Continuous preparation method and continuous preparation device of few-walled carbon nanotubes

Abstract

The application discloses a continuous preparation method and a continuous preparation device of few-walled carbon nanotubes. The continuous preparation method comprises the following steps: contacting first carbon nanotubes with an etchant, and forming a continuous reaction bed moving along a specified direction; applying a first transient current to a first selected segment of the continuous reaction bed to generate a first transient high temperature, and at least the outermost layer of the wall of the first carbon nanotubes is etched and removed by the etchant, so that the second carbon nanotubes with fewer walls are continuously obtained. The continuous preparation method and the device of the few-walled carbon nanotubes provided by the application can make the carbon nanotubes form a continuous reaction bed, and apply a transient current to the selected segment in the continuous reaction bed. The outer layer of the wall of the carbon nanotubes is etched and removed to obtain the carbon nanotube product with fewer walls. The few-walled carbon nanotubes are obtained by using the relatively cheap multi-walled carbon nanotubes, and sufficient and cheap carbon nanotube materials can be provided for the development of the related application field.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of inorganic carbon material preparation, and particularly relates to a continuous preparation method and a continuous preparation device of few-wall carbon nanotubes. BACKGROUND

[0002] Carbon nanotubes, also known as Buckminsterfullerene tubes, are one-dimensional nanomaterials with special structures (the radial dimension is nanometer level, the axial dimension is micrometer level, and the two ends of the tube are basically sealed). Carbon nanotubes are mainly composed of carbon atoms arranged in a hexagonal shape, forming a coaxial circular tube with several to dozens of layers, or directly forming a single-layer circular tube.

[0003] As one-dimensional nanomaterials, carbon nanotubes are light in weight, have perfect hexagonal structure connection, and have excellent mechanical, electrical and chemical properties. In recent years, with the deepening of research on carbon nanotubes and nanomaterials, the broad application prospects have been constantly revealed.

[0004] According to the number of walls, carbon nanotubes can be divided into single-wall carbon nanotubes, double-wall carbon nanotubes or multi-wall carbon nanotubes. Among them, the performance of single-wall carbon nanotubes, such as mechanical properties and electrical conductivity, is usually higher than that of carbon nanotubes with more walls, so single-wall carbon nanotubes have extremely broad application market in batteries, field emission displays, high-strength fibers and composite reinforcing materials.

[0005] At present, the main preparation methods of single-wall carbon nanotubes mainly include arc method, laser evaporation method and chemical vapor deposition method. These three preparation methods have one or two short boards in terms of purity, yield and cost, and cannot realize low-cost mass industrialization of high-purity single-wall carbon nanotubes. Therefore, the market vacancy of single-wall carbon nanotubes is extremely large, and the price can reach 1000 million / ton, which is 50 times the price of multi-wall carbon nanotubes. Not only limited to single-wall carbon nanotubes, in general, the lower the wall number of carbon nanotube products, the greater the use value.

[0006] Therefore, developing a batch and continuous single-wall carbon nanotube preparation method plays a crucial role in the application and development of single-wall carbon nanotubes, and not only limited to obtaining single-wall carbon nanotubes, but also continuous batch preparation of carbon nanotubes with fewer walls is also of great significance. SUMMARY

[0007] In view of the deficiencies of the prior art, the purpose of the present application is to provide a continuous preparation method and a continuous preparation device of few-wall carbon nanotubes.

[0008] To achieve the foregoing purposes of the application, the technical solutions adopted by the present application include:

[0009] In a first aspect, the present application provides a continuous preparation method of few-walled carbon nanotubes, comprising:

[0010] contacting first carbon nanotubes with wall number ≥2 with an etchant, and forming a continuous reaction bed moving in a specified direction;

[0011] contacting a first electrode group with the continuous reaction bed in motion, and applying a first transient electric current to a first selected segment of the continuous reaction bed, so that the first selected segment generates a first transient high temperature, under the action of which at least the outermost wall of the first carbon nanotubes is etched and removed by the etchant, thereby continuously obtaining second carbon nanotubes with fewer walls than the first carbon nanotubes.

[0012] In a second aspect, the present application also provides a continuous preparation device of few-walled carbon nanotubes, comprising:

[0013] a continuous motion module for contacting first carbon nanotubes with wall number ≥2 with an etchant, and forming a continuous reaction bed moving in a specified direction;

[0014] a current application module comprising a first electrode group, which can be in motion with the continuous reaction bed, and apply a first transient electric current to a first selected segment of the continuous reaction bed, so that the first selected segment generates a first transient high temperature, under the action of which at least the outermost wall of the carbon nanotubes is etched and removed by the etchant, thereby continuously obtaining second carbon nanotubes with fewer walls than the first carbon nanotubes.

[0015] Based on the above technical solutions, compared with the prior art, the present application has at least the following beneficial effects:

[0016] The continuous preparation method and device of few-walled carbon nanotubes provided by the present application can form a continuous reaction bed of carbon nanotubes, and apply a transient electric current to a selected segment in the continuous reaction bed, under the action of which the outer wall of the carbon nanotubes is etched and removed, to obtain carbon nanotubes with fewer walls. The few-walled carbon nanotubes with higher commercial value and use value are obtained from relatively inexpensive multi-walled carbon nanotubes, which can provide sufficient and inexpensive carbon nanotube materials for the development of related application fields.

[0017] The above description is only a summary of the technical solutions of the present application. In order for those skilled in the art to more clearly understand the technical means of the present application, and to implement the content of the specification, the following describes the preferred embodiments of the present application with reference to the detailed drawings as follows. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 is a process schematic diagram of the continuous preparation method provided by a typical embodiment of the present application;

[0019] Figure 2 is a structural schematic diagram of a continuous preparation device provided by an embodiment of the present application;

[0020] Figure 3 is a structural schematic diagram of a continuous preparation device provided by another embodiment of the present application;

[0021] Figure 4 is a transmission electron microscope image of a single-wall carbon nanotube provided by an embodiment of the present application;

[0022] Figure 5 is a transmission electron microscope image of a single-wall carbon nanotube provided by another embodiment of the present application. DETAILED DESCRIPTION

[0023] In view of the deficiencies in the prior art, the present inventors have, through long-term research and a large number of practices, come up with the technical solution of the present application. The technical solution, its implementation process and principles will be further explained as follows.

[0024] In the following description, a large number of specific details are set forth in order to facilitate a thorough understanding of the present application, however, the present application can also be implemented in other ways different from those described herein, and therefore, the scope of protection of the present application is not limited by the specific embodiments disclosed below.

[0025] Moreover, relational terms such as "first" and "second" and the like are used only to distinguish one from another of a same name, and do not necessarily require or imply any such actual relationship or order between the parts or method steps.

[0026] The core idea of the present application is to use multi-wall carbon nanotubes prepared in an industrial batch as raw materials, to use the transient Joule heat generated by the multi-wall carbon nanotubes when they bear high-power current to heat themselves, to generate ultra-high temperature, and to combine the use of a small amount of etching agent to promote the pyrolysis or etching removal of the outer wall of the multi-wall carbon nanotubes, thereby converting them into few-wall or even single-wall carbon nanotubes. On this basis, combined with raw material supply equipment, conveying equipment, special current supply equipment and collection equipment, the continuous supply of raw material multi-wall carbon nanotubes, the continuous conversion process and the continuous collection of products are carried out, and finally the continuous, batch and low-cost manufacturing of single-wall / few-wall carbon nanotubes is realized. Based on this, as shown in Figure 1 The embodiment of the present application provides a continuous preparation method of few-wall carbon nanotubes, which comprises the following steps:

[0027] The first carbon nanotube with a wall number ≥2 is contacted with an etching agent, and a continuous reaction bed moving in a specified direction is formed;

[0028] The first electrode group is brought into contact with the continuous reaction bed, and a first transient current is applied to a first selected section of the continuous reaction bed to cause the first selected section to generate a first transient high temperature, under the action of which at least the outermost tube wall of the first carbon nanotube is etched and removed by the etchant, thereby continuously obtaining a second carbon nanotube with a wall number less than that of the first carbon nanotube.

[0029] The few-walled carbon nanotube refers to a carbon nanotube product with a wall number less than that of the initial carbon nanotube used as a raw material. The wall number is not strictly limited, for example, a carbon nanotube with 10 wall layers is used to prepare a carbon nanotube with 8 wall layers, which can also be referred to as "few-walled". However, according to industrial requirements, the final goal is to prepare a carbon nanotube with a significantly smaller wall number, and the optimal choice is to obtain a double-walled or single-walled carbon nanotube by adjusting the process conditions or multiple preparations.

[0030] It should be noted that the effect of the current is to generate a transient high temperature, which requires the current to have the characteristics of short time and high power, for example, pulse transient current, short time high current discharge of high power direct current power supply, short time discharge of large capacity capacitor, etc., all of which meet the standard of current that can form a transient high temperature. Specifically, it is generally required that the temperature rise rate (slope of temperature / time curve) caused by the current meets the requirements. Regarding the definition of transient high temperature, in the field of carbon material processing, a high temperature of 500°C or above within 1s is usually used as the standard, and a temperature rise and fall rate of 10 3 -10 5 °C / s can be referred to as "transient" high temperature, but it is not absolutely limited to this standard. Under the guidance of the concept of the present application, the use of relatively rapid temperature rise to meet the requirement of etching the outermost layer is within the protection scope of the present application.

[0031] The combination of the etchant and the transient high temperature is the key to realizing the selective etching described above. In experiments, it is found that if a high-power transient high temperature is not used, some etchants, especially liquid etchants, are easily volatilized or moved away from the surface of the carbon nanotube in the process of slow temperature rise, and no longer have a selective etching effect. The transient high temperature makes the etchant volatilize, which does not have time to diffuse away and produce a selective etching effect on the outer tube wall of the carbon nanotube.

[0032] In some embodiments, the macroscopic morphology of the first carbon nanotube includes any one of powder, fiber, and film.

[0033] In some embodiments, the etchant includes any one or a combination of two or more of water, hydrogen peroxide, oxygen, ozone, and hydrogen.

[0034] In some embodiments, the etchant in liquid state is adsorbed into the continuous reaction bed before the first selected segment;

[0035] In some embodiments, at least the first selected segment is in an atmosphere containing the etchant in gaseous state.

[0036] In some embodiments, the mass ratio of the etchant in liquid state to the first carbon nanotubes in the continuous reaction bed is 1:100-10000;

[0037] In some embodiments, the volume fraction of the etchant in gaseous state in the atmosphere is 0.01-1%.

[0038] The proper selection of the etchant and its concentration setting is important, which ensures a proper etching degree, which is sufficient to remove the outermost tube wall, and does not cause damage or depletion of the carbon nanotubes due to over-etching.

[0039] In some embodiments, the peak temperature of the first transient high temperature is 500-3500°C, the first transient current is a pulse current, the pulse frequency is 0.1 Hz-1 MHz, the duty cycle is 0.1-0.9, and the duration is 10 -6 -600s.

[0040] In some embodiments, the preparation method can further comprise:

[0041] After the first selected segment, a second selected segment of the continuous reaction bed is applied with a second transient current by a second electrode group in the specified direction, the second transient current is used to generate a second transient high temperature, and the second transient high temperature makes the crystallinity of the carbon nanotubes in the second selected segment higher than that in the first selected segment;

[0042] In some embodiments, the peak temperature of the second transient high temperature is 1500-3500°C, the second transient current is a pulse current, the pulse frequency is 0.1 Hz-1 MHz, the duty cycle is 0.1-0.9, and the duration is 10 -6 -600s.

[0043] Corresponding to the above continuous preparation method, see Figure 2 and Figure 3 The embodiments of the present application also provide a continuous preparation device for few-walled carbon nanotubes, which comprises:

[0044] A continuous movement module is used to contact the first carbon nanotubes with wall number ≥2 with an etchant, and form a continuous reaction bed moving in a specified direction;

[0045] a current applying module comprising a first electrode group capable of being in moving contact with the continuous reaction bed and applying a first transient current to a first selected section of the continuous reaction bed to generate a first transient high temperature for the first selected section, under the action of which at least the outermost tube wall of the carbon nanotube is etched and removed by the etchant, thereby continuously obtaining a second carbon nanotube with a wall number less than that of the first carbon nanotube.

[0046] In some embodiments, the continuous movement module comprises a raw material supply device, a conveying device and a collecting device; the raw material supply device is used to provide the first carbon nanotube to the conveying device; the conveying device is used to continuously convey the first carbon nanotube to the collecting device to form the continuous reaction bed; and the collecting device is used to collect the generated second carbon nanotube.

[0047] In some embodiments, the current applying module further comprises a second electrode group arranged behind the first electrode group along the specified direction, for applying a second transient current to a second selected section of the continuous reaction bed to generate a second transient high temperature.

[0048] In some embodiments, the conveying device is insulated from the first carbon nanotube, and the current applying module comprises a first rotating electrode and a second rotating electrode which are in rolling contact with the continuous reaction bed in the same direction along the specified direction in sequence; at least the first rotating electrode and the second rotating electrode constitute the first electrode group.

[0049] In some embodiments, a third rotating electrode is further arranged behind the second rotating electrode and in rolling contact with the continuous reaction bed in the same direction, and at least the second rotating electrode and the third rotating electrode constitute the second electrode group.

[0050] In this embodiment, the flow direction of the current is along the specified direction, i.e. along the extension direction of the continuous reaction bed, and a large number of carbon nanotubes can be included between the two electrodes, and the applied current can simultaneously bring thermal energy to a large number of carbon nanotubes, so that the processing efficiency of this current applying method is higher, and it is more conducive to batch production.

[0051] In addition, the above-mentioned current applying method has a long working distance, so that the application time range of the transient ultra-high temperature can be better controlled, thereby controlling the etching effect. At the same time, the amorphous carbon and catalyst particles inside the carbon nanotube can also be more easily volatilized, so that the product is relatively clean. However, this method cannot apply pressure to the carbon nanotube when the transient ultra-high temperature is generated, and the carbon nanotube in the fluffy state is almost not fused when the transient ultra-high temperature is processed. Moreover, the current density of this method is low, so that the content of the single-walled carbon nanotube formed by one-time continuous preparation is low, and it often needs to be repeated multiple times.

[0052] Alternatively, the transmission device is in electrical contact with the first carbon nanotube, and the current application module comprises a fourth rotating electrode in rolling contact with the continuous reaction bed in the same direction, and the transmission device and the fourth rotating electrode constitute the first electrode group;

[0053] In some embodiments, the current application module further comprises a fifth rotating electrode, and the transmission device and the fifth rotating electrode constitute the second electrode group.

[0054] In this embodiment, the direction of current conduction is along the thickness direction perpendicular to the specified direction, the spacing distance between the electrodes is short, and the volume of the region acting on the continuous reaction bed is extremely small (only a very low amount of electricity is needed to rapidly heat up), which can bring better and excellent transient heating effect, and can more rapidly cool down after leaving the electrode region. Due to the short action distance, small action volume, and small mass of carbon nanotubes in the action range, the temperature change and the change of the current present a very strong correlation, which can more accurately adjust the applied transient high temperature, obtain a better wall number regulation effect, and be beneficial to improving the product quality.

[0055] And the energy density of the above current application method is high, and the content of single-walled carbon nanotubes obtained after one preparation is relatively higher. At the same time, by adjusting the height of the rotating electrode, a certain pressure can be given to the carbon tubes below, promoting the fusion of the carbon tubes under the transient ultrahigh temperature to form large-diameter single-walled tubes. However, this method is short in time, amorphous carbon, and catalyst volatilization time, so the product will be more complex, that is, the residual amount of amorphous carbon and catalyst is higher.

[0056] In some embodiments, the transmission device comprises a conveyor belt with a surface of conductive material, and the conductive material is in rolling electrical contact with at least a sixth rotating electrode;

[0057] In some embodiments, the sixth rotating electrode also serves as a roller at one end of the conveyor belt.

[0058] In some embodiments, the material of the contact surface between the first rotating electrode and / or the third rotating electrode and the continuous reaction bed comprises any one or a combination of two or more of graphite, molybdenum, and tungsten; and the material of the contact surface between the second rotating electrode and the continuous reaction bed comprises any one or a combination of two or more of graphite, copper, silver, molybdenum, and tungsten.

[0059] In some embodiments, the material of the contact surface between the fourth rotating electrode and / or the transmission device and the continuous reaction bed comprises any one or a combination of two or more of graphite, molybdenum, and tungsten, and the material of the contact surface between the fifth rotating electrode and the continuous reaction bed comprises any one or a combination of two or more of graphite, copper, silver, molybdenum, and tungsten.

[0060] As some typical application examples of the above-mentioned embodiments, the specific implementation steps of the preparation of single-walled carbon nanotubes using the above-mentioned continuous preparation device are as follows:

[0061] (1) The multi-walled carbon nanotube powder is loaded into the raw material supply device, and the multi-walled carbon nanotube is supplied to the conveying device at a constant rate. In this step, the original carbon nanotubes used can be double-walled or multi-walled carbon nanotubes with a wall number of 2-30.

[0062] (2) The conveying device operates at a constant rate to continuously and stably convey the carbon nanotube powder to the electrode for transient ultra-high temperature heating to continuously etch and peel off at least the wall of the multi-walled carbon nanotube or even a single wall.

[0063] (3) The main structure of the entire device is in a sealed container, which is vacuumed and then filled with argon to atmospheric pressure, and this vacuum-argon filling operation is repeated 3 times to remove air in the preparation device, and then the internal pressure of the preparation device is kept at a negative pressure state (0.5-1.01 MPa); the gas filled can be argon, nitrogen or other inert gases, and the number of repeated argon filling-vacuuming can be 1-20, or the repeated operation process of argon filling-vacuuming can also be replaced by a long-time argon filling treatment mode, which can remove oxygen in the reaction environment and avoid undesirable oxidation.

[0064] (4) A small amount of water is added to the multi-walled carbon nanotubes, and the mass ratio of water to multi-walled carbon nanotubes is 1:100-10000. Water can be replaced by other etchants, including hydrogen peroxide, oxygen, ozone, hydrogen and mixtures thereof, and the addition method can be, for example, to adsorb the liquid etchant on the carbon nanotube raw material, or to mix the gaseous etchant in the gas atmosphere;

[0065] (5) A high-power pulse current is passed through the multi-walled carbon nanotubes using a rotating electrode to generate a transient ultra-high temperature of the carbon nanotubes, with a peak temperature of 500-3500°C, a pulse frequency of 0.1 Hz-1 MHz, and a duty cycle of 0.1-0.9, so that the outer wall of the multi-walled carbon nanotubes reacts with the etchant, for example, C+H2O→CO↑+H2↑, thereby etching and removing the outer wall; corresponding to the different amounts of oxidizing agents passed in, the corresponding etching reactions are as follows:

[0066] Water: C+H2O→CO↑+H2↑.

[0067] Hydrogen peroxide: 2C+H2O2→2CO↑+H2↑, C+H2O2↑→CO2↑+H2, 2C+H2→2CH↑.

[0068] Oxygen: 2C+O2→2CO↑, C+O2↑→CO2↑.

[0069] Ozone: 3C + O3→ 3CO↑, 3C + 2O3↑→ 3CO2↑.

[0070] Hydrogen: 2C + H2→ 2CH↑, C + 2H2→ CH4↑.

[0071] And, in the multi-walled carbon nanotubes into high-power pulse current, carbon nanotubes produce transient ultra-high temperature, can be replaced by fast rising and falling DC power supply or capacitor discharge.

[0072] (6) combined with two rotating electrodes and conveying device, to achieve continuous supply of multi-walled carbon nanotubes, with continuous transient ultra-high temperature treatment, to achieve continuous production.

[0073] (7) using a collection device / container to collect the generated product, and Raman spectroscopy detection, to determine the etching, single-walled carbon nanotube content and crystallinity meet the requirements. If not, adjust the parameters in step (2), (4), (5), to increase the etchant ratio or increase the temperature and reduce the conveying device running speed; if it meets the requirements, then with this process parameters to achieve continuous preparation of single-walled carbon nanotubes.

[0074] Among them, the two rotating electrodes can be located above the carbon nanotube powder, and press on the continuous carbon nanotube powder, the conveying device using high temperature resistant insulating material, so that Figure 2 As shown in the rotating electrode 1 (the first rotating electrode) - carbon nanotube powder - rotating electrode 2 (the second rotating electrode) to form a conductive channel, to produce transient ultra-high temperature in the carbon nanotube powder; or, two rotating electrodes can be one located above the carbon nanotube powder, and press on the carbon nanotube powder, the other as a conveying device, the surface of the transmission mechanism using high conductivity material, so that as shown in Figure 3 As shown in the rotating electrode 1 (the fourth rotating electrode) - carbon nanotube powder - conveying belt (a specific conveying mechanism) - rotating electrode 2 (the fifth rotating electrode) to form a conductive channel, to produce transient ultra-high temperature in the carbon nanotube powder, to achieve continuous preparation of single-walled carbon nanotubes.

[0075] To further improve product quality, some implementation schemes apply two transient high-temperature processes. The first process aims to remove at least the outermost tube wall, while the second process aims to increase the crystallinity of the product. These two processes are performed continuously in the same equipment, allowing for the efficient acquisition of high-quality single-walled / few-walled carbon nanotube products. Specifically, this can be achieved by adding another rotating electrode after the aforementioned rotating electrode. The optimal form is for the two sets of rotating electrodes to share a common rotating electrode or a common conveying device. Of course, the two sets of electrodes can also be set up completely independently. Furthermore, to ensure that the two sets of currents do not interfere with each other when sharing the electrode, the pulse periods of the two sets of currents can be staggered. For example, when one set of currents is applied, the other set of currents is in an open-circuit state.

[0076] For example, Figure 2 The three rotating electrodes in the device shown in Figure 1 can be made of high-temperature resistant conductive materials such as graphite, molybdenum, and tungsten, and the conveying mechanism can be made of high-temperature resistant insulating ceramic material or have high-temperature resistant insulating ceramic material attached to its surface. Figure 3 The first rotating electrode in the device shown in Figure 2 can be made of high-temperature resistant conductive materials such as graphite, molybdenum, and tungsten; the second rotating electrode can be made of highly conductive materials such as graphite, copper, silver, molybdenum, and tungsten; and the conveying mechanism can be made of high-temperature resistant conductive materials such as graphite, molybdenum, and tungsten, or have such materials attached to its surface. Figure 3 The rotating electrode 3 can be connected to the power supply equipment, or any other form of electrical connection.

[0077] The technical solution of the present invention will be further described in detail below through several embodiments and in conjunction with the accompanying drawings. However, the selected embodiments are only for illustrating the present invention and do not limit the scope of the present invention.

[0078] Example 1:

[0079] (1) Adopt Figure 2 The No. 1 device shown in the figure loads multi-walled carbon nanotube powder into the raw material supply device. After the entire set of equipment is evacuated, argon gas is introduced to atmospheric pressure. This evacuation-argon gas introduction operation is repeated 3 times to remove air from the preparation device. After that, the preparation device is kept under negative pressure with a pressure of 0.5 MPa.

[0080] (2) Add a trace amount of water to the multi-walled carbon nanotubes, with a mass ratio of water to multi-walled carbon nanotubes of 1:100.

[0081] (3) Start the raw material supply device and the conveying device, and feed the multi-walled carbon nanotube powder from the supply device into the conveying device at a constant rate of 1 g / s. At the same time, the conveying device moves at a rate of 0.1 m / min and conveys the carbon nanotube powder to the electrode.

[0082] (4) rotating the electrodes 1 and 2 at the same linear speed as the conveyor belt, and connecting the power supply 1 to pass a high-power pulse current through the multi-walled carbon nanotubes to generate transient super-high temperature in the carbon nanotubes, with a peak temperature of 1200°C, a pulse frequency of 1 MHz, and a duty cycle of 30%, so that the outer wall of the multi-walled carbon nanotubes reacts with the etchant to be etched and removed;

[0083] (5) rotating the electrodes 3 and 4 at the same speed as the conveyor belt, and connecting the power supply 2 to pass a high-power pulse current through the multi-walled carbon nanotubes to generate transient super-high temperature in the carbon nanotubes, with a peak temperature of 3000°C, a pulse frequency of 1 MHz, and a duty cycle of 30%, so that the carbon nanotubes are crystallized to improve the quality of the single-walled carbon nanotubes.

[0084] (6) to ensure that the etching and peeling process and the recrystallization process do not affect each other, and the operation of the power supply 1 and the power supply 2 is not affected by each other, the duty cycles of the operation of the two power supplies are staggered, i.e. when the power supply 1 discharges, the power supply 2 does not discharge, and when the power supply 2 discharges, the power supply 1 does not discharge.

[0085] (7) sampling the collected product for Raman spectrum detection to determine the content of single-walled carbon nanotubes in the product and the crystallinity to meet the requirements, and continuously processing to realize the continuous batch production of single-walled carbon nanotubes.

[0086] The transmission electron microscope of the prepared carbon nanotube product is shown in Figure 4 From which it can be seen that the product is relatively pure, without obvious catalysts, amorphous carbon and other impurities, but the proportion of single-walled carbon nanotubes obtained after one treatment is relatively low, and multiple repeated treatments are needed to more easily obtain a product containing more single-walled carbon nanotubes.

[0087] Example 2:

[0088] This example is basically the same as Example 1, the main difference being that:

[0089] Adjust the power supply 1 so that the corresponding peak temperature is 500°C, the pulse frequency is 0.1 Hz, and the duty cycle is 90%, and adjust the electrode spacing so that the current acts on the carbon nanotubes for 600 s;

[0090] Adjust the power supply 2 so that the corresponding peak temperature is 1500°C, the pulse frequency is 0.1 Hz, and the duty cycle is 10%, and adjust the electrode spacing so that the current acts on the carbon nanotubes for 600 s.

[0091] Finally, a few-walled carbon nanotube with significantly fewer walls than the carbon nanotube raw material can still be obtained.

[0092] Example 3:

[0093] (1) using the method as shown in Figure 3The No. 2 device shown, the multi-walled carbon nanotube powder is loaded into the raw material supply device, the whole equipment is vacuumed and then argon is introduced to the atmospheric pressure, and the vacuum-argon introduction operation is repeated 3 times to remove the air in the preparation device, and then the internal pressure of the preparation device is kept at a negative pressure of 0.5 MPa;

[0094] (2) A small amount of water is added to the multi-walled carbon nanotubes, and the mass ratio of water to multi-walled carbon nanotubes is 1:1000;

[0095] (3) The raw material supply device and the conveying device are started, and the multi-walled carbon nanotube powder is put into the conveying device from the supply device at a constant rate of 1 g / s, while the conveying device moves at a speed of 0.1 m / min and conveys the carbon nanotube powder to the electrode;

[0096] (4) Rotate the electrode 1 at the same speed as the conveying belt, and connect the power supply 1 to introduce a high-power pulse current into the multi-walled carbon nanotubes, so that the carbon nanotubes generate a transient ultra-high temperature, the peak temperature is 1200℃, the pulse frequency is 1 MHz, and the duty cycle is 30%, so that the outer wall of the multi-walled carbon nanotubes reacts with the etchant and the outer wall is etched away;

[0097] (5) Rotate the electrode 2 at the same speed as the conveying belt, and connect the power supply 2 to introduce a high-power pulse current into the multi-walled carbon nanotubes, so that the carbon nanotubes generate a transient ultra-high temperature, the peak temperature is 2000℃, the pulse frequency is 1 MHz, and the duty cycle is 30%, so that the carbon nanotubes are crystallized and the quality of the single-walled carbon nanotubes is improved.

[0098] (6) The collected product is sampled and detected by Raman spectroscopy to determine the content and crystallinity of the single-walled carbon nanotubes in the product to meet the requirements, and the continuous batch production of single-walled carbon nanotubes is realized.

[0099] The transmission electron microscope of the carbon nanotube product prepared is shown in Figure 5 From which it can be seen that the single-walled carbon nanotube content of the product obtained by single treatment in this embodiment is high, but the content of residual catalyst, amorphous carbon and other impurities is high.

[0100] Example 4:

[0101] This embodiment is basically the same as Example 1, the main difference is:

[0102] Adjust the power supply 1 so that the corresponding peak temperature is 3500℃, the pulse frequency is 1000Hz, and the duty cycle is 50%;

[0103] Adjust the power supply 2 so that the corresponding peak temperature is 3500℃, the pulse frequency is 1000Hz, and the duty cycle is 50%.

[0104] Finally, a few-walled carbon nanotube with a significantly less number of walls than the carbon nanotube raw material can be obtained.

[0105] Based on the above embodiments, it can be clear that the continuous preparation method and device of the few-walled carbon nanotube provided by the embodiments of the present application can make the carbon nanotubes form a continuous reaction bed, and apply a transient current to selected segments in the continuous reaction bed. Under the action of the transient current, the outer walls of the carbon nanotubes are etched and removed to obtain carbon nanotube products with fewer walls. The few-walled carbon nanotube with higher commercial value and use value is obtained from the relatively inexpensive multi-walled carbon nanotube, which can provide sufficient and inexpensive carbon nanotube materials for the development of related application fields.

[0106] It should be understood that the above embodiments are only to illustrate the technical concepts and characteristics of the present application, and the purpose is to enable those skilled in the art to understand the content of the present application and to implement it, and cannot limit the protection scope of the present application. Any equivalent changes or modifications made in accordance with the spirit and essence of the present application shall be covered within the protection scope of the present application.

Claims

1. A method for continuous production of few-walled carbon nanotubes, characterized by, The method comprises the following steps: contacting a first carbon nanotube with wall number ≥2 with an etchant, and forming a continuous reaction bed moving along a specified direction; contacting a first electrode group with the continuous reaction bed, and applying a first transient current to a first selected segment of the continuous reaction bed, so that the first selected segment generates a first transient high temperature, under the action of which at least the outermost wall of the first carbon nanotube is etched and removed by the etchant, thereby continuously obtaining a second carbon nanotube with wall number less than the first carbon nanotube; The etchant includes any one or a combination of two or more of water, hydrogen peroxide, oxygen, ozone, and hydrogen. The liquid etchant is adsorbed into the continuous reaction bed in front of the first selected segment. The mass ratio of the liquid etchant to the first carbon nanotube in the continuous reaction bed is 1:100-10,000. At least the first selected segment is in an atmosphere containing gaseous etchant. The volume fraction of the gaseous etchant in the atmosphere is 0.01-1%. The first transient high temperature is a temperature reaching 500°C or above within 1 s, a temperature rising rate reaching 10 3 -10 5 °C / s, a peak temperature of the first transient high temperature being 500-3,500°C, and the first transient current being a pulse current with a pulse frequency of 0.1 Hz-1 MHz, a duty cycle of 0.1-0.9, and a duration of 10 -6 -600 s.

2. The continuous manufacturing process of claim 1, wherein, The macroscopic morphology of the first carbon nanotube includes any one of powder, fiber, and film.

3. The continuous manufacturing process of claim 1, wherein, The method further comprises the following steps: After the first selected segment, a second selected segment of the continuous reaction bed is applied with a second transient current by a second electrode group along the specified direction, and the second transient current is used to generate a second transient high temperature, which makes the crystallinity of the carbon nanotube in the second selected segment higher than that of the carbon nanotube in the first selected segment.

4. The continuous manufacturing process of claim 3, wherein, The peak temperature of the second transient high temperature is 1500-3500℃, the second transient current is a pulse current, the pulse frequency is 0.1 Hz-1 MHz, the duty cycle is 0.1-0.9, and the duration is 10 -6 -600 s.

5. An apparatus for the continuous production of few-walled carbon nanotubes for the implementation of the continuous production process according to any one of claims 1 to 4, characterized in that The method comprises the following steps: a continuous movement module is used to contact a first carbon nanotube with wall number ≥2 with an etchant, and form a continuous reaction bed moving along a specified direction; a current application module comprises a first electrode group, which can be in moving contact with the continuous reaction bed, and apply a first transient current to a first selected segment of the continuous reaction bed, so that the first selected segment generates a first transient high temperature, under the action of which at least the outermost wall of the carbon nanotube is etched and removed by the etchant, thereby continuously obtaining a second carbon nanotube with wall number less than the first carbon nanotube.

6. The continuous manufacturing apparatus of claim 5, wherein, The continuous movement module comprises a raw material supply device, a conveying device, and a collecting device; The raw material supply device is used to provide the first carbon nanotube to the conveying device; the conveying device is used to continuously convey the first carbon nanotube to the collecting device to form the continuous reaction bed; and the collecting device is used to collect the generated second carbon nanotube.

7. The continuous manufacturing apparatus of claim 6, wherein, The current application module further comprises a second electrode group arranged after the first electrode group along the specified direction, which is used to apply a second transient current to a second selected segment of the continuous reaction bed to generate a second transient high temperature.

8. The continuous manufacturing apparatus of claim 7, wherein, The conveying device is insulated from the first carbon nanotube, and the current application module comprises a first rotating electrode and a second rotating electrode which are in same-direction rolling contact with the continuous reaction bed along the specified direction in sequence; At least the first rotating electrode and the second rotating electrode constitute the first electrode group.

9. The continuous manufacturing apparatus of claim 8, wherein, After the second rotating electrode, a third rotating electrode is further included which is in same-direction rolling contact with the continuous reaction bed, and at least the second rotating electrode and the third rotating electrode constitute the second electrode group.

10. The continuous manufacturing apparatus of claim 9, wherein, The material of the contact surface of the first rotating electrode and / or the third rotating electrode with the continuous reaction bed comprises any one or a combination of two or more of graphite, molybdenum, and tungsten; and the material of the contact surface of the second rotating electrode with the continuous reaction bed comprises any one or a combination of two or more of graphite, copper, silver, molybdenum, and tungsten.

11. The continuous manufacturing apparatus of claim 7, wherein, The transfer device is in electrical contact with the first carbon nanotube, and the current application module includes a fourth rotating electrode in rolling contact with the continuous reaction bed in the same direction as the continuous reaction bed, and the transfer device and the fourth rotating electrode constitute the first electrode group.

12. The continuous manufacturing apparatus of claim 11, wherein, The current application module further includes a fifth rotating electrode, and the transfer device and the fifth rotating electrode constitute the second electrode group.

13. The continuous manufacturing apparatus of claim 12, wherein, The transfer device includes a transfer belt with a surface of an electrically conductive material in rolling electrical contact with at least a sixth rotating electrode. The sixth rotating electrode also serves as a roller at one end of the transfer belt.

14. The continuous manufacturing apparatus of claim 13, wherein, The material of the contact surface of the fourth rotating electrode and / or the transfer device with the continuous reaction bed includes any one or a combination of two or more of graphite, molybdenum, and tungsten, and the material of the contact surface of the fifth rotating electrode with the continuous reaction bed includes any one or a combination of two or more of graphite, copper, silver, molybdenum, and tungsten.

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