JPH04284851A - Photo-catalyst body - Google Patents

Abstract

PURPOSE:To obtain a photo-catalyst having sufficiently high mechanical strength and extremely enhanced in photo-catalytic activity by using porous nickel as a substrate and using fluoroplastics as a binder, and laminating and bonding porous nickel to a mixture of a photo-catalyst powder and fluoroplastics under pressure. CONSTITUTION:A sintered nickel plate formed by sintering a nickel powder or a foamed nickel plate having a three-dimensional reticulated structure obtained by decomposing polyurethane to which the electroless plating of nickel is applied under heating, is used as a substrate 1. A mixture 2 of a fluoroplastic binder such as polytetrafluoroethylene and a photo-catalyst powder such as a TiO2 or ZnO powder is placed on the substrate 1 to be pressed. The photo- catalyst thus obtained is strong and hardly generates rust or corrosion in water or air and has high activity.

Description

[Detailed description of the invention]

0001

FIELD OF INDUSTRIAL APPLICATION This invention relates to a photocatalyst used for sterilization, deodorization, wastewater treatment, inhibition of algae growth, various organic chemical reactions, and the like.

0002

BACKGROUND ART When a semiconductor is irradiated with light of a suitable wavelength having an energy greater than its band gap, electrons are transferred from the valence band to a conductor due to photoexcitation, and at the same time, holes are generated in the valence band. A so-called charge separation occurs. Also, when a semiconductor is exposed to water or a solution while being irradiated with light, a junction similar to a Schottky barrier is formed, and holes are transferred to the semiconductor if the semiconductor is n-type, and electrons are transferred if the semiconductor is p-type. It is well known that the particles gather on the surface of the solid-liquid interface. In the case of n-type semiconductors, holes extract electrons from water or solution species,
As a result, water decomposes and solutes in the solution are oxidized. Further, in the case of a p-type semiconductor, electrons are added to adjacent water or solution, and a reduction reaction of the water or solution species occurs. A semiconductor that promotes a photooxidation-reduction reaction in this way is particularly called a semiconductor photocatalyst or simply a photocatalyst.

Conventionally, as redox reactions or redox reaction operations using photocatalysts, water decomposition reactions, microorganism killing reactions, deodorizing reactions, sterilization reactions, water purification and wastewater treatment, and various other organic chemical reactions have been proposed. ing. Specifically, titanium oxide as an n-type semiconductor is used as a photocatalyst.
Most widely used because of its chemical stability. Titanium oxide may be used in powdered form suspended in a solution or supported on some kind of substrate. From the standpoint of photocatalytic activity, the former is generally more active due to its larger surface area;
From a practical standpoint, it is often necessary to adopt the latter method over the former method due to its ease of handling.

Various methods have been proposed for supporting photocatalysts on substrates. For example, (A) nitrocellulose,
Glass, polyvinyl chloride, nylon, methacrylic resin,
A method of attaching fine titanium oxide powder to a substrate in the form of a film, bead, board, fiber, etc. made of a light-transmitting material such as polypropylene (Japanese Patent Laid-Open No. 62-6686)
1), (B) A method of holding and fixing to a porous glass support by impregnating a porous glass support with an alcohol solution of titanium (IV) tetrabutoxy oxide and heating it to form anatase-type titanium oxide. (Unexamined Japanese Patent Publication No. 2-5
(C) By press-fitting, impregnating, adhering, etc. into a porous polymer membrane (e.g., polyfluoroethylene resin) having a photosensitizer such as a dye or a metal complex as a sidewall,
Method for holding and fixing semiconductor catalyst powder (JP-A-58-1
25602), (D) A method of supporting titanium oxide on a filtration filter made of polypropylene fiber or ceramic (Japanese Unexamined Patent Publication No. 2-68190), (E) Quartz, glass,
A method of holding and fixing titanium oxide powder in a tangle of plastic fibers and covering both sides with light-transmitting glass (U.S. Patent No. 4,888,101), (F) Sputtering platinum onto an alumina substrate. Fix it,
A mixed dispersion of anatase-type titanium oxide powder and an organic solvent solution of methyl methacrylate is applied onto it by spin coating, and then methyl methacrylate as a binder is thermally decomposed and anatase-type oxidation is performed. Method of converting titanium into rutile-type titanium oxide《Robert E. Hetrick - Robert E. H
etrick, Applied Physics C
communications, 5, (3), 177
-187 (1985)》, (G) A method of spraying and depositing titanium oxide on the surface of polyester cloth using a low-temperature spraying method (Tsukasa Sakurada, Surface Technology Vol. 41, No. 10, P60 (1990))
etc. have been proposed.

[0005]

[Problems to be Solved by the Invention] When considering the conventional methods of holding and fixing photocatalysts on substrates as described above, first of all, in any case, the substrate is not necessarily a wall cell such as an organic polymer film, glass, or ceramic. Because these materials are made of non-transparent materials, practical problems often occur when attempting to install these substrates holding and fixing photocatalysts into redox reactors. Furthermore, except for method (B) or (G), the strength with which the photocatalyst powder is held and fixed to the substrate is insufficient for practical use in each of the above-mentioned methods. Furthermore,
What all of the above methods have in common is that generally by holding and fixing the photocatalyst on a substrate, the catalytic activity is relatively reduced compared to when the photocatalyst powder is suspended in a liquid. That's what it means.

[0006]

[Means for Solving the Problems] The present invention attempts to solve the above-mentioned problems by using porous nickel as a base and laminating and pressing a layer of a mixture of photocatalyst powder and a fluororesin binder onto this base. It is something.

[0007]

[Operation] The photocatalyst according to the present invention is characterized by sufficiently high mechanical strength and extremely high photocatalytic activity. Hereinafter, the manufacturing process, structure, and significance of the photocatalyst according to the present invention will be explained in detail.

Porous nickel substrates include sintered nickel plates obtained by sintering nickel powder, and three-dimensional network structures obtained by electrolessly plating nickel on polyurethane and then thermally decomposing the polyurethane. So-called foamed nickel plates with a nickel-foamed material, or nickel fibers obtained by chatter vibration processing, etc., are made into paper and then sintered. Applicable. The porous nickel substrate is made of a nickel wire or expanded nickel core, a mixture of nickel powder and a glue such as a viscous aqueous solution of methylcellulose is applied to the surface, and then sintered. Things can also be effective. In the case of a porous nickel substrate obtained using expanded nickel as a core, the entire surface of the substrate is not covered with a porous nickel layer, and openings in the expanded nickel remain. A mixture of a semiconductor photocatalyst powder and a fluororesin binder is coated on this porous nickel substrate, or a mixture of a semiconductor photocatalyst powder and a fluororesin binder is made into a sheet shape in advance to form the porous nickel substrate. After placing it on a nickel base, it is pressed to produce a porous nickel base-semiconductor photocatalyst double layer body. Semiconductor photocatalyst powders include TiO2 (anatase type, rutile type), ZnO, SrTiO3, CdS, GaP, GaI
All conventionally known materials such as nP and GaAs can be applied to the present invention. As the fluororesin binder, polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-ethylene copolymer, etc. may be used alone or in mixtures. Further, these fluororesins are used in the form of an aqueous suspension, a liquid suspended in an organic solvent, or a powder. After pressing or during pressing, it is also effective to heat the fluororesin at a temperature of 100 to 300° C. in order to increase the binding strength of the fluororesin.

When a linear porous nickel substrate is used, a photocatalyst layer is formed on the surface of the substrate to form a linear photocatalyst. Although this may be used as is, it may be formed into a spiral shape or Braiding may be effective.

In the photocatalyst thus obtained, the significance of using the porous nickel substrate is, first, that it is more robust than conventional organic porous polymer films, glass fibers, ceramics, etc.; Second, it is difficult to rust or corrode under the environment in which the photocatalyst is placed, such as in water or in the air. Third, it is porous (6
Since it has plasticity with a porosity of 0 to 90%, the porous nickel base layer and mixed catalyst layer are firmly bonded when laminating and pressing a mixed layer of photocatalyst powder and fluororesin binder. Fourthly, when an n-type semiconductor is used as a photocatalyst, porous nickel contributes to charge separation.

The significance of using these porous nickel substrates is that, for example, when a photocatalyst powder-fluororesin mixed layer is pressure-bonded to a glass fiber or ceramic substrate, the substrate will be destroyed; This can be understood from the fact that when using a metal plate, strong bonding with the photocatalyst layer cannot be achieved due to lack of plasticity. The fourth charge separation will be explained as follows. In other words, conventionally, for example, when a titanium oxide powder with platinum supported on a portion of its surface is suspended in water under light irradiation, holes move to the exposed surface of the titanium oxide due to charge separation, generating oxygen. It is well known that the electrons transfer to the platinum portion and promote the generation of hydrogen. Platinum sputtered onto an alumina substrate as in the conventional example (F) described above also exhibits a similar effect. The porous nickel of the present invention plays a role similar to that of platinum. This will be described in detail later, but in experiments on the effectiveness of photocatalysts against algae death, the porous nickel of the present invention plays a role similar to that of platinum. This is also inferred from the fact that when comparing the case where a porous polytetrafluoroethylene sheet was used in place of the porous nickel substrate with the case where a porous polytetrafluoroethylene sheet was used instead of the porous nickel substrate, the former showed much more pronounced efficacy than the latter. Note that, as a matter of course, platinum is generally expensive, while nickel is cheaper, and it is generally relatively technically difficult to manufacture a porous body with platinum.

Next, the significance of the photocatalyst powder-fluororesin mixed layer is that, as is already well known in various fields, it is possible to mix the layer by using a fluororesin as a binder, which has strong binding strength and good corrosion resistance. In addition to the robustness of the layer, the photocatalytic activity is extremely high and the durability of the activity is good.

Conventionally, most experiments regarding photocatalysts have been carried out using powdered photocatalysts suspended in solutions.
The explanation of the reaction mechanism is that the solution species undergo oxidation or reduction on the surface of the photocatalyst. Therefore, 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 bigger the better. From this perspective, the photocatalyst is added to the solution,
It means that it is better to "get wet easily". The reason why no attempts have been made to apply water-repellent treatment to photocatalysts is thought to be because it was thought that water-repellent treatment would make them "difficult to get wet" and, as a result, reduce the effective reaction area of the photocatalyst. Among the conventional methods for supporting a photocatalyst on a substrate, in method (F), titanium oxide powder is attached to the substrate together with an organic solvent solution of methyl methacrylate, which is a water-repellent binder, but after the following It is unclear why this methyl methacrylate is thermally decomposed in the process, but if methyl methacrylate remains, the titanium oxide powder will become wet with the solution (in this case, water vapor). This may be due to the fact that the catalyst area was thought to be smaller. In contrast, the inventors of the present application found that when photocatalyst powder is bound with a highly water-repellent binder such as fluororesin, although the photocatalyst powder clearly becomes "difficult to wet," a surprising phenomenon occurs. In fact, they discovered that the photocatalytic activity was higher. in particular,
Even if the same photocatalyst powder is used, it is better to bind it with a fluororesin binder as in the present invention than to use it as a powder or to use it as a powder or to spray it by low-temperature thermal spraying, which does not have water repellency. The more water-repellent the catalyst is, the higher the catalytic activity will be. Although the relationship between the water repellency and activity of photocatalysts has not been theoretically elucidated so far, one hypothesis is that in the case of conventional photocatalysts that do not have water repellency, radicals are generated from adsorbed species at certain sites. However, whereas the radicals were involved in the redox reaction of the solution species, in the case of water repellency, the radical movement or decomposition site is different, the speed is faster, or the radical is dissolved in the aqueous solution. In the case of a redox reaction of a species, if the solubility of the species in water is low, it may be easier to approach sites close to the water-repellent sites of the photocatalyst, and as a result, the redox reaction may proceed more easily. can also be considered.

[0014] Among the conventional methods, for example, the above-mentioned (C
) method, even if the photocatalyst is held and fixed in the porous polymer membrane by a method such as press-fitting, impregnation, or deposition, it will not be possible to bind the photocatalyst powder with a fluororesin binder as in the present invention. No water repellent effect can be obtained. In addition, when an organic polymer other than fluororesin is used as a support for the photocatalyst,
Although it is known that the photocatalytic effect causes the organic polymer itself to undergo oxidation and become brittle, fluororesins exhibit better resistance to the photocatalytic effect.

[0015]

[Example] <Example 1> So-called carbonyl nickel powder obtained by thermal decomposition of nickel carbonyl and methyl A mixture of an aqueous solution of cellulose and a glue material is applied, and then heated to 85% in ammonia decomposition gas (mixed gas of hydrogen and nitrogen).
A porous sintered nickel substrate having a porosity of 85% and a thickness of 1.5 mm was obtained by sintering at 0°C. On the other hand, titanium oxide powder (particle size: 0
．． 3 μm), add 300 ml of polytetrafluoroethylene suspended in water (solid content 60%, specific gravity approximately 1.5), stir thoroughly, and then add alcohol.
Agglomeration proceeded to obtain a slurry-like kneaded material.

[0016] Next, this kneaded material was
After coating (6 g of titanium oxide) with a trowel on one side of the porous sintered nickel substrate cut out by the method of
Press at a pressure of 00 kg/cm2, and then press at a pressure of 150 kg/cm2.
Heat treatment was performed at ℃ for 1 hour. By this pressing, the thickness of the porous sintered nickel substrate, which was originally 1.5 mm, was compressed to 1.0 mm. In this way, a polar and robust photocatalyst body having a double structure of a porous nickel substrate, a photocatalyst powder/fluororesin mixed photocatalyst layer as shown in FIG. 1 was obtained. In FIG. 1, (1) is a porous nickel plate, and (2) is a titanium oxide powder/fluororesin mixed layer.

For comparison, a mat (thickness, 0.5 mm) made of glass fiber instead of the porous sintered nickel substrate and polytetrolafluoroethylene were obtained by the above-mentioned operation. Using nonwoven fabric (thickness, 0.5 mm), photocatalyst powder and fluororesin mixture were applied.
When pressed, the glass mat of the former was destroyed during the pressing process, and the latter was so-called cloth-like and too flexible.

<Example 2> In Example 1, a linear porous nickel substrate was manufactured in the following manner. That is, first, a mixture of nickel powder and a viscous aqueous solution of carboxymethyl cellulose (gluing material) was applied to the surface of a nickel wire with a wire diameter of 0.1 mm, and then the same process as in Example 1 was applied. sintered. Next, a mixed suspension of titanium oxide powder and polytetrafluoroethylene similar to that in Example 1 (however, the amount of water was relatively increased) was sprayed onto the linear porous nickel substrate. ,
Then, it was roll pressed. Its cross-sectional shape is shown in FIG. Moreover, an external view of this linear photocatalyst body made into a spiral shape is shown in FIG.

Example 3 In Example 1, an expanded nickel core was used as the porous nickel substrate, and a porous nickel layer was formed on the surface thereof in the same manner as in Example 2. Its cross-sectional shape is shown in FIG. In FIG. 4, 6 is an expanded nickel core, 7 is a porous nickel layer, and 8 is an opening, through which the solution or gas to be reacted can easily pass.

<Example of test on photocatalytic efficacy> Often, people are confused by excessive growth of algae due to photosynthesis in ponds, etc. In order to prevent the excessive growth of algae, the following experiment was conducted. I tried. First, fill a transparent glass beaker with 1 liter of water, add fresh green algae (camonvar), add various photocatalysts, and place it next to a transparent glass window so that sunlight will illuminate the beaker. A comparative experiment was conducted to compare the photocatalytic effect on the death of algae.

As the photocatalyst, the present invention product (A) described in the above-mentioned Examples, the photocatalyst material (B) prepared by coating a titanium oxide-polytetrafluoroethylene mixture on a polytetrafluoroethylene nonwoven fabric, and the polyester fabric surface coated with a low temperature A photocatalyst (C) to which rutile-type titanium oxide was attached by thermal spraying, a rutile-type titanium oxide powder (suspended in water) identical to the product of the present invention (A), and (D) were used. For comparison, a sample (E) that did not use any photocatalyst was also prepared. Note that the amount of titanium oxide used was the same in all cases.

The following table shows changes over time in the color and tissue condition of the algae.

From the above table, it can be seen that the photocatalysts (A, B) in which titanium oxide is bound with polytetrofluoroethylene to have water repellency as in the present invention exhibit a photocatalytic effect on the death of algae. On the other hand, it is clear that conventional products (C, D) in which titanium oxide powder (rutile) is suspended or sprayed by low-temperature spraying have no or little effect. In addition, the difference in effectiveness between A and B is that porous nickel
This shows that it has a certain effect on charge separation.

[0024] As described above, it was discovered for the first time by the inventors of the present application that a photocatalyst is effective in killing algae. Without exception, conventional research on the photocatalytic effect has only focused on cases in which the target species undergoes redox at the point of contact with the photocatalyst. However, in the above experiment, it was found that the photocatalyst and algae were not directly catalyzed. Since there is no,
This algae death phenomenon cannot be explained by conventional reaction mechanisms. In other words, the above-mentioned phenomenon cannot be explained unless we consider that some oxidized species is once generated by the photocatalyst and then diffused through the water to the point where the algae floating in the water are located. Until now, there have been no reports of such oxidizing species diffusing from the photocatalyst surface to offshore, and as a matter of course, it has not been confirmed what kind of substance the oxidizing species is. The inventors have discovered that OH- is adsorbed on the photocatalyst surface, and then OH* radicals are formed, which combine to produce H2O2, which diffuses offshore and attacks algae. I'm guessing, but so far I haven't been able to confirm it. In any case, it is presumed that there is some correlation between the diffusion of the oxidized species underwater and offshore, the binding of the photocatalyst powder of the present invention by the fluororesin, and eventually the water repellency. In other words, in the general technical field, it is common practice to use fluororesin to bind a certain powder material while imparting water repellency to it, but as mentioned above, the use of fluororesin in photocatalysts is common practice. It should be understood that the effects are based on new discoveries that go beyond these general effects.

[0024] As described above, in producing the photocatalyst, the present invention uses porous nickel as a substrate, fluororesin as a binder, etc., and the individual steps of the material and manufacturing method themselves are , are conventionally known in other technical fields, but by combining them, they exhibit completely new functions and effects as a semiconductor photocatalyst.

The field of application of the present photocatalyst is mainly redox reaction systems in an aqueous solution system, but it can also be applied to reactions in a gas phase, such as in deodorizers.

[Detailed explanation of drawings]

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

FIG. 2 is a sectional view of a photocatalyst according to Example 2 of the present invention.

FIG. 3 is an external view of a photocatalyst according to Example 2 of the present invention.

FIG. 4 is a diagram showing a cross-sectional structure of a porous nickel substrate according to Example 3 of the present invention.

[Explanation of symbols]

1 Porous nickel plate 2 Titanium oxide powder-fluororesin mixed layer 3 Nickel wire 4 Porous nickel layer 5 Titanium oxide powder-fluororesin mixed layer 6 Expanded nickel core portion 7 Porous nickel layer 8 Opening

Claims (1)

[Claims] Claim: A photocatalyst body comprising a porous nickel substrate and a mixture of photocatalyst powder and a fluororesin binder laminated and pressed together.