JP2000072422A - Method for refining carbon nano tube and apparatus therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method efficiently sorting and recovering carbon nano tubes(CNTs) from a carbon material mixture obtd. by an arc discharge method, etc., and an apparatus therefor. SOLUTION: A DC electrophoresis refining apparatus 26 consists of a main body vessel 6 which is filled with a migration liquid and induces electrophoresis, electrodes which are arranged on the opposite surfaces of this vessel 6, a DC power source 8 which impresses DC to one of these electrodes to an anode 10 and the other to a cathode 12, a dispersion migration liquid supplying means 30 which supplies the dispersion migration liquid dispersed with the carbon material mixture into the main body vessel 6 and fluidizes the dispersion migration liquid in one direction between the electrodes and a recovering means 38 which is disposed in the position where the carbon nano tubes gather in the outlet side of the dispersion migration liquid. The apparatus is so constituted that the carbon material mixture contg. the carbon nano tubes(CNTs) are separated and coordinated by every kind in the inter-electrode direction by the electrophoresis and that the carbon nano tubes are sorted and recovered by the recovering means.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for purifying carbon nanotubes, and more particularly, to a method for selectively separating and recovering carbon nanotubes by electrophoresis from a carbon material mixture containing carbon nanotubes obtained by arc discharge or the like. The present invention relates to a purification method and an apparatus therefor.

[0002]

2. Description of the Related Art Diamond, graphite and amorphous carbon are known as stable allotropes of carbon, and their structures have been almost determined by X-ray diffraction analysis or the like. However, in the steam cooling product obtained by irradiating graphite with a high-energy laser in 1985, the discovery of fullerene carbon atoms arranged in like a soccer ball, was to be written in C _60. Furthermore, in 1991, carbon nanotubes in which carbon atoms were arranged in a cylindrical shape were found in cathode deposits generated by DC arc discharge.

FIG. 11 is a block diagram of a DC arc discharge method, in which two carbon rods 5 having different diameters are provided at the center of a chamber 52.
4 and 56 are horizontally opposed. A carbon rod 54 having a diameter of 6.5 mm is used as an anode by a DC power
A 1 mm carbon rod 56 is used as a cathode. Helium gas is introduced into the chamber 52 in the direction of arrow a, exhausted by an oil rotary pump in the direction of arrow b, and adjusted so that the gas pressure becomes constant at 200 Torr while being measured by the pressure gauge 60. The cathode carbon rod 56 is finely moved in the direction of arrow c by the stepping motor 62, and the distance between the electrodes is finely adjusted by the ammeter 64 until the discharge current becomes constant. As an example, when the DC voltage is 26 V and the current is 70 A, an arc discharge starts between the carbon rods 54 and 56, and carbon atoms are released from the anode carbon rod 54 and deposited on the opposite surface of the cathode carbon rod 56, and the anode is discharged. Gradually wears out.

FIG. 12 shows a cathode carbon rod 56 of an arc plasma.
It is a schematic diagram of the vicinity. Region III is an arc plasma region in which carbon ions i and electrons e coexist in a plasma state to form a positive column. The region II is called a pre-sheath region, in which the neutral carbon atoms n dissociate into ions i and electrons e due to the collision of thermoelectrons e jumping out of the cathode, and has a thickness of mean free path. The region I is called a sheath region, and carbon ions i surround the vicinity of the cathode with a thickness of the Debye distance, and are deposited on the cathode while being neutralized. Therefore, the anode gradually wears out and deposits grow on the cathode.

FIG. 13 shows an anode carbon rod 54 and a cathode carbon rod 56.
FIG. The tip surface of the anode carbon rod 54 is roughened because it is consumed by the discharge, while a deposit 66 is growing on the tip of the cathode carbon rod 56. This deposit 66 is concentrically separated into two layers. The peripheral deposit 68 is made of hard glassy graphite having a gray metallic luster, and the central deposit 70 is a brittle black substance, which contains carbon nanotubes (CNT). A carbon material such as carbon nanoparticles (CP) is included in addition to the carbon nanotube, and the constituent material of the central portion 70 is called a carbon material mixture.

A carbon nanotube (CNT) is a cylindrical substance having a quasi-one-dimensional structure with a diameter of several nm to several tens of nm and a length of several μm, as shown in FIG. 14 from a transmission electron microscope photograph. It turns out that it has various shapes. (A) is a polyhedral closed end, (b) is open, (c) is a conical closed end,
In (d), the tip is closed in a beak shape. It is also known that there is a semi-doughnut type. Due to such a shape, the rigidity in the central axis direction and the radial direction is high, and it is extremely chemically and thermally stable like other carbon allotropes.

It has been found that the atomic arrangement of carbon nanotubes is a cylinder having a helical structure in which a graphite sheet is displaced and rounded. It can be seen that in order to close the end face of the CNT cylinder, six 5-membered rings should be inserted. The various shapes of the tip as shown in FIG. 14 indicate that the arrangement of the five-membered ring is various. FIG. 15 shows an example of the tip structure of the carbon nanotube,
By disposing the six-membered ring around the five-membered ring, it changes from a flat surface to a curved surface, and the structure has a closed end. The circles are carbon atoms, the solid line part corresponds to the front side, and the dotted line part corresponds to the back side. Since there are various types of arrangements of the five-membered ring, diversity of the tip structure appears.

[0008]

Since carbon nanotubes have a quasi-one-dimensional structure as described above, they have high rigidity and extremely good electronic characteristics. An idea of utilizing the carbon nanotubes as a probe of a scanning tunneling microscope (STM) utilizing the rigidity and electronic characteristics, an idea of utilizing the carbon nanotubes as an electron emitter, and the like have been proposed. However, it is currently extremely difficult to make a carbon nanotube alone without being mixed with other carbon allotropes. Even in the DC arc discharge method, carbon nanotubes are mixed with other carbon materials such as carbon nanoparticles (CP). Always. Since carbon nanotubes are insoluble in a solvent and do not evaporate, it is extremely difficult to select and handle the carbon nanotubes. Therefore, it is required to quickly establish a method for selectively separating carbon nanotubes from these carbon substance mixtures, that is, a method for purifying carbon nanotubes.

[0009]

Means for Solving the Problems The present invention has been made to achieve the above object, and a method of purifying carbon nanotubes according to the present invention comprises dispersing a carbon material mixture containing carbon nanotubes in an electrophoresis liquid. A first step of forming the dispersed electrophoresis liquid, a second step of supplying the dispersed electrophoresis liquid and flowing the dispersed electrophoresis liquid between the electrodes to which a voltage is applied, and electrophoresis of the carbon material in the direction between the electrodes during the flow. It is characterized in that it comprises a third step of electrically separating and coordinating the carbon nanotubes from other carbon substances, and a fourth step of selectively collecting the carbon nanotubes from the position where the carbon nanotubes are concentrated.

As the voltage, a DC voltage and an AC voltage can be used. Particularly, when an AC voltage is applied, the electrodes are arranged so as to form a non-uniform electric field between the electrodes. Further, when supplying the dispersed electrophoresis liquid, it is also possible to simultaneously supply a pure electrophoresis liquid to which the carbon substance mixture is not added.

Specific DC electrophoresis purification devices include:
A main body container for generating electrophoresis filled with an electrophoresis solution, electrodes arranged on opposing surfaces of the main body container, a DC power supply for applying one of the electrodes to the anode and the other to the cathode, and also inside the main body container. Dispersion electrophoresis liquid supply means for supplying a dispersion electrophoresis liquid in which a carbon material mixture is dispersed and causing the dispersion electrophoresis liquid to flow in one direction between the electrodes, and a position where the carbon nanotubes are concentrated on the exit side of the dispersion electrophoresis liquid are provided. And collection means.

As the AC / DC electrophoretic purification apparatus, there are provided a cylindrical main body container for generating electrophoresis filled with an electrophoresis solution, a central axis electrode provided at a central axis position of the cylindrical main body vessel, and a central axis electrode. And a power supply for applying a DC voltage or an AC voltage to the central axis electrode and the cylindrical electrode, and a dispersed electrophoresis liquid in which a carbon material mixture is dispersed in the cylindrical main body container. And a collection means provided at a position where the carbon nanotubes are concentrated on the outlet side of the dispersed electrophoresis liquid.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have conducted intensive studies on a method for purifying carbon nanotubes from a carbon material mixture obtained by an arc discharge method or the like, and as a result, have found that carbon nanotubes and carbon nanoparticles can be separated by electrophoresis. The present invention has been made based on this finding.

The carbon material mixture used as a raw material for purification in the present invention is, for example, a black center deposit among cathode deposits produced by an arc discharge method. It has been confirmed by a scanning electron microscope that carbon nanotubes (CNT) and carbon nanoparticles (CP) are mixed in the central deposit. The arc discharge method is an extremely versatile method used when performing carbon deposition with a normal vacuum apparatus, and is suitable for mass production of a carbon material mixture containing carbon nanotubes. Moreover, these carbon substance mixtures are unnecessary substances which have been conventionally discarded, and the significance of the present invention in which CNTs are selectively recovered using the unnecessary substances as raw materials can be understood.

By improving the arc discharge method and mixing a catalytic metal into the anode, a single-walled carbon nanotube can be obtained. In addition to the arc discharge method, carbon nanotubes can be synthesized by a CVD method using fine particles of catalytic metal such as nickel or cobalt as a base material. Furthermore, it has been found that single-walled carbon nanotubes can be synthesized by irradiating high-power laser light to graphite mixed with a catalyst metal at a high temperature. In the present invention, a carbon material mixture containing these carbon nanotubes can be used as a raw material for purification as in the case of the arc discharge method.

According to the study by the inventors, the following three conditions are important for increasing the density of carbon nanotubes in the central sediment. The first condition is to increase the pressure of the gas (for example, helium gas) in the chamber, so that the number density and the diameter of the carbon nanotubes increase. At 150 Torr, CP exists at a high density, but at 200 Torr, the CNT density increases,
Its length also increases. At 300 Torr, the CNT density sharply increases, and the diameter increases and the cylinder becomes thicker. The second condition is that the arc discharge is stable and the temperature of the cathode carbon rod is kept low. For this purpose, the cathode carbon rod may be cooled by water cooling or the like. The third condition is to reduce the discharge current density. It has been found that when the current density is increased, the amount of the graphite-like carbon and CP increases, and the length of the generated CNTs is reduced to less than 1 μm and further reduced.

The carbon material mixture having a high CNT density obtained as described above was collected and used as a raw material to be purified. The carbon material mixture was ultrasonically dispersed in order to finely disperse it in the solvent, and then centrifuged to take out only the supernatant. The carbon material that has become larger due to the fusion of the CNTs and CPs can be removed by this centrifugation, and it can be considered that the CNTs and CPs are present alone in the supernatant. By finely dispersing in this manner, a single CNT can be efficiently recovered.

As the solvent, any substance can be used as long as it can disperse a carbon substance mixture and the carbon substance mixture electrophoreses in the liquid. That is, the solvent is not only a dispersion liquid but also an electrophoresis liquid. As the solvent, an aqueous solvent, an organic solvent or a mixed solvent thereof can be used, and for example, known solvents such as water, acidic solution, alkaline solution, alcohol, ether, petroleum ether, benzene, ethyl acetate, chloroform and the like can be used. More specifically, general-purpose organic solvents such as isopropyl alcohol (IPA), ethyl alcohol, acetone, and toluene can be used. As an example, in the case of IPA, a carboxyl group is considered as an ion species for electrophoresis. As described above, the solvent may be selected in consideration of the electrophoretic performance and dispersion performance of the carbon material mixture, dispersion stability and safety, and the like.

First, in order to evaluate the DC electrophoresis performance, a test was performed using the DC electrophoresis apparatus 2 shown in FIG.
After ultrasonically dispersing the carbon material mixture in isopropyl alcohol, the mixture is centrifuged, and the supernatant is used as dispersion electrophoresis liquid 4. The container 6 is filled with the dispersing electrophoresis liquid 4 and electrodes are arranged on a pair of opposing surfaces. DC power supply 8 applies one to anode 10 and the other to cathode 12. In this experiment, the electric field (electric field strength) was 2250 V / cm. The dispersed electrophoresis liquid 4 contains countless carbon nanotubes (CNTs) and carbon nanoparticles (CPs) which are invisible to the naked eye but are extremely small. In this device, a uniform electric field is formed between the two electrodes. However, even if a non-uniform electric field is formed, the device can be used as a DC electrophoresis device. This is because electrophoresis is possible in a non-uniform electric field only when the migration speed is not constant.

FIG. 2 is a sketch of a scanning electron micrograph of a state in which CNT and CP have been electrophoresed. CNT and CP
It can be seen that electrophoresis is biased toward the cathode 12. Also, a branch-like continuation is seen from the cathode 12 toward the anode 10.
It can be understood that this branch-like series is such that the CNTs are continuous with each other in the vertical direction, and are oriented parallel to the electric field direction d. This orientation is a phenomenon that occurs when a rod-shaped object moves in a fixed direction in a stationary solvent because it takes the direction with the least resistance. Thus, since CNT and CP exhibited the electrophoresis phenomenon, it is understood that these particles are dispersed in IPA as colloid particles.

Since the CNTs and the CP showed migration toward the cathode side, it is considered that electric charges as shown in FIG. 3 are distributed at the interface between the colloidal particles. Colloid particles 14
Has a positive charge, so its surface potential is Ψ. It is. The positive charges attract negative charges in the solvent, and the boundary surface h is called a Stern plane (thickness: δ). However, the ions outside the positive ions also approach the colloid particles due to the effect of thermal motion. Usually, when the colloid particles move in the solvent, the solvent boundary surface f that moves integrally with the colloid particles is called a shift surface. The sum of the charges inside the shift surface f becomes the effective charge of the colloid particles that are sensitive to electrophoresis. The potential of this shift surface f is called ζ (zeta) potential,
It is a constant determined by the surface state of the colloid particles and the properties of the solvent. The length of the positive charge of the colloid particles 14 shielded by the charge of the solvent is referred to as the Debye distance λ, and is represented by the shielding surface g. Outside the shielding surface g (r> δ +
λ) is a region in which thermal motion is dominant and positive and negative ions have a Boltzmann distribution.

From the observation of DC electrophoresis of CNT and CP,
It was found that the electrophoretic mobility of CNT was larger than that of CP. That is, the CNT reaches the cathode earlier than the CP. In general, it is known that the electrophoretic velocity V is proportional to the electric field strength E.
Is given by V / E. In other words, since it means the speed increment per unit electric field, if the μ values of CNT and CP are different,
As time elapses, the CNT and the CP separate from each other in the direction of the electric field.

When the CNT and the CP are separated between the electrodes, it becomes possible to selectively collect both. Although CNT and CP cannot be observed with the naked eye, since both exist at different positions between the positive and negative electrodes, if the electrophoresis liquid is caused to flow in a direction orthogonal to the electrophoresis direction, for example, in the direction of gravity, the colloid particles will be in the direction of gravity. Migrate between the electrodes while flowing through. When the electrophoresis liquid is collected at a plurality of positions between the electrodes when the colloid particles reach the lower surface of the electrodes, colloid particles having a specific shape concentrated at each position can be selectively collected. The flow direction may be orthogonal to the electrophoresis direction, and need not be the direction of gravity. When the electrophoresis running liquid is not allowed to flow, as shown in FIG.
Since both NT and CP reach the cathode in a mixed state, it becomes difficult to separate and collect CNT and CP. However, when fluidized, CNT and CP can be separated and recovered. Although CNT and CP are slightly mixed in the first-stage separation and recovery, CNTs can be selectively recovered with high purity by repeating the second and third stages.

The difference in electrophoretic mobility obtained from the experiment was examined theoretically. Assuming that the spherical and rod-shaped particles have the same 粒子 potential, we solved Henry's electrophoresis equation. When certain conditions are satisfied, the electrophoretic mobility μ becomes 1.
It was found that the difference was about five times. The condition is
The rod-shaped particles are oriented parallel to the electric field, and the value of the κa product of the spherical particles is 10 or less. κ is the reciprocal of the Debye length λ, and a is the radius of the spherical particle. The radius of the carbon nanoparticles is 10 to 100 nm, and κ is 1/200 nm
Therefore, it can be seen that κa <10 is sufficiently satisfied. Thus, both CNT and CP experimentally and theoretically
It was proved that there was a difference in the electrophoretic mobilities of the two, and the two could be separated.

Next, in order to evaluate the AC electrophoresis performance, a test was performed using the AC electrophoresis apparatus 16 shown in FIG. After ultrasonically dispersing the carbon material mixture in isopropyl alcohol, the mixture is centrifuged, and the supernatant is used as dispersion electrophoresis liquid 4. The dispersion electrophoresis liquid 4 is filled in the cylindrical main body container 18. A cylindrical electrode 20 is provided on the outer or inner circumference of the container 18, and a central axis electrode 22 is disposed at a central axis position. The cylindrical main body container 18 itself may be used as a cylindrical electrode. An AC power supply 24 is provided to apply an AC voltage to the cylindrical electrode 20 and the center axis electrode 22.

The reason why the apparatus 16 is composed of the cylindrical electrode 20 and the central axis electrode 22 is to form a non-uniform electric field between the two electrodes. Due to the application of the AC voltage, the lines of electric force flow radially from the central axis electrode 22 toward the circumference of the cylindrical electrode 20, and the density of electric lines of force (electric field) gradually decreases as the distance from the center increases. That is, the electrodes may be arranged so that the interval between the lines of electric force is not uniform between the two electrodes, and is not limited to the central axis electrode and the cylindrical electrode. This device with an inhomogeneous electric field is configured for AC power supply, but when a DC power supply is connected, colloidal particles can migrate to the cathode side even in an inhomogeneous electric field and can be used as a DC electrophoresis device. it can.

An electric field of about 2250 V /
cm and the frequency is 100Hz and 10MHz,
Applied between both electrodes. The sketch of the electrophoresis at each frequency is shown in FIG. The direction of the arrow i is the direction of the electric field. The upper part of the figure shows the vicinity of the electrodes 20 and 22, and the lower part shows the intermediate position between the two electrodes. At 100 Hz, colloid particles are concentrated near the electrode, and almost no colloid particles are found at the intermediate position. Moreover, CNT and C near the electrode
P coexists and it is difficult to separate them. On the other hand, 10MH
At z, it was found that CNT concentrated near the electrode and CP concentrated at the intermediate position. This result means that CNT and CP can be separated by using a high frequency.

The frequency dependence of electrophoresis was examined in detail. FIG. 6 shows the frequency dependence of the ratio of CNT to all particles near the electrode. The value of CNT / (CNT + CP) increases when the frequency exceeds 10 kHz,
It reaches up to 30% around MHz. Therefore, it means that the separation of the CNT and the CP becomes extremely easy if a high frequency is applied.

Further, the deviation angle (orientation angle) of the CNT from the electric field direction i was examined. FIG. 7 shows the frequency dependence of the standard deviation of 1200 CNTs, with the average value of the orientation angles being 0 degrees. When the frequency exceeds 10 kHz, the standard deviation rapidly decreases, and at 5 to 10 MHz, the standard deviation drops to about 16 degrees. The parallelism in the direction of the electric field becomes extremely high. FIG. 8 is a semilogarithmic graph showing the dependence of the standard deviation of the orientation angle on the CNT length ignoring the frequency. It shows that the standard deviation of the orientation angle decreases exponentially as the length of the CNT increases. That is, it means that the longer the length of the CNT, the more the CNT is oriented in the electric field direction.

The reason for the above frequency dependence will be considered. In the electrophoretic phenomenon, it is necessary to consider the behavior of the charge induced in the colloid particles and the whole of the adsorbed ion vesicles surrounding the charge. In the low-frequency region, the electric field shifts the adsorbed ion vesicles relative to the colloid particles, causing polarization to form dipoles. The dipole moves in response to the inhomogeneous electric field. These movements are toward the electrode closer to the particle. Assuming that the carboxyl group in isopropyl alcohol is an ion, its mobility can be estimated to be about 10 ⁻⁴ to 10 ⁻⁵ cm ² / Vs, and the frequency at which the movement of the ion can follow is 1 kHz.
It is about. In the high frequency region beyond this, the displacement of the adsorbed ion vesicles can be ignored, only the polarization inside the colloid particles is induced, and the dipole feels a non-uniform electric field and electrophoreses. In other words, the effect of the difference in the shape of the colloidal particles is small at low frequencies due to the displacement of the adsorbed ion vesicles,
At high frequencies, the difference in shape has a direct effect. It is considered that the critical value is about 10 kHz.

In summary, the carbon nanotube (CNT) migrates near the electrode and is oriented parallel to the electric field. The higher the frequency of the electric field and the longer the length of the CNT, the better the degree of orientation in the direction of the electric field. The CNT abundance in the vicinity of the electrode increases as the frequency increases. In particular, CNTs and CPs migrate due to a non-uniform electric field, and have a property of moving toward a closer electrode as viewed from the colloid particles.

In the apparatus shown in FIG. 4, it is difficult to selectively recover CNTs since the disperse electrophoresis liquid is not allowed to flow.
In order to recover this, it is necessary to flow the dispersed electrophoresis liquid between the two electrodes, as in the case of DC electrophoresis. If CNTs and CPs are electrically separated during this flow, and if a collection vessel is arranged at the concentration position of each particle near the end of the electrode, CN
T and CP can be selectively and continuously collected in the container. Also, continuously supply the dispersed electrophoresis liquid from one end,
If the sorting and collecting are continuously performed from the other end, the sorting and collecting of CNTs can be industrially mass-produced.

[0033]

Embodiment 1 <DC Electrophoresis Purification Apparatus> FIG. 9 is a simplified perspective view of a DC electrophoresis purification apparatus 26, and the same parts as those in FIG. Electrodes are attached to a pair of opposing surfaces of the main container 6 filled with the electrophoresis running solution, and one is set to the anode 10 and the other is set to the cathode 12 by the DC power supply 8. An injector 28 is provided on the upper part of the main body container 6, and the dispersed electrophoresis liquid supply means 30 and the pure electrophoresis liquid supply means 32 are connected to the injector 28.
From the dispersing electrophoresis liquid supply means 30, the dispersing electrophoresis liquid in which the carbon substance mixture is dispersed in the direction of arrow j is injected into the dispersion injection chamber 34, and then supplied into the container 6. From the pure electrophoresis liquid supply means 32, a pure electrophoresis liquid is supplied to the container 6 through the pure injection chamber 36 in the direction of arrow k.

A collecting means 38 for carbon nanotubes is provided below the main body container 6, and the collecting means 38 is composed of a plurality of suction chambers 38a and a collecting container 38b arranged in parallel in a direction between electrodes (electrophoresis direction). . The dispersed electrophoresis liquid is supplied to the center of the container 6, and flows downward while being mixed with the pure electrophoresis liquid supplied at the same time. The pure electrophoresis liquid is supplied for adjusting the concentration and the flow rate of the colloid particles. But,
When concentration adjustment and flow rate adjustment can be performed only with the dispersed electrophoresis liquid, the pure electrophoresis liquid may not be supplied. Electrode 10 during flow
-Electrophoresis between 12 and CNT move between electrodes while separating from CP. Before the CNT reaches the cathode 12,
The CNT reaches the lower end of the container 6, and is collected in the collection container 38b via the suction chamber 38a at that position. Therefore, CNTs having substantially the same shape are collected in the same collection container 38b, and sorting and collection can be performed according to the length of the CNTs. When CPs are mixed in the CNTs, the recovered disperse electrophoresis liquid is further supplied as a raw material, and the second-stage purification is performed. If necessary, the purification purity can be increased in more stages.

Example 2 [Dual-Purpose Electrophoretic Purification Apparatus] FIG. 10 is a simplified perspective view of a bi-directional electrophoresis purification apparatus 40, and the same parts as those in FIGS. A cylindrical electrode 20 is provided on the outer periphery of the cylindrical main body container 18 filled with the electrophoresis liquid, and a central axis electrode 22 is provided at a central axis position. The center axis electrode 22 is grounded, and an AC power supply 24 is connected to the cylindrical electrode 20. Therefore, an AC voltage is applied between the electrodes 20 and 22. Dispersion electrophoresis liquid supply means 3
0 and the pure electrophoresis liquid supply means 32 are connected. A dispersed electrophoresis liquid in which a carbon material mixture is dispersed in the direction of arrow m is supplied to the container 18 from the dispersed electrophoresis liquid supply means 30, and a pure electrophoresis liquid is supplied to the container 18 in the direction of arrow n from the pure electrophoresis liquid supply means 32. Is done. The reason for supplying the pure electrophoresis running solution is the same as in Example 1, and the description thereof is omitted.

At the lower part of the container 18, a carbon nanotube collecting means 42 is arranged. The collecting means 42 includes a peripheral collecting means 44 and a valve 4 arranged at a peripheral position.
4a, a center collecting means 46 and a valve 46a arranged at the center position. Dispersion electrophoresis solution is in container 1
8 and simultaneously flows downward while being mixed with the pure electrophoresis liquid supplied to the center. Electrophoresis occurs between the electrodes 20 and 22 during the flow, and the CNT concentrates near the electrodes due to the high frequency voltage, and the CP concentrates in an intermediate portion between the electrodes. Therefore, the CNT and the CP are separated and the container 18
Reaches the lower end of the CNT, and the CNTs are collected around and around the center 4
According to 4, 46, it is sorted and collected in the direction of arrow p.

The recovery flow rate is equal to the inflow flow rate of the dispersed electrophoresis liquid and the pure electrophoresis liquid, and the recovery efficiency can be appropriately changed by adjusting the flow rate. Since the recovered CNTs also contain some CP, if the recovered electrophoresis liquid is introduced as a dispersed electrophoresis liquid into the second-stage sorting apparatus, the CNT isolation efficiency can be increased. Of course, it is possible to freely increase the number of stages. Since the obtained CNTs are dispersed in the electrophoresis running solution, the CNTs can be taken out of the CNTs by concentrating them with a high-speed centrifugal separator or drying them out by evaporating the solvent.

Although the second embodiment uses an AC power supply, a DC power supply may be used. An inhomogeneous electric field is formed between the center axis electrode 22 and the cylindrical electrode 20 at the center and weak at the periphery. In the case of an AC voltage, the dipole of the colloidal particles is moved to the closer electrode by the non-uniform electric field. In the case of a DC power supply, the situation of the non-uniform electric field does not change, but in the case of the DC power supply, the colloid particles are concentrated on the cathode, and the CNT electrophoreses on the cathode.

The present invention is not limited to the above-described embodiment, but includes various modifications and changes within the scope of the present invention without departing from the technical concept of the present invention. It is.

[0040]

According to the present invention, as described in detail above, carbon nanotubes can be easily selected from a carbon substance mixture by electrophoresis. Carbon material mixtures containing carbon nanotubes are produced in large quantities every day by an arc discharge method or the like, and these carbon material mixtures have been discarded as unnecessary materials. The present invention separates and collects carbon nanotubes, which can be used for a tip of a scanning tunneling microscope (STM), an electron emitter element, and the like, from a carbon material mixture, which is a waste material. Nanotubes can be mass-produced. Accordingly, an inexpensive and highly efficient industrially useful method for purifying carbon nanotubes and an apparatus therefor have been realized.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a DC electrophoresis apparatus.

FIG. 2 is a sketch of a scanning electron micrograph of a state in which carbon nanotubes and carbon nanoparticles have been electrophoresed.

FIG. 3 shows a charge distribution diagram and a potential distribution diagram at an interface of colloid particles.

FIG. 4 is a schematic configuration diagram of an AC electrophoresis apparatus.

FIG. 5 is a sketch of a scanning electron micrograph of a state in which carbon nanotubes and carbon nanoparticles have been electrophoresed at two types of AC frequencies.

FIG. 6 is a characteristic diagram showing the frequency dependence of the ratio of carbon nanotubes to all particles near an electrode.

FIG. 7 is a characteristic diagram showing the frequency dependence of the standard deviation of the orientation angle of carbon nanotubes.

FIG. 8 is a semilogarithmic graph showing the dependence of the standard deviation of the orientation angle of the carbon nanotube on the length of the carbon nanotube.

FIG. 9 is a simplified perspective view of a DC electrophoresis purification device.

FIG. 10 is a simplified perspective view of an AC / DC electrophoretic purification device.

FIG. 11 is a configuration diagram of a DC arc discharge method.

FIG. 12 is a schematic diagram showing the vicinity of a cathode carbon rod of arc plasma.

FIG. 13 is an enlarged view of an anode carbon rod and a cathode carbon rod.

FIG. 14 is a schematic view of various tip shapes of a carbon nanotube.

FIG. 15 is an example of an atomic arrangement of a carbon nanotube, showing an arrangement of a five-membered ring and a six-membered ring.

[Explanation of symbols]

 2 DC electrophoresis apparatus 4 Dispersion electrophoresis liquid 6 Main container 8 DC power supply 10 Anode 12 Cathode 14 Colloid particles 16 AC electrophoresis apparatus 18 Cylindrical main body container 20 Cylindrical electrode 22 Center axis electrode 24 AC power supply 26 DC electrophoresis purification apparatus 28 Injector 30 Dispersion electrophoresis liquid supply means 32 Pure electrophoresis liquid supply means 34 Dispersion injection chamber 36 Pure injection chamber 38 Recovery means 38a Suction chamber 38b Recovery container 40 AC / DC electrophoresis purification device 42 Recovery means 44 Peripheral recovery means 44a Valve 46 Central recovery Means 46a Valve 52 Chamber 54 Anode carbon rod 56 Cathode carbon rod 58 DC power supply 60 Pressure gauge 62 Stepping motor 64 Ammeter 66 Deposit 68 Peripheral deposit 70 Central deposit

Claims (6)

[Claims] 1. A first step of dispersing a carbon material mixture containing carbon nanotubes in an electrophoretic liquid to form a disperse electrophoretic liquid, and supplying the disperse electrophoretic liquid and applying the disperse electrophoretic liquid between electrodes to which a voltage is applied. A second step of flowing, a third step in which the carbon material is electrophoresed in the direction between the electrodes during the flow to electrically separate and coordinate the carbon nanotubes with other carbon materials, and a carbon step from the position where the carbon nanotubes are concentrated. A method for purifying carbon nanotubes, comprising a fourth step of sorting and recovering nanotubes. 2. The purification method according to claim 1, wherein a DC voltage is applied between the electrodes, and the carbon material is separated and coordinated for each type by utilizing a difference in electrophoretic mobility between the carbon nanotube and another carbon material. Method. 3. The method according to claim 1, wherein the electrodes are arranged so as to form a non-uniform electric field between the electrodes, and an AC voltage or a DC voltage is applied between the two electrodes to separate and coordinate the carbon material for each type. Purification method. 4. The purification method according to claim 1, wherein a pure electrophoresis liquid to which no carbon substance mixture is added is supplied simultaneously when supplying the dispersed electrophoresis liquid. 5. A main body container for generating electrophoresis filled with an electrophoresis running solution, electrodes arranged on opposite surfaces of the main body container, a DC power supply for applying one of the electrodes to an anode and the other to a cathode, Also, a dispersing electrophoresis liquid supply means for flowing the dispersing electrophoresis liquid in one direction between the electrodes while supplying the dispersing electrophoresis liquid in which the carbon substance mixture is dispersed in the main body container, and the carbon nanotubes are concentrated at the outlet side of the disperse electrophoresis liquid. A collecting means provided at a position, wherein a carbon material mixture containing carbon nanotubes is separated and coordinated for each type in a direction between electrodes by electrophoresis, and the carbon nanotubes are selectively collected by the collecting means. Nanotube purification equipment. 6. A cylindrical main body container for generating electrophoresis filled with an electrophoresis running solution, a central axis electrode provided at a central axis position of the cylindrical main body container, and arranged so as to surround the central axis electrode. A cylindrical electrode, a power supply for applying an AC voltage or a DC voltage to the central axis electrode and the cylindrical electrode, and a dispersing electrophoresis liquid in which a carbon material mixture is dispersed in a cylindrical main body container are supplied to perform dispersive migration between the electrodes. A dispersing electrophoresis liquid supply means for flowing the liquid in the axial direction; and a recovery means provided at a position where the carbon nanotubes are concentrated on the outlet side of the dispersing electrophoresis liquid. A carbon nanotube refining apparatus characterized in that carbon nanotubes are separated and coordinated for each type in a direction, and carbon nanotubes are selectively collected by a collecting means.