| There has been a growing interesting recently in new methods to prepare thin film at ambient temperature in aqueous solution, as they are expected to develop novel processing method and manufacturing process, which are low cost and environmentally friendly. It is well known that the photocatalytic activity of TiO2 thin films strongly depends on the preparing methods, the properties of substrates and post-treatment conditions, since they give decisive influence on the chemical and physical properties of TiO2 thin films. Therefore, it is necessary to elucidate the influence of the preparation process, the properties of substrates, and post-treatment conditions on the photocatalytic activity and surface microstructures of the films.In the present work, we have prepared titania thin films on different substrates from a (NH4) 2TiF6 aqueous solution upon addition of boric acid by liquid phase deposition (LPD) method under the ambient temperature. The as-prepared TiO2 thin films were characterized by Infrared absorption spectra (FTIR), X-ray diffraction (XRD) patterns, UV-Vis transmittance and reflectance spectra (UV-vis), thermogravimetry (TG), scanning electron micrographs (SEM), Photoluminescence spectra (PL), and X-ray photoelectron spectroscopy (XPS). The photocatalytic activity of the samples was evaluated by the photocatalytic oxidation of nitrogen monoxide in the gaseous phase and the photocatalytic decolorization of methyl orange solution in the aqueous phase, respectively.The titania thin films on fused quartz were prepared by LPD method and then calcined at different temperatures. The results showed that the dense and uniform titania thin films can be deposited on quartz substrate. The as-prepared TiO2 thin films contained not only Ti and O elements, but also a small amount of F, N and Si elements. The F and N came from the precursor solution and the amount of F decreased with increasing calcination temperature. Two sources of Si were identified. One was from the SiF62- ions, which were formed by a reactionbetween the treatment solution and quartz substrate. The other was attributed to the diffusion of Si from the surface of quartz substrate into TiO2 thin film at 700 C or higher calcination temperatures. The calcination temperatures had a significant effect on the potocatalytic activity of TiO2 thin films. With increasing calcination temperature, the photocatalytic activity of the TiO2 thin films gradually increased due to the improvement of crystallization of the anatase TiO2 thin films. At 700 C, the TiO2 thin film showed the highest photocatalytic activity due to the increasing amount of SiO2 as an adsorbent center and better crystallization of TiO2 in the composite thin film. Moreover, the SiO2/TiO2 composite thin film showed the lowest PL intensity due to a decrease in the recombination rate of photo-generated electrons and holes under UV light irradiation, which further confirmed the film with the highest photocatalytic activity at 700 C. When the calcination temperature was higher than 700 C, the decrease in photocatalytic activity was due to the formation of rutile and the sintering and growth of TiO2 crystallites resulting in the decrease of surface area. The iron doped titania thin films on stainless steel were obtained by LPD method. It was found that some Fe3+ was in situ doped in the TiO2 thin films, showing obvious influence on the photocatalytic activity of the samples. The source of Fe 3+ was from two contributions, one from the [FeFg]3- ions formed by a reaction between the treatment solution and the stainless steel substrate and the other from the diffusion of Fe element from the stainless steel substrate into the TiO2 thin film at 500 C or a higher calcination temperature. The iron doped TiO2 thin films showed almost no photocatalytic activity for the photodegradation of NO in the gaseous phase when the calcination temperature was lower than 400 C. This was due to the fact that the phase structure of the film was amorphous. At 400 C, the film appeared obviously photoactive du...
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