Influence of Structural Determinants of Dihydrogen Adsorption and Isotopologue Separation in Metal-Organic Frameworks

Efficient separation of hydrogen isotopologues, particularly D₂, is critical for applications in energy, nuclear technology, and environmental sciences. Conventional methods, such as cryogenic distillation, are energy-intensive and provide limited selectivity (S ≈ 1.4). Here, we report a systematic evaluation of diverse MOFs with ultramicropores, open metal sites (OMS), and framework flexibility for D₂/H₂ separation. Thermal desorption spectroscopy and adsorption studies revealed that ultramicroporous MOFs enable preferential D2 adsorption via kinetic quantum sieving, while Ni-MOF-74(Co) achieves exceptional selectivity (S = 52 at 77 K) through OMS-driven chemical affinity quantum sieving. Flexible MOFs, [Cu₂(nPr-trz-ia)₂] and [Cu₂(Et-trz-ia)₂], showed temperature-responsive cryogenic flexibility with selectivity of 1.4-2.3 ~ 77 K. These findings highlight structural design as the key to advancing isotopologue separation at practical temperatures.