One-pot synthesized multi-functional graphene oxide as a water-tolerant and efficient metal-free heterogeneous catalyst for cycloaddition reaction

A series of functional graphene oxide (F-GO) materials were prepared by silylanization of graphene oxide (GO) with chlorine-terminal silanes and subsequent nucleophilic substitution reaction with tertiary amine in a one-pot approach. The quaternary ammonium salt was generated and immobilized simultaneously in situ, and the primary amine is beneficial to improve the number of surface functionalities on GO. This is the first time that a multi-functional GO material was designed, prepared and used for the synthesis of cyclic carbonates through the cycloaddition of carbon dioxide (CO₂) to epoxides. The F-GO catalyst can be easily separated and reused for at least five times without significant loss of activity (TOF = 46.4 h⁻¹). The excellent performance is attributed to the synergetic effect of silanol group and halide anion for ring opening of epoxide as well as the role of amine for CO₂ adsorption and activation. A possible mechanism is proposed for the cycloaddition reaction over F-GO.