Visible-LED-light-driven photocatalytic activation of peroxydisulfate by magnetic ZnFe2O4/Ag nanocomposite for efficient tetracycline degradation

Heterogeneous photocatalysis/persulfate oxidation process has been regarded as a promising technology for antibiotic contaminants removal. Magnetic ZnFe 2 O 4 /Ag composite catalyst was synthesized to activate peroxydisulfate (PDS) toward tetracycline (TC) degradation under the visible-LED-light irradiation. The synergistic effect of ZnFe 2 O 4 and Ag endowed the optimized ZFO/Ag-15 with excellent photocatalytic performance for PDS activation and TC degradation, and 90.06 % of TC (20 mg/L) was efficiently degraded after 80 min of reaction. Ag can enhance the visible light absorption of ZnFe 2 O 4 and accelerate the separation of photo-induced electron/hole pairs, thereby promoting the generation of O 2 − and SO 4 − radicals. In addition, Ag can directly activate PDS to generate SO 4 − . Although the catalytic performance of magnetic ZFO/Ag-15 gradually decreased after each cycle due to the corrosion of Ag and the formation of inactive AgO, the catalytic activity of used catalyst was partially recovered by heat treatment. Quenching experiments and EPR tests indicated that the free radical (O 2 − , SO 4 − and OH) and non-free radical ( 1 O 2 , h + ) oxidation processes cooperated to degrade TC in Vis-ZFO/Ag-15/PDS system. The effect of operational factors (PDS concentration, temperature, solution pH, coexisting inorganic anions and humic acid) on TC degradation was investigated, and TC removal from the different water matrices (river water, tap water and secondary effluent) was also evaluated. The degradation products were detected using LC-MS and the possible TC degradation pathways were established.