New Process In Preparation Of Graphene By Liquid-phase Exfoliation Method

Graphene,with the two-dimensional(2D)atomic crystal structure,has attracted widespread interests and investigations in the basic preparation processes and applications owing to its unique properties and potential application value in many fields,such as electricity,thermal,mechanical and chemical.This work reports the study on the new technologies of preparing graphene by liquid-phase exfoliation method.The research contents consist two parts:1.We investigate the effects of pretreatment of graphite and exfoliated conditions on the structure and properties of graphene during the exfoliating by rotating packed bed(RPB),and optimize the scalable process that can prepare high-quality graphene.In addition,we also make a comparison with the graphene prepared by general exfoliation method.2.We explore the routes of preparing graphene by RPB and rotor-stator mixer(RSM)in graphite derivative/water system respectively,and we make a comparison between them as well.The details and the conclusions are as follows:(1)The exfoliation time,initial concentration of the edge-oxidized graphite(EOG)and the dosage of surfactant are main factors for the as-prepared edge-oxidized graphene(R-EOGN)in the exfoliation process by RPB.The concentration of R-EOGN can reach 1.0 mg mL-1 with the optimum conditions which the exfoliation time is 8 h,the concentration of EOG and surfactant are 20 mg·mL-1 and 17 mg·mL-1 respectively.The graphene(R-GN)is obtained after reduction of R-EOGN,which flake thickness mostly distributes in 3-4 layers with fewer defects.Significantly,the R-GN displays an excellent specific capacitance of 104 F·g-1 and small equivalent series resistance(ESR)of 5 Ω,in addition,the capacitance retention of R-GN hold 87%.Compared with the graphene(S-GN)exfoliated EOG by ultrasonic method,the lateral size of R-GN is about 2.5 times than S-GN under the same exfoliation condition,the flake thickness is only half of it and structural defects is significantly reduced.Compared with the graphene(R-rGO)exfoliated graphite oxide by RPB,the ESR of R-G is only 1/14 of R-rGO and capacitance retention rate of R-G increases by 11%.So RPB shows obvious advantages in graphene preparation.(2)The graphene named R-GNs and H-GNs are successfully exfoliated from graphite in graphite derivative/water system by both RPB and RSM respectively.After post-treatment,the defects of R-GNs and H-GNs are significantly reduced.Compared with them,the concentration of H-GNs is about 5.7 times higher than that of R-GNs,and the lateral size is 3 times than R-GNs.Besides,both of them exhibit higher specific capacitance above 110 F·g-1 and good retention capability above 94%.It can be concluded that the graphite derivatives can stabilize the dispersion of graphene,and the combination with RPB and RSM provides a green and high efficiency technology for the preparation of graphene.