KR20150107262A - Metal-carbon nanofiber and methods of fabricating the same - Google Patents

Abstract

The present invention provides a method for fabricating metal-carbon nanofibers, which can realize an oxidation resistance characteristic and process simplification, the method comprising the steps of: forming metal precursor-organic material nanofibers containing a metal precursor and an organic material; and forming metal-carbon nanofibers by performing selective oxidative thermal treatment for the metal precursor-organic material nanofibers to oxidize the carbon of the organic material and simultaneously deoxidize the metal precursor into metal, wherein the metal has lower oxidation reactivity than the carbon; the selective oxidative thermal treatment is preformed according to one thermal treatment step, not multiple thermal treatment steps; and the metal-carbon nanofibers may be formed to have different structures according to the size of oxygen partial pressure at which the selective oxidation thermal treatment is performed.

Description

METAL-CARBON NANOFIBER AND METHOD FOR MANUFACTURING THE SAME

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nanofiber and a manufacturing method thereof, and more particularly, to a metal-carbon nanofiber and a manufacturing method thereof.

Because nanostructures have a high surface area per volume, they can perform better in energy, electronics, chemical, and environmental applications than common materials. According to the structure, 0D structure is classified into 2D structure. In particular, 1D nanostructure has a different conduction characteristic depending on the aspect ratio. In particular, the electrical properties of 1D nanostructures are affected by the resistance of the structure itself and the contact resistance between the structures. The longer and thinner the 1D nanostructure, the better the electrical conductivity. The electrical conduction mechanism of 1D nanostructures is based on the percolation theory. More specifically, as nanostructures grow longer, the number of contacts present in series within a certain distance decreases. The thinner the contact, the greater the number of contacts present in parallel within a certain distance, and the effect of inducing a reduction of the total resistance according to the series and parallel distribution of such contacts can be obtained. The 1D nanostructures can be classified into nanorods, nanowires, and nanofibers according to the aspect ratio. Among them, the nanowire has a limitation that it is not easy to control the aspect ratio because the thickness and the length of the wire itself are determined as the concentration of the solute in the solution. Since the length of the nanowire is also 10 micrometers, the aspect ratio is not so large and the nanostructure itself has a limit in electrical conductivity.

In this context, the nanofiber fabricated through electrospinning is one of the highest aspect ratios of 1D nanostructures. Nanofibers are important because they can provide a solution that can overcome the limitations of conventional nanowires. Nanofibers are fabricated through electrospinning. Electrospinning is a solution-based method of fabricating nanofibers and has the advantage of producing large quantities of nanostructures at low process costs. Electrospinning produces nanofibers by applying a high voltage of several tens kV to the solution and pressing the syringe through a pump in the state of inducing electrostatic repulsion. In particular, the thickness of nanofibers can be easily controlled by adjusting the voltage applied to the solution, and the aspect ratio is large because the length is also 100 micrometers or more. In addition to this, it is possible to improve the properties through the arrangement of nanofibers. Basically, the solution used for electrospinning is composed of a polymer matrix and a solvent for constituting nanofibers. In order to fabricate nanofibers containing materials such as semiconductors, precursors or nanoparticles must be dissolved in the solution. After the electrospinning, the composition, phase, and structure of the material contained in the nanofiber can be controlled through a subsequent heat treatment process (calcination).

The present invention proposes a metal-carbon nanofiber and a manufacturing method thereof. The carbon nanofibers themselves exhibit electrical conductivity and can be applied to various fields such as energy, electrons, sensors and catalysts depending on the kind of metal. For the fabrication of metal-carbon nanofibers, a subsequent heat treatment process is required for nanofibers immediately after electrospinning, which consists of a metal precursor and a polymer matrix. The present invention proposes a condition control method in a subsequent heat treatment process and various types of metal-carbon nanofibers therefrom.

In order to increase the functionality of the nanofiber, it is necessary to have a technique of forming a secondary structure including a core / shell, a hollow and a porous structure, and a composite material of various materials into a nanofiber. First, in the case of the secondary structure, the core / shell can realize the dual characteristics by configuring the materials inside and outside differently. The hollow and porous structure have the advantage of increasing the surface area of nanofibers. These can be produced by coaxial electrospinning. This is a method of simultaneously pumping the syringe using different kinds of solutions, and conditions such as miscibility of the solution and volatility of the solvent should be controlled depending on the kind of the secondary structure. The combination of materials can be combined with various materials such as metals, semiconductors, polymers, and carbon-based materials, and has the advantage that properties according to the types can be realized. This can be done through gas-solid reaction, sol-gel method, direct-dispersion, in-situ photoreduction, and the like. In the conventional methods of forming the secondary structure and the composite material, there is a limit in that the process itself is sensitive to external conditions and is complicated. And there is no efficient production method that can implement both methods at the same time. In addition, since the raw materials required for fabricating each structure or composite material are different, practicality is low.

Disclosure of Invention Technical Problem [8] Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and it is an object of the present invention to provide a method of simultaneously forming a secondary structure of a nanofiber and a composite material. In particular, we will systematize the process through variable control of oxygen partial pressure in the subsequent heat treatment, and show the structure and characteristics of the metal - carbon nanofibers formed according to each condition. The nanofibers formed by this process can be subject to extreme thermal damage due to the sequential heat treatment of the two opposite phases of oxidation and reduction. The subsequent heat treatment process proposed in the present invention can reduce the conventional two-step heat treatment process to one step, and thus, the process efficiency is excellent.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems. However, these problems are exemplary and do not limit the scope of the present invention.

A process for producing a metal-carbon nanofiber according to one aspect of the present invention is provided. The method of fabricating the metal-carbon nanofibers includes forming a metal precursor-organic nanofiber including a metal precursor and an organic material, and oxidizing the carbon of the organic material, and simultaneously, the metal precursor- Forming a metal-carbon nanofiber by selectively oxidizing the organic nanofibers, wherein the metal has a lower oxidation reactivity than carbon, and the selective oxidation heat treatment is performed in one heat treatment step instead of a plurality of heat treatment steps , The metal-carbon nanofibers having a structure different from each other depending on the magnitude of the oxygen partial pressure to be subjected to the selective oxidation heat treatment may be formed.

In the method for manufacturing the metal-carbon nanofiber, the metal may include copper, nickel, cobalt, iron or silver, which is a metal having a lower oxidation reaction than carbon.

In the method for producing the metal-carbon nanofibers, the selective oxidation heat treatment is performed in an atmosphere of a first oxygen partial pressure to a second oxygen partial pressure, and the metal precursor-organic nanofibers in the atmosphere of oxygen partial pressure lower than the first oxygen partial pressure, The metal of the metal precursor is reduced and the carbon of the organic material is also reduced. When the metal precursor-organic nanofiber is heat-treated in an atmosphere having an oxygen partial pressure higher than the second oxygen partial pressure, Can be oxidized and the carbon of the organic substance can also be oxidized.

In the method for producing a metal-carbon nanofiber, when the metal precursor-organic nanofiber is heat-treated in the atmosphere of the first oxygen partial pressure to the second partial pressure of oxygen, the carbon remaining in the metal precursor- The carbon may support the structure of the metal-carbon nanofiber, and when the metal precursor-organic nanofiber is heat-treated in an atmosphere having an oxygen partial pressure higher than the second oxygen partial pressure, carbon in the metal precursor- The residual carbon remaining after oxidation can not support the structure of the metal-carbon nanofibers.

In the method for producing a metal-carbon nanofiber, the selective oxidation heat treatment is performed in an atmosphere having a first oxygen partial pressure higher than the first partial pressure of oxygen and lower than a third partial pressure of oxygen less than the second partial pressure of oxygen, When the metal precursor-organic nanofiber is heat-treated in the atmosphere, the carbon in the metal precursor-organic nanofiber is oxidized and the carbon is diffused according to the concentration gradient of the residual carbon, And the metal-carbon nanofibers formed by selectively oxidizing the metal precursor-organic nanofibers in an atmosphere at a temperature above the first oxygen partial pressure and lower than the third oxygen partial pressure, And a structure in which metal particles are uniformly dispersed and disposed on the outer surface of the carbon body.

In the method for producing the metal-carbon nanofiber, the selective oxidation heat treatment is performed in an atmosphere having a third oxygen partial pressure higher than the third oxygen partial pressure and lower than a fourth oxygen partial pressure lower than the second partial pressure of oxygen, When the metal precursor-organic nanofiber is heat-treated in the atmosphere, the carbon in the metal precursor-organic nanofiber is oxidized to generate a hollow in the interior of the metal-carbon nanofiber by the concentration gradient of the remaining carbon, The metal in the carbon nanofibers diffuses not only to the core of the metal-carbon nanofiber but also to the outer surface thereof, and the metal precursor-organic nanofibers are subjected to selective oxidation heat treatment in an atmosphere of the third oxygen partial pressure or higher and lower than the fourth oxygen partial pressure The metal-carbon nanofiber formed may be such that the metal particles form the core, It may have a shell (core-shell) structure surrounding the particle core to form the shell.

In the method for producing the metal-carbon nanofibers, the selective oxidation heat treatment is performed in an atmosphere having a fourth oxygen partial pressure higher than the fourth oxygen partial pressure and lower than a fifth oxygen partial pressure lower than the second partial pressure of oxygen, When the metal precursor-organic nanofiber is heat-treated in the atmosphere, the carbon in the metal precursor-organic nanofiber is oxidized to generate a hollow in the interior of the metal-carbon nanofiber by the concentration gradient of the remaining carbon, The metal-carbon nanotubes formed by selectively oxidizing the metal precursor-organic nanofibers in an atmosphere at a temperature above the fourth oxygen partial pressure and lower than the fifth oxygen partial pressure, The nanofibers may be formed by a method in which metal particles are dispersed in the base of a tube- It may have a structure are distributed in the outer surface and the hollow.

In the method of manufacturing the metal-carbon nanofibers, the selective oxidation heat treatment is performed in an atmosphere having the fifth oxygen partial pressure and lower than the second partial pressure of oxygen, and the metal precursor- Carbon nanofiber is oxidized by selective oxidative heat treatment in an atmosphere at a temperature lower than the oxygen partial pressure of the metal-carbon nanofibers, and a concentration gradient of the residual carbon remaining in the metal precursor- A part of the outer surface of the fiber may have a structure in which the thickness thereof is thinned and rupted to disperse the metal on the outer surface of the carbon body and the hollow.

In the method for producing the metal-carbon nanofibers, the selective oxidation heat treatment can be induced not only by pressure but also by time. A structure in which metal particles are uniformly dispersed and disposed on the inside of a base of a fibrous carbon body having no hollow and on the outer surface of the carbon body even when the heat treatment time is increased at a constant pressure, A core-shell structure for forming a surrounding shell, a structure in which metal particles are dispersed and disposed on the inside of a tube-shaped carbon body defining the hollow, on the outer surface of the carbon body and in the hollow, Carbon nanofibers can be formed in the order of a structure in which a portion of the outer surface of the metal-carbon nanofiber is thinned and rupted so that the outer surface of the carbon body and the metal are dispersed in the hollow. This tendency can vary with the pressure at which the structure is formed. At higher pressures, hollows are formed at a faster rate, the higher the pressure, the faster the four structures can be formed in the metal-carbon nanofibers. This is because the higher the pressure, the greater the amount of decomposition of the carbon during the same time, the larger the concentration gradient, and thus the greater the amount of external diffusion of carbon, the faster the hollow is formed.

Wherein the metal precursor comprises copper (Cu (CH ₃ COO) ₂ ) which is a copper precursor, and the organic material is polyvinyl alcohol (PVA, polyvinyl alcohol) forming a hydrogen bond with copper acetate, poly vinyl alcohol).

In the method for producing a metal-carbon nanofiber, a metal-carbon nanofiber is formed by selectively oxidizing the metal precursor-organic nanofiber so that the carbon of the organic substance is oxidized and the metal precursor is reduced to a metal , The step of autoclaving the copper precursor to copper using carbon monoxide (CO) generated by the selective oxidation heat treatment from the acetate functional group of the copper precursor as a reducing agent.

The step of forming the metal-carbon nanofibers by selectively oxidizing the metal precursor-organic nanofibers in the process for producing the copper-carbon nanofibers may include a step of thermally decomposing a part of the carbon constituting the metal precursor- pyrolysis) into combustion that is not combustion.

A metal-carbon nanofiber according to another aspect of the present invention is provided. The metal-carbon nanofibers are fabricated by the above-described manufacturing method.

According to an embodiment of the present invention as described above, it is possible to provide a method of manufacturing metal-carbon nanofibers capable of realizing oxidation resistance characteristics and process simplification. The secondary structure and the composite material implementation for improving the functionality of the nanofiber can be simultaneously realized through variable control in the process. The present invention can be applied to various fields depending on the structure of the metal-carbon nanofibers formed by the present process. It is needless to say that the scope of the present invention is not limited by these effects.

1 is a flow chart illustrating a method of manufacturing a metal-carbon nanofiber according to embodiments of the present invention.
2 is a diagram illustrating a step of forming copper precursor-organic nanofibers through electrospinning in a method of making copper-carbon nanofibers according to some embodiments of the present invention.
FIG. 3 is a graph showing the results of the selective oxidation heat treatment process by controlling the oxygen partial pressure in the one-step heat treatment and the copper-carbon nanofiber according to the comparative examples of the present invention in the method of manufacturing the copper-carbon nanofiber according to some embodiments of the present invention. And schematically illustrating the concept of the heat treatment process according to the manufacturing method.
FIG. 4 is a conceptual diagram illustrating a heat treatment process through control of oxygen partial pressure in the two-step heat treatment in the process for producing copper nanofibers according to the comparative example of the present invention.
FIG. 5 is a conceptual illustration of a self-reducing heat treatment process by controlling the oxygen partial pressure in the one-step heat treatment in the process for producing copper-carbon nanofibers according to the comparative example of the present invention.
FIG. 6 is a conceptual illustration of a selective oxidation heat treatment process through oxygen partial pressure control in a one-step heat treatment in a method of manufacturing copper-carbon nanofibers according to some embodiments of the present invention.
7 is a diagram illustrating a phase change pattern of copper in a method of manufacturing copper-carbon nanofibers according to some embodiments of the present invention and a comparative example.
8 is a graph showing the weight ratio of copper to carbon in the copper-carbon nanofiber realized by the method of manufacturing copper-carbon nanofibers according to some embodiments of the present invention and a comparative example.
FIG. 9 is a diagram illustrating a mechanism for forming copper-carbon nanofibers in the method for manufacturing copper-carbon nanofibers according to the first embodiment of the present invention.
10 is a diagram illustrating a mechanism of forming copper-carbon nanofibers in a method of manufacturing a copper-carbon nanofiber according to a second embodiment of the present invention.
11 is a diagram illustrating a mechanism of forming a copper-carbon nanofiber in a method of manufacturing a copper-carbon nanofiber according to a third embodiment of the present invention.
FIG. 12 is a diagram illustrating a mechanism of forming copper-carbon nanofibers in a method of manufacturing a copper-carbon nanofiber according to a fourth embodiment of the present invention.
FIG. 13 is a photograph of a copper-carbon nanofiber fabricated by a method of manufacturing a copper-carbon nanofiber according to some embodiments of the present invention.
14 is a photograph of a copper-carbon nanofiber fabricated by a manufacturing method according to process parameters of pressure and time of copper-carbon nanofiber according to some embodiments of the present invention.
15 is a diagram illustrating an aspect of resistance according to oxygen partial pressure in selective oxidation heat treatment using oxygen gas in a method of manufacturing copper-carbon nanofibers according to some embodiments of the present invention.
FIG. 16 is a diagram illustrating a result of evaluating the oxidation resistance of copper-carbon nanofibers formed by selective oxidation heat treatment in the method of manufacturing copper-carbon nanofibers according to an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. It should be understood, however, that the invention is not limited to the disclosed embodiments, but may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, Is provided to fully inform the user. Also, for convenience of explanation, the components may be exaggerated or reduced in size.

The method of manufacturing a metal-carbon nanofiber according to the technical idea of the present invention includes the steps of forming a metal precursor-organic nanofiber including a metal precursor and an organic material, and oxidizing the carbon of the organic material, Carbon nanofibers by selectively oxidizing the metal precursor-organic nanofibers to form the metal-carbon nanofibers, wherein the metal has a lower oxidation reactivity than carbon, and the selective oxidation heat treatment is performed at a temperature Heat treatment step.

The selective oxidation heat treatment is performed in an atmosphere of a first oxygen partial pressure to a second oxygen partial pressure, and in particular, metal-carbon nanofibers having a structure different from each other depending on the magnitude of the oxygen partial pressure to be subjected to the selective oxidation heat treatment may be formed . The criterion for the first oxygen partial pressure and the second oxygen partial pressure is as follows.

When the metal precursor-organic nanofiber is heat-treated in an atmosphere having an oxygen partial pressure lower than the first oxygen partial pressure, the metal of the metal precursor is reduced and carbon of the organic material is also reduced.

When the metal precursor-organic nanofibers are heat-treated in an atmosphere having an oxygen partial pressure higher than the second oxygen partial pressure, the metal of the metal precursor is oxidized and the carbon of the organic material is also oxidized.

When the metal precursor-organic nanofiber is heat-treated in the atmosphere of the first oxygen partial pressure to the second oxygen partial pressure, the residual carbon remaining in the metal precursor-organic nanofiber is oxidized to form the structure of the metal-carbon nanofiber When the metal precursor-organic nanofiber is heat-treated in an atmosphere having an oxygen partial pressure higher than the second partial pressure of oxygen, the carbon in the metal precursor-organic nanofiber is oxidized and the residual carbon remaining in the metal precursor- The structure of the fiber can not be supported.

The above-mentioned metal should have lower oxidation reactivity than carbon, for example, the metal may include copper, nickel, cobalt, iron or silver. Hereinafter, for convenience of explanation, various embodiments will be described in the case where the metal is copper. However, the technical idea of the present invention can be applied not only to copper but also to any metal having lower oxidation reactivity than carbon.

1 is a flow chart illustrating a method of manufacturing a metal-carbon nanofiber according to embodiments of the present invention.

Referring to FIG. 1, a method of fabricating a metal-carbon nanofiber according to embodiments of the present invention includes providing a solution including a copper precursor, an organic material, and a solvent (S10) (S20) of forming the copper precursor-organic nanofibers from the solution by electrospinning using electrostatic repulsion, and a step (S20) of oxidizing the carbon of the organic substance and simultaneously forming the copper precursor into copper (S30) by selectively oxidizing the copper precursor-organic nanofibers to reduce the copper-carbon nanofibers. In particular, the selective oxidation heat treatment is performed in one heat treatment step rather than a plurality of heat treatment steps.

2 is a diagram illustrating a step of forming copper precursor-organic nanofibers through electrospinning in a method of making copper-carbon nanofibers according to some embodiments of the present invention.

Referring to FIG. 2, a solution 22 made by mixing a metal precursor, organic matter, and a solvent in a syringe 10 for electrospinning is placed. Electrospinning is a simple and highly efficient method of making nanofibers 24_1 using electrostatic repulsion by applying a high voltage to solution 22. The solution 22 used to produce the nanofibers 24_1 may comprise a metal solid solution such as a metal precursor, an organic matrix (organic), and a solvent.

The metal solid solution is a material containing the ions of the metal nanofibers to be formed, and the combination between the functional groups in the solid solution and the organic matrix is important. Thus, it may be desirable to select materials having the same or similar types of functional groups and to make the dispersion of the metal solid solution uniform. For example, the metal precursor may comprise copper acetate (Cu (CH ₃ COO) ₂ ) to make copper nanofibers.

The organic material, that is, the organic matrix, serves as a skeleton of the nanofibers 24_1 formed through electrospinning. For example, to make copper nanofibers, the organic matrix forms a hydrogen bond with an acetate group (-CH ₃ COO-) of copper acetate (CuAc) and a polyvinyl alcohol (PVA) with a relatively low decomposition temperature .

The solvent should be able to dissolve both the metal solid solution and the organic matrix. For example, to make copper nanofibers, the solvent may use distilled water because the solubility of copper acetate and polyvinyl alcohol in water is relatively high.

For example, the copper precursor-organic nanofibers 24_1 are fabricated through electrospinning to produce electrostatic repulsion force on the solution 22 to form fibers. The copper precursor-organic nanofiber 24_1 formed by electrospinning may be subjected to oxidation and reduction followed by calcination to obtain a copper-carbon nanofiber. In the electrospinning, the thickness of the nanofibers generated according to the magnitude of the voltage of several tens kV applied to the solution 22 can be easily controlled, and the length can also be more than 100 μm. Further, the nanofiber array has an advantage that the transmittance and the conductivity can be further improved. These metal nanofibers are important because they can provide a solution that can overcome the limitations of existing nanowires.

The process of forming the nanofibers 24_1 is greatly influenced by the parameters of the solution 22. The shape of the nanofibers 24_1 produced by electrospinning depends on the viscosity of the solution 22, the surface tension, the concentration of the organic matter, the molecular weight, and the conductivity of the solvent. Among them, the viscosity of the solution (22) may have the greatest influence on the solution variables. If the viscosity is very low or very high, a bead is formed in the nanofiber 24_1, which is not suitable for the transparent electrode. Furthermore, in order to obtain the nanofiber form suitable for the transparent electrode, the conditions must be optimized by adjusting the viscosity of the solution and other solution parameters.

On the other hand, in the process of forming the nanofibers 24_1, there are electrospinning process variables and environmental variables in addition to the solution parameters. Environmental variables include humidity and temperature, because the optimal conditions for electrospinning are fixed, so that the atmosphere can be controlled by creating an environment that can meet them.

The variables affecting nanofibers (24_1) more directly than environmental variables are electrospinning process variables. The electrospinning process parameters include the magnitude of the voltage applied by the high voltage source 12, the distance between the tip 11 and the collector 14, and the feeding rate of the solution 22. Of these, the applied voltage is related to the electrostatic repulsive force which directly affects the formation of the nanofibers 24_1 in the solution 22. The larger the applied voltage is, the smaller the diameter of the nanofibers 24_1 is. However, if the applied voltage is too large, the nanofibers 24_1 cause instability in the electrospinning itself. Therefore, it is possible to form optimized nanofibers that can be applied to transparent electrodes by establishing the condition of these solution variables and process variables.

On the other hand, as a method of forming the metal precursor-organic nanofibers 24_1, various methods other than the above-described electrospinning method are possible. For example, a direct dispersion method using a solution in which metal particles are dispersed, a gas-solid reaction method using metal ions and inorganic nanoparticles, a reduction reaction by irradiating a metal precursor with ultraviolet light In-situ photoreduction method for inducing a metal precursor and a second metal precursor, a sol-gel method for performing electrospinning and heat treatment on a solution containing a first metal precursor and a second metal precursor, Organic nanofiber 24_1 can be formed.

Next, a process of selectively oxidizing and annealing the copper precursor-organic nanofibers 24_1 in order to realize oxidation-resistant copper-carbon nanofibers by a one-step heat treatment will be described. First, before describing the selective oxidation heat treatment method according to the technical idea of the present invention, a two-step heat treatment method in which an oxidation heat treatment and a reduction heat treatment are sequentially performed is referred to as Comparative Example 1, and a self-reduction heat treatment The method will be described below as Comparative Example 2.

FIG. 3 is a graph showing the results of the selective oxidation heat treatment process by controlling the oxygen partial pressure in the one-step heat treatment and the copper-carbon nanofiber according to the comparative examples of the present invention in the method of manufacturing the copper-carbon nanofiber according to some embodiments of the present invention. FIG. 4 is a conceptual illustration of a heat treatment process through control of oxygen partial pressure in the two-step heat treatment in the process for producing copper nanofibers according to Comparative Example 1 of the present invention FIG.

Referring to FIGS. 3 and 4, the copper precursor-organic nanofibers 24_1 are composed of copper 24a constituting copper acetate, which is a metal precursor, and carbon 24b constituting an organic polyvinyl alcohol. to be. The copper precursor-organic nanofibers (24_1) need to be subjected to a subsequent heat treatment process in order to make them into copper nanofibers.

The carbon 24b existing in the copper precursor-organic nanofiber 24_1 is oxidized and decomposed to proceed the heat treatment in the atmosphere containing the oxygen 30. [ As a result, the copper 24a in the metal precursor is oxidized to copper oxide (CuO), and the carbon 24b of the organic matter is oxidized in the form of carbon dioxide 35 and decomposed from the copper precursor-organic nanofiber 24_1 And finally becomes copper oxide (CuO) nanofiber 24_3. This copper oxide nanofiber (24_3) must be reduced again to pure copper nanofiber. Therefore, the final copper nanofiber can be formed by performing heat treatment in a hydrogen (H ₂ ) gas atmosphere for reduction.

That is, in order to produce the metal nanofibers, two steps of oxidation and reduction are required (FIG. 4 shows only the heat treatment in the oxidation step). The reasons for the oxidation and reduction are as follows. First, the oxidation is to remove the organic material 24b containing carbon in the form of an organic matrix used to make the nanofiber structure in electrospinning. Hydrogen gas is used to reduce the copper oxide formed in this process again. The same nanofibers are subjected to two successive heat treatments opposite to each other for oxidation and reduction, resulting in severe damage. Further, the manufacturing process is complicated and manufacturing costs are increased. As a method for solving this, as a comparative example 2 of the present invention for comparison with an embodiment of the present invention, a self-reduction heat treatment method for reducing both carbon and oxygen will be described.

5 is a conceptual illustration of a self-reducing heat treatment process by controlling the oxygen partial pressure in the one-step heat treatment in the process for producing copper-carbon nanofibers according to Comparative Example 2 of the present invention.

3 and 5, Comparative Example 2 of the present invention is characterized in that in the first heat treatment in Comparative Example 1, the oxygen partial pressure is extremely lowered to induce auto-reduction in an atmosphere where oxidation does not occur . The autoxidation refers to a heat treatment method of directly reducing copper to copper (24a) using a copper precursor having an acetate functional group such as copper acetate. Such self-reducible metals satisfy the conditions that the oxidation reactivity is lower than that of carbon such as nickel, cobalt, and iron, including copper. In the present invention, a basic experiment in which a copper precursor (CuAc) was autolored and applied to the production of nanofibers was conducted. When the oxygen partial pressure is lowered to below the reference value at which the copper 24a and the carbon 24b can be oxidized by using argon gas, a part of the carbon 24b undergoes pyrolysis reaction, and the copper precursor The copper 24a does not become an oxide by self-reduction but directly becomes a copper 24a. The copper-carbon nanofibers (24_4) fabricated through this method exhibit a constant ohmic contact behavior as in a conventional conductor. However, the copper-carbon nanofibers produced by the autothermal reduction compared to the copper nanofibers produced by the two-step heat treatment in Comparative Example 1 were not completely decomposed because the carbon was not oxidized, and the influence of the residual carbon And the electrical conductivity is lowered.

FIG. 6 is a conceptual illustration of a selective oxidation heat treatment process through oxygen partial pressure control in a one-step heat treatment in a method of manufacturing copper-carbon nanofibers according to some embodiments of the present invention.

Referring to FIGS. 3 and 6, the selective oxidation heat treatment process according to one embodiment of the present invention is introduced to solve the above-described problems. That is, in one embodiment of the present invention, a method of making a nanofiber having a high oxidation stability by controlling a partial pressure of oxygen in a heat treatment process after electrospinning by a single heat treatment process is proposed. This is possible by fully understanding and applying the oxidation reactivity and change of copper and carbon with oxygen partial pressure. In the conventional two-stage heat treatment (Comparative Example 1), both the copper 24a and the carbon 24b are oxidized under the condition of the heat treatment for oxidation. This causes the carbon 24b to be oxidized altogether, but the copper 24a is oxidized, so that additional heat treatment for reduction is required. The ordinary copper nanofibers produced through such a process are directly exposed to the outside of the crystalline copper, and the oxidation proceeds very rapidly because the surface area per volume is large.

Conversely, pure copper can be obtained immediately after the first-stage heat treatment in an atmosphere in which the copper (24a) and carbon (24b) are all reduced by lowering the oxygen partial pressure to induce self-reduction. However, since the carbon 24b is oxidized and decomposed by pyrolysis rather than being completely decomposed into combustion, a considerable amount of residual carbon remains. The nanofibers produced by this method are formed in such a structure that the copper nanoparticles are densely dispersed in the amorphous carbon. It is known that electrical conduction of copper (24a) nanoparticles arranged in this amorphous carbon matrix is achieved through electron hopping. In the case of copper-carbon nanofibers (24_4) formed through self-reduction, the amount of remaining carbon (24b) was large, and thus the electric resistance was relatively high, which was confirmed to be an ohmic contact when the actual resistance was measured. Is not good.

The two types of subsequent heat treatment methods introduced in the above comparative examples are different from the heat treatment methods proposed in the embodiment of the present invention in that both copper and carbon are oxidized or reduced. In an embodiment of the present invention, a selective oxidation method is proposed in which copper 24a is reduced and carbon 24b is oxidized and decomposed using the difference in oxidation reactivity between carbon and copper.

This is significant because it has both advantages of heat treatment in air atmosphere and advantages of heat treatment through self reduction. That is, since the copper 24a is directly reduced through the one-step heat treatment through the self-reduction, the carbon 24b can be decomposed through oxidation, so that the amount of the remaining carbon 24b is reduced. That is, the copper 24a is agglomerated in a line along an axis parallel to the copper-carbon nanofibers 24_2 and the surface of the copper 24a is surrounded by amorphous carbon 24b serving as an oxidation preventing film . The nanofibers having an electric conductivity higher than that of the self-reduction can be manufactured together with the antioxidant function that the copper nanofibers realized in these comparative examples have not.

In the method for producing copper-carbon nanofibers according to an embodiment of the present invention, the selective oxidation heat treatment process is performed in an atmosphere of a first oxygen partial pressure to a second oxygen partial pressure (i.e., a first oxygen partial pressure and a second partial pressure of oxygen) When the copper precursor-organic nanofibers 24_1 are heat-treated in an atmosphere having an oxygen partial pressure lower than the first oxygen partial pressure, the copper 24a of the copper precursor is reduced and the carbon 24b of the organic precursor is reduced, When the copper precursor-organic nanofiber 24_1 is heat-treated in an atmosphere having an oxygen partial pressure higher than the partial pressure, the copper 24a of the copper precursor is oxidized and the carbon 24b of the organic matter is also oxidized. For example, the first oxygen partial pressure may be an oxygen partial pressure corresponding to an oxidation point of the carbon 24b, and the second oxygen partial pressure may be an oxygen partial pressure corresponding to an oxidation point of the copper 24a.

When the copper precursor-organic nanofiber 24_1 is heat-treated in the atmosphere of the first oxygen partial pressure to the second partial pressure of oxygen, the carbon 24b in the copper precursor-organic nanofiber 24_1 is oxidized and the remaining carbon 24b is oxidized, If the copper precursor-organic nanofiber 24_1 is heat-treated in an atmosphere having an oxygen partial pressure higher than that of the second oxygen partial pressure, the copper precursor-organic nanofiber 24_2 The carbon 24b in the fibers 24_1 is oxidized, so that the structure of the nanofibers is collapsed or the nanofibers are formed.

According to one embodiment of the present invention, copper 24a constituting the copper precursor is reduced and only carbon 24b constituting the organic matter is oxidized using the difference in oxidation reactivity between carbon 24b and copper 24a And the selective oxidation method which has the advantages of the heat treatment in the conventional air atmosphere and the advantages of the heat treatment through the autothermal reduction are all significant.

The copper-carbon nanofiber 24_2 embodied by the selective oxidation heat treatment is formed so that the nanoparticles of the copper 24a in the nanofiber composed of the amorphous carbon 24b are oriented in the longitudinal direction of the nanofiber 24a to prevent oxidation of the copper 24a As shown in FIG. Furthermore, the nanoparticles of the copper 24a disposed on the copper-carbon nanofiber 24_2 have a relatively higher density inside the nanofiber corresponding to the core portion of the nanofiber, So as to have a relatively lower density. In addition, the nanoparticles of the copper (24a) aggregated in a line in the core (core) are arranged to be connected to each other, thereby securing the electrical conductivity characteristics of the nanofibers.

On the other hand, as shown in FIG. 5, in the copper-carbon nanofiber 24_4 realized by the autothermal reduction treatment, the nanoparticles of the copper 24a are uniformly distributed throughout the fiber without having a high dispersion density in the core of the fiber . Further, in the copper-carbon nanofiber (24_4) realized by the self-reduction heat treatment, the distribution of the nanoparticles of the copper (24a) is not connected to each other but is arranged in a spaced manner, The electric conductivity is relatively lower than that of the nanofiber 24_2 realized by the selective oxidation heat treatment including the copper (24a) nanoparticles. Therefore, the copper-carbon nanofiber 24_2 realized by the selective oxidation heat treatment can have improved electrical conductivity than the self-reduction with the antioxidant function that the copper nanofibers have in these comparative examples.

The process for reducing copper in the selective oxidation heat treatment process according to an embodiment of the present invention may include a reaction represented by Chemical Formulas 1 to 4.

(Formula 1)

Cu (CH ₃ COO) _{2 -} > CuCO ₃ + CH ₃ COCH ₃

(2)

CuCO _{3 -} > CuO + CO ₂

(Formula 3)

CH ₃ COCH _{3 -} > CO + C ₂ H ₆

(Formula 4)

CuO + CO → Cu + CO ₂

By this reaction, a reducing agent (for example, carbon monoxide (CO)) is automatically generated in the acetate, and a pure copper phase can be obtained during the heat treatment process.

Hereinafter, it will be described from the thermodynamic point of view that a selective oxidation heat treatment process can be performed in the process for producing copper-carbon nanofibers according to an embodiment of the present invention.

The reduction of copper acetate (CuAc), which is a metal precursor used in the selective oxidation heat treatment, is due to carbon monoxide (CO), which is a reducing agent generated during the heat treatment in the acetate functional group. That is, copper is reduced by self-reduction even in the selective oxidation heat treatment process. Therefore, in order to find the oxygen partial pressure required in this heat treatment, the reaction of copper generated in the autothermal reduction should be considered.

  First, when copper acetate is decomposed, copper oxide is reduced by carbon monoxide (CO) after copper oxide (CuO) is formed. Therefore, the Gibbs free energy for the oxidation reaction of carbon monoxide must be confirmed in the Elling diagram. In the actual E-ring diagram, the oxidation reaction of carbon monoxide is not shown, so it is necessary to utilize the reaction in which carbon is oxidized to form carbon monoxide and carbon dioxide. When the reaction of forming carbon monoxide in the reaction of forming carbon dioxide is reversed, it becomes possible to know the Gibbs energy in the reaction in which the actual carbon monoxide is oxidized to carbon dioxide at a given temperature and pressure. It should be noted that as the autoregression proceeds, the graph of the oxidation reactivity of carbon monoxide increases. This is due to the ratio of carbon monoxide and carbon dioxide in the Elling diagram, which is the result of carbon monoxide being consumed by autothermal reduction, resulting in carbon dioxide. In order to find the oxygen partial pressure for the selective oxidation heat treatment, the Gibbs free energy for the oxidation reaction of the carbon monoxide obtained through a series of processes can be shown in the Elling diagram, which can be compared with the actual oxidation reaction of copper.

FIG. 7 is a diagram illustrating a phase change pattern of copper in a method of manufacturing copper-carbon nanofibers according to some embodiments of the present invention and a comparative example, and FIG. Graph showing the weight ratio of copper to carbon in the copper-carbon nanofiber realized by the method for producing copper-carbon nanofibers. Specifically, in an oxygen partial pressure atmosphere of 1.0 x 10 ^-2 Torr, 2.5 x 10 ^-2 Torr, 6.0 x 10 ^-2 Torr, or 1.0 x 10 ^-1 Torr within the range of the first oxygen partial pressure to the second partial pressure of oxygen, Carbon nanofibers according to some embodiments of the present invention formed by oxidative heat treatment and a self-reducing heat treatment in an oxygen partial pressure atmosphere of 1.0 x 10 < ^{-2 &} gt ^; Torr, which is lower than the first oxygen partial pressure, The nanofibers and the nanofibers according to the comparative example of the present invention formed by ordinary heat treatment in an oxygen partial pressure atmosphere of 7.6 x 10 ² Torr higher than the second oxygen partial pressure were shown.

7, copper is oxidized only in the nanofibers formed by ordinary heat treatment in an oxygen partial pressure atmosphere higher than the second oxygen partial pressure, and in the nanofiber formed by heat treatment in an oxygen partial pressure atmosphere lower than the second oxygen partial pressure, copper is oxidized .

Referring to FIG. 8, the amount of copper and carbon was measured using XPS to analyze the degree of decomposition of carbon in the selective oxidation heat treatment. The main mechanism of carbon decomposition was changed from pyrolysis to combustion Is within the range of the above-described first oxygen partial pressure to the second oxygen partial pressure. On the other hand, in the nanofibers according to the comparative example of the present invention formed by heat treatment in an oxygen partial pressure atmosphere higher than the second oxygen partial pressure, most of the carbon is decomposed into burning, and the weight ratio of carbon in the nanofiber is remarkably lowered.

On the other hand, the present inventors have found that it is possible to form metal-carbon nanofibers having various structures different from each other according to the oxygen partial pressure even within the range of the first oxygen partial pressure to the second oxygen partial pressure, In the following, this will be described in detail.

9 to 12 are diagrams illustrating a mechanism of formation of copper-carbon nanofibers in a method of manufacturing copper-carbon nanofibers according to embodiments of the present invention.

Referring to FIG. 9, the copper precursor-organic nanofibers are selectively oxidized (for example, at a pressure of 1.0 x 10 < ^-2 > Torr) in an atmosphere above the first oxygen partial pressure and below the third oxygen partial pressure, A copper-carbon nanofiber (24_2) according to the first embodiment of the present invention formed by heat treatment is disclosed.

When the metal precursor-organic nanofibers are heat-treated in an atmosphere having an oxygen partial pressure equal to or higher than the third oxygen partial pressure, the carbon in the copper precursor-organic nanofibers is oxidized and the carbon is diffused according to the concentration gradient of the residual carbon. Hollows (H in Figs. 10 to 12) are generated inside the carbon nanofibers. Since the carbon is oxidized more at the outer surface than the core of the copper-carbon nanofiber and the concentration of carbon at the outer surface is lower than that of the core, diffusion of carbon becomes more active outside of the nanofiber, A hollow H is generated.

The copper-carbon nanofibers 24_2 according to the first embodiment of the present invention, formed by selective oxidation heat treatment of the copper precursor-organic nanofibers 24_1 in the atmosphere above the first oxygen partial pressure and below the third oxygen partial pressure, The carbon particles 24b are present in a hollow fiber-free form and the copper particles 24a are in contact with the inside of the carbon body 24b and the carbon bodies 24b. 24b on the outer surface thereof. Particularly, the copper-carbon nanofibers 24_2 shown in FIG. 9 (b) are formed by the copper-carbon nanofibers 24_2 shown in FIG. 9 (a) ) In the outer surface direction. This diffusion is caused by the relaxation of the stress due to the difference in thermal expansion coefficient between copper and carbon.

10, the third oxygen partial pressure is not more than the first in an atmosphere of less than 4 small oxygen partial pressure than the second oxygen partial pressure (e.g., 2.5 x 10 ^-2 Torr), the copper precursor-selective oxidation of organic nanofibres A copper-carbon nanofiber (24_2) according to a second embodiment of the present invention formed by heat treatment is disclosed.

When the copper precursor-organic nanofiber is annealed in the atmosphere of the oxygen partial pressure equal to or higher than the fourth oxygen partial pressure, the carbon in the copper precursor-organic nanofiber is oxidized and the concentration of the residual carbon is reduced, Hollows (H in FIGS. 11 to 12) are produced, and the copper 24a in the copper-carbon nanofiber can diffuse not only into the core of the copper-carbon nanofiber but also to the outer surface.

The copper-carbon nanofibers 24_2 according to the second embodiment of the present invention, formed by selectively oxidizing the copper precursor-organic nanofibers 24_1 in the atmosphere above the third oxygen partial pressure and below the fourth oxygen partial pressure, Shell structure in which the particles 24a form a core of the nanofibers and the carbon 24b forms a shell surrounding the copper 24a particles. Particularly, the copper-carbon nanofibers 24_2 shown in FIG. 10 (b) are formed by the copper-carbon nanofibers 24_2 shown in FIG. 10 (a) ) In the direction of the core. This diffusion is caused by the relaxation of the stress due to the difference in thermal expansion coefficient between copper and carbon. Further, it is observed that among the copper (24a) particles, a small particle to a large particle is converted, which can be understood as a so-called Ostwald ripening phenomenon.

Referring to FIG. 11, the copper precursor-organic nanofibers are selectively oxidized (for example, 5.0 x 10 < ^-2 > Torr) in an atmosphere above the fourth oxygen partial pressure and below the fifth oxygen partial pressure, A copper-carbon nanofiber (24_2) according to a third embodiment of the present invention formed by heat treatment is disclosed.

In the case where the copper precursor-organic nanofiber is annealed in the atmosphere of the oxygen partial pressure equal to or higher than the fifth oxygen partial pressure, the carbon in the copper precursor-organic nanofiber is oxidized and the residual carbon concentration gradient, A hollow (H in Fig. 12) is generated, and a part of the outer surface of the copper-carbon nanofiber becomes thinner and can be ruptured (R in Fig. 12).

The copper-carbon nanofibers 24_2 according to the third embodiment of the present invention, formed by selectively oxidizing the copper precursor-organic nanofibers 24_1 in the atmosphere above the fourth oxygen partial pressure and below the fifth oxygen partial pressure, The carbon particles 24a may have a structure in which the particles are dispersed and arranged in the interior of the base of the tubular shaped carbon body 24b defining the hollow H and on the outer surface of the carbon body 24b and in the hollow H, In this case, the tube-shaped carbon body 24b defining the hollow H has a thickness enough to allow the copper 24a particles to be disposed therein.

Particularly, the copper-carbon nanofibers 24_2 shown in FIG. 11 (b) are formed by the copper-carbon nanofibers 24_2 shown in FIG. 11 (a) In the core direction or the outer surface. This diffusion is caused by the relaxation of the stress due to the difference in thermal expansion coefficient between copper and carbon. Further, this diffusion may be performed through a nanochannel 25 formed inside the base of the tube-shaped carbon body 24b. It can also be observed that the so-called Ostwald ripening phenomenon converts from small copper (24a) particles to large copper (24a) particles.

Referring to FIG. 12, in the present invention, formed by selectively oxidizing the copper precursor-organic nanofibers in an atmosphere having the fifth oxygen partial pressure above the second oxygen partial pressure but below the second oxygen partial pressure (for example, 6.0 x 10 ^-2 Torr) A carbon-carbon nanofiber (24_2) according to the fourth embodiment is disclosed.

The copper-carbon nanofibers 24_2 according to the fourth embodiment of the present invention formed by selective oxidation heat treatment of the copper precursor-organic nanofibers 24_1 in the atmosphere above the fifth oxygen partial pressure and below the second oxygen partial pressure, 24a may have a structure in which the particles are dispersed on the outer surface of the tube-like carbon body 24b defining the hollow H and in the hollow H. In this case, the tubular carbon body 24b defining the hollow H can not secure a thickness enough to allow the copper 24a particles to be disposed inside the base, and a part of the outer surface is thinned to be ruptured (R) .

Particularly, the copper-carbon nanofibers 24_2 shown in FIG. 12 (b) are formed by the copper-carbon nanofibers 24_2 shown in FIG. 12 (a) In the core direction or the outer surface. This diffusion is caused by the relaxation of the stress due to the difference in thermal expansion coefficient between copper and carbon. Further, this diffusion may be performed through a nanochannel formed inside the base of the tube-shaped carbon body 24b. It can also be observed that the so-called Ostwald ripening phenomenon converts from small copper (24a) particles to large copper (24a) particles.

FIG. 13 is a photograph of a copper-carbon nanofiber fabricated by the method of manufacturing a copper-carbon nanofiber according to some embodiments of the present invention. Specifically, FIG. 13 (a) shows the result of selective oxidation treatment of the copper precursor-organic nanofiber 24_1 in an oxygen partial pressure atmosphere of 1.0 x 10 ^-2 Torr, which is the atmosphere above the first oxygen partial pressure and below the third oxygen partial pressure FIG. 13B is a photograph of the copper-carbon nanofiber 24_2 according to the first embodiment of the present invention. FIG. 13B is a photograph of the copper-carbon nanofiber 24_2 according to the first embodiment of the present invention, Carbon nanofibers 24_2 according to the second embodiment of the present invention formed by selective oxidation heat treatment in an oxygen partial pressure atmosphere of 2.5 x 10 ^-2 Torr, which is an atmosphere below the oxygen partial pressure, ) Is formed by selectively oxidizing the copper precursor-organic nanofibers 24_1 in an oxygen partial pressure atmosphere of 5.0 x 10 < ^{-2 &} gt ^; Torr, which is the atmosphere above the fourth oxygen partial pressure and below the fifth oxygen partial pressure, Copper- Of bovine nanofibers (24_2) a photo deulyimyeo, 13 record the (d) a copper precursor of organic nanofibres (24_1) of at least said fifth oxygen partial pressure atmosphere of less than said second oxygen partial pressure, 6.0 x 10 ^-2 Carbon nanofibers 24_2 according to the fourth embodiment of the present invention formed by selective oxidation heat treatment in an oxygen partial pressure atmosphere of Torr. Since the structure of these nanofibers has been described above, the explanation is omitted here.

Fig. 14 shows the structure formation pattern at the pressure and time of the selective oxidation heat treatment. According to this structure, even when the heat treatment time is increased at a constant pressure, the first structure (for example, the structure disclosed in FIG. 9) in which the metal particles are uniformly dispersed and disposed on the inside of the base of the fibrous carbon body without hollow and on the outer surface of the carbon body, , A second structure in the form of a core-shell (for example, the structure disclosed in FIG. 10) in which metal particles form the core and carbon forms a shell surrounding the metal particles, (For example, the structure disclosed in Fig. 11) dispersed in the hollow and on the outer surface of the carbon body and the inside of the tube-shaped carbon body defining the hollow, a hollow is generated inside the nanofiber , A portion of the outer surface of the metal-carbon nanofiber is formed in the order of a fourth structure (for example, the structure disclosed in FIG. 12) in which the thickness is thinned and rupted to disperse the metal on the outer surface of the carbon body and the hollow .

For example, in the selective oxidation heat treatment of the copper precursor-organic nanofibers in an oxygen partial pressure atmosphere of 2.5 x 10 ^-2 Torr, which is the atmosphere above the third oxygen partial pressure and below the fourth oxygen partial pressure, And at least a part of the copper-carbon nanofibers having the fourth structure is sequentially formed.

Of course, this tendency can vary with the pressure at which the structure is formed. The hollow is formed at a higher pressure at a higher pressure, and the higher the pressure, the faster the four structures of the first to fourth structures are formed in the metal-carbon nanofiber. This is because the higher the pressure, the greater the amount of decomposition of the carbon during the same time, the larger the concentration gradient, and thus the greater the amount of external diffusion of carbon and the faster the hollow is formed.

15 is a diagram illustrating an aspect of resistance according to oxygen partial pressure in selective oxidation heat treatment using oxygen gas in a method of manufacturing copper-carbon nanofibers according to some embodiments of the present invention.

15, the copper precursor-organic nanofibers 24_1 are subjected to a selective oxidation heat treatment in an oxygen partial pressure atmosphere of 2.5 x 10 < ^{-2 &} gt ^; Torr, which is the atmosphere above the third oxygen partial pressure and below the fourth oxygen partial pressure, It is understood that the copper-carbon nanofiber according to the second embodiment exhibits the lowest sheet resistance because the copper (24a) particles have a conductive structure concentrated in a line in the core of the nanofiber.

16 is a graph illustrating a result of evaluating the oxidation resistance of the copper-carbon nanofibers formed by the selective oxidation heat treatment in the method of manufacturing the copper-carbon nanofiber according to the second embodiment of the present invention.

16, the copper precursor-organic nanofibers 24_1 are subjected to selective oxidation heat treatment in an oxygen partial pressure atmosphere of 2.5 x 10 < ^{-2 &} gt ^; Torr, which is the atmosphere above the third oxygen partial pressure and below the fourth oxygen partial pressure, The oxidation resistance of the copper-carbon nanofibers according to the second embodiment was evaluated. The evaluation conditions were as follows: at room temperature and atmospheric conditions similar to those of general devices, and by measuring the sheet resistance for 28 days, Respectively. As a control, copper nanofibers were used.

As a result of examining the change in resistance due to the oxidation of copper in the two nanofibers, it was confirmed that the resistance was increased to about 10% for 28 days in the copper-carbon nanofibers unlike the copper nanofiber set as the control group. In the case of the copper nanofiber set as the control group, the resistance increased at a very rapid rate, which is 12 times higher than that of the conventional copper nanofiber.

In order to prevent oxidation of copper nanofibers as well as the control group, we compared the results with reference to the research data on the prevention of oxidation by covering the coating film with ALD method. In this experiment, oxidation was also carried out at room temperature, atmospheric pressure, and air atmosphere, where the pure copper nanofibers increased by 60% after 28 days. Therefore, when these control groups are checked, it can be judged that the copper-carbon nanofiber according to an embodiment of the present invention has a certain antioxidant ability.

In the case of the copper-carbon nanofibers according to the embodiment of the present invention, it is significant in that an oxidation-preventive film is formed from the PVA added to the solution in order to fabricate the nanofiber structure. In the case of covering the outer film with ALD for oxidation resistance, the process is further added and the material is ineffective. However, the method proposed in the present embodiments is a method of completely decomposing the carbon film of the nanofiber formed by electrospinning However, it is significant in that it is controlled by selective oxidation heat treatment with an effective structure and thickness to prevent oxidation.

The oxidation-resistant copper-carbon (Cu-C) nanofiber formed through the first-stage heat treatment process is of great significance in that it solves the very large problem of oxidization that was previously caused by the copper material. In contrast to the conventional process of adding a new process by coating a coating film on the outside in order to solve the oxidation problem, the technique has been used to reuse the material necessary for making the nanofiber, In addition, it can be applied to various fields where copper can be used as an electrode at present.

Further, as described above, the metal-carbon nanofibers having various structures that are different from each other depending on the oxygen partial pressure can be formed even within the range of the first oxygen partial pressure to the second oxygen partial pressure, in which the selective oxidation heat treatment is performed As a result, it can be applied to various applications depending on each structure.

For example, as shown in Fig. 9, a structure in which metal particles 24a such as nickel, cobalt or iron are uniformly dispersed and disposed on the inside of the base of the hollow carbon fiber body 24b and on the outer surface of the carbon body 24b The metal-carbon nanofibers 24_2 having the carbon nanofibers 24-2 can be applied to an energy field such as a battery.

For example, as shown in Fig. 10, a metal core 24a having a core-shell structure in which metal particles 24a such as copper form a core and carbon 24b forms a shell surrounding the metal particles 24a The metal-carbon nanofiber 24_2 can be applied to an electronic product using a transparent electrode.

11, particles of copper, zinc oxide, and aluminum oxide are formed on the inside of the tube-shaped carbon body 24b defining the hollow H, on the outer surface of the carbon body 24b, H), the metal-carbon nanofibers 24_2 can be applied to an environmental field for reducing carbon dioxide.

For example, as shown in FIG. 12, particles of copper and palladium are dispersed on the outer surface of the tube-like carbon body 24b defining the hollow H and in the hollow H, (24_2) can be applied to a chemical field that senses gas.

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the invention. Accordingly, the true scope of the present invention should be determined by the technical idea of the appended claims.

24_1: Copper Precursor - Organic Nanofibers
24_2: Copper-carbon nanofibers
24a: Copper
24b: Carbon

Claims (14)

Forming a metal precursor-organic nanofiber comprising a metal precursor and an organic material; And
Carbon nanofibers by selectively oxidizing the metal precursor-organic nanofibers such that the carbon of the organic material is oxidized and the metal precursor is reduced to a metal,
The metal has lower oxidation reactivity than carbon,
The selective oxidation heat treatment is performed in one heat treatment step, not in a plurality of heat treatment steps,
Carbon nanofibers having different structures depending on oxygen partial pressure and / or time to which the selective oxidation heat treatment is performed,
Method for manufacturing metal - carbon nanofibers. The method according to claim 1,
Wherein the metal comprises copper, nickel, cobalt, iron or silver which is a metal having a lower oxidation reactivity than carbon. The method according to claim 1,
Wherein the selective oxidation heat treatment is performed in an atmosphere of a first oxygen partial pressure to a second oxygen partial pressure,
When the metal precursor-organic nanofibers are heat-treated in an atmosphere having an oxygen partial pressure lower than the first oxygen partial pressure, the metal of the metal precursor is reduced and the carbon of the organic material is reduced,
Wherein the metal precursor of the metal precursor is oxidized and the carbon of the metal precursor is oxidized when the metal precursor-organic nanofiber is heat-treated in an atmosphere having an oxygen partial pressure higher than the second oxygen partial pressure. The method of claim 3,
When the metal precursor-organic nanofiber is heat-treated in the atmosphere of the first oxygen partial pressure to the second oxygen partial pressure, the residual carbon remaining in the metal precursor-organic nanofiber is oxidized to form the structure of the metal-carbon nanofiber Lt; / RTI >
When the metal precursor-organic nanofibers are heat-treated in an atmosphere having an oxygen partial pressure higher than the second partial pressure of oxygen, the carbon remaining in the metal precursor-organic nanofibers is oxidized and the residual carbon remains in the structure of the metal-carbon nanofibers A method for producing a metal-carbon nanofiber. The method of claim 3,
Wherein the selective oxidation heat treatment is performed in an atmosphere having a first oxygen partial pressure higher than the first oxygen partial pressure and lower than a third oxygen partial pressure lower than the second partial pressure of oxygen,
When the metal precursor-organic nanofiber is heat-treated in an atmosphere of oxygen partial pressure equal to or higher than the third oxygen partial pressure, the carbon in the metal precursor-organic nanofiber is oxidized and the carbon is diffused according to a concentration gradient of the residual carbon, A hollow is formed inside the carbon nanofiber,
The metal-carbon nanofibers formed by selective oxidation heat treatment of the metal precursor-organic nanofibers in an atmosphere at a temperature above the first oxygen partial pressure and below the third oxygen partial pressure, Having a structure in which metal particles are uniformly dispersed and arranged on the outer surface of the substrate
Method for manufacturing metal - carbon nanofibers. 6. The method of claim 5,
Wherein the selective oxidation heat treatment is performed in an atmosphere having a third oxygen partial pressure and a fourth oxygen partial pressure lower than the second partial pressure of oxygen,
When the metal precursor-organic nanofiber is heat-treated in an atmosphere of oxygen partial pressure equal to or higher than the fourth oxygen partial pressure, the carbon in the metal precursor-organic nanofiber is oxidized and the concentration of residual carbon in the metal precursor- The metal in the metal-carbon nanofiber diffuses not only into the core of the metal-carbon nanofiber but also to the outer surface,
The metal-carbon nanofibers formed by selective oxidation heat treatment of the metal precursor-organic nanofibers in an atmosphere of the third oxygen partial pressure or higher and lower than the fourth oxygen partial pressure are formed such that the metal particles form the core, Having a core-shell structure forming an encapsulating shell,
Method for manufacturing metal - carbon nanofibers. The method according to claim 6,
Wherein the selective oxidation heat treatment is performed in an atmosphere having a fourth oxygen partial pressure higher than the fourth partial pressure of oxygen and lower than the second partial pressure of oxygen,
When the metal precursor-organic nanofiber is heat-treated in an atmosphere of oxygen partial pressure equal to or higher than the fifth oxygen partial pressure, the carbon in the metal precursor-organic nanofiber is oxidized and the residual carbon concentration gradient of the metal- Carbon nanofibers are partially hollowed out and rupture, and the metal-carbon nano-
The metal-carbon nanofibers formed by selectively oxidizing the metal precursor-organic nanofibers in an atmosphere having a fourth oxygen partial pressure or higher and lower than the fifth oxygen partial pressure, A carbon body, an outer surface of the carbon body, and a structure dispersedly disposed in the hollow,
Method for manufacturing metal - carbon nanofibers. 8. The method of claim 7,
Wherein the selective oxidation heat treatment is performed in an atmosphere having the fifth oxygen partial pressure and lower than the second partial pressure of oxygen,
Wherein the metal precursor-organic nanofibers are selectively oxidized in an atmosphere of the second oxygen partial pressure or higher and the second oxygen partial pressure is higher than the fifth oxygen partial pressure to oxidize the carbon in the metal precursor- Carbon nanofibers having a structure in which a hollow is formed inside the carbon nanofiber and a part of an outer surface of the metal carbon nanofiber is thinned and ruptured to disperse the metal on the outer surface of the carbon body and in the hollow, ≪ / RTI > The method according to claim 1,
Depending on the time during which the selective oxidation heat treatment is performed,
A structure in which the metal is uniformly dispersed and disposed on the inside of a base of a fibrous carbon body having no hollow and on an outer surface of the carbon body;
A core-shell structure in which the metal forms a core and carbon forms a shell surrounding the metal;
A structure in which the metal is dispersed and arranged in the base of the tubular carbon body defining the hollow, on the outer surface of the carbon body, and in the hollow; And
A hollow is formed inside the nanofiber, a part of the outer surface of the metal-carbon nanofiber is thinned and rupted, and the metal is dispersedly disposed on the outer surface of the carbon body and in the hollow;
Wherein the metal-carbon nanofibers are sequentially formed. 10. The method of claim 9,
Wherein the oxygen partial pressure is constant while the selective oxidation heat treatment is performed. The method according to claim 1,
Wherein the metal precursor comprises copper acetate (Cu (CH ₃ COO) ₂ ), which is a copper precursor, and the organic material comprises a metal-carbon (PEC) material comprising polyvinyl alcohol (PVA) A method for producing nanofibers. 12. The method of claim 11,
The step of forming the metal-carbon nanofibers by selectively oxidizing the metal precursor-organic nanofibers such that the carbon of the organic material is oxidized and the metal precursor is reduced to a metal,
Carbon-nanofiber production comprising the step of autoclaving the copper precursor to copper using carbon monoxide (CO) generated as a reducing agent from the acetate functional group of the copper precursor by the selective oxidation heat treatment. Way. The method according to claim 1,
The step of forming the metal-carbon nanofibers by selective oxidation heat treatment of the metal precursor-organic nanofibers may include decomposing a part of carbon constituting the metal precursor-organic nanofibers into combustion rather than pyrolysis ≪ / RTI > carbon nanofibers. 14. The metal-carbon nanofiber as claimed in any one of claims 1 to 13.

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