Rational Pore Design in Multivariate Metal-Organic Frameworks for CH/CH 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 CH/CH ideal adsorption solution theory (IAST) selectivity of 2.25 due to the overall distribution of alkoxy chains that can form multiple interaction sites with CH. Breakthrough experiments demonstrate that MLMOF enables the effective separation of CH/CH mixtures, achieving the productivity of 19.7 L kg for high-purity CH (>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.