KR102224146B1 - Method for producing carbon nanotube-carbon nanofiber composite and carbon nanotube-carbon nanofiber composite produced by the same - Google Patents

Abstract

The present invention relates to a method for manufacturing a carbon nanotube-carbon nanofiber composite to allow a carbon nanotube to be grown from a surface of a carbon nanofiber, and a carbon nanotube-carbon nanofiber composite manufactured thereby. According to the present invention, the method comprises: a first step of dissolving an alkali metal precursor in a solvent to prepare an alkali metal precursor solution; a second step of preparing a spinning solution by dissolving a carbon-containing polymer in the alkali metal precursor solution; a third step of electrospinning the spinning solution to prepare a carbon-containing polymer nanofiber having the alkali metal precursor bonded to the surface thereof; a fourth step of heat-treating the carbon-containing polymer nanofibers to prepare carbon nanofibers having the alkali metal precursor bonded thereto; and a fifth step of performing heat treatment while supplying a carbon source to the carbon nanofibers to activate the alkali metal precursors to be activated as an alkali metal nanocatalyst and allowing the carbon source to be bonded to the surface of carbon nanofibers by the nanocatalyst to be crystalized and grown into carbon nanotubes, thereby manufacturing the carbon nanofibers having the carbon nanotubes bonded to the surface thereof.

Description

Method for producing carbon nanotube-carbon nanofiber composite and carbon nanotube-carbon nanofiber composite produced by the same}

The present invention relates to a method of manufacturing a carbon nanotube-carbon nanofiber composite, and a carbon nanotube-carbon nanofiber composite manufactured thereby.

Carbon is a substance that exists in various forms, and the structure and physical properties of the substance change depending on the method of bonding between carbon atoms. The carbon atom has 4 electrons consisting of 2 2s orbitals and 2 other 2p orbitals, and various allotropes exist by bonding electrons with adjacent carbon atoms in various covalent bonds. That is, when a carbon atom is covalently bonded with another atom, four electrons present in the outermost shell form sp ³ , sp ² and sp hybrid orbitals by the hybridization of s orbitals and p orbitals.

Representative carbon allotropes of each hybrid orbital are ^{diamond consisting of sp 3} hybrid orbitals, ^{graphite consisting of sp 2} hybrid orbitals, carbin consisting of sp hybrid orbitals. In addition, carbon nanofibers (CNF), carbon nanotubes (CNT), and fullerenes as carbon nanomaterials that have recently been in the spotlight are ^{composed of sp 2} hybrid orbitals, but their structural form is Because they are different, there are differences in the properties of substances.

Among them, carbon nanofibers are in the spotlight as a reinforcing component of fiber reinforced materials because of their excellent mechanical strength and conductivity.

Carbon nanotubes are attracting attention as high-performance materials because they have superior mechanical strength, superior elasticity, thermal and electrical properties, and low density than carbon nanofibers. There has been a lot of effort so far for carbon nanotubes, but to be used in a wider variety of fields, there is a prerequisite problem that it must be able to manufacture much longer and cheaper than now. In recent years, research on composite materials using carbon nanotubes and polymers has been conducted. However, since carbon nanotubes have a large specific surface area, the contact interface between polymers and composites becomes large, and if perfect dispersion is not achieved, carbon nanotubes have a large specific surface area. Since it is difficult to realize high thermal conductivity, which is a unique physical property of the tube, it is difficult to disperse carbon nanotubes in the polymer, making practical application difficult. A lot of research is still needed until development.

Because of these circumstances, a composite material formed of carbon nanotubes on carbon nanofibers can combine the advantages of both, and can extend excellent electrical and mechanical properties not only in the longitudinal direction of the carbon nanofibers, but also in the direction perpendicular to the carbon nanofibers. It can serve as an ideal two-dimensional fiber reinforcement component. Furthermore, since these composite materials can utilize the relatively large surface area of carbon nanotubes, it is possible to substantially expand the bonding area, and because functional groups can be introduced into the carbon nanotubes, the compatibility of fiber-reinforced materials with polymers can be improved. It is expected that a material with excellent mechanical strength is expected, so even though it is expected to greatly contribute to the industrial field where high-performance composite materials are required, the bonding strength between the carbon nanotubes and carbon nanofibers is in order for the composite material of carbon nanotubes to function properly. There is a problem that should be excellent, but not.

Until now, composite materials of carbon nanotubes and carbon nanofibers have suggested a solution to the problem of dispersing carbon nanotubes in polymers, but the bonding strength between carbon nanotubes and carbon nanofibers is weak, and they are not aligned carbon nanotubes. When it is made of a composite material, there is a problem that the mechanical strength is rather weak.

In particular, since most of the non-alkali metal catalysts such as iron (Fe), nickel (Ni), cobalt (Co) and palladium (Pd) are used, a number of non-alkali metal catalyst particles are formed as impurities in the carbon nanotube after being synthesized as a composite material. Will remain. This can be confirmed through FIG. 1 showing a defect occurring in a conventional composite material of carbon nanotubes and carbon nanofibers in a TEM photograph, and a defective part caused by non-alkali metal catalyst particles in the part indicated by the arrow in FIG. 1 Is confirmed.

For this reason, a high concentration of acid treatment is required to remove the non-alkali metal catalyst particles, but there is a hassle to proceed multiple times continuously because the non-alkali metal catalyst particles are not completely removed with a single acid treatment. There is a problem in that washing water is required each time, which adds to the environmental cost, and it is difficult to mass-produce a composite material of carbon nanotubes and carbon nanofibers.

Therefore, it is the time to desperately require research on technology development for a new composite material that can grow carbon nanotubes on carbon nanofibers by breaking away from the existing composite materials of carbon nanotubes and carbon nanofibers.

Registered Korean Patent Publication No. 10-0829001, as of May 6, 2008.

The present invention was invented to solve the above problems, and a method of manufacturing a carbon nanotube-carbon nanofiber composite that allows carbon nanotubes to grow from the surface of a carbon nanofiber, and a carbon nanotube-carbon manufactured thereby Providing a nanofiber composite is a technical challenge.

In order to solve the above technical problem, the present invention comprises: a first step of preparing an alkali metal precursor solution by dissolving an alkali metal precursor in a solvent; A second step of preparing a spinning solution by dissolving a carbon-containing polymer in the alkali metal precursor solution; A third step of electrospinning the spinning solution to prepare carbon-containing polymer nanofibers to which the alkali metal precursor is bonded to the surface; A fourth step of heat-treating the carbon-containing polymer nanofibers to prepare carbon nanofibers in which the alkali metal precursor is bonded to the surface; And heat treatment while supplying a carbon source to the carbon nanofibers, so that the alkali metal precursor is activated with an alkali metal nanocatalyst, and the carbon source is bonded to the surface of the carbon nanofiber by the nanocatalyst to form a carbon nanotube. It provides a method for producing a carbon nanotube-carbon nanofiber composite comprising; a fifth step of crystallizing and growing to produce carbon nanofibers to which the carbon nanotubes are bonded to the surface.

In the present invention, the alkali metal precursor is characterized in that it is selected from the group consisting of a lithium precursor (Li precursor), a sodium precursor (Na precursor), a potassium precursor (K precursor) and a mixture thereof.

In the present invention, the carbon-containing polymer is polyacrylonitrile (PAN), polyvinyl acetate (PVA), polyvinyl pyrrolidone (PVP), polycarbonate (PC). , Polyvinyl chloride (PVC), cellulose (cellulose), cellulose acetate (cellulose acetate) and characterized in that selected from the group consisting of a mixture thereof.

In the present invention, the carbon source is a liquid, gaseous or solid carbon source, and the liquid carbon source is ethanol (C ₂ H ₆ O), benzene (C ₆ H ₆ ), xylene, toluene (C ₇ H ₈ ) and is selected from the group consisting of its mixture, the gaseous carbon source is methane (CH _4), propylene (C ₃ H _6), Pro pine (C ₃ H _4), propane (C ₃ H _8), butane (C ₄ H ₁₀ ), butylene (C ₄ H ₈ ), butadiene (C ₄ H ₆ ), ethylene (C ₂ H ₂ ) and a mixture thereof, and the solid carbon source is camphor (C ₁₀ H ₁₆ O) It is characterized by being.

In the present invention, between the third step and the fourth step, the carbon-containing polymer nanofibers are subjected to preliminary heat treatment at a temperature in the range of 100 to 300°C.

In the present invention, in the fourth step, the carbon-containing polymer is carbonized by heat treatment at a temperature in the range of 800 to 1,200°C in an inert gas atmosphere.

In order to solve the above other technical problems, the present invention provides a carbon nanotube-carbon nanofiber composite, characterized in that produced by the above method.

The method of manufacturing a carbon nanotube-carbon nanofiber composite of the present invention by means of solving the above problems, and a carbon nanotube-carbon nanofiber composite manufactured thereby has the following effects.

First, non-alkali metals of groups 8, 9, and 10 such as iron (Fe), cobalt (Co), and nickel (Ni), that is, lithium (Li) and potassium (K) without using a transition metal-based catalyst. In particular, because alkali metal-based catalysts such as sodium (Na) are used, catalyst particles such as sodium are simply dissolved in water and can be easily removed, making it easier to synthesize metal-free carbon nanotube-carbon nanofiber composites. After completion, there is no need to go through a cleaning process such as acid treatment, so there is an effect of reducing environmental costs.

Second, it is possible to easily grow carbon nanotubes from the surface of carbon nanofibers only by manufacturing carbon-containing polymer nanofibers with an alkali metal precursor bonded to the surface through electrospinning, carbonizing them, and heat treatment while supplying a carbon source. , There is an effect that can mass-produce carbon nanotube-carbon nanofiber composites.

Third, by growing carbon nanotubes from carbon nanofibers through a nano-catalyst, the carbon nanofibers and carbon nanotubes are not separated due to the high binding force between the carbon nanofibers and the carbon nanotubes, thus improving the lifespan when applied to a battery. There is.

Fourth, the carbon nanotube-carbon nanofiber composite manufactured through the present invention is an emission source of various devices, VFD (Vacuum Fluorescent Display), white light source, FED (Field Emission Display), lithium ion battery electrode, hydrogen storage fuel cell, There is an effect that can be widely used in various energy application fields, such as nanowires, gas sensors, microparts for biomedical engineering, and high-functional composites.

1 is a TEM photograph showing defects occurring in a conventional composite material of carbon nanotubes and carbon nanofibers.
Figure 2 is a flow chart showing the manufacturing process of the carbon nanotube-carbon nanofiber composite according to the present invention.
Figure 3 is a schematic diagram showing the manufacturing process of the carbon nanotube-carbon nanofiber composite according to the present invention.
4 is a structure of a crown ether coordinated with an alkali metal cation of the present invention.
5 is a conceptual diagram of electrospinning according to the present invention.
6 is a photograph of a carbonization heat treatment furnace.
7 is a photograph of a heat treatment furnace for growing carbon nanotubes on carbon nanofibers.
8 is a SEM photograph of a carbon nanotube-carbon nanofiber composite prepared according to Example 1 of the present invention.
9 is a SEM photograph of a carbon nanotube-carbon nanofiber composite prepared according to Example 2 of the present invention.
10 is a SEM photograph showing the length of carbon nanotubes grown on carbon nanofibers.
11 is a SEM photograph showing the density of carbon nanotubes grown on carbon nanofibers.

Hereinafter, the present invention will be described in detail.

Figure 2 is a flow chart showing the manufacturing process of the carbon nanotube-carbon nanofiber composite according to the present invention, Figure 3 is a schematic diagram showing the manufacturing process of the carbon nanotube-carbon nanofiber composite according to the present invention, see this In the carbon nanotube-carbon nanofiber composite of the present invention, the first step (S10) of preparing an alkali metal precursor solution by dissolving an alkali metal precursor in a solvent, and preparing a spinning solution by dissolving a carbon-containing polymer in the alkali metal precursor solution The second step (S20), the third step (S30) of producing a carbon-containing polymer nanofiber in which an alkali metal precursor is bonded to the surface by electrospinning a spinning solution, an alkali metal precursor on the surface by heat treatment of the carbon-containing polymer nanofiber In the fourth step (S40) of manufacturing carbon nanofibers combined with carbon nanofibers and heat treatment while supplying a carbon source to the carbon nanofibers, the alkali metal precursor is activated as an alkali metal nanocatalyst, and the carbon source is converted into carbon nanofibers by the nanocatalyst. As it is bonded to the surface of the fiber, it is crystallized and grown into carbon nanotubes, and is manufactured through the fifth step (S50) of manufacturing carbon nanofibers in which carbon nanotubes are bonded to the surface, and the characteristics of each step are as follows. .

First, an alkali metal precursor is dissolved in a solvent to prepare an alkali metal precursor solution (S10).

Conventionally, non-alkali metals of groups 8, 9 and 10 such as iron (Fe), cobalt (Co), and nickel (Ni), such as iron (Fe), cobalt (Co), and nickel (Ni), are mainly used as catalysts based on transition metals. When the synthesis and growth of the carbon nanotubes are completed by making the non-alkali metal catalyst in the form of nanoparticles, an additional process such as acid treatment is required to remove the nanoparticles remaining in the metal state of the non-alkali metal catalyst. To do this, washing water is also required, so there has been a burden due to the increase in environmental costs.

Accordingly, in this step, an alkali metal precursor based on an element of Group 1 excluding hydrogen is dissolved in a solvent to prepare an alkali metal precursor solution, so that the alkali metal of this alkali metal precursor solution is activated as a nano catalyst in the fifth step and carbon Since the carbon nanotubes can be grown from the surface of the nanofibers and are easily dissolved and removed in water without removing the nanocatalyst through a separate process such as acid treatment later, the synthesis of high-purity carbon nanotube-carbon nanofiber composites is possible. It is possible.

The alkali metal precursor is selected from the group consisting of a lithium precursor, a sodium precursor, a potassium precursor, and a mixture thereof. That is, the alkali metal precursor is one or more alkali metal salts selected from the group consisting of lithium (Li), sodium (Na) and potassium (K), alkali metal organic compounds, or alkali metal inorganic compounds. It can be said to consist of alkali metal inorganic compounds.

For example, in the case of a lithium precursor, which is a compound containing lithium, it is selected from the group consisting of lithium benzoate, lithium chloride (LiCl), and mixtures thereof. In the case, it is selected from the group consisting of sodium benzoate, sodium chloride (NaOH), sodium bicarbonate (NaHCO ₃ ), and mixtures thereof. In the case of a potassium precursor, a compound containing potassium, potassium benzoate It is selected from the group consisting of Potassium benzoate, Potassium chloride, Potassium hydroxide, and mixtures thereof.

The solvent is composed of a polar solvent or a non-polar solvent, and is a polar solvent selected from the group consisting of water, dimethylformamide (DMF), a lower alcohol having 1 to 5 carbon atoms, and a mixture thereof, or xylene, benzene ( benzene), toluene, and mixtures thereof.

The alkali metal precursor solution in which the alkali metal precursor is mixed with the solvent is prepared in the following two ways.

First, an alkali metal precursor solution is prepared by dissolving an alkali metal precursor in a polar solvent such as dimethylformamide.

In this case, the amount of the alkali metal precursor is not particularly limited, but if it is mixed with less than 0.01 mol per 1 liter of the solvent, the alkali metal precursor cannot be activated or functionalized with the alkali metal nano catalyst when the heat treatment in the fifth step is performed. Not only does it take a lot of time from the surface to the point at which carbon nanotubes can grow, but there are cases where the carbon source supplied in the fifth step cannot be grown into carbon nanotubes, so it is limited to be applied to the field of energy application. In particular, if the alkali metal precursor is added in an excessively small amount, the reaction rate cannot be increased, which is not preferable in terms of production efficiency.

On the other hand, if the alkali metal precursor per 1 liter of solvent exceeds 0.05 mol, the alkali metal precursor is activated or functionalized with the alkali metal nano catalyst during the heat treatment in the fifth step, and then the nano catalyst remains partially attached to the carbon nanotube. As a result, the purity of carbon nanotubes grown on carbon nanofibers is lowered.

For this reason, it is preferable to dissolve the alkali metal precursor in the range of 0.01 to 0.05 mol per 1 liter of the solvent, and 0.02 mol is most preferable in consideration of the optimum activity as a nano catalyst.

Second, the alkali metal cation of the alkali metal precursor is coordinated in the cavity of the crown ether by the addition of crown ether to form a complex, so that the alkali metal cation is solvated to prepare an alkali metal precursor solution. It's the way.

Crown ether (x-Crown ether-y; x is the number of all atoms in the ring, y is the number of oxygen atoms) is an oligomer of ethylene oxide in which ethyleneoxy _{(-CH 2} CH _{2 O-) units are repeated (} oligomer), which forms a stable structure with alkali metal cations by putting the alkali metal cations in the alkali metal precursor solution into the cavity in the center of the crown ether, so that the alkali metal cations are solvated and dissolved, especially in a non-polar solvent. It increases the solubility of the phosphorus alkali metal precursor. In other words, since crown ether forms a ^{stable complex with metal ions, that is, alkali metal cations such as Li + , Na +} , and K ⁺ , alkali metal precursors such as benzene, xylene, and toluene that are not soluble in non-polar solvents composed of hydrocarbons can be easily dissolved. It becomes possible to plum blossom.

When an alkali metal precursor is dissolved in a solvent through crown ether, it is converted into a transparent alkali metal precursor solution, and in order to dissolve as much of the alkali metal precursor as possible, it is recommended to adjust the ratio with the crown ether (e.g., alkali metal precursor and The weight ratio of crown ether may be 1:0.1~100.), it is also possible to control the solubility of the alkali metal precursor solution by adjusting the amount of crown ether. However, the amount in which the alkali metal precursor and the crown ether can be mixed is not limited.

In the case of crown ether, it can be used by selecting from the group consisting of 12-Crown-4, 15-Crown-5, 18-Crown-6, and a mixture thereof, which is the structure of the crown ether coordinated with the alkali metal cation of the present invention. It can be confirmed through the shown Figure 4. FIG. 4(a) exemplarily shows 12-Crown-4 forming a complex with ^{Li +,} and FIG. 4(b) exemplarily shows 15-Crown-5 forming a complex with ^{Na +,} Figure 4(c) shows an example of 18-Crown-6 forming a complex with ^{K +.} Referring to FIG. 4, it can be seen that the oxygen atom constituting the crown assists in coordinating alkali metal cations in the cavity within the crown, and the types of ions in which stable complexes are formed are different depending on the size of the crown. That is, Li ⁺ forms the most stable complex with 12-Crown-4, Na ⁺ forms the most stable complex with 15-Crown-5, and K ⁺ forms the most stable complex with 18-Crown-6. It is possible to check.

In particular, since the solvents such as water or dimethylformamide presented in the first method are polar, alkali metal precursors are well soluble, but since alkali metal precursors do not dissolve in polar solvents and other non-polar solvents (e.g. xylene), crown ether is solute. It plays an important role in increasing the solubility by solvating.

Next, a spinning solution is prepared by dissolving a carbon-containing polymer in an alkali metal precursor solution (S20).

A spinning solution capable of electrospinning is prepared by adding 1 to 15 wt% of a polymer containing carbon to 85 to 99 wt% of an alkali metal precursor solution and dissolving it while stirring.

In particular, if the carbon-containing polymer is less than 1 wt%, it is difficult to make a homogeneous carbon-containing polymer nanofiber even if the spinning solution is electrospun, and if it exceeds 15 wt%, the alkali metal precursor solution is relatively small. The amount of activated nanocatalyst is also relatively reduced, so that the amount of carbon nanotubes that can be grown from the surface of carbon nanofibers is also reduced. In other words, if the alkali metal precursor solution is less than 85wt%, the amount of activated nanocatalyst decreases, so the amount of carbon nanotubes that can be grown is also reduced.If the alkali metal precursor solution exceeds 99wt%, the carbon nanoparticles There is a disadvantage in that the growth of carbon nanotubes cannot be stably achieved due to insufficient space in which the nanocatalyst can be formed in the fiber. In order to stably grow carbon nanotubes on carbon nanofibers after complete molding into carbon-containing polymer nanofibers, it is most preferable to include 9 wt% of the carbon-containing polymer in consideration of volatilization of the solvent in the alkali metal precursor solution.

Carbon-containing polymers can be referred to as carbon nanofiber precursors, such as polyacrylonitrile (PAN), polyvinyl acetate (PVA), polyvinyl pyrrolidone (PVP), and polycarbonate. PC), polyvinyl chloride (PVC), cellulose (cellulose), cellulose acetate (cellulose acetate), and may be selected from the group consisting of a mixture thereof, and in the present invention, polyacrylonitrile was applied, but carbon It is not particularly limited as long as it is a carbon-containing polymer that can be formed of nanofibers.

Next, the spinning solution is electrospinned to prepare a carbon-containing polymer nanofiber to which an alkali metal precursor is bonded to the surface (S30).

This step is to prepare a fiber-type carbon-containing polymer nanofiber by using the spinning solution, and referring to FIG. 5 showing a conceptual diagram of electrospinning according to the present invention, first (+) or (-) in the nozzle for electrospinning. If a sufficiently high voltage is applied while the high voltage terminal is connected and ground is connected to the conductor, an electromagnetic field is formed between the nozzle and the conductor, and the spinning solution inside the nozzle is affected, and the electromagnetic force is applied to the surface tension and viscosity of the spinning solution. When it is larger, a taylor cone is formed and stretched at the end to form a composite nanofiber, a nano-sized composite fiber. However,'composite nanofibers' and'nano-sized composite fibers' referred to in the present invention mean'carbon-containing polymer nanofibers in which an alkali metal precursor is bonded to the surface'.

For the production of nano-sized composite fibers through electrospinning, the molecular weight of the carbon-containing polymer, the properties of the spinning solution, the voltage, the distance between the nozzle and the conductor, the fluid amount and concentration of the carbon-containing polymer, the parameters, the movement of the nozzle, the conductor It is desirable to satisfy the size and nozzle size conditions, and each condition will be described in detail below.

The molecular weight conditions of the carbon-containing polymer are as follows. That is, when the molecular weight ( M _w ) of the polymer containing carbon is less than 45,000 or exceeds 1,000,000, it is difficult to uniformly form the composite nanofibers, so it is preferable to make it in the range of 45,000 to 1,000,000.

The characteristic conditions of the spinning solution are as follows. Regarding the viscosity of the spinning solution, if it is less than 1Pa·s, the viscosity is too low and the spinning solution breaks before being formed into nano-sized composite fibers in the process of electrospinning, making it into droplets rather than composite nanofibers. If it exceeds s, the viscosity becomes too high, so more electromagnetic force is required to elute from the nozzle, and as a result, an overcurrent occurs and the experimental equipment may be burned. Therefore, having a viscosity in the range of 1 to 1,000 Pa·s is desirable. Regarding the conductivity of the spinning solution, if it exceeds 53 µs/cm, it is not suitable for carbon nanofiber formation, so it is preferable that the spinning solution has a conductivity of 53 µs/cm or less. Regarding the surface tension of the spinning solution, if it exceeds 450 dyn/cm, the electromagnetic force becomes smaller than the surface tension of the spinning solution, and the tailor cone is not formed, making it difficult to form a composite nanofiber shape.Therefore, the surface tension of the spinning solution is It is preferably made of 450 dyn/cm or less.

Voltage conditions are as follows. If a voltage of 30kV or less is applied for electrospinning of the spinning solution, an electromagnetic field is formed between the nozzle and the conductor, so there is no need to apply a voltage exceeding 30kV.

The distance between the nozzle and the conductor is as follows. That is, when the distance between the nozzle containing the spinning solution and the conductor is 30 cm or less, it is formed of nano-sized composite fibers. If the distance between the nozzle and the conductor exceeds 30cm, the distance between the nozzle and the conductor is too far, so the electromagnetic force is small, making it difficult to make the nano-size of the composite fiber uniform. have.

The fluid amount and concentration conditions of the carbon-containing polymer are as follows. When the amount of fluid is less than 25ml/min, the spinning solution is formed into a tailor cone and stretches well with nanofibers. However, if the amount exceeds 25ml/min, the amount of stretching is small due to the amount of fluid being too large, resulting in uneven nanofibers. As the probability increases, the defect rate can also increase. In the case of the concentration, 30wt% is sufficient to be made into nano-sized composite fibers.

The parameter conditions are as follows. The parameters are related to basic environmental aspects such as temperature, humidity, air flow, etc., in the case of a temperature of 35°C or less, humidity of 60% or less, and an air flow of 1 or less, alkali metal precursors are bound to the surface through electrospinning. It can be manufactured from carbon-containing polymer nanofibers.

The conditions for the movement of the nozzle and the size of the conductor are as follows. First, the spinning solution is stably stretched to the conductor through electrospinning only when the movement of the nozzle is less than 0.1mm/min, and the composite nanofibers that are electrospun from the nozzle are stably collected in the conductor even if the size of the conductor is 10cm or more. Can be done. However, if the size of the conductor is less than 10 cm2, there is a disadvantage in that the area is too small to secure a space for sufficiently collecting the composite nanofibers.

The nozzle size conditions are as follows. If the nozzle size is less than 0.01mm or exceeds 1.7mm, it does not help to form the carbon-containing polymer nanofibers in which the alkali metal precursor is bonded to the surface, so the nozzle size is preferably made in the range of 0.01 to 1.7mm.

Next, the carbon-containing polymer nanofibers are heat-treated to prepare carbon nanofibers to which an alkali metal precursor is bonded to the surface (S40).

Prior to this step, before producing the carbon nanofibers through carbonization, the carbon-containing polymer nanofibers with an alkali metal precursor bonded to the surface were heated to 100 to 300°C at a temperature rising rate of 8 to 12°C/min in the atmosphere for 20 minutes to The carbon-containing polymer is stabilized through preliminary heat treatment for 1 hour. At this time, if the pre-heat treatment is less than 100°C, it is difficult to stabilize the carbon-containing polymer nanofibers, and if the pre-heat treatment is performed above 300°C, the temperature is higher than necessary and may cause deterioration in the shape or physical properties of the carbon-containing polymer nanofiber . In the case of the heating rate, it may be 8 to 12° C./min, and 10° C./min is most preferred. In addition, if the pre-heat treatment is performed in less than 20 minutes, it is difficult to stabilize the carbon-containing polymer of the carbon-containing polymer nanofibers as in the temperature condition. It does not work. In particular, there is an advantage that the oxygen supply is smooth only when preheating is performed in an oxygen environment in the atmosphere, so that the carbon-containing polymer nanofibers can be formed at a high speed.

After the formation of the carbon-containing polymer nanofibers stabilizing the carbon-containing polymer, it was then carbonized through an additional heat treatment for 30 minutes to 1 hour and 30 minutes by making it to 800 to 1,200°C at a heating rate of 3 to 7°C/min in an inert gas atmosphere. Next, the production of carbon nanofibers is completed through a natural cooling process. Carbonization herein refers to a heat treatment process that increases the carbon/hydrogen ratio of the carbon-containing polymer constituting the carbon-containing polymer nanofiber, and refers to a process of converting a carbon-containing component into carbon.

Regarding the heat treatment temperature for carbonization, if the heat treatment is less than 800°C, it takes a long time to complete the carbonization of the carbon-containing polymer due to incomplete carbonization, and complete carbonization cannot be expected, and thus the surface of the carbon nanofibers is damaged. On the other hand, if the temperature exceeds 1,200℃, the temperature is rather high than necessary, so that the carbon-containing polymer is not sufficiently converted to carbon, or the degree of improvement in the physical properties of the carbon nanofiber is reduced due to excessive heat treatment. Alkali metal precursors contained in are vaporized and disappear, making it difficult to form a nanocatalyst in the future. For complete carbonization, it is most preferable to perform heat treatment at 1,000°C.

Regarding the rate of temperature increase for carbonization, the reason why the rate of temperature increase is relatively slow compared to the preliminary heat treatment for stabilizing the carbon-containing polymer nanofibers as 3 to 7°C/min. This is to check whether there is no problem in forming the carbon nanofibers and to prevent the physical properties of the carbon nanofibers from deteriorating. Most preferably, it is performed at 5° C./min for stable production of carbon nanofibers.

Regarding the heat treatment time for carbonization, if it is made less than 30 minutes, the target carbonization effect is insignificant, and if it exceeds 1 hour and 30 minutes, the inefficient aspect of the process is highlighted due to too long time. In terms of process efficiency, most preferably, carbonization is performed by heat treatment for 60 minutes.

In the carbonization process, the inert gas atmosphere may be, for example, a gas such as helium, nitrogen, argon, or carbon dioxide, and more specifically, a nitrogen (N ₂ ) gas. That is, the carbon-containing polymer of the carbon-containing polymer nanofibers can be converted into carbon nanofibers by being carbonized by heat treatment in an inert atmosphere.

Finally, the alkali metal precursor is activated by the alkali metal nano catalyst by heat treatment while supplying a carbon source to the carbon nanofibers, and the carbon source is bonded to the surface of the carbon nanofibers by the nano catalyst and crystallized into carbon nanotubes to grow. Thus, to prepare carbon nanofibers to which carbon nanotubes are bonded to the surface (S50).

First, conventionally, for the growth of carbon nanotubes on carbon nanofibers, a non-alkali metal catalyst such as iron (Fe) is coated on carbon nanofibers, and carbon atoms are dissolved in iron particles while passing carbon dioxide and other carbon-containing gases. In the end, the process of forming a vertical tube of carbon atoms around the carbon nanofibers, and the method in which the carbon nanotubes are grown was the main one. However, in this case, there is a disadvantage that the iron particles remain in the carbon nanotubes, so that the acid treatment for removing the iron particles must be repeated several times.

In order to improve this, in this step, in simple terms, the alkali metal of the alkali metal precursor is activated with a nano catalyst, and through this nano catalyst, the carbon source is crystallized into carbon nanotubes so that it can be grown from the surface of the carbon nanofiber.

Regarding the heat treatment temperature conditions, if the temperature is less than 700℃, the alkali metals of the alkali metal precursor cannot be activated or functionalized with the nanocatalyst, and rather remain as impurities in the grown carbon nanotubes, and if it exceeds 800℃, it induces overreaction. As a result, the activity of the nano-catalyst cannot be stabilized, thereby hindering the growth of carbon nanotubes.

Regarding the heat treatment time conditions, if less than 15 minutes is insufficient time to induce the activation of the nanocatalyst, it is not possible to secure a sufficient time for the carbon nanotubes to grow, and if it exceeds 30 minutes, the length of the carbon nanotubes to be grown Since is too long, it is difficult to achieve optimal properties, and unnecessary side reactions may be generated, so it is preferable to heat treatment within 30 minutes.

Although the nanocatalyst is an alkali metal, especially sodium, which is the alkali metal of the alkali metal precursor applied in the present invention, is soluble in water, it is not necessary to remove it using a separate acid, so it is a metal-free carbon. It is important to be synthesized as a nano-tooth-carbon nanofiber composite. That is, even if the nanocatalyst is partially left on the carbon nanotubes, it is possible to remove it by dissolving it in general water, not by acid treatment, due to the high reactivity of the alkali metal cations.

In addition, since the nanocatalyst can be removed by simply vaporizing or evaporating at the temperature of the fifth step of heat treatment, only pure carbon nanotubes can be grown from the surface of the carbon nanofibers. By growing carbon nanotubes from carbon nanofibers through such a nanocatalyst, high binding strength between carbon nanofibers and carbon nanotubes is created, so that carbon nanofibers and carbon nanotubes are not separated, so that carbon nanofibers and carbon nanotubes are bound to each other. There is no need for a separate means to do so.

The carbon source that can grow and synthesize carbon nanotubes from the surface of carbon nanofibers is one of a liquid type liquid carbon source, a gas type gaseous carbon source, and a solid type solid carbon source. Choose one or more to use. The liquid carbon source is selected from the group consisting of ethanol (C ₂ H ₆ O), benzene (C ₆ H ₆ ), xylene, toluene (C ₇ H ₈ ), and mixtures thereof. Gas-phase carbon sources include methane (CH4), propylene (C3H6), propane (C ₃ H ₄ ), propane (C ₃ H ₈ ), butane (C ₄ H ₁₀ ), butylene (C ₄ H _8). ), butadiene (C ₄ H ₆ ), ethylene (C ₂ H ₂ ), and mixtures thereof. As the solid carbon source, camphor (C ₁₀ H ₁₆ O), which is one of the monoterpene ketones, can be used.

Therefore, the alkali metal precursor is activated as an alkali metal nano catalyst only by heat treatment in the presence of a carbon source that helps the growth of carbon nanotubes without the need to separately prepare Group 1 elements except hydrogen, especially sodium, as a catalyst in the form of particles. As the carbon source is crystallized into carbon nanotubes by the nano-catalyst, it can grow from the surface of the carbon nanofibers, and eventually, a carbon nanotube-carbon nanofiber composite in which the carbon nanotubes are bonded to the surface of the carbon nanofibers is produced.

As the carbon source is grown from the carbon nanofibers to the carbon nanotubes in this way, the nanocatalyst may be vaporized and removed, so the nanocatalyst is not attached or attached to the carbon nanotubes grown on the carbon nanofibers. Therefore, there is no need to remove the nanocatalyst by performing an additional heat treatment or post-treatment process such as acid treatment. Even if a part of the nanocatalyst remains in the carbon nanotube, the advantage of the process is maintained because the alkali metal ion has a high reactivity with water, so that it is only necessary to dissolve and remove it in water rather than acid treatment.

Hereinafter, an embodiment of the present invention will be described in more detail as follows. However, the following examples are merely illustrative to aid in understanding of the present invention, and the scope of the present invention is not limited thereby.

<Example 1> Preparation of carbon nanotube-carbon nanofiber composite

After dissolving sodium benzoate (Sigma Aldrich, BioXtra,> 99.5%) in DMF (Sigma Aldrich, for molecular biology,> 99%) solution at 0.02 mol/L, 9 wt% of PAN (Sigma Aldrich, Mw 150,000 Typical) The spinning solution was prepared by dissolving again at a ratio.

Adjust the movement of the nozzle with a size of 0.01mm≤D≤1.7mm to F≥0.1mm/min, and the size of the conductor as A≥10cm2, and fix the distance between the nozzle and the conductor to 30cm or less, and then the fluid volume ( V _f ) A spinning solution having a concentration of 25 ml/min or less and a concentration (C) of 30 wt% or less was electrospinned by applying a voltage of 30 kV or less to prepare a carbon-containing polymer nanofiber stretched while forming a tailor cone.

The carbon-containing polymer nanofibers were heat-treated at 200℃ for 40 minutes at a heating rate of 10℃/min in the atmosphere, and then heat-treated at 1,000℃ for 60 minutes at a heating rate of 5℃/min in an _{N 2 atmosphere, and then naturally cooled and carbonized.} Carbon nanofibers were prepared. This carbonization process was performed using a heat treatment furnace as shown in the carbonization heat treatment furnace picture of FIG. 6.

Subsequently, after placing a tube SUS pipe (diameter 5 cm, length 20 cm) in the center of the furnace as shown in Fig. 7 showing a photo of a heat treatment furnace for growing carbon nanotubes on carbon nanofibers, the temperature inside the SUS pipe is 700 The carbon nanotubes were grown on the surface of the carbon nanofibers by supplying the ethanol vapor generated by heating ethanol using a heater to the _{inside of the SUS pipe for 15 minutes through N 2 bubbling.} A carbon nanotube-carbon nanofiber composite was prepared.

<Example 2> Preparation of carbon nanotube-carbon nanofiber composite

In Example 2, a spinning solution was prepared using sodium benzoate and other sodium bicarbonate of Example 1 as an alkali metal precursor. That is, after dissolving sodium bicarbonate (Sigma Aldrich, BioXtra,> 99.5%) in DMF (Sigma Aldrich, for molecular biology,> 99%) solution at 0.02 mol/L, 9 wt. A spinning solution was prepared by dissolving again in% ratio.

Adjust the movement of the nozzle with a size of 0.01mm≤D≤1.7mm to F≥0.1mm/min, and the size of the conductor as A≥10cm2, and fix the distance between the nozzle and the conductor to 30cm or less, and then the fluid volume ( V _f ) A spinning solution having a concentration of 25 ml/min or less and a concentration (C) of 30 wt% or less was electrospinned by applying a voltage of 30 kV or less to prepare a carbon-containing polymer nanofiber stretched while forming a tailor cone.

The carbon-containing polymer nanofibers were heat-treated at 200℃ for 40 minutes at a heating rate of 10℃/min in the atmosphere, and then heat-treated at 1,000℃ for 60 minutes at a heating rate of 5℃/min in an _{N 2 atmosphere, and then naturally cooled and carbonized.} Carbon nanofibers were prepared. This carbonization process was performed using the same heat treatment furnace shown in the carbonization heat treatment furnace photograph of FIG. 6 mentioned in Example 1.

Subsequently, after placing a tube SUS pipe (diameter 5 cm, length 20 cm) in the center of the furnace as shown in Fig. 7 showing a photo of a heat treatment furnace for growing carbon nanotubes on carbon nanofibers, the temperature inside the SUS pipe is 700 The carbon nanotubes were grown on the surface of the carbon nanofibers by supplying the ethanol vapor generated by heating ethanol using a heater to the _{inside of the SUS pipe for 15 minutes through N 2 bubbling.} A carbon nanotube-carbon nanofiber composite was prepared.

8 is a SEM photograph of a carbon nanotube-carbon nanofiber composite prepared according to Example 1 of the present invention. In FIGS. 8(a), 8(b), and 8(c), it is possible to confirm the growth of carbon nanotubes by crystallization of carbon nanofibers. 9 is a SEM photograph of a carbon nanotube-carbon nanofiber composite manufactured according to Example 2 of the present invention. In FIGS. 9(a), 9(b), and 9(c), carbon nanofibers are carbon nanofibers. As the tube is combined, it is possible to check the shape of the growth.

Looking at the SEM photographs shown in FIGS. 8 and 9, a number of curly-shaped carbon nanotubes having a length of several hundred nanometers having a uniform diameter are very densely grown on the surface of the carbon nanofibers to form a hierarchical network structure. It can be seen that, through this, it can be seen that the carbon nanotubes can improve the flexibility and specific surface area of the carbon nanotube-carbon nanofiber composite.

10 is an SEM photograph showing the length of carbon nanotubes grown on carbon nanofibers. FIG. 10(a) shows a carbon nanotube-carbon nanofiber composite produced when all conditions in Example 1 were set the same, but heat-treated with only carbon nanotube growth time less than 5 minutes, as an SEM photograph, FIG. 10(b) is an SEM image by further magnifying FIG. 10(a), and FIG. 10(c) is an SEM image by further magnifying FIG. 10(b). When the heat treatment time is less than 5 minutes, carbon It is observed that the length of the carbon nanotubes grown on the surface of the nanofibers is remarkably shortened. Through this, it can be seen that the longer the heat treatment time under the supply of the carbon source increases the length as the carbon nanotubes grow.

11 is an SEM photograph showing the density of carbon nanotubes grown on carbon nanofibers. 11(a) shows the carbon nanotube-carbon nanofiber composite produced when the concentration of sodium benzoate, which is an alkali metal precursor soluble in DMF, is reduced to 1/5, except that all conditions in Example 1 are set the same. Fig. 11(b) is an SEM picture by further magnifying Fig. 11(a), and Fig. 11(c) is an SEM picture by further enlargement of Fig. 11(b), dissolved in DMF It can be seen that the density of carbon nanotubes grown from the surface of the carbon nanofibers can be controlled according to the concentration of the alkali metal precursor.

As described above, the present invention relates to a method of manufacturing a carbon nanotube-carbon nanofiber composite and a carbon nanotube-carbon nanofiber composite produced thereby, by electrospinning a spinning solution in which a carbon-containing polymer is dissolved in an alkali metal precursor solution. After preparing a carbon-containing polymer nanofiber with an alkali metal precursor bonded to the surface, the carbon-containing polymer nanofiber is heat-treated to produce a carbon nanofiber, which is then heat treated while supplying a carbon source to the carbon nanofiber. The precursor is activated with an alkali metal nano-catalyst, and a carbon source is bonded to the surface of the carbon nanofiber by the nano-catalyst to crystallize and grow into carbon nanotubes.

Thus, the present invention does not use a non-alkali metal such as iron (Fe), cobalt (Co), nickel (Ni), that is, a transition metal-based catalyst, and Since an alkali metal-based catalyst is used, catalyst particles such as sodium are simply dissolved in water and easily removed, so it is of great significance that a metal-free carbon nanotube-carbon nanofiber composite can be synthesized. .

Therefore, according to the present invention, since it is not necessary to perform a cleaning process such as acid treatment to remove catalyst particles, cleaning water is not required, so environmental costs can be reduced, and carbon nanotubes can be easily grown from the surface of carbon nanofibers. In addition, the carbon nanotube-carbon nanofiber composite can be mass-produced, so it is expected to be widely used in various energy applications.

The above description is merely illustrative of the technical idea of the present invention, and those of ordinary skill in the art to which the present invention pertains will be able to make various modifications and variations without departing from the essential characteristics of the present invention.

Accordingly, the embodiments disclosed in the present invention are not intended to limit the technical idea of the present invention, but to explain the technical idea, and the scope of the technical idea of the present invention is not limited by these embodiments.

The scope of protection of the present invention should be construed by the claims, and all technical thoughts within the scope equivalent thereto should be construed as being included in the scope of the present invention.

Claims (7)

A first step of dissolving an alkali metal precursor in a solvent to prepare an alkali metal precursor solution;
A second step of preparing a spinning solution by dissolving a carbon-containing polymer in the alkali metal precursor solution;
A third step of electrospinning the spinning solution to prepare carbon-containing polymer nanofibers to which the alkali metal precursor is bonded to the surface;
A fourth step of heat-treating the carbon-containing polymer nanofibers to prepare carbon nanofibers in which the alkali metal precursor is bonded to the surface; And
The alkali metal precursor is activated by an alkali metal nano catalyst by heat treatment while supplying a carbon source to the carbon nanofibers, and the carbon source is bonded to the surface of the carbon nanofiber by the nano catalyst to crystallize into carbon nanotubes. A method for producing a carbon nanotube-carbon nanofiber composite, comprising: a fifth step of producing carbon nanofibers to which the carbon nanotubes are bonded to the surface of the carbon nanotubes. The method of claim 1,
The alkali metal precursor,
Lithium precursor (Li precursor), sodium precursor (Na precursor), potassium precursor (K precursor), characterized in that selected from the group consisting of a mixture of carbon nanotube-carbon nanofiber composite method. The method of claim 1,
The carbon-containing polymer,
Polyacrylonitrile (PAN), polyvinyl acetate (PVA), polyvinyl pyrrolidone (PVP), polycarbonate (PC), polyvinyl chloride (PVC), A method for producing a carbon nanotube-carbon nanofiber composite, characterized in that it is selected from the group consisting of cellulose, cellulose acetate, and a mixture thereof. The method of claim 1,
The carbon source is a liquid, gaseous or solid carbon source,
The liquid carbon source is _{selected from the group consisting of ethanol (C 2} H ₆ O), benzene (C ₆ H ₆ ), xylene, toluene (C ₇ H ₈ ), and a mixture thereof,
The gaseous carbon source is methane (CH ₄ ), propylene (C ₃ H ₆ ), propane (C ₃ H ₄ ), propane (C ₃ H ₈ ), butane (C ₄ H ₁₀ ), butylene (C ₄ H ₈ ), butadiene (C ₄ H ₆ ), ethylene (C ₂ H ₂ ) and a mixture thereof,
The method of manufacturing a carbon nanotube-carbon nanofiber composite, characterized in that the solid carbon source is camphor (C ₁₀ H _{16 O).} The method of claim 1,
Between the third step and the fourth step,
Method for producing a carbon nanotube-carbon nanofiber composite, characterized in that the preliminary heat treatment at a temperature in the range of 100 to 300 ℃ the carbon-containing polymer nanofibers. The method of claim 1,
In the fourth step,
A method for producing a carbon nanotube-carbon nanofiber composite, characterized in that the carbon-containing polymer is carbonized by heat treatment at a temperature in the range of 800 to 1,200°C in an inert gas atmosphere. A carbon nanotube-carbon nanofiber composite, characterized in that it is produced by the method of any one of claims 1 to 6.

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