A single-walled carbon nanotube and its continuous preparation method

Abstract

This invention belongs to the field of carbon nanotube technology, and relates to a method for the continuous preparation of single-walled carbon nanotubes based on methane and a floating catalyst. The method includes: continuously injecting a metal catalyst precursor and optional additives into an evaporation chamber via spraying; introducing a first carrier gas (an inert gas) into the resulting mixed gas stream to accelerate its flow, thus obtaining a raw material stream; continuously injecting the raw material stream, a second carrier gas, and a silicon source precursor into a high-temperature tubular reactor for a high-temperature vapor-phase deposition reaction; the second carrier gas containing methane, hydrogen, and an inert gas; during the high-temperature vapor-phase deposition reaction, the metal catalyst precursor decomposes to form active catalyst nanoparticles, and the methane undergoes catalytic cracking and deposition, thereby continuously growing single-walled carbon nanotubes. This method can improve the yield and purity of single-walled carbon nanotubes, and the obtained single-walled carbon nanotubes have a uniform diameter distribution.

Description

Technical Field

[0001] This invention belongs to the field of carbon nanotube technology, specifically relating to a single-walled carbon nanotube and a continuous preparation method of single-walled carbon nanotubes based on methane and a floating catalyst. Background Technology

[0002] Single-walled carbon nanotubes (SWCNTs) have broad application prospects in nanoelectronic devices, aerospace materials, energy storage and conversion, and biomedicine due to their excellent optical, electrical, thermal, mechanical properties and chemical stability. Achieving low-cost, controllable, and large-scale preparation of high-quality SWCNTs is key to their practical application.

[0003] Currently, the commonly used methods for preparing SWCNTs mainly include arc discharge, laser evaporation, and chemical vapor deposition (CVD). Among them, CVD is considered the most promising method due to its stable and controllable reaction conditions and its ability to be mass-produced. Floating catalyst chemical vapor deposition (FCCVD) is a derivative of CVD. Its main feature is that the catalyst precursor and promoter are evaporated at a certain temperature to form gas or vapor, which is then introduced into a high-temperature reaction zone along with the carbon source gas. The carbon source is decomposed into carbon atoms, which directly form catalyst nanoparticles in the gas phase environment and catalyze the growth of SWCNTs (Parametric analysis of chirality families and diameter distributions insingle-wall carbon nanotube production by the floating catalyst method[J].Ranadeep, Bhowmick, and, et al. Carbon, 2008, 46(6):907-922.). Floating catalyst chemical vapor deposition avoids the use of a substrate and can realize the continuous and large-scale preparation of SWCNTs, which is especially suitable for scenarios requiring high yield, high purity, and direct application.

[0004] Methane, as a simple hydrocarbon, is an ideal carbon source for growing high-quality, low-defect SWCNTs. However, the methane molecule is extremely stable, and the cracking process requires high energy, higher reaction temperatures, and more efficient catalysts. In the existing preparation technology, the FCCVD method using methane as a carbon source to prepare SWCNTs mainly faces the following challenges: (1) The overall efficiency of the catalyst is not high, resulting in a low final yield of single-walled carbon nanotubes; (2) The process parameters are highly coupled, making it difficult to control them precisely and resulting in poor repeatability; (3) The catalyst particle size distribution is not uniform, resulting in excessively large diameters and wide chiral distributions of SWCNTs; (4) Amorphous carbon, carbon black, graphite flakes, and other byproducts are more likely to be generated at high temperatures. These byproduct impurities are easy to cover the catalyst surface, causing catalyst poisoning, thereby terminating carbon nanotube growth and affecting the purity of the product.

[0005] CN120057903A discloses an aerosol-assisted preparation system and method for single-walled carbon nanotubes. The method obtains uniform and fine catalyst particles through atomization and sieving, with the highest G / D ratio of the single-walled carbon nanotubes being only 16 and a purity of 72%. The single-walled carbon nanotubes obtained using this method have poor quality and low purity, possibly due to the catalyst particles failing to achieve a uniform and fine state.

[0006] CN114162804A discloses an apparatus and method for preparing single-walled carbon nanotubes by scalable floating catalytic cracking. This method first prepares catalyst nanoparticles with a narrow size distribution, and then uses a catalyst pretreatment unit to feed these narrow-size-distribution catalyst nanoparticles into a reaction chamber to react with a carbon source gas mixture before they grow further. The highest G / D ratio of the single-walled carbon nanotubes obtained using this method is 78, with a purity of around 80%. However, the quality and purity of the single-walled carbon nanotubes are not high, and the actual catalyst particles may not achieve the ideal size distribution. The G / D ratio is calculated based on Raman spectroscopy, with the G peak at 1580 cm⁻¹. -1 The peak D represents the ordered and complete sp2 hybrid carbon structure in single-walled carbon nanotubes, which is an indicator of the degree of graphitization and crystallinity quality; -1 The G peak represents the disordered, defective, or sp3 hybridized carbon structure in a single-walled carbon nanotube, and it is an indicator of defect density. The intensity ratio of the G peak to the D peak (G / D) can reflect the degree of defect. Generally speaking, the higher the quality of the single-walled carbon nanotube, the larger the G / D ratio.

[0007] In floating catalyst chemical vapor deposition (CVD), the diameter of single-walled carbon nanotubes (SUVs) is primarily determined by the size of the catalyst nanoparticles in the active liquid (or quasi-liquid) state that interact with them during nucleation. Small catalyst nanoparticles typically exhibit high activity, but may precipitate carbon too quickly due to carbon supersaturation, leading to the introduction of five- or seven-membered ring defects, incomplete tube walls, or even the formation of amorphous carbon. Large catalyst nanoparticles have longer carbon diffusion paths, potentially resulting in slower growth rates or excessive carbon accumulation and deactivation, and may also be more prone to encapsulating amorphous carbon due to their lower surface energy. In existing technologies, the size distribution of catalyst nanoparticles during the reaction process is far from ideal, exhibiting the core characteristics of being "wide, numerous, variable, and mixed." This non-ideal distribution is the direct cause of the non-uniform structure of SUVs. Therefore, controlling the generation of nanoscale catalyst particles with moderate size and uniform distribution is crucial for the controllable preparation of high-quality SUVs. Existing technologies have made some progress in controlling the size of catalyst nanoparticles, but controllability and reproducibility are poor, failing to achieve the ideal state of moderately sized and uniformly distributed catalyst particles.

[0008] Therefore, developing a new method to overcome the above-mentioned defects and to efficiently, controllably, and continuously prepare high-quality single-walled carbon nanotubes using methane and floating catalysts has significant technical and economic value. Summary of the Invention

[0009] The primary objective of this invention is to overcome the shortcomings of existing technologies that use methane as a carbon source in the preparation of single-walled carbon nanotubes via floating catalyst chemical vapor deposition, which result in low yield and purity and uneven diameter distribution. Instead, this invention provides a continuous preparation method for single-walled carbon nanotubes based on methane and a floating catalyst. This method can improve the yield and purity of single-walled carbon nanotubes, and the obtained single-walled carbon nanotubes have a uniform diameter distribution.

[0010] A second objective of the present invention is to provide single-walled carbon nanotubes prepared by the above method.

[0011] The continuous preparation method of single-walled carbon nanotubes based on methane and a floating catalyst provided by this invention includes the following steps:

[0012] S1. The metal catalyst precursor and optional additives are continuously injected into the evaporation chamber by spraying, so that the raw materials evaporate to form a mixed gas flow containing the metal catalyst precursor and optional additives. A first carrier gas is introduced into the obtained mixed gas flow to accelerate the gas flow. The first carrier gas is an inert gas to obtain the raw material flow.

[0013] S2. The raw material stream, the second carrier gas, and the silicon source precursor are continuously injected into a high-temperature tubular reactor for high-temperature vapor deposition reaction. The second carrier gas contains methane, hydrogen, and inert gas. During the high-temperature vapor deposition reaction, the metal catalyst precursor decomposes to form active catalyst nanoparticles, and methane undergoes catalytic cracking and deposition, thereby continuously growing single-walled carbon nanotubes.

[0014] The beneficial effects of this invention are as follows: Single-walled carbon nanotubes are prepared using a floating catalyst chemical vapor deposition method. A metal catalyst precursor and optional additives are sprayed into an evaporation chamber, causing the metal catalyst precursor and optional additives to vaporize instantaneously, forming a highly uniform and discrete mixed gas flow of metal catalyst precursor and optional additives. This gas flow is transported under the action of a first carrier gas and injected into a high-temperature tubular reactor along with a second carrier gas and silicon source precursor for a high-temperature vapor deposition reaction. The metal catalyst precursor decomposes at high temperature to form nanoscale active catalyst particles, while methane cracks and deposits on the surface of the catalyst particles, thereby efficiently growing high-quality single-walled carbon nanotubes. This method can significantly improve the yield and purity of single-walled carbon nanotubes and improve the uniformity of diameter distribution. The reason for this is speculated to be twofold: Firstly, by spraying the metal catalyst precursor and optional additives into the evaporation chamber, the kinetic energy of the high-speed airflow can be used to break up, disperse, and transport the aggregated powder through shearing, impact, and carrying effects, forming a stable and uniform powder cloud-like morphology. This cloud-like morphology is then stably sprayed into the evaporation chamber at a flow rate of g / min, where it instantly vaporizes to form a highly uniform and discrete catalyst vapor / aerosol. This method can effectively control the catalyst flux entering the reaction zone, achieving precise catalyst delivery and laying the foundation for the subsequent formation of uniformly sized active catalyst nanoparticles in the high-temperature reaction tube. Secondly, the metal catalyst... The catalyst precursor decomposes at high temperature to generate metal atoms or clusters, which serve as active sites for SWCNT growth. These metal atoms or clusters tend to agglomerate into larger particles, which is not conducive to the nucleation and growth of SWCNTs. The silicon source precursor decomposes in the gas phase at high temperature to generate SiO2 nanoparticles. SiO2 nanoparticles have a high specific surface area and surface defects, which can act as "anchors" to effectively capture these metal atoms or clusters and prevent them from agglomerating into large particles. This "confinement effect" helps to control the size distribution of catalyst particles, thereby forming uniformly sized and highly active metal nanoparticles and obtaining single-walled carbon nanotubes with uniform diameter distribution. Attached Figure Description

[0015] Figure 1 The image shows the macroscopic morphology of the single-walled carbon nanotubes obtained in Example 1.

[0016] Figure 2 The image shows a scanning electron microscope (SEM) image of the single-walled carbon nanotubes obtained in Example 1.

[0017] Figure 3 The image shows the Raman spectrum of the single-walled carbon nanotubes obtained in Example 1.

[0018] Figure 4 SEM image of single-walled carbon nanotubes obtained in Example 2;

[0019] Figure 5 The image shows the Raman spectrum of the single-walled carbon nanotubes obtained in Example 2.

[0020] Figure 6 SEM image of single-walled carbon nanotubes obtained in Example 3;

[0021] Figure 7 The image shows the Raman spectrum of the single-walled carbon nanotubes obtained in Example 3.

[0022] Figure 8 SEM image of single-walled carbon nanotubes obtained in Example 4;

[0023] Figure 9 The Raman spectrum of the single-walled carbon nanotubes obtained in Example 4;

[0024] Figure 10 SEM image of single-walled carbon nanotubes obtained in Example 5;

[0025] Figure 11 The image shows the Raman spectrum of the single-walled carbon nanotubes obtained in Example 5.

[0026] Figure 12 SEM image of single-walled carbon nanotubes obtained in Example 6;

[0027] Figure 13 The image shows the Raman spectrum of the single-walled carbon nanotubes obtained in Example 6.

[0028] Figure 14 SEM images of single-walled carbon nanotubes obtained for Comparative Example 1;

[0029] Figure 15 The Raman spectrum of the single-walled carbon nanotubes obtained in Comparative Example 1 is shown below.

[0030] Figure 16 SEM images of single-walled carbon nanotubes obtained for Comparative Example 2;

[0031] Figure 17 The image shows the Raman spectrum of the single-walled carbon nanotubes obtained in Comparative Example 2. Detailed Implementation

[0032] The continuous preparation method of single-walled carbon nanotubes based on methane and a floating catalyst provided by this invention includes the following steps:

[0033] S1. The metal catalyst precursor and optional additives are continuously injected into the evaporation chamber by spraying, so that the raw materials evaporate to form a mixed gas flow containing the metal catalyst precursor and optional additives. A first carrier gas is introduced into the obtained mixed gas flow to accelerate the gas flow. The first carrier gas is an inert gas to obtain the raw material flow.

[0034] S2. The raw material stream, the second carrier gas, and the silicon source precursor are continuously injected into a high-temperature tubular reactor for high-temperature vapor deposition reaction. The second carrier gas contains methane, hydrogen, and inert gas. During the high-temperature vapor deposition process, the metal catalyst precursor decomposes to form active catalyst nanoparticles, and methane undergoes catalytic cracking and deposition, thereby continuously growing single-walled carbon nanotubes.

[0035] In the aforementioned continuous preparation process of single-walled carbon nanotubes based on methane and a floating catalyst, the metal catalyst precursor and the auxiliary agent can be injected into the evaporation chamber separately by spraying, or they can be premixed first and then injected into the evaporation chamber by spraying; the latter is preferred. That is, the continuous preparation method of single-walled carbon nanotubes based on methane and a floating catalyst further includes premixing the metal catalyst precursor and optional auxiliary agent before spraying them into the evaporation chamber. The premixing method can be ball milling, stirring, etc., and is not particularly limited, but ball milling is preferred. In a preferred embodiment, the premixing method includes loading the metal catalyst precursor, optional auxiliary agent, and zirconia milling balls into a stainless steel ball mill jar, setting the temperature of the cooling medium to 5℃~12℃ to effectively dissipate frictional heat, and by adjusting the ball milling speed and time, etc., under the synergistic effect of mechanical shearing and impact force, achieving three-dimensional uniform dispersion of the material at the submicron scale, ultimately obtaining an ideal homogeneous powder raw material.

[0036] In the aforementioned continuous preparation process of single-walled carbon nanotubes based on methane and a floating catalyst, the metal catalyst precursor and optional additives are continuously injected into the evaporation chamber via spraying. A precision-controlled powder sprayer utilizes the kinetic energy of a high-speed airflow to break up, disperse, and transport the aggregated powder through shearing, impact, and carrying actions, forming a stable and uniform powder cloud, which is then stably sprayed into the evaporation chamber at a flow rate of g / min. The raw materials are instantaneously vaporized within the evaporation chamber, forming a highly uniform and discrete catalyst vapor / aerosol. This uniform gas-phase mixture enters the reaction zone and undergoes uniform thermal decomposition with a more controllable decomposition path, which is beneficial for generating clean activated carbon species, thereby reducing non-target carbon byproducts and improving the purity of the single-walled carbon nanotubes. Furthermore, this method effectively controls the catalyst flux entering the reaction zone, laying the foundation for the subsequent formation of uniformly sized active catalyst nanoparticles in a high-temperature reaction tube.

[0037] In the aforementioned continuous preparation process of single-walled carbon nanotubes based on methane and a floating catalyst, the silicon source precursor decomposes into dynamically suspended SiO2 nanoparticles at high temperature. Its core function is to confine and stabilize the ultrafine metal catalyst particles, thereby constructing numerous mobile "metal@SiO2" composite aerosol microreactors. This provides excellent auxiliary effects for the size stabilization and control of the metal catalyst particles, offering an essential physical and chemical environment for the efficient, continuous, and controllable growth of single-walled carbon nanotubes. The silicon source precursor can be injected into the high-temperature tubular reactor either at the inlet or in the middle. However, since the temperature at the inlet of the high-temperature tubular reactor is typically low (100℃~200℃), the silicon source precursor cannot be effectively decomposed into SiO2 nanoparticles. Therefore, when the silicon source precursor is injected into the high-temperature tubular reactor from the inlet, the yield of single-walled carbon nanotubes is low. In a preferred embodiment, the silicon source precursor is injected into a thin tube located in a high-temperature tubular reactor at a flow rate of microliters per minute. The thin tube is positioned such that the temperature difference between the outlet of the thin tube and the temperature of the high-temperature vapor deposition reaction does not exceed 200°C. At this temperature, the silicon source precursor can rapidly, fully, and effectively decompose into SiO2 nanoparticles in the high-temperature tubular reactor, which is more conducive to improving the yield of single-walled carbon nanotubes. The thin tube can be positioned such that the temperature difference between the outlet of the thin tube and the temperature of the high-temperature vapor deposition reaction is 200°C, 180°C, 160°C, 140°C, 120°C, 100°C, 80°C, 60°C, 40°C, 20°C, 10°C, 50°C, 0°C, or any value between them. The flow rate of the silicon source precursor injected into the capillary is 1~100 μL / min (i.e., on the order of microliters / minute), specifically 1 μL / min, 5 μL / min, 10 μL / min, 15 μL / min, 20 μL / min, 25 μL / min, 30 μL / min, 35 μL / min, 40 μL / min, 45 μL / min, 50 μL / min, 55 μL / min, 60 μL / min, 65 μL / min, 70 μL / min, 75 μL / min, 80 μL / min, 85 μL / min, 90 μL / min, 95 μL / min, 100 μL / min or any value between them.

[0038] In the continuous preparation process of single-walled carbon nanotubes based on methane and a floating catalyst described above, the mass ratio of the metal catalyst precursor to the auxiliary agent is preferably 1:(0.04~0.2), such as 1:0.04, 1:0.06, 1:0.08, 1:0.1, 1:0.12, 1:0.14, 1:0.16, 1:0.18, 1:0.2, or any value between them. The ratio of the total amount of the metal catalyst precursor and the auxiliary agent to the amount of the silicon source precursor is preferably 40mg:(1~10)μL, such as 40mg:1μL, 40mg:2μL, 40mg:4μL, 40mg:6μL, 40mg:8μL, 40mg:10μL, or any value between them.

[0039] In the above-described continuous preparation process of single-walled carbon nanotubes based on methane and a floating catalyst, the metal catalyst precursor can be any existing compound that can decompose into metal atoms or clusters capable of catalyzing the formation of single-walled carbon nanotubes from methane during floating catalyst chemical vapor deposition. The metal in the metal catalyst precursor is typically a transition metal, preferably at least one of iron, cobalt, and nickel. From the perspective of raw material availability, specific examples of the metal catalyst precursor include, but are not limited to, at least one of ferrocene, cobalt-diocene, nickel-diocene, iron acetylacetone, and nonacarbonyl-2-ferric.

[0040] In the above-described continuous preparation process of single-walled carbon nanotubes based on methane and a floating catalyst, the silicon source precursor can be any existing material capable of decomposing to generate SiO2 nanoparticles during high-temperature chemical vapor deposition, preferably at least one of hexamethyldisiloxane, polymethylsiloxane, trimethylsilane, tetramethylsilane, tetramethoxysilane, tetraethoxysilane, tetraethyl orthosilicate, and octamethylcyclotetrasiloxane. The SiO2 nanoparticles generated by the high-temperature vapor-phase decomposition of the silicon source precursor can effectively capture metal atoms or clusters formed by the decomposition of the metal catalyst precursor, preventing these metal atoms or clusters from excessively agglomerating into large particles. The SiO2 nanoparticles can stably anchor small metal atoms or clusters, thereby controlling the size distribution of the catalyst particles and resulting in uniform diameter single-walled carbon nanotubes.

[0041] In the continuous preparation process of single-walled carbon nanotubes based on methane and a floating catalyst, the auxiliary agent plays a role in promoting the growth of carbon nanotubes and improving the yield and uniformity of their diameter distribution. The auxiliary agent is generally a sulfur-containing compound, specifically including at least one of thiourea, sulfur powder, and diphenyl disulfide.

[0042] In the above-mentioned continuous preparation process of single-walled carbon nanotubes based on methane and a floating catalyst, the first carrier gas is an inert gas, specifically argon and / or nitrogen. The second carrier gas contains methane, hydrogen, and an inert gas, wherein the inert gas can be argon and / or nitrogen. This invention uses methane as the main carbon source and introduces a certain proportion of hydrogen, which plays multiple roles: (a) as a reducing agent, promoting the decomposition of the metal catalyst precursor into zero-valent metal nanoparticles; (b) as an etching agent, selectively removing amorphous carbon impurities such as amorphous carbon generated during the reaction, improving the crystallinity and purity of SWCNTs; and (c) adjusting the surface energy and fluidity of the catalyst particles, affecting the nucleation and growth kinetics of SWCNTs.

[0043] In the above-mentioned continuous preparation process of single-walled carbon nanotubes based on methane and floating catalyst, the flow rate of the first carrier gas is preferably 500 sccm to 2000 sccm, such as 500 sccm, 800 sccm, 1000 sccm, 1200 sccm, 1400 sccm, 1600 sccm, 1800 sccm, 2000 sccm or any value between them. The preferred total flow rate of the second carrier gas is 2200 sccm to 11000 sccm, such as 2200 sccm, 3000 sccm, 3500 sccm, 4000 sccm, 4500 sccm, 5000 sccm, 5500 sccm, 6000 sccm, 6500 sccm, 7000 sccm, 7500 sccm, 8000 sccm, 8500 sccm, 9000 sccm, 9500 sccm, 10000 sccm, 10500 sccm, 11000 sccm, or any value between them. The second carrier gas contains methane, hydrogen, and inert gases. The inert gases dilute the reaction gases, alleviate local overheating, and prevent catalyst sintering and deactivation. Hydrogen, within an appropriate range, helps remove carbon deposits on the catalyst surface and maintains the exposure of active sites. Excessive methane content may lead to carbon buildup, while insufficient methane content may weaken its regulatory effect on the reaction pathway. The preferred volume percentage of methane in the second carrier gas is 5-12%, such as 5%, 6%, 8%, 10%, 12%, or any value between them; the preferred volume percentage of hydrogen is 48-60%, such as 48%, 50%, 52%, 54%, 56%, 58%, 60%, or any value between them; and the preferred volume percentage of inert gas is 30-50%, such as 30%, 32%, 34%, 36%, 38%, 40%, 42%, 44%, 46%, 48%, 50%, or any value between them. Controlling the content of methane, hydrogen, and inert gas in the second carrier gas within the above preferred ranges can achieve a balance between reactivity and catalyst protection, guiding the reaction towards the target product and reducing side reactions.

[0044] In the above-described continuous preparation process of single-walled carbon nanotubes based on methane and a floating catalyst, the temperature at which the raw materials evaporate to form a mixed gas flow is preferably 150℃~300℃, such as 150℃, 180℃, 200℃, 220℃, 240℃, 260℃, 280℃, 300℃, or any value between them. The conditions for the high-temperature vapor deposition reaction preferably include a reaction temperature of 1000℃~1200℃, such as 1000℃, 1020℃, 1040℃, 1060℃, 1080℃, 1100℃, 1120℃, 1140℃, 1160℃, 1180℃, 1200℃, or any value between them; a reaction pressure of atmospheric pressure; and a residence time of the material in the reactor of 3s~10s, such as 3s, 4s, 5s, 6s, 7s, 8s, 9s, 10s, or any value between them. Controlling the temperature of the high-temperature vapor deposition reaction at 1000℃~1200℃ can ensure the effective cracking of methane and improve the yield of single-walled carbon nanotubes.

[0045] In the aforementioned continuous preparation process of single-walled carbon nanotubes (SWCNTs) based on methane and a floating catalyst, a high-speed rotating, high-temperature resistant collection shaft can be installed at the outlet of the high-temperature tubular reactor or behind a specific growth zone. As the shaft continues to rotate, SWCNTs gradually accumulate on the shaft into a continuous cylindrical roll. This overturns the traditional batch growth-processing model, enabling "growth and collection simultaneously," theoretically allowing for the production of infinitely long SWCNT materials, significantly improving production efficiency. The entire process, from raw material delivery to product collection, is completely continuous without interrupting the reaction, making it ideal for large-scale industrial production. Through the synergistic effect of a uniformly mixed catalyst and methane / hydrogen system, the grown SWCNTs exhibit high graphitization and few defects, and the product purity is significantly improved due to the etching effect of hydrogen on amorphous carbon.

[0046] The present invention also provides single-walled carbon nanotubes prepared by the above method.

[0047] The present invention will be described in detail below through embodiments.

[0048] Example 1

[0049] This embodiment illustrates the continuous preparation method of single-walled carbon nanotubes based on methane and a floating catalyst provided by the present invention.

[0050] The metal catalyst precursor (ferrocene) and the auxiliary agent (thiourea) were loaded into a stainless steel ball mill jar at a mass ratio of 1:0.1 and ball-milled until uniform. The resulting premix was continuously sprayed into an evaporation chamber at a temperature of 260°C using a powder sprayer at a rate of 40 mg / min, so that the raw materials evaporated to form a mixed gas flow. At the same time, argon gas with a flow rate of 1000 sccm was introduced as the first carrier gas to obtain the raw material flow. The feed stream is continuously drawn from the evaporation chamber and mixed with a second carrier gas (total flow rate of 6000 sccm, the second carrier gas being a mixture of methane, hydrogen, and argon, with methane accounting for 10% by volume, hydrogen for 50% by volume, and argon for 40% by volume) at the inlet of a high-temperature tubular reactor. This mixture is then injected into the preheated high-temperature tubular reactor at 1150°C, with a residence time controlled at 5 seconds. A glass capillary (outer diameter 8 mm, inner diameter 6 mm, length 20 cm) is installed deep within the high-temperature tubular reactor. Simultaneously with the injection of the feed stream and the second carrier gas, tetraethoxysilane is stably injected into this glass capillary at a rate of 10 μL / min using a precision injection pump. The temperature at the outlet of this glass capillary is 1000°C. All feed materials undergo high-temperature vapor deposition in the high-temperature tubular reactor. The resulting product is blown to the outlet by the gas flow and collected by a rotating shaft collection device at the rear, yielding single-walled carbon nanotubes with a yield of 5.2 g / h.

[0051] The macroscopic morphology of the single-walled carbon nanotube is shown in the figure. Figure 1 ,from Figure 1 As can be seen, the single-walled carbon nanotubes exhibit a black, fluffy, sponge-like appearance. The microstructure of these single-walled carbon nanotubes was characterized using scanning electron microscopy, and the results are shown in [Figure number missing]. Figure 2 ,from Figure 2 As can be seen, the single-walled carbon nanotubes are distributed in bundles with very few amorphous carbon impurities, and are generally quite clean. The Raman spectra of these single-walled carbon nanotubes are shown below. Figure 3 ,from Figure 3 Calculations show that its G / D ratio is 120 (Raman data are shown in Table 1), indicating a high degree of graphitization, few defects, and high overall crystal quality, with a range of 100-300 cm⁻¹. -1 The presence of RBM breathing peaks preliminarily identifies it as a single-walled carbon nanotube. Furthermore, the RBM breathing peaks exhibit a few very sharp and intense peaks, each corresponding to a narrow diameter distribution. This indicates that the catalyst particle size is highly concentrated, resulting in good uniformity of the diameter distribution of the obtained single-walled carbon nanotubes.

[0052] Example 2

[0053] This embodiment illustrates the continuous preparation method of single-walled carbon nanotubes based on methane and a floating catalyst provided by the present invention.

[0054] The metal catalyst precursor (cobalt decene) and the additive (sulfur powder) were loaded into a stainless steel ball mill jar at a mass ratio of 1:0.2 and ball-milled until uniform. The resulting premix was continuously sprayed into an evaporation chamber at a temperature of 150°C using a powder sprayer at a rate of 40 mg / min, so that the raw materials evaporated to form a mixed gas flow. At the same time, argon gas with a flow rate of 500 sccm was introduced as the first carrier gas to obtain the raw material flow. The feed stream is continuously drawn from the evaporation chamber and mixed with a second carrier gas (total flow rate of 2200 sccm, the second carrier gas being a mixture of methane, hydrogen, and argon, with methane accounting for 10% by volume, hydrogen for 60% by volume, and argon for 30% by volume) at the inlet of a high-temperature tubular reactor. This mixture is then injected into the preheated high-temperature tubular reactor at 1000°C, with a residence time controlled at 10 s. A glass capillary (outer diameter 8 mm, inner diameter 6 mm, length 20 cm) is installed deep within the high-temperature tubular reactor. Simultaneously with the injection of the feed stream and the second carrier gas, hexamethyldisiloxane is stably injected into this capillary at a rate of 1 μL / min using a precision injection pump. The temperature at the outlet of this capillary is 1000°C. All feed materials undergo high-temperature vapor deposition in the high-temperature tubular reactor. The resulting product is blown to the outlet by the gas flow and collected by a rotating shaft collection device at the rear, yielding single-walled carbon nanotubes with a yield of 5.0 g / h.

[0055] The single-walled carbon nanotubes exhibit a black, fluffy, sponge-like morphology. The microstructure of these single-walled carbon nanotubes was characterized using scanning electron microscopy, and the results are shown in [Figure number missing]. Figure 4 ,from Figure 4 As can be seen, the single-walled carbon nanotubes are distributed in bundles with very few amorphous carbon impurities, and are generally quite clean. The Raman spectrum of these single-walled carbon nanotubes is shown below. Figure 5 ,from Figure 5 Calculations show that the average G / D ratio of this single-walled carbon nanotube is 115 (Raman data are shown in Table 1), indicating a high degree of graphitization, few defects, and high overall crystallinity. The Raman spectrum of this single-walled carbon nanotube is in the range of 100-300 cm⁻¹. -1 The presence of RBM breathing peaks at the location indicates that the material is a single-walled carbon nanotube. Furthermore, the RBM breathing peaks exhibit a few very sharp and intense peaks, each corresponding to a narrow diameter distribution. This suggests that the catalyst particles are highly concentrated in size, resulting in a uniform diameter distribution of the obtained single-walled carbon nanotubes.

[0056] Example 3

[0057] This embodiment illustrates the continuous preparation method of single-walled carbon nanotubes based on methane and a floating catalyst provided by the present invention.

[0058] The metal catalyst precursor (nonacarbonyl ferric) and the auxiliary agent (diphenyl disulfide) were loaded into a stainless steel ball mill jar at a mass ratio of 1:0.04 and ball-milled until uniform. The resulting premix was continuously sprayed into an evaporation chamber at a temperature of 300°C using a powder sprayer at a rate of 40 g / min, so that the raw materials evaporated to form a mixed gas flow. At the same time, argon gas with a flow rate of 2000 sccm was introduced as the first carrier gas to obtain the raw material flow. The feed stream is continuously drawn from the evaporation chamber and mixed with a second carrier gas (total flow rate of 11000 sccm, the second carrier gas being a mixture of methane, hydrogen, and argon, with methane accounting for 5% by volume, hydrogen for 48% by volume, and argon for 47% by volume) at the inlet of a high-temperature tubular reactor. This mixture is then injected into the preheated high-temperature tubular reactor at 1200°C, with a residence time controlled at 3 seconds. A glass capillary (outer diameter 8 mm, inner diameter 6 mm, length 20 cm) is installed deep within the high-temperature tubular reactor. Simultaneously with the injection of the feed stream and the second carrier gas, octamethylcyclotetrasiloxane is stably injected into this glass capillary at a rate of 8 μL / min using a precision injection pump. The temperature at the outlet of this glass capillary is 1150°C. All feed materials undergo high-temperature vapor deposition in the high-temperature tubular reactor. The resulting product is blown to the outlet by the gas flow and collected by a rotating shaft collection device at the rear, yielding single-walled carbon nanotubes with a yield of 5.15 g / h.

[0059] The single-walled carbon nanotubes exhibit a black, fluffy, sponge-like morphology. The microstructure of these single-walled carbon nanotubes was characterized using scanning electron microscopy, and the results are shown in [Figure number missing]. Figure 6 ,from Figure 6 As can be seen, the single-walled carbon nanotubes are distributed in bundles with very few amorphous carbon impurities, and are generally quite clean. The Raman spectrum of these single-walled carbon nanotubes is shown below. Figure 7 ,from Figure 7 Calculations show that the G / D ratio of this single-walled carbon nanotube is 117 (Raman data are shown in Table 1), indicating a high degree of graphitization, few defects, and high overall crystallinity. The Raman spectrum of this single-walled carbon nanotube is in the range of 100-300 cm⁻¹. -1 The presence of RBM breathing peaks at the location indicates that the material is a single-walled carbon nanotube. Furthermore, the RBM breathing peaks exhibit a few very sharp and intense peaks, each corresponding to a narrow diameter distribution. This suggests that the catalyst particles are highly concentrated in size, resulting in a uniform diameter distribution of the obtained single-walled carbon nanotubes.

[0060] Example 4

[0061] Single-walled carbon nanotubes were prepared according to the method of Example 1, except that the volume percentage of methane in the second carrier gas was adjusted to 15%, the volume percentage of hydrogen to 45%, and the volume percentage of argon to 40%, while the other conditions were the same as in Example 1. Single-walled carbon nanotubes were obtained with a yield of 5.6 g / h.

[0062] The single-walled carbon nanotubes exhibit a black, fluffy, sponge-like morphology. The microstructure of these single-walled carbon nanotubes was characterized using scanning electron microscopy, and the results are shown in [Figure number missing]. Figure 8 ,from Figure 8 As can be seen, the single-walled carbon nanotube has a clear structure, but the amount of attached metal and carbon impurities is slightly increased. The Raman spectrum of this single-walled carbon nanotube is shown below. Figure 9 ,from Figure 9 The calculated G / D ratio of this single-walled carbon nanotube is 100 (Raman data are shown in Table 1). Although it still exhibits a high degree of graphitization and overall high crystallinity, the G / D ratio is slightly lower than that of Example 1. This indicates that the growth rate can be accelerated under higher carbon source concentration and slightly lower hydrogen etching conditions, but this will introduce slightly more defects and generate carbon impurities. The Raman spectrum of this single-walled carbon nanotube is in the range of 100-300 cm⁻¹. -1 The presence of RBM breathing peaks at the location indicates that it is a single-walled carbon nanotube. Furthermore, the RBM breathing peaks exhibit a few very sharp and intense peaks, each corresponding to a narrow diameter distribution. This suggests that the catalyst particle size is highly concentrated, resulting in a good uniformity in the diameter distribution of the obtained single-walled carbon nanotubes.

[0063] Example 5

[0064] Single-walled carbon nanotubes were prepared according to the method of Example 1, except that the hydrogen in the second carrier gas was replaced with argon of the same volume percentage. The other conditions were the same as in Example 1, and single-walled carbon nanotubes were obtained with a yield of 5.5 g / h.

[0065] The single-walled carbon nanotubes exhibit a black, fluffy, sponge-like morphology. The microstructure of these single-walled carbon nanotubes was characterized using scanning electron microscopy, and the results are shown in [Figure number missing]. Figure 10 ,from Figure 10 As can be seen, the single-walled carbon nanotubes are distributed in bundles with very few amorphous carbon impurities, and are generally quite clean. The Raman spectrum of these single-walled carbon nanotubes is shown below. Figure 11 ,from Figure 11 Calculations show that the G / D ratio of this single-walled carbon nanotube is 80 (Raman data are shown in Table 1), indicating that under etching conditions without hydrogen, the formed single-walled carbon nanotubes have more defects and a higher carbon impurity content, especially in the 100-300 cm⁻¹ range. -1 The presence of RBM breathing peaks preliminarily identifies them as single-walled carbon nanotubes. Furthermore, the RBM breathing peaks exhibit a few very sharp and intense peaks, each corresponding to a narrow diameter distribution. This indicates that the catalyst particle size is highly concentrated, resulting in good uniformity of the diameter distribution of the obtained single-walled carbon nanotubes.

[0066] Example 6

[0067] Single-walled carbon nanotubes were prepared according to the method of Example 1, except that no additive (thiourea) was added, and the other conditions were the same as in Example 1, and single-walled carbon nanotubes were obtained with a yield of 5.0 g / h.

[0068] The single-walled carbon nanotubes exhibit a black, fluffy, sponge-like morphology. The microstructure of these single-walled carbon nanotubes was characterized using scanning electron microscopy, and the results are shown in [Figure number missing]. Figure 12 ,from Figure 12 As can be seen, the single-walled carbon nanotubes are distributed in bundles with very few amorphous carbon impurities, and are generally clean, although a few larger diameter tubes appear in some areas. The Raman spectrum of these single-walled carbon nanotubes is shown below. Figure 13 ,from Figure 13 Calculations show that the G / D ratio of this single-walled carbon nanotube is 98 (Raman data are shown in Table 1), indicating a high degree of graphitization, few defects, and high overall crystal quality, especially within the 100-300 cm⁻¹ range. -1 The presence of RBM breathing peaks preliminarily identifies them as single-walled carbon nanotubes. The RBM breathing peaks also exhibit a few very sharp and intense peaks, each corresponding to a narrow diameter distribution. This indicates that the catalyst particle size is highly concentrated. However, there are also a few weak peaks, suggesting the presence of a small number of large-diameter nanotubes. Without the addition of additives, it may be easier to introduce large-diameter carbon nanotubes, which may slightly affect the uniformity of the nanotube diameter.

[0069] Comparative Example 1

[0070] Single-walled carbon nanotubes were prepared according to the method of Example 1, except that the premix formed by the metal catalyst precursor (ferrocene) and the auxiliary agent (thiourea) was not sprayed using a sprayer, but was directly placed in an evaporation chamber at a temperature of 260°C for evaporation. The other conditions were the same as in Example 1, and single-walled carbon nanotubes were obtained with a yield of 4.9 g / h, which was significantly reduced.

[0071] The single-walled carbon nanotubes exhibit a black, fluffy, sponge-like morphology. The microstructure of these single-walled carbon nanotubes was characterized using scanning electron microscopy, and the results are shown in [Figure number missing]. Figure 14 ,from Figure 14 As can be seen, this single-walled carbon nanotube contains a large number of carbon-coated iron nanoparticles and amorphous carbon, indicating low purity. The Raman spectrum of this single-walled carbon nanotube is shown below. Figure 15 ,from Figure 15 The calculation shows that its G / D ratio is 75 (Raman data are shown in Table 1). The RBM breathing peak is broadened and is generally weak, without any sharp or high-intensity peaks. This indicates that the generated SWCNTs have a wide diameter distribution, which indirectly indicates that the catalyst size is not uniform. At the same time, the intensity ratio of the G peak to the D peak is significantly reduced. Low-quality SWCNTs with a wide diameter distribution usually have a lower IG / ID value, indicating that the catalyst control is worse.

[0072] Comparative Example 2

[0073] Single-walled carbon nanotubes were prepared according to the method of Example 1, except that the silicon source precursor tetraethoxysilane was not added. The other conditions were the same as in Example 1, and single-walled carbon nanotubes were obtained with a yield of 5.0 g / h, which was significantly reduced.

[0074] The single-walled carbon nanotubes exhibit a black, fluffy, sponge-like morphology. The microstructure of these single-walled carbon nanotubes was characterized using scanning electron microscopy, and the results are shown in [Figure number missing]. Figure 16 ,from Figure 16 As can be seen, the single-walled carbon nanotubes are distributed in bundles with very few amorphous carbon impurities, and are generally quite clean. The Raman spectrum of these single-walled carbon nanotubes is shown below. Figure 17 ,from Figure 17 The calculated G / D ratio is 80 (Raman data are shown in Table 1). The RBM breathing peak shows a broad envelope and a large number of dense weak peaks, indicating that the generated SWCNTs have a wide diameter distribution, which indirectly indicates that the catalyst size is not uniform and the tube diameter uniformity of the obtained single-walled carbon nanotubes is poor. This proves that the introduction of silica at high temperature can regulate and stabilize the catalyst particle size distribution, improve the compatibility between carbon source and metal catalyst, and is conducive to the efficient growth of high-quality single-walled carbon nanotubes.

[0075] Table 1

[0076]

[0077] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention without departing from the principles and spirit of the present invention.

Claims

1. A continuous preparation method for single-walled carbon nanotubes based on methane and a floating catalyst, characterized in that, The method includes the following steps: S1. The metal catalyst precursor and optional additives are continuously injected into the evaporation chamber by spraying, so that the raw materials evaporate to form a mixed gas flow containing the metal catalyst precursor and optional additives. A first carrier gas is introduced into the obtained mixed gas flow to accelerate the gas flow. The first carrier gas is an inert gas to obtain the raw material flow. S2. The raw material stream, the second carrier gas, and the silicon source precursor are continuously injected into a high-temperature tubular reactor for high-temperature vapor deposition. The silicon source precursor is selected from at least one of hexamethyldisiloxane, polymethylsiloxane, trimethylsilane, tetramethylsilane, tetramethoxysilane, tetraethoxysilane, tetraethyl orthosilicate, and octamethylcyclotetrasiloxane. The silicon source precursor is injected into the high-temperature tubular reactor at a flow rate of 1-100 μL / min into a thin tube located in the high-temperature tubular reactor. The thin tube is positioned such that the temperature difference between the outlet of the thin tube and the temperature of the high-temperature vapor deposition reaction does not exceed 200°C. The second carrier gas contains methane, hydrogen, and inert gases. During the high-temperature vapor deposition reaction, the metal catalyst precursor decomposes to form active catalyst nanoparticles, and methane undergoes catalytic cracking and deposition, thereby continuously growing single-walled carbon nanotubes.

2. The method for continuous preparation of single-walled carbon nanotubes based on methane and a floating catalyst according to claim 1, characterized in that, The method also includes premixing the metal catalyst precursor and optional additives before spraying them into the evaporation chamber.

3. The continuous preparation method of single-walled carbon nanotubes based on methane and a floating catalyst according to claim 1, characterized in that, The mass ratio of the metal catalyst precursor to the auxiliary agent is 1:(0.04~0.2); the ratio of the total amount of the metal catalyst precursor and the auxiliary agent to the amount of the silicon source precursor is 40mg:(1~10)μL.

4. The continuous preparation method of single-walled carbon nanotubes based on methane and a floating catalyst according to claim 1, characterized in that, The metal catalyst precursor is selected from at least one of ferrocene, cobalt dicene, nickel dicene, iron acetylacetonate, and nonacarbonyl ferric oxide; the promoter is a sulfur-containing compound.

5. The continuous preparation method of single-walled carbon nanotubes based on methane and a floating catalyst according to claim 1, characterized in that, The flow rate of the first carrier gas is 500 sccm to 2000 sccm; the total flow rate of the second carrier gas is 2200 sccm to 11000 sccm.

6. The continuous preparation method of single-walled carbon nanotubes based on methane and a floating catalyst according to claim 1, characterized in that, The second carrier gas contains 5-12% methane, 48-60% hydrogen, and 30-50% inert gas by volume.

7. The continuous preparation method of single-walled carbon nanotubes based on methane and a floating catalyst according to any one of claims 1 to 6, characterized in that, The temperature at which the raw materials evaporate to form a mixed gas flow is 150℃~300℃; the conditions for the high-temperature vapor deposition reaction include a reaction temperature of 1000℃~1200℃, a reaction pressure of atmospheric pressure, and a residence time of the material in the reactor of 3s~10s.

8. Single-walled carbon nanotubes prepared by the method according to any one of claims 1 to 7.

Images