Our Research Active materials for heavy metal extraction from water

The research team of this project created 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 were active and could be switched by oxidation to a state wherein they had a greatly reduced affinity for the metal ions. The materials incorporated thioether groups that are established as being able to extract mercury from water. Different chemical structures were 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 was also investigated. Cyclic structures have lower entropic energetic penalties with their organized binding of metal ions. Polymer composites were produced that incorporate structures that promote free volume and 3- dimensional ion diffusion in the polymer network.

These structures were formed by electrostatic assembly of the electroactive polymers in their oxidized cationic state with a novel polyelectrolyte that had been recently developed in the Swager group. The electrostatic assembly was also useful because reduction of the electroactive polymer resulted in an uncompensated charge from the sulfonate groups. This helped the material to actively recruit cationic metal ions and when combined with the high affinity of the incorporated thioethers, the system strongly bound mercury and lead. These materials can be studied as immobilized films or membranes on electrodes. These studies allowed the determination of how metal binding affects the electrochemical potential of the electroactive polymers. Additionally, by depositing films on interdigitated electrodes it was possible to see if the electrical conductivity is dependent on the target metal ions. The composite materials could also be synthesized as colloidal particles that can be cycled between their binding and release of metal ions by treatment with oxidants and reductants. The team also investigated 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.