Ni/S co-modified nanoscale Fe⁰ enables selective reaction pathways for complete dehalogenation

Nano-zero-valent iron (nFe⁰)-based materials can dehalogenate halogenated organic contaminants (HOCs) through hydrogen atom transfer (HAT) and direct electron transfer (DET) pathways. However, the mechanistic contributions of DET and HAT to the reductive dehalogenation, particularly for sterically hindered contaminants like tetrabromobisphenol A (TBBPA), along with effective regulatory strategies for robust reduction performance, remain poorly understood. Here, we report a surface-engineered strategy that constructs Fe-Ni_xS_y nanomaterials with dual Ni/S active sites to regulate DET and HAT pathways. Notably, the optimal Fe-Ni₃S₇ achieved over 109.9-fold higher reactivity and 359.7-fold greater electron efficiency than pristine nFe⁰, while maintaining high stability, which is governed by the interplay of the reaction pathway, material characteristics, and contaminant properties. Molecular dynamics simulations and density functional theory calculations revealed that DET is severely constrained by steric shielding of the bulky C(CH₃)₂ group within the TBBPA framework, whereas HAT bypasses these constraints with a substantially lower energy barrier (3.5 vs. 1.0 eV). This work provides an effective and sustainable strategy for the targeted remediation of sterically hindered HOCs in groundwater.