WO2013039117A1 - Continuous synthesis method for metal core and oxide shell core-shell structure nanoparticles, continuous synthesis apparatus for same, and core-shell structure nanoparticles - Google Patents

Abstract

This invention addresses the problem of providing a method and apparatus for continuously synthesizing nanoparticles in few processes and without causing variation in particle size or aggregation, as well as providing a core-shell structure nanoparticle. This invention concerns a continuous synthesis method for core-shell structure nanoparticles, a continuous synthesis apparatus, and core-shell structure nanoparticles synthesized by this continuous synthesis method and/or this continuous synthesis apparatus, wherein: the continuous synthesis method for core-shell structure nanoparticles continuously synthesizes metal nanoparticles having a diameter of 1-100 nM through an initial stage flow-type reaction tube (3) comprising at least a single stage flow-type reaction tube, hydrolyzes an oxide precursor in a subsequent stage flow-type reaction tube (10) comprising at least a single stage flow-type reaction tube, and uniformly heats at least the flow-type reaction tube (3) through microwaves; and the continuous synthesis apparatus has initial and subsequent stage flow-type reaction tubes (3, 10), and has a means for uniformly heating at least the flow-type reaction tube (3) through microwaves, the flow-type reaction tube (3) being a reaction tube for metal core synthesis, and the other flow-type reaction tube (10) being a reaction tube for oxide shell synthesis.

Description

Continuous synthesis method and apparatus for core-shell structured nanoparticles of metal core / oxide shell and core-shell structured nanoparticles

The present invention relates to a core / shell nanoparticle of a metal core / oxide shell, a continuous synthesis method and a continuous synthesis apparatus for composite nanoparticles, and a core / shell nanoparticle.

By making the metal particles nano-sized, unique electronic, electrical, catalytic, and optical properties are manifested, so they can be used in a wide range of fields such as electronic materials, catalysts, sensors, biomaterials, molecular labels, and diagnostic markers. Has been expanded. Since metal nanoparticles have a chemically very active surface, they are easily altered by chemical substances, temperature, light, pH, etc., and aggregation between particles is likely to occur. However, it can be stabilized by coating with a suitable shell. In addition, with this coating, in the case of gold or silver nanoparticles, it is possible to adjust the distance between core particles when applying high-intensity absorption and emission due to plasmon resonance coupling between particles to markers and molecular labels. Become. Among shell materials, oxide shells are considered to be excellent shell materials because they are thermally and mechanically stable and transparent.
In general, the metal melting temperature decreases the melting temperature of the substance. For catalyst applications, it is desirable that metal nanoparticles maintain a stable shape even at high temperatures. Therefore, by covering the surface of the metal nanoparticles with a shell, it is possible to suppress melting or to restore the original shape even when melted. It is thought that it will be possible to keep.
There are several reports as a method of coating the nanoparticle core with an oxide shell. One is a method in which the core raw material solution is atomized and coated on the core particles, and is fixed by heat treatment after drying (see Patent Document 1). Further, a method using a sol-gel process in which silane alkoxide is used as a shell precursor and hydrolyzed is proposed. For example, a method is disclosed in which mercaptopropyltrimethoxysilane is used for the cadmium sulfide nanoparticles, and this is introduced into the core particle surface, and then the trimethoxysilyl moiety is hydrolyzed and coated with a silica layer (Patent Document 2). reference). Furthermore, a method of coating metal nanoparticles such as silver with a shell of titanium, silica, or zirconia as a crystal layer by adjusting the hydrolysis rate of metal alkoxide is disclosed (see Patent Document 3).
In another document, a method for producing core-shell particles in which silver nanoparticles are coated with a silica layer is reported. An aqueous solution containing silver perchlorate and sodium citrate is reduced with sodium borohydride to obtain silver nanoparticles. Thereafter, silver nanoparticles are added to an ethanol solution of tetraethoxysilane (TEOS), and the target core-shell structure is obtained by hydrolyzing TEOS with methylamine (see Non-Patent Document 1).
All of the disclosed methods for producing core-shell type nanoparticles or composite nanoparticles of metal particles and oxides are batch-type synthesis, which is a two-step reaction between the synthesis of the core particles and the shell formation.

JP 2006-232919 A JP 2003-251599 A Special table 2009-519374

In the conventional method, in the method for synthesizing the core-shell type nanoparticles and composite nanoparticles, synthesis has been performed by improving the order of introducing raw materials, the method for producing nanoparticles, and the reduction method based on a batch method. However, the batch method requires many steps and can be applied to a small amount of synthesis, but there is a limit to large-scale continuous synthesis. There are problems such as possible alteration and aggregation by the stage. Also, the batch method tends to cause variation in particle size and aggregation.
The present invention relates to a method and an apparatus for continuously synthesizing nanoparticles in which metal nanoparticles are the core and the oxide forms a shell layer of the outer skin without any variation in particle diameter or aggregation, and with fewer steps, and It is an object to provide core-shell structured nanoparticles.

The present inventors have so far researched and proposed a reaction apparatus and a reaction method using microwave energy. Japanese Patent Application Laid-Open No. 2005-322582 has proposed a device that irradiates a specific portion of a microwave in a concentrated manner by using a single mode cavity that forms a standing wave. The cavity has a metallic cylindrical resonance space, and places the reaction tube in the central portion of the cylinder, thereby concentrating the electric field on the central axis of the reaction tube. There has also been proposed an apparatus and a method in which a reaction solution is made to flow through a flow pipe and a liquid sample is continuously directly heated with high efficiency (see JP 2010-207735 A). Furthermore, a method for synthesizing metal nanoparticles having a uniform particle diameter by heating a solution in which a metal precursor is dissolved using this apparatus has been found (Japanese Patent Application Laid-Open No. 2011-137226, Japanese Patent Application No. 2011-153214). issue). These microwave heating methods have a feature that the reaction solution in circulation can be heated quickly and uniformly.
The present inventors use at least two microwave heating flow reaction devices in series, or at least one microwave heating flow reaction device as a previous flow reaction tube including at least one flow reaction tube. And at least one reaction tube as a subsequent flow reaction tube including at least one flow reaction tube, and 1) synthesis of metal core particles by microwave heating, and 2) formation of an oxide film are performed consistently. In this way, unstable metal nanoparticles are continuously sent to the next oxide coating coating stage, and core-shell structured nanoparticles of metal core / oxide shell (hereinafter also referred to as metal core / oxide shell nanoparticles) are continuously produced. Based on this finding, the present inventors have made the present invention.

That is, the present invention provides the following means.
(1) Continuously synthesizing metal nanoparticles having a diameter of 1 to 100 nanometers using a previous flow reaction tube including at least one flow reaction tube, and subsequent flow reaction including at least one flow reaction tube. A method for continuously synthesizing core / shell nanoparticles of metal core / oxide shell, wherein an oxide film is continuously formed around metal nanoparticles by hydrolyzing an oxide precursor in a tube, comprising: A continuous synthesis method of core-shell structured nanoparticles of a metal core / oxide shell, characterized in that a flow-type reaction tube is uniformly heated by microwaves.
(2) The continuous core-shell structured nanoparticles of the metal core / oxide shell according to (1), wherein the first-stage flow-type reaction tube and the second-stage flow-type reaction tube are uniformly heated by microwaves. Synthesis method.
(3) After a mixer is arranged between the preceding and following flow-type reaction tubes, the oxide precursor is mixed with the solution containing the metal core particles flowing out from the previous flow-type reaction tube using the mixer. The continuous synthesis method of core-shell structured nanoparticles of metal core / oxide shell according to (1) or (2), wherein the flow-through reaction tube is allowed to flow into the latter-stage flow-type reaction tube.
(4) The method for continuously synthesizing core-shell structured nanoparticles of metal core / oxide shell according to any one of (1) to (3), wherein the surface of the metal core particles is protected with a polymer dispersant .
(5) The metal core according to any one of (1) to (4), wherein the oxide film is formed by allowing the product solution recovered from the subsequent flow reaction tube to stand. A continuous synthesis method of core-shell structured nanoparticles of an oxide shell.
(6) The thickness of the oxide film is controlled by diluting the product solution collected from the subsequent flow-type reaction tube with water or an alcohol compound. A method for continuously synthesizing core-shell structured nanoparticles of the metal core / oxide shell described.
(7) The method for continuously synthesizing core-shell structured nanoparticles of metal core / oxide shell according to any one of (1) to (6), wherein the thickness of the oxide film is controlled to 1 to 100 nanometers.
(8) The method for continuously synthesizing core-shell structured nanoparticles of silver core / oxide shell according to any one of (1) to (7), wherein the metal core has silver nanoparticles and the shell has an oxide.
(9) The method for continuous synthesis of core-shell structured nanoparticles of platinum core / oxide shell according to any one of (1) to (7), wherein the metal core is platinum nanoparticles and the shell is an oxide.
(10) The method for continuously synthesizing core-shell structured nanoparticles of palladium core / oxide shell according to any one of (1) to (7), wherein the metal core has palladium nanoparticles and the shell has oxide.
(11) The method for continuously synthesizing core-shell structured nanoparticles of nickel core / oxide shell according to any one of (1) to (7), wherein the metal core has nickel nanoparticles and the shell has an oxide.
(12) It has a front and rear flow type reaction tube each including at least one flow type reaction tube, and has means for uniformly heating at least the previous flow type reaction tube by microwave, and the previous flow type reaction tube An apparatus for continuous synthesis of core-shell structured nanoparticles, wherein the tube is a reaction tube for synthesizing a metal core, and the flow-through reaction tube in the latter stage is a reaction tube for synthesizing an oxide shell.
(13) The continuous synthesis apparatus for core-shell structured nanoparticles according to (12), wherein at least one mixer is inserted between the upstream and downstream flow-type reaction tubes.
(14) The continuous synthesis apparatus for core-shell structured nanoparticles according to (13), wherein a plurality of the mixers are connected.
(15) The continuous-synthesizing device for core-shell structured nanoparticles according to any one of (12) to (14), which has a measuring means capable of measuring the particle size of the nanoparticles and / or the thickness of the oxide shell .
(16) The core-shell structured nanoparticle according to any one of (12) to (15), wherein a product solution outlet for taking out a product solution that has flowed through the subsequent flow reaction tube is provided. Continuous synthesizer.
(17) The core-shell structured nanoparticle according to any one of (12) to (16), wherein at least one mixer and / or the upstream and downstream flow-type reaction tubes are detachable. Continuous synthesizer.
(18) The method for continuously synthesizing the core-shell structured nanoparticles of the metal core / oxide shell according to any one of (1) to (11) and / or the core-shell structured nanoparticle according to any one of (12) to (17) A core-shell structured nanoparticle synthesized using a continuous particle synthesizer.

The above and other features and advantages of the present invention will become more apparent from the following description with reference to the accompanying drawings as appropriate.

ADVANTAGE OF THE INVENTION According to this invention, the method and apparatus which synthesize | combines the nanoparticle which forms a core-shell structure with a metal nanoparticle as a core, and an oxide is a shell, cheaply, and a metal core and oxide shell nanoparticle with uniform particle size Particles can be provided. The present invention provides nanoparticles of metal cores and oxide shells with a particle size useful for electronic materials, catalysts, sensors, biomaterials, molecular labels, diagnostic markers, imaging materials, optical materials, semiconductors, and industrial catalysts. It can be used as a method and apparatus for efficient and efficient synthesis with high yield.

BRIEF DESCRIPTION OF THE DRAWINGS It is explanatory drawing which shows in partial cross section one preferable embodiment of the continuous synthesis apparatus of the core-shell structure nanoparticle of this invention used in Example 1. FIG. It is explanatory drawing which shows other one Embodiment of the continuous synthesis | combination apparatus of the core-shell structure nanoparticle of this invention with a partial cross section figure. It is explanatory drawing which shows further another one Embodiment of the continuous synthesis | combination apparatus of the core-shell structure nanoparticle of this invention with a partial cross section figure. 4 is a graph showing the relationship between the TEM image of the silver core / silica shell nanoparticles synthesized in Example 1, the thickness of the silica shell layer, and the retention time. 2 is a graph showing a TEM image and a spectrophotometric spectrum of silver core / silica shell nanoparticles synthesized in Example 2. FIG. 4 is a TEM image of platinum core / silica shell nanoparticles synthesized in Example 3. FIG. 4 is a TEM image of platinum core / silica shell nanoparticles synthesized in Example 3. FIG. 4 is a TEM image of composite nanoparticles synthesized in Example 4. FIG. 6 is a TEM image of composite nanoparticles synthesized in Example 5. FIG. 6 is a TEM image of each of the platinum core / silica shell nanoparticles synthesized in Example 6 by changing the DMA concentration in the reaction solution. 6 is a TEM image of palladium core / silica shell nanoparticles synthesized in Example 7. FIG. 6 is a TEM image of nickel core / silica shell nanoparticles synthesized in Example 8. FIG.

In the present invention, core-shell nanoparticles are continuously synthesized by continuously generating metal fine particles in the flow-through reaction tube in the former stage and further coating the metal fine particles with oxide in the flow-through reaction tube in the subsequent stage. At this time, the preceding flow reaction tube is heated by microwaves. That is, the present invention continuously synthesizes metal nanoparticles having a diameter of 1 to 100 nanometers in the former flow type reaction tube, and hydrolyzes the oxide precursor in the latter flow type reaction tube. In the continuous synthesis method of the core-shell structure nanoparticles of the metal core / oxide shell, the oxide film is continuously heated at least when the flow-type reaction tube in the previous stage is uniformly heated by microwaves. In the present invention, the first-stage flow-type reaction tube and the second-stage flow-type reaction tube are arranged in series, and metal fine particles are continuously generated in the first-stage flow-type reaction tube. It is preferable to coat the fine particles with an oxide. FIG. 1 shows an explanatory view of a preferred embodiment of the continuous synthesis apparatus for core-shell structured nanoparticles of the present invention. An embodiment of the present invention will be described with reference to this.
In FIG. 1, two microwave heating devices are arranged in series, and a mixer 9 is arranged between the two microwave heating devices to connect flow- type reaction tubes 3 and 10. The reaction tubes 3 and 10 are preferably made of a material that easily transmits microwaves, and examples thereof include glass, quartz, and Teflon (registered trademark), but are not limited thereto. The reaction tubes 3 and 10 are preferably millimeter-sized flow tubes having an inner diameter of 2.9 mm or less and more preferably 0.5 to 1.5 mm when the microwave frequency to be irradiated is 2.4 to 2.5 GHz.

The microwave heating apparatus mainly includes a microwave oscillator / irradiation port 5 and a TM ₀₁₀ cavity 4. The cavity is configured as a metal cavity resonator having a cylindrical space inside. The internal dimensions of this space can be set as appropriate so that a standing wave called _TM010 can be formed. Standing wave TM ₀₁₀ are concentrated electric field in the cylindrical central part, along the axis and has a uniform electric field intensity distribution. A reaction tube 3 is installed as a flow-through reaction tube in the previous stage in FIG. 1 so as to penetrate along the central axis. A liquid feed pump 1 is attached to one side so that the reaction solution 2 can flow through the reaction tube 3. A radiation thermometer is attached as the thermometer 7 so that the temperature of the reaction tube 3 can be measured. An electric field monitor 6 is attached to measure the electric field strength inside. The microwave generated from the microwave oscillator / irradiation port 5 is applied to the cylindrical TM ₀₁₀ cavity 4. The oscillation frequency or the inner diameter of the cylindrical cavity 4 of the microwave in this case, it is possible to adjust the cavity 4 inside so that it can form standing waves TM ₀₁₀ is. At this time, based on a signal from the field monitor 6, it is possible to know whether the standing wave of TM ₀₁₀ is formed. If a standing wave is not formed, the standing wave is formed by changing the microwave oscillation frequency oscillated from the microwave oscillator / irradiation port 5 or adjusting the cavity inner diameter. Feedback control may be performed.
As a method for synthesizing metal nanoparticles using a microwave heating apparatus, which is a reaction by the reaction tube 3 in the previous stage, a method described in JP2011-137226A can be used.

Examples of the metal that becomes the metal core of the core-shell structured nanoparticles that can be produced by the method of the present invention include Ag, Au, Ir, Pt, Pd, Rh, Re, Ru, and Os in transition metal and typical metal complexes. Transition metals such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, Nb, Mo, Tc, and W, Al, In, Ga, Zn , Cd, Sb, Sn, Ge, Be, Mg and other typical metals may be used.
The metal core of the core-shell structured nanoparticle is formed using a metal particle precursor (sometimes referred to as a metal precursor in the present invention). As the precursor of the metal particles, for example, at least one selected from the group consisting of chlorides, nitrates, acetates, and chloro complexes of metals such as the transition metals and the typical metals is preferably used.

The metal precursor is dispersed or dissolved in a solvent having a reducing action on the metal and irradiated with electromagnetic waves. Such solvents include alcohols (methanol, ethanol, ethylene glycol, diethylene glycol, propylene glycol, tetraethylene glycol, glycerol, benzyl alcohol, dipropylene glycol, etc.), inorganic acids (boron hydroxide salt, dimethylaminoborane, phosphorous acid) Acid, hypophosphorous acid, sulfurous acid, sodium thiosulfate, Fe ion complex, hydrazine, etc.), organic acids (citric acid, malic acid, oxalic acid, formic acid, etc.), saccharides and the like.
As the solvent, a solvent having a high boiling point is preferably used, and these solvents may be mixed and used. When a solvent is used, the amount of the solvent used is preferably set so that the concentration of the metal precursor falls within the range described below.

In addition, by adding a dispersant to the liquid containing the metal precursor and coexisting the dispersant with the metal precursor in the preceding flow reaction tube, the surface of the generated metal nanoparticles is protected and aggregation is prevented. It is also preferable to increase the dispersion stability. Examples of such a dispersant include polyvinyl pyrrolidone, polyethylene glycol, polyvinyl alcohol, and a polymer dispersant. The polymer dispersant is a high molecular weight polymer into which a functional group having high affinity for the pigment surface is introduced, and is an amphiphilic one having a structure including a solvent-affinity moiety. As a polymer dispersing agent, it is soluble in a solvent that absorbs microwaves, and it can capture and disperse the fine particles generated instantaneously by an extremely fast reduction reaction in the solvent without agglomeration. It is preferable that the copolymer is effective for long-term stability, and the average molecular weight of the polymer dispersant is preferably 1,000 to 1,000,000, and particularly preferably 10,000 to 50,000. Examples of the polymer dispersant include those exemplified in JP-A-11-80647. Preferred polymer dispersants (commercially available products) include DISPERBYK 102, 108, 116, 145 manufactured by BYK Chemie. 180, 190, 191, 2096, 2155, etc., BYK154, 9076, 9077, etc., and Kyoeisha Chemical Co., Ltd. Floren G700, G900, etc. can be mentioned. The amount of the dispersing agent used is preferably 0.05 to 5000 mM, more preferably 0.5 to 500 mM, per monomer unit.

In the present invention, the concentration of the metal precursor substance in the reaction solution is preferably 0.01 mM to 1M, more preferably 0.1 mM to 100 mM.
If the reaction time is too short, the desired nanometer-sized microparticles cannot be obtained, and if the reaction time is too long, the particle size will not be uniform or the reaction solution will boil. 1 mL / h to 5 L / h, more preferably 5 to 200 mL / h. The reaction time is preferably 1 to 60 seconds.
The reaction temperature is not particularly limited but is preferably 140 to 250 ° C.
By doing so, nanometer-sized metal nanoparticles can be synthesized. In the present invention, the core metal nanoparticles have a diameter of 1 to 100 nanometers, that is, from 1 nanometer to 50 nanometers and from 50 nanometers to 100 nanometers, preferably 5 to 20 nanometers. In addition, the diameter of the metal nanoparticle in this invention means the average value measured from 100 particle | grains image | photographed by the transmission electron microscope image. In addition, metal nanoparticles having a narrow particle size distribution can be obtained with high efficiency.
The particle size distribution of the metal nanoparticles is preferably 50% or less in terms of CV value. In the present invention, when the obtained metal nanoparticles have a particle size distribution in the above range, it is said that the particle size is uniform. be able to. The CV value is a value (%) obtained by dividing the standard deviation of the diameter of the metal nanoparticles by the diameter and multiplying by 100. The standard deviation can be calculated from the particle size of 100 particles obtained from an electron microscope image.

The solution containing the metal nanoparticles synthesized by the microwave heating device for the flow-through reaction tube in the previous stage is mixed with the oxide precursor by the mixer 9. An oxide film (also referred to as an oxide shell layer) is formed by hydrolyzing the oxide precursor. The hydrolysis of the oxide precursor can employ a known method without any particular limitation. In the hydrolysis of the oxide precursor, in addition to water and the oxide precursor, for example, an amine solution can be mixed as a catalyst for promoting the hydrolysis. When the oxide coating is silica, the silica precursors include tetramethoxysilane, tetraethoxysilane, tetra (n-propoxy) silane, tetra (i-propoxy) silane, tetra (n-butoxy) silane, tetra (t- Butoxy) silane, trimethoxysilane, triethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, propyltrimethoxysilane, propyltriethoxysilane, isobutyltriethoxysilane, cyclohexyltrimethoxy Silane, cyclohexyltriethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, allyltrimethoxysilane, allyltrieth Shishiran, dimethyldimethoxysilane, dimethyldiethoxysilane, diphenyldimethoxysilane, and the like diphenyl diethoxy silane. Of these, tetraethoxysilane (TEOS) is particularly preferable. Examples of the amine solution include ammonia, methylamine, dimethylamine, and trimethylamine. The oxide precursor and the amine solution may be dissolved in alcohols and then fed to the mixer 9. As the solution concentration after mixing with the mixer, the metal concentration is preferably 0.00001M to 10M, and the amine solution is preferably 0.001mM to 2mM, more preferably 0.01M to 2M. The oxide precursor is preferably 0.0001M to 1M, and the water is preferably 1M to 20M. In FIG. 1, a four-way static mixer is used as the mixer 9. However, the mixer 9 is not limited to this as long as it is in a form capable of homogeneous mixing. Reference numeral 8 denotes a liquid feed pump for adding an oxide precursor or the like.

While the solution mixed by the mixer is flowing through the subsequent flow reaction tube 10 in FIG. 1, hydrolysis occurs and an oxide shell is formed on the surface of the metal core particles. Moreover, hydrolysis is accelerated | stimulated by microwave-heating the flow-type reaction tube 10 of a back | latter stage. The oxide shell is also formed on the surface of the metal nanoparticles by collecting the product solution 11 in the container from the outlet of the flow-type reaction tube 10 in the latter stage and allowing it to stand. Further, the thickness of the oxide film can be controlled by diluting a solution in the middle of the formation of the oxide film with water or alcohols. Furthermore, the thickness of the oxide film can also be adjusted by the holding time in which the product solution taken out from the downstream flow reaction tube 10 is allowed to stand at room temperature.
FIG. 1 shows a configuration in which the latter-stage flow-type reaction tube 10 is also provided with a microwave heating apparatus. Wave heating may not be performed. In this case, the subsequent flow type reaction tube may not be equipped with microwave heating means such as the TM ₀₁₀ cavity 4 and the microwave oscillator / irradiation port 5.

The film thickness of the oxide coating is preferably 1 to 100 nanometers, more preferably 5 to 20 nanometers. That is, the core-shell structure nanoparticles preferably have a diameter (also referred to as an average particle diameter) of 5 to 250 nanometers, and more preferably 10 to 100 nanometers. The particle size distribution of the core-shell structure nanoparticles is preferably 50% or less in terms of the CV value. In the present invention, if the obtained core-shell structure nanoparticles have a particle size distribution in the above range, “the particle size is uniform. It can be said. The CV value is as described above, and the standard deviation can be calculated from the particle diameter of 100 particles obtained from an electron microscope image.
The flow rate of the reaction solution in the subsequent flow reaction tube is preferably 50 to 2000 mL / h, and can also be 50 to 400 mL / h. Further, the reaction time in this flow-type reaction tube is preferably 0.1 to 6 seconds, and may be 0.5 to 6 seconds.
The reaction temperature in the subsequent flow reaction tube is not particularly limited, but is preferably 50 to 100 ° C. when heated.
The product solution that has passed through the front and rear flow-type reaction tubes is recovered from the product solution outlet 16 that opens to the downstream end of the rear-stage flow reaction tube.
According to the present invention, core-shell structured nanoparticles having a narrow particle size distribution can be finally obtained with high efficiency.

As described above, the continuous synthesis apparatus of the present invention has front and rear flow type reaction tubes, and has means for uniformly heating at least the previous flow type reaction tube with microwaves. The first-stage flow reaction tube is used for the synthesis of the metal core particles, and the second-stage flow reaction tube is used for the synthesis of the oxide shell. It is preferable that at least one mixer is inserted between the front and rear flow-type reaction tubes.

FIG. 2 shows a second configuration example of the continuous synthesis apparatus of the present invention. It is also possible to connect a plurality of mixers 9 in succession. For example, the oxide precursor is homogeneously mixed with the solution containing metal nanoparticles in the first mixer, and the amine solution is mixed in the second and subsequent mixers. You may mix. The same reference numerals as those in FIG.

FIG. 3 shows a third configuration example of the continuous synthesis apparatus of the present invention. In the third configuration example, a further reaction tube 12 is provided after the outlet of the reaction tube 10 as a subsequent flow type reaction tube, and an absorptiometer capable of online measurement at a position of an arbitrary length of the reaction tube 12 or the like The measuring device 15 capable of measuring the thickness of the oxide shell is connected to the mixer 14. In the case of a metal core / oxide shell nanoparticle in which the absorbance changes with the change in the thickness of the oxide film, the pump 13 at the position where the desired absorbance, that is, the thickness of the desired oxide film is obtained. By feeding water or an alcohol compound, formation of an oxide film can be suppressed, and metal core / oxide shell nanoparticles having an arbitrary oxide shell thickness can be continuously synthesized. The measurement device 15 measures the parameters corresponding to the particle size and particle size distribution of the nanoparticles, controls the conditions such as the intensity, distribution, and frequency of the microwave given to the flow-through reaction tube in the previous stage, and the flow rate of the reaction solution It is possible to control the production conditions such as the particle size, variation of the nanoparticles, thickness of the oxide film, density, etc. As an alcohol compound, what was mentioned as alcohols with the said solvent can be used.
Although there is no restriction | limiting in particular as the measuring instrument 15, In addition to what can measure the thickness of an oxide film, what can measure the particle size of a nanoparticle etc. is preferable. Alternatively, a mode in which a plurality of measuring devices are provided and the core particle diameter and the thickness of the oxide film are respectively measured is possible.

Next, the present invention will be described in more detail by way of examples, but the present invention is not limited to these examples.

Example 1
Silver core / silica shell nanoparticles were synthesized using the apparatus shown in FIG. The analysis of the particles was performed by an absorption spectrum using an ultraviolet-visible absorption spectrometer (trade name: U-3310, manufactured by Hitachi, Ltd.) and observation with a transmission electron microscope (TEM, manufactured by FEI, trade name: TECNAI G ² ). went. A reaction tube was installed along the central axis of a _TM010 single mode cavity with an inner diameter designed based on a microwave frequency of 2.45 GHz. Teflon (registered trademark), which is a representative product of a tetrafluoroethylene resin having an inner diameter of 1 mm and an outer diameter of 3 mm, was used for all the reaction tubes in this configuration example. A liquid solvent containing a metal precursor and a polymer dispersant was supplied from one side of the Teflon reaction tube with a syringe pump. The reaction raw material was irradiated with microwaves having a uniform energy distribution in a section of 100 mm and heated homogeneously. By using silver nitrate as the metal precursor and adding polyvinylpyrrolidone (average molecular weight 10,000) as the polymer dispersant, the particle size was adjusted and the silver nanoparticles were stabilized. The concentration of silver nitrate was 10 mM, and the concentration of polyvinylpyrrolidone was 300 mM per monomer unit. Ethylene glycol was used as a reaction solution solvent. Silver nanoparticles (average diameter 15 nanometers, standard deviation 1.7) were synthesized by feeding a solution obtained by mixing them into the previous reaction tube 3 with a syringe pump and heating them with microwaves. As for the particle size distribution, the CV value was 11%, and nanoparticles having a uniform particle size were obtained. The heating temperature was 140 ° C., and the liquid feeding speed was 6 mL / h.

A solution containing silver nanoparticles synthesized in the previous reaction tube 3 (production density (amount) of silver nanoparticles 0.1 wt%) was fed to a four-way static mixer. An ethanol solution containing TEOS, an ethanol solution containing water and dimethylamine, and a solution containing silver nanoparticles were mixed from three directions and fed to the reaction tube 10 at the subsequent stage. The flow rate after mixing with the mixer was 320 mL / h, the silver concentration was 0.0002M, the TEOS concentration was 0.014M, the dimethylamine concentration was 0.4M, and the water was 12M. The subsequent reaction tube 10 was heated by microwaves at 70 ° C., and the product solution was recovered in a container, and the state was kept at room temperature. FIG. 4 shows a TEM image of the synthesized core-shell structured nanoparticles with respect to the retention time, which is the elapsed time from the start of retention at room temperature. From the TEM image (a) of the particles having a retention time of 5 minutes after that shown in FIG. 4, it was found that silver nanoparticles were formed at the center and a homogeneous silica shell was formed on the surface of the silver nanoparticles. It has been confirmed that the thickness of the silica shell is constant after the holding time of 10 minutes and there is no change in appearance even after one week.
FIG. 4 shows TEM images (b) to (f) of the core-shell structured nanoparticles when the product solution is collected in a container without performing microwave heating in the subsequent reaction tube 10 and left standing. It was confirmed that the silica shell was formed after the retention time of 6 minutes and the shell thickness was constant after 20 minutes. When the time change of the thickness of the silica shell layer with and without microwave heating in FIG. 4 was compared, it was found that the formation time of the silica shell layer was shortened by microwave heating.
The particle size distribution of the core-shell structure nanoparticles (average diameter 51 nanometers, standard deviation 3.5) had a CV value of 7%, and nanoparticles with uniform particle sizes were obtained.

Example 2
The product solution in the middle of the formation of the silica shell obtained in the same manner as in Example 1 was subjected to ethanol retention at 7 minutes, 8 minutes, and 10 minutes after the retention time, which was the elapsed time from the start of retention at room temperature. FIG. 5 shows TEM images (g) to (i) and absorption spectra observed after 10-fold dilution and further maintained at room temperature for 24 hours. When the holding time is 7 minutes, a silica shell with a thickness of 5 nm is formed. By diluting after an arbitrary holding time, the silica shell is arbitrarily controlled with a thickness of 5 nm or more. It was confirmed that the thickness of the shell could be maintained. Further, from the absorption spectrum, as the silica shell layer becomes thicker, the peak intensity increases and it is confirmed that the peak wavelength is shifted to the higher wavelength side, so when using the apparatus shown in FIG. From the value of the absorption spectrum, it can be said that silver core / silica shell nanoparticles having an arbitrary silica shell thickness can be continuously synthesized.

Example 3
An apparatus configuration example shown in FIG. 2 (however, a downstream flow-type reaction tube 10 is arranged downstream of the second mixer 9, and includes a microwave heating means, a _TM010 cavity 4, a microwave oscillator, The platinum core / silica shell nanoparticles were synthesized using the irradiation port 5 and the like. The fluid type reaction tubes 3 and 10 are the same as the reaction tube of Example 1. Hexachloroplatinic acid (10 mM), which is a chloro complex, is used as a metal precursor, polyvinylpyrrolidone (50 mM per monomer unit, average molecular weight 40,000) as a polymer dispersant, and the size of platinum nanoparticles are controlled. Sodium nitrate (50 mM) for dissolution in ethylene glycol, which is a reaction solution solvent, is sent to the previous reaction tube 3 with a syringe pump, and is heated by microwaves to form platinum nanoparticles (average diameter 10 nanometer, The particle size distribution was 20% in terms of CV value). The heating temperature was 170 ° C., and the liquid feeding speed was 6 mL / h. The solution containing platinum nanoparticles synthesized in the previous reaction tube 3 was sent to the first static mixer 9, and the solution containing platinum nanoparticles and the same amount of ethanol were mixed. Subsequently, an ethanol solution containing TEOS and an ethanol solution containing water and dimethylamine were mixed in the second static mixer 9 and fed to the reaction tube 10 at the subsequent stage. The flow rate after mixing with the mixer was 600 mL / h, the platinum concentration was 0.0001M, the TEOS concentration was 0.0088M, the dimethylamine concentration was 0.06M, and water was 12M. The platinum core / silica shell nanoparticles (average diameter 60 nanometers, CV value 12%) when the solution is collected in a container without performing microwave heating in the subsequent reaction tube 10 and kept at room temperature for 1 hour are different magnifications. The TEM images taken in Fig. 6 are shown in Figs. 6a and 6b. As shown in FIGS. 6a and 6b, it can be seen that a platinum nanoparticle is formed at the center, and a silica shell (thickness 25 nm) is formed on the surface of the platinum nanoparticle.

In Examples 4 to 6 below, among the composite nanoparticles composed of platinum and silica synthesized by changing the TEOS concentration and the dimethylamine (DMA) concentration, the platinum core silica in which the platinum nanoparticles are coated with a silica shell Composite nanoparticles in which platinum nanoparticles are attached to the surface of shell nanoparticles, composite nanoparticles in which silica particles and platinum nanoparticles are aggregated and silica particles are coated around the platinum nanoparticles, and have an arbitrary average particle size An example of synthesis of platinum core / silica shell nanoparticles will be shown. The composition of the reaction raw materials used in each example is as shown in Table 1.

Example 4
Example 4 is a synthesis example of platinum-silica composite nanoparticles in which platinum nanoparticles are coated with a silica shell and platinum nanoparticles not coated with silica are attached to the surface of the silica shell. It is. In Example 4, conditions other than the composition shown in Table 1 were set basically in the same manner as in Example 3 to synthesize platinum core / silica shell nanoparticles (average diameter 60 nm, CV value 11%). In addition, the diameter of the platinum nanoparticles was 10 nanometers, and the particle size distribution was 20% in terms of CV value. FIG. 7 shows a TEM image of the composite nanoparticles of platinum and silica synthesized in Example 4. In FIG. 7, it can be confirmed that there are two or three 10 nanometer platinum nanoparticles appearing in black around the 60 nanometer platinum core / silica shell nanoparticles appearing translucently. . When the TEOS concentration is lowered in the composition of the reaction raw material, the number of silica particles decreases, and the number of platinum nanoparticles relatively increases. It is also possible to adjust the number density of platinum nanoparticles adhering to the surface of the platinum core / silica shell nanoparticles by adjusting the TEOS concentration.

Example 5
Example 5 is a synthesis example of composite nanoparticles having a form in which the periphery of a platinum core is coated by attaching particulate silica to the surface of platinum nanoparticles. In Example 5, conditions other than the composition shown in Table 1 were set basically in the same manner as in Example 3 to synthesize composite nanoparticles (average diameter 140 nm, CV value 45%). In addition, the diameter of the platinum nanoparticles was 10 nanometers, and the particle size distribution was 20% in terms of CV value. FIG. 8 shows a TEM image of the composite nanoparticles synthesized in Example 5. According to FIG. 8, it can be seen that a large number of nanoparticles having a diameter of 10 nanometers appearing in black are dispersed in silica particles having a diameter of about 140 nanometers appearing in a translucent gray color. It can be seen that when the TEOS concentration and the DMA concentration in the reaction solution are lowered in the composition of the reaction raw material, composite silica particles covering the periphery of the metal core can be obtained by attaching particulate silica to the surface of the platinum nanoparticles. It was.

Example 6
Example 6 is a synthesis example of platinum core / silica shell nanoparticles having an arbitrary average particle size. Example 6 consists of four types of Examples 6-1 to 6-4 in which the concentration of MDA in the reaction solution was changed. Conditions other than the composition shown in Table 1 were basically set in the same manner as in Example 3, and platinum was used. Core silica shell nanoparticles were synthesized. In addition, the diameter and particle size distribution (CV value%) of platinum nanoparticles, and the average particle diameter and particle size distribution (CV value%) of platinum core / silica shell nanoparticles (referred to as core-shell structure nanoparticles in Table 1). Is shown in Table 1. FIG. 9 shows TEM images of the platinum core / silica shell nanoparticles synthesized in Examples 6-1 to 6-4. It was found that platinum core / silica shell particles having an arbitrary average particle diameter of 20 nm to 140 nm can be synthesized by changing the DMA concentration in the reaction solution. In addition, the tendency which the synthetic | combination amount of the platinum nanoparticle which does not have a silica shell increases as the DMA density | concentration in a reaction liquid is made high was confirmed.

Example 7
An apparatus configuration example shown in FIG. 2 (however, a flow type reaction tube 10 is arranged downstream of the second mixer 9, and heating means by microwave, _TM010 cavity 4, microwave oscillator / irradiation port 5 may not be provided.) Was used to synthesize palladium core / silica shell nanoparticles. The fluid type reaction tubes 3 and 10 are the same as the reaction tube of Example 1. Using palladium chloride (2 mM) as a metal precursor, polyvinyl pyrrolidone (50 mM per monomer unit, average molecular weight 40,000) as a polymer dispersant is dissolved in ethylene glycol as a reaction solution solvent, The solution was sent to the reaction tube 3 and heated with microwaves to synthesize palladium nanoparticles (average diameter: 8 nanometers, CV value: 13%). The heating temperature was 170 ° C., and the liquid feeding speed was 6 mL / h. The solution containing the palladium nanoparticles synthesized in the previous reaction tube 3 was sent to the first static mixer 9, and the solution containing the palladium nanoparticles and the same amount of ethanol were mixed. Subsequently, TEOS and an ethanol solution containing water and dimethylamine were mixed in the second static mixer 9 and fed to the reaction tube 10 at the subsequent stage. After mixing with the mixer, the palladium concentration was 0.00004M, the TEOS concentration was 0.0088M, the dimethylamine concentration was 0.06M, water was 12M, and the flow rate was 300 mL / h. FIG. 10 shows a TEM image of the palladium core / silica shell nanoparticles when the solution was collected in a container without performing microwave heating in the subsequent reaction tube 10 and kept at room temperature for 1 hour. As shown in FIG. 10, it can be seen that palladium nanoparticles are present at the center, and a silica shell (thickness 20 nm) is formed on the surface of the palladium nanoparticles. The particle size distribution of the palladium core / silica shell under these synthesis conditions was an average diameter of 48 nanometers and a CV value of 7%.

Example 8
An apparatus configuration example shown in FIG. 2 (however, a flow type reaction tube 10 is arranged downstream of the second mixer 9, and heating means by microwave, _TM010 cavity 4, microwave oscillator / irradiation port 5 may not be provided), and nickel core / silica shell nanoparticles were synthesized. The fluid type reaction tubes 3 and 10 are the same as the reaction tube of Example 1. Nickel acetate tetrahydrate (5 mM) is used as a metal precursor, polyvinylpyrrolidone (100 mM per monomer unit, average molecular weight 40,000) as a polymer dispersant, and dioctyl for controlling the size of nickel nanoparticles Amine (10 mM) is dissolved in ethylene glycol, which is a reaction solvent, and is sent to the previous reaction tube 3 with a syringe pump, and heated by microwaves to form nickel nanoparticles (average diameter 15 nm, CV value 13%) ) Was synthesized. The heating temperature was 170 ° C., and the liquid feeding speed was 1 mL / h. The solution containing nickel nanoparticles synthesized in the previous reaction tube 3 was sent to the first static mixer 9, and the solution containing nickel nanoparticles and the same amount of ethanol were mixed. Subsequently, TEOS and an ethanol solution containing water and dimethylamine were mixed in the second static mixer 9 and fed to the reaction tube 10 at the subsequent stage. The flow rate after mixing with the mixer was 50 mL / h, the nickel concentration was 0.0001M, the TEOS concentration was 0.0088M, the dimethylamine concentration was 0.06M, and water was 12M. FIG. 11 shows a TEM image of the nickel core / silica shell nanoparticles when the solution was collected in a container without performing microwave heating in the subsequent reaction tube 10 and kept at room temperature for 1 hour. As shown in FIG. 11, it can be seen that nickel nanoparticles (particle diameter: 15 nanometers) are present at the center, and a silica shell (thickness: 20 nanometers) is formed on the surface of the nickel nanoparticles. The particle size distribution of the nickel core / silica shell synthesized under these conditions was an average diameter of 55 nanometers and a CV value of 8%.

In the above description, the present invention has been described with reference to an embodiment in which the production is divided into the former stage and the latter stage. However, as described above, this embodiment can be applied to the first-stage flow reaction tube and the second-stage flow reaction tube. A case where a plurality of each or any one of them is provided is also included. For example, as shown in FIG. 3, the subsequent stage may be performed with a plurality of flow-type reaction tubes. At this time, the number of flow-type reaction tubes before and after the microwave heating is not particularly limited. For example, at least one or a plurality or all of the flow reaction tubes at the front and rear stages may be heated by microwaves. In addition, a mode in which a plurality of front and rear flow-type reaction tubes are provided is not particularly limited, and a plurality of front and rear flow-type reaction tubes may be arranged in series or in parallel.
In addition to the flow reaction tubes at the front and rear stages, a flow tube for circulating or mixing a raw material such as a metal precursor, a solvent, an oxide precursor, an amine solution, or a solution containing metal nanoparticles may be provided. Good. For example, a flow tube can be provided further upstream than the flow reaction tube of the previous step. Moreover, a flow pipe can be provided between the front and rear flow type reaction tubes. Furthermore, a flow tube can be provided further downstream of the flow reaction tube at the subsequent stage.
It is preferable that at least a flow type reaction tube and a mixer are detachably provided. By doing so, it is possible to diversify the types and forms of the nanoparticles to be produced, to easily control the quality, and to further reduce the production cost, thereby further enhancing the effects of the present invention. it can.
In the above description, silica has been described as an example of the oxide. However, the oxide is not limited to silica because the oxide precursor can be hydrolyzed, and there are alumina, zirconia, and the like. Particles and composite nanoparticles can be synthesized.
The present invention has been described above including the embodiments. However, the present invention is not limited to this, and many variations are possible based on the technical idea of the present invention. Composite nanoparticles synthesized using a synthesis method and / or a continuous synthesis apparatus also belong to the present invention. This composite nanoparticle is a nanoparticle composed of different types of nanoparticles and oxide particles, for example, composite nanoparticles in which the nanoparticles are metal particles and the oxide is attached to a part of the surface. It is done. More specifically, the composite nanoparticles include composite nanoparticles in which platinum nanoparticles not coated with silica are attached to the surface of the core-shell structured nanoparticles as in Example 4, and platinum as in Example 5. Examples include composite nanoparticles in which particulate silica adheres to the surface of the nanoparticles and covers the periphery of the platinum core. Therefore, the continuous synthesis method and / or continuous synthesis apparatus of the present invention can synthesize such composite nanoparticles. The core-shell structured nanoparticles of the present invention can be used in various chemical reaction processes due to the activity of the catalyst, which is one of their uses.

Metal core / oxide shell structure nanoparticles and composite nanoparticles synthesized by the continuous synthesis method and continuous synthesis apparatus of the present invention are converted into electronic materials, catalysts, sensors, biomaterials, molecular labels (molecular labels), diagnostic markers, By using it as an image forming material, an optical material, a semiconductor, or an industrial catalyst, it is possible to further improve the quality and cost of products in this field.

While this invention has been described in conjunction with its embodiments, we do not intend to limit our invention in any detail of the description unless otherwise specified and are contrary to the spirit and scope of the invention as set forth in the appended claims. I think it should be interpreted widely.

This application claims priority based on Japanese Patent Application No. 2011-198001 filed in Japan on September 12, 2011, all of which are incorporated herein by reference. As part of.

1 Liquid feed pump 2 Reaction liquid 3 Reaction tube 4 TM ₀₁₀ cavity 5 Microwave oscillator / irradiation port 6 Electric field monitor 7 Thermometer 8 Liquid feed pump 9 Mixer 10 Reaction tube 11 Product solution 12 Reaction tube 13 Liquid feed pump (for dilution)
14 Mixer (for dilution)
15 Equipment for measuring oxide shell thickness 16 Product solution outlet

Claims (18)

1. Metal nanoparticles having a diameter of 1 to 100 nanometers are continuously synthesized by a preceding flow reaction tube including at least one flow reaction tube, and oxidized in a subsequent flow reaction tube including at least one flow reaction tube. A metal core / oxide shell core-shell structured nanoparticle continuous synthesis method in which an oxide film is continuously formed around metal nanoparticles by hydrolyzing a precursor of the metal precursor, and at least the previous flow-type reaction A method for continuously synthesizing core-shell structured nanoparticles of metal core / oxide shell, characterized in that the tube is uniformly heated by microwaves.
2. The method for continuously synthesizing core-shell structured nanoparticles of a metal core / oxide shell according to claim 1, wherein the first-stage flow-type reaction tube and the second-stage flow-type reaction tube are uniformly heated by microwaves.
3. A mixer is disposed between the upstream and downstream flow-type reaction tubes, and after mixing the oxide precursor into the solution containing the metal core particles flowing out of the upstream flow-type reaction tube, the post-stage 3. The method for continuously synthesizing core-shell structured nanoparticles of a metal core / oxide shell according to claim 1 or 2, wherein
4. 4. The method for continuously synthesizing core-shell structured nanoparticles of a metal core / oxide shell according to claim 1, wherein the surface of the metal core particles is protected with a polymer dispersant.
5. The metal core / oxide shell according to any one of claims 1 to 4, wherein an oxide film is formed by allowing the product solution recovered from the subsequent flow reaction tube to stand still. Of continuous synthesis of core-shell structured nanoparticles.
6. The metal according to any one of claims 1 to 5, wherein the thickness of the oxide film is controlled by diluting the product solution recovered from the subsequent flow-type reaction tube with water or an alcohol compound. A continuous synthesis method for core / shell nanoparticles of core / oxide shell.
7. The method for continuously synthesizing core / shell nanoparticles of metal core / oxide shell according to any one of claims 1 to 6, wherein the thickness of the oxide film is controlled to 1 to 100 nanometers.
8. The method for continuously synthesizing core-shell structured nanoparticles of a silver core / oxide shell according to any one of claims 1 to 7, wherein the metal core has silver nanoparticles and the shell has an oxide.
9. The method for continuously synthesizing core-shell structured nanoparticles of platinum core / oxide shell according to any one of claims 1 to 7, wherein the metal core has platinum nanoparticles and the shell has oxide.
10. The method for continuously synthesizing core-shell structured nanoparticles of palladium core / oxide shell according to any one of claims 1 to 7, wherein the metal core has palladium nanoparticles and the shell has oxide.
11. The method for continuously synthesizing core-shell structured nanoparticles of nickel core / oxide shell according to any one of claims 1 to 7, wherein the metal core has nickel nanoparticles and the shell has oxide.
12. A front and rear flow type reaction tube each including at least one flow type reaction tube; and at least means for heating the previous flow type reaction tube by microwaves, wherein the previous flow type reaction tube is a metal An apparatus for continuous synthesis of core-shell structured nanoparticles, characterized in that it is a reaction tube for core synthesis, and the downstream reaction tube is a reaction tube for oxide shell synthesis.
13. The apparatus for continuous synthesis of core-shell structured nanoparticles according to claim 12, wherein at least one mixer is inserted between the front and rear flow-type reaction tubes.
14. 14. The continuous synthesis apparatus for core-shell structured nanoparticles according to claim 13, wherein a plurality of the mixers are connected.
15. 15. The apparatus for continuously synthesizing core-shell structured nanoparticles according to any one of claims 12 to 14, further comprising measuring means capable of measuring the particle diameter of the nanoparticles and / or the thickness of the oxide shell.
16. The continuous synthesis apparatus for core-shell structured nanoparticles according to any one of claims 12 to 15, further comprising a product solution outlet for taking out a product solution that has flowed through the downstream flow reaction tube. .
17. The apparatus for continuous synthesis of core-shell structured nanoparticles according to any one of claims 12 to 16, wherein at least one mixer and / or the upstream and downstream flow-type reaction tubes are detachably provided. .
18. The method for continuously synthesizing the core-shell structured nanoparticles of the metal core / oxide shell according to any one of claims 1 to 11 and / or the continuation of the core-shell structured nanoparticles according to any one of claims 12 to 17. A core-shell structured nanoparticle synthesized using a synthesizer.

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