Sol-gel prepared InTaO 4 and its photocatalytic characteristics
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Hsin-Yu Lin Department of Materials Science and Engineering, National Dong Hwa University, Hualien, Taiwan 97401 (Received 9 October 2007; accepted 30 January 2008)
InTaO4 is an efficient visible-light photocatalyst, which used to be synthesized by solid-state fusion at over 1100 °C. However, irregular morphology and severe agglomeration of particles were acquired due to nonuniform fusion of solid precursors. In this study, InTaO4 was synthesized by two sol-gel routes, the thermal hydrolysis and esterification methods. The precursors were indium (III) nitrate pentahydrate [In(NO3)3] and tantalum(V) butoxide [Ta(OC4H9)5] dissolved in solutions. The InTaO4 powders with a uniform grain size of 17.7 nm were successfully synthesized using the esterification method at a calcination temperature of 950 °C. A uniform InTaO4 thin film nearly 40 nm thick formed on an optical fiber at 1100 °C using the sol prepared by the esterification method. For the first time, InTaO4 was evaluated by the photocatalytic activity of CO2 photo reduction, which was conducted in aqueous solution under visible light irradiation. Cocatalyst NiO was loaded on the surface of InTaO4 to further enhance the methanol yield. The methanol yields of NiO/InTaO4 by esterification method were significantly higher than those by solid-state fusion. The esterification method provided homogeneous mixing of Ta(OC4H9)5 and In(NO3)3, resulting in nano-sized InTaO4 with uniform crystallinity and superior photocatalytic activity.
I. INTRODUCTION
Fossil fuels have always been the main source of energy for human beings. In recent centuries, thriving industrial developments create a large amount of pollutants, including carbon dioxide, nitric oxide, etc. One of the greenhouse gases, CO2, is the primary cause of global warming. Simultaneously, the reserve of fossil fuel has decreased dramatically. Owing to the serious energy shortage and environment problems, decomposing chemical compounds photocatalytically under sunlight by using oxide semiconductors has received a lot of attention recently. Since the first experiment of H2 evolution via TiO2 photocatalyst several decades ago,1 abundant research has been directed towards the development of photocatalysts capable of splitting water into H2 and O2. Besides water splitting, researchers have also shown that CO2 can be photocatalytically reduced to hydrocarbons in solvent or water vapor by photocatalysts such as ZnS and TiO2.2,3 Equation (1) shows an example of the overall reaction. a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2008.0172 1364 J. Mater. Res., Vol. 23, No. 5, May 2008 http://journals.cambridge.org Downloaded: 03 Aug 2014
CO2 + 2H2O → CH3OH +
3 O . 2 2
(1)
The process for photocatalysis of semiconductors is considered a direct absorption of photons following the generation of electron–hole pairs in the semiconductor particles. The excitation of an electron from the valence band to the conduction band is initiated by light absorption with energy equal to or great
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