Taming Flexibility: Synergistic Pore and Polarity Engineering in a MOF for High‐Efficiency Xe/Kr Separation

ABSTRACT The separation of xenon (Xe) and krypton (Kr), two inert gases with nearly identical physicochemical properties, remains a formidable industrial challenge. Flexible metal–organic frameworks (MOFs) offer guest‐specific recognition via structural responsiveness; however, their application in low‐concentration separations is limited by intrinsic flexibility and high gate‐opening pressures, as exemplified by ZIF‐7. Herein, we propose and experimentally substantiate a synergistic regulation strategy that concurrently modulates the pore size and polarity of the framework, thereby overcoming the intrinsic flexibility of MOFs and enabling exceptional Xe/Kr separation performance. By incorporating 20% chlorine into the framework (ZIF‐7‐Cl(20)), the pore environment is effectively polarized, promoting highly selective Xe recognition while preserving adsorption capacity. The optimized material exhibits an IAST selectivity of 30.8 for Xe/Kr (20/80, v/v). Grand Canonical Monte Carlo simulations reveal strong Xe─Cl interactions as the origin of the enhanced selectivity. Dynamic breakthrough experiments further demonstrate excellent separation performance, affording high‐purity Kr (>99.9%) with a productivity of 129 L kg ^{− 1} and a retention time of 84 min g ^{− 1} . This work provides a generalizable strategy for converting flexible MOFs into high‐performance adsorbents for challenging gas separations.