Method for producing purified carbon nanotubes using xenon light irradiation

Abstract

The present invention relates to a method for producing purified carbon nanotubes using xenon light irradiation, the method comprising: a first step of applying xenon light with an energy density of 1–4 J / J / cm2 for 0.2–50 seconds to carbon nanotubes containing impurities to remove amorphous carbon impurities; and a second step of applying xenon light with an energy density of at least 4 J / cm2 for at least 10 seconds to the carbon nanotubes from which carbon impurities have been removed, to eliminate inorganic impurities. The method for producing purified carbon nanotubes using xenon light irradiation of the present invention enables selective oxidation and removal of amorphous carbon particles and inorganic impurities in a short time under atmospheric pressure in a dry manner, thereby improving the purity and crystallinity of carbon nanotubes while simplifying and efficiently performing a purification process.

Description

Method for producing purified carbon nanotubes using xenon light irradiation

[0001] The present invention relates to a method for manufacturing purified carbon nanotubes using xenon light irradiation to remove amorphous carbon and catalyst impurities from carbon nanotubes through xenon light irradiation in order to improve the purity and electrical conductivity of carbon nanotubes.

[0002] Carbon nanotubes are an allotrope of carbon, each carbon atom bonded to another in a hexagonal honeycomb pattern to form a tube. These tubes are extremely small, measuring in the nanometer range in diameter. Carbon nanotubes possess high electrical conductivity, high surface area, exceptional mechanical properties, and excellent physical and chemical stability, making them useful in diverse applications, including electron emitters, secondary batteries, fuel cells, composites, chemical / biosensors, and transparent electrodes.

[0003] To synthesize carbon nanotubes, catalyst metals such as iron, cobalt, and nickel are essential. To control the structure such as diameter, length, yield, and crystallinity, cocatalysts such as molybdenum and sulfur and supports such as alumina, magnesia, and silica are used together. Ultimately, carbon nanotube composite products inevitably contain inorganic impurities of catalysts, cocatalysts, and supports in addition to amorphous carbon particle impurities, and these impurities cause a deterioration in the properties of carbon nanotube applications.

[0004] For high-purity carbon nanotube applications, a purification process is performed to selectively remove impurities. Generally, carbon impurities are removed through oxidation using air atmosphere heat treatment, and inorganic impurities are removed through etching using strong acid or high-temperature vacuum heat treatment.

[0005] A carbon impurity purification process based on oxidation is introduced in the prior art (paper: YSPark et al., Carbon 39 (2001) 655-661) by utilizing the difference in oxidation energy between amorphous carbon impurities and crystalline carbon nanotubes. Oxidation of amorphous carbon impurities occurs at a relatively lower energy than that of carbon nanotubes.

[0006] In addition, the process of purifying inorganic impurities using strong acid, such as Korean Patent No. 10-0790839 (non-destructive purification method of carbon nanotubes), generally requires a long processing time of 1 to 15 hours and has problems such as recycling of strong acid solution and occurrence of defects in carbon nanotubes.

[0007] In addition, a purification process based on a high-temperature vacuum heat treatment method, such as Korean Patent No. 10-1766156 (carbon nanotube purification method), melts and vaporizes inorganic impurities under high-temperature vacuum conditions of approximately 1500 degrees Celsius or higher, thereby removing them. However, the processing time is long and the manufacturing cost may increase due to the extreme environment of high temperature and high vacuum.

[0008] Accordingly, there is an increasing need for reducing manufacturing costs and simplifying the process by selectively removing amorphous carbon and inorganic impurities from carbon nanotubes in a short period of time without using acid solutions or high temperatures or vacuum conditions. Therefore, the inventors of the present invention have developed a method for manufacturing purified carbon nanotubes using xenon light irradiation, which improves the purity and crystallinity of carbon nanotubes and increases electrical conductivity by effectively removing amorphous carbon and inorganic impurities in a short period of time at atmospheric pressure using a xenon flash lamp, and have completed the present invention.

[0009] The present invention was invented to solve the above problems, and its technical task is to provide a method for manufacturing purified carbon nanotubes using xenon light irradiation.

[0010] In order to solve the above technical problem, the present invention,

[0011] Carbon nanotubes containing impurities have an energy density of 1–4 J / cm 2 The first step is to remove amorphous carbon impurities by irradiating the xenon light for 0.2 to 50 seconds; and

[0012] The energy density of the carbon nanotube from which the above carbon impurities have been removed is at least 4 J / cm 2 A method for manufacturing purified carbon nanotubes using xenon light irradiation is provided, characterized in that it comprises a second step of removing inorganic impurities by irradiating the carbon nanotubes with xenon light for at least 10 seconds.

[0013] The method of manufacturing purified carbon nanotubes using xenon light irradiation according to the present invention as a means for solving the above problem has the effect of selectively oxidizing and removing amorphous carbon particles and inorganic impurities in a dry manner at atmospheric pressure in a short period of time, thereby improving the purity and crystallinity of carbon nanotubes and making the purification process simple and efficient.

[0014] Figure 1 is a schematic diagram of a method for manufacturing purified carbon nanotubes according to the present invention.

[0015] Figure 2 is a graph showing the surface temperature of a carbon nanotube irradiated with xenon light according to the present invention.

[0016] Figure 3 is a Raman analysis result of MWCNT irradiated with xenon light according to one embodiment of the present invention.

[0017] Figure 4 is a TGA result of MWCNT irradiated with xenon light according to one embodiment of the present invention.

[0018] FIG. 5 is a Raman analysis result measuring recrystallization of MWCNTs irradiated with xenon light according to one embodiment of the present invention.

[0019] Figure 6 is a Raman analysis result of SWCNTs irradiated with xenon light according to one embodiment of the present invention.

[0020] Figure 7 is a TGA result of SWCNT irradiated with xenon light according to one embodiment of the present invention.

[0021] The present invention is susceptible to various modifications and takes various forms, and thus, embodiments are described in detail herein. However, this is not intended to limit the present invention to a specific disclosed form, and it should be understood that all modifications, equivalents, and alternatives fall within the spirit and technical scope of the present invention.

[0022] Throughout the specification, whenever a part is said to "include" a component, this does not mean that it excludes other components, but rather that it may include other components, unless otherwise stated.

[0023] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Terms defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant technology, and will not be interpreted in an idealized or overly formal sense unless explicitly defined herein.

[0024] The terminology used herein is merely used to describe specific embodiments and is not intended to limit the invention. Singular expressions include plural expressions unless the context clearly dictates otherwise.

[0025] In the present invention, xenon light is light output from a xenon flash lamp, has a wavelength range of 300 to 1000 nm, a main wavelength range of 400 to 800 nm in the visible light range, and has a voltage of 400 to 1000 V and a light energy of 0.5 to 6 J / cm. 2 , the investigation time is more than 0.01 seconds.

[0026] In the present invention, the carbon nanotube may be one or more of a single-walled carbon nanotube (SWCNT), a double-walled carbon nanotube (DWCNT), and a multi-walled carbon nanotube (MWCNT).

[0027]

[0028] According to one aspect of the present invention, a carbon nanotube containing impurities has an energy density of 1 to 4 J / cm. 2 A first step of removing amorphous carbon impurities by irradiating xenon light for 0.2 to 50 seconds; and an energy density of at least 4 J / cm in the carbon nanotube from which the carbon impurities have been removed. 2 A method for manufacturing purified carbon nanotubes using xenon light irradiation is provided, characterized in that it comprises a second step of removing inorganic impurities by irradiating the carbon nanotubes with xenon light for at least 10 seconds.

[0029] First, the energy density of carbon nanotubes containing impurities is 1 to 4 J / cm. 2 Amorphous carbon impurities are removed by irradiating the material with xenon light for 0.2 to 50 seconds.

[0030] In the present invention, in purifying carbon nanotubes, amorphous carbon impurities are first removed by irradiating low-energy-density xenon light. In the first step, carbon nanotubes containing impurities are irradiated with an energy density of 1 to 4 J / cm. 2 Amorphous carbon impurities are removed by irradiating the xenon light for 0.2 to 50 seconds. More preferably, the energy density is 2.5 to 4 J / cm. 2 The xenon light can be irradiated for 5 to 30 seconds.

[0031] The energy density of xenon light is 1 J / cm 2 When it is less than 4 J / cm, not enough heat energy is generated to oxidize amorphous carbon impurities, and the energy density is less than 4 J / cm.2 When it is excessive, not only amorphous carbon impurities but also crystalline carbon nanotubes are oxidized, which is undesirable.

[0032] Peak value 1350 cm in Raman analysis -1 The D band appearing nearby indicates a defect in the carbon material, with a peak value of 1590 cm -1 The G band appearing nearby indicates crystalline carbon material, and the relative ratio of the D band and the G band can be used to determine whether amorphous carbon impurities have been removed and the degree of crystallinity of the carbon nanotube.

[0033] In the first step of the present invention, the 1 to 4 J / cm 2 The instantaneous temperature of the surface of a carbon nanotube irradiated with xenon light is 560 to 1100°C, and when light of multiple wavelengths is irradiated on the carbon nanotube, the irradiated portion rapidly rises to a high temperature, and by reacting with oxygen, the effect of selectively oxidizing amorphous carbon particles can be obtained.

[0034] The first step of removing the above carbon impurities can be accomplished by irradiating the carbon nanotube composite containing the impurities with xenon light in an atmospheric atmosphere and an oxygen-containing gas atmosphere at normal pressure. Oxygen is essential for the oxidation of amorphous carbon, and the concentration is 1 to 4 J / cm. 2 Xenon light irradiation can efficiently remove amorphous carbon impurities from carbon nanotubes in a dry manner at atmospheric pressure within a short period of time.

[0035] Next, the energy density is at least 4 J / cm 2 Remove inorganic impurities by irradiating with xenon light for at least 10 seconds.

[0036] After removing amorphous carbon impurities by irradiating low-energy density xenon light, inorganic impurities are removed by irradiating high-energy density xenon light. In the second step, the carbon nanotubes from which the carbon impurities have been removed are irradiated with an energy density of at least 4 J / cm. 2Irradiate the inorganic impurities with xenon light for more than 10 seconds. Preferably, the energy density is at least 4 to 6 J / cm. 2 Xenon light can be irradiated for 10 to 100 seconds. The energy density of xenon light is 4 J / cm. 2 When it is less than this, it is not desirable because not enough heat energy is generated to remove inorganic impurities.

[0037] In the second step of the present invention, the temperature of the portion irradiated with the xenon light is at least 1100°C, and carbon nanotubes are instantaneously expressed at 1100°C or higher using high-energy density xenon light.

[0038] The second stage can be carried out at atmospheric pressure, and the gas atmosphere can be an oxygen atmosphere or an inert gas (argon, nitrogen) atmosphere. However, in the case of an oxygen atmosphere, the energy density should be 4 J / cm to prevent oxidation of carbon nanotubes. 2 It is desirable to use xenon light, and in an inert gas atmosphere (argon, nitrogen), without any energy density restrictions, at least 4 J / cm 2 Inorganic impurities can be removed by irradiating with xenon light for more than 10 seconds.

[0039] Additionally, in the second step of the present invention, inorganic impurities such as catalysts, co-catalysts, and supports can be selectively removed by additionally adding hydrogen halide.

[0040] In the present invention, the hydrogen halide may be at least one selected from the group consisting of HCl, HBr, HF, and HI. In the hydrogen halide, hydrogen plays a role in promoting the reduction of the inorganic impurities, and the halogen element plays a role in removing the reduced inorganic impurities. Specifically, a metal oxide impurity (MO) is reduced to a metal (M) by hydrogen, and the reduced metal impurity (M) combines with a halogen to form a metal halide (MCl). x) is formed and the metal halide is removed through sublimation.

[0041] As described above, the present invention is characterized in that it manufactures purified carbon nanotubes by removing amorphous carbon impurities through a first step using low-energy-density xenon light and removing inorganic impurities through a second step using high-energy-density xenon light.

[0042] In addition, the present invention has an energy density of at least 4 J / cm 2 A third step may further include recrystallizing by re-irradiating the xenon light for at least 30 seconds.

[0043] The third step of the present invention is to recrystallize defects occurring during the synthesis of carbon nanotubes and defects occurring during the removal of impurities, and the energy density is at least 4 J / cm. 2 The xenon light is re-irradiated for at least 30 seconds. That is, the method for manufacturing purified carbon nanotubes of the present invention can improve the crystallinity of carbon nanotubes and increase their purity by additionally re-irradiating them with xenon light after the second step of removing the inorganic impurities. At this time, the xenon light irradiation is preferably performed in an inert gas atmosphere (argon, nitrogen).

[0044] The above-mentioned first to third steps are carried out at atmospheric pressure, and have a technical feature in that the efficiency of the process is improved by rapidly removing carbon and catalyst impurities from the carbon nanotube composite product in a dry manner through xenon light irradiation.

[0045]

[0046] Hereinafter, embodiments of the present invention will be described in more detail. However, the following embodiments are provided merely to aid understanding of the present invention, and the scope of the present invention is not limited thereby.

[0047]

[0048] <Example 1>

[0049] (1) Purification of carbon impurities in MWCNT composites

[0050] 50 mg of MWCNT composite (JENOTUBE 8B, J.O. Co., Ltd.) was placed in a vial and carbon impurities were removed by xenon light irradiation in an air atmosphere. Afterwards, 0.5, 1, 2.5, 4, and 5 J / cm 2 Each xenon light was irradiated for 10 seconds.

[0051] (2) Purification of inorganic impurities in MWCNT composite products from which carbon impurities have been removed

[0052] 50 mg of the MWCNT composite product from which the carbon impurities were removed was placed in a vial, 5 ml of HCl was added, and inorganic impurities were removed through xenon light irradiation. Afterwards, 3, 4, and 5 J / cm 2 Each xenon light was irradiated for 10 seconds.

[0053] (3) Improvement of crystallinity of MWCNT composite products with carbon and inorganic impurities removed

[0054] The MWCNT composite product from which the above carbon and inorganic impurities were removed was placed in a vial with 50 mg, and the vial was filled with argon. Then, the crystallinity of the MWCNT was improved through xenon light irradiation. Afterwards, 3, 4, and 5 J / cm 2 Each xenon light was irradiated for 30 seconds.

[0055]

[0056] <Example 2>

[0057] (1) Purification of carbon impurities in SWCNT composites

[0058] 50 mg of SWCNT composite (TUBALL 80%, OCSiAl) was placed in a vial and carbon impurities were removed by xenon light irradiation in an air atmosphere. Afterwards, 0.5, 1, 2.5, 4, and 5 J / cm 2 Each xenon light was irradiated for 10 seconds.

[0059] (2) Purification of inorganic impurities in SWCNT composite products from which carbon impurities have been removed

[0060] 50 mg of the SWCNT composite product from which the carbon impurities were removed was placed in a vial, 5 ml of HCl was added, and inorganic impurities were removed through xenon light irradiation. Afterwards, 3, 4, and 5 J / cm 2 Each xenon light was irradiated for 10 seconds.

[0061]

[0062] Results and Evaluation

[0063] CNT surface temperature according to energy density

[0064] Figure 2 is a graph showing the surface temperature of carbon nanotubes irradiated with xenon light according to the present invention. Referring to Figure 2, the surface temperature of carbon nanotubes could be rapidly increased to 500 to 1200°C within 0.5 milliseconds, depending on the energy density of the irradiated xenon light.

[0065]

[0066] MWCNT

[0067] Figure 3 shows the results of a Raman analysis of MWCNTs irradiated with xenon light according to Example 1 of the present invention. Since carbon impurities are composed of an amorphous rather than a crystalline substance, the quality of the synthetic product improves when the carbon impurities are removed, and the crystallinity of the synthetic product can be determined through Raman analysis.

[0068] Referring to Figure 3, the characteristic peak D peak (~1350 cm) that appears in a material made of carbon -1 ) and G peak (~1590cm -1 ) can be used to infer the crystallinity of carbon nanotubes. In Fig. 3, the D / G ratio of pristine is approximately 1.41 and 0.5 J / cm 2 Considering that the photon irradiance sample is 1.36, 0.5 J / cm 2 It can be seen that carbon impurities are not effectively removed at energy densities of 1 to 4 J / cm 2It can be confirmed that carbon impurities are removed by significantly reducing the D / G ratio in the light irradiation. 5 J / cm 2 In , it can be seen that not only carbon impurities but also carbon nanotubes are oxidized or defective, increasing the D / G ratio.

[0069] Figure 4 shows the TGA results of MWCNTs irradiated with xenon light according to Example 1 of the present invention in an oxygen atmosphere. The content of inorganic impurities can be quantitatively measured through TGA (thermogravimetric analysis) by utilizing the principle that inorganic impurities are not removed below 900°C, whereas carbon nanotubes are removed through oxidation.

[0070] Referring to Figure 4, in the case of Pristine, approximately 10.5 wt% of inorganic impurities remain, and the energy density is 3 J / cm. 2 Even for the photo-irradiated sample, 9.1 wt% of residue was detected, at 3 J / cm 2 At an energy density of 4 J / cm, it can be concluded that sufficient thermal energy is not generated, making it difficult to remove impurities. In contrast, at 4 J / cm 2 At 1.5 wt%, 5 J / cm 2 In , there is an inorganic impurity content of 0.5 wt%, and it can be confirmed that effective impurity removal is achieved.

[0071] Figure 5 is a Raman analysis result measuring the recrystallization of MWCNTs irradiated with xenon light according to Example 1 of the present invention. Defects in carbon nanotubes that may occur during the carbon nanotube synthesis and light irradiation treatment process can be recrystallized through additional light irradiation in an inert gas atmosphere. Referring to Figure 5, the Raman D / G ratio is 3 J / cm. 2 4~5 J / cm compared to 2 It can be confirmed that recrystallization is effectively achieved at an energy density of .

[0072]

[0073] SWCNT

[0074] Figure 6 is the Raman analysis result of SWCNT irradiated with xenon light according to Example 2 of the present invention. Referring to Figure 6, the D / G ratio of pristine is approximately 0.21 and 0.5 J / cm 2 Considering that the light irradiation sample is 0.18, 0.5 J / cm 2 At energy densities of 1–4 J / cm, carbon impurities are not effectively oxidized. In contrast, at 1–4 J / cm 2 It can be confirmed that carbon impurities are removed by significantly reducing the D / G ratio in the light irradiation. 5 J / cm 2 In , it can be seen that not only carbon impurities but also carbon nanotubes are oxidized or defective, increasing the D / G ratio.

[0075] Figure 7 is a TGA result of SWCNT irradiated with xenon light according to Example 2 of the present invention. Referring to Figure 7, in the case of Pristine, approximately 23.9 wt% of inorganic impurities are present and the energy density is 3 J / cm. 2 From the results showing that 20.6 wt% remained in the photoirradiation, 3 J / cm 2 At an energy density of 4 J / cm, it can be seen that sufficient heat energy is not generated, making it difficult to remove impurities. In contrast, at 4 J / cm 2 At 7.7 wt%, 5 J / cm 2 In , there is an inorganic impurity content of 5.3 wt%, and it can be confirmed that effective impurity removal is achieved.

[0076]

[0077] Thus, the method for manufacturing purified carbon nanotubes of the present invention has the technical feature of improving the purity and crystallinity of carbon nanotubes by selectively oxidizing and removing amorphous carbon particles and inorganic impurities in a dry manner at atmospheric pressure in a short period of time using xenon light, and enabling the purification process to be carried out simply and efficiently.

[0078]

[0079] The above description is merely an illustrative description of the technical idea of ​​the present invention, and those skilled in the art will appreciate that various modifications and variations can be made without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are not intended to limit the technical idea of ​​the present invention, but rather to illustrate it, 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 interpreted by the claims, and all technical ideas within a scope equivalent thereto should be interpreted as being included in the scope of the rights of the present invention.

Claims

1. Energy density of 1-4 J / cm in carbon nanotubes containing impurities 2 The first step is to remove amorphous carbon impurities by irradiating the xenon light for 0.2 to 50 seconds; and The energy density of the carbon nanotube from which the above carbon impurities have been removed is at least 4 J / cm 2 A method for producing purified carbon nanotubes using xenon light irradiation, characterized in that it comprises a second step of removing inorganic impurities by irradiating the carbon nanotubes with xenon light for at least 10 seconds.

2. In paragraph 1, The above carbon nanotubes are, A method for producing a purified carbon nanotube using xenon light irradiation, characterized in that the carbon nanotube is at least one of a single-walled carbon nanotube (SWCNT), a double-walled carbon nanotube (DWCNT), and a multi-walled carbon nanotube (MWCNT).

3. In paragraph 1, A method for producing purified carbon nanotubes using xenon light irradiation, characterized in that the second step is performed by further adding hydrogen halide.

4. In paragraph 1, In the above first step, the temperature of the part irradiated with the xenon light is 560 to 1100°C, A method for producing purified carbon nanotubes using xenon light irradiation, characterized in that the temperature of the portion irradiated with xenon light in the second step is at least 1100°C.

5. In paragraph 1, After the second step, the carbon nanotubes from which inorganic impurities have been removed have an energy density of at least 4 J / cm. 2 A method for producing purified carbon nanotubes using xenon light irradiation, characterized in that it further comprises a third step of producing recrystallized purified carbon nanotubes by re-irradiating the carbon nanotubes with xenon light for at least 30 seconds.

6. In paragraph 5, A method for producing purified carbon nanotubes using xenon light irradiation, characterized in that the first to third steps are performed at atmospheric pressure.

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