Persulfate activation by sulfide-modified nanoscale zero-valent iron for metronidazole degradation: Mechanism, major radicals and toxicity assessment

Sulfide-modified nanoscale zero-valent iron (SnZVI) is considered to be an effective method for persulfate (PS) activation. Here, the catalytic activity was evaluated in view of the potential influencing factors, including the sulfidation regent, Fe/S molar ratio, initial solution pH value, catalyst dosage, PS dosage, initial MNZ concen-tration and common anion species. The complete removal was obtained when Na2S was chosen at Fe/S molar ratio of 0.05 with 1.5 g center dot L-1 SnZVI and 1.5 mM PS. SnZVI exhibited a promising application owing to the high pH adaptation and the outstanding reusability. The high and persistent release of Fe2+ and FexSy generated on the surface, which accelerated the electron transfer rate for PS activation. The main reactive oxygen species, including center dot OH, SO4 center dot-, O-2(-) and O-1(2), were further determined. However, center dot OH rather than SO4 (-)was the dominant reactive radical in our study. Finally, the degradation products and possible pathways were predicted based on the intermediate analysis. The T.E.S.T theoretical calculation indicated that the ecotoxicity of the various in-termediate products of MNZ were greatly reduced. These results demonstrated that SnZVI/PS was a promising strategy for practical application in the remediation of MNZ contaminated water.