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Controlled Synthesis and Self-Assembly of Nanosized Titania and Silica

Author: YuKaiFeng
Tutor: WangZiChen
School: Jilin University
Course: Physical and chemical
Keywords: Silica Controlled synthesis Titania Hydrothermal Nanorods Amorphous Tartaric acid Nanocrystalline Anatase Morphology
CLC: O613.72
Type: PhD thesis
Year: 2005
Downloads: 1218
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Abstract


The preparation of nano-materials is a great challenge in the fields of synthetic chemistry and materials science, because materials at the nano-and micro-scale lengths have unique structural, mechanical, electronic, and optical properties. Various nano-and micro devices were built up based on nanomaterials. To utilize and optimize the chemical/physical properties of nano-scale materials, a number of workers have focused on the control of the size and/or shape of nanoparticles as well as their self-assembly into ordered structures by developing effective synthetic techniques. The alkoxide sol-gel synthesis of nanostructured TiO2 has been studied systematically to examine the processing parameters that control crystallite size and phase. A hydrothermal method has been proposed to prepare uniform and unaggregated nanocrystals of pure anatase in nitric acidic medium. Hydrolysis and polycondensation of titanium n-butoxide (Ti (OC4H9) 4) has been performed in the presence of polyethylene glycol (PEG). The use of polyethylene glycol (PEG) and the effect of its concentrations on the formation of anatase phase have been described in detail using X-ray diffraction and transmission electron microscopy. It was found that nanocrystalline anatase particle (about 5 nm) derived by hydrothermal processing at 160 oC for 5 h. Controlling over crystal structure, size, shape, and organization of TiO2 nanocrystals has been achieved by means of wet chemistry. Hydrolysis and polycondensation of titanium n-butoxide (Ti (OR) 4) has been performed in the presence of polyethylene glycol (PEG). The self-assemble propensity of the controlled shape and size distribution of the titania nanoparticles makes the oriented particles organise to ordered structures (nanorods) by a hydrolysis-hydrothermal route. The procedure offers the possibility of a generalized approach to the production of patterned organization of single and complex oxide nanoparticles with tunable size and morphology. A novel and simple method for preparing nanosized TiO2 was developed by hydrolysis of titanium n-butoxide (Ti (OR) 4) modified with tartaric acid. The TiO2 powders were characterized by differential thermal analysis-thermogravimetry (DTA-TG), X-ray, transmission electron microscopy (TEM). The results showed the crystallinity of rutile was improved upon tartaric acid modified titanium n-butoxide. Moreover, tartaric acid prohibited the formation of anatase phase. A novel approach was employed in the fabrication of silica nanocubes with controlled size and shape. The silica nanocubes were highly dispersed with width of about 30 nm and product with high purity. A small amount of tartaric acid was introduced in the TEOS hydrolysis process. In this work tartaric acid as the organic template, was formation on the surface of hydrous silica colloidal particles. The organic template ordered by carboxyl, made the self-assembly of amorphous silicasol encapsulated into cubic matrixes, and the organic template was packed into 3D structure. Since the discovery of carbon nanotubes in 1991, many other nanosized tubular materials have been synthesized. To date, various preparation methods have been used to synthesize silica nanotubes. In our previous work, we have presented a relatively easy and inexpensive synthesis procedure for silica nanotubes by converting layered kaolin clay. But all the silica nanotubes are amorphous. Single crystal silica nanotubes, however, have not yet been reported. Here we report the result of an X-ray diffraction study and TEM study of silica nanotubes that has been heated to 471K in the present of glycol and potassium hydroxide. We observe the occurrence of single crystal silica nanotube which structure is tridymite. Finally, we have prepared the composite of nanosized titania and silica nanotubes. We used hydrothemal and peptizing method to precipitate nanosized anatase on the surface of amorphous silica nanotubes.

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CLC: > Mathematical sciences and chemical > Chemistry > Inorganic Chemistry > Non-metallic elements and their compounds > Part Ⅳ family of non-metallic elements (carbon and silicon ) and its compounds > Si Si
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