Microwave-assisted synthesis of hierarchical BiOBr/BiOF Z-scheme heterojunction with abundant oxygen vacancies for activating peroxymonosulfate toward photodegradation of the refractory levofloxacin

Abstract

Herein, a novel Z-scheme BiOBr/BiOF heterojunction was synthesized via one-step microwave-assisted hydrothermal method, which was integrated with peroxymonosulfate (PMS) to design a sulfate radical (•SO₄⁻) based advanced oxidation processes (AOPs) system through PMS activation (BiOBr/BiOF-PMS) toward Levofloxacin (LFX) photodegradation. In order to achieving an optimal degradation efficiency, the formed BiOBr/BiOF-PMS was systematically investigated and the operational parameters for LFX photodegradation were thoroughly optimized. Thereby, the optimal BiOBr/BiOF exhibits a higher photodegradation efficiency of 89.8 % toward LFX via PMS activation compared to others including PMS alone, BiOBr, BiOF and BiOBr/BiOF with varied ratios. Furthermore, the BiOBr/BiOF has superior stability for multiple cycles and universal applicability for degrading various contaminants. This can mainly be attributed that the formed heterojunction between BiOBr and BiOF and the enhanced concentration of oxygen vacancies (OVs) of BiOBr/BiOF heterojunction, which can synchronously promote the separation and transmission of the photogenerated charges (e⁻/h⁺) and thereby lead to more reactive oxygen species (ROS). As well, the expanded optical responsiveness and increased specific surface area of BiOBr/BiOF are also mainly responsible for the improved photodegradation capability. Free radical capture experiments and ESR technique verify that the •O₂⁻ is the primary ROS and •SO₄⁻ and •OH play subordinative role. The photodegradation pathways of LFX were unraveled based on the identified intermediates with a liquid-chromatography-mass (LC-MS) technique. Consequently, this study offers a novel route by developing Bi-based heterojunction photocatalyst to activate PMS for refractory antibiotic photodegradation.