Double Z-scheme FeVO<inf>4</inf>/Bi<inf>4</inf>O<inf>5</inf>Br<inf>2</inf>/BiOBr ternary heterojunction photocatalyst for simultaneous photocatalytic removal of hexavalent chromium and rhodamine B

Abstract

Hypothesis: Fabrication of the heterojunction photocatalyst with appropriate band potentials as a promising method of inhibiting electron-hole pair recombination leading to enhanced photocatalytic properties. Experiments: Herein, BiOBr, Bi4O5Br2, and binary BiOBr/Bi4O5Br2 composite were selectively synthesized by employing a one-step microwave irradiation method. Then, double Z-scheme FeVO4/Bi4O5Br2/BiOBr ternary composites with different weight percentages (%wt) of FeVO4 were fabricated and their photocatalytic applications were studied. The photodegradation of organic compounds (rhodamine B (RhB), methylene blue (MB) and salicylic acid (SA)), along with the photoreduction of hexavalent chromium (Cr(VI)) were investigated. Findings: Comparing with the single and binary photocatalysts, and a commercial TiO2, the 1 %wt-FeVO4/Bi4O5Br2/BiOBr photocatalyst demonstrated superior visible-light-driven photocatalytic performance. In a Cr(VI)/RhB combined system, Cr(VI) photoreduction was further improved and coexisting RhB molecules were simultaneously degraded. Removal of Cr(VI) and RhB were maximized by adjusting both pH values and catalyst dosages. Based on UV–vis diffuse reflectance spectroscopy, photoluminescence spectroscopy, electrochemical investigations, active-species trapping, nitrotetrazolium blue transformation, and silver photo-deposition experiments, a double Z-scheme charge transfer mechanism with an RhB-sensitized effect was proposed. This special mechanism has led to significant enhancement in charge segregation and migration, along with higher redox properties of the ternary composite, which were responsible for the excellent photocatalytic activity.