Polymers of intrinsic microporosity with internal dihedral lock for efficient gas separation

Abstract

Polymers of intrinsic microporosity (PIMs) stand out as promising membrane materials with exceptional separation performance. In this study, we crafted a highly efficient gas separation membrane using an emerging material, called cyclohexyl-fused spirobiindane-based PIM (CCS-PIM). The CCS-PIM features a robust and rigid microporous structure with a high specific surface area (S_BET ​= ​704.6 ​m²/g), exhibiting excellent CO₂-selective adsorption capacity. The CO₂ adsorption uptake is 0.78 ​mmol/g at 273 ​K and 0.15 ​bar, leading to IAST selectivity of 25.2 for CO₂/N₂ (15/85 v/v) and 16.7 for CO₂/CH₄ (50/50 v/v) at 298 ​K. The precisely tuned pore size of the CCS-PIM membrane leads to an enhanced molecular sieving effect, showcasing superior selectivity across various gas pair separations. It demonstrates an O₂/N₂ selectivity of 6.03 and a CO₂/CH₄ selectivity of 26.1, surpassing the 2008 Robeson upper bounds. This study suggests a strategic method to improve gas separation efficiency by customizing a locked PIM structure with precise molecular sieving through the insertion of variously sized rings.