JP2019167595A - Production method of nano-particles of precious metal - Google Patents

Abstract

To provide a method capable of producing particles of a precious metal having smaller particle size.SOLUTION: A method of producing nano-particles of a precious metal by mixing a liquid containing a precious metal ion and a liquid containing a reduction agent, the production method including: a step of mixing a liquid containing a precious metal ion and a liquid containing a reducing agent by converging a first flow path 11 transporting a liquid containing a precious metal ion, and a second flow path 12 transporting a liquid containing a reducing agent; a first heating step of heating the liquid containing the reducing agent before mixing; and a second heating step of heating the liquid after mixing, in which the first heating step and the second heating step heat the flow paths at a temperature set at 100°C or higher.SELECTED DRAWING: Figure 1

Description

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

The demand for noble metal particles having a small particle diameter is increasing in various applications. For example, etching has been used to form a fine conductor pattern on a circuit board. Recently, an ink composition to which noble metal particles are added is sprayed to form a conductor pattern. In addition, conductive films in which noble metal particles having a small particle diameter are blended are also used for touch screens that require conductivity and transparency.

The above-mentioned noble metal particles having a small particle diameter are, for example, silver, liquefied silver with an acid or the like and a reducing agent are put into a container such as a flask and heated while stirring with a stir bar. , Produced by reducing silver ions into silver particles. Silver particles obtained by such a batch-type method have a large variation in particle size, and many particles having a particle size of 40 to 50 nm are contained.

Moreover, for example, as described in Patent Document 1, a method of continuously producing metal particles having a small particle diameter using a microreactor is also known. In this method, the liquid A containing the first metal ion and the second metal ion and the liquid B containing the reducing agent are mixed using a microreactor. According to this method, copper particles having a number average particle diameter of 20 nm can be produced.

JP 2015-48494 A

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

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

A method of producing a noble metal nanoparticle by mixing a liquid containing a noble metal ion and a liquid containing a reducing agent, the production method comprising a flow path for conveying a liquid containing a noble metal ion, A step of mixing the liquid containing the noble metal ion and the liquid containing the reducing agent by joining the flow path for transporting the liquid containing the reducing agent, and the step of heating the liquid containing the reducing agent before mixing. A first heating step and a second heating step for heating the mixed liquid, wherein the first heating step and the second heating step heat the flow path at a set temperature of 100 ° C. or higher. The above problem is solved by a method for 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. In the above manufacturing method, it is preferable that the mixed liquid is transported by the flow path, and the flow path for transporting the mixed liquid is configured to bypass.

ADVANTAGE OF THE INVENTION According to this invention, the method which can manufacture the particle | grains of a noble metal with a smaller particle diameter can be provided.

It is a figure which shows the structure of one Embodiment of the manufacturing apparatus of the noble metal nanoparticle. It is a figure which shows the cross section of the principal part of the connection part of FIG. It is a figure which shows the particle size distribution of the suspension of the silver particle manufactured by the method of Example 1 or Comparative Example 1. 2 is a TEM photograph (magnification of 250,000 times) of silver particles produced by the method of Example 1. FIG. 4 is a TEM photograph (magnification of 250,000 times) of gold particles produced by the method of Example 2. FIG. 2 is a TEM photograph (magnification of 250,000 times) of silver particles produced by the method of Comparative Example 1. FIG. 4 is a TEM photograph (magnification of 250,000 times) of platinum particles produced by the method of Example 3. FIG.

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

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

The method of the present embodiment includes a liquid containing a noble metal ion and a liquid containing a reducing agent by joining a flow path that carries a liquid containing noble metal ions and a flow path that carries a liquid containing a reducing agent. , A first heating step for heating the liquid containing the reducing agent before mixing, and a second heating step for heating the liquid after mixing. And in a 1st heating process and a 2nd heating process, a channel is heated at preset temperature of 100 ° C or more.

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 to increase the temperature of the liquid containing the reducing agent in advance. In the 2nd heating process, it carries out in order to prevent the temperature of a liquid mixture falling.

In both the first heating step and the second heating step, each channel is heated at a set temperature of 100 ° C. or higher, for example, a nanoscale noble metal having an average particle diameter of 10 nm or less, more preferably 6 nm or less. Particles can be produced. Here, the average particle diameter is an average particle diameter of primary particles of noble metal. The average particle diameter is calculated by selecting a plurality of primary particles from a transmission electron micrograph of the particles. The major axis diameter of the selected particle shape is measured using image analysis software. The sum of the values of the major axis diameters is divided 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 precious metal ions before mixing and the liquid after mixing becomes low, the yield of nanoscale precious metal particles having an average particle diameter of 10 nm or less is lowered. 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 reduced. Conversely, when the set temperature in the first heating step and the second heating step increases, the amount of nanoscale noble metal particles having an average particle diameter of 10 nm or less tends to increase. For this reason, 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 reaches a peak even if the temperature is excessively increased and energy is wasted. It is preferable to set it as follows, It is more preferable to set it as 150 degrees C or less, It is further more preferable to set it as 130 degrees C or less.

In the first heating process and the second heating process, when heating each flow path, 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 becomes equal to the set temperature before reaching the back pressure valve. For that purpose, it is necessary to make each flow path long. However, if the flow path is lengthened, the flow path becomes longer. For this reason, it is preferable to make the flow path which conveys the liquid containing a noble metal ion into 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.

Nanoscale noble metal particles have a small particle size, and may aggregate after production depending on conditions. For this reason, the liquid containing a noble metal ion, 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 nanofiber, polyvinylpyrrolidone and the like can be used.

Any noble metal ion may be used as long as it is reduced by a reducing agent. For example, one or more types of noble metal ions selected from the group consisting of Cu, Ag, Au, Ni, Pd, Pt, Co, Ir, Ru, CoNi, and FeNi can be given. These metals are homologous or close to each other. It is common for elements of the same family and adjacent groups to be reduced in the same reaction system.

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

Examples of the reducing agent include hydrazine, formic acid, sodium borohydride, or alcohols such as ethanol and methanol. As a solvent for 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 such that the temperature is higher than the boiling point of the liquid containing the noble metal ions and the liquid containing the reducing agent and the pressurizing condition.

The method for producing noble metal nanoparticles of the above-described embodiment can be performed by, for example, the noble metal nanoparticle production apparatus shown in FIG.

The nanoparticle production apparatus 1 in FIG. 1 includes a first channel 11 that transports a liquid containing noble metal ions, a second channel 12 that transports a liquid containing a reducing agent, a first channel 11, and a first channel 11. It has the connection part 13 of the two flow paths 12, the 3rd flow path 14 which conveys the liquid mixed by the connection part 13, and the back pressure valve 15 provided in the 3rd flow path 14. FIG.

The first flow path may be configured to be able to transport a liquid containing noble metal ions. For example, as shown in FIG. 1, the first flow path can be configured from a tube configured to allow liquid to flow through an interior configured to allow liquid flow. A liquid containing noble metal ions stored in the first container 17 can be supplied to the first flow path 11 using, for example, a pump 16. In the example of FIG. 1, a beaker is used as the first container. As the first container, other containers such as a flask can be used.

The second flow path may be configured to be able to transport a liquid containing a reducing agent. For example, as shown in FIG. 1, the 2nd flow path 12 can be comprised from the pipe | tube comprised so that liquid flow was possible. For example, a liquid containing a reducing agent stored in the second container 19 can be supplied to the second flow path 12 by using a pump 18. In the example of FIG. 1, a beaker is used as the second container. Other containers such as flasks can be used as the second container.
The

The connecting portion 13 joins the first flow path 11 and the second flow path 12, and the liquid containing noble metal ions transferred from the first flow path 11 and the reducing agent transferred from the second flow path 12 are used. What is necessary is just to set it as the structure which can mix the liquid to contain. As the connection unit 13, for example, as shown in FIG. 2, one configured such 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 the connection part. In the example of FIG. 2, a T-shaped microreactor in which the first pipeline 21, the second pipeline 22, and the third pipeline 23 merge at one point is used. In addition, a microreactor having a Y-shaped junction may be used. In the example of FIG. 1, the first pipe line 21 is connected to the first flow path 11, the second pipe line 22 is connected to the second flow path 12, and the third pipe line 23 is the third flow path. 14.

The 3rd flow path 14 should just be set as the structure which conveys said liquid mixed in the connection part 13. As shown in FIG. For example, the 3rd flow path 14 can be comprised from the hollow pipe | tube comprised so that liquid flow was possible.

The back pressure valve 15 is configured to be able to prevent the volume of the liquid from expanding when the liquid containing the liquid containing the precious metal ions before mixing and the liquid containing the liquid after mixing are heated. That's fine. For example, it is possible to use a valve that urges a shut-off device such as a diaphragm with an elastic body such as a spring and shuts off communication in the flow path with 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 line communicates, and the liquid is discharged. Is 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 heat apparatus 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 that is the connection portion 13 is installed in the dry heat apparatus 2. When the dry heat apparatus 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 manufacturing apparatus 1 described above, it is preferable that the second flow path 12 has a bypass portion 121. That is, it is preferable that the flow path for transporting the liquid containing the reducing agent has a detour shape. Moreover, it is preferable that the third flow path 14 has a bypass 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 increasing 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, and even more preferably 8 m or more from the viewpoint of heating the liquid containing the reducing agent to 100 ° C. or more. . The upper limit of the length of the second flow path 12 is not particularly limited, but 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 ions, and the deposited noble metal to 100 ° C. or more. More preferably, it is 8 m or more. The upper limit of the length of the third flow path 14 is not particularly limited, but is preferably 30 m or less from the viewpoint of space saving. The length here refers to the length of the flow path in a state where the detour portion is linearly extended.

The residence time from when the liquid is supplied to the second flow path 12 until it is discharged 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 preferable to set it to 480 seconds or more. The upper limit of the residence time is not particularly limited, but is preferably 1800 seconds or less from the viewpoint of increasing the production amount of silver particles within a unit time.

A 1st flow path, a 2nd flow path, or a 3rd flow path can be comprised from 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, an example is given and it demonstrates more concretely.

As a device shown in FIG. 1, a microreactor was used to produce noble metal particles. The microreactor has a T-shaped bottleneck similar to that shown in FIG. 2, and the inner diameter of the pipe is 140 μm. Each pipe line is connected to the first flow path, the second flow path, and the third flow path. The first channel is inserted into a flask for storing an aqueous solution containing noble metal ions. The aqueous solution containing noble metal ions is conveyed through the first flow path by a pump. The 2nd channel is inserted in the flask which stores the methanol aqueous solution which is a reducing agent. A back pressure valve is provided at the end of the third flow path so that when the second flow path and the third flow path are heated, liquid in each flow path boils and bubbles are not generated. Has been.

The microreactor and the first channel, the second channel, and the third channel connected to the microreactor are installed in the dry heat apparatus. The second flow path and the third flow path are provided with detours so that the liquid flowing through each flow path is heated until it becomes equal to the set temperature of the dry heat apparatus. 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 polytetrafluoroethylene resin.

[Example 1]
Silver particles were produced under the following conditions using an apparatus in which the above microreactor and dry heat apparatus were combined. 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 a room temperature of about 10 to 26 ° C. The dry heat apparatus was set to 120 ° C., and the first flow path, the second flow path, and the third flow path were preheated. After completion of preheating, the pump was operated to supply an aqueous solution containing silver nitrate from the first channel at a flow rate of 1 ml / min, and a methanol solution 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 liquid discharged from the back pressure valve was received in a flask storing 100 ml of an aqueous solution containing 1 g of polyvinylpyrrolidone K30 (manufactured by Wako Pure Chemical Industries, Ltd.), and this was successively subjected to ultrafiltration and concentrated. . The solid content was collected and suspended in 50 ml of an aqueous solution to obtain a suspension of silver particles.

[Example 2]
Gold particles were produced under the following conditions using an apparatus in which the above microreactor and dry heat apparatus were combined. That is, an aqueous solution containing 0.5 mM tetrachloroauric acid tetrahydrate is stored in a 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 a room temperature of about 10 to 26 ° C. The dry heat apparatus was set to 120 ° C., and the first flow path, the second flow path, and the third flow path were preheated. After completion of preheating, 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 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 liquid discharged from the back pressure valve was received in a flask storing 100 ml of an aqueous solution containing 1 g of polyvinylpyrrolidone K30 (manufactured by Wako Pure Chemical Industries, Ltd.), and this was successively subjected to ultrafiltration and concentrated. . The solid content was collected and suspended in 50 ml of an aqueous solution to obtain a suspension of gold particles.

[Example 3]
Platinum particles were produced under the following conditions using an apparatus in which the above microreactor and dry heat apparatus were combined. 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 a room temperature of about 10 to 26 ° C. The dry heat apparatus was set to 120 ° C., and the first flow path, the second flow path, and the third flow path were preheated. After completion of preheating, the pump is operated to supply an aqueous solution containing hexachloroplatinic acid hexahydrate from the first channel at a flow rate of 1 ml / min, and methanol solution from the second channel at a flow rate of 1 ml / min. did. The methanol solution and the aqueous solution containing hexachloroplatinic acid hexahydrate are fluidly mixed at the connection portion. The mixed liquid discharged from the back pressure valve was received in a flask storing 100 ml of an aqueous solution containing 1 g of polyvinylpyrrolidone K30 (manufactured by Wako Pure Chemical Industries, Ltd.), and this was successively subjected to ultrafiltration and concentrated. . The solid content was collected and suspended in 50 ml of an aqueous solution to obtain a suspension of platinum particles.

[Comparative Example 1]
A silver particle suspension was produced in the same manner as in Example 1 except that the set temperature of the dry heat apparatus was changed to 80 ° C.

A suspension of silver particles obtained by the method of Example 1, Example 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 adjusted using and the electron micrograph was image | photographed using the transmission electron micrograph apparatus (TEM) (JEOL Co., Ltd. JEM-2100). 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 addition, when taking a TEM photograph, sample adjustment was performed as follows. A few drops of each suspension was dropped onto a copper mesh with a carbon support film (Ultra High Reso Carbon manufactured by Oken Shoji Co., Ltd.) and air-dried to obtain an observation sample.

From the photographed electron microscopic images, 50 particles with clear and dark and capable of discriminating the contour of the particles were selected, and the major axis diameter of the particles was measured using image analysis software and 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 a particle size distribution calculated by image analysis of a TEM photograph.

As shown in the particle size distribution of FIG. 3, the average particle diameter of the silver particles obtained in Example 1 and the upper limit value of the particle distribution range and the lower limit value of the particle distribution range are smaller than those in Comparative Example 1. I understand that. Moreover, it turns out that the average particle diameter of the gold particle obtained 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 laser light, 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 laser light, only a very small optical path of the laser due to the Tyndall phenomenon was observed. Therefore, in the method of Comparative Example 1, it was necessary to collect the mixed fluid discharged from the microreactor in a large amount (approximately 20 times the liquid amount of the method of Example 1) and to concentrate by ultrafiltration. From this, it can be seen that the method of Example 1 is superior 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 with high yield. Moreover, according to the method of Example 3, nanoscale platinum particles having an average particle diameter of 6 nm or less can be obtained efficiently. Silver particles, gold particles, or platinum particles having a small particle diameter 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 silver particles, gold particles, or platinum particles are used as a catalyst, the amount of silver particles, gold particles, or platinum particles used can be reduced.

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

Further, for example, in a conductive film for a touch screen, the light transmittance improves as the particle diameter of silver particles, gold particles, or platinum particles to be blended decreases.

Silver particles, gold particles, or platinum particles produced by the methods of the above-described embodiments have a smaller particle size than conventional ones, and the variation in particle size is also small. For this reason, it can be suitably used for various applications. Moreover, in the method of Example 1, Example 2, and Example 3, since it is excellent in a yield, the silver particle, gold particle, or platinum particle whose average particle diameter is 6 nm or less is manufactured for a short time and continuously. be able to.

Claims (3)

A method of producing a noble metal nanoparticle by mixing a liquid containing a noble metal ion and a liquid containing a reducing agent,
The manufacturing method mixes a liquid containing noble metal ions and a liquid containing reducing agents by combining a flow path for transferring liquids containing noble metal ions and a flow path for transferring liquids containing a reducing agent. And a process of
A first heating step of heating the liquid containing the reducing agent before mixing;
A second heating step of heating the liquid after mixing,
A 1st heating process and a 2nd heating process are the manufacturing methods of the noble metal nanoparticle which heats a flow path at the preset temperature of 100 degreeC or more. The method for producing nanoparticles of noble metal according to claim 1, wherein the flow path for transporting the liquid containing the reducing agent has a detour shape. 3. The method for producing noble metal nanoparticles according to claim 1 or 2, wherein the flow path for transporting the mixed liquid has a detour shape.