Efficient removal of ciprofloxacin by peroxymonosulfate/Mn3O4-MnO2 catalytic oxidation system

• A novel and efficient Mn3O4-MnO2/PMS system was designed for CIP removal.
• PMS was activated via redox cycle: Mn(III)/Mn(II) and Mn(IV)/Mn(III).
• Sulfate radical played a major role in degradation process.
• The CIP degradation pathways in PMS/Mn3O4-MnO2 system were proposed.

In this work, the novel multivalent Mn3O4-MnO2 composite catalyst was synthesized and employed for peroxymonosulfate (PMS) activation to realize ciprofloxacin (CIP) degradation. Results showed that 97.6% of CIP (50 μM) was removed in PMS/Mn3O4-MnO2 system by adsorption and further degradation within 25 min at the dosage of 1 mM PMS and 0.1 g/L Mn3O4-MnO2. The CIP degradation followed the pseudo-first-order kinetic model and the highest kinetic constant of 0.139 min−1 was achieved. Moreover, the effects of solution pH, coexisting anions and natural organic matter on CIP removal were investigated. The optimum pH in PMS/Mn3O4-MnO2 system for CIP removal was neutral. The coexisting anions such as HCO3−, NO3− and SO42− inhibited the degradation process while Cl− enhanced the process. The natural organic matter (NOM) presented positive effect on CIP degradation at 1.0 mg/L and detrimental effect at 3.0 and 5.0 mg/L. Furthermore, the mechanism of PMS activation by Mn3O4-MnO2 was interpreted. The PMS was highly activated to sulfate and hydroxide radicals by the redox pairs of Mn(III)/Mn(II) and Mn(IV)/Mn(III) in Mn3O4-MnO2 composite. Accordingly, the transformation products of CIP were determined and the degradation pathways in PMS/Mn3O4-MnO2 system were proposed. These findings would make a significant contribution towards removing antibiotics from water through PMS oxidation system.

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