Highly C2/C1-Selective Covalent Organic Frameworks Substituted with Azo Groups

A series of covalent organic frameworks substituted with azo groups (AzoCOFs) have been synthesized via imine condensation. The obtained frameworks show crystallinity and high stability. More importantly, the AzoCOFs exhibit exceptionally high ideal adsorption solution theory (IAST) selectivity in adsorption of C2H2 (35–2891) over CH4 at 273 K and 1 bar, owing to the favorable interactions between azo groups and acetylene molecules. The dependence of the gas adsorption property on pore size and polarity of the frameworks was also studied. The triethylene glycol substituted Tg-AzoCOF shows the highest C2H2/CH4 selectivity (IAST selectivity of 2891), which represents the highest reported for all porous materials. The AzoCOFs also exhibit high IAST adsorption selectivity of C2H4/CH4 (11–20), C2H6/CH4 (15–22), and CO2/CH4 (12–37), which is comparable with most porous materials, thus showing their great potential in gas separation applications.