WO2020153399A1 - Photocatalyst, photocatalyst cluster, and photocatalyst production method - Google Patents

Abstract

This photocatalyst is provided with: a carrier transport body; a plurality of negative electrode active materials which have a smaller particle size than the carrier transport body and which partially cover the carrier transport body; and a plurality of positive electrode active materials which have a smaller particle size than the carrier transport body and which partially cover the carrier transport body.

Description

Photocatalyst, photocatalyst cluster, and method for producing photocatalyst

The present disclosure relates to a Z-scheme type (two-step photoexcitation type) photocatalyst using a negative electrode active material and a positive electrode active material, a photocatalytic cluster, and a method for producing the same. This international application claims priority based on Japanese Patent Application No. 2019-11344, Japanese Patent Application No. 2019-011352, and Japanese Patent Application No. 2019-011354 filed on January 25, 2019, respectively. All the contents disclosed in Japanese Patent Application No. 2019-11344, Japanese Patent Application No. 2019-011352, and Japanese Patent Application No. 2019-011354 are incorporated in the present international application.

Demand for safety and security in daily life is increasing, while there are demands for energy saving and resource reduction. Photocatalytic sterilization and antibacterial effects are used as conventional technology.

A Z-scheme type photocatalyst is known as a type of photocatalyst. Patent Document 1 discloses a photocatalyst material, in which first photocatalyst particles for hydrogen generation and second photocatalyst particles for oxygen generation are connected by conductive particles, as a photocatalyst for generating hydrogen and oxygen by water decomposition. It is disclosed. In this photocatalyst material, the conductive particles serve as a carrier transporter that moves carriers (electrons) between the first photocatalyst particles and the second photocatalyst particles. Further, as the conductive particles, those having a smaller particle size than the catalyst particles (first photocatalyst particles and second photocatalyst particles) are used.

JP, 2017-124393, A

In the photocatalyst of Patent Document 1, in order to sufficiently exhibit the Z scheme effect of the first photocatalyst particles and the second photocatalyst particles, the first photocatalyst particles and the second photocatalyst particles respectively increase the coverage of the conductive particles, The movement paths of carriers of the first photocatalyst particles and the second photocatalyst particles must be increased. On the other hand, the first photocatalyst particles and the second photocatalyst particles each increase the coverage of the conductive particles, so that the conductive particles prevent contact between the substance to be decomposed and the first photocatalyst particles or the second photocatalyst particles. It As a result, the reaction efficiency of the first photocatalyst particles and the second photocatalyst particles decreases.

The present disclosure has been made in view of the above problems, and an object thereof is to provide a photocatalyst with improved reaction efficiency and a method for producing the same.

In order to solve the above problems, a photocatalyst according to one embodiment of the present disclosure is a carrier transporter, a plurality of negative electrode active materials that are smaller than the particle size of the carrier transporter and cover a part of the carrier transporter, and a carrier. A plurality of positive electrode active materials each having a particle size smaller than that of the transporter and covering a part of the carrier transporter.

According to one aspect of the present disclosure, a photocatalyst with improved reaction efficiency, a photocatalyst cluster including the photocatalyst, and a method for producing the photocatalyst are realized.

3 is a schematic cross-sectional view showing the configuration of the photocatalyst of Embodiment 1. FIG. 4 is a flowchart showing a manufacturing process of the photocatalyst according to the first embodiment. 3 is a schematic cross-sectional view showing the configuration of another embodiment of the photocatalyst according to Embodiment 1. FIG. FIG. 6 is a schematic cross-sectional view showing the structure of the photocatalyst according to the second embodiment. (a)-(c) is a figure which shows the preparation process of the secondary particle of the negative electrode active material or positive electrode active material of the photocatalyst which concerns on Embodiment 2. FIG. 9 is a schematic cross-sectional view showing the structure of the photocatalyst according to the third embodiment. (A)-(d) is a figure which shows the manufacturing process of the photocatalyst which concerns on Embodiment 3. FIG. 11 is a graph showing the results of an acetaldehyde decomposition experiment using the photocatalyst according to the third embodiment. It is a schematic cross section which shows the structure of the photocatalyst which concerns on Embodiment 4. (A)-(d) is a figure which shows the manufacturing process of the photocatalyst which concerns on Embodiment 4. 11 is a graph showing the results of an acetaldehyde decomposition experiment using the photocatalyst according to the fourth embodiment. It is a schematic cross section which shows the structure of the photocatalyst which concerns on Embodiment 5.

[Embodiment 1]
Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing the configuration of the photocatalyst 10 according to the first embodiment.

[Structure of Photocatalyst 10]
The photocatalyst 10 is composed of the negative electrode active material 2, the positive electrode active material 3, and the carrier transporter 4. Specifically, the photocatalyst 10 is a composite particle in which the surface of the carrier transporter 4 in the form of particles is covered with the negative electrode active material 2 and the positive electrode active material 3 which are both in the form of particles. The negative electrode active material 2 and the positive electrode active material 3 have smaller particle sizes than the carrier transporter 4.

The average particle size of the negative electrode active material 2 and the positive electrode active material 3 is preferably 5 nm or more and 60 μm or less. When the average particle diameter of the negative electrode active material 2 and the positive electrode active material 3 is less than 5 nm, sufficient light absorption may not be obtained. Further, when the average particle diameter of the negative electrode active material 2 and the positive electrode active material 3 exceeds 60 μm, it is necessary to design the particle diameter of the carrier transport body 4 to be larger, which may reduce the carrier transport efficiency. Further, it is preferable that the average particle size of the negative electrode active material 2 and the average particle size of the positive electrode active material 3 do not differ greatly, and the particle size ratio of the negative electrode active material 2 and the positive electrode active material 3 is 1:5 to 5:1. It is preferably in the range of.

The average particle size of the carrier transporter 4 is preferably 50 nm or more and 100 μm or less. When the average particle diameter of the carrier transporter 4 is less than 50 nm, the numbers of the negative electrode active material 2 and the positive electrode active material 3 which coat the carrier transporter 4 may be small. On the other hand, if the average particle diameter of the carrier transport material 4 exceeds 100 μm, the carrier transport efficiency may decrease.

The particle size ratio of the negative electrode active material 2 and the positive electrode active material 3 to the carrier transporter 4 (negative electrode active material 2 or positive electrode active material 3/carrier transporter 4) is preferably 0.05 or more and 1 or less, respectively. It is more preferably 0.1 or more and 0.5 or less. When this particle size ratio is less than 0.1, the surface areas of the negative electrode active material 2 and the positive electrode active material 3 are smaller than the volume of the carrier transporter 4 in the photocatalyst 10. As a result, the reaction efficiency of the photocatalyst 10 is reduced. On the other hand, when the particle size ratio exceeds 0.5, the surface areas of the portions of the negative electrode active material 2 and the positive electrode active material 3 that are not electrically connected (not in contact) with the carrier transporter 4 increase. In this case, both the negative electrode active material 2 and the positive electrode active material 3 can function as a photocatalyst in response to visible light, but the Z scheme effect is reduced. Also in this case, the reaction efficiency of the photocatalyst 10 is reduced. That is, the surface area of the negative electrode active material 2 and the positive electrode active material 3 in the photocatalyst 10 becomes appropriate by setting the respective particle diameter ratios of the negative electrode active material 2, the positive electrode active material 3, and the carrier transporter 4 in an appropriate range, The reaction efficiency of the photocatalyst 10 can be improved.

The coverage of the carrier transporter 4 is preferably 50% or more, more preferably 90% or less. When the coverage of the carrier transporter 4 is less than 50%, the surface area on which the photocatalyst 10 functions becomes insufficient and the reaction efficiency becomes low. When the coverage of the carrier transporting material body 4 exceeds 90%, the probability that the negative electrode active material 2 and the positive electrode active material 3 contact each other becomes high, electron transfer occurs between both particles, and the Z scheme effect is reduced.

The negative electrode active material 2 is an electrode for reducing a decomposed substance and is a photocatalyst having a reducing ability. The negative electrode active material 2 is preferably a material having a conduction band level that is lower than the redox potential of hydrogen. Moreover, the valence band level of the negative electrode active material 2 is not particularly limited, but is preferably more base. Thereby, the light absorption wavelength of the negative electrode active material 2 can be made longer. Such negative electrode active material 2 preferably contains, for example, any one of titanium oxide, strontium titanate, and tantalate. An example of the tantalate salt is potassium tantalate.

In order to make the conduction band level of the negative electrode active material 2 more base than the redox potential of the decomposed substance, the negative electrode active material 2 contains a platinum group element such as Pt, Rh, Ru, Pd, Os, Ir or the like. The negative electrode active material 2 may be doped with lanthanoid such as La or Ce by 0.5% to 10%. Further, the negative electrode active material 2 may carry a sensitizing dye in order to widen the wavelength range capable of absorbing light. As the sensitizer, a sensitizer used in the field of dye-sensitized solar cells can be appropriately used. The material of the sensitizer is not particularly limited, but a wider absorption wavelength width is preferable. Specifically, organic sensitizers such as organic dyes and metal complex dyes, commonly used inorganic sensitizers such as SbCl ₄ and quantum dots can be used.

The positive electrode active material 3 is an electrode for oxidizing a decomposed substance and is a photocatalyst having an oxidizing ability. The positive electrode active material 3 is preferably a material having a valence band level that is nobler than the redox potential of oxygen. The conduction band level of the positive electrode active material 3 is not particularly limited, but it is preferably noble. This is because the light absorption wavelength of the positive electrode active material 3 can be made longer. Such a positive electrode active material 3 preferably contains, for example, any one of iron (III) oxide, tungsten oxide, and vanadate. Bismuth vanadate can be mentioned as an example of vanadate. Like the negative electrode active material 2, the positive electrode active material 3 may carry a sensitizer.

The carrier transporter 4 is a material that serves as a carrier transport path between the negative electrode active material 2 and the positive electrode active material 3. Here, the carrier may be an electron or a hole. The carrier transporter 4 is not particularly limited as long as it is a material generally used for carrier transport, and for example, an inorganic material such as copper iodide (CuI) or nickel oxide (NiO) can be used. Alternatively, the carrier transporter 4 is any one of PEDOT (polyethylenedioxythiophene), PEDOT-PSS (poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid)), and Spiro-OMeTAD. A hole transporting material including can be used. Alternatively, the carrier transporter 4 may use an electron transporting material containing any of fullerene, fullerene derivative, silole compound, and triazine compound.

Further, in order to carry out carrier transport efficiently, the Fermi level of the carrier transporter 4 is at a position more negative than the electron energy level at the upper end of the valence band of the negative electrode active material 2, and the conduction band of the positive electrode active material 3. The position is more positive than the electron energy level at the lower end.

[Production process of photocatalyst 10]
Next, the manufacturing process of the photocatalyst 10 according to the first embodiment will be described with reference to FIG. FIG. 2 is a process diagram showing a manufacturing procedure of the photocatalyst 10 according to the first embodiment. In addition, the material of each member of the photocatalyst 10 described here and the method used in each step are examples.

As shown in FIG. 2, the manufacturing process of the photocatalyst 10 includes a negative electrode active material preparation process, a positive electrode active material preparation process, a carrier transporter preparation process, and a composite particle formation process. The negative electrode active material preparation step is a step of preparing the negative electrode active material 2. The positive electrode active material preparation step is a step of preparing the positive electrode active material 3. The carrier transporter preparation step is a step of preparing the carrier transporter 4. These steps can be carried out independently. The composite particle forming step is a step of forming the photocatalyst 10 which is a composite particle from the prepared negative electrode active material 2, positive electrode active material 3 and carrier transporter 4. Hereinafter, each step will be described.

[Negative electrode active material preparation step]
Hereinafter, an example of using SrTiO ₃ doped with La and Rh as the negative electrode active material 2 will be described. The particles are not limited to this example, and commercially available particles may be used as long as they can be used for the negative electrode active material 2.

Sr:Ti=1 with strontium carbonate powder (Kanto Kagaku, purity 99.9%, powder baked in advance at 200° C. for 1 hour) and rutile titanium oxide powder (Kanto Kagaku, purity 99.0%). First, SrTiO ₃ powder was obtained by mixing in a mortar so as to have a molar ratio of 0.055 and baking at 1150° C. for 10 hours. Furthermore, the obtained SrTiO ₃ powder and lanthanum oxide were adjusted so that Sr:La=0.96:0.04 (molar ratio) and Ti:Rh=0.96:0.04 (molar ratio). The powder and rhodium oxide (Rh ₂ O ₃ , purity 99.9%) were mixed in ethanol, and the dried powder was calcined at 1100° C. for 6 hours. Thus, as the negative electrode active material 2, a powder composed of 4% La and 4% Rh-doped SrTiO ₃ (Sr _0.96 La _0.04 Ti _0.96 Rh _0.04 O ₃ ) particles was produced. As the lanthanum oxide powder (La ₂ O ₃ ), a powder having a purity of 99.99% manufactured by Kanto Kagaku Co., Ltd., which was previously baked at 1000° C. for 10 hours was used.

[Cathode active material preparation step]
BiVO ₄ particles carrying CoO _x were prepared by a liquid-solid method. Specifically, first, K ₂ CO ₃ (manufactured by Kanto Kagaku Co., 99.5%) and V ₂ O ₅ (manufactured by Wako Pure Chemical Industries, 99.0%) were mixed with K:V=3.03:5 (molar ratio). ) Was placed in a mortar and pestle, ethanol (10 mL) was added, and the mixture was mixed for 30 minutes. Then, the obtained mixture was put in a magnetic crucible and fired in an electric furnace at 450° C. in the atmosphere for 5 hours. After firing, the fired body was allowed to cool to room temperature and then crushed. The resulting powder, 100 ml of water and _{Bi (NO 3) 3 · 5H} 2 O ( manufactured by Wako Pure Chemical Industries, Ltd., 99.9%) was placed in the entered was 300ml Erlenmeyer flask (Bi: V = 1: 1 ), The mixture was stirred at 70° C. for 10 hours at 1500 rpm using a stirring bar. The obtained precipitate was collected by suction filtration, washed with water, and then dried at 60° C. for 12 hours in a drier to obtain BiVO ₄ powder. 0.5 g of the obtained BiVO4 powder was placed in a magnetic crucible, and Co(NO ₃ ) ₂ (manufactured by Wako Pure Chemical Industries, 99.5%) was used as a cocatalyst raw material so that CoO was 0.5 wt %. Then, a small amount of pure water was added. The BiVO ₄ powder was thoroughly suspended by ultrasonic waves and then evaporated to dryness in a water bath. Finally, it was baked in an electric furnace at 300° C. in the atmosphere for 2 hours. Thus, BiVO ₄ powder carrying CoO _x as the positive electrode active material 3 was produced.

[Carrier transporter preparation process]
A copper iodide solution was prepared by dissolving copper iodide (CuI) in acetonitrile (both manufactured by Sigma-Aldrich) so as to be 1 mol/L and stirring. A copper iodide solution was dropped on a glass substrate placed on a hot plate set at 100° C. to obtain a white powder. This white powder was pulverized with a bead mill to prepare copper iodide fine particles having an average particle diameter of 2.5 μm as the carrier transporter 4.

[Composite particle forming step]
In the composite particle forming step, the negative electrode active material 2, the positive electrode active material 3, and the carrier transporter 4 are mixed while applying the shearing force obtained in each of the above steps. By mixing while applying shearing force, the negative electrode active material 2 and the positive electrode active material 3 having a small particle size are attached to the surface of the carrier transport body 4, and the negative electrode active material 2 and the positive electrode active material 3 are attached to the surface of the carrier transport body 4. The photocatalyst 10 fixed so as to be embedded can be manufactured.

As a device for mixing the negative electrode active material 2, the positive electrode active material 3, and the carrier transporter 4 while applying a shearing force, a high speed air impact method is used for the hybridization system of Nara Machinery Co., Ltd. A mixer equipped with a high-speed stirring blade such as a mechanofusion system of Hosokawa Micron Co., Ltd. that utilizes a crusher is suitable. The rotation speed of the high-speed stirring blade can be set arbitrarily depending on the mixer used and the combination of the materials to be mixed, but when a hybridization system is used, the peripheral speed may be about 10 to 130 m/s.

In the photocatalyst 10 according to the first embodiment, the surface of the carrier transporter 4 has a plurality of negative electrode active materials 2 each having a smaller particle size than the carrier transporter 4, and a plurality of smaller than the particle size of the carrier transporter 4. The positive electrode active material 3 is used for coating.

By providing the above configuration, it is possible to increase the surface area of the photocatalyst 10 capable of receiving the light of the negative electrode active material 2 and the positive electrode active material 3. Further, since one carrier transporter 4 is coated with the plurality of negative electrode active materials 2 and the positive electrode active materials 3, the transport paths in the negative electrode active material 2 and the positive electrode active material 3 increase. Therefore, the photocatalyst 10 can improve the Z scheme effect and the reaction efficiency more than the conventional Z scheme type photocatalyst.

In the conventional (patent document 1) photocatalyst material, the surface of the catalyst particles which are large particles is coated with the conductive particles (carrier transporter) which is the small particle. There was a trade-off relationship between the effect and the reaction efficiency of the catalyst particles.

Further, in the photocatalyst 10 manufactured by the method for manufacturing a photocatalyst according to the first embodiment, the plurality of negative electrode active materials 2 and the plurality of positive electrode active materials 3 randomly cover the surface of the carrier transporter 4, and Since the coverage of the surface of the carrier transporter 4 with the negative electrode active material 2 and the positive electrode active material 3 is larger than in the conventional case, the light is absorbed by the negative electrode active material 2 or the positive electrode active material 3 regardless of the direction of light irradiation. This can be suppressed and the Z scheme effect can be exhibited.

Further, in the photocatalyst 10 manufactured by the method for manufacturing a photocatalyst according to the first embodiment, the adhesion between the carrier transporter 4 and the negative electrode active material 2 and the positive electrode active material 3 is also improved. This is because the negative electrode active materials 2 or the positive electrode active materials 3 are bonded to each other on the surface of the carrier transporter 4 and the bonding prevents the peeling of the negative electrode active material 2 and the positive electrode active material 3.

In addition, the photocatalyst 10 according to the first embodiment does not require a base material or the like for supporting the photocatalyst 10, and the photocatalyst 10 can be easily manufactured into particles. The photocatalyst 10 produced in the form of particles can be used by being dispersed in a solvent and used in a wide variety of applications such as spraying.

Further, FIG. 3 is a schematic cross-sectional view showing the configuration of another embodiment of the photocatalyst 10 according to the first embodiment. Like the photocatalyst 10 in the first embodiment, the photocatalyst 10A is a composite particle in which the surface of the particulate carrier transporter 4 is covered with the negative electrode active material 2 and the positive electrode active material 3 which are both particulate. However, in the photocatalyst 10A, the negative electrode active material 2 and the positive electrode active material 3 do not have to have the same ratio, and an appropriate ratio is selected depending on their respective absorption wavelength ranges, the decomposition ability as the visible light responsive photocatalyst, and the like. ..

For example, when the negative electrode active material 2 is Rh-doped SrTiO ₃ and the positive electrode active material 3 is BiVO ₄ , the ratio of Rh-doped SrTiO ₃ and BiVO ₄ is selected according to the quantum yield of visible light. Thereby, the number of photoexcited holes generated in the negative electrode active material 2 and the number of photoexcited electrons generated in the positive electrode active material 3 are balanced, and the photocatalyst 10A can function as an efficient Z scheme type photocatalyst.

The ratio (weight ratio) of the negative electrode active material 2 and the positive electrode active material 3 is preferably in the range of 2:8 to 8:2. Outside of this range, the carriers transported between the negative electrode active material 2 and the positive electrode active material 3 may have a large distance passing through the carrier transport body 4, and the reaction efficiency in the photocatalyst 11 may decrease.

[Embodiment 2]
FIG. 4 is a schematic cross-sectional view showing the configuration of the photocatalyst 10B according to the second embodiment. Like the photocatalyst 10 in the first embodiment, the photocatalyst 10B is a composite particle in which the surface of the particulate carrier transporter 4 is covered with the negative electrode active material 2 and the positive electrode active material 3 which are both particulate. .. However, in the photocatalyst 10B, the negative electrode active material 2 and the positive electrode active material 3 are each configured by secondary particles (aggregates of primary particles) in which the primary particles 21 and the primary particles 31 are aggregated. Note that only one of the negative electrode active material 2 and the positive electrode active material 3 may be the secondary particles formed by aggregating the primary particles 21 and 31.

When the negative electrode active material 2 or the positive electrode active material 3 is a secondary particle in which the primary particles 21 and 31 are aggregated, the primary particles 21 and 31 distant from the carrier transporter 4 are present in the secondary particles. Therefore, from the viewpoint of electrical connection, the secondary particles may contain the carrier transporting material 4a in advance. Further, the carrier transport substance 4 a contained in the secondary particles comes into contact with the carrier transport body 4. The average particle size of the carrier transport material 4a is larger than the average particle size of the carrier transport body 4 and smaller than the average particle size of the negative electrode active material 2 or the positive electrode active material 3. By doing so, the carriers generated in the secondary particles can be efficiently transported to the carrier transporter 4 through the carrier transport material 4a.

Further, in this case, the carrier transporter 4 and the carrier transport substance 4a may be the same substance or different substances. For example, when the negative electrode active material 2 is a secondary particle, the carrier transport material 4a contained in the negative electrode active material 2 may be a hole transport material, and when the positive electrode active material 3 is a secondary particle, the positive electrode active material 3 is used. The carrier-transporting substance 4a contained in may be an electron-transporting substance. However, the Fermi level of each carrier transport substance 4a needs to be selected so that carriers are transported.

FIG. 5 is a diagram showing a manufacturing process of the negative electrode active material 2 or the positive electrode active material 3 to be the secondary particles. This will be described below with reference to FIG. However, the materials and methods used in the following manufacturing steps are examples.

First, as shown in FIG. 5A, the porous body layer 7 made of the primary particles 21 or 31 of the negative electrode active material 2 or the positive electrode active material 3 is formed on the base material 6. For example, when the negative electrode active material 2 is produced, a titanium oxide paste (manufactured by Solaronix, product name: D/SP) having an average particle diameter of 20 nm, which is the primary particle 21, is applied onto the base material 6 by screen printing, and 120 After drying at ℃, it is baked at 500 ℃ for 1 h. When the positive electrode active material 3 is manufactured, an aqueous slurry containing fine particles of tungsten oxide (WO ₃ ) (particle size: 100 μm, manufactured by Kishida Chemical Co., Ltd.) is applied by the doctor blade method and then dried at 120° C.

In order to include the carrier transport substance 4a in the porous body layer 7 thus formed, as shown in FIG. 5B, a copper iodide (CuI) solution 8 is dropped onto the porous body layer 7 and spin coated ( 2000 rpm, 30s) and so on. This copper iodide solution is prepared, for example, by dissolving copper iodide (CuI) in acetonitrile so as to be 1 mol/L and stirring. The copper iodide solution dropped onto the porous body layer 7 permeates into the porous body layer 7.

In this way, the substrate 6 on which the porous layer 7 containing the carrier transport substance 4a is formed is immersed in a container (not shown) containing pure water, and as shown in FIG. It is crushed by laser ablation by irradiating laser light L having a wavelength of 1024 nm and a frequency of 14000 Hz. As a device for irradiating the laser light L, for example, a device manufactured by Seishin Shoji can be used. As a result, the porous body layer 7 is pulverized into fine particles while peeling off the porous body layer 7 from the base material 6. As a result, the negative electrode active material 2 or the positive electrode active material 3 as secondary particles as shown in FIG. 4 can be produced.

The manufacturing process of the negative electrode active material 2 or the positive electrode active material 3 to be the secondary particles described above can be applied to the [negative electrode active material preparation step] and the [positive electrode active material preparation step] in FIG. That is, in the [negative electrode active material preparation step] or the [positive electrode active material preparation step], if the negative electrode active material 2 or the positive electrode active material 3 to be the secondary particles is produced, the same [composite particle forming step] as that of the first embodiment is performed. ], the photocatalyst 10B according to the second embodiment can be manufactured.

In the above-described photocatalyst 10B, when the light absorption width in the negative electrode active material 2 or the positive electrode active material 3 is small and the current is low, a sensitizer for widening the light absorption wavelength in the negative electrode active material 2 serving as secondary particles. May be supported.

In the photocatalyst 10B, when a sensitizer is carried on the negative electrode active material 2 which becomes the secondary particles, after forming a porous layer made of the primary particles 21 of the negative electrode active material 2 on the substrate, a copper iodide solution Before dripping, it may be immersed in a solution containing a sensitizer prepared in advance for 24 hours.

Note that the sensitizer can be supported on the positive electrode active material 3 to be the secondary particles by the same method. Further, the negative electrode active material 2 or the positive electrode active material 3 carrying the sensitizer is preferably in contact with the carrier transporter 4.

In the [composite particle forming step] shown in FIG. 2, Coulomb interaction may be used to prevent the negative electrode active material 2 and the positive electrode active material 3 from aggregating with each other. Specifically, a method in which the carrier transporter 4 contains an anionic polymer and the negative electrode active material 2 and the positive electrode active material 3 contain a cationic polymer can be considered.

For example, when the particles of the carrier transporter 4 are prepared in the [carrier transporter preparing step] of FIG. 2, by dispersing the anionic polymer in acetonitrile as a solvent, the carrier transporter 4 containing the anionic polymer is obtained. Can be produced. Further, regarding the negative electrode active material 2 and the positive electrode active material 3, these are used as the secondary particles described in the third embodiment, and the cationic polymer is dispersed in the carrier transport material 4a contained in the secondary particles. The negative electrode active material 2 and the positive electrode active material 3 containing a conductive polymer can be produced.

As described above, in the [composite particle forming step], the carrier transporter 4 and the negative electrode active material 2 and the positive electrode active material 3 interact with the carrier transporter 4 due to Coulomb interaction between different charges of the polymers adsorbed on the surface. The negative electrode active material 2 and the positive electrode active material 3 attract each other, and the carrier transporters 4 and the negative electrode active materials 2 and/or the positive electrode active materials 3 repel each other. This prevents the negative electrode active material 2 and the positive electrode active material 3 from aggregating in the [composite particle forming step], and the negative electrode active material 2 and the positive electrode active material 3 satisfactorily coat the surface of the carrier transporter 4. You can The polymer used in the above manufacturing process may be removed by heating or baking the photocatalyst after the [composite particle forming step].

[Embodiment 3]
Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. FIG. 6 is a schematic cross-sectional view showing the structure of the photocatalyst 10C according to the third embodiment. The photocatalyst 10C includes a carrier transporter 4, a negative electrode 20 provided on a part of the surface of the carrier transporter 4, and a positive electrode 30 provided on another part of the surface of the carrier transporter 4. The negative electrode 20 and the positive electrode 30 are separated from each other via the carrier transporter 4.

The negative electrode 20 is an electrode for reducing a substance to be decomposed, and is formed by sintering a granular negative electrode active material 2. More specifically, the negative electrode 2 is preferably formed from two or more types of negative electrode active materials 2 having different average particle sizes. In the following example, the negative electrode 20 is composed of a set of the first negative electrode active material 2a and the second negative electrode active material 2b. The carriers generated by the first negative electrode active material 2a and the second negative electrode active material 2b are conducted to the carrier transporter via the respective contact points. In the present embodiment, it is more preferable that the average particle size of the first negative electrode active material 2a is larger than the average particle size of the second negative electrode active material 2b.

The average particle size of the first negative electrode active material 2a is preferably 100 nm or more and 600 nm or less. The average particle size of the second negative electrode active material 2b is preferably 5 nm or more and 100 nm or less, and more preferably 10 nm or more and 50 nm or less. That is, the particle size distribution of the negative electrode active material 2 in the negative electrode 20 has at least two peaks. Here, the average particle size of the first negative electrode active material 2a and the second negative electrode active material 2b can be measured by a laser diffraction/scattering particle size distribution measuring device or the like.

The density of the negative electrode active material 2 contained in one photocatalyst 10C is preferably 1×10 ⁷ pieces/mm ² to 1×10 ¹³ pieces/mm ² per unit area of the carrier transporter 4. The density of the negative electrode active material 2 contained in one photocatalyst 10C can be measured by an electron beam microanalyzer or the like.

The first negative electrode active material 2a and the second negative electrode active material 2b to be the negative electrode active material 2 can be appropriately selected from the negative electrode active materials 2 listed in the first embodiment. The first negative electrode active material 2a and the second negative electrode active material 2b may be the same kind of compounds or different kinds of compounds. It is more preferable to use the same kind of compound, because the negative electrode 20 can be formed without considering the energy level relationship between the first negative electrode active material 2a and the second negative electrode active material 2b and the degree of adhesion.

The mixing ratio of the second negative electrode active material 2b with respect to the total of the first negative electrode active material 2a and the second negative electrode active material 2b is preferably 10% to 90%, more preferably 30% to 70%. .. When the mixing ratio of the second negative electrode active material 2b to the total of the first negative electrode active material 2a and the second negative electrode active material 2b is less than 10%, the pore diameter of the negative electrode 2 increases and the surface area of the negative electrode 20 decreases. Therefore, there is concern that the reaction efficiency may decrease. On the other hand, when the mixing ratio of the second negative electrode active material 2b with respect to the total of the first negative electrode active material 2a and the second negative electrode active material 2b exceeds 90%, the pore diameter in the negative electrode 20 becomes small, resulting in a reaction product or formation. There is concern that the diffusion of substances may be hindered and the reaction efficiency may decrease.

Further, the negative electrode 20 may carry a sensitizer for broadening the absorption wavelength of light. The sensitizer can be appropriately selected from the materials listed in Embodiment Mode 1.

The carrier transporter 4 is not particularly limited as long as it is a material generally used for carrier transport, and can be appropriately selected from the carrier transporters 4 listed in the first embodiment. In the case of Embodiment 4, the thickness of the carrier transporter 4 is preferably 0.5 μm to 50 μm.

The positive electrode 30 is an electrode for oxidizing a substance to be decomposed, and is formed as a layer containing the positive electrode active material 3. The positive electrode 30 is preferably a porous layer and has a surface area of preferably 10 m ² /g to 100 m ² /g. The particle size of the granular positive electrode active material 3 contained in the positive electrode 30 is preferably 10 nm to 500 μm. The aggregate of the granular positive electrode active materials 3 allows the carriers to be conducted to the carrier transporter 4 via the contact points of the respective positive electrode active materials 3. The material used for the positive electrode active material 3 is appropriately selected from the materials listed as the positive electrode active material 3 in the first embodiment.

The coverage of the carrier transporter 4 with respect to the positive electrode 30 is preferably 5 to 80%. The coverage of the carrier transporter 4 can be measured by observing a cross-section SEM or the like.

As described above, the photocatalyst 10C is a composite particle having the negative electrode 20, the carrier transporter 4, and the positive electrode 30, and the average particle size S (see FIG. 6) of the photocatalyst 10C is 100 nm to 1000 μm. Thereby, the redox reaction can be efficiently performed in the photocatalyst 10C which is the composite particle. When the average particle size S of the photocatalyst 10C is too small, the light absorption ability of the photocatalyst 10C is small and the catalyst ability may be reduced. On the other hand, if the average particle size S of the photocatalyst 10C is too large, the surface area may decrease, and the reaction efficiency of the catalytic reaction may decrease. In the method for measuring the average particle size S of the photocatalyst 1, first, an SEM image of the photocatalyst 10C is taken by using SEM. After that, a plurality of (for example, 10) particles are randomly extracted from the SEM image using image analysis software, and the areas of these particles are obtained. Next, assuming that each of the extracted particles is spherical, the average particle size S is obtained.

Next, the manufacturing process of the photocatalyst 10C according to the third embodiment will be described with reference to FIG. Note that the material used for each member of the photocatalyst 10C and the method used in each step described with reference to FIG. 7 are examples.

(Negative electrode film forming step)
FIG. 7A shows a negative electrode film forming step of forming the negative electrode film 200 to be the negative electrode 20 on the base material 100. In this negative electrode film forming step, a paste containing the first negative electrode active material 2a which becomes the negative electrode active material 2 and a second negative electrode active material 2b which becomes the negative electrode active material 2 and has an average particle diameter smaller than that of the first negative electrode active material 2a. The paste-like first solution in which the containing paste is mixed at a predetermined ratio is applied onto the substrate 100, dried, and then baked at a predetermined temperature for a predetermined time. As a result, the negative electrode film 200 is formed on the base material 100. The method of applying the paste containing the first negative electrode active material 2a and the second negative electrode active material 2b to the base material 100 is not particularly limited, but may be screen printing or a doctor blade method. When a sensitizer is applied to the negative electrode 2, after that, the base material 100 having the negative electrode film 200 formed thereon is dipped in a solution containing a sensitizer prepared in advance to form the negative electrode 20 carrying the sensitizer. The negative electrode film 200 is formed.

(Carrier transport film forming process)
FIG. 7B shows the carrier transport film forming step of forming the carrier transport film 400 containing the carrier transport material, which becomes the carrier transport body 4, on the negative electrode film 200. In the carrier transport film forming step, for example, the carrier transport material is dissolved in an organic solvent and stirred to form a second solution containing the carrier transport material. Then, a solution containing the carrier transport material is dropped on the negative electrode film 200, and spin coating (2000 rpm, 30 s) or the like is performed. As a result, the carrier transport film 400 is formed on the negative electrode film 200. As a method of applying the solution containing the carrier transport material onto the negative electrode film 200, a dip coating method or a drop casting method can be used in addition to the spin coating method. Further, in the carrier transport film forming step, since the negative electrode film 200 is a porous body formed by sintering a mixture of the first negative electrode active material 2a and the second negative electrode active material 2b, it is dropped onto the negative electrode film 200. Part of the carrier transport material penetrates into the negative electrode film 200.

(Positive electrode film forming step)
FIG. 7C shows a positive electrode film forming step of forming the positive electrode film 300 to be the positive electrode 30 on the carrier transport film 400. In this positive electrode film forming step, for example, an aqueous slurry as a third solution containing fine particles of the positive electrode active material 3 is applied to the carrier transport film 400 and then dried. The method of applying the water slurry containing fine particles of the positive electrode active material 3 to the carrier transport film 400 is not particularly limited, but it can be performed by screen printing or a doctor blade method. As a result, the positive electrode film 300 is formed on the carrier transport film 400.

(Particulation process)
Thus, the base material 100 on which the laminated body including the negative electrode film 200, the carrier transporting film 400, and the positive electrode film 300 is formed is immersed in a container (not shown) containing pure water, and the wavelength is, for example, 300 nm to 11000 nm and the frequency is 10000 nm. It is crushed by laser ablation by irradiating a laser beam L of up to 1,000,000 Hz (see FIG. 7D). As a device for irradiating the laser light L, for example, a device manufactured by Seishin Shoji can be used. As a result, the laminate is pulverized into fine particles while peeling the laminate from the base material 100. As a result, the photocatalyst particles 10C shown in FIG. 6 are formed. The step of forming fine particles is not limited to the above method. For example, the laminated body may be cut off to be separated from the substrate, and then finely divided by pulverizing with a mill or the like.

In the manufacturing process described above, the negative electrode film 200, the carrier transporting film 400, and the positive electrode film 300 are laminated in this order on the base material 100. However, the stacking order may be reversed, and the positive electrode film 300, the carrier transporting film 400, and the negative electrode film 200 may be stacked in this order on the base material 100. However, in this case, since it becomes difficult for the carrier transport film 300 to permeate into the negative electrode film 200 that is finally stacked, it is preferable to stack in the order shown in FIG. 7. Further, by stacking in the order shown in FIG. 7, it becomes easy to support the sensitizer only on the negative electrode film 200.

In the photocatalyst 10C according to the third embodiment, the negative electrode 20 is formed of two types of negative electrode active materials 2 having different average particle sizes, that is, the first negative electrode active material 2a and the second negative electrode active material 2b. Then, by adjusting the mixing ratio of the first negative electrode active material 2a and the second negative electrode active material 2b, it becomes easy to adjust the size of the pores in the negative electrode 20, and as a result, the carrier transporter to the negative electrode 2 can be obtained. It becomes easy to adjust the degree of penetration of No. 4 appropriately. Specifically, if the proportion of the second negative electrode active material 2b, which is a smaller particle, is reduced, the pores of the negative electrode 20 become larger, and the permeability of the carrier transporter 4 becomes larger (permeation becomes easier). On the contrary, if the proportion of the second negative electrode active material 2b is increased, the pores of the negative electrode 20 become smaller, and the permeability of the carrier transporter 4 becomes smaller (it becomes difficult for the carrier transporter 4 to permeate).

The effect will be described below based on a specific example of the third embodiment.

(Example 1)
A commercially available titanium paste containing titanium oxide particles having an average particle diameter of 400 nm (trade name: PST-400C, manufactured by JGC Catalysts and Chemicals) as the first negative electrode active material 2a and titanium oxide having an average particle diameter of 20 nm as the second negative electrode active material 2b. A titanium oxide paste containing particles (manufactured by Solaronix, trade name: D/SP) was used, and the ratio of the second negative electrode active material 2b to the total of the first negative electrode active material 2a and the second negative electrode active material 2b was 30%. The following titanium oxide paste was prepared.

After that, the above titanium oxide paste is applied by screen printing to a 20 mm×40 mm substrate (Blue plate glass, manufactured by Nippon Sheet Glass Co., Ltd.) 100, dried at 120° C., and baked at 500° C. for 1 h to give a thickness on the substrate. A 6 μm negative electrode film 200 was formed.

Next, copper iodide (manufactured by Sigma-Aldrich) was dissolved in propyl sulfide (manufactured by Sigma-Aldrich) as a carrier transport material to prepare a copper iodide solution having a copper iodide content of 1 mol/L. The copper iodide solution prepared above was dropped onto the negative electrode film 200, and a carrier transporting film 400 having a thickness of 6 μm was formed on the negative electrode film 200 by a spin coater (Mikasa, 2000 rpm, 30 s).

Next, an aqueous slurry prepared by dispersing tungsten oxide (particle size 100 nm, manufactured by Kishida Chemical Co., Ltd.) in 1 ml of water as the positive electrode active material 3 is applied on the carrier transport film 400 by the doctor blade method, and then dried at 120° C. for 10 minutes. It was Thus, the positive electrode film 300 having a thickness of 18 μm was formed on the carrier transport film 400.

Next, the laminated body in which the base material 100, the negative electrode film 200, the carrier transporting film 300, and the positive electrode film 400 are laminated is permeated into a container containing pure water, and pure water is obtained by using a laser irradiation device (manufactured by Seishin Trading Co., Ltd.). The laminated body immersed in water was irradiated with laser light having a wavelength of 1024 nm and a frequency of 14000 Hz for 60 seconds to pulverize the laminated body. After the pulverization, the peeled base material 100 and the photocatalyst 10C in which the negative electrode 20, the carrier transporter 4, and the positive electrode 30 were laminated in this order were separated by a sieve having a diameter of 500 μm to obtain the photocatalyst of Example 1.

Then, 8 mg of the powder of the photocatalyst prepared in Example 1 was used as the sample of Example 1.

(Example 2)
Example 2 was performed in the same manner as in Example 1 except that the titanium oxide paste was adjusted such that the ratio of the second negative electrode active material 2b to the total of the first negative electrode active material 2a and the second negative electrode active material 2b was 50%. The photocatalyst particles of Example 1 and the sample of Example 2 were obtained.

(Example 3)
In the same manner as in Example 1, except that the titanium oxide paste was adjusted such that the ratio of the second negative electrode active material 2b to the total of the first negative electrode active material 2a and the second negative electrode active material 2b was 70%. The photocatalyst and the sample of Example 3 were obtained.

(Example 4)
A sample of Example 4 was obtained in the same manner as in Example 1 except that the titanium oxide paste containing only the first negative electrode active material 2a was used. That is, in the photocatalyst negative electrode 20 of Example 4, the ratio of the second negative electrode active material 2b to the total of the first negative electrode active material 2a and the second negative electrode active material 2b was 0%.

(Example 5)
A sample of Example 5 was obtained in the same manner as in Example 1 except that the titanium oxide paste containing only the second negative electrode active material 2b was used. That is, in the photocatalyst negative electrode 20 of Comparative Example 2, the ratio of the second negative electrode active material 2b to the total of the first negative electrode active material 2a and the second negative electrode active material 2b was 100%.

(Evaluation method)
The following evaluations were performed to evaluate the reaction efficiency of the samples obtained in Examples 1 to 5.

Each sample of Examples 1 to 5 and acetaldehyde gas, which is a substance to be decomposed, were enclosed in a bag so that the acetaldehyde gas was 100 ppm, allowed to stand at room temperature, and irradiated with a fluorescent lamp 500 lx to decompose the aldehyde. The time taken was measured. The decomposition of aldehyde was visually confirmed by a gas detector tube (formaldehyde formaldehyde 91, manufactured by Gastec).

FIG. 8 is a graph showing the results of an acetaldehyde decomposition experiment using the photocatalyst 10C according to Examples 1 to 5. In the graph of FIG. 8, the horizontal axis represents the small particle ratio (the ratio of the second negative electrode active material 2b included in the negative electrode 20), and the vertical axis represents the time (day) required for acetaldehyde decomposition. The small particle ratio is shown by the area ratio of the first negative electrode active material 2a and the second negative electrode active material 2b in the SEM image of the negative electrode 20.

As shown in FIG. 8, when the small particle ratio is 0% (Example 4, negative electrode 2 is the first negative electrode active material 2a only), the acetaldehyde decomposition time is 6 days, and the small particle ratio is 30%. , The acetaldehyde decomposition time decreases as it increases to 50%, and it becomes about 3 days when the small particle ratio is 50%. Furthermore, the acetaldehyde decomposition time increases as the small particle proportion increases to 70% and 100%, and when the small particle proportion is 100% (Comparative Example 2, negative electrode 2 is the second particle 2b only), it takes about 10 days. There is.

From this, the reaction rate in the photocatalyst 10C varies depending on the small particle ratio in the negative electrode 20, that is, the mixing ratio of the first negative electrode active material 2a and the second negative electrode active material 2b, and the small particle ratio is too large. It has been revealed that the reaction rate is lowered if it is too much. This is because the size of the pores in the negative electrode 2 is adjusted by adjusting the mixing ratio of the first negative electrode active material 2a and the second negative electrode active material 2b, and the carrier transport efficiency in the carrier transporter 4 and the negative electrode 20 reaction efficiency. It is thought that this was due to the balance being maintained.

In addition, a method of adjusting the mixing ratio of the first negative electrode active material 2a and the second negative electrode active material 2b is to strictly adjust the average particle diameter of each of the first negative electrode active material 2a and the second negative electrode active material 2b. It is a method of easily adjusting the size of the pores in the negative electrode 2. Therefore, it is possible to use the commercially available negative electrode active material 2 as the first negative electrode active material 2a and the second negative electrode active material 2b.

In the above description, the case where the negative electrode 20 is formed of two types of the first negative electrode active material 2a and the second negative electrode active material 2b is illustrated, but the negative electrode 20 is formed into three or more types of negative electrode active materials having different average particle sizes. It may be formed by adjusting the mixing ratio of three or more kinds of negative electrode active materials.

[Embodiment 4]
FIG. 9 is a side view showing the configuration of the photocatalyst 10D according to the fourth embodiment. The photocatalyst 1D includes a carrier transporter 4, a negative electrode 20A provided on a part of the surface of the carrier transporter 4, and a positive electrode 4 provided on another part of the surface of the carrier transporter 4. The negative electrode 20A and the positive electrode 4 are separated from each other via the carrier transporter 4. Photocatalyst particles 10D according to the fourth embodiment have a structure having negative electrode 20A in place of negative electrode 20 in the third embodiment, and carrier transporter 4 and positive electrode 30 are similar to photocatalyst 1 in the first embodiment. The composition.

The negative electrode 20A is formed of a first negative electrode active material 2a having a large average particle size and a second negative electrode active material 2b having a small average particle size, as in the negative electrode 20 in the third embodiment. However, while the negative electrode 20 has a single-layer structure formed by mixing the first negative electrode active material 2a and the second negative electrode active material 2b, the negative electrode 20A has a first layer mainly containing the first negative electrode active material 2a. 2A and the second layer 2B mainly containing the second negative electrode active material 2b have a multilayer structure. In the negative electrode 20A, the first layer 2A is formed on the carrier transporter 4, and the second layer 2B is formed on the first layer 2A.

The layer thickness of the negative electrode 20A is preferably 100 nm to 50 μm. When the layer thickness of the negative electrode 20A is less than 100 nm, the amount of light absorption decreases and the reaction efficiency decreases. On the other hand, when the layer thickness exceeds 50 μm, the diffusion distance of the reaction product and the product increases, and the reaction efficiency decreases. The ratio of the layer thickness of the second layer 2B in the negative electrode 20A is preferably 10% to 90%, more preferably 20% to 80%.

Next, the manufacturing process of the photocatalyst 10D according to the fourth embodiment will be described with reference to FIG. Note that the material used for each member of the photocatalyst 10D and the method used in each step described with reference to FIG. 10 are examples.

(Negative electrode film forming step)
FIG. 10A is a negative electrode film forming step of forming a first negative electrode film 200a to be the first layer 2A of the negative electrode 20A and a second negative electrode film 200b to be the second layer 2B of the negative electrode 2 on the base material 100. Is shown. In this negative electrode film forming step, first, a paste containing the second particles 2b that is the negative electrode active material 2 is applied onto the substrate 10, dried, and then baked at 300° C. to 550° C. for 30 minutes to 2 hours. The two negative electrode film 200b is formed. Further, a paste containing the first negative electrode active material 2a, which is the negative electrode active material 2 and has an average particle size larger than that of the second negative electrode active material 2b, is applied on the second negative electrode film 200b by screen printing, dried, and then dried. The first negative electrode film 200a is formed by baking at 550° C. for 30 minutes to 2 hours. When a sensitizer is applied to the negative electrode 2, after that, the first negative electrode film 200a and the second negative electrode film 200b carrying the sensitizer are immersed in a solution containing a sensitizer prepared in advance for 24 hours. Form.

(Carrier transport film forming process, positive electrode film forming process, fine particle forming process)
FIG. 10B shows a carrier transport film forming step of forming the carrier transport film 400, which becomes the carrier transport body 4, and which contains the carrier transport material, on the first negative electrode film 200a. FIG. 10C shows a positive electrode film forming step of forming the positive electrode film 300 to be the positive electrode 30 on the carrier transport film 400. These steps are the same as the steps for manufacturing the photocatalyst 10C in the first embodiment.

In this way, the base material 100 on which the laminated body including the second negative electrode film 200b, the first negative electrode film 200a, the carrier transport film 400, and the positive electrode film 300 is formed is immersed in a container (not shown) containing pure water, for example, Then, it is pulverized by laser ablation by irradiating laser light L having a wavelength of 300 nm to 11000 nm and a frequency of 10000 Hz to 1000000 Hz (see FIG. 10D). As a result, the laminate is pulverized into fine particles while peeling the laminate from the base material 100. As a result, the photocatalyst 10D shown in FIG. 9 is formed.

In the photocatalyst 10D according to the fourth embodiment, the negative electrode 20A has a multilayer structure including a first layer 2A mainly containing the first negative electrode active material 2a and a second layer 2B mainly containing the second negative electrode active material 2b. ing. In this case, in the first layer 2A, the pores of the negative electrode 20B become large, and the penetration degree of the carrier transporter 4 becomes large (it becomes easy to penetrate). On the contrary, in the second layer 2B, the pores of the negative electrode 20A are small, and the permeability of the carrier transporter 4 is small (it becomes difficult for them to penetrate). As a result, in the first layer 2A near the carrier transporter 4, the pore diameter is large and the carrier transporting material easily permeates into the negative electrode 20A, so that the carrier transporting efficiency can be increased and the second layer separated from the carrier transporter 4 can be used. In the layer 2B, since the pore diameter is small and the surface area is large, the reaction efficiency of decomposition by light can be increased. Furthermore, by adjusting the thickness ratio of the first layer 2A and the second layer 2B, it becomes easy to balance the carrier transport efficiency in the carrier transporter 4 and the reaction efficiency of the negative electrode 20A.

The effects will be described below based on a concrete example of the fourth embodiment.

(Example 6)
Titanium oxide paste (manufactured by Solaronix, product name: D/SP) containing titanium oxide particles having an average particle diameter of 20 nm as the second negative electrode active material 2b was screen-printed to a 20 mm×40 mm substrate (blue plate glass, manufactured by Nippon Sheet Glass Co., Ltd.). And dried at 120° C. and baked at 500° C. for 1 h to form a second film 200B of the negative electrode film 200 having a thickness (second film thickness) of 3 μm on the base material.

Next, a commercially available titanium paste containing titanium oxide particles having an average particle diameter of 400 nm (manufactured by JGC Catalysts & Chemicals Co., Ltd., trade name: PST-400C) was applied onto the second layer by screen printing as the first negative electrode active material 2a, After drying at 120° C., it was baked at 500° C. for 1 h to form a first film 200A of a negative electrode film having a thickness (thickness of the first film 200A) of 7 μm on the second film 200B. Thus, a negative electrode film having a film thickness ratio of the first film 200A and the second film 200B of 7:3 was formed.

After the formation of the negative electrode film 200, the photocatalyst 10D of Example 6 was obtained through the carrier transport film forming process, the positive electrode film forming process, and the microparticulation process as in Example 1. Then, in the same manner as in Example 1, a sample of Example 6 was obtained.

(Example 7)
The total film thickness of the first film 200A and the second film 200B was the same as that of the negative electrode film of Example 6, and the film thickness ratio between the first film 200A and the second film 200B was 5:5. The photocatalyst 10D of Example 7 and the sample of Example 7 were obtained in the same manner as in Example 6.

(Example 8)
The total thickness of the first film 200A and the second film 200B was the same as that of the negative electrode film 200 of Example 6, and the film thickness ratio between the first film 200A and the second film 200B was 3:7. A photocatalyst of Example 8 and a sample of Example 8 were obtained in the same manner as in Example 6.

(Evaluation method)
In order to evaluate the efficiency of the decomposition reactions of Examples 6 to 8, the samples of Examples 6 to 8 were evaluated in the same manner as the samples of Examples 4 and 5.

FIG. 11 is a graph showing the results of an acetaldehyde decomposition experiment using the photocatalyst 10D according to the fourth embodiment. In the graph of FIG. 11, the horizontal axis represents the second layer thickness ratio (thickness ratio of the second layer 2B in the thickness of the negative electrode 20A), and the vertical axis represents the time (day) required for acetaldehyde decomposition.

As shown in FIG. 11, when the second layer thickness ratio is 0% (Example 4, negative electrode 20 is the first negative electrode active material 2a only), the acetaldehyde decomposition time is 6 days, and the second layer thickness is The acetaldehyde decomposition time decreases as the ratio increases to 30% and 50%, and is about 2 days when the second layer thickness ratio is 50%. Furthermore, the acetaldehyde decomposition time increases as the second layer thickness ratio increases to 70% and 100%, and when the second layer thickness ratio is 100% (Example 5, negative electrode 20 is the second negative electrode active material 2b only). It has been about 10 days.

From this, it is clear that the reaction rate in the photocatalyst 10D changes depending on the second layer thickness ratio in the negative electrode 20, and that the reaction rate decreases if the second layer thickness ratio is too small or too large. .. It is considered that this is because the carrier transport efficiency in the carrier transporter 4 and the reaction efficiency of the negative electrode 20 were balanced by adjusting the second layer thickness ratio.

In the photocatalyst 10D according to the fourth embodiment, the shortest acetaldehyde decomposition time is about 2 days, which is shorter than the shortest acetaldehyde decomposition time (about 3 days) of the photocatalyst 10C according to the third embodiment. Has become. As a result, the negative electrode 20A has a multi-layered structure, and the reaction field of light absorption and decomposition material (that is, the second layer 2B) and the field that carries carrier transport (that is, the first layer 2A) are separated, and the effect as a photocatalyst is obtained. It is suggested that can be improved.

In addition, the method of adjusting the thickness ratio of the first layer 2A and the second layer 2B does not require strict adjustment of the average particle diameter of each of the first negative electrode active material 2a and the second negative electrode active material 2b, and This is a method that can easily adjust the balance between the carrier transport efficiency of the transporter 4 and the reaction efficiency of the negative electrode 2. Therefore, it is possible to use commercially available negative electrode active materials as the first negative electrode active material 2a and the second negative electrode active material 2b.

In the photocatalyst 10D of the fourth embodiment, the negative electrode 20A has a two-layer structure including the first layer 2A and the second layer 2B. Further, the first layer 2A is composed of only the first negative electrode active material 2a, and the second layer 2B is composed of only the second negative electrode active material 2b. However, the present disclosure is not limited to this, and the first layer 2A and the second layer 2B are formed by mixing the first negative electrode active material 2a and the second negative electrode active material 2b, respectively. The mixing ratios may be different from each other. That is, the structure may be such that the small particle proportion of the second layer 2B separated from the carrier transport body 4 is made larger than the small particle proportion of the first layer 2A close to the carrier transport body 4. For example, the structure may be such that the small particle ratio in the first layer 2A is 30% and the small particle ratio in the second layer 2B is 70%. Of course, the first layer 2A may be composed of only the first negative electrode active material 2a and the second layer 2B may be composed of the first negative electrode active material 2a and the second negative electrode active material 2b. It may be composed of the first negative electrode active material 2a and the second negative electrode active material 2b, and the second layer 2B may be composed of only the second negative electrode active material 2b.

Further, the negative electrode 20A may have a multi-layer structure having three or more layers. In this case, the structure may be such that the layer closer to the carrier transporter 4 has a smaller proportion of small particles, and the layer further away from the carrier transporter 4 has a larger proportion of small particles.

The above third and fourth embodiments have a structure in which the negative electrode 20 includes two or more kinds of negative electrode active materials 2 having different average particle sizes. However, the present disclosure is not limited thereto, and the positive electrode 30 may have a structure including two or more kinds of positive electrode active materials having different average particle diameters depending on the substance to be decomposed. That is, the particle size distribution of the positive electrode active material 3 in the positive electrode 30 may have two or more peaks.

[Embodiment 5]
FIG. 12 is a side view showing the configuration of the photocatalyst 10E according to the fifth embodiment. The photocatalyst 10E covers the carrier transporter, the negative electrode 20 provided on a part of the surface of the carrier transporter, the positive electrode 30 provided on another part of the surface of the carrier transporter 4, and the surface of the negative electrode 20. The first insulating layer 5A and the second insulating layer 5B that covers the surface of the positive electrode 4 are provided. Since the configuration is the same as that of the third or fourth embodiment except that the first insulating layer 5A and the second insulating layer 5B are provided, the description thereof will be omitted.

The first insulating layer 5A and the second insulating layer 5B are formed of a porous body containing an insulating material. As the insulating substance, for example, a material having a high conduction band level such as glass, zirconium oxide, silicon oxide, aluminum oxide, or niobium oxide can be used. Further, both the first insulating layer 5A and the second insulating layer 5B are light-transmitting porous bodies. The insulating layers 5A and 5B are preferably formed by sintering insulating particles 5p made of a large number of insulating substances. The average particle size of the insulating particles 5p is preferably 1 nm or more and 600 nm or less, and more preferably 200 nm or more and 600 nm or less. When the average particle diameter of the insulating particles 5p is less than 1 nm, the decomposition target may be clogged in the holes of the insulating layers 5A and 5B. The particle diameters of the insulating particles 5p are preferably as uniform as possible (small particle size distribution).

In the manufacturing method of the present embodiment, before the [negative electrode film forming step] of the third embodiment, the insulating film 500A to be the insulating layer 5A is formed on the base material 100 [first insulating film forming step]. Including. Further, in the manufacturing method of the present embodiment, in the [negative electrode film forming step] of the third embodiment, the negative electrode film 200 to be the negative electrode 20 is not formed on the substrate 100, but the negative electrode film is formed on the insulating film 500A. Form 200. Further, in the manufacturing method of the present embodiment, in the positive electrode film forming step of the third embodiment, the insulating film 500B to be the insulating layer 5B is further formed on the positive electrode film 300 [second insulating film forming step]. including.

[First insulating film forming step]
In the first insulating film forming step, a paste containing insulating particles 5p (for example, a paste containing zirconia particles (manufactured by Sigma-Aldrich)) is prepared. Then, a paste containing the insulating particles 5p is applied on the substrate 100, dried at 100° C. to 150° C., and then baked at 300° C. to 700° C. for several hours. As a result, the insulating film 500A is formed on the base material 100. The solvent contained in the paste containing the insulating particles 5p can be appropriately selected from an aqueous solvent or an organic solvent. The method of applying the paste containing the insulating particles 5p to the base material 100 may be a known method, and examples thereof include screen printing.

[Second insulating film forming step]
After the positive electrode film forming step, in the second insulating film forming step, a paste containing the insulating particles 5p is prepared as in the first insulating film forming step. Then, a paste containing the insulating particles 5p is applied on the positive electrode film 300, dried at 100° C. to 150° C., and then baked at 300° C. to 700° C. for several hours. As a result, the insulating film 500B is formed on the positive electrode film 300.

After the [second insulating film forming step], the photocatalyst 10E according to the present embodiment is obtained by going through the atomizing step as in the third embodiment.

The photocatalyst according to the tenth embodiment includes an insulating layer 5A formed so as to cover a part of the surface of the negative electrode and an insulating layer 5B formed so as to cover a part of the surface of the positive electrode. Therefore, it is possible to suppress direct contact between one negative electrode of the two photocatalysts and the other positive electrode in the state where the plurality of photocatalysts are dispersed in the dispersion medium or in the dispersion medium or in the state where clusters are formed. it can. That is, it is possible to suppress the generation of leak current between the one negative electrode of the two photocatalysts and the other positive electrode, and to keep the reaction efficiency of the photocatalyst high.

Although the photocatalyst disclosed in the present embodiment includes both the insulating layer 5A and the insulating layer 5B, the photocatalyst includes a porous insulating layer that covers at least one of the negative electrode and the positive electrode. May be.

The above-mentioned photocatalysts 10 to 10E are preferably used in a state in which a plurality of photocatalysts are dispersed in a dispersion medium or in a state in which a plurality of photocatalysts are fixed to each other in random directions to form clusters. Here, the dispersion medium may be an aqueous dispersion medium such as water or an organic dispersion medium such as ethanol, methanol or terpineol. Each of the photocatalysts 10 to 10E, which have random directions in the dispersion medium or the clusters, can exhibit the photocatalytic function regardless of the incident direction of light.

Claims (22)

1. A carrier transporter,
   A plurality of negative electrode active materials smaller than the particle size of the carrier transporter and covering a part of the carrier transporter,
   A photocatalyst comprising a plurality of positive electrode active materials each having a particle size smaller than that of the carrier transporter and covering a part of the carrier transporter.
2. A negative electrode in which the plurality of negative electrode active materials are assembled,
   The photocatalyst according to claim 1, further comprising a positive electrode in which the plurality of positive electrode active materials are aggregated.
3. The photocatalyst according to claim 2, wherein the particle size distribution of the negative electrode active material in the negative electrode has two or more peaks.
4. The negative electrode is
   A first negative electrode active material,
   The photocatalyst according to claim 3, comprising a second negative electrode active material having an average particle size smaller than that of the first negative electrode active material.
5. The negative electrode is
   A first negative electrode layer that covers a part of the carrier transporter and mainly contains the first negative electrode active material;
   The 2nd negative electrode layer which covers a part of said 1st negative electrode layer, and mainly contains the said 2nd negative electrode active material, The photocatalyst of Claim 4 provided.
6. The average particle size of the first negative electrode active material is 100 nm or more and 600 nm or less,
   The photocatalyst according to claim 4 or 5, wherein an average particle diameter of the second negative electrode active material is 5 nm or more and 100 nm or less.
7. The photocatalyst according to any one of claims 2 to 6, wherein the particle size distribution of the positive electrode active material in the positive electrode has two or more peaks.
8. The photocatalyst according to claim 2, further comprising a porous insulating layer that covers at least one of the negative electrode and the positive electrode.
9. The photocatalyst according to any one of claims 1 to 8, wherein the particle size ratio of the negative electrode active material to the carrier transporter is 0.05 or more and 1 or less.
10. The photocatalyst according to claim 1, wherein the carrier transporter has an average particle size of 50 nm or more and 100 μm or less.
11. The photocatalyst according to any one of claims 1 to 10, wherein the weight ratio of the total weight of the negative electrode active material and the total weight of the positive electrode active material is in the range of 2:8 to 8:2.
12. The Fermi level of the carrier transporter is a position more negative than the electron energy level at the upper end of the valence band of the negative electrode active material, and is more positive than the electron energy level at the lower end of the conduction band of the positive electrode active material. The photocatalyst according to any one of claims 1 to 11, which is
13. The photocatalyst according to any one of claims 1 to 12, wherein the carrier transporter has a hole transport material containing any of copper iodide, nickel oxide, PEDOT, PEDOT-PSS, and spiro-OMeTAD.
14. The photocatalyst according to any one of claims 1 to 13, wherein the carrier transporter is an electron transporting material containing any of fullerene, fullerene derivative, silole compound and triazine compound.
15. The photocatalyst according to any one of claims 1 to 14, wherein the negative electrode active material contains any one of titanium oxide, strontium titanate, and tantalate.
16. The photocatalyst according to any one of claims 1 to 15, wherein the positive electrode active material contains any one of iron oxide (III), tungsten oxide, and vanadate.
17. The photocatalyst according to any one of claims 1 to 16, further comprising a sensitizer supported on at least one of the negative electrode active material and the positive electrode active material.
18. A plurality of photocatalysts according to any one of claims 1 to 18 are included,
    A photocatalytic cluster in which the photocatalysts adhere to each other in random directions to form clusters.
19. While imparting a shearing force, the carrier transporter, a particle size smaller than the particle size of the carrier transporter, a plurality of negative electrode active materials covering a part of the carrier transporter, and smaller than the particle size of the carrier transporter, And a step of mixing a plurality of positive electrode active materials that cover a part of the carrier transporter, the method for producing a photocatalyst.
20. Applying a first solution containing one of a plurality of negative electrode active materials and a plurality of positive electrode active materials to a substrate to form a first electrode film on the substrate;
    Applying a second solution containing a carrier transporter to the first electrode film to form the carrier transport film on the first electrode film;
    When the first solution contains the negative electrode active material, the first solution contains the positive electrode active material,
    When the first solution contains the positive electrode active material, a step of applying a third solution containing the negative electrode active material to the carrier transport film to form a second electrode film on the carrier transport film,
    A method for producing a photocatalyst, comprising a step of peeling a laminate including the first electrode film, the carrier transport film, and the second electrode film from the substrate and crushing the laminate.
21. The method for producing a photocatalyst according to claim 20, wherein
    The substrate includes a first insulating film including first insulating particles,
    In the step of forming the first electrode film, the method of manufacturing a photocatalyst, wherein the first solution is applied to the first insulating film.
22. The method for producing the photocatalyst according to claim 20 or 21,
    The substrate may further include applying second insulating particles to the second electrode film to form a second insulating film.
    The photocatalyst manufacturing method, wherein the stacked body further includes the second insulating film.

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