachim; Eckert, Juergen; Bačić, Zlatko

    2012-07-01

    We report rigorous quantum five-dimensional (5D) calculations of the coupled translation-rotation (T-R) eigenstates of a H2 molecule adsorbed in metal organic framework-5 (MOF-5), a prototypical nanoporous material, which was treated as rigid. The anisotropic interactions between H2 and MOF-5 were represented by the analytical 5D intermolecular potential energy surface (PES) used previously in the simulations of the thermodynamics of hydrogen sorption in this system [Belof et al., J. Phys. Chem. C 113, 9316 (2009), 10.1021/jp901988e]. The global and local minima on this 5D PES correspond to all of the known binding sites of H2 in MOF-5, three of which, α-, β-, and γ-sites are located on the inorganic cluster node of the framework, while two of them, the δ- and ɛ-sites, are on the phenylene link. In addition, 2D rotational PESs were calculated ab initio for each of these binding sites, keeping the center of mass of H2 fixed at the respective equilibrium geometries; purely rotational energy levels of H2 on these 2D PESs were computed by means of quantum 2D calculations. On the 5D PES, the three adjacent γ-sites lie just 1.1 meV above the minimum-energy α-site, and are separated from it by a very low barrier. These features allow extensive wave function delocalization of even the lowest translationally excited T-R eigenstates over the α- and γ-sites, presenting significant challenges for both the quantum bound-state calculations and the analysis of the results. Detailed comparison is made with the available experimental data.

  18. Structural changes of silica mesocellular foam supported amine-functionalized CO2 adsorbents upon exposure to steam.

    PubMed

    Li, Wen; Bollini, Praveen; Didas, Stephanie A; Choi, Sunho; Drese, Jeffrey H; Jones, Christopher W

    2010-11-01

    Three classes of amine-functionalized mesocellular foam (MCF) materials are prepared and evaluated as CO(2) adsorbents. The stability of the adsorbents under steam/air and steam/nitrogen conditions is investigated using a Parr autoclave reactor to simulate, in an accelerated manner, the exposure that such adsorbents will see under steam stripping regeneration conditions at various temperatures. The CO(2) capacity and organic content of all adsorbents decrease after steam treatment under both steam/air and steam/nitrogen conditions, primarily due to structural collapse of the MCF framework, but with additional contributions likely associated with amine degradation during treatment under harsh conditions. Treatment with steam/air is found to have stronger effect on the CO(2) capacity of the adsorbents compared to steam/nitrogen.

  19. Molecular Weight Distribution Effects on the Structure of Strongly Adsorbed Polymers by Monte Carlo Simulation

    NASA Astrophysics Data System (ADS)

    Kuppa, Vikram

    2012-02-01

    Monte Carlo simulations are used to investigate the adsorption of polymers from solution onto strongly attractive, perfectly smooth substrates. Using a coarse-grained united atom model for freely rotating polymer chains, three systems with different polydispersities are studied. The structure of the adsorbed layers, exemplified by density profiles, bond orientation order parameters, radii of gyration, and distribution of the adsorbed chain fractions, is shown to be highly dependent on the molecular weight distribution of the polymer phase. The results for the more monodisperse polymer systems are qualitatively similar to experimental and theoretical investigations, but devolve from very different chain conformations and statistics. For the first time ever, equilibrium polymer adsorption on highly attractive surface is studied, with all molecules in the adsorbed layers demonstrated to be indistinguishable from each other. The ergodicity of states explored by the polymer chains is in contrast to the kinetically constrained viewpoint of irreversible adsorption, and the observed behavior is explained in the context of the competition between polymers to make contact with the surface.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. The role of surface oxygenated-species and adsorbed hydrogen in the oxygen reduction reaction (ORR) mechanism and product selectivity on Pd-based catalysts in acid media.

    PubMed

    Rahul, R; Singh, R K; Bera, B; Devivaraprasad, R; Neergat, M

    2015-06-21

    Oxygen reduction reaction (ORR) is investigated on bulk PdO-based catalysts (oxides of Pd and Pd3Co) in oxygen-saturated 0.1 M HClO4 to establish the role of surface oxides and adsorbed hydrogen in the activity and product selectivity (H2O/H2O2). The initial voltammetric features suggest that the oxides are inactive toward ORR. The evolution of the ORR voltammograms and potential-dependent H2O2 generation features on the PdO catalyst suggest gradual and parallel in situ reduction of the bulk PdO phase below ∼0.4 V in the hydrogen underpotential deposition (Hupd) region; the reduction of the bulk PdO catalyst is confirmed from the X-ray photoelectron spectra (XPS) and X-ray diffraction (XRD) patterns. The potential-dependent H2O2 generation features originate due to the presence of surface oxides and adsorbed hydrogen; this is further confirmed using halide ions (Cl(-) and Br(-)) and peroxide as the external impurities.

  7. Metal organoclays with compacted structure for truly physical capture of hydrogen

    NASA Astrophysics Data System (ADS)

    Tahir, M. Nazir; Sennour, Radia; Arus, Vasilica Alisa; Sallam, Lamyaa M.; Roy, René; Azzouz, Abdelkrim

    2017-03-01

    Truly reversible capture of hydrogen was achieved at ambient conditions on Pd-loaded organo-montmorillonites obtained by photo-addition of different thiols on propargylated-TRIS cations already grafted on the clay surface. TEM insights showed that more than 90% of Pd0 incorporated occur as 0.3-0.5 nm subnanoparticles (PdSNPs). XPS and NMR analyses revealed simultaneous strong S:Pd0 and O:Pd0 interactions that "cement" the organic moiety around PdSNPs. The significant decrease in porosity suggests a compacted structure that impedes not only metal aggregation, but also hydrogen diffusion in the metal bulk. Thus, hydrogen appears to adsorb mainly via physical condensation around PdSNPs. These thiol-clay matrices showed hydrogen surface affinity factors of up to 0.51 mmol m-2 at ambient temperature and pressure. This is higher than those reported for much more sophisticated materials. DSC measurements showed very low desorption heat between 20 and 80 °C. Hydrogen release was achieved merely under vacuum or slight heating starting from 40 °C and was almost completed up to 85 °C. This provides a proof of concept of truly reversible capture of hydrogen for concentration and/or storage purposes. Such a performance has never been achieved at ambient temperature and pressure. These findings open new prospects to develop low-cost materials for reversible hydrogen storage without energy and safety constraints.

  8. 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.

  9. 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].

  10. Adsorbate-induced structural changes in 1-3 nm platinum nanoparticles.

    PubMed

    Lei, Yu; Zhao, Haiyan; Rivas, Rosa Diaz; Lee, Sungsik; Liu, Bin; Lu, Junling; Stach, Eric; Winans, Randall E; Chapman, Karena W; Greeley, Jeffrey P; Miller, Jeffrey T; Chupas, Peter J; Elam, Jeffrey W

    2014-07-02

    We investigated changes in the Pt-Pt bond distance, particle size, crystallinity, and coordination of Pt nanoparticles as a function of particle size (1-3 nm) and adsorbate (H2, CO) using synchrotron radiation pair distribution function (PDF) and X-ray absorption spectroscopy (XAS) measurements. The ∼1 nm Pt nanoparticles showed a Pt-Pt bond distance contraction of ∼1.4%. The adsorption of H2 and CO at room temperature relaxed the Pt-Pt bond distance contraction to a value close to that of bulk fcc Pt. The adsorption of H2 improved the crystallinity of the small Pt nanoparticles. However, CO adsorption generated a more disordered fcc structure for the 1-3 nm Pt nanoparticles compared to the H2 adsorption Pt nanoparticles. In situ XANES measurements revealed that this disorder results from the electron back-donation of the Pt nanoparticles to CO, leading to a higher degree of rehybridization of the metal orbitals in the Pt-adsorbate system.

  11. 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.

  12. a Monte Carlo Study of Carbon Monoxide Layers Adsorbed on Ionic Substrates:. Structures and Phase Transitions

    NASA Astrophysics Data System (ADS)

    Vu, Ngoc-Thanh; Jack, David B.

    We have studied the order-disorder phase transitions of carbon monoxide layers adsorbed on sodium chloride and lithium flouride substrates using the Metropolis Monte Carlo method. The simulations have been performed in the temperature range from 5 K to 60 K. At low temperature and monolayer coverage, both of these systems form ordered phases which disorder as the temperature is increased. The transition temperature (Tc) is between 30 K and 35 K for CO/NaCl, and from 40 K to 45 K for CO/LiF. Below Tc, both systems have an ordered p(2 × 1) type structure due to correlated azimuthal orientations. Above Tc, both systems undergo a phase transition to an azimuthally disordered p(1 × 1) structure, i.e. one with no preferred orientation in the surface plane. The heat capacity shows a characteristic divergence at the transition temperature. Coverages of less than a monolayer of the CO/NaCl system have also been studied. The CO molecules are found to aggregate and form islands with an ordered structure in the middle of the islands. These islands also undergo an order-disorder transition but at lower temperatures. Multilayer systems were found to destabilize the p(2 × 1) structure of the bottommost layer in favor of a p(1 × 1) structure with the upper layers adopting the bulk structure.

  13. Crystal structure of tris-(piperidinium) hydrogen sulfate sulfate.

    PubMed

    Lukianova, Tamara J; Kinzhybalo, Vasyl; Pietraszko, Adam

    2015-12-01

    In the title molecular salt, 3C5H12N(+)·HSO4 (-)·SO4 (2-), each cation adopts a chair conformation. In the crystal, the hydrogen sulfate ion is connected to the sulfate ion by a strong O-H⋯O hydrogen bond. The packing also features a number of N-H⋯O hydrogen bonds, which lead to a three-dimensional network structure. The hydrogen sulfate anion accepts four hydrogen bonds from two cations, whereas the sulfate ion, as an acceptor, binds to five separate piperidinium cations, forming seven hydrogen bonds.

  14. 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.

  15. Effect of Various Factors on Hydrogen Embrittlement of Structural Steels

    NASA Astrophysics Data System (ADS)

    Khanzhin, V. G.; Turilina, V. Yu.; Rogachev, S. O.; Nikitin, A. V.; Belov, V. A.

    2015-07-01

    Results of studies of hydrogen embrittlement of structural steels of different strength are presented. The effect of various factors on delayed hydrogen fracture is analyzed using the results of investigations by the methods of acoustic emission, metallography and fractography of bolts under the conditions of tension with bending after galvanic hydrogen charging.

  16. Effect of edge structure on the activity for hydrogen evolution reaction in MoS2 nanoribbons

    NASA Astrophysics Data System (ADS)

    Liu, Lili; Li, Xiuyan; Xu, Li-Chun; Liu, Ruiping; Yang, Zhi

    2017-02-01

    Density functional theory (DFT) was carried out to investigate the effect of edge structure on the catalytic activity and electronic properties of MoS2 nanoribbons for hydrogen evolution reaction (HER). There are two stable configurations of MoS2 nanoribbons, MoS2NR-L and MoS2NR-R, with an energy barrier of 0.035 eV. Four hydrogen adsorbed configurations are obtained by adsorbing the hydrogen atom at the different adsorption sites of two configurations. By calculating the Gibbs free energy and exchange current densities, it is found that these four adsorbed configurations have varied catalytic activity for HER, which demonstrates that location of edge atoms has significantly effect on the catalytic activity for HER. The optimization in HER activities originates from the suitable binding between hydrogen atom and S atom, corresponding to that Gibbs free energy is close to zero. Our results signify that the edge structures play a key role on the HER activity in MoS2 nanoribbons.

  17. Thiphene hydrodesulfurization over rhenium surfaces: The effects of structure and adsorbates (C and S)

    SciTech Connect

    Bussell, M.E.; Somorjai, G.A. )

    1989-03-09

    Thiophene hydrodesulfurization (HDS) has been investigated over rhenium single crystals and polycrystalline foils and was found to be a structure-sensitive reaction over these surfaces. Rhenium single crystals are 1-6 times more active than molybdenum single crystals, which is in agreement with previous studies using rhenium disulfide and molybdenum disulfide catalysts. Adsorbed carbon and sulfur overlayers decrease the activity of the rhenium single crystals, suggesting that the catalyst surface remain free of strongly bound deposits of carbon and/or sulfur. The trend in HDS activity measured for the Re catalyst can be explained by considering the difference in coordination of the top layer rhenium atoms in the single-crystal surfaces.

  18. Hydrogen and the structure of transition aluminas

    SciTech Connect

    Sohlberg, K.; Pennycook, S.J.; Pantelides, S.T.

    1999-08-25

    {alpha}-Alumina results from the complete dehydration of several minerals of the form Al{sub 2}O{sub 3}{center{underscore}dot}nH{sub 2}O. The ``transition'' aluminas, {gamma}-alumina, {eta}-alumina, and {delta}-alumina are known to have a spinel structure but the possibility that they contain hydrogen (H) has been the subject of debate. The authors present a series of density-functional theory calculations which, together with available experimental data, show that the spinel aluminas exist over a range of hydrogen content captured by the empirical formula H{sub 3m}Al{sub 2{minus}m}O{sub 3}, with a different greek-letter phases corresponding to different distributions of the Aluminum (Al) ions on the two cation sublattices. Calculations of densities and vibrational frequencies of bulk OH bonds are in excellent agreement with available data. The theory reconciles seemingly inconsistent data and reveals a remarkable property of the spinel aluminas: They are ``reactive sponges'' in that they can store and release water in a reactive way. This chemical activity offers a basis for understanding long-standing puzzles in the behavior of aluminas in catalytic systems.

  19. Theoretical predictions of structures in dispersions containing charged colloidal particles and non-adsorbing polymers.

    PubMed

    Xie, Fei; Turesson, Martin; Woodward, Clifford E; van Gruijthuijsen, Kitty; Stradner, Anna; Forsman, Jan

    2016-04-28

    We develop a theoretical model to describe structural effects on a specific system of charged colloidal polystyrene particles, upon the addition of non-adsorbing PEG polymers. This system has previously been investigated experimentally, by scattering methods, so we are able to quantitatively compare predicted structure factors with corresponding experimental data. Our aim is to construct a model that is coarse-grained enough to be computationally manageable, yet detailed enough to capture the important physics. To this end, we utilize classical polymer density functional theory, wherein all possible polymer configurations are accounted for, subject to a mean-field Boltzmann weight. We make efforts to counteract drawbacks with this mean-field approach, resulting in structural predictions that agree very well with computationally more demanding simulations. Electrostatic interactions are handled at the fully non-linear Poisson-Boltzmann level, and we demonstrate that a linearization leads to less accurate predictions. The particle charge is an experimentally unknown parameter. We define the surface charge such that the experimental and theoretical gel point at equal polymer concentration coincide. Assuming a fixed surface charge for a certain salt concentration, we find very good agreements between measured and predicted structure factors across a wide range of polymer concentrations. We also present predictions for other structural quantities, such as radial distribution functions, and cluster size distributions. Finally, we demonstrate that our model predicts the occurrence of equilibrium clusters at high polymer concentrations, but low particle volume fractions and salt levels.

  20. 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.

  1. Theoretical study of successive hydrogenations of small platinum clusters: structure and energetics

    SciTech Connect

    Minot, C.; Bigot, B.; Hariti, A.

    1986-01-22

    The successive hydrogenations, up to saturation, of the most stable small platinum clusters Pt/sub n/ (n = 2-13) are studied by the extended Huckel method with (EHT-SO) and without (EHT) spin-orbit coupling. For each hydrogenation step, a large number of possible structures has been calculated in order to determine the stereochemistry of the best stepwise hydrogenated compounds. The results indicate that the energies of the first successive steps of dihydrogen adsorptions on the small clusters decrease stepwise with the hydrogenation rate, except for a few steps which are discussed. In these conditions, if the hydrogenation reactions are either under thermodynamic control or under kinetic control with activation energies related to the reaction enthalpies, all the clusters of a given size will absorb a first H/sub 2/ molecule before one of them can adsorb a second molecule. Another remarkable point is that the energy of first absorption varies with the cluster size. It shows a peak for Pt/sub 3/ and Pt/sub 4/ that makes the Pt/sub 3/ and Pt/sub 4/ species the most likely clusters to be hydrogenated first in a collection of clusters of different size. 19 references, 9 figures, 5 tables.

  2. Hydrogen-induced atomic structure evolution of the oxygen-chemisorbed Cu(110) surface

    NASA Astrophysics Data System (ADS)

    Shan, Weitao; Liu, Qianqian; Li, Jonathan; Cai, Na; Saidi, Wissam A.; Zhou, Guangwen

    2016-12-01

    Using a combination of scanning tunneling microscopy (STM) and density functional theory (DFT) modeling, we determine the mechanism of the atomic structural evolution of the oxygenated Cu(110) surface induced by the reaction of adsorbed hydrogen with chemisorbed oxygen in the Cu(110)-c(6 × 2)-O structure. Our STM observations show that the reconstructed Cu(110)-c(6 × 2)-O surface undergoes a phase transition to the (2 × 1)-O reconstruction in the course of oxygen loss induced by the reaction with H2 gas. Using DFT modeling, we find that the surface phase transition is initiated via the adsorption of molecular hydrogen on the chemisorbed oxygen, which results in the formation of H2O molecules that desorb spontaneously from the surface. The loss of chemisorbed oxygen induces the c(6 × 2) → (2 × 1) transition that involves the diffusion of Cu―O―Cu chains along the ⟨1 ¯ 10 ⟩ direction.

  3. Hydrogen spillover on Rh/TiO2: the FTIR study of donated electrons, co-adsorbed CO and H/D exchange.

    PubMed

    Panayotov, D; Ivanova, E; Mihaylov, M; Chakarova, K; Spassov, T; Hadjiivanov, K

    2015-08-28

    Hydrogen dissociation and spillover on supported metal nanoparticles have received renewed interest because these chemical processes are closely related to applications in heterogeneous catalysis and hydrogen storage. In heterogeneous catalysis, spillover can control the reaction rate and selectivity of a wide range of reactions, e.g. hydrogenation, synthesis of methanol and hydroisomerization. In this work, we combine three spectroscopic approaches, i.e. the FT-IR spectroscopy of donated electrons, co-adsorbed CO and H/D exchange, to obtain detailed information on the dynamics of hydrogen interaction with a model 1.3% Rh/TiO2 catalyst. Our spectroscopic results helped us to build a physical picture of the processes occurring during the H-spillover on Rh/TiO2. It was found that molecular H2 dissociates on nanocrystalline Rh; H atoms spillover onto the titania thus protonating the semiconductor, while donating electrons to shallow trap (ST) states and the conduction band (CB) of TiO2. These donated electrons are observed by their specific IR features. By simultaneously monitoring the changes in the vibrational modes of CO, and, the infrared absorbance due to transitions involving CB and ST electrons, we found that both CO-reduced and partially re-oxidized Rh nanocrystallites promote the H-spillover and thus the n-doping of TiO2 materials. Upon evacuation, the process reverses: hydrogen atoms spillover back to Rh nanoparticles where they recombine to form H2 molecules that desorb from the surface. These new mechanistic insights into the process of H2 dissociation and spillover on the powder Rh/TiO2 catalyst call for further model surface science studies with model metal nanoparticle-single crystal substrate systems, in which a detailed picture of energetics and spatial distribution of hydrogen and injected electrons could be obtained.

  4. 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.

  5. 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.

  6. Structural characterisation of parotid and whole mouth salivary pellicles adsorbed onto DPI and QCMD hydroxyapatite sensors.

    PubMed

    Ash, Anthony; Burnett, Gary R; Parker, Roger; Ridout, Mike J; Rigby, Neil M; Wilde, Peter J

    2014-04-01

    In this study we investigated the differences in the properties of pellicles formed from stimulated parotid saliva (PS), which contains little or no mucin; and stimulated whole mouth saliva (WMS), which contains mainly two types of mucin: MUC5B and MUC7. By contacting WMS and PS with quartz-crystal microbalance with dissipation monitoring (QCM-D) and dual polarisation interferometer (DPI) hydroxyapatite (the main component of enamel) coated sensors, we observed the formation and structure of the respective salivary pellicles. As this was the first time that DPI hydroxyapatite sensors have been used to measure salivary pellicle adsorption; the techniques combined allowed us to measure the hydrated mass, dry mass, thickness and viscoelastic properties of the pellicle; but also to record the density of the PS and WMS formed pellicles. Subsequently, the PS pellicle was shown to form a denser layer than WMS pellicle; which would suggest that the proteins present in PS are also responsible for forming the dense basal layer of the acquired enamel pellicle. Whereas proteins present in the WMS are more likely to help form the softer outer layer of the pellicle. The data presented help to further define the mechanisms leading to the multi-layered structure of the salivary pellicle and demonstrate that salivary composition has an important effect on the structural properties of the adsorbed pellicle.

  7. 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.

  8. Effects of surface curvature and surface chemistry on the structure and activity of proteins adsorbed in nanopores.

    PubMed

    Sang, Lung-Ching; Coppens, Marc-Olivier

    2011-04-14

    The interactions of proteins with the surface of cylindrical nanopores are systematically investigated to elucidate how surface curvature and surface chemistry affect the conformation and activity of confined proteins in an aqueous, buffered environment. Two globular proteins, lysozyme and myoglobin, with different catalytic functions, were used as model proteins to analyze structural changes in proteins after adsorption on ordered mesoporous silica SBA-15 and propyl-functionalized SBA-15 (C(3)SBA-15) with carefully controlled pore size. Liquid phase ATR-FTIR spectroscopy was used to study the amide I and II bands of the adsorbed proteins. The amide I bands showed that the secondary structures of free and adsorbed protein molecules differ, and that the secondary structure of the adsorbed protein is influenced by the local geometry as well as by the surface chemistry of the nanopores. The conformation of the adsorbed proteins inside the nanopores of SBA-15 and C(3)SBA-15 is strongly correlated with the local geometry and the surface properties of the nanoporous materials, which results in different catalytic activities. Adsorption by electrostatic interaction of proteins in nanopores of an optimal size provides a favorably confining and protecting environment, which may lead to considerably enhanced structural stability and catalytic activity.

  9. Structural and Immunological Analysis of Anthrax Recombinant Protective Antigen Adsorbed to Aluminum Hydroxide Adjuvant

    PubMed Central

    Wagner, Leslie; Verma, Anita; Meade, Bruce D.; Reiter, Karine; Narum, David L.; Brady, Rebecca A.; Little, Stephen F.

    2012-01-01

    New anthrax vaccines currently under development are based on recombinant protective antigen (rPA) and formulated with aluminum adjuvant. Because long-term stability is a desired characteristic of these vaccines, an understanding of the effects of adsorption to aluminum adjuvants on the structure of rPA is important. Using both biophysical and immunological techniques, we compared the structure and immunogenicity of freshly prepared rPA-Alhydrogel formulations to that of formulations stored for 3 weeks at either room temperature or 37°C in order to assess the changes in rPA structure that might occur upon long-term storage on aluminum adjuvant. Intrinsic fluorescence emission spectra of tryptophan residues indicated that some tertiary structure alterations of rPA occurred during storage on Alhydrogel. Using anti-PA monoclonal antibodies to probe specific regions of the adsorbed rPA molecule, we found that two monoclonal antibodies that recognize epitopes located in domain 1 of PA exhibited greater reactivity to the stored formulations than to freshly prepared formulations. Immunogenicity of rPA-Alhydrogel formulations in mice was assessed by measuring the induction of toxin-neutralizing antibodies, as well as antibodies reactive to 12-mer peptides spanning the length of PA. Mice immunized with freshly prepared formulations developed significantly higher toxin-neutralizing antibody titers than mice immunized with the stored preparations. In contrast, sera from mice immunized with stored preparations exhibited increased reactivity to nine 12-mer peptides corresponding to sequences located throughout the rPA molecule. These results demonstrate that storage of rPA-Alhydrogel formulations can lead to structural alteration of the protein and loss of the ability to elicit toxin-neutralizing antibodies. PMID:22815152

  10. 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). Copyright © 2015 Elsevier Inc. All rights reserved.

  11. Structural study and wetting behavior of ethane and tetrafluoromethane thick films adsorbed on graphite (0001)

    NASA Astrophysics Data System (ADS)

    Gay, Jean-Marc; Suzanne, Jean; Pepe, Gérard; Meichel, Thierry

    1988-10-01

    We present a quantitative study of the diffraction patterns (LEED, RHEED and neutron) of ethane and tetrafluoromethane thick films adsorbed on graphite (0001). We propose to interpret the streak-like RHEED patterns of C 2H 6 and CF 4 with tabular crystallites epitaxially grown on the thin underlying film. The growth of flat ethane crystallites is explained by a partial agreement of the lattice parameters, the symmetry and the molecule orientations between the bilayer structure deduced from static energy calculations and the structure within the 3D (011) plane which appears as the interfacial plane. The change in the CF 4 RHEED pattern observed at T = 37 K and previously considered as the signature of a wetting transition might be due to a change of interfacial plane. It could be the 3D (100) or (001) plane in which a hexagonal or quasi-hexagonal symmetry in the molecule packing appears for T > 37 K. At lower temperature, T < 37 K, this symmetry could be lost with the (101¯) interfacial plane which presents a quasi-square molecule packing. We would like to emphasize the caution necessary for interpreting RHEED results. The determination of the growth mode requires the combination of different methods of measurements in order to draw conclusions without ambiguities. These two molecular systems show rather well the difficulties for interpreting experimental results on the wetting phenomenon.

  12. Adsorption dynamics for the system hydrogen/palladium and its relation to the surface electronic structure

    NASA Astrophysics Data System (ADS)

    Resch, Ch.; Berger, H. F.; Rendulic, K. D.; Bertel, E.

    1994-09-01

    We have determined differential sticking coefficients for a monoenergetic nozzle beam of hydrogen on Pd(111) and Pd(110). In particular the energy dependence and the angular variation of the initial sticking coefficient were measured. The results indicate that adsorption of hydrogen on palladium occurs in parallel processes through a direct path with an activation barrier of perhaps 50 meV or less and a precursor path. There is relatively little difference in the adsorption properties of the (111) and the (110) plane. The appearance of a molecular precursor on the (111) plane can be related to the electronic structure of palladium, in particular to the absence of occupied Shockley surface states, as compared to Ni (111) and Pt (111). Pre-adsorbed potassium on a (110) plane acts as an inhibitor to adsorption. Different inhibiting mechanisms are observed for the direct adsorption path and the precursor path. At high potassium coverage the precursor path is completely suppressed.

  13. Scanning Tunneling Microscopy Study of the Structure and Interaction Between Carbon Monoxide and Hydrogen on the Ru(0001) Surface

    DOE PAGES

    Lechner, Barbara A. J.; Feng, Xiaofeng; Feibelman, Peter J.; ...

    2017-07-28

    Here, we use scanning tunneling microscopy (STM) to investigate the spatial arrangement of carbon monoxide (CO) and hydrogen (H) co-adsorbed on a model catalyst surface, Ru(0001). We find that at cryogenic temperatures CO forms small triangular islands of up to 21 molecules with hydrogen segregated outside of the islands. Furthermore, whereas for small island sizes (3-6 CO molecules) the molecules adsorb at hcp sites, a registry shift towards top sites occurs for larger islands (10-21 CO molecules). To characterize the CO structures better and to help interpret the data, we carried out density functional theory (DFT) calculations of the structuremore » and simulations of the STM images, which reveal a delicate interplay between the repulsions of the different species.« less

  14. Computational methods to determine the structure of hydrogen storage materials

    NASA Astrophysics Data System (ADS)

    Mueller, Tim

    2009-03-01

    To understand the mechanisms and thermodynamics of material-based hydrogen storage, it is important to know the structure of the material and the positions of the hydrogen atoms within the material. Because hydrogen can be difficult to resolve experimentally computational research has proven to be a valuable tool to address these problems. We discuss different computational methods for identifying the structure of hydrogen materials and the positions of hydrogen atoms, and we illustrate the methods with specific examples. Through the use of ab-initio molecular dynamics, we identify molecular hydrogen binding sites in the metal-organic framework commonly known as MOF-5 [1]. We present a method to identify the positions of atomic hydrogen in imide structures using a novel type of effective Hamiltonian. We apply this new method to lithium imide (Li2NH), a potentially important hydrogen storage material, and demonstrate that it predicts a new ground state structure [2]. We also present the results of a recent computational study of the room-temperature structure of lithium imide in which we suggest a new structure that reconciles the differences between previous experimental and theoretical studies. [4pt] [1] T. Mueller and G. Ceder, Journal of Physical Chemistry B 109, 17974 (2005). [0pt] [2] T. Mueller and G. Ceder, Physical Review B 74 (2006).

  15. 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.

  16. Synthesis of adsorbent with zeolite structure from red mud and rice husk ash and its properties

    NASA Astrophysics Data System (ADS)

    Quyen, Dinh Thi Ngoc; Loc, Luu Cam; Ha, Huynh Ky Phuong; Nga, Dang Thi Hang; Tri, Nguyen; Van, Nguyen Thi Thuy

    2017-09-01

    There are many researches in the modification of red mud as adsorbent for treatment of wastewater or waste gases. Yet, most of them have to face up with a thorny problem caused by remaining alkali in red mud. In this study, the material with zeolite structure was synthesized by fusion method using red mud with the remaining alkali and rice husk ash as raw materials. It comprised alkaline fusion followed by hydrothermal treatment with step - change of synthesis temperature. The synthesized materials were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), BET and CO2 adsorption capacity. The influences on the quality of these materialswere investigated under various calcination temperatures, calcination times and the ratios of raw materials (based on SiO2/Al2O3 ratio). The optimum reaction parameters were determined. The results depicted that the sample treated at 600 °C for 2 hours with the ratio of SiO2/Al2O3 of 1.8 had the best adsorption capacity and total specific surface area compared with the others.

  17. Structure and dynamics of confined flexible and unentangled polymer melts in highly adsorbing cylindrical pores

    SciTech Connect

    Carrillo, Jan-Michael Y.; Sumpter, Bobby G.

    2014-08-21

    Coarse-grained molecular dynamics simulations are used to probe the dynamic phenomena of polymer melts confined in nanopores. The simulation results show excellent agreement in the values obtained for the normalized coherent single chain dynamic structure factor, (S(Q,Δt))/(S(Q,0)) . In the bulk configuration, both simulations and experiments confirm that the polymer chains follow Rouse dynamics. However, under confinement, the Rouse modes are suppressed. The mean-square radius of gyration 〈R{sub g}{sup 2}〉 and the average relative shape anisotropy 〈κ{sup 2}〉 of the conformation of the polymer chains indicate a pancake-like conformation near the surface and a bulk-like conformation near the center of the confining cylinder. This was confirmed by direct visualization of the polymer chains. Despite the presence of these different conformations, the average form factor of the confined chains still follows the Debye function which describes linear ideal chains, which is in agreement with small angle neutron scattering experiments (SANS). The experimentally inaccessible mean-square displacement (MSD) of the confined monomers, calculated as a function of radial distance from the pore surface, was obtained in the simulations. The simulations show a gradual increase of the MSD from the adsorbed, but mobile layer, to that similar to the bulk far away from the surface.

  18. Structure and dynamics of confined flexible and unentangled polymer melts in highly adsorbing cylindrical pores

    SciTech Connect

    Carrillo, Jan-Michael Y; Sumpter, Bobby G

    2014-01-01

    Coarse-grained molecular dynamics simulations are used to probe the dynamic phenomena of polymer melts confined in nanopores. The simulation results show excellent agreement in the values obtained for the normalized coherent single chain dynamic structure factor, S(Q,t) S(Q,0) . In the bulk configuration, both simulations and experiments confirm that the polymer chains follow Rouse dynamics. However, under confinement, the Rouse modes are suppressed. The mean-square radius of gyration R2 g and the average relative shape anisotropy 2 of the conformation of the polymer chains indicate a pancake-like conformation near the surface and a bulk-like conformation near the center of the confining cylinder. This was confirmed by direct visualization of the polymer chains. Despite the presence of these different conformations, the average form factor of the confined chains still follows the Debye function which describes linear ideal chains, which is in agreement with small angle neutron scattering experiments (SANS). The experimentally inaccessible mean-square displacement (MSD) of the confined monomers, calculated as a function of radial distance from the pore surface, was obtained in the simulations. The simulations show a gradual increase of the MSD from the adsorbed, but mobile layer, to that similar to the bulk far away from the surface.

  19. Structure and Hydrogen Adsorption Properties of SBA-15 Doped with Pd Nanoparticles.

    PubMed

    Lee, Sang-Hwa; Park, Taehee; Yi, Whikun; Kim, Jaeyong

    2015-11-01

    Hydrogen adsorption properties of Pd-doped Santa Barbara amorphous No. 15 (Pd-SBA-15) were investigated and the results were compared with pure SBA-15 ones in terms of change of its structure and Pd concentration. Pd-SBA-15 samples were prepared by a hydrothermal reaction, using mixture of PEO20PPO70PEO20 (P123) and tetraethyl orthosilicate (TEOS). For the doping of Pd on SBA-15, PdC2 solution was added into the mixture of P123 and TEOS, and the solution was annealed at 80 degrees C for 2 hours under 800 Torr of hydrogen atmosphere. According to the X-ray diffraction and transmission electron microscope data, Pd-doped SBA-15 samples form a hexagonal array of mesoporous structure with 20-30 nm size of Pd particles. Values of specific surface area decreased from 630 to 414 m2/g as increasing the Pd doping level due to the increasing of the volume density. In fact, the volume density increased from 0.103 to 0.276 g/cc as increasing the mass ratio of PdCl2 to TEOS from 0 to 0.5. For the Pd-doped SBA-15, the amount of adsorbed hydrogen significantly increased from 0.49 to 0.99 wt% as increasing the Pd doping level from 0 to 0.5 demonstrating that Pd doping is an effect method for SBA-1 5 as a potential use of hydrogen storage application.

  20. Structural Studies of Clean and Adsorbate-Covered Fcc Metal Surfaces

    NASA Astrophysics Data System (ADS)

    Statiris, Panayiotis Athanasiou

    We have used medium energy ion scattering (MEIS) to study the structural and vibrational properties of the clean metal surfaces of Ni(110) and Ag(111), the structural changes induced by the presence of small amounts ( {~}1 atomic layer) of heteroatoms on the Ni(001) and Ni(110) surfaces (Cs, K, K and CO on Ni(110) and Au on Ni(001)) as well as the arrangement of the heteroatoms on the surface. The thesis consists of five chapters two of which serve as an introduction and provide general information about metal surfaces and medium energy ion scattering (chapters 1 and 2) and three chapters (3, 4, 5) in which the experimental results are being presented, and structural models are proposed for the surfaces studied. The purpose of the material contained in chapter one is to familiarize the reader with the general concepts, and provide an overview of the progress (experimental and theoretical) in the field of clean and adsorbate covered metal surfaces. The second chapter contains an extensive discussion about the principles and applications of medium energy ion scattering. A study of the structure of the clean Ni(001) surface and the K/Ni(110) and K/CO/Ni(110) surfaces is presented in chapter 3. Both the K/Ni(110) and K/CO/Ni(110) exhibit the missing row reconstruction. The change in the surface unit cell observed upon adsorption of CO atoms on the K/Ni(110) surface observed with low energy electron diffraction is due to the ordering of the CO molecules. The growth and structure of thin Au films (0.35 -3 layers) deposited on the Ni(001) surface is the subject of chapter 4. Au forms an almost incommensurate overlayer with a c(2 times 8) unit cell whose structure resembles that of fcc Au(111). The Au atoms exhibit unusually high vibrational amplitudes, indicating the presence of a soft phonon mode as predicted by theoretical work. The growth mode resembles the Stranski-Krastanov mode without exactly following it. The temperature dependence of the vibrational amplitudes

  1. Sum frequency generation and solid-state NMR study of the structure, orientation, and dynamics of polystyrene-adsorbed peptides

    PubMed Central

    Weidner, Tobias; Breen, Nicholas F.; Li, Kun; Drobny, Gary P.; Castner, David G.

    2010-01-01

    The power of combining sum frequency generation (SFG) vibrational spectroscopy and solid-state nuclear magnetic resonance (ssNMR) spectroscopy to quantify, with site specificity and atomic resolution, the orientation and dynamics of side chains in synthetic model peptides adsorbed onto polystyrene (PS) surfaces is demonstrated in this study. Although isotopic labeling has long been used in ssNMR studies to site-specifically probe the structure and dynamics of biomolecules, the potential of SFG to probe side chain orientation in isotopically labeled surface-adsorbed peptides and proteins remains largely unexplored. The 14 amino acid leucine-lysine peptide studied in this work is known to form an α-helical secondary structure at liquid-solid interfaces. Selective, individual deuteration of the isopropyl group in each leucine residue was used to probe the orientation and dynamics of each individual leucine side chain of LKα14 adsorbed onto PS. The selective isotopic labeling methods allowed SFG analysis to determine the orientations of individual side chains in adsorbed peptides. Side chain dynamics were obtained by fitting the deuterium ssNMR line shape to specific motional models. Through the combined use of SFG and ssNMR, the dynamic trends observed for individual side chains by ssNMR have been correlated with side chain orientation relative to the PS surface as determined by SFG. This combination provides a more complete and quantitative picture of the structure, orientation, and dynamics of these surface-adsorbed peptides than could be obtained if either technique were used separately. PMID:20628016

  2. Prediction of electronic structure of van der Waals interfaces: Benzene adsorbed monolayer MoS2, WS2 and WTe2

    NASA Astrophysics Data System (ADS)

    You, Baiqing; Wang, Xiaocha; Chen, Guifeng; Zheng, Zhida

    2017-04-01

    The electronic structure of benzene adsorbed monolayer MoS2, WS2 and WTe2 has been investigated by first-principles calculations with van der Waals forces. The benzene adsorbed monolayer MoS2, WS2 and WTe2 with spin-orbital coupling are found to be direct-band-gap semiconductors. All the benzene adsorbed model show the semiconducting characteristic. The band gap and spin splitting of the benzene adsorbed monolayer MoS2, WS2 and WTe2 are slightly regulated. The calculated results show the potential applications in the optoelectronic devices, spin-filter devices, etc.

  3. Two-step adsorption on jungle-gym-type porous coordination polymers: dependence on hydrogen-bonding capability of adsorbates, ligand-substituent effect, and temperature.

    PubMed

    Uemura, Kazuhiro; Yamasaki, Yukari; Onishi, Fumiaki; Kita, Hidetoshi; Ebihara, Masahiro

    2010-11-01

    A preliminary study of isopropanol (IPA) adsorption/desorption isotherms on a jungle-gym-type porous coordination polymer, [Zn(2)(bdc)(2)(dabco)](n) (1, H(2)bdc = 1,4-benzenedicarboxylic acid, dabco =1,4-diazabicyclo[2.2.2]octane), showed unambiguous two-step profiles via a highly shrunk intermediate framework. The results of adsorption measurements on 1, using probing gas molecules of alcohol (MeOH and EtOH) for the size effect and Me(2)CO for the influence of hydrogen bonding, show that alcohol adsorption isotherms are gradual two-step profiles, whereas the Me(2)CO isotherm is a typical type-I isotherm, indicating that a two-step adsorption/desorption is involved with hydrogen bonds. To further clarify these characteristic adsorption/desorption behaviors, selecting nitroterephthalate (bdc-NO(2)), bromoterephthalate (bdc-Br), and 2,5-dichloroterephthalate (bdc-Cl(2)) as substituted dicarboxylate ligands, isomorphous jungle-gym-type porous coordination polymers, {[Zn(2)(bdc-NO(2))(2)(dabco)]·solvents}(n) (2 ⊃ solvents), {[Zn(2)(bdc-Br)(2)(dabco)]·solvents}(n) (3 ⊃ solvents), and {[Zn(2)(bdc-Cl(2))(2)(dabco)]·solvents}(n) (4 ⊃ solvents), were synthesized and characterized by single-crystal X-ray analyses. Thermal gravimetry, X-ray powder diffraction, and N(2) adsorption at 77 K measurements reveal that [Zn(2)(bdc-NO(2))(2)(dabco)](n) (2), [Zn(2)(bdc-Br)(2)(dabco)](n) (3), and [Zn(2)(bdc-Cl(2))(2)(dabco)](n) (4) maintain their frameworks without guest molecules with Brunauer-Emmett-Teller (BET) surface areas of 1568 (2), 1292 (3), and 1216 (4) m(2) g(-1). As found in results of MeOH, EtOH, IPA, and Me(2)CO adsorption/desorption on 2-4, only MeOH adsorption on 2 shows an obvious two-step profile. Considering the substituent effects and adsorbate sizes, the hydrogen bonds, which are triggers for two-step adsorption, are formed between adsorbates and carboxylate groups at the corners in the pores, inducing wide pores to become narrow pores. Interestingly, such

  4. 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

  5. The structure of adsorbed bromide concurrent with the underpotential deposition (UPD) of Cu on Pt(111)

    NASA Astrophysics Data System (ADS)

    Marković, Nenad M.; Lucas, Chris A.; Gasteiger, Hubert A.; Ross, Philip N.

    1997-02-01

    The adsorption of bromide anions concurrent with the underpotential deposition (UPD) of Cu on Pt(111) was examined utilizing ex-situ LEED and in-situ surface X-ray scattering for structure determination, in combination with coverage determination by rotating ring disk flux measurements with the Pt(111) single crystal as the disk electrode. The results show definitively that Cu UPD on Pt(111) in the presence of bromide is a two-step process, with the total amount of Cu deposited at underpotentials ˜0.95 ± 5% ML (1 ML = 1 adatom per Pt atom). The results also indicate that the surface coverage by adsorbed bromide undergoes only a small (<0.05 ML) change upon the deposition of Cu, even up to a nominal monolayer. We propose a model wherein the first stage of deposition occurs by displacement of the close-packed hexagonal layer of Br adatoms by Cu adatoms through a "turn-over" process, in which Cu is sandwiched between the Pt surface and the Br overlayer, leading to the formation of an ordered Pt(111)CuBr bilayer intermediate phase which closely resembles the (111) planes of the Cu(I)Br crystal. The coverage of both Cu and Br in this intermediate phase is ˜0.5 ML. The second stage is the filling-in of the Cu plane of the bilayer to form a pseudomorphic (1 × 1) Cu monolayer and a disordered Br adlayer with a coverage of ˜0.4 ML. The same mechanism is suggested for Cu UPD on Pt(111) in solutions containing chloride anions.

  6. 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.

  7. 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

  8. Ionic strength affects tertiary structure and aggregation propensity of a monoclonal antibody adsorbed to silicone oil-water interfaces.

    PubMed

    Gerhardt, Alana; Bonam, Kurt; Bee, Jared S; Carpenter, John F; Randolph, Theodore W

    2013-02-01

    Therapeutic proteins formulated in prefilled syringes lubricated with silicone oil come in contact with silicone oil-water interfaces for their entire shelf lives. Thus, the interactions between protein and silicone oil were studied to determine the effect of silicone oil on a monoclonal antibody's stability, both at the interface and in the bulk solution. The influence of ionic strength on these interactions was also investigated through the addition of various monovalent and divalent salts to sample formulations. The tertiary structure of the antibody was perturbed when it adsorbed to the silicone oil-water interface in solutions at low ionic strength. However, the tertiary structure of the antibody at the interface was not perturbed when the ionic strength of the formulation was increased. Even at low ionic strength, the secondary structure of the antibody adsorbed to the silicone oil-water interface was retained, suggesting that at low ionic strength, the adsorbed antibody assumes a molten globule-like conformation. This partially unfolded species was aggregation-prone, especially during agitation. Silicone oil-induced aggregation of the antibody was inhibited at higher ionic strength. Copyright © 2012 Wiley Periodicals, Inc.

  9. 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.

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

    Treesearch

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

    2004-01-01

    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...

  11. Reliable determination of oxygen and hydrogen isotope ratios in atmospheric water vapour adsorbed on 3A molecular sieve.

    PubMed

    Han, Liang-Feng; Gröning, Manfred; Aggarwal, Pradeep; Helliker, Brent R

    2006-01-01

    The isotope ratio of atmospheric water vapour is determined by wide-ranging feedback effects from the isotope ratio of water in biological water pools, soil surface horizons, open water bodies and precipitation. Accurate determination of atmospheric water vapour isotope ratios is important for a broad range of research areas from leaf-scale to global-scale isotope studies. In spite of the importance of stable isotopic measurements of atmospheric water vapour, there is a paucity of published data available, largely because of the requirement for liquid nitrogen or dry ice for quantitative trapping of water vapour. We report results from a non-cryogenic method for quantitatively trapping atmospheric water vapour using 3A molecular sieve, although water is removed from the column using standard cryogenic methods. The molecular sieve column was conditioned with water of a known isotope ratio to 'set' the background signature of the molecular sieve. Two separate prototypes were developed, one for large collection volumes (3 mL) and one for small collection volumes (90 microL). Atmospheric water vapour was adsorbed to the column by pulling air through the column for several days to reach the desired final volume. Water was recovered from the column by baking at 250 degrees C in a dry helium or nitrogen air stream and cryogenically trapped. For the large-volume apparatus, the recovered water differed from water that was simultaneously trapped by liquid nitrogen (the experimental control) by 2.6 per thousand with a standard deviation (SD) of 1.5 per thousand for delta(2)H and by 0.3 per thousand with a SD of 0.2 per thousand for delta(18)O. Water-vapour recovery was not satisfactory for the small volume apparatus.

  12. Rotary adsorbers for continuous bulk separations

    DOEpatents

    Baker, Frederick S [Oak Ridge, TN

    2011-11-08

    A rotary adsorber for continuous bulk separations is disclosed. The rotary adsorber includes an adsorption zone in fluid communication with an influent adsorption fluid stream, and a desorption zone in fluid communication with a desorption fluid stream. The fluid streams may be gas streams or liquid streams. The rotary adsorber includes one or more adsorption blocks including adsorbent structure(s). The adsorbent structure adsorbs the target species that is to be separated from the influent fluid stream. The apparatus includes a rotary wheel for moving each adsorption block through the adsorption zone and the desorption zone. A desorption circuit passes an electrical current through the adsorbent structure in the desorption zone to desorb the species from the adsorbent structure. The adsorbent structure may include porous activated carbon fibers aligned with their longitudinal axis essentially parallel to the flow direction of the desorption fluid stream. The adsorbent structure may be an inherently electrically-conductive honeycomb structure.

  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. Effect of peptide secondary structure on adsorption and adsorbed film properties on end-grafted polyethylene oxide layers.

    PubMed

    Binazadeh, M; Zeng, H; Unsworth, L D

    2014-01-01

    Poly-l-lysine (PLL), in α-helix or β-sheet configuration, was used as a model peptide for investigating the effect of secondary structures on adsorption events to poly(ethylene oxide) (PEO) modified surfaces formed using θ solvents. Circular dichroism results showed that the secondary structure of PLL persisted upon adsorption to Au and PEO modified Au surfaces. Quartz crystal microbalance with dissipation (QCM-D) was used to characterize the chemisorbed PEO layer in different solvents (θ and good solvents), as well as the sequential adsorption of PLL in different secondary structures (α-helix or β-sheet). QCM-D results suggest that chemisorption of PEO 750 and 2000 from θ solutions led to brushes 3.8 ± 0.1 and 4.5 ± 0.1 nm thick with layer viscosities of 9.2 ± 0.8 and 4.8 ± 0.5 cP, respectively. The average number of H2O per ethylene oxides, while in θ solvent, was determined as ~0.9 and ~1.2 for the PEO 750 and 2000 layers, respectively. Upon immersion in good solvent (as used for PLL adsorption experiments), the number of H2O per ethylene oxides increased to ~1.5 and ~2.0 for PEO 750 and 2000 films, respectively. PLL adsorbed masses for α-helix and β-sheet on Au sensors was 231 ± 5 and 1087 ± 14 ng cm(-2), with layer viscosities of 2.3 ± 0.1 and 1.2 ± 0.1 cP, respectively; suggesting that the α-helix layer was more rigid, despite a smaller adsorbed mass, than that of β-sheet layers. The PEO 750 layer reduced PLL adsorbed amounts to ~10 and 12% of that on Au for α-helices and β-sheets respectively. The PLL adsorbed mass to PEO 2000 layers dropped to ~12% and 4% of that on Au, for α-helix and β-sheet respectively. No significant differences existed for the viscosities of adsorbed α-helix and β-sheet PLL on PEO surfaces. These results provide new insights into the fundamental understanding of the effects of secondary structures of peptides and proteins on their surface adsorption.

  15. Ground-state structures of atomic metallic hydrogen.

    PubMed

    McMahon, Jeffrey M; Ceperley, David M

    2011-04-22

    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 (r(s)=1.23) that remains stable to 1 TPa (r(s)=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 (r(s)=0.92).

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

    DOEpatents

    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.

  17. 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.

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

    SciTech Connect

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

    2016-05-23

    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 4G{sub 0} to 2G{sub 0} suggesting its applications for the fabrications of organic sensor devices based on the Au atomic layers.

  19. 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.

  20. 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.

  1. 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

  2. Structural characterization of irreversibly adsorbed polymer layers at the polymer/solid interface - In-situ grazing incidence angle x-ray scattering studies

    NASA Astrophysics Data System (ADS)

    Jiang, Naisheng; Chen, Fen; Chen, Xiameng; Han, Zexi; Liang, Chen; Gin, Peter; Asada, Mitsunori; Endoh, Maya; Koga, Tad

    2012-02-01

    In recent years, great attention has been paid to irreversibly adsorbed polymer layers formed on solid substrates since they can modify various properties of polymeric materials confined at the nanometer scale. In this talk, by the combined use of in-situ grazing incidence small angle x-ray scattering and x-ray reflectivity techniques, we aim to characterize the detailed structures of the adsorbed layers composed of different homopolymers (polystyrene, polybutadiene, poly (ethylene oxide), and poly (methyl methacrylate)) prepared on silicon substrates. We will highlight the generality/differences in the structures, leading to a better understanding of the formation process of the adsorbed layers at the impenetrable solid interfaces.

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

    SciTech Connect

    Peterson, Eric Scott

    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.

  4. 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.

  5. Effective adsorbent for arsenic removal: core/shell structural nano zero-valent iron/manganese oxide.

    PubMed

    Bui, Trung Huu; Kim, Choonsoo; Hong, Sung Pil; Yoon, Jeyong

    2017-09-09

    Recently, nano zero-valent iron (nZVI) has emerged as an effective adsorbent for the removal of arsenic from aqueous solutions. However, its use in various applications has suffered from reactivity loss resulting in a decreased efficiency. Thus, the aim of this study was to develop an effective arsenic adsorbent as a core/shell structural nZVI/manganese oxide (or nZVI/Mn oxide) to minimize the reactivity loss of the nZVI. As the major result, the arsenic adsorption capacities of the nZVI/Mn oxide for As(V) and As(III) were approximately two and three times higher than that of the nZVI, respectively. In addition, the As(V) removal efficiency of the nZVI/Mn oxide was maintained through 4 cycles of regeneration whereas that of the nZVI was decreased significantly. The enhanced reactivity and reusability of the nZVI/Mn oxide can be successfully explained by the synergistic interaction of the nZVI core and manganese oxide shell, in which the manganese oxides participate in oxidation reactions with corroded Fe(2+) and subsequently retard the release of aqueous iron providing additional surface sites for arsenic adsorption. In summary, this study reports the successful fabrication of a core/shell nZVI/Mn oxide as an effective adsorbent for the removal of arsenic from aqueous solutions.

  6. The structural and electronic properties of Ag-adsorbed (SiO2)n (n=1-7) clusters.

    PubMed

    Zhao, Gao-feng; Zhi, Li-li; Guo, Ling-ju; Zeng, Zhi

    2007-12-21

    Equilibrium geometries, charge distributions, stabilities, and electronic properties of the Ag-adsorbed (SiO(2))(n) (n=1-7) clusters have been investigated using density functional theory with generalized gradient approximation for exchange-correlation functional. The results show that the Ag atom preferably binds to silicon atom with dangling bond in nearly a fixed direction, and the incoming Ag atoms tend to cluster on the existing Ag cluster leading to the formation of Ag islands. The adsorbed Ag atom only causes charge redistributions of the atoms near itself. The effect of the adsorbed Ag atom on the bonding natures and structural features of the silica clusters is minor, attributing to the tendency of stability order of Ag(SiO(2))(n) (n=1-7) clusters in consistent with silica clusters. In addition, the energy gaps between the highest occupied and lowest unoccupied molecular orbitals remarkably decrease compared with the pure (SiO(2))(n) (n=1-7) clusters, eventually approaching the near infrared radiation region. This suggests that these small clusters may be an alternative material which has a similar functionality in treating cancer to the large gold-coated silica nanoshells and the small Au(3)(SiO(2))(3) cluster.

  7. 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.

  8. 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.

  9. 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.

  10. 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

  11. 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.

  12. 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.

  13. Hydrogen Chemical Configuration and Thermal Stability in Tungsten Disulfide Nanoparticles Exposed to Hydrogen Plasma.

    PubMed

    Laikhtman, Alex; Makrinich, Gennady; Sezen, Meltem; Yildizhan, Melike Mercan; Martinez, Jose I; Dinescu, Doru; Prodana, Mariana; Enachescu, Marius; Alonso, Julio A; Zak, Alla

    2017-06-01

    The chemical configuration and interaction mechanism of hydrogen adsorbed in inorganic nanoparticles of WS2 are investigated. Our recent approaches of using hydrogen activated by either microwave or radiofrequency plasma dramatically increased the efficiency of its adsorption on the nanoparticles surface. In the current work we make an emphasis on elucidation of the chemical configuration of the adsorbed hydrogen. This configuration is of primary importance as it affects its adsorption stability and possibility of release. To get insight on the chemical configuration, we combined the experimental analysis methods with theoretical modeling based on the density functional theory (DFT). Micro-Raman spectroscopy was used as a primary tool to elucidate chemical bonding of hydrogen and to distinguish between chemi- and physisorption. Hydrogen adsorbed in molecular form (H2) was clearly identified in all the plasma-hydrogenated WS2 nanoparticles samples. It was shown that the adsorbed hydrogen is generally stable under high vacuum conditions at room temperature, which implies its stability at the ambient atmosphere. A DFT model was developed to simulate the adsorption of hydrogen in the WS2 nanoparticles. This model considers various adsorption sites and identifies the preferential locations of the adsorbed hydrogen in several WS2 structures, demonstrating good concordance between theory and experiment and providing tools for optimizing of hydrogen exposure conditions and the type of substrate materials.

  14. Scanning Tunneling Microscopy Study of the Structure and Interaction between Carbon Monoxide and Hydrogen on the Ru(0001) Surface.

    PubMed

    Lechner, Barbara A J; Feng, Xiaofeng; Feibelman, Peter J; Cerdá, Jorge I; Salmeron, Miquel

    2017-09-29

    We use scanning tunneling microscopy (STM) to investigate the spatial arrangement of carbon monoxide (CO) and hydrogen (H) coadsorbed on a model catalyst surface, Ru(0001). We find that at cryogenic temperatures, CO forms small triangular islands of up to 21 molecules with hydrogen segregated outside of the islands. Furthermore, whereas for small island sizes (3-6 CO molecules) the molecules adsorb at hcp sites, a registry shift toward top sites occurs for larger islands (10-21 CO molecules). To characterize the CO structures better and to help interpret the data, we carried out density functional theory (DFT) calculations of the structure and simulations of the STM images, which reveal a delicate interplay between the repulsions of the different species.

  15. Mg/Ti multilayers: Structural and hydrogen absorption properties

    NASA Astrophysics Data System (ADS)

    Baldi, A.; Pálsson, G. K.; Gonzalez-Silveira, M.; Schreuders, H.; Slaman, M.; Rector, J. H.; Krishnan, G.; Kooi, B. J.; Walker, G. S.; Fay, M. W.; Hjörvarsson, B.; Wijngaarden, R. J.; Dam, B.; Griessen, R.

    2010-06-01

    Mg-Ti alloys have uncommon optical and hydrogen absorbing properties, originating from a “spinodal-like” microstructure with a small degree of chemical short-range order in the atomic distribution. In the present study we artificially engineer short-range order by depositing Pd-capped Mg/Ti multilayers with different periodicities. Notwithstanding the large lattice mismatch between Mg and Ti, the as-deposited metallic multilayers show good structural coherence. On exposure to H2 gas a two-step hydrogenation process occurs with the Ti layers forming the hydride before Mg. From in situ measurements of the bilayer thickness Λ at different hydrogen pressures, we observe large out-of-plane expansions of Mg and Ti layers on hydrogenation, indicating strong plastic deformations in the films and a consequent shortening of the coherence length. On unloading at room temperature in air, hydrogen atoms remain trapped in the Ti layers due to kinetic constraints. Such loading/unloading sequence can be explained in terms of the different thermodynamic properties of hydrogen in Mg and Ti, as shown by diffusion calculations on a model multilayered systems. Absorption isotherms measured by hydrogenography can be interpreted as a result of the elastic clamping arising from strongly bonded Mg/Pd and broken Mg/Ti interfaces.

  16. Crystal structure and vibrational spectra of betaine hydrogen selenate monohydrate

    NASA Astrophysics Data System (ADS)

    Baran, J.; Drozd, M.; Lis, T.; Śledź, M.; Barnes, A. J.; Ratajczak, H.

    1995-11-01

    The crystal structure of betaine hydrogen selenate monohydrate, (C 5H 12NO 2) +·(HSeO 4) -·(H 2O), BHSeH 2O, has been determined by X-ray diffraction as monoclinic, space group {P2 1}/{c} with a = 6.674(6), b = 11.912(9), c = 14.156(14) A, β = 100.61(4)° and Z = 4. It comprises protonated betaine moieties (betainium cations), hydrogen selenate anions and water molecules which are held together by a number of hydrogen bonds and form infinite chains. Two types of four-membered centrosymmetric rings are distinguished in the chain. The two rings share a common side. Powder FT-IR and FT-Raman spectra were measured for the title crystal, the dehydrated crystal (betaine hydrogen selenate, BHSe) and their deuterated analogues. Assignments of the observed bands to vibrations of the hydrogen bonds and internal vibrations of the hydrogen selenate anions and the betainium cations are proposed. DSC data are also presented.

  17. 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.

  18. 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.

  19. Some features of raman scattering by molecules adsorbed on metal crystal faces and a fine light structure

    NASA Astrophysics Data System (ADS)

    Polubotko, A. M.

    2013-07-01

    The paper analyzes some experiments on Raman scattering by molecules adsorbed on the face (111) of silver monocrystals performed by A. Campion et al. From the existence of the forbidden line A 2 u of benzene, the conclusion about existence of the surface field, caused by atomic structure of the surface is made. The relatively large intensity of this line allows to make a conclusion about large influence of the electromagnetic field spatial inhomogeneity in crystals on their optical properties. The difference between this field and a regular plane wave, which usually describes propagation of electromagnetic field in solids is named as a fine light structure. The influence of this structure on optical properties of solids is pointed out.

  20. Hydrogenation of graphitic nanocarbons

    NASA Astrophysics Data System (ADS)

    Berber, Savas; Tománek, David; Kim, Eunja; Weck, Philippe F.; Miller, Glen P.

    2008-03-01

    We apply ab initio density functional calculations to study the hydrogenation of graphitic nanocarbons including fullerenes, onions and nanotubes using diethylenetriamine (DETA) as hydrogenation reagent. Our results indicate that transfer of atomic hydrogen from the amine end-group of chemisorbed DETA molecules to nanocarbons is an exothermic reaction. We explore the optimum pathway for the hydrogenation reaction and find the activation energy associated with sigmatropic rearrangement of chemisorbed hydrogen atoms to lie near 1 eV, thus facilitating formation of energetically favorable adsorbate structures by surface diffusion. Chemisorbed hydrogen assists in a local sp^2 to sp^3 bonding conversion of the graphitic nanocarbons, causing large-scale structural changes ranging from local relaxations in nanotubes to shell opening in multi-wall onions.

  1. Immunogenicity of Structurally Perturbed Hen Egg Lysozyme Adsorbed to Silicone Oil Microdroplets in Wild-Type and Transgenic Mouse Models.

    PubMed

    Chisholm, Carly F; Soucie, Kaitlin R; Song, Jane S; Strauch, Pamela; Torres, Raul M; Carpenter, John F; Ragheb, Jack A; Randolph, Theodore W

    2017-02-16

    Silicone oil microdroplets may act as adjuvants, promoting unwanted immune responses against both foreign and self-proteins. Proteins often unfold upon adsorption to silicone oil microdroplets, but it is unclear how such unfolding might affect the immune response. In this study, we found that hen egg lysozyme (HEL) readily adsorbed to silicone oil microdroplets and perturbed the conformation of HEL. We compared the immune response to injections of HEL formulated in the presence and absence of silicone oil microdroplets in both wild-type mice and transgenic littermates that express a soluble form of HEL (sHEL), thus rendering them immunologically tolerant to this nominal self-antigen. Following 2 subcutaneous injections of a HEL formulation containing silicone oil microdroplets, wild-type mice exhibited a stronger IgG1 antibody response against HEL compared to the response in wild-type mice that administered an oil-free HEL formulation. However, when HEL was subcutaneously administered to sHEL-transgenic mice, immunological tolerance to sHEL was not broken in the presence of silicone oil microdroplets. Thus, although structural perturbations in proteins adsorbed to silicone oil microdroplets may augment the immune response, in the case of endogenously expressed proteins, such structural perturbations may not be sufficient to result in a breach of immunological tolerance.

  2. Model study of the effect of pore structure and condensation on multilayer adsorbate transport in porous media.

    PubMed

    Papadopoulos, George K; Petropoulos, John H

    2007-12-18

    A single-pore model approach to multilayer adsorbate transport in mesoporous media, previously shown to be capable of interpreting the observed behavior of relative vapor permeability PHs/PHL (or of the corresponding surface diffusion coefficient Ds), has been incorporated in a model pore network. The resulting more sophisticated model can simulate realistically the effect on PHs/PHL or Ds (i) of salient structural features of the porous medium (notably pore size dispersion and network connectivity) and (ii) of vapor condensation, which inevitably accompanies multilayer adsorbate transport in reality. An extensive generic parametric study of these effects has been performed on this basis. The results indicate that the aforementioned effects are ordinarily unlikely to induce substantial deviations of observed PHs/PHL behavior from the single-pore model benchmark. Thus, the utility of this simple model as a good basis for data analysis is confirmed, while the network model offers the possibility of exploiting external structural and other available information for a more refined interpretation of PHs/PHL behavior in particular mesoporous solid-vapor systems.

  3. 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.

  4. 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.

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

    SciTech Connect

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

    2016-07-01

    Here, 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.

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

    DOE PAGES

    Hong, Sung -Young; Xu, Pan; Camillone, Nina R.; ...

    2016-07-01

    Here, 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 probabilitymore » 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.« less

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

    SciTech Connect

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

    2016-07-01

    Here, 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.

  8. 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.

  9. Change in hydrogen bonding structures of a hydrogel with dehydration

    NASA Astrophysics Data System (ADS)

    Naohara, Ryo; Narita, Kentaro; Ikeda-Fukazawa, Tomoko

    2017-02-01

    To investigate the mechanisms of structural changes in polymer network and water during dehydration, X-ray diffraction of poly-N,N-dimethylacrylamide (PDMAA) hydrogels was measured. The variation process in the individual structures of water and PDMAA were analyzed by decomposition of the diffraction patterns to separate the respective contributions. The results show that the short-range structures of PDMAA expand during dehydration, whereas the network structure as a whole shrinks. The average length of the hydrogen bonds between water molecules increases with the process. The present results provide a direct evidence of the structural changes of water and polymer in the hydrogel during dehydration.

  10. Structural changes in borohydride hydrogen storage materials

    NASA Astrophysics Data System (ADS)

    Kumar, Ravhi; Cornelius, Andrew; Nicol, Malcolm

    2008-03-01

    Angle dispersive powder x-ray diffraction and Raman experiments were performed on ABH4 (A = K, Rb) at high pressures up to 27 GPa. We demonstrate that KBH4 exhibits structural phase transitions from the ambient α-KBH4 phase (cubic Fm-3m) to β-KBH4 (tetragonal-P421c) at 3.8 GPa and to γ-KBH4 phase (orthorhombic-Pnma) at 6.8 GPa which is similar to the phase transition sequence observed for NaBH4 earlier [1]. However, RbBH4 undergoes two successive pressure induced structural transitions from the ambient cubic Fm-3m phase to an orthorhombic Pnma phase around 2.9 GPa and then to a monoclinic phase above 8 GPa. The high pressure monoclinic phase is found to be stable up to 27 GPa. The experimental results reveal the phase transition sequence exhibited by RbBH4 is different from the pressure induced changes observed in similar cubic compounds NaBH4 and KBH4. The results further show that both the transition pressure and the structural ordering at high pressures are influenced by the atomic size of the alkali cation in these compounds. [1]. R.S. Kumar and Andrew L. Cornelius, App.Phys.Lett., 2005, 87, 261916.

  11. Cellular structure of lean hydrogen flames in microgravity

    NASA Technical Reports Server (NTRS)

    Patnaik, G.; Kailasanath, K.

    1990-01-01

    Detailed, time-dependent, two-dimensional numerical simulations of premixed laminar flames have been used to study the initiation and subsequent development of cellular structures in lean hydrogen-air flames. The model includes detailed hydrogen-oxygen combustion with 24 elementary reactions of eight reactive species and a nitrogen diluent, molecular diffusion of all species, thermal conduction, viscosity, and convection. This model has been used to study the nonlinear evolution of cellular flame structure and shows that cell splitting, as observed in experiments, can be predicted numerically for sufficiently reactive mixtures. The structures that evolved also resembled the cellular structures observed in experiments. The present study shows that the 'cell-split limit' postulated from experimental observations is an intrinsic property of the mixture and that external factors such as heat losses are not necessary to cause this limit.

  12. Hydrogen

    PubMed Central

    Bockris, John O’M.

    2011-01-01

    The idea of a “Hydrogen Economy” is that carbon containing fuels should be replaced by hydrogen, thus eliminating air pollution and growth of CO2 in the atmosphere. However, storage of a gas, its transport and reconversion to electricity doubles the cost of H2 from the electrolyzer. Methanol made with CO2 from the atmosphere is a zero carbon fuel created from inexhaustible components from the atmosphere. Extensive work on the splitting of water by bacteria shows that if wastes are used as the origin of feed for certain bacteria, the cost for hydrogen becomes lower than any yet known. The first creation of hydrogen and electricity from light was carried out in 1976 by Ohashi et al. at Flinders University in Australia. Improvements in knowledge of the structure of the semiconductor-solution system used in a solar breakdown of water has led to the discovery of surface states which take part in giving rise to hydrogen (Khan). Photoelectrocatalysis made a ten times increase in the efficiency of the photo production of hydrogen from water. The use of two electrode cells; p and n semiconductors respectively, was first introduced by Uosaki in 1978. Most photoanodes decompose during the photoelectrolysis. To avoid this, it has been necessary to create a transparent shield between the semiconductor and its electronic properties and the solution. In this way, 8.5% at 25 °C and 9.5% at 50 °C has been reached in the photo dissociation of water (GaP and InAs) by Kainthla and Barbara Zeleney in 1989. A large consortium has been funded by the US government at the California Institute of Technology under the direction of Nathan Lewis. The decomposition of water by light is the main aim of this group. Whether light will be the origin of the post fossil fuel supply of energy may be questionable, but the maximum program in this direction is likely to come from Cal. Tech. PMID:28824125

  13. Method for fabricating MNOS structures utilizing hydrogen ion implantation

    NASA Astrophysics Data System (ADS)

    Saks, N. S.

    1984-05-01

    An improved method for reducing the density of electronic trapping states and fixed insulator charge in the thin oxide layer of an MNOS structure is discussed. The method includes the steps of implanting hydrogen ions in field region of the oxide layer and annealing the MNOS structure at 400 deg C to cause the ions to diffuse laterally into the gate region of the oxide layer.

  14. Electronic Structures of Clusters of Hydrogen Vacancies on Graphene.

    PubMed

    Wu, Bi-Ru; Yang, Chih-Kai

    2015-10-15

    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.

  15. Electronic Structures of Clusters of Hydrogen Vacancies on Graphene

    NASA Astrophysics Data System (ADS)

    Wu, Bi-Ru; Yang, Chih-Kai

    2015-10-01

    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.

  16. 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

  17. Determining the Mechanism and Efficiency of Industrial Dye Adsorption through Facile Structural Control of Organo-montmorillonite Adsorbents.

    PubMed

    Huang, Peng; Kazlauciunas, Algy; Menzel, Robert; Lin, Long

    2017-08-09

    The structural evolution of cost-effective organo-clays (montmorillonite modified with different loadings of CTAB (cetyltrimethylammonium bromide)) is investigated and linked to the adsorption uptake and mechanism of an important industrial dye (hydrolyzed Remazol Black B). Key organo-clay characteristics, such as the intergallery spacing and the average number of well-stacked layers per clay stack, are determined by low-angle X-ray diffraction, while differential thermogravimetric analysis is used to differentiate between surface-bound and intercalated CTAB. Insights into the dye adsorption mechanism are gained through the study of the adsorption kinetics and through the characterization of the organo-clay structure and surface charge after dye adsorption. It is shown that efficient adsorption of anionic industrial dyes is driven by three key parameters: (i) sufficiently large intergallery spacing to enable accommodation of the relatively large dye molecules, (ii) crystalline disorder in the stacking direction of the clay platelets to facilitate dye access, (iii) and positive surface charge to promote interaction with the anionic dyes. Specifically, it is shown that, at low modifier loadings (0.5 cation exchange capacity (0.5CEC)), CTAB molecules exclusively intercalate as a monolayer into the clay intergallery spaces, while, with increasing modifier loadings, the CTAB molecules adopt a bilayer arrangement and adsorb onto the exterior clay surface. Bilayer intercalation results in sufficiently large expansion of the intergallery spaces and significant disordering along the (001) stacking direction to enable high and relatively fast dye uptake via intraparticle diffusion. Poor and slow dye uptake is observed for the organo-clays with a monolayer structure, suggesting relatively inefficient dye adsorption at the clay edges. The optimized bilayer organo-clays (montmorillonite modified with 3CEC of CTAB) also show enhanced adsorption efficiencies for other important

  18. 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 (√3x√3)R30° 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(√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.

  19. 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).

  20. Hydrogen storage in metal-organic frameworks: An investigation of structure-property relationships

    NASA Astrophysics Data System (ADS)

    Rowsell, Jesse

    Metal-organic frameworks (MOFs) have been identified as candidate hydrogen storage materials due to their ability to physisorb large quantities of small molecules. Thirteen compounds (IRMOF-1, -2, -3, -6, -8, -9, -11, -13, -18, -20, MOF-74, MOF-177 and HKUST-1) have been prepared and fully characterized for the evaluation of their dihydrogen (H2) adsorption properties. All compounds display approximately type I isotherms with no hysteresis at 77 K up to 1 atm. The amount adsorbed ranges from 0.89 to 2.54 wt%; however, saturation is not achieved under these conditions. The influences of link functionalization, catenation and topology are examined for the eleven MOFs composed of Zn4O(O2C-)6 clusters. Enhanced H2 uptake by catenated compounds is rationalized by increased overlap of the surface potentials within their narrower pores. This is corroborated by the larger isosteric heat of adsorption of IRMOF-11 compared to IRMOF-1. Inelastic neutron scattering spectroscopic analysis of four Zn4O-based materials (IRMOF-1, -8, -11, and MOF-74) under a range of H2 loading suggests the presence of multiple localized adsorption sites on both the inorganic and organic moieties. To determine the structural details of the adsorption sites, variable temperature single crystal X-ray diffraction was used to analyze adsorbed argon and dinitrogen molecules in IRMOF-1. The principle binding site was found to be the same for both adsorbates and is located on faces of the octahedral Zn4O(O2C-)6 clusters with close contacts to three carboxylate groups. A total of eight symmetry-independent adsorption sites were identified for argon at 30 K. Similar sites were observed for dinitrogen, suggesting that they are good model adsorbates for the behaviour of dihydrogen. Two additional materials composed of inorganic clusters with coordinatively unsaturated metal sites (MOF-74, HKUST-1) were examined and their increased capacities and isosteric heats of adsorption provide further evidence that the

  1. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

    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(CH3)2) and deactivating (NO2) 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 (Hhcp) 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.

  3. A Newtonian Explanation of the Hydrogen Fine Structure

    NASA Astrophysics Data System (ADS)

    Fisher, Paul; Espinosa, James; Woodyard, James

    2010-10-01

    The Hydrogen spectrum as seen by low dispersion spectrometers is correctly described by a classical theory founded on Ritz's magnetic model. With increasingly powerful instruments, individual lines are split into smaller groupings that are three orders of magnitude smaller. Arnold Sommerfeld was the first to develop a theory based on the mass variation of the electron to correctly describe this ``fine'' structure. A few years later, Vannevar Bush pointed out that Weber's force law could be used instead of Einstein's theory of relativity. We will utilize this line of approach to present a purely classical theory of the fine structure of the Hydrogen atom. Ritz's theory of electromagnetism replaces Weber's law; we will summarize all the other atomic physics experiments that our classical theory already describes correctly. Finally we will show how this fine structure theory logically paves the way for an explanation of the linear Stark effect.

  4. 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.

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

    PubMed

    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, KEET, between selected identical pairs of crystalline silicon quantum dots systems, either bare, doped with Al or P, or adsorbed with Ag and Ag3, 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 Ag3 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) KEET 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.

  6. Probing the hydrogen bonding structure in the Rieske protein.

    PubMed

    El Khoury, Youssef; Trivella, Aurélien; Gross, Julien; Hellwig, Petra

    2010-10-25

    The use of the far-infrared spectral range presents a novel approach for analysis of the hydrogen bonding in proteins. Here it is presented for the analysis of Fe--S vibrations (500-200 cm(-1)) and of the intra- and intermolecular hydrogen bonding signature (300-50 cm(-1)) in the Rieske protein from Thermus thermophilus as a function of temperature and pH. Three pH values were adequately chosen in order to study all the possible protonation states of the coordinating histidines. The Fe--S vibrations showed pH-dependent shifts in the FIR spectra in line with the change of protonation state of the histidines coordinating the [2Fe--2S] cluster. Measurements of the low-frequency signals between 300 and 30 K demonstrated the presence of a distinct overall hydrogen bonding network and a more rigid structure for a pH higher than 10. To further support the analysis, the redox-dependent shifts of the secondary structure were investigated by means of an electrochemically induced FTIR difference spectroscopic approach in the mid infrared. The results confirmed a clear pH dependency and an influence of the immediate environment of the cluster on the secondary structure. The results support the hypothesis that structure-mediated changes in the environment of iron--sulfur centers play a critical role in regulating enzymatic catalysis. The data point towards the role of the overall internal hydrogen bonding organization for the geometry and the electronic properties of the cluster.

  7. Capillary wave theory of adsorbed liquid films and the structure of the liquid-vapor interface.

    PubMed

    MacDowell, Luis G

    2017-08-01

    In this paper we try to work out in detail the implications of a microscopic theory for capillary waves under the assumption that the density is given along lines normal to the interface. Within this approximation, which may be justified in terms of symmetry arguments, the Fisk-Widom scaling of the density profile holds for frozen realizations of the interface profile. Upon thermal averaging of capillary wave fluctuations, the resulting density profile yields results consistent with renormalization group calculations in the one-loop approximation. The thermal average over capillary waves may be expressed in terms of a modified convolution approximation where normals to the interface are Gaussian distributed. In the absence of an external field we show that the phenomenological density profile applied to the square-gradient free energy functional recovers the capillary wave Hamiltonian exactly. We extend the theory to the case of liquid films adsorbed on a substrate. For systems with short-range forces, we recover an effective interface Hamiltonian with a film height dependent surface tension that stems from the distortion of the liquid-vapor interface by the substrate, in agreement with the Fisher-Jin theory of short-range wetting. In the presence of long-range interactions, the surface tension picks up an explicit dependence on the external field and recovers the wave vector dependent logarithmic contribution observed by Napiorkowski and Dietrich. Using an error function for the intrinsic density profile, we obtain closed expressions for the surface tension and the interface width. We show the external field contribution to the surface tension may be given in terms of the film's disjoining pressure. From literature values of the Hamaker constant, it is found that the fluid-substrate forces may be able to double the surface tension for films in the nanometer range. The film height dependence of the surface tension described here is in full agreement with results of

  8. Capillary wave theory of adsorbed liquid films and the structure of the liquid-vapor interface

    NASA Astrophysics Data System (ADS)

    MacDowell, Luis G.

    2017-08-01

    In this paper we try to work out in detail the implications of a microscopic theory for capillary waves under the assumption that the density is given along lines normal to the interface. Within this approximation, which may be justified in terms of symmetry arguments, the Fisk-Widom scaling of the density profile holds for frozen realizations of the interface profile. Upon thermal averaging of capillary wave fluctuations, the resulting density profile yields results consistent with renormalization group calculations in the one-loop approximation. The thermal average over capillary waves may be expressed in terms of a modified convolution approximation where normals to the interface are Gaussian distributed. In the absence of an external field we show that the phenomenological density profile applied to the square-gradient free energy functional recovers the capillary wave Hamiltonian exactly. We extend the theory to the case of liquid films adsorbed on a substrate. For systems with short-range forces, we recover an effective interface Hamiltonian with a film height dependent surface tension that stems from the distortion of the liquid-vapor interface by the substrate, in agreement with the Fisher-Jin theory of short-range wetting. In the presence of long-range interactions, the surface tension picks up an explicit dependence on the external field and recovers the wave vector dependent logarithmic contribution observed by Napiorkowski and Dietrich. Using an error function for the intrinsic density profile, we obtain closed expressions for the surface tension and the interface width. We show the external field contribution to the surface tension may be given in terms of the film's disjoining pressure. From literature values of the Hamaker constant, it is found that the fluid-substrate forces may be able to double the surface tension for films in the nanometer range. The film height dependence of the surface tension described here is in full agreement with results of

  9. Character and Structure of Hydrogen Bonding in Liquid Water

    NASA Astrophysics Data System (ADS)

    Guo, Jinghua; Luo, Yi; Augustsson, Andreas; Rubensson, Jan-Erik; Sathe, Conny; Agren, Hans; Siegbahn, Hans; Nordgren, Joseph

    2003-03-01

    Pauling stated in the 50s that electron sharing between water molecules results in a covalency in the hydrogen bond. Many attempts have been made in the past to verify PaulingÂ's prediction, but without much success due to the limitation of experimental access to the electronic structure of liquids. We reported the first X-ray emission spectra of liquid water. X-ray emission is a direct probe of the local electronic structure of complex systems. Our experimental and theoretical studies on liquid water provide clear evidence that an electron sharing takes place between water molecules. Such a sharing mainly involves the so-called 3a1 orbital, which is a mixing of oxygen 2p and hydrogen 2s atomic orbitals. The outermost "lone pair" orbital (1b_1), however, hardly shows any change upon solvation, which is in contradiction with the normal definition of so-called coordinate-covalent bonding (also called donor-acceptor or Lewis acid-base bonding). Moreover, the X-ray emission spectra of liquid water nicely show the origin for the increasing of dipole moment in liquid water, and they have also been used to separately determine a particular structure with broken hydrogen bonding.

  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. Micro structure processing on plastics by accelerated hydrogen molecular ions

    NASA Astrophysics Data System (ADS)

    Hayashi, H.; Hayakawa, S.; Nishikawa, H.

    2017-08-01

    A proton has 1836 times the mass of an electron and is the lightest nucleus to be used for accelerator in material modification. We can setup accelerator with the lowest acceleration voltage. It is preferable characteristics of Proton Beam Writer (PBW) for industrial applications. On the contrary ;proton; has the lowest charge among all nuclei and the potential impact to material is lowest. The object of this research is to improve productivity of the PBW for industry application focusing on hydrogen molecular ions. These ions are generated in the same ion source by ionizing hydrogen molecule. There is no specific ion source requested and it is suitable for industrial use. We demonstrated three dimensional (3D) multilevel micro structures on polyester base FPC (Flexible Printed Circuits) using proton, H2+ and H3+. The reactivity of hydrogen molecular ions is much higher than that of proton and coincident with the level of expectation. We can apply this result to make micro devices of 3D multilevel structures on FPC.

  13. Electronic structure and enthalpy of hydrogen and helium mixtures

    NASA Astrophysics Data System (ADS)

    Ross, M.; Klepeis, J. E.; Schafer, K. J.; Barbee, T. W., III

    1992-11-01

    The first local density approximation (LDA) calculations of the electronic structure, equation of state, and enthalpy of mixing were carried out for a number of different compositions of hydrogen and helium in bcc and fcc lattices. These are fully quantum mechanical, self-consistent calculations utilizing state-of-the-art methods of electron band theory, which make no assumptions regarding pressure ionization. The major approximation in the LDA method is that the exchange and correlation energy is given by a free electron functional in terms of the local electron density. The majority of previous mixture calculations start with the assumption that both hydrogen and helium are pressure-ionized so that the electronic structure is approximately that of free or weakly screened electrons in the presence of positive ions. Stevenson used a hard-sphere mixture model for the ions with an ion-ion pseudopotential to account for electron screening and predicted that a mixture containing 7% helium by number, the composition believed to be present in Jupiter and Saturn, would phase separate at a temperature of about 7000 K at 8 Mbar. Subsequent calculations carried out for the fully ionized mixture and for a mixture of screened ions (linear response theory) have all arrived at predictions similar to those of Stevenson. MacFarlane and Hubbard performed Thomas-Fermi-Dirac calculations for mixing enthalpies of hydrogen and helium in bcc and fcc lattices and predicted that phase separation would not occur at any temperature.

  14. Proton-structure corrections to hyperfine splitting in muonic hydrogen

    SciTech Connect

    Carlson, Carl E.; Nazaryan, Vahagn; Griffioen, Keith

    2011-04-15

    We present the derivation of the formulas for the proton structure-dependent terms in the hyperfine splitting of muonic hydrogen. We use compatible conventions throughout the calculations to derive a consistent set of formulas that reconcile differences between our results and some specific terms in earlier work. Convention conversion corrections are explicitly presented, which reduce the calculated hyperfine splitting by about 46 ppm. We also note that using only modern fits to the proton elastic form factors gives a smaller than historical spread of Zemach radii and leads to a reduced uncertainty in the hyperfine splitting. Additionally, hyperfine splittings have an impact on the muonic hydrogen Lamb shift and proton radius measurement, however the correction we advocate has a small effect there.

  15. Structure determination by diffuse LEED of disordered CO adsorbed on Ru(001) at low coverages

    NASA Astrophysics Data System (ADS)

    Piercy, P.; Heimann, P. A.; Michalk, G.; Menzel, D.

    1989-09-01

    Diffuse LEED scattering from the low coverage, disordered CO/Ru(001) system has been measured using a multichannel, angle-resolving, energy-dispersive electron analyzer. The incident beam was off-normal and diffuse intensities were measured in the plane of incidence, for different azimuthal angles of incidence, and for different beam energies. A detailed multiple scattering analysis was carried out using the DLEED and TAUMOL programs of Saldin and Pendry. By performing and analyzing measurements at absolute CO coverages of 5%, 10% and 20% of a monolayer and at temperatures T = 120 and 330 K, the diffuse LEED technique of structure determination was tested under different controlled experimental conditions. While for 10% ML the comparison with theory was best when Y-functions were used, the 5% coverage could be successfully analysed by comparing relative intensities; for 20% ML partial ordering disturbed the analysis. By combination of data sets at two energies an unequivocal decision between sites and a determination of structural and non-structural (inner potential) parameters was possible. From the complete data, the favoured adsorption structure has CO linearly bonded to the on-top site with a perpendicular Ru-C distance of 2.0 ±0.15 Å, in close agreement with the ordered √3-structure at θ = {1}/{3}. This result is nontrivial and furthermore provides a positive test of the diffuse LEED technique in general as well as of our particular approach.

  16. Determination of Adsorbate Structures from 1,4-Phenylene Diisocyanide on Gold.

    PubMed

    Kestell, John; Abuflaha, Rasha; Boscoboinik, J Anibal; Garvey, Michael; Bennett, Dennis W; Tysoe, Wilfred T

    2014-10-16

    The structure of the 1-D oligomer chains that form on a Au(111) surface following adsorption of 1,4-phenylene diisocyanide (PDI) is explored using reflection-absorption infrared spectroscopy and scanning tunneling microscopy (STM). The experimental work is complemented by first-principles density functional theory calculations, which indicate that the previously proposed gold-PDI oligomer chains in which the PDI molecule bridged gold adatoms are thermodynamically stable. In addition, the calculated vibrational modes for this structure are in excellent agreement with the experimental infrared data. The linkage of the PDI units by gold adatoms is confirmed by comparing STM images collected as a function of tip bias with images for the calculated structure by the Bardeen method.

  17. Supported Ag nanoparticles as trace iodide adsorbent from acetic acid

    NASA Astrophysics Data System (ADS)

    Qian, Qingli; Shao, Shouyan; Yan, Fang; Ling, Chen; Yan, Fengwen; Cao, Hongbing; Guo, Cun-Yue; Yuan, Guoqing

    2012-09-01

    Ag nanoparticles (AgNPs) were used as adsorbent to remove trace iodide from acetic acid. Under identical conditions, AgNPs adsorbent with 0.5 wt % Ag has the same performance as commercial adsorbent with 10 wt % Ag+. In addition, Ag loss of AgNPs adsorbent is remarkably lower than that of commercial adsorbent. The Ag content in AgNPs adsorbent affects its adsorption performance, and the optimal content is 1.0 wt %. Saturated AgNPs adsorbent can be regenerated by hydrogen reduction and reused with satisfying performance. The properties of AgNPs adsorbent are based on surface effect of nanoparticles, differing from commercial Ag+ type adsorbents. In a word, AgNPs adsorbent is of high efficiency, low Ag loss and easy recycling, thus making it "green adsorbent" for removing iodide from acetic acid.

  18. Group V adsorbate structures on vicinal Ge(001) surfaces determined from the optical spectrum

    NASA Astrophysics Data System (ADS)

    Banerjee, S.; Patterson, C. H.; McGilp, J. F.

    2017-06-01

    Vicinal Ge(001) is the standard substrate for the fabrication of high-performance solar cells by metal-organic vapour phase epitaxy, where growth of the III-V material on single domain Ge surfaces, with a single dimer orientation, minimizes the formation of anti-phase domain defects. Reflectance anisotropy spectroscopy has proved to be a powerful and sensitive optical probe of such anisotropic surface structures, but moving beyond fingerprinting to atomic structure determination from the optical spectra has been held back by the high computational cost. It is shown that an empirical, local-orbital-based hybrid density functional theory approach produces very good agreement between the theory and the experiment for (2 × 1)-As and (2 × 1)-Sb structures grown on vicinal Ge(001). These results, when taken together with previous work on Si interfaces, show that this computationally efficient approach is likely to prove to be an important general technique for determining the structure of anisotropic semiconductor surfaces and interfaces by comparing the experimental and calculated optical spectrum.

  19. Hydrogenation induced structure and property changes in GdGa

    SciTech Connect

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

    2016-07-15

    Hydrides GdGaH{sub x} 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 NdGaH{sub 1.66} 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 NdGaH{sub 1.66} 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 GdGaH{sub 1.66}. 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 GdGaH{sub 1.66}, takes place at lower temperatures. Consequently, GdGaH{sub 1.66} desorbs H above T=200 °C. Without the presence of hydrogen, hydrides GdGaH{sub x} decompose at temperatures above 300 °C into GdH{sub 2} 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 GdGaH{sub 1.66} were obtained. The former indicates antiferromagnetic interactions, the latter attains a value of ~8 μ{sub B} which is typical for compounds containing Gd{sup 3+}ions. - Graphical abstract: Ferromagnetic GdGa absorbs hydrogen in two steps to yield antiferromagnetic GdGaH{sub 1.66}. Display Omitted - Highlights: • Elucidation of hydrogen uptake behavior of the rare earth gallide

  20. The Effect of monoglycerides on structural and topographical characteristics of adsorbed beta-casein films at the air-water interface.

    PubMed

    Fernández, Marta Cejudo; Sánchez, Cecilio Carrera; Rodríguez Niño, M Rosario; Rodríguez Patino, Juan M

    2006-02-01

    The effect of monoglycerides (monopalmitin and monoolein) on the structural and topographical characteristics of beta-casein adsorbed film at the air-water interface has been analyzed by means of surface pressure (pi)-area (A) isotherms and Brewster angle microscopy (BAM). At surface pressures lower than that for the beta-casein collapse (pi(c)(beta-casein)), attractive interactions between beta-casein and monoglycerides were observed. At higher surface pressures, the collapsed beta-casein is partially displaced from the interface by monoglycerides. However, beta-casein displacement by monoglycerides is not quantitative at the monoglyceride concentrations studied in this work. From the results derived from these experiments, we have concluded that interactions, miscibility, and displacement of proteins by monoglycerides in adsorbed mixed monolayers at the air-water interface depend on the particular protein-monoglyceride system, the interactions between film-forming components being higher for adsorbed than for spread films. The adsorbed films are more segregated than spread films, and both collapsed protein domains and monoglyceride domains in adsorbed films are smaller than for spread films.

  1. Effect of reducible oxide-metal cluster charge transfer on the structure and reactivity of adsorbed Au and Pt atoms and clusters on anatase TiO2

    NASA Astrophysics Data System (ADS)

    Wang, Honghong; An, Taicheng; Selloni, Annabella

    2017-05-01

    We carried out density functional theory calculations to study the influence of oxide-metal charge transfers on the structure, energetics, and reactivity of Au and Pt atoms, dimers, and trimers adsorbed on the (101) surface of reduced anatase TiO2. Pt clusters interact much more strongly with the TiO2 support than Au clusters, and, with the exception of single Pt adatoms, generally behave as electron acceptors on reduced TiO2, whereas Au clusters can both accept and donate charge on the reduced surface. The reactivity of the supported clusters was probed by considering their interaction with CO and co-adsorbed O2. The effect of surface reduction on the interaction with CO is particularly significant when the CO adsorption site is an interfacial metal atom directly in contact with the TiO2 surface and/or in the presence of co-adsorbed O2. Pt clusters interact strongly with co-adsorbed O2 and form Pt-O2 complexes that can easily accept electrons from reduced surfaces. In contrast, Au clusters donate charge to co-adsorbed O2 even in the presence of excess electrons from a reduced support. The computed differences in the properties of the supported Pt and Au clusters are consistent with several experimental observations and highlight the important role of excess surface electrons in the behavior of supported metal catalysts on reducible oxides.

  2. A Link between Protein Structure and Enzyme Catalyzed Hydrogen Tunneling

    NASA Astrophysics Data System (ADS)

    Bahnson, Brian J.; Colby, Thomas D.; Chin, Jodie K.; Goldstein, Barry M.; Klinman, Judith P.

    1997-11-01

    We present evidence that the size of an active site side chain may modulate the degree of hydrogen tunneling in an enzyme-catalyzed reaction. Primary and secondary kH/kT and kD/kT kinetic isotope effects have been measured for the oxidation of benzyl alcohol catalyzed by horse liver alcohol dehydrogenase at 25 degrees C. As reported in earlier studies, the relationship between secondary kH/kT and kD/kT isotope effects provides a sensitive probe for deviations from classical behavior. In the present work, catalytic efficiency and the extent of hydrogen tunneling have been correlated for the alcohol dehydrogenase-catalyzed hydride transfer among a group of site-directed mutants at position 203. Val-203 interacts with the opposite face of the cofactor NAD+ from the alcohol substrate. The reduction in size of this residue is correlated with diminished tunneling and a two orders of magnitude decrease in catalytic efficiency. Comparison of the x-ray crystal structures of a ternary complex of a high-tunneling (Phe-93 --> Trp) and a low-tunneling (Val-203 --> Ala) mutant provides a structural basis for the observed effects, demonstrating an increase in the hydrogen transfer distance for the low-tunneling mutant. The Val-203 --> Ala ternary complex crystal structure also shows a hyperclosed interdomain geometry relative to the wild-type and the Phe-93 --> Trp mutant ternary complex structures. This demonstrates a flexibility in interdomain movement that could potentially narrow the distance between the donor and acceptor carbons in the native enzyme and may enhance the role of tunneling in the hydride transfer reaction.

  3. Hydrogenation and hydrogen intercalation of hexagonal boron nitride on Ni(1 1 1): reactivity and electronic structure

    NASA Astrophysics Data System (ADS)

    Späth, F.; Gebhardt, J.; Düll, F.; Bauer, U.; Bachmann, P.; Gleichweit, C.; Görling, A.; Steinrück, H.-P.; Papp, C.

    2017-09-01

    We investigate the reactivity of hexagonal boron nitride (h-BN) on a Ni(1 1 1) single crystal towards atomic hydrogen over a wide exposure range. Near edge x-ray absorption fine structure and x-ray photoelectron spectroscopy (XPS) show that for low hydrogen exposures hydrogenation of the h-BN sheet is found. In contrast, intercalation of hydrogen between h-BN and the Ni(1 1 1) substrate occurs for high exposures. For intermediate regimes, a mixture of intercalation and hydrogenation is observed. From temperature-programmed desorption and temperature-programmed XPS experiments, we conclude that the hydrogen covalently bound to h-BN is rather stable with a desorption temperature of 600 K, while intercalated hydrogen is desorbing already at 390 K. Further insight into the structural arrangements and the thermodynamics of the system is obtained by comparing our experimental results with extensive density-functional theory calculations. Together with ultraviolet photoelectron spectroscopy measurements, the calculations provide detailed insight into the influence of hydrogenation on the electronic structure of h-BN.

  4. The electronic structure and catalytic properties of molybdenum sulfides in the coal hydrogenation process

    SciTech Connect

    A.M. Gyul'maliev; M.A. Gyul'malieva; A.S. Maloletnev; M.Ya. Shpirt

    2008-08-15

    Comparative analysis of the electronic structure of molybdenum sulfides and their catalytic activity in hydrogenation reactions was performed from the results of Hartree-Fock ab initio quantum-chemical calculations using the STO 3-21G and 6-311G basis sets with geometry optimization. The model reactions of hydrogenation of aromatic and saturated hydrocarbons with hydrogen and hydrogen sulfide were studied. It was shown that the hydrogenation reactions of aromatic hydrocarbons with hydrogen sulfide must occur at a higher rate (with lower activation energy) as compared to those with molecular hydrogen.

  5. 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.

  6. Characterization of Cross-Linked Cellulosic Ion-Exchange Adsorbents: 1. Structural Properties

    PubMed Central

    Angelo, James M.; Cvetkovic, Aleksandar; Gantier, Rene; Lenhoff, Abraham M.

    2014-01-01

    The structural characteristics of the HyperCel family of cellulosic ion-exchange materials (Pall Corporation) were assessed using methods to gauge the pore dimensions and the effect of ionic strength on intraparticle architecture. Inverse size exclusion chromatography (ISEC) was applied to the S and STAR AX HyperCel derivatives. The theoretical analysis yielded an average pore radius for each material of about 5 nm, with a particularly narrow pore-size distribution. Electron microscopy techniques were used to visualize the particle structure and relate it to macroscopic experimental data. Microscopy of Q and STAR AX HyperCel anion exchangers presented some qualitative differences in pore structure that can be attributed to the derivatization using conventional quaternary ammonium and salt-tolerant ligands, respectively. Finally, the effect of ionic strength was studied through the use of salt breakthrough experiments to determine to what extent Donnan exclusion plays a role in restricting the accessible pore volume for small ions. It was determined that Donnan effects were prevalent at total ionic strengths (TIS) less than 150 mM, suggesting the presence of a ligand-containing partitioning volume within the pore space. PMID:24188996

  7. MgO-based adsorbents for CO2 adsorption: Influence of structural and textural properties on the CO2 adsorption performance.

    PubMed

    Elvira, Gutiérrez-Bonilla; Francisco, Granados-Correa; Víctor, Sánchez-Mendieta; Alberto, Morales-Luckie Raúl

    2017-07-01

    A series of MgO-based adsorbents were prepared through solution-combustion synthesis and ball-milling process. The prepared MgO-based powders were characterized using X-ray diffraction, scanning electron microscopy, N2 physisorption measurements, and employed as potential adsorbents for CO2 adsorption. The influence of structural and textural properties of these adsorbents over the CO2 adsorption behaviour was also investigated. The results showed that MgO-based products prepared by solution-combustion and ball-milling processes, were highly porous, fluffy, nanocrystalline structures in nature, which are unique physico-chemical properties that significantly contribute to enhance their CO2 adsorption. It was found that the MgO synthesized by solution combustion process, using a molar ratio of urea to magnesium nitrate (2:1), and treated by ball-milling during 2.5hr (MgO-BM2.5h), exhibited the maximum CO2adsorption capacity of 1.611mmol/g at 25°C and 1atm, mainly via chemisorption. The CO2 adsorption behaviour on the MgO-based adsorbents was correlated to their improved specific surface area, total pore volume, pore size distribution and crystallinity. The reusability of synthesized MgO-BM2.5h was confirmed by five consecutive CO2 adsorption-desorption times, without any significant loss of performance, that supports the potential of MgO-based adsorbent. The results confirmed that the special features of MgO prepared by solution-combustion and treated by ball-milling during 2.5hr are favorable to be used as effective MgO-based adsorbent in post-combustion CO2 capture technologies. Copyright © 2016. Published by Elsevier B.V.

  8. 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.

  9. 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.

  10. Structural Evolution of a Recoverable Rhodium Hydrogenation Catalyst

    SciTech Connect

    Shaw, Wendy J.; Chen, Yongsheng; Fulton, John L.; Linehan, John C.; Gutowska, Anna; Bitterwolf, Thomas E.

    2008-06-01

    N-isopropylacrylamide was utilized as a ligand to affect recoverability into a rhodium hydrogenation catalyst. The catalyst ligand structure was characterized in situ using NMR, XAFS and IR. Model compounds including glycine, cysteamine and methionine methyl ester were also investigated to aid in the interpretation. The investigation revealed a ligand switch from RNH2 to RSR’ when the catalyst is placed in water as opposed to organic solvents. The catalyst continued to transform with time, creating Rh clusters of up to 4 rhodium atoms, with no Rh metal detected. Over the time and solvents investigated, the catalyst ligands evolve from 1-Cl, 1-NH2, and 2-CO’s to 3-Rh, 1-RSR’ and 1-CO. Upon introduction of the alkene for hydrogenation catalysis, the Rh cluster is lost, favoring instead the interaction with the reactant. The kinetics of the hydrogenation reaction were measured using a novel high pressure flow through NMR system and the catalyst was found to have a TOF of 3000/hr at 25 ºC. This work was supported by the Laboratory Directed Research and Development Program at the Pacific Northwest National Laboratory operated by Battelle for the U.S. Department of Energy.

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

    PubMed

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

    2009-01-01

    A three-electrode based CO(2) 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 CO(2) 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.

  12. Controlling the Electronic Structure of Graphene Using Surface-Adsorbate Interactions

    DTIC Science & Technology

    2015-07-21

    et al., Layer Area, Few- Layer Graphene Films on Arbitrary Substrates by Chemical Vapor Deposition . Nano Letters, 2009. 9(8): p. 3087-3087. 18...the underlying layer . 44. Gamo, Y., et al., Atomic structure of monolayer graphite formed on Ni(111). Surface Science, 1997. 374(1-3): p. 61-64. 45... atomic orbitals in graphene on Ni(111) opens a large energy gap of ≈2.8 eV between non-hybridized states at the K-point. Here we use alkali metal

  13. Oligoethylene-bridged diferrocene on Ag(110): Monolayer structures and adsorbate-induced faceting

    SciTech Connect

    Zhong, D. Y.; Fuchs, H.; Wang, W. C.; Dou, R. F.; Chi, L. F.; Wedeking, K.; Erker, G.

    2007-11-15

    The self-assembly of a ferrocene (Fc) derivative, oligoethylene-bridged diferrocene (diFc), Fc(CH{sub 2}){sub 14}Fc, on Ag(110) surface has been investigated by scanning tunneling microscopy (STM) under ultrahigh vacuum. Three ordered structures, the majority {beta} and the minorities {alpha} and {gamma}, are formed at monolayer coverage. In {alpha} and {gamma}, a unit cell contains one molecule and the molecules are parallel to each other so that the distances between Fc groups and between oligoethylene chains are reduced. A unit cell contains five molecules in {beta}: four of them are parallel to each other but not parallel to the fifth. The interaction between diFc and Ag(110), which is relatively strong in comparison to the intermolecular interaction, is dominant for the assembly of the ordered structures. The adsorption of diFc molecules induces the reorganization of substrate steps, which prefer to follow the directions of the superstructure lattice vectors, i.e. ({+-}1,2) and ({+-}3,2) of the Ag(110) surface. The (12 13-1) facet is formed due to step bunching at regions with high step density. By using in situ STM, the process of step reorganization and faceting has been observed in real time. It is concluded that the Ag adatoms play a key role on the substrate reorganization.

  14. Oligoethylene-bridged diferrocene on Ag(110): Monolayer structures and adsorbate-induced faceting

    NASA Astrophysics Data System (ADS)

    Zhong, D. Y.; Wang, W. C.; Dou, R. F.; Wedeking, K.; Erker, G.; Chi, L. F.; Fuchs, H.

    2007-11-01

    The self-assembly of a ferrocene (Fc) derivative, oligoethylene-bridged diferrocene (diFc), Fc(CH2)14Fc , on Ag(110) surface has been investigated by scanning tunneling microscopy (STM) under ultrahigh vacuum. Three ordered structures, the majority β and the minorities α and γ , are formed at monolayer coverage. In α and γ , a unit cell contains one molecule and the molecules are parallel to each other so that the distances between Fc groups and between oligoethylene chains are reduced. A unit cell contains five molecules in β : four of them are parallel to each other but not parallel to the fifth. The interaction between diFc and Ag(110), which is relatively strong in comparison to the intermolecular interaction, is dominant for the assembly of the ordered structures. The adsorption of diFc molecules induces the reorganization of substrate steps, which prefer to follow the directions of the superstructure lattice vectors, i.e., (∓1,2) and (±3,2) of the Ag(110) surface. The (1213-1) facet is formed due to step bunching at regions with high step density. By using in situ STM, the process of step reorganization and faceting has been observed in real time. It is concluded that the Ag adatoms play a key role on the substrate reorganization.

  15. 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.

  16. The spiral structure of the outer Milky Way in hydrogen.

    PubMed

    Levine, E S; Blitz, Leo; Heiles, Carl

    2006-06-23

    We produce a detailed map of the perturbed surface density of neutral hydrogen in the outer Milky Way disk, demonstrating that the Galaxy is a non-axisymmetric multiarmed spiral. Spiral structure in the southern half of the Galaxy can be traced out to at least 25 kiloparsecs, implying a minimum radius for the gas disk. Overdensities in the surface density are coincident with regions of reduced gas thickness. The ratio of the surface density to the local median surface density is relatively constant along an arm. Logarithmic spirals can be fit to the arms with pitch angles of 20 degrees to 25 degrees .

  17. Structured rf hydrogen plasma induced by magnetic field.

    SciTech Connect

    Barnat, Edward V.

    2007-11-01

    Images of the spatial structure of a capacitively coupled hydrogen discharge are presented for various strengths of applied magnetic field. With increasing magnetic field, we find that not only does the distribution of emission change because of the confinement of the electrons by the magnetic field, but we also find 'dark-bands' regions that form in the discharge. By using narrowband interference filters (10 nm bandwidth), we examine how the relative optical emission centered on H{sub {alpha}} and H{sub {beta}} (with respect to the total optical emission) change with the applied magnetic field.

  18. Low-temperature adsorption/storage of hydrogen on FAU, MFI, and MOR zeolites with various Si/Al ratios: effect of electrostatic fields and pore structures.

    PubMed

    Jhung, Sung Hwa; Yoon, Ji Woong; Lee, Ji Sun; Chang, Jong-San

    2007-01-01

    Several zeolites, such as faujasite, mordenite, and ZSM-5, with various aluminum contents have been used to analyze the effect of aluminum or cation concentration (strength of electrostatic field) on hydrogen adsorption at low temperature. Irrespective of the zeolite structure, the adsorption capacity, isosteric heat of adsorption (-DeltaHads), surface coverage, and micropore occupancy increase with increasing aluminum content of a zeolite. Zeolites with a higher amount of aluminum favorably adsorb hydrogen at relatively low pressures. For zeolites with similar aluminum contents, the adsorption capacity, isosteric heat of adsorption, surface coverage, and micropore occupancy are in the order of mordenite>ZSM-5>faujasite, probably due to differing pore sizes and the presence or absence of pore intersections. This work demonstrates that zeolites with strong electrostatic fields and narrow pores without intersections are beneficial for high hydrogen uptake.

  19. 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.

  20. 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.

  1. 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

  2. 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.

  3. 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.

  4. Theoretical simulations of structure and X-ray photoelectron spectra of glycine and diglycine adsorbed on Cu(110).

    PubMed

    Carravetta, Vincenzo; Monti, Susanna; Li, Cui; Ågren, Hans

    2013-08-13

    The study of adsorption of glycine and glycylglycine (or diglycine) on a copper surface is an important step for the comprehension of mechanisms that determine the stability of biological functionalizers on metal substrates. These two molecules can be considered as prototypes and essential models to investigate, theoretically and experimentally, the adaptability of flexible short peptide chains to a definite interface. In this work, we have improved and updated earlier molecular dynamics simulations by including reactivity of the various species and the comparison of ab initio calculated C, N, and O core photoelectron chemical shifts with the ones found in previous studies. New diglycine-copper bonding is predicted, and the results of the chemical shift analysis are, in all cases, fully compatible with structural information obtained through experimental measurements. Moreover, we have found that the process of proton transfer, which is fundamental in the dynamics of amino acids and peptides, occurs mainly by intermolecular interaction between the first and second layer of the adsorbate.

  5. 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.

  6. 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.

  7. Hydrogen atoms in protein structures: high-resolution X-ray diffraction structure of the DFPase

    PubMed Central

    2013-01-01

    Background Hydrogen atoms represent about half of the total number of atoms in proteins and are often involved in substrate recognition and catalysis. Unfortunately, X-ray protein crystallography at usual resolution fails to access directly their positioning, mainly because light atoms display weak contributions to diffraction. However, sub-Ångstrom diffraction data, careful modeling and a proper refinement strategy can allow the positioning of a significant part of hydrogen atoms. Results A comprehensive study on the X-ray structure of the diisopropyl-fluorophosphatase (DFPase) was performed, and the hydrogen atoms were modeled, including those of solvent molecules. This model was compared to the available neutron structure of DFPase, and differences in the protein and the active site solvation were noticed. Conclusions A further examination of the DFPase X-ray structure provides substantial evidence about the presence of an activated water molecule that may constitute an interesting piece of information as regard to the enzymatic hydrolysis mechanism. PMID:23915572

  8. Hydrogen atoms in protein structures: high-resolution X-ray diffraction structure of the DFPase.

    PubMed

    Elias, Mikael; Liebschner, Dorothee; Koepke, Jurgen; Lecomte, Claude; Guillot, Benoit; Jelsch, Christian; Chabriere, Eric

    2013-08-02

    Hydrogen atoms represent about half of the total number of atoms in proteins and are often involved in substrate recognition and catalysis. Unfortunately, X-ray protein crystallography at usual resolution fails to access directly their positioning, mainly because light atoms display weak contributions to diffraction. However, sub-Ångstrom diffraction data, careful modeling and a proper refinement strategy can allow the positioning of a significant part of hydrogen atoms. A comprehensive study on the X-ray structure of the diisopropyl-fluorophosphatase (DFPase) was performed, and the hydrogen atoms were modeled, including those of solvent molecules. This model was compared to the available neutron structure of DFPase, and differences in the protein and the active site solvation were noticed. A further examination of the DFPase X-ray structure provides substantial evidence about the presence of an activated water molecule that may constitute an interesting piece of information as regard to the enzymatic hydrolysis mechanism.

  9. Acetylene hydrogenation over structured Au-Pd catalysts.

    PubMed

    McCue, Alan J; Baker, Richard T; Anderson, James A

    2016-07-04

    AuPd nanoparticles were prepared following a methodology designed to produce core-shell structures (an Au core and a Pd shell). Characterisation suggested that slow addition of the shell metal favoured deposition onto the pre-formed core, whereas more rapid addition favoured the formation of a monometallic Pd phase in addition to some nanoparticles with the core-shell morphology. When used for the selective hydrogenation of acetylene, samples that possessed monometallic Pd particles favoured over-hydrogenation to form ethane. A sample prepared by the slow addition of a small amount of Pd resulted in the formation of a core-shell structure but with an incomplete Pd shell layer. This material exhibited a completely different product selectivity with ethylene and oligomers forming as the major products as opposed to ethane. The improved performance was thought to be as a result of the absence of Pd particles, which are capable of forming a Pd-hydride phase, with enhanced oligomer selectivity associated with reaction on uncovered Au atoms.

  10. Unveiling subsurface hydrogen-bond structure of hexagonal water ice

    NASA Astrophysics Data System (ADS)

    Otsuki, Yuji; Sugimoto, Toshiki; Ishiyama, Tatsuya; Morita, Akihiro; Watanabe, Kazuya; Matsumoto, Yoshiyasu

    2017-09-01

    The phase-resolved sum-frequency-generation (SFG) spectrum for the basal face of hexagonal ice is reported and is interpreted by molecular dynamics simulations combined with ab initio quantum calculations. Here, we demonstrate that the line shape of the SFG spectra of isotope-diluted OH chromophores is a sensitive indicator of structural rumpling uniquely emerging at the subsurface of hexagonal ice. In the outermost subsurface between the first (B1) and second (B2) bilayer, the hydrogen bond of OB 1-H ⋯OB 2 is weaker than that of OB 1⋯H -OB 2 . This implies that subsurface O-O distance is laterally altered, depending on the direction of O-H bond along the surface normal: H-up or H-down, which is in stark contrast to bulk hydrogen bonds. This new finding uncovers how water molecules undercoordinated at the topmost surface influence on the subsurface structural rumpling associated with orientational frustration inherent in water ice.

  11. Hydrogen sensing characteristics of Cu-PS-Si structures

    NASA Astrophysics Data System (ADS)

    Dzhafarov, T. D.; Omur, B. Can; Oruc, C.; Allahverdiev, Z. A.

    2002-12-01

    The effect of ambient humidity on the current-voltage characteristics of Cu-PS (porous silicon) structures was investigated. The humidity-voltaic effect, i.e. generation of humid voltage (Voc) in Cu-PS interface in humid atmosphere (up to 300 mV at 95% relative humidity) in dark and day-light illumination is discovered. Humidity-stimulated voltage generation is caused by the hydrogen component of water vapour of ambient. A possible mechanism of hydrogen-stimulated voltage generation in Cu-PS interface is suggested. Besides the effect of annealing in the range of 60-200°C in air on Voc of Cu-PS structures was studied and decrease of values of Voc depending on duration of annealing was discovered. These changes were attributed to diffusion of oxygen from air and oxidation of the copper film. (Voc-t) data were used for estimation of the diffusion coefficients of oxygen in the Cu film. The temperature dependence of the oxygen diffusion coefficient in Cu films is described by the relation D = 5.2×10-7exp(-0.44/kT).

  12. Rapid visualization of hydrogen positions in protein neutron crystallographic structures.

    PubMed

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

    2012-01-01

    Neutron crystallography is a powerful technique for experimental visualization of the positions of light atoms, including hydrogen and its isotope deuterium. In recent years, structural biologists have shown increasing interest in the technique as it uniquely complements X-ray crystallographic data by revealing the positions of D atoms in macromolecules. With this regained interest, access to macromolecular neutron crystallography beamlines is becoming a limiting step. In this report, it is shown that a rapid data-collection strategy can be a valuable alternative to longer data-collection times in appropriate cases. Comparison of perdeuterated rubredoxin structures refined against neutron data sets collected over hours and up to 5 d shows that rapid neutron data collection in just 14 h is sufficient to provide the positions of 269 D atoms without ambiguity.

  13. Adsorptive Removal of Pharmaceuticals and Personal Care Products from Water with Functionalized Metal-organic Frameworks: Remarkable Adsorbents with Hydrogen-bonding Abilities

    NASA Astrophysics Data System (ADS)

    Seo, Pill Won; Bhadra, Biswa Nath; Ahmed, Imteaz; Khan, Nazmul Abedin; Jhung, Sung Hwa

    2016-10-01

    Adsorption of typical pharmaceuticals and personal care products (PPCPs) (such as naproxen, ibuprofen and oxybenzone) from aqueous solutions was studied by using the highly porous metal-organic framework (MOF) MIL-101 with and without functionalization. Adsorption results showed that MIL-101s with H-donor functional groups such as –OH and –NH2 were very effective for naproxen adsorption, despite a decrease in porosity, probably because of H-bonding between O atoms on naproxen and H atoms on the adsorbent. For this reason, MIL-101 with two functional groups capable of H-bonding (MIL-101-(OH)2) exhibited remarkable adsorption capacity based on adsorbent surface area. The favorable contributions of –OH and –(OH)2 on MIL-101 in the increased adsorption of ibuprofen and oxybenzone (especially based on porosity) confirmed again the importance of H-bonding mechanism. The adsorbent with the highest adsorption capacity, MIL-101-OH, was very competitive when compared with carbonaceous materials, mesoporous materials, and pristine MIL-101. Moreover, the MIL-101-OH could be recycled several times by simply washing with ethanol, suggesting potential application in the adsorptive removal of PPCPs from water.

  14. Adsorptive Removal of Pharmaceuticals and Personal Care Products from Water with Functionalized Metal-organic Frameworks: Remarkable Adsorbents with Hydrogen-bonding Abilities.

    PubMed

    Seo, Pill Won; Bhadra, Biswa Nath; Ahmed, Imteaz; Khan, Nazmul Abedin; Jhung, Sung Hwa

    2016-10-03

    Adsorption of typical pharmaceuticals and personal care products (PPCPs) (such as naproxen, ibuprofen and oxybenzone) from aqueous solutions was studied by using the highly porous metal-organic framework (MOF) MIL-101 with and without functionalization. Adsorption results showed that MIL-101s with H-donor functional groups such as -OH and -NH2 were very effective for naproxen adsorption, despite a decrease in porosity, probably because of H-bonding between O atoms on naproxen and H atoms on the adsorbent. For this reason, MIL-101 with two functional groups capable of H-bonding (MIL-101-(OH)2) exhibited remarkable adsorption capacity based on adsorbent surface area. The favorable contributions of -OH and -(OH)2 on MIL-101 in the increased adsorption of ibuprofen and oxybenzone (especially based on porosity) confirmed again the importance of H-bonding mechanism. The adsorbent with the highest adsorption capacity, MIL-101-OH, was very competitive when compared with carbonaceous materials, mesoporous materials, and pristine MIL-101. Moreover, the MIL-101-OH could be recycled several times by simply washing with ethanol, suggesting potential application in the adsorptive removal of PPCPs from water.

  15. Adsorptive Removal of Pharmaceuticals and Personal Care Products from Water with Functionalized Metal-organic Frameworks: Remarkable Adsorbents with Hydrogen-bonding Abilities

    PubMed Central

    Seo, Pill Won; Bhadra, Biswa Nath; Ahmed, Imteaz; Khan, Nazmul Abedin; Jhung, Sung Hwa

    2016-01-01

    Adsorption of typical pharmaceuticals and personal care products (PPCPs) (such as naproxen, ibuprofen and oxybenzone) from aqueous solutions was studied by using the highly porous metal-organic framework (MOF) MIL-101 with and without functionalization. Adsorption results showed that MIL-101s with H-donor functional groups such as –OH and –NH2 were very effective for naproxen adsorption, despite a decrease in porosity, probably because of H-bonding between O atoms on naproxen and H atoms on the adsorbent. For this reason, MIL-101 with two functional groups capable of H-bonding (MIL-101-(OH)2) exhibited remarkable adsorption capacity based on adsorbent surface area. The favorable contributions of –OH and –(OH)2 on MIL-101 in the increased adsorption of ibuprofen and oxybenzone (especially based on porosity) confirmed again the importance of H-bonding mechanism. The adsorbent with the highest adsorption capacity, MIL-101-OH, was very competitive when compared with carbonaceous materials, mesoporous materials, and pristine MIL-101. Moreover, the MIL-101-OH could be recycled several times by simply washing with ethanol, suggesting potential application in the adsorptive removal of PPCPs from water. PMID:27695005

  16. Carbon-mineral adsorbents prepared by pyrolysis of waste materials in the presence of tetrachloromethane.

    PubMed

    Leboda, Roman; Charmas, Barbara; Skubiszewska-Zieba, Jadwiga; Chodorowski, Stanislaw; Oleszczuk, Patryk; Gun'ko, Vladimir M; Pokrovskiy, Valery A

    2005-04-01

    Natural bentonite spent in the process of plant oil bleaching was used as an initial material for preparation of carbon-mineral adsorbents. The spent bleaching earth was treated using four procedures: T (thermal treatment); H (hydrothermal treatment); C (thermal treatment with addition of CCl4 vapor); M (modification of porous structure). Raw bentonite, RB (raw bleaching earth), and carbon materials prepared using plant oil were compared. The physicochemical characteristics of the adsorbents were determined using different methods: nitrogen adsorption/desorption, XRD, TEM, and MS-TPD. Carbon-mineral adsorbents contain from 5.23 to 19.92% C (w/w) and carbon adsorbents include from 84.2 to 91.18% C (w/w). Parallel processes of organic substance carbonization, porous structure modification, sublimation or evaporation of metal chlorides, and removal of hydrogen chloride take place during pyrolysis of waste mineral materials in the CCl4 atmosphere.

  17. Microscopic analyses of complexes formed in adsorbent for Mo and Zr separation chromatography

    NASA Astrophysics Data System (ADS)

    Abe, Ryoji; Nagoshi, Kohei; Arai, Tsuyoshi; Watanabe, Sou; Sano, Yuichi; Matsuura, Haruaki; Takagi, Hideaki; Shimizu, Nobutaka; Koka, Masashi; Sato, Takahiro

    2017-08-01

    Molybdenum and zirconium obstruct the efficient recovery of minor actinides (MA(III): Am(III) and Cm(III)) by extraction chromatography; hence, the removal of these elements prior to MA(III) recovery is desirable. The use of an adsorbent impregnated with bis(2-ethylhexyl) hydrogen phosphate (HDEHP) for Mo and Zr decontamination was evaluated in this report. The adsorption/elution and column separation experiments showed that Mo and Zr in the simulated HLLW were selectively adsorbed on the particles, and that Mo was eluted by H2O2. EXAFS analysis and SAXS patterns of the adsorbent containing Zr revealed that the Zr-HDEHP complex had a crystal-like periodic structure similar to the structure of the precipitate produced in the solvent extraction system. Micro-PIXE analysis revealed that distribution of the residual Zr on the adsorbent was uniform.

  18. Structural, optical, and electrical characterization of improved amorphous hydrogenated germanium

    NASA Astrophysics Data System (ADS)

    Turner, W. A.; Jones, S. J.; Pang, D.; Bateman, B. F.; Chen, J. H.; Li, Y.-M.; Marques, F. C.; Wetsel, A. E.; Wickboldt, P.; Paul, W.; Bodart, J.; Norberg, R. E.; El Zawawi, I.; Theye, M. L.

    1990-06-01

    High-quality amorphous hydrogenated germanium has been deposited using the diode rf glow discharge method out of a gas plasma of GeH4 and H2. The optical, electrical, and structural properties of this material have been extensively characterized. The optical and electrical properties are all consistent with material containing a low density of defect related states in the energy gap. In particular, this material has an ημτ=3.2×10-7 cm2/V, ratio of photocurrent to dark current of 1.3×10-1, and flux dependence of the photocurrent with γ=0.79 at 1.25 eV measured using photoconductivity, a μτ=4×10-8 cm2/V measured using time of flight, an Urbach energy of 51 meV and α at 0.7 eV of 8.3 cm-1 measured using photothermal deflection spectroscopy, a dangling bond spin density of 5×1016 cm-3 measured using electron spin resonance, photoluminescence with a peak energy position of 0.81 eV and full width at half maximum of 0.19 eV, an activation energy of 0.52 eV and σ0 of 6.1×103 (Ω cm)-1 measured using dark conductivity, and an E04 band gap of 1.24 eV measured by optical absorption. The structural measurements indicate a homogeneous material lacking any island/tissue and columnar structure when investigated using transmission and scanning electron microscopy, respectively. Hydrogen concentrations calculated from infrared and gas evolution measurements can only by reconciled by postulating a large quantity of unbonded hydrogen whose presence is confirmed using deuteron magnetic resonance. The bonded deuterium component, as seen in this film using DMR, has a spin-lattice relaxation time of the order of 4000 s. The differential scanning calorimetry measurement shows crystallization occurring at 421 °C and the presence of large compressive stresses has been confirmed using a bending-beam method. The experimental details necessary to interpret the quantities quoted here are set out in the text which follows. It is considered that the very good optical and electrical

  19. Ab initio study of structural and mechanical property of solid molecular hydrogens

    NASA Astrophysics Data System (ADS)

    Ye, Yingting; Yang, Li; Yang, Tianle; Nie, Jinlan; Peng, Shuming; Long, Xinggui; Zu, Xiaotao; Du, Jincheng

    2015-06-01

    Ab initio calculations based on density functional theory (DFT) were performed to investigate the structural and the elastic properties of solid molecular hydrogens (H2). The influence of molecular axes of H2 on structural relative stabilities of hexagonal close-packed (hcp) and face-centered cubic (fcc) structured hydrogen molecular crystals were systematically investigated. Our results indicate that for hcp structures, disordered hydrogen molecule structure is more stable, while for fcc structures, Pa3 hydrogen molecular crystal is most stable. The cohesive energy of fcc H2 crystal was found to be lower than hcp. The mechanical properties of fcc and hcp hydrogen molecular crystals were obtained, with results consistent with previous theoretical calculations. In addition, the effects of zero point energy (ZPE) and van der Waals (vdW) correction on the cohesive energy and the stability of hydrogen molecular crystals were systematically studied and discussed.

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

    SciTech Connect

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

    2016-08-04

    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. NEAþMP docking complexes are imaged using scanning tunneling 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. In conclusion, 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.

  1. 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.

  2. 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

    2016-08-04

    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.

  3. 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

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

    DOE PAGES

    Mahapatra, Mausumi; Burkholder, Luke; Garvey, Michael; ...

    2016-08-04

    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. NEAþMP docking complexes are imaged using scanning tunneling 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 bindingmore » of the C=C of the enol tautomer of MP to the surface, while simultaneously optimizing C=O...H2N hydrogen-bonding interactions. In conclusion, 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.« less

  5. Dynamics and mechanism of structural diffusion in linear hydrogen bond.

    PubMed

    Chaiwongwattana, Sermsiri; Phonyiem, Mayuree; Vchirawongkwin, Viwat; Prueksaaroon, Supakit; Sagarik, Kritsana

    2012-01-15

    Dynamics and mechanism of proton transfer in a protonated hydrogen bond (H-bond) chain were studied, using the CH(3)OH(2)(+)(CH(3)OH)(n) complexes, n = 1-4, as model systems. The present investigations used B3LYP/TZVP calculations and Born-Oppenheimer MD (BOMD) simulations at 350 K to obtain characteristic H-bond structures, energetic and IR spectra of the transferring protons in the gas phase and continuum liquid. The static and dynamic results were compared with the H(3)O(+)(H(2)O)(n) and CH(3)OH(2)(+)(H(2)O)(n) complexes, n = 1-4. It was found that the H-bond chains with n = 1 and 3 represent the most active intermediate states and the CH(3)OH(2)(+)(CH(3)OH)(n) complexes possess the lowest threshold frequency of proton transfer. The IR spectra obtained from BOMD simulations revealed that the thermal energy fluctuation and dynamics help promote proton transfer in the shared-proton structure with n = 3 by lowering the vibrational energy for the interconversion between the oscillatory shuttling and structural diffusion motions, leading to a higher population of the structural diffusion motion than in the shared-proton structure with n = 1. Additional explanation on the previously proposed mechanisms was introduced, with the emphases on the energetic of the transferring proton, the fluctuation of the number of the CH(3)OH molecules in the H-bond chain, and the quasi-dynamic equilibriums between the shared-proton structure (n = 3) and the close-contact structures (n ≥ 4). The latter prohibits proton transfer reaction in the H-bond chain from being concerted, since the rate of the structural diffusion depends upon the lifetime of the shared-proton intermediate state. Copyright © 2011 Wiley Periodicals, Inc.

  6. Structure and properties of hydrogen-intercalated YBa2Cu3O y

    NASA Astrophysics Data System (ADS)

    Bobylev, I. B.; Naumov, S. V.; Zyuzeva, N. A.

    2017-07-01

    The effect of hydrogenation at 150 and 200°C on the structure and magnetic susceptibility of YBa2Cu3Oy (123) with different hydrogen contents has been studied. Upon the incorporation of hydrogen, the phase transition of the 123 phase into a defect tetragonal 124 phase occurs. In contrast to the transition upon hydration, the phase transition upon hydrogenation takes place only for compounds characterized by high oxygen contents (y > 6.5). Depending on the compound structure and oxygen content, hydrogen atoms can both occupy interstitials in Cu-O planes to form HYBa2Cu3O6 and join with oxygen to form an oxide-hydroxide. In contrast to hydration, upon hydrogenation of YBa2Cu3Oy, the substitution of europium for yttrium and alloying with cerium and zirconium oxides do not block the intercalation of hydrogen into the structure of the 123 compound.

  7. Hydrogen bond rotations as a uniform structural tool for analyzing protein architecture

    NASA Astrophysics Data System (ADS)

    Penner, Robert C.; Andersen, Ebbe S.; Jensen, Jens L.; Kantcheva, Adriana K.; Bublitz, Maike; Nissen, Poul; Rasmussen, Anton M. H.; Svane, Katrine L.; Hammer, Bjørk; Rezazadegan, Reza; Nielsen, Niels Chr.; Nielsen, Jakob T.; Andersen, Jørgen E.

    2014-12-01

    Proteins fold into three-dimensional structures, which determine their diverse functions. The conformation of the backbone of each structure is locally at each Cα effectively described by conformational angles resulting in Ramachandran plots. These, however, do not describe the conformations around hydrogen bonds, which can be non-local along the backbone and are of major importance for protein structure. Here, we introduce the spatial rotation between hydrogen bonded peptide planes as a new descriptor for protein structure locally around a hydrogen bond. Strikingly, this rotational descriptor sampled over high-quality structures from the protein data base (PDB) concentrates into 30 localized clusters, some of which correlate to the common secondary structures and others to more special motifs, yet generally providing a unifying systematic classification of local structure around protein hydrogen bonds. It further provides a uniform vocabulary for comparison of protein structure near hydrogen bonds even between bonds in different proteins without alignment.

  8. 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.

  9. 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

  10. 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

    2000-12-01

    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.

  11. 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.

  12. CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES: Adsorption Mechanism of Hydrogen on Boron-Doped Fullerenes

    NASA Astrophysics Data System (ADS)

    Yu, Liu-Min; Shi, Guo-Sheng; Wang, Zhi-Gang; Ji, Guang-Fu; Lu, Zhi-Peng

    2009-08-01

    The C35BH-H2 complex and two other possible isomers, C34BCaH-H2 and C34BCbH-H2, are investigated using the local-spin-density approximation (LSDA) method. The results indicate that a single hydrogen molecule could be strongly adsorbed on two isomers, C34BCaH and C34BCbH, with binding energies of 0.42 and 0.47 eV, respectively, and that these calculated binding energies are suitable for reversible hydrogen adsorption/desorption near room temperature. However, it is difficult for the H2 molecule to be firmly adsorbed on C35BH. We analyze the interaction between C34BCxH (x = a, b) and the H2 molecule using dipole moments and molecular orbitals. The charge analysis showed there was a partial charge (about 0.32e) transfer from H2 to the doped fullerenes. These calculation results should broaden our understanding of the mechanisms of hydrogen storage using boron-doped fullerenes.

  13. Angle-resolved UV photoemission studies of the two-dimensional band structures of sulfur, selenium, and tellurium monolayers adsorbed on aluminium (111)

    NASA Astrophysics Data System (ADS)

    Jacobi, K.; Muschwitz, C. V.; Kambe, K.

    1980-03-01

    On A1(111) surfaces adsorbate layers of S, Se, and Te were prepared by reaction with H 2S and evaporation of selenium and tellurium. Two condensation processes of different rate were found by measuring the photoemission intensity of the adsorbate p-levels as a function of dosis or evaporation time. The first process was identified as the build-up of a monolayer. By LEED and angular resolved UPS it was found that the atoms of the monolayers are hexagonally close packed and aligned to, but not in registry with the substrate. The nearest neighbour distances are 0.35 nm for S, 0.37 nm for Se, and 0.40 nm for Te. These distances are only somewhat smaller than the Van der Waals diameters. By measuring the kinetic energy and emission angle of photoelectrons from the adsorbate p-levels using polarized and unpolarized Hel (21.2eV) radiation the two-dimensional band structures could be constructed. They were found to be similar for all three adsorbate systems and only shifted as a whole to lower binding energies with increasing Z. The two-dimensional band structures were also calculated using a simple tight-binding model. The main features of the experimentally obtained bands could be reproduced by a calculation using only two parameters. The main differences between the calculated and experimentally evaluated bands could be attributed to the interaction of the monolayer with the substrate. For Te no important influence of the spin-orbit coupling was found.

  14. Structural effects of drying and rehydration for enzymes in soils: a kinetics-FTIR analysis of alpha-chymotrypsin adsorbed on montmorillonite.

    PubMed

    Noinville, S; Revault, M; Quiquampoix, H; Baron, M H

    2004-05-15

    The effects of desiccation and rehydration cycles encountered by extracellular enzymes in soils are studied on -chymotrypsin adsorbed on montmorillonite. The controlled hygrometric FTIR cell used in this study enables to monitor drying and rehydration steps undergone by the -chymotrypsin-montmorillonite suspension or by the enzyme alone. Relative humidity (RH) determines the amount of deuterated water in the FTIR cell atmosphere. The molar water/protein ratio (W/P) as well as the conformational and solvation states of the enzyme have been determined using H/D exchange monitored by FTIR-transmission spectroscopy. When the W/P ratio decreases from 3500 to approximately 400, unfolding of beta-secondary structure in three different domains involves about 8% of the polypeptide backbone with respect to the most solvated states. Desiccation induces beta-unfolding, which opens channels allowing free vapor water molecules to diffuse into the enzyme at 15% RH. On drying to 0% RH, displacements of internal water (H2O) in the enzyme are demonstrated by reverse peptide isotopic exchanges (COND ==> CONH). Specific beta-structures, only formed in highly solvated states, sequester around 20 internal H2O molecules. Indeed, most of the unfolded secondary structures during the drying step are refolded at W/P approximately 1000 during rehydration. However, self-association hinders the recovery of the initial closed tertiary structure. The pD-dependent structural changes controlling inward and outward water diffusion are suppressed, whether the protein is initially in an adsorbed state or in solution. Changes in secondary structures encountered during desiccation/rehydration cycle are similar for the protein either free or in the adsorbed state. Thus domains that are unfolded by adsorption are not concerned by the desiccation/rehydration cycle.

  15. 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.

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

    PubMed

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

    2015-11-26

    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.

  17. Synergistic adsorption of phenol from aqueous solution onto polymeric adsorbents.

    PubMed

    Ming, Zhang W; Long, Chen J; Cai, Pan B; Xing, Zhang Q; Zhang, B

    2006-02-06

    Adsorption of phenol from aqueous solution onto a nonpolar adsorbent, aminated adsorbent and weak base adsorbent (Amberlite XAD4, NDA103 and Amberlite IRA96C, respectively) at temperatures from 293 to 313K was studied for the weak interactions between the phenol molecules and the polymeric adsorbents. Isotherms of Langmuir and Freundlich equation with characteristic parameters for different adsorbents were well fitted to the batch equilibrium adsorption data. The adsorption capacity on NDA103 driven by hydrogen bonding and van der Waals interaction together is higher than that on IRA96C driven by hydrogen bonding interaction only and on XAD4 driven by van der Waals interaction only. For evaluating synergistic adsorption for phenol-water systems onto polymeric adsorbents, the adsorption capacity is normalized to the amounts of specific surface area and amino groups of adsorbents. The synergistic effect with other weak interactions would contribute more to the adsorption as acting simultaneously than that of acting individually.

  18. 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.

  19. 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

  20. Probing Electrochemical Adsorbate Structure and Reactions with In-Situ Atomic-Resolution Scanning Microscopy: Some Progress and Prospects

    DTIC Science & Technology

    1992-10-01

    adsorbate systems. Illustrative results of the former type are presented for the potential-dependent adsorption of iodide at low-index gold electrodes. The...between the former and latter atomic arrangements can be deduced with high precision. The suitability of in-situ STH for examining real- space dynamics of...presented for the potential-dependent adsorption of iodide at low-index gold electrodes. The virtues of acquiring "composite-domain" STM images, where

  1. 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. © 2015 The Protein Society.

  2. 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

  3. The structure, energetics, and nature of the chemical bonding of phenylthiol adsorbed on the Au(111) surface: implications for density-functional calculations of molecular-electronic conduction.

    PubMed

    Bilić, Ante; Reimers, Jeffrey R; Hush, Noel S

    2005-03-01

    The adsorption of phenylthiol on the Au(111) surface is modeled using Perdew and Wang density-functional calculations. Both direct molecular physisorption and dissociative chemisorption via S-H bond cleavage are considered as well as dimerization to form disulfides. For the major observed product, the chemisorbed thiol, an extensive potential-energy surface is produced as a function of both the azimuthal orientation of the adsorbate and the linear translation of the adsorbate through the key fcc, hcp, bridge, and top binding sites. Key structures are characterized, the lowest-energy one being a broad minimum of tilted orientation ranging from the bridge structure halfway towards the fcc one. The vertically oriented threefold binding sites, often assumed to dominate molecular electronics measurements, are identified as transition states at low coverage but become favored in dense monolayers. A similar surface is also produced for chemisorption of phenylthiol on Ag(111); this displays significant qualitative differences, consistent with the qualitatively different observed structures for thiol chemisorption on Ag and Au. Full contours of the minimum potential energy as a function of sulfur translation over the crystal face are described, from which the barrier to diffusion is deduced to be 5.8 kcal mol(-1), indicating that the potential-energy surface has low corrugation. The calculated bond lengths, adsorbate charge and spin density, and the density of electronic states all indicate that, at all sulfur locations, the adsorbate can be regarded as a thiyl species that forms a net single covalent bond to the surface of strength 31 kcal mol(-1). No detectable thiolate character is predicted, however, contrary to experimental results for alkyl thiols that indicate up to 20%-30% thiolate involvement. This effect is attributed to the asymptotic-potential error of all modern density functionals that becomes manifest through a 3-4 eV error in the lineup of the adsorbate and

  4. Hydrogen dimer structures in the far-infrared spectra of Jupiter and Saturn

    NASA Technical Reports Server (NTRS)

    Frommhold, L.; Samuelson, R.; Birnbaum, G.

    1984-01-01

    On the basis of a spectral line shape computation and radiative transfer calculations, it is shown that the unexplained, diminutive structures seen in the Voyager IRIS Jovian spectra near the hydrogen S0(0) and S0(1) rotational frequencies are due to bound-free transitions involving hydrogen dimers. The absorption intensities of these transitions, as well as of the collision-induced background, are given. These dimer structures may possibly prove to be useful for determining the helium/hydrogen ratio and the para-hydrogen fraction in the atmospheres of the outer planets.

  5. Surface structural-chemical characterization of a single-site d0 heterogeneous arene hydrogenation catalyst having 100% active sites

    PubMed Central

    Williams, Linda A.; Guo, Neng; Motta, Alessandro; Delferro, Massimiliano; Fragalà, Ignazio L.; Miller, Jeffrey T.; Marks, Tobin J.

    2013-01-01

    Structural characterization of the catalytically significant sites on solid catalyst surfaces is frequently tenuous because their fraction, among all sites, typically is quite low. Here we report the combined application of solid-state 13C-cross-polarization magic angle spinning nuclear magnetic resonance (13C-CPMAS-NMR) spectroscopy, density functional theory (DFT), and Zr X-ray absorption spectroscopy (XAS) to characterize the adsorption products and surface chemistry of the precatalysts (η5-C5H5)2ZrR2 (R = H, CH3) and [η5-C5(CH3)5]Zr(CH3)3 adsorbed on Brønsted superacidic sulfated alumina (AlS). The latter complex is exceptionally active for benzene hydrogenation, with ∼100% of the Zr sites catalytically significant as determined by kinetic poisoning experiments. The 13C-CPMAS-NMR, DFT, and XAS data indicate formation of organozirconium cations having a largely electrostatic [η5-C5(CH3)5]Zr(CH3)2+···AlS− interaction with greatly elongated Zr···OAlS distances of ∼2.35(2) Å. The catalytic benzene hydrogenation cycle is stepwise understandable by DFT, and proceeds via turnover-limiting H2 delivery to surface [η5-C5(CH3)5]ZrH2(benzene)+···AlS− species, observable by solid-state NMR and XAS. PMID:23269836

  6. Synthesis of FeH5: A layered structure with atomic hydrogen slabs.

    PubMed

    Pépin, C M; Geneste, G; Dewaele, A; Mezouar, M; Loubeyre, P

    2017-07-28

    High pressure promotes the formation of polyhydrides with unusually high hydrogen-to-metal ratios. These polyhydrides have complex hydrogenic sublattices. We synthesized iron pentahydride (FeH5) by a direct reaction between iron and H2 above 130 gigapascals in a laser-heated diamond anvil cell. FeH5 exhibits a structure built of atomic hydrogen only. It consists of intercalated layers of quasicubic FeH3 units and four-plane slabs of thin atomic hydrogen. The distribution of the valence electron density indicates a bonding between hydrogen and iron atoms but none between hydrogen atoms, presenting a two-dimensional metallic character. The discovery of FeH5 suggests a low-pressure path to make materials that approach bulk dense atomic hydrogen. Copyright © 2017 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.

  7. Titanium defect structure change after gas-phase hydrogenation at different temperatures and cooling rates

    NASA Astrophysics Data System (ADS)

    Mikhaylov, Andrey A.; Laptev, Roman S.; Kudiiarov, Viktor N.; Volokitina, Tatiana L.

    2016-11-01

    Influence of gas-phase hydrogenation temperature and cooling rate on defect structure of commercially pure titanium alloy was experimentally studied by means of positron annihilation spectroscopy. The change of temperature in the process of gas-phase hydrogenation was in the range of 500-700°C, while the change of cooling rate was in the range of 0.4-10.4°C/min. With increasing of gas-phase hydrogenation temperature, significant increase of hydrogen sorption rate was found. High temperature gas-phase hydrogenation of commercially pure titanium alloy lead to the formation of vacancy and hydrogen-vacancy complexes. For the same concentration of hydrogen, temperature variation or variation of cooling rate had no effect on the type of defect. However, this variation provides significant changes in defect concentration.

  8. Synthesis of FeH5: A layered structure with atomic hydrogen slabs

    NASA Astrophysics Data System (ADS)

    Pépin, C. M.; Geneste, G.; Dewaele, A.; Mezouar, M.; Loubeyre, P.

    2017-07-01

    High pressure promotes the formation of polyhydrides with unusually high hydrogen-to-metal ratios. These polyhydrides have complex hydrogenic sublattices. We synthesized iron pentahydride (FeH5) by a direct reaction between iron and H2 above 130 gigapascals in a laser-heated diamond anvil cell. FeH5 exhibits a structure built of atomic hydrogen only. It consists of intercalated layers of quasicubic FeH3 units and four-plane slabs of thin atomic hydrogen. The distribution of the valence electron density indicates a bonding between hydrogen and iron atoms but none between hydrogen atoms, presenting a two-dimensional metallic character. The discovery of FeH5 suggests a low-pressure path to make materials that approach bulk dense atomic hydrogen.

  9. 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.

  10. 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.

  11. 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.

  12. Parameter-Free Hydrogen-Bond Definition to Classify Protein Secondary Structure.

    PubMed

    Haghighi, Hasti; Higham, Jonathan; Henchman, Richard H

    2016-08-25

    DSSP is the most commonly used method to assign protein secondary structure. It is based on a hydrogen-bond definition with an energy cutoff. To assess whether hydrogen bonds defined in a parameter-free way may give more generality while preserving accuracy, we examine a series of hydrogen-bond definitions to assign secondary structure for a series of proteins. Assignment by the strongest-acceptor bifurcated definition with provision for unassigned donor hydrogens, termed the SABLE method, is found to match DSSP with 95% agreement. The small disagreement mainly occurs for helices, turns, and bends. While there is no absolute way to assign protein secondary structure, avoiding molecule-specific cutoff parameters should be advantageous in generalizing structure-assignment methods to any hydrogen-bonded system.

  13. A grazing incidence surface X-ray absorption fine structure (GIXAFS) study of alkanethiols adsorbed on Au, Ag, and Cu

    NASA Astrophysics Data System (ADS)

    Floriano, Pierre N.; Schlieben, Olaf; Doomes, Edward E.; Klein, Ingo; Janssen, J.; Hormes, Josef; Poliakoff, E. D.; McCarley, Robin L.

    2000-04-01

    Self-assembled monolayers of n-alkanethiols, CH 3-(CH 2) x-SH, on Au, Ag, and Cu have been studied with GIXAFS at the sulfur K-edge. For both pentanethiol and decanethiol monolayers on Ag and Cu, the three-fold hollow site is found to be the most probable sulfur binding site. However, observations for octadecanethiol indicate that the three-fold hollow site is not the exclusive binding site. In addition, the possible existence of disulfide bonds on the metal surface (adsorbed dialkyldisulfides) is not supported by the data. Preliminary results from monolayers on Au are also reported.

  14. Nanocomposite polymer structures for optical sensors of hydrogen sulfide

    NASA Astrophysics Data System (ADS)

    Sergeev, A. A.; Mironenko, A. Yu.; Nazirov, A. E.; Leonov, A. A.; Voznesenskii, S. S.

    2017-08-01

    Composite coatings based on gold and silver nanoparticles reduced in situ in the film of chitosan polysaccharide are studied. In the presence of hydrogen sulfide, the maximum of plasmon resonance of the nanoparticles that is proportional to the analyte concentration decreases. The detection limits for hydrogen sulfide are 0.1 and 5 ppm for the chitosan/silver and chitosan/gold nanocomposites, respectively.

  15. Topological hydrogen-bond definition to characterize the structure and dynamics of liquid water.

    PubMed

    Henchman, Richard H; Irudayam, Sheeba Jem

    2010-12-23

    A definition that equates a hydrogen bond topologically with a local energy well in the potential energy surface is used to study the structure and dynamics of liquid water. We demonstrate the robustness of this hydrogen-bond definition versus the many other definitions which use fixed, arbitrary parameters, do not account for variable molecular environments, and cannot effectively resolve transition states. Our topology definition unambiguously shows that most water molecules are double acceptors but sizable proportions are single or triple acceptors. Almost all hydrogens are found to take part in hydrogen bonds. Broken hydrogen bonds only form when two molecules try to form two hydrogen bonds between them. The double acceptors have tetrahedral geometry, lower potential energy, entropy, and density, and slower dynamics. The single and triple acceptors have trigonal and trigonal bipyramidal geometry and when considered together have higher density, potential energy, and entropy, faster dynamics, and a tendency to cluster. These calculations use an extended theory for the entropy of liquid water that takes into account the variable number of hydrogen bonds. Hydrogen-bond switching is shown to depend explicitly on the variable number of hydrogen bonds accepted and the presence of interstitial water molecules. Transition state theory indicates that the switching of hydrogen bonds is a mildly activated process, requiring only a moderate distortion of hydrogen bonds. Three main types of switching events are observed depending on whether the donor and acceptor are already sharing a hydrogen bond. The switch may proceed with no intermediate or via a bifurcated-oxygen or cyclic dimer, both of which have a broken hydrogen bond and symmetric and asymmetric forms. Switching is found to be strongly coupled to whole-molecule vibration, particularly for the more mobile single and triple acceptors. Our analysis suggests that even though water is heterogeneous in terms of the

  16. Hydrogenated graphene and hydrogenated silicene: computational insights.

    PubMed

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

    2015-06-08

    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. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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

    SciTech Connect

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

    2010-03-01

    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.

  18. Analyzing and tracking burning structures in lean premixed hydrogen flames.

    PubMed

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

    2010-01-01

    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 multiresolution 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 reprocessing the data for each set of parameters. The resulting statistics enable scientists to select appropriate parameters and provide insight into the sensitivity of the results with respect 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 counterintuitively 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.

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

    NASA Astrophysics Data System (ADS)

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

    2009-12-01

    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.

  20. 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.

  1. Nano-structured Mg-doped Fe2O3-ferrihydrite powder--a new adsorbent for cation removal from aqueous solutions.

    PubMed

    Mohapatra, M; Mohapatra, L; Hariprasad, D; Anand, S; Mishra, B K

    2012-01-01

    The present studies were undertaken with a view to developing a low-cost, efficient adsorbent for removal of heavy metal ions from aqueous solutions. A new cost-effective nano-structured Mg-doped Fe2O3-ferrihydrite adsorbent exhibiting high uptake capacities for various cations was synthesized. After preliminary testing of a series of Mg-doped (0.38 to 0.98%) samples for Pb(II), Cd(II), Cu(II) or Co(II) adsorption, a typical sample containing 55.7% Fe and 0.38% Mg was chosen for detailed characterization studies (XRD, TG-DTA, FTIR and TEM techniques). The adsorption behaviour of cations on the prepared nano powder was studied under various experimental conditions. The generated data were fitted to kinetic and isotherm models. The Langmuir monolayer capacities were 99.1, 83.3, 111.1 and 151.5 mg/g for Pb(II), Cd(II), Cu(II) and Co(II), respectively. It is the first time that such a high loading capacity for Co(II) has been reported. The effect of the presence of chloride or sulphate was dependent on the nature of the cation. Lead(II) adsorption was endothermic in nature with increased randomness at the solid-liquid interface, while for the rest of the three cations the adsorption process was exothermic. The XRD and FTIR studies on the loaded samples revealed structural changes during the adsorption process. The high cation loading capacities along with the stability of the loaded adsorbent make the synthesized ferrihydrite-Fe2O3 nano powder a potential candidate for contaminated water purification.

  2. Combining photocatalytic hydrogen generation and capsule storage in graphene based sandwich structures

    NASA Astrophysics Data System (ADS)

    Yang, Li; Li, Xiyu; Zhang, Guozhen; Cui, Peng; Wang, Xijun; Jiang, Xiang; Zhao, Jin; Luo, Yi; Jiang, Jun

    2017-07-01

    The challenge of safe hydrogen storage has limited the practical application of solar-driven photocatalytic water splitting. It is hard to isolate hydrogen from oxygen products during water splitting to avoid unwanted reverse reaction or explosion. Here we propose a multi-layer structure where a carbon nitride is sandwiched between two graphene sheets modified by different functional groups. First-principles simulations demonstrate that such a system can harvest light and deliver photo-generated holes to the outer graphene-based sheets for water splitting and proton generation. Driven by electrostatic attraction, protons penetrate through graphene to react with electrons on the inner carbon nitride to generate hydrogen molecule. The produced hydrogen is completely isolated and stored with a high-density level within the sandwich, as no molecules could migrate through graphene. The ability of integrating photocatalytic hydrogen generation and safe capsule storage has made the sandwich system an exciting candidate for realistic solar and hydrogen energy utilization.

  3. Combining photocatalytic hydrogen generation and capsule storage in graphene based sandwich structures.

    PubMed

    Yang, Li; Li, Xiyu; Zhang, Guozhen; Cui, Peng; Wang, Xijun; Jiang, Xiang; Zhao, Jin; Luo, Yi; Jiang, Jun

    2017-07-06

    The challenge of safe hydrogen storage has limited the practical application of solar-driven photocatalytic water splitting. It is hard to isolate hydrogen from oxygen products during water splitting to avoid unwanted reverse reaction or explosion. Here we propose a multi-layer structure where a carbon nitride is sandwiched between two graphene sheets modified by different functional groups. First-principles simulations demonstrate that such a system can harvest light and deliver photo-generated holes to the outer graphene-based sheets for water splitting and proton generation. Driven by electrostatic attraction, protons penetrate through graphene to react with electrons on the inner carbon nitride to generate hydrogen molecule. The produced hydrogen is completely isolated and stored with a high-density level within the sandwich, as no molecules could migrate through graphene. The ability of integrating photocatalytic hydrogen generation and safe capsule storage has made the sandwich system an exciting candidate for realistic solar and hydrogen energy utilization.

  4. 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.

  5. Structural, electronic and optical properties of CO adsorbed on the defective anatase TiO2 (101) surface; a DFT study

    NASA Astrophysics Data System (ADS)

    Rafique, Muhammad; Shuai, Yong; Hassan, Muhammad

    2017-08-01

    This paper illustrates the study of stable structural, electronic and optical properties of carbon mono oxide (CO) molecule adsorbed on pure anatase TiO2 (101) surface and CO molecule adsorbed on defective anatase TiO2 (101) surface containing oxygen (O) atom subsurface vacancy using first-principles study calculations based on density functional theory (DFT) method. A foreign molecule CO was added in the interstitial space of anatase TiO2 (101) surface. It was observed that, adsorption of CO molecule is not favorable on pure anatase TiO2 (101) surface, however adsorption process is improved when subsurface contains O atom vacancy defect. In case of anatase TiO2 (101) surface containing subsurface vacancy, adsorption process is exothermic, resulting in stable structures. The adsorption energies calculated for CO molecules adsorbed at O2c site, at defect site and at Ti5c site of anatase surface containing subsurface O vacancy are 0.16 eV (at O2c), 0.32 eV (at defect site) and 0.43 eV (at Ti5c) site. DOS and PDOS plots are calculated for all the structures. Results indicated that CO molecule adsorption introduces surface states at the Fermi energy level (EF) as shown in partial density of states (PDOS) plots. The dielectric matrix and absorption coefficient (α) for defective anatase TiO2 (101) surface, CO adsorbed at O2c site, at defect site and at Ti5C site of anatase TiO2 (101) surface containing O atom subsurface vacancy has been calculated within the random phase approximation (RPA) using VASP (Vienna ab-initio simulation package) code. It was observed that upon CO adsorption at defective anatase surface, real and imaginary dielectric function peaks were shifted towards lower energy level and a small absorption peak was observed at 1.1 eV energy level which is not present in case of defective anatase (101) surface. CO adsorption produces a red shift in the absorption spectrum of anatase TiO2 (101) surface containing subsurface O atom vacancy.

  6. Structure and stabilization of hydrogen-rich transverse.

    SciTech Connect

    Lyra, Sgouria; Wilde, B; Kolla, Hemanth; Seitzman, J.; Lieuwen, T. C.; Chen, Jacqueline H.

    2014-07-01

    This paper reports the results of a joint experimental and numerical study of the ow characteristics and flame stabilization of a hydrogen rich jet injected normal to a turbulent, vitiated cross ow of lean methane combustion products. Simultaneous high-speed stereoscopic PIV and OH PLIF measurements were obtained and analyzed alongside three-dimensional direct numerical simulations of inert and reacting JICF with detailed H2/CO chemistry. Both the experiment and the simulation reveal that, contrary to most previous studies of reacting JICF stabilized in low-to-moderate temperature air cross ow, the present conditions lead to an autoigniting, burner-attached flame that initiates uniformly around the burner edge. Significant asymmetry is observed, however, between the reaction zones located on the windward and leeward sides of the jet, due to the substantially different scalar dissipation rates. The windward reaction zone is much thinner in the near field, while also exhibiting significantly higher local and global heat release than the much broader reaction zone found on the leeward side of the jet. The unsteady dynamics of the windward shear layer, which largely control the important jet/cross flow mixing processes in that region, are explored in order to elucidate the important flow stability implications arising in the reacting JICF. Vorticity spectra extracted from the windward shear layer reveal that the reacting jet is globally unstable and features two high frequency peaks, including a fundamental mode whose Strouhal number of ~0.7 agrees well with previous non-reacting JICF stability studies. The paper concludes with an analysis of the ignition, ame stabilization, and global structure of the burner-attached flame. Chemical explosive mode analysis (CEMA) shows that the entire windward shear layer, and a large region on the leeward side of the jet, are highly explosive prior to ignition and are dominated by non-premixed flame structures after

  7. Simulation of hydrogen diffusion in TiH x structures

    NASA Astrophysics Data System (ADS)

    Rokhmanenkov, A. S.; Kuksin, A. Yu.; Yanilkin, A. V.

    2017-01-01

    Quantum-mechanical calculations of the energies of the formation of Frenkel pairs and barriers for hydrogen migration via different mechanisms in the titanium hydride δ-TiH x and in the α phase of titanium have been carried out. Using the potential of interaction developed for the molecular-dynamic simulation, diffusion coefficients of hydrogen in fcc and hcp lattices of TiH x were calculated depending on the temperature. The opportunity to approximate the coefficients of hydrogen self-diffusion has been analyzed in terms of the model of non-interacting point defects. For δ-TiH x , the range of concentrations and temperatures was separated where the self-diffusion of hydrogen becomes liquid-like (ceases be dependent on the hydrogen concentration), upon the transition into which there takes place a sharp increase in the isochoric heat capacity. The effect of defects in the Ti sublattice on the coefficient of self-diffusion of H has been investigated.

  8. 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.

  9. 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.

  10. Accessing the structural and thermodynamic properties of ultra-thin layers of C32 adsorbed on a SiO2 surface

    NASA Astrophysics Data System (ADS)

    Gutierrez-Maldonado, Sebastian E.; Garate, Jose Antonio; Retamal, Maria Jose; Cisternas, Marcelo A.; Volkmann, Ulrich G.; Perez-Acle, Tomas

    2017-04-01

    Medium-chain alkanes are important molecules with applications in biology and industry. Notably, their structural properties are scarcely understood. To assess structural and thermodynamic properties of dotriacontane (C32) molecules adsorbed on a SiO2 surface, we conducted all-atom molecular dynamics (MD) simulations. By analyzing potentials of mean force, order parameters and self-diffusion, we compared the stability and preferential orientation between ordered and disordered systems. Our data confirm the presence of one parallel layer of C32 followed by a mixture of disordered C32 segments exhibiting no thermodynamic preference. This semi-ordered structural model shed light to the interactions between C32 and a SiO2 surface.

  11. Bioinspired synthesis of hierarchically micro/nano-structured CuI tetrahedron and its potential application as adsorbent for Cd(II) with high removal capacity.

    PubMed

    Gao, Shuyan; Yang, Jianmao; Li, Zhengdao; Jia, Xiaoxia; Chen, Yanli

    2012-04-15

    An environment friendly bioinspired strategy for synthesizing hierarchically micro/nano-structured CuI tetrahedron has been developed by combining the stabilization and the reduction performances of l-tryptophan together. A possible growth mechanism of such hierarchical tetrahedron is tentatively proposed. Remarkably, such CuI tetrahedron is found to possess high removal capacity for poisonous Cd(II) ions, 136.3mg/g, and ideal reusability. This is ascribed to the hierarchical micro/nano-structure and chemical adsorption mechanism, which shows great advantages over the traditional nano-scaled adsorbents. These interesting results stand out the promising applications of such hierarchically micro/nano-structured materials in environment. It is also a good example for the organic combination of green chemistry and nanotechnologies for the treatment of contaminated water.

  12. 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

    2014-12-07

    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(+) 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.

  13. 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.

  14. 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.

  15. 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.

  16. Grand canonical Monte Carlo simulations of the distribution and chemical shifts of xenon in the cages of zeolite NaA. II. Structure of the adsorbed fluid

    NASA Astrophysics Data System (ADS)

    Jameson, Cynthia J.; Jameson, A. Keith; Lim, Hyung-Mi; Baello, Bernoli I.

    1994-04-01

    The quantitative agreement between the results of a grand canonical Monte Carlo (GCMC) simulation and the various direct experimental measures of the distribution of the Xe atoms between adsorbed phase and gas phase, of intrazeolitic xenon among the alpha cages, and of the distribution of n Xe atoms in a Xen cluster within one alpha cage permit us to consider the structure of the adsorbed fluid in the GCMC simulation as a reasonable description of the actual structure. We provide here the adsorption sites for a single Xe atom in the alpha cage of zeolite NaA, the transition states between these adsorption sites, the one-body distribution functions for the individual clusters Xen inside the alpha cage, the Xe-Xe pair distribution functions for Xe2 through Xe8 at two temperatures, and some of the local minima in the configuration space of the clusters Xe2 through Xe8, i.e., some of the minimum energy configurations of the clusters.

  17. Structural and microscopic relaxation processes in liquid hydrogen fluoride.

    PubMed

    Angelini, R; Giura, P; Monaco, G; Ruocco, G; Sette, F; Verbeni, R

    2002-06-24

    The high frequency collective dynamics of liquid hydrogen fluoride is studied by inelastic x-ray scattering on the coexistence curve at T = 239 K. The comparison with existing molecular dynamics simulations shows the existence of two active relaxation processes with characteristic time scales in the subpicosecond range. The observed scenario is very similar to that found in liquid water. This suggests that hydrogen bonded liquids behave similarly to other very different systems as simple and glass forming liquids, thus indicating that these two relaxation processes are universal features of the liquid state.

  18. Double hydrogen bond mediating self-assembly structure of cyanides on metal surface

    NASA Astrophysics Data System (ADS)

    Wang, Zhongping; Xiang, Feifei; Lu, Yan; Wei, Sheng; Li, Chao; Liu, Xiaoqing; Liu, Lacheng; Wang, Li

    2016-10-01

    Cyanides with different numbers of -C≡N, 1,2,4,5-Tetracyanobenzene (TCNB) and 2,3-Dicyanonaphthalene (2,3-DCN) deposited on Ag(111) and Ag(110) surfaces, have been investigated by room temperature scanning tunneling microscopy (RTSTM), respectively. High resolution STM images show double hydrogen bond is the main driving force to form variety of self-assembly structures, indicating the double hydrogen bond affects the electron distribution of cyanides and leads to a more stable structure with lower energy. In addition, the difference between Ag(111) and Ag(110) surfaces in their lattice structure induces a bigger assembly structural change of 2,3-DCN than that of 1,2,4,5-TCNB, which confirms the fact that the opposite double hydrogen bond formation formed by 1,2,4,5-TCNB is more stable than the neighboring double hydrogen bond formation formed by molecule 2,3-DCN.

  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. Proton Transfer and Structure-Specific Fluorescence in Hydrogen Bond-Rich Protein Structures.

    PubMed

    Pinotsi, Dorothea; Grisanti, Luca; Mahou, Pierre; Gebauer, Ralph; Kaminski, Clemens F; Hassanali, Ali; Kaminski Schierle, Gabriele S

    2016-03-09

    Protein structures which form fibrils have recently been shown to absorb light at energies in the near UV range and to exhibit a structure-specific fluorescence in the visible range even in the absence of aromatic amino acids. However, the molecular origin of this phenomenon has so far remained elusive. Here, we combine ab initio molecular dynamics simulations and fluorescence spectroscopy to demonstrate that these intrinsically fluorescent protein fibrils are permissive to proton transfer across hydrogen bonds which can lower electron excitation energies and thereby decrease the likelihood of energy dissipation associated with conventional hydrogen bonds. The importance of proton transfer on the intrinsic fluorescence observed in protein fibrils is signified by large reductions in the fluorescence intensity upon either fully protonating, or deprotonating, the fibrils at pH = 0 or 14, respectively. Thus, our results point to the existence of a structure-specific fluorophore that does not require the presence of aromatic residues or multiple bond conjugation that characterize conventional fluorescent systems. The phenomenon may have a wide range of implications in biological systems and in the design of self-assembled functional materials.

  1. Structure of hydrogen-bonded associates in supercritical water under low and high pressures

    NASA Astrophysics Data System (ADS)

    Antipova, M. L.; Gurina, D. L.; Petrenko, V. E.

    2013-03-01

    The character and structural features of hydrogen-bonded associates in sub- and supercritical water are studied by analyzing distributions of the dipole moments of water molecules at P = 40, 80, and 100 MPa and T = 373-773 K, calculated using Car-Parrinello molecular dynamics. The main types of hydrogen-bonded structures and their changes upon isobaric heating are determined. It is shown that clusters with tetrahedral configurations exist in supercritical water only under high pressure.

  2. Atomic Scale Structure of (001) Hydrogen-Induced Platelets in Germanium

    NASA Astrophysics Data System (ADS)

    David, Marie-Laure; Pizzagalli, Laurent; Pailloux, Fréderic; Barbot, Jean François

    2009-04-01

    An accurate characterization of the structure of hydrogen-induced platelets is a prerequisite for investigating both hydrogen aggregation and formation of larger defects. On the basis of quantitative high resolution transmission electron microscopy experiments combined with extensive first principles calculations, we present a model for the atomic structure of (001) hydrogen-induced platelets in germanium. It involves broken Ge-Ge bonds in the [001] direction that are dihydride passivated, vacancies, and trapped H2 molecules, showing that the species involved in platelet formation depend on the habit plane. This model explains all previous experimental observations.

  3. Conformers of hydrogenated SiC honeycomb structure: A first principles study

    NASA Astrophysics Data System (ADS)

    Banerjee, Seemita; Majumder, Chiranjib

    2013-08-01

    The structural and electronic properties of fully hydrogenated SiC graphane-like nano-structures have been investigated. The objective of this study is to underscore the relative stability of different conformers of hydrogenated SiC sheet. All calculations are carried out using plane wave based pseudo-potential approach under the density functional theory. The results reveal that the fully hydrogenated SiC sheet forms five stable isomers, and the chair conformer is most stable. Further study through molecular dynamic simulation strategy demonstrates that even at room temperature the chair conformer remains stable.

  4. Adsorption of hydrogen and porous structure of active carbons

    SciTech Connect

    Gavrilov, V. Yu.

    1995-09-01

    Adsorption of hydrogen on active carbons is investigated at 77.4 K. The main features of the comparative method are described for treating the sorption isotherms obtained for the solids with a well developed surface in super micropores and mesopores.

  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. Thermodynamics, structure, and charge state of hydrogen-vacancy complexes in δ-plutonium

    NASA Astrophysics Data System (ADS)

    Taylor, Christopher D.; Francis, Michael F.; Schwartz, Daniel S.

    2014-06-01

    Hydrogen-vacancy complexes can form in a material due to the exothermic binding of hydrogen atoms to vacancy sites. We explore the structure and electronic properties of hydrogen-vacancy complexes in δ-Pu using a density functional theory supercell approach, with up to eight hydrogen atoms stored in the vacancy site. We find that the hydrogen atoms bind to the inner edge of the vacancy site, preferring pseudo-octahedral configurations that optimize the Pu-H bond length. Hydrogen binding to the vacancy site remains exothermic, with binding energies around -0.4 eV/H atom. A statistical mechanics analysis is derived and applied to reveal the range of hydrogen chemical potentials that would lead to hydrogen-vacancy complex formation. We find that these chemical potentials are higher than those required to form the hydride phase, indicating that hydriding should occur before any appreciable concentration of vacancy-hydrogen complexes is realized. Some remarks are made comparing this theoretical finding to the experimental work on this topic, with suggestions given for future work that may help reconcile some apparent contradictions.

  7. Improved estimates of separation distances to prevent unacceptable damage to nuclear power plant structures from hydrogen detonation for gaseous hydrogen storage. Technical report

    SciTech Connect

    Not Available

    1994-05-01

    This report provides new estimates of separation distances for nuclear power plant gaseous hydrogen storage facilities. Unacceptable damage to plant structures from hydrogen detonations will be prevented by having hydrogen storage facilities meet separation distance criteria recommended in this report. The revised standoff distances are based on improved calculations on hydrogen gas cloud detonations and structural analysis of reinforced concrete structures. Also, the results presented in this study do not depend upon equivalencing a hydrogen detonation to an equivalent TNT detonation. The static and stagnation pressures, wave velocity, and the shock wave impulse delivered to wall surfaces were computed for several different size hydrogen explosions. Separation distance equations were developed and were used to compute the minimum separation distance for six different wall cases and for seven detonating volumes (from 1.59 to 79.67 lbm of hydrogen). These improved calculation results were compared to previous calculations. The ratio between the separation distance predicted in this report versus that predicted for hydrogen detonation in previous calculations varies from 0 to approximately 4. Thus, the separation distances results from the previous calculations can be either overconservative or unconservative depending upon the set of hydrogen detonation parameters that are used. Consequently, it is concluded that the hydrogen-to-TNT detonation equivalency utilized in previous calculations should no longer be used.

  8. Activity of catalase adsorbed to carbon nanotubes: effects of carbon nanotube surface properties.

    PubMed

    Zhang, Chengdong; Luo, Shuiming; Chen, Wei

    2013-09-15

    Nanomaterials have been studied widely as the supporting materials for enzyme immobilization. However, the interactions between enzymes and carbon nanotubes (CNT) with different morphologies and surface functionalities may vary, hence influencing activities of the immobilized enzyme. To date how the adsorption mechanisms affect the activities of immobilized enzyme is not well understood. In this study the adsorption of catalase (CAT) on pristine single-walled carbon nanotubes (SWNT), oxidized single-walled carbon nanotubes (O-SWNT), and multi-walled carbon nanotubes (MWNT) was investigated. The adsorbed enzyme activities decreased in the order of O-SWNT>SWNT>MWNT. Fourier transforms infrared spectroscopy (FTIR) and circular dichrois (CD) analyses reveal more significant loss of α-helix and β-sheet of MWNT-adsorbed than SWNT-adsorbed CAT. The difference in enzyme activities between MWNT-adsorbed and SWNT-adsorbed CAT indicates that the curvature of surface plays an important role in the activity of immobilized enzyme. Interestingly, an increase of β-sheet content was observed for CAT adsorbed to O-SWNT. This is likely because as opposed to SWNT and MWNT, O-SWNT binds CAT largely via hydrogen bonding and such interaction allows the CAT molecule to maintain the rigidity of enzyme structure and thus the biological function.

  9. Metallacarboranes: Towards promising hydrogen storage metal organic framework

    NASA Astrophysics Data System (ADS)

    Singh, Abhishek; Sadrzadeh, Arta; Yakobson, Boris

    2011-03-01

    Using first principles calculations we show the high hydrogen storage capacity of metallacarboranes, where the transition metal (TM) atoms bind hydrogen via Kubas interaction. The average binding energy of ~ 0.3 eV/H favorably lies within the reversible adsorption range The Sc and Ti are found to be the optimum metal atoms maximizing the number of stored H2 molecules. Depending upon the structure, metallacarboranes can adsorb up to 8 wt% of hydrogen, which exceeds DOE goal for 2015. Being integral part of the cage, TMs do not suffer from the aggregation problem. Furthermore, the presence of carbon atom in the cages permits linking the metallacarboranes to form metal organic frameworks (MOF), thus able to adsorb hydrogen via Kubas interaction, in addition to van der Waals physisorption. A. K. Singh, A. Sadrzadeh, and B. I. Yakobson, Metallacarboranes: Toward Promising Hydrogen Storage Metal Organic Frameworks, JACS 132,14126 (2010).

  10. 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.

  11. Modeling adsorption: Investigating adsorbate and adsorbent properties

    NASA Astrophysics Data System (ADS)

    Webster, Charles Edwin

    1999-12-01

    Surface catalyzed reactions play a major role in current chemical production technology. Currently, 90% of all chemicals are produced by heterogeneously catalyzed reactions. Most of these catalyzed reactions involve adsorption, concentrating the substrate(s) (the adsorbate) on the surface of the solid (the adsorbent). Pore volumes, accessible surface areas, and the thermodynamics of adsorption are essential in the understanding of solid surface characteristics fundamental to catalyst and adsorbent screening and selection. Molecular properties such as molecular volumes and projected molecular areas are needed in order to convert moles adsorbed to surface volumes and areas. Generally, these molecular properties have been estimated from bulk properties, but many assumptions are required. As a result, different literature values are employed for these essential molecular properties. Calculated molar volumes and excluded molecular areas are determined and tabulated for a variety of molecules. Molecular dimensions of molecules are important in the understanding of molecular exclusion as well as size and shape selectivity, diffusion, and adsorbent selection. Molecular dimensions can also be used in the determination of the effective catalytic pore size of a catalyst. Adsorption isotherms, on zeolites, (crystalline mineral oxides) and amorphous solids, can be analyzed with the Multiple Equilibrium Analysis (MEA) description of adsorption. The MEA produces equilibrium constants (Ki), capacities (ni), and thermodynamic parameters (enthalpies, ΔHi, and entropies, ΔSi) of adsorption for each process. Pore volumes and accessible surface areas are calculated from the process capacities. Adsorption isotherms can also be predicted for existing and new adsorbate-adsorbent systems with the MEA. The results show that MEA has the potential of becoming a standard characterization method for microporous solids that will lead to an increased understanding of their behavior in gas

  12. Hydrogen Embrittlement of a 1500-MPa Tensile Strength Level Steel with an Ultrafine Elongated Grain Structure

    NASA Astrophysics Data System (ADS)

    Nie, Yihong; Kimura, Yuuji; Inoue, Tadanobu; Yin, Fuxing; Akiyama, Eiji; Tsuzaki, Kaneaki

    2012-05-01

    A deformation of a tempered martensitic structure ( i.e., tempforming) at 773 K (500 °C) was applied to a 0.6 pct C-2 pct Si-1 pct Cr steel. The hydrogen embrittlement (HE) property of the tempformed (TF) steel was investigated by a slow strain rate test (SSRT) and an accelerated atmospheric corrosion test (AACT). Hydrogen content within the samples after SSRT and AACT was measured by thermal desorption spectrometry (TDS). The tempforming at 773 K (500 °C) using multipass caliber rolling with an accumulative are reduction of 76 pct resulted in the evolution of an ultrafine elongated grain (UFEG) structure with a strong <110>//rolling direction (RD) fiber deformation texture and a dispersion of spheroidized cementite particles. The SSRT of the pre-hydrogen-charged notched specimens and the AACT demonstrated that the TF sample had superior potential for HE resistance to the conventional quenched and tempered (QT) sample at a tensile strength of 1500 MPa. The TDS analysis also indicated that the hydrogen might be mainly trapped by reversible trapping sites such as grain boundaries and dislocations in the TF sample, and the hydrogen trapping states of the TF sample were similar to those of the QT sample. The QT sample exhibited hydrogen-induced intergranular fracture along the boundaries of coarse prior-austenite grains. In contrast, the hydrogen-induced cracking occurred in association with the UFEG structure in the TF sample, leading to the higher HE resistance of the TF sample.

  13. Adsorbed poly(ethyleneoxide)-poly(propyleneoxide) copolymers on synthetic surfaces: spectroscopy and microscopy of polymer structures and effects on adhesion of skin-borne bacteria.

    PubMed

    Marsh, Lorraine H; Coke, Mark; Dettmar, Peter W; Ewen, Richard J; Havler, Michael; Nevell, Thomas G; Smart, John D; Smith, James R; Timmins, Barry; Tsibouklis, John; Alexander, Cameron

    2002-09-15

    Poly(ethyleneoxide)-copoly(propyleneoxide) (PEO-PPO) polymer coatings were evaluated for their resistance to the attachment of the marker organism Serratia marcescens and the skin-borne bacteria Staphylococcus epidermidis. The copolymers were adsorbed onto poly(styrene) films-chosen as simplified physicochemical models of skin surfaces-and their surface characteristics probed by contact angle goniometry, attenuated total reflectance-Fourier transform infrared (ATR-FTIR), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). These functional surfaces were then presented to microbial cultures, bacterial attachment was assessed by fluorescence microscopy and AFM, and the structures of the polymer films examined again spectroscopically. Surface characterization data suggest that the adsorbed copolymer was partially retained at the surface and resisted bacterial attachment for 24 h. Quantitative evaluation of cell attachment was carried out by scintillation counting of (14)C-labeled microorganisms in conjunction with plate counts. The results show that a densely packed layer of PEO-PPO copolymer can reduce attachment of skin commensals by an order of magnitude, even when the coating is applied by a simple adsorptive process. The work supports the hypothesis that adhesion of microorganisms to biological substrates can be reduced if a pretreatment with an appropriate copolymer can be effected in vivo.

  14. Manufacturing of agarose-based chromatographic adsorbents--effect of ionic strength and cooling conditions on particle structure and mechanical strength.

    PubMed

    Ioannidis, Nicolas; Bowen, James; Pacek, Andrzej; Zhang, Zhibing

    2012-02-01

    The effect of ionic strength of agarose solution and quenching temperature of the emulsion on the structure and mechanical strength of agarose-based chromatographic adsorbents was investigated. Solutions of agarose containing different amounts of NaCl were emulsified at elevated temperature in mineral oil using a high-shear mixer. The hot emulsion was quenched at different temperatures leading to the gelation of agarose and formation of soft particles. Analysis of Atomic Force Microscopy (AFM) images of particle surfaces shows that pore size of particles increases with ionic strength and/or high quenching temperature. Additionally it has been found that the compressive strength of particles measured by micromanipulation also increases with ionic strength of the emulsion and/or high quenching temperature but these two parameters have no significant effect on the resulting particle size and particle size distribution. Results from both characterization methods were compared with Sepharose 4B, a commercial agarose-based adsorbent. This is the first report examining the effect of ionic strength and cooling conditions on the microstructure of micron-sized agarose beads for bioseparation.

  15. Water hydrogen bond structure near highly charged interfaces is not like ice.

    PubMed

    Nihonyanagi, Satoshi; Yamaguchi, Shoichi; Tahara, Tahei

    2010-05-26

    Imaginary chi(2) spectra of HOD at air/charged surfactant/aqueous interfaces highly resemble the IR spectrum of the bulk liquid HOD, showing no indication of the "ice-like" structure. Clearly, the hydrogen bond structures at highly charged interfaces are not like ice but very similar to the structure in the bulk.

  16. Growth and structure of hydrogenated carbon films containing fullerene-like structure

    NASA Astrophysics Data System (ADS)

    Wang, Peng; Wang, Xia; Liu, Weimin; Zhang, Junyan

    2008-04-01

    Hydrogenated carbon films were prepared by magnetron sputtering of a titanium target in methane and argon atmosphere. The film grown at -800 V bias exhibits excellent mechanical properties with a hardness of 20.9 GPa and an elastic recovery as high as 85%. Its structure, characterized by high-resolution transmission electron microscopy, Raman spectrum, and x-ray photoelectron spectroscopy, can be described as fullerene-like structures uniformly dispersed in an amorphous carbon matrix. In order to reveal the evolution of fullerene-like structures in our films, different bias voltages were introduced. The results show that high bias voltage leads to the accumulation of high compressive internal stress in the film and promotes the evolution of fullerene-like structures. Although the film grown at -800 V bias presents high sp2 bonding content, it exhibits good mechanical properties with high hardness and high elasticity at the same time; we attribute it to the unique structure of the film, in which a fullerene-like structure, just like a molecule spring dispersed in the film, reserves the elastic energy during distortion through reversible bond rotation and bond angle deflection, while the amorphous carbon matrix restrains the relaxation of the rigid C-C network and compressive stress and restricts the slip of graphene sheets.

  17. Two-stage production of olefins utilizing a faujasite structure zeolite in hydrogenation stage

    SciTech Connect

    Kreuter, W.; Mansmann, M.; Watson, A.; Weber, H.; Wernicke, H.J.

    1980-02-12

    A process is disclosed for the production of olefins in two stages. In the first stage, heavy petroleum fractions are hydrogenated in the presence of hydrogen and a hydrogenation catalyst and, in the second stage, the thus-hydrogenated fractions are subjected to thermal cracking the presence of steam. The improvement comprises employing as the hydrogenation catalyst a zeolite of the faujasite structure combined with elements from groups VIB, VIIB and VIII of the periodic table of the elements, wherein the alkali component of the zeolite is exchanged at least partially for ammonium, hydronium, alkaline earth and/or rare earth ions, and the elements are present in a metallic, ionic, oxidic and/or sulfidic form.

  18. Ab initio study revealing a layered structure in hydrogen-rich KH6 under high pressure

    NASA Astrophysics Data System (ADS)

    Zhou, Dawei; Jin, Xilian; Meng, Xing; Bao, Gang; Ma, Yanming; Liu, Bingbing; Cui, Tian

    2012-07-01

    By adding small amounts of potassium to hydrogen, the energetically preferred compound KH6 forms above 70 GPa and metalizes within 166 GPa. Two-layered C2/m and C2/c structures of KH6 discovered here contain H2 and H3 units under high pressure. The metallic C2/c phase is found to be a one-dimensional conductor with a conducting hydrogen-bonded network and an insulating potassium chain. The layered hydrogen-dominant compound KH6 is found to be a good example of pressure-induced metallization, which originates from a hydrogen sublattice at lower pressures than those in pure hydrogen system due to the ``chemical precompression'' from heavier element potassium.

  19. Measurements of the structure of an ionizing shock wave in a hydrogen-helium mixture

    NASA Technical Reports Server (NTRS)

    Leibowitz, L. P.

    1972-01-01

    Shock structure during ionization of a hydrogen-helium mixture was studied using hydrogen line and continuum emission measurements. A reaction scheme is proposed which includes hydrogen dissociation and a two-step excitation-ionization mechanism for hydrogen ionization by atom-atom and atom-electron collisions. Agreement was achieved between numerical calculations and measurements of emission intensity as a function of time for shock velocities from 13 to 20 km/sec in a 0.208 H2 - 0.792 He mixture. The electron temperature was found to be significantly different from the heavy particle temperature during much of the ionization process. Similar time histories for H beta and continuum emission indicate upper level populations of hydrogen in equilibrium with the electron concentration during the relaxation process.

  20. Measurements of the structure of an ionizing shock wave in a hydrogen-helium mixture.

    NASA Technical Reports Server (NTRS)

    Leibowitz, L. P.

    1973-01-01

    Shock structure during ionization of a hydrogen-helium mixture has been followed using hydrogen line and continuum emission measurements. A reaction scheme is proposed which includes hydrogen dissociation and a two-step excitation-ionization mechanism for hydrogen ionization by atom-atom and atom-electron collisions. Agreement has been achieved between numerical calculations and measurements of emission intensity as a function of time for shock velocities from 13 to 20 km/sec in a 0.208 H2-0.792 He mixture. The electron temperature was found to be significantly different from the heavy particle temperature during much of the ionization process. Similar time histories for H beta and continuum emission indicate upper level populations of hydrogen in equilibrium with the electron concentration during the relaxation process.

  1. Primary Structure Effects on Peptide Group Hydrogen Exchange

    PubMed Central

    Bai, Yawen; Milne, John S.; Mayne, Leland; Englander, S. Walter

    2012-01-01

    The rate of exchange of peptide group NH hydrogens with the hydrogens of aqueous solvent is sensitive to neighboring side chains. To evaluate the effects of protein side chains, all 20 naturally occurring amino acids were studied using dipeptide models. Both inductive and steric blocking effects are apparent. The additivity of nearest-neighbor blocking and inductive effects was tested in oligo-and polypeptides and, surprisingly, confirmed. Reference rates for alanine-containing peptides were determined and effects of temperature considered. These results provide the information necessary to evaluate measured protein NH to ND exchange rates by comparing them with rates to be expected for the same amino acid sequence is unstructured oligo- and polypeptides. The application of this approach to protein studies is discussed. PMID:8234246

  2. Crystal structure of iso-butyl-ammonium hydrogen oxalate hemihydrate.

    PubMed

    Dziuk, Błażej; Zarychta, Bartosz; Ejsmont, Krzysztof

    2014-11-01

    In the title hydrated mol-ecular salt, C4H12N(+)·C2HO4 (-)·0.5H2O, the O atom of the water mol-ecule lies on a crystallographic twofold axis. The dihedral angle between the CO2 and CO2H planes of the anion is 18.47 (8)°. In the crystal, the anions are connected to each other by strong near-linear O-H⋯O hydrogen bonds. The water mol-ecules are located between the chains of anions and iso-butyl-amine cations; their O atoms participate as donors and acceptors, respectively, in O-H⋯O and N-H⋯O hydrogen bonds, which form channels (dimensions = 4.615 and 3.387 Å) arranged parallel to [010].

  3. Hydrogen decoration of radiation damage induced defect structures

    SciTech Connect

    Kirnstötter, S.; Faccinelli, M.; Hadley, P.; Schustereder, W.; Laven, J. G.; Schulze, H.-J.

    2014-02-21

    The defect complexes that are formed when protons with energies in the MeV-range were implanted into high-purity silicon were investigated. After implantation, the samples were annealed at 400 °C or 450 °C for times ranging between 15 minutes and 30 hours. The resistivity of the samples was then analyzed by Spreading Resistance Profiling (SRP). The resistivity shows minima where there is a high carrier concentration and it is possible to extract the carrier concentration from the resistivity data. Initially, there is a large peak in the carrier concentration at the implantation depth where most of the hydrogen is concentrated. For longer anneals, this peak widens as the hydrogen diffuses away from the implantation depth. Following the changes in resistivity as a function of annealing time allows us to characterize the diffusion of hydrogen through these samples. Differences in the diffusion were observed depending on whether the silicon was grown by the magnetic Czochralski (m:Cz) method or the Float zone (Fz) method.

  4. Structural, electronic, and magnetic properties of transition-metal atom adsorbed two-dimensional GaAs nanosheet

    NASA Astrophysics Data System (ADS)

    Luo, Jia; Xiang, Gang; Yu, Tian; Lan, Mu; Zhang, Xi

    2016-09-01

    By using first-principles calculations within the framework of density functional theory, the electronic and magnetic properties of 3d transitional metal (TM) atoms (from Sc to Zn) adsorbed monolayer GaAs nanosheets (GaAsNSs) are systematically investigated. Upon TM atom adsorption, GaAsNS, which is a nonmagnetic semiconductor, can be tuned into a magnetic semiconductor (Sc, V, and Fe adsorption), a half-metal (Mn adsorption), or a metal (Co and Cu adsorption). Our calculations show that the strong p-d hybridization between the 3d orbit of TM atoms and the 4p orbit of neighboring As atoms is responsible for the formation of chemical bonds and the origin of magnetism in the GaAsNSs with Sc, V, and Fe adsorption. However, the Mn 3d orbit with more unpaired electrons hybridizes not only with the As 4p orbit but also with the Ga 4p orbit, resulting in a stronger exchange interaction. Our results may be useful for electronic and magnetic applications of GaAsNS-based materials. Project supported by the National Natural Science Foundation of China (Grant No. 11174212).

  5. Structure and hydrogen bond dynamics of water-dimethyl sulfoxide mixtures by computer simulations

    NASA Astrophysics Data System (ADS)

    Luzar, Alenka; Chandler, David

    1993-05-01

    We have used two different force field models to study concentrated dimethyl sulfoxide (DMSO)-water solutions by molecular dynamics. The results of these simulations are shown to compare well with recent neutron diffraction experiments using H/D isotope substitution [A. K. Soper and A. Luzar, J. Chem. Phys. 97, 1320 (1992)]. Even for the highly concentrated 1 DMSO : 2 H2O solution, the water hydrogen-hydrogen radial distribution function, gHH(r), exhibits the characteristic tetrahedral ordering of water-water hydrogen bonds. Structural information is further obtained from various partial atom-atom distribution functions, not accessible experimentally. The behavior of water radial distribution functions, gOO(r) and gOH(r) indicate that the nearest neighbor correlations among remaining water molecules in the mixture increase with increasing DMSO concentration. No preferential association of methyl groups on DMSO is detected. The pattern of hydrogen bonding and the distribution of hydrogen bond lifetimes in the simulated mixtures is further investigated. Molecular dynamics results show that DMSO typically forms two hydrogen bonds with water molecules. Hydrogen bonds between DMSO and water molecules are longer lived than water-water hydrogen bonds. The hydrogen bond lifetimes determined by reactive flux correlation function approach are about 5 and 3 ps for water-DMSO and water-water pairs, respectively, in 1 DMSO : 2 H2O mixture. In contrast, for pure water, the hydrogen bond lifetime is about 1 ps. We discuss these times in light of experimentally determined rotational relaxation times. The relative values of the hydrogen bond lifetimes are consistent with a statistical (i.e., transition state theory) interpretation.

  6. Hydrogen absorption and structural analysis of TiZrNiV quasicrystals.

    PubMed

    Lee, Sang-Hwa; Jo, Youngsoo; Kim, Jaeyong

    2014-12-01

    Ti-based quasicrystals are known to store a high capacity of hydrogen exceeding the density of liquid hydrogen. Because TiZrNi quasicrystals contain a large number of tetrahedral sites formed with Ti and Zr atoms that are chemically favorable to hydrogen, these materials retain strong advantages for hydrogen storage applications in structurally and chemically. In fact, TiZrNi quasicrystals are known to absorb hydrogen maximum of the hydrogen to host metal ratio (H/M) value of near 2.0. The critical disadvantage, however, is that the equilibrium vapor pressure of hydrogen is very low (less than 1 Torr). To overcome this engineering drawback, we added a small amount of vanadium (V) in Ti(53-x)Zr27Ni20V(x), alloys (where x = 0 to 15) and rapidly quenched the molten ingots to form quasicrystals, and investigated the effects of V in terms of changes of structure, the H/M values, and an equilibrium vapor pressure of hydrogen. As the results, an equilibrium vapor pressure significantly increased from 0.84 to 2.16 Torr while the maximum H/M value decreased from 1.32 to 1.11 as increasing x = 0 to 8. After hydrogenation, the main peaks shifted evenly to the lower angle of 20 in X-ray diffraction patterns with uniform expansion of the quasilattice constants which demonstrates that hydrogen atoms homogeneously diffused into the samples. A Laves phase starts to form at x = 13 and the samples completely transformed to the phase at x = 15 suggesting the similarity between the quasicrystal and the Laves phase.

  7. Perfluorobutane sulfonic acid hydration and interactions with O2 adsorbed on Pt3.

    PubMed

    Yan, Liuming; Balbuena, Perla B; Seminario, Jorge M

    2006-04-06

    The side chain of NAFION, a proton conductive membrane used as electrolyte in low-temperature fuel cells, is modeled with perfluorobutane sulfonic acid. Density functional theory is used to characterize structures and energetics of hydration of the model system interacting with a proton solvated with up to 24 water molecules and analyze interactions of some of these hydrated complexes with O(2) adsorbed on Pt(3). It is found that at least three water molecules are needed to ionize the sulfonic acid, and higher degrees of hydration induce the formation of cages where the water molecules are held together via complex hydrogen-bond networks. The interaction between the complex formed by the ionized acid and the hydrated proton, in contact with a bridge-adsorbed O(2)-Pt(3), promotes the protonation of the adsorbed O(2). Upon protonation, the O(2)-Pt(3) system evolves from hydrophobic to hydrophilic behavior, which may facilitate further interfacial contact.

  8. Structure-acidity correlation of supported tungsten(VI)-oxo-species: FT-IR and TPD studies of adsorbed pyridine and catalytic decomposition of 2-propanol

    NASA Astrophysics Data System (ADS)

    Zaki, M. I.; Mekhemer, G. A. H.; Fouad, N. E.; Rabee, A. I. M.

    2014-07-01

    The amount of 10 wt%-WO3 was supported on alumina, titania or silica by impregnation with aqueous solution of ammonium paratungstate and subsequent calcination at 500 °C for 10 h. Tungstate-related chemical and physical changes in the calcination products were resolved by ex-situ infrared (IR) spectroscopy. Nature of exposed surface acid sites were probed by in-situ IR spectroscopy of adsorbed pyridine (Py) molecules at room temperature (RT). The relative strength of the acid sites thus probed was gauged by combining results of temperature-programmed desorption (TPD) measurements of the RT-adsorbed Py with those communicated by in-situ IR spectra of residual Py on the surface after a brief thermoevacuation at high temperatures (100-300 °C). Reactivity of the surface acid sites was tested toward 2-propanal catalytic decomposition, and observed by in-situ IR gas phase spectra. Results obtained were correlated with predominant structures assumed by the supported tungstate species. Accordingly, polymerization of the supported tungstate into 2-/3-dimensional structures, was found to be relatively most advanced on favorable locations of titania surfaces as compared to the case on alumina or silica surfaces. Consequently, the Lewis acidity was strengthened, and strong Bronsted acidity was evolved, leading to a 2-propanol dehydration catalyst (tungstate/titania) of optimal activity and selectivity. Strong tungstate/support interfacial interactions were found to hamper the formation of the strongly acidic and catalytically active polymeric structures of the supported tungstate (i.e., the case on alumina or silica).

  9. Structure and hydrogen adsorption properties in low density nanoporous carbons from simulations

    SciTech Connect

    Peng, L.; Morris, James R

    2012-01-01

    We systematically model the hydrogen adsorption in nanoporous carbons over a wide range of carbon bulk densities (0.6 - 2.4 g/cm3) by using tight binding molecular dynamics simulations for the carbon structures and thermodynamics calculations of the hydrogen adsorption. The resulting structures are in good agreement with the experimental data of ultra-microporous carbon (UMC), a wood-based activated carbon, as indicated by comparisons of the microstructure at atomic level, pair distribution function, and pore size distribution. The hydrogen adsorption calculations in carbon structures demonstrate both a promising hydrogen storage capacity (excess uptake of 1.33 wt% at 298K and 5 MPa, for carbon structures at the lower range of densities) and a reasonable heat of adsorption (12-22 kJ/mol). This work demonstrates that increasing the heat of adsorption does not necessarily increase the hydrogen uptake. In fact, the available adsorption volume is as important as the isosteric heat of adsorption for hydrogen storage in nanoporous carbons.

  10. Correlation of structural order, anomalous density, and hydrogen bonding network of liquid water.

    PubMed

    Bandyopadhyay, Dibyendu; Mohan, S; Ghosh, S K; Choudhury, Niharendu

    2013-07-25

    We use extensive molecular dynamics simulations employing different state-of-the-art force fields to find a common framework for comparing structural orders and density anomalies as obtained from different water models. It is found that the average number of hydrogen bonds correlates well with various order parameters as well as the temperature of maximum densities across the different models, unifying apparently disparate results from different models and emphasizing the importance of hydrogen bonding in determining anomalous properties and the structure of water. A deeper insight into the hydrogen bond network of water reveals that the solvation shell of a water molecule can be defined by considering only those neighbors that are hydrogen-bonded to it. On the basis of this view, the origin of the appearance of a non-tetrahedral peak at a higher temperature in the distribution of tetrahedral order parameters has been explained. It is found that a neighbor that is hydrogen-bonded to the central molecule is tetrahedrally coordinated even at higher temperatures. The non-tetrahedral peak at a higher temperature arises due to the strained orientation of the neighbors that are non-hydrogen-bonded to the central molecule. With the new definition of the solvation shell, liquid water can be viewed as an instantaneously changing random hydrogen-bonded network consisting of differently coordinated hydrogen-bonded molecules with their distinct solvation shells. The variation of the composition of these hydrogen-bonded molecules against temperature accounts for the density anomaly without introducing the concept of large-scale structural polyamorphism in water.

  11. Evidences for Cooperative Resonance-Assisted Hydrogen Bonds in Protein Secondary Structure Analogs

    NASA Astrophysics Data System (ADS)

    Zhou, Yu; Deng, Geng; Zheng, Yan-Zhen; Xu, Jing; Ashraf, Hamad; Yu, Zhi-Wu

    2016-11-01

    Cooperative behaviors of the hydrogen bonding networks in proteins have been discovered for a long time. The structural origin of this cooperativity, however, is still under debate. Here we report a new investigation combining excess infrared spectroscopy and density functional theory calculation on peptide analogs, represented by N-methylformamide (NMF) and N-methylacetamide (NMA). Interestingly, addition of the strong hydrogen bond acceptor, dimethyl sulfoxide, to the pure analogs caused opposite effects, namely red- and blue-shift of the N-H stretching infrared absorption in NMF and NMA, respectively. The contradiction can be reconciled by the marked lowering of the energy levels of the self-associates between NMA molecules due to a cooperative effect of the hydrogen bonds. On the contrary, NMF molecules cannot form long-chain cooperative hydrogen bonds because they tend to form dimers. Even more interestingly, we found excellent linear relationships between changes on bond orders of N-H/N-C/C = O and the hydrogen bond energy gains upon the formation of hydrogen bonding multimers in NMA, suggesting strongly that the cooperativity originates from resonance-assisted hydrogen bonds. Our findings provide insights on the structures of proteins and may also shed lights on the rational design of novel molecular recognition systems.

  12. Control of changes in the defect structure of titanium saturated with hydrogen

    NASA Astrophysics Data System (ADS)

    Larionov, V. V.; Lider, A. M.; Laptev, R. S.

    2016-06-01

    The hydrogenated samples of technical titanium were investigated using the EPA method and the measurements of the thermal electromotive force for these samples saturated with a different amount of hydrogen. The structure of the hydrogenated samples was studied by the X-ray diffraction method. The results have shown that the hydrogenated titanium structure starts changing at the same time, depending on the amount of added hydrogen. The intensity of the annihilation process increases with the increase in the hydrogen concentration in a-titanium up to the values of 4% wt and does not change up to the values of 5% wt (α + δ) - titanium. At the same time, the value of the thermal electromotive force decreases in this range of values. The annihilation intensity is stabilized for the values of 5% wt, and the value of the thermal electromotive force is increased. The inflection point for the thermal electromotive force versus the hydrogen concentration corresponds to the formation of δ - hydrides. The increase in the positron lifetime starts in the concentration range of 6-8% and moves to the stable level up to the concentrations of 21-22%. In this range, there is a transition from the (α + β) to the (α + δ) phase. The lifetime of positrons and the number of defects are increased, the value of the thermal electromotive force is reduced (up to the concentration of 24%), then there is a stabilization mode for all these parameters up to the values 32% wt.

  13. Evidences for Cooperative Resonance-Assisted Hydrogen Bonds in Protein Secondary Structure Analogs

    PubMed Central

    Zhou, Yu; Deng, Geng; Zheng, Yan-Zhen; Xu, Jing; Ashraf, Hamad; Yu, Zhi-Wu

    2016-01-01

    Cooperative behaviors of the hydrogen bonding networks in proteins have been discovered for a long time. The structural origin of this cooperativity, however, is still under debate. Here we report a new investigation combining excess infrared spectroscopy and density functional theory calculation on peptide analogs, represented by N-methylformamide (NMF) and N-methylacetamide (NMA). Interestingly, addition of the strong hydrogen bond acceptor, dimethyl sulfoxide, to the pure analogs caused opposite effects, namely red- and blue-shift of the N−H stretching infrared absorption in NMF and NMA, respectively. The contradiction can be reconciled by the marked lowering of the energy levels of the self-associates between NMA molecules due to a cooperative effect of the hydrogen bonds. On the contrary, NMF molecules cannot form long-chain cooperative hydrogen bonds because they tend to form dimers. Even more interestingly, we found excellent linear relationships between changes on bond orders of N−H/N−C/C = O and the hydrogen bond energy gains upon the formation of hydrogen bonding multimers in NMA, suggesting strongly that the cooperativity originates from resonance-assisted hydrogen bonds. Our findings provide insights on the structures of proteins and may also shed lights on the rational design of novel molecular recognition systems. PMID:27849028

  14. Nanostructure and hydrogen spillover of bridged metal-organic frameworks.

    PubMed

    Tsao, Cheng-Si; Yu, Ming-Sheng; Wang, Cheng-Yu; Liao, Pin-Yen; Chen, Hsin-Lung; Jeng, U-Ser; Tzeng, Yi-Ren; Chung, Tsui-Yun; Wu, Hsiu-Chu

    2009-02-04

    The metal-organic frameworks (MOF) with low and medium specific surface areas (SSA) were shown to be able to adsorb hydrogen via bridged spillover at room temperature (RT) up to an amount of full coverage of hydrogen in the MOF. Anomalous small-angle X-ray scattering was employed to investigate the key relationship between the structures and storage properties of the involved materials. It was found that the tunable imperfect lattice defects and the 3D pore network in the MOF crystal are the most critical structures for RT hydrogen uptake rather than the known micropores in the crystal, SSA, and Pt catalyst structure.

  15. Effect of gravity on the stability and structure of lean hydrogen-air flames

    NASA Technical Reports Server (NTRS)

    Patnaik, G.; Kailasanath, K.

    1991-01-01

    Detailed, time-dependent, 2D numerical simulations with full hydrogen-oxygen chemistry are used to investigate the effects of gravity on the stability and structure of laminar flames in lean, premixed hydrogen-air mixtures. The calculations show that the effects of gravity becomes more important as the lean flammability limit is approached. In a 12 percent hydrogen-air mixture, gravity plays only a secondary role in determining the multidimensional structure of the flame with the stability and structure of the flame controlled primarily by the thermo-diffusive instability mechanism. However, in leaner hydrogen-air mixtures gravity becomes more important. Upward-propagating flames are highly curved and evolve into a bubble rising upwards in the tube. Downward-propagating flames are flat or even oscillate between structures with concave and convex curvatures. The zero-gravity flame shows only cellular structures. Cellular structures which are present in zero gravity can be suppressed by the effect of buoyancy for mixtures leaner than 11 percent hydrogen. These observations are explained on the basis of an interaction between the processes leading to buoyancy-induced Rayleigh-Taylor instability and the thermo-diffusive instability.

  16. Effect of gravity on the stability and structure of lean hydrogen-air flames

    NASA Technical Reports Server (NTRS)

    Patnaik, G.; Kailasanath, K.

    1991-01-01

    Detailed, time-dependent, 2D numerical simulations with full hydrogen-oxygen chemistry are used to investigate the effects of gravity on the stability and structure of laminar flames in lean, premixed hydrogen-air mixtures. The calculations show that the effects of gravity becomes more important as the lean flammability limit is approached. In a 12 percent hydrogen-air mixture, gravity plays only a secondary role in determining the multidimensional structure of the flame with the stability and structure of the flame controlled primarily by the thermo-diffusive instability mechanism. However, in leaner hydrogen-air mixtures gravity becomes more important. Upward-propagating flames are highly curved and evolve into a bubble rising upwards in the tube. Downward-propagating flames are flat or even oscillate between structures with concave and convex curvatures. The zero-gravity flame shows only cellular structures. Cellular structures which are present in zero gravity can be suppressed by the effect of buoyancy for mixtures leaner than 11 percent hydrogen. These observations are explained on the basis of an interaction between the processes leading to buoyancy-induced Rayleigh-Taylor instability and the thermo-diffusive instability.

  17. Hydrogen storage in graphite nanofibers

    SciTech Connect

    Park, C.; Tan, C.D.; Hidalgo, R.; Baker, R.T.K.; Rodriguez, N.M.

    1998-08-01

    Graphite nanofibers (GNF) are a type of material that is produced by the decomposition of carbon containing gases over metal catalyst particles at temperatures around 600 C. These molecularly engineered structures consist of graphene sheets perfectly arranged in a parallel, perpendicular or at angle orientation with respect to the fiber axis. The most important feature of the material is that only edges are exposed. Such an arrangement imparts the material with unique properties for gas adsorption because the evenly separated layers constitute the most ordered set of nanopores that can accommodate an adsorbate in the most efficient manner. In addition, the non-rigid pore walls can also expand so as to accommodate hydrogen in a multilayer conformation. Of the many varieties of structures that can be produced the authors have discovered that when gram quantities of a selected number of GNF are exposed to hydrogen at pressures of {approximately} 2,000 psi, they are capable of adsorbing and storing up to 40 wt% of hydrogen. It is believed that a strong interaction is established between hydrogen and the delocalized p-electrons present in the graphite layers and therefore a new type of chemistry is occurring within these confined structures.

  18. Structural and energy properties of interstitial molecular hydrogen in single-crystal silicon

    SciTech Connect

    Melnikov, V. V.

    2015-06-15

    The structural and energy characteristics of interstitial molecular hydrogen in single-crystal silicon are theoretically studied. The dependence of the potential energy of the system on the position and orientation of the interstitial defect is investigated, and the mechanism of interaction of a hydrogen molecule with a silicon crystal is considered. A three-dimensional model is employed to calculate the energy spectrum of H{sub 2} in Si, and the obtained dispersion law is analyzed.

  19. Acoustic Emission Monitoring of the DC-XA Composite Liquid Hydrogen Tank During Structural Testing

    NASA Technical Reports Server (NTRS)

    Wilkerson, C.

    1996-01-01

    The results of acoustic emission (AE) monitoring of the DC-XA composite liquid hydrogen tank are presented in this report. The tank was subjected to pressurization, tensile, and compressive loads at ambient temperatures and also while full of liquid nitrogen. The tank was also pressurized with liquid hydrogen. AE was used to monitor the tank for signs of structural defects developing during the test.

  20. Effects of edge hydrogenation on structural stability, electronic, and magnetic properties of WS2 nanoribbons

    NASA Astrophysics Data System (ADS)

    Ouyang, Fangping; Ni, Xiang; Yang, Zhixiong; Chen, Yu; Zheng, Xiaojuan; Xiong, Xiang

    2013-12-01

    Using density functional theory based first-principles, we have investigated the structural stability, electronic, and magnetic properties of tungsten disulfide nanoribbons (WS2NRs). When the edges are bare, Zigzag-edge WS2 nanoribbons (ZWS2NRs) and Armchair-edge WS2 nanoribbons (AWS2NRs) are ferromagnetic metal and nonmagnetic semiconductor, respectively. After edge hydrogenation, WS2NRs exhibit different structural stabilities and electronic structures according the patterns of edge hydrogenation. Hydrogenated ZWS2NRs keep ferromagnetic and metallic while AWS2NRs convert from nonmagnetic to magnetic when at least one edge is partially hydrogenated. The transition of AWS2NRs is contributed to the unpaired valence electrons. With the change of nanoribbon width n, magnetic moment of edge fully hydrogenated ZWS2NRs shows nearly periodical variation, the band gap of bare AWS2NRs oscillates like three distinct families and owing to the ever-present edge effect it converges to 0.5 eV as n increases. Compared with bare AWS2NRs, edge fully hydrogenated AWS2NRs have the same scaling rule of band-gap variation when n ≤12, while the band gap oscillates up and down when n > 12 because of the more obvious edge asymmetric effect than quantum confinement effect. These findings are essential for applications of WS2NRs in nanoelectronics and spintronics.

  1. Structures and optical properties of solid hydrogen at ultrahigh pressures

    NASA Astrophysics Data System (ADS)

    Nagara, H.

    2003-09-01

    The electronic energy bands in structures whose primitive cell contains up to four molecules are studied with full optimization of the structures on the basis of GGA and LDA band calculations. Above 250 GPa, the eventual optimal structure obtained by the GGA or the LDA calculation is Cmca, which is a layered structure with the molecular bonds lying in planes and which has a metallic band structure with no band gaps. The metallic property of the band structure remains unchanged even if the molecular bonds in the plane of the Cmca are inclined so that the atoms in the molecule lie out of the plane. The electronic bands of the Cmca structure and those of some other candidate structures are discussed in the light of recent experimental results. Effects of the occupation of electronic states on the predicted optimal structures are also studied.

  2. Deterministic features of side-chain main-chain hydrogen bonds in globular protein structures.

    PubMed

    Eswar, N; Ramakrishnan, C

    2000-04-01

    A total of 19 835 polar residues from a data set of 250 non-homologous and highly resolved protein crystal structures were used to identify side-chain main-chain (SC-MC) hydrogen bonds. The ratio of the number of SC-MC hydrogen bonds to the total number of polar residues is close to 1:2, indicating the ubiquitous nature of such hydrogen bonds. Close to 56% of the SC-MC hydrogen bonds are local involving side-chain acceptor/donor ('i') and a main-chain donor/acceptor within the window i-5 to i+5. These short-range hydrogen bonds form well defined conformational motifs characterized by specific combinations of backbone and side-chain torsion angles. (a) The Ser/Thr residues show the greatest preference in forming intra-helical hydrogen bonds between the atoms O(gamma)(i) and O(i-4). More than half the examples of such hydrogen bonds are found at the middle of alpha-helices rather than at their ends. The most favoured motif of these examples is alpha(R)alpha(R)alpha(R)alpha(R)(g(-)). (b) These residues also show great preference to form hydrogen bonds between O(gamma)(i) and O(i-3), which are closely related to the previous type and though intra-helical, these hydrogen bonds are more often found at the C-termini of helices than at the middle. The motif represented by alpha(R)alpha(R)alpha(R)alpha(R)(g(+)) is most preferred in these cases. (c) The Ser, Thr and Glu are the most frequently found residues participating in intra-residue hydrogen bonds (between the side-chain and main-chain of the same residue) which are characterized by specific motifs of the form beta(g(+)) for Ser/Thr residues and alpha(R)(g(-)g(+)t) for Glu/Gln. (d) The side-chain acceptor atoms of Asn/Asp and Ser/Thr residues show high preference to form hydrogen bonds with acceptors two residues ahead in the chain, which are characterized by the motifs beta (tt')alphaR and beta(t)alpha(R), respectively. These hydrogen bonded segments, referred to as Asx turns, are known to provide stability to type I

  3. Two solvent-induced porous hydrogen-bonded organic frameworks: solvent effects on structures and functionalities.

    PubMed

    Wang, Hailong; Bao, Zongbi; Wu, Hui; Lin, Rui-Biao; Zhou, Wei; Hu, Tong-Liang; Li, Bin; Zhao, John Cong-Gui; Chen, Banglin

    2017-09-05

    Two solvent-induced porous hydrogen-bonded organic frameworks have been obtained, and their synthesis, crystal structures, gas sorption behaviours and fluorescence sensing applications have been systematically investigated to elucidate the solvent effects on the structures and functionalities of HOFs.

  4. Enhanced hydrogen storage in sandwich-structured rGO/Co1-xS/rGO hybrid papers through hydrogen spillover

    NASA Astrophysics Data System (ADS)

    Han, Lu; Qin, Wei; Jian, Jiahuang; Liu, Jiawei; Wu, Xiaohong; Gao, Peng; Hultman, Benjamin; Wu, Gang

    2017-08-01

    Reduced graphene oxide (rGO) based two-dimensional (2D) structures have been fabricated for electrochemical hydrogen storage. However, the effective transfer of atomic hydrogen to adjacent rGO surfaces is suppressed by binders, which are widely used in conventional electrochemical hydrogen storage electrodes, leading to a confining of the performance of rGO for hydrogen storage. As a proof of concept experiment, a novel strategy is developed to fabricate the binder-free sandwich-structured rGO/Co1-xS/rGO hybrid paper via facile ball milling and filtration process. Based on the structure investigation, Co1-xS is immobilized in the space between the individual rGO sheets by the creation of chemical ;bridges; (Csbnd S bonds). Through the Csbnd S bonds, the atomic hydrogen is transferred from Co1-xS to rGO accompanying a Csbnd H chemical bond formation. When used as an electrode, the hybrid paper exhibits an improved hydrogen storage capacity of 3.82 wt% and, most importantly, significant cycling stability for up to 50 cycles. Excluding the direct hydrogen storage contribution from the Co1-xS in the hybrid paper, the hydrogen storage ability of rGO is enhanced by 10× through the spillover effects caused by the Co1-xS modifier.

  5. In situ study of structural and optical properties of Pd thin film during hydrogen exposure

    NASA Astrophysics Data System (ADS)

    Pelizzo, Maria Guglielmina; Corso, Alain J.; Bazzan, Marco; Zuppella, Paola; Garoli, Denis; Martucci, Alessandro

    2016-09-01

    When Palladium film is exposed to hydrogen, it becomes palladium hydride. A change in the complex permittivity of the metal film results in a change of the optical properties that depends on hydrogen concentration. Ellipsometry is the technique of choice to measure the optical constants prior and during hydrogenation. Sensors are then usually designed and optimized to measure changes in transmittance or reflectance of the palladium films. Films of different thicknesses have been realized and tested to verify potential applications in hydrogen sensing by studying the optical response prior, during and after hydrogenation, to assess in particular the reversibility of the process. Within this work a deep analysis carried out by x-ray reflectance (XRR) shows that during hydrogenation the films change also their thickness, and the amount has been assessed for a specific hydrogen concentration. Ellipsometric measurements have been therefore corrected taking into account such variation to determine the optical constants. Such structural property of the palladium hydride may be exploited in surface plasmon resonance transducers, which are sensitive also to the change of the sensing film thickness during detection.

  6. Effect of Water on the Structure and Stability of Hydrogen-Bonded Oxalic Acid Dimer.

    PubMed

    Hu, Yuan-Chun; Zhang, Xiu-Hui; Li, Quan-Song; Zhang, Yun-Hong; Li, Ze-Sheng

    2017-10-06

    As the simplest and the most abundant dicarboxylic acids in the atmosphere, oxalic acid (OA) not only plays a key role in aerosol nucleation, but also acts as a prototypical compound for the investigation of intra- and intermolecular hydrogen bonding interactions. In this work, a systematic theoretical study on the hydrated OA dimers were carried out using density functional theory (DFT) at the M06-2X/6-311++G(3df, 2p) level. The properties of the hydrogen bonds in clusters were inspected through topological analysis using atoms in molecules (AIM) theory. The most stable OA dimer involves a cyclic structure with two intermolecular hydrogen bonds. Our calculations show that one H2O has slightly effect on the hydrogen bonds, while two water molecules weaken and three water molecules even break the two intermolecular hydrogen bonds between OAs. Furthermore, there are no hydrogen bond interactions between OAs in almost all stable clusters when the H2O number increases to four and five. Additionally, the ionization and the isomerization of OA through water-assisted proton transfer phenomena were observed in tetrahydrates and pentahydrates. Our work has provided new insights into the conversion process of anhydrous OA to hydrated clusters, which are helpful for further understanding the atmospheric nucleation process and the nature of hydrogen bond. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  7. A Classical Description of the Hyperfine Structure of the Hydrogen Atom

    NASA Astrophysics Data System (ADS)

    Chaney, Andrea; Espinosa, James; Woodyard, James

    2010-10-01

    As stronger dispersion gratings are utilized, the Hydrogen spectrum is broken into small groupings. At first, the fine structure was successfully described by Sommerfeld by utilizing the special theory of relativity. The fine structure groupings are three orders of magnitude smaller than the series separations as described by Balmer and others. With even further powerful instruments, Michelson was the first to split these lines into further groupings which are a further two orders of magnitude smaller. It was almost fifty years before Breit used quantum mechanics to describe this hyperfine structure. It is almost universally believed that classical theory utterly fails to describe this phenomenon. We will show how our classical Hydrogen atom based on Ritz's magnetic model can account for the splitting of the 1s state, which is famous for its use by radio astronomers to map out the distribution of hydrogen in the universe.

  8. Dinuclear complexes formed by hydrogen bonds: synthesis, structure and magnetic and electrochemical properties.

    PubMed

    Williams, Alan Francis; Granelli, Matteo; Downward, Alan M; Huber, Robin; Guenée, Laure; Besnard, Céline; Krämer, Karl W; Decurtins, Silvio; Liu, Shi-Xia; Thompson, Laurence K

    2017-03-20

    The synthesis is reported of a series of homo- and hetero-dinuclear octahedral complexes of the ligand 1, 1,2-bis(1-methyl-benzimidazol-2-yl) ethanol, where the two metal centres are linked by hydrogen bonds between coordinated alcohols and coordinated alkoxides. Homonuclear divalent M(II)M(II), mixed valent M(II)M(III) and heteronuclear M(II)M'(III) species are prepared. The complexes have been characterised by X-ray crystallography and show unusually short O…O distances for the hydrogen bonds. Magnetic measurements show the hydrogen bond bridges can lead to ferromagnetic or antiferromagnetic coupling. The electrochemistry of the dinuclear species is significantly different from the mononuclear systems: the latter show irreversible waves in cyclic voltammograms as a result of the need to couple proton and electron transfer. The dinuclear species, in contrast, show reversible waves which are attributed to rapid intramolecular proton transfer facilitated by the hydrogen bonded structure.

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

    SciTech Connect

    Dunphy, James Christopher

    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(2xl) 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.

  10. EDITORIAL: Nanoscale phenomena in hydrogen storage Nanoscale phenomena in hydrogen storage

    NASA Astrophysics Data System (ADS)

    Vajo, John; Pinkerton, Fred; Stetson, Ned

    2009-05-01

    Future energy technologies that use hydrogen as an energy carrier offer the tantalizing prospect of operating essentially free of pollutant and greenhouse gas emissions while utilizing hydrogen produced from a diverse range of renewable sources. To realize these technologies, such as hydrogen proton exchange membrane (PEM) fuel cells, improved approaches are needed for the high-capacity storage of hydrogen at temperatures ranging from near ambient to about 100 °C and at pressures below about 100 bar. These conditions favor storage based on the interaction of hydrogen with solid materials, rather than storage based on compressed or liquid hydrogen, which requires high pressures (700 bar) or low temperatures (20 K), respectively. Significant advances have recently been made, both in materials that store hydrogen as H2 molecules adsorbed on suitable supports and in materials that bind hydrogen chemically in the form of atoms, protons (cations) or hydride anions. Advances in molecular storage have come largely from a detailed understanding of the structures and bonding processes in traditional adsorbents and the development of new high-surface-area adsorbent materials with structures tailored on the molecular scale. Much of the emphasis has been on further increasing the number of adsorption sites to improve storage capacity. The low adsorption energies of current materials present another challenge because the weakly bound H2 can achieve technologically significant capacities only at cryogenic temperatures (50-80 K). Ongoing efforts to improve the thermodynamics of adsorption are primarily focused on composition and structure modifications. For chemically bound hydrogen, advances have come from investigation into light-element binary and complex hydrides, which inherently have high hydrogen capacities. The polar covalent bonding that characterizes these hydrides leads to very slow kinetics for hydrogen exchange, so here the emphasis is on improving kinetics through

  11. The intermolecular hydrogen-hydrogen structure of chain-molecule liquids from neutron diffraction

    NASA Astrophysics Data System (ADS)

    Londono, J. D.; Annis, B. K.; Turner, J. Z.; Soper, A. K.

    1994-11-01

    Neutron diffraction isotopic substitution experiments on liquid n-decane (C10H22) and n-eicosane (C20H42) are described. The intermolecular H-H structure function hHH(Q) and the intermolecular H-H correlation function ginterHH(r) are obtained without recourse to models of the intramolecular structure. The structure of the ginterHH(r) found at 2.5, 5.0, and 7.0 Å corresponds to different shells in the H-H pair correlation function. In addition, ginterHH(r)<1 for a considerable range, due to the screening of intermolecular correlations by intramolecular correlations. This ``correlation hole'' effect is accentuated by extrapolation of the structure functions to the expected infinite wavelength limit, and shows good agreement with values determined from small-angle neutron scattering (SANS) data. All of these features are in good agreement with the results of molecular dynamics simulations for the closely related system C13H28.

  12. Structures and segregation patterns of Ag-Cu and Ag-Ni nanoalloys adsorbed on MgO(0 0 1)

    NASA Astrophysics Data System (ADS)

    Bochicchio, Davide; Ferrando, Riccardo; Panizon, Emanuele; Rossi, Giulia

    2016-02-01

    Low-energy geometric structures and segregation patterns of Ag-Cu and Ag-Ni nanoparticles adsorbed on MgO(0 0 1) are searched for by global optimisation methods within an atomistic potential model. Sizes betwen 100 and 300 atoms are considered for several compositions. In all cases, Ag segregates to the nanoparticle surface, so that Cu@Ag and Ni@Ag core-shell arrangements are found, with off-centre cores for Ag-rich compositions. The behaviours of Ag-Cu and Ag-Ni differ at the interface with the MgO substrate. For Ag-Cu, some Cu atoms are at the interface even for compositions that are very rich in Ag, where Ag-Ni nanoparticles present an interface completely made of Ag atoms. Ag-Ni and Ag-Cu also differ concerning their geometric structures. With increasing Ag content, in Ag-Cu we find the structural sequence faulted fcc \\to icosahedral \\to fcc, while in Ag-Ni we find the sequence hcp \\to faulted fcc-faulted hcp \\to icosahedral \\to fcc.

  13. Influence of hydrogen oxidation kinetics on hydrogen environment embrittlement

    NASA Technical Reports Server (NTRS)

    Walter, R. J.; Kendig, M. W.; Meisels, A. P.

    1992-01-01

    Results are presented from experiments performed to determine the roles of hydrogen absorption and hydrogen electron transfer on the susceptibility of Fe- and Ni-base alloys to ambient-temperature hydroen embrittlement. An apparent independence is noted between hydrogen environment embrittlement and internal hydrogen embrittlement. The experiments were performed on Inconel 718, Incoloy 903, and A286. The electrochemical results obtained indicate that Inconel 718 either adsorbs hydrogen more rapidly and/or the electrochemical oxidation of the adsorbed hydrogen occurred more rapidly than in the other two materials.

  14. Protein structure change studied by hydrogen-deuterium exchange, functional labeling, and mass spectrometry

    PubMed Central

    Englander, Joan J.; Del Mar, Charyl; Li, Will; Englander, S. Walter; Kim, Jack S.; Stranz, David D.; Hamuro, Yoshitomo; Woods, Virgil L.

    2003-01-01

    An automated high-throughput, high-resolution deuterium exchange HPLC-MS method (DXMS) was used to extend previous hydrogen exchange studies on the position and energetic role of regulatory structure changes in hemoglobin. The results match earlier highly accurate but much more limited tritium exchange results, extend the analysis to the entire sequence of both hemoglobin subunits, and identify some energetically important changes. Allosterically sensitive amide hydrogens located at near amino acid resolution help to confirm the reality of local unfolding reactions and their use to evaluate resolved structure changes in terms of allosteric free energy. PMID:12773622

  15. Hydrogen Diffusion Behavior in Titanium-Chromium Hydrides with Laves Structures

    SciTech Connect

    Bowman Jr., R.C.; Craft, B.D.; Attalla, A.; Johnson, J.R.

    1981-03-31

    Extensive NMR measurements of the proton relaxation times have been performed on low (i.e., alpha-phase) and intermediate (i.e., alpha'-phase) hydrogen concentrations in TiCr{sub}2H{sub}x with both the hexagonal Cl4 and cubic Cl5 Laves structures. The relaxation times indicate rapid diffusion rates above 200 K for all the TiCr{sub}2H{sub}x phases; however, large differences in the diffusion activation energies are observed. This behavior is associated with the hydrogen interstitial site occupancies and diffusion pathways becoming restricted in the Cl4 structure.

  16. Protein structure change studied by hydrogen-deuterium exchange, functional labeling, and mass spectrometry.

    PubMed

    Englander, Joan J; Del Mar, Charyl; Li, Will; Englander, S Walter; Kim, Jack S; Stranz, David D; Hamuro, Yoshitomo; Woods, Virgil L

    2003-06-10

    An automated high-throughput, high-resolution deuterium exchange HPLC-MS method (DXMS) was used to extend previous hydrogen exchange studies on the position and energetic role of regulatory structure changes in hemoglobin. The results match earlier highly accurate but much more limited tritium exchange results, extend the analysis to the entire sequence of both hemoglobin subunits, and identify some energetically important changes. Allosterically sensitive amide hydrogens located at near amino acid resolution help to confirm the reality of local unfolding reactions and their use to evaluate resolved structure changes in terms of allosteric free energy.

  17. Effects of hydrogen and rf power on the structural and electrical properties of rf sputtered hydrogenated amorphous silicon carbide films

    NASA Astrophysics Data System (ADS)

    Choi, W. K.; Loo, F. L.; Loh, F. C.; Tan, K. L.

    1996-08-01

    The effects of the rf power (100 to 600 W) and the hydrogen partial pressure (PH=0.15 to 0.6 Pa.) on the deposition rate and the structural and electrical properties of rf sputtered hydrogenated amorphous silicon carbide (a-Si1-xCx:H) films were investigated. The films were deposited in an argon plus hydrogen ambient. The deposition rate increased with increasing rf power, but decreased with increasing PH. The refractive index increases from 1.85-3.6 as the rf power increases from 100-600 W and from 2.8 to 3.5 as PH increases from 0.15-0.6 Pa. The optical gap increases from 1.5 to 2.15 eV as PH increases from 0.15-0.6 Pa, but decreases from 2.8-1.38 eV as the rf power increases from 100-600 W. The Si-C bond gave the most prominent absorption peak in the infrared spectra, and increased with increasing rf power but not affected by changes in PH. The Si-H bonds increases from 3.06×1021 to 1.64×1022 cm-3 as PH was increased from 0.15-0.6 Pa. The optical gap increases from 1.5-2.15 eV and the conductivity reduces from 7.3×10-9 to 1.9×10-11 Ω-1 cm-1 accordingly. No C-Hn stretching mode was detected in all the films and this was attributed to the low carbon content of the films. We conclude that rf sputtering technique is not effective in varying the carbon content in a-Si1-xCx:H films.

  18. Doped penta-graphene and hydrogenation of its related structures: a structural and electronic DFT-D study.

    PubMed

    Quijano-Briones, J J; Fernández-Escamilla, H N; Tlahuice-Flores, A

    2016-06-21

    The structure of penta-graphene (penta-C), an irregular pentagonal two-dimensional (2D) structure, has been predicted recently. In this communication we carried out a dispersion-corrected density functional theory (DFT-D) study of the penta-C doped with Si, Ge and Sn atoms and its related hydrogenated penta-C structures (H-penta-C-X). We predict various new structures as thermally stable based on Born-Oppenheimer molecular dynamics (BOMD) calculations. Moreover, their dynamical stability is attested by phonon dispersions spectra. In general, we found that the bandgap value of doped structures reduces, while H-penta-C-X show large bandgap values. This feature can be exploited for potential uses of hydrogenated doped-penta-C structures as dielectric layers in electronic devices.

  19. Local atomic structure modulations activate metal oxide as electrocatalyst for hydrogen evolution in acidic water.

    PubMed

    Li, Yu Hang; Liu, Peng Fei; Pan, Lin Feng; Wang, Hai Feng; Yang, Zhen Zhong; Zheng, Li Rong; Hu, P; Zhao, Hui Jun; Gu, Lin; Yang, Hua Gui

    2015-08-19

    Modifications of local structure at atomic level could precisely and effectively tune the capacity of materials, enabling enhancement in the catalytic activity. Here we modulate the local atomic structure of a classical but inert transition metal oxide, tungsten trioxide, to be an efficient electrocatalyst for hydrogen evolution in acidic water, which has shown promise as an alternative to platinum. Structural analyses and theoretical calculations together indicate that the origin of the enhanced activity could be attributed to the tailored electronic structure by means of the local atomic structure modulations. We anticipate that suitable structure modulations might be applied on other transition metal oxides to meet the optimal thermodynamic and kinetic requirements, which may pave the way to unlock the potential of other promising candidates as cost-effective electrocatalysts for hydrogen evolution in industry.

  20. Local atomic structure modulations activate metal oxide as electrocatalyst for hydrogen evolution in acidic water

    PubMed Central

    Li, Yu Hang; Liu, Peng Fei; Pan, Lin Feng; Wang, Hai Feng; Yang, Zhen Zhong; Zheng, Li Rong; Hu, P.; Zhao, Hui Jun; Gu, Lin; Yang, Hua Gui

    2015-01-01

    Modifications of local structure at atomic level could precisely and effectively tune the capacity of materials, enabling enhancement in the catalytic activity. Here we modulate the local atomic structure of a classical but inert transition metal oxide, tungsten trioxide, to be an efficient electrocatalyst for hydrogen evolution in acidic water, which has shown promise as an alternative to platinum. Structural analyses and theoretical calculations together indicate that the origin of the enhanced activity could be attributed to the tailored electronic structure by means of the local atomic structure modulations. We anticipate that suitable structure modulations might be applied on other transition metal oxides to meet the optimal thermodynamic and kinetic requirements, which may pave the way to unlock the potential of other promising candidates as cost-effective electrocatalysts for hydrogen evolution in industry. PMID:26286479

  1. Local atomic structure modulations activate metal oxide as electrocatalyst for hydrogen evolution in acidic water

    NASA Astrophysics Data System (ADS)

    Li, Yu Hang; Liu, Peng Fei; Pan, Lin Feng; Wang, Hai Feng; Yang, Zhen Zhong; Zheng, Li Rong; Hu, P.; Zhao, Hui Jun; Gu, Lin; Yang, Hua Gui

    2015-08-01

    Modifications of local structure at atomic level could precisely and effectively tune the capacity of materials, enabling enhancement in the catalytic activity. Here we modulate the local atomic structure of a classical but inert transition metal oxide, tungsten trioxide, to be an efficient electrocatalyst for hydrogen evolution in acidic water, which has shown promise as an alternative to platinum. Structural analyses and theoretical calculations together indicate that the origin of the enhanced activity could be attributed to the tailored electronic structure by means of the local atomic structure modulations. We anticipate that suitable structure modulations might be applied on other transition metal oxides to meet the optimal thermodynamic and kinetic requirements, which may pave the way to unlock the potential of other promising candidates as cost-effective electrocatalysts for hydrogen evolution in industry.

  2. Partial high-resolution structure of phosphorylated and non-phosphorylated leucine-rich amelogenin protein adsorbed to hydroxyapatite

    SciTech Connect

    Masica, David L.; Gray, Jeffrey J.; Shaw, Wendy J.

    2011-07-21

    The formation of biogenic materials requires the interaction of organic molecules with the mineral phase. In forming enamel, the amelogenin proteins contribute to the mineralization of hydroxyapatite (HAp). Leucine-rich amelogenin protein (LRAP) is a naturally occurring splice variant of amelogenin that comprises amelogenin’s predicted HAp binding domains. We determined the partial structure of phosphorylated and non-phosphorylated LRAP variants bound to HAp using combined solid-state NMR (ssNMR) and ssNMR-biased computational structure prediction. The ssNMR measurements indicate a largely extended structure for both variants, though some measurements are consistent with a partially helical N-terminal segment. Structure prediction was biased using 21 ssNMR measurements at five HAp crystal faces. The predicted fold of LRAP is similar at all HAp faces studied, regardless of phosphorylation. LRAP’s predicted structure is relatively extended with a helix-turn-helix motif in the N-terminal domain and some helix in the C-terminal domain. The N-terminal domain of the phosphorylated variant binds HAp more tightly than the N-terminal domain of the non-phosphorylated variant. Both variants are predicted to preferentially bind the {010} HAp crystal face providing further evidence that amelogenins block crystal growth on the a and b faces to allow elongated crystals in the c-axis. Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy.

  3. Infrared spectral evidence and DFT calculations of hydrogen-bonding and molecular structures of acetogenins

    NASA Astrophysics Data System (ADS)

    Afonso, Sabrina; Silva, Fabiano B.; Silva, Arnaldo F.; Scarminio, Ieda S.; Bruns, Roy E.

    2017-02-01

    FTIR spectra have been measured for 31 different five component - simplex centroid design solvent mixture extracts of shaded and sun-exposed Annonaceous leaves harvested in all four seasons. The spectral frequencies are characteristic of anonnaceous acetogenins known to be a major component of these leaves. Osbnd H stretching spectral bands in the 3100-3600 cm-1 region provide evidence of notable intensity changes for the shaded and sun-exposed leaves. Chemometric principal component analysis involving 264 spectra show that shaded samples tend to have more intense Osbnd H stretching bands than those grown in the sun. B3LYP density functional calculations indicate significant Osbnd H stretching band changes in this region owing to hydrogen bond formation. Weak Osbnd H intensity enhancements, around 40 km mol-1, occur when an Osbnd H group forms a hydrogen bond with the oxygen atom of an adjacent tetrahydrofuran ring oxygen atom. Much more intense enhancements, 400-500 km mol-1, are predicted to occur for acetogenins with two tetrahydrofuran rings for which the Osbnd H group hydrogen bonds with its fartherest removed tetrahydrofuran ring oxygen. Whereas weak or moderate H-bond stretching intensities are obtained for acetogenins with slightly bent carbon chain structures the strongest hydrogen bond intensities are calculated for molecules with a 45° V-type backbone structure. These important structural modifications as well as significant changes in bond lengths and angles owing to hydrogen bonding are detailed.

  4. Hydrogen storage in microporous metal-organic frameworks.

    PubMed

    Rosi, Nathaniel L; Eckert, Juergen; Eddaoudi, Mohamed; Vodak, David T; Kim, Jaheon; O'Keeffe, Michael; Yaghi, Omar M

    2003-05-16

    Metal-organic framework-5 (MOF-5) of composition Zn4O(BDC)3 (BDC = 1,4-benzenedicarboxylate) with a cubic three-dimensional extended porous structure adsorbed hydrogen up to 4.5 weight percent (17.2 hydrogen molecules per formula unit) at 78 kelvin and 1.0 weight percent at room temperature and pressure of 20 bar. Inelastic neutron scattering spectroscopy of the rotational transitions of the adsorbed hydrogen molecules indicates the presence of two well-defined binding sites (termed I and II), which we associate with hydrogen binding to zinc and the BDC linker, respectively. Preliminary studies on topologically similar isoreticular metal-organic framework-6 and -8 (IRMOF-6 and -8) having cyclobutylbenzene and naphthalene linkers, respectively, gave approximately double and quadruple (2.0 weight percent) the uptake found for MOF-5 at room temperature and 10 bar.

  5. Hydrogen Storage in Microporous Metal-Organic Frameworks

    NASA Astrophysics Data System (ADS)

    Rosi, Nathaniel L.; Eckert, Juergen; Eddaoudi, Mohamed; Vodak, David T.; Kim, Jaheon; O'Keeffe, Michael; Yaghi, Omar M.

    2003-05-01

    Metal-organic framework-5 (MOF-5) of composition Zn4O(BDC)3 (BDC = 1,4-benzenedicarboxylate) with a cubic three-dimensional extended porous structure adsorbed hydrogen up to 4.5 weight percent (17.2 hydrogen molecules per formula unit) at 78 kelvin and 1.0 weight percent at room temperature and pressure of 20 bar. Inelastic neutron scattering spectroscopy of the rotational transitions of the adsorbed hydrogen molecules indicates the presence of two well-defined binding sites (termed I and II), which we associate with hydrogen binding to zinc and the BDC linker, respectively. Preliminary studies on topologically similar isoreticular metal-organic framework-6 and -8 (IRMOF-6 and -8) having cyclobutylbenzene and naphthalene linkers, respectively, gave approximately double and quadruple (2.0 weight percent) the uptake found for MOF-5 at room temperature and 10 bar.

  6. Hydrogen Storage in Titanium-decorated Boron Buckyball

    NASA Astrophysics Data System (ADS)

    Li, Jia; Zhou, Gang; Duan, Wenhui; Lee, Hoonkyung; Ihm, Jisoon

    2008-03-01

    Using first-principles electronic structure calculations, we investigate the potential of Ti-decorated B80 for hydrogen storage medium. The Ti-decorated B80 has the merit of an unexpected large binding energy of a Ti atom to B80 which can overcome the problem of metal clustering. Up to four hydrogen molecules are found to be adsorbed on a single Ti atom coated on B80. At high Ti coverage, we show that the Ti-decorated B80 can adsorb up to 5 wt% hydrogen and the calculated binding energy falls in the desirable range of 0.2-0.6eV/H2 which is suitable for reversible hydrogen storage at room-temperature, near-ambient-pressure conditions.

  7. Structural analysis of diheme cytochrome c by hydrogen-deuterium exchange mass spectrometry and homology modeling.

    PubMed

    Zhang, Ying; Majumder, Erica L-W; Yue, Hai; Blankenship, Robert E; Gross, Michael L

    2014-09-09

    A lack of X-ray or nuclear magnetic resonance structures of proteins inhibits their further study and characterization, motivating the development of new ways of analyzing structural information without crystal structures. The combination of hydrogen-deuterium exchange mass spectrometry (HDX-MS) data in conjunction with homology modeling can provide improved structure and mechanistic predictions. Here a unique diheme cytochrome c (DHCC) protein from Heliobacterium modesticaldum is studied with both HDX and homology modeling to bring some definition of the structure of the protein and its role. Specifically, HDX data were used to guide the homology modeling to yield a more functionally relevant structural model of DHCC.

  8. Structure dependent hydrogen induced etching features of graphene crystals

    NASA Astrophysics Data System (ADS)

    Thangaraja, Amutha; Shinde, Sachin M.; Kalita, Golap; Papon, Remi; Sharma, Subash; Vishwakarma, Riteshkumar; Sharma, Kamal P.; Tanemura, Masaki

    2015-06-01

    H2 induced etching of graphene is of significant interest to understand graphene growth process as well as to fabricate nanoribbons and various other structures. Here, we demonstrate the structure dependent H2 induced etching behavior of graphene crystals. We synthesized graphene crystals on electro-polished Cu foil by an atmospheric pressure chemical vapor deposition process, where some of the crystals showed hexagonal shaped snowflake-dendritic morphology. Significant differences in H2 induced etching behavior were observed for the snowflake-dendritic and regular graphene crystals by annealing in a gas mixture of H2 and Ar. The regular graphene crystals were etched anisotropically creating hexagonal holes with pronounced edges, while etching of all the dendritic crystals occurred from the branches of lobs creating symmetrical fractal structures. The etching behavior provides important clue of graphene nucleation and growth as well as their selective etching to fabricate well-defined structures for nanoelectronics.

  9. Quasiparticle band structure of infinite hydrogen fluoride and hydrogen chloride chains.

    PubMed

    Buth, Christian

    2006-10-21

    We study the quasiparticle band structure of isolated, infinite (HF)(infinity) and (HCl)(infinity) bent (zigzag) chains and examine the effect of the crystal field on the energy levels of the constituent monomers. The chains are one of the simplest but realistic models of the corresponding three-dimensional crystalline solids. To describe the isolated monomers and the chains, we set out from the Hartree-Fock approximation, harnessing the advanced Green's function methods local molecular orbital algebraic diagrammatic construction (ADC) scheme and local crystal orbital ADC (CO-ADC) in a strict second order approximation, ADC(2,2) and CO-ADC(2,2), respectively, to account for electron correlations. The configuration space of the periodic correlation calculations is found to converge rapidly only requiring nearest-neighbor contributions to be regarded. Although electron correlations cause a pronounced shift of the quasiparticle band structure of the chains with respect to the Hartree-Fock result, the bandwidth essentially remains unaltered in contrast to, e.g., covalently bound compounds.

  10. 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.

  11. Isomers and Conformers of H(NH₂BH₂)(n)H Oligomers: Understanding the Geometries and Electronic Structure of Boron-Nitrogen-Hydrogen Compounds as Potential Hydrogen Storage Materials

    SciTech Connect

    Li, Jun; Kathmann, Shawn M.; Schenter, Gregory K.; Gutowski, Maciej S.

    2007-02-07

    Boron-nitrogen-hydrogen (BNHx) materials are polar analogs of hydrocarbons with potential applications as media for hydrogen storage. As H(NH₂BH₂)nH oligomers result from dehydrogenation of NH₃BH₃ and NH₄BH₄ materials, understanding the geometries, stabilities, and electronic structure of these oligomers is essential for developing chemical methods of hydrogen release and regeneration of the BNHx-based hydrogen storage materials. In this work we have performed computational modeling on the H(NH₂BH₂)nH (n = 1 – 6) oligomers using density functional theory (DFT). We have investigated linear chain structures and the stabilizing effects of coiling, biradicalization, and branching through Car-Parrinello molecular dynamics simulations and geometry optimizations. We find that the zig-zag linear oligomers are unstable with respect to the coiled, square-wave chain, and branched structures, with the coiled structures being the most stable. Dihydrogen bonding in oligomers, where protic Hδ⁺(N) hydrogens interact with hydridic Hδ⁻(B) hydrogens, plays a crucial role in stabilizing different isomers and conformers. The results are consistent with structures of products that are seen in experimental NMR studies of dehydrogenated ammonia borane.

  12. Structure sensitivity in the nonscalable regime explored via catalysed ethylene hydrogenation on supported platinum nanoclusters

    SciTech Connect

    Crampton, Andrew S.; Rötzer, Marian D.; Ridge, Claron J.; Schweinberger, Florian F.; Heiz, Ueli; Yoon, Bokwon; Landman, Uzi

    2016-01-28

    The sensitivity, or insensitivity, of catalysed reactions to catalyst structure is a commonly employed fundamental concept. Here we report on the nature of nano-catalysed ethylene hydrogenation, investigated through experiments on size-selected Ptn (n=8-15) clusters soft-landed on magnesia and first-principles simulations, yielding benchmark information about the validity of structure sensitivity/insensitivity at the bottom of the catalyst size range. Both ethylene-hydrogenation-to-ethane and the parallel hydrogenation–dehydrogenation ethylidyne-producing route are considered, uncovering that at the <1 nm size-scale the reaction exhibits characteristics consistent with structure sensitivity, in contrast to structure insensitivity found for larger particles. The onset of catalysed hydrogenation occurs for Ptn (n≥10) clusters at T>150 K, with maximum room temperature reactivity observed for Pt13. Structure insensitivity, inherent for specific cluster sizes, is induced in the more active Pt13 by a temperature increase up to 400 K leading to ethylidyne formation. As a result, control of sub-nanometre particle size may be used for tuning catalysed hydrogenation activity and selectivity.

  13. Structure sensitivity in the nonscalable regime explored via catalysed ethylene hydrogenation on supported platinum nanoclusters

    DOE PAGES

    Crampton, Andrew S.; Rötzer, Marian D.; Ridge, Claron J.; ...

    2016-01-28

    The sensitivity, or insensitivity, of catalysed reactions to catalyst structure is a commonly employed fundamental concept. Here we report on the nature of nano-catalysed ethylene hydrogenation, investigated through experiments on size-selected Ptn (n=8-15) clusters soft-landed on magnesia and first-principles simulations, yielding benchmark information about the validity of structure sensitivity/insensitivity at the bottom of the catalyst size range. Both ethylene-hydrogenation-to-ethane and the parallel hydrogenation–dehydrogenation ethylidyne-producing route are considered, uncovering that at the <1 nm size-scale the reaction exhibits characteristics consistent with structure sensitivity, in contrast to structure insensitivity found for larger particles. The onset of catalysed hydrogenation occurs for Ptn (n≥10)more » clusters at T>150 K, with maximum room temperature reactivity observed for Pt13. Structure insensitivity, inherent for specific cluster sizes, is induced in the more active Pt13 by a temperature increase up to 400 K leading to ethylidyne formation. As a result, control of sub-nanometre particle size may be used for tuning catalysed hydrogenation activity and selectivity.« less

  14. Crystal structure and cyclic hydrogenation property of Pr4MgNi19.

    PubMed

    Iwase, Kenji; Terashita, Naoyoshi; Mori, Kazuhiro; Yokota, Hitoshi; Suzuki, Tetsuya

    2013-12-16

    The hydrogen absorption-desorption property and the crystal structure of Pr4MgNi19 was investigated by pressure-composition isotherm measurement and X-ray diffraction (XRD). Pr4MgNi19 consisted of two phases: 52.9% Ce5Co19-type structure (3R) and 47.0% Gd2Co7-type structure (3R). Sm5Co19-type structure (2H) and Ce2Ni7-type structure (2H) were not observed in the XRD profile. The Mg atoms substituted at the Pr sites in a MgZn2-type cell. The maximum hydrogen capacity reached 1.14 H/M (1.6 mass%) at 2 MPa. The hysteresis factor, Hf = ln(Pabs/Pdes), was 1.50. The cyclic hydrogenation property of Pr4MgNi19 was investigated up to 1000 absorption-desorption cycles. After 250, 500, 750, and 1000 cycles, the retention rates of hydrogen were reduced to 94%, 92%, 91%, and 90%, respectively. These properties were superior to those of Pr2MgNi9 and Pr3MgNi14.

  15. Structure sensitivity in the nonscalable regime explored via catalysed ethylene hydrogenation on supported platinum nanoclusters

    PubMed Central

    Crampton, Andrew S.; Rötzer, Marian D.; Ridge, Claron J.; Schweinberger, Florian F.; Heiz, Ueli; Yoon, Bokwon; Landman, Uzi

    2016-01-01

    The sensitivity, or insensitivity, of catalysed reactions to catalyst structure is a commonly employed fundamental concept. Here we report on the nature of nano-catalysed ethylene hydrogenation, investigated through experiments on size-selected Ptn (n=8–15) clusters soft-landed on magnesia and first-principles simulations, yielding benchmark information about the validity of structure sensitivity/insensitivity at the bottom of the catalyst size range. Both ethylene-hydrogenation-to-ethane and the parallel hydrogenation–dehydrogenation ethylidyne-producing route are considered, uncovering that at the <1 nm size-scale the reaction exhibits characteristics consistent with structure sensitivity, in contrast to structure insensitivity found for larger particles. The onset of catalysed hydrogenation occurs for Ptn (n≥10) clusters at T>150 K, with maximum room temperature reactivity observed for Pt13. Structure insensitivity, inherent for specific cluster sizes, is induced in the more active Pt13 by a temperature increase up to 400 K leading to ethylidyne formation. Control of sub-nanometre particle size may be used for tuning catalysed hydrogenation activity and selectivity. PMID:26817713

  16. Combining photocatalytic hydrogen generation and capsule storage in graphene based sandwich structures

    PubMed Central

    Yang, Li; Li, Xiyu; Zhang, Guozhen; Cui, Peng; Wang, Xijun; Jiang, Xiang; Zhao, Jin; Luo, Yi; Jiang, Jun

    2017-01-01

    The challenge of safe hydrogen storage has limited the practical application of solar-driven photocatalytic water splitting. It is hard to isolate hydrogen from oxygen products during water splitting to avoid unwanted reverse reaction or explosion. Here we propose a multi-layer structure where a carbon nitride is sandwiched between two graphene sheets modified by different functional groups. First-principles simulations demonstrate that such a system can harvest light and deliver photo-generated holes to the outer graphene-based sheets for water splitting and proton generation. Driven by electrostatic attraction, protons penetrate through graphene to react with electrons on the inner carbon nitride to generate hydrogen molecule. The produced hydrogen is completely isolated and stored with a high-density level within the sandwich, as no molecules could migrate through graphene. The ability of integrating photocatalytic hydrogen generation and safe capsule storage has made the sandwich system an exciting candidate for realistic solar and hydrogen energy utilization. PMID:28681839

  17. Quantum mechanical electronic structure calculation reveals orientation dependence of hydrogen bond energy in proteins.

    PubMed

    Mondal, Abhisek; Datta, Saumen

    2017-06-01

    Hydrogen bond plays a unique role in governing macromolecular interactions with exquisite specificity. These interactions govern the fundamental biological processes like protein folding, enzymatic catalysis, molecular recognition. Despite extensive research work, till date there is no proper report available about the hydrogen bond's energy surface with respect to its geometric parameters, directly derived from proteins. Herein, we have deciphered the potential energy landscape of hydrogen bond directly from the macromolecular coordinates obtained from Protein Data Bank using quantum mechanical electronic structure calculations. The findings unravel the hydrogen bonding energies of proteins in parametric space. These data can be used to understand the energies of such directional interactions involved in biological molecules. Quantitative characterization has also been performed using Shannon entropic calculations for atoms participating in hydrogen bond. Collectively, our results constitute an improved way of understanding hydrogen bond energies in case of proteins and complement the knowledge-based potential. Proteins 2017; 85:1046-1055. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

  18. Structural and optical properties of silicon nanoparticles prepared by pulsed laser ablation in hydrogen background gas

    NASA Astrophysics Data System (ADS)

    Makino, T.; Inada, M.; Yoshida, K.; Umezu, I.; Sugimura, A.

    We studied the structural and optical properties of silicon (Si) nanoparticles (np-Si) prepared by pulsed laser ablation (PLA) in hydrogen (H2) background gas. The mean diameter of the np-Si was estimated to be approximately 5 nm. The infrared absorption corresponding to Si-Hn (n=1,2,3) bonds was observed at around 2100 cm-1, and a Raman scattering peak corresponding to crystalline Si was observed at around 520 cm-1. These results indicate that nanoparticles are not an alloy of Si and hydrogen but Si nanocrystal covered by hydrogen or hydrogenated silicon. This means that surface passivated Si nanoparticles can be prepared by PLA in H2 gas. The band-gap energy of np-Si prepared in H2 gas (1.9 eV) was larger than that of np-Si prepared in He gas (1.6 eV) even though they are almost the same diameter. After decreasing the hydrogen content in np-Si by thermal annealing, the band-gap energy decreased, and reached the same energy level as np-Si prepared in He gas. Thus, the optical properties of np-Si were affected by the hydrogenation of the surface of np-Si.

  19. Effect of boron and hydrogen on the electronic structure of Ni{sub 3}Al

    SciTech Connect

    Kioussi, N.; Watanabe, H.; Hemker, R.G.; Gourdin, W.: Gonis, A.; Johnson, P.E.

    1993-11-19

    Using first-principles electronic structure calculations based on the Linear-Muffin-Tin Orbital (LMTO) method, we have investigated the effects of interstitial born and hydrogen on the electronic structure of the Ll{sub 2} ordered intermetallic Ni{sub 3}Al. When it occupies an octahedral interstitial site entirely coordinated by six Ni atoms, we find that boron enhances the charge distribution found in the strongly-bound ``pure`` Ni{sub 3}Al crystal: Charge is depleted at Ni and Al region. Substitution Al atoms for two of the Ni atoms coordinating the boron, however, reduces the interstitial charge density between atomic planes. In contrast to boron, hydrogen appears to deplete the interstitial charge, even when fully coordinated by Ni atoms. We suggest that these results are broadly consistent with the notion of boron as a cohesion enhancer and hydrogen as an embrittler.

  20. Efficient direct solar-to-hydrogen conversion by in situ interface transformation of a tandem structure.

    PubMed

    May, Matthias M; Lewerenz, Hans-Joachim; Lackner, David; Dimroth, Frank; Hannappel, Thomas

    2015-09-15

    Photosynthesis is nature's route to convert intermittent solar irradiation into storable energy, while its use for an industrial energy supply is impaired by low efficiency. Artificial photosynthesis provides a promising alternative for efficient robust carbon-neutral renewable energy generation. The approach of direct hydrogen generation by photoelectrochemical water splitting utilizes customized tandem absorber structures to mimic the Z-scheme of natural photosynthesis. Here a combined chemical surface transformation of a tandem structure and catalyst deposition at ambient temperature yields photocurrents approaching the theoretical limit of the absorber and results in a solar-to-hydrogen efficiency of 14%. The potentiostatically assisted photoelectrode efficiency is 17%. Present benchmarks for integrated systems are clearly exceeded. Details of the in situ interface transformation, the electronic improvement and chemical passivation are presented. The surface functionalization procedure is widely applicable and can be precisely controlled, allowing further developments of high-efficiency robust hydrogen generators.

  1. Hydrogenation of Nano-Structured TiO2 Photocatalyst Through an Electrochemical Method.

    PubMed

    He, Ke Feng; Xu, En Ni; Liu, Yong; Chen, Wan Ping

    2015-01-01

    Nano-structured photocatalyst P25 was electrochemically hydrogenated through being immersed in 0.01 M NaOH solution to act as cathode to electrolyze water. With its color changed from white to bluish, its absorption in visible light range was obviously enhanced after the treatment, and its solar-driven photocatalytic activity was significantly improved for photo-degradation of methylene blue and rhodamine B. XPS spectra analyses were conducted and the photocurrent was measured, which indicate the formation of Ti3+ and oxygen vacancies, and increased separation efficiency of photoactivated electrons and holes in electrochemically hydrogenated P25. These changes are proposed responsible for the improved photocatalytic activity of P25. Electrochemical hydrogenation has been proven a facile and effective method for improving the photocatalytic activity of nano-structured TiO2 photocatalyst.

  2. Efficient direct solar-to-hydrogen conversion by in situ interface transformation of a tandem structure

    PubMed Central

    May, Matthias M.; Lewerenz, Hans-Joachim; Lackner, David; Dimroth, Frank; Hannappel, Thomas

    2015-01-01

    Photosynthesis is nature's route to convert intermittent solar irradiation into storable energy, while its use for an industrial energy supply is impaired by low efficiency. Artificial photosynthesis provides a promising alternative for efficient robust carbon-neutral renewable energy generation. The approach of direct hydrogen generation by photoelectrochemical water splitting utilizes customized tandem absorber structures to mimic the Z-scheme of natural photosynthesis. Here a combined chemical surface transformation of a tandem structure and catalyst deposition at ambient temperature yields photocurrents approaching the theoretical limit of the absorber and results in a solar-to-hydrogen efficiency of 14%. The potentiostatically assisted photoelectrode efficiency is 17%. Present benchmarks for integrated systems are clearly exceeded. Details of the in situ interface transformation, the electronic improvement and chemical passivation are presented. The surface functionalization procedure is widely applicable and can be precisely controlled, allowing further developments of high-efficiency robust hydrogen generators. PMID:26369620

  3. [GC-FTIR analysis of structural isomers from hydrogenation products of p-phenylphenol].

    PubMed

    Xin, Jun-Na; Xu, Qiang; Zhang, Hua; Yang, Xi-Chuan; Lü, Lian-Hai

    2008-04-01

    The hydrogenation of p-phenylphenol is a consecutive and parallel complex reaction. Owing to the difference in the hydrogenation ability of the two benzene rings in pphenylphenol, the hydrogenation products contained several structural isomers, which can not be identified by normal analytical method. However, the reaction mixture was effectively separated and identified by GC-FTIR technique. According to the characteristic wave numbers of benzene ring substituted at different positions, the main product was confirmed to be p-cyclohexylphenol, and the two typical by-products were p-phenylcyclohexanol and p-cyclohexylcyclohexanol, respectively. Each product has several stereo-isomers. GC-MS, melting point measurement and NMR proved the accuracy of GC-FTIR results, indicating that GC-IR is an useful and rapid method for analyzing structural isomers of organic compounds.

  4. Advanced fabrication techniques for hydrogen-cooled engine structures. Final report, October 1975-June 1982

    SciTech Connect

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

    1985-11-01

    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.

  5. Efficient direct solar-to-hydrogen conversion by in situ interface transformation of a tandem structure

    NASA Astrophysics Data System (ADS)

    May, Matthias M.; Lewerenz, Hans-Joachim; Lackner, David; Dimroth, Frank; Hannappel, Thomas

    2015-09-01

    Photosynthesis is nature's route to convert intermittent solar irradiation into storable energy, while its use for an industrial energy supply is impaired by low efficiency. Artificial photosynthesis provides a promising alternative for efficient robust carbon-neutral renewable energy generation. The approach of direct hydrogen generation by photoelectrochemical water splitting utilizes customized tandem absorber structures to mimic the Z-scheme of natural photosynthesis. Here a combined chemical surface transformation of a tandem structure and catalyst deposition at ambient temperature yields photocurrents approaching the theoretical limit of the absorber and results in a solar-to-hydrogen efficiency of 14%. The potentiostatically assisted photoelectrode efficiency is 17%. Present benchmarks for integrated systems are clearly exceeded. Details of the in situ interface transformation, the electronic improvement and chemical passivation are presented. The surface functionalization procedure is widely applicable and can be precisely controlled, allowing further developments of high-efficiency robust hydrogen generators.

  6. Structure of hydrogenous liquids: separation of coherent and incoherent cross sections using polarised neutrons

    NASA Astrophysics Data System (ADS)

    Stunault, A.; Vial, S.; Pusztai, L.; Cuello, G. J.; Temleitner, L.

    2016-04-01

    The determination of the coherent structure factor of hydrogenous liquids is very difficult: while X-rays are barely sensitive to hydrogen, neutrons results still lack accuracy due to the contamination of the scattering intensities by a huge spin-incoherent signal from the 1H atoms. Using polarised neutrons with polarisation analysis, one can experimentally separate the coherent and incoherent contributions to the scattered intensity. We present the upgrade of the D3 polarised hot neutron diffractometer at ILL to study hydrogenated liquids. We show first data obtained from a test sample of water and detail the data reduction leading to an unprecedented accuracy in the extraction of the coherent signal, representative of the structure.

  7. 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.

  8. Promotion of CO oxidation on PdO(101) by adsorbed H2O

    NASA Astrophysics Data System (ADS)

    Choi, Juhee; Pan, Li; Mehar, Vikram; Zhang, Feng; Asthagiri, Aravind; Weaver, Jason F.

    2016-08-01

    We investigated the influence of adsorbed H2O on the oxidation of CO on PdO(101) using temperature programmed reaction spectroscopy (TPRS), reflection absorption infrared spectroscopy (RAIRS) and density functional theory (DFT) calculations. We find that water inhibits CO adsorption on PdO(101) by site blocking, but also provides a more facile pathway for CO oxidation compared with the bare oxide surface. In the presence of adsorbed H2O, the oxidation of CO on PdO(101) produces a CO2 TPRS peak that is centered at a temperature 50 K lower than the main CO2 TPRS peak arising from CO oxidation on clean PdO(101) ( 330 vs. 380 K). RAIRS shows that CO continues to adsorb on atop-Pd sites of PdO(101) when H2O is co-adsorbed, and provides no evidence of other reactive intermediates. DFT calculations predict that the CO oxidation mechanism follows the same steps for CO adsorbed on PdO(101) with and without co-adsorbed H2O, wherein an atop-CO species recombines with an oxygen atom from the oxide surface lattice. According to DFT, hydrogen bonding interactions with adsorbed H2O species stabilize the carboxyl-like transition structure and intermediate that result from the initial recombination of CO and O on the PdO(101) surface. This stabilization lowers the energy barrier for CO oxidation on PdO(101) by 10 kJ/mol, in good agreement with our experimental estimate.

  9. Molecular Adsorber Coating

    NASA Technical Reports Server (NTRS)

    Straka, Sharon; Peters, Wanda; Hasegawa, Mark; Hedgeland, Randy; Petro, John; Novo-Gradac, Kevin; Wong, Alfred; Triolo, Jack; Miller, Cory

    2011-01-01

    A document discusses a zeolite-based sprayable molecular adsorber coating that has been developed to alleviate the size and weight issues of current ceramic puck-based technology, while providing a configuration that more projects can use to protect against degradation from outgassed materials within a spacecraft, particularly contamination-sensitive instruments. This coating system demonstrates five times the adsorption capacity of previously developed adsorber coating slurries. The molecular adsorber formulation was developed and refined, and a procedure for spray application was developed. Samples were spray-coated and tested for capacity, thermal optical/radiative properties, coating adhesion, and thermal cycling. Work performed during this study indicates that the molecular adsorber formulation can be applied to aluminum, stainless steel, or other metal substrates that can accept silicate-based coatings. The coating can also function as a thermal- control coating. This adsorber will dramatically reduce the mass and volume restrictions, and is less expensive than the currently used molecular adsorber puck design.

  10. Magnetocaloric properties of distilled gadolinium: Effects of structural inhomogeneity and hydrogen impurity

    SciTech Connect

    Burkhanov, G. S.; Kolchugina, N. B.; Chzhan, V. B.; Chistyakov, O. D.; Tereshina, E. A.; Tereshina, I. S.; Politova, G. A.; Badurski, D.; Drulis, H.; Paukov, M.; Havela, L.

    2014-06-16

    High-purity Gd prepared by distillation is a structurally inhomogeneous system consisting of needle-shaped crystals of cross section 0.5–2.5 μm with near-c-axis orientation embedded in a matrix of nanosized (30–100 nm) grains. By measuring the magnetocaloric effect (MCE) directly, we find that the MCE values differ markedly for the plate-shaped samples cut out of a distillate along and perpendicular to the crystals. The effect of small controlled amounts of impurity (hydrogen) on the properties of distilled Gd is further studied. We observe opposite trends in the MCE response to hydrogen charging with respect to the crystal's orientation within the samples and discuss mechanisms interrelating the unique structural morphology with the impurity behavior. As an overall assessment, the Curie temperatures of α-GdH{sub x} solid solutions increase from 291 K up to 294 K when increasing hydrogen concentration x from 0 to 0.15. Hydrogenation is found to broaden the ferromagnetic-to-paramagnetic phase transition. Hydrogen-containing specimens demonstrate reversibility of MCE at these temperatures.

  11. Metal Hydride Nanoparticles with Ultrahigh Structural Stability and Hydrogen Storage Activity Derived from Microencapsulated Nanoconfinement.

    PubMed

    Zhang, Jiguang; Zhu, Yunfeng; Lin, Huaijun; Liu, Yana; Zhang, Yao; Li, Shenyang; Ma, Zhongliang; Li, Liquan

    2017-06-01

    Metal hydrides (MHs) have recently been designed for hydrogen sensors, switchable mirrors, rechargeable batteries, and other energy-storage and conversion-related applications. The demands of MHs, particular fast hydrogen absorption/desorption kinetics, have brought their sizes to nanoscale. However, the nanostructured MHs generally suffer from surface passivation and low aggregation-resisting structural stability upon absorption/desorption. This study reports a novel strategy named microencapsulated nanoconfinement to realize local synthesis of nano-MHs, which possess ultrahigh structural stability and superior desorption kinetics. Monodispersed Mg2 NiH4 single crystal nanoparticles (NPs) are in situ encapsulated on the surface of graphene sheets (GS) through facile gas-solid reactions. This well-defined MgO coating layer with a thickness of ≈3 nm efficiently separates the NPs from each other to prevent aggregation during hydrogen absorption/desorption cycles, leading to excellent thermal and mechanical stability. More interestingly, the MgO layer shows superior gas-selective permeability to prevent further oxidation of Mg2 NiH4 meanwhile accessible for hydrogen absorption/desorption. As a result, an extremely low activation energy (31.2 kJ mol(-1) ) for the dehydrogenation reaction is achieved. This study provides alternative insights into designing nanosized MHs with both excellent hydrogen storage activity and thermal/mechanical stability exempting surface modification by agents. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  12. Simulating Hydrogen-Bond Structure and Dynamics in Glassy Solids Composed of Imidazole Oligomers.

    PubMed

    Harvey, Jacob A; Auerbach, Scott M

    2014-07-01

    We simulated structural and dynamical properties of imidazoles tethered to aliphatic backbones to determine how chain length influences the competition between extended hydrogen-bond networks and imidazole reorientation dynamics. We performed molecular dynamics simulations on hypothetical solids using the GAFF Amber force field over the temperature range 300-800 K, for chain lengths varying from monomers to pentamers. We investigated the effect of heterogeneity by simulating monodisperse and polydisperse solids with the same average chain length. We computed hydrogen-bond cluster sizes and percolation ratios; orientational order parameters associated with imidazole rings, tethering linkers, and backbones; and orientational correlation functions for imidazole rings. We found the surprising result that chain-length heterogeneity negligibly affects system density at standard pressure, the fraction of percolating hydrogen-bonded clusters, and the order parameters for backbone, linker, and imidazole ring. Decreasing oligomer chain length from pentamers to shorter chains decreases the tendency to form percolating hydrogen-bond networks while dramatically decreasing imidazole ring reorientation times from a broad range of 100-700 ps for pentamers down to 20 ps for monomers, hence quantifying the competition between hydrogen-bond cluster size and reorientation rate. The computed orientational order parameters suggest the following hierarchy of structural excitations: imidazole ring reorientation in the range 400-500 K, linker motion around 500-600 K, and backbone relaxation at 600-700 K in this model. The question remains for this class of systems which of these motions is crucial for facile proton transport.

  13. Quantum simulation of structure, transport properties, and melting in dense hydrogen

    NASA Astrophysics Data System (ADS)

    Kang, Dongdong; Dai, Jiayu; Yuan, Jianmin

    2016-10-01

    Due to the low mass, hydrogen exhibits significant nuclear quantum effects (NQEs), especially under low temperatures and high pressures. NQEs on structure and transport properties of dense liquid hydrogen under extreme conditions are investigated using the improved centroid path integral molecular dynamics (PIMD) simulations. The results show that with the inclusion of NQEs, the radial distribution functions are obviously broadened. The self-diffusion is largely higher while the shear viscosity is notably lower than the results of without the inclusion of NQEs due to the lower collision cross sections even when the NQEs have little effects on the static structures. The electrical conductivity is also significantly affected by NQEs. Quantum nuclear character induces complex behaviors for ionic transport properties of dense liquid hydrogen. In addition, the melting temperature of dense hydrogen is also investigated using the two-phase approach based on the PIMD with the Yukawa potential describing the interaction between ions. The results show that the NQEs have a significant impact on the melting of dense hydrogen, which largely lower the melting temperature by 10% at the density range of 10-1000 g/cm3.

  14. Hydrogen-induced structural transformation of AuCu nanoalloys probed by synchrotron X-ray diffraction techniques.

    PubMed

    Yamauchi, M; Okubo, K; Tsukuda, T; Kato, K; Takata, M; Takeda, S

    2014-04-21

    In situ X-ray diffraction measurements reveal that the transformation of a AuCu nanoalloy from a face-centered-cubic to an L10 structure is accelerated under a hydrogen atmosphere. The structural transformation rate for the AuCu nanoalloy under hydrogen above 433 K was found to be 100 times faster than that in a vacuum, which is the first quantitative observation of hydrogen-induced ordering of nanoalloys.

  15. Hydrogen program overview

    SciTech Connect

    Gronich, S.

    1997-12-31

    This paper consists of viewgraphs which summarize the following: Hydrogen program structure; Goals for hydrogen production research; Goals for hydrogen storage and utilization research; Technology validation; DOE technology validation activities supporting hydrogen pathways; Near-term opportunities for hydrogen; Market for hydrogen; and List of solicitation awards. It is concluded that a full transition toward a hydrogen economy can begin in the next decade.

  16. The structure and reactivity of adsorbates on stepped Rh and Pt surfaces investigated by LEED, HREELS, TPD, XPS and STM

    SciTech Connect

    Batteas, J.D. |

    1995-06-01

    Defects on surfaces such as steps play an important role in surface chemistry. In order to obtain an understanding of the influence of steps in surface chemical reactions, the structure and reactivity of small molecules (O{sub 2}, CO, H{sub 2}S, and C{sub 2}H{sub 4}) on atomically stepped surfaces of RH and Pt have been investigated. The detailed structures of CO and oxygen bonded to the Rh(110) surface were determined. The CO molecules bond near the short bridge sites with the CO molecular axis tilted approximately 24{degree} from the surface normal. Oxygen atoms are bound asymmetrically in the 3-fold fcc hollow-sites to the (111) facets of the steps. The interactions of CO and oxygen on the Rh(311) surface were examined. The reaction of CO with the ordered phases of O shows two distinct reaction channels, a low temperature reaction limited channel (200 K) and a high temperature diffusion limited channel (350 K). Models of the reaction geometry and dynamics are proposed. The thermal decomposition of ethylene was examined on the Rh(311) surface. The stable decomposition species (C{sub 2}H, CH and C{sub 2}) are formed near 300 K, approximately 100 K lower on the stepped Rh(311) than on the flatter Rh(111) surface. The formation of these species at lower temperatures is attributed to the stepped nature of the surface. Finally, in situ STM was used to examine surface structural changes of a stepped Pt(111) crystal under coadsorption of sulfur and CO. This is the first direct evidence for a new mechanism by which a surface covered with an unreactive, strongly chemisorbed overlayer can form new sites, for bonding and reactions to occur, by massive surface restructuring at the step edges. This new surface phenomenon answers some of the puzzles of metal surface catalysis and its implications are described. 278 refs.

  17. A DFT study of halogen atoms adsorbed on graphene layers.

    PubMed

    Medeiros, Paulo V C; Mascarenhas, Artur J S; de Brito Mota, F; de Castilho, Caio M C

    2010-12-03

    In this work, ab initio density functional theory calculations were performed in order to study the structural and electronic properties of halogens (X = fluorine, chlorine, bromine or iodine) that were deposited on both sides of graphene single layers (X-graphene). The adsorption of these atoms on only one side of the layer with hydrogen atoms adsorbed on the other was also considered (H,X-graphene). The results indicate that the F-C bond in the F-graphene system causes an sp(2) to sp(3) transition of the carbon orbitals, and similar effects seem to occur in the H,X-graphene systems. For the other cases, two configurations are found: bonded (B) and non-bonded (NB). For the B configuration, the structural arrangement of the atoms was similar to F-graphene and H-graphene (graphane), although the electronic structures present some differences. In the NB configuration, the interaction between the adsorbed atoms and the graphene layer seems to be essentially of the van der Waals type. In these cases, the original shape of the graphene layer presents only small deviations from the pristine form and the adsorbed atoms reach equilibrium far from the sheet. The F-graphene structure has a direct bandgap of approximately 3.16 eV at the Γ point, which is a value that is close to the value of 3.50 eV that was found for graphane. The Cl-graphene (B configuration), H,F-graphene and H,Cl-graphene systems have smaller bandgap values. All of the other systems present metallic behaviours. Energy calculations indicate the possible stability of these X-graphene layers, although some considerations about the possibility of spontaneous formation have to be taken into account.

  18. The new metal complex templated polyoxoborate(s) (POB(s)) structures. Synthesis, structural characterization, and hydrogen storage capacities

    NASA Astrophysics Data System (ADS)

    Ali Köse, Dursun; Yurdakul, Ömer; Şahin, Onur; Öztürk, Zeynel

    2017-04-01

    The polyoxoborate(s) (POB(s)) structures, including a neutral ligand-metal complex compound as a template, were synthesized and the structural characterizations were performed via single crystal X-ray diffraction, FTIR, 11B-NMR, solid state UV-Vis spectroscopy, SEM and elemental analysis methods. Moreover, the stabilization features were determined via TGA/DTA method. In addition, nitrogen and hydrogen adsorption measurements provided the realization to determine the pore size distribution, BET surface area, and hydrogen storage capacities. The molecular formulas of compounds were estimated as [Cu(C12H8N2)2(C2H3O2)][B5O6(OH)4]·2H3BO3·H2O (I) and [Ni(C12H8N2)2(H2O)2]·(B7O9(OH)5)·5H2O (II) and the existence of two different POB(s) structures as pentaborate (B5O6(OH)4) and heptaborate (B7O9(OH)5) within the compounds were observed. At last, it was found that the both structures have micro and mesoporosity with 0.407 and 1.480 m2/g BET surface areas, for the compound I and II, respectively. Moreover, within the same conditions, compound II could uptake 0.19 wt% hydrogen at 77 K and at the relative pressure of 1 while compound II uptakes 0.035 wt% hydrogen.

  19. The structure of N2 adsorbed on the rumpled NaCl(100) surface—A combined LEED and DFT-D study

    NASA Astrophysics Data System (ADS)

    Vogt, Jochen

    2012-11-01

    The structure of N2 physisorbed on the NaCl(100) single crystal surface is investigated by means of quantitative low-energy electron diffraction (LEED) in combination with dispersion corrected density functional theory (DFT-D). In the temperature range between 20 K and 45 K, a p(1 × 1) structure is observed in the LEED experiment. According to the structure analysis based on the measured diffraction spot intensity profiles, the N2 molecules are adsorbed over the topmost Na+ ions. The experimental distance of the lower nitrogen to the Na+ ion underneath is (2.55 ± 0.07) Å; the corresponding DFT-D value is 2.65 Å. The axes of the molecules are tilted (26 ± 3)° with respect to the surface normal, while in the zero Kelvin optimum structure from DFT-D, the molecules have a perpendicular orientation. The experimental monolayer heat of adsorption, deduced from a Fowler-Guggenheim kinetic model of adsorption is -(13.6 ± 1.6) kJ mol-1, including a lateral molecule-molecule interaction energy of -(2.0 ± 0.4) kJ mol-1. The zero Kelvin adsorption energy from DFT-D, including zero point energy correction, is -15.6 kJ mol-1; the molecule-molecule interaction is -2.4 kJ mol-1. While the rumpling of the NaCl(100) surface is unchanged upon adsorption of nitrogen, the best-fit root mean square thermal displacements of the ions in the topmost substrate layer are significantly reduced.

  20. The structure of N2 adsorbed on the rumpled NaCl(100) surface--a combined LEED and DFT-D study.

    PubMed

    Vogt, Jochen

    2012-11-07

    The structure of N(2) physisorbed on the NaCl(100) single crystal surface is investigated by means of quantitative low-energy electron diffraction (LEED) in combination with dispersion corrected density functional theory (DFT-D). In the temperature range between 20 K and 45 K, a p(1 × 1) structure is observed in the LEED experiment. According to the structure analysis based on the measured diffraction spot intensity profiles, the N(2) molecules are adsorbed over the topmost Na(+) ions. The experimental distance of the lower nitrogen to the Na(+) ion underneath is (2.55 ± 0.07) Å; the corresponding DFT-D value is 2.65 Å. The axes of the molecules are tilted (26 ± 3)° with respect to the surface normal, while in the zero Kelvin optimum structure from DFT-D, the molecules have a perpendicular orientation. The experimental monolayer heat of adsorption, deduced from a Fowler-Guggenheim kinetic model of adsorption is -(13.6 ± 1.6) kJ mol(-1), including a lateral molecule-molecule interaction energy of -(2.0 ± 0.4) kJ mol(-1). The zero Kelvin adsorption energy from DFT-D, including zero point energy correction, is -15.6 kJ mol(-1); the molecule-molecule interaction is -2.4 kJ mol(-1). While the rumpling of the NaCl(100) surface is unchanged upon adsorption of nitrogen, the best-fit root mean square thermal displacements of the ions in the topmost substrate layer are significantly reduced.

  1. Hydrogen trapping in δ-Pu: insights from electronic structure calculations.

    PubMed

    Taylor, Christopher D; Hernandez, Sarah C; Francis, Michael F; Schwartz, Daniel S; Ray, Asok K

    2013-07-03

    Density functional theory calculations have been performed to provide details of the structural and charge-transfer details related to the solid solution of hydrogen in (δ)-plutonium. We follow the Flanagan model that outlines the process by which hydrogen interacts with a metal to produce hydride phases, via a sequence of surface, interstitial and defect-bound (trapped) states. Due to the complexities of the electronic structure in plutonium solid-state systems, we take the pragmatic approach of adopting the 'special quasirandom structure' to disperse the atomic magnetic moments. We find that this approach produces sound structural and thermodynamic properties in agreement with the available experimental data. In δ-Pu, hydrogen has an exothermic binding energy to all of the states relevant in the Flanagan model, and, furthermore, is anionic in all these states. The charge transfer is maximized (i.e. most negative for hydrogen) in the hydride phase. The pathway from surface to hydride is sequentially exothermic, in the order surface < interstitial < grain boundary < vacancy < hydride (hydride being the most exothermic state). Thus, we find that there is no intermediate state that involves an endothermic increase in energy, consistent with the general experimental observations that the hydriding reaction in plutonium metal can proceed with zero apparent activation barrier.

  2. The quadrupole coupling constant of HNC. [hydrogen isocyanide hyperfine structure measurements

    NASA Technical Reports Server (NTRS)

    Snyder, L. E.; Hollis, J. M.; Buhl, D.

    1977-01-01

    The letter reports resolved measurements of the quadrupole hyperfine structure of HNC (hydrogen isocyanide). These measurements were made in the direction of the cool interstellar dust cloud L134, and were used to make an experimental determination of a fundamental spectroscopic constant of HNC, its quadrupole coupling constant.

  3. Influence of surface chemistry on the structural organization of monomolecular protein layers adsorbed to functionalized aqueous interfaces.

    PubMed Central

    Lösche, M; Piepenstock, M; Diederich, A; Grünewald, T; Kjaer, K; Vaknin, D

    1993-01-01

    The molecular organization of streptavidin (SA) bound to aqueous surface monolayers of biotin-functionalized lipids and binary lipid mixtures has been investigated with neutron reflectivity and electron and fluorescence microscopy. The substitution of deuterons (2H) for protons (1H), both in subphase water molecules and in the alkyl chains of the lipid surface monolayer, was utilized to determine the interface structure on the molecular length scale. In all cases studied, the protein forms monomolecular layers underneath the interface with thickness values of approximately 40 A. A systematic dependence of the structural properties of such self-assembled SA monolayers on the surface chemistry was observed: the lateral protein density depends on the length of the spacer connecting the biotin moiety and its hydrophobic anchor. The hydration of the lipid head groups in the protein-bound state depends on the dipole moment density at the interface. Images FIGURE 1 FIGURE 2 FIGURE 3 FIGURE 5 FIGURE 11 FIGURE 12 FIGURE A1 PMID:8298041

  4. Hydrophobic Porous Material Adsorbs Small Organic Molecules

    NASA Technical Reports Server (NTRS)

    Sharma, Pramod K.; Hickey, Gregory S.

    1994-01-01

    Composite molecular-sieve material has pore structure designed specifically for preferential adsorption of organic molecules for sizes ranging from 3 to 6 angstrom. Design based on principle that contaminant molecules become strongly bound to surface of adsorbent when size of contaminant molecules is nearly same as that of pores in adsorbent. Material used to remove small organic contaminant molecules from vacuum systems or from enclosed gaseous environments like closed-loop life-support systems.

  5. ATR-FTIR and density functional theory study of the structures, energetics, and vibrational spectra of phosphate adsorbed onto goethite.

    PubMed

    Kubicki, James D; Paul, Kristian W; Kabalan, Lara; Zhu, Qing; Mrozik, Michael K; Aryanpour, Masoud; Pierre-Louis, Andro-Marc; Strongin, Daniel R

    2012-10-16

    Periodic plane-wave density functional theory (DFT) and molecular cluster hybrid molecular orbital-DFT (MO-DFT) calculations were performed on models of phosphate surface complexes on the (100), (010), (001), (101), and (210) surfaces of α-FeOOH (goethite). Binding energies of monodentate and bidentate HPO(4)(2-) surface complexes were compared to H(2)PO(4)(-) outer-sphere complexes. Both the average potential energies from DFT molecular dynamics (DFT-MD) simulations and energy minimizations were used to estimate adsorption energies for each configuration. Molecular clusters were extracted from the energy-minimized structures of the periodic systems and subjected to energy reminimization and frequency analysis with MO-DFT. The modeled P-O and P---Fe distances were consistent with EXAFS data for the arsenate oxyanion that is an analog of phosphate, and the interatomic distances predicted by the clusters were similar to those of the periodic models. Calculated vibrational frequencies from these clusters were then correlated with observed infrared bands. Configurations that resulted in favorable adsorption energies were also found to produce theoretical vibrational frequencies that correlated well with experiment. The relative stability of monodentate versus bidentate configurations was a function of the goethite surface under consideration. Overall, our results show that phosphate adsorption onto goethite occurs as a variety of surface complexes depending on the habit of the mineral (i.e., surfaces present) and solution pH. Previous IR spectroscopic studies may have been difficult to interpret because the observed spectra averaged the structural properties of three or more configurations on any given sample with multiple surfaces.

  6. Hydrogen peroxide-induced structural alterations of RNAse A.

    PubMed

    Lasch, P; Petras, T; Ullrich, O; Backmann, J; Naumann, D; Grune, T

    2001-03-23

    Proteins exposed to oxidative stress are degraded via proteolytic pathways. In the present study, we undertook a series of in vitro experiments to establish a correlation between the structural changes induced by mild oxidation of the model protein RNase A and the proteolytic rate found upon exposure of the modified protein toward the isolated 20 S proteasome. Fourier transform infrared spectroscopy was used as a structure-sensitive probe. We report here strong experimental evidence for oxidation-induced conformational rearrangements of the model protein RNase A and, at the same time, for covalent modifications of amino acid side chains. Oxidation-related conformational changes, induced by H(2)O(2) exposure of the protein may be monitored in the amide I region, which is sensitive to changes in protein secondary structure. A comparison of the time- and H(2)O(2) concentration-dependent changes in the amide I region demonstrates a high degree of similarity to spectral alterations typical for temperature-induced unfolding of RNase A. In addition, spectral parameters of amino acid side chain marker bands (Tyr, Asp) revealed evidence for covalent modifications. Proteasome digestion measurements on oxidized RNase A revealed a specific time and H(2)O(2) concentration dependence; at low initial concentration of the oxidant, the RNase A turnover rate increases with incubation time and concentration. Based on these experimental findings, a correlation between structural alterations detected upon RNase A oxidation and proteolytic rates of RNase A is established, and possible mechanisms of the proteasome recognition process of oxidatively damaged proteins are discussed.

  7. Hydrogen Bonding Between FNO and H2O: Structure and Energetics

    NASA Astrophysics Data System (ADS)

    Ting, Melodie; Peters, Nancy J. S.

    2009-09-01

    Nitrosyl fluoride, of some interest in atmospheric chemistry, has three atoms which could potentially serve as proton acceptors in the formation of hydrogen bonds. The optimized structure of FNO and H2O was determined at the MP4/6-31G** level of calculation. In the resulting structure, the hydrogen bonds at the fluorine with an energy of 5.15 kcal/mol, contrary to the prediction that less electronegative atoms make better proton acceptors/electron donors but consistent with results of proton affinity studies and with the contribution of a resonance structure with no bond between the N and F and a negative charge on the fluorine atom. The resulting structure also shows a significant increase in the length of the NF bond from 1.51 to 1.61 Å.

  8. Bonding, structures, and band gap closure of hydrogen at high pressures

    NASA Astrophysics Data System (ADS)

    Goncharov, Alexander F.; Tse, John S.; Wang, Hui; Yang, Jianjun; Struzhkin, Viktor V.; Howie, Ross T.; Gregoryanz, Eugene

    2013-01-01

    We have studied dense hydrogen and deuterium experimentally up to 320 GPa and using ab initio molecular dynamic (MD) simulations up to 370 GPa between 250 and 300 K. Raman and optical absorption spectra show significant anharmonic and quantum effects in mixed atomic and molecular dense phase-IV of hydrogen. In agreement with these observations, ab initio MD simulations near 300 K show extremely large atomic motions, which include molecular rotations, hopping, and even pair fluctuations, suggesting that phase IV may not have a well-defined crystalline structure. The structurally diverse layers (molecular and graphenelike) are strongly coupled, thus opening an indirect band gap; moreover, at 300 GPa, we find fast synchronized intralayer structural fluctuations. At 370 GPa, the mixed structure collapses to form a metallic molecular Cmca-4 phase, which exhibits a new interstitial valence charge bonding scheme.

  9. Hydrogen adsorption and desorption with 3D silicon nanotube-network and film-network structures: Monte Carlo simulations

    SciTech Connect

    Li, Ming; Kang, Zhan; Huang, Xiaobo

    2015-08-28

    Hydrogen is clean, sustainable, and renewable, thus is viewed as promising energy carrier. However, its industrial utilization is greatly hampered by the lack of effective hydrogen storage and release method. Carbon nanotubes (CNTs) were viewed as one of the potential hydrogen containers, but it has been proved that pure CNTs cannot attain the desired target capacity of hydrogen storage. In this paper, we present a numerical study on the material-driven and structure-driven hydrogen adsorption of 3D silicon networks and propose a deformation-driven hydrogen desorption approach based on molecular simulations. Two types of 3D nanostructures, silicon nanotube-network (Si-NN) and silicon film-network (Si-FN), are first investigated in terms of hydrogen adsorption and desorption capacity with grand canonical Monte Carlo simulations. It is revealed that the hydrogen storage capacity is determined by the lithium doping ratio and geometrical parameters, and the maximum hydrogen uptake can be achieved by a 3D nanostructure with optimal configuration and doping ratio obtained through design optimization technique. For hydrogen desorption, a mechanical-deformation-driven-hydrogen-release approach is proposed. Compared with temperature/pressure change-induced hydrogen desorption method, the proposed approach is so effective that nearly complete hydrogen desorption can be achieved by Si-FN nanostructures under sufficient compression but without structural failure observed. The approach is also reversible since the mechanical deformation in Si-FN nanostructures can be elastically recovered, which suggests a good reusability. This study may shed light on the mechanism of hydrogen adsorption and desorption and thus provide useful guidance toward engineering design of microstructural hydrogen (or other gas) adsorption materials.

  10. Hydrogen adsorption and desorption with 3D silicon nanotube-network and film-network structures: Monte Carlo simulations

    NASA Astrophysics Data System (ADS)

    Li, Ming; Huang, Xiaobo; Kang, Zhan

    2015-08-01

    Hydrogen is clean, sustainable, and renewable, thus is viewed as promising energy carrier. However, its industrial utilization is greatly hampered by the lack of effective hydrogen storage and release method. Carbon nanotubes (CNTs) were viewed as one of the potential hydrogen containers, but it has been proved that pure CNTs cannot attain the desired target capacity of hydrogen storage. In this paper, we present a numerical study on the material-driven and structure-driven hydrogen adsorption of 3D silicon networks and propose a deformation-driven hydrogen desorption approach based on molecular simulations. Two types of 3D nanostructures, silicon nanotube-network (Si-NN) and silicon film-network (Si-FN), are first investigated in terms of hydrogen adsorption and desorption capacity with grand canonical Monte Carlo simulations. It is revealed that the hydrogen storage capacity is determined by the lithium doping ratio and geometrical parameters, and the maximum hydrogen uptake can be achieved by a 3D nanostructure with optimal configuration and doping ratio obtained through design optimization technique. For hydrogen desorption, a mechanical-deformation-driven-hydrogen-release approach is proposed. Compared with temperature/pressure change-induced hydrogen desorption method, the proposed approach is so effective that nearly complete hydrogen desorption can be achieved by Si-FN nanostructures under sufficient compression but without structural failure observed. The approach is also reversible since the mechanical deformation in Si-FN nanostructures can be elastically recovered, which suggests a good reusability. This study may shed light on the mechanism of hydrogen adsorption and desorption and thus provide useful guidance toward engineering design of microstructural hydrogen (or other gas) adsorption materials.

  11. Structure and Energetics of Benzene Adsorbed on Transition-Metal Surfaces: Density-Functional Theory with Screened van der Waals Interactions

    NASA Astrophysics Data System (ADS)

    Liu, Wei; Ruiz-López, Victor G.; Zhang, Guo-Xu; Ren, Xinguo; Scheffler, Matthias; Tkatchenko, Alexandre

    2012-02-01

    The adsorption of benzene on metal surfaces is an important benchmark system for more complex hybrid inorganic/organic interfaces. Here, the recently developed DFT+vdW\\surfcirc method (density-functional theory including screened van der Waals (vdW) interactions) [1] is used to study the structure and energetics of benzene on transition-metal surfaces (Cu, Ag, Au, Pd, Pt, Rh, and Ir). Benzene adsorbs in a planar configuration at coinage metal surfaces, with almost zero distortion and a flat potential-energy surface. In contrast, benzene is strongly bound to the (111) surface of Pd, Pt, Rh, and Ir, and located at the bridge-30^o site. The vdW interactions significantly enhance the binding energy by more than 0.75 eV for all metals. The screening of the vdW energy plays a critical role in coinage metals, shortening the equilibrium distance by 0.2 å, and lowering the binding energy by 0.25 eV. The validity of our results is confirmed by comparison with calculations using the random-phase approximation including renormalized single excitations (EX+cRPA+rSE scheme [2]), and the experimental data from temperature-programmed desorption and calorimetry measurements. [1] V. G. Ruiz-L'opez et al., submitted. [2] X. Ren et al., Phys. Rev. Lett. 106, 153003 (2011).

  12. An X-ray Absorption Fine Structure study of Au adsorbed onto the non-metabolizing cells of two soil bacterial species

    SciTech Connect

    Song, Zhen; Kenney, Janice P.L.; Fein, Jeremy B.; Bunker, Bruce A.

    2015-02-09

    Gram-positive and Gram-negative bacterial cells can remove Au from Au(III)-chloride solutions, and the extent of removal is strongly pH dependent. In order to determine the removal mechanisms, X-ray Absorption Fine Structure (XAFS) spectroscopy experiments were conducted on non-metabolizing biomass of Bacillus subtilis and Pseudomonas putida with fixed Au(III) concentrations over a range of bacterial concentrations and pH values. X-ray Absorption Near Edge Structure (XANES) and Extended X-ray Absorption Fine Structure (EXAFS) data on both bacterial species indicate that more than 90% of the Au atoms on the bacterial cell walls were reduced to Au(I). In contrast to what has been observed for Au(III) interaction with metabolizing bacterial cells, no Au(0) or Au-Au nearest neighbors were observed in our experimental systems. All of the removed Au was present as adsorbed bacterial surface complexes. For both species, the XAFS data suggest that although Au-chloride-hydroxide aqueous complexes dominate the speciation of Au in solution, Au on the bacterial cell wall is characterized predominantly by binding of Au atoms to sulfhydryl functional groups and amine and/or carboxyl functional groups, and the relative importance of the sulfhydryl groups increases with increasing pH and with decreasing Au loading. The XAFS data for both microorganism species suggest that adsorption is the first step in the formation of Au nanoparticles by bacteria, and the results enhance our ability to account for the behavior of Au in bacteria-bearing geologic systems.

  13. Dynamic adsorption and structure of interfacial bilayers adsorbed from lipopeptide surfactants at the hydrophilic silicon/water interface: effect of the headgroup length.

    PubMed

    Jia, Donghui; Tao, Kai; Wang, Jiqian; Wang, Chengdong; Zhao, Xiubo; Yaseen, Mohammed; Xu, Hai; Que, Guohe; Webster, John R P; Lu, Jian R

    2011-07-19

    Lipopeptides are an important group of biosurfactants expressed by microorganisms. Because they are well-known for being biocompatible, biodegradable, and highly surface active, they are attractive for a wide range of applications. Natural lipopeptide surfactants are however impure; it is hence difficult to use them for exploring the structure-function relation. In this work, a series of cationic lipopeptide surfactants, C(14)K(n) (n = 1-4), where C denotes the myristic acyl chain and K denotes lysine (Lys), have been synthesized, and their interfacial behavior has been characterized by studying their adsorption at the silicon/water interface (bearing a thin native oxide layer) using spectroscopic ellipsometry and neutron reflection (NR). The dynamic adsorption was marked by an initial fast step within the first 2-3 min followed by a slow molecular relaxation process over the subsequent 20-30 min. The initial rate of time-dependent adsorption and the equilibrated adsorbed amount showed a steady decrease with increasing n, indicating the impact of the molecular size, structure, and charge. NR revealed the formation of sandwiched bilayers from C(14)K(n), similar to conventional surfactants such as nonionic C(12)E(6) and cationic C(16)TAB. However, the electrostatic attraction between K and the silica surface caused confinement of the K groups, forcing the head segments into a predominantly flat-on conformation. This characteristic structural feature was confirmed by the almost constant thickness of the headgroup regions ranging from 8 to 11 Å as determined from NR combined with partial deuterium labeling to the acyl tail. An increase in area per molecular pair with n resulted directly from increasing the footprint. As a result, the hydrophobic back-to-back tail mixing and acyl chain tilting rose with n. The extent of chain-head intermixing became so intensified that the C(14)K(4) bilayer could be approximated to a uniform layer distribution.

  14. Structural insights into DNA replication without hydrogen bonds.

    PubMed

    Betz, Karin; Malyshev, Denis A; Lavergne, Thomas; Welte, Wolfram; Diederichs, Kay; Romesberg, Floyd E; Marx, Andreas

    2013-12-11

    The genetic alphabet is composed of two base pairs, and the development of a third, unnatural base pair would increase the genetic and chemical potential of DNA. d5SICS-dNaM is one of the most efficiently replicated unnatural base pairs identified to date, but its pairing is mediated by only hydrophobic and packing forces, and in free duplex DNA it forms a cross-strand intercalated structure that makes its efficient replication difficult to understand. Recent studies of the KlenTaq DNA polymerase revealed that the insertion of d5SICSTP opposite dNaM proceeds via a mutually induced-fit mechanism, where the presence of the triphosphate induces the polymerase to form the catalytically competent closed structure, which in turn induces the pairing nucleotides of the developing unnatural base pair to adopt a planar Watson-Crick-like structure. To understand the remaining steps of replication, we now report the characterization of the prechemistry complexes corresponding to the insertion of dNaMTP opposite d5SICS, as well as multiple postchemistry complexes in which the already formed unnatural base pair is positioned at the postinsertion site. Unlike with the insertion of d5SICSTP opposite dNaM, addition of dNaMTP does not fully induce the formation of the catalytically competent closed state. The data also reveal that once synthesized and translocated to the postinsertion position, the unnatural nucleobases again intercalate. Two modes of intercalation are observed, depending on the nature of the flanking nucleotides, and are each stabilized by different interactions with the polymerase, and each appear to reduce the affinity with which the next correct triphosphate binds. Thus, continued primer extension is limited by deintercalation and rearrangements with the polymerase active site that are required to populate the catalytically active, triphosphate bound conformation.

  15. Structural Insights into DNA Replication Without Hydrogen-Bonds

    PubMed Central

    Betz, Karin; Malyshev, Denis A.; Lavergne, Thomas; Welte, Wolfram; Diederichs, Kay; Romesberg, Floyd E.; Marx, Andreas

    2014-01-01

    The genetic alphabet is comprised of two base pairs, and the development of a third, unnatural base pair would increase the genetic and chemical potential of DNA. d5SICS-dNaM is one of the most efficiently replicated unnatural base pairs identified to date, but its pairing is mediated by only hydrophobic and packing forces, and in free duplex DNA it forms a cross-strand intercalated structure that makes its efficient replication difficult to understand. Recent studies of the KlenTaq polymerase revealed that the insertion of d5SICSTP opposite dNaM proceeds via a mutually induced-fit mechanism, where the presence of the triphosphate induces the polymerase to form the catalytically competent closed structure, which in turn induces the pairing nucleotides of the developing unnatural base pair to adopt a planar Watson-Crick-like structure. To understand the remaining steps of replication, we now report the characterization of the pre-chemistry complexes corresponding to the insertion of dNaMTP opposite d5SICS, as well as multiple post-chemistry complexes in which the already formed unnatural base pair is positioned at the post-insertion site. Unlike with the insertion of d5SICSTP opposite dNaM, addition of dNaMTP does not fully induce the formation of the catalytically competent closed state. The data also reveal that once synthesized and translocated to the post-insertion position, the unnatural nucleobases again intercalate. Two modes of intercalation are observed, depending on the nature of the flanking nucleotides, and are each stabilized by different interactions with the polymerase, and each appear to reduce the affinity with which the next correct triphosphate binds. Thus, continued primer extension is limited by de-intercalation and rearrangements with the polymerase active site that are required to populate the catalytically active, triphosphate bound conformation. PMID:24283923

  16. Aniline adsorption, hydrogenation, and hydrogenolysis on the Ni(100) surface

    SciTech Connect

    Huang, S.X.; Gland, J.L.; Fischer, D.A.

    1996-06-13

    The bonding and reactions of adsorbed aniline have been characterized on the Ni(100) surface both in hydrogen and in vacuum with a combination of surface spectroscopies. The structure of adsorbed aniline and derived intermediates has been characterized by near-edge X-ray absorption fine structure (NEXAFS) and X-ray photoemission spectroscopy (XPS). The dominant surface reactions have been studied using temperature-programmed reaction spectroscopy (TPRS) and in-situ temperature-programmed fluorescence yield near- edge spectroscopy (TP FYNES). Competition between hydrogenation, hydrogenolysis, and dehydrogenation of aniline in the 300-400 K temperature range depends markedly on hydrogen pressures in the vacuum to 0.01 Torr range. In the absence of external hydrogen, dehydrogenation dominates with increasing temperature. Both hydrogenation and hydrogenolysis of aniline-derived surface intermediates are enhanced dramatically by hydrogen atmospheres. For aniline coverages up to 1 monolayer, hydrogenolysis to form benzene at 475 K is dominant over a broad hydrogen pressure range (> 10{sup -6} Torr). Ultrasoft X-ray absorption spectra above the carbon K edge of the aniline-derived surface intermediates reveal that the precursor for hydrogenolysis is a hydrogenated aniline-derived species indistinguishable from cyclohexylamine. 34 refs., 12 figs., 2 tabs.

  17. Crystal structure of peroxiredoxin from Aeropyrum pernix K1 complexed with its substrate, hydrogen peroxide.

    PubMed

    Nakamura, Tsutomu; Kado, Yuji; Yamaguchi, Takafumi; Matsumura, Hiroyoshi; Ishikawa, Kazuhiko; Inoue, Tsuyoshi

    2010-01-01

    Peroxiredoxin (Prx) reduces hydrogen peroxide and alkyl peroxides to water and corresponding alcohols, respectively. The reaction is dependent on a peroxidatic cysteine, whose sulphur atom nucleophilically attacks one of the oxygen atoms of the peroxide substrate. In spite of the many structural studies that have been carried out on this reaction, the tertiary structure of the hydrogen peroxide-bound form of Prx has not been elucidated. In this paper, we report the crystal structure of Prx from Aeropyrum pernix K1 in the peroxide-bound form. The conformation of the polypeptide chain is the same as that in the reduced apo-form. The hydrogen peroxide molecule is in close contact with the peroxidatic Cys50 and the neighbouring Thr47 and Arg126 side chain atoms, as well as with the main chain nitrogen atoms of Val49 and Cys50. Bound peroxide was also observed in the mutant C50S, in which the peroxidatic cysteine was replaced by serine. Therefore, the sulphur atom of the peroxidatic cysteine is not essential for peroxide binding, although it enhances the binding affinity. Hydrogen peroxide binds to the protein so that it fills the active site pocket. This study provides insight into the early stage of the Prx reaction.

  18. Hydrogen trapping in δ-Pu: insights from electronic structure calculations

    NASA Astrophysics Data System (ADS)

    Taylor, Christopher D.; Hernandez, Sarah C.; Francis, Michael F.; Schwartz, Daniel S.; Ray, Asok K.

    2013-07-01

    Density functional theory calculations have been performed to provide details of the structural and charge-transfer details related to the solid solution of hydrogen in (δ)-plutonium. We follow the Flanagan model that outlines the process by which hydrogen interacts with a metal to produce hydride phases, via a sequence of surface, interstitial and defect-bound (trapped) states. Due to the complexities of the electronic structure in plutonium solid-state systems, we take the pragmatic approach of adopting the ‘special quasirandom structure’ to disperse the atomic magnetic moments. We find that this approach produces sound structural and thermodynamic properties in agreement with the available experimental data. In δ-Pu, hydrogen has an exothermic binding energy to all of the states relevant in the Flanagan model, and, furthermore, is anionic in all these states. The charge transfer is maximized (i.e. most negative for hydrogen) in the hydride phase. The pathway from surface to hydride is sequentially exothermic, in the order surface < interstitial < grain boundary < vacancy < hydride (hydride being the most exothermic state). Thus, we find that there is no intermediate state that involves an endothermic increase in energy, consistent with the general experimental observations that the hydriding reaction in plutonium metal can proceed with zero apparent activation barrier.

  19. Facile synthesis of hydrogenated carbon nanospheres with a graphite-like ordered carbon structure.

    PubMed

    Xiao, Junping; Yao, Mingguang; Zhu, Kai; Zhang, Dong; Zhao, Shijia; Lu, Shuangchen; Liu, Bo; Cui, Wen; Liu, Bingbing

    2013-11-21

    We report a synthesis of hydrogenated carbon nanospheres (HCNSs) via a facile solvothermal route at low temperatures (60-100 °C), using CHCl3 as the carbon source and potassium (K) as the reductant. Selective cleavage of the relatively lower stable C-Cl bonds (compared to C-H bonds) of the carbon precursor (CHCl3) by K metal results in the growth of HCNSs. The diameter of HCNSs ranges from 40 to 90 nm. The HCNSs have a graphite-like ordered carbon structure in spite of their high degree of hydrogenation. The HCNSs exhibit an average Brunauer-Emmett-Teller (BET) surface area of 43 m(2) g(-1), containing a small amount of mesopores and macropores in the structure. The nanospheres' sample as an anode material for lithium ion batteries (LIBs) has been studied. It exhibits a high discharge capacity (3539 mA h g(-1) in the first cycle, 978 mA h g(-1) after 50 cycles) and good cycling stability, demonstrating advantages as a promising candidate for anode materials in LIBs. The high capacity of the HCNSs is due to their unique nanostructures and high percentage hydrogenation, as well as hydrogenation induced structural defects.

  20. Blister formation in Mo/Si multilayered structures induced by hydrogen ions

    NASA Astrophysics Data System (ADS)

    van den Bos, R. A. J. M.; Lee, C. J.; Benschop, J. P. H.; Bijkerk, F.

    2017-07-01

    We report on blister formation in nanometer thick Mo/Si multilayer structures due to exposure to hydrogen ion fluxes. The influence of hydrogen flux and ion energy for blister formation have been measured and compared to a blister model. The blister number density increases significantly around 100 eV when increasing the ion energy from 50 to 200 eV. This stepwise behavior could be explained by the fact that for energies  >100 eV hydrogen ions could directly penetrate to the depth where delamination takes place. From the blister model also the blisters internal pressure and surface energy was calculated to be around 100-800 MPa and γ =1.87~\\text{J}~{{\\text{m}}-2} respectively.

  1. Electronic Structure Calculations of Hydrogen Storage in Lithium-Decorated Metal-Graphyne Framework.

    PubMed

    Kumar, Sandeep; Dhilip Kumar, Thogluva Janardhanan

    2017-08-30

    Porous metal-graphyne framework (MGF) made up of graphyne linker decorated with lithium has been investigated for hydrogen storage. Applying density functional theory spin-polarized generalized gradient approximation with the Perdew-Burke-Ernzerhof functional containing Grimme's diffusion parameter with double numeric polarization basis set, the structural stability, and physicochemical properties have been analyzed. Each linker binds two Li atoms over the surface of the graphyne linker forming MGF-Li8 by Dewar coordination. On saturation with hydrogen, each Li atom physisorbs three H2 molecules resulting in MGF-Li8-H24. H2 and Li interact by charge polarization mechanism leading to elongation in average H-H bond length indicating physisorption. Sorption energy decreases gradually from ≈0.4 to 0.20 eV on H2 loading. Molecular dynamics simulations and computed sorption energy range indicate the high reversibility of H2 in the MGF-Li8 framework with the hydrogen storage capacity of 6.4 wt %. The calculated thermodynamic practical hydrogen storage at room temperature makes the Li-decorated MGF system a promising hydrogen storage material.

  2. Multiscale structural and electronic control of molybdenum disulfide foam for highly efficient hydrogen production

    PubMed Central

    Deng, Jiao; Li, Haobo; Wang, Suheng; Ding, Ding; Chen, Mingshu; Liu, Chuan; Tian, Zhongqun; Novoselov, K. S.; Ma, Chao; Deng, Dehui; Bao, Xinhe

    2017-01-01

    Hydrogen production through water splitting has been considered as a green, pure and high-efficient technique. As an important half-reaction involved, hydrogen evolution reaction is a complex electrochemical process involving liquid-solid-gas three-phase interface behaviour. Therefore, new concepts and strategies of material design are needed to smooth each pivotal step. Here we report a multiscale structural and electronic control of molybdenum disulfide foam to synergistically promote the hydrogen evolution process. The optimized three-dimensional molybdenum disulfide foam with uniform mesopores, vertically aligned two-dimensional layers and cobalt atoms doping demonstrated a high hydrogen evolution activity and stability. In addition, density functional theory calculations indicate that molybdenum disulfide with moderate cobalt doping content possesses the optimal activity. This study demonstrates the validity of multiscale control in molybdenum disulfide via overall consideration of the mass transport, and the accessibility, quantity and capability of active sites towards electrocatalytic hydrogen evolution, which may also be extended to other energy-related processes. PMID:28401882

  3. Multiscale structural and electronic control of molybdenum disulfide foam for highly efficient hydrogen production

    NASA Astrophysics Data System (ADS)

    Deng, Jiao; Li, Haobo; Wang, Suheng; Ding, Ding; Chen, Mingshu; Liu, Chuan; Tian, Zhongqun; Novoselov, K. S.; Ma, Chao; Deng, Dehui; Bao, Xinhe

    2017-04-01

    Hydrogen production through water splitting has been considered as a green, pure and high-efficient technique. As an important half-reaction involved, hydrogen evolution reaction is a complex electrochemical process involving liquid-solid-gas three-phase interface behaviour. Therefore, new concepts and strategies of material design are needed to smooth each pivotal step. Here we report a multiscale structural and electronic control of molybdenum disulfide foam to synergistically promote the hydrogen evolution process. The optimized three-dimensional molybdenum disulfide foam with uniform mesopores, vertically aligned two-dimensional layers and cobalt atoms doping demonstrated a high hydrogen evolution activity and stability. In addition, density functional theory calculations indicate that molybdenum disulfide with moderate cobalt doping content possesses the optimal activity. This study demonstrates the validity of multiscale control in molybdenum disulfide via overall consideration of the mass transport, and the accessibility, quantity and capability of active sites towards electrocatalytic hydrogen evolution, which may also be extended to other energy-related processes.

  4. A revised structure and hydrogen bonding system in cellulose II from a neutron fiber diffraction analysis

    SciTech Connect

    Langan, P.; Nishiyama, Y.; Chanzy, H.

    1999-11-03

    The crystal and molecular structure and hydrogen bonding system in cellulose II have been revised using new neutron diffraction data extending to 1.2 {angstrom} resolution collected from two highly crystalline fiber samples of mercerized flax. Mercerization was achieved in NaOH/H{sub 2}O for one sample and in NaOD/D{sub 2}O for the other, corresponding to the labile hydroxymethyl moieties being hydrogenated and deuterated, respectively. Fourier difference maps were calculated in which neutron difference amplitudes were combined with phases calculated from two revised X-ray models of cellulose II. The revised phasing models were determined by refinement against the X-ray data set of Kolpak and Blackwell, using the LALS methodology. Both models have two antiparallel chains organized in a P2{sub 1} space group and unit cell parameters: a = 8.01 {angstrom}, b = 9.04 {angstrom}, c = 10.36 {angstrom}, and {gamma} = 117.1{degree}. One has equivalent backbone conformations for both chains but different conformations for the hydroxymethyl moieties: gt for the origin chain and tg for the center chain. The second model based on the recent crystal structures of cellotetraose, has different conformations for the two chains but nearly equivalent conformations for the hydroxymethyl moieties. On the basis of the X-ray data alone, the models could not be differentiated. From the neutron Fourier difference maps, possible labile hydrogen atom positions were identified for each model and refined using LALS. The second model is significantly different from previous proposals based on the crystal structures of cellotetraose, MD simulations of cellulose II, and any potential hydrogen-bonding network in the structure of cellulose II determined in earlier X-ray fiber diffraction studies. The exact localization of the labile hydrogen atoms involved in this bonding, together with their donor and acceptor characteristics, is presented and discussed. This study provides, for the first time

  5. Probing the structure, stability and hydrogen storage properties of calcium dodecahydro-closo-dodecaborate

    SciTech Connect

    Stavila, Vitalie; Her, Jae-Hyuk; Zhou Wei; Hwang, Son-Jong; Kim, Chul; Ottley, Leigh Anna M.; Udovic, Terrence J.

    2010-05-15

    Calcium borohydride can reversibly store up to 9.6 wt% hydrogen; however, the material displays poor cyclability, generally associated with the formation of stable intermediate species. In an effort to understand the role of such intermediates on the hydrogen storage properties of Ca(BH{sub 4}){sub 2}, calcium dodecahydro-closo-dodecaborate was isolated and characterized by diffraction and spectroscopic techniques. The crystal structure of CaB{sub 12}H{sub 12} was determined from powder XRD data and confirmed by DFT and neutron vibrational spectroscopy studies. Attempts to dehydrogenate/hydrogenate mixtures of CaB{sub 12}H{sub 12} and CaH{sub 2} were made under conditions known to favor partial reversibility in calcium borohydride. However, up to 670 K no notable formation of Ca(BH{sub 4}){sub 2} (during hydrogenation) or CaB{sub 6} (during dehydrogenation) occurred. It was demonstrated that the stability of CaB{sub 12}H{sub 12} can be significantly altered using CaH{sub 2} as a destabilizing agent to favor the hydrogen release. - Graphical abstract: Calcium dodecahydro-closo-dodecaborate, CaB{sub 12}H{sub 12} (1), was isolated by dehydration/desolvation of [Ca(H{sub 2}O){sub 7}][B{sub 12}H{sub 12}].H{sub 2}O (2) or [Ca(H{sub 2}O){sub 5}(MeCN){sub 2}][B{sub 12}H{sub 12}] (3). The crystal structure of 1 was determined by powder X-ray diffraction and confirmed by neutron vibrational spectroscopy and first-principles calculations. Hydrogen storage properties of 1 in the presence of calcium hydride were elucidated.

  6. Scanning tunneling microscopy characterization of the geometric and electronic structure of hydrogen-terminated silicon surfaces

    NASA Technical Reports Server (NTRS)

    Kaiser, W. J.; Bell, L. D.; Hecht, M. H.; Grunthaner, F. J.

    1988-01-01

    Scanning tunneling microscopy (STM) methods are used to characterize hydrogen-terminated Si surfaces prepared by a novel method. The surface preparation method is used to expose the Si-SiO2 interface. STM images directly reveal the topographic structure of the Si-SiO2 interface. The dependence of interface topography on oxide preparation conditions observed by STM is compared to the results of conventional surface characterization methods. Also, the electronic structure of the hydrogen-terminated surface is studied by STM spectroscopy. The near-ideal electronic structure of this surface enables direct tunnel spectroscopy measurements of Schottky barrier phenomena. In addition, this method enables probing of semiconductor subsurface properties by STM.

  7. Crystal structure and hydrogen-bonding patterns in 5-fluoro­cytosinium picrate

    PubMed Central

    Mohana, Marimuthu; Thomas Muthiah, Packianathan; McMillen, Colin D.

    2017-01-01

    In the crystal structure of the title compound, 5-fluoro­cytosinium picrate, C4H5FN3O+·C6H2N3O7 −, one N heteroatom of the 5-fluoro­cytosine (5FC) ring is protonated. The 5FC ring forms a dihedral angle of 19.97 (11)° with the ring of the picrate (PA−) anion. In the crystal, the 5FC+ cation inter­acts with the PA− anion through three-centre N—H⋯O hydrogen bonds, forming two conjoined rings having R 2 1(6) and R 1 2(6) motifs, and is extended by N—H⋯O hydrogen bonds and C—H⋯O inter­actions into a two-dimensional sheet structure lying parallel to (001). Also present in the crystal structure are weak C—F⋯π inter­actions. PMID:28316809

  8. Electronic structure characterization and bandgap engineeringofsolar hydrogen materials

    SciTech Connect

    Guo, Jinghua

    2007-11-01

    Bandgap, band edge positions as well as the overall band structure of semiconductors are of crucial importance in photoelectrochemical and photocatalytic applications. The energy position of the band edge level can be controlled by the electronegativity of the dopants, the pH of the solution (flatband potential variation of 60 mV per pH unit), as well as by quantum confinement effects. Accordingly, band edges and bandgap can be tailored to achieve specific electronic, optical or photocatalytic properties. Synchrotron radiation with photon energy at or below 1 keV is giving new insight into such areas as condensed matter physics and extreme ultraviolet optics technology. In the soft x-ray region, the question tends to be, what are the electrons doing as they migrated between the atoms. In this paper, I will present a number of soft x-ray spectroscopic study of nanostructured 3d metal compounds Fe{sub 2}O{sub 3} and ZnO.

  9. Recognizing molecular patterns by machine learning: An agnostic structural definition of the hydrogen bond

    SciTech Connect

    Gasparotto, Piero; Ceriotti, Michele

    2014-11-07

    The concept of chemical bonding can ultimately be seen as a rationalization of the recurring structural patterns observed in molecules and solids. Chemical intuition is nothing but the ability to recognize and predict such patterns, and how they transform into one another. Here, we discuss how to use a computer to identify atomic patterns automatically, so as to provide an algorithmic definition of a bond based solely on structural information. We concentrate in particular on hydrogen bonding – a central concept to our understanding of the physical chemistry of water, biological systems, and many technologically important materials. Since the hydrogen bond is a somewhat fuzzy entity that covers a broad range of energies and distances, many different criteria have been proposed and used over the years, based either on sophisticate electronic structure calculations followed by an energy decomposition analysis, or on somewhat arbitrary choices of a range of structural parameters that is deemed to correspond to a hydrogen-bonded configuration. We introduce here a definition that is univocal, unbiased, and adaptive, based on our machine-learning analysis of an atomistic simulation. The strategy we propose could be easily adapted to similar scenarios, where one has to recognize or classify structural patterns in a material or chemical compound.

  10. Recognizing molecular patterns by machine learning: an agnostic structural definition of the hydrogen bond.

    PubMed

    Gasparotto, Piero; Ceriotti, Michele

    2014-11-07

    The concept of chemical bonding can ultimately be seen as a rationalization of the recurring structural patterns observed in molecules and solids. Chemical intuition is nothing but the ability to recognize and predict such patterns, and how they transform into one another. Here, we discuss how to use a computer to identify atomic patterns automatically, so as to provide an algorithmic definition of a bond based solely on structural information. We concentrate in particular on hydrogen bonding--a central concept to our understanding of the physical chemistry of water, biological systems, and many technologically important materials. Since the hydrogen bond is a somewhat fuzzy entity that covers a broad range of energies and distances, many different criteria have been proposed and used over the years, based either on sophisticate electronic structure calculations followed by an energy decomposition analysis, or on somewhat arbitrary choices of a range of structural parameters that is deemed to correspond to a hydrogen-bonded configuration. We introduce here a definition that is univocal, unbiased, and adaptive, based on our machine-learning analysis of an atomistic simulation. The strategy we propose could be easily adapted to similar scenarios, where one has to recognize or classify structural patterns in a material or chemical compound.

  11. Hydrogen-induced structural transition in single layer ReS2

    NASA Astrophysics Data System (ADS)

    Yagmurcukardes, M.; Bacaksiz, C.; Senger, R. T.; Sahin, H.

    2017-09-01

    By performing density functional theory-based calculations, we investigate how structural, electronic and mechanical properties of single layer ReS2 can be tuned upon hydrogenation of its surfaces. It is found that a stable, fully hydrogenated structure can be obtained by formation of strong S-H bonds. The optimized atomic structure of ReS2H2 is considerably different than that of the monolayer ReS2 which has a distorted-1T phase. By performing phonon dispersion calculations, we also predict that the Re2-dimerized 1T structure (called 1T {{}\\text{R{{\\text{e}}2}}} ) of the ReS2H2 is dynamically stable. Unlike the bare ReS2 the 1T {{}\\text{R{{\\text{e}}2}}} -ReS2H2 structure which is formed by breaking the Re4 clusters into separated Re2 dimers, is an indirect-gap semiconductor. Furthermore, mechanical properties of the 1T {{}\\text{R{{\\text{e}}2}}} phase in terms of elastic constants, in-plane stiffness (C) and Poisson ratio (ν) are investigated. It is found that full hydrogenation not only enhances the flexibility of the single layer ReS2 crystal but also increases anisotropy of the elastic constants.

  12. DFT STUDY OF HYDROGEN STORAGE ON Li- AND Na-DOPED C59B HETEROFULLERENE

    NASA Astrophysics Data System (ADS)

    Zahedi, Ehsan; Mozaffari, Majid

    2014-05-01

    Effect of light alkali metal (Li and Na) decorated on the C59B heterofullerene for hydrogen storage is considered using DFT-MPW1PW91 method. Results show that Li and Na atoms strongly prefer to adsorb on top of five-member and six-member ring where a carbon atom is replaced by a boron atom. Significant charge transfer from the alkali metal to the C59B compensates for the electron deficiency of C59B and makes the latter aromatic in nature. Corrected binding energies of hydrogen molecule on the alkali-doped C59B using counterpoise method, structural properties and NBO analysis indicate that first hydrogen molecule is adsorbed physically and does not support minimal conditions of DOE requirement. Finally, positive values of binding energies for the adsorption of a second hydrogen molecule show that alkali doped C59B are capable of storing a maximum of one hydrogen molecule.

  13. Polyaniline as a material for hydrogen storage applications.

    PubMed

    Attia, Nour F; Geckeler, Kurt E

    2013-07-12

    The main challenge of commercialization of the hydrogen economy is the lack of convenient and safe hydrogen storage materials, which can adsorb and release a significant amount of hydrogen at ambient conditions. Finding and designing suitable cost-effective materials are vital requirements to overcome the drawbacks of investigated materials. Because of its outstanding electronic, thermal, and chemical properties, the electrically conducting polyaniline (PANI) has a high potential in hydrogen storage applications. In this review, the progress in the use of different structures of conducting PANI, its nanocomposites as well as activated porous materials based on PANI as hydrogen storage materials is presented and discussed. The effect of the unique electronic properties based on the π-electron system in the backbone of these materials in view of the hydrogen uptake and the relevant mechanisms are highlighted. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  14. Frequent side chain methyl carbon-oxygen hydrogen bonding in proteins revealed by computational and stereochemical analysis of neutron structures.

    PubMed

    Yesselman, Joseph D; Horowitz, Scott; Brooks, Charles L; Trievel, Raymond C

    2015-03-01

    The propensity of backbone Cα atoms to engage in carbon-oxygen (CH · · · O) hydrogen bonding is well-appreciated in protein structure, but side chain CH · · · O hydrogen bonding remains largely uncharacterized. The extent to which side chain methyl groups in proteins participate in CH · · · O hydrogen bonding is examined through a survey of neutron crystal structures, quantum chemistry calculations, and molecular dynamics simulations. Using these approaches, methyl groups were observed to form stabilizing CH · · · O hydrogen bonds within protein structure that are maintained through protein dynamics and participate in correlated motion. Collectively, these findings illustrate that side chain methyl CH · · · O hydrogen bonding contributes to the energetics of protein structure and folding. © 2014 Wiley Periodicals, Inc.

  15. Effect of chain structure on hydrogen bonding in vinyl acetate - vinyl alcohol copolymers

    NASA Astrophysics Data System (ADS)

    Merekalova, Nadezhda D.; Bondarenko, Galina N.; Denisova, Yuliya I.; Krentsel, Liya B.; Litmanovich, Arkadiy D.; Kudryavtsev, Yaroslav V.

    2017-04-01

    FTIR spectroscopy and semi-empirical AM1 method are used to study hydrogen bonding in multiblock and random equimolar copolymers of vinyl acetate and vinyl alcohol. An energetically beneficial zip-holder complex, built on multiple inter- and intrachain hydroxyl-hydroxyl bonds and an intrachain hydroxyl-acetyloxy bond, can be formed between two vinyl alcohol sequences. As a result, multiblock copolymers reveal stronger degree of association that affects crystallinity, as well as various rheological and relaxation properties discussed in the literature. Macromolecular complexes in random copolymers are weak and tend to be destroyed in the presence of residual DMF solvent and adsorbed water. Nevertheless, a rather stable interchain quaternary complex can be formed that includes vinyl alcohol and vinyl acetate units and DMF and water molecules. For a single chain it is shown that an H-bond between neighboring vinyl alcohol and vinyl acetate monomer units mostly engages a carbonyl oxygen atom of the vinyl acetate, if the vinyl alcohol belongs to a short (<5 units) sequence, and an ether oxygen atom in the other case. On the whole, the quantum chemistry calculations shed much light on the origin of distinctions in the copolymer FTIR spectra, which may seem subtle when considered standalone.

  16. Intramolecular hydrogen bond stabilization of hemiaminal structures, precursors of imidazo[1,2- a]pyridine

    NASA Astrophysics Data System (ADS)

    Velázquez, Manuel; Salgado-Zamora, Héctor; Pérez, Cuauhtémoc; Campos-A, Ma Elena; Mendoza, Patricia; Jiménez, Hugo; Jiménez, Rogelio

    2010-08-01

    A theoretical study supported by calculations at the B3LYP/6-31+G and B3LYP/6-311++G(d,p) levels demonstrated that an attractive interaction involving a hydrogen bond between a hydroxyl group and an acceptor halogen atom (O-H⋯Cl) is present in 2,3-dihydro-2-hydroxy-2-chloromethylimidazo[1,2- a]pyridinium salts, which have an hemiaminal structure. However, the conformers obtained from a dihedral angle analysis performed upon these hemiaminal structures showed relatively small differences in energy among them, indicating that the hydrogen bonding interaction is not entirely responsible for preventing the aromatization process. Calculations were carried out on the gas phase of the hemiaminal cation 6b and the corresponding fully aromatic heterocycle cation 8b. It was found that the difference in energy between the two species is rather small, suggesting that other factors must be contributing to the hemiaminal isolation. The fact that a hydrogen bond is a stabilizing element of the hemiaminal suggests that the formation process of this compound should be favored in aprotic solvents. Accordingly, the condensation of several 2-aminopyridines with 3-bromo-1,1,1-trifluoroacetone was revised. The reaction performed in dry acetone (a non-competing hydrogen bond solvent) proceeded to the hemiaminal derivative, thus confirming the prediction made by theoretical calculations.

  17. Hydrogen segregation and its roles in structural stability and metallization: silane under pressure

    NASA Astrophysics Data System (ADS)

    Cui, Wenwen; Shi, Jingming; Liu, Hanyu; Yao, Yansun; Wang, Hui; Iitaka, Toshiaki; Ma, Yanming

    2015-08-01

    We present results from first-principles calculations on silane (SiH4) under pressure. We find that a three dimensional P-3 structure becomes the most stable phase above 241 GPa. A prominent structural feature, which separates the P-3 structure from previously observed/predicted SiH4 structures, is that a fraction of hydrogen leaves the Si-H bonding environment and forms segregated H2 units. The H2 units are sparsely populated in the system and intercalated with a polymeric Si-H framework. Calculations of enthalpy of formation suggest that the P-3 structure is against the decomposition into Si-H binaries and/or the elemental crystals. Structural stability of the P-3 structure is attributed to the electron-deficient multicenter Si-H-Si interactions when neighboring silicon atoms are linked together through a common hydrogen atom. Within the multicenter bonds, electrons are delocalized and this leads to a metallic state, possibly also a superconducting state, for SiH4. An interesting outcome of the present study is that the enthalpy sum of SiH4 (P-3 structure) and Si (fcc structure) appears to be lower than the enthalpy of disilane (Si2H6) between 200 and 300 GPa (for all previously predicted crystalline forms of Si2H6), which calls for a revisit of the stability of Si2H6 under high pressure.

  18. Hydrogen segregation and its roles in structural stability and metallization: silane under pressure

    PubMed Central

    Cui, Wenwen; Shi, Jingming; Liu, Hanyu; Yao, Yansun; Wang, Hui; Iitaka, Toshiaki; Ma, Yanming

    2015-01-01

    We present results from first-principles calculations on silane (SiH4) under pressure. We find that a three dimensional P-3 structure becomes the most stable phase above 241 GPa. A prominent structural feature, which separates the P-3 structure from previously observed/predicted SiH4 structures, is that a fraction of hydrogen leaves the Si-H bonding environment and forms segregated H2 units. The H2 units are sparsely populated in the system and intercalated with a polymeric Si-H framework. Calculations of enthalpy of formation suggest that the P-3 structure is against the decomposition into Si-H binaries and/or the elemental crystals. Structural stability of the P-3 structure is attributed to the electron-deficient multicenter Si-H-Si interactions when neighboring silicon atoms are linked together through a common hydrogen atom. Within the multicenter bonds, electrons are delocalized and this leads to a metallic state, possibly also a superconducting state, for SiH4. An interesting outcome of the present study is that the enthalpy sum of SiH4 (P-3 structure) and Si (fcc stru