Nitrogen-rich covalent organic polymers and potassium iodide for efficient chemical fixation of CO2 into epoxides under mild conditions

Abstract

Resource utilization of carbon dioxide (CO₂) to add value to the chemicals used in the preparation of cyclic carbonates has gained significant interest in sustainable chemistry and environmental preservation. Herein, new nitrogen-rich urea covalent organic polymers (NUP-1, NUP-2, NUP-3) with multiple urea groups simultaneously acting as acidic nodes were designed and synthesized in a simple method. These synthesized NUPs were characterized using FT-IR spectroscopy, ¹³C CP MAS NMR, SEM, PXRD, TGA, XPS spectroscopy, CO₂ adsorption and nitrogen adsorption–desorption. The novel NUP-3 catalyst was particularly effective in the cycloaddition reactions having obtained a 93% yield of cyclic carbonate after 24 h at 90 °C with 0.1 MPa of pressure, using 1.0 mol% of KI and 70 mg of NUP-3. The results showed that the functionalized NUP-3 used as a catalyst for the cycloaddition reaction of CO₂ and epoxide with an alkali-metal salt, exhibited good activity under mild conditions. In addition, a mechanistic insight into the effects of urea groups on the activation of both epoxide and CO₂ was gained using DFT calculations.