Effect of increased basicity of activated carbon surface on valeric acid adsorption from aqueous solution activated carbon

Two types of activated carbons of different origins were used to study the adsorption of valeric acid from aqueous solution. Nitrogen-containing basic groups were introduced into the surface by impregnating the initial samples with urea followed by heat treatment at 1223 K. Characterization of the surface was done using the following techniques: Boehm titration, potentiometric titration, thermal analysis and sorption of nitrogen. Valeric acid adsorption isotherms were measured at 333 K and fitted to the Freundlich equation. A direct correlation of the capacity coefficients with both the total number of groups and the volume of micropores smaller than 10 Angstrom was found. The amount of valeric acid adsorbed on activated carbons, calculated from the isotherms, showed similar trend. The results obtained from DTG analysis showed that the strongly adsorbed amount of valeric acid per unit surface area increases with an increase in the density of basic groups. On the other hand, the amount adsorbed decreases with an increase in the density of acidic groups on the surface. This is related to attractive/repulsive interactions of adsorbate with surface species.