WO2011074606A1 - Metal nanoparticles and method for producing metal nanoparticles - Google Patents

Abstract

Disclosed are metal nanoparticles which have a zeta potential of 0-5 mV, an average particle diameter of 0.5-10 nm, and a particle size distribution with a CV value of 0-25%.

Description

Metal nanoparticles and method for producing metal nanoparticles

The present invention provides metal nanoparticles and a method for producing metal nanoparticles.

Metal nanoparticles are expected to be used differently from bulk metals as materials exhibiting unique electrical and optical properties and catalytic activity.
For example, gold nanoparticles are known to be used as various catalysts, dyes, biosensors, biomolecule labeling substances, and the like.

In addition, a composite (polymer nanocomposite) in which metal nanoparticles are dispersed in a conductive polymer such as polypyrrole, polyaniline, and polythiophene is used as a catalyst, a quantum dot, an electrode, or the like of a fuel cell.
Specifically, for example, it is known that metal nanoparticles dispersed in a conductive polymer can be used as a fuel cell catalyst (see Japanese Patent Application Laid-Open No. 2004-359724 (Patent Document 1)). .

In the production of metal nanoparticles, particularly gold nanoparticles, the present inventors reduced chloroauric acid using aniline as a reducing agent to oxidize aniline itself to form polyaniline, in which gold nanoparticles are contained. It has been found that aggregates of retained gold nanoparticles can be obtained (Non-patent Documents 1 and 2).

JP 2004-359724 A

The present inventors can extract metal nanoparticles because polyaniline is peroxidized and decomposed by electrolyzing the aggregate of metal nanoparticles produced using aniline or an aniline derivative as a reducing agent. And the present invention was completed.

Therefore, the present invention provides metal nanoparticles having a zeta potential of 0 to 5 mV, an average particle size of 0.5 to 10 nm, and a particle size distribution with a CV value of 0 to 25%.

The present invention also provides metal nanoparticle aggregates covered with polyaniline or polyaniline derivatives by reducing metal ions using aniline or aniline derivatives as a reducing agent, and obtained metal nanoparticle aggregates. A method for producing metal nanoparticles is provided, which includes a step of obtaining metal nanoparticles not covered with polyaniline or a polyaniline derivative by electrolysis.

In the present specification, the “metal nanoparticles” have an average particle diameter of about 0.5 nm to 10 nm, more preferably 0.5 nm to 7.5 nm. In general, metal particles are called “metal nanoparticles”, and particles smaller than about 100 nm are referred to as “metal clusters”. As used herein, the term “metal nanoparticles” is intended to include particles in the range of both “metal nanoparticles” and “metal clusters” that are commonly used. For example, in the case of gold, particles larger than about 1.4 nm (number of atoms or magic number 55) are usually called “gold nanoparticles”, and particles with a particle size of about 1.4 nm or less (magic number 55 or less) are called. In the present specification, these so-called gold nanoparticles and gold clusters are collectively referred to as “gold nanoparticles” for convenience.

The metal nanoparticle production method of the present invention makes it possible to obtain metal nanoparticles having a relatively uniform particle size and a small size. In addition, since the obtained metal nanoparticles are not covered with polyaniline, they are not covered with other organic substances, so that they have high catalytic activity and high reactivity with biomolecules such as proteins and nucleic acids. It is done. Therefore, there is a high possibility that biomolecules can be labeled more easily using a metal nanoparticle obtained by the method of the present invention, and a fuel cell with high reaction efficiency can be manufactured.

It is a schematic diagram of the polyaniline formed with the aggregate of a metal nanoparticle (for example, gold nanoparticle). It is a transmission electron micrograph of the aggregate of the gold nanoparticles obtained by reducing (A) for 5 minutes and (B) for 10 minutes (Example 1). It is a transmission electron micrograph of the aggregate of the gold nanoparticle obtained by reducing for 20 minutes (Example 2). It is a photograph which shows an example of the electrolyzer which can be used in the method of this invention. (A) Transmission electron micrograph of gold nanoparticles obtained by electrolysis for 3 hours, (B) 4 hours, (C) 6 hours, (D) 8 hours and (E) 9 hours (implementation) Example 3). (A) Aggregates of platinum nanoparticles obtained by electrolysis for 0 hour and (B) 9 hours and transmission electron micrographs of platinum nanoparticles (Example 4). It is the photograph which shows an example of the electrolyzer which can be used in the method of this invention, and a schematic cross section of an electrochemical cell. It is a transmission electron micrograph of gold nanoparticles obtained by electrolysis for 56 hours. It is a transmission electron micrograph of the gold nanoparticle aggregate produced in (A) Example 5, (B) Example 6 and (C) Example 7. It is a transmission electron micrograph of the gold nanoparticle aggregate produced in (A) Example 8, (B) Example 9 and (C) Example 10. (A) The result of the particle size distribution measurement of the gold nanoparticle obtained by the method of this invention and (B) the gold cluster obtained by the known method is shown (Example 11). It is a schematic cross section of the electrochemical cell used in this invention. It is a figure which shows the measurement result of the cyclic voltammetry obtained in Example 12. 4 is a transmission electron micrograph of gold nanoparticles prepared in Example 13. FIG. It is a figure which shows the result of the particle size distribution measurement of the gold nanoparticle created in Example 13. (A) It is a figure which shows the measurement result of the IR spectrum of the gold cluster obtained by the known method, and (b) the gold nanoparticle obtained by the method of this invention.

The method for producing metal nanoparticles of the present invention comprises reducing metal ions using aniline or an aniline derivative as a reducing agent, and separating the metal nanoparticles from an aggregate of metal nanoparticles retained in the obtained polyaniline. It can be taken out as
When metal ions are reduced using aniline or an aniline derivative, the amino group of aniline or aniline derivative is oxidized to become an electrophilic group and polymerized with another aniline or aniline derivative molecule to form polyaniline or polyaniline derivative (Fig. 1). The presence of this as a matrix between the reduced metal nanoparticles forms aggregates of metal nanoparticles in polyaniline or polyaniline derivatives.

As used herein, “aniline derivative” means a derivative of aniline having one or more substituents at the ortho, meta, and / or para positions with respect to the amino group of aniline. The plurality of substituents may be the same or different. The above substituents may be any substituents that do not impair the basicity of the amino group of aniline, that is, the electric discharge property. Such substituents include C ₁ -C ₅ alkyl groups such as methyl, ethyl, isopropyl, tert-butyl groups, amino groups, carboxy groups, hydroxy groups, and the like. These substituents are preferably in the ortho position and / or the meta position with respect to the amino group of aniline. Moreover, these substituents may be one or more, and preferably one or two.
Examples of the aniline derivatives include o-aminotoluene, o-ethylaniline, m-ethylaniline, o-aminophenol, o-aminobenzoic acid, m-aminobenzoic acid, 2,4-dimethylaniline, 2, Examples include 6-dimethylaniline and 4-tert-butylaniline.

In the present specification, “polyaniline or polyaniline derivative” is a molecule formed by polymerizing the above aniline or aniline derivative.

In this specification, the “aggregate of metal nanoparticles” refers to a state in which a plurality of metal nanoparticles are held in polyaniline or polyaniline derivative using polyaniline or polyaniline derivative as a matrix.

In this specification, “metal nanoparticles alone” and “metal nanoparticles not covered with polyaniline or polyaniline derivatives” are dispersed metal nanoparticles that are not covered by a matrix of polyaniline or polyaniline derivatives. It is. It can be confirmed that the metal nanoparticles are not covered with the matrix of polyaniline or polyaniline derivative and are dispersed by observation with an electron microscope or measurement of the zeta potential of the metal particles by Nicomp 380ZLS or Particle Sizing Systems.

In the method of the present invention, metal ions are reduced using aniline or an aniline derivative as a reducing agent.
Examples of metal ions include noble metal ions such as gold, platinum, palladium, rhodium, ruthenium and silver, and non-noble metal ions such as copper. Among these, noble metal ions are preferable, and gold and platinum ions are more preferable.
Said reduction process can be performed by mixing aniline or an aniline derivative with a metal ion containing compound. Metal ion-containing compounds include chloroauric acid (HAuCl ₄ ), chloroplatinic acid (H ₂ PtCl ₆ ), hexaamine platinum chloride (Pt (NH ₃ ) ₆ Cl ₄ ), dinitrodiamine platinum (Pt (NO ₂ ) ₂ ( NH ₃ ) ₂ ), palladium chloride (PdCl ₂ , H ₂ PdCl ₄ ), tetraamine palladium chloride (Pd (NH ₃ ) ₄ Cl ₂ ), rhodium chloride (RhCl ₃ ), ruthenium chloride (RuCl ₃ ), silver nitrate ( Including noble metal ion-containing compounds such as AgNO ₃ ) and non-noble metal ion-containing compounds such as copper sulfate (CuSO ₄ ).

In the present invention, since metal nanoparticles having a lower zeta potential can be easily obtained, either chloroauric acid (HAuCl ₄ ) or chloroplatinic acid (H ₂ PtCl ₆ ) is used as the metal ion-containing compound. It is preferable. From the same viewpoint, it is preferable to use aniline and any of aniline derivatives such as aminotoluene, ethylaniline, aminophenol, and aminobenzoic acid as a reducing agent.

When the metal ion-containing compound is mixed with aniline or an aniline derivative, the concentration of the metal ion is preferably 10 ⁻⁶ to 10 ⁻³ (M), more preferably 7 × 10 ⁻⁵ to 6 × 10 ⁻⁴ Can be used.

The aniline or aniline derivative and the metal ion-containing compound are preferably mixed in such an amount that the molar ratio of the aniline or aniline derivative and the metal ion is preferably 10 to 100: 1, more preferably 20 to 50: 1. .

The above reduction is preferably performed at a temperature of room temperature (25 ° C.) to 80 ° C., more preferably 60 ° C. to 80 ° C., preferably 1 minute to 60 minutes, more preferably 1 minute to 30 minutes, even more preferably 2 Can be performed for 30 minutes. By shortening the reaction time, the particle diameter of the metal nanoparticles produced in the polyaniline or polyaniline derivative can be reduced, that is, a so-called metal cluster can be obtained.

The above reduction can be performed in an appropriate solvent capable of dissolving the metal ion-containing compound and aniline or aniline derivative. As such a solvent, water or a mixed solution of water and an organic solvent is preferable, and toluene, benzene, hexane, or the like can be used as the organic solvent. When water and an organic solvent are mixed, the mixing ratio of water and the organic solvent is preferably 1: 1 to 10 (volume ratio), more preferably 1: 1 to 5 (volume ratio).

In addition, toluene is preferable as the organic solvent because a desired aggregate can be easily obtained. On the other hand, these solvents may appropriately contain other substances such as an electrolyte, a dispersant such as polyvinyl alcohol, and a pH adjuster such as sodium hydroxide as long as the metal nanoparticles of the present invention can be obtained. Good.

When a mixed solution is used as the reaction solution, the reduction is performed by bringing an aqueous solution containing metal ions into contact with an organic solution containing aniline or an aniline derivative.

Next, the aggregate of metal nanoparticles obtained by the above reduction is electrolyzed.
The electrolysis is not particularly limited as long as the electrolysis is performed by flowing a current through a pair of electrodes arranged in the electrolyte solution.
The electrolyte solution is not particularly limited as long as it is an electrolyte solution that can decompose polyaniline or a polyaniline derivative without affecting the electrolysis of the above-mentioned aggregate of metal nanoparticles. As the solvent of the electrolyte solution, water is preferable because metal nanoparticle aggregates can be dispersed. As the electrolyte solution, an aqueous sodium hydroxide solution, an aqueous potassium hydroxide solution, or the like can be used. The electrolyte solution preferably has a pH of 12.0 to 14.0.

In the present invention, other substances may be included as long as desired electrolysis can be performed and the metal nanoparticles of the present invention can be obtained.

In addition, since desired metal nanoparticles can be easily obtained, electrolysis is preferably performed at a temperature of about room temperature, and 10 to 50 mg of the aggregate is preferably dispersed in a solvent of about 10 to 100 ml.

Electrolysis can be performed by applying a potential in the range of preferably 1.5 to 2.2 V, more preferably 1.5 to 2.0 V, more preferably 1.8 to 2.0 V to the working electrode. The potential in this range is preferably kept constant during electrolysis. The electrolysis is preferably performed for 1 to 20 hours, more preferably 1 to 15 hours, more preferably 3 to 10 hours, and even more preferably 4 to 9 hours. By performing electrolysis under such conditions, the polyaniline or polyaniline derivative can be sufficiently peroxidized and decomposed, and appropriately dispersed metal nanoparticles can be obtained.

Electrolysis can also be applied by applying a pulse-shaped potential that gives a constant high potential for a fixed period of 0.001 to 10 seconds and then repeatedly applies a constant low potential to the working electrode for a fixed period of 0.001 to 10 seconds. It can be carried out. The low potential side is preferably in the range of −2.0 to 0 V, and the high potential side is preferably in the range of 1.5 to 2.2 V, more preferably in the range of 1.8 to 2.0 V. Both the low potential side and the high potential side have one potential. To give a pulse-shaped potential. Thereby, when a high potential is applied, an electrode contaminated by adsorption of a decomposition reaction product of polyaniline or a polyaniline derivative can be electrolyzed while being cleaned by reducing at a low potential.

The electrode used for electrolysis is not particularly limited as long as it is used for normal electrolysis. As a material for the counter electrode and the working electrode, metals such as carbon (glassy carbon or conductive diamond), tungsten, molybdenum, tantalum, niobium, titanium, cobalt, and the like can be used. A reference electrode may be used for the electrolysis, and an electrode such as silver / silver chloride or mercury / mercury chloride can be used as the reference electrode.

The metal nanoparticles produced by the method of the present invention have a zeta potential on the surface of 0 to 5 mV, more preferably 0.1 mV to 3 mV.
The surface of conventional metal nanoparticles is covered with an organic substance, but the metal nanoparticles obtained by the method of the present invention have a very low zeta potential, so that the surface is almost covered with other substances. It is considered that the metal is not exposed. Since such metals are likely to interact with sulfur (S), nitrogen (N) atoms, etc., the metal nanoparticles obtained by the method of the present invention have very high binding properties with biomolecules such as proteins and nucleic acids. It is considered to be suitable as a labeling substance for these biomolecules.

Specifically, reduction of citric acid, ascorbic acid, NaBH _{4 and the} like in the presence of a protective agent such as conventional PVP (polyvinyl pyrrolidone), PVA (polyvinyl alcohol), and glutathione in a solvent such as MeOH (methanol) and water. In the method for producing nanometal particles using an agent, the obtained metal nanoparticles have a high zeta potential, and a protective layer of a protective agent is present on the surface thereof.

On the other hand, in the present invention, since the metal nanoparticles are produced using the production method described above, the metal nanoparticles of the present invention have a very low zeta potential. Moreover, as the electrolysis of the present invention proceeds, the zeta potential of the metal nanoparticles decreases. This indicates that the metal nanoparticles covered with polyaniline or polyaniline derivative are changed to metal nanoparticles not covered with them.

It can also be confirmed by measuring the IR spectrum of the metal nanoparticles that the metal nanoparticles are not covered with polyaniline or polyaniline derivatives. Specifically, when the IR spectrum of metal nanoparticles having a protective layer is measured, various peaks derived from the protective layer are confirmed. On the other hand, the metal nanoparticle of the present invention cannot substantially confirm a peak derived from the protective layer. That is, the metal nanoparticles of the present invention substantially have no peak derived from the organic compound in the IR chart obtained by measuring the metal nanoparticles.

In the present invention, the “peak derived from an organic compound” means a peak derived from a substituent and a skeleton structure of an organic compound containing atoms such as general carbon, hydrogen, oxygen, nitrogen, and sulfur. Substituents of organic compounds are —OH, —NH ₂ , —SH, —COH, —COOH, —CH _3, etc., and skeleton structures are C—C, C═C, C—H, C—N, C ═N, C—O, C═O, C—H and the like. On the other hand, since aniline and aniline derivatives are usually soluble in water or an organic solvent, they are not substantially present on the surface of the nanometal particles of the present invention.

Also, a "substantially no peak derived from the organic compound", when the IR measurement of the metal nanoparticles in the 4000 cm ^-1 ~ 700 cm ^-1, in the resulting IR chart, the transmittance (% T ) Is preferably 20% or less, more preferably 30% or less. The IR measurement method of the present invention will be described in detail in Examples.

The metal nanoparticles produced by the method of the present invention have an average particle size of 0.5 nm to 10 nm, preferably 0.5 nm to 7.5 nm. In this specification, the average particle diameter of the metal nanoparticles is a value measured using a transmission electron microscope.
Since the above metal nanoparticles have such a small particle diameter, the surface area per weight can be increased, and it is considered that the metal nanoparticles have high catalytic activity.
Moreover, by having such a small particle diameter, the melting point of the metal nanoparticles is significantly lower than that of the metal in the bulk state. Therefore, the metal nanoparticles can be melted at a lower temperature.

On the other hand, the particle diameter of the metal nanoparticles of the present invention is preferably in the range of 0.3 to 50 nm, more preferably 0.5 to 10 nm as a whole. When included in the above range, it may have higher catalytic activity as well.

Also, the metal nanoparticles of the present invention have a very narrow particle size distribution. Specifically, the metal nanoparticles of the present invention have a CV value particle size distribution of 0 to 25%, preferably 0 to 15%, more preferably 0 to 10%. For this reason, similarly, the metal nanoparticles of the present invention can have a larger surface area per weight, and as a result, may have higher catalytic activity. Moreover, according to the present invention, metal nanoparticles having an extremely narrow particle size distribution can be easily produced in large quantities.

In the present invention, polyaniline or polyaniline derivative is substantially removed from the surface by electrolyzing the aggregate of metal nanoparticles covered with polyaniline or polyaniline derivative. Can be obtained more easily. For this reason, the metal nanoparticles of the present invention are extremely fine and have a narrow particle size distribution, that is, nanoparticles excellent in monodispersity.

Since the metal nanoparticles obtained by the method for producing metal nanoparticles of the present invention have the above-described characteristics, they can be suitably used for catalysts, fuel cells, biomolecular labeling substances, metal plating, and the like.

In particular, the metal nanoparticles of the present invention may have a high catalytic activity. Specifically, since the metal nanoparticles of the present invention do not substantially have a protective layer on the surface thereof, when used as a catalyst, firing for removing them is not required. For this reason, a catalyst having high activity can be easily produced by easily supporting metal nanoparticles on a catalyst carrier containing carbon or silicon oxide. In particular, by utilizing the above properties, the metal nanoparticles of the present invention can be suitably used as an electrode catalyst or the like in electrochemical or fuel cells.

Similarly, the metal nanoparticles of the present invention can be used as a biomolecule labeling substance by utilizing the binding property with an antibody or the like. For example, the metal nanoparticles of the present invention and an antibody having a thiol group (—SH) or amino group (—NH ₂ ) that can be directly bonded to the surface of the metal nanoparticles can be easily bonded in one step. . For this reason, the antibody can be easily labeled by immunochromatography. That is, the metal nanoparticles of the present invention can be used as a simple test kit for influenza or a pregnancy test kit.

Furthermore, since the metal nanoparticles of the present invention are extremely fine and have a narrow particle size distribution, they can be suitably used as metal plating. For example, due to the above characteristics, the metal nanoparticles of the present invention can be applied to a fine material and can be easily adhered to a plastic material. Specifically, it can also be used as a material for anisotropic conductive film (ACF), conductive beads for ACF, nanoparticle plating and the like.

As materials such as conductive beads and nanoparticle plating,
"Green Electroless Plating Method Using Gold Nanoparticles for Conducting Microbeads: Application to Anisotropic Conductive Films", S. Tokonami, Y. Yamamoto, Y. Mizutani, I. Ota, H. Shiigi, T. Nagaoka, J. Electrochem. Soc., 156 (12), D558-D563 (2009) and "A Novel Electroless Plating Method for Conducting Microbeads by Using Gold Nanoparticle", Y. Yamamoto, S. Takeda, H. Shiigi, T. Nagaoka, J. Electrochem. Soc., 154 (9), D462-D466 (2007), "Characterization of Au Nanoparticle Film Electrodes Prepared on Polystyrene", Y. Yamamoto, H. Shiigi, T. Nagaoka, Electroanalysis, 17 (24), 2224-2230 (2005) It can be used as the metal nanoparticles described.

On the other hand, since the metal nanoparticles of the present invention have substantially no protective layer on the surface, they are excellent in water dispersibility. For this reason, these can be used conveniently also in the use using an aqueous solvent etc.

Hereinafter, the present invention will be described with some embodiments, but the present invention is not limited thereto.

<Measuring method of average particle diameter>
Using a transmission electron microscope (manufactured by JEOL Ltd., product name JEM-2000FXII), the metal nanoparticles are photographed at a magnification of 150,000 times or more. The particle size of 100 metal nanoparticles is measured arbitrarily from the obtained image, and the average value is taken as the average particle size of the metal nanoparticles.

<Measurement method of CV value>
Using a particle size distribution measuring device (manufactured by Otsuka Electronics Co., Ltd., product name: ELSZ, Zetapotential & Particle size Analyzer), the CV value corresponding to the coefficient of variation is calculated by the following formula.
Coefficient of variation CV (%) = (standard deviation / average particle size) x 100

<Method for measuring zeta potential>
The zeta potential is calculated by electrophoresis using a zeta potential measuring device (product name: Nicomp 380ZLS, Zeta Potential Analyzer, manufactured by Particle Sizing Systems).
More specifically, the zeta potential is calculated by measuring the moving speed (electrophoretic speed) with laser light and determining the moving speed per unit electric field (electrophoretic mobility).

<IR measurement method>
Place the pellet for measurement, KBr plate (mini KBr plate, manufactured by Jusco Engineering Co., Ltd.) on the pressure holder part of a dedicated press machine (mini press, manufactured by Jusco Co., Ltd.), add 0.001 g of metal nanoparticles, Further, it is made by sandwiching between KBr plates and pressing. Next, the surface of the metal nanoparticles is observed by a transmission method using an infrared spectrometer (FT / IR-4200, manufactured by Jusco).

Example 1
30 ml of a 1% by weight chloroauric acid tetrahydrate (manufactured by Wako Pure Chemical Industries) aqueous solution as a metal ion-containing compound and 9 ml of toluene containing 0.01 M aniline (manufactured by Wako Pure Chemical Industries, Ltd.) were mixed (39 ml in total), Gold ions were reduced by leaving them in a constant temperature bath at 60 ° C. for 5 minutes or 10 minutes. Then, it centrifuged at 8500 rpm and 5 degreeC for 30 minutes, and rinsed with the ultrapure water. This washing operation was repeated three times.
The result of observing the aggregate of the gold nanoparticles in the obtained polyaniline with a transmission electron microscope (JEM-2000FXII, manufactured by JEOL Ltd.) is shown in FIG. In FIG. 2, (A) shows the aggregate obtained by reducing for 5 minutes, and (B) shows the aggregate obtained by reducing for 10 minutes.
The particle size of the gold nanoparticles in the obtained agglomerate was measured with an electron microscope and measured with a particle size distribution measuring device. After 5 minutes of reduction, the average particle size was about 0.92 nm (CV value 5%) (cluster) ) After 10 minutes of reduction, the average particle size was about 2.70 nm (CV value 13%) (nanoparticles).

Example 2
Ultrapure water was added to 76 μl of an aqueous solution of 1 wt% chloroauric acid tetrahydrate (manufactured by Wako Pure Chemical Industries) as a metal ion-containing compound and 500 μl of 0.1 M aniline (manufactured by Wako Pure Chemical Industries, Ltd.) to a total volume of 25 ml, 60 The mixture was stirred for 20 minutes while maintaining the temperature to reduce gold ions. Then, it centrifuged at 8500 rpm and 5 degreeC for 30 minutes, and rinsed with the ultrapure water. This washing operation was repeated three times. 40 ml of a 0.1 M aqueous sodium hydroxide solution (manufactured by Wako Pure Chemical Industries, Ltd.) containing polyvinyl alcohol (manufactured by Wako Pure Chemical Industries, Ltd.) was added to the precipitate of aggregates of the obtained gold nanoparticles and mixed, and the mixture was allowed to stand for 12 hours.
The result of having observed the obtained aggregate with the transmission electron microscope similarly to Example 1 is shown in FIG.
The particle size of the gold nanoparticles in the obtained aggregate was about 5.52 nm (CV value 15%) as measured with an electron microscope and measured with a particle size distribution measuring device.

Example 3
The aggregate of gold nanoparticles in the polyaniline obtained in Example 2 was electrolyzed using the electrolysis apparatus shown in FIG. The apparatus shown in FIG. 3 is an H-shaped type using Ag / AgCl as a reference electrode, a tantalum wire (manufactured by Niraco) as a counter electrode, and a carbon cloth (GF-20-S9, manufactured by Shin Nippon Carbon Co., Ltd.) 0.29 g as a working electrode. Cell. A 0.1 M aqueous sodium hydroxide solution (pH 13) was used as the electrolyte solution.
The electrolysis conditions were a constant potential of 1.85 V, 3, 4, 6, 8 or 9 hours.
Further, 10 to 50 mg of the aggregate obtained in Example 2 was added to 40 ml of 0.1 M sodium hydroxide aqueous solution containing 0.01% polyvinyl alcohol (manufactured by Wako Pure Chemical Industries, Ltd.), and uniformly dispersed using ultrasonic waves for 10 minutes. Then, electrolysis was performed at room temperature (25 ° C.).
The result of observing the gold nanoparticles obtained by electrolysis with a transmission electron microscope in the same manner as in Example 1 is shown in FIG. FIG. 5 shows electron micrographs of gold nanoparticles electrolyzed (A) 3 hours, (B) 4 hours, (C) 6 hours, (D) 8 hours and (E) 9 hours.

Table 1 shows the results of measuring the zeta potential of the gold nanoparticles electrolyzed in this example using Nicomp 実 施 380ZLS and Zeta Potential Analyzer. Table 1 also shows the particle diameter (average particle diameter) of the gold nanoparticles measured by observation with an electron microscope.

From the results of Table 1, it can be seen that the zeta potential of the gold nanoparticles decreases as the electrolysis time increases. Since the aggregate of gold nanoparticles that has not been electrolyzed is covered with polyaniline, the surface has a positive charge. However, it can be seen that by performing electrolysis, gold on the surface of the gold nanoparticles is exposed and the zeta potential is lowered.

In addition, the CV value of the gold nanoparticles after the electrolysis time of 0, 3, 4, 6, 8 and 9 hours was measured by a particle size distribution measuring device, respectively 15%, 15%, 17%, 20%, 18% and 20%.

Example 4
76 μl of the 1 wt% chloroauric acid tetrahydrate aqueous solution of Example 2 was changed to 760 μl of a 1 wt% aqueous solution of chloroplatinic acid tetrahydrate (manufactured by Wako Pure Chemical Industries, Ltd.), and 5 ml of 0.1M aniline was used at 80 ° C. A platinum nanoparticle aggregate in polyaniline was obtained in the same procedure as in Example 2 except that the reduction was carried out for 30 minutes.
The obtained platinum nanoparticle aggregate was electrolyzed in the same manner for 9 hours using the same electrolysis apparatus as used in Example 3.
The results obtained by observing the obtained platinum nanoparticle aggregates and platinum nanoparticles with a transmission electron microscope in the same manner as in Example 1 are shown in FIGS. 6 (A) and 6 (B), respectively.

Table 2 shows the results of measuring the particle size (average particle size) and zeta potential of platinum nanoparticles electrolyzed for 9 hours.

From the results in Table 2, it can be seen that polyaniline was decomposed by electrolysis for 9 hours to obtain platinum nanoparticles.

The CV values of the gold nanoparticles after the lapse of 0 and 9 hours of electrolysis were 14% and 14%, respectively, as measured by a particle size distribution measuring device.

Reference example Ag / AgCl as the reference electrode, tantalum wire (manufactured by Niraco) as the counter electrode, 0.068 g of carbon cloth (GF-20-S9, Shin Nippon Carbon) as the working electrode, porous Vycor glass (manufactured by Corning) ) "Enantioselective uptake of amino acids using an electromodulated column packed with carbon fibers modified with overoxidised polypyrrole", B. Deore, H. Yakabe, H. Shiigi, T. Nagaoka, Analyst, 127, 935-939 (2002) A syringe type flow cell electrolysis apparatus was prepared by a known method described in 1). A 0.1M sodium hydroxide aqueous solution (pH 13) containing the gold nanoparticle aggregate obtained in Example 2 was circulated at 5 ml / min using a peristaltic pump (SJ-1211H, manufactured by Ato), and a constant potential of 1.85 V. For 56 hours. A photograph of the electrolyzer used is shown in FIG.
The results obtained by observing the obtained substance with a transmission electron microscope in the same manner as in Example 1 are shown in FIG.
In addition, Table 3 shows the results of measuring the zeta potential and average particle diameter of the obtained substance.

8 and Table 3 show that if the electrolysis time is too long, the polyaniline is sufficiently decomposed to lower the zeta potential, but the gold particles are fused to increase the particle size.

The CV values of the gold nanoparticles after the electrolysis time of 0 and 56 hours were 15% and 30%, respectively, as measured with a particle size distribution measuring device.

Examples 5-7
0.1M o-aminotoluene (manufactured by Wako Pure Chemical Industries, Ltd.) in 25 ml of an aqueous solution containing 76 μl of 1 wt% chloroauric acid tetrahydrate (manufactured by Wako Pure Chemical Industries, Ltd.) as a metal ion-containing compound Toluene containing 5 ml was added to make a total volume of 30 ml, and the mixture was stirred for 20 minutes while maintaining at 60 ° C. to reduce gold ions. Subsequently, it was centrifuged at 8500 rpm and 5 ° C. for 30 minutes and rinsed with ultrapure water. This washing was performed 3 times (Example 5).
Also, gold nanoparticle aggregates were prepared in the same manner as described above using o-ethylaniline (Example 6) and m-ethylaniline (Example 7) instead of o-aminotoluene.
The results of observing the obtained aggregates with a transmission electron microscope in the same manner as in Example 1 are shown in FIG. FIG. 9 is a photograph of the gold nanoparticle aggregate prepared in (A) Example 5, (B) Example 6 and (C) Example 7.
The particle diameters of the gold nanoparticles in the aggregates obtained in Examples 5, 6 and 7 were measured with an electron microscope and measured with a particle size distribution measuring device, and the average particle diameter was 7.22 nm (CV value 22%), respectively. , 7.42 nm (CV value 20%), and 7.14 nm (CV value 17%).

Examples 8-10
Add ultrapure water to 76 μl of 1 wt% chloroauric acid tetrahydrate (manufactured by Wako Pure Chemical Industries) as a metal ion-containing compound and 500 μl of 0.1 M o-aminophenol (manufactured by Wako Pure Chemical Industries, Ltd.) The mixture was stirred for 20 minutes while maintaining the temperature at 60 ° C. to reduce gold ions. Subsequently, it was centrifuged at 8500 rpm and 5 ° C. for 30 minutes and rinsed with ultrapure water. This washing was performed 3 times (Example 8).
Also, gold nanoparticle aggregates were prepared in the same manner as described above using o-aminobenzoic acid (Example 9) and m-aminobenzoic acid (Example 10) instead of o-aminophenol.
The results of observation of the obtained aggregates with a transmission electron microscope in the same manner as in Example 1 are shown in FIG. FIG. 10 is a photograph of the gold nanoparticle aggregate prepared in (A) Example 8, (B) Example 9 and (C) Example 10.
The particle diameters of the gold nanoparticles in the aggregates obtained in Examples 8, 9 and 10 were measured with an electron microscope and measured with a particle size distribution measuring device, respectively, and the average particle diameter was 5.52 nm (CV value 16%). 3.79 nm (CV value 16%) and 4.85 nm (CV value 21%).

From the results of Examples 5 to 10, it can be seen that metal nanoparticles can be produced using an aniline derivative as a reducing agent.

Example 11
Using the same electrolysis apparatus as used in Example 3, the aggregate of gold nanoparticles (average particle size: 0.92 nm, CV value: 5%) in polyaniline obtained in Example 1 was similarly used as an electrolyte solution. Was electrolyzed at a constant potential of 1.85 V for 18 hours using a 0.1 M aqueous sodium hydroxide solution (pH 13). The zeta potential of this particle was 0.20 mV.
FIG. 11A shows the result of measuring the particle size distribution of the obtained gold nanoparticles using ELSZ, Zetapotential & Particle size Analyzer manufactured by Otsuka Electronics.

For comparison, "Glutathione-Protected Gold Clusters Revisited: Bridging the Gap between Gold (I) -Thiolate Complexes and Thiolate-Protected Gold Nanocrystals", Y. Negishi, K. Nobusada, T. Tsukuda, J. Am. Chem. Soc. , 127, 5261-5270 (2005), gold nanoparticles were prepared by a known method.
Specifically, 1 mmol of glutathione (0.306 g) as a protective agent was added to 50 ml of 5 mM chloroauric acid (solvent; methanol) as a metal ion-containing compound, and the mixture was cooled and stirred (0 to 4 ° C.) for 30 minutes, and then reduced. As an agent, 12.5 ml of 0.2M NaBH ₄ was added and stirred for an additional hour while cooling to reduce gold ions to obtain gold particles. The solution was then centrifuged at 8500 rpm at 5 ° C. for 30 minutes and rinsed with methanol. This washing was performed 3 times. The precipitate thus obtained was dried at 60 ° C. Subsequently, it was added to 20 ml of ultrapure water and dispersed by ultrasonic treatment. The zeta potential of this particle was −37.76 mV.
FIG. 11B shows the result of measuring the particle size distribution of the obtained particles using ELSZ, Zetapotential & Particle size Analyzer manufactured by Otsuka Electronics.

From the results of FIG. 11, the average particle size of the gold nanoparticles prepared by the method of the present invention is 1.3 nm (CV value 23%), and the average particle size of the gold clusters prepared by the known method is 1.6 nm. (CV value 31%). It was found that gold nanoparticles having a narrow particle size distribution can be produced according to the method of the present invention as compared with gold clusters produced by a known method. That is, according to the method of the present invention, metal nanoparticles having a desired particle diameter can be efficiently produced.

Example 12
<Use of gold nanoparticles as catalyst>
Using the same electrolysis apparatus as used in Example 3, the aggregate of gold nanoparticles (average particle size 5.52 nm, CV value 15%) in polyaniline obtained in Example 2 was used in the same manner as the electrolyte solution. Gold nanoparticles (average particle size 6.31 nm, CV value 20%) obtained by electrolysis at a constant potential of 1.85 V for 9 hours using 0.1 M sodium hydroxide aqueous solution (pH 13) as 8500 rpm at 5 ° C The mixture was centrifuged for 30 minutes and rinsed with ultrapure water. This washing was performed 3 times. The precipitate thus obtained was again dispersed in 0.5 ml of ultrapure water. 10 μl of this dispersion was dropped onto an electrode (diameter 1 mm, GCE glassy carbon electrode, manufactured by BAS) and vacuum dried for 30 minutes. Thus obtained glassy carbon electrode fixed with gold nanoparticles was obtained (a).

For comparison, "Glutathione-Protected Gold Clusters Revisited: Bridging the Gap between Gold (I) -Thiolate Complexes and Thiolate-Protected Gold Nanocrystals '', Y. Negishi, K. Nobusada, T. Tsukum,. , 127, 5261-5270) (2005), gold nanoparticles were prepared by a known method.

Specifically, 1 mmol of glutathione (0.306 g) as a protective agent was added to 50 ml of 5 mM chloroauric acid (solvent; methanol) as a metal ion-containing compound, and the mixture was cooled and stirred (0 to 4 ° C.) for 30 minutes, and then reduced. As an agent, 12.5 ml of 0.2M NaBH ₄ was added and stirred for an additional hour while cooling to reduce gold ions to obtain gold particles. This solution was centrifuged at 8500 rpm and 5 ° C. for 30 minutes and rinsed with methanol. This washing was performed 3 times. The precipitate thus obtained was dried at 60 ° C. Subsequently, it was added to 20 ml of ultrapure water and dispersed by ultrasonic treatment. 10 μl of this dispersion was dropped onto an electrode (diameter 1 mm, GCE glassy carbon electrode, manufactured by BAS) and vacuum dried for 30 minutes.

"The humidity dependence of the electrical conductivity of a solublepolyaniline-poly (vinyl alcohol) composite film", K. Ogura, T. Saino, M. Nakayama, H. Shiigi, J. Mater. Chem., 7, 2363 ～ 2363 ～ 2363 ～ 1997) to prepare a polyaniline powder.

Specifically, 100 ml of a 0.1 M paratoluenesulfonic acid aqueous solution containing 0.15 M ammonium persulfate was slowly added to 100 ml of a 0.1 M paratoluenesulfonic acid aqueous solution containing 0.15 M aniline, followed by stirring at room temperature (25 ° C.) for 8 hours. The resulting precipitate was filtered under reduced pressure and washed thoroughly with a 0.1 M paratoluenesulfonic acid aqueous solution until the color of the solution became colorless. Next, the powder remaining on the filter paper was vacuum-dried.
0.01 g of this powder was added to 20 ml of ultrapure water and subjected to ultrasonic treatment for 30 minutes for dispersion. 10 μl of this dispersion solution was dropped on the glassy carbon electrode fixed with gold nanoparticles using a microsyringe and vacuum-dried for 3 hours (b).
These polyaniline-coated glassy carbon electrodes were used as working electrodes, electrochemical measurements were performed using the electrochemical cell shown in FIG. 12, Ag / AgCl as the reference electrode, and tantalum wire (manufactured by Niraco) as the counter electrode. . A 0.05 M sulfuric acid aqueous solution (pH 1.2) was used as the electrolyte solution. Cyclic voltammetry was performed using an electrochemical apparatus (potentiogalvanostat HZ3000, manufactured by Hokuto Denko) at an insertion range of -0.2 to 0.8 V and an insertion speed of 10 mV / s. The result is shown in FIG.

Example 13
In the same manner as in Example 1, 30 ml of a 1 wt% chloroauric acid tetrahydrate (manufactured by Wako Pure Chemical Industries) aqueous solution as a metal ion-containing compound and 9 ml of toluene containing 0.01 M aniline (manufactured by Wako Pure Chemical Industries, Ltd.) The mixture was mixed (39 ml in total) and left in a constant temperature bath at 60 ° C. for 10 minutes to reduce gold ions. Then, it centrifuged at 8500 rpm and 5 degreeC for 30 minutes, and rinsed with the ultrapure water. This washing operation was repeated three times.
FIGS. 14a and 14b show the results of observation of the aggregates of gold nanoparticles in the obtained polyaniline with a transmission electron microscope (JEM-2000FXII, manufactured by JEOL Ltd.).
The particle size of the gold nanoparticles in the obtained aggregate was approximately 1.10 nm (CV value 9.1%) after 10 minutes of reduction, as measured with an electron microscope and measured with a particle size distribution analyzer. It was.
40 ml of 0.1M sodium hydroxide aqueous solution (manufactured by Wako Pure Chemical Industries) containing polyvinyl alcohol (manufactured by Wako Pure Chemical Industries) was added to the precipitate of the aggregates of the obtained gold nanoparticles and mixed, and the mixture was allowed to stand for 12 hours. Electrolysis was carried out using an electrolysis apparatus of a syringe type flow cell.
A 0.1 M aqueous sodium hydroxide solution (pH 13) containing gold nanoparticle aggregates was electrolyzed at a constant potential of 1.85 V for 18 hours while circulating at 5 ml / min using a peristaltic pump (SJ-1211H, manufactured by Ato). Then, it centrifuged at 15000 rpm and 5 degreeC for 30 minutes, and rinsed with the ultrapure water. This washing operation was repeated three times. The precipitate thus obtained was again dispersed in 1.0 ml of ultrapure water.
The result obtained by observing the obtained substance with a transmission electron microscope in the same manner as in Example 1 is shown in FIG. 14c. Gold nanoparticles having an average particle diameter of 1.13 nm (CV value of 10%) were obtained by observation with an electron microscope and measurement with a particle size distribution measuring apparatus.
In addition, Table 4 shows the results of measuring the zeta potential and particle size of the obtained substance.

FIG. 15 shows the result of measuring the particle size distribution of the obtained particles using ELSZ, Zetapotential & Particle Analyzer manufactured by Otsuka Electronics Co., Ltd.

Electrolysis of polyaniline occurs at the working electrode during electrolysis, but using an electrochemical cell with a structure like a syringe type flow cell improves the contact efficiency of the aggregate to the working electrode and electrolysis of polyaniline. Therefore, it is possible to suppress an increase in average particle size and CV value due to an increase in electrolysis time.

Example 14
Aggregates of gold nanoparticles (average particle size 5.52 nm, CV value 15%) in polyaniline obtained in Example 2 were prepared as an electrolyte solution using the same electrolysis apparatus as used in Example 3. Similarly, gold nanoparticles (average particle size 6.31 nm, CV value 20%) obtained by electrolysis at a constant potential of 1.85 V for 9 hours using M sodium hydroxide aqueous solution (pH 13), 8500 rpm, 5 ° C And then rinsed with ultrapure water. This washing was performed 3 times. The precipitate thus obtained was vacuum-dried at 60 ° C. for 3 days.
For comparison, "Glutathione-Protected Gold Clusters Revisited: Bridging the Gap between Gold (I) -Thiolate Complexes and Thiolate-Protected Gold Nanocrystals", Y. Negishi, K. Nobusada, T. Tsukuda, J. Am. Chem. Soc. , 127, 5261-5270 (2005), gold nanoparticles were prepared by a known method.
Specifically, 1 mmol of glutathione (0.306 g) as a protective agent was added to 50 ml of 5 mM chloroauric acid (solvent; methanol) as a metal ion-containing compound, and the mixture was cooled and stirred (0 to 4 ° C.) for 30 minutes, and then reduced. As an agent, 12.5 ml of 0.2M NaBH ₄ was added and stirred for another 1 hour while cooling to reduce gold ions to obtain gold particles. This solution was centrifuged at 8500 rpm and 5 ° C. for 30 minutes and rinsed with methanol. This washing was performed 3 times. The precipitate thus obtained was vacuum dried at 60 ° C. for 3 days.
The surface of the gold nanoparticles was observed by a transmission method using an infrared spectrometer (FT / IR-4200, manufactured by Jusco). For the pellets for measurement, place a KBr plate (mini KBr plate, manufactured by Jusco Engineering) on a special press machine (mini press, manufactured by Jusco), add 0.001 g of gold nanoparticle powder, It was produced by sandwiching and pressing. The result is shown in FIG. In the comparative gold nanoparticles, a peak based on glutathione forming a protective layer was observed, but in the gold nanoparticles according to the present invention, only a peak of adsorbed water was obtained, and a peak indicating the presence of an organic compound due to aniline was obtained. I couldn't.

a1 Counter electrode a2 Reference electrode a3 Working electrode a4 Polyaniline gold nanoparticle aggregate solution

b1 Reference electrode b2 Counter electrode b3 Working electrode b4 Polyaniline gold nanoparticle aggregate solution b5 Reference electrode Ag | AgCl
b6 Working electrode Carbon cloth b7 Electrolyte b8 Working electrode Lead wire b9 Counter electrode Tantalum wire b10 Vycor glass tube b11 Load

c1% of particles
c2 Average particle size (nm)
c3% of particles
c4 Average particle size (nm)

d1 Working electrode: Glassy carbon (GC) electrode d2 Reference electrode: Ag | AgCl
d3 Counter electrode: Platinum wire d4 Electrolyte solution d5 Beaker d6 GC electrode d7 Insulating resin d8 Cross section d9 Electrode surface d10 GC

e1 × 10 ^-6 A current e2 potential / V vs. Ag | AgCl

f1 a before electrolysis f2 b before electrolysis f3 c after 18h electrolysis

g1% of particles
g2 Average particle size (nm)

h1 wave number (cm ^-1 )
h2 wave number (cm ^-1 )

Claims (12)

1. Metal nanoparticles having a zeta potential of 0 to 5 mV, an average particle size of 0.5 to 10 nm, and a particle size distribution with a CV value of 0 to 25%.
2. The metal nanoparticle according to claim 1, wherein the metal nanoparticle contains either gold or platinum.
3. The metal nanoparticle according to claim 1, wherein the metal nanoparticle has substantially no peak derived from an organic compound in an IR chart obtained by measuring the metal nanoparticle.
4. Metal nanoparticles,
   Metal ions are reduced using aniline or aniline derivatives as a reducing agent to obtain aggregates of metal nanoparticles covered with polyaniline or polyaniline derivatives,
   The metal nanoparticles according to claim 1, which are obtained by a production method including a step of obtaining metal nanoparticles not covered with polyaniline or a polyaniline derivative by electrolyzing the obtained aggregate of metal nanoparticles.
5. A catalyst comprising the metal nanoparticles according to claim 1.
6. Metal ions are reduced using aniline or aniline derivatives as a reducing agent to obtain aggregates of metal nanoparticles covered with polyaniline or polyaniline derivatives,
   A method for producing metal nanoparticles, comprising electrolyzing the obtained aggregate of metal nanoparticles to obtain metal nanoparticles not covered with polyaniline or a polyaniline derivative.
7. The method according to claim 6, wherein the reduction is carried out by bringing an aqueous solution containing metal ions into contact with an organic solution containing aniline or an aniline derivative.
8. The method according to claim 6, wherein the electrolysis is performed in an electrolyte solution containing an aggregate of metal nanoparticles.
9. The method according to claim 6, wherein the electrolyte solution has a pH of 12.0 to 14.0.
10. The method according to claim 6, wherein the electrolysis is performed at a potential of 1.5 to 2.2 V for 1 hour to 20 hours.
11. The method according to claim 6, wherein the electrolysis is performed at a potential of 1.5 to 2.0 V for 1 hour to 15 hours.
12. The method according to claim 6, wherein the metal is a noble metal containing gold and platinum.

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