Elucidating Liquid‐Phase Guest Transport Across MOF Single Crystals: Interplay of Adsorption, Desorption, and Intracrystalline Diffusion

ABSTRACT Although metal–organic frameworks (MOFs) provide molecular selectivity in separations, understanding diffusion within these materials remains challenging due to the intertwined contributions of inherent pore architecture and grain boundaries in packed‐bed systems. To isolate the intracrystalline diffusion behavior, molecular transport across MOF single crystals was investigated in binary and ternary liquid‐phase systems. Diffusion rates were found to vary significantly even among guest molecules with identical kinetic diameters. By isolating the intracrystalline diffusion process, the slow transport is attributed to strong guest–framework interactions rather than pore clogging. This is corroborated by the increase in diffusion rates upon reducing the guest–framework interactions through selection of a more strongly interacting solvent. This study provides mechanistic insights into intrinsic diffusion in MOFs and benchmark behavior to calibrate computational approaches.