Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Metal – metal oxide or metal hydroxide
Patent
1998-05-18
2000-09-19
Bell, Mark L.
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Metal, metal oxide or metal hydroxide
502325, 502339, 502344, 502347, 502350, 252514, 423403, 423546, B01J 2358, B01J 2300, H01B 102, C01C 1245, C01B 2126
Patent
active
061211915
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a photocatalyst which can clean the environment by decomposing environmental contaminants, etc., and more particularly to a technical field of a photocatalyst which causes a conspicuous improvement in photocatalytic efficiency in quantum-mechanical terms by supporting nano-scale ultra-fine metal particles, which are capable of realizing a quantum size effect, on fine particles of a photocatalyst, and a highly functional base material which can clean the environment with high efficiency by holding the photocatalyst supporting ultra-fine metal particles on the surface of such a material.
BACKGROUND ART
A photocatalytic reaction of titanium dioxide was reported in Nature in 1972 and became known world-wide as the Honda-Fujishima effect. Since then, research has been conducted on the production of hydrogen and carbon dioxide by the decomposition of water or the decomposition of aqueous solutions of organic matter by means of titanium dioxide under irradiation with light; and today, a technique in which fine particles of titanium dioxide are held in the form of a thin film on tiles or window glass is in the process of being adapted for practical use in the decomposition of environmental contaminants, i. e., tobacco tar and organic matter such as bacteria, toxins produced by bacteria, etc.
Titanium dioxide is a powder-form metal oxide and is used after being dispersed in a solution in the case of decomposition of water or solutions. However, it is desirable that titanium dioxide adhere to window glass and bathroom tiles, or to the surfaces of construction materials, in the form of a uniform thin film even when titanium dioxide is used in particle form. Accordingly, methods such as sol-gel methods, spray pyrolysis methods using titanium acetate, etc., and dip coating methods, etc. have been developed. These techniques are described in "Oyo Butsuri (Applied Physics)", Vol. 64, No. 8, p. 803 (1995), "Kayak to Kogyo (Chemistry and Industry)", Vol. 48, No. 10, p. 1256 (1995), and "Kayak to Kogyo (Chemistry and Industry)", Vol. 49, No. 6, p. 764 (1996). It has been shown that adhering oils and tobacco tar can be decomposed while being irradiated with ultraviolet light using a glass, etc. covered with such titanium dioxide. It is difficult to decompose inorganic matter such as dirt and dust, etc.; however, it has been reported that since such inorganic matter adheres with organic substances such as oils, etc. as a binder, the decomposition of organic matter also tends to prevent the adhesion of inorganic matter.
The principle of the action of fine particles of titanium dioxide on materials such as tiles, etc. is based on the photocatalytic characteristics of titanium dioxide as a semiconductor. If titanium dioxide is irradiated with light which exceeds the band gap energy, e. g., ultraviolet light, then the electrons in the valence electron band are excited and undergo a transition to the conduction band, so that positively charged holes are left in the valence electron band, thus producing electron-hole pairs. These electrons and holes move through the titanium dioxide and reach the surface; and the electrons are supplied to oxygen in the air so that O.sub.2.sup.- (super-oxide anion) is produced and other substances are reduced. The holes not only cause direct oxidative decomposition of organic matter but also oxidize water molecules adhering to the surface so that strongly oxidizing hydroxyl radicals are formed, and other substances are oxidized by the oxidizing power of these hydroxyl radicals. The O.sub.2.sup.- reportedly participates in this oxidation process; however, the detailed reaction circuit is still being studied. Thus, organic matter is decomposed into carbon dioxide and water by electron-hole pairs excited by light.
In this research, instances have been found in which the electrons and holes re-couple and disappear prior to the oxidation-reduction of external substances in cases where titanium oxide is used alone. Accordingly, it has been indicated tha
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Harada Akio
Komatsu Teruo
Ueyama Ryosuke
Bell Mark L.
Daiken Chemical Co., Ltd.
Hailey Patricia L.
Komatsu Teruo
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