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.
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