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Nanocrystalline metal chalcogenide Preparation and Properties of

Author: NiuHongYan
Tutor: BaoJianChun；HanMin
School: Nanjing Normal University
Course: Inorganic Chemistry
Keywords: Chalcogenide semiconductor liquid-liquid interface nanoparticles fluorescence Electrochemiluminescence(ECL) hydrothermal reaction
CLC: TB383.1
Type: Master's thesis
Year: 2011
Downloads: 72
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Abstract


The physicochemical properties of nanomaterials are mainly dependent on their size, shape and phase structure. In order to better manipulating the physicochemical properties of a desired material, the size and shape as well as phase structure controlled synthesis of special nanomaterials becomes the hot research area in current chemistry and material science. As a class of important functional materials, chalcogenide semiconductor nanocrystals have been attracted much attention because they exhibit novel optical and electrical properties compared to their bulk counterparts. They have potential applications in many fields, sunch as optics, electronics, optoelectronic conversion, thermoelectric, chemical sensing, and medical diagnosis. Up to now, many methods have been developed to synthesize chalcogenide semiconductor nanostuctures. It is noted that most of them choose homogeneous system as reaction medium. In this thesis, we use liquid-liquid interface strategy to controllable synthesize chalcogenide semiconductor nanomaterials. The main results are as follows:(1) Cd-oleate complex and CdCl2.2H2O are chosen as cadmium soure. And the thioacetamide and trioctylphophine selenium are used as sulfur and selenium source. Using the developed liquid-liquid interface synthethic method (glycol as polar phase and 1-octadecene as non-polar phase), CdS nanocrystals, CdSe quantum dots and tetrahedron-like CdSe nanocrystals have been successfully synthesized by controlling the experimental parameters, such as reaction temperature, time, the molar ratio of precursors and viscosity. The obtained products are characterized by energy dispersive X-ray spectroscopy (EDS), powder X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), ultraviolet-visible spectroscopy (UV-vis), Fourier transform infrared spectroscopy (FT-IR) and fluorescence spectroscopy. Compared with their bulk counterparts, the absorption spectral of the obtained CdS and CdSe nanocrystals are blue-shifted, which is attributed to the quantum size effect. Moreover, excited by the light with a special wavelength, strong green light emission are observed in both the CdS and CdSe nanocrystals.(2) Pb(Ac)2 are chosen as lead soure and trioctylphophine selenium are used as selenium source, respectively. Using the above-mentioned liquid-liquid interface synthethic method, 1D nanospiral PbSe nanocrystals have been successfully synthesized by controlling reaction temperature. The obtained products are characterized by energy dispersive X-ray spectroscopy (EDS), powder X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM). Moreover, we found that the reaction temperature also has a great impact on the phase structure of the obtained PbSe nanocrystals. Electrogenerated chemiluminescence (ECL) measurements demonstrate that ECL intensity of cubic phase PbSe nanocrystals is stronger than that of mixed phase PbSe nanocrystals.(3) In polyethylene glycol-water system, the NiSe2 nanosheet cluster structures have been synthesized by the reaction of NiSO4.6H2O and SeO2 in the presence of NaH2PO2 under hydrothermal condition. The component, phase structure and shape of the obtained product were characterized by X-ray energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and transmission electron microscopy (TEM), respectively. The pH value, the concentration of PEG and the ratio of NiSO4 to SeO2 have a great impact on the morphology of the final products. Time-dependent experimental results demonstrate that the NiSe2 nanosheet cluster structures are evolved from the initial formed sheet-like structure during the ripening process. Moreover, the optical and electrochemical properties of the obtained NiSe2 nanosheet cluster structures are studied.

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