A stable ultra-microporous hafnium-based metal-organic framework with high performance for CO2 adsorption and separation

By utilizing a winding carboxylic acid ligand as the linker and 12-connected Hf6 clusters as the metal node, we successfully construct a novel hafnium-based metal-organic framework [Hf6O4(OH)4(DCPB)6]·(Hf-MOF, 1,3-di(4-carboxyphenyl)benzene (H2DCPB)) with ultra-microporous structure. Benefitting from the strong coordination bond between Hf6 clusters and the carboxylic acid ligand, the synthesized Hf-MOF displays extraordinarily high thermal and chemical stability, in which the Hf-MOF can maintain high crystallinity under both acidic and basic aqueous solutions, and its decomposition temperature is as high as about 400 °C. Moreover, the interpenetrated framework can endow the Hf-MOF with ultra-microporous pores, which can provide multiple adsorption sites and play a role in the size sieving effect of CO2 molecules. Thus, the Hf-MOF displays excellent CO2 adsorption and separation performance, in which the maximum CO2 adsorption amount can reach up to 65.5 cm3 g−1 at 273 K and 1 bar, and the selectivities for CO2/CH4 = 0.5/0.5 and CO2/CH4 = 0.05/0.95 are as high as 6.9 and 6.0 under 1 bar at 298 K, respectively, and surpass many reported water stable MOF materials. The commendable stability and the CO2 adsorption/separation ability are of extreme importance for its practical industrial applications.