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Study on the Preparation, Morphology and Formation Mechanism of TiO2 Nanotubes and TiO2 Nanotube Arrays

Author: ZhouChengFeng
Tutor: WangZhiYi
School: Qingdao University of Science and Technology
Course: Materials Physics and Chemistry
Keywords: tetrabutyl titanate alkoxide hydrolysis precipitation method TiO2 nanotubes hydrothermal method TiO2 nanotube arrays anodic oxidation
CLC: TB383.1
Type: Master's thesis
Year: 2009
Downloads: 168
Quote: 1
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Abstract


Titania nanotube have aroused much attention for their excellent properties of photoelectricity, catalysis, gas sensitivity, and the potential applications in areas such as solar cell, photocatalyst, environmental purification, and gas sensors. TiO2 nanotube arrays, a new type of titania nanomaterials, have attracted wide attention due to their distinctive structure and notable property recently.In this paper, the preparation methods and formation mechanism of TiO2 nanotubes and TiO2 nanotube arrays were studied. Pure TiO2 nanopowders were prepared by controlled alkoxide hydrolysis precipitation method, and well-grown hollow TiO2 nanotubes with ringent pipe end were successfully synthesized in different alkali liquor by hydrothermal method. TiO2 nanotube arrays and nanorod arrays with various forms were prepared by effectively controlling electrolyte concentration as well as anodization time in acidic, neutral and ethyleneglycol electrolyte. The main results of this paper are summarized as follows:1. TiO2 nanopowders with particle size about 10nm were synthesized by calcining TiO2 precursor at 450℃for 2 h prepared by controlled alkoxide hydrolysis precipitation method using tetrabutyl titanate as raw materials. Results show that the TiO2 nanopowders as-obtained are pure, ultra-fine and narrow distributed, and the preparation process is simple and time-saving.2. TiO2 nanotubes were successfully prepared by hydrothermal method using anatase-type TiO2 powders which mentioned above as precursor. The effects of species and concentration of alkali liquor, reaction temperature and time as well as acidwashing process on the morphology of TiO2 nanotubes were studied in detail. Results show that well-grown hollow TiO2 nanotubes, with outer diameters of 5 nm to 7 nm, wall thicknesses of about 1 nm , lengthes of 200 nm to 300 nm and ringent pipe ends, were obtained by hydrothermal treating anatase-type TiO2 powders in sodium hydroxide solution（10 mol/L） at 120℃for 48 h and then acidwashing in 0.1 mol/L hydrochloric acid. TiO2 nanotubes with the same morphology were obtained in potassium hydroxide solution （10 mol/L） at a higher temperature（140℃）. The conclusion is that monovalent alkaline solution can be used as reaction medium to prepare TiO2 nanotubes with the same formation mechanism that TiO2 nanoparticles are changed to flake product which curled to nanotubes the length of which gradually increased with the extension of reaction time according to solution-imbibition mechanism. The transformation temperature from lamellar product to nanotubes are different for the alkali metal ions with different field strength have different restraining effects on the lamellar structure. Compared with K+, H3O+ can change for Na+ more easily, so the formatiom temperatures of TiO2 nanotubes are lower in sodium hydroxide solution.3. The highly ordered TiO2 nanotube arrays were fabricated by anodic oxidation of titanium foil. The influences of species and concentration of electrolyte as well as anodization time on the morphology of TiO2 nanotube arrays had been studied, and the growth mechanics were analyzed. Results show that regular ordered TiO2 nanotube arrays can be prepared in hydrofluoric acidic solution, the pipe diameters are uniform and the surfaces are smooth, but the lengthes are limlited in the range of 300350 nm. The interesting thing is that TiO2 nanotube arrays and nanorod arrays can be obtained in high concentrate hydrofluoric acidic solution. TiO2 nanotube arrays with high slenderness ratios and bad surface smoothness can be prepared in sodium fluoride and sodium sulfate electrolyte, whose lengthes of 700 nm are longer than those prepared in hydrofluoric acidic electrolyte. TiO2 nanotube arrays can also be prepared in glycol, ammonium fluoride and water ethyleneglycol electrolyte, whose pipe diameters are about 150 nm and lengthes can reach 6μm. But the top of TiO2 nanotube arrays gather together for the existance of glycol. The tubular structures array more orderly in the bottom than the top. The formation of TiO2 nanotube arrays undergo three stages named formation of oxidizing layers, formation of nanopores and steady growth of nanotubes, which is the result of dynamic balance achieved by interactions of field oxidation, field dissolution and chemical dissolution.

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