Boosting charge transfer promotes photocatalytic peroxymonosulfate activation of S-doped CuBi2O4 nanorods for ciprofloxacin degradation: Key role of Ov–Cu–S and mechanism insight

The regulation of the metal–oxygen tetrahedron active center in spinel catalysts is crucial for enhancing the photocatalytic activation of peroxymonosulfate (PMS) to degrade organic pollutants. Herein, S−doped CuBi₂O₄ (CBOS) catalysts with surface oxygen vacancies (O_v) were prepared via a one-step hydrothermal method. The cycling of Cu(I)/Cu(II) and the trapping of photogenerated electrons by O_v significantly enhance the migration of photogenerated carriers. Density functional theory (DFT) calculations revealed that the synergistic effect of S doping and O_v successfully modulated the charge distribution around the Cu site in Cu−O tetrahedron. Furthermore, the exceptional adsorption and activation abilities of O_v−Cu−S on PMS greatly enhanced the photocatalytic activation of S−doped CuBi₂O₄, which resulted in the degradation of ciprofloxacin (CIP). The optimal CBOS2 was capable of removing 95.3 % of CIP in 60 min, a 40.7 % increase compared to pure CuBi₂O₄. Electron paramagnetic resonance (EPR) spectroscopy and quenching tests confirmed the synergistic effect of radical and non-radical mixed pathways (SO₄^•−, •OH, ¹O₂) on the removal of CIP. The potential pathways for CIP degradation were further explored using liquid chromatography-mass spectrometry (LC−MS) test results. This study offers a novel perspective for the research and application of spinel-based catalysts in water treatment.