Facile preparation of cross-linked polyimide aerogels with carboxylic functionalization for CO₂ capture

In this study, highly cross-linked and completely imidized polyimide aerogels containing carboxyl groups were successfully synthesized using a mild sol-gel method at room temperature from 3,5-diaminobenzoic (DABA) and biphenyl-3,3′,4,4′-tetracarboxylic (BPDA) and cross-linked with 1,3,5-triaminophenoxybenzene. The densities of the obtained polyimide aerogels are between 0.116 and 0.386 g/cm³, the specific surface areas range from 173 to 461 m²/g, and the porosities are as high as 97%. The CO₂ adsorption-desorption isotherms are reversible, and the CO₂ uptakes at 25 °C and 1 bar are as high as 21.10 cm³/g, which are comparable to those of previously reported microporous organic polymers. The high CO₂ adsorptions are attributed to the abundance of electron-rich heteroatoms in the polyimide networks and to the presence of carboxyl groups, a type of CO₂-philic group. The facile preparation and high CO₂ adsorptive capacity indicate that polyimide aerogels may be ideal candidates for capturing CO₂.