Method for manufacturing silver-coated copper nanowires having core-shell structure using chemical reduction method

Abstract

The present invention relates to a silver-coated copper nanowire having a core-shell structure using chemical reduction and a method for preparing the same. More particularly, the present invention relates to a method for preparing a silver-coated copper nanowire and a silver-coated copper nanowire having a core-shell structure produced by the method, the method comprising chemically producing a copper nanowire and coating a copper surface with silver using a silver ammonia complex solution and a reducing agent, thus, oxidation of the copper nanowire is prevented by chemical reduction. In addition, since the copper nanowire can be produced by reusing the solution, the production cost can be reduced. The method for preparing a silver-coated copper nanowire having a core-shell structure according to the present invention can avoid deterioration of conductivity by preventing oxidation even in air or at high temperatures, and thus is useful for the production of an electromagnetic shielding paste requiring high conductivity or a high-conductivity paste.

Description

[0001] This application is a divisional application of Chinese patent application No. 201780041973.1 (filed on May 30, 2017, entitled: Method for manufacturing silver-coated copper nanowires with core-shell structure using a chemical reduction method). Technical Field

[0002] This invention relates to a method for preparing silver-coated copper nanowires with a core-shell structure using chemical reduction, and more specifically to a method for preparing silver-coated copper nanowires, the method comprising chemically producing copper nanowires and coating the copper surface with silver using a silver ammonia complex solution and a reducing agent, thereby preventing oxidation of the copper nanowires by chemical reduction. Background Technology

[0003] Nanowires are nanomaterials with diameters of a few nanometers and lengths ranging from hundreds of nanometers to hundreds of micrometers. Due to their ease of manipulation, these materials have attracted much attention as core materials for the production of next-generation nanodevices. Recently, metallic nanowires such as copper, silver, and nickel nanowires have been usefully used as alternatives to indium tin oxide (ITO), conductive polymers, carbon nanotubes, graphite, and others due to their properties such as conductivity and transparency.

[0004] Copper nanowires have emerged as an alternative to indium tin oxide (ITO), which is primarily used in displays, due to their advantages such as high conductivity, flexibility, transparency, and low cost. In particular, because copper nanowires are transparent conductors, they can be used in a wide variety of applications, including low-emissivity windows, touch-sensitive control panels, solar cells, and electromagnetic shielding materials.

[0005] Copper nanowires have conventionally been produced using various methods, such as electrochemical reactions, chemical vapor deposition, hard template-assisted methods, and colloidal and hydrothermal processes. However, conventional manufacturing methods suffer from problems such as high equipment investment costs, difficulty in controlling nanowire dimensions, and low productivity.

[0006] Recently, methods for manufacturing copper nanowires via chemical synthesis have been known. Korean Patent No. 10-73808 discloses a method for preparing copper nanowires, which involves mixing an amine ligand, a reducing agent, a surfactant, and a nonpolar organic solvent with an aqueous CuCl2 solution, transferring the reaction solution to a high-pressure reactor, and reacting at 80ºC to 200ºC for 24 hours. The copper nanowires produced by this method have lengths of 10 to 50 µm and diameters of 200 to 1,000 nm. However, this production method uses a high-pressure reactor, which may lead to increased production costs and make it unsuitable for mass production.

[0007] Korean Patent No. 1334601 discloses a method for preparing copper nanowires using a polyol process employing ethylene glycol (EG) and polyvinylpyrrolidone (PVP). However, this production method raises environmental concerns due to the use of toxic solvents compared to methods using aqueous solutions, and also suffers from reduced economic efficiency due to increased production costs.

[0008] International Patent Publication No. 2011-071885 discloses a method for manufacturing copper nanowires having a length of 1 to 500 µm and a diameter of about 20 to 300 nm by mixing a copper ion precursor, a reducing agent, a capping agent, and a pH adjuster, and then reacting them at a predetermined temperature to obtain copper nanowires comprising copper rods attached to spherical copper nanoparticles. However, this method still has drawbacks, such as low yield and low quality uniformity of the resulting copper nanowires.

[0009] On the other hand, when copper nanowires are exposed to air for extended periods, they oxidize to form copper oxide. This oxidation process accelerates with increasing temperature. This copper oxide is significantly less conductive than pure copper. To prevent the formation of this copper oxide, International Patent Publication No. 2011-071885 and Korean Patent Publication No. 1334601 disclose methods for producing copper nanowires and surface-treating them with metals such as nickel, gold, tin, zinc, silver, platinum, titanium, aluminum, tungsten, cobalt, or the like. However, improvements in the overall process efficiency and quality uniformity of copper nanowires are still needed.

[0010] Therefore, as a result of extensive efforts to solve the above problems, the inventors of this invention have developed a method for chemically synthesized copper nanowires to be coated with silver to prevent oxidation by using a silver ammonia complex solution and a reducing agent for chemical reduction. They have also found that, compared with conventional methods for producing copper nanowires, this method enables the production of silver-coated copper nanowires with high economic efficiency, productivity, and high oxidation resistance, thus completing this invention. Summary of the Invention

[0011] Therefore, the present invention was realized in view of the above problems, and the object of the present invention is to provide a method for preparing silver-coated copper nanowires with high economic efficiency, productivity and high antioxidant properties.

[0012] To achieve the above objectives, the present invention provides a method for preparing silver-coated copper nanowires with a core-shell structure, the method comprising: (a) stirring an aqueous solution containing (1) an alkali, (2) a copper compound and (3) a capping agent; (b) producing copper nanowires by adding a reducing agent to the aqueous solution to reduce copper ions; (c) washing and drying the produced copper nanowires; (d) removing an oxide film from the copper nanowires produced in step (c); (e) adding a reducing agent to the solution in step (d), adjusting the pH and then forming a silver coating by adding a silver nitrate-ammonia complex solution dropwise; and (f) washing and drying the silver-coated copper nanowires prepared in step (e). Attached Figure Description

[0013] Figure 1 This is a scanning electron microscope (SEM) image of the copper nanowires produced in Example 1.

[0014] Figure 2 The image shows a scanning electron microscope-energy dispersive spectroscopy (SEM-EDS) image illustrating the content analysis results of the copper nanowires produced in Example 1.

[0015] Figure 3 This is a scanning electron microscope (SEM) image of the copper nanowires produced in Example 2.

[0016] Figure 4 The image shows a scanning electron microscope-energy dispersive spectroscopy (SEM-EDS) image illustrating the content analysis results of the copper nanowires produced in Example 2.

[0017] Figure 5 This is a scanning electron microscope (SEM) image of silver-coated copper nanowires produced using Cu(OH)2 as a copper precursor.

[0018] Figure 6 This is a scanning electron microscope (SEM) image of the copper nanowires synthesized in Example 4 by reusing NaOH solution once.

[0019] Figure 7 This is a scanning electron microscope (SEM) image of the copper nanowires synthesized in Example 4 by reusing NaOH solution twice.

[0020] Figure 8 This is a scanning electron microscope (SEM) image of the copper nanowires synthesized in Example 5 by reusing NaOH solution once.

[0021] Figure 9 This is a scanning electron microscope (SEM) image of the copper nanowires synthesized in Example 5 by reusing NaOH solution twice.

[0022] Figure 10 This is a scanning electron microscope (SEM) image of the silver-coated copper nanowires with a core-shell structure produced in Example 6.

[0023] Figure 11 The image shows a scanning electron microscope-energy dispersive spectroscopy (SEM-EDS) image illustrating the content analysis results of the silver-coated copper nanowires with a core-shell structure produced in Example 6.

[0024] Figure 12 This is an ion beam scanning electron microscope (FIB) image showing the thickness of the silver coating on the silver-coated copper nanowires with a core-shell structure produced in Example 6.

[0025] Figure 13 This is a scanning electron microscope (SEM) image of silver-coated copper nanowires with a core-shell structure produced in Comparative Example 1.

[0026] Figure 14 The image shows a scanning electron microscope-energy dispersive spectroscopy (SEM-EDS) image illustrating the content analysis results of silver-coated copper nanowires with a core-shell structure produced in Comparative Example 1.

[0027] Figure 15 This is a scanning electron microscope (SEM) image of silver-coated copper nanowires with a core-shell structure produced in Comparative Example 2.

[0028] Figure 16 The image shows a scanning electron microscope-energy dispersive spectroscopy (SEM-EDS) image illustrating the content analysis results of silver-coated copper nanowires with a core-shell structure produced in Comparative Example 2.

[0029] Figure 17 This is a scanning electron microscope (SEM) image of the silver-coated copper nanowires with a core-shell structure produced in Example 7.

[0030] Figure 18 The image shows a scanning electron microscope-energy dispersive spectroscopy (SEM-EDS) image illustrating the content analysis results of the silver-coated copper nanowires with a core-shell structure produced in Example 7.

[0031] Figure 19 This is an ion beam scanning electron microscope (FIB) image showing the thickness of the silver coating on the silver-coated copper nanowires with a core-shell structure produced in Example 7.

[0032] Figure 20 This is a scanning electron microscope (SEM) image of the silver-coated copper nanowires with a core-shell structure produced in Example 8.

[0033] Figure 21 The image shows a scanning electron microscope-energy dispersive spectroscopy (SEM-EDS) image illustrating the content analysis results of the silver-coated copper nanowires with a core-shell structure produced in Example 8.

[0034] Figure 22 This is an ion beam scanning electron microscope (FIB) image showing the thickness of the silver coating on the silver-coated copper nanowires with a core-shell structure produced in Example 8.

[0035] Figure 23 This is a scanning electron microscope (SEM) image of the silver-coated copper nanowires with a core-shell structure produced in Example 9.

[0036] Figure 24 The image shows a scanning electron microscope-energy dispersive spectroscopy (SEM-EDS) image illustrating the content analysis results of the silver-coated copper nanowires with a core-shell structure produced in Example 9.

[0037] Figure 25 This is an ion beam scanning electron microscope (FIB) image showing the thickness of the silver coating on the silver-coated copper nanowires with a core-shell structure produced in Example 9.

[0038] Figure 26 This is a scanning electron microscope (SEM) image of the silver-coated copper nanowires with a core-shell structure produced in Example 10.

[0039] Figure 27 The image shows a scanning electron microscope-energy dispersive spectroscopy (SEM-EDS) image illustrating the content analysis results of the silver-coated copper nanowires with a core-shell structure produced in Example 10.

[0040] Figure 28 This is a scanning electron microscope (SEM) image of the silver-coated copper nanowires with a core-shell structure produced in Example 11.

[0041] Figure 29 The image shows a scanning electron microscope-energy dispersive spectroscopy (SEM-EDS) image illustrating the content analysis results of the silver-coated copper nanowires with a core-shell structure produced in Example 11.

[0042] Figure 30 This is a scanning electron microscope (SEM) image of the silver-coated copper nanowires with a core-shell structure produced in Example 12.

[0043] Figure 31 The image shows a scanning electron microscope-energy dispersive spectroscopy (SEM-EDS) image illustrating the content analysis results of the silver-coated copper nanowires with a core-shell structure produced in Example 12.

[0044] Figure 32 This image shows the results of a spectral profile scan of the silver-coated copper nanowires with a core-shell structure produced in Example 6, performed using an energy-dispersive spectrometer mounted on a transmission electron microscope (TEM) in Experimental Example 2. Detailed Implementation

[0045] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as understood by one of skill in the art to which this invention relates. Generally, the nomenclature used herein is well-known and commonly used in the art.

[0046] In this invention, piperazine and / or hexamethylenediamine are used as end-capping agents to prepare copper nanowires. The oxide film on the copper nanowires is then removed, and the copper nanowires are subsequently chemically coated with silver to produce core-shell silver-coated copper nanowires. Therefore, it has been found that silver-coated copper nanowires with a core-shell structure exhibit better oxidation stability than conventional copper nanowires and can be produced at a lower cost than silver nanowires with similar physical properties.

[0047] Therefore, the present invention relates to a method for preparing silver-coated copper nanowires, the method comprising (a) stirring an aqueous solution containing (1) an alkali, (2) a copper compound and (3) a capping agent; (b) producing copper nanowires by adding a reducing agent to the aqueous solution to reduce copper ions; (c) washing and drying the produced copper nanowires; (d) removing an oxide film from the copper nanowires produced in step (c); (e) adding a reducing agent to the solution of step (d), adjusting the pH and forming a silver coating while adding a silver nitrate-ammonia complex solution dropwise; and (f) washing and drying the silver-coated copper nanowires prepared in step (e).

[0048] In this invention, the method may further include (c') resynthesizing copper nanowires after step (c) by adding a copper precursor and a reducing agent to the solution separated from the copper nanowires. Even after the synthesis of copper nanowires, a considerable amount of copper precursor and reducing agent remains in the solution separated from the copper nanowires. Furthermore, because the alkaline solution used for this reaction should be supplied at a high concentration, there are costs associated with purchasing or disposing of new alkaline solution when the untreated alkaline solution is discarded. Therefore, production costs can be significantly reduced when the copper precursor and reducing agent are additionally supplied to the separated solution for the reaction. Moreover, production costs are preferably minimized by repeating step (c) two or more times to synthesize copper nanowires.

[0049] In step (d) of the present invention, a mixed solution of ammonia and ammonium sulfate can be used as the solution for removing the oxide film. Copper nanowires are oxidized after production, thereby forming an oxide film (copper oxide) on their surface. This oxide film may reduce the conductivity of the copper nanowires and may interfere with contact with the silver coated on the surface. Therefore, it is preferable to remove the oxide film before coating with silver. In this case, the concentration of the mixed solution of ammonia and ammonium sulfate is more preferably 0.001 to 0.3 M. When the concentration of the mixed solution of ammonia and ammonium sulfate is less than 0.001 M, the oxide film may not be properly removed, and therefore the silver coating may not form or the conductivity of the copper nanowires may decrease. When the concentration is higher than 0.3 M, the copper nanowires may decompose, and therefore, the overall yield may decrease due to high copper consumption. Furthermore, the solution can be a substance containing amines rather than a solution containing ammonium ions. The solution may further include other amine-based substances or additives, but the present invention is not limited thereto. Furthermore, step (d) for removing the oxide film is preferably performed for 1 to 60 minutes. When the reaction time is less than 1 minute, the oxide film cannot be removed, and when the reaction time exceeds 60 minutes, the copper nanowires may dissolve.

[0050] In this invention, in step (e), a reducing agent is added to the copper nanowire solution from which the oxide film has been removed in step (d), the pH is adjusted, and the silver ammonia complex solution is fed at a rate of 0.5 to 500 ml / min while stirring at 50 to 1,600 rpm. Step (e) is used to form a silver coating on the copper nanowires from which the oxide film has been removed in step (d). When the silver ammonia complex solution is fed at a rate less than 0.5 ml / min, the amount of silver to be reduced is small, thereby forming a dense silver coating. When the silver ammonia complex solution is fed at a rate greater than 500 ml / min, silver cannot be coated onto the copper nanowires and silver-free particles may form in the solution.

[0051] Furthermore, when the stirring rate of the solution is less than 50 rpm, the diffusion rate of the silver ammonia complex decreases, and a silver coating is not sufficiently formed on the surface of the copper nanowires. When the stirring rate is higher than 1,600 rpm, the flowability of the solution may become unstable, and therefore the reactivity may decrease.

[0052] In this invention, the pH of the solution in which copper nanowires are dispersed can be between 8 and 11. When the pH is less than 8, a silver coating cannot be properly formed on the copper nanowires. When the pH is greater than 11, copper may dissolve and the yield may decrease. In this case, the reagent used to adjust the pH is at least one selected from NaOH, KOH, ammonia, and the like. Preferably, the pH is adjusted with ammonia, but the invention is not limited thereto. The concentration of ammonia in the solution in which the copper nanowires are dispersed can be between 0.001 and 0.1 M, but the invention is not limited thereto. When the concentration of ammonia is less than 0.001 M, silver coating cannot be properly performed on the surface of the copper nanowires. When the concentration is greater than 0.1 M, the copper nanowires may dissolve and the yield may deteriorate.

[0053] In this invention, the reducing agent in step (e) can be selected from the group consisting of: oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, octanoic acid, azelaic acid, sebacic acid, tridecanoic acid, dodecanoic acid, hexadecanoic acid, maleic acid, fumaric acid, gluconic acid, tufalicic acid, mucoconic acid, mucopicroic acid, citrate, mesoconic acid, aspartic acid, glutamic acid, diaminopimelic acid, malonic acid, arabinaric acid, gluconic acid, mesooxalic acid, oxaloacetic acid, acetone dicarboxylic acid, phthalic acid, isophthalic acid, terephthalic acid, biphenyl phthalic acid, tartaric acid, potassium sodium tartrate, ascorbic acid, hydroquinone, glucose, hydrazine, etc. Any reducing agent can be used without restriction as the reducing agent in step (e), as long as the reducing agent can reduce silver for silver coating. However, the use of a weak reducing agent allows for the uniform formation of a silver coating, and the weak reducing agent is preferably sodium potassium tartrate.

[0054] In this invention, the concentration of the reducing agent in step (e) can be from 0.001 to 3 M. When the concentration of the reducing agent is less than 0.001 M, the reduction reaction deteriorates and therefore no silver coating is formed. When the concentration of the reducing agent is higher than 3 M, the economic and environmental losses are significant due to the large consumption of reagents.

[0055] In this invention, a silver-ammonia complex solution is prepared by mixing a silver nitrate solution with ammonia. The principle of forming a silver coating on copper nanowires is based on chemical plating. To coat copper nanowires with silver, a silver-ammonia complex solution should be applied, and ammonia can be added to the silver nitrate solution.

[0056] Specifically, a silver ammonia complex solution is produced by adding ammonia water to a silver nitrate solution. This reaction can be described by reaction scheme 2. [Ag(NH3)2] + It is a silver ammonia complex, which is formed according to step 3) of reaction scheme 2.

[0057] [Reaction Scheme 2]

[0058] 1) 2AgNO3+ 2NH4OH → Ag2O ↓ +H2O + 2NH4NO3

[0059] 2) Ag2O + 4NH4OH → 2[Ag(NH3)2]OH + 3H2O

[0060] 3) [Ag(NH3)2]OH + NH4NO3→ [Ag(NH3)2]NO3 + NH4OH

[0061] Copper nanowires are coated with silver atoms using a chemical plating principle, wherein [Ag(NH3)2] is formed in reaction scheme 2, step 3). + The Ag ions in the complex are reduced by electrons derived from the copper nanowires. This reaction is described by the following reaction scheme 3.

[0062] [Reaction Scheme 3]

[0063] Cu + 2[Ag(NH3)2]NO3→ [Cu(NH3)4](NO3)2 + 2Ag ↓

[0064] In this invention, the concentration of silver nitrate in the silver ammonia complex solution can be from 0.001 to 1 M, and the concentration of ammonia can be from 0.01 to 0.3 M. When the concentration of silver nitrate is less than 0.001 M or greater than 1 M, or when the concentration of ammonia is less than 0.01 M or greater than 0.3 M, it is difficult to form a complex.

[0065] In this invention, the alkali in step (a) can be NaOH, KOH, or Ca(OH)₂. Preferably, the concentration of the alkali solution in step (a) is in the range of 2.5 to 25 M. When the concentration of the alkali solution is less than 2.5 M, the solution does not maintain pH and therefore the reduction reaction of copper ions will not occur properly. When the concentration of the alkali solution is higher than 25 M, the alkali reacts with copper, and therefore nanowires are not formed as desired.

[0066] In this invention, the copper compound can be copper hydroxide, copper nitrate, copper sulfate, copper sulfite, copper acetate, copper chloride, copper bromide, copper iodide, copper phosphate, or copper carbonate, preferably copper nitrate. This copper compound provides the copper ions necessary for the growth of copper nanowires. In this invention, the copper compound can have a concentration based on copper ions from 0.004 to 0.5 M. When the concentration of copper ions is less than 0.004 M, copper nanowires cannot be properly formed, and copper nanoparticles may form instead. When the concentration of copper ions is higher than 0.5 M, the reaction with the reducing agent does not occur completely because copper ions are present in excess in the solution.

[0067] In this invention, the capping agent (3) can be piperazine (C4H ...5H4H5H4H5H5H4H5H5H5H5H6H5H5H5H6H5H5H5H6H5H5H5H6H5H5H5H6H5H5 10 N2) or hexamethylenediamine (C6H) 16 N2). To enable the copper ions contained in copper compounds to form nanowires, the shape of the copper nanowires should be controlled by the amine groups contained in the capping agent. This capping agent is bound to the copper nanostructure, and the copper grows longitudinally, thus obtaining the nanowire morphology. The preferred copper capping agent used here is piperazine (C4H2O). 10 N2) and / or hexamethylenediamine (C6H) 16 N2). Piperazine (C4H) 10 N2) and hexamethylenediamine (C6H) 16 N2) can be expressed by Equation 1 and Equation 2 respectively:

[0068] [Formula 1]

[0069]

[0070] [Equation 2]

[0071]

[0072] In this invention, (3) the concentration of the capping agent can be from 0.008 to 2.0 M. When the concentration of the capping agent is less than 0.008 M, copper disks and copper nanowires can be formed, and when the concentration of the capping agent is higher than 2.0 M, disk-shaped copper can be formed.

[0073] In this invention, stirring in step (a) is performed to ensure that all materials added to the aqueous solution are well dissolved, and this can be done using a conventional stirrer, but the invention is not limited thereto. The stirring rate is preferably 200 to 400 rpm and the stirring time is preferably 5 to 30 minutes. However, the stirring rate and time are freely selectable depending on the amount of aqueous solution, reaction time, etc.

[0074] In this invention, the reducing agent in step (b) can be hydrazine, ascorbic acid, L(+)-ascorbic acid, isoascorbic acid, ascorbic acid derivatives, oxalic acid, formic acid, phosphite, phosphoric acid, sulfite, or sodium borohydride, preferably hydrazine.

[0075] The process by which hydrazine reduces copper ions to copper in the presence of an alkaline solution is described by the following reaction scheme 1:

[0076] [Reaction Scheme 1]

[0077] 2Cu 2+ + N2H4 + 4OH - 2Cu + N2 + 4H2O

[0078] In this invention, the concentration of the reducing agent in step (b) can be from 0.01 to 1.0 M, and the addition rate of the reducing agent can be from 0.1 to 500 ml / min. When the concentration of the reducing agent is less than 0.01 M or greater than 1.0 M, or when the addition rate of the reducing agent is less than 0.1 ml / min or greater than 500 ml / min, copper nanoparticles may be formed instead of copper nanowires. In step (b), after adding the reducing agent, copper ions are reduced by stirring for 30 minutes to 2 hours, preferably 1 hour. When the reaction time is less than 30 minutes, the thickness and length of the copper nanowires are unsuitable. When the reaction time is greater than 2 hours, the remaining copper ions on the surface of the copper nanowires are reduced, which may result in the wire having an uneven surface.

[0079] Furthermore, step (b) can be carried out at temperatures between 0°C and 100°C. When the reaction temperature is below 0°C or above 100°C during reduction, copper reduction occurs, but copper nanoparticles may form instead of nanowires.

[0080] In this invention, in step (c), the resulting copper nanowires are washed and dried. In step (c), impurities are removed from the surface of the copper nanowires, and the copper nanowires are dried. During the synthesis of the copper nanowires, materials for removing surface impurities, preferably distilled water and an ethanol solution, can be used to wash and dry the copper nanowires. During the washing of the copper nanowires, the impurities on the surface are washed several times with distilled water, washed once or twice with ethanol for rapid drying, and dried in a vacuum oven at room temperature for 12 to 30 hours, but the invention is not limited thereto.

[0081] In this invention, step (f) is used to wash and dry the silver-coated copper nanowires produced in step (e), and is performed by the same cleaning steps as in step (c).

[0082] In this invention, the method for manufacturing silver-coated copper nanowires with a core-shell structure can be carried out by batch reaction, plug flow reaction, or continuous stirred tank reaction, but the invention is not limited thereto.

[0083] The present invention will now be described in more detail with reference to embodiments. However, it will be apparent to those skilled in the art that these embodiments are provided merely to illustrate the invention and should not be construed as limiting the scope of the invention.

[0084] [Example]

[0085] The specifications of the equipment used in the embodiments and the method for measuring physical properties are as follows:

[0086] 1) Morphological and structural measurements: using scanning electron microscopy (SEM; FEI, SIRION) and transmission electron microscopy (TEM; FEI, TECNAI G). 2 The morphology and structure of silver-coated copper nanowires with a core-shell structure were measured using the T-20S method.

[0087] 2) Composition measurement: Scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS; FEI, SIRION) and transmission electron microscopy-energy dispersive spectroscopy (TEM-EDS; FEI, TECNAI G) were used. 2 The composition of silver-coated copper nanowires with a core-shell structure was measured using the iCAP 6500 (T-20S) method. Furthermore, the silver and copper content of the silver-coated copper nanowires with the core-shell structure was analyzed by inductively coupled plasma atomic emission spectrometry (ICP-AES; iCAP 6500, Thermo Scientific).

[0088] 3) Thin film resistance: The thin film resistance was measured using a four-point thin film resistance meter (Loresta-GP, MCP-T610, Mitsubishi Chemical Analysis Technology Co., Ltd.).

[0089] 4) Thickness measurement: The thickness of the silver-coated copper nanowires with a core-shell structure was measured using a focused ion beam (FIB) scanning electron microscope (LYRA3 XMU, TESCAN).

[0090] 5) Content analysis: The silver and copper content of the silver-coated copper nanowires with core-shell structure was measured using inductively coupled plasma atomic emission spectrometry (ICP-AES, iCAP 6500 duo, Thermo Technologies).

[0091] Example 1: Using piperazine (C4H) 10 N2) Production of copper nanowires

[0092] 2,000 ml of ultrapure water was fed into a 3,000 ml round-bottom flask, and 1,200 g (15 M) sodium hydroxide (NaOH, manufactured by Samchun Pure Chemical Co., Ltd.) was added while stirring with a stirrer. The reactor, heated by the exothermic reaction, was cooled to an internal temperature of 50°C or less. Then, 3.8 g (0.0079 M) copper nitrate (II) (Cu(NO3)2·3H2O, manufactured by Samchun Pure Chemical Co., Ltd.) was dissolved in 100 ml of ultrapure water, and the resulting solution was fed into the reactor. Then, 9.7 g (0.268 M) piperazine (C4H) was added. 10 N2 (Sigma Aldrich Corporation) was dissolved in 100 ml of water (ultrapure water), and the resulting solution was fed into the reactor and stirred at a uniform stirring rate of 300 rpm for 10 minutes. After raising the reactor temperature to 70ºC, 4 ml of hydrazine (N2H4, Samchun Purification Chemical Co., Ltd.) was mixed with 240 ml (0.04 M) of water (ultrapure water), and the resulting mixture was fed into the reactor using a syringe pump at a rate of 4 ml / min for one hour. After maintaining the reactor at 70ºC and then completing the reaction, the reaction solution was slowly cooled to room temperature. The copper nanowires were then separated from the solution and washed with distilled water and 2 L of ethanol. The copper nanowires were then dried in a vacuum oven (JEIO Tech, OV-12) at 25ºC for 24 hours. The results of scanning electron microscopy (SEM) of the resulting copper nanowires are shown in the figures from... Figure 1 As can be seen, copper nanowires with lengths of 5 to 10 μm and diameters of 200 to 300 nm have been produced. (As seen from...) Figure 2 As can be seen from the results of analysis of the composition and content of the copper nanowires using scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), unoxidized copper nanowires were produced.

[0093] Example 2: Using hexamethylenediamine (C6H) 16 N2) Production of copper nanowires

[0094] 2,000 ml of ultrapure water was fed into a 3,000 ml round-bottom flask, and 1,200 g of sodium hydroxide (NaOH, manufactured by Samchun Purification Chemical Co., Ltd.) was added while stirring with a stirrer. The reactor, heated by the exothermic reaction, was cooled to an internal temperature of 50ºC or less. Then, 3.8 g of copper nitrate(II) (Cu(NO3)2·3H2O, manufactured by Samchun Purification Chemical Co., Ltd.) was dissolved in 100 ml of ultrapure water, and the resulting solution was fed into the reactor. Then, 62.25 ml (0.268 M) of hexamethylenediamine (C6H2O) was added to the solution. 16 N2 (Sigma-Aldrich), was added and then stirred at an average stirring rate of 300 rpm for 10 minutes. After the reactor temperature reached 35ºC, 4 ml of hydrazine (N2H4, Samchun Purification Chemical Co., Ltd.) was mixed with 240 ml of water (ultrapure water), and the resulting mixture was fed into the reactor at a rate of 4 ml / min using a syringe pump for one hour. After the reactor temperature was raised to 70ºC, the reaction proceeded for one hour. After the reaction was complete, the reaction solution was slowly cooled to room temperature. The copper nanowires were then washed with distilled water and 2 L of ethanol. The copper nanowires were then dried in a vacuum oven (JEIO Tech, OV-12) at 25ºC for 24 hours. The results of scanning electron microscopy (SEM) of the resulting copper nanowires are shown in the figures from... Figure 3 As can be seen, copper nanowires with lengths of 2 to 5 μm and diameters of 200 to 300 nm have been produced. (As seen from...) Figure 4 As can be seen from the results of analysis of the composition and content of the copper nanowires using scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), unoxidized copper nanowires were produced.

[0095] Example 3: Production of copper nanowires using copper precursor Cu(OH)2

[0096] Copper nanowires were produced in the same manner as in Example 1, except that copper hydroxide (Cu(OH)2, Samchun Chemical Co., Ltd.) was used instead of copper nitrate(II) as the copper precursor.

[0097] like Figure 5 As shown, the formation of copper nanowires was identified using scanning electron microscopy (SEM).

[0098] Example 4: Synthesis of copper nanowires by reusing NaOH (using copper(II) nitrate as a copper precursor)

[0099] The components that account for the largest portion of the cost for synthesizing silver-coated copper nanowires with a core-shell structure are the silver precursor and NaOH. In this invention, 15 M (1,200 g) NaOH is added to copper nanowires to synthesize them. In this respect, NaOH is reused for process improvement. After synthesizing the copper nanowires as in Example 1, the copper nanowires are separated from the solution, and the copper(II) nitrate precursor and reducing agent are added again to the resulting solution to synthesize copper nanowires. This time, the copper precursor and reducing agent are added in a controlled equivalence ratio so that no reducing agent remains in the solution. Therefore, although only the reducing agent and copper precursor are added to the already reacted solution, copper nanowires can be synthesized by reusing them once and twice.

[0100] Figure 6 This illustrates a case where copper nanowires are synthesized by reusing NaOH solution once, and... Figure 7 These are scanning electron microscope (SEM) images obtained when copper nanowires were synthesized by reusing NaOH twice. These images show that copper nanowires were successfully synthesized by injecting only the copper precursor and reducing agent into the solution left after the synthesis of copper nanowires. This demonstrates that NaOH solution can be reused only when the copper precursor and reducing agent are supplied in a controlled equivalence ratio. As shown in this embodiment, the cost of synthesizing silver-coated copper nanowires with a core-shell structure can be reduced by reusing NaOH several times.

[0101] Example 5: Synthesis of copper nanowires by reusing NaOH (using copper hydroxide as a copper precursor)

[0102] Following the same procedure as in Example 3, after synthesizing the copper nanowires, the copper nanowires were separated from the solution, and a copper hydroxide precursor and a reducing agent were added to the remaining solution to synthesize copper nanowires. This time, the copper precursor and reducing agent were added in a controlled equivalence ratio to prevent any reducing agent from remaining in the solution. Therefore, although only the reducing agent and copper precursor are added to the already reacted solution, copper nanowires can be synthesized by reusing them once or twice.

[0103] Figure 8 This illustrates a case where copper nanowires are synthesized by reusing NaOH solution once, and... Figure 9 These are scanning electron microscope (SEM) images obtained when copper nanowires were synthesized by reusing NaOH twice. These images show that copper nanowires were successfully synthesized by injecting only the copper precursor and reducing agent into the solution left after the synthesis of copper nanowires. This demonstrates that NaOH solution can be reused only when the copper precursor and reducing agent are supplied in a controlled equivalence ratio. As shown in this embodiment, the cost of synthesizing silver-coated copper nanowires with a core-shell structure can be reduced by reusing NaOH several times.

[0104] Example 6: Production of silver-coated copper nanowires with a core-shell structure in a reaction solution with pH 10

[0105] 100 ml of water (ultrapure water) and 1.0 g of copper nanowires prepared in Example 1 were added to a 500 ml Erlenmeyer flask and dispersed by stirring at 900 rpm for 3 hours using an ultrasonic cleaner (Youngjin Bath Ultrasonic Instrument (SK7210HP)). 0.0094 M ammonium hydroxide ((NH4)2SO4, Samseon Pure Chemical Industries, Co., Ltd.) and 0.0376 M ammonia (NH4OH) were added to remove the oxide film from the copper nanowires, and the mixture was stirred at 800 rpm for 3 minutes. At this point, the solution turned blue as the oxide film was removed. 0.028 M potassium sodium tartrate (C4H4KNaO6·4H2O, Samseon Pure Chemical Industries, Co., Ltd.) was added as a reducing agent, and the pH was adjusted to 10 using potassium hydroxide (KOH, Samseon Pure Chemical Industries, Co., Ltd.), and the mixture was stirred at 800 rpm for 3 minutes.

[0106] To form a silver coating on copper nanowires from which the oxide film had been removed, water (ultrapure water) was mixed with nitric acid (AgNO3, Juntech) to prepare a 0.18 M silver nitrate solution. 1.5 ml of ammonia (NH4OH, Samchun Purification Chemical Co., Ltd.) was added to obtain a clear solution, and the resulting solution was stirred for one minute to prepare a silver-ammonia complex solution. At this point, Cu and Ag were added at a ratio of 55:45. While stirring the copper nanowire solution from which the oxide film had been removed at 800 rpm, the silver coating solution was added at a rate of 1 ml / min. Although the entire volume of the silver coating solution was injected over approximately 44 minutes, the silver coating solution was allowed to react for one hour to achieve sufficient coating time. After the reaction was complete, the resulting solution was washed with 2 L of water (ultrapure water) using filter paper and dried at room temperature for 24 hours to obtain silver-coated copper nanowires.

[0107] like Figure 10 As shown, the formation of a silver coating on the surface of copper nanowires was identified using scanning electron microscopy (SEM). The results of scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) of the silver-coated copper nanowires are shown below. Figure 11 The film shows approximately 88% silver coating. At this point, the measured film resistance is 4.2 × 10⁻⁶. -2Ω / sq. Therefore, it can be seen that when the pH of the reaction solution is adjusted to 10 during silver coating, a dense silver coating is formed compared to Example 3, and the sheet resistance is reduced by an order of magnitude.

[0108] Furthermore, the thickness of the silver coating on silver-coated copper nanowires with a core-shell structure was measured. Therefore, as from... Figure 12 As can be seen, copper wire exists in the inner portion, and the outer portion of the copper wire is coated with silver to a thickness of about 75 nm.

[0109] Comparative Example 1: Production of silver-coated copper nanowires with a core-shell structure in a reaction solution with pH 6

[0110] Silver-coated copper nanowires with a core-shell structure were produced in the same manner as in Example 6, except that the pH of the reaction solution was adjusted to 6 using hydrochloric acid (HCl, Samchun Chemical Co., Ltd.) before forming the silver coating on the copper nanowires.

[0111] like Figure 13 As shown, the formation of a silver coating on the surface of copper nanowires was identified using scanning electron microscopy (SEM). The results of scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) of the silver-coated copper nanowires are shown below. Figure 14 The result showed that the silver coating was approximately 37%, a reduction of about 50% compared to Example 5. At this point, the measured film resistivity was 3.3 × 10⁻⁶. -2 Ω / sq. Therefore, it is evident that when the pH of the reaction solution is adjusted to 6 during silver coating, the silver coating ratio decreases, and the film resistivity increases by 10 Ω / sq. 4 Times or more.

[0112] Comparative Example 2: Production of silver-coated copper nanowires with a core-shell structure in a reaction solution with pH 12

[0113] Silver-coated copper nanowires with a core-shell structure were produced in the same manner as in Example 6, except that the pH of the reaction solution was adjusted to 12 using potassium hydroxide before forming the silver coating on the copper nanowires.

[0114] like Figure 15 As shown, the formation of a silver coating on the surface of copper nanowires was identified using scanning electron microscopy (SEM). The results of scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) of the silver-coated copper nanowires are shown below. Figure 16 The result showed that the silver coating was approximately 31%, a reduction of approximately 57% compared to Example 6. At this point, the measured film resistance was 1.1 × 10⁻⁶. -1 Ω / sq. Therefore, it can be seen that the yield is reduced by about 10% compared to Example 6, in which silver coating is performed at a pH adjusted to 10.

[0115] Example 7: Production of silver-coated copper nanowires with a core-shell structure using 0.14 M silver nitrate

[0116] In this embodiment, experiments were conducted to reduce the amount of silver coated on the copper nanowires to improve economic efficiency. Silver-coated copper nanowires with a core-shell structure were produced in the same manner as in Example 6, except that 0.14 M silver nitrate was used to prepare the silver-ammonia complex solution, as in Example 5. In Example 6, the concentration of silver nitrate in the feed was 0.18 M, indicating that silver was added at 45% by weight relative to copper, and in this Example 7, 0.14 M silver nitrate was added, indicating that silver was added at 40% by weight relative to copper. That is, silver-coated copper nanowires with a core-shell structure were produced while the silver content was reduced by approximately 5%.

[0117] like Figure 17 As shown, the formation of a silver coating on the surface of copper nanowires was identified using scanning electron microscopy (SEM). The results of scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) of the silver-coated copper nanowires are shown below. Figure 18 The film shows approximately 70% silver coating. At this point, the measured film resistance is 5.3 × 10⁻⁶. -2 Ω / sq. Therefore, it can be seen that the sheet resistance of the silver-coated copper nanowire with the core-shell structure is similar to that of the silver-coated copper nanowire produced in Example 7.

[0118] Furthermore, the thickness of silver coated on silver-coated copper nanowires with a core-shell structure was measured. Therefore, as from... Figure 19 As can be seen, a copper wire exists in the internal portion, and the external portion of the copper wire is coated with silver to a thickness of approximately 66 nm. Because the amount of silver nitrate fed during silver coating was reduced from 0.18 M to 0.14 M compared to Example 5, the thickness of the silver coating was also reduced from approximately 75 nm to approximately 66 nm.

[0119] Example 8: Production of silver-coated copper nanowires with a core-shell structure using a 0.14 M silver coating solution

[0120] Silver-coated copper nanowires with a core-shell structure were produced in the same manner as in Example 6, except that 0.11 M silver nitrate was used to prepare the silver ammonia complex solution. In Example 8, the concentration of silver nitrate in the feed was 0.11 M, indicating that silver was added in an amount of 35% relative to the weight of copper. That is, silver-coated copper nanowires with a core-shell structure were produced, while the silver content was reduced by approximately 10% compared to Example 5.

[0121] like Figure 20As shown, the formation of a silver coating on the surface of copper nanowires was identified using scanning electron microscopy (SEM). The results of scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) of the silver-coated copper nanowires are shown below. Figure 21 The film shows approximately 57% silver coating. At this point, the measured film resistance is 3.7 × 10⁻⁶. -2 Ω / sq. Therefore, it can be seen that the sheet resistance of the silver-coated copper nanowire with the core-shell structure is similar to that of the silver-coated copper nanowire produced in Example 6.

[0122] Furthermore, the thickness of silver coated on silver-coated copper nanowires with a core-shell structure was measured. Therefore, as from... Figure 22 As can be seen, a copper wire exists in the internal portion, and the external portion of the copper wire is coated with silver to a thickness of approximately 48 nm. Because the amount of silver nitrate fed during silver coating was reduced from 0.18 M to 0.14 M compared to Example 6, the thickness of the silver coating was also reduced from approximately 75 nm to approximately 48 nm.

[0123] Example 9: Production of silver-coated copper nanowires with a core-shell structure using a 0.09 M silver coating solution

[0124] Silver-coated copper nanowires with a core-shell structure were produced in the same manner as in Example 6, except that 0.09 M silver nitrate was used to prepare the silver ammonia complex solution, as in Example 5. In Example 9, the concentration of silver nitrate in the feed was 0.09 M, indicating that silver was added at 30% of the weight of copper. That is, silver-coated copper nanowires with a core-shell structure were produced, while the silver content was reduced by approximately 15% compared to Example 5.

[0125] from Figure 23 As can be seen, the formation of a silver coating on the surface of copper nanowires was identified using scanning electron microscopy (SEM). The results of scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) of the silver-coated copper nanowires are shown below. Figure 24 The film shows approximately 43% silver coating. At this point, the measured film resistance is 4.4 × 10⁻⁶. -2 Ω / sq. Therefore, it can be seen that the sheet resistance of the silver-coated copper nanowire with the core-shell structure is similar to that of the silver-coated copper nanowire produced in Example 6.

[0126] Furthermore, the thickness of silver coated on silver-coated copper nanowires with a core-shell structure was measured. Therefore, as from... Figure 25As can be seen, a copper wire exists in the inner portion, and the outer portion of the copper wire is coated with silver to a thickness of approximately 30.6 nm. Because the amount of silver nitrate fed during silver coating was reduced from 0.18 M to 0.09 M compared to Example 6, the thickness of the silver coating was also reduced from approximately 75 nm to approximately 30.6 nm.

[0127] Example 10: Production of silver-coated copper nanowires with a core-shell structure using tartaric acid as a reducing agent.

[0128] Silver-coated copper nanowires with a core-shell structure were produced in the same manner as in Example 6, except that tartaric acid (C4O6H6, Samchun Chemical Co., Ltd.) was used instead of sodium potassium tartrate (C4H4KNaO6·4H2O, Samchun Chemical Co., Ltd.) as the reducing agent ....

[0129] from Figure 26 As can be seen, the formation of a silver coating on the surface of copper nanowires was identified using scanning electron microscopy (SEM). The results of scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) of the silver-coated copper nanowires are shown below. Figure 27 The film shows approximately 72% silver coating. At this point, the measured film resistance is 1.3 × 10⁻⁶. -1 Ω / sq.

[0130] Example 11: Production of silver-coated copper nanowires with a core-shell structure using 0.14 M silver nitrate and tartaric acid as a reducing agent.

[0131] Silver-coated copper nanowires with a core-shell structure were produced in the same manner as in Example 7, except that tartaric acid (C4O6H6, Samchun Chemical Co., Ltd.) was used instead of sodium potassium tartrate (C4H4KNaO6·4H2O, Samchun Chemical Co., Ltd.) as the reducing agent ....

[0132] like Figure 28 As shown, the formation of a silver coating on the surface of copper nanowires was identified using scanning electron microscopy (SEM). The results of scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) of the silver-coated copper nanowires are shown below. Figure 29 The film shows approximately 60% silver coating. At this point, the measured film resistance is 1.5 × 10⁻⁶. -1 Ω / sq.

[0133] Example 12: Production of silver-coated copper nanowires with a core-shell structure using 0.11 M silver nitrate and tartaric acid as a reducing agent.

[0134] Silver-coated copper nanowires with a core-shell structure were produced in the same manner as in Example 8, except that tartaric acid (C4O6H6, Samchun Chemical Co., Ltd.) was used instead of sodium potassium tartrate (C4H4KNaO6·4H2O, Samchun Chemical Co., Ltd.) as the reducing agent ....

[0135] like Figure 30 As shown, the formation of a silver coating on the surface of copper nanowires was identified using scanning electron microscopy (SEM). The results of scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) of the silver-coated copper nanowires are shown below. Figure 31 The film shows approximately 51% silver coating. At this point, the measured film resistance is 2.5 × 10⁻⁶. -1 Ω / sq.

[0136] Experimental Example 1: Oxidation Test of Silver-Coated Copper Nanowires with Core-Shell Structure

[0137] To evaluate the oxidation properties of silver-coated copper nanowires with a core-shell structure, copper nanowires produced by the method of Example 1 and silver-coated copper nanowires with a core-shell structure produced by the methods of Examples 7, 8 and 9 were each laminated onto a GF filter and then heated at 200ºC for one hour.

[0138] Table 1 shows the sheet resistance of the copper nanowires produced in Example 1 before and after heating, as well as the silver-coated copper nanowires with a core-shell structure produced in Examples 7, 8, and 9. As shown in Table 1, the sheet resistance of the copper nanowires before heating is 2.6 × 10⁻⁶. -2 The resistivity of the thin film is Ω / sq, but after heating, it increases to 8.7 × 10 Ω / sq. 6 Ω / sq. This means that the copper nanowire is oxidized when left to stand for a long time or heated. On the other hand, when the silver-coated copper nanowires with a core-shell structure produced in the methods of Examples 7 to 9 are oxidized under the same conditions, the silver-coated copper nanowires of all examples have a Ω / sq. -2 The sheet resistance is Ω / sq, which is similar to that before heating. This means that the silver-coated copper nanowires with a core-shell structure produced by this invention are not oxidized.

[0139] [Table 1]

[0140]

[0141] Experimental Example 2: Analysis results of silver and copper content in silver-coated copper nanowires with core-shell structure produced according to the example.

[0142] To determine whether the silver-coated copper nanowires with core-shell structures produced according to Examples 7 to 9 were silver-coated, the silver and copper content of the produced silver-coated copper nanowires was analyzed using high-frequency inductively coupled plasma atomic emission spectrometry (ICP-AES) and energy dispersive spectroscopy mounted on a transmission electron microscope.

[0143] First, in order to detect the silver and copper content, high-frequency inductively coupled plasma torch (ICP-AES) was used to analyze the silver-coated copper nanowires with core-shell structure produced by the methods of Examples 7 to 9.

[0144] Table 2 shows the results of inductively coupled plasma atomic emission spectroscopy (ICP-AES) analysis of silver-coated copper nanowires with core-shell structures produced by the methods of Examples 7 to 9. The analysis results show that, as shown in Table 2, the silver content coated on the copper nanowires gradually decreased in the order of 54.7%, 47%, and 40.2% as the amount of silver nitrate during silver coating gradually decreased in the order of 0.14 M, 0.11 M, and 0.09 M.

[0145] [Table 2]

[0146]

[0147] Furthermore, to determine whether silver was formed on the copper nanowires in a core-shell structure, the silver-coated copper nanowires with a core-shell structure produced in Example 7 were subjected to spectral profile scanning using an energy-dispersive spectroscopy system mounted on a transmission electron microscope. Therefore, as from... Figure 30 As can be seen, silver-coated copper nanowires with a core-shell structure are formed, wherein copper exists in the inner part and the outer part of the copper nanowire is coated with silver.

[0148] Industrial applicability

[0149] The method for preparing silver-coated copper nanowires with a core-shell structure according to the present invention can prevent the degradation of conductivity by preventing oxidation even in air or at high temperatures, and thus provides copper nanowires with higher economic efficiency compared to pure silver nanoparticles or nanowires.

[0150] Although specific configurations of the invention have been described in detail, those skilled in the art will understand that this specification is provided for illustrative purposes as a preferred embodiment and should not be construed as limiting the scope of the invention. Therefore, the essential scope of the invention is defined by the appended claims and their equivalents.

[0151] This disclosure relates to the following implementation plan:

[0152] 1. A method for preparing silver-coated copper nanowires with a core-shell structure, the method comprising:

[0153] (a) Stir an aqueous solution containing (1) alkali, (2) copper compound and (3) capping agent;

[0154] (b) Copper nanowires are produced by adding a reducing agent to the aqueous solution to reduce copper ions;

[0155] (c) Wash and dry the produced copper nanowires;

[0156] (d) Remove the oxide film from the copper nanowires produced in step (c);

[0157] (e) Add a reducing agent to the solution from step (d), adjust the pH, and then form a silver coating while adding a silver nitrate-ammonia complex solution dropwise; and

[0158] (f) The silver-coated copper nanowires prepared in step (e) are washed and dried.

[0159] 2. The method for preparing silver-coated copper nanowires with a core-shell structure according to item 1 further includes (c') resynthesizing copper nanowires after step (c) by adding a copper precursor and a reducing agent to a solution separated from the copper nanowires.

[0160] 3. The method for preparing silver-coated copper nanowires with a core-shell structure according to item 2, wherein the copper nanowires are synthesized by repeating step (c') two or more times.

[0161] 4. The method for preparing silver-coated copper nanowires with a core-shell structure according to item 1, wherein a mixed solution of ammonia and ammonium sulfate is used as a solution for removing oxide films in step (d).

[0162] 5. The method for preparing silver-coated copper nanowires with a core-shell structure according to item 4, wherein the concentration of the mixed solution of ammonia and ammonium sulfate in step (d) is from 0.001 to 0.3 M.

[0163] 6. The method for preparing silver-coated copper nanowires with a core-shell structure according to item 4, wherein step (d) is performed for 1 to 60 minutes.

[0164] 7. The method of preparing silver-coated copper nanowires with a core-shell structure according to item 1, wherein in step (e), the reducing agent is added to the copper nanowire solution from which the oxide film has been removed in step (d), the pH is adjusted, and the silver nitrate-ammonia complex solution is injected at a rate of 0.5 to 500 ml / min while stirring at 50 to 1600 rpm.

[0165] 8. The method for preparing silver-coated copper nanowires with a core-shell structure according to item 1, wherein the reducing agent in step (e) is selected from the group consisting of: oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, octanoic acid, azelaic acid, sebacic acid, tridecanoic acid, dodecanoic acid, hexadecanoic acid, maleic acid, fumaric acid, gluconic acid, tufalicic acid, mucoconic acid, mucopicroic acid, citrate, mesoconic acid, aspartic acid, glutamic acid, diaminopimelic acid, malonic acid, arabinoic acid, gluconic acid, mesooxalic acid, oxaloacetic acid, acetone dicarboxylic acid, phthalic acid, isophthalic acid, terephthalic acid, biphenyl phthalic acid, tartaric acid, potassium sodium tartrate, ascorbic acid, hydroquinone, glucose, and hydrazine.

[0166] 9. The method of preparing silver-coated copper nanowires with a core-shell structure according to item 8, wherein the concentration of the reducing agent is from 0.001 M to 3 M.

[0167] 10. The method of preparing silver-coated copper nanowires with a core-shell structure according to item 7, wherein the pH of the copper nanowire solution is 8 to 11.

[0168] 11. The method for preparing silver-coated copper nanowires with a core-shell structure according to item 7, wherein the silver nitrate-ammonia complex solution is prepared by mixing a silver nitrate solution and ammonia.

[0169] 12. The method of preparing silver-coated copper nanowires with a core-shell structure according to item 11, wherein the concentration of silver nitrate in the silver nitrate-ammonia complex solution is from 0.001 to 1 M.

[0170] 13. The method for preparing silver-coated copper nanowires with a core-shell structure according to item 7, wherein the concentration of ammonia in the silver nitrate-ammonia complex solution is 0.01-0.3 M.

[0171] 14. The method for preparing silver-coated copper nanowires with a core-shell structure according to item 1, wherein the base in step (a) (1) is NaOH, KOH or Ca(OH)2.

[0172] 15. The method for preparing silver-coated copper nanowires with a core-shell structure according to item 1, wherein the concentration of the (1) base is 2.5 to 25 M.

[0173] 16. The method for preparing silver-coated copper nanowires with a core-shell structure according to item 1, wherein the copper compound in step (a) (2) is copper hydroxide, copper nitrate, copper sulfate, copper sulfite, copper acetate, copper chloride, copper bromide, copper iodide, copper phosphate or copper carbonate.

[0174] 17. The method of preparing silver-coated copper nanowires with a core-shell structure according to item 1, wherein the concentration of the copper compound in step (a) is based on copper ions from 0.004 to 0.5 M.

[0175] 18. The method for preparing silver-coated copper nanowires with a core-shell structure according to item 1, wherein the (3) end-capping agent is piperazine (C4H4H4O2). 10 N2) or hexamethylenediamine (C6H) 16 N2).

[0176] 19. The method of preparing silver-coated copper nanowires with a core-shell structure according to item 18, wherein the concentration of the capping agent is from 0.008 to 2.0 M.

[0177] 20. The method for preparing silver-coated copper nanowires with a core-shell structure according to item 1, wherein the reducing agent in step (b) is hydrazine, ascorbic acid, L(+)-ascorbic acid, isoascorbic acid, ascorbic acid derivative, oxalic acid, formic acid, phosphite, phosphoric acid, sulfite or sodium borohydride.

[0178] 21. The method for preparing silver-coated copper nanowires with a core-shell structure according to item 1, wherein the concentration of the reducing agent in step (b) is from 0.01 to 1.0 M.

[0179] 22. The method of preparing silver-coated copper nanowires with a core-shell structure according to item 1, wherein the reducing agent in step (b) is added at a rate of 0.1 to 500 ml / min.

[0180] 23. The method of preparing silver-coated copper nanowires with a core-shell structure according to item 1, wherein step (b) is carried out at a temperature of 0 to 100ºC.

[0181] 24. A method for preparing silver-coated copper nanowires with a core-shell structure according to any one of items 1 to 23, wherein the silver-coated copper nanowires are prepared by a batch reaction, a plug flow reaction, or a continuous stirred tank reaction process.

Claims

1. A method for preparing silver-coated copper nanowires with a core-shell structure, the method comprising: (a) Stir an aqueous solution containing (1) alkali, (2) copper compound and (3) capping agent; (b) Copper nanowires are produced by adding a reducing agent to the aqueous solution to reduce copper ions; (c) Wash and dry the produced copper nanowires; (d) Remove the oxide film from the copper nanowires produced in step (c) in a copper nanowire solution; (e) Add a reducing agent to the solution from step (d) to adjust the pH to 8 to 10, and then form a silver coating by adding a silver nitrate-ammonia complex solution dropwise; and (f) The silver-coated copper nanowires prepared in step (e) are washed and dried.

2. The method for preparing silver-coated copper nanowires with a core-shell structure according to claim 1, further comprising (c') after step (c) resynthesizing copper nanowires by adding a copper precursor and a reducing agent to a solution separated from the copper nanowires; and synthesizing copper nanowires by repeating step (c') two or more times.

3. The method for preparing silver-coated copper nanowires with a core-shell structure according to claim 1, wherein, In step (d), a mixed solution of ammonia and ammonium sulfate is used as the solution for removing the oxide film, and The concentration of the mixed solution of ammonia and ammonium sulfate in step (d) is 0.001 to 0.3 M.

4. The method for preparing silver-coated copper nanowires with a core-shell structure according to claim 1, wherein, Step (b) is performed at a temperature of 0 to 100ºC, and step (d) is performed for 1 to 60 minutes.

5. The method for preparing silver-coated copper nanowires with a core-shell structure according to claim 1, wherein, In step (e), the reducing agent is added to the copper nanowire solution from which the oxide film was removed in step (d), the pH is adjusted, and the silver nitrate-ammonia complex solution is injected at a rate of 0.5 to 500 ml / min while stirring at 50 to 1600 rpm. The silver nitrate-ammonia complex solution is prepared by mixing silver nitrate solution and ammonia water. The concentration of silver nitrate in the silver nitrate-ammonia complex solution is between 0.001 and 1 M. The concentration of ammonia in the silver nitrate-ammonia complex solution is 0.01-0.3 M.

6. The method for preparing silver-coated copper nanowires with a core-shell structure according to claim 1, wherein, The reducing agent in step (e) is selected from the group consisting of the following: oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, octanoic acid, azelaic acid, sebacic acid, tridecanoic acid, dodecanoic acid, hexadecanoic acid, maleic acid, fumaric acid, gluconic acid, tufalicic acid, mucoconic acid, mucoisocyanic acid, citrate, mesocarboxylic acid, aspartic acid, glutamic acid, diaminopimelic acid, malonic acid, arabinoic acid, gluconic acid, mesooxalic acid, oxaloacetic acid, acetone dicarboxylic acid, phthalic acid, isophthalic acid, terephthalic acid, biphenyl phthalic acid, tartaric acid, potassium sodium tartrate, ascorbic acid, hydroquinone, and glucose. The concentration of the reducing agent is from 0.001 M to 3 M.

7. The method for preparing silver-coated copper nanowires with a core-shell structure according to claim 1, wherein, In step (a), the base in (1) is NaOH, KOH, or Ca(OH)2. The concentration of the (1) base is 2.5 to 25 M.

8. The method for preparing silver-coated copper nanowires with a core-shell structure according to claim 1, wherein, The copper compound in step (a) (2) is copper hydroxide, copper nitrate, copper sulfate, copper sulfite, copper acetate, copper chloride, copper bromide, copper iodide, copper phosphate, or copper carbonate. The concentration of the copper compound in step (a) is based on copper ions from 0.004 to 0.5 M.

9. The method for preparing silver-coated copper nanowires with a core-shell structure according to claim 1, wherein, The (3) capping agent is piperazine (C4H) 10 N2) or hexamethylenediamine (C6H) 16 N2), The concentration of the capping agent is 0.008 to 2.0 M.

10. The method for preparing silver-coated copper nanowires with a core-shell structure according to claim 1, wherein, The reducing agent in step (b) is hydrazine, ascorbic acid, L(+)-ascorbic acid, isoascorbic acid, ascorbic acid derivatives, oxalic acid, formic acid, phosphite, phosphoric acid, sulfite, or sodium borohydride. The concentration of the reducing agent in step (b) is 0.01 to 1.0 M, and The reducing agent in step (b) is added at a rate of 0.1 to 500 ml / min.

11. The method for preparing silver-coated copper nanowires with a core-shell structure according to any one of claims 1 to 10, wherein, The silver-coated copper nanowires were prepared by batch reaction, plug flow reaction or continuous stirred tank reaction process.

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