Preparation method of high specific surface area carbon nanotube

Abstract

The application discloses a preparation method of high specific surface area carbon nanotubes, which comprises the following steps: (1) adding low specific surface area carbon nanotubes into alkaline solution, mixing through ultrasonic dispersion to obtain black suspension; (2) performing solid-liquid separation and drying on the black suspension in step (1) to obtain adsorbed carbon nanotubes; and (3) performing ball milling treatment on the carbon nanotubes obtained in step (2), and then performing washing, drying and calcination to obtain the high specific surface area carbon nanotubes. The method is simple in operation, small in pollution, high in specific surface area of the obtained carbon nanotubes, and has a good application prospect.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of carbon materials, and relates to a preparation method of high specific surface area carbon nanotubes. BACKGROUND

[0002] Carbon nanotubes have unique hollow structure, strong adsorption capacity and excellent electrical conductivity, and are ideal catalyst carriers and have the potential of separating photo-generated electrons and holes. The preparation methods of carbon nanotubes mainly include arc method, chemical vapor deposition method, laser evaporation method, solar energy method and low-temperature solid pyrolysis method. However, the common deficiency of the carbon nanotubes prepared by the above methods is that the specific surface area is small, especially for multi-walled carbon nanotubes, and the specific surface area is generally not more than 200 m 2 / g without special treatment, which seriously affects the application performance of the carbon nanotubes in the fields of adsorption separation and electrode, because the materials usually require a large specific surface area to accommodate adsorbents and electrolyte. For example, the specific surface area of the carbon nanotubes used as hydrogen storage materials is of decisive significance.

[0003] Physical Chemistry (2006, 22(1): 43-47) uses KOH as an activator to significantly improve the specific surface area of multi-walled carbon nanotubes after high-temperature treatment; Carbon (2002, 40: 1597-1617) obtains carbon nanotubes with a specific surface area of about 1000 m 2 / g by using the KOH high-temperature activation method. The preparation process of the above alkali high-temperature activation method is complicated, the graphite structure of the obtained carbon nanotubes is inevitably damaged to a certain extent, and a large amount of strong alkali is used, which pollutes the environment.

[0004] CN200710043671.6 mixes carbon nanotubes with strong alkali with a mass of 5-50 times of the carbon nanotubes, ball-mills and then obtains modified carbon nanotubes through post-treatment. The modification method is beneficial to improve the specific surface area of the carbon nanotubes, but when the solid-phase mixing is used, the strong alkali is difficult to enter the inside of the carbon nanotubes, so the modification only occurs on the surface of the carbon nanotubes, and the effect on the inner surface of the carbon nanotubes is limited. Meanwhile, a large amount of strong alkali is used in the method, which seriously pollutes the environment. SUMMARY

[0005] In view of the deficiencies of the prior art, the present application provides a preparation method of high specific surface area carbon nanotubes. The method of the present application is simple in operation, small in pollution, has high specific surface area of the obtained carbon nanotubes, and has a good application prospect.

[0006] The preparation method of high specific surface area carbon nanotubes of the present application comprises the following contents:

[0007] (1) adding low specific surface carbon nanotubes into alkali solution, mixing through ultrasonic dispersion to obtain black suspension;

[0008] (2) the black suspension of step (1) is subjected to solid-liquid separation and drying to obtain carbon nanotubes after adsorption;

[0009] (3) the carbon nanotubes obtained in step (2) are subjected to ball milling, and then are washed, dried and calcined to obtain the high specific surface area carbon nanotubes.

[0010] In the method, the low specific surface area carbon nanotubes of step (1) are commercially available or self-made multi-walled carbon nanotubes, with a length of 5-30 μm, an inner diameter of 3-25 nm, a wall thickness of 5-25 nm, a specific surface area of 10-300 m 2 / g, and an aspect ratio of 200-1500.

[0011] In the method, the alkali liquor of step (1) comprises inorganic alkali, water, low carbon alcohol and amide; the mass percentage of each component in the alkali liquor is as follows: the inorganic alkali is 10%-40%, the water is 40%-80%, the low carbon alcohol is 5%-20%, and the amide is 1-10%.

[0012] The inorganic alkali is one or more of sodium hydroxide, potassium hydroxide, rubidium hydroxide and cesium hydroxide. The low carbon alcohol is monohydric alcohol and polyhydric alcohol with a carbon number of not more than 5, and is preferably one or more of methanol, ethanol or propanol.

[0013] The amide is one or more of formamide, acetamide or dimethylformamide. In the method, the amount of the alkali liquor of step (1) is determined to ensure that the carbon nanotube powder can be sufficiently wetted, and the loading amount of the alkali in the final alkali is 10%-100% of the mass of the carbon nanotubes, and further preferably the impregnation solid-liquid mass ratio is determined according to the equal volume impregnation method, and the loading amount of the alkali is 30%-50%.

[0014] In the method, the ultrasonic dispersion treatment condition of step (1) is as follows: the ultrasonic treatment time is 5-60 minutes, the ultrasonic power is 40-720 W, the ultrasonic frequency is 20-100 kHz, and the ultrasonic temperature is 5-90℃. The ultrasonic dispersion treatment condition is preferably as follows: the time is 10-30 minutes, the power is 40-100 W, the ultrasonic frequency is 20-60 kHz, and the ultrasonic temperature is 10-60℃.

[0015] In the method, the solid-liquid separation of step (2) is a conventional dry method, including but not limited to filtration, centrifugation, precipitation and the like.

[0016] In the method, the drying condition of step (2) is as follows: the drying temperature is 30-200℃, and the drying time is 1-24 hours, preferably the drying temperature is 100-150℃, and the drying time is 3-12 hours.

[0017] The drying in step (2) is further preferably vacuum drying, and the operating conditions are: pressure 0-100 Pa, temperature 20-200℃, and time 3-24 hours, preferably pressure 0-40 Pa, temperature 100-150℃, and time 6-12 hours.

[0018] In the method of the present application, the ball milling treatment in step (3) is carried out under the following conditions: ball milling rotation speed 200-5000 r / min, ball-to-material mass ratio 25-500:1, and ball milling time 2-48 hours. Preferably, the ball milling rotation speed is 200-3000 r / min, the ball-to-material mass ratio is 50-300:1, and the ball milling time is 6-12 hours.

[0019] In the method of the present application, the washing in step (3) is a conventional process, and water is preferably used until the washing liquid is neutral or nearly neutral. The drying conditions are: temperature 100-150℃, and time 6-12 hours. The calcination conditions are: under the protection of an inert atmosphere, temperature 300-800℃, preferably 450-650℃, and time 1-12 hours, preferably 3-6 hours; wherein the inert atmosphere is an inert gas and / or nitrogen.

[0020] The high specific surface area carbon nanotubes prepared by the method of the present application have the following properties: length 2-30 μm, inner diameter 2-20 nm, wall thickness 3-25 nm, specific surface area 600-2000 m 2 / g, and aspect ratio of nanotube 100-1400.

[0021] Compared with the prior art, the method of the present application has the following advantages: the low carbon alcohol contained in the alkaline solution can reduce the surface tension of the solution, and in combination with the ultrasonic effect, the carbon nanotubes can fully adsorb the alkaline solution inside and outside, and the amount of alkali used in the present application is less, which is conducive to environmental protection; the amide contained in the alkaline solution used in the present application can inhibit the aggregation of the alkaline solution in the subsequent drying process, so that the alkali can be uniformly dispersed on the inner and outer surfaces of the carbon nanotubes, which is conducive to improving the uniformity of the ball milling modification; the local high temperature generated by the ball milling extrusion can etch the carbon nanotubes with alkali to produce defects, thereby increasing the specific surface area. The method of the present application is simple in operation, safe and environmentally friendly, and the obtained carbon nanotubes have a high specific surface area, which is conducive to widening the application range and improving the application performance. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 Transmission electron microscope image of the carbon nanotubes prepared in Example 1. DETAILED DESCRIPTION

[0023] The present application will be described in more detail by examples, but the scope of protection of the present application is not limited to these examples. The length, diameter, inner diameter, aspect ratio and wall thickness of the nanotubes are measured according to the transmission electron microscope images, and the average value is calculated by measuring at least 20 groups of data. The loading amount of the carbon nanotube base 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 BET calculation formula.

[0024] Example 1

[0025] The base solution is prepared by weighing a certain amount of potassium hydroxide, water, ethanol and formamide. The proportion of each component is 30% of potassium hydroxide, 55% of water, 10% of ethanol and 5% of formamide by mass. The carbon nanotubes are immersed in the base solution, and an ultrasonic dispersing machine (100W, 40KHz) is used to disperse at room temperature (20℃) for 10 minutes. The amount of base solution should be enough to fully wet the carbon nanotube powder. 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 base solution, they are filtered, then dried at 120℃ for 6 hours. The final loading amount of the base is 35% of the mass of the carbon nanotubes. The dried carbon nanotube powder is placed in a ball mill for grinding, with a ball-to-material mass ratio of 200:1 and a rotation speed of 500r / min. The grinding time is set to 6 hours. After grinding, the carbon nanotubes are washed with distilled water, filtered, dried at 120℃ for 6 hours, and then calcined at 500℃ for 3 hours under nitrogen protection. After natural cooling, the high specific surface area carbon nanotubes are obtained. The average length is 8.5μm, the inner diameter is 7.6nm, the wall thickness is 4.6nm, the aspect ratio is 505, and the specific surface area is 775m 2 / g.

[0026] Example 2

[0027] The base solution is prepared by weighing a certain amount of sodium hydroxide, water, ethanol and formamide. The proportion of each component is 20% of sodium hydroxide, 45% of water, 15% of ethanol and 8% of formamide by mass. The carbon nanotubes are immersed in the base solution, and an ultrasonic dispersing machine (100W, 40KHz) is used to disperse at 30℃ for 20 minutes. The amount of base solution should be enough to fully wet the carbon nanotube powder. 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, the carbon nanotubes were fully adsorbed with the lye, then filtered, and dried at 100°C for 8 hours. The final loading of the lye was 30% of the mass of the carbon nanotubes, calculated based on the dried carbon nanotubes. The dried carbon nanotube powder was placed in a ball mill, the ball-to-material mass ratio was 200:1, the rotation speed was 800 r / min, and the ball milling time was set to 8 hours. After the grinding, the carbon nanotubes were fully washed with distilled water, filtered, dried at 100°C for 8 hours, and then calcined at 400°C for 4 hours under nitrogen protection. The high specific surface area carbon nanotubes were obtained after natural cooling. The average length was 9.2 μm, the inner diameter of the tube was 7.8 nm, the wall thickness was 4.7 nm, the aspect ratio of the nanotube was 535, and the specific surface area was 674 m 2 / g.

[0028] Example 3

[0029] A lye was prepared by weighing a certain amount of rubidium hydroxide, water, ethanol, and formamide, and the proportions of the components were as follows: rubidium hydroxide 35%, water 50%, ethanol 20%, and formamide 10% by mass. The carbon nanotubes were immersed in the lye, and an ultrasonic dispersing machine (100 W, 40 KHz) was used to disperse at 40°C for 30 minutes. The amount of the lye was sufficient to fully wet the carbon nanotube powder. The used carbon nanotubes were commercially available products, the average length was 10.2 μm, the inner diameter of the tube was 8 nm, the wall thickness was 4.8 nm, the aspect ratio of the nanotube was 607, and the specific surface area was 39 m 2 / g, the carbon nanotubes were fully adsorbed with the lye, then filtered, and dried at 150°C for 10 hours. The final loading of the lye was 40% of the mass of the carbon nanotubes, calculated based on the dried carbon nanotubes. The dried carbon nanotube powder was placed in a ball mill, the ball-to-material mass ratio was 200:1, the rotation speed was 1000 r / min, and the ball milling time was set to 6 hours. After the grinding, the carbon nanotubes were fully washed with distilled water, filtered, dried at 150°C for 10 hours, and then calcined at 300°C for 5 hours under nitrogen protection. The high specific surface area carbon nanotubes were obtained after natural cooling. The average length was 7.6 μm, the inner diameter of the tube was 7.7 nm, the wall thickness was 4.5 nm, the aspect ratio of the nanotube was 455, and the specific surface area was 584 m 2 / g.

[0030] Example 4

[0031] A base solution was prepared by weighing a certain amount of cesium hydroxide, water, ethanol, and formamide. The proportions of the components were 40% cesium hydroxide, 60% water, 10% ethanol, and 5% formamide by mass. The carbon nanotubes were immersed in the base solution and dispersed using an ultrasonic disperser (100 W, 40 KHz) at 50°C for 40 minutes. The amount of base solution used was sufficient to wet the carbon nanotube powder. The carbon nanotubes used were 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 had absorbed the base solution, they were filtered and then dried at 150°C for 15 hours. The final loading of base was 45% of the mass of the carbon nanotubes. The dried carbon nanotube powder was placed in a ball mill and ground at a ball-to-material mass ratio of 200:1 at a rotation speed of 2000 r / min for 8 hours. After grinding, the carbon nanotubes were washed with distilled water, filtered, dried at 150°C for 12 hours, and then calcined at 600°C for 3 hours under nitrogen. The high-surface-area carbon nanotubes were obtained after natural cooling. The average length of the carbon nanotubes was 8.1 μm, the inner diameter was 7.2 nm, the wall thickness was 4.1 nm, the aspect ratio was 526, and the specific surface area was 1137 m 2 / g.

[0032] Example 5

[0033] Example 1 except that the final loading of base was 110% of the mass of the carbon nanotubes. The specific surface area of the carbon nanotubes was 524 m 2 / g.

[0034] Comparative Example 1

[0035] Example 1 except that no low-carbon alcohol or amide was added. The specific surface area of the resulting product was 439 m 2 / g.

[0036] Comparative Example 2

[0037] Example 1 except that no low-carbon alcohol was added. The specific surface area of the resulting product was 491 m 2 / g.

[0038] Comparative Example 3

[0039] The carbon nanotubes were modified using KOH as an activating agent according to the method of Physical Chemistry (2006, 22(1): 43-47). The amount of base used was 200% of the amount of carbon nanotubes, the activation temperature was 500°C, and the time was 3 hours. The specific surface area of the resulting product was 354 m 2 / g.

[0040] Comparative Example 4

[0041] Carbon nanotubes were modified according to the method of Example 1 of CN200710043671.6. The resulting product had a specific surface area of 95 m 2 / g, and the amount of alkali used was much higher than in the present application, with serious pollution.

Claims

1. A method for preparing high specific surface area carbon nanotubes, characterized by The method comprises the following steps: (1) adding multi-walled carbon nanotubes into an alkali solution, mixing by ultrasonic dispersion to obtain a black suspension; (2) performing solid-liquid separation and drying on the black suspension of step (1) to obtain carbon nanotubes after adsorption; (3) placing the carbon nanotubes of step (2) in a microwave heating device, and performing microwave treatment under the conditions of an inert atmosphere and a closed condition to obtain carbon nanotubes with a high specific surface area; the alkali solution of step (1) comprises an inorganic base, water, a low-carbon alcohol and an amide; the mass percentage of each component in the alkali solution is as follows: the inorganic base is 10%-40%, the water is 40%-80%, the low-carbon alcohol is 5%-20%, and the amide is 1%-10%.

2. The method of claim 1, wherein: The multi-walled carbon nanotube of step (1) has a length of 5-30 μm, an inner tube diameter of 3-25 nm, a wall thickness of 5-25 nm, a specific surface area of 10-300 m 2 / g, and an aspect ratio of the nanotube of 200-1500.

3. The method of claim 1, wherein: The inorganic base is one or more of sodium hydroxide, potassium hydroxide, rubidium hydroxide and cesium hydroxide.

4. The method of claim 1, wherein: The low-carbon alcohol is a monohydric alcohol and a polyhydric alcohol with a carbon number of not more than 5.

5. The method of claim 1, wherein: The amide is one or more of formamide, acetamide and dimethylformamide.

6. The method of claim 1, wherein: The amount of the alkali solution of step (1) is required to ensure that the carbon nanotube powder can be fully wetted, and the final alkali loading amount is 10%-100% of the mass of the carbon nanotubes.

7. The method of claim 1, wherein: The ultrasonic dispersion treatment conditions of step (1) are as follows: the ultrasonic treatment time is 5-60 minutes, the ultrasonic power is 40-720 W, the ultrasonic frequency is 20-100 kHz, and the ultrasonic temperature is 5-90℃.

8. The method of claim 1, wherein: The drying conditions of step (2) are as follows: the drying temperature is 30-200℃, and the drying time is 1-24 hours.

9. The method of claim 1, wherein: The microwave treatment conditions of step (3) are as follows: the microwave frequency is 0.3-100 GHz, the microwave power is 200-4000 W, the treatment time is 5-60 minutes, and the treatment temperature is 200-500℃.

10. The method of claim 1, wherein: The microwave treatment conditions of step (3) are as follows: the microwave frequency is 2.40-2.50 GHz, the microwave power is 400-2500 W, the treatment time is 10-30 minutes, and the treatment temperature is 300-450℃.

11. The method of claim 1, wherein: The inert atmosphere of step (3) is an inert gas and / or nitrogen.

12. High specific surface area carbon nanotubes prepared according to the method of any one of claims 1 to 11, characterized in that having the following properties: length 2-30 μm, inner diameter of the tube 2-20 nm, wall thickness 3-25 nm, specific surface area 800-2000 m 2 / g, aspect ratio of the nanotubes 100-1400.

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