A method for preparing small-diameter single-walled carbon nanotubes

Abstract

The application provides a preparation method of small-diameter single-walled carbon nanotubes, and relates to the technical field of carbon nanometer materials. The nanometer catalyst, high-purity graphite powder and liquid carbon source binder are mixed, and then forming and sintering are sequentially performed to obtain a mixed graphite rod; the nanometer catalyst contains metal elements, and the metal elements are transition metal elements and / or aluminum elements; the mixed graphite rod is used as an anode, a pure graphite rod is used as a cathode, and plasma catalytic pyrolysis is performed to obtain small-diameter single-walled carbon nanotubes. The preparation method provided by the application has high yield (the mass proportion of single-walled carbon nanotubes in the crude product is high), and can be used to prepare single-walled carbon nanotubes with smaller diameters. The results of examples show that, when the single-walled carbon nanotubes are prepared by using the preparation method provided by the application, the mass proportion of single-walled carbon nanotubes in the crude product can reach 79%, and the diameter of the single-walled carbon nanotubes can be as low as 1.2nm.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of carbon nanomaterials, and particularly to a preparation method of small-diameter single-walled carbon nanotubes. BACKGROUND

[0002] Single-walled carbon nanotubes (SWCNT) are tubular structures formed by rolling up a single layer of graphene composed of carbon atoms, and have excellent electronic, mechanical, and mechanical properties. The arc discharge method is an important method for preparing single-walled carbon nanotubes, and its principle is to evaporate solid carbon source into carbon atoms under high temperature conditions. The bottleneck of industrialization of this method is the low yield of carbon nanotubes (i.e. the mass fraction of carbon nanotubes in the crude product is generally not more than 30%). On the other hand, the thinner the diameter of SWNTs, the lower the conductivity threshold when used as a conductive filler, which can be as low as one ten-thousandth, which is beyond the reach of existing conventional materials. The diameter of SWCNTs prepared by traditional arc discharge method is usually more than 1.4 nm. The preparation of fine-diameter carbon nanotubes is also an important difficulty in this field. SUMMARY

[0003] Therefore, the present application aims to provide a preparation method of small-diameter single-walled carbon nanotubes. The preparation method provided by the present application has high yield (high mass fraction of single-walled carbon nanotubes in the crude product) and can prepare single-walled carbon nanotubes with smaller diameter.

[0004] In order to achieve the above-mentioned application purposes, the present application provides the following technical solutions:

[0005] The present application provides a preparation method of small-diameter single-walled carbon nanotubes, comprising the following steps:

[0006] Mixing a nanoscale catalyst, high-purity graphite powder, and a liquid carbon source binder, and sequentially performing molding and sintering to obtain a mixed graphite rod; the nanoscale catalyst contains a metal element, and the metal element is a transition metal element and / or an aluminum element;

[0007] Carrying out plasma catalytic pyrolysis with the mixed graphite rod as an anode and a pure graphite rod as a cathode to obtain small-diameter single-walled carbon nanotubes.

[0008] Preferably, the transition metal element is selected from one or more of iron element, cobalt element, nickel element, yttrium element, zinc element, chromium element, manganese element, copper element, and molybdenum element.

[0009] Preferably, the nanoscale catalyst is selected from one or more of a metal element corresponding to a metal element, an alloy formed by two or more metal elements, and a compound containing the metal element.

[0010] Preferably, the alloy formed by the two or more transition metal elements comprises Ni4Y, Ni5Y or Ni3Y.

[0011] Preferably, the particle size of the nanoscale catalyst is 1-100 nm.

[0012] Preferably, the particle size of the high-purity graphite powder is 1 nm-500 μm.

[0013] Preferably, the high-purity graphite powder comprises one or more of a first graphite powder, a second graphite powder, a third graphite powder and a fourth graphite powder, the particle sizes of the first, second, third and fourth graphite powders being different; the particle size of the first graphite powder is 100-500 μm, the particle size of the second graphite powder is 10-100 μm, the particle size of the third graphite powder is 1-10 μm, and the particle size of the fourth graphite powder is 1-999 nm.

[0014] Preferably, the molar amount of the nanoscale catalyst is 0.1-1% of the total molar amount of the nanoscale catalyst and the high-purity graphite powder.

[0015] Preferably, the gas used in the plasma catalytic pyrolysis is one or more of helium, argon and neon, and the gas pressure is 1-200 kPa; the discharge arc voltage of the plasma catalytic pyrolysis is 10-40 V, and the current is 10-400 A.

[0016] Preferably, the tube diameter of the small-diameter single-walled carbon nanotube is 1.2-1.4 nm.

[0017] The present application provides a method for preparing a small-diameter single-walled carbon nanotube.

[0018] Compared with a micron-sized large-particle catalyst, the nanoscale catalyst can reduce the content of carbon impurities (such as amorphous carbon or even fullerene) in the product other than the single-walled carbon nanotube; in addition, the use of the nanoscale catalyst can reduce the amount of catalyst used, thereby improving the mass proportion of the single-walled carbon nanotube in the product. The method of plasma catalytic pyrolysis provided by the present application can provide high plasma energy for the growth of graphite into carbon nanotubes, realize more efficient production of single-walled carbon nanotubes, and, in combination with the small size of the catalyst, obtain single-walled carbon nanotubes with smaller tube diameters. The method provided by the present application has high yield (high mass proportion of single-walled carbon nanotubes in the crude product) and can produce single-walled carbon nanotubes with smaller tube diameters.

[0019] The results of the examples show that, by using the method provided by the present application to prepare single-walled carbon nanotubes, the mass proportion of single-walled carbon nanotubes in the crude product can reach 79%, and the tube diameter of the single-walled carbon nanotube can be as low as 1.2 nm. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 A scanning electron microscope image of the crude product obtained in Example 1;

[0021] Figure 2 A TEM image of the crude product obtained in Example 1;

[0022] Figure 3 A Raman spectrum of the crude product obtained in Example 1;

[0023] Figure 4 A scanning electron microscope image of the crude product obtained in Example 21. DETAILED DESCRIPTION

[0024] The present application provides a preparation method of small-diameter single-walled carbon nanotubes, comprising the following steps:

[0025] The nanoscale catalyst, high-purity graphite powder and liquid carbon source binder are mixed, and then are sequentially subjected to molding and sintering to obtain a mixed graphite rod; the nanoscale catalyst contains a metal element, and the metal element is a transition metal element and / or an aluminum element;

[0026] The mixed graphite rod is used as an anode, and a pure graphite rod is used as a cathode to perform plasma catalytic pyrolysis, so as to obtain small-diameter single-walled carbon nanotubes.

[0027] In the present application, if no special description is given, all the raw materials involved are commercially available products.

[0028] The nanoscale catalyst, high-purity graphite powder and liquid carbon source binder are mixed, and then are sequentially subjected to molding and sintering to obtain a mixed graphite rod.

[0029] In the present application, the particle size of the nanoscale catalyst is preferably 1-100 nm, and can be 1, 3, 5, 10, 20, 50 or 80 nm. In the present application, the nanoscale catalyst is used, and compared with the micron-sized large-particle catalyst, the content of carbon impurities (such as amorphous carbon, even fullerene) of non-single-walled carbon nanotubes in the product can be reduced; in addition, the use of the nanoscale catalyst can reduce the catalyst consumption, so as to improve the yield of single-walled carbon nanotubes in the product.

[0030] In this invention, the nanoscale catalyst contains a metal element, which is a transition metal element and / or aluminum. Preferably, the transition metal element is selected from one or more of iron (Fe), cobalt (Co), nickel (Ni), yttrium (Y), zinc (Zn), chromium (Cr), manganese (Mn), copper (Cu), and molybdenum (Mo). The nanoscale catalyst is preferably selected from one or more of the elemental metals corresponding to the stated metal elements, alloys formed from two or more of the stated metal elements, and compounds containing the stated metal elements; the compounds containing the stated metal elements can be oxides, sulfides, or carbides containing the stated metal elements. As an embodiment of this invention, the nanoscale catalyst is a mixture of elemental metals corresponding to two or more of the stated metal elements, preferably a mixture of elemental metals corresponding to two or more transition metal elements. This invention does not have a particular requirement for the mixing ratio between the elemental metals in the mixture; for example, it can be a mixture of nickel and yttrium, where the molar ratio of nickel to yttrium in the nickel-yttrium mixture can be 3~5:1, specifically 3:1, 4:1, or 5:1. In one embodiment of the present invention, the nanoscale catalyst is an alloy formed by two or more metallic elements, preferably an alloy formed by two or more transition metallic elements. The present invention does not have a particular requirement for the proportion of metallic elements in the alloy, and it can be Ni4Y, Ni5Y, or Ni3Y. In the present invention, the alloy-form nanoscale catalyst has a lower melting point and weaker thermal conductivity than a single metal, thus making it easier to trigger the reaction (the lower melting point allows it to co-evaporate with carbon atoms at a lower temperature, and the weaker thermal conductivity makes energy easier to concentrate), and the alloy can achieve a more uniform composite of metallic elements. In another embodiment of the present invention, the nanoscale catalyst is a mixture of the alloy and the metallic element. The alloy can be Ni4Y, and the metallic element can be aluminum, zinc, chromium, manganese, copper, or molybdenum. The molar ratio of the alloy to the metallic element can be (90~99.5):(10:0.5), such as 99.5:0.5, 99:1, 98:2, 95:5, or 90:10. The present invention does not have any special requirements on the source of the nanoscale catalyst, which can be prepared using commercially available products or methods known to those skilled in the art.

[0031] In this invention, the particle size of the high-purity graphite powder (i.e., purity of 99.99% or higher) is preferably 1 nm to 500 μm. In this invention, the high-purity graphite powder preferably includes one or more of a first graphite powder, a second graphite powder, a third graphite powder, and a fourth graphite powder, wherein the particle sizes of the first graphite powder, the second graphite powder, the third graphite powder, and the fourth graphite powder are different; the particle size of the first graphite powder is preferably 100 to 500 μm, more preferably 300 to 400 μm; the particle size of the second graphite powder is preferably 10 to 100 μm, more preferably 50 to 60 μm; the particle size of the third graphite powder is preferably 1 to 10 μm, more preferably 5 to 6 μm; and the particle size of the fourth graphite powder is preferably 1 to 999 nm, more preferably 40 to 100 nm. In an embodiment of this invention, the fourth graphite powder is Super P. In this invention, when the high-purity graphite powder includes several of the following: first graphite powder, second graphite powder, third graphite powder, and fourth graphite powder, the high-purity graphite powder is preferably a mixture of the first, second, third, and fourth graphite powders, or a mixture of the second, third, and fourth graphite powders. When the high-purity graphite powder is preferably a mixture of the first, second, third, and fourth graphite powders, the mass ratio of the first, second, third, and fourth graphite powders in the mixture is preferably 95:4:0.8:0.2. When the high-purity graphite powder is a mixture of the second, third, and fourth graphite powders, the mass ratio of the second, third, and fourth graphite powders in the mixture is preferably 95:4:1. This invention uses a blend of graphite powders of varying particle sizes, which reduces the porosity of the graphite powder, thereby ensuring close contact between the catalyst and the graphite powder and increasing the mass proportion of nanotubes in the crude product.

[0032] In this invention, the molar amount of the nano-scale catalyst is preferably 0.1% to 1% of the total molar amount of the nano-scale catalyst and high-purity graphite powder (calculated as C), and can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, or 1%. By controlling the amount of nano-scale catalyst added within the above range, this invention helps to reduce the use of useless catalyst, thereby increasing the mass proportion of nanotubes in the crude product.

[0033] This invention does not impose any special requirements on the liquid carbon source binder; any liquid carbon source binder well-known to those skilled in the art can be used, such as asphalt, tar, petroleum, kerosene, diesel, gasoline, paraffin wax, liquid butadiene rubber (i.e., cis-butadiene rubber, molecular weight 5000~50000), bisphenol A type epoxy resin, phenolic resin, unsaturated polyester resin, polyvinyl alcohol, or polycarbonate. In this invention, the preferred mass of the liquid carbon source binder is 0.1~10% of the mass of high-purity graphite powder, and can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%.

[0034] In this invention, the preferred method for mixing the nanoscale catalyst, high-purity graphite powder, and liquid carbon source binder is to: mix the high-purity graphite powder and the nanoscale catalyst evenly; then add the liquid carbon source binder and mix evenly (the liquid carbon source binder fills the gaps).

[0035] In this invention, the forming method is preferably extrusion, and in this embodiment of the invention, it is specifically extruded into a mixed graphite rod blank with a diameter of 20 mm.

[0036] In this invention, the sintering temperature is preferably 1000℃, the holding time is preferably 4 hours, and the sintering is preferably carried out in an argon atmosphere; in an embodiment of this invention, the sintering is carried out in a high-temperature furnace. After sintering, a dense and uniform graphite rod of catalyst and graphite mixture is formed, namely the mixed graphite rod.

[0037] After obtaining the mixed graphite rod, the present invention uses the mixed graphite rod as the anode and the pure graphite rod as the cathode to perform plasma catalytic pyrolysis to obtain small-diameter single-walled carbon nanotubes (SWCNTs).

[0038] In this embodiment of the invention, the diameter of the pure graphite rod is 40 mm.

[0039] This invention places the anode and cathode within a plasma generator for plasma catalytic pyrolysis. In this invention, the gas used for plasma catalytic pyrolysis is preferably one or more of helium, argon, and neon. The gas pressure is preferably 1-200 kPa, and can be 50, 70, 100, 150, or 200 kPa. The discharge arc voltage for plasma catalytic pyrolysis is preferably 10-40 V, and can be 10, 20, 30, or 40 V. The current is preferably 10-400 A, and can be 50, 100, 200, 300, or 400 A. The discharge time is preferably 5-60 min, and can be 5, 10, 15, 20, 30, 40, 50, or 60 min. During the plasma catalytic pyrolysis process, the high-energy ions in the plasma drive the reaction, promoting the dissociation of the carbon source (graphite). Under the action of the catalyst, single-walled carbon nanotubes are generated in large quantities and controllably. This invention employs controlled plasma-enhanced catalytic pyrolysis (CPECP) to further control the current and voltage of the plasma generator, thereby producing single-walled carbon nanotubes with controllable diameter.

[0040] In this invention, the diameter of the small-diameter single-walled carbon nanotubes is 1.2~1.4 nm. In this invention, the diameter of the small-diameter single-walled carbon nanotubes is the peak value calculated based on the radial breathing peak (RBM) of the Raman spectrum.

[0041] The preparation method provided by this invention can obtain high-quality (high content of single-walled carbon nanotubes in the crude product, i.e., increased yield of single-walled carbon nanotubes in the obtained product, and reduced content of amorphous carbon and metal catalyst) and small-diameter single-walled carbon nanotubes with controllable size. The diameter of the obtained single-walled carbon nanotubes is smaller than that of similar products.

[0042] To further illustrate the present invention, the preparation method of small-diameter single-walled carbon nanotubes provided by the present invention will be described in detail below with reference to examples, but these should not be construed as limiting the scope of protection of the present invention.

[0043] Example 1

[0044] The preparation of small-diameter single-walled carbon nanotubes involves the following steps:

[0045] Step 1: Using a mixture of 99.99% high-purity graphite powder (300μm graphite powder: 50μm graphite powder: 5μm graphite powder: 40nm super P=95:4:0.8:0.2 (mass ratio)) and nano-Ni4Y alloy catalyst (particle size 5nm) as raw materials, mix them evenly according to the molar ratio (C:Ni4Y = 99.2:0.8), then add liquid butadiene rubber (molecular weight 20000) and mix and extrude into a graphite rod blank with a diameter of 20mm. The amount of liquid butadiene rubber added is 10% of the mass of the high-purity graphite powder mixture. Place the graphite rod blank in a high-temperature furnace under argon protection and sinter at 1000℃ for 4h to obtain an anode graphite rod.

[0046] Step 2: Place the anode graphite rod prepared in Step 1 into a plasma generator. The cathode is a pure graphite rod with a diameter of 40 mm. The plasma gas used is a mixture of helium and neon, with helium accounting for 99.9% of the volume and the gas pressure being 70 kPa. The discharge current is 100 A, the voltage is 30 V, and the discharge time is 5 min, yielding crude single-walled carbon nanotubes. In the crude product, single-walled carbon nanotubes (SWCNTs) account for 79% of the mass, and the diameter distribution of SWCNTs is 1.2 ± 0.4 nm (where 1.2 nm is the peak value calculated from the radial breathing peak (RBM) of the Raman spectrum, and the other diameter distributions are represented similarly).

[0047] Figure 1 The image shows a scanning electron microscope (SEM) image of the crude product obtained in Example 1 (where the filaments are single-walled carbon nanotubes and the granules are impurities). It can be seen that the crude product contains a high proportion of carbon nanotubes and relatively few impurities.

[0048] Figure 2 The image shown is a TEM image of the crude product obtained in Example 1. It can be seen that the product prepared in Example 1 is a single-walled carbon nanotube with a relatively small diameter of approximately 1.2 nm.

[0049] Figure 3 The image shows the Raman spectrum of the crude product obtained in Example 1. The diameter of the tube can be calculated to be approximately 1.2 nm based on the peak value data from the Raman breath peak.

[0050] Examples 2-16

[0051] Examples 2-16 are the same as the SWCNT preparation steps in Example 1, the difference being the type of catalyst used. The types of catalysts used in Examples 2-16, the mass ratio of SWCNTs in the crude product, and the diameter distribution of SWCNTs are shown in Table 1. In Table 1, the catalyst ratios corresponding to Examples 4-16 in the "Catalyst Type" column are all molar ratios.

[0052] Table 1. Catalyst types used in Examples 2-16, and the mass percentage and diameter distribution of SWCNTs in the crude products obtained.

[0053]

[0054] Examples 2-16 follow the same steps as the SWCNT preparation process in Example 1, except for the type of catalyst used. As shown in Table 1, different catalyst types have a significant impact on the SWCNT yield and the diameter of the SWCNT tube.

[0055] Examples 17-21

[0056] Examples 17-21 follow the same SWCNT preparation steps as Example 1, the difference being the size of the catalyst used. Table 2 shows the size of the catalyst used in Examples 17-21, the mass percentage of SWCNTs in the crude product, and the diameter distribution of SWCNTs.

[0057] Table 2 Catalyst sizes used in Examples 17-21, and the mass percentage and diameter distribution of SWCNTs in the crude products obtained.

[0058]

[0059] Examples 17-21 follow the same SWCNT preparation steps as Example 1, the difference being the size of the catalyst used. As can be seen from the results in Table 2, the size of the catalyst used has a significant impact on the SWCNT yield and the diameter of the SWCNT tube.

[0060] Figure 4 The image shown is a scanning electron microscope (SEM) image of the crude product obtained in Example 21, which shows that it contains a large number of impurities.

[0061] Examples 22-26

[0062] Examples 22-26 are the same as the SWCNT preparation steps in Example 1, the difference being the different molar ratios of carbon source (high-purity graphite powder mixture) and catalyst in the raw materials. The molar ratios of carbon source and catalyst (carbon:catalyst) in Examples 22-26, as well as the mass percentage of SWCNTs and the diameter distribution of SWCNTs in the crude product, are shown in Table 3.

[0063] Table 3. Molar ratio of carbon source to catalyst in Examples 22-26, and mass percentage and diameter distribution of SWCNTs in the crude products obtained.

[0064]

[0065] Examples 22-26 follow the same SWCNT preparation steps as Example 1, except for the different ratios of carbon source and catalyst. As can be seen from the data in Table 3, the different ratios of carbon source and catalyst have a significant impact on the SWCNT yield.

[0066] Examples 27-31

[0067] Examples 27-31 follow the same SWCNT preparation steps as Example 1, except that the carbon source (a mixture of high-purity graphite powder) used is different. The carbon source used in Examples 27-31 and the mass percentage and diameter distribution of SWCNTs in the crude product are shown in Table 4.

[0068] Table 4. Mass percentage and diameter distribution of SWCNTs in the carbon source and crude product obtained in Examples 27-31

[0069]

[0070] Examples 27-31 follow the same SWCNT preparation steps as Example 1, the difference being the use of different carbon sources. As can be seen from the results in Table 4, the use of different carbon sources has a significant impact on the yield.

[0071] Examples 32-35

[0072] Examples 32-35 follow the same SWCNT preparation steps as Example 1, except that the current and voltage used in the preparation process are different. The current and voltage used in Examples 32-35, as well as the mass ratio of SWCNTs and the diameter distribution of SWCNTs in the crude product obtained, are shown in Table 5.

[0073] Table 5. Current and voltage in Examples 32-35, and the mass percentage and diameter distribution of SWCNTs in the crude product.

[0074]

[0075] Examples 32-35 follow the same SWCNT preparation steps as Example 1, except for the different current and voltage used. As shown in Table 5, the different current and voltage used have a significant impact on the yield.

[0076] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing small-diameter single-walled carbon nanotubes, characterized in that, Includes the following steps: Nanoscale catalyst, high-purity graphite powder and liquid carbon source binder are mixed and then successively molded and sintered to obtain a mixed graphite rod; Using the mixed graphite rod as the anode and the pure graphite rod as the cathode, plasma catalytic pyrolysis was performed to obtain small-diameter single-walled carbon nanotubes. The nanoscale catalyst has a particle size of 1~100nm; the nanoscale catalyst is a mixture of nickel and yttrium, wherein the molar ratio of nickel to yttrium in the mixture is 3~5:1, or the nanoscale catalyst is Ni4Y, Ni5Y or Ni3Y, or the nanoscale catalyst is a mixture of an alloy and a metallic element, wherein the alloy is Ni4Y, and the metallic element is aluminum, zinc, chromium, manganese, copper or molybdenum, wherein the molar ratio of the alloy to the metallic element is (90~99.5):(10~0.5); The high-purity graphite powder is a mixture of first graphite powder, second graphite powder, third graphite powder, and fourth graphite powder, or a mixture of second graphite powder, third graphite powder, and fourth graphite powder; when the high-purity graphite powder is a mixture of first graphite powder, second graphite powder, third graphite powder, and fourth graphite powder, the mass ratio of the first graphite powder, second graphite powder, third graphite powder, and fourth graphite powder in the mixture is 95:4:0.8:0.2; when the high-purity graphite powder is a mixture of second graphite powder, third graphite powder, third graphite powder, and fourth graphite powder, the mass ratio of the first graphite powder, second graphite powder, third graphite powder, and fourth graphite powder in the mixture is 95:4:0.8:0.

2. When a mixture of third and fourth graphite powders is used, the mass ratio of the second, third, and fourth graphite powders in the mixture is 95:4:1; the first, second, third, and fourth graphite powders have different particle sizes; the first graphite powder has a particle size of 100~500μm, the second graphite powder has a particle size of 10~100μm, the third graphite powder has a particle size of 1~10μm, and the fourth graphite powder has a particle size of 1~999nm; The gas used in the plasma catalytic pyrolysis is one or more of helium, argon and neon, and the gas pressure is 1~200kPa; the discharge arc voltage of the plasma catalytic pyrolysis is 10~40V and the current is 10~400A; the diameter of the small-diameter single-walled carbon nanotube is 1.2~1.4nm.

2. The preparation method according to claim 1, characterized in that, The molar amount of the nanoscale catalyst is 0.1 to 1% of the total molar amount of the nanoscale catalyst and high-purity graphite powder.

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