Boosting peroxymonosulfate activation over Co-N-C@Co9S8 double-shelled nanocages for ciprofloxacin degradation: Insights into catalytic performance, degradation mechanism and routes

In order to achieve a clean water environment in line with the development strategy of the United Nations Sustainable Development Goals, a novel Double-Shell Nanocage (Co-N-C@Co₉S₈) was prepared in this study and applied to the activation of peroxymonosulfate (PMS) to achieve efficient degradation of ciprofloxacin (CIP). 94.9 % of CIP was removed within 10 min, which was adaptable to a wide pH range. Free radical quenching experiments and electron paramagnetic resonance (EPR) results indicated that the active species such as SO₄^•-, •OH, O₂^•-and ¹O₂ were the key to the degradation of CIP, with SO₄^•- playing a dominant role, and the cumulative concentration of SO₄^•- reached 3.43 μM at 7 min. Electrochemical characterization demonstrated that the Co-N-C@Co₉S₈ possessed a higher capacity to promote the transfer of electrons and enhanced the electron-hole pair separation. Twenty-four possible intermediates were deduced using liquid chromatography-mass spectrometry (LC-MS), including two new substances that have not been reported, and a novel CIP degradation pathway was proposed in the paper, while the toxicity of the intermediates was evaluated using quantitative conformational relationship prediction methods. Co-N-C@Co₉S₈ showed good degradation performance (CIP removal > 70 %) in both actual aquaculture wastewater and natural water, and maintained a high CIP removal (82.1 %) after four cycles of experiments. The very high utilization efficiency of the catalyst (0.0902 mmol·g⁻¹·min⁻¹) was calculated, and the results indicated that Co-N-C@Co₉S₈ has good practicality and economy, and can be applied to the treatment of difficult-to-degrade antibiotics after primary and secondary water treatments through further exploration in the future. This work provides a new approach for the development of catalysts with non-homogeneous high catalytic performance with shell-like structure.