Purification method of single-walled carbon nanotube

Abstract

The invention discloses a purification method of a single-walled carbon nanotube. The purification method comprises the following steps: S1, mixing and stirring oxidizing acid and a single-walled carbon nanotube crude product, and refluxing I to obtain a suspension; and S2, mixing a non-oxidizing acid and the suspension, continuing reflux II, and carrying out solid-liquid separation to obtain the product. According to the method, oxidizing acid and non-oxidizing acid are combined, firstly, the oxidizing acid and a single-walled carbon nanotube crude product are subjected to reflux reaction, a carbon coating layer of metal oxide is rapidly and effectively opened, and most amorphous carbon is degraded. The non-oxidizing acid is added for reflux, the non-oxidizing acid dissolves the exposed metal catalyst with the mild protonic acid characteristic and actively inhibits excessive erosion to the carbon tube body, amorphous carbon and fully exposed residual metal catalyst particles can be fully dissolved and removed, and the high purity is achieved while the residual metal catalyst particles are fully exposed. The inherent structure and intrinsic performance of the carbon nano tube are protected to the maximum extent, and deep removal of metal impurities is achieved.

Description

Technical Field

[0001] This invention relates to the field of carbon nanotube purification technology, and in particular to a method for purifying single-walled carbon nanotubes. Background Technology

[0002] The purification methods for single-walled carbon nanotubes in related technologies include liquid-phase oxidation, gradient oxidation, and density gradient centrifugation. Liquid-phase oxidation uses strong acid oxidation, but this method easily damages the carbon nanotube structure and impairs its intrinsic properties. Gradient oxidation struggles to remove stubborn amorphous carbon or carbon coatings and cannot remove metallic impurities. Density gradient centrifugation is time-consuming, costly, and difficult to scale up.

[0003] Therefore, it is necessary to develop a purification method for single-walled carbon nanotubes that can efficiently remove metal impurities while preserving the complete structure of the carbon nanotubes to the maximum extent. Summary of the Invention

[0004] The present invention aims to at least solve one of the technical problems existing in the prior art. To this end, the first aspect of the present invention proposes a purification method for single-walled carbon nanotubes, which can achieve efficient removal of metal impurities while preserving the complete structure and excellent properties of the carbon nanotubes to the maximum extent.

[0005] According to a first aspect of the present invention, a method for purifying single-walled carbon nanotubes is provided, comprising the following steps: S1. Mix and stir the oxidizing acid and crude single-walled carbon nanotubes, and reflux them to obtain a suspension; S2. Mix the non-oxidizing acid and the suspension and continue reflux II to obtain the solid-liquid separation.

[0006] According to a preferred embodiment of the present invention, the molar ratio of the oxidizing acid to the non-oxidizing acid is (1~4):1.

[0007] According to a preferred embodiment of the present invention, the total concentration of the oxidizing acid and the non-oxidizing acid is 0.1~3.5 mol / L.

[0008] According to a preferred embodiment of the present invention, the total concentration of the oxidizing acid and the non-oxidizing acid is 1~3 mol / L.

[0009] According to a preferred embodiment of the present invention, the oxidizing acid includes nitric acid and / or sulfuric acid.

[0010] According to a preferred embodiment of the present invention, the non-oxidizing acid includes at least one of hydrochloric acid, acetic acid, or oxalic acid.

[0011] According to a preferred embodiment of the present invention, the reflux time is 0.5h to 1.5h.

[0012] According to a preferred embodiment of the present invention, the reflux II time is 2h to 4h.

[0013] According to a preferred embodiment of the present invention, the reaction temperatures of reflux I and reflux II are independently selected from 90°C to 130°C.

[0014] According to a preferred embodiment of the present invention, in step S1, the stirring speed is 50-800 rpm.

[0015] According to a preferred embodiment of the present invention, the solid-liquid separation step includes filtration, washing, and drying.

[0016] According to a preferred embodiment of the present invention, the washing refers to washing the filter cake multiple times with deionized water until the pH value of the filtrate stabilizes between 6 and 7.

[0017] The purification method according to embodiments of the present invention has at least the following beneficial effects: This invention combines oxidizing and non-oxidizing acids. First, the oxidizing acid and crude single-walled carbon nanotubes undergo a reflux reaction, rapidly and effectively opening the carbon coating layer of the metal oxide and degrading most of the amorphous carbon. Then, a non-oxidizing acid is added and refluxed. The non-oxidizing acid, with its mild protic acid properties, dissolves the exposed metal catalyst and actively inhibits excessive erosion of the carbon nanotubes. This allows for the thorough dissolution and removal of amorphous carbon and fully exposed residual metal catalyst particles. Simultaneously, as the non-oxidizing acid gradually becomes dominant, the overall oxidizing power of the system automatically decreases, thus protecting the structure of the single-walled carbon nanotubes. In other words, while achieving high purity, the inherent structure and intrinsic properties of the carbon nanotubes are preserved to the maximum extent, achieving deep removal of metal impurities.

[0018] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. Attached Figure Description

[0019] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 This is a SEM image of the crude carbon nanotubes of the present invention; Figure 2 This is a SEM image of the purified carbon nanotubes from Example 1 of the present invention; Figure 3 This is the Raman spectrum of the crude carbon nanotubes of the present invention; Figure 4This is the Raman spectrum of the purified carbon nanotubes of Example 1 of the present invention. Detailed Implementation

[0020] The following are specific embodiments of the present invention, and the technical solutions of the present invention will be further described in conjunction with the embodiments, but the present invention is not limited to these embodiments.

[0021] Unless otherwise specified, the reagents, methods and equipment used in this invention are all conventional reagents, methods and equipment in this technical field.

[0022] In some embodiments of the present invention, a method for purifying single-walled carbon nanotubes is provided, comprising the following steps: S1. Mix and stir the oxidizing acid and crude single-walled carbon nanotubes, and reflux them to obtain a suspension; S2. Mix the non-oxidizing acid and the suspension and continue reflux II to obtain the solid-liquid separation.

[0023] Understandably, this invention combines oxidizing and non-oxidizing acids. First, the oxidizing acid and crude single-walled carbon nanotubes undergo a reflux reaction, rapidly and effectively opening the carbon coating layer of the metal oxide and degrading most of the amorphous carbon. Then, a non-oxidizing acid is added and refluxed. This non-oxidizing acid, with its mild protic acid properties, dissolves the exposed metal catalyst and actively inhibits excessive erosion of the carbon nanotubes. This allows for the thorough dissolution and removal of amorphous carbon and fully exposed residual metal catalyst particles. Simultaneously, as the non-oxidizing acid gradually becomes dominant, the overall oxidizing power of the system automatically decreases, thereby protecting the structure of the single-walled carbon nanotubes. In other words, while achieving high purity, the inherent structure and intrinsic properties of the carbon nanotubes are preserved to the maximum extent, achieving deep removal of metal impurities.

[0024] In some embodiments of the present invention, the molar ratio of the oxidizing acid to the non-oxidizing acid is (1~4):1. For example, it includes sub-ranges of 1:1, 1.5:1, 2:1, 2.5:1, 3.0:1, 3.5:1, 4:1 or any two of the above ratios.

[0025] Therefore, a ratio lower than 1:1 results in a low concentration of oxidizing acid, insufficient oxidizing power, and poor purification effect. A ratio higher than 4:1 means that the addition of a small amount of non-oxidizing acid cannot effectively inhibit carbon nanotube destruction, easily leading to carbon nanotube damage and a decrease in yield and performance.

[0026] In some embodiments of the present invention, the molar ratio of the oxidizing acid to the non-oxidizing acid is (1~2):1. Therefore, within this concentration range, impurity removal and structural protection of the single-walled carbon nanotubes can be guaranteed.

[0027] In some embodiments of the present invention, the total concentration of the oxidizing acid and the non-oxidizing acid is 0.1 to 3.5 mol / L. For example, it includes sub-ranges such as 0.1 mol / L, 0.2 mol / L, 0.5 mol / L, 0.8 mol / L, 1.0 mol / L, 1.5 mol / L, 1.7 mol / L, 2 mol / L, 2.5 mol / L, 2.8 mol / L, 3.0 mol / L, 3.5 mol / L, or any two of the above values.

[0028] In some embodiments of the present invention, the total concentration of the oxidizing acid and the non-oxidizing acid refers to the concentration expressed in H⁺. + Ion concentration calculation.

[0029] In some embodiments of the present invention, the total concentration of the oxidizing acid and the non-oxidizing acid is 1 to 3 mol / L. For example, it includes 1.0 mol / L, 1.5 mol / L, 1.7 mol / L, 2 mol / L, 2.5 mol / L, 2.8 mol / L, 3.0 mol / L, or any sub-range consisting of two of the above values.

[0030] Therefore, an acid concentration of 1-3 mol / L provides a sufficiently high proton (H) concentration. + ) and oxidizing agents (such as NO3) - NO2 produced in hot acid + The concentration of the oxidizing acid is crucial; too low a concentration will result in a slow reaction, excessively long purification time, and incomplete purification. Too high a concentration, meaning a higher concentration of oxidizing acid, will lead to an excessively strong oxidation potential, causing indiscriminate attack on intact carbon nanotubes.

[0031] In some embodiments of the present invention, the oxidizing acid includes nitric acid and / or sulfuric acid.

[0032] Therefore, nitric acid has a relatively mild oxidizing effect and causes less damage to the carbon nanotubes themselves. It tends to selectively oxidize defect sites and amorphous carbon with higher reactivity, exposing the carbon nanotubes tightly encased in a carbon shell. Sulfuric acid can remove water from organic matter and can insert into carbon nanotube bundles, allowing the internal metal catalyst particles to be more fully exposed and dissolved.

[0033] In some embodiments of the present invention, the non-oxidizing acid includes at least one of hydrochloric acid, acetic acid, or oxalic acid.

[0034] In some embodiments of the present invention, the reflux I time is 0.5h to 1.5h. For example, it includes 0.5h, 0.7h, 0.8h, 1h, 1.2h, 1.5h, or any subrange consisting of two of the above values.

[0035] Thus, before the carbon nanotube body is significantly eroded, the efficiency of impurity removal is maximized, balancing purity and structural integrity.

[0036] In some embodiments of the present invention, the reflux II time is 2h to 4h. This includes sub-ranges such as 2h, 2.2h, 2.4h, 2.5h, 2.8h, 3.0h, 3.2h, 3.4h, 3.6h, 3.8h, 4h, or any two of the above values.

[0037] Therefore, the exposed metal ions can be largely dissolved within this time, while the carbon nanotubes are chemically passivated and protected.

[0038] In some embodiments of the present invention, the reaction temperatures of reflux I and reflux II are independently selected from 90°C to 130°C. For example, they include 90°C, 95°C, 100°C, 105°C, 110°C, 115°C, 120°C, 125°C, 130°C, or any sub-range composed of any two of the above values.

[0039] In some embodiments of the present invention, in step S1, the stirring speed is 50-800 rpm. For example, it includes 50 rpm, 60 rpm, 70 rpm, 80 rpm, 90 rpm, 100 rpm, 150 rpm, 250 rpm, 350 rpm, 400 rpm, 450 rpm, 500 rpm, 550 rpm, 600 rpm, 650 rpm, 700 rpm, 750 rpm, 800 rpm, or any sub-range of any two of the above values.

[0040] In some embodiments of the present invention, the solid-liquid separation steps include filtration, washing, and drying.

[0041] In some embodiments of the present invention, the washing refers to washing the filter cake multiple times with deionized water until the pH value of the filtrate stabilizes between 6 and 7.

[0042] The crude carbon nanotubes of the present invention are prepared by a controlled plasma-enhanced catalytic pyrolysis method to produce crude single-walled carbon nanotubes. For the specific preparation method, please refer to Example 1 of CN120039867A.

[0043] Example 1 This example provides a method for purifying single-walled carbon nanotubes, including the following steps: S1. First, mix nitric acid and 10g of crude carbon nanotubes, and stir at a constant speed of 300 rpm. React under reflux (100℃) for 1 hour to obtain a suspension. S2. Add hydrochloric acid to the above suspension and continue reflux for 3 hours to obtain a mixture. Filter the mixture through a 0.8-8 μm microporous membrane and wash the filter cake repeatedly with deionized water until the pH of the washing solution is approximately 7 as measured by pH paper. Collect the filter cake and dry it to obtain the purified single-walled carbon nanotubes.

[0044] The total concentration of nitric acid and hydrochloric acid is 2 mol / L, and the molar ratio is 2:1.

[0045] Examples 2-10 Examples 2-10 provide a series of purification methods for single-walled carbon nanotubes. The specific steps are the same as in Example 1, and other conditions are shown in Table 1.

[0046] Table 1

[0047] Comparative Examples 1-9 Comparative Examples 1-9 provide a series of purification methods for single-walled carbon nanotubes. The specific steps are the same as in Example 1, and other conditions are shown in Table 2.

[0048] Table 2

[0049] Comparative Example 10 This example provides a method for purifying single-walled carbon nanotubes, including the following steps: S1. First, mix nitric acid and 10g of crude carbon nanotubes, stir at a constant speed of 300 rpm, react under reflux (100℃) for 1 hour, and then filter to obtain the intermediate. S2. Refluxing hydrochloric acid and the intermediate for 3 hours yields a mixture. Filter the mixture through a 0.8-8 μm microporous membrane and repeatedly wash the filter cake with deionized water until the pH of the washing solution is approximately 7 as measured by pH paper. Collect the filter cake and dry it to obtain purified single-walled carbon nanotubes.

[0050] The total concentration of nitric acid and hydrochloric acid is 2 mol / L, and the molar ratio is 2:1.

[0051] Performance testing First, the prepared crude single-walled carbon nanotubes were subjected to SEM testing, and the results are as follows: Figure 1 As shown, a large number of amorphous carbon impurities and metal particles can be seen in the crude product.

[0052] The purified single-walled carbon nanotubes from Example 1 of this invention were then subjected to SEM testing, and the results are as follows: Figure 2 As shown, the purified single-walled carbon nanotubes have a smooth surface with no impurities attached.

[0053] Furthermore, the single-walled carbon nanotube products of the embodiments and comparative examples of the present invention were taken and their total metal content was detected by ICP-OES (inductively coupled plasma optical emission spectroscopy) method, and the metal removal rate was calculated (metal removal rate % = [(initial metal content - purified metal content) / initial metal concentration] * 100, the initial metal content of crude single-walled carbon nanotubes was 20%).

[0054] Furthermore, through the Raman spectrum I G / I D The integrity of the single-walled carbon nanotube structure before and after purification during the purification process was compared. Figure 3 Raman spectrum of crude single-walled carbon nanotubes; Figure 4 The image shows the Raman spectrum of the purified single-walled carbon nanotubes from Example 1. The same testing method was used to test the Ig of the remaining single-walled carbon nanotubes from the examples and comparative examples. G / I D The results are shown in Table 3.

[0055] Table 3

[0056] As can be seen from the data in Table 3, the purification methods in the comparative examples either have low metal impurity removal rates or damage the integrity of single-walled carbon nanotubes. However, the purification method for single-walled carbon nanotubes in this embodiment of the invention can both ensure high metal impurity removal rates and prevent damage to the single-walled carbon nanotubes.

[0057] The present invention has been described in detail above with reference to the embodiments of the present invention. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A method for purifying single-walled carbon nanotubes, characterized in that, Includes the following steps: S1. Mix and stir the oxidizing acid and crude single-walled carbon nanotubes, and reflux them to obtain a suspension; S2. Mix the non-oxidizing acid and the suspension and continue reflux II to obtain the solid-liquid separation.

2. The purification method according to claim 1, characterized in that, The molar ratio of the oxidizing acid to the non-oxidizing acid is (1~4):

1.

3. The purification method according to claim 1, characterized in that, The total concentration of the oxidizing acid and the non-oxidizing acid is 0.1~3.5 mol / L.

4. The purification method according to claim 1, characterized in that, The oxidizing acids include nitric acid and / or sulfuric acid.

5. The purification method according to claim 1, characterized in that, The non-oxidizing acid includes at least one of hydrochloric acid, acetic acid, or oxalic acid.

6. The purification method according to claim 1, characterized in that, The reflux time is 0.5h to 1.5h.

7. The purification method according to claim 1, characterized in that, The reflux II time is 2h to 4h.

8. The purification method according to claim 1, characterized in that, The reaction temperatures for reflux I and reflux II are independently selected from 90℃ to 130℃.

9. The purification method according to claim 1, characterized in that, In step S1, the stirring speed is 50-800 rpm.

10. The purification method according to claim 1, characterized in that, The solid-liquid separation steps include filtration, washing, and drying.

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