Enhanced oxidative degradation of norfloxacin using peroxymonosulfate activated by oily sludge carbon-based nanoparticles CoFe₂O₄/OSC

In this study, oily sludge (OS) was pyrolyzed into an environmentally friendly OS carbon (OSC) material, which was used as the carrier of CoFe₂O₄ nanoparticles to prepare a heterogeneous catalyst CoFe₂O₄/OSC, and it was used to catalyze the degradation of norfloxacin (NFC) by peroxymonosulfate (PMS). X-ray diffraction (XRD) and transmission electron microscope (TEM) characterization results show that CoFe₂O₄/OSC had a spinel structure under high temperature pyrolysis conditions. The effects of initial pH, PMS dosage, catalyst dosage, and temperature on NFC degradation efficiency were also studied. Under a temperature of 25 °C, an initial pH of 7, a catalyst amount of 0.5 g/L, and a PMS dosage of 0.8 mM, the reaction rate constant reached 0.051 min⁻¹, and the degradation efficiency and total organic carbon of NFC reached 90.8% and 62%, respectively, within 60 min. Trace amounts of Co and Fe ions were leached from the system (both less than 30 μg/L). After ten cycles, the degradation efficiency of NFC decreased to 69.8%. Radical quenching experiments, electron paramagnetic resonance, and X-ray fluorescence spectroscopy characterization proved that free-radical (^[rad]OH, SO₄^[rad]−, and O₂^[rad]−) and nonradical (¹O₂) active species were present in the system. Moreover, the CoFe₂O₄/OSC/PMS system involved the participation of two pairs of redox couples (Fe(II)/Fe(III) and Co(III)/Co(II)). Results from matrix-assisted laser desorption ionization time-of-flight mass spectrometry and ion chromatography proved that the main oxidation pathways of NFC were formed through the fragmentation of heterocycles, defluorination of benzene rings, decarboxylation reactions, and piperazine ring-opening process. At the same time, NFC was eventually oxidized to fluoride. This study provides potential for the resource utilization of OS and the application of sludge-type catalysts in PMS-activated oxidation systems.