JP4878196B2 - Method for producing metal fine particles using conductive nanodot electrode - Google Patents

Description

The present invention relates to a method for producing a metal comprising copper, silver, nickel, cobalt, iron, zinc, tin, silver, gold, platinum, palladium, iridium, rhodium, osmium, ruthenium, etc., and in particular, electrochemistry in a liquid phase The present invention relates to a method for producing typical nano-sized metal fine particles.

  It is known that nano-sized metal particles (particle size of 1 μm or less) have various unique characteristics not found in bulk materials. Various engineering applications that take advantage of this property are now highly expected in fields such as electronics, biotechnology, and energy.

  As methods for producing such nano-sized metal fine particles, two types of production methods, a gas phase synthesis method and a liquid phase synthesis method, are widely known. Here, the gas phase synthesis method is a method of forming solid metal fine particles from metal vapor introduced into the gas phase, while the liquid phase synthesis method is to reduce metal ions dispersed in a solution. This is a method of depositing metal fine particles.

  Among them, in the vapor phase synthesis method, metal vapor is generally supplied to the reaction vessel by CVD, gas evaporation, laser ablation, sputtering, etc., and metal fine particles are generated, but these reaction apparatuses are generally expensive, It has been found that there is a problem that the production amount (that is, the yield) relative to the amount of raw material used is poor and the production cost is high. Furthermore, it has been pointed out that the obtained metal fine particles have a problem that the particle size distribution is wide.

Further, in the liquid phase synthesis method, generally, as a reduction method for reducing the metal ion, a method using a reducing agent such as alcohol, polyol, aldehyde, hydrazine, sodium borohydride, or the like, and an electrochemical cathode electrode Methods for performing the above reduction are known. Among them, the electrochemical reduction method can easily adjust the shape and size of the generated metal fine particles by adjusting the reduction rate according to the amount of current, and also by adjusting the amount of current, In recent years, it has attracted much attention because it is easy to produce composite (alloy) particles.
JP 2005-281781 Japanese Patent Laid-Open No. 2003-147417 JP 2005-248204 A MTReetz et al., J. Am. Chem. Soc. Vol.116 (1994) p7401-7402, MTReetz et al., Chem. Mater. Vol.7 (1995) p2227-2228 A. Pietrikova et al., Metallic Materials Vol. 29 (1991) p262-272

  However, in the technique known so far as this electrochemical reduction method, the problem is that the reduced metal grows in a dendrite shape or when the particles are produced in large quantities, the particles are enlarged. Has been pointed out.

  Therefore, the object of the present invention is to produce granular nano-sized fine metal particles without producing enlarged particles when the reduced metal does not grow into dendrites (dendrites) and the particles are produced in large quantities. It is providing the manufacturing method of the copper nanoparticle which can be manufactured efficiently.

The inventor conducted extensive research on the above-described conventional problems. As a result, instead of the cathode electrode made of metal such as plate-like or rod-like platinum that has been used in the conventional electrochemical liquid phase reduction method, a cathode electrode made of nanodot metal made up of a large number of nano-sized metal protrusions is used. Thus, it was found that granular nanosized metal fine particles can be efficiently produced by electrochemical reduction of metal ions. At this time, the amount of metal fine particles to be obtained can be controlled by appropriately adding ions of the metal to be produced to the electrolytic solution for electrochemical reduction. If an organic dispersion medium such as pyrrolidone or polyacrylic acid is added, it is possible to reduce the aggregation of the generated particles. Further, when the applied current is changed to a pulsed current and the reaction solution and the cathode electrode are vibrated ultrasonically, it is obtained. It has been found that the shape uniformity of the metal fine particles is further improved. The present invention has been made based on the research results described above.

The first aspect of the production method of the present invention comprises at least one metal selected from copper, nickel, cobalt, iron, zinc, tin, silver, gold, platinum, palladium, iridium, rhodium, osmium, and ruthenium. An anode that is a metal to be manufactured, and a cathode that is made of a number of conductive nanodot electrodes insulated from each other with a maximum length of 1 μm or less made of platinum or carbon,
Furthermore, the anode and the cathode, in a conductive aqueous solution, a method for producing metal fine particles by producing metal fine particles by energization,
The conductive aqueous solution contains a metal ion to be manufactured,
Further , the present invention is a method for producing fine metal particles, wherein an amide polymer such as polyvinylpyrrolidone and polyethyleneimine are added as an organic dispersion medium .

According to a second aspect of the production method of the present invention, the cathode is a conductive nanodot electrode made of platinum and the anode is an electrode made of a copper sheet. Further, as a supporting electrolyte, a dilute sulfuric acid aqueous solution is used as an organic dispersion medium. 2. The method for producing fine metal particles according to claim 1, wherein the fine copper particles are produced using polyvinylpyrrolidone and a conductive aqueous solution to which copper acetate is added as a metal ion raw material to be produced.

According to a third aspect of the production method of the present invention, in the method for producing metal fine particles for producing copper fine particles according to claim 2, polyvinylpyrrolidone 0.5 as an organic dispersion medium is used with respect to 200 parts by mass of dilute sulfuric acid aqueous solution. 3. The metal fine particles according to claim 2, wherein copper particles having an average particle diameter of 50 nm are produced using parts by weight and a conductive aqueous solution added with 0.5 parts by weight of copper acetate as a metal ion raw material to be produced. It is a manufacturing method.

According to a fourth aspect of the manufacturing method of the present invention, the energization is performed with a pulse current having a frequency of 1 Hz or higher, or ultrasonic vibration is applied to the conductive aqueous solution and the cathode during the energization, or the energization is performed with a frequency of 1 Hz or higher. 4. The fine metal particles according to claim 3, wherein copper fine particles having an average particle diameter of 15 to 30 nm are produced by a method of applying ultrasonic vibration to the conductive aqueous solution and the cathode during the energization simultaneously with the pulse current of It is a manufacturing method.

According to the present invention, since metal ions are electrochemically reduced using a cathode (cathode electrode) made up of a large number of nano-sized conductive electrodes, it is possible to efficiently produce granular nano-sized metal fine particles.

Furthermore, according to the present invention, the applied current is changed to a pulse current, and the reaction solution and the electrode are vibrated ultrasonically, so that the shape uniformity of the obtained metal fine particles is further improved.

A method for producing copper nanoparticles that are one of the metal fine particles according to the present invention will be described with reference to the drawings.
The first aspect of the method for producing copper nanoparticles of the present invention is characterized in that, in a conductive aqueous solution containing an organic dispersion medium, an anode made of copper and a cathode electrically insulated from each other are energized. This is a method for producing copper nanoparticles.

The cathodes described above are conductive electrodes that are insulated from each other so that the maximum length is 1 μm or less. For example, a cylindrical electrode having a diameter of 1 μm or less or a rectangular electrode having a length of one side of 1 μm or less and electrically insulated conductive electrodes. The cathode made of the electrically insulated conductive electrode is formed by a nano-imprinting method, a hole is formed in the Si substrate by a focused ion beam (FIB) apparatus, and embedded by plating. There are a forming method, a forming method by arranging nano-sized metal fine particles to be manufactured by a Langmuir-Blodgett (LB) method, and the like.
In the present invention, metal ions are electrochemically reduced using nanodot electrodes composed of a large number of nano-sized conductive electrodes. In the following, the difference in particles obtained when a plate-like platinum electrode is used and when a nanodot platinum electrode is used will be described by way of examples.

( Manufacturing method of nanodot platinum electrode)
The nanodot platinum electrode used as a pole in the present invention was prepared by the following procedure as shown in FIGS. 1 (a) to 1 (c).
First, the surface of the platinum plate-like substrate 1 was coated with an insulating resin 2 (FIG. 1A). Thereafter, a pattern substrate 3 composed of a large number of square holes 4 each having a side length of about 1 μm was formed by nanoimprinting (FIG. 1B). By applying electrochemical plating to the pattern substrate thus formed, platinum was embedded in the hole portion described above to form a conductive electrode to obtain a nanodot platinum electrode 5 (FIG. 1C).

(Differences in the particles obtained when using a plate-like platinum electrode and when using a nanodot platinum electrode)
When the plate-like platinum electrode was used and when the nanodot platinum electrode was used, the difference in the obtained particles was confirmed by the following copper nanoparticle production experiment.

（電気化学還元法によって得られた銅微粒子の特徴）
表１から明らかなように、カソード電極にナノドット白金電極を使用して金属イオンの電気化学的還元を行うと、粒子形状は球状で、平均粒径は５０ｎｍであるのに対して、カソード電極に板状白金電極を使用して同様に電気化学的還元を行うと、粒子形状は棒状（または樹枝状）で、平均粒径は２００ｎｍである。従って、カソード電極にナノドット白金電極を用いて金属イオンの電気化学的還元を行うと、粒状で、ナノサイズの金属微粒子を効率よく製造することができる。
更に、この発明においては、印加する電流をパルス電流にし、さらに反応溶液およびカソード電極を超音波振動させる。以下に、印加電流をパルスにした時の効果および反応溶液およびカソード電極を超音波振動させた時の効果を実施例によって説明する。
First, a conductive aqueous solution containing copper ions by adding 0.5 g of polyvinylpyrrolidone (PVP) as an organic dispersion medium and 0.5 g of copper acetate as a metal ion raw material to be produced to 200 g of an aqueous solution containing a small amount of dilute sulfuric acid as a supporting electrolyte. A reaction solution was prepared. Subsequently, in this solution, an anode (anode electrode) made of a 2 cm square copper sheet and a cathode (cathode electrode) made of a platinum nanodot substrate prepared by the above production method were energized for 30 minutes. At this time, the applied voltage was 1 V with respect to the reference electrode, and the current density was 0.1 mA / cm2. Thereafter, the obtained colloid solution was collected on an aluminum mesh to which a carbon support film was attached, and after removing the solvent by drying, the generated fine particles were observed using a transmission electron microscope (TEM). Further, when a plate-like platinum electrode was used as the cathode (cathode electrode), copper nanoparticles were produced under the same conditions.
The results obtained from the above experiment are shown in Table 1.

( Characteristics of copper fine particles obtained by electrochemical reduction method)
As is apparent from Table 1, when a metal dot is electrochemically reduced using a nanodot platinum electrode as the cathode electrode, the particle shape is spherical and the average particle diameter is 50 nm. When electrochemical reduction is similarly performed using a plate-like platinum electrode, the particle shape is rod-shaped (or dendritic), and the average particle size is 200 nm. Therefore, when a metal dot is electrochemically reduced using a nanodot platinum electrode as a cathode electrode, granular nanosized metal fine particles can be efficiently produced.
Furthermore, in the present invention, the applied current is changed to a pulse current, and the reaction solution and the cathode electrode are vibrated ultrasonically. Hereinafter, the effect when the applied current is made into a pulse and the effect when the reaction solution and the cathode electrode are vibrated ultrasonically will be described by way of examples.

表２から明らかなように、直流電流を印加した場合の平均粒径が５０ｎｍであるのに対して、パルス電流を印加した場合の平均粒径は３０ｎｍである。従って、印加する電流をパルス電流にすることによって、得られる金属微粒子の形状均一性が一層向上している。
(Effect when applying current to pulse)
The effect when the applied current was changed to a pulse current was confirmed by the following experiment.
The nanodot platinum electrode prepared in Example 1 is used as the cathode electrode, and the voltage amplitude is 1 V, the current density (ip) is 0.1 mA / cm2, and the frequency is 100 Hz as shown in FIG. A pulse current (Toff = Ton) was applied . The colloidal solution obtained after the energization for 30 minutes was collected on an aluminum mesh to which a carbon support film was attached, and after removing the solvent by drying, the generated particles were observed using a transmission electron microscope (TEM). The results are shown in Table 2.

As is apparent from Table 2, the average particle diameter when a direct current is applied is 50 nm, whereas the average particle diameter when a pulse current is applied is 30 nm. Therefore, by making the applied current a pulse current, the shape uniformity of the obtained metal fine particles is further improved.

表３から明らかなように、反応溶液およびカソード電極を振動させないで直流電流を使用したとき、平均粒径５０ｎｍの球状の粒子であるのに対して、直流電流を使用し、反応溶液およびカソード電極を超音波振動させた時は、平均粒径２０ｎｍの球状の粒子である。更に、直流電流の代わりにパルス電流を印加すると、反応溶液およびカソード電極を超音波振動させた時は、平均粒径１５ｎｍの球状の粒子である。即ち、印加電流をパルスにした時の効果および反応溶液およびカソード電極を超音波振動させると、金属微粒子の形状均一性がより一層向上する。
上述したように、適当な有機保護剤（例えばポリビニルピロリドン）を分散させた電解質溶液中（例えば、水、THFなど）で、ナノサイズの白金ドット電極からなるカソードと、対象金属のバルク体からなるアノードに通電することで、有機保護剤に被膜された金属微粒子を得ることができる。この時、通電する電流をパルス電流にすることで、さらには反応溶液および電極を振動させることにより、得られる金属微粒子の粒径がより小さくまた形状がより球状になる。
(Effect when the reaction solution and cathode electrode are vibrated ultrasonically)
The effect of ultrasonically vibrating the reaction solution and the cathode electrode was confirmed by the following experiment. The nanodot platinum electrode prepared in Example 1 was used as the cathode electrode, and electrochemical reduction was performed under the same conditions as in Examples 2 and 3 while vibrating the reaction solution with an ultrasonic vibration device. The obtained colloid solution was collected on an aluminum mesh to which a carbon support film was attached, and after removing the solvent by drying, the generated particles were observed using a transmission electron microscope (TEM). The results are shown in Table 3.

As is apparent from Table 3, when direct current is used without vibrating the reaction solution and the cathode electrode, the direct current is used for the reaction solution and the cathode electrode, while the spherical particles have an average particle diameter of 50 nm. Is a spherical particle having an average particle diameter of 20 nm. Furthermore, when a pulse current is applied instead of a direct current, when the reaction solution and the cathode electrode are vibrated ultrasonically, they are spherical particles having an average particle diameter of 15 nm. That is, when the applied current is pulsed and when the reaction solution and the cathode electrode are vibrated ultrasonically, the shape uniformity of the metal fine particles is further improved.
As described above, in an electrolyte solution (for example, water, THF, etc.) in which an appropriate organic protective agent (for example, polyvinylpyrrolidone ) is dispersed, a cathode composed of a nano-sized platinum dot electrode and a bulk body of the target metal By energizing the anode, fine metal particles coated with an organic protective agent can be obtained. At this time, the current to be energized is changed to a pulse current, and further, the reaction solution and the electrode are vibrated, whereby the resulting metal fine particles have a smaller particle size and a more spherical shape.

According to the present invention, since metal ions are electrochemically reduced using a large number of nano-sized conductive nanodot electrodes , granular nano-sized metal fine particles can be efficiently produced. Furthermore, since the applied current is changed to a pulse current, and the reaction solution and the cathode electrode are ultrasonically vibrated, the shape uniformity of the obtained metal fine particles is further improved, and thus the industrial applicability is great.

FIG. 1 is a schematic view for explaining a method for producing a nanodot platinum electrode. FIG. 2 is a diagram showing a pulse current.

Explanation of symbols

1 platinum plate-like substrate 2 insulating resin 3 pattern substrate 4 hole 5 nanodot platinum electrode

Claims (4)

An anode, which is a metal to be manufactured, made of at least one metal selected from copper, nickel, cobalt, iron, zinc, tin, silver, gold, platinum, palladium, iridium, rhodium, osmium, and ruthenium, and platinum or carbon A cathode consisting of a number of electrically conductive nanodot electrodes insulated from each other with a maximum length of 1 μm or less,
Furthermore, the anode and the cathode, in a conductive aqueous solution, a method for producing metal fine particles by producing metal fine particles by energization,
The conductive aqueous solution contains a metal ion to be manufactured,
Furthermore, a method for producing fine metal particles, characterized in that an amide polymer such as polyvinylpyrrolidone and polyethyleneimine are added as an organic dispersion medium .   The cathode is a conductive nanodot electrode made of platinum, the anode is an electrode made of a copper sheet, and further, an aqueous solution of dilute sulfuric acid as a supporting electrolyte, polyvinylpyrrolidone as an organic dispersion medium, and acetic acid as a metal ion raw material to be produced. 2. The method for producing fine metal particles according to claim 1, wherein the fine copper particles are produced using a conductive aqueous solution to which copper is added.   In the manufacturing method of the metal microparticle which manufactures the copper microparticle of Claim 2, with respect to 200 mass parts of dilute sulfuric acid aqueous solution, 0.5 weight part of polyvinylpyrrolidone as an organic dispersion medium, and acetic acid as a metal ion raw material to be manufactured The method for producing fine metal particles according to claim 2, wherein copper particles having an average particle diameter of 50 nm are produced using a conductive aqueous solution added with 0.5 parts by weight of copper. The energization is performed with a pulse current having a frequency of 1 Hz or higher, the ultrasonic vibration is applied to the conductive aqueous solution and the cathode during the energization, or the energization is performed with the pulse current having a frequency of 1 Hz or more and simultaneously with the energization, 4. The method for producing metal fine particles according to claim 3, wherein copper fine particles having an average particle diameter of 15 to 30 nm are produced by a method of applying ultrasonic vibration to the conductive aqueous solution and the cathode.

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