Photocatalyst, method for producing the same, photocatalytic coating agent using the same, photocatalyst dispersion, and photocatalyst body

The present invention relates to a photocatalyst, a method for producing the same, a photocatalyst coating agent using the same, a photocatalyst dispersion, and a photocatalyst, and more specifically, a photocatalyst having excellent catalytic activity even when irradiated with light such as a white fluorescent lamp.

The photocatalyst is excited when irradiated with light having a wavelength having an energy equal to or higher than the band gap, and exhibits strong catalytic activity. In particular, since it has a large oxidizing and decomposing power of some inorganic substances such as organic substances and NOx, it is low cost as an energy source, and it can use light with a very small environmental load, it has been used for environmental purification, deodorization, antifouling, sterilization, etc. in recent years. The application is in progress. Further, it has been found that when the photocatalyst is excited, its surface becomes hydrophilic and the contact angle with water decreases, and application to antifogging, antifouling, etc. is being promoted by utilizing this action. As the photocatalyst, metal compounds such as oxides and sulfides, particularly fine particles of titanium oxide and zinc oxide having high photocatalytic activity are generally used. Titanium oxide, zinc oxide, etc. are in the ultraviolet region where the wavelength of the excitation light is 400 nm or less. For example, a technique is known in which an iron compound such as iron oxide, iron hydroxide, or iron oxyhydroxide is contained inside and / or on the surface of titanium oxide particles to improve photocatalytic activity (see Patent Document 1). In addition, a technique for increasing the efficiency of sunlight utilization by supporting 10 to 100 Å of ferric oxide fine particles on the surface of titanium oxide particles (see Patent Document 2), ferrous oxide on the surface of anatase-type titanium oxide particles, A technique of supporting iron oxides such as ferric oxide and magnetite to obtain high activity by irradiation with visible light (see Patent Document 3) has also been proposed.

<p><patcit num="1"><text>Japanese Unexamined Patent Publication No. 7-303835</text></patcit><patcit num="2"><text>Japanese Unexamined Patent Publication No. 6-39285</text></patcit><patcit num="3"><text>Japanese Unexamined Patent Publication No. 2003-190811</text></patcit></p>

<p> A photocatalyst having photocatalytic activity by irradiation with visible light does not require a special light source such as an ultraviolet lamp, and a light source such as sunlight or a white fluorescent lamp can be used. Therefore, it is expected that the application fields of the photocatalyst will be further expanded. However, the photocatalysts described in Patent Documents 2 and 3 do not have sufficient photocatalytic activity under light irradiation such as a white fluorescent lamp. Therefore, an object of the present invention is to provide a photocatalyst having excellent photocatalytic activity by irradiation with a white fluorescent lamp or the like and a method for producing the same.</p>

<p> Based on the above-mentioned Patent Document 1, the present inventors have conducted intensive studies to develop a titanium oxide photocatalyst having excellent activity even in a white fluorescent lamp, and as a result, among various iron compounds, the light of the white fluorescent lamp is used. By using iron oxyhydroxide that absorbs light with a wavelength of 400 to 500 nm, the photocatalyst containing iron oxyhydroxide and titanium oxide can generate iron oxyhydroxide under the light irradiation of a white fluorescent lamp. The present invention was completed by finding that it has about twice or more photocatalytic activity as compared with titanium oxide measured under the same conditions without using it.</p><p> That is, the present invention is characterized in the following points. (1) A photocatalyst containing at least iron oxyhydroxide and titanium oxide, which is a photocatalyst in which titanium oxide exhibits photocatalytic activity when iron oxyhydroxide absorbs light having a wavelength of 400 to 500 nm. In such a photocatalyst, the acetaldehyde decomposition reaction rate constant when irradiated with light from a white fluorescent lamp containing light having a wavelength of 400 to 500 nm is higher than the acetaldehyde decomposition reaction rate constant of titanium oxide measured under the same conditions. It has about twice or more photocatalytic activity. (2) In the method for producing a photocatalyst of the present invention, at least iron oxyhydroxide and titanium oxide are mixed, and more preferably, a medium solution containing titanium oxide containing an alkali metal element and / or an alkaline earth metal element. Iron oxyhydroxide and titanium oxide are contained by adding an iron compound to the inside and causing a reaction to carry iron oxyhydroxide on the surface of the titanium oxide particles. (3) A photocatalyst coating agent can be obtained by adding a binder to a photocatalyst containing at least iron oxyhydroxide and titanium oxide, and a photocatalyst dispersion can be obtained by adding a dispersion medium. Further, a photocatalyst containing at least iron oxyhydroxide and titanium oxide can be molded or fixed on a base material.</p>

<p> Since the photocatalyst of the present invention has excellent photocatalytic activity under light irradiation of a white fluorescent lamp or the like having a wavelength of 400 to 500 nm, the photocatalyst of the present invention does not require a special light source such as an ultraviolet lamp and is used in a fluorescent lamp or the like. Even indoor lighting and sunlight effectively decompose NOx and organic environmental pollutants. Since it can be expected to have a hydrophilic effect, it is suitable as a purifying material, a deodorizing material, an antifouling material, a bactericidal material, an antifogging material, and the like. Further, since relatively inexpensive materials such as titanium oxide and iron oxyhydroxide are used, a low-cost photocatalyst can be provided. Further, the photocatalyst of the present invention can be a liquid composition such as a coating agent or a dispersion, or can be molded or fixed to a base material to be a photocatalyst, and these can be used. It is possible to impart functionality such as antifouling property and hydrophilicity.</p>

<figref num="1">It is a differential absorption spectrum of the sample B of Example 2.</figref><figref num="2">It is a differential absorption spectrum of the sample I of Comparative Example 4.</figref><figref num="3">It is a differential absorption spectrum of the sample J of Comparative Example 5.</figref>

The present invention is a photocatalyst containing at least iron oxyhydroxide and titanium oxide, and titanium oxide exhibits photocatalytic activity when iron oxyhydroxide absorbs light having a wavelength of 400 to 500 nm. Therefore, as an evaluation standard for photocatalytic activity, the acetaldehyde decomposition reaction rate constant when irradiated with light from a white fluorescent lamp containing light having a wavelength of 400 to 500 nm was measured (see Evaluation 1 below), thereby determining the activity. evaluate. The activity of the photocatalyst of the present invention evaluated in this manner is preferably about 2 times or more, more preferably about 5 times, the activity of titanium oxide itself (evaluated by the acetaldehyde decomposition reaction rate constant) measured under the same conditions. As mentioned above, it is more preferably about 7 times or more, and most preferably about 10 times or more. The photocatalyst of the present invention may contain at least iron oxyhydroxide and titanium oxide, but iron oxyhydroxide absorbs light having a wavelength of 400 to 500 nm so that titanium oxide exhibits photocatalytic activity. , The state in which iron oxyhydroxide and titanium oxide are bonded to the extent that they interact with each other is preferable, and the state in which they are firmly bonded is more preferable. In order to obtain such a state, it is preferable to mix iron oxyhydroxide and titanium oxide, more preferably the mixture using a mixer, and further preferably iron oxyhydroxide and titanium oxide in a suspended state. Mix using a stirrer or the like. Preferably, iron oxyhydroxide is supported on the surface of the titanium oxide particles. The supporting mode of iron oxyhydroxide is not limited, and it may be in a state of being adsorbed on the surface of titanium oxide particles or in a state of being strongly bonded by hydrogen bonding with the hydroxyl group of the titanium oxide particles on the surface. .. The photocatalyst, photocatalytic coating agent, photocatalytic dispersion, and photocatalyst of the present invention may appropriately contain photocatalytic substances such as zinc oxide and cadmium sulfide, and various adsorbents in addition to iron oxyhydroxide and titanium oxide. , The content form thereof is not particularly limited.

The iron oxyhydroxide contained in the photocatalyst of the present invention is FeOOH or Fe.₂O₃ NH₂A compound represented by the chemical formula of O, which is crystalline such as α-state, β-state, γ-state, or amorphous, can be used. In particular, α-iron hydroxide is preferable because it has a high absorption effect of light having a wavelength of 400 to 500 nm and provides a photocatalyst having more excellent activity. The content of iron oxyhydroxide can be set as appropriate, but it is preferably in the range of 0.01 to 5% by weight in terms of Fe with respect to the total amount of iron oxyhydroxide and titanium oxide, and further in the range of 0.05 to 2% by weight. preferable. Whether titanium oxide contains or supports iron oxyhydroxide, and more specifically, whether it contains or supports α-state iron oxyhydroxide is confirmed by, for example, Mössbauer spectroscopy or an electron microscope. be able to.

The titanium oxide contained in the photocatalyst of the present invention includes those called anhydrous titanium oxide, titanium hydroxide-containing, hydrated titanium oxide, titanium hydroxide, titanium acid, etc., in addition to general titanium oxides. There is no limitation on the crystal form such as anatase type and rutile type, and it may be an indefinite form or a mixture thereof. Among these, those having particularly high crystallinity are preferable because they have high photocatalytic activity, and titanium oxide having rutile-type crystals is more preferable because the wavelength of the excitation light of rutile-type titanium oxide is slightly larger than that of anatase-type titanium oxide. Further, a part of titanium oxide may be a composite oxide such as an alkali metal titanate or an alkaline earth metal titanate, and inside such titanium oxide, an alkali metal element constituting the composite oxide may be used. , Alkaline earth metal elements are contained, which is preferable. In addition, titanium oxide may contain one or more different elements selected from V, Fe, Co, Ni, Cu, Zn, Ru, Rh, Pd, Ag, and Au as long as they do not adversely affect the excitation. Compounds of dissimilar elements such as oxides may be contained. The size of titanium oxide is not limited, but the specific surface area by the BET method is 10 to 400 m.²It is preferably in the range of about / g, 10 ~ 200m²A range of about / g is more preferable, 10 to 100 m²A range of about / g is more preferable, 30 to 80 m.²The range of about / g is the most preferable. If the specific surface area is too small, the adsorption power of the substance to be treated such as organic substances and nitrogen oxides is lowered and the decomposition efficiency is lowered, which is not preferable. If the specific surface area is too large, the substance becomes too fine and the crystallinity is high. Is not preferable because it is difficult to obtain.

The particle shape of titanium oxide is also not limited, and fixed-sized particles such as true spherical, substantially spherical, and anisotropic shapes, and amorphous particles such as agglomerates can be used. In particular, those having an anisotropic shape are preferable because excellent photocatalytic activity can be easily obtained. The "anisometric shape" referred to in the present invention is generally called a spindle-shaped particle, a rod-shaped particle, a needle-shaped particle, a plate-shaped particle, or the like, and one primary particle is flat in the most stable state. The image is stationary on the plane, the projected image on the plane is sandwiched between two parallel lines, and the distance when the distance between the parallel lines is minimized is the width of the particle or the minor axis diameter w, in the direction perpendicular to these two parallel lines. If the distance between two parallel lines is the particle length or major axis diameter l, and the distance between the two parallel lines is the particle height h, then l&gt; w h. Say what you meet. The major axis diameter, minor axis diameter, and height can be obtained from the electron micrographs of the primary particles by the arithmetic mean value of about 1000 particles. The size of titanium oxide having an anisotropic shape used in the present invention has a specific surface area of 10 to 200 m by the BET method as described above.²A range of about / g is more preferable, 10 to 100 m²A range of about / g is more preferable, 30 to 80 m.²The range of about / g is the most preferable. Such anisotropically shaped particles preferably have an average major axis diameter in the range of 10 to 500 nm and an average minor axis diameter in the range of 1 to 25 nm, and among them, an axial ratio (average major axis diameter /). Spindle-shaped particles, rod-shaped particles, and needle-shaped particles having an average minor axis diameter of 1.5 or more are preferable, and an axial ratio in the range of 1.5 to 10 is more preferable, and more preferably in the range of 2 to 7.

Further, it is preferable that the photocatalyst containing titanium oxide and iron oxyhydroxide contains an alkali metal element and / or an alkaline earth metal element because it can have excellent photocatalytic activity. The alkali metal element and the alkaline earth metal element may be contained on the surface of the titanium oxide particles, may be contained inside as described above, and may be further contained inside the iron oxyhydroxide. It may be present on the surface of iron hydroxide, or may be present in any two or more locations selected from these. In particular, it is preferable to have it inside and / or on the surface of titanium oxide because it can have excellent photocatalytic activity such as being able to firmly support iron oxyhydroxide. Further, a part of titanium oxide may be a composite oxide of an alkali metal titanate or an alkaline earth metal titanate. Examples of the alkali metal element include sodium, potassium, lithium and the like, and examples of the alkaline earth metal element include calcium, magnesium, barium, strontium, beryllium and the like. Of these, sodium is preferable because it easily produces iron oxyhydroxide that absorbs light having a wavelength of 400 to 500 nm. The content of alkali metal elements and / or alkaline earth metal elements is converted into oxides with respect to the total amount of iron oxyhydroxide and titanium oxide (for example, Na).₂OK₂O, Li₂In terms of O, CaO, MgO, BaO, SrO, BeO, etc.), the range of 0.01 to 30% by weight is preferable, the range of 0.05 to 15% by weight is more preferable, and the range of 0.05 to 5% by weight is most preferable. The content form of the alkali metal element and the alkaline earth metal element is not limited to any of ions, metals, and compounds such as oxides, hydroxides, and chlorides. The chemical composition in the present invention is an analytical value by fluorescent X-ray, including the content of iron oxyhydroxide.

Next, in order to produce the photocatalyst of the present invention containing at least iron oxyhydroxide and titanium oxide, (a) the pre-produced iron oxyhydroxide and titanium oxide are mixed with a Henschel mixer, a Reidge mixer, an Erich mixer, and a Raikai. Mixing means using a mixer such as a machine, a mixing means using a milk bowl / milk stick, etc., a method of mixing using a crushing mixer such as a ball mill or a colloid mill, or using a stirrer or the like in a suspended state of iron oxyhydroxide and titanium oxide. Method of mixing, (b) Method of mixing a mixed solution of titanium compound and iron compound and a basic compound described later, neutralizing and reacting to precipitate both iron oxyhydroxide and titanium oxide, ( c) A method of adding an iron compound to a pre-made titanium oxide suspension and reacting it to generate iron oxyhydroxide in the presence of titanium oxide, (d) a pre-made iron oxyhydroxide suspension. A method of adding a titanium compound to the mixture and reacting it to produce titanium oxide in the presence of iron oxyhydroxide can be used. In these methods, a photocatalytic substance such as zinc oxide and cadmium sulfide, various adsorbents and the like may be included, if necessary.

To pre-produce iron oxyhydroxide, add sodium hydroxide, potassium hydroxide, ammonia, amine, sodium carbonate, etc. to a solution of ferrous compounds such as ferrous sulfate, ferrous nitrate, and ferrous chloride. A method in which a basic compound is added to neutralize a part or all of the ferrous compound, and then a gas such as air or oxygen is blown into the compound while adjusting the pH to oxidize the ferrous compound. A basic compound such as sodium hydroxide, potassium hydroxide, ammonia, amine, or sodium carbonate is added to a solution of a ferrous compound such as ferric chloride, and the ferric compound is heated to a temperature of, for example, about 10 to 70 ° C. A known method such as a aging treatment, a heat treatment, or a hydrothermal treatment after neutralization with the above can be used. It is preferable to use a basic sodium compound because it easily produces iron oxyhydroxide that absorbs light at 400 to 500 nm. The aging treatment in this method is a treatment in which the neutralization product is held for a certain period of time while maintaining the neutralization temperature to produce iron oxyhydroxide, and the aging time is appropriately about 10 minutes to 5 hours. The heat treatment is a treatment in which the neutralized product is heated in a medium solution in a range of about 50 to 200 ° C, more preferably in a range of about 70 to 100 ° C to generate iron oxyhydroxide, and the heating time is long. About 10 minutes to 5 hours is appropriate. If the temperature of the heat treatment is lower than 50 ° C, dehydration does not proceed in a short time and ferric hydroxide is not sufficiently modified to iron oxyhydroxide, which is not preferable. In hydrothermal treatment, the neutralized product is heated at about 100 ° C. or higher, more preferably at about 150 to 200 ° C. using a high-temperature and high-pressure device such as an autoclave, and oxyhydroxide is applied under steam pressure according to the temperature. It is a process to generate iron, and the heating time is appropriately about 10 minutes to 5 hours. If the temperature of the hydrothermal treatment is higher than 200 ° C, dehydration proceeds too much and it is easily denatured into ferric oxide, which is not preferable. The obtained iron oxyhydroxide may be appropriately subjected to operations such as filtration, washing, and drying by a method usually used.

A known method can be used to produce titanium oxide in advance, for example, (1) a method of neutralizing titanium chloride or the like, (2) a method of heat-hydrolyzing titanium sulfate, titanyl sulfate or the like, (3). ) A method of calcining or hydrolyzing the product obtained by the methods (1) and (2) above can be used. Further, titanium oxide having an anisotropic shape can also be produced by a known method. For example, after treating titanium hydroxide-containing with a basic sodium compound such as sodium hydroxide, sodium carbonate or sodium oxalate, the mixture can be used. , A method of treating with hydrochloric acid can be used. Titanium oxide obtained by such a method is fine particles and is so-called spindle-shaped, and is therefore preferably used. The obtained titanium oxide may be appropriately subjected to operations such as filtration, washing, and drying by a method usually used.

The titanium oxide containing the alkali metal element and the alkaline earth metal element used in the method (B) described later is the titanium oxide obtained by the above method or the titanium oxide precursor described below, and the alkali metal and alkali. It is obtained by mixing an earth metal hydroxide, carbonate, sulfate, chloride, oxide or the like with a sodium compound and firing. The titanium oxide precursor refers to a compound that becomes titanium oxide by firing, and examples thereof include titanium sulfate, titanyl sulfate, titanium chloride, and titanium alkoxide. When titanium hydroxide and titanium hydroxide are fired to obtain titanium oxide, titanium hydroxide and titanium hydroxide belong to the titanium oxide precursor. Further, titanium oxide containing an alkali metal element and an alkaline earth metal element in advance is obtained by neutralizing titanium chloride with a large excess of alkali metal and alkaline earth metal basic compounds in the method (1) above. More preferably, it can also be obtained by adding titanium chloride to a solution of a basic compound of an alkali metal or an alkaline earth metal to neutralize it. Similarly, for titanium oxide having an anisotropic shape, after treating titanium hydroxide or titanium chloride with a large excess of a basic sodium compound, preferably, titanium hydroxide is added to a solution of the basic sodium compound. After the treatment, it can be obtained by a method of treating with hydrochloric acid. In titanium oxide having an anisotropic shape obtained by this method, it is considered that sodium is contained inside the particles as ions.

As the titanium oxide of the present invention, the one obtained by firing titanium oxide in advance and the one obtained by firing the titanium oxide precursor have high crystallinity of titanium oxide, and the amount of hydroxyl groups and water contained therein is appropriately reduced. This is preferable because the photocatalytic activity is further improved. The firing temperature is preferably in the range of 200 to 700 ° C. If the firing temperature is too lower than this range, it is difficult to obtain the effect of improving the photocatalytic activity, which is not preferable. Not only is it difficult, but it is not preferable because sintering of the formed or grown photocatalyst particles is likely to occur. A more preferred firing temperature range is 200 to 600 ° C, and a more preferred range is 300 to 600 ° C. Conditions such as the firing time and the firing atmosphere can be appropriately set. The firing time is, for example, about 1 to 10 hours, and the firing atmosphere is an atmosphere of air or an oxygen-containing gas or an inert gas such as nitrogen or argon. It is appropriate to carry out in an active gas atmosphere.

In the present invention, when an iron compound is added to a suspension of titanium oxide prepared in advance as described in (c) above and reacted to generate iron oxyhydroxide in the presence of titanium oxide, titanium oxide is produced. It is more preferable because iron oxyhydroxide is easily supported on the particle surface, and the carried iron oxyhydroxide and titanium oxide can interact with each other to exhibit excellent photocatalytic activity. More preferable methods in this method include (A) a method of adding an iron compound in a medium solution containing titanium oxide and reacting by oxidation or aging treatment, heat treatment or hydrothermal treatment, (B) alkali metal element and /. Alternatively, titanium oxide containing an alkaline earth metal element is used to contact the iron compound, and the alkali metal element or alkaline earth metal element eluted from the titanium oxide neutralizes the iron compound and oxidizes the neutralized product. A method of reacting by aging treatment, heat treatment or hydrothermal treatment, and (C) a compound of titanium oxide and an alkali metal element and / or an alkaline earth metal element is contained in the medium solution, and then an iron compound is added. Examples thereof include a method of neutralizing and reacting the neutralized product by oxidation or aging treatment, heat treatment or hydrothermal treatment. The method described in (B) does not require the addition of a basic compound as a neutralizing agent, the process is rational, and is the most preferable method in the present invention. Further, according to the methods described in (B) and (C), iron oxyhydroxide can be supported on the surface of titanium oxide particles, and an alkali metal element and / or an alkaline earth metal element can be contained. In the method (C), the iron compound and the alkali metal element and / or the alkaline earth metal element may be added separately to the medium solution, or may be added in parallel at the same time.

In the above methods (A), (B), and (C), as the medium solution, an inorganic or organic solution such as water, alcohol, or toluene can be used, but water is industrially handled. Easy and preferable. A ferrous compound is used as the iron compound, and a basic compound such as sodium hydroxide, potassium hydroxide, ammonia, amine, or sodium carbonate is added to the solution to neutralize part or all of the ferrous compound , and then , While adjusting the pH, gas such as air or oxygen may be blown to oxidize the titanium oxide particles to support ferric hydroxide, but if a ferrous compound is used, the step of oxidizing is unnecessary. Therefore, it is preferable. When an aqueous medium is used, it is preferable to use a water-soluble iron compound. Examples of the water-soluble ferric compound include ferric nitrate, ferric sulfate, ferric chloride and the like. Examples of the alkali metal compound and the alkaline earth metal compound include these hydroxides, carbonates, sulfates, chlorides and oxides, and in the present invention, the photocatalyst contains sodium as an alkali metal element. It is preferable to use a sodium compound. In the contact between the titanium oxide and the iron compound, the alkali metal element and the alkaline earth metal element contained inside and outside the titanium oxide particles are easily released, and the reaction with the iron compound is promoted. It is preferable to carry out with. The pH of the medium solution is preferably 3 or less, and more preferably 2 or less. Sulfuric acid, hydrochloric acid, nitric acid, hydrofluoric acid and the like can be used for pH adjustment.

When the product containing titanium oxide and iron oxyhydroxide thus obtained is made into a powder, operations such as filtration, washing, and drying may be appropriately performed by a usual method, and it is necessary. Grinding may be performed accordingly. Drying is carried out at a temperature at which iron oxyhydroxide does not denature into ferric oxide, and is preferably carried out at a temperature of, for example, 200 ° C. or lower. When filtering and cleaning, it is preferable to adjust the pH of the medium solution to around neutral, preferably around 7, because titanium oxide aggregates and the cleaning property is improved, but it is preferable in the medium solution. If an unreacted iron compound is present in the water, iron hydroxide precipitates. Therefore, the unreacted iron compound is removed by filtering and washing in advance, and then the unreacted iron compound is redispersed in the medium solution to bring the pH of the medium solution to near neutral. It is preferred to adjust, filter and wash. As the neutralizing agent, basic alkali metal compounds such as hydroxides and carbonates, basic alkaline earth metal compounds, ammonia, amines and the like can be used. Water is also preferable as the medium solution used for redispersion.

When the photocatalyst of the present invention is actually used for a photocatalytic reaction, it is convenient to fix it on a base material or to mold and granulate the photocatalyst and use it as a molded product, if necessary. The base material is made of various materials such as metal, tile, enamel, cement, concrete, glass, plastic, fiber, wood, and paper, and its shape is plate-like, corrugated-plate, or honeycomb. Various shapes such as a shape, a spherical shape, and a curved shape can be used.

In order to fix the photocatalyst on the base material, a method can be used in which the photocatalyst is used as a photocatalyst coating agent, the coating agent is applied or sprayed on the surface of the base material, and then dried or fired. The photocatalyst coating agent contains at least a binder, and as the binder, an inorganic resin or an organic resin can be used, and a binder that is not easily decomposed by a photocatalytic reaction, for example, a polymerizable silicon compound, cement, concrete, plaster, or silicone. Resins, fluororesins and the like are preferable, and among them, polymerizable silicon compounds are preferable because they have high durability, are relatively easy to handle, and have high versatility. Examples of the polymerizable silicon compound include hydrolyzable silane or a hydrolyzed product thereof or a partial condensate thereof, water glass, colloidal silica, organopolysiloxane, and the like, and even if one of these is used, Two or more types may be mixed and used. The hydrolyzable silane contains at least one hydrolyzable group such as an alkoxy group and a halogen group. Among them, the alkoxysilane is preferable in terms of stability and economy, and in particular, tetraalkoxysilane such as tetramethoxysilane and tetraethoxysilane. Silane is preferable because of its high reactivity. As the water glass, sodium-silicate type, potassium-silicate type, lithium-silicate type and the like can be used, and among them, sodium-silicate type is preferable because it has high stability. Sodium-silicate waterglass is Na₂O and SiO₂When the molar ratio is in the range of 2 to 4, the curability is high, and the No. 3 water glass having the molar ratio of 3 is particularly preferable from the viewpoint of the balance between stability and curability. As colloidal silica and organopolysiloxane, those having a silanol group can be used. The coating agent may further contain water or a non-aqueous solvent such as alcohols, hydrocarbons, ethers, ether alcohols, esters, ether esters, and ketones as a dispersion medium, and may contain a binder. A mixed solvent containing one or more of these is appropriately selected and used depending on the compatibility of the above. The solid content concentration in the coating agent is preferably in the range of 0.05 to 50% by weight, more preferably in the range of 0.1 to 40% by weight. The photocatalyst is preferably contained in the solid content in an amount of 20 to 95% by weight, more preferably in the range of 40 to 95% by weight.

In addition to photocatalysts and binders and dispersion media, coating agents include pH adjusters, dispersants, defoamers, emulsifiers, colorants, bulking agents, fungicides, and curing agents, as long as the effects of the present invention are not impaired. Various additives such as auxiliaries and thickeners, fillers and the like may be contained. If these additives or fillers are non-volatile, it is preferable to select inorganic ones that are not easily decomposed by photocatalytic action.

The photocatalyst of the present invention can also be a dispersion previously dispersed in a dispersion medium. It is preferable to prepare a photocatalytic coating agent using a dispersion because a high degree of dispersibility can be easily obtained. Alternatively, the photocatalyst can be fixed to the base material by diluting the dispersion to an appropriate concentration, applying or spraying the dispersion on the surface of the base material, drying and firing, without using a binder. As the dispersion medium of the dispersion, one of the same type as the dispersion medium contained in the coating agent or one having high compatibility is selected. Further, a dispersant may be blended in the dispersion, and the dispersant type is appropriately selected according to the dispersion medium. Examples of the dispersant include (1) surfactants ((a) anionic (carboxylates, sulfates, sulfonates, phosphates, etc.)) and (b) cationics (alkylamine salts, alkyls). Aquarium quaternary ammonium salt, aromatic quaternary ammonium salt, heterocyclic quaternary ammonium salt, etc.), (c) amphoteric (betaine type, amino acid type, alkylamine oxide, nitrogen-containing heterocyclic type, etc.), (d) nonion Systems (ether type, ether ester type, ester type, nitrogen-containing type, etc.), (2) Silicone-based dispersants (alkyl-modified polysiloxane, polyoxyalkylene-modified polysiloxane, etc.), (3) Phosphate-based dispersants (Sodium phosphate, sodium pyrophosphate, sodium orthophosphate, sodium metaphosphate, sodium tripolyphosphate, etc.), (4) Alkanolamines (aminomethylpropanol, aminomethylpropanediol, etc.), etc. Among them, carboxylate type Of the surfactants in the above, particularly high molecular weight ones are preferable because they can disperse titanium oxide to a high degree. Specifically, polyacrylate ([CH)₂CH (COOM)]_n: M is alkali metal, alkaline earth metal, ammonium, etc., and so on), acrylate-acrylamide copolymer ([CH₂CH (COOM)]_n-[CH₂CH (CONH₂)]_m), Acrylic acid-maleate copolymer ([CH₂CH (COOH)]_n-[CH₂CH (COOM) CH (COOM)]_m), Ethylene-maleate copolymer ([CH₂CH₂]_n-[CH (COOM) CH (COOM)]_m), Olefin-maleate copolymer ([CH₂CH (R)]_n-[CH (COOM) CH (COOM)]_m), Styrene-maleate copolymer ([CH₂CH (C₆H₅)]_n-[CH (COOM) CH (COOM)]_m) Etc. can be mentioned. The blending amount of the photocatalyst in the dispersion is preferably in the range of 5 to 90% by weight, more preferably in the range of 10 to 80% by weight. The amount of the dispersant compounded is preferably in the range of 0.01 to 20% by weight, more preferably 0.01 to 10% by weight, based on the photocatalyst.

When the photocatalyst is molded and used, it can be molded into an arbitrary shape after being mixed with a binder such as clay, diatomaceous earth, organic resin, or inorganic resin, if necessary.

Example Next, the present invention will be further described by way of examples, but these are not limited to the present invention.

Example 1 (1) TiO₂As a 200 g / liter concentration of titanium tetrachloride aqueous solution to 700 ml, Na₂An aqueous sodium hydroxide solution having a concentration of 100 g / liter was added as O. Then, after adjusting the pH of the system to 7, it was filtered, washed until the conductivity of the filtrate became 100 μS / cm, and dried to obtain titanium oxide. This titanium oxide has an average major axis diameter of 64 nm, an average minor axis diameter of 13 nm (axial ratio 4.9), and a specific surface area of 160 m.²Spindle-shaped titanium dioxide with rutile-type crystals of / g, with sodium inside the titanium oxide particles.₂It contained 1.7% by weight as O. (2) To 0.5 liter of pure water, 50 g of the above-mentioned spindle-shaped titanium dioxide was added and stirred to prepare a dispersion, and the pH was adjusted to 1 with sulfuric acid. Next, an aqueous ferric nitrate solution equivalent to 0.2% by weight in Fe equivalent to titanium oxide was added and mixed to neutralize ferric nitrate with the sodium component contained in titanium oxide, and then at 90 ° C. Heat treatment was performed for 1 hour. After the heat treatment, it was filtered, and the obtained dehydrated cake of titanium oxide particles was redispersed in 0.5 liter of pure water. The pH of the redispersion solution is neutralized with sodium hydroxide to around 7, then filtered, washed, dried at 110 ° C for one day and night, and then pulverized with a Raikai machine to obtain the photocatalyst of the present invention ( Sample A) was obtained. In this sample A, it was confirmed by analysis by Mössbauer spectroscopy that α-iron oxyhydroxide was supported on the surface of titanium oxide particles. In sample A, α-oxyiron hydroxide is 0.2% by weight in terms of Fe, and sodium is Na.₂It contained 1.7% by weight as O.

Example 2 The unfired spindle-shaped titanium dioxide used in Example 1 was fired at 350 ° C for 5 hours, and the specific surface area was 63 m.²/ g, average major axis diameter is 38 nm, average minor axis diameter is 19 nm (axis ratio 2.0), sodium content is Na₂A calcined spindle-shaped titanium dioxide (sample a) having 0.26% by weight of rutile-type crystals as O was obtained. The photocatalyst (Sample B) of the present invention was obtained in the same manner as in Example 1 except that this calcined spindle-shaped titanium dioxide was used instead of the unfired spindle-shaped titanium dioxide. In this sample B, it was confirmed by analysis by Mössbauer spectroscopy that α-oxyiron hydroxide was supported on the surface of titanium oxide particles. In sample B, α-oxyiron hydroxide was 0.19% by weight in terms of Fe, and sodium was Na.₂It contained 0.26% by weight as O.

Example 3 (1) 1 liter of an 80 g / liter aqueous solution of titanyl sulfate was heated to a temperature of 85 ° C and held for 3 hours to hydrolyze titanyl sulfate. The hydrolysis product thus obtained was filtered, washed and dried to give titanium oxide. This titanium oxide is spherical titanium oxide having anatase-type crystals, and has an average particle diameter of 4.5 nm and a specific surface area of 320 m.²Having / g, alkali metal elements and alkaline earth metal elements were not analyzed. (2) To 0.5 liter of pure water, 50 g of the above-mentioned spherical titanium dioxide was added and stirred to prepare a dispersion, and the pH was adjusted to 1 with sulfuric acid. Next, ferric nitrate aqueous solution equivalent to 0.2% by weight in Fe conversion and sodium hydroxide were added to and mixed with titanium oxide to neutralize ferric nitrate, and then heat-treated at 90 ° C for 1 hour. Was done. After the heat treatment, the cake was filtered and the obtained dehydrated titanium oxide cake was redispersed in 0.5 liters of pure water. The pH of the redispersion solution is neutralized with sodium hydroxide to around 7, then filtered, washed, dried at 110 ° C for one day and night, and then pulverized with a Raikai machine to obtain the photocatalyst of the present invention (the photocatalyst of the present invention). Sample C) was obtained. In this sample C, it was confirmed by analysis by Mössbauer spectroscopy that α-oxyiron hydroxide was supported on the surface of titanium oxide particles. In addition, sample C contained 0.25% by weight of α-oxyiron hydroxide in terms of Fe, but alkali metal elements such as sodium and alkaline earth metal elements were not analyzed.

Example 4 The spindle-shaped titanium dioxide used in Example 1 and α-oxyoxide iron (manufactured by Ishihara Sangyo Co., Ltd .: N-600) were mixed using a Raikai machine to obtain the photocatalyst (Sample D) of the present invention. The presence of α-oxyferroxide in this sample D was confirmed by analysis by Mössbauer spectroscopy. In sample D, α-oxyiron hydroxide was 0.75% by weight in terms of Fe, and sodium was Na.₂It contained 1.19% by weight as O.

Example 5 The suspension of spindle-shaped titanium dioxide used in Example 1 and the suspension of α-oxyferroxide (manufactured by Ishihara Sangyo Co., Ltd .: N-600) are placed in a container equipped with a stirrer and mixed, and then. , Filtered, washed, dried at 110 ° C. for one day and night, and then pulverized with a Raikai machine to obtain the photocatalyst (Sample E) of the present invention. The presence of α-oxyferroxide in this sample E was confirmed by analysis by Mössbauer spectroscopy. In sample E, α-oxyiron hydroxide was 0.75% by weight in terms of Fe, and sodium was Na.₂It contained 1.19% by weight as O.

Comparative example 1 The spindle-shaped titanium oxide used in Example 1 was used as a comparative sample (Sample F).

Comparative example 2 The calcined spindle-shaped titanium oxide used in Example 2 was used as a comparative sample (Sample G).

Comparative example 3 The spherical titanium oxide used in Example 3 was used as a comparative sample (Sample H).

Comparative example 4 A photocatalyst (Sample I) was obtained in the same manner as in Example 2 except that the heat treatment was not performed after the addition of ferric nitrate. It was confirmed by analysis by Mössbauer spectroscopy that ferric hydroxide was supported on Sample I.

Comparative example 5 The sample B obtained in Example 2 was heated in air at a temperature of 350 ° C. for 1 hour to obtain a photocatalyst (Sample J). It was confirmed by analysis by Mössbauer spectroscopy that ferric oxide was supported on sample J.

Comparative example 6 The α-oxyoxide iron (manufactured by Ishihara Sangyo Co., Ltd .: N-600) used in Example 4 was used as a comparative sample (K).

Evaluation 1: Evaluation of acetaldehyde decomposition activity 0.1 g of the samples (A to K) obtained in Examples 1 to 5 and Comparative Examples 1 to 6 were uniformly spread on a petri dish of 6 cmφ. A flexible bag with a capacity of 2 liters was filled with acetaldehyde and synthetic air, and the acetaldehyde concentration was adjusted to 210 ppm. After installing the petri dish in a 500 ml separable flask, it was connected to a flexible bag, and the gas in the system was circulated by a pump at a speed of 3 liters / minute to carry out the reaction. After reaching the adsorption equilibrium under dark conditions (about 30 minutes), the light was irradiated with a white fluorescent lamp of 5700 lux for 500 hours. The gas in the system was collected from the sampling port with a syringe, and the acetaldehyde concentration was measured with a gas chromatograph. The rate of decrease constant (k) of acetaldehyde concentration was calculated by the following equation 1 to evaluate the photocatalytic activity. The larger the decomposition reaction rate constant of acetaldehyde, the better the photocatalytic activity. The results are shown in Table 1. It was found that the photocatalyst obtained in the present invention has high photocatalytic activity under light irradiation of a white fluorescent lamp because it contains titanium oxide and iron oxyhydroxide. Further, since the photocatalyst of the present invention has high photocatalytic activity under ultraviolet irradiation, it was found that the photocatalyst has excellent photocatalytic activity because visible light can be effectively used in addition to ultraviolet light. Equation 1: ln (C / Co) = -kt k: Reaction rate constant (l / h) t: Reaction time (h) C: Acetaldehyde concentration after light irradiation (ppm) Co: Acetaldehyde concentration (ppm) at the start of light irradiation

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The reflection spectra of Samples B, I, and J obtained in Example 2 and Comparative Examples 4 and 5 and the reflection spectrum of titanium oxide (Sample a) used in Example 2 were measured in a wavelength region of 400 to 700 nm. The absorption spectrum of the iron compound contained in Samples B, I, and J was obtained by subtracting the reflection spectrum of titanium oxide (Sample a) from the reflection spectra of Samples B, I, and J at each wavelength. The results are shown in FIGS. 1 to 3. Sample B carrying α-oxyferroxide was found to have a high absorption peak in the range of 400 to 500 nm. From this absorption peak, it was found that iron oxyhydroxide absorbs light having a wavelength of 400 to 500 nm contained in the light of a white fluorescent lamp, and titanium oxide exhibits photocatalytic activity by this absorption. From these facts, when the photocatalyst of the present invention is used in combination with iron oxyhydroxide that absorbs light having a wavelength of 400 to 500 nm contained in the light of a white fluorescent lamp, the photocatalytic activity under light irradiation of the white fluorescent lamp can be increased. It turned out to be expensive.

Using the samples A and B obtained in Examples 1 and 2, a coating agent was prepared using colloidal silica as a binder and pure water as a dispersion medium. Further, pure water was used as a dispersant and a polyacrylate-based polymer was used as a dispersant to obtain a dispersion. These coating agents and aqueous dispersions were added dropwise to a 6 cmφ petri dish, spread uniformly, and then dried at a temperature of 110 ° C. for 12 hours to obtain a photocatalyst. After that, when the test was conducted in the same manner as in Evaluation 1, all of them were subjected to the light irradiation of the white fluorescent lamp by using iron oxyhydroxide, which absorbs the light of the wavelength of 400 to 500 nm contained in the light of the white fluorescent lamp. It has been confirmed that the photocatalytic activity is high and stable, and since the photocatalytic activity under ultraviolet irradiation is also high, visible light can be effectively used in addition to ultraviolet light, so that it has excellent photocatalytic activity. I confirmed that it was there.

Oxygen that absorbs light with a wavelength of 400 to 500 nm contained in the light of a white fluorescent lamp even when the samples A and B obtained in Examples 1 and 2 are molded and granulated using clay to form a photocatalyst molded body. By using iron hydroxide together, it was confirmed that the photocatalytic activity under the light irradiation of a white fluorescent lamp was high and stable, and the photocatalytic activity under the ultraviolet irradiation was also high. It was confirmed that it has excellent photocatalytic activity because it can effectively use visible light.

The photocatalyst of the present invention has excellent photocatalytic activity against light irradiation of a white fluorescent lamp or the like by using iron oxyhydroxide which absorbs light having a wavelength of 400 to 500 nm contained in the light of a white fluorescent lamp or the like in combination. It has and can be used for a wide range of purposes as a purifying material, a deodorizing material, an antifouling material, a sterilizing material, an antifogging material, etc. in an environment irradiated with visible light (light having a wavelength of 400 to 800 nm). Preferred embodiments of the present invention are as follows. 1. A method for producing a photocatalyst, which comprises adding an iron compound to a medium solution containing titanium oxide and reacting the mixture to support iron oxyhydroxide on the surface of the titanium oxide particles. 2. An iron compound is added and reacted in a medium solution containing titanium oxide containing an alkali metal element and / or an alkaline earth metal element to support iron oxyhydroxide on the surface of the titanium oxide particles. A characteristic method for producing a photocatalyst. 3. It is characterized in that an iron compound is added and reacted in a medium solution containing a compound of titanium oxide and an alkali metal and / or an alkaline earth metal to support iron oxyhydroxide on the particle surface of the titanium oxide. A method for producing a photocatalyst. Four. The method for producing a photocatalyst according to any one of 1 to 3, wherein the pH of the medium solution containing titanium oxide is adjusted to be acidic, and then an iron compound is added. 5. The method for producing a photocatalyst according to 4, which comprises adjusting the pH of the medium solution to 3 or less. 6. The method for producing a photocatalyst according to any one of 1 to 3, wherein the medium solution is heated after adding an iron compound. 7. The method for producing a photocatalyst according to 6, wherein the heating temperature is in the range of 50 to 200 ° C. 8. The method for producing a photocatalyst according to any one of 1 to 3, wherein titanium oxide having an anisotropic shape is used. 9. The method for producing a photocatalyst according to any one of 1 to 3, wherein titanium oxide obtained by firing titanium oxide or a titanium oxide precursor is used. Ten. A photocatalyst in which iron oxyhydroxide is supported on the surface of titanium oxide particles. Titanium oxide is a photocatalyst that develops photocatalytic activity when iron oxyhydroxide absorbs light with a wavelength of 400 to 500 nm. The acetaldehyde decomposition reaction rate constant when the photocatalyst is irradiated with light from a white fluorescent lamp containing light having a wavelength of 400 to 500 nm is more than twice the acetaldehyde decomposition reaction rate constant of the titanium oxide measured under the same conditions. A photocatalyst coating agent containing at least a photocatalyst and a binder. 11. A photocatalyst in which iron oxyhydroxide is supported on the surface of titanium oxide particles. Titanium oxide is a photocatalyst that develops photocatalytic activity when iron oxyhydroxide absorbs light with a wavelength of 400 to 500 nm. The acetaldehyde decomposition reaction rate constant when the photocatalyst is irradiated with light from a white fluorescent lamp containing light having a wavelength of 400 to 500 nm is more than twice the acetaldehyde decomposition reaction rate constant of the titanium oxide measured under the same conditions. A photocatalytic dispersion containing at least a photocatalyst and a dispersion medium. 12. A photocatalyst in which iron oxyhydroxide is supported on the surface of titanium oxide particles. Titanium oxide is a photocatalyst that develops photocatalytic activity when iron oxyhydroxide absorbs light with a wavelength of 400 to 500 nm. The acetaldehyde decomposition reaction rate constant when the photocatalyst is irradiated with light from a white fluorescent lamp containing light having a wavelength of 400 to 500 nm is more than twice the acetaldehyde decomposition reaction rate constant of the titanium oxide measured under the same conditions. A photocatalyst molded product containing at least a photocatalyst. 13. A photocatalyst in which iron oxyhydroxide is supported on the surface of titanium oxide particles. Titanium oxide is a photocatalyst that develops photocatalytic activity when iron oxyhydroxide absorbs light with a wavelength of 400 to 500 nm. The acetaldehyde decomposition reaction rate constant when the photocatalyst is irradiated with light from a white fluorescent lamp containing light having a wavelength of 400 to 500 nm is more than twice the acetaldehyde decomposition reaction rate constant of the titanium oxide measured under the same conditions. A photocatalyst in which a photocatalyst is fixed on a substrate.