Tailoring Pore Aperture and Structural Defects in Zirconium-Based Metal-Organic Frameworks for Krypton/Xenon Separation

Krypton and xenon are important gases in many applications, including, but not limited to, electronics, lighting, and medicine. Separation of these two gases by cryogenic distillation is highly energy-intensive; however, adsorption-based separation processes provide an alternative strategy for isolating gases in high purity. The absence of strong interactions between these molecules and porous adsorbents has impeded the advancement of adsorptive separation of krypton and xenon. Herein, we capitalized on the modular nature of metal-organic frameworks (MOFs) to design a porous material which relies on gas confinement to separate krypton/xenon (Kr/Xe) mixtures. We solvothermally synthesized a new zirconium-based MOF, NU-403, which comprises a three-dimensional linker, bicyclo[2.2.2]octane-1,4-dicarboxylic acid. Comprehensive gas adsorption measurements revealed that the linker dimensionality and MOF pore aperture dramatically affect the separation of xenon from krypton owing to the confinement of gas molecules inside the framework. Moreover, Kr/Xe selectivity increased significantly after postsynthetic defect healing, which further enhanced gas-framework interactions, demonstrating an effective strategy for enhancing krypton and xenon separation.