Synthesis And Characterization Of Graphene Sheets And The Raman Properties Of Nitrogen-Doped Graphene Sheets

Graphene, a single layer of sp2-bonged carbon atoms packed in a honeycomb lattice, since the first fabrication via a "Scotch tape" method in 2004, has triggered great research interests. The fascinating properties of graphene, such as high thermal conductivity (5000W/mK), fast charge carrier mobility (200,000 cm2V-1s-1), high surface area(2630m2/g) and anomalous quantum Hall effect, have been well described. The graphene prepared by chemical methods are not pure but chemically modified to different extents, We normally refer to them as the reduced graphene oxide (RGO). However, for simplicity we hereafter refer to them as the graphene in this paper. Graphene and reduced graphene oxide, RGO (also called chemically modified graphene, CMG) are promising nanomaterials in applications, such as energy-storage materials, catalyst supports and electronic devices. Doping graphene with various chemical species is an effective approach to tailor its band structure and physicochemical properties, and doped graphene has numerous fascinating properties and widespread potential applications, such as in superconduction and ferromagnetism. Two approaches are typically used for the chemical doping of graphene: (1) the adsorption of gas or metal onto the graphene surface and (2) substitutional doping.In this paper, hydrothermal method was used to synthesis graphene and Nitrogen-doped graphene (NG). The morphology and structure of them were characterized by X-ray diffraction(XRD), Field-emission scanning electron microscopy (FESEM), Transmission electron microscope (TEM), Energy dispersive spectrometer(EDS) and Raman spectrometer. Its main contents include the following sections:1. Synthesis and characterization of graphene sheets:graphene sheets were synthesized by a simple hydrothermal method at different temperatures, with graphite oxide (GO), prepared by the modified Hummers method, served as the raw material. Structural and morphological studies on graphene sheets indicate the degree of reduction is dependent on the temperature, which is also verified by Raman analysis. The variation in interlayer distance and the intensity ratio of the D to G Raman modes (ID/IG) indicates higher reaction temperature can accelerate the reduction of GO more thoroughly. The conductivity also varies with the degree of reduction, as verified by electrochemical analyzer. Moreover, the reaction process affects organic functional groups, and the mechanism during the reaction process is also discussed.2. The Raman properties of nitrogen-doped graphene sheets:Nitrogen-doped graphene (NG) with different nitrogen levels was synthesized by using a simple hydrothermal method. Graphite oxide (GO), prepared by the modified Hummers method, served as the raw material, and urea served as both the reducing reagent and dopant. The variation in structures and morphologies indicates the successful incorporation of nitrogen in graphene, and found urea can accelerate the reduction in GO. The optical properties of NG vary with the doping level, as verified by Raman analysis. Depth study the Raman spectra properties of NG, namely the changes in D peak, G peak,2D peak and S3 peak. The intensity ratio (ID/IG) of the D to G Raman modes also changes with increasing nitrogen doping level because of defects induced by doping. In addition, the relationship between the qualities of urea and the crystallite size of the as-produced NG was also studied in detail, and through this relationship, further study the effects of the amount of urea on the product defects.3. The last part of this paper also briefly introduces one other work of myselves: Hydrothermal synthesis of FeS2 nanomaterials and the study of their properties.