Activated peroxydisulfate by sulfidated zero-valent iron for enhanced organic micropollutants removal from water

Recently, sulfidation of zerovalent iron (S-ZVI) has gained increasing attention due to its merits to mediate the electron transfer from Fe⁰ core to reactants at the water-particle interface. However, few studies have attempted so far to use the unique properties of S-ZVI to activate peroxydisulfate (PDS) under both oxic and anoxic conditions. Hence, in this study, the performance of S-ZVI in activating PDS was systematically evaluated at various conditions. As expected, under oxic conditions, S-ZVI could enhance the acetaminophen (ACT) removal rate by 2.4–5.1 folds compared to unmodified ZVI, and this enhancing effect works well over the tested initial pH range of 3.0–8.5. Likewise, under anoxic conditions, S-ZVI still performed better than unmodified ZVI. But interestingly, both ZVI and S-ZVI achieved better PDS activation with the absence of O₂, despite in which comparable or much less Fe⁰ were consumed. This may be ascribed to the multiple roles of O₂ which could not only enhance the Fe⁰ to generate Fe²⁺ but also compete with PDS significantly for the generated Fe²⁺. Through quenching experiments and electron spin resonance spectra analysis, SO₄^•− and HO^• were identified to be involved in Fe⁰/PDS process. Moreover, taking PMSO as a probe, Fe(IV) was also confirmed to be generated in both ZVI/PDS and S-ZVI/PDS systems. Taking four other microcontaminants and a real groundwater sample, the broad applicability of S-ZVI/PDS was further evaluated. All these results would favor the fundamental understanding of Fe⁰/PDS process and thus help to facilitate its application.