Magnetic MnFe2O4 nanoparticles anchored on sludge-derived biochar in activating peroxydisulfate for levofloxacin degradation: Mechanism, degradation pathways and cost analysis

The sludge-derived biochar (SBC) was prepared by a low-cost microwave pyrolysis process, and then MnFe2O4 nanoparticles were anchored onto the surface of SBC through a hydrothermal route to construct a magnetic MnFe2O4/SBC composite catalyst. As-obtained MnFe2O4/SBC catalysts were characterized by XRD, FT-IR, Raman, FE-SEM, BET surface area and XPS. The optimized MnFe2O4/SBC(1:3) catalyst showed a higher catalytic activity to activate peroxydisulfate (PDS) for levofloxacin (LVF) degradation than that of SBC, MnFe2O4 and reported magnetic composite catalysts. After 80 min of reaction, 79.5% of LVF in water (10 mg/L) was degraded by MnFe2O4/SBC(1:3) in the presence of PDS (1.5 g/L), and LVF degradation followed the pseudo-second-order kinetics. Calcium carbonate (CaCO3) in SBC participates in PDS activation. XPS analysis, oxidative species capture experiments, EPR and linear sweep voltammetry (LSV) tests confirmed that LVF degradation in MnFe2O4/SBC-PDS oxidation system was achieved through the non-radical (electron transfer, 1O2) and radical (SO4•−, ∙OH and O2•−) pathways, with the former playing a dominant role. The degradation routes of LVF were established based on the degradation intermediates. LVF removal efficiency from real water matrices was improved by means of increasing catalyst dosage and reaction temperature. Cost analysis indicates that MnFe2O4/SBC-PDS oxidation process is a cost-effective method to eliminate the antibiotics in water.