A Polyphenol-Based Hydrogel for Enabling Enhanced Metal Ion Sorption, Antimicrobial Activity, and Water Remediation

Abstract

Naturally derived, highly functional, and widely accessible materials represent enabling technologies for sustainable development. However, current bio-derived materials often present a trade-off between sustainability potential and functional performance. Sorbents that can remove potentially toxic elements (PTEs) and inhibit bacterial growth to enable water remediation exemplify this dilemma. Conventional plant-based biopolymer materials are attractive for their low cost and environmental compatibility, but many require additional specialized synthetic components to impart the requisite performance. We now report an approach for preparing majority plant polyphenol hydrogels composed of the widely available tannic acid (TA) at an unprecedented 75% content. A minority seaweed alginate (Alg) matrix is used to bind TA into conveniently handled beads. Convenient application is also demonstrated by conducting all experiments with dried beads rehydrated directly during use. Multifold enhancements in water swelling, sorption of a suite of PTEs, and antimicrobial activity are found with increasing TA content. Moreover, we report a novel additional enhancement of antimicrobial activity based on TA-induced iron incorporation, as characterized by XPS, SEM, TGA, and EDX. Further enhancement of sorption for a PTE in this Alg-TA-Fe matrix is also demonstrated. Our hydrogels can be produced at room temperature in low resource settings and exhibit performance generally superior to other biopolymer sorbents and on par with those combining synthetic functionalities. A qualitative evaluation of our polyphenol hydrogels' sustainability potential is performed based on their novel functionalities, greenhouse gas emissions, environmental compatibility, material abundance, and potential for localized production.