Method for effectively purifying single-walled carbon nanotubes through multi-step treatment

Abstract

The invention discloses a method for effectively purifying a single-walled carbon nanotube through multi-step treatment, and belongs to the field of separation and purification of carbon nanotube materials, and the method comprises the following steps: calcining under the condition of carbon dioxide gas to remove redundant amorphous carbon; the method comprises the following steps of: adding a single-walled carbon nanotube into a reaction kettle, refluxing and filtering by using methylbenzene to realize high separation of the single-walled carbon nanotube, simultaneously adding concentrated acid and polyvinylpyrrolidone to remove metal impurities, washing to be neutral by using distilled water, and filtering to remove redundant acid, thereby further purifying the single-walled carbon nanotube. And finally, calcining at a high temperature of 600-900 DEG C to decompose residual polyvinylpyrrolidone, so that the purity of the single-walled carbon nanotube is improved, the metal residue in the purified single-walled carbon nanotube is 1.5%, and the yield of the method for effectively purifying the single-walled carbon nanotube through multi-step treatment provided by the invention can reach 80%.

Description

Technical Field

[0001] The invention belongs to the field of separation and purification of carbon nanotube materials, and particularly relates to a method for effectively purifying single-walled carbon nanotubes through multi-step treatment. Background Art

[0002] In the 30 years since single-walled carbon nanotubes were developed, they have been widely used in many fields such as nanoelectronics, biosensors, and energy equipment due to their excellent physical and chemical properties. Single-walled carbon nanotube samples prepared on a large scale usually contain a large amount of impurities, of which carbon impurities and metal impurities are the two most common types. Carbon impurities include graphite particles, carbon nanoparticles, and amorphous carbon formed during the growth of carbon nanotubes. Metal impurities come from transition metal catalysts, and the presence of these impurities seriously affects the properties and applications of single-walled carbon nanotubes.

[0003] Therefore, developing efficient purification methods is crucial to obtaining high-purity single-walled carbon nanotube products. During the purification process, chemical, physical and thermal treatment methods can be used to remove impurities. For example, carbon impurities on the surface of carbon nanotubes can be removed by acid treatment, while acid washing and high-temperature treatment can remove metal catalysts. In order to obtain high-purity single-walled carbon nanotube products, in addition to paying attention to large-scale preparation processes, purification processes are equally important. The development of efficient purification methods can remove carbon and metal impurities in carbon nanotubes, thereby improving their properties and application potential.

[0004] In view of the serious impact of metal impurities in carbon nanotubes on their properties and applications, there are currently several different methods for purifying single-walled carbon nanotubes. First, physical purification methods include centrifugal separation, electrophoresis purification, filtration purification, and spatial exclusion chromatography. These methods are based on the difference in physical properties between metal impurities and single-walled carbon nanotubes, and improve the purity of single-walled carbon nanotubes by separation and screening. The advantage of physical purification methods is that the separation is rapid, but the separation is not thorough, and there are more metal residues. Secondly, chemical purification methods include gas phase oxidation purification methods, liquid phase oxidation purification methods, etc. These methods use the characteristics of metal impurities that are easy to dissolve in acid or sublimate at high temperature to purify single-walled carbon nanotubes by oxidizing or dissolving metal impurities. Compared with physical purification methods, chemical purification methods are more thorough, but still need to be further improved. Finally, comprehensive purification methods include acid treatment combined with gas phase oxidation, acid treatment combined with high temperature annealing, acid treatment combined with gas phase oxidation and high temperature annealing, acid treatment combined with electrophoresis, microporous filtration combined with electrolysis, etc. By combining these methods with a variety of purification methods, the purity and efficiency of single-walled carbon nanotubes can be improved. However, the purification reagents and conditions of the comprehensive purification method need to be further determined and selected to improve the carbon utilization rate of crude single-walled carbon nanotubes under the condition that metal and carbon impurities are reduced to a lower level. During the purification process of single-walled carbon nanotubes, it is necessary to prevent the carbon tubes from being oxidized and destroyed, and to ensure the high efficiency of the method.

[0005] Studies have shown that the most effective method for removing metal impurities is to acidify the carbon nanotubes. The acidification treatment has a low temperature, relatively low equipment requirements, and is more economical and scalable than high-temperature purification methods. However, the acidification treatment cannot deeply dissolve the metal particles wrapped in the inner wall of the carbon nanotubes, and other auxiliary methods are needed to reduce the impurity content. Therefore, the development of a more suitable purification method is necessary to completely destroy the carbon layer on the surface of the metal particles to fully dissolve them while maintaining the structural integrity of the single-walled carbon nanotubes, and to significantly improve the purity of the single-walled carbon nanotubes. Summary of the invention

[0006] The purpose of the present invention is to provide a multi-step treatment method for effectively purifying single-walled carbon nanotubes to solve the problems existing in the above-mentioned prior art.

[0007] The present invention provides the following solutions:

[0008] A multi-step treatment method for effectively purifying single-walled carbon nanotubes comprises the following steps: placing crude single-walled carbon nanotubes in a reactor, introducing inert nitrogen gas, heating, introducing weak oxidizing gas, calcining, placing the calcined product in toluene, refluxing to remove impurities, centrifuging the suspension obtained after reflux, removing the supernatant, washing to neutrality, adding polyvinyl pyrrolidone and concentrated acid to the washed product, stirring for 30 minutes, washing to neutrality after reaction, drying, and calcining again to obtain purified single-walled carbon nanotubes.

[0009] First, the crude single-walled carbon nanotubes are calcined under carbon dioxide for a period of time. Then, the single-walled carbon nanotubes are refluxed in toluene to remove fullerenes and soluble impurities. The liquid oxides, fullerenes and soluble impurities of amorphous carbon are removed after being refluxed and washed with distilled water until neutral. The metal particles not protected by amorphous carbon are removed by adding a concentrated acid reagent and polyvinyl pyrrolidone to the washed product; the purpose of adding polyvinyl pyrrolidone is to disperse the transition metal nanoparticles coated with the terminal carbon cap, which is more conducive to the removal of metal catalyst impurities.

[0010] Reflux in toluene for 16 hours to remove other types of carbon materials in the single-walled carbon nanotubes. Reflux in toluene can improve the reaction efficiency. Through the reflux technology, the crude single-walled carbon nanotubes in the reaction system can be kept at a certain temperature and pressure for continuous reaction, effectively improving the reaction efficiency. During the reflux process, the condenser can cool the generated gas or volatiles into liquid, so that it can flow back into the reaction system, avoiding the loss of crude single-walled carbon nanotubes. The reflux technology can regulate the anti-initiation conditions of the reaction temperature and reaction pressure, which helps to control and optimize the reaction.

[0011] Preferably, the weak oxidizing gas is carbon dioxide, and the carbon dioxide enters the reactor at a flow rate of 800 sccm until the partial pressure of the carbon dioxide reaches 0.1 MPa.

[0012] Preferably, the heating temperature is 600-900°C, and the calcination time is 3 hours. More preferably, the heating temperature is 750-900°C.

[0013] Preferably, the mass ratio of the washed product to polyvinyl pyrrolidone is 4:100.

[0014] Preferably, the usage ratio of the polyvinyl pyrrolidone and the concentrated acid is 1 g: 25 mL.

[0015] Preferably, the concentrated acid is selected from sulfuric acid, nitric acid, hydrochloric acid, aqua regia or hydrofluoric acid.

[0016] The concentrations of the sulfuric acid, nitric acid, hydrochloric acid, aqua regia and hydrofluoric acid are 40%, 60%, 50%, 50% and 60% respectively.

[0017] Preferably, the re-calcination temperature is 600-900°C.

[0018] The purpose of re-calcination is to remove residual polyvinyl pyrrolidone.

[0019] Beneficial effects of the present invention:

[0020] Compared with the conventional technology, the improvement of the present invention is that a method for effectively purifying single-walled carbon nanotubes by multi-step treatment is disclosed. First, calcination is carried out under the condition of carbon dioxide gas to remove excess amorphous carbon. Then, toluene is used for reflux and filtration to achieve a high degree of separation of single-walled carbon nanotubes. Next, concentrated acid and polyvinyl pyrrolidone are added simultaneously to remove metal impurities, distilled water is used to wash to neutrality, and excess acid is removed by filtration to further purify the single-walled carbon nanotubes. Finally, calcination is carried out under high temperature conditions of 600-900°C to decompose the residual polyvinyl pyrrolidone, thereby improving the purity of the single-walled carbon nanotubes. The residual metal content in the purified single-walled carbon nanotubes is 1.5%. The yield of the method for effectively purifying single-walled carbon nanotubes by multi-step treatment provided by the present invention can reach 80%. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0022] Figure 1 A purification process roadmap for the multi-step treatment method for effectively purifying single-walled carbon nanotubes provided by the present invention;

[0023] Figure 2 This is a SEM comparison diagram of the single-walled carbon nanotubes before and after purification in Example 1 of the present invention;

[0024] Figure 3 This is a SEM comparison picture of the single-walled carbon nanotubes before and after purification in Example 2 of the present invention. DETAILED DESCRIPTION

[0025] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0026] It should be understood that the terms described in the present invention are only for describing special embodiments and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. Each smaller range between the intermediate value in any stated value or stated range and any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0027] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0028] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to those skilled in the art. The present application description and examples are exemplary only.

[0029] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0030] In order to overcome the shortcomings of traditional purification processes, the present invention provides a method for effectively purifying single-walled carbon nanotubes through multi-step treatment, which comprises calcining under carbon dioxide gas conditions to remove excess amorphous carbon, then refluxing and filtering with toluene to achieve a higher degree of separation between the single-walled carbon nanotubes, then adding concentrated acid and polyvinyl pyrrolidone at the same time to remove more metal impurities, washing with distilled water to neutrality and then filtering to remove excess acid to obtain further purified single-walled carbon nanotubes, and finally calcining under high temperature conditions, the purpose of which is to decompose the residual polyvinyl pyrrolidone in the product under high temperature conditions, thereby improving the purity of the single-walled carbon nanotube product.

[0031] Example 1 A multi-step process for effectively purifying single-walled carbon nanotubes

[0032] S1. 5 g of crude single-walled carbon nanotubes were placed in a tube furnace and calcined at 600 ° C with a flow rate of 800 sccm of carbon dioxide for 3 h;

[0033] S2. The calcined sample obtained in S1 was added to 50 mL of toluene and refluxed for 16 h;

[0034] S3. The suspension after reflux is centrifuged to remove the supernatant and washed to neutrality;

[0035] S4. Add 20g polyvinyl pyrrolidone and 500mL concentrated nitric acid (60wt%) at the same time, stir for 30min until uniform, wash with distilled water until neutral and then dry; calcine at 600℃ for 5h to remove residual polyvinyl pyrrolidone, and obtain 2g purified single-walled carbon nanotubes with a yield of 40%.

[0036] Figure 1 A purification process roadmap for the multi-step treatment method for effectively purifying single-walled carbon nanotubes provided by the present invention; Figure 2 The SEM comparison diagram of the single-walled carbon nanotubes before and after purification in Example 1 is shown in FIG. Figure 1 It can be seen that the single-walled carbon nanotubes are in a bundle state, but are easy to agglomerate and are not evenly dispersed.

[0037] The carbon tube content in the purified single-walled carbon nanotubes obtained in this example was measured by TGA method, and the content was 62%, and the metal impurity content was 5%.

[0038] Example 2

[0039] S1. 5 g of crude single-walled carbon nanotubes were placed in a tube furnace and calcined at 900 ° C with carbon dioxide at a flow rate of 800 sccm for 3 h;

[0040] S2. The calcined sample obtained in S1 was added to 50 mL of toluene and refluxed for 16 h;

[0041] S3. The suspension after reflux is centrifuged to remove the supernatant and washed to neutrality;

[0042] S4. Add 20g polyvinyl pyrrolidone and 500mL concentrated nitric acid (60wt%) at the same time, stir for 30min until uniform, wash with distilled water until neutral and then dry; calcine at 900℃ for 5h to remove residual polyvinyl pyrrolidone, and obtain 4g purified single-walled carbon nanotubes with a yield of 80%.

[0043] Figure 3 This is a SEM comparison of the single-walled carbon nanotubes before and after purification in Example 2. Figure 3 It can be seen that the single-walled carbon nanotubes are in a bundle state, have fewer impurities and are relatively evenly dispersed.

[0044] The carbon tube content in the purified single-walled carbon nanotubes obtained in this example was measured by TGA method, and the content was 80%, and the content of metal impurities was 1.5%.

[0045] Example 3

[0046] S1. 5 g of crude single-walled carbon nanotubes were placed in a tube furnace and calcined at 750 ° C for 3 h with carbon dioxide flowing at a flow rate of 800 sccm;

[0047] S2. The calcined sample obtained in S1 was added to 50 mL of toluene and refluxed for 16 h;

[0048] S3. The suspension after reflux is centrifuged to remove the supernatant and washed to neutrality;

[0049] S4. Add 20g polyvinyl pyrrolidone and 500mL concentrated nitric acid (60wt%) at the same time, stir for 30min until uniform, wash with distilled water until neutral and then dry; calcine at 600℃ for 5h to remove residual polyvinyl pyrrolidone, and obtain 3.1g purified single-walled carbon nanotubes with a yield of 62%.

[0050] Comparative Example 1

[0051] The same as Example 2, except that the carbon dioxide in S1 was replaced by water vapor, and 3.4 g of purified single-walled carbon nanotubes were obtained with a yield of 68%.

[0052] The carbon tube content in the purified single-walled carbon nanotubes obtained in this comparative example was measured by TGA method, and the content was 72%, and the content of metal impurities was 4.2%.

[0053] Comparative Example 2

[0054] The same as Example 2, except that the carbon dioxide in S1 was replaced by air, and 3.8 g of purified single-walled carbon nanotubes were obtained with a yield of 76%.

[0055] The carbon tube content in the purified single-walled carbon nanotubes obtained in this comparative example was measured by TGA method, and the content was 73%, and the content of metal impurities was 4.1%.

[0056] Comparative Example 3

[0057] The same as Example 2, except that no polyvinyl pyrrolidone was added to S4, and 3.9 g of purified single-walled carbon nanotubes were obtained with a yield of 78%.

[0058] The carbon tube content in the purified single-walled carbon nanotubes obtained in this comparative example was measured by TGA method, and the content was 60%, and the content of metal impurities was 4.6%.

[0059] Comparative Example 4

[0060] 5 g of crude single-walled carbon nanotubes were purified with reference to Example 1 in patent CN 109650379 A to obtain 2.5 g of purified single-walled carbon nanotubes with a yield of 50%.

[0061] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A multi-step process for effectively purifying single-walled carbon nanotubes, characterized in that: The method comprises the following steps: placing a crude single-walled carbon nanotube in a reactor, introducing inert nitrogen gas, heating, introducing weak oxidizing gas, calcining, placing the calcined product in toluene, refluxing to remove impurities, centrifuging the suspension obtained after reflux, removing the supernatant, washing to neutrality, adding polyvinyl pyrrolidone and concentrated acid to the washed product, stirring for 30 minutes, washing to neutrality after reaction, drying, and calcining again to obtain purified single-walled carbon nanotubes.

2. The multi-step treatment method for effectively purifying single-walled carbon nanotubes according to claim 1, characterized in that: The weak oxidizing gas is carbon dioxide, which enters the reactor at a flow rate of 800 sccm until the partial pressure of the carbon dioxide reaches 0.1 MPa.

3. The multi-step treatment method for effectively purifying single-walled carbon nanotubes according to claim 1, characterized in that: The heating temperature is 600-900° C., and the calcination time is 3 hours.

4. The multi-step treatment method for effectively purifying single-walled carbon nanotubes according to claim 1, characterized in that: The mass ratio of the washed product to polyvinyl pyrrolidone is 4:

100.

5. The multi-step treatment method for effectively purifying single-walled carbon nanotubes according to claim 1, characterized in that: The usage ratio of the polyvinyl pyrrolidone to the concentrated acid is 1 g: 25 mL.

6. The multi-step treatment method for effectively purifying single-walled carbon nanotubes according to claim 1, characterized in that: The concentrated acid is selected from sulfuric acid, nitric acid, hydrochloric acid, aqua regia or hydrofluoric acid.

7. The multi-step treatment method for effectively purifying single-walled carbon nanotubes according to claim 1, characterized in that: The re-calcination temperature is 600-900°C.

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