Sodium-Selective Channels Enabled by De Novo Encapsulated Azamacrocycles for Boosting Osmotic Energy Harvesting.

Similar to the selective filter of biological ion channels, crown ethers have numerous dipole moments arranged around its interior, forming spatially confined electronegativity capable of attracting target ions while rejecting other species. In this light, crown-ether-based membranes have the potential to render both benign ion selectivity and high throughput and therefore enable highly efficient osmotic energy harvesting, however not yet implemented. Herein, we develop biomimetic sodium-selective channels via de novo encapsulation of diazacrown ethers into UiO-66 membranes. The embedding of such azamacrocycles exclusively enhances Na+ flux while blocking other cations, leading to the concurrent enhancement of Na+ selectivity and permeability. This can be ascribed to the interplay between ion dehydration and azamacrocycle-cation recognition, which resulted in a lower energy barrier for Na+ transport in contrast to other cations. The optimized permeability-selectivity combination enables the azamacrocycle-encapsulated membranes highly favorable in terms of osmotic energy harvesting, where an impressive output power density of 11.5 W m-2 is achieved by mixing natural seawater and river water. This work presents a methodology for developing high-performance ion-selective membranes with biomimetic channel structures, suitable for applications involving complicated separation processes and energy conversion systems.