| Luminescent materials have drawn great attention for their applications in areas such as optical elements, chemical sensors, biosensors, catalysis and biomedical analysis, due to the extensive research on these materials and their rapid development.Nanomaterials with luminescent properties, as a group of new materials, exhibit high fluorescence intensity, excellent light stability, and the unique advantages of such as macroscopic quantum tunneling effect, quantum size effect, surface effect and dielectric confined effect. They normally have extra properties that not possessed by the traditional fluorescent dyes and produce new development opportunities for the fields of physics, chemistry, biology and medicine. Among various luminescent nanomaterials, the most extensively studied, the most rapidly developed and the most widely used luminescent nanomaterials include semiconductor quantum dots and carbon quantum dots. Inorganic semiconductor quantum dots are extremely popular for their good fluorescence, small sizes, excellent photostability and tunable emission wavelength. However, heavy metal ions such as Cd, Pb, which are toxic normally contained, and it is necessary to develop new preparation methods or surface modification processes to reduce their toxicity. Carbon quantum dots, because of their low toxicity, good biocompatibility and relatively stable chemical properties, have become the new focus of researchers. In recent years, the development of novel preparation methods, improvement of the luminescent properties and exploration of the luminescence mechanism are the main topic of the related research. In this dissertation, based on the work of predecessors, we successfully prepared a series of luminescent carbon quantum dots with different raw materials through fast microwave pyrolysis method, the fluorescent properties of these nanomaterials were characterized systematically. Furthermore, capillary electrophoresis has been introduced as an effective way to explore the photoluminescent mechanism. Meanwhile, we also reduce the toxicity of semiconductor quantum dots by good biocompatibility polymer coated and extend the application of semiconductor quantum dots.The dissertation consists of six chapters.Chapter 1: The concept of luminescent nanomaterials was described briefly. The physical and chemical properties, synthesis methods, developing and application status of semiconductor quantum dots and carbon quantum dots were introduced in detail.Chapter 2: In this work we used citric acid as the carbon source, cysteamine hydrochloride as the nitrogen source to prepare two kinds of fluorescent material with similar fluorescence properties but completely different morphology by microwave pyrolysis method and hydrothermal method. The product of microwave pyrolysis exhibited the typical characteristics of carbon quantum dots reported previously, and the product of hydrothermal method is a kind of pure organic small molecules, TPCA,which with strong fluorescence. By separation characterization, the main component of two kinds of products was identified as the same molecule through capillary electrophoresis. Various properties of TPCA and possible applications were also examined. The results indicate that the hydrothermal method can be used as an effective and simple synthetic route for fluorescent small molecules. Based on TPCA and silver nanoparticles, we have established a quick new method for the detection of dopamine.Chapter 3: Carbon quantum dots with novel fluorescence properties were prepared via a microwave pyrolysis method by use citric acid as carbon source and aniline hydrochloride as nitrogen source. The photoluminescence quantum yield was67.12%. The product exhibited different spectral behavior in ethanol and water. Based on this difference, the carbon quantum dots were used for evaluation of the amount of water in ethanol. In addition, the fluorescence intensity of the carbon quantum dots is sensitive to p H. They give almost no fluorescence in acidic aqueous solution, but show strong blue fluorescence in neutral and alkaline media. The cell imaging experiment successfully proved that the carbon quantum dots can be used to monitor the intracellular p H level.Chapter 4: We used citric acid as carbon source and methylamine hydrochloride as nitrogen source under microwave pyrolysis to get blue fluorescent carbon quantum dots in this chapter. Through spiking of suitable amount of lanthanum in the raw material, the color of the fluorescence of as-prepared carbon quantum dots can be shifted to yellow. This is an alternative way to adjust the fluorescence emission wavelength of carbon quantum dots. Lanthanum doped carbon quantum dots has a good response to the p H, present different fluorescence color under different p H(under UV 365 nm light). The lanthanum doped carbon quantum dots were also proved to be an effective fluorescence probe for the fast and sensitive detection of Fe3+, the limit of detection for Fe3+ is 91.2 nmol/L.Chapter 5: We used citric acid as carbon source and methylamine hydrochloride as nitrogen source to prepare fluorescent carbon quantum dots under microwave pyrolysis. This prepared carbon quantum dots showed evident excitation dependence,with the increase of the excitation wavelength, emission wavelength shifted toward the red direction gradually, showed different fluorescence color. Particularly, the prepared carbon quantum dots exhibited effective catalytic performance, can significantly catalyze the reduction reaction of methylene blue by hydrazine hydrate.The catalytic performance of carbon quantum dots is comparable with metal nanometer catalyst. The carbon quantum dots were also used successfully for catalyticreduction of methylene blue in Yellow River.Chapter 6: A successful synthesis of water soluble and polyacrylamide coated Cd Te(S) quantum dots with high quantum yields via one-step mild photochemical route was described in this chapter. The precursor solution of mixed acrylamide,thioglycolic acid, cadmium chloride and freshly prepared sodium hydrogen telluride was subjected directly to the UV irradiation using a 500 W high-pressure mercury lamp. Polyacrylamide functionalized alloyed Cd Te(S) quantum dots were formed within 40 min. This quantum dots was used as an effective probe to detect 2,4,6-trinitrotoluene in tap water, pond water, dust and soil. |
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