Revealing the charge transfer mechanism in Er ion-doped Bi₄O₅Br₂/g-C₃N₅ nanocomposite for efficient photocatalytic degradation of antibiotic tetracycline

Pharmaceutical products occurring in freshwater bodies create numerous problems for the water bodies owing to their bio-toxic nature. In order to remove such pharmaceutical pollutants, a novel Er-doped Bi₄O₅Br₂/g-C₃N₅ nanocomposite was prepared by one-pot synthesis and applied for the photocatalytic removal process. The Er ions doped on the surface of Bi₄O₅Br₂/g-C₃N₅ nanocomposite exhibited 97% degradation of tetracycline in 60 min under visible light irradiation, which is higher than pure g-C₃N₅ and Bi₄O₅Br₂ photocatalysts. The improved photocatalytic properties are attributed to the outstanding visible light harvesting capacity and quick charge carrier separation efficiency which greatly reduced the recombination rate in the heterojunctions. Based on radical trapping experiments, the ^•O₂⁻, h⁺ and •OH radicals played a prominent role in the photodegradation reactions under visible light. Finally, the ternary Er-doped Bi₄O₅Br₂/g-C₃N₅ nanocomposite is effectively recyclable with quite a stable photocatalytic removal rate. This work enables a new perspective on the rational design of rare-earth-based nanocomposites for various pharmaceutical pollutants treatment processes.