| Chemical oxygen demand (COD), one of the synthetical indicators to evaluate water pollution level, refers to, in certain conditions, the amount of oxygen in water consumed in the oxidation of organic compounds by strong oxidizing agents. With rapid developments of industry and agriculture and fast urbanization in China, environmental pollution is getting worse. At present, the standard method in China of detecting COD is potassium dichromate method. The advantages of this method are accurate, reproductive and widely used. But the disadvantages are also obvious:time consuming, high cost, serious secondary pollution, and hardly analyzing numbers of samples at the same time because of the restriction of appliance for backflow. Therefore, it is necessary to develop fast, sensitive and easy new method to shorten the analysis time and realize on-line monitor of COD. Applying nano-materials, such as carbon nanomaterials, nanostructured metals and metal oxides, organic polymeric membranes and their composite materials, to chemically modified electrodes is a new way to improve the sensitivity and selectivity. Considering this advantage, I construct two novel chemically modified electrodes that can detect COD of surface water quickly, sensitively and easily. The details and results are mentioned in the following:1. Using Co(NO3)2as the precursor, Cobalt oxide nanoparticles were in situ prepared on the surface of glassy carbon electrode (GCE) via potentiostatic method. We use lake water to harvest data of deposition potential, electrolyte, deposition time.. Besides, how the concentration of Co2+affect the signal of COD is studied. Interestingly, the shape of cobalt oxide nanoparticles was successfully regulated. As a result, cobalt oxide nanoparticles remarkably improved the electrochemical response of COD and a rapid, sensitive and simple electrochemical method was developed for COD using amperometric detection. The linear range was froml.7mg L-1to170mg L-1,and the limit of detection was as low as1.1mg L-1.To verify the practical application of cobalt oxide nanoparticles modified GCE, this new method was applied to detect the COD values of different lake water samples, and the results were in good agreement with those obtained by conventional dichromate method.2. Using Co(N03)2and CuCl2as the precursors, micro-nano Cu-Co sensitive membrane was in situ prepared on the surface of gold electrode via galvanic deposition. Based on this, the enhancement effect of micro-nano Cu-Co to the oxidation behavior of glucose, a standard compound for evaluating the COD, was investigated. Meanwhile, the oxidation of glucose was successfully tunned by variation of metal ion concentration, deposition current, electrolyte and deposition time. As a result, the newly fabricated micro-nano Cu-Co sensitive membrane can remarkably enhance the electrochemical response of COD and a rapid electroanalytical method was developed for COD using amperometric detection. The linear range was from1.92mg L-1to768mg L-1, and the limit of detection was as low as0.609mg L-1. Finally, this method was applied to detect the COD values of different water samples, and the results were testified by the standard dichromate method.3. Carbon dots, as a new nanomaterial, have attracted tremendous attention these years, the particle size of which is always less than10nm. Compared with conventional organic fluorescent dyes and semiconductor quantum dots, carbon dots have many advanced characters, including high fluorescence intensity, high photostability, wavelength tunable fluorescence emission, high solvency and nice biocompatibility. Therefore, the carbon dots were more and more widely applied in cell imaging, drug delivery, sensing of small molecules and bioscience. The forth chapter of the article reports that using glucose and folic acid as the precursors, P-doped carbon dots were synthesized by pyrolysis whose quantum yield were measured to be21.82%. The fabricated carbon quantum dots can be quenched selectively by Fe3+and based on that a fluorescent system had been established for detection of Fe3+. Meanwhile, the fluorescence intensity and detecting efficiency of quantum dots was tunned by the concentration of phosphate buffer, the pH of phosphate buffer, pyrolysis time and pyrolysis temperature. Applying this new method to detect values of iron in serums, the results were in good agreement with those obtained by flame atomic absorption spectrometry. At last, the fluorescent carbon quantum dots were applied in cell imaging, and the result showed that PC12cells emitted homogeneous blue fluorescent lights. |
