Catalysis Letters, Vol.150, No.7, 1909-1922, 2020
Amine Functionalized Graphene Oxide Stabilized Pickering Emulsion for Highly Efficient Knoevenagel Condensation in Aqueous Medium
A Pickering emulsion catalytic system was developed using amphiphilic amine-functionalized graphene oxide (GO-NH2) for a Knoevenagel condensation in aqueous medium instead of organic solvent. The properties of GO-NH2 and the Pickering emulsion stabilized by GO-NH2 were characterized by Fourier-transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA), X-ray diffraction (XRD) analysis, X-ray photoelectron spectroscopy (XPS), organic elemental analysis (OEA), contact angle (CA), Brunauer-Emmett-Teller surface area, and optical microscopy. The results indicated that the properties of the as-prepared Pickering emulsion system, such as droplet density, size, and distribution, were greatly affected by the amount of GO-NH2 and the oil-water ratio, which were closely related to the catalytic performance for Knoevenagel condensation reactions. Furthermore, this Pickering emulsion system for the Knoevenagel condensation in an aqueous medium exhibited a much higher catalytic activity than those of GO-NH2 in organic solvents under the same reaction conditions. The reaction rate constant (k) in the Pickering emulsion system was calculated to be 0.043 min(-1) at 50 degrees C. The enhanced activity of the Pickering emulsion was mainly attributed to large interfaces between GO-NH2 and reactants in the emulsion, and the clear confinement effect. Furthermore, GO-NH2 remained stable for preparing Pickering emulsion systems after recycling in six runs, exhibiting its good reusability. Graphic A novel Pickering emulsion catalytic system was developed using amphiphilic amine functionalized graphene oxide (GO-NH2) for Knoevenagel condensation in aqueous medium instead of organic solvents. It exhibited excellent catalytic performance in the reaction. [GRAPHICS] .