Silicate-Confined Hydrogen on Nanoscale Zerovalent Iron for Efficient Defluorination Reactions

Defluorination reactions are increasingly vital due to the extensive use of organofluorine compounds with robust carbon-fluorine (C-F) bonds; particularly, the efficient defluorination of widespread and persistent per- and polyfluoroalkyl substances under mild conditions is crucial due to their accumulation in the environment and human body. Herein, we demonstrate that surface-modified silicate of pronounced proton affinity can confine active hydrogen (•H) onto nanoscale zerovalent iron (nZVI) by withdrawing electrons from nZVI to react with bound protons, generating confined active hydrogen (•H^*) for efficient defluorination under ambient conditions. The exposed silicon cation (Si^σ+) of silicate functions as a Lewis acid site to activate the C-F bond by forming Si^σ+...F^--C and substantially lowers the energy barrier of nucleophilic •H^* attack, thereby facilitating selective C-F hydrodefluorination and subsequent fluorine immobilization. In a column flow reactor, silicate-modified nZVI efficiently removes perfluorooctanoic acid (PFOA) of concentrations ranging from 0.24 to 24 μmol/L with 75-92% defluorination efficiencies, 8 times higher than those of nZVI, generating environmentally friendly alkyl carboxylic acids as the primary products. Besides PFOA, this novel nZVI also realizes deep defluorination of other organofluorine compounds, including perfluorooctanesulfonates and fluoroquinolones, demonstrating its superior defluorination potential.