A study of acetaldehyde adsorption on activated carbons

Three samples of activated carbons of various origins were used in this stu dy. 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 anal ysis. Then adsorption of acetaldehyde was studied by means of inverse gas c hromatography 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 th e carbon matrix, interactions of acetaldehyde are strongest. This is due to the contribution of hydrogen bonding to dispersive interactions of hydroca rbon moiety with the activated carbon pore walls. After oxidation, for the carbons with unaltered or decreased surface area the isosteric heat of acet aldehyde adsorption decreased due to an increase in the density of oxygen-c ontaining groups resulting in a decrease in dispersive interactions and blo cking of the pore entrances. Oxidation of carbon surfaces results also in a n increase in the amount of acetaldehyde adsorbed under saturation conditio ns. (C) 2001 Academic Press.