The Application Of Functionalized Graphene Nanocomposite Materials In Electrochemical Sensors

Graphene is the monolayer graphite which the thickness is just only one carbon atom. It is made up of sp2-hybridized carbon atoms. The carbon atoms can connect to each other by covalent bonds. Graphene has attracted much attention since it was found, because of some unique properties, such as large specific surface area, high heat conductivity, good conductivity, excellent mechanical strength. The nanocomposites based on graphene have been widely used in optics, electricity, biomedicine, catalysis, sensors, energy storage and other fields. However, the chemical stability of graphene is very high, which makes graphene be in an inert state. At the same time, the strong van der Waals force and electrostatic force between graphene sheets make graphene powders agglomerate very easily. However, with the appropriate surface treatment or surface functionalization, not only the agglomeration of single layer graphene can be prevented, but also some functionalized graphene nanocomposites can be fabricated. In this paper, we prepared the graphene nanocomposites through chemical modification and characterized their electrochemical performance, and moreover, we explored the potential applications of the functionalized graphene nanocomposites as novle electrode materials for electrochemical sensors.(1) Simultaneous determination of hydroquinone and catechol based on glassy carbon electrode modified with gold-graphene nanocompositesFirstly, we synthesized the nearly monodispersed gold-graphene nanocomposites by a single-step chemical reduction method in aqueous dimethylformamide solution. Sodium borohydride reduced both graphene oxide and chloroauric acid at the same time. It should be noted that nearly monodispersed Au nanoparticles were uniformly distributed over the2D graphene nanosheets without aggregation. Then, the morphologies and structures of the as-prepared nanocomposites were characterized by transmission electron microscope and X-ray powder diffractometer. The electrochemical behavior of the nanocomposites was characterized by AC impedance spectroscopy, cyclic voltammetry and other electrochemical methods. Moreover, the electrochemical sensor of simultaneous detennination of hydroquinone and catechol was constructed based on gold-graphene nanocomposites. A glassy carbon electrode was modified with the nanocomposites and the as-fabricated modified electrode displayed high electrocatalytic activity and extraordinary electronic transport properties. The CVs of the present modified electrode show two pairs of well defined, quasi-reversible redox peaks, with the significantly enhanced peak currents for the redox reactions of hydroquinone and catechol. Due to the large separation of oxidation peak potentials, the concentrations of hydroquinone and catechol can be easily determined simultaneously. The oxidation peak currents for both hydroquinone and catechol increase linearly with the respective concentrations in the concentration range from1.0umol/L to0.1mmol/L, with the detection limits of0.2and0.15μmol/L (S/N=3), respectively. In addition, the proposed method was suitable for determining the contents of hydroquinone and catechol in tap water samples with satisfactory results, demonstrating that the nanocomposite is a promising sensing material for high performance electrochemical sensor applicable to the selective detection of some environmental pollutants.(2) Application of gold-polyaniline-graphene nanocompositcs in nitrite electrochemical sensorFirst of all, using graphene oxide as the precursor, the polyaniline modified graphene oxide composite materials were prepared, in which the agglomeration of graphene sheets can be prevented effectively. Then, the polyaniline-graphene oxide composites were reduced to polyaniline-graphene composites by green pollution-free electrochemical reduction method. Finally, a thin layer of nearly monodispersed Au nanoparticles with uniform size (around12nm) were modified on the surface of polyaniline-graphene nanocomposites. Moreover, the nitrite electrochemical sensor was constructed based on gold-polyanilinc-graphcne nanocomposites. When using the nanocomposite modified the glass carbon electrode for the detection of nitrite, an obvious oxidation peak can be found and the peak current was obviously larger as compared with other common modified electrodes. In addition, the linear range is0.1to205.8μmol/L, with the detection limit of1.0×10-8mol/L (S/N=3). All the results show that the nanocomposites play a very good catalytic activity towards the oxidation of nitrite. Besides, the reaction mechanism of nitrite on the modified electrodes was also studied. This series of studies widen the application of graphene nanocomposite materials in the electrochemical detection of environmental pollutants.