Synthesis Of II-VI Group Semiconductor Nanocrystals: Applications In Cu(II) Detection And Photocatalysis Of Organic Pullutants

In this dissertation, many efforts had been devoted to the synthesis of II-VI group semiconductor nanocrystals based on the correlations of separate nanocrystal constituents between structural and functional speciality. A series of II-VI group semiconductor nanocrystals are successfully synthesized, and their physical and chemical properties are systematically studied, such as optical properties and photocatalytic activities. Further study shows that the chemical, physical or optical properties of theses semiconductor nanocrystals have been largely enhanced or modified, or even resulting in novel functionality.1. Aqueous synthesis of highly luminescent amorphous CdSe nanocrystals at low temperatureWe utilize CdC12·3/2H2O and Na2SeO3 as Cd and Se sources, repectively. MSA was stabilzers and ligands, NaBH4 was reducing agent. Aqueous CdSe nanocrystals was prepared at low temperature (low than 100℃) with high PL QYs. The reaction temperature and heating speed had distinctive effect on QYs of CdSe NCs.We prepared a series of CdSe NCs at temperature between 25 and 60℃through water bath and microwave irradiation. The experimental results showed that water bath at 40℃was the suitable method for preparing highly fluorescent CdSe NCs. The PL QYs of prepared CdSe NCs were as high as 30%. But more high temperature is not suitable for preparing highly fluorescent CdSe NCs. Microwave irradiation that is a fast heating method was not suitable for preparing CdSe NCs with high PL QYs. CdSe NCs obtained through fast heating method had unobvious exciton absorption peak. CdSe NCs were not crystalloid. XRD patterns of CdSe NCs prepared at 20-60℃had no obvious diffraction peaks. HRTEM pictures did not show clear crystal stripes. CdSe NCs prepared at high temperature had good crystalline but with poor fluorescent quality. The PL of CdSe NCs should be defect related emission.In summary, synthesis of CdSe NCs at low temperature through water bath resulting in high fluorescence.2. One-pot microwave assisted synthesis of homogeneously alloyed CdSexTe1-x nanocrystals with tunable photoluminescenceMany factors affect the photoluminescence quantum yields (PL QYs) of nanocrystals (NCs), such as crystalline, surface state, solution surroundings, reaction conditions, et al. In our reaction system, we focus on the microwave heating methods which had obvious influence on nucleation of CdSexTe1-x NCs. As a result, the NCs had distinctly different PL QYs output. Conventionally, synthesis of CdSe or CdTe NCs in organic solvents is realized always at high temperature through fast nucleation and fast growth. Microwave can heat rapidly and uniformly, which could accelerate fast nucleation of CdSexTe1-x NCs similarly. The temperature and time of the first process were 80℃and 15s-120s, respectively. We fixed 120℃as the temperature of the second process, which was regulated as the optimum condition according to the QYs of obtained CdSexTe1-x NCs. Microwave heating at 80℃for a few seconds can evidently improve the PL QYs of CdSexTe1-x NCs. Different x had special corresponding heating time.The lattice distance (d) of (111) peaks from XRD patterns of CdSexTe1-x NCs show segmental linear relationship with x When 0