Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Metal – metal oxide or metal hydroxide
Reexamination Certificate
1999-07-15
2001-10-23
Bell, Mark L. (Department: 1755)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Metal, metal oxide or metal hydroxide
C423S610000, C106S436000, C501S134000
Reexamination Certificate
active
06306796
ABSTRACT:
TECHNICAL FIELD
The invention relates to a titanium dioxide photocatalyst, a process thereof, and a multifunctional material.
BACKGROUND ART
Pollution by malodor, deleterious materials in the air, etc. has become a problem in recent years. Also, water pollution by domestic waste water, industrial waste water, etc. has spread widely. Thus, environmental pollution has become a serious social problem.
In removing malodor or deleterious materials, absorption process using acid or alkali, and adsorption process using an adsorbent have been employed conventionally. In these processes, however, it is necessary to treat a waste liquid or spent adsorber. On the other hand, it is known that when a semiconductor device is irradiated with light, electrons having strong reducing action and holes having strong oxidizing action are formed and the molecular species after having been in contact with the semiconductor device are decomposed by oxidation-reduction action. Such a photocatalytic action of the semiconductor is applicable to decomposition and removal of deleterious materials.
JP-B-9850/1990 discloses to decompose deleterious materials in waste by using a photocatalyst such as titanium oxide. JP-B-78326/1992 discloses to eliminate toilet night soil odor, tobacco odor, etc. by using a photocatalyst such as titanium oxide.
In addition, a number of titanium oxide photocatalysts are disclosed in JP-A-199524/1994, 205974/1994, 279026/1994, 819/1995, 241475/1995, 275704/1995, 303835/1995, 99041/1996, 81222/1996, 126845/1996, and 182934/1996.
JP-A-131834/1996 discloses a titanium oxide sol for photocatalyst and a multifunctional material having photocatalytic action.
The above conventional titanium oxide photocatalysts are, however, ones which employ titanium oxide, e.g., anatase-type titanium oxide, rutile-type titanium oxide, brookite-type titanium oxide, amorphous titanium oxide, metatitanic acid and orthotitanic acid, titanium hydroxide, or hydrate titanium oxide. It has been therefore demanded a novel photocatalyst having superior activity and a multifunctional material using the same.
Accordingly, it is an object of the invention to provide a novel photocatalyst having superior activity, a process thereof, and a multifunctional material using the same.
DISCLOSURE OF THE INVENTION
The present invention provides a titanium dioxide photocatalyst having a monoclinic crystal structure, a process thereof, and a multifunctional material using the same.
The titanium dioxide of a photocatalyst of the invention is characterized in that its crystal structure is monoclinic and its lattice constant is expressed by: a=12.163 Å, b=3.735 Å, c=6.513 Å, &agr;=&ggr;=90°, and &bgr;=107.29°. This monoclinic titanium dioxide differs from the known anatase-type, rutile-type, or brookite-type titanium dioxide in crystal structure. The single crystal of the monoclinic titanium dioxide of the invention is normally of a size from 0.005 &mgr;m to 0.1 &mgr;m, preferably from about 0.007 &mgr;m to 0.05 &mgr;m. The monoclinic titanium dioxide may be of a polycrystal which is the assembly of single crystals.
A monoclinic titanium dioxide of the invention is obtained by subjecting a titanium dioxide hydrate fiber to a heat treatment at a temperature in the range of 80 to 350° C. and then further heat treatment at a temperature in the range of 360 to 650° C. Titanium dioxide hydrate as a starting material is not specifically limited. This is obtained in a manner well known in the art, for example, a method in which alkali metal titanate is treated with water, warm water, inorganic acid, organic acid, or a mixture of at least two of them, to remove the alkali metal content. A monoclinic 8-titanic acid is obtained by subjecting titanium dioxide hydrate to heat treatment at a specific temperature range of usually 80 to 350° C., preferably 110 to 200° C. Below 80° C., the composition of 8-titanic acid cannot be obtained. Above 350° C., there is a possibility that the shape of a monoclinic 8-titanic acid is impaired. No specific limitations are imposed on heating time, however, it is usually two or more hours, preferably from about 3 to 50 hours, more preferably from about 10 to 30 hours. After heating, it may be allowed to cool. No specific limitations are imposed on cooling, and any known manner can be employed, e.g., air cooling, mechanical cooling, or in a combination of these.
Subsequently, the above monoclinic 8-titanic acid is subjected to heat treatment at a temperature of 360 to 650° C., preferably 500 to 650° C., to obtain a monoclinic titanium dioxide of the invention. When a heating temperature is less than 360° C., crystallization does not proceed sufficiently to give a substance of low crystallinity, failing to obtain the desired compound of the invention. On the other hand, when it exceeds 650° C., anatase-type or rutile-type titanium dioxide is formed and thus fails to obtain the present compound.
A monoclinic titanium dioxide of the invention may be in any forms, for example, in the form of particle, fiber, whisker or bar. For particulate form, its suitable size is generally in the range of 0.005 to 50 &mgr;m, preferably about 0.01 to 10 &mgr;m. For fibrous or whisker form, its suitable fiber diameter is in the range of 0.05 to 2 &mgr;m, preferably 0.1 to 1 &mgr;m, and its suitable fiber length is usually in the range of 0.5 to 30 &mgr;m, preferably about 1 to 20 &mgr;m, although it is possible to obtain ones having about hundreds of &mgr;m.
A monoclinic titanium dioxide of the invention has a specific surface area of about 1 to 500 m
2
/g, preferably about 3 to 300 m
2
/g, more preferably about 5 to 200 m
2
/g. Even when the monoclinic titanium dioxide has a small specific surface area, it has a great photocatalytic activity and thus exhibits an extremely large activity per unit specific surface area.
In applying a photocatalyst of the invention to a variety of photocatalytic reactions, such as the synthetic reaction of organic materials and the decomposition reaction of deleterious materials, or reaction affording hydrophilic property, the photocatalyst is irradiated with light of a wavelength which has energy greater than the band gap of the photocatalyst, in the presence of a material to be treated. The photocatalyst can take an arbitrary form depending on the place of utilization. For example, it may be suspended in a solvent, retained or coated on a substrate. Alternatively, it may be in powder form, and such powder may be pulverized or molded.
Examples of deleterious materials which are decomposed or oxidized by photocatalytic reaction by use of titanium oxide and then removed, are materials having adverse effect upon human body and living environment, and materials which might have such adverse effect. For instance, there are a variety of biochemical oxygen demand materials; environmental pollution materials such as air pollution materials; materials of various agricultural chemicals such as herbicide, bactericide, insecticide and nematocide; and microorganism such as bacteria, actinomyces, funguses, algaes and molds. Examples of environmental pollution materials are organic halogen compounds, organic phosphorus compounds, other organic compounds, and inorganic compounds such as nitrogen compounds, sulfur compounds, cyanide and chromium compounds. Examples of organic halogen compounds are polychlorinated biphenyl, fleon, trihalomethanes, trichloroethylene, and tetrachloroethylene. Examples of organic compounds other than organic halogen compounds and organic phosphorous compounds are surface active agents, hydrocarbons such as oils, aldehydes, mercaptans, alcohols, amines, amino acid, and protein. Examples of nitrogen compounds are ammonia and nitrogen oxide.
By utilizing hydrophilic reaction, it is possible to prevent mirrors, glass or spectacle lens from being clouded, and prevent dirt of external walls. This is also applicable to treatment for cancer cells by using an endoscope or the like.
As the light of wavelength having energy great
Aki Minoru
Suzue Masayoshi
Torii Katsura
Arent Fox Kintner & Plotkin & Kahn, PLLC
Bell Mark L.
Hailey Patricia L.
Otsuka Kagaku Kabushiki Kaisha
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