Rational Pore Design in Multivariate Metal-Organic Frameworks for C₂H₆/C₂H₄ Separation

The arrangement of pores within the framework plays a crucial role in the gas separation and adsorption of metal-organic frameworks (MOFs), determining their overall performance. In this study, the impact on gas separation efficiency is compared using two multivariate MOF (MTV-MOF) systems with controlled pore arrangements. These systems employ two types of ligands with differing bulkiness: one is the core-shell MOF composite (CSMOF), sequentially synthesized with the bulkier ligand located at the shell, and the other is the mixed-linker MOF (MLMOF), synthesized via a one-pot reaction. Interestingly, in MLMOFs, it is confirmed that the distribution of bulky ligands increases gradually from the center to the surface, rather than being randomly distributed, forming a framework with finely tuned pores. MLMOFs exhibit a high C₂H₆/C₂H₄ ideal adsorption solution theory (IAST) selectivity of 2.25 due to the overall distribution of alkoxy chains that can form multiple interaction sites with C₂H₆. Breakthrough experiments demonstrate that MLMOF enables the effective separation of C₂H₆/C₂H₄ mixtures, achieving the productivity of 19.7 L kg^-1 for high-purity C₂H₄ (>99.9%) under dry conditions. This study indicates that pore space partitioning utilizing MTV-MOFs can be effectively applied to maximize performance in specific gas separations.