Niobium and tantalum doped titania particles
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um and tantalum doped anatase were prepared by thermal hydrolysis of peroxotitanium complex aqueous solutions containing of niobium or tantalum peroxocomplexes at 100 C for 3 days. Niobium-doping increased the unit cell constants of anatase and changed the morphology of TiO2 from spindle-like to rectangular or square cross section. Nb and Ta doping in the TiO2 nanostructure increases the anatase to rutile transformation temperature to >1000 C. In the visible region, the photocatalytic activity is directly proportional to the concentration and increases with increasing of Nb concentration. The niobium addition enhances the photocatalytic activity of titania in the visible light region.
I. INTRODUCTION
Several ultraviolet (UV)/semiconductor systems have been used for photocatalytic degradation of organic pollutants. Most of these semiconductor particles are metal oxides, such as TiO2, WO3, ZnO, and Fe2O3, and metal chalcogenides such as CdS and MoS2. Titanium dioxide is predominantly used as photocatalyst because TiO2 has high catalytic activity due to the long lifetime of e–/hþ pairs and the appropriate band edge position. More specifically, TiO2 assisted photocatalysis offers the following advantages: TiO2 is inexpensive, nontoxic, biologically stable, the light required to activate the photocatalyst is near ultraviolet radiation, making the use of solar light possible and the TiO2 surface is fully hydroxylated with these hydroxyl groups being the precursors of the OH radicals. The photocatalytic decomposition of organic matter depends on the creation of OH radicals on the surface of TiO2 particles. The band gap of anatase is 3.2 eV and lies in the UV range so that only 5–8% of sunlight photons have the required energy to activate the catalyst. This relatively large band gap has significantly limited application, particularly in indoor situations. An effective way to improve the TiO2 photocatalytic activity is to introduce dopants into its lattice. Depending on the dopant type and concentration, the band gap of TiO2 can be tailored to extend the photo-responsiveness into the visible light region. The interest in Nb-doped TiO2 derives from the fact that Nb doping leads to enhanced photocatalytic activity in the destruction of many organic pollutants.1 According to the available literature, the most a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2010.0252 J. Mater. Res., Vol. 25, No. 10, Oct 2010
common methods of preparation of TiO2 are based on organometallic compounds of titanium. Nb-doped titania (3%) was prepared from alkoxides precursors via the sol-gel route in dry nitrogen from titanium isopropoxide (IV) Ti[OCH(CH3)2]3 and niobium ethoxide Nb(OC2H5)5 with a 99.99% purity.2 It has been also reported that Nbdoped titania shows higher sensitivity toward oxygen and shorter response time than pure TiO2.3 The study4 evaluated the possibility of preparing the pure rutile phase of Nb5þ and Ta5þ doped TiO2 at low temperature (400 C) by the sol-gel process. The doping o
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