Cu₂S-modified iron sludge with high activity and stability for ciprofloxacin removal in a Fenton-like system

Pyrolysis-derived Fenton-like catalysts show promise for the resourceful utilization of iron sludge. However, catalysts prepared directly from iron sludge often exhibit limited performance due to an inefficient Fe(III)/Fe(II) redox cycle. In this work, a solvothermal Cu₂S-modified iron-sludge-based catalyst/hydrogen peroxide (H₂O₂) system was developed for ciprofloxacin (CIP) degradation. Specifically, FC-160-3, synthesized with a Cu₂S to iron sludge-derived carbon mass ratio of 3:10 and subjected to a hydrothermal temperature of 160 °C, demonstrated the best activation performance. The FC-160-3/H₂O₂ system removed 98.1 % of CIP within 90 min, with a rate constant of 0.0455 min^-1, outperforming the unmodified iron-sludge-based catalyst/H₂O₂ (0.0007 min^-1) and Cu₂S/H₂O₂ system (0.0152 min^-1). Meanwhile, FC-160-3 exhibited low metal ion leaching and excellent stability. Additionally, Cu₂S modification induced structural distortion and carbon skeleton disruption in the iron-sludge-based catalyst, which increased the surface abundance of C=O, pyrrolic-N, graphitic-N, and oxygen vacancies (O_V). The synergistic interaction between Cu₂S and iron sludge enhanced a shift in the oxidation pathway from a radical-dominated mechanism to a non-radical mechanism. Besides, Short-chain intermediates were generated with lower molecular weight and reduced toxicity during the catalytic process. The research provides a scientific approach for developing iron sludge-based catalysts for wastewater treatment.