Preparation Of Graphene By Liquid Phase Exfoliation With Assistance Of Supercritical Carbon Dioxide

Graphene has wide application prospect because of its unique mechanical,electrical and thermal properties.Recently,It has attracted many attentions from the research community and industry.The point of the research and application of graphene is how to prepare high quality graphene with massive production,no pollution and low cost.Liquid phase method has the advantage of simple technology,low pollution and high quality.In this paper,supercritical CO₂as a green solvent is used to assist liquid phase method to exfoliate natural powder.The dosage of solvent is reduced by this way.In addition,CO₂ molecules can be intercalated into graphite layers coupled with mechanical shear to improve production yield.The main research works are as follows:?1?The preparation process was optimized in Supercritical CO₂-organic solvent system.Effect of pressure,temperature,time and the kind of solvent were studied with fixed graphite powder,organic solvent,and amount of glass beads in the preparation of graphene.The experimental results showed that thinner graphene was exfoliated in higher pressure,higher temperature,longer shear time and solvent whose surface tension matched the surface tension of graphene.The highest concentration was 0.0576 mg/mL within experiments at its operating conditions as follows:200 mg graphite powder,20 mL NMP,3 g glass beads,40 ^oC,19 MPa,24 h,1000 r/min rotating speed and 30min ultrasound time.Most of graphene was few-layer whose thickness was 0.8-1.2 nm having edge defects.?2?Effect of the subsequent sonic time and centrifugal speed in the separation process were studied after pressure relief.All of these experiments were operated in supercritical CO₂-NMP system fixing other operation parameters.The result showed that yield grew with the increase in ultrasonic time,but graphene sheets were broken.What's more,the higher centrifugal speed was,the thinner layer and product gained.In addition,graphene became aggregation and larger lateral size.The optimal operating conditions were as follows:30 min ultrasonic time,4000 r/min centrifugal speed and 30min centrifugal time.Meanwhile,the type of paddle was investigated to make sure what was the most suitable for exfoliation.The yield and quality of graphene installed the propeller was superior to the turbine blade.?3?Research about the preparation of graphene in supercritical CO₂-ionic liquid system.Different exfoliation time was studied in three kind of ionic liquid including[Bmim]PF₆,[BzMim]BF₄.The result showed that three kinds of ionic liquids could exfoliate graphite into few-layer graphene.Large shear force was created which was benefit to exfoliate because of high viscosity.Meanwhile,the mixture system of[BzMim]BF₄ with benzene rings and NMP gained the thinnest sheet which has more than 60%few-layer graphene,consistent with literature reports.In comparison with pure ionic liquids system,supercritical CO₂-ionic liquid made graphene concentration decrease due to carbon dioxide.It proved that volume expansion of the ionic liquid was small after joining in CO₂ because of cavitation in ionic liquid.CO₂ in the hole couldn't insert into graphite layer and weakened the ultrasonic cavitation effect after relief pressure.The CO₂ did not assist ionic liquid to exfoliate.