Interactions between hydrogenated diamond surface and adsorbates with different concentration of NO2 molecules: A first‐principles study

To elucidate the effects of NO₂ and H₂O molecules on the surface conductivity of hydrogenated diamond film, models of various adsorbates containing different molecular ratio of NO₂ and H₂O on hydrogenated diamond (100) surfaces were constructed. The adsorption energies, equilibrium geometries of adsorbates, density of states, and atomic Mulliken populations were studied by using first‐principles method. The results showed that H₂O molecule in the adsorbate could weaken the interactions between the adsorbates and hydrogenated diamond surface significantly. Compared with H₂O molecule, NO₂ molecule relaxes more dramatically when adsorbed on hydrogenated diamond surface. In addition, density of states for C(100):H–2NO₂, C(100):H–NO₂, and C(100):H–NO₂ + H₂O systems are very similar to each other, which indicates an obvious peak at valence band maximum level for all the three samples. It can be attributed to mainly single occupied molecule orbital of NO₂ molecule and slightly C–H bond of C(100):H substrate. When the adsorbates contain one NO₂ and two H₂O molecules, the peak shifts slightly into valence band, but its intensity increases significantly. All the samples exhibit p‐type surface conductivity when adsorbed with pure NO₂ molecules, and the surface conductivity remains as H₂O molecules added into the NO₂ adsorbate layer. However, for oxygenated diamond surface, very week interactions generate between diamond surface and various adsorbates. All the oxygenated diamond (100) surfaces with various adsorbates containing different NO₂ and H₂O molecules on it exhibit an insulating property.     

Surface interaction of H2O and H2S onto Ca12O12 nanocluster: Quantum‐chemical analyses

To find the selectivity of H₂S, we explicate the adsorption properties of water (H₂O) and hydrogen sulfide (H₂S) molecules on the external surfaces of free Ca₁₂O₁₂ nanocages using the density functional theory method. More specifically, binding energies, natural bond orbital charge transfer, dipole moment, molecular electrostatic potential, frontier molecular orbitals, density of states, and global indices of activities are calculated to deeply understand the impacts of the aforementioned molecules on the electronic and chemical properties of Ca₁₂O₁₂ nanocages. Our theoretical findings indicate that although H₂O seems to be adsorbed in molecular form, the H₂S molecule is fully dissociated during the adsorption process because of the weak bond between sulfur and hydrogen atoms of the molecule. Interestingly, the highest occupied molecular orbital–lowest unoccupied molecular orbital energy gap of the nanocage is decreased by 1.87 eV upon H₂S adsorption, indicating that the electrical conductivity of the nanocage is strongly increased by the dissociation process. In addition, the values of softness and electrophilicity for the H₂S‐Ca₁₂O₁₂ complex are higher than those for the free nanocage. Our results suggest that Ca₁₂O₁₂ nanoclusters show promise in the adsorption/dissociation of H₂S molecules, which can be used further for designing its selective sensor.     

A boundary for reaction mechanisms within the transition metals interacting with nitrogen oxides is observed in DSIMS experiments

Summary Dynamic secondary ion mass spectrometry (DSIMS) investigations have been carried out with Cr, Mn, Fe, Co, Mo, Rh, W, Re, Os and Ir under 4 mPa N₂O, NO and 3 mPa NO₂ as reactant gases. Results indicate similar behaviour in adsorption for Cr, Mn, Fe, Mo, W on the one hand and for Co, Rh, Os and Ir on the other. For the first group of metals the nitrogen oxide molecules are always totally destroyed in adsorption whereas the second group shows evidence for surface compounds such as MeNO (Me=metal) indicating only a partial dissociation in the case of N₂O and NO₂, and molecular adsorption under NO respectively. Re does not belong uniquely to either group because it reacts with N₂O and NO₂ dissociatively whereas under NO only partial dissociation is observed.Abbreviations SIMS Secondary ion mass spectrometry - SSIMS Static SIMS - AES Auger electron spectroscopy - EELS Electron energy-loss spectroscopy - LEED Low energy electron diffraction - TDS Thermal desorption spectroscopy - XPS, UPS X-ray/Ultraviolet photoelectron spectroscopy     

Dissociative Adsorption of H2S on Li(110) Surface Using Density Functional Theory Calculations and Car-Parrinello Molecular Dynamics Simulations

The information concerning dissociative adsorption of H₂S on Li surface is inadequate and the mechanistic insight for its complete dissociation is yet to be explored. The present investigation aims to scrutinize the dissociative adsorption of H₂S on Li(110) surface using density functional theory calculations. The climbing image nudged elastic band calculation was employed to unveil the relative energy profiles for S−H dissociation. To elucidate the components of interaction energy responsible for stabilizing the adsorbed moieties on the surface, periodic energy decomposition analysis was performed. A Car-Parrinello molecular dynamics (CPMD) simulation was performed to understand the dynamic behaviour of H₂S on Li(110). Results vividly demonstrates: (i) partially dissociated product with perpendicular S−H is comparatively stable than the parallel SH, (ii) completely dissociated moieties H/H/S are the most stable among all, (iii) dissociation of first S−H is barrierless and the second S−H dissociation is a low energy barrier reaction, (iv) complete dissociation of H₂S occurs in a stepwise manner, (v) orbital and electrostatic contributions of the interaction energy plays a vital role in stabilizing the dissociated moieties, and (vi) stepwise dissociation of H₂S was further reinforced by CPMD.     

Spectroscopic Monitoring of the Acidity of Water Films on Ru(0001): Orientation‐Specific Acidity of Adsorbed Water

We examined the acid–base properties of water films adsorbed onto a Ru(0001) substrate by using surface spectroscopic methods in vacuum environments. Ammonia adsorption experiments combined with low‐energy sputtering (LES), reactive ion scattering (RIS), reflection–absorption infrared spectroscopy (RAIRS) and temperature‐programmed desorption (TPD) measurements showed that the adsorbed water is acidic enough to transfer protons to ammonia. Only the water molecules in an intact water monolayer and water clusters larger than the hexamer exhibit such acidity, whereas small clusters, a thick ice film or a partially dissociated water monolayer that contains OH, H₂O and H species are not acidic. The observations indicate the orientation‐specific acidity of adsorbed water. The acidity stems from water molecules with H‐down adsorption geometry present in the monolayer. However, the dissociation of water into H and OH on the surface does not promote but rather suppresses the proton transfer to ammonia.     

Zirconyl-containing microspheric silica gel surfaces

The adsorption properties of two samples of zirconyl-containing silica gels derived from zirconium oxychloride, polyetoxysiloxane oligomer 3% ZrOCl₂/SiO₂ (composite 1) and tetraetoxysilane 5% ZrOCl₂/SiO₂ (composite 2) were investigated by gas chromatography at low surface coverages. n-Alkanes and n-alkenes (C₆–C₈), C₆H₆ were used as test adsorbates, along with polar compounds whose molecules had different donor-acceptor interaction abilities. The dispersion and specific (electron-donor and electronacceptor) components of the energy of intermolecular interactions for the studied systems were determined from the experimental data on chromatographic retention. It was shown that composite 2 had a higher dispersion potential and higher surface energy characteristics of the surface’s electron-donating and electronacceptor centers, as compared to composite 1.     

First-principles study on the effect of arsenic impurity on oxidation of pyrite surfaces

Arsenic (As) frequently exists in pyrite (FeS₂) in the form of impurities. The oxidation behavior of As in FeS₂ is important in environmental science, mineral processing, and other related fields. The adsorption behaviors of H₂O and O₂ molecules on the As-bearing pyrite (100) surface (As FeS₂(100)) are studied using the density functional theory (DFT). The results show that As prefers the S site on the pyrite (100) surface (FeS₂(100)). In the absence of O₂, an isolated H₂O molecule does not dissociate when adsorbed at an iron (Fe) site and is repelled at an As site. Furthermore, the surface area around the As atoms exhibits a hydrophobic behavior. Adsorption energy analysis reveals that the presence of As atoms is unfavorable for the adsorption of H₂O molecules on the pure FeS₂ surface, and that the adsorption of H₂O molecules on the As FeS₂(100) is physical adsorption. In the absence of H₂O, it is suggested that the O₂ molecule easily dissociates on both the pure FeS₂(100) and As FeS₂(100). The adsorption of O₂ on the As-bearing surface is weaker than that on the pure FeS₂(100). For the co-adsorption of H₂O and O₂, the adsorption energy on the As-bearing surface is more negative than that on the pure surface. This indicates that the presence of As promotes surface oxidation. Additionally, two  OH and O (AsO or SO) or  O (Fe O) species are formed on the surface of pyrite when the H₂O molecule is dissociated.     

H2分子在LaFeO3表面吸附的第一性原理研究

基于密度泛函理论的第一性原理方法,通过计算表面能确定LaFeO₃(010)表面为最稳定的吸附表面,研究了H₂分子在LaFeO₃(010)表面的吸附性质。LaFeO₃(010)表面存在LaO和FeO₂两种终止表面,但吸附主要发生在FeO₂终止表面,由于LaFeO₃(010)表面弛豫的影响,使得凹凸不平的表面层增加了表面原子与H原子的接触面积,表面晶胞的纵向体积增加约2.5%,有利于H原子向晶体内扩散。研究发现,H₂分子在LaFeO₃(010)表面主要存在3种化学吸附方式:第一种吸附发生在O-O桥位,2个H原子分别吸附在2个O原子上,形成2个-OH基,这是最佳吸附位置,此时H原子与表面O原子的作用主要是H1s与O2p轨道杂化作用的结果,H-O之间为典型的共价键。H₂分子的解离能垒为1.542 eV,说明表面需要一定的热条件,H₂分子才会发生解离吸附;第二种吸附发生在Fe-O桥位,1个H原子吸附在O原子上形成1个-OH基,另一个H原子吸附在Fe原子上形成金属键;第三种吸附发生在O顶位,2个H原子吸附在同一个O原子上,形成H₂O分子,此时H₂O分子与表面形成物理吸附,H₂O分子逃离表面后容易形成氧空位。此外,H₂分子在LaFeO₃(010)表面还可以发生物理吸附。     

Effect of Hydrogen on O2 Adsorption and Dissociation on a TiO2 Anatase (001) Surface

The effect of hydrogen on the adsorption and dissociation of the oxygen molecule on a TiO₂ anatase (001) surface is studied by first‐principles calculations coupled with the nudged elastic band (NEB) method. Hydrogen adatoms on the surface can increase the absolute value of the adsorption energy of the oxygen molecule. A single H adatom on an anatase (001) surface can lower dramatically the dissociation barrier of the oxygen molecule. The adsorption energy of an O₂ molecule is high enough to break the O?O bond. The system energy is lowered after dissociation. If two H adatoms are together on the surface, an oxygen molecule can be also strongly adsorbed, and the adsorption energy is high enough to break the O?O bond. However, the system energy increases after dissociation. Because dissociation of the oxygen molecule on a hydrogenated anatase (001) surface is more efficient, and the oxygen adatoms on the anatase surface can be used to oxidize other adsorbed toxic small gas molecules, hydrogenated anatase is a promising catalyst candidate.     

Adsorption of water isotopomers H<Subscript>2</Subscript>O and D<Subscript>2</Subscript>O on hypercross-linked polystyrene MN-272

Adsorption of light and heavy water (H₂O and D₂O) on porous hypercross-linked polystyrene MN-272 was studied by gas chromatography. For the estimation of the properties of this polymer surface, n-alkanes (C6—C9), C_{6 6}, and polar compounds (CHCl₃, MeNO₂, MeCN, Me₂CO, EtCOOCH₃, Et₂O) were used as test adsorbates. The contributions of energies of dispersion and specific (donor-acceptor) intermolecular interactions to the total energy of adsorption were determined on the basis of experimental data on the retention of the sorbates. The electron-donor and electron-acceptor characteristics of the hypercross-linked polystyrene MN-272 surface were estimated. Hypercross-linked polystyrene MN-272 was found to be a weakly specific adsorbent with predomination of electron-donating properties. The adsorption isotherms of H₂O and D₂O were measured on this polymer at 50, 60, and 70 °C. The dependences of the isosteric heats of adsorption on the amount adsorbed were determined. The contribution of the energy of specific interactions to the total energy of adsorption for all polar adsorbates (except for acetone, light and heavy water) does not exceed 20%. Adsorption of H₂O on hypercross -linked polystyrene MN-272 is slightly weaker than that of D ₂O.     

Density Functional Theory Study for Adsorption of Oxygen and Water Molecules on 6H-SiC(0001) Surface

6H-SiC is an important semiconductor material. The 6H-SiC wafer is always exposed to a high-humidity environment and the effect from the absorbed water molecule and some relative adsorbates is not negligible. Here, the oxygen and water molecules absorbed on the 6H-SiC(0001) surface and the dissociation process were studied with density functional theory. On the 6H-SiC(0001) surface, absorbed O₂ is spontaneously dissociated into O^*, which is absorbed on a hollow site, and further transforms the 6H-SiC(0001) surface into SiO₂. The absorbed H₂O is spontaneously broken into OH^*and H^*, which are both absorbed on the top of the Si atom, and OH^* is further reversibly transformed into O^* and H^*. The H^* could saturate the dangling Si bond and change the absorption type of O^*, which could stabilize the 6H-SiC(0001) surface and prevent it from transforming into SiO₂.     

Surface Chemistry of Ga(CH3)3 on Pd(111) and Effect of Pre-covered H and O

The adsorption and decomposition of trimethylgallium (Ga(CH₃)₃, TMG) on Pd(111) and the effect of pre-covered H and O were studied by temperature programmed desorption spectroscopy and X-ray photoelectron spectroscopy. TMG adsorbs dissociatively at 140 K and the surface is covered by a mixture of Ga(CH₃)_x (x=1, 2 or 3) and CHx(a) (x=1, 2 or 3) species. During the heating process, the decomposition of Ga(CH₃)₃ on clean Pd(111) follows a progressive Ga-C bond cleavage process with CH₄ and H₂ as the desorption products. The desorption of Ga-containing molecules (probably GaCH₃) is also identi ed in the temperature range of 275-325 K. At higher annealing temperature, carbon deposits and metallic Ga are left on the surface and start to di use into the bulk of the substrate. The presence of precovered H(a) and O(a) has a signi cant effect on the adsorption and decomposition behavior of TMG. When the surface is pre-covered by saturated H₂, CH₄, and H₂ desorptions are mainly observed at 315 K, which is ascribed to the dissociation of GaCH₃ intermediate. In the case of O-precovered surface, the dissociation mostly occurs at 258 K, of which a Pd-O-Ga(CH₃)₂ structure is assumed to be the precusor. The presented results may provide some insights into the mechanism of surface reaction during the lm deposition by using trimethylgallium as precursor.     

Water Interaction with Iron Oxides

We present a mechanistic study on the interaction of water with a well‐defined model Fe₃O₄(111) surface that was investigated by a combination of direct calorimetric measurements of adsorption energies, infrared vibrational spectroscopy, and calculations bases on density functional theory (DFT). We show that the adsorption energy of water (101 kJ mol⁻¹) is considerably higher than all previously reported values obtained by indirect desorption‐based methods. By employing ¹⁸O‐labeled water molecules and an Fe₃O₄ substrate, we proved that the generally accepted simple model of water dissociation to form two individual OH groups per water molecule is not correct. DFT calculations suggest formation of a dimer, which consists of one water molecule dissociated into two OH groups and another non‐dissociated water molecule creating a thermodynamically very stable dimer‐like complex.     

5‐Aminonaphthalene‐1‐sulfonic acid and its manganese,nickel and cobalt salts

5‐Ammonionaphthalene‐1‐sulfonate monohydrate, C₁₀H₉NO₃S·H₂O, contains layers of zwitterionic molecules with the acidic sulfonic acid H atom transferred to the amine N atom. Within each layer, the charged groups (NH₃⁺ and SO₃⁻) are directed to the surface of the layer and are inverted on adjacent molecules. The naphthalene rings in a given layer are all parallel. The layers are held together by N—H...O and O—H...O hydrogen bonds involving the ammonium, sulfonate and water atoms. The Mn and Ni salts crystallize as fully aquated trihydrates, namely hexaaquamanagnese(II) bis(5‐aminonaphthalene‐1‐sulfonate) trihydrate, [Mn(H₂O)₆](C₁₀H₈NO₃S)₂·3H₂O, (II), and hexaaquanickel(II) bis(5‐aminonaphthalene‐1‐sulfonate) trihydrate, [Ni(H₂O)₆](C₁₀H₈NO₃S)₂·3H₂O, (III), in which layers of hexaaquametal(II) complexes alternate with layers of 5‐aminonaphthalene‐1‐sulfonate anions. The cations reside on twofold rotation axes and display regular octahedral coordination. The additional water molecules are found in the inorganic layer between the complex cations, one on a twofold axis and one in a general position. The anions are packed in a herring‐bone arrangement with the rings of neighboring rows of anions approximately 43° out of parallel. The NH₂ and SO₃⁻ groups line the surface of the layer, where they participate in numerous hydrogen bonds with the water molecules. Whereas the Mn and Ni salts are orthorhombic, the Co salt, hexaaquacobalt(II) bis(5‐aminonaphthalene‐1‐sulfonate) dihydrate, [Co(H₂O)₆](C₁₀H₈NO₃S)₂·2H₂O, (IV), crystallizes in a triclinic cell of similar dimensions, with the cations situated on centers of inversion. The overall packing is very similar to that of the Mn and Ni salts, with the main differences being the absence of the solvent water molecule on the special position and subtle modifications in the positioning of the anions within their layers. This series of salts is compared with those of the same metals with the 5‐aminonaphthalene‐2‐sulfonate and 4‐aminonaphthalene‐1‐sulfonate isomers, allowing for similarities and differences in packing to be discussed on the basis of the differing substitution of the naphthalene ring and, in some cases, differing degrees of hydration.     

Quantum chemical study of dissociation of H2 on C3H3V organometallic compound

We have studied H₂ adsorption on C₃H₃V organometallic compound using density functional method at B3LYP/LanL2Dz level of theory. It was found that H₂ molecule dissociates and adsorbed in dihydride form on this organometallic compound. Potential energy surface for H₂ dissociation process was obtained and different properties such as HOMO–LUMO gap, dipole moment, interaction energies between different molecules and atoms, vibrational frequencies, and atomic charges during the dissociation process were studied. It was found that the C₃H₃V(H₂) structure is most stable at H? V? H angle of 66.3°. Many‐body analysis was also carried out to determine the two‐body energies, three‐body energies, relaxation energy, and binding energy of the structures for each point on the potential surface. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

A DFT study of adsorption and decomposition of nitroamine molecule on Mg(001) surface

The adsorption and dissociation mechanism of NH₂NO₂ on the Mg surface have been investigated by the generalized gradient approximation of density functional theory. Calculations employ a supercell (3 × 3 × 3) slab model and three-dimensional periodic boundary conditions. The strong attractive force between oxygen and Mg atoms induces the N–O bond of the NH₂NO₂ to decompose. The dissociated oxygen atoms and radical fragment of NH₂NO₂ oxidize readily Mg atoms. The largest adsorption energy is ?860.5 kJ/mol. The largest charge transfer is 3.76 e from surface Mg atoms to fragments of NH₂NO₂. The energy barriers of N–O bond dissociation are in a range of 11.6–36.5 kJ/mol. The adsorption energy of NH₂NO₂ on the Mg surface compensates the energy needed for the N–O bond dissociation.     

Nb(110)表面氧原子覆盖度对氧分子解离的影响

用基于密度泛函理论的第一性原理方法研究了Nb(110)表面氧原子覆盖度分别为0.25、0.50、0.75 和1.00单层时对氧分子解离的影响. 结果表明, 在氧原子覆盖度不大于0.50单层时, 由于氧分子和表面铌原子的较强相互作用, 使它们能够自发解离. 然而在氧原子覆盖度为0.75单层时, 氧分子只能够在未占据的洞位附近解离, 同时发生严重的晶格畸变. 在形成一个氧原子单层后(1.00 单层), 氧分子只能弱吸附在Nb(100)表面上,此时氧原子向内扩散成为氧分子继续解离的速率决定步骤. 这些结果从理论上解释了在形成一个氧原子单层后, Nb(110)表面氧分子吸收速率迅速下降的原因.     

二维TiC 层表面H2的化学吸附与物理吸附

第一性原理计算研究发现由于二维TiC 单原子层具有高的比表面积与大量的暴露在表面的Ti 原子,其是一种非常有潜力的储氢材料. 计算结果显示H₂可以在二维TiC 单原子层表面进行物理吸附与化学吸附. 其中化学吸附能为每个氢分子0.36 eV,物理吸附能是每个氢分子0.09 eV. 覆盖度为1和1/4层（ML）时,H₂分子在二维TiC 单原子层表面的离解势垒分别为1.12 和0.33 eV. 因此,除了物理吸附与化学吸附,TiC 表面还存在H单原子吸附. 最大的H₂储存率可以达到7.69%（质量分数）. 其中,离解的H原子、化学吸附的H₂、物理吸附的H₂的储存率分别为1.54%、3.07%、3.07%. 符合Kubas吸附特征的储存率为3.07%. 化学吸附能随覆盖度的变化非常小,这有利于H₂分子的吸附与释放.     

Stability of molecular form of HCl in water vapor: A computer simulation

The free energy and entropy of the dissociation of HCl molecule into ions in water vapor, HCl(H₂O) _n + mH₂O → H₃O + (H₂O) _n+m -1Cl^?, were calculated. The dependences of various parameters on the interionic distance at 273 K and various vapor pressures were obtained. A detailed model taking into account unpaired covalent-type interactions, polarization interactions, charge transfer effect, and hydrogen bonds was applied. The numerical values of the parameters were reconstructed from the experimental data on the free energy and enthalpy of the first reactions of addition of vapor molecules to ions, and also from the results of quantum-chemical calculations of the energy and geometry of locally stable configurations of clusters HCl(H₂O) _n . Despite lower internal energy of the dissociated state, the molecular form is absolutely stable in clusters of water molecules. The dissociated state is relatively stable. Accumulation of unrecombined ion pairs in clusters is possible with a decrease in the temperature to 200 K.     

O2 dissociative adsorption on the Cu‐, Ag‐, and W‐doped Al(111) surfaces from DFT computation

The O₂ adsorption and dissociation on M‐doped (M = Cu, Ag, W) Al(111) surface were studied by density functional theory. The adsorption energy of adsorbate, the average binding energy and surface energy of Al surface, and the doping energy of doping atom were calculated. All the doped atoms can be stably combined with Al atoms, while being slightly embedded in the surface to a certain depth. The TOP‐type surfaces are the most stable doped surfaces for O₂ adsorption, which is related to the orbital hybridization between the adsorbate and the surface atoms, the electronegativity, and the orbital energy level of the doping atoms. Moreover, the O atoms and doping atoms contribute significantly to the density of states (DOS), especially the O‐p orbital electrons and the d orbital electrons of doping atoms. The degree of O₂ dissociation is related to the doping atoms on Al surfaces, and the doping atoms actually resist the dissociation of O₂. W atoms have the best resistance effect on the O₂ dissociation as compared with Cu and Ag atoms, especially W‐1NN surface, which has both large barrier energy and reaction energy.