Catalyst and preparation method thereof, carbon nanotube and preparation method thereof

Abstract

This application relates to the field of carbon nanotube catalyst materials, specifically disclosing a catalyst and a preparation method thereof, and carbon nanotubes and a preparation method thereof. A carbon nanotube catalyst is formed into amorphous nanocrystals, wherein the amorphous nanocrystals include microwave-active metal ions. The catalyst preparation method comprises: S1, raw material preparation; S2, microwave-assisted coprecipitation; S3, calcination treatment. A carbon nanotube is prepared using the above-mentioned catalyst; the carbon nanotube powder has a resistivity greater than 20 mΩ·cm and less than 30 mΩ·cm. The carbon nanotubes prepared using the catalyst of this application have a high yield and excellent electrical conductivity.

Description

Technical Field

[0001] The present application relates to the field of carbon nanotube catalyst materials, and in particular to a catalyst and a preparation method thereof, and carbon nanotubes and a preparation method thereof. Background Art

[0002] As a new material, carbon nanotubes (CNTs) have enormous potential for application in nanocomposites, supercapacitors, flat-panel displays, electron microscope probes, nanowires, and hydrogen storage. Generally speaking, CNTs can be divided into array-type CNTs and clustered CNTs based on their microscopic aggregation state.

[0003] The main methods for producing carbon nanotubes include direct current arc (DC) ablation, laser ablation, and catalytic chemical vapor deposition (CCVD). DC arc and laser ablation methods produce straighter carbon nanotubes with a higher degree of graphitization, but their yields are extremely low and their purity is poor, making continuous production impossible. In contrast, CCVD offers higher yields and higher purity, enabling industrialized, large-scale, continuous production.

[0004] A related Chinese invention patent, CN106379886A, discloses a high-loading carbon nanotube catalyst and a method for preparing carbon nanotubes using the same, belonging to the field of nanomaterials. The high-loading carbon nanotube catalyst uses a low-valent metal salt from a variable-valent metal salt as a precursor, synthesized under inert gas protection and then calcined at high temperature. The low-valent metal element accounts for 10-90% of the total metal element mass of the catalyst. The high-loading carbon nanotube catalyst is then used to synthesize carbon nanotubes using a vapor deposition method. This invention not only increases the loading of the low-valent metal element in the carbon nanotube catalyst, simplifies the catalyst production process, and increases catalyst yield, but also produces carbon nanotubes with small diameter and uniform quality. The process is simple and the yield is high, showing good prospects in the industrial production of carbon nanotubes.

[0005] In response to the above-mentioned related technologies, the inventors believe that the existing catalysts have defects in the process of catalytically preparing carbon nanotubes, such as slow reaction speed, long aging time, and large crystal particle size, which are not conducive to the growth of high-quality and high-yield carbon nanotubes. Summary of the Invention

[0006] In order to improve the defects of the existing carbon nanotube catalyst process such as slow reaction speed, long aging time, and large crystal particle size, the present application provides a catalyst and a preparation method thereof, carbon nanotubes and a preparation method thereof.

[0007] In a first aspect, the present application provides a catalyst for carbon nanotubes, which adopts the following technical solution:

[0008] A catalyst for carbon nanotubes is formed into amorphous nanocrystals. The amorphous nanocrystals contain metal ions with microwave activity.

[0009] By employing the aforementioned technical solution, the present application optimizes the structure of the catalyst material and prepares the catalyst into amorphous nanocrystals. Since the catalyst significantly influences the structural properties of carbon nanotubes during their actual growth and production, the amorphous nanocrystals prepared from the optimized microwave-active metal ions in the present application exhibit higher activity and are more suitable for mass production of carbon nanotubes with superior yield and conductivity.

[0010] The technical solution of the present application selects metal ions with microwave activity to prepare the amorphous nanocrystals, so that during the actual production process of this type of catalyst, a thermal effect is generated by stimulating the dipole steering polarization and interface polarization of polar microscopic particles, thereby effectively improving the preparation efficiency of the catalyst material.

[0011] Preferably, the metal ions having microwave activity include one or more of Fe, Co, Ni, Mg, Al, Mo, and La.

[0012] By adopting the above technical solution, the present application further optimizes the metal ions with microwave activity. The catalyst material prepared by the above-mentioned metal ions with microwave activity can continuously vibrate and move under the auxiliary conditions of microwave heating, thereby accelerating the preparation speed of the prepared catalyst material and reducing the defects of the catalyst material itself.

[0013] In a second aspect, the present application provides a method for preparing a catalyst for carbon nanotubes, comprising the following preparation steps:

[0014] S1. Raw material preparation: mixing metal ion salt solutions containing at least two metal ions having microwave activity to prepare a mixed solution;

[0015] S2. Microwave-assisted coprecipitation: adding an alkaline salt solution to the mixed solution under a microwave environment, maintaining the temperature and stirring for coprecipitation reaction, and after the coprecipitation reaction, allowing the mixture to stand for aging to obtain a coprecipitation reaction product;

[0016] S3. Calcination treatment: The coprecipitated reactants are washed and dried, and after calcination treatment, allowed to stand and cool to room temperature, and then ground and sieved to prepare a catalyst for carbon nanotubes.

[0017] By adopting the above-mentioned technical solution, the present application prepares catalyst materials for carbon nanotubes with the assistance of microwaves. Since the microwave radiation generated by microwave assistance has the characteristic of rapid heating, the polar molecules can quickly obtain energy and intensify their movement, which significantly shortens the crystallization time, thereby saving the time of catalyst production and reaction and improving production efficiency.

[0018] Secondly, during the growth of carbon nanotubes using catalytic chemical vapor deposition, if the carbon source decomposition and diffusion rate exceeds the carbon nanotube growth rate, the carbon atoms diffused through the metal particles will not have enough time to grow into well-structured carbon nanotubes, resulting in a relatively coarse tube wall structure. Therefore, the technical solution of this application uses a salt solution containing at least two microwave-active metal ions when selecting raw materials. The purpose is to enhance the activity of the prepared catalyst material, thereby achieving an appropriate decomposition rate during the catalytic production of carbon nanotubes, and thus obtaining carbon nanotubes with a better microstructure.

[0019] Preferably, the alkaline salt solution in step S2 includes one or two of sodium carbonate solution, sodium bicarbonate solution, ammonium carbonate solution, ammonium bicarbonate solution or urea solution.

[0020] By adopting the above technical solution, the present application optimizes the type of alkaline salt solution, and prepares a catalyst material with excellent structure by co-precipitation of the alkaline salt solution and a metal ion salt with microwave activity under microwave conditions, thereby producing carbon nanotube products with high rate and good conductivity.

[0021] Preferably, the microwave heating in step S2 includes: adjusting the microwave power to 500-3000 W, controlling the microwave heating reaction temperature to 55° C.-100° C., and the microwave reaction time to 0.5-6 h.

[0022] By adopting the above technical solution, the present application further optimizes the microwave-assisted solution and adjusts the microwave power, temperature and time. Due to the long-term high-power effect, the movement of polar molecules will be intensified, the interaction between them and the layers will be enhanced, while the van der Waals effect between the layers will be weakened, so that the orderliness along the stacking direction of the laminate will be reduced, so it is necessary to control the microwave power, temperature and time well. Prolonging the crystallization time or increasing the crystallization power will lead to incomplete material structure of crystallization production, so it is necessary to adjust the microwave-assisted conditions so that the regularity of the catalyst prepared by it is effectively improved, so that the catalyst can produce a carbon nanotube product with high rate and good electrical conductivity.

[0023] Preferably, the temperature of the static aging in step S2 is 60-100° C., and the static aging time is 1-12 hours.

[0024] By adopting the above technical solution, the present invention further optimizes the temperature of static aging, and by adjusting the temperature of static aging, the OH- or CO3 generated by ionization or hydrolysis in the alkaline salt solution is 2- The catalyst reacts and co-precipitates with microwave-active metal ions. Under alkaline conditions, the nanocrystalline particles are continuously precipitated and grown, and the growth rate of the catalyst is increased under microwave-assisted conditions, so that the catalyst can produce carbon nanotube products with high rate and good conductivity.

[0025] Preferably, the calcination temperature in step S3 is 400-900° C., and the calcination time is 0.5-5 h.

[0026] By adopting the above-mentioned technical solution, the present application further optimizes the calcination temperature and time. Since calcination optimizes the activity of the catalyst material, but long-term high-temperature treatment may be affected by the generated spinel phase, the present application optimizes the calcination temperature and time, which can effectively improve its activity without destroying the activity of the catalyst of the present application.

[0027] In a third aspect, the present application also provides a carbon nanotube prepared by using the above catalyst;

[0028] Preferably, the resistivity of the carbon nanotube powder is greater than 20 mΩ·cm and less than 30 mΩ·cm.

[0029] By adopting the above technical solution, the present application prepares carbon nanotubes by catalysis with a high rate and excellent conductive properties.

[0030] In a fourth aspect, the present application further provides a method for preparing carbon nanotubes, comprising the following preparation steps:

[0031] The catalyst is placed in a reactor, and the temperature is programmed to 700-750° C. under protective gas. Then, the protective gas is stopped and replaced with carbon source gas. The catalytic reaction is carried out at 700-750° C. for 20-50 minutes to obtain the carbon nanotubes.

[0032] By adopting the above technical solution, the present application optimizes the preparation method of carbon nanotubes. By selecting carbon source gas as raw material for preparation, the prepared carbon nanotubes have a higher rate and relatively excellent conductive properties.

[0033] Preferably, the mass ratio of the carbon nanotubes to the catalyst is greater than 15, that is, the ratio is greater than 15; more preferably, the ratio is between 15-50.

[0034] By adopting the above technical solution, the present application optimizes the addition ratio between carbon nanotubes and catalysts, which can further improve the production efficiency of carbon nanotubes while reducing the usage ratio of catalysts, thereby effectively improving the performance and quality of the produced carbon nanotubes.

[0035] In summary, this application has the following beneficial effects:

[0036] First, by employing the aforementioned technical solution, this application optimizes the structure of the catalyst material, preparing it into amorphous nanocrystals. Since the catalyst significantly influences the structural properties of carbon nanotubes during their actual growth and production, the amorphous nanocrystals prepared from the optimized microwave-active metal ions in this application exhibit higher activity, making them more suitable for mass production of carbon nanotubes with superior yield and conductivity.

[0037] The technical solution of the present application selects metal ions with microwave activity to prepare the amorphous nanocrystals, so that during the actual production process of this type of catalyst, a thermal effect is generated by stimulating the dipole steering polarization and interface polarization of polar microscopic particles, thereby effectively improving the preparation efficiency of the catalyst material.

[0038] Second, the present application uses microwave-assisted preparation of catalyst materials for carbon nanotubes. Since the microwave radiation generated by microwave assistance has the characteristic of rapid heating, polar molecules can quickly obtain energy and intensify their movement, which significantly shortens the crystallization time, thereby saving catalyst production and reaction time and improving production efficiency.

[0039] Secondly, during the growth of carbon nanotubes using catalytic chemical vapor deposition, if the carbon source decomposition and diffusion rate exceeds the carbon nanotube growth rate, the carbon atoms diffused through the metal particles will not have enough time to grow into well-structured carbon nanotubes, resulting in a relatively coarse tube wall structure. Therefore, the technical solution of this application uses a salt solution containing at least two microwave-active metal ions when selecting raw materials. The purpose is to enhance the activity of the prepared catalyst material, thereby achieving an appropriate decomposition rate during the catalytic production of carbon nanotubes, and thus obtaining carbon nanotubes with a better microstructure.

[0040] Third, the present application further optimizes the microwave-assisted scheme and adjusts the microwave power, temperature and time. Since long-term high-power action will intensify the movement of polar molecules, enhance their interaction with the interlayer, and weaken the van der Waals interaction between the layers, so that the order along the stacking direction of the laminate is reduced, it is necessary to control the microwave power, temperature and time well. Prolonging the crystallization time or increasing the crystallization power will lead to incomplete material structure of crystallization production, so it is necessary to adjust the microwave-assisted conditions so that the regularity of the microstructure of the catalyst prepared is effectively improved, so that the catalyst can produce carbon nanotube products with high rate and good electrical conductivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is a SEM image of the catalyst prepared in Example 1 of the present application;

[0042] Figure 2 This is a SEM image of the carbon nanotubes prepared in Example 1 of the present application;

[0043] Figure 3 This is a SEM image of the catalyst prepared in Example 4 of the present application;

[0044] Figure 4 This is the SEM image of the carbon nanotubes prepared in Example 4 of the present application. DETAILED DESCRIPTION

[0045] The present application is further described in detail below with reference to the embodiments. Example

[0046] Example 1

[0047] The raw materials of a carbon nanotube catalyst are aluminum nitrate nonahydrate and sodium carbonate.

[0048] A method for preparing a catalyst for carbon nanotubes:

[0049] S1. Prepare raw materials: dissolve 20 g of aluminum nitrate nonahydrate in 500 mL of deionized water to form solution A, and dissolve 50 g of anhydrous sodium carbonate in 500 mL of deionized water to form solution B;

[0050] S2. Microwave-assisted coprecipitation: Solution A was added to a microwave reactor, stirred, and microwave heated at 500 W. After heating to 50°C, Solution B was slowly added dropwise to the reactor, maintaining the microwave heating temperature at 50°C for 0.5 h. After the reaction, stirring was stopped, the microwave reactor temperature was set to 50°C, and aging was continued for 1 h. The reactants were removed, cooled to room temperature, filtered, washed until neutral, and dried.

[0051] S3. Calcination treatment: The dried precursor is placed in a high-temperature muffle furnace and calcined at 400° C. for 0.5 h, then cooled to room temperature. The obtained solid is ground into 100 mesh to obtain a catalyst for carbon nanotubes.

[0052] Carbon nanotubes are prepared by the following scheme: 0.5 g of a catalyst is added to a quartz boat, the quartz boat is placed in a fixed-bed reactor, the temperature is raised to 700° C. at 20° C. / min under nitrogen protection, the nitrogen flow is stopped, ethylene is introduced instead, and the reaction is carried out at 700° C. for 20 minutes to prepare the carbon nanotubes.

[0053] Example 2

[0054] The raw materials of a carbon nanotube catalyst are cobalt nitrate hexahydrate and sodium carbonate.

[0055] A method for preparing a catalyst for carbon nanotubes:

[0056] S1. Prepare raw materials: dissolve 20 g of cobalt nitrate hexahydrate in 500 mL of deionized water to form solution A, and dissolve 50 g of anhydrous sodium carbonate in 500 mL of deionized water to form solution B;

[0057] S2. Microwave-assisted coprecipitation: Solution A was added to a microwave reactor, stirred, and microwave heated at 500 W. After heating to 50°C, Solution B was slowly added dropwise to the reactor, maintaining the microwave heating temperature at 50°C for 0.5 h. After the reaction, stirring was stopped, the microwave reactor temperature was set to 50°C, and aging was continued for 1 h. The reactants were removed, cooled to room temperature, filtered, washed until neutral, and dried.

[0058] S3. Calcination treatment: The dried precursor is placed in a high-temperature muffle furnace and calcined at 400° C. for 0.5 h, then cooled to room temperature. The obtained solid is ground into 100 mesh to obtain a catalyst for carbon nanotubes.

[0059] Carbon nanotubes are prepared by the following scheme: 0.5 g of a catalyst is added to a quartz boat, the quartz boat is placed in a fixed-bed reactor, the temperature is raised to 720° C. at 20° C. / min under nitrogen protection, the nitrogen flow is stopped, ethylene is introduced instead, and the reaction is carried out at 720° C. for 30 minutes to prepare the carbon nanotubes.

[0060] Example 3

[0061] The raw materials of a carbon nanotube catalyst are ferric nitrate nonahydrate and sodium carbonate.

[0062] A method for preparing a catalyst for carbon nanotubes:

[0063] S1. Prepare raw materials: dissolve 20 g of ferric nitrate nonahydrate in 500 mL of deionized water to form solution A, and dissolve 50 g of anhydrous sodium carbonate in 500 mL of deionized water to form solution B;

[0064] S2. Microwave-assisted coprecipitation: Solution A was added to a microwave reactor, stirred, and microwave heated at 500 W. After heating to 50°C, Solution B was slowly added dropwise to the reactor, maintaining the microwave heating temperature at 50°C for 0.5 h. After the reaction, stirring was stopped, the microwave reactor temperature was set to 50°C, and aging was continued for 1 h. The reactants were removed, cooled to room temperature, filtered, washed until neutral, and dried.

[0065] S3. Calcination treatment: The dried precursor is placed in a high-temperature muffle furnace and calcined at 400° C. for 0.5 h, then cooled to room temperature. The obtained solid is ground into 100 mesh to obtain a catalyst for carbon nanotubes.

[0066] Carbon nanotubes are prepared by the following scheme: 0.5 g of a catalyst is added to a quartz boat, the quartz boat is placed in a fixed-bed reactor, the temperature is raised to 750° C. at 20° C. / min under nitrogen protection, the nitrogen flow is stopped, ethylene is introduced instead, and the reaction is carried out at 750° C. for 50 minutes to prepare the carbon nanotubes.

[0067] Example 4

[0068] The raw materials of a carbon nanotube catalyst are aluminum nitrate nonahydrate, cobalt nitrate hexahydrate, iron nitrate nonahydrate and sodium carbonate.

[0069] A method for preparing a catalyst for carbon nanotubes:

[0070] S1. Prepare raw materials: dissolve 10 g of aluminum nitrate nonahydrate, 9 g of cobalt nitrate hexahydrate, and 8 g of ferric nitrate nonahydrate in 500 mL of deionized water to form solution A; dissolve 50 g of anhydrous sodium carbonate in 500 mL of deionized water to form solution B;

[0071] S2. Microwave-assisted coprecipitation: Solution A was added to a microwave reactor, stirred, and microwave heated at 500 W. After heating to 50°C, Solution B was slowly added dropwise to the reactor, maintaining the microwave heating temperature at 50°C for 0.5 h. After the reaction, stirring was stopped, the microwave reactor temperature was set to 50°C, and aging was continued for 1 h. The reactants were removed, cooled to room temperature, filtered, washed until neutral, and dried.

[0072] S3. Calcination treatment: The dried precursor is placed in a high-temperature muffle furnace and calcined at 400° C. for 0.5 h, then cooled to room temperature. The obtained solid is ground into 100 mesh to obtain a catalyst for carbon nanotubes.

[0073] Carbon nanotubes are prepared by the following scheme: 0.5 g of a catalyst is added to a quartz boat, the quartz boat is placed in a fixed-bed reactor, the temperature is raised to 720° C. at 20° C. / min under nitrogen protection, the nitrogen flow is stopped, ethylene is introduced instead, and the reaction is carried out at 720° C. for 30 minutes to prepare the carbon nanotubes.

[0074] Example 5

[0075] The raw materials of a carbon nanotube catalyst are aluminum nitrate nonahydrate, magnesium nitrate hexahydrate, cobalt nitrate hexahydrate, iron nitrate nonahydrate and sodium carbonate.

[0076] A method for preparing a catalyst for carbon nanotubes:

[0077] S1. Prepare raw materials: dissolve 0.8 g of ammonium molybdate heptahydrate, 14 g of magnesium nitrate hexahydrate, 10 g of cobalt nitrate hexahydrate, and 9 g of ferric nitrate nonahydrate in 500 mL of deionized water to form solution A, and dissolve 50 g of anhydrous sodium carbonate in 500 mL of deionized water to form solution B;

[0078] S2. Microwave-assisted coprecipitation: Solution A was added to a microwave reactor, stirred, and microwave heated at 500 W. After heating to 50°C, Solution B was slowly added dropwise to the reactor. The microwave heating temperature was maintained at 50°C for 0.5 h. After the reaction, stirring was stopped, the microwave reactor temperature was set to 50°C, and aging was continued for 1 h. The reactants were removed and cooled to room temperature, then filtered, washed until neutral, and dried.

[0079] S3. Calcination treatment: The dried precursor is placed in a high-temperature muffle furnace and calcined at 400° C. for 0.5 h, then cooled to room temperature. The obtained solid is ground into 100 mesh to obtain a catalyst for carbon nanotubes.

[0080] Carbon nanotubes are prepared by the following scheme: 0.5 g of a catalyst is placed in a quartz boat, the quartz boat is placed in a fixed-bed reactor, the temperature is raised to 700° C. at 20° C. / min under nitrogen protection, the nitrogen is stopped and propylene is introduced instead, and the reaction is carried out at 700° C. for 30 minutes to prepare the carbon nanotubes.

[0081] Example 6

[0082] A carbon nanotube catalyst uses the following raw materials: Solution A: 10g of aluminum nitrate nonahydrate, 14g of magnesium nitrate hexahydrate, 10g of ferric nitrate nonahydrate and 1g of ammonium molybdate heptahydrate are dissolved in 500mL of deionized water to form solution A.

[0083] Solution B: Dissolve 20 g of anhydrous sodium carbonate and 30 g of sodium bicarbonate in 500 mL of deionized water to form solution B.

[0084] Example 7

[0085] A carbon nanotube catalyst uses the following raw materials: Solution A: 10g of zinc nitrate hexahydrate, 14g of lanthanum nitrate hexahydrate, 10g of nickel nitrate hexahydrate and 1g of ammonium molybdate heptahydrate are dissolved in 500mL of deionized water to form solution A.

[0086] Solution B: Dissolve 20 g of ammonium carbonate and 30 g of ammonium bicarbonate in 500 mL of deionized water to form solution B.

[0087] Example 8

[0088] The raw materials of a carbon nanotube catalyst are aluminum nitrate nonahydrate, magnesium nitrate hexahydrate, cobalt nitrate hexahydrate, iron nitrate nonahydrate and sodium carbonate.

[0089] The difference from Example 4 is that the microwave power used in the microwave-assisted coprecipitation is 1750 W, the microwave heating temperature is 75° C., the microwave reaction time is 3 h, the aging temperature is 80° C., the aging time is 6 h, and the calcination temperature is 750° C., and the calcination time is 2.5 h.

[0090] Example 9

[0091] The raw materials of a carbon nanotube catalyst are aluminum nitrate nonahydrate, magnesium nitrate hexahydrate, cobalt nitrate hexahydrate, iron nitrate nonahydrate and sodium carbonate.

[0092] The difference from Example 4 is that the microwave power used in the microwave-assisted coprecipitation is 3000 W, the microwave heating temperature is 100° C., the microwave reaction time is 6 h, the aging temperature is 100° C., the aging time is 12 h, and the calcination temperature is 900° C., and the calcination time is 5 h.

[0093] It should be noted that the protective gas includes but is not limited to nitrogen or one or a combination of several inert gases.

[0094] The carbon source gas includes, but is not limited to, any one of methane, ethane, propane, ethylene and propylene.

[0095] Comparative Example

[0096] Comparative Example 1

[0097] A catalyst for carbon nanotubes, which differs from Example 1 in that microwave-assisted heating is not used in Comparative Example 1, is used to produce carbon nanotubes. The specific preparation steps are as follows:

[0098] 0.5 g of catalyst was placed in a quartz boat, which was then placed in a fixed-bed reactor. The temperature was raised to 720°C at 20°C / min under nitrogen protection. The nitrogen was stopped and replaced with ethylene. The reaction was continued at 720°C for 30 minutes to prepare carbon nanotubes.

[0099] Performance testing

[0100] The carbon nanotubes prepared in Examples 1 to 9 and Comparative Example 1 were tested, specifically their resistivity and specific resistance (specific resistance refers to the ratio of the mass of the prepared carbon nanotubes to the mass of the catalyst). The test results are shown in Table 1 below; the catalysts and carbon nanotubes prepared in Examples 1 and 4 were tested by scanning electron microscopy. Figures 1 to 4 shown.

[0101] Table 1 Performance test table

[0102]

[0103] Figure 1 、 Figure 3 Schematic diagram of the catalyst structure.

[0104] Figure 2 and Figure 4 It shows that the microstructure of carbon nanotubes is a clustered structure.

[0105] Combined with Examples 1 to 9, Comparative Example 1, Figures 1 to 4 Compared with the performance test table in Table 1, we can find that:

[0106] Examples 1 to 3, Examples 4 to 5, Examples 6 to 7, Examples 8 to 9 and Comparative Example 1 were used as a comparison group for comparison, as follows:

[0107] (1) First, the performance of Examples 1 to 3 was compared with that of Comparative Example 1. As can be seen from the data in Table 1, the data of Examples 1 to 3 are significantly better than that of Comparative Example 1, indicating that the technical solution of the present application optimizes the structure of the catalyst material by preparing the catalyst into amorphous nanocrystals. Since the catalyst can significantly affect the structural properties of carbon nanotubes during the actual growth and preparation process, the amorphous nanocrystals prepared by the optimized microwave-active metal ions of the present application have higher activity and are more suitable for mass production of carbon nanotubes with better yield and conductivity.

[0108] The technical solution of the present application selects metal ions with microwave activity to prepare the amorphous nanocrystals, so that during the actual production process of this type of catalyst, a thermal effect is generated by stimulating the dipole steering polarization and interface polarization of polar microscopic particles, thereby effectively improving the preparation efficiency of the catalyst material.

[0109] (2) Comparing Examples 4 to 5, Example 1 and Comparative Example 1, the data of Examples 4 to 5 further reflect that when selecting raw materials, the present application uses a salt solution containing at least two metal ions with microwave activity, the purpose of which is to improve the activity of the prepared catalyst material so that it has a suitable cracking rate when catalyzing the production of carbon nanotubes, thereby obtaining carbon nanotubes with better microstructure.

[0110] (3) Comparing Examples 6 to 7 with Example 4, and combining the data in Table 1, it can be found that the technical solution of the present application optimizes the type of alkaline salt solution, and can prepare a catalyst material with an excellent structure by co-precipitating the alkaline salt solution with a metal ion salt having microwave activity under microwave conditions, thereby producing a carbon nanotube product with high rate and good conductivity.

[0111] (4) Comparing Examples 8 to 9 with Example 4, and combining the data in Table 1, it can be found that the technical solution of the present application further optimizes the microwave-assisted solution and adjusts the microwave power, temperature, and time. Since long-term high-power application will intensify the movement of polar molecules, enhance their interaction with the layers, and weaken the van der Waals interaction between the layers, reducing the order along the stacking direction of the layers, it is necessary to well control the microwave power, temperature, and time. However, extending the crystallization time or increasing the crystallization power will lead to incomplete structure of the crystallized material. Therefore, it is necessary to adjust the microwave-assisted conditions to effectively improve the regularity of the catalyst prepared, so that the catalyst can produce carbon nanotube products with high yield and good conductivity.

[0112] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A method for preparing carbon nanotubes, characterized in that: The preparation method comprises the following preparation steps: The catalyst is placed in a reactor, and the temperature is programmed to 700-750° C. under protective gas, and then the protective gas is stopped and replaced with a carbon source gas, and the catalytic reaction is carried out at 700-750° C. for 20-50 minutes to obtain the carbon nanotubes; The catalyst is formed into amorphous nanocrystals, and the amorphous nanocrystals include metal ions having microwave activity; The metal ions having microwave activity include two or more of Fe, Co, Ni, Mg, Al, Mo, and La; The preparation method of the catalyst comprises the following preparation steps: S1. Raw material preparation: mixing metal ion salt solutions containing at least two metal ions having microwave activity to prepare a mixed solution; S2. Microwave-assisted coprecipitation: adding an alkaline salt solution to the mixed solution under a microwave environment, maintaining the temperature and stirring for coprecipitation reaction, and after the coprecipitation reaction, allowing the mixture to stand for aging to obtain a coprecipitation reaction product; S3, calcination treatment: taking the coprecipitated reactant, washing and drying it, calcining it, letting it stand and cool to room temperature, grinding and sieving it to prepare the catalyst; The microwave heating in step S2 includes: adjusting the microwave power to 500-3000W, controlling the microwave heating reaction temperature to 55°C-100°C, and the microwave reaction time to 0.5-6h; The alkaline salt solution in step S2 includes one or two of sodium carbonate solution, sodium bicarbonate solution, ammonium carbonate solution or ammonium bicarbonate solution; The calcination temperature in step S3 is 400-900° C., and the calcination time is 0.5-5 h.

2. The method for preparing carbon nanotubes according to claim 1, wherein: The temperature of the static aging in step S2 is 60-100° C., and the static aging time is 1-12 hours.

3. The method for preparing carbon nanotubes according to claim 1, wherein: The mass ratio of the carbon nanotubes to the catalyst is greater than 15.

4. A carbon nanotube prepared by the preparation method according to any one of claims 1 to 3, characterized in that: The carbon nanotube powder has a resistivity greater than 20 mΩ·cm and less than 30 mΩ·cm.

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