Estimation of the influence of structural elements of activated carbons on the energetic components of adsorption

The general mechanisms for the adsorption of organic molecules on the surface of solids are well known for flat/smooth non-porous materials. They depend on low energy dispersive interactions (London-Van der Waals) responsible for reversible physical adsorption and specific forces of greater energy associated with dipolar or acid/base interactions. However in the case of activated carbons (ACs) the study of these mechanisms is considerably hindered by their microporosity. The pores increase the surface area considerably but impede the study of the surface itself. The comparative study of inverse gas chromatography (IGC) at infinite dilution and a capillary wetting method shows that the dispersive component of the surface energy is greatly influenced by the porosity. The specific adsorption forces liable to intervene in the adsorption of alkenes do not appear due to steric hindrance. However alcohols are better adsorbed than alkanes, even more so as the surface overlap increases. A method for estimating adsorption energy based on capillary wetting shows clearly that porosity is responsible for an increase in the dispersive adsorption energies and that the non-specific hydrophobic component is much more important than acid/base interactions susceptible to intervene with the surface functional groups of ACs. (C) 2001 Elsevier Science Ltd. All rights reserved.