Intrinsic Effects of Sulfidation on the Reactivity\nof Zero-Valent Iron With Trichloroethene: A DFT Study

Sulfidation represents\na promising approach to enhance the selectivity\nand longevity of zero-valent iron (ZVI) in water treatment, particularly\nfor nanoscale ZVI (nZVI). While previous mechanistic studies have\nprimarily concentrated on the impact of sulfidation on the (n)ZVI\nhydrophobicity, the fundamental effects of sulfidation on the (n)ZVI\nreactivity with target contaminants remain poorly understood. Herein,\nwe employed density functional theory to elucidate reaction mechanisms\nof trichloroethene (TCE) dechlorination at various (n)ZVI surface\nmodels, ranging from pristine Fe0 to regularly sulfidated\nFe surfaces. Our findings indicate that sulfidation intrinsically\nhinders the TCE dechlorination by (n)ZVI, which aligns with prior\nobservations of sulfur poisoning in transition metal catalysts. We\nfurther demonstrate that the positive effects of sulfidation emerge\nwhen the surface of (n)ZVI undergoes corrosion. Notably, S sites exhibit\nhigher reactivity compared to the sites typically present on the surface\nof (n)ZVI oxidized in water. Additionally, S sites protect nearby\nFe sites against oxidation and make them more selective for direct\nelectron transfer. Overall, our results reveal that the reactivity\nof sulfidated (n)ZVI is governed by an interplay of intrinsic inhibitory\neffects and corrosion protection. A deeper understanding of these\nphenomena may provide new insights into the selectivity of sulfidated\n(n)ZVI for specific contaminants.