TiO2 catalysed reduction of Cr(VI) in aqueous solutions under ultraviolet illumination

The photoassisted reduction of Cr(VI) to Cr(III) in aqueous suspensions of TiO₂ under ultraviolet (UV) illumination has been studied by determining the amount of Cr(VI) photoreduced at different irradiation times, the mass of catalyst in suspension, the Cr(VI) initial concentration and the pH. Samples of wastes from metal-surface treatment industries have been used to test this photocatalytic procedure for Cr(VI) elimination in a real ease. It has been observed that the presence in these samples of certain species such as Fe(III) and Cr(III) at low concentrations can increase significantly the yield of Cr(VI) photoreduction. It is assumed that these cations act by maintaining the pH during the photoreduction process, preventing the alkalization by hydrolysis of the solution.