Charged Covalent Triazine Frameworks for CO₂ Capture and Conversion

Abstract

The quest for the development of new porous materials addressing both CO₂ capture from various sources and its conversion into useful products is a very active research area and also critical in order to develop a more sustainable and environmentally-friendly society. Here, we present the first charged covalent triazine framework (cCTF) prepared by simply heating nitrile functionalized dicationic viologen derivatives under ionothermal reaction conditions using ZnCl₂ as both solvent and trimerization catalyst. It has been demonstrated that the surface area, pore volume/size of cCTFs can be simply controlled by varying the synthesis temperature and the ZnCl₂ content. Specifically, increasing the reaction temperature led to controlled increase in the mesopore content and facilitated the formation of hierarchical porosity, which is critical to ensure efficient mass transport within porous materials. The resulting cCTFs showed high specific surface areas up to 1247 m² g^-1, and high physicochemical stability. The incorporation of ionic functional moieties to porous organic polymers improved substantially their CO₂ affinity (up to 133 mg g^-1, at 1 bar and 273 K) and transformed them into hierarchically porous organocatalysts for CO₂ conversion. More importantly, the ionic nature of cCTFs, homogeneous charge distribution together with hierarchical porosity offered a perfect platform for the catalytic conversion of CO₂ into cyclic carbonates in the presence of epoxides through an atom economy reaction in high yields and exclusive product selectivity. These results clearly demonstrate the promising aspect of incorporation of charged units into the porous organic polymers for the development of highly efficient porous organocatalysts for CO₂ capture and fixation.