Facile synthesis of carboxyl- and hydroxyl‑functional carbon nitride catalyst for efficient CO2 cycloaddition

With the aim of green chemistry and sustainable development, the coupling of CO 2 with epoxides to cyclic carbonate is an attractive and promising CO 2 fixation without byproducts. Solvent- and metal-free heterogeneous catalysts offer an environmentally friendly and convenient separation alternative to traditional metal-based or homogeneous catalysts. Hence, hydrolyzed carbon nitride (HCN) was successfully synthesized via urea-derived carbon nitride (CN) hydrolyzed in NaOH solution and the freeze-drying (FD) method was adopted to obtain the HCN-FD catalyst. The composition and chemical properties of HCN-FD were thoroughly characterized by different analysis methods. The synergistic effects of hydrogen-bond donors of –COOH, –OH and –NH X in HCN-FD resulted in improved acidity sites characterized by NH 3 -TPD. Compared with CN, HCN-FD combined with tetrabutylammonium iodide cocatalyst displayed satisfactory catalytic performance in the CO 2 cycloaddition due to more exposed active sites (–COOH, –OH and –NH X ). Moreover, the recyclability and versatility of the HCN-FD catalyst were excellent in CO 2 cycloaddition reaction. Thus, the HCN-FD catalyst was a potential candidate for the practical utilization of CO 2 fixation due to its advantage of facile synthetic method, inexpensive raw material and environmental friendliness.