Mechanisms for ·[Formula: see text] and ·OH Production on Flowerlike BiVO4 Photocatalysis Based on Electron Spin Resonance

Xuan Xu; Yaofang Sun; Zihong Fan; Deqiang Zhao; Shimin Xiong; Bingyao Zhang; Shiyu Zhou; Guotao Liu

doi:10.3389/fchem.2018.00064

Mechanisms for ·[Formula: see text] and ·OH Production on Flowerlike BiVO₄ Photocatalysis Based on Electron Spin Resonance

Front Chem. 2018 Mar 26:6:64. doi: 10.3389/fchem.2018.00064. eCollection 2018.

Authors

Xuan Xu^{1

2}, Yaofang Sun^{1

2}, Zihong Fan³, Deqiang Zhao^{1

2}, Shimin Xiong^{1

2}, Bingyao Zhang^{1

2}, Shiyu Zhou^{1

2}, Guotao Liu^{1

2}

Affiliations

¹ Key Laboratory of Three Gorges Reservoir Region's Eco-Environment, Ministry of Education, Chongqing University, Chongqing, China.
² National Centre for International Research of Low-Carbon and Green Buildings, Chongqing University, Chongqing, China.
³ College of Environmental and Resources, Chongqing Technology and Business University, Chongqing, China.

Abstract

Many studies have focused on the use of BiVO₄ as a photocatalyst, but few have investigated the production of free radicals during the photocatalytic process. Following synthesis of flowerlike BiVO₄ and characterization by X-ray diffraction (XRD), Raman spectroscopy, Scanning electron microscopy (SEM) Scanning electron microscopy (EDX), UV-Vis and XPS, we successfully prepared BiVO₄. Then we used electron spin resonance (ESR) to determine the production and degradation of individual active free radicals, including the superoxide radical (·[Formula: see text]) and the hydroxyl radical (·OH). In the first experiment, we used ESR to detect the signals of free radicals (·[Formula: see text] and ·OH) under varying oxygen conditions. The results shown that in addition to production by ·[Formula: see text], ·OH could also be produced by oxidation of h⁺ to OH^-. In the next experiment, we detected ·OH under varying pH to identify the result of the first experiment, and found that signal intensities increased with increasing pH, indicating the mechanism for ·OH production. Finally, we conducted a trapping experiment to examine free radical degradation mechanisms. We identified ·OH and h⁺ as the main active free radicals and showed the complete production about ·OH. These results improve current knowledge of free radical production mechanisms, which can be used to enhance the photocatalytic performance of BiVO₄.

Keywords: bismuth vanadate (BiVO4); degradation mechanism; electron spin resonance (ESR); hydroxyl radical (·OH); superoxide radical (·O−2).