Simultaneous photocatalytic Cr(VI) reduction and dye oxidation in a TiO2 slurry reactor

The semiconductor photocatalytic reduction is a relatively new technique for the removal of dissolved metal ions, such as Cr(VI) and organic compounds in wastewater. Many studies concern only the catalytic activity of TiO2 with single substrates. However, for practical applications it is necessary to evaluate the photocatalytic simultaneous reduction and oxidation reactions. In this paper, we report the results of a study on the simultaneous Cr(VI) reduction and the Luranzol S Kong dye (from the tannery industry) oxidation by photocatalysis, The experiments were performed in a UV reactor system with a lamp of 150 W, using TiO2 as a catalyst. We evaluated the effect of pH and concentration of pollutants on the kinetics of the reactions. Isolated tests showed that both Cr(VI) and Luranzol S Kong are degraded in acidic pH, according to the Langmuir-Hinshelwood kinetic model, In neutral pH, the Cr(VI) is not reduced, but this might be explained by the fact that Cr(VI) is not adsorbed on TiO2 surface. The dye is almost completely degraded by both acidic and neutral pH. Under UV irradiation, photo-induced Cr(VI) reduction is observed in both Cr(VI)-TiO2 and dye-Cr(VI)-TiO2, and dye oxidation is observed in both dye-TiO2 and dye-Cr(VI)-TiO2. The concentration of Cr(VI) and dye, and the pH are the main parameters influencing both reactions. In the simultaneous reduction-oxidation process, the reduction of Cr(VI) proceeds quicker than it does in the single process, showing synergism between the oxidation and reduction reactions, (C) 2002 Elsevier Science B,V. All rights reserved.