Preparation Of Graphene By Supercritical Carbon Dioxide Assisted Mechanical Exfoliation And Its Application

The graphene can be applied into many fields due to its unique structure and properties.So it is particularly important to prepare high quality graphene in large-scale production.In this paper,high-quality and large graphene sheets were successfully prepared by supercritical carbon dioxide(SC CO2)assisted mechanical exfoliation.The effect of preparation conditions on the yield of graphene was systematically studied to determine the optimum preparation conditions.Then the graphene products were characterized and the mechanism of preparation was explored.Furthermore,the applications of the graphene products were studied.Firstly,the effects of preparation conditions,such as SC CO2 pressure,the weight of initial expanded graphite,ultrasonic power and time on graphene yield were studied.It was found that when the pressure of the high-pressure reactor was 12 MPa,the weight of initial expanded graphite was 0.5 g,the ultrasonic power and time were 180 W and 90 min respectively,the highest yield of graphene was obtained.Secondly,the morphology of the graphene products was characterized by SEM,TEM and AFM.The SEM results showed that the transverse dimension of the graphene products prepared from 80 mesh expanded graphite was larger than 20 μm.The TEM and AFM results showed that few layers of graphene and some single-layer graph ene were successfully prepared.It was found that the yield of graphene was 92%within 10 layers,16%within 3 layers,respectively.The structure of th e graphene products was characterized by XRD,Raman and FTIR.XRD and FTIR results indicated that the SC CO2 assisted mechanical exfoliation process was a physical process with no structural damage and introduction of functional groups.According to Raman results,the value of ID/IG was only 0.04,which indicated that there were very few defects of the product obtained in this process.The electrochemical cyclic voltammetry of the product was also tested.Wh en the scan rate is 5 mV/s,the specific capacitance reaches 7.87 mF/cm2.Then,the role of the venturi-like stripper in the preparation of graphene was studied.It was showed from XRD and Raman characterization that the quality of the graphene products was obviously improved by adding venturi-like tube stripper.Then the impact of pressure difference on the quality of graphene products was studied by changing the internal flow of the venturi-like stripper.When the pressure difference was increased,the product quality tended to decline.The layer statistical distribution of the graphene products obtained under the venting state indicated that the yield of graphene within 10 layers decreased to 70%,which further proved that the increase of pressure difference will reduce the stripping effect of the venturi-like stripper.The hydrodynamic calculations showed that under ideal conditions,the throat velocity of the venturi-like stripper could reach 392 m/s and the internal pressure reached-4.83×107 Pa.Finally,the applications of graphene products prepared by SC CO2 assisted mechanical exfoliation,including conductive film,flexible film and biosensors,were explored.When the mass ratio of polystyrene to graphene was 5:1,the conductivity of the prepared graphene-polystyrene composite film reached 4.63×104 S/m.When the mass fraction of graphene was 40%,the prepared graphene-polystyrene composite film has good mechanical property.The graphene-chitosan modified electrode could sensitize the hydrogen peroxide solution well,especially at the lower concentration of h ydrogen peroxide solution.