Two carbons of different origins (wood and coal) were oxidized with nitric acid. The materials were
characterized using sorption of nitrogen, Boehm titration, 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 using virial equation. The results showed that
the isosteric heats of water adsorption are affected by surface chemical heterogeneity only at low surface
coverage. The shapes of heats obtained indicate strong water−water interactions 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 condensation (45 kJ/mol) was obtained.
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