Comparative Study of the Theoretical Predictions of Mixed-Gas Adsorption Equilibria from Pure Component Adsorption Data: Vacancy Solution Theory

Simple methods for describing mixed-gas adsorption equilibria based on a knowledge of single gas adsorption are still needed for gas separation processes. The present paper describes the possibilities of the Vacancy Solution Theory (VST) approach. The VST predictions are compared with results obtained using the IAS, IE and PT approaches as presented earlier by the author

Application of the Dubinin–Astakhov Equation to the Study of the Geometric Structure, Energetic Surface Heterogeneity and Surface Topography of Carbonaceous Adsorbents

The new theoretical approach to multisite-occupancy adsorption on heterogeneous surfaces, developed recently by Rudziński and Everett, is generalized for the case of adsorption systems characterized by non-Gaussian adsorption energy distributions. Attention is focused on the adsorption energy distribution which, in the case of one-site-occupancy adsorption, leads to the Dubinin–Astakhov isotherm equation. In effect, a generalized form of that isotherm equation is developed for the common case of multisite-occupancy adorption in actual adsorption systems. The generalized equation is sensitive to surface topography; hence, fitting it to experimental adsorption isotherms creates a chance to study the surface topography of carbonaceous surfaces. An example of such computer exercises is reported here before a more systematic study is published

Application of the Dubinin–Radushkevich Equation for Describing Adsorption from Solutions on to Various Carbons

Dozens of papers have been published recently describing adsorption processes from solutions on to solid surfaces, but a certain lack of understanding of this problem is still observed. This article deals with the description of adsorption from binary solutions of non-electrolytes on to solids. This description covers adsorption both on homogeneous and heterogeneous surfaces from ideal and non-ideal liquid mixtures. Some important factors determining the adsorption process, i.e. the heterogeneity of the solid surface, interactions between the species in the bulk and surface phases, differences in molecular sizes of the adsorbate molecules, etc., have been discussed. The main attention has been focused on the Dubinin–Radushkevich equation and its application in the description of adsorption from solutions on to energetically, heterogeneous adsorbents. Numerous model calculations have been reported for this equation and several experimental systems have been analyzed. The application of the Dubinin–Radushkevich equation in characterizing liquid adsorption on to various carbons has been demonstrated

Heterogeneity of multiwalled carbon nanotubes based on adsorption of simple aromatic compounds from aqueous solutions

The surface heterogeneity of multiwalled carbon nanotubes (MWCNTs) is studied on the basis of adsorption isotherms from dilute aqueous phenol and dopamine solutions at various pH values. The generalized Langmuir-Freundlich (GLF) isotherm equation was applied to investigate the cooperative effect of the surface heterogeneity and the lateral interactions between the adsorbates. The theoretical isosteric heats of adsorption were obtained assuming that the heat of adsorption profile reveals both the energetic heterogeneity of the adsorption system and the strength of the interactions between the neighboring molecules. The adsorption energy distribution (AED) functions were calculated by using algorithm based on a regularization method. The great advantage of this method is that the regularization makes no assumption about the shape of the obtained energy distribution functions. Analysis of the isosteric heats of adsorption for MWCNTs showed that the influence of the surface heterogeneity is much stronger than the role of the lateral interactions. The most typical adsorption heat is 20-22 kJ/mol for both phenol and dopamine. After purification of nanotubes, heat value for phenol dropped to 16-17 kJ/mol. The range of the energy distribution is only slightly influenced by the surface chemistry of the nanotubes in the aqueous conditions