KR20130056852A - Nickel-cobalt nanoparticle and manufacturing method therefor - Google Patents

Abstract

The nickel-cobalt nanoparticles include a core substantially made of nickel and a shell made of substantially cobalt substantially covering the entire surface of the core. The method for producing nickel-cobalt nanoparticles is a step of heating a mixture containing nickel salts or nickel fine particles, cobalt salts, and primary amines to obtain a reaction solution, or by heating a mixture of cobalt salts and primary amines. And a step of heating the reaction solution to obtain a nickel-cobalt nanoparticle slurry.

Description

Nickel-Cobalt Nanoparticles and Manufacturing Method Thereof {NICKEL-COBALT NANOPARTICLE AND MANUFACTURING METHOD THEREFOR}

The present invention relates to nanoparticles having a core-shell structure composed of dissimilar metals.

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, so that they are suitable for various catalysts, magnetic materials, electrodes in fuel cells, multilayer ceramic capacitors, and the like. It is expected to use. However, since cobalt is a rare metal and considerably more expensive than nickel particles, it is desired to develop cobalt particles and a method of manufacturing the same, which can draw cobalt performance in a smaller amount. In order to derive the performance of cobalt well, its particle size or shape should be controlled to be uniform.

In general, methods for producing metal nanoparticles are broadly classified into physical methods and chemical methods. A physics method is a method (pulverization method) which grinds a bulk metal and manufactures nanoparticles, and a chemical method is a method (generation method) which produces | generates a metal atom and controls the aggregation. In the pulverization by the physics method, there is a limit in reducing the particle size, and the shape of the particles is also different, so that uniform ones are hardly formed. For this reason, the chemical method is advantageous for controlling the shape and particle diameter of the particles.

In addition, the manufacturing method of a metal nanoparticle by the chemical method is classified into a wet method and a dry method. In the dry method of the chemical method, CVD (chemical vapor growth) method, gas evaporation method, laser method, sputtering method, metal droplet spraying method, and the like are known, and the particles produced are spherical because of high temperature treatment, and crystals While the property is good, the particle size is wide and the productivity is low. On the other hand, in the wet method represented by the chemical reduction method, since the productivity is higher than the dry method and there is an advantage that it is easy to control a particle diameter, much research is performed with the development of the recent nanotechnology.

By the way, the examination of the binary type nanoparticle (metal composite nanoparticle) which is expected to express further physical property compared with a single metal nanoparticle is progressing widely. In addition, considering that it is required to have specific properties as the surface layer metal of the particles depending on the use of the nanoparticles, the formation of the core and the shell with heterogeneous metals as binary nanoparticles has also been studied.

As a metal nanoparticle having such a core-shell structure, for example, a metal nano containing a copper core and a thin film layer of metals such as silver, palladium, platinum, and gold which surrounds the copper core and has a higher reduction potential than copper. Particles are disclosed (Patent Document 1). This metal nanoparticle manufacturing method is a copper precursor which consists of copper complexes, such as copper nitrate, copper chloride, and copper formate, using tert- butylhydroxytoluene, ascorbic acid, a flavonoid, etc. as a reducing agent in the solution containing a primary amine. And forming a thin film layer of a metal having a higher reduction potential than copper on the surface of the copper nanoparticles. Since the metal nanoparticle which has the core-shell structure obtained makes copper particle into a core and coat | covers this with a noble metal, since the content rate of copper can be made high, preventing the oxidation of copper, it is excellent in economics, and is more electric than copper. Since the thin film layer contains a metal such as silver having excellent conductivity, it is said to have an advantage that a wiring having better electrical conductivity than copper can be formed.

Further, for example, a metal precursor containing a first metal (for example cobalt), which is a nanoparticle, and a second metal (for example, platinum) having a higher reduction potential than the first metal, may be dissolved in a suitable organic solvent, respectively. The method of manufacturing the metal nanoparticle of a core-shell structure by the metal substitution reaction between a 1st metal and a 2nd metal by mixing each formed solution is disclosed (patent document 2).

Patent Literatures 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 different techniques. However, it is not certain whether the metal nanoparticles of the core-shell structure which consist of another dissimilar metal can be suitably obtained using the manufacturing method of patent document 1, 2. In particular, it is hard to think that the same method as Patent Documents 1 and 2 can be applied to dissimilar metals having similar redox potentials, such as nickel and cobalt, for example.

On the other hand, the present inventors studied and reported about Cu-Ni alloy which has copper as a core and nickel which has a reduction potential lower than copper in a shell (nonpatent literature 1, 2). According to the nonpatent literature 2 which further advanced the examination of nonpatent literature 1, the manufacturing method of a Cu-Ni alloy mixes copper formate and nickel formate separately with oleylamine separately, and it is room temperature with respect to the liquid mixture of copper formate, About the mixed liquid of nickel formate, it forms a complex by heating at 393K, prepares a precursor, mixes with 1-octanol, and then rapidly heats with a microwave and obtains a nanoparticle. Since reduction and particle formation occur at different temperatures from the difference in the redox potential of copper and nickel (Cu ²⁺ 433 K, Ni ^{2 +} 463 K), copper nanoparticles are first produced, and the copper nanoparticles are nucleated as the temperature is raised. It is considered that the shell of nickel is formed on the surface thereof. It was confirmed that the obtained nanoparticles have a high nickel concentration in the vicinity of the particle surface.

Japanese Unexamined Patent Publication No. 2007-224420 Japanese Unexamined Patent Publication No. 2003-055703

 Tomohiyama Yamachi, Yasunori Tsukahara, Yuji Wada, `` Synthesis and Magnetic Properties of Cu-Ni Alloy Nanoparticles Using Microwave Heating '', Japan Chemical Society 89th Spring Banquet (2009) Preview, 2D2-34  Yamauchi Tomohisa, Yasunori Tsukahara, Yuji Wada, et al., `` Synthesis and Magnetic Properties of Cu Core-Ni Shell Nanoparticles Using Microwaves, '' 3rd Symposium of Japan Electromagnetic Engineering Society Symposium, P190, 2009. 18-20 days per month

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

The nickel-cobalt nanoparticle which concerns on this invention is equipped with the core which consists of nickel substantially, and the shell which consists of cobalt substantially covering the whole surface of the core.

Moreover, the nickel-cobalt nanoparticle which concerns on this invention becomes like this. Preferably nickel content exists in the range of 30-90 mass%, cobalt content exists in the range of 10-70 mass%, and the average particle diameter is 10-200 nm. It is in the range, It is characterized in that the thickness of the said shell exists in the range of 1-50 nm.

Moreover, the manufacturing method of the nickel-cobalt nanoparticle which concerns on this invention is a process of heating a mixture containing nickel salt, cobalt salt, and a primary amine, and obtaining a complexing reaction liquid, and heating the said complexing reaction liquid, and nickel-cobalt It is equipped with the process of obtaining a nanoparticle slurry.

Moreover, the manufacturing method of the nickel-cobalt nanoparticle which concerns on this invention is a process of heating a mixture containing nickel microparticles | fine-particles, cobalt salt, and a primary amine, and obtaining a complexing reaction liquid, and heating the said complexing reaction liquid, and nickel-cobalt It is equipped with the process of obtaining a nanoparticle slurry.

Moreover, the manufacturing method of the nickel-cobalt nanoparticle which concerns on this invention heats the process containing a cobalt salt and a primary amine to obtain a complexing reaction liquid, and after adding nickel fine particles to the said complexing reaction liquid, it heats, To obtain a nickel-cobalt nanoparticle slurry.

Moreover, in the manufacturing method of the nickel-cobalt nanoparticle which concerns on this invention, Preferably, the said nickel salt and the cobalt salt are respectively represented by the linear carboxylic acid group of 1-3 carbon atoms, and group represented by following structural formula (1). It is characterized by having either one.

[Formula 1]

(Here, 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 different from each other.)

Moreover, in the manufacturing method of the nickel-cobalt nanoparticle which concerns on this invention, Preferably, the said carboxylic acid group is a formic acid group or an acetic acid group, and group represented by the said structural formula (1) is acetylacetonato.

In the method for producing nickel-cobalt nanoparticles according to the present invention, microwaves are preferably used as a heating means in the step of obtaining the slurry of nickel-cobalt nanoparticles.

Since the nickel-cobalt nanoparticles related to the present invention are composed of a core of nickel and a shell of cobalt, the nickel-cobalt nanoparticles are suitable for use in, for example, a catalyst, a magnetic material, an electrode and the like. Moreover, by adjusting cobalt content according to these uses, cost can be made moderate and the performance of cobalt can be pulled out to the maximum in each said use.

Moreover, according to the manufacturing method of the nickel-cobalt nanoparticle which concerns on this invention, the nickel-cobalt nanoparticle which concerns on this invention can be obtained preferably.

FIG. 1: is a figure which shows the structure of each nickel acetate complex, (a) is a bidentate coordination, (b) is a single seat coordination, (c) shows the state which the carboxylic acid ion coordinated in the outer region, respectively.
FIG. 2A is a transmission electron microscope (TEM) photograph of 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.
It is a figure which shows the mapping image by STEM-EDS of the nickel- cobalt nanoparticle obtained in Example 1. FIG.
4 is a diagram showing a line analysis result by STEM-EDS of the nickel-cobalt nanoparticles obtained in Example 1. FIG.
FIG. 5: is a figure which shows the SQUID susceptibility measurement result of the nickel-cobalt nanoparticles of Examples 1 and 2, the nickel particle of the comparative example 8, and commercially available cobalt particle.
FIG. 6: is a figure which shows the mapping image by STEM-EDS of the nickel- cobalt nanoparticle obtained in Example 2. FIG.
FIG. 7: is a figure which shows the mapping image by STEM-EDS of the nickel-cobalt nanoparticle obtained in Example 4. FIG.

Embodiments of the present invention will be described below.

[Nickel-Cobalt Nanoparticles]

The nickel-cobalt nanoparticles (hereinafter sometimes referred to simply as "nanoparticles") according to the present embodiment include a core made of nickel and a shell made of substantially cobalt substantially covering the entire surface of the core. Include. Here, the nanoparticles do not exclude the form in which the core contains a small amount of cobalt and the shell contains a small amount of nickel. In other words, the term "substantially made of nickel" allows the presence of a small amount of cobalt inevitably contained in the core, but most means made of nickel, and "substantially made of cobalt" means inevitable in the shell. Although small amounts of nickel are allowed to be present, it is mostly made of cobalt. In addition, it is preferable that the shell of a nanoparticle covers the whole surface of a core, It is not limited to this, The form in which some nickel is exposed is not excluded. In short, the term "substantially covering the entire surface of the core" means not only the form in which the shell completely covers the core, but also the shell is discontinuously formed in a range that does not impair the effect (function of the nanoparticles) of the present invention, and partially. Although the core allows the exposed form, most of the surface of the nickel-cobalt nanoparticles is made of a shell. Moreover, the structure which has an inner shell between a cobalt shell and nickel may be sufficient as a nanoparticle.

The nanoparticle which concerns on this embodiment is 30-90 mass% of nickel content, and 10-70 mass% of cobalt content, for example. The cobalt content of the nanoparticles can be appropriately set in consideration of the characteristics required for the application, the cost, and the like. However, when the cobalt content of the nanoparticles is less than 10% by mass, the core is largely exposed from the shell, and thus the catalyst performance and magnetic properties There exists a possibility that an effect may not be fully acquired, and when it exceeds 70 mass%, cost will become high.

The average particle diameter of a nanoparticle is 10-200 nm, for example, Preferably it is 10-150 nm. If the average particle diameter of the nanoparticles is less than 10 nm, aggregation may be severe and dispersibility may deteriorate, and for example, the average particle diameter may be unsuitable for paste materials such as catalysts and electrodes. On the other hand, when the average particle diameter of a nanoparticle exceeds 200 nm, a specific surface area becomes small and there exists a possibility that high catalyst performance may not be exhibited, for example. In addition, the nanoparticles have a Cv value [coefficient of variation; It is preferable that the ratio (sigma / d) of the average particle diameter (d) and the standard deviation (σ) is 0.01 ≦ σ / 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 there is a possibility that the catalytic activity and magnetic properties originally possessed by cobalt cannot be sufficiently exhibited. On the other hand, when it exceeds 50 nm, cost will become high.

The shape of the nanoparticles is, for example, spherical, spherical, elongated, cuboid, truncated tetrahedral, biangular abstract, octahedral, octahedral, and icosahedral. Although various shapes, such as a body shape, may be sufficient, spherical shape or spherical shape is preferable, and spherical shape is more preferable from a viewpoint of the improvement of the packing density, for example when nickel nanoparticles are used for the electrode of an electronic component. Here, the shape of a nanoparticle can be confirmed by observing with a scanning electron microscope (SEM).

The nanoparticle which concerns on this embodiment demonstrated above can adjust cobalt content according to the use of a catalyst, a magnetic material, an electrode, etc., and can moderate cost, and can also derive the performance of cobalt suitably.

[Method for Producing Nickel-Cobalt Nanoparticles]

Next, the manufacturing method of nickel-cobalt nanoparticles for obtaining a nickel-cobalt nanoparticle preferably is demonstrated. As a manufacturing method of the nickel-cobalt nanoparticle which concerns on this embodiment (hereinafter, it may only be called "the manufacturing method of a nanoparticle"), a 1st example-a 3rd example are mentioned.

<1st example>

The first example of the method for producing nanoparticles is a step of heating a mixture containing nickel salt, cobalt salt, and a primary amine to obtain a complex reaction solution, and a step of heating a complex reaction solution to obtain a nickel-cobalt nanoparticle slurry. Has

<2nd example>

The second example of the method for producing nanoparticles is a step of heating a mixture containing nickel fine particles, cobalt salt and a primary amine to obtain a complex reaction solution, and a process of heating a complex reaction solution to obtain a nickel-cobalt nanoparticle slurry. Has That is, nickel fine particles are used instead of the nickel salt of the first example.

<Third example>

A third example of the method for producing nanoparticles is a step of heating a mixture containing cobalt salt and a primary amine to obtain a complex reaction solution, and adding nickel fine particles to the complex reaction solution, followed by heating to form nickel-cobalt nanoparticles. It has a process of obtaining a slurry. That is, the nickel fine particles of the second example are added in the process of producing the nickel-cobalt nanoparticle slurry, not in the complexing reaction liquid generation process.

Although the 2nd example and the 3rd example are both preferred embodiments, when adding nickel microparticles | fine-particles, it is necessary to disperse | distribute nickel microparticles | fine-particles in a complexing reaction liquid, and when it is inadequate, it will not perform uniform formation of a cobalt shell. There is a risk of not. In that sense, the first example, which does not need to be highly dispersed, is the most preferred method.

[Step of Obtaining Complexation Reaction Liquid]

In this step, the mixture containing nickel salt, cobalt salt and primary amine is heated (first example), the mixture containing nickel fine particles, cobalt salt and primary amine is heated (second example), or By heating (third example) the mixture containing cobalt salt and primary amine, a complex of nickel and / or cobalt is produced to obtain a complex reaction solution. Here, a complexing reaction liquid means the reaction production liquid (reaction product) produced | generated by reaction of a nickel salt and / or cobalt salt, and a primary amine. The complexing reaction liquid is considered to contain a nickel complex and a cobalt complex in the first example and a cobalt complex in the second and third examples as the complex. By heating the complexing reaction liquid, the nickel ions and / or cobalt ions of the nickel complex and / or cobalt complex are reduced, and the carboxylic acid ions coordinated to the ions are simultaneously decomposed, and finally zero valent Ni and / or zero False Co is produced, producing nanoparticles of core-shell structure.

(Nickel salt, cobalt salt)

Although both nickel salt and cobalt salt do not specifically limit, It is preferable to have either one or both of the C1-C3 linear carboxylic acid group or group represented by following structural formula (1). The group represented by the following structural formula (1) is a 1,3-diketonato group (β-diketonato ligand). The nickel salt and the cobalt salt may be the same kind of salts or different kinds of salts. In addition, an anhydride may be sufficient as a nickel salt and cobalt salt, and a hydrate may be sufficient as it.

[Formula 2]

(Here, 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 different from each other.)

Specifically, the nickel salt which has a C1-C3 linear carboxylic acid group is nickel formate, nickel acetate, or nickel propionate, It is preferable to use nickel formate or nickel acetate especially. In addition, the cobalt salt which has a C1-C3 linear carboxylic acid group is specifically cobalt formate, cobalt acetate, or cobalt propionate, It is preferable to use cobalt formate or cobalt acetate especially. Anhydrous may be sufficient as these nickel carboxylate and carboxylate cobalt, and a hydrate may be sufficient as it. Instead of nickel carbonate or cobalt carbonate, nickel chloride (cobalt chloride), nickel nitrate (cobalt nitrate), nickel sulfate (cobalt sulfate), nickel carbonate (cobalt carbonate), nickel hydroxide (cobalt hydroxide) It is conceivable to use inorganic salts, but in the case of inorganic salts, since dissociation (decomposition) takes place at a high temperature, an additional high temperature in the process of reducing nickel ions (or nickel complexes) or cobalt ions (or cobalt complexes) after dissociation is achieved. It is not desirable because it requires heating at.

Examples of the group represented by the structural formula (1) include 2,4-pentanedioato (alias: acetylacetonato), 2,4-hexadioato, 3,5-heptadioato, 1-phenyl-1, Although 3-butanedionato, 1-chlor-1,3-butanedionato, etc. are mentioned, It is preferable to use acetylacetonato among these.

It is preferable that the compounding quantity of a nickel salt and a cobalt salt shall be 30-90 mass parts of nickel and 10-70 mass parts of cobalt with respect to 100 mass parts of total amounts of nickel and cobalt in a complex reaction liquid, for example in metal conversion, and nickel It is more preferable to set it as 50-80 mass parts and 20-50 mass parts of cobalt. Although the compounding quantity of cobalt can be set suitably in consideration of the characteristic, cost, etc. which are calculated | required in the use of a nanoparticle, when a metal is less than 10 mass parts with respect to 100 mass parts of total amounts of nickel and cobalt, a core will be, for example. There is a possibility that it is greatly exposed from the shell and the effect of the catalytic performance and the magnetic properties may not be sufficiently obtained. On the other hand, if it exceeds 70 parts by mass, the cost is high.

(Nickel fine particles)

Although the nickel microparticles | fine-particles used by the 2nd example and the 3rd example of the manufacturing method of a nanoparticle do not limit the magnitude | size of a particle size, it is preferable to use the thing of 5-200 nm particle diameter, for example. When the particle diameter is less than 5 nm, aggregation is severe and there is a possibility that the particle size may not be dispersed well in the liquid. On the other hand, when the particle diameter exceeds 200 nm, the specific surface area of the particles is too small, and there is a fear that sufficient reaction may not be achieved. In addition, although the shape of nickel fine particles is preferable, for example, spherical shape, pseudo sphere shape, etc., spherical shape is most preferable.

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

(Primary amine)

The primary amine can form a complex with nickel ions or cobalt ions, and exhibits a reducing ability to nickel complexes (or nickel ions) effectively. On the other hand, since secondary amines have large steric hindrances, there is a risk of inhibiting favorable formation of nickel complexes and cobalt complexes, and since tertiary amines do not have reduction ability of nickel ions and cobalt ions, they cannot be used.

The primary amine is not particularly limited as long as it can form a complex with nickel ions or cobalt ions, and a solid or liquid can be used at room temperature. Here, normal temperature means 20 degreeC +/- 15 degreeC. The primary amine, which is liquid at normal temperature, also functions as an organic solvent when forming a nickel complex or cobalt complex. Moreover, even if it is a solid primary amine which is solid at normal temperature, if it is a liquid by melt | dissolution by heating at 100 degreeC or more, there will be no problem in particular.

Since the primary amine also functions as a dispersant and can disperse the nickel complex and the cobalt complex in the reaction solution well, the aggregation of the particles when the nickel complex or the cobalt complex is heated and decomposed after complex formation to obtain nanoparticles. Can be suppressed. Although an aromatic primary amine may be sufficient as a primary amine, an aliphatic primary amine is preferable from a viewpoint of the ease of nickel complex formation and cobalt complex formation in a reaction liquid. An aliphatic primary amine can control the particle diameter of the nanoparticle produced | generated by adjusting the length of the carbon chain, for example, and is especially advantageous when producing nanoparticles whose average particle diameter is 10-200 nm. From the viewpoint of controlling the particle diameter of the nanoparticles, the aliphatic primary amine is preferably selected from those having 6 to 20 carbon atoms. The larger the carbon number, the smaller the particle diameter of the obtained nanoparticles. As such an amine, octylamine, trioctylamine, dioctylamine, hexadecylamine, dodecylamine, tetradecylamine, stearylamine, oleylamine, myristylamine, laurylamine, etc. are mentioned, for example. have. For example, since oleylamine exists as a liquid state under the temperature conditions in a nanoparticle formation process, reaction in a homogeneous solution can be advanced efficiently.

Since primary amines function as surface modifiers in the production of nanoparticles, secondary aggregation can be suppressed even after removal of primary amines. In addition, a primary amine is preferable also from the viewpoint of the ease of processing operation in the washing | cleaning process which isolate | separates the solid component of the produced nanoparticle after a reduction reaction, a solvent, or an unreacted primary amine. In addition, it is preferable that a primary amine has a boiling point higher than a reduction temperature from a viewpoint of the ease of reaction control at the time of reducing a nickel complex and a cobalt complex and obtaining a nanoparticle. That is, in an aliphatic primary amine, it is preferable that boiling point is 200 degreeC or more, and it is preferable that carbon number is 9 or more. Here, for example, the boiling point of C ₉ H ₂₁ N (nonylamine) of aliphatic amine having 9 carbon atoms is 201 ° C. The amount of the primary amine is preferably 2 mol or more, more preferably 2.5 mol or more, and even more preferably 4 mol or more, based on 1 mol of the total amount of nickel and cobalt in terms of metal. The upper limit of the amount of the primary amine is not particularly limited. For example, from the viewpoint of productivity, the upper limit of the amount of the primary amine is preferably about 20 mol or less relative to 1 mol of the total amount of nickel and cobalt in terms of metal.

Divalent nickel ions are known as ligand-substituted active species, and the ligands of the complexes formed may possibly change complex formation by ligand exchange depending on temperature and concentration. For example, in the step of heating a mixture of nickel carboxylic acid and a primary amine to obtain a reaction solution, in consideration of steric hindrance such as carbon chain length of the amine to be used, for example, a carb as shown in FIG. In the case where the acid ions (R ₁ COO, R ₂ COO) are coordinated in any one of the coordination coordination (a) or the monodentation coordination (b), and the concentration of the amine is excessively excessive, the carboxylic acid in the outer region There is a possibility of taking the structure (c) in which ions are present. In order to make a homogeneous solution at the target reaction temperature (reduction temperature), at least one of the ligands of A, B, C, D, E, and F needs to be coordinated with a primary amine. In order to take the state, it is necessary for the primary amine to be present in the reaction solution excessively, at least 2 mol or more per 1 mol of nickel ions is preferred, and more preferably 2.5 mol or more, It is more preferable to exist 4 mol or more.

It is thought that cobalt ions behave similarly to nickel ions and form complexes. For this reason, the primary amine needs to be present in an excessive amount even with respect to cobalt ions, preferably at least 2 mol with respect to at least 1 mol of nickel ions, more preferably at least 2.5 mol, more preferably at least 4 mol. It is more preferable to do.

Although complex formation reaction can be advanced also at room temperature, in order to perform reaction reliably and more efficiently, it is preferable to heat at the temperature of 100 degreeC or more. This heating is particularly advantageous when a carboxylate nickel hydrate such as nickel acetate tetrahydrate or a hydrate of cobalt carboxylate is used as the nickel salt or the cobalt salt. Coordination water and primary amine coordinated with nickel carboxylate and carboxylate cobalt by making heating temperature become temperature exceeding 100 degreeC preferably, More preferably, it is 105 degreeC or more. The ligand substitution reaction of can be carried out efficiently, so that the water molecules as the complex ligand can be dissociated, and the water can be sent out of the system so that the complex can be formed efficiently. For example, nickel acetate tetrahydrate has a complex structure in which two coordinating water and two acetic acid ions, which are two-coordinate ligands, and two water molecules exist in the outer space at room temperature, so these two coordination water and primary amine In order to complex-form by the ligand substitution of, it is preferable to dissociate the water molecule as this complex ligand by heating at a temperature higher than 100 degreeC. In addition, the heating temperature is 175 ° C. or less from the viewpoint of reliably separating the subsequent process of heat reduction of the nickel complex (or nickel ion) and the cobalt complex (or cobalt ion) and completing the complex formation reaction of the previous stage. desirable. Therefore, it is preferable to perform heating at the time of complex formation, for example at 105-175 degreeC. More preferably, heating temperature is 125-160 degreeC.

Although heating time can be suitably determined according to heating temperature and content of each raw material, it is preferable to set it as 15 minutes or more from a viewpoint of completing a complex formation reaction reliably. Although there is no upper limit in particular of a heating time, heating for a long time is waste from a viewpoint of saving energy consumption and process time. In addition, this heating method is not specifically limited, For example, the heating by heat mediums, such as an oil bath, may be sufficient, and the heating by microwave irradiation may be sufficient.

Complexation reaction can be confirmed by the color change of a solution, when the solution obtained by mixing a nickel salt and / or cobalt salt, and a primary amine is heated. In addition, this complex formation reaction uses the ultraviolet-visible absorption spectrum measuring apparatus, for example, measures the wavelength of absorption maximum of the absorption spectrum observed in the wavelength range of 300 nm-750 nm, and the maximum absorption wavelength of a raw material. It can confirm by observing the shift of reaction liquid with respect to (for example, the maximum absorption wavelength in nickel acetate tetrahydrate is 710 nm).

After the complex formation of the nickel salt and / or cobalt salt and the primary amine is made, the resulting reaction solution is heated by a method such as microwave irradiation, as described later, so that the nickel ions and / or cobalt complexes of the nickel complex are Cobalt ions are reduced, and carboxylic acid ions coordinated with nickel ions and cobalt ions are decomposed simultaneously, and finally nanoparticles containing nickel and / or cobalt having zero oxidation number are produced. In general, nickel carboxylic acid and cobalt carboxylic acid are poorly soluble under conditions other than water as a solvent, and a solution containing nickel carboxylic acid and cobalt carboxylic acid as a preliminary step of the heat reduction reaction by microwave irradiation. It is necessary to make it a homogeneous reaction solution. In contrast, the primary amine used in the present embodiment is considered to be a liquid under operating temperature conditions, and is liquefied by coordinating with nickel ions or cobalt ions to form a homogeneous reaction solution.

(Organic solvent)

In order to advance reaction in a homogeneous solution more efficiently, you may add the organic solvent separate from a primary amine newly. When using an organic solvent, you may mix an organic solvent simultaneously with a nickel salt, cobalt salt, and a primary amine, but if nickel salt, cobalt salt, and a primary amine are mixed first, and after complex formation, if an organic solvent is added, 1 It is more preferable because the tertiary amine is efficiently coordinated to nickel ions and cobalt ions. As an organic solvent which can be used, if it does not inhibit the complex formation of a primary amine, nickel ion, or cobalt ion, it will not specifically limit, For example, a C4-C30 ether type organic solvent, C7-C30 Saturated or unsaturated hydrocarbon organic solvents, alcohol organic solvents having 8 to 18 carbon atoms, and the like can be used. In addition, it is preferable to select a thing whose boiling point is 170 degreeC or more from the viewpoint of being able to use even under the heating conditions by microwave irradiation etc., More preferably, select the thing in the range of 200-300 degreeC. It is good. As a specific example of such an organic solvent, tetraethylene glycol, n-octyl ether, etc. are mentioned, for example.

[Step of obtaining nickel-cobalt nanoparticle slurry]

In this step, by heating the complexing reaction liquid, the nickel complex and / or cobalt complex (nickel ions and / or cobalt ions) are reduced to metal to produce nanoparticles. For example, in the first example, when the mixture of nickel complex and cobalt complex is reduced and pyrolyzed, the nickel complex is pyrolyzed at a lower temperature than the cobalt complex and reduced by amine so that the nickel particles become a core, and It is believed 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, under the over-oleyl amine it is present, and a Ni catalyst to the cobalt complex is reduced in a Co from Co ^{2 +} (a 0), a temperature lower than the normal (is this complex dissociated).

By heating the complexing reaction liquid, the complexing reaction liquid is reduced, and the complex is thermally decomposed. From a viewpoint of performing a reduction reaction efficiently, heating temperature becomes like this. Preferably it is 200 degreeC or more, More preferably, it is 220 degreeC or more. From a viewpoint of performing a process efficiently, Preferably it is 270 degrees C or less, More preferably, it is about 250 degrees C or less. For example, when nickel is described as an example, in order to produce nanoparticles having a uniform particle size, uniformly and sufficiently generate nickel complexes in a process of obtaining a complexing reaction solution, and heat the complexing reaction solution to form nickel-cobalt. In the process of obtaining a nanoparticle slurry, it is necessary to perform simultaneous generation and growth of the nuclei of Ni (zero valent) generated by reduction of nickel ions. That is, by adjusting the heating temperature of the process of obtaining a complexing reaction liquid within the said specific range, and making it surely lower than the heating temperature of the process of obtaining a nickel-cobalt nanoparticle slurry, particle | grains with a uniform particle size and a shape are produced | generated. easy. For example, when the heating temperature is too high in the process of obtaining the complexing reaction liquid, the formation of the nickel complex and the reduction reaction to Ni (0) proceed simultaneously to produce the finely grained particles in the process of obtaining the nickel-cobalt nanoparticle slurry. This may be difficult. In addition, when the heating temperature in the process of obtaining the nickel-cobalt nanoparticle slurry is too low, the rate of reduction to Ni (zero-valent) is slowed down, resulting in less nucleus generation. not.

In this step, the heating source may be an oil bath or the like, but is preferably microwave. When microwaves are irradiated to the complexing reaction liquid, microwaves penetrate into the complexing reaction liquid, and rapid heating and uniform heating are performed by internal heating. As a result, the entire complexing reaction liquid can be made uniform at a desired temperature, and the processes of reduction, nucleation, and nucleation of nickel and cobalt particles are simultaneously generated in the entire solution. As a result, monodisperse particles having a narrow particle size distribution are obtained. Can be easily produced in a short time. In addition, the use wavelength of a microwave is not specifically limited, For example, it is 2.45 GHz.

The nanoparticle slurry obtained by heating a complexing reaction liquid is left still, for example, after removing a supernatant liquid, wash | cleaning using a suitable solvent, and drying, a nanoparticle is obtained.

In the process of obtaining a nickel-cobalt nanoparticle slurry, you may add the organic solvent mentioned above to a complexing reaction liquid as needed. In addition, as above-mentioned, using the primary amine used for complex formation reaction as it is as an organic solvent is preferable embodiment of this invention. The solvent added as needed in the process of heating a complexing reaction liquid is not specifically limited, For example, alcohol, such as an octanol (octyl alcohol), a nonpolar solvent, etc. can be used. As described above, when oleylamine is used as the primary amine, the solvent may be omitted.

The manufacturing method of the nanoparticle of this embodiment can include arbitrary processes other than the said process. For example, arbitrary processes, such as addition of a surface modifier, can be performed as mentioned later. In addition, since the manufacturing method of the nanoparticle of this embodiment adopts the reduction method by heating using a microwave etc. in the process of obtaining a nickel-cobalt nanoparticle slurry, use of a strong reducing agent is not necessary. However, the substance which has a reducing effect may exist in a complex formation reaction liquid in the range which does not inhibit the effect of this invention.

(Addition of surface modifier)

In the method for producing nanoparticles according to the present embodiment, as a surface modifier for controlling the particle diameter of the nanoparticles, for example, polymer resins such as polyvinylpyrrolidone (PVP), polyethyleneimine, polyacrylamide, and the like Long chain carboxylic acids or carboxylates such as list acid and oleic acid may be added. However, when the amount of surface modification of the obtained nanoparticles is large, since there is a possibility that it may adversely affect as an impurity depending on a use, it is preferable that the amount of surface modification after washing the obtained nanoparticles is as small as possible. For example, when used for the conductive paste for nickel electrodes, when the nickel particles are pasted and calcined at a high temperature, the packing density may be reduced, causing interlayer peeling or cracking. Therefore, it is preferable to make the addition amount of a surface modifier into 0.1 or more and 100 mass parts or less with respect to 100 mass parts of total amounts of a nickel element. Although a surface modifier may be added at the stage of the mixture of the nickel carboxylic acid and a primary amine in a complex reaction liquid formation process, you may add to the complex reaction liquid obtained by a complex reaction liquid formation process, Preferably addition timing It is good after silver complexation reaction or after production | generation of nickel nanoparticle.

By the manufacturing method of the nickel-cobalt nanoparticle which concerns on this embodiment demonstrated above, an average particle diameter is 10-200 nm and Cv value [coefficient of variation; A nickel-cobalt nanoparticle comprising a core of nickel and a shell of cobalt having a narrow particle size distribution in which the ratio σ / d of the average particle diameter d and the standard deviation σ is 0.01 ≦ σ / d ≦ 0.5 can be obtained. .

Example

Although an Example and a comparative example are given and this invention is further demonstrated, this invention is not limited to the Example demonstrated below.

The particle size of a nanoparticle photographed the nanoparticle powder with the transmission electron microscope (TEM), 200 were randomly extracted from it, and the average particle diameter and standard deviation were calculated | required. Moreover, Cv value (= (sigma) / d) was obtained from this result. In addition, by the scanning transmission electron microscope (STEM-EDS) equipped with an energy dispersive X-ray analyzer, the presence or concentration of nickel and cobalt in the obtained particles were confirmed by surface analysis and ray analysis. As shown in FIG. 4, the thickness of the cobalt shell layer computed the linear nickel and cobalt atomic concentration which crosses 1 particle by STEM-EDS. In this line analysis technique, the atomic concentration of only the core portion of the generated spherical particles cannot be calculated. In other words, the analysis near the particle surface shows a simple particle surface concentration, but the analysis result near the particle center adds together the concentrations of the metal element on the particle surface and the inside (core). Therefore, in this analysis result, the average value of the thickness of the layer whose cobalt strength becomes higher than nickel was made into the thickness of a cobalt shell layer. The composition of the obtained particles was analyzed by Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES).

(Example 1)

275 mmol of oleylamine was added to 12.5 mmol of cobalt formate dihydrate and 12.5 mmol of nickel acetate tetrahydrate, and the complexing reaction liquid was obtained by heating at 120 degreeC for 20 minutes under nitrogen flow. Subsequently, this complexing reaction liquid was heated to 225 degreeC using microwave, and the nanoparticle slurry was obtained by maintaining the temperature for 30 minutes. The nanoparticle slurry was left to stand still, the supernatant was removed, and then washed three times using hexane. Then, it dried in the vacuum drier maintained at 60 degreeC for 6 hours, and obtained nanoparticle.

The TEM (Transmission Electron Microscope) photograph of the obtained nanoparticle is shown in FIG. 2A, and the ED (electron diffraction) pattern is shown in FIG. 2B. Spherical uniform particles having an average particle diameter of 82 nm were formed. In addition, it can be seen from the ED pattern that the nanoparticles are fcc-structured metals containing no oxides. Moreover, when the metal composition of the particle | grains obtained by ICP-AES was confirmed, since it is 47.6 mass% and 47.3 mass% of Ni and Co, respectively, a mol ratio is Ni / Co = 1.0 and a raw material ratio (injection ratio of Ni salt and Co salt) (Mol%)). The photograph of the STEM-EDS mapping image is likewise shown in FIG. 3. It can be seen that the distribution of nickel is a nanoparticle having a Ni (core) -Co (shell) structure because the distribution of nickel is largely distributed in the center of the nanoparticles and the surface of the nanoparticles.

In addition, it is understood from the line analysis results of the particles shown in FIG. 4 that the thickness of the cobalt shell layer (shell) is approximately 13 nm. In addition, the result of the saturation magnetization (unit: emu / g) obtained by SQUID magnetization rate measurement was shown in FIG. Although the saturation magnetization is lower than that of commercially available cobalt nanoparticles (particle size of 50 nm or less, manufactured by Aldrich), it can be seen that the saturation magnetization is greatly increased as compared with the nanoparticles of Comparative Example 8 described later.

(Examples 2-7, Comparative Examples 1-8)

In Examples 2-7 and Comparative Examples 1-8, according to Example 1 except having changed the kind of nickel salt and cobalt salt, and the kind of heating source and reaction temperature (heating temperature) in the process of obtaining a nanoparticle slurry. Nanoparticles were prepared. The result was shown in Table 1 with Example 1. FIG. In addition, in each Example and each comparative example, the mol ratio of oleylamine / (Ni salt + Co salt) is all ten. In addition, all the heating methods of a complexing reaction liquid were performed by microwave heating except Example 3 which used the oil bath.

In addition, 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 a TEM photograph of the nickel-cobalt nanoparticles obtained in Example 2 is shown. 6 and 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, acetate or acetylacetone salt as nickel salts and cobalt salts. In addition, it was 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 diameter of 100 nm and a Cv value of 0.14 (without using a cobalt salt), a complexation reaction was obtained from nickel acetate tetrahydrate according to the first example, followed by heating. 125 mmol of oleylamine was added to one particle: comparative example 8), and the complexing reaction liquid was obtained by heating at 120 degreeC for 20 minutes under nitrogen flow. Subsequently, the complexing reaction liquid was heated to 225 degreeC using microwave, and the nickel-cobalt nanoparticle slurry was obtained by maintaining the temperature for 30 minutes.

The nickel-cobalt nanoparticle slurry was left still to remove the supernatant, and then washed three times using hexane. Then, it dried in the vacuum drier maintained at 60 degreeC for 6 hours, and obtained nickel-cobalt nanoparticle. The average particle diameter of the obtained nickel-cobalt nanoparticles was 120 nm, 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 the complexing reaction liquid was obtained by heating at 120 degreeC for 20 minutes under nitrogen flow. Subsequently, 25 mmol of nickel particles having an average particle diameter of 100 nm and a Cv value of 0.14 were used for the complexing reaction solution (particles obtained by obtaining a complexing reaction from nickel acetate tetrahydrate without using a cobalt salt and heating it; Comparative Example 8 ) Was added and stirred well, and then it heated to 225 degreeC using microwave, and maintained the temperature for 30 minutes, and obtained the nickel-cobalt nanoparticle slurry.

The nickel-cobalt nanoparticle slurry was left still to remove the supernatant, and then washed three times using hexane. Then, it dried in the vacuum drier maintained at 60 degreeC for 6 hours, and obtained nickel-cobalt nanoparticle. The average particle diameter of the obtained nickel-cobalt nanoparticles was 117 nm, Cv value of the particle size distribution was 0.15, and the thickness of the cobalt shell layer was 15 nm.

As mentioned above, although embodiment of this invention was described in detail for the purpose of illustration, this invention is not restrict | limited to the said embodiment. This international application claims priority based on Japanese Patent Application No. 2010-60773 for which it applied on March 17, 2010, and uses the whole content here.

Claims (9)

A nickel-cobalt nanoparticle having a core substantially made of nickel and a shell made of substantially cobalt substantially covering the entire surface of the core. The method of claim 1,
Nickel content exists in the range of 30-90 mass%, cobalt content exists in the range of 10-70 mass%, average particle diameter exists in the range of 10-200 nm, and the thickness of the said shell is 1-50 nm Nickel-cobalt nanoparticles in range. Obtaining a complexing reaction solution by heating a mixture containing nickel salt, cobalt salt and primary amine,
A method for producing nickel-cobalt nanoparticles comprising the step of heating the complexing reaction liquid to obtain a nickel-cobalt nanoparticle slurry. Obtaining a complexing reaction liquid by heating a mixture containing nickel fine particles, cobalt salt and a primary amine,
A method for producing nickel-cobalt nanoparticles comprising the step of heating the complexing reaction liquid to obtain a nickel-cobalt nanoparticle slurry. Obtaining a complexing reaction liquid by heating a mixture containing cobalt salt and a primary amine,
The nickel-cobalt nanoparticle manufacturing method provided with the process of adding nickel fine particle to the said complexing reaction liquid, and heating and obtaining a nickel-cobalt nanoparticle slurry. 6. The method according to any one of claims 3 to 5,
The said nickel salt has any one of the C1-C3 linear carboxylic acid group and group represented by following structural formula (1), The manufacturing method of the nickel-cobalt nanoparticle.
[Formula 1]

(Here, 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 different from each other.) 7. The method according to any one of claims 3 to 6,
The method for producing nickel-cobalt nanoparticles, wherein the cobalt salt has any one of a linear carboxylic acid group having 1 to 3 carbon atoms and a group represented by the following structural formula (1).
(2)

(Here, 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 different from each other.) The method according to claim 6 or 7,
A method for producing nickel-cobalt nanoparticles 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,
The manufacturing method of the nickel-cobalt nanoparticles using a microwave as a heating means in the process of obtaining the said nickel-cobalt nanoparticle slurry.

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