Visible light-responsive photocatalyst

Abstract

To provide a visible light-responsive photocatalyst having high photocatalytic activity.SOLUTION: A visible light-responsive photocatalyst of the present invention comprises at least one tungsten oxide particle and at least one cocatalyst particle carried on a surface of the tungsten oxide particle. Out of a plurality (100 or more) of cocatalyst particles whose primary particle diameter can be measured on an electron microscope image of the visible light-responsive photocatalyst, 20% or more of cocatalyst particles are non-aggregate, and have a primary particle diameter of 6 nm or more and 20 nm or less.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a visible light-responsive photocatalyst.

Background Art

[0002] A photocatalyst in which platinum particles (Pt particles) are supported on tungsten oxide particles is known (see, for example, Patent Document 1). In this photocatalyst, aggregates of a plurality of platinum particles having a primary particle diameter of about 5 nm are attached to the surface of the tungsten oxide particles.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the conventional photocatalyst, since aggregates of platinum particles are attached to the surface of tungsten oxide particles, the effect of separating photoexcited electrons and holes by the cocatalyst in the tungsten oxide particles becomes small, and the photocatalytic activity may be low. The present invention has been made in view of such circumstances, and provides a visible light-responsive photocatalyst having high photocatalytic activity.

Means for Solving the Problems

[0005] The present invention provides a visible light-responsive photocatalyst including at least one tungsten oxide particle and at least one cocatalyst particle supported on the surface of the tungsten oxide particle, wherein 20% or more of a plurality of 100 or more cocatalyst particles whose primary particle diameter can be measured in the electron microscope image of the visible light-responsive photocatalyst are non-aggregates, and have a primary particle diameter of 6 nm or more and 20 nm or less. The present invention also provides a visible light-responsive photocatalyst, characterized in that the average primary particle diameter of a plurality of cocatalyst particles, which are non-aggregated particles whose primary particle diameter can be measured from an electron microscope image of the visible light-responsive photocatalyst, is 6 nm or more and 20 nm or less. The present invention also provides a visible light-responsive photocatalyst, in which among 100 or more tungsten oxide particles from which the aspect ratio (the ratio of the major axis b to the minor axis a of the primary particle (b / a)) can be calculated from an electron microscope image of the visible light-responsive photocatalyst, 50% or more of the tungsten oxide particles have an aspect ratio of 1.3 or more and 10 or less.

Advantages of the Invention

[0006] The visible light-responsive photocatalyst of the present invention has high photocatalytic activity.

Brief Description of the Drawings

[0007]

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Mode for Carrying Out the Invention

[0008] First Embodiment The visible light-responsive photocatalyst of the present embodiment is a visible light-responsive photocatalyst comprising at least one tungsten oxide particle and at least one cocatalyst particle supported on the surface of the tungsten oxide particle, wherein 20% or more of a plurality of cocatalyst particles, of which the primary particle diameter can be measured in the electron microscope image of the visible light-responsive photocatalyst, are non-aggregates, and have a primary particle diameter of 6 nm or more and 20 nm or less, or the average primary particle diameter of a plurality of non-aggregate cocatalyst particles, of which the primary particle diameter can be measured in the electron microscope image of the visible light-responsive photocatalyst, is 6 nm or more and 20 nm or less. In the present specification, a primary particle is the smallest unit particle whose particle diameter can be measured in an electron microscope image. A secondary particle is an aggregate of a plurality of primary particles. A primary particle may be a particle that does not constitute a secondary particle. Further, in the present specification, a non-aggregate means that the smallest unit particles whose shape can be measured in an electron microscope image are dispersed to such an extent that they have no contact with other particles or have little contact and do not form agglomerates.

[0009] A visible light-responsive photocatalyst is a photocatalyst that generates photocatalytic activity by receiving visible light, and comprises a plurality of tungsten oxide particles and a plurality of cocatalyst particles supported on the surface of the tungsten oxide particles. The visible light-responsive photocatalyst may be in powder form, may be dispersed in a dispersion medium, or may be contained in a photocatalyst layer. For example, it may be processed so as to ensure air permeability with glass fiber and then filtered, and the photocatalyst may be supported on the filter to form a photocatalyst filter having a photocatalyst layer.

[0010] The tungsten oxide particles are tungsten trioxide (WO3 ) particles. Tungsten oxide may have a composition deviated from the stoichiometric composition as long as it has photocatalytic activity. Also, the tungsten oxide content of the photocatalyst may be 90 wt% or more.

[0011] Among 100 or more plural tungsten oxide particles whose primary particle diameters can be measured from the electron microscope image of the visible light-responsive photocatalyst, 90% or more of the tungsten oxide particles can have a primary particle diameter of 5 nm or more and 400 nm or less. The electron microscope image is, for example, an SEM (scanning electron microscope) image, a TEM (transmission electron microscope) image, a STEM (scanning transmission electron microscope) image, an elemental mapping image by electron microscope energy dispersive X-ray spectroscopy (SEM-EDX, TEM-EDX, etc.) (the same applies to the electron microscope images described later). The primary particle diameter of the tungsten oxide particles may be measured using image analysis software, or the primary particle diameter may be measured using the scale bar of the image. When the tungsten oxide particles have a major axis and a minor axis, the primary particle diameter of the tungsten oxide particles can be the major axis of the particles. Also, the "100 or more plural tungsten oxide particles" are particles randomly selected from particles whose primary particle diameters can be measured in a plurality of electron microscope images and the entire outer periphery of the particles can be observed.

[0012] Among 100 or more plural tungsten oxide particles whose aspect ratio (the ratio of the major axis b to the minor axis a of the primary particle (b / a)) can be calculated from the electron microscope image of the visible light-responsive photocatalyst, 50% or more of the tungsten oxide particles can have an aspect ratio of 1.3 or more and 10 or less. The aspect ratio of the tungsten oxide particles may be measured and calculated using image analysis software, or may be calculated from the primary particle diameters (major axis and minor axis) measured using the scale bar of the image. Also, the "100 or more plural tungsten oxide particles" are particles randomly selected from particles for which the aspect ratio of a plurality of electron microscope images can be calculated or all particles.

[0013] Among 100 or more tungsten oxide particles from which the circularity can be calculated from the electron microscope image of the visible light-responsive photocatalyst, 70% or more of the tungsten oxide particles may have a circularity of 0.2 or more and 0.8 or less. The circularity of the tungsten oxide particles may be measured and calculated using image analysis software, or may be measured and calculated using the scale bar of the image. Further, the "100 or more tungsten oxide particles" are particles randomly selected from particles for which the circularity of a plurality of electron microscope images can be measured and the entire outer periphery of the particles can be observed, or all the particles. The circularity is a value representing roundness, and the closer it is to 1, the closer it is to a circle. The circularity is calculated using the formula: circularity = 4π × (area) ÷ (perimeter length). 2 It can be calculated using

[0014] The co-catalyst particles are particles supported on the surface of the tungsten oxide particles. Specifically, they are metal particles containing platinum, metal oxide particles containing platinum, metal particles containing at least one of gold, silver, ruthenium, rhodium, iridium, and palladium, metal oxide particles containing at least one of gold, silver, ruthenium, rhodium, iridium, and palladium, and the like. In the visible light-responsive photocatalyst, the mass ratio of the plurality of co-catalyst particles to the plurality of tungsten oxide particles is preferably 0.01 wt% or more and 2.0 wt% or less.

[0015] Among 100 or more co-catalyst particles from which the primary particle diameter can be measured in the electron microscope image of the visible light-responsive photocatalyst, 20% or more of the co-catalyst particles are non-aggregates and have a primary particle diameter of 6 nm or more and 20 nm or less. The primary particle diameter of the co-catalyst particles may be measured using image analysis software, or may be measured using the scale bar of the image. When the co-catalyst particles have a major axis and a minor axis, the primary particle diameter of the co-catalyst particles can be the major axis of the particles. Further, the "100 or more co-catalyst particles" are particles randomly selected from particles for which the primary particle diameter of a plurality of electron microscope images can be measured and the entire outer periphery of the particles can be observed, or all the particles.

[0016] In the electron microscope image of the visible light-responsive photocatalyst, it is preferable that 50% or more of a plurality of 10 or more, preferably 100 or more, cocatalyst particles, the primary particle diameter of which can be measured, are not in contact with other cocatalyst particles. Whether the cocatalyst particles are in contact with other cocatalyst particles can be confirmed from the electron microscope image. Further, the "plurality of 10 or more cocatalyst particles" or "plurality of 100 or more cocatalyst particles" are particles randomly selected from particles that can determine whether they are in contact with other cocatalyst particles in a plurality of electron microscope images. This particle may be a primary particle.

[0017] Second Embodiment The visible light-responsive photocatalyst of the present embodiment includes tungsten oxide particles and a plurality of cocatalyst particles supported on the surface of the tungsten oxide particles. Among 100 or more tungsten oxide particles, the primary particle diameter of which can be calculated from the electron microscope image of the visible light-responsive photocatalyst, 50% or more of the tungsten oxide particles have an aspect ratio (the ratio of the major axis b to the minor axis a of the primary particle (b / a)) of 1.3 or more and 10 or less. Further, it is preferable that the circularity of 70% or more of 100 or more tungsten oxide particles, the circularity of which can be calculated from the electron microscope image of the visible light-responsive photocatalyst, is 0.2 or more and 0.8 or less. Since the visible light-responsive photocatalyst, tungsten oxide particles, cocatalyst particles, aspect ratio, circularity, etc. have been described in the first embodiment, they are omitted here.

[0018] Preparation of Photocatalyst for Example 1 (Grinding process) Using a bead mill (media agitation type wet ultrafine grinding and dispersing machine "MS C50" manufactured by Nippon Coke & Engineering Co., Ltd.), tungsten oxide powder (specifically WO 3 , manufactured by Kinoshita Chemical Co., Ltd.) was dispersed in ion-exchanged water to primarily grind the tungsten oxide particles to obtain a dispersion of tungsten oxide.

[0019] (Cocatalyst loading process) A dispersion of tungsten oxide was dissolved with hexachloroplatinum(VI) hexahydrate (manufactured by Kishida Chemical Co., Ltd., solid content concentration: 98.5%). The addition amount of hexachloroplatinum(VI) hexahydrate was an amount such that the content rate of elemental platinum was 0.1% by mass with respect to the mass of the prepared tungsten oxide particles (W-A). Next, the dispersion was heated at 100 °C to evaporate the water. Thereby, a lump of tungsten oxide carrying platinum was obtained.

[0020] Preparation of Photocatalyst for Example 2 Ultrasonic irradiation was performed on a dispersion obtained by dispersing tungsten oxide powder (specifically WO 3 , manufactured by Kishida Chemical Co., Ltd.) in water. This dispersion was centrifuged using a centrifuge for 10 minutes (1000 rpm), and particles with a large particle diameter were sedimented and separated and removed from the dispersion. The obtained dispersion was dried to obtain tungsten oxide powder. This tungsten oxide powder was dispersed in water, and an aqueous solution of hexachloroplatinic acid was added to 40 mL of the prepared tungsten oxide dispersion so that Pt was 0.1 part by mass with respect to 100 parts by mass of the tungsten oxide particles. Further, 5 mL of isopropyl alcohol was added to this dispersion. While stirring the dispersion after the addition, visible light was irradiated to the dispersion for 24 hours. A blue LED was used as the light source. Thereafter, the dispersion was dried at 80 °C to obtain a powdered Pt-supported tungsten oxide photocatalyst.

[0021] Preparation of Photocatalyst for Example 3 (Grinding process) Using a bead mill (media stirring type wet ultrafine grinding and dispersing machine "MS C50" manufactured by Nippon Coke & Engineering Co., Ltd.), tungsten oxide powder (specifically WO 3 , manufactured by Kishida Chemical Co., Ltd.) was dispersed in ion-exchanged water to perform primary grinding of the tungsten oxide particles to obtain a dispersion of tungsten oxide.

[0022] (Promoter supporting process) An aqueous solution of hexachloroplatinic acid was added to 40 mL of a tungsten oxide dispersion prepared in the grinding step so that the amount of Pt was 0.1 part by mass with respect to 100 parts by mass of tungsten oxide particles, and further, 5 mL of isopropyl alcohol was added to this dispersion. The dispersion after the addition was irradiated with visible light for 24 hours while stirring. A blue LED was used as the light source. Thereafter, a powdered Pt-supported tungsten oxide photocatalyst was obtained by drying at 80°C.

[0023] Preparation of Photocatalyst for Comparative Example 1 Tungsten oxide powder (specifically, WO 3 , manufactured by Kishida Chemical Co., Ltd.) was dispersed in water, and the dispersion was irradiated with ultrasonic waves. This dispersion was centrifuged for 10 minutes using a centrifuge (1000 rpm), and particles with a large particle diameter were sedimented and separated and removed from the dispersion. The obtained dispersion was dried to obtain tungsten oxide powder. Hexachloroplatinum(VI) hexahydrate (manufactured by Kishida Chemical Co., Ltd., solid content concentration: 98.5%) was dissolved in a dispersion obtained by dispersing this tungsten oxide powder in water. The addition amount of hexachloroplatinum(VI) hexahydrate was such that the content rate of elemental platinum was 0.1% by mass with respect to the mass of the tungsten oxide particles (W-A) to be prepared. Next, the dispersion was heated at 100°C to evaporate the water. Thereby, a lump of tungsten oxide supporting platinum was obtained.

[0024] Electron Microscopic Observation of Photocatalyst for Example 1 The photocatalyst of Example 1 was observed with a scanning electron microscope (SEM). After observing the photocatalyst with SEM, the minor axis a, major axis b, aspect ratio (b / a), perimeter, area, and circularity of the tungsten oxide particles were measured and calculated using the image analysis application "A Image-kun". In addition, the photocatalyst of Example 1 was observed with a scanning transmission electron microscope (STEM), and the primary particle diameter of the Pt particles was measured from the photographed image.

[0025] Figs. 1(a) and 1(b) are STEM images of the photocatalyst of Example 1, and Fig. 1(c) is a table showing the primary particle diameters of seven Pt particles whose primary particle diameters can be measured in the images of Figs. 1(a) and 1(b). As can be seen from Fig. 1, in the photocatalyst of Example 1, a plurality of Pt particles having a primary particle diameter of 4 nm or less aggregate and adhere to the surface of tungsten oxide particles (as secondary particles).

[0026] Figs. 2(a) and 2(b) are SEM images of the photocatalyst of Example 1. Further, Fig. 3 is a table showing the minor axis a (minimum width), major axis b (maximum length), aspect ratio (b / a), perimeter, area, and circularity of ten tungsten oxide particles whose primary particle diameters can be measured in the images of Figs. 2(a) and 2(b). As shown in the table of Fig. 3, 60% of the ten tungsten oxide particles had an aspect ratio of 1.3 or more.

[0027] The circularity is a value representing roundness, and the closer it is to 1, the closer it is to a circle. The circularity can be calculated using the formula: circularity = 4π × (area) ÷ (perimeter). 2 As shown in the table of Fig. 3, the circularities of the ten tungsten oxide particles in the images of Figs. 2(a) and 2(b) were in the range of 0.2 to 0.8.

[0028] Acetaldehyde Gas Decomposition Experiment Using Photocatalyst of Example 1 An acetaldehyde gas decomposition experiment was conducted using the photocatalyst of Example 1 to evaluate the photocatalytic activity. Specifically, as the photocatalytic activity, the decomposition activity of acetaldehyde (C 2 H 4 O) caused by the photocatalyst irradiated with visible light was evaluated. Specifically, a petri dish (diameter 60 mm) was filled with an amount of the composition such that the mass of the photocatalyst contained in the composition was 0.05 g, and the composition was dried at 80°C for 30 minutes. In this way, the water in the composition was evaporated. A petri dish containing the dried composition was placed in a transparent gas bag with a volume of 5 L. The gas bag was filled with acetaldehyde gas (air-diluted) at a concentration of 600 ppm.

[0029] Next, light (center wavelength: 450 nm, illuminance: 4500 lux) was irradiated onto the composition in the gas bag. The concentration of acetaldehyde in the gas bag was measured before the light irradiation (0.0 hours), and 2 hours and 4 hours after the start of the light irradiation. For the measurement of the acetaldehyde concentration, a gas detector tube for acetaldehyde ("92" manufactured by Gastec Corporation) was used. The gas decomposition rate was calculated using the following formula. Formula: Gas decomposition rate = (LN value of the measured value of C 2 H 4 O concentration at 2 hours - LN value of the measured value of C 2 H 4 O concentration at 4 hours) ÷ 2 The higher the photocatalytic activity, the greater this gas decomposition rate. Note that when the concentration becomes 0, the LN value cannot be calculated, so the gas decomposition rate was calculated assuming 0.2 ppm, which is the minimum detection amount of the detector tube used.

[0030] Figure 4(a) is a graph showing the change in the residual rate (%) of acetaldehyde in the acetaldehyde gas decomposition experiment conducted using the photocatalyst of Example 1. Figure 4(b) shows a table of the acetaldehyde concentration measured in this acetaldehyde gas decomposition experiment and the gas decomposition rate calculated using the above formula.

[0031] In this experiment, as shown in Figure 4(b), the acetaldehyde gas concentration after 4 hours of light irradiation was 195 ppm and the gas decomposition rate was 0.33. Therefore, it was found that the photocatalyst of Example 1 has excellent photocatalytic activity.

[0032] Electron Microscopic Observation of Photocatalyst for Example 2 The photocatalyst of Example 2 was observed with a scanning electron microscope (SEM). After observing the photocatalyst with SEM, the minor axis a, major axis b, aspect ratio (b / a), perimeter, area, and circularity of tungsten oxide particles were measured and calculated using the image analysis application "A-Image-kun". In addition, the photocatalyst of Example 2 was observed with a scanning transmission electron microscope (STEM), and the primary particle diameter of Pt particles was measured from the photographed image.

[0033] Figure 5(a) is a STEM image of the photocatalyst of Example 2, and Figure 5(b) is a table showing the primary particle diameters of eight Pt particles for which the primary particle diameter could be measured in the image of Figure 5(a). In the image of Figure 5(a), the primary particle diameters of all eight Pt particles attached to the tungsten oxide particles were 7 nm or more. Also, each Pt particle does not seem to be in contact with other Pt particles.

[0034] Figures 6(a) and (b) are SEM images of the photocatalyst of Example 2. Also, Figure 7 is a table showing the minor axis a (minimum width), major axis b (maximum length), aspect ratio (b / a), perimeter, area, and circularity of ten tungsten oxide particles for which the primary particle diameter could be measured in the images of Figures 6(a) and (b). In this image, as shown in the table of Figure 7, 70% of the ten tungsten oxide particles had an aspect ratio of 1.3 or less, and 70% of the tungsten oxide particles had a circularity greater than 0.8.

[0035] Acetaldehyde Gas Decomposition Experiment Using Photocatalyst of Example 2 An acetaldehyde gas decomposition experiment was conducted using the photocatalyst of Example 2, and the photocatalytic activity was evaluated. The experimental method and the method for calculating the gas decomposition rate were the same as those of the acetaldehyde gas decomposition experiment using the photocatalyst of Example 1.

[0036] Figure 8(a) is a graph showing the change in the acetaldehyde residual rate (%) in the acetaldehyde gas decomposition experiment conducted using the photocatalyst of Example 2, and Figure 8(b) shows a table of the acetaldehyde concentration measured in this acetaldehyde gas decomposition experiment and the gas decomposition rate calculated using the above formula. In this experiment, as shown in Figure 8(b), the acetaldehyde gas concentration after 4 hours of light irradiation was 14 ppm, and the gas decomposition rate was 1.25. Therefore, it was found that the photocatalyst of Example 2 has excellent photocatalytic activity.

[0037] Electron Microscopic Observation of Photocatalyst for Example 3 The photocatalyst of Example 3 was observed with a scanning electron microscope (SEM). After observing the photocatalyst with SEM, the minor axis a, major axis b, aspect ratio (b / a), perimeter, area, and circularity of tungsten oxide particles were measured and calculated using the image analysis application "A Image-kun". In addition, the photocatalyst of Example 3 was observed with a scanning transmission electron microscope (STEM), and the primary particle size of Pt particles was measured from the captured images.

[0038] Figure 9(a) is a STEM image of the photocatalyst of Example 3, and Figure 9(b) is a table showing the primary particle sizes of 11 Pt particles for which the primary particle size could be measured in the image of Figure 9(a). In the image of Figure 9(a), the primary particle sizes of 6 out of 11 (54%) Pt particles attached to tungsten oxide particles were 6 nm or more. Also, each Pt particle does not seem to be in contact with other Pt particles.

[0039] Figures 10(a) and (b) are SEM images of the photocatalyst of Example 3. Also, Figure 11 is a table showing the minor axis a (minimum width), major axis b (maximum length), aspect ratio (b / a), perimeter, area, and circularity of 10 tungsten oxide particles for which the primary particle size could be measured in the images of Figures 10(a) and (b). In this image, as shown in the table of Figure 11, 60% of the 10 tungsten oxide particles had an aspect ratio of 1.5 or more, and all 10 tungsten oxide particles had a circularity of 0.2 or more and 0.8 or less.

[0040] Acetaldehyde Gas Decomposition Experiment Using Photocatalyst of Example 3 An acetaldehyde gas decomposition experiment was performed using the photocatalyst of Example 3 to evaluate the photocatalytic activity. The experimental method and the method for calculating the gas decomposition rate are the same as those in the acetaldehyde gas decomposition experiment using the photocatalyst of Example 1.

[0041] Fig. 12(a) is a graph showing the change in the residual rate (%) of acetaldehyde in the acetaldehyde gas decomposition experiment conducted using the photocatalyst of Example 3, and Fig. 12(b) shows the table of the acetaldehyde concentration measured in this acetaldehyde gas decomposition experiment and the gas decomposition rate calculated using the above formula. In this experiment, as shown in Fig. 12(b), the acetaldehyde gas concentration after 4 hours of light irradiation was 0 ppm and the gas decomposition rate was 3.11. Therefore, it was found that the photocatalyst of Example 3 has excellent photocatalytic activity.

[0042] Electron Microscopic Observation of Photocatalyst for Comparative Example 1 The photocatalyst of Comparative Example 1 was observed with a scanning electron microscope (SEM). After observing the photocatalyst with SEM, the minor axis a, major axis b, aspect ratio (b / a), perimeter, area, and circularity of tungsten oxide particles were measured and calculated using the image analysis application "A-Image-kun". In addition, the photocatalyst of Comparative Example 1 was observed with a scanning transmission electron microscope (STEM), and the primary particle diameter of Pt particles was measured from the photographed image.

[0043] Fig. 13(a) is a STEM image of the photocatalyst of Comparative Example 1, and Fig. 13(b) is a table showing the primary particle diameters of 5 Pt particles for which the primary particle diameter can be measured in the image of Fig. 13(a). As can be seen from Fig. 13, in the photocatalyst of Comparative Example 1, a plurality of Pt particles having a primary particle diameter of 3 nm or less are aggregated and attached to the surface of tungsten oxide particles (as secondary particles).

[0044] Figs. 14(a) and (b) are SEM images of the photocatalyst of Comparative Example 1. Fig. 15 is a table showing the minor axis a (minimum width), major axis b (maximum length), aspect ratio (b / a), perimeter, area, and circularity of 8 tungsten oxide particles for which the primary particle diameter can be measured in the images of Figs. 14(a) and (b). In this image, as shown in the table of Fig. 15, all 8 tungsten oxide particles had an aspect ratio of less than 1.3, and 50% of the tungsten oxide particles had a circularity of greater than 0.8.

[0045] Acetaldehyde Gas Decomposition Experiment Using Photocatalyst of Comparative Example 1 An acetaldehyde gas decomposition experiment was conducted using the photocatalyst of Comparative Example 1, and the photocatalytic activity was evaluated. The experimental method and the calculation method of the gas decomposition rate were the same as those of the acetaldehyde gas decomposition experiment using the photocatalyst of Example 1.

[0046] Fig. 16(a) is a graph showing the change in the residual rate (%) of acetaldehyde in the acetaldehyde gas decomposition experiment conducted using the photocatalyst of Comparative Example 1, and Fig. 16(b) shows the table of the acetaldehyde concentration measured in this acetaldehyde gas decomposition experiment and the gas decomposition rate calculated using the above formula. In this experiment, as shown in Fig. 16(b), the acetaldehyde gas concentration after 4 hours of light irradiation was 260 ppm, and the gas decomposition rate was 0.18.

Claims

1. A visible light responsive photocatalyst comprising at least one tungsten oxide particle and at least one promoter particle supported on a surface of the tungsten oxide particle, A visible light responsive photocatalyst, characterized in that 20% or more of a plurality of promoter particles, of which 100 or more promoter particles have a measurable primary particle diameter in an electron microscope image of the visible light responsive photocatalyst, are non-aggregates and have a primary particle diameter of 6 nm or more and 20 nm or less.

2. A visible light responsive photocatalyst comprising tungsten oxide particles and a plurality of co-catalyst particles supported on the surfaces of the tungsten oxide particles, A visible light responsive photocatalyst, characterized in that the average primary particle diameter of a plurality of non-aggregated cocatalyst particles, the primary particle diameter of which can be measured in an electron microscope image of the visible light responsive photocatalyst, is 6 nm or more and 20 nm or less.

3. 2. The visible light responsive photocatalyst according to claim 1, wherein 50% or more of a plurality of promoter particles of 100 or more whose primary particle diameters can be measured in an electron microscope image of the visible light responsive photocatalyst are not in contact with other promoter particles on the tungsten oxide particle on which the promoter particle is supported.

4. 2. The visible light responsive photocatalyst according to claim 1, wherein a mass ratio of the plurality of promoter particles to the plurality of tungsten oxide particles is 0.01 wt % or more and 2.0 wt % or less.

5. 2. The visible light responsive photocatalyst according to claim 1, wherein the co-catalyst particles are metal particles or metal oxide particles containing at least platinum.

6. 6. The visible light responsive photocatalyst according to any one of claims 1 to 5, wherein 90% or more of a plurality of tungsten oxide particles, the primary particle diameter of which can be measured in an electron microscope image of the visible light responsive photocatalyst, have a primary particle diameter of 5 nm or more and 400 nm or less.

7. A visible light responsive photocatalyst comprising tungsten oxide particles and a plurality of co-catalyst particles supported on the surfaces of the tungsten oxide particles, A visible light responsive photocatalyst, in which 50% or more of a plurality of tungsten oxide particles out of 100 or more tungsten oxide particles whose aspect ratio (ratio (b / a) of the major axis b to the minor axis a of the primary particle) can be calculated from an electron microscope image of the visible light responsive photocatalyst, have an aspect ratio of 1.3 or more and 10 or less.

8. 8. The visible light responsive photocatalyst according to claim 7, wherein the circularity of 70% or more of 100 or more tungsten oxide particles whose circularity can be calculated from an electron microscope image of the visible light responsive photocatalyst is 0.2 or more and 0.8 or less.

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