The Preparation Of Au-based Composite Catalysts And Their Performance In Electrocatalytic Oxidation Toward Alcohols And Detection For Small Biomolecules

Although Au is traditionally considered to be chemically inert, recent studies show that Au in nanoscale has exhibited good catalytic activity. Factualy, Au nanoparticles could exhibit unusual activity and selectivity in a wide array of reactions, such as the CO oxidation, oxygen reduction reaction and alcohols electrooxidation. Especially for the alcohols electrooxidation, the Au nanoparticles usually exhibit high catalytic activity in alkaline medium, even can surpass platinum. Many researchers devote to the preparation of Au-based catalysts and their electrocatalytic oxidation toward some small molecular alcohols, such as methanol, ethanol, propanol, 2-propanol and so on. Au is not prone to get poisoned by COads during the process of alcohols oxidation. Meanwhile, in order to improve the catalytic performance of catalysts, much attention is paid on the development of Au-based composite catalysts that are obtained by coupling some surporting materials with Au nanoparticles.On the other hand, because of well biocompatibility, Au nanoparticles are also widely applied in the field of biomedical. Au with high redox potential has strong ability of electronic capture, which make the electro-chemical reactions are prone to happen between Au nanoparticles and biomolecules. Hence, nanostructured Au is also paid much attention in the field of biosensors. For example, it has excellent prospects in application of the simultaneous determination of ascorbic acid(AA), dopamine(DA) and uric acid(UA).In this thesis, a series of Au-based composite nanocatalysts were prepared through coupling Au nanoparticles with some surporting materials, such as metal oxides, graphene and conductive polumers. Also their catalytic performances toward ethanol, 2-propanol and biomolecules like AA, DA and UA were invetiaged, respectively. The main research contents are as below:(1) Three kinds of nanoscaled metal oxides, Zn O, Mn O2 and Ti O2, were prepared by chemical method. Then they were combined with Au nanoparticles. As following, the catalysts were assembled onto glassy carbon electrode(GCE). The catalytic performance toward ethanol electrooxidation was investigated. Results show that Au-Zn O/GCE has the best catalytic performance toward ethanol electrooxidation, and the pure Au/GCE has better catalytic performance than Au-MnO2/GCE and Au-Ti O2/GCE.(2) A three-dimensional Au nanoparticles/graphene/carbon fibers hybrid electrode was fabricated by a layer-by-layer method, denoted as Au0.5/RGO/Au0.5/RGO/CF. It was found that two layers of reduced graphene oxide(RGO) sheets and two layers of Au nanoparticles were assembled alternately on carbon fibers. The catalytic performances of as-prepared electrode were evaluated via the cyclic voltammetry(CV) and chronopotentiometry(CA) measurements. It was also demonstrated that the activity of Au nanoparticles was not affected by the covered graphene layers. The synergetic interaction between RGO sheets and Au nanoparticles enhanced the catalytic activity of the electrode. Meanwhile, the excellent electron conductivity of RGO sheets benefited to the electron transfer and the oxidation removal of the intermediate species during the ethanol electrooxidation, which was good to the catalytic activity. Because of the effects of the above multiple factors, the Au0.5/RGO/Au0.5/RGO/CF electrode exhibited well catalytic performances.(3) Ag@Au nanoparticles were fabricated via a simple two-step method of electrodeposition of Ag nanoparticles and subsequently partial galvanic replacement reaction. The results of physical characterization showed that the as-prepared Ag@Au nanostructure possessed core-shell structure and has numerous nanofringes at the bord. A series of Ag@Au catalysts, Ag@Au10, Ag@Au20, Ag@Au40, Ag@Au60, were obtained by simply controlling the replace reaction time, and their catalytic performances toward ethanol oxidation were evaluated. Ag@Au40/CF showed the highest catalytic activity among the serial catalysts, and its mass current density even surpassed the commercial JM-Pt/C catalyst.(4) A facile one-pot strategy was proposed for the synthesis of well-defined Au-PEDOT(poly(3,4-ethylenedioxythiophene)) nanonets. Morphology observation shows that the Au nanoparticles with average diameters of 3.23 nm are evenly deposited on the PEDOT nanonets. Ethanol and isopropanol elelctrooxidation on the Au-PEDOT electrode was studied by cyclic voltammetry and chronoamperometry. The Au-PEDOT electrode exhibits much higher catalytic activity for ethanol and isopropanol electrooxidation than pure Au nanoparticles prepared by electrodeposition, which is owing to its unique 3D nanonetwork structure.(5) A facile Au nanoparticles and reduced graphene oxide(RGO) modified glassy carbon electrode(GCE) was fabricated via a simple electrochemical method, denoted as Au/RGO/GCE. The Au/RGO/GCE electrode was used for the simultaneous detection of ascorbic acid(AA), dopamine(DA) and uric acid(UA). The modified electrodes fabricated by different methods presented different morphologies and performances for determination of AA, DA, and UA. Three well-defined voltammetric peaks along with remarkable increasing electrooxidation currents were obtained on the Au/RGO/GCE with needle-like Au nanoparticles in differential pulse voltammetry(DPV) measurements. It is found that there are linear relationships between the peak currents and the concentrations in the range of 2.4 × 10-4 – 1.5 × 10-3 M(AA), 6.8 × 10-6 – 4.1 × 10-5 M(DA), and 8.8 × 10-6 – 5.3 × 10-5 M(UA), and the limits of simultaneous determination(based on S/N = 3) are 5.1 × 10-5 M, 1.4 × 10-6 M, and 1.8 × 10-6 M for AA, DA and UA, respectively. Additionally, the Au/RGO/GCE electrode presents well anti-interference ability, stability and reproducibility.