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Study on the synthesis and properties of nano titanium dioxide and Its Composites

Author: WangZhiFeng
Tutor: ZhangMing
School: Yangzhou University
Course: Physical and chemical
Keywords: nano-titania polymer composite controlled crystallization photocatalysis electric field inducement
CLC: TB33
Type: PhD thesis
Year: 2010
Downloads: 145
Quote: 2
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Abstract


As a well-known semiconductor material, the significance of titania (TiO2) nanoparticles in areas of photocatalysts, pigments, cosmetics, photovoltaics conversion, gas sensors and photochromic devices has drawn great attention to the controlled synthesis for defined crystallinity, particle size and mophorology. Polymer-based nanosized titania composites have received increased interest owing to the complex advantage of TiO2and polymer matrix. The composite of nanosized TiO2and polymer is an important way to realize the practical application of nano-titania. In present dissertation, the research work was carried out as follows, focused on the controlled synthesis of nano-titania and the performance of its composites.(1). Well-crystallized TiO2from peroxotitanic acid were synthesized via a hydrothermal process in the presence of PVA. The effects of solution pH, dosage and molecular weight of PVA on crystal structure, morphology and particle size distribution of TiO2particles were investigated. High acidic condition is favorable for formation of rutile TiO2, while under the same acidic environment the addition of PVA can result in the transformation from rutile to anatase type, including the formation of mixed phase of TiO2. Crystal structure of TiO2is independent of PVA addition in weak acid, neutral and alkaline conditions. Solution pH affects the morphologies of TiO2via its effect on the absorption quantity of PVA.(2). TiO2films were fabricated on the surface of PMMA from the TiOSO4precursor solution using urea as precipitator. The differences in morphologies of TiO2 films on PMMA surface were analyzed based on the examination of solution pH variation on time. The increase of urea amount accelerates the formation of TiO2films, while excessive urea addition affect the formatiom of thick films. The photocatalytic degradation rate of methyl orange with TiO2@PMMA composite is low because of the poor crystallinity of TiO2. Microwave irradiation can improve the crystallinity of TiO2films on PMMA surface to some extent and speed up the degradation rate.(3). A new protocol to prepare crystalline TiO2rods at low temperature and without any additives or surfactants was studied. Phase-pure rutile is obtained at75℃while phase-pure anatase is at80℃. The formation of crystalline phases is highly dependent on the reaction temperature and concentration. Low concentration and temperature favor the formation rutile phase, while high concentration and temperature result in anatase and brookite phase. The phase formation closely follows the diffusion rate model in which the diffusion rate is influenced by reaction temperature and concentration. This method is suitable to fabricate TiO2coating on the low heat-resistant substrates and to develop organic-inorganic composite materials with different functionalities, such as UV-blocking and photocatalysts.(4). Crystalline TiO2with different phase composition were successfully fabricated on the surface of carbon fibers at low temperature. All loaded TiO2show absorption band in UV region. And the TiO2-loaded carbon fibers exhibit different photocatalytic activities on the degradation of MO under UV irradiation. The carbon fibers loaded with mixed-phase TiO2show the best photocatalytic performance. Additionally, acidic solution can accelerate the degradation rate of MO and the TiO2-loaded carbon fibers prepared in this work can be recycled facilely. They are potentially employable in the continuous photocatalytic degradation process.(5). PMMA/TiO2composite containing oriented titania nanorods was prepared by applying an external DC electric field. The orientation degree of TiO2nanorods in PMMA matrix increases with electric field strength. The orientation of TiO2nanorods in PMMA matrix induced by electric field can reduce the scatter of light and enhance the transmittance in the direction parallel to electric field. At the same direction, the dielectric constant of composite was also improved.

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