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SDK Develops TiO2 Photocatalyst Responsive to Visible Light

December 3, 2002

Showa Denko K.K. (SDK) has developed a new photocatalyst responsive to visible light, using brookite titanium dioxide nanoparticles.

The product uses brookite TiO2 particles with diameter of 10 nanometers (1 nm: one-billionth of a meter) manufactured by SDK's subsidiary, Showa Titanium Co., Ltd., in Toyama Prefecture, Japan. Showa Titanium is the world's first producer of brookite TiO2 in commercial quantities, producing one ton a month.

After special treatment, those TiO2 particles become responsive to visible light from a wide range of sources, including sunlight on a cloudy day and a fluorescent light. SDK has also developed an aqueous slurry of those TiO2 particles stable in the neutral pH range (pH: 5-9) as well as a colorless and transparent photocatalytic film from the slurry.

Conventional TiO2 photocatalysts comprise anatase TiO2 particles that respond only to ultraviolet rays. (The anatase-crystalline phase is a tetragonal system while the brookite-crystalline phase is an orthorhombic system.)

Existing visible-light-responsive photocatalysts have the problem of coloring as a result of doping and introduction of oxygen defect. Furthermore, when TiO2 photocatalyst is mixed with paint in a slurry using water or solvents, the slurry tends to gelatinize in the neutral pH area.

SDK's new product based on brookite TiO2, sold under the trade name of "NTB™," which stands for "Nano Titania Brookite," has solved these problems. SDK has also developed an inorganic binder to be used for formation of a photocatalytic film at ordinary temperatures from the slurry. While conventional acidic coating materials cannot be used for coating metals, the combination of our neutral and aqueous TiO2 slurry and the binder can be applied to metals. It will also contribute toward improving the environment for film formation work with coating materials.

At present, photocatalysts are used outdoors for removing stain from building materials, paints, noise barriers, automotive outside mirrors, etc., mainly by the ultraviolet rays in sunlight.

Photocatalysts are also being used together with ultraviolet lamps in deodorizing equipment (air cleaners) as well as in devices for treating exhaust gases and wastewater. For these applications, SDK's NTB™ will enable the use of less expensive light sources, including a fluorescent light.

In addition, NTB™ can be used indoors, with visible light (sunlight, fluorescent) as light source, for stainproofing, deodorization, and sterilization purposes for interior materials (paint, building materials, porcelain, glass, etc.), furniture, electric appliances and electric lamps. The product can also be used in cars for stainproofing, deodorization, and sterilization purposes.

As the photocatalyst market is expected to expand to the order of ¥1 trillion, SDK is planning to sell ¥5 billion worth a year of photocatalysts by 2007, centering on visible-light-responsive products for environmental goods applications. NTB™ will become one of SDK's strategic growth businesses under the new medium-term consolidated business plan, named the "Sprout Project," that starts in 2003.

For further information, contact:
Ceramics Division (Phone: 0263-52-0976) (For customers)