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The Syntheses and Applications of Nanao Cadmium Sulfide Based on the Green Chemical Concept

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Tutor: YangLin;GuoYuMing
School: Henan Normal
Course: Inorganic Chemistry
Keywords: green chemistry,CdS QDs,amino acid,potocatalytic,cytotoxicity
CLC: O614.242
Type: Master's thesis
Year:  2011
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As one of the most important and popular group II-IV semiconductors, cadmium sulfide (CdS) has a large direct band gap of 2.4 eV at room temperature and exhibits excellent photoelectric properties. Based on these properties, it has been studied extensively during the past decades. Currently, CdS is widely used in nonlinear optics, solar cells, light-emitting diodes for flat-panel displays, lasers, and thin film transistors. In addition, CdS quantum dots (QDs) show the widely potential applications in biomedical and chemical analysis based on its excellent photoluminescent (PL) activity. However, most of the existing preparation methods involve the severe conditions including high pressures and temperatures, the toxic organic stabilizers and solvents, the complicated procedures for the synthesis of the stabilizers and the QDs, and the following purification process. These significantly limit the applications of these methods. Therefore, it is urgently to construct a facile method to prepare the stable and good dispersed QDs. Based on the concept of the green chemistry, the current study will focus on the design and development of the facile one-pot environment-friendly method to the green synthesis of the CdS QDs. The innovation of this thesis can be summarized to three aspects. Firstly, the environment-friendly amino acids with good biocompatibility were selected as the additives, but not the toxic organic sulfhydryl reagent. Secondly, the water was selected as the environment-friendly reaction media, but not the generally used toxic organic solvent. Thirdly, the preparation was performed under the mild conditions, including the comparatively low temperature and short reaction time, but not the generally used high temperature and pressure conditions.In summary, the study of the thesis mainly focused on the following aspects:(1) Using cystine as the additive and water as the reaction media, the CdS microspheres with hierachical structure were successfully prepared under the mild conditions through a simple method. Based on the XRD, SEM, and TEM characterization results, the as-prepared CdS microspheres were the typical cubic CdS phase. The diameters were in the range of 4~8μm and the thickness of nanosheets was in the range of 60-80 nm. According to the optical determination, the as-prepared CdS microspheres exhibited a broad absorption band from 200 to 500 nm and a strong green emission near 528 nm when excited with wavelength 202 nm. In addition, the possible formation mechanism was proposed based on the FTIR determination and the time-dependent SEM observation.(2) According to the difference of the polarity and structure of R base inα-amino acids, the essential amino acids can be classified into five categories. In this thesis, two kinds of amino acid in each category were selected as the stabilizing agent to prepare the CdS QDs through a facile one-pot strategy in aqueous media, respectively. Based on the XRD analysis results, the as-prepared CdS QDs exhibited similar XRD patterns, which can be assigned to the cubic CdS phase. Moreover, the size distribution analysis results showed that the CdS QDs prepared in the presence of the amino acid with aromatic rings, imidazole rings or bicarboxyl structures exhibited the better dispersion and smaller size. In addition, the FTIR spectroscopy analysis suggested that there are certain coordination interactions between the QDs and the carbonyl groups of the amino acids. From the data of the UV-visible and PL spectra, the sequence of the UV absorption intensities of the CdS QDs is Glu-CdS > Trp-CdS > Arg-CdS > Thr-CdS > Val-CdS > His-CdS > Phy-CdS > Pro-CdS > Met-CdS > Asp-CdS. And the sequence of the PL intensities is Arg-CdS≥Pro-CdS > Met-CdS > Thr-CdS≥Val-CdS > His-CdS > Phe-CdS > Glu-CdS > Asp-CdS > Trp-CdS. The PL intersities of the CdS QDs showed obvious correlation to the particle size, i.e. the smaller the size of the QDs, the stronger the PL intensities.(3) Because of the strong photo absorption properties of the as-prepared CdS QDs, the phtocatalytic activities to degrade the organic pollutant rhodamine B under visible light irradiation were studied in detail. Based on the photodegradation activities, the CdS QDs prepared in the presence of ten different amino acids can be divided into two groups, the high-active group and the low-active group. The high-active group consists of the QDs through five different amino acids, including Trp, Glu, His, Asp, and Phe. While the low-active group consists of the QDs through the other five different amino acids, including Pro, Thr, Val, Arg, and Met. In addition, through the mediation of the hydroxyl radicals produced by the photogenerated holes and electrons, the as-prepared CdS QDs showed different photocatalytic activities and good recycling stability under visible light irradiation, suggesting the potential application in the effectively treatment of the organic pollutants in wastewater under visible-light irradiation.(4) Based on the cell biology studies, except for the QDS from Arg, the CdS QDs from other amino acids possessed good biocompatiblities and might be used in biological fluorescence labeling. KEY WORDS: green chemistry, CdS QDs, amino acid, potocatalytic, cytotoxicity
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