Fabrication Of Graphene Dispersion And Self-organization Phenomenon In Graphene Dispersion

Graphene is a flat monolayer of carbon atoms tightly packed into a two-dimensional(2D) honeycomb lattice, and is a basic building block for carbon materials，which canbe wrapped up into0D fullerenes, rolled into1D nanotubes or stacked into3Dgraphite. It is a new two-dimensional (2D) nanomaterials with novel physicalproperties for its structure in monolayers. It is a hot topic on the methods of producinggraphene in large-scale and novel properties, since the prepararion of graphene frombulk graphite via micromechanical cleavage by K. S. Novoselov and A. K. Geim in2004. Graphene possess remarkable properties, such as high values of Young’smodulus (~1,100GPa), fracture strength (125GPa), pecific surface area (calculatedvalue,2,630m2g-1), thermal conductivity (~5,000W m-1K-1), mobility of chargecarriers (200,000cm2V-1s-1). Owing to graphene’s unusual physicochemicalproperties and tremendous potential for applications, it is an important and urgent onthe preparation of graphene with mass production, low cost, and high yield.In this dissertation, the stable graphene dispersion with high concentration wasprepared by the exfoliation of pretreated microcrystalline graphite. A spontaneous,macroscopic and dynamic self-organization phenomenon was discovered in thesurface of graphene dispersion, and preliminary research in grapheneself-organization phenomenon was performed. Moreover, macroscopic, free-standingAg-reduced graphene oxide Janus films prepared by evaporation-inducedself-assembly (EISA) is also fabricated.Firstly, the stable graphene dispersion with high concentration was fabricated byusing polyvinyl pyrrolidone (PVP) as dispersants and stabilizer by the directexfoliation of microcrystalline graphite in different organic solvents.Based on the fact that the graphene is dispersed effectively and exist steadily indifferent organic solvents, the microcrystalline graphite was pretreated by proper heattreatment in N-methyl-2-pyrrolidone (NMP). Graphene dispersion with higherconcentration was obtained by the exfoliation of pretreated graphite using polyvinylpyrrolidone (PVP) as dispersants and stabilizer. The results acquired by X-raydiffraction (XRD) indicated that the interlayer spacing of graphite increased after theheat treatment. The enlargement of the interlayer spacing of graphite is favourable tothe organic moleculors entering into the lattice of graphite, and is helpful to the exfoliation of graphite for the produce of graphene. It was found that the qualities ofgraphite were equivalent to that of the pristine graphite via detected by Ramanspectrum and X-ray diffraction (XRD). It suggested that no defects and impuritieswere introduced into graphite lattice in the process of the heat treatment. However,the results of graphene by Raman demonstrated that a few defects were introducedinto the two-dimensional (2D) honeycomb lattice of graphene, and implied that thehoneycomb lattice was destroyed in the process of ultrasonication. Fortunately, theintensity rate of D peak and G peak (ID/IG) is keep with in0.52. Therefore, it mayprovides a method for the mass production of grapheneA spontaneous, dynamic, and macroscopic self-organizing phenomenon withspatiotemporal patterns is observed on the surface of the graphene dispersion, whichwe named as graphene gush. The self-organizing patterns in graphene dispersion canoccur spontaneously, move continuously, bubble furiously and float out like a springfrom the interior of graphene dispersion. Neither extra power provided from outsideambient nor any external conditions is required to drive the operation of the graphenegush. The motion rate of graphene gush was greatly changed with environmentaltemperature, accelerated with the increasing of environmental temperature, andmaintained to move even at the environmental temperature of0-5oC. The graphenegush would continue to travel without end until the solvents in the systems wasevaporated thoroughly. Moreover, a spontaneous and dynamic liquid crystal flow(LCF) with helical structure was observed in mesoscopic scale. It is important thatboth the macroscopic self-organization and the liquid crystal flow are sensitive to anapplied magnetic. Meanwhile, self-organization in graphene dispersion ischaracterized by chiral properties, dynamic polarized light and light scattering. Aself-organizing mechanism of graphene was proposed according to the results ofpreliminary researches. Self-organizing phenomenon in graphene dispersion is a newphenomenon in graphene dispersion, which was not reported as yet. A sample andtheoretical models will be provided for the investigation of self-organization theory,which will be promoted to the development of the self-organization theory. It is alsowould be promoted to the development of a new theories in physics, mesoscopicdispersion system, thermodynamic and dynamic process by the study of the magneticeffect of the self-organization system of graphene dispersion.Finally, macroscopic, free-standing Ag-reduced graphene oxide Janus films wasprepared by evaporation-induced self-assembly (EISA). The resullts, characterized byscanning electron microscope (SEM) and energy dispersive spectrometer (EDS), implied that Ag-reduced graphene oxide Janus films composed of Ag layer andgraphene layer, which were banded together closely. The results analysed via cyclicvoltammetry (CV) suggested that the reaction between graphene oxide (GO) andTollens-reagent took place. A mechanism was proposed for the explanation of theEISA process. The potential application of the Janus films as substrates forsurface-enhanced Raman scattering (SERS) was also studied. It was found that theAg-reduced graphene oxide Janus films could be used for the detection of melamine,the Raman signals of the molecules are detected even though the concentration is aslow as10-8mol/L. The methods could be used for the other materials and to developednew design parameters of novel nanostructures for potential applications.