A new and efficient method of graphene oxide immobilized with ionic liquids: Promoted catalytic activity for CO2 cycloaddition

In this work, both hydroxyl and epoxy groups on graphene oxide (GO) were simultaneously employed to immobilize ionic liquids (ILs) via a one-step Bronsted acid catalysis. The resulting materials, consisting of ILs immobilized on GO, were characterized by atomic force microscopy, Fourier transform infrared spectroscopy, thermogravimetry and X-ray photoelectron spectroscopy. The results indicate that the ILs were immobilized on the GO through both the ring opening of epoxy groups and the silylanization of hydroxyl groups in a single step. The amount of IL per unit mass of GO was greatly enhanced by Bronsted acid catalysis compared to the amount deposited without acid catalysis. These materials were applied to the cycloaddition of CO2 with propylene oxide to form propylene carbonate, and exhibited enhanced catalytic activity. The catalyst prepared using a H+ concentration of 80 mmol/L during the Bronsted acid catalysis was approximately 26% more active during the reaction relative to a control prepared without acid catalysis.