Carbon surface polarity from immersion calorimetry

A series of carbons with various oxygen- and/or nitrogen-containing surface groups has been prepared and analyzed by water vapor adsorption, acid–base titration, immersion calorimetry, and XPS. These techniques led to coherent description of the surfaces and of their chemistry. It has been found that the total concentration of surface oxygen and nitrogen correlates with the acid–base properties. At the same time, a simple correlation exists between the enthalpy of immersion into water for such modified activated carbons and specific interactions with the solid. These interactions correspond to the acidic (with oxygen) and basic (without oxygen or with nitrogen) sites. The value of water interaction with the carbon surface is ca. 21 kJ mol−1 of surface species.