Functionalized poly(ionic liquid)s-covalent organic framework materials for catalyzing CO2 cycloaddition reaction

CO 2 capture and utilization has received worldwide attention in view of the goals of sustainable development and carbon neutrality. Ionic liquid-functionalized covalent-organic frameworks (IL-COFs) possess high adsorption performance and catalytic activity, which overcome the drawbacks of cycling difficulty for pure ILs as homogeneous catalysts and deficient catalytic active sites for COFs. In this work, BpCOF is first rapidly synthesized by solvothermal-scCO 2 -assisted activation method. Afterwards, poly(ionic liquid)s and metal sites are introduced into BpCOF to obtain Zn-R-PIL-BpCOF (R = COOH, CH 3 ) materials through two-step modification including free radical polymerization and metallization. Then the CO 2 adsorption performance, catalytic activity for CO 2 cycloaddition with epichlorohydrin and catalytic recyclability of the materials are investigated. The excellent diffusion behavior of supercritical CO 2 and extremely low surface tension contribute to the rapid synthesis of highly crystalline BpCOF. The crystal structure and micromorphology of the materials are preserved after the two-step modification while the specific surface area and pore volume are decreased. The isosteric heat of adsorption of CO 2 for the typical sample Zn-COOH-PIL-BpCOF is higher than that of BpCOF, indicating the enhanced interaction with CO 2 by the integrated poly(ionic liquid)s and metal sites. Then Zn-COOH-PIL-BpCOF serves as catalyst and the yield of cyclic chloropropylene carbonate reaches 99.3 % at 90 °C and 2.0 MPa for 16 h under solvent-free and co-catalyst-free conditions. The carboxyl hydrogen-bond donors (HBDs), Zn 2+ Lewis acidic sites and Br − nucleophilic group in Zn-COOH-PIL-BpCOF play the roles synergistically. Zn-COOH-PIL-BpCOF exhibits excellent catalytic sustainability and reusability with the product yield exceeding 95 % after six cycles.