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

Abstract

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.