JP2020132504A - Purification method and purification device of carbon nanotube - Google Patents

Abstract

To provide a purification method and a purification device of carbon nano-tubes, which can largely reduce a risk of accident by precipitating as liquid drops or solid powder even when a vapor pressure of an etching agent is lower than 100 Pa at 25°C and the etching agent leaks by any chance.SOLUTION: In a purification method of carbon nano-tubes, a catalyst metal-containing carbon nano-tubes 1 synthesized with a catalyst metal 2, and a metal halide 15 are heated, vapor of the metal halide 15 is contacted with catalyst metal-containing carbon nano-tubed 1 to remove the catalyst metal 2.SELECTED DRAWING: Figure 2

Description

The present invention relates to a method and an apparatus for purifying carbon nanotubes.

Carbon nanotubes (hereinafter, also referred to as CNTs) have a unique one-dimensional nanostructure and excellent thermal, electrical, and mechanical properties, so that they can be mixed with battery electrodes, capacitors, transistors, polymers, etc. Various applications such as strength materials are expected. There are known physical vapor deposition (PVD) methods in which solid carbon is sublimated and then cooled to synthesize CNTs, and chemical vapor deposition (CVD) methods in which hydrocarbons and the like are thermally decomposed to synthesize CNTs. The method also uses metal nanoparticles as a catalyst. Usually, the synthesized CNT product contains several to several tens of wt% of the catalyst metal used for the synthesis as an impurity. If the catalyst metal is still contained, the physical properties of the nanomaterial will decrease and the weight will increase. Therefore, it is important to remove the catalyst metal by a purification treatment or the like.

Since most of the catalytic metals as impurities are mixed in a state of being covered with a carbon shell such as graphite carbon or amorphous carbon, conventionally, the process of oxidizing the carbon shell to remove all or part of it and the metal A purification method in which the acid dissolution step of dissolving the above-mentioned carbon is repeated is common. However, in the process of repeating these steps, in addition to damaging the CNT, it is immersed in the solution during the treatment with acid, so that the CNT is densely aggregated due to the surface tension of the solution during drying after purification, and redispersion is difficult. It has many problems such as becoming.

In recent years, a method for purifying CNTs has been proposed in which catalyst metal-containing carbon nanotubes containing a catalyst metal are heated in a dry state and brought into contact with chlorine gas (Cl ₂ gas) to remove the catalyst metal as a metal chloride. (For example, Patent Document 1).

Furthermore, the present inventors have developed a method for purifying CNTs using bromine (Br ₂ ), which is a liquid at normal temperature and pressure (25 ° C., 1 atm) (for example, Patent Document 2). This method is a purification method for removing a catalyst metal as a metal bromide by heating the catalyst metal-containing carbon nanotubes containing the catalyst metal in a dry state and bringing them into contact with Br ₂ gas.

International Publication No. WO2008 / 126534 International Publication No. WO2017 / 146218

In the method for purifying CNT with Cl ₂ gas disclosed in Patent Document 1, since the toxicity of Cl ₂ gas is high, the equipment becomes complicated and the cost increases, or if Cl ₂ gas leaks, a serious accident occurs. There was a problem in putting mass-produced equipment into practical use, especially from the viewpoint of equipment and operational safety, such as the possibility of connection.

In the method for purifying CNT with Br ₂ gas disclosed in Patent Document 2, since Br ₂ is a liquid at normal temperature and pressure, it is easier to deal with leakage than Cl ₂ which is a gas at normal temperature and pressure. Br ₂ has a high vapor pressure of 30.4 kPa even at room temperature of 25 ° C., and there is a risk that vapor may be diffused at the time of leakage, and a safer purification method has been desired.

The present invention has been made in view of such circumstances, and the vapor pressure of the etching agent is as low as less than 100 Pa at room temperature of 25 ° C., and even if the etching agent leaks, it is precipitated as droplets or solid powder. Therefore, it is an object of the present invention to provide a purification method and a purification apparatus for carbon nanotubes, which can significantly reduce the risk of accidents.

In order to solve such a problem, the present invention is a method for purifying carbon nanotubes, wherein a catalyst metal-containing carbon nanotube synthesized by using a catalyst metal and a metal halide are heated, and the vapor of the metal halide is heated. Provided is a method including an etching step of removing the catalyst metal by contacting the carbon nanotubes containing a catalyst metal.

In the purification method according to the present invention, the vapor pressure of the halide may be less than 100 Pa at 25 ° C.

In the purification method according to the present invention, the halide may be a solid at normal temperature and pressure.

The purification method according to the present invention may further include a vacuum heating step of heating the carbon nanotubes purified by the etching step in a vacuum state.

In the purification method according to the present invention, the metal halide may contain one or more of Fe, Ti, Cu, Zr, W, Si, Ge, Sn and Bi.

In the purification method according to the present invention, the metal halide may be selected from the group consisting of fluorides, chlorides, bromides or iodides, and mixtures thereof.

In the purification method according to the present invention, the catalytic metal-containing carbon nanotubes may be synthesized by a flame synthesis method, an arc discharge method, or a chemical vapor deposition (CVD) method.

In the present invention, a reactor, a carbon nanotube supply means for supplying a catalyst metal-containing carbon nanotube synthesized using a catalyst metal into the reactor, and an etching agent for supplying a metal halide into the reactor. The reactor includes a supply means, the catalyst metal-containing carbon nanotube, and a heating means for heating the metal halide, and the steam of the catalyst metal-containing carbon nanotube and the metal halide heated in the reactor is provided. Provided is a carbon nanotube purification apparatus which is brought into contact with each other to remove the catalyst metal.

The purification apparatus according to the present invention may further include a vacuum heating means for heating the purified carbon nanotubes in contact with the heated catalyst metal-containing carbon nanotubes and the vapors of the metal halide in a vacuum state.

In the present invention, an etching agent having a vapor pressure of less than 100 Pa at 25 ° C. is used, and the vapor is brought into contact with carbon nanotubes containing a catalytic metal in a heated state. Therefore, even if the etching agent leaks, it is dropleted. Alternatively, provide a method and apparatus for purifying carbon nanotubes, which can significantly reduce the risk of accidents by precipitating as a solid powder, have a high removal rate of catalytic metal, and can obtain high-quality carbon nanotubes having excellent crystallinity. be able to.

It is a schematic diagram which shows the appearance that the catalyst metal is covered with the carbon shell in the catalyst metal-containing carbon nanotube which is the object of purification processing by the purification method and the purification apparatus of the carbon nanotube of this invention. It is a schematic diagram which shows how the catalyst metal is removed by the etching agent in the heated catalyst metal-containing carbon nanotube. It is a schematic diagram which shows the state of the CNT which has the hollow carbon shell from which the catalyst metal was removed, obtained after the purification process by the purification method and the purification apparatus of the carbon nanotube of this invention. It is a schematic diagram which shows one preferable embodiment of the apparatus for performing the purification process by the etching process in the purification method and the purification apparatus of carbon nanotube of this invention. It is a schematic diagram which shows one preferable embodiment of the apparatus for performing the purification process by the vacuum heating step in the purification method and the purification apparatus of carbon nanotube of this invention. It is a graph and the table which shows the processing condition of the etching process in the purification method and purification apparatus of carbon nanotube of this invention. It is a graph which shows the change of the content rate of Fe in CNT before and after the purification process by the etching process with respect to Example 1 in the method and apparatus for purification of carbon nanotube of this invention. It is a graph which shows the result of the laser microscopic Raman spectroscopic analysis before performing the purification process by the etching process about Example 1 in the purification method and purification apparatus of the carbon nanotube of this invention. It is a graph which shows the result of the laser microscopic Raman spectroscopic analysis after the purification process by the etching process with respect to Example 1 in the purification method and purification apparatus of the carbon nanotube of this invention. It is a graph which expanded the horizontal axis of the result of the laser microscopic Raman spectroscopic analysis before performing the purification process by the etching process about Example 1 in the carbon nanotube purification method and the purification apparatus of this invention. It is a graph which expanded the horizontal axis of the result of the laser microscopic Raman spectroscopic analysis after the purification process by the etching process about Example 1 in the carbon nanotube purification method and the purification apparatus of this invention. In the method and apparatus for purifying carbon nanotubes of the present invention, a graph showing the results of thermogravimetric analysis (TG) for CNTs before the purification process and the CNTs after the purification process by the etching step and a weight loss rate with respect to Example 1 are shown. .. It is a graph and the table which show the processing condition of the vacuum heating step with respect to Example 1 in the carbon nanotube purification method and purification apparatus of this invention. FIG. 5 is a graph showing changes in the Cl content in CNTs before and after the purification treatment by the vacuum heating step with respect to Example 1 in the carbon nanotube purification method and purification apparatus of the present invention. FIG. 5 is a graph showing changes in the Fe content in CNTs before and after the purification treatment by the vacuum heating step with respect to Example 1 in the carbon nanotube purification method and purification apparatus of the present invention. It is a TEM image photograph of CNT taken by the transmission electron microscope (TEM) with respect to Example 1 and before the purification process by the purification method and the purification apparatus of the carbon nanotube of this invention. It is a TEM image photograph of CNT after the purification process by the etching process and the vacuum heating process, which was taken by the transmission electron microscope (TEM) with respect to Example 1 in the carbon nanotube purification method and the purification apparatus of this invention. In the method and apparatus for purifying carbon nanotubes of the present invention, there is a graph showing the results of thermogravimetric analysis (TG) for CNTs before the purification process and the CNTs after the purification process by the etching step and a weight loss rate for Example 2. .. FIG. 2 is a TEM image photograph of CNTs taken with a transmission electron microscope (TEM) with respect to Example 2 before the carbon nanotube purification method of the present invention and the purification treatment by the purification apparatus are performed. It is a TEM image photograph of CNT after the purification process by the etching process and the vacuum heating process, which was taken by the transmission electron microscope (TEM) with respect to Example 2 in the carbon nanotube purification method and the purification apparatus of this invention. In the method and apparatus for purifying carbon nanotubes of the present invention, a graph showing the results of thermogravimetric analysis (TG) for CNTs before the purification process and the CNTs after the purification process by the etching step and a weight loss rate with respect to Example 3 are shown. .. FIG. 3 is a TEM image photograph of CNTs taken with a transmission electron microscope (TEM) with respect to Example 3 before the carbon nanotube purification method of the present invention and the purification treatment by the purification apparatus are performed. It is a TEM image photograph of the CNT after the purification process by the etching process and the vacuum heating process, which was taken by the transmission electron microscope (TEM) with respect to Example 3 in the carbon nanotube purification method and the purification apparatus of this invention.

Hereinafter, preferred embodiments of the method for purifying carbon nanotubes (hereinafter, also referred to as CNT) and the purification apparatus of the present invention will be described with reference to the drawings and examples.

In the present embodiment, the catalyst metal-containing carbon nanotube is a CNT before the purification treatment by the purification method of the present invention, and contains, for example, a catalyst metal derived from a raw material used in the synthesis of the CNT as an impurity. As shown in FIG. 1, most of the catalyst metal 2 exists in a state of being covered with the carbon shell 3. The catalyst metal-containing carbon nanotubes 1 include CNTs 5 in which the catalyst metal 2 remains in the carbon shell 3 at the end 6 without removing the catalyst metal 2, particles 7 in which the catalyst metal 2 is covered with the carbon shell 3 and adheres to the CNTs 5. In addition, the catalyst metal 2 includes particles 8 that are covered with a carbon shell 3 and exist apart from the CNT 5. The carbon shell 3 may be a single layer or a multi-layer. Some CNTs 5 exist independently, while others exist as a plurality of CNTs 5 intertwined or bundled. Further, as impurities, the catalyst metal-containing carbon nanotube 1 includes a catalyst metal 2 covered with a carbon shell 3, a catalyst metal 2 not covered with a carbon shell 3, and carbon that has not been decomposed during the synthesis of CNT. It may also include a source, a catalyst source that was also undecomposed during the synthesis of CNTs, and the like.

The method for purifying carbon nanotubes according to the present embodiment includes an etching step (see FIGS. 1 to 3) for removing the catalyst metal 2 from the catalyst metal-containing carbon nanotubes 1. In the etching step, first, the catalyst metal-containing carbon nanotube 1 synthesized using the catalyst metal 2 and the metal halide 15 as an etching agent having a vapor pressure of less than 100 Pa at 25 ° C. (see FIG. 4) are heated. To do. From the viewpoint of safety, the vapor pressure of the metal halide as an etching agent at 25 ° C. is preferably less than 10 Pa, and more preferably less than 1 Pa. While the catalytic metal-containing carbon nanotube 1 is heated, the vapor of the metal halide 15 is brought into contact with the catalytic metal-containing carbon nanotube 1. An etching product is produced by a chemical reaction described later, and the catalyst metal 2 is removed.

As for the purification treatment temperature for heating the catalyst metal-containing carbon nanotube 1 and the metal halide 15 having a vapor pressure of less than 100 Pa at 25 ° C., the higher the temperature, the more the purification proceeds. When iron chloride (FeCl ₃ ) is used as an etching agent, the purification treatment temperature is preferably 600 ° C. or higher, more preferably 800 ° C. or higher, and even more preferably 1000 ° C. or higher. When the purification treatment temperature is 600 ° C. or higher, the reaction between the etching agent and the catalyst metal proceeds, and when the purification treatment temperature is 1000 ° C. or higher, the reaction proceeds further.

The method for purifying carbon nanotubes according to the present embodiment can further include a vacuum heating step of heating the carbon nanotubes 110 (see FIG. 5) purified by the etching step in a vacuum state after the etching step. By performing the purification treatment by the vacuum heating step, the content of the halogen element and the catalytic metal element remaining in the CNT 110 after the purification treatment by the etching step can be further reduced.

The principle of etching the catalyst metal 2 by the etching step of the present embodiment will be described with reference to FIGS. 1 to 3. FIG. 1 is a conceptual diagram showing a state of the catalyst metal-containing carbon nanotube 1 in which the catalyst metal 2 is covered with a carbon shell 3. When the catalyst metal-containing carbon nanotube 1 is heated and the temperature rises, the movement of the catalyst metal atom, the carbon atom, and the etching molecule becomes active so that the atom and the molecule can diffuse through the carbon shell 3 covering the particles of the catalyst metal 2. become. For example, when the catalyst metal 2 is Fe, the vapor pressure at 25 ° C. is less than 100 Pa, and the chloride 15 (FeCl ₃ ) of Fe, which is solid at normal temperature and pressure, is used as an etching agent to obtain Fe of the catalyst metal 2. FeCl _{3 of the} etching agent 15 reacts to produce FeCl _{2 as} an etching product (FIG. 2). Since FeCl ₂ has a high vapor pressure in a high temperature field, it separates from the catalyst metal-containing carbon nanotube 1 as steam, and as a result, Fe of the catalyst metal 2 in the catalyst metal-containing carbon nanotube 1 is removed, and the carbon shell 3 having a hollow structure is formed. A CNT 4 is formed, which includes a CNT 25 having a CNT 25, a particle 27 having a hollow structure carbon shell 3 attached to the CNT 25, and a particle 28 having a hollow structure carbon shell 3 and existing apart from the CNT 25. (Fig. 3). In this case, the reaction formula between Fe, which is the catalyst metal 2, and chloride 15 (FeCl ₃ ) of Fe, which is the etching agent, is represented by the following formula (1). FeCl ₂ , which is an etching product, has a negligibly low vapor pressure at 25 ° C. and is a solid at normal temperature and pressure.

Examples of the catalyst metal 2 include Fe, Co, Ni, Y, Cr, Mo, Nb, Cu, Ag, Au, and alloys thereof.

The metal of the metal halide 15 may be the same as or different from the catalyst metal 2 to be removed, and is not particularly limited. For example, Fe, Ti, Cu, Zr, W, Si, Ge, etc. Examples include Sn and Bi.

The metal halide 15 as an etching agent is a halide of a metal having a plurality of valences, and may have a vapor pressure of less than 100 Pa at 25 ° C. The metal halide 15 as an etching agent is particularly preferably solid at normal temperature and pressure, and has a high vapor pressure in a heated state (for example, 100 Pa or more at 600 ° C. or higher). The metal halide 15 as an etching agent is a fluoride, chloride, bromide or iodide having a vapor pressure of less than 100 Pa at 25 ° C., and a mixture thereof. Specifically, for example, FeCl ₃ or FeBr. _{3, TiI 4, CuCl 2,} ZrI 4, WCl 5, SiI 4, GeI 4, SnBr 4, BiF 5, include BiCl _3, BiBr 3 and BiI _3. These halides react with the catalyst metal 2 to change to lower valence halides, and the catalyst metal 2 is etched as a halide. Further, the metal halide as an etching product after etching also has a low vapor pressure of less than 100 Pa at 25 ° C., and can be particularly selected from solid metal halides at normal temperature and pressure. In that case, the vapor pressure at normal temperature is high. Is low (for example, 1 Pa or less) and the vapor pressure is high in the heated state (for example, 100 Pa or more at 600 ° C. or higher).

The catalyst metal-containing carbon nanotube 1 can be synthesized by a flame synthesis method, an arc discharge method, or a chemical vapor deposition (CVD) method, but is not particularly limited to these manufacturing methods.

FIG. 4 shows a preferred embodiment of the carbon nanotube purification apparatus 10 according to the present invention. FIG. 4 is a schematic view showing a simple purification apparatus as an example of an apparatus having a function of removing the catalyst metal 2 from the catalyst metal-containing carbon nanotubes 1 by the carbon nanotube purification method of the present embodiment. If the carbon nanotube purification apparatus 10 of the present invention can heat the catalyst metal-containing carbon nanotube 1 and the metal halide 15 and bring the vapor of the halide 15 into contact with the catalyst metal-containing carbon nanotube 1. The configuration is not limited to that shown in FIG.

In the reactor 11, a carbon nanotube supply means 13 for supplying the catalyst metal-containing carbon nanotube 1 synthesized by using the catalyst metal 2, which is the target of the purification treatment, is installed. Further, an etching agent supply means 16 for supplying a metal halide 15 as an etching agent is installed in the reactor 11.

The carbon nanotube supply means 13 may supply the catalyst metal-containing carbon nanotubes 1 in the reactor 11 as shown in FIG. 4, or the catalyst metal-containing carbon nanotubes 1 may be supplied into the reactor 11 from the outside of the reactor 11. It may be configured to supply 1. Similarly, the etching agent supply means 16 may supply the metal halide 15 in the reactor 11 as shown in FIG. 4, or the metal halide 15 may be supplied into the reactor 11 from the outside of the reactor 11. May be configured to supply.

In the reactor 11, for example, heat-resistant wool 18 may be arranged between the carbon nanotube supply means 13 and the etching agent supply means 1 and the opening 19. The steam flow is rectified to suppress thermal convection so that the vapor of the metal halide 15 does not flow out of the reactor 11. By this rectification, the flow of gas in the reactor 11 is restricted, the vapor of the metal halide 15 is efficiently brought into contact with the catalyst metal-containing carbon nanotube 1, and the efficiency of CNT purification can be improved.

The heating means 20 heats the catalyst metal-containing carbon nanotube 1 and the metal halide 15. The method and configuration of the heating means 20 are not particularly limited as long as the catalyst metal-containing carbon nanotube 1 and the metal halide 15 can be heated.

Since the vapor pressure of the metal halide 15 as an etching agent is less than 100 Pa at 25 ° C., even if the etching agent leaks from the inside of the reactor 11 during the purification process, it should be precipitated as droplets or solid powder. Can be done. For example, further, the etching product produced by bringing the steam of the heated catalytic metal-containing carbon nanotube 1 and the metal halide 15 into contact with each other in the reactor 11 is also etched if the vapor pressure at 25 ° C. is as low as less than 100 Pa. Should a material leak out of the reactor 11 during the purification process, it can also be precipitated as droplets or solid powder. Further, if the etching agent is a solid at normal temperature and pressure, even if the etching agent leaks from the inside of the reactor 11 during the purification process, it can be precipitated as a solid powder. Furthermore, if the etching product is also solid at normal temperature and pressure, even if the etching product leaks from the reactor 11 during the purification process, it can also be precipitated as a solid powder. Therefore, according to the carbon nanotube purification method and purification apparatus of the present embodiment, there is no risk of a person inhaling the leaked gas, so that an accident due to leakage is eliminated as compared with the conventional purification method using Cl ₂ gas or Br ₂ gas. Damage and its risk can be significantly reduced.

In the device as the vacuum heating means 100 shown in FIG. 5, the heated catalytic metal-containing carbon nanotube 1 and the vapor of the metal halide 15 are brought into contact with each other to purify the CNT 110 in a vacuum state in the reactor 111. Heat. The CNT supply means 113 supplies the CNT 110. By connecting the opening 119 of the reactor 111 to a vacuum pump (not shown) as a vacuuming means and operating the vacuum pump, the inside of the quartz glass tube 112 can be evacuated. Further, the vacuum heating means 100 is configured by providing the heating means 120 for heating the CNT 110 in the reactor 111. By heating the CNT 110 in a vacuum state by the vacuum heating means 100, the contents of the halogen element and the catalytic metal element remaining in the CNT 110 can be further reduced.

The content of each element remaining in the CNT can be measured, for example, by analyzing the composition using an energy dispersive X-ray analysis (EDX) apparatus attached to a scanning electron microscope (SEM).

The crystallinity of CNTs can be analyzed, for example, by laser microscopic Raman spectroscopy. In laser microscopic Raman spectroscopy, the peak that appears near 1590 cm ^-1 is called the G-band and is derived from the in-plane stretching vibration of a carbon atom having a six-membered ring structure. In addition, the peak that appears near 1350 cm ^-1 is called D-band, and it is more likely to appear if the six-membered ring structure is defective. The relative crystallinity of CNTs can be evaluated by the peak intensity ratio of G-band to D-band, I _G / I _D (G / D ratio). It can be said that the higher the G / D ratio, the higher the crystallinity of CNT. The peak that appears around 200 cm ^-1 is peculiar to single-walled CNT called RBM (Radial Breathing Mode), and is a mode that vibrates in the diameter direction of the tube.

The metal content of the catalyst metal 2 in the CNT is significantly reduced in the CNT 110 after purification by the etching step of the present embodiment as compared with the catalyst metal-containing carbon nanotube 1 before purification. Moreover, by purifying so as to remove the catalyst metal 2 while leaving the carbon shell 3, the surface area of the carbon shell 3 can be effectively used in addition to the surface area of the CNT, and the performance is improved in the application device using the surface area. Has an effect. Applications that utilize the surface area include electric double layer capacitors, various gas and ion adsorbents, gas and biosensor materials, and for example, in the case of electric double layer capacitors, their capacities can be increased.

As described above, in the present invention, the vapor pressure of the etching agent is less than 100 Pa at 25 ° C., and even if the etching agent leaks, it will settle as droplets or solid powder, so that the risk of accident is greatly reduced. can do. Further, since the catalyst metal 2 is removed without destroying the carbon shell 3, damage to the CNTs can be reduced. Furthermore, since there is no wet step of wetting the CNTs with a liquid, the CNTs do not become densified, and the CNTs can be kept in a low-density and easily dispersed state.

All references referred to herein are incorporated herein by reference in their entirety. The examples described herein illustrate embodiments of the invention and should not be construed as limiting the scope of the invention.

In Examples 1 to 3, CNTs having different synthesis methods were purified by the carbon nanotube purification method and purification apparatus according to the present embodiment. The details of the purification apparatus, the conditions of the purification process, and the evaluation results will be described below.

The carbon nanotube purification apparatus used in the examples will be described with reference to FIGS. 4 and 5.

As the reactor 11, a horizontal tube composed of a quartz glass tube 12 as shown in FIG. 4 was used. As the carbon nanotube supply means 13, a CNT container 14 which is a ceramic boat-shaped container made of silica and alumina was used.

FeCl ₃ was used as the metal halide 15 having a vapor pressure of less than 100 Pa at 25 ° C. FeCl ₃ is a solid at normal temperature and pressure. FeCl ₃ was placed directly on the quartz plate 17 as the etching agent supply means 16 provided in the quartz glass tube 12. The CNT container 14 was also placed on the quartz plate 17. As the heat-resistant wool 18, ceramic wool made of aluminum and silica was used.

As the heating means 20, an electric furnace 21 was used on the outer periphery of the quartz glass tube 12, and the inside of the quartz glass tube 12 was heated to raise the temperatures of the catalyst metal-containing carbon nanotube 1 and the metal halide 15.

In the apparatus as the vacuum heating means 100 for further purification, as shown in FIG. 5, a quartz glass tube 112 having the same configuration as the CNT purification apparatus 10 of FIG. 4, a CNT container 114 as the CNT supply means 113, and an apparatus , Quartz plate 117 was used. The opening 119 of the quartz glass tube 112 was connected to a vacuum pump (not shown) as a vacuuming means. Further, an electric furnace 121 as a heating means 120 was arranged on the outer circumference of the quartz glass tube 12.

The content of each element in the CNT was measured by the following method and laser microscopic Raman spectroscopic analysis was performed, and the evaluation was performed in Examples 1 to 3.

(Content rate measurement)
The content of each element in CNT is determined by scanning electron microscope (SEM) (model number: S-4800, manufactured by Hitachi High-Technologies Corporation) -energy dispersive X-ray analysis (EDX) device (model number: EDAX Genesis, manufactured by AMETEK). Was measured using. In order to reduce the influence of the substrate, in Examples 1 and 2, CNTs are sandwiched between two copper plates, pressure is applied from above and below to attach them to the copper plates, one copper plate is removed, and CNTs are placed on the other copper plate. The measurement was carried out in a state where. In Example 3, the CNTs were sandwiched between Ti meshes, pressed, and measured through the gaps in the Ti meshes. SEM-EDX analysis was performed at an accelerating voltage of 20 kV and a magnification of 300 times (Examples 1 and 2) to 500 times (Example 3) to evaluate the elemental composition of each element. After observing at a predetermined point, the observation points are measured at a distance of about 1.5 to 2 mm, and this is repeated to measure at 15 points in Example 1 and 5 points in Examples 2 and 3. It was.

(Laser microscopic Raman spectroscopic analysis)
A CNT powder sample was placed on a laser microscopic Raman spectrometer (model number: HR-800, manufactured by Horiba Seisakusho), and laser microscopic Raman spectroscopic analysis was performed using a laser wavelength of 488 nm. The CNT is placed on a silicon substrate, and 2-3 drops of ethanol are dropped on the CNT. Then, ethanol was dried on a hot plate, and CNT was brought into close contact with the silicon substrate. In the laser microscopic Raman spectroscopic analysis of CNT, variations may occur depending on the measurement points of CNT, so 10 points were measured, and the G / D ratio and RBM were measured at each point. The G / D ratio was evaluated by taking the total sum of the I _G / I _D values at 10 points.

(Thermogravimetric analysis)
Thermogravimetric analysis (TG) was performed on the CNT powder sample before the etching process and the CNT powder sample after the etching process using a thermal analyzer (model number: TGB210, manufactured by Rigaku), and the temperature rise rate was 5 ° C / under air flow. The weight loss rate due to carbon combustion was measured in min.

(Example 1) Purification treatment of TUBALL (registered trademark) single-walled carbon nanotubes 1. Etching Treatment A purification treatment of the etching process was performed using TUBALL (registered trademark) single-walled carbon nanotubes (OCSiAl) as a sample. The carbon nanotubes have a diameter of 1.6 ± 0.4 nm. In this example, first, 5 mg of CNT was placed in a CNT container, and the CNT container and 100 mg of FeCl ₃ were placed on a quartz plate. As shown in FIG. 6, the inside of the quartz glass tube was sucked into a vacuum and then replaced with Ar gas for 10 minutes to discharge the oxygen in the quartz glass tube. Next, the inside of the quartz glass tube was heated by an electric furnace to raise the temperature to 200 ° C., and the temperature was kept under reduced pressure for 5 minutes to evaporate only the water in the quartz glass tube, and the water in the quartz glass tube was removed. By removing the water in the quartz glass tube, it is possible to prevent the formation of Fe oxide due to the reaction between water and FeCl ₃ . Then, the replacement with Ar gas for 10 minutes was performed twice, and the temperature was raised to 1000 ° C. over 15 minutes while satisfying Ar at normal pressure (760 Torr). After the temperature was raised, the inside of the quartz glass tube was maintained at 1000 ° C. under normal pressure (760 Torr), and etching treatment with FeCl ₃ was performed for 60 minutes. Then, the mixture was cooled to room temperature at normal pressure (760 Torr) for 15 minutes, finally sucked into vacuum, and then replaced with Ar gas for 10 minutes twice.

Table 1 shows the measurement results of the content of C, O, Cl and Fe in the CNTs before the purification treatment by the etching step and the CNTs after the purification treatment by the etching step. FIG. 7 is a graph showing the measurement results of the Fe content among these measurement results. The content of Fe remaining in the CNT after the purification treatment by the etching step was 3.3 wt%, which was 76% less than 13.5 wt% before the purification treatment by the etching step.

FIG. 8 is a graph showing the results of laser microscopic Raman spectroscopic analysis before the purification process by the above etching step. FIG. 9 is a graph showing the results of laser microscopic Raman spectroscopic analysis after the purification process by the above vacuum heating step. The total added average of the I _G / I _D values, which are the G / D ratios at 10 points, was 25.4 before the purification treatment and 37.0 after the purification treatment. As a result of the purification treatment by the etching process, I _G The / _ID value increased by 46%, the crystallinity of the CNT did not decrease, and the CNT was not damaged.

FIG. 10 is an enlarged view of the vicinity of 200 cm ^-1 in the graph of FIG. From the graph, RBM is confirmed at all 10 points, and it can be seen that TUBALL (registered trademark) is a single-walled CNT. Further, it can be seen that the RBM of TUBALL (registered trademark) appears in a wide wave number range, and the distribution of the diameter of the CNT of TUBALL (registered trademark) is large. FIG. 11 is an enlarged view of the vicinity of 200 cm ^-1 in the graph of FIG. When the CNTs are treated at a high temperature of 1600 ° C. or higher, the diameter of the single-walled CNTs becomes large, and the CNTs may eventually change to multi-walled CNTs. From the graph of FIG. 11, RBM was confirmed at all 10 points, and it can be seen that the CNTs did not change to multi-walled CNTs even after the purification treatment by the etching step. Further, as compared with the RBM of FIG. 10, almost no change is observed in the peak position and the like, so that it can be seen that the diameter of the CNT is hardly changed even after the purification treatment by the etching step.

FIG. 12 shows the results of thermogravimetric analysis (TG) of CNTs before the purification treatment by the etching step (broken line) and after the purification treatment by the etching step (solid line). The weight loss rate of CNTs before the purification treatment by the etching step was 83.75%, and the residual amount was 16.25%. The weight loss rate of CNTs after the purification treatment by the etching step was 96.84%, and the residual amount was 3.16%. From the result of thermogravimetric analysis (TG), it can be seen that the residual amount of catalyst in CNT, which causes residue, was reduced to 1/5 or less by the etching process.

2. 2. Purification treatment after etching treatment Using the CNTs after the purification treatment by the above etching step, the purification treatment by the vacuum heating step was performed. First, the CNTs purified by the etching process were placed in a CNT container, and the CNT container was placed on a quartz plate. As shown in FIG. 13, after sucking the inside of the quartz glass tube into a vacuum, replacement with Ar gas was performed twice for 10 minutes, and oxygen in the quartz glass tube was discharged. Then, the inside of the quartz glass tube was heated in a vacuum state by an electric furnace, and the temperature was raised to 1000 ° C. over 15 minutes. After the temperature was raised, the inside of the quartz glass tube was kept at 1000 ° C. for 60 minutes in a vacuum state. Then, the mixture was cooled to room temperature in a vacuum state for 15 minutes, and finally replaced with Ar gas for 10 minutes twice.

Table 2 shows the measurement results of the contents of C, O, Cl and Fe in the CNTs before the purification treatment by the vacuum heating step and the CNTs after the purification treatment by the vacuum heating step. FIG. 14 is a graph showing the measurement result of the Cl content among these measurement results, and FIG. 15 is a graph showing the measurement result of the Fe content. The content of Cl remaining in the CNT after the purification treatment by the vacuum heating step was 0.6 wt%, which was 73% lower than the 2.2 wt% before the purification treatment by the vacuum heating step. The content of Fe remaining in the CNT after the purification treatment by the vacuum heating step was 1.8 wt%, which was 45% less than 3.3 wt% before the purification treatment by the vacuum heating step. As a result of the purification treatment by the etching step and the vacuum heating step, the content of Fe remaining in the CNT after the purification treatment is reduced by 87% from 13.5 wt% before the purification treatment by the etching step. did.

FIG. 16 is a TEM image photograph of the CNT before the purification process, which was taken with a transmission electron microscope (TEM). As shown by the arrow, it can be confirmed that the particles of the catalyst metal remain in the carbon shell. FIG. 17 is a TEM image photograph of the CNT after the purification treatment by the etching step and the vacuum heating step. As shown by the arrow, a hollow carbon shell from which the catalyst metal in the carbon shell has been removed can be confirmed.

3. 3. Summary of Example 1 From the above, the catalyst metal can be removed from the CNTs of TUBALL (registered trademark) by the purification process by the etching process using FeCl ₃ as an etching agent, and the diameter of the CNTs can be increased or the number of layers can be increased. It was confirmed that the crystallinity can be enhanced without causing damage such as conversion. Furthermore, it was confirmed that the catalyst metal can be further removed and the Cl content can be reduced by the purification treatment by the vacuum heating step.

(Example 2) Purification treatment of carbon nanotubes synthesized by the arc discharge method 1. Etching process A single-walled carbon nanotube synthesized by the arc discharge method was used as a sample to purify the etching process. The carbon nanotubes have a diameter of 1 to 2 nm. In this example, 5 mg of CNT and 100 mg of FeCl ₃ were used, and the purification treatment was carried out under the same purification treatment conditions as in Example 1 using the same purification equipment as in Example 1.

Table 3 shows the measurement of the contents of C, O, Y, S, Cl, Fe and Ni in the CNTs before the purification treatment by the etching step and the CNTs after the purification treatment by the etching step. The result is shown. The content of Ni remaining in the CNT after the purification treatment by the etching step was 6.9 wt%, which was 82% lower than the 38.5 wt% before the purification treatment by the etching step.

FIG. 18 shows the results of thermogravimetric analysis (TG) of CNTs before the purification treatment by the etching step (broken line) and after the purification treatment by the etching step (solid line). The weight loss rate of CNTs before the purification treatment by the etching step was 34.86%, and the residual amount was 65.14%. The weight loss rate of CNTs after the purification treatment by the etching step was 75.59%, and the residual amount was 24.41%. From the results of thermogravimetric analysis (TG), it can be seen that the amount of catalyst residue in CNTs, which causes residues, was reduced to about 1/3 by the etching process.

2. 2. Purification treatment after etching treatment Using the CNTs after the purification treatment by the above etching step, the purification treatment by the vacuum heating step was performed. The purification treatment was carried out under the same purification treatment conditions as in Example 1 using the same purification equipment as in Example 1.

FIG. 19 is a TEM image photograph of the CNT before the purification process, which was taken with a transmission electron microscope (TEM). As shown by the arrow, it can be confirmed that the particles of the catalyst metal remain in the carbon shell. FIG. 20 is a TEM image photograph of the CNT after the purification treatment by the etching step and the vacuum heating step. As shown by the arrow, a hollow carbon shell from which the catalyst metal in the carbon shell has been removed can be confirmed.

3. 3. Summary of Example 2 From the above, it is possible to remove the catalyst metal from the CNT synthesized by the arc discharge method by the purification treatment by the etching process using FeCl ₃ as an etching agent and the purification treatment by the vacuum heating step. It was confirmed that it could be done.

(Example 3) Purification treatment of carbon nanotubes synthesized by chemical vapor deposition (CVD) method 1. Etching treatment The multi-walled carbon nanotubes synthesized by the CVD method were used as samples to purify the etching process. The carbon nanotubes have a diameter of 10 to 30 nm and an average diameter of about 20 nm. In this example, 5 mg of CNT and 100 mg of FeCl ₃ were used, and the purification treatment was carried out under the same purification treatment conditions as in Example 1 using the same purification equipment as in Example 1.

Table 4 shows the measurement results of the contents of C, O, Mg, Al, Cl and Fe in the CNTs before the purification treatment by the etching step and the CNTs after the purification treatment by the etching step. Shown. The content of Fe remaining in the CNT after the purification treatment by the etching step was 0.1 wt%, which was 99% less than 7.2 wt% before the purification treatment by the etching step.

FIG. 21 shows the thermogravimetric analysis (TG) results of CNTs before the purification treatment by the etching step (broken line) and after the purification treatment by the etching step (solid line). The weight loss rate of CNTs before the purification treatment by the etching step is 89.01%, and the residual amount is 10.99%. The weight loss rate of CNTs after the purification treatment by the etching step was 96.12%, and the residual amount was 3.88%. From the results of thermogravimetric analysis (TG), it can be seen that the amount of catalyst residue in CNTs, which causes residues, was reduced to 1/2 or less by the etching process.

2. 2. Purification treatment after etching treatment Using the CNTs after the purification treatment by the above etching step, the purification treatment by the vacuum heating step was performed. The purification treatment was carried out under the same purification treatment conditions as in Example 1 using the same purification equipment as in Example 1.

FIG. 22 is a TEM image photograph of the CNT before the purification process, which was taken with a transmission electron microscope (TEM). As shown by the arrow, it can be confirmed that the particles of the catalyst metal remain in the carbon shell. FIG. 23 is a TEM image photograph of the CNT after the purification treatment by the etching step and the vacuum heating step. As shown by the arrow, a hollow carbon shell from which the catalyst metal in the carbon shell has been removed can be confirmed.

3. 3. Summary of Example 3 From the above, the catalyst metal can be removed from the CNT synthesized by the CVD method by the purification treatment by the etching process using FeCl ₃ as an etching agent and the purification treatment by the vacuum heating step. Was confirmed.

Although the present invention has been described above based on the embodiments and examples, the present invention can be modified in various ways. For example, the heating means 20 may separately include a CNT heating means (not shown) for heating the catalyst metal-containing carbon nanotube 1 and a halide heating means (not shown) for heating the metal halide 15. ..

1 Catalytic metal-containing carbon nanotube 2 Catalytic metal 3 Carbon shell 4 CNT having a hollow carbon shell
5 CNT
6 End 7 Particles whose catalyst metal is covered with carbon shells and adhered to CNTs 8 Particles whose catalyst metal is covered with carbon shells and exists away from CNTs
10 Carbon nanotube purification equipment
11 Reactor
12 Quartz glass tube
13 Carbon nanotube supply means
14 CNT container
15 Metal halides
16 Etching agent supply means
17 Quartz plate
18 Heat resistant wool
20 Heating means
21 electric furnace
25 CNTs with hollow carbon shells
27 Particles with a hollow carbon shell and attached to CNTs
28 Particles with a hollow carbon shell that exist apart from CNTs
100 vacuum heating device
112 Quartz glass tube
113 Carbon nanotube supply means
114 CNT container
117 Quartz plate
120 Heating means
121 electric furnace

Claims (9)

An etching step of heating the catalyst metal-containing carbon nanotubes synthesized using the catalyst metal and the metal halide and bringing the vapor of the metal halide into contact with the catalyst metal-containing carbon nanotubes to remove the catalyst metal. Methods for purifying carbon nanotubes, including. The method for purifying carbon nanotubes according to claim 1, wherein the vapor pressure of the metal halide is less than 100 Pa at 25 ° C. The method for purifying carbon nanotubes according to claim 1 or 2, wherein the halide is a solid at normal temperature and pressure. The method for purifying carbon nanotubes according to any one of claims 1 to 3, further comprising a vacuum heating step of heating the carbon nanotubes purified by the etching step in a vacuum state. The method for purifying carbon nanotubes according to any one of claims 1 to 4, wherein the metal halide contains one or more of Fe, Ti, Cu, Zr, W, Si, Ge, Sn and Bi. The method for purifying carbon nanotubes according to any one of claims 1 to 5, wherein the metal halide is selected from the group consisting of fluoride, chloride, bromide or iodide, and a mixture thereof. The method for purifying carbon nanotubes according to any one of claims 1 to 6, wherein the catalytic metal-containing carbon nanotubes are synthesized by a flame synthesis method, an arc discharge method, or a chemical vapor deposition (CVD) method. Reactor and
A carbon nanotube supply means for supplying the catalyst metal-containing carbon nanotubes synthesized using the catalyst metal into the reactor, and
An etching agent supply means for supplying a metal halide into the reactor, and
The catalyst metal-containing carbon nanotube and a heating means for heating the metal halide are provided.
A carbon nanotube refining apparatus for removing the catalytic metal by bringing the heated catalyst metal-containing carbon nanotube and the vapor of the metal halide into contact with each other in the reactor. The carbon nanotube refining apparatus according to claim 8, further comprising a vacuum heating means for heating the heated carbon nanotubes containing the catalyst metal and the carbon nanotubes purified by contacting the vapors of the metal halide in a vacuum state.