Mesoporous carbon nitride grafted with n-bromobutane: a high-performance heterogeneous catalyst for the solvent-free cycloaddition of CO2 to propylene carbonate
A new type of mesoporous-C4N4-based catalyst (n-butBr/mp-C3N4) was prepared by simple grafting of n-bromobutane. The N2 adsorption–desorption and X-ray diffraction characterizations indicate that, in comparison with the parent mp-C3N4, the textual and structural properties have been well retained by n-butBr/mp-C3N4. In the cycloaddition of CO2 with propylene epoxide, the n-butBr/mp-C3N4 exhibits high catalytic conversion as well as a high selectivity to propylene carbonate. The maximum TOF value obtained over n-butBr/mp-C3N4 is 10.7 h−1 at 6 h under 140 °C, which compares favorably to other reported C3N4-based catalysts. In addition to n-bromobutane, mp-C3N4 materials grafted with other alkyl halides also provide high catalytic activities. According to the Fourier transform infrared and X-ray photoelectron spectroscopy measurements, it is speculated that the catalytic active sites of n-butBr/mp-C3N4 are uncondensed amines and Br anions which originate from the reaction between n-bromobutane and the N-containing heterocycles of mp-C3N4.