The Preparation And Its Application Of Carbon Nanotube/Polymer Chemically Modified Electrodes

Carbon nanotubes (CNT) is generated by rolling a single or several layers of graphite into a seamless and hollow cylinder. Because of the large ratio of surface area to volume, the good electric conductivity, the strong electrocatalysis, and its ability to decrease the overpotential, it has attracted much attention in the perspective of electrochemical sensor design. Polymer film not only provides much electroactivity center, but also possesses three-dimensional (3-D) spatial structure and offers much available potential energy making it is possible to react at 3-D space. It can be immobilized covalently by many electroactive groups, and is not strict in the electrode surface. Therefore, polymer film has attracted lots of attention. Both of CNT and polymer have been widely used in modified electrode, such as biomolecular sensor and gas sensor. However, they are not widely used as sensors for food and cosmetic products. In this thesis, we have done some work in this field and the main results are expressed as follows:1. A multiwall carbon nanotube/Nafion composite modified glassy carbon electrode (MWNT/Nafion/GCE) was prepared and characterized by Atomic Force Microscopy (AFM) and Transmission Electron Microscope (TEM). This voltammetric sensor exhibited strong catalytic effect toward the oxidation of 8-hydroxyquinoline(8-HQ) in HAc-NaAc buffer solution (0.2 M, pH 3.6). A new analytical method for determining 8-HQ was established. Under the optimized condition, the anodic peak current was linear with the concentration of 8-HQ in the range of 2×10-8～1.0×10-5 mol/L with a detection limit of 9×10-9 mol/L. The practical application of MWNT/Nafion/GCE was carried out for determining 8-HQ in cosmetic sample with satisfactory results. The number of electron and proton taking part in the reaction was calculated, and then the electrode reaction mechanism was confirmed by UV-vis spectra.2. Safranine T was polymerized electrochemically on a glassy carbon electrode and characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) respectively. Poly (safranine T)/Nafion film modified glassy carbon electrode (PST/Nafion/GCE) was prepared and showed catalytic effect toward the electro-oxidation of caffeine in H2SO4 solution (pH1.0). A new analytical method for determining caffeine was established. The peak currents showed a linear relationship with the caffeine concentrations in the range of 3×10-7mol/L and 1×10-4 mol/L with a detection limit of 1×10-7 mol/L. The practical application of PST/Nafion/GCE was carried out for determining caffeine in tea sample with satisfactory results. The effects of preparation method, including the water temperature, infusion time and times on the caffeine content in drinking tea were studied.