A novel red mud-based Co3O4–Fe2O3–Co2AlO4 composite as a peroxymonosulfate activator for effective degradation of lomefloxacin hydrochloride

Abstract

In this study, red mud (RM), an industrial waste, was used as a raw material to prepare a novel red mud-based Co₃O₄–Fe₂O₃–Co₂AlO₄ (Co–Fe/RM) catalyst using a simple solid-phase method, and lomefloxacin hydrochloride (LOMH) was degraded by using Co–Fe/RM to activate peroxymonosulfate (PMS). The optimum preparation conditions of the mass ratio of Co(NO₃)₂·6H₂O to RM, calcination temperature and calcination time were 1.5 : 1 (1.5 g of Co(NO₃)₂·6H₂O and 1 g of RM), 700 °C, and 2 h, respectively. The characterization results showed that Fe₂O₃, Co₃O₄ and Co₂AlO₄ were the main active components in Co–Fe/RM, and Co–Fe/RM could expose more reaction sites compared with RM. The Co–O–Al bonds that existed on the Co–Fe/RM could facilitate the redox cycle between Co(II) and Co(III), thus improving the Co–Fe/RM catalytic activity. For 10 mg L⁻¹ LOMH solution with a volume of 100 mL, the maximal removal ratio of LOMH (89.3%) was obtained at 20 min under the optimal parameters (0.3 g L⁻¹ Co–Fe/RM dosage, 1 mmol L⁻¹ PMS concentration, initial pH 5.5, and 30 °C of reaction temperature) in a Co–Fe/RM/PMS system. The trapping experiments proved that SO₄˙⁻, ¹O₂ and O₂˙⁻ dominated the degradation of LOMH, and a possible catalytic mechanism of activating PMS using the prepared catalysts was proposed. For LOMH in the Co–Fe/RM/PMS system, degradation pathways were analyzed via density functional theory (DFT) calculations and liquid chromatography–mass spectrometry (LC–MS). A toxicity estimation software tool (TEST) and the Chlorella pyrenoidosa cultivation experiment were used to evaluate the biological toxicity of the treated LOMH solution. The recycling experiments found that the Co–Fe/RM had distinguished reusability and excellent stability. The mineralization assessment showed that organic carbon contents could be effectively diminished in the treated LOMH solution. This study provided a viable way for the beneficial use of RM to activate PMS and offered a low-cost and efficient catalyst for the degradation of pollutants in wastewater.