Statistical-mechanical derivation of generalised langmuir equation and its application for the interpretation of chromatographic data for the adsorption of water and methanol on non-porous carbon materials

The chromatographic method is applied to the study of water and methanol adsorption on non-porous carbon materials—graphitised carbon black and thermally expanded graphite. It is shown that the processing of the experimental isotherms in coordinates of the classic Langmuir equation results in their linearization in two ranges of relative pressure, indicating the presence of two types of adsorption centres on the surface, which can be identified as the carboxyl and phenolic hydroxyl groups, respectively. A generalised Langmuir equation based on a statistical-mechanical approach is proposed, capable for the description of both monomolecular and polymolecular adsorption on the surface. It is shown that this equation provides for a better description of the adsorption of polar molecules on non-porous carbon materials.