Photoreduction of toxic chromium using TiO2-immobilized under natural sunlight: effects of some hole scavengers and process parameters

This work focuses on the photocatalytic reduction of Cr(VI)–Cr(III) using TiO2-immobilized onto glass slides under natural sunlight. The commercial TiO2 Degussa P25 was used as a photocatalyst in this work. The effects of some additives as hole scavengers for Cr(VI) reduction are studied. The results show that their presence enhances the reduction rate in the order: tartaric acid > oxalic acid > EDTA > ethanol > methanol > no-additive. The optimization of tartaric acid concentration is determined. The effect of process parameters such as Cr(VI) concentration, pH, and the presence of interfering substances such as inorganic anions (SO42-, CO32-, NO3-, Cl- and PO43-) and metallic cations (Fe3+, Cu2+, Zn2+, and Mn2+) is investigated. The results show that the removal rate is maximum at pH 1.5. On the other hand, the coexistence of interfering ions with Cr(VI) decreases the reduction rate except for the Fe3+. Finally, the results show that the TiO2-immobilized can be reused several times.