A theoretical investigation on sulfidated nanoscale zero valent iron for removal of cis-DCE and PCE

The organochlorine contaminants in wastewater can be degraded by using sulfidated nanoscale zero-valent iron. However, the specific role of S dopants and the underlying degradation mechanism are largely unknown. In this study, we applied ab initio molecular dynamics and density functional theory to investigate the remediation mechanism of two chlorinated organic compounds, cis-dichloroethene and tetrachloroethene, focusing on the role of sulfur dopant coverage on the nZVI surface, represented by a stepped Fe(211) facet, and compare it to a flat (110) surface. Our results revealed that low S coverage facilitates the dissociation of the contaminants due to stronger interaction with the iron surface. Conversely, high S coverage initially hinders dissociation but promotes adsorption of the contaminants for later dissociation, suggesting a potential benefit for remediation. By comparing with the water molecule adsorption energies, we demonstrate that S doping enhances selectivity towards these contaminants only at high S coverage. Our theoretical findings, therefore, highlight the importance of optimizing S coverage for effective wastewater treatment using sulfidated nanoscale zero-valent iron.