WATER-ADSORPTION ON ACTIVATED CARBONS WITH DIFFERENT DEGREES OF OXIDATION

A typical activated carbon, derived from olive stones, has been oxidiz ed to different degrees with (NH4)(2)S2O8 and analysed by water vapour adsorption, immersion calorimetry, acid-base titration and temperatur e-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 deco mposed into type I and V contributions and analysed in terms of the Du binin-Astakhov equation. The corresponding calculated enthalpies of im mersion into water are in agreement with the experimental values. The number of carboxyl, lactone, phenol and basic groups identified by tit ration, 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 tota l number of sites identified on the surface.