Visible light-responsive photocatalytic particles and method for producing the same

Abstract

To provide visible light-responsive photocatalyst particles that are small in particle size, have a narrow particle size distribution, and exhibit high catalytic activity, as well as a method for producing the same. [Solution] A visible light-responsive photocatalytic particle characterized by comprising a core-shell type nanoparticle consisting of silica nanoparticles forming a core and a photocatalytic layer coating the silica nanoparticles, and co-catalytic nanoparticles supported on the surface of the core-shell type nanoparticle.

Description

[Technical Field]

[0001] The present invention relates to visible light-responsive photocatalytic particles and a method for producing the same. [Background technology]

[0002] Photocatalysts are substances that use light energy to accelerate chemical reactions. Representative photocatalytic materials include titanium dioxide (TiO2) and zinc oxide (ZnO), which are widely researched and used due to their excellent photocatalytic properties. The main characteristics of photocatalysts are their high activity, stability, and low environmental impact.

[0003] The basic principle of photocatalysis begins with the absorption of light (mainly ultraviolet light), which excites electrons within the photocatalytic material, causing them to move from the valence band to the conduction band. This creates electron vacancies called holes. These electrons and holes have the ability to trigger reduction and oxidation reactions, respectively. For example, when ultraviolet light strikes titanium dioxide photocatalyst, water is oxidized to produce hydroxyl radicals (·OH) and superoxide ions (O2). - These reactive oxygen species are highly reactive and are used in a variety of applications, such as the decomposition of organic matter, sterilization of bacteria, and removal of unpleasant odors.

[0004] Photocatalytic technology is attracting particular attention in the fields of environmental remediation and energy conversion. In the field of environmental remediation, the use of photocatalysts for water and air purification is becoming widespread. By using photocatalytic filters, volatile organic compounds (VOCs) and nitrogen oxides (NOx) can be removed. x Furthermore, it is possible to effectively decompose harmful microorganisms. In water purification, technology is advancing that uses photocatalysis to decompose and neutralize pollutants.

[0005] In the field of energy conversion, artificial photosynthesis and hydrogen production using photocatalysts are being researched. Artificial photosynthesis is a process that mimics plant photosynthesis to convert light energy into chemical energy, aiming to produce useful compounds from carbon dioxide and water. In hydrogen production, technologies are being explored to efficiently produce hydrogen, a clean energy source, by using photocatalysts to decompose water into hydrogen and oxygen.

[0006] In the application of photocatalysts, research is actively being conducted to maximize their activity. For example, the development of visible light-responsive photocatalysts is progressing. While ordinary titanium dioxide only shows activity in the ultraviolet region, visible light-responsive photocatalysts exhibit activity in the visible light region, which accounts for about half of sunlight. This enables more efficient energy utilization, and expectations for practical application are rising.

[0007] Furthermore, the integration of nanotechnology is also an important theme in photocatalysis research. Nano-sized photocatalytic particles have a large surface area, which improves reaction efficiency and selectivity for specific reactions. By utilizing these properties, the development of higher-performance and multi-functional photocatalytic materials is progressing.

[0008] Overall, photocatalysts are expected to play an increasingly important role in the future due to their environmental friendliness and versatility. In particular, further development and application of photocatalytic technology are needed as a clean technology for realizing a sustainable society.

[0009] For example, Non-Patent Document 1 discloses photocatalytic technology. Patent Document 1 discloses a modified carbon particle / titania core-shell composite with excellent visible light activity. Patent Document 2 discloses a core-shell type powder in which the core is an organic complex particle and the shell is at least one thin film of a metal oxide thin film, a semiconductor oxide film, a metal nitride thin film, or a semiconductor nitride film. [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] Japanese Patent No. 7018643 [Patent Document 2] Japanese Unexamined Patent Application Publication No. 2022-39938 [Non-Patent Document]

[0011] [Non-Patent Document 1] S.Ko et al., Compos. B. Eng., 42 (2011) 579-583. [Summary of the Invention] [Problems to be Solved by the Invention]

[0012] In photocatalysis technology, there has been a concern that due to polydispersity and particle aggregation caused by nanoparticle formation to enhance reactivity, the catalytic activity is non-uniform for each particle. For example, it has been difficult to synthesize titanium oxide particles with a nanosize and a uniform shape. Therefore, when titanium oxide is used as photocatalytic particles, there is a concern that the catalytic activity will be non-uniform for each particle. In addition, there is also a concern that it is inactive under visible light, and there are problems such as little or no utilization of sunlight, or inability to absorb it, not only indoor light.

[0013] Therefore, an object of the present invention is to provide visible light-responsive photocatalytic particles that are visible light-responsive, have a small particle size, a narrow particle size distribution, and high catalytic activity, and a method for producing the same. [Means for Solving the Problems]

[0014] As a result of intensive research by the present inventors, silica particles obtained by hydrolyzing and condensing tetraalkoxysilane have a narrow particle size distribution, little aggregation, and little change in particle curvature even when the particle size is reduced. Therefore, by forming a photocatalytic layer on the surface of silica nanoparticles as core particles, the composition of the compound having photocatalytic ability is not limited, the particle size distribution is narrow, and the change in particle curvature is small. Therefore, the catalytic activity is likely to be uniform, and visible light-responsive photocatalytic particles that retain surface plasmon resonance and can absorb visible light can be obtained, and a production method thereof has been found.

[0015] Specifically, silica allows for the relatively easy creation of uniform nano-sized particles. Therefore, by using silica nanoparticles as the core and forming a catalyst layer made of photocatalytic material as the shell, a core-shell structure can be obtained, resulting in photocatalytic particles with small particle size, a narrow particle size distribution, and a small aspect ratio. Furthermore, by supporting metal nanoparticles as co-catalysts using a metal substitution method, neither photodeposition nor chemical reduction, we succeeded in placing the co-catalyst nanoparticles on the surface of the photocatalyst without aggregation. Through these methods, we found that visible light-responsive photocatalytic particles with high catalytic activity and small variation in catalytic activity can be obtained.

[0016] The above problems are solved by the present invention as described below. In other words, the present invention (1) is, A core-shell type nanoparticle comprising silica nanoparticles forming a core and a photocatalytic layer coating the silica nanoparticles, Co-catalyst nanoparticles supported on the surface of the core-shell type nanoparticles, This invention provides visible light-responsive photocatalytic particles characterized by containing [a specific compound / component].

[0017] Furthermore, the present invention (2) provides visible light-responsive photocatalytic particles of (1), characterized in that the photocatalytic layer contains one or more selected from titanium dioxide, zinc oxide, tungsten oxide, indium oxide, iron oxide, bismuth oxide, molybdenum sulfide, strontium titanate, silicon, gallium phosphide, gallium arsenide, cadmium sulfide, cadmium selenide, and silicon carbide.

[0018] Furthermore, the present invention (3) provides visible light-responsive photocatalytic particles of (1), characterized in that the co-catalyst nanoparticles are one or more selected from the group consisting of Ag, Cu, Ni, Au, Pt, Pd, Rh, and Ru.

[0019] Furthermore, the present invention (4) provides visible light-responsive photocatalytic particles of (1) characterized in that the average particle diameter of the visible light-responsive photocatalytic particles is 6 to 700 nm, the dispersion is 2 to 20%, and the aspect ratio is 1 to 10.

[0020] Furthermore, the present invention (5) provides visible light-responsive photocatalytic particles of (1), characterized in that the supported area ratio of the co-catalyst nanoparticles is 10 to 80% in transmission electron microscopy (TEM) observation.

[0021] Furthermore, the present invention (6) includes a core particle generation step of mixing a tetraalkoxysilane or a derivative thereof with an alkaline catalyst to obtain silica nanoparticles, A core-shell nanoparticle production step involves forming a photocatalytic layer on the surface of the silica nanoparticles to obtain core-shell nanoparticles, A co-catalyst introduction step to obtain visible light-responsive photocatalyst particles by supporting co-catalyst nanoparticles on the surface of the core-shell type nanoparticles, This invention provides a method for producing visible light-responsive photocatalytic particles, characterized by having [a specific characteristic].

[0022] Furthermore, the present invention (7) provides a method for producing visible light-responsive photocatalytic particles according to (6), characterized in that the core-shell type nanoparticle production step involves adding tetraalkoxytitanium or a derivative thereof and an alkaline catalyst to a colloidal solution of silica nanoparticles to form a photocatalytic layer coating the silica nanoparticles, thereby obtaining the core-shell type nanoparticles.

[0023] Furthermore, the present invention (8) provides a method for producing visible light-responsive photocatalyst particles according to (6), characterized in that the co-catalyst introduction step involves adding a substance containing reducing metal ions having a lower standard electrode potential than the co-catalyst metal to an aqueous solution of the core-shell nanoparticles to adsorb the reducing metal ions onto the surface of the core-shell nanoparticles, then adding metal ions of the co-catalyst metal to reduce the metal ions of the co-catalyst metal through an oxidation-reduction reaction between the reducing metal ions and the metal ions of the co-catalyst metal to generate the co-catalyst nanoparticles, thereby obtaining a colloidal solution of visible light-responsive photocatalyst particles on which the co-catalyst nanoparticles are supported on the surface of the core-shell nanoparticles.

[0024] Furthermore, the present invention (9) provides a method for producing visible light-responsive photocatalytic particles according to (7), characterized in that, after the core-shell nanoparticle generation step and before the co-catalyst introduction step, the core-shell nanoparticles are heat-treated at 200 to 1000°C for 0.5 to 24 hours. [Effects of the Invention]

[0025] According to the present invention, it is possible to provide visible light-responsive photocatalyst particles that are small in particle size, have a narrow particle size distribution, and have high catalytic activity, as well as a method for producing the same. [Brief explanation of the drawing]

[0026] [Figure 1] A schematic diagram illustrating an example of a method for producing visible light-responsive photocatalytic particles of the present invention. [Figure 2] Figure showing TEM images of SiO2 nanoparticles in the example. [Figure 3] A diagram showing DLS of SiO2 nanoparticles in the example. [Figure 4] Figure showing TEM images of the SiO2 / TiO2 nanoparticles in the example. [Figure 5] A diagram showing the UV-vis of SiO2 / TiO2 nanoparticles in the example. [Figure 6] A figure showing TG-DTA of SiO2 / TiO2 nanoparticles in the example. [Figure 7]Figure showing TEM images of the SiO2 / TiO2 nanoparticles in the example. [Figure 8] A figure showing the XRD of the SiO2 / TiO2 nanoparticles in the example. [Figure 9] Figure showing TEM images of the SiO2 / TiO2 / Ag nanoparticles in the example. [Figure 10] This figure shows a STEM image of the SiO2 / TiO2 / Ag nanoparticles from the example. [Figure 11] A diagram showing UV-bis emission of SiO2 / TiO2 / Ag nanoparticles from the example. [Figure 12] A figure showing the XRD of the SiO2 / TiO2 / Ag nanoparticles in the example. [Figure 13] A diagram showing a calibration curve illustrating the relationship between absorbance and MB concentration. [Figure 14] This figure shows TEM images of SiO2 particles, SiO2 / Ag nanoparticles, SiO2 / TiO2 nanoparticles, and TiO2 particles from the comparative example, and SiO2 / TiO2 / Ag nanoparticles from the example. [Figure 15] This figure shows the photocatalytic activity evaluation of SiO2 particles, SiO2 / Ag nanoparticles, SiO2 / TiO2 nanoparticles, and TiO2 particles in comparative examples, and SiO2 / TiO2 / Ag nanoparticles in examples. [Figure 16] This figure shows the photocatalytic activity evaluation of SiO2 particles, SiO2 / Ag nanoparticles, SiO2 / TiO2 nanoparticles, and TiO2 particles in comparative examples, and SiO2 / TiO2 / Ag nanoparticles in examples. [Modes for carrying out the invention]

[0027] The visible light-responsive photocatalytic particles of the present invention are A core-shell type nanoparticle comprising silica nanoparticles forming a core and a photocatalytic layer coating the silica nanoparticles, Co-catalyst nanoparticles supported on the surface of the core-shell type nanoparticles, These are visible light-responsive photocatalytic particles characterized by containing [a specific compound / component].

[0028] The core-shell type nanoparticles constituting the visible light-responsive photocatalytic particles of the present invention have silica nanoparticles forming the core. By using silica nanoparticles to form the core of the visible light-responsive photocatalytic particles, the particle size of the core can be standardized on a nanoscale, and the particle size can be made uniform. Furthermore, the silica nanoparticles can be spherical.

[0029] In the visible light-responsive photocatalytic particles of the present invention, the average particle diameter of the silica nanoparticles forming the core of the core-shell type nanoparticles is 1 to 300 nm, preferably 3 to 90 nm. Furthermore, in the visible light-responsive photocatalytic particles of the present invention, the dispersion degree of the silica nanoparticles forming the core of the core-shell type nanoparticles is 2 to 20%, preferably 2 to 10%. Furthermore, in the visible light-responsive photocatalytic particles of the present invention, the aspect ratio of the silica nanoparticles forming the core of the core-shell type nanoparticles is 1 to 10, preferably 1 to 3. By having the average particle diameter and dispersion degree of the silica nanoparticles in the visible light-responsive photocatalytic particles of the present invention within the above ranges, the variation in the catalytic activity of the visible light-responsive photocatalytic particles is reduced, and the catalytic activity is increased. Furthermore, by having the aspect ratio of the silica nanoparticles in the visible light-responsive photocatalytic particles of the present invention within the above ranges, the variation in the catalytic activity of the visible light-responsive photocatalytic particles is reduced, and the catalytic activity is increased.

[0030] Silica is preferred as the core material, but it is not particularly limited as long as it is easy to synthesize materials with a similar particle size distribution and shape in the nanoscale. Suitable core materials include chemically and physically stable materials, such as cerium oxide, iron oxide, zinc oxide, aluminum oxide, zirconium oxide, and various metal nanoparticles.

[0031] The core-shell type nanoparticles constituting the visible light-responsive photocatalytic particles of the present invention have a photocatalytic layer coating the core silica nanoparticles. The photocatalytic layer is present on the surface of the core silica nanoparticles and coats the silica nanoparticles to form a shell.

[0032] In the visible light-responsive photocatalytic particles of the present invention, the photocatalytic layer of core-shell type nanoparticles is composed of photocatalytic particles. The photocatalytic particles are particles that function as photocatalysts, mainly by absorbing ultraviolet light, which excites electrons, causing them to move from the valence band to the conduction band, and triggering reduction and oxidation reactions with electrons and holes. There are no restrictions on the material of the particles that can be used as photocatalysts, but well-known examples include titanium dioxide, zinc oxide, tungsten oxide, indium oxide, iron oxide, bismuth oxide, molybdenum sulfide, strontium titanate, silicon, gallium phosphide, gallium arsenide, cadmium sulfide, cadmium oxide, cadmium selenide, and silicon carbide. In particular, titanium dioxide, zinc oxide, and tungsten oxide are preferred from the viewpoint of ease of handling (safe and secure substances) and excellent photocatalytic activity. The shell material formed on the silica nanoparticles can be in any state, including inorganic, organic, and polymer materials, as long as it has photocatalytic activity, and there are no particular restrictions on the manufacturing method.

[0033] The presence of a core-shell structure in the core-shell nanoparticles of the visible light-responsive photocatalyst particles of the present invention can be confirmed using a transmission electron microscope (TEM).

[0034] The thickness of the photocatalytic layer in the core-shell type nanoparticles of the visible light-responsive photocatalytic particles of the present invention is 1 to 200 nm, preferably 3 to 50 nm. The thickness of the photocatalytic layer in the core-shell type nanoparticles can be measured using a transmission electron microscope (TEM).

[0035] The average particle size of the core-shell nanoparticles of the visible light-responsive photocatalyst particles of the present invention is 5 to 500 nm, preferably 9 to 115 nm. The dispersion degree of the core-shell nanoparticles of the visible light-responsive photocatalyst particles of the present invention is 2 to 20%, preferably 2 to 10%. The aspect ratio of the core-shell nanoparticles of the visible light-responsive photocatalyst particles of the present invention is 1 to 10, preferably 1 to 3. Because the average particle size and dispersion degree of the core-shell nanoparticles of the visible light-responsive photocatalyst particles of the present invention are within the above ranges, the variation in catalytic activity of the visible light-responsive photocatalyst particles is reduced, resulting in higher catalytic activity, and thus making it easier to set reaction conditions. Furthermore, because the aspect ratio of the core-shell nanoparticles of the visible light-responsive photocatalyst particles of the present invention is within the above range, the variation in catalytic activity of the visible light-responsive photocatalyst particles is reduced, resulting in higher catalytic activity, and thus making it easier to set reaction conditions.

[0036] The visible light-responsive photocatalyst particles of the present invention have co-catalyst nanoparticles supported on the surface of a core-shell type nanoparticle. The co-catalyst nanoparticles are supported on a photocatalyst layer that constitutes the shell of the core-shell type nanoparticle. The co-catalyst nanoparticles are particles that function as co-catalysts and are present on the surface of the photocatalyst layer to broaden the light absorption wavelength range of the visible light-responsive photocatalyst particles of the present invention. Because the co-catalyst nanoparticles are supported on the surface of the core-shell type nanoparticle, the visible light-responsive photocatalyst particles of the present invention can function as a visible light-responsive photocatalyst that can utilize visible light, which represents most of sunlight.

[0037] The co-catalyst nanoparticles of the visible light-responsive photocatalyst particles of the present invention are, for example, nanoparticles of metals such as silver (Ag), copper (Cu), nickel (Ni), gold (Au), platinum (Pt), palladium (Pd), rhodium (Rh), and ruthenium (Ru), and preferably silver (Ag), copper (Cu), and nickel (Ni) nanoparticles. The co-catalyst nanoparticles undergo surface plasmon resonance and absorb visible light, so that the visible light-responsive photocatalyst particles of the present invention can function as a photocatalyst that responds to visible light.

[0038] The average particle size of the co-catalyst nanoparticles in the visible light-responsive photocatalyst particles of the present invention is 1.5 to 200 nm, preferably 2 to 50 nm. Furthermore, the dispersion degree of the co-catalyst nanoparticles in the visible light-responsive photocatalyst particles of the present invention is 2 to 50%, preferably 2 to 20%. By having the average particle size and dispersion degree of the co-catalyst nanoparticles in the visible light-responsive photocatalyst particles of the present invention within the above ranges, the co-catalyst function is easily expressed, resulting in cost-effective and easily synthesized co-catalyst nanoparticles.

[0039] The area ratio of co-catalyst nanoparticles in the visible light-responsive photocatalyst particles of the present invention is 1 to 80%, preferably 10 to 50%. By having the area ratio of co-catalyst nanoparticles in the visible light-responsive photocatalyst particles of the present invention within the above range, visible light can be effectively utilized. The area ratio of co-catalyst nanoparticles in the visible light-responsive photocatalyst particles of the present invention is determined by measuring the area occupied by the visible light-responsive photocatalyst particles and the area occupied by the co-catalyst nanoparticles for 100 arbitrarily selected visible light-responsive photocatalyst particles in TEM images obtained using a transmission electron microscope (TEM) (JEM-2100, manufactured by JEOL Ltd.) under conditions of an acceleration voltage of 200 kV, and is defined as the area ratio of co-catalyst nanoparticles to the total area of ​​visible light-responsive photocatalyst particles (%) ((area of ​​co-catalyst nanoparticles / total area of ​​visible light-responsive photocatalyst particles) × 100).

[0040] The average particle size of the visible light-responsive photocatalyst particles of the present invention is 6 to 700 nm, preferably 10 to 120 nm. The dispersion of the visible light-responsive photocatalyst particles of the present invention is 2 to 20%, preferably 2 to 10%. The aspect ratio of the visible light-responsive photocatalyst particles of the present invention is 1 to 10, preferably 1 to 3. Because the average particle size and dispersion of the visible light-responsive photocatalyst particles of the present invention are within the above ranges, the variation in catalytic activity of the visible light-responsive photocatalyst particles is reduced, resulting in high catalytic activity, and thus making it easier to set reaction conditions. Because the aspect ratio of the visible light-responsive photocatalyst particles of the present invention is within the above range, the variation in catalytic activity of the visible light-responsive photocatalyst particles is reduced, resulting in high catalytic activity, and thus making it easier to set reaction conditions.

[0041] The method for producing visible light-responsive photocatalytic particles of the present invention is as follows: A core particle generation step of mixing a tetraalkoxysilane or its derivative with an alkaline catalyst to obtain silica nanoparticles, A core-shell nanoparticle production step involves forming a photocatalytic layer on the surface of the silica nanoparticles to obtain core-shell nanoparticles, A co-catalyst introduction step to obtain visible light-responsive photocatalyst particles by supporting co-catalyst nanoparticles on the surface of the core-shell type nanoparticles, This is a method for producing visible light-responsive photocatalytic particles, characterized by having [a specific characteristic].

[0042] Figure 1 is a schematic diagram illustrating an example of a method for producing visible light-responsive photocatalytic particles according to the present invention. First, silica nanoparticles obtained by hydrolysis and condensation of tetraalkoxysilane are used as core particles, and a photocatalytic layer is formed on their surface to obtain core-shell type nanoparticles. Next, Sn is applied to the surface of the core-shell type nanoparticles (the surface of the photocatalytic layer). 2+ It adsorbs. Then, Sn 2+ and Ag + Through a redox reaction with Ag + The material is reduced to generate Ag nanoparticles (co-catalyst nanoparticles) on the surface of the core-shell type nanoparticles (the surface of the photocatalyst layer).

[0043] The present invention provides a method for producing visible light-responsive photocatalytic particles, comprising a core particle generation step, a core-shell type nanoparticle generation step, and a co-catalyst introduction step.

[0044] The core particle generation step in the method for producing visible light-responsive photocatalytic particles of the present invention is a step of mixing a tetraalkoxysilane or its derivative with an alkaline catalyst, and obtaining a colloidal solution of silica nanoparticles by hydrolyzing and condensing the tetraalkoxysilane or its derivative.

[0045] The tetraalkoxysilane used in the core particle generation process is not particularly limited, and for example, the following general formula (1): Si(OR 1 )4(1) Examples include tetraalkoxysilanes represented by . In general formula (1), R 1may be the same or different. R 1 is an alkyl group, preferably an alkyl group having 1 to 8 carbon atoms, more preferably an alkyl group having 1 to 4 carbon atoms, still more preferably an alkyl group having 1 to 3 carbon atoms. R 1 Specific examples include a methyl group, an ethyl group, a propyl group, an isobutyl group, a butyl group, a pentyl group, and a hexyl group. As the tetraalkoxysilane represented by the general formula (1), in terms of obtaining a dense shell, R 1 tetramethoxysilane (TMOS) in which R is a methyl group, R 1 tetraethoxysilane (TEOS) in which R is an ethyl group are more preferred. Further, examples of the derivative of the tetraalkoxysilane used in the core particle generation step include low condensates obtained by partially hydrolyzing alkoxysilane. The tetraalkoxysilane or its derivative may be used alone or in combination of two or more.

[0046] Examples of the alkali catalyst used in the core particle generation step include ammonium hydroxide, methylamine, dimethylamine, ethylenediamine, ethylenediaminetetraacetic acid and its sodium salt, diethylenetriamine, sodium hydroxide, potassium hydroxide, arginine, and lysine. The alkali catalyst may be used alone or in combination of two or more. The concentration of the alkali catalyst in the reaction solution is appropriately selected, but is preferably 0.01 to 20.0% by mass, more preferably 0.05 to 15.0% by mass, and still more preferably 0.10 to 10.0% by mass.

[0047] In the core particle generation process, examples of solvents used when hydrolyzing and condensing tetraalkoxysilane or its derivatives include water, methanol, ethanol, n-propanol, isopropanol, ethylene glycol, propylene glycol, alcohols such as 1,4-butanediol, ketones such as acetone and methyl ethyl ketone, and esters such as ethyl acetate. Among these, alcohols are preferred, and methanol, ethanol, and isopropanol are more preferred. It is even more preferable to use the same type of alcohol as that produced by the hydrolysis of the silicon compound as the solvent. By using the same type of alcohol as that produced by the hydrolysis of the silicon compound, the solvent can be easily recovered and reused. The solvent can be used individually or as a mixture of two or more solvents.

[0048] The average particle size of the silica nanoparticles obtained by the core particle generation process is 1 to 300 nm, preferably 3 to 90 nm. The dispersion of the silica nanoparticles obtained by the core particle generation process is 2 to 20%, preferably 2 to 10%. The aspect ratio of the silica nanoparticles obtained by the core particle generation process is 1 to 10, preferably 1 to 3. By having the average particle size and dispersion of the silica nanoparticles obtained by the core particle generation process within the above ranges, the variation in the catalytic activity of the visible light-responsive photocatalyst particles is reduced, resulting in higher catalytic activity. Furthermore, by having the aspect ratio of the silica nanoparticles obtained by the core particle generation process within the above range, the variation in the catalytic activity of the visible light-responsive photocatalyst particles is reduced, resulting in higher catalytic activity.

[0049] In the core particle generation process, the reaction temperature and reaction time when hydrolyzing and condensing tetraalkoxysilane or its derivative are appropriately selected and preferably adjusted so that the average particle size of the resulting silica nanoparticles falls within the above range.

[0050] In the core particle generation process, tetraalkoxysilane or its derivatives are used as raw materials and subjected to hydrolysis and condensation. As a result, silica nanoparticles can be obtained that have small particle sizes, low aggregation, a narrow particle size distribution, and a small aspect ratio.

[0051] The core-shell nanoparticle production step in the method for producing visible light-responsive photocatalytic particles of the present invention is a step of forming a photocatalytic layer on the surface of silica nanoparticles obtained by the core particle production step to obtain core-shell nanoparticles.

[0052] In the core-shell nanoparticle production process, the photocatalytic material used to form the photocatalytic layer is not particularly limited as long as it can be used as a photocatalytic material, but examples include titanium dioxide, zinc oxide, tungsten oxide, indium oxide, iron oxide, bismuth oxide, molybdenum sulfide, strontium titanate, silicon, gallium phosphide, gallium arsenide, cadmium sulfide, cadmium oxide, cadmium selenide, and silicon carbide. In particular, titanium dioxide, zinc oxide, and tungsten oxide are preferred from the viewpoint of ease of handling (safe and secure substances) and excellent photocatalytic activity. The photocatalytic material formed on the surface of the silica nanoparticles may be inorganic, organic, polymer, etc., in addition to those listed above, as long as it has photocatalytic activity.

[0053] In the core-shell nanoparticle production process, the amount of photocatalytic layer formed on silica nanoparticles is 3 to 99.9% by mass, preferably 18 to 99.9% by mass, in terms of the mass ratio of the amount of photocatalyst to the silica nanoparticles.

[0054] In the core-shell nanoparticle production process, the thickness of the photocatalytic layer formed on the surface of the silica nanoparticles is 1 to 200 nm, preferably 3 to 50 nm. The thickness of the photocatalytic layer formed on the surface of the silica nanoparticles can be measured using a transmission electron microscope (TEM).

[0055] The average particle size of the core-shell nanoparticles obtained by the core-shell nanoparticle production process is 5 to 500 nm, preferably 9 to 115 nm. The dispersion of the core-shell nanoparticles obtained by the core-shell nanoparticle production process is 2 to 20%, preferably 2 to 10%. The aspect ratio of the core-shell nanoparticles obtained by the core-shell nanoparticle production process is 1 to 10, preferably 1 to 3. Because the average particle size and dispersion of the core-shell nanoparticles obtained by the core-shell nanoparticle production process are within the above ranges, the variation in catalytic activity of the visible light-responsive photocatalyst particles is reduced, resulting in higher catalytic activity, which in turn makes it easier to set reaction conditions. Furthermore, because the aspect ratio of the core-shell nanoparticles obtained by the core-shell nanoparticle production process is within the above range, the variation in catalytic activity of the visible light-responsive photocatalyst particles is reduced, resulting in higher catalytic activity, which in turn makes it easier to set reaction conditions.

[0056] One of the first forms of the core-shell nanoparticle production process is to add tetraalkoxytitanium or its derivative and an alkaline catalyst to a colloidal solution of silica nanoparticles obtained in the core particle production process, and to form a photocatalytic layer coating the silica nanoparticles by a sol-gel method in which the tetraalkoxytitanium or its derivative is hydrolyzed and condensed, thereby obtaining core-shell nanoparticles.

[0057] The tetraalkoxytitanium used in the first form of the core-shell type nanoparticle production process is not particularly limited, and for example, the following general formula (2): Ti(OR 2 )4(2) Examples include tetraalkoxytitanium represented by . In general formula (2), R 2 They may be the same or different. 2 R is an alkyl group, preferably an alkyl group having 1 to 8 carbon atoms, more preferably an alkyl group having 1 to 4 carbon atoms, and even more preferably an alkyl group having 1 to 3 carbon atoms. 2Specifically, these include methyl, ethyl, propyl, isobutyl, butyl, pentyl, and hexyl groups. As tetraalkoxytitanium represented by general formula (2), tetra-i-propoxytitanium (Ti[OCH(CH3)2]4) and tetra-n-butoxytitanium (TBT) (Ti(OCH2CH2CH2CH3)4) are preferred as raw materials for TiO2 shell formation when producing SiO2 / TiO2 nanoparticles, and tetrakis(2-ethylhexyloxy)titanium Ti[OCH2CH(C2H5)C4H9]4, tetraethoxytitanium Ti(OHC2H5)4, tetramethoxytitanium Ti(OCH3)4, and (2-propoxy)(2-ethylhexane-1,3-diolato)titanium are also preferably used. Furthermore, as derivatives of tetraalkoxytitanium, low condensates obtained by partially hydrolyzing alkoxytitanium can be exemplified. Tetraalkoxytitanium or its derivatives may be used alone or in combination of two or more.

[0058] Examples of alkaline catalysts used in the first form of the core-shell nanoparticle production process include ammonium hydroxide, methylamine, dimethylamine, ethylenediamine, ethylenediaminetetraacetic acid and its sodium salt, diethylenetriamine, sodium hydroxide, potassium hydroxide, arginine, and lysine. The alkaline catalyst may be used alone or in a mixture of two or more types. The concentration of the alkaline catalyst in the reaction solution can be appropriately selected, but is preferably 0.01 to 20.0% by mass, more preferably 0.05 to 15.0% by mass, and even more preferably 0.10 to 10.0% by mass.

[0059] In the first embodiment of the core-shell nanoparticle production process, examples of solvents used when hydrolyzing and condensing tetraalkoxytitanium or its derivatives include water, methanol, ethanol, n-propanol, isopropanol, ethylene glycol, propylene glycol, alcohols such as 1,4-butanediol, ketones such as acetone and methyl ethyl ketone, and esters such as ethyl acetate. Among these, alcohols are preferred, and methanol, ethanol, and isopropanol are more preferred. It is even more preferable to use the same type of alcohol as that produced by the hydrolysis of the silicon compound as the solvent. By using the same type of alcohol as that purified by the hydrolysis of the silicon compound, the solvent can be easily recovered and reused. The solvent can be used individually or as a mixture of two or more solvents.

[0060] In the first embodiment of the core-shell type nanoparticle production process, it is preferable to add tetraalkoxy titanium or a derivative thereof such that the thickness of the photocatalyst layer on the silica nanoparticles is preferably 1 to 200 nm, more preferably 3 to 50 nm.

[0061] In the first embodiment of the core-shell nanoparticle production process, the reaction temperature and reaction time when hydrolyzing and condensing tetraalkoxytitanium or its derivatives are appropriately selected and preferably adjusted so that the average particle size of the resulting core-shell nanoparticles falls within the above range.

[0062] A second form of the core-shell nanoparticle production process involves adding tetraalkoxytitanium or its derivative and an alkaline catalyst to a colloidal solution of silica nanoparticles obtained in the core particle production process, and forming a photocatalytic layer coating the silica nanoparticles by hydrothermal synthesis under high temperature and high pressure to hydrolyze and condense the tetraalkoxytitanium or its derivative, thereby obtaining core-shell nanoparticles.

[0063] The tetraalkoxy titanium, alkaline catalyst, and solvent used in the second form of the core-shell nanoparticle production process are the same as those used in the first form of the core-shell nanoparticle production process.

[0064] In the second form of the core-shell nanoparticle production process, the reaction temperature of the hydrothermal synthesis method is preferably 100 to 400°C, more preferably 130 to 350°C.

[0065] In the second embodiment of the core-shell type nanoparticle production process, it is preferable to add tetraalkoxy titanium or a derivative thereof such that the thickness of the photocatalyst layer on the silica nanoparticles is preferably 1 to 200 nm, more preferably 3 to 50 nm.

[0066] In the core-shell nanoparticle production process, silica nanoparticles with small particle size but low aggregation, a narrow particle size distribution, and a small aspect ratio are used as the core, and a photocatalytic layer is formed on its surface. This makes it possible to obtain core-shell nanoparticles with small particle size, a narrow particle size distribution, and a small aspect ratio.

[0067] In the method for producing visible light-responsive photocatalytic particles of the present invention, when the first form of the core-shell nanoparticle generation step is performed, the obtained core-shell nanoparticles may be heat-treated at 200 to 1000°C for 0.5 to 24 hours after performing the first form of the core-shell nanoparticle generation step. By heat-treating at the above temperature range and time, the titanium dioxide in the photocatalytic layer coating the silica nanoparticles crystallizes from amorphous to anatase crystal, thereby increasing the catalytic activity.

[0068] The co-catalyst introduction step in the method for producing visible light-responsive photocatalyst particles of the present invention is a step of supporting co-catalyst nanoparticles on the surface of core-shell nanoparticles obtained by the core-shell nanoparticle generation step to obtain visible light-responsive photocatalyst particles.

[0069] In the co-catalyst introduction step, the co-catalyst nanoparticles supported on the surface of the core-shell type nanoparticles are, for example, nanoparticles of metals such as silver (Ag), copper (Cu), nickel (Ni), gold (Au), platinum (Pt), palladium (Pd), rhodium (Rh), and ruthenium (Ru), and preferably silver (Ag), copper (Cu), and nickel (Ni) nanoparticles.

[0070] In the co-catalyst introduction process, the amount of co-catalyst nanoparticles supported on the core-shell type nanoparticles is selected as appropriate.

[0071] In the co-catalyst introduction step, the average particle size of the co-catalyst nanoparticles supported on the surface of the core-shell type nanoparticles is 1.5 to 200 nm, preferably 2 to 50 nm. Furthermore, the dispersion degree of the co-catalyst nanoparticles supported on the surface of the core-shell type nanoparticles is 2 to 50%, preferably 2 to 20%. By having the average particle size and dispersion degree of the co-catalyst nanoparticles supported on the surface of the core-shell type nanoparticles within the above ranges, the co-catalyst function is easily exhibited, resulting in cost-effective and easily synthesized co-catalyst nanoparticles.

[0072] The area ratio of co-catalyst nanoparticles supported on the surface of core-shell type nanoparticles is 1-80%, preferably 10-50%. This area ratio is an indicator of the uniform dispersion of the co-catalyst nanoparticles. By having the above area ratio of co-catalyst nanoparticles supported on the surface of core-shell type nanoparticles, the variation in catalytic activity of visible light-responsive photocatalyst particles is reduced, resulting in higher catalytic activity, and thus making it easier to set reaction conditions.

[0073] As a first form of the co-catalyst introduction process, a substance containing reducing metal ions having a lower standard electrode potential than the co-catalyst metal is added to an aqueous dispersion of core-shell nanoparticles obtained by the core-shell nanoparticle generation process, causing the reducing metal ions to adsorb onto the surface of the core-shell nanoparticles. Subsequently, metal ions of the co-catalyst metal are added, and the metal ions of the co-catalyst metal are reduced by an oxidation-reduction reaction between the reducing metal ions and the metal ions of the co-catalyst metal to generate the co-catalyst nanoparticles, thereby obtaining a colloidal solution of visible light-responsive photocatalyst particles in which the co-catalyst nanoparticles are supported on the surface of the core-shell nanoparticles.

[0074] In the first form of the co-catalyst introduction process, the reducing metal refers to a metal ion whose standard electrode potential is lower than that of the metal forming the co-catalyst nanoparticles (co-catalyst metal) that are supported on the surface of the core-shell type nanoparticles. For example, when Ag nanoparticles are supported as co-catalyst nanoparticles, the reducing metal ion is Sn 2+ You can use it.

[0075] In the first form of the co-catalyst introduction process, first, a substance containing reducing metal ions is added to an aqueous solution of core-shell nanoparticles to adsorb the reducing metal ions onto the surface of the core-shell nanoparticles. The reducing metal ions are not particularly limited as long as they are metal ions with a standard electrode potential lower than that of the co-catalyst metal, but for example, Sn 2+ Fe 2+ , Cr 3+ Mn 2+ , Ru 2+ These are examples. Substances containing reducing metal ions include salts containing these reducing metal ions, such as chloride salts, sulfates, nitrates, oxalates, acetates, chlorides, and fluorides of reducing metal ions.

[0076] In the first form of the co-catalyst introduction process, the amount of substance containing reducing metal ions added is appropriately selected according to the amount of co-catalyst nanoparticles to be supported.

[0077] In the first form of the co-catalyst introduction process, the temperature and time for adding a substance containing reducing metal ions to an aqueous dispersion of core-shell nanoparticles to adsorb the reducing metal ions onto the surface of the core-shell nanoparticles are appropriately selected.

[0078] In the first form of the co-catalyst introduction process, metal ions of the co-catalyst metal are then added, and the metal ions of the co-catalyst metal are reduced by an oxidation-reduction reaction between the reducing metal ions and the co-catalyst metal ions, thereby generating co-catalyst nanoparticles on the surface of the core-shell type nanoparticles, and supporting the co-catalyst nanoparticles on the surface of the core-shell type nanoparticles.

[0079] In the first form of the co-catalyst introduction process, the co-catalyst metal is not particularly limited as long as it has a higher standard electrode potential than the reducing metal ions and is a metal used as a co-catalyst in photocatalysis. Examples include silver (Ag), copper (Cu), nickel (Ni), gold (Au), platinum (Pt), palladium (Pd), rhodium (Rh), and ruthenium (Ru). Then, the metal ions of the co-catalyst metal are added by adding a substance containing metal ions of the co-catalyst metal, such as chloride salts, sulfates, nitrates, oxalates, acetates, chlorides, fluorides, etc. of these metal ions of the co-catalyst metal.

[0080] In the first form of the co-catalyst introduction process, the amount of metal ions of the co-catalyst metal added is appropriately selected according to the amount of co-catalyst nanoparticles supported.

[0081] In the first form of the co-catalyst introduction process, metal ions of the co-catalyst metal are added to an aqueous dispersion of core-shell type nanoparticles, and the temperature and time for reducing the metal ions of the co-catalyst metal are appropriately selected.

[0082] In the first form of the co-catalyst introduction process, a redox reaction occurs between the reducing metal ions present on the surface of the core-shell nanoparticles and the metal ions of the co-catalyst metal. This reduces the metal ions of the co-catalyst metal at the positions where the reducing metal ions were adsorbed, generating the co-catalyst metal, and simultaneously oxidizing the reducing metal ions, causing them to detach from the surface of the core-shell nanoparticles. This results in visible light-responsive photocatalyst particles with co-catalyst nanoparticles supported on the surface of the core-shell nanoparticles. Furthermore, in the first form of the co-catalyst introduction process, since the reducing metal ions are adsorbed onto the surface of the core-shell nanoparticles beforehand, the reducing metal ions can be uniformly and well-dispersed on the surface of the core-shell nanoparticles. Then, by reacting the metal ions of the co-catalyst metal with these reducing metal ions to generate the co-catalyst metal, the co-catalyst nanoparticles can be supported on the surface of the photocatalyst layer with high uniform dispersion and minimal aggregation.

[0083] In the present invention's method for producing visible light-responsive photocatalytic particles, tetraalkoxysilane or a derivative thereof is used as a raw material and subjected to hydrolysis and condensation to obtain silica nanoparticles with small particle size, low aggregation, a narrow particle size distribution, and a small aspect ratio. These silica nanoparticles are then used as a core to form a photocatalytic layer. Therefore, in the present invention's method for producing visible light-responsive photocatalytic particles, granular photocatalysts with small particle size, low aggregation, a narrow particle size distribution, and a small aspect ratio are obtained, resulting in less variation in the catalytic activity of the photocatalytic particles. Furthermore, in the present invention's method for producing visible light-responsive photocatalytic particles, the granular photocatalyst on which the co-catalytic nanoparticles are supported has small particle size, a narrow particle size distribution, and a small aspect ratio, making it easier for the co-catalytic nanoparticles to be uniformly supported on the surface of the granular photocatalyst. Therefore, the present invention's method for producing visible light-responsive photocatalytic particles enhances the effect of reducing variation in the catalytic activity of the photocatalytic particles and increases photocatalytic activity.

[0084] Note that the average particle diameter d of silica nanoparticles (core particles), core-shell type nanoparticles, co-catalyst nanoparticles, and the visible light-responsive photocatalyst particles of the present invention is specified. nand a method for measuring the degree of dispersion. In a TEM image obtained under the condition of an acceleration voltage of 200 kV using a transmission electron microscope (TEM) (JEM-2100, manufactured by JEOL Ltd.), the minor axis diameters of arbitrarily selected 100 particles are measured, and the obtained values are averaged to obtain the average particle diameter d n is determined. Also, as described above, from the values obtained by measuring the minor axis diameters of arbitrarily selected 100 silica nanoparticles, the standard deviation σ of the particle diameter is determined. Then, from the obtained values of d n and σ, the degree of dispersion is calculated according to the formula "degree of dispersion = (σ / d n ) × 100" to obtain the degree of dispersion. Further, a method for measuring the aspect ratio of silica nanoparticles (core particles), core-shell type nanoparticles, and the visible light-responsive photocatalyst particles of the present invention is as follows. As described above, the minor axis diameter and the major axis diameter of arbitrarily selected 100 particles are measured, the ratio of the major axis diameter to the minor axis diameter is calculated, and the average value of the ratio is obtained to determine the aspect ratio.

[0085] Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to these examples.

Examples

[0086] (Example 1) <Production of SiO2 nanoparticles> 12.57 mL of ethanol and 10.314 mL of distilled water were mixed, and the mixture was stirred for 5 minutes. Next, 1.175 mL of tetraethoxysilane (TEOS) as a SiO2 source was added to the above mixture, and the mixture was stirred for 5 minutes. Furthermore, 0.936 mL of an NH4OH aqueous solution as a basic catalyst was added and stirred for 3 hours. The obtained reaction solution was subjected to solid-liquid separation by centrifugation at 24,000 rpm for 30 minutes × 3 times, and the solid matter was redispersed in ethanol to prepare 25 mL of a SiO2 colloidal solution. The final concentrations were TEOS 0.20 M and NH4OH 0.6 M.

[0087] <Production of SiO2 / TiO2 nanoparticles> To 12.42 mL of ethanol, 7.14 mL of the above SiO2 colloidal solution and 14.28 mL of acetonitrile were added, and the mixture was stirred for 5 minutes. Next, 0.035 mL of an aqueous methylamine (MA) solution as a basic catalyst and 0.126 mL of distilled water as an initiator were added and stirred for 5 minutes. Furthermore, 0.36 mL of ethanol and 5.64 mL of tetraisopropyl orthotitanate (TTIP) as a TiO2 source were added and stirred for 24 hours. Solid-liquid separation was carried out by centrifugation at 20000 rpm for 30 minutes × 3 times, and the solid was redispersed in ethanol to prepare 40 mL of a SiO2 coated with TiO2 (denoted as SiO2 / TiO2) colloidal solution. The final concentrations were MA 0.01 M, distilled water 0.2 M, and TTIP 0.03 M.

[0088] <Heat treatment of SiO2 / TiO2 nanoparticles> The above SiO2 / TiO2 nanoparticles were heat-treated at 500 °C, 600 °C, and 700 °C for 3 hours, respectively.

[0089] <Preparation of SiO2 / TiO2 / Ag nanoparticles> To 2.50 mL of distilled water, 0.0270 g of the powder of the above heat-treated SiO2 / TiO2 nanoparticles was added at 35 °C. Furthermore, 35.84 mL of distilled water, 0.16 mL of acetic acid, and an aqueous solution (the first aqueous solution) prepared with 0.76 g of SnCl2 as a Sn source were added in 22.5 mL, and the mixture was stirred for 45 minutes and solid-liquid separated by centrifugation at 20000 rpm for 30 minutes × 2 times. 2+ Next, 2.50 mL of distilled water was added, and 22.5 mL of an aqueous solution (the second aqueous solution) prepared with 0.24 mL of an aqueous solution of [Ag(NH3)2] as an Ag source and 22.61 mL of distilled water were added, and the mixture was stirred for 5 minutes and then stirred at 20000 rpm for 30 minutes. Furthermore, 2.50 mL of distilled water and 22.5 mL of the above first aqueous solution were added, and the mixture was stirred for 45 minutes and solid-liquid separated by centrifugation at 20000 rpm for 30 minutes × 2 times. 2+ Next, 2.50 mL of distilled water was added, and 22.5 mL of an aqueous solution (the second aqueous solution) prepared with 0.24 mL of an aqueous solution of [Ag(NH3)2] as an Ag source and 22.61 mL of distilled water were added, and the mixture was stirred for 5 minutes and then stirred at 20000 rpm for 30 minutes. Furthermore, 2.50 mL of distilled water and 22.5 mL of the above first aqueous solution were added, and the mixture was stirred for 45 minutes and solid-liquid separated by centrifugation at 20000 rpm for 30 minutes × 2 times. Furthermore, 2.50 mL of distilled water and 22.5 mL of the above second aqueous solution were added, stirred for 5 minutes, and subjected to solid-liquid separation by centrifugation at 20,000 rpm for 30 minutes × 2 times to prepare 25 mL of a colloidal solution in which Ag atoms are present on the surface of SiO2 / TiO2 particles (denoted as SiO2 / TiO2 / Ag). The final concentration was 0.17 mM of Ag.

[0090] <TEM Observation of SiO2 Nanoparticles> The above SiO2 nanoparticles were observed using a transmission electron microscope (TEM) (JEM-2100, manufactured by JEOL Ltd.).

[0091] <DLS Measurement of SiO2 Nanoparticles> The above SiO2 nanoparticles were subjected to DLS measurement using a Zetasizer nano ZS90, manufactured by Malvern.

[0092] <TEM Observation of SiO2 / TiO2 Nanoparticles> The above SiO2 / TiO2 nanoparticles were observed using a transmission electron microscope (TEM) (JEM-2100, manufactured by JEOL Ltd.).

[0093] <UV-Vis Spectrophotometric Analysis of SiO2 / TiO2 Nanoparticles> The above SiO2 / TiO2 nanoparticles were subjected to UV-vis spectrophotometric analysis using a UV-visible spectrophotometer (UV-2600i, manufactured by Shimadzu Corporation).

[0094] <TG-DTA Analysis of SiO2 / TiO2 Nanoparticles> The above SiO2 / TiO2 nanoparticles were subjected to TG-DTA analysis using a thermogravimetry-differential thermal analyzer (TG8120, manufactured by Rigaku Corporation).

[0095] <TEM Observation of Heat-Treated SiO2 / TiO2 Nanoparticles> The above heat-treated SiO2 / TiO2 nanoparticles were observed using a transmission electron microscope (TEM) (JEM-2100, manufactured by JEOL Ltd.).

[0096] <XRD Analysis of SiO2 / TiO2 Nanoparticles after Heat Treatment> The SiO2 / TiO2 nanoparticles after the above heat treatment were subjected to XRD analysis using an X-ray diffractometer (Ultima IV, manufactured by Rigaku Corporation).

[0097] <TEM Observation of SiO2 / TiO2 / Ag Nanoparticles> The SiO2 / TiO2 / Ag nanoparticles were observed using a transmission electron microscope (TEM) (JEM-2100, manufactured by JEOL Ltd.).

[0098] <STEM Observation of SiO2 / TiO2 / Ag Nanoparticles> The SiO2 / TiO2 / Ag nanoparticles were observed using a scanning transmission electron microscope (STEM) (HD-2000, manufactured by Hitachi High-Technologies Corporation).

[0099] <UV-Vis Spectrophotometric Analysis of SiO2 / TiO2 / Ag Nanoparticles> The SiO2 / TiO2 / Ag nanoparticles were subjected to UV-vis spectrophotometric analysis using a UV-visible spectrophotometer (UV-2600i, manufactured by Shimadzu Corporation).

[0100] <XRD Analysis of SiO2 / TiO2 / Ag Nanoparticles> The SiO2 / TiO2 / Ag nanoparticles were subjected to XRD analysis using an X-ray diffractometer (Ultima IV, manufactured by Rigaku Corporation).

[0101] <Measurement of Average Particle Size, Dispersion Degree and Aspect Ratio> The SiO2 nanoparticles, the SiO2 / TiO2 nanoparticles, and the SiO2 / TiO2 / Ag nanoparticles were observed using a transmission electron microscope (TEM) (JEM-210, manufactured by JEOL Ltd.) under the condition of an acceleration voltage of 200 kV. In the obtained TEM images, the minor diameters of 100 arbitrarily selected silica nanoparticles were measured, and the obtained values were averaged to obtain the average particle size d nThe standard deviation σ of the particle size was determined from the values ​​obtained by measuring the short diameter of 100 arbitrarily selected silica nanoparticles as described above. Then, the obtained d n And from the value of σ, "Depth of dispersion = (σ / d n The degree of dispersion was calculated using the formula "() × 100". In addition, the short and long diameters of 100 arbitrarily selected silica nanoparticles were measured as described above, the ratio of long diameter to short diameter was calculated, and the aspect ratio was obtained by averaging these values. The results are shown in Table 1.

[0102] <Result> As shown in Figure 2, TEM images confirmed that spherical SiO2 nanoparticles with a particle size of approximately 84 nm and a dispersion of 13% were fabricated. As shown in Figure 3, a single peak representing the particle size of the fabricated SiO2 nanoparticles was confirmed from the DLS measurement. This suggests that no aggregates were formed. As shown in Figure 4, high contrast was observed around the SiO2 particles in the TEM image. This suggests that a TiO2 coating was formed on the surface of the SiO2 nanoparticles. As shown in Figure 5, UV-bis analysis revealed absorption in the ultraviolet region below 380 nm. This suggests the generation of TiO2. As shown in Figure 6, TG-DTA analysis revealed a peak at around 600°C that is attributed to crystallization. This suggests crystallization from amorphous to anatase form of TiO2. As shown in Figure 7, the SiO2 / TiO2 nanoparticles after heat treatment were monodisperse, and there was no particle growth due to the heat treatment. As shown in Figure 8, XRD analysis suggests that the TiO2 crystallized in the anatase form after heat treatment at 600°C and 700°C. The crystallite size of the anatase form of TiO2 remained unchanged at 14.8 nm at both heat treatment temperatures of 600°C and 700°C. This confirmed that no crystal growth (condensation) occurred due to the increase in heat treatment temperature. As shown in FIGS. 9 and 10, small-sized particles with high contrast were confirmed around the particles from the TEM image and STEM image. The formation of SiO2 / TiO2 / Ag nanoparticles and the loading of Ag nanoparticles were confirmed. As shown in FIG. 11, an absorption peak derived from Ag nanoparticles was confirmed from the UV-vis analysis. As shown in FIG. 12, no peak attributed to Ag was detected from the XRD. It is presumed that there was a small amount of Ag due to the low AgNO3 concentration.

[0103]

Table 1

[0104] As can be seen from Table 1, silica nanoparticles (SiO2) obtained by hydrolyzing and condensing tetraethoxysilane, which is a tetraalkoxysilane, with an alkali catalyst have a small particle size, a small particle size distribution, and a small aspect ratio. By using the silica nanoparticles as a core, the shape characteristics of having a small particle size, a small particle size distribution, and a small aspect ratio are reflected in the shape of the core-shell type nanoparticles (SiO2 / TiO2) formed with a titanium oxide layer as a photocatalyst on the surface of the silica particles, and the visible light-responsive photocatalyst particles (SiO2 / TiO2 / Ag) loaded with Ag nanoparticles on the surface of the photocatalyst layer.

[0105] <UV-vis Analysis of SiO2 / TiO2 / Ag Nanoparticles (Photocatalytic Activity Evaluation)> 1.56×10 13 of the above SiO2 / TiO2 / Ag nanoparticles were added to an aqueous solution of methylene blue (MB), and after adsorbing MB onto the particles in the dark, the photocatalytic activity was investigated by observing the change over time of the MB concentration with respect to the visible light irradiation time. Visible light with a wavelength of 420 - 700 nm was used. Also, the change over time of the MB concentration was measured using UV-vis (UV-2600i, manufactured by Shimadzu Corporation). FIG. 13 shows a calibration curve representing the relationship between the absorbance at a wavelength of 655 nm and the MB concentration. Photocatalytic activity was evaluated by comparing the rate constants of the MB decomposition reaction. The reaction rate constant was calculated using the integral method based on the following equation. First-order reaction -dC A / dt=kC A → -ln(C A / C0)=kt (C A :MB concentration after irradiation time A minutes, C0: initial concentration) The results are shown in Figures 15 and 16. In Figure 15, the MB concentrations at 0 minutes are listed in descending order from highest to lowest: SiO2 / Ag, SiO2 / TiO2, SiO2, SiO2 / TiO2 / Ag, and P25 (at 240 minutes, P25 has the highest MB concentration, and SiO2 / TiO2 / Ag has the lowest). In Figure 16, the MB concentrations at 125 minutes are shown as -ln(C A The values ​​of / C0) in descending order are SiO2 / TiO2 / Ag, SiO2 / TiO2, SiO2 / Ag, SiO2, and P25.

[0106] (Comparative Example 1) The intermediate product of Example 1, SiO2 nanoparticles, was divided into 1.56 × 10⁻⁶ units. 13 In addition, UV-vis analysis was performed by irradiating with visible light (wavelength: 420-700 nm) in the same manner as the UV-vis analysis (photocatalytic activity evaluation) described in Example 1 (UV-2600i, manufactured by Shimadzu Corporation).

[0107] (Comparative Example 2) A mixed solution of SnCl2 was prepared by adding SnCl2 and acetic acid to H2O. Furthermore, by adding AgNO3 and NH4OH to H2O, [Ag(NH3)2] + An aqueous solution was prepared. Next, add the SiO2 nanoparticle colloidal solution and the SnCl2 mixed solution to H2O, stir for 45 minutes, and then centrifuge wash with H2O to obtain the SiO2 / SnCl2 2+ A colloidal solution was prepared. Next, SiO2 / Sn 2+ H2O and [Ag(NH3)2] in a colloidal solution +An aqueous solution was added and the mixture was stirred for 5 minutes. The reaction temperature was 35°C. Subsequently, SiO2 / Ag nanoparticle powder was prepared by centrifugal washing with H2O and vacuum drying. The obtained SiO2 / Ag nanoparticles were divided into 1.56 × 10⁻⁶ units. 13 In addition, UV-vis analysis was performed by irradiating with visible light (wavelength: 420-700 nm) in the same manner as the UV-vis analysis (photocatalytic activity evaluation) described in Example 1.

[0108] (Comparative Example 3) The intermediate product of Example 1, SiO2 / TiO2 nanoparticles, was divided into 1.56 × 10⁻⁶ units. 13 In addition, the samples were irradiated with visible light (wavelength: 420-700 nm) and UV-vis analysis was performed in the same manner as the UV-vis analysis (photocatalytic activity evaluation) described in Example 1.

[0109] (Comparative Example 4) For comparative studies of photocatalytic activity, commercially available reagent-grade TiO2 (99.5%, Thermo Scientific Chemicals, P25) was used as TiO2 nanoparticles, and the TiO2 nanoparticles were divided into 1.56 × 10⁶ units. 13 In addition, UV-vis analysis was performed by irradiating with visible light (wavelength: 420-700 nm) in the same manner as the UV-vis analysis (photocatalytic activity evaluation) described in Example 1.

[0110] Table 2 shows the particle weight, added weight, and number of particles for Example 1 and Comparative Examples 1-4. TEM images of the nanoparticles from Example 1 and Comparative Examples 1-4 are shown in Figure 14.

[0111] [Table 2]

[0112] <Result> As shown in Figures 15 and 16, the SiO2 / TiO2 / Ag nanoparticles of Example 1 showed a significant decrease in MB concentration and a change in the MB decomposition reaction rate constant, confirming that they possess outstanding catalytic activity under visible light. It is presumed that the photoelectric field enhancement due to plasmon resonance excited electrons in the TiO2 conductor, resulting in the manifestation of catalytic activity.

Claims

1. A core-shell type nanoparticle comprising silica nanoparticles forming a core and a photocatalytic layer coating the silica nanoparticles, Co-catalyst nanoparticles supported on the surface of the core-shell type nanoparticles, Visible light-responsive photocatalytic particles characterized by containing the following:

2. The visible light-responsive photocatalytic particle according to claim 1, characterized in that the photocatalytic layer contains one or more selected from titanium dioxide, zinc oxide, tungsten oxide, indium oxide, iron oxide, bismuth oxide, molybdenum sulfide, strontium titanate, silicon, gallium phosphide, gallium arsenide, cadmium sulfide, cadmium selenide, and silicon carbide.

3. The visible light-responsive photocatalytic particle according to claim 1, characterized in that the co-catalyst nanoparticles are one or more selected from the group consisting of Ag, Cu, Ni, Au, Pt, Pd, Rh, and Ru.

4. The visible light-responsive photocatalyst particles according to claim 1, characterized in that the average particle diameter of the visible light-responsive photocatalyst particles is 6 to 700 nm, the degree of dispersion is 2 to 20%, and the aspect ratio is 1 to 10.

5. The visible light-responsive photocatalytic particle according to claim 1, characterized in that the supported area ratio of the co-catalyst nanoparticles is 1 to 80% in transmission electron microscopy (TEM) observation.

6. A core particle generation step of mixing a tetraalkoxysilane or its derivative with an alkaline catalyst to obtain silica nanoparticles, A core-shell nanoparticle production step involves forming a photocatalytic layer on the surface of the silica nanoparticles to obtain core-shell nanoparticles, A co-catalyst introduction step to obtain visible light-responsive photocatalyst particles by supporting co-catalyst nanoparticles on the surface of the core-shell type nanoparticles, A method for producing visible light-responsive photocatalytic particles, characterized by having the following characteristics.

7. The method for producing visible light-responsive photocatalytic particles according to claim 6, characterized in that the core-shell nanoparticle production step involves adding tetraalkoxytitanium or a derivative thereof and an alkaline catalyst to a colloidal solution of silica nanoparticles to form a photocatalytic layer coating the silica nanoparticles, thereby obtaining the core-shell nanoparticles.

8. The method for producing visible light-responsive photocatalyst particles according to claim 6, characterized in that the co-catalyst introduction step involves adding a substance containing reducing metal ions having a lower standard electrode potential than the co-catalyst metal to an aqueous solution of the core-shell nanoparticles to adsorb the reducing metal ions onto the surface of the core-shell nanoparticles, then adding metal ions of the co-catalyst metal to reduce the metal ions of the co-catalyst metal through an oxidation-reduction reaction between the reducing metal ions and the metal ions of the co-catalyst metal to generate the co-catalyst nanoparticles, thereby obtaining a colloidal solution of visible light-responsive photocatalyst particles in which the co-catalyst nanoparticles are supported on the surface of the core-shell nanoparticles.

9. The method for producing visible light-responsive photocatalyst particles according to claim 7, characterized in that, after the core-shell nanoparticle generation step and before the co-catalyst introduction step, the core-shell nanoparticles are heat-treated at 200 to 1000°C for 0.5 to 24 hours.

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