Boosting peroxymonosulfate activation by FeOCl/CuS composite for ciprofloxacin removal

The addition of CuS could enhance the catalytic activity of FeOCl. • The FeOCl/CuS/PMS can completely degrade ciprofloxacin within 4 min. • The FeOCl/CuS/PMS could work efficiently at pH 3–9. • FeOCl/CuS/PMS system contained reactive species (·OH, SO 4 ·- and O 2 ·- ). FeOCl serves as an effective iron-based catalyst in peroxymonosulfate (PMS) activation for antibiotic removal. However, its catalytic efficiency is hindered by the sluggish redox cycling between Fe 3+ and Fe 2+ . To overcome this limitation, a composite catalyst of FeOCl/CuS was synthesized to enhance catalytic activity. At an optimal mass ratio of FeCl 3 ·6H 2 O to CuS of 1:2, the FeOCl/CuS system achieved complete degradation of ciprofloxacin (CIP) within 4 min. Notably, the catalyst exhibited high degradation efficiency across a broad pH range, demonstrating strong environmental adaptability. Although common co-existing anions and humic acid exerted inhibitory effects on CIP degradation to varying extents, the system remained robust under complex water matrices. Radical quenching experiments and electron paramagnetic resonance (EPR) analyses confirmed that hydroxyl radicals (·OH), sulfate radicals (SO 4 ·- ), and superoxide anions (O 2 ·- ) were the dominant reactive species responsible for pollutant degradation. The incorporation of CuS significantly accelerated the Fe 3+ /Fe 2+ redox cycle, thereby improving PMS activation efficiency. Reaction pathway analysis revealed that CIP was degraded via two primary routes, generating 16 intermediate products, the majority of which showed reduced ecotoxicity compared to the parent compound. Furthermore, the FeOCl/CuS catalyst maintained excellent stability and reusability, retaining over 93% CIP degradation efficiency after four consecutive cycles. These results collectively highlight the promising potential of the FeOCl/CuS/PMS system for practical wastewater treatment applications.