Degradation of levofloxacin in aqueous solution by non-thermal plasma combined with Ag3PO4/activated carbon fibers: Mechanism and degradation pathways

Degradation of quinolone antibiotic levofloxacin (LFX) in water falling film dielectric barrier discharge (DBD) plasma combined with Ag3PO4 loaded activated carbon fibers (Ag3PO4/ACFs) system was studied. The prepared Ag3PO4/ACFs were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD) and Brunauer-Emmett-Teller (BET). The results showed that the cubic Ag3PO4 was well loaded on surface of the ACFs with a large specific surface area. Effects of initial concentration of LFX, discharge voltage, initial pH, liquid circulation flow rate, and catalyst dosage on the removal rate of LFX were discussed. The results showed that the degradation efficiency of LFX at 18 min could reach 93% with the addition of Ag3PO4/ACFs compared with 63% by single DBD plasma (discharge voltage 10 kV, initial concentration of LFX 20 mg/L). The addition of Ag3PO4/ACFs increased the mineralization rate of LFX from 11% to 46%. The possible degradation pathways of LFX were derived by Gaussian calculation and high-performance liquid chromatography-mass spectrometry (HPLC-MS) analysis, decarboxylation, demethylation, dehydroxylation, side chain decomposition, and ring cleavage involved in the degradation process of LFX.