| Anodic TiO2 nanotube arrays (TNAs) have attracted significant interest due to their impressive properties for applications in the fields of photocatalysis, sensing, photoelectrolysis, polymer-based bulk heterojunction photovoltaics, dye-sensitized solar cells, biofluids filtration and drug delivery, and also have been highly valued because of the abundant raw materials, low cost, and simple preparation technology. But because of the limited understanding of the growth mechanism, it is difficult to synthesize the nanotube arrays with high photo-electric conversion efficiency. In this dissertation, series of morphology controllable and precisely oriented TiO2 nanotube arrays were prepared under suitable anodic conditions. A new growth mechanism, layer-by-layer model was presented. It reveals the TiO2 nanotube growth process and also can be served as guidance for the TiO2 nanotube arrays preparation. The main contents of the dissertation are listed as follows:(1) Ti foils were ultrasonic-assisted polished in the solution prepared by HF, HNO3 and DI water (volume ratio 1:1:2) for 5 S. Results show that the surfaces are smooth and without the oxide remnant. The influences of anodic conditions on TNAs morphology were studied. Prepared in electrolyte with low ionic concentration and mobility, the TNAs show the uniform tube external diameter, close ridge interval, reduced inner diameter from tube mouth to bottom, rough surface, and long tube length, but contrary of those prepared in the electrolyte with high ionic concentration and mobility.(2) The current data were recorded by self-made I-t recorder with high accuracy, multi measuring range and low time interval. The multiplied I-t curves were plotted, and not only the second stage (the stage in which the current increases for the first time) of curve can be found for the samples prepared in electrolyte with high ionic concentration and mobility but also the fluctuations showed in the third stage (the stage in which the TNAs grow steadily) of curves for the samples prepared in electrolyte with low ionic concentration and mobility. The results of current curve fitting show that the first order exponential decay is suitable for the sample prepared in the most water containing electrolyte without stirring while the first order exponential decay isn't suitable for the sample prepared in the lowest water containing electrolyte with stirring. The two exponential forms suggest the complex influences on the current during the anodic process.(3) The influences of the heat treatment and ultrasonic-assisted wash on the TNA morphology were studied, and the results show that the ultrasonic-assisted wash can clean the TNA surface.(4) A new growth mechanism, layer-by-layer model, of titania nanotube arrays is presented, in which the key processes can be described as:(a) Establishment and breakdown of each oxide layer subsequently. (b) Pores formation due to the longitudinal prolongation and the lateral expansion of the pits. (c) Tubes formation after pores separation and the ridges formation between adjacent layers.(5) The TNAs which can be used for photo-catalysis were fabricated by controlling anodic conditions. The influences of morphology and annealing on the photo-catalysis efficiency were also studied and discussed.The primary novelties of the dissertation are as follows:(1) For the first time, the fine depth and 3D digital microscope was used to characterize the influence of chemical polish on the TNA surface roughness. The methods of Ti foil annealed in vacuum and polished with ultrasonic assistance were tried and the good results were obtained.(2) The current data were recorded by self-made I-t recorder with high accuracy, multi measuring range and low time interval. The current curve fitting results revealed the important information of the TNA growth and provided key proofs for the layer-by-layer model.(3) A new growth mechanism, layer-by-layer model, of titania nanotube arrays is presented and reasonably explained.
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