Red mud-based CoFe2O4 activated by ball milling as effective peroxymonosulfate activator for the degradation of lomefloxacin hydrochloride: Preparation & activation, application and degradation mechanism

In this study, red mud-based CoFe2O4 (CoFe2O4/RM) was firstly prepared via a sol–gel method, and then activated through ball milling to obtain the catalyst of Ball-milled CoFe2O4/RM (BM-CoFe2O4/RM). The BM-CoFe2O4/RM catalyst was applied as a high-efficiency activator of peroxymonosulfate (PMS) for the degradation of lomefloxacin hydrochloride (LOM-HCl). The LOM-HCl (100 mg/L) could be removed 86.36 % after 12 min treatment under the optimal reaction parameters (BM-CoFe2O4/RM dosage of 1.33 g/L, PMS concentration of 5 mmol/L and nature pH 6.59 ± 0.1). The comparative experiments revealed that the apparent rate constant of LOM-HCl degradation of BM-CoFe2O4/RM (0.1091 min−1) was approximately 1.6 times that of CoFe2O4/RM (0.0701 min−1). A series of characterizations demonstrated that the physicochemical properties of CoFe2O4/RM, including defective structures, crystallinity of high active components, exposures of Co (II) and Fe (II) and electrical conductivity, could be improved via ball milling, causing the increase of the catalytic activity of CoFe2O4/RM. Combined with the results of Electron spin resonance (ESR), X-ray photoelectron spectrometer (XPS) and quenching experiments, the possible catalytic mechanism of PMS activated by BM-CoFe2O4/RM for LOM-HCl degradation was proposed. Combined with the density functional theory (DFT) calculation and liquid chromatography-mass spectrometer (LC-MS), the possible vulnerable sites and possible degradation pathways of LOM-HCl were obtained. The recycling experiments and XPS demonstrated that BM-CoFe2O4/RM had good stability, and the catalytic activity of the BM-CoFe2O4/RM after use could be regenerated by thermal treatment. The biological toxic experiment suggested that the toxicity of LOM-HCl solution treated by the BM-CoFe2O4/RM + PMS system was effectively reduced. The work not only provides a simple and high-efficiency method for improving the catalytic activity of CoFe2O4/RM, but also opens novel insights into the Ball-milled CoFe2O4/RM as an effective PMS activator for antibiotic wastewater treatment.