Activation of persulfate by magnetic zirconium-doped manganese ferrite for efficient degradation of tetracycline

Tetracycline (TC) is a typical antibiotic that is eco-toxic and easily causes bacterial resistance, and thus it is necessary to eliminate tetracycline from the water environment. In this study, an innovative TC removal approach was developed by activation of persulfate (PDS) using oxide-based materials fabricated via low-temperature co-precipitation: Zr oxide/MnFe2O4 (ZrO2/MnFe2O4). The effects of Fe/Zr molar ratio, the dose of ZrO2/MnFe2O4 and PDS, initial pH, TC concentration, co-existing anions, natural organic matter on TC degradation were investigated. Under optimal conditions (Fe/Zr = 10, PDS = 6.0 mM, ZrO2/MnFe2O4-10 = 0.20 g/L, and pH = 7.1), the TC degradation efficiency of 85.2% could be achieved after 120 min. Besides, the TC degradation efficiency was different extents inhibited by inorganic anions (H2PO4- >HCO3- > NO3- > Cl-) and organic substances (EDTA > HA). Furthermore, the results of quenching experiments, electron paramagnetic resonance (EPR) analysis, and X-ray photoelectron spectroscopy (XPS) spectra analysis demonstrated that three radicals (hydroxyl radicals (·OH), sulfate radicals (SO4·-), and superoxide radicals (O2·-)) contribute to rapid TC degradation in ZrO2/MnFe2O4-10/PDS system. Particularly, the ZrO2/MnFe2O4-10 exhibited superparamagnetic property and excellent stability, which was conducive to the effective recovery and utilization of the catalyst through the external magnetic field. Based on the degradation products determined by ultra-performance liquid chromatography-mass spectrometry (UPLC-MS), the possible four degradation pathways of TC degradation were proposed in the ZrO2/MnFe2O4-10/PDS system. This study indicates the ZrO2/MnFe2O4 composite is an efficient and environmentally catalyst for PDS oxidation of organic pollutants.