Metal-organic framework based membranes for selective separation of target ions

Abstract

Metal-organic frameworks (MOFs) are an increasingly popular class of porous materials due to their tailorable structure comprised of ordered porous cavities, high specific surface areas, and versatile functional organic ligands. Implementation of these porous materials into membrane separation technologies can create an energy-efficient alternative for ion-selective separation. However, their low stability in aqueous environments and other challenges has limited their industrial breakthrough. In the past five years, many developments have improved MOF-based membranes for the selective separation of target ions. Novel insight into MOF-based membranes' structure-property relationships improves dispersibility, stability, size-sieving, electrostatic repulsion, and ionic conductivity for ideal membrane performance. The latest design principles for MOF-based membrane use advanced confinement conversion, in situ self-assembly, layer-by-layer assembly, and interfacial polymerization methods for enhanced separation performance. Analysis of separation mechanisms in MOF-based membranes now extends applications to desalination, lithium extraction, removal of heavy metal ions, and separation of ions from organic solvents. Overall, further development of MOF-based membranes presents numerous opportunities and challenges in target ion separation.