Dense packing of xenon in an ultra-microporous metal–organic framework for benchmark xenon capture and separation

Abstract

For adsorptive separation of xenon/krypton mixture, it still remains a daunting challenge to target both high Xe adsorption and selectivity in a single adsorbent because of their close size and inert nature. Herein, we report an ultra-microporous alkyl Cu-based MOF-11 with suitable pore architecture for benchmark Xe capture and separation. MOF-11 features small pore channels (4.4 Å) close to the kinetic diameter of Xe, in which a large number of alkyl cavities and oppositely adjacent open Cu-metal sites are densely arranged along the pore channels in staggered mode. Such unique pore system can not only introduce strong binding affinity with Xe, but also enable the dense packing of Xe inside the pores. This material shows the highest Xe storage density of 2826 g/L at ambient conditions, record-high Xe uptake (4.0 mmol g−1at 0.2 bar and 298 K) and one of the highest Xe/Kr selectivity (19.1). The Xe locations within MOF-11 were visually identified by single-crystal X-ray diffraction experiment, which unveils the dense packing mechanism of Xe within the pores accountable for the record Xe capture capacity. The breakthrough experiments confirm that MOF-11 exhibits the exceptional separation performance for 20/80Xe/Kr mixture with both record-high Xe uptake capacity (3.46 mmol g−1) and Kr productivity (350 cm3 g−1).