Experimental study of water adsorption on activated carbons

Two carbons of different origins (wood and coal) were oxidized with nitric acid. The materials were characterized using sorption of nitrogen, Boehm ti tration, and potentiometric titration. The water adsorption isotherms were measured at various temperatures close to ambient (relative pressure from 0 .001 to 0.3). From these isotherms heats of adsorption were calculated usin g virial equation. The results showed that the isosteric heats of water ads orption are affected by surface chemical heterogeneity only at low surface coverage. The shapes of heats obtained indicate strong water-water interact ions as a result of adsorption on secondary sites and cluster formation. In all cases the limiting heat of adsorption equal to the heat of water conde nsation (45 kJ/mol) was obtained.