Design and synthesis of carbazole-based conjugated microporous polymers for CO2 capture

Conjugated microporous polymers (CMPs) with electron-rich heteroatoms in the skeleton have been receiving continuous attention for their huge potential in carbon dioxide (CO₂) capture with high selectivity. Herein, we designed and synthesized three CMPs (MFCM-CMP, FFCM-CMP, and FFC-CMP-1) for CO₂ capture. The MFCM-CMP and FFCM-CMP were obtained by the reaction between the similar carbazole- and fluorine-based building blocks and cyanuric chloride, while the FFC-CMP-1 was synthesized by self-polymerization of 9,9′-(9,9-difluoro-9H-fluorene-2,7-diyl)bis(9H-carbazole) (FFC) building blocks. The as-prepared CMPs had high specific surface areas (SA_BET = 688-1245 m²/g), and hierarchical porous skeletons with average pore sizes from 2.7 to 3.2 nm. Furthermore, all the CMPs exhibited excellent gas (CO₂, N₂, CH₄) uptake capacity. Remarkably, FFCM-CMP performed the CO₂, N₂, and CH₄ uptake for 74.5 cm³/g, 4.2 cm³/g, and 17.4 cm³/g at 273 K, 1.0 bar, and the CO₂ capture selectivity could achieve 19.6 and 4.3 from CO₂/N₂ (15/80) and CO₂/CH₄ (50/50) mixture at 298 K, 1.0 bar, respectively. The gas breakthrough test carried out in CO₂/N₂/Ar (15/80/5) disclosed evidently that the synthesized CMPs with triazine groups exhibited outstanding CO₂ capture selectivity. This work provides a new strategy for porous organic adsorbent for improving CO₂ selectivity from the molecular level.