JP7141095B2 - photocatalyst - Google Patents

Description

The present invention relates to a photocatalyst and its production technology.

Patent Document 1 describes a technique relating to porous silica having pores with a diameter of 0.5 nm to 2.0 nm.

In Patent Document 2, a first substance capable of exhibiting a photocatalytic function and a second substance having a bandgap smaller than the first substance are joined together to increase the photocatalytic ability compared to the case of the first substance alone. A possible technique is described.

Japanese Patent No. 5647669 JP 2016-87522 A

In order to improve the activity of the photocatalyst, it is expected that it is effective to configure the photocatalyst particles from quantum dots of 0.5 nm to 2.0 nm. However, the expected improvement in activity was not observed. Therefore, it is necessary to devise quantum dots that are effective in improving the activity of photocatalysts.

Other problems and novel features will become apparent from the description of the specification and the accompanying drawings.

The photocatalyst in one embodiment includes a support having pores having a diameter that serves as a template for quantum dots having a diameter that causes the quantum size effect, a first portion inserted into the pores, and the first portion. and a second portion protruding outside the pores.

In one embodiment, the photocatalyst is in contact with a carrier formed with pores having a diameter that serves as a template for quantum dots having a diameter that causes the quantum size effect, the quantum dots inserted into the pores, and the quantum dots, and a catalyst material having nanoparticles disposed outside the pores.

A method for producing a photocatalyst according to one embodiment includes (a) a step of placing a carrier having pores having a diameter that causes a quantum size effect in a container, and (b) a step of injecting a precursor of a photocatalyst material into the container. and (c) drying the inside of the container into which the precursor has been injected under reduced pressure.

In one embodiment, the method for producing a photocatalyst includes (a) a first pore having a diameter that causes the quantum size effect, and a diameter that is larger than the diameter of the first pore and does not cause the quantum size effect. (b) a step of drying the structure after the step (a); and (c) a step of (b) and then firing the structure.

According to one embodiment, it is possible to improve the activity of the photocatalyst.

1 is a diagram showing a schematic structure of a photocatalyst in Embodiment 1. FIG. FIG. 2 shows bands of a photocatalyst having the structure shown in FIG. 1; 4 is a flow chart for explaining a manufacturing process of a photocatalyst according to Embodiment 1. FIG. 3(a) to 3(d) are diagrams showing the steps of manufacturing a photocatalyst in Example 1. FIG. (a) to (c) are a photocatalyst material composed of quantum dots and nanoparticles in porous silica having pores by going through the manufacturing process of the photocatalyst shown in FIGS. and is a diagram schematically showing the process of forming a complex containing. 1 is a TEM image of a photocatalyst in Example 1. FIG. It is a graph which shows the relationship between the irradiation time of an ultraviolet-ray, and hydrogen generation amount. 4 is a graph showing the relationship between the ultraviolet irradiation time and the amount of hydrogen generated when the concentration of the titanium chloride aqueous solution is varied from 5% by weight to 20% by weight. FIG. 9 is a graph showing the relationship between the amount of hydrogen generated and the concentration of the titanium chloride aqueous solution when the UV irradiation time in FIG. 8 is 270 minutes. 1 is a TEM image showing a state in which titanium oxide is formed inside and outside pores of porous silica when the concentration of the titanium chloride aqueous solution is 10% by weight. Fig. 10 is a TEM image showing a state in which a "jellyfish structure" is not formed inside and outside pores of porous silica when the concentration of the titanium chloride aqueous solution is 5% by weight. 4 is a graph showing the relationship between the ultraviolet irradiation time and the amount of carbon dioxide (CO ₂ ) produced by decomposing isopropyl alcohol upon irradiation with ultraviolet rays. FIG. 5 is a diagram schematically showing a photocatalyst in a modified example of Embodiment 1; It is a graph which shows the relationship between the irradiation time of an ultraviolet-ray, and hydrogen generation amount. FIG. 5 is a diagram showing a schematic structure of a photocatalyst in Embodiment 2; 5 is a flow chart showing a manufacturing process of a photocatalyst in Embodiment 2. FIG. (a) to (c) are diagrams showing morphological changes during photocatalyst production in Example 2. FIG. 4 is an SEM image of a photocatalyst in Embodiment 2. FIG. 4 is an SEM image of a photocatalyst in Embodiment 2. FIG. It is a graph which shows the relationship between the irradiation time of an ultraviolet-ray, and hydrogen generation amount.

In principle, the same members are denoted by the same reference numerals throughout the drawings for describing the embodiments, and repeated description thereof will be omitted. In order to make the drawing easier to understand, even a plan view may be hatched.

(Embodiment 1)
<Photocatalyst>
Photocatalysts, for example, emit nitrogen oxides (NO _x ), sulfur oxides (SO _x ), greenhouse gases such as methane gas, air pollutants, volatile organic compounds (VOC), oils and fats, etc. by light such as sunlight. It can be used for the detoxification treatment of fatty acids, odorants, dioxins, etc., and for the production of hydrogen by decomposing water. For this reason, photocatalysts are attracting attention from the viewpoints of air purification, prevention of global warming, antifouling, deodorization, sterilization, and the like. Photocatalysts are composed of semiconductor materials, and when irradiated with light having energy greater than the potential difference (bandgap) between the lower end of the conduction band and the upper end of the valence band, electrons are excited from the valence band to the conduction band. As a result, electrons are generated in the conduction band and holes are generated in the valence band. In the photocatalyst, electrons and holes generated by light irradiation induce photocatalytic activity. Specifically, in a photocatalyst made of a semiconductor material, electrons are excited from the valence band to the conduction band by irradiation with light having energy equal to or greater than the bandgap. As a result, when the photocatalyst is irradiated with light having energy higher than the bandgap, holes are formed in the valence band and electrons are excited in the conduction band, resulting in electron-hole pairs (excitons). ) will be generated. Various processes are conceivable as reactions occurring after this, but the following reaction occurs as an example. For example, if the level of holes formed in the valence band is lower than the oxidation level of hydroxide ions (OH ^- ), the holes transfer electrons from the hydroxide ions (OH ^- ). By robbing (by transferring an electron from the hydroxide ion to a hole), the hydroxide ion becomes a radical (.OH). Since these radicals have a strong oxidizing power (the property of taking electrons), organic compounds that come into contact with the photocatalyst can be decomposed into carbon dioxide and the like by the strong oxidizing power of the radicals. Thus, the photocatalyst will function. In order to expand the application range of photocatalysts having such properties, catalyst materials exhibiting high activity are desired.

For example, titanium oxide (TiO ₂ ) can be mentioned as a representative photocatalyst used on the market. This titanium oxide is used for self-cleaning by coating on the outer wall, odor purification by an air purifying device, and the like.

However, commercially available highly active photocatalysts are fine powders, and it is necessary to use a binder in order to apply them to walls or incorporate them into equipment. However, there is concern that the binder will also be decomposed by the decomposing power of the photocatalyst itself, and as decomposition progresses, it is assumed that the detachment of the photocatalyst will lead to deterioration of the performance of the photocatalyst and health hazards due to the scattering of fine powder. . In addition, in order to ensure sufficient adhesion, it is necessary to increase the amount of binder, which tends to cause a decrease in activity due to a decrease in the amount of catalyst.

<Usefulness of porous silica>
In order to solve such a problem, it is conceivable to fix a photocatalyst inside pores formed in a carrier that does not exhibit catalytic activity and is transparent to light in the visible region to the ultraviolet region. For example, porous silica is promising as a material that realizes such a configuration. Since porous silica also serves as an adsorbent, the use of porous silica makes it possible to combine an adsorbent and a photocatalyst. That is, by using porous silica, organic substances such as malodorous substances can be efficiently collected by the adsorption function of the porous silica, and the organic substances can be transferred to the photocatalyst embedded in the pores provided in the porous silica. Since the probability of contact can be increased, it is expected that the activity of the photocatalyst can be improved.

<Application of quantum dots>
Here, efficiency is important for putting photocatalysts on a commercial basis. In this regard, it is useful to reduce the size of the catalyst particles to increase the specific surface area in order to improve the activity of the photocatalyst. In addition, since the molecular size of many volatile organic compounds (VOCs) is 1 nm or less, porous silica with pores of around 1 nm is effective for adsorbing volatile organic compounds that cause offensive odors. . The present inventor has so far developed porous silica (super microporous silica: SMPS) having pores (super micropores) with a diameter of about 0.5 nm to 2.0 nm, and has a high VOC adsorption capacity. It is reported that

Therefore, by combining this porous silica (SMPS) and a photocatalyst, aiming to improve the activity by quantum dots in which the diameter of the photocatalyst particle is reduced to about 0.5 nm to 2.0 nm, it is also possible It is considered to be effective because it has advantages such as expansion of the site and increase in specific surface area. Furthermore, by introducing the photocatalyst material into the pores of the porous silica (SMPS), the porous silica as a carrier is interposed between the binder and the photocatalyst material, so that the photocatalyst material and the binder direct contact is suppressed. As a result, it is considered effective from the viewpoint of suppressing decomposition of the binder due to direct contact between the photocatalyst material and the binder.

The present inventor has previously succeeded in forming photocatalyst materials such as tungsten oxide and titanium oxide with quantum dots of about 0.5 nm to 2.0 nm using the pores of porous silica (SMPS). there is For example, when a photocatalyst material made of tungsten oxide is formed with quantum dots, photoreduction of oxygen and photoreduction of protons, which do not proceed with the photocatalyst material in the bulk state, proceed with the photocatalyst material of the quantum dots. I found That is, in the case of tungsten oxide, the photocatalytic function of bulk photocatalytic materials is realized by the strong oxidizing power of radicals (.OH, etc.) generated by holes, but the energy of excited electrons Excited electrons cannot be effectively used because the level is lower than the reduction level of protons and oxygen. In contrast, the photocatalyst material composed of quantum dots not only has a photocatalytic function realized by the strong oxidizing power of radicals (OH, etc.) generated due to holes formed in the valence band, but also A photocatalytic function realized by highly reactive superoxide anion radicals (O ₂ ^- , etc.) generated by binding of electrons excited in the conduction band to oxygen is also exhibited. As a result, it is expected that the photocatalyst material composed of quantum dots will enhance the synergistic effect between the photocatalyst function caused by holes and the photocatalyst function caused by electrons, and can improve the activity of the photocatalyst. That is, in the photocatalyst material composed of quantum dots, due to the expansion of the bandgap due to the quantum size effect, for example, the upper end level of the valence band is lower than the upper end level of the valence band of the bulk photocatalyst material. lower. This means that, for example, the level of holes formed in the valence band is lower than the oxidation level of hydroxide ions in a photocatalytic material composed of quantum dots than in a photocatalytic material composed of a bulk. means. This means that electrons are more likely to move from hydroxide ions to holes, and this is because the photocatalyst material composed of quantum dots has a stronger oxidizing power than the bulk photocatalyst material. This means that radicals (.OH, etc.) are easily formed (advantage 1). Furthermore, in a photocatalyst material composed of quantum dots, due to the expansion of the bandgap due to the quantum size effect, for example, the bottom level of the conduction band becomes higher than the bottom level of the conduction band of the bulk photocatalyst material. . As a result, for example, the energy difference between the lower end of the conduction band of the photocatalytic material made of quantum dots and the reduced level of oxygen is higher than the energy difference between the lower end of the conduction band of the photocatalytic material made of bulk and the reduced level of oxygen. energy difference increases. In the photocatalyst material consisting of quantum dots, the probability of occurrence of a phenomenon in which the electron excited in the conduction band transitions to the reduction level of oxygen and the oxygen is reduced in the photocatalyst material consisting of the quantum dots is higher than that of the conduction band. This means that the electrons excited in the band are more likely to transition to the reduction level of oxygen and reduce oxygen. As a result, in the photocatalyst material composed of quantum dots, electrons excited in the conduction band are supplied to oxygen, and oxygen is reduced, resulting in generation of highly reactive superoxide anion radicals (O ₂ -, etc.). easier. Therefore, due to the expansion of the bandgap due to the quantum size effect, the photocatalyst material composed of quantum dots exhibits a photocatalytic function realized by superoxide anion radicals (O ₂ -, etc.) more than the bulk photocatalyst material. (advantage 2).

From the above, it is considered that the photocatalyst material composed of quantum dots can improve the activity of the photocatalyst due to the synergistic effect of the above-mentioned (advantage 1) and (advantage 2).

As described above, the composite material of the photocatalyst material composed of quantum dots and the porous silica (SMPS) is a composite of the high-performance adsorbent and the photocatalyst material. It is considered to be effective for various photocatalytic reactions such as decomposition.

<Room for improvement>
However, in our research, when forming quantum dots made of titanium oxide inside the pores of porous silica (SMPS), the photocatalytic activity is significantly higher than that of bulk titanium oxide or nanoparticle titanium oxide. was found to decrease to That is, as described above, in a photocatalytic material composed of quantum dots, it is expected that the photocatalytic activity can be improved by the synergistic effect of the photocatalytic function caused by holes and the photocatalytic function caused by electrons. On the other hand, in reality, a phenomenon occurs in which the photocatalytic activity is greatly reduced.

The cause of this decrease in photocatalytic activity is considered as follows. That is, in the case of a photocatalyst material composed of quantum dots, the particle size becomes very small, and as a result, the particle size becomes smaller than the Bohr radius of excitons. This means that the electron-hole pairs generated by light irradiation are more likely to recombine. In other words, in photocatalyst materials composed of quantum dots, the distance between electron-hole pairs generated by light irradiation is shorter than the distance at which stable excitons are formed, so the electron-hole pairs are stable as excitons. are unable to exist within each other and are more likely to recombine as they approach each other. In other words, in the case of a photocatalyst material composed of quantum dots, since the particle size is extremely small, spatial charge separation of electrons and holes in electron-hole pairs generated by light irradiation becomes difficult. For this reason, it is believed that photocatalytic activity decreases in photocatalytic materials composed of quantum dots due to an increase in the recombination probability of electron-hole pairs. Thus, the photocatalytic material composed of quantum dots has the potential to significantly improve the activity of the photocatalyst due to the synergistic effect of the photocatalytic function caused by the holes and the photocatalytic function caused by the electrons. Factors unique to quantum dots with small particle sizes actually reduce the photocatalytic activity.

Therefore, in a photocatalyst material composed of quantum dots formed inside the pores of porous silica (SMPS), if spatial charge separation of electron-hole pairs can be realized, the photocatalytic activity can be dramatically improved. it is conceivable that. Therefore, in Embodiment 1, a photocatalyst material composed of quantum dots, which has the potential to significantly improve photocatalytic activity, is devised to achieve spatial charge separation of electron-hole pairs. . In the following, the technical idea of the first embodiment with this contrivance will be described.

<Structure of photocatalyst>
FIG. 1 is a diagram showing a schematic structure of a photocatalyst 20 according to the first embodiment. In FIG. 1, the photocatalyst 20 in Embodiment 1 has a carrier made of, for example, porous silica (SiO ₂ ) 10, and the carrier has a quantum dot template with a diameter that causes the quantum size effect. Pores 11 having different diameters are formed. For example, the diameter of the pores 11 formed in the carrier made of the porous silica 10 is 0.5 nm or more and 2.0 nm or less, preferably about 1.0 nm.

As shown in FIG. 1, the pores 11 formed in the porous silica are filled with, for example, quantum dots of titanium oxide 12a. That is, the pores 11 formed in the porous silica are embedded with quantum dots exhibiting a quantum size effect, and the quantum dots are composed of titanium oxide 12a, which is a photocatalyst material.

Furthermore, the photocatalyst 20 in Embodiment 1 shown in FIG. Titanium oxide 12b consisting of nanoparticles protruding from 11 is formed. At this time, as shown in FIG. 1, the titanium oxide 12a made of quantum dots and the titanium oxide 12b made of nanoparticles are integrally formed. As described above, the photocatalyst 20 in the first embodiment includes the titanium oxide 12a (first portion) composed of the quantum dots embedded in the pores 11 formed in the porous silica, and the Titanium oxide 12b made of nanoparticles.

Here, the particle size of the titanium oxide 12a forming the quantum dots is smaller than the particle size of the titanium oxide 12b forming the nanoparticles. In other words, the particle size of the titanium oxide 12b forming the nanoparticles is larger than the particle size of the titanium oxide 12a forming the quantum dots. For example, the particle diameter of the titanium oxide 12a forming the quantum dots is 0.5 nm or more and 2.0 nm or less. On the other hand, for example, the particle diameter of the titanium oxide 12b forming the nanoparticles is 5 nm or more and 50 nm or less.

<Mechanism of spatial charge separation>
Next, the fact that the photocatalyst 20 having the structure shown in FIG. 1 can achieve spatial charge separation of electron-hole pairs generated by irradiating the photocatalyst 20 with light will be described.

FIG. 2 is a diagram showing bands of the photocatalyst 20 having the structure shown in FIG. In FIG. 2, a band of titanium oxide 12a composed of quantum dots embedded in pores 11 is shown adjacent to a support composed of porous silica 10, and adjacent to this titanium oxide 12a composed of quantum dots. A band of titanium oxide 12b consisting of nanoparticles is shown.

In FIG. 2, in the titanium oxide 12a composed of quantum dots, a quantum size effect occurs in which the bandgap expands. On the other hand, in the titanium oxide 12b composed of nanoparticles, the quantum size effect is not exhibited and the bandgap is not expanded. As a result, as shown in FIG. 2, the band is tilted in the boundary region between the titanium oxide 12a composed of quantum dots and the titanium oxide 12b composed of nanoparticles. Specifically, since the bandgap of the titanium oxide 12a made of quantum dots is widened, the conduction band of the titanium oxide 12a made of quantum dots exists at a higher energy position than the conduction band of the titanium oxide 12b made of nanoparticles. do. As a result, as shown in FIG. 2, the conduction band is tilted downward from the titanium oxide 12a composed of quantum dots toward the titanium oxide 12b composed of nanoparticles.

Here, when the titanium oxide 12a made of quantum dots is irradiated with light, electrons are excited from the valence band to the conduction band. It moves along the conduction band sloping downward toward the titanium oxide 12b composed of nanoparticles. That is, as shown in FIG. 2, electrons excited in the conduction band of the titanium oxide 12a composed of quantum dots move to the conduction band of the titanium oxide 12b composed of nanoparticles with lower energy. As a result, holes generated in the valence band of the titanium oxide 12a composed of quantum dots and electrons transferred from the conduction band of the titanium oxide 12a composed of quantum dots to the conduction band of the titanium oxide 12b composed of nanoparticles. the spatial distance between them increases. This means that the recombination probability of electron-hole pairs generated by light irradiation is reduced. Therefore, according to the photocatalyst 20 of the first embodiment, it is possible to suppress the increase in the recombination probability of electron-hole pairs due to the structure (size reduction structure) peculiar to the photocatalyst material composed of quantum dots. A synergistic effect can be obtained between the photocatalyst function caused by electrons and the photocatalyst function caused by electrons, thereby greatly improving the activity of the photocatalyst.

The basic concept of the first embodiment is basically based on the premise that a photocatalyst material composed of quantum dots capable of obtaining a synergistic effect between the photocatalyst function caused by holes and the photocatalyst function caused by electrons is adopted. do. The basic idea of the first embodiment is to solve the problem of the difficulty of spatial charge separation of electron-hole pairs, which is manifested in quantum dots, by, for example, oxidizing quantum dots as shown in FIG. The idea is to solve the problem by forming the titanium oxide 12b made of nanoparticles so as to be integrated with the titanium 12a. That is, the basic idea in the first embodiment is to integrally connect the titanium oxide 12a made of quantum dots and the titanium oxide 12b made of nanoparticles. According to the basic idea of the first embodiment, the conduction band of the titanium oxide 12a made of quantum dots whose bandgap is widened by the quantum size effect is shifted from the conduction band of the titanium oxide 12b made of nanoparticles in which the quantum size effect does not appear. A gradient can be produced between the conduction band. As a result, according to the basic concept of the first embodiment, the electrons generated in the titanium oxide 12a made of quantum dots can be transferred to the titanium oxide 12b made of nanoparticles by utilizing the gradient of the conduction band. It is possible to increase the spatial distance between the holes localized in the titanium oxide 12a made of titanium oxide and the electrons moved to the titanium oxide 12b made of nanoparticles. Therefore, according to the basic concept of the first embodiment, it is possible to solve the problem manifested in quantum dots that the spatial charge separation of electron-hole pairs is difficult. A synergistic effect can be obtained between the photocatalytic function caused by holes and the photocatalytic function caused by electrons. That is, according to the basic idea of the first embodiment, the excellent photocatalytic function inherent in the photocatalytic material composed of quantum dots can be brought out, and as a result, the photocatalytic activity can be significantly improved.

Thus, in Embodiment 1, for example, as shown in FIG. While forming the titanium oxide 12a, a photocatalyst material composed of nanoparticles is formed on the surface of the porous silica 10 to obtain a photocatalyst 20 composed of a composite. Thereby, electron-hole pairs generated by light irradiation can be spatially separated into quantum dots and nanoparticles. As a result, for example, it is possible to obtain photocatalytic activity that is several tens to several hundred times higher than that of commercially available titanium oxide. In the photocatalyst 20 according to Embodiment 1, the composite photocatalyst material is formed on the carrier made of the porous silica 10, so that the porous silica has a high adsorption capacity and the composite photocatalyst material The synergistic effect with high photocatalytic activity results in very high activity for photodegradation reactions of, for example, volatile organic compounds (VOCs).

<Method for producing photocatalyst>
Next, a method for producing a photocatalyst according to Embodiment 1 will be described.

FIG. 3 is a flow chart for explaining the flow of the photocatalyst manufacturing process according to the first embodiment. As shown in FIG. 3, first, a carrier having pores having a diameter that serves as a template for quantum dots having a diameter that causes the quantum size effect is formed by a known method, and then the carrier is placed in a container (S101). . Next, the precursor of the photocatalyst material is injected into the container containing the carrier (S102). Then, the inside of the container into which the precursor is injected is dried under reduced pressure (S103). Subsequently, after taking out the carrier from the container (S104), the carrier is calcined (S105). A photocatalyst can be produced as described above.

<<Example 1>>
Specific Example 1 of the method for producing a photocatalyst will be described below.

4(a) to (d) are schematic diagrams showing the flow of the photocatalyst manufacturing process in Example 1. FIG. FIGS. 5(a) to (c) show photocatalyst materials composed of quantum dots in porous silica having pores and nanoparticles by going through the photocatalyst manufacturing process shown in FIGS. 4(a) to (d). FIG. 4 is a diagram schematically showing the process of forming a composite containing a photocatalyst material.

First, porous silica 10 (SMPS) having pores with an average diameter of 1.0 nm is produced by a known method. Specifically, 8 g (0.038 mol; 1 eq) of tetraethoxysilane (TEOS) as a silica source is placed in a polypropylene container. Subsequently, hexyltrimethylammonium bromide (C6TAB) (0.0075 mol to 0.038 mol), which is a surfactant, is dispersed and stirred. Then, 2.74 g (0.152 mol; 4 eq) of water adjusted to pH 2 using hydrochloric acid is added thereto and stirred at room temperature to gel. The gel is dried at 60° C. and baked at 600° C. for 3 hours to remove the surfactant. Thereby, the porous silica 10 having pores (supermicropores) with an average diameter of 1.0 nm can be obtained.

Next, the photocatalyst in Example 1 is produced using the porous silica 10 produced in this way. In Example 1, titanium oxide is used as the photocatalyst material, and a titanium (III) chloride aqueous solution (20% by weight) is used as the precursor of this titanium oxide. In Example 1, a vacuum impregnation method is used as a method for synthesizing a photocatalyst.

Specifically, first, porous silica 10 having pores with an average diameter of 1.0 nm is pulverized in a mortar into powder. Subsequently, as shown in FIG. 4( a ), powdered porous silica 10 is placed in a container (eggplant flask) 30 . Thereafter, the powdery porous silica 10 is dried under reduced pressure for one day and night to remove the adsorbed water adsorbed on the porous silica 10 . Pores 11 formed in this porous silica 10 are shown in FIG. 5(a).

After that, as shown in FIG. 4(b), in a state where the container 30 is depressurized, an aqueous solution of titanium chloride in an amount equal to the volume of the pores 11 formed in the porous silica 10 is injected with a syringe. By stirring, part of the titanium chloride aqueous solution is allowed to penetrate into the pores 11 of the porous silica 10. FIG. 5(b) shows a state in which the precursor 31 made of the aqueous titanium chloride solution is infiltrated into the pores 11 and the precursor 31 made of the aqueous titanium chloride solution is present outside the pores 11 as well. It is

Subsequently, the interior of the container 30 is gradually evacuated using, for example, a vacuum pump. At this time, it is sufficient for the vacuum pump to have a capacity of 0.5 Pa or more, and the evacuation time is, for example, within 30 minutes. After that, the porous silica 10 impregnated with the precursor 31 is dried in a time range of less than 3 days while the inside of the container 30 is maintained in a vacuum state. Here, the drying time is desirably about 1 day, and depending on the degree of vacuum, about 5 hours is sufficient. By going through this step, the precursor 31 is dried while maintaining the protruding state (FIG. 5(c)).

Next, after taking out the dried porous silica 10 from the container 30, the photocatalyst 20 in Example 1 can be produced by calcining it in the air at 450°C. Specifically, in FIG. 5( c ), a dried titanium oxide precursor 12 a ′ composed of quantum dots is formed in the pores 11 of the porous silica 10 , and the nanoparticles protrude from the pores 11 . A photocatalyst precursor 20' is shown from which a dried precursor 12b' is formed.

6 is a TEM image of the photocatalyst in Example 1. FIG. From FIG. 6, the first part (“(a)”) consisting of quantum dots with a diameter of 0.5 nm to 2.0 nm and the second part (“(b)”) consisting of nanoparticles with a diameter of 5 nm to 50 nm It can be seen that the photocatalyst is composed of the complex containing

<Comparative Example 1>
The photocatalyst in Comparative Example 1 is a commercially available p25 titanium oxide (0.1 g) manufactured by degussa.

<Comparative Example 2>
The photocatalyst in Comparative Example 2 is a photocatalyst in which a photocatalyst material made of titanium oxide is added to porous silica having pores with an average diameter of 3 nm (hereinafter referred to as mesoporous silica). Specifically, the photocatalyst in Comparative Example 2 is produced as follows. That is, the mesoporous silica powder is dried under reduced pressure in an eggplant flask for a whole day and night to remove the water adsorbed on the mesoporous silica. Then, under reduced pressure, an aqueous solution of titanium chloride in an amount equal to the pore volume of the mesoporous silica is injected with a syringe, and the powder is stirred to allow the aqueous titanium chloride solution to permeate into the pores. Then, the photocatalyst in Comparative Example 2 can be obtained by drying again under reduced pressure for one day and night, and then calcining the dried sample in the air at 450°C.

<Comparative Example 3>
The photocatalyst in Comparative Example 3 is a photocatalyst in which a photocatalyst material is formed only in the pores of porous silica. Specifically, the photocatalyst in Comparative Example 3 is produced as follows. That is, porous silica having an average diameter of 1.1 nm is immersed in an aqueous titanium (III) chloride solution (20% by weight). Then, the surface of the porous silica is washed with ethanol. Next, after drying under reduced pressure, the photocatalyst in Comparative Example 3 can be obtained by firing at 600° C. for 3 hours.

The spectral absorption edge of the photocatalyst in Comparative Example 3 is 3.5 eV, and the particle size calculated from the bandgap is about 1.1 nm. From this, it can be seen that in the photocatalyst of Comparative Example 3, quantum dots having approximately the same size as the diameter of the pores formed in the porous silica are formed. On the other hand, in the photocatalyst of Comparative Example 3, since no absorption of 3.2 eV due to bulk titanium oxide was observed, bulk titanium oxide did not exist outside the pores. It can be seen that quantum dots made of titanium oxide are formed only inside the pores formed in the porous silica.

<Comparative Example 4>
The photocatalyst in Comparative Example 4 was prepared in the same manner as the photocatalyst in Example 1, except that the concentration of the precursor titanium chloride aqueous solution was reduced from 20% by weight to 5% by weight.

<Verification of effect>
Next, the superiority of the photocatalyst in Example 1 will be described by comparing Example 1 and Comparative Examples 1 to 4 described above. In particular, the predominance of the photocatalyst in Example 1 is carried out in hydrogen production by water splitting containing a sacrificial reagent. Specifically, 0.1 g of the sample (photocatalyst) was put into water containing 20% by volume of the sacrificial reagent (ethanol), and then argon gas was bubbled for one hour while stirring to remove the dissolved gas and the gas in the headspace. is replaced with argon. After that, an ultra-high pressure mercury lamp is used to irradiate ultraviolet rays. The amount of hydrogen in the system is measured by analyzing the change over time of the gas components in the headspace with a gas chromatograph.

The amount of titanium oxide in the porous silica is determined using the bulk FP method of a fluorescent X-ray device. Also, the average diameter of the pores formed in the porous silica is determined by the GCMC analysis method of the N ₂ adsorption method.

FIG. 7 is a graph showing the relationship between the irradiation time of ultraviolet rays and the amount of hydrogen generated. Graph (a) in FIG. 7 shows the results when the photocatalyst in Example 1 was used. On the other hand, graph (b) in FIG. 7 shows the results when the photocatalyst in Comparative Example 1 is used, and graph (c) shows the results when the photocatalyst in Comparative Example 2 is used. Graph (d) in FIG. 7 shows the results when the photocatalyst in Comparative Example 3 is used, and graph (e) shows the results when the photocatalyst in Comparative Example 4 is used.

As shown in FIG. 7, the amount of hydrogen generated when the photocatalyst in Example 1 is used is significantly larger than the amount of hydrogen generated when the photocatalysts in Comparative Examples 1-4 are used. This means that the performance of the photocatalyst in Example 1 is superior to the performance of the photocatalysts in Comparative Examples 1-4. Furthermore, when examined in detail, the photocatalyst in Comparative Example 2 is a photocatalyst in which a photocatalyst material made of titanium oxide is added to porous silica having pores with an average diameter of 3 nm, and the particle size of titanium oxide is large. Therefore, no significant quantum size effect occurs. In the photocatalyst of Comparative Example 2, as shown in the graph (c) of FIG. 7, almost no hydrogen was generated. From this, like the photocatalyst of Example 1, a photocatalyst material composed of quantum dots of 0.5 nm or more and 2.0 nm or less in which the quantum size effect is remarkably expressed, and a photocatalyst composed of nanoparticles having a diameter of 5 nm or more and 50 nm or less From the viewpoint of improving the photocatalytic activity, it is important to form a composite with the material. The photocatalyst in Comparative Example 3 is a photocatalyst in which quantum dots made of titanium oxide are formed only inside pores of porous silica having pores with an average diameter of 1.1 nm. With the photocatalyst in Comparative Example 3, as shown in the graph (e) of FIG. 7, it can be seen that almost no hydrogen is generated. Therefore, like the photocatalyst in Comparative Example 3, in a photocatalyst in which quantum dots made of titanium oxide are formed only inside pores of porous silica having pores with an average diameter of 1.1 nm, hydrogen is generated. It can be seen that there is almost no contributing photocatalytic function. From this, like the photocatalyst of Example 1, a photocatalyst material composed of quantum dots of 0.5 nm or more and 2.0 nm or less in which the quantum size effect is remarkably expressed, and a photocatalyst composed of nanoparticles having a diameter of 5 nm or more and 50 nm or less It can be seen that a high photocatalyst function that contributes to the generation of hydrogen can be realized when it is combined with a material.

In addition, in the photocatalyst of Comparative Example 4, the concentration of the titanium chloride aqueous solution, which is the precursor, was lowered to 5% by weight, and in this case as well, as shown in the graph (e) of FIG. is doing. More specifically, even when the concentration of the titanium chloride aqueous solution was decreased from 20% by weight to 10% by weight, the bonding between the quantum dots and the nanoparticles was observed. %, no bonding between quantum dots and nanoparticles is observed. A large amount of hydrogen is generated even when the concentration of the aqueous titanium chloride solution is decreased from 20% by weight to 10% by weight, while hydrogen is hardly generated when the concentration of the aqueous titanium chloride solution is further decreased to 5% by weight. The result is that This can be attributed to the fact that due to the lack of precursors, the bonding between the quantum dots and the nanoparticles did not occur, and effective charge separation of the electron-hole pairs did not occur.

From the above, it is confirmed that the photocatalyst in Example 1 can improve the photocatalytic activity more than the photocatalysts in Comparative Examples 1-4. That is, from the results shown in FIG. 7, it can be seen that the photocatalyst in Example 1 is superior to the photocatalysts in Comparative Examples 1 to 4 from the viewpoint of improving the photocatalytic activity.

Further, the relationship between the irradiation time of ultraviolet rays and the amount of hydrogen generated will be described in detail when the concentration of the titanium chloride aqueous solution, which is the precursor, is changed.

FIG. 8 is a graph showing the relationship between the ultraviolet irradiation time and the amount of hydrogen generated when the concentration of the titanium chloride aqueous solution is varied from 5% by weight to 20% by weight. In FIG. 8, graph (a) is a graph showing the relationship between the ultraviolet irradiation time and the amount of hydrogen generated when the concentration of the titanium chloride aqueous solution is 10% by weight, and the graph (b) is a graph showing the relationship between the concentration of the titanium chloride aqueous solution It is a graph which shows the relationship between ultraviolet irradiation time and the amount of hydrogen generation in the case of 20 weight%. In FIG. 8, graph (c) is a graph showing the relationship between the ultraviolet irradiation time and the amount of hydrogen generated when the concentration of the titanium chloride aqueous solution is 15% by weight, and graph (d) is the titanium chloride aqueous solution. 4 is a graph showing the relationship between the UV irradiation time and the amount of hydrogen generated when the concentration is 7% by weight. Graph (e) is a graph showing the relationship between the ultraviolet irradiation time and the amount of hydrogen generated when the concentration of the titanium chloride aqueous solution is 5% by weight.

As shown in FIG. 8, when the concentration of the titanium chloride aqueous solution is less than 10% by weight (graph (d)), compared to when the concentration of the titanium chloride aqueous solution is 10% by weight or more (graphs (a) to (c)) ~ (e)), it can be seen that the amount of hydrogen generation is small. Therefore, from the viewpoint of improving the photocatalytic activity, it is desirable that the concentration of the precursor titanium chloride aqueous solution is 10% by weight or more. Here, FIG. 9 is a graph showing the relationship between the amount of hydrogen generated and the concentration of the titanium chloride aqueous solution when the ultraviolet irradiation time in FIG. 8 is "270 minutes".

8 and 9, the amount of hydrogen generated is a value per unit gram of photocatalyst. When the concentration of the aqueous titanium chloride solution is 10% by weight or more, the amount of hydrogen generated is almost the same. However, in FIG. Therefore, apparently, the amount of hydrogen generated per unit gram of photocatalyst appears to decrease. From this, it can be seen that the amount of hydrogen generated is large when the concentration of the titanium chloride aqueous solution is 10% by weight or more. On the other hand, it can be seen from FIG. 9 that when the concentration of the aqueous titanium chloride solution falls below 10% by weight, the amount of hydrogen generated decreases sharply. This can be attributed to the fact that due to the lack of precursors, no bonding between the quantum dots and nanoparticles occurs, and effective electron-hole pair charge separation does not occur. Actually, FIG. 10 is a TEM image showing a state in which titanium oxide is formed inside and outside the pores of porous silica when the concentration of the titanium chloride aqueous solution is 10% by weight. In FIG. 10, the dot-shaped regions indicate regions where titanium oxide exists. As shown in FIG. 10, titanium oxide is formed inside and outside the pores of the porous silica, resulting in quantum dots inside the pores. and nanoparticles outside the pores (“jellyfish structure”).

In contrast, FIG. 11 is a TEM image showing a state in which no "jellyfish structure" is formed inside and outside the pores of the porous silica when the concentration of the titanium chloride aqueous solution is 5% by weight. In FIG. 11, the dot-shaped regions indicate regions where titanium oxide exists. As shown in FIG. It can be seen that a “jellyfish structure”, which is a bonding structure with nanoparticles, does not occur.

Therefore, looking at the results of FIGS. 8 to 11 together, when the concentration of the precursor titanium chloride aqueous solution is 10% by weight or more, the bonding structure between the quantum dots inside the pores and the nanoparticles outside the pores is formed, and as a result of effective charge separation of electron-hole pairs caused by this "jellyfish structure", it is possible to achieve a dramatic improvement in photocatalytic activity. It can be seen that

Furthermore, FIG. 12 is a graph showing the relationship between the ultraviolet irradiation time and the amount of carbon dioxide (CO ₂ ) produced by decomposing isopropyl alcohol upon irradiation with ultraviolet rays. In FIG. 12, graph (a) is the result when the photocatalyst in Example 1 is used, and graph (b) is the result when the photocatalyst in Comparative Example 1 is used.

As shown in FIG. 12, the amount of carbon dioxide generated when the photocatalyst in Example 1 is used is significantly greater than the amount of carbon dioxide generated when the photocatalyst in Comparative Example 1 is used. This means that the performance of the photocatalyst in Example 1 is superior to the performance of the photocatalyst in Comparative Example 1. This FIG. 12 also confirms that the photocatalyst in Example 1 can improve the photocatalytic activity more than the photocatalyst in Comparative Example 1. That is, it can be seen from the results shown in FIG. 12 that the photocatalyst in Example 1 is superior to the photocatalyst in Comparative Example 1 from the viewpoint of improving photocatalytic activity.

<Modification>
Next, a modified example of Embodiment 1 will be described.

FIG. 13 is a diagram schematically showing a photocatalyst in a modified example of Embodiment 1. FIG.

As shown in FIG. 13, the photocatalyst 20 in this modified example has a carrier made of, for example, porous silica 10, and the carrier is formed with pores 11 having a diameter that causes the quantum size effect. . Then, as shown in FIG. 13, the pores 11 formed in the porous silica are filled with, for example, titanium oxide 12a and tungsten oxide 40 made of quantum dots.

That is, the pores 11 formed in the porous silica are embedded with quantum dots exhibiting a quantum size effect, and the quantum dots are composed of titanium oxide 12a and tungsten oxide 40, which are photocatalyst materials. . In other words, in the photocatalyst 20 of this modified example, in addition to the titanium oxide 12a, a catalyst material different in type from the titanium oxide 12a and in contact with the titanium oxide 12a is inserted inside the pores 11. . Specifically, this catalytic material is tungsten oxide 40 . This point is the difference between the photocatalyst 20 in this modified example and the photocatalyst in the first embodiment.

Furthermore, in the photocatalyst 20 in this modification shown in FIG. Titanium oxide 12b composed of nanoparticles is also formed on the surface of (porous silica 10). At this time, as shown in FIG. 13, titanium oxide 12a composed of quantum dots and titanium oxide 12b composed of nanoparticles are integrally formed. Thus, in the photocatalyst 20 in this modification, titanium oxide 12a and tungsten oxide 40 composed of quantum dots embedded in the pores 11 formed in porous silica, and nanoparticles protruding outside the pores 11 and titanium oxide 12b.

According to the photocatalyst 20 in this modified example configured in this way, it is possible to further improve the photocatalytic activity as compared with the photocatalyst in the first embodiment.

This point will be described below. For example, in the photocatalyst 20 according to the present modification, similarly to the photocatalyst 20 according to Embodiment 1, electrons are excited from the valence band to the conduction band when the titanium oxide 12a made of quantum dots is irradiated with light. , the electrons excited in the conduction band move along the conduction band sloping downward from the titanium oxide 12a composed of quantum dots toward the titanium oxide 12b composed of nanoparticles. That is, the electrons excited in the conduction band of the titanium oxide 12a composed of quantum dots move to the conduction band of the titanium oxide 12b composed of nanoparticles with lower energy (see FIG. 2). Furthermore, electrons generated by light irradiation in the tungsten oxide 40 also move to the conduction band of the titanium oxide 12b, which is composed of nanoparticles with lower energy, via the titanium oxide 12a, which is composed of quantum dots. As a result, holes generated in the valence band of the titanium oxide 12a made of quantum dots and the tungsten oxide 40 and titanium oxide 12b made of nanoparticles from the conduction band of the titanium oxide 12a made of quantum dots and the tungsten oxide 40 are formed. The spatial distance between electrons that have moved to the conduction band increases. Further, in this modification, as shown in FIG. 13, not only the titanium oxide 12a but also the tungsten oxide 40 are embedded inside the pores 11 having a size that causes the quantum size effect. Here, the hole mobility in the tungsten oxide 40 is higher than the hole mobility in the titanium oxide 12a. Also, quantum size effects in tungsten oxide mainly lead to elevation of the conductor bottom. On the other hand, in the case of titanium oxide, the conductor and valence bands rise and fall, respectively. Therefore, the upper end of the valence band of tungsten oxide 40 is located higher than the upper end of the valence band of titanium oxide 12a. As a result, holes generated in the valence band of the titanium oxide 12 a move toward the tungsten oxide 40 due to the irradiation of light. This is because the tungsten oxide 40 has a higher hole mobility than the titanium oxide 12a, and the upper end of the valence band of the tungsten oxide 40 is located on the negative side of the upper end of the valence band of the titanium oxide 12a. Because it does. From this, in the photocatalyst 20 according to the present modification, among the electron-hole pairs generated in the titanium oxide 12a composed of quantum dots by irradiation of light (ultraviolet light or visible light), electrons are narrowed due to the gradient of the conduction band. It moves to the side of titanium oxide 12b made of nanoparticles protruded outside the hole 11 . On the other hand, among the electron-hole pairs, holes move to the tungsten oxide 40 side due to the factors described above. Therefore, in the photocatalyst 20 of the present modification, the spatial charge separation between electrons and holes is greater than in the photocatalyst 20 of the first embodiment by the amount that the holes move toward the tungsten oxide 40 side. Therefore, according to the photocatalyst 20 of this modified example, the recombination probability of electron-hole pairs generated by light irradiation can be reduced more than the photocatalyst 20 of the first embodiment. Therefore, according to the photocatalyst 20 in this modification, it is possible to further suppress the increase in the recombination probability of electron-hole pairs due to the structure (size reduction structure) peculiar to the photocatalyst material composed of quantum dots, The activity of the photocatalyst can be improved more than the photocatalyst 20 in the first embodiment.

FIG. 14 is a graph showing the relationship between the irradiation time of ultraviolet rays and the amount of hydrogen generated. Graph (a) in FIG. 14 shows the results when the photocatalyst in the modified example is used. On the other hand, graph (b) in FIG. 7 shows the results when the photocatalyst in Example 1 was used.

As shown in FIG. 14, the amount of hydrogen generated when the photocatalyst in the modified example is used is significantly larger than the amount of hydrogen generated when the photocatalyst in Example 1 is used. This means that the performance of the photocatalyst in the modified example is superior to the performance of the photocatalyst in the first example. That is, from the results shown in FIG. 14, by forming the tungsten oxide 40 in addition to the titanium oxide 12a in the pores 11 shown in FIG. 13, the spatial electrical separation between electrons and holes can be increased. , it can be said that the activity of the photocatalyst can be significantly improved as compared with the first embodiment.

(Embodiment 2)
<Structure of photocatalyst>
FIG. 15 is a diagram showing a schematic structure of the photocatalyst 25 according to the second embodiment. In FIG. 15, the photocatalyst 25 in Embodiment 2 includes, as a carrier, porous silica nanoparticles 50 having pores 51 with diameters that exhibit the quantum size effect, for example. Then, the photocatalyst 25 in the second embodiment is in contact with the titanium oxide 52 made of quantum dots inside the pores 51 of the porous silica nanoparticles 50, and in contact with the titanium oxide 52, and around the porous silica nanoparticles 50 and a titanium oxide 53 made of nanoparticles arranged in the inter-particle voids.

<Method for producing photocatalyst>
Next, a method for producing a photocatalyst according to Embodiment 2 will be described.

FIG. 16 is a flow chart for explaining the flow of the photocatalyst manufacturing process according to the second embodiment. As shown in FIG. 16, first, by a known method, a first pore having a diameter that causes the quantum size effect and a second pore having a diameter that is larger than the diameter of the first pore and does not cause the quantum size effect. A structure having two pores is prepared (S201). Next, this structure is immersed in a precursor of a photocatalyst material (S202). After drying the structure (S203), the structure is fired (S204). A photocatalyst can be produced as described above.

<<Example 2>>
Example 2, which is a specific example of the method for producing a photocatalyst, will be described below.

FIGS. 17(a) to 17(c) are schematic diagrams showing morphological changes during production of the photocatalyst in Example 2. FIG. First, a container made of polypropylene is charged with 8 g (0.038 mol; 1 eq) of tetraethoxysilane (TEOS) as a silica source. Subsequently, hexyltrimethylammonium bromide (C6TAB) (0.0075 mol to 0.038 mol) as a surfactant and polyethylene glycol (average molecular weight: 1000) (0.0075 mol to 0.038 mol) are dispersed and stirred. Then, 2.74 g (0.152 mol; 4 eq) of water adjusted to pH 2 using hydrochloric acid is added thereto and stirred at room temperature to obtain a precursor sol. Next, this precursor sol is injected into a 20% aqueous ammonia solution using a syringe. At this time, the precursor sol gels at the moment of contact with aqueous ammonia. The gel is then dried at 60° C. and baked at 600° C. for 3 hours to remove the surfactant and polyethylene glycol. As a result, porous silica nanoparticles 50 having pores (supermicropores) with an average diameter of 1.0 nm and pores (mesopores) with an average diameter of 10 nm to 50 nm can be obtained (see FIG. 17(a)). .

Next, the photocatalyst in Example 2 is produced using the porous silica nanoparticles 50 produced in this way. Specifically, first, the monolithic porous silica nanoparticles 50 are immersed in an aqueous titanium (III) chloride solution (20%). By this operation, it is possible to prepare a sample in which the titanium chloride aqueous solution 54 is infiltrated into pores (supermicropores) with an average diameter of 1.0 nm and pores (mesopores) with an average diameter of 10 nm to 50 nm (Fig. 17(b)). Then, after drying the sample under reduced pressure, it is baked at 600 ° C. for 3 hours, so that titanium oxide made of quantum dots is in contact with the titanium oxide inside the pores of the porous silica nanoparticles 50, and porous A photocatalyst 25 having titanium oxide 53 composed of nanoparticles arranged around silica nanoparticles 50 can be produced (see FIG. 17(c)). In this photocatalyst 25, the ratio of silicon (Si) to titanium (Ti) (Si:Ti) by fluorescent X-ray analysis is, for example, 60:40.

18 and 19 are SEM images of the photocatalyst in the second embodiment. From Figures 18 and 19, it can be seen that the porous silica nanoparticles consist of particles of approximately 50 nm. In addition, in the photocatalyst according to the second embodiment, it can be seen from FIGS. 18 and 19 that titanium oxide (nanoparticles) having a size of about 10 nm to 20 nm is produced on the surfaces of the porous silica nanoparticles.

<Comparative Example 5>
The photocatalyst in Comparative Example 5 was prepared in the same manner as the photocatalyst in Example 2, except that the concentration of the precursor titanium chloride aqueous solution was reduced from 20% to 2%.

<Verification of effect>
FIG. 20 is a graph showing the relationship between the irradiation time of ultraviolet rays and the amount of hydrogen generated. Graph (a) in FIG. 20 shows the results when the photocatalyst in Example 1 was used. On the other hand, graph (b) in FIG. 20 shows the results when the photocatalyst in Example 2 is used, and graph (c) shows the results when the photocatalyst in Comparative Example 1 is used. Graph (d) in FIG. 20 shows the results when the photocatalyst in Comparative Example 5 was used.

As shown in FIG. 20, the amount of hydrogen generated when the photocatalyst in Example 2 is used is significantly greater than the amount of hydrogen generated when the photocatalyst in Comparative Example 1 and the photocatalyst in Comparative Example 5 are used. This means that the performance of the photocatalyst in Example 2 is superior to the performance of the photocatalyst in Comparative Example 1 and the photocatalyst in Comparative Example 5. Furthermore, when examined in detail, in the photocatalyst of Comparative Example 5, the concentration of the precursor titanium chloride aqueous solution was reduced to 2%. In this case, as shown in the graph (d) of FIG. outbreak has almost disappeared. This can be attributed to the lack of precursors, which prevented contact between the quantum dots and the nanoparticles, resulting in ineffective electron-hole pair charge separation.

From the above, it is supported that the photocatalyst in Example 2 can improve the photocatalytic activity more than the photocatalyst in Comparative Example 1 and the photocatalyst in Comparative Example 5. That is, from the results shown in FIG. 20, it can be seen that the photocatalyst in Example 2 is superior to the photocatalyst in Comparative Example 1 and the photocatalyst in Comparative Example 5 from the viewpoint of improving the photocatalytic activity.

Although the invention made by the present inventor has been specifically described based on the embodiment, the invention is not limited to the above embodiment, and can be variously modified without departing from the gist of the invention. Needless to say.

Although titanium oxide has been described as an example of the photocatalyst material in the above embodiment, the technical idea of the above embodiment is not limited to this. For example, photocatalyst materials include copper oxide, tungsten oxide, zirconium oxide, zinc oxide, gallium oxide, tin oxide, tantalum oxide, niobium oxide, silver phosphate, silicon carbide, gallium phosphide, gallium arsenide, cadmium sulfide, cadmium selenium, Germanium oxide, strontium oxide, molybdenum sulfide, indium oxide, bismuth oxide, barium oxide, ruthenium oxide, hafnium oxide, scandium oxide, yttrium oxide, lanthanum oxide, and the like can also be used.

Furthermore, metal particles such as platinum, gold, silver, and copper can be supported as an auxiliary catalyst on the photocatalytic material described above.

The embodiment includes the following modes.

(Appendix)
a carrier formed with pores having a diameter that causes the quantum size effect;
a catalyst material having quantum dots inserted into the pores and nanoparticles in contact with the quantum dots and positioned outside the pores;
Photocatalyst, including

10 porous silica 11 pore 12a titanium oxide 12b titanium oxide 20 photocatalyst 25 photocatalyst 30 container 31 precursor 40 tungsten oxide 50 porous silica nanoparticles 51 pore 52 titanium oxide 53 titanium oxide

Claims (7)

a carrier formed with pores having a diameter that causes the quantum size effect;
a first catalyst material having quantum dots inserted into the pores and nanoparticles in contact with the quantum dots and protruding outside the pores;
including
The pores have a diameter of 0.5 nm or more and 1.0 nm or less,
The photocatalyst , wherein the particle diameter of the particles constituting the quantum dots is smaller than the particle diameter of the particles constituting the nanoparticles . In the photocatalyst according to claim 1,
The photocatalyst, wherein the carrier is porous silica. In the photocatalyst according to claim 1,
The photocatalyst, wherein the first catalyst material is titanium oxide. In the photocatalyst according to claim 1 ,
The particle diameter of the particles constituting the quantum dots is 0.5 nm or more ,
The photocatalyst, wherein the particles constituting the nanoparticles have a particle diameter of 5 nm or more and 50 nm or less. In the photocatalyst according to claim 1,
A photocatalyst, wherein the bandgap of the quantum dots is larger than the bandgap of the nanoparticles . In the photocatalyst according to claim 1,
A photocatalyst, wherein a second catalyst material different in type from the first catalyst material and in contact with the quantum dots of the first catalyst material is further inserted into the pores. In the photocatalyst according to claim 6 ,
The photocatalyst, wherein the second catalyst material is tungsten oxide.

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