Agile Construction of Porous Organic Frameworks Pending Carboxylic Acids and Imidazolium-Based Ionic Liquids for the Efficient Fixation of CO2 to Cyclic Carbonates

Abstract

The design and facile preparation of ionic liquids (ILs)-functionalized polymer materials is a hot research topic due to their potential wide applications. Herein, taking the reaction advantage of a cyclic anhydride with an alcoholic compound to atom-economically generate a carboxyl ester pending a carboxylic acid moiety, porous organic framework (POF) materials pending carboxylic acids and imidazolium-based ILs (CILs-POFm) were facile synthesized via the acylation reaction of hydroxyl group-functionalized ILs with a styrene maleic anhydride copolymer. The CILs-POFm material properties were facilely adjusted by changing the molar ratio of the mono-hydroxyl-functionalized ILs to the dihydroxyl-functionalized ILs. CILs-POFm materials showed abundant mesoporous structures with a porous diameter of approximately 23.83–48.16 nm, a surface area of up to 274.4 m2 g–1, and a superior CO2 adsorption capacity of 1.71–2.14 mmol g–1 at 273 K and 1 atm. As a proof of concept application, the coupling reaction of epoxides with CO2 to produce cyclic carbonates was studied by using the CILs-POFm materials as catalysts under solvent-free and co-catalyst-free conditions. The findings indicated that the CILs-POF0.5 exhibited a satisfactory catalytic activity and reusability for a large scope of epoxides. Based on the experimental results and density functional theory (DFT) simulations, a synergetic catalytic mechanism was proposed based on the pended carboxylic acidic groups and IL groups. This study not only provided an atom-economic strategy to prepare POFs pending both carboxylic acids and ILs, but also showed new insights into the design of functionalized POF materials with great application potential in energy storage materials, separation, and green catalysis.