Titania nanoparticles and their manufacturing method

Abstract

To provide a photocatalyst which is prepared without use of silver salt and includes titanium oxide having fine silver nanoparticles supported thereon, does not exhibit precipitation in water, ensuring its stable presence, and is highly transparent.SOLUTION: A titania nanoparticle production method includes the steps of (A) mixing a substance containing titanium, an organic acid, and water to give an aqueous dispersion, (B) heating the aqueous dispersion given in the step (A) at a temperature of higher than 80°C, and (C) after the step (B), mixing silver (metal silver, or silver particles) into the aqueous dispersion and irradiating the resultant silver-containing aqueous dispersion with visible light or ultraviolet light to cause the titanium (titania nanoparticles) to support the silver (the metal silver or the silver particles).SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to titania nanoparticles and a method for producing the same. [Background technology]

[0002] In recent years, with the increase in awareness of hygiene, photocatalysts have been put to practical use to impart pathogen resistance to indoor building materials, daily necessities, etc., and paints containing photocatalysts are applied to the surfaces of indoor building materials, daily necessities, etc.

[0003] When photocatalysts are irradiated with light, they generate reactive oxygen species that lead to antimicrobial activity, for example, from oxygen and moisture on the catalyst surface. Photocatalysts are utilized as highly sustainable antimicrobial materials because the photocatalyst itself does not change before and after the generation of antimicrobial active species. Photocatalysts generally refer to catalysts that absorb ultraviolet light and exhibit photocatalytic activity.

[0004] In addition, photocatalysts are designed for use in environments where ultraviolet rays are difficult to reach, such as indoors. Visible light catalysts that exhibit photocatalytic activity in response to light in the visible light region have been actively developed. The most commonly used visible light catalysts are metal-containing titanium oxide powders or metal-containing titanium oxide sols, which are titanium oxide powders or titanium oxide sols that contain metals such as iron, platinum, gold, copper, or silver.

[0005] In addition, as photocatalysts, in indoor environments and when everyday items are used, there are environments where there is no light, such as in the shade or at night, so metal-containing titanium oxide powders and metal-containing titanium oxide sols containing anti-microbiotic metal species such as silver and copper have also been developed to exhibit anti-microbiotic properties even in dark places.

[0006] Meanwhile, photocatalytic coating films for indoor building materials, daily necessities, etc., are required to be easily applied as a one-component system, to be highly transparent without impairing the design freedom of the substrate, and to have adhesion and crack resistance so that they do not slip off or crack when touched by hands, etc.

[0007] However, when a suspension of titanium oxide powder containing metals, such as those marketed by Lumiresh (Showa Denko K.K.) or Cellmuse (Daicel Miraize Co., Ltd.), dispersed in water is applied to a glass substrate or a highly transparent resin substrate, the white color of the titanium oxide powder is strongly observed, and the transparency of the glass substrate can be impaired. Furthermore, when the coating film formed in this way is rubbed with a finger, the powder can slide off. Thus, when metal-containing titanium oxide powder is used as a coating, there are issues with transparency and substrate adhesion when used alone.

[0008] One method to address this issue is to use a polymeric organic compound or a porous inorganic compound as a binder, fix the metal-containing titanium oxide powder in the binder, and form a coating film. However, polymeric organic compound binders coat the surface of the metal-supported titanium oxide, which reduces the photocatalytic activity. Porous inorganic compound binders, while having more voids than polymeric organic compound binders and therefore less likely to reduce activity, are hard and brittle, resulting in poor crack resistance and accelerated catalyst slippage, shortening the service life. Thus, using a binder in a photocatalyst can impair the inherent durability and antimicrobial activity of the metal-supported titanium oxide.

[0009] For example, Patent Document 1 discloses a virus inactivating agent containing a photocatalytic substance on the surface of which a mixture containing a monovalent copper compound and a divalent copper compound is supported. The examples in Patent Document 1 exemplify an example in which Cu2O powder is used and an example in which Cu2O powder is mixed with a silica-based binder, and disclose an example in which these are applied to a glass plate and brought into contact with viruses under the same conditions for 30 minutes. When Cu2O is used alone, 10 6 When the binder was used, the virus infectivity decreased by 10 5 It is disclosed that the activity only decreased by about 10 times when a material carrier was used in combination with a binder.

[0010] Therefore, a method has been proposed in which an antimicrobial metal is supported on titanium oxide sol, which can be applied in a one-component system without using a binder, and a coating film of the antimicrobial metal-supported titanium oxide sol is formed by applying the one-component system. However, titanium oxide sol has problems such as cloudiness and cracks in the coating film, making it difficult to achieve a coating film that is highly transparent and durable.

[0011] In fact, when a water-soluble titanium oxide sol with an X-ray particle diameter of 7 nm (product name: CSB, Sakai Chemical Industry Co., Ltd.) was applied to a glass substrate, the coating became cloudy. Furthermore, when titanium oxide synthesized by the method described in Non-Patent Document 1 was applied, cracks occurred.

[0012] As described above, when using metal-containing titanium oxide powder and titanium oxide sol, it is currently difficult to form a binderless (without using a binder) coating material that is highly transparent, crack-resistant, and highly adhesive.

[0013] As mentioned above, metal-supported titanium oxide powders and sols for indoor coatings have problems such as low substrate adhesion and crack resistance when used alone, and although these can be reinforced by adding a binder or the like, there are problems such as the binder coating the catalyst surface or causing the catalyst to slide off, and at present, this impairs the inherent antimicrobial activity and activity sustainability of metal-containing titanium oxide.

[0014] Furthermore, while many indoor building materials, daily necessities, and the like require design in terms of color, metal-containing titanium oxide powder is a cloudy white powder, which means that the range of design possibilities is extremely limited.

[0015] Therefore, there is a demand for a highly transparent visible light catalyst that is binderless, adheres to a substrate, and has high physical resistance as a coating film.

[0016] Another problem with metal-containing titanium oxide powders and titanium oxide sols is the instability of the metal components contained separately from titanium oxide. For example, as disclosed in Patent Document 2, when a silver complex is added to an aqueous solution in which titanium oxide is dispersed, the color of the solution gradually changes, and eventually silver precipitation is observed. This phenomenon of precipitation due to instability of the metal component is often seen with elements with low ionization tendency, such as silver and copper.

[0017] Therefore, a method has been proposed in which silver and copper are combined and quaternary ammonium is incorporated into titanium oxide sol to stabilize the metal components with a stabilizer (Patent Document 2). However, the method disclosed in Patent Document 2 raises safety concerns because it contains quaternary ammonium ions, which are highly toxic to the human body.

[0018] Also proposed is a method of coating the surface of silver with a thiol-based ligand or titanium oxide (Non-Patent Document 2). However, the method of coating the surface of silver with a thiol-based ligand or titanium oxide disclosed in Non-Patent Document 2 has the problem that, if the surface is completely coated, the elution of silver, which is an antimicrobial metal, is prevented, resulting in a loss of antimicrobial activity, and, on the other hand, if the surface is only partially coated, the antimicrobial metal silver is repeatedly eluted and reprecipitated, causing discoloration and precipitation.

[0019] Furthermore, when silver salts are used to support silver in photocatalysts, problems such as safety, coloration, and corrosivity arise. Most inorganic silver salts are toxic substances. For example, nitrate is the most commonly used silver salt, but nitrate is a toxic substance that, when it comes into contact with hands, becomes sensitive to light and deposits black compounds. Furthermore, when nitrate decomposes and generates acid, it can lead to corrosion of metals, etc. Furthermore, silver salts have poor storage stability, so they must be shielded from light, and are preferably stored in low-oxygen environments at low temperatures. If they are altered, they cannot be used to synthesize silver nanoparticles, so they require a lot of care.

[0020] When silver is supported on a photocatalyst, it is expected that the smaller the particle size, the higher the activity. On the other hand, silver is more likely to form aggregates than platinum and other metals. Platinum particles of 5 nm or less can generally be produced relatively easily. Compared to platinum, silver is less likely to form independent particles of 20 nm or less.

[0021] As described above, there is a need for a method for easily and safely producing a visible light catalyst that allows antimicrobial metal components with low ionization tendency, such as silver and copper, to exist stably in a titanium oxide solution without causing precipitation and that does not prevent the elution of these metals. [Prior art documents] [Patent documents]

[0022] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-166705 [Patent Document 2] Japanese Patent Application Laid-Open No. 2008-260684 [Non-patent literature]

[0023] [Non-Patent Document 1] Journal of the Society of Inorganic Materials, Japan 11.313 (2004): 481-488. [Non-patent document 2] Journal of the Japan Color Materials Association, 2014, Vol. 87, No. 2, 43-49 Summary of the Invention [Problem to be solved by the invention]

[0024] The present invention aims to provide a highly transparent photocatalyst that does not use silver salts, but instead supports fine silver nanoparticles on titanium oxide, which does not precipitate in water and exists stably. [Means for solving the problem]

[0025] With the above-mentioned object in mind, the present inventors conducted extensive research and found that uniform and highly transparent silver-loaded titanium oxide can be synthesized simply by stirring metallic silver with a dispersion of titania nanoparticles in the presence of visible or ultraviolet light, wherein at least some of the titanium atoms present on the surface have acetoxy groups bonded thereto and wherein the mass loss at 200°C or higher when heated to 600°C using a simultaneous differential thermal and thermogravimetric analyzer is 5% by mass or more.

[0026] The inventors then conducted further research and completed the present invention.

[0027] That is, the present invention includes the following configurations.

[0028] Section 1. A method for producing titania nanoparticles, comprising: a step of adding silver particles to an aqueous dispersion of titania nanoparticles and stirring the mixture to support silver on the titania nanoparticles; The titania nanoparticles have acetoxy groups bonded to at least some of the titanium atoms present on the surface, and when heated to 600°C using a thermogravimetric and differential thermal analyzer, the mass loss at 200°C or higher is 5% by mass or more. Manufacturing method.

[0029] Section 2. A method for producing titania nanoparticles, comprising: (A) mixing a titanium-containing substance, an organic acid, and water to obtain an aqueous dispersion; (B) heating the aqueous dispersion obtained in step (A) at a temperature higher than 80°C; and (C) After the step (B), a step of mixing silver (metallic silver, silver particles) with the aqueous dispersion and irradiating the silver-containing aqueous dispersion with visible light or ultraviolet light to support the silver (metallic silver, silver particles) on the titanium (titania nanoparticles). A manufacturing method comprising:

[0030] Section 3. 3. The method according to Item 2, wherein the aqueous dispersion in step (A) contains 50% by mass or more of water.

[0031] Section 4. 4. The method according to any one of items 1 to 3, wherein the pH of the aqueous dispersion in step (A) is 2 or more and 5 or less.

[0032] Section 5. 5. The method according to any one of items 1 to 4, wherein the silver is silver particles having a particle size of 1 μm or more and 1 mm or less.

[0033] Section 6. Titania nanoparticles, Titania nanoparticles are loaded with silver, The titania nanoparticles have acetoxy groups bonded to at least some of the titanium atoms present on the surface, and when heated to 600°C using a thermogravimetric and differential thermal analyzer, the mass loss at 200°C or higher is 5% by mass or more. Titania nanoparticles. [Effects of the Invention]

[0034] According to the present invention, a uniform, highly transparent, and storage-stable dispersion of silver-supported titanium oxide nanoparticles can be easily obtained without using silver salts, which are unsafe and susceptible to deterioration.

[0035] The silver-supported titanium oxide nanoparticle dispersion obtained by the present invention has high substrate adhesion and crack resistance, and can be used to obtain a highly transparent photocatalytic coating film. [Brief explanation of the drawings]

[0036] [Figure 1] 1 is a diagram illustrating an embodiment of the present invention. FIG. 1 shows the results of ESCA analysis of the metallic Ag obtained in Example 1. Metallic Ag is generated. [Figure 2] 2 is a diagram illustrating an embodiment of the present invention. Fig. 2 shows the silver-containing aqueous dispersion in which silver nanoparticles are supported on titania obtained in Example 1. The silver-containing aqueous dispersion was uniform, and maintained its uniformity and transparency even after 3 months. [Figure 3]3 is a diagram illustrating an embodiment of the present invention. Fig. 3 shows the results of TEM observation of titania nanoparticles supported by silver nanoparticles obtained in Example 1. The primary particles of Ag were 3 nm to 7 nm. [Figure 4] 4 is a diagram illustrating an embodiment of the present invention. Fig. 4 shows the results of TEM observation of titania nanoparticles supported by silver nanoparticles obtained in Example 1. Ag was found to be 10 nm to 20 nm in the aggregated secondary particles. [Figure 5] 5 shows the results of TEM observation of the dispersion liquid carrying metallic Ag obtained in Comparative Example 1. The Ag was in the form of aggregates of Ag nanoparticles with primary particles of 40 nm to 50 nm. [Figure 6] 6 is a diagram showing a comparative example. Fig. 6 shows the titania aqueous dispersion obtained in Comparative Example 3. In the titania aqueous dispersion, a supernatant and a precipitate were observed. DETAILED DESCRIPTION OF THE INVENTION

[0037] The present invention will be described in detail below.

[0038] In this specification, the terms "comprise" and "contain" are concepts that encompass all of "comprise," "consist essentially of," and "consist only of."

[0039] In this specification, when a numerical range is expressed as "A to B," it means "not less than A and not more than B."

[0040] 1. Manufacturing method of titania nanoparticles (silver-loaded titania nanoparticles) The method for producing titania nanoparticles of the present invention comprises the steps of: The method includes a step of adding silver (metallic silver, silver particles) to an aqueous dispersion of titanium (titania nanoparticles) and stirring the mixture to support the silver on the titanium, The titanium has acetoxy groups bonded to at least some of the titanium atoms present on the surface, and when heated to 600°C using a thermogravimetric and differential thermal analyzer, the mass loss at 200°C or higher is 5% by mass or more.

[0041] The method for producing titania nanoparticles of the present invention comprises the steps of: (A) mixing a titanium-containing substance, an organic acid, and water to obtain an aqueous dispersion; (B) heating the aqueous dispersion obtained in step (A) at a temperature higher than 80°C; and (C) After the step (B), a step of mixing silver (metallic silver, silver particles) with the aqueous dispersion and irradiating the silver-containing aqueous dispersion with visible light or ultraviolet light to support the silver (metallic silver, silver particles) on the titanium (titania nanoparticles). Equipped with.

[0042] In this specification, "titanium oxide" or "titania" does not refer only to titanium dioxide (TiO2), but also includes titanium dioxide with oxygen deficiency, such as titanium trioxide (Ti2O3), titanium monoxide (TiO), Ti4O7, and Ti5O9. "Titanium oxide" or "titania" may contain groups other than Ti-O-Ti, such as terminal OH groups, that result from the synthesis of titanium oxide. "Titanium oxide" or "titania" also includes those in which an organic acid or the like is bonded to the terminal OH group.

[0043] The titania nanoparticles (silver-supported titania nanoparticles) of the present invention are a composite in which silver nanoparticles are supported on the surface of titania nanoparticles, and the titania nanoparticles have acetoxy groups bonded to at least some of the titanium atoms present on the surface, and when the titania nanoparticles are heated to 600°C using a thermogravimetric and differential thermal analyzer, they experience a mass loss of 5% by mass or more at temperatures above 200°C.

[0044] Conventionally, when synthesizing such a composite, titanium oxide and silver salt are made to coexist in water, and a reducing agent is added or light is irradiated.

[0045] In the method for producing titania nanoparticles (composite) of the present invention, titanium oxide is preferably used as the titanium-containing substance. Titanium oxide preferably has a particle size of 1 nm to 10 nm, a large specific surface area, and acetoxy groups bonded to the surface, and is used in the form of an aqueous dispersion.

[0046] In the method for producing titania nanoparticles (composite) of the present invention, silver is not used in the production of silver, but preferably metallic silver is used in the presence of a titanium-containing substance and stirred.

[0047] In the method for producing titania nanoparticles of the present invention, minute amounts of silver ions are gradually released from metallic silver, which are then precipitated as silver nanoparticles on the surface of titanium oxide, which has a large specific surface area.In the method for producing titania nanoparticles of the present invention, finer silver nanoparticles are supported on the surface of titanium oxide compared to conventional techniques.

[0048] (1) Titania nanoparticles Generally, water, inorganic acids, free organic acids, etc. volatilize almost completely at temperatures below 200°C.

[0049] On the other hand, the titania nanoparticles that constitute the metal-supported titania nanoparticles of the present invention have acetoxy groups bonded to at least some of the titanium atoms present on the surface, and therefore the acetoxy groups bonded to the titanium atoms gradually detach in the range of 200°C to 600°C.

[0050] The titania nanoparticles constituting the metal-supported titania nanoparticles of the present invention have acetoxy groups bonded to at least some of the titanium atoms present on the surface, which prevents aggregation of the titania nanoparticles during drying or firing. This makes them less susceptible to cracking, peeling, etc., and they are particularly excellent in coatability and transparency.

[0051] Titania nanoparticles can suppress cracking, peeling, and the like, and furthermore, as they can easily support the metal described below firmly, they also have excellent visible light catalytic activity.

[0052] Conventionally, the presence of acetoxy groups on the surface reduces the visible light catalytic activity.

[0053] As explained above, titania nanoparticles can suppress aggregation of titania nanoparticles during drying or calcination, and therefore have a particularly excellent effect of suppressing cracking, peeling, and the like. In addition, they can easily firmly support metals (described below), and therefore can also improve visible light photocatalytic activity despite having acetoxy groups.

[0054] Titania nanoparticles preferably have a large number of acetoxy groups bonded to titanium atoms present on the surface. When acyloxy groups are present on at least some of the titanium atoms present on the surface, as explained above, the acyloxy groups present on the titanium atoms gradually leave the range of 200°C to 600°C, and therefore, when heated using a thermogravimetric differential thermal analyzer (TG-DTA), a large mass loss occurs above 200°C.

[0055] In the present invention, when titania nanoparticles are heated using a thermogravimetric differential thermal analyzer (TG-DTA), the mass loss at 200°C or higher indicates the number of acetoxy groups bonded to titanium atoms present on the surface. Therefore, when titania nanoparticles are heated to 600°C using a thermogravimetric differential thermal analyzer (TG-DTA), the mass loss at 200°C or higher is 5% by mass or more, preferably 7% by mass to 20% by mass. The detailed conditions for the thermogravimetric differential thermal analyzer (TG-DTA) are: atmosphere: air, heating rate: 3°C / min.

[0056] As described above, titania nanoparticles have acetoxy groups bonded to at least some of the titanium atoms present on the surface. Other acyloxy groups may also be present in titania nanoparticles. Examples of other acyloxy groups include monocarboxylic acids such as formic acid, acetic acid, propionic acid, and butyric acid, and hydroxycarboxylic acids such as glycolic acid, lactic acid, and 3-hydroxybutyric acid. The transparency of titania nanoparticles can be further enhanced by using or subsequently adding lactic acid as another acyloxy group.

[0057] The average particle size of the titania nanoparticles is preferably 1 nm to 10 nm, more preferably 2 nm to 6 nm The average particle size of the titania nanoparticles is measured by observation with a transmission electron microscope (TEM).

[0058] In the present invention, by setting the average particle size of the titania nanoparticles within this range, it is easier to support the metals (silver and copper) appropriately and more firmly, and it is easier to form a film with higher visible light catalytic activity and higher transparency.

[0059] Generally, when titania nanoparticles have a small average particle size, they tend to shrink significantly when heated, resulting in cracks and peeling from the substrate.

[0060] The metal-supported titania nanoparticles of the present invention are a material that exhibits excellent coating properties even when titania nanoparticles having a small average particle size are used.

[0061] The specific surface area of ​​the titania nanoparticles is preferably 150 m 2 / g~500m 2 / g, more preferably 200m 2 / g~400m 2 The specific surface area of ​​the titania nanoparticles is measured by the BET method.

[0062] In the present invention, by setting the specific surface area of ​​the titania nanoparticles within this range, it becomes easier to support the metals (silver and copper) appropriately and more firmly, and it becomes easier to increase the visible light catalytic activity.

[0063] The titania nanoparticles can have a concentration of each of the elements N, Cl, and S of preferably 0 ppm to 5000 ppm, more preferably 0 ppm to 1000 ppm. The concentrations of the elements N, Cl, and S of the titania nanoparticles are measured by WDX (fluorescent X-ray).

[0064] In the present invention, by setting the concentrations of N, Cl, and S elements in the titania nanoparticles within this range, corrosion of the substrate can be easily suppressed. This condition means that impurities derived from acidic titania precursors such as TiCl4 and TiOSO4 are absent or present in very small amounts.

[0065] The crystalline form of titania nanoparticles is preferably anatase type. In the present invention, by adopting anatase type, the visible light catalytic activity can be particularly improved. For the same reason, the crystalline form of titania nanoparticles is preferably 100% anatase type, with no other crystalline form being present.

[0066] (2) Method for producing metal-loaded titania nanoparticles and photocatalysts In the present invention, the method for supporting silver on titania nanoparticles involves mixing metallic silver with titania nanoparticles in the presence of visible light or ultraviolet light.

[0067] Specifically, the metal-supported titania nanoparticles and photocatalyst of the present invention are (A) mixing a titanium-containing substance, an organic acid, and water to obtain an aqueous dispersion; (B) heating the aqueous dispersion obtained in step (A) at a temperature higher than 80°C; (C) A step of mixing the aqueous dispersion obtained in the step (B) with silver in the presence of visible light or ultraviolet light. The method can be manufactured by the method comprising the steps of:

[0068] In step (C), the loading efficiency can be improved by heating. If the heating temperature is too high, the hydration water of the titania nanoparticles tends to be removed, resulting in an increase in viscosity and a decrease in dispersibility. The reaction temperature in step (C) is usually 0°C to 100°C, preferably 10°C to 50°C, and more preferably 15°C to 40°C.

[0069] (2-1) Process (A) In step (A), a titanium-containing substance, an organic acid, and water are mixed to obtain an aqueous dispersion.

[0070] The titanium-containing substance to be used is not particularly limited as long as it becomes titanium oxide when heated. That is, the titanium-containing substance is preferably titanium oxide and / or a titanium oxide precursor. Specific examples of titanium-containing substances include titanium oxide; titanium hydroxide; titanium alkoxide; titanium halides such as titanium trichloride and titanium tetrachloride (especially those neutralized with a base); and metallic titanium. These titanium-containing substances can be used alone or in combination of two or more.

[0071] Among these titanium-containing substances, titanium alkoxide, titanium hydroxide, or titanium halide (particularly those neutralized with a base) is preferred from the viewpoints of dispersibility, coatability, transparency, and visible light photocatalysis of the resulting titania, and titanium alkoxide is more preferred from the viewpoints of purity, dispersibility, coatability, transparency, and visible light photocatalysis.

[0072] Preferred examples of titanium alkoxides include titanium tetraisopropoxide, titanium tetra n-butoxide, titanium tetra n-propoxide, and titanium tetraethoxide. From the viewpoints of cost, water solubility of by-products, coatability, and visible light catalytic properties, titanium tetraisopropoxide is more preferred.

[0073] Depending on the combination of titanium alkoxide and organic acid, the resulting titania may act as a catalyst to liberate ester compounds that are poorly soluble in water, but the titania itself is not a problem. For example, when titanium tetra-n-butoxide and acetic acid are combined, butyl acetate tends to be produced and liberated when mixed and heated.

[0074] From the viewpoint of obtaining a uniform dispersion, it is preferable to employ a combination of an organic acid and a titanium alkoxide that can provide an organic acid alkoxide with excellent water solubility.

[0075] Regarding titanium halides (titanium tetrachloride, titanium trichloride, etc.), from the viewpoints of impurities (halogens), corrosion of a reactor during mass production, crystallinity control, coatability, transparency, and visible light catalysis, the titanium halide is preferably neutralized with a base and the precipitate is washed before use. In this case, from the viewpoint of dispersibility of the obtained titania, the washed titanium halide is preferably used without drying.

[0076] When a solid such as titanium oxide or metallic titanium is used as the titanium-containing substance, the average particle size is preferably 10 nm or less, more preferably 6 nm or less. There is no particular lower limit for the average particle size of the titanium-containing substance, but it is usually about 1 nm. The average particle size of solids such as titanium oxide or metallic titanium is measured by observation with a transmission electron microscope (TEM). When the particle size of the titanium-containing substance is large, it can be ground using a planetary ball mill, paint shaker, or the like, in a dry or wet manner before use.

[0077] The concentration of the titanium-containing substance in the dispersion produced in step (A) is preferably 0.01 mol / L to 5 mol / L, more preferably 0.05 mol / L to 3 mol / L, from the viewpoints of productivity, viscosity of the reaction liquid, coatability, transparency, and visible light catalytic properties.

[0078] The acid used in the reaction is an organic acid, preferably a volatile acid, and more preferably acetic acid. The acid used in the reaction may be, for example, acetic acid in combination with formic acid, lactic acid, butyric acid, hydroxybutyric acid, or the like.

[0079] From the viewpoints of dispersibility, coatability, transparency, visible light catalytic activity, and cost, the amount of organic acid used is adjusted so that the number of moles of acetoxy groups per mole of titanium in the titanium-containing substance is preferably 1 mole or more, more preferably 1.5 moles or more. The more organic acid used, the easier it is to improve stability over time, coatability, transparency, etc. The upper limit of the amount of organic acid used is not particularly limited. The upper limit of the amount of organic acid used is adjusted so that the number of moles of acetoxy groups per mole of titanium in the titanium-containing substance is preferably 10 moles or less.

[0080] The concentration of the organic acid (such as acetic acid) in the dispersion obtained in step (A) is preferably 0.02 mol / L to 10 mol / L, and more preferably 0.1 mol / L to 7 mol / L, from the viewpoints of dispersibility, coatability, transparency, visible light catalytic properties, and cost.

[0081] In the present invention, the aqueous dispersion in step (A) preferably contains water in an amount of 50% by mass or more. The reaction solvent preferably contains an aqueous solvent such as water as the main component. Specifically, the reaction solvent may contain an aqueous solvent such as water in an amount of, for example, 50% by mass or more. The reaction solvent may contain an alcohol or an ester during the reaction.

[0082] For example, when titanium tetraisopropoxide is used as a raw material, it reacts with organic acids to produce isopropyl alcohol, and heating can also produce isopropyl esters of organic acids.

[0083] An alcohol or ester may be added to the dispersion obtained in step (A), or may be generated in the reaction system. The alcohol or ester may be removed by heating in an open system at 100°C or below, or by reducing the pressure, or may remain in the reaction solution.

[0084] When alcohol is contained in the dispersion, the average particle size of the obtained titania nanoparticles and the silver-supported titania nanoparticles of the present invention tends to be small, and therefore alcohol may be intentionally added to control the average particle size.

[0085] In the present invention, it is preferable not to use inorganic acids (particularly strong inorganic acids) such as nitric acid, hydrochloric acid, and sulfuric acid, which are generally used in hydrothermal synthesis reactions of titania nanoparticles, not only because the crystal forms of the obtained titania nanoparticles are a mixture of anatase and brookite types, but also from the viewpoints of storage stability of the obtained dispersion, corrosion of the equipment, impurities, wastewater, etc.

[0086] In the present invention, when the dispersibility, transparency, uniformity, etc. of the raw material are improved to facilitate handling, an inorganic acid can be used supplementarily, for example, in a range of 0.01 mol / L or less, as long as the effect is not impaired. In this case, the concentrations of N, Cl, and S elements in the dispersion obtained in step (A) are all 0.01 mol / L or less.

[0087] The pH of the aqueous dispersion obtained in step (A) is preferably 2 or more and less than 6, from the viewpoints of corrosion of the equipment, handling safety, dispersibility, etc. The pH of the aqueous dispersion is more preferably 2 or more and 5 or less, and even more preferably 2.1 or more and 5 or less.

[0088] In step (A), the method for preparing the aqueous dispersion is not particularly limited. In the method for preparing the aqueous dispersion in step (A), the titanium-containing substance, the organic acid, and water (solvent) may be mixed simultaneously or sequentially. In the method for preparing the aqueous dispersion in step (A), for example, on a mass production scale, from the viewpoints of preventing aggregation and forming large lumps and facilitating continuous stirring, the method for preparing the aqueous dispersion in step (A) preferably involves mixing the organic acid and water (solvent) and then adding the titanium-containing substance while stirring. In the method for preparing the aqueous dispersion in step (A) on a laboratory scale, for example, preferably involves mixing the titanium-containing substance and the organic acid and then adding water while stirring.

[0089] (2-2) Process (B) In step (B), the aqueous dispersion obtained in step (A) is heated at a temperature higher than 80° C., preferably for 1 hour or longer.

[0090] Step (B) may be carried out under normal pressure or under pressure in a sealed container. From the viewpoint of reducing the average particle size of the titania nanoparticles and the metal nanoparticle-supported titania nanoparticles of the present invention, step (B) is preferably carried out under normal pressure, specifically, under conditions of 0.09 MPa to 0.11 MPa. When step (B) is carried out under pressure, from the viewpoint of easily forming a film having high visible light catalytic activity and high transparency, the reaction is carried out for a short time (for example, about 5 to 30 minutes) at preferably 0.2 MPa or less, more preferably 0.11 MPa to 0.2 MPa.

[0091] The heating in step (B) is preferably performed with stirring in order to sufficiently react the titanium-containing substance with the organic acid (acetic acid, etc.) and water. The stirring method is not particularly limited and can be performed according to a conventional method.

[0092] The stirring time (reaction time) is preferably 1 hour or more, more preferably 1.5 hours or more, from the viewpoint of sufficiently reacting the titanium-containing substance with the organic acid (acetic acid, etc.) and water. The upper limit of the stirring time is not particularly limited, but is usually 240 hours.

[0093] The heating in step (B) is carried out at a temperature higher than 80°C, preferably at a temperature of 82°C or higher. By setting the heating temperature higher than 80°C, the crystallization of the resulting metal-supported titania nanoparticles and the surface functional group reaction are completed, and the reaction solution has excellent stability over time. On the other hand, if the heating temperature is below 80°C, cracks are likely to occur, the coating properties are poor, and the coating falls off easily, making it difficult to form a coating film. There is no particular upper limit to the heating temperature, and when the reaction is carried out at normal pressure, it is usually 120°C.

[0094] The pH of the aqueous dispersion obtained in step (B) is preferably 2 or more and less than 6, from the viewpoints of preventing corrosion of the apparatus, safety in handling the apparatus, dispersibility of the aqueous dispersion, etc. The pH of the aqueous dispersion is more preferably 2 or more and 5 or less, and even more preferably 2.1 or more and 5 or less.

[0095] (2-3) Process (C) In step (C), the aqueous dispersion obtained in step (B) is mixed with silver (metallic silver, silver particles) in the presence of ultraviolet light or visible light.

[0096] In step (C), the silver is preferably silver particles having a particle size of 1 μm or more and 1 mm or less. When silver particles are used, the particle size is preferably 1 μm to 1 mm from the viewpoint of cost.

[0097] The pH of the aqueous dispersion obtained in step (C) is preferably 1 or more and 4 or less from the viewpoint of preventing corrosion of the equipment.

[0098] As the reaction in step (C) progresses, the reaction solution turns yellow, which indicates the presence of silver nanoparticles with small particle sizes.

[0099] After step (C), titania nanoparticles can be obtained in which silver is supported on the titania nanoparticles, acetoxy groups are bonded to at least some of the titanium atoms present on the surface of the titania nanoparticles, and when heated to 600°C using a thermogravimetric and differential thermal analyzer, the mass loss at 200°C or higher is 5% by mass or more.

[0100] In the metal-supported titania nanoparticles (titania nanoparticles supported with silver) of the present invention, the particle size of the silver (metallic silver, silver particles) supported on the titania nanoparticles is preferably 20 nm or less. When the particle size of the silver supported on the titania nanoparticles falls within this range, the metal-supported titania nanoparticles have transparency and high stability over time. Furthermore, because the particle size of the silver supported on the titania nanoparticles is extremely small, they exhibit excellent antibacterial properties.

[0101] 2. Silver nanoparticle-loaded titania nanoparticle dispersion The metal-supported titania nanoparticle dispersion (particularly, photocatalyst dispersion, and further, visible light-responsive photocatalyst dispersion) of the present invention can be made even more uniform by using the reaction liquid that has undergone the above steps (A), (B), and (C), and adding a dispersion step such as ultrasonic dispersion as necessary.

[0102] In the present invention, the metal-supported titania nanoparticle dispersion is sufficiently dispersed before step (C), and strong dispersion or the addition of a dispersant is not necessarily required, and a transparent metal-supported titania nanoparticle dispersion can be obtained.

[0103] The metal-supported titania nanoparticle dispersion of the present invention has good dispersibility, resulting in excellent crack resistance of the coating.The metal-supported titania nanoparticle dispersion of the present invention does not require the addition of a dispersant, making it possible to form a dense titania coating, and has excellent coatability and transparency, as well as excellent visible light catalytic activity.

[0104] After step (C), an organic solvent may be added to the dispersion of metal-supported titania nanoparticles to increase the wettability and facilitate coating, and to increase the stability of silver.

[0105] The organic solvent used in the dispersion liquid is preferably alcohol, ether, ketone, etc. From the viewpoint of affinity with titania, the organic solvent is more preferably an alcohol having 4 or less carbon atoms.

[0106] Preferred examples of the alcohol include monohydric alcohols such as methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, sec-butyl alcohol, and tert-butyl alcohol; and polyhydric alcohols such as ethylene glycol, propylene glycol, and glycerin.

[0107] Preferred examples of the ether include ethylene glycol monomethyl ether, propylene glycol monomethyl ether, ethylene glycol dimethyl ether, propylene glycol dimethyl ether, 3-methoxy-1,2-propanediol, 1,3-dimethoxy-2-propanol, and trimethoxymethane.

[0108] The ketone preferably includes, for example, acetylacetone.

[0109] These organic solvents can be used alone or in combination of two or more.

[0110] Among the organic solvents used in the dispersion, methanol, ethanol, 1-propanol, 2-propanol, 2-butanol, tert-butyl alcohol, and the like are more preferred.

[0111] From the viewpoints of safety when applying the coating liquid of the present invention and affinity with titania, the organic solvent used in the dispersion preferably contains at least ethanol, 2-propanol, 1-propanol, etc. In the present invention, the sum of ethanol, 2-propanol, and 1-propanol is preferably 50% by mass to 100% by mass, and more preferably 60% by mass to 100% by mass, where the total amount of the organic solvent is 100% by mass.

[0112] The viscosity of the silver-supported titania nanoparticle dispersion of the present invention can be adjusted depending on the application, and the dispersion can be used as a coating material. When the silver-supported titania nanoparticle dispersion is applied by spin coating, dip coating, spraying, or the like, the silver-supported titania nanoparticle dispersion preferably has a low viscosity. When the silver-supported titania nanoparticle dispersion is applied by brush coating, squeegeeing, or the like, the silver-supported titania nanoparticle dispersion is preferably adjusted to have a higher viscosity. When the silver-supported titania nanoparticle dispersion is applied by screen printing, the silver-supported titania nanoparticle dispersion is preferably adjusted to have an even higher viscosity to suppress fluidity. The coating film of the present invention obtained in this manner is a dense coating.

[0113] There are no particular limitations on the coated products provided with the coating film of the present invention thus obtained, and examples of the coated products of the present invention include building materials, building exteriors, building interiors, window frames, window glass, various lenses, structural members, building equipment such as housing, cooking utensils, textile products, furniture, displays, display protective films, plumbing members, vehicle lamp covers and window glass, exteriors of mechanical devices or articles, dustproof covers and coatings, display devices, their covers, traffic signs, various display devices, signs such as billboards, sound insulation walls for roads and railways, exteriors and coatings of bridges and guardrails, interiors and coatings of tunnels, insulators, solar cell covers, solar hot water heater heat collector covers, and other exterior parts of electronic and electrical devices used outdoors, particularly transparent members, exteriors of vinyl greenhouses, greenhouses, etc. [Example]

[0114] The present invention will be specifically described based on examples.

[0115] The present invention is not limited to these.

[0116] [Example 1] 120 g (2 mol) of acetic acid was added to 142.1 g (0.5 mol) of titanium tetraisopropoxide, and the mixture was stirred for 60 minutes, after which 538 g of water was added. The dispersion had a titanium tetraisopropoxide concentration of 0.625 mol / L, an acetic acid concentration of 2.5 mol / L, and a pH of 2.2.

[0117] In this dispersion, a large amount of translucent precipitate was generated, but when the dispersion was stirred for 60 minutes and then heated, all of the precipitate dissolved at 70° C. In this dispersion, the concentrations of the inorganic acid and the elements N, Cl, and S were all 0 mol / L.

[0118] After that, the mixture was stirred at normal pressure (0.10 MPa) and 99°C for 3 hours, and a translucent, uniform titania dispersion was obtained without using any organic dispersant.

[0119] When this dispersion was subjected to ultrasonic dispersion, the viscosity was reduced and the transparency increased. The pH of this dispersion was 2.2.

[0120] This dispersion was dried to obtain titania nanoparticles. The BET specific surface area of ​​these titania nanoparticles was measured and found to be 256 m 2 / g. TEM observation revealed that the average particle size was approximately 3 nm. Crystallinity analysis of the obtained titania nanoparticles by X-ray diffraction revealed that they were 100% anatase, with no other crystal forms present.

[0121] This dispersion was held at 200°C using a moisture meter and dried until no mass loss was observed. TG-DTA of the titania nanoparticles was measured by heating them in an air atmosphere at a rate of 3°C / min up to 600°C. The mass loss above 200°C was 13% by mass. This mass loss above 200°C is due to the desorption of acetic acid, an organic acid. Since the released acetic acid almost completely volatilizes below 200°C, the 13% mass loss above 200°C suggests that a large number of acetyl groups, which are acyloxy groups, are bonded to titanium atoms in the form of -OCOCH3 on the surface of the titania nanoparticles.

[0122] In an air atmosphere, an equal amount of water was added to 50 g of this dispersion (titania 5.0 mass %) to prepare 100 g of a 2.5 mass % dispersion.

[0123] To this dispersion, 0.125 g of silver particles (50 μm) was added and stirred indoors. The reaction to support the silver particles on the titania nanoparticles was carried out using only indoor light (approximately 1000 lx) without irradiation with ultraviolet light. After 3 hours, the dispersion turned yellowish, indicating that the silver nanoparticles had been supported on the titania nanoparticles.

[0124] The titania nanoparticles carrying silver nanoparticles were dried under reduced pressure at 80°C, and the resulting powder was analyzed by XRD (X-ray diffraction). Peaks were observed at 2θ = 44-45° and 64-65°, indicating the formation of metallic Ag. Furthermore, semi-quantitative analysis revealed that approximately 0.2% by mass of Ag was supported on TiO2.

[0125] Furthermore, ESCA (X-ray photoelectron spectroscopy) analysis revealed that the binding energy was 368.1 eV, suggesting that metallic Ag was formed (Figure 1).

[0126] After removing the excess Ag, the dispersion was found to be homogeneous, and maintained its homogeneity and transparency even after 3 months (Fig. 2).

[0127] TEM observation of the synthesized material revealed that the primary particles of Ag were 3 nm to 7 nm in size, and even the aggregated secondary particles were at most 10 nm to 20 nm in size, which was consistent with the color of the liquid (silver nanoparticles are generally yellow when they are 30 nm or less, and as the particle size increases, they become more reddish and turn orange) (Figures 3 and 4).

[0128] [Comparative Example 1] The reaction was carried out in the same manner as in Example 1, without irradiation with ultraviolet light, but only under room light (approximately 1000 lx), except that 0.193 g of silver acetate was used instead of 0.125 g of silver particles.

[0129] In Comparative Example 1, a dispersion liquid carrying metallic Ag with a pale bluish-purple color was obtained after 8 hours. TEM analysis of Comparative Example 1 showed that the Ag was in the form of aggregates of Ag nanoparticles with primary particles of 40 nm to 50 nm (FIG. 5). In Comparative Example 1, the dispersion liquid was uniform after the reaction, but became turbid after one week, and a slight supernatant was observed after three months.

[0130] Comparative Example 2 The test was carried out in the same manner as in Example 1, except that a mixture of 2.5 g of commercially available titania (P25: manufactured by Nippon Aerosil) and 47.5 g of water was used instead of 50 g of the dispersion (5.0 mass % titania).

[0131] In Comparative Example 2, there was no change in color after 3 hours, and no change occurred even when stirring was extended to 60 hours. In Comparative Example 2, when the dispersion was left to stand for 4 hours, a supernatant and a precipitate were observed.

[0132] Comparative Example 3 The test was carried out in the same manner as in Example 1, except that 50 g of the dispersion (5.0 mass % titania) was replaced with a mixture of 2.5 g of commercially available titania (P25: manufactured by Nippon Aerosil), 7.5 g of acetic acid, and 40 g of water.

[0133] In Comparative Example 3, there was no change in color after 3 hours, and no change occurred even when stirring was extended to 60 hours. In Comparative Example 3, when the dispersion was left to stand for 4 hours, a supernatant and a precipitate were observed (Figure 6). [Industrial Applicability]

[0134] The method for producing titania nanoparticles of the present invention makes it possible to easily obtain a uniform, highly transparent, and storage-stable dispersion of silver-supported titanium oxide nanoparticles without using silver salts, which are unsafe and easily altered.

[0135] The silver-supported titanium oxide nanoparticle dispersion obtained by the method for producing titania nanoparticles of the present invention has high substrate adhesion and crack resistance, and can be used to obtain a highly transparent photocatalytic coating film.

Claims

1. A method for producing titania nanoparticles, comprising: a step of adding silver particles having a particle size of 1 μm or more and 1 mm or less to an aqueous dispersion of titania nanoparticles and stirring the mixture to support silver on the titania nanoparticles; The titania nanoparticles have acetoxy groups bonded to at least some of the titanium atoms present on the surface, and when heated to 600°C using a thermogravimetric and differential thermal analyzer, the mass loss at 200°C or higher is 5% by mass or more. Manufacturing method.

2. A method for producing titania nanoparticles, comprising: (A) mixing a titanium-containing substance, an organic acid, and water to obtain an aqueous dispersion; (B) heating the aqueous dispersion obtained in the step (A) at a temperature higher than 80°C; and (C) After the step (B), a step of mixing silver particles having a particle size of 1 μm or more and 1 mm or less into the aqueous dispersion and irradiating the silver-containing aqueous dispersion with visible light or ultraviolet light to support silver on titanium. A manufacturing method comprising:

3. The method according to claim 2 , wherein the aqueous dispersion in step (A) contains 50% by mass or more of water.

4. The method according to claim 2 or 3, wherein the pH of the aqueous dispersion in steps (A) and (B) is 2 or more and 5 or less.

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