Revisiting the effect of surface chemistry on adsorption of water on activated carbons

A sample of Westvaco carbon was oxidized with ammonium persulfate and both initial and oxidized samples were washed with methanol. The samples were ch aracterized using sorption of nitrogen, Boehm titration, potentiometric tit ration, IGC, FTIR, TPD, and thermal analysis. Then water adsorption isother ms were measured at various temperatures close to ambient (relative pressur e from 0.001 to 0.3). The isotherms were analyzed in terms of the thermodyn amic consistency, presence of equilibrium, and water-activated carbon surfa ce interactions. The results showed that washing with methanol significantl y modifies the surface chemistry of carbons, creating phenols and new, very easily hydrolyzed esters. The latter, when in contact with water, is hydro lyzed, creating carboxylic acids and methanol. This may result in unjustifi ed application of the Clausius-Clapeyron equation to calculate the isosteri c heat of adsorption.