| Since its discovery in 2004, graphene has emerged as a rapidly rising star in the field of material science. It has been widely investigated as a promising candidate in the fabrication of chemically modified electrodes due to its large surface area, good conductivity and compatibility, wide potential window and good electrocatalytical activities. Graphene oxide is one of the most crucial derivatives of graphene, and bears lots of electroactive oxygen containing functional groups and disorder at the basal planes and edges of graphene. Generally, graphene oxide is the main intermediate product for the preparation of graphene nanomaterials from graphite. Sometimes, graphene oxide itself is used as the final material, i.e., for electrochemical sensing; usually the oxygen-containing groups are used as starting points for further functionalization. It also possesses the properties of large surface area and good chemical stability. Thus, it has overwhelming physical and chemical applications in a variety of fields.In this thesis, some other substances were combined with graphene oxide, which was used as the main modifier. Based on this, various electrochemical voltammetric sensors were fabricated and used for quick and sensitive determination of some useful materials. The main contents of the thesis can be given as follows:(1) First, graphite oxide (GO) was synthesized by ourselves from graphite powder. The characterization of synthesized graphene oxide was performed by the spectrum of FT-IR and atomic force microscopy (AFM). A new voltammetric sensor, by dipping Nafion combined with GO on the surface of a glassy carbon electrode, was fabricated and used to examine the electrochemical oxidation of caffeine. This sensor exhibited a good electrochemical response towards caffeine, which was from the affinity of Nafion and excellent electrocatalytic character of GO. Under the optimal experimental contidions, this sensor had a wide linear range response for caffeine with a low detection limit, and showed good stability, reproducibility and high sensitivity. A new electroanalytical method of caffeine was erected and successfully applied to the quantitative determination of caffeine in beverage samples with satisfactory results.(2) The possibility of the simultaneous determination of theophylline and caffeine was investigated using the modified electrode fabricated previously. The results showed that the modified electrode could discriminate the oxidation potentials of the two molecules significantly, with a peak-to-peak separation of 150 mV. As a result, the modified electrode can be used to detect theophylline and caffeine simultaneously and sensitively. Also, the contents of theophylline and caffeine in the real samples were determinated using the proposal method and the results were tested by UV. Finally the possibility of the simultaneous determination of o-, m-, p-nitrophenol was preliminarily studied using the same electrode. Although generally it was difficult to determinate o-, m-, p-nitrophenol simultaneously in electroanalysis because of their similar molecular structures, this electrochemical sensor can distinguish the three molecules effectively, which offers a promising future.(3) A new voltammetric sensor for matrine was fabricated via the polymerization of L-cysteine on graphene oxide, which served as the templates. This sensor could improve the oxidation of matrine intensively. The oxidation process of matrine was studied and some dynamic parameters were calculated using various electrochemical techniques. The calibration curve of matrine was established in the optimal conditions and the modified electrode was successfully applied in the quantitative determination of matrine in matrine injection with satisfactory results. |
