Jan. 21, 2025
Ion-exchange is one of the more prominent highly selective treatment technologies, but it requires periodic chemical backwashing to regenerate binding sites due to specific, irreversible interactions with target species. Other ion-selective technologies include supported liquid membranes and polymer inclusion membranes, which rely on complexing agents to selectively bind to the target species at the membrane interface and shuttle it to the other side. The downfall of these membranes is their poor stability, limited lifetime, and/or low throughput.
Ryan’s research demonstrates how design principles from biological ion channels can overcome the limitations of the aforementioned technologies. Ryan incorporates selective functional groups into a thin polymer coating on top of porous supports. The membranes obtain remarkable separation factors (> 50) in diffusion dialysis between like-charge species that are similar in hydrated size (< 0.05Å different). Using experimental characterization and simulations, Ryan demonstrates the significant role of intermolecular interactions between the metal and the membrane in controlling selectivity. Additionally, Ryan has found that high permeability and selectivity require that the membrane be very thin, similar to the sub-nanometer length of selectivity filters in biological ion channels.
Future work will aim to produce ultrathin, robust membranes that are highly selective in an electro-driven process to maximize ion throughput. Such a process would provide a continuous, chemical-free approach for high-precision separations. These membranes could improve the viability of recovering valuable metals from wastewater and future ion-selective membranes could enable targeted removal of harmful contaminants or recovery of other precious resources.
