S-scheme heterojunction g-C3N4/Bi2WO6 highly efficient degradation of levofloxacin: Performance, mechanism and degradation pathway

Abstract

g-C₃N₄/Bi₂WO₆ (MCN/BWO) heterojunction photocatalysts were synthesized via a one-step hydrothermal method for the degradation of levofloxacin (LEV). Under simulated sunlight irradiation, the degradation rate of LEV by MCN/BWO with a molar ratio of 1 : 1 reached 98.14 %, which was attributed to the formation of an S-scheme heterojunction between MCN and BWO. In situ XPS analysis and surface work function measurements confirmed that the electron transfer pathway follows the S-scheme heterojunction mechanism. The internal electric field (IEF) generated by the S-scheme heterojunction in the MCN/BWO system facilitates direct transfer of photogenerated electrons (e⁻) from the conduction band (CB) of BWO to the valence band (VB) of MCN. This process enables efficient separation of photogenerated electron-hole (e⁻-h⁺) pairs, with h⁺ accumulating on the VB of BWO and e⁻ accumulating on the CB of MCN. Free radical trapping experiments demonstrated that the superoxide free radical (·O₂⁻) and h⁺ were the primary active species. Besides exhibiting superior photocatalytic performance, the catalyst maintained excellent stability over three consecutive cycles. To elucidate the degradation mechanism, liquid chromatography-mass spectrometry (LC-MS) and quantitative structure-activity relationship (QSAR) analysis were employed to identify degradation pathways, intermediates, and potential toxicity. This study provides a theoretical foundation for wastewater treatment applications.