Visible-Light-Driven Peroxydisulfate Activation By Fe₂O₃/Bi₂WO₆ For Boosting Tetracycline Degradation

Peroxydisulfate（PDS）can be activated to produce highly active SO₄^·-by transition metals,heat,ultraviolet light,electrolysis,so PDS-based advanced oxidation process can degrade organic pollutants quickly and efficiently.Fe is a cheap and widely available transition metal.Fe²⁺can activate PDS efficiently,but it is easily oxidized to Fe³⁺.The activation efficiency of Fe³⁺for PDS is low.Therefore,if the conversion of Fe³⁺/Fe²⁺can be realized,the application of Fe³⁺in the field of PDS activation can be improved.Photocatalysis is considered to be an effective way to assist transition metals to activate PDS due to its simplicity,high efficiency and no secondary pollution risk.However,UV only has a 4%occupancy ratio in solar spectroscopy and UV radiation alone requires a lot of energy,so photocatalysts responded to visible light（vis）have higher research value.In this study,the Fe₂O₃/Bi₂WO₆ composite materials that can respond to visible light were prepared by hydrothermal method,and the removal of tetracycline（TC）in water by Fe₂O₃/Bi₂WO₆/PDS/vis system was investigated accordingly.（1）In this study,the composite materials were prepared through different preparation ways,and the effect of these materials on TC removal by activating PDS under visible light was studied.The optimal preparation conditions were determined as follows:the synthesis temperature was 160℃,the synthesis time was 24 h,and the mass ratio of Fe₂O₃/Bi₂WO₆ was 1/100.（2）The visible light source was simulated by a 300 W Xe lamp,and TC was removed under the condition of 0.3 g/L Fe₂O₃/Bi₂WO₆,0.3 g/L PDS,20mg/L TC and natural pH.A rapid degradation of TC with the rate constant4.2×10² min^-1 was implemented,which was 8.5-fold and 16.6-fold higher than that of Fe₂O₃/Bi₂WO₆/vis and Fe₂O₃/Bi₂WO₆/PDS system,respectively.The factors such as catalyst dosage,PDS concentration,initial TC concentration,initial pH of reaction and coexisting anions in water were analyzed.Moreover,the as-prepared composite still maintained good stability and reusability after 5 cycling experiments.（3）The mineralization of TC was measured by total organic carbon（TOC）.The intermediates,the final products and the degradation pathways of TC were identified by a liquid chromatography-mass spectrometry（LC-MS）.A possible catalytic mechanism was proposed based on quenching experiments and electron spin resonance（ESR）tests.SO ₄^·-and·OH played a major role in the degradation of TC.Besides,electron-hole pairs,O₂^·-,and ¹O₂ also had a certain contribution.This study explored a sustainable and environmentally-friendly strategy for enhanced Fe²⁺/Fe³⁺cycle driven by visible light,and provided an idea to activate PDS by using Fe³⁺-based materials.