JP6551495B2 - Continuous synthesis method and continuous synthesis apparatus for core-shell structured nanoparticles of metal core / oxide shell and core-shell structured nanoparticles - Google Patents

Description

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

Metal particles are applied to a wide range of fields such as electronic materials, catalysts, sensors, biomaterials, molecular labels, diagnostic markers, etc., because their unique electronic, electrical, catalytic and optical properties are expressed by making them nano-sized. Is deployed. 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 luminescence due to plasmon resonance coupling between particles to markers and molecular labels. Become. Among the shell materials, the oxide shell is considered to be an excellent shell material because it is thermally and mechanically stable and transparent.
In general, the metal melting temperature decreases the melting temperature of the substance. In catalytic applications, metal nanoparticles are desired to maintain a stable shape even at high temperatures, so by covering the metal nanoparticle surface with a shell, suppression of melting and the original shape even when melted are desired. It is believed that it will be possible to keep it.
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). In addition, a method using a sol-gel process in which a silane alkoxide is used as a shell precursor and which is 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, there is disclosed a method of coating a metal nanoparticle such as silver with a shell of titanium, silica or zirconia as a crystal layer by adjusting the hydrolysis rate of the metal alkoxide (see Patent Document 3).
In another document, a method of 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 TEOS is hydrolyzed with methylamine to obtain a target core-shell structure (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 JP2003-251599A Special table 2009-519374

Journal of Colloid and Interface Science, 2005, 283, 392-396

In the conventional method, in the method of synthesizing the core-shell type nanoparticles and the composite nanoparticles, the synthesis has been performed by improving the order of introduction of raw materials, the method of forming nanoparticles, and the reduction method under 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 An object of the present invention is 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 an apparatus that concentrates and irradiates a microwave to a specific part 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 allowed to flow through a flow pipe and a liquid sample is continuously directly heated with high efficiency (see JP 2010-207735 A). Furthermore, the method which synthesize | combined the metal nanoparticle with uniform particle diameter by heating the solution which melt | dissolved the metal precursor using this apparatus was discovered (Unexamined-Japanese-Patent 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 synthesize metal nanoparticles having a diameter of 1 to 100 nanometers using a preceding flow reaction tube including at least one flow reaction tube, and then perform a 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, an oxide precursor is mixed with the solution containing the metal core particles flowing out of the previous flow-type reaction tube using the mixer. A continuous synthesis method of core-shell structured nanoparticles of metal core / oxide shell according to (1) or (2), which is made to flow into the downstream flow type reaction tube.
(4) A continuous synthesis method of core-shell structured nanoparticles of metal core / oxide shell according to any one of (1) to (3), characterized in that the surface of the metal core particle is protected by 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. Continuous synthesis method of oxide shell core-shell structured nanoparticles.
(6) The product solution recovered from the subsequent flow-type reaction tube is diluted with water or an alcohol compound, thereby controlling the thickness of the oxide film (1) to (5) A method for continuously synthesizing core-shell structured nanoparticles of the metal core / oxide shell described.
(7) The continuous synthesis method of core-shell structured nanoparticles of metal core / oxide shell according to any one of (1) to (6), wherein the film thickness of the oxide film is controlled to 1 to 100 nm.
(8) A method for continuously synthesizing a core / shell structured nanoparticle of a 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 continuously synthesizing a core / shell structured nanoparticle of a platinum core / oxide shell according to any one of (1) to (7), which has platinum nanoparticles as the metal core and an oxide as the shell.
(10) A continuous synthesis method of a core-shell structured nanoparticle of a palladium core-oxide shell according to any one of (1) to (7), wherein the metal core has a palladium nanoparticle and the shell has an oxide.
(11) The continuous synthesis method of 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 A continuous synthesis apparatus of core-shell structured nanoparticles, wherein the pipe is a reaction pipe for metal core synthesis, and the flow-through type reaction pipe at the latter stage is a reaction pipe for oxide shell synthesis.
(13) An apparatus for continuously synthesizing core-shell structured nanoparticles according to (12), wherein at least one mixer is inserted between the front and rear flow-through 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 synthesis apparatus of core-shell structured nanoparticles according to any one of (12) to (14), characterized by having 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 nanoparticles according to any one of (12) to (16), wherein at least one mixer and / or the upstream and downstream flow-type reaction tubes are detachably provided. Continuous synthesizer.
(18) The method for continuous synthesis of the core-shell structure nanoparticles of the metal core / oxide shell according to any one of (1) to (11) and / or the core-shell structure nanostructure according to any one of (12) to (17) A core-shell structured nanoparticle synthesized using a continuous particle synthesizer.
In addition, the inventors have filed a divisional application for the following claims. At least a part of the claims in this divisional application is realized by using a continuous synthesis method of core-shell structured nanoparticles of metal core / oxide shell produced by uniformly heating at least the preceding flow-type reaction tube with microwaves It can be done.
The invention according to claim 1 is a core-shell structure nanoparticle of a metal core / oxide shell having a metal nanoparticle as a core and an oxide as a shell, wherein the metal core has Ag, Au, Ir, Pt, Pd, Rh, Transition metals such as Re, Ru, and Os, transition metals such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, Nb, Mo, Tc, W, Al, In, Ga , Zn, Cd, Sb, Sn, Ge, Be, Mg, etc., at least one selected from typical metals, and the precursor thereof is tetramethoxysilane, tetraethoxysilane, tetra (n Propoxy) silane, tetra (i-propoxy) silane, tetra (n-butoxy) silane, tetra (t-butoxy) silane, trimethoxysilane, triethoxysilane, methyltri Toxisilane, methyltriethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, propyltrimethoxysilane, propyltriethoxysilane, isobutyltriethoxysilane, cyclohexyltrimethoxysilane, cyclohexyltriethoxysilane, phenyltrimethoxysilane, phenyltriethoxy Examples include silane, vinyltrimethoxysilane, vinyltriethoxysilane, allyltrimethoxysilane, allyltriethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, diphenyldimethoxysilane, and diphenyldiethoxysilane. Particularly preferred among these are core-shell structured nanoparticles of a metal core / oxide shell, characterized in that it is composed of an oxide whose raw material is at least one selected from tetraethoxysilane (TEOS). is there.
The invention according to claim 2 is characterized in that, in the core-shell structured nanoparticles of the metal core / oxide shell according to claim 1, the oxide shell contains an oxide having TEOS as a precursor. It is a core-shell structured nanoparticle of a metal core / oxide shell.
The invention according to claim 3 is the core-shell structure nanoparticle of the metal core / oxide shell according to claim 1 or 2, wherein the core-shell structure nanoparticle of the metal core / oxide shell is placed inside the outermost oxide shell. It is a core-shell structure nanoparticle of a metal core / oxide shell characterized by containing particles.

  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 an inexpensive method for efficiently synthesizing with high yield.

FIG. 1 is an explanatory view showing a preferable embodiment of the continuous synthesis apparatus of core-shell structured nanoparticles of the present invention used in Example 1 partially in cross section. It is explanatory drawing which shows one part another embodiment of the continuous synthesis | combination apparatus of the core-shell structure nanoparticle of this invention in sectional drawing. It is an explanatory view showing a partial cross-sectional view of still another embodiment of the continuous synthesis apparatus of core-shell structured nanoparticles of the present invention. It is a graph which shows the relationship between the TEM image of the silver core * silica shell nanoparticle synthesize | combined in Example 1, and thickness of a silica shell layer, and retention time. FIG. 6 is a graph showing a TEM image and an absorption spectrum of silver core / silica shell nanoparticles synthesized in Example 2. FIG. 7 is a TEM image of platinum core-silica shell nanoparticles synthesized in Example 3. FIG. 7 is a TEM image of platinum core-silica shell nanoparticles synthesized in Example 3. FIG. 7 is a TEM image of composite nanoparticles synthesized in Example 4. FIG. 7 is a TEM image of the composite nanoparticle synthesized in Example 5. FIG. FIG. 14 is a TEM image of each of platinum core / silica shell nanoparticles synthesized by changing the DMA concentration in the reaction solution in Example 6. FIG. FIG. 16 is a TEM image of palladium core-silica shell nanoparticles synthesized in Example 7. FIG. FIG. 16 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 flow-through type reaction tube at the front stage is heated by microwave. That is, according to the present invention, metal nanoparticles having a diameter of 1 to 100 nm are continuously synthesized by the upstream flow type reaction tube, and metal nanoparticles are hydrolyzed in the downstream flow type reaction tube by hydrolyzing the oxide precursor. 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. One embodiment of the present invention will be described with reference to this.
In FIG. 1, two microwave heating devices are disposed in series, and a mixer 9 is disposed 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. As the reaction tubes 3 and 10, when the microwave frequency to be irradiated is 2.4 to 2.5 GHz, a millimeter-sized flow tube having an inner diameter of 2.9 mm or less is preferable, and 0.5 to 1.5 mm is more preferable.

The microwave heating apparatus mainly includes a microwave oscillator / irradiation port 5 and a TM010 cavity 4. The cavity is configured as a metal cavity resonator having a cylindrical space inside. The internal dimensions of this space can be appropriately set so that a standing wave called TM010 can be formed. The standing wave of TM010 has an electric field concentrated at the center of the cylinder, and has a uniform electric field strength distribution along the axis. 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 TM010 cavity 4. At this time, the oscillation frequency of the microwave or the inner diameter of the cylindrical cavity 4 can be adjusted so that a standing wave of TM010 can be formed inside the cavity 4. At this time, based on the signal from the electric field monitor 6, it can be known whether a TM010 standing wave is formed. If the 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.
The method described in JP 2011-137226 A can be used 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.

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. And the like are most preferable, but transition metals such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, Nb, Mo, Tc, 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 described above is favorably 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. Such dispersants include polyvinyl pyrrolidone, polyethylene glycol, polyvinyl alcohol, polymer dispersants and the like. 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 the long-term stability of the polymer, 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 Big 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 dispersant used is preferably 0.05 to 5000 mM, and 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. The metal nanoparticles to be the core in the present invention have a diameter of 1 to 100 nm, that is, 1 to 50 nm and more than 50 nm to 100 nm or less, preferably 5 to 20 nm. 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 with 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 CV value, and 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 upstream flow type reaction tube is mixed with the oxide precursor in the mixer 9. The oxide precursor (also referred to as an oxide shell layer) is formed by hydrolyzing the oxide precursor. For hydrolysis of the oxide precursor, known methods can be employed without 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 film 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. Among these, tetraethoxysilane (TEOS) is particularly preferable. As an amine solution, ammonia, methylamine, dimethylamine and trimethylamine can be mentioned. The oxide precursor and the amine solution may be dissolved in the alcohol and then sent 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, and more preferably 0.01M to 2M. The oxide precursor is preferably 0.0001 M to 1 M, and the water is preferably 1 M to 20 M. 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. The code | symbol 8 is a liquid feeding pump for adding an oxide precursor etc.

While the solution mixed by the mixer flows through the downstream flow type reaction tube 10 in FIG. 1, hydrolysis occurs and an oxide shell is formed on the surface of the metal core particle. Moreover, hydrolysis is accelerated | stimulated by microwave heating the subsequent flow type reaction tube 10. FIG. 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 be adjusted also by the holding time in which the product solution taken out from the downstream flow reaction tube 10 is left 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 device. However, the latter-stage flow-type reaction tube 10 has a micro-core according to the core-shell structure nanoparticles to be manufactured, its specifications, physical properties, etc. Sometimes there is no wave heating. In this case, the flow type reaction tube in the latter stage may not be provided with a heating means by microwaves, for example, the TM010 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 structured nanoparticles preferably have a diameter (also referred to as average particle diameter) of 5 to 250 nm, and more preferably 10 to 100 nm. 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. Moreover, as reaction time in this flow-through type reaction tube, 0.1 to 6 second is preferable, and it can also be 0.5 to 6 second.
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 finally having a narrow particle size distribution can be obtained with high efficiency.

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

  The 2nd structural example of the continuous synthesizer of this invention is shown in FIG. It is also possible to connect a plurality of mixers in series, 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.

The 3rd structural example of the continuous synthesizer of this invention is shown in FIG. In the third configuration example, an additional reaction tube 12 is provided after the outlet of the reaction tube 10 as a downstream flow-through reaction tube, and an absorptiometer capable of online measurement at 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 parameters corresponding to the particle size and particle size distribution of the nanoparticles are measured by the measuring device 15, and conditions such as the intensity, distribution, and frequency of microwaves given to the flow-through type reaction tube in the previous stage are controlled. 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 the alcohol compound, those exemplified as alcohols in the above-mentioned 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.
(Example)

  EXAMPLES The present invention will next be described in more detail by way of examples, which should not be construed as limiting the invention thereto.

Example 1
Silver core / silica shell nanoparticles were synthesized using the apparatus shown in FIG. The analysis of the particles is performed by observation with an absorption spectrum using an ultraviolet-visible absorption spectrum meter (manufactured by Hitachi, Ltd., trade name: U-3310) and observation with a transmission electron microscope (TEM, manufactured by FEI, trade name: TECNAI G2). It was. A reaction tube was installed along the central axis of a TM010 single mode cavity having 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 by a syringe pump from one side of a Teflon (registered trademark) reaction tube. The reaction raw material was irradiated with microwaves having a uniform energy distribution in a section of 100 mm, and was uniformly heated. By using silver nitrate as the metal precursor and adding polyvinylpyrrolidone (average molecular weight: 10,000) as the polymer dispersant, adjustment of particle size and stabilization of silver nanoparticles were achieved. The concentration of silver nitrate was 10 mM, and the concentration of polyvinyl pyrrolidone was 300 mM per monomer unit. Ethylene glycol was used as a reaction solution solvent. The solution which mixed these was sent to the reaction tube 3 of a front | former stage with a syringe pump, and the silver nanoparticle (average diameter 15 nanometer, standard deviation 1.7) was synthesize | combined by carrying out microwave heating. 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 transfer rate was 6 mL / h.

A solution containing silver nanoparticles synthesized in the reaction tube 3 in the preceding stage (the formation 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 mixer mixing was 320 mL / h, the silver concentration was 0.0002 M, the TEOS concentration was 0.014 M, the dimethylamine concentration was 0.4 M, and the water was 12 M. The subsequent reaction tube 10 was subjected to microwave heating at 70 ° C., and the product solution was collected in a container, and the state was maintained 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 after 5 minutes in which the retention time is shown in FIG. 4, it was found that a uniform silica shell was formed on the surface of the silver nanoparticles having silver nanoparticles at the center. 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 6 minutes of holding time, and the thickness of the shell became constant after 20 minutes. When the time change of the thickness of the silica shell layer with and without the microwave heating of FIG. 4 was compared, it was found that the formation time of the silica shell layer was shortened by the microwave heating.
The particle size distribution of the core-shell structured nanoparticles (average diameter 51 nm, standard deviation 3.5) had a CV value of 7%, and nanoparticles with uniform particle size were obtained.

Example 2
The resulting solution during formation of the silica shell obtained in the same manner as in Example 1 is treated with ethanol for 7 minutes, 8 minutes and 10 minutes after each holding time which is an elapsed time from the start of holding at room temperature. FIG. 5 shows TEM images (g) to (i) and an absorption spectrum 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. In addition, it is confirmed from the absorption spectrum that as the silica shell layer becomes thicker, the peak intensity becomes higher and 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 disposed downstream of the second mixer 9, and includes heating means using microwaves, TM010 cavity 4, microwave oscillator / irradiation. The core 5 and the silica shell nanoparticles were synthesized using the nozzle 5 and the like. The flow 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, Particle size distribution synthesized CV value 20%). The heating temperature was 170 ° C., and the liquid transfer rate was 6 mL / h. The solution containing the platinum nanoparticles synthesized in the reaction tube 3 in the previous stage was sent to the first static mixer 9, and the same amount of ethanol was mixed with the solution containing the platinum nanoparticles. 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 at the center, and a silica shell (25 nm thick) 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 the synthesis of platinum core-silica shell nanoparticles is shown. The composition of the reaction raw material used for each Example is as 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. The conditions of Example 4 other than the composition shown in Table 1 were set basically the same as those of 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 of 10 nm in diameter, which are black, are dispersed in the translucent, gray, silica particles of about 140 nm in diameter. 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 examples 6-1 to 6-4 in which the concentration of MDA in the reaction solution is changed, and the conditions other than the composition shown in Table 1 are set basically the same as in Example 3 and platinum Core and 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 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 disposed downstream of the second mixer 9, and heating means by microwave, TM010 cavity 4, microwave oscillator / irradiation port 5 are provided. Etc.) 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 transfer rate was 6 mL / h. The solution containing palladium nanoparticles synthesized in the reaction tube 3 in the previous stage was sent to the first static mixer 9, and the same amount of ethanol was mixed with the solution containing palladium nanoparticles. Subsequently, in the second static mixer 9, TEOS and an ethanol solution containing water and dimethylamine were mixed, and the solution was sent to the reaction tube 10 in the latter stage. The palladium concentration after mixer mixing was 0.00004 M, the TEOS concentration was 0.0088 M, the dimethylamine concentration was 0.06 M, the water was 12 M, and the flow rate was 300 mL / h. FIG. 10 shows a TEM image of palladium core-silica shell nanoparticles in the case where the solution is collected in a container without microwave heating in the latter reaction tube 10 and held 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 disposed downstream of the second mixer 9, and heating means by microwave, TM010 cavity 4, microwave oscillator / irradiation port 5 are provided. Etc.) was used to synthesize nickel core / silica shell nanoparticles. 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 transfer rate was 1 mL / h. The solution containing the nickel nanoparticles synthesized in the reaction tube 3 in the previous stage was sent to the first static mixer 9, and the same amount of ethanol was mixed with the solution containing the nickel nanoparticles. 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 mixer mixing was 50 mL / h, the nickel concentration was 0.0001 M, the TEOS concentration was 0.0088 M, the dimethylamine concentration was 0.06 M, and the water was 12 M. A solution is collected in a container without microwave heating in the reaction tube 10 in the latter stage, and a TEM image of nickel core / silica shell nanoparticles in the case of holding at room temperature for 1 hour is shown in FIG. 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 plurality of each or any one is provided, and the case where it carries out 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 more or all of the flow through reaction tubes in the front and rear flow through reaction tubes may be microwave-heated. 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. The composite nanoparticles are nanoparticles of different types of nanoparticles and oxide particles combined, for example, composite nanoparticles in which the nanoparticles are metal particles and the oxide is attached to a part of the surface thereof. 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 its applications.

  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 for an image forming material, an optical material, a semiconductor, and an industrial catalyst, it is possible to further promote quality improvement and cost reduction of products in the relevant 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 that it should be interpreted broadly without.

  This application claims the priority based on Japanese Patent Application No. 2011-198001 for which it applied for a patent in Japan on September 12, 2011, and these are all referred to here for description of this specification. As part of.

1: liquid feed pump 2: reaction liquid 3: reaction tube 4: TM010 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: Delivery pump (for dilution)
14: Mixer (for dilution)
15: Equipment for measuring oxide shell thickness 16: Product solution outlet

Claims (3)

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 method of continuously synthesizing core-shell structure nanoparticles of a metal core / oxide shell, in which an oxide film is continuously formed around metal nanoparticles by hydrolyzing a precursor of the product, and
  A mixer in which at least the first-stage flow-type reaction tube is uniformly heated by microwaves and disposed between the first-stage and second-stage flow-type reaction tubes in a solution containing metal core particles flowing out of the first-stage flow-type reaction tube Is a continuous synthesis method of core-shell structured nanoparticles of metal core / oxide shell, in which the formation of core-shell structured nanoparticles to be introduced into the subsequent flow-type reaction is performed consistently after mixing the oxide precursor using ,
The continuous synthesis method of core-shell structured nanoparticles of metal core / oxide shell characterized in that the shell is formed using oxide nanoparticles. 2. The method of continuously synthesizing core-shell structure nanoparticles of a metal core / oxide shell according to claim 1, wherein at least one of an average diameter of the metal core, an average outer diameter of the core-shell structure nanoparticles, and a shell thickness of the core-shell structure nanoparticles is selected. A means for controlling and / or means for measuring at least one of the average diameter of the metal core, the average outer diameter of the core-shell structured nanoparticles, and the shell thickness of the core-shell structured nanoparticles, Continuous synthesis method of core-shell structured nanoparticles. 3. The method of continuously synthesizing core-shell structure nanoparticles of metal core / oxide shell according to claim 1 or 2, wherein a plurality of core-shell structure nanoparticles are arranged inside the outermost shell. A continuous synthesis method of core-shell structured nanoparticles of metal core / oxide shell characterized by having at least one core-shell structured nanoparticle.