Functional Chain Engineering in MOFs: Balancing Pore Size and Affinity for Noble Gas Separation

ABSTRACT The efficient separation of Xe from Kr requires adsorbents with optimized pore environments that maximize van der Waals interactions with Xe atoms. To achieve this, a series of five metal–organic frameworks (MOFs) are synthesized using a mixed‐ligand strategy that systematically incorporates bulky C8 alkoxy substituents into the IRMOF‐1 framework through varying ratios of terephthalic acid (BDC) and 2,5‐bis(octyloxy)‐1,4‐benzenedicarboxylic acid (C8BDC). Increasing the C8BDC content progressively reduces the pore size, and ML‐80C8 (20% BDC and 80% C8BDC) provides the optimal pore environment for selective Xe adsorption. ML‐80C8 exhibits the best Xe/Kr separation performance, achieving a high Xe uptake of 0.96 mmol g − 1 and a markedly elevated Xe/Kr selectivity of 12.1, comparable to that of high‐performing benchmark MOFs. It demonstrates excellent Xe/Kr separation performance under dynamic mixture conditions, outstanding stability, and easy regenerability. These results highlight the potential of mixed‐ligand MOFs for tailored pore designs in noble gas separation.