Bioinspired Amphoteric Sorbent for Water Remediation

According to UN estimates, 4 billion people will lack access to safe drinking water by the year 2025. This projection can be attributed to rising population and industrialization, resulting in an insurgence of pollutant deposition in water bodies. Heavy metals have been identified as common inorganic contaminants produced in significant amounts by battery manufacturing, metal plating, and mining industries, among other industries. Consumption of these dissolved species in ultra-trace amounts is hazardous to human health. Current water treatment methods such as ion exchange and reverse osmosis are time consuming, generate waste, and costly. Presently, adsorption technology has been adopted in water purification systems to remove heavy metals from water resources due to its effectiveness and low cost, but lacking the high adsorption, environmental sustainability, and versatility. This project aims at overcoming these technical barriers by developing a novel sorbent from biomass by products with high porosity, and high surface area with amphoteric surface properties for selective cleansing of heavy metals in surface water. The sorbent of hierarchical microstructures with a robust metal-organic framework was synthesized by catenating the naturally occurring tannic acid with iron (II) acetate in an aqueous media. The synthesis method follows the green chemistry principles, offering an energy-efficient versatile synthesis method. The chemical composition, shape, physicochemical properties, and colloidal stability of microstructures were investigated using a wide range of characterization techniques. Supporting their amphoteric sorption, Fe (III)-TA microstructures efficiently removed Ag⁺and Cd⁺² from a highly alkaline synthetic water, with > 96% removal efficiency. Experimental data fitted into Langmuir, Freundlich, and Temkin adsorption isotherms and Pseudo first and second order kinetic models suggests a monolayer adsorption of Ag⁺and Cd⁺²onto the surface of the microstructures. The effective adsorption of metal ions onto the microstructures is attributed to the highly branched and hydroxyl dense polytopic tannic acid ligand, which provides multiple bonding sites through diverse chemical interactions. These highly porous, amphoteric polyphenol-based metal organic coordination polymers synthesized under environmentally benign conditions are cost-effective and easy to scale-up for pilot or industrial applications. Thus, they offer a great potential for use in tertiary treatment of water remediation.