Sol-gel-derived photosensitive TiO 2 and Cu/TiO 2 using homogeneous hydrolysis technique
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Titania and copper-loaded titania were synthesized by an improved sol-gel method using a homogeneous hydrolysis technique. Unlike the conventional sol-gel procedure that added water directly, the esterification of anhydrous butanol and glacial acetic acid provided the hydrolyzing water. In addition, acetic acid also served as a chelating ligand to stabilize the hydrolysis-condensation process and minimize the agglomeration of titania. Fourier transform infrared spectra confirmed the presence of bidental ligand. The sol was dried, then calcined at 500 °C to remove organics and transformed to anatase titania. Transmission electron microscopy revealed that the titania particles were uniform, and the particle size ranged from 10 to 25 nm. The band gaps of TiO2 and Cu/TiO2 ranged from 3.01 to 3.17 eV based on the diffusive reflective ultraviolet-visible spectrometry. X-ray photoelectron spectroscopy analysis showed a positive shift of binding energy of Ti 2p3/2 and a negative shift of Cu 2p3/2 in Cu/TiO2. The redistribution of electric charge is due to the Schottky barrier of Cu and TiO2.
I. INTRODUCTION
The sol-gel process is one of the versatile methods for preparing ceramic materials. Currently, the sol-gel process is employed quite often for synthesis of nano-sized catalytic materials. The incorporation of an active metal in the sol during the gelation stage allows the metal to have a direct interaction with support; therefore the material posseses special catalytic properties. As is well known, titania is a photoexcited catalyst. Although titania-supported metal catalysts have been extensively studied, their photocatalytic properties are still of great interest. Greenhouse gases such as CO2, CH4, and chlorofluorocarbons (CFCs) largely account for global warming. Much research has been reported that CO2 can be transformed to light hydrocarbons by photocatalysts such as TiO2 in an aqueous solution.1,2 Titania-supported copper plays a significant role in promoting the reducing CO2.3 Cu/TiO2 was also reported as an effective photocatalyst in purification of contaminated ground water. Enhancing photoreaction of titania is one of the most challenging tasks in environmental catalysts. One of the difficulties in sol-gel procedures is that the hydrolysis of titanium alkoxide is very sensitive to water. Even if the solution of titanium alkoxide is stirred viga)
Address all correspondence to this author. e-mail: [email protected] J. Mater. Res., Vol. 16, No. 2, Feb 2001
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orously, the hydrolysis rate is so fast that titania particles precipitate once water is added. This study presents an improved method of preparing TiO2 sol by controlling the hydrolysis of titanium alkoxide through the slowly released esterification of water from acetic acid and butanol. Furthermore, Brinker and Scherer reported that the use of acetic acid also resulted in the formation of stable complexes between the alkoxide and the acetate.4 Such a concept could also apply to other metal alkoxi
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