Energy Electronics Institute (EEI) of National Institute of Advanced Industrial Science and Technology (AIST), an independent administrative institution, succeeded first in the world to synthesize crystalline metal oxide (MO) composite porous materials, that is, composite nanoporous materials with a framework of crystalline MO with tailored 3-dimensional structures having regularly arranged nanopores and forming a porous framework.

Photo: A transmission electron microgram of microcrystalline composite nano-porous powder of TiO2-P2O5 with 3-D structures and high specific surface area.

The newly developed material is expected to be applicable to catalyst carrier, adsorbent, photocatalyst, dye-sensitized solar cell, sensor, energy storage device, and so on through the utilization of its electronic and chemical properties as well as molecular sieve features of nanopores.

The nanoporous metal oxide materials (porous MO materials) was developed in 1995 by a research group in the Massachusetts Institute of Technology (MIT), U.S. and came under the spotlight because of 3D structure with regularly arranged nanopores and high specific surface area. However, as the framework holding nanopores is made of chemically stable amorphous (non-crystalline) solid, various electronic and chemical features derived from regular atomic arrays of crystal could not be utilized. A number of study groups in the world made a lot of efforts to tailor crystalline phase into a framework but no success was achieved because the epitaxial growth of metal oxide in nanometer order disturbed regular 3D arrangement owing to failure in grain size control.

Normally, nanoporous MO materials are synthesized by using templates. Based on a new concept, the EEI-AIST succeeded in synthesizing nanoporous materials of 3D structure with regularly arranged nanopores and crystalline MO framework, by adding a small amount of glass phase precursor, triethyl phosphorate, PO(OC₂H₅)₃, or tetraethyl o-silicate Si(OC₂H₅)₄ to an original mix of the conventional process, and by sintering at higher temperatures. The glass phase of material can be doped with functional ingredient providing ionic or electronic conductivity and other innovative properties. This process can be applied to a variety of materials.

The integration of electronic and chemical features of crystalline MO with molecular sieve property of nanoporous structure is expected to open the way to a broad spectrum of applications, including catalyst carrier, adsorbent, photocatalyst, dye-sensitized solar cell, sensor, energy storage device, and so on. (Patent pending).

NB: The result of this study was published in a British science journal, Nature Materials, January 2004.