▎ 摘　　要

Based on the synergetic effects among hydrogen bond donors, halide anions and suitable amines for the CO2 cycloaddition reaction, the multi-functionalized graphene oxide (containing silanol group, quaternary ammonium salt and tertiary amine) were synthesized by a "in-situ approach". Hexamethylenetetramine that is nontoxic, cheap and rich in tertiary amine was used as precursor for quaternary ammonium salt. Then, further quaternization was conducted by adding halohydrocarbon for the formation of multi-cationic quaternary ammonium salt functionalized graphene oxide (F-GO) heterogeneous catalysts. As characterized by X-ray photoelectron spectroscopy and elemental analysis, the loading of quaternary ammonium salt and tertiary amine was up to 2.23 and 2.49 mmol.g(-1) respectively. The "multi-cationic approach" is proved to be beneficial to improve the amount of ionic liquids and catalytic activity. The F-GO was used as metal-free heterogeneous catalyst for the synthesis of cyclic carbonates through the cycloaddition of CO, towards propylene epoxide under mild conditions without solvent and co-catalyst. The yield of propylene carbonate was up to 99.2% (100 degrees C, 2 MPa, 4 h). The synergetic effects was investigated by comparing the catalytic activity of F-GO functionalized with different groups. A plausible mechanism was proposed for the CO2 cycloaddition reaction over F-GO. In addition, F-GO is a water-tolerant and stable catalyst for the cycloaddition reaction, and there was no significant loss of catalytic activity after six runs.