Current membrane technology is based primarily on pore size and chemical functionality. Naturally occurring protein channels far exceed any man-made engineering pores with selectivities exceeding parts per million and flow rates 10,000 fold faster. The PI proposes to imitate natural protein channel structures and nanometer scale electrode geometries to increase flow. If successful, this could potentially revolutionize membrane function by providing a solution to the long standing trade-off between high chemical selectivity and high processing rate.
Two promising material platforms are Carbon Nanotube (CNT) Membranes and nm-scale electrode multilayers on anodized aluminum oxide (AAO). There are three key attributes unique to Carbon Nanotube (CNT) membranes: 1) atomically flat hydrophobic graphitic core that induces a near perfect slip layer for dramatic fluid flow 2) functional chemistry by necessity is at the cut entrances to the CNT cores for gatekeeper activity and 3) CNTs are conductive allowing for electrochemical transformation and application of electric field. Needed is a method to generate fluid flow (with chemical interaction or selectivity) in the entrance to CNT pores and have the plug flow rapidly transfer down the fast CNT core. Electro-osmotic pumping is found to have similar flow enhancements as pressure driven pumping and can accelerate selectively bound species within plug flow Peptide libraries allow the screening of 109 peptide combinations to find highly selective affinity chemistry far beyond what is achieved with simple coordination chemistry. However, strong binding coefficients result in kinetics too slow for monolayer-based pumping cycles. The PIs have found that modest voltages are sufficient to release cationic bound rare-earth ions, from high surface area conductive AAO surface. Multilayer electrodes allow for pumping cycles to direct strong electric fields in a high porosity AAO system. This allows for a very general separation system based on rapid cycles of binding targets to specific peptides at the pore entrances followed by electrostatic release pumping across the membrane. Due to the large breadth of peptide affinity libraries, this concept is applied to a large number of commercially relevant applications in energy storage, energy processing, chemical sensors, selective pharmaceutical separations, drug delivery and water purification. Support of this research area will enable many educational opportunities related to novel nanometer scale materials fabrication, characterization and application into separations science and engineering.
