DFT study of oxygen adsorption on modified nanostructured gold pyramids

Periodic DFT calculations are used to predict and investigate the adsorption behavior of molecular oxygen on Au, Au/Pt, and Pt surfaces. To obtain an array of pyramids containing surface atoms with the lowest possible coordination number, a nano-modified surface consisting of a symmetrically "modified" (100) surface was used. The effect of atom substitution (organized alloying) is investigated. The adsorption of molecular oxygen on a pure gold pyramid is exothermic by 0.77 eV for the end-on adsorption mode. In the case of a pure platinum pyramid, the end-on adsorption mode was found to dissociate; however, a side-on geometry was encountered with an energy of adsorption of 2.3 eV. This value is in line with the fact that the adsorption energy of small molecules does not vary much on Pt surfaces with different indices. Additionally, some geometrically related trends of the surface deformation in relation to its composition and after adsorption of molecular oxygen are highlighted.     

Methane and carbon dioxide adsorption on edge-functionalized graphene: A comparative DFT study

With a view towards optimizing gas storage and separation in crystalline and disordered nanoporous carbon-based materials, we use ab initio density functional theory calculations to explore the effect of chemical functionalization on gas binding to exposed edges within model carbon nanostructures. We test the geometry, energetics, and charge distribution of in-plane and out-of-plane binding of CO(2) and CH(4) to model zigzag graphene nanoribbons edge-functionalized with COOH, OH, NH(2), H(2)PO(3), NO(2), and CH(3). Although different choices for the exchange-correlation functional lead to a spread of values for the binding energy, trends across the functional groups are largely preserved for each choice, as are the final orientations of the adsorbed gas molecules. We find binding of CO(2) to exceed that of CH(4) by roughly a factor of two. However, the two gases follow very similar trends with changes in the attached functional group, despite different molecular symmetries. Our results indicate that the presence of NH(2), H(2)PO(3), NO(2), and COOH functional groups can significantly enhance gas binding, making the edges potentially viable binding sites in materials with high concentrations of edge carbons. To first order, in-plane binding strength correlates with the larger permanent and induced dipole moments on these groups. Implications for tailoring carbon structures for increased gas uptake and improved CO(2)/CH(4) selectivity are discussed.     

Protein adsorption on a nanoparticle with a nanostructured surface

In the present study, the adsorption of a protein on a nanoparticle with a nanostructured surface, which is created using successively patterned Gaussian pillars (GPs), is simulated by considering the charge regulation within the electrical double layer of a silica nanoparticle (NP). Namely, the mathematical models for the adsorption mechanism, such as classical Langmuir model, extended Langmuir model, and two-state model, are coupled with charge regulation model. By this means, size and pH variables are able to included to the calculations. Moreover, free space, surface curvature, and conformational changes are also taken into account. For systematic investigation, the solution's pH, surface charge density, initial protein concentration, electrostatic charge of the protein, and the diameter of the spherical NP are varied. As a result, the vital properties of a nanoparticle, such as protonation/deprotonation, polarization, topography, and morphology, are considered in the current simulations. The surface charge density and surface chemistry change with NP and GP sizes. The present results reveal that the protein adsorption on an NP with a smooth surface reaches a faster complete surface coverage than an NP with a nanostructured surface. Both states of conformational changes are also affected by the presence of the GP.     

Carbon dioxide adsorption on carbon nanomaterials

The adsorption of CO₂ on a number of activated carbons, thermal carbon black, and oxide materials at 195 K was studied using static and dynamic techniques. The landing surface areas ω(CO₂) ≈ 0.19 nm² on thermal carbon black and the absolute values of sorption for P/P ₀ < 0.4 were determined. The density of adsorbed CO₂ in the micropore volume was estimated at ρ(CO₂) = 0.91 g/cm³. It was demonstrated that the previously found effect of a weakening of the sorption interaction of nitrogen molecules with thin-walled materials (which manifested itself in an analysis of sorption isotherms by a comparative method) was pronounced to a lesser degree for the sorption of CO₂. At the same time, the presence of supermicropores in activated carbon samples resulted in overestimated values of surface areas. A dynamic method was proposed to measure the spectra of CO₂ desorption at 195–260 K using a SORBI-MS system for evaluating the binding energy of sorbate molecules with the surface.     

Organic probe molecule adsorption on extended Au(111) surface: a theoretical DFT study

Research on Chemical Intermediates - The cluster approach has been applied to mimic the interactions of probe trans-1,2-bis-(4-pyridyl) ethylene on a gold surface with the aim of discriminating the...     

Atomic carbon adsorption on Ni nanoclusters: a DFT study

Atomic carbon is a key intermediate interacting with transition metal clusters during the growth of carbon nanotube (CNT). Present density functional calculations studied the initial carbon adsorption on four Ni nanoclusters (N₁₃, N₁₅, N₃₈, and N₅₅). Our results show that carbon atoms preferentially adsorb on high-coordination sites, and carbon adsorption energies are larger on smaller Ni clusters. Ni cluster reconstruction plays an important role in creating more stable subsurface adsorption sites. The migration of adsorbed carbon atom on the surface threefold hollow site into the underlying interstitial subsurface positions is thermodynamically and kinetically feasible. The results indicate that the investigation of CNT growth mechanism should include both surface and subsurface carbon atoms, coupled with surface reconstruction of Ni nanoclusters.     

DFT study of the adsorption of microsolvated glycine on a hydrophilic amorphous silica surface

Density functional theory (DFT) periodic ab initio molecular dynamics calculations are used to study the adsorption of gaseous and microsolvated glycine on a hydroxylated, hydrophilic silica surface. The silica model is presented and the interaction of water with surface silanols is studied. The heat of interaction of water is higher with the associated silanols (be they terminal or geminal ones) studied here than with isolated silanols presented in past works. Glycine is stabilized in a parallel mode on the hydroxylated surface. Terminal silanols do not allow the stabilization of the zwitterionic form, whereas geminal silanols do. Molecular dynamics (MD) first-principle calculations show that microsolvated zwitterion glycine directly binds through the carboxylate function to a surface silanol rather than through water molecules. The adsorption mode, whether with or without additional water molecules, is parallel to the surface. The ammonium function does not interact directly with the silanol groups but rather through water molecules. Thus, the carboxylate and ammonium functions exhibit two different reactivities towards silanols. The calculated free energies, taking into account the chemical potentials of water and glycine in the gas phase, suggest the existence of a thermodynamic domain in which the glycine is present in the gas phase as well as strongly adsorbed on specific sites of the surface.     

Hydrogen adsorption on Ce/SWCNT systems: a DFT study

The adsorption of H(2) on Ce doped single-walled carbon nanotubes (SWCNT) and graphene are investigated by using density functional theory. For both systems, it is found that Ce preferentially occupies the hollow site on the outside. The results indicate that Ce/SWCNT system is a good candidate for hydrogen storage where six H(2) per Ce can be adsorbed and 5.14 wt% H(2) can be stored in the Ce(3)/SWCNT system. Among metal-doped SWCNTs, Ce exhibits the most favorable hydrogen adsorption characteristics in terms of the adsorption energy and the uptake capacity. The hybridization of the Ce-4f and Ce-5d orbitals with the H orbital contributes to the H(2) binding where Ce-4f electrons participate in the hybridization due to the instability of the 4f state. The interaction between H(2) and Ce/SWCNT is balanced by the electronic hybridization and electrostatic interactions. Curvature of SWCNT changes the size of the binding energy of Ce and C and the adsorption energy of H(2) on Ce.     

Oxygen adsorption induced superhydrophilic-to-superhydrophobic transition on hierarchical nanostructured CuO surface

Hierarchical nanostructured CuO surface was embellished to amplify the wettability. The pristine superhydrophilic CuO surface spontaneously transited to be superhydrophobic after exposed in air at room temperature for about 3 weeks. The wettability change is attributed to the adsorption of oxygen molecules on the topmost layer according to the surface chemical analysis. The adsorbed oxygen molecules could be removed by dipping the sample into l-Ascorbic acid solution for 10 s, leading to the recovery of the pristine superhydrophilicity.     

Carbon dioxide hydrogenation catalyzed by a ruthenium dihydride: a DFT and high-pressure spectroscopic investigation

Reaction pathways during CO(2) hydrogenation catalyzed by the Ru dihydride complex [Ru(dmpe)(2)H(2)] (dmpe=Me(2)PCH(2)CH(2)PMe(2)) have been studied by DFT calculations and by IR and NMR spectroscopy up to 120 bar in toluene at 300 K. CO(2) and formic acid readily inserted into or reacted with the complex to form formates. Two formate complexes, cis-[Ru(dmpe)(2)(OCHO)(2)] and trans-[Ru(dmpe)(2)H(OCHO)], were formed at low CO(2) pressure (<5 bar). The latter occurred exclusively when formic acid reacted with the complex. A RuHHOCHO dihydrogen-bonded complex of the trans form was identified at H(2) partial pressure higher than about 50 bar. The trans form of the complex is suggested to play a pivotal role in the reaction pathway. Potential-energy profiles along possible reaction paths have been investigated by static DFT calculations, and lower activation-energy profiles via the trans route were confirmed. The H(2) insertion has been identified as the rate-limiting step of the overall reaction. The high energy of the transition state for H(2) insertion is attributed to the elongated Ru--O bond. The H(2) insertion and the subsequent formation of formic acid proceed via Ru(eta(2)-H(2))-like complexes, in which apparently formate ion and Ru(+) or Ru(eta(2)-H(2))(+) interact. The bond properties of involved Ru complexes were characterized by natural bond orbital analysis, and the highly ionic characters of various complexes and transition states are shown. The stability of the formate ion near the Ru center likely plays a decisive role for catalytic activity. Removal of formic acid from the dihydrogen-bonded complex (RuHHOCHO) seems to be crucial for catalytic efficiency, since formic acid can easily react with the complex to regenerate the original formate complex. Important aspects for the design of highly active catalytic systems are discussed.     

Uranyl adsorption on solvated edge surfaces of pyrophyllite: a DFT model study

In a computational study we addressed the adsorption of uranyl UO(2)(2+) on solvated (110) and (010) edge surfaces of pyrophyllite, applying a density functional approach to periodic slab models. We explored bidentate adsorption complexes on various partially deprotonated adsorption sites: octahedral Al(O,OH), tetrahedral Si(O,OH), and mixed AlO-SiO. Aluminol sites were determined to be most favorable on the (110) surface of pyrophyllite, while on the (010) surface mixed AlO-SiO sites are preferred. The structural parameters of all low-energy complexes on both surfaces agree rather well with EXAFS results for the structurally similar mineral montmorillonite. We calculate the average U-O distance to surface and aqua ligand oxygen atoms to increase with the increasing coordination number of uranyl whereas EXAFS results indicate the opposite trend. According to our results, several adsorption species, with different coordination numbers on different edge faces, may coexist on clay minerals. This computational finding rationalizes why earlier spectroscopic studies indicated the existence of more than one adsorption species, whereas a single type of adsorption complex was suggested from most EXAFS results.     

甲氧基在Rh(111)表面吸附的密度泛函研究

采用密度泛函理论(DFT)的B3LYP方法,以原子簇Rh13(9,4)为模拟表面,在6-31G(d,p)与Lanl2dz基组水平上,对甲氧基在Rh(111)表面的四种吸附位置(fcc、hcp、top、bridge)的吸附模型进行了几何优化、能量计算、Mulliken电荷布局分析以及前线轨道的计算。结果表明,当甲氧基通过氧与金属表面相互作用时,在bridge位的吸附能最大,吸附体系最稳定,在top位转移的电子数最多;吸附于Rh(111)面的过程中C—O键被活化,C—O键的振动频率发生红移。     

Carbon dioxide adsorption on the microporous ACC carbon adsorbent

Adsorption isotherms of carbon dioxide on the microporous ACC carbon adsorbent and the adsorption deformation of the adsorbent were measured. The heats of adsorption at temperatures raising from 243 to 393 K and pressures from 1 to 5⋅10⁶ Pa were measured. In the low-temperature region (243 K), an increase in the amount adsorbed is accompanied by adsorbent contraction, and at high micropore fillings (a > 10 mmol g⁻¹) the ACC carbon adsorbent expands. At high temperatures, adsorbent expansion is observed in the whole region of micropore filling. At 243 K in the low filling region (a < 1 mmol g⁻¹), the heat of adsorption decreases smoothly from 27 to 24 kJ mol⁻¹. The heat of adsorption remains virtually unchanged in the interval 2 mmol g⁻¹ < a < 11 mmol g⁻¹ and then decreases to 8 kJ mol⁻¹ at a = 12 mmol g⁻¹. Taking into account the nonideal character of the gas phase and adsorbent deformation the heats of adsorption are strongly temperature-dependent in a region of high pressures. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1331–1335, June, 2005.     

Olefin adsorption on silica-supported silver salts--a DFT study

Recent experiments have shown that silver salts supported on mesoporous silicas display excellent adsorption selectivities of ethylene over ethane and propylene over propane. Employing the techniques of density functional theory, we have investigated the fundamental bases of this separation process by examining silver salts dispersed on model silica surfaces. Our model system includes Ag+ cations, their counteranions, silica supports, and surface silanols. Both adsorption geometries and energetics of ethylene and propylene were explored. Our results indicate that the nature of the Ag-olefin interaction is predominantly hybridization between Ag d and olefin pi states, which is supported by analyses of electron density difference plots and density of states. The counteranions, such as NO3- were found to interact strongly with surface silanols through multiple hydrogen bonds but have limited effect on the adsorption energy of olefins on the Ag+ cations. The current work supports recent experiments, which indicate that Ag-salt/silica may be a very promising adsorbent for olefin/paraffin separation.     

金镍六原子团簇吸附CO的密度泛函研究

在UBP86/LAN2DZ水平上计算了金镍二元团簇(AunNi6-n,n=0～6)吸附CO的稳定构型和相关性质.计算结果表明,AunNi6-nCO团簇的最低能量结构是在AunNi6-n团簇最低能量结构或亚稳态结构基础上吸附CO分子而形成.优化结构中C-O键长表明,吸附后的CO没有解离,即CO分子在AunNi6-n团簇表...     

Coverage-dependent adsorption of atomic sulfur on Fe(110): a DFT study

Adsorption of atomic sulfur at different coverages on the Fe(110) surface is examined using density functional theory (DFT) in order to investigate the effect that adsorbate-adsorbate interactions may have on the surface properties. S is adsorbed in the high-symmetry adsorption sites: 4-fold hollow, bridge, and atop sites in the following surface arrangements: c(2 x 2) and p(1 x 1) which correspond to coverages of 1/2 and 1 monolayer, respectively. The binding energy, work function change, adsorption geometry, charge density distribution, magnetic properties, and density of states are examined and compared to our previous study of S adsorbed at 1/4 monolayer coverage and p(2 x 2) arrangement [Spencer et al. Surf. Sci. 2003, 540, 420]. It was found that S forms polar covalent bonds to the surface. The bonding goes from being S-Fe dominated at the low coverages to being S-S dominated at the higher coverages where the S atoms are located closer together on the surface and interact with each other.     

A DFT study of acetonitrile adsorption and decomposition on the TiO2 (110) surface

The adsorption and decomposition of acetonitrile on the TiO₂ (110) surface have been investigated with first principles calculations. Our results reveal that both C?N and C? C bonds of acetonitrile become weakened after adsorption. Acetonitrile behaves as an electron donor, and electrons transfer from acetonitrile to substrate is obvious. The reaction mechanism of further decomposition of acetonitrile on TiO₂ (110) surface is also investigated, and the result shows that acetonitrile can decompose into CH₃ and CN fragments and form OCH₃ and NCO groups on the TiO₂ (110) surface, which consists with the experimental results. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

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.     

CO adsorption on CoMo and NiMo sulfide catalysts: a combined IR and DFT study

Experimental IR spectra of carbon monoxide adsorbed on a series of Mo/Al2O3, CoMo/Al2O3, and NiMo/Al2O3 sulfided catalysts have been compared to ab initio DFT calculations of CO adsorption on CoMo and NiMo model surfaces. This approach allows the main IR features of CO adsorbed on the sulfide phase to be assigned with an uncertainty of 15 cm(-1). On the CoMo system, the band at 2070 cm(-1) is specific of the promotion by Co and is assigned to CO interacting either with a Co atom or with a Mo atom adjacent to a Co atom. On the NiMo system, CO adsorption on Ni centers of the promoted phase leads to a high-wavenumber band at approximately 2120 cm(-1) that strongly overlaps the band at 2110 cm(-1) characteristic of nonpromoted Mo sites. For NiMo and CoMo catalysts, broad shoulders at low wave numbers (below 2060 cm(-1)) are characteristic of Mo centers adjacent to promoter atoms, indicating a partial decoration of the MoS2 edges by the promoter.