Tailoring Molecular Diffusion in Core‐Shell Zeolite Imidazolate Framework Composites Realizes Efficient Kinetic Separation of Xylene Isomers.

The separation of xylene isomers is a critical and energy‐intensive process in the petrochemical industry, primarily due to their closely similar molecular structures and boiling points. In this work, we report the synthesis and application of a novel core–shell zeolitic imidazolate framework (ZIF) composite, ZIF‐65@ZIF‐67, designed to significantly enhance the kinetic separation of xylene isomers through a synergistic "shell‐gated diffusion and core‐facilitated transport" strategy. The external ZIF‐67 shell selectively restricts the diffusion of larger isomers (MX and OX), while the internal ZIF‐65 core accelerates the diffusion of PX, thereby amplifying the diffusion differences among the isomers. This architecture yields remarkable improvements in both selectivity and diffusion rates, as demonstrated by vapor‐phase adsorption studies and molecular dynamics simulations. The ZIF‐65@ZIF‐67 composite exhibits up to 12.5 times higher PX/OX selectivity in liquid‐phase adsorption and 3.4 times higher dynamic selectivity in fixed‐column breakthrough experiments compared to the individual ZIF components. Theoretical simulations further corroborate the heterogeneous diffusion control mechanism, revealing the time‐dependent diffusion regulation within the core–shell architecture. This work underscores the great potential of core–shell MOF composites in optimizing molecular sieving processes for industrially significant separations and highlights a new route for enhancing kinetic separation efficiency in complex multicomponent systems. [ABSTRACT FROM AUTHOR]