Enhanced visible-light activity of bismuth-rich oxybromide photocatalysts: Focus on synthesis, characterization, and modeling

Abstract

Abstract

Bismuth oxybromides (BiOBr) are promising visible light activated photocatalysts for degradation of pharmaceuticals in water. However, light absorption of BiOBr is limited to a narrow range of visible light and the rate of electron-hole recombination is quite high. Bi-rich bismuth oxybromides, such as Bi3O4Br and Bi24O31Br10 as an improvement to BiOBr are expected to show better band structure, optical properties, and charge carrier separation efficiency. In this study, BiOBr, Bi3O4Br, and Bi24O31Br10 were synthesized using a controlled solvothermal method. The photocatalysts were synthesized at 110 °C, 160 °C, and 180 °C for 18 hours. It was found that pH and temperature affect the structure, morphology, and crystallinity of the final products. BiOBr is achieved at pH around 1, while alkaline pH leads to formation of bismuth-rich oxybromides such as Bi3O4Br and Bi24O31Br10. An increase in the Bi/Br atomic ratio leads to changes in electronic band structure and better photocatalytic activity in paracetamol degradation. Among the photocatalysts, Bi3O4Br-160 °C demonstrated superior visible light activity with 80 % degradation of paracetamol and 50 % total organic carbon removal in 360 min. Based on the characterization and DFT modeling, this photocatalyst had highest conduction band minimum improving superoxide formation and better charge carrier separation efficiency. This study provides in-depth and detailed characterization of the BiOBr, Bi3O4Br, and Bi24O31Br10 and shows their activity as visible light driven photocatalysts.