Interaction Of Atomic Hydrogen Research Articles

Effect of Titanium Doping of Al(111) Surfaces on Alane Formation, Mobility, and Desorption

Alanes are critical intermediates in hydrogen storage reactions for mass transport during the formation of complex metal hydrides. Titanium has been shown to promote hydrogen desorption and hydrogenation, but its role as a catalyst is not clear. Combining surface infrared (IR) spectroscopy and density functional theory (DFT), the role of Ti is explored during the interaction of atomic hydrogen with Ti-doped Al(111) surfaces. Titanium is found to reduce the formation of large alanes, due to a decrease of hydrogen mobility and to trapping of small alanes on Ti sites, thus hindering oligomerization. For high doping levels ({approx}0.27 ML Ti) on Al(111), only chemisorbed AlH{sub 3} is observed on Ti sites, with no evidence for large alanes. Titanium also dramatically lowers the desorption temperature of large alanes from 290 to 190 K, due to a more restricted translational motion of these alanes.

Interaction of Gas-phase Atomic Hydrogen with Chemisorbed Oxygen Atoms on a Silicon Surface

The reaction of gas-phase atomic hydrogen with oxygen atoms chemisorbed on a silicon surface is studied by use of the classical trajectory approach. We have calculated the probability of the OH formation and energy deposit of the reaction exothermicity in the newly formed OH in the gas-surface reaction H(g) + O(ad)/Si → OH(g) + Si. All reactive events occur in a single impact collision on a subpicosecond scale, following the EleyRideal mechanism. These events occur in a localized region around the adatom site on the surface. The reaction probability is dependent upon the gas temperature and shows the maximum near 1000 K, but it is essentially independent of the surface temperature. The reaction probability is also independent upon the initial excitation of the O-Si vibration. The reaction energy available for the product state is carried away by the desorbing OH in its translational and vibrational motions. When the initial excitation of the O-Si vibration increases, translational and vibrational energies of OH rise accordingly, while the energy shared by rotational motion varies only slightly. Flow of energy between the reaction zone and the solid has been incorporated in trajectory calculations, but the amount of energy propagated into the solid is only a few percent of the available energy released in the OH formation.

Hydration of OH radical in high temperature water

Molecular dynamics simulation study on the hydration and hydrogen-bonding of the OH radical is presented for the 25 MPa isobar and the temperature ranging from 373 to 673 K. For the first time the water molecule and the radical have been described by the flexible three- and two-site models, respectively, which account for short-range interaction of the hydrogen atom. We have found that the mechanism of hydration and the degree of radical–water hydrogen-bonding are closely related to the structural transformations occurring in the hydrogen-bonded network of the solvent. Compact and ordered network, typical for the liquid phase, favours the cavity localization. Up to 573 K the decrease in the number of water–water hydrogen bonds has been associated with the increase in the number of radical–water H-bonds. Unlike the hydration in the condensed liquid phase the low density of supercritical water at 673 K stimulates the radical behaviour as a structure-maker. In the presence of OH the structural inhomogeneity of the solvent has been noticeably reduced. Our work showed the importance of short-range interaction of hydrogen atoms in hydration and hydrogen bonding of OH at high temperatures and proved that neglect of the angular condition greatly overestimates the number of radical–water H-bonds, mostly of the H-acceptor type.

Investigation of the adsorption and diffusion interaction of atomic hydrogen with low-index surfaces of crystal aluminum nanoplates

By the method of density functional in the local density and generalized gradient approximation, the dependences of the potential energy of interaction of atomic hydrogen with low-index surfaces of aluminum nanoplates have been calculated. The spatial configurations of hydrogen atoms and surface layers of the plate corresponding to the stable structures formed by adsorption and diffusion have been determined. It has been shown that atomic hydrogen is adsorbed irreversibly on the Al surface, releasing energy of 2.8–3.1 eV whose value is determined by the atomic structure of the surface. On the atomic planes (100) and (110), the bridge form of chemisorption has the minimum energy. For the (111) surface, the energy-stable state is realized in the threefold coordinated position of the hydrogen atom. Diffusion of hydrogen is an activated process in which energy of 0.5–0.8 eV is absorbed depending on the atomic structure of the plate. Atomic hydrogen moves through interatomic voids sequentially occupying octa- and tetrahedral positions. It has been established that the transient state between stable Oh and Td positions in the bulk of the plate is the geometrical configuration of the hydrogen atom having third-order symmetry.

Biosorption of Cd(II) and Pb(II) ions by aqueous solutions of novel alkalophillic Streptomyces VITSVK5 spp. biomass

Discharge of heavy metals from metal processing industries is known to have adverse effects on the environment. Biosorption of heavy metals by metabolically inactive biomass of microbial organisms is an innovative and alternative technology for removal of these pollutants from aqueous solution. The search of marine actinobacteria with potential heavy metal biosorption ability resulted in the identification of a novel alkalophilic Streptomyces VITSVK5 species. The biosorption property of Streptomyces VITSVK5 spp. was investigated by absorbing heavy metals Cadmium (Cd) and Lead (Pb). Physiochemical characteristics and trace metal concentration analysis of the backwater showed the concentrations of different metals were lead 13±2.1 μg L−1, cadmium 3.1±0.3μg L−1, zinc 8.4±2.6μg L−1 and copper 0.3±0.1μg L−1, whereas mercury was well below the detection limit. The effect of pH and biomass dosage on removal efficiency of heavy metal ions was also investigated. The optimum pH for maximal biosorption was 4.0 for Cd (II) and 5.0 for Pb (II) with 41% and 84% biosorption respectively. The biosorbent dosage was optimized as 3 g L-1 for both the trace metals. Fourier transform infrared absorption spectrum results indicated the chemical interactions of hydrogen atoms in carboxyl (-COOH), hydroxyl (-CHOH) and amine (-NH2) groups of biomass with the metal ions. This could be mainly involved in the biosorption of Cd (II) and Pb (II) onto Streptomyces VITSVK5 spp. The results of our study revealed Streptomyces metabolites could be used to develop a biosorbent for adsorbing metal ions from aqueous environments.

Interaction of atomic hydrogen with carbon grains

Laboratory studies on the interaction of atomic hydrogen with aliphatic and aromatic hydrogenated carbon grains are discussed. When exposed to atomic hydrogen, both types of hydrogenated carbon grains act as catalysts for molecular hydrogen formation. In the first case, an exchange reaction with hydrogen chemisorbed in aliphatic carbon sites is the formation route to H2 formation. For aromatic carbon grains, the formation of molecular hydrogen takes place through a two-step reaction sequence: 1) super hydrogenation of the aromatic carbon islands of grains 2) exchange reactions on these islands. This mechanism represents a good approximation of molecular hydrogen formation on large neutral PAHs.

Influence of a high electric field on the interaction of hydrogen with small palladium clusters: DFT studies

The effect of an external electric field of 25 V/nm on the interaction of atomic hydrogen with palladium clusters consisting of four and six atoms was investigated using the density-functional theory. The equilibrium geometry found for the systems under investigation is in good agreement with other computational studies carried out for extended systems, however the values obtained for the adsorption energy are overestimated. A comparison with the results obtained for clusters not affected by an external electric field shows that the effect of the field is a decrease of the energy barrier for incorporation of hydrogen into the clusters. The changes of the electronic structure induced by the electric field and the nature of the bonding between H and Pd atoms are analysed in a discussion of the density of states of the systems.

Molecular Dynamics Simulation of Hydrogen Injection onto Diamond Surfaces

We demonstrate the chemical interaction of hydrogen atoms with single-crystal diamond by performing classical molecular dynamics (CMD) simulations based on the modified Brenner reactive empirical bond order (REBO) potential. Erosion of the diamond structure is shown not to occur for hydrogen injection energies Ein < 5 eV, which is consistent with Yada's experimental results. We also clarify that the increase in the temperature of diamond depends on the surface of diamond. This finding is similar to our previous simulation results that chemical sputtering of graphite depends on the surface of graphite. In addition, we obtain the time dependence of the temperature of diamond Tdia, which is saturated.

Molecular dynamics study of the hydration of the hydroxyl radical at body temperature

Classical molecular dynamics (MD) simulation of ˙OH in liquid water at 37 °C has been performed using flexible models of the solute and solvent molecules. We derived the Morse function describing the bond stretching of the radical and the potential for ˙OH-H(2)O interactions, including short-range interactions of hydrogen atoms. Scans of the potential energy surface of the ˙OH-H(2)O complex have been performed using the DFT method with the B3LYP functional and the 6-311G(d,p) basis set. The DFT-derived partial charges, ±0.375e, and the equilibrium bond-length, 0.975 Å, of ˙OH resulted in the dipole moment of 1.76 D. The radical-water radial distribution functions revealed that ˙OH is not built into the solvent structure but it rather occupies distortions or cavities in the hydrogen-bonded network. The solvent structure at 37 °C has been found to be the same as that of pure water. The hydration cage of the radical comprises 13-14 water molecules. The estimated hydration enthalpy -42 ± 5 kJ mol(-1) is comparable with the experimental value -39 ± 6 kJ mol(-1) for 25 °C. Inspection of hydrogen bonds showed the importance of short-range interaction of hydrogen atoms and indicated that neglect of the angular condition greatly overestimates the number of the H-acceptor radical-water bonds. The mean number ̅n = 0.85 of radical-water H-bonds has been calculated using geometric definition of H-bond and ̅n = 0.62 has been obtained when the energetic condition, E(da)≤-8 kJ mol(-1), was additionally considered. The continuous lifetimes of 0.033 ps and 0.024 ps have been estimated for the radical H-donor and the H-acceptor bonds, respectively. Within statistical uncertainty the radical self-diffusion coefficient, (2.9 ± 0.6) × 10(-9) m(2) s(-1), is the same as (3.1 ± 0.5) × 10(-9) m(2) s(-1) calculated for water in solution and in pure solvent. To the best of our knowledge, this is the first study of the ˙OH(aq) properties at a biologically relevant body temperature.

Interaction of Atomic and Molecular Hydrogen with Tholin Surfaces at Low Temperatures

We study the interaction of atomic and molecular hydrogen with a surface of tholin, a man-made polymer considered to be an analogue of aerosol particles present in Titan's atmosphere, using thermal programmed desorption at low temperatures below 30 K. The results are fitted and analyzed using a fine-grained rate equation model that describes the diffusion, reaction, and desorption processes. We obtain the energy barriers for diffusion and desorption of atomic and molecular hydrogen. These barriers are found to be in the range of 30-60 meV, indicating that atom/molecule-surface interactions in this temperature range are dominated by weak adsorption forces. The implications of these results for the understanding of the atmospheric chemistry of Titan are discussed.

Experimental evaluation of total hydrogen capacity for fullerite C 60

The fullerene is the fourth allotropic modification of carbon and its properties, as volume, gravimetric and electrochemical capacities, are in excess of many similar properties of metal hydrides and hydrocarbons. The solution of the problem of the reversible hydrogenation of each carbon atom in the frame of fullerene molecule will allow to create the hydrogen storage with the capacity up to 7.7 wt.% H. A series of experiments have been conducted to evaluate the full hydrogenation of fullerite C 60; hydrofullerenes have been produced experimentally with the variable content of hydrogen. The optimum regime of C 60 hydrogenation has been determined resulting in the full hydrogenation of fullerene molecule C 60. As was apparent after the tests, the sequence of formation of hydrogenated fullerene molecule C 60H 60 in fullerite has been going in the following order: the molecular hydrogen dissolution in octahedral interstices of fcc lattice of fullerite, the dissociation of hydrogen molecules in going from octa- to tetrahedral interstices, the interaction of hydrogen atoms with fullerene molecule. It has been demonstrated that chemisorption process of hydrogen by molecule C 60 is limited by diffusive processes in fullerite after hydrogen concentration conformed to C 60H 36. The spectral analysis have shown that the second stage process of chemisorption follows the compressive shell model. The suggestion of the model of processes going on at the interaction between H 2 and fullerite C 60 has been made. The mechanism for the definition of hydrogenation degree of molecule C 60 has been proposed in the present paper.

Nanotexture Switching of Single‐Layer Hexagonal Boron Nitride on Rhodium by Intercalation of Hydrogen Atoms

Playing nano-tectonics: The interaction of atomic hydrogen with a single layer of hexagonal boron nitride on rhodium leads to the removal of the h-BN surface corrugation (see picture; blue region: corrugated, orange region: flat). This change of surface texture arises from the intercalation of hydrogen atoms between the h-BN skin and the metal, and can be restored by annealing to about 600 K to expel the hydrogen atoms.

Adsorption and dissociation of H 2 on the Cu 2O(1 1 1) surface: A density functional theory study

Interactions of atomic and molecular hydrogen with perfect and deficient Cu 2O(1 1 1) surfaces have been investigated by density functional theory. Different kinds of possible modes of H and H 2 adsorbed on the Cu 2O(1 1 1) surface and possible dissociation pathways were examined. The calculated results indicate that O SUF, Cu CUS and O vacancy sites are the adsorption active centers for H adsorbed on the Cu 2O(1 1 1) surface, and for H 2 adsorption over perfect surface, Cu CUS site is the most advantageous position with the side-on type of H 2. For H 2 adsorption over deficient surface, two adsorption models of H 2, H 2 adsorbing perpendicularly over O vacancy site and H 2 lying flatly over singly-coordinate Cu–Cu short bridge, are typical of non-energy-barrier dissociative adsorption leading to one atomic H completely inserted into the crystal lattice and the other bounded to Cu CUS atom, suggesting that the dissociative adsorption of H 2 is the main dissociation pathway of H 2 on the Cu 2O(1 1 1) surface. Our calculation result is consistent with that of the experimental observation. Therefore, Cu 2O(1 1 1) surface with oxygen vacancy exhibits a strong chemical reactivity towards the dissociation of H 2.

H ATOM IRRADIATION OF CARBON GRAINS UNDER SIMULATED DENSE INTERSTELLAR MEDIUM CONDITIONS: THE EVOLUTION OF ORGANICS FROM DIFFUSE INTERSTELLAR CLOUDS TO THE SOLAR SYSTEM

We present the results of experiments aimed at studying the interaction of hydrogen atoms at 80 K with carbon grains covered with a water ice layer at 12 K. The effects of H processing have been analyzed, using IR spectroscopy, as a function of the water ice layer. The results confirm that exposure of the samples to H atoms induces the activation of the band at 3.47 μm with no evidence for the formation of aromatic and aliphatic C-H bonds in the CH2 and CH3 functional groups. The formation cross section of the 3.47 μm band has been estimated from the increase of its integrated optical depth as a function of the H atom fluence. The cross section decreases with increasing thickness of the water ice layer, indicating an increase of adsorption of H atoms in the water ice layer. A penetration depth of 100 nm has been estimated for H atoms in the porous water ice covering carbon grains. Sample warm-up at room temperature causes the activation of the IR features due to the vibrations of the CH2 and CH3 aliphatic functional groups. The evolution of the 3.47 μm band carrier has been evaluated for dense and diffuse interstellar clouds, using the estimated formation cross section and assuming that the destruction cross section by energetic processing is the same as that derived for the 3.4 μm band. In both environments, the presence of the 3.47 μm band carrier is compatible with the evolutionary timescale limit imposed by fast cycling of materials between dense and diffuse regions of the interstellar medium. In diffuse regions the formation of the CH2 and CH3 aliphatic bands, inhibited in dense regions, takes place, masking the 3.47 μm band. The activation of the CH2 and CH3 aliphatic vibrational modes at the end of H processing after sample warm-up represents the first experimental evidence supporting an evolutionary connection between the interstellar carbon grain population, which is responsible for the 3.4 μm band (diffuse regions) and contributes to the absorption at 3.47 μm (dense regions), and the organics observed in interplanetary dust particles and cometary Stardust grains.

Quantum-chemical study of interaction of hydrogen atoms with graphene

The dependence of the binding energy and the activation energy of adsorption of hydrogen atoms on the number of previously adsorbed particles and their position—on one or both sides of a cluster, on nearest or distant neighbors (carbon atoms)—is investigated by quantum-chemical modeling. A hypothesis of the formation of adsorption sites (islands) on graphene at the initial stage of its saturation by hydrogen is discussed.

Molecular dynamics simulation of low-energy atomic hydrogen on tungsten surface

The trapping and release of hydrogenic particles is a crucial issue in the application of tungsten (W) as plasma-facing materials (PFM) in current fusion devices. To study the interaction of low-energy atomic hydrogen with W surface, molecular dynamics (MD) simulations were performed adopting a bond-order interatomic potential. Energetic hydrogen atoms with a series of energies ranged from 0.5 eV to 50 eV were projected on the W (0 0 1) surface at normal incidence. The particle and energy reflection coefficients as well as mean range distribution as a function of incident energy have been discussed. Also calculated were the interstitial hydrogen formation energies and the migration energy. For an interstitial hydrogen atom in W, the most favorable configuration is in the tetrahedral position and the migration energy is obtained as about 0.30 eV, in agreement with experimental data.

Synthesis and characterization of new zirconium 4-sulfophenylphosphonates

New way for the preparation of 4-sulfophenylphosphonic acid is proposed based on the hydrolysis of sulfamoylphenylphosphonic acid under hydrothermal conditions. 4-Sulfophenylphosphonic acid was successfully used for the preparation of zirconium sulfophenylphosphonate and zirconium phosphate sulfophenylphosphonate with formulae Zr(HO 3SC 6H 4PO 3) 2·2H 2O and Zr(HPO 4) 0.7(HO 3SC 6H 4PO 3) 1.3·2H 2O. Both compounds are layered with the interlayer distances of around 19.9 Å, which agrees well with the presumed structure derived from the structure of the alpha modification of zirconium phosphate monohydrate (α-ZrP). The inorganic part of the title compounds is identical with that of α-ZrP, with the sulfophenyl groups jutting out of the layers into the interlayer space. Both compounds were further characterized by FTIR and solid-state NMR, which confirmed the presence of strongly acidic hydrogen on the sulfonic group. Based on the NMR findings, the structure of hydrogen bonding in the interlayer space was proposed. The 2D 1H– 1H spin-exchange and double-quantum NMR experiments further revealed various mutually interacting hydrogen atoms differing in their mobility. In contrast to α-ZrP, protons in the newly prepared systems exhibit significantly higher dynamics. The proton conductivity ( σ) of both compounds was determined at 100 °C as a function of relative humidity (RH) in the range 50–90% and as a function of temperature between 70 and 150 °C, at RH = 75%. The phosphate phosphonate compound is more conductive than the pure phosphonate compound, the highest σ values being 0.063 S cm − 1 (at 100 °C and 90% RH) and 0.073 S cm − 1 (at 150 °C and 75% RH). Due to their insolubility in water, good thermal stability and the considerably high protonic conductivity the described layered compounds are promising candidates for application as components of composite proton exchange membranes in fuel cells.

Modification of single wall carbon nanotubes (SWNT) for hydrogen storage

Due to unique structural, mechanical and electrical properties of single wall carbon nanotubes, SWNTs, they have been proposed as promising hydrogen storage materials especially in automotive industries. This research deals with investing of CNT’s and some activated carbons hydrogen storage capacity. The CNT’s were prepared through natural gas decomposition at a temperature of 900˚C over cobalt-molybdenum nanoparticles supported by nanoporous magnesium oxide (Co–Mo/MgO) during a chemical vapor deposition (CVD) process. The effects of purity of CNT (80–95%wt.) on hydrogen storage were investigated here. The results showed an improvement in the hydrogen adsorption capacity with increasing the purity of CNT’s. Maximum adsorption capacity was 0.8%wt. in case of CNT’s with 95% purity and it may be raised up with some purification to 1%wt. which was far less than the target specified by DOE (6.5%wt.). Also some activated carbons were manufactured and the results compared to CNTs. There were no considerable H 2-storage for carbon nanotubes and activated carbons at room-temperature due to insufficient binding between H 2 molecules carbon nanostructures. Therefore, hydrogen must be adsorbed via interaction of atomic hydrogen with the storage environment in order to achieve DOE target, because the H atoms have a very stronger interaction with carbon nanostructures.

Dependency of Tritium Retention in Graphite on Temperature Control of Molecular Dynamics

AbstractWe have investigated the carbon plasma facing material and hydrogen atom interaction by the use of molecular dynamics simulation to clarify chemical erosion processes on divertor plate. The present paper is our first try at elucidation of temperature dependence by the molecular dynamics. Temperature was controlled by using Langevin thermostat method. As a result, the retention of hydrogen atom achieve steady state, and the CH4 was generated, which was not found MD simulations without a temperature control method. About 30 percent of injected hydrogen atoms are retained. CH4 yields has a peak at 600 K, which accords with experimental results. A dominant path of CH4 generation found by the present molecular dynamics simulation is as follows: a CH is detached from eroded surface and then it grows into CH4 adsorbing hydrogen atoms via CH2 and CH3. In addition, we propose the problem that the hydrogen atom retention and CH𝓍 yields depend on the thermal relaxation time in MD simulation using temperature control methods (© 2010 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

First-Principle Study of Atomic Hydrogen Interaction with a Fluorinated Corannulene Radical

In this work, we study fluorination effects on atomic hydrogen interactions with the fluorinated corannulene radical (C15H10F5), which was built as a model for a partially fluorinated nanotube (or fullerene). Complete active space self-consistent field and multi-reference configuration interaction methods are employed to calculate the potential energy surfaces for both ground and excited electronic states, and the R-matrix quantum dynamics method is used to investigate the atomic hydrogen transmission and reflection dynamics through the five-membered ring in the fluorinated corannulene radical, which includes resonance effects as well as non-adiabatic transitions between the ground and excited electronic states. We also investigate hydrogen adsorptions at two sites in the middle five-membered ring, namely, on top of a carbon atom and in the middle of a carbon–carbon bond. We found that on carbon-top site, the adsorption is almost barrierless, whereas in the middle bond site, there is a barrier to hydrogen adsorption.