Synthesis of Bi2O3/BiVO4 heterojunction with enhanced photocatalytic activity via single-step hydrothermal method

Abstract

The single-step hydrothermal method was used to synthesize Bi2O3/BiVO4 heterojunctions (BBVs) with various Bi2O3/BiVO4 molar ratios. The surface characteristics of the prepared photocatalysts were analyzed by X-ray diffractometry (XRD), scanning electron microscopy, transmission electron microscopy, ultraviolet (UV)-visible-light (Vis.) spectrophotometry, surface area analysis, X-ray photoelectron spectroscopy and fluorescence spectrophotometry. C.I. Reactive Red 2 (RR2) was used as the parent compound to evaluate the photocatalytic activity of photocatalysts under UV and Vis. irradiation. The XRD peak intensity of BiVO4 declined as the amount of Bi2O3 in the BBVs increased. The surface areas of all BBVs exceeded those of Bi2O3 and BiVO4 and all of the samples exhibited strong absorption in the Vis. region. The optimal Bi2O3/BiVO4 molar ratio was 0.25 and the corresponding photocatalyst was denoted as 0.25 BBV. The RR2 photodegradation rate constant of 0.25 BBV was 1.9 times that of BiVO4 under UV irradiation, which was in turn 3.5 times that of BiVO4 under Vis. irradiation. The improved photodegradation efficiency of BBVs is attributed to the effective separation of photo-generated carriers by the formed heterojunction. The results of a radical-trapping experiment revealed that the photo-generated holes and superoxide anion radicals were the primary reactive species in the BBV photocatalytic systems.