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 Hf-6 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 Hf-6 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 degrees 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 cm(3) 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.