Oxygen-free wastewater treatment system constructed using FeWO4@CN S-scheme heterojunction photocatalyst coupled with H2O2 activation

Abstract

The construction of a novel, low-cost, anoxic catalytic oxidation system, in which light-assisted heterogeneous catalysis is employed to regulate the activation of H₂O₂, holds potential application value for water purification. In this study, an oxygen-free FeWO₄@CN/H₂O₂/Vis system was designed for the advanced treatment of ofloxacin (OFL)-contaminated wastewater. XPS, ESR, and UPS analyses demonstrated that the S-scheme charge transfer pathway greatly accelerated the charge transfer rate within the heterojunction. The FeWO₄@CN-20 photocatalyst demonstrated 99% removal of OFL within 20 minutes, significantly outperforming monomeric CN. The degradation rate of OFL by FeWO₄@CN-20 was approximately 7.5 times higher than that by CN and 10.8 times higher than that by FeWO₄. ROS -capturing experiments in an anaerobic environment revealed that the generated ˙O₂⁻ and ¹O₂ played predominant roles in degrading OFL. Moreover, the Fe²⁺/Fe³⁺ redox cycle synergistically enhanced H₂O₂ activation, ensuring both the efficiency and stability of the photo-Fenton reaction. In situ Raman and ESR spectroscopies further revealed the catalytic mechanism by which synergistic visible-light irradiation enhanced the H₂O₂ activation efficiency. Continuous membrane reactor experiments confirmed that the FeWO₄@CN/H₂O₂/Vis system significantly enhanced photo-Fenton activity and OFL degradation stability compared with the FeWO₄@CN/H₂O₂ and CN/H₂O₂/Vis systems. Moreover, the FeWO₄@CN/H₂O₂/Vis system not only exhibited photothermal effects but also showed excellent resistance to ion interference and continuous degradation under hypoxic conditions. The degradation products exhibited low or no toxicity, suggesting the system's potential for practical applications. Overall, this study offers valuable insights into the development of heterojunction photocatalysts to remediate fluoroquinolone antibiotic pollutants in aquatic environments.