Hollow NiCo₂S₄ microspheres synergistically promote peroxymonosulfate activation for efficient ofloxacin degradation: Performance, mechanism and degradation pathways

Ofloxacin (OFX), a widely used antibiotic, poses significant ecological risks due to its persistence in the environment. Therefore, developing simple, efficient, and durable catalysts for the removal of such pollutants remains a pressing challenge. Herein, hollow NiCo₂S₄ microspheres composed of nanosheets were successfully synthesized via a facile hydrothermal method and employed as efficient catalysts to directly activate peroxymonosulfate (PMS) for rapid OFX degradation. Experiments results revealed that the NiCo₂S₄/PMS system exhibited excellent removal performance toward a variety of representative organic pollutants. Specifically, 82.1 % of OFX was removed within 20 min under optimal conditions. Moreover, the system maintained high catalytic activity across various water matrices and retained 80.5 % efficiency after five consecutive cycles, demonstrating its excellent stability and potential for practical applications. Mechanistic investigations revealed that both non-radical species ( 1 O 2 ) and radical species (SO 4 •- , ·OH, O 2 •- ) synergistically contributed to the rapid degradation of OFX. The degradation mechanism of OFX in the NiCo₂S₄/PMS system was attributed to the synergistic catalytic effects of Ni 2+ /Ni 3+ and Co 2+ /Co 3+ redox cycles, along with sulfur species facilitating the cyclic conversion of Ni 3+ /Co 3+ to Ni 2+ /Co 2+ , thereby enhancing PMS activation. Furthermore, intermediates were identified by LC-MS, potential degradation pathways were proposed, and toxicity assessments were conducted, revealing a gradual decrease in toxicity. This study not only presents a novel strategy for designing high-performance hollow bimetallic sulfide catalysts but also offers a sustainable and efficient approach for the removal of persistent organic pollutants in complex water matrices, effectively addressing key challenges in water pollution treatment and remediation.