| Semiconductor materials have some excellent properties, such as thermo sensitivity, light sensitivity and doping property, this three properties supply the semiconductor materials with excellent photoelectric properties. TiO2 as a kind of typical n-type semiconductor has outstanding photoelectric properties also, thus attracted widely attentions of scientific workers. TiO2 has broad application prospect in the area of photocatalysis, gas sensitive sensor and photoelectric conversion due to its excellent physical and chemical properties, TiO2 nanotubes have the more excellent photoelectric properties while compared with TiO2 particles, because TiO2 has smaller particle size and larger specific surface area.There are some methods to prepare TiO2 nanotubes, such as template-assisted synthesis method, hydrothermal synthesis method and anodic oxidation method. Among them; the anodic oxidation method attracted extensive interests due to its many advantages, such as convenient operation, lower cost, TiO2 nanotubes arranged by array form which was highly ordered, and TiO2 nanotubes are easy to recycle because of that they were cohered on the substrate. However, similar to TiO2 material, the forbidden bandwidth of TiO2 nanotubes is large which leads to the defect that the utilization rate of solar energy is low. Therefore, TiO2 nanotubes are needed to be modified to reduce its forbidden bandwidth, in order to expand the application scope of TiO2 nanotubes. In this paper, we used anodic oxidation process to prepare TiO2 nanotube arrays with controllable morphology, rare earth ions (La3+, Er3+) were used to dope the TiO2 nanotube arrays, and nonmetallic element (C) was used to modify the TiO2 nanotube arrays. The specific contents are as follows:(1) Ti substrate was put into ethylene glycol which contains F to prepare TiO2 nanotube arrays with one-dimensional nanostructure through anodic oxidation process. The structure and morphology of samples were researched by using X-ray diffraction (XRD) and field emission scanning electron microscope (FESEM). The composition was analyzed by energy dispersive X-ray spectroscopy (EDS). The absorption of ultraviolet light and visible light was measured by using ultraviolet and visible spectrophotometer. We explored the influence of preparation parameters on the structure and morphology of TiO2 nanotube arrays, the preparation parameters contain the concentration of F, anodic oxidation voltage, anodic oxidation time, annealing temperature. And we realized the controllable preparation of TiO2 nanotube arrays through adjusting the preparation parameters in a little scope. We found that the concentration of F is the main factor that influence the morphology of TiO2 nanotube arrays. The anodic oxidation voltage influenced the inner-diameter of the TiO2 nanotube arrays mainly, the inner-diameter of TiO2 nanotube arrays increased with the increasing of anodic oxidation voltage. The anodic oxidation time influenced the morphology of TiO2 nanotube arrays also. The increasing of annealing temperature will accelerate the growth of crystalline grain and play a decisive role on the crystal of TiO2. The best preparation parameters of TiO2 nanotube arrays are as follows:the concentration of F is 5 wt%, the anodic oxidation voltage is 30 V, the anodic oxidation time is 1 h and the annealing temperature is 450℃. The pipe diameter of the TiO2 nanotube arrays prepared under the best conditions is about 70-100nm, and the length of the nanotube is about 2.12μm. The prepared TiO2 nanotube arrays had a strong absorption on ultraviolet light, and the absorption on visible light is weak. The photo-degradation rate of TiO2 nanotube arrays on methylene blue can reach to 92% at 240 min, almost the twice of the P25, so the TiO2 nanotube arrays have excellent photocatalytic performance.(2) La(NO3)3·6H2O was selected as the source of La3+, and some amount electrolyte contains certain concentration of La3+ was prepared, then we prepared TiO2 nanotube arrays contain La3+ in the electrolyte which contains La3+ through anodic oxidation process successfully. We found that the doping La3+ would decrease the degree order of TiO2 nanotube arrays, and make the nanotube orifice being rough, but the influence of different concentration of La3+ within a certain range on the morphology of TiO2 nanotube arrays have no obvious difference. XRD result shows that the doping La3+ has no obvious influence on the structure of TiO2 nanotube arrays, it is assumed that was caused by the little amount of doping La3+. EDS result shows that a little amount of La3+ was doped into TiO2 nanotube arrays successfully, the relative atomic mass fraction percentage and the relative atomic number percentage of La3+ is 3.09% and 0.76%, relatively. UV-Vis result shows that TiO2 nanotube arrays doped with La3+ have a great enhancement on the absorption of visible light whose scope is ranging from 400nm to 800 nm. The photo-degradation rate of TiO2 nanotube arrays on methylene blue can reach to 91.9% after irradiating under ultraviolet and visible light for 240 min, and has a improvement about 3.1% while comparing with the pristine TiO2 nanotube arrays among the same batch test samples, which means that TiO2 nanotube arrays doped with appropriate amount of La3+could have a great improvement on the photocatalytic performance.(3) Er(NO3)3-6H2O was selected as the source of Er3+, and some amount electrolyte contains certain concentration of Er3+ was prepared, then we prepared TiO2 nanotube arrays contain Er3+ in the electrolyte which contains Er3+ through anodic oxidation process. We found that the doping Er3+ could decrease the degree order of TiO2 nanotube arrays also. XRD result shows that the diffraction peaks of TiO2 nanotube arrays doped with Er3+ have a little movement towards the left, which means that Er3+ was doped into the crystal lattice of TiO2. EDS result shows that a little amount of Er3+ was doped into TiO2 nanotube arrays successfully, the relative atomic mass fraction percentage and the relative atomic number percentage of Er3+ is 2.94% and 0.56%, relatively. UV-vis result shows that TiO2 nanotube arrays doped with Er3+ have a great enhancement on the absorption of visible light whose scope is ranging from 400 nm to 800 nm. The forbidden bandwidth of TiO2 nanotube arrays is about 2.87 eV when the concentration of doping Er3+ is 3 mg/mL, which means that the doping Er3+ could reduce the forbidden bandwidth of TiO2 nanotube arrays. The photocatalytic property of TiO2 nanotube arrays is the best while prepared under the condition that the concentration of the doping Er3+ is 1 mg/mL, the photo-degradation rate of TiO2 nanotube arrays on methylene blue can reach to 91.9% at this time, and has a improvement about 4.9% while comparing with the pristine TiO2 nanotube arrays among the same batch test samples, which means that TiO2 nanotube arrays doped with appropriate amount of Er3+ could have a great improvement on the photocatalytic performance.(4) TiO2 nanotube arrays were prepared through anodic oxidation process, then put the TiO2 nanotube arrays into the solution which contains certain concentration of urea for a period of time, evaporated the water and put the sample in the tube furnace which was protected under N2 atmosphere to calcine for 2 hours under 350℃, and then we could obtain the TiO2 nanotube arrays modified by C. We found that the modified carbon could decrease the degree order of TiO2 nanotube arrays, the orifice of modified TiO2 nanotube arrays being rough. TiO2 nanotube arrays couldn’t be seen when the concentration of urea is overlarge, the surface of TiO2 nanotube arrays was covered with a layer of carbon film. XRD result shows that the crystallinity of TiO2 nanotube arrays increased after modifying by carbon, and the carbon modification could promote the growth on the crystal face of (002). EDS result shows that the TiO2 nanotube arrays was modified by a little amount of carbon successfully, the relative atomic mass fraction percentage and the relative atomic number percentage of carbon is 4.95% and 10.85%, relatively. UV-Vis result shows that TiO2 nanotube arrays modified by carbon have a great enhancement on the absorption of visible light. The forbidden bandwidth of TiO2 nanotube arrays prepared is about 2.50 eV and 2.11 eV when the concentration of urea is 20 wt% and 40 wt%, relatively. Which means that the carbon modification could reduce the forbidden bandwidth of TiO2 nanotube arrays obviously, thus to improve the absorption of TiO2 nanotube arrays on visible light. The photo-degradation rate of TiO2 nanotube arrays on methylene blue improved after modifying by carbon, the photocatalytic property of TiO2 nanotube arrays is the best when the concentration of urea is 20 wt%, and has a improvement about 7.9% while comparing with the pristine TiO2 nanotube arrays among the same batch test samples. The photocatalytic property of sample declined when the concentration of urea rose to 40 wt%. Which means that urea with appropriate concentration could improve the photocatalytic property of TiO2 nanotube arrays.In a word, the TiO2 nanotube arrays prepared via anodic oxidation method is highly ordered, and its photocatalytic property is excellent. La3+, Er3+ which belongs to the rare earth ions can improve the photocatalytic performance of TiO2 nanotube arrays, the modified carbon is also beneficial to the photocatalytic performance of TiO2 nanotube arrays. |
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