Synthesis And Properties Of Iron Oxide, Semiconductor Quantum Dots And Their Composites

During the past decades, numerous novel materials and methods have emerged as the development of nanomaterial science. Dramatic progress has made in synthesizing materials with enhanced properties. Multiple functional nanomaterials present various properties and show large potential in many application fields. They have drawn much attention, and turned out to be a focus. Meanwhile, scientists are being confronted with a great challenge that let the brand-new nanotechnology enter a commercial stage to make them more common and life-oriented.In this thesis, we choose iron oxide and semiconductor quantum dots for their extensive applications in many areas and their own novel properties. We aim to gain the nanomaterials with high properties, novel structure and multiple functions, as well as the potential in applications by some simple and green methods. The structure, component, morphologies, magnetic properties, optical properties and porosity of the products were characterized by X-ray diffraction analysis (XRD), Mossbauer spectrum analysis, differential thermal analysis-thermogravimetric analysis (DTA-TGA), X-ray energy dispersive spectrum analysis (EDS), transmission electron microscopy (TEM), atomic force microscopy (AFM), a vibrating sample magnetometer (VSM), a ultraviolet-visible spectrophotometer, a fluorescence spectrophotometer, a Fourier transform infrared spectra (FT-IR) and a surface area analyzer. The main results and conclusions are listed as follows:1.α-Fe2O3 nanoparticles were prepared by high-energy ball milling using a-FeOOH as raw materials in the air. The XRD and TEM results showed that after 90 h millingα-Fe2O3 nanoparticles were obtained, and the particle size is about 20 nm. The mechanism of reaction during milling is proposed from Mossbauer spectroscopy that the initialα-FeOOH powder turned smaller and smaller by the high-speed collision during ball milling, later these particles turned to be superparamagnetic, at last these superparamagnetic a-FeOOH particles were dehydrated and transformed intoα-Fe2O3. 2. Fe3O4 nanoporous particles assembled from small Fe3O4 nanoparticles were prepared by thermal decomposition of iron acetylacetonate in the presence of polyethylene glycol 4000. The size of the spherical nanoporous particles is 100-200 nm. Surface area measurement shows that these Fe3O4 nanoporous particles have a high surface area of 87.5m2/g. Magnetization measurement and Mossbauer spectrum indicate that these particles are nearly superparamagnetic at room temperature. It is found that the morphology of the products is greatly influenced by polyethylene glycol concentration and the polymerization degree of polyethylene glycol. Polyethylene glycol molecules are believed to facilitate the formation of the spherical assembly.3. Optical performances of reductive glutathione coated CdSe quantum dots were studied under different ageing conditions. The enhancements of luminescence were obviously occurred for the samples ageing under illumination. The quantum yield of CdSe was enhanced continuously over 44 days at room temperature, and reached as high as 36.6%. O2 was proved to make a certain contribute to the enhancement. The evolutions of the systems during the ageing time were deduced according to the variations of pH values with ageing time and the XRD results of the samples ageing in air with illumination. We conferred that the reduction of surface defects resulted from the photo-induced decomposition of CdSe quantum dots was the main reason for the enhancement of fluorescence. The production of CdO as a result of the surface reaction with O2 made contributions to the enhancement for a certain extent. The curves of quantum yield versus ageing time were fitted with a stretched exponential function. It was found that the course of fluorescence enhancement accorded with the dynamics of system with strongly coupled hierarchical degrees of freedom.4. CdS/a-Fe2O3 composite was synthesis by in-situ preparation. The composite was formed by nearly 5nm CdS nanoparticles attaching onto the surfaces of a-Fe2O3 with 50nm in size. EDS results showed the quantity of CdS nanoparticles could changed with the amount of the raw materials. The emission wavelengths were slightly different possibly due to the tiny different in the size of CdS nanoparticles. The photocatalysis results showed the composite had the improved degradation of methyl orange, and charge separation might be the cause of the improvement..5. A new type of magnetic-fluorescent composite was prepared using starch-stabilized Fe3O4 and GSH-stabilized CdSe. AFM and TEM showed the group size of the Fe3O4-CdSe composite was about 100 nm. The composites were easily attracted by magnet, and the magnetization of the composites could reach 48emu/g. The composites with green-emitting or red-emitting quantum dots could emit distinguished fluorescence when composed, and the quantum yields are 7.6% and 6.3%. The formation mechanism of the composite was proposed to be the hydrogen bonds between OH of starch and NH of GSH and partial esterification. The adsorption of anticancer drug doxorubicin (DOX) onto the composite was studied. The saturate adsorption could reach 1.18mg DOX/mg composite in PBS7.4 buffer. FT-IR and adsorption kinetics analysis indicated that both chemical and physical adsorption existed between DOX and the composites, and physical adsorption is the main type in the saturate adsorption sample. DOX could release from the composite in PBS7.4 buffer, and the released rate was 65.2% after 94 hours. Moreover, the saturate adsorption sample showed a saturate magnetism of 28.3emu/g. All the result shows the Fe3O4-CdSe composite has a promising application in biomedical region.