KR101671049B1 - Nickel-cobalt nanoparticle and manufacturing method therefor - Google Patents

Abstract

The nickel-cobalt nanoparticles include a core substantially composed of nickel and a shell substantially consisting of cobalt substantially covering the entire surface of the core. The method for producing nickel-cobalt nanoparticles comprises the steps of heating a mixture containing a nickel salt or a nickel fine particle, a cobalt salt and a primary amine to obtain a reaction liquid, or a step of heating a mixture of a cobalt salt and a primary amine, And a step of heating the reaction liquid to obtain a slurry of nickel-cobalt nano particles.

Description

TECHNICAL FIELD [0001] The present invention relates to nickel-cobalt nanoparticles and nickel-cobalt nanoparticles,

The present invention relates to a nanoparticle having a core-shell structure made of a dissimilar metal.

Cobalt nanoparticles are cheaper than silver nanoparticles, are more chemically stable than copper nanoparticles, and have higher catalytic activity and saturation magnetization than nickel particles. Therefore, it is desirable to use cobalt nanoparticles for various catalysts, magnetic materials, electrodes in fuel cells or multilayer ceramic capacitors Use is expected. However, since cobalt is a rare metal, which is considerably higher in price than nickel particles, development of cobalt particles and a production method thereof which can draw the performance of cobalt to a smaller amount is desired. In order to draw out the performance of the cobalt well, the particle size and the shape of the cobalt should be controlled to be uniform.

In general, the production method of metal nanoparticles is largely divided into physics and chemistry. The physical method is a method (milling method) of producing nanoparticles by pulverizing a bulk metal, and a chemical method is a method (agglomeration method) of producing metallic atoms by controlling aggregation thereof. In the pulverization by the physical method, there is a limit in decreasing the particle diameter, and the shape of the particles is also varied, and uniformity is not well formed. Therefore, the chemical method is advantageous for controlling the shape and particle size of the particles.

The production method of metal nanoparticles by a chemical method is classified into a wet method and a dry method. As the dry method of the chemical method, a CVD (chemical vapor deposition) method, a gas evaporation method, a laser method, a sputtering method, a metal droplet atomization method, and the like are known, and the produced particles are spherical, While the properties are good, the distribution of the particle diameters is wide and the productivity is low. On the other hand, the wet process represented by the chemical reduction method has a higher productivity than the dry process and has an advantage in that the particle size can be easily controlled. Therefore, much research has been conducted with the recent development of nanotechnology.

However, studies on binary nanoparticles (metal composite nanoparticles), which are expected to exhibit additional physical properties as compared with single-metal nanoparticles, have been extensively studied. In addition, attention has been paid to the fact that, depending on the use of the nanoparticles, it is required to have specific properties as the surface layer metal of the particles, and the core and the shell are made of a binary metal as the binary metal.

As such metal nanoparticles having a core-shell structure, for example, there are a copper core and a metal nano-particle including a thin film layer of a metal such as silver, palladium, platinum, gold or the like surrounding the copper core and having a reduction potential higher than copper (Patent Document 1). The method for producing the metal nanoparticles comprises the steps of reacting a copper precursor comprising copper complexes such as copper nitrate, copper chloride and copper formate with tert-butylhydroxytoluene, ascorbic acid, flavonoid or the like in a solution containing primary amine as a reducing agent And forming a thin film of a metal having a reducing potential higher than copper on the surface of the copper nanoparticles. The metal nanoparticles having a core-shell structure thus obtained are coated with a noble metal by using copper particles as a core. Since the content of copper can be increased while preventing the oxidation of copper, the economical efficiency is excellent. Further, And has a merit of being able to form a wiring having an electric conductivity higher than that of copper because it contains a metal such as silver having excellent conductivity in the thin film layer.

Further, for example, a metal precursor containing nanoparticles of a first metal (for example, cobalt) and a second metal having a reduction potential higher than that of the first metal (for example, platinum) is dissolved in an appropriate organic solvent (Patent Document 2) discloses a method of preparing metal nanoparticles having a core-shell structure by a metal substitution reaction between a first metal and a second metal by mixing each of the formed solutions.

Patent Documents 1 and 2 realize metal nanoparticles having a core made of a metal having a low reduction potential and a shell made of a metal having a high reduction potential by a different technique. However, it is not certain whether the metal nanoparticles of the core-shell structure made of different dissimilar metals can be suitably obtained by using the production methods of Patent Documents 1 and 2. Particularly, it is hard to imagine that the same technique as in Patent Documents 1 and 2 can be applied to a dissimilar metal having a similar oxidation-reduction potential, for example, nickel and cobalt.

On the other hand, the present inventors have studied and reported on Cu-Ni alloys having copper as the core and nickel in the shell having a lower reduction potential than copper (Non-Patent Documents 1 and 2). According to Non-Patent Document 2 in which the examination of Non-Patent Document 1 is further carried out, the copper-nickel alloy is produced by mixing copper formate and nickel formate separately with oleylamine, and with respect to the mixed solution of copper formate, The mixture of nickel formate and nickel formate is heated at 393 K to form a precursor, which is mixed with 1-octanol, and then heated rapidly by microwave to obtain nanoparticles. (Cu ²⁺ 433 K, Ni ^{2 +} 463 K), copper nanoparticles are formed first, and copper nanoparticles are formed at nuclei due to the difference in redox potential between copper and nickel And a shell of nickel is formed on the surface. It was confirmed that the resulting nanoparticles had a high nickel concentration in the vicinity of the particle surface.

Japanese Patent Application Laid-Open No. 2007-224420 Japanese Patent Application Laid-Open No. 2003-055703

 Yamauchi Tomohisa, Tsukahara Yasunori, Wada Yasu, "Synthesis and Magnetic Properties of Cu-Ni Alloy Nanoparticles Using Microwave Heating", Bulletin of the 89th Spring Meeting of the Chemical Society of Japan (2009), 2D2-34  Yamauchi Tomohisa, Tsukahara Yasunori, Wada Yasu et al., "Synthesis and Magnetic Property of Cu core-Ni shell nanoparticles using microwaves", Proc. Of the 3rd Symposium of the Japan Society of Electromagnetic Energy and Applied Physics, P190, 2009 From 18th to 20th of month

The object of the present invention is to provide nickel-cobalt nanoparticles in which nickel is a core and cobalt is a shell layer, which can be suitably used for applications such as catalysts, magnetic materials and electrodes, and a method for producing the same.

The nickel-cobalt nanoparticles according to the present invention comprise a core consisting essentially of nickel and a shell consisting essentially of cobalt substantially covering the entire surface of the core.

The nickel-cobalt nanoparticles according to the present invention preferably have a nickel content within a range of 30 to 90 mass%, a cobalt content within a range of 10 to 70 mass%, an average particle size of 10 to 200 nm And the thickness of the shell is in the range of 1 to 50 nm.

The method for producing nickel-cobalt nanoparticles according to the present invention comprises the steps of: heating a mixture containing a nickel salt, a cobalt salt and a primary amine to obtain an complex reaction solution; and heating the complex reaction solution to prepare nickel- And a step of obtaining a nanoparticle slurry.

The method for producing nickel-cobalt nanoparticles according to the present invention comprises the steps of: heating a mixture containing nickel fine particles, a cobalt salt and a primary amine to obtain an complex reaction solution; and heating the complex reaction solution to prepare nickel- And a step of obtaining a nanoparticle slurry.

The method for producing nickel-cobalt nanoparticles according to the present invention includes the steps of: heating a mixture containing a cobalt salt and a primary amine to obtain an complex reaction solution; and adding nickel fine particles to the complex reaction solution, Thereby obtaining a nickel-cobalt nano-particle slurry.

The method for producing nickel-cobalt nanoparticles according to the present invention is characterized in that the nickel salt and the cobalt salt are preferably selected from the group consisting of a straight chain carboxylic acid group having 1 to 3 carbon atoms and a group represented by the following structural formula (1) It is characterized by having either one.

[Chemical Formula 1]

(Wherein the substituents Ra to Rc are groups selected from the group consisting of methyl, ethyl, phenyl and halogen), the substituents Ra to Rc may be the same or may be different from each other)

In the method for producing nickel-cobalt nanoparticles according to the present invention, preferably, the carboxylic acid group is a formic acid group or an acetic acid group, and the group represented by the structural formula (1) is acetylacetonato.

The method for producing nickel-cobalt nanoparticles according to the present invention preferably uses microwaves as the heating means in the step of obtaining the slurry of nickel-cobalt nano particles.

The nickel-cobalt nanoparticles according to the present invention are composed of a core of nickel and a shell of cobalt, and thus are suitable for use in, for example, catalysts, magnetic materials, electrodes and the like. Further, by adjusting the content of cobalt in accordance with these applications, the cost can be appropriately adjusted, and the performance of cobalt can be maximized in each of the above applications.

Further, according to the method for producing nickel-cobalt nanoparticles according to the present invention, the nickel-cobalt nanoparticles according to the present invention can be preferably obtained.

Fig. 1 is a diagram showing the structure of each nickel acetate complex. Fig. 2 (a) shows the two-coordinate coordinate system, Fig. 2 (b) shows the one-way coordinate system and Fig.
FIG. 2A is a transmission electron microscope (TEM) photograph of the nickel-cobalt nanoparticles obtained in Example 1. FIG.
FIG. 2B is a diagram showing an electron diffraction (ED) pattern from the TEM photographic region of FIG. 2A. FIG.
3 is a diagram showing a mapping image by STEM-EDS of the nickel-cobalt nanoparticles obtained in Example 1. Fig.
4 is a diagram showing the result of line analysis by STEM-EDS of the nickel-cobalt nanoparticles obtained in Example 1. Fig.
5 is a graph showing SQUID susceptibility measurement results of nickel-cobalt nanoparticles of Examples 1 and 2 and nickel particles of Comparative Example 8 and commercially available cobalt particles.
6 is a diagram showing a mapping image of the nickel-cobalt nanoparticles obtained in Example 2 by STEM-EDS.
7 is a diagram showing a mapping image of STEM-EDS of the nickel-cobalt nanoparticles obtained in Example 4. FIG.

Embodiments of the present invention will be described below.

[Nickel-Cobalt Nanoparticles]

The nickel-cobalt nanoparticles (hereinafter, simply referred to as " nanoparticles ") according to the present embodiment include a core substantially composed of nickel and a shell substantially consisting of cobalt substantially covering the entire surface of the core . Here, the nanoparticles do not exclude a form in which the core contains a small amount of cobalt and the shell contains a small amount of nickel. That is, the term " substantially nickel-made core " means that a small amount of cobalt contained in the core is allowed to exist in the core, but most of the core is made of nickel. The term " substantially consisting of cobalt " It means that a small amount of nickel is allowed to exist, but most of it is made of cobalt. Further, it is preferable that the shell of the nanoparticle covers the whole surface of the core, but the present invention is not limited to this, and it is not excluded that a form in which some nickel is exposed. In short, " substantially covering the entire surface of the core " means that the shell is discontinuously formed within a range that does not impair the effect of the present invention (function of the nanoparticle) as well as the shape in which the shell completely covers the core, , But most of the surface of the nickel-cobalt nanoparticles is made up of the shell. The nanoparticles may also have an inner shell between the shell and the nickel of cobalt.

The nanoparticles according to this embodiment have, for example, a nickel content of 30 to 90 mass% and a cobalt content of 10 to 70 mass%. The content of cobalt in the nanoparticles can be appropriately set in consideration of the characteristics required for the intended application, cost, etc. If the content of cobalt is less than 10% by mass, for example, the core may be exposed to a large extent from the shell, There is a possibility that the effect can not be sufficiently obtained. On the other hand, if it exceeds 70% by mass, the cost becomes high.

The average particle diameter of the nanoparticles is, for example, 10 to 200 nm, preferably 10 to 150 nm. If the average particle diameter of the nanoparticles is less than 10 nm, the nanoparticles may be agglomerated to deteriorate dispersibility and may be inadequate for paste materials such as catalysts and electrodes. On the other hand, when the average particle diameter of the nanoparticles exceeds 200 nm, the specific surface area becomes small, and for example, high catalyst performance may not be exhibited. The nanoparticles have a Cv value (coefficient of variation; It is preferable that the ratio? / D of the average particle diameter (d) to the standard deviation (?) Is 0.01?? / D? 0.5.

The thickness of the shell of the nanoparticles is, for example, 1 to 50 nm, preferably 5 to 20 nm. When the thickness of the shell layer of the nanoparticles is less than 1 nm, the amount of cobalt is too small, and the catalyst activity and magnetic properties inherently possessed by cobalt may not be sufficiently exhibited. On the other hand, if it exceeds 50 nm, the cost becomes high.

The shape of the nanoparticles may be, for example, a spherical shape, a spherical shape, a long spherical shape, a cube shape, a truncated pyramidal shape, a biconvex abstract, an octahedron shape, Shape, or the like. From the viewpoint of improving the filling density when nickel nanoparticles are used for electrodes of electronic components, for example, spherical or spherical shapes are preferable, and spherical shapes are more preferable. Here, the shape of the nanoparticles can be confirmed by observing with a scanning electron microscope (SEM).

The nanoparticles according to the present embodiment described above can adjust the content of cobalt depending on applications such as a catalyst, a magnetic material, an electrode, etc., so that the cost can be appropriately adjusted, and the performance of cobalt can be preferably obtained.

[Method for producing nickel-cobalt nanoparticles]

Next, a method for producing nickel-cobalt nanoparticles for obtaining nickel-cobalt nanoparticles is described. The first to third examples are given as the method for producing nickel-cobalt nanoparticles according to the present embodiment (hereinafter, simply referred to as "method for producing nanoparticles").

≪ Example 1 >

A first example of the method for producing nanoparticles comprises the steps of heating a mixture containing a nickel salt, a cobalt salt and a primary amine to obtain an complex reaction solution, and a step of heating the complex reaction solution to obtain a nickel-cobalt nano particle slurry Respectively.

<Example 2>

A second example of the method for producing nanoparticles comprises a step of heating a mixture containing nickel fine particles, a cobalt salt and a primary amine to obtain an complex reaction solution, and a step of heating the complex reaction solution to obtain a nickel-cobalt nanoparticle slurry Respectively. Namely, nickel fine particles are used instead of the nickel salt of the first example.

<Example 3>

A third example of the method for producing nanoparticles comprises the steps of: heating a mixture containing a cobalt salt and a primary amine to obtain an complex reaction solution; adding nickel fine particles to the complex reaction solution and then heating to form nickel-cobalt nanoparticles And a step of obtaining a slurry. That is, the nickel microparticles of the second example are added not in the course of the complex reaction, but in the process of producing the nickel-cobalt nano-particle slurry.

The second and third examples are all preferred embodiments. However, in the case of adding nickel fine particles, it is necessary to highly disperse the nickel fine particles in the complexing reaction solution, and if it is insufficient, uniform formation of the cobalt shell is not performed There is a fear of not being able to do. In this sense, the first example in which there is no need to perform highly dispersed processing is the most preferable method.

[Step of obtaining complex reaction solution]

In this step, a mixture containing a nickel salt, a cobalt salt and a primary amine is heated (first example), or a mixture containing nickel fine particles, a cobalt salt and a primary amine is heated (second example) A complex containing nickel and / or cobalt is produced by heating the mixture containing the cobalt salt and the primary amine (the third example) or obtaining the complexation reaction solution. Here, the complex reaction liquid refers to a reaction product (reaction product) produced by the reaction of a nickel salt and / or a cobalt salt with a primary amine. It is considered that the complex reaction solution contains a nickel complex and a cobalt complex in the first example, and a cobalt complex in the second example and the third example as the complex. The nickel ion and / or the cobalt ion of the nickel complex and / or the cobalt complex is reduced, and the carboxylic acid ions coordinated to the ion are simultaneously decomposed by heating the complex reaction solution, and ultimately the zero valent Ni and / or 0 Co of Co is generated, and nanoparticles of the core-shell structure are produced.

(Nickel salt, cobalt salt)

The nickel salt and the cobalt salt are not particularly limited, but preferably have either one or both of a straight chain carboxylic acid group having 1 to 3 carbon atoms or a group represented by the following structural formula (1). The group represented by the structural formula (1) below is a 1,3-diketonato group (? -Diketonato ligand). The nickel salt and the cobalt salt may be a homogeneous salt or a different kind of salt. The nickel salt and the cobalt salt may all be anhydrides or hydrates.

(2)

(Wherein the substituents Ra to Rc are groups selected from the group consisting of methyl, ethyl, phenyl and halogen), the substituents Ra to Rc may be the same or may be different from each other)

Specific examples of the nickel salt having a straight chain carboxylic acid group having 1 to 3 carbon atoms include nickel formate, nickel acetate or nickel propionate, and particularly nickel formate or nickel acetate is preferably used. The cobalt salt having a straight chain carboxylic acid group having 1 to 3 carbon atoms is specifically cobalt formate, cobalt acetate or cobalt propionate, and it is particularly preferable to use cobalt formate or cobalt acetate. These carboxylic acid nickel and carboxylic acid cobalt may be anhydrides or hydrates. (Cobalt chloride), nickel nitrate (cobalt nitrate), nickel sulfate (cobalt sulfate), nickel carbonate (cobalt carbonate), nickel hydroxide (cobalt hydroxide) and the like can be used in place of nickel carboxylate or cobalt carboxylate. (Or a nickel complex) or a cobalt ion (or a cobalt complex) after dissociation because the dissociation (decomposition) takes place at a high temperature in the case of an inorganic salt. It is not preferable because heating is required.

Examples of the group represented by the above structural formula (1) include 2,4-pentanedionato (acetylacetonato), 2,4-hexadionato, 3,5-heptadionato, 3-butanedionato, 1-chlor-1,3-butanedionato and the like, among which acetylacetonato is preferably used.

The amount of the nickel salt and the cobalt salt is preferably 30 to 90 parts by mass of nickel and 10 to 70 parts by mass of cobalt relative to 100 parts by mass of the total amount of nickel and cobalt in the complexing reaction solution, More preferably 50 to 80 parts by mass, and cobalt 20 to 50 parts by mass. When the amount of cobalt is less than 10 parts by mass based on 100 parts by mass of the total amount of nickel and cobalt in terms of the metal, There is a fear that the catalyst is largely exposed from the shell and the effect of the catalyst performance or the magnetic property is not sufficiently obtained. On the other hand, if it exceeds 70 parts by mass, the cost becomes high.

(Nickel fine particles)

The nickel fine particles used in the second and third examples of the method for producing nanoparticles do not limit the size of the particle size, but for example, those having a particle diameter of 5 to 200 nm are preferably used. When the particle diameter is less than 5 nm, coagulation is severe and there is a fear that the particles are not dispersed well in the liquid. On the other hand, if the particle size exceeds 200 nm, the specific surface area of the particles becomes too small, and there is a possibility that sufficient reaction is not achieved. The shape of the nickel fine particles is preferably spherical, spherical, or the like, but is most preferably spherical.

The amount of the nickel fine particles to be added is preferably 30 to 90 parts by mass, more preferably 50 to 80 parts by mass, in terms of the metal, based on 100 parts by mass of the total amount of nickel and cobalt in the complexing reaction liquid.

(Primary amine)

The primary amine can form a complex with a nickel ion or a cobalt ion, and can effectively exhibit a reducing ability to a nickel complex (or a nickel ion). On the other hand, since the secondary amine has a large steric hindrance, there is a fear that the formation of a nickel complex or a cobalt complex is not favorably formed, and the tertiary amine does not have a reducing ability of nickel ion or cobalt ion.

The primary amine is not particularly limited as long as it can form a complex with nickel ion or cobalt ion, and a solid or liquid at room temperature can be used. Here, the room temperature refers to 20 캜 15 캜. The primary amine, which is a liquid at room temperature, also functions as an organic solvent for forming a nickel complex or a cobalt complex. A primary amine which is solid at normal temperature is not particularly problematic as long as it is a liquid by heating at 100 DEG C or higher or is dissolved by using an organic solvent.

The primary amine also functions as a dispersant and can disperse the nickel complex or the cobalt complex well in the reaction solution. Therefore, after the complex is formed, the nickel complex or the cobalt complex is heated and decomposed to aggregate the particles when the nanoparticles are obtained Can be suppressed. The primary amine may be an aromatic primary amine, but an aliphatic primary amine is preferable from the viewpoint of ease of nickel complex formation and cobalt complex formation in the reaction solution. The aliphatic primary amine can control the particle diameter of the nanoparticles formed by, for example, adjusting the length of the carbon chain, and is particularly advantageous when nanoparticles having an average particle diameter of 10 to 200 nm are produced. From the viewpoint of controlling the particle diameter of the nanoparticles, the aliphatic primary amine is preferably selected from those having about 6 to 20 carbon atoms. The larger the carbon number, the smaller the particle size of the resulting nanoparticles. Examples of such amines include octylamine, trioctylamine, dioctylamine, hexadecylamine, dodecylamine, tetradecylamine, stearylamine, oleylamine, myristylamine and laurylamine have. For example, oleylamine is present in a liquid state under temperature conditions in the process of producing nanoparticles, so that the reaction in the homogeneous solution can be efficiently advanced.

Since the primary amine functions as a surface modifier when the nanoparticles are formed, the secondary aggregation can be suppressed even after the removal of the primary amine. The primary amine is also preferable from the viewpoint of easiness of treatment in the cleaning step of separating the solid component of the produced nanoparticles after the reduction reaction and the solvent or the unreacted primary amine. It is also preferable that the primary amine has a boiling point higher than the reduction temperature in view of ease of reaction control when reducing the nickel complex or the cobalt complex to obtain the nanoparticles. That is, the aliphatic primary amine preferably has a boiling point of 200 ° C or higher, and preferably has a carbon number of 9 or higher. Here, for example, the boiling point of C ₉ H ₂₁ N (nonylamine) of an aliphatic amine having 9 carbon atoms is 201 ° C. The amount of the primary amine is preferably 2 moles or more, more preferably 2.5 moles or more, and further preferably 4 moles or more, relative to the total amount of nickel and cobalt in terms of metals. The upper limit of the amount of the primary amine is not particularly limited, but it is preferably about 20 mol or less with respect to the total amount of 1 mol of nickel and cobalt in terms of the metal from the viewpoint of productivity.

The divalent nickel ion is known as a ligand-substituting active species, and the ligand of the complex to be formed is likely to be easily changed by ligand exchange depending on the temperature and the concentration. Considering the steric hindrance such as the carbon chain length of the amine used in the step of heating the mixture of the nickel carboxylate and the primary amine to obtain the reaction solution, for example, as shown in Fig. 1, There is a possibility that the complex acid ion (R ₁ COO, R ₂ COO) is coordinated in either the two-coordinate configuration (a) or the monoclinic configuration (b), and if the concentration of the amine is excessively excessive, There is a possibility of taking structure (c) in which ions exist. At least one of the ligands of A, B, C, D, E and F needs to have a primary amine coordination in order to obtain a homogeneous solution at the target reaction temperature (reduction temperature). In order to take such a state, it is necessary that the primary amine exists in excess in the reaction solution. It is preferably at least 2 mol, more preferably 2.5 mol or more, relative to 1 mol of the nickel ion, More preferably 4 mol or more.

It is considered that a complex is formed by taking similar behavior to nickel ions also for cobalt ions. For this reason, the primary amine needs to be present in an excessive amount relative to the cobalt ion, and it is preferably at least 2 mol or more, more preferably 2.5 mol or more, more preferably 4 mol or more Is more preferable.

The complexing reaction can proceed even at room temperature, but in order to reliably and more efficiently carry out the reaction, it is preferable to carry out heating at a temperature of 100 캜 or higher. This heating is particularly advantageous when a hydrate of nickel carboxylate or a hydrate of cobalt carboxylate such as nickel acetate tetrahydrate is used as a nickel salt or a cobalt salt. The heating temperature is preferably set to a temperature exceeding 100 ° C, and more preferably, to a temperature of 105 ° C or more, whereby coordination water (coordination water) coordinated with nickel carboxylate or cobalt carboxylate and primary amine The ligand substitution reaction of the complex ligand can be efficiently carried out and the water molecule as the complex ligand can be dissociated and the water can be discharged out of the system to efficiently form the complex. For example, nickel acetate tetrahydrate has two coordination numbers at room temperature, two acetic acid ions as two-coordinate ligands, and a complex structure in which two water molecules are present in the outer potion. Therefore, the two coordination numbers and the primary amine , It is preferable to dissociate the water molecule as the complex ligand by heating at a temperature higher than 100 ° C. The heating temperature is preferably 175 ° C or lower from the viewpoint of ensuring separation of the subsequent nickel complex (or nickel ion) and cobalt complex (or cobalt ion) from the heating and reduction process and completing the complexation reaction of the previous step desirable. Therefore, the heating at the time of complex formation is preferably carried out at, for example, 105 to 175 ° C. More preferably, the heating temperature is 125 to 160 ° C.

The heating time can be appropriately determined depending on the heating temperature and the content of each raw material, but is preferably 15 minutes or longer from the viewpoint of surely completing the complexing reaction. The upper limit of the heating time is not particularly limited, but heating for a long time is a waste in terms of saving energy consumption and processing time. The heating method is not particularly limited and may be heating by a heating medium such as an oil bath or heating by microwave irradiation.

The complex formation reaction can be confirmed by changing the color of the solution when a solution obtained by mixing a nickel salt and / or a cobalt salt with a primary amine is heated. The complex formation reaction can be carried out by measuring the wavelength at which the absorption spectrum observed in the wavelength range of 300 nm to 750 nm is maximized, for example, using an ultraviolet / visible absorption spectrum measuring apparatus, (For example, the maximum absorption wavelength in nickel acetate tetrahydrate is 710 nm).

After the nickel salt and / or the cobalt salt and the primary amine have been formed, the resulting reaction solution is heated by microwave irradiation or the like to form nickel ions and / or cobalt complexes of nickel complexes The cobalt ions of nickel and cobalt ions are reduced and carboxylic acid ions coordinated to nickel ions and cobalt ions are simultaneously decomposed to finally produce nanoparticles containing nickel and / or cobalt whose oxidation number is zero. In general, nickel carboxylate or cobalt carboxylate is poorly soluble under conditions other than the use of water as a solvent, and a solution containing nickel carboxylate or cobalt carboxylate as a preliminary step of a heating and reducing reaction by microwave irradiation It is necessary to prepare a homogeneous reaction solution. On the other hand, it is considered that the primary amine used in the present embodiment is a liquid at the use temperature condition and is liquefied by coordination with nickel ion or cobalt ion to form a uniform reaction solution.

(Organic solvent)

An organic solvent separate from the primary amine may be newly added in order to more efficiently proceed the reaction in the homogeneous solution. When an organic solvent is used, an organic solvent may be mixed with a nickel salt or a cobalt salt and a primary amine at the same time. However, when a nickel salt or a cobalt salt and a primary amine are mixed first, It is more preferable that the quaternary amine is efficiently coordinated to the nickel ion or the cobalt ion. The organic solvent that can be used is not particularly limited as long as it does not inhibit the formation of a primary amine and nickel ion or cobalt ion, and includes, for example, an ether organic solvent having 4 to 30 carbon atoms, an organic solvent having 7 to 30 carbon atoms Saturated or unsaturated hydrocarbon-based organic solvents, and alcohol-based organic solvents having 8 to 18 carbon atoms. The organic solvent to be used is preferably selected so as to have a boiling point of 170 캜 or higher, more preferably 200 캜 to 300 캜, from the viewpoint of being usable under heating conditions by microwave irradiation or the like It is good. Specific examples of such an organic solvent include, for example, tetraethylene glycol, n-octyl ether, and the like.

[Step of obtaining nickel-cobalt nanoparticle slurry]

In this step, by heating the complex reaction solution, the nickel complex and / or the cobalt complex (nickel ion and / or cobalt ion) is reduced with a metal to produce nanoparticles. For example, in the first example, when the mixture of the nickel complex and the cobalt complex is reduced and pyrolyzed, the nickel complex is pyrolyzed at a lower temperature than the cobalt complex and reduced by the amine, so that the nickel particles become the core, It is considered that a shell of cobalt is formed on the surface of the core. Typically, the cobalt complex is the ligand is dissociated by pyrolysis, the nanoparticles of Co (0 A) is formed from a complex of Co ^{+ 2.} On the other hand, in the present invention, the cobalt complex is reduced from Co ^{2 +} to Co (O) by using Ni as a catalyst in the presence of excess oleylamine, and is usually reduced at a lower temperature (the complex dissociates).

By heating the complex reaction solution, the complex reaction solution is reduced and the complex is pyrolyzed. The heating temperature is preferably 200 占 폚 or higher, more preferably 220 占 폚 or higher, from the viewpoint of efficiently carrying out the reduction reaction. It is preferably 270 DEG C or lower, more preferably 250 DEG C or lower from the viewpoint of efficiently carrying out the treatment. For example, in the case of using nickel as an example, in order to produce nanoparticles having a uniform particle size, it is necessary to uniformly and sufficiently produce a nickel complex in the step of obtaining an complex reaction solution, and to heat the complex reaction solution to nickel- It is necessary to co-generate and grow nuclei of Ni (0 a) produced by the reduction of nickel ions in the step of obtaining the nanoparticle slurry. That is, by adjusting the heating temperature in the step of obtaining the complex reaction solution within the above-mentioned specific range to be certainly lower than the heating temperature in the step of obtaining the nickel-cobalt nano-particle slurry, particles with uniform particle size and shape are produced easy. For example, if the heating temperature is excessively high in the step of obtaining the complex reaction solution, formation of a nickel complex and a reduction reaction to Ni (O) are simultaneously progressed to produce particles having a uniform particle shape in the step of obtaining a nickel- This may cause difficulties. If the heating temperature in the step of obtaining the nickel-cobalt nanoparticle slurry is too low, the rate of reduction reaction to Ni (O) is slowed and the generation of nuclei is reduced, so that not only is the particle size increased but also in terms of the yield of nanoparticles not.

In this step, the heating source may be an oil bath or the like, but it is preferably a microwave. When the microwave is irradiated to the complex reaction solution, the microwave penetrates into the complex reaction solution, and rapid heating and uniform heating are performed by internal heating. As a result, the entire complex reaction solution can be made uniform at a desired temperature, and the reduction, nucleation, and nucleation of the nickel or cobalt particles can be simultaneously generated in the entire solution. As a result, Can be easily produced in a short time. The wavelength of use of the microwave is not particularly limited and is, for example, 2.45 GHz.

The nanoparticle slurry obtained by heating the complex reaction solution is removed by, for example, standing still, removing the supernatant, washing with an appropriate solvent, and drying the nanoparticle slurry to obtain nanoparticles.

In the step of obtaining the nickel-cobalt nano-particle slurry, the above-mentioned organic solvent may be added to the complexing reaction liquid, if necessary. As described above, it is a preferred embodiment of the present invention that the primary amine used in the polymerization reaction is used as an organic solvent. The solvent to be added in the step of heating the complex reaction solution is not particularly limited, and for example, alcohol such as octanol (octyl alcohol), a nonpolar solvent and the like can be used. As described above, when oleylamine is used as the primary amine, the solvent may be omitted.

The nanoparticle production method of the present embodiment may include an optional step in addition to the above-described steps. In addition, any treatment such as addition of a surface modifier as described later can be performed, for example. In addition, the method of producing nanoparticles of the present embodiment does not require the use of a strong reducing agent because it employs a reducing method by heating with microwave or the like in the step of obtaining the nickel-cobalt nanoparticle slurry. However, a substance having a reducing action may be present in the complexing reaction liquid within the range not hindering the effect of the invention.

(Addition of surface modifier)

In the method for producing nanoparticles according to the present embodiment, as the surface modifier for controlling the particle diameter of the nanoparticles, for example, a polymer resin such as polyvinylpyrrolidone (PVP), polyethyleneimine, polyacrylamide, And long-chain carboxylic acids or carboxylates such as lauric acid and oleic acid. However, if the amount of the surface water of the obtained nanoparticles is large, there is a fear that adverse effects may be given as impurities depending on the application. Therefore, the amount of surface water after cleaning the obtained nanoparticles is preferably as small as possible. For example, in the case of use in a conductive paste for a nickel electrode, if the nickel particles are pasted and fired at a high temperature, the filling density is decreased, and there is a possibility of delamination and cracking. Therefore, the addition amount of the surface modifier is preferably in the range of 0.1 to 100 parts by mass with respect to 100 parts by mass of the total amount of the nickel elements. The surface modifier may be added at the stage of the mixture of nickel carboxylate and primary amine in the complexation reaction liquid forming step or may be added to the complexing reaction solution obtained in the complexation reaction liquid forming step, May be after the complexing reaction or after the formation of the nickel nanoparticles.

According to the method for producing nickel-cobalt nanoparticles according to the embodiment described above, the average particle diameter is 10 to 200 nm and the Cv value (coefficient of variation; It is possible to obtain nickel-cobalt nanoparticles composed of a core of nickel and a shell of cobalt having a narrow particle size distribution such that a ratio σ / d of an average particle diameter (d) and a standard deviation (σ) is 0.01 ≦ σ / d ≦ 0.5 .

Example

EXAMPLES The present invention will be further described by way of examples and comparative examples, but the present invention is not limited to the examples described below.

The particle size of the nanoparticles was determined by taking a photograph of the nanoparticle powder by a transmission electron microscope (TEM), randomly extracting 200 pieces of the nanoparticle powder, and calculating the average particle size and standard deviation thereof. From this result, a Cv value (= sigma / d) was obtained. Also, presence or individual concentrations of nickel and cobalt in the obtained particles were confirmed by surface analysis and line analysis by a scanning transmission electron microscope (STEM-EDS) equipped with an energy dispersive X-ray analyzer. The thickness of the cobalt shell layer was calculated by STEM-EDS for nickel and cobalt atom concentrations on the line traversing one particle, as shown in Fig. In this line analysis method, the atomic concentration of only the core portion of the generated spherical particles can not be calculated. That is, in the analysis near the particle surface, the concentration of the surface of the particle is simply shown, but the result of the analysis near the center of the particle is that the concentration of the metal element in the particle surface and the inner (core) are added together. Therefore, in the result of this analysis, the average value of the thickness of the layer in which the strength of cobalt is higher than that of nickel is defined as the thickness of the cobalt shell layer. The composition of the obtained particles was analyzed by ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry).

(Example 1)

12.5 mmol of cobalt formate dihydrate and 12.5 mmol of nickel acetate tetrahydrate were added 275 mmol of oleylamine and heated at 120 캜 for 20 minutes under a nitrogen flow to obtain a complex reaction solution. Subsequently, the complex reaction solution was heated to 225 DEG C using microwave, and the temperature was maintained for 30 minutes to obtain a nanoparticle slurry. The nanoparticle slurry was separated by cessation, and the supernatant was removed, followed by washing three times with hexane. Thereafter, it was dried in a vacuum dryer maintained at 60 캜 for 6 hours to obtain nanoparticles.

A TEM (transmission electron microscope) photograph of the obtained nanoparticles is shown in Fig. 2A, and an ED (electron diffraction) pattern is shown in Fig. 2B. Spherical uniform particles having an average particle size of 82 nm were formed. It can also be seen from the ED pattern that the nanoparticles are metals of the fcc structure which do not contain oxides. The metal composition of the particles obtained by ICP-AES was 47.6% by mass and 47.3% by mass, respectively. As a result, the molar ratio was Ni / Co = 1.0 and the ratio of raw materials (Mol%)). A photograph of the STEM-EDS mapping image is also shown in Fig. It can be seen that the distribution of nickel is a nanoparticle having a Ni (core) -Co (shell) structure at the center of the nanoparticles and a large distribution of cobalt on the surface of the nanoparticles.

From the line analysis results of the particles shown in Fig. 4, it can be seen that the thickness of the cobalt shell layer (shell) is approximately 13 nm. The results of saturation magnetization (unit: emu / g) obtained by SQUID susceptibility measurement are shown in Fig. Compared with the commercially available cobalt nanoparticles (particle diameter 50 nm or less, manufactured by Aldrich), the saturation magnetization is low, but the saturation magnetization is remarkably increased as compared with the nanoparticles of Comparative Example 8 described later.

(Examples 2 to 7 and Comparative Examples 1 to 8)

Examples 2 to 7 and Comparative Examples 1 to 8 were prepared in the same manner as in Example 1 except that the kind of the nickel salt and the cobalt salt and the type of the heating source in the step of obtaining the nanoparticle slurry and the reaction temperature Nanoparticles were prepared. The results are shown in Table 1 together with Example 1. In each of Examples and Comparative Examples, molar ratios of oleylamine / (Ni salt + Co salt) were all 10. The heating method of the complex reaction solution was all microwave heating except for Example 3 using an oil bath.

The SQUID susceptibility measurement results of the nickel-cobalt nanoparticles of Examples 1 and 2, the nickel particles of Comparative Example 8, and the commercially available cobalt particles are shown in FIG. 5, and the TEM pictures of the nickel-cobalt nano particles obtained in Example 2 6, TEM photographs of the nickel-cobalt nanoparticles obtained in Example 4 are shown in Fig. 7, respectively.

From Table 1, it was confirmed that nickel-cobalt nanoparticles having an average particle diameter of 10 to 200 nm and a cobalt shell layer of 1 to 50 nm were obtained by using formic acid, acetic acid salt or acetylacetone salt as the nickel salt and the cobalt salt. It is also confirmed from Fig. 5 that the nickel-cobalt nanoparticles of Examples 1 and 2 are similar to the saturation magnetization of cobalt.

(Example 8)

12.5 mmol of cobalt formate dihydrate and 25 mmol of nickel particles having an average particle size of 100 nm and a Cv value of 0.14 (a complex reaction was obtained from nickel acetate tetrahydrate in the same manner as in Example 1, without using a cobalt salt, One particle: Comparative Example 8), 125 mmol of oleylamine was added, and the mixture was heated under a nitrogen flow at 120 占 폚 for 20 minutes to obtain a complex reaction solution. Then, the complex reaction solution was heated to 225 DEG C using microwave, and the temperature was maintained for 30 minutes to obtain a nickel-cobalt nanoparticle slurry.

The nickel-cobalt nanoparticle slurry was allowed to stand, the supernatant was removed, and the mixture was washed three times with hexane. Thereafter, it was dried in a vacuum dryer maintained at 60 캜 for 6 hours to obtain nickel-cobalt nanoparticles. The average particle diameter of the obtained nickel-cobalt nanoparticles was 120 nm, the Cv value of the particle size distribution was 0.15, and the thickness of the cobalt shell layer was 17 nm.

(Example 9)

125 mmol of oleylamine was added to 12.5 mmol of cobalt formate dihydrate and heated at 120 캜 for 20 minutes under a nitrogen flow to obtain a complex reaction solution. Subsequently, 25 mmol of nickel particles having an average particle size of 100 nm and a Cv value of 0.14 (particles obtained by heating the mixture to an ignition reaction from nickel acetate tetrahydrate without using a cobalt salt, Comparative Example 8 ) Was added and stirred well. The mixture was heated to 225 ° C using microwave, and the temperature was maintained for 30 minutes to obtain a nickel-cobalt nanoparticle slurry.

The nickel-cobalt nanoparticle slurry was allowed to stand, the supernatant was removed, and the mixture was washed three times with hexane. Thereafter, it was dried in a vacuum dryer maintained at 60 캜 for 6 hours to obtain nickel-cobalt nanoparticles. The average particle diameter of the obtained nickel-cobalt nanoparticles was 117 nm, the Cv value of the particle size distribution was 0.15, and the thickness of the cobalt shell layer was 15 nm.

Although the embodiments of the present invention have been described in detail for the purpose of illustration, the present invention is not limited to the above embodiments. This international application claims priority based on Japanese Patent Application No. 2010-60773 filed on March 17, 2010, the entire contents of which are incorporated herein by reference.

Claims (9)

delete delete A step of heating a mixture containing a nickel salt, a cobalt salt and a primary amine to obtain an complex reaction solution,
And a step of heating the complex reaction solution to obtain a slurry of nickel-cobalt nanoparticles,
Wherein the average particle diameter of the nickel-cobalt nanoparticles is 10 nm or more and 200 nm or less, nickel in the nickel-cobalt nanoparticles forms a core, cobalt is a shell, and the thickness of the shell is 1 nm or more and 50 nm or less. Method for preparing cobalt nanoparticles. A step of heating a mixture containing nickel fine particles, cobalt salt and primary amine to obtain an complex reaction solution;
And a step of heating the complex reaction solution to obtain a slurry of nickel-cobalt nanoparticles,
Wherein the average particle diameter of the nickel-cobalt nanoparticles is 10 nm or more and 200 nm or less, nickel in the nickel-cobalt nanoparticles forms a core, cobalt is a shell, and the thickness of the shell is 1 nm or more and 50 nm or less. Method for preparing cobalt nanoparticles. A step of heating a mixture containing a cobalt salt and a primary amine to obtain an complex reaction solution;
And a step of adding nickel fine particles to the complexing reaction solution and then heating to obtain a nickel-cobalt nano-particle slurry,
Wherein the average particle diameter of the nickel-cobalt nanoparticles is 10 nm or more and 200 nm or less, nickel in the nickel-cobalt nanoparticles forms a core, cobalt is a shell, and the thickness of the shell is 1 nm or more and 50 nm or less. Method for preparing cobalt nanoparticles. The method of claim 3,
Wherein the nickel salt has either one of a straight chain carboxylic acid group having 1 to 3 carbon atoms and a group represented by the following structural formula (1).
[Chemical Formula 1]

(Wherein the substituents Ra to Rc are groups selected from the group consisting of methyl, ethyl, phenyl and halogen), the substituents Ra to Rc may be the same or may be different from each other) 6. The method according to any one of claims 3 to 5,
Wherein the cobalt salt has either one of a straight chain carboxylic acid group having 1 to 3 carbon atoms and a group represented by the following structural formula (1).
(2)

(Wherein the substituents Ra to Rc are groups selected from the group consisting of methyl, ethyl, phenyl and halogen), the substituents Ra to Rc may be the same or may be different from each other) The method according to claim 6,
Wherein the linear carboxylic acid group having 1 to 3 carbon atoms is a formic acid group or an acetic acid group and the group represented by the structural formula (1) is acetylacetonato. 6. The method according to any one of claims 3 to 5,
Wherein the nickel-cobalt nanoparticle slurry is obtained by using a microwave as a heating means.

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