Dai Sun,Yu-Le Wang,Peng-Yue Zhu,Hai-Tao Ren,Yong Liu,Song-Hai Wu,Shao-Yi Jia,Xu Han
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).
Tian-Yu Liu,Cong Wang,Yong-Zhe Han,Chang Bai,Hai-Tao Ren,Yong Liu,Xu Han
Bi 2+x WO 6 are a group of reactive photocatalysts in the photooxidation of various contaminants. However, their catalytic reactivity in the persulfate (PS)-based oxidation processes in the absence of light is still unknown. In this study, Bi 2.15 WO 6 shows a high reactivity in the catalytic oxidation of bisphenol A (BPA) by PS in the absence of light under alkaline conditions, and 20 mg L -1 BPA can be rapidly removed within 30 min at pH 10.0 with the low stoichiometry ratio of 1.79 between consumed PS and removed BPA. Characterizations of the oxidation products indicate that 98.4% of soluble BPA has been oxidatively polymerized to BPA polymers, instead of being oxidized to CO 2 and H 2 O. FTIR, Raman, XPS and electrochemical analyses confirm that surface Bi(III) is the reactive site for the adsorption of BPA and PS, which then initiates reactions between BPA and PS. DFT calculations reveal that the O-O bond in PS is moderately activated via the nonradical pathway after adsorbing on Bi(III), instead of being decomposed to SO 4 •− , followed by H-abstraction from BPA by the activated PS with the formation of phenoxyl radicals and the subsequent polymerization to BPA polymers. The apparently lower energy barrier from adsorbed BPA (Δ G = 0.056 eV) than that from dissolved BPA (Δ G = 0.263 eV) further reveals that H-abstraction from adsorbed BPA to the activated PS on the surface of Bi 2.15 WO 6 is more favorable than that from dissolved BPA. This study gives new insight on the efficient removal of recalcitrant contaminants via the H-abstraction pathway.
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