Enhanced degradation of diazinon with a WO3-Fe3O4/g-C3N4-persulfate system under visible light: Pathway, intermediates toxicity and mechanism

In this study, the WO3-Fe3O4/g-C3N4 catalyst was investigated for activating PS in degradation of diazinon under visible light. Characteristics of the synthesized catalyst were analyzed via XRD, BET, TEM, FESEM, EDS, VSM, FTIR and XPS techniques. With the WO3-Fe3O4/g-C3N4-PS system, under optimal conditions (diazinon 5 mg L-1, catalyst dosage 0. 4 g L-1, PS 1 mM, pH 5) a diazinon degradation efficiency of 95% and mineralization of 69% could be achieved after 60 min. The results displayed that the removal of diazinon followed pseudo-first-order (PFO) kinetics, and compared with WO3-Fe3O4/g-C3N4, PS activated with WO3-Fe3O4/gC3N4 exhibited diazinon removal with higher reaction rate. The quenching experiment confirmed that the main active species were sulfate radicals (SO4 center dot-), hydroxyl radicals (OH center dot) and singlet oxygen (1O2) and a possible reaction mechanism was suggested. Based on the intermediate products identified by LC-MS/MS, the main reaction pathway was proposed. In addition, the catalyst indicated good reusability after four consecutive experiments. Finally, the by-product toxicity was estimated by the Chlorella vulgaris. This work presented a catalyst with excellent efficiency in the PS activation, implying a new system for degradation of other organic contaminants.