Mechanisms involved in the photocatalytic oxidation of As­(III) are complicated in that various oxidizing species (such as h+, •OH, and O2 •–) have been suggested to play important roles in different photocatalytic systems. In this study, Bi2.15WO6 shows high reactivity in the photocatalytic oxidation of As­(III) under visible light. Quenching experiments indicate that apart from h+, the surface superoxo (Bi–OO•) and peroxo species (Bi–OOH) formed on Bi2.15WO6 also contribute to As­(III) oxidation. The increased production of H2O2 with increasingly consumed As­(III) or with the addition of H-donors such as glucose and various phenolics further reveals that H-abstraction from As­(III) or H-donors to Bi–OO• and then to Bi–OOH is an important pathway involved in H2O2 production and As­(III) oxidation. In addition, various characterizations confirm that the As­(III)–O–Bi­(III) surface complexes formed on Bi2.15WO6 enhance the photocatalytic reactivity of Bi2.15WO6 via the ligand-to-metal charge transfer pathway. We therefore suggest that dissolved oxygen is sequentially reduced to Bi–OO• and then to Bi–OOH on Bi2.15WO6, accompanied by H-abstraction from adsorbed or aqueous As­(III) to Bi–OO• and Bi–OOH with the formation of H2O2 and the oxidation of As­(III). This work enriches our understanding of the mechanisms involved in the photocatalytic oxidation of As­(III).

In this study, Bi2.15WO6 with different morphologies was successfully synthesized and used for the selective photooxidation of benzyl alcohol to benzaldehyde in aqueous solutions. High conversion (85%) and selectivity (85%) can be simultaneously achieved under alkaline conditions by adding ethylenediamine to protect the produced benzaldehyde from overoxidation. In the oxidation process, Bi–OO• and Bi–OOH on Bi2.15WO6, instead of OH• and O2 •–, are the primary oxidizing species to sequentially abstract two H (H+ + e–) from benzyl alcohol, accompanied by the formation of H2O2. Meanwhile, h+ and OH– also minorly contribute to the selective oxidation of benzyl alcohol via the H-abstraction pathway. This study enriches our understanding of the oxidizing species involved in the selective photooxidation of benzyl alcohol to benzaldehyde.