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

Abstract

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.