Thermodynamic Separation of Hydrogen Isotopes Using Hofmann-Type Metal-Organic Frameworks with High-Density Open Metal Sites

Abstract

Hydrogen isotope separation with nanoporous materials is a very challenging yet promising approach. To overcome the limitation of the conventional isotope separation strategy, quantum sieving-based separation using nanoporous materials has been investigated recently. In this study, to see the thermodynamic deuterium separation phenomena attributed to the chemical affinity quantum sieving effect, we examine Hofmann-type metal-organic frameworks (MOFs), Co(pyz)[M(CN)(4)] (pyz = pyrazine, M = Pd2+, Pt2+, and Ni2+), which have microporosity (4.0 x 3.9 angstrom(2)) and an extraordinarily high density of open metal sites (similar to 9 mmol/cm(3)). Owing to the preferential adsorption of D-2 over H2 at strongly binding open metal sites, the Hofmann-type MOF, Co(pyz)[Pd(CN)(4)] exhibited a high selectivity (S-D2/H2) of 21.7 as well as a large D-2 uptake of 10 mmol/g at 25 K. This is the first study of Hofmann-type MOFs to report high selectivity and capacity, both of which are important parameters for the practical application of porous materials toward isotope separation.