A Gate‐Opening Control Strategy via Nitrate–Chloride Anion Exchange for Enhanced Hydrogen Isotope Separation in Metal‐Organic Frameworks

Efficient separation of hydrogen isotopes, especially deuterium (D2), is pivotal for advancing industries such as nuclear fusion, semiconductor processing, and metabolic imaging. Current technologies, including cryogenic distillation and Girdler sulfide processes, suffer from significant limitations in selectivity and cost‐effectiveness. Herein, we introduce a novel approach utilizing an imidazolium‐based Metal‐Organic Framework (MOF), JCM‐1, designed to enhance D2/H2 separation through temperature‐dependent gate‐opening controlled by ion exchange. By substituting NO3⁻ ions in JCM‐1(NO3⁻) with Cl⁻ ions to form JCM‐1(Cl⁻), we precisely modulate the gate‐opening threshold, achieving a significant enhancement in isotope selectivity. JCM‐1(NO3⁻) exhibited a D2/H2 selectivity (SD2/H2) of 14.4 at 30 K and 1 bar, while JCM‐1(Cl⁻) achieved an exceptional selectivity of 27.7 at 50 K and 1 mbar. This heightened performance is attributed to the reduced pore aperture and higher gate‐opening temperature resulting from the Cl⁻ exchange, which optimizes the selective adsorption of D2. Our findings reveal that JCM‐1 frameworks, with their tunable gate‐opening properties, offer a highly efficient and adaptable platform for hydrogen isotope separation. This work not only advances the understanding of ion‐exchanged MOFs but also opens new pathways for targeted applications in isotope separation and other gas separation processes.