Preparation Of Graphene In Supercritical Fluid System

Graphene is a quasi two-dimensional single atomic layer structure composed ofsp2 carbon atoms with a honeycomb lattice.Because of the special structure of grapheme,it has special electrical,optical,mechanical,thermal properties,in electronics,aerospace,military,biological,new energy,semiconductor and other fields shows a broad application prospects.The special properties of graphene makes it also show remarkable ability in environmental pollution control.In this paper,the main preparation methods of graphene are briefly introduced.including mechanical stripping,chemical vapor deposition,chemical oxidation reduction,SiC epitaxial growth and so on,but these methods cannot meet the needs of large-scale preparation,low cost and high quality at the same time.In this paper,graphene was prepared by the method of supercritical fluid intercalation-exfoliation.In this paper,we studied the effect of graphite raw materials on the product.In supercritical carbon dioxide system,the effects of reaction temperature,pressure,time.surfactant type and graphite quality on the experimental results were studied;under the optimal conditions.the graphite were exfoliated in repeated several times;The exfoliation of graphite by supercritical methanol,ethanol,isopropanol,acetone and water was studied;explored two supercritical fluid to exfoliation graphite at the same time:of product of all kinds of fluid preparation were analyzed by SEM.TEM,Raman.AFM,XRD characterization.The main work and achievements of this paper are as follows:1?The influence of graphite raw materialsThe natural flake graphite and expandable graphite used in this experiment have a relatively obvious layered structure,the size of natural flake graphite is mostly a few microns,the size of the expandable graphite is more uniform,concentrated in the ten to twenty microns.The difference in size is also reflected in the product graphene above,that is,the amount of graphene prepared with expandable graphite is relatively large.Comprehensive consideration.we use expandable graphite as raw material.2.The influence of experimental conditions in supercritical carbon dioxide systemUnder different conditions,the density,viscosity and diffusion coefficient of supercritical CO2 vary greatly.In the supercritical carbon dioxide system,the influence of reaction temperature,pressure,time,surfactant type and graphite quality on the exfoliation results was studied by the control variable method.The optimum reaction conditions were temperature 80?,pressure 15MPa,reaction time 2h,the surfactant type is PVP,the raw material quality is 50mg.The layers of graphene prepared under the optimum reaction conditions is about 8 layers,and the number of layers reduced to 3 to 4 layers after 3 times exfoliation.3.Using other supercritical fluids for exfoliationIn this paper,graphite is exfoliated of solvent such as supercritical methanol,ethanol,isopropanol,acetone and water.The best exfoliation effect is ethanol.the minimum layer is 3?4 layer.Two kinds of supercritical fluids(ethanol + helium)were investigated.TEM and AFM characterization showed that the graphene prepared by supercritical ethanol and helium minimum layer is 2 to 3 layers.4.Characterization analysisThe samples were characterized by SEM.TEM,Raman,AFM and XRD.The images of SEM show that the distribution and size of the samples after the exfoliation are even more uniform,with many folds and overlapping,and the color becomes lighter.The results of AFM show that the thickness of the graphene exfoliation by carbon dioxide is about 8 layers,and the number of layers after the three exfoliation is reduced to 3 to 4 layers,the layer of graphene exfoliation by supercritical ethanol is about 3 to 4 layers too.The graphene prepared by supercritical ethanol and helium minimum layer is 2 to 3 layers.Under the HR-TEM image,we can see the dark line of the folded edge of the lamina,the number of dark lines represents the number of graphene.The number of graphene layers prepared by carbon dioxide is at least 3 to 5 layers,and the minimum number of layers of graphene prepared by supercritical ethanol is 2 to 4 layers,Raman spectroscopy results show that the ratio of G peak to 2D peak is reduced,which indicates that the number of layers decreases.The ratio of graphene prepared by supercritical ethanol is more obvious,indicating that the effect is better.The XRD pattern of the sample after exfoliation is not as complete as graphite,indicating that the long-range order of the graphite after exfoliation is destroyed and the exfoliation has a certain effect.