Sculpting the Pores of a Metal–Organic Framework to Enhance Mixture Separation: An Illustrative Study based on Xe/Kr Separation

Postsynthetic modification (PSM) of metal–organic frameworks (MOFs) is an attractive approach for enhancing functionality and boosting performance of these nanoporous materials. Often PSM relies on elaboration of either metal nodes or organic linkers of candidate MOFs. Herein, we introduce an alternative approach, sculpting the pores of a zirconium-based MOF, NU-903, with a size-matching Keggin polyoxometalate (POM) and apply the approach to separation of Xe/Kr mixtures as a test application. The computationally optimized structure of POM@NU-903 showed that the original 3-dimensional pore network was sculpted to a 2-dimensional pore. Although the pore volume decreased by 20%, Xe and Kr uptake capacities were nearly doubled at 298 K and 1 bar, with significantly boosted selectivity and heat of adsorption. Given the agreement between computational and experimental results and the great variety of MOFs and POMs, we envision a sizable library of pore-sculpted MOFs for demonstration and optimization of desired chemical separations.