A Study On Liquid Phase Exfoliation Of Two And Few Layer Graphene

Graphene is one of the hot spots in recent development and researches,and itsunique structure endows many interesting properties,such as excellent mechanical,electrical,optical and thermal properties.Currently,graphene has shown great application prospect in functional composite materials,energy storage and conversion,and environmental monitoring and governance,which bring broad market demand for graphene.However,there are three main problems in the liquid phase preparation of graphene:?i?the selectivity of graphene is poor,and there are few reports on single-layer,double-layer or three-layer graphene;?ii?the yield of graphene is relatively low,and it is difficult to achieve mass production;?iii?the preparation period of graphene is long,the reaction temperature is high,and the process is energy-consuming.In response to some of the existing problems,high yield of graphene was prepared at room temperature by liquid phase exfoliation in the present work.The main contents are as follows:1.The optimization of the preparation conditions for the stage-2 graphiteintercalation compounds was systematically studied at room temperature.The high-quality bi-layer graphene with high selectivity and high yield was prepared by using chemical intercalation-expansivity-liquid phase exfoliation.The mechanism of graphene preparation was studied by means of Charge density difference?CDD?,Electron localization functions?ELFs?and control experiments.It was shown that the electrostatic interactions between the graphene sheets and CrO₂Cl₂ were the main driving force for the formation of the stage-2graphite intercalation compounds.2.A new type of aqueous tetramethyl urea solution was developed for the liquidphase exfoliation of graphite,and graphene with few-layer structure was obtained.The effect of volume fractions of water on the effect of graphite stripping was systematically studied.It was shown that when the volume fraction of water was 0.3,the concentration of graphene came to the largest.The mechanism of the graphite exfoliation in aqueous tetramethyl urea solution is also investigated,and the formation of?TMU·3H₂O?_n aggregates was suggested to play a decisive role in the exfoliation of graphene.3.A new system,SOCl₂/H₂SO₄/?NH₄?S₂O₈,was developed to prepare the expandedgraphite by chemical oxidation method,and then graphene was prepared by liquid phase exfoliation,which the yield of grpahene is 72%.The characterization of XRD,Raman,XPS,HR-TEM and AFM indicate that the graphene has a few-layer structure.Compared with other gas expansion methods,this process of preparing expanded graphite is stable,simple and less toxic.