Single-walled carbon nanotube purification method

Abstract

The invention relates to the technical field of carbon nanomaterials, in particular to a single-walled carbon nanotube purification method. Introducing a solvent into the initial sample of the single-walled carbon nanotube: putting the single-walled carbon nanotube with the mass A into a container, adding the solvent with the mass B, and fully stirring to obtain a wet material; low-temperature oxidation in a strong oxidizing atmosphere: putting the wet single-walled carbon nanotube material into a reactor, continuously introducing inert gas, heating the reactor to a relatively low temperature T1, introducing strong oxidizing gas after the temperature is stable, and stopping introducing the strong oxidizing gas after reacting for a certain time; and acid treatment: dispersing the obtained sample into an acid solution, stirring for reaction, and then filtering and drying to obtain the purified single-walled carbon nanotube. According to the method, the purification efficiency, retention rate and purity of the single-walled carbon nanotubes are greatly improved.

Description

Technical Field

[0001] The present application relates to the technical field of carbon nanomaterials, and in particular to a method for purifying single-walled carbon nanotubes. Background Art

[0002] Single-walled carbon nanotubes are one-dimensional carbon nanomaterials with a unique hollow tubular structure. They not only have excellent mechanical, thermal, mechanical, electrical and chemical properties, but also show excellent application prospects in many fields, including electronic devices, composite materials, conductive films and catalyst carriers.

[0003] At present, the main methods for preparing single-walled carbon nanotubes are chemical vapor deposition, plasma and arc discharge. Regardless of the method, the single-walled carbon nanotubes obtained are usually accompanied by more or less impurities, which mainly include impure carbon and metal catalysts. In industrial production, the difficulty of producing high-purity single-walled carbon nanotubes has greatly hindered the large-scale application and performance research of single-walled carbon nanotubes.

[0004] At present, many purification methods of single-walled carbon nanotubes have been proposed, such as centrifugation, microwave method and high temperature oxidation method etc. of regulating centrifugal rate. Especially the single-walled carbon nanotube gradient oxidation purification method (CN109650379) proposed recently has greatly improved the preparation efficiency of high-purity single-walled carbon nanotubes. However, in these purification technologies mentioned above, the biggest problem is that high-purity single-walled carbon nanotubes are difficult to realize large-scale mass production under the premise of ensuring low cost and limited equipment space. The main reason is that in a given limited space, when increasing the single-walled carbon nanotube treatment capacity for improving efficiency, carbon nanotubes are easily accumulated, making it difficult for the inside to contact strong oxidizing gas, and metal impurities can not be fully exposed. Therefore, under the premise of ensuring single-walled carbon nanotube retention rate and purity, seeking a single-walled carbon nanotube purification method that is efficient and suitable for industrial mass production has very important significance and value. Summary of the invention

[0005] In order to improve the purification efficiency, purity and retention rate, the present application provides a single-walled carbon nanotube purification method.

[0006] The present application provides a method for purifying single-walled carbon nanotubes, which adopts the following technical scheme: A method for purifying single-walled carbon nanotubes comprises the following steps: (1) Introducing a solvent into an initial sample of single-walled carbon nanotubes: placing single-walled carbon nanotubes of mass A in a container, adding a solvent of mass B, and stirring the mixture thoroughly to obtain a wet material; (2) Low-temperature oxidation in a strong oxidizing atmosphere: The wet single-walled carbon nanotube material is placed in a reactor, and an inert gas is continuously introduced. The reactor is heated to a relatively low temperature T1, and a strong oxidizing gas is introduced after the temperature stabilizes. After a certain reaction time, the introduction of the strong oxidizing gas is stopped; (3) Acid treatment: The sample obtained in step (2) is dispersed in an acid solution, stirred for reaction, and then filtered and dried to obtain purified single-walled carbon nanotubes.

[0007] The above technical solution provides a low-cost, large-scale single-walled carbon nanotube pretreatment and re-oxidation purification method, which is to fully contact the single-walled carbon nanotube initial sample with a solvent, then low-temperature oxidation in a strong oxidizing atmosphere, and finally remove metal impurities in the carbon nanotubes through acid washing.

[0008] Preferably, the ratio of A to B in step (1) is (1-10):(5-500).

[0009] Preferably, the solvent in step (1) is selected from at least one of pure water, ethanol, methanol or N-methylpyrrolidone.

[0010] Preferably, in step (2), T1 is 400°C to 600°C.

[0011] Preferably, in step (2), the strong oxidizing gas is selected from at least one of oxygen, air, chlorine or ozone.

[0012] Preferably, the acid solution in step (3) is selected from at least one of a nitric acid solution, a hydrochloric acid solution or a sulfuric acid solution.

[0013] Preferably, in step (2), the inert gases are independently selected from at least one of nitrogen, argon and helium.

[0014] Preferably, in step (3), the reaction temperature is from room temperature to 95°C.

[0015] Preferably, when a strong oxidizing gas is introduced in step (2), the oxidizing gas accounts for 1% to 100% of the total volume of the gas introduced into the reactor, and the remainder is an inert gas.

[0016] In summary, this application has the following beneficial effects: 1. Compared with conventional purification methods, the method of the present application first pre-treats a large number of single-walled carbon nanotube initial samples, fully contacts them with a solvent, and then oxidizes the single-walled carbon nanotube wet material under low temperature conditions. The introduction of solvent during pre-treatment can not only improve the treatment efficiency of impurity carbon under the premise of protecting the surface of carbon nanotubes from damage, but also can deeply introduce a large amount of strong oxidizing gas during the high-temperature volatilization of the solvent in the case of serious accumulation of a large number of single-walled carbon nanotubes, further treat the impurity carbon and solve the problem that the metal particles coated in the crystalline graphite layer are difficult to expose, thereby greatly improving the purification efficiency (realizing one-time large-scale purification), retention rate and purity of single-walled carbon nanotubes in industry.

[0017] 2. The method of the present application is suitable for the purification of industrial-grade large quantities of single-walled carbon nanotube initial samples. The method is simple, the gas used is cheap and easy to obtain, and can be recycled, which greatly reduces the purification cost and can be industrially scaled up. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The process flow chart of the present application method is as follows; Figure 2 The transmission electron microscope (TEM) images of the single-walled carbon nanotubes in Example 1 are corresponding to the initial sample, before acid treatment, and after purification treatment, wherein (a) is the TEM image of the single-walled carbon nanotube initial sample 1; (b) is the TEM image of the single-walled carbon nanotube before acid treatment; (c) is the TEM image of the single-walled carbon nanotube after purification treatment; Figure 3 1 and 2 are Raman images of the single-walled carbon nanotubes in Example 1 before and after purification, wherein (a) is the Raman image of the single-walled carbon nanotube initial sample 1, and (b) is the Raman image of the single-walled carbon nanotubes after purification. DETAILED DESCRIPTION

[0019] The following examples further illustrate the content of this application, but should not be construed as limiting this application. Without departing from the spirit and substance of this application, modifications or substitutions made to the methods, steps or conditions of this application are within the scope of this application.

[0020] Unless otherwise specified, the technical means used in the examples are conventional means well known to those skilled in the art; unless otherwise specified, the reagents used in the examples are commercially available.

[0021] Example 1 Take 400g of the initial sample of single-walled carbon nanotubes and place it in a container. The purity of the initial sample is 82.07%. Add solvent to the container. The solvent is an aqueous solution with a 50% ethanol content. The mass ratio of carbon tubes to solvent is 1:5. Stir thoroughly and soak for 24 hours. Then put the semi-wetted single-walled carbon nanotube wet material on a quartz boat, and put the quartz boat into a tube furnace. Raise the temperature to 450°C under a nitrogen atmosphere, introduce air after the temperature stabilizes, and react for 2 hours. After the reaction is completed, cut off the air feed, and allow the reactor to cool to room temperature under nitrogen protection. Take out the sample and weigh it. The weight loss is only 5.45%. Put the sample in a 2M hydrochloric acid solution and stir at room temperature for 24 hours. Then filter and dry to obtain the purified product. The initial sample 1 and the purified product are characterized by TEM and Raman spectroscopy. The results are as follows: Figure 2 (a), (b) and (c), Figure 3 As shown in (a) and (b). Figure 2 From the results of (a) and (b), it can be seen that a large amount of impurity carbon in the initial sample was removed by oxidation, while the iron particles coated with carbon were fully exposed and removed by acid treatment. Figure 3 The results of (a) and (b) show that the low-quality impurity carbon is fully removed, the surface carbon lattice of the purified carbon nanotubes is not destroyed, and the Raman value is as high as 126.18. The residual amount of metal impurities in the purified single-walled carbon nanotubes is only 0.17%.

[0022] Example 2 Take 40g of the initial sample of single-walled carbon nanotubes and place it in a container. The purity of the initial sample is 82.07%. Add solvent to the container. The solvent is an aqueous solution with 50% ethanol content. The mass ratio of carbon tubes to solvent is 1:5. Stir and soak for 24 hours. Then put the wet single-walled carbon nanotubes on a quartz boat and put the quartz boat into a tube furnace. Heat to 450℃ under nitrogen atmosphere, introduce air after the temperature stabilizes, and react for 2 hours. After the reaction is completed, cut off the air feed and cool the reactor to room temperature under nitrogen protection. Take out the sample and weigh it. The weight loss is 7.32%. Put the sample in 2M hydrochloric acid solution and stir at room temperature for 24 hours. Then filter and dry to obtain the purified product, and characterize the purity and Raman spectrum of the purified product. The residual amount of metal impurities in the purified single-walled carbon nanotubes is only 0.15%.

[0023] Example 3 Take 400g of the initial sample of single-walled carbon nanotubes and place it in a container. The purity of the initial sample is 82.07%. Add solvent to the container. The solvent is an aqueous solution with 50% ethanol content. The mass ratio of carbon tubes to solvent is 1:10. Stir and soak for 24 hours. Then put the wet single-walled carbon nanotubes on a quartz boat and put the quartz boat into a tube furnace. Heat to 450℃ under nitrogen atmosphere, introduce air after the temperature stabilizes, and react for 2 hours. After the reaction is completed, cut off the air feed and cool the reactor to room temperature under nitrogen protection. Take out the sample and weigh it. The weight loss is 6.55%. Put the sample in 2M hydrochloric acid solution and stir at room temperature for 24 hours. Then filter and dry to obtain the purified product, and characterize the purity and Raman spectrum of the purified product. The residual amount of metal impurities in the purified single-walled carbon nanotubes is only 0.75%.

[0024] Example 4 Take 400g of the initial sample of single-walled carbon nanotubes and place it in a container. The purity of the initial sample is 70.16%. Add solvent to the container. The solvent is an aqueous solution with 50% ethanol content. The mass ratio of carbon tubes to solvent is 1:5. Stir and soak for 24 hours. Then put the wet single-walled carbon nanotubes on a quartz boat and put the quartz boat into a tube furnace. Heat to 450℃ under nitrogen atmosphere, introduce air after the temperature stabilizes, and react for 2 hours. After the reaction is completed, cut off the air feed, and cool the reactor to room temperature under nitrogen protection. Take out the sample and weigh it. The weight loss is 9.87%. Put the sample in 2M hydrochloric acid solution and stir at room temperature for 24 hours, then filter and dry to obtain the purified product, and characterize the purity and Raman spectrum of the purified product. The residual amount of metal impurities in the purified single-walled carbon nanotubes is only 0.33%.

[0025] Example 5 Take 400g of the initial sample of single-walled carbon nanotubes and place it in a container. The purity of the initial sample is 82.07%. Add 10% N-methylpyrrolidone aqueous solution to the container, the mass ratio of carbon tubes to solvent is 1:5, fully stir and soak for 24 hours, then put the wet single-walled carbon nanotubes on a quartz boat, and put the quartz boat into a tube furnace. Heat to 450℃ under nitrogen atmosphere, introduce air after the temperature stabilizes, and react for 2 hours. After the reaction is completed, cut off the air feed, and cool the reactor to room temperature under nitrogen protection. Take out the sample and weigh it. The weight loss is only 6.76%. Put the sample in 2M hydrochloric acid solution and stir at room temperature for 24 hours, then filter and dry to obtain the purified product, and characterize the purity and Raman spectrum of the purified product. The residual amount of metal impurities in the purified single-walled carbon nanotubes is only 0.72%.

[0026] Comparative Example 1 The single-walled carbon nanotube initial sample was purified according to the method of Example 1, except that the single-walled carbon nanotube initial sample was not pretreated, and the amount of single-walled carbon nanotubes used was 40 g. The specific steps were as follows: 40g of the initial sample of single-walled carbon nanotubes was placed on a quartz boat, and the quartz boat was placed in a high-temperature tube furnace. The temperature was raised to 450°C in a nitrogen atmosphere, and air was introduced after the temperature stabilized, and the reaction was carried out for 2 hours. After the reaction was completed, the air feed was cut off, and the reactor was cooled to room temperature under nitrogen protection. The sample was taken out and weighed, and the weight loss was 4.86%. The sample was placed in a 2M hydrochloric acid solution and stirred at room temperature for 24 hours, and then filtered and dried to obtain a purified product. The purified product was characterized by thermogravimetric analysis. The results showed that a small amount of the initial sample of single-walled carbon nanotubes was not pretreated, directly oxidized at low temperature and then acid-washed, and the metal content was as high as 0.97%.

[0027] Comparative Example 2 The single-walled carbon nanotube initial sample is purified according to the method of Example 1, except that the single-walled carbon nanotube initial sample is not pretreated. The specific steps are as follows: 400g of the initial sample of single-walled carbon nanotubes was placed on a quartz boat, and the quartz boat was placed in a high-temperature tube furnace. The temperature was raised to 450°C in a nitrogen atmosphere, and air was introduced after the temperature stabilized, and the reaction was carried out for 2 hours. After the reaction was completed, the air feed was cut off, and the reactor was cooled to room temperature under nitrogen protection. The sample was taken out and weighed, and the weight loss was 2.57%. The sample was placed in a 2M hydrochloric acid solution and stirred at room temperature for 24 hours, and then filtered and dried to obtain a purified product. The purified product was characterized by thermogravimetric analysis. The results showed that a large number of initial samples of single-walled carbon nanotubes were not pretreated, directly oxidized at low temperature and then acid-washed, and the metal content was as high as 11.68%.

[0028] Comparative Example 3 The single-walled carbon nanotube initial sample was purified according to the method of Comparative Example 1, except that the single-walled carbon nanotube initial sample was oxidized at low temperature and then oxidized at high temperature before acid washing. The specific steps are as follows: 40g of the initial sample of single-walled carbon nanotubes was placed on a quartz boat, and the quartz boat was placed in a high-temperature tube furnace. The temperature was raised to 450°C in a nitrogen atmosphere, and air was introduced after the temperature stabilized. The reaction was continued for 2 hours, and then the air feed was cut off. The temperature was raised to 850°C in an argon atmosphere, and the reaction was continued for 1 hour. After the reaction was completed, the reactor was cooled to room temperature under the protection of argon. The sample was taken out and weighed, and the weight loss was 17.73%. The sample was placed in a 2M hydrochloric acid solution and stirred at room temperature for 24 hours, and then filtered and dried to obtain a purified product. The purified product was characterized by thermogravimetric analysis. The results showed that a small amount of the initial sample of single-walled carbon nanotubes was not pretreated, and was directly oxidized at low temperature and then oxidized at high temperature and then acid washed, and the metal content was as low as 0.26%.

[0029] Comparative Example 4 The single-walled carbon nanotube initial sample was purified according to the method of Comparative Example 2, except that the single-walled carbon nanotube initial sample was oxidized at low temperature and then oxidized at high temperature before acid washing. The specific steps are as follows: 400g of the initial sample of single-walled carbon nanotubes was placed on a quartz boat, and the quartz boat was placed in a high-temperature tube furnace. The temperature was raised to 450°C in a nitrogen atmosphere, and air was introduced after the temperature stabilized. The reaction was continued for 2 hours, and then the air feed was cut off. The temperature was raised to 850°C in an argon atmosphere, and the reaction was continued for 1 hour. After the reaction was completed, the reactor was cooled to room temperature under the protection of argon. The sample was taken out and weighed, and the weight loss was 13.08%. The sample was placed in a 2M hydrochloric acid solution and stirred at room temperature for 24 hours, and then filtered and dried to obtain a purified product. The results showed that a large number of initial samples of single-walled carbon nanotubes were not pretreated, directly oxidized at low temperature and then oxidized at high temperature and then acid washed, and the metal content was as high as 7.88%.

[0030] Comparative Example 5 The initial sample of single-walled carbon nanotubes was purified according to the method of Example 1, except that the mass ratio of carbon nanotubes to solvent was 1:20. The specific steps were as follows: 400g of the initial sample of single-walled carbon nanotubes was placed in a container. The purity of the initial sample was 82.07%. A solvent was added to the container. The solvent was an aqueous solution with a 50% ethanol content. The mass ratio of carbon tubes to solvent was 1:20. The single-walled carbon nanotubes were fully stirred and soaked for 24 hours. Then the fully soaked single-walled carbon nanotubes were placed on a quartz boat, and the quartz boat was placed in a tube furnace. The temperature was raised to 450°C under a nitrogen atmosphere. After the temperature stabilized, air was introduced and the reaction was carried out for 2 hours. After the reaction was completed, the air feed was cut off, and the reactor was cooled to room temperature under nitrogen protection. The sample was taken out and weighed. The weight loss was 5.29%. The sample was placed in a 2M hydrochloric acid solution and stirred at room temperature for 24 hours. Then it was filtered and dried to obtain a purified product. The purified product was characterized by thermogravimetric analysis. The results showed that the initial sample of single-walled carbon nanotubes was pretreated with a mass ratio of carbon tubes to solvent of 1:20, directly oxidized at low temperature and then acid-washed, and the metal content was as high as 9.46%.

[0031] Comparative Example 6 The difference from Example 1 is that the ratio of A to B is 1:50.

[0032] Comparative Example 7 The difference from Example 1 is that the ratio of A to B is 1:500.

[0033] Comparative Example 8 The difference from Example 1 is that the ratio of A to B is 2:1.

[0034] Comparative Example 9 The difference from Example 1 is that in step (2), T1 is 400°C.

[0035] Comparative Example 10 The difference from Example 1 is that in step (2), T1 is 600°C.

[0036] Comparative Example 11 The difference from Example 1 is that the strong oxidizing gas is chlorine.

[0037] Table 1 shows the oxidation of single-walled carbon nanotubes in experimental examples and comparative examples. Retention rate, purity and Raman-based characterization results As shown in Table 1, compared with Example 3, Comparative Examples 5, 6, 7, and 8, the mass ratio of single-walled carbon nanotubes to solvent in the pretreatment of single-walled carbon nanotubes in Example 1 is preferably 1:5-1:10. When the ratio is too low, the single-walled carbon nanotubes are not fully in contact with the solvent, and the introduction of strong oxidizing gas is small during the later low-temperature oxidation, resulting in poor oxidation effect. When the ratio is too high, the solvent evaporates in large quantities in a short period of time, resulting in carbon tube agglomeration and poor oxidation effect. Compared with Example 2, Comparative Examples 1, 2, 3, and 4, in a limited space, a small amount of single-walled carbon nanotubes can be obtained by low-temperature oxidation or step oxidation to obtain high-purity carbon tubes. However, when the amount of single-walled carbon nanotubes increases, it is difficult to fully treat the initial sample of single-walled carbon nanotubes by low-temperature oxidation or step oxidation. By changing the type of solvent or the type of strong oxidizing gas, a good purification effect can still be achieved. The purity of the high-purity carbon nanotubes obtained by the single-walled carbon nanotube initial sample of the present invention after appropriate pretreatment and reoxidation purification method is maintained at more than 99%, and the one-time processing amount and retention rate are excellent. In industry, continuous purification operations can be carried out to greatly increase the production capacity of high-purity carbon nanotubes.

[0038] 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 modifications to the present embodiment without any creative contribution as needed, but such modifications are protected by the patent law as long as they are within the scope of the claims of the present application.

Claims

1. A method for purifying single-walled carbon nanotubes, characterized in that: The steps include: (1) Introducing a solvent into the initial sample of single-walled carbon nanotubes: placing single-walled carbon nanotubes of mass A in a container, adding a solvent of mass B, and stirring thoroughly to obtain a wet material; (2) Low-temperature oxidation in a strong oxidizing atmosphere: Place the wet single-walled carbon nanotube material in a reactor, continuously introduce inert gas, heat the reactor to a relatively low temperature T1, and introduce strong oxidizing gas after the temperature stabilizes. After a certain period of reaction, stop introducing strong oxidizing gas. (3) Acid treatment: The sample obtained in step (2) is dispersed in an acid solution, stirred for reaction, and then filtered and dried to obtain purified single-walled carbon nanotubes.

2. The method for purifying single-walled carbon nanotubes according to claim 1, characterized in that: The ratio of A to B in step (1) is (1-10):(5-500).

3. The method for purifying single-walled carbon nanotubes according to claim 1, characterized in that: In step (1), the solvent is selected from at least one of pure water, ethanol, methanol or N-methylpyrrolidone.

4. The method for purifying single-walled carbon nanotubes according to claim 1, characterized in that: In step (2), T1 is 400°C to 600°C.

5. The method for purifying single-walled carbon nanotubes according to claim 1, characterized in that: In step (2), the strong oxidizing gas is selected from at least one of oxygen, air, chlorine or ozone.

6. The method for purifying single-walled carbon nanotubes according to claim 1, characterized in that: In step (3), the acid solution is selected from at least one of a nitric acid solution, a hydrochloric acid solution or a sulfuric acid solution.

7. The method for purifying single-walled carbon nanotubes according to claim 1, characterized in that: In step (2), the inert gases are independently selected from at least one of nitrogen, argon and helium.

8. The method for purifying single-walled carbon nanotubes according to claim 1, characterized in that: In step (3), the reaction temperature is from room temperature to 95°C.

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