Enhancing Effects of Ultrasound Treatment on the Preparation of TiO 2 Photocatalysts
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Enhancing Effects of Ultrasound Treatment on the Preparation of TiO2 Photocatalysts Sung-Yeon Kim Æ Tae-Sun Chang Æ Chae-Ho Shin
Received: 3 April 2007 / Accepted: 17 June 2007 / Published online: 17 July 2007 Springer Science+Business Media, LLC 2007
Abstract TiO2 nanoparticles were synthesized by the hydrolysis and condensation of TiCl4 in a mixed solvent of iso-propyl alcohol and water with or without ultrasound treatment. As-prepared powders were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy filtering transmission electron microscopy (EF-TEM), particle size analysis and BET surface area analysis. The specific surface area, thermal stability and crystallization of the as-prepared samples treated with ultrasound were higher than those of samples treated without ultrasound. To examine the photocatalytic activity of the as-prepared TiO2, the photodegradation of MB which is a typical dye resistant to biodegradation has been investigated on TiO2 powders in aqueous heterogeneous suspensions. The photocatalytic degradation of a aqueous solution of methylene blue shows a remarkable increase when it is carried out with ultrasound in all cases. Keywords TiO2 Photoactivity Methylene blue Ultrasound TiCl4
1 Introduction TiO2 has a variety of functional applications ranging from pigments to photoconductors, sensor materials and S.-Y. Kim C.-H. Shin (&) Department of Chemical Engineering, Chungbuk National University, Cheongju, Chungbuk 361-763, Korea e-mail: [email protected] T.-S. Chang (&) Advanced Chemical Technology Division, Korea Research Institute of Chemical Technology, Daejeon 350-343, Korea e-mail: [email protected]
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dielectric ceramics. The material has also been studied extensively in recent years as a photocatalyst to deal with environmental pollution, water purification, wastewater treatment, hazardous waste control and air purification. The photocatalytic activity of TiO2 nanoparticle is greatly influenced by its crystal structure, particle size, surface are and porosity. When the size of TiO2 particle is decreased to nanometer scale, the catalytic activity is enhanced because the optical band gap is widened due to the quantum size effect, combined with the increased surface area [1]. Titania has three different crystalline phases; rutile, anatase and brookite, among which rutile is in the thermodynamically stable state while the latter two phases are in the metastable state. Various kinds of methods including the sol–gel method [2], vapor decomposition of titanium alkyloxides or TiCl4 in oxygen [3, 4], the hydrothermal technique [5], the reversed micelle method titania nanostructures [6], and oxidation of metallic Ti powder [7] were used to prepare titania nanostructures. The sol–gel method is widely used to prepare nanometer TiO2, but the precipitates derived by sol–gel are amorphous in nature, and require further treatment to induce crystallization. The hydrothermal technique is widely employed to enhance crystallization at bot
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