JP2008043828A - Metal material containing photocatalyst coated with silicon oxide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a metal material having an excellent photocatalytic activity as compared with products employing photocatalysts containing titanium oxide alone. <P>SOLUTION: The metal material contains a photocatalyst in the surface layer. The photocatalyst comprises a substrate having a photocatalyst and a silicon oxide film coating the substrate and essentially no pores and has a content of alkali metals of 1-1,000 ppm. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to a metal material having photocatalytic activity.

  Metal oxide semiconductors such as titania and zinc oxide have a property of absorbing light having energy corresponding to the bandwidth. In recent years, attention has been focused on high reactivity due to holes and electrons generated by excitation by light irradiation, and water purification, antifouling, antibacterial, deodorization, air purification, etc., using the metal oxide semiconductor as a “photocatalyst”. Attempts have been made to apply it to environmental purification. Attempts have been made to apply a finely divided photocatalyst to the surface of a metal material to immobilize the photocatalyst and to impart antifouling, antibacterial, deodorizing and antifungal functions to the metal material.

  For example, a method of sequentially laminating an anodic oxide film and a titanium oxide powder-containing thin film on a substrate surface (see Patent Document 1), a method of depositing titanium oxide on a substrate surface by a CVD method, or a method of performing plasma spraying (Patent Document) 2), and a method of forming a mica layer in which titanium oxide fine particles are dispersed on the surface of a metal substrate (see Patent Document 3) has been proposed, both of which are very expensive to manufacture. Further, since titanium oxide is used as a photocatalyst, the heat resistance is poor, the photocatalytic activity is insufficient, and a metal material using a new photocatalyst has been demanded.

  As a new photocatalyst, organohydrogenpolysiloxane is supplied to the photocatalyst in the gas phase to form a silica-based coating, and even when coated, the bactericidal activity under light irradiation conditions is higher than the activity of the original photocatalyst It is disclosed that it increases (see Patent Document 4). A titanium oxide photocatalyst that selectively removes basic gases such as ammonia gas and amine-based gas is described (see Patent Document 5). The photocatalyst described in this document has a core made of titanium oxide particles having photocatalytic activity, and a silica hydrate coating layer surrounding the core. This coating layer is supposed to function so as to enhance the basic gas removal capability of the entire photocatalyst by selectively adsorbing the basic gas and efficiently supplying it to the active sites of the titanium oxide core.

However, the photocatalysts described in Patent Documents 4 and 5 do not have sufficient photolysis performance for organic substances, and the photocatalyst described in Patent Document 5 has insufficient adsorption capacity for harmful gases other than basic gases. Met. This is thought to be due to the insufficient mechanical strength and durability of the photocatalyst structure obtained by the method described in Patent Document 5 or the silica hydrate coating layer.
Japanese Patent No. 10-121266 JP-A-6-210170 JP 2004-43924 A Japanese Patent Laid-Open No. 62-260717 JP 2002-159865 A

  This invention is made | formed in view of such a situation, and makes it a subject to provide the metal material which has photocatalytic activity.

As a result of intensive studies to solve the above problems, the present inventors have
A substrate having photocatalytic activity;
By forming the photocatalyst in a metal material, which has a silicon oxide film that substantially covers no pores and covers the substrate, and has an alkali metal content of 1 ppm or more and 1000 ppm or less. As compared with the case of only the photocatalyst, it was found that high photocatalytic activity can be maintained, and the present invention has been completed.

  That is, according to the present invention, a photocatalyst having a substrate having photocatalytic activity and a silicon oxide film substantially covering no pores covering the substrate and having an alkali metal content of 1 ppm or more and 1000 ppm or less. Is provided. A photocatalyst-containing metal material is provided.

  According to the present invention, it is possible to provide a metal material having a photocatalytic function, which has significantly higher photocatalytic activity than a photocatalyst using only titanium oxide.

The metallic material of the present invention has a photocatalytic activity (a photocatalyst having a substrate having photocatalytic activity and a silicon oxide film having substantially no pores covering the substrate and having an alkali metal content of 1 ppm or more and 1000 ppm or less). Hereinafter, the surface layer appropriately includes abbreviated as “silicon oxide-coated photocatalyst”.
The silicon oxide-coated photocatalyst means one obtained by coating the surface of a substrate having a photocatalytic function with a film made of silicon oxide. Therefore, the photocatalyst is formed later in the presence of silicon oxide, which is produced by immobilizing the photocatalyst on silicon oxide, and the composite formed by forming silicon oxide and photocatalyst in parallel in the same container are included. I can't.

A mode in which the silicon oxide film covers the substrate is not particularly limited, and includes both a mode in which a part of the substrate is coated and a mode in which the substrate is entirely coated. From the viewpoint of obtaining higher photolytic activity, the surface of the substrate is It is preferable that the film is uniformly coated with a film made of silicon oxide.
Here, the silicon oxide film may be in the form of an unfired film or a fired film. In the present invention, a fired film of silicon oxide after firing is preferred.

  As a substrate having photocatalytic activity (hereinafter abbreviated as “substrate” as appropriate), a metal compound photo semiconductor can be used. Examples of the metal compound optical semiconductor include titanium oxide, zinc oxide, tungsten oxide, and strontium titanate. Among these, titanium oxide is preferable because of its excellent photocatalytic activity, harmlessness and excellent stability. Examples of the titanium oxide include amorphous, anatase, rutile, and brookite types. Of these, the anatase type or rutile type, which are excellent in photocatalytic activity, or a mixture thereof is more preferable, and these may contain a small amount of amorphous substance.

  As a substrate, one having one or more transition metals added to a metal compound optical semiconductor, one or more typical elements of group 14, 15, and / or group 16 added to a metal compound optical semiconductor, two or more A semiconductor composed of a metal compound and a mixture of two or more metal compound optical semiconductors can also be used.

Further, as the substrate, it is preferable to use particles of metal compound optical semiconductor, also, the specific surface area of the substrate, preferably at least ^{30 m} 2 / g, more preferably 120~400m ² / g, most preferably The thing containing 120-300 m < ² > / g metal compound optical semiconductor is preferable. When the specific surface area of the substrate is within the above range, good catalytic activity can be maintained.

  If the substrate can be clearly recognized as particles, the specific surface area of the substrate can be calculated by a general BET method. Otherwise, the specific surface area of the substrate is calculated by X-ray diffraction analysis and Scherrer formula, or based on the primary particle diameter obtained from the observation of the primary particles using an electron microscope, the “surface area” is calculated in spherical form, In addition, the specific surface area can be obtained by grasping the crystal phase from diffraction analysis of X-rays or electron beams and calculating the “weight” from the true density of the crystal phase and the volume obtained from the spherical conversion. .

  When the substrate is a particle, the primary particle size is preferably 1 nm to 50 nm, more preferably 2 nm to 30 nm. When the primary particle size of the substrate is within this range, good catalytic activity can be maintained.

  In the present invention, examples of the alkali metal include lithium, sodium, potassium, rubidium, cesium, and francium. These alkali metals may contain 1 type, and may contain 2 or more types of these. Among these, sodium and / or potassium are preferable, and sodium is more preferable.

The alkali metal content in the photocatalyst can be quantified using an atomic absorption photometer (AA), an inductively coupled plasma emission analyzer (ICP), a fluorescent X-ray analyzer (XRF) or the like. The alkali metal content in the silicon oxide-coated photocatalyst is preferably 1 ppm or more, and more preferably 10 ppm or more. If it is 1 ppm or more, the improvement effect of photodegradation activity will be acquired, and if it is 10 ppm or more, this improvement effect of photolysis activity will become remarkable. The reason why the photodegradation activity is improved by containing a predetermined amount of alkali metal is not necessarily clear, but is thought to be due to an improvement in the adsorption rate of the decomposition target. On the other hand, the upper limit of the alkali metal content is preferably 1000 ppm or less, more preferably 500 ppm or less, and even more preferably 200 ppm or less. By setting it to 1000 ppm or less, elution of the silicon oxide film can be suppressed. Moreover, by setting it as 500 ppm or less, generation | occurrence | production of sintering of the photocatalyst by the baking process in the temperature range over 800 degreeC can be suppressed, and sintering of a photocatalyst can further be hard to advance by setting it as 200 ppm or less.
The alkali metal content contained in the silicon oxide film is preferably 1 ppm to 500 ppm, more preferably 1 ppm to 200 ppm.

  “Substantially free of pores” means a photocatalytic activity substrate used as a raw material when producing a photocatalyst coated with a silicon oxide film, and an oxidation prepared using the photocatalytic activity substrate. When comparing the pore size distribution in the region of 20 to 500 angstroms with the photocatalyst coated with the silicon film, it means that the pores are not substantially present in the silicon oxide film.

  Specifically, the pore size distribution of a photocatalytic substrate coated with a photocatalytic activity and a photocatalyst coated with a silicon oxide film is ascertained by pore distribution measurement such as a nitrogen adsorption method, and these are compared to form a silicon oxide film. It can be determined whether or not the pores are substantially absent.

  More specifically, the grasping method in the nitrogen adsorption method can determine the presence or absence of pores in the silicon oxide film by the following methods (1) to (4). Here, an example in which photocatalyst particles are used as the substrate will be described.

(1) After drying the photocatalyst particles at 200 ° C., the N ₂ adsorption isotherm in the desorption process is measured;
(2) measuring the N ₂ adsorption isotherm during the desorption process of the photocatalyst coated with the silicon oxide film;
(3) Analyzing the two N ₂ adsorption isotherms by a BJH (Barrett-Joyner-Halenda) method to obtain a log differential pore volume distribution curve in a region of 20 to 500 angstroms;
(4) A region in which two log differential pore volume distribution curves are compared, and the log differential pore volume of the photocatalyst coated with the silicon oxide film is 0.1 ml / g or more larger than the log differential pore volume of the photocatalyst particle When there is no pore, it is determined that the silicon oxide film has substantially no pores, and when there is a region larger than 0.1 ml / g, it is determined that the silicon oxide film has pores. The reason why the concentration is 0.1 ml / g or more is that, in the pore distribution measurement by the nitrogen adsorption method, a measurement error of about 0.1 ml / g width often occurs in the log differential pore volume value.

  If two log differential pore volume distribution curves are compared in the range of 20 to 500 angstroms, the presence or absence of pores in the silicon oxide film can be substantially determined.

  The two log differential pore volume distribution curves were compared, and the log differential pore volume of the photocatalyst coated with the silicon oxide film in the region of 10 to 1000 angstroms was less than the log differential pore volume of the photocatalyst particles. More preferably, there is no region larger than 1 ml / g.

  Here, when the silicon oxide film has pores, it is difficult to improve the photolytic activity. The reason for this is not necessarily clear, but the presence of pores facilitates light scattering and reflection at the silicon oxide film, reduces the amount of ultraviolet light reaching the photocatalytic activity substrate, This is probably due to a decrease in the amount of electrons generated. Also, when coated with the same amount of silicon oxide, the one with pores is decomposed from the substrate with photocatalytic activity as a result of the increase in the thickness of the silicon oxide film by the volume of the pores compared to the one without pores. It is presumed that sufficient photodegradation activity cannot be obtained because the physical distance from the organic substance that is the object increases.

The amount of silicon supported per 1 m ² of the surface area of the silicon oxide-coated photocatalyst according to the present invention is a calculated value calculated from the amount of silicon contained in the silicon oxide-coated photocatalyst and the surface area of the silicon oxide-coated photocatalyst. Silicon supported amount per surface area of 1m ² of the silicon oxide coated photocatalyst, the surface area of 1m silicon supported per ² or more 0.10 mg, and at 2.0mg or less, preferably 0.12mg above, 1.5 mg or less, more Preferably they are 0.16 mg or more and 1.25 mg or less, More preferably, they are 0.18 mg or more and 1.25 mg or less. If it is less than 0.10 mg, the photocatalytic activity improvement effect by the silicon oxide film is small. On the other hand, if it exceeds 2.0 mg, the proportion of the substrate in the silicon oxide-coated photocatalyst is too low, so that the photocatalytic function is hardly improved. By making the silicon loading amount in the above range, the photocatalytic activity improvement effect by the silicon oxide film becomes remarkable.

  The surface area of the substrate and the silicon oxide-coated photocatalyst can be measured using a BET specific surface area measuring apparatus by nitrogen adsorption / desorption after heat treatment at 150 ° C. for 15 minutes in a dry gas stream having a dew point of −195.8 ° C. or less. it can.

  In the method for producing a silicon oxide-coated photocatalyst of the present invention, when a silicon oxide film is coated on a substrate existing in an aqueous medium using a silicate, the pH of the mixed solution containing both the substrate and the silicate is 5 or less. It is characterized by maintaining.

  In the above production method, examples of the aqueous medium include water or a mixed solution containing water as a main component and containing an organic solvent that is soluble in water among aliphatic alcohols, aliphatic ethers, and the like. Specific examples of the aqueous medium include water and a mixed solution of water and methyl alcohol, water and ethyl alcohol, water and isopropanol, and the like. Of these, water is preferred. Moreover, these water and a liquid mixture can be used individually by 1 type or in combination of 2 or more types. Further, in order to improve the dispersibility or solubility of the photocatalyst, the aqueous medium includes an organic solvent that can be dissolved in water among aliphatic alcohols and aliphatic ethers, aliphatic amines, and aliphatic polymers. Surfactants such as ethers and gelatins can also be mixed.

  As the silicate, silicic acid and / or an oligomer salt thereof may be used, and two or more kinds may be mixed and used. Sodium salts and potassium salts are preferred from the viewpoint of industrial availability, and an aqueous sodium silicate solution (JIS K1408 “water glass”) is more preferred because the dissolution step can be omitted.

  When a silicon oxide film is coated with a silicate on a substrate present in an aqueous medium, the aqueous medium, the substrate, and the silicate are mixed, and then this mixed solution is aged.

Specifically,
(i) an aqueous medium containing a substrate and a silicate,
(ii) an aqueous medium containing a silicate and a substrate, and
(iii) an aqueous medium containing a substrate and an aqueous medium containing a silicate,
A coating method comprising a step of mixing at least one set of the above and a step of aging the mixed solution. In the aging step, the coating of the silicon oxide film on the substrate gradually proceeds.

  At this time, it is necessary to maintain the pH of the aqueous medium containing both the substrate and the silicate at 5 or less, and it is more preferable to set the pH to 4 or less. When the pH is maintained at 5 or lower in the absence of the substrate, the condensate of the silicic acid compound hardly precipitates alone from silicic acid, silicic acid ions and / or oligomers thereof. On the other hand, when the pH is maintained at 5 or lower in the presence of the substrate, the surface of the substrate acts as a condensation catalyst for the silicate compound, and a silicon oxide film is rapidly formed only on the surface of the substrate. That is, the acidic region having a pH of 5 or less is a region where a solution containing a silicate compound can be stably present and silicon oxide can be formed in a film shape on the surface of the substrate.

  Even in a basic region having a pH of 11 or more, as in the acidic region having a pH of 5 or less, when a liquid containing silicic acid, silicate ions and / or oligomers thereof is ripened, the condensate of the silicate compound hardly precipitates. However, since only a part of the used silicate forms a silicon oxide film, it is not preferable. Further, in the pH 6 to 11 region, a condensate of a silicate compound, that is, silicon oxide fine particles and / or gel is likely to be generated, so that the silicon oxide film becomes porous or the silicon oxide locally on the surface of the substrate. Is not preferable.

  When an organic medium such as alcohol is present in the aqueous medium, the pH cannot be accurately measured with a water pH electrode, and therefore, measurement is performed using a pH electrode for an aqueous solution containing the organic medium. Separately, it is also possible to measure the pH by replacing the organic medium with the same volume of water.

  As a method of maintaining the mixed solution containing both the substrate and the silicate at a pH of 5 or less, the pH of the aqueous medium is constantly measured when mixing and aging the substrate, the silicate, and the aqueous solvent, and an acid and a base are appropriately used. It is possible to adjust by adding. However, it is easy to neutralize the total amount of the base components contained in the silicate used for the production, and to make a sufficient amount of acid present in the aqueous medium in advance so that the pH is 5 or lower.

  Although any acid can be used, mineral acids such as hydrochloric acid, nitric acid, and sulfuric acid are preferably used. Only one kind of acid may be used, or two or more kinds of acids may be mixed and used. Of these, hydrochloric acid and nitric acid are preferred. When sulfuric acid is used, if a large amount of sulfur remains in the photocatalyst, the adsorption efficiency may deteriorate over time. The sulfur content in the photocatalyst is preferably 0.5% by weight or less, more preferably 0.4% by weight or less, based on the total weight of the photocatalyst.

  When using the above-described method in which a sufficient amount of acid is previously present in the aqueous medium to neutralize the total amount of the base components contained in the silicate and then to have a pH of 5 or lower. There is no need to use it separately. However, when a base is used, any base can be used. Of these, alkali metal hydroxides such as potassium hydroxide and sodium hydroxide are preferably used.

  The reaction conditions such as reaction temperature and reaction time when the mixed solution is aged and the silicon oxide film is coated on the substrate are not particularly limited as long as they do not adversely affect the production of the target silicon oxide-coated photocatalyst. . The reaction temperature is preferably 10 ° C. or higher and 200 ° C. or lower, and more preferably 20 ° C. or higher and 80 ° C. or lower. When the temperature is less than 10 ° C., the condensation of the silicate compound is difficult to proceed, so that the formation of the silicon oxide film is remarkably delayed and the productivity of the silicon oxide-coated photocatalyst may be deteriorated. When the temperature is higher than 200 ° C., a condensate of a silicate compound, that is, silicon oxide fine particles and / or gel is likely to be generated, so that the silicon oxide film becomes porous or silicon oxide is locally formed on the substrate surface. It may be done.

  The aging time is preferably 10 minutes or more and 500 hours or less, and more preferably 1 hour or more and 100 hours or less. If it is less than 10 minutes, the coating with the silicon oxide film does not proceed sufficiently, and the effect of improving the photolytic activity by the coating may not be sufficiently obtained. If it is longer than 500 hours, the substrate having the photocatalytic function is sufficiently covered with the silicon oxide film and the photodecomposing function is improved, but the productivity of the silicon oxide-coated photocatalyst may be deteriorated.

  The concentration of the substrate having photocatalytic activity contained in the mixed solution is preferably 1% by weight to 50% by weight, and more preferably 5% by weight to 30% by weight. When the amount is less than 1% by weight, the productivity of the silicon oxide-coated photocatalyst deteriorates. When the concentration is higher than 50% by weight, the coating of the silicon oxide film on the substrate does not proceed uniformly, and the effect of improving the photolytic activity is sufficient. May not be obtained. The concentration of silicon contained in the mixed solution is preferably 0.05% by weight or more and 5% by weight or less, and more preferably 0.1% by weight or more and 3% by weight or less. When the silicon concentration is less than 0.05% by weight, the condensation of the silicate compound is delayed, and the substrate may not be sufficiently covered with the silicon oxide film. If the silicon concentration is higher than 5% by weight, the coating of the silicon oxide film on the substrate may not proceed uniformly.

In the production method of the present invention, the ratio of the amount of the substrate having photocatalytic activity and the amount of silicate used is 0.01 mg / m ² or more and 0.50 mg / m ² or less as silicon atoms per 1 m ² of the surface area of the substrate. Preferably there is. If manufactured at a ratio in this range, a step of forming a silicon oxide film on the surface of the substrate, that is, an aqueous medium containing the substrate and a silicate, an aqueous medium containing the silicate, the substrate, and an aqueous system containing the substrate In the step of mixing and aging at least one of a medium and an aqueous medium containing silicate, a desired silicon oxide film can be formed on the surface of the substrate, and it remains unreacted without being condensed on the surface of the substrate. In addition, since the amount of silicic acid, silicate ions, and / or oligomers thereof can be suppressed, a silicon oxide film having pores is rarely formed. In the range of 0.50 mg / m ² or more and 5.0 mg / m ² or less, as the ratio increases, the amount of unreacted material may increase and a silicon oxide film having pores may be formed. It can be avoided by shortening the treatment time that the condensation of the product proceeds to generate pores.

If the production method of the silicon oxide-coated photocatalyst of the present invention is shown more specifically, for example,
(Step a) A step of mixing at least one set of an aqueous medium containing a substrate and a silicate, an aqueous medium containing a silicate and a substrate, and an aqueous medium containing a substrate and an aqueous medium containing a silicate,
(Step b) A step of aging this mixed solution and coating the substrate with a silicon oxide film,
(Step c) A step of separating and washing the silicon oxide-coated photocatalyst from the aqueous medium without neutralizing the mixed solution,
(Step d) comprising a step of drying and baking the silicon oxide-coated photocatalyst,
And the manufacturing method which maintains the pH of the aqueous medium containing both the said base | substrate and a silicate at 5 or less in the process a and the process b is mentioned.

  When the silicon oxide-coated photocatalyst is separated from the aqueous medium, neutralization reduces the alkali metal content reduction efficiency in the washing process, and the silicon compound remaining dissolved in the aqueous medium is condensed and gelled. The problem is that a porous silica film is formed. Dealkali the silicate solution in advance, prepare this dealkalized liquid and use it in production, and reduce or reduce the ratio of the amount of the substrate having the photocatalytic function and the silicate, thereby minimizing the above problem It is also possible to However, it is preferable to separate the silicon oxide-coated photocatalyst from the aqueous medium without neutralization because the above problem can be avoided and the production method is simple.

  A method for separating the silicon oxide-coated photocatalyst from the mixed solution is not particularly limited, and known methods such as a natural filtration method, a vacuum filtration method, a pressure filtration method, and a centrifugal separation method can be suitably used.

  The method for cleaning the silicon oxide-coated photocatalyst is not particularly limited, and for example, redispersion in pure water and repeated filtration, desalting cleaning by ion exchange treatment, and the like can be suitably used. Further, depending on the use of the silicon oxide-coated photocatalyst, the cleaning step can be omitted.

  The method for drying the silicon oxide-coated photocatalyst is not particularly limited, and for example, air drying, reduced pressure drying, heat drying, spray drying, and the like can be suitably used. Further, depending on the use of the silicon oxide-coated photocatalyst, the drying step can be omitted.

  The firing method of the silicon oxide-coated photocatalyst is not particularly limited, and for example, reduced-pressure firing, air firing, nitrogen firing and the like can be suitably used. Usually, baking can be performed at a temperature of 200 ° C. or higher and 1200 ° C. or lower, but 400 ° C. or higher and 1000 ° C. or lower is preferable, and 400 ° C. or higher and 800 ° C. or lower is more preferable. When the firing temperature is less than 200 ° C., a desired fired silicon oxide film is not formed on the surface of the substrate, resulting in an unstable structure. Furthermore, due to the presence of a large amount of water around the silicon oxide, the gas adsorption performance is not sufficiently exhibited, and at the same time, sufficient photolytic activity cannot be obtained. When the firing temperature is higher than 1200 ° C., sintering of the silicon oxide-coated photocatalyst proceeds and sufficient photolytic activity cannot be obtained.

  The water content contained in the silicon oxide-coated photocatalyst is preferably 7% by weight or less. 5% by weight or less is more preferable, and 4% by weight or less is most preferable. When the water content is 7% by weight or more, a large amount of water is present around the silicon oxide, so that the gas adsorption performance is not sufficiently exhibited, and at the same time, sufficient photolytic activity cannot be obtained.

  The silicon oxide-coated photocatalyst thus obtained can adsorb any of acidic gases such as acetic acid, basic gases such as ammonia, and nonpolar gases such as toluene, and is excellent in photocatalytic performance.

  As described above, the method for producing a silicon oxide-coated photocatalyst of the present invention reduces the pH, uses the silicate concentration, the substrate concentration, and uses in order to obtain a silicon oxide film having substantially no pores. It is necessary to appropriately select conditions such as the acidic solution to be used, the firing temperature after film formation, and the firing time.

  Regarding a method for producing a metal material having a surface layer containing a silicon oxide-coated photocatalyst, a method of forming a silicon oxide-coated photocatalyst on the surface of the metal material, or if the metal used has a low melting point, the metal material itself and the silicon oxide coating Various methods such as a method of producing a molded product by mixing photocatalysts can also be used. Although it will not specifically limit if a photocatalyst can exist in the metal material surface so that high photocatalytic activity can be exhibited by light irradiation, For example, it can manufacture as follows. Here, the surface means an exposed surface of the metal material and can come into contact with harmful substances and odor components.

  The method for forming a silicon oxide-coated photocatalyst on the surface of the metal material is not particularly limited, but includes a spray coating method, a spin coating method, a roll coating method, a dip coating method, a sputtering method, a brush coating method, etc. It can be implemented by a general method.

  For example, a silicon oxide-coated photocatalyst and a binder are dispersed in a solvent such as water, a polar organic solvent such as alcohol, or a nonpolar organic solvent such as toluene, and the dispersion is applied to a metal material having a desired shape. A heat treatment is performed at a temperature of 1000 ° C. to obtain a metal material having photocatalytic activity. More preferably, the heat treatment is performed at room temperature to 800 ° C., more preferably at room temperature to 600 ° C., and the film containing the silicon oxide-coated photocatalyst is firmly fixed to the metal surface, and durability required for practical use such as wear resistance and chemical durability. Make sure to add sex. In order to improve the adhesion during film formation, it is also possible to use a method such as forming an oxide film on the surface of the metal material and forming a photocatalyst.

  The metal material is not particularly limited and includes, for example, aluminum, iron, nickel, cobalt, chromium, copper, zinc, manganese, tin, titanium, magnesium, gold, silver, platinum, or an alloy thereof, Carbon steel, aluminum alloy, titanium alloy, Hastelloy, stainless steel, etc. can be used. The metal material can be applied to any shape as long as it can absorb light. For example, a flat plate, a corrugated plate, a honeycomb, a mesh, a tube, a sphere, a foil, a rod, a tube, etc. Things can be used.

  Binders adversely affect the photocatalytic activity of organic systems such as methylcellulose, polyethylene oxide, polyethylene glycol, polyvinyl alcohol, vinyl acetate, xanthan gum, sodium acrylate, inorganic systems such as water glass, colloidal silica, alumina sol, zirconia sol, and silicon resin. Any of them can be used as long as it is not affected. The concentration of the binder may be about 0.1 to 20% by weight of the dispersion. The concentration of the silicon oxide-coated photocatalyst may be in the range of 0.01 to 40% by weight, preferably 0.05 to 35% by weight, more preferably 0.1 to 30% by weight with respect to the dispersion. .

The amount of the silicon oxide coated photocatalyst per metal material surface area is preferably 0.01~30g / ^{m 2,} more preferably 0.1 to 20 g / ^{m 2.} When the amount of the silicon oxide-coated photocatalyst is too large, the photocatalyst easily peels from the surface of the metal material, and when it is too small, the effect of the photocatalytic function cannot be exhibited.

  By having the surface layer containing the silicon oxide-coated photocatalyst obtained as described above, a metal material having a photocatalytic function can be obtained. If the film thickness of the film containing the silicon oxide-coated photocatalyst is 50 nm to 2 μm, the photocatalytic activity and high durability are retained, but more preferably, the film thickness is set to 50 nm to 1 μm so that it is high in one film formation. Since the oxide film which has durability is obtained, it is more preferable.

The metal material having photocatalytic activity is, for example, a metal sizing material for exterior (body or wheel) of an automobile train, anti-fouling, aircraft exterior (airframe), ship exterior or building exterior. , Pre-coating metal, metal roof, sash, wire mesh, antenna, faucet fitting, mold for molding, intersection mirror or curve mirror, metal road material, lamp, fluorescent lamp, tunnel lighting fixture, road lamp, street lamp, etc. Metal parts, air conditioners for the purpose of air purification, refrigerators, humidifiers, dehumidifiers, air purifiers, dust collectors, or sterilization and sterilization of drinking water, drinking water, etc. It can be used as a metal filter or metal filler for products and devices intended to decompose organic matter such as wastewater.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto.
[Preparation of photocatalyst]
Photocatalysts were prepared and their properties were evaluated.

First, the evaluation method will be described.
(i) Alkali metal content The alkali metal content was measured using a fluorescent X-ray analyzer (LAB CENTER XRE-1700, Shimadzu Corporation), and the atomic absorption photometer (Z- 5000, Hitachi, Ltd.). In addition, about the alkali metal which was not detected, description was abbreviate | omitted.
(Ii) Silicon, sulfur content Silicon and sulfur content were quantified using a fluorescent X-ray analysis method (LAB CENTER XRE-1700, Shimadzu Corporation).
(Iii) Specific surface area The specific surface area was measured with a BET specific surface area measuring device.

  Hereinafter, production examples of the photocatalyst will be described.

The photocatalyst shown below has a structure in which raw material titanium dioxide is covered with a fired film of silicon oxide except for the photocatalyst 27. That is, after a silicon oxide precursor film is formed on the surface of raw material titanium dioxide, firing is performed to form a silicon oxide fired film.
(Photocatalyst 1)
200 g of water and 66.9 g of 1N hydrochloric acid aqueous solution were added to a glass flask, and titanium dioxide (ST-01, Ishihara Sangyo Co., Ltd., adsorbed water content 9% by weight, specific surface area 300 m ² / g by BET specific surface area measuring device) 24. 5 g was dispersed to prepare a liquid A. In a beaker, 100 g of water and 10.7 g of water glass No. 1 (SiO ₂ content 35 to 38% by weight, JIS-K1408) were added and stirred to obtain a liquid B. The liquid B was dripped at 2 ml / min while the liquid A was kept at 35 ° C. and stirred to obtain a mixed liquid C. At this time, the pH of the mixed solution C was 2.3. Stirring was continued for 3 days while maintaining the mixed solution C at 35 ° C. Thereafter, the mixture C was filtered under reduced pressure, and the obtained filtrate was washed by repeating redispersion in 500 mL of water and vacuum filtration four times, and then allowed to stand at room temperature for 2 days. The obtained solid was pulverized in a mortar and then subjected to a baking treatment at 600 ° C. for 3 hours to obtain a photocatalyst 1. When the sodium content of this photocatalyst 1 was quantified with an atomic absorption photometer (Z-5000, Hitachi, Ltd.), the sodium content was 87 ppm. Further, when the silicon content and sulfur content of the photocatalyst 1 were quantified by fluorescent X-ray analysis (LAB CENTER XRE-1700, Shimadzu Corporation), the silicon content was 6.9% by weight and the sulfur content was 0.06. % By weight. It was 212.8 m < ² > / g when the specific surface area was measured with the BET method specific surface area measuring apparatus. Therefore, the amount of silicon supported per 1 m ² of the surface area of the photocatalyst 1 was 0.33 mg. The result of measuring the pore distribution of the photocatalyst 1 is shown in FIG.
(Photocatalyst 2)
A photocatalyst 2 was obtained in the same manner as the photocatalyst 1 except that the amount of titanium dioxide was 82.1 g and the pH of the mixed solution C was 4.0. This photocatalyst 2 had a sodium content of 56 ppm, a silicon content of 2.4% by weight, and a specific surface area of 133.8 m ² / g. Therefore, silicon supported amount per surface area of 1 m ² of photocatalytic 2 was 0.18 mg.
(Photocatalyst 3)
A photocatalyst 3 was obtained in the same manner as the photocatalyst 1 except that the amount of titanium dioxide was 38.9 g and the pH of the mixed solution C was 2.8. This photocatalyst 3 had a sodium content of 85 ppm, a silicon content of 4.6% by weight, and a specific surface area of 194.9 m ² / g. Therefore, the amount of silicon supported per 1 m ² of the surface area of the photocatalyst 3 was 0.24 mg.

(Photocatalyst 4)
A photocatalyst 4 was obtained in the same manner as the photocatalyst 1 except that the amount of titanium dioxide was 12.2 g and the pH of the mixed solution C was 2.5. This photocatalyst 4 had a sodium content of 160 ppm, a silicon content of 9.6% by weight, and a specific surface area of 244.2 m ² / g. Therefore, the amount of silicon supported per 1 m ² of the surface area of the photocatalyst 4 was 0.39 mg.
(Photocatalyst 5)
As titanium dioxide, 75.0 g of P25 (Nippon Aerosil Co., Ltd., a mixture of anatase: rutile ratio 8: 2, purity 99.5%, specific surface area 50 m ² / g by BET specific surface area measuring device) was used. The photocatalyst 5 was obtained in the same manner as the photocatalyst 1 except that 6.5 g of an aqueous sodium silicate solution was used and the pH of the mixed solution C was 2.6. This photocatalyst 5 had a sodium content of 34 ppm, a silicon content of 1.4% by weight, and no sulfur content detected, and the specific surface area was 61.1 m ² / g. Therefore, the amount of silicon supported per 1 m ² of the surface area of the photocatalyst 5 was 0.22 mg. The result of measuring the pore distribution of the photocatalyst 5 is shown in FIG.
(Photocatalyst 6)
As titanium dioxide, 70.5 g of PC-102 (Titanium Industry Co., Ltd., anatase type, adsorbed water content 5%, specific surface area 137 m ² / g by BET specific surface area measuring device) was used, and the pH of the mixed solution C was The photocatalyst 6 was obtained in the same manner as the photocatalyst 1 except that the mixture became 3.8 and the mixture C was aged by stirring for 16 hours. This photocatalyst 6 had a sodium content of 12 ppm, a silicon content of 2.2% by weight, a sulfur content of 0.19% by weight, and a specific surface area of 127.8 m ² / g. Therefore, the amount of silicon supported per 1 m ² of the surface area of the photocatalyst 6 was 0.18 mg.

(Photocatalyst 7)
As titanium dioxide, 25.0 g of AMT-100 (Taika Co., Ltd., anatase type, adsorbed water content 11%, specific surface area 290 m ² / g by BET specific surface area measuring device) was used, and pH of the mixture C was 2 The photocatalyst 7 was obtained in the same manner as in the production method of the photocatalyst 6 except that the ratio was 4. This photocatalyst 7 had a sodium content of 17 ppm, a silicon content of 5.5% by weight, a sulfur content of 0.07% by weight, and a specific surface area of 207.2 m ² / g. Therefore, the amount of silicon supported per 1 m ² of the surface area of the photocatalyst 7 was 0.27 mg.
(Photocatalyst 8)
As titanium dioxide, 25.0 g of TKP-101 (Taika Co., Ltd., anatase type, adsorbed water content 11%, specific surface area 300 m ² / g by BET specific surface area measuring device) was used, and pH of the mixture C was 2 The photocatalyst 8 was obtained in the same manner as the photocatalyst 6 production method except that the amount of the photocatalyst 6 was 1. This photocatalyst 8 had a sodium content of 50 ppm, a silicon content of 6.7 wt%, a sulfur content of 0.38 wt%, and a specific surface area of 194.2 m ² / g. Therefore, the amount of silicon supported per 1 m ² of the surface area of the photocatalyst 8 was 0.34 mg.
(Photocatalyst 9)
A photocatalyst 9 was obtained in the same manner as the photocatalyst 1 except that the mixture C was aged by stirring for 16 hours. This photocatalyst 9 had a sodium content of 180 ppm, a silicon content of 5.7 wt%, and a specific surface area of 246.2 m ² / g. Therefore, the silicon content per 1 m ² of the surface area of the photocatalyst 9 was 0.23 mg.

(Photocatalyst 10)
Photocatalyst 10 was obtained in the same manner as in the production method of photocatalyst 8, except that redispersion in 500 mL of water and filtration under reduced pressure were repeated 7 times. This photocatalyst 10 had a sodium content of 120 ppm, a silicon content of 5.7 wt%, and a specific surface area of 231.4 m ² / g. Therefore, the amount of silicon supported per 1 m ² of the surface area of the photocatalyst 10 was 0.25 mg.
(Photocatalyst 11)
Photocatalyst 11 was obtained in the same manner as in the production method of photocatalyst 8, except that washing was performed by performing redispersion in 500 mL of water and filtration under reduced pressure once. This photocatalyst 11 had a sodium content of 210 ppm, a silicon content of 5.7 wt%, and a specific surface area of 231.4 m ² / g. Therefore, the amount of silicon supported per 1 m ² of the surface area of the photocatalyst 11 was 0.24 mg.
(Photocatalyst 12)
A photocatalyst 12 was obtained in the same manner as in the production method of the photocatalyst 1 except that the baking treatment was performed at 400 ° C. for 3 hours. This photocatalyst 12 had a sodium content of 93 ppm, a silicon content of 6.9% by weight, and a specific surface area of 255.5 m ² / g. Therefore, the amount of silicon supported per 1 m ² of the surface area of the photocatalyst 12 was 0.27 mg.

(Photocatalyst 13)
A photocatalyst 13 was obtained in the same manner as in the production method of the photocatalyst 1 except that the baking treatment was performed at 800 ° C. for 3 hours. This photocatalyst 13 had a sodium content of 98 ppm, a silicon content of 6.9% by weight, and a specific surface area of 150.7 m ² / g. Therefore, the amount of silicon supported per 1 m ² of the surface area of the photocatalyst 13 was 0.46 mg.
(Photocatalyst 14)
A photocatalyst 14 was obtained in the same manner as in the production method of the photocatalyst 1 except that the baking treatment was performed at 900 ° C. for 3 hours. This photocatalyst 14 had a sodium content of 96 ppm, a silicon content of 6.9 wt%, and a specific surface area of 108.2 m ² / g. Therefore, the amount of silicon supported per 1 m ² of the surface area of the photocatalyst 14 was 0.64 mg.
(Photocatalyst 15)
A photocatalyst 15 was obtained in the same manner as in the production method of the photocatalyst 1 except that the baking treatment was performed at 1000 ° C. for 3 hours. This photocatalyst 15 had a sodium content of 92 ppm, a silicon content of 6.9% by weight, and a specific surface area of 55.3 m ² / g. Therefore, the amount of silicon supported per 1 m ² of the surface area of the photocatalyst 15 was 1.25 mg. The result of measuring the pore distribution of the photocatalyst 15 is shown in FIG.

(Photocatalyst 16)
A photocatalyst 16 was obtained in the same manner as the photocatalyst 9 except that the same amount of 1N nitric acid aqueous solution was used instead of the 1N hydrochloric acid aqueous solution, and the pH of the mixed solution C became 3.2. . This photocatalyst 16 had a sodium content of 480 ppm, a silicon content of 6.7% by weight, and a specific surface area of 207.4 m ² / g. Therefore, the amount of silicon supported per 1 m ² of the surface area of the photocatalyst 16 was 0.32 mg.
(Photocatalyst 17)
81.7 g of 1N nitric acid aqueous solution was used instead of 66.9 g of 1N hydrochloric acid aqueous solution, sodium silicate aqueous solution of different composition (SiO ₂ content 29.1 wt%, Na ₂ O content 9.5 wt%, Photocatalyst 17 was obtained in the same manner as in the production method of photocatalyst 9 except that 13.3 g of JIS K1408 “Water Glass 3” was used. This photocatalyst 17 had a sodium content of 150 ppm, a silicon content of 3.4% by weight, and a specific surface area of 210.5 m ² / g. Therefore, the amount of silicon supported per 1 m ² of the surface area of the photocatalyst 17 was 0.16 mg.
(Photocatalyst 18)
Photocatalyst 18 was obtained in the same manner as in the production method of photocatalyst 2 except that the calcination temperature was changed to 200 ° C instead of 600 ° C. This photocatalyst 18 had a sodium content of 56 ppm, a silicon content of 2.4% by weight, and a specific surface area of 237.3 m ² / g. Therefore, the amount of silicon supported per 1 m ² of the surface area of the photocatalyst 18 was 0.10 mg.

(Photocatalyst 19)
Photocatalyst 19 was obtained in the same manner as the production method of photocatalyst 17 except that 13.8 g of potassium silicate solution (Wako Pure Chemical Industries, SiO ₂ content 28 wt%) was used instead of water glass No. 3. It was. When the sodium and potassium contents of the photocatalyst 19 were quantified with an atomic absorption photometer (Z-5000, Hitachi, Ltd.), the sodium content was 74 ppm and the potassium content was 90 ppm. As a result, it was confirmed that the photocatalyst 19 contained potassium in the silicon oxide film. Further, when the silicon content of the photocatalyst 19 was quantified by fluorescent X-ray analysis (LAB CENTER XRE-1700, Shimadzu Corporation), the silicon content was 4.9% by weight, and the specific surface area was determined by the BET specific surface area. It was 193.9 m < ² > / g when measured with the measuring apparatus. Therefore, the amount of silicon supported per 1 m ² of the surface area of the photocatalyst 19 was 0.25 mg. The result of measuring the pore distribution of the photocatalyst 19 is shown in FIG.

(Photocatalyst 20)
Commercially available titanium dioxide (Ishihara Sangyo Co., Ltd., ST-01) was dried at 200 ° C. for 3 hours to obtain a photocatalyst 20. This photocatalyst 20 had a sodium content of 1400 ppm and a specific surface area of 214.3 m ² / g.

(Photocatalyst 21)
Commercially available titanium dioxide (Nippon Aerosil Co., Ltd., P25) was dried at 200 ° C. for 3 hours to obtain a photocatalyst 21. In this photocatalyst 21, no alkali metal was detected. The specific surface area was 50.2 m ² / g.
As a result, it was confirmed that the photocatalyst 5 contained sodium in the fired silicon oxide film, and the photocatalyst 19 contained potassium in the fired silicon oxide film.
Photocatalysts 22 to 26 were prepared in order to confirm the difference in performance depending on the presence or absence of pores derived from the silicon oxide film in the region of sodium content or 20 to 500 angstroms.
(Photocatalyst 22)
ST-01 (Ishihara Sangyo Co., Ltd., adsorbed water content 9% by weight, specific surface area 300 m ² / g) as titanium dioxide in accordance with Example (Production Example 1) of Patent Document 4 (Japanese Patent Laid-Open No. 62-260717) The photocatalyst 22 was obtained. This photocatalyst 22 had a sodium content of 1200 ppm, a silicon content of 5.8 wt%, and a specific surface area of 187.3 m ² / g. Therefore, the amount of silicon supported per 1 m ² of the surface area of the photocatalyst 22 was 0.31 mg. The result of measuring the pore distribution of the photocatalyst 22 is shown in FIG.
(Photocatalyst 23)
In accordance with Example (Production Example 1) of Patent Document 4 (Japanese Patent Application Laid-Open No. Sho 62-260717), P25 (Nippon Aerosil Co., Ltd., purity 99.5%, specific surface area 50.8 m ² / g) as titanium dioxide The photocatalyst 23 was obtained. In this photocatalyst 23, no alkali metal was detected. Further, this photocatalyst 23 had a silicon content of 2.2% by weight and a specific surface area of 38.7 m ² / g. Therefore, the amount of silicon supported per 1 m ² of the surface area of the photocatalyst 23 was 0.56 mg. The result of measuring the pore distribution of the photocatalyst 23 is shown in FIG.

(Photocatalyst 24)
Add 250 g of water and 0.05 g of 0.1N sodium hydroxide aqueous solution to a glass flask, and disperse 24.5 g of titanium dioxide (ST-01, Ishihara Sangyo Co., Ltd., adsorbed water content 9% by weight, specific surface area 300 m ^{2 /} g). A liquid A was obtained. In a beaker, 100 g of water and 10.7 g of an aqueous sodium silicate solution (SiO ₂ content 36.1 wt%, Na ₂ O content 17.7 wt%, JIS K1408 “Water Glass No. 1”) were added, stirred, and solution B It was. The liquid B was dripped at 2 ml / min while the liquid A was kept at 35 ° C. and stirred to obtain a mixed liquid C. At this time, the pH of the mixed solution C was 11.5. Stirring was continued for 3 days while maintaining the mixed solution C at 35 ° C. Thereafter, the mixture C was filtered under reduced pressure, and the obtained filtrate was washed by repeating redispersion in 500 mL of water and vacuum filtration four times, and then allowed to stand at room temperature for 2 days. The obtained solid was pulverized in a mortar and then subjected to baking treatment at 600 ° C. for 3 hours to obtain a photocatalyst 24. This photocatalyst 24 had a sodium content of 14000 ppm, a silicon content of 3.4% by weight, and a specific surface area of 126.1 m ² / g. Therefore, the amount of silicon supported per 1 m ² of the surface area of the photocatalyst 24 was 0.27 mg. The result of measuring the pore distribution of the photocatalyst 24 is shown in FIG.
(Photocatalyst 25)
100 g of water was put in a glass flask, and 10.0 g of titanium dioxide (P-25, Nippon Aerosil Co., Ltd., purity 99.5%, specific surface area 50.8 m ^{2 /} g by BET specific surface area measuring device) was dispersed, It was set as A liquid. A 4N aqueous sodium hydroxide solution was added dropwise thereto to adjust the pH to 10.5. Then, the solution was heated to 75 ° C. and maintained at 75 ° C., while an aqueous sodium silicate solution (SiO ₂ content 29.1 wt%, Na ₂ O content 9.5 wt%, JIS K1408 “Water Glass No. 3”) ) 14.8 g was added and stirred to give solution B. The liquid B was heated to 90 ° C., and while maintaining the temperature at 90 ° C., a 1N aqueous sulfuric acid solution was added dropwise at a rate of 2 ml / min to obtain a liquid C. As the sulfuric acid aqueous solution was dropped, the pH of the mixed solution gradually decreased from 10.5 to the acidic side, and finally the pH of the C solution became 5. Thereafter, stirring was continued for 1 hour while the liquid C was kept at 90 ° C., and aged. Next, C liquid after aging was filtered under reduced pressure, and the obtained filtrate was washed by repeating redispersion in 250 mL of water and vacuum filtration four times, and then dried at 120 ° C. for 3 hours. The obtained solid was pulverized in a mortar and then subjected to a baking treatment at 600 ° C. for 3 hours to obtain a photocatalyst 25. This photocatalyst 25 had a sodium content of 2500 ppm, a silicon content of 13.0% by weight, and a specific surface area of 68.4 m ² / g. Therefore, the amount of silicon supported per 1 m ² of the surface area of the photocatalyst 25 was 1.90 mg.
(Photocatalyst 26)
100 g of water was put into a glass flask, and 4.2 g of titanium dioxide (ST-01, Ishihara Sangyo Co., Ltd., adsorbed water content 9% by weight, specific surface area 300 m ^{2 /} g by BET specific surface area measuring device) was dispersed. A liquid was used. In a beaker, 43 g of water and 5.6 g of a sodium silicate aqueous solution (SiO ₂ content 29.1 wt%, Na ₂ O content 9.5 wt%, JIS K1408 “Water Glass No. 3”) were added, stirred, and liquid B It was. Next, the liquid A was kept at 35 ° C., and the liquid B was added dropwise at a rate of 2 ml / min while stirring. At this time, 1N nitric acid aqueous solution was appropriately added dropwise so that the pH of the mixed solution was 6-8. The pH of the mixed liquid at the completion of the dropwise addition of the B liquid was 7.0. Thereafter, the mixture was aged by continuing stirring for 16 hours while maintaining the mixed solution at 35 ° C. Thereafter, the mixed liquid was filtered under reduced pressure, and the obtained residue was washed by repeating redispersion in 250 mL of water and vacuum filtration four times, and then dried at 120 ° C. for 3 hours. The obtained solid was pulverized in a mortar and then subjected to a baking treatment at 600 ° C. for 3 hours to obtain a photocatalyst 26. This photocatalyst 26 had a sodium content of 5900 ppm, a silicon content of 12.0% by weight, and a specific surface area of 258.3 m ² / g. Therefore, the amount of silicon supported per 1 m ² of the surface area of the photocatalyst 26 was 0.47 mg. The result of measuring the pore distribution of the photocatalyst 26 is shown in FIG.

(Photocatalyst 27)
In order to confirm the difference from the silica hydrate coating, referring to Example 1 of Patent Document 5, a titanyl sulfate aqueous solution was thermally hydrolyzed to prepare a metatitanic acid slurry having a crystal particle diameter of 6 nm. The temperature was raised to 40 ° C. The 100 ml (100 g / l in terms of TiO ₂₎ The metatitanic acid slurry, constant speed 200 g / l of sodium silicate solution 5 ml _(SiO 2 / TiO ₂ weight ratio = 0.1) as a SiO ₂ In 10 minutes. After the addition, the pH was adjusted to 4.0 with sodium hydroxide, and the mixture was stirred for 30 minutes while maintaining 40 ° C. Thereafter, the slurry was filtered and washed with water. The obtained cake was dried at 110 ° C. for 12 hours and then pulverized using a sample mill to obtain a photocatalyst 27. This photocatalyst 27 had a sodium content of 210 ppm, a silicon content of 5.1 wt%, and a specific surface area of 140.0 m ² / g. Therefore, the amount of silicon supported per 1 m ² of the surface area of the photocatalyst 27 was 0.36 mg.

  The characteristics of the obtained photocatalysts 1 to 27 are summarized in Table 1.

<Evaluation of photocatalysts 1-27>
[1. Methylene blue photolytic activity evaluation]
Photocatalysts 1 to 27 were suspended in an aqueous methylene blue solution. Thereafter, light irradiation was performed, and the photodegradation activity was tested by quantifying the concentration of methylene blue in the liquid by spectroscopic analysis. The detailed test operation method is as follows.
(Preparation of photocatalyst suspension)
45 g of methylene blue aqueous solution having a concentration of 40 × 10 ⁻⁶ mol / L was weighed into a 100 cc polyethylene wide-mouthed bottle in which a fluororesin stirrer was previously placed. Next, 10 mg of photocatalyst was added with stirring by a magnetic stirrer. Then, after stirring vigorously for 5 minutes, the stirring strength was adjusted to such an extent that the liquid did not scatter and stirring was continued.
(Preliminary adsorption treatment)
Starting from the moment when the photocatalyst was added, stirring was continued for 60 minutes without light irradiation. After 60 minutes, 3.0 cc of the suspension was collected and used as a sample before light irradiation.
(Photolytic treatment)
3.5 cc of the suspension after the pre-adsorption treatment was extracted, and a quartz standard spectroscopic cell (Tosoh Quartz Co., Ltd., outer dimensions 12.5 × 12.5 × 45 mm, optical path width 10 mm, which was previously filled with a fluororesin stirrer. , Optical path length 10 mm, volume 4.5 cc), and stirred with a magnetic stirrer. Next, light was irradiated for 5 minutes from the outside / lateral direction of the spectroscopic cell. Light irradiation was performed through a quartz filter container filled with pure water using a light source device SX-UI151XQ (USHIO Inc., 150 W xenon short arc lamp) as a light source. The amount of irradiation light was 5.0 mW / cm ² with an ultraviolet illuminance meter UVD-365PD (USHIO INC., Test wavelength 365 nm). After irradiation, the suspension in the spectroscopic cell was collected and used as a sample after light irradiation.
(Quantitative determination of methylene blue)
A membrane filter (Toyo Roshi Kaisha, DISMIC-13HP) was attached to an all-plastics 10 cc syringe. The sample suspension before and after the light irradiation was put into this, respectively, and extruded with a piston to remove the photocatalyst. At that time, the first half amount of the filtrate was discarded, and the latter half amount of the filtrate was collected in a semi-micro type disposable cell for visible light analysis (made of polystyrene, optical path width 4 mm, optical path length 10 mm, volume 1.5 cc). Then, using a UV-visible spectroscopic analyzer (UV-2500, Shimadzu Corporation), the absorbance at a wavelength of 680 nanometers was measured, and the methylene blue concentration was calculated.

  The photolytic activity was evaluated by the methylene blue concentration after light irradiation with respect to the methylene blue concentration before light irradiation. Table 1 shows the methylene blue removal rate as the photolytic activity. The methylene blue adsorption rate was calculated from the methylene blue concentration before light irradiation based on the charged concentration of methylene blue (concentration of methylene blue before adding the photocatalyst), and is also shown in Table 1.

[2. Determination of presence or absence of pores derived from silicon oxide film by pore distribution measurement]
Using an autosorb (manufactured by Cantachrome), nitrogen adsorption isotherms of the photocatalysts 1 to 27 in the desorption process under liquid nitrogen (77K) were measured.
As pretreatment of each photocatalyst, vacuum deaeration at 100 ° C. was performed. Next, the measurement result of each photocatalyst was analyzed by the BJH method, and a log differential pore volume distribution curve was obtained.
Next, the presence or absence of pores derived from the silicon oxide film of the photocatalysts 1 to 27 was determined. Specifically, a photocatalyst used as a raw material is compared with a log differential pore volume distribution curve of a photocatalyst coated with a silicon oxide film prepared using this photocatalyst as a base (base catalyst). The presence or absence of the derived pores was determined.

  Table 1 shows the presence or absence of pores derived from the silicon oxide film in the region of 20 to 500 Å of the photocatalysts 1 to 27.

It was confirmed that the photocatalysts 1 to 19 exhibited good catalytic activity.

[3. Differential thermal balance analysis]
In order to examine the water content of the silicon oxide-coated photocatalyst, differential thermal balance analysis (Thermoplus TG8120, Rigaku) was performed. The temperature was raised from room temperature to 600 ° C. in an air flow of 50 ml / min at 10 ° C./min, and the weight loss rate at that time was measured.
Each sample was measured after drying or baking and cooling for 1 hour in order to eliminate the influence of moisture adsorption after drying or baking as much as possible. Table 2 shows the water contents of the photocatalysts 1, 5, 18, and 27.

For some of the photocatalysts obtained above, metal plates containing a photocatalytic film were produced.

  2 g of photocatalyst 1 was mixed and stirred in 100 g of an ethanol solution containing 2% by weight of tetraethoxysilane, 0.6% by weight of water, and 0.06% by weight of 60% nitric acid to prepare a coating solution. 1 g of this solution is formed on a stainless steel plate (SUS304) of 4 cm in length and width by a spin coater, dried at 250 ° C. for 1 hour, and baked at 500 ° C. for 1 hour to form a photocatalyst film having a thickness of 100 nm. The containing metal plate 1 was obtained.

A metal plate 2 containing a photocatalytic film having a film thickness of 190 nm was obtained in the same manner as in Example 1 except that film formation was performed twice using a spin coater.

A metal plate 3 containing a photocatalytic film having a film thickness of 105 nm was obtained in the same manner as in Example 1 except that the photocatalyst 5 was used.

A metal plate 4 containing a photocatalyst film having a thickness of 110 nm was obtained in the same manner as in Example 1 except that the photocatalyst 19 was used.

(Comparative Example 1)
A metal plate 5 containing a photocatalyst film having a film thickness of 100 nm was obtained in the same manner as in Example 1 except that the photocatalyst 20 was used.
(Comparative Example 2)
A metal plate 6 containing a photocatalyst film having a film thickness of 105 nm was obtained in the same manner as in Example 1 except that the photocatalyst 24 was used.

[Acetaldehyde photodegradation activity evaluation]
The metal plates 1 to 6 were irradiated with light in the presence of acetaldehyde gas, and the photodegradation activity was tested by quantifying the acetaldehyde concentration in the gas with a gas chromatograph. The detailed test operation method is as follows.
The metal plates 1 to 6 were irradiated with ultraviolet rays of 5.4 mW / cm ² for 3 hours in an air atmosphere. A 27 W black light blue lamp (Sankyo Electric, FPL27BLB) was used as the light source, and UVA-365 (manufactured by Custom Corp.) was used for the ultraviolet intensity measurement.

  Then, prepare three 1-liter Tedlar (DuPont registered trademark) bags with one silicon packing connector and a minicock, cut one side of the Tedlar (DuPont registered trademark) bag, Each of the molded products 1 to 3 subjected to the irradiation treatment was put and pasted on the center of the bag with a 5 mm square double-sided tape. And it sealed with the heat sealer. Subsequently, the internal air was extracted from the mini-cock using a vacuum pump, and then the cock was closed and left in the dark overnight.

Next, a wet mixed gas in which a mixed gas of 20% oxygen and 80% nitrogen is immersed in 15 ° C. ion exchange water and a 1% acetaldehyde / nitrogen mixed gas are mixed to prepare a gas having an acetaldehyde concentration of 100 ppm. did. 600 mL of this gas was collected and injected into a bag containing a photocatalyst sample plate, and then the bag was left in the dark for 20 hours. Thereafter, the acetaldehyde concentration of the gas inside the bag was measured. A gas chromatograph (Shimadzu Corporation, GC-14) was used for concentration measurement. After the analysis, the photocatalyst sample plate stored in the bag was irradiated with light using a full white fluorescent lamp (Matsushita Electric Works, 10W, FL10N), and the gas inside the bag was analyzed every 2 hours of light irradiation. . At this time, the surface of the photocatalyst sample plate on which the photocatalyst was immobilized was placed at a distance of 4 cm from the fluorescent lamp. The ultraviolet intensity measured at the same place using one film as the bag as a filter was 11 μW / cm ² . Table 3 shows the photolysis evaluation results.

For some of the photocatalysts obtained above, metal beads containing a photocatalytic film were produced.

10 g of the photocatalyst 1 was mixed and stirred in 500 g of an ethanol solution containing 2% by weight of tetraethoxysilane, 0.6% by weight of water, and 0.06% by weight of 60% nitric acid to prepare a coating solution. Next, 80 g of commercially available Φ3 mm stainless beads were applied onto the surface of the stainless beads while spraying the coating liquid using a tumbling granulator, and baked at 250 ° C. for 30 minutes and at 500 ° C. for 30 minutes, to thereby produce photocatalyst 1. Immobilized on stainless steel beads (metal beads 1). The weight of the photocatalyst 1 fixed to the metal beads 1 was 2.5 g / m 2 −beads.
(Comparative Example 3)
A metal bead 2 was obtained in the same manner as in Example 5 except that the photocatalyst 1 was changed to the photocatalyst 20. The weight of the photocatalyst 2 fixed to the metal beads 2 was 2.4 g / m 2 -beads.

[Tricuruloethylene Decomposition Evaluation Test]
30 g of metal beads fixed with a photocatalyst and 30 ml of a 20 mg / L trichloroethylene aqueous solution were placed in a petri dish having an inner diameter of 7 cm, and light irradiation was performed from the upper surface of the cell using black light (Sankyo Electric Co., Ltd., 27 W) as a light source. The amount of irradiation light was 1.0 mW / cm 2 with an ultraviolet illuminance meter UVD-365PD (USHIO INC., Test wavelength 365 nm). The content of trichlorethylene in the solution 10 hours after the start of irradiation was measured using a gas chromatograph to determine the decomposition rate of trichlorethylene. The results are shown in Table 4.

It is a figure which shows the log differential pore volume distribution curve (solid line) of the photocatalyst 1, and the log differential pore volume distribution curve (dotted line) of the photocatalyst (photocatalyst 20) which does not have the silicon oxide film applicable to the base of this photocatalyst. . It is a figure which shows the log differential pore volume distribution curve (solid line) of the photocatalyst 5, and the log differential pore volume distribution curve (dotted line) of the photocatalyst (photocatalyst 21) which does not have the silicon oxide film applicable to the base of this photocatalyst. . It is a figure which shows the log differential pore volume distribution curve (solid line) of the photocatalyst 15, and the log differential pore volume distribution curve (dotted line) of the photocatalyst (photocatalyst 20) which does not have the silicon oxide film applicable to the base of this photocatalyst. . It is a figure which shows the log differential pore volume distribution curve (solid line) of the photocatalyst 19, and the log differential pore volume distribution curve (dotted line) of the photocatalyst (photocatalyst 20) which does not have the silicon oxide film applicable to the base of this photocatalyst. . It is a figure which shows the log differential pore volume distribution curve (solid line) of the photocatalyst 22, and the log differential pore volume distribution curve (dotted line) of the photocatalyst (photocatalyst 20) which does not have the silicon oxide film applicable to the base | substrate of this photocatalyst. . It is a figure which shows the log differential pore volume distribution curve (solid line) of the photocatalyst 23, and the log differential pore volume distribution curve (dotted line) of the photocatalyst (photocatalyst 21) which does not have the silicon oxide film applicable to the base of this photocatalyst. . It is a figure which shows the log differential pore volume distribution curve (solid line) of the photocatalyst 24, and the log differential pore volume distribution curve (dotted line) of the photocatalyst (photocatalyst 20) which does not have the silicon oxide film applicable to the base | substrate of this photocatalyst. . It is a figure which shows the log differential pore volume distribution curve (solid line) of the photocatalyst 26, and the log differential pore volume distribution curve (dotted line) of the photocatalyst (photocatalyst 20) which does not have the silicon oxide film applicable to the base | substrate of this photocatalyst. .

Claims (13)

A metal material containing a photocatalyst in the surface layer,
The photocatalyst is
A substrate having photocatalytic activity;
A silicon oxide film that covers the substrate and has substantially no pores,
The metal material whose alkali metal content of this photocatalyst is 1 ppm or more and 1000 ppm or less. The metal material according to claim 1, wherein the silicon oxide film is a fired film of silicon oxide. The metal material according to claim 2, wherein the silicon oxide film is a fired film obtained by firing at a temperature of 200 ° C. or higher and 1200 ° C. or lower. The metal material according to any one of claims 1 to 3, wherein pores derived from a silicon oxide film are not present in pore diameter distribution measurement in a region of 20 to 500 angstroms by a nitrogen adsorption method. The metal material according to any one of claims 1 to 4, wherein the substrate is an anatase type, a rutile type, or a titanium oxide containing a mixture thereof. The metal material according to claim 1, wherein the alkali metal is sodium and / or potassium. The metal material according to claim 1, wherein the substrate is a particle. 8. The metal material according to claim 1, wherein the amount of silicon supported per 1 m ² of the surface area of the photocatalyst is 0.10 mg or more and 2.0 mg or less. The metal material according to claim 8, wherein the amount of silicon supported per 1 m ² of the surface area of the photocatalyst is 0.18 mg or more and 1.25 mg or less. 10. The metal material according to claim 9, wherein a specific surface area of the substrate is 120 m ² / g or more and 400 m ² / g or less. 11. The metal material according to claim 1, wherein the content of sulfur atoms is 0.5% by weight or less based on the total weight of the photocatalyst. The metal material according to claim 1, wherein the silicon oxide film contains an alkali metal. The metal material according to claim 12, wherein the content of alkali metal contained in the silicon oxide film is 1 ppm or more and 200 ppm or less based on the total weight of the photocatalyst.

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