Method for manufacturing silver nanoparticles

Abstract

To provide a production method of silver nanoparticles, capable of producing silver nanoparticles having a small and uniform particle diameter from silver ions at a high concentration to reduce production cost through high-volume production.SOLUTION: The production method of silver nanoparticles includes exposing a reaction liquid to microwaves. The reaction liquid contains silver ions (i), 500 mM or more of a reducing solvent (ii), and a protective agent having one or more functional groups selected from the group consisting of a carboxy group and an amide group, with a concentration ratio between the reducing solvent and the silver ions (Concentration of reducing solvent / Concentration of silver ions) of 5 or more, and a ratio of dielectric loss between the protective agent and the reducing solvent (Dielectric loss of protective agent / Dielectric loss of reducing solvent) of 0.0004 or more. The output power of irradiation source of the microwaves to which the reaction liquid is exposed is 30 W / mL or more based on the total volume of the reaction liquid.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for producing silver nanoparticles.

Background Art

[0002] In recent years, metal nanoparticles having properties different from those of bulk materials, particularly silver nanoparticles having various excellent physical and chemical properties in terms of functionality, have been used and studied in various applications such as catalysts, ink materials, and electronic component members.

[0003] For example, Patent Document 1 discloses a method for producing silver nanoparticles by adding a reducing agent for reducing silver ions to silver and a polymer adsorbent for adsorbing to the reduced silver to a solution containing silver ions to precipitate silver. In this method, a reducing agent having a standard electrode potential in the range of 0.03 V to 0.8 V is used as the reducing agent, polyvinylpyrrolidone having a weight average molecular weight of 10,000 to 40,000 is used as the polymer adsorbent, the reducing agent and the polymer adsorbent are added to the solution containing silver ions, and the resulting mixture is irradiated with microwaves to precipitate silver from the silver ions while producing plate-like silver nanoparticles.

[0004] Non-Patent Document 1 discloses the properties of reducing agents and protective agents in a method for synthesizing silver particles using sodium borohydride and a method for synthesizing silver particles using organic acids such as citric acid and amino acids.

[0005] In the field of electronics mounting, metal nanoparticles are also being studied as lead-free bonding materials that can be bonded at low temperatures. Although it is difficult to bond lead-free solder at 250°C or lower, lead-free solder containing metal nanoparticles can utilize the properties of metal nanoparticles, that is, having a lower melting point compared to bulk materials and having the melting point of a bulk material when sintered for use in bonding, to enable bonding at 250°C or lower.

[0006] For example, Patent Document 2 discloses a method for producing silver particles, which includes the steps of: obtaining a mixed solution by mixing at least a silver compound, a reducing agent and a dispersant in order to improve the packing properties (particle packing density) of spherical silver nanoparticles and obtain high bonding strength by using silver nanoparticles as metal nanoparticles; and heating the mixed solution to react the silver compound and the reducing agent to produce sheet-like or plate-like first silver particles and second silver particles that have a shape closer to or more spherical than the first silver particles and have a particle diameter smaller than the maximum side length of the first silver particles. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2018-135566 [Patent Document 2] Japanese Patent Publication No. 2017-025391 [Non-patent literature]

[0008] [Non-Patent Document 1] Restrepo, Cindy Vanessa and Cristian C. Villa, "Synthesis of silver nanoparticles, influence of capping agents, and dependence on size and shape: A review." Environmental Nanotechnology, Monitoring&Management, 2021, 100428 [Overview of the project] [Problems that the invention aims to solve]

[0009] Conventional methods for synthesizing silver nanoparticles are complex and rigorous due to gas generation and rapid reaction rates. For example, the method for synthesizing silver particles using sodium borohydride, as used in Non-Patent Document 1, has a fast reaction rate, making it difficult to achieve uniform particle size, and also generates a large amount of gas. Furthermore, the method for synthesizing silver particles using citric acid or amino acids, as used in Non-Patent Document 1, is limited to synthesis conditions using low concentrations of silver ions due to salt formation (insolubilization) between silver ions and citric acid or amino acids. In addition, when silver ions are used at high concentrations, there is concern that particle growth will be accelerated, i.e., the particles will become coarser, due to a decrease in the frequency of contact between silver nanoparticles and protective agents in the system.

[0010] Furthermore, as a strategy for using silver nanoparticles as a high heat-resistant bonding material, Patent Document 2 mentions the synthesis of bimodal silver nanoparticles, but generally, the goal is to make the melting point of the silver nanoparticles constant and as low as possible. In order to make the melting point of the silver nanoparticles constant and as low as possible, it is necessary to make the particle size of the silver nanoparticles small and uniform (here, uniform particle size means a narrow particle size distribution).

[0011] Therefore, the object of the present invention is to provide a method for producing silver nanoparticles that can use a high concentration of silver ions to reduce manufacturing costs through mass production, and that can produce silver nanoparticles that are small in size and uniform in size. [Means for solving the problem]

[0012] As a result of various investigations into means to solve the above-mentioned problems, the present inventors have found that, in a method for producing silver nanoparticles by irradiating a reaction solution with microwaves, by using specific amounts of the solvent and a reducing solvent acting as a reducing agent, using a protective agent having a specific functional group as a protective agent, and further adjusting the ratio of dielectric loss between the protective agent and the reducing solvent (dielectric loss of the protective agent / dielectric loss of the reducing solvent), it is possible to stably produce silver nanoparticles with small and uniform particle size, thus completing the present invention.

[0013] In other words, the gist of this invention is as follows: (1) A method for producing silver nanoparticles by irradiating a reaction solution with microwaves, The reaction solution is (i) Silver ions and, (ii) A reducing solvent with a concentration of 500 mM or higher, (iii) A protective agent having one or more functional groups selected from the group consisting of carboxyl groups, hydroxyl groups, amino groups and amide groups. Includes, The ratio of the reducing solvent concentration to the silver ion concentration (concentration of reducing solvent / concentration of silver ions) is 5 or greater. The ratio of the dielectric loss of the protective agent to the reducing solvent (dielectric loss of the protective agent / dielectric loss of the reducing solvent) is 0.0004 or greater. The output power of the microwave irradiation source used to irradiate the reaction solution is 30 W / mL or more, based on the total volume of the reaction solution. method. (2) The method according to (1), wherein the protective agent has an amide group. (3) The method according to (1) or (2), wherein the reducing solvent is an organic compound having one or more functional groups selected from amino groups, hydroxyl groups, and carboxyl groups, or an organic compound that decomposes upon microwave irradiation to produce a compound having one or more functional groups selected from amino groups, hydroxyl groups, and carboxyl groups, and has a melting point of 60°C or lower. (4) The method according to (3), wherein the reducing solvent is N,N-dimethylformamide (DMF) or propanol. (5) The method according to any one of (1) to (4), wherein the output of the microwave irradiation source that irradiates the reaction solution is 50 W / mL or more, based on the total volume of the reaction solution. (6) The method according to any one of (1) to (5), wherein the concentration of silver ions in the reaction solution is 50 mM or higher. [Effects of the Invention]

[0014] The present invention provides a method for producing silver nanoparticles, which can use high-concentration silver ions to reduce manufacturing costs through mass production and can generate silver nanoparticles with small and uniform particle sizes.

Brief Description of Drawings

[0015] [Figure 1] It is a graph showing the relationship between the ratio of the dielectric loss of the protective agent to the reducing solvent (dielectric loss of the protective agent / dielectric loss of the reducing solvent) and the average particle size of silver nanoparticles for the silver nanoparticles prepared in Comparative Examples 1 to 2, Examples 1 to 2, and Reference Example 3. [Figure 2] It is a graph showing the particle size distribution of the silver nanoparticles prepared in Example 5. [Figure 3] It is a TEM photograph of the silver nanoparticles prepared in Example 5. [Figure 4] It is a graph showing the relationship between the concentration of DMF as the reducing solvent in the reaction solution and the average particle size of silver nanoparticles for the silver nanoparticles prepared in Comparative Example 3 and Examples 4 to 6. [Figure 5] It is a graph showing the relationship between the output of the microwave irradiation source and the average particle size of silver nanoparticles for the silver nanoparticles prepared in Examples 7 to 8 and Comparative Example 4.

Modes for Carrying Out the Invention

[0016] Hereinafter, preferred embodiments of the present invention will be described in detail. In this specification, the features of the present invention will be described with reference to the drawings as appropriate. Note that the method for producing silver nanoparticles of the present invention is not limited to the following embodiments, and can be implemented in various forms with modifications and improvements made by those skilled in the art without departing from the gist of the present invention.

[0017] The present invention relates to a method for producing silver nanoparticles by irradiating a reaction solution with microwaves, wherein the reaction solution comprises (i) silver ions, (ii) a reducing solvent with a concentration of 500 mM or more, and (iii) a protective agent having one or more functional groups selected from the group consisting of carboxyl groups and amide groups, the ratio of the concentrations of the reducing solvent to the silver ions (concentration of the reducing solvent / concentration of silver ions) is 5 or more, the ratio of the dielectric loss of the protective agent to the reducing solvent (dielectric loss of the protective agent / dielectric loss of the reducing solvent) is 0.0004 or more, and the output of the microwave irradiation source that irradiates the reaction solution is 30 W / mL or more based on the total volume of the reaction solution.

[0018] Here, the raw materials for the silver ions contained in the reaction solution are not limited as long as they can dissolve in the solvent described below and generate silver ions, but examples include inorganic salts of silver such as hydrochloride, sulfate, nitrate, and phosphate, and organic salts such as carboxylates and sulfonates. The raw materials for silver nanoparticles may be prepared, for example, by dissolving a material containing metallic silver or silver salts with an acid such as nitric acid or ammonia water. As the raw material for silver ions, it is preferable to use inexpensive silver nitrate.

[0019] The concentration of silver ions in the reaction solution is not limited as long as the ratio to the reducing solvent is within a specific range, as explained below, and may be low, for example, usually 0.1 mmol / L (mM) or higher, preferably 1 mM or higher. When considering the reduction of manufacturing costs through mass production, the concentration of silver ions in the reaction solution is usually 50 mM or higher, preferably 80 mM or higher, and more preferably 100 mM or higher. The upper limit of the concentration of silver ions in the reaction solution is not limited as long as the silver ion raw material exists as silver ions in the reaction solution, but is usually 500 mM, preferably 400 mM.

[0020] By setting the concentration of silver ions in the reaction solution within the aforementioned range, the variability of the resulting silver nanoparticles is reduced, or in other words, the particle size distribution of the resulting silver nanoparticles becomes narrower.

[0021] The reducing solvent contained in the reaction solution is a compound that acts as both a solvent, which is the reaction field in the reaction solution, and a reducing agent, which reduces silver ions to silver with an oxidation state of 0 through a redox reaction.

[0022] The reducing solvent is not limited as long as it has the above-mentioned properties, dissolves silver ion raw materials and protective agents, and can absorb microwaves. Preferred reducing solvents are organic compounds having one or more functional groups selected from amino groups, hydroxyl groups, and carboxyl groups, or organic compounds that decompose upon microwave irradiation, i.e., by absorbing microwaves, to produce compounds having one or more functional groups selected from amino groups, hydroxyl groups, and carboxyl groups. Furthermore, organic compounds having a melting point of 60°C or lower are preferred as reducing solvents. Examples of reducing solvents include N,N-dimethylformamide (DMF), acetic acid, propanol, for example, n-propyl alcohol and 2-propyl alcohol, ethanol, formic acid, ethylene glycol, and mixtures of two or more of these. DMF or propanol are preferred as reducing solvents.

[0023] DMF undergoes hydrolysis upon temperature increase due to heating, thereby exhibiting its reducing ability. Therefore, by using DMF as a reducing solvent, the DMF, rapidly heated by microwaves, reduces silver ions all at once. As a result, nucleation of silver nanoparticles occurs uniformly in the solvent, and the resulting silver nanoparticles are small and uniform in size.

[0024] The concentration of the reducing solvent in the reaction solution is sufficient for both the solvent and the reducing agent, i.e., 500 mM or more, preferably 1000 mM or more, and more preferably 1500 mM or more. The upper limit of the concentration of the reducing solvent in the reaction solution is not limited; for example, only the reducing solvent may be used as the solvent in the reaction solution.

[0025] The ratio of the reducing solvent concentration to the silver ion concentration (concentration of reducing solvent / concentration of silver ions) is 5 or greater, preferably 10 or greater.

[0026] By adjusting the concentration of the reducing solvent in the reaction solution to the aforementioned range, small-particle silver nanoparticles can be produced.

[0027] The protective agent contained in the reaction solution is a compound that binds to part or all of the surface of the silver nanoparticles generated in the reaction solution, and is a compound that suppresses aggregation of the silver nanoparticles. The protective agent is an organic compound having one or more functional groups selected from the group consisting of carboxyl groups, hydroxyl groups, amino groups, and amide groups, preferably from the group consisting of carboxyl groups and amide groups. Examples of protective agents include polyvinylpyrrolidone (PVP), polyacrylamide (PAA), polyvinyl alcohol (PVA), and mixtures of two or more of these. PVP or PAA is preferred as the protective agent.

[0028] The protective agent has carboxyl groups and / or amide groups, which allows these functional groups to efficiently absorb microwaves, improving the adsorption rate of the protective agent to silver nanoparticles and enabling the generation of small-particle-sized silver nanoparticles.

[0029] The weight-average molecular weight of the protective agent is not limited and can be changed depending on the desired particle size of the silver nanoparticles, but is typically 300 g / mol to 100,000 g / mol, preferably 1,500 g / mol to 50,000 g / mol.

[0030] By setting the weight-average molecular weight of the protective agent within the aforementioned range, the protective agent effectively coordinates to the generated silver nanoparticles, suppressing grain growth and resulting in a uniform particle size distribution.

[0031] The amount of protective agent is not limited and can be changed depending on the desired particle size of the silver nanoparticles, but is usually 0.1 to 2000 times, preferably 0.2 to 1000 times, the amount of silver.

[0032] By using the protective agent with the aforementioned weight-average molecular weight and amount, aggregation of the generated silver nanoparticles can be suppressed.

[0033] The ratio of dielectric loss of the protective agent to the reducing solvent (dielectric loss of the protective agent / dielectric loss of the reducing solvent) is 0.0004 or higher, preferably 0.00040 or higher, and more preferably 0.001 or higher. The upper limit of the ratio of dielectric loss of the protective agent to the reducing solvent (dielectric loss of the protective agent / dielectric loss of the reducing solvent) is not limited because the particle size of the protective agent becomes smaller as it absorbs microwaves more easily, but it is usually 0.005.

[0034] Table 1 summarizes the dielectric loss of compounds that can be used as protective agents.

[0035] [Table 1]

[0036] The dielectric loss of the protective agent is not limited, but is usually 0.0030 or higher, preferably 0.0050 or higher. Table 2 summarizes the dielectric losses of compounds that can be used as reducing solvents.

[0037] [Table 2]

[0038] The dielectric loss of the reducing solvent is not limited, but is usually 1 or more, preferably 5 or more.

[0039] By setting the ratio of the dielectric loss of the protective agent to that of the reducing solvent within the aforementioned range, it is possible to prevent the dielectric loss of the protective agent from becoming too small compared to that of the reducing solvent, thereby preventing delays in the adsorption rate and particle coarsening.

[0040] Furthermore, the dielectric loss coefficient due to microwaves is given by the following formula Dielectric loss coefficient = ε r ·tanσ ε r : Relative permittivity of a dielectric (e.g., protective agent or reducing solvent) tanσ: Dielectric loss loss tangent of a dielectric material It can be calculated using the following method.

[0041] This formula allows us to estimate the dielectric loss coefficients of both the reducing solvent and the protective agent. The dielectric loss coefficient represents the microwave absorption characteristics; materials with a larger dielectric loss coefficient absorb microwave power more easily and are more easily heated. Therefore, by setting the ratio of the dielectric loss of the protective agent to the reducing solvent (dielectric loss of the protective agent / dielectric loss of the reducing solvent) within the aforementioned range, heating around the protective agent is promoted, creating conditions that facilitate the adsorption of the protective agent immediately after the formation of silver nanoparticles, thus enabling the synthesis of silver nanoparticles that are small in size and uniform in shape.

[0042] The reaction solution may consist of the silver ions, reducing solvent, and protective agent described above, but it may also contain additives that are commonly used in reaction solutions for producing silver nanoparticles by conventional microwave irradiation methods.

[0043] For example, the reaction solution may further contain additives such as a chelating agent, for example, ethylenediaminetetraacetic acid (EDTA) and / or its salt, a pH adjuster, and so on.

[0044] In this invention, the order of addition of each material, the addition temperature, the mixing method, and the mixing time in the preparation of the reaction solution are not limited, and the mixture is prepared in such a way that a homogeneous reaction solution is obtained. In this invention, the reaction is started after a homogeneous reaction solution has been prepared.

[0045] In this invention, the reaction solution described above is irradiated with microwaves using a microwave synthesis device to allow the reaction to proceed. When microwaves are irradiated onto the reaction solution, the polar solvent (reducing solvent) contained in the reaction solution absorbs the microwaves and generates heat energy by converting it into thermal energy.

[0046] In a microwave synthesis apparatus, the material of the container holding the reaction solution is not limited as long as the reaction solution can be uniformly irradiated with microwaves. For example, when microwaves are irradiated into the reaction solution from outside the reactor through the reactor, materials that transmit microwaves, such as ceramics or glass, can be used. When microwaves are irradiated directly into the reaction solution from above, materials that reflect microwaves, such as aluminum or stainless steel, can be used.

[0047] Microwaves are generated from a microwave source (microwave oscillator (magnetron)), and the microwave source can be either a single-mode system or a multi-mode system.

[0048] The output of the microwave irradiation source is 30 W / mL or more, preferably 50 W / mL or more, based on the total volume of the reaction solution. The upper limit of the output of the microwave irradiation source is not limited, but is usually 10 kW / mL, preferably 1 kW / mL, and more preferably 500 W / mL, based on the total volume of the reaction solution.

[0049] By setting the output of the microwave irradiation source within the aforementioned range, small-particle silver nanoparticles can be produced.

[0050] The frequency of microwaves generated from a microwave irradiation source can be changed as appropriate and is not limited, but is usually 1 GHz to 10 GHz, preferably 2 GHz to 6 GHz. In this invention, it is more preferable to use 2.45 GHz as the frequency of the microwave, which is the frequency of an industrial microwave power supply.

[0051] The temperature of the reaction solution, which is raised by microwave irradiation, can be appropriately changed depending on the reaction conditions and is not limited. The temperature of the reaction solution should be below the boiling point of the solvent.

[0052] The microwave irradiation time to the reaction solution can be adjusted as appropriate depending on the reaction conditions and is not limited once the reaction is complete, but is usually 1 to 200 minutes, preferably 1 to 80 minutes. Alternatively, the reaction solution can be irradiated with microwaves to maintain the desired temperature. The completion of the reaction can be confirmed by analyzing the absence of silver ions, the starting material, in the solution using ICP-AES.

[0053] The total reaction time, including microwave irradiation time, can be appropriately changed depending on the reaction conditions and is not limited to, but is, for example, 1 minute to 300 minutes, preferably 1 minute to 80 minutes.

[0054] In this invention, by using a microwave synthesis apparatus, the entire reaction field can be heated uniformly.

[0055] In this invention, it is preferable to stir the reaction solution using a stirring mechanism, such as a propeller-type stirrer or a vibrating stirrer. By stirring the reaction solution, the silver nanoparticles generated in the reaction solution can be uniformly dispersed, and the reaction solution can be kept uniform.

[0056] The present invention may be carried out in a batch or flow manner. The present invention is preferably carried out in a batch manner. By carrying it out in a batch manner, the synthesis reaction itself can be completed, and the yield of the resulting silver nanoparticles can be improved. Furthermore, the concentration of the reaction solution can be increased, preventing the problem of silver nanoparticle blockage in the piping that can occur in a flow manner.

[0057] The solution containing silver nanoparticles obtained by the present invention can be separated and purified (e.g., by salting out or centrifugation) by methods known in the art to obtain the desired silver nanoparticles and / or a dispersion containing silver nanoparticles.

[0058] The silver nanoparticles produced by the present invention have small particle sizes, with an average particle size of 5 nm to 30 nm when measured by TEM (where the average particle size refers to the average particle size of 300 or more particles when the particle size is the average of the major and minor axes). Furthermore, the particle size is uniform, i.e., it has a narrow particle size distribution, for example, the standard deviation σ of the particle size distribution measured by TEM is 20 or less.

[0059] The silver nanoparticles produced by this invention can be used not only as conventional catalysts, electronic component materials, and ink materials, but also as a high-temperature-resistant, lead-free bonding material in the field of electronics packaging. [Examples]

[0060] The following describes some embodiments of the present invention, but the present invention is not intended to be limited to those shown in these embodiments.

[0061] 1. Examination of protective agents and reducing solvents Example 1 (1) Silver nitrate, PVP (weight-average molecular weight: 40,000 g / mol) as a protective agent, and DMF as a reducing solvent were added to a sample tube so that the concentrations in the reaction solution were 100 mM silver nitrate, 600 mM PVP, and 2,000 mM DMF, respectively, and then stirred and mixed.

[0062] (2) The stirring reaction solution was irradiated with microwaves at 200 W / mL based on the total volume of the reaction solution for approximately 2 seconds until it reached 90°C. The reaction solution temperature of 90°C was then maintained for 10 minutes to synthesize silver nanoparticles.

[0063] Example 2 Silver nanoparticles were synthesized in the same manner as in Example 1, except that PAA (weight-average molecular weight: 5000 g / mol) was used as a protective agent in step (1) of Example 1.

[0064] reference Example 3 Silver nanoparticles were synthesized in the same manner as in Example 1, except that n-propyl alcohol was used as the reducing solvent in step (1) of Example 1.

[0065] Comparative Example 1 Silver nanoparticles were synthesized in the same manner as in Example 1, except that ethanol was used as the reducing solvent in step (1) of Example 1.

[0066] Comparative Example 2 Silver nanoparticles were synthesized in the same manner as in Example 1, except that polyvinyl alcohol (PVA, weight-average molecular weight: 1700 g / mol) was used as a protective agent and ethanol was used as the reducing solvent in step (1) of Example 1.

[0067] Example 1~ 2 and Reference Example 3 and For the silver nanoparticles of Comparative Examples 1 and 2, UV-vis spectral measurements and transmission electron microscopy (TEM) measurements were performed. In the TEM measurements, the particle size was calculated as the average of the major and minor axes of the particle, and the average particle size was calculated from the results of measuring the particle size of 300 or more particles.

[0068] The results are shown in Table 3.

[0069] [Table 3]

[0070] Furthermore, Figure 1 shows the relationship between the ratio of dielectric loss of the protective agent and the reducing solvent (dielectric loss of the protective agent / dielectric loss of the reducing solvent) and the average particle size of silver nanoparticles.

[0071] Table 3 and Figure 1 show that when the ratio of dielectric loss of the protective agent to the reducing solvent (dielectric loss of protective agent / reducing solvent) is 0.0004 or higher, the average particle size of the resulting silver nanoparticles becomes smaller.

[0072] 2. Examination of the concentration of the reducing solvent Comparative Example 3 (1) Silver nitrate, PVP (weight-average molecular weight: 40,000 g / mol) as a protective agent, and DMF as a reducing solvent were added to a sample tube so that the concentrations in the reaction solution were 100 mM silver nitrate, 600 mM PVP, and 300 mM DMF, respectively, and the mixture was stirred and mixed.

[0073] (2) The stirring reaction solution was irradiated with microwaves at 200 W / mL based on the total volume of the reaction solution for approximately 2 seconds until it reached 90°C. The reaction solution temperature of 90°C was then maintained for 10 minutes to synthesize silver nanoparticles.

[0074] Example 4 Silver nanoparticles were synthesized in the same manner as in Comparative Example 3, except that in step (1) of Comparative Example 3, the concentration of DMF as the reducing solvent in the reaction solution was changed to 500 mM.

[0075] Example 5 Silver nanoparticles were synthesized in the same manner as in Comparative Example 3, except that the concentration of DMF as the reducing solvent in the reaction solution was changed to 2000 mM in step (1) of Comparative Example 3.

[0076] Example 6 Silver nanoparticles were synthesized in the same manner as in Comparative Example 3, except that in step (1) of Comparative Example 3, the concentration of DMF as the reducing solvent in the reaction solution was changed to 4000 mM.

[0077] For Comparative Example 3 and Examples 4-6, UV-vis spectral measurements and transmission electron microscopy (TEM) measurements were performed. In the TEM measurements, the particle size was defined as the average value of the major and minor axes of the particles, and the average particle size and particle size distribution were calculated from the results of measuring the particle size of 300 or more particles.

[0078] The results are shown in Table 4.

[0079] [Table 4]

[0080] Furthermore, Figure 2 shows the particle size distribution of the silver nanoparticles prepared in Example 5 based on TEM, Figure 3 shows a TEM image of the silver nanoparticles prepared in Example 5, and Figure 4 shows the relationship between the concentration of DMF as a reducing solvent in the reaction solution and the average particle size of the silver nanoparticles.

[0081] Table 4 and Figures 2-4 show that when the concentration of DMF as the reducing solvent in the reaction solution exceeds 500 mM, the average particle size of the resulting silver nanoparticles decreases, and the particle size distribution becomes narrower.

[0082] 3. Output of the microwave irradiation source Comparative Example 4 (1) Silver nitrate, PVP (weight-average molecular weight: 40,000 g / mol) as a protective agent, and DMF as a reducing solvent were added to a sample tube so that the concentrations in the reaction solution were 100 mM silver nitrate, 600 mM PVP, and 4,000 mM DMF, respectively, and the mixture was stirred and mixed.

[0083] (2) The stirring reaction solution was irradiated with microwaves at 10 W / mL based on the total volume of the reaction solution for approximately 2 seconds until it reached 90°C. The reaction solution was then maintained at 90°C for 10 minutes to synthesize silver nanoparticles.

[0084] Example 7 Silver nanoparticles were synthesized in the same manner as in Comparative Example 4, except that in step (2) of Comparative Example 4, the output of the microwave irradiation source was changed to 50 W / mL based on the total volume of the reaction solution.

[0085] Example 8 Silver nanoparticles were synthesized in the same manner as in Comparative Example 4, except that in step (2) of Comparative Example 4, the output of the microwave irradiation source was changed to 100 W / mL based on the total volume of the reaction solution.

[0086] For Comparative Example 4 and Examples 7-8, UV-vis spectral measurements and transmission electron microscopy (TEM) measurements were performed. In TEM measurements, the particle size was calculated as the average of the major and minor diameters of the particles, and the average particle size was calculated from the results of measuring the particle size of 300 or more particles.

[0087] The results are shown in Table 5.

[0088] [Table 5]

[0089] Furthermore, Figure 5 shows the relationship between the output of the microwave irradiation source and the average particle size of silver nanoparticles.

[0090] Table 5 and Figure 5 show that when the output of the microwave irradiation source is 30 W / mL or more, preferably 50 W / mL or more, based on the total volume of the reaction solution, the average particle size of the resulting silver nanoparticles becomes smaller.

Claims

1. A method for producing silver nanoparticles by irradiating a reaction solution with microwaves, The reaction solution is (i) Silver ions and, (ii) A reducing solvent that is 500 mM or higher, (iii) A protective agent having one or more functional groups selected from the group consisting of carboxyl groups and amide groups. Includes, The ratio of the reducing solvent concentration to the silver ion concentration (concentration of reducing solvent / concentration of silver ions) is 5 or greater. The ratio of the dielectric loss of the protective agent to the reducing solvent (dielectric loss of the protective agent / dielectric loss of the reducing solvent) is 0.001 or greater. The reducing solvent is N,N-dimethylformamide. The protective agent is polyvinylpyrrolidone, polyacrylamide, or a mixture thereof. The output power of the microwave irradiation source used to irradiate the reaction solution is 30 W / mL or more, based on the total volume of the reaction solution. method.

2. The method according to claim 1, wherein the output of the microwave irradiation source that irradiates the reaction solution is 50 W / mL or more, based on the total volume of the reaction solution.

3. The method according to claim 1, wherein the concentration of silver ions in the reaction solution is 50 mM or more.

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