Enhanced visible light photocatalysis of Bi2O3/BiVO4 and Bi2O3/Ag3VO4 heterojunctions: effects of synthetic procedures

In this investigation, different synthetic procedures were used to generate Bi2O3 (BOS)/BiVO4 (BVO) and BOS/Ag3VO4 (AVO) composites. The BOS/BVO composites that were produced by single-step and two-step processes were denoted as BB1 and BB2, respectively; the BOS/AVO composites that were formed by these processes were denoted as BA1 and BA2, respectively. All photocatalysts were prepared by a hydrothermal process, except for BOS, which was prepared by a solvothermal process. The prepared composites were characterized by X-ray diffraction, scanning electron microscopy, photoluminescence spectroscopy, UV-vis diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy, and specific surface area analysis. C.I. Reactive Red 2 (RR2) was used as the parent compound in photocatalytic reactions to compare the photoactivities of the photocatalysts. The RR2 photodegradation exhibited pseudo-first-order kinetics. Under visible light irradiation, the RR2 photodegradation rate constants of BVO, AVO, BOS, BB1, BB2, BA1, and BA2 were 0.120, 0.168, 0.042, 0.750, 0.354, 1.062, and 1.244 h(-1), respectively. The improvement of photocatalytic activity was attributed to the prolongation of the lifetime of photo-generated electron-hole pairs in BOS/BVO and BOS/AVO composites. The findings of this study suggest that the photo-generated holes and superoxide anion radicals are the dominant reactive species in the oxidative degradation of RR2 in the UV/BB2 system; additionally, hydroxyl radicals are the dominant oxidative species in the UV/BA2 system.