Ionic Sieving at Sub-Angstrom Precision Enabled by Metal Organic Frameworks

The demand for cesium is expanding rapidly in light of its necessity in high-tech industries. Thus, technologies that can efficiently extract cesium from the sources are critically needed. Here, the metal-organic framework (MOF) membranes created from -Cl and -NH₂ functionalized MIL-53 enabled highly selective transport of cesium ions. The angstrom-scale pore windows in these MOFs conduct Cs⁺ ions at high throughput, 2 orders of magnitude faster than other marginally larger ions. Ascribed to size sieving effects, MIL-53-NH₂ containing 6.6 Å size channels realized an exceedingly high Cs⁺/Li⁺ selectivity up to ∼315. The rapid transport of Cs⁺ ions relative to other ions is greatly dependent on the precision of the angstrom-scale pores. Our work highlights the enormous potential of realizing high ion selectivity with MOFs and drives the further development of these materials in a variety of advanced separations.