| Highly ordered nanomaterials are currently in great attention in many research fields. The nanotube structure with large surface area can enhance the working efficiency in different applications. Anodization is a commonly used method to form porous structure oxides on valve metals including titanium, zirconium, etc. Anodic titania (TiO2) nanotubes exhibits promising performance in applications of lithium batteries, water splitting, solar cells, photocatalysts, etc. Anodic zirconia (ZrO2) nanotubes may improve their properties in different applications, such as gas sensors, fuel cells, thermal barrier coatings, refractory materials, and catalysts, etc. In this paper, TiO2 nanotubes and ZrO2 nanotubes have been prepared via an anodization method and the functionalization related to the nanotubes has also been investigated in detail.The main results are as below:High density, well ordered and uniform TiO2 nanotube arrays were fabricated by anodization on a pure titanium sheet in the aqueous electrolyte (NaF+Na2SO4+H2SO4) and non-aqueous organic electrolyte (NH4F+H2O+glycol solution) at room temperature. The morphologies of the TiO2 nanotubes were investigated by scanning electron microscopy (SEM). The results showed that the average tubes diameter increaseed with anodizing voltage. The deviation of the tubes diameter is redused after two-step anodizing. TiO2 nanotubes prepared in ethylene glycol have a smooth surface and a very high aspect ratio comparing to that made in an aqueous electrolyte. The freestanding TiO2 nanotube membrane can be obtained by an ultrasonication process. After anodization for 48 h at 60 V, the freestanding membrane has 115.9?m in length.Morphological evolution and phase transformations of TiO2 nanotubes on a Ti substrate and that of freestanding TiO2 membranes during the calcinations process were studied by SEM, transmission electron microscopy (TEM), and X-ray diffraction microscopy (XRD). The detailed results and mechanisms on the morphology and crystalline structure were presented. Our results show that a compact layer exists between the tubular layer and Ti substrate at 600?, and the length of the nanotubes shortens dramatically at 750?. The freestanding membranes have many particles on their tubes during calcinations from 450 to 900?. The TiO2 nanotubes on the Ti substrate transform to rutile crystals at 600?, while the freestanding TiO2 membranes retain an anatase crystal with increasing temperature to 800?.Zirconia (ZrO2) nanotubes have been synthesized using a facile anodizing process in organic electrolyte systems containing small amounts of fluoride. Morphological nanoarchitecture evolution of ZrO2 nanotubes was measured at different anodization times (1 h-24 h) by SEM. A fluoride-rich compact layer was found between Zr substrate and upper tubular layer for 1 h anodization. For 3 h anodization, the fluoride-rich compact layer disappeared and ZrO2 nanotubes with uniform structure from top to bottom were obtained. And a random layer with lots of defeats existed instead of the uniform tubular layer for 18 h and 24 h anodization. Due to part of the fluoride-rich compact layer was not dissolved, the retained compact layer yielded O-rings on the outer surface of the nanotubes and double-walled ZrO2 nanotubes were obtained.Integrated freestanding ZrO2 membrane was fabricated via a two-step electrochemical anodization with a Zr foil, followed by a simple and safe detachment of the formed ZrO2 membrane. The resulting membrane consists of highly ordered, vertically aligned, and one-side open ZrO2 nanotube arrays. The effect of heat treatment on the morphology and crystalline structure of the integrated freestanding ZrO2 membranes was studied using SEM, TEM and XRD. These results showed that the nanotubes were stable up to be annealed at 500?and then gradually transformed to wires along their long axis from 600 to 900?. The as-prepared samples possess amorphous structure, while both monoclinic and tetragonal phases were found after annealing when ZrO2 nanotubes were annealed at a temperature between 400?and 900?.A chemical etching step is used to open the closed bottom end of freestanding TiO2 films and yields two-end opened membranes. Using the two-end opened membranes as template, dense NiTiO3/TiO2 nanotubes were sucessfully prepared for the first time by a sol-gel method. Ordered Cu nanowire structures were fabricated by a simple electroplating method inside high aspect-ratio anodic TiO2 membrane. SEM, TEM and XRD were employed to characterize the resulting samples. Detailed results and the possible mechanism are presented.The photoluminescence properties of the TiO2 nanotube arrays were discussed. There are two optical centers for the TiO2 nanotubes, the first originates from the F centers located at 465 nm, and the second is correlated with the electron transition in TiO2 nanotubes from the bottom of the conduction band to the top of the valence band. The photoluminescence of the TiO2 nanotubes was also affected by the calcination temperatures, as two main emission peaks appeared at about 387.0 and 465.0 nm when the temperature was less than 500?, while at 700?the PL spectra of TiO2 nanotubes showed four peaks at 368.0 nm, 407.0 nm,465.0 nm, and 510.5 nm. The two peaks at 368.0 nm and 407.0 nm are blue shifted due to quantum size effects.The photocatalysis activities of TiO2 nanotube arrays were characterized by quantifying the degradation of methyl orange dye solution. A set of conditions such as pH of the solution, the volume of H2O2 added to the solution, and the calcination temperatures were investigated. The result indicated that the photocatalytic activity depend on the adsorption of dyes on the TiO2 nanotubes and hydroxyl radicals in the solution. Due to the anatase crystals in the tubular layer and rutile crystals in the compact layer, TiO2 nanotubes annealed at 450?with pure anatase crystals have a better photocatalytic activity than those annealed at 600?or 750?. The TiO2 nanotube on the Ti substrate can be easily used circularly.The TiO2 nanotubes were used as negative materials for lithium-ion battery, whose charge-discharge properties, cyclic voltammetry, electrochemical impedance spectroscopy and cycle performance were examined in detail. Ag/TiO2 nanotube was also prepared from TiO2 nanotube array by thermal decomposition. The physical properties of the synthesized Ag/TiO2 nanotubes were characterized by SEM. The results indicated that the addition of Ag to TiO2 nanotube could significantly improve the electronic conductivity, charge-discharge capacity, and cycle stability of TiO2 nanotube. |
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