Preparation and characterization of visible light sensitive Fe- and Ta-codoped TiO 2 photocatalyst
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Titania (TiO2) was modified by codoping of Fe3+ and Ta5+ to absorb visible light. The codoped titania [(Fe,Ta)xTi1–xO2, 0 x 1] were prepared by a solid state reaction or by the polymer complex method. With increased codoping, the optical absorption spectra are red-shifted and the color ranges from white to brown via yellow. Also, the codoped titania (0 < x 0.05) possesses photocatalytic activity for organic decomposition under visible light irradiation. The codoped titania (x = 0.01) with yellow color shows the highest activity among the codoped titania (0 x 1) and a higher activity than the 1% Fe3+-doped TiO2 with orange brown color. I. INTRODUCTION
Titania (TiO2) is widely applied for cosmetics, paints, photocatalysts, and so on, because this oxide is harmless and inexpensive.1–6 In photocatalysis, electrons in the valence band (VB) of TiO2 are excited to the conduction band (CB) by UV (ultraviolet) light irradiation and holes are generated in the VB. The holes have an oxidizing potential strong enough to decompose harmful organics into harmless substances, such as CO2 and H2O.7 Using these properties, TiO2 photocatalysts have been available for self-cleaning outdoor walls, windows, and so on.1 At present, however, usage of this photocatalyst is almost completely limited to outdoor application because TiO2 is not sensitive to visible light and UV light is little emitted by indoor illumination. To overcome this problem, development of photocatalysts with visible light sensitivity has been investigated8–15 because indoor illumination emits a much stronger intensity of visible light. Doping of a metal ion, such as Cr3+, Fe3+, or V5+, into a Ti-containing oxide is one method of narrowing the band gap.16–20 However, doping of an aliovalent cation including Cr3+ often leads to the formation of defects, and improvement of the photocatalytic activity is limited. In the case of Cr3+-doped materials, codoping of a pentavalent ion is promising because charges are compensated for and the formation of defects decreases by codoping. For example, Cr3+- and Ta5+-codoped SrTiO3 was reported to have a better activity for H2 evolution from a)
Address all correspondence to this author. e-mail: [email protected] This author was an editor of this focus issue during the review and decision stage. For the JMR policy on review and publication of manuscripts authored by editors, please refer to http:// www.mrs.org/jmr_policy DOI: 10.1557/JMR.2010.0004 110
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J. Mater. Res., Vol. 25, No. 1, Jan 2010 Downloaded: 14 Mar 2015
water under visible light irradiation by photocatalytic reduction, in comparison with Cr3+-doped SrTiO3.21 For this codoped oxide, however, photocatalytic oxidation for organic contaminants has not been reported, and Cr3+ is not suitable for application of harmful organic gas oxidation and decomposition because this ion is harmful. In this study, harmless Fe3+ was selected as a doping cation and Fe3+- and Ta5+-codoped TiO2 was prepared as a candidate visible light sensitive ph
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