Facile synthesis of magnetic ZnFe2O4/AC composite to activate peroxydisulfate for dye degradation under visible light irradiation

Heterogeneous photocatalysis/persulfate oxidation process has been considered as a promising technology for dye contaminants removal. The magnetic ZnFe2O4/active carbon (AC) composites were hydrothermally synthesized and firstly used to activate peroxydisulfate (PDS) for rhodamine B (RhB) degradation under visible LED light irradiation. The optimized Vis-ZnFe2O4/AC(4/1)-PDS system can enhance the RhB degradation efficiency by 32.01% and 13.87% compared with Vis-ZnFe2O4-PDS and Vis-AC-PDS systems, respectively. The influence of operational parameters such as catalyst dosage (0.2 - 0.4 g L-1), PDS concentration (1.0 - 2.0 g L-1), temperature (25 - 45 °C), solution pH (2.7 - 10.9), and coexisting inorganic ions (Cl-, NO3-, HCO3-, PO43-, Cu2+, Fe3+, and Ca2+) on RhB degradation was studied, and 100% of RhB (20 mg L-1) was degraded after 80 min at operational condition: 0.30 g L-1 of ZnFe2O4/AC(4/1) and 1.5 g L-1 of PDS, solution pH of 2.74, reaction temperature of 25 °C. The quenching experiments, EPR test, and XPS analysis were employed to reveal the proposed mechanism, which demonstrated that 1O2 played a more important role than other reactive species (SO4•-, •OH, O2•-, and h+) in RhB degradation. The generation of 1O2 via the two routes was as follows: (i) the in situ formed active oxygen (O*) reacted with HSO5- to produce 1O2; (ii) O2•- was oxidized by h+ to form 1O2. After five consecutive cycles, the photodegradation efficiency of RhB by ZnFe2O4/AC(4/1) catalyst slightly decreased from 88.52 to 83.92%, indicating the excellent reusability of ZnFe2O4/AC(4/1) photocatalyst. As designed, Vis-ZnFe2O4/AC-PDS oxidation system can effectively remove RhB from the different real water matrices, and the degradation efficiency of RhB in tap water, river water, and secondary effluent was 78.24%, 79.55%, and 74.53% after 80 min of reaction, respectively.