Photocatalytic reduction of hexavalent chromium (Cr(VI)) using rotating TiO₂ mesh

Abstract

An immobilized TiO₂ electrode for photocatalytic hydrogen production is applied to reduce toxic Cr(VI) to non toxic Cr(III) in aqueous solution under UV irradiation. To overcome the limitation of powder TiO₂, a novel technique of immobilization based on anodization was applied and investigated under various experimental conditions. The anodization was performed with three different electrolytes (single or mixed), and then the anodized samples were annealed under an oxygen stream. Among the three kinds of anodized/annealed TiO₂ on Ti foil, Sample II (anodized at 20 V in 0.5% HF for 45 min at 5 °C, and annealed at 450 °C for 5 hr in ambient oxygen at a flow rate of 400 mL/min) was more effective for both Cr(VI) reduction than the other samples. Based on the electrolyte compositions, nanotubular TiO₂ grown on Ti meshes was fabricated for the purpose of its light-harvesting ability and efficiency, where the anodized/annealed TiO₂ on meshes were rotated in the center of the reactor and Cr(VI) could be effectively reduced at rotation speeds ranging from 0 to 64 rpm. In case of Sample II, it was found that up to 98 % of the Cr(VI) was reduced in 30 min at 64 rpm.