Selective removal of heavy metals from wastewater using polyphenol nano-microspheres: Enhancing sequestration and regeneration performance through pH-responsive coordinated structural changes

Abstract

The proficient advancement of nanoscale adsorbents assumes a pivotal role in the enhanced elimination of heavy metals to trace concentrations. Nevertheless, within the realm of engineering, the attainment of elevated selectivity and effective regeneration remains an arduous endeavor. In this context, we propose a novel structure-tunable sorption/regeneration mechanism by designing TA cross-linked polyphenolic nano-microspheres (PTA). These PTAs exhibit tunable pH-responsive metal coordination structures, enabling high sequestration and purification in removing heavy metals, and facilitating efficient regeneration. Taking Pb(II) as an example, under neutral conditions, the PTAs form a six-coordination configuration with Pb(II) ions, resulting in larger selectivity of Kd: 84400 mL/g with a 99 % removal efficiency even in the presence of various cations, anions, and organic acids. This performance far surpasses that of the commercial ion exchanger D001, exhibiting an enhancement factor of nearly 250 times, rendering it amenable for deployment in a wide array of contaminated water sources, encompassing lake water and industrial wastewater. Notably, the PTA also demonstrates exceptional practical utility, affording a voluminous treatment capacity of 5250 L per kilogram of adsorbent in wastewater scenarios. Furthermore, under acidic conditions, the transformation of PTA's metal coordination into a weaker two-coordination facilitates the efficient desorption of Pb(II) with an impressive efficiency of up to 99.0 % across multiple cycles. In contrast, commercial cheated resins D401 and D418 experience a significant 70 % decrease in reuse performances after the first cycle. This study provides a new perspective and platform for efficient adsorbent development through coordinated structural changes, it holds the potential to alleviate the challenges associated with deep restoration of heavy metal-contaminated wastewater.