Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Metal – metal oxide or metal hydroxide
Reexamination Certificate
1998-03-17
2002-05-14
Bell, Mark L. (Department: 1755)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Metal, metal oxide or metal hydroxide
C502S349000, C502S232000, C502S240000, C502S242000, C428S428000, C428S432000, C428S702000, C427S235000, C427S255391, C427S276000, C427S430100
Reexamination Certificate
active
06387844
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a titanium dioxide photocatalyst structure that has excellent photocatalytic actions and light transmissivity (or transmittance) and enables members of various substances, which require transparency particularly, to have photocatalytic actions. The present invention further relates to a lighting device and a window glass which employ such a titanium dioxide photocatalyst structure.
BACKGROUND ART
Heretofore, there have been known photocatalysts that exhibit activities, by which the decomposition and oxidation of substances are accelerated, when irradiated with light. Recently, attempts or the like have been made to remove air pollutants such as sulfur oxides and nitrogen oxides by utilizing the photocatalysts. Moreover, attempts have been further made to use titanium dioxides as the photocatalysts (see, for example, Japanese Patent Laid-Open Nos. 6-385/1994, 6-49677/1994 and 6-39285/1994 Official Gazettes).
By the way, in recent years, there has been a growing interest in globally environmental pollution. Meanwhile, the demand for removing substances such as CO
2
, NO
X
and SO
X
has grown. Moreover, a plan for creating amenity space by eliminating toxic substances has been devised. Thus, the demands for deodorizing living space and for making the living space antibacterial, soil-resistant and mildew-proof have grown increasingly.
It is accordingly conceived that the aforementioned titanium dioxide photocatalyst is utilized for removing such pollutants. However, in the case of the conventional titanium dioxide photocatalysts, generally, gaseous or liquid materials to be treated are introduced into a container accommodating the photocatalyst and are thus made to be in contact with the photocatalyst, and simultaneously, light is introduced from the exterior thereto and is applied onto the photocatalyst.
Further, in such a case, for the purpose of increasing the contact area between the material to be treated and the photocatalyst and efficiently applying the light onto the photocatalyst, attempts or the like have been made to produce the photocatalyst in minute-particle form or to hold the photocatalyst on a transparent base material.
However, in the case of the aforementioned conventional titanium dioxide photocatalyst, although the contact area between the photocatalyst and the material to be treated can be increased by, for instance, producing the photocatalyst in minute-particle form, the effective area of the photocatalyst, by which light is received, cannot be increased very much. Consequently, it is difficult to largely enhance the total catalysis effects thereof
Further, in the case where the titanium dioxide photocatalyst is formed in film form on, for example, a glass substrate or the like, the titanium dioxide photocatalyst itself has low transparency. This is because it has been heretofore considered that methods suitable for forming a photocatalyst in film form to thereby obtain practical photocatalysis are limited to a method of forming a titanium dioxide sol on the substrate by sintering and a method of producing titanium dioxide in fine powder form, dissolving the powder by using a binder and then applying the dissolved powder onto the substrate. However, in the case of employing the former method, a photocatalyst, which has high activity and a certain measure of transparency, can be obtained, though it is necessary for obtaining the film, whose strength is sufficient for practical use, to set a sintering temperature at a value which is not lower than the softening temperature of glass. Thus, at least, it is impossible to form the photocatalyst on the glass substrate. Besides, regarding the light transmissivity, this photocatalyst tends to become clouded. It is difficult for this photocatalyst to transmit visible light to such an extent that the transparency can be obtained. In this sense, this photocatalyst is close to opaque. In contrast, in the case of the latter method, although the step of sintering is unnecessary, the photocatalyst becomes clouded and opaque because fine titanium dioxide powder is applied to the substrate.
Further, in the case of titanium dioxide produced in film form by performing a sol-gel method and CVD method which have been well known in the field of such a kind heretofore, the transparency can be ensured, whereas the activity of the catalyst, which has a practical level, is not obtained.
Thus, all of the conventional titanium dioxide photocatalysts, which exhibit the photocatalytic activities of practical levels, are substantially opaque. Therefore, even in the case that this conventional photocatalyst is formed on, for example, the front surface of a transparent glass substrate or the like, light applied from the back surface of the glass substrate cannot effectively reach the front surface portion of the photocatalyst. Consequently, only light applied from the front surface portion, on which the photocatalyst is formed, of the substrate can be utilized. Hence, in the case that the cleaning of indoor air is performed by forming this photocatalyst on, for instance, the surface of a window pane, it naturally follows that the photocatalyst is formed on the surface of the glass, which faces the inside of a room. Thus, only light applied from the inside of the room that can be utilized for obtaining the photocatalytic activity. Consequently, there has been a serious defect that sunlight cannot be utilized therefor.
Thus, in the case of the conventional titanium dioxide photocatalyst, titanium dioxide, which performs the photocatalysts, itself is substantially opaque. Consequently, there occurs a limit to the enhancement of the photocatalytic activity. Moreover, the range of application of the photocatalyst is extremely limited.
Furthermore, there has been made an attempt to apply powdered photocatalyst to the outer surface of a discharge lamp to thereby impart a deodorization function thereto (see Japanese Patent Laid-Open No.1-169866 Official Gazette). Additionally, there has been made another attempt to cover the periphery of an illuminating lamp with a net constituted by a glass filter, which is coated with a photocatalyst (see Japanese Patent Laid-Open No.1-139139 Official Gazette), thereby performing a deodorization by utilizing a photocatalytic action at a place where illuminance is high, namely, at a place closer to the illuminating lamp. Besides, there has been made still another attempt to decompose ambient offensive odor (or malodor) substances by depositing a titanium dioxide film on the surfaces of spectacle lenses according to a sputtering method (see Japanese Patent Laid-Open No.2-223909 Official Gazette).
However, the discharge lamp described in the aforementioned Japanese Patent Laid-Open No.1-169866 Official Gazette is configured only by applying anatase-type titanium dioxide powder, whose grain diameter is 500 Å, onto the outer surface of a discharge container. Thus, this discharge lamp is inferior to other lamps in light transmissivity and abrasion resistance. It is obvious that, even if the applied titanium dioxide is baked, a high temperature is needed and there are obtained only discharge lamps which are inferior to other lamps in light transmissivity. Therefore, in the case of this discharge lamp, the photocatalyst has little effect. Further, this discharge lamp is in a state in which the powder adheres to the surface thereof and the degree of the unevenness of the surface thereof is high. With such a structure, this discharge lamp is easily stained and is liable to gather dusts.
Moreover, regarding the air-cleaning spectacle described in the Japanese Patent Laid-Open No. 2-223909 Official Gazette, although the titanium dioxide films are formed on the surfaces of the spectacle lenses by a physical method such as an ion plating method, the objective device configuration and data concerning the identification of titanium dioxide, the crystalline structure of the (thin) films and the judgement on the deodorization effects are not sufficiently disclosed in this of
Fujishima Akira
Fukayama Shigemichi
Hashimoto Kazuhito
Iyoda Tomokazu
Saitoh Tokuyoshi
Bell Mark L.
Frank Robert J.
Hailey Patricia L.
Venable
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