High-concentration niobium (V) doping into TiO 2 nanoparticles synthesized by thermal plasma processing
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Masashi Ikeda Nano Ceramic Center, National Institute for Materials Science, Tsukuba, Ibaraki 305-0044, Japan; and Department of Materials Chemistry, Hosei University, Koganei, Tokyo 184-8584, Japan
Tetsuo Uchikoshi Nano Ceramic Center, National Institute for Materials Science, Tsukuba, Ibaraki 305-0047, Japan
Ji-Guang Li Nano Ceramic Center, National Institute for Materials Science, Tsukuba, Ibaraki 305-0044, Japan
Takayuki Watanabe Department of Environmental Chemistry and Engineering, Tokyo Institute of Technology, Yokohama, Kanagawa 226-8502, Japan
Takamasa Ishigakia) Nano Ceramic Center, National Institute for Materials Science, Tsukuba, Ibaraki 305-0044, Japan; and Department of Chemical Science and Technology, Hosei University, Koganei, Tokyo 184-8584, Japan (Received 11 October 2010; accepted 10 January 2011)
High-concentration niobium (V)-doped titanium dioxide (TiO2) nanoparticles of the nonequilibrium chemical composition have been synthesized via Ar/O2 radio-frequency thermal plasma oxidation of mist precursor solutions with various Nb5+ concentrations (Nb/(Ti + Nb) 5 0–25.0 at.%). The solubility as high as ;25.0 at.% has not been achieved before by wet-chemical techniques. The preferable anatase formation was attained in the plasma-synthesized powders and was enhanced by the niobium doping. All the powders were heated at high temperatures (600–800 °C) to investigate their phase transformation, band gap variation, inter-particulate binding behavior, and photocatalytic stability. The transformation from anatase to rutile was effectively inhibited by increasing the Nb5+ content. The Nb5+ doping prevented the band gap of TiO2 from narrowing after the heating. At high temperatures, Nb5+ doping could not only preserve particle size but also prevent inter-particulate binding. High concentration (25.0 at.%) Nb5+ doping retained the photocatalytic performance almost invariably irrespective of being thermally treated.
I. INTRODUCTION
Titanium dioxide, TiO2, as one of the well-known oxide semiconductor materials has been extensively investigated for many applications, such as photocatalysis,1 solar energy,2 gas sensors,3 phosphors,4 and dilute magnetism,5 because of its outstanding properties including remarkable chemical and thermal stabilities, high transparency in the visible region, and high refractive index. It usually exists in two polymorphs: anatase (tetragonal, space group:D19 4h ) and rutile (tetragonal, space group:D14 4h ). These phases present quite different arrangements of structure-building blocks (Ti–O octahedrons).6 Specifically, in rutile, each a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2011.16 658
J. Mater. Res., Vol. 26, No. 5, Mar 14, 2011
http://journals.cambridge.org
Downloaded: 14 Mar 2015
octahedron provides two opposing edges, which are shared to form linear chains along the [001] direction, thus TiO6 chains are linked to each other via corner connection, whereas anatase has four shared edges per octahedron instead of shared co
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