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

The general mechanisms for the adsorption of organic molecules on the surfa ce of solids are well known for flat/smooth non-porous materials. They depe nd on low energy dispersive interactions (London-Van der Waals) responsible for reversible physical adsorption and specific forces of greater energy a ssociated with dipolar or acid/base interactions. However in the case of ac tivated carbons (ACs) the study of these mechanisms is considerably hindere d by their microporosity. The pores increase the surface area considerably but impede the study of the surface itself. The comparative study of invers e gas chromatography (IGC) at infinite dilution and a capillary wetting met hod shows that the dispersive component of the surface energy is greatly in fluenced by the porosity. The specific adsorption forces liable to interven e in the adsorption of alkenes do not appear due to steric hindrance. Howev er alcohols are better adsorbed than alkanes, even more so as the surface o verlap increases. A method for estimating adsorption energy based on capill ary wetting shows clearly that porosity is responsible for an increase in t he dispersive adsorption energies and that the non-specific hydrophobic com ponent is much more important than acid/base interactions susceptible to in tervene with the surface functional groups of ACs. (C) 2001 Elsevier Scienc e Ltd. All rights reserved.