Facile Synthesis And Application Of Graphene And Its Metal Composite

Graphene has attracted enormous attention due to its unique structure andextraordinary properties, such as high carrier mobility, high surface area, good opticaltransparency, high Young’s modulus and excellent thermal conductivity. Sincesuccessful isolation of graphene by the mechanical exfoliation of graphite, manymethods have been developed to synthesize graphene, including chemical vapordeposition (CVD), chemical reduction graphene oxides, organic synthesis from micromolecule, etc. To date, however, rational synthesis of graphene with high quality andlarge quantity at low cost is still a key issue in the pratical applications of graphene. Inthis thesis, the endeavor has been mainly focused on the development of two syntheticstrategies of graphene, chemical redox method and CVD approach.We have firstly studied the oxidation level of the graphene oxide in the modifiedHummer method. The amount of oxygenated functional groups in the GO can be variedby changing the amount of oxidant. FTIR and Raman results show the sp3C domainsincrease with the increase in oxidation level. The oxygenated functional groups in GOsignificantly alter the potential of GO; the higher oxidation level of GO, the lowerpotential. In addition, electrostatic repulsion between the GO nanosheets is an importantfactor on the GO dispersibility in aqueous solution.So far, a number of chemical reductants have been developed to chemicalreduction of GO. For example, hydrazine or its derivatives as strong reducing agentwere used for the reduction of GO. However, these reductants are highly toxic andexplosive, which limited their usage. In third chapter, a simple chemical approach hasbeen developed for the synthesis of graphene through a mild reduction of grapheneoxide (GO) using metal nanoparticles as a catalyst for the hydrolysis reaction of NaBH4at room temperature. The morphology and structure of the graphene were characterizedwith atomic force microscopy and transmission electron microscopy. The reductionprocess and quality of graphene were followed and examined by UV-Vis absorption spectroscopy, X-ray photoelectron spectroscopy, Raman spectroscopy and X-raydiffraction. By this method, graphene can be prepared in large quantity without usingtoxic reducing agents such as hydrazine or its derivatives, making it environmentallybenign. The reaction is conducted under mild conditions (room temperature), resultingin the formation of fewer defects. The method can be easily scaled up and the metalcatalyst can be recycled.Graphene@metal nanoparticles (NPs) composites have attracted great interests invarious applications such as catalyst, electrode, sensor, etc. due to their uniquestructures and extraordinary properties. A facile synthesis of graphene/metal-NPscomposite with good control of size and morphology of metal NPs is critical to thepractical applications. A simple method to synthesize graphene/metal-NPs undercontrollable manner via a self-catalysis reduction at room temperature has beendeveloped in fourth chaprter. At first, metal NPs with desirable size and morphologywere decorated on GO, and then used the metal NPs as catalyst to accelerate thehydrolysis reaction of NaBH4to reduce the graphene oxide. Compared to the existingmethods, the method reported here features the several advantages whichgraphene/metal are prepared without using toxic and explosive reductant such ashydrazine or its derivatives, making it environmentally benign and the reaction can beprocessed at room temperature with high efficiency and in a large range of pH value.The approach has been demonstrated to successfully synthesize graphene compositewith various metal NPs at large quantity, which opens up a novel and simple way toprepare large-scale graphene/metal or graphene/metal oxide composite under a mildcondition for the practical applications. For example, graphene/AuNPs compositesynthesized by the method shows excellent performance in the catalysis and solar cellapplications.Direct formation of high-quality and wafer scale graphene on dielectric substrate isemergent for electronic application of graphene. In fivth chapter, we report atransfer-free method to directly synthesize graphene on dielectric substrate usingpolycyclic aromatic hydrocarbons (PAHs)(e.g. ADN, HAT-CN, NPB) or GO as thesolid carbon source and Cu layer as the catalyst covering on the solid carbon source.The effects of different carbon source, growth temperature, H2content, thickness ofcatalyst and carbon source, have been investigated. According to the results, HAT-CNcan be used to synthesize graphene at relatively low temperature. The monolayer graphene has been obtained with5nm carbon source. With increase the thickness ofcarbon source, the quality of graphene will decrease. By this method, N-doping andpatented growth of graphene can be easily achieved.