Study On The Preparation Of Functionalized Graphene Oxide And Its Application In Pickering Emulsion

Knoevenagel condensation reaction refers to the condensation reaction of carbonyl compounds and active methylene compounds to formα,β-unsaturated compounds which play an important role in the synthesis of fine chemicals.Most of the reactions are carried out under basic catalysts.However,during this process of catalysis,it still has some problems,such as the resistance of mass transfer.Pickering emulsion prepared by solid catalyst particles can reduce the mass transfer resistance in the process of reaction by increasing the contact area between the substrate and the catalyst.The system which uses the water as the solvent can greatly reduce the cost of reaction and the catalyst can be recycled.Nitrogen-doped GO was perparaed by urea under hydrothermal conditions.A series of NGO_{（x）-（Y）}-NH₂ catalysts are preparaed by APTMS grafted on nitrogen-doped GO.Pickering emulsion catalytic systems prepared by NGO_{（x）-（Y）}-NH₂ are used for the catalysis of Knoevenagel condensation in aqueous medium instead of organic solvent.The Properties of prepared NGO_{（x）-（Y）}-NH₂ and Pickering emulsion NGO_{（x）-（Y）}-NH₂are 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）,and Optical microscopy.The results indicated that the properties of the as-prepared Pickering emulsion system（droplet density size and distribution）were greatly affected by the amount of Urea and hydrothermal time,thus affacting the catalytic of Pickering emulsion.As the increase of the amount of nitrogen,conversion rate of benzaldehyde firstly increases and then gradually decreases.Among of all the catalysts,the Pickering emulsion prepared by NGO_0.8-3h-NH₂ exhibits best catalytic activity.This is due to two aspects.On the one hand,The introduction of nitrogen atoms can increase the basic sites in the catalyst.On the other hand,an appropriate amount of urea can increase the lipophilicity of the catalyst surface,so that NGO_0.8-3h-NH₂ can prepare a O/W Pickering emulsion catalytic system with the smallest droplet size,highest density,and narrowest distribution.Silanes with different carbon chain lengths（methylsilane,propylsilane,and hexylsilane）were respectively used to modify amine graphene oxide to prepare GO-NH₂-CX.The Pickering emulsion catalytic systems are prepared by GO-NH₂-CX,which are used to catalyze the Knoevenagel condensation reaction of benzaldehyde and malononitrile.The catalytic activity of this system is determined by the number of active sites and the length of the carbon chain of the grafted silane.Pickering emulsion prepared by GO-NH₂-C3 shows high catalytic activity after four runs,exhibiting its good reusability.