Catalyst – solid sorbent – or support therefor: product or process – Miscellaneous
Reexamination Certificate
2000-10-04
2003-02-25
Silverman, Stanley S. (Department: 1754)
Catalyst, solid sorbent, or support therefor: product or process
Miscellaneous
C502S350000
Reexamination Certificate
active
06524997
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a photocatalyst-bearing material usable for environmental cleanup of the air, water, etc. and effective utilization of light energy such as solar energy, and to a method of producing the same.
2. Related Art
When photocatalyst particles are irradiated with a light having an energy of at least the band gap thereof, electrons and holes come into existence in the conduction band and valence band, respectively, of the photocatalyst particles due to light excitation. The electrons produced in the conduction band have a strong reducing power, while the holes produced in the valence band have a strong oxidizing power. Thus, these photocatalyst particles are utilized for the purposes of cleanup of harmful substances, deodorization of malodorous substances, decomposition of water, sterilization, etc. [see Kazuhito Hashimoto, Akira Fujishima, “Application of Photocatalytic Reactions to Water Purification,” Journal of Water and Waste, Vol. 36, No. 10, pp. 851-857 (1994); Sadao Murasawa, “Deodorization Method Using Photocatalyst,” Environmental Management, Vol. 32, No. 8, pp. 929-934 (1996); Kazuhiro Sayama, Hironori Arakawa, “Stoichiometric Decomposition of Water over Semiconductor Photocatalyst,” Catalysts and Catalysis, Vol. 39, No. 3, pp. 252-256 (1997); etc.]. Incidentally, photocatalytic reactions are mainly oxidation reactions basically attributed to holes excited by photons, which reactions usually proceed only on the surfaces of photocatalyst particles and more particularly only on sites thereof irradiated with a light such as ultraviolet rays.
Such photocatalyst particles must be easily handleable, and easily separable and recoverable from a liquid treated therewith in most cases. For this reason, photocatalyst particles are generally used in such a state that they are supported or coated on a carrier such as a flat plate, a granular material, a honeycomb structure or a three-dimensional reticular structure. Methods of supporting photocatalyst particles on a carrier include one involving precipitating and fixing photocatalyst particles on a carrier [see Japanese Patent Laid-Open No. 5-96181 published on Apr. 20, 1993; and Masayuki Murabayashi, Kazuo Okamura, “Degradation of Chloroorganic Compounds by Using Fixed Photocatalyst,” Journal of Water and Waste, Vol. 36, No. 10, pp. 877-882 (1994)], a sol-gel method involving supporting a photocatalytic chemical substance produced on a carrier by heat decomposition of an organic compound such as titanium tetraisopropoxide [see Katsuhiko Yoshida, Kazuo Okamura, Koji Hirano, Kiyoshi Iguchi, Kiminori Itoh & Masayuki Murabayashi, “Photocatalytic Degradation of Trichloroethylene in Water by Using Thin-film TiO
2
Prepared by Sol-Gel Process,” Journal of Japan Society on Water Environment, Vol. 17, No. 5, pp. 324-329 (1994)], and one involving preliminary dispersion of photocatalyst particles in a carrier material [see Japanese Patent Laid-Open No. 8-208414 published on Aug. 13, 1996].
The method involving precipitating and fixing photocatalyst particles on a carrier leaves much to be desired as these particles are readily released, or dislodged, so that the total area of particles wherein photocatalysis can be manifested is decreased in keeping with an increasing number of sites released of photocatalyst particles, thereby lowering the reaction efficiency. The sol-gel method is so complicated in preparation operations as to be unfit for mass production, and cannot give rise to a sufficient activity of photocatalyst because the amount of supported photocatalyst is limited. Further, in this method, a heat-resistant material (glass, metal or the like), which is difficult to handle and expensive, must disadvantageously be used as the carrier material because heating up to at least 300° C. must usually be done for heat decomposition of the organic compound. The method involving preliminary dispersion of photocatalyst particles in a carrier material is gravely wasteful because photocatalyst particles are unnecessarily buried inside the carrier.
An object of the present invention, which has been made in view of the foregoing various shortcomings of the prior art, is to provide a photocatalyst-bearing material capable of exhibiting a high photocatalysis for a long period of time, and an inexpensive method of producing the same.
SUMMARY OF THE INVENTION
As a result of intensive investigations with a view to doing away with the foregoing shortcomings of the prior art, the inventors of the present invention have found out that bearing particles (B) capable of photocatalysis in and on surface portions of a carrier (A) of thermoplastic polymer by fusion bonding enables the particles (B) to be firmly borne, or supported, on the carrier (A) in such a state that multiple particles (B) are stacked in directions perpendicular to the surfaces of the carrier (A). The present invention has been completed based on this finding.
Specifically, the present invention provides a photocatalyst-bearing material characterized in that particles (B) capable of photocatalysis are fusion-bonded to surface portions of a carrier (A) of thermoplastic polymer in such a state that multiple particles (B) are stacked in directions perpendicular to the surfaces of the carrier (A); and a method of producing a photocatalyst-bearing material, characterized by comprising mixing and contacting a carrier (A) of thermoplastic polymer with particles (B) capable of photocatalysis to fusion-bond the particles (B) to surface portions of the carrier (A) in such a manner that multiple particles (B) are stacked in directions perpendicular to the surfaces of the carrier (A).
The photocatalyst-bearing material of the present invention, which is different from a simple mixture of the carrier (A) with particles (B), is a material having particles (B) borne in and on surface portions of the carrier (A) by fusion bonding, and maintaining a state that particles (B) are partly exposed from the surfaces of the carrier (A) [see FIGS.
1
and
2
]. Since multiple particles (B) are stacked in and on a surface portion of every grain of the carrier (A), release, or dislodgment (exfoliation), of some particles (B), even when brought about because of deterioration of the surface of that grain of the photocatalyst-bearing material, lets particles (B) thereunder be sequentially exposed from the surface. Thus, the photocatalyst-bearing material of the present invention can continuously maintain the photocatalysis thereof over a long period of time. Moreover, the method of producing a photocatalyst-bearing material according to the present invention is simply and easily operable to be favorably usable for mass production thereof.
The process of formation of the foregoing photocatalyst-bearing material by the method of producing a photocatalyst-bearing material according to the present invention will be described to be as follows: Surface portions of the carrier (A) are fused, or molten, by heating. Simultaneously, the carrier (A) and particles (B) are mixed and stirred together to fusion-bond some particles (B) to the molten surfaces of the carrier (A). Upon further heating, some melt of the thermoplastic polymer of the carrier (A) is oozed out from between particles (B) fusion-bonded to the surfaces of the carrier (A), thereby further fusion-bonding some other particles (B) to the oozed-out melt of the thermoplastic polymer of the carrier (A). According to the foregoing mechanism that is repeated, multiple particles (B) are stacked and borne on the carrier (A) to produce the photocatalyst-bearing material of the present invention.
The shapes of the carrier (A) and the photocatalyst-bearing material of the present invention may be arbitrary, but are preferably substantially spherical or disk-like from the viewpoint of simplicity of the production procedure. Substantially spherical ones are preferred in respect of handleability, while substantially disk-like ones are preferred bec
Higo Yuji
Yano Daisaku
Johnson Edward M.
Norris & McLaughlin & Marcus
Organo Corporation
Silverman Stanley S.
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