JP7278539B2 - Carbon nanotube purification method and purification apparatus - Google Patents

Description

TECHNICAL FIELD The present invention relates to a purification method and purification apparatus for carbon nanotubes.

Carbon nanotubes (hereinafter also referred to as CNTs) have a unique one-dimensional nanostructure and excellent thermal, electrical and mechanical properties. Various applications such as strength materials are expected. A physical vapor deposition (PVD) method in which solid carbon is sublimated and then cooled to synthesize CNTs, and a chemical vapor deposition (CVD) method in which CNTs are synthesized by pyrolyzing hydrocarbons or the like are known. The method also uses metal nanoparticles as catalysts. Generally, the synthesized CNT product contains several to several tens of wt % of catalyst metal used for synthesis as an impurity. If the catalyst metal remains contained, the physical properties of the nanomaterial will decrease and the weight will increase, so it is important to remove the catalyst metal by refining or the like.

Since most catalyst metals as impurities are mixed in a state covered with a carbon shell such as graphite carbon or amorphous carbon, conventionally, a process of oxidizing the carbon shell to remove all or part of it and a metal A common purification method is to repeat the acid dissolution step of dissolving with an acid. However, in the process of repeating these processes, the CNTs are damaged, and since they are immersed in a solution during the acid treatment, the CNTs aggregate densely due to the surface tension of the solution during drying after purification, making re-dispersion difficult. There are many problems such as becoming

In recent years, a method for purifying CNTs has been proposed in which catalytic metal-containing carbon nanotubes are heated in a dry state and brought into contact with chlorine gas ( _Cl2 gas) to remove the catalytic metal as a metal chloride. (For example, Patent Document 1).

Furthermore, the present inventors have developed a CNT purification method using bromine (Br ₂ ), which is liquid at normal temperature and normal pressure (25° C., 1 atm) (for example, Patent Document 2). This method is a purification method in which the catalytic metal-containing carbon nanotubes containing the catalytic metal are heated in a dry state and brought into contact with Br ₂ gas to remove the catalytic metal as a metal bromide.

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

In the method for purifying CNTs using _Cl2 gas disclosed in Patent Document 1, the toxicity of _Cl2 gas is high, which complicates equipment and increases costs, and if _Cl2 gas leaks, serious accidents may occur. There were problems in putting mass-production equipment into practical use, especially from the standpoint of equipment and operational safety, such as the risk of being connected.

In the CNT refining method using _Br2 gas disclosed in Patent Document 2, since _Br2 is liquid at normal temperature and pressure, it is easier to deal with leakage than _Cl2 , which is 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 the vapor will diffuse when leaking, so a safer purification method has been desired.

The present invention has been made in view of such circumstances, and the vapor pressure of the etchant is as low as less than 100 Pa at room temperature 25 ° C., and even if the etchant leaks, it will settle as droplets or solid powder. Therefore, an object of the present invention is to provide a carbon nanotube refining method and a refining apparatus that can greatly reduce the risk of accidents.

In order to solve such problems, the present invention provides a method for purifying carbon nanotubes, which comprises heating a catalytic metal-containing carbon nanotube synthesized using a catalytic metal and a metal halide, and removing the vapor of the metal halide from the A method is provided comprising an etching step of contacting with a catalytic metal-containing carbon nanotube to remove said catalytic 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 solid at normal temperature and normal 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 invention, said 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.

The present invention comprises a reactor, a carbon nanotube supplying means for supplying catalyst metal-containing carbon nanotubes synthesized using a catalyst metal into the reactor, and an etchant supplying a metal halide into the reactor. a supply means, and a heating means for heating the catalytic metal-containing carbon nanotubes and the metal halide, wherein the heated vapor of the catalytic metal-containing carbon nanotubes and the metal halide is heated in the reactor. Provided is a carbon nanotube purifier for contacting to remove the catalyst metal.

The purification apparatus according to the present invention may further include vacuum heating means for heating the purified carbon nanotubes in a vacuum state by contacting the heated catalytic metal-containing carbon nanotubes and the vapor of the metal halide.

The present invention uses an etching agent having a vapor pressure of less than 100 Pa at 25° C., and by bringing the vapor into contact with the catalyst metal-containing carbon nanotubes in a heated state, even if the etching agent leaks, it can be released into droplets. Alternatively, a carbon nanotube refining method and a refining apparatus are provided, which can greatly reduce the risk of an accident by allowing the carbon nanotube to settle as a solid powder, has a high catalyst metal removal rate, and obtains a high-quality carbon nanotube with excellent crystallinity. be able to.

FIG. 1 is a schematic diagram showing a state in which a catalytic metal is covered with a carbon shell in a catalytic metal-containing carbon nanotube to be purified by the carbon nanotube purification method and the purification apparatus of the present invention. FIG. 2 is a schematic diagram showing how catalyst metals are removed by an etchant from heated carbon nanotubes containing catalyst metals. FIG. 2 is a schematic diagram showing the appearance of CNTs having hollow carbon shells from which catalytic metals have been removed, obtained after purification by the method and apparatus for purifying carbon nanotubes of the present invention. 1 is a schematic view showing a preferred embodiment of an apparatus for performing a purification treatment by an etching step in the method and apparatus for purifying carbon nanotubes of the present invention; FIG. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram showing a preferred embodiment of an apparatus for performing purification treatment by a vacuum heating step in the method and apparatus for purifying carbon nanotubes of the present invention. 4 is a graph and a table showing processing conditions for an etching step in the method and apparatus for purifying carbon nanotubes of the present invention. 4 is a graph showing changes in the Fe content in CNTs before and after purification by an etching step in Example 1 in the method and apparatus for purifying carbon nanotubes of the present invention. 1 is a graph showing the results of laser microscopic Raman spectroscopic analysis before performing a purification treatment by an etching process in relation to Example 1 in the method and apparatus for purifying carbon nanotubes of the present invention. 1 is a graph showing the results of laser microscopic Raman spectroscopic analysis after performing a purification treatment by an etching process in relation to Example 1 in the method and apparatus for purifying carbon nanotubes of the present invention. 4 is a graph showing the result of laser microscopic Raman spectroscopic analysis before performing a purification treatment by an etching process in Example 1 in the method and apparatus for purifying carbon nanotubes of the present invention, with the horizontal axis enlarged. 4 is a graph showing the result of laser microscopic Raman spectroscopic analysis after performing a purification treatment by an etching process in Example 1 in the method and apparatus for purifying carbon nanotubes of the present invention, with the horizontal axis enlarged. 2 is a graph showing the results of thermogravimetric analysis (TG) on CNTs before and after purification by an etching step, and the weight reduction rate, in the method and apparatus for purifying carbon nanotubes of the present invention in Example 1. FIG. . 4 is a graph and a table showing the processing conditions of the vacuum heating step in Example 1 in the method and apparatus for purifying carbon nanotubes of the present invention. 4 is a graph showing changes in the Cl content in CNTs before and after purification by a vacuum heating step in Example 1 in the method and apparatus for purifying carbon nanotubes of the present invention. 4 is a graph showing changes in the Fe content in CNTs before and after purification by a vacuum heating step in Example 1 in the method and apparatus for purifying carbon nanotubes of the present invention. 1 is a TEM image photograph of CNTs before purification treatment by the carbon nanotube purification method and purification apparatus of the present invention, taken with a transmission electron microscope (TEM), in relation to Example 1. FIG. 1 is a TEM image photograph of CNTs after purification treatment by an etching step and a vacuum heating step, taken with a transmission electron microscope (TEM) in relation to Example 1 in the method and apparatus for purifying carbon nanotubes of the present invention. FIG. 10 is a graph showing the results of thermogravimetric analysis (TG) on CNTs before and after purification by an etching step, and the weight reduction rate, in Example 2 of the carbon nanotube purification method and purification apparatus of the present invention. FIG. . FIG. 10 is a TEM image photograph of CNTs before purification treatment by the carbon nanotube purification method and purification apparatus of the present invention, taken with a transmission electron microscope (TEM), in relation to Example 2. FIG. FIG. 10 is a TEM image photograph of CNTs after purification treatment by an etching process and a vacuum heating process, taken with a transmission electron microscope (TEM) in relation to Example 2 in the method and apparatus for purifying carbon nanotubes of the present invention. FIG. 10 is a graph showing the results of thermogravimetric analysis (TG) on CNTs before and after purification by an etching step, and the weight reduction rate, in Example 3 of the carbon nanotube purification method and purification apparatus of the present invention. FIG. . FIG. 10 is a TEM image photograph of CNTs before purification treatment by the carbon nanotube purification method and purification apparatus of the present invention, taken with a transmission electron microscope (TEM), relating to Example 3. FIG. FIG. 10 is a TEM image photograph of CNTs after purification treatment by an etching step and a vacuum heating step, taken with a transmission electron microscope (TEM) in relation to Example 3 in the method and apparatus for purifying carbon nanotubes of the invention.

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of the carbon nanotube (hereinafter also referred to as CNT) purification method and purification apparatus of the present invention will be described below based on the drawings and examples.

In the present embodiment, the catalytic metal-containing carbon nanotubes are CNTs before being purified by the purification method of the present invention, and contain, as impurities, catalytic metals derived from the raw materials used in the synthesis of the CNTs, for example. As shown in FIG. 1, most of the catalytic metal 2 exists in a state covered with a carbon shell 3 . The catalytic metal-containing carbon nanotubes 1 are composed of CNTs 5 in which the catalytic metal 2 remains in the carbon shell 3 at the end 6 without being removed, particles 7 in which the catalytic metal 2 is covered with the carbon shell 3 and attached to the CNTs 5, And, the catalyst metal 2 includes particles 8 which are particles covered with the carbon shell 3 and exist apart from the CNTs 5 . The carbon shell 3 may be a single layer or multiple layers. Some CNT5 exist independently, while others exist as a plurality of CNT5 intertwined or bundled. In addition to the catalyst metal 2 covered with the carbon shell 3, the catalyst metal-containing carbon nanotube 1 contains, as impurities, for example, the catalyst metal 2 not covered with the carbon shell 3, and carbon that has not been decomposed during the synthesis of the CNT. It may also include sources, such as sources of catalyst that were not decomposed during the synthesis of the CNTs.

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

Regarding 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 progresses. For example, when iron chloride (FeCl ₃ ) is used as an etchant, the purification treatment temperature is preferably 600° C. or higher, more preferably 800° C. or higher, and even more preferably 1000° C. or higher. If the refining treatment temperature is 600° C. or higher, the reaction between the etchant and the catalyst metal proceeds, and if it is 1000° C. or higher, the reaction proceeds further.

The carbon nanotube purification method according to the present embodiment may further include a vacuum heating process of heating the carbon nanotubes 110 (see FIG. 5) purified by the etching process in a vacuum state after the etching process. By performing the purification treatment by the vacuum heating process, it is possible to further reduce the contents of the halogen element and the catalytic metal element remaining in the CNT 110 after the purification treatment by the etching process.

The principle of etching the catalyst metal 2 by the etching process of this embodiment will be described with reference to FIGS. 1 to 3. FIG. FIG. 1 is a conceptual diagram showing the appearance of a catalytic metal-containing carbon nanotube 1 in which the catalytic metal 2 is covered with a carbon shell 3. As shown in FIG. When the catalytic metal-containing carbon nanotubes 1 are heated to raise the temperature, the motion of the catalytic metal atoms, carbon atoms, and etching molecules increases, allowing atoms and molecules to diffuse through the carbon shells 3 covering the particles of the catalytic metal 2. become. For example, when the catalyst metal 2 is Fe, the vapor pressure at 25° C. is less than ₁₀₀ Pa and solid at normal temperature and pressure. The FeCl ₃ of the etchant 15 reacts to form the etching product FeCl ₂ (FIG. 2). Since FeCl ₂ has a high vapor pressure in a high-temperature field, it leaves the catalyst metal-containing carbon nanotube 1 as vapor. a CNT 25 having a hollow structure, a particle 27 having a hollow carbon shell 3 attached to the CNT 25, and a particle 28 having a hollow carbon shell 3 and existing away from the CNT 25. (Fig. 3). In this case, the reaction formula of Fe, which is the catalyst metal 2, and Fe chloride 15 (FeCl ₃ ), which is the etchant, is represented by the following formula (1). The etching product, FeCl ₂ , has negligible vapor pressure at 25° C. and is 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. Examples include Fe, Ti, Cu, Zr, W, Si, Ge, Sn and Bi are included.

The metal halide 15 as an etchant is a metal halide having multiple valences, and may have a vapor pressure of less than 100 Pa at 25°C. The metal halide 15 as an etchant is particularly preferably solid at normal temperature and normal pressure, and preferably has a high vapor pressure in a heated state (for example, 100 Pa or higher at 600° C. or higher). Metal halides 15 as etching agents are fluorides, chlorides, bromides or iodides having a vapor pressure of less than 100 Pa at 25° C. and mixtures thereof, specifically FeCl ₃ and FeBr ₃ , _TiI4 , _CuCl2 , _ZrI4 , _WCl5 , _SiI4 , GeI4, _SnBr4 , _BiF5 , _{BiCl3 , BiBr3} and _BiI3 . These halides react with the catalytic metal 2 to convert to lower valence halides, and the catalytic metal 2 is etched as a halide. In addition, the metal halide as an etching product after etching has a low vapor pressure of less than 100 Pa at 25 ° C., and can be selected from metal halides that are particularly solid at normal temperature and normal pressure. It is preferable that the viscosity is low (for example, 1 Pa or less) and the vapor pressure in a heated state is high (for example, 100 Pa or more at 600° C. or more).

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

FIG. 4 shows a preferred embodiment of a carbon nanotube purification apparatus 10 according to the present invention. FIG. 4 is a schematic diagram showing a simple refining apparatus as an example of an apparatus having a function of removing the catalytic metal 2 from the catalytic metal-containing carbon nanotube 1 by the carbon nanotube refining method of the present embodiment. Incidentally, in the carbon nanotube purification apparatus 10 of the present invention, if the catalyst metal-containing carbon nanotube 1 and the metal halide 15 can be heated and the vapor of the halide 15 can be brought into contact with the catalyst metal-containing carbon nanotube 1, It is not limited to the configuration of FIG.

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

The carbon nanotube supply means 13 may supply the catalyst metal-containing carbon nanotubes 1 within the reactor 11 as shown in FIG. 1 may be provided. Similarly, the etchant supply means 16 may supply the metal halide 15 within the reactor 11 as shown in FIG. may be configured to provide

In the reactor 11, between the carbon nanotube supply means 13 and the etchant supply means 1 and the opening 19, for example, a refractory wool 18 may be arranged. To prevent the vapor of the metal halide 15 from flowing out of the reactor 11, the flow of the vapor is rectified to suppress heat convection. This rectification restricts the gas flow in the reactor 11, allows the vapor of the metal halide 15 to efficiently come into contact with the catalytic metal-containing carbon nanotubes 1, and improves the efficiency of CNT purification.

Heating means 20 heats catalyst metal-containing carbon nanotubes 1 and metal halide 15 . As long as the heating means 20 can heat the catalytic metal-containing carbon nanotube 1 and the metal halide 15, the method and configuration are not particularly limited.

Since the metal halide 15 as an etchant has a vapor pressure of less than 100 Pa at 25° C., even if the etchant leaks from the reactor 11 during the refining process, it will settle out as droplets or solid powder. can be done. For example, if the vapor pressure at 25° C. is as low as less than 100 Pa, the etching product produced by contacting the vapors of the heated catalytic metal-containing carbon nanotubes 1 and the metal halide 15 in the reactor 11 can be produced by etching. Should material leak out of reactor 11 during the purification process, it can also settle out as droplets or a solid powder. Furthermore, if the etchant is solid at normal temperature and normal pressure, even if the etchant leaks from the reactor 11 during the refining process, it can be precipitated as a solid powder. In addition, if the etching product is also solid at normal temperature and normal 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 refining method and refining _apparatus of the present embodiment, there is no risk of human beings inhaling the _leaked gas. damage and its risk can be significantly reduced.

The apparatus as the vacuum heating means 100 shown in FIG. heat up. CNT supplying means 113 supplies CNTs 110 . The quartz glass tube 112 can be evacuated by connecting the opening 119 of the reactor 111 to a vacuum pump (not shown) as an evacuation means and operating the vacuum pump. Furthermore, the vacuum heating means 100 is configured by providing the heating means 120 for heating the CNTs 110 in the reactor 111 . By heating the CNTs 110 in a vacuum with the vacuum heating means 100, the contents of halogen elements and catalytic metal elements remaining in the CNTs 110 can be further reduced.

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

The crystallinity of CNTs can be analyzed, for example, by laser micro-Raman spectroscopy. In the laser microscopic Raman spectroscopic analysis, the peak appearing near 1590 cm ^-1 is called G-band, which is derived from in-plane stretching vibration of carbon atoms having a six-membered ring structure. Also, a peak appearing near 1350 cm ^-1 is called D-band, and it tends to appear when there is a defect in the six-membered ring structure. The relative crystallinity of CNTs can be evaluated by the peak intensity ratio I _G /I _D (G/D ratio) of the G-band to the D-band. It can be said that the higher the G/D ratio, the higher the crystallinity of the CNT. The peak appearing near 200 cm ⁻¹ is called RBM (Radial Breathing Mode), which is peculiar to single-walled CNTs and is a mode in which the tube diametrically oscillates.

The CNT 110 purified by the etching process of this embodiment has a significantly reduced metal content of the catalytic metal 2 in the CNT compared to the catalytic metal-containing carbon nanotube 1 before purification. Moreover, by refining 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 of the application device using the surface area can be improved. have an effect. Applications that utilize surface area include electric double layer capacitors, various gas and ion adsorbents, gas and biosensor materials, etc. For example, in the case of electric double layer capacitors, their capacity can be increased.

As described above, according to the present invention, the vapor pressure of the etchant is less than 100 Pa at 25°C, and even if the etchant leaks, it settles as droplets or solid powder, which greatly reduces the risk of accidents. can do. Moreover, since the catalyst metal 2 is removed while leaving the carbon shell 3 unbroken, damage to the CNT can be reduced. Furthermore, since there is no wet process for wetting the CNTs with a liquid, the CNTs are not densified, and the CNTs can be kept in a state of low density and easy to disperse.

All documents mentioned herein are hereby incorporated by reference in their entirety. The examples described herein are illustrative of embodiments of the invention and should not be construed as limiting the scope of the invention.

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

An apparatus for purifying carbon nanotubes used in the examples will be described with reference to FIGS. 4 and 5. FIG.

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 metal halide 15 whose vapor pressure is less than 100 Pa at 25°C. _FeCl3 is a solid at normal temperature and pressure. The FeCl ₃ was placed directly on a quartz plate 17 as an etchant supply means 16 provided within the quartz glass tube 12 . A CNT container 14 was also placed on the quartz plate 17 . Ceramic wool made of aluminum and silica was used as the heat-resistant wool 18 .

As a heating means 20, an electric furnace 21 was used around the quartz glass tube 12 to heat the inside of the quartz glass tube 12, thereby raising the temperatures of the catalyst metal-containing carbon nanotube 1 and the metal halide 15.

As shown in FIG. 5, the apparatus as the vacuum heating means 100 for further purification includes a quartz glass tube 112 having the same configuration as the CNT purification apparatus 10 of FIG. , a quartz plate 117 was used. An opening 119 of the quartz glass tube 112 was connected to a vacuum pump (not shown) as a means for evacuating. Further, an electric furnace 121 as a heating means 120 was arranged around the quartz glass tube 12 .

Measurement of the content of each element in the CNT and laser microscopic Raman spectroscopic analysis were performed by the following methods, and evaluated in Examples 1 to 3.

(Content rate measurement)
The content of each element in CNT was measured using a 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, the CNTs were sandwiched between two copper plates and pressure was applied from above and below to adhere them to the copper plates. was adhered to the measurement. In Example 3, the CNTs were sandwiched between Ti meshes, pressed, and measured from the gaps between the Ti meshes. SEM-EDX analysis was performed at an acceleration voltage of 20 kV and a magnification of 300 (Examples 1 and 2) to 500 (Example 3) to evaluate the elemental composition of each element. After observing at a predetermined point, measurement was also performed at a point about 1.5 to 2 mm away, and this was repeated to measure at 15 points in Example 1 and at 5 points in Examples 2 and 3. rice field.

(laser microscopic Raman spectroscopic analysis)
A CNT powder sample was set in a laser micro-Raman spectrometer (model number: HR-800, manufactured by Horiba, Ltd.), and laser micro-Raman spectroscopic analysis was performed using a laser wavelength of 488 nm. A CNT is placed on a silicon substrate, and two to three drops of ethanol are dropped on it. After that, the ethanol was dried on a hot plate to adhere the CNTs onto the silicon substrate. Since the laser micro-Raman spectroscopic analysis of CNTs may vary depending on the measurement points of the CNTs, 10 points were measured and the G/D ratio and RBM were measured at each point. The G/D ratio was evaluated by averaging the I _G /I _D values at 10 points.

(Thermogravimetric analysis)
The CNT powder sample before the etching process and the CNT powder sample after the etching process were subjected to thermogravimetric analysis (TG) using a thermal analysis device (model number: TGB210, manufactured by Rigaku), and the temperature was raised at a rate of 5°C/5°C under air circulation. The weight loss rate due to carbon combustion was measured at min.

(Example 1) Purification process of TUBALL (registered trademark) single-walled carbon nanotubes 1. Etching Treatment TUBALL (registered trademark) single-walled carbon nanotubes (OCSiAl Co.) were used as samples for purification treatment in the etching step. The carbon nanotubes are 1.6±0.4 nm in diameter. In this example, 5 mg of CNTs were first 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, after the inside of the quartz glass tube was evacuated, the oxygen inside the quartz glass tube was discharged by replacing it with Ar gas for 10 minutes. Next, the inside of the quartz glass tube was heated to 200° C. in an electric furnace, and held under reduced pressure for 5 minutes to evaporate only the water inside the quartz glass tube and remove the water inside the quartz glass tube. By removing the water in the quartz glass tube, it is possible to prevent the formation of oxides of Fe due to the reaction between water and _FeCl3 . Then, replacement with Ar gas for 10 minutes was carried out twice, and the temperature was raised to 1000° C. over 15 minutes while filling with Ar at normal pressure (760 Torr). After the temperature was raised, the inside of the quartz glass tube was held at 1000° C. under normal pressure (760 Torr) and etched with FeCl ₃ for 60 minutes. After that, it was cooled to room temperature over 15 minutes under normal pressure (760 Torr), and finally, after being vacuumed, it was replaced twice with Ar gas for 10 minutes.

Table 1 shows the measurement results of the contents of C, O, Cl and Fe in the CNTs before the purification treatment by the etching process and the CNTs after the purification treatment by the etching process. 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 refining treatment by the etching process was 3.3 wt%, which was 76% lower than 13.5 wt% before the refining treatment by the etching process.

FIG. 8 is a graph showing the results of laser microscopic Raman spectroscopic analysis before the purification treatment by the etching process described above. FIG. 9 is a graph showing the results of laser micro-Raman spectroscopic analysis after the purification treatment by the vacuum heating process described above. The total arithmetic average of the values of I _G /I _D , which is the G / D ratio at 10 points, was 25.4 before refining treatment and 37.0 after refining treatment _. The /I _D value was increased by 46%, the CNT crystallinity was not decreased, and the CNTs were not damaged.

FIG. 10 is an enlarged view near 200 cm ⁻¹ in the graph of FIG. 8 . From the graph, RBM was confirmed at all 10 points, indicating that TUBALL (registered trademark) is a single-walled CNT. Moreover, it can be seen that the RBM of TUBALL (registered trademark) appears in a wide range of wavenumbers, and the diameter distribution of TUBALL (registered trademark) CNTs is large. FIG. 11 is an enlarged view near 200 cm ⁻¹ in the graph of FIG. 9 . If the CNTs are treated at a high temperature of 1600° C. or higher, the diameter of the single-walled CNTs may increase, eventually changing 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 multilayer CNTs even after the purification treatment by the etching process. Moreover, even when compared with the RBM of FIG. 10, almost no change is observed in the position of the peak, etc., so it can be seen that the diameter of the CNTs has hardly changed even after the purification treatment by the etching process.

FIG. 12 shows the results of thermogravimetric analysis (TG) of CNTs before (dashed line) the refining treatment by the etching process described above and after (solid line) the refining treatment by the etching process. The CNT had a weight reduction rate of 83.75% and a residue amount of 16.25% before the purification treatment by the etching process. The weight reduction rate of CNT after the purification treatment by the etching process was 96.84%, and the amount of residue was 3.16%. From the results of thermogravimetric analysis (TG), it can be seen that the amount of catalyst remaining in the CNTs, which causes residues, was reduced to 1/5 or less by the etching process.

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

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

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

3. Summary of Example 1 From the above, it can be concluded that the purification treatment by an etching process using _FeCl3 as an etchant can remove the catalyst metal from the CNTs of TUBALL®, resulting in the CNTs with enlarged diameter and multi-layered structure. It was confirmed that crystallinity can be improved without giving damage such as quenching. Furthermore, it was confirmed that the purification treatment by the vacuum heating process can further remove the catalyst metal and also reduce the Cl content.

(Example 2) Purification treatment of carbon nanotubes synthesized by arc discharge method1. Etching Treatment Single-walled carbon nanotubes synthesized by the arc discharge method were used as samples and subjected to purification treatment in the etching step. The carbon nanotubes are 1-2 nm in diameter. In this example, 5 mg of CNT and 100 mg of FeCl ₃ were used, and the purification treatment was performed under the same purification conditions as in Example 1 using the same purification apparatus 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 process and in the CNTs after the purification treatment by the etching process. Show the results. The content of Ni remaining in the CNT after the purification treatment by the etching process was 6.9 wt%, which was 82% lower than the 38.5 wt% before the purification treatment by the etching process.

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

2. Purification Treatment after Etching Treatment Using the CNTs after purification treatment in the etching step, purification treatment in a vacuum heating step was performed. Purification treatment was performed under the same purification treatment conditions as in Example 1 using the same purification apparatus as in Example 1.

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

3. Summary of Example 2 From the above, it can be seen that the catalyst metal can be removed from the CNTs synthesized by the arc discharge method by the purification treatment by the etching process using FeCl ₃ as an etchant and the purification process by the vacuum heating process. confirmed to be possible.

(Example 3) Purification of carbon nanotubes synthesized by chemical vapor deposition (CVD) method 1. Etching Treatment A multi-walled carbon nanotube synthesized by the CVD method was used as a sample and purified in the etching step. The carbon nanotubes are 10-30 nm in diameter with 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 performed under the same purification treatment conditions as in Example 1 using the same purification apparatus 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 process and in the CNTs after the purification treatment by the etching process. show. The content of Fe remaining in the CNT after the purification treatment by the etching process was 0.1 wt%, which was 99% lower than 7.2 wt% before the purification treatment by the etching process.

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

2. Purification Treatment after Etching Treatment Using the CNTs after purification treatment in the etching step, purification treatment in a vacuum heating step was performed. Purification treatment was performed under the same purification treatment conditions as in Example 1 using the same purification apparatus as in Example 1.

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

3. Summary of Example 3 From the above, it is possible to remove the catalyst metal from the CNTs synthesized by the CVD method by the purification treatment by the etching process using FeCl ₃ as an etchant and the purification treatment by the vacuum heating process. 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 catalytic metal-containing carbon nanotubes 1 and a halide heating means (not shown) for heating the metal halide 15. .

1 Catalyst metal-containing carbon nanotube 2 Catalyst metal 3 Carbon shell 4 CNT having hollow carbon shell
5 CNTs
6 Terminal 7 Particles in which the catalytic metal is covered with a carbon shell and adhered to the CNT 8 Particles in which the catalytic metal is covered with a carbon shell and exists apart from the CNT
10 Carbon nanotube refiner
11 reactor
12 quartz glass tube
13 Carbon Nanotube Supply Means
14 CNT container
15 metal halides
16 Etchant supply means
17 quartz plate
18 heat resistant wool
20 heating means
21 electric furnace
25 CNT with a hollow carbon shell
27 Particles having a hollow carbon shell attached to CNTs
28 Particles with a hollow carbon shell that exist apart from the CNT
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 a catalyst metal-containing carbon nanotube synthesized using a catalyst metal and a metal halide, and bringing the vapor of the metal halide into contact with the catalyst metal-containing carbon nanotube to remove the catalyst metal. A method for purifying carbon nanotubes, comprising:
the metal halide has a vapor pressure of less than 100 Pa at 25°C;
The metal halide is solid or liquid at normal temperature and pressure,
supplying the catalytic metal-containing carbon nanotubes and the metal halide into a reactor;
A method for purifying carbon nanotubes, wherein the temperature is raised in an inert gas atmosphere and the purification treatment is performed at a purification treatment temperature of 600° C. or higher . After the catalyst metal-containing carbon nanotubes and the metal halide are supplied into the reactor and before the temperature is raised, the reactor is evacuated, replaced with an inert gas, and heated to remove water. The method for purifying carbon nanotubes according to claim 1, wherein 3. The method for purifying carbon nanotubes according to claim 1 , further comprising a vacuum heating step of heating the carbon nanotubes purified by said etching step in a vacuum state. The method for purifying carbon nanotubes according to any one of claims 1 to 3 , 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 4 , wherein the metal halide is selected from the group consisting of fluorides, chlorides, bromides or iodides, and mixtures thereof. The method for purifying carbon nanotubes according to any one of claims 1 to 5, 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. a reactor;
Carbon nanotube supply means for supplying catalyst metal-containing carbon nanotubes synthesized using a catalyst metal into the reactor;
an etchant supply means for supplying a metal halide into the reactor;
Heating means for heating the inside of the reactor to raise the temperature of the catalyst metal-containing carbon nanotube and the metal halide,
An apparatus for purifying carbon nanotubes, wherein the heated catalytic metal-containing carbon nanotubes and vapor of the metal halide are contacted in the reactor to remove the catalytic metal,
the metal halide has a vapor pressure of less than 100 Pa at 25°C;
The metal halide is solid or liquid at normal temperature and pressure,
supplying the catalyst metal-containing carbon nanotubes and the metal halide into the reactor by the carbon nanotube supply means and the etchant supply means;
An apparatus for purifying carbon nanotubes, wherein the temperature is raised in an inert gas atmosphere by the heating means and the purification treatment is performed at a purification treatment temperature of 600° C. or higher. After the catalyst metal-containing carbon nanotubes and the metal halide are supplied into the reactor and before the temperature is raised, the inside of the reactor is evacuated, replaced with an inert gas, and heated by the heating means. 8. The apparatus for purifying carbon nanotubes according to claim 7, wherein the water is removed by 9. The purification of carbon nanotubes according to claim 7 or 8, further comprising vacuum heating means for heating the carbon nanotubes purified by contacting the heated catalyst metal-containing carbon nanotubes and the vapor of the metal halide in a vacuum state. Device.

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