JP6480778B2 - Method of manufacturing copper nanostructure - Google Patents

Description

  The present invention relates to a method for producing a wire-like copper nanostructure by reduction precipitation reaction in an aqueous alkaline solvent.

  In the present specification, fine metal particles having a shape elongated in one direction and having a minor axis length of 1000 nm or less and an aspect ratio represented by a major axis length / minor axis length of 10 or more are described as “wire-like metal nanostructure Say "body".

  The wire-like metal nanostructure is expected to be used in various applications such as a transparent conductive film, a heat dissipation sheet, a conductive paint, an electrode for a solar cell, and a catalyst. Among them, silver nano-structures have been developed for mass production of thin and long wire-shaped ones, and have been put to practical use in applications such as touch panels. However, silver is an expensive metal. Silver also has migration problems. Furthermore, the reflection of light specific to silver causes a reduction in clear visibility (haze characteristic) of a display such as a touch panel.

  On the other hand, copper is mentioned as an element which can synthesize | combine a wire-like nanostructure with metals other than silver. However, it is not always easy to synthesize wire-like copper nanostructures on an industrial scale with high productivity.

  For example, Patent Documents 1 to 3 disclose a method of reducing and depositing copper in the form of a wire in an alkaline aqueous solution. According to these methods, it is possible to synthesize a wire-like copper nanostructure in a one-step reduction process. However, the amount (feed amount) of copper as a raw material that can be added to the solvent before the reaction is very small. For mass production of copper nanostructures, a large amount of solution is required depending on the production volume. In order to increase the production volume per charge, it is also necessary to increase the scale of the reaction vessel.

Patent Document 4 discloses a method of reducing and depositing copper in the form of a wire in a solution containing a copolymer having a polyethyleneimine skeleton and a polyethylene glycol skeleton. This method requires a step of synthesizing the above-mentioned specific copolymer.
Patent Document 5 discloses a method of reducing and depositing copper in the form of a wire in a polyol solvent. In this method, it takes a long time to reduce and deposit metallic copper. In the example, metallic copper is deposited over 5 days.

International Publication No. 2013/187384 Japanese Patent Publication No. 2013-513220 Publication JP, 2014-37602, A JP, 2013-194290, A JP, 2014-148716, A

As described above, various techniques for synthesizing wire-like copper nanostructures have been proposed, but there are problems to be improved in order to synthesize them on an industrial scale with good productivity.
The present invention discloses a new synthesis method that can efficiently obtain a large amount of wire-like copper nanostructures in one charge reaction.

In the present invention, copper (II) is prepared by heating an aqueous alkaline solution containing a water-soluble copper (II) compound and an alkylglyoxime (RC (N = OH) C (N = OH)-R '). Is reduced to copper (I) to obtain a solution in which copper (I) is present (first reduction),
Adding a reducing agent to a solution containing copper (I) generated by the first reduction, and depositing and growing a wire-like copper nanostructure (second reduction),
A method of producing a copper nanostructure is provided.

  It has been found that it is simple and extremely effective to use the change in color of the solution as a method of determining the timing of addition of the reducing agent. That is, the method of adding a reducing agent to the liquid in which presence of copper (I) produced | generated by 1st reduction was confirmed by monitoring the change of the color of a liquid can be employ | adopted suitably. In addition, it is also effective to add a reducing agent to a solution in which the presence of copper (I) generated in the first reduction is confirmed by measuring the change in absorbance of the solution within a wavelength range of 500 to 800 nm. .

It is more preferable to set the time at which the first reduction proceeds until the absorbance change rate ΔAbs determined by (X) below reaches a range of 60 to 95% as the time of adding the reducing agent.
(X) for a sample S ₁ of the first reduction before starting the liquid sample S ₀ and the first liquid time after initiation reduction, then diluted to 5 to 50 times by weight in each aqueous solution of sodium hydroxide, spectral When the absorbance integral value I of the absorption spectrum at 612 to 624 nm is measured under the same conditions by absorptiometry using a photometer, the value determined by the following equation (1) is taken as the absorbance change rate ΔAbs of the solution after the reduction starts .
Δ Abs (%) = (I ₀ −I ₁ ) / I ₀ × 100 (1)
Here, I ₀ and I ₁ are the absorbance integrals I for the sample S ₀ of the solution before the start of reduction and the sample S ₁ of the solution after the start of the reduction, respectively.
As a spectrophotometer, an ultraviolet and visible spectrophotometer can be used.

  In the actual operation, for example, by obtaining the relationship between the elapsed time and the ΔAbs in advance according to the synthesis conditions by preliminary experiments, the absorbance change rate determined by the above (X) can be determined without performing the absorbance measurement for each operation charge. A second reducing agent can be added to the solution where ΔAbs is 60 to 95%.

As the second reducing agent, for example, one or more of hydrazine, a hydrazine compound, glucose and ascorbic acid can be used.
The aqueous alkali solution to be subjected to the first reduction can be, for example, a 40-48% by mass aqueous solution of sodium hydroxide mixed with a water-soluble copper (II) compound and an alkylglyoxime.

  The heating temperature at which the first reduction is performed is preferably 85 ° C. or more and the boiling point or less of the liquid, and more preferably 100 ° C. or more and 115 ° C. or less. The second reduction is preferably performed at a temperature of 50 ° C. or more and a boiling point or less.

Examples of the alkylglyoxime include dimethylglyoxime (CH ₃ C (N = OH) C (N = OH) CH ₃ ). In this case, the molar ratio [DGO] / [Cu (II)] of dimethylglyoxime and copper (II) in the alkaline aqueous solution to be subjected to the first reduction is preferably 0.3 to 1.0. Further, the molar ratio [Cu (II)] / [OH ⁻ ] of copper (II) and hydroxide ion can be, for example, 1 × 10 ⁻⁴ to 2 × 10 ⁻² .

  According to the present invention, it is possible to significantly increase the preparation amount of copper with respect to the amount of solvent, as compared with the conventional general method of reducing and precipitating a wire-like copper nanostructure in an alkaline aqueous solution solvent. The recovery rate of copper recovered as a copper nanostructure is also high, for example, about 99% with respect to the input amount. Since a small amount of solvent is required to obtain a certain amount of wire-like copper nanostructures, mass production using relatively small scale reactors is possible. Also, no special copolymer is required. The reaction time is also short, around 1 h. Thus, the present invention is suitable for industrial mass production of wire-like copper nanostructures.

The figure which showed typically the formation reaction of the copper (II) complex which makes an alkyl glyoxime a ligand. The figure for demonstrating the reaction mechanism which the intermediate body A produces | generates by 1st reduction | restoration. The figure for demonstrating the postulated route of the case (case outside this invention object) where copper (I) of the intermediate body A is reduce | restored to metallic copper by intramolecular reduction. The figure for demonstrating the assumption route of the case (the case of the present invention) where copper (I) of intermediate A is reduced to metallic copper by external reduction with a reducing agent. SEM photograph of the copper nanostructure obtained in Example 1. FIG. SEM photograph of the copper nanostructure obtained in Example 2. SEM photograph of the copper nanostructure obtained in Example 3. SEM photograph of the copper nanostructure obtained in Example 4. SEM photograph of the copper nanostructure obtained in Example 5. SEM photograph of the copper nanostructure obtained in Example 6. SEM photograph of the copper nanostructure obtained in Example 7. SEM photograph of the copper nanostructure obtained in Comparative Example 1. SEM photograph of the copper nanostructure obtained in Comparative Example 2.

In the present specification, divalent copper is described as "copper (II)" and monovalent copper is described as "copper (I)".
The reaction mechanism by which the wire-like copper nanostructure is synthesized according to the present invention is not necessarily elucidated, but at present it is considered as follows.

[First reduction]
When a water-soluble copper (II) compound and an alkylglyoxime are mixed in an aqueous solvent, the alkylglyoxime is coordinated to copper (II) with two nitrogen atoms serving as coordination sites to form a copper (II) complex. It is conceivable (Fig. 1). When the copper (II) by heating the complex in alkaline solution to impart thermal energy, hydroxide ions OH present in large amounts in the liquid ^- is a copper (II) in coordinating one alkyl glyoxime " The reaction for depriving the proton (H ⁺ ) from —O—H ”occurs (symbol a in FIG. 2), and a double bond is formed between O and N (symbol b in FIG. 2). At the same time, while N and C become single bonds, double bonds are formed between carbon atoms, and the electrons are conjugated and stabilized (symbol c in FIG. 2). At the same time, another double bond of N and C becomes a single bond, whereby the surplus N unpaired electrons are shared with Cu, and copper (II) is reduced to copper (I) (Fig. 2 symbol d). Thus, an intermediate A having copper (I) is formed. Intermediate A has a structure having a nitroso group (-N = O) at one end of the skeleton derived from alkylglyoxime. This first reduction can be said to be "intramolecular reduction" because it is a reduction by giving electrons to copper (II) which were present in the molecule of the copper (II) complex.

Examples of the alkylglyoximes include dialkylglyoximes such as dimethylglyoxime and diethylglyoxime.
Examples of water-soluble copper (II) compounds include copper (II) chloride, copper (II) nitrate, copper (II) sulfate, copper (II) acetate and the like.

To advance the intramolecular reduction of the large amount of hydroxide ions only enough to take the proton from "-O-H" - there is a need exists in the liquid ^(OH). Therefore, it is desirable to use a strong alkaline aqueous solution as a solvent. As the alkali substance, an alkali metal hydroxide such as KOH or NaOH, a mixture of dimethylformamide and a diol, or the like may be used. For example, in the case of NaOH, it is preferable to add a water-soluble copper (II) compound and an alkylglyoxime to it using a 40 to 48% by mass aqueous solution of sodium hydroxide as a solvent.

  In addition, thermal energy is required to cause the reaction of depriving protons from the above "-O-H". If the temperature of the solution is low, the reaction does not occur, or the progress of the reaction takes a long time and is not practical. As a result of various studies, it is preferable to heat the temperature of the solution to 85 ° C. or more, and more preferably 90 ° C. or more. As the temperature increases, the reaction rate also increases, but it becomes difficult to accurately determine the reducing agent addition timing for shifting to the second reduction. The first reduction can be performed at a temperature equal to or lower than the boiling point by using a method of monitoring the color of the liquid, which will be described later. In consideration of both the reaction efficiency and the determination of the reducing agent addition time, for example, when using dimethylglyoxime, it is more preferable to maintain the temperature range of 100 ° C. or more and 115 ° C. or less.

The molar ratio [alkylglyoxime] / [Cu (II)] of alkylglyoxime and copper (II) in the aqueous alkali solution to be subjected to the first reduction may be set in the range of 0.3 to 2.5. It is more preferable to set it as the range of 0.5-1.0.
The molar ratio [Cu (II)] / [OH ⁻ ] of copper (II) and hydroxide ion in the aqueous alkali solution to be subjected to the first reduction is set in the range of 1 × 10 ⁻⁴ to 2 × 10 ⁻² do it. More preferably, it is in the range of 1 × 10 ⁻³ to 1 × 10 ⁻² .

[Second reduction]
In the present specification, the reduction process from copper (I) to metallic copper produced in the first reduction is referred to as a second reduction. When constant heat energy is continuously applied to the above intermediate A as it is, intramolecular reduction of Cu (I) to metallic copper proceeds. However, the copper nanostructure obtained thereby is in the form of a contaminating substance in which particles, rods, wires and the like are mixed. Therefore, in the present invention, a technique is applied that avoids the second reduction by intramolecular reduction.

Here, first, a pattern in which the second reduction proceeds by the intramolecular reduction (a reduction aspect which is not the object of the present invention) will be described.
When heat energy is continuously applied to the solution containing the intermediate A generated in the first reduction, protons (H ⁺ ) are also in the solution from the non-nitroso group “-O-H”. of OH ^- lost to, it places the electronic in the molecule. The electrons are supplied to copper (I) and copper (I) is reduced to metallic copper. At this time, the skeleton derived from the alkylglyoxime becomes O = N−C = C−N = O, and forms a π conjugated system to be stabilized. However, since it is an intramolecular reduction and the O = N-C = C-N = O skeleton is formed by releasing electrons to a Cu atom, the electron density of the π conjugated system is low, and a nitroso group is formed first. It is believed that the N in the form of N tends to be difficult to adsorb to metallic copper. Therefore, the probability that a case (Pathway I in FIG. 3) in which the O = N-C = C-N = O skeleton is adsorbed to the metallic copper only at one N portion is selected is large. There are also cases where a case (Pathway II in FIG. 3) of adsorbing to metal copper at two N parts is selected.

  In Pathways I and II, the electron density of the conjugated system is low, and the probability of capping with N as a coordination site is low. Besides this, capping with an oxygen atom as a coordination site is also possible. The case where one N of O = N-C = C-N = O skeleton capping one (110) face of a copper crystal and the case where one N of a (001) face is capped can be assumed. It is difficult to precisely control the selectivity of these two adsorption modes. Therefore, the copper nanostructure obtained is in the form of a commingled form in which particles, rods, wires and the like are mixed, and the shape of the nanostructure can not be controlled uniformly.

Therefore, in the present invention, a reducing agent is added at the stage where intermediate A is formed, and the copper (I) constituting intermediate A is reduced to metallic copper by the electrons supplied from the reducing agent. Since the electrons are supplied from the outside of the molecule of intermediate A, this reduction mode can be called "external reduction" as opposed to the above-mentioned "intramolecular reduction". In the external reduction, as shown in FIG. 4, electrons are directly supplied from the outside to the Cu atom of intermediate A (symbol a in FIG. 4), and the skeleton derived from alkylglyoxime is O ⁻ —N = C—C = N -O ^- a form of. Since the electrons are received from the outside, the electron density of the π conjugated system increases. Along with that, the electron density of N atoms also increases, and it becomes easy to be adsorbed to metallic copper evenly by two N parts (Pathway III in FIG. 4). In this case, as the reduction of copper (I) to metallic copper proceeds, the O ^-- N = C-C = N-O ^- skeleton (glyoxime) is regenerated, and this skeleton is the (100) plane of the copper crystal. It is considered that the tendency for capping is strong. As a result, growth of the (100) plane is preferably inhibited, and crystal growth occurs preferentially on the (110) plane, and a wire-like copper nanostructure is obtained.

As the reducing agent, various ones capable of reducing copper (I) constituting the intermediate A to metallic copper are targeted. At present, it has been confirmed that good results can be obtained by using one or more of hydrazine, a hydrazine compound, glucose and ascorbic acid. Future investigations will find the applicability of more types of reductants. Hydrazine compounds include hydrazine hydrate (N ₂ H ₄ · H ₂ O), neutral hydrazine sulfate ((N ₂ H ₂ ) ₂ · H ₂ SO ₄ ), hydrazine sulfate (N ₂ H ₄ · H) ₂ SO ₄ ) etc. can be illustrated. The addition amount of the reducing agent is preferably set in the range of 0.5 to 2.0 molar equivalents in terms of chemical equivalents in the case of reducing all the copper atoms present in the solution to one to zero. 5-1.0 molar equivalent is more preferable.

  In order to lead to Pathway III without advancing the second reduction to Pathway I or II, the timing of addition of the reducing agent is important. If the reducing agent is added too early, it is reduced from copper (II) to metallic copper by the reducing agent and can not proceed to Pathway III. If the timing of addition of the reducing agent is too late, it will be easy to proceed to the pathway I or II reduction route, especially when the temperature is high. Therefore, it is desirable to introduce a reducing agent at a time when intermediate A is sufficiently formed while controlling the temperature.

  It was found that the method of monitoring the color of the solution was effective as a method of confirming that intermediate A was generated, that is, copper (I) was generated in the first reduction. The copper (II) ion aqueous solution exhibits a deep blue color (wavelength 500 to 800 nm). On the other hand, the copper (I) ion aqueous solution is transparent. Thus, while the color of the solution begins to fade, the first reduction is underway while it is changing towards transparency. It is necessary to wait for at least the first reduction to start before adding the reducing agent. When a large amount of copper (II) remains, the addition of a reducing agent increases the amount of copper nanostructures that are reduced directly to copper metal copper without using Pathway III. The yield is poor. Therefore, it is preferable to add a reducing agent at the time when the color of the liquid is discolored and becomes clear. However, as described above, the higher the temperature of the solution, the easier it is to go to the pathway of Pathway I or II. The solution is suspended when metallic copper is formed. It is necessary to add the reducing agent at the latest before the solution begins to suspend.

  It is effective to measure the absorbance of the solution in order to quantitatively know the degree of change in the color of the solution. As a result of various studies, for example, by measuring the absorption spectrum at 612 to 624 nm, the presence of Intermediate A can be accurately grasped. Specifically, it is effective to add the reducing agent to the solution when the absorbance change rate ΔAbs obtained by the equation (1) becomes 60 to 95% by the method shown in the above (X).

The second reduction using a reducing agent can be performed, for example, in a temperature range of 50 ° C. or more and a boiling point or less. When a boiling point is higher than 120 degreeC, it is preferable to set it as the range of 50-120 degreeC. The range of 80 to 120 ° C. is more effective, and may be controlled to the range of 90 to 110 ° C.
The first reduction and the second reduction are performed while stirring the solution. It is preferable to use a nitrogen atmosphere for the gas phase space in contact with the liquid level during the reaction.

  The liquid after completion of the second reduction is subjected to solid-liquid separation by a method such as filtration, centrifugation or the like to recover a solid content mainly comprising a wire-like copper nanostructure. The obtained solid content may be thoroughly washed and, if necessary, stored in a suitable liquid medium. For example, the dispersion liquid of a wire-like copper nanostructure can be obtained by using an aqueous solution of pH 6 to 8 containing about 1% of PVP (polyvinylpyrrolidone) as a dispersant.

Example 1
A 300 mL conical beaker was used as a reaction vessel. In a reaction vessel, 120 g (80 mL) of a 48% by mass aqueous solution of sodium hydroxide was placed, and 0.4 g of copper chloride · dihydrate (molecular weight: 170.48) was added to the solution. The molar ratio [Cu (II)] / [OH ⁻ ] of copper (II) and hydroxide ion in this solution is 1.6 × 10 ⁻³ . The reaction vessel is immersed in an oil bath, the upper part is covered with a fluorocarbon resin sealing material, and nitrogen gas is introduced into the liquid at a flow rate of 0.1 L / min and bubbling while bubbling the liquid at 500 rpm with a fluorine resin stirring blade It stirred. Temperature raising was started in this state, and 0.2 g of dimethylglyoxime (manufactured by Wako Pure Chemical Industries, Ltd., molecular weight: 116.12) was added when the liquid temperature reached 80 ° C. At this time, the molar ratio [DGO] / [Cu (II)] of dimethylglyoxime and copper (II) present in the solution is 0.73. A small amount of sample S ₀ for absorbance measurement was collected from the solution before the start of the first reduction.

Nitrogen gas introduction and stirring were continued after addition of dimethylglyoxime. It was visually observed that the solution temperature reached 105 ° C. about 0.5 h after the start of the temperature rise and the color of the solution was starting to fade from dark blue to clear greenish blue. This fading is due to the progress of the reduction reaction (first reduction) from copper (II) to copper (I). Thereafter, the solution temperature was maintained in the range of 105 to 115 ° C., and a small amount of the sample S ₁ for absorbance measurement was collected from the solution at the time when the discoloration progressed. Using the above samples S ₀ and S ₁ , the rate of change in absorbance ΔAbs was rapidly determined by the method described in (X) above. At that time, 48% by mass sodium hydroxide was used for the aqueous alkali solution for 5-fold dilution, and an ultraviolet and visible spectrophotometer HITACHI Spectrophotometer U-3210 was used for the absorbance measurement apparatus. The absorbance change rate ΔAbs of the liquid at the time of collecting the sample S ₁ was 80%.

  As soon as the measurement result of the rate of change in absorbance ΔAbs was found, 0.20 mL of 17% by mass hydrazine was added as a reducing agent to initiate the second reduction. The color of the solution at the time of addition of this reducing agent was dark in blue as compared to the color sample of ΔAbs 95%. The concentration of hydrazine in the solution is 26.5 mmol / L. The addition time was 0.75 h after the start of the temperature rise. After addition of the reducing agent, after stirring for 30 seconds at 500 rpm, the stirring was stopped. The introduction of nitrogen gas continued thereafter. In order to complete the second reduction, after stopping the stirring, the solution temperature was kept at 100 to 105 ° C. for 0.5 h to complete the heating.

  After the liquid temperature falls to around normal temperature, the reaction product (floating solid content) that floated near the liquid surface (floating solid content) is solid-liquid separated by a filter paper with a retaining particle diameter of 3 μm (Watman No. 131) and recovered did. The recovered solid content was washed three times with water, and then immersed in a 1% by mass PVP aqueous solution, and 0.5 M nitric acid was added to adjust the pH of the solution to 6 to 8 to obtain a copper nanostructure dispersion.

What dried this dispersion liquid was observed with SEM (scanning electron microscope) (Nippon Electron, JSM-IT300LV). The SEM photograph is illustrated in FIG. The scale (hereinafter simply referred to as “scale”) indicated by white lines at the bottom of the left picture is 5 μm, and the scale of the right picture is 1 μm. It was confirmed that a wire-like copper nanostructure was obtained.
Moreover, after diluting the filtrate obtained by said solid-liquid separation 20 times and making it nitric acid acid, it analyzed by inductively-coupled-plasma-spectrometer (SEIKO INSTRUMENT, SPS5100), and measured copper concentration. As a result of calculating | requiring the recovery of copper collect | recovered as a copper nanostructure from the copper addition amount of the initial stage and copper concentration of the filtrate, copper recovery was 99% or more.

Example 2
In Example 1, hydrazine was used as the reducing agent, but D-glucose (C ₆ H ₁₂ O ₆ ) (Wako Pure Chemical Industries, special grade reagent) was used here.
The difference from Example 1 is that 180 g (120 mL) of the 48 mass% aqueous solution of sodium hydroxide and 0.6 g of copper chloride dihydrate were added ([Cu (II)] / [ OH ⁻ ] is 1.6 × 10 ⁻³ ), the addition amount of dimethylglyoxime is 0.3 g, the above-mentioned D-glucose is added as a reducing agent at 27 mmol / L in liquid concentration, the second reduction The solid-liquid separation after completion of the above was performed by centrifugation at 3500 rpm for 10 minutes. A copper nanostructure was synthesized under the same conditions as Example 1 except for the above. In this example, the molar ratio [DGO] / [Cu (II)] of dimethylglyoxime and copper (II) is 0.73.
The SEM photograph of the obtained copper nanostructure is illustrated in FIG. The scale of the photograph on the left is 10 μm, and the scale of the photograph on the right is 1 μm. Although some granular copper particles were mixed, it was confirmed that the method was effective as a method of synthesizing wire-like copper nanostructures.

[Example 3]
Copper nanostructure under the same conditions as in Example 2 except that L-ascorbic acid (C ₆ H ₈ O ₆ ) (manufactured by Wako Pure Chemical Industries, special grade reagent) as a reducing agent was added at a concentration of 27 mmol / L in the solution I synthesized the body.
The SEM photograph of the obtained copper nanostructure is illustrated in FIG. The scale of the photograph on the left is 5 μm, and the scale of the photograph on the right is 1 μm. Although some granular copper particles were mixed, it was confirmed that the method was effective as a method of synthesizing wire-like copper nanostructures.

Example 4
This example is an example scaled up more than Example 1 using hydrazine as a reducing agent.
A 1 L beaker was used as a reaction vessel. 900 g (0.6 L) of a 48% by mass aqueous solution of sodium hydroxide was placed in a reaction vessel, and 3.0 g of copper chloride · dihydrate (molecular weight: 170.48) was added to the solution. The molar ratio [Cu (II)] / [OH ⁻ ] of copper (II) and hydroxide ion in this solution is 1.6 × 10 ⁻³ . The reaction vessel was placed on the heater. Cover the top of the reaction vessel with a stainless steel lid, introduce nitrogen gas into the liquid at a flow rate of 1.5 L / min and bubbling while bubbling the liquid at a rotational speed of 500 rpm or more with a titanium two-stage turbine stirring blade It stirred. A baffle is also installed in the container. Temperature rising was started in this state. The liquid temperature was controlled by PDI by measuring the temperature with a resistance temperature detector inserted in the liquid. The ultimate temperature of the liquid temperature was set to 110 ° C. When the liquid temperature reached 80 ° C., 1.5 g of dimethylglyoxime (manufactured by Wako Pure Chemical Industries, Ltd., molecular weight: 116.12) was added. At this time, the dimethylglyoxime concentration is 21.5 mmol / L, and the molar ratio of dimethylglyoxime to copper (II) present in the solution [DGO] / [Cu (II)] is 0.73. A small amount of sample S ₀ for absorbance measurement was collected from the solution before the start of the first reduction.

Nitrogen gas introduction and stirring were continued after addition of dimethylglyoxime. When the liquid temperature reached 110 ° C., a small amount of sample S ₁ for absorbance measurement was collected. Using the samples S ₀ and S ₁ , the rate of change in absorbance ΔAbs was rapidly determined in the same manner as in Example 1. As a result, the rate of change in absorbance ΔAbs of the solution at the time of collection of sample S ₁ was 90%, and the progress of the first reduction from copper (II) to copper (I) was confirmed.

  As soon as the measurement result of the absorbance change rate ΔAbs was found, 3.0 mL of 17% by mass hydrazine was added as a reducing agent to start the second reduction. The color of the solution at the time of addition of this reducing agent was dark in blue as compared to the color sample of ΔAbs 95%. The concentration of hydrazine in the solution is 26.6 mmol / L. The addition time was 1 h after the start of the temperature rise. After adding the reducing agent, stirring was performed at 500 rpm for 20 seconds, and then the stirring was stopped. The introduction of nitrogen gas continued thereafter. In order to complete the second reduction, after the stirring was stopped, the liquid temperature was set to 105 ° C. and held for 0.5 h to complete heating.

  After the liquid temperature falls to around normal temperature, the reaction product (floating solid content) that floated near the liquid surface (floating solid content) is solid-liquid separated by a filter paper with a retaining particle diameter of 3 μm (Watman No. 131) and recovered did. The recovered solid content was washed three times with water, and then immersed in a 1% by mass PVP aqueous solution, and 0.5 M nitric acid was added to adjust the pH of the solution to 6 to 8 to obtain a copper nanostructure dispersion.

This dispersion was observed by SEM in the same manner as in Example 1. The SEM photograph is illustrated in FIG. The scale of the left picture is 1 μm and the scale of the right picture is 100 nm. It was confirmed that a wire-like copper nanostructure was obtained.
Moreover, as a result of calculating | requiring the recovery of copper collect | recovered as a copper nanostructure by the method similar to Example 1, copper recovery was 99% or more.

[Example 5]
This example is an example scaled up more than Example 2 using D-glucose as a reducing agent.
Except that 2.88 g (27 mmol / L in concentration in liquid) D-glucose used in Example 2 as a reducing agent was added, and the holding temperature in the second reduction was 110 ° C., and the holding time was 5 minutes. Copper nanostructures were synthesized under the same conditions as in Example 4 (scale-up using hydrazine). However, when D-glucose is used, granular copper particles tend to coexist more easily than when hydrazine is used. Here, after dispersing the obtained dispersion for 10 minutes with ultrasonic waves, a solution in which the solid content filtered through 5 A filter paper (made by ADVANTEC, holding particle diameter 7 μm) was dispersed again in the PVP solution was subjected to SEM observation. The SEM photograph is illustrated in FIG. The scale of the photograph on the left is 5 μm, and the scale of the photograph on the right is 1 μm. It was confirmed that a wire-like copper nanostructure was obtained.

[Example 6]
This example is an example in which the concentration of copper chloride dihydrate added to the aqueous sodium hydroxide solution is doubled.
In Examples 1 to 5, the initial concentration of added copper chloride dihydrate (molecular weight 170.48) was 5 g / L (29 mmol / L), but here it was 10 g / ml (59 mmol / L). . The difference from Example 1 is that 360 g (240 mL) of a 48% by mass aqueous solution of sodium hydroxide and 2.4 g of copper chloride dihydrate were added ([Cu (II)] / [ OH ⁻ ] is 3.3 × 10 ^-3 ), the addition amount of dimethylglyoxime is 0.6 g, the rotation speed of the stirrer is 600 rpm, and the supply amount of nitrogen is 0.8 L / min. The point is that the heating was continued at 100 ° C. for 0.75 h, and the above-mentioned D-glucose as a reducing agent was added at a concentration of 58 mmol / L. A copper nanostructure was synthesized under the same conditions as Example 1 except for the above. In this example, the molar ratio [DGO] / [Cu (II)] of dimethylglyoxime and copper (II) is 0.37.
The SEM photograph of the obtained copper nanostructure is illustrated in FIG. The scale of the picture is 5 μm. Although some granular copper particles were mixed, it was confirmed that the method was effective as a method of synthesizing wire-like copper nanostructures.

[Example 7]
This example is an example in which the concentration of copper chloride dihydrate added to the aqueous sodium hydroxide solution is increased threefold.
The initial concentration of copper chloride dihydrate (molecular weight: 170.48) was 15 g / ml (88 mmol / L). Changes in Example 6, except that the amount of copper chloride dihydrate was 3.6g ([Cu (II)] / [OH -] is 4.9 × 10 ^-3), dimethylglyoxime The addition amount of oxime is 0.95 g, heating at 100 ° C. for 0.5 h, and addition of 87 mmol / L of D-glucose as a reducing agent at a concentration in the solution. A copper nanostructure was synthesized under the same conditions as Example 6 except for the above. In this example, the molar ratio [DGO] / [Cu (II)] of dimethylglyoxime and copper (II) is 0.39.
The SEM photograph of the obtained copper nanostructure is illustrated in FIG. The scale of the picture is 1 μm. Although some granular copper particles were mixed, it was confirmed that the method was effective as a method of synthesizing wire-like copper nanostructures.

Comparative Example 1
This example is an example in which the reducing agent is added in the state where the first reduction is not achieved.
A 300 mL conical beaker was used as a reaction vessel. The reaction vessel was charged with 180 g (120 mL) of a 48% by mass aqueous solution of sodium hydroxide, and 0.6 g of copper chloride · dihydrate (molecular weight: 170.48) was added to the solution. The molar ratio [Cu (II)] / [OH ⁻ ] of copper (II) and hydroxide ion in this solution is 1.6 × 10 ⁻³ . In the same manner as in Example 1, nitrogen gas was introduced into the solution and the solution was stirred at 500 rpm by a fluororesin stirring blade while bubbling. Temperature rising was started in this state, and 0.3 g of dimethylglyoxime (manufactured by Wako Pure Chemical Industries, Ltd., molecular weight: 116.12) was added when the liquid temperature reached 80 ° C. At this time, the molar ratio [DGO] / [Cu (II)] of dimethylglyoxime and copper (II) present in the solution is 0.73. A small amount of sample S ₀ for absorbance measurement was collected from the solution at this stage.

After the addition of dimethylglyoxime, the liquid temperature was maintained at 80 ° C. without further raising the temperature, and held for 4 hours while continuing the nitrogen gas introduction and stirring. During this time, the color of the solution remained dark blue. And small amount of collected sample S ₁ for absorbance measurements from liquid 4h retention time. Using the samples S ₀ and S ₁ , the rate of change in absorbance ΔAbs was rapidly determined in the same manner as in Example 1. As a result, it was confirmed that the absorbance change rate ΔAbs of the liquid at the time of collecting the sample S ₁ was 0%, and the first reduction from copper (II) to copper (I) did not proceed.

  Thereafter, 0.6 mL of 17% by mass hydrazine was added as a reducing agent. The concentration of hydrazine in the solution is 26.5 mmol / L. After addition of the reducing agent, after stirring for 30 seconds at 500 rpm, the stirring was stopped. The introduction of nitrogen gas continued thereafter. After the stirring was stopped, the liquid temperature was maintained at 80 ° C., held for 0.5 h, and heating was completed.

  After the liquid temperature dropped to around normal temperature, solid-liquid separation, washing, and preparation of a dispersion were performed by the same method as in Example 1, and the dispersion was observed by SEM. The SEM photograph is illustrated in FIG. The scale of the picture is 5 μm. The metallic copper was crystal-grown in a rod-like or particulate form. The intramolecular reduction with dimethylglyoxime does not proceed in 4 h due to insufficient application of heat energy, and the obtained copper nanostructure does not go through intermediate A, but directly from copper (II) by a reducing agent It has been reduced to metallic copper. It is believed that dimethylglyoxime only functions as a capping agent. However, the capping effect is insufficient to obtain wire-like copper nanostructures.

Comparative Example 2
This example is an example in which metallic copper is formed by intramolecular reduction after the first reduction and before addition of the reducing agent.
The same conditions as in Comparative Example 1 were performed until the addition of dimethylglyoxime at 80 ° C. After the addition of dimethylglyoxime, the temperature was further raised, and the mixture was kept at 120 ° C. for 2 h while stirring was continued. At this stage, reduction to metallic copper was already in progress, and absorbance measurement was impossible because of the generated particles. Thereafter, heating was finished without adding a reducing agent, and after the liquid temperature fell to around normal temperature, the recovered solid content was washed and observed by SEM. The SEM photograph is illustrated in FIG. The scale of the picture is 1 μm. The deposited metallic copper was a complex mainly composed of a rod-like structure with many irregularities. After intermediate A is formed, it is considered that the intramolecular reduction proceeded through the above-mentioned pathway in which Pathways I and II compete because they were maintained at high temperature.

Claims (12)

A process of reducing copper (II) to copper (I) by heating an aqueous alkali solution containing a water-soluble copper (II) compound and an alkylglyoxime to obtain a solution in which copper (I) is present (No. 1) Reduction of),
A wire having a minor axis length of 1000 nm or less and an aspect ratio represented by a major axis length / minor axis length of 10 or more by adding a reducing agent to a solution containing copper (I) generated by the first reduction Depositing and growing copper nanostructures (second reduction),
The manufacturing method of the copper nanostructure which has.   The manufacturing method of the copper nanostructure of Claim 1 which adds a reducing agent to the liquid in which presence of copper (I) produced | generated by 1st reduction was confirmed by monitoring the change of the color of a liquid.   The copper according to claim 1, wherein the reducing agent is added to a solution in which the presence of copper (I) produced in the first reduction is confirmed by measuring the change in absorbance of the solution in the wavelength range of 500 to 800 nm. Method of manufacturing nanostructures. The method for producing a copper nanostructure according to claim 1, wherein a reducing agent is added to a solution in which the first reduction proceeds and the absorbance change rate ΔAbs determined by (X) below is 60 to 95%.
(X) for a sample S ₁ of the first reduction before starting the liquid sample S ₀ and the first liquid time after initiation reduction, then diluted to 5 to 50 times by weight in each aqueous solution of sodium hydroxide, spectral When the absorbance integral value I of the absorption spectrum at 612 to 624 nm is measured under the same conditions by absorptiometry using a photometer, the value determined by the following equation (1) is taken as the absorbance change rate ΔAbs of the solution after the reduction starts .
Δ Abs (%) = (I ₀ −I ₁ ) / I ₀ × 100 (1)
Here, I ₀ and I ₁ are the absorbance integrals I for the sample S ₀ of the solution before the start of reduction and the sample S ₁ of the solution after the start of the reduction, respectively.   The method for producing a copper nanostructure according to any one of claims 1 to 4, wherein one or more of hydrazine, a hydrazine compound, glucose and ascorbic acid are used as a reducing agent.   The aqueous alkali solution to be subjected to the first reduction is a mixture of a 40-48% by mass aqueous sodium hydroxide solution, a water-soluble copper (II) compound, and an alkylglyoxime, according to any one of claims 1 to 5. Method of producing copper nanostructures.   The manufacturing method of the copper nanostructure as described in any one of Claims 1-6 which sets heating temperature which performs 1st reduction to 85 degreeC or more and the boiling point or less of a liquid.   The manufacturing method of the copper nanostructure as described in any one of Claims 1-6 which hold | maintains the heating temperature which performs 1st reduction at 100 degreeC or more and 115 degrees C or less.   The method for producing a copper nanostructure according to any one of claims 1 to 8, wherein the second reduction is performed at a temperature of 50 ° C or more and a boiling point or less.   The method for producing a copper nanostructure according to any one of claims 1 to 9, wherein dimethylglyoxime is used as the alkylglyoxime.   11. The copper nano-particles according to claim 10, wherein the molar ratio [DGO] / [Cu (II)] of dimethylglyoxime and copper (II) in the alkaline aqueous solution subjected to the first reduction is 0.3 to 1.0. Method of manufacturing structure. In alkaline aqueous solution to be subjected to a first reduction of copper (II) the molar ratio of hydroxide ions [Cu (II)] / [ OH -] is claim is 1 × 10 ^-4 ~2 × 10 ^-2 The manufacturing method of the copper nanostructure as described in 10 or 11.