Immobilization poly(ionic liquid)s into hierarchical porous covalent organic frameworks as heterogeneous catalyst for cycloaddition of CO₂ with epoxides

The chemical fixation of CO₂ into high value-added chemicals is of significant potential and sustainability to address the energy and ecological issues. To achieve great catalytic performance on the transformation of CO₂, it is pivotal to strategically integrating several multifunctional and synergetic functionalities into the catalyst design and catalytic system construction. Herein, the poly(ionic liquid)-hierarchical porous covalent organic framework (PIL-HPCOF) hybrids were successfully synthesized via the formation of HPCOF through hard-template method, followed by in-situ polymerization of mono-vinyl decorated ionic liquids (ILs). The resultant PIL-HPCOF hybrids possess excellent versatility, with micropores providing high surface area to enhance CO₂ uptake capacity and macropores supplying sufficient pore volume to promote mass transport of substrates. As a proof of concept, the conversion of CO₂ with epoxides to produce cyclic carbonates was selected as a model reaction, which catalytic performance was obviously promoted by using PIL-HPCOF hybrids as the catalyst as compared to those of independent PIL and the PIL-COF hybrids with only micropores. Thus, it enables such a metal-free catalysis proceeds under much mild conditions (CO₂ (1 MPa), 90 °C) and with broad substrates tolerance. These results supply the basis to design efficient and stable catalysts for CO₂ conversion.