Adsorption of Chromium(VI) Ions on to TiO2 from Aqueous Solution

Abstract

The study of the adsorption of the CrVI ion on to TiO2 not only provides information on the removal of heavy metal ions from polluted aqueous solutions; but is also useful for further investigation of the photocatalytic decontamination of the CrVI ion or of CrVI–organic species which co-exist as pollutants with TiO2 when the latter is used as a stable and highly efficient photocatalyst. It has been found that dark adsorption of the CrVI ion on to TiO2 is mainly dependent on the acidity of the system and the initial concentration of the CrVI ion. As the pH of the system increases, so the extent of adsorption of the CrVI ion decreases. The greatest adsorption was obtained with an initial CrVI ion concentration of ca. 300 μmol/l. The presence of phosphate or acetate ions in the system dramatically decreases the adsorption efficiency of the CrVI ion. In contrast, the addition of formic acid leads to a limited increase in the extent of CrVI ion adsorption. Other organic ions and organic compounds examined showed no interference in CrVI ion adsorption. FT-IR spectroscopic methods were used for the characterization of CrVI ion adsorption on to TiO2.