Single-walled carbon nanotube and preparation method thereof

Abstract

The present invention belongs to the technical field of carbon nanotube materials, and specifically relates to a single-walled carbon nanotube and a method thereof. The method fully mixes paraffin wax with a catalyst and a co-catalyst, compresses them into a reaction raw material, then turns on a plasma arc, preheats the reaction chamber of the arc furnace to a certain temperature, and then transports the reaction raw material in the storage tank to a graphite crucible in the arc furnace. Under the action of the electric arc, the catalyst and the carbon source evaporate simultaneously and interact to generate single-walled carbon nanotubes. At the same time, a carrier gas is introduced into the plasma arc system, and the reaction product is taken out by the airflow. The beneficial effect of the present invention is that the method selects paraffin wax that is easy to evaporate as a carbon source, and fully mixes it with a catalyst, so that the carbon source and the catalyst evaporate more evenly and contact more fully, which is conducive to the synthesis of high-quality single-walled carbon nanotubes. The I of the single-walled carbon nanotubes G / I D The ratio is not less than 37, and the TG residue of the obtained product is less than 40.0%.

Description

Technical Field

[0001] The invention belongs to the technical field of carbon nanotube materials, and in particular relates to a single-walled carbon nanotube and a preparation method thereof. Background Art

[0002] The geometric structure of single-walled carbon nanotubes (SWCNTs) can be regarded as a single layer of graphene curled up, with excellent electronic, mechanical, and mechanical properties. At the same time, changes in the atomic scale can lead to changes in the properties of single-walled carbon nanotubes. One-dimensional carbon nanotubes have a large aspect ratio. After regulation, they can obtain a large specific surface area and a high degree of graphitization. They are widely used in supercapacitors, catalyst carriers, hydrogen storage, carp-ion batteries, functional coatings and other fields.

[0003] The main methods for preparing single-walled carbon nanotubes include arc ablation, laser evaporation and chemical vapor deposition. The single-walled carbon nanotubes prepared by arc ablation have a high degree of graphitization and few structural defects. The disadvantage is that carbon nanotubes are often mixed with by-products such as amorphous carbon and nanocarbon particles, which are not easy to separate and purify. In addition, the carbon source of this method is high-purity graphite, the boiling point of graphite is as high as 4830°C, and the energy consumed during evaporation is high. There are also reports that graphitizable carbon powder is mixed with iron powder and pressed into carbon rods, and then sintered in an inert atmosphere to fully graphitize the carbon powder to obtain a carbon electrode rod containing an iron catalyst as a reaction raw material, but this method is complicated and has a high energy consumption during the sintering process. The advantage of the laser evaporation method is that the obtained carbon nanotubes are of good quality, but because the laser required for the laser evaporation method requires high energy and expensive equipment, it is not suitable for the large-scale preparation of carbon nanotubes. Chemical vapor deposition is the most common method for preparing carbon nanotubes. The generally accepted growth mechanism is: at high temperature, the gaseous carbon source decomposes on the surface of the transition metal catalyst, and the formed carbon dissolves in the catalyst particles. As the carbon continues to dissolve, when it reaches supersaturation, it precipitates from the metal to form carbon nanotubes. Since this type of transition metal catalyst is usually prepared by impregnation, it is inevitable that this type of catalyst will agglomerate and grow under high temperature conditions, resulting in the growth of carbon nanotubes with different diameters and large diameters. Summary of the invention

[0004] The present invention discloses a single-walled carbon nanotube and a preparation method thereof, so as to solve any of the above and other potential problems in the prior art.

[0005] To achieve the above-mentioned purpose, the technical scheme of the present invention is: a method for preparing single-walled carbon nanotubes, wherein paraffin is used as a carbon source, paraffin, a catalyst and a co-catalyst are first mixed in a certain proportion to prepare a reaction raw material, the reaction raw material is placed in an electric arc furnace, and a mixed carrier gas is introduced, under the action of the electric arc, the paraffin, the catalyst and the co-catalyst are evaporated at the same time, and interact with each other to generate single-walled carbon nanotubes, and then the generated single-walled carbon nanotubes are taken out by the mixed carrier gas, so as to obtain single-walled carbon nanotubes.

[0006] Further, the method is specifically as follows:

[0007] S1) paraffin, catalyst and co-catalyst are weighed respectively according to the designed ratio, mixed evenly, pressed into block or granular particles as reaction raw materials, and loaded into a storage tank of a plasma arc furnace for standby use;

[0008] S2) firstly introduce an inert gas to evacuate, then introduce a mixed carrier gas into the plasma arc furnace at a certain flow rate, then start the plasma arc, form a plasma arc between the anode and the cathode, and heat the reaction chamber in the arc furnace to a certain temperature;

[0009] S3) feeding the reaction raw materials in the storage tank into the anode graphite crucible of the plasma arc furnace through the feed pipe, under the action of the electric arc, the catalyst and paraffin are evaporated to generate single-walled carbon nanotubes, and the reaction product is taken out from the discharge port by the airflow of the mixed carrier gas, so as to obtain single-walled carbon nanotubes.

[0010] Furthermore, in said S1), the mass percentage of paraffin in the reaction raw materials is 1%-99%, and the mass ratio of the catalyst to the co-catalyst is 5:1-50:1.

[0011] Furthermore, the catalyst is one or more of iron powder, iron oxide, nickel powder, nickel oxide, cobalt powder, and cobalt oxide; and the promoter is sulfur powder.

[0012] Furthermore, the flow rate of the mixed carrier gas in S2) is 10-1000 L / min, and the temperature of the reaction chamber is heated to 800-2000°C.

[0013] Furthermore, the mixed carrier gas includes hydrogen, water vapor and inert gas; wherein the volume of the mixed carrier gas occupies 5-50% of the hydrogen, the volume of the mixed carrier gas occupies 0.1-10% of the water vapor, and the volume of the mixed carrier gas occupies 40-95% of the inert gas.

[0014] Furthermore, the inert gas is one or more of nitrogen, argon and helium.

[0015] Furthermore, the power of the arc in S3) is not less than 10kW, the voltage is 30-150V, and the current is 200-2000A.

[0016] A single-walled carbon nanotube is prepared by the above-mentioned preparation method.

[0017] Further, the single-walled carbon nanotubes G / I D The ratio is not less than 37, and the TG residue of the obtained product is less than 40.0%.

[0018] The principle of the present invention is: under the high temperature of plasma arc, paraffin and catalyst are evaporated into steam, which escapes in the reaction chamber to form a mixed steam of carbon source-catalyst. As the steam diffuses to a position far away from the arc, the temperature drops rapidly, and the catalyst steam condenses into nanoparticles to catalyze the growth of carbon nanotubes. Since the catalyst and carbon source evaporate from the anode crucible at the same time, the two can be fully mixed. There is a large amount of carbon source steam around the condensed nanocatalyst particles, which is conducive to preventing the further growth of the catalyst particles and forming a uniform aerosol. This carbon source steam-catalyst particle aerosol is conducive to increasing the contact between the carbon source and the catalyst and improving the efficiency of the catalyst, thereby obtaining high-quality single-walled carbon nanotubes. When using a gaseous carbon source, the repulsive force generated by the huge expansion of the gas volume caused by the high temperature of the arc will hinder the carbon source gas from entering the high temperature area of ​​the arc and contacting the catalyst, so that the catalytic efficiency is difficult to improve. In addition, during the reaction, the mixed carrier gas is continuously introduced into the reaction chamber, which can keep the atmosphere in the reaction chamber relatively stable on the one hand, and the reaction products can be taken out of the reaction chamber in time, so that the reaction is carried out continuously. By adjusting the components, proportions and flow of the carrier gas, the state of the reaction can be adjusted, affecting the yield and quality of the product. Paraffin is a mixture of hydrocarbons with a carbon number of about 18 to 30. The main components are straight-chain alkanes (about 80% to 95%), as well as a small amount of alkanes with individual branches and monocyclic cycloalkanes with long side chains. The melting point of paraffin is 100-200°C, and it can be gasified at less than 400°C. Under the action of high temperature and catalyst, paraffin can undergo catalytic cracking reaction to produce shorter carbon chains, and then continue to interact with the catalyst to generate single-walled carbon nanotubes. Compared with graphite, the energy required for paraffin evaporation is lower. Paraffin has low chemical activity, is neutral, and has stable chemical properties. Compared with gaseous hydrocarbons such as methane, ethane, and ethylene, it is safer and easier to transport.

[0019] Compared with the prior art, the present invention has the following advantages and technical effects: the raw material of the present invention selects paraffin wax with low boiling point and easy evaporation as the carbon source, and the carbon source and the catalyst are evaporated at the same time under the action of the electric arc to form a uniform vapor, thereby increasing the contact between the carbon source and the catalyst; the reaction product is taken out of the reaction chamber by introducing a carrier gas, thereby preventing the product from staying in the reaction chamber for a long time and being burned, which is conducive to continuous production, and the I of the prepared single-walled carbon nanotubes is G / I DThe ratio is not less than 37, and the TG residue of the obtained product is less than 40.0%. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The present invention is a flowchart of a method for preparing single-walled carbon nanotubes.

[0021] Figure 2 This is a scanning electron microscope image of the single-walled carbon nanotubes prepared in Example 1 of the present invention.

[0022] Figure 3 This is the thermogravimetric curve of the single-walled carbon nanotubes prepared in Example 3 of the present invention.

[0023] Figure 4 This is a transmission electron microscope image of the single-walled carbon nanotubes prepared in Example 5 of the present invention.

[0024] Figure 5 This is a Raman spectrum of the single-walled carbon nanotubes prepared in Example 5 of the present invention. DETAILED DESCRIPTION

[0025] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0026] The invention discloses a method for preparing single-walled carbon nanotubes. The method uses paraffin as a carbon source. Paraffin, a catalyst and a co-catalyst are first mixed in a certain proportion to prepare a reaction raw material. The reaction raw material is placed in an electric arc furnace and a carrier gas is introduced. Under the action of the electric arc, the paraffin, the catalyst and the co-catalyst are evaporated simultaneously and interact with each other to generate single-walled carbon nanotubes. The generated single-walled carbon nanotubes are then taken out by airflow to obtain the single-walled carbon nanotubes.

[0027] like Figure 1 The method for preparing single-walled carbon nanotubes is as follows:

[0028] S1) Weigh paraffin, catalyst and co-catalyst according to the designed ratio and mix them evenly

[0029] The particles pressed into blocks or granules are used as reaction raw materials and loaded into the storage tank of the plasma arc furnace for standby use;

[0030] S2) firstly introduce an inert gas to evacuate, then introduce a mixed carrier gas into the plasma arc furnace at a certain flow rate, and then start the plasma arc to form a plasma arc between the anode and the cathode, and heat the reaction chamber in the arc furnace to a certain temperature;

[0031] S3) feeding the reaction raw materials in the storage tank into the anode graphite crucible of the plasma arc furnace through the feed pipe, under the action of the electric arc, the catalyst and paraffin are evaporated to generate single-walled carbon nanotubes, and the reaction product is taken out from the discharge port by the airflow of the carrier gas, so as to obtain single-walled carbon nanotubes.

[0032] In the S1), the mass percentage of paraffin in the reaction raw materials is 1%-99%, and the mass ratio of the catalyst to the co-catalyst is 5:1-50:1.

[0033] The catalyst is one or more of iron powder, iron oxide, nickel powder, nickel oxide, cobalt powder and cobalt oxide; the promoter is sulfur powder.

[0034] The flow rate of the mixed carrier gas in S2) is 10-1000 L / min, and the temperature of the reaction chamber is heated to 800-2000°C.

[0035] The mixed carrier gas includes hydrogen, water vapor and inert gas; wherein the volume of the mixed carrier gas is 5-50% by hydrogen, the volume of the mixed carrier gas is 0.1-10% by water vapor, and the volume of the mixed carrier gas is 40-95% by inert gas.

[0036] The inert gas is one or more of nitrogen, argon and helium.

[0037] The power of the arc in S3) is not less than 10kW, the voltage is 30-150V, and the current is 200-2000A.

[0038] A single-walled carbon nanotube is prepared by the above-mentioned preparation method.

[0039] The single-walled carbon nanotubes G / I D The ratio is not less than 37, and the TG residue of the obtained product is less than 40.0%.

[0040] Example 1

[0041] Weigh a certain amount of paraffin wax, iron powder, and sulfur powder in a mass ratio of 90:9:1, mix them on a V-type mixer for 24 hours, and then use a tablet press to press them into discs with a diameter of 8mm and a thickness of 10mm. Put the pressed discs into the graphite crucible of the plasma arc furnace, first introduce Ar to exhaust the air in the furnace chamber, and then introduce a mixed carrier gas of Ar / H2 / water vapor, with flow rates of 20L / min, 2L / min, and 1L / min, respectively, and a total carrier gas flow rate of 23L / min. Turn on the arc, set the arc furnace current to 280A, the voltage to 40V, heat to 1000℃, add the reaction raw materials in the storage tank into the graphite crucible, and under the action of the arc, the carbon source and catalyst in the reaction raw material particles evaporate to form single-walled carbon nanotubes, which are taken out of the reaction chamber with the carrier gas, and the single-walled carbon nanotube products are collected at the discharge port.

[0042] Raman spectroscopy can be used to characterize the quality of single-walled carbon nanotubes. -1The G peak at 1340 cm represents the completeness of the SP2 hybrid bond structure in the structure. -1 The D peak at is caused by incomplete crystallites, structural defects, and unsaturated carbon atoms at the edge, and represents the degree of defects in carbon nanotubes. The intensity ratio of the G peak to the D peak is commonly used. G / I D To judge the degree of graphite structure integrity of carbon nanotubes, I G / I D The larger the value of , the better the crystallinity of the carbon nanotubes.

[0043] Thermogravimetry can be used to characterize the purity of the product. The sample is heated to 900°C in air. During this process, the carbon nanotubes are oxidized by oxygen in the air to become carbon dioxide and escape, leaving behind metal catalyst particles. The weight of the remaining catalyst can be used to infer the content of single-walled carbon nanotubes in the product.

[0044] It can be seen from Table 1 that the average I of the product obtained in Example 1 G / I D The ratio was 52, and the TG residue of the obtained product was 23.1%.

[0045] Figure 2 This is a scanning electron microscope image of the single-walled carbon nanotube prepared in Example 1 of the method of the present invention.

[0046] Example 2

[0047] Weigh a certain amount of paraffin wax, nickel powder, and sulfur powder in a mass ratio of 93:6:1, mix them on a V-type mixer for 24 hours, and then use a tablet press to press them into discs with a diameter of 8 mm and a thickness of 10 mm. Put the pressed discs into the graphite crucible of the plasma arc furnace, first introduce N2 to exhaust the air in the furnace chamber, and then introduce a mixed carrier gas of N2 / H2 / water vapor, with flow rates of 20L / min, 2L / min, and 2L / min, respectively, and the total carrier gas flow rate is 24L / min. Turn on the arc, set the arc furnace current to 285A, the voltage to 40V, heat to 1500℃, add the reaction raw materials in the storage tank to the graphite crucible, and under the action of the arc, the carbon source and catalyst in the reaction raw material particles evaporate to form single-walled carbon nanotubes, which are taken out of the reaction chamber with the carrier gas, and the single-walled carbon nanotube products are collected at the discharge port.

[0048] It can be seen from Table 1 that the average I of the product obtained in Example 2 G / I D The ratio was 45, and the TG residue of the obtained product was 35.4%.

[0049] Example 3

[0050] Weigh a certain amount of paraffin wax, cobalt powder, and sulfur powder in a mass ratio of 92:7:1, mix them on a V-type mixer for 24 hours, and then use a tablet press to press them into discs with a diameter of 8 mm and a thickness of 10 mm. Put the pressed discs into the graphite crucible of the plasma arc furnace, first introduce N2 to exhaust the air in the furnace chamber, and then introduce a mixed carrier gas of Ar / H2 / water vapor, with flow rates of 40L / min, 8L / min, and 2L / min, respectively, and the total carrier gas flow rate is 50L / min. . Turn on the arc, set the arc furnace current to 290A, the voltage to 35V, heat to 1200℃, add the reaction raw materials in the storage tank into the graphite crucible, and under the action of the arc, the carbon source and catalyst in the reaction raw material particles evaporate to form single-walled carbon nanotubes, which are taken out of the reaction chamber with the carrier gas, and the single-walled carbon nanotube products are collected at the discharge port.

[0051] Figure 3 The thermogravimetric curve of the initial product of single-walled carbon nanotubes prepared in Example 3 of the method of the present invention has a TG residue of 39.8%, so that the purity of the carbon nanotubes can be estimated to be 60%.

[0052] It can be seen from Table 1 that the average I of the products obtained in Example 3 G / I D The ratio is 40.

[0053] Example 4

[0054] Weigh a certain amount of paraffin wax, iron oxide, and sulfur powder in a mass ratio of 85:18:2, mix them on a V-type mixer for 30 hours, and then use a tablet press to press them into discs with a diameter of 8 mm and a thickness of 10 mm. Put the pressed discs into the graphite crucible of the plasma arc furnace, first introduce Ar to exhaust the air in the furnace chamber, and then introduce a mixed carrier gas of N2 / H2 / water vapor, with flow rates of 20L / min, 10L / min, and 0.5L / min, respectively, and the total carrier gas flow rate is 30.5L / min. . Turn on the arc, set the arc furnace current to 290A, the voltage to 40V, heat to 1100℃, add the reaction raw materials in the storage tank into the graphite crucible, and under the action of the arc, the carbon source and catalyst in the reaction raw material particles evaporate to form single-walled carbon nanotubes, which are taken out of the reaction chamber with the carrier gas, and the single-walled carbon nanotube products are collected at the discharge port.

[0055] It can be seen from Table 1 that the average I of the products obtained in Example 4 G / I D The ratio was 37, and the TG residue of the obtained product was 40.1%.

[0056] Example 5

[0057] Weigh a certain amount of paraffin wax, iron oxide, and sulfur powder in a mass ratio of 80:17:3, mix them on a V-type mixer for 30 hours, and then use a tablet press to press them into discs with a diameter of 8mm and a thickness of 10mm. Put the pressed discs into the graphite crucible of the plasma arc furnace, first introduce Ar to exhaust the air in the furnace chamber, and then introduce a mixed carrier gas of Ar / H2 / water vapor, with flow rates of 30L / min, 2L / min, and 3L / min, respectively, and the total carrier gas flow rate is 35L / min. . Turn on the arc, set the arc furnace current to 280A, the voltage to 45V, heat to 900℃, add the reaction raw materials in the storage tank into the graphite crucible, and under the action of the arc, the carbon source and catalyst in the reaction raw material particles evaporate to form single-walled carbon nanotubes, which are taken out of the reaction chamber with the carrier gas, and the single-walled carbon nanotube products are collected at the discharge port.

[0058] Figure 4 This is a transmission electron microscope image of the single-walled carbon nanotube prepared in Example 5 of the method of the present invention.

[0059] Figure 5 The Raman spectrum of the single-walled carbon nanotubes prepared in Example 5 of the method of the present invention is located at 1580 cm -1 The G peak at 1340 cm represents the completeness of the SP2 hybrid bond structure in the structure. -1 The D peak at is caused by incomplete crystallites, structural defects, and unsaturated carbon atoms at the edge, and represents the degree of defects in carbon nanotubes. The intensity ratio of the G peak to the D peak is commonly used. G / I D To judge the degree of graphite structure integrity of carbon nanotubes, I G / I D The larger the value of is, the better the crystallinity of the carbon nanotubes is. G / I D =67, indicating that the prepared single-walled carbon nanotubes have good crystallinity.

[0060] It can be seen from Table 1 that the TG residue of the product obtained in Example 5 is 31.5%.

[0061] Table 1: Properties of single-walled carbon nanotubes prepared in the examples of the present invention

[0062]

[0063]

[0064] The above is a detailed introduction to a single-walled carbon nanotube and a preparation method thereof provided in the embodiments of the present application. The description of the above embodiments is only used to help understand the method and its core idea of ​​the present application; at the same time, for a person skilled in the art, according to the idea of ​​the present application, there will be changes in the specific implementation method and application scope. In summary, the content of this specification should not be understood as limiting the present application.

[0065] If certain words are used in the specification and claims to refer to specific components, hardware manufacturers may use different nouns to refer to the same component. This specification and claims do not use differences in names as a way to distinguish components, but use differences in the functions of components as the criteria for distinction. As mentioned throughout the specification and claims, "including" and "comprising" are open-ended terms, so they should be interpreted as "including / including but not limited to". "Approximately" means that within an acceptable error range, those skilled in the art can solve the technical problem within a certain error range and basically achieve the technical effect. The subsequent description of the specification is a preferred embodiment of the present application, but the description is for the purpose of illustrating the general principles of the present application, and is not used to limit the scope of the present application. The scope of protection of the present application shall be determined by the attached claims.

[0066] It should also be noted that the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a product or system including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such a product or system. In the absence of more restrictions, the elements defined by the sentence "comprises a ..." do not exclude the existence of other identical elements in the product or system including the elements.

[0067] It should be understood that the term "and / or" used in this article is only a description of the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0068] The above description shows and describes several preferred embodiments of the present application, but as mentioned above, it should be understood that the present application is not limited to the form disclosed herein, and should not be regarded as excluding other embodiments, but can be used in various other combinations, modifications and environments, and can be modified within the scope of the application concept described herein through the above teachings or the technology or knowledge of the relevant field. The changes and modifications made by those skilled in the art do not deviate from the spirit and scope of the present application, and should be within the scope of protection of the claims attached to the present application.

Claims

1. A method for preparing single-walled carbon nanotubes, characterized in that: The method uses paraffin as a carbon source, firstly mixes paraffin, a catalyst and a co-catalyst in a certain ratio to prepare a reaction raw material, places the reaction raw material in an electric arc furnace, and introduces a carrier gas, under the action of the electric arc, the paraffin, the catalyst and the co-catalyst evaporate simultaneously, and interact with each other to generate single-walled carbon nanotubes, and then uses the airflow to take out the generated single-walled carbon nanotubes, that is, to obtain single-walled carbon nanotubes. The method is specifically as follows: S1) paraffin, catalyst and co-catalyst are weighed respectively according to the designed ratio, mixed and evenly pressed into block or granular particles as reaction raw materials, and loaded into a storage tank of a plasma arc furnace for standby use; The mass percentage of the paraffin wax to the reaction raw materials is 1%-99%, and the mass ratio of the catalyst to the co-catalyst is 5:1-50:1; S2) firstly introduce an inert gas to evacuate, then introduce a mixed carrier gas into the plasma arc furnace at a certain flow rate, and then start the plasma arc to form a plasma arc between the anode and the cathode, and heat the reaction chamber in the arc furnace to a certain temperature; S3) feeding the reaction raw materials in the storage tank into the anode graphite crucible of the plasma arc furnace through the feed pipe, under the action of the electric arc, the catalyst and paraffin are evaporated to generate single-walled carbon nanotubes, and the reaction product is taken out from the discharge port by the airflow of the mixed carrier gas, so as to obtain single-walled carbon nanotubes.

2. The method according to claim 1, characterized in that The catalyst is one or more of iron powder, iron oxide, nickel powder, nickel oxide, cobalt powder and cobalt oxide; the promoter is sulfur powder.

3. The method according to claim 1, characterized in that The flow rate of the mixed carrier gas in S2) is 10-1000 L / min, and the temperature of the reaction chamber is heated to 800-2000°C.

4. The method according to claim 3, characterized in that The mixed carrier gas includes hydrogen, water vapor and inert gas; wherein the volume of the mixed carrier gas is 5-50% by hydrogen, the volume of the mixed carrier gas is 0.1-10% by water vapor, and the volume of the mixed carrier gas is 40-95% by inert gas.

5. The method according to claim 4, characterized in that The inert gas is one or more of nitrogen, argon and helium.

6. The method according to claim 1, characterized in that The power of the arc in S3) is not less than 10kW, the voltage is 30-150V, and the current is 200-2000A.

7. A single-walled carbon nanotube, characterized in that: The single-walled carbon nanotubes are prepared by the preparation method according to any one of claims 1 to 6.

8. The single-walled carbon nanotube according to claim 7, characterized in that: The single-walled carbon nanotubes G / I D The ratio is not less than 37, and the TG residue of the obtained product is less than 40.0%.

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