Graphene And High Quality Graphene:Controllable Synthesis, Characterization,Properties And Application

In October5,2010, the Royal Swedish Academy of Sciences announced that they will award2010Nobel Prize in physics to British scientist Andre Heim and Konstantin coming from the University of Manchester to commend their research in graphene materials. Graphene is a single layer of carbon packed in a hexagonal (honeycomb) lattice. The unique two-dimensional structure endows them excellent properties in physical, chemical, mechanical and so on. For example:, high specific surface area (calculated value,2,630m2g-1), thermal conductivity (~5,000Wm-1K-1), mobility of charge carriers (exceeding200,000cm2/Vs) at room temperature, high values of Young's modulus (~1,100GPa) and intrinstic breaking strength (125GPa), the tansparent greater than95%light transmittance in the100-3000nm wavelength range. Graphene is called "star material" due to these excellent properties, and expected to be widely used in the area of reinforced composite, nano electronic devices, optoelectronic devices, energy storage material, catalysis, etc.Since2004, Andre Heim and Konstantin Novoselov had obtained the single layered graphene by mechanical exfoliation for the first time, the preparation, performance, and application of graphene have been the research hotspot in the world. Based on the full understanding of graphene and carbon materials, and combining with some international frontier hotspots in the area of graphene research, we conducted systematic and in-depth researches on graphene preparation, characterization, properties, and application, In this research, we developed flame combustion method to prepare graphene and N doped graphene. We developed a new method to prepare high quality graphene in large scale by hot-pressing. We introduced an approach to simply and effectively determine the mechanical property and number of layers of graphene by using an instrumented nanoindentation. We explored the graphene application in photocatalysis and energy storage and conversion. For the first time we presented a concept "nanogenerator based on the strain-band engineering effect of graphene".This dissertation includes ten chapters.An introduction is given in chapter one, including the research background, origin, significance of the subject, and the discovery, structure, properties and applicaion of graphene. Subsequently, the research status and progress about controllable preparation, characterization and application of graphene were also summarized.The experimental materials and methods, characterization methods and test equipment in this research are described in the second chapter. It includes several parts:The methods of preparing graphene and N-doped graphene by flame, by chemical exfoliation, by CVD, and high quality graphene by hot-pressing; The measurement of mechanical property and number of layers of graphene by nanoindentation; The preparation and characterization of graphene/TiO2photocatalyst; The preparation and characterization of graphene based nanogenerator. In addition, the characterization and measurement of graphene and related samples by SEM, EDS, TEM, HRTEM, XRD, XPS, Raman, FTIR, UV-Vis were also introduced.In the third chapter, a simple process is described for directly synthesizing pure graphene and N-doped graphene sheets from ethanol flame and amine plus ethanol flames respectively. The microstructures and nitrogen contents of the graphene were characterized in detail. The results reveal that:Compared with other methods, the graphene sheets from flame have more surface defects due to the environmental conditions and introduction of nitrogen atoms; N-doped graphene sheets have a dominant "pyridine-type" structure. It also provides a new mechanism for preparation of graphene by flame.In the forth chapter, we report a simple and effective route to convert graphene oxide sheets to good quality graphene sheets using hot pressing. The micro structure, formation mechanism, and electrical property of high quality graphene have been studied. The graphene sheets produced had a much higher electron mobility (1000cm2V-1S-1) than other chemically modified graphenes. In addition, the application of high quality graphene in photocatalysis, supercapacitor, reinforce composites have been explored.In the fifth chapter, we introduce an approach to simply and effectively determine the mechanical property and number of layers of graphene simultaneously by using an instrumented nanoindenter. Nanoindentation technique is high precise and sensitive, which can be used to measure the mechanical property of nano materials. The mechanical property of graphene can be obtained by nanoindentation without separated from substrate. In addition, it is found that there exist a linear relationship between the number of layers and the hardness of graphene, which provide a novel and also effective method for judging the number of graphene layers.Graphene based photocatalyst has triggered extensive research interest recently. In the sixth chapter, the preparation of graphene/TiO2composite powers by heat treatment and composite films by spin-coating were introduced. The morphology and micro structure of composite were charactered by SEM, HRTEM, XRD and XPS. The graphene/TiO2composite powers were prepared from heat treatment of graphene oxide. C atoms have substituted some of the Ti atoms in the TiO2lattice during the composite preparation. Graphene/TiO2layer-by-layer composite was able to overcome the disadvantages of nano powers that difficult to separate and recycle, and reduce the band gap of TiO2. The graphene/TiO2layer by layer composite exhibited excellent photocatalytic properties in visible light.In the seventh chapter, on the basis of the relationship between the strain-band strucute-electrical transport-electrochemical performance, we presented a concept "nanogenerator based on the strain-band engineering effect of graphene" for the first time, we developed two kinds of new nanogenerator based on graphene strain-band engineering.1) The first one is based on the tensile-strain effect. This nanogenerator realized the charge output and transfer by tensile strain. It was found that an electric potential difference between stretched and static monolayer graphene sheets reached8mV when the strain was5%.2) The second one is based on the friction-strain effect. This nanogenerator realized the charge output and transfer by friction between the graphene and electrolyte.3) The amplification and adjustable of the current and voltage could be realized by changing the electrolyte concentration, stirring speed, and the circuit assembly.The following eighth chapter and the ninth chapter are the introductions about author's research work on photocatalysis involved in National Basic Research Program of China (973Program). As segment content during graduate study, they are included in this dissertation.In the eight chapter, we report a novel "bud-on-branch" BiaWO6-TiO2nanofibers fabricated via a facile and large-scale electrospinning technique from a biphased precursor. Forming by surface-decorating continuous TiO2nanofibers with~13nm well-crystallized Bi2WO6nanoparticles, the as-synthesized Bi2WO6-TiO2nanofibers achieved an evidently increased specific surface area and excellent photocatalytic activity.In the nine chapter, we introduces a facile and novel route to synthesize the N+Ni codoped anatase TiO2nanocrystals with exposed {001} facets through two-step hydrothermal reaction.The results revealed that the elements N and Ni have been successfully codoped into the anatase TiO2with exposed {001} facets. The size of the TiO2reached to a narrow range of5-15nm; and the codoped TiO exhibited an additional visible light absorption band from400nm to500nm, which greatly improved the photocatalytic activity.Chapter ten is a full summary.Finally, a brief introduction of published papers, participated projects, honors and awards, curriculum vitae and acknowledgements in the graduate were given.