Facile synthesis and enhanced photocatalytic activity of a novel FeVO<inf>4</inf>/Bi<inf>4</inf>O<inf>5</inf>Br<inf>2</inf> heterojunction photocatalyst through step-scheme charge transfer mechanism

Abstract

Construction of a step-scheme (S-scheme) heterojunction photocatalyst is currently under investigation as it is known to facilitate a decrease in the e–/h+ recombination rate and preserves a strong redox ability. This research work has reported on the use of microwave irradiation combined with the wet impregnation synthesis of FeVO4/Bi4O5Br2 heterojunctions at different weight percentages (%wt) of FeVO4 (0.5%, 1%, 3% and 5%wt). The visible-light-driven photocatalytic activities for the photoreduction of Cr(VI), and the decontamination of certain organic pollutants (bisphenol A; BPA, rhodamine B; RhB, and tetracycline hydrochloride; TC) were also investigated. Ethylene glycol that was used as a reaction medium in the microwave synthesis process played a key role in the formation control of a flower-like structure of bismuth-rich Bi4O5Br2. Among the heterojunction photocatalysts, FeVO4/Bi4O5Br2 with 1%wt of FeVO4 markedly maximized the photocatalytic activity. Specifically, 95% of Cr(VI) was reduced by a reduction rate that was 6.0 times higher than that of Bi4O5Br2. Similarly, this photocatalyst was able to degrade 90%, 97%, and 88% of BPA, RhB, and TC at degradation rates that were 2.0, 1.2, and 1.6 times higher than Bi4O5Br2, respectively. Trapping experiments indicated that •O2− and h+ were the main active species responsible for the organic pollutant degradation, while •OH played a minor role in this process. These outcomes were confirmed with the use of the nitrotetrazolium blue transformation method and the terephthalic acid photoluminescence probing technique. Enhancement in the photo-activity of 1%wt-FeVO4/Bi4O5Br2 was attributed to the extended visible-light absorption range as well as the efficient generation, separation, and migration of photo-generated charge carriers through the S-scheme charge transfer mechanism which was supported by the results from the trapping experiments, XPS and UV–vis DRS analyses, Ag and PbO2 photo-deposition experiments, and electrochemical studies, along with the consideration of the reduction potentials of reactive oxygen species.