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Breakthrough Method for Synthesizing Nanotechnology Materials (Press Release)

Release Date
11 Jul, 2011
  • BL15XU (WEBRAM)
- Manufacturing highly functional titanium oxide nanoparticles at a low cost

National Institute for Materials Science

A research group of the National Institute for Materials Science (NIMS; President, Sukekatsu Ushioda) succeeded, for the first time in the world, in synthesizing reduced titanium oxide (Ti2O3) nanoparticles with a crystal structure different from that of titanium dioxide*1 (TiO2) nanoparticles used as the precursor, while maintaining the nanosize structure (hereafter, nanostructure) of the TiO2 nanoparticles. Also, the reaction mechanism was determined using the beamlines at SPring-8. The research group of Satoshi Tominaka (Researcher), Yoshihiro Tsujimoto (Researcher), Yoshitaka Matsushita (Senior Engineer), and Kazunari Yamaura (Senior Researcher) of NIMS obtained this research result.

Reduced titanium oxide Ti2O3 is known to have attractive properties such as high electron conductivity and the absorption of visible light. It is hoped that it can be used in a wide range of applications such as materials for solar and fuel cells, if its nanostructure can be synthesized. However, it is difficult to synthesize nanostructured Ti2O3 using conventional synthesis methods because heating to a high temperature is required.

The research group developed a method of synthesizing black Ti2O3 nanoparticles by reducing white TiO2 nanoparticles with a rutile structure and a diameter of 10-30 nm while maintaining the morphology and size of this precursor. The precursor is mixed and reacted with calcium hydride*2 powder, which has a strong reducing ability even at a low temperature of 350 oC, which is much lower than the conventional reducing temperature (T > 800 oC). This reaction is unique in that the nanostructure is maintained even though the crystal structure is transformed from a tetragonal to a hexagonal system. High-resolution synchrotron X-ray powder diffraction*3 measurement using NIMS beamline BL15XU at SPring-8 (wide-energy beamline for the research of advanced materials) played an important role in analyzing the unique reaction mechanism involved in maintaining the nanostructure.

This breakthrough achievement will provide a new method for synthesizing highly functional and homogenous nanooxides, leading to the synthesis of materials used in a wide range of applications such as solar and fuel cells.

The original paper of this study was published online in the international journal Angewandte Chemie International Edition published by the German Chemical Society.

Publication:
"Synthesis of Nanostructured Reduced Titanium Oxide: Crystal Structure Transformation Maintaining Nano-morphology"
Satoshi Tominaka, Yoshihiro Tsujimoto, Yoshitaka Matsushita, Kazunari Yamaura
Angewandte Chemie International Edition, 50, (32), 418–7421 (2011), published online 29 June 2011

<<Glossary>>
*1　Titanium dioxide
Titanium dioxide (TiO2) is an insulator. Three different structures, i.e., rutile, anatase, and brookite, each with the same composition, are known. The anatase structure is a low-temperature phase, which undergoes a transition to the rutile structure at 800 oC or higher. Once TiO2 takes a rutile structure, the structure is stable even after it is cooled to room temperature. Anatase TiO2 is widely used as a photocatalytic material.

*2　Calcium hydride
Calcium hydride (CaH2) is a white solid. It vigorously reacts with water, and can thus be used to remove water dissolved in an organic solvent.

*3　Synchrotron X-ray powder diffraction
Synchrotron X-ray powder diffraction is a technique for observing the structure of materials. The crystal structure (arrangement of atoms) of a sample is determined by measuring the diffraction intensity obtained by irradiating synchrotron radiation X-rays on the sample.

<<Figures>>

Fig. 1 Comparison between conventional method and new method adopted in this study
Fig. 1 Comparison between conventional method and new method adopted in this study

The particles are enlarged when reduced titanium oxide Ti2O3 is synthesized by the conventional method involving high-temperature treatment, leading to the difficulty of its use in various applications. They succeeded in synthesizing reduced titanium oxide Ti2O3 nanoparticles that absorb visible light using the new method.

Fig. 2　Crystal structure, optical micrograph, and transmission electron microscope image of rutile TiO2 nanoparticles used as a precursor (a) and obtained Ti2O3 nanoparticles (b), and crystal structure of intermediate Magneli phase, Ti4O7 (c)

Fig. 2 Crystal structure, optical micrograph, and transmission
electron microscope image of rutile TiO2 nanoparticles
used as a precursor (a) and obtained Ti2O3 nanoparticles (b),
and crystal structure of intermediate Magneli phase, Ti4O7 (c)

Fig. 3 Synchrotron X-ray diffraction patterns obtained at room temperature
Fig. 3 Synchrotron X-ray diffraction patterns obtained at room temperature

Precursor before reaction, rutile TiO2 (lower), product (Ti2O3 + Ti4O7) obtained by reduction at 350 oC for five days (middle), and reduced titanium oxide Ti2O3 obtained by reduction at 350 oC for 15 days (upper).



For more information, please contact:
　Dr. Yoshihiro Tsujimoto (NIMS)
　　E-mail：mail