Enhanced D ₂ /H ₂ Separation in Isomorphic Copper-Based Metal–Organic Frameworks via Optimized Pore Architecture and Open Metal Sites

Efficient separation of hydrogen isotopes remains a formidable challenge due to their nearly identical physicochemical properties. Porous materials exploiting the quantum sieving effect, particularly those involving open metal sites (OMSs), offer a promising platform for isotopes separation. Herein, we report a systematic investigation of three isoreticular Cu-based metal-organic frameworks-Cu-TDPAT, NOTT-115, and PCN-61-featuring distinct Cu²⁺ OMSs densities (3.73, 3.23, and 3.61 mmol g^-1, respectively) and progressively enlarged pore sizes. By combining static adsorption measurements, thermodynamic analysis, and dynamic breakthrough experiments, we elucidate the cooperative roles of OMSs density and pore architecture of the OMSs in governing hydrogen isotopes separation. Among the studied materials, PCN-61 exhibits the best overall separation performance, achieving a separation time of 28.5 min g^-1 and a selectivity of 1.53 for a D₂/H₂/Ne (3/3/94) mixture at 77 K. Kinetic adsorption studies further confirm that sufficiently large pores, together with a high density of accessible Cu²⁺ OMSs, are essential for efficient dynamic isotopes separation. These findings establish clear structure-performance relationships and provide practical guidelines for the rational design of porous materials for hydrogen isotopes separation.