Preparation And Performance Studies Of Functionalized Graphene Nanocomposites

Graphene, one of carbon nanomaterials with two-dimensional honeycomb crystal structure, is called as "the thinnest material in our universe". Due to its unique optical, electrical, mechanical and thermal properties, graphene has attracted widespread attention of researchers from chemistry and material fields. In this dissertation, we adopted several different ways to prepare the functionalized graphene nanocomposites using graphene oxide as the precursor. The morphology and structure of graphene were characterized by a variety of analytical techniques. The obtained graphene nanocomposites were used as the electrode modified materials to investigate their potential application in electrochemical sensors and electrochemical polymerization.Chapter1:The development history of carbon nanomaterials was briefly introduced. Preparation methods, functionalization of graphene and its application in sensors and dye removal aspect were summarized in detail.Chapter2:Neutral red covalently-functionalized graphene nanosheets (NR-FGN) were prepared via the acyl-chlorination and amination reaction using NR as "the source of amino functional group. The obtained NR-FGN nanocomposites were characterized by UV-vis, Fourier transform infrared (FT-IR), Raman spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM) and Electrochemical impedance (EIS). The results indicate that NR grafted onto the graphene not only improves the solubility and stability of graphene but also enhances the electron transfer rate to have the good electrocatalytic performance towards uric acid. In phosphate buffer solution (pH5.0), the good linear response between the peak current of uric acid and its concentration was obtained in the range of0.125～12.25μM (Ip=0.06689+0.02899C, R-0.9927). The detection limit is0.062μM. Moreover, the current response is rapidly and the time required to reach the95%steady-state response is only5s. Chapter3:A simple and an effective method for preparing well-decorated polyvinylpyrrolidone (PVP) functionalized graphene nanosheets with metal nanoparticles (Ag, Pd and Cu) was demonstrated by one-step solvothermal synthesis. The obtained graphene-PVP-M nanocomposites were characterized by UV-vis, Raman spectroscopy, XRD, TEM and Scanning electron microscopy (SEM), which all verified that metal nanoparticles have been successfully anchored on the graphene nanosheets. Methanol and glucose were selected as the model molecules to investigate the electrocatalytic capability of three graphene-PVP-M nanocomposites. The results showed that graphene-PVP nanosheets decorated with Pd possessed excellent electrocatalytic activity towards the oxidation of methanol and glucose than that of decorated with Ag or Cu, implying its potential application of graphene-PVP-Pd nanocomposites in direct methanol fuel cells and electrochemical sensors.Chapter4:A simple and rapidly wet-strategy for synthesis of Graphene/SnO2nanocomposites was developed by employing citric acid as a protective agent, stannous chloride together with citric acid as reducing agent. UV-vis, FT-IR, Raman spectroscopy, TEM, SEM, XRD and X-ray photo-electron spectroscopy (XPS) were used to characterize the obtained Graphene/SnO2nanocomposites. The results confirmed that SnO2nanoparticles were homogeneously anchored on the surface of graphene nanosheets using a facile spontaneous redox reaction. The obtained Graphene/SnO2nanocomposites showed higher adsorption performance towards methylene blue and crystal violet. The adsorption equilibrium could be reached about ten minutes. By comparison, it was found that the adsorption properties of Graphene/SnO2nanocomposites towards methylene blue and crystal violet were96%and90%, respectively, which were increased by10%and14%than graphene oxide. This suggested that SnO2nanoparticles anchored on the graphene caused the increase of surface area of nanomaterials, leading to the enhancement of adsorption performance for dye molecules. This research will provide necessary theoretical basis for the application of graphene nanocomposites in the treatment of dye wastewaterChapter5:Sulfonated calix[6]arene functionalized graphene nanocomposites (SCX6-GN) were synthesized and characterized by UV-vis, FTIR, Raman spectroscopy, TEM, SEM, XPS and atomic force microscopy (AFM). The possible interaction force between graphene and sulfonated calix[6]arene was discussed. It was found that SCX6-GN showed the better electrochemical performance for tryptophan. In PBS buffer solution (pH7.4), the good linear response between the peak current of tryptophan and its concentration was obtained in the range of2×10-6～1×10-4M and the detection limit was0.7μM.Chapter6:The electrochemical polymerization behaviors of VB6on GO, GO/Nafion, GR/Nafion modified electrode and bare carbon glass electrode were studied using cyclic voltammetry. The possible electrochemical polymerization mechanism of VB6was discussed. The cyclic voltammetry results displayed that the electrochemical polymerizations of VB6on GO and GO/Nafion modified electrode are very easy, however, it is not obvious at the GR/Nafion modified electrode, implying that the presence of oxygen-containing groups on the GO surface provide a suitable polymerization site for VB6. Furthermore, the pH values of the solution have apparent influence on the polymerization process. The main reason is that VB6exists different forms in different media, which will lead to different monomer polymerization process.Chapter7:The electrochemical polymerization behaviors of luminol on GO/Nafion, GR/Nafion modified electrode and bare carbon glass electrode were studied by cyclic voltammetry. The effect of the initial scan potential was investigated. The results showed that luminol was prone to polymerize at the GR/Nafion modified electrode when the initial scan potential was-0.2V. However, when the initial scan potential was-1.0V, the polymer oxidation peak current at GO/Nafion modified electrode gradually increased, moreover, this modified electrode helped to improve the electrochemical signal of potassium ferricyanide, suggesting that GO has been converted into graphene which will lead to the enhancement of conductivity while also promote the electrochemical polymerization of luminol.