JP6932045B2 - Photocatalyst and method for manufacturing photocatalyst - Google Patents

Description

The present invention relates to a photocatalyst and a method for producing a photocatalyst.

Photocatalysts that exhibit activity by irradiation with sunlight and room light are being studied. Patent Document 1 describes a semiconductor photocatalytic substance. This semiconductor photocatalytic substance is titanium oxide in which aluminum oxide and copper oxide are supported as cocatalysts.

JP-A-2010-119920

However, the semiconductor photocatalytic substance described in Patent Document 1 is insufficient in terms of photocatalytic activity.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a photocatalyst exhibiting excellent photocatalytic activity. Another object of the present invention is to provide a method for producing a photocatalyst exhibiting excellent photocatalytic activity.

The photocatalyst of the present invention includes a plurality of first particles and a plurality of second particles. The first particles include at least the first tungsten oxide particles. The second particles include at least tungsten dioxide particles. The activity of the second particle is lower than the activity of the first particle.

The method for producing a photocatalyst of the present invention includes a first particle forming step of forming a plurality of first particles, a second particle forming step of forming a plurality of second particles, and a plurality of the first particles and a plurality of the first particles. Includes a mixing step of mixing the two particles. The first particles include at least the first tungsten oxide particles. The second particles include at least tungsten dioxide particles. The activity of the second particle is lower than the activity of the first particle.

According to the photocatalyst of the present invention, the photocatalytic activity can be improved. Further, according to the method for producing a photocatalyst of the present invention, a photocatalyst having improved photocatalytic activity can be produced.

It is sectional drawing which shows the 1st particle and 2nd particle schematically, and these 1st particle and 2nd particle are included in the photocatalyst which concerns on 1st Embodiment of this invention. It is a figure which shows another example of the 1st particle shown in FIG. 1 schematically. It is an enlarged view which shows another example of the co-catalyst particle included in the 1st particle shown in FIG. 1 schematically. It is sectional drawing which shows the 1st particle and 2nd particle schematically, and these 1st particle and 2nd particle are included in the photocatalyst which concerns on 2nd Embodiment of this invention. It is sectional drawing which shows the 1st particle and 2nd particle schematically, and these 1st particle and 2nd particle are included in the photocatalyst which concerns on 3rd Embodiment of this invention. It is sectional drawing which shows the 1st particle and 2nd particle schematically, and these 1st particle and 2nd particle are included in the photocatalyst which concerns on 4th Embodiment of this invention. It is a graph which shows the time-dependent change of the acetaldehyde residual rate and the time-dependent change of the carbon dioxide production rate. It is a graph which shows the time-dependent change of the acetaldehyde residual rate and the time-dependent change of the carbon dioxide production rate. It is a graph which shows the time-dependent change of the acetaldehyde residual rate and the time-dependent change of the carbon dioxide production rate. It is a graph which shows the time-dependent change of the acetaldehyde residual rate and the time-dependent change of the carbon dioxide production rate.

Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments. The present invention can be carried out with appropriate modifications within the scope of the object of the present invention. In addition, although the description may be omitted as appropriate for the parts where the description is duplicated, the gist of the invention is not limited.

<First Embodiment>
Hereinafter, the photocatalyst 10 of the first embodiment of the present invention will be described with reference to FIG. The photocatalyst 10 is a visible light responsive type that absorbs visible light and exhibits photocatalytic activity. FIG. 1 shows a schematic cross-sectional view of the first particle 1 and the second particle 2 contained in the photocatalyst 10. For convenience of illustration, in FIG. 1, the first particle 1 and the second particle 2 are not in contact with each other, but the first particle 1 and the second particle 2 may be in contact with each other.

The photocatalyst 10 includes a plurality of first particles 1 and a plurality of second particles 2. The first particle 1 contains at least the first tungsten oxide particle 3. The second particle 2 contains at least the tungsten dioxide particle 5. The activity of the second particle 2 is lower than that of the first particle 1.

As used herein, the term "activity" refers to photocatalytic activity. More specifically, the activity refers to the decomposition activity of acetaldehyde into carbon dioxide caused by a photocatalyst irradiated with visible light. The lower the activity, the lower the decomposition activity of acetaldehyde into carbon dioxide caused by the photocatalyst irradiated with visible light, and the lower the carbon dioxide production rate of the photocatalyst per unit mass. When comparing the first particle 1 and the second particle 2 of the same mass, the carbon dioxide production rate caused by the second particle 2 irradiated with visible light is the carbon dioxide produced by the first particle 1 irradiated with visible light. It is lower than the carbon production rate. The carbon dioxide production rate of the first particle 1 and the carbon dioxide production rate of the second particle 2 are measured by the method described in the examples.

The photocatalyst 10 exhibits excellent photocatalytic activity. The reason is presumed as follows. The first particle 1 absorbs visible light and generates an electric charge. The generated charge directly or indirectly decomposes acetaldehyde. Charges that did not contribute to the decomposition of acetaldehyde may remain on the surface of the first particle 1 as surplus charges. The excess charge may cause the first particle 1 to be discolored and deteriorated. Here, the second particle 2 also absorbs visible light to generate an electric charge and exhibits acetaldehyde decomposition activity. However, since the activity of the second particle 2 is lower than the activity of the first particle 1, the oxidizing power of the second particle 2 is lower than the oxidizing power of the first particle 1. Therefore, the excess charge on the surface of the first particle 1 is absorbed by the second particle 2. As a result, the deterioration of the first particle 1 caused by the excess charge can be suppressed, and the photocatalytic activity can be improved.

In the first embodiment, the first particle 1 includes the first tungsten oxide particle 3 and one or more co-catalyst particles 4. Hereinafter, the co-catalyst particles 4 contained in the first particles 1 may be referred to as the first co-catalyst particles 4. The first auxiliary catalyst particles 4 are provided on the surface of the first tungsten oxide particles 3. In the first embodiment, the second particle 2 contains the tungsten dioxide particles 5, and does not contain the co-catalyst particles (both the first co-catalyst particles 4 and the co-catalyst particles other than the first co-catalyst particles 4). Since the first particle 1 contains the first auxiliary catalyst particle 4, and the second particle 2 does not contain the auxiliary catalyst particle (both the first auxiliary catalyst particle 4 and the auxiliary catalyst particle other than the first auxiliary catalyst particle 4). , The activity of the second particle 2 is lower than the activity of the first particle 1. Another embodiment in which the activity of the second particle 2 is lower than the activity of the first particle 1 will be described later in the second embodiment, the third embodiment and the fourth embodiment. The reason why it is presumed to exhibit excellent photocatalytic activity in the second embodiment, the third embodiment and the fourth embodiment is the same as the reason described in the first embodiment.

(First particle)
The first tungsten oxide particles 3 contain tungsten oxide. Tungsten oxide is not particularly limited as long as it has photocatalytic activity by irradiation with visible light. Examples of tungsten oxide include WO ₃ (tungsten trioxide), WO ₂ (tungsten dioxide), WO, W ₂ O ₃ , W ₄ O ₅ , W ₄ O ₁₁ , W ₂₅ O ₇₃ , W ₂₀ O ₅₈ , and so on. W ₂₄ O ₆₈ , as well as mixtures thereof. The first tungsten oxide particles 3 may contain only one type of tungsten oxide, or may contain two or more types. _{WO 3} is preferable as the tungsten oxide contained in the first tungsten oxide particles 3 in order to improve the photocatalytic activity.

The crystal structure of tungsten oxide contained in the first tungsten oxide particles 3 is not particularly limited. Examples of the crystal structure of tungsten oxide include monoclinic crystals, triclinic crystals, orthorhombic crystals, and mixed crystals of at least two of these.

FIG. 2 shows another example of the first tungsten oxide particles 3. As shown in FIG. 2, the first tungsten oxide particles 3 may be aggregated particles. The agglomerated particles are agglomerates of the primary particles of the first tungsten oxide particles 3. Further, the first tungsten oxide particles 3 may be primary particles instead of aggregated particles.

As described above, the surface of the first tungsten oxide particles 3 is provided with one or more first co-catalyst particles 4. Thereby, the photocatalytic activity of the first particle 1 with respect to the irradiation of visible light can be improved. The first co-catalyst particles 4 contain a metal having an electron-withdrawing property. Examples of the metal contained in the first auxiliary catalyst particles 4 include transition metals, and more specifically, copper, platinum (Pt), palladium (Pd), iron, silver, gold, nickel, ruthenium (Ru), and the like. Examples include iridium, niobium, zirconium and molybdenum (Mo). These metals, for example, in the form of complexes, chlorides, bromides, iodides, oxides, hydroxides, sulfates, nitrates, carbonates, phosphates, or organic acid salts, form the first cocatalyst particles 4. It may be contained.

The first co-catalyst particles 4 preferably include platinum particles, palladium particles, molybdenum particles, ruthenium particles, or particles of oxides thereof, and more preferably platinum particles. Examples of the molybdenum oxide particles include molybdenum oxide particles, and more specifically, molybdenum trioxide particles. Examples of the ruthenium oxide particles include ruthenium oxide particles, and more specifically, ruthenium (IV) oxide particles and ruthenium (VIII) oxide particles. The surface of the first tungsten oxide particles 3 may be provided with only one type of the first auxiliary catalyst particles 4, or may be provided with two or more types. When two or more types of the first auxiliary catalyst particles 4 are provided, the combination of the two types of the first auxiliary catalyst particles 4 includes a combination of platinum particles and palladium particles, a combination of platinum particles and ruthenium oxide particles, and platinum. Examples thereof include a combination of particles and molybdenum oxide particles.

The first auxiliary catalyst particles 4 may be provided on the surface of the first tungsten oxide particles 3 as aggregated particles. FIG. 3 is an enlarged view schematically showing another example of the first co-catalyst particles 4. The first auxiliary catalyst particles 4 may be provided on the surface of the first tungsten oxide particles 3 in the form of aggregated particles, for example. The agglomerated particles are agglomerates of the primary particles of the first co-catalyst particles 4. Further, the first auxiliary catalyst particles 4 may be provided on the surface of the first tungsten oxide particles 3 in a state in which each of the first auxiliary catalyst particles 4 is independent, not in the state of aggregated particles.

The average particle size of the first auxiliary catalyst particles 4 is preferably smaller than the average particle size of the first tungsten oxide particles 3. Thereby, the first auxiliary catalyst particles 4 can be suitably fixed to the surface of the first tungsten oxide particles 3.

The content of the first auxiliary catalyst particles 4 with respect to the mass of the first tungsten oxide particles 3 (hereinafter, may be referred to as the first auxiliary catalyst loading ratio) is larger than 0.000% by mass and 0.250% by mass or less. It is preferable to have. The first auxiliary catalyst support rate is calculated from the calculation formula "first auxiliary catalyst support rate (unit: mass%) = 100 x mass of first auxiliary catalyst particles 4 / mass of primary tungsten oxide particles 3". When the support rate of the first auxiliary catalyst is 0.250% by mass or less, the content of the auxiliary catalyst can be reduced, and a cost merit can be obtained. Further, since the photocatalyst 10 contains the first particle 1 and the second particle 2, it exhibits excellent photocatalytic activity even when the first auxiliary catalyst loading ratio is 0.250% by mass or less.

The first co-catalyst carrying ratio is more preferably less than 0.030% by mass, further preferably 0.024% by mass or less, further preferably 0.020% by mass or less, and 0.010. It is even more preferably mass% or less, and particularly preferably 0.005 mass% or less. The lower the support rate of the first co-catalyst, the lower the content of the co-catalyst can be while maintaining the photocatalytic activity. As a result, a cost advantage can be obtained. The support rate of the first auxiliary catalyst can be, for example, 0.001% by mass or more. The first co-catalyst carrying ratio was 0.250% by mass, 0.030% by mass, 0.024% by mass, 0.020% by mass, 0.010% by mass, 0.005% by mass, and 0.001. It is also preferable that it is within the range of two values selected from% by mass.

In order to improve the photocatalytic activity, the volume median diameter D ₅₀ of the first particle 1 is preferably 2.000 μm or less, more preferably 1.000 μm or less, and 0.500 μm or less. Is even more preferably 0.340 μm or less, even more preferably 0.337 μm or less, even more preferably 0.270 μm or less, and even more preferably 0.264 μm or less. , 0.250 μm or less, even more preferably 0.245 μm or less, even more preferably 0.180 μm or less, even more preferably 0.178 μm or less, 0. It is particularly preferably .176 μm or less, and most preferably 0.175 μm or less. For the same reason, the volume median diameter D ₅₀ of the first particle 1 is preferably larger than 0.000 μm, more preferably 0.050 μm or more, further preferably 0.100 μm or more, and 0. It is particularly preferably 143 μm or more. For the same reason, the volume median diameter D ₅₀ of the first particle 1 is 2.000 μm, 1.000 μm, 0.500 μm, 0.340 μm, 0.337 μm, 0.310 μm, 0.304 μm, 0.270 μm, 0. .265 μm, 0.264 μm, 0.261 μm, 0.250 μm, 0.248 μm, 0.245 μm, 0.180 μm, 0.179 μm, 0.178 μm, 0.176 μm, 0.175 μm, 0.172 μm, 0.143 μm , 0.100 μm, and 0.050 μm. The volume median diameter D ₅₀ of the first particle 1 is measured, for example, by the method described in Examples. The volume median diameter D ₅₀ of the first particle 1 is adjusted by, for example, changing one or both of the peripheral speed of the disperser in the first particle dispersion forming step described later and the processing time by the disperser. The faster the peripheral speed of the disperser in the first particle dispersion forming step, the smaller _{the volume median diameter D 50 of the first particle 1.} The longer the processing time by the disperser in the first particle dispersion forming step, the smaller _{the volume median diameter D 50 of the first particle 1.}

The photocatalyst 10 may contain only one of the first particles 1. Further, the photocatalyst 10 may contain 2 types, 3 types, or 4 types or more of the first particles 1.

(Second particle)
As described above, when the photocatalyst 10 contains the second particle 2, the photocatalyst activity can be improved. Further, since the photocatalyst 10 includes the second particle 2 having no co-catalyst particles (both the first co-catalyst particles 4 and the co-catalyst particles other than the first co-catalyst particles 4), the photocatalyst 10 is co-catalyst with respect to the total mass of the photocatalyst 10. The content of the particles can be reduced, and a cost advantage can be obtained.

The tungsten dioxide particles 5 of the second particles 2 contain tungsten oxide. Specific examples and suitable examples of tungsten oxide contained in the tungsten dioxide particles 5 are the same as specific examples and suitable examples of tungsten oxide contained in the first tungsten oxide particles 3. The tungsten oxide contained in the tungsten dioxide particles 5 may be the same as or different from the tungsten oxide contained in the first tungsten oxide particles 3. In order to simplify the manufacturing process, it is preferable that the tungsten oxide contained in the tungsten dioxide particles 5 is the same as the tungsten oxide contained in the first tungsten oxide particles 3. In order to simplify the manufacturing process, the first tungsten oxide particles 3 before the first auxiliary catalyst particles 4 may be used as the fifth tungsten dioxide particles 5.

The average particle size of the tungsten dioxide particles 5 may be the same as or different from the average particle size of the first tungsten oxide particles 3. The preferred range of the volume median diameter D ₅₀ of the tungsten dioxide particles 5 is the same as the preferred range of the volume median diameter D _{50 of the second particles 2 described later.}

In order to improve the photocatalytic activity, the volume median diameter D ₅₀ of the second particle 2 is preferably 2.000 μm or less, more preferably 1.000 μm or less, and 0.500 μm or less. Is even more preferably 0.200 μm or less, even more preferably 0.175 μm or less, even more preferably 0.150 μm or less, and even more preferably 0.149 μm or less. , 0.137 μm or less, and even more preferably 0.136 μm or less. For the same reason, the volume median diameter D ₅₀ of the second particle 2 is preferably larger than 0.000 μm, more preferably 0.050 μm or more, further preferably 0.100 μm or more, and 0. It is particularly preferably 135 μm or more. For the same reason, the volume median diameter D ₅₀ of the second particle 2 is 2.000 μm, 1.000 μm, 0.500 μm, 0.200 μm, 0.175 μm, 0.150 μm, 0.149 μm, 0.137 μm, 0. It is also preferably within the range of two values selected from .136 μm, 0.135 μm, 0.100 μm, and 0.050 μm. The volume median diameter D ₅₀ of the second particle 2 is measured, for example, by the method described in Examples. The volume median diameter D ₅₀ of the second particle 2 is adjusted by, for example, changing one or both of the peripheral speed of the disperser in the second particle dispersion forming step described later and the processing time by the disperser. The faster the peripheral speed of the disperser in the second particle dispersion forming step, the smaller _{the volume median diameter D 50 of the second particle 2.} The longer the processing time by the disperser in the second particle dispersion forming step, the smaller _{the volume median diameter D 50 of the second particle 2.}

Second grain 2 having a volume median diameter D ₅₀ may be the same as the volume median diameter D ₅₀ of the first particles 1, may be different. Volume median diameter D ₅₀ of the second particles 2 is preferably substantially the same as the volume median diameter D ₅₀ of the first particle 1. The percentage of the volume median diameter D ₅₀ of the second particle 2 to the volume median diameter D ₅₀ of the first particle 1 is preferably 40.0% or more and 120.0% or less. The percentage of the volume median diameter D ₅₀ of the second particle 2 to the volume median diameter D ₅₀ of the first particle 1 is 40.0%, 44.2%, 49.3%, 52.5%, 60.5. %, 76.5%, 85
.. It is also preferably within the range of two values selected from 2%, 87.2%, 100.0%, 104.9%, 116.7% and 120.0%.

The photocatalyst 10 may contain only one of the second particles 2. Further, the photocatalyst 10 may contain 2 types, 3 types, or 4 types or more of the second particles 2.

(Mixing ratio of first particle and second particle)
The content of the second particle 2 with respect to the sum of the mass of the first particle 1 and the mass of the second particle 2 is preferably larger than 0.0% by mass and 50.0% by mass or less. The content of the second particle 2 with respect to the sum of the mass of the first particle 1 and the mass of the second particle 2 is calculated by the formula "Content rate of the second particle 2 (unit: mass%) = (100 x second particle 2). (Mass) / (mass of first particle 1 + mass of second particle 2) ”. When the content of the second particle 2 with respect to the sum of the mass of the first particle 1 and the mass of the second particle 2 is 50.0% by mass or less, the content of the co-catalyst is reduced and the photocatalytic activity is further improved. Can be made to.

In order to improve the photocatalytic activity, the content of the second particle 2 with respect to the sum of the mass of the first particle 1 and the mass of the second particle 2 is preferably 10.0% by mass or less, preferably 9.1. It is more preferably 0% by mass or less, further preferably 9.0% by mass or less, further preferably 8.0% by mass or less, and even more preferably 7.0% by mass or less. It is particularly preferable that it is 6.0% by mass or less. For the same reason, the content of the second particle 2 with respect to the sum of the mass of the first particle 1 and the mass of the second particle 2 is preferably 0.1% by mass or more, preferably 0.5% by mass or more. More preferably, it is more preferably 1.0% by mass or more, further preferably 2.0% by mass or more, further preferably 3.0% by mass or more, and 4.5% by mass. The above is particularly preferable. For the same reason, the content of the second particle 2 with respect to the sum of the mass of the first particle 1 and the mass of the second particle 2 is 50.0% by mass, 10.0% by mass, 9.1% by mass, 9. 0% by mass, 8.0% by mass, 7.0% by mass, 6.0% by mass, 5.0% by mass, 4.8% by mass, 4.5% by mass, 3.0% by mass, 2.0% by mass It is also preferable that it is within the range of two values selected from%, 1.0% by mass, 0.5% by mass, 0.1% by mass, and more than 0.0% by mass.

In order to improve the photocatalyst activity, in the photocatalyst 10, the first _{auxiliary catalyst particles 4 are platinum particles, the volume median diameter D 50} of the first particles 1 is 0.245 μm or less, and the mass of the first particles 1 is increased. The content of the second particle 2 with respect to the sum of the mass of the second particle 2 and the mass of the second particle 2 is preferably 2.0% by mass or more and 9.0% by mass or less.

In order to improve the photocatalyst activity, in the photocatalyst 10, the first _{auxiliary catalyst particles 4 are platinum particles, and the mass median diameter D 50} of the first particles 1 is 0.310 μm or more and 0.500 μm or less. It is also preferable that the content of the second particle 2 with respect to the sum of the mass of the particle 1 and the mass of the second particle 2 is 2.0% by mass or more and 9.0% by mass or less.

The photocatalyst 10 may further contain an additive, if necessary. Additives include, for example, silicon compounds, aluminum compounds, aluminosilicates, alkaline earth metals, calcium phosphate, molecular sieves, and activated carbon. The photocatalyst 10 of the first embodiment has been described above.

(Manufacturing method of photocatalyst)
Next, the method for producing the photocatalyst 10 of the first embodiment will be described. The method for producing the photocatalyst 10 includes, for example, a first particle forming step, a second particle forming step, and a mixing step. Hereinafter, the first particle forming step, the second particle forming step, and the mixing step will be described.

(First particle formation step)
In the first particle forming step, a plurality of first particles 1 are formed. The first particle forming step preferably includes, for example, a first tungsten oxide particle dispersion forming step, a supporting step, and a first particle dispersion forming step.

[Step of forming first tungsten oxide particle dispersion]
In the step of forming the first tungsten oxide particle dispersion, a dispersion containing the first tungsten oxide particles 3 is formed. Specifically, by dispersing the first tungsten oxide particles 3 in a dispersion medium, a dispersion containing the first tungsten oxide particles 3 is formed. Examples of the dispersion medium include water and ethanol. Examples of the dispersion of the first tungsten oxide particles 3 include a dispersion liquid and a slurry. Examples of the disperser for dispersing the first tungsten oxide particles 3 in the dispersion medium include a homogenizer, an ultrasonic disperser, a bead mill and a jet mill.

In order to suitably promote the support of the first auxiliary catalyst particles 4 with respect to the first tungsten oxide particles 3, the content of the first tungsten oxide particles 3 with respect to the mass of the first tungsten oxide particle dispersion is 25.0% by mass. It is preferably 24.0% by mass or less, more preferably 23.5% by mass or less, still more preferably 23.0% by mass or less. For the same reason, the content of the tungsten oxide particles 3 with respect to the mass of the tungsten oxide particle dispersion is preferably larger than 0.0% by mass, more preferably 5.0% by mass or more, and 10% by mass. It is even more preferably 9.0% by mass or more, and particularly preferably 16.0% by mass or more. For the same reason, the contents of the tungsten oxide particles 3 with respect to the mass of the tungsten oxide particle dispersion are 25.0% by mass, 24.0% by mass, 23.5% by mass, 23.0% by mass, and 16. It is also preferable that it is within the range of two values selected from 0.0% by mass, 10.0% by mass, and 5.0% by mass.

In the step of forming the first tungsten oxide particle dispersion, the first tungsten oxide particles 3 may be pulverized in addition to the dispersion of the first tungsten oxide particles 3 in the dispersion medium. By pulverizing the first tungsten oxide particles 3, the first tungsten oxide particles 3 are made into fine particles. As a result, the first co-catalyst particles 4 are suitably supported on the first tungsten oxide particles 3.

In order to favorably proceed with the support of the first auxiliary catalyst particles 4 on the first tungsten oxide particles 3, the D ₉₀ of the first tungsten oxide particles 3 after pulverization must be 0.200 μm or more and 0.500 μm or less. It is preferably 0.200 μm or more and 0.230 μm or less, more preferably. For the same reason, the volume median diameter D ₅₀ of the first tungsten oxide particles 3 after pulverization is preferably 0.100 μm or more and 0.300 μm or less, and more preferably 0.100 μm or more and 0.150 μm or less. .. D ₉₀ and medium volume diameter D ₅₀ are 90% particle size and 50% particle size from the fine particle side of the cumulative particle size distribution based on the volume of the particles, respectively. D ₉₀ and median volume diameter D ₅₀ are measured by the methods described in the Examples.

If necessary, the tungsten oxide particles 3 may be preheated before forming the dispersion containing the tungsten oxide particles 3. By preheating, the crystal structure of the first tungsten oxide particles 3 can be prepared. The temperature of the preheating is preferably 1500 ° C. or lower, more preferably 500 ° C. or higher and 1500 ° C. or lower, and further preferably 800 ° C. or higher and 1000 ° C. or lower. The preheating time is preferably 1 hour or more and 24 hours or less, and more preferably 1 hour or more and 5 hours or less.

[Supporting process]
In the supporting step, one or a plurality of first auxiliary catalyst particles 4 are supported on the surface of the first tungsten oxide particles 3. As a result, the first particle 1 is obtained. Examples of the supporting method include a method of heat treatment, a method of light-precipitating with ultraviolet rays, and a method of light-precipitating with visible light.

An example of the supporting method when the supporting method is heat treatment will be described. The first auxiliary catalyst particles 4 are added to the first tungsten oxide particle dispersion obtained in the step of forming the first tungsten oxide particle dispersion. As a result, a dispersion containing the first tungsten oxide particles 3 and the first co-catalyst particles 4 is obtained.
The obtained dispersion is heat-treated to support one or more first co-catalyst particles 4 on the surface of the first tungsten oxide particles 3. The temperature of the heat treatment is preferably 30 ° C. or higher and 900 ° C. or lower, and more preferably 80 ° C. or higher and 600 ° C. or lower. The heat treatment time is preferably 1 hour or more and 96 hours or less. The heat treatment may be performed only once or twice or more. When the heat treatment is performed twice or more, the conditions of each heat treatment may be changed. When the heat treatment is performed two or more times, the temperature of the second and subsequent heat treatments is preferably higher than the temperature of the first heat treatment. The temperature of the second heat treatment is preferably 200 ° C. or higher.

Instead of the first auxiliary catalyst particles 4, the precursor of the first auxiliary catalyst particles 4 may be added in the supporting step. When the precursor of the first auxiliary catalyst particles 4 is heated, it changes into the first auxiliary catalyst particles 4, and the first auxiliary catalyst particles 4 are supported on the surface of the first tungsten oxide particles 3. When the first auxiliary catalyst particles 4 are platinum particles, the precursors of the first auxiliary catalyst particles 4 include, for example, platinum oxide (II), platinum oxide (IV), platinum chloride (II), and platinum chloride (IV). , Platinum chloride acid, hexachloroplatinic acid, or tetrachloroplatinic acid, or complexes thereof can be added.

[First particle dispersion forming step]
In the first particle dispersion forming step, the first particle dispersion containing the first particle 1 is formed. Specifically, the first particles 1 obtained in the supporting step are dispersed in a dispersion medium to form a dispersion containing the first particles 1. As a result, the mixing of the first particle 1 and the second particle 2 can be suitably promoted, and the photocatalytic activity can be improved.

Examples of the dispersion medium include water and ethanol. Examples of the dispersion of the first particle 1 include a dispersion liquid and a slurry. Examples of the disperser for dispersing the first particle 1 in the dispersion medium include a homogenizer, a mixer, an ultrasonic disperser, a bead mill and a jet mill. The peripheral speed of the disperser is preferably 8 m / sec or more and 50 m / sec or less. The time for dispersing the first particles 1 in the dispersion medium (dispersion treatment of the first particles 1) is preferably 30 minutes or more and 420 minutes or less.

The dispersion treatment of the first particle 1 may be performed only once, twice, or three or more times. When the dispersion treatment of the first particle 1 is performed twice or more, the conditions of each dispersion treatment may be the same or different. The conditions of the distributed processing include, for example, the type of the disperser, the peripheral speed of the disperser, and the time of the distributed processing.

In order to improve the photocatalytic activity, in the first particle dispersion forming step, the first particles 1 are dispersed in a dispersion medium until _{the volume median diameter D 50 of the first particles 1 is within a suitable range.} It is preferable to form a particle dispersion. The preferred range of the volume median diameter D ₅₀ of the first particle 1 is as described above. In the first particle dispersion forming step, _{it is preferable to disperse the first particle 1 in the dispersion medium until the volume median diameter D 50} of the first particle 1 becomes 1.000 μm or less, and the volume median of the first particle 1 It is more preferable to disperse the first particle 1 in the dispersion medium until the diameter D ₅₀ becomes 0.337 μm or less, and the first particle 1 is kept until the volume median diameter D ₅₀ of the first particle 1 becomes 0.178 μm or less. It is more preferable to disperse in a dispersion medium. When the dispersion treatment of the first particle 1 is performed twice or more, the volume of the first particle 1 _{after the second and subsequent dispersion treatments is larger than the volume medium diameter D 50} of the first particles 1 after the first dispersion treatment. It is preferable that the medium diameter D _{50 is small.}

In order to improve the photocatalytic activity, in the first particle dispersion forming step _{, the first particle 1 is dispersed in a dispersion medium until the D 90} of the first particle 1 becomes 0.200 μm or more and 2.000 μm or less. It is preferable to form a first particle dispersion. _{The D 90} of the first particle 1 after the first particle dispersion forming step is more preferably 1.000 μm or less, and further preferably 0.230 μm or less.

In order to suitably proceed with the mixing of the first particle 1 and the second particle 2 and particularly improve the photocatalytic activity, the content of the first particle 1 with respect to the mass of the first particle dispersion is 26.0% by mass. It is preferably less than or equal to, more preferably 25.0% by mass or less, further preferably 24.0% by mass or less, further preferably 21.0% by mass or less, and 20.0% by mass. It is particularly preferable that it is% or less. For the same reason, the content of the first particle 1 with respect to the mass of the first particle dispersion is preferably larger than 0.0% by mass, and more preferably 10.0% by mass or more. For the same reason, the content of the first particle 1 with respect to the mass of the first particle dispersion is 26.0% by mass, 25.0% by mass, 24.0% by mass, 23.0% by mass, and 22.0% by mass. , 21.0% by mass, 20.0% by mass, 19.0% by mass, 15.0% by mass, 10.0% by mass, 5.0% by mass, and 1.0% by mass. It is also preferable that it is within the range of.

The first particles 1 obtained in the supporting step may be added in the mixing step without performing the first particle dispersion forming step.

(Second particle formation step)
In the second particle forming step, a plurality of second particles 2 are formed. The second particle forming step includes, for example, a second particle dispersion forming step.

[Second particle dispersion forming step]
In the second particle dispersion forming step, a second particle dispersion containing the second particle 2 is formed. Specifically, by dispersing the second particles 2 in a dispersion medium, a dispersion containing the second particles 2 is formed. Examples of the dispersion medium include water and ethanol. Examples of the dispersion of the second particle 2 include a dispersion liquid and a slurry. Examples of the disperser for dispersing the second particle 2 in the dispersion medium include a homogenizer, an ultrasonic disperser, a bead mill, and a jet mill. In the step of forming the second particle dispersion, in addition to the dispersion of the second particle 2 in the dispersion medium, the second particle 2 may be pulverized. By crushing the second particle 2, the particle size of the second particle 2 can be adjusted.

In order to preferably advance the mixing of the first particle 1 and the second particle 2 to improve the photocatalytic activity, the content of the second particle 2 with respect to the mass of the second particle dispersion is 25.0% by mass or less. It is more preferably 24.0% by mass or less, further preferably 23.5% by mass or less, further preferably 20.0% by mass or less, and 15.0% by mass. The following is particularly preferable. For the same reason, the content of the second particle 2 with respect to the mass of the second particle dispersion is preferably larger than 0.0% by mass, more preferably 5.0% by mass or more, and 8.0% by mass. The above is more preferable, and 10.0% by mass or more is further preferable. For the same reason, the content of the second particle 2 with respect to the mass of the second particle dispersion is 25.0% by mass, 24.0% by mass, 23.5% by mass, 20.0% by mass, and 15.0% by mass. It is also preferable that the value is within the range of two values selected from 1, 10.0% by mass, 8.0% by mass, 5.0% by mass, and 1.0% by mass.

If necessary, the tungsten dioxide particles 5 may be preheated before forming the dispersion containing the tungsten dioxide particles 5. By preheating, the crystal structure of the tungsten dioxide particles 5 can be prepared. The temperature of the preheating is preferably 1500 ° C. or lower, more preferably 500 ° C. or higher and 1500 ° C. or lower, and further preferably 800 ° C. or higher and 1000 ° C. or lower. The preheating time is preferably 1 hour or more and 24 hours or less, and more preferably 1 hour or more and 5 hours or less.

The second particle dispersion obtained in the second particle dispersion forming step may be used as it is in the mixing step. Further, the second particle dispersion obtained in the second particle dispersion forming step may be dried and the second particles 2 which are powders may be used in the mixing step.

Even if the dispersion containing the first tungsten oxide particles 3 before the first auxiliary catalyst particles 4 is provided, which is obtained in the step of forming the first tungsten oxide particle dispersion, is used as the second particle dispersion. good. As a result, it is possible to omit performing the second particle dispersion forming step separately from the forming of the first tungsten oxide particle dispersion, and it is possible to simplify the manufacturing method.

(Mixing process)
In the mixing step, the plurality of first particles 1 and the plurality of second particles 2 are mixed. As a result, the photocatalyst 10 is obtained. A photocatalyst 10 having stable and excellent photocatalytic activity can be obtained by a simple method of mixing a plurality of first particles 1 and a plurality of second particles 2. In addition, a photocatalyst 10 having stable and excellent photocatalytic activity can be obtained even when no special treatment other than mixing is performed. Examples of the mixing method include mixing by stirring, mixing by shaking, and mixing by vibration. Further, as a method of mixing, a method using a homogenizer, an ultrasonic disperser, a bead mill, a jet mill or a ball mill can be mentioned.

When the first particle dispersion forming step and the second particle dispersion forming step are performed, the first particle dispersion containing the first particle 1 and the second particle dispersion containing the second particle 2 are mixed. By mixing, the plurality of first particles 1 and the plurality of second particles 2 can be mixed. As a result, the mixing of the first particle 1 and the second particle 2 can be suitably promoted to improve the photocatalytic activity. After mixing the first particle dispersion and the second particle dispersion, the dispersion medium may be removed to obtain the photocatalyst 10 which is a powder. Further, after mixing the first particle dispersion and the second particle dispersion, the photocatalyst 10 which is a dispersion may be obtained without removing the dispersion medium. The photocatalyst 10 which is a dispersion is, for example, a slurry or a dispersed liquid.

When the first particle dispersion forming step and the second particle dispersion forming step are omitted, the first particle 1 obtained in the supporting step of the first particle forming step and the first particle 1 obtained in the second particle forming step were obtained. By mixing the second particle 2, the plurality of first particles 1 and the plurality of second particles 2 can be mixed. By omitting the first particle dispersion forming step and the second particle dispersion forming step, the production method can be simplified. When the first particle dispersion forming step and the second particle dispersion forming step are omitted, a dispersion containing the first particle 1 and the second particle 2 may be formed in the mixing step. The method of forming the dispersion in the mixing step is the same as the method of forming the first particle dispersion in the first particle dispersion forming step.

Depending on the characteristics of the photocatalyst 10 to be manufactured, unnecessary steps or operations may be omitted. Further, if necessary, a known step or operation may be added to the method for producing the photocatalyst 10. The method for producing the photocatalyst 10 of the first embodiment has been described above.

<Second embodiment>
Next, the photocatalyst 20 according to the second embodiment of the present invention will be described with reference to FIG. For convenience of explanation, in the second embodiment and the third and fourth embodiments described later, the same configurations as those described in the first embodiment are designated by the same reference numerals, and the description thereof will be omitted. ..

The photocatalyst 20 includes a plurality of first particles 1 and a plurality of second particles 22. The first particle 1 includes the first tungsten oxide particle 3 and one or more first co-catalyst particles 4. The first auxiliary catalyst particles 4 are provided on the surface of the first tungsten oxide particles 3. The second particle 22 includes the tungsten dioxide particle 5 and one or more second auxiliary catalyst particles 26. The second auxiliary catalyst particles 26 are provided on the surface of the tungsten dioxide particles 5. The content of the second auxiliary catalyst particles 26 with respect to the mass of the tungsten dioxide particles 5 (hereinafter, may be referred to as the second auxiliary catalyst loading ratio) is the first auxiliary catalyst particles 4 with respect to the mass of the primary tungsten oxide particles 3. It is lower than the content rate (first co-catalyst support rate). Since the support rate of the second auxiliary catalyst is lower than the support rate of the first auxiliary catalyst, the activity of the second particle 22 is lower than the activity of the first particle 1.

In addition to the second co-catalyst carrying rate being lower than the first co-catalyst carrying rate, the second co-catalyst carrying rate is preferably 0.250% by mass or less, and preferably less than 0.030% by mass. More preferably, it is 0.024% by mass or less, further preferably 0.020% by mass or less, further preferably 0.010% by mass or less, and 0.005% by mass or less. It is particularly preferable to have. The lower the support rate of the second co-catalyst, the lower the content of the co-catalyst can be while maintaining the photocatalytic activity. Further, the lower the support rate of the second auxiliary catalyst than the support rate of the first auxiliary catalyst, the lower the activity of the second particle 22 can be lower than the activity of the first particle 1. For the same reason, the support rate of the second auxiliary catalyst can be, for example, such that the support rate of the second auxiliary catalyst is lower than the support rate of the first auxiliary catalyst and 0.001% by mass or more. For the same reason, in addition to the second co-catalyst support rate being lower than the first co-catalyst support rate, the second co-catalyst support rate is 0.250% by mass, 0.030% by mass, 0.024% by mass. , 0.020% by weight, 0.010% by weight, and 0.005% by weight. For the same reason, it is preferable that the supporting ratio of the first auxiliary catalyst is 0.024% by mass or more and 0.250% by mass or less, and the supporting ratio of the second auxiliary catalyst is 0.005% by mass or more and less than 0.024% by mass. ..

The type of the second auxiliary catalyst particles 26 may be the same as or different from the type of the first auxiliary catalyst particles 4.

The specific example of the second auxiliary catalyst particle 26 is the same as the specific example of the first auxiliary catalyst particle 4 of the first embodiment. The specific example of the volume median diameter D ₅₀ of the second particle 22 is the same as the specific example _{of the volume median diameter D 50} of the second particle 2 of the first embodiment. Specific examples of the content of the second particle 22 with respect to the sum of the mass of the first particle 1 and the mass of the second particle 22 are the mass of the first particle 1 and the mass of the second particle 2 described in the first embodiment. It is the same as the specific example of the content rate of the second particle 2 with respect to the sum of.

The method for producing the photocatalyst 20 is the same as the method for producing the photocatalyst 10 of the first embodiment, except that the second particle forming step is changed. In the second particle forming step, a plurality of second particles 22 are formed. The second particle forming step preferably includes, for example, a step of forming a tungsten dioxide particle dispersion, a step of carrying the second particle dispersion, and a step of forming the second particle dispersion. The step of forming the first tungsten dioxide particle dispersion was carried out in the same manner as the step of forming the first tungsten oxide particle dispersion of the first embodiment, except that the first tungsten oxide particle 3 was changed to the fifth tungsten dioxide particle 5. It is said. The supporting step is the same as the supporting step of the first embodiment, except that the first tungsten oxide particles 3 are changed to the second tungsten dioxide particles 5 and the first auxiliary catalyst particles 4 are changed to the second auxiliary catalyst particles 26. It is done in the same way. The second particle dispersion forming step is performed in the same manner as the second particle dispersion forming step of the first embodiment except that the first particle 1 is changed to the second particle 22. The dispersion containing the first tungsten oxide particles 3 before the first auxiliary catalyst particles 4 was provided, which was obtained in the step of forming the first tungsten oxide particle dispersion, was used as the first tungsten dioxide particle dispersion. May be good. As a result, it is possible to omit the step of forming the tungsten dioxide particle dispersion separately from the step of forming the first tungsten oxide particle dispersion, and the production method can be simplified.

<Third Embodiment>
Next, the photocatalyst 30 according to the third embodiment of the present invention will be described with reference to FIG. The photocatalyst 30 includes a plurality of first particles 1 and a plurality of second particles 32. The first particle 1 includes the first tungsten oxide particle 3 and one or more first co-catalyst particles 4. The first auxiliary catalyst particles 4 are provided on the surface of the first tungsten oxide particles 3. The second particle 32 includes the tungsten dioxide particle 5 and one or more second auxiliary catalyst particles 36. The second auxiliary catalyst particles 36 are provided on the surface of the tungsten dioxide particles 5. The type of the second auxiliary catalyst particle 36 is different from the type of the first auxiliary catalyst particle 4. Since the type of the second auxiliary catalyst particle 36 is different from the type of the first auxiliary catalyst particle 4, the activity of the second particle 32 is lower than that of the first particle 1.

The type of the first auxiliary catalyst particle 4 and the type of the second auxiliary catalyst particle 36 can be selected so that the activity of the second particle 32 is lower than the activity of the first particle 1. In order for the activity of the second particle 32 to be lower than that of the first particle 1, the first auxiliary catalyst particle 4 contains platinum particles or platinum oxide particles, and the second auxiliary catalyst particle 36 is palladium. It preferably contains particles, molybdenum particles, or ruthenium particles, or particles of these oxides. Further, the combination of the type of the first auxiliary catalyst particle 4 and the loading ratio of the first auxiliary catalyst, the type of the second auxiliary catalyst particle 36, and the like so that the activity of the second particle 32 is lower than the activity of the first particle 1 It is also possible to select a combination of the second co-catalyst support rate.

The first co-catalyst support rate may be the same as or different from the second co-catalyst support rate. For example, the support rate of the second co-catalyst may be lower than the support rate of the first co-catalyst.

The specific example of the second auxiliary catalyst particle 36 is the same as the specific example of the first auxiliary catalyst particle 4 of the first embodiment. The specific example of the volume median diameter D ₅₀ of the second particle 32 is the same as the specific example _{of the volume median diameter D 50} of the second particle 2 of the first embodiment. Specific examples of the content of the second particle 32 with respect to the sum of the mass of the first particle 1 and the mass of the second particle 32 are the mass of the first particle 1 and the mass of the second particle 2 described in the first embodiment. It is the same as the specific example of the content rate of the second particle 2 with respect to the sum of.

The method for producing the photocatalyst 30 is the same as the method for producing the photocatalyst 10 of the first embodiment, except that the second particle forming step is changed. In the second particle forming step, a plurality of second particles 32 are formed. The second particle forming step preferably includes, for example, a step of forming a tungsten dioxide particle dispersion, a step of carrying the second particle dispersion, and a step of forming the second particle dispersion. The step of forming the first tungsten dioxide particle dispersion was carried out in the same manner as the step of forming the first tungsten oxide particle dispersion of the first embodiment, except that the first tungsten oxide particle 3 was changed to the fifth tungsten dioxide particle 5. It is said. The supporting step is the same as the supporting step of the first embodiment, except that the first tungsten oxide particles 3 are changed to the second tungsten dioxide particles 5 and the first auxiliary catalyst particles 4 are changed to the second auxiliary catalyst particles 36. It is done in the same way. The second particle dispersion forming step is performed in the same manner as the second particle dispersion forming step of the first embodiment except that the first particle 1 is changed to the second particle 32. The dispersion containing the first tungsten oxide particles 3 before the first auxiliary catalyst particles 4 was provided, which was obtained in the step of forming the first tungsten oxide particle dispersion, was used as the first tungsten dioxide particle dispersion. May be good. As a result, it is possible to omit the step of forming the tungsten dioxide particle dispersion separately from the step of forming the first tungsten oxide particle dispersion, and the production method can be simplified.

<Fourth Embodiment>
Next, the photocatalyst 40 according to the fourth embodiment of the present invention will be described with reference to FIG. The photocatalyst 40 includes a plurality of first particles 41 and a plurality of second particles 2. The first particles 41 include the first tungsten oxide particles 3. The second particle 2 contains the tungsten dioxide particle 5. The first particle 41 is heat-treated, and the second particle 2 is not heat-treated. Alternatively, the first particle 41 is heat-treated, and the second particle 2 is heat-treated under milder conditions than the first particle 41.

The method for producing the photocatalyst 40 includes, for example, a first particle forming step, a second particle forming step, and a mixing step.

(First particle formation step)
In the first particle forming step, a plurality of first particles 41 are formed. The first particle forming step includes, for example, a first tungsten oxide particle dispersion forming step, a first heat treatment step, and a first particle dispersion forming step.

[Step of forming first tungsten oxide particle dispersion]
In the step of forming the first tungsten oxide particle dispersion, a dispersion containing the first tungsten oxide particles 3 is formed. The step of forming the first tungsten oxide particle dispersion of the fourth embodiment can be carried out in the same manner as the step of forming the first tungsten oxide particle dispersion of the first embodiment.

[First heat treatment process]
In the first heat treatment step of the fourth embodiment, the first tungsten oxide particles 3 are heated. As a result, the first particle 41 is obtained. As described above, the first particle 41 may be heat-treated, and the second particle 2 may be heat-treated under milder conditions than the first particle 41. An example of a condition more lenient than the first particle 41 is that the temperature of the heat treatment for obtaining the second particle 2 is lower than the temperature of the heat treatment for obtaining the first particle 41. Another example of conditions that are milder than the first particle 41 is that the heat treatment time for obtaining the second particle 2 is shorter than the heat treatment time for obtaining the first particle 41. Yet another example of conditions more lenient than the first particle 41 is that the number of heat treatments to obtain the second particle 2 is less than the number of heat treatments to obtain the first particle 41. Yet another example of conditions more lenient than the first particles 41 is that the heat input rate to the tungsten dioxide particles 5 for obtaining the second particles 2 is the tungsten oxide particles 3 for obtaining the first particles 41. It is slower than the heat input rate to. In yet another example of the condition more lenient than that of the first particle 41, the difference between the amount of heat input to the surface layer portion and the amount of heat input to the deep layer portion of the tungsten dioxide particle 5 for obtaining the second particle 2 is first. This is different from the difference between the amount of heat input to the surface layer portion and the amount of heat input to the deep layer portion of the first tungsten oxide particles 3 for obtaining the particles 41. By adjusting the dispersion conditions of the first tungsten oxide particles 3 and the dispersion conditions of the second tungsten dioxide particles 5, the particle size of the first tungsten dioxide particles 5 (and thus the particle size of the second particles 2) is changed to that of the first tungsten oxide particles 3. By changing the particle size (and thus the particle size of the first particle 41), the heat input rate and the difference between the heat input amount to the surface layer portion and the heat input amount to the deep layer portion can be adjusted. The particle size of the first tungsten oxide particles 3 used in the first heat treatment step and the particle size of the second tungsten dioxide particles 5 used in the second heat treatment step described later are, for example, 0.100 μm or more and 10 mm or less, respectively. The first tungsten oxide particles 3 used in the first heat treatment step and the fifth tungsten dioxide particles used in the second heat treatment step described later are, for example, spherical.

The temperature of the heat treatment is preferably 30 ° C. or higher and 1500 ° C. or lower, and more preferably 80 ° C. or higher and 600 ° C. or lower. The heat treatment time is preferably 1 hour or more and 95 hours or less. The heat treatment may be performed only once or twice or more. When the heat treatment is performed twice or more, the conditions of each heat treatment may be changed. When the heat treatment is performed two or more times, the temperature of the second and subsequent heat treatments is preferably higher than the temperature of the first heat treatment. The temperature of the second heat treatment is preferably 200 ° C. or higher.

[First particle dispersion forming step]
The first particle dispersion forming step of the fourth embodiment can be performed by the same method as the first particle dispersion forming step of the first embodiment except that the first particle 1 is changed to the first particle 41. ..

(Second particle formation step)
In the second particle forming step, a plurality of second particles 2 are formed. The second particle forming step includes, for example, a step of forming a tungsten dioxide particle dispersion, a second heat treatment step, and a second particle dispersion forming step. When the first particle 41 is heat-treated and the second particle 2 is not heat-treated, the second heat treatment step is omitted.

[Step of forming a tungsten dioxide particle dispersion]
The step of forming the tungsten dioxide particle dispersion of the fourth embodiment can be carried out in the same manner as the step of forming the tungsten dioxide particle dispersion of the first embodiment.

[Second heat treatment process]
In the second heat treatment step of the fourth embodiment, the first tungsten oxide particles 3 were changed to the fifth tungsten dioxide particles 5, the first particles 41 were changed to the second particles 2, and the first particles 41 were heated. It can be carried out by the same method as the first heat treatment step of the fourth embodiment except that the conditions are changed to be gentler than the treatment.

[Second particle dispersion forming step]
The second particle dispersion forming step of the fourth embodiment can be performed in the same manner as the second particle dispersion forming step of the first embodiment.

The specific example of the first particle 41 is the same as the specific example of the first tungsten oxide particle 3 of the first embodiment. The specific example of the volume median diameter D ₅₀ of the first particle 41 is the same as the specific example _{of the volume median diameter D 50} of the first particle 1 of the first embodiment. Specific examples of the content of the second particle 2 with respect to the sum of the mass of the first particle 41 and the mass of the second particle 2 are the mass of the first particle 1 and the mass of the second particle 2 described in the first embodiment. It is the same as the specific example of the content rate of the second particle 2 with respect to the sum of.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the present invention is not limited to the scope of the examples. The median volume diameters D ₅₀ and D ₉₀ were measured using a laser diffraction / scattering particle size distribution measuring device (“Microtrack (registered trademark) MT3300EXII” manufactured by Microtrack Bell Co., Ltd.).

The photocatalysts (A-1) to (A-14) shown below are specific examples of the first embodiment. Evaluation of material composition and photocatalytic activity of photocatalysts (A-1) to (A-14), and reference examples of photocatalysts (B-1a) to (B-11a) and (B-1b) to (B-11b). The results are shown in Tables 1-12. Hereinafter, each photocatalyst will be described with reference to each table.

<Photocatalyst (A-1)>
The photocatalyst (A-1) was produced by the following method.

(First particle formation step)
As the first particle forming step, the first tungsten oxide particle dispersion forming step, the supporting step, and the first particle dispersion forming step described in the first embodiment were performed.

[Step of forming first tungsten oxide particle dispersion]
The first tungsten oxide particles (tungsten trioxide sold by Takagi Co., Ltd.) were preheated at 900 ° C. in an air atmosphere. Preheated tungsten oxide particles and ion-exchanged water were charged into a bead mill so that the content of the tungsten oxide particles with respect to the mass of the tungsten oxide particle dispersion was 23.0% by mass. The tungsten oxide particles were dispersed in ion-exchanged water using a bead mill to obtain a tungsten oxide particle dispersion. Zirconia beads (0.1 mm in diameter) were used as the medium of the bead mill. The obtained first tungsten oxide particle dispersion was in the form of a slurry. _{The volume median diameter D 50} of the first tungsten oxide particles in the obtained tungsten oxide particle dispersion was 0.150 μm, and D ₉₀ was 0.230 μm. The peripheral speed and processing time of the bead mill were adjusted so that the first tungsten oxide particles having medium volume diameters D ₅₀ and D _{90 could be obtained.}

[Supporting process]
Hexachloroplatinic (IV) acid hexahydrate (manufactured by Tanaka Kikinzoku Kogyo Co., Ltd., platinum concentration) was added to the tungsten oxide particle dispersion so that platinum was 0.025% by mass with respect to the mass of the first tungsten oxide particles. 0.1 g / mL ± 5 wt%) was added and dispersed. As a result, a dispersion was obtained. The dispersion was heat-treated at 110 ° C. for 21 hours to obtain flakes. The flakes were crushed using a mixer to obtain a powder. The powder was heat treated at 400 ° C. As a result, the first particle was obtained. The first particles include first tungsten oxide particles (specifically, tungsten trioxide particles) and first auxiliary catalyst particles (specifically, platinum particles) provided on the surface of the first tungsten oxide particles. I was out.

[First particle dispersion forming step]
The obtained first particles and ion-exchanged water were charged into a homogenizer so that the content of the first particles with respect to the mass of the first particle dispersion was 19.8% by mass. The first particles were dispersed in ion-exchanged water using a homogenizer to obtain a dispersion. _{The volume median diameter D 50} of the first particle in the obtained dispersion was 0.343 μm, and D ₉₀ was 1.782 μm. The peripheral speed and processing time of the homogenizer were adjusted so that the first particles having medium volume diameters D ₅₀ and D _{90 could be obtained.} The resulting dispersion was then further dispersed using a bead mill. As a result, a slurry-like first particle dispersion was obtained. _{The volume median diameter D 50} of the first particle contained in the first particle dispersion was 0.143 μm, and D ₉₀ was 0.223 μm. The peripheral speed and processing time of the bead mill were adjusted so that the first particles having such medium volume diameters D ₅₀ and D _{90 could be obtained.}

(Second particle formation step)
The second particle forming step was as follows. The first tungsten oxide particle dispersion before the co-catalyst particles, which was obtained in the first tungsten oxide particle dispersion forming step without performing the second particle dispersion forming step according to the first embodiment, can be obtained. Used as a second particle dispersion. _{The volume median diameter D 50} of the second particle contained in the second particle dispersion was 0.150 μm, and D ₉₀ was 0.230 μm. The content of the second particle with respect to the mass of the second particle dispersion was 23.0% by mass.

(Mixing process)
The first particle dispersion and the second particle obtained in the first particle dispersion forming step in an amount such that the first particle in the container is 95.0 parts by mass and the second particle is 5.0 parts by mass. The second particle dispersion in the dispersion forming step was placed in a container. The contents of the container were mixed for 90 seconds by shaking the container by hand. The mixture was dried at 95 ° C. for 1 hour. As a result, a powder photocatalyst (A-1) was obtained. In the photocatalyst (A-1), the content of the second particle with respect to the sum of the mass of the first particle and the mass of the second particle was 5.0% by mass.

<Photocatalysts (A-2) and (A-3)>
Photocatalysts (A-2) and (A-3) were produced by the following methods.

(First particle formation step)
The first particle forming steps of the photocatalysts (A-2) and (A-3) were carried out in the same manner as the first particle forming step of the photocatalyst (A-1).

(Second particle formation step)
The second particle forming step of the photocatalysts (A-2) and (A-3) was the same as the second particle forming step of the photocatalyst (A-1).

(Mixing process)
The photocatalysts (A-2) and (A-3) were produced in the same manner as in the production of the photocatalyst (A-1) except that the following points were changed. By changing the mass of the first particle dispersion (and thus the mass of the first particle) and the mass of the second particle dispersion (and thus the mass of the second particle) added in the mixing step, the mass of the first particle The content of the second particle with respect to the sum of and the mass of the second particle was changed to the value shown in Table 1.

<Photocatalyst (B-1a)>
The photocatalyst (B-1a) was produced by the same method as that for the photocatalyst (A-1) except that the following points were changed. The second particle forming step and the mixing step were not carried out. The first particle dispersion obtained in the first particle dispersion forming step was dried to obtain a photocatalyst (B-1a).

<Photocatalyst (B-1b)>
The first tungsten oxide particle dispersion obtained in the step of forming the first tungsten oxide particle dispersion of the photocatalyst (A-1) before containing the cocatalyst particles was used as the second particle dispersion. The second particle dispersion was dried to obtain a photocatalyst (B-1b).

<Evaluation of photocatalytic activity: Photocatalysts (A-1) to (A-3) and (B-1a) to (B-1b)>
The decomposition activity of acetaldehyde into carbon dioxide was evaluated as the photocatalytic activity of the photocatalysts (A-1) to (A-3) and (B-1a) to (B-1b). Specifically, a petri dish containing 1.3 g of a photocatalyst was placed in a gas bag having a capacity of 5 L. Acetaldehyde was introduced into the gas bag so that the acetaldehyde concentration in the gas bag was 300 ppm. Next, while irradiating the gas bag with a blue LED (wavelength 450 μm, irradiance 7 mW / cm ² ), the change over time in the acetaldehyde concentration in the gas bag was measured using a gas detector tube for acetaldehyde. In addition, the change over time in the carbon dioxide concentration in the gas bag was measured using a carbon dioxide gas detector tube. From the measured acetaldehyde concentration and carbon dioxide concentration, the acetaldehyde residual rate and the carbon dioxide production rate were determined, respectively.

In addition, the improvement rate of photocatalytic activity was obtained from the following calculation formula (1). In formula (1), R _A represents a carbon dioxide generation rate after 1.50 hours of a photocatalyst comprising a first particle and a second particle, R _B photocatalyst without the second particles comprise a first particle The carbon dioxide production rate after 1.50 hours is shown. Improvement of the photocatalytic activity _{(%) = 100 × (R} A -R B) / R B ··· (1)

Specifically, photocatalyst _{R A} in formula (1) (A-1) , substituting the carbon dioxide production rate after 1.50 hours (A-2) or (A-3), _{R B} The carbon dioxide production rate after 1.50 hours of the photocatalyst (B-1a) was substituted into. The higher the improvement rate of the photocatalytic activity, the more the photocatalytic activity of the photocatalyst containing the first particle and the second particle is improved with respect to the photocatalyst containing the first particle and not containing the second particle. When the carbon dioxide production rate of the photocatalyst containing only the second particle (for example, the photocatalyst (B-1b)) is lower than the carbon dioxide production rate of the photocatalyst containing only the first particle (for example, the photocatalyst (B-1a)). , Indicates that the activity of the second particle is lower than the activity of the first particle.

Photocatalysts (A-1) to (A-3) and (B-) 1.50 hours after the start of blue LED irradiation
The carbon dioxide production rate (unit:%) and improvement rate (unit:%) of 1a) to (B-1b) are shown in Tables 1 and 2. Further, the time course of the acetaldehyde residual rate and the time change of the carbon dioxide production rate of the photocatalysts (A-1) to (A-3) and (B-1a) are shown in FIG. In FIG. 7, the vertical axis indicates the acetaldehyde residual rate (unit:%) and the carbon dioxide production rate (unit:%). In FIG. 7, the horizontal axis indicates the elapsed time (unit: h) from the start of irradiation of the blue LED. As is clear from FIG. 7, the photocatalysts (A-1) to (A-3) containing the first particle and the second particle generate carbon dioxide as compared with the photocatalyst (B-1a) not containing the second particle. The change with time of the rate and the change with time of the acetaldehyde residual rate were large, and the photocatalytic activity was excellent. Further, as is clear from FIG. 7, the photocatalyst (A) in which the content of the second particle with respect to the sum of the mass of the first particle and the mass of the second particle is more than 0.0% by mass and 10.0% by mass or less. In -1) to (A-3), the change over time in the carbon dioxide production rate and the change over time in the residual rate of acetaldehyde were larger than those in the photocatalyst (B-1a), and the photocatalytic activity was excellent.

In addition, the acetaldehyde decomposition rate constant was determined by the following method. Specifically, a graph was created with the logarithmic display of the measured acetaldehyde concentration on the vertical axis and the elapsed time from the start of irradiation of the blue LED on the horizontal axis. In the created graph, the slope between the point where the elapsed time was 0.25 hours and the point where the elapsed time was 0.50 hours was calculated. The obtained slope was defined as the acetaldehyde decomposition rate constant (unit: h ^-1 ). The acetaldehyde decomposition rate constants of the photocatalysts (A-1), (A-2), (A-3), and (B-1a) are 5.07, 4.33, 5.50, and 3.86, respectively. Met.

In Tables 1 and 2 and Tables 3 to 16 described later, the meanings of the terms are as follows. “Wt%” indicates mass%. “First particle D ₅₀ ” indicates the volume median diameter of the first particle contained in the first particle dispersion. The volume median diameter of the first particle was measured after the first particle dispersion forming step. "Tungsten trioxide particle / tungsten oxide particle dispersion" indicates the content ratio (unit: mass%) of the tungsten oxide particles with respect to the mass of the tungsten oxide particle dispersion. "First particle / first particle dispersion" indicates the content ratio (unit: mass%) of the first particle with respect to the mass of the first particle dispersion. “Second particle D ₅₀ ” indicates the volume median diameter of the second particle contained in the second particle dispersion. The volume median diameter of the second particle was measured after the second particle dispersion forming step. "Tungsten dioxide particles / Tungsten dioxide particle dispersion" indicates the content ratio (unit: mass%) of the tungsten dioxide particles with respect to the mass of the tungsten dioxide particle dispersion. "Second particle / second particle dispersion" indicates the content ratio (unit: mass%) of the second particle with respect to the mass of the second particle dispersion. "Second particle / (first particle + second particle)" indicates the content ratio (unit: mass%) of the second particle with respect to the sum of the mass of the first particle and the mass of the second particle. The CO ₂ production rate indicates the carbon dioxide production rate. "-" Indicates that it is not contained or measured.

<Photocatalyst (A-4)>
A photocatalyst (A-4) was produced by the following method.

(First particle formation step)
As the first particle forming step, the first tungsten oxide particle dispersion forming step, the supporting step, and the first particle dispersion forming step described in the first embodiment were performed.

[Step of forming first tungsten oxide particle dispersion]
The first tungsten oxide particles (tungsten trioxide sold by Takagi Co., Ltd.) were preheated at 900 ° C. in an air atmosphere. Preheated tungsten oxide particles and ion-exchanged water were charged into a bead mill so that the content of the tungsten oxide particles with respect to the mass of the tungsten oxide particle dispersion was 15.8% by mass. The tungsten oxide particles were dispersed in ion-exchanged water using a bead mill to obtain a tungsten oxide particle dispersion. Zirconia beads (0.1 mm in diameter) were used as the medium of the bead mill. The obtained first tungsten oxide particle dispersion was in the form of a slurry. _{The volume median diameter D 50} of the first tungsten oxide particles in the obtained tungsten oxide particle dispersion was 0.150 μm, and D ₉₀ was 0.230 μm. The peripheral speed and processing time of the bead mill were adjusted so that the first tungsten oxide particles having medium volume diameters D ₅₀ and D _{90 could be obtained.}

[Supporting process]
Hexachloroplatinic (IV) acid hexahydrate (manufactured by Tanaka Kikinzoku Kogyo Co., Ltd., platinum concentration) was added to the tungsten oxide particle dispersion so that platinum was 0.025% by mass with respect to the mass of the first tungsten oxide particles. 0.1 g / mL ± 5 wt%) was added and dispersed. As a result, a dispersion was obtained. The dispersion was heat-treated at 110 ° C. for 21 hours to obtain flakes. The flakes were crushed using a mixer to obtain a powder. The powder was heat treated at 400 ° C. As a result, the first particle was obtained. The first particles include first tungsten oxide particles (specifically, tungsten trioxide particles) and first auxiliary catalyst particles (specifically, platinum particles) provided on the surface of the first tungsten oxide particles. I was out.

[First particle dispersion forming step]
The obtained first particles and ion-exchanged water were charged into a homogenizer so that the content of the first particles with respect to the mass of the first particle dispersion was 20.2% by mass. The first particles were dispersed in ion-exchanged water using a homogenizer to obtain a dispersion. _{The volume median diameter D 50} of the first particle in the obtained dispersion was 0.343 μm, and D ₉₀ was 1.782 μm. The peripheral speed and processing time of the homogenizer were adjusted so that the first particles having medium volume diameters D ₅₀ and D _{90 could be obtained.} The resulting dispersion was then further dispersed using a mixer. As a result, a slurry-like first particle dispersion was obtained. _{The volume median diameter D 50} of the first particle contained in the first particle dispersion was 0.172 μm, and D ₉₀ was 0.769 μm. The peripheral speed and processing time of the mixer were adjusted so that the first particles having such medium volume diameters D ₅₀ and D _{90 could be obtained.}

(Second particle formation step)
The second particle forming step was as follows. The first tungsten oxide particle dispersion obtained in the first tungsten oxide particle dispersion forming step before the first co-catalyst particles are provided without performing the second particle dispersion forming step is used as the second particle dispersion. Used as. The content of the second particle with respect to the mass of the second particle dispersion was 10.1% by mass.

(Mixing process)
The first particle dispersion obtained in the first particle forming step and the second particle forming step in an amount such that the first particle in the container is 95.0 parts by mass and the second particle is 5.0 parts by mass. The second particle dispersion obtained in the above was placed in a container. The contents of the container were mixed for 90 seconds by shaking the container by hand. The mixture was dried at 95 ° C. for 1 hour. As a result, a powder photocatalyst (A-4) was obtained. In the photocatalyst (A-4), the content of the second particle with respect to the sum of the mass of the first particle and the mass of the second particle was 5.0% by mass.

<Photocatalyst (B-2a)>
The photocatalyst (B-2a) was produced by the same method as that for the photocatalyst (A-4) except that the following points were changed. The second particle forming step and the mixing step were not carried out. The first particle dispersion obtained in the first particle dispersion forming step was dried to obtain a photocatalyst (B-2a).

<Photocatalyst (B-2b)>
The first tungsten oxide particle dispersion obtained in the step of forming the first tungsten oxide particle dispersion of the photocatalyst (A-4) before the cocatalyst particles were provided was used as the second particle dispersion. The second particle dispersion was dried to obtain a photocatalyst (B-2b).

<Evaluation of photocatalytic activity: Photocatalysts (A-4) and (B-2a) to (B-2b)>
Photocatalysts (A-4) and (B-2a) to (B-2b) in the same manner as the photocatalytic activity evaluation of the photocatalysts (A-1) to (A-3) and (B-1a) to (B-1b). ) Photocatalytic activity was evaluated. The carbon dioxide production rate (unit:%) and improvement rate (unit:%) of the photocatalysts (A-4) and (B-2a) to (B-2b) 1.50 hours after the start of irradiation of the blue LED are determined. It is shown in Table 3. Incidentally, in the calculation of the improvement, of substituting carbon dioxide generation rate after 1.50 hours of photocatalyst (A-4) to _{R A} in formula (1), photocatalyst _{R B} (B-2a) 1 The carbon dioxide production rate after 50 hours was substituted. Further, the time course of the acetaldehyde residual rate and the time change of the carbon dioxide production rate of the photocatalysts (A-4) and (B-2a) are shown in FIG. In FIG. 8, the vertical axis indicates the acetaldehyde residual rate (unit:%) and the carbon dioxide production rate (unit:%). In FIG. 8, the horizontal axis indicates the elapsed time (unit: h) from the start of irradiation of the blue LED. As is clear from FIG. 8, in the photocatalyst (A-4) containing the first particle and the second particle, the change over time in the carbon dioxide production rate and acetaldehyde as compared with the photocatalyst (B-2a) not containing the second particle. The residual rate changed significantly with time, and the photocatalytic activity was excellent. Further, as is clear from FIG. 8, the photocatalyst (A) in which the content of the second particle with respect to the sum of the mass of the first particle and the mass of the second particle is more than 0.0% by mass and 10.0% by mass or less. In -4), the change over time in the carbon dioxide production rate and the change over time in the residual rate of acetaldehyde were larger than those in the photocatalyst (B-2a), and the photocatalytic activity was excellent.

<Photocatalyst (A-5)>
A photocatalyst (A-5) was produced by the following method.

(First particle formation step)
As the first particle forming step, the first tungsten oxide particle dispersion forming step, the supporting step, and the first particle dispersion forming step described in the first embodiment were performed.

[Step of forming first tungsten oxide particle dispersion]
The step of forming the first tungsten oxide particle dispersion of the photocatalyst (A-5) was performed in the same manner as the step of forming the first tungsten oxide particle dispersion of the photocatalyst (A-4) except that the following points were changed. rice field. By changing the amount of preheated tungsten oxide particles added and the amount of ion-exchanged water added, the content of tungsten oxide particles with respect to the mass of the tungsten oxide particle dispersion can be increased from 15.8% by mass. It was changed to 23.8% by mass.

[Supporting process]
The step of supporting the photocatalyst (A-5) was carried out in the same manner as the step of supporting the photocatalyst (A-4).

[First particle dispersion forming step]
The first particle dispersion forming step of the photocatalyst (A-5) was carried out in the same manner as the first particle dispersion forming step of the photocatalyst (A-4) except that the following points were changed. By changing the amount of the first particles added and the amount of ion-exchanged water added, the content of the first particles with respect to the mass of the first particle dispersion was changed from 20.2% by mass to 25.6% by mass. By changing the peripheral speed and the processing time of the mixer, the volume median diameter D ₅₀ of the first particle was changed to the value shown in Table 4.

(Second particle formation step)
The second particle forming step was as follows. The first tungsten oxide particle dispersion obtained in the first tungsten oxide particle dispersion forming step before the co-catalyst particles are provided is used as the second particle dispersion without performing the second particle dispersion forming step. bottom. By adjusting the peripheral speed and the processing time of the mixer step of forming the first tungsten oxide particle dispersion, the volume median diameter D ₅₀ of the first tungsten oxide particles (corresponding to the second particles) to the values shown in Table 4 changed. The content of the second particle with respect to the mass of the second particle dispersion was 23.8% by mass.

(Mixing process)
The first particle dispersion obtained in the first particle forming step and the second particle forming step in such an amount that the first particle in the container is 95.2 parts by mass and the second particle is 4.8 parts by mass. The second particle dispersion obtained in the above was placed in a container. The contents of the container were mixed for 90 seconds by shaking the container by hand. The mixture was dried at 95 ° C. for 1 hour. As a result, a powder photocatalyst (A-5) was obtained. In the photocatalyst (A-5), the content of the second particle with respect to the sum of the mass of the first particle and the mass of the second particle was 4.8% by mass.

<Photocatalyst (A-6)>
A photocatalyst (A-6) was produced by the following method.

(First particle formation step)
The first particle forming step of the photocatalyst (A-6) was carried out in the same manner as the first particle forming step of the photocatalyst (A-5).

(Second particle formation step)
The second particle forming step of the photocatalyst (A-6) was the same as the second particle forming step of the photocatalyst (A-5).

(Mixing process)
The photocatalyst (A-6) was produced in the same manner as the photocatalyst (A-5) except that the following points were changed. By changing the mass of the first particle dispersion (and thus the mass of the first particle) and the mass of the second particle dispersion (and thus the mass of the second particle) added in the mixing step, the mass of the first particle The content of the second particle with respect to the sum of the mass of the second particle and the mass of the second particle was changed from 4.8% by mass to 9.1% by mass.

<Photocatalyst (B-3a)>
The photocatalyst (B-3a) was produced by the same method as that for the photocatalyst (A-5) except that the following points were changed. The second particle forming step and the mixing step were not carried out. The first particle dispersion obtained in the first particle dispersion forming step was dried to obtain a photocatalyst (B-3a).

<Photocatalyst (B-3b)>
The first tungsten oxide particle dispersion obtained in the step of forming the first tungsten oxide particle dispersion of the photocatalyst (A-5) before containing the cocatalyst particles was used as the second particle dispersion. The second particle dispersion was dried to obtain a photocatalyst (B-3b).

<Evaluation of photocatalytic activity: Photocatalysts (A-5) to (A-6) and (B-3a) to (B-3b)>
Photocatalysts (A-5) to (A-6) and (B-3a) in the same manner as the photocatalytic activity evaluation of photocatalysts (A-1) to (A-3) and (B-1a) to (B-1b). )-(B-3b) were evaluated. Carbon dioxide production rate (unit:%) and improvement rate (unit:%) and improvement rate of photocatalysts (A-5) to (A-6) and (B-3a) to (B-3b) 1.50 hours after the start of irradiation of the blue LED. Unit:%) is shown in Table 4. Incidentally, in the calculation of the improvement ratio, by substituting the carbon dioxide production rate after 1.50 hours photocatalysts in _{R A} in formula (1) (A-5) or (A-6), photocatalyst _{R B} ( The carbon dioxide production rate after 1.50 hours of B-3a) was substituted. In addition, the time course of the acetaldehyde residual rate and the time change of the carbon dioxide production rate of the photocatalysts (A-5), (A-6) and (B-3a) are shown in FIG. In FIG. 9, the vertical axis indicates the acetaldehyde residual rate (unit:%) and the carbon dioxide production rate (unit:%). In FIG. 9, the horizontal axis indicates the elapsed time (unit: h) from the start of irradiation of the blue LED. As is clear from FIG. 9, the photocatalyst (A-5) and (A-6) containing the first particle and the second particle generate carbon dioxide as compared with the photocatalyst (B-3a) not containing the second particle. The change with time of the rate and the change with time of the acetaldehyde residual rate were large, and the photocatalytic activity was excellent. Further, as is clear from FIG. 9, the photocatalyst (A) in which the content of the second particle with respect to the sum of the mass of the first particle and the mass of the second particle is more than 0.0% by mass and 10.0% by mass or less. In -5) and (A-6), the change over time in the carbon dioxide production rate and the change over time in the residual rate of acetaldehyde were larger than those in the photocatalyst (B-3a), and the photocatalytic activity was excellent.

<Photocatalyst (A-7)>
A photocatalyst (A-7) was produced by the following method.

(First particle formation step)
As the first particle forming step, the first tungsten oxide particle dispersion forming step, the supporting step, and the first particle dispersion forming step described in the first embodiment were performed.

[Step of forming first tungsten oxide particle dispersion]
The step of forming the first tungsten oxide particle dispersion of the photocatalyst (A-7) was performed in the same manner as the step of forming the first tungsten oxide particle dispersion of the photocatalyst (A-4) except that the following points were changed. rice field. By changing the amount of preheated tungsten oxide particles added and the amount of ion-exchanged water added, the content of tungsten oxide particles with respect to the mass of the tungsten oxide particle dispersion can be increased from 15.8% by mass. It was changed to 23.8% by mass.

[Supporting process]
The step of supporting the photocatalyst (A-7) was carried out in the same manner as the step of supporting the photocatalyst (A-4).

[First particle dispersion forming step]
The first particle dispersion forming step of the photocatalyst (A-7) was carried out in the same manner as the first particle dispersion forming step of the photocatalyst (A-4) except that the following points were changed. By changing the amount of the first particles added and the amount of ion-exchanged water added, the content of the first particles with respect to the mass of the first particle dispersion was changed from 20.2% by mass to 25.2% by mass. By changing the peripheral speed and the processing time of the mixer, the volume median diameter D ₅₀ of the first particle was changed to the value shown in Table 5.

(Second particle formation step)
The second particle forming step was as follows. The first tungsten oxide particle dispersion obtained in the first tungsten oxide particle dispersion forming step before the co-catalyst particles are provided is used as the second particle dispersion without performing the second particle dispersion forming step. bottom. By adjusting the peripheral speed and the processing time of the mixer step of forming the first tungsten oxide particle dispersion, the volume median diameter D ₅₀ of the first tungsten oxide particles (corresponding to the second particles) to the values shown in Table 5 changed. The content of the second particle with respect to the mass of the second particle dispersion was 23.8% by mass.

(Mixing process)
The photocatalyst (A-7) was produced by the same method as that for the photocatalyst (A-4) except that the following points were changed. By changing the mass of the first particle dispersion (and thus the mass of the first particle) and the mass of the second particle dispersion (and thus the mass of the second particle) added in the mixing step, the mass of the first particle The content of the second particle with respect to the sum of the mass of the second particle and the mass of the second particle was changed from 5.0% by mass to 4.8% by mass.

<Photocatalyst (B-4a)>
The photocatalyst (B-4a) was produced by the same method as that for the photocatalyst (A-7) except that the following points were changed. The second particle forming step and the mixing step were not carried out. The first particle dispersion obtained in the first particle dispersion forming step was dried to obtain a photocatalyst (B-4a).

<Photocatalyst (B-4b)>
The first tungsten oxide particle dispersion obtained in the step of forming the first tungsten oxide particle dispersion of the photocatalyst (A-7) before containing the cocatalyst particles was used as the second particle dispersion. The second particle dispersion was dried to obtain a photocatalyst (B-4b).

<Evaluation of photocatalytic activity: Photocatalysts (A-7) and (B-4a) to (B-4b)>
Photocatalysts (A-7) and (B-4a) to (B-4b) in the same manner as the photocatalytic activity evaluation of photocatalysts (A-1) to (A-3) and (B-1a) to (B-1b). ) Photocatalytic activity was evaluated. The carbon dioxide production rate (unit:%) and improvement rate (unit:%) of the photocatalysts (A-7) and (B-4a) to (B-4b) 1.50 hours after the start of irradiation of the blue LED are determined. It is shown in Table 5. Incidentally, in the calculation of the improvement, of substituting carbon dioxide generation rate after 1.50 hours of photocatalyst (A-7) to _{R A} in formula (1), photocatalyst _{R B} (B-4a) 1 The carbon dioxide production rate after 50 hours was substituted.

<Photocatalyst (A-8)>
A photocatalyst (A-8) was produced by the following method.

(First particle formation step)
As the first particle forming step, the first tungsten oxide particle dispersion forming step, the supporting step, and the first particle dispersion forming step described in the first embodiment were performed.

[Step of forming first tungsten oxide particle dispersion]
The step of forming the first tungsten oxide particle dispersion of the photocatalyst (A-8) was performed in the same manner as the step of forming the first tungsten oxide particle dispersion of the photocatalyst (A-4) except that the following points were changed. rice field. By changing the amount of preheated tungsten oxide particles added and the amount of ion-exchanged water added, the content of tungsten oxide particles with respect to the mass of the tungsten oxide particle dispersion can be increased from 15.8% by mass. It was changed to 23.8% by mass.

[Supporting process]
The step of supporting the photocatalyst (A-8) was carried out in the same manner as the step of supporting the photocatalyst (A-4).

[First particle dispersion forming step]
The first particle dispersion forming step of the photocatalyst (A-8) was carried out in the same manner as the first particle dispersion forming step of the photocatalyst (A-4) except that the following points were changed. By changing the amount of the first particles added and the amount of ion-exchanged water added, the content of the first particles with respect to the mass of the first particle dispersion was changed from 20.2% by mass to 21.1% by mass. By changing the peripheral speed and the processing time of the mixer, the volume median diameter D ₅₀ of the first particle was changed to the value shown in Table 6.

(Second particle formation step)
The second particle forming step was as follows. The first tungsten oxide particle dispersion obtained in the first tungsten oxide particle dispersion forming step before the co-catalyst particles are provided is used as the second particle dispersion without performing the second particle dispersion forming step. bottom. By adjusting the peripheral speed and the processing time of the mixer step of forming the first tungsten oxide particle dispersion, the volume median diameter D ₅₀ of the first tungsten oxide particles (corresponding to the second particles) to the values shown in Table 6 changed. The content of the second particle with respect to the mass of the second particle dispersion was 23.8% by mass.

(Mixing process)
The photocatalyst (A-8) was produced by the same method as that for the photocatalyst (A-4) except that the following points were changed. By changing the mass of the first particle dispersion (and thus the mass of the first particle) and the mass of the second particle dispersion (and thus the mass of the second particle) added in the mixing step, the mass of the first particle The content of the second particle with respect to the sum of the mass of the second particle and the mass of the second particle was changed from 5.0% by mass to 4.8% by mass.

<Photocatalyst (B-5a)>
The photocatalyst (B-5a) was produced by the same method as that for the photocatalyst (A-8) except that the following points were changed. The second particle forming step and the mixing step were not carried out. The first particle dispersion obtained in the first particle dispersion forming step was dried to obtain a photocatalyst (B-5a).

<Photocatalyst (B-5b)>
The first tungsten oxide particle dispersion obtained in the step of forming the first tungsten oxide particle dispersion of the photocatalyst (A-8) before containing the cocatalyst particles was used as the second particle dispersion. The second particle dispersion was dried to obtain a photocatalyst (B-5b).

<Evaluation of photocatalytic activity: Photocatalyst (A-8) and (B-5a) to (B-5b)>
Photocatalysts (A-8) and (B-5a) to (B-5b) in the same manner as the photocatalytic activity evaluation of photocatalysts (A-1) to (A-3) and (B-1a) to (B-1b). ) Photocatalytic activity was evaluated. The carbon dioxide production rate (unit:%) and improvement rate (unit:%) of the photocatalysts (A-8) and (B-5a) to (B-5b) 1.50 hours after the start of irradiation of the blue LED are determined. It is shown in Table 6. Incidentally, in the calculation of the improvement, of substituting carbon dioxide generation rate after 1.50 hours of photocatalyst (A-8) to _{R A} in formula (1), photocatalyst _{R B} (B-5a) 1 The carbon dioxide production rate after 50 hours was substituted. Further, the time course of the acetaldehyde residual rate and the time change of the carbon dioxide production rate of the photocatalysts (A-8) and (B-5a) are shown in FIG. In FIG. 10, the vertical axis shows the acetaldehyde residual rate (unit:%) and the carbon dioxide production rate (unit:%). In FIG. 10, the horizontal axis indicates the elapsed time (unit: h) from the start of irradiation of the blue LED. As is clear from FIG. 10, in the photocatalyst containing the first particle and the second particle (A-8), the change over time in the carbon dioxide production rate and acetaldehyde as compared with the photocatalyst not containing the second particle (B-5a). The residual rate changed significantly with time, and the photocatalytic activity was excellent. Further, as is clear from FIG. 10, the photocatalyst (A) in which the content of the second particle with respect to the sum of the mass of the first particle and the mass of the second particle is more than 0.0% by mass and 10.0% by mass or less. In -8), the change over time in the carbon dioxide production rate and the change over time in the residual rate of acetaldehyde were larger than those in the photocatalyst (B-5a), and the photocatalytic activity was excellent.

<Photocatalyst (A-9)>
A photocatalyst (A-9) was produced by the following method.

(First particle formation step)
As the first particle forming step, the first tungsten oxide particle dispersion forming step, the supporting step, and the first particle dispersion forming step described in the first embodiment were performed.

[Step of forming first tungsten oxide particle dispersion]
The first tungsten oxide particles (tungsten trioxide sold by Takagi Co., Ltd.) were preheated at 900 ° C. in an air atmosphere. Preheated tungsten oxide particles and ion-exchanged water were charged into a bead mill so that the content of the tungsten oxide particles with respect to the mass of the tungsten oxide particle dispersion was 21.7% by mass. The tungsten oxide particles were dispersed in ion-exchanged water using a bead mill to obtain a tungsten oxide particle dispersion. Zirconia beads (0.1 mm in diameter) were used as the medium of the bead mill. The obtained first tungsten oxide particle dispersion was in the form of a slurry. _{The volume median diameter D 50} of the first tungsten oxide particles in the obtained tungsten oxide particle dispersion was 0.149 μm, and D ₉₀ was 0.227 μm. The peripheral speed and processing time of the bead mill were adjusted so that the first tungsten oxide particles having medium volume diameters D ₅₀ and D _{90 could be obtained.}

[Supporting process]
Hexachloroplatinic (IV) acid hexahydrate (manufactured by Tanaka Kikinzoku Kogyo Co., Ltd., platinum concentration) was added to the tungsten oxide particle dispersion so that platinum was 0.025% by mass with respect to the mass of the first tungsten oxide particles. 0.1 g / mL ± 5 wt%) was added and dispersed. As a result, a dispersion was obtained. The dispersion was heat-treated at 110 ° C. for 21 hours to obtain flakes. The flakes were crushed using a mixer to obtain a powder. The powder was heat treated at 400 ° C. As a result, the first particle was obtained. The first particles include first tungsten oxide particles and first auxiliary catalyst particles (specifically, platinum particles) provided on the surface of the first tungsten oxide particles (specifically, tungsten trioxide particles). I was out.

[First particle dispersion forming step]
The obtained first particles and ion-exchanged water were added to the homogenizer so that the content of the first particles with respect to the mass of the first particle dispersion was 24.8% by mass. Using a homogenizer, the first particles were dispersed in ion-exchanged water to obtain a slurry-like first particle dispersion. The volume median diameter D ₅₀ of the first particles contained in the first particle dispersion are shown in Table 7. Note that the first particles having such a volume median diameter D ₅₀ as obtained was adjusted peripheral speed and processing time of the homogenizer.

(Second particle formation step)
The second particle forming step was as follows. The first tungsten oxide particle dispersion obtained in the first tungsten oxide particle dispersion forming step before the co-catalyst particles are provided is used as the second particle dispersion without performing the second particle dispersion forming step. bottom. The content of the second particle with respect to the mass of the second particle dispersion was 7.3% by mass.

(Mixing process)
The first particle dispersion obtained in the first particle forming step and the second particle forming step in such an amount that the first particle in the container is 95.2 parts by mass and the second particle is 4.8 parts by mass. The second particle dispersion obtained in the above was placed in a container. The contents of the container were mixed for 90 seconds by shaking the container by hand. The mixture was dried at 95 ° C. for 1 hour. As a result, a powder photocatalyst (A-9) was obtained. In the photocatalyst (A-9), the content of the second particle with respect to the sum of the mass of the first particle and the mass of the second particle was 4.8% by mass.

<Photocatalyst (B-6a)>
The photocatalyst (B-6a) was produced by the same method as that for the photocatalyst (A-9) except that the following points were changed. The second particle forming step and the mixing step were not carried out. The first particle dispersion obtained in the first particle dispersion forming step was dried to obtain a photocatalyst (B-6a).

<Photocatalyst (B-6b)>
The first tungsten oxide particle dispersion obtained in the step of forming the first tungsten oxide particle dispersion of the photocatalyst (A-9) before containing the cocatalyst particles was used as the second particle dispersion. The second particle dispersion was dried to obtain a photocatalyst (B-6b).

<Evaluation of photocatalytic activity: Photocatalyst (A-9) and (B-6a) to (B-6b)>
Photocatalysts (A-9) and (B-6a) to (B-6b) in the same manner as the photocatalytic activity evaluation of the photocatalysts (A-1) to (A-3) and (B-1a) to (B-1b). ) Photocatalytic activity was evaluated. The carbon dioxide production rate (unit:%) and improvement rate (unit:%) of the photocatalysts (A-9) and (B-6a) to (B-6b) 1.50 hours after the start of irradiation of the blue LED are determined. It is shown in Table 7. Incidentally, in the calculation of the improvement, of substituting carbon dioxide generation rate after 1.50 hours of photocatalyst (A-9) to _{R A} in formula (1), photocatalyst _{R B} (B-6a) 1 The carbon dioxide production rate after 50 hours was substituted.

<Photocatalyst (A-10)>
A photocatalyst (A-10) was produced by the following method.

(First particle formation step)
As the first particle forming step, the first tungsten oxide particle dispersion forming step, the supporting step, and the first particle dispersion forming step described in the first embodiment were performed.

[Step of forming first tungsten oxide particle dispersion]
The step of forming the first tungsten oxide particle dispersion of the photocatalyst (A-10) was performed in the same manner as the step of forming the first tungsten oxide particle dispersion of the photocatalyst (A-4) except that the following points were changed. rice field. By changing the amount of preheated tungsten oxide particles added and the amount of ion-exchanged water added, the content of tungsten oxide particles with respect to the mass of the tungsten oxide particle dispersion can be increased from 15.8% by mass. It was changed to 23.0% by mass.

[Supporting process]
The photocatalyst (A-10) was supported by the same method as the photocatalyst (A-4), except that the following points were changed. By changing the addition amount of the first tungsten oxide particle dispersion and the addition amount of hexachloroplatinic (IV) acid hexahydrate, the primary cocatalyst loading ratio of the first particles was increased from 0.025% by mass to 0.020. Changed to mass%.

[First particle dispersion forming step]
The first particle dispersion forming step of the photocatalyst (A-10) was carried out in the same manner as the first particle dispersion forming step of the photocatalyst (A-4) except that the following points were changed. By changing the amount of the first particles added and the amount of ion-exchanged water added, the content of the first particles with respect to the mass of the first particle dispersion was changed from 20.2% by mass to 26.2% by mass. By changing the peripheral speed and the processing time of the mixer, the volume median diameter D ₅₀ of the first particle was changed to the value shown in Table 8.

(Second particle formation step)
The second particle forming step was as follows. The first tungsten oxide particle dispersion obtained in the first tungsten oxide particle dispersion forming step before the co-catalyst particles are provided is used as the second particle dispersion without performing the second particle dispersion forming step. bottom. The content of the second particle with respect to the mass of the second particle dispersion was 23.0% by mass.

(Mixing process)
The mixing step of the photocatalyst (A-10) was carried out in the same manner as the mixing step of the photocatalyst (A-4). As a result, a photocatalyst (A-10) was obtained.

<Photocatalyst (B-7a)>
The photocatalyst (B-7a) was produced by the same method as that for the photocatalyst (A-10) except that the following points were changed. The second particle forming step and the mixing step were not carried out. The first particle dispersion obtained in the first particle dispersion forming step was dried to obtain a photocatalyst (B-7a).

<Photocatalyst (B-7b)>
The first tungsten oxide particle dispersion obtained in the step of forming the first tungsten oxide particle dispersion of the photocatalyst (A-10) before the co-catalyst particles were provided was used as the second particle dispersion. The second particle dispersion was dried to obtain a photocatalyst (B-7b).

<Evaluation of photocatalytic activity: Photocatalysts (A-10) and (B-7a) to (B-7b)>
Photocatalysts (A-10) and (B-7a) to (B-7b) in the same manner as the photocatalytic activity evaluation of the photocatalysts (A-1) to (A-3) and (B-1a) to (B-1b). ) Photocatalytic activity was evaluated. The carbon dioxide production rate (unit:%) and improvement rate (unit:%) of the photocatalysts (A-10) and (B-7a) to (B-7b) 1.50 hours after the start of irradiation of the blue LED are determined. It is shown in Table 8. Incidentally, in the calculation of the improvement, of substituting carbon dioxide generation rate after 1.50 hours of photocatalyst (A-10) to _{R A} in formula (1), photocatalyst _{R B} (B-7a) 1 The carbon dioxide production rate after 50 hours was substituted.

<Photocatalyst (A-11)>
A photocatalyst (A-11) was produced by the following method.

(First particle formation step)
As the first particle forming step, the first tungsten oxide particle dispersion forming step, the supporting step, and the first particle dispersion forming step described in the first embodiment were performed.

[Step of forming first tungsten oxide particle dispersion]
The step of forming the first tungsten oxide particle dispersion of the photocatalyst (A-11) was performed in the same manner as the step of forming the first tungsten oxide particle dispersion of the photocatalyst (A-4) except that the following points were changed. rice field. By changing the amount of preheated tungsten oxide particles added and the amount of ion-exchanged water added, the content of tungsten oxide particles with respect to the mass of the tungsten oxide particle dispersion can be increased from 15.8% by mass. It was changed to 16.0% by mass.

[Supporting process]
The photocatalyst (A-11) was supported by the same method as the photocatalyst (A-4), except that the following points were changed. By changing the addition amount of the first tungsten oxide particle dispersion and the addition amount of hexachloroplatinic (IV) acid hexahydrate, the primary cocatalyst loading ratio of the first particles was increased from 0.025% by mass to 0.005. Changed to mass%.

[First particle dispersion forming step]
The first particle dispersion forming step of the photocatalyst (A-11) was carried out in the same manner as the first particle dispersion forming step of the photocatalyst (A-4) except that the following points were changed. By changing the amount of the first particles added and the amount of ion-exchanged water added, the content of the first particles with respect to the mass of the first particle dispersion was changed from 20.2% by mass to 20.0% by mass. By changing the peripheral speed and the processing time of the mixer, the volume median diameter D ₅₀ of the first particle was changed to the value shown in Table 9.

(Second particle formation step)
The second particle forming step was as follows. The first tungsten oxide particle dispersion obtained in the first tungsten oxide particle dispersion forming step before the co-catalyst particles are provided is used as the second particle dispersion without performing the second particle dispersion forming step. bottom. The content of the second particle with respect to the mass of the second particle dispersion was 16.0% by mass.

(Mixing process)
The mixing step of the photocatalyst (A-11) was carried out in the same manner as the mixing step of the photocatalyst (A-4). As a result, a photocatalyst (A-11) was obtained.

<Photocatalyst (B-8a)>
The photocatalyst (B-8a) was produced by the same method as that for the photocatalyst (A-11) except that the following points were changed. The second particle forming step and the mixing step were not carried out. The first particle dispersion obtained in the first particle dispersion forming step was dried to obtain a photocatalyst (B-8a).

<Photocatalyst (B-8b)>
The first tungsten oxide particle dispersion before providing the cocatalyst particles obtained in the step of forming the first tungsten oxide particle dispersion of the photocatalyst (A-11) was used as the second particle dispersion. The second particle dispersion was dried to obtain a photocatalyst (B-8b).

<Evaluation of photocatalytic activity: Photocatalyst (A-11) and (B-8a) to (B-8b)>
Photocatalysts (A-11) and (B-8a) to (B-8b) in the same manner as the photocatalytic activity evaluation of the photocatalysts (A-1) to (A-3) and (B-1a) to (B-1b). ) Photocatalytic activity was evaluated. The carbon dioxide production rate (unit:%) and improvement rate (unit:%) of the photocatalysts (A-11) and (B-8a) to (B-8b) 1.50 hours after the start of irradiation of the blue LED are determined. It is shown in Table 9. Incidentally, in the calculation of the improvement, of substituting carbon dioxide generation rate after 1.50 hours of photocatalyst (A-11) to _{R A} in formula (1), photocatalyst _{R B} (B-8a) 1 The carbon dioxide production rate after 50 hours was substituted.

<Photocatalyst (A-12)>
A photocatalyst (A-12) was produced by the following method.

(First particle formation step)
As the first particle forming step, the first tungsten oxide particle dispersion forming step, the supporting step, and the first particle dispersion forming step described in the first embodiment were performed.

[Step of forming first tungsten oxide particle dispersion]
The step of forming the first tungsten oxide particle dispersion of the photocatalyst (A-12) was performed in the same manner as the step of forming the first tungsten oxide particle dispersion of the photocatalyst (A-4) except that the following points were changed. rice field. By changing the amount of preheated tungsten oxide particles added and the amount of ion-exchanged water added, the content of tungsten oxide particles with respect to the mass of the tungsten oxide particle dispersion can be increased from 15.8% by mass. It was changed to 16.0% by mass.

[Supporting process]
The photocatalyst (A-12) was supported by the same method as the photocatalyst (A-4), except that the following points were changed. By changing the addition amount of the first tungsten oxide particle dispersion and the addition amount of hexachloroplatinic (IV) acid hexahydrate, the primary cocatalyst loading ratio of the first particles was increased from 0.025% by mass to 0.250. Changed to mass%.

[First particle dispersion forming step]
The first particle dispersion forming step of the photocatalyst (A-12) was carried out in the same manner as the first particle dispersion forming step of the photocatalyst (A-4) except that the following points were changed. By changing the amount of the first particles added and the amount of ion-exchanged water added, the content of the first particles with respect to the mass of the first particle dispersion was changed from 20.2% by mass to 20.0% by mass. By changing the peripheral speed and the processing time of the mixer, the volume median diameter D ₅₀ of the first particle was changed to the value shown in Table 10.

(Second particle formation step)
The second particle forming step was as follows. The first tungsten oxide particle dispersion obtained in the first tungsten oxide particle dispersion forming step before the co-catalyst particles are provided is used as the second particle dispersion without performing the second particle dispersion forming step. bottom. The content of the second particle with respect to the mass of the second particle dispersion was 16.0% by mass.

(Mixing process)
The mixing step of the photocatalyst (A-12) was carried out in the same manner as the mixing step of the photocatalyst (A-4). As a result, a photocatalyst (A-12) was obtained.

<Photocatalyst (B-9a)>
The photocatalyst (B-9a) was produced by the same method as that for the photocatalyst (A-12) except that the following points were changed. The second particle forming step and the mixing step were not carried out. The first particle dispersion obtained in the first particle dispersion forming step was dried to obtain a photocatalyst (B-9a).

<Photocatalyst (B-9b)>
The first tungsten oxide particle dispersion obtained in the step of forming the first tungsten oxide particle dispersion of the photocatalyst (A-12) before containing the cocatalyst particles was used as the second particle dispersion. The second particle dispersion was dried to obtain a photocatalyst (B-9b).

<Evaluation of photocatalytic activity: Photocatalyst (A-12) and (B-9a) to (B-9b)>
Photocatalysts (A-12) and (B-9a) to (B-9b) in the same manner as the photocatalytic activity evaluation of the photocatalysts (A-1) to (A-3) and (B-1) to (B-1b). ) Photocatalytic activity was evaluated. The carbon dioxide production rate (unit:%) and improvement rate (unit:%) of the photocatalysts (A-12) and (B-9a) to (B-9b) 1.50 hours after the start of irradiation of the blue LED are determined. It is shown in Table 10. Incidentally, in the calculation of the improvement, of substituting carbon dioxide generation rate after 1.50 hours of photocatalyst (A-12) to _{R A} in formula (1), photocatalyst _{R B} (B-9a) 1 The carbon dioxide production rate after 50 hours was substituted.

<Photocatalyst (A-13)>
A photocatalyst (A-13) was produced by the following method.

(First particle formation step)
As the first particle forming step, the first tungsten oxide particle dispersion forming step, the supporting step, and the first particle dispersion forming step described in the first embodiment were performed.

[Step of forming first tungsten oxide particle dispersion]
The first tungsten oxide particles (tungsten trioxide sold by Takagi Co., Ltd.) were preheated at 900 ° C. in an air atmosphere. Preheated tungsten oxide particles and ion-exchanged water were charged into a bead mill so that the content of the tungsten oxide particles with respect to the mass of the tungsten oxide particle dispersion was 10.0% by mass. The tungsten oxide particles were dispersed in ion-exchanged water using a bead mill to obtain a tungsten oxide particle dispersion. Zirconia beads (0.1 mm in diameter) were used as the medium of the bead mill. The obtained first tungsten oxide particle dispersion was in the form of a slurry. _{The volume median diameter D 50} of the first tungsten oxide particles in the obtained tungsten oxide particle dispersion was 0.150 μm, and D ₉₀ was 0.230 μm. The peripheral speed and processing time of the bead mill were adjusted so that the first tungsten oxide particles having medium volume diameters D ₅₀ and D _{90 could be obtained.}

[Supporting process]
Palladium (manufactured by Kishida Chemical Co., Ltd.) was added to and dispersed in the obtained tungsten oxide particle dispersion so that palladium was 0.010% by mass with respect to the mass of the first tungsten oxide particles. As a result, a dispersion was obtained. The dispersion was heat-treated at 110 ° C. for 21 hours to obtain flakes. The flakes were crushed using a mixer to obtain a powder. The powder was heat treated at 400 ° C. As a result, the first particle was obtained. The first particles include first tungsten oxide particles (specifically, tungsten trioxide particles) and first auxiliary catalyst particles (specifically, palladium particles) provided on the surface of the first tungsten oxide particles. I was out.

[First particle dispersion forming step]
The obtained first particles and ion-exchanged water were added to the mixer so that the content of the first particles with respect to the mass of the first particle dispersion was 20.0% by mass. Using a mixer, the first particles were dispersed in ion-exchanged water to obtain a slurry-like first particle dispersion. _{The volume median diameter D 50} of the first particle contained in the first particle dispersion was 0.150 μm, and D ₉₀ was 0.230 μm. The peripheral speed and processing time of the mixer were adjusted so that the first particles having such medium volume diameters D ₅₀ and D _{90 could be obtained.}

(Second particle formation step)
The second particle forming step was as follows. The first tungsten oxide particle dispersion obtained in the first tungsten oxide particle dispersion forming step before the co-catalyst particles are provided is used as the second particle dispersion without performing the second particle dispersion forming step. bottom. The content of the second particle with respect to the mass of the second particle dispersion was 10.0% by mass.

(Mixing process)
The mixing step of the photocatalyst (A-13) was carried out in the same manner as the mixing step of the photocatalyst (A-4). As a result, a photocatalyst (A-13) was obtained.

<Photocatalyst (B-10a)>
The photocatalyst (B-10a) was produced by the same method as that for the photocatalyst (A-13) except that the following points were changed. The second particle forming step and the mixing step were not carried out. The first particle dispersion obtained in the first particle dispersion forming step was dried to obtain a photocatalyst (B-10a).

<Photocatalyst (B-10b)>
The first tungsten oxide particle dispersion obtained in the step of forming the first tungsten oxide particle dispersion of the photocatalyst (A-13) before containing the cocatalyst particles was used as the second particle dispersion. The second particle dispersion was dried to obtain a photocatalyst (B-10b).

<Evaluation of photocatalytic activity: Photocatalyst (A-13) and (B-10a) to (B-10b)>
Photocatalysts (A-13) and (B-10a) to (B-10b) in the same manner as the photocatalytic activity evaluation of the photocatalysts (A-1) to (A-3) and (B-1a) to (B-1b). ) Photocatalytic activity was evaluated. Table 11 shows the carbon dioxide production rate (unit:%) and improvement rate (unit:%) of the photocatalysts (A-13) and (B-10a) to (B-10b) 4 hours after the start of irradiation of the blue LED. Shown in. Incidentally, in the calculation of the improvement ratio, by substituting the carbon dioxide production rate after 4 hours of photocatalyst _{R A} in formula (1) (A-13) , 4 hours after the photocatalyst (B-10a) to _{R B} The carbon dioxide production rate of was substituted.

<Photocatalyst (A-14)>
A photocatalyst (A-14) was produced by the following method.

(First particle formation step)
As the first particle forming step, the first tungsten oxide particle dispersion forming step, the supporting step, and the first particle dispersion forming step described in the first embodiment were performed.

[Step of forming first tungsten oxide particle dispersion]
The step of forming the first tungsten oxide particle dispersion of the photocatalyst (A-14) was carried out in the same manner as the step of forming the first tungsten oxide particle dispersion of the photocatalyst (A-13).

[Supporting process]
The step of forming the first tungsten oxide particle dispersion of the photocatalyst (A-14) was performed in the same manner as the step of forming the first tungsten oxide particle dispersion of the photocatalyst (A-13) except that the following points were changed. rice field. Instead of 0.010% by mass of palladium with respect to the mass of tungsten primary oxide particles, 0.010% by mass of molybdenum trioxide (VI) (MоO _{3) with respect to the mass of tungsten primary oxide particles} , Kishida Chemical Co., Ltd.) was added. As a result, the first particle was obtained. The first particles include first tungsten oxide particles (specifically, tungsten trioxide particles) and first auxiliary catalyst particles (specifically, molybdenum trioxide particles) provided on the surface of the first tungsten oxide particles. Included.

[First particle dispersion forming step]
The first particle dispersion forming step of the photocatalyst (A-14) was carried out in the same manner as the first particle dispersion forming step of the photocatalyst (A-13).

(Second particle formation step)
The second particle forming step of the photocatalyst (A-14) was the same as the second particle forming step of the photocatalyst (A-13).

(Mixing process)
The mixing step of the photocatalyst (A-14) was carried out in the same manner as the mixing step of the photocatalyst (A-13). As a result, a photocatalyst (A-14) was obtained.

<Photocatalyst (B-11a)>
The photocatalyst (B-11a) was produced by the same method as that for the photocatalyst (A-14) except that the following points were changed. The second particle forming step and the mixing step were not carried out. The first particle dispersion obtained in the first particle dispersion forming step was dried to obtain a photocatalyst (B-11a).

<Photocatalyst (B-11b)>
The first tungsten oxide particle dispersion obtained in the step of forming the first tungsten oxide particle dispersion of the photocatalyst (A-14) before containing the cocatalyst particles was used as the second particle dispersion. The second particle dispersion was dried to obtain a photocatalyst (B-11b).

<Evaluation of photocatalytic activity: Photocatalyst (A-14) and (B-11a) to (B-11b)>
Photocatalysts (A-14) and (B-11a) to (B-11b) in the same manner as the photocatalytic activity evaluation of the photocatalysts (A-1) to (A-3) and (B-1a) to (B-1b). ) Photocatalytic activity was evaluated. Table 12 shows the carbon dioxide production rate (unit:%) and improvement rate (unit:%) of the photocatalysts (A-14) and (B-11a) to (B-11b) 4 hours after the start of irradiation of the blue LED. Shown in. Incidentally, in the calculation of the improvement ratio, by substituting the carbon dioxide production rate after 4 hours of photocatalyst _{R A} in formula (1) (A-14) , 4 hours after the photocatalyst (B-11a) to _{R B} The carbon dioxide production rate of was substituted.

The photocatalyst (A-15) shown below is a specific example of the second embodiment. Table 13 shows the material composition and photocatalytic activity evaluation results of the photocatalyst (A-15) and the photocatalysts (B-12a) and (B-12b) which are reference examples. Hereinafter, each photocatalyst will be described with reference to Table 13.

<Photocatalyst (A-15)>
A photocatalyst (A-15) was produced by the following method.

(First particle formation step)
As the first particle forming step, the forming step and the supporting step of the first tungsten oxide particle dispersion described in the second embodiment were performed.

[Step of forming first tungsten oxide particle dispersion]
The first tungsten oxide particles (tungsten trioxide manufactured by Nippon Shinkinzoku Co., Ltd.) were preheated at 900 ° C. in an air atmosphere. Preheated tungsten oxide particles and ion-exchanged water were charged into a bead mill so that the content of the tungsten oxide particles with respect to the mass of the tungsten oxide particle dispersion was 21.0% by mass. The tungsten oxide particles were dispersed in ion-exchanged water using a bead mill to obtain a tungsten oxide particle dispersion. Zirconia beads (0.1 mm in diameter) were used as the medium of the bead mill. The obtained first tungsten oxide particle dispersion was in the form of a slurry. _{The volume median diameter D 50} of the first tungsten oxide particles in the obtained tungsten oxide particle dispersion was 0.150 μm, and D ₉₀ was 0.230 μm. The peripheral speed and processing time of the bead mill were adjusted so that the first tungsten oxide particles having medium volume diameters D ₅₀ and D _{90 could be obtained.}

[Supporting process]
Hexachloroplatinic (IV) acid hexahydrate (manufactured by Tanaka Kikinzoku Kogyo Co., Ltd., platinum concentration) was added to the tungsten oxide particle dispersion so that platinum was 0.030% by mass with respect to the mass of the first tungsten oxide particles. 0.1 g / mL ± 5 wt%) was added and dispersed. As a result, a dispersion was obtained. The dispersion was heat-treated at 110 ° C. for 21 hours to obtain flakes. The flakes were crushed using a mixer to obtain a powder. The powder was heat treated at 400 ° C. As a result, the first particle was obtained. The first particles include first tungsten oxide particles (specifically, tungsten trioxide particles) and first auxiliary catalyst particles (specifically, platinum particles) provided on the surface of the first tungsten oxide particles. I was out.

(Second particle formation step)
As the second particle forming step, the forming step and the supporting step of the tungsten dioxide particle dispersion described in the second embodiment were performed.

[Step of forming a tungsten dioxide particle dispersion]
The tungsten oxide particle dispersion obtained in the step of forming the tungsten dioxide particle dispersion of the photocatalyst (A-15) was used as the tungsten dioxide particle dispersion of the photocatalyst (A-15).

[Supporting process]
The step of supporting the second particle of the photocatalyst (A-15) was carried out in the same manner as the step of supporting the first particle of the photocatalyst (A-15) except that the following points were changed. By changing the addition amount of the tungsten dioxide particle dispersion and the addition amount of hexachloroplatinic (IV) acid hexahydrate, the support rate of the second auxiliary catalyst of the second particles was increased from 0.030% by mass to 0.020% by mass. Changed to%. As a result, the second particle was obtained.

(Mixing process)
50.0 parts by mass of the first particles obtained in the supporting step of the first particle forming step, 50.0 parts by mass of the second particles obtained in the supporting step of the second particle forming step, and ion-exchanged water. It was put into a bead mill. Using a bead mill, the first particles and the second particles were dispersed in ion-exchanged water to obtain a slurry-like dispersion. The volume median diameter D ₅₀ of the first particles and mixed particles of the second particles contained in the obtained dispersion are shown in Table 13. The mixing particles of the first particle and the second particle of such volume median diameter D ₅₀ as obtained was adjusted peripheral speed and processing time of a bead mill. Then, the dispersion was dried to obtain a powder photocatalyst (A-15). In the photocatalyst (A-15), the content of the second particle with respect to the sum of the mass of the first particle and the mass of the second particle was 50.0% by mass.

<Photocatalyst (B-12a)>
The photocatalyst (B-12a) was produced by the same method as that for the photocatalyst (A-15) except that the following points were changed. The second particle forming step and the mixing step were not carried out. The first particles obtained in the step of supporting the first particles were used as a photocatalyst (B-12a).

<Photocatalyst (B-12b)>
The photocatalyst (B-12b) was produced by the same method as that for the photocatalyst (A-15) except that the following points were changed. The first particle forming step and the mixing step were not carried out. The second particle obtained in the step of supporting the second particle was used as a photocatalyst (B-12b).

<Evaluation of photocatalytic activity: Photocatalyst (A-15) and (B-12a) to (B-12b)>
Photocatalysts (A-15) and (B-12a) to (B-12b) in the same manner as the photocatalytic activity evaluation of the photocatalysts (A-1) to (A-3) and (B-1a) to (B-1b). ) Photocatalytic activity was evaluated. Table 13 shows the carbon dioxide production rate (unit:%) and improvement rate (unit:%) of the photocatalysts (A-15) and (B-12a) to (B-12b) 4 hours after the start of irradiation of the blue LED. Shown in. Incidentally, in the calculation of the improvement, of substituting carbon dioxide production rate after 1.5 hours of the photocatalyst (A-15) to _{R A} in formula (1), photocatalyst _{R B} (B-12a) 1 The carbon dioxide production rate after 5 hours was substituted.

The photocatalysts (A-16) to (A-18) shown below are specific examples of the third embodiment. Materials for photocatalysts (A-16) to (A-18), and reference examples of photocatalysts (B-13a), (B-15a), (B-13b), (B-14b) and (B-15b). The composition and the evaluation results of the photocatalytic activity are shown in Tables 14 to 16. Hereinafter, each photocatalyst will be described with reference to each table.

<Photocatalyst (A-16)>
A photocatalyst (A-16) was produced by the following method.

(First particle formation step)
As the first particle forming step, the first tungsten oxide particle dispersion forming step, the supporting step, and the first particle dispersion forming step described in the third embodiment were performed.

[Step of forming first tungsten oxide particle dispersion]
The step of forming the first tungsten oxide particle dispersion of the photocatalyst (A-16) was carried out in the same manner as the step of forming the first tungsten oxide particle dispersion of the photocatalyst (A-13).

[Supporting process]
Hexachloroplatinum (IV) acid hexahydrate (manufactured by Kishida Chemical Co., Ltd.) was added to the tungsten oxide particle dispersion so that platinum was 0.010% by mass with respect to the mass of the tungsten oxide particles. , Distributed. As a result, a dispersion was obtained. The dispersion was heat-treated at 110 ° C. for 21 hours to obtain flakes. The flakes were crushed using a mixer to obtain a powder. The powder was heat-treated at 400 ° C. under an atmosphere of an inert gas. As a result, the first particle was obtained. The first particles include first tungsten oxide particles and first auxiliary catalyst particles (specifically, platinum particles) provided on the surface of the first tungsten oxide particles (specifically, tungsten trioxide particles). I was out.

[First particle dispersion forming step]
The obtained first particles and ion-exchanged water were added to the mixer so that the content of the first particles with respect to the mass of the first particle dispersion was 10.0% by mass. Using a mixer, the first particles were dispersed in ion-exchanged water to obtain a slurry-like first particle dispersion. The volume median diameter D ₅₀ of the first particles contained in the first particle dispersion are shown in Table 14. Note that the first particles having such a volume median diameter D ₅₀ as obtained was adjusted peripheral speed and processing time of the mixer.

(Second particle formation step)
As the second particle forming step, the forming step, the supporting step, and the second particle dispersion forming step of the tungsten dioxide particle dispersion described in the third embodiment were performed.

[Step of forming a tungsten dioxide particle dispersion]
Tungsten dioxide particles (tungsten trioxide sold by Takagi Co., Ltd.) were preheated at 900 ° C. in an air atmosphere. Preheated tungsten dioxide particles and ion-exchanged water were charged into a bead mill so that the content of the tungsten dioxide particles with respect to the mass of the tungsten dioxide particle dispersion was 10.0% by mass. Tungsten dioxide particles were dispersed in ion-exchanged water using a bead mill to obtain a tungsten dioxide particle dispersion. Zirconia beads (0.1 mm in diameter) were used as the medium of the bead mill. The obtained tungsten dioxide particle dispersion was in the form of a slurry. _{The volume median diameter D 50} of the tungsten dioxide particles in the obtained tungsten dioxide particle dispersion was 0.150 μm, and D ₉₀ was 0.230 μm. The peripheral speed and processing time of the bead mill were adjusted so that the tungsten dioxide particles having medium volume diameters D ₅₀ and D _{90 could be obtained.}

[Supporting process]
Palladium (manufactured by Kishida Chemical Co., Ltd.) was added to and dispersed in the obtained tungsten dioxide particle dispersion so that palladium was 0.010% by mass with respect to the mass of the tungsten dioxide particles. As a result, a dispersion was obtained. The dispersion was heat-treated at 110 ° C. for 21 hours to obtain flakes. The flakes were crushed using a mixer to obtain a powder. The powder was heat-treated at 400 ° C. under an atmosphere of an inert gas. As a result, the second particle was obtained. The second particle contained a second tungsten dioxide particle (specifically, a tungsten trioxide particle) and a second auxiliary catalyst particle (specifically, a palladium particle) provided on the surface of the second tungsten dioxide particle. ..

[Second particle dispersion forming step]
The obtained second particles and ion-exchanged water were added to the mixer so that the content of the second particles with respect to the mass of the second particle dispersion was 20.0% by mass. Using a mixer, the second particles were dispersed in ion-exchanged water to obtain a slurry-like second particle dispersion. The volume median diameter D ₅₀ of the second particles contained in the second particle dispersion are shown in Table 14. Incidentally, the second particles of such volume median diameter D ₅₀ as obtained was adjusted peripheral speed and processing time of the mixer.

(Mixing process)
The mixing step of the photocatalyst (A-16) was carried out in the same manner as the mixing step of the photocatalyst (A-1). As a result, a photocatalyst (A-16) was obtained.

<Photocatalyst (B-13a)>
The photocatalyst (B-13a) was produced by the same method as that for the photocatalyst (A-16) except that the following points were changed. The second particle forming step and the mixing step were not carried out. The first particle dispersion obtained in the first particle dispersion forming step was dried to obtain a photocatalyst (B-13a).

<Photocatalyst (B-13b)>
The photocatalyst (B-13b) was produced in the same manner as the photocatalyst (A-16) except that the following points were changed. The first particle forming step and the mixing step were not carried out. The second particle dispersion obtained in the second particle dispersion forming step was dried to obtain a photocatalyst (B-13b).

<Evaluation of photocatalytic activity: Photocatalysts (A-16), (B-13a) and (B-13b)>
Photocatalysts (A-16), (B-13a) and (B-13b) in the same manner as the photocatalytic activity evaluation of the photocatalysts (A-1) to (A-3) and (B-1a) to (B-1b). ) Photocatalytic activity was evaluated. Table 14 shows the carbon dioxide production rate (unit:%) and improvement rate (unit:%) of the photocatalysts (A-16), (B-13a) and (B-13b) 4 hours after the start of irradiation of the blue LED. Shown in. Incidentally, in the calculation of the improvement ratio, by substituting the carbon dioxide production rate after 4 hours of photocatalyst _{R A} in formula (1) (A-16) , 4 hours after the photocatalyst (B-13a) to _{R B} The carbon dioxide production rate of was substituted.

<Photocatalyst (A-17)>
A photocatalyst (A-17) was produced by the following method.

(First particle formation step)
The first particle forming step of the photocatalyst (A-17) was carried out in the same manner as the first particle forming step of the photocatalyst (A-16).

(Second particle formation step)
As the second particle forming step, the forming step, the supporting step, and the second particle dispersion forming step of the tungsten dioxide particle dispersion described in the third embodiment were performed.

[Step of forming a tungsten dioxide particle dispersion]
The step of forming the tungsten dioxide particle dispersion of the photocatalyst (A-17) was carried out in the same manner as the step of forming the tungsten dioxide particle dispersion of the photocatalyst (A-16).

[Supporting process]
The step of supporting the second particle of the photocatalyst (A-17) was carried out in the same manner as the step of supporting the second particle of the photocatalyst (A-16) except that the following points were changed. Instead of 0.010% by mass of palladium with respect to the mass of tungsten dioxide particles, 0.010% by mass of molybdenum trioxide (VI) (MоO ₃ , xida) with respect to the mass of tungsten dioxide particles (Manufactured by Chemical Co., Ltd.) was added. As a result, the second particle was obtained. The second particles include tungsten dioxide particles (specifically, tungsten trioxide particles) and second auxiliary catalyst particles (specifically, molybdenum trioxide particles) provided on the surface of the tungsten dioxide particles. I was out.

[Second particle dispersion forming step]
The second particle dispersion forming step of the photocatalyst (A-17) was carried out in the same manner as the second particle dispersion forming step of the photocatalyst (A-16).

(Mixing process)
The mixing step of the photocatalyst (A-17) was carried out in the same manner as the mixing step of the photocatalyst (A-1). As a result, a photocatalyst (A-17) was obtained.

<Photocatalyst (B-14b)>
The photocatalyst (B-14b) was produced by the same method as that for the photocatalyst (A-17) except that the following points were changed. The first particle forming step and the mixing step were not carried out. The second particle dispersion obtained in the second particle dispersion forming step was dried to obtain a photocatalyst (B-14b).

<Evaluation of photocatalytic activity: photocatalysts (A-17), (B-13a) and (B-14b)>
Photocatalysts (A-17), (B-13a) and (B-14b) in the same manner as the photocatalytic activity evaluation of photocatalysts (A-1) to (A-3) and (B-1a) to (B-1b). ) Photocatalytic activity was evaluated. Table 15 shows the carbon dioxide production rate (unit:%) and improvement rate (unit:%) of the photocatalysts (A-17), (B-13a) and (B-14b) 4 hours after the start of irradiation of the blue LED. Shown in. The photocatalyst (B-13a) has already been shown in Table 14, but is shown again in Table 15 for reference. Incidentally, in the calculation of the improvement ratio, by substituting the carbon dioxide production rate after 4 hours of photocatalyst _{R A} in formula (1) (A-17) , 4 hours after the photocatalyst (B-13a) to _{R B} The carbon dioxide production rate of was substituted.

<Photocatalyst (A-18)>
A photocatalyst (A-18) was produced by the following method.

(First particle formation step)
The first particle forming step of the photocatalyst (A-18) was carried out in the same manner as the first particle forming step of the photocatalyst (A-16) except that the following points were changed. In the step of carrying the first particles of the photocatalyst (A-16), the heat treatment at 400 ° C. was performed in an inert gas atmosphere, but in the step of carrying the first particles of the photocatalyst (A-18), the heat treatment at 400 ° C. was performed. I went in the air atmosphere.

(Second particle formation step)
As the second particle forming step, the forming step, the supporting step, and the second particle dispersion forming step of the tungsten dioxide particle dispersion described in the third embodiment were performed.

[Step of forming a tungsten dioxide particle dispersion]
The step of forming the tungsten dioxide particle dispersion of the photocatalyst (A-18) was carried out in the same manner as the step of forming the tungsten dioxide particle dispersion of the photocatalyst (A-16).

[Supporting process]
The step of supporting the second particle of the photocatalyst (A-18) was carried out in the same manner as the step of supporting the second particle of the photocatalyst (A-16) except that the following points were changed. Instead of 0.010% by mass of palladium with respect to the mass of the tungsten primary oxide particles, 0.010% by mass of ruthenium oxide (IV) (RuO ₂ ) with respect to the mass of the tungsten primary oxide particles. Kishida Chemical Co., Ltd.) was added. Further, in the step of carrying the second particles of the photocatalyst (A-16), the heat treatment at 400 ° C. was performed in an inert gas atmosphere, but in the step of carrying the second particles of the photocatalyst (A-18), the heat treatment was performed at 400 ° C. The treatment was performed in an air atmosphere. As a result, a second particle was obtained. The second particles include tungsten dioxide particles (specifically, tungsten trioxide particles) and second auxiliary catalyst particles (specifically, ruthenium (IV) oxide particles) provided on the surface of the tungsten dioxide particles. Included.

[Second particle dispersion forming step]
The second particle dispersion forming step of the photocatalyst (A-18) was carried out in the same manner as the second particle dispersion forming step of the photocatalyst (A-16).

(Mixing process)
The mixing step of the photocatalyst (A-18) was carried out in the same manner as the mixing step of the photocatalyst (A-1). As a result, a photocatalyst (A-18) was obtained.

<Photocatalyst (B-15a)>
The photocatalyst (B-15a) was produced in the same manner as the photocatalyst (A-18) except that the following points were changed. The second particle forming step and the mixing step were not carried out. The first particle dispersion obtained in the first particle dispersion forming step was dried to obtain a photocatalyst (B-15a).

<Photocatalyst (B-15b)>
The photocatalyst (B-15b) was produced in the same manner as the photocatalyst (A-18) except that the following points were changed. The first particle forming step and the mixing step were not carried out. The second particle dispersion obtained in the second particle dispersion forming step was dried to obtain a photocatalyst (B-15b).

<Evaluation of photocatalytic activity: photocatalysts (A-18), (B-15a) and (B-15b)>
Photocatalysts (A-18), (B-15a) and (B-15b) in the same manner as the photocatalytic activity evaluation of photocatalysts (A-1) to (A-3) and (B-1a) to (B-1b). ) Photocatalytic activity was evaluated. Table 16 shows the carbon dioxide production rate (unit:%) and improvement rate (unit:%) of the photocatalysts (A-18), (B-15a) and (B-15b) 4 hours after the start of irradiation of the blue LED. Shown in. Incidentally, in the calculation of the improvement ratio, by substituting the carbon dioxide production rate after 4 hours of photocatalyst _{R A} in formula (1) (A-18) , 4 hours after the photocatalyst (B-15a) to _{R B} The carbon dioxide production rate of was substituted.

Each of the photocatalysts (A-1) to (A-18) contained a plurality of first particles and a plurality of second particles. The first particles contained at least the first tungsten oxide particles. The second particles contained at least tungsten dioxide particles. The activity of the second particle was lower than that of the first particle. Specifically, the carbon dioxide production rate of the photocatalyst of only the second particle (see, for example, the photocatalyst (B-1b) in Table 2) is the carbon dioxide production rate of the photocatalyst of only the first particle (for example, the photocatalyst of Table 2). It was lower than (see (B-1a)). Therefore, as is clear from Tables 1 to 16, the improvement rate of the photocatalytic activity was 2.9% or more in each of the photocatalysts (A-1) to (A-18), and the photocatalytic activity was improved. ..

Since each of the photocatalysts (A-1) to (A-14) contains second particles having no cocatalyst particles, the content of the cocatalyst with respect to the total mass of the photocatalyst was reduced. Since the photocatalyst (A-15) contains the second particles having a second auxiliary catalyst loading ratio lower than that of the first auxiliary catalyst loading ratio, the content of the cocatalyst with respect to the total mass of the photocatalyst is reduced. Nevertheless, the photocatalytic activity was improved in each of the photocatalysts (A-1) to (A-15).

Each of the photocatalysts (A-1) to (A-14) contained second particles without co-catalyst particles, and the volume median diameter of the first particles was 0.337 μm or less. Therefore, in each of the photocatalysts (A-1) to (A-14), the improvement rate of the photocatalytic activity was 2.9% or more, and the photocatalytic activity was improved.

Each of the photocatalysts (A-1), (A-4), (A-5) and (A-10) contained second particles without co-catalyst particles. The co-catalyst particles included in the first particles were platinum particles. The volume median diameter of the first particle was 0.245 μm or less. The content of the second particle with respect to the sum of the mass of the first particle and the mass of the second particle was 2.0% by mass or more and 9.0% by mass or less. Therefore, in each of the photocatalysts (A-1), (A-4), (A-5) and (A-10), the improvement rate of the photocatalytic activity is 44.7% or more, and the photocatalytic activity is particularly excellent. rice field.

The photocatalyst (A-9) contained second particles without co-catalyst particles. The co-catalyst particles included in the first particles were platinum particles. The volume median diameter of the first particle was 0.310 μm or more and 0.500 μm or less. The content of the second particle with respect to the sum of the mass of the first particle and the mass of the second particle was 2.0% by mass or more and 9.0% by mass or less. Therefore, in the photocatalyst (A-9), the improvement rate of the photocatalytic activity was 56.8%, and the photocatalytic activity was particularly excellent.

Each of the photocatalysts (A-1) to (A-3), (A-4) and (A-10) contains second particles without co-catalyst particles, and the volume median diameter of the first particles is 0. It was .178 μm or less. Therefore, each of the photocatalysts (A-1) to (A-3), (A-4) and (A-10) had a carbon dioxide production rate of 113.9% or more, and the photocatalytic activity was particularly excellent. ..

From the above, it was shown that the photocatalyst according to the present invention has excellent photocatalytic activity. Further, it was shown that according to the method for producing a photocatalyst according to the present invention, a photocatalyst excellent in a photoactive catalyst can be produced.

The photocatalyst according to the present invention can be used for visible light responsive photocatalytic functional products such as building materials, interior materials for automobiles, home appliances and textile products.

1,41 First particle 2, 22, 32 Second particle 3 Tungsten trioxide particle 4 Auxiliary catalyst particle (first auxiliary catalyst particle)
5 Tungsten dioxide particles 26, 36 Second auxiliary catalyst particles 10, 20, 30, 40 Photocatalyst

Claims (9)

Contains a plurality of first particles and a plurality of second particles,
The first particles contain at least the first tungsten oxide particles and contain at least the first tungsten oxide particles.
The second particles contain at least tungsten dioxide particles and
The first particles further include one or more co-catalyst particles provided on the surface of the first tungsten oxide particles.
The second particle is a photocatalyst that does not contain the co-catalyst particles. The photocatalyst according to claim 1, wherein the content of the second particle with respect to the sum of the mass of the first particle and the mass of the second particle is more than 0.0% by mass and 50.0% by mass or less. The photocatalyst according to claim 1, wherein the content of the co-catalyst particles with respect to the mass of the first tungsten oxide particles is more than 0.000% by mass and 0.250% by mass or less. The photocatalyst according to any one of claims 1 to 3, wherein the content of the co-catalyst particles with respect to the mass of the first tungsten oxide particles is more than 0.000% by mass and less than 0.030% by mass. The photocatalyst according to any one of claims 1 to 4, wherein the co-catalyst particles include platinum particles, palladium particles, molybdenum particles, ruthenium particles, or particles of oxides thereof. The photocatalyst according to any one of claims 1 to 5, wherein the volume median diameter of the first particle is 0.337 μm or less. The first particle forming step of forming a plurality of first particles, and
A support step of supporting one or more co-catalyst particles on the surface of the first particles, and
A second particle forming step of forming a plurality of second particles,
Including a mixing step of mixing the plurality of the first particles and the plurality of the second particles.
The first particles contain at least the first tungsten oxide particles and contain at least the first tungsten oxide particles.
The second particles contain at least tungsten dioxide particles and
The second particle is a method for producing a photocatalyst, which does not contain the co-catalyst particles. The first particle forming step includes a first particle dispersion forming step of forming a first particle dispersion containing the first particle.
The second particle forming step includes a second particle dispersion forming step of forming a second particle dispersion containing the second particle, and in the mixing step, the first particle dispersion and the second particle dispersion. The method for producing a photocatalyst according to claim 7 , wherein is mixed with. In the first particle dispersion forming step, the first particles are dispersed in a dispersion medium until the volume median diameter of the first particles becomes 0.337 μm or less to form the first particle dispersion. Item 8. The method for producing a photocatalyst according to Item 8.

Images