Preparation of benzodiimidazole-containing covalent triazine frameworks for enhanced selective CO₂ capture and separation

Covalent triazine frameworks (CTFs) were frequently prepared by carbonitriles polymerization reaction under the ionothermal condition, and the functionalized CTFs were achieved through the rational design of monomer to improve the gas capture and separation performance. In this paper, a class of porous benzodiimidazole-containing covalent triazine frameworks (CTF-DIs) was successfully prepared via ionothermal trimerizations from benzo[1,2-d:4,5-d']diimidazole based dicyano monomer (BCBDI). The N₂ adsorption isotherms at 77 K reveal high BET surface areas of CTF-DIs up to 1877 m² g⁻¹. The effects of reaction temperature and the ratio of monomer to ZnCl₂ on the pore characteristics of the CTF-DIs were investigated. The highest uptake value for CO₂ is 89.2 cm³ g⁻¹ for CTF-DI-7 at 273 K and 1 bar. Excitingly, CTF-DI-6 demonstrates the highest CO₂/N₂ selectivity of 53 and the significant CO₂/CH₄ selectivity of 15 at 273 K and 1 bar, according to IAST, due to the existence of abundant active nitrogen species. These results clearly demonstrate the CTF-DIs are likely to be promising candidates for CO₂ capture and separation field.