Method for producing platinum nano-particle solution, antibacterial agent, and antibacterial product

Abstract

Provided is a method for producing a platinum nano-particle solution, the method comprising: adding a reducing agent to a solution containing platinum ions derived from platinic chloride or a platinic chloride salt to reduce the platinum ions, thereby preparing platinum nano-particles; and adding an inorganic acid to the platinum nano-particles. Also provided are: an antibacterial agent in which a platinum nano-particle solution comprising platinum nano-particles, an inorganic acid and water is used; and an antibacterial product to which the antibacterial agent is applied.

Description

Method for producing platinum nanoparticle solution, antibacterial agent, and antibacterial product

[0001] One embodiment of the present invention relates to a method for producing a platinum nanoparticle solution. Another embodiment of the present invention relates to an antibacterial agent and an antibacterial product using platinum nanoparticles.

[0002] Metal nanoparticles are metal particles typically having an average particle size of 1 to 100 nm. Because they have properties different from bulk metals, they have recently attracted attention for a variety of applications, including electronic materials, electrode materials, and catalyst materials. In particular, noble metal nanoparticles have excellent adsorption capabilities for fine substances and are known to have properties such as antibacterial, deodorizing, and antiviral properties. Therefore, in recent years, various studies have been conducted on the use of noble metal nanoparticles for a wide range of applications related to food, clothing, and shelter.

[0003] For example, liquid preparations containing nanoparticles of precious metals such as gold, silver, or copper, or antibacterial products to which precious metal nanoparticles are attached, have been known. Meanwhile, platinum nanoparticles have recently attracted attention because they can maintain their antibacterial and other action properties for a long period of time and are highly safe for the human body, and the development of liquid preparations of antibacterial agents, humidifiers, air purifiers, antibacterial products, and the like that utilize platinum nanoparticles is progressing.

[0004] A liquid agent containing platinum nanoparticles is prepared as a colloidal solution (hereinafter referred to as "platinum nanoparticle solution") in which platinum nanoparticles are uniformly dispersed in a solvent such as water. The method for producing platinum nanoparticles is not particularly limited, and any known method for producing metal nanoparticles can be applied. Specifically, platinum nanoparticles may be produced by either a breakdown method such as dry pulverization or wet pulverization, or a build-up method such as a liquid phase method or a gas phase method. Among these, the liquid phase method is preferably applied from the viewpoint of easily obtaining a platinum nanoparticle solution.

[0005] In the liquid-phase production of platinum nanoparticles, a reducing agent is added to a solution containing platinum ions derived from platinate salts or the like, and the platinum ions are reduced to form platinum nanoparticles. Therefore, the reaction solution used in the production of platinum nanoparticles can be used as is as a platinum nanoparticle solution. However, platinum nanoparticle solutions often contain protective agents such as surfactants or polymer compounds, which adhere to the surface of the platinum nanoparticles to suppress aggregation and maintain dispersibility (see, for example, Patent Document 1).

[0006] Japanese Patent Application Laid-Open No. 2002-001095

[0007] However, when the platinum nanoparticle solution is used for applications such as antibacterial agents, the surfactant or protective agent may reduce the adsorption ability of the platinum nanoparticles, potentially reducing their antibacterial and other properties. Furthermore, depending on the type of surfactant or protective agent, there are concerns about their effects on the human body. Therefore, there is a demand for a platinum nanoparticle solution that has better properties and is safe for the human body, for a wide range of applications related to food, clothing, and shelter.

[0008] On the other hand, in order to easily obtain the antibacterial and other effects of platinum nanoparticles, it is preferable to increase the content of platinum nanoparticles in the platinum nanoparticle solution. However, if a surfactant or protective agent is not used during the preparation of the platinum nanoparticle solution, aggregation and precipitation tend to occur as the content of platinum nanoparticles increases over time. As a result, the platinum nanoparticle solution tends to change color (discoloration over time) from a nearly transparent state to light gray and then dark black.

[0009] When preparing an antibacterial agent using a platinum nanoparticle solution, the platinum nanoparticle solution is typically used as is, or diluted with a solvent such as water as needed. However, as described above, if the platinum nanoparticle solution discolors over time, problems are likely to occur when it is applied to white materials. For example, if a discolored platinum nanoparticle solution is applied to white materials such as paper, cloth, or fiber, problems such as stains (darkening) at the contact area of ​​the solution are likely to occur. Therefore, in order to expand the range of use of antibacterial agents, it is necessary to improve the discoloration of the platinum nanoparticle solution over time.

[0010] Therefore, in view of the above circumstances, one embodiment of the present invention provides a method for producing a platinum nanoparticle solution that can suppress discoloration over time. Another embodiment of the present invention provides an antibacterial agent and an antibacterial product that use the platinum nanoparticle solution and have excellent effects and can suppress discoloration over time.

[0011] The present inventors have conducted extensive research to solve the above problems and have completed the present invention. That is, embodiments of the present invention relate to the following. However, the present invention is not limited to the embodiments described below and includes various embodiments.

[0012] One embodiment of the present invention relates to a method for producing a platinum nanoparticle solution, which includes adding a reducing agent to a solution containing platinum ions derived from chloroplatinic acid or a chloroplatinate to reduce the platinum ions, and adding an inorganic acid.

[0013] [1] A method for producing a platinum nanoparticle solution, comprising adding a reducing agent to a solution containing platinum ions derived from chloroplatinic acid or a chloroplatinate to reduce the platinum ions, and adding an inorganic acid.

[0014] [2] The method for producing a platinum nanoparticle solution according to [1] above, wherein the chloroplatinate salt comprises at least one selected from the group consisting of sodium chloroplatinate, potassium chloroplatinate, sodium chloroplatinate (II), potassium chloroplatinate (II), and ammonium chloroplatinate.

[0015] [3] The method for producing a platinum nanoparticle solution according to [1] above, wherein the pH of the platinum nanoparticle solution is adjusted to within a range of 4 to 6 by adding the inorganic acid.

[0016] [4] The method for producing a platinum nanoparticle solution according to any one of [1] to [3] above, wherein the inorganic acid is dilute hydrochloric acid.

[0017] [5] The reducing agent comprises at least one selected from the group consisting of ascorbic acid or ascorbic acid salts, alginic acid or alginic acid salts, dicarboxylic acids, alcohols, and polysaccharides. [1] - [4] The method for producing a platinum nanoparticle solution according to any one of the above.

[0018] [6] The method for producing a platinum nanoparticle solution according to any one of [1] to [5] above, wherein citric acid or a citrate salt is further added in the reduction treatment.

[0019] [7] An antibacterial agent comprising platinum nanoparticles, an inorganic acid, and water.

[0020] [8] The antibacterial agent according to [7] above, wherein the inorganic acid is dilute hydrochloric acid.

[0021] [9] The antibacterial agent according to [7] or [8] above, further comprising chloroplatinic acid or a chloroplatinate.

[0022]

[10] The antibacterial agent according to any one of [7] to [9] above, further comprising potassium iodide.

[0023]

[11] A paint containing the antibacterial agent according to any one of [7] to

[10] above.

[0024]

[12] An antibacterial product in which the antibacterial agent according to any one of [7] to

[10] above or the paint according to

[11] above is applied to an everyday item made of a material selected from the group consisting of synthetic or natural fibers, plastics, ceramics, and wood.

[0025]

[13] The antibacterial product according to

[12] above, which is a mask, gauze, toothbrush, cup, or disinfecting sheet.

[0026] According to an embodiment of the present invention, a method for producing a platinum nanoparticle solution capable of suppressing discoloration over time can be provided. In addition, an antibacterial agent and an antibacterial product capable of suppressing discoloration over time can be provided by using the platinum nanoparticle solution.

[0027] Fig. 1 is a photograph showing the state of discoloration over time of an antibacterial agent containing platinum nanoparticles (after 4 months of storage), (a) is the antibacterial agent of Example 1 (with dilute hydrochloric acid added), and (b) is the antibacterial agent of Comparative Example 1 (without dilute hydrochloric acid added). Fig. 2 is a photograph showing the state of discoloration over time of an antibacterial agent containing platinum nanoparticles (after 6 months of storage), (a) is the antibacterial agent of Example 1 (with dilute hydrochloric acid added), and (b) is the antibacterial agent of Comparative Example 1 (without dilute hydrochloric acid added).

[0028] Embodiments of the present invention are described below. However, the present invention is not limited to the following embodiments. (Method for Producing a Platinum Nanoparticle Solution) One embodiment relates to a method for producing a platinum nanoparticle solution, which includes adding a reducing agent to a solution containing platinum ions derived from chloroplatinic acid or chloroplatinic acid salts to reduce the platinum ions, and adding an inorganic acid. According to the above embodiment, adding an inorganic acid to a solution containing platinum nanoparticles obtained by reduction treatment makes it possible to improve undesirable changes over time, such as discoloration, that occur during storage of the platinum nanoparticle solution. Therefore, the stock solution of the platinum nanoparticle solution after storage can be used directly, or diluted with a solvent such as water as needed, and suitably used as a liquid agent such as an antibacterial agent. The water used for dilution is preferably deionized water.

[0029] The amount of inorganic acid added to the solution containing platinum nanoparticles is not particularly limited, but is preferably adjusted so that the pH of the solution after reduction treatment is weakly acidic. In one embodiment, the pH of the solution after reduction treatment may be 4 or higher and 6 or lower. When the pH of the solution containing platinum nanoparticles after reduction treatment is adjusted to a range of 4 to 6, aggregation of nanoplatinum particles (particle enlargement) is easily suppressed. Furthermore, when an antibacterial agent is prepared using the above solution, an excellent disinfecting effect can be easily obtained. Furthermore, when the above solution is sprayed or applied, undesirable effects on the target object can be easily suppressed.

[0030] In the manufacturing method of the above embodiment, the pH of the solution after the reduction treatment may be preferably in the range of 4.2 to 5.8, more preferably in the range of 4.3 to 5.6, and even more preferably in the range of 4.4 to 5.4. In one embodiment, the pH of the solution may more preferably be in the range of 4.4 to 5.0.

[0031] The inorganic acid is not particularly limited as long as it can adjust the pH of the solution. For example, hydrochloric acid can be used as the inorganic acid, and dilute hydrochloric acid is particularly suitable. The dilute hydrochloric acid may be commercially available. Commercially available dilute hydrochloric acid has a hydrogen chloride concentration of approximately 10% by mass. Therefore, an aqueous solution in which the hydrogen chloride concentration is adjusted to 9.5 to 10.5% by mass may be used.

[0032] As described below, the source of platinum ions may preferably be chloroplatinic acid or a chloroplatinate salt, and for example, a solution of potassium chloroplatinate(II) can be suitably used. In a solution of potassium chloroplatinate(II), ionization of nanoplatinum reduces nanoPt(II) to nanoPt(0) over time, making it more susceptible to aggregation. In the manufacturing method of this embodiment, discoloration of the solution over time can be suppressed by adding an inorganic acid such as dilute hydrochloric acid to the solution in this state. Without being bound by theory, it is presumed that the addition of an inorganic acid suppresses the heterogenization reaction represented by the following formula (1), maintaining ionic bonding in the nanoPt(II) state. Formula (1) 2K ２ [Pt(II)Cl ４ ] → K ２ [Pt(IV)Cl ６ ]+Pt(0)+2KCl

[0033] The average particle size of the platinum nanoparticles may be 100 nm or less. In one embodiment, the average particle size of the platinum nanoparticles may be preferably 1 to 50 nm, more preferably 2 to 20 nm, and even more preferably 5 to 10 nm. The average particle size of the platinum nanoparticles is preferably as small as possible, from the viewpoint of improving the catalytic effect by increasing the contact area. When the average particle size of the platinum nanoparticles is adjusted within the above range, aggregation and precipitation of the platinum nanoparticles in water can be easily suppressed, and good dispersibility can be easily maintained. By adjusting the conditions during platinum nanoparticle production, platinum nanoparticles having the desired average particle size can be easily obtained. From the viewpoints of the form of use (e.g., spraying) and raw materials, as described above, it is preferable that the platinum nanoparticles be as small a powder as possible and have an average particle size. However, from the viewpoints of cost and availability, it is not necessary to make the particle size uniform in reality, and the particle size may be non-uniform.

[0034] In the above embodiment, the solution containing platinum ions can be prepared by dissolving a water-soluble platinum complex in a solvent containing at least water. In one embodiment, the water is preferably deionized water. The source of platinum ions may preferably be chloroplatinic acid or a chloroplatinate, which dissolves in water to produce platinum ions. Chloroplatinic acid or a chloroplatinate well known in the art can be used. Among them, chloroplatinate is more preferred. As a specific example, chloroplatinic acid (H ２ PtCl ６ ), chloroplatinic acid hexahydrate (H ２ PtCl ６ (H ２ O) ６ ), sodium chloroplatinate (potassium hexachloroplatinate, Na ２ PtCl ６ ), potassium chloroplatinate (potassium hexachloroplatinate, Na ２ PtCl ６ ), sodium chloroplatinate(II) (sodium tetrachloroplatinate, Na ２ PtCl ４ ), potassium chloroplatinate(II) (potassium tetrachloroplatinate, K ２ PtCl４ ), and ammonium chloroplatinate ((NH ４ ) ２ PtCl ６ In one embodiment, the chloroplatinate may be at least one selected from the group consisting of sodium chloroplatinate, potassium chloroplatinate, sodium chloroplatinate(II), potassium chloroplatinate(II), and ammonium chloroplatinate. Chloroplatinic acid or chloroplatinate may be commercially available or may be prepared according to methods well known in the art.

[0035] The reduction treatment of platinum ions can be carried out according to methods well known in the art. For example, first, a solution containing platinum ions is prepared by dissolving chloroplatinic acid or a chloroplatinate in a solvent containing at least water. In one embodiment, the concentration of platinum ions in the solution may be, for example, 0.001 to 0.1 mol / L, calculated from the amount of chloroplatinic acid or chloroplatinate used. The concentration of platinum ions may preferably be 0.005 to 0.1 mol / L, more preferably 0.01 to 0.1 mol / L. Next, a reducing agent or a solution containing a reducing agent is added to the solution containing platinum ions, and the two are mixed to perform a reduction treatment of the platinum ions, thereby obtaining a platinum nanoparticle solution. The reduction treatment can be carried out at room temperature or under heat.

[0036] The reducing agent that can be used in the reduction treatment of the above embodiment is not particularly limited as long as it can reduce platinum ions, but organic compounds with reducing properties can be preferably used. In one embodiment, the reducing agent can be one selected from the group consisting of ascorbic acid or ascorbic acid salts, alginic acid or alginate salts, dicarboxylic acids, alcohols, and polysaccharides. More specifically, the ascorbic acid can be L-ascorbic acid. The ascorbic acid salt can be, for example, sodium ascorbate, calcium ascorbate, potassium ascorbate, etc. The alginate salt can be, for example, sodium alginate. The dicarboxylic acid can be, for example, formic acid, oxalic acid, etc. The alcohol can be, for example, glucose, tetraethylene glycol, ethanol, etc. The polysaccharide can be, for example, xylitol, glycerol, chitosan, etc. Among these, ascorbic acid can be preferably used. The amount of the reducing agent added may be preferably 2 to 10 times the concentration of platinum ions derived from chloroplatinic acid or chloroplatinate in the solution.

[0037] In one embodiment, it is preferable to further add a hydroxycarboxylic acid or a salt thereof, such as citric acid or a citrate, during the reduction treatment. Adding a hydroxycarboxylic acid or a salt thereof during the reduction treatment facilitates stabilizing the dispersibility of the platinum nanoparticles produced by the reduction. Although not particularly limited, citric acid or a citrate can be preferably used. Examples of citrates include sodium citrate and potassium citrate. Citric acid can function as both a stabilizer and a binder. Here, the binder improves the adhesion between the solution and the object to be sprayed or applied when the solution is used by spraying or applying it, thereby promoting the effect of the solution remaining on the object for a longer period of time.

[0038] The amount of hydroxycarboxylic acid or its salt added to the solution is not particularly limited. In one embodiment, the amount may be preferably 2 to 3 times the concentration of platinum ions derived from chloroplatinic acid or chloroplatinate in the solution. In another embodiment, the amount may be 0.4 to 0.6 g per 1 L of solution.

[0039] The inorganic acid may be added either during or after the reduction treatment. In one embodiment, from the viewpoint of efficiently obtaining platinum nanoparticles, it is preferable to add the inorganic acid during the reduction treatment. The pH of the solution during the reduction treatment is not particularly limited, and may be adjusted to a weak acidity. For example, the pH of the solution may preferably be 4 to 6.

[0040] As described above, in one embodiment, ascorbic acid can be suitably used as a reducing agent. However, undiluted ascorbic acid is brown or black. Therefore, in order to avoid discoloration of the produced platinum nanoparticle solution, it is preferable to use as little as possible of ascorbic acid. In investigating a method for suppressing discoloration of a platinum nanoparticle solution over time, the present inventors have found that adding an inorganic acid to the solution can suppress discoloration over time. Furthermore, they have also found that the amount of ascorbic acid used can be reduced by adding an inorganic acid.

[0041] From this perspective, in the manufacturing method of this embodiment, it is preferable that the inorganic acid is added together with the reducing agent during the reduction treatment. According to such an embodiment, since the inorganic acid can also function as a reducing agent, it is thought that the reduction treatment can be carried out well even if the amount of ascorbic acid used is reduced. In another embodiment, from the viewpoint of improving the dispersion stability of the platinum nanoparticles in the solution, the inorganic acid may be added to the solution containing the platinum nanoparticles obtained after the reduction treatment.

[0042] In one embodiment, the amount of inorganic acid added may be preferably 4 to 12 times the platinum ion concentration in the solution. In one embodiment, as described above, the platinum nanoparticle solution preferably further contains citric acid from the viewpoint of stabilization. In this case, the amount of inorganic acid added may be about 2 to 6 times the amount of citric acid added. In either case, the amount of inorganic acid added is preferably adjusted so that the pH of the platinum nanoparticle solution is 4 to 6.

[0043] In the platinum nanoparticle solution of the above embodiment, the content of platinum nanoparticles is not particularly limited and can be adjusted by the amount of chloroplatinic acid or chloroplatinic acid salt used during the production of the platinum nanoparticle solution. According to the production method of the above embodiment, a solution containing a high concentration of platinum nanoparticles can be easily prepared. However, sufficient effects can be obtained even with a platinum nanoparticle concentration of approximately 0.001 to 0.1 mol / L in the solution. In one embodiment, the concentration of platinum nanoparticles in the solution may be approximately 0.01 mol / L.

[0044] In one embodiment, the platinum nanoparticle solution obtained after the reduction treatment may contain a portion of the chloroplatinic acid or chloroplatinate used as the raw material in its original (unreduced) state. The coexistence of platinum nanoparticles and chloroplatinic acid or chloroplatinate in the platinum nanoparticle solution makes it easier to increase the stability of the platinum nanoparticles in the platinum nanoparticle solution.

[0045] In one embodiment, the method for producing a platinum nanoparticle solution includes (i) adding a reducing agent to a solution containing platinum ions derived from chloroplatinic acid or chloroplatinic acid salts to reduce the platinum ions, and (ii) adding an inorganic acid to the solution containing platinum nanoparticles obtained by the reduction. Furthermore, if necessary, after step (ii), the solution is preferably filtered and then stirred for at least 5 minutes. Filtering the solution can prevent problems such as aggregation or precipitation due to solid components in the solution, making it easier to improve the storage stability of the platinum nanoparticle solution.

[0046] One embodiment of the present invention relates to a platinum nanoparticle solution comprising an inorganic acid and a solution obtained by reducing a solution containing platinum ions derived from chloroplatinic acid or a chloroplatinate. Another embodiment relates to a platinum nanoparticle solution obtained by mixing a solution containing platinum ions derived from chloroplatinic acid or a chloroplatinate, a reducing agent containing ascorbic acid or an ascorbate, citric acid or a citrate, and an inorganic acid. In this embodiment, the platinum nanoparticle solution may further comprise citric acid or a citrate. Yet another embodiment relates to a platinum nanoparticle solution comprising platinum nanoparticles and an inorganic acid. These platinum nanoparticle solutions can each be obtained by the above-mentioned method for producing a platinum nanoparticle solution. The platinum nanoparticle solution may further comprise chloroplatinic acid or a chloroplatinate.

[0047] The platinum nanoparticle solution exhibits antibacterial, deodorant, and antiviral effects due to the catalytic action of the platinum nanoparticles, and can therefore be used in a variety of applications. For example, in one embodiment, the platinum nanoparticle solution can be suitably used as a liquid agent such as an antibacterial agent. Hereinafter, an embodiment of the antibacterial agent will be described as an example.

[0048] (Antibacterial Agent) The antibacterial agent may be a platinum nanoparticle solution containing platinum nanoparticles, an inorganic acid, and water. In an embodiment of the antibacterial agent, the platinum nanoparticle solution may be used as it is at a high concentration (stock solution) without dilution, or may be diluted to a desired concentration with a solvent such as water as needed. In one embodiment, the concentration of platinum nanoparticles in the platinum nanoparticle solution (stock solution) may be, for example, K ２ PtCl ４ The Pt(0) content in 0.265 g of platinum nanoparticle solution using the above may be approximately 0.05 g / L. This stock solution can be diluted, for example, 100 to 1000 times with water and used as an antibacterial agent. The dilution with water can be adjusted appropriately depending on the application.

[0049] The antibacterial agent of the above embodiment has excellent storage stability even when the concentration of platinum nanoparticles in the platinum nanoparticle solution is high, and can maintain good dispersibility of the platinum nanoparticles. Therefore, according to the above embodiment, an antibacterial agent can be provided in which undesirable changes over time in the platinum nanoparticle solution, such as a decrease in effectiveness and discoloration after storage, are suppressed. Note that, as the amount of platinum nanoparticles (Pt(0)) in the solution increases, a more excellent antibacterial effect can be obtained. On the other hand, from the viewpoint of further enhancing the stability of the platinum nanoparticles in the solution, the antibacterial agent may further contain, for example, chloroplatinic acid or chloroplatinic acid. In one embodiment, the platinum nanoparticle solution used as the antibacterial agent contains, for example, K ２ PtCl ４ may be contained at 0.2 g to 0.4 g / L.

[0050] When an antibacterial agent using a platinum nanoparticle solution is applied or sprayed onto a surface to be treated, the antibacterial agent dries (the solvent evaporates), causing platinum nanoparticles to adhere to the surface of the object. The catalytic action of the platinum nanoparticles adhered to the surface provides the surface with antibacterial properties. In one embodiment, deionized water can be suitably used as a solvent for diluting the platinum nanoparticle solution. The use of an alcohol such as ethanol in combination, if necessary, can facilitate the drying of the antibacterial agent.

[0051] The antibacterial agent may further contain other components in addition to platinum nanoparticles, inorganic acid, and a solvent such as deionized water. In one embodiment, the antibacterial agent preferably further contains potassium iodide. Potassium iodide itself exhibits excellent antibacterial activity in its liquid state. Therefore, when potassium iodide is added to the antibacterial agent, in addition to the antibacterial activity of the platinum nanoparticles that is exhibited after the antibacterial agent is dried, the antibacterial activity can be exhibited even before the antibacterial agent is dried (in its liquid state), thereby further enhancing the antibacterial activity of the antibacterial agent. The amount of potassium iodide added is not particularly limited. In one embodiment, the amount of potassium iodide added may be preferably 0.1 to 10 mass% based on the total mass of the antibacterial agent (platinum nanoparticle solution).

[0052] In one embodiment, the antibacterial agent can be added to a paint to form a paint containing the antibacterial agent. The paint may have a typical composition used in various applications, and the use of the antibacterial agent can impart antibacterial properties to the coating film. The paint can be applied to structures such as buildings, electrical appliances such as office automation equipment, and everyday items, without being particularly limited thereto.

[0053] One embodiment of the present invention relates to an antibacterial product to which the antibacterial agent of the above embodiment is applied. The antibacterial product can be produced by applying an antibacterial agent using a platinum nanoparticle solution to a workpiece and fixing the platinum nanoparticles to the surface of the workpiece. The method of applying the antibacterial agent to the workpiece can be carried out according to a method well known in the art. The application method may be, but is not limited to, painting or spraying. After application of the antibacterial agent, a drying step can be carried out as needed to promote the fixing of the platinum nanoparticles.

[0054] The treated object is not particularly limited and may be an article made of various materials. For example, it may be everyday items made of synthetic or natural fibers, plastics, ceramics, wood, etc. Although not particularly limited, examples of antibacterial products include hygiene products such as masks, gauze, toothbrushes, cups, and disinfecting wipes. These antibacterial products exhibit excellent antibacterial, deodorizing, and antiviral properties due to the catalytic action of platinum nanoparticles attached to their surfaces, and these effects can be maintained for a long period of time.

[0055] Hereinafter, the embodiments of the present invention will be described in more detail with reference to examples. However, the embodiments of the present invention are not limited to the following description and include various embodiments.

[0056] <1> Preparation of platinum nanoparticle solution and antibacterial agent (Example 1) (1) Preparation of platinum nanoparticle solution Potassium chloroplatinate (II) (K ２ PtCl ４) 0.40 g was dissolved in 100 mL of water (pure water) to prepare a solution A containing platinum ions (platinum ion concentration 0.01 mol / L, 0.05 g / L in terms of Pt (0)). Meanwhile, 1.77 g of ascorbic acid was dissolved in 100 mL of water to prepare a solution B with an ascorbic acid concentration of 0.1 mol / L. Furthermore, 0.26 g of citric acid was dissolved in 100 mL of water to prepare a solution C with a citric acid concentration of 0.01 mol / L. Next, 100 mL of the above solution A, 100 mL of solution B, and 100 mL of solution C were added to a reaction vessel and stirred at room temperature (25 ° C) for 5 minutes. Then, dilute hydrochloric acid was added while stirring the reaction solution, and a platinum nanoparticle solution (1) with a pH of 4.7 was obtained. (2) Preparation of antibacterial agent To 100 mL of the platinum nanoparticle solution (1) prepared above, a 1% aqueous solution of potassium iodide was added so that the potassium iodide concentration in the solution was 0.15 g / L, and these were mixed to prepare antibacterial agent (1).

[0057] (Comparative Example 1) (1) Preparation of Platinum Nanoparticle Solution A platinum nanoparticle solution (C1) was obtained in the same manner as in Example 1, except that dilute hydrochloric acid was not added in the preparation of the platinum nanoparticle solution described in Example 1. That is, 100 mL of solution A, 100 mL of solution B, and 100 mL of solution C were added, and the temperature in the reaction vessel was maintained at room temperature (20 ° C.) while stirring for 5 minutes to obtain a platinum nanoparticle solution (C1). (2) Preparation of Antibacterial Agent An antibacterial agent (C1) was prepared by adding water to 100 mL of the platinum nanoparticle solution (C1). The amount of water was adjusted so that the concentration of platinum nanoparticles in the antibacterial agent (C1) was the same as that of the antibacterial agent (1) of Example 1.

[0058] (Comparative Example 2) (1) Preparation of Platinum Nanoparticle Solution A platinum nanoparticle solution (C1) was prepared in the same manner as in Comparative Example 1. (2) Preparation of Antibacterial Agent A 1% aqueous solution of potassium iodide was added to 100 mL of platinum nanoparticle solution (C1) so that the platinum nanoparticle solution had a potassium iodide equivalent of 0.15 g / L, and the mixture was mixed to prepare an antibacterial agent (C2). The amounts of the platinum nanoparticle solution (C1) and the aqueous potassium iodide solution used were adjusted so that the platinum nanoparticle concentration and potassium iodide concentration in the antibacterial agent (C2) were the same as those of the antibacterial agent in Example 1.

[0059] <2> Evaluation of Storage Stability (Discoloration of Solution Over Time) Each antibacterial agent prepared in Example 1 and Comparative Example 1 was placed in a transparent container, sealed, and stored for a long period of time under the same conditions (room temperature), and the changes in the solution were observed. Immediately after the start of storage, all solutions were nearly transparent. However, one week after the start of storage, the antibacterial agent of Comparative Example 1 began to discolor. The antibacterial agent of Comparative Example 1 became light brownish after four months of storage and further darkened brownish after six months. In contrast, the antibacterial agent of Example 1 remained nearly transparent even after four and six months of storage. Figure 1 shows a photograph illustrating the discoloration of the antibacterial agent over time after four months of storage, and Figure 2 shows a photograph illustrating the discoloration of the antibacterial agent over time after six months of storage. In Figures 1 and 2, (a) shows the antibacterial agent (1) of Example 1 (with dilute hydrochloric acid added), and (b) shows the antibacterial agent (C1) of Comparative Example 1 (without dilute hydrochloric acid added). As is clear from the comparison of (a) and (b) shown in Figures 1 and 2, (b) shows discoloration, which deepens over time. On the other hand, (a) shows almost no discoloration even after six months, maintaining a transparent state. This shows that dilute hydrochloric acid contributes to the prevention of discoloration over time.

[0060] <3> Evaluation of Antibacterial Agent Properties The antibacterial agents prepared in Example 1 and Comparative Examples 1 and 2 were evaluated for various properties according to the following methods. (Antibacterial Activity (1)) The antibacterial activity of each of the antibacterial agents prepared in Example 1 and Comparative Examples 1 and 2 was tested according to the method of JIS Z 2801:20105. Specifically, each antibacterial agent was first applied to a polyethylene film and then dried to prepare a test specimen. Next, the test specimen was inoculated with test bacteria and cultured at room temperature (25°C). The test bacteria were Staphylococcus aureus (NBRC 12732) and Escherichia coli O157:H7 (ATCC 43888). The antibacterial activity value was calculated from the viable cell counts immediately after inoculation, 0.5 hours after inoculation, and 24 hours after inoculation. An untreated polyethylene film without any antibacterial agent was used as a control.

[0061] The results are shown in Tables 1 and 2.

[0062]

[0063] As shown in Tables 1 and 2, the antibacterial activity values ​​after 24 hours of incubation for the test pieces coated with the antibacterial agent (1) of Example 1 were approximately equal to or better than those for the test pieces coated with the antibacterial agents (C1) and (C2) of Comparative Examples 1 and 2. This indicates that the catalytic action of the platinum nanoparticles is expressed as the antibacterial agent dries, but the antibacterial activity does not decrease due to the addition of dilute hydrochloric acid. In contrast, for the antibacterial activity values ​​after 0.5 hours of incubation, the test pieces of Example 1 exhibit significantly superior antibacterial activity compared to the test pieces of Comparative Examples 1 and 2. The increase in the antibacterial activity value after 0.5 hours of incubation after 24 hours of incubation is thought to be due to the catalytic action of the platinum nanoparticles being expressed as the antibacterial agent dries, but it is thought that the antibacterial activity before the antibacterial agent dries is due to the dilute hydrochloric acid. From the above, it can be seen that the addition of an inorganic acid such as dilute hydrochloric acid can enable the antibacterial agent to exhibit excellent antibacterial activity even before it is dried, and can also effectively suppress discoloration over time for a long period of time even after the antibacterial agent has dried, without reducing its original antibacterial activity.

[0064] (Antibacterial Activity (2)) Deionized water was added to the antibacterial agent (1) prepared in Example 1 to prepare three types of antibacterial agents (1-1), (1-2), and (1-3), each with a different dilution ratio. Specifically, the antibacterial agent (1-1) was diluted 50 times, the antibacterial agent (1-2) was diluted 100 times, and the antibacterial agent (1-3) was diluted 200 times. The antibacterial activity of these antibacterial agents against two types of test bacteria was evaluated according to the same method as above. The results are shown in Tables 3 and 4.

[0065]

[0066]

[0067] As shown in Tables 3 and 4, it can be seen that excellent antibacterial activity was obtained for all test pieces. This shows that antibacterial agent (1) exhibits excellent antibacterial activity even when diluted 50 to 200 times. From the above, it can be seen that the addition of an inorganic acid can effectively suppress discoloration over time for a long period of time without reducing the original antibacterial activity.

[0068] According to the present invention, a platinum nanoparticle solution capable of suppressing discoloration over time can be provided. This platinum nanoparticle solution has the properties of platinum nanoparticles, such as antibacterial properties, and can suppress discoloration over time for a long period of time, making it suitable for use in antibacterial agents, antibacterial products, and the like.

Claims

1. A method for producing a platinum nanoparticle solution, comprising adding a reducing agent to a solution containing platinum ions derived from chloroplatinic acid or a chloroplatinic acid salt to reduce the platinum ions, and adding an inorganic acid.

2. The method for producing a platinum nanoparticle solution according to claim 1, wherein the chloroplatinic acid salt contains at least one selected from the group consisting of sodium chloroplatinate, potassium chloroplatinate, sodium chloroplatinate (II), potassium chloroplatinate (II), and ammonium chloroplatinate.

3. The method for producing a platinum nanoparticle solution according to claim 1, wherein the pH of the platinum nanoparticle solution is adjusted to a range of 4 to 6 by adding the inorganic acid.

4. The method for producing a platinum nanoparticle solution according to claim 1 or 2, wherein the inorganic acid is dilute hydrochloric acid.

5. The method for producing a platinum nanoparticle solution according to claim 1 or 2, wherein the reducing agent contains at least one selected from the group consisting of ascorbic acid or an ascorbate, alginic acid or an alginate, dicarboxylic acids, alcohols, and polysaccharides.

6. The method for producing a platinum nanoparticle solution according to claim 1 or 2, wherein citric acid or a citrate is further added in the reduction treatment.

7. An antibacterial agent comprising platinum nanoparticles, an inorganic acid, and water.

8. The antibacterial agent according to claim 7, wherein the inorganic acid is dilute hydrochloric acid.

9. The antibacterial agent according to claim 7, further comprising chloroplatinic acid or a chloroplatinic acid salt.

10. The antibacterial agent according to claim 7, further comprising potassium iodide.

11. A paint comprising the antibacterial agent according to claim 7.

12. An antibacterial product obtained by applying the antibacterial agent according to any one of claims 7 to 10 or the paint according to claim 11 to a daily necessity made of a material selected from the group consisting of synthetic or natural fibers, plastics, ceramics, and wood.

13. The antibacterial product according to claim 12, wherein the antibacterial product is a mask, gauze, toothbrush, cup, or antibacterial sheet.