JP6206918B2 - Method for synthesizing Prussian blue-type complex nanoparticles and Prussian blue-type complex nanoparticles synthesized by the method - Google Patents

Description

  The present invention relates to a method for synthesizing Prussian blue-type complex nanoparticles and Prussian blue-type complex nanoparticles synthesized by the method.

  A coordination polymer is a complex having a continuous structure composed of a ligand and a metal ion. Among the coordination polymers, Prussian blue-type complex nanoparticles represented by Prussian blue are electrochromic utilizing the property of removing the radioactive cesium scattered by the nuclear power plant accident and changing the color electrochemically. Research and development as a material is underway.

  For example, when attention is focused on the use of radioactive cesium as a scavenger, there are a wide variety of systems in which radioactive cesium is scattered due to accidents at nuclear power plants, including soil, rivers, seawater, and incinerated ash. These include other metals such as potassium and sodium. Contains a large amount of ions. Prussian blue-type complex nanoparticles have high cesium selectivity, and preferentially adsorb radioactive cesium from these objects (Patent Document 1).

  Coordination polymers are also used as electrochromic materials that can be driven with low voltage and low power. Among them, the Prussian blue type complex varies in color and color depending on the constituent metal ions, and an appropriate Prussian blue type complex can be selected according to the application (Patent Document 2). Moreover, the color tone can be changed by synthesizing a Prussian blue-type complex nano containing a plurality of metal elements.

  Further, Prussian blue type complexes have been studied as secondary battery electrodes, biosensor transducers, gas adsorbents, and the like.

  As described above, the Prussian blue type complex is being researched and developed for application to various uses. In particular, the nanoparticulation has attracted much attention. For example, dispersibility in a solvent can be improved by forming nanoparticles and modifying the surface thereof. It has been shown that if this feature is utilized, a dispersion liquid dispersed in a solvent can be used as ink and film formation can be performed by printing and coating, and in particular, it becomes easy to produce a thin film for an electrochromic device.

  The method for controlling the particle size of Prussian blue complex nanoparticles is not always clear. Non-Patent Document 1 shows that the electrochromic reaction is stabilized by reducing the particle size of zinc-substituted Prussian blue complex nanoparticles. However, the method used here classifies nanoparticles having various particle sizes once synthesized by a centrifugal separation method. Although this could certainly yield small nanoparticles, it was a small part of the composite and had the problem of poor yield.

Among Prussian blue-type complexes, it is known that Prussian blue nanoparticles having a small particle size are relatively easy to synthesize. For example, according to Non-Patent Document 2, it is reported that, in addition to flow synthesis, a batch method in which two liquids are simply mixed can obtain a particle size of 7 nm or less.
However, for Prussian blue-type complexes other than Prussian blue, it was difficult to synthesize nanoparticles of 15 nm or less. For example, Patent Document 2 has a description of the synthesis of various Prussian blue complex nanoparticles of metal M, and Example 3 describes the case of M = Cu. Is 45 nm. In Example 4, an example of M = Co is described. In this case, the particle size is 30 nm. Although there is a description that the particle size is reduced by adding ammonia, even in that case, it is 17 nm, and the addition of such other materials may cause deterioration during use. It is desirable to avoid it if possible. Further, there is a description that the particle diameter in the case of M = Ni is also 20 nm. Non-Patent Document 1 describes the case of M = Zn. In this case, the particle size is 182 nm before classification. As described above, for materials other than Prussian blue, it was difficult to synthesize nanoparticles of 15 nm or less without additives other than the nanoparticle synthesis element.

JP 2013-160666 A International Publication No. 2008/081923

Kyoung Moo Lee, Hisashi Tanaka, Kyong Ho Kim, Midori Kawamura, Yoshi Abe, Tohru Kawamoto, Applied Physics Letters, Vol. 102, P141901 (2013). Hokuto Hashio, Toru Kawamoto, Akira Takahashi, Kimiko Minami, Kazunori Yamada, “Physical Properties of Prussian Blue Nanoparticles by Flow Synthesis”, Nihon University College of Industrial Science, December 1, 2012

  Thus, it has been shown that the function of Prussian blue complex nanoparticles is improved by controlling the particle size. However, with the exception of Prussian Blue, there is no known method for efficiently synthesizing nanoparticles having a small particle diameter, and the function as a radioactive cesium adsorbent other than electrochromism, for example, is converted into nanoparticles. It was not always clear whether it would improve by doing.

  The present invention has been made in view of such a situation, and the particle size of Prussian blue complex nanoparticles is efficiently controlled, and after ensuring a sufficient yield, the nanoparticles are used as a radioactive cesium adsorbent. It is an object of the present invention to provide a synthesis method for expressing a high function, and Prussian blue complex nanoparticles synthesized by the method.

  The inventors have clarified that it is important to perform a uniform reaction continuously in order to obtain particles having a small particle diameter in Prussian blue-type complex nanoparticles through various studies. As a result of further earnest studies to achieve such conditions, the present inventors can swiftly stir by generating turbulent flow when mixing the liquid when synthesizing the Prussian blue type complex. It was found that particles having a smaller particle diameter can be obtained by performing flow synthesis.

The present invention has been completed based on these findings, and according to the present invention, the following inventions are provided.
[1] A liquid mixing device having two or three or more inlets, joined inside, and having one or more outlets, and made of a salt solution containing metal M First solution and a second solution consisting of a salt solution containing hexacyanoiron ions ([Fe (CN) ₆ ]) are allowed to flow from separate inlets and mixed inside to obtain Prussian blue complex nanoparticles. A method for synthesizing Prussian blue-type complex nanoparticles, which is synthesized by a method that satisfies the following conditions a or b.
a. Mixing is performed under a condition that the Reynolds number after mixing of the first solution and the second solution in the mixing apparatus is 2000 or more.
b. A baffle plate is provided in the mixing device.
[2] The method for synthesizing Prussian blue complex nanoparticles according to [1], wherein the metal M is copper.
[3] The method of synthesizing Prussian blue complex nanoparticles according to [1] or [2], wherein a flow path radius in the mixing apparatus is 0.5 mm or less.
[4] Prussian blue-type complex nanoparticles obtained by the synthesis method according to any one of [1] to [3].
[5] A cesium adsorbent comprising Prussian blue-type complex nanoparticles obtained by the synthesis method according to any one of [1] to [3].
[6] An electrochromic material comprising Prussian blue-type complex nanoparticles obtained by the synthesis method according to any one of [1] to [3].

  According to the present invention, nanoparticles having a small particle size can be synthesized. Further, by using the nanoparticles, a cesium adsorbent with higher adsorption performance can be provided.

Schematic diagram of a mixing device when using a micromixer with a Y-shaped tube The figure which shows the Reynolds number dependence of the average particle diameter of a copper Prussian blue type complex nanoparticle in Example 1 The figure which shows the cerium adsorption rate of the copper Prussian blue type | mold complex nanoparticle obtained in Example 1 as a function of time and Reynolds number

Hereinafter, the present invention will be described in detail.
The Prussian blue-type complex in the present invention is a mixture of a salt 1 solution containing metal M (first solution) and a salt 2 solution containing hexacyanoiron ion [Fe (CN) ₆ ] (second solution). The composition is expressed by A _x M [Fe (CN) ₆ ] _y · zH ₂ O. Here, A represents a cation such as Li ion, Na ion, K ion, NH ₄ ion, Rb ion, or Cs ion. In addition, a material other than the composition such as a solvent other than water and other ions included as impurities may be included. x is preferably in the range of 0 to 3, particularly preferably in the range of 0 to 2. y is preferably in the range of 0.3 to 1.5, particularly preferably in the range of 0.4 to 1. z is preferably in the range of 0 to 5, particularly preferably in the range of 0 to 4. However, x, y, and z must be evaluated with their effects removed, for example, when a salt is included as an impurity or the material has moisture that is not taken into the internal structure of the Prussian blue complex.

  The salt 1 should just contain the metal M as a cation. Here, M is one or two of V, Cr, Mn, Fe, Ru, Co, Ph, Ni, Pd, Pt, Cu, Ag, Zn, La, Eu, Gd, Lu, Ba, Sr, and Ca. Above, Fe, Co, Ni, Cu, Zn, and Mn are preferable, and Ni, Cu, Zn, and Mn are particularly preferable. As the anion contained in the salt 1, it is sufficient that the salt 1 is dispersed in a solvent. For example, nitrate ion, chlorine ion, or the like can be used.

  The salt 2 contains hexacyanoiron ions and may be dispersed in a solvent. For example, potassium ferrocyanide, potassium ferricyanide, sodium ferrocyanide, sodium ferricyanide, ammonium ferrocyanide, ammonium ferricyanide and the like can be used.

  The concentration of the first solution and the second solution is preferably 10 g / L, and more preferably 100 g / L. Although there is no particular upper limit, it is practically 1000 g / L or less. The solvent used in the first solution and the second solution is not limited as long as the salt 1 and the salt 2 are dissolved, and water, methanol, and the like can be used.

The synthesis of the Prussian blue complex that is the subject of the present invention is achieved by mixing two or more raw material liquids. As the shape of the mixing apparatus, it is sufficient that there are two or more inflow ports and one or more outflow ports, and it is sufficient that the first solution and the second solution can be mixed inside.
As a specific example, FIG. 1 shows a device diagram in the case where a micromixer having a Y-shaped tube is used as a mixing device.
There is no particular limitation on the shape as long as efficient mixing can be achieved, but it may be a structure in which nanoparticles synthesized inside accumulate. Further, from the viewpoint of mixing efficiency, the ratio of the mixed liquids is desirably 1000 times or less, and more desirably 100 times or less. Actually, it is 10 times or less. Although there is no restriction | limiting in a material, in order to prevent the obstruction | occlusion of the pipe | tube by adhesion of particle | grains, a thing with low affinity with the particle | grains synthesize | combined is desirable. For example, stainless steel (SUS316L, SUS304, etc.), PEEK, etc. can be used.

  In the present invention, it is important to generate turbulent flow during synthesis. As a method for generating turbulent flow, a baffle plate is installed in the pipe. Further, when it is difficult to install a baffle plate in the pipe such as using a micromixer as the mixing section, it is possible to use a turbulent state with a Reynolds number of 2000 or more. Specifically, in the case of the apparatus shown in FIG. 1, it is necessary to make a turbulent state by increasing the Reynolds number immediately after the mixing section, that is, at the position of the arrow * shown in FIG. By setting it as a turbulent flow state, it becomes possible to mix two liquids uniformly at high speed, and the particle diameter of the nanoparticle obtained as a result can be made small. The Reynolds number Re is particularly preferably 2000 or more, and more preferably 5000 or more. There is no particular upper limit, but 1000000 or less is realistic.

  Here, the Reynolds number Re indicates an amount defined for the flow in the pipe through which the Prussian blue complex nanoparticles after mixing pass, and (liquid density) × (liquid flow velocity) × (piping diameter) ) / (Dimensionless amount expressed by (viscosity of liquid)). It is known that the higher the Reynolds number, the more likely it becomes a turbulent state, which can be used for evaluation of the mixed state.

  The desirable particle size of the Prussian blue complex nanoparticles is preferably a primary average particle size of 30 nm or less, more preferably 20 nm or less, and particularly preferably 15 nm or less. In addition, depending on the type of M, for example, when M = Zn, it may be difficult to synthesize nanoparticles of 100 nm or less without the addition of substances other than the constituents of the nanoparticles or without classification work such as centrifugation. In this case, the present invention is not limited to the above-described particle size, and according to the present invention, the present invention can be used to synthesize particles having a smaller particle size than the conventional technology. In the present invention, the primary particle diameter means the diameter of the primary particles, and the equivalent circle diameter can be calculated from the half width of the peak of the powder X-ray structure analysis. Moreover, although the ligand etc. may adsorb | suck to the particle | grain surface, in that case, as a primary particle size, the particle size except a ligand shall be pointed out.

Hereinafter, the present invention will be described in more detail based on examples, but the present invention should not be construed as being limited thereto.
Example 1
<Reynolds number dependence of the primary particle size of copper Prussian blue complex nanoparticles>
Copper-iron cyano complex nanoparticles (Cu ₃ [Fe (CN) ₆ ] ₂ ) were prepared as follows. A solution prepared by dissolving 140 g of copper sulfate pentahydrate in 500 mL with pure water and 104 g of potassium ferrocyanide trihydrate in 500 mL with pure water was prepared. The flow rate was adjusted to 4.7, 9.4, 37, 94 mL / min, and synthesized by the flow method. Here, the Y-shaped micromixer (VICI's micro volume connector “1/16 Y PEEK, product number MY1XCPK” and the connection part of “1/16 Y SUS, product number MY1XCS6” are joined together. The density of the liquid was 1100 kg / m ³ , the diameter of the piping was 1.5 × 10 ⁻⁴ m, and the viscosity was 2 × 10 ⁻³ Pa / s. When the Reynolds number at each flow rate is calculated from these, it corresponds to 389, 778, 3180, and 7780.

The obtained liquid was centrifuged at 10,000 rpm for 15 minutes, and the resulting precipitate was washed with pure water and then vacuum dried to obtain reddish brown powders P1, P2, P3, and P4.
When the obtained P1, P2, P3, and P4 were evaluated by an X-ray diffractometer, all coincided with the K ₂ Cu ₃ [Fe (CN) ₆ ] ₂ peak position in the database.
Further, the average primary particle diameters of the obtained P1, P2, P3, and P4 were calculated by the Scherrer equation from the peak width of the powder X-ray diffraction. Scherrer's formula is expressed as follows.
d = K × λ / (β × cos θ)
(d: primary particle size, K: Scherrer constant, λ: X-ray wavelength, θ: diffraction angle of peak)

  The obtained results are shown in FIG. As can be seen from FIG. 2, the higher the Reynolds number, the smaller the result. When the Reynolds number was smaller than 2000, the Reynolds number was increased and the particle size became smaller. However, when the Reynolds number exceeded 2000, the particle size became almost constant.

(Example 2)
<Cesium adsorption ability of copper Prussian blue complex nanoparticles>
The cesium adsorption ability of P1, P2, P3, and P4 obtained in Example 1 was examined by the following method.
Each powder (0.1 g) was added to 500 mL of a 2 mg / L CsNO ₃ aqueous solution, and a lenticular test was performed at 200 rpm. In the experiment, TAITEC TS-20 was used as a shinto device. For comparison, a test using Prussian blue nanoparticles described in Patent Document 2 was performed in the same manner. A sample is taken in the middle of the measurement, and the Cs concentration in the liquid is measured by an inductively coupled plasma mass spectrometer (NexION300D, Perkin Elmer) to measure the Cs concentration in the liquid. The amount of Cs adsorption in the solid was calculated.
The obtained results are shown in FIG. As is clear from FIG. 3, it was found that the amount of cesium adsorbed earlier as the Reynolds number at the time of synthesis increased, and the amount of Cs adsorbed in the equilibrium state was larger.

Claims (5)

First solution comprising a salt solution containing metal M using a liquid mixing device having two or three or more inlets, combined inside, and having one or more outlets And a second solution composed of a salt solution containing hexacyanoiron ions ([Fe (CN) ₆ ]) from different inlets and mixed inside to synthesize Prussian blue complex nanoparticles And a method for synthesizing Prussian blue-type complex nanoparticles, which is synthesized by a method that satisfies the following condition a .
a. Mixing is performed under a condition that the Reynolds number after mixing of the first solution and the second solution in the mixing apparatus is 2000 or more .   The method for synthesizing Prussian blue-type complex nanoparticles according to claim 1, wherein the metal M is copper.   The method for synthesizing Prussian blue complex nanoparticles according to claim 1 or 2, wherein a flow path radius in the mixing apparatus is 0.5 mm or less. A method for producing a cesium adsorbent comprising Prussian blue-type complex nanoparticles , wherein the Prussian blue-type complex nanoparticles are synthesized by the synthesis method according to claim 1. A method for producing an electrochromic material comprising Prussian blue-type complex nanoparticles , wherein the Prussian blue-type complex nanoparticles are synthesized by the synthesis method according to claim 1.

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