Analyzing degradation pathways in the conversion of trichloroethylene to vinyl chloride: The role of S/Fe ratios

Abstract

The long-standing contradiction between the mineralization of organic pollutants and the reduction of CO₂ emissions has prompted the exploration of sustainable solutions. In this study, the concept of green sustainable restoration (GSR) was applied to the groundwater remediation of trichloroethylene (TCE). Sulfurized nano zero-valent iron (S-nZVI), with S/Fe ratios of 0.00088, 0.00880, 0.08800, separately, was applied as catalyst, to construct a peroxymonosulfate (PMS) based resource conversion system. The etching of nZVI with Na₂S effectively enhanced the catalytic conversion of TCE. The rough spherical morphology, intact core-shell structure, and amorphous sulfide species were all observed. The S-nZVI/PMS system facilitated a non-free radical pathway dominated by ¹O₂, driven by endogenous Cl^-, enabling the resource conversion of TCE into vinyl chloride (VC). This innovative approach highlighted the potential for achieving dual environmental benefits. Specifically, at S/Fe ratios of 0.00088 and 0.08800, PMS was converted to ¹O₂ through a one-step process. In contrast, at S/Fe ratio of 0.00880, the conversion involves a two-step process, where superoxide radicals (·O₂^-) served as intermediates, notably with amorphous sulfide species facilitating the transition. Importantly, our resource conversion system demonstrated resilience, being independent of both pH and temperature fluctuations. This research advanced our understanding of pollutant reduction pathways and underscored the potential for enhancing the synergistic performance of pollution control while concurrently mitigating CO₂ emissions. By effectively regulating resource conversion pathways, this study laid the groundwork for innovative remediation strategies that aligned with sustainable environmental goals.