Method for producing carbon dioxide reduction photocatalytic particles

Abstract

To provide a method for producing carbon dioxide reduction photocatalytic particles that exhibit excellent catalytic performance. [Solution] A method for producing carbon dioxide reduction photocatalyst particles, comprising the following steps: a step of producing co-catalyst-supported matrix particles by supporting metallic silver particles as a co-catalyst on the surface of matrix particles; and a step of producing carbon dioxide reduction photocatalyst particles by irradiating a dispersion containing the co-catalyst-supported matrix particles with ultrasound.

Description

[Technical Field]

[0001] This invention relates to a method for producing carbon dioxide reduction photocatalytic particles. [Background technology]

[0002] Water splitting and carbon dioxide reduction technologies using semiconductor photocatalytic particles are attracting attention as technologies that can solve energy and environmental problems. In particular, photocatalytic particles consisting of matrix particles supported with co-catalysts such as silver (Ag) particles are expected to have the effect of trapping electrons generated by photoexcitation to promote charge separation and the effect of selectively producing carbon dioxide reduction products. For example, in a normal photocatalyst, water is decomposed into hydrogen (H2) and oxygen (O2) by light irradiation. In contrast, in a photocatalyst supported with Ag particles, carbon monoxide (CO) is produced along with hydrogen (H2) by the reduction of carbon dioxide (CO2).

[0003] Carbon monoxide (CO) is an important starting material in the chemical industry and other industrial sectors, and various fuels and chemical substances can be synthesized by reacting it with hydrogen. Therefore, in carbon dioxide reduction photocatalysts, a high carbon monoxide production rate, i.e., a high CO selectivity, is desirable. Here, CO selectivity is the ratio of the rate of carbon monoxide (CO) gas production to the sum of the rate of hydrogen (H2) gas production (amount produced) and the rate of carbon monoxide (CO) gas production produced by the reduction reaction, as shown in equation (1) below.

[0004]

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[0005] As a carbon dioxide reduction photocatalyst, Patent Document 1 discloses a gallium oxide photocatalyst supported with silver (Claim 1 of Patent Document 1). In this photocatalyst, the silver is supported by photoelectrodeposition or impregnation (Claim 2 of Patent Document 1). Non-Patent Document 1 discloses that an Al-doped SrTiO3 (Ag / Al-SrTiO3) photocatalyst supported with 1.0 wt% Ag, prepared by chemical reduction, showed an excellent CO generation ratio (Abstract of page 8779 of Non-Patent Document 1). [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2012-192302 [Non-patent literature]

[0007] [Non-Patent Document 1] Shuying Wang et al., Optimized Synthesis of Ag-Modified Al-Doped SrTiO3 Photocatalyst for the Conversion of CO2 Using H2O as an Electron Donor, ChemistrySelect, 2020, 5, 8779-8786 [Overview of the project] [Problems that the invention aims to solve]

[0008] As described above, photocatalysts consisting of matrix particles supporting co-catalysts such as Ag particles have been proposed conventionally, but there was room for improvement in conventional photocatalysts. Specifically, as mentioned above, a high carbon monoxide generation rate (CO selectivity) is desired in carbon dioxide reduction photocatalysts. At the same time, a high carbon monoxide generation rate (CO generation rate) is also desired. However, conventional photocatalysts had limitations in improving these catalytic performance aspects.

[0009] In view of such conventional problems, the present inventors have conducted intensive studies. As a result, they have found that photocatalytic particles exhibiting excellent catalytic performance can be obtained by supporting metal silver particles as a cocatalyst on the surface of base material particles and then performing ultrasonic irradiation treatment thereafter.

[0010] The present invention has been completed based on such findings, and an object thereof is to provide a method for producing carbon dioxide reduction photocatalytic particles exhibiting excellent catalytic performance.

Means for Solving the Problems

[0011] The present invention includes the following aspects (1) to (5). In this specification, the expression "~" includes the numerical values at both ends. That is, "X~Y" is synonymous with "X or more and Y or less".

[0012] (1) A method for producing carbon dioxide reduction photocatalytic particles, comprising the following steps; A step of supporting metal silver particles as a cocatalyst on the surface of base material particles to produce cocatalyst-supported base material particles, and A method including a step of irradiating a dispersion liquid containing the cocatalyst-supported base material particles with ultrasonic waves to produce carbon dioxide reduction photocatalytic particles.

[0013] (2) In the step of producing the cocatalyst-supported base material particles, a mixed liquid containing water, base material particles, a water-soluble silver salt, and a reducing agent is prepared, a chemical reduction reaction is caused in the obtained mixed liquid, and the metal silver particles generated thereby are supported on the surface of the base material particles. The method according to (1) above.

[0014] (3) The base material particles include SrNb2O6, Al-SrTiO3, K2YTa5O

[0015] , y , , , and Zn x Ta2O y (However, x and y satisfy 0 < x ≦ 1.0 and 0 < y ≦ 6.0.) The method according to (1) or (2) above, which contains as a main component a compound selected from the group consisting of.

[0015] (4) Any of the methods (1) to (3) above, wherein the average particle size of the metallic silver particles is 1 nm or more and 50 nm or less.

[0016] (5) Any of the methods (1) to (4) above, wherein the amount of metallic silver particles supported is greater than 0% by mass and 8.0% by mass or less relative to the base material particles. [Effects of the Invention]

[0017] According to the present invention, a method for producing carbon dioxide reduction photocatalytic particles exhibiting excellent catalytic performance is provided. [Brief explanation of the drawing]

[0018] [Figure 1] This illustrates the mechanism of the photocatalytic reaction. [Figure 2] This is a schematic cross-sectional view showing an example of an evaluation device. [Figure 3] This shows the XRD pattern of the photocatalytic particles. [Figure 4] This shows a STEM image of photocatalytic particles. [Figure 5] The diffuse reflectance spectrum of the photocatalytic particles is shown. [Figure 6] This shows the CO2 reduction photocatalytic performance of the photocatalytic particles. [Modes for carrying out the invention]

[0019] Specific embodiments of the present invention (hereinafter referred to as "these embodiments") are described below. However, the present invention is not limited to the following embodiments, and various modifications are possible without altering the essence of the invention. Furthermore, in this specification, any combination of preferred embodiments can be adopted as long as technical consistency can be maintained. For example, one of the preferred numerical ranges can be arbitrarily combined with the other.

[0020] <<1. Method for producing carbon dioxide reduction photocatalytic particles>> The method for manufacturing the carbon dioxide reduction photocatalyst particles of the present embodiment includes the following steps: a step of supporting metal silver (Ag) particles as a cocatalyst on the surface of base particles to produce cocatalyst-supported base particles (cocatalyst support step), and a step of irradiating an ultrasonic wave to a dispersion liquid containing the cocatalyst-supported base particles to produce carbon dioxide reduction photocatalyst particles (ultrasonic irradiation step). Details of each step will be described below.

[0021] <Cocatalyst Support Step> In the cocatalyst support step, metal silver (Ag) particles are supported as a cocatalyst on the surface of base particles to produce cocatalyst-supported base particles. Even when the base particles themselves have little reducing action on water and have an oxidizing action, by supporting silver (Ag), which is a reduction site for CO2, oxygen generation due to oxidation of water occurs on the surface of the base particles, and CO generation occurs due to CO2 reduction on the surface of the Ag cocatalyst, thereby improving the catalytic performance.

[0022] The base particles function as a main catalyst. As the base particles, those made of known materials used for carbon dioxide reduction photocatalysts can be used. For example, gallium oxide (Ga2O3), strontium niobate (SrNb2O6), aluminum-doped strontium titanate (Al-SrTiO3), K2YTa5O 15 , tantalum oxide (Ta2O5), sodium tantalate (NaTaO3), and zinc tantalate (Zn x Ta2O y (where 0 < x ≦ 1.0 and 0 < y ≦ 6.0 are satisfied.) Compounds selected from the group consisting of are exemplified. Among these, SrNb2O6, Al-SrTiO3, K2YTa5O 15 , and Zn x Ta2O y (where x and y satisfy the conditions of 0 < x ≦ 1.0 and 0 < y ≦ 6.0) Compounds containing one kind selected from the group consisting of as the main component are preferred. The main component means a component that occupies 50% by mass or more in the base particles. The higher the proportion of the main component in the base particles, the better. The proportion of the main component may be 60% by mass or more, 70% by mass or more, 80% by mass or more, or 90% by mass or more.

[0023] Among these, Al-SrTiO3 is a photocatalyst with two different crystal planes, and oxidation and reduction proceed separately on each plane, which allows for efficient charge separation. When using a material containing Al-SrTiO3 as the matrix particle, the molar ratio of Al to the total amount of Al and Ti contained in Al-SrTiO3 (Al / (Al+Ti)) is preferably 0.5% to 10.0%.

[0024] The size of the base material particles is not particularly limited. For example, the average particle size may be 0.3 to 5.0 μm. Furthermore, the shape of the particles is not limited. Examples include spherical, irregularly shaped, and anisotropic (rod-shaped, plate-shaped, etc.). If the particles are rod-shaped, for example, those with a major axis diameter of 1.0 to 5.0 μm and a minor axis diameter of 0.3 to 1.0 μm can be used.

[0025] The loading of metallic silver (Ag) particles (co-catalyst) can be carried out by known methods. For example, loading can be done by chemical reduction, impregnation, or photoelectrodeposition. When loading Ag by chemical deposition, known methods can be used. For example, a mixture containing water, matrix particles, a water-soluble Ag salt, and a reducing agent can be prepared. A chemical reduction reaction occurs in the resulting mixture, and the resulting metallic silver particles are loaded onto the surface of the matrix particles. Examples of water-soluble Ag salts include silver nitrate (AgNO3). As reducing agents, sodium phosphinate (NaPH2O2), sodium borohydride, ascorbic acid, hydrazine, etc. can be used. If necessary, the product may be recovered and dried from the resulting slurry.

[0026] When Ag loading is performed by the Impregnation P method, known methods can be employed. For example, a mixture containing water, an aqueous solution of Ag salt, and a base material particle can be prepared, and the resulting mixture can be dried and calcined. This will yield Ag-supported base material particles. Examples of water-soluble Ag salts include silver nitrate. When Ag loading is performed by the Photodeposition method, known methods can also be employed. For example, an aqueous solution containing Ag in which the base material particles are dispersed can be irradiated with UV light. Upon UV irradiation, Ag ions in the mixture precipitate and are supported on the surface of the base material particles. Examples of water-soluble Ag salts include silver nitrate.

[0027] <Ultrasonic irradiation process> In the ultrasonic irradiation process, photocatalytic particles that reduce carbon dioxide are produced by irradiating a dispersion containing the obtained co-catalyst-supported matrix particles with ultrasound. By irradiating with ultrasound after supporting the co-catalyst, photocatalytic particles exhibiting excellent catalytic performance can be obtained. The reason for this, although it should not be interpreted restrictively, is thought to be that the adhesion between the metal Ag particles (co-catalyst) and the matrix particles is improved. In other words, Ag particles supported on the surface of the matrix particles have low adhesion to the matrix particles as they are. However, by performing ultrasonic irradiation treatment, the adhesion between the Ag particles and the matrix particles is improved, and as a result, catalytic performance (CO generation rate, CO selectivity, etc.) is improved.

[0028] To explain this point, when ultrasound is irradiated, compression waves are generated in the dispersion, and these compression waves generate repeated positive and negative pressure. During negative pressure cycles, countless tiny bubbles are generated in the liquid due to evaporation. During positive pressure cycles, these bubbles collapse, exerting a strong impact force on the surroundings. This phenomenon is called ultrasonic cavitation. Cavitation generates tiny, high-temperature, and high-pressure hot spots. It has been reported that the hot spots generated by ultrasound reach temperatures of nearly 5000°C, and it is easy to predict that even a momentary action by such high-temperature hot spots will change the morphology of the Ag particles and their adhesion to the matrix particles. As a result of the improved adhesion between the Ag particles and the matrix particles, ideally, hemispherical Ag particles are supported on the matrix particles. It is speculated that this results in smoother electron movement compared to point-contact Ag co-catalysts with the matrix particles, leading to superior catalytic performance.

[0029] It is also conceivable to improve the adhesion between Ag particles (co-catalysts) and base material particles by applying energy other than ultrasound, such as high-temperature heat treatment. However, such methods have disadvantages, such as damaging the semiconductor particles (base material particles) and causing aggregation of co-catalyst Ag particles. Therefore, improving adhesion by ultrasonic irradiation is more advantageous for improving catalyst performance.

[0030] No special equipment is required for ultrasonic treatment; any device equipped with a standard ultrasonic source will suffice. For example, a commercially available ultrasonic cleaner can be used. The treatment can also be carried out under normal conditions. For example, the ultrasonic frequency may be 20-200 kHz or 26-45 kHz. The ultrasonic treatment may be performed continuously at the same frequency, or the frequency may be switched midway through the treatment using a frequency oscillation switching mode. The frequency may be switched once or multiple times. By using a frequency oscillation switching mode (for example, a 28 kHz / 45 kHz dual-frequency switching oscillation mode), it is possible to further improve the dispersibility of the base material particles in the liquid. The ultrasonic output may be 10-500 W or 50-200 W. Furthermore, the treatment time may be 1-10 hours.

[0031] As long as the promoter-supporting base material particles are irradiated with ultrasonic waves, the type of the dispersion medium of the dispersion liquid is not particularly limited. It may be water or a non-aqueous solvent (organic solvent). However, alcohols such as ethanol and propanol with low toxicity and easy availability are preferred. Also, a mixture of alcohols and water can be used.

[0032] The promoter-supporting base material particles subjected to ultrasonic treatment exist in a state of being dispersed or precipitated in the dispersion liquid. Therefore, the product (promoter-supporting base material particles) may be recovered from the dispersion liquid and dried. For the recovery, known separation means such as filtration or centrifugation may be used. Also, the drying may be performed under conditions where the Ag particles do not cause excessive grain growth, for example, at 100 °C or lower.

[0033] In this way, photocatalyst particles composed of the ultrasonic-treated promoter-supporting base material particles can be obtained. According to the production method of the present embodiment, the adhesion between the metal Ag particles and the base material particles is high, and therefore, photocatalyst particles exhibiting excellent catalytic performance (CO generation rate, CO selectivity, etc.) can be obtained.

[0034] <<2. Carbon Dioxide Reduction Photocatalyst Particles>> The carbon dioxide reduction photocatalyst particles of the present embodiment include base material particles and metal silver (Ag) particles supported on the surface of the base material particles. The details of the base material particles that function as the main catalyst are as described above. That is, those made of known materials can be used as the base material particles, and among them, SrNb2O6, Al-SrTiO3, K2YTa5O 15 , and Zn x Ta2O y (However, x and y satisfy 0 < x ≤ 1.0 and 0 < y ≤ 6.0). Those containing as a main component a compound selected from the group consisting of are preferred.

[0035] Metallic Ag particles function as co-catalysts. By supporting co-catalyst Ag particles, the catalytic performance of photocatalytic particles is enhanced. Even if the base material particles themselves have little water-reducing activity and more oxidizing activity, supporting Ag, which is a CO2 reduction site, causes oxygen generation through water oxidation on the surface of the base material particles. At the same time, CO generation occurs through CO2 reduction on the surface of the Ag co-catalyst, thereby improving catalytic performance.

[0036] The average particle size of the metallic Ag particles is preferably between 1 nm and 50 nm, and more preferably between 1 nm and 30 nm. Supporting fine Ag particles improves catalytic performance. Conversely, if the Ag particle size is larger than the order of nanometers, problems may arise such as a decrease in the function as a co-catalyst or a reduction in the number of surface active sites of the base material particles. The average particle size is the number average particle size of the Ag particles. Specifically, it is determined by observing the photocatalytic particles with a TEM to measure the particle size of the supported metallic Ag particles, and then calculating the number average particle size from the measured particle size.

[0037] The amount of metal Ag particles (co-catalyst) supported is preferably greater than 0% by mass and less than or equal to 8.0% by mass relative to the base material particles. By increasing the supported amount to a certain extent, the effect of the co-catalyst can be fully exerted. Specifically, when photocatalytic particles are used for CO2 reduction, it becomes possible to significantly increase the CO generation rate and CO selectivity. On the other hand, by moderately suppressing the supported amount, the decrease in the CO generation rate can be suppressed. A supported amount of 0.1% by mass or more and less than or equal to 1.0% by mass is more preferable. The supported amount can be adjusted by controlling the conditions in the co-catalyst loading process, for example, by controlling the Ag supply source.

[0038] The carbon dioxide reduction photocatalyst particles of this embodiment are preferably manufactured by the method described above. Specifically, they are preferably manufactured by a method including the following steps: a step of supporting metallic silver (Ag) particles as a co-catalyst on the surface of a base material particle to produce a co-catalyst-supported base material particle (co-catalyst-supporting step); and a step of irradiating the co-catalyst-supported base material particle with ultrasound in a liquid to produce carbon dioxide reduction photocatalyst particles (ultrasonic irradiation step). This makes it possible to obtain excellent catalytic performance (CO generation rate, CO selectivity, etc.).

[0039] The photocatalytic particles of this embodiment exhibit a peak A located in the wavelength range of 200 nm to 300 nm and a peak B located in the wavelength range of 350 nm to 500 nm in the diffuse reflectance spectrum, and the intensity of peak A (I A The intensity of peak B relative to (I B ) ratio (I B / I A ) may be 20% or less.

[0040] The photocatalytic particles of this embodiment exhibit excellent catalytic performance, particularly in terms of CO selectivity. For example, in CO2 reduction photocatalytic performance evaluation tests, the CO selectivity is 50% or higher. This makes it possible to increase the proportion of CO gas generated by CO2 reduction. The CO selectivity may be 60% or higher, 70% or higher, 80% or higher, or even 90% or higher. There is no particular upper limit to the CO selectivity, but for example, it may be 99% or less.

[0041] The photocatalytic particles of this embodiment are thought to exhibit excellent catalytic performance due to the high adhesion between the metal Ag particles (co-catalyst) and the base material particles. Furthermore, the particle size and electronic transition state of the Ag particles are unique, which is also thought to contribute to the excellent catalytic performance. This will be explained based on the mechanism of CO2 reduction of metal Ag particle-supported photocatalytic particles (Figure 1). As shown in Figure 1, when light with energy hν is irradiated onto the particles, electrons (e) are released into the semiconductor photocatalytic particles. - ) and holes (h + ) occurs. At this time, the metal Ag particles (co-catalyst) perform charge separation (electron e- and hole h + Promotes the separation of holes (h + As a result of the reaction between the oxygen (O2) and the surrounding water (H2O), the reaction shown in equation (2) below proceeds to the right, and oxygen (O2) and protons (H2O) are produced. + ) and are produced. On the other hand, electrons (e - ) are carbon dioxide (CO2) and protons (H + As a result of the reaction with (), the reactions shown in equations (3) and (4) below proceed to the right, producing carbon monoxide (CO), water (H2O), and hydrogen (H2). Furthermore, if the reactions in equations (2) to (4) below are combined, in principle the reaction shown in equation (5) below will proceed.

[0042]

number

number

number

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[0043] If the reactions in equation (3) and (4) occur to the same extent, the CO selectivity (CO evolution rate / (H2 evolution rate + CO evolution rate)) will be constant, as shown in equation (5) above. However, in reality, these reactions do not necessarily occur to the same extent. The reaction in equation (3) occurs preferentially, resulting in a higher CO selectivity.

[0044] In the reaction of equation (3) above, it has been reported that carbon dioxide (CO2) is adsorbed on the catalyst surface as a carbonate species, and upon light irradiation, it is transformed into a formate species, which is a reaction intermediate, and then interacts with water molecules to become carbon monoxide (CO). This report also suggests that the Ag co-catalyst promotes the formation of the reaction intermediate. Therefore, it is expected that by enhancing the charge separation effect and the reaction intermediate formation effect of the metallic Ag particles (co-catalyst), the reaction of equation (3) above will occur preferentially, and the CO selectivity will be further improved. In this regard, it is speculated that the photocatalytic particles of this embodiment have fine supported Ag particles with unique electronic transition states, and that these combine to enhance the charge separation effect and the reaction intermediate formation effect.

[0045] The CO2 reduction photocatalyst performance evaluation test can be performed using a known evaluation apparatus. An example of an evaluation apparatus is shown in Figure 2. The evaluation apparatus (2) consists of a tank (4) and a high-pressure mercury (Hg) lamp (6) installed inside the tank (4). An evaluation solution (22) is placed inside the tank (4). The tank (4) is also equipped with a gas inlet pipe (8), a gas outlet pipe (10), a pH meter (12), a rubber stopper (14), and a stirrer (16). A bubbling filter (18) is provided at the end of the gas inlet pipe (8). The mercury lamp (6) is cooled by cooling water (20) flowing around it.

[0046] The evaluation test should be carried out as follows: Prepare an evaluation solution (22) by mixing pure water, sodium bicarbonate (NaHCO3), and the sample (photocatalytic particles). Place this evaluation solution (22) into the tank (4) of the evaluation apparatus (2) and stir with a stirrer (16). Blow in carbon dioxide (CO2) gas (30) through the gas inlet pipe (8), and at the same time irradiate the evaluation solution (22) with UV light from a high-pressure Hg lamp (6). After irradiation for a predetermined time, introduce the generated gas (32) through the gas outlet pipe (10) into a gas chromatograph (34) and analyze it there. From this analysis, determine the generation rate (amount produced) of hydrogen (H2), oxygen (O2), and carbon monoxide (CO). Using the obtained generation rates, calculate the CO selectivity based on equation (1) above.

[0047] Furthermore, the photocatalytic particles of this embodiment have a high CO generation rate. For example, in a CO2 reduction photocatalyst performance evaluation test, when 0.5 g of photocatalytic particles were dispersed in 1 L of aqueous solution and irradiated with UV light from a 400 W high-pressure Hg lamp that cuts out light with a wavelength of 300 nm or less, the CO generation rate was 1.0 μmolh. -1 It is extremely high. The CO generation rate is 2.0 μmolh -1 The above is acceptable. There is no particular upper limit to the CO generation rate, but for example, 50.0 μmolh -1 The following applies: [Examples]

[0048] The present invention will be described in more detail using the following examples and comparative examples. However, the present invention is not limited to the following examples.

[0049] (1) Preparation of carbon dioxide reduction photocatalytic particles [Example 1] In Example 1, Al-SrTiO3 particles were used as the base material particles. Ag particles, which were reduced and produced by a chemical reduction method, were then supported on the surface of the base material particles. Subsequently, the Ag-supported base material particles were irradiated with ultrasound to produce photocatalytic particles. The Ag concentration (supported amount) relative to the base material particles (Al-SrTiO3 particles) was set to 1.0 mass%. Specifically, samples were prepared using the following procedure.

[0050] <Promoter-supporting process> First, Al-SrTiO3 particles with an Al / (Al + Ti) molar ratio of 4% were prepared. Next, the prepared Al-SrTiO3 particles (average particle size of about 300 nm, 0.75 g) and ultrapure water (50 mL) were placed in a flask and heated to 80°C using a water bath. An aqueous silver nitrate (AgNO3) solution (0.1 M, 695 μL) was then dropped therein, and immediately thereafter, an aqueous sodium phosphinate (NaPH2O2) solution (0.4 M, 747 μL) was dropped. After the dropping, the solution was stirred at 80°C for 1.5 hours to react. Thereafter, the product particles (Ag(1 mass%) / Al-SrTiO3) were collected by filtration, and the obtained product particles (promoter-supporting base particles) were air-dried at room temperature overnight.

[0051] <Ultrasonic irradiation process> The product particles obtained in the promoter-supporting process and ethanol (50 mL) were placed in a flask and subjected to ultrasonic treatment using an ultrasonic device (Honda Electronics Co., Ltd., WT-100-M). The ultrasonic treatment was performed with two-frequency switching oscillation of 28 kHz and 45 kHz under the condition of an output of 100 W. The treatment time was 3 hours. At this time, the temperature of the reaction solution was maintained at 40°C. Next, after the product was collected by filtration, it was washed with ethanol (10 mL) and dried under the condition of 60°C in the air for 0.5 hours. <​​​​​​​​​​​​​​​​​​​​The sample was analyzed by X-ray diffraction (XRD) method to examine its crystal phase. The analysis was carried out under the following conditions.

[0056] - X-ray diffractometer: Spectris Co., Ltd., X’Pert PRO MRD - Radiation source: CuKα radiation - Tube voltage: 45 kV - Tube current: 40 mA - Scanning speed: 5.5° / min - Scanning range (2θ): 20~60°

[0057] <STEM Observation> The sample was observed using a scanning transmission electron microscope (STEM; Hitachi High-Technologies Corporation, HD2700). The observation was carried out under the condition of an acceleration voltage of 200 kV with a transmission electron image.

[0058] <Diffuse Reflection Spectrum> The diffuse reflection spectrum of the sample in the solid state was measured in the wavelength range of 200~800 nm using an ultraviolet-visible spectrophotometer (Hitachi High-Technologies Science, UH4150).

[0059] <CO2 Reduction Photocatalytic Performance> The CO2 reduction photocatalytic performance of the sample was evaluated using the evaluation apparatus shown in Figure 2. First, ultrapure water (1 L), NaHCO3 (0.1 M), and photocatalytic particles (0.5 g) were mixed to prepare an evaluation solution. Next, this evaluation solution was placed in the tank of the evaluation apparatus, and while blowing carbon dioxide (CO2) gas at a flow rate of 30 mL / min, UV light was irradiated with a 400 W high-pressure Hg lamp. At this time, a Pyrex jacket was used to cut off light with a wavelength of 300 nm or less. The gas generated after 1 hour of irradiation was analyzed using gas chromatography (Shimadzu Corporation, GC-8A) to determine the generation rates of H2, O2, and CO. Then, the CO selectivity was calculated based on the above equation (1).

[0060] (3) Evaluation Results <X-ray Diffraction (XRD)> The X-ray diffraction (XRD) patterns obtained for Example 1 and Comparative Example 1 are shown in Fig. 3 together with the pattern of silver (Ag). An enlarged view of the XRD pattern is shown at the bottom of Fig. 3. In Example 1, a pattern consistent with silver (Ag) was observed slightly near 2θ = 44.5°. However, in Comparative Example 1, the silver peak was not detected. This suggests that the crystallinity of the silver nanoparticles was increased by ultrasonic irradiation.

[0061] <STEM Observation> The STEM photographs obtained for the samples of Example 1 and Comparative Example 1 are shown in Fig. 4 respectively. In both samples, Ag nanoparticles were supported on the surface of the Al-SrTiO3 particles. The particles obtained in Example 1 were observed such that the Ag nanoparticles and the Al-SrTiO3 particles were in surface contact.

[0062] <Diffuse Reflection Spectrum> The diffuse reflection spectra obtained for Example 1 and Comparative Example 1 are shown in Fig. 5. In both Example 1 and Comparative Example 1, peaks were observed at wavelengths of 400 to 550 nm. Also, no difference was seen in this peak intensity.

[0063] <CO2 Reduction Photocatalytic Performance> The CO2 reduction photocatalytic performance (gas generation rate and CO selectivity) obtained for Example 1 and Comparative Example 1 are shown in Fig. 6. The sample after ultrasonic irradiation in Example 1 had a significantly higher CO generation rate and also a slightly higher CO selectivity compared to the sample without ultrasonic irradiation in Comparative Example 1. From this result, it is considered that by changing the adhesion of the Ag nanoparticles by ultrasonic irradiation, it effectively acted as a cocatalyst.

[0064] From the above results, it is understood that according to this embodiment, a method for producing carbon dioxide reduction photocatalytic particles showing excellent catalytic performance is provided.

Description of Reference Numerals

[0065] 2 Evaluation Apparatus 4 Tank 6 Mercury (Hg) Lamp 8. Gas inlet pipe 10 Gas discharge pipe 12 pH meter 14 Rubber stopper 16 Stirrers 18 Bubbling Filter 20 Cooling water 22 Evaluation solution 30 CO2 gas 32. Generated gases 34. Gas chromatography

Claims

1. A method for producing carbon dioxide reduction photocatalytic particles, comprising the following steps: A process for producing catalyst-supported matrix particles by supporting metallic silver particles as a co-catalyst on the surface of matrix particles, and A method comprising the step of irradiating a dispersion containing the aforementioned co-catalyst-supported matrix particles with ultrasound to produce carbon dioxide reduction photocatalyst particles.

2. The method according to claim 1, wherein in the step of producing the co-catalyst-supported matrix particles, a mixed solution containing water, matrix particles, a water-soluble silver salt, and a reducing agent is prepared, a chemical reduction reaction is carried out in the obtained mixed solution, and the resulting metallic silver particles are supported on the surface of the matrix particles.

3. The base material particles are SrNb ２ O ６ , Al - SrTiO ３ , K ２ YTa ５ O １５ , and Zn ｘ Ta ２ O ｙ (where x and y satisfy 0 < x ≤ 1.0 and 0 < y ≤ 6.0). The method according to claim 1 or 2, comprising as a main component a compound selected from the group consisting of.

4. The method according to claim 1 or 2, wherein the average particle size of the metallic silver particles is 1 nm or more and 50 nm or less.

5. The method according to claim 1 or 2, wherein the amount of supported metallic silver particles is greater than 0% by mass and 8.0% by mass or less relative to the base material particles.

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