Different paths lead to the same destination: The mechanism of photocatalytic oxidation of As(III) by polyoxometalates

Abstract This study revealed the mechanism of the photocatalytic oxidation of As(III) by phosphotungstic acid (PTA) via experiments and density functional theory (DFT) simulations. All the experimental results were highly consistent with the simulated data. The results showed that hydroxyl radical ( OH)was the main reactive species for the photocatalytic oxidation of As(III) by PTA. Interestingly, when 2-propanol was added to the system, the main reactive species was converted to peroxide species (-OOH). The effect of the O2, H-sites, radicals, and light irradiation time were studied in this research and a 5 steps -OOH mechanism of oxidation of As(III) was first proposed and proved. This mechanism included the adsorption of O2 on H-sites of the catalyst surface; the formation of the peroxide species -OOH; the -OOH dissociated from catalyst surface and reacted with As(III) to form HOO-As(III) compound; the transformation of the HOO-As(III) to As(V); and the regeneration of the catalyst. What represented in this study should provide a rational theoretical support for oxidation of As(III) to As(V).