Hierarchical porous metal-organic frameworks (MOFs) integrating micro- and mesopores hold promise for advanced separations but often suffer from understudied negative pore synergy, where interconnected pores compromise selectivity and diffusion. Using the zirconium-based porous coordination network (PCN) PCN-608 as a model, we identify that rapid analyte translocation between meso-hexagonal and micro-triangular channels induces chaotic diffusion, undermining separation efficiency. A channel-isolation strategy is then developed via solvent-assisted installation of barrier ligands (BDC/NH2BDC) at interconnecting windows. PCN-608-BDC with isolated pores exhibit 8-13 times higher diffusion coefficients for xylene isomers than the pristine PCN-608 monitored by inverse gas chromatography (IGC). Molecular dynamics simulations confirm the restriction of cross-pore migration and the acceleration of diffusion kinetics in PCN-608-BDC. The PCN-608-BDC shows obviously better performance than the pristine material as GC stationary phases and breakthrough adsorbents in separation xylene isomers. All PCN-608 series with a micro-mesoporous mixed structure exhibit excellent xylene uptake. Similar improvements in separation performance are also observed for NU-1000 with isolated pores, validating the universality of the phenomena. By balancing pore connectivity and active site availability, this work establishes channel isolation as a generalizable design principle for optimizing hierarchical MOFs to eliminate the negative pore synergy, offering simultaneous enhancements in selectivity, and stability for gas separations. Here authors show that isolating interconnected channels in metal-organic frameworks eliminates inefficient molecular shuttling, greatly improving diffusion and separation performance. The strategy enhances isomer separation and material stability.
Liu et al. (Wed,) studied this question.