Enhancement of microplastics degradation with MIL-101 modified BiOI photocatalyst under light and dark alternated system

The composite material combining BiOI with metal-organic frameworks, was developed as catalyst for microplastics degradation. The preparation was modified to achieve the optimal composite catalyst BiOI/MIL-101-40%. The composites exhibited a larger surface area, superior photo-activity, and a distinct heterojunction structure, which accelerated the separation of electrons and holes. Besides, the inclusion of Fe(II) within MIL-101 could construct a photo-Fenton reaction upon the addition of H2O2 in the solution. The carbonyl index of treated polyethylene microplastics increased by 0.127 after 6 h reaction, which was 5.3 and 3.7 times higher than monomer BiOI and MIL-101, respectively. Efficient electron-hole separation and Fe(III)/Fe(II) conversion improved the rate-limiting step of the Fenton process, leading to a synergistic effect between photocatalysis and Fenton reaction, significantly enhancing PE degradation efficiency. Electron spin resonance spectroscopy and selective radical quenching experiments were performed to detect the active components, and the main active species proved to be the hydroxyl radical and the hole. The band structure of the photocatalyst and intermediate products in the reaction solution were subsequently analyzed, leading to the inference of potential reaction mechanisms and pathways. The catalyst-built Fenton system demonstrated outstanding proficiency even under alternating light and dark conditions. The extracted microplastic samples also confirmed the feasibility of this system for complex samples. In conclusion, this study highlighted a green and efficient approach that may be used in future industrial applications to combat microplastic pollution.