Mild Preparation Of Reduced Graphene Oxide-Noble Metal Nanocomposites For Electroanalysis Applications

Graphene is a two-dimensional honeycomb crystal structure carbon nanomaterial with large surface area,high electron mobility and high conductivity. Noble metal nanoparticles possess good biocompatibility, conductivity, catalytic activity and optical properties. Because graphene-noble metal nanocomposites can integrate the excellent physical and chemical characteristics of graphene and noble metal nanoparticles, they have been widely used in the fields of energy, biosensors and electroanalysis. In this thesis, we briefly review the recent progress of graphene and graphene–noble metal nanocomposites, and study the facile preparation of several reduced graphene oxide-noble metal nanocomposites directly on the surface of the electrode at room temperature for analytical applications. The main contents are as follows.1. Reduced graphene oxide-Au nanoparticles composites were prepared facilely by co-reduction of graphene oxide sheets and HAuCl4 at room temperature. Glucose oxidase(GOx) and then chitosan were cast-coated on the electrode to yield a chitosan/GOx/rGO-AuNPs/Au enzyme electrode. The first-generation and second-generation biosensing properties of the enzyme electrode as well as the direct electron transfer of GOx were studied. In the first-generation biosensing mode, the enzyme electrode exhibited a linear amperometric response to glucose concentration from 10.0 μM to 4.15 mM with a sensitivity of 99.9 μA mM-1 cm-2 and a limit of detection(S/N = 3) of 0.2 μM, excellent reproducibility, storage stability, selectivity and good results of assay in real samples. Excellent analytical performance was also obtained in the second-generation biosensing mode. In the presence of 4 mM ferrocenecarboxylic acid(FcMA), the LDR was favorably extended to 18 mM with a sensitivity of 64.6 μA mM-1 cm-2(R2=0.991); in the presence of 4 mM benzoquinone(BQ), the LDR was favorably extended to 22 mM with a sensitivity of 80.3 μA mM-1 cm-2(R2=0.996). The enzyme electrode based on rGO-AuNPs nanocomposites can also realize the direct electrochemistry of GOx. A pair of well-defined redox peak was observed for GOx immobilized at chitosan/GOx/rGO-AuNPs/Au electrode in N2 saturated PBS(p H 7.0), and the electron transfer rate constant(ks) of GOx at this electrode is calculated to be 2.63 s-1.2. A rGO-PtNPs/Au electrode was mildly constructed directly on the surface of the Au electrode at room temperature through chemical reduction method. The electrocatalytic and electroanalysis properties of rGO-PtNPs/Au electrode for ethanol in alkaline media were investigated by cyclic voltammetry and chronoamperometry. Results show that the rGO-PtNPs/Au electrode exhibits a linear amperometric response to ethanol concentration from 20.0 μM to 18.1 mM with a sensitivity of 132 μA mM-1 cm-2(R2=0.994) and a limit of detection(S/N = 3) of 0.93 μM in 1 M NaOH, indicating that the rGO-PtNPs composites have excellent catalytic activity and electroanalysis properties for ethanol.3. With NaBH4 as a reductant, rGO-PdNPs composites were synthesized facilely by co-reduction of graphene oxide and H2PdCl4 mixture solution. The rGO-PdNPs composites were characterized by UV-Vis, FTIR, as well as the electrochemical methods. The results revealed that the Pd nanoparticles are dispersed uniformly on the reduced graphene oxide sheets. The electrocatalytic properties of rGO-PdNPs/Au electrode for the oxidation of formic acid in acidic media were investigated by cyclic voltammetry and chronoamperometry. Electrochemical experiments show that the rGO-PdNPs composites has excellent catalytic activity and good stability for formic acid oxidation, indicating that the rGO-Pd NPs composites material is a good carrier for direct formic acid fuel cell(DFAFC).