| Graphene is a kind of carbon material with a two-dimensional honeycomb lattice structure stacked by single layer carbon atom sp2 hybridization,it has extraordinary electrical,thermal,mechanical and other properties.The distinctive electronic property of graphene has great potential applications in energy storage devices and electronic components.Up to now,several fabrication routes for the production of graphene have been established,such as mechanical exfoliation,chemical reduction method,epitaxial growth and chemical vapor deposition?CVD?.Among them,chemical oxidation-reduction method is suitable for large-scale preparation and has potential industrial prospects.The most common methods for the oxidation stage of graphite in the redox process are Hummers method and Tours method.the manganese oxide?Mn2O7?which is heated and explosive will be produced during oxidation process,and the risk factor is high in preparation process.The conductivity of graphene prepared by oxidation-reduction method reported in most literatures is not ideal(2007500 S m-1).In order to overcome the above problems,the main research work of this paper includes the following two aspects:Aiming at the explosive problems in Hummers method and Tours method,a relatively safe graphene oxide?GO?preparation method is proposed in this paper.A larger amount of water is added to the reaction system to avoid the formation of Mn2O7 and improve the safety of the preparation process.Firstly,the influence of different reaction systems on the oxidation degree of GO was discussed,the optimal reaction system was determined to be concentrated sulfuric acid?H2SO4?/H2O system with water content of 20%.Then explored the influence of different preparation processes on GO.It was found that by adding quartz sand,increasing the stirring rate and increasing the ultrasonic time,the shearing force and peeling force of the reaction system can be effectively increased,which is beneficial to further improve the water content of the reaction system.The water content of the concentrated H2SO4/H2O system can be increased to 30%.In addition,we found that in the presence of concentrated phosphoric acid?H3PO4?,the acidity of the system decreased,and the manganese phosphate?MnPO4·H2O?insolubles with manganese ion of+3 valence was formed,which affected the oxidation efficiency of potassium permanganate.Therefore,the used of concentrated H3PO4 was abandoned,and the oxidation efficiency of KMnO4 and the yield of GO were improved.In view of the low conductivity of graphene in the traditional chemical oxidation-reduction method,we believe that in the graphite oxidation stage,the edge of graphite sheet is oxidized preferentially and the oxidation degree of GO edge is higher than that of the middle region.Therefore,in the reduction stage,the edge portion of the GO sheet is preferentially reduced,while the middle region is reduced slowly,forming a hydrophilic structure in middle region and a hydrophobic structure at edge portion.The?-?conjugation between the hydrophobic portions tend to aggregate them,hindering the reduction of the intermediate region of GO,resulting in reduction degree of graphene is low and the conductivity is poor.Therefore,we designed a technical route to prepare graphene in non-aqueous medium:using GO as raw material,hydrazine hydrate as reducing agent,and preparing GO in non-aqueous mixed medium of non-ionic surfactant alkylphenol polyoxyethylene?7?ether?OP-7?and polar organic solvent 2-methoxyethanol?EGM?.The EGM provides a good dispersion of GO and OP-7,while the?-?interaction between the?-electrons in OP-7 aromatic ring structure and the?-electrons in graphene make the hydrophobic regions of graphene well dispersed and prevent aggregation.Finally,the graphene with complete reduction was prepared and its conductivity could reach 14000 S m-1.The effects of OP-7 and EGM with different ratios on the conductivity of graphene were discussed.It was found that the optimum volume ratio of OP-7/EGM was 3:7. |
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