Graphene With Controlled Microstructures And Their Applications

Graphene is an atom-thick two-dimensional graphitic crystal. The unique structure and excenlent properties of graphene make it has a variety of applications. In order to improve the performances of graphene materials, the structures of graphene sheets and the interfacial microstructures of graphene composites need to be modulated and optimized. This dissertation mainly studies the mechanisms and techniques of controlling the sizes, porous structures and composite interfaces of graphene sheets, and reveal the infulences of microstructures on the optical, electronical, mehcanical and catalystic peroperties of graphene composites.A one-step technique for size fractionation of graphene oxide(GO) sheets was developed by adjusting the p H value of GO aqueous solution. After 4 h sedimentation in the aqueous solution with p H=4, more than 90% large GO sheets(> 40 μm2) were selectively separated. The factinaation method is cheap, simple and environmantal, which is suitable for large-scale industrial applications. The sizes of graphene sheets have strong effects on the properties of graphene materilas: the LB films of larger reduced GO(r GO) sheets showed higher electrical conductivity and lower optical transparancy, and the filtrated GO papers have better mechanical properties and more ordered microstructure.Graphene nanomeshes(GNMs) have been prepared by refluxing r GO sheets in nitric acid solution. The pore sizes can be modulated by refluxing time, they are in the range of a few to several hundred nanometers. Compared with traditional graphene, porous graphene has more carboxyl functional groups, more compact conjugation structure and better dispersi bility. Assembled GNM films also have higher transmittances and smaller d-spacings. The method of producing GNMs is controllable and prepared in large scale.Cellular nacre-mimic films have been prepared by blending r GO sheets into chitosan films. The microstructures of composite interfaces can be effectively controlled by hydrogen bonding, thus improving the mechanical and electrical properties of composites. The cellular composite containing 6%(by weight) presented strongest interfacial interactions and its mechanical properties partially surpassed that of natural nacre. Furthermore, the interfacial microstructers connected conductive networks in chitosan matrix, and the cellular composite film showed a conductivity of 1.28 S m?1.Graphene/calcium carbonate composite crystals were prepared via a hydrothermal process. Graphene sheets acted as a molecular template to induce the mineralization of calcium carbonate crystals. The crystal polymorph can be selectively formed by modulating the interface of graphene/calcium carbonate composites. On the other hand, the hexagonal graphene/calcium carbonate composite crystals can be filled into membrane, and the Young’s modulus were far more than that of nacre.Pt nanoparticles has been in-situ prepared in three-dimensional graphene-gel/nickel foam for methanol fuel cell. The porous structure of three-dimensional assembled graphene materials improved the interfacial utilization of catalysts/reactors, and provided effecitive channel for ions/electrons transportation. Compared with traditional 2D catalysts, the 3D composite catalyst system had better electrochemical activity, stability and resistance to carbon monoxide poisoning.