Method for manufacturing metal nanoparticles

Abstract

To provide a technology for easily and efficiently manufacturing metal nanoparticles having a small average particle diameter and little variation in particle diameter.SOLUTION: A method for manufacturing metal nanoparticles includes the steps of: preparing a transparent base liquid that contains micelles of a nonionic surfactant by mixing a metal extraction reagent of the target metal, which has hydrophilicity, with the nonionic surfactant; and bringing the base liquid into contact with a metal solution that contains ions of the target metal to generate a microemulsion liquid in which micelles that contain the ions of the target metal are dispersed.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present application relates to a method for producing metal nanoparticles.

Background Art

[0002] Conventionally, metal nanoparticles have been widely used in various applications. For example, noble metal nanoparticles such as palladium (Pd) and platinum (Pt) are used in automotive exhaust gas purification catalysts, hydrogen storage alloys, electrode catalysts for solid polymer fuel cells, electronic components such as memories, biosensors, medical materials, and the like.

[0003] As manufacturing techniques for metal nanoparticles, for example, a vapor phase growth method disclosed in Non-Patent Document 1, a spray pyrolysis method disclosed in Non-Patent Document 2, a continuous countercurrent foam separation method disclosed in Non-Patent Document 3, and the like are known. In addition, various techniques have been proposed as manufacturing techniques for metal nanoparticles.

[0004] For example, in Patent Document 1 below, a technique using yeast that adsorbs noble metals is proposed. In Patent Document 2 below, a technique for producing palladium sub-nanoparticles using dendrimer molecules is proposed. Further, in Patent Document 3 below, a technique for generating platinum group nanoparticles using reverse micelles obtained by stirring a mixed solution containing an aqueous phase, an oil phase, and a surfactant is proposed.

Prior Art Documents

Patent Documents

[0005]

Non-Patent Document 1

Non-Patent Document 2

Non-Patent Document 3

Non-Patent Document 4

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, in the vapor phase growth method and spray pyrolysis method of the above Non-Patent Documents 1 and 2, since high-temperature treatment is involved in the manufacturing process, there are problems such as the enlargement of the device and the increase in energy consumption. In addition, in the technology using yeast of the above Patent Document 1, there are problems that the particle size of the obtained metal nanoparticles is likely to vary, and it is not easy to increase the recovery rate from the raw material of the metal constituting the metal nanoparticles.

[0007] In the case of the technology using dendrimer molecules of the above Patent Document 2, since an organic solvent is used, there is a problem that it is not easy to reduce the manufacturing cost and environmental load. In addition, regarding the technology using reverse micelles of the technology of the above Patent Document 3, since an organic solvent is used, there are the same problems as the technology of the above Patent Document 2. There is also a problem that the recovery rate of platinum recovered as platinum group nanoparticles from the raw material is about 50%, which is not high at all.

[0008] Thus, in the manufacturing technology of metal nanoparticles, there is still room for improvement in reducing the environmental impact, facilitating the manufacturing process, and enhancing the manufacturing efficiency. Also, in the manufacturing technology of metal nanoparticles, there is still room for improvement in reducing the average particle diameter of metal nanoparticles and suppressing the variation in the average particle diameter.

[0009] An object of the present invention is to provide a technique capable of easily and efficiently manufacturing metal nanoparticles having a small average particle diameter and little variation in particle diameter.

Means for Solving the Problems

[0010] The present invention can be realized, for example, in the following forms.

[0011] [First Embodiment] The first embodiment of the present invention is provided as a method for manufacturing metal nanoparticles. The manufacturing method of the first embodiment includes a step of preparing a transparent base liquid containing micelles of the nonionic surfactant by mixing a metal extraction reagent of a target metal having hydrophilicity and a nonionic surfactant, and a step of bringing the base liquid into contact with a metal solution containing ions of the target metal to generate a microemulsion liquid in which micelles containing ions of the target metal are dispersed. According to the manufacturing method of the first embodiment, even in an environment of normal temperature and pressure, a microemulsion liquid in which micelles containing metal ions are dispersed can be easily generated without using a large amount of organic solvent. According to this microemulsion liquid, by reducing the metal ions captured in the micelles, metal nanoparticles with suppressed variation in particle diameter and a small average particle diameter can be easily obtained.

[0012] [Second Embodiment] In the manufacturing process of the first embodiment, the average ethylene oxide chain length of the nonionic surfactant may be greater than 7 and 25 or less. According to the manufacturing method of the second embodiment, in the step of generating the base liquid, it is possible to suppress the micelles from growing too large and the base liquid from becoming semi-turbid, so that a transparent base liquid cannot be obtained. Therefore, the production of metal nanoparticles is made easier.

[0013] [Third Embodiment] In the manufacturing method according to any one of the first and second embodiments above, the micelles in the microemulsion solution may have an average particle size of 30 nm or less and be monodispersed. According to the manufacturing method of the third embodiment, metal nanoparticles having an average particle size smaller than 30 nm and a small variation in particle size can be obtained.

[0014] [Fourth Embodiment] In the manufacturing method according to any one of the first, second, and third embodiments above, the base liquid and the microemulsion liquid may exhibit the Tyndall phenomenon when irradiated with light in a dark place. According to the manufacturing method of the fourth embodiment, metal nanoparticles having a small average particle size and a small variation in particle size can be obtained more reliably, and the production efficiency of the metal nanoparticles can be further increased.

[0015] [Fifth Embodiment] In the manufacturing method according to any one of the first, second, third, and fourth embodiments above, the step of generating the microemulsion liquid may include: (i) in a separation tower, continuously generating foam of the base liquid from the liquid layer of the base liquid stored below, thereby forming a foam layer in which the foam moves successively from below to above; and (ii) supplying the metal solution and the base liquid to the foam layer, thereby generating the microemulsion liquid on the surface of the rising foam, flowing out and recovering the microemulsion liquid together with the foam from above the separation tower, and flowing the base liquid containing impurities back to the liquid layer below. According to the manufacturing method of the fifth embodiment, by the continuous countercurrent foam separation method, a microemulsion liquid in which micelles containing metal ions are dispersed can be continuously and efficiently generated. Therefore, the production efficiency of metal nanoparticles can be further increased.

[0016] [Sixth Embodiment] In the production method according to any one of the first, second, third, fourth, and fifth embodiments, the nonionic surfactant may be polyoxyethylene octyl phenyl ether (POOPE) or polyoxyethylene nonyl phenyl ether (PONPE). According to the production method of the sixth embodiment, a base liquid in a better state can be easily obtained. Therefore, the production of metal nanoparticles is facilitated, and the production efficiency can be further increased.

[0017] [Seventh Embodiment] In the production method according to any one of the first, second, third, fourth, fifth, and sixth embodiments, the target metal is palladium, and the metal extraction reagent may be thiodiglycolamide. According to the production method of the seventh embodiment, palladium nanoparticles with a small average particle diameter and suppressed particle diameter variation can be easily and efficiently obtained.

[0018] [Eighth Embodiment] In the production method according to any one of the first, second, third, fourth, fifth, sixth, and seventh embodiments, the concentration of the metal extraction reagent in the base liquid is 0.05 g / L or more and 5.00 g / L or less, the concentration of the nonionic surfactant is 0.50 g / L or more and 10.00 g / L or less, and the concentration of the target metal in the metal solution may be 1000 ppm or less. According to the production method of the eighth embodiment, metal nanoparticles with a small average particle diameter and suppressed particle diameter variation can be obtained more reliably.

[0019] [Ninth Embodiment] The production method according to any one of the first, second, third, fourth, fifth, sixth, seventh, and eighth embodiments may further include a step of generating nanoparticles of the target metal by drying the microemulsion solution. According to the production method of the ninth embodiment, metal nanoparticles can be easily obtained from the microemulsion liquid.

[0020] [Embodiment 10] The manufacturing method according to any one of the first, second, third, fourth, fifth, sixth, seventh, and eighth embodiments further includes mixing the base material particles and the microemulsion solution, stirring and drying them, and then firing them to generate a carrier having the nanoparticles of the target metal supported on the base material particles. According to the manufacturing method of the tenth embodiment, a carrier having metal nanoparticles supported thereon can be easily manufactured.

[0021] [Embodiment 11] The eleventh embodiment of the present invention is provided as an apparatus for manufacturing metal nanoparticles. The manufacturing apparatus of the eleventh embodiment includes a base liquid supply unit that supplies a transparent base liquid in which a nonionic surfactant and a metal extraction reagent of a target metal having hydrophilicity are mixed and the nonionic surfactant is dispersed as micelles, a metal solution supply unit that supplies a metal solution containing ions of the target metal, and a generation unit that is connected to the base liquid supply unit and the metal solution supply unit and brings the base liquid supplied from the base liquid supply unit into contact with the metal solution supplied from the metal solution supply unit to generate a microemulsion liquid in which micelles containing ions of the target metal are dispersed. According to the manufacturing apparatus of the eleventh embodiment, even in an environment of normal temperature and pressure, a microemulsion liquid in which micelles containing metal ions are dispersed can be easily generated without using an organic solvent. According to this microemulsion liquid, by reducing the metal ions captured in the micelles, metal nanoparticles with suppressed variation in particle size and a small average particle size can be easily obtained.

[0022] The present invention can be realized in various forms other than the method and apparatus for manufacturing metal nanoparticles. The present invention can be realized, for example, as a method for manufacturing a base liquid for generating metal nanoparticles, a method for manufacturing a microemulsion liquid, a method for separating and recovering a target metal from a metal solution, a method for manufacturing a carrier of metal nanoparticles, and a manufacturing apparatus for executing these methods. In addition, the present invention can be realized, for example, in the form of a recycling method of metal nanoparticles, metal nanoparticles manufactured by the above-described manufacturing method and manufacturing apparatus, a carrier of metal nanoparticles, a catalyst using metal nanoparticles, electronic components, and other products.

Brief Description of Drawings

[0023]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0024] Hereinafter, embodiments of a method for manufacturing metal nanoparticles according to the present invention will be described with reference to the drawings.

[0025] 1. Embodiment: 1-1. Manufacturing process of metal nanoparticles: FIG. 1 is a process flow diagram of a method for manufacturing metal nanoparticles. In the manufacturing method of this embodiment, a microemulsion liquid in which micelles containing metal ions are dispersed is generated by bringing a base liquid containing a metal extraction reagent into contact with a metal solution, and metal nanoparticles are generated by reducing the metal ions contained in the micelles. Hereinafter, the detailed steps will be described. Note that the following steps P1 to P2 can be carried out in an environment of normal temperature and normal pressure.

[0026] In step P1, a base liquid is prepared. The base liquid is prepared by adding a metal extraction reagent of the target metal to be nanoparticulated and a nonionic surfactant to an inorganic solvent such as a hydrochloric acid solution and stirring with a stirrer such as a magnetic stirrer.

[0027] The base liquid is obtained as a transparent liquid in which micelles of the nonionic surfactant are uniformly dispersed. Here, "transparent" means a state in which fine particles cannot be visually confirmed, and is not limited to being colorless. The base liquid is preferably in a state of a microemulsion in which micelles are uniformly dispersed to such an extent that the Tyndall phenomenon can be confirmed when irradiated with light in a dark place.

[0028] In the manufacturing method of this embodiment, in order to form micelles of the nonionic surfactant in the base liquid, a hydrophilic metal extraction reagent is used. Here, "having hydrophilicity" means showing higher hydrophilicity than hydrophobicity by introducing a hydrophilic group.

[0029] When the target metal is palladium (Pd), as the hydrophilic metal extraction reagent, for example, Pd-EX manufactured by Wako Chemicals, which is a kind of thiodiglycolamide, can be used. Pd-EX is known as a high-performance reagent that achieves both high selectivity and rapid extraction from a multi-component solution of the target metal.

[0030] Here, generally, the metal extraction reagent added to the organic phase in the solvent extraction method has high hydrophobicity. When a metal extraction reagent with high hydrophobicity is dropped into an aqueous solution, it forms large droplets and does not stick to or dissolve on the oil-water interface or the inner wall surface of the container. This suppresses the distribution of the metal extraction reagent not only in the organic phase but also in the aqueous phase, thereby preventing a decrease in separation efficiency. In the solvent extraction method, usually, a metal extraction reagent with high hydrophobicity is used also to reduce extraction inhibition due to emulsion formation (emulsification phenomenon).

[0031] On the other hand, for those having hydrophilicity to such an extent that no emulsion is formed, like the above-mentioned Pd-EX, they are likely to line up at the oil-water interface, so the extraction rate can be increased. When such a hydrophilic metal extraction reagent is added to an aqueous solution, it does not dissolve but forms oil droplets.

[0032] Through repeated research, the inventor of the present invention found that by appropriately adding such a hydrophilic metal extraction reagent and a properly selected nonionic surfactant to an inorganic solvent in an appropriate amount, micelles of the nonionic surfactant can be formed around the minute oil droplets of the metal extraction reagent. And when a base liquid in a transparent state where such micelles are uniformly dispersed in an aqueous solution as microemulsions is brought into contact with a metal solution containing a target metal, ions of the target metal are trapped in the micelles, and it was found that metal nanoparticles can be generated from the micelles.

[0033] Examples of candidates for nonionic surfactants capable of forming such micelles in the base liquid include the following.

[0034] <Examples of nonionic surfactants> Polyoxyethylene octyl phenyl ether (POOPE), polyoxyethylene nonyl phenyl ether (PONPE), polyoxyethylene monooleyl ether (POOE), polyoxyethylene monododecyl ether (PODE), polyoxyethylene monocetyl ether (POCE), etc.

[0035] The nonionic surfactant is not limited to the above, and may be appropriately selected according to the metal extraction reagent to be mixed. The nonionic surfactant may be any one that does not cause phase separation, precipitation, colloid, etc. when the metal extraction reagent is mixed, forms minute micelles, and can make the base liquid in the above-mentioned transparent state.

[0036] The average chain length of ethylene oxide of the nonionic surfactant is preferably greater than 7 and 25 or less. If the average chain length of ethylene oxide is within the above-mentioned preferred range, it is possible to suppress the situation where the micelles of the nonionic surfactant become too large, resulting in a semi-turbid state and the inability to obtain a transparent base liquid.

[0037] The components of the base liquid may be appropriately adjusted so that the base liquid becomes the above-mentioned transparent liquid. For the preparation of the base liquid, for example, a metal extraction reagent and a nonionic surfactant may be added to an inorganic solvent at a mass ratio of 1:5 to 15. When 0.05 to 0.10 g of the metal extraction reagent is added, 0.25 to 1.5 g of the nonionic surfactant may be added.

[0038] In step P2, the base liquid obtained in step P1 is brought into contact with a metal solution containing the target metal. As the metal solution, for example, a solution obtained by dissolving the target metal in an inorganic solvent such as a hydrochloric acid solution can be used. The concentration of the target metal in the metal solution may be, for example, 1000 ppm or less. Here, 1 ppm can be approximately converted to 1 mg / L. Note that the metal solution may contain metals other than the target metal. Even in this case, it is possible to separate and recover the nanoparticles of the target metal from other metals.

[0039] When the base liquid is brought into contact with the metal solution, a microemulsion liquid in which micelles containing metal extraction reagents in the base liquid disperse and micelles containing ions of the target metal inside are generated due to the action of the metal extraction reagents. In the case of the microemulsion liquid when the target metal is Pd, Pd becomes divalent ions, interacts with the metal extraction reagent to form a hydrochloric acid complex, and the micelles of the surfactant surround the hydrochloric acid complex. Specific examples of the method of bringing the base liquid into contact with the metal solution will be described later.

[0040] The microemulsion liquid obtained in step P2 is preferably transparent like the base liquid. Since metal nanoparticles are generated based on the micelles of the microemulsion liquid in the subsequent step P3, if the microemulsion liquid is transparent, it is possible to obtain metal nanoparticles with a small average particle size and a small variation in particle size.

[0041] Also, the microemulsion liquid obtained in step P2 preferably exhibits the Tyndall phenomenon when irradiated with light in a dark place, like the base liquid. With this microemulsion liquid, it is possible to obtain metal nanoparticles with an even smaller average particle size and a smaller variation in particle size.

[0042] The microemulsion liquid obtained in step P2 is preferably monodispersed with an average particle size of 30 nm or less. According to this microemulsion liquid, in the subsequent step P3, it is possible to obtain metal nanoparticles with an average particle size smaller than 30 nm and a better state in which the generation of variation in particle size is more suppressed.

[0043] In step P3, metal nanoparticles are generated from the microemulsion liquid obtained in step P2. In step P3 of the present liquid, metal nanoparticles supported on the base material particles are generated from the microemulsion liquid obtained in step P2.

[0044] In Process P3, first, the base material particles and the microemulsion solution are mixed, stirred, and dried. Then, by firing, a carrier is produced in which the nanoparticles of the target metal are supported on the base material particles. As the base material particles, for example, particles such as aluminum oxide, cerium oxide, and cerium-zirconium composite oxide can be used. Further, the firing can be carried out in an oxidizing atmosphere, but the firing method is not particularly limited.

[0045] In another embodiment, in Process P3, by drying the microemulsion solution, metal nanoparticles in a state of being dispersed in each other may be generated. For example, by applying the microemulsion solution to the surface of a substrate and drying it, metal nanoparticles may be deposited on the surface of the substrate. In this case, a known reducing agent for reducing the ions of the target metal may be added to the microemulsion solution before drying.

[0046] 1-2. Method for generating microemulsion solution: Hereinafter, a method for generating a microemulsion solution by bringing a base solution and a metal solution into contact with each other in Process P2, and a specific example of the apparatus will be described in order.

[0047] 1-2-1. Method by dropping: FIG. 2 is a schematic view showing an example of a microemulsion solution generating apparatus 10a for carrying out the first method.

[0048] In the first method, a microemulsion solution is generated by dropping the metal solution ML into the base solution BL and stirring. The generating apparatus 10a includes a storage unit 12 in which the base solution BL is stored, a dropping unit 13 that supplies the metal solution ML to the base solution BL by dropping, and a stirring unit 16 that is disposed in the storage unit 12 and stirs the base solution BL.

[0049] The storage section 12 corresponds to a generation section where the microemulsion liquid is generated. The storage section 12 is constituted by, for example, a beaker or the like. Although not shown, a base liquid supply section for supplying the base liquid BL into the storage section 12 may be connected to the storage section 12.

[0050] The dropping section 13 corresponds to a metal solution supply section. The dropping section 13 has a pipe section 14 through which the metal solution ML flows out. The pipe section 14 is disposed above the storage section 12 and opens toward the storage section 12. The dropping section 13 is configured to continuously drop droplets of the metal solution ML having a preset volume from the pipe section 14 at a preset period. Note that the pipe section 14 is preferably not made of a material containing an organic material such as a plasticizer, for example, made of vinyl chloride.

[0051] The stirring section 16 is constituted by, for example, a magnetic stirrer. The stirring section 16 stirs the base liquid by rotating a rotor immersed in the base liquid BL at a preset rotation speed. The stirring section 16 may be constituted by a homogenizer.

[0052] In the generation device 10a, while stirring the base liquid BL stored in the storage section 12 by the stirring section 16, the metal solution ML is continuously dropped from the dropping section 13, whereby a microemulsion liquid is generated in the storage section 12. The dropping speed of the metal solution ML is preferably, for example, 50 ml / min or less, and more preferably less than 10 ml / min.

[0053] According to the generation device 10a, a microemulsion liquid can be easily generated with a simple configuration. The generation device 10a is suitable for generating a small amount of microemulsion liquid.

[0054] 1-2-2. Method by Microreactor: FIG. 3 is a schematic view showing an example of a microemulsion liquid generation device 10b for carrying out the second method.

[0055] In the second method, a microemulsion liquid is generated by bringing a metal solution into contact with a base liquid in a microreactor having three flow channels. The generation device 10b is configured as a microreactor and includes a first flow channel section 21 that supplies the base liquid, a second flow channel section 22 that supplies the metal solution, and a third flow channel section 23 that discharges the microemulsion liquid.

[0056] Each of the flow channel sections 21, 22, and 23 has a tubular configuration. The downstream ends of the first flow channel section 21 and the second flow channel section 22 merge at a merging section 25. The upstream end of the third flow channel section 23 is also connected to the merging section 25.

[0057] The first flow channel section 21 corresponds to a base liquid supply section that supplies the base liquid, and the second flow channel section 22 corresponds to a metal solution supply section that supplies the metal solution. The second flow channel section 22 is made of, for example, metal or glass. It is preferable that the second flow channel section 22 is not made of a material containing an organic material such as a plasticizer like vinyl chloride. The merging section 25 corresponds to a generation section where the microemulsion liquid is generated.

[0058] In the generation device 10b, the base liquid and the metal solution are each supplied to the merging section 25 at a preset flow rate through the first flow channel section 21 and the second flow channel section 22 and are mixed in the merging section 25. As a result, a microemulsion liquid is generated in the merging section 25 and is discharged through the third flow channel section 23.

[0059] According to the generation device 10b, a microemulsion liquid in a predetermined state can be continuously generated by adjusting the concentration and flow rate of the base liquid and the metal solution. Therefore, metal nanoparticles can be easily and efficiently produced.

[0060] 1-2-3. Method by continuous countercurrent foam separation method: FIG. 4 is a schematic diagram showing an example of a microemulsion liquid generation device 10c for implementing the third method.

[0061] In the third method, a microemulsion liquid is continuously generated by a continuous countercurrent foam separation method. As described below, in the continuous countercurrent foam separation method, on the surface of the foam BB of the base liquid BL continuously generated, the base liquid BL and the metal solution ML come into contact to generate the microemulsion liquid EL.

[0062] The generation device 10c executes a continuous countercurrent foam separation method. The generation device 10c includes a separation tower 30 constituted by a hollow cylindrical container, a first supply unit 31 for supplying the base liquid BL into the separation tower 30, a second supply unit 40 for supplying the metal solution ML into the separation tower 30, and a foam generation unit 45 for generating the foam BB of the base liquid BL in the separation tower 30. The generation device 10c further includes a recovery unit 50 for recovering the microemulsion liquid EL generated in the separation tower 30 and a drainage unit 55 for discharging the base liquid BL from the separation tower 30.

[0063] The separation tower 30 is arranged with its central axis along the gravitational direction. The separation tower 30 functions as a generation unit that brings the base liquid BL supplied from the first supply unit 31 into contact with the metal solution ML supplied from the second supply unit 40 to generate the microemulsion liquid EL.

[0064] The first supply unit 31 includes a base liquid storage tank 32 for storing the base liquid BL supplied to the separation tower 30, a lower supply unit 33 connected to the lower end of the separation tower 30, and an upper supply unit 36 connected above the separation tower 30. The first supply unit 31 supplies the base liquid BL to the separation tower 30 through the lower supply unit 33 and the upper supply unit 36. In the present embodiment, the lower supply unit 33 and the upper supply unit 36 supply the base liquid BL from a common base liquid storage tank 32 to the separation tower 30. In other embodiments, one base liquid storage tank 32 may be individually provided for each of the lower supply unit 33 and the upper supply unit 36.

[0065] The lower supply section 33 includes a lower supply pipe 34 connecting the base liquid storage tank 32 and the lower end of the separation tower 30, and a lower liquid feed pump 35 provided in the lower supply pipe 34. The lower supply section 33 supplies the base liquid BL in the base liquid storage tank 32 to the lower end of the separation tower 30 by the driving force of the lower liquid feed pump 35. Thereby, a liquid layer LL of the base liquid BL is formed at the lower end of the separation tower 30.

[0066] The upper supply section 36 includes an upper supply pipe 37 connecting the base liquid storage tank 32 and the separation tower 30, and an upper liquid feed pump 38 provided in the upper supply pipe 37. The upper supply pipe 37 is connected above the connection site of the central supply pipe 42 provided in the second supply section 40 with respect to the separation tower 30. In the present embodiment, the upper supply pipe 37 is connected at a position above the central portion in the height direction of the separation tower 30. The upper supply section 36 supplies the base liquid BL in the base liquid storage tank 32 to the foam layer LB formed in the separation tower 30 by the driving force of the upper liquid feed pump 38. The upper supply section 36 supplies the base liquid BL at a small flow rate such that the foam BB in the foam layer LB does not break. Thereby, in the foam layer LB of the separation tower 30, a flow of the base liquid BL from above to below is formed between the foams BB.

[0067] The second supply section 40 includes a metal solution storage tank 41 for storing the metal solution ML supplied to the separation tower 30, a central supply pipe 42 connecting the metal solution storage tank 41 and the separation tower 30, and a central liquid feed pump 43 provided in the central supply pipe 42. The central supply pipe 42 is connected below the connection site of the upper supply pipe 37 provided in the upper supply section 40 of the first supply section 31 with respect to the separation tower 30. In the present embodiment, the central supply pipe 42 is connected to the central portion in the height direction of the separation tower 30.

[0068] The second supply unit 40 supplies the metal solution ML in the metal solution storage tank 41 to the foam layer LB formed in the separation tower 30 by the driving force of the central liquid feed pump 43. Thereby, in the separation tower 30, the base liquid BL of the foam layer LB and the metal solution ML come into contact with each other. Note that the supply of the metal solution ML by the second supply unit 40 is started after the foam layer LB is formed in the separation tower 30 by the foam generation unit 45 described below and the foam BB is stabilized.

[0069] The foam generation unit 45 includes a gas disperser 46 disposed in the separation tower 30, an air pump 47 that sends out air, an air supply pipe 48 that connects the gas disperser 46 and the air pump 47, and a flow meter 49 provided in the air supply pipe 48. The gas disperser 46 is immersed in the liquid layer LL of the base liquid BL at the lower end of the separation tower 30. The air pump 47 takes in outside air and sends it out to the gas disperser 46 in the separation tower 30 through the air supply pipe 48. The measurement result of the flow meter 49 is used for driving control of the air pump 47.

[0070] When the air supplied from the air pump 47 is discharged into the liquid layer LL through the gas disperser 46, foam BB of the base liquid BL is generated on the liquid layer LL. By continuously generating the foam BB of the base liquid BL, a foam layer LB filled with the foam BB moving successively from below to above is formed above the liquid layer LL in the separation tower 30.

[0071] The recovery unit 50 is connected to the upper end of the separation tower 30 and includes a discharge flow path 51 through which the foam BB of the foam layer LB is discharged, a foam breaker 52 connected to the downstream end of the discharge flow path 51, and a recovery tank 53 disposed below the foam breaker 52. As will be described later, micelles containing ions of the target metal adhere to the surface of the foam BB that reaches the upper end of the separation tower 30. The foam BB flows into the foam breaker 52 through the discharge flow path 51 and is broken, and is recovered by the recovery tank 53 as a microemulsion liquid EL in which the micelles are dispersed.

[0072] The liquid discharging section 55 includes a drain pipe 56 connected to the lower end of the separation tower 30, a liquid level adjusting section 57 connected to the drain pipe 56, and a waste liquid storage section 58 for storing the base liquid BL discharged through the drain pipe 56 and the liquid level adjusting section 57. In the separation tower 30, the base liquid BL is discharged from the liquid discharging section 55 while being supplied from the first supply section 31. The amount of the base liquid BL discharged from the liquid discharging section 55 is adjusted by the liquid level adjusting section 57 so that the liquid level of the liquid layer LL in the separation tower 30 is kept constant.

[0073] Referring to FIG. 5, the mechanism for generating the microemulsion liquid in the separation tower 30 will be described. FIG. 5 schematically shows one of the foams BB constituting the foam layer LB in the separation tower 30.

[0074] The micelles MC of the nonionic surfactant containing the metal extraction reagent contained in the base liquid BL are arranged so as to line up on the surface of the foam BB of the base liquid BL. The metal solution ML supplied from the second supply section 40 flows on the surface of the foam BB of the foam layer LB, and the ions MI of the target metal contained in the metal solution ML are captured inside the micelles MC on the surface of the foam BB. Thereby, a microemulsion liquid in which the micelles MC containing the ions MI of the target metal are dispersed is generated on the surface of the foam BB.

[0075] The micelles MC containing the ions MI of the target metal are adsorbed on the surface of the foam BB and move upward in the separation tower 30 together with the foam BB as indicated by the arrow FA. The foam BB that has reached the upper end of the separation tower 30 flows into the foam breaker 52 through the discharge flow path 51 of the recovery section 50 shown in FIG. 4 and is broken, and the microemulsion liquid EL that constituted the foam BB is recovered in the recovery tank 53.

[0076] As described above, the base liquid BL is also supplied to the separation column 30 from the upper supply section 36 of the first supply section 31. As a result, between the foams BB of the foam layer LB, as indicated by the arrow FB in FIG. 5, a flow of the base liquid BL occurs from above along the surface of the foam BB downward. Impurities CT such as ions other than the ions MI of the target metal contained in the metal solution ML are not adsorbed by the foam BB and flow downward in the separation column 30 along with the flow.

[0077] As shown in FIG. 4, in the liquid layer LL at the lower end of the separation column 30, while the base liquid BL containing the impurities CT is discharged to the drainage section 55, new base liquid BL is continuously supplied from the lower supply section 33 of the first supply section 31. Therefore, the base liquid BL in the separation column 30 is maintained in a good state.

[0078] As described above, in the production device 10c, (i) in the separation column 30, by continuously generating the foam BB of the base liquid BL from the liquid layer LL of the base liquid BL stored below, a foam layer LB is formed in which the foams BB continuously move upward from below; and (ii) by supplying the metal solution ML and the base liquid BL to the foam layer LB, a microemulsion liquid is generated on the surface of the rising foam BB, and the foam BB and the microemulsion liquid are discharged and recovered from the upper part of the separation column 30, and the base liquid BL containing the impurities CT is made to flow to the lower liquid layer LL. It can be interpreted that these steps are being executed. Also, on the surface of the foam BB of the production device 10c, it can also be interpreted that a configuration of a microreactor as shown in the production device 10b in FIG. 3 is realized, in which the microchannel through which the base liquid BL flows and the microchannel through which the metal solution ML flows merge and come into contact.

[0079] According to the continuous countercurrent foam separation method realized in the generating device 10c, by continuously supplying the metal solution ML while generating the foam BB of the base liquid BL, the microemulsion liquid EL can be continuously generated and recovered. Further, since the reaction field where the metal extraction reagent in the base liquid BL contacts the metal solution ML is limited to an extremely small region on the surface of the foam BB, the ions MI of the target metal can be efficiently captured by the micelles MC containing the metal extraction reagent with a short diffusion distance. Therefore, the recovery efficiency of the ions MI of the target metal from the metal solution ML can be increased.

[0080] Furthermore, as described above, the ions MI of the target metal and the inclusions CT contained in the metal solution ML can be efficiently separated by the liquid flow generated in the foam layer LB indicated by the arrows FA and FB in FIG. 5. Therefore, a high-quality microemulsion liquid EL with suppressed inclusion of inclusions CT can be efficiently obtained.

[0081] 1-3. Summary of this embodiment: As described above, according to the manufacturing method of this embodiment, in an environment of normal temperature and normal pressure, by bringing the base liquid into contact with the metal solution, a microemulsion liquid in which minute micelles incorporating the ions of the target metal are uniformly dispersed can be easily obtained. Further, by drying the microemulsion liquid, nanoparticles of the target metal with a small average particle diameter and a small variation in particle diameter can be easily obtained. According to the manufacturing method of this embodiment, since the use of a large amount of an organic solvent with a high environmental load is suppressed, it is possible to reduce the environmental load during the production of metal nanoparticles.

[0082] Also, according to the microemulsion liquid obtained in the manufacturing method of this embodiment, by mixing with the base material particles, drying, and firing, a carrier in which nanoparticles of the target metal are supported on the base material particles can be easily obtained. Therefore, according to this manufacturing method, a carrier supporting nanoparticles of a noble metal such as palladium or platinum, which is used as a catalyst, can be easily and efficiently obtained.

[0083] According to the manufacturing method of the present embodiment, catalyst particles and hydrogen storage alloys with a small average particle size and a small variation in particle size can be easily obtained. According to these catalyst particles and hydrogen storage alloys, since the specific surface area increases as the particle size is reduced, high reaction activity can be obtained. Also, it is possible to meet the demand for resource conservation.

[0084] Further, according to the manufacturing method of the present embodiment, by controlling the particle size of the micelles in the base liquid, it is possible to easily control the particle size of the obtained metal nanoparticles. Therefore, by controlling the particle size of the metal nanoparticles supported on the catalyst particles, it is also possible to significantly improve catalyst performance such as redox activity, for example.

[0085] By the way, in the manufacturing process of nanoparticles of platinum group metals used for automotive exhaust gas purification catalysts, those after disposal may be recovered and recycled. Generally, in that recycling process, platinum group metals are extracted by a wet process that combines a solvent extraction method, an adsorption method, a precipitation method, an electrodeposition method, etc. after a dry process involving a high-temperature treatment called the Rose process.

[0086] However, in this recycling process, drainage containing trace amounts of platinum group metals for which the recovery is not profitable is discarded, and a technique for easily recovering platinum group metals from such drainage is required. Also, in the manufacturing processes of industrial catalysts, electrical and electronic parts, dental and jewelry products, etc. that use platinum group metals, the current domestic recycling rate of platinum group metals is said to be around 30 - 50%, and a technique for easily recovering platinum group metals from drainage in the manufacturing process and refining process is required.

[0087] According to the manufacturing method of the present embodiment described above, by using a base liquid with a platinum group metal as the target metal, it is possible to easily and efficiently recover nanoparticles of platinum group metals from the drainage generated in the recycling process described above. Therefore, it is possible to increase the recycling rate of platinum group metals.

Example

[0088] 2. Experimental Examples by the Inventor of the Present Invention: 2-1. Base Solution: Table 1 shows the experimental results regarding the preparation examples of the base solution by the inventor of the present invention. The inventor of the present invention used Pd-EX as a metal extraction reagent, and combined various nonionic surfactants shown in Table 1 with the metal extraction reagent to try to obtain a transparent base solution in which the micelles of the nonionic surfactant are uniformly dispersed.

[0089]

Table 1

[0090] Each of the solutions BL01 to BL10 in Table 1 was prepared under the following conditions. <Preparation Conditions> · Inorganic Solvent: Concentration: 1 mol / L hydrochloric acid solution · Type of Nonionic Surfactant: Any one of POOPE10, PONPE10, PONPE20, POOE10, POOE2, POOE7, POOE20, POOE50, POCE23, PODE25 (all are commercially available products manufactured by Tokyo Chemical Industry Co., Ltd. The number at the end indicates the average chain length of ethylene oxide.) · Type of Metal Extraction Reagent: Pd-EX (Commercially available product manufactured by Wako Chemical Co., Ltd.) · Addition Amount of Nonionic Surfactant: 2.5 g · Addition Amount of Metal Extraction Reagent: 0.45 g · Stirring in a beaker with a stirrer for 24 hours at 400 rpm

[0091] In Table 1, the columns of "oil droplets", "turbidity", and "Tyndall phenomenon" show the evaluation results for the solutions obtained under the above preparation conditions. "○" in the "oil droplets" column indicates that no oil droplets were visually confirmed, and "×" indicates that oil droplets visible on the gas-liquid interface, the inner wall surface of the glass, etc. were confirmed. "○" in the "turbidity" column indicates that the solution was visually confirmed to be transparent, "△" indicates that slight turbidity occurred and it was semi-transparent, and "×" indicates that the solution was visually confirmed to be cloudy. "○" in the "Tyndall phenomenon" column indicates that the Tyndall phenomenon was confirmed when the solution was irradiated with light in a dark place, and "×" indicates that the Tyndall phenomenon could not be confirmed.

[0092] For solutions BL01, BL02, BL03, and BL04 using POOPE10, PONPE10, POOE10, and POOE20 as nonionic surfactants respectively, no presence of oil droplets or turbidity was confirmed, and they were transparent. For solutions BL01, BL02, BL03, and BL04, the occurrence of the Tyndall phenomenon could also be confirmed.

[0093] For solutions BL05, BL06, and BL07 using PONPE20, POCE23, and PODE25 as nonionic surfactants, the presence of oil droplets was confirmed, but there was no turbidity and they were transparent. However, for solutions BL05, BL06, and BL07, the Tyndall phenomenon could not be confirmed.

[0094] For solution BL08 using POOE50 as a nonionic surfactant, the presence of oil droplets was confirmed and slight turbidity occurred. Also, for solution BL08, the Tyndall phenomenon could not be confirmed. For solutions BL09 and BL10 using POOE2 and POOE7 as nonionic surfactants, the presence of oil droplets in the solution was confirmed and they were cloudy. Also, for solutions BL09 and BL10, the Tyndall phenomenon could not be confirmed.

[0095] In the case of Solutions BL01 to BL07, although those in which oil droplets were confirmed were included, since they were transparent, it is considered that they were in a state where minute micelles containing the metal extraction reagent were dispersed, and they can be used as the base liquid. Among them, Solutions BL01 to BL04 have no oil droplets, are transparent, and the Tyndall phenomenon has also been confirmed. They are in a state where minute micelles containing the metal extraction reagent are uniformly dispersed, and it can be said that they are base liquids of higher quality.

[0096] Both Solutions BL09 and BL10, which became turbid and did not become transparent, had an average ethylene oxide chain length of 7 or less for the nonionic surfactant. From this, it can be seen that it is preferable that the average ethylene oxide chain length of the nonionic surfactant is greater than 7. Also, as described above, in all solutions where the average ethylene oxide chain length of the nonionic surfactant was 25 or less, turbidity was not confirmed and they became transparent. From this, it can be seen that it is preferable that the average ethylene oxide chain length of the nonionic surfactant is 25 or less.

[0097] 2-2. Comparative Examples of Base Liquids: Table 2 shows the evaluation results of the solutions prepared as comparative examples of the base liquid.

[0098]

Table 2

[0099] In this comparative example, a solution was prepared by adding a metal extraction reagent having no hydrophilicity to an inorganic solvent and a nonionic surfactant. The preparation conditions of this solution are the same as those of each of Solutions BL01 to BL10 shown in Table 1, except that a metal extraction reagent having hydrophilicity was used.

[0100] As the metal extraction reagents, phosphoric acid-based D2EHPA, TBP, TOPO, PC88A, and TOA were used. Commercially available products were used for all the metal extraction reagents. As the nonionic surfactant, the 10 types of nonionic surfactants shown in Table 1 were used for each of the above metal extraction reagents.

[0101] The display of the evaluation results of "oil droplets" in Table 2 is the same as that in Table 1. In this comparative example, none of the metal extraction reagents were miscible with the nonionic surfactant, and visible oil droplets were dispersed on the gas-liquid interface and did not become transparent. Thus, metal extraction reagents without hydrophilicity were unable to form micelles of the nonionic surfactant containing the metal extraction reagent.

[0102] 2-3. Microemulsion liquid: 2-3-1. Generation by dropping: Table 3 shows the conditions and results when a Pd metal solution was brought into contact with each of the solutions BL01 to BL10 shown in Table 1 by "dropping" as described with reference to FIG. 2.

[0103]

Table 3

[0104] Each of the solutions E01 to E12 in Table 3 was prepared under the following conditions. <Preparation conditions> · Base liquid: Solutions BL01 to BL10 shown in Table 1 · Metal solution: Standard solution for atomic absorption of Pd with a concentration of 100 ppm · Dropping rate of the metal solution: 1 ml / min or 60 ml / min · While stirring 100 ml of the base liquid at 400 rpm with a stirrer, the metal solution was dropped

[0105] Using solutions BL01 and BL02 as the base liquid and dropping the metal solution at a rate of 1 ml / min, solutions E01 and E02 were obtained as clear, yellowish transparent liquids without turbidity. Also, in solutions E01 and E02, the Tyndall phenomenon was confirmed when irradiated with light in a dark place. This result indicates that solutions E01 and E02 were obtained as high-quality microemulsion liquids in which fine micelles containing Pd were uniformly dispersed.

[0106] Using solutions BL03 to BL10 as the base solution, for solutions E03 to E10 obtained by dropping the metal solution at a rate of 1 ml / min, yellow turbidity was confirmed in all of them. Among them, for solutions E04, E07, E08, and E09, it was confirmed that a part of the oil droplets was phase-separated and floating in the solution.

[0107] Using solutions BL01 and BL02 as the base solution, in solutions E11 and E12 obtained by dropping the metal solution at a rate of 60 ml / min, yellowish precipitates were immediately formed and accumulated at the bottom of the container. Solutions E11 and E12 differ from solutions E01 and E02 only in the dropping rate of the metal solution. From this result, it is considered preferable that the rate of bringing the base solution and the metal solution into contact is appropriately controlled according to the conditions such as the concentration of the base solution and the metal solution when producing the microemulsion solution.

[0108] 2-3-2. Generation by continuous countercurrent foam separation method: Table 4 summarizes the preparation conditions and evaluation results of solutions E13 to E18 prepared by the "continuous countercurrent foam separation method" described with reference to FIG. 4. The recovery rate shown in Table 4 is the percentage of the mass of the metal contained in the solution recovered by the recovery unit 50 of the production apparatus 10c with respect to the mass of the metal contained in the metal solution measured before being introduced into the production apparatus 10c.

[0109]

Table 4

[0110] The continuous countercurrent foam separation method was carried out using the production apparatus 10c described in FIG. 4. The inner diameter of the separation tower 30 was 3 cm and the height was 93 cm. Also, the operating conditions in the production apparatus 10c are as follows.

[0111] <Operating conditions> · Bubble diameter: 1.5 mm · Air flow rate in the foam generation section 45: 45 ml / min · Flow rate of the base solution in the lower supply section 33: 13 ml / min · Flow rate of the base solution in the upper supply section 36: 0.18 ml / min ·Supply flow rate of the metal solution: 0.28 ml / min

[0112] Solution E13 was prepared by bringing a metal solution, which uses solution BL01 in Table 1 containing nonionic surfactant POOPE10 as the base solution and is a 1 mol / L hydrochloric acid solution containing Pd at a concentration of 20 ppm, into contact with the continuous countercurrent foam separation method under the above operating conditions. The metal solution before being brought into contact with the base solution did not contain any surfactant or Pd-EX at all.

[0113] Solution E13 was yellow in color, but had no turbidity and was transparent. In solution E13, the Tyndall phenomenon was observed when irradiated with light in the dark. This result indicates that solution E13 is a microemulsion liquid in which fine micelles containing a hydrochloric acid complex of divalent Pd ions are uniformly dispersed. The recovery rate of Pd in solution E13 was 100%.

[0114] Solution E14 was prepared by bringing a multi-component metal solution, which uses solution BL01 in Table 1 as the base solution, into contact with the continuous countercurrent foam separation method under the above operating conditions. The multi-component metal solution was a 1 mol / L hydrochloric acid solution containing Pd, platinum (Pt), iron (Fe), copper (Cu), and zinc (Zn) at concentrations of 20 ppm each.

[0115] Solution E14 was yellow in color, but had no turbidity and was transparent. In solution E14, the Tyndall phenomenon was confirmed when irradiated with light in the dark. This result indicates that solution E14 is a microemulsion liquid in which micelles containing Pd are uniformly dispersed.

[0116] In solution E14, the concentration of Pd was 55 ppm, and the concentrations of the other metals Pt, Fe, Cu, and Zn were less than 1 ppm. In solution E14, the recovery rate of Pd was 100%. Also, the recovery rates of the remaining Pt, Fe, Cu, and Zn were 0.02%, 0.51%, 0.14%, and 0.11% respectively. Thus, in solution E14, the target metal Pd was almost completely separated and extracted from the multi-component metal solution.

[0117] Solution E15 was prepared under substantially the same conditions as Solution E14, except that Solution BL02 in Table 1 containing nonionic surfactant PONPE10 was used as the base solution.

[0118] Similar to Solution E14, Solution E15 was yellow in color, clear without turbidity. Also, in Solution E15, the Tyndall phenomenon was confirmed when irradiated with light in the dark, similar to Solution E14. This result indicates that Solution E15, like Solution E14, is a microemulsion solution in which Pd-containing micelles are uniformly dispersed.

[0119] In Solution E15, the concentration of Pd was 45 ppm, and the concentrations of other metals Pt, Fe, Cu, and Zn were less than 1 ppm. In Solution E15, the recovery rate of Pd was 99.4%. Also, the recovery rates of the remaining Pt, Fe, Cu, and Zn were 0.06%, 0.50%, 0.14%, and 0.16% respectively. Thus, in Solution E15, similar to Solution E14, Pd, the target metal, was almost completely separated and extracted from the multi-component metal solution.

[0120] Solution E16 was prepared under substantially the same conditions as Solution E14, except that the metal solution did not contain Pd, the target metal. Solution E16 was colorless and transparent. Also, in Solution E16, the concentrations of Pt, Fe, Cu, and Zn were less than 1 ppm, and the recovery rate of any metal was less than 1%.

[0121] Solutions E17 and E18 were prepared under substantially the same preparation conditions as Solutions E14 and E15, except that the base solutions did not contain the metal extraction reagent. The base solutions of Solutions E17 and E18 were prepared under the same conditions as Solutions BL01 and BL02, except that the metal extraction reagent Pd-EX was not mixed.

[0122] Solutions E17 and E18 were colorless and transparent, but the concentrations of Pd, Pt, Fe, Cu, and Zn were all less than 1 ppm, and the recovery rate of each metal was less than 1%. The results of Solutions E17 and E18 indicate that in the production method of the present invention, the target metal is extracted by the action of the metal extraction reagent contained in the base liquid.

[0123] Figure 6 shows a graph indicating the measurement results of the particle size of the micelles contained in the microemulsion liquid of Solution E13 in Table 4. These measurement results were obtained by the Dynamic Light Scattering (DLS) method. The solid line graph Ga in Figure 6 shows the measurement results immediately after Solution E13 was produced, and the dashed-dotted line graph Gb shows the measurement results after 7 months had passed since production.

[0124] As shown by graph Ga, in Solution E13, tiny micelles with a particle size of about several nm to 10 nm were monodispersed. Also, as shown by graph Gb, those micelles did not disappear even after 7 months had passed, and remained dispersed in the solution with almost no change from immediately after they were produced. For Solutions E14 and E15 in Table 4, as a result of DLS measurement, almost the same results as those of Solution E13 were obtained.

[0125] As described above, the results shown in Table 3, Table 4, and Figure 6 indicate that according to the production method of the present invention, a microemulsion liquid in which micelles containing the target metal, having a small average particle size and a small variation in particle size, are uniformly dispersed can be easily and efficiently obtained.

[0126] 2-4. Metal Nanoparticles: Figure 7 shows a Transmission Electron Microscope (TEM) image of the Pd nanoparticles recovered from Solution E14. These Pd nanoparticles in the image were recovered on the TEM grid by immersing the TEM grid in the liquid surface of Solution E14 and reducing the pressure. These nanoparticles correspond to the nanoparticles of the target metal produced by drying the microemulsion solution.

[0127] In this image, it can be observed that Pd nanoparticles with a size of about 3 to 10 nm are dispersed. This result is consistent with the result of the DLS measurement shown in FIG. 6.

[0128] As shown in the photographed image of FIG. 7, according to the manufacturing method of the present invention, based on the fine micelles uniformly dispersed in the microemulsion liquid, it is possible to easily obtain nanoparticles of the target metal with a small average particle size, a small variation in particle size, and extremely high dispersibility.

[0129] 2-5. Carrier for metal nanoparticles: Table 5 summarizes the manufacturing conditions of production examples M1 and M2 of the carrier for metal nanoparticles.

[0130]

Table 5

[0131] In production example M1, solution E14 shown in Table 4 was used as the raw material solution for the metal nanoparticles to be supported on the base material particles. In production example M2, a standard solution for atomic absorption containing palladium chloride (PdCl2) was used as the raw material solution.

[0132] In production examples M1 and M2, the above raw material solution was added to the cerium oxide (CeO2) powder serving as the base material particles so that the weight percentage of Pd with respect to CeO2 was 0.5% by weight, and an impregnation operation was performed. The mixture was dried in an air atmosphere for 72 hours while stirring using a stirrer, and then fired under the conditions of a firing temperature of 600 ° C and a firing time of 3 hours.

[0133] Table 6 shows the measurement results of the oxidation-reduction activity for each of production examples M1 and M2. In Table 6, the temperature at which 10% of each of the reactants carbon monoxide (CO), propylene (C3H6), and nitrogen monoxide (NO) is converted by the reaction with production examples M1 and M2 is shown as T 10 [°C], and the temperature at which 50% is converted is shown as T 50It is shown as [℃].

[0134]

Table 6

[0135] As shown in Table 6, the temperature of T in Production Example M1 10 was higher than the temperature of T in Production Example M2 10 , but the temperature of T for C3H6 and NO 50 became lower than that in Production Example M2. According to Non-Patent Document 4, the reversal of the activity order in such a high-temperature range indicates that the turnover frequency (TOF) showing the reaction rate per unit amount of Pd is higher in Production Example M1.

[0136] 2-6. Summary: As described above, by mixing a hydrophilic metal extraction reagent and a nonionic surfactant, a transparent base liquid in which the micelles formed around the oil droplets of the metal extraction reagent are uniformly dispersed was obtained. Further, by bringing the base liquid into contact with a metal solution of the target metal, a microemulsion liquid in which the micelles containing the ions of the metal solution are uniformly dispersed was generated. Then, the nanoparticles of the target metal could be recovered from the microemulsion liquid, and a carrier having the metal nanoparticles supported on the base material particles could also be manufactured.

[0137] 3. Other Embodiments: The present invention is not limited to the configurations of the above-described embodiments and examples, and can be implemented, for example, in the following forms. In the following, all the configurations described as other embodiments are also positioned as one example of implementing the present invention, similar to the above-described embodiments and examples.

[0138] 3-1. Other Embodiment 1: The target metal is not limited to Pd. The target metal may be platinum (Pt), other platinum group metals, or precious metals. Further, the target metal may be a metal other than precious metals.

[0139] 3-2. Other Embodiment 2: The base particles for supporting metal nanoparticles are not limited to CeO2 powder. Further, the carrier of the metal nanoparticles is not limited to the catalysts described in the above embodiments and examples, and may be other types of catalysts, or particles having functions other than catalysts.

Description of Reference Numerals

[0140] 10a, 10b, 10c... generating device, 12... storage section, 13... dropping section, 14... pipe section, 16... stirring section, 21... first flow path section, 22... second flow path section, 23... third flow path section, 25... confluence section, 30... separation tower, 31... first supply section, 32... base liquid storage section, 33... lower supply section, 34... lower supply pipe, 35... lower liquid feed pump, 36... upper supply section, 37... upper supply pipe, 38... upper liquid feed pump, 40... second supply section, 41... metal solution storage tank, 42... central supply pipe, 43... central liquid feed pump, 45... foam generation section, 46... gas disperser, 47... air pump, 48... air supply pipe, 49... flow meter, 50... recovery section, 51... discharge flow path, 52... foam breaker, 53... recovery tank, 55... liquid discharge section, 56... liquid discharge pipe, 57... liquid level adjustment section, 58... waste liquid storage section, BB... foam, BL... base liquid, CT... impurity, ML... metal solution, MC... micelle, EL... microemulsion liquid, LB... foam layer, LL... liquid layer

Claims

1. A method for producing metal nanoparticles, comprising: preparing a transparent base liquid containing micelles of the nonionic surfactant by mixing a metal extraction reagent of the target metal having hydrophilicity and a nonionic surfactant; contacting the base liquid with a metal solution containing ions of the target metal to generate a microemulsion liquid in which micelles containing ions of the target metal are dispersed; A manufacturing method comprising:

2. The manufacturing method according to claim 1, wherein: the average ethylene oxide chain length of the nonionic surfactant is greater than 7 and 25 or less.

3. The manufacturing method according to claim 1, wherein: the micelles of the microemulsion solution have an average particle diameter of 30 nm or less and are monodispersed.

4. The manufacturing method according to claim 1, wherein: the base liquid and the microemulsion liquid exhibit the Tyndall phenomenon when irradiated with light in a dark place.

5. The manufacturing method according to claim 1, wherein: the step of generating the microemulsion liquid includes: (i) forming a foam layer in which the foam of the base liquid continuously moves upward from the liquid layer of the base liquid stored below in a separation tower; (ii) supplying the metal solution and the base liquid to the foam layer to generate the microemulsion liquid on the surface of the rising foam, flowing out and recovering the microemulsion liquid from above the separation tower together with the foam, and flowing the base liquid containing impurities back to the liquid layer below.

6. The manufacturing method according to any one of claims 1 to 5, wherein: The manufacturing method wherein the nonionic surfactant is polyoxyethylene octyl phenyl ether (POOPE) or polyoxyethylene nonyl phenyl ether (PONPE).

7. The manufacturing method according to claim 6, wherein the target metal is palladium and the metal extraction reagent is thioglycolamide.

8. The manufacturing method according to claim 7, wherein the concentration of the metal extraction reagent in the base liquid is 0.05 g / L or more and 5.00 g / L or less, and the concentration of the nonionic surfactant is 0.50 g / L or more and 10.00 g / L or less, and the concentration of the target metal in the metal solution is 1000 ppm or less.

9. The manufacturing method according to any one of claims 1 to 5, further comprising a step of generating nanoparticles of the target metal by drying the microemulsion solution.

10. The manufacturing method according to any one of claims 1 to 5, further comprising a step of generating a carrier in which nanoparticles of the target metal are supported on the base material particles by mixing the base material particles and the microemulsion solution, stirring, drying, and then firing.

Images