Polystyrene sulfonate mediated the synthesis of nano zero-valent iron via tea-polyphenols and their application for lead removal from aqueous media

This study aims to improve the applicability of green-synthesized nano zero-valent iron (GT-nZVI) for wastewater treatment under natural pH conditions by developing a novel -nZVI composite stabilized with polystyrene sulfonate (PSS) and green tea polyphenols (GT-nZVI@PSS) at different PSS/Fe mass ratios (0.01–0.5) for Pb(II) removal. Particular emphasis was placed on elucidating the influences of humic acid (HA) and sulfate ubiquitous constituents in wastewaters on Pb(II) removal performance, with the underlying mechanisms of their effects systematically clarified. Results demonstrated that GT-nZVI@PSS (PSS/Fe = 0.05) exhibited excellent Pb(II) removal at neutral pH, primarily driven by enhanced Pb(II) reduction and Pb 0 precipitation. This performance is mainly attributed to improved dispersibility resulting from the synergistic effects of PSS and tea polyphenols on the particle surface. HA and sulfate exerted opposing effects on Pb(II) removal by GT-nZVI@PSS. At low concentrations, HA enhanced Pb(II) uptake by increasing the surface negative charge, improving particle dispersion, and providing additional active sites for the formation of Fe–HA/Pb complexes. In contrast, sulfate inhibited Pb(II) removal by disrupting the polyphenol coating and forming surface sulfate–iron species and PbSO 4 precipitates, thereby accelerating passivation and reducing Fe release. However, at high concentrations, excessive HA molecules formed large aggregates that enveloped the particle surfaces, ultimately hindering Pb(II) access to the active sites of GT-nZVI@PSS. Conversely, high concentrations of sulfate promoted GT-nZVI@PSS corrosion, facilitating Fe 0 release and thereby enhancing Pb(II) removal. These findings highlight the crucial role of water matrix constituents in modulating the performance of GT-nZVI@PSS, as an eco-friendly and cost-effective material.