Study of water adsorption on activated carbons with different degrees of surface oxidation

A carbon of wood origin was oxidized with different oxidizing agents (nitri c acid, hydrogen peroxide, and ammonium persulfate). The microstructural pr operties of the starting material and the oxidized samples were characteriz ed using sorption of nitrogen. The surface acidity was determined using Boe hm titration and potentiometric titration. The changes in the surface chemi stry were also studied by diffuse reflectance FTIR. Water adsorption isothe rms were measured at three different temperatures close to ambient (relativ e pressure from 0.001 to 0.3). From the isotherms the heats of adsorption w ere calculated using a virial equation. The results indicated that the isos teric heats of water adsorption are affected by the surface heterogeneity o nly at low surface coverage. In all cases the limiting heat of adsorption w as equal to the heat of water condensation (45 kJ/mol). (C) 1999 Academic P ress.