The Preparation Of Self-cleaning Titanium Dioxide Films By Sol-gel

As one kinds of oxide semiconductor thin film materials, the Titanium dioxide(TiO₂) thin films are studied in the most broad, it's super-hydrophilic ability and self-cleaning effect lead to a new research field in the photocatalysis function thin film materials. First, This thesis introduced the current research situation at home and abroad, the existed questions and the developing prospects. Then the photocatalyst and super-hydrophilicity's working principles and effect factors of TiO₂ are introduces in detailed.Because of the wide band gap(3.2eV), the absorption thresholds correspond to 380nm for the TiO₂ consequently, only the ultraviolet fraction of the solar irradiation can be active in the photo-excitation processes using pure TiO₂ solid. The high recombination rate of charge carrier, low efficiency of quantization and the recovery of TiO₂ thin film's hydrophilicity are also the deficiencies of the pure TiO₂. For the TiO₂ thin film's self-clean ability need to improve, this paper focus on the doped TiO₂ and structural modification by using sol-gel method combined dip-coating on glass slides, and to compose the TiO₂ thin film and Si-doped TiO₂, Fe-doped TiO₂, SiO₂/Fe₂O₃/TiO₂ composite films, the X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy and the contact angle meter are used to express the photocatalytic activity and ultra-hydrophilic-property, and have discussed the relationships of the compositions of TiO₂ complex thin films, the structural and the properties.The experimental results show that: while increasing the SiO₂ contents, the crystal phase have a trend to low-temperature phase (anatase), with the size of crystal particles decreased and become uniform. The thinning particles promote effective separation of the electronic-hole pairs, with the TiO₂'s BET increased, which enhance the absorption of reactants abilities, so improved the SiO₂/TiO₂ complex powder's photocatalitic activities. Special for the molar concentration of SiO₂-doped is 5% , and heat-treatment at 450℃, the SiO₂/TiO₂ composite powder have an excellent photocatalytic activity abilities for degrading the methyl orange (10mg/L) under the UV-light irradiation, 4h later, the degradation rate is 36.7%. For the surface roughness and acidity had increased, the SiO₂/TiO₂ composite complex thin films surface can be absorbed more hydroxy water, and show its excellent super-hydrophilic ability. Special for the 4 layers SiO₂/TiO₂ composite complex thin films, the light-induced super-hydrophilic ability is the best, and the water contact angle decreased from 44.46°to 6.42°after 80 minute UV-light illumination.As to the Fe-doped TiO₂ composite films, when the Fe energy level intervenes the TiO₂ composite thin films, the electronic transition energy level is changed. The absorption band to the light have a little red shift, which can improve the photocatalitic activities and the super-hydrophilic abilities of TiO₂ under the visible light irradiating. While the doping quantities of Fe³⁺ ion increasing, the degradation rate of the Fe-doped TiO₂ composite powder for the methyl orange solution exist a trend, rising at first and getting down at the end. Special for the molar concentration of Fe-doped is 0.5%, the photocatalitic degradation effect under the UV-light irradiation is the best, and the degradation rate is 42.4% 4h later. Because of the Fe³⁺ ions become Shallow potential capture Center, the action restrains the Photo-generated electron-hole pairs to recompound, so the high concentration of oxide holes existed the Fe-doped TiO₂ composite thin films surface, and the hydrophilic ability is enhanced. The experimental results confirm that the best adulterate molar concentration of Fe is 0.5%, under the UV-light irradiation, 6 hours later, the water contact angle decreases to 7.07°.The Fe-doped can improve the TiO₂ complex thin film's Photosensitivity, and the doped Si-doped can ameliorate the super-hydrophilic ability of the complex films, but the (Si-Fe) co-doped can not improve the photosensitivity and the hydrophilic ability of the TiO₂ complex thin film at the same time.At the last, the work in dissertation was generalized and the problems which were unsolved in paper were represented base of this, and the orientation of research which is to improve the photocatalytic activity or super-hydrophilic ability of the TiO₂ complex thin film in future was pointed out.