JP7054138B2 - Method for manufacturing precious metal nanoparticles - Google Patents

Description

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

Precious metal particles with a small particle size are in increasing demand for various applications. For example, etching has been used to form a minute conductor pattern of a circuit board, but recently, an ink composition containing precious metal particles is sprayed to form a conductor pattern. Further, a conductive film or the like containing precious metal particles having a small particle diameter is also used for a touch screen that requires conductivity and transparency.

For the precious metal particles having a small particle size as described above, for example, silver is liquefied with an acid or the like and a reducing agent is put into a container such as a flask and heated while stirring with a stirrer. , Manufactured by reducing silver ions into silver particles. The silver particles obtained by such a batch method have a large variation in particle size, and include many particles having a particle size of 40 to 50 nm.

Further, for example, as described in Patent Document 1, a method of continuously producing metal particles having a small particle diameter by using a microreactor is also known. In this method, a liquid A containing a first metal ion and a second metal ion and a liquid B containing a reducing agent are mixed using a microreactor. It is said that this method can produce copper particles having a number average particle diameter of 20 nm.

JP-A-2015-48494A

The number average particle size obtained by the method of Patent Document 1 is 20 nm, and precious metal particles having a smaller particle size are desired.

It is an object of the present invention to provide a method capable of producing particles of a noble metal having a smaller particle size.

A method for producing noble metal nanoparticles by mixing a liquid containing noble metal ions and a liquid containing a reducing agent, and the production method includes a flow path for transporting the liquid containing noble metal ions. The step of mixing the liquid containing the noble metal ion and the liquid containing the reducing agent by merging with the flow path for transporting the liquid containing the reducing agent, and the step of heating the liquid containing the reducing agent before mixing. The first heating step and the second heating step include a first heating step and a second heating step of heating the liquid after mixing, and the first heating step and the second heating step are for heating the flow path at a set temperature of 100 ° C. or higher. The above-mentioned problems are solved by the method of producing particles.

In the above manufacturing method, it is preferable that the flow path for transporting the liquid containing the reducing agent has a detour shape. Further, in the above manufacturing method, it is preferable that the mixed liquid is conveyed by the flow path, and the flow path for conveying the mixed liquid is detoured.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a method capable of producing particles of a noble metal having a smaller particle size.

It is a figure which shows the structure of one Embodiment of the manufacturing apparatus of the nanoparticle of a noble metal. It is a figure which shows the cross section of the main part of the connection part of FIG. It is a figure which shows the particle size distribution of the suspension of silver particles produced by the method of Example 1 or Comparative Example 1. 6 is a TEM photograph (magnification of 250,000 times) of silver particles produced by the method of Example 1. 6 is a TEM photograph (magnification of 250,000 times) of gold particles produced by the method of Example 2. 6 is a TEM photograph (magnification of 250,000 times) of silver particles produced by the method of Comparative Example 1. 3 is a TEM photograph (magnification of 250,000 times) of platinum particles produced by the method of Example 3.

Hereinafter, preferred embodiments of the present invention will be described.

The method of the present embodiment is a method of producing nanoscale noble metal particles (noble metal nanoparticles) by mixing a liquid containing noble metal ions and a liquid containing a reducing agent.

In the method of the present embodiment, a flow path for transporting a liquid containing a noble metal ion and a flow path for transporting a liquid containing a reducing agent are merged to form a liquid containing a noble metal ion and a liquid containing a reducing agent. A step of heating the liquid containing the reducing agent before mixing, and a second heating step of heating the liquid after mixing are included. Then, in the first heating step and the second heating step, the flow path is heated at a set temperature of 100 ° C. or higher.

In the method of the above embodiment, the flow path is heated at a set temperature of 100 ° C. or higher in both the first heating step and the second heating step. The first heating step is performed in order to raise the temperature of the liquid containing the reducing agent in advance. The second heating step is performed in order to prevent the temperature of the mixed solution from dropping.

By heating each flow path at a set temperature of 100 ° C. or higher in both the first heating step and the second heating step, for example, a nanoscale noble metal having an average particle size of 10 nm or less, more preferably 6 nm or less. Particles can be produced. Here, the average particle size is the average particle size of the primary particles of the noble metal. As a method for calculating the average particle size, a plurality of primary particles are selected from the transmission electron micrographs of the particles. The shape of the selected particles is measured for the major axis diameter using image analysis software. Divide the sum of the values of each major axis diameter by the number to obtain the average particle diameter.

The set temperature for heating in the first heating step and the second heating step is 100 ° C. or higher. When the temperature of the liquid containing the noble metal ion before mixing and the liquid after mixing becomes low, the yield of nanoscale noble metal particles having an average particle diameter of 10 nm or less decreases. This is because when the temperature is lowered, the amount of nanoscale noble metal particles having an average particle diameter of 10 nm or less is lowered. On the contrary, when the set temperature in the first heating step and the second heating step becomes high, the amount of nanoscale noble metal particles having an average particle diameter of 10 nm or less tends to increase. Therefore, it is more preferable that the first heating step and the second heating step heat the flow path at a temperature of 110 ° C. or higher. The first heating step and the second heating step are preferably heated under pressure from the viewpoint of enabling high temperature heating. The upper limit of the set temperature when heating the flow path in the first heating step and the second heating step is 180 ° C. because the effect of improving the yield even if the temperature is excessively raised reaches a plateau and energy is wasted. The temperature is preferably as follows, more preferably 150 ° C. or lower, and even more preferably 130 ° C. or lower.

When heating each flow path in the first heating step and the second heating step, it is preferable that the temperature of the liquid flowing through each flow path is equal to the set temperature. In the second heating step, it is preferable that the temperature of the liquid reaches the set temperature up to the back pressure valve. For that purpose, it is necessary to configure each flow path long. However, if the flow path is lengthened, the flow path becomes long. Therefore, it is preferable that the flow path for transporting the liquid containing the noble metal ion has a detoured shape. Similarly, it is preferable that the flow path for transporting the mixed liquid has a detoured shape. Examples of the detoured shape include a shape in which the flow path is curved so as to have a zigzag shape or a spiral shape.

Since nanoscale noble metal particles have a small particle size, they may aggregate after production depending on the conditions. Therefore, the liquid containing noble metal ions, the liquid containing a reducing agent, or the liquid discharged from the back pressure valve may contain a dispersant. As the dispersant, for example, polyvinyl alcohol, cellulose nanofibers, polyvinylpyrrolidone and the like can be used.

The noble metal ion may be one that is reduced by a reducing agent. For example, ions of one or more precious metals selected from the group consisting of Cu, Ag, Au, Ni, Pd, Pt, Co, Ir, Ru, CoNi, and FeNi can be mentioned. These metals are of the same family or close to each other. Homogeneous elements and elements of neighboring groups are generally reduced in the same reaction system.

In the liquid containing noble metal ions, the source of the noble metal ions includes nitrates, sulfates, acetates of noble metals, halides of noble metals, complexes of halogens and noble metals, and the like. Since they are soluble in polar solvents such as water, they can be suitably used for fluid mixing. Examples of the source of ions of the noble metal include silver nitrate, tetrachlorogold acid tetrahydrate, hexachloroplatinic acid hexahydrate and the like.

Examples of the reducing agent include hydrazine, formic acid, sodium borohydride, and alcohols such as ethanol and methanol. As the solvent of the reducing agent, for example, water can be used. Since the above reducing agent is soluble in a polar solvent such as water, it can be suitably used for fluid mixing.

The heating in the first heating step and the second heating step is preferably performed so that the temperature is equal to or higher than the boiling point of the liquid containing the noble metal ion and the liquid containing the reducing agent and the pressure conditions are met.

The method for producing nanoparticles of noble metal according to the above embodiment can be carried out by, for example, the apparatus for producing nanoparticles of noble metal shown in FIG.

In the nanoparticle manufacturing apparatus 1 of FIG. 1, the first flow path 11 for transporting a liquid containing a noble metal ion, the second flow path 12 for transporting a liquid containing a reducing agent, the first flow path 11 and the first flow path 11 It has a connection portion 13 of the two flow paths 12, a third flow path 14 for transporting the liquid mixed in the connection portion 13, and a back pressure valve 15 provided in the third flow path 14.

The first flow path may be configured to be capable of transporting a liquid containing noble metal ions. For example, as shown in FIG. 1, the first flow path can be composed of a tube configured to allow liquid to flow inside, which is configured to allow liquid to pass through. For example, a pump 16 can be used to supply the noble metal ion-containing liquid stored in the first container 17 to the first flow path 11. In the example of FIG. 1, a beaker is used as the first container. As the first container, another container such as a flask can be used.

The second flow path may be configured to be capable of transporting a liquid containing a reducing agent. For example, as shown in FIG. 1, the second flow path 12 can be composed of a tube configured to allow liquid to pass through. For example, a pump 18 can be used to supply the liquid containing the reducing agent stored in the second container 19 to the second flow path 12. In the example of FIG. 1, a beaker is used as the second container. As the second container, another container such as a flask can be used.
To.

The connecting portion 13 joins the first flow path 11 and the second flow path 12 to combine the liquid containing the noble metal ion conveyed from the first flow path 11 and the reducing agent conveyed from the second flow path 12. It may be configured so that it can be mixed with the contained liquid. As the connecting portion 13, for example, as shown in FIG. 2, one configured so that the first pipeline 21, the second pipeline 22, and the third pipeline 23 merge can be used. When manufacturing on a small scale, a microreactor can be suitably used as a connection part. In the example of FIG. 2, a T-shaped microreactor in which the first line 21, the second line 22, and the third line 23 meet at one point was used. In addition, a microreactor having a Y-shaped confluence may be used. In the example of FIG. 1, the first pipeline 21 is connected to the first flow path 11, the second pipeline 22 is connected to the second flow path 12, and the third pipeline 23 is connected to the third flow path. It is connected to 14.

The third flow path 14 may be configured to convey the above liquid mixed by the connecting portion 13. For example, the third flow path 14 can be composed of a hollow tube configured to allow liquid to pass through.

The back pressure valve 15 has a configuration capable of preventing the volume of the liquid containing the noble metal ion before mixing and the liquid containing the liquid after mixing from expanding when the liquid is heated. Just do it. For example, it is possible to use a valve in which a barrier such as a diaphragm is urged by an elastic body such as a spring and the communication in the flow path is blocked by the diaphragm. In such a valve, when the pressure in the pipeline exceeds the urging force of the elastic body, the breaker is pushed up against the urging force of the elastic body, the blocked pipeline communicates, and the liquid is discharged. Will be done.

In the above manufacturing apparatus, if at least the second flow path 12 and the third flow path 14 are heated by a heating unit such as a dry heating device or an electric heating coil, the liquid containing the reducing agent before mixing is mixed with the liquid after mixing. It is possible to heat the liquid. In FIG. 1, the microreactor, which is the connection portion 13, is installed in the dry heat device 2. When the drying heat device 2 is operated, the first flow path 11, the second flow path 12, and the third flow path 14 connected to the microreactor are heated.

In the above-mentioned manufacturing apparatus 1, it is preferable that the second flow path 12 has a detour portion 121. That is, it is preferable that the flow path for transporting the liquid containing the reducing agent has a detour shape. Further, it is preferable that the third flow path 14 has a detour portion 141. That is, it is preferable that the flow path for transporting the mixed liquid has a detour shape. This makes it possible to configure the second flow path or the third flow path in a space-saving manner while gaining the residence time of the liquid in the second flow path or the third flow path.

The length of the second flow path 12 is preferably 2 m or more, more preferably 5 m or more, still more preferably 8 m or more, from the viewpoint of heating the liquid containing the reducing agent to 100 ° C. or higher. .. There is no particular upper limit to the length of the second flow path 12, but it is preferably 20 m or less from the viewpoint of space saving. The length of the third flow path 14 is preferably 2 m or more, more preferably 5 m or more, from the viewpoint of heating the liquid containing the reducing agent, the noble metal ion, and the precipitated noble metal to 100 ° C. or higher. It is more preferably 8 m or more. There is no particular upper limit to the length of the third flow path 14, but it is preferably 30 m or less from the viewpoint of space saving. The length here means the length of the flow path in a state where the detour portion is extended in a straight line.

The residence time from the supply of the liquid to the second flow path 12 to the discharge from the third flow path 14 is 300 seconds or more from the viewpoint of heating the liquid containing the reducing agent and the silver salt to 100 ° C. or higher. It is preferably 480 seconds or longer. There is no particular upper limit to the residence time, but it is preferably 1800 seconds or less from the viewpoint of increasing the production amount of silver particles within a unit time.

The first flow path, the second flow path, or the third flow path can be made of various materials. For example, the first flow path, the second flow path, or the third flow path is preferably composed of a metal material such as stainless steel or a synthetic resin such as polytetrafluoroethylene.

The inner diameter of the first flow path, the second flow path, or the third flow path is preferably 0.01 to 1 mm.

Hereinafter, a more specific description will be given with reference to examples.

A microreactor was used as the apparatus shown in FIG. 1 to produce precious metal particles. The microreactor has a T-shaped conduit similar to that shown in FIG. 2, and the inner diameter of the conduit is 140 μm. Each pipeline is connected to a first flow path, a second flow path, and a third flow path. The first flow path is inserted into a flask for storing an aqueous solution containing noble metal ions. The aqueous solution containing noble metal ions is conveyed in the first flow path by a pump. The second flow path is inserted into a flask for storing an aqueous solution of methanol as a reducing agent. A back pressure valve is provided at the end of the third flow path so that the liquid in each flow path does not boil and bubbles are generated when the second flow path and the third flow path are heated. Has been done.

The microreactor and the first flow path, the second flow path, and the third flow path connected to the microreactor are installed in the dry heat device. The second flow path and the third flow path are provided with detour portions so that the liquid flowing through each flow path is heated until the temperature becomes equal to the set temperature of the drying heat device. The length of the detour portion of the second flow path is 10 m, and the length of the detour portion of the third flow path is 5 m. The first flow path, the second flow path, and the third flow path are made of a polytetrafluoroethylene resin.

[Example 1]
Using a device combining the above microreactor and a drying and heating device, silver particles were produced under the following conditions. That is, an aqueous solution containing 3.5 mM silver nitrate was stored in the flask connected to the first flow path, and 99.8% (special grade) methanol solution was stored in the flask connected to the second flow path. .. The liquid temperature of both liquids is about 10 to 26 ° C. at room temperature. The dry heat device was set to 120 ° C., and the first flow path, the second flow path, and the third flow path were preheated. After the preheating was completed, the pump was operated to supply an aqueous solution containing silver nitrate at a flow rate of 1 ml / min from the first channel, and a methanol solution was supplied from the second channel at a flow rate of 1 ml / min. The methanol solution and the aqueous solution containing silver nitrate are fluidly mixed at the connection portion. The mixed solution discharged from the back pressure valve was received in a flask containing 100 ml of an aqueous solution containing 1 g of polyvinylpyrrolidone K30 (manufactured by Wako Pure Chemical Industries, Ltd.), and this was sequentially subjected to ultrafiltration and concentrated. .. The solid content was collected and suspended in a 50 ml aqueous solution to obtain a suspension of silver particles.

[Example 2]
Gold particles were produced under the following conditions using a device combining the above microreactor and a drying and heating device. That is, an aqueous solution containing 0.5 mM tetrachloroauric acid tetrahydrate is stored in the flask connected to the first flow path, and 99.8% (special grade) is stored in the flask connected to the second flow path. ) The methanol solution was stored. The liquid temperature of both liquids is about 10 to 26 ° C. at room temperature. The dry heat device was set to 120 ° C., and the first flow path, the second flow path, and the third flow path were preheated. After the preheating is completed, the pump is operated to supply an aqueous solution containing tetrachloroauric acid tetrahydrate from the first channel at a flow rate of 1 ml / min, and a methanol solution is supplied from the second channel at a flow rate of 1 ml / min. Supplied. The methanol solution and the aqueous solution containing tetrachloroauric acid tetrahydrate are fluidly mixed at the connection portion. The mixed solution discharged from the back pressure valve was received in a flask containing 100 ml of an aqueous solution containing 1 g of polyvinylpyrrolidone K30 (manufactured by Wako Pure Chemical Industries, Ltd.), and this was sequentially subjected to ultrafiltration and concentrated. .. The solid content was collected and suspended in a 50 ml aqueous solution to obtain a suspension of gold particles.

[Example 3]
Platinum particles were produced under the following conditions using a device combining the above microreactor and a drying and heating device. That is, an aqueous solution containing 0.04 mM hexachloroplatinic acid hexahydrate is stored in the flask connected to the first flow path, and 99.8% (special grade) is stored in the flask connected to the second flow path. The methanol solution was stored. The liquid temperature of both liquids is about 10 to 26 ° C. at room temperature. The dry heat device was set to 120 ° C., and the first flow path, the second flow path, and the third flow path were preheated. After the preheating is completed, the pump is operated to supply an aqueous solution containing hexachloroplatinic acid hexahydrate at a flow rate of 1 ml / min from the first flow path, and a methanol solution is supplied from the second flow rate at a flow rate of 1 ml / min. bottom. The methanol solution and the aqueous solution containing hexachloroplatinic acid hexahydrate are fluidly mixed at the connection portion. The mixed solution discharged from the back pressure valve was received in a flask containing 100 ml of an aqueous solution containing 1 g of polyvinylpyrrolidone K30 (manufactured by Wako Pure Chemical Industries, Ltd.), and this was sequentially subjected to ultrafiltration and concentrated. .. The solid content was collected and suspended in a 50 ml aqueous solution to obtain a suspension of platinum particles.

[Comparative Example 1]
A suspension of silver particles was produced in the same manner as in Example 1 except that the set temperature of the drying device was changed to 80 ° C.

A suspension of silver particles obtained by the methods of Examples 1, 2 and Comparative Example 1, a suspension of gold particles obtained by the method of Example 2, and a suspension of platinum particles of Example 3. The sample was prepared using and, and an electron micrograph was taken using a transmission type electron micrograph (TEM) (JEM-2100 manufactured by Nippon Denshi Co., Ltd.). The electron micrograph of Example 1 is shown in FIG. 4, the electron micrograph of Example 2 is shown in FIG. 5, the electron micrograph of Comparative Example 1 is shown in FIG. 6, and the electron micrograph of Example 3 is shown in FIG. In taking the TEM photograph, the sample was adjusted as follows. A few drops of each suspension were dropped onto a copper mesh with a carbon support film (Ultra High Reso Carbon manufactured by Ohken Shoji Co., Ltd.), and the air-dried sample was used as an observation sample.

From the captured electron microscope images, 50 particles whose light and darkness was clear and the contours of the particles could be discriminated were selected, the major axis diameters of the particles were measured using image analysis software, and the particles were averaged. The average particle size of Example 1 was 2.5 nm, and the average particle size of Comparative Example 1 was 6.5 nm. The average particle size of Example 2 was 2.6 nm. The average particle size of Example 3 was 5.11 nm (standard deviation ± 1.19 nm). FIG. 3 shows the particle size distribution calculated by image analysis of TEM photographs.

As shown in the particle size distribution in FIG. 3, the average particle diameter of silver particles obtained in Example 1 and the upper limit of the particle distribution range and the lower limit of the particle distribution range are smaller in Example 1 than in Comparative Example 1. You can see that. Further, it can be seen that the average particle size of the obtained gold particles in Example 2 is smaller than that in Comparative Example 1.

In the method of Example 1, when the mixed fluid discharged from the microreactor was irradiated with the laser beam, the optical path of the laser due to the Tyndall phenomenon was clearly confirmed. On the other hand, in the method of Comparative Example 1, when the mixed fluid discharged from the microreactor was irradiated with the laser beam, the optical path of the laser due to the Tyndall phenomenon was observed only slightly. Therefore, in the method of Comparative Example 1, it was necessary to collect a large amount of the mixed fluid discharged from the microreactor (a liquid volume about 20 times that of the method of Example 1) and concentrate it by ultrafiltration. From this, it can be seen that the method of Example 1 is excellent in yield, and the method of Comparative Example 1 is inferior in yield.

According to the method of Example 1 or Example 2, nanoscale silver particles or gold particles having an average particle diameter of 5 nm or less can be obtained in good yield. Further, according to the method of Example 3, nanoscale platinum particles having an average particle diameter of 6 nm or less can be efficiently obtained. Silver particles, gold particles or platinum particles having a small particle size have a large surface area per unit weight. For example, when silver particles are used as an antibacterial agent, the amount of silver particles used can be reduced. Further, when the silver particles, the gold particles or the platinum particles are used as a catalyst, the amount of the silver particles, the gold particles or the platinum particles used can be reduced.

Further, for example, in the case of a suspension of silver particles, gold particles or platinum particles, the smaller the particle size of the silver particles, gold particles or platinum particles, the more the liquid and the silver particles, gold particles or platinum particles are separated. It takes longer time. If the silver particles, gold particles or platinum particles have a smaller particle size, the silver particles, gold particles or platinum particles can maintain a stable state for a long period of time.

Further, for example, in a conductive film for a touch screen, the smaller the particle size of the silver particles, gold particles or platinum particles to be blended, the better the light transmission.

The silver particles, gold particles, or platinum particles produced by the methods of each of the above examples have a smaller particle size than the conventional one, and the variation in particle size is also small. Therefore, it can be suitably used for various purposes. Further, since the methods of Example 1, Example 2, and Example 3 are excellent in yield, silver particles, gold particles, or platinum particles having an average particle diameter of 6 nm or less are continuously produced in a short time. be able to.

Claims (3)

A method for producing nanoparticles of a noble metal by mixing a liquid containing a noble metal ion and a liquid containing a reducing agent.
In the manufacturing method, a flow path for transporting a liquid containing noble metal ions and a flow path for transporting a liquid containing a reducing agent are merged to mix a liquid containing noble metal ions and a liquid containing a reducing agent. And the process of transporting the mixed liquid through the flow path,
The first heating step of heating the liquid containing the reducing agent before mixing, and
Including a second heating step of heating the liquid after mixing,
In the first heating step and the second heating step, the flow path is heated at a set temperature of 100 ° C. or higher, and the flow path is set to a temperature equal to or higher than the boiling point of the liquid containing the reducing agent and under pressure conditions. A method for producing nanoparticles of a noble metal to be heated . The method for producing nanoparticles of a noble metal according to claim 1, wherein the flow path for transporting the liquid containing the reducing agent is curved so as to gain time for the liquid to stay in the flow path . The method for producing nanoparticles of a noble metal according to claim 1 or 2, wherein the flow path for transporting the liquid after mixing is curved so as to gain time for the liquid to stay in the flow path .

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