Hierarchically Porous Co-MOF-74 Hollow Nanorods for Enhanced Dynamic CO₂ Separation

Metal–organic frameworks (MOFs) with coordinatively unsaturated (open) metal sites have been intensively investigated in gas separations because their active sites can selectively interact with targeted molecules such as CO2. Although such MOFs have shown to exhibit exceptional CO2 uptake capacity at equilibrium, the dynamic separation behavior is often not satisfactory to be considered in practical applications. Herein, we report a facile and efficient self-sacrifice template strategy based on the nanoscale Kirkendall effect to form novel Co-MOF-74 hollow nanorods enabling adsorption/desorption of gas molecules in a facilitated manner. The time-dependent microscopic and diffraction examinations were performed to elucidate the formation mechanism of Co-MOF-74 hollow nanorods and to obtain insights into the factors critical to maintaining the rodlike morphology. Such nanostructured MOF exhibited much sharper CO2 molecular separation behavior than conventional MOF bulk crystals under a dynamic flow condition, because of its enhanced adsorption kinetics through the shortened diffusion distance. Such enhanced dynamic molecular separation behavior was further confirmed by chromatographic separations where a significant peak narrowing was demonstrated.