Study On Photocatalytic Properties Of Rare Earth Ions Doped Titanium Dioxide Nanotubes Made By Template Method

Nanometer TiO₂ is a new type of semiconductor material. It is a kind of ideal semiconductor photocatalyst becase of its properties such as stable, poisonless, difficultly soluble and cheap. It has wide application prospects in solar energy storage and utilization, photoelectric conversion, photochromism, photocatalysis in degradation of pollutants in atmosphere and water and so on. But the electron-hole pairs can only be excited by ultraviolet light or near ultraviolet rays because of its 3.2eV forbidden band, The recombination rate of charge carriers is rapid and this mostly occur within picosecond and nanosecond, so lead to its low photocatalysis activity and can not be applied widely and actually. At present, it is one of main directions to improve the photocatalysis property of nanometer TiO₂, the research mainly focus on the modification of nanometer powders and nanometer films, but the photocatalysis property is still low. TiO₂ nanotubes have more specific surface area than nanometer powders and nanometer films, it is a kind of new approach to improve the photocatalysis property of nanometer TiO₂ by prepare nanometer TiO₂ to nanotube, but there are seldom researches about this at home and abroad. The researches on the preparation and photocatalysis property of rare earth ions doped TiO₂ nanotubes is scarcely reported.In this thesis, the rare earth ions doped titanium dioxide nanotubes are prepared by sol-gel method using Anodic Aluminum Oxide (AAO) film as template. The photocatalytic properties of doped and undoped nanotubes and nanopowders were researched by degrading the methyl orange solution. The degradation mechanism and the influence mechanism of photocatalytic properties by rare earth ions doped are researched. The main researches of this thesis include the preparations and studies of templates and nanotubes:AAO films were prepared by two-step anodizing in sulfuric and oxalic acid solutions. The AAO films can be used as template of TiO₂ nanotube, which thickness is about 1～4μm and the apertures on it are about 100nm and uniform. The samples are observed by field emission scanning electron microscope (SEM), transmission electron microscope (TEM) and X-ray diffraction(XRD).The formation mechanism of film and array holes is researched. The formation of the AAO film and array holes could be explained based on the present experiment and some former models. The La-doped, Ce-doped and La-Ce co-doped anatase TiO₂ nanotubes and nanopowders are prepared by sol-gel method using porous anodic alumina as template with C₁₆H₃₆O₄Ti as precursors. The samples are observed by field emission scanning electron microscope (SEM), transmission electron microscope (TEM), specific surface area measurement (BET), fluorescence spectrometer(FS) and X-ray diffraction(XRD).The formation mechanism and influencing factors are researched.The external diameters of TiO₂ nanotubes are 80～130nm and the internal diameters are 50～70nm, the diameters are uniform in this experiment condition. The TiO₂ nanopowders are made by sol-gel method at the same conditions, their particle sizes are 20～30nm and the diameters are uniform.At the irradiation of 15W ultraviolet light source, after 150min, the results of photodegradation show that the photocatalytic properties of TiO₂ nanotubes are better than those of nanopowders, the doped nanotubes are better than those of undoped nanotube. The degradation rate of La-doped anatase TiO₂ nanotubes is 89.11%, the degradation rate of Ce-doped anatase TiO₂ nanotubes is 76.87%, the degradation rate of 0.3%La-1.5%Ce doped anatase TiO₂ nanotubes is 95.24%. The orthogonal test shows that the photocatalytic property is optimal at the 0.3%La-1.5%Ce doped content.The photocatalytic properties of TiO₂ are improved because that the TiO₂ electron-hole pairs of recombination probability is reduced with the rare earth ions doped in. The specific surface areas of TiO₂ are greatly increased when it become to nanotube, this made the catalytic activities increasing and the photocatalytic properties improved further.This research provides a kind of new approach to improve the photocatalysis property of TiO₂ and made the application of nano TiO₂ to become extensive and substantive in many fields.