Synthesis Of TiO₂-based Nano-sized Photocatalysts And Their Applications In Photocatalysis And Superhydrophilicity

In order to improve the photocatalytic activity and super-hydrophilicity of TiO2, the following three parts of work have been done:(1) In the present work, a series of silica-embedded nanocrystalline titania powders with variable Si/Ti ratios have been prepared by ultrasound-assisted hydrolysis. The prepared samples were characterized by thermal analysis (DTA-TG), X-ray diffraction (XRD), FTIR spectroscopy, scanning electron microscopy (SEM), X-ray energy dispersive spectrometer, and nitrogen adsorption-desorption. Photocatalytic activity was checked by the photocatalytic oxidation of formaldehyde in air. Correlations between the microstructure and the photocatalytic activity of the prepared powders were observed. The results showed that improved photocatalytic activity relative to titania-only materials can be made by fabricating silica/titania composite materials through ultrasound-assisted hydrolysis processing, the highest photocatalytic activity was obtained when silica content was 10 wt.% and three times higher than that of Degussa P25. The improved photocatalytic activity was achieved by quantization of particle size, increase of surface area and hydroxyl content through embedding silica into anatase titania matrix. Ultrasonic irradiation obviously enhances the photocatalytic activity of the prepared powders due to the fact that ultrasonic irradiation enhances hydrolysis of the alkoxide and crystallization of the gel.(2) The wettability of solid surfaces is a very important property governed by both the chemical composition and the geometrical structure of the surfaces. In this work, a mesh-like structure of aligned titania nanofiber film was synthesized by a sol-gel template process. The surface of the synthesized nanofibers, with the modification by trimethychlorosilane, was irradiated by UV light, and as-designed superhydrophilic surfaces were formed. The retention of hydrophilicity of nanofiber TiO2 is longer than plane TiO2. It is believed that the combination of the micro- and nanostructure of the nanofibers enhances the wettability. The retention of hydrophilicity of nanofiber TiO2 with SiO2 film is longer than nanofiber TiO2 without SiO2 film. This is attributed to that surface SiO2 contain a large quantity of Si-OH on its outermost surface.(3)The use of glass fibers in the form of woven cloth (GFC), as a new type of catalytic support, was studied for the decomposition of formaldehyde. Anatase TiO2 nanocrystalline thin films were deposited on GFC via the sol-gel method, and were characterized by X-ray diffraction, scanning electron microscopy, and UV-visible spectrophotometer. The removal efficiencies of TiO2 films were evaluated by the photocatalytic decomposition of gaseous formaldehyde in a continuous reactor. The results show that The average grain size is about 18nm of the resultant film, which exhibits excellence absorption (300-400 nm) in the UV spectral region, and the photocatalytic ability of the thin films was drastically changed with the coating amount and was capable of efficiently decomposing gaseous formaldehyde when the coating cycles reached 10 times.