Preparation method of small-diameter single-wall carbon nanotube

Abstract

The invention provides a preparation method of a small-diameter single-walled carbon nanotube, and relates to the technical field of carbon nanomaterials. The preparation method comprises the following steps: mixing a nanoscale catalyst, high-purity graphite powder and a liquid carbon source binder, and sequentially molding and sintering to obtain a mixed graphite rod; the nanoscale catalyst contains metal elements, and the metal elements are transition metal elements and / or aluminum elements; and carrying out plasma catalytic pyrolysis by taking the mixed graphite rod as an anode and a pure graphite rod as a cathode to obtain the small-diameter single-wall carbon nanotube. The preparation method provided by the invention is high in yield (the mass ratio of the single-walled carbon nanotubes in a crude product is high), and the single-walled carbon nanotubes with smaller tube diameters can be prepared. Results of the embodiment show that when the preparation method provided by the invention is adopted to prepare the single-walled carbon nanotube, the mass ratio of the single-walled carbon nanotube in a crude product can reach 79%, and the diameter of the single-walled carbon nanotube can be as low as 1.2 nm.

Description

Technical Field

[0001] The present invention relates to the technical field of carbon nanomaterials, and particularly to a method for preparing single-walled carbon nanotubes with a small tube diameter. Background Art

[0002] Single-walled carbon nanotubes (SWCNTs) are tubular structures formed by curling a single layer of graphene composed entirely of carbon atoms, and they have excellent electrical, mechanical, and mechanical properties. The arc discharge method is an important method for preparing single-walled carbon nanotubes. Its principle is to evaporate solid carbon sources into carbon atoms under high-temperature conditions. The bottleneck in the industrialization of this method lies in the low yield of carbon nanotubes (that is, the mass ratio of carbon nanotubes in the crude product is low, generally not exceeding 30%). On the other hand, the smaller the diameter of SWNTs, the lower the conductivity threshold when they are used as conductive fillers. The conductivity threshold can be as low as one ten-thousandth, which is unattainable by existing conventional materials. The diameter of SWCNTs prepared by the traditional arc discharge method is usually above 1.4 nm. The preparation of carbon nanotubes with a small diameter is also an important difficulty in this field. Summary of the Invention

[0003] In view of this, the purpose of the present invention is to provide a method for preparing single-walled carbon nanotubes with a small tube diameter. The preparation method provided by the present invention has a high yield (the mass ratio of single-walled carbon nanotubes in the crude product is high), and can prepare single-walled carbon nanotubes with a smaller tube diameter.

[0004] To achieve the above-mentioned invention purpose, the present invention provides the following technical solutions: The present invention provides a method for preparing single-walled carbon nanotubes with a small tube diameter, including the following steps: Mix a nanoscale catalyst, high-purity graphite powder, and a liquid carbon source binder, and perform molding and sintering in sequence 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; Use the mixed graphite rod as the anode and a pure graphite rod as the cathode to perform plasma catalytic pyrolysis to obtain single-walled carbon nanotubes with a small tube diameter.

[0005] 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.

[0006] Preferably, the nanoscale catalyst is selected from one or more of the metal corresponding to the metal element, an alloy formed by two or more of the metal elements, and a compound containing the metal element.

[0007] Preferably, the alloy formed by two or more transition metal elements includes Ni 4 Y, Ni 5 Y or Ni 3 Y.

[0008] Preferably, the particle size of the nanoscale catalyst is 1 to 100 nm.

[0009] Preferably, the particle size of the high-purity graphite powder is 1 nm to 500 μm.

[0010] Preferably, the high-purity graphite powder includes one or more of first graphite powder, second graphite powder, third graphite powder, and fourth graphite powder, and the particle sizes of the first graphite powder, second graphite powder, third graphite powder, and fourth graphite powder are different; the particle size of the first graphite powder is 100 to 500 μm, the particle size of the second graphite powder is 10 to 100 μm, the particle size of the third graphite powder is 1 to 10 μm, and the particle size of the fourth graphite powder is 1 to 999 nm.

[0011] Preferably, the molar amount of the nanoscale catalyst is 0.1 to 1% of the total molar amount of the nanoscale catalyst and the high-purity graphite powder.

[0012] Preferably, the gas used for the plasma catalytic pyrolysis is one or more of helium, argon, and neon, and the air pressure of the gas is 1 to 200 kPa; the discharge arc voltage of the plasma catalytic pyrolysis is 10 to 40 V, and the current is 10 to 400 A.

[0013] Preferably, the tube diameter of the small-diameter single-walled carbon nanotube is 1.2 to 1.4 nm.

[0014] The present invention provides a method for preparing small-diameter single-walled carbon nanotubes. Compared with the prior art, the present invention has the following beneficial effects: The present invention uses a nanoscale catalyst. Compared with a micron-sized large-particle catalyst, it can reduce the content of carbon impurities (such as amorphous carbon and even fullerenes) in the product that are not single-walled carbon nanotubes; in addition, using a nanoscale catalyst can reduce the amount of catalyst used, thereby increasing the mass ratio of single-walled carbon nanotubes in the product. The present invention uses the method of plasma catalytic pyrolysis. Its high plasma energy can provide the energy for graphite to grow into carbon nanotubes, realizing more efficient production of single-walled carbon nanotubes, and cooperating with a nanoscale small-size catalyst to obtain single-walled carbon nanotubes with a smaller tube diameter. The preparation method provided by the present invention has a high yield (the mass ratio of single-walled carbon nanotubes in the crude product is high), and can prepare single-walled carbon nanotubes with a smaller tube diameter.

[0015] The results of the examples show that when using the preparation method provided by the present invention to prepare single-walled carbon nanotubes, the mass ratio of single-walled carbon nanotubes in the crude product can reach 79%, and the tube diameter of the single-walled carbon nanotubes can be as low as 1.2 nm. Description of the Drawings

[0016] Figure 1SEM image of the crude product obtained in Example 1; Figure 2 TEM image of the crude product obtained in Example 1; Figure 3 Raman spectrum of the crude product obtained in Example 1; Figure 4 SEM image of the crude product obtained in Example 21. Detailed implementation mode

[0017] The present invention provides a method for preparing small-diameter single-walled carbon nanotubes, comprising the following steps: Mix a nano-sized catalyst, high-purity graphite powder, and a liquid carbon source binder, and perform shaping and sintering in sequence to obtain a mixed graphite rod; the nano-sized catalyst contains a metal element, and the metal element is a transition metal element and / or an aluminum element; Use the mixed graphite rod as the anode and a pure graphite rod as the cathode to perform plasma catalytic pyrolysis to obtain small-diameter single-walled carbon nanotubes.

[0018] In the present invention, unless otherwise specified, all raw materials involved are commercially available products.

[0019] The present invention mixes a nano-sized catalyst, high-purity graphite powder, and a liquid carbon source binder, and performs shaping and sintering in sequence to obtain a mixed graphite rod.

[0020] In the present invention, the particle size of the nano-sized catalyst is preferably 1 to 100 nm, and can be 1, 3, 5, 10, 20, 50, or 80 nm. By using a nano-sized catalyst in the present invention, compared with a micron-sized large-particle catalyst, the content of carbon impurities (such as amorphous carbon, and even fullerenes) in the product that are not single-walled carbon nanotubes can be reduced; in addition, using a nano-sized catalyst can reduce the amount of catalyst used, thereby increasing the yield of single-walled carbon nanotubes in the product.

[0021] In the present invention, the nano-catalyst contains a metal element, and the metal element is a transition metal element and / or aluminum element. In the present invention, the transition metal element is preferably selected from one or more of iron element (Fe), cobalt element (Co), nickel element (Ni), yttrium element (Y), zinc element (Zn), chromium element (Cr), manganese element (Mn), copper element (Cu), and molybdenum element (Mo). In the present invention, the nano-catalyst is preferably selected from one or more of the metal simple substances corresponding to the metal elements, alloys formed by two or more of the metal elements, and compounds containing the metal elements; the compounds containing the metal elements can be oxides, sulfides, or carbides containing the metal elements. As an embodiment of the present invention, the nano-catalyst is a mixture of metal simple substances corresponding to two or more of the metal elements, preferably a mixture of metal simple substances corresponding to two or more transition metal elements. The present invention has no particular requirement for the mixing ratio between the metal simple substances in the mixture. For example, it can be a mixture of nickel and yttrium, and the molar ratio of nickel to yttrium in the mixture of nickel and yttrium can be 3-5:1, specifically 3:1, 4:1, or 5:1. As an embodiment of the present invention, the nano-catalyst is an alloy formed by two or more metal elements, preferably an alloy formed by two or more transition metal elements. The present invention has no particular requirement for the proportion of the metal elements in the alloy, and it can be Ni 4 Y, Ni 5 Y or Ni 3 Y. In the present invention, the nano-catalyst in the form of an alloy has a lower melting point and weaker thermal conductivity than a single metal, resulting in it being easier to trigger a reaction than a single metal (where the low melting point causes it to co-evaporate with carbon atoms at a lower temperature, and the weak thermal conductivity causes energy to be more concentrated), and the alloy can achieve a more uniform combination of metal elements. As an embodiment of the present invention, the nano-catalyst is a mixture of the alloy and the metal simple substance. The alloy can be Ni 4 Y, and the metal simple substance can be aluminum, zinc, chromium, manganese, copper, or molybdenum. The molar ratio of the alloy to the metal simple substance 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 has no particular requirement for the source of the nano-catalyst, and it can be obtained by using commercially available products or by using methods well-known to those skilled in the art.

[0022] In the present invention, the particle size of the high-purity graphite powder (i.e., with a purity of over 99.99%) is preferably 1 nm to 500 μm. In the present invention, the high-purity graphite powder preferably comprises one or several of a first graphite powder, a second graphite powder, a third graphite powder, and a fourth graphite powder, and 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, the particle size of the fourth graphite powder is preferably 1 to 999 nm, more preferably 40 to 100 nm. In an embodiment of the present invention, the fourth graphite powder is super P. In the present invention, when the high-purity graphite powder comprises several of the first graphite powder, the second graphite powder, the third graphite powder, and the fourth graphite powder, the high-purity graphite powder is preferably a mixture of the first graphite powder, the second graphite powder, the third graphite powder, and the fourth graphite powder or a mixture of the second graphite powder, the third graphite powder, and the fourth graphite powder; when the high-purity graphite powder is preferably a mixture of the first graphite powder, the second graphite powder, the third graphite powder, and the fourth graphite powder, the mass ratio of the first graphite powder, the second graphite powder, the third graphite powder, and the fourth graphite powder in the mixture is preferably 95:4:0.8:0.2; when the high-purity graphite powder is a mixture of the second graphite powder, the third graphite powder, and the fourth graphite powder, the mass ratio of the second graphite powder, the third graphite powder, and the fourth graphite powder in the mixture is preferably 95:4:1. The present invention uses a compounding of graphite powders with different particle sizes, which can reduce the voids of the graphite powder, so that the catalyst is in close contact with the graphite powder, thereby increasing the mass ratio of nanotubes in the crude product.

[0023] In the present invention, the molar amount of the nano-sized catalyst is preferably 0.1% to 1% of the total molar amount of the nano-sized catalyst and the 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%. The present invention controls the addition amount of the nano-sized catalyst within the above range value, which is beneficial to reducing the use of useless catalysts, thereby increasing the mass ratio of nanotubes in the crude product.

[0024] The present invention has no special requirements for the liquid carbon source binder, and a liquid carbon source binder well-known to those skilled in the art can be used, such as asphalt, tar, petroleum, kerosene, diesel, gasoline, paraffin, liquid butadiene rubber (i.e., cis-butadiene rubber, molecular weight 5000 - 50000), bisphenol A epoxy resin, phenolic resin, unsaturated polyester resin, polyvinyl alcohol or polycarbonate. In the present invention, the mass of the liquid carbon source binder is preferably 0.1 - 10% of the mass of the high-purity graphite powder, and can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%.

[0025] In the present invention, the method for mixing the nano-catalyst, high-purity graphite powder and liquid carbon source binder is preferably: mixing the high-purity graphite powder and nano-catalyst evenly; then adding the liquid carbon source binder thereto and mixing evenly (the liquid carbon source binder fills the voids).

[0026] In the present invention, the forming method is preferably extrusion, and specifically in the embodiments of the present invention, it is extruded into a mixed graphite rod blank with a diameter of 20 mm.

[0027] In the present invention, the sintering temperature is preferably 1000 °C, the heat preservation time is preferably 4 h, and the sintering is preferably carried out in an argon atmosphere; in the embodiments of the present invention, the sintering is carried out in a high-temperature furnace. After the sintering, a dense and uniform graphite rod mixed with the catalyst and graphite is formed, that is, the mixed graphite rod.

[0028] After obtaining the mixed graphite rod, the present invention uses the mixed graphite rod as the anode and a pure graphite rod as the cathode to carry out plasma catalytic pyrolysis to obtain small-diameter single-walled carbon nanotubes (SWCNT).

[0029] In the embodiments of the present invention, the diameter of the pure graphite rod is 40 mm.

[0030] In the present invention, the anode and the cathode are placed in a plasma generator for plasma catalytic pyrolysis. In the present invention, the gas used for the plasma catalytic pyrolysis is preferably one or more of helium, argon and neon, and the gas pressure is preferably 1-200 kPa, which can be 50, 70, 100, 150 or 200 kPa; the discharge arc voltage of the plasma catalytic pyrolysis is preferably 10-40 V, which can be 10, 20, 30 or 40 V, the current is preferably 10-400 A, which can be 50, 100, 200, 300 or 400 A, and the discharge time is preferably 5-60 min, which can be 5, 10, 15, 20, 30, 40, 50 or 60 min. During the plasma catalytic pyrolysis process, high-energy ions in the plasma drive the reaction to promote the dissociation of the carbon source (graphite). Under the action of the catalyst, single-walled carbon nanotubes are macroscopically and controllably generated. The present invention adopts a controllable plasma enhanced catalytic pyrolysis method (CPECP) to further control the current and voltage of the plasma generator to produce single-walled carbon nanotubes with controllable diameters.

[0031] In the present invention, the diameter of the small-diameter single-walled carbon nanotubes is 1.2-1.4 nm. In the present invention, the diameter of the small-diameter single-walled carbon nanotubes is the peak value calculated according to the radial breathing mode (RBM) of the Raman spectrum.

[0032] The preparation method provided by the present invention can obtain high-quality (the content of single-walled carbon nanotubes in the crude product is high, that is, the yield of single-walled carbon nanotubes in the obtained product increases, and the content of amorphous carbon and metal catalyst decreases) and small-diameter single-walled carbon nanotubes with controllable sizes. The diameter of the obtained single-walled carbon nanotubes is smaller than that of similar products.

[0033] To further illustrate the present invention, the following examples are used to describe in detail the preparation method of the small-diameter single-walled carbon nanotubes provided by the present invention, but they should not be construed as limiting the protection scope of the present invention.

[0034] Example 1 The preparation of small-diameter single-walled carbon nanotubes is carried out as follows: Step 1: Using a 99.99% high-purity graphite powder mixture (300 μm graphite powder: 50 μm graphite powder: 5 μm graphite powder: 40 nm super P = 95:4:0.8:0.2 (mass ratio)), nano-Ni 4 Y alloy catalyst (particle size 5 nm) as raw materials, according to the molar ratio (C∶Ni 4 Y is 99.2∶0.8), after mixing evenly, liquid butadiene rubber (molecular weight 20000) is added and mixed and extruded into a graphite rod blank with a diameter of 20 mm. The addition amount of liquid butadiene rubber is 10% of the mass of the high-purity graphite powder mixture; the graphite rod blank is placed in a high-temperature furnace protected by argon and sintered at 1000 °C for 4 h to obtain an anode graphite rod.

[0035] Step 2: Place the anodic graphite rod prepared in Step 1 into a plasma generator. Use a pure graphite rod with a diameter of 40 mm as the cathode. The gas used in the plasma is a mixture of helium and neon. The volume ratio of helium in the mixture is 99.9%. The pressure of the mixture is 70 kPa. The discharge current is 100 A, the voltage is 30 V, and the discharge time is 5 min to obtain crude single-walled carbon nanotubes. In the obtained crude product, the mass ratio of single-walled carbon nanotubes (SWCNT) is 79%, and the diameter distribution of SWCNT is 1.2 ± 0.4 nm (where 1.2 nm is the peak value calculated based on the radial breathing mode peak RBM of the Raman spectrum, and the other diameter distribution representations are similar to this).

[0036] Figure 1 It is the scanning electron microscope image of the crude product obtained in Example 1 (where the filaments are single-walled carbon nanotubes and the granular ones are impurities). It can be seen that the proportion of carbon nanotubes in the obtained crude product is large and the impurities are few.

[0037] Figure 2 It is the TEM image of the crude product obtained in Example 1. It can be seen that what is prepared in Example 1 is single-walled carbon nanotubes, and the tube diameter is small, about 1.2 nm.

[0038] Figure 3 It is the Raman spectrum of the crude product obtained in Example 1. The tube diameter size can be calculated to be about 1.2 nm through the peak value data in the Raman breathing peak.

[0039] Examples 2 - 16 The preparation steps of SWCNT in Examples 2 - 16 are the same as those in Example 1, the difference is that different types of catalysts are selected. The types of catalysts used in Examples 2 - 16 and the mass ratio of SWCNT and the diameter distribution of SWCNT in the obtained crude products are shown in Table 1. In the column of "Catalyst type" in Table 1, the catalyst ratios corresponding to Examples 4 - 16 are all molar ratios.

[0040] Table 1 Types of catalysts used in Examples 2 - 16 and the mass ratio of SWCNT and the diameter distribution of SWCNT in the obtained crude products

[0041] The preparation process steps of SWCNT in Examples 2 - 16 are the same as those in Example 1, the difference is that different types of catalysts are selected. It can be seen from the results in Table 1 that different types of catalysts will have a greater impact on the yield of SWCNT and the tube diameter of SWCNT.

[0042] Examples 17 - 21 Examples 17 to 21 have the same SWCNT preparation steps as Example 1, except that the sizes of the catalysts selected are different. The sizes of the catalysts used in Examples 17 to 21, as well as the mass percentage of SWCNT and the SWCNT diameter distribution in the crude product obtained, are shown in Table 2.

[0043] Table 2 Sizes of the catalysts used in Examples 17 to 21, as well as the mass percentage of SWCNT and the SWCNT diameter distribution in the crude product obtained

[0044] Examples 17 to 21 have the same SWCNT preparation steps as Example 1, except that the sizes of the catalysts selected are different. As can be seen from the results in Table 2, different sizes of the catalysts selected have a great influence on the SWCNT yield and the tube diameter of SWCNT.

[0045] Figure 4 Figure 12 is the SEM image of the crude product obtained in Example 21, from which it can be seen that there are many impurities.

[0046] Examples 22 to 26 Examples 22 to 26 have the same SWCNT preparation steps as Example 1, except that the molar ratio of the carbon source (high-purity graphite powder mixture) to the catalyst in the raw materials selected is different. The molar ratio of the carbon source to the catalyst (carbon: catalyst) in Examples 22 to 26, as well as the mass percentage of SWCNT and the SWCNT diameter distribution in the crude product obtained, are shown in Table 3.

[0047] Table 3 Molar ratio of the carbon source to the catalyst in Examples 22 to 26, as well as the mass percentage of SWCNT and the SWCNT diameter distribution in the crude product obtained

[0048] Examples 22 to 26 have the same SWCNT preparation steps as Example 1, except that the ratio of the carbon source to the catalyst is different. As can be seen from the data in Table 3, different ratios of the carbon source to the catalyst have a great influence on the SWCNT yield.

[0049] Examples 27 to 31 Examples 27 to 31 have the same SWCNT preparation steps as Example 1, except that the carbon source (high-purity graphite powder mixture) selected is different. The carbon sources used in Examples 27 to 31, as well as the mass percentage of SWCNT and the SWCNT diameter distribution in the crude product obtained, are shown in Table 4.

[0050] Table 4 Carbon sources in Examples 27 to 31, as well as the mass percentage of SWCNT and the SWCNT diameter distribution in the crude product obtained

[0051] Examples 27 to 31 have the same SWCNT preparation steps as Example 1, except that different carbon sources are selected. It can be seen from the results in Table 4 that different carbon sources selected have a great influence on the yield.

[0052] Examples 32 to 35 Examples 32 to 35 have the same SWCNT preparation steps as Example 1, except that the current voltages in the preparation process are different. The current voltages used in Examples 32 to 35, as well as the mass ratio of SWCNT in the obtained crude product and the SWCNT diameter distribution, are shown in Table 5.

[0053] Table 5 Current voltages in Examples 32 to 35, as well as the mass ratio of SWCNT in the obtained crude product and the SWCNT diameter distribution

[0054] Examples 32 to 35 have the same SWCNT preparation steps as Example 1, except that different current voltages are selected. It can be seen from the results in Table 5 that different current voltages selected have a great influence on the yield.

[0055] The above are only the preferred embodiments of the present invention and do not impose any form of limitation on the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing small-diameter single-walled carbon nanotubes, characterized in that: The following steps are involved: A nano-scale catalyst, high-purity graphite powder and a liquid carbon source binder are mixed, and molded and sintered in sequence to obtain a mixed graphite rod; the nano-scale catalyst contains a metal element, and the metal element is a transition metal element and / or an aluminum element; The mixed graphite rod is used as an anode and the pure graphite rod is used as a cathode to carry out plasma catalytic pyrolysis to obtain small-diameter single-walled carbon nanotubes.

2. The preparation method according to claim 1, characterized in that: The transition metal element is selected from one or more of iron, cobalt, nickel, yttrium, zinc, chromium, manganese, copper and molybdenum.

3. The preparation method according to claim 1 or 2, characterized in that: The nano-scale catalyst is selected from one or more of the metal element corresponding to the metal element, an alloy formed by two or more of the metal elements, and a compound containing the metal element.

4. The preparation method according to claim 3, characterized in that: The alloy formed by the two or more metal elements includes Ni4Y, Ni5Y or Ni3Y.

5. The preparation method according to claim 1, characterized in that: The particle size of the nano-scale catalyst is 1-100 nm.

6. The preparation method according to claim 1, characterized in that: The particle size of the high-purity graphite powder is 1 nm to 500 μm.

7. The preparation method according to claim 6, characterized in that: The high-purity graphite powder includes one or more of a first graphite powder, a second graphite powder, a third graphite powder and a fourth graphite powder, and the first graphite powder, the second graphite powder, the third graphite powder and the fourth graphite powder have different particle sizes; the particle size of the first graphite powder is 100~500μm, the particle size of the second graphite powder is 10~100μm, the particle size of the third graphite powder is 1~10μm, and the particle size of the fourth graphite powder is 1~999nm.

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

9. The preparation method according to claim 1, characterized in that: The gas used for 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.

10. The preparation method according to claim 1, characterized in that: The diameter of the small-diameter single-walled carbon nanotube is 1.2-1.4 nm.

Images