CN102811829B - Nickel-cobalt nanometer particle and manufacture method thereof - Google Patents

Abstract

Nickel-cobalt nanometer particle of the present invention comprises the core that formed by nickel in fact and covers in fact whole of core and the shell formed by cobalt in fact.The manufacture method of nickel-cobalt nanometer particle of the present invention has following operation: the mixture heating containing nickel salt or nickel particle, cobalt salt and primary amine is obtained the operation of reactant liquor or the mixture of cobalt salt and primary amine is heated the operation obtaining reactant liquor; With operation reactant liquor heating being obtained nickel-cobalt nanometer particle slurry.

Description

Nickel-cobalt nanoparticle and its production method

technical field

The present invention relates to nanoparticles having a core-shell structure formed from dissimilar metals.

Background technique

Cobalt nanoparticles are cheaper than silver nanoparticles, chemically more stable than copper nanoparticles, and have higher catalytic activity and magnetic saturation than nickel particles, so they are used in various catalysts, magnetic materials, fuel cells, laminates Utilization in electrodes and the like in ceramic capacitors is expected. However, cobalt is a rare metal and is more expensive than nickel particles. Therefore, development of cobalt particles capable of exhibiting the performance of cobalt with a smaller amount and a method for producing the same has been desired. In order to give full play to the performance of cobalt, its particle size and particle shape must be controlled uniformly.

In general, methods for producing metal nanoparticles can be broadly classified into physical methods and chemical methods. The physical method is a method of pulverizing bulk metal to produce nanoparticles (pulverization method), and the chemical method is a method of producing metal atoms and controlling their aggregation (aggregation method). When pulverization is performed by a physical method, there is a limit to reduction in particle size, and the shape of particles also becomes uneven, making it difficult to form uniform particles. Therefore, chemical methods are more advantageous for controlling the shape or diameter of particles.

In addition, the manufacturing method of the metal nanoparticle by a chemical method can be divided into a wet method and a dry method. For the dry method of chemical method, there are known CVD (Chemical Vapor Deposition) method, evaporation method in gas, laser method, sputtering method, metal droplet spray method, etc., because the generated particles are spherical and crystallized after high temperature treatment. However, on the other hand, the particle size distribution is wide and the productivity is low, which are disadvantages. On the other hand, the wet method represented by the chemical reduction method has the advantages of high productivity and easy particle size control compared with the dry method, so a lot of research has been carried out with the development of nanotechnology in recent years.

In addition, studies on binary nanoparticles (metal composite nanoparticles) that can be expected to exhibit further physical properties than single metal nanoparticles are being extensively conducted. In addition, focusing on the need to have a metal having specific properties as the surface metal of the particle depending on the application of the nanoparticle, as a binary nanoparticle, a binary nanoparticle having a core and a shell made of a different metal has also been studied.

As such a metal nanoparticle having a core-shell structure, for example, a metal nanoparticle including a copper core and a thin film layer of a metal such as silver, palladium, platinum, or gold that surrounds the copper core and has a reduction potential higher than that of copper is disclosed. (Patent Document 1). The method for producing metal nanoparticles comprises the steps of: using tert-butylhydroxytoluene, ascorbic acid, flavonoids, etc. a step of forming copper nanoparticles from a copper precursor composed of a substance; and a step of forming a thin film layer of a metal having a reduction potential higher than that of copper on the surface of the copper nanoparticles. The obtained metal nanoparticles with a core-shell structure have the following advantages: Since the copper particles are used as the core and covered with a noble metal, the copper content can be increased while preventing the oxidation of copper, so the economy is excellent, Furthermore, since metal such as silver, which is superior in electrical conductivity to copper, is contained in the thin film layer, wiring having superior electrical conductivity to copper can be formed.

In addition, for example, a method is also disclosed in which a metal precursor containing a first metal (such as cobalt) as nanoparticles and a second metal (such as platinum) having a higher reduction potential than the first metal is separately dissolved in an appropriate organic solvent. , the resulting solutions were mixed, and a metal nanoparticle with a core-shell structure was produced by a metal substitution reaction between the first metal and the second metal (Patent Document 2).

Patent Documents 1 and 2 realize metal nanoparticles having a core formed of a metal with a low reduction potential and a shell formed of a metal with a high reduction potential by different methods. However, it is unclear whether metal nanoparticles having a core-shell structure made of other dissimilar metals can be obtained appropriately using the production methods of Patent Documents 1 and 2. In particular, it is difficult to think that the same method as in Patent Documents 1 and 2 can be applied to dissimilar metals having similar oxidation-reduction potentials, such as nickel and cobalt.

On the other hand, the inventors of the present invention have studied and reported Cu-Ni alloys having copper as the core and nickel having a lower reduction potential than copper in the shell (Non-Patent Documents 1 and 2). According to Non-Patent Document 2, which further deepens the research of Non-Patent Document 1, the Cu-Ni alloy is prepared as follows: Copper formate and nickel formate are mixed with oleylamine respectively, and the mixed solution of copper formate is heated at room temperature 1. Heating the mixed solution of nickel formate at 393K to perform complexation (that is, form a complex) to prepare a precursor, mix with 1-octanol, and then obtain nanoparticles by rapid heating with microwaves. Due to the different redox potentials of copper and nickel, the reduction and particle formation occur at different temperatures (433K for Cu ²⁺ and 463K for Ni ²⁺ ), so it is believed that copper nanoparticles are formed first, and copper nanoparticles are formed as the temperature increases. The particle is a core and a nickel shell is formed on the surface. It was confirmed that the obtained nanoparticles had a high nickel concentration near the particle surface.

prior art literature

patent documents

Patent Document 1: Japanese Patent Laid-Open No. 2007-224420

Patent Document 2: Japanese Patent Laid-Open No. 2003-055703

non-patent literature

Non-Patent Document 1: Tomoyo Yamauchi, Yasutoku Tsukahara, and Yuji Wada, "Synthesis and Magnetic Properties of Cu-Ni Alloy Nanoparticles Using Microwave Heating" Properties)", the 89th Spring Annual Meeting of the Chemical Society of Japan (2009) Preparatory Papers, 2D2-34

Non-Patent Document 2: Tomoo Yamauchi, Yasutoku Tsukahara, Yuji Wada, and another, "Synthesis and Magnetic Properties of Cu Core-Ni Shell Nanoparticles Using Microwaves (マイクロ波を用いた Cu core-Nishell nanoparticleのSynthesisとMagnetic properties)", the 3rd symposium of the Japan Society for the Application of Electromagnetic Wave Energy, preparatory manuscript collection, P190, November 18-20, 2009

Contents of the invention

The technical problem to be solved by the invention

An object of the present invention is to provide a nickel-cobalt nanoparticle in which nickel forms a core and cobalt forms a shell, and a method for producing the same, which is suitable for applications such as catalysts, magnetic materials, and electrodes.

Means used to solve technical problems

The nickel-cobalt nanoparticle of the present invention includes a core substantially made of nickel, and a shell substantially made of cobalt covering substantially the entire surface of the core.

In addition, the nickel-cobalt nanoparticles of the present invention are characterized in that, preferably, the nickel content is within the range of 30 to 90% by mass, the cobalt content is within the range of 10 to 70% by mass, and the average particle diameter is within the range of 10 to 200nm. , and the thickness of the shell is in the range of 1 to 50 nm.

In addition, the method for producing nickel-cobalt nanoparticles of the present invention includes the steps of: heating a mixture containing nickel salt, cobalt salt, and primary amine to obtain a complex reaction solution; and heating the complex reaction solution to obtain nickel - Process of cobalt nanoparticle slurry.

In addition, the method for producing nickel-cobalt nanoparticles of the present invention includes the steps of: heating a mixture containing nickel particles, cobalt salts, and primary amines to obtain a complex reaction solution; and heating the complex reaction solution to obtain nickel - Process of cobalt nanoparticle slurry.

In addition, the manufacturing method of the nickel-cobalt nanoparticles of the present invention has the following steps: a step of heating a mixture containing a cobalt salt and a primary amine to obtain a complex reaction solution; A process of heating to obtain a nickel-cobalt nanoparticle slurry.

In addition, the method for producing nickel-cobalt nanoparticles of the present invention is characterized in that it is preferable that the above-mentioned nickel salt and cobalt salt each have a straight-chain carboxylic acid group having 1 to 3 carbon atoms or a compound represented by the following structural formula (1). any of the groups.

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

In addition, in the method for producing nickel-cobalt nanoparticles of the present invention, it is preferable that the above-mentioned carboxylic acid group is a formate group or an acetate group, and the group represented by the above-mentioned structural formula (1) is an acetylacetonate ligand. the

In addition, in the method for producing nickel-cobalt nanoparticles of the present invention, it is preferable to use microwaves as heating means in the step of obtaining the above-mentioned nickel-cobalt nanoparticle slurry.

Invention effect

The nickel-cobalt nanoparticles of the present invention are composed of a nickel core and a cobalt shell, and thus are suitable for applications such as catalysts, magnetic materials, electrodes, and the like. In addition, by adjusting the cobalt content according to these uses, the cost can be made reasonable, and the performance of cobalt can be brought into full play in each of the above-mentioned uses.

Moreover, according to the manufacturing method of the nickel-cobalt nanoparticle of this invention, the nickel-cobalt nanoparticle of this invention can be obtained suitably.

Description of drawings

Fig. 1 is a diagram showing the structure of each nickel acetate complex, (a) showing binary mesh coordination, (b) showing single mesh coordination, and (c) showing a state where carboxylate ions are coordinated to the outer ring.

FIG. 2A is a transmission electron microscope (TEM: Transmission Electron Microscope) photograph of nickel-cobalt nanoparticles obtained in Example 1. FIG.

FIG. 2B is a diagram showing an electron diffraction (ED: Electron diffraction) pattern from the TEM photograph region of FIG. 2A .

3 is a diagram showing a mapping image obtained by STEM-EDS of nickel-cobalt nanoparticles obtained in Example 1.

4 is a graph showing the results of line analysis by STEM-EDS of nickel-cobalt nanoparticles obtained in Example 1. FIG.

5 is a graph showing the results of SQUID magnetic susceptibility measurements of nickel-cobalt nanoparticles of Examples 1 and 2, nickel particles of Comparative Example 8, and commercially available cobalt particles.

FIG. 6 is a diagram showing a mapping image obtained by STEM-EDS of nickel-cobalt nanoparticles obtained in Example 2. FIG.

FIG. 7 is a diagram showing a mapping image obtained by STEM-EDS of nickel-cobalt nanoparticles obtained in Example 4. FIG.

detailed description

Embodiments of the present invention will be described below.

[Nickel-Cobalt Nanoparticles]

The nickel-cobalt nanoparticles of this embodiment (hereinafter sometimes simply referred to as “nanoparticles”) include a core substantially made of nickel, and a shell substantially made of cobalt covering substantially the entire surface of the core. Here, the nanoparticle does 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, "a core formed substantially of nickel" means that the existence of a small amount of cobalt inevitably contained in the core is allowed, but most of it is formed of nickel, and "a shell formed of substantially cobalt" means that the unavoidable amount of cobalt in the shell is allowed. The ground contains a small amount of nickel, but the majority is formed of cobalt. In addition, the shell of the nanoparticle preferably covers the entire surface of the core, but it is not limited thereto, and a form in which part of the nickel is exposed is not excluded. In other words, "substantially covering the entire surface of the core" not only refers to the form in which the shell completely covers the core, but also allows the shell to be formed discontinuously and the core partially exposed form, but most of the surface of nickel-cobalt nanoparticles is formed by the shell. In addition, the nanoparticles may have an inner shell between a cobalt shell and nickel.

The nanoparticles of the present embodiment have, for example, a nickel content of 30 to 90% by mass and a cobalt content of 10 to 70% by mass. The cobalt content of the nanoparticle can be appropriately set in consideration of the characteristics required in the applicable application, cost, etc., but if it is less than 10% by mass, for example, the core may be largely exposed from the shell and it may not be sufficiently catalyzed. performance, magnetic properties, and when it exceeds 70% by mass, the cost will increase.

The average particle diameter of the nanoparticles is, for example, 10 to 200 nm, preferably 10 to 150 nm. When the average particle size of the nanoparticles is less than 10 nm, the aggregation is severe and the dispersibility becomes poor, and it may not be suitable as a paste material such as a catalyst or an electrode. On the other hand, when the average particle diameter of the nanoparticle exceeds 200 nm, the specific surface area becomes small, and there is a possibility that, for example, high catalytic performance cannot be exhibited. In addition, the nanoparticle preferably has a Cv value [coefficient of variation; ratio σ/d of the average particle diameter (d) to the standard deviation (σ)] of 0.01≦σ/d≦0.5.

The thickness of the shell of the nanoparticle is, for example, 1 to 50 nm, preferably 5 to 20 nm. When the thickness of the shell layer of the nanoparticle is less than 1 nm, the amount of cobalt is too small, and the catalytic activity and magnetic properties of cobalt itself may not be fully exhibited. And when it exceeds 50nm, the cost will increase.

The shape of nanoparticles can be spherical, pseudo-spherical, prolate spherical, cube-like, truncated tetrahedron-like, bipyramidal, regular octahedron-like, regular decahedron-like, regular icosahedron-like and other shapes, but from For example, from the viewpoint of increasing the packing density when nickel nanoparticles are used in electrodes of electronic devices, spherical or pseudo-spherical shapes are preferable, and spherical shapes are more preferable. Here, the shape of the nanoparticles can be confirmed by observation with a scanning electron microscope (SEM).

The nanoparticles of the present embodiment described above can adjust the cobalt content according to the application such as catalyst, magnetic material, electrode, etc. to make the cost reasonable, and can also exhibit the performance of cobalt suitably.

[Manufacturing method of nickel-cobalt nanoparticles]

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

<First example>

The first example of the method for producing nanoparticles has the following steps: a step of heating a mixture containing a nickel salt, a cobalt salt, and a primary amine to obtain a complex reaction solution; and heating the complex reaction solution to obtain a nickel-cobalt nanoparticle slurry material process.

<Second example>

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

<Third example>

The third example of the method for producing nanoparticles has the following steps: a step of heating a mixture containing a cobalt salt and a primary amine to obtain a complex reaction liquid; adding nickel fine particles to the complex reaction liquid and then heating to obtain nickel-cobalt The process of nanoparticle slurry. That is, the nickel fine particles of the second example are not added during the production of the complex reaction solution, but are added during the production of the nickel-cobalt nanoparticle slurry.

Both the second example and the third example are preferred embodiments, but when adding nickel particles, it is necessary to highly disperse the nickel particles in the complexation reaction solution, and if the dispersion is insufficient, the uniform formation of the cobalt shell may not be possible. . This means that the first example, which does not require high dispersion treatment, is the most preferable method.

[Step of Obtaining Complexation Reaction Liquid]

In this step, by heating a mixture containing nickel salt, cobalt salt and primary amine (first example), heating a mixture containing nickel particles, cobalt salt and primary amine (second example), or heating a mixture containing cobalt The mixture of the salt and the primary amine is heated (the third example), thereby generating a nickel and/or cobalt complex to obtain a complex reaction solution. Here, the complexation reaction liquid refers to the reaction product liquid (reaction product) produced by reaction of nickel salt and/or cobalt salt and primary amine. It is considered that the complexation reaction solution contains a nickel complex and a cobalt complex as complexes in the first example, and contains a cobalt complex as a complex in the second and third examples. By heating the complexation reaction solution, the nickel ions and/or cobalt ions of the nickel complex and/or cobalt complex are reduced, and the carboxylate ions coordinated on the ions are simultaneously decomposed, finally generating 0-valent Ni and/or 0-valent Co to generate core-shell nanoparticles.

(nickel salt, cobalt salt)

Both the nickel salt and the cobalt salt are not particularly limited, and preferably have either 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). A group represented by the following structural formula (1) is a 1,3-diketo group (β-diketo ligand). The nickel salt and the cobalt salt may be the same salt or different salts. In addition, both the nickel salt and the cobalt salt may be anhydrous or hydrate.

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

The nickel salt having a straight-chain carboxylic acid group with 1 to 3 carbon atoms is specifically nickel formate, nickel acetate or nickel propionate, and nickel formate or nickel acetate is particularly preferably used. In addition, 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 cobalt formate or cobalt acetate is particularly preferably used. These nickel carboxylate and cobalt carboxylate may be anhydrous or hydrate. In addition, nickel chloride (cobalt chloride), nickel nitrate (cobalt nitrate), nickel sulfate (cobalt sulfate), nickel carbonate (cobalt carbonate), nickel hydroxide (cobalt hydroxide) and other inorganic salts can also be considered instead Nickel carboxylate or cobalt carboxylate, but in the case of inorganic salts, since the dissociation (decomposition) is high temperature, the dissociated nickel ion (or nickel complex) or cobalt ion (or cobalt complex) ) needs to be heated at a higher temperature during the reduction process, so it is not preferred.

Examples of the group represented by the above structural formula (1) include 2,4-pentanedione (alias: acetylacetonate ligand), 2,4-hexanedione, 3,5-heptanedione group, 1-phenyl-1,3-butanedionyl group, 1-chloro-1,3-butanedionyl group, etc., among which acetylacetone ligand is preferably used.

Regarding the compounding quantity of nickel salt and cobalt salt, for example, in terms of metal, relative to 100 parts by mass of the total amount of nickel and cobalt in the complexation reaction solution, it is preferably set to 30 to 90 parts by mass for nickel and 10 to 30 parts by mass for cobalt. 70 parts by mass, more preferably 50 to 80 parts by mass of nickel and 20 to 50 parts by mass of cobalt. The compounding quantity of cobalt can consider the characteristics required for the use of nanoparticles, cost, etc., and can set it suitably, but when it is less than 10 mass parts with respect to the total amount of nickel and cobalt 100 mass parts in terms of metal, for example, There is a possibility that the core is largely exposed from the shell and the effects of catalytic performance and magnetic properties cannot be sufficiently obtained, and when it exceeds 70 parts by mass, the cost will increase.

(nickel particles)

The nickel microparticles used in the second example and the third example of the method for producing nanoparticles are not limited in particle size, but nickel microparticles having a particle diameter of, for example, 5 to 200 nm are preferably used. When the particle diameter is less than 5 nm, the aggregation may be severe and it may be difficult to disperse in liquid. On the other hand, when the particle diameter exceeds 200 nm, the specific surface area of the particles becomes too small, and there is a possibility that a sufficient reaction cannot proceed. In addition, the shape of nickel fine particles is preferably spherical, pseudo-spherical, etc., but spherical is most preferable.

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

(primary amine)

Primary amines can form complexes with nickel ions or cobalt ions, and effectively exert their reducing ability to nickel complexes (or nickel ions). On the other hand, secondary amines may hinder the good formation of nickel complexes or cobalt complexes due to their large steric hindrance, and tertiary amines cannot be used because they do not have the reducing ability of nickel ions or cobalt ions.

The primary amine is not particularly limited as long as it can form a complex with nickel ions or cobalt ions, and primary amines that are solid or liquid at normal temperature can be used. Here, normal temperature means 20°C±15°C. The primary amine, which is liquid at normal temperature, also functions as an organic solvent when forming a nickel complex or a cobalt complex. In addition, even if it is a primary amine that is solid at normal temperature, there is no particular problem as long as it becomes a liquid by heating at 100° C. or higher or is dissolved in an organic solvent.

The primary amine also acts as a dispersant, which can make the nickel complex or cobalt complex disperse well in the reaction solution, so it can inhibit the heating of the nickel complex or cobalt complex after the complex is formed. Aggregation between particles when decomposing to obtain nanoparticles. The primary amine may be an aromatic primary amine, but an aliphatic primary amine is preferable from the viewpoint of easiness of forming a nickel complex or a cobalt complex in the reaction liquid. The primary aliphatic amine can control the particle diameter of the generated nanoparticles by, for example, adjusting the length of its carbon chain, and is particularly advantageous when producing nanoparticles with an average particle diameter of 10 to 200 nm. From the viewpoint of controlling the particle size of the nanoparticles, the primary aliphatic amine is preferably selected from primary amines having about 6 to 20 carbon atoms. The larger the number of carbon atoms, the smaller the particle size of the obtained nanoparticles. Examples of such amines include octylamine, trioctylamine, dioctylamine, cetylamine, dodecylamine, tetradecylamine, stearylamine, oleylamine, myristylamine, and laurylamine. Oleylamine, for example, can efficiently react in a homogeneous solution because it exists in a liquid state under the temperature conditions during nanoparticle formation.

Since primary amines function as surface modifiers during the formation of nanoparticles, secondary aggregation can be suppressed even after primary amines are removed. In addition, primary amines are also preferable from the viewpoint of ease of handling operation in the washing step of separating the solid content of nanoparticles produced after the reduction reaction from the solvent or unreacted primary amines. In addition, the primary amine is preferably a primary amine having a boiling point higher than the reduction temperature from the viewpoint of easiness of reaction control when reducing a nickel complex or a cobalt complex to obtain nanoparticles. That is, among primary aliphatic amines, primary aliphatic amines having a boiling point of 200° C. or higher are preferable, and those having 9 or more carbon atoms are preferable. Here, for example, the boiling point of an aliphatic amine C ₉ H ₂₁ N (nonylamine) 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, most preferably 4 mol or more, in terms of metal, based on 1 mol of the total amount of nickel and cobalt. The upper limit of the amount of primary amine is not particularly limited, but is preferably set to about 20 mol or less in terms of metal relative to 1 mol of the total amount of nickel and cobalt, for example, from the viewpoint of productivity.

Divalent nickel ions are known as ligand substitution active species, and the ligands of the formed complexes may easily change complexation by ligand exchange depending on the temperature and concentration. For example, in the process of heating a mixture of nickel carboxylate and primary amine to obtain a reaction solution, if the steric hindrance such as the carbon chain length of the amine used is considered, the carboxylate ion (R ₁ COO, R ₂ COO) may be coordinated by any of two-dentate coordination (a) or single-dentate coordination (b), and when the concentration of amine is excessive, it may also adopt a structure in which carboxylate ions exist in the outer ring (c). In order to obtain 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 adopt this state, the primary amine needs to be present in excess in the reaction solution, preferably at least 2 mol or more, more preferably 2.5 mol or more, most preferably 4 mol or more, based on 1 mol of nickel ions.

It is believed that cobalt ions also behave similarly to nickel ions to form complexes. Therefore, the primary amine also needs to be present in excess relative to cobalt ions, preferably at least 2 mol or more, more preferably 2.5 mol or more, most preferably 4 mol or more, based on 1 mol of cobalt ions.

The complexation reaction can proceed at room temperature, but it is preferable to heat at a temperature of 100° C. or higher in order to proceed the reaction reliably and more efficiently. This heating is particularly advantageous when, for example, a nickel carboxylate hydrate such as nickel acetate tetrahydrate or a cobalt carboxylate hydrate is used as the nickel salt or the cobalt salt. By setting the heating temperature preferably at a temperature exceeding 100°C, more preferably at a temperature of 105°C or higher, the coordination water coordinated on the nickel carboxylate or cobalt carboxylate and the ligand substitution reaction of the primary amine are effectively This dissociates the water molecule which is the ligand of the complex, and the water can be discharged out of the system, so that the complex can be efficiently formed. For example, nickel acetate tetrahydrate has a complex structure of 2 coordination waters and 2 acetate ions as double-entangled ligands at room temperature, and 2 water molecules in the outer ring. Therefore, in order to pass through these 2 coordination Potential water is substituted with the ligand of the primary amine to perform complexation efficiently, and it is preferable to dissociate the water molecule that is the complex ligand by heating at a temperature higher than 100°C. In addition, the heating temperature is preferably 175° C. from the viewpoint of reliably separating from the subsequent heating reduction process of the nickel complex (or nickel ion) and cobalt complex (or cobalt ion) and completing the complexation reaction in the previous stage. the following. Therefore, it is preferable to perform heating at the time of complex formation, for example at 105-175 degreeC. More preferably, the heating temperature is 125 to 160°C.

The heating time can be appropriately determined according to the heating temperature and the content of each raw material, but it is preferably set to 15 minutes or more from the viewpoint of reliably completing the complexation reaction. The upper limit of the heating time is not particularly limited, but heating for a long time is not beneficial from the viewpoint of saving energy consumption and process time. In addition, the heating method is not particularly limited, and may be, for example, heating by a heat medium such as an oil bath, or heating by microwave irradiation.

The complexation reaction can be confirmed by the color change of the solution obtained by heating the solution obtained by mixing the nickel salt and/or cobalt salt and the primary amine. In addition, this complex reaction can also be confirmed by the following method: for example, using an ultraviolet-visible absorption spectrometer, measuring the wavelength of the maximum absorption of the absorption spectrum observed in the wavelength region of 300nm to 750nm, by observing the maximum wavelength relative to the raw material It is confirmed by the shift of the reaction liquid with absorption wavelength (for example, nickel acetate tetrahydrate, whose maximum absorption wavelength is 710nm).

After the complexation of the nickel salt and/or cobalt salt with the primary amine is carried out, the obtained reaction solution is heated by microwave irradiation or the like as described later to complex the nickel ion and/or cobalt of the nickel complex. The cobalt ions of the compound are reduced, and the carboxylate ions coordinated on the nickel ions or cobalt ions are simultaneously decomposed, finally generating nanoparticles containing nickel and/or cobalt with an oxidation value of 0. Generally, nickel carboxylate and cobalt carboxylate are poorly soluble in conditions other than water as a solvent, and a solution containing nickel carboxylate or cobalt carboxylate needs to be made into a uniform reaction solution as a pre-stage of heating reduction reaction by microwave irradiation. On the other hand, it is considered that the primary amine used in the present embodiment is a liquid under the temperature conditions of use, and is liquefied by coordinating with nickel ions or cobalt ions to form a uniform reaction solution.

(Organic solvents)

In order to carry out the reaction in the homogeneous solution more efficiently, an organic solvent different from the primary amine may be newly added. When using an organic solvent, the organic solvent can be mixed with the nickel salt or cobalt salt and the primary amine at the same time, but if the nickel salt or cobalt salt is first mixed with the primary amine for complexation and then the organic solvent is added, the primary amine will effectively coordinate On nickel ions or cobalt ions, thus more preferred. The organic solvent that can be used is not particularly limited as long as it does not hinder the complexation of primary amines with nickel ions or cobalt ions. For example, ether-based organic solvents with 4 to 30 carbon atoms, carbon atom Saturated or unsaturated hydrocarbon-based organic solvents with 7-30 carbon atoms, alcohol-based organic solvents with 8-18 carbon atoms, and the like. In addition, from the viewpoint of being usable under heating conditions such as microwave irradiation, the organic solvent to be used is preferably an organic solvent having a boiling point of 170° C. or higher, more preferably an organic solvent having a boiling point in the range of 200 to 300° C. . Specific examples of such an organic solvent include tetraethylene glycol, n-octyl ether, and the like.

[Process of Obtaining Nickel-Cobalt Nanoparticle Slurry]

In this step, the complex reaction solution is heated to reduce the nickel complex and/or cobalt complex (nickel ion and/or cobalt ion) to metal to generate nanoparticles. For example, in the first example, when the mixture of the nickel complex and the cobalt complex is considered to be reduced and thermally decomposed, the nickel complex is first thermally decomposed at a lower temperature than the cobalt complex. Reduced by the amine, the nickel particles form a core, on the surface of which a shell of cobalt is formed. Usually, the cobalt complex is thermally decomposed to dissociate the ligands, and Co (0-valent) nanoparticles are formed from the Co ²⁺ complex. In contrast, in the present invention, in the presence of excess oleylamine, using Ni as a catalyst, the ^cobalt complex is reduced from Co to Co (0 valence) at a lower temperature than usual (complex dissociation ).

By heating the complex reaction liquid, the complex reaction liquid is reduced and the complex is thermally decomposed. From the viewpoint of efficiently advancing the reduction reaction, the heating temperature is preferably 200°C or higher, more preferably 220°C or higher. From the viewpoint of efficient treatment, the heating temperature is preferably 270°C or lower, and more preferably about 250°C or lower. For example, taking nickel as an example, in order to generate nanoparticles with a uniform particle size, it is necessary to uniformly and sufficiently generate the nickel complex in the process of obtaining the complex reaction solution, and to obtain the complex compound by heating the complex reaction solution. The nuclei of Ni (zero valence) generated by the reduction of nickel ions in the process of the nickel-cobalt nanoparticle slurry occurred and grew simultaneously. That is, by adjusting the heating temperature of the step of obtaining the complex reaction liquid within the above-mentioned specific range, making it lower than the heating temperature of the step of obtaining the nickel-cobalt nanoparticle slurry, it is easy to generate the particle size and shape. Uniform particles. For example, when the heating temperature is too high in the process of obtaining the complex reaction liquid, the generation of the nickel complex and the reduction reaction to Ni (0 valence) proceed simultaneously, and it may be difficult to obtain the nickel-cobalt nanoparticle slurry. Particles with uniform particle shape are generated in the process. In addition, when the heating temperature in the process of obtaining the nickel-cobalt nanoparticle slurry is too low, the reduction reaction rate to Ni (0 valence) becomes slow and the generation of nuclei decreases, so not only the particles become larger, but also the particles from the nanoparticles become larger. It is also not preferable from the viewpoint of yield.

In this step, the heating source may be other than the oil bath, but is preferably microwave. When the complex reaction liquid is irradiated with microwaves, the microwave penetrates into the complex reaction liquid, and rapid heating and uniform heating are performed by internal heating. Thus, the entire complexation reaction solution can be uniformly brought to the required temperature, and the processes of reduction, nucleation, and nucleation of nickel or cobalt particles can be simultaneously produced in the entire solution. As a result, it can be easily produced in a short time. Monodisperse particles with a narrow particle size distribution. In addition, the use wavelength of the microwave is not particularly limited, for example, it is 2.45 GHz.

The nanoparticle slurry obtained by heating the complexation reaction liquid is, for example, separated by standing to remove the supernatant, washed with an appropriate solvent, and dried to obtain nanoparticles.

In the step of obtaining the nickel-cobalt nanoparticle slurry, the above-mentioned organic solvent may be added to the complexation reaction liquid as needed. In addition, as described above, it is a preferred embodiment of the present invention to use the primary amine used in the complexation reaction as an organic solvent as it is. The solvent added as needed in the step of heating the complex reaction liquid is not particularly limited, for example, alcohols such as octanol (octyl alcohol) or non-polar solvents can be used. As mentioned above, when oleylamine is used as the primary amine, the solvent can be omitted.

The method for producing nanoparticles according to the present embodiment may include any steps other than the above-mentioned steps. In addition, arbitrary treatments such as addition of a surface modifier may also be performed, for example, as described later. In addition, since the method for producing nanoparticles of this embodiment employs a reduction method of heating by microwaves or the like in the step of obtaining the nickel-cobalt nanoparticle slurry, it is not necessary to use a strong reducing agent. However, it does not matter that there is a reducing substance in the complexation reaction solution within the range that does not impair the effect of the 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 nanoparticles, polymer resins such as polyvinylpyrrolidone (PVP), polyethyleneimine, and polyacrylamide can be added, Myristic acid, oleic acid and other long-chain carboxylic acids or carboxylates, etc. However, when the amount of surface modification of the obtained nanoparticles is large, it may be adversely affected as an impurity depending on the application. Therefore, the amount of surface modification of the obtained nanoparticles after washing is preferably as small as possible. For example, when used in a conductive paste for nickel electrodes, if nickel particles are made into a paste and fired at a high temperature, the filling density will decrease, and delamination or cracks may occur. Therefore, it is preferable to set the addition amount of a surface modifier in the range of 0.1-100 mass parts with respect to 100 mass parts of nickel elements total amount. The surface modifier can be added at the stage of the mixture of nickel carboxylate and primary amine in the complex reaction liquid formation process, and can also be added in the complex reaction liquid obtained in the complex reaction liquid formation process, but the timing of addition is preferably complex After the synthesis reaction, or after the generation of nickel nanoparticles.

According to the manufacturing method of the nickel-cobalt nanoparticles of the present embodiment described above, the average particle diameter can be obtained as 10 to 200 nm, which has a Cv value [coefficient of variation: the ratio σ of the average particle diameter (d) and the standard deviation (σ). /d] is a nickel-cobalt nanoparticle having a narrow particle size distribution of 0.01≦σ/d≦0.5 and consisting of a nickel core and a cobalt shell.

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

Regarding the particle diameter of the nanoparticles, a photograph of the nanoparticle powder was taken with a transmission electron microscope (TEM), and 200 of them were randomly selected, and the average particle diameter and standard deviation thereof were obtained. In addition, the Cv value (=σ/d) value was obtained from this result. In addition, the presence or concentration of nickel and cobalt in the obtained particles was confirmed by surface analysis and line analysis using a scanning transmission electron microscope (STEM-EDS) equipped with an energy dispersive X-ray analyzer. Regarding the thickness of the cobalt shell layer, as shown in FIG. 4 , the atomic concentrations of nickel and cobalt on a line crossing one particle were calculated by STEM-EDS. According to this line analysis method, it is impossible to calculate the atomic concentration only in the core portion of the produced spherical particles. That is, the concentration near the particle surface alone can be shown by analysis near the particle surface, but the analysis result near the center of the particle is the sum of the concentration of metal elements on the particle surface and inside (core). Therefore, in the results of this analysis, the average value of the thicknesses of the layers having higher cobalt strength than nickel was taken as the thickness of the cobalt shell layer. The composition of the obtained particles was analyzed by Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES: Inductively Coupled Plasma-Atomic Emission Spectrometry).

(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 heated at 120° C. for 20 minutes under nitrogen flow to obtain a complex reaction liquid. Next, the complex reaction solution was heated to 225° C. with microwaves, and the temperature was maintained for 30 minutes to obtain a nanoparticle slurry. The nanoparticle slurry was separated by standing, and the supernatant was removed, followed by washing with hexane three times. After that, it was dried with a vacuum dryer maintained at 60° C. for 6 hours to obtain nanoparticles.

A TEM (Transmission Electron Microscope, transmission electron microscope) photograph of the obtained nanoparticles is shown in FIG. 2A, and an ED (Electron diffraction: Electron diffraction) pattern is shown in FIG. 2B. Spherical uniform particles with an average particle diameter of 82 nm were formed. In addition, from the ED pattern, it can be seen that the nanoparticles are metals with an fcc structure that does not contain oxides. In addition, the metal composition of the obtained particles was confirmed by ICP-AES. As a result, Ni and Co were 47.6% by mass and 47.3% by mass, respectively, so the mol ratio was Ni/Co=1.0, and the raw material ratio (Ni salt and Co salt Feed ratio (mol%)) is very consistent. A photograph of the STEM-EDS mapping image is also shown in FIG. 3 . Nickel is distributed in the center of the nanoparticle and cobalt is distributed in a large amount on the surface of the nanoparticle. From this, it can be seen that the nanoparticle has a Ni (core)-Co (shell) structure.

In addition, from the results of the line analysis of the particles shown in FIG. 4 , it was found that the thickness of the cobalt shell layer (shell) was about 13 nm. In addition, the results of magnetic saturation (unit: emu/g) obtained by SQUID magnetic susceptibility measurement are shown in FIG. 5 . It can be seen that the magnetic saturation is lower than that of commercially available cobalt nanoparticles (particle size: 50 nm or less, manufactured by Aldrich), but the magnetic saturation is significantly increased 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, except changing the kind of nickel salt and cobalt salt and the kind of heating source and the reaction temperature (heating temperature) in the process of obtaining nanoparticle slurry, according to Example 1 to prepare nanoparticles. The results are shown in Table 1 together with Example 1. In addition, the mol ratio of oleylamine/(Ni salt+Co salt) was 10 in each of Examples and Comparative Examples. In addition, with respect to the heating method of the complexation reaction liquid, except for Example 3 which used an oil bath, microwave heating was performed for all.

In addition, the results of the SQUID magnetic susceptibility measurement of the nickel-cobalt nanoparticles of Examples 1 and 2, the nickel particles of Comparative Example 8, and commercially available cobalt particles are shown in FIG. 5 , and the nickel-cobalt nanoparticles obtained in Example 2 A TEM photograph of the particles is shown in FIG. 6 , and a TEM photograph of the nickel-cobalt nanoparticles obtained in Example 4 is shown in FIG. 7 .

It was confirmed from Table 1 that by using formic acid, acetate, or acetylacetonate as the nickel salt and cobalt salt, nickel-cobalt nanoparticles with an average particle diameter of 10 to 200 nm and a cobalt shell layer of 1 to 50 nm can be obtained. In addition, it was confirmed from FIG. 5 that the nickel-cobalt nanoparticles of Examples 1 and 2 were close to the magnetic saturation of cobalt.

Table 1

(Embodiment 8)

12.5mmol of cobalt formate dihydrate and 25mmol of nickel particles with an average particle size of 100nm and a Cv value of 0.14 (without using cobalt salts, obtain the complex reaction solution from nickel acetate tetrahydrate according to the first example above, and heat it And the prepared particles; Comparative Example 8) was added with 125 mmol of oleylamine, and heated at 120° C. for 20 minutes under a nitrogen stream to obtain a complex reaction solution. Next, the complex reaction solution was heated to 225° C. with microwaves, and the temperature was maintained for 30 minutes to obtain a nickel-cobalt nanoparticle slurry.

The above-mentioned nickel-cobalt nanoparticle slurry was separated by standing, and after removing the supernatant, it was washed three times with hexane. Thereafter, it was dried with a vacuum dryer maintained at 60° C. 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° C. for 20 minutes under a nitrogen stream to obtain a complex reaction liquid. Next, 25 mmol of nickel particles having an average particle diameter of 100 nm and a Cv value of 0.14 were added to the complex reaction liquid (particles obtained by heating the complex reaction liquid obtained from nickel acetate tetrahydrate without using cobalt salts) ; Comparative Example 8) and fully stirred, heated to 225° C. with microwaves, and kept the temperature for 30 minutes to obtain a nickel-cobalt nanoparticle slurry.

The above-mentioned nickel-cobalt nanoparticle slurry was separated by standing, and after removing the supernatant, it was washed three times with hexane. Thereafter, it was dried with a vacuum dryer maintained at 60° C. 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.

As mentioned above, although the embodiment of this invention was described in detail for the purpose of illustration, this invention is not 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)

1. A method for producing nickel-cobalt nanoparticles, the nickel-cobalt nanoparticles having a core formed substantially of nickel, and a shell substantially formed of cobalt covering substantially the entire surface of the core, the The manufacturing method has the following steps: A step of heating a mixture containing nickel salt, cobalt salt and primary amine to obtain a complex reaction solution; and a step of heating the complex reaction solution to obtain a nickel-cobalt nanoparticle slurry. 2. A method for producing nickel-cobalt nanoparticles, the nickel-cobalt nanoparticles having a core formed substantially of nickel, and a shell substantially formed of cobalt covering substantially the entire surface of the core, the The manufacturing method has the following steps: A step of heating a mixture containing nickel particles, cobalt salt and primary amine to obtain a complex reaction solution; and a step of heating the complex reaction solution to obtain a nickel-cobalt nanoparticle slurry. 3. A method for producing nickel-cobalt nanoparticles, the nickel-cobalt nanoparticles having a core formed substantially of nickel, and a shell substantially formed of cobalt covering substantially the entire surface of the core, the The manufacturing method has the following steps: A process of heating a mixture containing cobalt salt and primary amine to obtain a complex reaction solution; and a process of adding nickel particles to the complex reaction solution and heating to obtain a nickel-cobalt nanoparticle slurry. 4. The method for producing nickel-cobalt nanoparticles according to any one of claims 1 to 3, wherein the nickel content of the nickel-cobalt nanoparticles is in the range of 30 to 90% by mass, and the cobalt content is 10% by mass. ~70% by mass, the average particle diameter is in the range of 10~200nm, and the thickness of the shell is in the range of 1~50nm. 5. The method for producing nickel-cobalt nanoparticles according to claim 1, wherein the nickel salt has a straight-chain carboxylic acid group with 1 to 3 carbon atoms and a group represented by the following structural formula (1) any of the Wherein, the substituents Ra to Rc are groups selected from methyl, ethyl, phenyl and halogen, and the substituents Ra to Rc may be the same or different from each other. 6. according to the manufacture method of the described nickel-cobalt nano-particle according to any one of claim 1～3, wherein, described cobalt salt has carbon atom number and be the linear carboxylic acid group of 1～3 and following structural formula (1 ), any of the groups shown in ), Wherein, the substituents Ra to Rc are groups selected from methyl, ethyl, phenyl and halogen, and the substituents Ra to Rc may be the same or different from each other. 7. the manufacture method of nickel-cobalt nanoparticle according to claim 5, wherein, the linear carboxylic acid group that described carbon number is 1～3 is formic acid group or acetic acid group, shown in described structural formula (1) The group is the acetylacetonate ligand. 8. the manufacture method of nickel-cobalt nanoparticle according to claim 6, wherein, the linear carboxylic acid group that described carbon number is 1～3 is formic acid group or acetic acid group, shown in described structural formula (1) The group is the acetylacetonate ligand. 9. The method for producing nickel-cobalt nanoparticles according to any one of claims 1 to 3, wherein microwaves are used as heating means in the step of obtaining the nickel-cobalt nanoparticle slurry.