A tunable ionic covalent organic framework platform for efficient CO2 catalytic conversion

The cycloaddition reaction between epoxides and CO2 is an effective method to utilize CO2 resource. Covalent organic frameworks (COFs) provide a promising platform for the catalytic CO2 transformations on account of their remarkable chemical and physical properties. Herein, a family of novel vinylene-linked ionic COFs named TE-COFs (TTE-COF, TME-COF, TPE-COF, TBE-COF) has been facilely synthesized from N-ethyl-2,4,6-trimethylpyridinium bromide and a series of triphenyl aromatic aldehydes involving different numbers of nitrogen atoms in the central aromatic ring. The resulting catalyst TTE-COF with excellent adsorption capacity (45.6 cm3·g−1, 273 K) exhibited outstanding catalytic performance, remarkable recyclability and great substrate tolerance. Moreover, it was also observed that the introduction of nitrogen atom in the precursor led to a great improvement in the crystallinity and CO2 adsorption capacity of TE-COFs, thus resulting to a progressively improved catalytic performance. This work not only illustrated the influence of monomer nitrogen content on the crystallinity and CO2 adsorption capacity of TE-COFs but also provided a green heterogeneous candidate for catalyzing the cycloaddition between CO2 and epoxides, which shed a light on improving the catalytic performance of the CO2 cycloaddition reaction by designing the covalent organic frameworks structures.