JP7164391B2 - Method for producing copper nanowires - Google Patents

Description

The present disclosure relates to a method for manufacturing copper nanowires.

Metal nanowires are extremely fine elongated materials with a diameter of usually 20 nm or less and an aspect ratio (that is, length/diameter ratio) of usually 100 or more. It is used for applications such as high-performance ink (ink for electronic circuits, etc.) and high thermal conductivity coolant for automobiles. Among them, copper nanowires have the advantage of being relatively inexpensive while having good electrical and thermal conductivity.

Patent Document 1 describes a method for producing copper nanowires, characterized by mixing a copper salt, a polyol and an alkylamine and reducing the copper salt in the presence of chloride ions.

Patent Document 2 discloses copper nanorods or nanowires by heating metallic copper and a molybdenum substrate coated with a carbon thin film to a temperature range of 800 to 850° C. in vacuum to generate copper nanorods or nanowires. A method of making nanowires is described.

Patent Document 3 describes a first step of reacting a precursor containing at least a copper complex with water in supercritical or subcritical carbon dioxide to form a nanowire-like hydroxide, and and a second step of reducing.

In Patent Document 4, metal nanowires flow along with the flow of a liquid medium in a tubular channel having a porous ceramic filter having an average pore diameter of 1.0 μm or more by a mercury intrusion method on the channel wall surface, and the flow Some of the metal nanowires are discharged out of the tubular channel through the porous ceramic filter together with a part of the liquid medium, and the metal nanowires that have flowed through the channel without being discharged out of the tubular channel. A method for producing metal nanowires is described, in which the is recovered.

JP 2014-148716 A JP 2004-263318 A JP 2011-168817 A JP 2016-055283 A

In copper nanowire products, there are usually impurities such as granular or low aspect ratio copper crystals other than the desired copper nanowires. In order for copper nanowires to exhibit high electrical conductivity and thermal conductivity per unit mass, it is necessary to reduce such impurities in copper nanowire products, but the methods described in Patent Documents 1 to 3 However, there is still room for improvement in the purity of copper nanowires (that is, the desired ratio of copper nanowires in the resulting copper crystals). On the other hand, the method described in Patent Document 4 relates to providing a high-purity metal nanowire product. is complicated.

Accordingly, an object of the present disclosure is to provide a method for producing copper nanowires, which is a simple process and capable of producing copper nanowires with high yield and high purity.

Aspects of the present disclosure include the following aspects.
<Aspect 1>
Mixing at least a copper (II) salt, a metal chloride, a reducing agent, and water to prepare liquid A;
Mixing at least an alkylamine, an unsaturated fatty acid, and ethanol to prepare a liquid B;
Mixing A liquid and B liquid to prepare C liquid, and heating C liquid to generate copper nanowires,
including
A method for producing copper nanowires, wherein the ratio of Cl ⁻ ion concentration to Cu ²⁺ ion concentration [Cl ⁻ ]/[Cu ²⁺ ] in the solution A is 3.0 or more and 5.0 or less.
<Aspect 2>
A method according to aspect 1 above, wherein the metal chloride is sodium chloride.
<Aspect 3>
3. The method according to aspect 1 or 2 above, wherein the reducing agent is glucose.

According to the present disclosure, it is possible to provide a method for producing copper nanowires, which is a simple process and capable of producing copper nanowires with high yield and high purity.

FIG. 1 shows scanning electron microscope (SEM) images of copper crystals obtained in Examples 1 and 2 and Comparative Examples 1-5.

Although exemplary aspects of the present disclosure will be described below, the present disclosure is not limited to the following aspects.
One aspect of the present disclosure is
Mixing at least a copper (II) salt, a metal chloride, a reducing agent, and water to prepare liquid A;
Mixing at least an alkylamine, an unsaturated fatty acid, and ethanol to prepare a liquid B;
Mixing A liquid and B liquid to prepare C liquid, and heating C liquid to generate copper nanowires,
including
Provided is a method for producing copper nanowires, wherein the liquid A has a ratio of Cl ⁻ ion concentration to Cu ²⁺ ion concentration [Cl ⁻ ]/[Cu ²⁺ ] of 3.0 or more and 5.0 or less.

The generation mechanism of copper nanowires is considered as follows. That is, when copper ions and a reducing agent coexist, the copper ions are reduced to form copper crystal nuclei. When copper ions and a reducing agent are further applied to the crystal nuclei in the presence of a morphology control agent, anisotropic grains are formed due to the contribution of the morphology control agent when crystal growth occurs due to the precipitation of copper on the crystal nuclei. Grown, the anisotropic particles grow into nanowires by further reductive deposition of copper ions in the presence of a morphology control agent.

In order to obtain copper nanowires with few impurities in a simple process with high yield and high purity, the present inventors use part of the copper (II) salt as a raw material for copper nanowires as a material for crystal nuclei. that the reduction reaction from copper ions to copper proceeds slowly (that is, excessive generation of crystal nuclei is suppressed), thereby reducing the generation of impurities itself; The inventors focused on the fact that by performing the etching in a system in which the ion concentration ratio is controlled within a specific range, moderate oxidative etching of the precipitated copper crystals is caused to selectively generate copper nanowires of a desired shape.

That is, in the method according to one aspect of the present disclosure, a copper (II) salt, which is a raw material for copper nanowires, is combined with a metal chloride, a reducing agent, an alkylamine, and an unsaturated fatty acid under hydrothermal conditions, A moderate rate of reductive deposition of copper ions and moderate progress of oxidative etching of the deposited copper crystals occurs. Thereby, according to the said method, the copper nanowire with few impurities can be manufactured with a high yield by a simple process. Without being bound by theory, it is believed that copper ions form stable complexes with alkylamines and unsaturated fatty acids to facilitate the slow reduction of copper ions to copper under hydrothermal conditions.

Each step of the method according to one aspect is described below.

<Preparation of liquid A>
Liquid A is obtained by mixing at least a copper (II) salt, a metal chloride, a reducing agent, and water. In one aspect, liquid A contains a water-soluble component among the components used in the method for producing copper nanowires of the present disclosure.

Copper (II) salts include copper chloride, copper nitrate, copper sulfate, copper phosphate, copper carbonate, copper carboxylate (e.g., copper acetate, copper oxalate, etc.), etc. Copper chloride and copper nitrate are particularly preferred. .

In one aspect, the amount of copper (II) salt in liquid A is 5 mmol/L or more, or 10 mmol/L or more, or 20 mmol/L or more, or 30 mmol/L or more, from the viewpoint of efficient production of copper nanowires. , or 40 mmol/L or more, and from the viewpoint of suppressing generation of impurities, it is 500 mmol/L or less, or 300 mmol/L or less, or 100 mmol/L or less, or 80 mmol/L or less, or 60 mmol/L or less. In one aspect, the amount of copper (II) salt in solution C is preferably 5 mmol/L or more, or 10 mmol/L or more, or 20 mmol/L or more, or 30 mmol/L or more, preferably 500 mmol/L or less, Alternatively, it is adjusted to be 300 mmol/L or less, 100 mmol/L or less, 80 mmol/L or less, 60 mmol/L or less, or 50 mmol/L or less.

Metal chlorides are used as the chloride ion source. In typical embodiments, the metal chloride is a chloride of a metal other than copper. Examples of metal chlorides include sodium chloride, potassium chloride, calcium chloride and the like, preferably sodium chloride. Chloride ions have the effect of redissolving the surface of copper crystals produced by the reduction of copper ions (also referred to as oxidative etching in the present disclosure). Oxidative etching mainly re-dissolves impurities (that is, low-aspect-ratio copper crystals) in copper crystals, and contributes to improving the ratio of desired copper nanowires.

In one embodiment, the amount of metal chloride in liquid A is 5 mmol/L or more, or 10 mmol/L or more, or 30 mmol/L or more, or 50 mmol/L or more, from the viewpoint of good progress of oxidative etching. , 1000 mmol/L or less, or 500 mmol/L or less, or 300 mmol/L or less, or 200 mmol/L or less, or 150 mmol/L or less. In one aspect, the amount of metal oxide in solution C is preferably 10 mmol/L or more, or 20 mmol/L or more, or 40 mmol/L or more, or 60 mmol/L or more, preferably 1000 mmol/L or less, or 500 mmol/L. /L or less, or 200 mmol/L or less, or 150 mmol/L or less, or 100 mmol/L or less.

In solution A, if the ratio of the chloride ion concentration to the copper (II) ion concentration is too large, not only the impurities but also the desired copper nanowires are etched, and moreover, the granular particles are more stable than the copper nanowires. The percentage of copper nanowires in the recovered copper crystals becomes low due to the fact that they remain without being etched. On the other hand, if the above ratio is too small, copper crystals are formed even if the copper (II) salt concentration is relatively low, but only a part of the impurities are redissolved, resulting in a low ratio of copper nanowires in the recovered copper crystals. . From this point of view, in liquid A, the ratio of chloride ion concentration to copper (II) ion concentration [Cl ⁻ ]/[Cu ²⁺ ] is 3.0 or more and 5.0 or less, preferably 3.0 4.0 or less. In liquid A, copper (II) ions are derived from copper (II) salts, and chloride ions are derived from metal chlorides. Copper chloride is included in the concepts of both copper(II) salts and metal chlorides, providing both copper(II) ions and chloride ions in Part A.

The chloride ion concentration in liquid A is preferably 10 mmol/L or more, or 50 mmol/L or more, or 100 mmol/L or more, or 150 mmol/L or more, from the viewpoint of good progress of oxidative etching. From the viewpoint of avoiding oxidative etching and producing copper nanowires at a high yield, it is preferably 1000 mmol/L or less, 500 mmol/L or less, 300 mmol/L or less, or 250 mmol/L or less. In one aspect, the chloride ion concentration in solution C is preferably 20 mmol/L or more, or 50 mmol/L or more, or 100 mmol/L or more, or 130 mmol/L or more, or 150 mmol/L or more, preferably 2000 mmol/L or more. L or less, or 1000 mmol/L or less, or 500 mmol/L or less, or 300 mmol/L or less, or 250 mmol/L or less, or 200 mmol/L or less.

Examples of the reducing agent include reducing sugars such as glucose, fructose, glyceraldehyde, lactose, arabinose and maltose, and polyols such as ethylene glycol, propylene glycol and diethylene glycol, preferably glucose.

The reducing agent concentration in liquid A is 5 mmol/L or more, or 10 mmol/L or more, or 20 mmol/L or more, or 30 mmol/L or more, or 40 mmol/L or more, and 500 mmol/L or less, or 300 mmol/L or less. , or 100 mmol/L or less, or 80 mmol/L or less, or 60 mmol/L or less. In one aspect, the amount of the reducing agent in solution C is preferably 5 mmol/L or more, or 10 mmol/L or more, or 20 mmol/L or more, or 30 mmol/L or more, preferably 500 mmol/L or less, or 300 mmol/L. L or less, or 100 mmol/L or less, or 80 mmol/L or less, or 60 mmol/L or less, or 50 mmol/L or less.

In liquid A, the molar ratio of the reducing agent to the copper (II) salt is preferably 0.5 or more, or 0.7 or more, or 0.8 or more, or 0.9, from the viewpoint of good progress of the reduction reaction. or more, or 0.95 or more, and from the viewpoint of suppressing excessive formation of crystal nuclei, it is preferably 1.5 or less, or 1.3 or less, or 1.2 or less, or 1.1 or less, or 1.1. 05 or less.

Liquid A can be prepared by mixing the above components at room temperature, for example, under stirring. It is not excluded that the liquid A contains optional components other than the above components within a range that does not impair the effects of the present invention.

<Preparation of liquid B>
Liquid B is obtained by mixing at least alkylamine, unsaturated fatty acid and ethanol. In one aspect, the B liquid contains water-insoluble and ethanol-soluble components among the components used in the method for producing copper nanowires of the present disclosure.

Alkylamine contributes to suppression of excessive formation of crystal nuclei. Although not bound by theory, alkylamine suppresses the formation of crystal nuclei by forming a stable complex with copper ions together with unsaturated fatty acids in solution C, which is a mixture of solutions A and B. may have contributed to The number of carbon atoms in the alkyl group in the alkylamine is preferably 5 or more, or 10 or more, or 15 or more, and preferably 30 or less, or 25 or less, or 20 or less, from the viewpoint of obtaining a good stabilizing effect of copper ions. is. In a preferred embodiment, the alkylamine is oleylamine.

In one embodiment, the amount of alkylamine in liquid B is preferably 5 parts by volume or more, or 10 parts by volume or more, or 20 parts by volume or more, or 30 parts by volume or more with respect to 100 parts by volume of ethanol in liquid B. or 40 volume parts or more, or 50 volume parts or more, preferably 500 volume parts or less, or 300 volume parts, or 100 volume parts or less, or 80 volume parts or less, or 70 volume parts or less. In one aspect, the amount of alkylamine is preferably 1 or more, or 3 or more, or 5 or more, or 6 or more, preferably 20 or less, or 15 or less, or 10 or less, or 8 or less, or 7 or less.

Unsaturated fatty acids contribute to suppression of excessive formation of crystal nuclei. Although not bound by theory, unsaturated fatty acids form stable complexes with alkylamines and copper ions in liquid C, which is a mixture of liquids A and B, to generate crystal nuclei. may contribute to suppression. The number of carbon atoms of the unsaturated hydrocarbon group in the unsaturated fatty acid is preferably 5 or more, or 10 or more, or 15 or more, and preferably 30 or less, or 25 or less, from the viewpoint of obtaining a good stabilizing effect of copper ions. , or 20 or less. In preferred embodiments, the unsaturated fatty acid is oleic acid.

In one aspect, the amount of unsaturated fatty acid in liquid B is preferably 0.05 parts by volume or more, or 0.1 parts by volume, or 0.3 parts by volume or more with respect to 100 parts by volume of ethanol in liquid B. or 0.5 volume parts or more, preferably 5.0 volume parts or less, or 3.0 volume parts or less, or 1.0 volume parts or less, or 0.7 volume parts or less. In one aspect, the amount of unsaturated fatty acid is preferably 0.01 or more, or 0.03 or more, or 0.05 or more, preferably 0.2 or less, or a molar ratio to copper ions in solution C, or The amount is adjusted to 0.15 or less, or 0.1 or less, or 0.08 or less.

Liquid B can be prepared by mixing the above components at room temperature, for example, under stirring. It is not excluded that the B liquid contains optional components other than the above components within the range that does not impair the effects of the present invention.

<Preparation of solution C>
Next, liquid A, which is an aqueous solution, and liquid B, which is an ethanol solution, are stirred and mixed to prepare liquid C. The volume ratio of liquid A: liquid B is preferably 1:1 to 10:1, or 3:1 to 8:1, or 5:1 to 7:1. The mixing temperature may generally be from room temperature to 70° C., eg 50° C., the mixing time may generally be 1 hour to 10 hours, eg 6 hours, and the mixing pressure may generally be normal pressure. In one aspect, Liquid C is obtained as a uniform emulsion. In one aspect, in solution C, copper ions derived from copper (II) salt and alkylamine and unsaturated fatty acid form a complex.

<Generation of copper nanowires>
Next, the liquid C is heated to advance the reduction reaction of copper ions and deposit copper nanowires. In a typical embodiment, heating is under pressure using a pressure vessel. The heating temperature is usually 140-170° C., and the heating time is usually 6-36 hours. The resulting copper crystals are cooled and washed with deionized water, hexane, or the like to obtain the desired copper nanowires.

In a typical embodiment, the copper nanowires have a diameter of 20 nm or less and an aspect ratio (length/diameter ratio) of 100 or more. The aspect ratio (length/diameter ratio) of the copper nanowires is preferably 150 or more, or 200 or more, or 500 or more, or 1000 or more from the viewpoint of obtaining excellent conductive performance. It is preferably 10,000 or less, or 5,000 or less, or 3,000 or less. In one aspect, the ratio of the number of copper crystals having a diameter of 20 nm or less and an aspect ratio of 100 or more to the total number of copper crystals after washing is, for example, 75% or more, or 80% or more, without any special impurity removal treatment. or 85% or more, or 90% or more. The number and size of copper crystals can be measured on scanning electron microscope (SEM) images.

EXAMPLES Hereinafter, the present disclosure will be described more specifically with reference to Examples, but the present disclosure is not limited to these Examples.

<Preparation of liquid A>
In 80 ml of ^deionized water, an amount of ^copper (II) chloride dihydrate ⁽ Cu ²⁺ source and Cl ⁻ source) (but not used in Comparative Example 1), copper (II) nitrate trihydrate (as Cu ²⁺ source), and sodium chloride (as Cl ⁻ source), and as reducing agent Glucose (4 mmol) was added and dissolved by sufficiently stirring at room temperature to obtain liquid A.

<Preparation of liquid B>
To 14 ml of ethanol, 8 ml of oleylamine (about 24.32 mmol) and 0.08 ml of oleic acid (about 0.25 mmol) were added and thoroughly stirred at room temperature for dissolution to obtain liquid B.

<Preparation of solution C>
Liquid A and liquid B were mixed and mixed with stirring at 50° C. for 12 hours using a hot stirrer to obtain liquid C.

<Generation of copper nanowires>
Liquid C was placed in a stainless steel pressure vessel with a Teflon (registered trademark) inner cylinder, placed in an oven, heated at a constant temperature of 150° C. for 6 hours, and then cooled to room temperature. The contents were centrifuged at 12,000 rpm for 15 minutes to collect the precipitate, and washing operation (deionized water once, hexane three times) was performed to obtain copper crystals.

Scanning Electron Microscope (SEM) Observation After the surface treatment of the copper crystal, it was dispersed in a fluorocarbon (FC) fluid to obtain a sample for SEM observation.

Using a scanning electron microscope (SEM), the morphology was observed at an acceleration voltage of 15 kV, and the morphology image shown in FIG. 1 was obtained. In the morphological image, the aspect ratio of the copper crystal was measured. Copper crystals with an aspect ratio of 100 or more were determined to be nanowires. The ratio of the number of copper crystals determined to be nanowires among the total number of copper crystals in the measurement field was defined as the nanowire ratio (%), and the value obtained by subtracting the nanowire ratio (%) from 100% was defined as the impurity ratio (%). Table 1 shows the results.

In Comparative Example 1 in which only copper (II) nitrate trihydrate was used as the copper source and the [Cl ⁻ ]/[Cu ²⁺ ] ratio of solution A was 0, no copper nanowires were obtained, and only cubic particles were obtained. was generated. Further, in Comparative Examples 2 to 4 in which the [Cl ⁻ ]/[Cu ²⁺ ] ratio was too low and in Comparative Example 5 in which the [Cl ⁻ ]/[Cu ²⁺ ] ratio was too high, the ratio of nanowires was low. On the other hand, in Examples 1 and 2 in which the [Cl ⁻ ]/[Cu ²⁺ ] ratio was 3.0 and 4.0, while recovering the entire amount of the precipitated copper crystals (that is, without removing impurities), Nanowire ratios as high as 80% and 90% could be achieved. That is, in Examples 1 and 2, it can be seen that the desired copper nanowires could be produced with high yield and high purity.

Claims (3)

Mixing at least a copper (II) salt, a metal chloride, a reducing agent, and water to prepare liquid A;
Mixing at least an alkylamine, an unsaturated fatty acid, and ethanol to prepare a liquid B;
Mixing A liquid and B liquid to prepare C liquid, and heating C liquid to generate copper nanowires,
including
A method for producing copper nanowires, wherein the ratio [Cl ⁻ ]/[Cu ²⁺ ] of Cl ⁻ ion concentration to Cu ²⁺ ion concentration in the liquid A is 3.0 or more and 5.0 or less. 2. The method of claim 1, wherein the metal chloride is sodium chloride. 3. The method of claim 1 or 2, wherein the reducing agent is glucose.

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