Research On Controllable Synthesis Of Graphene And Functional Structure And Its Foundational Application

Graphene, a two-dimensional nano-material comprises a single layer carbon atomsarranged in six-membered rings with the thickness of0.34nm. It is considered as anessence of cell of other carbon materials. It exhibits many excellent physical andchemical properties which can be used both in fundamental researches andindustrial applications. Since the the properties are strongly depended on thestructure, the first and the most important thing is preparation of graphene withspecial structure if we want to make the unique properties of graphene become areality. In this thesis, we have focused on the main technology of controllablesynthesis of graphene, chemcial derived graphite oxide (GO) method and chemcialvapor deposition (CVD). Further, we develop a new approach to synthesis of dopedgraphene. Thereby, as-synthesized graphene and its functional structures wereapplied for electrode materials, gas sensor and construction structures.Firstly, we have synthesized the GO by modified Hummers’ method. The GOsheets with single-layer and more than100μm in lateral size were achieved byoptimization of the reaction parameters and precursors. Also, the different sizes ofGO sheets were separated via gradient centrifugation technology, which suppliedthe proper materials for its applications.The effect of the parametres such as properties of catalyst, geometry of chamber,growth temperature, concentrate of carbon source and growth time on the graphenevia CVD, was investigated in detail. Large-scale graphene films with uniformthickness and tens of micrometers of single crystalline domains were synthesized.The graphene films exhibit high transparency (93.3%~96.5%at550nm) and lowsheet resistence (540.5~652.6Ω/sq), which achieved a tradeoffs betweentransparency and conductivity.The mechanism of grwoth graphene on Cu foil using methane as precursor by atmosphere pressure chemcial vapor deposition was investigated. The resultsshowed that the lateral size and layer number of graphene were increasing as growthtime. Meanwhile, we found for the first time that the C-Cu alloy particles suppliedthe carbon sources for the growth of graphene. The hypothesized mechanism,epitaxial graphene layer on the sub-layer under the high concentrate precursor, isproposed based on our experimental results.We have successfully developed a general approach for low temperature growthof large area doped graphene film. The approach involves a free radical reaction.High quality single layer N-doped graphene film with a high N content of7.3at%was successfully synthesized at230oC. S-doped graphene film with S content of1.54at%was also obtained at300oC using this low temperature growth technique.These doped graphenes exhibit controlled electrical properties and outstandingoxygen reduction reaction activity. Our approach also provides an efficient andscalable avenue to synthesize high level doped graphenes with characteristics of lowenergy consumption and low cost, which are key features needed forcommercializationBased on the as-synthesized GO, we have developed a method for fabrication ofpatterned GO thin films array using soft-lithography technique. The properties ofpatterned GO films can be regulated by annealing in different atmosphere. And theintegrated field effect transistors based on annealed GO films can be fabricatedsimply by evaporation of electrodes with shield mask. Then, the devices were usedto detect ammonia gas and achieved a quite good sensitivity of10ppm and stability.In addition, the titanium dioxide (TiO2) was hybrid with as-made graphene filmand formed a heterojunction device, and it was used as oxygen (O2) sensor. Thesensor could achieve a fast response and high sensitivity operated at atmospherepressure and room temperature, benefit by high carrier mobility in grapheme filmaccompany with photoelectric property of TiO2. In detail, the response and recovery time were estimated to be193s and135s, and the detected limitation was down to0.0134%. In addition, it has a quite good linear relationship between theresponsivity of the device and the concentration of O2in the range of0.0134%-100%.Graphene sheets with low defect were exfoliated by electrochemical method,and incorporated into poly(vinyl alcohol, PVA) to form a nacre-like composite film.And then, the PVA/graphene fibers were twist-spun from the composite films. Itwas found the content of PVA had an important effect on the mechanical propertiesof the fiber. When the content increased to~66%, a spring-like PVA/graphene fibercan be achieved. The spring-like fiber shows a super stretchable (160%~400%) andtoughness (298.23~639.44J/g). The elongation and toughness of the fiber haveincreased by20~40times and30~60times, respectively, comparing with those ofthe fiber derived from GO. At last, we have investigated the macro-and micro-structure of the PVA/graphene composite fiber to interpret the mechanism ofenhancement of the mechanical properties.The foundations and results in this thesis would provide some theoretical andtechnical support for synthesis of graphene and its applications.