DNAPL-Responsive Hydrogel Nanoreactor Encapsulating nZVI for Enhanced Degradation of Chlorinated Contaminants in Groundwater.

The remediation of dense nonaqueous phase liquids (DNAPLs) in groundwater presents a persistent challenge, as conventional technologies suffer from side reactions with bulk water rather than chlorinated solvents within DNAPL source zones. By engineering DNAPL-responsive poly(N-isopropylacrylamide) (PNIPAM) hydrogels with precisely controlled hydrophobic domains, we fabricated nanoscale zerovalent iron (nZVI) reactors (nZVI@PNIPAM) via in situ reduction of incorporated Fe3+ ions. The hydrogel encapsulation enabled nZVI to remain well-dispersed, spontaneously penetrated porous media, and significantly suppressed side reactions with water. Crucially, the nanoreactors leveraged the selective interaction between DNAPLs and PNIPAM's hydrophobic functional groups as a trigger, exposing encapsulated reactive nZVI exclusively at contamination interfaces through a rapid conformational transition and dehydration of PNIPAM. This interfacial interaction yields unprecedented efficiency, achieving 4.4-12.3-fold higher electron utilization for degradation of seven typical chlorinated solvents than conventional nZVI while suppressing water corrosion over 600-fold. Field-relevant evaluations demonstrated consistent performance across broad hydrochemical conditions (pH 6-9, 0-1000 mg L-1 KCl, 0-200 mg L-1 natural organic matter), with over 90% DNAPL removal in real contaminated groundwater. Our mechanistic discovery of pollutant-responsive activation represents a significant advance over current diffusion-limited approaches, potentially revolutionizing targeted in situ groundwater remediation strategies.