Graphene-based Metal Nanocomposites:Synthesis And Their Electrical Properties

Graphene, a monolayer of carbon atoms packed into a dense two-dimensional honeycomb crystal structure, was found in2004by two scientists A. K. Geim and K. S. Novoselov at University of Manchester in UK. The discovery of graphene filled the gap on the two-dimensional field of carbon-based materials. Due to the unique nanostructure and extraordinary properties, graphene has attracted tremendous attention in both the experiment and theoretical scientific communications in recent years, and considered to be a new promise material to replace silicon in the future. Graphene-based composite materials have been shown a great of potential applications in electronics, optics, magnetics, biomedicine, catalysis, sensors, energy storage etc. In this thesis, the chemical modified graphene-graphene oxide was used as precursor to prepare graphene-based metal nanocomposites by different methods. The obtained graphene-based composite materials show many outstanding physical properties. The content focused on:1. Chemical preparation of graphene oxide.Graphite oxide was first synthesized using Hummers’method, then was dispersed in aqueous by sonication to get an exfoliated graphene oxide dispersion and characterized by Fourier transform infrared spectra, Raman spectra, X-ray diffraction, and field emission scanning electron microscopy.2. Using different methods to fabricate graphene nanosheets (GNs).(1) Oxidation-reduction method. The single-dispersed graphene oxide was reduced by two different kinds of reducing agents, sodium borohydride and hydrazine hydrate, to prepare graphene nanosheets. The results of conductivity test showed that reduced graphene recovered original graphite structure and conductive properties.(2) Physical ultrasonic exfoliation. The original graphite was exfoliated into single or multilayer graphene by means of physical micro-machined ultrasound. The result confirmed that the lamellar graphite materials can be exfoliated layer to layer by small organic or benzene ring molecules.3. Fabicate graphene-based Ag nanofilm by simultaneous reduction method.Graphene-metal nanoparticle (Ag) composites were synthesized using graphene oxide sheets as precursor and metal nanoparticles as building blocks in the water system. In this system, the free metal positive ions were first adsorbed noto the functional groups of graphene oxide, and then reduced into matel nanoparticles under the action of reducing agent. The oxygen functional groups disappeared simultaneously. Ag nanoparticles, as the electrical transmission bridge between the graphene layers, are adsorbed on the edges of graphene to form a connected graphene film. The nanoparticles effectively prevent the aggregation of the graphene nano-sheets. The modified graphene shows good electrical conductivity and thermal stability properties.4. Graphene-based Ag2S metal semiconductor nanocomposites were synthesized through the in situ adsorption of silver nitrate and crystal growth of Ag on the edge of graphene oxide sheets. The results show that Ag2S semiconductor nanoparticles functionalized graphene has a high specific capacitance and is an ideal supercapacitor materials in the future.5. Hydrothermal method synthesis Ag/Ag2S/graphene nanocomposite materials, results indicate that three-phase composite material has a more complex interface structure and behavior. Because of the close relationship between microstructure and macroscopic properties of the composite, the interface is bound tois a hot topic in materials science research.