Growth method of single-walled carbon nanotube

Abstract

The invention relates to a growth method of a single-walled carbon nanotube. The growth method comprises the following steps: step 1, injecting a carbon source, an argon-carried catalyst precursor, an auxiliary agent and hydrogen into a reaction furnace; 2, preheating the mixed gas in the reaction furnace, so that the catalyst precursor, the auxiliary agent and the carbon source are pre-cracked or decomposed in the reaction furnace, and the heating temperature in the reaction furnace is higher than the temperature required by the pre-cracking or decomposition of the catalyst precursor, the auxiliary agent and the carbon source; step 3, carrying the pre-cracked or decomposed carbon source, the catalyst precursor and the auxiliary agent into a high-temperature heating vacuum furnace by argon carrier gas, heating the pre-cracked or decomposed carbon source, the catalyst precursor and the auxiliary agent by a heat source of the high-temperature heating vacuum furnace to grow single-walled carbon nanotube powder, and controlling the heating temperature of the high-temperature heating vacuum furnace to be the growth temperature of the single-walled carbon nanotube powder; the mixed gas reaches a critical state by preheating the mixed gas in the reaction furnace, and the method can pre-split or decompose a catalyst precursor, an auxiliary agent and a carbon source in the preheating stage, so that the growth efficiency and purity are improved.

Description

Technical Field

[0001] The invention relates to the technical field of single-walled carbon nanotube growth, and in particular to a method for growing single-walled carbon nanotubes. Background Art

[0002] Single-walled carbon nanotubes (SWCNTs) have been widely used in nanoelectronics, composite materials, energy storage, and other fields due to their excellent electrical, mechanical, and thermal properties. Currently, the main methods for preparing SWCNTs include arc discharge, laser ablation, and chemical vapor deposition (CVD). CVD has become the mainstream technology due to its high controllability and suitability for large-scale production.

[0003] According to Chinese patent CN119390058A, a method for continuously preparing single-walled carbon nanotubes is disclosed. The method comprises mixing an organic metal with a growth promoter to form a catalyst for standby use; adding the uniformly mixed catalyst to a precision dust injection device, and connecting the device to a preheating furnace via a pipeline; connecting pipelines for organic gas, reducing gas, and inert gas to the preheating furnace, respectively, with the outlet of the preheating furnace connected to the feed inlet of a vertical tube furnace via a pipeline; first introducing inert gas 2 and residual air, and then heating the preheating furnace and the vertical tube furnace separately under an inert gas atmosphere, the preheating furnace being heated to 100°C-300°C and the vertical tube furnace being heated to 1100°C-1300°C; opening the precision dust injection device, adjusting the gas velocity so that the catalyst enters the preheating furnace, and adjusting the pipeline so that the inert gas carrying the organic gas and reducing gas enters the preheating furnace before entering the vertical tube furnace, the entire pipeline remaining heated, and finally maintaining the preheating furnace and the vertical tube furnace at a constant temperature to achieve continuous growth of single-walled carbon nanotubes.

[0004] As can be seen from the above, the mixed raw materials are first heated to 100°C-300°C in a preheating furnace, and then heated to 1100°C-1300°C in a vertical tubular furnace before generating single-walled carbon nanotubes. However, the preheating stage of this method makes it difficult to fully pre-cracking or decomposing the catalyst and carbon source, affecting the growth efficiency and purity of single-walled carbon nanotubes.

[0005] Therefore, it is necessary to develop a method for growing single-walled carbon nanotubes to solve the above problems. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for growing single-walled carbon nanotubes with improved growth efficiency and purity.

[0007] To achieve the above object, the present invention provides the following technical solution: a method for growing single-walled carbon nanotubes, characterized in that it comprises the following steps: Step 1: injecting carbon source, argon-carried catalyst precursor and promoter, and hydrogen into the reactor; Step 2: Electromagnetic induction heating of graphite in the reactor preheats the mixed gas by heat conduction. The heating time is 0.02-0.08s, so that the catalyst precursor, the auxiliary agent and the carbon source are pre-cracked or decomposed in the reactor. The heating temperature in the reactor is higher than the temperature required for the catalyst precursor, the auxiliary agent and the carbon source to be pre-cracked or decomposed. Step 3: The pre-cracked or decomposed carbon source, catalyst precursor and additive are carried by argon carrier gas into a high-temperature heating vacuum furnace, where they are heated by the heat source of the high-temperature heating vacuum furnace to grow single-walled carbon nanotube powder. The heating temperature of the high-temperature heating vacuum furnace is the growth temperature of the single-walled carbon nanotube powder, which is less than or equal to the preheating temperature of 100-500°C in the reactor through which the same batch of single-walled carbon nanotube powder passes.

[0008] Furthermore, in step 2, the preheating temperature in the reaction furnace is 600°C to 2000°C.

[0009] Furthermore, in step three, the growth temperature of the high-temperature heating vacuum furnace is 500°C to 1500°C.

[0010] Furthermore, in step 2, the reaction furnace is provided with a magnetic induction heating or plasma heating system with a length of 5-20 cm.

[0011] Furthermore, the reaction furnace is connected to the high-temperature heating vacuum furnace, and the absolute pressure is maintained at 50-150Kpa.

[0012] Furthermore, in step one, the carrier gas carries the sublimated, vaporized or evaporated catalyst precursor and auxiliary agent.

[0013] Furthermore, the catalyst precursor is selected from organic substances such as Fe-Co, Ni-Mo, Fe, and auxiliary agents such as thiophene or sulfur or sulfur-containing organic substances.

[0014] Furthermore, the molar ratio of the catalyst precursor to the auxiliary agent is 1:1 to 10000:1.

[0015] Furthermore, the carbon source is hydrocarbons such as ethanol, methanol, benzene, xylene, acetylene, ethylene, and methane.

[0016] Furthermore, the molar ratio of the catalyst precursor to the carbon source is 1:1 to 1:100.

[0017] Compared with the prior art, the beneficial effects of the present invention are: a method for growing single-walled carbon nanotubes of the present invention has the characteristics of improving growth efficiency and purity. The mixed gas is preheated by the heat source in the reactor, so that the catalyst precursor, auxiliary agent and carbon source are pre-cracked or decomposed in the reactor, and reach a critical state. The pre-cracked or decomposed carbon source, catalyst precursor and auxiliary agent are carried by argon carrier gas to a high-temperature heating vacuum furnace, and the heat source of the high-temperature heating vacuum furnace heats them, and high-quality single-walled carbon nanotube powder begins to grow in large quantities. This method can fully pre-crack or decompose the catalyst precursor, auxiliary agent and carbon source in the preheating stage, thereby improving the growth efficiency and purity of single-walled carbon nanotubes. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0019] Figure 1 This is a Raman spectrum of single-walled carbon nanotubes prepared by a single-walled carbon nanotube growth method of the present invention; Figure 2 This is a scanning electron microscope image of single-walled carbon nanotubes prepared by a single-walled carbon nanotube growth method of the present invention; Figure 3 Another scanning electron microscope image of single-walled carbon nanotubes prepared by a single-walled carbon nanotube growth method of the present invention; Figure 4 A transmission electron microscope image of single-walled carbon nanotubes prepared by a single-walled carbon nanotube growth method of the present invention; Figure 5 This is a thermogravimetric analysis chart of single-walled carbon nanotubes prepared by a single-walled carbon nanotube growth method of the present invention; Figure 6 A BET diagram of single-walled carbon nanotubes prepared by a single-walled carbon nanotube growth method of the present invention; Figure 7 This is the Raman spectrum of single-walled carbon nanotubes using the conventional preheating method; Figure 8 This is a transmission electron microscope image of single-walled carbon nanotubes produced using a conventional preheating method; Figure 9 This is a thermogravimetric analysis chart of single-walled carbon nanotubes using a conventional preheating method; Figure 10 Another transmission electron microscope image of single-walled carbon nanotubes using the conventional preheating method; Figure 11This is the BET diagram of single-walled carbon nanotubes using the conventional preheating method; Figure 12 A schematic diagram of the cross-sectional structure of the equipment used in the method for growing single-walled carbon nanotubes of the present invention; Figure 13 for Figure 12 Schematic diagram of the partial structure of the equipment used in the growth method of single-walled carbon nanotubes; Figure 14 for Figure 12 Another partial structural diagram of the equipment used in the method for growing single-walled carbon nanotubes; Figure 15 for Figure 12 A schematic diagram of a three-dimensional structure including a partial cross-sectional view of an apparatus used in a method for growing single-walled carbon nanotubes; Figure 16 for Figure 12 Another schematic diagram of the three-dimensional structure including a partial cross-sectional view of the equipment used in the method for preparing single-walled carbon nanotubes. DETAILED DESCRIPTION

[0020] To further illustrate the technical means and effectiveness of the present invention in achieving its intended objectives, the following, in conjunction with the accompanying drawings and preferred embodiments, describes in detail the single-walled carbon nanotube growth method according to the present invention, including its specific implementation, structure, features, and effectiveness. In the following description, references to different "one embodiment" or "another embodiment" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics of one or more embodiments may be combined in any suitable manner.

[0021] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

[0022] The specific scheme of the method for growing single-walled carbon nanotubes provided by the present invention is described in detail below with reference to the accompanying drawings.

[0023] Please see Figures 12 to 16 The present invention is a method for growing single-walled carbon nanotubes, which is achieved through a reaction furnace 100 and a high-temperature heating vacuum furnace 200.

[0024] The reaction furnace 100 includes an outer shell 1 , a feeding portion 2 extending into the outer shell 1 , a heating portion 3 and a heat-insulating portion 4 located in the outer shell 1 .

[0025] Housing 1 includes a shell 11, a flange 12 mounted on one end of shell 11, and a ceramic hanger plate 13 mounted on the other end of shell 11. Shell 11 is made of high-temperature resistant material and is hollow and cylindrical. Flange 12 is mounted on the top of shell 11 and fixedly connected by bolts or screws. Ceramic hanger plate 13 is mounted on the bottom of shell 11 and fixedly connected by bolts or screws. Specifically, a cooling element 14 is laid on the upper surface of flange 12. Cooling element 14 forms a cavity inside. When cooling is required, coolant is added to the cavity to reduce the temperature.

[0026] Please see Figures 12 to 14 The feed part 2 includes a ceramic tube 21 and a feed port 22 connected to the ceramic tube 21. The ceramic tube 21 passes through the flange 12 and the ceramic hanger plate 13. The feed port 22 is connected to the ceramic tube 21 from the side of the ceramic tube 21. Specifically, a limiting member 23 is sleeved on the top of the ceramic tube 21. The outer surface of the limiting member 23 forms an external thread. A fixing member 15 is installed on the upper surface of the flange 12. The interior of the fixing member 15 forms an internal thread. The ceramic tube 21 is screwed with the thread of the fixing member 15 through the external thread of the limiting member 23 to fix the position of the ceramic tube 21. Furthermore, the limiting member 23 has an annular groove 231 formed by being recessed inward from the outer surface. A sealing ring 24 is provided in the annular groove 231. The number of the annular grooves 231 is a pair, and a sealing ring 24 is installed in each of them.

[0027] Please see Figure 12 and Figure 14 The heating unit 3 includes a heating coil 31 and a graphite 32 corresponding to the heating coil 31. The graphite 32 is disposed outside the end of the ceramic tube 21 and surrounds the ceramic tube 21. The heating coil 31 is located outside the graphite 32 and surrounds the graphite 32. Specifically, the graphite 32 is in the shape of a T-shaped sleeve and includes a vertical section 321 and a horizontal section 322. The vertical section 321 and the horizontal section 322 are integrally formed. The vertical section 321 is parallel to the ceramic tube 21 and its length can be adjusted according to needs. One end of the horizontal section 322 is fixedly connected to the top of the vertical section 321, and the other end extends perpendicularly and radially.

[0028] The inner diameter of the graphite 32 is larger than the outer diameter of the ceramic tube 21 , and a gap is formed between the graphite 32 and the ceramic tube 21 .

[0029] The heating coil 31 is made of a conductive material, preferably copper, and includes a conductor segment 311 and a surrounding segment 312. Both segments are formed from one or more deformed copper wires. The surrounding segment 312 is positioned outside the graphite 32, maintaining a certain distance from the graphite 32. The conductor segments 311 extend outward from both ends of the surrounding segment 312, passing through the flange 12 and connected to a power source. When high-frequency alternating current is applied to the heating coil 31, the generated alternating magnetic field induces eddy currents in the graphite 32, causing the graphite 32 to heat due to its own electrical resistance or through plasma heating. Specifically, the graphite 32 is heated to a temperature of 600°C to 2000°C, and the height of the surrounding ceramic tube 21 is 5 to 20 cm.

[0030] The heating part 3 also includes a temperature measuring element 33. In this embodiment, the temperature measuring element 33 is a thermocouple. The temperature measuring element 33 extends into the ceramic tube 21, and its end is close to the area where the graphite 32 is heated. Specifically, the temperature measuring element 33 is located at the center of the ceramic tube 21.

[0031] Please see Figure 12 The insulation portion 4 includes a first insulation layer 41, a second insulation layer 42, and a third insulation layer 43, which are sequentially installed in the housing 1. Specifically, the first insulation layer 41 surrounds the ceramic tube 21 and is arranged along the ceramic tube 21, with its bottom abutting against the top of the graphite 32. The second insulation layer 42 is located outside the first insulation layer 41 and is sleeved on the first insulation layer 41. Its bottom abuts against the outer surface of the graphite 32. The third insulation layer 43 is located outside the second insulation layer 42 and is sleeved on the second insulation layer 42.

[0032] Specifically, the inner surface of the second insulation layer 42 contacts the outer surface of the first insulation layer 41, and the bottom of the second insulation layer 42 is provided with a first installation groove 421 and a second installation groove 422. The second installation groove 422 is located outside the first installation groove 421. The first installation groove 421 is formed by being recessed inward from the inner surface of the second insulation layer 42. The graphite 32 is arranged in the first installation groove 421, the second installation groove 422 is arranged inside the second insulation layer 42, and the heating coil 31 is arranged in the second installation groove 422.

[0033] A passing area 44 is formed between the inner surface of the third insulation layer 43 and the outer surface of the second insulation layer 42. The wire segment 311 of the heating coil 31 passes through the second insulation layer 42 from the second mounting groove 422 into the passing area 44 and extends out of the shell 1 along the passing area 44.

[0034] The heat-insulating portion 4 further includes a heat-insulating block 45 , which is disposed below the second heat-insulating layer 42 , and an upper surface of an inner circle of the heat-insulating block 45 contacts the bottom of the graphite 32 .

[0035] The high-temperature vacuum furnace 200, located below the aforementioned structures, includes a feed pipe 51 and a heating and insulation structure located outside the feed pipe 51. Specifically, the top of the feed pipe 51 communicates with the ceramic tube 21, and its bottom forms a discharge port 511. The heating structure heats the feed pipe 51 to a temperature between 500°C and 1500°C, maintaining an absolute pressure between 50 and 150 kPa.

[0036] Please see Figures 15 and 16 The material tube 51 extends in an S-shaped or spirally curved manner, thereby prolonging the growth time of the single-walled carbon nanotubes.

[0037] The growth steps of single-walled carbon nanotubes are: Step 1: injecting a carbon source, argon-carrying catalyst precursor and promoter, and hydrogen into the reaction furnace 100; Step 2: The graphite 32 is heated by the heating coil 31 to heat the graphite 32. The graphite 32 conducts heat to the ceramic tube 21. The temperature measuring component 33 detects in real time whether the ceramic tube 21 reaches the predetermined temperature. After reaching the predetermined temperature, the carbon source, argon-carrying catalyst precursor and additive, and hydrogen enter the ceramic tube 21 from the feed port 22, and enter the heated area of ​​the graphite 32 along the ceramic tube 21 for preheating. The heating temperature is 600°C to 2000°C, so that the catalyst precursor, additive, and carbon source are pre-cracked or decomposed. The preheating time of the cracked or decomposed carbon source, catalyst precursor, and additive is 0.02-0.08s. Step 3: The preheated mixed gas flows into the feed pipe 51 of the high-temperature vacuum furnace 5. The heating structure heats the feed pipe 51 to a temperature of 500°C to 1500°C. The absolute pressure is maintained at 50 to 150 kPa. SWCNT powder begins to grow in large quantities in the reaction furnace. The preheating temperature is always 100-500°C higher than the growth temperature.

[0038] In step 2, electromagnetic heating uses an electric field to generate a magnetic field, which heats the graphite. The graphite then radiates or conducts the heat to the catalyst and carbon nanotubes. The heating range of electromagnetic heating is uniform at +-5°, which is easy to control. At the same time, high-quality carbon nanotubes can be grown at a relatively low temperature.

[0039] In steps 2 and 3, the preheating temperature experienced by the single-walled carbon nanotube powders grown in the same batch is greater than the growth temperature. For example: when the growth temperature of the single-walled carbon nanotube powder in a high-temperature vacuum furnace is 500-800°C, the preheating temperature in the reactor is 800-2000°C; when the growth temperature of the single-walled carbon nanotube powder in a high-temperature vacuum furnace is 800-1200°C, the preheating temperature in the reactor is 1200-2000°C; when the growth temperature of the single-walled carbon nanotube powder in a high-temperature vacuum furnace is 1200-1500°C, the preheating temperature in the reactor is 1500-2000°C.

[0040] Specifically, in terms of the preparation of catalyst precursors and additives, unlike the traditional liquid catalyst injection atomization method, a carrier gas is used to carry out sublimation, vaporization or evaporation of the catalyst precursor. The catalysts are organic substances such as Fe-Co, NiMo, Fe, and additives such as thiophene, sulfur or sulfur-containing organic substances. The molar ratio of the catalyst precursor to the additive is 1:1 to 10000:1; the molar ratio of the catalyst precursor to the carbon source is 1:1 to 1:100.

[0041] The carbon source is ethanol, methanol, benzene, xylene, acetylene, ethylene, methane and other hydrocarbons.

[0042] Please see Figures 1 to 5 , single-walled carbon nanotubes were tested by SEM, TEM and Raman spectroscopy. SEM and TEM were used to characterize the diameter of the product, while the G / D ratio of Raman spectroscopy was used to characterize the degree of defects of the product.

[0043] Please see Figure 1 and Figure 7 Compared with the Raman spectrum of single-walled carbon nanotubes using the conventional preheating method, it was found from the RAMAN (Raman) data that the crystallinity IG / ID of single-walled carbon nanotube powder increased from 36.5 to 80.

[0044] Please see Figure 5 and Figure 9 , single-walled carbon nanotubes were tested by thermogravimetric method and TG curves were obtained. From the comparison of TG (thermogravimetric analysis) data, it was found that the purity of single-walled carbon nanotubes increased from 46% to about 78%.

[0045] Please see Figure 3 and Figure 10 , TME (transmission electron microscopy evaluation) test was performed on single-walled carbon nanotubes, and the diameter range of single-walled carbon nanotubes was reduced from 0.6-1.8nm to 1.5±0.4nm.

[0046] Please see Figure 6 and Figure 11 , BET test was conducted on single-walled carbon nanotubes. The BET test is used to describe the isotherm of gas adsorption on the solid surface, express the relationship between pressure and volume, and calculate the specific surface area. After comparison, it was found that the specific surface area of ​​single-walled carbon nanotubes decreased from 439.3m2 / g to 369.3m2 / g, both of which are greater than 300 m2 / g.

[0047] The present invention provides a method for growing single-walled carbon nanotubes, which has the characteristics of improving growth efficiency and purity. The mixed gas is preheated by a heat source in a reaction furnace, so that a catalyst precursor, an auxiliary agent and a carbon source are pre-cracked or decomposed in the reaction furnace. When a critical state is reached, the pre-cracked or decomposed carbon source and catalyst are carried by argon carrier gas to a high-temperature heating vacuum furnace. The heat source of the high-temperature heating vacuum furnace heats them, and high-quality single-walled carbon nanotube powder begins to grow in large quantities. This method can fully pre-crack or decompose the catalyst precursor, the auxiliary agent and the carbon source in the preheating stage, thereby improving the growth efficiency and purity of the single-walled carbon nanotubes.

[0048] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for growing single-walled carbon nanotubes, characterized in that: The following steps are involved: Step 1: injecting carbon source, argon-carried catalyst precursor and promoter, and hydrogen into the reactor; Step 2: Electromagnetic induction heating of graphite in the reactor preheats the mixed gas by heat conduction. The heating time is 0.02-0.08s, so that the catalyst precursor, the auxiliary agent and the carbon source are pre-cracked or decomposed in the reactor. The heating temperature in the reactor is higher than the temperature required for the catalyst precursor, the auxiliary agent and the carbon source to be pre-cracked or decomposed. Step 3: The pre-cracked or decomposed carbon source, catalyst precursor and additive are carried by argon carrier gas into a high-temperature heating vacuum furnace, where they are heated by the heat source of the high-temperature heating vacuum furnace to grow single-walled carbon nanotube powder. The heating temperature of the high-temperature heating vacuum furnace is the growth temperature of the single-walled carbon nanotube powder, which is 100-500°C lower than the preheating temperature in the reactor that the same batch of single-walled carbon nanotube powder passes through.

2. The method for growing single-walled carbon nanotubes according to claim 1, wherein: In step 2, the preheating temperature in the reaction furnace is 600°C to 2000°C.

3. The method for growing single-walled carbon nanotubes according to claim 1 or 2, characterized in that: In step 3, the growth temperature of the high-temperature heating vacuum furnace is 500°C to 1500°C.

4. The method for growing single-walled carbon nanotubes according to claim 2, wherein: In step 2, the reaction furnace is provided with a magnetic induction heating or plasma heating system with a length of 5-20 cm.

5. The method for growing single-walled carbon nanotubes according to claim 3, wherein: The reaction furnace is connected to the high-temperature heating vacuum furnace, and the absolute pressure is maintained at 50-150Kpa.

6. The method for growing single-walled carbon nanotubes according to claim 1, wherein: In step 1, the carrier gas carries the sublimated, vaporized or evaporated catalyst precursor and auxiliary agent.

7. The method for growing single-walled carbon nanotubes according to claim 1, wherein: The catalyst precursor is selected from organic substances such as Fe-Co, Ni-Mo, Fe, and auxiliary agents such as thiophene or sulfur or sulfur-containing organic substances.

8. The method for growing single-walled carbon nanotubes according to claim 7, wherein: The molar ratio of the catalyst precursor to the auxiliary agent is 1:1 to 10000:

1.

9. The method for growing single-walled carbon nanotubes according to claim 1, wherein: The carbon source is hydrocarbons such as ethanol, methanol, benzene, xylene, acetylene, ethylene, and methane.

10. The method for growing single-walled carbon nanotubes according to claim 1, wherein: The molar ratio of the catalyst precursor to the carbon source is 1:1 to 1:100.

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