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 the non-specific interactions between the liquid and the solid. The study of a variety of active carbons oxidized to different degrees with (NH4)(2)S2O8, HNO3 and H2O2, reveals a simple correlation between the enthalpy of immersion, Delta(i)H(H2O), the oxygen content of the surface, the basic groups, the micropore filling and the wetting of the external (non-microporous) surface. 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 oxygen. The basic groups on the surface, which contain no oxygen, have an interaction energy with water of 10.3 kJ/HCl eq of base. The non-specific filling of the micropores by water corresponds to 0.8 kJ/mol of water. Preliminary results show that the correlation also holds for oxidized carbon blacks with 10.7 kJ/mol for the oxygen-water interaction and 0.035 J/m(2) for the wetting of the pure carbon surface. (C) 2000 Elsevier Science Ltd. All rights reserved.