Synthesis and characterization of TiO 2 nanocrystalline powder prepared by homogeneous precipitation using urea
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Hang Chul Jung and Jong Kook Leea) Division of Metallurgical and Materials Engineering, Chosun University, Gwangju 501-759, Korea (Received 12 August 2002; accepted 12 November 2002)
TiO2 nanocrystalline powder was synthesized by homogeneous precipitation method using urea, and its characteristics were investigated through comparison with the powder prepared by conventional precipitation using ammonia. The homogeneously precipitated powder was anatase-type TiO2 with a particle size of 4–5 nm and a uniform spherical particle shape. The fact that the transformation from anatase to rutile was prohibited at elevated temperatures in the homogeneously precipitated powder can be useful to prepare anatase-type TiO2 thin films by calcination at high temperatures. With increasing heat-treatment temperature, the particle size of the homogeneously precipitated powder was smaller than that of the conventionally precipitated powder, and the particle shape was more uniform. The homogeneously precipitated powder showed good photocatalytic activity for Ag ion photoadsorption because the powder had both good crystallinity and a large specific surface area of 280 m2/g.
I. INTRODUCTION
In recent years, titania has been a well-known material with high photocatalytic activities, in which electrons and holes, generated by ultraviolet-visible light, subsequently initiate oxidation and reduction.1 Titania has been widely studied for applications in water purification by degradation of hazardous contaminants or spilled oil, and in air purification, such as decomposition of NOx and improvement of living conditions by removal of various pollutants.2,3 In addition, the reason why titania has had considerably more attention than ZnO,4 CdS,5 and ZrTiO46 photocatalysts is because it has characteristics such as chemical stability, endurance, thin-film transparency, and lower production costs.7 TiO2 is a polymorphic substance present in three crystalline phases of anatase, rutile, and brookite, each with different structures and properties. Of these, anatase or rutile phase TiO2 has been mostly applied for photodecomposition as photocatalysts; however, it is generally accepted that anatase shows higher photocatalytic activity than rutile.8 One of the most important requirements for good photocatalysts is that TiO2 powder has good crystallinity with a large specific surface area. As the photocatalytic reaction occurs at the TiO2 surface, the reaction area a)
Address all correspondence to this author. e-mail: [email protected] J. Mater. Res., Vol. 18, No. 3, Mar 2003
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between the surface of particle and the target materials (that is, the specific surface area) needs to be large for more effective photocatalytic activity. We recently synthesized anatase- and rutile-type TiO2 nanocrystalline powders with large specific surface area at low temperatures by aging titanium hydroxide precipitates obtained from the reaction between TiOCl2 and NH4OH solutions.9,10 Instead of using NH4OH as a pr
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