Modulating Surface Architecture of Sulfidated Nanoscale Zerovalent Iron for Synergistic Enhancement of Dechlorination Reactivity, Electron Selectivity, and Colloid Stability

Sulfidated nanoscale zerovalent iron (S-nZVI) has shown great promise in the remediation of chlorinated solvents-impacted groundwater, yet its performance is hindered by the trade-off between electron selectivity and colloidal stability. Here, we resolve this dilemma with a simple solution, that is, using cyclodextrin (CD) as a template in S-nZVI synthesis to regulate the surface architecture. The CD-modified S-nZVI (CD-S-nZVI) prepared using sodium sulfide as the sulfur precursor exhibits high electron selectivity toward the dechlorination of trichloroethylene (TCE), a legacy groundwater contaminant, while maintaining high colloidal stability. Mechanistic assays with additional S-nZVI materials prepared by varying CD dosage and using alternative sulfur precursor (sodium dithionite) show that the binding of Fe2+ to CD provides abundant sulfidation sites during S-nZVI formation, thus rendering a higher sulfur content and more uniform FeS coating. This suppresses hydrogen evolution and improves electron selectivity. The incorporation of CD also facilitates accumulation of TCE onto S-nZVI, due to partitioning into the hydrophobic cavities of CD molecules. Moreover, steric stabilization endows CD-S-nZVI with a much higher colloidal stability than S-nZVI without CD. The CD-S-nZVI demonstrates adaptability to a broad range of aqueous chemistry conditions and excellent longevity. This new strategy has important implications for the design of highly deployable groundwater remediation nanomaterials.