Insights into enhanced removal of TCE utilizing sulfide-modified nanoscale zero-valent iron activated persulfate

Sulfide-modified nanoscale zero-valent iron (NZVI-S) has been considered as a promising material for in-situ chemical reduction processes (ISCRPs) for groundwater remediation. However, studies utilizing NZVI-S for in-situ chemical oxidation processes (ISCOPs) were relative rare. In this study, NZVI-S was synthesized and utilized to activate persulfate (PS) for the degradation of TCE. The effects of Fe/S molar ratio, initial pH on TCE removal and dechlorination by NZVI-S activated PS were studied. The results showed that, compared with bare NZVI, NZVI-S showed better properties in activating PS which included better pH adaptiveness, higher TCE removal and mineralization efficiency, and faster removal rate. The Fe/S molar ratio significantly influenced the TCE degradation, and the highest TCE degradation was observed at Fe/S molar ratio of 25–30. The underlying mechanisms of NZVI-S exceling NZVI in activating PS were elucidated through spectroscopic analyses that accounted for the higher iron dissolution rates and iron sulfides (e.g., FeS and FeSx) generated on its surface, which elevated the quantity and accelerated the transfer rate of electrons for activating PS. Besides, hydroxyl radical was observed as a dominant reactive radical in degrading TCE at various pH conditions, but sulfate radical also played an important part especially under acidic condition. Finally, the degradation products of TCE were analyzed and the possible pathways of TCE degradation were illustrated. And the slight influence of natural substances in groundwater on the degradation process suggests NZVI-S activated PS would be a promising approach for groundwater remediation.