JP3211083B2 - Photocatalyst - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photocatalyst used for sterilization, deodorization, wastewater treatment, inhibition of algae growth, various organic chemical reactions, and the like.

[0002]

2. Description of the Related Art When a semiconductor is irradiated with light of an appropriate wavelength having energy greater than its band gap, electrons are transferred from the valence band to the conductor by photoexcitation, and at the same time, holes are generated in the valence band. So-called charge separation occurs. When a semiconductor is irradiated with light while being brought into contact with water or a solution, a junction similar to a Schottky barrier is formed. When the semiconductor is n-type, holes are formed. When the semiconductor is p-type, electrons are formed. It is well known that they gather on the surface on the solid-liquid interface side. Then, in the case of an n-type semiconductor, holes extract electrons from water or a solution species,
As a result, water is decomposed and solutes in the solution are oxidized.
In the case of a p-type semiconductor, electrons are given to adjacent water or solution species, and a reduction reaction of the water or solution species occurs. Such a semiconductor that promotes the photooxidation-reduction reaction is particularly called a semiconductor photocatalyst or simply a photocatalyst.

Conventionally, as a redox reaction or a redox reaction operation using a photocatalyst, a water decomposition reaction, a reaction for killing microorganisms, a deodorization reaction, a sterilization reaction, a water purification wastewater treatment, and various other organic chemical reactions have been proposed. ing. As the photocatalyst, specifically, titanium oxide as an n-type semiconductor,
Most widely used because of its chemical stability. Titanium oxide may be used in the form of a powder suspended in a solution or in the form of being supported on some substrate. From the viewpoint of photocatalytic activity, the former is generally more active because of its surface area,
From a practical point of view, it is often necessary to adopt the latter rather than the former because of its ease of handling.

Various methods have been proposed for supporting a photocatalyst on a substrate. For example, (A) nitrocellulose,
Glass, polyvinyl chloride, nylon, methacrylic resin,
A method in which titanium oxide fine powder is adhered to a film-like, bead-like, board-like, fiber-like, or other substrate made of a light-transmitting material such as polypropylene (Japanese Patent Application Laid-Open No. 62-6686).
1), (B) a method in which a porous glass support is impregnated with an alcohol solution of titanium (IV) tetrabutoxy oxide, heated and converted to anatase-type titanium oxide to be held and fixed to the porous glass support. (Japanese Patent Laid-Open No. 2-50
154), (C) The semiconductor catalyst powder is pressed into a porous polymer film (for example, polyfluoroethylene resin) having a photosensitizer such as a dye or a metal complex as a side chain, by impregnation, deposition, or the like. Method of holding and fixing (Japanese Patent Laid-Open No. 58-12 / 1983)
5602), (D) a method of supporting titanium oxide on a filtration filter made of polypropylene fiber or ceramic (Japanese Patent Application Laid-Open No. 2-68190), (E) holding titanium oxide powder in a bundle of quartz, glass, and plastic fibers. A method of fixing and holding both surfaces with light-transmitting glass (US Pat. No. 4,888,101). (F) Platinum is fixed to an alumina substrate by a sputtering method, and then anatase type titanium oxide powder and methyl A method in which a mixed dispersion of a methacrylate and an organic solvent solution is applied by a spin coating method, and thereafter, methyl methacrylate as a binder is thermally decomposed, and anatase-type titanium oxide is converted to rutile-type titanium oxide. Robert E. Hetrick, Applied
Physics Communications, 5 ,, (3), 177-187 (1985)》,
(G) A method of spray-supporting titanium oxide on the surface of a polyester cloth by a low-temperature spraying method (T. Sakurada, Surface Technology Vol. 41, 10
No., P60 (1990)).

[0005]

Considering the conventional method of holding and fixing the photocatalyst to the substrate as described above, first, in any case, the substrate is not necessarily robust, such as an organic polymer film, glass, or ceramic. Since no such material is used, mounting a photocatalyst holding or fixing the photocatalyst on these substrates often causes practical problems when mounted on the oxidation-reduction reactor. Except for the method (B) or (G), the strength of holding and fixing the photocatalyst powder to the substrate in each of the above methods is practically insufficient.

Further, what is common in any of the above-mentioned methods is that the photocatalyst is generally held and fixed on a substrate, so that the catalytic activity is higher than when the photocatalyst powder is suspended in a liquid. Is relatively reduced.

[0007]

According to the present invention, there is provided a foamed nickel base having a three-dimensional network structure, a mixture of a photocatalyst powder and a fluororesin binder is kneaded into the pores of the base, and the whole is pressed. By doing so, the above-mentioned problem is solved.

[0008]

The features of the photocatalyst according to the present invention are that the mechanical strength is sufficiently high and the photocatalytic activity is extremely high. Hereinafter, the production process, configuration, and significance of the photocatalyst according to the present invention will be described in detail.

As the foamed nickel substrate, a so-called nickel foamed plate having a three-dimensional network structure obtained by electroless plating nickel on polyurethane and then thermally decomposing the polyurethane can be used. A mixture of a semiconductor photocatalyst powder and a fluororesin binder is kneaded into the pores of the three-dimensional network structure of the foamed nickel substrate, and then pressed to produce a foamed nickel substrate-semiconductor photocatalyst composite. Semiconductor photocatalyst powders include TiO ₂ (anatase type, rutile type), ZnO, SrTiO ₃ , CdS,
Conventionally known materials such as GaP, InP, and GaAs can all be applied to the present invention. As the fluororesin binder, polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-ethylene copolymer or the like may be used alone or in a mixture. These fluororesins are used in the form of an aqueous suspension, an organic solvent suspension, or a powder. After pressing or at the time of pressing, heating at a temperature of 100 to 300 ° C. is also effective in order to increase the binding strength of the fluororesin.

When a linear nickel foam substrate is used,
A linear photocatalyst is obtained by kneading a mixture of a photocatalyst and a fluororesin into the pores, and this may be used as it is. For example, it may be effective to form a spiral or braid.

In the photocatalyst thus obtained, first, the significance of using a foamed nickel substrate is firstly that the photocatalyst itself is more robust than conventional organic porous polymer films, glass fibers, ceramics and the like. 2
Third, it is difficult for rust or corrosion to occur in an environment where the photocatalyst is placed, for example, in water or in the air. Third, since it is porous (60-90% porosity) and plastic, the photocatalyst powder When kneading and pressing the mixture of the resin and the fluororesin binder, the foamed nickel substrate and the photocatalyst are firmly bonded. Fourth, when the n-type semiconductor is used as the photocatalyst, the foamed nickel is charged. And a large number of reduction reaction sites are scattered on the photocatalyst body surface. For example,
When a photocatalyst powder / fluorine resin mixed layer is pressed against glass fiber or ceramic as a substrate, the substrate is broken, and when a nonporous ordinary metal plate is used, there is no plasticity. It can be understood from the fact that a strong bond with the layer is not successful. 4th
In the following, the charge separation will be described.
That is, conventionally, for example, when a titanium oxide powder having platinum supported on a partial surface is suspended in water under light irradiation, holes move to the exposed surface of the titanium oxide due to charge separation and generate oxygen. It is well known that electrons move to the platinum portion to promote the generation of hydrogen. Platinum sputtered on an alumina substrate as in the above-mentioned conventional example (F) exhibits the same effect. The foamed nickel in the present invention plays a role similar to that of such platinum, which will be described in detail later. In the experiment of the effect of the photocatalyst on the death of algae, the foamed nickel substrate of the present invention was used. When comparing the case and the case of using a porous polyester nonwoven fabric instead of the foamed nickel substrate, the former is:
It is inferred from the fact that it showed much more pronounced efficacy than the latter. Naturally, platinum is generally expensive, while nickel is less expensive, and it is generally technically relatively difficult to produce a porous body from platinum.

Next, the significance of the photocatalyst powder-fluororesin mixture is that, as is well known in various fields, a mixed layer formed by using a fluororesin having a strong binding force and good corrosion resistance as a binder. In addition to the robustness, the photocatalytic activity is extremely high, and the activity lasts well.

Conventionally, experiments on photocatalysts have been mostly conducted in the form of a powdery photocatalyst suspended in a solution.
The explanation of the reaction mechanism is that the solution species undergoes oxidation or reduction at the surface of the photocatalyst, and thus the activity of the photocatalyst depends on its surface area, and if the contact area between the photocatalyst and the solution is large, It has been said that the larger the better. From this point of view, the photocatalyst is in solution,
It means that "wet" is better. It is presumed that conventionally, no attempt has been made to apply a water-repellent treatment to the photocatalyst, because the water-repellent treatment has been considered to make the photocatalyst less likely to wet, resulting in a reduction in the effective reaction area of the photocatalyst. Among the above-mentioned conventional methods for supporting a photocatalyst on a substrate, in the method (F), even if the titanium oxide powder is adhered to the substrate together with an organic solvent solution of methyl methacrylate as a water-repellent binder, The reason why the methyl methacrylate is thermally decomposed in the process is unknown, but if methyl methacrylate remains, the titanium oxide powder is less likely to wet the solution species (in this case, water vapor). It may be due to the idea that the contact area with it is reduced. In contrast, the inventors of the present application have surprisingly found that when the photocatalyst powder is bound with a binder having a very high water repellency such as a fluororesin, the photocatalyst powder becomes apparently “hard to wet”. In fact, they discovered that the photocatalytic activity was higher. More specifically, even when the same photocatalyst powder is used, it is used in the form of a fluororesin as in the present invention, compared to a case where the same photocatalyst powder is used as suspended as it is or does not have water repellency as sprayed by a low-temperature spraying method. The catalyst activity is higher if the binder is used to provide water repellency. Although the theoretical relationship between the water repellency and activity of the photocatalyst has not been elucidated so far, one hypothesis is that in the case of a conventional photocatalyst without water repellency, radicals are generated from adsorbed species at a specific site. When the radicals participate in the oxidation-reduction reaction of the solution species, but have water repellency, the sites of radical transfer or decomposition are different, the rate is faster, or the radicals dissolve in the aqueous solution. In the case of the type of redox reaction, if the solubility of that type in water is small, it is easy to approach the site close to the site with water repellency of the photocatalyst, and as a result, the redox reaction may be easier to proceed Is also conceivable. Further, by combining the photocatalyst powder-fluororesin mixture with the foamed nickel substrate, active sites similar to the catalyst in which platinum is supported on a part of the surface of the above-mentioned titanium oxide powder are to be widely generated. . In other words, since the catalyst mixture portion and the metal nickel portion coexist on the surface of the photocatalyst, a titanium oxide surface that is thought to function as an oxidation site of a redox reaction that proceeds by light irradiation and a metal surface that is thought to function as a reduction site This is because it is considered that a large number of highly active reaction sites having a certain fixed distance exist.

In the conventional method, for example, even if the photocatalyst is retained and fixed by a method such as press-fitting, impregnation, or deposition into the porous polymer membrane by the above-described method (C), as in the present invention. The water-repellent effect unlike the case where the photocatalyst powder is bound with a fluororesin binder cannot be obtained. In addition, when an organic polymer other than a fluororesin is used as a photocatalyst carrier, it is known that the organic polymer itself is oxidized and becomes brittle due to the photocatalytic effect.
Shows better resistance to photocatalytic effects.

[0015]

【Example】

<Examples> 1.0 mol / l nickel sulfate + 0.2 was used as a cathode, a nickel plate as an anode, a polyurethane porous material electrode provided by applying a graphite powder to polyurethane and having conductivity as a cathode.
After nickel was electrolytically reduced and produced at 50 ° C. in a mol / l boric acid solution, heat treatment was performed at 300 ° C. for 3 hours to obtain a foamed nickel plate having a three-dimensional network structure. On the other hand, 100 g of titanium oxide powder (particle size: 0.3 μm), which is an n-type semiconductor having a rutile crystal structure, is mixed with 300 m of a water suspension of polytetrafluoroethylene (solid content: 60%, specific gravity: about 1.5).
After the mixture was stirred sufficiently, alcohol was further added to promote agglomeration to obtain a muddy mixture.

Next, the kneaded material was cut into a size of 90 × 90 (mm), kneaded with a trowel from one side of the nickel foam plate into holes, and pressed at a pressure of 100 kg / cm ² , and further pressed for 150 minutes. Heat treatment was performed at 1 ° C. for 1 hour. With this press, the thickness of the foamed nickel substrate was initially 2.0
mm was compressed to 1.0 mm. Thus, an extremely robust photocatalyst consisting of a three-dimensional composite of a nickel foam foam-photocatalyst powdered fluororesin mixed photocatalyst as shown in FIG. 1 was obtained. In FIG. 1, (1) is a metal nickel portion, and (2) is a titanium oxide powder fluororesin mixture portion.

<Test Example of Photocatalytic Efficacy> There is often a situation in which it is difficult to overgrow algae due to photosynthesis in ponds and the like, but in order to suppress the overgrowth of the algae, the following experiment was conducted. Tried. First, 1 liter of water is put into a transparent glass beaker, fresh green algae (cum bar) are put in it, and various photocatalysts are put in. Then, it is put near the window of the transparent glass, and sunlight is irradiated on the beaker. And compared the photocatalytic effect on algal mortality.
As the photocatalyst, the product of the present invention (A) described in the above-described Examples, a photocatalyst (B) obtained by applying a titanium oxide-polytetrafluoroethylene mixture to a polyester nonwoven fabric and pressing the same, and the product of the present invention ( The same rutile type titanium oxide powder (suspended in water) and (C) as in A) were used. For comparison, a sample (D) using no photocatalyst was also prepared. The amount of titanium oxide used was the same in all cases.

The changes in algal color and tissue condition over time are shown in the following table.

[Table 1]

From the above table, as shown in the present invention, the photocatalysts (A, B) in which titanium oxide is bound with polytetrafluorofluoroethylene to give water repellency exhibit a photocatalytic effect on algal death. On the other hand, it is clear that a suspension of titanium oxide powder (rutile) as in the conventional product (C) does not show much effect. Also, the difference in potency between A and B indicates that porous nickel has a significant effect on charge separation.

As described above, the present inventors have found for the first time that the photocatalyst shows its effectiveness against the death of algae. Conventional photocatalytic research has been considered without exception to the case where the target species undergoes redox at the contact with the photocatalyst, but in the above experiment, the photocatalyst does not directly contact the algae. Therefore, this phenomenon cannot be explained by the conventional reaction mechanism. That is, the above-mentioned phenomenon cannot be explained unless it is considered that some oxidized species is once generated by the photocatalyst, and the oxidized species diffuses in the water to the point where there is an algae floating in the water. Heretofore, there have been no reports that such oxidizing species diffuse from the surface of the photocatalyst to offshore, and as a result, it has not been confirmed what kind of oxidizing species is diffused. The present inventors have discovered that OH ^- is adsorbed on the photocatalyst surface and then OH ^* radicals are formed, which associate to form H ₂ O ₂ , which diffuses off the water and removes algae. We are guessing for an attack, but have yet to confirm. In any case, it is presumed that there is some correlation between the diffusion of the oxidized species off the water and the binding of the photocatalyst powder of the present invention by the fluororesin, and furthermore, the water repellency. In other words, in the general technical field, it is a common practice to use a fluororesin to bind a powder material while imparting water repellency, but as described above, the fluororesin in the photocatalyst is used. It should be understood that the effects are based on new discoveries that go beyond these general effects.

As described above, according to the present invention, when manufacturing a photocatalyst, the material and the individual process itself such as using a foamed nickel plate as a base and using a fluororesin as a binder are used. Conventionally known in other technical fields, a combination thereof provides a completely new function and effect as a semiconductor photocatalyst. The field of application of the present photocatalyst is mainly an oxidation-reduction reaction system in an aqueous solution system, but it is also applicable to a reaction in a gas phase such as a deodorizer.

[Detailed description of drawings]

FIG. 1 is a sectional view of a photocatalyst according to an embodiment of the present invention.

[Explanation of symbols]

 1 Metal Nickel Part 2 Titanium Oxide-Fluororesin Mixture Part 3 Titanium Oxide Particles 4 Fluoro Resin Fiber

────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI B01J 35/02 B01J 35/04 331Z 35/04 331 A01M 29/00 Z // A01M 29/00 B01D 53/36 J (56) References JP-A-4-2844851 (JP, A) JP-A-2-107339 (JP, A) JP-A-2-213351 (JP, A) JP-A-62-66861 (JP, A) JP-A-58 -125602 (JP, A) JP-A-2-68190 (JP, A) JP-A-1-139139 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) A61L 2/16 A61L 2/02 B01J 35/02 B01J 35/04 331 B01D 53/86 A61L 9/01 A01N 25/34 A01M 29/00

Claims (1)

(57) [Claims] 1. A photocatalyst comprising kneading a mixture of a photocatalyst powder and a fluororesin binder into pores of a nickel foam substrate having a three-dimensional network structure and pressing the whole. body.