Method for producing metal nanoparticles and apparatus for producing metal nanoparticles

Abstract

To provide a method for efficiently producing metal nanoparticles and an apparatus for performing the method.SOLUTION: There are provided: a method for continuously synthesizing metal nanoparticles by irradiating microwaves while feeding a raw material solution into a pipe, wherein the pipe comprises a microwave irradiation unit for irradiating microwaves to the raw material solution flowing through the pipe, a raw material solution introduction unit disposed upstream of the microwave irradiation part and a heat insulating cooling part disposed downstream of the microwave irradiation unit, and when a fixed amount of the raw material solution and / or metal nanoparticles adheres to the inner wall of the piping, the position of the microwave irradiation unit is moved; and an apparatus for performing the method.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method and an apparatus for producing metal nanoparticles. [Background technology]

[0002] Metal nanoparticles are being used and investigated for a variety of applications, such as catalysts, ink materials, and electronic component materials.

[0003] For example, Patent Document 1 discloses a method for continuously synthesizing core-shell structured nanoparticles having a metal core and an oxide shell, which comprises continuously synthesizing metal nanoparticles having a diameter of 1 to 100 nanometers in a front-stage flow-type reaction tube including at least one flow-type reaction tube, and continuously forming an oxide coating around the metal nanoparticles by hydrolyzing an oxide precursor in a rear-stage flow-type reaction tube including at least one flow-type reaction tube, and which is characterized in that at least the front-stage flow-type reaction tube is uniformly heated by microwaves.

[0004] Patent document 2 discloses a method for producing metal microparticles, in which a reaction liquid containing a metal precursor is circulated through a flow pipe, and electromagnetic waves are irradiated uniformly and intensively into the flow pipe along the length of the flow pipe, thereby uniformly heating the electromagnetic wave-irradiated space within the flow pipe along the flow direction, thereby generating metal microparticles. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2013 / 039117 [Patent Document 2] Japanese Patent Application Laid-Open No. 2011-137226 Summary of the Invention [Problem to be solved by the invention]

[0006] A method for producing metal nanoparticles using a flow system in which a raw material solution is circulated through a resin tube and heated using a microwave heating device has been investigated. However, this method tends to result in adhesion of the metal nanoparticles and raw materials to the inner walls of the tube, causing clogging of the tube, abnormal heating, and reduced yield.

[0007] The present invention aims to provide a method for efficiently producing metal nanoparticles and an apparatus for carrying out the method. [Means for solving the problem]

[0008] The inventors conducted extensive research to solve the above-mentioned problems and discovered that in a method for continuously synthesizing metal nanoparticles by irradiating microwaves from a microwave irradiation section of a pipe while a raw material solution is being fed into the pipe, once a certain amount of raw material solution and / or metal nanoparticles has adhered to the inner wall of the pipe, by moving the position of the microwave irradiation section upstream, metal nanoparticles can be efficiently produced without reducing productivity, leading to the present invention.

[0009] An example aspect of this embodiment is described as follows. (1) A method for continuously synthesizing metal nanoparticles by irradiating microwaves onto a raw material solution while feeding the raw material solution through a pipe, the method comprising the steps of: a microwave irradiation section for irradiating microwaves onto the raw material solution flowing through the pipe; a raw material solution introduction section disposed upstream of the microwave irradiation section; and a heat-retaining / cooling section disposed downstream of the microwave irradiation section; and moving the position of the microwave irradiation section when a certain amount of raw material solution and / or metal nanoparticles adheres to the inner wall of the pipe. (2) The method according to (1), wherein the position of the microwave irradiation unit is moved upstream. (3) The method according to (1) or (2), wherein the length of the heat-retaining / cooling section is kept constant while the position of the microwave irradiation section is moved. (4) An apparatus for producing metal nanoparticles by irradiating a raw material solution with microwaves, the apparatus comprising a raw material solution storage tank, a metal nanoparticle recovery tank, and piping connecting the raw material solution storage tank and the metal nanoparticle recovery tank, the piping comprising a microwave irradiation unit that irradiates microwaves onto the raw material solution flowing through the piping, a raw material solution introduction unit located upstream of the microwave irradiation unit, and a heat-retaining cooling unit located downstream of the microwave irradiation unit, and the microwave irradiation unit is movable. (5) The device described in (4) further comprises an adjustment mechanism for maintaining the length of the heat-retaining / cooling section constant. (6) The apparatus according to (4) or (5), further comprising a device for detecting the raw material solution and / or metal nanoparticles attached to the inner wall of the pipe. (7) The apparatus according to (6), wherein the microwave irradiation unit moves upstream when the detection device detects adhesion of a certain amount of raw material solution and / or metal nanoparticles to the inner wall of the pipe. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a method for efficiently producing metal nanoparticles and an apparatus for carrying out the method. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a diagram showing an outline of an embodiment of a manufacturing apparatus of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] Preferred embodiments of the present invention will now be described in detail. In this specification, the features of the present invention will be described with reference to the drawings as appropriate. In the drawings, the dimensions and shapes of each part are exaggerated for clarity and do not accurately depict the actual dimensions and shapes. Therefore, the technical scope of the present invention is not limited to the dimensions and shapes of each part shown in these drawings. The method and apparatus for producing metal nanoparticles of the present invention are not limited to the following embodiments, and can be embodied in various forms incorporating modifications and improvements that can be made by those skilled in the art without departing from the spirit of the present invention. Furthermore, although each embodiment described in this specification is independent, two or more of each embodiment can also be combined to form one embodiment of the present invention.

[0013] The symbol "to" used herein means a range having the numerical values ​​before and after it as the upper and lower limits. In numerical ranges described in stages in this specification, the upper or lower limit described in one numerical range may be replaced with the upper or lower limit described in another stage. The upper or lower limit of a numerical range described herein may be replaced with a value shown in the examples.

[0014] First, the method for producing metal nanoparticles of the present invention will be described. The method of the present invention relates to a method for continuously synthesizing metal nanoparticles by irradiating a raw material solution with microwaves while feeding the raw material solution through a pipe.

[0015] In the present invention, the raw material solution is not particularly limited as long as it is a solution from which metal nanoparticles can be obtained by heating with microwaves.

[0016] The solvent is not limited as long as it dissolves materials such as a metal nanoparticle precursor, an organic dispersant, and a reducing agent, and is a polar solvent or ionic liquid that can absorb microwaves. Examples of solvents used in the raw material solution include low-boiling-point solvents with a boiling point of 300°C or less at one atmosphere. Examples of low-boiling-point solvents include, but are not limited to, water, alcohols such as methanol and ethanol, polyhydric alcohol solvents such as ethylene glycol, ketone solvents such as acetone, dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), other organic solvents, and mixtures of two or more of these low-boiling-point polar solvents.

[0017] The metal nanoparticle precursor is not limited as long as it dissolves in a solvent and generates metal ions, such as ions of precious metals, base metals, and alloys, such as gold, silver, platinum, copper, nickel, iron, and cobalt, or ions of two or more of these metals. Examples of metal nanoparticle precursors include inorganic metal salts such as metal halides (e.g., fluorides, chlorides, bromides, and iodides), metal sulfates, metal nitrates, metal phosphates, and metal cyanides; organic metal salts such as metal carboxylates and metal sulfonates; and metal complexes, including metal complex salts. Inexpensive metal nitrates, such as nickel nitrate and silver nitrate, are preferred as metal nanoparticle precursors. Alternatively, formates with reducing properties, such as nickel formate, can be used as the metal nanoparticle precursor.

[0018] The concentration of metal ions in the raw material solution is not limited as long as it is equal to or less than the saturated concentration, but is usually 0.05 mol / L (M) or more and usually 2.0 M or less, for example, 0.05 M to 2.0 M, 0.05 M to 1.0 M in one embodiment, 0.05 M to 0.5 M in one embodiment, and 0.05 M to 0.3 M in another embodiment.

[0019] The raw material solution contains an organic substance as a dispersant. Examples of dispersants include, but are not limited to, one or more dispersants selected from polyvinylpyrrolidone (PVP), dodecylamine (DDA), thiol-based polymers, polyvinyl alcohol (PVA), polyacrylic acid, polyacrylates, cyclodextrin, aminopectin, methylcellulose, polyethyleneimine cellulose, aliphatic amines, aliphatic carboxylic acids, and tannic acid. When the dispersant is a polymer, the molecular weight of the dispersant is, but is not limited to, for example, a weight-average molecular weight (Mw) of typically 1,000 or more, in one embodiment 8,000 or more, and in one embodiment 10,000 or more, and typically 50,000 or less, in one embodiment 40,000 or less, for example 1,000 to 50,000, in one embodiment 8,000 to 50,000, and in one embodiment 10,000 to 40,000.

[0020] The concentration of the dispersant in the raw solution is not limited, but is usually 3000 mmol / L (mM) or less, and in one embodiment, 1000 mM or less. Since the amount of dispersant in the raw solution is preferably small, the lower limit is not limited, but is usually 0.1 mM or more.

[0021] Furthermore, the raw material solution may contain a reducing agent.

[0022] The reducing agent is not limited. Examples of the reducing agent include citric acid or citrates such as trisodium citrate, disodium citrate, and monosodium citrate; oxalic acid or oxalate salts such as sodium oxalate; ascorbic acid or ascorbate salts such as sodium ascorbate; formic acid or formate salts such as sodium formate; DMF, NaBH4, hydrazine, and mixtures of two or more thereof. In one embodiment, the reducing agent for metal ions, particularly silver ions, is DMF. When the raw material solution contains DMF, DMF can function as both a solvent and a reducing agent.

[0023] The amount of reducing agent is not limited as long as it can reduce metal ions to a metal whose oxidation number is 0 through a redox reaction, but is typically 1.0 equivalent or more, and in one embodiment 4.0 equivalents or more, and typically 20 equivalents or less, and in one embodiment 15 equivalents or less, for example, 1.0 to 20 equivalents, and in one embodiment 4.0 to 15 equivalents, relative to the metal ions. Note that when the reducing agent for metal ions contains one or more functional groups capable of interacting with metals, such as a carboxy group, a hydroxy group, or an ether group, it can also function as a dispersant.

[0024] The raw material solution may further contain a base. The base functions as a pH adjuster, and examples thereof include 2-amino-1-butanol, sodium hydroxide, magnesium hydroxide, potassium hydroxide, and calcium hydroxide. The base may be a mixture of two or more types. The base may be used as a basic solution containing a base dissolved in a solvent such as water or alcohol. When the raw material solution contains a base, it is possible to promote the reduction reaction and increase the reaction rate, thereby enabling metal nanoparticles to be produced efficiently at a high concentration.

[0025] When the raw material solution further contains a base, the concentration of the base in the raw material solution is not limited as long as it is not more than the saturated concentration, but is usually 1 mmol / L (mM) or more, and in one embodiment, 50 mM or more and usually 250 mM or less. The concentration of the base in the raw material solution is, for example, 1 mM to 250 mM, and in one embodiment, 50 mM to 250 mM.

[0026] The pH of the raw material solution is not limited, but is usually pH5 to pH14.

[0027] The raw material solution may be composed of the metal nanoparticle precursor, solvent, dispersant, and optionally a reducing agent and base described above. In addition to these materials, the raw material solution may further contain additives that are commonly used in conventional methods for producing metal nanoparticles by microwave irradiation, such as chelating agents, such as ethylenediaminetetraacetic acid (EDTA) and / or salts thereof. The amount of additive is not limited. The amount of additive is typically 10 wt % or less, and in one embodiment, 3 wt % or less, based on the total weight of the raw material solution. Because additives do not necessarily need to be added, there is no lower limit for the amount of additive. However, if the raw material solution further contains an additive, the amount of additive is typically 0.1 wt % or more, based on the total weight of the raw material solution.

[0028] In the present invention, the order of addition of the materials, the addition temperature, the mixing method, the mixing time, etc. in preparing the raw material solution are not limited, and the materials are mixed so as to prepare a uniform raw material solution.

[0029] Next, the prepared raw material solution is passed through a pipe, and the raw material solution is irradiated with microwaves to heat the raw material solution and cause the reaction to proceed.

[0030] The piping is equipped with a microwave irradiation section that irradiates microwaves to the raw material solution flowing through the piping to cause a reaction, a raw material solution inlet section located upstream of the microwave irradiation section, and a heat-retaining / cooling section located downstream of the microwave irradiation section. Note that "upstream" refers to the direction of the location where the raw material solution begins to flow before the synthesis of metal nanoparticles, and "downstream" refers to the direction of the location where the suspension after the synthesis of metal nanoparticles is finally collected and stored.

[0031] The piping may be a straight pipe or a spiral pipe, and the size and shape of the piping are not limited as long as the piping is configured such that the microwaves are irradiated uniformly throughout the piping.

[0032] The average inner diameter of the pipe is usually 2 mm or more, and in one embodiment 4 mm or more, and usually 10 mm or less, and in one embodiment 8 mm or less, for example, 2 mm to 10 mm, and in one embodiment 4 mm to 10 mm.

[0033] The length of the piping is not limited, and is usually 1 m to 30 m, and in one embodiment, 10 m to 20 m.

[0034] The thickness of the pipe is not limited, and is usually 1 mm to 3 mm, and in one embodiment, 1 mm to 2 mm.

[0035] The material of the piping is not limited as long as it can uniformly irradiate the raw material solution with microwaves, and is, for example, a material that transmits microwaves, i.e., does not absorb microwaves, such as ceramic materials, ceramic materials made of silicon oxide such as glass and quartz, and non-conductive materials with a small relative dielectric constant ε and a dielectric loss angle tanδ, such as resin.

[0036] Examples of the resin include fluororesins such as PFA (perfluoroalkoxy fluororesin), PTFE (polytetrafluoroethylene), and FEP (tetrafluoroethylene-hexafluoropropylene copolymer), nylon resin, silicone resin, polyethylene resin, acrylic resin, or mixtures thereof.

[0037] The arithmetic mean roughness Ra of the inner wall of the pipe is usually 0.01 μm or more and usually less than 0.1 μm. The maximum height roughness Rz of the inner wall of the pipe is usually 0.1 μm or more and usually less than 1.0 μm. By using pipes with inner wall Ra and Rz within the above ranges, it is possible to prevent the produced metal nanoparticles from adhering to the pipe.

[0038] In the piping, the microwave irradiation section is equipped with a microwave irradiation device, and is a section that irradiates microwaves to the raw material solution flowing through the microwave irradiation section in the piping using the microwave irradiation device, thereby heating the raw material solution in the irradiated piping. The raw material solution is usually reduced by the heating, thereby producing metal nanoparticles.

[0039] The microwave irradiation device is not particularly limited as long as it is a device that can irradiate microwaves to the microwave irradiation section of the piping, but a device that can irradiate microwaves continuously is usually used.

[0040] The microwave absorption power (E) of the raw material solution is usually 20 W / mL or more and usually 500 W / mL or less, for example, 20 W / mL to 500 W / mL, relative to the volume of the raw material solution.

[0041] Here, the microwave absorption power E of the raw material solution is calculated by dividing the microwave intensity (W) absorbed by the raw material solution, i.e., the value obtained by subtracting the reflected wave power irradiated and reflected from the raw material solution from the output of the microwave irradiation source (output - reflected wave power), by the volume (mL) of the raw material solution irradiated with that output. The reflected wave power can be measured using a power monitor in the microwave irradiation device.

[0042] In the microwave irradiation section, the raw material solution is heated to the reaction temperature. The reaction temperature to which microwave irradiation raises the temperature can be appropriately changed depending on the reaction conditions (such as the type of solvent and the pressure during the reaction) and is not limited. The reaction temperature is usually 25°C or higher, and in one embodiment, 80°C or higher. The upper limit of the reaction temperature is not limited, but is usually below the boiling point of the solvent. For example, when the solvent is water, the reaction temperature is usually in the range of 25°C or higher and lower than 100°C at atmospheric pressure, and in one embodiment, 80°C to 90°C. Note that, in the present invention, when pressure is applied to the raw material solution, the reaction temperature can be higher than the boiling point of the solvent under atmospheric pressure. The boiling point of the solvent under the applied pressure may vary depending on the pressure. Therefore, in one embodiment, the reaction temperature is equal to or higher than the boiling point of the solvent under atmospheric pressure and lower than the boiling point of the solvent under the applied pressure.

[0043] The length of the microwave irradiation unit is not limited and can be changed depending on the microwave irradiation device configured. The length of the microwave irradiation unit is usually 0.1 m to 0.5 m.

[0044] In the piping, the raw material solution inlet section is a section that is disposed upstream of the microwave irradiation section and is used to introduce the prepared raw material solution into the microwave irradiation section.

[0045] The raw material solution introduction section is usually a section where the raw material solution before reaction flows, and is at room temperature, for example, in the temperature range of 0°C to 40°C.

[0046] In the present invention, the raw material solution introduction section includes a portion that can become a new microwave irradiation section when the microwave irradiation section is moved, particularly upstream, after the raw material solution reacts in the microwave irradiation section and a certain amount of raw material solution and / or metal nanoparticles adheres to the inner wall of the pipe. Therefore, the raw material solution introduction section is preferably longer than the microwave irradiation section before the microwave irradiation section is moved so that the movement distance of the microwave irradiation section can be equal to or greater than the length of the microwave irradiation section. For example, the length of the raw material solution introduction section before the microwave irradiation section is usually 0.2 m to 0.6 m.

[0047] In the piping, the heat-retaining / cooling section is a section that is placed downstream of the microwave irradiation section and is used to keep the metal nanoparticles (post-reaction suspension) produced in the raw material solution warm.

[0048] The heat-retaining / cooling section may be composed of piping only, or may include a heat-retaining device such as a heater or a cooler.

[0049] The temperature maintained in the heat-retaining / cooling section is not limited, but is usually below the reaction temperature, and the heat-retaining / cooling section has a temperature gradient from the reaction temperature to room temperature, for example, usually from 80°C to 0°C. The lower limit of the temperature maintained is not limited, but is usually 0°C or higher, and in one embodiment, 20°C or higher. For example, when the solvent is water, the temperature maintained at atmospheric pressure is usually in the range of 80°C to 10°C, and in one embodiment, 60°C to 20°C.

[0050] The length of the heat-retaining / cooling section is not limited. In one embodiment, the length of the heat-retaining / cooling section is long enough to cool the reaction mixture from the reaction temperature to room temperature. The length of the heat-retaining / cooling section is usually 1 m to 10 m.

[0051] By keeping the post-reaction suspension warm using a heat-retaining device, the growth of nuclei of metal nanoparticles in the resulting post-reaction suspension can be promoted, and the metal nanoparticles can be further homogenized (ripened).

[0052] The method of flowing the raw material solution is not limited as long as the raw material solution flows, for example, from the raw material solution inlet (upstream) to the heat-retaining / cooling section (downstream). The raw material solution can be flowed at a constant speed through a pipe, for example, a straight pipe or a spiral pipe.

[0053] The flow rate of the raw material solution flowing through the piping is not limited, but is usually 70 mL / min to 300 mL / min, and in one embodiment, 120 mL / min to 180 mL / min.

[0054] In one embodiment, pressure may be applied to the raw material solution. By applying pressure, the flow rate can be easily adjusted. In one embodiment, the pressure is 0.1 MPa to 1.0 MPa.

[0055] In the present invention, a reaction proceeds in the microwave irradiation section, producing metal nanoparticles in the raw material solution, and thereafter, when a certain amount of raw material solution and / or metal nanoparticles adheres to the inner wall of the pipe, particularly the microwave irradiation section where the reaction is occurring, the position of the microwave irradiation section is moved, particularly in a direction in which the raw material solution and / or metal nanoparticles adhere to the inner wall of the pipe less. In one embodiment, the raw material solution introduction section, microwave irradiation section, and heat retention / cooling section in the pipe are each pipes arranged in a straight line, for example, a straight pipe, a spiral pipe, etc., and the microwave irradiation section is movable horizontally relative to the pipe.

[0056] The adhesion of a certain amount of raw material solution and / or metal nanoparticles to the inner wall of the pipe can be detected, for example, by visual inspection, pressure, reaction temperature, reaction time, or the like.

[0057] The term "certain amount" refers to an amount of the precursor solution and / or metal nanoparticles deposited on the inner wall of the pipe that makes it impossible to maintain the synthesis conditions for metal nanoparticles. In one embodiment, the term "certain amount" refers to an amount of the precursor solution and / or metal nanoparticles deposited on the inner wall of the pipe that accounts for 1% or more of the cross-sectional area of ​​the pipe (the area through which the precursor solution flows). In one embodiment, the term "certain amount" refers to an amount of deposition when the pressure applied to the precursor solution is 5% or more higher than the set pressure. In one embodiment, the term "certain amount" refers to an amount of deposition when the reaction temperature is 5% or more higher than the set temperature. In one embodiment, the term "certain amount" refers to an amount of deposition when the reaction time exceeds a certain time, for example, 30 minutes, 1 hour, 2 hours, or 3 hours. When the amount of deposition is determined based on the reaction time, the amount of deposition may be empirically determined through experiments. A person skilled in the art can calculate the amount of the precursor solution and / or metal nanoparticles deposited on the inner wall of the pipe per unit of time through several experiments and determine the reaction time required to reach the certain amount.

[0058] The adhesion of a certain amount of raw material solution and / or metal nanoparticles to the pipe, particularly the inner wall of the pipe in the microwave irradiation section, may be detected, for example, by a detection device such as a pressure gauge, a thermometer, or a clock, without any particular limitation. The installation location of the detection device is not limited, and it is installed in a location where each condition and physical property can be appropriately measured.

[0059] The position of the microwave irradiation unit may be moved upstream, i.e., toward the raw material solution inlet, or downstream, i.e., toward the heat-retaining / cooling unit. However, because adhesion of the raw material solution and / or metal nanoparticles is likely to occur in areas with high temperatures, it is preferable to move the position of the microwave irradiation unit upstream, i.e., toward the raw material solution inlet where metal nanoparticles are not generated.

[0060] The moving distance of the microwave irradiation unit is not limited, but is usually equal to or greater than the length of the microwave irradiation unit. In one embodiment, the microwave irradiation unit is moved at a point where adhesion of a certain amount of raw material solution and / or metal nanoparticles to the inner wall of the pipe is detected so as to prevent further adhesion of the raw material solution and / or metal nanoparticles due to further reaction of the raw material solution in the microwave irradiation unit.

[0061] By moving the position of the microwave irradiation unit, metal nanoparticles can be produced continuously without reducing productivity.

[0062] In one embodiment, the length of the heat-retaining / cooling section downstream of the microwave irradiation section is adjusted to be kept constant as the position of the microwave irradiation section is moved. That is, when the position of the microwave irradiation section is moved upstream, the length of the heat-retaining / cooling section downstream of the microwave irradiation section after the movement is adjusted to be shorter by the amount by which the position of the microwave irradiation section is moved upstream. When the position of the microwave irradiation section is moved downstream, the length of the heat-retaining / cooling section downstream of the microwave irradiation section after the movement is adjusted to be longer by the amount by which the position of the microwave irradiation section is moved downstream.

[0063] By maintaining the length of the heat-retaining / cooling section constant as the position of the microwave irradiation section moves, the temperature gradient from the reaction temperature to room temperature is also maintained constant, the maturation time of the metal nanoparticles is maintained constant, and the quality of the metal nanoparticles is also maintained constant.

[0064] Next, one embodiment of a metal nanoparticle production apparatus for carrying out the production method of the present invention will be described with reference to FIG. 1. As shown in FIG. 1, the production apparatus produces metal nanoparticles by irradiating a raw material solution L with microwaves. FIG. 1A schematically shows the production apparatus before a certain amount of raw material solution L and / or metal nanoparticles adheres to the inner wall of piping 30. FIG. 1B schematically shows the production apparatus after a certain amount of raw material solution L and / or metal nanoparticles adheres to the inner wall of piping 30, and after the microwave irradiator 32 (housing 40 and irradiator 41) has been moved toward the raw material solution inlet 31 and the recovery tank 50 has been moved toward the heat-retaining cooling unit 33 to maintain a constant length of the heat-retaining cooling unit 33. The metal nanoparticle production method of this embodiment can be easily carried out by using the metal nanoparticle production apparatus of this embodiment.

[0065] The production apparatus includes a storage tank 10 that stores a raw material solution L, a pump 20 that sucks and pumps the raw material solution L from the storage tank 10, a recovery tank 50 that recovers and stores the produced slurry suspension containing metal nanoparticles, and a pipe 30 that connects the storage tank 10 to the recovery tank 50. The pipe 30 is composed of a raw material solution inlet section 31, a microwave irradiation section 32, and a heat-retaining cooling section 33. The raw material solution L flows from the storage tank 10 through the raw material solution inlet section 31, then passes through the microwave irradiation section 32 to become a slurry suspension containing metal nanoparticles, and then passes through the heat-retaining cooling section 33 to flow to the recovery tank 50. In this embodiment, for convenience, all fluids flowing through the pipe 30 will be referred to as raw material solutions L (before and after the reaction).

[0066] The raw material solution introduction section 31 is an upstream section of the microwave irradiation section 32, and is the section up to where the raw material solution L is introduced into the microwave irradiation section 32. The temperature of the microwave irradiation section 32 is room temperature (RT).

[0067] The microwave irradiation unit 32 includes a housing 40 for accommodating the microwave irradiation unit 32 through which the raw material solution L flows, and an irradiation device 41 for irradiating microwaves to the microwave irradiation unit 32 in the housing 40. Furthermore, as described above, the manufacturing apparatus, particularly the microwave irradiation unit 32, may be provided with a detection device (not shown) for detecting the raw material solution L and / or metal nanoparticles adhering to the inner wall of the pipe 30.

[0068] The raw material solution L, which is pumped by the pump 20 and flows through the microwave irradiation unit 32, is irradiated with microwaves by the irradiation device 41 along with the microwave irradiation unit 32. The materials of the piping 30, particularly the microwave irradiation unit 32, are as described above. Furthermore, the raw material solution introduction unit 31 and the heat-retaining / cooling unit 33 of the piping 30 may be made of metals such as aluminum and stainless steel, in addition to the materials described above, except for the portion that becomes the new microwave irradiation unit 32 when the microwave irradiation unit 32 is moved, as described above. Furthermore, the microwave irradiation unit 32 may be a straight pipe, but may also be, for example, a spiral pipe. This can improve the microwave irradiation efficiency compared to a straight pipe. The average inner diameter, thickness, length, etc. of the pipe are as described above.

[0069] 1A are configured so that, as the synthesis of metal nanoparticles progresses, a certain amount of raw material solution L and / or metal nanoparticles adhere to the inner wall of pipe 30, particularly microwave irradiation section 32, and therefore they can be moved upstream as shown in FIG. 1B or downstream (not shown). For example, housing 40 and irradiation device 41 may be programmed to be moved upstream or downstream when a detection device detects that raw material solution L and / or metal nanoparticles have adhered to the inner wall of pipe.

[0070] Downstream of the microwave irradiation section 32 is the heat-retaining / cooling section 33. The post-reaction raw solution L (specifically, a slurry-like suspension containing metal nanoparticles) flowing through the microwave irradiation section 32 has been heated by the irradiation device 41, and the heat-retaining / cooling section 33 is a section that keeps the raw solution L at the temperature maintained in the method of the present invention described above, i.e., the raw solution L having a temperature gradient from the reaction temperature to room temperature. Specifically, the raw solution L flowing through the heat-retaining / cooling section 33 is optionally kept warm or cooled using a heat-retaining device (not shown), and the raw solution L maintained at a predetermined temperature, for example, room temperature, is released into the recovery tank 50. The heat-retaining / cooling section 33 may be equipped with a heat-retaining device such as a heater or a cooler.

[0071] Furthermore, as described above, it is preferable that the heat-retaining cooling unit 33 is configured so that its length can be adjusted in accordance with the upstream or downstream movement of the housing 40 and the irradiation device 41. For example, as shown in Fig. 1B, when the microwave irradiation unit 32 (housing 40 and irradiation device 41) moves a distance n upstream, the heat-retaining cooling unit 33 is adjusted to be shorter by the moved distance n. For example, when the microwave irradiation unit 32 (housing 40 and irradiation device 41) moves downstream, the heat-retaining cooling unit 33 is adjusted to be longer by the amount of the movement.

[0072] The raw material solution L sent by the pump 20 is pumped into the microwave irradiation unit 32. At this time, the pumped raw material solution L may be adjusted to a pressurized state by providing a pressure adjusting device (not shown) downstream of the heat-retaining / cooling unit 33. [Example]

[0073] The present embodiment will be described below with reference to examples, but the present invention is not limited to these examples.

[0074] Metal nanoparticles were synthesized according to the table below. The raw material solution used was silver nitrate as a precursor for the metal nanoparticles, PVP as a dispersant, and DMF as a reducing agent. The synthesis temperature was 90°C. The apparatus shown in Figure 1 was used for the synthesis in Example 1. In Table 1, "stage change" means moving the position of the microwave irradiation unit. As a result, it was found that in Example 1, even if the synthesis time was shortened by 0.4 hours, metal nanoparticles could be synthesized while suppressing the occurrence of abnormal heating in the microwave irradiation part.

[0075] [Table 1]

[0076] The method and manufacturing apparatus of the present invention can deal with the adhesion of metal nanoparticles and the like to piping immediately after the adhesion, and therefore can synthesize metal nanoparticles continuously without significantly reducing the manufacturing efficiency.

Claims

1. A method for continuously synthesizing metal nanoparticles by irradiating a raw material solution with microwaves while feeding the raw material solution through a pipe, comprising: the piping includes a microwave irradiation unit that irradiates microwaves onto the raw material solution flowing through the piping, a raw material solution introduction unit that is disposed upstream of the microwave irradiation unit, and a heat-retaining / cooling unit that is disposed downstream of the microwave irradiation unit; A method characterized by moving the position of the microwave irradiation unit when a certain amount of raw material solution and / or metal nanoparticles adheres to the inner wall of the pipe.

2. The method according to claim 1 , wherein the position of the microwave irradiation unit is moved upstream.

3. The method according to claim 1 or 2, wherein the length of the heat-retaining / cooling section is maintained constant while the position of the microwave irradiation section is moved.

4. An apparatus for producing metal nanoparticles by irradiating a raw material solution with microwaves, The apparatus includes a raw material solution storage tank, a metal nanoparticle recovery tank, and piping connecting the raw material solution storage tank and the metal nanoparticle recovery tank, the piping includes a microwave irradiation unit that irradiates microwaves onto the raw material solution flowing through the piping, a raw material solution introduction unit that is disposed upstream of the microwave irradiation unit, and a heat-retaining / cooling unit that is disposed downstream of the microwave irradiation unit; The microwave irradiation unit is movable. Device.

5. 5. The apparatus according to claim 4, further comprising an adjustment mechanism that maintains a constant length of the heat-retaining / cooling section, and a detection device that detects the raw material solution and / or metal nanoparticles adhering to the inner wall of the pipe, wherein the microwave irradiation section moves upstream when the detection device detects that a certain amount of the raw material solution and / or metal nanoparticles has adhered to the inner wall of the pipe.

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