Hydroxyl-functionalized ionic liquid-modified covalent organic frameworks for efficient CO2 cycloaddition conversion

Abstract

Converting CO2 into high-value chemicals is an essential way to mitigate greenhouse impact and realize sustainable utilization of resources. In this work, the COF materials named X-QCOF (X = OH, OCH3) were synthesized by a three-component Povarov reaction, followed by chemical grafting of hydroxyl‑functionalized ionic liquid into the COFs neutral backbone via quaternization to obtain the hybrid materials IL-X-QCOF (X = OH, OCH3). The resultant IL-X-QCOF can efficiently catalyze the cycloaddition reaction of CO2 and epoxides in the absence of metals, additives and solvents. Among them, IL-OH-QCOF exhibits a yield of 97.2% of cyclochloroallyl carbonate with a high turnover frequency (TOF) value of 217.7. The inherent high specific surface area of the COF-based materials promotes mass transfer efficiency, and meanwhile the abundant hydroxyl groups and bromine anions occurring in the backbone create excellent catalytic effect. Attributed to the chemical grafting approach, the product yield keeps over 90% when IL-OH-QCOF is reused for 6 cycles.