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

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 Bi 3 O 4 Br and Bi 24 O 31 Br 10 as an improvement to BiOBr are expected to show better band structure, optical properties, and charge carrier separation efficiency. In this study, BiOBr, Bi 3 O 4 Br, and Bi 24 O 31 Br 10 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 Bi 3 O 4 Br and Bi 24 O 31 Br 10 . 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, Bi 3 O 4 Br-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, Bi 3 O 4 Br, and Bi 24 O 31 Br 10 and shows their activity as visible light driven photocatalysts. • The bismuth-rich photocatalysts exhibited high activity in paracetamol degradation. • The greater the Bi/Br atomic ratio, the better the performance of the photocatalyst. • Synthesis temperature and pH can be considered as structure-controlling parameters.