Surface changes in coals after oxidation. 2. H2O sorption studies

This paper presents a quantitative characterization of the effects of oxidiation on the surface of coal based on water sorption measurements. Two coals of different rank were examined before and after oxidation with H 2 O 2 and KMnO 4 . A theoretical model describing sorption equilibria, as the effect of adsorption in submicropores and absorption in the elastic phase of coal, was applied to evaluate structural and enegetic parameters of the sorption systems. Oxidation results in a noticeable increase in the adsorption capacity of the studied coals and practically does not affect the absorption. This is due to creation of new oxygen-containig surface groups on the coal surface, as was shown by XPS measurements. A significant increase in the adsorption energy together with much smaller changes in concentration of water molecules on the coal surface was seen. This suggests an increase in the number of double bonds between adsorbed water molecules and oxygen-containig surface groups.