A metal-organic framework with suitable pore size and dual functionalities for highly efficient post-combustion CO₂ capture

Capturing carbon dioxide (CO₂) from flue gases with porous materials has been considered as a viable alternative technology to replace traditional liquid amine adsorbents. A large number of microporous metal-organic frameworks (MOFs) have been developed as CO₂-capturing materials. However, it is challenging to target materials with both extremely high CO₂ capture capacity and gas selectivity (socalled trade-off) along with moderate regeneration energy. Herein, we developed a novel porous material, [Cu(dpt)₂(SiF₆)]_n (termed as UTSA-120; dpt = 3,6-di(4-pyridyl)-1,2,4,5-tetrazine), which is isoreticular to the net of SIFSIX-2-Cu-i. This material exhibits simultaneously high CO₂ capture capacity (3.56 mmol g^-1 at 0.15 bar and 296 K) and CO₂/N-2 selectivity (similar to 600), both of which are superior to those of SIFSIX-2-Cu-i and most other MOFs reported. Neutron powder diffraction experiments reveal that the exceptional CO₂ capture capacity at the low-pressure region and the moderate heat of CO₂ adsorption can be attributed to the suitable pore size and dual functionalities (SiF6^2- and tetrazine), which not only interact with CO₂ molecules but also enable the dense packing of CO₂ molecules within the framework. Simulated and actual breakthrough experiments demonstrate that UTSA-120a can efficiently capture CO2 gas from the CO₂/N₂ (15/85, v/v) and CO₂/CH₄ (50/50) gas mixtures under ambient conditions.