Hazardous or toxic waste destruction or containment – Containment – Solidification – vitrification – or cementation
Reexamination Certificate
1999-12-30
2002-07-02
Griffin, Steven P. (Department: 1754)
Hazardous or toxic waste destruction or containment
Containment
Solidification, vitrification, or cementation
C204S157440, C204S157630, C423S210000, C423S239100, C423S245100, C423S245300, C423S247000
Reexamination Certificate
active
06414213
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an interior member or indoor equipment using a titanium oxide particle as a photocatalyst. More specifically, the present invention enables an organic material or nitrogen oxide adhering to the surface of an interior member or indoor equipment to be decomposed by the irradiation of a weak ultraviolet ray.
BACKGROUND OF THE INVENTION
Photocatalysis is a reaction of decomposing an organic material or nitrogen oxide present in air or water using light energy in the presence of a photocatalyst. Thus, photocatalysis is a technique which uses an ultraviolet ray present in the light emitted from sunlight or an interior room illuminator such as a fluorescent lamp and an incandescent lamp, and studies thereon are being made broadly, for example, on the application to architectural materials or the cleaning of water or air.
As the photocatalyst, zinc oxide, cadmium selenide, gallium arsenide and the like are known but titanium dioxide (hereinafter referred to as “titanium oxide”) is usually used. Titanium oxide is known to assume three kinds of crystal structures, and in any structure, a distorted octahedron formed by the 6-coordination of oxygen atoms to titanium atom is fundamental. The three kinds of crystal structures are a tetragonal anatase type for low temperature, a rutile type for high temperature and a rhombic brookite type for a temperature between those two types. Among these, anatase titanium oxide is considered to be most excellent as a photocatalyst and a large number of studies have heretofore been made thereon.
It is known that the decomposing action of titanium oxide on contamination caused by adhesion of an organic material or on the generation of mold is generally accelerated by the action of an ultraviolet ray present in sunlight (see, Unexamined Re-Published International Patent Application WO96-29375). The mechanism in the decomposing action of titanium oxide is not yet fully understood, however, the decomposition presently is considered to proceed as follows.
When titanium oxide absorbs an ultraviolet ray, two kinds of electric charges (carriers) of an electron and a hole are generated inside and the hole is induced on the surface thereof. This hole acts with water on the particle surface to generate an OH radical having a strong oxidizing power on the surface of the particle and the pollutant positioned on the particle surface, such as nitrogen oxide, is decomposed by the OH radical into carbon dioxide gas, water or a low molecular weight material. These decomposition products accumulate on the particle surface and are washed out by rain or the like. As a result, the photocatalytic action of the particle is regenerated. Thus, the photocatalytic function of titanium oxide can be continuously maintained. (See, Akira Fukushima, Kazuhito Hashimoto and Toshiya Watanabe,
Titanium Oxide Photocatalysis Fundamentals and Applications
, BKC Inc., (1998)).
SUMMARY OF THE INVENTION
The present inventors have found that titanium oxide particles containing a brookite-type crystal exhibit a strong photocatalytic effect even under a weak ultraviolet ray. The present invention has been accomplished based on this finding.
An anatase titanium oxide as a photocatalyst has been mainly used. Irradiation energy of at least 0.005 mW/cm
2
at a wavelength of 365 nm is needed to exhibit the function of a photocatalyst. Therefore anatase titanium oxide as a photocatalyst has been only adopted on sunshiny areas such as the windows side of an indoor place or in an outdoor place. Brookite titanium oxide used in the present invention exhibits its photocatalytic function under the condition of a weak ultraviolet ray having an irradiation energy of, for example, 0.001 mW/cm
2
and under the conditions of light in indoor places.
The present inventors have thought that since the photocatalytic property of a titanium oxide particle is influenced by the OH radical concentration on the surface thereof or the like, selection of the crystal structure, surface shape or particle size of titanium oxide and control of the shape are matters of importance.
In other words, the generation of OH radicals is governed by the generation density of holes and the life thereof in the above-described mechanism and the generation density and life of a hole is governed by the band gap thereof. Therefore, the photo-functional property of titanium oxide is considered to be dependent on the crystal system. It is well known that a rutile-type crystal has a band gap of 3.0 eV and an anatase-type crystal has a band gap of 3.2 eV.
Furthermore, the OH radical is generated by the reaction of a hole with water, accordingly, the hole potential (corresponding to the potential of an electric charge depletion layer in the valence band) on the surface of titanium oxide plays an important factor. This potential is governed by the band system in the crystal structure, therefore, also in this point, the photo-functional property of titanium oxide is inferred to be dependent on the crystal system.
However, in the case of decomposing organic material or the like adsorbed, for example, on an interior member by letting titanium oxide be present on the surface of an interior member or indoor equipment in a room, a tunnel, a car, a plane or a ship, the ultraviolet ray which can be used is a weak ray emitted from an interior room illuminator and the like. Accordingly, unless a specific ultraviolet ray source such as a strong ultraviolet ray lamp is installed, sufficiently high percentage decomposition cannot be attained.
The present invention has been made under these circumstances and a primary object of the present invention is to obtain an interior member or indoor equipment capable of decomposing an organic material or nitrogen oxide adsorbed on wall paper, floor member or gauges, with the irradiation of a weak ultraviolet ray.
Another object of the present invention is to provide an interior member or indoor equipment where titanium oxide particles containing a brookite-type crystal are present on the surface thereon.
Still another object of the present invention is to provide a method of using titanium oxide particles containing a brookite-type crystal under the condition of irradiation with an ultraviolet ray having irradiation energy of from 0.001 to 0.2 mW/cm
2
at a wavelength of 365 nm.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The titanium oxide particles for use in the present invention contain brookite-type crystal. The titanium oxide particle is not particularly limited as long as brookite titanium oxide particle is present. The brookite titanium oxide particle may be used alone or a rutile or anatase titanium oxide particle may also be present. In the case of a rutile or anatase titanium oxide particle is present, the ratio of the brookite titanium oxide particle in the titanium oxide particles is not particularly limited but it is usually from 1 to 100 wt %, preferably from 10 to 100 wt %, more preferably from 50 to 100 wt %. This is because the brookite titanium oxide is superior in photocatalytic activity to rutile or anatase titanium oxide.
The titanium oxide particles containing a brookite-type crystal may be produced by a vapor-phase production process where anatase titanium oxide particles are heat-treated to obtain titanium oxide particles containing a brookite-type crystal, or by a liquid-phase production process where a solution of a titanium compound such as titanium tetrachloride, titanium trichloride, titanium alkoxide or titanium sulfate is neutralized or hydrolyzed to obtain a titanium oxide sol having dispersed therein titanium oxide particles.
The production process is not particularly limited as far as titanium oxide particles containing a brookite-type crystal can be obtained. However, taking account of the photocatalytic activity and manageability of the material obtained and in the case of forming a titanium oxide thin film, transparency and adhesion, a production process previously found by the present inventors (Japanese Patent Application Nos. 9-231
Nakamura Hidenori
Ohmori Masahiro
Griffin Steven P.
Showa Denko K.K.
Strickland Jonas N.
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