An experimental and molecular-statistical study of the adsorption of the iodobenzene, 2-iodothiophene, and isomeric iodoadamantane molecules on the graphite basal face surface

The thermodynamic characteristics of adsorption of iodobenzene, 2-iodothiophene, and 1- and 2-iodoadamantanes on the surface of graphitized thermal carbon black were determined experimentally. The influence of the special features of the molecular structure of the adsorbates on the thermodynamic characteristics of adsorption was studied. The atom-atom approximation of the semiempirical molecular-statistical theory of adsorption was used to calculate the thermodynamic characteristics of adsorption of the adsorbates using the newly determined potential function parameters of pair intermolecular interaction (φ(r)) of I with C atoms of the basal graphite face. For the example of isostructural monohalogenated benzenes, thiophenes, and adamantanes, a comparative analysis of the contributions of the F, Cl, Br, and I atoms to the thermodynamic characteristics of adsorption was performed for the nonspecific adsorption of these compounds on a plane graphitized carbon black surface.     

Adsorption of tetramethylsilane molecules on the basal face of graphite

The thermodynamic adsorption characteristics of tetramethylsilane (TMS) molecules on graphitized carbon black (GCB) were for the first time determined experimentally and by molecular statistics methods. The potential function parameters of pair molecular interactions (φ(r)) between Si and C atoms on the basal face of graphite were calculated in the atom-atom approximation of the semiempirical molecular-statistical theory of adsorption. The contributions of Si and C atoms to thermodynamic adsorption characteristics are compared for the example of nonspecific adsorption of TMS and isostructural neopentane molecules on the flat surface of GCB.     

Molecular statistical calculation of thermodynamic characteristics of adsorption of polymantane molecules on the basis face of graphite

The thermodynamic characteristics of adsorption (TCA) of polymantane molecules and their some derivatives on the basis face of graphite were calculated for the first time in terms of the atom-atomic approximation of the semiempirical molecular statistical theory of adsorption. The graphite surface exhibits high structural selectivity to isomeric polymantanes. A model for adsorption of cage molecules on the planar surface was proposed. The model is based on the idea that contributions of atoms of the adsorbate molecule to the total adsorption energy can be discriminated according to the distance of these atoms from the surface of a solid. Advantages and limitations of using the data on adsorption of molecules of isomeric alkanes, including rotamers, for the analysis of equilibrium TCA values of isomeric polymantanes on graphite are discussed. The possibility of separation of representatives of the polymantane hydrocarbon family by gas adsorption chromatography on columns with graphitized thermal carbon black was suggested on the basis of the calculated TCA values and logarithmic retention indices.     

Adsorption of nitrobenzene, aniline and nitroanilines on the surface of a basal face of graphite

Thermodynamic characteristics of the adsorption of nitrobenzene, aniline, and isomeric nitro-anilines are determined experimentally and from molecular statistics in the range of the closest packing of a graphite surface according to equilibrium gas adsorption chromatography. It is found that graphitized thermal carbon black is characterized by high selectivity upon the chromatographic separation of isomeric nitro-anilines (retention increases in the series of ortho, meta, and para isomers). Using the atom-atomic approximation of the semi-empirical molecular statistical theory of adsorption, parameters are calculated for the potential function of the pair intermolecular interaction of the NO₂ group in nitrobenzene and the N atom in aniline with the C atoms in a basal face of graphite. The effect of the NH₂ and NO₂ groups on the parameters of adsorption for isomeric nitroanilines as a result of direct polar conjugation is demonstrated and must be assumed when performing molecular statistical calculations.     

Calculation op the adsorption energy of nonpolar molecules on graphite

Summary The details of an earlier theoretical calculation of the energy of adsorption of simple and complex non-polar molecules on graphite were presented. The power sums of type were calculated for different distances of the adsorbate molecule from the external base plane of graphite, at n=6, 8, 10 and 12, as were also the exponential sums of type , at =0.28 A. Using approximate quantum mechanics equations, we calculated the constants of three terms of the energy of dispersive attraction, and also the constants of repulsion from the equilibrium condition. The additive scheme was used to calculate the potential curves and equilibrium adsorption energies of complex molecules.     

Thermodynamic parameters of adsorption of isomeric chloronaphthalenes on graphitized thermal carbon black

Henry's constants and the heats of adsorption of isomeric chloronaphthalenes on graphitized thermal carbon black were calculated by the semiempirical molecular statistical method. The calculated data were compared with experimental results. The best agreement was achieved when corrections for the interaction of the Cl atom with the C atom of the adjacent benzene ring and the presence of other Cl atoms inortho-positions are introduced in calculations of the atom-atomic potential. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 8, pp. 1484–1489, August, 1999.     

Thermodynamic study of adsorption of nickel complexes with Schiff bases from acetonitrile solutions on uncharged graphite surface

Adsorption of nickel N,N-ethylenebis(salicylideneimine) complex from acetonitrile solution on expanded natural graphite powder at 273–313 K is studied.Translated from Zhurnal Prikladnoi Khimii, Vol. 77, No. 10, 2004, pp. 1643–1646.Original Russian Text Copyright © 2004 by Afanasev, Aleksandrova, Akulova, Logvinov.     

The influence of arrangement of substituents in isomeric chlorobenzenes on their adsorption on graphite

Henry's constants and the heats of adsorption of benzene chloro derivatives on graphitized thermal carbon black were calculated by the semiempirical molecular statistical theory of adsorption. The best agreement between the experimental and calculated data was achieved by introducing corrections for the presence of other chlorine atoms in theortho-positions into the calculation of the atom-atomic potential of the intermolecular interaction of the chlorine atom with the carbon atom of graphite. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 672–676, April, 1999.     

The adsorption of polar molecules on the surface of graphite modified with a monomolecular layer of a mesogen

An equation for the potential energy of the interaction of a quasi-solid polar adsorbate molecule with a semiinfinite graphite crystal containing a monomolecular layer of polar anisometric particles on its surface was obtained. Adsorbate-modifier electrostatic interactions were considered in the dipole-dipole approximation. Dispersion interactions were described using the Lennard-Jones potentials (6, 12). The suggestion was made that a modifier monolayer impermeable to adsorbate molecules could be modeled by force centers that formed a two-dimensional translationally periodic lattice and by force centers uniformly distributed in a plane parallel to the outer face of graphite crystals.     

Chiral pair monolayer adsorption of iodine-substituted octadecanol molecules on graphite

High-resolution scanning tunneling microscopy has been used to examine the adsorbate structures formed when a racemic mixture of (9R,10R)-9,10-diiodooctadecan-1-ol and (9S,10S)-9,10-diiodooctadecan-1-ol is adsorbed at the basal plane of highly ordered pyrolytic graphite. The herringbone structure characteristic of the adsorption of long-chain molecules on graphite is observed. Close examination of the micrographs indicates a unique structure in which the chiral molecules adsorb in pairs, with one enantiomer filling half of the unit cell, and the other enantiomer filling the other half. Instead of forming separate chiral domains, as is sometimes observed when a racemic mixture adsorbs on an achiral surface, chiral pairs are formed and the pairs form an ordered monolayer, exposing opposite faces of the same molecule. An achiral racemic mixture is observed to form a chiral structure on an achiral surface in the regions of the surface examined here.     

Thermodynamic analysis of ordered and disordered monolayer of argon adsorption on graphite

We presented a detailed thermodynamic analysis of argon adsorption on a graphitized carbon black with a kinetic Monte Carlo scheme. In this study, we particularly paid attention to the formation of a hexagonal two-dimensional molecular layer on a graphite surface and discuss conditions of its stability and thermodynamic properties of the adsorbed phase as a function of loading. It is found that the simulation results are substantially affected by the dimensions of the simulation box when the monolayer forms a hexagonal ordered structure. This is due to the fact that the lattice constant is constrained by the dimensions of the surface. To circumvent this, we presented a thermodynamic technique, which allows for the variation of the box size as a function of loading, to determine the "intrinsic" lattice constant (rather than apparent average value because of the fixed dimensions of the simulation box) and the thermodynamic functions for the adsorbed phase: the Helmholtz free energy, the chemical potential, and the surface tension. The tangential and normal pressures as a function of the distance from the surface are also discussed.     

Thermodynamic investigation of the adsorption of amides on graphite from their liquids and binary mixtures

We report a thermodynamic investigation of the adsorption of saturated and unsaturated (cis- and trans-) alkyl amides onto the surface of graphite from their pure liquids and from binary mixtures. We identify the formation of solid monolayers of the amides at temperatures when the bulk materials are liquid. The extent of this presolidification is much more extensive than other related materials, indicating that these amide layers are significantly more stable. The monolayer stability is found to be greatest for saturated amides. In addition, the stability of unsaturated amides is extremely sensitive to the location of the double bonds in the alkyl chain of the molecules, and trans isomers are found to be more stable than cis. We also address the preferential adsorption and mixing behavior of amide mixtures and amides mixed with other species coadsorbed onto graphite from binary solution. The results indicate that the amide molecules appear to be adsorbed with their principal axis parallel to the graphite surface and that amides are found to be strongly preferentially adsorbed with respect to alkanes. Interestingly the amides appear to mix rather better than might have been expected. There is also evidence of a number of other transitions in the adsorbates.     

Modeling the surface of polystyrene and the adsorption of dye molecules on this surface

Models of the structures of complexes of the Nile red dye (NR) molecule on the surface of various types of polystyrene (PS) were constructed by molecular dynamics (MD). The surface of a polystyrene film and the surfaces of clumps of isolated polystyrene chains were examined as surfaces. The film and the clumps were obtained as a result of molecular-dynamics trajectories. The atomistic version of molecular dynamics was used. The surface of the film was comparatively uniform, and the clumps were irregular ellipsoids with varied local surface form. The variety of the surface forms makes it possible to obtain complexes of PS with local environments having different structures. A method of constructing the solvent-accessible surface (SAS) was proposed as method of evaluating the potential sensor characteristics of the material. In the PS clumps the NR molecule is almost completely submerged in the upper layer, while in the film the aromatic fragment of the dye is partly accessible to the analyte.     

Calculation of the adsorption of interacting molecules on a stepped surface

A theory of adsorption which allows simultaneously for the nonuniformity of a surface and for lateral interactions between the adsorbed species is able to account for the main features of a stepped surface. The effect of the above factors on the adsorption isotherm and the heat of adsorption is investigated. A sudden increase in the heat of adsorption is predicted when an ordered distribution of the adsorbed species has been realized.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 1943–1948, September, 1989.     

Adsorption of isomeric aryl- and diadamantane molecules on the surface of graphitized thermal carbon black

The thermodynamic characteristics of adsorption of isomeric molecules of 1,1??-, 1,2??-, and 2,2??-diadamantanes, 1- and 2-phenyladamantanes, and 1-cyclohexyladamantane on the surface of graphitized thermal carbon black (GTC) were experimentally determined. The influence of the molecular structure of adsorbates on their adsorption on the basis face of graphite was considered. A high selectivity of the GTC surface for the gas chromatographic separation of mixtures of the considered structural isomers was shown.     

Interaction model for the adsorption of organic molecules on the silver surface

Adsorption of organics on a silver surface is simulated. An Embedded Atom Model is used for the metal, a standard force field for the organics, and a combination of the charge equilibration model and the Morse potential for their electrostatic and nonbonding interactions. The only adjustable parameters of this approach appear in the Morse potential. They are tuned to reproduce experimental and high level quantum chemical data. The adsorption energies of 13 molecules on the Ag(111) surface are obtained with an average error of less than 1 kcal mol(-1). The model should be transferable to molecules with the same chemical groups used in regressing the potential parameters when physisorption or weak chemisorption, i.e., no bond breaking, occur, and also to other Ag surfaces. When used to simulate perylene tetracarboxylic acid dianhydride (PTCDA) on Ag(111), correct geometry of mono- and multilayers are observed in molecular dynamics simulations at room temperature.