Theoretical Study Of Adsorption Research Articles

Theoretical study of adsorption of ethanol and acetone molecules by perfect and defected h-BN nanosheet

Abstract Density functional theory-dispersion corrected (DFT-D3) calculations was used to provide an understanding of interaction strength of various solvents (ethanol, acetone and water) with hexagonal-boron nitride (h-BN) nanosheet. To evaluate the adsorption ability of h-BN nanosheet in considered solvents, the binding characteristics of interacting entities, the charge transfer, the electronic structure, and the specific role of atom in molecule (AIM) analyses were investigated. The accuracy of our implemented method was validated against experimental and theoretical results at the coupled cluster with a full treatment singles and doubles (CCSD(T)) level. It was found that perfect h-BN could not strongly adsorb the selected solvents, energy of adsorption (Eads) of −4 to −8 kcal/mol. Adsorption strength, however, was enhanced significantly upon the introducing defects in the h-BN lattice with Eads of about −20 kcal/mol for ethanol and −12 kcal/mol for water adsorption as the consequence of strong interaction between polar solvents adsorbates and h-BN surface.

A theoretical study of adsorption on iron sulfides towards nanoparticle modeling.

Surface modification of zero-valent iron (nZVI) nanoparticles, which are frequently used in the removal of chlorinated hydrocarbons from contaminated groundwater, can increase their surface stability without significant loss of reactivity. Sulfidation is a process during which thin iron sulfide phases are formed on nZVI particles. In this work, the adsorption capability of two iron sulfide minerals (mackinawite and pyrite) and ZVI with respect to two small polar molecules (H2O and H2S) and trichloroethylene (TCE) was modeled by using the quantum mechanics (QM) approach. High-level QM methods used on cluster models helped in benchmarking and validation of density functional theory methods used on periodic slab models of the (001) surfaces of iron sulfides and the (111) surface of ZVI. This careful computational treatment was necessary for achieving reliable results because modeled iron containing compounds represent computationally demanding systems. The results showed that adsorption was strongly affected by surface topology, accessibility of surface sites, and the shape of adsorbed molecular species. The mackinawite surface is practically hydrophobic having weak interactions with polar molecules (about -5/-6 kcal mol-1), in contrast to the surfaces of pyrite and ZVI (adsorption energies are about three times larger). On the other hand, the adsorption of weakly polar planar TCE molecule is relatively strong and similar for all three surfaces (in the range of -11 to -17 kcal mol-1). Moreover, it was shown that the dominant component of the adsorption energy of TCE had originated from dispersion interactions, which were less important for small polar molecules.

Importance of the interaction adsorbent –adsorbate in the dyes adsorption process and DFT modeling

Abstract The objective of this work is to highlight the importance of the textural and functional groups present in the carbon surface for the adsorption process of basic, acid and reactive dyes through experimental and theoretical adsorption studies. The adsorption of dyes on activated carbon prepared from peach endocarp shell by simple carbonization (CP) and chemical activation of the precursor by impregnation with CaCl2 (CPCa) were compared with theoretical calculations under the DFT framework. The carbonaceous materials were characterized with TGA, FTIR, XRD, SEM/EDX and the textural parameters by N2 isotherms. The adsorbents used in this study presented a higher adsorption capacity for the basic dye when compared with the reactive and acid dyes evaluated. The CPCa carbon had a higher adsorption capacity and surface area (943 m2 g−1) than the CP carbon. The adsorptive properties of the material obtained are a result of the combination of the high specific surface area of the carbon and the presence of CaCO3, Ca(OH)2 and the abundance of oxygenated moieties on the material’s surface. The theoretical calculation showed that the adsorption stability of anionic dyes on adsorbent is due to the interplay of dispersion, charge transfer and electrostatic intermolecular effects; this behavior is not sustained for the cationic dyes, where the adsorption stability is entirely reached by dispersion forces. These results support the relevance of the functionalization of the carbon surface.

Theoretical study of adsorption and dehydrogenation of C2H4 on Cu(410)

Adsorption and dehydrogenation of ethylene on Cu(410) surface are investigated with first-principles calculations and micro-kinetics analysis. Ethylene dehydrogenation is found to start from the most stable π-bonded state instead of the previously proposed di-σ-bonded state. Our vibrational frequencies calculations verify the π-bonded adsorption at step sites at low coverage and low surface temperature and di-σ-bonded ethylene on C−C dimer (C2H4-CC) is proposed to be the species contributing to the vibrational peaks experimentally observed at high coverage at 193 K. The presence of C2H4-CC indicates that the dehydrogenation of ethylene on Cu(410) can proceed at temperature as low as 193 K.

Theoretical study of adsorption of organic phosphines on transition metal surfaces

ABSTRACTThe adsorption properties of organic phosphines on transition metal (TM) surfaces (Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Ir, Pt, and Au) have been studied to explore the possibility of building novel heterogeneous chiral catalytic systems based on organic phosphines. Preferred adsorption sites, adsorption energies and surface electronic structures of a selected set of typical organic phosphines adsorbed on TM surfaces are calculated with density-functional theory to obtain a systematic understanding on the nature of adsorption interactions. All organic phosphines considered are found to chemically adsorb on these TM surfaces with the atop site as the most preferred one, and the TM–P bond is formed via the lone-pair electrons of the P atom and the directly contacted TM atom. These findings imply that it is indeed possible to build heterogeneous chiral catalytic systems based on organic phosphines adsorbed on TM surfaces, which, however, requires a careful design of molecular structure of organic phosphines.

A theoretical study of adsorption of tyrosol derivatives as antioxidant drugs on the boron nitride (BN)-nanotube (9, 0) surface

ABSTRACTThe delivery of tyrosol by BN-nanotube was investigated by density functional theory in the gas phase. The antioxidant activity of tyrosol was investigated in the gas phase and water. The effects of NHMe, OMe, and tert-butyl substituents on the antioxidant activity and delivery of tyrosol were investigated. Results showed that BN-nanotube interacted with tyrosols effectively and adsorption of tyrosol derivatives on BN-nanotube were exothermic and possible from the energetic viewpoint. Also, replacement of the NHMe group at the x position of tyrosol was suitable scheme the sensitivity of tyrosol toward BN-nanotube surface. The NHMe and OMe substitutions decreased the BDE and IP values and increased the antioxidant activity of tyrosol. The BDE an IP values of tyrosols have linear dependencies with Ead values of tyrosols. These linear dependencies proposed the novel tyrosol derivatives with high level of antioxidant activity.

Theoretical study of adsorption and dissociation of NH3 on pentanuclear Fe(111) surface

Theoretical study regarding the adsorption and dissociation of NH3 molecule on Fe(111) surface has been carried out. The method used was DFT-B3LYP, and the basis sets used were ECP and 6-311G**. This research aimed at giving the theoretical understanding of adsorption and dissociation of NH3 molecule on Fe(111) surface. The adsorption and dissociation were studied based on the energetic parameter, bond length, electron population, vibration and orbital interaction. The result of theoretical calculation revealed that the on top position is the interaction position with the minimum energy for the adsorption of NH3 molecule on Fe(111) surface. The analysis of electron population of the two composing molecular orbitals indicated that the transfer of electron has an important role in the mechanism of adsorption. The visualization of molecular orbital showed that the transfer of electron occurred in the electron pairs of the interacting orbital. Relating to the adsorption mechanism and the overlapping of interaction orbitals, NH3 molecule provides the Highest Occupied Molecular Orbital (HOMO) as the interaction pair for the Lowest Unoccupied Molecular Orbital (LUMO) on Fe surface. The insignificant difference between the oxidation state of N and H atoms as well as the higher hemolytic N-H bond dissociation energy (compared to heterolytic dissociation) cause the adsorption mechanism of NH3 on Fe(111) model to occur through homolytic-dissociative chemisorption.

Electrochemical and theoretical studies of adsorption and corrosion inhibition of aniline violet compound on carbon steel in acidic solution

The inhibition ability of 4-[bis[4-(dimethylamino)phenyl]methyl]-N,N-dimethylaniline (Mv10B) on carbon steel in 1 M HCl solution was studied by electrochemical techniques. Mv10B inhibited carbon steel corrosion in 1 M HCl solution significantly and the inhibition efficiency increased with Mv10B concentration. Potentiodynamic polarization results showed that Mv10B was a mixed-type inhibitor. The adsorption of Mv10B on steel surface followed Langmuir adsorption isotherm. The inhibition performance of Mv10B was also evidenced by AFM images. Computational investigations of studied inhibitor are performed by using HF method with 6-31++G(d,p) and 6-311++G(d,p) basis sets.

An experimental and theoretical study of adsorption of aromatic alcohols and amines on graphitized thermal carbon black

The Henry constants have been calculated for nonrigid molecules of benzyl alcohol, 1-phenylethanol, benzylamine, and 1-phenylethylamine on graphitized thermal carbon black (GTCB). It has been shown that remarkable changes in geometry for stable conformers in the adsorbed state depend on the height of the barrier to internal rotation around the labile bond and the presence of an intermolecular hydrogen bond. The parameters of atom-atom potential (AAP) characterizing the intermolecular hydrogen bond of the OH-group with π-electrons of GTCB with the assumption of direction have been determined. The experimental values of the Henry constant have been compared with the results of a molecular statistical calculation for the aromatic alcohols and amines being studied on GTCB.

Electrochemical and Theoretical Studies of Adsorption and Corrosion Inhibition of N,N′-Bis(2-hydroxyethoxyacetophenone)-2,2-dimethyl-1,2-propanediimine on Low Carbon Steel (API 5L Grade B) in Acidic Solution

Schiff base N,N′-bis(2-hydroxyethoxyacetophenone)-2,2-dimethyl-1,2-propanediimine (H2(hppnptn)) as corrosion inhibitor for API 5L grade B low carbon steel in hydrochloric acid solutions has been studied using electrochemical techniques and surface techniques. Results showed that the inhibition occurs through adsorption of the inhibitor molecules on the metal surface. Thermodynamic parameters for adsorption and activation processes were determined. Polarization data indicated that this compound acts as mixed-type inhibitors, and the adsorption isotherm basically obeys the Langmuir adsorption isotherm. The calculations of reactivity indices of H2(hppnptn) such as the localization of frontier molecular orbitals, EHOMO, ELUMO, energy gap (ΔE), dipole moment (D), hardness (η), softness (σ), the fractions of electrons transferred (ΔN), electrophilicity index (ω), total energy change (ΔET), and natural bond orbital (NBO) charge distributions together with local reactivity by means of Fukui indices were used to explain the electron transfer mechanism between the H2(hppnptn) molecules and the steel surface.

The influence of fluctuation inhomogeneity in a volume phase on one-layer adsorption

A theoretical study of adsorption was performed using a model of two-dimensional lattice liquid. One-layer adsorption from a binary solution was considered. As a result, the temperature dependence of the coefficient of the degree of filling close to the critical binary solution stratification point was found taking into account nonlocal liquid properties. Correlation effects that arise close to the critical point were shown to influence adsorption substantially.

Theoretical Study of Adsorption and Diffusion of Group IIIA Metals on Si(111)

Adsorption of group IIIA elements (M = B, Al, Ga, and In) on a model Si(111) surface was studied by density functional theory calculations. Eight stable structures were determined for the M adsorbed species. The incorporation of the M atoms on the Si surface is investigated, and the energy barriers for the incorporation are calculated. The binding energy of the lowest calculated minimum of chemisorbed M at Si(111), after correcting for the basis set superposition error, is 6.3 (B, S5 substitutional site), 3.4 (Al, T4 adsorption site), 2.9 (Ga, T4), and 2.5 (In, T4) eV. Our results are in good agreement with previous experimental work, where available. The activation energy barrier from the T4 to the H3 adsorption site is 1.2 (Al), 1.1 (Ga), and 0.7 eV (In); the activation energy barrier from the lowest energy structure with M connected to the surface at a dangling bond to a precursor of T4 is 0.5 (B), 1.6 (Al), 1.7 (Ga), and 1.9 eV (In).

Theoretical study of adsorption and dissociation of NH3 on the Ir{110}(1×2) surface

The adsorption and dissociation of NH3 on Ir{110}(1×2) have been investigated using the density-functional calculations at a coverage of 0.25 ML. The adsorption sites, energy, and geometries were obtained for NH3, NH2, and H adsorptions on the surface. The transition state for NH3 dissociation on Ir{110}(1×2) was also identified. It was found that NH3 is adsorbed preferentially at the ridge atop site, while NH2 and H are adsorbed at the ridge bridge site. The activation barrier of NH3 dissociation is 78.4 kJ/mol, which is very close to the NH3 adsorption energy of 90.0 kJ/mol. This indicates that the desorption and dissociation of NH3 on Ir{110}(1×2) are very competitive, which is consistent with the recent experimental results.

Theoretical study of adsorption on activated carbon from a supercritical fluid by the SLD–ESD approach

The simplified local density (SLD) theory is combined with the Elliott, Suresh, Donohue (ESD) equation of state to model adsorption of solutes from supercritical carbon dioxide onto activated carbon. The model is fit to adsorption isotherms of toluene + CO 2 and benzene + CO 2 over wide temperature and pressure ranges by adjusting only two temperature-independent parameters for each binary. We present a systematic analysis of adsorption characteristics for finite and infinite dilution conditions in supercritical CO 2 by selecting the toluene/CO 2 as a model system. Competitive adsorption between solvent and solute is investigated. The effects of temperature, pressure, bulk solute concentration, and the adsorbent structure size on the adsorption behavior are presented.

Hydrogen adsorption energies on bimetallic overlayer systems at the solid–vacuum and the solid–liquid interface

Atomic hydrogen adsorption energies on bimetallic overlayer systems have been determined by periodic density functional theory calculations within the generalized gradient approximation. On the pseudomorphic Pd/Cu(1 1 1) surface, both the substrate interaction and the lattice compression of the Pd overlayer lead to smaller hydrogen binding energies. For pseudomorphic Cu/Pd(1 1 1), on the other hand, the strong Cu–Pd interaction results in larger binding energies. Hence, both Pd/Cu(1 1 1) and Cu/Pd(1 1 1) exhibit an intermediate behavior between pure Cu(1 1 1) and pure Pd(1 1 1). In addition, we have determined the atomic hydrogen adsorption on Pd/Au(1 1 1) in the presence of a water overlayer. The hydrogen adsorption energies are changed by less than 60 meV by the most stable H 2O bilayer compared to the clean surface. This indicates that theoretical adsorption studies at the solid–vacuum interface might also be relevant for the solid–liquid interface.

The mechanism of CO 2 chemisorption on zigzag carbon active sites: A computational chemistry study

A computational chemistry study was carried out to evaluate the various options for CO 2 adsorption on one or two adjacent zigzag sites in a graphene layer. Density functional theory was used with the 6-31G(d) basis set, as implemented in the Gaussian software package in conjunction with GaussView and Chem3D. Various electronic environments of a four-ring model, with and without surface oxygen and with special emphasis on carbene-like structures, were analyzed. The resulting optimized geometries were quite sensitive to such electronic configurations. In agreement with long-standing experimental evidence, dissociative CO 2 adsorption was found to be particularly favorable; furthermore, dissociation was found to be favored on isolated carbene-like zigzag sites. It is recommended that such a pathway, rather than dual-site adsorption and C—CO 2 complex formation, deserves the dominant attention in further theoretical studies of adsorption, reaction and desorption processes during CO 2 gasification of carbons.

A theoretical study of adsorption and the surfactant effect of Sb on the Ag(100) surface

The adsorption and the surfactant effect of Sb on the Ag(100) surface are studied using first-principles calculations. Our calculated results show that the pre-adsorbed Sb atoms act as nucleation centres for the deposited Ag atoms, and surface-substitutional Sb atoms repel on-fcc-site Ag atoms nearby. We suggest that the Sb repulsion network reduces the Ag-adatom mobility and leads to a high density of Ag islands which improve the smoothness of the layer-by-layer growth.

On the porous structure of coals: Evidence for an interconnected but constricted micropore system and implications for coalbed methane recovery

An experimental and theoretical study of adsorption and diffusion of carbon dioxide and methane in coals of widely varying rank was carried out. Low pressures adsorption isotherms of CO2 were obtained and analyzed using Dubinin's theory of volume filling of micropores. High-pressure adsorption isotherms of CH4 were obtained and analyzed using tracer pulse chromatography in conjunction with an appropriate adsorption/diffusion model. A preliminary129Xe NMR analysis of chemical shifts experienced by xenon atoms in particles of different sizes is also reported.

Simulation Studies of a Lennard-Jones Liquid in Micropores

Abstract In this paper grand canonical ensemble Monte Carlo and molecular dynamics simulation techniques are used to establish the degree to which the equilibrium and transport properties of fluids in micropores are influenced both by confinement in the narrow pore space and by the lattice structure of the pore wall. Partition coefficients, solvation forces, and diffusion coefficients for a Lennard-Jones liquid confined within two model cylindrical pores are determined over a range of effective micropore sizes. In one model the cylindrical pore wall is described by a structureless, continuum interaction potential similar to that which is frequently employed in theoretical studies of adsorption. In the second model a single embedded layer of lattice atoms is placed at the solid/fluid interface. The results obtained are compared with the prediction of a bulk fluid approximation and the Fischer-Methfessel approximation to the Yvon-Born-Green equation and the recently developed kinetic theory of Davis for mic...