Core-shell BiOBr/BiOI/MIL-53(Fe)-min double Z-type heterojunction for efficient and stable photocatalytic degradation from small molecules to microplastics

The persistent accumulation of organic pollutants in aquatic environments poses serious risks to ecosystems and public health. In this study, a double Z-type photocatalyst BiOBr/BiOI/MIL-53(Fe)-min was successfully fabricated by a two-step solvothermal-hydrothermal synthesis method. Characterization revealed tightly stacked BiOBr/BiOI nanosheets uniformly coating rod-like the 2-methylimidazole-modified metal–organic framework MIL-53(Fe) (MIL-53(Fe)-min), forming a core-shell structure with intimate interface contact. The formation of a unique double Z-type heterojunction significantly inhibited the recombination of photogenerated electron-hole pairs and optimized the charge carrier transfer pathway. Meanwhile, the surface stacked catalyst nanosheets not only improve the utilization efficiency of photons, but also greatly increase the contact area between active radicals and reactants. Under visible light irradiation, BBF-20 composite photocatalyst demonstrated a tetracyclines (TC) degradation rate of 90.6% within 100 min, with 80.3% of its activity retained after five cycles. Notably, polyethylene terephthalate (PET) microplastics achieved 56% weight loss after being treated by BBF-20 for 8 h. The main active species during degradation process were determined through quenching experiment and EPR tests. HPLC-MS analysis proposed the possible degradation pathways for TC and PET microplastics. Based on experimental results, a double Z-type heterojunction mechanism was proposed. This work presents a novel strategy for designing efficient photocatalysts to degrade antibiotics and microplastics in complex aquatic environments.