Preparation, Properties And Applications Of Graphene And Graphene Composites

Graphene is a two-dimensional nanomaterial, consisted of only one atom thick layer of graphite. This material has great potential in various applications, due to its excellent features in a high electrical and thermal conductivity, high mechanical strength, high carrier mobility, high transparency and huge specific surface area. Graphene shows a great prospect in many ways, such as transparent conductive film, electronic devices, energy storage, catalysis, bio-medicine, etc.. In this dissertation, we focus on the synthesis, properties, applications of graphene, including low temperature reduction of graphene, direct exfoliation of graphite, and preparation of graphene composite material. The main innovative work and specific research results are summarized as follows:Highly reduced graphene oxide (RGO) and RGO film were prepared by Na-NH3solution. The solvated electrons in Na-NH3solution can effectively facilitate the de-oxygenation of GO and the restoration of π-conjugation to produce RGO samples with an oxygen content of5.6wt%at low temperature. Electrical characterization of single RGO flakes demonstrates a high hole-mobility of123cm2/Vs. To probe the fundamental mechanism for the reduction of GO with solvated electrons, we have carried out detailed Fourier transform infrared spectroscopy (FTIR) study to monitor the evolution of the functional groups in GO during the reduction process. Additionally, we show that the pre-formed GO thin film can be directly reduced to form RGO film with a combined low sheet resistance (～350Ω/square with～80%transmittance) in few minutes. We also have fabricated the graphene-carbon nanotube composite films using this method. We have prepared the RGO-based ultracapacitors with specific capacitance of263F/g and produced the Pt/RGO composites as high-efficient catalyst for methanol oxidation.High quality graphene was prepared by direct exfoliation of the graphite without oxidizing and damaging the graphene sheets through a grinding-assisted chemical bursting-process when the pre-intercalated oleum was ignited by sodium. The definitive evidence that the as-made graphene sheets are only a single atomic layer thickness was observed with atomic force microscopy (AFM) and high-resolution TEM (HRTEM). The high quality of the graphene sheets were supported by selected area electron diffraction (SAED), Raman, FTIR, and X-ray photoelectron spectroscopy (XPS), which also demonstrate our graphene samples with less defects or oxides. Using the exfoliated graphene, we are able to fabricate high performance graphene-based ultracapacitors (120F/g), transparent conductive film (～760Ω/square with～85%transmittance) and Pt/graphene nanocomposites as high-efficient catalyst for methanol oxidation. In addition, we slao use the vapor of the metallic sodium to directly exfoliate the oleum pre-intercalated graphite.By in situ chemical reduction of the graphite oxide (GO) mixed with poly(vinyl alcohol)(PVA), we successfully fabricated reduced graphene oxide (rGO)-PVA composite hydrogels with improved dispersion and load transfer in their composites. The rGO-PVA composite wires were made by thermal-drawing or by directly drawing from rGO-PVA dispersion and their mechanical properties were rapidly evaluated using a microfabricated tuning fork device. It was found that the Young’s modulus of the polymer composites increase by ca.200%with only0.68vol%addition of the rGO. The thermal properties of the composites were studied by differential scanning calorimetry (DSC), and it was observed that the addition of graphene to PVA highly improves the thermal stability of the composites. Raman spectroscopy revealed the existence of an interaction between the graphene and the polymer via the shift in the vibration bands of the graphene in the composites.