Visible light CrO42- reduction using the new CuAlO2/CdS hetero-system

In this study, 64% of hexavalent chromium Cr(VI) reduction from the initial concentration (10(-4) M) is reported under visible light using the (CuAlO2/CdS) hetero-system. In this new hetero-system, low doped CuAlO2 delafossite, synthesized by sol-gel works as an electrons reservoir with a wide space charge region (440 nm). In this case, the electron transfer to chromate is mediated via the hexagonal CdS variety, whose conduction band level is at -1.08 V with respect to the saturated calomel electrode which is more negative than the CrO42-/Cr3+ level. This high reduction rate is achieved under optimized pH and CuAlO2 percentage. Moreover, salicylic acid gives the best performance among hole scavengers and CuAlO2 approaches 100% photostability at pH 7.5. The photo-catalytic process follows a pseudo first order kinetic with a half life of 2 h. The reaction products are identified by UV-visible spectrophotometry and linear voltametry at a platinum rotating electrode. The results reveal the presence of Cr3+ after irradiation. (C) 2012 Published by Elsevier B.V.