New Insights into Heavy Metal Sequestration Through Metal-Phenolic Network-Confined Nano-HFO: Overlooking Iron Utilization and Modulating Electron Density.

Abstract

Reducing toxic metal concentrations to trace levels remains a critical challenge in water remediation, largely due to the underutilization of hydrous ferric oxide (HFO), particularly within its inner layers. Herein, we present a novel strategy to enhance HFO utilization by in situ confinement of nano-HFO within polystyrene beads using a tannic acid-zirconium (TA-Zr) metalphenolic network, forming PS-Fe@TA-Zr. The TAZr network generates a highly negative microenvironment with tunable electron density at oxygen sites, facilitating Pb(II) enrichment and activating inner-layer Fe sites. Depth-profiling reveals a significant increase in the Pb/Fe ratio from 7.6% at the surface to 18.8% at 10 nm depth, highlighting the contribution of previously inaccessible active sites. The TAZr confinement also modulates electron density at Fe and O sites, enabling stronger hybridization with Pb 4f orbitals and enhancing Pb(II)HFO interactions. Compared with PS-Fe, PS-Fe@TA-Zr exhibits over 8-fold higher selectivity (Kd = 15,278 mL g^-1), 5-fold faster kinetics, and can treat up to 1,680 L kg^-1 with effective regeneration across six cycles in actual industrial wastewater. This work provides new insights into metalphenolic network-assisted design of nanocomposites for highly efficient iron utilization in heavy metal removal.