JP2002219769A - Metal plate having photocatalytic activity and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a metal plate more efficiently developing the decompositional removal, deodorizing, antistaining and sterilizing actions of an environmental pollutant originating from photocatalytic action. SOLUTION: The metal plate having photocatalytic action is characterized by that, in a metal plate having a film with a thickness of 0.5-5.0 μm on its surface, the film comprises a material having photocatalytic action or contains the same and has a surface state having a stepped structure, or has a two- layered structure consisting of an inner layer, which comprises the material having photocatalytic action, and an outer layer, which comprises a light pervious material held to the surface state having the stepped structure, both of which are formed so as to go from the metal plate to a surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal plate having a photocatalytic activity imparted to the surface of the metal plate and a method for producing the same.

[0002]

2. Description of the Related Art Photocatalytic materials such as titanium oxide are known to exhibit the effects of decomposition and removal of environmental pollutants, deodorization, antifouling, and sterilization by a strong oxidation reaction as a result of ultraviolet light excitation. Application and practical application are under consideration. When the photocatalytic material is photoexcited, electrons and holes generated in proportion to the number of irradiated photons cause an oxidation-reduction reaction on the photocatalytic material surface. When the generated electrons and holes recombine,
It does not contribute to the oxidation-reduction reaction on the surface, which lowers the efficiency.

In general, the efficiency (quantum yield) of the photooxidation-reduction reaction of titanium oxide has a correlation with the intensity of irradiation light, but is expected to be at most about 10% (see "Development of titanium oxide photocatalyst and environmental・ Application development to energy field ”published by Technical Information Association, 1997). That is, at present, only 10% or less of the irradiated light is available for the photocatalytic reaction. Moreover, sunlight, expressed in total 3% energy per 1 cm ² in UV, but about 1mW outdoors, according to long-term standing as an outdoor construction material, the photocatalytic effect such as antifouling effect at present ("Photocatalytic mechanism", published by Nihon Jitsugyo Publishing Co., Ltd., 2000). However, when used indoors, under indoor lighting such as fluorescent lamps, the UV intensity is three orders of magnitude lower than 1 μW or less, and the activity of conventional photocatalyst materials is not enough to exhibit the antibacterial and antifouling effects of photocatalyst indoors. It was enough.

[0004] Therefore, a photocatalytic material having higher activity has been demanded. Attempts have been made to increase the surface area to increase the efficiency of the reaction. For example, JP-A-5-3415
No. 63 discloses that an anatase porous membrane having pores is prepared by adding polyethylene glycol or ethylene oxide to titania sol, coating the substrate with a sol-gel method, and sintering at 600 to 700 ° C. in the air. There is a description. Further, in JP-A-6-293519, 15 to 25 nm
About titanium oxide fine particles are suspended in the solution, and after application,
There is a description that it is baked at a temperature of about 450 ° C. and fixed to a substrate. In either case, the specific surface area of the titanium oxide film surface is increased to increase the total reaction amount.

[0005] However, since these crystal surfaces are crystallized and grown in the air or in an aqueous solution, they are sufficiently stabilized and have relatively few defects serving as reaction sites. Further, since a high temperature of about 500 ° C. is required for firing, there is a limit of application to a metal plate such as stainless steel. In the above-mentioned sol-gel method, the thickness of the formed film tends to change depending on the viscosity of the paint and the application conditions. There is a problem that adhesion between the material and the surface of the material is reduced and the material is easily peeled off. Further, in order to enhance the crystallinity of the titanium oxide film, three steps of drying after the coating and firing are essential, and the anatase phase, which is considered to have high photocatalytic activity, is stably formed in the titanium oxide film. In general, it was necessary to perform the calcination at a high temperature of 500 ° C. or higher in the atmosphere. Furthermore, the film thickness obtained by one application is often about 0.1 μm, and in order to obtain a thick film, it is necessary to go through complicated steps such as repeating the above-mentioned application, drying and baking several times. Was. If fired many times in air at high temperature, diffusion of elements from the substrate is inevitable, especially
In the case of a film having a thickness of about μm, there is a problem that elements in the base material diffuse into the entire film and the photocatalytic activity of titanium oxide is reduced. For example, in the case of stainless steel, it is known that Cr diffuses into a titanium oxide film.

As described above, the conventional film has a limit in the efficiency of the reaction, which hinders its practical use in a wide range. Also,
As for the film forming method, there is a limit in improving the homogeneity and adhesion of the film, the processing steps are complicated, and an efficient manufacturing method has been desired.

[0007]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above circumstances, and has been developed to decompose and remove environmental pollutants derived from photocatalysis, to prevent odors, prevent stains, and sterilize. An object of the present invention is to provide a metal plate that has been more efficiently exhibited and a method for manufacturing the same.

[0008]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to achieve the above-mentioned object, and as a result, by providing a number of active steps on the film surface to increase the efficiency of the photocatalytic reaction. The inventors have found that it is significantly increased, and have accomplished the present invention. That is, a metal plate having a film having a thickness of 0.5 μm to 5.0 μm on the surface, wherein the film is made of a material having photocatalytic activity or includes the material, and is a surface state having a step structure. Is a metal plate having photocatalytic activity. Further, a metal plate having a coating having a thickness of 0.5 μm to 5.0 μm on the surface, wherein the coating is directed from the metal plate toward the surface, an inner layer made of a material having photocatalytic activity, and a surface state having a step structure. A metal plate having photocatalytic activity, which has a two-layer structure including an outer layer made of a certain translucent material.

Further, the material having photocatalytic activity is anatase type titanium oxide, rutile type titanium oxide, or Fe ₂ O ₃ , Cu ₂ O, In ₂ O ₃ , WO ₃ , PbO, V ₂ O ₅ , Bi ₂ O ₃ , FeT
iO ₃ , SrTiO ₃ , Nb ₂ O ₃ , ZnO, at least one selected from SnO ₂ or ZrO ₂ , wherein the metal plate is carbon steel, stainless steel, a metal plate having photocatalytic activity that is titanium or a titanium-based alloy. It is.

[0010] The present invention also relates to a method for forming a film on a metal plate having photocatalytic activity, wherein a PVD method for separately controlling the partial pressures of metal vapor or ionized metal vapor and oxygen under reduced pressure is used. A method for producing a metal plate having photocatalytic activity, characterized in that a film is formed at a temperature of the metal plate of not more than ° C. Further, the present invention is a method for producing a metal plate having photocatalytic activity, wherein the PVD method is sputtering or ion plating.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A step is a step having different lattice planes at an atomic level, a place where two-dimensional periodicity is interrupted, and a large number of dangling bonds (bonds having no covalent bond partner) exist. Location. A dangling bond is an active site where it is chemically active and holes generated by the photoexcitation reaction preferentially undergo an oxidation reaction. Also, adsorption of atoms on the surface occurs preferentially. As schematically shown in Sample A and Sample B in FIG. 1, when observed in a plane, it is shown as a curve, and in the cross section, it is recognized as a step between terraces. In large-scale integrated circuit technology, it must be excluded in the sense of maintaining the flatness of the silicon wafer surface.Therefore, understanding of the arrangement and behavior of steps has been advanced by various surface observation means such as SEM and STM (for example, Ogino et al., Applied Physics, Vol. 66,
No. 12, p. 1289, 1997). The formation of a step is characteristically observed when a crystal is formed by epitaxial or heteroepitaxial growth, and is difficult to be formed in a thermal equilibrium state such as firing in the air.

When the photocatalytic material is excited by the irradiated photons, holes and electrons are generated corresponding to the photon amount. In particular, holes decompose substances that come into contact with the surface due to strong oxidizing action, but cannot participate in the reaction if they recombine and disappear with electrons or impurities before reaching the active site on the surface. When there are many active sites on the surface, the recombination of holes is reduced, and the efficiency of the photocatalytic oxidation action is increased. The steps formed on the surface are important in that they create many active sites for this reaction. When the surface on which the steps are formed is observed on a plane as shown in FIGS. 1 and 2, when the total length of the steps connected in a curve is equal to or greater than the sum of the length and width of the observation surface, this It can be said that a large number of steps are formed on the surface, and a photocatalytic reaction having high activity can be expected, which is preferable. For example,
As shown in FIG. 1, the vertical length a (μm), the horizontal length is also a (μm)
Is observed, and when the steps are formed concentrically, the total length of the steps observed planarly is 5πa / 4 (μm), which is the sum of the vertical and horizontal lengths, 2a (μm )
Greater than. It is important that the surface is formed in such a large number of steps. The material of the surface composed of a number of steps may be a photocatalyst material, or may be a translucent material without being a photocatalyst material. Photocatalytic materials include anatase type titanium oxide, rutile type titanium oxide, Fe ₂ O ₃ , Cu ₂ O, In ₂ O ₃ , WO ₃ , PbO, V ₂ O ₅ , Bi ₂ O ₃ , FeT
iO ₃ , SrTiO ₃ , Nb ₂ O ₃ , ZnO, SnO ₂ , ZrO _2, etc. are preferred because they are relatively easy to produce and have excellent photocatalytic effects.

As the material of the outermost surface, basically any material can be used as long as it is translucent and a step structure can be formed stably. For example, SiO ₂ , Al ₂ O ₃ , TiO ₂ , YAG, KNbO ₃ Such inorganic oxide materials are preferable because they are chemically stable and have excellent corrosion resistance and mechanical strength. The thickness of the film on the surface of the metal plate is 0.5 μm to 5.0 μm. If the thickness is less than 0.5 μm, the photocatalytic effect is small, and if the thickness is more than 5.0 μm, the effect does not change, which is uneconomic. With a thickness of 0.5 μm or more, it can efficiently absorb light and function as a photocatalyst. 1.0 μm or more is more desirable for the most efficient light absorption. If the film thickness exceeds 5.0 μm, deformation and bending workability are extremely poor, so that the thickness is preferably 5.0 μm or less. Most preferably, 3.0 μm
It is as follows. In the case of a two-layer structure, the light-transmitting material of the outer layer is preferably 1.0 μm or less, and when it is thicker, the light transmission efficiency is reduced, and holes and electrons generated in the inner layer are efficiently formed on the surface of the outer layer. Can not respond to In the decomposition of water, etc., it is known that the reaction efficiency increases when a noble metal such as platinum is supported on the photocatalytic material.However, when the reaction efficiency is increased by supporting the noble metal, even when applied to the film of the present invention, No problem.

In the photocatalytic reaction, it is important that electrons generated together with holes by photoexcitation move from the reaction site without remaining on the surface. When electrons have no escape place and are charged up in a so-called material, the efficiency of the reaction is reduced. For this purpose, the substrate is preferably conductive. Considering application to actual members, a metal plate is optimal, and among them, carbon steel, stainless steel, titanium, or a titanium-based alloy excellent in versatility, workability, and functionality is preferable. These are already used as various members used for building materials, air conditioning equipment, exhaust gas equipment, water purification equipment and the like, and have a proven track record, so that they are easy to apply.

The metal plate having photocatalytic activity as described above can be manufactured by forming a film on the surface of the metal plate by a PVD (Physical Vapor Deposition) method or the like. PVD method is
It is characterized in that the load on the substrate due to temperature is small, and a crystalline film composed of dense and fine grains can be formed. As the PVD method suitable for the film formation, specifically, various methods such as vacuum deposition, sputtering, and ion plating are suitable. In order to avoid problems such as deformation of the metal plate substrate due to heat and deterioration of photocatalytic activity due to diffusion of elements from the metal plate substrate into the film, the substrate temperature at the time of film formation is 500 ° C. or less. Each of the above three methods can form a film at a substrate temperature of 500 ° C or less, provides sufficient film adhesion and crystallinity of the film, deforms the metal plate substrate due to heat, Problems such as deterioration of photocatalytic activity due to diffusion of elements into the film are unlikely to occur. The above three methods use a deposition rate of 0.02 μm / min.
It is practically 5 to 50 minutes to obtain a film of about 1 μm, for example, 1 μm.

When the PVD method is applied to the formation of the above-mentioned film,
Dissolving and evaporating the metal with an electron beam or the like under reduced pressure, and separately supplying metal vapor and oxygen, such as introducing oxygen as a reaction gas, have excellent controllability of the composition of the photocatalytic material,
Are suitable. As the film exhibiting photocatalytic activity, the above-mentioned oxides are preferable, but among these, another oxide may be formed stably due to the difference in the ratio between oxygen and metal. The composition controllability of the process is important.
For example, when producing Fe ₂ O ₃ , FeO or Fe ₃ O ₄ may also be produced depending on the ratio of iron to oxygen. In this case, it is important to react with iron vapor or ionized vapor by controlling the partial pressure of oxygen to generate Fe ₂ O ₃ without excess or deficiency.

In this process, the crystal phase to be formed is easily controlled, and no post heat treatment or the like is required. For example,
When the substrate temperature during film formation is 490 ° C, the electron beam current for evaporating metallic titanium is 200 mA (acceleration voltage 20 KV), and the oxygen pressure is
When ionization was performed at 40 V and 10 A with an arc discharge activated ion plating device at 0.05 Pa, a stainless steel SUS304 sample placed 45 cm above the titanium evaporation source was used as a substrate, and a film was formed for 10 minutes. In this case, a rutile-based film having a thickness of 0.8 μm can be formed. On the other hand, when a film is formed with the same apparatus and sample at a substrate temperature of 300 ° C. for 20 minutes, a film mainly composed of anatase of about 1.5 μm can be formed. As described above, in the PVD method, the crystal phase and the film thickness can be adjusted to the desired values by keeping the ionization and the atmospheric pressure at an appropriate level, and controlling the temperature of the substrate, the film formation time, and the like. Since the film forming speed is high, there is no need to repeat the same process, and compared to the conventional sol-gel method, it is simple, short, and easy to manage, and the manufacturing cost can be reduced.

Film formation under reduced pressure is important for promoting the formation reaction of the photocatalytic material. In addition, it is preferable to heat the metal plate substrate at 500 ° C. or lower during film formation because the adhesion and crystallinity of the film are improved while suppressing deterioration of the substrate due to the temperature. Since the heating of the substrate is performed under reduced pressure, the surface of the substrate is less oxidized than in the case of firing in the air. By reducing the pressure, the metal can be efficiently evaporated.

Vacuum deposition is a method in which a metal is melted in a vacuum using a heat source such as an electron beam to generate a vapor of the metal, and the vapor is deposited on a substrate. The equipment configuration is relatively simple, and the film formation cost is the lowest among the above three methods. Sputtering is a method in which a target metal is irradiated with a gas component such as ionized argon or the like, and a metal component hit from the target is deposited on a substrate. Ion plating is a method in which a metal source is melted using a heat source such as an electron beam, a metal vapor is generated, and a metal component ionized by plasma is reacted on the substrate to form a film. This attracts ions, which is advantageous for forming a dense film, and provides high adhesion even at a low substrate temperature. In the ion plating method, it is easy to form a film made of fine-grained crystals. For example, an arc discharge activated ion plating method, which is a type of ion plating method, is used. In a 1 μm-thick anatase film formed at Pa, the crystal grains become fine particles of about 0.01 μm. As described above, a film forming method can be selected according to the characteristics of a target film. Of the above three methods,
In the sputtering and ion plating methods, metal vapor is ionized or excited and activated by plasma, so it is highly reactive, and even if the substrate temperature is low, high film crystallinity and adhesion can be obtained, and the film is dense. And composed of fine grains. From the viewpoint of the film formation rate, vacuum evaporation or ion plating using an electron gun evaporation source is advantageous. For example, in order to form a film mainly composed of an anatase phase at a practical film forming rate, the temperature of the substrate is set to 200 ° C. to 450 ° C.,
It is preferable to form a film at a pressure of 0.02 to 0.08 Pa in an oxygen atmosphere while the evaporation rate of titanium is 0.06 μm to 0.15 μm per minute.

[0020]

EXAMPLES Examples of the present invention and comparative examples are shown below.
Industrial pure titanium plate, carbon steel SS41 and stainless steel SUS304
Is used as a metal plate substrate, a film is formed by a PVD method or the like, and the properties of the film (configuration, film thickness, crystal layer,
The adhesion was examined, and the photocatalytic activity (degree of potassium iodide decomposition, deodorizing effect, antibacterial activity) was evaluated for each sample. Table 1 shows the conditions and evaluation results for film formation.
Shown in Titanium-based alloys are Al, Zr, Hf, V, Nb, Ta, M
Generally, the alloy contains 0.5% to 5% by mass of n, Fe, Co, Ni, Cr, etc. Here, a titanium-based alloy containing 0.5% by mass of Al was used.

The composition, thickness and crystal layer of the film are determined by Auger electron spectroscopy, X-ray photoelectron spectroscopy, glow discharge emission spectroscopy,
It was determined by Raman scattering analysis and X-ray diffraction. The adhesion was evaluated by a 45-degree bending test. As a substrate for evaluation of adhesion, a disc-shaped substrate of SUS304 having a diameter of 30 mm and a thickness of 0.3 mm was used, and a film was formed on this surface. Bending angle 45
Each part was deformed and processed, and the most deformed part (bent part) was observed with a reflection microscope at a magnification of 100 times. When the film was completely peeled, the adhesion was evaluated as X. When the film was partially peeled and the film was partially adhered, the adhesion was evaluated. ○

For the evaluation of photocatalytic activity, a titanium oxide film was formed on a SUS304 stainless steel plate (40 mm square, 1 mm thick) by the sol-gel method described below, and the relative evaluation with this photocatalytic activity was performed. The sol-gel method was used to make flowers ("Sol-gel method science", Agne Shofusha, 1988). Specifically, dilute titanium tetraisopropoxide to a concentration of 284 g / L with 100 mL of absolute ethanol, and with stirring, 2N hydrochloric acid 2m
L was dropped into a solution diluted with 100 mL of absolute ethanol to prepare a transparent sol. Next, dip coating-drying (10
(0 ° C.), a gel-like compound was formed on the substrate, and baked at 650 ° C. for 5 hours in an electric furnace. The thickness of the film formed repeatedly five times was 0.6 μm.

The degree of decomposition of potassium iodide was determined by immersing each sample in a 100 mM potassium iodide aqueous solution and irradiating the sample with black light (4 mW / cm ² ) having a high ultraviolet intensity so that the iodine complex ion (I ₃ ⁻ ) was generated. The production was evaluated. Based on the amount of iodine complex ions produced by the above method, the film produced by the sol-gel method was evaluated as a reference, and the amount of iodine tested in each sample was evaluated to be 0.5 times or less of the reference amount. ×, 0.5 to 1.5 times Up to △ and 1.5 times or more as ○.

Regarding the deodorizing effect, ultraviolet rays at a constant speed (black light: 5 W / c) were applied from outside the quartz tube where each sample was placed.
While irradiating m ² ), a constant flow rate of aldehyde was allowed to flow, and the residual aldehyde concentration at the outlet was measured to evaluate. Based on the residual aldehyde concentration tested by the above method for the film formed by the sol-gel method, the residual concentration tested in each sample was evaluated as x or more than twice the reference concentration.
Up to 2 times was rated as △, and up to 0.5 times as ○.

With respect to the antibacterial activity, physiological saline in which Escherichia coli is suspended at a constant concentration is dropped on the surface of each sample, and ultraviolet light is irradiated.
Evaluation was made by the survival rate of Escherichia coli after irradiation for 1 hour.
Based on the survival rate of Escherichia coli tested by the above method for the film formed by the sol-gel method, the survival rate of Escherichia coli tested in each sample was evaluated as 1.5 times or more of the reference concentration ×, 0.5 times to 1.
ま で up to 5 times and ○ up to 0.5 times or less.

The surface on which the steps are formed (sample A,
When B) is observed on a plane as shown in FIG. 2, when the total length of steps connected in a curve is equal to or greater than the sum of the length and width of the observation surface, a large number of steps are formed on this surface. Table 1 shows that the Observation was performed at random with five fields of view at a magnification of 50,000 times using a high-resolution SEM. No.1 in Table 1
Nos. 8 to 8 are comparative examples, and Nos. 9 to 18 are examples. In the examples, both the adhesion and the photocatalytic activity were equal to or better than those of the sol-gel method. No. 1 is the evaluation result of the blank substrate itself on which no film was formed.

In the film formation method, in the sputtering method, a metal was used as a target, and oxygen gas was introduced as a reaction gas. The plasma was activated with argon gas, and the gas pressure was 1 Pa. When the composition was different between the inner layer and the outer layer, the target was replaced with the target metal when the outer layer was formed.
A plurality of targets can be placed in the apparatus, and can be performed without breaking a vacuum.

The formation of the film by vacuum deposition and ion plating is performed in an oxygen atmosphere at a pressure of 0.05 Pa.
Below, metal evaporation with an electron gun was performed. The film thickness was controlled by changing the deposition time. The film thickness increases linearly with increasing deposition time. The deposition rate was, for example, 0.05 μm / min in the ion plating of No. 17, which was almost the same as the evaporation rate of titanium metal.

The coating of No. 2 by the sol-gel method is performed by a chemical modification alkoxide method (Ceramics, Vol. 30, 1995, No. 1).
1, p. 1021), and prepared using a precursor solution obtained by adding 5% by mass of polyethylene glycol having a molecular weight of 4000 to a solution composed of titanium tetraisopropoxide, ethanol, diethanolamine, and water. In No. 3 thermal spraying, titanium oxide particles were irradiated with plasma. In order to avoid an increase in the temperature of the substrate, thermal spraying was performed quickly while cooling the substrate from behind with compressed air. In the thermal spraying method, since there is a limit in forming a dense and thin film with good controllability, sufficient adhesion cannot be obtained.

FIG. 3 shows the result of observing the surface of No. 17 film with a high-resolution SEM. It can be observed that a fine step structure is formed overlapping within a crystal grain of 0.1 μm or less. Similarly, FIG. 4 shows the result of observing the surface of No. 2 film with a high-resolution SEM. X-ray diffraction confirmed that crystals had been formed, but the surface structure was very different in that the surface was porous, no step structure was observed, and there were few microscopic irregularities.

As is apparent from the examples (Nos. 9 to 18) in Table 1, the thickness of the surface film is 0.5 μm to 5.0 μm, and at least the inner layer has photocatalytic activity on the conductive metal plate, By forming a film whose surface is formed in a number of steps, a metal plate having excellent photocatalytic activity can be obtained. They are,
It can be seen that the PVD method in which the partial pressures of metal vapor or ionized metal vapor and oxygen are separately controlled can be efficiently and effectively produced.

[0032]

[Table 1]

[0033]

According to the present invention, a metal plate having photocatalytic activity can be put to practical use in a wide range. By forming a large number of steps on the film surface, the efficiency of the reaction is improved, and a metal plate having a sufficient catalytic activity even when used indoors can be provided. In addition, the process of forming a film is easy to control, which is advantageous for reducing manufacturing costs and improving work efficiency.Because the temperature of the metal plate substrate at the time of forming the film is low, deformation of the metal plate and changes in design due to heat, A decrease in photocatalytic activity and the like can be avoided.

[Brief description of the drawings]

FIG. 1 is a step observation on a plane.

FIG. 2 is a schematic view of a step.

FIG. 3 shows the results of observation of the film surface in Examples.

FIG. 4 is a result of observation of a coating surface of a comparative example.

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Claims (8)

[Claims] 1. A photocatalyst comprising a metal plate having on its surface a coating having a thickness of 0.5 μm to 5.0 μm, said coating comprising a material having photocatalytic activity and being in a surface state having a step structure. An active metal plate. 2. A metal plate having a coating having a thickness of 0.5 μm to 5.0 μm on its surface, wherein the coating is made of a material having photocatalytic activity and has a surface state having a step structure. An active metal plate. 3. A metal plate having a coating having a thickness of 0.5 μm to 5.0 μm on the surface, the coating having an inner layer made of a material having photocatalytic activity from the metal plate toward the surface, and a step structure. A metal plate having photocatalytic activity, which has a two-layer structure including an outer layer made of a light-transmitting material in a surface state. 4. The material having photocatalytic activity is anatase type titanium oxide or rutile type titanium oxide.
4. The metal plate having photocatalytic activity according to any one of 1 to 3. 5. The material having photocatalytic activity is Fe
₂ O ₃ , Cu ₂ O, In ₂ O ₃ , WO ₃ , PbO, V ₂ O ₅ , Bi ₂ O ₃ , FeTiO ₃ , S
_{rTiO 3, Nb 2 O 3,} ZnO, metal plate having a photocatalytic activity according to any one of claims 1 to 3 is at least one selected from SnO ₂ or ZrO _2. 6. The method according to claim 1, wherein the metal plate is made of carbon steel, stainless steel,
4. The metal plate having photocatalytic activity according to claim 1, which is titanium or a titanium-based alloy. 7. The method for forming a film on a metal plate having photocatalytic activity according to claim 1, wherein the partial pressures of metal vapor or ionized metal vapor and oxygen are separately controlled under reduced pressure. A method for producing a metal plate having photocatalytic activity, wherein a film is formed at a temperature of 500 ° C. or less by using a PVD method. 8. The method for producing a metal plate having photocatalytic activity according to claim 7, wherein the PVD method is sputtering or ion plating.