Method for removing metal catalyst in carbon nanotube crude product

Abstract

The invention provides a method for removing a metal catalyst in a carbon nanotube crude product, and belongs to the technical field of carbon nanotubes. The method comprises the following steps: mixing a carbon nanotube crude product with a rolling medium, and rolling to obtain a disentangled material; mixing the disentangled material with a dispersing agent to obtain slurry; and carrying out magnetic separation on the slurry. In the rolling process, the carbon nanotubes in the carbon nanotube crude product are disentangled with the metal catalyst, meanwhile, oriented carding of the carbon nanotubes is carried out, and the carbon nanotubes are separated from the metal catalyst, so that subsequent magnetic separation is facilitated, the removal rate of the metal catalyst is improved, and if oriented carding is not carried out, the carbon nanotubes are separated from the metal catalyst. The entangled network structure of the carbon nanotubes can intercept part of the metal catalyst, so that the removal rate of the metal catalyst is influenced, and the purity of the carbon nanotubes is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of carbon nanotubes, and in particular to a method for removing metal catalysts from crude carbon nanotubes. Background Art

[0002] Carbon nanotubes have a large specific surface area, light weight, super strong mechanical strength, excellent electrical conductivity, and good physical and chemical stability. They are a new type of material that has attracted much attention and have broad application prospects in many fields. Currently, carbon nanotubes can be prepared by chemical vapor deposition (CVD). However, metal catalysts are required in the process of preparing carbon nanotubes by CVD. After the preparation is completed, the metal catalyst is easy to remain and enter the product along with the carbon nanotubes. This seriously hinders the application of carbon nanotubes in some industries that have high requirements for metal impurities.

[0003] In order to reduce the impact of residual metal catalysts, carbon nanotubes are usually purified. Existing carbon nanotube purification methods are mainly divided into chemical methods, physical methods and methods combining physics and chemistry. The chemical method has attracted people's attention due to its simple purification process, large purification volume and scalability. The main problem of this method is that the intrinsic structure of carbon nanotubes is also destroyed in the process of removing impurities. In addition, since the chemical pickling method will produce a large amount of acidic waste liquid, it will cause environmental pollution, or the cost of waste liquid treatment is too high; the method combining physics and chemistry also has the shortcomings of the chemical method; the physical method includes centrifugation, filtration, screening, etc. The physical method is economical and green, can be industrialized, and is a commonly used method for purifying carbon nanotubes, but there is a problem of low metal catalyst removal rate. Summary of the invention

[0004] In view of this, the object of the present invention is to provide a method for removing metal catalysts from crude carbon nanotubes. The removal method of the present invention disentangles the carbon nanotubes by rolling and oriented combing, thereby improving the removal rate of the metal catalysts.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a method for removing metal catalysts from crude carbon nanotubes, comprising the following steps:

[0007] The crude carbon nanotubes are mixed with a rolling medium and then rolled to obtain a disentangled material;

[0008] mixing the disentangled material with a dispersant to obtain a slurry;

[0009] The slurry is subjected to magnetic separation.

[0010] Preferably, the rolling medium includes one or more of water, ethanol, acetone, isopropanol, N-methylpyrrolidone, glycerol, paraffin, polyvinyl alcohol, sodium carboxymethyl cellulose, sodium alginate, starch, polyethylene glycol, polyacrylic acid, polymaleic anhydride, polymethyl methacrylate and gelatin.

[0011] Preferably, the mass ratio of the crude carbon nanotubes to the rolling medium is 1:1000 to 100:1.

[0012] Preferably, the mass ratio of the crude carbon nanotubes to the rolling medium is 1:50 to 50:1.

[0013] Preferably, the mass content of the metal catalyst in the crude carbon nanotubes is 2% to 50%, and the metal elements in the metal catalyst include one or more of iron, cobalt and nickel.

[0014] Preferably, the rolling is performed 1 to 25 times.

[0015] Preferably, the rolling is performed 3 to 24 times.

[0016] Preferably, the dispersant includes one or more of water, ethanol, acetone, dichloromethane, tetrahydrofuran, isopropanol, N-methylpyrrolidone, petroleum ether and N,N-dimethylformamide.

[0017] Preferably, the concentration of the slurry is 0.01-200 g / L.

[0018] Preferably, the magnetic field strength of the magnetic separation is 3000-12000 Gs, and the feeding speed is 0.1-20 L / s.

[0019] The invention provides a method for removing metal catalysts from crude carbon nanotubes, comprising the following steps: mixing the crude carbon nanotubes with a rolling medium and then rolling to obtain a disentangled material; mixing the disentangled material with a dispersant to obtain a slurry; and magnetically separating the slurry.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] In the rolling process of the present invention, the carbon nanotubes and the metal catalyst in the crude carbon nanotubes are disentangled, and the carbon nanotubes are oriented and combed at the same time, so that the carbon nanotubes are separated from the metal catalyst, which is beneficial to the subsequent magnetic separation and improves the removal rate of the metal catalyst. If there is no oriented combing, the entangled network structure of the carbon nanotubes will intercept part of the metal catalyst, thereby affecting the removal rate of the metal catalyst and reducing the purity of the carbon nanotubes. In addition, the removal method of the present invention is simple, efficient, industrializable, economical and green, and the obtained metal catalyst can be reused, which can reduce the preparation cost of the carbon nanotubes. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is the SEM image of crude SWCNT;

[0023] Figure 2 is a SEM image of the disentangled material in Example 1;

[0024] Figure 3 This is the SEM image of the final product obtained in Example 1. DETAILED DESCRIPTION

[0025] The present invention provides a method for removing metal catalysts from crude carbon nanotubes, comprising the following steps:

[0026] The crude carbon nanotubes are mixed with a rolling medium and then rolled to obtain a disentangled material;

[0027] mixing the disentangled material with a dispersant to obtain a slurry;

[0028] The slurry is subjected to magnetic separation.

[0029] In the present invention, unless otherwise specified, the raw materials used are all commercially available products in the art.

[0030] The present invention mixes the crude carbon nanotubes with a rolling medium and then performs rolling to obtain a disentangled material.

[0031] In the present invention, the crude carbon nanotube is preferably a crude single-walled carbon nanotube (SWCNT) or a crude multi-walled carbon nanotube. Single-walled carbon nanotube (SWCNT) has unique physical and chemical properties and excellent electrical and mechanical properties due to its unique structure, and has broad application prospects in the fields of nanoelectronic components, field emission and composite materials. All these attractive application prospects are based on the acquisition of high-purity, large quantities and cheap single-walled carbon nanotubes. The three traditional methods for preparing single-walled carbon nanotubes include chemical vapor deposition, arc method and laser evaporation method. The single-walled carbon nanotubes prepared by the above three methods have low purity (the product contains amorphous carbon, metal catalyst and SWCNT), so finding a simple, efficient and industrially purifiable method for purifying single-walled carbon nanotubes has become a bottleneck restricting the industrial application of single-walled carbon nanotubes. The removal method of the present invention is to carry out orientation combing of carbon nanotubes while disentangling by rolling, thereby improving the removal rate of metal catalysts.

[0032] In the present invention, the mass content of the metal catalyst in the crude carbon nanotubes is preferably 2% to 50%, specifically 2%, 5%, 8%, 10%, 12%, 15%, 20%, 22%, 30%, 40 or 50%, and the metal elements in the metal catalyst include one or more of iron, cobalt and nickel.

[0033] In the present invention, the magnetic catalyst preferably exists in the form of iron, cobalt, nickel, iron oxide, cobalt oxide, nickel oxide, iron carbide, cobalt carbide, nickel carbide, and one or more alloys, compounds and complexes formed by one or more of iron, cobalt and nickel and other elements, and the other elements include one or more of tungsten, yttrium, molybdenum, manganese, scandium, vanadium, silicon and sulfur.

[0034] In the present invention, the mass content of carbon nanotubes in the crude carbon nanotubes is preferably 20-80%, specifically 20%, 30%, 40%, 50%, 60%, 64%, 68%, 70% or 80%; the crude carbon nanotubes also preferably include other carbon materials, and the mass content of other carbon materials in the crude carbon nanotubes is preferably 10-15%, specifically 10%, 12%, 14% or 15%, and the other carbon materials preferably include one or more of amorphous carbon, an outer carbon shell of a metal catalyst and carbon nanoparticles, and the outer carbon shell coated on the surface of the metal catalyst is removed along with the removal of the metal catalyst during the subsequent magnetic separation process and is separated from the carbon nanotubes.

[0035] In the present invention, the rolling medium preferably includes one or more of water, ethanol, acetone, isopropanol, N-methylpyrrolidone, glycerol, paraffin, polyvinyl alcohol, sodium carboxymethyl cellulose, sodium alginate, starch, polyethylene glycol, polyacrylic acid, polymaleic anhydride, polymethyl methacrylate and gelatin.

[0036] In the present invention, when the rolling medium is preferably solid, the present invention preferably adopts the form of a solid material film layer or a gel film to roll the rolling medium and the crude carbon nanotube product. Specifically, when the rolling medium is polyvinyl alcohol, a polyvinyl alcohol film is used to roll the crude carbon nanotube product, or a gel film made of polyvinyl alcohol and water is used to roll the crude carbon nanotube product.

[0037] In the present invention, the mass ratio of the crude carbon nanotubes to the rolling medium is preferably 1:1000-100:1, more preferably 1:50-50:1, specifically 1:1000, 1:50, 1:1, 5:1, 50:1 or 100:1.

[0038] In the present invention, the number of rolling is preferably 1 to 25 times, more preferably 3 to 24 times, specifically 1, 3, 8, 12, 18, 24 or 25 times. The present invention preferably folds the crude product after the previous rolling and repeats the rolling.

[0039] In the present invention, the rolling is preferably carried out in the same direction.

[0040] During the rolling process of the present invention, the carbon nanotubes and the metal catalyst in the crude carbon nanotubes are disentangled, and the carbon nanotubes are oriented and combed to form a larger tube bundle, which is beneficial to the subsequent magnetic separation and improves the removal rate of the metal catalyst. If there is no oriented combing, the entangled network structure of the carbon nanotubes will intercept part of the metal catalyst, thereby affecting the removal rate of the metal catalyst and reducing the purity of the carbon nanotubes. In addition, the type of rolling medium, the mass ratio of the crude carbon nanotubes to the rolling medium, and the number of rolling times in the present invention have a great influence on the removal rate of the metal catalyst.

[0041] In the present invention, the roller gap width of the rolling is preferably 0.1 to 0.9 of the thickness of the feed material, specifically 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 or 0.9. The roller gap width limited within the above range can promote the orientation and combing of carbon nanotubes, which is beneficial to the separation of metal catalysts from carbon nanotubes. The feed material refers to a mixture of crude carbon nanotubes and rolling medium.

[0042] In the present invention, the rolling is preferably carried out in a roller press, more preferably in a multi-roll mill.

[0043] After obtaining the disentangled material, the present invention mixes the disentangled material with a dispersant to obtain a slurry.

[0044] In the present invention, the dispersant preferably includes one or more of water, ethanol, acetone, dichloromethane, tetrahydrofuran, isopropanol, N-methylpyrrolidone, petroleum ether and N,N-dimethylformamide.

[0045] In the present invention, the concentration of the slurry is preferably 0.01-200 g / L, specifically 0.01, 0.1, 10, 50, 100, 150 or 200 g / L. The concentration of the slurry limited to the above range can improve the removal rate of the metal catalyst.

[0046] In the present invention, the magnetic field strength of the magnetic separation is preferably 3000-12000Gs, specifically 3000, 5000, 8000, 10000 or 12000Gs. The magnetic separation strength of the magnetic separation is limited within the above range to improve the removal rate of the metal catalyst; the feeding rate is preferably 0.1-20L / s, specifically 0.1, 1, 5, 10, 15 or 20L / s.

[0047] In the present invention, the magnetic separation is preferably carried out in a high gradient magnetic separator.

[0048] After the magnetic separation is completed, the present invention preferably filters, dries and collects the obtained liquid in sequence. The present invention has no special limitation on the specific methods of filtering, drying and collecting, and methods familiar to those skilled in the art can be used.

[0049] The technical solutions in the present invention will be described clearly and completely below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0050] The metal catalyst in the crude SWCNT used in the embodiment of the present invention includes alloy nanoparticles formed by Ni and Y and Ni carbide, the mass content of the metal catalyst in the crude single-walled carbon nanotube is 20%, the mass content of the single-walled carbon nanotube is 68%, and the mass content of other carbon materials (carbon shell wrapped around the outer layer of the metal catalyst) is 12%; the metal catalyst in the crude multi-walled carbon nanotube includes Fe and Fe carbide nanoparticles, the mass content of the metal catalyst in the crude multi-walled carbon nanotube is 22%, the mass content of the multi-walled carbon nanotube is 64%, and the mass content of other carbon materials (carbon shell wrapped around the outer layer of the metal catalyst) is 14%;

[0051] The average molecular weight of the polyvinyl alcohol used in the embodiment of the present invention is 1750±50; paraffin was purchased from Aladdin, and petroleum ether was purchased from Guangzhou Chemical Reagent Factory.

[0052] Example 1

[0053] Step 1: Mix 10 g of SWCNT crude product with 10 g of polyvinyl alcohol, place in a roller press, roll in the same direction, repeat the rolling in the same direction for 12 times, and the roll gap width is 0.1 of the thickness of the mixed SWCNT crude product and polyvinyl alcohol.

[0054] Step 2: The disentangled material obtained in step 1 is mixed with water to form a 1 g / L slurry, and the slurry is passed through a high gradient magnetic separator with a magnetic field strength of 5000 Gs and a feed rate of 0.1 L / s to separate the metal catalyst from the SWCNT.

[0055] The removal rate of the metal catalyst and the purity of the SWCNTs in the final product are shown in Table 1.

[0056] Embodiments 2 to 10

[0057] The same as Example 1, the only difference is the types of rolling medium and dispersant, as shown in Table 1.

[0058] It can be seen from Table 1 that the removal rate of the metal catalyst is different when different types of rolling media and dispersants are selected, and the types of rolling media and dispersants also have a great influence on the purity of the final product.

[0059] Table 1 Effect of raw material type on metal catalyst removal rate and SWCNT purity in the final product

[0060]

[0061]

[0062] Examples 11 to 15

[0063] The same as Example 1, the only difference is the mass ratio of the crude SWCNT to the polyvinyl alcohol medium. The details are shown in Table 2.

[0064] Table 2 Effect of the mass ratio of crude SWCNT to polyvinyl alcohol on metal catalyst removal rate and SWCNT purity in the final product

[0065] Mass ratio of crude SWCNT to polyvinyl alcohol Metal catalyst removal rate Purity of SWCNT (wt%) Example 1 1：1 99.9％ 99％ Embodiment 11 5：1 91.9％ 92％ Example 12 50：1 89.7％ 88％ Embodiment 13 100：1 80.5％ 79％ Embodiment 14 1：50 99.2％ 99％ Embodiment 15 1：1000 99.6％ 99％

[0066] It can be seen from Table 2 that the removal rate of the metal catalyst is different when the mass ratio of the crude SWCNT product to the polyvinyl alcohol medium is different, and the mass ratio of the crude SWCNT product to the polyvinyl alcohol medium also has a great influence on the purity of the final product obtained.

[0067] Embodiments 16 to 20

[0068] The same as Example 1, the only difference is the number of rolling times.

[0069] Table 3 Effect of rolling times on metal catalyst removal rate and SWCNT purity in the final product

[0070] Rolling times Metal catalyst removal rate Purity of SWCNT (wt%) Example 1 12 99.9％ 99％ Example 16 0 27.4％ 29％ Embodiment 17 3 83.7％ 82％ Embodiment 18 8 92.5％ 34％ Embodiment 19 18 99.9％ 99％ Embodiment 20 24 99.8％ 99％

[0071] It can be seen from Table 3 that increasing the number of rolling times can improve the removal rate of the metal catalyst, and the number of rolling times also has a great influence on the purity of the final product. In Example 16, no rolling was performed, and the carbon nanotubes in the crude carbon nanotubes would not be disentangled with the metal catalyst, and the orientation combing of the carbon nanotubes would not occur. Therefore, the removal rate of the metal catalyst was low, and the purity of the carbon nanotubes in the final product was also low.

[0072] Examples 21 to 24

[0073] The same as Example 1, the only difference is the magnetic field strength.

[0074] Table 4 Effect of magnetic field strength on the removal rate of metal catalysts and the purity of SWCNT in the final product

[0075] Magnetic field strength Metal catalyst removal rate Purity of SWCNT (wt%) Example 1 5000Gs 99.9％ 99％ Embodiment 21 3000Gs 91.9％ 92％ Embodiment 22 8000Gs 98.7％ 99％ Embodiment 23 10000Gs 99.5％ 99％ Embodiment 24 12000Gs 99.2％ 99％

[0076] It can be seen from Table 4 that the removal rate of the metal catalyst is different with different magnetic field intensities, and the magnetic field intensity also has a great influence on the purity of the final product obtained.

[0077] Embodiments 25 to 29

[0078] The same as Example 1, the only difference is the concentration of the slurry. Specific details are shown in Table 5.

[0079] Table 5 Effect of slurry concentration on metal catalyst removal rate and purity of SWCNT in the final product

[0080] Slurry concentration Metal catalyst removal rate Purity of SWCNT (wt%) Example 1 1g / L 99.9％ 99％ Embodiment 25 0.01g / L 99.3％ 98％ Embodiment 26 0.1g / L 99.6％ 98％ Embodiment 27 10g / L 97.5％ 97％ Embodiment 28 100g / L 79.2％ 80％ Embodiment 29 200g / L 73.2％ 73％

[0081] It can be seen from Table 5 that the removal rate of the metal catalyst is different with different slurry concentrations, and the slurry concentration also has a great influence on the purity of the final product.

[0082] Embodiment 30

[0083] The same as Example 1, the only difference is that crude multi-walled carbon nanotubes are used. The details are shown in Table 6.

[0084] Table 6 Effect of different carbon nanotube raw materials on metal catalyst removal rate and purity of carbon nanotubes in the final product

[0085]

[0086] It can be seen from Table 6 that the metal catalyst can be removed to a certain extent for different types of crude carbon nanotubes, and the removal effect of single-walled carbon nanotubes is better.

[0087] Figure 1 This is the SEM image of the crude SWCNT, which shows that the granular metal catalyst is evenly attached to the SWCNT; Figure 2 This is a SEM image of the disentangled material in Example 1. It can be seen that the granular metal catalyst is separated from the SWCNT, and the SWCNT has a certain orientation and forms a larger tube bundle; Figure 3 This is the SEM image of the final product obtained in Example 1. It can be seen that the metal catalyst particles have been removed and the SWCNTs maintain a certain orientation.

[0088] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A method for removing metal catalysts from crude carbon nanotubes, characterized in that: The following steps are involved: The crude carbon nanotubes are mixed with a rolling medium and then rolled to obtain a disentangled material; dispersing the disentangled material in a dispersant to obtain a slurry; The slurry is subjected to magnetic separation.

2. The removal method according to claim 1, characterized in that: The rolling medium includes one or more of water, ethanol, acetone, isopropanol, N-methylpyrrolidone, glycerol, paraffin, polyvinyl alcohol, sodium carboxymethyl cellulose, sodium alginate, starch, polyethylene glycol, polyacrylic acid, polymaleic anhydride, polymethyl methacrylate and gelatin.

3. The removal method according to claim 1 or 2, characterized in that: The mass ratio of the crude carbon nanotubes to the rolling medium is 1:1000 to 100:

1.

4. The removal method according to claim 3, characterized in that: The mass ratio of the crude carbon nanotubes to the rolling medium is 1:50 to 50:

1.

5. The removal method according to claim 1, characterized in that: The mass content of the metal catalyst in the crude carbon nanotubes is 2% to 50%, and the metal elements in the metal catalyst include one or more of iron, cobalt and nickel.

6. The removal method according to claim 1, characterized in that: The number of times of rolling is 1 to 25 times.

7. The removal method according to claim 6, characterized in that: The number of times of rolling is 3 to 24 times.

8. The removal method according to claim 1, characterized in that: The dispersant includes one or more of water, ethanol, acetone, dichloromethane, tetrahydrofuran, isopropanol, N-methylpyrrolidone, petroleum ether and N,N-dimethylformamide.

9. The removal method according to claim 1, characterized in that: The concentration of the slurry is 0.01-200 g / L.

10. The removal method according to claim 1 or 9, characterized in that: The magnetic field strength of the magnetic separation is 3000-12000 Gs, and the feeding speed is 0.1-20 L / s.

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