Photocatalytic activity of TiO 2 prepared at low temperature by a photo-assisted sol-gel method
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TiO2 nanocrystals were prepared by a photo-assisted sol-gel process in which tetrabutoxide titanate was hydrolyzed in acidic medium under ultraviolet irradiation. X-ray diffraction and Raman spectra showed that the as-prepared TiO2 particles without further annealing were well-crystallized anatase. Such TiO2 particles were easily immobilized on dacron cloth and showed very high photocatalytic activity. In contrast, TiO2 particles were ill crystallized and showed lower activity when no light was introduced under otherwise equal conditions.
Titania has been an important object of the sol-gel chemistry partly due to its wide applications in environmental technology, including photocatalysts for degradation of organic pollutants, superhydrophilic coating, self-sterilizing materials, etc.1–3 Sol-gel derived TiO2 particles are generally amorphous or less-crystallized in nature, requiring further heat treatment to improve crystallinity. However, the annealing process makes it difficult to prepare high photoactive TiO2 coatings on thermolabile substrates, such as textiles, paper, and plastics, which are extensively used in many industrial and commercial fields. In particular, high photoactive TiO2 coated on the porous and ventilative textile may be very suitable for purifying waste water and air. So it would be very interesting and challenging to prepare wellcrystallized TiO2 nanoparticles at low temperatures. Recently, there has been much interest in applying ultraviolet irradiation in sol-gel synthesis of functional materials. Besides the photoreduced preparation of noble metal nanocrystals such as Au,4 Ag,5 and noble-metalbased nanocomposite materials,6 ultraviolet irradiation was also used to sharpen the size distribution of semiconductor nanoparticles including CdS, ZnS, and ZnO, etc. by photoetching process.7,8 More recently, it was found that ultraviolet irradiation could densify or even crystallize sol-gel-derived precursor coatings of SiO2, SiO2–TiO2, and ZrO2 at low temperatures.9–11 In this paper, we report a photo-assisted sol-gel method to prepare TiO2 nanocrystals at low temperatures. In a typical preparation procedure, a 500-W highpressure mercury lamp was used as an ultraviolet
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Address all correspondence to this author. e-mail: [email protected]. J. Mater. Res., Vol. 16, No. 4, Apr 2001
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irradiation source. Two milliliters of tetrabutoxide titanate (TBOT) dissolved in 20 ml of ethanol was mixed with 1 ml of concentrated hydrogen chloride under ultraviolet irradiation. The reaction temperature was controlled at 323 K, and the distance between lamp and reactor was about 10 cm. Ultraviolet irradiation persisted for an hour, and then the mixture was aged further at room temperature. The resulting sol was very stable for several months. For comparison, we also prepared TiO2 colloids by the conventional sol-gel process in which no irradiation was used during hydrolysis of TBOT. Both sols were dried in a rotary evaporation after aging for 24 h and used to c
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