Triphenylamine-based covalent imine framework for CO2 capture and catalytic conversion into cyclic carbonates

A series of covalent imine framework (CIF) comprised of triphenylamine (TPA) and triazine (T) moieties were synthesized under reflux and solvothermal conditions using different solvents: TPA-TCIF(DMF), TPA-TCIF(DM), and TPA-TCIF(BD) (DMF = dimethylformamide, DM = 1,4-dioxane:mesitylene mixture, and BD = 1-butanol:o-dichlorobenzene mixture). While TPA-TCIF(DM) and TPA-TCIF(DMF) were partially crystalline and amorphous, respectively, with a surface area of 935 and 388 m2 g−1, highly crystalline TPA-TCIF(BD) was formed with a surface area of 2907 m2 g−1 and high nitrogen content. TPA-TCIF(BD) showed a reasonable CO2 capture capacity of 77.3/50.2 mg g−1 at 1 bar and CO2 selectivity over N2 of 51.6/61.8 at 273/298 K, respectively. Subsequently, TPA-TCIF(BD) was used as catalyst support to anchor M2+ (Zn2+ and Co2+) ions for CO2 cycloaddition to various epoxides. The M2+-complexed catalysts with n-Bu4NBr showed an excellent catalytic activity with high selectivity to cyclic carbonates under mild reaction conditions. Zn/TPA-TCIF(BD) exhibited somewhat higher catalytic activity than Co/TPA-TCIF(BD), and the activity was maintained after five recycle runs.