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.
Shen et al. (Fri,) studied this question.