JPH10130887A - Production of porous titanium oxide film, porous titanium oxide film and photocatalyst for decomposing gaseous nox - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for forming a highly active porous titanium oxide film having innumerable micropores on the surface of titanium and having a large surface area and to furnish a photocatalyst applying the characteristic of the film and capable of efficiently decomposing gaseous NOx . SOLUTION: Titanium is anodized in an aq. soln. of the electrolyte consisting of a glycerophosphate and a metal acetate to form an anodic oxide film contg. a liq.-soluble substance and having at least 0.1μm thickness, and then the anodic oxide film is hydrothermally treated to elute the liq.-soluble substance. The acetate of an alkali metal or an alkaline-earth metal or lanthanum acetate is preferably used as the metal acetate. Further, the anodization is conducted by changing the concn. and composition ratio of the electrolyte. Porous titanium oxide film 1 is formed on a titanium substrate 5 or a titanium net and used as a photocatalyst for decomposing gaseous NOx .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a titanium oxide film applied to a wet solar cell utilizing a photocatalyst and a photosensitizing effect.

[0002]

2. Description of the Related Art Titanium oxide has various uses and has been put to practical use as a dielectric material, a white pigment (titanium white), and the like. Furthermore, since the excited holes on the surface of titanium oxide have a very high oxidation potential, their properties as semiconductors are attracting attention. For example, harmful substances such as antibacterial materials that break down oxygen and moisture in the air to generate active oxygen and kill mold and bacteria, photocatalysts that break down water to generate hydrogen or oxygen, and nitrogen oxides It is being studied as a decomposing photocatalyst.

Recently, a wet solar cell using a titanium oxide film coated with a dye has been studied. This is characterized by being cheaper and more efficient than a conventional solar cell using amorphous silicon. What is important in these applications is to increase the area of a part involved in a chemical reaction. In general, increasing the surface area increases the amount of chemical reaction, thus improving performance when incorporated into an apparatus or device. In order to increase the surface area, fine irregularities may be formed on the substrate holding titanium oxide, the titanium oxide film may be made porous, or the titanium oxide powder particles may be made fine.

[0004] When titanium oxide is applied to an apparatus or a device, it is convenient to handle the film or plate in a state of a powder or a plate rather than in a powder state because maintenance is easier. Conventionally, as a method of manufacturing an oxide film, a vacuum evaporation method, a chemical evaporation method (CVD)
), A gas phase method such as a sputtering method, a liquid phase method such as a spin coating method, and a solid phase method such as a thermal spraying method or a method using a solid phase reaction. In addition, as a method for producing an oxide plate material, a method in which oxide powder particles are mixed with a binder and then mechanically spread thinly, or a method in which the oxide powder particles are packed in a mold and fired at a high temperature. Bonding sintering methods are known.

[0005] As means for increasing the surface area of the film or plate, there is a method of forming a so-called porous structure having a fine uneven surface and an infinite number of pores, or a method of using finely divided powder particles as a raw material. Conventional porous titanium oxide films are often produced by a so-called sol-gel method in which a sol solution of titanium alkoxide is applied to a substrate and then heat-treated. Since this film is composed of very fine titanium oxide particles, its surface area is significantly larger than the apparent area. Accordingly, the contact area with the liquid or gas is increased, and the performance is improved.

On the other hand, there is an anodic oxidation method as a method for producing an oxide film. The anodic oxidation method is a method of forming an oxide of the metal on the surface of the metal.The film forming rate is faster than other methods of manufacturing a ceramic film, and the thickness is uniform even if the substrate has a large area. There is an advantage that a film can be formed. In addition, since a film can be formed on a substrate having a complicated shape, it is an industrially useful film forming method for forming a ceramic film.

Conventionally, when anodizing titanium in an electrolyte aqueous solution comprising phosphoric acid, sulfuric acid, or a mixed acid thereof, it is possible to stably anodize up to a high voltage of several hundred volts. It is known that a thick anodic oxide film is formed. It is known that when a titanium substrate is anodized at a high voltage, a large number of discharge marks are formed by spark discharge generated on the surface of the substrate and the substrate becomes porous.

The photocatalyst for decomposing the nitrogen oxide gas utilizes the properties of titanium oxide as a semiconductor. When fossil fuels such as petroleum and coal, which are used in large amounts as energy sources, are burned, large amounts of carbon dioxide, nitrogen oxides, sulfur oxides, and the like are emitted. As a result, carbon dioxide causes global warming, and nitrogen oxides and sulfur oxides react with atmospheric moisture to produce acid rain, which causes environmental destruction.

When titanium oxide is used as a photocatalyst, N
Nitrogen oxides such as O and NO ₂ (hereinafter collectively referred to as NO _x ) and sulfur oxides such as SO ₂ and SO ₃ can be rendered harmless or removed. Photocatalyst is a kind of semiconductor,
Holes and electrons are generated by absorbing energy above the band gap. The holes and electrons react with oxygen gas and water in the atmosphere to generate active oxygen such as oxygen atoms, oxygen radicals, and hydroxyl radicals. The active oxygen acts on the harmful gas to decompose the gas. By the above series of mechanisms (photocatalytic reaction), harmful gas can be decomposed in titanium oxide by irradiating light energy having a band gap energy of about 3 eV or more.

Conventionally of the NO _x cracking photocatalyst, mixed titanium oxide from the direction of the state of the plate than to use it handling ease in the form of powder, titanium oxide powder activated carbon particles and a fluorine resin and mechanically Then roll this to a thickness of 0.
It was made into a sheet of 5 to 1 mm. Further, in order to enhance the reaction efficiency, the titanium oxide powder may be miniaturized to increase the surface area, or the content of the titanium oxide powder may be increased.

[0011]

The conventional method for producing an oxide film has the following disadvantages. The vacuum deposition method
The material is heated and evaporated under a high vacuum, and the evaporated particles are deposited on the substrate.A substance having a high melting point such as an oxide is melted and evaporated under a high vacuum of about 10 ^-3 Pa. Equipment and maintenance costs are high.

The chemical vapor deposition method utilizes a reaction of a compound gas to vaporize a gaseous raw material or a liquid or solid raw material and form a film by performing a chemical reaction such as decomposition / bonding in a gas phase or on a substrate surface. And the cost of equipment and maintenance is large. The sputtering method uses, for example, gas atoms ionized in a high-frequency electric field as a target (raw material).
And strikes the raw material from the surface to deposit on the substrate. In this method, since it is not necessary to melt the raw material, a high melting point metal, oxide, nitride, or the like can be used as the raw material. However, the equipment itself becomes rather large, and the equipment and maintenance costs are high.

[0013] The spin coating method is a method for forming a film by a wet process.
This is a method in which a coating liquid (raw material) is scattered on a substrate such as a metal using centrifugal force due to rotation to form a film on the substrate. However, since it is necessary to rotate the substrate, it is difficult to form a film having a uniform thickness on a substrate having a large area or a complicated shape.

The thermal spraying method is a method in which a raw material powder is melted by plasma or the like and a molten raw material is sprayed on a substrate to form a film. This method can result in changes in the chemical composition of the coating due to the thermal decomposition of the raw materials and is also very costly to operate.

In the sol-gel method, the steps of coating and heating must be repeated many times in order to increase the thickness of the film, so that the film-forming speed is low and is not practical. Moreover, it is very difficult to form a film having a uniform thickness on a large-area substrate. On the other hand, when an oxide plate material is used for the purpose of a chemical reaction on its surface, there is more waste of material than an oxide film. However, since both the surface and the inside are made of the same material, there is an advantage that the surface layer hardly peels off and the performance does not deteriorate even if the surface layer falls off.

In the method of mixing oxide powder particles with a binder and mechanically processing the binder, the density of the oxide powder particles is reduced by the amount of the binder, so that the surface of the plate material can be effectively used. There is a disadvantage that it cannot be used. The sintering method is
The chemical composition of the plate may change due to thermal decomposition of the oxide powder particles as a raw material, and furthermore, a mold must be used, which is not suitable as a method for producing a plate having a large area or a complicated shape.

As described above, the anodic oxidation method is an industrially useful method for producing an oxide film, and the possibility of peeling and falling off of the film is very low. However, since the diameter of the discharge trace on the anodic oxide film formed by the conventional anodic oxidation is as large as about several μm, it does not contribute much to increasing the surface area. In order to increase the surface area of the coating, it is necessary to make the coating porous by forming countless very small pores of about several tens nm.

Further, the crystal phase of the conventional porous titanium oxide film is mainly a rutile phase, and this rutile phase has a relatively wide band gap and has a problem that its activity as a semiconductor is not so high. Therefore, the present invention provides a method for forming a porous titanium oxide film having a thickness of 0.1 μm or more on the surface of titanium at a thickness of 0.1 μm or more in which the actual surface area is increased by tens to hundreds of times at low cost. It is still another object of the present invention to provide a production method for making the porous titanium oxide film have high activity. Further, the present invention was applied a porous titanium oxide film according to the manufacturing method described above, and an object thereof is to provide efficiently short time photocatalyst can decompose NO _x.

[0019]

Means for Solving the Problems The present inventors have found that the step of anodizing titanium and the step of hydrothermally treating this anodized film at a high temperature and a high pressure can greatly increase the surface area of the anodized film. I paid attention. In the present invention, based on this, first, a titanium anodic oxide film containing a substance soluble in a liquid is prepared, and then a hydrothermal treatment is performed to elute the substance soluble in the liquid to produce a porous titanium oxide film. I found what I could do.

It has also been found that the crystal phase of the porous titanium oxide film can be controlled by selecting the conditions of the anodizing treatment, in particular, the type, concentration and composition ratio of the electrolyte. Therefore, the invention according to claim 1 of the present invention relates to a method comprising: “anodizing a titanium substrate in an aqueous solution of an electrolyte composed of glycerophosphate and metal acetate to contain a substance soluble in a liquid; A step of producing an anodized film having a thickness of, and the titanium substrate having the anodized film formed thereon is subjected to hydrothermal treatment in a liquid or in a vapor thereof to form a liquid-soluble substance in the anodized film. Eluted to form fine pores ".

The electrolyte used for the anodic oxidation is preferably a mixture of glycerophosphate and metal acetate. In particular, the metal acetate is preferably an alkali metal or alkaline earth metal acetate or lanthanum acetate. Preferred (claim 2). Further, sodium glycerophosphate is used as the glycerophosphate, the concentration in the aqueous solution is 0.001 to 0.15 mol / l, and the concentration of the metal acetate in the aqueous solution is 0.01 to 0.5 mol / l. ).

In the invention according to claims 4 to 6 of the present invention, a titanium substrate is replaced with a titanium net as an object to be processed.
This corresponds to the above-described inventions according to claims 1 to 3, respectively. The invention according to claim 7 of the present invention is formed by anodizing titanium in an aqueous solution of an electrolyte composed of glycerophosphate and metal acetate, and further performing a hydrothermal treatment in a liquid or a vapor thereof. "It is a porous titanium oxide film.
This coating contains countless micropores, at least
It has a thickness of 0.1 μm.

The above-mentioned porous titanium oxide film is preferably produced by using an alkali metal or alkaline earth metal acetate or lanthanum acetate as a metal acetate. Further, the above-mentioned porous titanium oxide film uses, in particular, sodium glycerophosphate, the concentration in the aqueous solution is 0.001 to 0.15 mol / l, and the concentration of the metal acetate in the aqueous solution is 0.01 to 0.5 mol / l. It is preferably manufactured (claim 9).

According to a tenth aspect of the present invention, there is provided a method for producing a titanium substrate or a titanium net, comprising the steps of: anodizing the titanium substrate or the titanium net in an aqueous solution of an electrolyte comprising glycerophosphate and a metal acetate; A photocatalyst for decomposing nitrogen oxide gas, comprising: a titanium oxide film having a thickness of at least 0.1 μm and containing a myriad of fine pores, formed by hydrothermal treatment in a liquid or its vapor.

The porous titanium oxide film constituting the photocatalyst for decomposing nitrogen oxide gas is preferably produced by using an alkali metal or alkaline earth metal acetate or lanthanum acetate as a metal acetate. Claim 1
1). Further, the porous titanium oxide film constituting the nitrogen oxide gas decomposition photocatalyst is, in particular, sodium glycerophosphate, and the concentration in the aqueous solution is 0.001 to 0.15.
mol / l, and the concentration of the metal acetate in the aqueous solution is 0.01 to
It is preferable to produce it as 0.5 mol / l (claim 12).

[0026]

BEST MODE FOR CARRYING OUT THE INVENTION The anodic oxidation performed in the present invention is performed by applying an electric field to a metal to be treated as an anode and an arbitrary metal as a cathode in an electrolyte, so that a metal having a thickness of several μm is formed on the surface of the metal on the anode side.
This is a technique for forming an oxide film. In the present invention, by incorporating a soluble substance dissolved in an electrolyte into a film formed by anodic oxidation, a heat treatment (hydrothermal treatment) is performed in a liquid or vapor to elute the soluble substance. Form a porous titanium oxide film.

In the present invention, any electrolyte can be used as long as the substance contained in the electrolyte is incorporated into the film during the anodization. However, as will be described in detail below, the anodized film of titanium depends on the anodizing conditions, particularly the voltage and the type and concentration of the electrolyte, the color of the film, the thickness of the film, the number and size of the pores, the crystal phase. There are differences in type and composition.

The color tone of the film is determined by the ratio of oxygen atoms and titanium atoms constituting titanium oxide. In TiO ₂ , the atomic ratio between oxygen and titanium is originally 2 and is white, but if titanium is excessive, the color tone becomes blackish. When a strong acid such as phosphoric acid, sulfuric acid, or a mixed acid thereof conventionally used for anodizing titanium is used, elution of titanium from the titanium substrate increases, and titanium oxide having a blackish color tone is obtained.

On the other hand, when a mixed solution of glycerophosphate and metal acetate is used as in the present invention, the elution of titanium is suppressed because the electrolyte solution is weakly alkaline, so that the atomic ratio of oxygen to titanium is reduced. It becomes almost 2, and exhibits a white color. When it is desired to increase the thickness of the film to about several μm, it is preferable to use phosphoric acid, sulfuric acid or a mixed acid thereof, or a mixed solution of glycerophosphate and metal acetate. A mixed solution of glycerophosphate and metal acetate is particularly preferred in terms of controlling the thickness of the anodic oxide film and making the film porous. Examples of the glycerophosphate include sodium glycerophosphate and calcium glycerophosphate, and sodium glycerophosphate is most preferable because it is very soluble in water.

Any kind of metal acetate can be used, but especially acetates of alkali metals (lithium, sodium, potassium, rubidium, cesium), acetates of alkaline earth metals (magnesium, calcium, strontium, barium), Further, lanthanum acetate or the like is preferable because it has a very high solubility in an aqueous solution of glycerophosphate and can stably anodize up to a high voltage.

When titanium is anodized using these electrolytes, an anodic oxide film is formed in which phosphorus ions or phosphate ions are taken in from phosphoric acid or glycerophosphate and metal ions are taken in from metal acetate. Among metal acetates, a large amount of alkaline earth metal ions or lanthanum ions can be taken into the film by using, in particular, an alkaline earth metal acetate or lanthanum acetate and increasing the concentration.

For example, when sodium β-glycerophosphate and strontium acetate are used for the electrolyte, an anodic oxide film containing P and Sr is formed, and its content is almost determined by the concentration of these electrolytes. Regardless of which electrolyte is used, there is a tendency that the higher the electrolyte concentration is, the more the amount of ions taken into the film is. The larger the amount of ions eluted from the film, the larger the diameter of pores formed in the anodized film. Therefore, the pore size can be controlled by the ratio of the soluble substance in the film, that is, the electrolyte concentration. The pore density (porosity) can be controlled by the composition of the electrolyte. For example, the content of P in the anodic oxide film is higher when 0.1 mol / l calcium acetate is added to this phosphoric acid than when phosphoric acid having a concentration of 0.26 mol / l is used alone as an electrolyte. A film having a significantly increased porosity is obtained.

The electrolyte concentration also depends on the anodic oxidation conditions. If the concentration of sodium glycerophosphate is lower than 0.001 mol / l, it becomes difficult for electric current to flow, and if it is higher than 0.15 mol / l, it reacts with acetate to precipitate. Tends to occur. When the concentration of the metal acetate is lower than 0.01 mol / l or higher than 0.5 mol / l, the anodic oxidation treatment becomes difficult. Therefore, in the present invention,
0.001 ~ 0.15mo concentration range of sodium glycerophosphate
l / l and the concentration range of the metal acetate were 0.01 to 0.5 mol / l.

When calcium acetate or strontium acetate is used as the electrolyte, calcium apatite or strontium apatite crystals may be deposited on the anodic oxide film by hydrothermal treatment depending on their concentrations. However, by adjusting the concentration of these acetates, no apatite crystals can be precipitated. That is, when the concentrations of the acetate and the sodium β-glycerophosphate are both reduced, crystals are not formed because the concentration of the eluted ions is too low. Alternatively, if the concentration of acetate is reduced from 1/5 to 1/20 with respect to the concentration of sodium β-glycerophosphate, crystals are not formed because the concentration ratio of the eluted ions is significantly different from the composition ratio of apatite crystals. Thus, it is desirable to adjust the electrolyte concentration so that apatite crystals do not precipitate on the surface of the anodic oxide film.

Before starting anodic oxidation using these electrolytes, the highest attainable voltage is set in advance. When the anodization is started, the voltage gradually increases. When the voltage reaches the maximum voltage, no current flows and the anodization is terminated. The time required for anodic oxidation can be completed in a shorter time as the current density is increased and the pressure is increased faster.
Make it relatively short, about 5 to 10 minutes. In order to increase the surface area of the anodic oxide film, it is more preferable that the thickness of the film is not less than a certain value, for example, not less than 1 μm. Since the thickness of the anodized film is proportional to the voltage, it is preferable to increase the film thickness by anodizing at a high voltage. However, if the film thickness is too large, anodic oxidation cannot be performed stably, so that about 500 V is the limit. When the voltage exceeds about 100 V, spark discharge occurs on the surface of the anodic oxide film, and the anodic oxide film is locally heated to a high temperature. As a result of repeatedly heating the film innumerably, the entire anodic oxide film is crystallized, and a titanium anodic oxide film having high crystallinity is formed. Incorporation of a soluble substance from the electrolyte into the anodic oxide film is also performed by heating by spark discharge. In the anodizing method,
Even if the titanium substrate has a large area or a complicated shape, a titanium oxide film having a uniform thickness can be formed, and a single reaction time is relatively short, about several minutes. In addition, since the treatment can be performed in an aqueous solution at room temperature without requiring a special device, the energy consumption can be extremely small.

As the elution method, the anodic oxide film is coated with a liquid or vapor in a closed container such as an autoclave for 100 to 100 minutes.
The so-called hydrothermal method of heating in the range of 500 ° C. is effective. If the heating temperature is lower than 100 ° C, the soluble substance hardly elutes. Also, heating the autoclave to a temperature higher than 500 ° C. is not common since the equipment becomes very large. The pressure in the container varies greatly depending on the heating temperature, depending on the type and amount of the liquid contained therein. In the present invention, the pressure range allowed in a normal autoclave was used. In general, pure water is used as the liquid, but the liquid is not limited to pure water, and may be made acidic or alkaline in order to promote elution of the soluble substance from the anodic oxide film. When the liquid is heated while being stirred, the elution is promoted. By dissolving the soluble substances taken into the titanium anodic oxide film by this hydrothermal treatment,
Since numerous pores are formed, the surface area of the coating can be significantly increased. Further, by heating, crystallization of the film proceeds, and the crystallinity further increases.

The crystalline phase of the porous titanium oxide film thus formed is usually composed of an anatase phase and a rutile phase, but the ratio depends on the electrolyte concentration in the aqueous solution and the composition ratio. . For example, even if the type of electrolyte is the same, by adjusting the concentration and composition ratio,
The proportion of the highly active anatase phase can be as high as 90-100%.

Hereinafter, the present invention will be described in more detail with reference to embodiments. In these embodiments, the object to be treated is plate-shaped titanium, but is not limited to plate-like titanium, and may be a fibrous, woven, or net-like or an aggregate obtained by combining these two-dimensionally and three-dimensionally with the object to be treated. can do. In the following embodiments, in the sixth and seventh embodiments, by using a titanium plate porous titanium oxide film according to the present invention is formed, it is described for the catalyst activity as the NO _x decomposition photocatalytic.

[First Embodiment] The anodizing conditions of a titanium substrate were as follows: an electrolyte aqueous solution consisting of sodium β-glycerophosphate at a concentration of 0.08 mol / l and strontium acetate at a concentration of 0.05 mol / l was used. the density of 50mA / cm ^2,
The voltage was up to 400V. Hydrothermal treatment conditions were 300 ° C. for 2 hours in high-pressure water.

FIG. 1 is a schematic diagram showing a cross section of the porous titanium oxide film after the above-mentioned treatment. The porous titanium oxide film 1 is composed of titanium oxide fine particles 2 and pores 3 formed at the boundaries thereof, and fine irregularities 4 are formed on the outermost surface. Since ions such as P and Sr are taken into the pores 3 at the time of anodic oxidation, an increase in the surface area of the porous titanium oxide film 1 mainly depends on fine irregularities 4 on the surface.

When these ions are eluted into high-temperature and high-pressure water by the hydrothermal treatment, the inside of the pores 3 becomes empty, so that the surface area of the porous titanium oxide film 1 further increases. FIG. 2 is an SEM photograph showing the surface structure of the porous titanium oxide film after the above treatment. This film is
The porous structure was composed of very fine titanium oxide fine particles with a particle size of about 40 nm, and pores exist between the fine particles. The crystal phase of the fine particles was of the anatase type.

The thickness of the porous titanium oxide film is about 12 μm.
m, and the results of elemental analysis showed that the diffraction peaks indicating elements such as P and Sr incorporated in the film during anodic oxidation showed low values, and it was clear that the sample was eluted from the film into water by hydrothermal treatment. It became. As described above, by eluting P and Sr from the anodic oxide film, a porous titanium oxide film having a large surface area was formed.

[Second Embodiment] The anodizing conditions for a titanium substrate were as follows: an electrolyte aqueous solution comprising 0.005 mol / l sodium β-glycerophosphate and 0.08 mol / l strontium acetate was used. the density of 50mA / cm ^2,
The voltage was up to 350V. Hydrothermal treatment conditions were 300 ° C. for 2 hours in high-pressure water.

The surface area after the completion of the anodic oxidation was 60 times as large as that of the untreated titanium substrate, and was 98 times after the completion of the hydrothermal treatment. Note that a nitrogen adsorption method was used as a surface area measuring method. [Third Embodiment] Anodizing conditions for a titanium substrate are as follows:
0.005mol / l β-glycerophosphate sodium and 0.13mol
The electrolyte temperature was 40 ° C., the current density was 50 mA / cm ² , and the voltage was up to 350 V using an aqueous solution of sodium acetate composed of 1 / l sodium acetate. Hydrothermal treatment conditions are 300 ° C, 2
Time.

The surface area after the anodization was 35 times larger than that of the untreated titanium substrate, and 63 times after the completion of the hydrothermal treatment. [Fourth Embodiment] The conditions for anodizing a titanium substrate are as follows:
0.02mol / l β-glycerophosphate sodium and 0.09mol
Using an aqueous electrolyte solution consisting of / l strontium acetate,
Electrolyte temperature 40 ° C., and a current density of 50mA / cm ^2, 350V voltage
Up to. Hydrothermal treatment conditions are 300
C. for 2 hours.

As a result, the thickness of the porous titanium oxide film is
It was 2.5 μm. When only the voltage was set to 400 V, the thickness of the porous titanium oxide film was 9.0 μm. That is, the film thickness increases as the anodic oxidation is performed up to a higher voltage. [Fifth Embodiment] The anodizing condition of the titanium substrate is β-
The concentration of sodium glycerophosphate was kept constant at 0.005 mol / l, the concentration of calcium acetate was changed in the range of 0 to 0.4 mol / l, and the other conditions were the same as in the first embodiment. The density was 50 mA / cm ² and the voltage was up to 350V. The conditions of hydrothermal treatment are as follows:
Time.

FIG. 3 is a diagram showing a change in the composition of the crystal phase of the porous titanium oxide film according to the present embodiment. As shown in FIG. 3, the composition ratio of the anatase phase and the rutile phase changes according to the concentration of calcium acetate. The composition ratio of the anatase phase, the concentration range of calcium acetate is 0.05 to 0.1 mol / l.
And it was 90-100%. The diffraction intensity of the anatase phase was maximized when the concentration of calcium acetate was 0.09 mol / l, and the composition ratio was 92%. But,
As the concentration of calcium acetate increases, the proportion of the rutile phase increases. Therefore, by limiting the concentration of calcium acetate to a certain range, the composition ratio of the anatase phase can be 90 to 100%. In this embodiment,
When the concentration range of calcium acetate was set to 0.05 to 0.1 mol / l, a porous titanium oxide film of almost anatase single phase was obtained, but depending on the type of metal acetate used and other anodic oxidation conditions, anatase phase was obtained. Therefore, it is necessary to select an appropriate condition because the composition ratio of the compound is different.

[Sixth Embodiment] In this embodiment, the width 20
mm, length 150mm, thickness 0.5mm titanium substrate (titanium plate)
It relates porous titanium oxide film formed by anodizing treatment and hydrothermal treatment of the present invention, the performance as the NO _x decomposition photocatalytic described. Anodizing conditions for the titanium substrate were as follows: using an aqueous electrolyte solution consisting of sodium β-glycerophosphate at a concentration of 0.02 mol / l and strontium acetate at 0.08 mol / l, at an electrolyte temperature of 40 ° C. and a current density of 50 mA / cm ² ,
The voltage was up to 400V. The time required for anodization was about 7 minutes. Next, the hydrothermal treatment conditions were 180 ° C. for 4 hours in high-pressure water. For hydrothermal treatment, use distilled water 0.9
An autoclave with a capacity of 1.3 l was used.

FIG. 4 shows the NO produced by the above process.
FIG. 3 is a partial cross-sectional view of an _x- decomposition photocatalyst. A porous titanium oxide film 1 is formed on the surface of a titanium substrate 5. The porous titanium oxide film 1 was composed of fine titanium oxide fine particles having a particle size of about 30 nm, had a porous structure in which pores exist between the fine particles, and were firmly bonded to the titanium substrate 5. The crystal phase of the fine particles was 100% anatase phase. The thickness of the porous titanium oxide film was about 8 μm, and the surface area was remarkably increased by 700 to 800 times.

Subsequently, the catalytic activity of the porous titanium oxide film after the above treatment was evaluated using a closed circulation system reactor. (A) Evaluation of Catalytic Activity by Fluorescent Light A titanium plate on which the above-mentioned porous titanium oxide was formed and a NO standard gas having a concentration of 10.5 ppm were introduced into the flask at about 650 mmHg and sealed. The flask was irradiated with 100 W fluorescent light to measure the concentration of NO gas over time.

FIG. 5 is a graph showing the change over time of the NO standard gas concentration when light is irradiated under three conditions.
The NO gas concentration decreases almost in proportion to the irradiation time, and the photocatalytic effect can be evaluated by the amount of the decrease. As shown in FIG. 5, when the light of the fluorescent lamp is irradiated for 24 hours, the initial concentration is 10.5 p.
pm NO standard gas was reduced to 2.2 ppm. Next, in order to investigate the possibility of spontaneous decomposition of NO gas by light, a blank experiment was conducted in which only a NO standard gas was inserted and light from a fluorescent lamp was applied. As a result, the NO standard gas having an initial concentration of 10.5 ppm was reduced to 8.6 ppm. Furthermore, in order to examine the adsorption to the catalyst and the flask, etc., a titanium plate on which porous titanium oxide was formed and a NO standard gas were placed in the flask, and a dark experiment was conducted in which external light was blocked. The NO standard gas was reduced to 8.7 ppm. From the above experimental results, it is considered that at least 6 ppm of NO gas was decomposed by photocatalysis after irradiation for 24 hours.

(B) Evaluation of catalytic activity by high-pressure mercury lamp light A titanium plate on which the porous titanium oxide was formed and a NO standard gas having a concentration of 10.0 ppm were introduced into the flask and sealed at about 650 mmHg. The flask was irradiated with light from a 450 W high-pressure mercury lamp, and the concentration of NO gas was measured over time. As shown in Fig. 5, when the light of a mercury lamp is irradiated for 1 hour, the initial concentration is 10.0p.
pm NO standard gas was reduced to 0.6 ppm. Next, in order to investigate the possibility of spontaneous decomposition of NO gas by light, a blank experiment was conducted in which only a NO standard gas was inserted and light from a mercury lamp was irradiated. After one hour, the NO standard gas having an initial concentration of 10.0 ppm was reduced to 9.4 ppm. Further, in order to examine adsorption to a catalyst, a flask, and the like, a titanium plate on which porous titanium oxide was formed and a NO standard gas were placed in the flask, and a dark experiment was performed. After 18 hours, the NO standard gas with an initial concentration of 10.0 ppm was reduced to 8.5 ppm. From the above experimental results, it is considered that at least 8 ppm of NO gas was decomposed by photocatalysis after 1 hour.

As described above, when a porous titanium oxide film having a high crystallinity of an anatase phase and a very large surface area per unit area is used for a photocatalyst, the number of NO molecules adsorbable on the surface is greatly increased. And the NO gas can be efficiently decomposed in a short time. [Seventh Embodiment] In this embodiment, the width is 20 mm and the length is 150 mm.
mm, relates porous titanium oxide film formed by anodizing treatment and hydrothermal treatment of the present invention to a titanium substrate having a thickness of 0.5 mm (titanium plate), it will be described performance as the NO _x decomposition photocatalytic.

Anodizing conditions for the titanium substrate are as follows:
Using an aqueous electrolyte solution consisting of l / l sodium β-glycerophosphate and 0.13 mol / l sodium acetate,
The temperature was 40 ° C., the current density was 50 mA / cm ² , and the voltage was 350 V. The time required for the anodization was about 5 minutes. next,
Hydrothermal treatment conditions were 300 ° C. for 2 hours in high-pressure water. For hydrothermal treatment, 0.2 l of distilled water was added, and the volume was 1.3 l
Autoclave was used.

Subsequently, the catalytic activity of the porous titanium oxide film after the above treatment was evaluated using a closed circulation system reactor. (C) Evaluation of catalytic activity by sunlight A titanium plate on which the porous titanium oxide was formed and a NO standard gas having a concentration of 10.5 ppm were placed in a flask having a capacity of 2 liters for about 6 hours.
50 mmHg was introduced and sealed. Irradiate the flask with sunlight,
The concentration of the NO gas was measured over time.

When irradiated with sunlight for a total of 24 hours, the initial concentration
10.0 ppm NO standard gas was reduced to 0.1 ppm. Next, to investigate the possibility of spontaneous decomposition of NO gas by light,
A blank experiment was conducted in which only the O standard gas was introduced and sunlight was irradiated. After 24 hours, the NO standard gas having an initial concentration of 10.5 ppm was reduced to 9.0 ppm. Further, in order to examine adsorption to a catalyst, a flask, and the like, a titanium plate on which porous titanium oxide was formed and a NO standard gas were placed in the flask, and a dark experiment was performed. After 24 hours, the NO standard gas with an initial concentration of 10.5 ppm was reduced to 10.0 ppm. From the above experimental results, it is considered that at least 8 ppm of NO gas was decomposed by photocatalysis after 24 hours by sunlight.

[0057] above, sixth and 7 NO _x decomposition photocatalytic described in the embodiment of, because of the high crystallinity of the porous titanium oxide film, an effect of improving the catalytic activity. Further, modifications such as loading of platinum, which is a cocatalyst usually used in the production of photocatalysts, can be applied to the photocatalyst of the present invention. As described above, the porous titanium oxide film of the present invention is not limited to only plate-like titanium, but may also be formed on the surface of a fibrous, woven, or net-like or an aggregate obtained by combining these two-dimensionally and three-dimensionally. It can be formed to a uniform thickness. With these configurations, it is possible to dispose the gas so as to block the gas flow path, and it is possible to remove NO _x by passing it through.

[0058]

According to the present invention, after a soluble substance dissolved in an electrolyte is incorporated into a film formed by anodic oxidation, a hydrothermal treatment is performed in a liquid or steam to elute the soluble substance. To form a porous titanium oxide film. This porous titanium oxide film can be formed with a uniform thickness on a titanium substrate having a large area and a complicated shape. Since numerous fine pores are formed in the porous titanium oxide film,
The actual surface area can be increased by more than 50 times the apparent area. Further, the composition ratio of the anatase phase having high activity can be increased only by controlling relatively few parameters such as the concentration and composition ratio of the electrolyte under anodizing conditions.

[0059] In the present invention, to form the porous titanium oxide film on the titanium substrate, which is applied to NO _x decomposition photocatalytic. The photocatalyst exhibit both high catalytic activity for NO _x decomposition even under natural light in artificial light irradiation, porous titanium oxide film are strongly bonded to the titanium substrate, or a porous titanium oxide film is peeled off from the substrate There is almost no dropout. Furthermore, it is not limited to plate-like titanium, but may be fibrous, woven, or net-like,
Since a porous titanium oxide film having a uniform thickness can be formed on the surface of the aggregate formed three-dimensionally and three-dimensionally, the degree of freedom of design when incorporating the same into an apparatus or a device is increased.

Further, the method for producing a porous titanium oxide film of the present invention is lower in equipment price, equipment operation cost and maintenance cost than other production methods.

[Brief description of the drawings]

FIG. 1 is a partial schematic view showing a cross section of a porous titanium oxide film according to a first embodiment.

FIG. 2 is an SEM photograph of a surface of a porous titanium oxide film according to the first embodiment.

FIG. 3 is a diagram showing a composition change of a crystal phase of a porous titanium oxide film according to a fifth embodiment.

4 is a partial cross-sectional view of the NO _x decomposition photocatalytic according to a sixth embodiment.

FIG. 5 is a view showing N when irradiated with light according to a sixth embodiment.
It is a graph which shows a temporal change of O standard gas concentration.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Porous titanium oxide film 2 ... Titanium oxide fine particles 3 ... Porosity 4 ... Fine unevenness 5 ... Titanium substrate

Claims (12)

[Claims] 1. Anodizing a titanium substrate in an aqueous solution of an electrolyte comprising glycerophosphate and a metal acetate to form an anodized film having a thickness of at least 0.1 μm and containing a substance soluble in a liquid. Performing a hydrothermal treatment of the titanium substrate on which the anodized film is formed in a liquid or a vapor thereof to elute a substance soluble in the liquid in the anodized film to form fine pores. A method for producing a porous titanium oxide film, comprising the steps of: 2. The method for producing a porous titanium oxide film according to claim 1, wherein the metal acetate is an alkali metal or alkaline earth metal acetate or lanthanum acetate. 3. The glycerophosphate is sodium glycerophosphate, wherein the concentration of the sodium glycerophosphate in the aqueous solution is 0.001 to 0.15 mol / l, and the concentration of the metal acetate in the aqueous solution is 0.01 to 0.5 mol / l. 2. The method for producing a porous titanium oxide film according to claim 1, wherein 4. A thickness of at least 0.1 μm containing a substance soluble in a liquid by anodizing a titanium net composed of fine titanium wires in an aqueous solution of an electrolyte comprising glycerophosphate and metal acetate. A step of producing an anodic oxide film of the above, the titanium net having the anodic oxide film formed thereon is subjected to a hydrothermal treatment in a liquid or a vapor thereof in the anodic oxide film,
A process of eluting a substance soluble in a liquid to form fine pores, comprising the steps of: 5. The method for producing a porous titanium oxide film according to claim 4, wherein the metal acetate is an alkali metal or alkaline earth metal acetate or lanthanum acetate. 6. The glycerophosphate salt is sodium glycerophosphate, wherein the concentration of the sodium glycerophosphate in the aqueous solution is 0.001 to 0.15 mol / l, and the concentration of the metal acetate in the aqueous solution is 0.01 to 0.5 mol / l. The method for producing a porous titanium oxide film according to claim 4, wherein 7. Titanium is anodized in an aqueous solution of an electrolyte composed of glycerophosphate and metal acetate, and is further treated with hydrothermal treatment in a liquid or in a vapor thereof to form an infinite number of minute pores. Contains at least 0.1μm
A porous titanium oxide film, characterized in that it is a titanium oxide film having a thickness of 3 mm. 8. The porous titanium oxide film according to claim 7, wherein the metal acetate is an alkali metal or alkaline earth metal acetate or lanthanum acetate. 9. The glycerophosphate is sodium glycerophosphate, wherein the concentration of the sodium glycerophosphate in the aqueous solution is 0.001 to 0.15 mol / l, and the concentration of the metal acetate in the aqueous solution is 0.01 to 0.5 mol / l. 8. The porous titanium oxide film according to claim 7, wherein the thickness is l. 10. Anodizing a titanium substrate or a titanium mesh in an aqueous solution of an electrolyte comprising glycerophosphate and a metal acetate, and subjecting the titanium substrate or the titanium mesh to a hydrothermal treatment in a liquid or in a vapor thereof. A titanium oxide film having a thickness of at least 0.1 μm and containing a myriad of fine pores formed thereby. 11. The photocatalyst for nitrogen oxide gas decomposition according to claim 10, wherein the metal acetate is an alkali metal or alkaline earth metal acetate or lanthanum acetate. 12. The glycerophosphate salt is sodium glycerophosphate, wherein the concentration of the sodium glycerophosphate in the aqueous solution is 0.001 to 0.15 mol / l, and the concentration of the metal acetate in the aqueous solution is 0.01 to 0.5 mol / l. 11. The photocatalyst for decomposing nitrogen oxide gas according to claim 10, wherein the photocatalyst is l.