Thermodynamic Characteristics Of Adsorption Research Articles

Influence of the structure of esters on their thermodynamic adsorption characteristics and chromatographic retention in HPLC

The chromatographic behavior of a series of esters was investigated in conditions of normal-phase and reversed-phase high-performance liquid chromatography. The dependence of the retention on the molecular structure of the investigated compounds and their physicochemical parameters is considered.

Influence of the structures of hydrogen-bonded dimeric molecules on their adsorption at graphitized thermal carbon

This study is devoted to the influence of the structures of hydrogen-bonded dimeric molecules on their adsorption at graphitized thermal carbon (GTC). The thermodynamic adsorption characteristics (TACs) of amino acid dimers and dimers of amino acids with acetic acid and formamide at GTC were determined. The results obtained for the adsorption of dimeric molecules at the carbon sorbent were compared with the calculated data for the molecules of the corresponding amino acids at GTC. The geometric parameters of dimeric molecules were varied to analyze the influence of the hydrogen bond lengths on the TACs of the compounds under study.

The thermodynamics of benzene adsorption on carbon obtained by the pyrolysis of hypercrosslinked polystyrene

The Glukauf chromatography method was used to study the adsorption of benzene on a microporous carbon material prepared by the pyrolysis of hypercrosslinked polystyrene. The thermodynamic characteristics of adsorption were determined as functions of the degree of pore filling. Over the range of relative pressures studied (<0.005), adsorption was shown to occur in ultramicropores by the mechanism of primary filling without condensed phase formation.

The thermodynamic characteristics of adsorption of hydrogen, sodium, and potassium chlorides at the aqueous solution-gas interface

Thermodynamic models of the adsorption of ions at the interphase boundary between a solution of a 1,1-electrolyte and a gas are suggested. The experimental surface tension isotherms and the isotherms of excess adsorption of hydrogen, sodium, and potassium chlorides from aqueous solutions were used to show that the formation of the surface layer followed both the mechanism of coadsorption of the anion and cation and the mechanism of predominant adsorption of one of the ions. The calculated total adsorption isotherms were used to obtain the dependences of the heats and entropies of adsorption on the amount of the ion adsorbed. The results are discussed in terms of the solvation and desolvation of electrolyte ions in bulk solution and at liquid-vapor interfaces.

The influence of intramolecular H-bond on chromatographic behavior of phenylalkylamines

The thermodynamic characteristics of adsorption on the surface of graphitized thermal carbon black at 300 K were determined by the molecular statistical method for three phenylalklylamines. The influence of the intramolecular H-bond on the conformation of the molecules compared with structurally related n-alkyl-benzenes was considered. It was shown that the conformations of the molecules could influence chromatographic retention. Conformational isomers stabilized by intramolecular H-bonds were found to retain their structure in adsorption on graphitized thermal carbon black.

The influence of an intramolecular H-bond on the adsorption of sulfur-containing amino acids on graphitized thermal carbon black

The thermodynamic characteristics of adsorption of sulfur-containing amino acids and their derivatives on the surface of graphitized thermal carbon black were calculated by the molecular statistical method. The parameters of the atom-atom potential function of intermolecular interaction between the S atom in amino acids and the graphite C atom were determined. It was shown that an intramolecular H-bond influenced the adsorption of amino acids on the surface of graphitized thermal carbon black.

The chromatographic behavior and thermodynamic characteristics of adsorption of profen enantiomers on silica gel with grafted eremomycin antibiotic

The chromatographic retention and thermodynamic characteristics of adsorption of several derivatives of 2-arylpropanoic acid on a chiral stationary phase with a grafted eremomycin antibiotic under the conditions of liquid chromatography with water-ethanol mobile phases were studied. The dependences of retention characteristics and selectivity on eluent pH were revealed. The difference between the adsorption mechanisms of acids with one and two benzene rings was demonstrated. Compensation effect manifestations in these systems are discussed.

Molecular statistical calculations of the adsorption of proline and its hydroxy derivatives on graphitized thermal carbon black

The thermodynamic characteristics of adsorption of proline and its hydroxy derivatives on the surface of graphitized thermal carbon black (GTCB) were calculated. The arrangement of hydroxyl groups in the amino acid molecule was shown to influence their adsorption on GTCB. The influence of internal rotation angles in proline and its hydroxy derivative molecules on their adsorption on GTCB was studied.

Experimental and molecular statistical study of alkyladamantane adsorption on graphitized thermal carbon black

Experimental measurements and molecular statistics methods were used to calculate thermodynamic characteristics of adsorption (TCA) of alkyladamantanes of different structure on the surface of hydrogen-treated graphitized thermal carbon black (GTCB) Carbopack C HT. High selectivity of separation of isomeric alkyladamantanes on GTCB is due to specific features of their geometry and electronic structure. The influence of the spatial structure of adsorbates on the TCA was established. Special attention was given to analysis of the heat capacities of adsorption. The best agreement between the experimental TCA and those calculated by the molecular statistics methods is achieved when the “cage effect“ in the adamantane ring is taken into account. The corresponding corrections are introduced into the parameters of the atom-atomic potential function of pair intermolecular interaction of the Me groups with the carbon atoms of the basal face of graphite, which are localized in the nodal positions of the lattice. The critical parameters for a large group of alkyladamantanes were calculated in terms of the additive group Lydersen method. A set of various topological indices used further for constructing structure-retention correlations on GTCB was obtained.

The thermodynamic characteristics of acetone adsorption on Raney nickel under liquid phase hydrogenation conditions

An adsorption-calorimetric study was performed to determine the thermodynamic characteristics of adsorption of acetone on Raney nickel from aqueous solutions of 2-propanol of various compositions directly during liquid-phase hydrogenation. At adsorbate concentrations below 3 × 10−3 M, adsorption occurred by the mechanism of the filling of the pore volume of the catalyst with saturated solutions of complex compositions. At higher concentrations, the process followed the mechanism of condensation interactions. Two-dimensional phase diagrams were obtained for Raney nickel surface layers involved in the adsorption of acetone. These diagrams substantiated the possibility of two-dimensional phase transitions in adsorption solutions.

The adsorption of chlorobenzene on a carbon adsorbent obtained by the pyrolysis of hypercrosslinked polystyrene

The adsorption of chlorobenzene vapor on an experimental D4609 (Purolite Int.) adsorbent prepared by the pyrolysis of hypercrosslinked polystyrene was studied. The adsorbent was characterized by a large specific surface area, a narrow pore size distribution with the predominant fraction of pore diameters 0.9–3.4 nm, and a high absorption ability with respect to chlorobenzene. The adsorption isotherms were measured over the temperature range 100–140°C, and the thermodynamic characteristics of adsorption were determined. In spite of the correspondence to the formal requirements of the theory of volume filling of micropores, the mechanism of adsorption in narrow micropores (<1.2—1.5 nm) was different from filling with a condensed phase.

A Correlation between the Kinetic and Thermodynamic Adsorption Characteristics of an Optical Brightener on a Pulp Surface

An attempt to find a correlation between the kinetic and thermodynamic terms (e.g. activation energy, pre-exponential factor, isosteric heat, entropy, etc.) of the chemisorption process involved in a commercial optical brightener/pulp system is presented. A linear inter-relationship between the kinetic and thermodynamic characteristics of the system was found. Based on the coefficients obtained in the thermodynamic investigation of the adsorption process, it was possible to calculate the kinetic coefficient of the surface inhomogeneity. The use of both a model employing uniformly inhomogeneous surfaces and an approach involving all the kinetic and thermodynamic data was confirmed by the results obtained.

The thermodynamic characteristics of retention of tricyclo[5.2.1.02,6]decane isomer molecules on different sorbents in gas chromatography

The thermodynamic characteristics of sorption of the isomeric tricyclo[5.2.1.02.6]decane (tetrahydrodicyclopentadiene, TDCPD) molecules were for the first time determined experimentally and by molecular statistical methods under the conditions of gas-adsorption chromatography on graphitized thermal carbon black and gas-liquid chromatography on stationary liquid phases of different polarities (Apiezon L and Carbowax 20M). The effects of the chemical nature of sorbents on the retention of the TDCPD isomers are considered. A procedure for calculating the thermodynamic characteristics of adsorption of molecules with a complex structure is suggested within the framework of the atom-atom approximation of the semiempirical molecular statistical theory of adsorption for the example of isostructural norbornane molecules. The procedure involves simultaneous variation of geometric parameters and refinement of the parameters that determine the special features of the electronic structure. This method was used to determine several geometric parameters of the TDCPD molecules for the first time. The results were in close agreement with the quantum-chemical data.

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.

The thermodynamic characteristics of adsorption and retention of adamantane derivatives on graphitized carbon black under the conditions of gas-adsorption chromatography

The experimentally determined thermodynamic characteristics of adsorption of adamantane derivatives with different numbers and chemical natures of functional groups on graphitized carbon black under the conditions of gas-adsorption chromatography were analyzed. The theoretical values of the entropy of adsorption calculated in terms of the two-dimensional ideal gas model were correlated with the corresponding experimental values, and some special features of the molecular structure of the compounds studied were determined. Using the method of structural fragments and sorption-structure correlations for the adamantane derivatives and cyclohexane, it was established that the adsorption potential of cage adamantane molecules was largely determined by the cyclohexane fragment with the largest number of substituents, which was situated in the immediate vicinity of the flat graphite-like adsorbent surface.

The thermodynamic characteristics of processes in Raney nickel surface layers with the participation of adsorbed hydrogen forms

Equilibria between adsorbed hydrogen forms on the surface of Raney nickel in aqueous solutions were studied by the potentiometric and adsorption-calorimetric methods. The establishment of equilibria between adsorbate forms was proved experimentally. The model of a surface with discrete inhomogeneity was used to determine the standard thermodynamic characteristics of surface equilibria and adsorption of particular hydrogen adsorption forms. The influence of pH of the bulk phase on the thermodynamic characteristics of adsorption of hydrogen on the surface of Raney nickel caused redistribution of adsorbed hydrogen forms.

A gas-chromatography study of adsorption properties of silica modified by stable nickel nanoparticles obtained in reverse micelles under γ-radiation

Stable nano-sized nickel particles are prepared using the radiation-chemical synthesis in reverse micelles. Adsorption properties of raw silica (silochrome, S-120), the silochrome modified by a micelle-forming compound (AOT), and the silochrome modified by the nano-sized nickel particles are studied using gas chromatography method. The retention times for different test-compounds at different temperatures are determined for these adsorbents. Specific retention volumes of the test-compounds, as well as the thermodynamic adsorption characteristics, are determined. After the modification, the initial adsorption heat for n-hydrocarbons increases, which points out to the higher surface roughness of the modified samples. For the nickel-nanoparticle-modified silica, the contribution of specific interactions of polar compounds is less than that for the unmodified silica; this can be explained by screening the active centers (OH-groups) of the silica gel by the metal nanoparticles. The silica polarity decreases after the modification. The gas chromatography method allows detecting the difference in the properties of nanocomposites containing Ni- and NiO-nanoparticles.

Adsorption of naproxen enantiomers on chemically modified cellulose

Adsorption of naproxen enantiomers on the Chiralcel OJ-H chiral stationary phase, being tris(4-methylbenzoate) cellulose coated on silica gel, was studied. The thermodynamic characteristics of adsorption were measured. The adsorption isotherms are described by the Langmuir equation within the concentration range under study.

Interaction between organic vapors and clinoptilolite–mordenite rich tuffs in parent, decationized, and lead exchanged forms

Scientific interest in adsorption phenomena of organic vapors has concentrated on synthetic zeolites. Solid–vapor systems containing natural zeolites deserve special attention due to their abundance and environmental applications. Adsorption thermodynamic characteristics for benzene, toluene, n-hexane, and CCl 4 were measured on clinoptilolite-rich zeolitic tuffs from Mexico (ZE) and Hungary (ZH) on parent, decationized, dealuminated, and lead-exchanged samples. The clinoptilolite structure released Na + and Ca 2+ by acid treatment and this was accompanied by dealumination to a greater extent on ZE than on ZH. The exchange isotherm of Pb 2+ on ZE exhibited a concave type “a” form and accomplished 95% exchange and the tuff was selective at X i ( s ) < 0.25 . The pattern of adsorption isotherms was the same on all tuffs: benzene > toluene > n-hexane > carbon tetrachloride. The − Δ H ¯ values were higher for toluene than for the other adsorbates. Curves of q isost vs coverage decreased with the increment of the adsorbed amount in practically all studied systems. The contributions to the solid–vapor interaction potential were examined using inverse gas chromatography. The specific interaction energy G sp was primarily due to adsorbate–framework and adsorbate–cation interactions at low adsorbate pressures producing low surface coverage.

The adsorption of organic compounds on a modified carbon adsorbent Carbopack B

The thermodynamic characteristics of adsorption of several organic compounds on the carbon adsorbent Carbopack B before and after its modification by a monomolecular layer of cholesteryl-n-pentyl oxybenzoate were determined by gas chromatography. The initial adsorbent was close in its properties to graphitized carbon black. Modification weakened adsorbate-adsorbent attraction and increased the mobility of adsorbed molecules, to a greater extent for nonpolar adsorbents and to a lesser extent for compounds capable of specifically interacting with modifier molecules.