Iron sludge-derived magnetic Fe⁰/Fe₃C catalyst for oxidation of ciprofloxacin via peroxymonosulfate activation

Iron sludge produced numerously from drinking water treatment plants can be recycled to create catalyst for peroxymonosulfate (PMS) activation. In this study, iron sludge-derived catalysts were synthesized via one-step pyrolysis process by self-reduction in argon atmosphere. The crystallite structures and catalytic performance of these catalysts were strongly dependent on the pyrolytic temperature. The product carbonized at 900 °C (Fe⁰/Fe₃C) exhibited a superior catalytic behavior with 99% ciprofloxacin (CIP, 10 mg/L) degradation in 20 min due to the synergistic effect of Fe⁰ and graphitic carbon. The influences of reaction parameters on the CIP degradation were further investigated and the Fe⁰/Fe₃C-PMS process had a wide efficient pH range from 3 to 9. The catalyst also exhibited excellent magnetic property and could be easily separated with external magnetic field. Radical quenching study and electron paramagnetic resonance (EPR) tests indicated that sulfate radical (SO₄^[rad]−), hydroxyl radical (^[rad]OH), superoxide radical (O₂^[rad]−) and singlet oxygen (¹O₂) contributed to the degradation of CIP. This study extended the application of Fe⁰/Fe₃C to catalytic oxidation of other typical refractory organic contaminants and confirmed its excellent catalytic activity. Overall, this study provided a cost-effective iron sludge reuse method to develop an environment-friendly catalyst for decontamination of organics pollutants, and also to relieve detrimental influences on aqueous environment by discharging the iron sludge.