Method for Separating Long Carbon Nanotubes and Short Carbon Nanotubes

Abstract

The present invention provides a method for separating long carbon nanotubes and short carbon nanotubes, which comprises the following steps: (1) preparing a composite dispersion of carbon nanotube raw materials in a container, wherein the composite dispersion contains a first surfactant, a second surfactant, carbon nanotube raw materials and a solvent; wherein the first surfactant is different from the second surfactant; (2) allowing the composite dispersion to stand still so that the long carbon nanotubes agglomerate and precipitate to the bottom of the container, and the short carbon nanotubes are suspended in the supernatant. The method of the present invention is convenient, efficient and low-cost. The method of the present invention does not rely on gel media and liquid chromatography equipment, and the yield of long carbon nanotubes can be increased by enlarging the volume of the container. The method of the present invention is also applicable to carbon nanotube raw materials with different diameters grown by different methods, and has universality.

Description

Technical Field

[0001] The present invention belongs to the field of materials. Specifically, the present invention relates to a method for separating long carbon nanotubes and short carbon nanotubes. Background Art

[0002] As a one-dimensional tubular carbon nanomaterial, carbon nanotubes not only have a nanoscale diameter but also an extremely high aspect ratio, and their diameters are usually between several hundred nanometers and several micrometers. Due to the extremely strong van der Waals interaction between carbon nanotubes, the synthesized carbon nanotube materials usually exist in the form of agglomerated bundles. How to effectively disperse the synthesized carbon nanotube bundles in an aqueous solution or an organic solution to prepare a monodisperse carbon nanotube dispersion is crucial for the further purification and application of carbon nanotube materials.

[0003] In order to achieve the effective dispersion of carbon nanotubes, various dispersant molecules, such as conjugated polymers, surfactants, and biomolecules, have been widely used. In the prior art, usually a surfactant is used to separate long carbon nanotubes and short carbon nanotubes, but this method using a single surfactant often requires the assistance of complex equipment (such as a liquid chromatograph) to separate long carbon nanotubes and short carbon nanotubes. For example, the method disclosed in the prior art US7131537 B2 discloses a method for separating the lengths of carbon nanotubes. The specific content involves loading a carbon nanotube dispersion into a gel column of polystyrene divinylbenzene resin. Due to the different flow paths of carbon nanotubes with different lengths in the gel column, long carbon nanotubes flow out of the gel column earlier than short carbon nanotubes. It can be seen that the prior art methods for separating long carbon nanotubes and short carbon nanotubes require a gel as the stationary phase, the separation effect strongly depends on the type of gel, and the separation operation requires expensive liquid chromatograph equipment, with a complex process and high cost.

[0004] How to simply and efficiently extract long carbon nanotubes from a carbon nanotube dispersion with a certain length distribution is a key technology for realizing their applications in high-performance optoelectronic devices. Some of the prior art also realizes the length separation of carbon nanotubes based on gel chromatography with a size screening effect, that is, under non-adsorbing conditions, long carbon nanotubes flow out of the gel column earlier than short carbon nanotubes. However, the resolution of the length of carbon nanotubes by this method is still very limited, resulting in that the obtained long carbon nanotube dispersion is always doped with some short carbon nanotubes, and this method requires a large amount of gel medium and expensive liquid chromatograph equipment, which greatly limits the further large-scale preparation of long carbon nanotube dispersions.

[0005] Therefore, there is an urgent need for a convenient, efficient, and low-cost method for separating long carbon nanotubes and short carbon nanotubes. Summary of the Invention

[0006] The object of the present invention is to provide a method for separating long carbon nanotubes and short carbon nanotubes, which is convenient, efficient and low-cost. The method of the present invention lays an important foundation for the large-scale preparation of long carbon nanotube dispersions and the realization of their applications in high-performance optoelectronic devices.

[0007] The above object of the present invention is achieved by the following technical solutions.

[0008] In the context of the present invention, the term "long carbon nanotube" refers to a carbon nanotube with a length of greater than or equal to 400 nanometers.

[0009] In the context of the present invention, the term "short carbon nanotube" refers to a carbon nanotube with a length of less than 400 nanometers.

[0010] The present invention provides a method for separating long carbon nanotubes and short carbon nanotubes, which comprises the following steps:

[0011] (1) Prepare a composite dispersion of carbon nanotube raw materials in a container, the composite dispersion comprising a first surfactant, a second surfactant, carbon nanotube raw materials and a solvent; wherein the first surfactant is different from the second surfactant;

[0012] (2) Let the composite dispersion stand still, so that the long carbon nanotubes agglomerate and precipitate to the bottom of the container, and the short carbon nanotubes are suspended in the supernatant.

[0013] The inventors of the present invention unexpectedly found that in a dual surfactant system (representative surfactants are sodium dodecyl sulfate and sodium cholate), the dispersibility of long carbon nanotubes is significantly lower than that of short carbon nanotubes. Within several hours to dozens of hours, the long carbon nanotubes with weak dispersibility undergo natural agglomeration, resulting in the appearance of flocs and precipitation to the bottom of the container; the short carbon nanotubes with strong dispersibility do not undergo natural agglomeration and precipitation, and are always isolated and suspended in the solution under the wrapping of the surfactant. Without wishing to be bound by theory, the method of the present invention is based on the different dispersibilities of carbon nanotubes with different lengths in the surfactant solution, and separates the long carbon nanotubes and short carbon nanotubes in the dispersion by adjusting the types and concentrations of surfactants. Since there is a certain competitive relationship between the dual surfactants in coating the carbon nanotubes. In the dual surfactant system, the combination and concentration of different types of surfactants directly determine the coating state of the dual surfactants on the surface of the carbon nanotubes, thereby affecting the dispersibility of the long carbon nanotubes and causing different degrees of agglomeration and precipitation.

[0014] Preferably, in the method of the present invention, the first surfactant and the second surfactant are each independently selected from any one of sodium cholate (SC), sodium deoxycholate (DOC), sodium dehydrocholate, sodium hyodeoxycholate (SHC), sodium chenodeoxycholate, sodium cholate hydrate, sodium dodecyl sulfate (SDS), sodium n-hexadecyl sulfate, sodium octyl sulfate, and sodium decyl sulfate.

[0015] Preferably, in the method of the present invention, the step of formulating the carbon nanotube raw material into a composite dispersion liquid in a container in step (1) is carried out by a method including the following steps:

[0016] (a) Dispersing the carbon nanotube raw material with a first surfactant solution to obtain an initial dispersion liquid;

[0017] (b) Adding a second surfactant to the initial dispersion liquid to obtain a composite dispersion liquid.

[0018] Preferably, in the method of the present invention, the step of dispersing the carbon nanotube raw material with the first surfactant solution in step (a) is carried out under ultrasonic conditions.

[0019] Preferably, in the method of the present invention, the ultrasonic treatment is carried out under the following conditions: the ultrasonic output power density is 2 - 40 W / cm 2 , and the ultrasonic time is 0.1 - 20 hours.

[0020] Preferably, in the method of the present invention, based on the weight of the composite dispersion liquid excluding the carbon nanotube raw material being 100%, the amount of the first surfactant accounts for 0.1% - 5%, preferably 0.2% - 2%; the amount of the second surfactant accounts for 1.2% - 5%, preferably 1.5% - 3%; the balance is a solvent;

[0021] Based on weight, the weight ratio of the carbon nanotube raw material to the weight of the composite dispersion liquid excluding the carbon nanotube raw material is 0.000001 - 0.005:1, preferably 0.00001 - 0.002:1.

[0022] Preferably, in the method of the present invention, the method further includes the following steps after step (2):

[0023] (3) Removing the supernatant obtained in step (2) to obtain a precipitate; subsequently dispersing the precipitate in a solution having a surfactant.

[0024] The present invention does not particularly limit the choice of the solvent, and conventional solvents in the art can be used, such as water. Of course, common organic solvents or other inorganic solvents in the art can also be used.

[0025] Preferably, in the method of the present invention, the carbon nanotube raw material is selected from at least one of CoMoCAT, HiPco, Plasma, and Arc-Discharge.

[0026] In a specific embodiment of the present invention, the ultrasonic treatment in step (a) is carried out using a water bath ultrasonic device or a cell disruptor.

[0027] In a specific embodiment of the present invention, when using a cell disruptor, the volume of the dispersion liquid is 1 - 1000 ml, the ultrasonic output power density is 2 - 40 W / cm 2 , and the ultrasonic time is 0.1 - 20 hours.

[0028] In the method of the present invention, the carbon nanotube raw material can be carbon nanotubes grown and synthesized by different methods, which can be non-functionalized carbon nanotubes or functionalized carbon nanotubes, and the diameter range can be 0.6 - 2.0 nanometers.

[0029] In a specific embodiment of the present invention, the composite dispersion liquid obtained in step (2) is allowed to stand, and the standing time is several hours to dozens of hours. In a specific embodiment of the present invention, the standing time is 4 - 48 hours. After flocculent precipitation occurs in the composite dispersion liquid, first slowly remove the supernatant from the container, then add the required surfactant solution to the precipitate, and disperse it by shaking or water bath ultrasonic treatment. For example, in a preferred embodiment, the added surfactant solution is sodium cholate.

[0030] The present invention has the following beneficial effects:

[0031] (1) Compared with the traditional gel chromatography method for screening the length of carbon nanotubes, the method of the present invention has the following advantages: by controlling the types and concentrations of the double surfactants, the content ratio of long carbon nanotubes in the precipitate is much higher than that of the long carbon nanotubes obtained by the gel chromatography method, showing a higher resolution for the length of carbon nanotubes.

[0032] (2) The method of the present invention does not rely on gel media and liquid chromatography equipment, and the yield of long carbon nanotubes can be increased by expanding the volume of the container.

[0033] (3) The method of the present invention is also applicable to carbon nanotube raw materials with different diameters grown by different methods, and has universality.

[0034] (4) The method of the present invention lays an important foundation for the large-scale preparation of long carbon nanotube dispersion liquids and the realization of their high-performance optoelectronic device applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Hereinafter, the embodiments of the present invention will be described in detail with reference to the drawings, wherein:

[0036] Figure 1 is the method for separating long carbon nanotubes and short carbon nanotubes adopted in Embodiments 1-4 of the present invention;

[0037] Figure 2 are the changes before and after the carbon nanotube dispersion liquid in Embodiment 1 of the present invention stands still, and the atomic force microscope characterizations of the carbon nanotubes in the supernatant and the precipitate after standing still;

[0038] Figure 3 are the photos of the carbon nanotubes after standing still under different dosages of the double surfactant system in Embodiment 2;

[0039] Figure 4 are the photos of the carbon nanotubes after standing still under the SDS+SHC and SDS+DOC double surfactant systems in Embodiment 3, and the atomic force microscope characterizations of the carbon nanotubes in the supernatant and the precipitate after standing still;

[0040] Figure 5 are the changes before and after the standing still of different types of carbon nanotube dispersion liquids in Embodiment 4, and the atomic force microscope characterizations of the carbon nanotubes in the supernatant and the precipitate after standing still;

[0041] Figure 6 are the photos of the carbon nanotubes after standing still under the single surfactant system in Comparative Example 1 and Comparative Example 2. Detailed Embodiments

[0042] The present invention will be further described in detail below in conjunction with the detailed embodiments. The provided embodiments are only for clarifying the present invention and not for limiting the scope of the present invention.

[0043] Example 1

[0044] 1) Weigh 40 mg of carbon nanotubes and 0.4 g of sodium cholate powder, and add them together to 39.6 g of water. Use a cell disruptor to ultrasonically disperse the above solution at a power of 30 W / cm 2 for 45 minutes at a temperature of 15°C. The carbon nanotube raw material is single-walled carbon nanotubes synthesized by the arc discharge method and commercially available from Sigma-Aldrich Company, USA.

[0045] 2) Centrifuge and purify to remove impurities such as metal catalyst particles, carbon nanotube bundles, and amorphous carbon in the dispersion liquid in Step 1). Set the centrifugal force to 210000×g and the centrifugation time to 60 minutes, and take out the supernatant.

[0046] 3) Add 4 g of sodium dodecyl sulfate to the supernatant obtained in Step 2), and adjust the surfactant in the carbon nanotube dispersion liquid to a composite surfactant of sodium dodecyl sulfate and sodium cholate (SDS+SC) by adding 156 g of pure water. The total mass of the surfactant solution is 200 g.

[0047] 4) After allowing the double surfactant-carbon nanotube dispersion in step 3) to stand for 48 hours, record the photos of the solution before and after standing, as Figure 2 shown in a.

[0048] 5) After recording the photos of each solution, following the Figure 1 procedure shown, take out the supernatant and then add an aqueous solution of sodium cholate into the container and shake until the precipitated carbon nanotubes are redispersed evenly.

[0049] 6) Characterize the two portions of carbon nanotubes obtained in step 5) using an atomic force microscope and label them as supernatant and precipitate respectively, as Figure 2 shown in b.

[0050] Example 2

[0051] 1) Weigh 40 mg of carbon nanotubes and 0.4 g of sodium cholate powder and add them together to 39.6 g of water. Use a cell disruptor to ultrasonically disperse the above solution at a power of 30 W / cm 2 for 45 minutes at a temperature of 15 °C. The carbon nanotube raw material is single-walled carbon nanotubes synthesized by the arc discharge method and commercially available from Sigma-Aldrich, USA.

[0052] 2) Centrifuge and purify to remove impurities such as metal catalyst particles, carbon nanotube bundles, and amorphous carbon in the dispersion in step 1). Set the centrifugal force to 210,000×g and the centrifugation time to 60 minutes, and take out the supernatant.

[0053] 3) Repeat steps 1) and 2) to obtain six portions of the same supernatant.

[0054] 4) Add 0.4 g, 2 g, 3 g, 4 g, 5 g, and 6 g of sodium dodecyl sulfate to the six portions of supernatant obtained in step 3) respectively, and adjust the total mass of the surfactant solution to 200 g by adding pure water.

[0055] 5) After allowing the six portions of double surfactant-carbon nanotube dispersions in step 4) to stand for 48 hours, record the photos of the solutions after standing, as Figure 3 shown.

[0056] From Figure 3As can be seen from the results, precipitation does not occur when the amount of sodium dodecyl sulfate is less than or equal to 2 g (i.e., based on the weight of the composite dispersion excluding the carbon nanotube raw material being 100%, the amount of sodium dodecyl sulfate accounts for 1%), and precipitation occurs when the amount of sodium dodecyl sulfate is greater than or equal to 3 g (i.e., based on the weight of the composite dispersion excluding the carbon nanotube raw material being 100%, the amount of sodium dodecyl sulfate accounts for 1.5%). Moreover, as the amount of sodium dodecyl sulfate increases, the precipitation amount of carbon nanotubes gradually increases.

[0057] Example 3

[0058] 1) Weigh 40 mg of carbon nanotubes and 0.4 g of sodium hyodeoxycholate (SHC), and add them together to 39.6 g of water. Use a cell disruptor at a power of 30 W / cm 2 Ultrasonically disperse the above two solutions at a temperature of 15 °C for 45 minutes. The carbon nanotube raw material is single-walled carbon nanotubes synthesized by arc discharge method and commercially available from Sigma-Aldrich, USA.

[0059] 2) Weigh 40 mg of carbon nanotubes and 0.4 g of sodium deoxycholate (DOC), and add them together to 39.6 g of water. Use a cell disruptor at a power of 30 W / cm 2 Ultrasonically disperse the above two solutions at a temperature of 15 °C for 45 minutes. The carbon nanotube raw material is single-walled carbon nanotubes synthesized by arc discharge method and commercially available from Sigma-Aldrich, USA.

[0060] 3) Centrifuge and purify to remove impurities such as metal catalyst particles, carbon nanotube bundles, and amorphous carbon in the two dispersions in steps 1) and 2). Set the centrifugal force to 210000×g and the centrifugation time to 60 minutes, and take out the supernatant.

[0061] 4) Add 4 g of sodium dodecyl sulfate to the two supernatants obtained in step 3), and adjust the surfactants in the carbon nanotube dispersions to composite surfactants of sodium dodecyl sulfate and sodium hyodeoxycholate, sodium deoxycholate (SDS+SHC and SDS+DOC) respectively by adding 156 g of pure water. The total mass of the surfactant solution is 200 g.

[0062] 5) After standing the two double-surfactant-carbon nanotube dispersions in step 4) for 48 hours, record the photos of the two solutions before and after standing, as Figure 4 shown in a and 4c.

[0063] 6) After recording the photos of each solution, according to the Figure 1 shown process, take out the supernatant and then add the sodium cholate aqueous solution to the container and shake until the precipitated carbon nanotubes are redispersed evenly.

[0064] 7) Characterize the carbon nanotubes in the supernatant and precipitate obtained under different combinations of double surfactants in step 6) using an atomic force microscope, and label them as supernatant and precipitate respectively, as shown in Figure 4 Figures 4b and 4d.

[0065] Example 4

[0066] 1) Weigh 40 mg of different types of carbon nanotubes, and add 0.4 g of sodium cholate powder to 39.6 g of water together. Use a cell disruptor at a power of 30 W / cm 2 Ultrasonically disperse the above two solutions at 15 °C for 45 minutes. The two carbon nanotube raw materials are CoMoCAT carbon nanotubes commercially available from Sigma-Aldrich and Hipco carbon nanotubes commercially available from NanoIntegris.

[0067] 2) Centrifuge and purify to remove impurities such as metal catalyst particles, carbon nanotube bundles, and amorphous carbon in the two carbon nanotube dispersions in step 1). Set the centrifugal force to 210,000 × g and the centrifugation time to 60 minutes, and take out the supernatant.

[0068] 3) Add 4 g of sodium dodecyl sulfate to the supernatant obtained in step 2), and adjust the surfactant in the four carbon nanotube dispersions to a composite surfactant of sodium dodecyl sulfate and sodium cholate (SDS+SC) by adding 156 g of pure water. The total mass of the surfactant solution is 200 g.

[0069] 4) After allowing the two double-surfactant-carbon nanotube dispersions in step 3) to stand for 48 hours, record the photos of the two solutions before and after standing, as shown in Figure 5 Figures 5a and 5c.

[0070] 5) After recording the photos of each solution, according to the Figure 1 procedure shown, take out the supernatant and then add an aqueous solution of sodium cholate to the container and shake until the precipitated carbon nanotubes are redispersed evenly.

[0071] 6) Characterize the supernatant and precipitate of the two carbon nanotubes obtained in step 5) using an atomic force microscope, and label them as supernatant and precipitate respectively, as shown in Figure 5 Figures 5b and 5d.

[0072] Comparative Example 1

[0073] 1) Weigh 40 mg of carbon nanotubes and 0.4 g of sodium cholate powder, and add them to 39.6 g of water together. Use a cell disruptor at a power of 30 W / cm 2The above solution was ultrasonically dispersed at a temperature of 15 °C for 45 minutes. The raw material of carbon nanotubes is single-walled carbon nanotubes synthesized by the arc discharge method and commercially available from Sigma-Aldrich, USA.

[0074] 2) The metal catalyst particles, carbon nanotube bundles, amorphous carbon and other impurities in the dispersion liquid in step 1) were removed by centrifugal purification. The centrifugal force was set at 210,000 × g and the centrifugation time was 60 minutes. The supernatant was taken out.

[0075] 3) 160 g of pure water was added to the first supernatant obtained in step 2) to adjust the amount of sodium cholate in the carbon nanotube dispersion liquid to be the same as that in Example 1, but without sodium dodecyl sulfate in Example 1.

[0076] 4) After the single surfactant-carbon nanotube dispersion liquid in step 3) was allowed to stand for 48 hours, a photo of the solution after standing was recorded, as Figure 6 shown in a.

[0077] Comparative Example 2

[0078] 1) Weigh 40 mg of carbon nanotubes and 0.8 g of sodium dodecyl sulfate powder, and add them together to 39.2 g of water. Using a cell disruptor at a power of 30 W / cm 2 The above solution was ultrasonically dispersed at a temperature of 15 °C for 45 minutes. The raw material of carbon nanotubes is single-walled carbon nanotubes synthesized by the arc discharge method and commercially available from Sigma-Aldrich, USA.

[0079] 2) The metal catalyst particles, carbon nanotube bundles, amorphous carbon and other impurities in the dispersion liquid in step 1) were removed by centrifugal purification. The centrifugal force was set at 210,000 × g and the centrifugation time was 60 minutes. The supernatant was taken out.

[0080] 3) 3.2 g of sodium dodecyl sulfate powder and 156.8 g of pure water were added to the second supernatant obtained in step 2) to adjust the amount of sodium dodecyl sulfate in the carbon nanotube dispersion liquid to be the same as that in Example 1, but without sodium cholate in Example 1.

[0081] 4) After the single surfactant-carbon nanotube dispersion liquid in step 3) was allowed to stand for 48 hours, a photo of the solution after standing was recorded, as Figure 6 shown in b.

Claims

1. A method for separating long carbon nanotubes and short carbon nanotubes, which comprises the following steps: (1) Prepare a composite dispersion of carbon nanotube raw materials in a container, the composite dispersion comprising a first surfactant, a second surfactant, carbon nanotube raw materials and a solvent; wherein the first surfactant is different from the second surfactant; (2) Let the composite dispersion stand, so that long carbon nanotubes agglomerate and precipitate to the bottom of the container, and short carbon nanotubes are suspended in the supernatant; Among them, The first surfactant and the second surfactant are each independently selected from any one of sodium cholate, sodium deoxycholate, sodium dehydrocholate, sodium hyodeoxycholate, sodium chenodeoxycholate, sodium cholate hydrate, sodium dodecyl sulfate, sodium n-hexadecyl sulfate, sodium octyl sulfate, and sodium decyl sulfate.

2. The method according to claim 1, wherein The step of preparing the composite dispersion of carbon nanotube raw materials in the container in step (1) is carried out by a method comprising the following steps: (a) Disperse the carbon nanotube raw materials with a first surfactant solution to obtain an initial dispersion; (b) Add a second surfactant to the initial dispersion to obtain a composite dispersion.

3. The method according to claim 2, wherein The step of dispersing the carbon nanotube raw materials with the first surfactant solution in step (a) is carried out under ultrasonic treatment.

4. The method according to claim 3, wherein The ultrasound is performed under the following conditions: the ultrasound output power density is 2 to 40 W / cm 2 , and the ultrasound time is 0.1 to 20 hours.

5. The method according to claim 1, wherein, Based on the weight of the composite dispersion excluding the carbon nanotube raw materials being 100%, the amount of the first surfactant accounts for 0.1% - 5%; the amount of the second surfactant accounts for 1.2% - 5%; the balance is the solvent; The weight ratio of the carbon nanotube raw materials to the composite dispersion excluding the carbon nanotube raw materials is 0.000001 - 0.005:

1.

6. The method according to claim 5, wherein The amount of the first surfactant accounts for 0.2% - 2%.

7. The method according to claim 5, wherein The amount of the second surfactant accounts for 1.5% - 3%.

8. The method according to claim 5, wherein The weight ratio of the carbon nanotube raw materials to the composite dispersion excluding the carbon nanotube raw materials is 0.00001 - 0.002:

1.

9. The method according to claim 1, wherein The method further comprises the following steps after step (2): (3) Remove the supernatant obtained in step (2) to obtain a precipitate; then disperse the precipitate in a solution with a surfactant.

10. The method according to claim 1, wherein, The carbon nanotube raw materials are selected from at least one of CoMoCAT, HiPco, Plasma, and Arc-Discharge.

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