Z-scheme charge transfer–driven peroxymonosulfate activation over MIL-53-NH₂(Fe)/Bi₂WO₆ for mechanistic degradation of polystyrene microplastics

The environmental persistence and potential toxicity of microplastics have raised serious concerns regarding their impacts on aquatic ecosystems and human health. Herein, a Z-scheme heterojunction photocatalyst, MIL-53-NH 2 (Fe)/Bi 2 WO 6 , was rationally constructed to promote directional charge separation and enhance redox reactivity under light irradiation. Interfacial coupling between MIL-53-NH 2 (Fe)/Bi 2 WO 6 facilitates an efficient Z-scheme charge-transfer pathway, preserving the strong oxidation ability of photogenerated holes on Bi 2 WO 6 and the high reduction potential of electrons on MIL-53-NH 2 (Fe). When coupled with peroxymonosulfate (PMS), the heterojunction effectively activates PMS via electron-mediated pathways, leading to the generation of reactive oxygen species (ROS), primarily sulphate radicals (SO 4 •⁻ ), accompanied by the generation of hydroxyl radicals ( • OH) and superoxide radicals( • O 2 ⁻ ). As a result, polystyrene (PS) microplastics undergo accelerated oxidative chain scission, surface oxidation, and mass loss, achieving a weight reduction of 45.36% in the presence of 5 mM PMS. Radical quenching experiments and electron paramagnetic resonance (EPR) spectroscopy collectively confirm the dominant role of PMS-derived ROS and validate the proposed Z-scheme-driven degradation mechanism. This study elucidates the synergistic interplay between heterojunction charge dynamics and PMS activation, offering mechanistic insights into the design of efficient photocatalytic systems for microplastic degradation in aquatic environments.