An intra-ligand charge redistribution strategy for ensuring polyhydroxyferrous iron regeneration and targeted redox-active heavy metal removal.

Abstract

Redox-active heavy metals remain challenging targets for water remediation due to their complex redox transformations and unstable speciation. Although ferrous iron is an effective reductant, its application is hindered by rapid oxidation and inefficient regeneration. Herein, we propose an intra-ligand charge redistribution strategy to achieve self-sustained Fe(II) regeneration and targeted heavy metal reduction. A polyphenol-coordinated polyhydroxyferrous iron (FHC) system was constructed, where tannic acid (TA) functions as both a coordination ligand and an intrinsic electron-regulating framework. Our strategy operates through a pollutant-coupled electron regulation mechanism, in which the electron demand driven by contaminant reduction dynamically governs charge redistribution within the ligand framework. This process sustains a continuous electron flux and maintains Fe(II) regeneration. As a result, the FHC system achieves removal efficiencies of up to 100% within 10 min, with a maximum removal capacity of 133.8 mg/g, a high reaction rate of 1.73 min-1, and a selectivity of 95.4%. Moreover, the practical applicability of this system is demonstrated by scalable synthesis, comprehensive life-cycle assessment (LCA) and techno-economic analysis (TEA), continuous-flow operation, and real mining wastewater treatment. This work establishes a new paradigm for designing iron-based remediation materials with intrinsic ligand-mediated electron-regulating capability, providing a sustainable and selective strategy for redox-active heavy metal removal.

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