Modification Of Electrodes With Nanocomposites And Study Of Their Electrocatalytic Properties

Nanomaterials have been studied extensively due to their large specific area, high surface activity, and strong affinity. Also they indicate the wide application prospect in electrocatalysis and sensor materials. The electrochemical responses of modification of electrodes are related to the electrode materials. Current response can be improved and detection limit extended when the nanomaterial modified electrodes are employed. The main work of this paper is focus on preparation of nanomaterial modified electrodes and study of the electrocatalytical properties. Compared with the traditional modified electrodes, the process of preparation is simple and convenient. Besides, the other emphasis of the work is to apply these nanomaterials modified electrodes to detect and analysize some analysts, such as oxygen, hydrogen peroxide, L-cysteine. The details are listed below:1. Preparation and characterization of Pt-polypyrrole nanocomposites for electrochemical reduction of oxygen.An easy and simple method of one-step reaction was employed to synthesize the platinum-adsorbed polypyrrole nanocomposite (PtPPy) in a cetyltrimethylammonium bromide (CTAB) solution. The prepared nanocomposites were characterized using UV-vis absorption spectroscopy(UV-vis), scanning electron microscopy(SEM), Fourier transform infrared spectroscopy(IR), thermogravimetric analysis(TA), and cyclic voltammetry(CV). Polypyrrole within nanocomposites could crosslink to improve its stability on the Au substrates. O₂ reduction was performed at Au electrodes modified PtPPy. The results clearly show that modification of PtPPy nanocomposites results in the enhancement of the electrocatalytic reduction of oxygen. The nanocomposites may provide a novel electrode material for application in fuel cells and oxygen sensors.2. Preparation of Au-polypyrrole composite nanoparticles and study of their electrocatalytical reduction to oxygen with (without) laccasse.Au nanoparticles are often employed to design self-assembling electrodes and prepare functionalized sensors due to their characteristics, such as the large surface-to-volume ratio, high activity and strong absorbtion. In the section, the colloids of Au-polypyrrole (AuPPy) composite nanoparticles were prepared by oxidizing pyrrole monomer with HAuCl₄ in a cetyltrimethylammonium bromide (CTAB) solution. Scanning electron microscopy (SEM) suggests the AuPPy nanoparticles in the form of regular spheres, approximately 200 run in diameter. The resulting colloid of AuPPy composite nanoparticles strongly adheres to the surface of Au electrodes and exhibits better electrocatalytical reduction of oxygen than bare Au electrodes. It means that the complex procedures of centrifuge and wash are avoided. Also, no linker molecules are needed and the immobilization of nanoparticles is achieved easily in a single-step procedure. The direct electron transfer of laccase is observed after it is immobilized on AuPPy modified electrodes by glutaraldehyde. With the help of mediator 2,2'-azino-bis-(3-ethylbenzothiazoline-sulfonic acid)(ABTS), laccase electrode gives an electrocatalytical reduction wave of oxygen. It is proved that these nanocomposites not only have a stable electric signal, but show the environmental compatibility for biomolecule. These materials are excellent choice for the design of metal nanoparticles modified electrodes or biosensors.3. Direct assembly and electrochemical study of Au-polypyrrole and Pt-polypyrrole composite nanoparticles in the colloids with bioderivative peptide polymyxin B as stabilizer.The amphipathic molecule polymyxin B(PMB) is employed dispersion nanopaticles. The hydrophilic property of PMB is excellent. The stable colloids of Au-polypyrrole or Pt-polypyrrole composite nanoparticles were prepared by oxidizing pyrrole monomer with HAuCl₄ or K₂PtCl₆ respectively in the presence of PMB. On the one hand, the Au-polypyrrole and Pt-polypyrrole composite nanoparticles are dispersed well in colloid solution due to excellent hydrophilic property of PMB. On the other hand, after the colloid solution is spread on Au surface followed by the evaporation of the solvent, the resulting composite nanoparticles strongly adhere to the Au surface due to the existence of polypyrrole. It is a facile and versatile route to immobilize Au-polypyrrole or Pt-polypyrrole nanoparticles. The composite nanoparticles exhibit better electron transfer and electrocatalytical reduction of oxygen than bare Au electrodes. It makes these polypyrrole-based composite nanomaterials an excellent choice to prepare noble metal nanoparticle-modified surface for electrocatalytical or electroanalytical applications.4. Electrochemistry of self-assembled hemin from hexadecyl trimethyl ammonium bromide (CTAB) water solution on single wall carbon nanotube modified glass carbon electrodes.The hemin is adsorbed on the surface of single-wall carbon nanotube modified GC electrodes by self-assembly. The modified electrodes exhibit a well-defined, reversible redox peaks with the reduction potential at -0.30V and potential separation of 61mV at pH 7.0. The peak current is found to increase linearly with the scan rate in the range of 25-200mV and the peak potential to be pH dependent. The modified electrodes exhibit obvious signal enhancement for the electrochemical reduction of O₂ and H₂O₂, and oxidation of cysteine, which is useful to develop their application in electroanalysis and biosensors.