The Electrodeposition Synthesis Of Titania Nanotubes And Their Composite Nanostructures

Titania (TiO₂) is an important wide-gap band semiconductor. It has been found wide use in the field of water photolysis, photocatalysis, dye-sensitized solar cells (DSSC), and so on. Compared with other morphologic forms of TiO₂, nanotube arrays and their compositions (such as core/shell structure) are expected to exhibit improved and novel functional characteristics, due to their higher surface area, highly ordered and new structures. Thus the systematical studies on the preparation and characterization of TiO₂ nanotube arrays and their compositions have both scientific and engineering significances.In this thesis, we fabricated TiO₂ nanotubes and their various compositions in AAO membranes by one or two steps electrodeposition. Then we studied their formation mechanism and application in DSSC. The main results are as follows:1. The electrodeposition synthesis of TiO₂ nanotubesTiO₂ nanotubes with uniform wall thickness could be obtained by electrodeposition in electrolyte with TiF4. The outer diameter and length of the TiO₂ nanotubes are dependent on the channels diameter and thickness of the AAO membranes, and the wall thickness could be controlled by the deposition time or the concentration of TiF4 in electrolyte. Under the negative potential, TiO₂ would deposit quickly on the whole inner surface of the AAO membranes, and nanotubes with about 60μm length (similar with the thickness of the AAO membranes) could be obtained after 5 min electrodeposition. Moreover, the top of the nanotubes prepared by electrodeposition is open and the bottom is connected with the Au film at the back of the AAO membranes directly. The TiO₂ nanotube with this structure is very similar with the AAO membranes, and could be used as the template to form the TiO₂ nanotube composited structures.2. The TiO₂ nanotubes are used as the template to fabricate various compositionsDifferent metals are filled into the TiO₂ nanotubes to form metal/TiO₂ core/shell structures by electrodeposition. The core/shell structures prepared by this method are high density, and the length of the core/shell structures is dependent on the deposition time. Moreover, metal/TiO₂ two-wall nanotube structures could also be obtained through changing the deposition conditions. Not only metals, but also other materials that could be electrodeposited in AAO membranes could also be filled into TiO₂ nanotubes to form various composited structures. So, this is a general method to fabricate TiO₂ nanotube composited structures.3. Fabrication of Ni/TiO₂ composition by one-step electrodepositionNi/TiO₂ core/shell structure could be obtained by one-step electrodeposition in electrolyte with TiF4 and NiCl2, the wall thickness and length of the core/shell structure could be controlled by adjusting the TiF4 concentration and deposition time. Moreover, Ni nanoparticle chains embedded in TiO₂ nanotubes could also be obtained by increasing the deposition potential. We studied the formation mechanism of these two structures. The deposition rate of TiO₂ is much faster than Ni, and Ni could be deposited in TiO₂ nanotubes that have formed earlier. When the H2 produced could diffuse out side the TiO₂ nanotubes in time, Ni could deposit in TiO₂ nanotubes continuously to form nanorods. On the other hand, when the H2 could not diffuse out side the TiO₂ nanotubes in time, Ni would form discontinuous nanoparticle chains in TiO₂ nanotubes. Beside Ni, other materials such as Co and CdS could also be filled in TiO₂ nanotubes to form composited structure by one-step electrodeposition.4. Fabrication of DSSC with TiO₂ nanotube arrays and Ni/TiO₂ core/shell structureTiO₂ nanotube arrays and Ni/TiO₂ core/shell structure are applied in DSSC, however, only the DSSC with TiO₂ nanotube arrays after annealing could work with low efficiency. More work need to be devoted to this area.