Water adsorption on activated carbons with different degrees of oxidation

A typical activated carbon, derived from olive stones, has been oxidized to different degrees with (NH₄)₂S₂O₈ and analysed by water vapour adsorption, immersion calorimetry, acid–base titration and temperature-programmed desorption of CO₂ and CO monitored by mass spectrometry. These techniques led to a coherent description of the surfaces and of their chemistry. The water adsorption isotherms, of type IV, were decomposed into type I and V contributions and analysed in terms of the Dubinin–Astakhov equation. The corresponding calculated enthalpies of immersion into water are in agreement with the experimental values. The number of carboxyl, lactone, phenol and basic groups identified by titration, can also be related to the parameters of the Dubinin–Astakhov equation and to the enthalpy of immersion into water. Finally, a good linear correlation is found between the amounts of CO₂ and CO desorbed from the surface, the enthalpies of immersion into water and the total number of sites identified on the surface.