Chlorinated hydrocarbons are the most frequently encountered contaminants in groundwater. The reductive dichlorination of chlorinated ethenes mediated by artificially injected materials (e.g., Fe(0)) or naturally-occurring minerals (e.g., iron sulfides and green rust) constitutes major abiotic degradation pathways. Although in situ remediation of chlorinated compounds using reduced iron minerals has been extensively studied in the past two decades, the key material attributes giving rise to the vast differences in reactivity and reduction capacity observed of various iron-containing materials are largely unknown, and their deployments at TCE or PCE-contaminated sites have seen sporadic success.

Our group seek to understand the mechanisms of reactions of chlorinated ethenes on iron surface. Specifically, we analyzed the prominent role of surfaces in generating and stabilizing activated hydrogen for the reduction of chlorinated ethenes and pointed out various deactivation pathways of catalytic iron materials (e.g., Pd-Fe and Ni-Fe) in groundwater matrices. These insights led us to examine sulfided iron materials, which have shown superior reactivity and selectivity for PCE and TCE dechlorination over conventional iron materials. To us, the sulfur-modified iron represents a very interesting system because it embodies several desirable features of environmental catalysis, namely high selectivity and efficiency in generating reactive hydrogen species, resistance against fouling and passivation, and amenability to control via biogeochemical means.