Influence of Structural Determinants on Dihydrogen Adsorption and Isotopologue Separation in Nanoporous Metal–Organic Frameworks

Efficient separation of dihydrogen isotopologues, particularly D₂, is critical for applications in nuclear energy 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 (TDS) and adsorption studies revealed that ultramicroporous MOFs enable preferential D₂ adsorption via kinetic quantum sieving, while bimetallic Ni-MOF-74(Co) achieves high 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], show temperature-responsive cryogenic flexibility with selectivities of 1.4-2.3 at 77 K. These findings highlight structural design as the key to advancing dihydrogen isotopologue separation at practical temperatures.