EFFECT OF SURFACE CHEMICAL GROUPS ON ENERGETIC HETEROGENEITY OF ACTIVATED CARBONS

Activated carbons from different origins have been oxidized with nitric acid at different temperatures. Some of the oxidized samples were heat treated at 873 K in inert atmosphere in order to partially reduce their oxidized surface. The changes in the number of surface species were determined by the Boehm titration method and X-ray photoelectron spectroscopy. Gas chromatography at infinite dilution and finite concentration was used to study the effect of surface groups on adsorption properties of the carbon samples. Oxidation was followed by decreases in the enthalpies and free energies of alkane adsorption. The results obtained indicate that surface chemical groups may hinder and/or perturb occupancy of adsorbed molecules on their energetically most favorable positions.