Efficient and selective capture of xenon over krypton by a window-cage metal-organic framework with parallel aromatic rings

Efficient capture and separation of xenon (Xe) and krypton (Kr) from nuclear fuel reprocessing plants is of great significance for the control of discharge of gaseous radioisotopes into the environment. However, due to the similar size and chemically inert spherical properties of Xe/Kr, the discovery of an adsorbent with both high adsorption capacity and high selectivity remains a challenge. Here, we report a microporous MOF (Ni-MOF, [(Ni2NiIII)-Ni-II(mu(3)-OH)(bdc)(3)(tpt)].guest) featuring two different cavities with an appropriate triangular hole window size. One is composed of parallel aromatic rings with spacings of approximately 4.3 angstrom comparable to the kinetic diameter of Xe (4.047 angstrom), affording excellent binding affinity for Xe while the larger one with narrow pore window provides sufficient space for gas adsorption. The Ni-MOF material exhibits an exceptionally high Xe uptake of 5.43 mmol/g and Xe/Kr selectivity of 7.66 at 298 K and 1 bar. The adsorption capacity is the highest among all MOFs without open-metal-sites. Furthermore, the sorption selectivity of Xe over Kr within Ni-MOF originates from a special sandwiched pi-Xe-pi interaction revealed by Van der Waals interaction calculations.