Reconstructing the PHI Surface Microenvironment for In Situ Immobilization of Ionic Liquids to Enhance CO₂ Conversion

Graphitic carbon nitride (CN) has emerged as a promising candidate for CO₂ capture and conversion due to its structural tenability and abundant surface active sites. However, CN suffers from inherent drawbacks such as poor catalytic activity, leading to unsatisfactory utilization. In this study, a rational strategy combining organic superbases as hydrogen bond acceptors with hydrolyzed high crystallinity CN (poly-(heptazine imide), PHI) derivatives as hydrogen bond donors was developed to form ionic liquid-functionalized PHI catalysts. This design strategically integrates amino and hydrogen bond functionalities within a single polymeric framework, thereby cooperatively accelerating the coupling of epoxides with CO₂. Under the conditions of 0.1 MPa CO₂, 90 °C, and 6 h, [PHI-NH]-[DBUH] achieved chloropropene carbonate (CPC) in 99% yield with 99% selectivity. Based on the multifunctional structure and experimental results of the catalyst, a plausible pathway emphasizing intramolecular cooperative activation was subsequently elucidated. Furthermore, the heterogeneous nature of the catalyst enabled facile recovery and reuse via simple solid-liquid separation. This work establishes a sustainable catalytic platform that merges ionic liquid functionality with polymeric semiconductor matrices for green chemical transformations.