Influence of Surface Composition and Pore Structure on Cr(III) Adsorption onto Activated Carbons

The adsorption of chromium(III) ions from aqueous solutions onto activated carbons prepared from air and CO 2 activation of Eucalyptus sawdust is studied. HNO 3 oxidation of these carbons greatly enhances their ability to retain Cr(III) mainly because of a significant increase of the concentration of carbon−oxygen surface groups. To characterize these surface groups, X-ray photoelectron spectroscopy and temperature-programmed desorption (TPD) were used. The influence of these carbon−oxygen surface groups on chromium adsorption is examined. Upon addition of acidic groups, some other functions of nonacidic character evolving as CO upon TPD seem to contribute to Cr(III) uptake. Modifications of the porous structure upon oxidation and chromium adsorption are investigated. Adsorption into the micropores appears to take place to a significant extent although oxidation of the active carbons leads to a narrowing of the average micropore widths.