Preparations, Properties And Applications Of Chemically Reduced Graphene Oxide And Its Derivatives

Graphene is a two-dimensional carbon materials, which is composed of monolayer of carbon atoms tightly packed with hexagnol symmetry, and has excellent electrical, optical, mechanical and thermal properties, and holds great potential for applications in electronic device, chemical/biological sensors, energy storage devices, and composites. Up to now, there have been several fabrication routes to graphene, such as micromechanical exfoliation, chemical vapour deposition, epitaxial growth, the reduction of graphene oxide (GO) solution, and organic synthesis. In comparison, the reduction of GO solution has advantages over other approaches including easy processing, large-scale yield and low cost, and is expected to be an effective way for large-scale preparation of graphene.In this thesis, to overcome the current scientific and technical problems exist in reduction of GO, an innovative route using L-ascorbic acid (L-AA) (vitamin C) as a reducing agent, which have mild reductive ability and nontoxic property, to achieve effective reduction of graphene oxide, and prepare the chemically reduced graphene oxide (CRG) having higher degree of reduction. Because its surface remained a small number of residual oxygen groups, in order to distinguish strict graphene, in this thesis, we call it chemically reduced graphene oxide, and, additionally, the chemically reduced graphene oxide/poly(N-vinyl pyrrolidone) (CRG/PVP) nanocomposites and so on have been prepared successfully. Meanwhile, the compositions, structures and electrical properties, and applications in enzyme immobilization and electrochemical sensing were explored systematically. The main results are as follows: 1. We demonstrated that graphite could be intercalated and oxidized to form graphite oxide. The graphite oxide could be exfoliated by ultrasonication in water into individual graphene oxide (GO) sheets. The composition, structure and morphology of as-generated GO were characterized using atomic force microscopy (AFM), transmission electron microscopy (TEM), FT-IR, Raman spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Solid-State 13C Magic-Angle Spinning (MAS) NMR. The results show that the as-prepared single-layered GO, has abundant oxygen-containing surface functional groups, and shows a good monodispersity in water.2. Using L-ascorbic acid as reductant, having a mild reductive ability and nontoxic property, the individual CRG sheets in water was prepared by the redction of GO without using any stabilizer. The morphology and structure of CRG were characterized using AFM, TEM, HRTEM, UV-vis, FT-IR, Raman spectroscopy, XRD and XPS. The electrical conductivity of CRG paper was measured by Four-Point probes, and the electrical conductivity of the individual CRG sheet was measured using conductive atomic force micr oscopy (CAFM). The results show that the prepared CRG has good electrical conductivity, and can be dispersed in water to form a stable suspension.3. Using water-soluble poly (N-vinyl pyrrolidone) (PVP) and GO as raw materials and L-AA as reductant and protonated reagent, the individual nanocomposite sheets of CRG and PVP, namely CRG/PVP, have been fabricated through a simple one-pot procedure. The structure of as-prepared CRG/PVP sheets were characterized using UV-vis, Raman spectroscopy, XPS, Solid-State 13C NMR, differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Water adsorption capability of individual CRG/PVP sheets was monitored in situ using AFM. The electrical conductivity of the individual CRG/PVP sheets was measured at different relative humidity (RH) using a CAFM system. The results show that the PVP molecules were chemically grafted on CRG surfaces, and the electrical conductivity of CRG/PVP sheet is sensitive to RH variation. 4. We illustrated that horseradish peroxidase (HRP) immobilization on GO sheets could take place readily without using any cross linking reagents and additional surface modification. The atomically flat surface of GO enabled us to observe the immobilized enzyme in native state directly using AFM. The catalytic activity of the immobilized HRP was assayed using phenol as catalytic reaction substrates. The results show that GO sheets is an ideal substrate for enzyme immobilization, and immobilized catalytic performance is mainly determined by the interactions of the enzyme molecules with the functional groups of GO.5. The electrochemical catalytic properties of glass carbon (GC) electrodes modified with PCRG (partially chemcailly reduced graphene oxide)-bound HRP were investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The results show that PCRG, which were prepared by reduction of GO via L-AA, were able to immobilize enzyme firmly without using any cross linking reagents, and CRG24H (GO was reduced for 24 hours) was an ideal material for modification of GC electrode, and may promote the direct electron transfer between enemzy and electrode, and the sensor based on HRP/CRG24H/GC electrode exhibites high biological activity toward H2O2, phenol and p-chlorophenol.