Controlling Pore Shape and Size of Interpenetrated Anion-Pillared Ultramicroporous Materials Enables Molecular Sieving of CO₂ Combined with Ultrahigh Uptake Capacity

The separation of carbon dioxide (CO₂) from hydrocarbons is a critical process for the production of clean energy and high-purity chemicals. Adsorption based on molecular sieving is an energy-saving separation process; however, most of molecular sieves with narrow and straight pore channels exhibit low CO₂ uptake capacity. Here, we report that a twofold interpenetrated copper coordination network with a consecutive pocket-like pore structure, namely, SIFSIX-14-Cu-i (SIFSIX = hexafluorosilicate, 14 = 4,4′-azopyridine, i = interpenetrated) is a remarkable CO₂/CH₄ molecular sieving adsorbent which completely blocks the larger CH₄ molecule with unprecedented selectivity, whereas it has excellent CO₂ uptake (172.7 cm³/cm³) under the ambient condition. The exceptional separation performance of SIFSIX-14-Cu-i is attributed to its unique pore shape and functional pore surface, which combine a contracted pore window (3.4 Å) and a relatively large pore cavity decorated with high density of inorganic anions. Dispersion-corrected density functional theory calculation and neutron powder diffraction were performed to understand the CO₂ binding sites. The practical feasibility of SIFSIX-14-Cu-i for CO₂/CH₄ mixtures separation was validated by experimental breakthrough tests. This study not only demonstrates the great potential of SIFSIX-14-Cu-i for CO₂ separation but also provides important clues for other gas separations