A study of acetaldehyde adsorption on activated carbons

Three samples of activated carbons of various origins were used in this study. The initial samples were oxidized with nitric acid to introduce oxygen-containing groups. The surface of sorbents was characterized using sorption of nitrogen, Boehm and potentiometric titrations, DRIFTS, and thermal analysis. Then adsorption of acetaldehyde was studied by means of inverse gas chromatography at infinite dilution. From the retention volumes the heats of acetaldehyde adsorption were calculated. The results showed that the heats differ depending on the pore structure and surface chemistry of materials. On materials with very small pores and surface groups incorporated into the carbon matrix, interactions of acetaldehyde are strongest. This is due to the contribution of hydrogen bonding to dispersive interactions of hydrocarbon moiety with the activated carbon pore walls. After oxidation, for the carbons with unaltered or decreased surface area the isosteric heat of acetaldehyde adsorption decreased due to an increase in the density of oxygen-containing groups resulting in a decrease in dispersive interactions and blocking of the pore entrances. Oxidation of carbon surfaces results also in an increase in the amount of acetaldehyde adsorbed under saturation conditions. (C) 2001 Academic Press.