Chloride-Induced Dual Electron Regulation on Zero-Valent Iron Surface for Highly Efficient Reductive Removal of Cr(VI)
Conventional zero-valent iron (ZVI) suffers from limited electron transfer due to its dense surface oxide layer. This study introduces a mechanochemical ball-milling strategy incorporating sodium chloride (NaCl) with ZVI to fabricate chloride-modified ZVI (Cl-ZVIbm). Using hexavalent chromium (Cr(VI)) as a model pollutant, Cl-ZVIbm exhibited a 76.5-fold enhancement in removal kinetics (0.0306 min−1 vs. 0.0004 min−1) compared to ball-milled ZVI (ZVIbm), achieving complete removal of 2 mg·L−1 Cr(VI) within 120 min. Spectroscopic characterization and density functional theory (DFT) calculations revealed dual regulation mechanisms: (1) Cl− substitution of surface hydroxyl groups alters coordination environments, enabling Cr(VI) adsorption via a bidentate binuclear configuration with adsorption energy reduced from –0.28 eV to –1.64 eV; (2) The strong electron-withdrawing effect of Cl− drives directional electron migration from the iron core to the surface, increasing surface Fe(II) content by 26.9% (67.5% vs. 53.2%) and facilitating direct electron transfer to reduce 99.5% of Cr(VI) into low-toxicity Cr(III). Notably, chloride leaching during reactions was only 0.0126 mmol·L−1, far below industrial wastewater discharge standards, confirming environmental compatibility. This work provides atomic-scale insights into chloride-mediated electronic modulation on ZVI surfaces, offering novel principles for interfacial engineering of environmental functional materials and a theoretical basis for heavy metal remediation technologies.