JP2019178355A - Method for manufacturing metal nanoparticle - Google Patents

Abstract

To provide a method for manufacturing metal nanoparticles, capable of forming a large amount of metal nanoparticles having a uniform particle size in a short time using a raw material solution including a metal compound at high concentration.SOLUTION: The method for manufacturing metal nanoparticles includes the step of irradiating a raw material solution with a microwave. The raw material solution comprises: a solvent; ethylenediamine tetraacetic acid; ethylenediamine triacetic acid; ethylenediamine diacetate; one or more kinds of chelating agents selected from those salts; and a metal compound. The molar ratio (material amount of chelating agent/material amount of metal) of the chelating agent to the metal in the metal compound is 0.067-3.00, and the raw material solution does not include a reducer selected from formic acid, citric acid and those salts.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a method for producing metal nanoparticles.

  In recent years, metal nanoparticles that may have different properties from bulk materials have been used in various applications such as catalysts and electronic component members.

  Various methods for producing metal nanoparticles have been devised.

  For example, Patent Document 1 discloses a step of dissociating at least one metal precursor selected from silver, gold, and palladium using an alkylamine, a step of reducing the dissociated metal precursor, and an alkylamine. Separating the capped metal nanoparticles, and a method for producing the metal nanoparticles.

  Patent Document 2 is a method for producing silver nanoparticles having a narrow particle size distribution, which includes a step of forming a mixture containing a silver compound, a carboxylic acid, and a chelating diamine compound, and optionally heating the mixture. A step of adding a hydrazine compound to the mixture and reacting the mixture to form silver nanoparticles, wherein the silver nanoparticles have a particle size distribution of about 30 nm or less. A method for producing silver nanoparticles is disclosed.

  Patent Document 3 is characterized in that ultrafine particles composed of a metal in the metal salt are produced by irradiating a solution obtained by dissolving or dispersing at least one metal salt in a solvent with microwaves. A method for producing ultrafine particles is disclosed.

JP 2009-30170 A JP 2010-43355 A JP 2000-256707 A

  However, the conventional techniques including Patent Documents 1 to 3 have a problem that the particle diameters of the obtained metal nanoparticles are not uniform.

  In the method of producing metal nanoparticles by reducing the metal nanoparticle precursor with a reducing agent, the reaction between the metal nanoparticle precursor and the reducing agent occurs very quickly. Therefore, when the reducing agent is simply added, the reaction starts locally from the added portion before the reducing agent diffuses throughout the reaction field by stirring. As a result, the resulting metal nanoparticles have non-uniform particle sizes.

  In the method described in Patent Document 1, a local reaction is suppressed by utilizing the capping effect of an amino group. However, the capping effect is an effect generated on the generated metal nanoparticles, and a local reaction at the time of generation of the metal nanoparticles cannot be sufficiently suppressed. Furthermore, since the binding force of the amino group is weak and the steric hindrance effect is small, sufficient particle size control cannot be performed. Moreover, since it heats using a heater, when it reacts by high concentration, a yield (reaction rate) is bad and reaction requires a long time.

  In the method described in Patent Document 2, a chelating diamine compound is used. However, the hydrazine compound used as the reducing agent is highly reducible and cannot sufficiently suppress local reactions. Moreover, since it heats using a hotplate, like patent document 1, when reaction is performed by high concentration, a yield (reaction rate) is bad and reaction requires a long time.

  In the method described in Patent Document 3, although microwaves are used for the reaction, the reaction rate is poor and metal nanoparticles cannot be generated efficiently.

  Therefore, the present invention provides a method for producing metal nanoparticles that can produce a large amount of metal nanoparticles with a uniform particle size in a short time using a raw material solution containing a metal compound at a high concentration. Let it be an issue.

  As a result of various studies on means for solving the above problems, the present inventors, as a raw material solution, in a method for producing metal nanoparticles by irradiating a raw material solution with microwaves, a metal compound and ethylenediaminetetraacetic acid ( EDTA), ethylenediaminetriacetic acid, ethylenediaminediacetic acid and a salt solution containing at least one chelating agent selected from salts thereof at a specific molar ratio were used to carry out the reaction. It was found that metal ions can be reduced to metal nanoparticles without adding a reducing agent selected from formic acid, citric acid and salts thereof, which can be dissolved in a solvent, and the present invention has been completed.

That is, the gist of the present invention is as follows.
(1) A method for producing metal nanoparticles comprising a step of irradiating a raw material solution with microwaves,
The raw material solution contains a solvent, one or more chelating agents selected from ethylenediaminetetraacetic acid, ethylenediaminetriacetic acid, ethylenediaminediacetic acid and their salts, and a metal compound,
The molar ratio of the chelating agent to the metal in the metal compound (the amount of the chelating agent / the amount of the metal) is 0.067 to 3.00,
The raw material solution does not contain a reducing agent selected from formic acid, citric acid and salts thereof;
Said method.

  In the method for producing metal nanoparticles of the present invention, the metal compound can be dissolved in a solvent at a high concentration by one or more chelating agents selected from ethylenediaminetetraacetic acid, ethylenediaminetriacetic acid, ethylenediaminediacetic acid and salts thereof. it can. Further, the chelating agent is used as a reducing agent by microwave irradiation, and further, the starting solution does not contain a reducing agent selected from formic acid, citric acid and their salts, whereby the start of the reaction is microwaved. Can be controlled by irradiation. For this reason, a local reaction does not occur. In addition, since the microwave acts directly on the reaction field, the reaction time is short. As a result, according to the method for producing metal nanoparticles of the present invention, a large amount of metal nanoparticles having a uniform particle diameter can be produced in a short time.

1 illustrates one embodiment of the present invention. The experimental procedure of Examples 1-9 and Comparative Examples 1-6 is shown. The reaction rate with respect to (amount of EDTA substance / amount of silver substance) in the preparation of Examples 1 to 9 and Comparative Examples 1 to 4 is shown. The TEM photograph of the silver nanoparticle obtained by Example 8 is shown. The TEM photograph of the silver nanoparticle obtained by Example 9 is shown. The TEM photograph of the silver nanoparticle obtained by the comparative example 5 is shown. The TEM photograph of the silver nanoparticle obtained by the comparative example 6 is shown.

Hereinafter, preferred embodiments of the present invention will be described in detail.
In the present specification, features of the present invention will be described with reference to the drawings as appropriate. Note that the method for producing metal nanoparticles of the present invention is not limited to the following embodiments, and can be variously modified and improved by those skilled in the art without departing from the gist of the present invention. Can be implemented.

  The present invention is a method for producing metal nanoparticles including a step of irradiating a raw material solution with microwaves, wherein the raw material solution is selected from a solvent, ethylenediaminetetraacetic acid, ethylenediaminetriacetic acid, ethylenediaminediacetic acid, and salts thereof. The molar ratio of the chelating agent to the metal in the metal compound is a specific value, and the raw material solution is selected from formic acid, citric acid and salts thereof This method does not contain a reducing agent.

  In the present invention, the amount of one or more chelating agents selected from ethylenediaminetetraacetic acid, ethylenediaminetriacetic acid, ethylenediaminediacetic acid and their salts in the raw material solution and the amount of the metal compound have a certain relationship. In the present invention, the molar ratio of the chelating agent to the metal in the metal compound (the amount of the chelating agent / the amount of the metal) is 0.067 to 3.00, preferably 0.067 to 2.67, more preferably. Is 0.10 to 2.00.

  When the molar ratio of the chelating agent to the metal in the metal compound satisfies the above relationship, the metal compound is secured after being dissolved by the chelating agent, and can be dissolved in the solvent at a high concentration. In addition, the chelating agent acts as a reducing agent when irradiated with microwaves, and can efficiently reduce metal ions in the metal compound to metal nanoparticles.

  Furthermore, in the present invention, the chelating agent serves as a reducing agent for metal ions by microwaves in addition to increasing the concentration of the metal compound in the raw material solution, which is the original role. , Free of reducing agents selected from citric acid and their salts.

  Here, the reducing agent selected from formic acid, citric acid, and salts thereof in the present invention is a powerful reduction that reduces a metal having a positive oxidation number in a metal compound to a metal at the moment of mixing with the metal compound. It is an agent. In this invention, it is preferable not to contain ascorbic acid etc. other than the said reducing agent. In the present invention, it is more preferable that the raw material solution does not contain a reducing agent.

  Since the raw material solution does not contain the reducing agent, local generation of particles that may occur at the moment when the reducing agent is added does not proceed. In addition, since the reducing agent, which is generally known for its short pot life (the maximum value that can be used after products that are supplied as separate components), is not used, can reduce manufacturing costs. it can.

  In the present invention, since uniform nucleation is promoted in the entire reaction field only by irradiating with microwaves, metal nanoparticles having a uniform particle size as compared with the prior art can be obtained.

  Furthermore, in the present invention, the raw material solution contains one or more chelating agents selected from ethylenediaminetetraacetic acid, ethylenediaminetriacetic acid, ethylenediaminediacetic acid and their salts, and is selected from formic acid, citric acid and their salts. Since the agent solution is not included, the precipitate that can be precipitated when the raw material solution does not contain the chelating agent and contains the reducing agent may vary depending on the combination of the solvent and the metal compound, but the concentration of the metal compound is 300 mM or more. Even if it becomes, it does not precipitate.

  In the present invention, materials described below are prepared and mixed to prepare a raw material solution.

  The solvent is a polar solvent that has a polar portion in the molecule and generates heat by absorbing microwaves and converting them into thermal energy when irradiated with microwaves.

  Examples of the solvent include, but are not limited to, alcohol solvents such as water, methanol, and ethanol, ketone solvents such as acetone, and polyhydric alcohol solvents such as DMSO, DMF, and ethylene glycol. In the present invention, it is preferable to use water which is generally inexpensive as a solvent.

  The chelating agent is at least one chelating agent selected from ethylenediaminetetraacetic acid, ethylenediaminetriacetic acid, ethylenediaminediacetic acid, and salts thereof, and easily reacts with metal ions in the metal compound to form a chelate compound. It is a compound having a multidentate ligand that can increase the solubility of the metal compound in the solvent, that is, it is possible to achieve a high concentration of the metal compound in the raw material solution.

  As the chelating agent, it is preferable to use ethylenediaminetetraacetic acid and its salt.

  The amount of the chelating agent is not limited as long as the molar ratio of the chelating agent to the metal in the metal compound is satisfied, but is usually 1 mM (mmol / L) to 2000 mM, preferably 2 mM to 800 mM in the raw material solution.

  A metal compound is a precursor of metal nanoparticles that are dissolved in a solvent, and the metal compound itself has polarity, and when irradiated with microwaves, it absorbs the microwaves and generates heat by converting them into thermal energy. .

  Examples of the metal compound include, but are not limited to, for example, metals such as gold, silver, platinum, copper, nickel, iron, and cobalt that form metal nanoparticles, such as hydrochloride, sulfate, nitrate, and phosphate. And inorganic salts such as carboxylate and sulfonate. In the present invention, it is preferable to use inexpensive silver nitrate as the metal compound, for example, as a silver metal compound.

  The amount of the metal compound is not limited as long as the molar ratio of the chelating agent to the metal in the metal compound is satisfied, but is usually 1 mM to 2000 mM, preferably 20 mM to 600 mM in the raw material solution.

  In the present invention, in addition to the above materials, an additive such as a dispersant can be added.

  The dispersant is a material that can control the particle size and / or shape of the metal nanoparticles to be generated and can disperse the metal nanoparticles generated in the solution. Even if metal nanoparticles are generated in the raw material solution, the dispersant can keep the raw material solution in a uniform state, and the particle size and / or shape of the generated metal nanoparticles can be kept constant.

  The preferred dispersant may differ depending on the type of metal nanoparticles to be produced, and is not limited, and examples thereof include polyvinylpyrrolidone (PVP), oleic acid, and amines.

  The amount of the dispersant is not limited, but is usually 0.1 to 20 times, preferably 0.2 to 10 times the amount of the metal in the metal compound.

  The total volume of the raw material solution varies depending on the conditions of the microwave to be irradiated and is not limited, but is usually adjusted to be 0.1 L to 100 L, preferably 0.2 L to 10 L.

  In the preparation of the raw material solution of the present invention, the order of addition of each material, the addition temperature, the mixing method, the mixing time and the like are not limited, and they are mixed so that a uniform raw material solution is prepared. For example, in the present invention, a raw material solution can be prepared as follows.

  A solvent and one or more chelating agents selected from ethylenediaminetetraacetic acid, ethylenediaminetriacetic acid, ethylenediaminediacetic acid and their salts are added and mixed in a container at 10 ° C to 40 ° C to prepare a mixed solution To do. Then, a uniform raw material solution is prepared by adding a metal compound slowly in a liquid mixture and stirring for 1 minute-30 minutes, for example until a metal compound melt | dissolves.

  In the present invention, the obtained raw material solution is irradiated with microwaves to advance the reaction.

  The material of the container for storing the raw material solution is not limited as long as the raw material solution can be uniformly irradiated with microwaves. For example, when the raw material solution is irradiated with microwaves from the outside of the reactor, Materials that transmit waves, such as ceramics and glass, can be used. When directly irradiating the raw material solution with microwaves from the top of the raw material solution, a material that reflects microwaves, such as metals such as aluminum and stainless steel, is used. Can be used.

  The microwave is generated from a microwave irradiation source (a microwave oscillator (magnetron)), and the microwave irradiation source can be used in either a single mode system or a multimode system.

  The output of the microwave irradiation source can be appropriately changed depending on the reaction conditions, such as the type of reaction, and is not limited, but is usually 100 W / L to 10 kW / L, preferably 100 W, based on the total volume of the raw material solution. / L to 5 kW / L.

  The frequency of the microwave generated from the microwave irradiation source can be appropriately changed and is not limited, but is usually 1 GHz to 10 GHz, preferably 2 GHz to 6 GHz. In the present invention, it is more preferable to use 2.45 GHz which is the frequency of an industrial microwave power source defined by Japanese regulations as the frequency of the microwave.

  The temperature of the raw material solution heated by microwave irradiation can be appropriately changed depending on the reaction conditions, and is not limited, but depends on the boiling point of the solvent usually used.

  The irradiation time of the microwave to the raw material solution can be appropriately changed depending on the reaction conditions and is not limited, but is usually 1 minute to 200 minutes, preferably 1 minute to 60 minutes. Alternatively, the raw material solution can be irradiated with microwaves so as to maintain the temperature of the target raw material solution.

  The total reaction time including the microwave irradiation time can be appropriately changed depending on the reaction conditions, and is not limited, but is, for example, 1 minute to 300 minutes, preferably 1 minute to 60 minutes.

  When irradiating the raw material solution with microwaves, the raw material solution is preferably stirred by a stirring mechanism such as a propeller stirrer or a vibration stirrer. By stirring the raw material solution, the metal nanoparticles generated in the raw material solution can be uniformly dispersed, and the raw material solution can be kept uniform.

  The present invention may be implemented in a batch system or a flow system. The present invention is preferably carried out batchwise. By carrying out in batch mode, the synthesis reaction itself can be completed and the yield of the metal nanoparticles obtained can be improved. Moreover, the concentration of the raw material solution can be increased, and the piping is not blocked by the metal nanoparticles.

  In the present invention, by irradiating the raw material solution with microwaves, a reduction reaction of metal ions in the metal compound is started, and precipitation of metal nanoparticles starts. In this reaction, the microwave is affected by the polar bond between one or more chelating agents selected from ethylenediaminetetraacetic acid, ethylenediaminetriacetic acid, ethylenediaminediacetic acid and their salts and the metal ion in the metal compound, and is inherently reducing. The chelating agent that does not have a reduction effect on metal ions.

One embodiment of the present invention is shown in FIG.
In FIG. 1, a metal having a good cost performance and a high solubility of the metal compound, one or more chelating agents selected from ethylenediaminetetraacetic acid, ethylenediaminetriacetic acid, ethylenediaminediacetic acid and salts thereof, and a metal having good cost performance A raw material solution containing a compound and a suitably selected dispersant is prepared, and the molar ratio of the chelating agent to the metal in the metal compound satisfies the above requirements, and the prepared raw material solution is adjusted based on the reaction system. The reaction is carried out at a time determined based on the temperature and the reaction rate adjusted depending on the reaction system by irradiating 2.45 GHz microwaves stipulated by Japanese law and Japanese regulations. Moreover, the stirring mechanism can use a propeller stirrer and the rotation speed in that case is adjusted to 100 rpm-300 rpm. Thereafter, the obtained metal nanoparticles are collected.

  The solution containing the metal nanoparticles obtained by the present invention is subjected to separation and purification (for example, salting out and centrifugation) by a method known in the art, and the target metal nanoparticles and / or metal nanoparticles are obtained. A dispersion containing particles can be obtained.

  The metal nanoparticles produced by the method for producing metal nanoparticles of the present invention are characterized by small dispersion of the particle size distribution.

  The metal nanoparticles produced by the method for producing metal nanoparticles of the present invention can be used as an electronic control unit (ECU) wiring as a high heat-resistant bonding material for a power control unit (PCU) in addition to conventional catalysts and electronic component members. As a material for a substrate, it can be used as a wiring material.

  Several examples relating to the present invention will be described below, but the present invention is not intended to be limited to those shown in the examples.

1. Preparation Examples 1-9 and Comparative Examples 1-6 of Silver Nanoparticles
Examples 1-9 and Comparative Examples 1-6 were implemented according to the experimental procedure shown in FIG. The experimental conditions of Examples 1-9 are summarized in Table 1, and the experimental conditions of Comparative Examples 1-6 are summarized in Table 2. The reaction time was set short in consideration of productivity.

(Experiment procedure of FIG. 2)
Ethylenediaminetetraacetic acid tetrasodium (EDTA-4Na) (1) (mM) as one or more chelating agents selected from ethylenediaminetetraacetic acid, ethylenediaminetriacetic acid, ethylenediaminediacetic acid and salts thereof in 50 mL of water as a polar solvent (In the examples, “mM” indicates the concentration in the raw material solution) to prepare a mixed solution. In the mixed solution, silver nitrate (2) (mM) as a metal compound, PVP as a dispersing agent (0.5 times mol with respect to the number of moles of silver (Ag)), and optionally formic acid, citric acid and those As a reducing agent selected from these salts, trisodium citrate (3) (mM) was added and stirred for 5 minutes to dissolve each material in water to prepare a raw material solution.

  The prepared raw material solution is put into a glass container and heated by a specific device (5) so that the raw material solution is maintained at a temperature of 80 ° C. for a certain time (4) (minutes) while stirring with a stirrer. did. After the reaction, silver nanoparticles were collected.

2. Reaction rate evaluation The reaction rate in preparation of Examples 1-9 and Comparative Examples 1-5 was computed in the following procedures.
(1) The produced silver nanoparticles were settled by centrifuging the raw material solution obtained after the reaction (20,000 rpm, 20 minutes).
(2) The amount of silver remaining in the supernatant was measured by ICP emission spectroscopy (ICP-AES, manufactured by HORIBA).
(3) The reaction rate was calculated from the amount of silver remaining in the supernatant.
The reaction rates in the preparation of Examples 1 to 9 and Comparative Examples 1 to 5 are summarized in Table 3. The rate is shown in FIG.

  From Table 3 and FIG. 3, it was found that there was an optimum value for the concentration of EDTA. In a reaction time as short as 10 minutes, the reaction rate is 30% or more when the molar ratio of EDTA to silver in silver nitrate (the amount of EDTA / the amount of silver) is 0.067 to 2.67. When the molar ratio of EDTA to silver in silver nitrate is 0.100 to 2.00, it is 50% or more, and when the molar ratio of EDTA to silver in silver nitrate is 0.300 to 1.300, It was found to be 80% or more. On the other hand, the reaction rate of Comparative Example 5, which is a conventional method, was less than 30%.

  Moreover, in the result of the comparative example 4 heated with the heater, the reaction rate became only 4% although it heated for a long time. From this, it turned out that the effect of Examples 1-9 is an effect acquired by combining a microwave and EDTA.

3. Particle Size Distribution Evaluation TEM photographs were taken for Examples 8 and 9 and Comparative Examples 5 and 6 synthesized in a high concentration region where the concentration of silver nitrate was 300 mM or more. A TEM photograph of the silver nanoparticles obtained in Example 8 is shown in FIG. 4, a TEM photograph of the silver nanoparticles obtained in Example 9 is shown in FIG. 5, and a TEM of the silver nanoparticles obtained in Comparative Example 5 is shown. A photograph is shown in FIG. 6, and a TEM photograph of the silver nanoparticles obtained in Comparative Example 6 is shown in FIG.

  4 and 5 are compared with FIG. 6, the silver nanoparticles obtained by the preparation methods of Examples 8 and 9 are the same as the silver nanoparticles obtained by the preparation method of Comparative Example 5 which is a conventional method. In comparison, it was found that the particle size distribution was uniform and the quality was high. Further, the silver nanoparticles obtained by the preparation method of Comparative Example 5 were intensely aggregated.

  Further, when FIG. 4 is compared with FIG. 7, the silver nanoparticles obtained by the preparation method of Example 8 have a uniform particle size distribution as compared with the silver nanoparticles obtained by the preparation method of Comparative Example 6. It was found to be high quality. In the preparation method of Comparative Example 6, since both trisodium citrate and EDTA are present in the raw material solution, there are two types of reduction: reduction by trisodium citrate and reduction by EDTA that occurs by irradiation with microwaves. It is considered that the generation of particles is varied and the particle size distribution is widened.

Claims (1)

A method for producing metal nanoparticles comprising a step of irradiating a raw material solution with microwaves,
The raw material solution contains a solvent, one or more chelating agents selected from ethylenediaminetetraacetic acid, ethylenediaminetriacetic acid, ethylenediaminediacetic acid and their salts, and a metal compound,
The molar ratio of the chelating agent to the metal in the metal compound (the amount of the chelating agent / the amount of the metal) is 0.067 to 3.00,
The raw material solution does not contain a reducing agent selected from formic acid, citric acid and salts thereof;
Said method.