Structural Control of Uniform MOF-74 Microcrystals for the Study of Adsorption Kinetics.

Metal-organic frameworks (MOFs) is a promising class of sorbent materials for swing adsorption gas separation. However, although sorption kinetics plays a major role in column breakthrough experiments, it is rarely studied with MOF materials. This is largely because the synthesis of uniform yet separation-relevant MOFs is a challenging task. Here, we report a dual-modulation approach for the synthesis of well-defined Mg-MOF-74 hexagonal rods with an extremely uniform size distribution (polydispersity index = 1.02). Through epitaxial growth and wet chemical etching, uniform hollow Ni-MOF-74 with plate-shaped caps were obtained. CO2 adsorption kinetic study shows that hollow Ni-MOF-74 exhibits 54% faster diffusion rate compared to solid Ni-MOF-74 due to a shortened diffusion length, despite their identical CO2 uptake capacity. This has led to a 21% extension of column breakthrough time during CO2/N2 separation under identical conditions.