Highly efficient visible light-induced photocatalytic oxidation of arsenite with nanosized WO3 particles in the presence of Cu2+ and CuO

Although WO3 appears to be one of the extensively studied photocatalysts, the low response of pure WO3 in aqueous solution under visible light limits its application remarkably. In this work, the enhancement of the efficiency of WO3 for the visible light-driven photocatalytic oxidation of arsenite was explored using Cu2+ ion and CuO as a co-catalyst. While the addition of Cu2+ was found effective for the suppression of dissolution of WO3, the efficiency of CuO appeared to be slightly lower. Significant improvement of the efficiency for the photocatalytic oxidation of As(III) with WO3 was noted when Cu2+ ions and CuO were added. The optimized conditions were WO3 in the presence of 10 mg L-1 Cu2+ ion and 1 wt% CuO coupled with WO3, respectively. The As(III) concentration of 10 mg L-1 could be lowered to less than 0.1 mg L-1 by the photocatalytic treatment. Acidic pH favours the oxidation of arsenite in the presence of Cu2+ whereas basic pH is suitable with CuO. Characterization techniques such as TEM, XPS, XRD and UV-DRS were used to characterize photocatalysts. The reactive species scavenger tests revealed that the photo-induced holes (h+) play a key role in the photocatalytic oxidation process while the effect of •OH is negligible. It was found that As(III) oxidation rate was remarkably suppressed in the nitrogen atmosphere. A mechanism for enhanced photocatalytic oxidation has been proposed based on the results of the reactive species scavenger tests. This research may contribute to the large-scale As(III) oxidation treatment in the groundwater.