Investigation On The Preparation Of TiO₂ Fibers And The Micro-nano TiO₂ Sheets Arraying On The Fibers

Titanium oxide possesses excellent photocatalytic properties, and it exhibits obvious advantages and has been widely used in pollutant degradation. At present, the main application forms of titanium oxide are nanopowders and thin films which have some drawbacks such as difficult recovery after reaction and poor fixed technology, and limit the application in photocatalysis area. The titanium oxide fibers can avoid these problems.Titanium oxide fiber is a kind of widely used oxide fiber in optical degradation, hydrogen production, solar cells and etc. It is the polycrystalline fibers composed with nanocrystals. Titanium oxide fiber can be free inspreading in the solution, realize the effective optical absorption and full contact with solution, and be easily separated from the water (the most important) in the photocatalytic reaction process. Hence, it could improve the reaction efficiency.Titanium oxide fibers were prepared successfully by the use of polyorganotitanium precursor method by our research group at the beginning of the century. The corresponding technique has been obtained a national invention patent. However, there are some disadvantages in the previous preparation process such as complicated preparation procedures, expensive raw materials, hard reaction conditions, long reaction time and etc. As part of continuous work, the preparation method of titanium oxide fibers was improved based on centrifugal-spinning technique with the polyorganotitanium precursor solution. Improved the preparation method of titanium oxide fibers and simplify the preparation process and reaction condition, meanwhile, the molecular structures of the precursors were assumed. Based on the modified titanium oxide fibers, for example, loaded the single crystal on the surfaces of titanium oxide fibers and doped with SiO2 and Fe2O3, the photocatalytic properties of titanium oxide fibers were improved. The main research contents of the thesis are as follows:1. Study on the preparation of titanium oxide fibersIn order to solve the complicated preparation procedures, using the different precursors, the titanium oxide fibers of excellent photocatalytic performance were preparedThe two kinds of precursors of titanium oxide fibers, polyacetylacetonatotitanium (PAT) and polyacetictitanium (PET) were prepared. The structures of the two precursors were conferred. The molecular structural formulas were provided. By the use of PAT and PET, the precursor fibers were prepared by comparison, one-pot PAT and 1:3 (MTC:MKAc) PET are better for obtaining titanium oxide fibers.Titanium oxide fibers were prepared by the use of PAT and PET, respectively. The crystallization, morphology, grain size distribution, pore size distribution and photocatalytic properties of titanium oxide fibers were characterized and compared with each other. The photocatalytic degradation activities of these samples followed the sequence of S1>P25>S3>S4>S2>S5>S6. The photocatalytic ability of S1 is best among them. The diameter of the fibers prepared from one-pot PAT precursor were about 2-5 μm. The crystallographic form is anatase and the configuration of the crystallographic grain was compact.2. Modification of the titanium oxide fibers to improve the photocatalytic propertiesIn order to improve the photocatalytic performance of titanium oxide fibers, loaded the single crystal on the surfaces of titanium oxide fibers, they were explored in the following aspects:First of all, PAT and PET as titanium sources, HF as the profile controlling agent, isopropyl alcohol as capping agent, titanium oxide single crystal particles were prepared under the alcohol thermal conditions. The grains (PAT as titanium source) are mainly dispersed single crystal flakes, the length of the particles was 50～80 run, the thickness was 15～30 nm. The microspheres were composed with single crystals when PET as titanium source preparation. The diameter of microspheres was 1～3 μm, the length of the single crystal flake is ～100 nm.Secondly, the preparation of single crystal flakes was combined with that of titanium oxide fiber using PAT and PET as’the titanium sources, HF as a capping agent, isopropyl alcohol as the solvent. The titanium oxide fibers were put into a Teflon-lined autoclave, and the mixture was kept at 180 ℃ for 24 hrs. The single crystal flakes (PAT) and microspheres (PET) were loaded onto the surfaces of titanium oxide fiber. The photocatalytic performance of the fibers has been greatly improved. The (001) crystal plane was confirmed by XRD, FE-SEM, HR-TEM and atomic force microscopy (AFM).The photocatalytic performance increased 3-5 times compared with that of P25 evaluated by the degradation of methyl orange under UV light irradiation with the help of a 350 W Hg lamp.Finally, diethylenetriamine (DETA) was doped into PAT with different ratios to adjust the crystallographic plane of the crystal particle for titanium oxide fiber. The grain morphology of titanium oxide fibers were compared by FE-SEM and etc with the different incorporations. The higher the mixed amount of DETA, the more ideal the grain morphologies. The crystallinity was decreased.3. Improve the photocatalytic performance of titanium oxide fibers by increasing the specific surface area or widening the absorption band of the fiberUsing PAT as the titanium source, ethyl orthosilicate tetraethyl silicate as the silicon source, Si-doped titanium oxide (TiO2-Si) fibers were prepared. The specific surface area of TiO2-Si fibers is one time higher than that of TiO2 fibers.The Fe-doped titanium oxide (TiO2-Fe) fibers was prepared using PAT as the titanium source and Fe(NO3)3 as the iron source. The main advantage of TiO2-Fe fibers was that the absorption band moved from ultraviolet to visible light range and the photocatalytic degradation of TO2-Fe fibers in the visible light region is much higher than that of pure TiO2 fibers.In the dissertation, the titanium oxide fibers were prepared by using polyorganotitanium precursor method. The method of one-step PAT is simple and the photocatalytic efficiency is better than that of P25. The titanium oxide single crystal particles with (001) and (101) were prepared under the alcohol thermal conditions. The sheets and microspheres with (001) and (101) were loaded onto the surfaces of the titanium oxide fibers successfully. The photocatalytic performance was improved significantly. Two kinds of titanium oxide fibers, TiO2-Si and TiO2-Fe fibers were prepared. Among them, the specific surface area of TiO2-Si fibers was increased significantly, and the absorption band of TiO2-Fe fibers was widened.