Active Materials for Heavy Metal Extraction from Water

Active Materials for Heavy Metal Extraction from Water
Timothy Swager, John D. MacArthur Professor of Chemistry, Department of Chemistry

Period of performance: 

September 2016 to August 2018

Abstract: 

This proposal seeks to create economically viable and scalable electroactive polymer compositions that have high affinities for soft heavy metal ions such as mercury and lead in their reduced state. The materials will be active and can be switched by oxidation to a state wherein they will have a greatly reduced affinity for the metal ions. The materials will incorporate thioether groups that are established as being able to extract mercury from water. As part of this development different chemical structures will be first evaluated at a small molecule level to determine if the redox active groups need to be directly incorporated into the metal binding group or can simply be proximate. The need for cyclic verses acyclic structures to bind the metal ions will also be investigated. Cyclic structures have lower entropic energetic penalties with their organized binding of metal ions. Polymer composites will be produced that incorporate structures that promote free volume and 3- dimensional ion diffusion in the polymer network.

These structures will be formed by electrostatic assembly of the electroactive polymers in their oxidized cationic state with a novel polyelectrolyte that has been recently developed in the Swager group. The electrostatic assembly is also useful because reduction of the electroactive polymer will result in an uncompensated charge from the sulfonate groups. This will help the material to actively recruit cationic metal ions and when combined with the high affility of the incorporated thioethers, we expect that the system will strongly bind mercury and lead. These materials can be studied as immobilized films or membranes on electrodes. These studies will allow determination of how metal binding affects the electrochemical potential of the electroactive polymers. Additionally, by depositing films on interdigitated electrodes it will be possible to see if the electrical conductivity is dependent on the target metal ions. The composite materials can also be synthesized as colloidal particles that can be cycled between their binding and release of metal ions by treatment with oxidants and reductants. It is also intriguing to see if new materials that contain electron acceptors can be used to transiently charge the electroative materials under sunlight. The latter would open up many new opportunities as it could lead to systems that do not require access to electrical power.