Preparation method of carbon nanotube with high specific surface area

Abstract

The invention discloses a preparation method of a carbon nanotube with a high specific surface area. The preparation method of the carbon nano tube with the high specific surface area comprises the following steps: (1) adding a multi-walled carbon nano tube into alkali liquor, and mixing through ultrasonic dispersion to obtain black turbid liquid; (2) carrying out solid-liquid separation and drying on the black turbid liquid obtained in the step (1) to obtain adsorbed carbon nanotubes; and (3) putting the carbon nano tube obtained in the step (2) into a microwave heating device, and carrying out microwave treatment in an inert atmosphere under a closed condition to obtain the carbon nano tube with the high specific surface area. According to the method, the carbon nanotubes adsorbing the alkali liquor with the specific formula are treated through microwaves, the specific surface area of the carbon nanotubes is greatly increased, operation is easy, the alkali dosage is small, pollution is small, and good application prospects are achieved.

Description

Technical Field

[0001] The invention belongs to the field of carbon materials, and specifically relates to a method for preparing carbon nanotubes with high specific surface area. Background Art

[0002] Carbon nanotubes have a unique hollow structure, strong adsorption capacity, and excellent electrical conductivity. They are ideal catalyst carriers and have the potential to separate photogenerated electrons and holes. The main methods for preparing carbon nanotubes include arc method, chemical vapor deposition method, laser evaporation method, solar method, and low-temperature solid-state pyrolysis method. However, the common disadvantage of carbon nanotubes prepared by the above methods is that the specific surface area is small, especially for multi-walled carbon nanotubes. If they are not specially treated, the specific surface area is generally not more than 200 m 2 / g, which seriously affects the application performance of carbon nanotubes in adsorption separation, electrodes, etc., because these fields usually require materials with a large specific surface area to accommodate adsorbates and electrolytes. For example, if carbon nanotubes are used as hydrogen storage materials, the size of their specific surface area is of decisive significance.

[0003] Chemical Industry Progress (2010, 29(4): 704-709) used water vapor as an activator and microwave carbonization under nitrogen protection to prepare activated nanocarbon fibers, whose specific surface area increased significantly, and the micropore volume accounted for a large proportion of the total pore volume; Electronic Components and Materials (2010, 29(6): 28-30) used petroleum coke as a raw material and KOH as an activator, and prepared an activated carbon electrode material with a large specific surface area through microwave heating activation. CN114477141A prepared a mixed slurry by mixing a carbon source, an organic iron catalyst and a co-catalyst, and passed it into a microwave plasma cloud reaction device using H2 or Ar / H2 mixed carrier gas, and continuously generated oligo-walled carbon nanotube fibers with a large specific surface area by in-situ reaction.

[0004] The above modification method is beneficial to increase the specific surface area of ​​carbon nanotubes, but the preparation process is cumbersome, the operation is complicated, and the effect of strong alkali on the inner surface of carbon nanotubes is limited. At the same time, a large amount of strong alkali seriously pollutes the environment. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention provides a method for preparing carbon nanotubes with high specific surface area. The present invention greatly improves the specific surface area of ​​carbon nanotubes by microwave treatment of carbon nanotubes adsorbing a specific formula of alkali solution, has simple operation, small alkali dosage, low pollution, and has good application prospects.

[0006] The method for preparing high specific surface area carbon nanotubes of the present invention comprises the following contents: (1) adding multi-walled carbon nanotubes into an alkaline solution and mixing them by ultrasonic dispersion to obtain a black suspension; (2) performing solid-liquid separation and drying on the black suspension of step (1) to obtain adsorbed carbon nanotubes; (3) Placing the carbon nanotubes obtained in step (2) in a microwave heating device and subjecting them to microwave treatment in an inert atmosphere and sealed conditions to obtain carbon nanotubes with a high specific surface area.

[0007] In the method of the present invention, the multi-walled carbon nanotubes in step (1) have a length of 5-30 μm, an inner diameter of 3-25 nm, a wall thickness of 5-25 nm, and a specific surface area of ​​10-300 m 2 / g, the aspect ratio of the nanotubes is 200-1500; the multi-walled carbon nanotubes can be commercially available or homemade.

[0008] In the method of the present invention, the alkali solution in step (1) comprises an inorganic base, water, a low-carbon alcohol and an amide; the mass percentages of the components based on the mass of the alkali solution are: 10%-40% of the inorganic base, 40%-80% of the water, 5%-20% of the low-carbon alcohol and 1%-10% of the amide.

[0009] The inorganic base is one or more of sodium hydroxide, potassium hydroxide, rubidium hydroxide and cesium hydroxide. The low-carbon alcohol is a monohydric alcohol or polyhydric alcohol with a carbon number not greater than 5, preferably one or more of methanol, ethanol or propanol.

[0010] The amide is one or more of formamide, acetamide or dimethylformamide. In the method of the present invention, the amount of the alkali solution in step (1) is to ensure that the carbon nanotube powder can be fully wetted, and the final alkali loading is 10%-100% of the mass of the carbon nanotubes. It is further preferred that the impregnation solid-liquid mass ratio is determined according to the equal volume impregnation method, and the alkali loading is 20%-40%.

[0011] In the method of the present invention, the ultrasonic dispersion treatment conditions in step (1) are: ultrasonic treatment time is 5-60 minutes, ultrasonic power is 40-720W, ultrasonic frequency is 20-100kHz, and ultrasonic temperature is 5-90°C. The ultrasonic dispersion treatment conditions are preferably: time is 10-30 minutes, power is 40-100W, ultrasonic frequency is 20-60kHz, and ultrasonic temperature is 10-60°C.

[0012] In the method of the present invention, the solid-liquid separation in step (2) is a conventional dry method, including but not limited to filtration, centrifugation, precipitation and the like.

[0013] In the method of the present invention, the drying conditions in step (2) are: drying temperature of 30-200° C., drying time of 1-24 hours, preferably drying temperature of 100-150° C., drying time of 3-12 hours.

[0014] The drying in step (2) is further preferably vacuum drying, and the operating conditions are pressure 0-100 Pa, temperature 20-200° C., and time 3-24 hours, preferably pressure 0-40 Pa, temperature 100-150° C., and time 6-12 hours.

[0015] In the method of the present invention, the microwave treatment conditions in step (3) are: microwave frequency of 0.3-100 GHz, microwave power of 200-4000 W, treatment time of 5-60 minutes, and treatment temperature of 200-500° C., preferably: microwave frequency of 2.40-2.50 GHz, microwave power of 400-2500 W, treatment time of 10-30 minutes, and treatment temperature of 300-450° C.

[0016] In the method of the present invention, the inert atmosphere in step (3) is an inert gas and / or nitrogen.

[0017] The high specific surface carbon nanotubes prepared by the method of the present invention have the following properties: length of 2-30 μm, inner diameter of the tube of 2-20 nm, wall thickness of 3-25 nm, specific surface area of ​​800-2000 m 2 / g, and the aspect ratio of the nanotubes is 100-1400.

[0018] Compared with the prior art, the method of the present invention has the following advantages: the multi-walled carbon nanotubes of the present invention greatly improve the specific surface area of ​​the product by adsorbing alkali solution of a specific formula and processing technology, with short reaction time, small amount of alkali used, safety and environmental protection. The low-carbon alcohol in the alkali solution can reduce the surface tension of the solution, and combined with the ultrasonic effect, the alkali solution can be fully adsorbed inside and outside the carbon nanotubes. The amide contained in the alkali solution can inhibit the aggregation of the alkali solution during the microwave treatment process and improve the uniformity of microwave modification; at the same time, activation in a closed inert atmosphere can cause the carbon nanotubes to microscopically expand, which is beneficial to the etching of the carbon nanotubes by the alkali, resulting in defects and increasing the specific surface area. Figure Description BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a scanning electron microscope (SEM) photograph of the carbon nanotubes with a high specific surface area obtained in Example 1. DETAILED DESCRIPTION

[0020] The present invention will be described in more detail through examples, but the protection scope of the present invention is not limited to these examples. The length, diameter, inner diameter, aspect ratio and wall thickness of the nanotubes are measured based on the transmission electron microscope images taken, and the average value is calculated by measuring at least 20 sets of data. The loading amount of carbon nanotube alkali is calculated by weighing method. The specific surface area is tested by low temperature nitrogen physical adsorption instrument, and the specific surface area is characterized according to the BET calculation formula. Example 1

[0021] Prepare alkali solution, weigh a certain amount of potassium hydroxide, water, ethanol, and formamide, the proportion of each component by mass is: 25% potassium hydroxide, 50% water, 15% ethanol, 10% formamide. Immerse the carbon nanotubes in the alkali solution and use an ultrasonic disperser (100W, 40KHz) to disperse them at room temperature (20°C) for 10 minutes. The amount of alkali solution must ensure that the carbon nanotube powder can be fully wetted. The carbon nanotubes used are commercially available products with an average length of 10.2μm, an inner diameter of 8nm, a wall thickness of 4.8nm, an aspect ratio of 607, and a specific surface area of ​​39m 2 / g,. After the carbon nanotubes fully absorb the alkali solution, filter and then dry at 120°C for 6 hours. Calculated based on the dried carbon nanotubes, the final alkali loading is 30% of the mass of the carbon nanotubes. The dried carbon nanotube powder is placed in a microwave radiation heating device, and in an inert gas atmosphere, microwave radiation heating is performed for 15 minutes to raise the temperature to 400°C and then kept warm for 30 minutes. The microwave frequency is 2.45GHz and the microwave power is 1500W.

[0022] After natural cooling, the carbon nanotubes with high specific surface area were obtained. According to the test, the average length was 9.8 μm, the inner diameter was 7.1 nm, the wall thickness was 3.8 nm, the aspect ratio of the nanotubes was 9:13, and the specific surface area was 1545 m 2 / g. Example 2

[0023] Prepare alkali solution, weigh a certain amount of sodium hydroxide, water, ethanol, and formamide, the proportion of each component by mass is: 20% sodium hydroxide, 50% water, 20% ethanol, 10% formamide. Immerse the carbon nanotubes in the alkali solution and use an ultrasonic disperser (100W, 40KHz) to disperse them at 30°C for 20 minutes. The amount of alkali solution must ensure that the carbon nanotube powder can be fully wetted. The carbon nanotubes used are commercially available products with an average length of 10.2μm, an inner diameter of 8nm, a wall thickness of 4.8nm, an aspect ratio of 607, and a specific surface area of ​​39m 2 / g,. After the carbon nanotubes fully absorb the alkali solution, filter and then dry at 100°C for 8 hours. Calculated based on the dried carbon nanotubes, the final alkali loading is 25% of the mass of the carbon nanotubes. The dried carbon nanotube powder is placed in a microwave radiation heating device, and in an inert gas atmosphere, microwave radiation heating is performed for 10 minutes to raise the temperature to 350°C and then kept warm for 30 minutes. The microwave frequency is 2.45GHz and the microwave power is 1000W.

[0024] After natural cooling, the carbon nanotubes with high specific surface area were obtained. According to the test, the average length was 8.7 μm, the inner diameter was 7.3 nm, the wall thickness was 4.0 nm, the aspect ratio of the nanotubes was 853, and the specific surface area was 1217 m 2 / g. Example 3

[0025] Prepare alkali solution, weigh a certain amount of potassium hydroxide, water, ethanol, and formamide, the proportion of each component by mass is: 30% potassium hydroxide, 55% water, 10% ethanol, and 5% formamide. Immerse the carbon nanotubes in the alkali solution and use an ultrasonic disperser (100W, 40KHz) to disperse them at 40°C for 30 minutes. The amount of alkali solution must ensure that the carbon nanotube powder can be fully wetted. The carbon nanotubes used are commercially available products with an average length of 10.2μm, an inner diameter of 8nm, a wall thickness of 4.8nm, an aspect ratio of 607, and a specific surface area of ​​39m 2 / g, after the carbon nanotubes fully absorb the alkali solution, filter and then dry at 150°C for 10 hours. Calculated based on the dried carbon nanotubes, the final alkali loading is 35% of the mass of the carbon nanotubes. The dried carbon nanotube powder is placed in a microwave radiation heating device, and in an inert gas atmosphere, microwave radiation heating is performed for 5 minutes to raise the temperature to 300°C and then kept warm for 30 minutes. The microwave frequency is 2.45GHz and the microwave power is 800W.

[0026] After natural cooling, the high specific surface carbon nanotubes were obtained. According to the test, the average length was 8.4 μm, the inner diameter was 7.3 nm, the wall thickness was 4.1 nm, the aspect ratio of the nanotubes was 620, and the specific surface area was 1048 m 2 / g. Example 4

[0027] Prepare alkali solution, weigh a certain amount of sodium hydroxide, water, ethanol, and formamide, the mass ratio of each component is: 35% sodium hydroxide, 55% water, 5% ethanol, and 5% formamide. Immerse the carbon nanotubes in the alkali solution and use an ultrasonic disperser (100W, 40KHz) to disperse them at 50°C for 40 minutes. The amount of alkali solution must ensure that the carbon nanotube powder can be fully wetted. The carbon nanotubes used are commercially available products with an average length of 10.2 μm, an inner diameter of 8 nm, a wall thickness of 4.8 nm, an aspect ratio of 607, and a specific surface area of ​​39 m 2 / g. After the carbon nanotubes fully absorb the alkali solution, they are filtered and then dried at 150°C for 15 hours. Calculated based on the dried carbon nanotubes, the final alkali loading is 40% of the mass of the carbon nanotubes. The dried carbon nanotube powder is placed in a microwave radiation heating device, and in an inert gas atmosphere, the temperature is raised to 450°C for 15 minutes and then kept warm for 30 minutes. The microwave frequency is 2.45GHz and the microwave power is 2000W.

[0028] After natural cooling, the high specific surface carbon nanotubes were obtained. According to the test, the average length was 7.5 μm, the inner diameter was 7.2 nm, the wall thickness was 3.9 nm, the aspect ratio of the nanotubes was 737, and the specific surface area was 962 m 2 / g. Example 5

[0029] The same as Example 1, except that the final alkali loading is 110% of the mass of the carbon nanotubes. The specific surface area of ​​the carbon nanotubes obtained by testing is 565 m 2 / g.

[0030] Comparative Example 1 The same as Example 1, except that no low-carbon alcohol and amide were added. The specific surface area of ​​the obtained carbon nanotubes was 508 m 2 / g.

[0031] Comparative Example 2 The same as Example 1, except that an electromagnetic heater was used to heat the carbon nanotubes instead of a microwave radiation heating device. The specific surface area of ​​the obtained carbon nanotubes was 376 m 2 / g.

[0032] Comparative Example 3 The same as Example 1, except that microwave heating was performed under air atmosphere, and the specific surface area of ​​the obtained carbon nanotubes was 593 m 2 / g.

Claims

1. A method for preparing high specific surface area carbon nanotubes, characterized in that The method comprises the following contents: (1) adding multi-walled carbon nanotubes into an alkaline solution and mixing them by ultrasonic dispersion to obtain a black suspension; (2) subjecting the black suspension obtained in step (1) to solid-liquid separation and drying to obtain adsorbed carbon nanotubes; and (3) placing the carbon nanotubes obtained in step (2) in a microwave heating device and subjecting them to microwave treatment in an inert atmosphere and sealed conditions to obtain carbon nanotubes with a high specific surface area.

2. The method according to claim 1, characterized in that: The multi-walled carbon nanotubes described in step (1) have a length of 5-30 μm, an inner diameter of 3-25 nm, a wall thickness of 5-25 nm, and a specific surface area of ​​10-300 m 2 / g, and the aspect ratio of the nanotubes is 200-1500.

3. The method according to claim 1, characterized in that: The alkali solution in step (1) comprises an inorganic base, water, a low-carbon alcohol and an amide; the mass percentage of each component based on the mass of the alkali solution is: 10%-40% of the inorganic base, 40%-80% of water, 5%-20% of the low-carbon alcohol and 1%-10% of the amide.

4. The method according to claim 4, characterized in that: The inorganic base is one or more of sodium hydroxide, potassium hydroxide, rubidium hydroxide and cesium hydroxide.

5. The method according to claim 4, characterized in that: The low-carbon alcohol is a monohydric alcohol or a polyhydric alcohol having a carbon number not greater than 5, preferably one or more of methanol, ethanol or propanol.

6. The method according to claim 4, characterized in that: The amide is one or more of formamide, acetamide or dimethylformamide.

7. The method according to claim 1, characterized in that: The amount of the alkali solution in step (1) should be sufficient to fully wet the carbon nanotube powder, and the final alkali loading is 10%-100% of the mass of the carbon nanotubes, preferably 20%-40%.

8. The method according to claim 1, characterized in that: The ultrasonic dispersion treatment conditions in step (1) are as follows: ultrasonic treatment time is 5-60 minutes, ultrasonic power is 40-720W, ultrasonic frequency is 20-100kHz, and ultrasonic temperature is 5-90°C.

9. The method according to claim 1, characterized in that: The drying conditions in step (2) are: drying temperature 30-200° C., and drying time 1-24 hours.

10. The method according to claim 1, characterized in that: The microwave treatment conditions in step (3) are as follows: microwave frequency of 0.3-100 GHz, microwave power of 200-4000 W, treatment time of 5-60 minutes, and treatment temperature of 200-500° C.; preferably, microwave frequency of 2.40-2.50 GHz, microwave power of 400-2500 W, treatment time of 10-30 minutes, and treatment temperature of 300-450° C.

11. The method according to claim 1, characterized in that: The inert atmosphere in step (3) is an inert gas and / or nitrogen.

12. The high specific surface area carbon nanotubes prepared by the method according to claims 1 to 11, characterized in that It has the following properties: length 2-30μm, inner diameter 2-20nm, wall thickness 3-25nm, specific surface area 800-2000m 2 / g, and the aspect ratio of the nanotubes is 100-1400.

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