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.