Chemistry of inorganic compounds – Oxygen or compound thereof – Metal containing
Reexamination Certificate
1999-08-24
2003-03-25
Bos, Steven (Department: 1754)
Chemistry of inorganic compounds
Oxygen or compound thereof
Metal containing
Reexamination Certificate
active
06537517
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
Titania (TiO
2
) is excellent in properties such as ultraviolet absorbability, adsorbability and the like. Accordingly, it has been widely used as a material in such applications as {circle around (1)} an ultraviolet absorber, a masking agent in an anti-sunburn agent, a paint, a film and the like; {circle around (2)} an absorber, an adsorbent, a deodorizer and the like.
Further, nowadays the superior photocatalytic activity of titania is given attention. The titania is applied to environmental cleanup or the like upon decomposition of carbonaceous gas or nitrogen oxides while utilizing the superior properties thereof, such as oxidation or reduction.
The improvement of the properties of titania, especially the photocatalytic activity in the above-mentioned usages has been in demand.
2. Description of Related Art
As one of the conventional technologies for improving the properties of titania, it is known that if titania is doped with SiO
2
, the specific surface area can be increased.
In order to improve the photocatalytic activity, the present inventors tried to chemically treat the TiO
2
powder obtained by a sol-gel method, having large specific surface area, with an NaOH aqueous solution to improve the photocatalytic activity, and reported this technology in the following literature.
(1) “Preprints of Symposium of Catalyst Chemistry related to Light”, Jun. 6, 1996, held by Rikagaku Kenkyusyo and Catalyst Academy, p. 24-25
(2) “Preprints of Annual Meeting of The Ceramic Society of Japan 1996”, Apr. 2 to 4, 1996, p. 170
SUMMARY OF THE INVENTION
Taking aim at improving the catalytic activity as the properties of crystalline titania, further investigations were made. Meanwhile, it has been found that where the crystalline titania is treated with an alkali, if certain conditions are met, a titania crystal in a nanotube form, which has hitherto been unknown, is formed, leading to the accomplishment of the present invention.
It has been hitherto considered that the crystal shape of crystalline titania has only a spherical shape or a needle shape, whether it is an anatase type or a rutile type, so long as the present inventors know.
The present invention is to provide crystalline titania of a nanotube which has a novel crystal shape. The diameter of the nanotube varies depending on the production conditions and the like. It is approximately between 5 and 80 nm in many cases. The crystal structure which is easy to obtain is an anatase type.
This nanotube is formed by treating crystalline titania with an alkali. In order to increase the yield, the alkali treatment can be conducted at a temperature of from 18 to 160° C. using from 13 to 65 percent by outer weight of sodium hydroxide.
Since the nanotube is a hollow crystal, the specific surface area is increased as compared with a solid crystal such as a needle crystal, and the specific surface area in the volume occupied is more increased. Accordingly, it is expected to markedly improve the properties of the crystalline titania. Further, this crystal is expected to find novel use in filters and the like upon utilizing the nanotube shape.
REFERENCES:
patent: 5897945 (1999-04-01), Lieber et al.
patent: 5958358 (1999-09-01), Tenne et al.
patent: 8-257399 (1996-10-01), None
patent: 9-70532 (1997-03-01), None
Journal of Materials Research, “Preparation of TiO2-based Powders with High Photocatalytic Activities”, Kasuga et al, vol. 12, No. 3, Mar., 1997, pp. 607-609.
Advanced Materials, “Semiconductor Nanotube Formation by a Two-Step Template Process”, Hoyer, pp. 857-859, 1996, Advanced Materials, vol. 8, No. 10.
Langmuir, “Formation of Titanium Dioxide Nanotube Array”, Hoyer, pp. 1411-11413, 1996.
Preprints of Annual Meeting of The Ceramic Society of Japan 1995, Apr. 1-3, 1995, p. 363, “Photocatalytic Property of TiO2-SiO2Powders Prepared by a Sol-Gel Method”, Kasuga et al.
Preprints of the 8th Autumn Symposium of The Ceramic Society of Japan 1996, Oct. 3-5, 1995, p. 167, “Photocatalytic Property of TiO2-SiO2Powders Leached with Aqueous NaOH”, Kasuga et al.
Preprints of Annual Meeting of The Ceramic Society of Japan 1996, Apr. 2-4, 1996, p. 170, “Improvement of Photocatalytic Activity of TiO2-based Powders Prepared by a Sol-Gel Method”, Kasuga et al.
Preprints of the 76th Catalyst Discussion Society (A), Oct. 7-8, 1995, held by Catalyst Academy and The Chemical Society of Japan, p. 67.
Preprints of Symposium of Catalyst Chemistry Related to Light, Jun. 6, 1996, held by Rikagaku Kenkyusyo and Catalyst Academy, pp. 24-25.
P. Hoyer: “Formation of Titanium Dioxide Nanotube Array”, Langmuir, vol. 12, 1996, pp. 1411-1413, XP002052967, 1996 American Chemical Society.
Lakshmi B.B. et al: “Sol-gel Template Synthesis of Semiconductor Nanostructures”, Chemistry of Materials, vol. 9, No. 3, Mar. 1997, pp. 857-862, XP000686528, 1997 American Chemical Society.
Kasuga: “Improvement of Photocatalytic Activity of TiO2-based Powders Prepared by a Sol-gel Method”, Preprints of Annual Meeting of the Ceramic Society of Japan, XP002052939, p. 170, no date.
Preprints of the 78th Catalyst Discussion Society (A), Oct. 9-11, 1996, held by Catalyst Academy and The Chemical Society of Japan, p. 67.
Hiramatsu Masayoshi
Kasuga Tomoko
Arent Fox Kintner Plotkin & Kahn
Bos Steven
Chuba Electric Power Co., Ltd.
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