WO2024162514A1 - Method for preparing copper nanowire having high aspect ratio and copper nanowire prepared thereby - Google Patents

Abstract

The present invention provides a method for preparing a copper nanowire having a high aspect ratio of an aspect ratio of 1:180 or more, the method comprising: a first step of forming a first solution containing a capping agent; a second step of forming a second solution containing a halogen catalyst and a reducing agent; a third step of forming a third solution containing a copper precursor compound; and a fourth step of mixing and heating the first solution to the third solution to synthesize a copper nanowire. The present invention may enable the formation of a copper nanowire with a uniform thickness through low-cost and simple solution processes, wherein pure copper has a yield close to 60 %. In addition, the present invention is the first study to apply CuC₂O₄ as a copper precursor, and not only is it expected to reduce costs, but also has the potential for high-yield copper nanowire synthesis through additional process control in the future.

Description

Method for manufacturing high aspect ratio copper nanowires and copper nanowires produced thereby

The present invention relates to a method for producing a copper nanowire having a high aspect ratio and a copper nanowire produced thereby, and more particularly, to a method for producing a copper nanowire having a high aspect ratio of 1:180 or more and a copper nanowire produced thereby.

Metal nanowires are one-dimensional nanomaterials that are attracting attention in various fields including catalysts, sensors, and electronic devices due to their excellent physical and chemical properties. Among them, copper not only has excellent electrical and thermal conductivity, but also has an advantage in price competitiveness due to its abundant reserves. In order for metal nanowires to be utilized in various fields, it is important to have a technology that satisfies physical properties such as shape uniformity, diameter, length, and aspect ratio while simultaneously producing them in mass quantities with excellent economic feasibility. In general, metal nanowires are induced to grow anisotropically due to the action of shape-controlling additives such as capping agents and halogen catalysts on metal seeds. In order to induce such growth, there have been problems in that many process steps are required and satisfactory yields are not obtained. Copper precursors commonly used in the synthesis of existing copper nanowires include copper compounds such as copper sulfate (CuSO ₄ ), copper chloride (CuCl ₂ ), and copper nitrate (Cu(NO ₃ ) ₂ ). The problem with these conventional technologies is that compounds that are combined with counterions such as chloride ions (Cl ^- ), sulfate ions (SO ₄ ^2- ), and nitrate ions ((NO ₃ ) ^2- ) form a large amount of reaction by-products due to reactions with additives, making it difficult to maintain the composition before and after the reaction, and a complex post-treatment process is required, which may cause environmental problems.

In order to solve the problems of the prior art, the copper nanowire manufacturing technology of the present invention aims to develop an economically advantageous copper _nanowire manufacturing method that can reduce the generation of reaction by-products and process costs while dramatically improving productivity by applying _CuC 2 O 4 as a copper precursor.

In order to solve the above problems, the purpose is to provide a method for manufacturing high aspect ratio copper nanowires.

In addition, the present invention aims to provide a high aspect ratio copper nanowire according to the above manufacturing method.

In order to achieve the above purpose, the present invention,

A first step of forming a first solution containing a capping agent;

A second step of forming a second solution containing a halogen catalyst and a reducing agent;

A third step of forming a third solution containing a copper precursor compound;

The present invention provides a method for producing high aspect ratio copper nanowires having an aspect ratio of 1:180 or higher, comprising a fourth step of mixing and heating the first to third solutions to synthesize copper nanowires.

In addition, in order to achieve the other objects described above, the present invention provides a high aspect ratio copper nanowire according to the manufacturing method described above.

The present invention can form copper nanowires of uniform thickness through a low-cost and simple solution process, and the formed pure copper has a yield of close to 60%. In addition, the present invention is the first study to apply CuC ₂ O ₄ as a copper precursor, and thus, not only can a cost-saving effect be expected, but also has the potential for high-yield copper nanowire synthesis through additional process control in the future.

FIG. 1 is a schematic diagram showing the production of copper nanowires according to one embodiment of the present invention.

FIG. 2 illustrates an SEM image of copper nanowires produced from copper oxalic acid according to one embodiment of the present invention.

FIG. 3 illustrates an SEM image of copper nanowires produced from copper oxalic acid according to one embodiment of the present invention.

Figure 4 illustrates an image of a copper shape produced after changing the solvent according to a comparative example of the present invention.

Figure 5 illustrates an image of a copper shape produced when NaCl was not added according to a comparative example of the present invention.

FIG. 6 illustrates the results of XRD analysis of copper nanowires produced from copper oxalic acid according to one embodiment of the present invention.

Hereinafter, the present invention will be described in more detail.

According to one aspect of the present invention, a method for producing high aspect ratio copper nanowires having an aspect ratio of 1:180 or more is provided, comprising: a first step of forming a first solution containing a capping agent; a second step of forming a second solution containing a halogen catalyst and a reducing agent; a third step of forming a third solution containing a copper precursor compound; and a fourth step of mixing and heating the first to third solutions to synthesize copper nanowires.

First, the first step is explained. The first solution is prepared by dissolving a capping agent in a polar organic solvent at room temperature.

The capping agent of the present invention is a compound that changes the assembly of growing copper atoms into an anisotropic state. It strongly adsorbs to a specific surface through a chemical reaction and inhibits growth through passivation, and the growth of nanowires occurs due to crystallization that continues while the cross-sectional surface is still exposed to the solution. Copper capping agents include polyvinylpyrrolidone (PVP), polyvinylalcohol (PVA), hexadecylamine, triethylenediamine, ethylenediamine, propane-1,3-diamine, butane-1,4-diamine, pentane-1,5-diamine, ethylenediamine tetraacetic acid, 1,2-cyclohexane diamine-N,N,N′,N′-tetraacetic acid, glycine, ascorbic acid, iminodiacetic acid, Nitrilotriacetic acid, alanine, arginine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, proline, serine, threonine, tryptophane, tyrosine, valine, gallic acid, boric acid, acetic acid, acetone oxime, acrylic acid, adipic acid, betaine, dimethyl Glyoxime, formic acid, fumaric acid, gluconic acid, glutaric acid, glyceric acid, glycolic acid, glyoxylic acid, isophthalic acid, itaconic acid, lactic acid, maleic acid, maleic anhydride, malic acid, malonic acid, mandelic acid, 2,4-pentandione, phenylacetic acid, phthalic acid, proline, propionic acid, pyrocatechol, pyromellitic acid, quinic acid, Includes at least one selected from the group consisting of sorbitol, succinic acid, tartaric acid, terephthalic acid, trimellitic acid, trimesic acid, xylitol, salts thereof, and derivatives thereof, but is not particularly limited thereto. In the present invention, the copper capping agent uses polyvinylpyrrolidone (PVP) and polyvinyl alcohol (PVA), most preferably polyvinylpyrrolidone.

In one embodiment of the present invention, PVP is a chain-shaped polymer material, and the Carbonyl group (C=O) of PVP is strongly adsorbed to the {100} plane of the copper seed having the FCC structure, forming a cross-section of the {111} plane and growing in the <110> direction. The molecular weight (Mw) is 10,000 to 60,000, preferably 30,000 to 60,000, and more preferably 40,000 to 60,000. As the molecular weight of PVP increases, a strong chemical adsorption of Cu2 ⁺ and the Carbonyl group (C=O) occurs, and it is stably adsorbed on the surface of the copper seed with excellent surface coating. In addition, since it improves the viscosity in the solution, a stable reaction can be induced. That is, when PVP having a large molecular weight is applied, an increase in the aspect ratio of the formed nanowire can be expected.

In addition, the concentration of the capping agent added in the present invention is 50 to 154 mM, preferably 80 to 120 mM, more preferably 100 to 120 mM. If the capping agent is added in an amount less than 50 mM, the yield of nanowires may decrease due to an increase in the concentration of copper particles on which the capping agent does not act, and if it is added in an amount exceeding 154 mM, there is a problem in that passivation of all facets may be induced, resulting in generation in the form of nanoparticles.

The solvent of the present invention is a polar organic solvent capable of dissolving all of the copper precursor, the capping agent, the halogen catalyst, and the reducing agent, and not only assists the action of the additive, but also assists the reduction of the metal precursor, and may be a polyhydric alcohol such as glycol or polyol. For example, it may be ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, etc., and preferably, ethylene glycol may be used to promote the reduction reaction of copper.

Next, the second step is described. The second solution is prepared by dissolving a halogen catalyst and a reducing agent in a polar organic solvent.

The halogen catalyst of the present invention is an additive containing a halogen ion (Cl ^- , Br ^-, etc.) and induces anisotropic growth. Separation into ions occurs in a polar organic solvent, and the halogen ion as an anion and the copper ion as a cation form an intermediate substance through bonding. This prevents supersaturation of free copper ions in the solution, thereby preventing random growth of particles. Through this ion provision rate control, a thermodynamically stable structure, a decahedron multiply-twinned particle, is formed. The multiply-twinned particle is a decahedron having five twin seeds with a mixture of {111} and {100} facets, and when a decahedral seed is generated, a nanowire having a pentagonal cross-section due to a single growth along the five-fold axis is generated.

In the present invention, the concentration of the halogen catalyst is preferably 5 to 15 mM. If the halogen catalyst is added in an amount less than 5 mM, the concentration of copper ions in the solution increases, thereby accelerating the formation rate of copper nanoparticles. If the halogen catalyst is added in an amount exceeding 15 mM, the concentration of copper ions in the solution is drastically reduced, which causes a problem of limiting the growth of nanowires.

The reducing agent of the present invention reacts with copper ions supplied from a copper precursor to form copper atoms. The reducing agent includes, but is not particularly limited to, at least one selected from the group consisting of fructose, potassium bromide, sodium borohydride, hydrazine, sodium chloride, sodium hydroxide, ammonium chloride, sodium phosphinate monohydrate, ascorbic acid, L(+)-ascorbic acid, an ascorbic acid derivative, oxalic acid, malic acid, formic acid, phosphite, glucose, sulfite, and cetytrimethyl ammonium bromide. In the present invention, ascorbic acid can be used as a reducing agent, and the concentration of the reducing agent is 30 to 80 mM, preferably 40 to 60 mM.

The solvent of the second step is a polar organic solvent identical to the solvent used in the first step, and may be a polyhydric alcohol such as glycol or polyol. For example, it may be ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, etc., and preferably, ethylene glycol may be used to promote the reduction reaction of copper.

Next, the third step is described. The third solution is prepared by dissolving a copper precursor compound in a polar organic solvent.

The copper precursor compound of the present invention provides copper ions to form copper nanowires. The copper precursor may be copper sulfate, copper chloride, copper nitrate, copper nitrite, copper acetate, copper bromide, copper iodide, copper carbonate, copper oxalic acid, and the like, and preferably, copper oxalic acid, which is an inorganic material having anti-ferromagnetic properties, may be used.

In one embodiment of the present invention, copper oxalic acid is used as a copper precursor, dissolved in an ethylene glycol solvent, and decomposed into copper ions and counter ions, oxalate ions (C ₂ O ₄ ^2- ), the copper ions are reduced to copper, and the oxalate ions are oxidized to CO ₂ and removed through evaporation.

The solvent of the third step is a polar organic solvent identical to the solvent used in the first and second steps, and may be a polyhydric alcohol such as glycol or polyol. For example, it may be ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, etc., and preferably, ethylene glycol may be used to promote the reduction reaction of copper.

When copper oxalic acid is used as a copper precursor as in one embodiment of the present invention, since CuC ₂ O ₄ decomposes at a temperature of 250° C. or higher, the solvent must have a boiling point higher than the decomposition temperature. For example, glycerol is a high-viscosity solvent with a boiling point of about 290° C., which has the advantage of being advantageous for reduction because it is higher than the decomposition temperature of CuC ₂ O _4. However, there is a problem in that high-viscosity solvents cause non-uniform chemical reactions, which limits the formation of nanowires.

On the other hand, ethylene glycol (EG) has a boiling point of approximately 190°C _, which is lower than the high decomposition temperature of _CuC2O4 . This problem was solved by reducing the high reduction temperature of _CuC2O4 by adding ascorbic acid, a reducing agent, _and Cu nanowires were successfully synthesized when EG was applied.

Next, the fourth step is described. The first to third solutions formed above are mixed and heated to synthesize copper nanowires.

First, before mixing the respective solutions formed in the first to third steps, each solution is heated to 60 to 100°C while stirring at 500 to 700 rpm. Then, the second solution is added to the first solution, and the stirring speed is increased to 600 to 800 rpm, and the third solution is added and the stirring speed is further increased to 700 to 900 rpm to induce uniform stirring. At this time, when mixing the first to third solutions, a surfactant may be further included in the mixed solution. The surfactant minimizes aggregation of copper nanowires, increases the length of the copper nanowires, and reduces the width of the copper nanowires. The surfactant usable in the present invention may include at least one selected from the group consisting of ethoxylate, alkoxylate, ethylene oxide, propylene oxide, and copolymers thereof, or at least one selected from the group consisting of sulfonate, sulfate, disulfonate salt, sulfosuccinate, phosphate ester, and fluorosurfactants, but is not particularly limited thereto.

The final temperature of the solution thus mixed is increased to 140 to 180°C, most preferably 160°C, then heated for 3 to 5 hours and cooled to room temperature to terminate the reaction. Cooling is performed at room temperature, and an alcohol organic solvent (such as methanol, ethanol, acetone, etc.) is applied in a washing process to remove residual reaction by-products. A preferable alcohol organic solvent in the present invention may be methanol. Since the surface of the nanowire is covered with a capping agent, which is a polymer organic material, methanol plays a role in removing the capping layer. The reaction by-products on the surface of the copper nanowire can be completely removed with only two washing processes.

According to another aspect of the present invention, a high aspect ratio copper nanowire is provided according to the above manufacturing method.

The copper nanowires of the present invention have an average diameter of 190 to 200 nm, an average length of 65 to 70 nm, an aspect ratio of 1:180 or more, preferably 1:350 or more, and a final production yield of about 60%.

Hereinafter, in order to specifically explain this specification, examples and comparative examples will be given in detail. However, the examples according to this specification may be modified in various different forms, and the scope of this specification is not construed as being limited to the examples described below. The examples of this specification are provided to more completely explain this specification to a person having average knowledge in the art.

<Example>

Example 1 - Preparation of copper nanowires

A first solution was prepared by dissolving 103 mM PVP (M _W = 10000) in 40 ml of EG (Ethylene Glycol) in a 100 ml reactor at room temperature, and a second solution was prepared by dissolving 10 mM NaCl and 52 mM AA in 10 ml of EG in a 50 ml reactor. Then, a third solution was prepared by dissolving 12.4 mM CuC ₂ O ₄ in 10 ml of EG in a 50 ml reactor, and each solution was heated to 80°C with stirring at 600 rpm, then the second solution was added to the first solution, and the stirring speed was increased to 700 rpm. After the third solution was added, the stirring speed was increased to 800 rpm to induce uniform stirring. After the final solution temperature was increased to 160°C, it was heated for 4 hours, and then cooled to room temperature to terminate the reaction. Afterwards, the solution in which the reaction was completed was divided into 10 ml portions in 50 ml conical tubes, and 30 ml of methanol was supplied to each conical tube to perform centrifugation. The solvent was discarded, methanol was supplied again to redisperse the copper nanowires, and then the solvent was discarded to obtain the manufactured copper nanowires.

Example 2 - Preparation of copper nanowires

A first solution was prepared by dissolving 103 mM PVP (M _W = 55000) in 40 ml of EG (Ethylene Glycol) in a 100 ml reactor at room temperature, and a second solution was prepared by dissolving 15 mM NaCl and 52 mM AA in 10 ml of EG in a 50 ml reactor. Then, a third solution was prepared by dissolving 12.4 mM CuC ₂ O ₄ in 10 ml of EG in a 50 ml reactor, and each solution was heated to 80°C with stirring at 600 rpm, then the second solution was added to the first solution, and the stirring speed was increased to 700 rpm. After the third solution was added, the stirring speed was increased to 800 rpm to induce uniform stirring. After the final solution temperature was increased to 160°C, it was heated for 4 hours, and then cooled to room temperature to terminate the reaction. Afterwards, the solution in which the reaction was completed was divided into 10 ml portions in 50 ml conical tubes, and 30 ml of methanol was supplied to each conical tube to perform centrifugation. The solvent was discarded, methanol was supplied again to redisperse the copper nanowires, and then the solvent was discarded to obtain the manufactured copper nanowires.

Comparative Example 1 - Preparation of copper nanowires using different solvents

A first solution was prepared by heating 50 ml of Glycerol in a 100 ml reactor to 200°C with stirring at 800 rpm. Then, 103 mM of PVP and 15 mM of NaCl were added at room temperature and dissolved in 10 ml of Glycerol to 100°C with stirring at 600 rpm. The first solution was added to the second solution and the temperature was raised to 250°C. Then, 12.4 mM of CuC ₂ O ₄ was added and heated for 1 hour, and the solution temperature was lowered to 100°C and additional heating was performed for 1 hour. Thereafter, the reaction was terminated by cooling to room temperature. The solution at the completion of the reaction was divided into 10 ml portions into 50 ml conical tubes, and 30 ml of methanol was supplied to each conical tube to perform centrifugation. After discarding the solvent, copper nanowires were redispersed by supplying methanol again, and then the solvent was discarded to obtain the manufactured copper nanowires.

Comparative Example 2 - Preparation of copper nanowires without using halogen catalyst

Copper nanowires were formed in the same manner as in Example 1 without adding NaCl.

Experimental Example 1 - Shape Analysis

The shape of the copper nanowires manufactured in Examples 1 and 2 above was observed using SEM.

Experimental Example 2 - XRD Analysis

XRD analysis was performed on the copper nanowires manufactured in Example 2 above.

<Results and Evaluation>

Shape Analysis

FIGS. 2 and 3 illustrate SEM images of copper nanowires manufactured from copper oxalic acid according to one embodiment of the present invention. Referring to FIGS. 2 and 3, copper nanowires manufactured using ethylene glycol as a solvent as in Examples 1 and 2 exhibited a nanowire shape, and it was confirmed that uniform copper nanowires whose thickness and length can be controlled by controlling the PVP molecular weight and the concentration of the halogen catalyst could be manufactured.

In Example 2, where copper nanowires were formed under optimized conditions based on Example 1, the average diameter was 192 nm, the average length was 68.10 μm, the aspect ratio was 354.08, and the final production yield was 57%.

Diameter, length, and final production yield of copper nanowires prepared from copper oxalate

	Average diameter (nm)	Average length (μm)	Aspect ratio	Final production rate (%)
Example 1	298.37	56.28	188.61	52
Example 2	192.33	68.10	354.08	57

Fig. 4 illustrates an image of a copper shape produced after changing the solvent according to a comparative example of the present invention. Referring to Fig. 4, copper produced using glycerol as a solvent, as in Comparative Example 1, exhibited a particle shape.

Figure 5 illustrates an image of a copper shape produced when NaCl was not added according to a comparative example of the present invention. Referring to Figure 5, when NaCl was not used as in Comparative Example 2, incomplete reduction of copper oxalate and copper of an uneven shape were formed.

XRD analysis

FIG. 6 illustrates the results of XRD analysis of copper nanowires manufactured from copper oxalic acid according to one embodiment of the present invention. Referring to FIG. 6, it was confirmed that the copper nanowire according to Example 2 was a copper nanowire having an FCC structure having (111), (200), (220) planes, as copper peaks were observed at (111), (200), and (220).

The foregoing has broadly described the features and technical advantages of the present invention so that the scope of the claims to be described later may be better understood. Those skilled in the art will appreciate that the present invention may be implemented in other specific forms without changing the technical idea or essential features thereof. Therefore, it should be understood that the embodiments described above are exemplary in all respects and not restrictive. The scope of the present invention is indicated by the claims described below rather than the detailed description above, and all changes or modifications derived from the claims and their equivalents should be construed as being included in the scope of the present invention.

Claims (6)

1. A first step of forming a first solution containing a capping agent;

   A second step of forming a second solution containing a halogen catalyst and a reducing agent;

   A third step of forming a third solution containing a copper precursor compound;

   A method for producing high aspect ratio copper nanowires having an aspect ratio of 1:180 or more, comprising a fourth step of mixing and heating the first to third solutions to synthesize copper nanowires.
2. In paragraph 1,

   The above steps 1 to 3 are a method for producing high aspect ratio copper nanowires, characterized in that a polyol solvent is used as a solvent in preparing a solution.
3. In paragraph 1,

   The above 4 steps are a method for producing high aspect ratio copper nanowires, characterized in that a surfactant can be additionally added.
4. A high aspect ratio copper nanowire manufactured by a manufacturing method according to any one of claims 1 to 3.
5. In paragraph 4,

   A high aspect ratio copper nanowire characterized in that the copper nanowire is anisotropic.
6. In paragraph 4,

   A high aspect ratio copper nanowire characterized by an aspect ratio of 1:180 or greater.

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