Enhancing Gas Sorption and Separation Performance via Bisbenzimidazole Functionalization of Highly Porous Covalent Triazine Frameworks

In this paper, a series of bisbenzimidazole-functionalized highly porous covalent triazine frameworks (CTF-BIBs) has been constructed from a new organic building block, 1,4-bis(5-cyano-1H-benzimidazole-2-yl)benzene, via ionothermal polymerization. The physical porosity and gas adsorption properties of these CTF-BIBs were characterized, and the resulting CTF-BIBs exhibit significantly high Brunauer–Emmett–Teller surface areas (1636–2088 m² g^–1) and notable CO₂ uptakes (86.4–97.6 cm³ g^–1 at 273 K and 1 bar; 48.5–56.8 cm³ g^–1 at 298 K and 1 bar). More importantly, these CTF-BIBs exhibit excellent selective separation abilities for CO₂/N₂, CO₂/CH₄, C₂H₆/CH₄, and C₃H₈/CH₄, particularly for equimolar mixtures C₃H₈/CH₄ (386.6 for CTF-BIB-1 under 1 bar and 298 K). Furthermore, transient breakthrough simulations were carried out for equimolar CO₂/C₃H₈/C₂H₆/CH₄ mixtures, and CTF-BIBs display good separation performance in industrial fixed bed adsorbers. These results clearly demonstrate that the synthesized CTF-BIBs may serve as potential materials for CO₂ capture and adsorptive separation for small hydrocarbons.