Design and synthesis of a multifunctional g-C3N4@MOF for enhanced CO2 cycloaddition: Synergistic effects of Lewis acid-base sites and ionic liquid functionalization

Abstract

The cycloaddition reaction of CO₂ to synthesize cyclic carbonates is highly valuable for greenhouse gas resource utilization. In this study, a multifunctional g-C₃N₄@MOFs layered catalyst (BCN-MIL-IMNH₂), containing Lewis acid-base sites and hydrogen bond donors (HBD), was prepared using a mild in-situ growth and covalent bonding strategy. At optimal performance conditions (120 °C, 1.5 MPa, 90 mg catalyst, 4 h), the BCN-MIL-IMNH₂–2 catalyst exhibited excellent catalytic performance (Y_PC = 96.5 %, S_PC = 99.0 %). The remarkable catalytic efficiency resulted from the combined effect of Lewis acid (B/Cr), Lewis base (Br⁻), and hydrogen bond donors (-NH₂) active groups. The introduced Cr and B were effective in activating and opening (via nucleophilic attack by Br⁻) epoxides. Besides, the -NH₂ group, serving as a hydrogen bond donor basic functional group, adsorbed and activated CO₂ to form an intermediate carbamate. The enhanced stability was attributed to the covalent bonding strategy, which effectively immobilizes the amino functionalized ionic liquids within the MOFs of the composite material, thereby enhancing structural stability and preventing dissociation during the reaction process. After five cycles, the catalyst maintained excellent performance with a yield of approximately 93 %.