Specific and non-specific interactions of water molecules with carbon surfaces from immersion calorimetry

The enthalpy of immersion of carbons into water reflects the specific and t he non-specific interactions between the liquid and the solid. The study of a variety of active carbons oxidized to different degrees with (NH4)(2)S2O 8, HNO3 and H2O2, reveals a simple correlation between the enthalpy of imme rsion, Delta(i)H(H2O), the oxygen content of the surface, the basic groups, the micropore filling and the wetting of the external (non-microporous) su rface. The specific interactions between the surface oxygen and water is 12 .1 kJ/mol of oxygen and it involves on average two molecules of water per o xygen. The basic groups on the surface, which contain no oxygen, have an in teraction energy with water of 10.3 kJ/HCl eq of base. The non-specific fil ling of the micropores by water corresponds to 0.8 kJ/mol of water. Prelimi nary results show that the correlation also holds for oxidized carbon black s with 10.7 kJ/mol for the oxygen-water interaction and 0.035 J/m(2) for th e wetting of the pure carbon surface. (C) 2000 Elsevier Science Ltd. All ri ghts reserved.