Design of hollow mesoporous TiO2@BiOBr/Bi4O5Br2 type-II/Z-scheme tandem heterojunctions under confinement effect: Improved space charge separation and enhanced visible-light photocatalytic performance

The new type of hollow mesoporous TiO2@BiOBr/Bi4O5Br2 type-II/Z-scheme tandem heterojunction is synthesized using MIL-125(Ti) as the precursor based on the confinement effect caused by the outward shrinkage induced by the interface. Among them, the BiOBr shell is an indispensable component of forming a cavity during the pyrolysis of MIL-125(Ti). Not only that, BiOBr is partially converted into Bi-rich Bi4O5Br2 at high temperature, and the remaining BiOBr acts as a bridge to connect TiO2 and Bi4O5Br2 to construct a type-II/Z-scheme tandem heterojunction. This new type of hollow mesoporous tandem heterojunction shows excellent degradation efficiency (95%) for 10 mg/L ciprofloxacin (CIP) within 40 min, with a rate constant (K) of 0.05930 min-1. The Fukui index is used to determine the attack site of CIP, and the possible degradation pathway is proposed through LC-MS analysis. The results of the culture of Vibrio qinghaiensis-Q67 showed that ciprofloxacin and its intermediate products have biological toxicity, and the toxicity is reduced with the progress of photodegradation. This method of synthesizing novel hollow mesoporous TiO2@BiOBr/Bi4O5Br2 type-II/Z-scheme tandem heterojunctions based on the confinement effect will provide a new idea for other use of MOF to synthesize hollow and high-efficiency heterojunctions.