Engineering an oxygen-vacancy-mediated step-scheme charge carrier dynamic coupling WO3−X/ZnFe2O4 heterojunction for robust photo-Fenton-driven levofloxacin detoxification

Abstract

Designing a heterojunction through oxygen vacancy (OV) has been considered as a well-accepted stratagem for enhanced photo-Fenton activity. Therefore, we have adopted a combination of hydrothermal and calcination methods to fabricate an abundant step-scheme photocatalyst by uniting ZnFe₂O₄ with an oxygen-defect-oriented WO₃ semiconductor and verified their activities towards levofloxacin (LVX) degradation under solar-light illumination. The as-synthesized 15%WO_3−X/ZnFe₂O₄ binary hybrid displayed increased photo-Fenton activity for LVX degradation (k_app value 4–7 times greater than that of pure semiconductors). The increased activity can be attributed to effective charge transmission occurring between the conduction band of defective WO_3−X and the valence band of ZnFe₂O₄ bridged through mediator-free OVs. The existence of OVs was well-supported with the assistance of Raman, XPS, and EPR characterization, whereas the proposed S-scheme charge transfer mechanism was proved by hydroxyl and super-oxide radical generation experiments. Furthermore, the photo-Fenton system constructed by H₂O₂ and continuous Fe(III)/Fe(II) conversion resulted in high concentration of ˙OH radical that ultimately encouraged faster LVX degradation. Through the identification of reaction intermediates via LC-MS analysis, the LVX degradation pathways were speculated.