Adsorption of Chromium(VI) Ions on to TiO 2 from Aqueous Solution

The study of the adsorption of the Cr VI ion on to TiO 2 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 Cr VI ion or of Cr VI –organic species which co-exist as pollutants with TiO 2 when the latter is used as a stable and highly efficient photocatalyst. It has been found that dark adsorption of the Cr VI ion on to TiO 2 is mainly dependent on the acidity of the system and the initial concentration of the Cr VI ion. As the pH of the system increases, so the extent of adsorption of the Cr VI ion decreases. The greatest adsorption was obtained with an initial Cr VI ion concentration of ca. 300 μmol/l. The presence of phosphate or acetate ions in the system dramatically decreases the adsorption efficiency of the Cr VI ion. In contrast, the addition of formic acid leads to a limited increase in the extent of Cr VI ion adsorption. Other organic ions and organic compounds examined showed no interference in Cr VI ion adsorption. FT-IR spectroscopic methods were used for the characterization of Cr VI ion adsorption on to TiO 2 .