Fabrication of mesoporous bulk composed of titanate nanotubes by hydrothermal hot-pressing technique
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Yuki Yamasaki Department of Materials Science, Osaka Prefectural College of Technology, Neyagawa-shi, Osaka 572-8572, Japan (Received 13 September 2006; accepted 18 January 2007)
In this study, bulky titanate nanotubes with dense microstructures were successfully fabricated by a hydrothermal hot-pressing (HHP) technique with water as a reactive solvent. Titanate-based nanotubes of about 10 nm outer diameter and 5 nm inner diameter and a few hundred nanometers in length were synthesized by a hydrothermal treatment of anatase-type TiO2 powder in a 10 M NaOH aqueous solution. From results of N2-adsorption and transmission electron microscopy observation, it was obvious that HHP processed samples were composed of nanotubular structures and that the obtained bulks possessed mesopores and high Brunauer–Emmett–Teller surface area. These results suggested that the obtained bulks possessed functionality as good as that of powders of titanate nanotubes. Thus, the HHP technique may be a useful method for fabricating bulky titanate nanotubes and may be applied in the solidification of the other some nanotubular materials. I. INTRODUCTION
The development of synthesis methods for various nanoscale materials is currently under intensive investigation. Titanate-based nanotubes, which are prepared by a hydrothermal treatment of TiO2 particles in a concentrated NaOH aqueous solution,1–4 are expected to be useful for various applications such as photocatalysts and solar cells, etc., due to their nanotubular structures and high surface areas. Recently, many studies have been performed on the development of the high photocatalytic and novel functional nanotube materials such as N2-doped titanate nanotubes5 and noble metals such as Pt-entrapped titanate nanotubes.6 In addition, the TiO 2 -derived nanotubes with layered structures (NaxH2−xTi3O7 or H2Ti3O7), synthesized by a soft chemical hydrothermal treatment of TiO2 with a NaOH aqueous solution, such as sodium or hydrogen titanate, exhibit ion exchange, optical, and magnetic properties.7 In addition, preparations of thin film for these nanotubes have been attempted.8,9 On another front, no study on fabrication of bulky titanate nanotubes has been performed. The application area of titanate nanotubes can be expected to expand if the fabrication of bulky titanate nanotubes becomes possible. Although fabrication of the bulky titanate nanotubes has been attempted by various a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2007.0160 1286
J. Mater. Res., Vol. 22, No. 5, May 2007
methods in our work, a bulk with high density and nanotubular structures was difficult to fabricate. For example, in the case of the bulks solidified with silicate, nanotubular structures were filled with amorphous phase as a binder. Also, the sintered body of titanate nanotubes could not be fabricated because they could not keep nanotubular structures at high heat. Therefore, it is necessary to develop a novel process for bulk nanotubes. In this study, we focused
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