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Bi2+xWO6 is a cost-effective and environmentally friendly photocatalyst that shows high reactivity in the oxidation of various contaminants under visible light. However, under alkaline conditions, the reactive oxidative species in the Bi2+xWO6 system are still not clear yet. In this study, it is observed that the oxidation rates of As(III) increase with increasing pH values in the Bi2.15WO6 system. Photoluminescence and the Mott–Schottky analyses confirm that OH− promotes the separation and transfer of photogenerated electron–hole pairs over Bi2.15WO6, thus facilitating the oxidation of As(III). Electron spin resonance spectra analysis and quenching experiments rule out contributions of •OH, O2˙−, 1O2 and superoxo species to As(III) oxidation and indicate that surface –OOH and/or H2O2 are indeed the predominant species under alkaline conditions. The improved production of H2O2 by H-donors such as glucose and phenol, as well as the UV-vis diffuse reflectance and Raman analyses, further confirms the formation of surface –OOH on Bi2.15WO6 under alkaline conditions. In the dark, the significant higher oxidation rate of As(III) by H2O2–Bi2.15WO6 than that by H2O2 alone reveals that surface −OOH, instead of H2O2, plays an important role in As(III) oxidation. This study enriches our understanding of the diversity of reactive oxygen species (ROS) in the Bi2.15WO6 system and gives new insight into the mechanism involved in the oxidation of As(III) under alkaline conditions. [ABSTRACT FROM AUTHOR]

Photocatalytic technology is a popular research area for converting solar energy into environmentally friendly chemicals and is considered the greenest approach for producing H 2 O 2 . However, the corresponding reactive oxygen species (ROS) and pathway involved in the photocatalytic generation of H 2 O 2 by the Bi 2.15 WO 6 -glucose system are still not clear. Quenching experiments have established that neither • OH nor h + contribute to the formation of H 2 O 2 , and show that the formed surface superoxo (≡Bi-OO • ) and peroxo (≡Bi-OOH) species are the predominant ROS in H 2 O 2 generation. In addition, various characterizations indicate the enhanced electron-transfer on the surface of Bi 2.15 WO 6 with increasing contents of glucose via the ligand-to-metal charge transfer pathway, confirming H-transfer from glucose to ≡Bi-OO • or ≡Bi-OOH. The increased production of H 2 O 2 with decreasing bond dissociation energy (BDE O-H ) values of various phenolic compounds again supports the H-transfer mechanism from phenolic compounds to ≡Bi-OO • and then to ≡Bi-OOH. DFT calculations further reveal that on the Bi 2.15 WO 6 surface, oxygen is sequentially reduced to ≡Bi-OO • and ≡Bi-OOH, while H-transfer from H 2 O or glucose to ≡Bi-OO • and ≡Bi-OOH, resulting in the production of H 2 O 2 . The lower energy barrier of H-transfer from adsorbed glucose (0.636 eV) than that from H 2 O (1.157 eV) indicates that H-transfer is more favorable from adsorbed glucose. This work gives new insight into the photocatalytic generation of H 2 O 2 by Bi 2.15 WO 6 in the presence of glucose/phenolic compounds via the H-abstraction pathway.

Conversion of aniline wastes to value-added products is always a promising method to treat aniline wastewater. In this study, a selective oxidation of aniline contaminants by Bi 2·15 WO 6 was carried out under visible light and alkaline conditions. Kinetic results show that the oxidation rates of aniline increase with increasing pH values under visible light. UV-vis absorption spectra and GC-MS analysis confirm that azobenzene is the primary oxidation product with aminophenol and N,N'-diphenylhydrazine as the secondary products. The analyses from Mott-Schottky, electrochemical impedance spectroscopy (EIS), transient photocurrent and photoluminescence (PL) further indicate that OH - promotes the separation and transfer of photogenerated electron-hole pairs on the surface of Bi 2·15 WO 6 , thus facilitating oxidation of aniline. Quenching experiments and electron spin resonance (ESR) analysis confirm that h + is the predominant specie in the Bi 2·15 WO 6 system and aniline radical cation (PhNH 2 •+ ) is an important intermediate. The Hammett and ΔBDE N-H plots further reveal that e - abstraction from aniline with the formation of PhNH 2 •+ , followed by H + abstraction from PhNH 2 •+ with the formation of anilino radicals (PhNH • ), is the prerequisite for the formation of N,N'-diphenylhydrazine, which is then oxidized to azobenzene via the hydrogen-abstraction pathway. This work provides a cost-effective method to selectively oxidize aniline to azobenzene., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Bi2+xWO6 is a cost-effective and environmentally friendly photocatalyst that shows high reactivity in the oxidation of various contaminants under visible light. However, under alkaline conditions, the reactive oxidative species in the Bi2+xWO6 system are still not clear yet. In this study, it is observed that the oxidation rates of As(iii) increase with increasing pH values in the Bi2.15WO6 system. Photoluminescence and the Mott-Schottky analyses confirm that OH- promotes the separation and transfer of photogenerated electron-hole pairs over Bi2.15WO6, thus facilitating the oxidation of As(iii). Electron spin resonance spectra analysis and quenching experiments rule out contributions of •OH, O2˙-, 1O2 and superoxo species to As(iii) oxidation and indicate that surface -OOH and/or H2O2 are indeed the predominant species under alkaline conditions. The improved production of H2O2 by H-donors such as glucose and phenol, as well as the UV-vis diffuse reflectance and Raman analyses, further confirms the formation of surface -OOH on Bi2.15WO6 under alkaline conditions. In the dark, the significant higher oxidation rate of As(iii) by H2O2-Bi2.15WO6 than that by H2O2 alone reveals that surface -OOH, instead of H2O2, plays an important role in As(iii) oxidation. This study enriches our understanding of the diversity of reactive oxygen species (ROS) in the Bi2.15WO6 system and gives new insight into the mechanism involved in the oxidation of As(iii) under alkaline conditions.