Design of hollow mesoporous TiO 2 @BiOBr/Bi 4 O 5 Br 2 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 TiO ₂ @BiOBr/Bi ₄ O ₅ Br ₂ 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 Bi ₄ O ₅ Br ₂ at high temperature, and the remaining BiOBr acts as a bridge to connect TiO ₂ and Bi ₄ O ₅ Br ₂ 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 TiO ₂ @BiOBr/Bi ₄ O ₅ Br ₂ 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.
Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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