Hierarchically mesoporous imidazole-functionalized covalent triazine framework: An efficient metal- and halogen-free heterogeneous catalyst towards the cycloaddition of CO2 with epoxides

The conversion of CO2 into value-added cyclic carbonates over metal- and halogen-free heterogeneous catalyst has attracted much attention but remains a huge challenge. Herein, a covalent triazine framework (CTF) with hierarchical microstructure was synthesized from cyanuric chloride and 1,4-phenylenediamine by a simple solvothermal approach compared to traditional ionothermal trimerization methods. While functionalizing the CTF framework with imidazole (IM) groups, the resultant CTF-IM exhibits excellent catalytic activity for the synthesis of cyclic carbonate from CO2 and epoxides under metal-, halogen- and solvent-free conditions. Under optimal reaction conditions, the representative epoxide, epichlorohydrin, afforded the corresponding cyclic carbonate in almost quantitative yield (94.6%), which is 5.4 times than that obtained over the parent CTF. The Lewis acidic C2-H and Lewis basic nitrogen atom play vital roles in the activation of epoxide and CO2, respectively, which help the cycloaddition reaction to proceed faster. In addition, CTF-IM has good chemical stability and recyclability, as well as could be applicable to a wide range of substituted epoxides.