Computational Modeling of Adsorption of Xe and Kr in M-MOF-74 Metal Organic Frame Works with Different Metal Atoms

Management of radioactive noble gases, i.e., Xe and Kr, needs special attention in the context of nuclear fuel reprocessing and postulated severe accident scenarios. Entrapment of these species in suitable matrix is generally difficult since Xe and Kr do not form bonds with substrates (physisorbed by van der Waals interactions) due to their chemical inertness. In recent years metal-organic frameworks (MOFs) are being actively discussed for adsorption/separation of various gases including noble gases. MOFs are considered superior in such applications owing to their high intake capacity, better selectivity and also the possibility of tuning the chemical properties by varying organic linkers or metal atoms. Theoretical modeling of MOFs and tailoring their properties appropriately for noble gas adsorption/separation are potentially useful to identify suitable candidates. In this regard, we investigate the binding energies of Xe and Kr in the well-known M-MOF-74 employing computer simulations. To understand the influence of different open metal sites on binding affinity, the central metal ion in M-MOF-74 are varied. Our results show that Xe binds stronger than Kr and binding strength changes with the nature of the central metal atom in the MOF. The adsorption behavior obtained from our calculations is in good agreement with previous experimental and theoretical observations. The binding strength at different adsorption sites are favored by van der Waals interactions between noble gas atoms with MOF network and each other. On the basis of our studies, efficient MOFs for noble gas separation can be obtained within the MOF series by incorporating suitable metal centers.