Efficient degradation of levofloxacin by a microwave–3D ZnCo2O4/activated persulfate process: Effects, degradation intermediates, and acute toxicity

Abstract

Three-dimensional ZnCo2O4 (3D ZCO) nanometer material was synthesized using a hydrothermal method. The obtained materials were characterized via XRD, XPS, SEM, HRTEM analysis techniques. 3D ZCO was used as heterogeneous persulfate (PS) activators under microwave irradiation for levofloxacin (LVF) degradation, in which influence factors, mechanism and probable degradation pathways were investigated in depth. Influences of reaction parameters such as initial pH, initial PS concentration, the dosage of ZCO and the influence of anions (NO3–, Cl–, CO32–, H2PO4–) were investigated. Radical quenching experiments and electron spin resonance studies proved that the contribution of active species was in descending order of SO4·− > ·O2− > ·OH in the microwave–3D ZnCo2O4/persulfate (MW–3D ZCO/PS) system. The feasible reaction mechanism of MW-3D ZCO/PS system was proposed according to the characterization and experiments analysis. The experimental optimum conditions ([LVF] = 10 mg/L, [ZCO] = 2 g/L, [PS] = 5 mM, [pH]0 = 5, MW = 700 W, T = 70 °C) of mineralization of levofloxacin, reaching a 69.8% TOC removal. The acute toxicity test showed that MW–3D ZCO/PS system was effective at reducing the toxic compounds of LVF solutions lead to a reduction in toxicity. By high-performance liquid chromatography tandem mass spectrometry analysis (HPLC–MS), eight products of LVF including H2O, CO2, inorganic ions and other small molecules were identified, and possible degradation pathways were then proposed. In short, this study provides a solution to decrease refractory antibiotic in water systems.