Single-walled carbon nanotube and preparation method thereof

Abstract

The invention relates to the technical field of nano material preparation and electrochemical energy storage, in particular to a single-walled carbon nanotube and a preparation method thereof. According to the preparation method, a floating catalyst chemical vapor deposition (FCCVD) method is adopted, a compound of ferrocene and sublimed sulfur is used as a catalyst precursor, a horizontal tube furnace with at least three independent temperature zones is adopted, and a specific staged programmed heating strategy is adopted, so that the high-temperature-resistant and high-temperature-resistant catalyst is obtained. And the temperatures of the precursor sublimation area, the catalyst formation and activation area and the main growth area are accurately controlled in sequence. Wherein the temperature of the main growth region is accurately controlled at an optimal window of 1000 DEG C. The method effectively inhibits the generation of multi-walled carbon nanotubes and defect structures, and can stably prepare single-walled carbon nanotubes with high graphitization degree and less metal residues. The method is high in process controllability, and a reliable scheme is provided for large-scale preparation of the high-performance single-walled carbon nanotubes.

Description

Technical Field

[0001] This invention relates to the field of nanomaterial preparation and electrochemical energy storage technology, specifically to a method for synthesizing high-quality single-walled carbon nanotubes (SWNTs) through precise temperature control, and a single-walled carbon nanotube prepared by the above method. Background Technology

[0002] Single-walled carbon nanotubes (SWCNTs) are tubular nanomaterials formed by rolling up a single layer of graphene, typically with diameters between 0.4 and 2 nm. Due to their excellent electrical conductivity (carrier mobility up to 10⁵ cm² / V·s), mechanical strength (elastic modulus approximately 1 TPa), and thermal conductivity (3500 W / m·K), SWCNTs have become a hot topic in nanomaterials research. With the rapid development of industries such as new energy vehicles and flexible electronics, the market demand for high-performance materials continues to rise, making the industrialization process of SWCNTs a focus of attention. However, the controllable preparation of high-quality SWNTs remains a core challenge. Current mainstream SWNT synthesis methods, such as arc discharge, laser ablation, and chemical vapor deposition (CVD), generally suffer from problems such as complex process control, high cost, and poor product purity and structural uniformity. In particular, the structural quality of SWNTs grown via CVD (e.g., degree of graphitization, defect density, chiral distribution) is extremely sensitive to growth temperature. Low temperatures (e.g., <900 ℃) typically lead to insufficient carbon source decomposition, inadequate catalyst activity, and a tendency to generate MWNTs or amorphous carbon with disordered structures and abundant defects. High temperatures (e.g., >1100 ℃) cause excessively rapid sintering and deactivation of catalyst particles, as well as an imbalance in carbon atom deposition rates, resulting in increased defects in the SWNT tube walls, wider diameter distribution, and severe amorphous carbon coating. Current technologies lack precise definition and control strategies for the "temperature window" during SWNT growth, making it difficult to stably and mass-produce "high-quality" SWNTs suitable for high-performance electrodes (which also possess high IT). G / I D High specific surface area, suitable diameter distribution, and low metal residue are desirable characteristics of high-performance lithium-ion batteries. Improper temperature control can lead to the formation of multi-walled carbon nanotubes (MWNTs) or structurally defective SWNTs, preventing the formation of an efficient conductive network in the battery and significantly limiting their practical application in high-end lithium-ion batteries. Therefore, developing a controllable synthesis method for high-quality, low-defect SWNTs is of great significance for promoting the development of high-performance lithium-ion batteries. Summary of the Invention

[0003] The purpose of this invention is to provide a floating catalytic chemical vapor deposition (FCCVD) method for the controllable preparation of high-quality single-walled carbon nanotubes. By employing a specific catalyst system and a multi-temperature zone precise temperature control process, the synthesis of SWNTs with high selectivity and low defects can be achieved.

[0004] To achieve the above objectives, the primary objective of this invention is to provide a method for synthesizing single-walled carbon nanotubes through precise temperature control.

[0005] Another object of the present invention is to provide single-walled carbon nanotubes prepared by the above method.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for preparing single-walled carbon nanotubes, characterized by employing a floating catalyst chemical vapor deposition method, comprising the following steps: S1. Ferrocene and sublimed sulfur are mixed at a mass ratio of 85:1 to 115:1, and the resulting catalyst precursor is placed in the preheating zone of a tube furnace. The tubular furnace is provided with at least three independently temperature-controlled zones along the airflow direction, which are, in order, a preheating zone for the sublimation of catalyst precursors, at least one transition reaction zone for the formation and activation of catalyst nanoparticles, and a main growth zone for the growth of single-walled carbon nanotubes. S2. The main growth zone is heated to a growth temperature of 950℃~1050℃ and kept stable, and the transition reaction zone is heated to a set temperature of 500℃~850℃; then, the preheating zone is heated to 160℃~220℃ at a rate of not less than 15℃ / min to sublimate the catalyst precursor. S3. A mixed reaction gas containing methane and hydrogen is introduced, carrying the gaseous catalyst precursor through the transition reaction zone and the main growth zone in sequence. By controlling the flow rate of the mixed reaction gas and the length of each temperature zone, the average passage time of the gaseous catalyst precursor in the transition reaction zone is 1.5-3 minutes, and the average passage time in the main growth zone is 5-10 minutes. The crude product of single-walled carbon nanotubes is then collected in the product collection unit and separated to obtain single-walled carbon nanotubes.

[0007] Preferably, in step S2, the target heating temperature of the main growth temperature zone is 1000℃±10℃.

[0008] Preferably, in step S2, the target heating temperature of the preheating zone is 190°C.

[0009] Preferably, the tubular furnace has five independently temperature-controlled zones, which are sequentially designated as the first temperature zone, the second temperature zone, the third temperature zone, the fourth temperature zone, and the fifth temperature zone along the airflow direction; wherein, the first temperature zone is the preheating zone, the second and third temperature zones are the transition reaction zones, and the fourth temperature zone is the main growth temperature zone; Step S2 is as follows: First, the fourth temperature zone is heated to a growth temperature of 950℃~1050℃, the second temperature zone is heated to 500℃, and the third and fifth temperature zones are heated to 800℃; then, the first temperature zone is heated to 160℃-220℃.

[0010] Preferably, the temperature of the fourth temperature zone is 1000℃±10℃.

[0011] Preferably, in step S3: The average passage time of the gaseous catalyst precursor in the second temperature zone is 30–60 seconds; The average passage time of the gaseous catalyst precursor in the third temperature zone is 60–120 seconds; The average passage time of the gaseous catalyst precursor in the fourth temperature zone is 5-10 minutes. The average passage time of the gaseous catalyst precursor in the fifth temperature zone is 60–120 seconds.

[0012] Preferably, the separation method in step S3 is as follows: the crude single-walled carbon nanotube product is purified by acid washing to obtain purified single-walled carbon nanotubes.

[0013] Preferably, the specific steps of step S3 are as follows: After purging the reaction pipeline with high-purity argon gas at a flow rate of 500 sccm for 10 minutes, the argon gas flow rate was adjusted to 200 sccm as the base carrier gas. A mixed reaction gas containing methane and hydrogen was then introduced, with a volume ratio of methane to hydrogen of 1:1 and a total flow rate of 50 sccm. This mixed reaction gas carried the gaseous catalyst precursor through the transition reaction zone and the main growth zone sequentially. The average passage time of the gaseous catalyst precursor was calculated as the ratio of the gas volume flow rate to the effective volume of the corresponding temperature zone. The above preparation method uses a ferrocene-sulfur / methane system. Methane has stronger CH bonds, requiring higher temperatures (thermodynamic thresholds) for cracking. The addition of sulfur alters the phase diagram and surface properties of the iron catalyst. Around 800℃, the Fe-S eutectic phase may be in a highly active but not optimally stable "metastable" or "pre-activated" state, where the methane cracking rate is low but selectivity may be good.

[0014] For a detailed explanation of the mechanisms of action in each temperature zone: The first temperature zone (160℃~220℃, preferably 190℃) is the sublimation zone of the catalyst precursor. The precise temperature and heating rate ensure that ferrocene and sublimed sulfur sublimate uniformly and slowly to form stable gaseous molecular clusters, avoiding uneven decomposition of the precursor caused by local overheating. The third temperature zone (800℃) and the fifth temperature zone (800℃) are “activation / regulation / buffering” zones, not the main growth zones.

[0015] For the catalyst: At this temperature, sulfur and iron interact fully to form nanoparticles with uniform size and moderate surface sulfur atom modification. This temperature ensures that the catalyst particles will not sinter due to excessively high temperatures (>1000℃ is prone to sintering) nor will they become insufficiently active due to excessively low temperatures.

[0016] For the carbon source: At 800°C, the cracking rate of methane is kinetically limited. Although there is a small amount of cracking, the resulting carbon atom flux is low. This is precisely what is beneficial for: (a) the formation of perfect graphene caps (nucleation) on the catalyst surface without the formation of multilayer nucleation units (MWNTs) or amorphous carbon deposition due to carbon atom supersaturation; and (b) for carbon nanotubes that have entered the Z4 region and begun rapid growth, the carbon source cracking rate drops sharply when they enter the Z5 region with the gas flow, which is equivalent to a "mild growth termination signal," which is beneficial for the formation of carbon nanotubes with complete structure and few defects, rather than stress caused by sudden cooling.

[0017] Fourth temperature zone (1000℃): "High-speed selective growth" zone.

[0018] For the carbon source: Optimal kinetic window for efficient thermal and catalytic cracking of methane is achieved. The carbon atom supply rate is significantly improved.

[0019] For catalysts: On activated catalyst particles, the carbon atom dissolution-precipitation process is accelerated. Most importantly, 1000℃ is the "optimal temperature window" for carbon atom diffusion and graphene sheet rearrangement in iron catalysts. At this temperature, carbon atoms have sufficient energy for surface migration and ordered arrangement, thus tending to form the lowest-energy, least-defect monolayer graphene structure (i.e., SWNT), and preferentially growing along specific crystal planes of the catalyst particles. Temperatures that are too low (e.g., 950℃) lack sufficient motive force for ordering (I... G / I D =25), if the temperature is too high (e.g., 1050℃), the catalyst is prone to sintering, and carbon deposition is too fast, leading to an increase in defects (I G / I D =40).

[0020] Regarding the selection of average transit time: Within the transition reaction zone, the average transit time determines whether ferrocene pyrolysis, sulfur incorporation, and Fe nanoparticle nucleation / aging are sufficient: if the time is too short, the Fe particles are too small and the sulfur does not have enough time to modify the surface; if the time is too long, the particles are over-aged and sintered and deactivated. Within the main growth temperature zone, the average passage time determines whether the carbon source cracking-diffusion-precipitation time is sufficient: if the time is too short, the tube length is insufficient; if the time is too long, the yield no longer increases, and instead, wall defects and multiple walls appear due to "overgrowth".

[0021] Regarding the setting method for average transit time: A quartz tube is a regularly shaped circular tube, and the fluid inside exhibits a parabolic laminar velocity profile. The average flow velocity can be calculated from the volumetric flow rate and cross-sectional area, while the volumetric flow rate depends on temperature and pressure. Therefore, after obtaining the desired passage time, the gas flow rate can be selected based on the quartz tube diameter, length, and zoned temperature. Furthermore, by adjusting the length of each zone, the average passage time can be matched, ensuring the parameters are calculable and reproducible.

[0022] Secondly, the present invention provides single-walled carbon nanotubes prepared by the above method.

[0023] Preferably, the Raman spectrum of this single-walled carbon nanotube is I G / I D The value is greater than 50.

[0024] Compared with the prior art, the present invention has the following significant advantages: Innovative Synthesis Process: By employing a ferrocene-sublimated sulfur composite catalyst and a multi-temperature gradient heating strategy, particularly with precise control of the main growth region, the growth window of SWNTs was precisely locked, effectively suppressing the formation of MWNTs and defect structures, and selectively generating SWNTs (Raman RBM characteristic peaks) and high graphitization (Raman I) peaks. G / I D High-quality SWNTs with >50% and low metal impurity content.

[0025] The process is highly scalable: the FCCVD method and subsequent slurry preparation process adopted are simple, environmentally friendly, and easy to scale up and produce continuously, providing a feasible technical path for high-performance SWNTs and their large-scale application in power batteries. Attached Figure Description

[0026] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a TEM data diagram of SWNTs-950 in Example 1.

[0028] Figure 2 This is a TEM data diagram of SWNTs-1000 in Example 2.

[0029] Figure 3 This is a TEM data diagram of SWNTs-1050 in Example 3.

[0030] Figure 4 The image shows the constant TEM data of SWNTs-1000 in Comparative Example 1.

[0031] Figure 5 The images show a comparison of the Raman spectra of Examples 1, 2, 3 and Comparative Example 1.

[0032] Figure 6 This is a schematic diagram of the principle of a multi-temperature zone tubular furnace. Detailed Implementation

[0033] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] In the specific embodiments described in this invention, unless otherwise specified, the term 'room temperature' refers to an ambient temperature of 15 °C to 30 °C.

[0035] The present invention will be further illustrated below with reference to specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in this technical field.

[0036] Example 1 High-quality single-walled carbon nanotubes (SWNTs-950) were synthesized at 950℃ using a multi-temperature zone FCCVD method. 1. Preparation of catalyst precursors: In a glove box filled with high-purity argon, accurately weigh 10.0 g of ferrocene (purity >99.5%) and 0.10 g of sublimed sulfur (purity >99.9%), and place them in a clean agate mortar. Manually grind and mix for 30 minutes until the mixture is uniform in color and free of visible particulate sulfur or ferrocene crystals. Seal the well-mixed precursor powder and store it in a brown glass bottle for later use. The mass ratio of ferrocene to sublimed sulfur is 100:1.

[0037] 2. Preparation of the FCCVD reaction system: A customized horizontal tubular FCCVD system was employed, the core of which was a multi-segment furnace with an inner diameter of 60 mm and a length of 1200 mm. This furnace was divided axially into five independent temperature control zones: Zone 1, Zone 2, Zone 3, Zone 4, and Zone 5 (referred to as Zone 1 to Zone 5 for simplicity). Each zone was precisely temperature-controlled (accuracy ±1℃) using an independent temperature controller and a type K thermocouple. A quartz tube with an inner diameter of 50 mm was used as the reaction chamber.

[0038] Considering process parameters: Zone 1, length 15 cm → Stay for 30–60 seconds Zone 2, 15 cm long → Stay for 30–60 seconds Zone 3 length 20cm → stay for 60–120s Zone 4, length 40cm → Stay for 5–10 minutes Zone 5, length 20 cm → stay for 60–120 seconds The length ratio of each temperature zone, Zone 1 : Zone 2 : Zone 3 : Zone 4 : Zone 5 ≈ 1 : 1 : 1.3 : 2.7 : 1. The residence time ratio of the catalyst precursor, Zone 1 : Zone 2 : Zone 3 : Zone 4 : Zone 5 ≈ 0.55 : 0.55 : 0.73 : 5.8 : 0.73 → 1 : 1 : 1.3 : 10.5 : 1.3.

[0039] Accurately weigh 2.50g of the catalyst precursor powder prepared in step 1 and place it in a quartz boat. Then, push the quartz boat into the quartz tube and position it at the center of Zone 1 (preheating zone). Place a porous alumina ceramic plug at the front and back of the catalyst boat in the quartz tube for flow equalization and heat preservation to prevent premature heat dissipation from the preheating zone.

[0040] 3. Synthesis process: (1) System cleaning and inertization: Seal both ends of the quartz tube and connect the gas line. First, purge with high-purity argon gas (99.999% purity) at a flow rate of 500 standard cubic centimeters per minute (sccm) for 10 minutes to thoroughly remove air and moisture from the reaction pipeline. Then, adjust the argon gas flow rate to 200 sccm as the base carrier gas.

[0041] (2) Multi-temperature zone staged temperature rise: First, Zone 4 (main growth zone) is heated to the target temperature of 950°C at a heating rate of 10°C / min, and held at this temperature for 10 minutes.

[0042] Once Zone 4 has stabilized, simultaneously begin the heating programs for Zones 2, 3, and 5. Heat Zone 2 to 500°C, Zone 3 to 800°C, and Zone 5 to 800°C at the same rate of 10°C / min. After reaching the set temperature, maintain each zone at that temperature for 1-2 minutes.

[0043] Finally, begin heating Zone 1 (preheating zone). Heat it to 190°C at a relatively fast heating rate of 20°C / min.

[0044] (3) Introduction of reactive gases and growth of SWNTs: When the temperature of Zone 1 rose to about 120°C, the solid precursor inside the quartz boat was observed to begin to sublimate significantly, producing yellow smoke.

[0045] At this point, switch the gas path: shut off the pure argon gas and immediately introduce a mixed reaction gas consisting of high-purity methane (CH4, 99.99%) and high-purity hydrogen (H2, 99.999%). The total flow rate of the mixed gas is 50 sccm, where the volume ratio of CH4 to H2 is approximately 1:1 (specifically, CH4: 25 sccm, H2: 25 sccm).

[0046] A mixed gas stream carries gaseous ferrocene-sulfur molecular clusters into the subsequent heating zone. In the high-temperature zone (Zones 2-5), ferrocene pyrolyzes to generate iron nanoparticles, with sulfur playing a regulating role, and methane catalytically cracking on the surface of the iron particles to provide a carbon source. The growth reaction is carried out for 20 minutes at a constant temperature of 950°C in Zone 4. The product is discharged from the reaction tube with the gas stream, and a large amount of fluffy black flocculent material is collected in the quartz wool filter (or cold trap) at the end of the reaction tube. This is the main target product prepared in this invention—high-quality single-walled carbon nanotubes.

[0047] (4) Reaction termination: After 20 minutes, first shut off the methane and hydrogen gas lines, then switch back to pure argon (200 sccm) to purge and protect the system.

[0048] Stop heating in all heating zones and allow the entire system to cool naturally to room temperature under an argon atmosphere (approximately 4-6 hours). After growth, a small amount of black, dense layer can be observed adhering to the inner wall of the middle section of the reaction tube (Zone 2 to Zone 4). This layer mainly consists of carbonaceous byproducts generated under non-ideal conditions and some deactivated catalyst particles, which can be physically scraped off and treated separately.

[0049] 4. Acid washing and purification: (1) Preparation of acid solution: dilute concentrated hydrochloric acid (mass fraction 37%) with deionized water at a volume ratio of 1:9 to prepare a dilute hydrochloric acid solution of about 0.4 mol / L.

[0050] (2) Acid treatment: The crude product SWNTs was immersed in a sufficient amount of dilute hydrochloric acid solution, placed in a constant temperature water bath at 80°C, and magnetically stirred (400 rpm) for 6 hours.

[0051] (3) Repeated washing: The above acid treatment process is repeated twice to ensure that the nano iron catalyst particles and their oxides are completely removed.

[0052] (4) Post-treatment: Transfer the acid-washed mixture to a sintered sand funnel (G4 specification) for vacuum filtration. Wash the filter cake repeatedly with plenty of deionized water until the pH of the filtrate reaches neutral (pH=7). Transfer the filter cake to a watch glass and dry it in a vacuum drying oven at 60°C for 12 hours.

[0053] (5) Final product: After drying, purified black, fluffy powder of SWNTs was obtained, labeled SWNTs-950. Transmission electron microscopy (TEM) characterization revealed that it contained multiple carbon nanotube bundles and a small amount of residual metal catalyst. Raman spectroscopy analysis showed that... G / I D =25.

[0054] It is important to note that the 20-minute reaction time in this embodiment refers to the duration of the reactant gas introduction, i.e., the "reaction window" of the entire system. Its decisive role lies in controlling the total supply of precursors and the "online" lifetime of the catalyst in the growth zone. In floating catalysis, catalyst particles are continuously generated, grown, and may deactivate. The reaction time determines: Continuous replenishment of catalyst particles: Within 20 minutes, new precursors are continuously introduced into the system, generating new catalyst particles, ensuring that the growth zone always has "fresh" active catalyst.

[0055] Termination of single carbon nanotube growth: For a single catalyst particle, the growth of carbon nanotubes on its surface may cease within seconds to minutes due to being coated with a carbon layer (deactivation). However, macroscopically, product collection is continuous due to the constant replenishment of new catalyst particles.

[0056] Total product amount: The reaction time is directly proportional to the total yield.

[0057] Relationship with "passage time": "Passage time" (e.g., 5–10 min in zone Z4) is a spatial residence time, while 20 minutes is the duration of the entire process. It can be understood that during the 20-minute reaction period, countless batches of "catalyst-carbon source" gas envelopes pass through zone Z4 sequentially, with each envelope staying in zone Z4 for approximately 5–10 minutes for growth.

[0058] Example 2 High-quality single-walled carbon nanotubes (denoted as SWNTs-1000) were synthesized at 1000℃ using a multi-temperature zone FCCVD method. 1. Preparation of catalyst precursors: Same as Example 1.

[0059] 2. Preparation of the FCCVD reaction system: Same as Example 1.

[0060] 3. Synthesis process: (1) System cleaning and inertization: Seal both ends of the quartz tube and connect the gas line. First, purge with high-purity argon gas (99.999% purity) at a flow rate of 500 standard cubic centimeters per minute (sccm) for 10 minutes to thoroughly remove air and moisture from the reaction pipeline. Then, adjust the argon gas flow rate to 200 sccm as the base carrier gas.

[0061] (2) Multi-temperature zone staged temperature rise: First, Zone 4 (main growth zone) is heated to the target temperature of 1000℃ at a heating rate of 10℃ / min, and held at this temperature for 10 minutes.

[0062] Once Zone 4 has stabilized, simultaneously begin the heating programs for Zones 2, 3, and 5. Heat Zone 2 to 500°C, Zone 3 to 800°C, and Zone 5 to 800°C at the same rate of 10°C / min. After reaching the set temperature, maintain each zone at that temperature for 1-2 minutes.

[0063] Finally, begin heating Zone 1 (preheating zone). Heat it to 190°C at a relatively fast heating rate of 20°C / min.

[0064] (3) Introduction of reactive gases and growth of SWNTs: When the temperature of Zone 1 rose to about 120°C, the solid precursor inside the quartz boat was observed to begin to sublimate significantly, producing yellow smoke.

[0065] At this point, switch the gas path: shut off the pure argon gas and immediately introduce a mixed reaction gas consisting of high-purity methane (CH4, 99.99%) and high-purity hydrogen (H2, 99.999%). The total flow rate of the mixed gas is 50 sccm, where the volume ratio of CH4 to H2 is approximately 1:1 (specifically, CH4: 25 sccm, H2: 25 sccm).

[0066] A mixed gas stream carries gaseous ferrocene-sulfur molecular clusters into the subsequent heating zone. In the high-temperature zone (Zones 2-5), ferrocene pyrolyzes to generate iron nanoparticles, with sulfur playing a regulating role, and methane catalytically cracking on the surface of the iron particles to provide a carbon source. The growth reaction is carried out for 20 minutes at a constant temperature of 1000°C in Zone 4. The product is discharged from the reaction tube with the gas stream, and a large amount of fluffy black flocculent material is collected in the quartz wool filter (or cold trap) at the end of the reaction tube. This is the main target product of this invention—high-quality single-walled carbon nanotubes.

[0067] (4) Reaction termination: After 20 minutes, first shut off the methane and hydrogen gas lines, then switch back to pure argon (200 sccm) to purge and protect the system.

[0068] Stop heating in all heating zones and allow the entire system to cool naturally to room temperature under an argon atmosphere (approximately 4-6 hours). After growth, a small amount of black, dense layer can be observed adhering to the inner wall of the middle section of the reaction tube (Zone 2 to Zone 4). This layer mainly consists of carbonaceous byproducts generated under non-ideal conditions and some deactivated catalyst particles, which can be physically scraped off and treated separately.

[0069] 4. Acid washing and purification: Steps (1)-(4) are the same as in Example 1.

[0070] (5) Final product: After drying, purified black, fluffy powder of SWNTs was obtained, labeled SWNTs-1000. Transmission electron microscopy (TEM) characterization showed that it consisted of single-walled carbon nanotubes with no metal catalyst residue. Raman spectroscopy revealed that... G / I D =70.

[0071] Example 3 High-quality single-walled carbon nanotubes (SWNTs-1050) were synthesized at 1050℃ using a multi-temperature zone FCCVD method. 1. Preparation of catalyst precursors: Same as Example 1.

[0072] 2. Preparation of the FCCVD reaction system: Same as Example 1.

[0073] 3. Synthesis process: (1) System cleaning and inertization: Seal both ends of the quartz tube and connect the gas line. First, purge with high-purity argon gas (99.999% purity) at a flow rate of 500 standard cubic centimeters per minute (sccm) for 10 minutes to thoroughly remove air and moisture from the reaction pipeline. Then, adjust the argon gas flow rate to 200 sccm as the base carrier gas.

[0074] (2) Multi-temperature zone staged temperature rise: First, Zone 4 (main growth zone) is heated to the target temperature of 1050℃ at a heating rate of 10℃ / min, and held at this temperature for 10 minutes.

[0075] Once Zone 4 has stabilized, simultaneously begin the heating programs for Zones 2, 3, and 5. Heat Zone 2 to 500°C, Zone 3 to 800°C, and Zone 5 to 800°C at the same rate of 10°C / min. After reaching the set temperature, maintain each zone at that temperature for 1-2 minutes.

[0076] Finally, begin heating Zone 1 (preheating zone). Heat it to 190°C at a relatively fast heating rate of 15°C / min.

[0077] (3) Introduction of reactive gases and growth of SWNTs: When the temperature of Zone 1 rose to about 120°C, the solid precursor inside the quartz boat was observed to begin to sublimate significantly, producing yellow smoke.

[0078] At this point, switch the gas path: shut off the pure argon gas and immediately introduce a mixed reaction gas consisting of high-purity methane (CH4, 99.99%) and high-purity hydrogen (H2, 99.999%). The total flow rate of the mixed gas is 50 sccm, where the volume ratio of CH4 to H2 is approximately 1:1 (specifically, CH4: 25 sccm, H2: 25 sccm).

[0079] A mixed gas stream carries gaseous ferrocene-sulfur molecular clusters into the subsequent heating zone. In the high-temperature zone (Zones 2-5), ferrocene pyrolyzes to generate iron nanoparticles, with sulfur playing a regulating role, and methane catalytically cracking on the surface of the iron particles to provide a carbon source. The growth reaction is carried out for 20 minutes at a constant temperature of 1050°C in Zone 4. The product is discharged from the reaction tube with the gas stream, and a large amount of fluffy black flocculent material is collected in the quartz wool filter (or cold trap) at the end of the reaction tube. This is the main target product of this invention—high-quality single-walled carbon nanotubes.

[0080] (4) Reaction termination: After 20 minutes, first shut off the methane and hydrogen gas lines, then switch back to pure argon (200 sccm) to purge and protect the system.

[0081] Stop heating in all heating zones and allow the entire system to cool naturally to room temperature under an argon atmosphere (approximately 4-6 hours). After growth, a small amount of black, dense layer can be observed adhering to the inner wall of the middle section of the reaction tube (Zone 2 to Zone 4). This layer mainly consists of carbonaceous byproducts generated under non-ideal conditions and some deactivated catalyst particles, which can be physically scraped off and treated separately.

[0082] 4. Acid washing and purification: Steps (1)-(4) are the same as in Example 1.

[0083] (5) Final product: After drying, purified black, fluffy powder of SWNTs was obtained, labeled SWNTs-1050. Transmission electron microscopy (TEM) characterization revealed that it consisted of single-walled carbon nanotubes with numerous defects and no residual metal catalyst. Raman spectroscopy showed that... G / I D =40.

[0084] Comparative Example 1 This comparative example uses uncontrolled FCCVD to synthesize high-quality single-walled carbon nanotubes (denoted as SWNTs-1000 constant) at 1000℃. 1. Preparation of catalyst precursors: Same as Example 1.

[0085] 2. Preparation of the FCCVD reaction system: Same as Example 1.

[0086] 3. Synthesis process: (1) System cleaning and inertization: Same as in Example 1.

[0087] (2) Programmed heating: First, Zone 4 (main growth zone) is heated to the target temperature of 1000℃ at a heating rate of 10℃ / min, and held at this temperature for 10 minutes.

[0088] Once Zone 4 has stabilized, simultaneously begin the heating programs for Zones 2, 3, and 5. Heat Zones 2, 3, and 5 to 1000℃ at the same rate of 10℃ / min. After reaching the set temperature, maintain each zone at that temperature for 1-2 minutes.

[0089] (3) Introduction of reactive gases and growth of SWNTs: When the temperature of Zone 1 rose to about 120°C, the solid precursor inside the quartz boat was observed to begin to sublimate significantly, producing yellow smoke.

[0090] At this point, switch the gas path: shut off the pure argon gas and immediately introduce a mixed reaction gas consisting of high-purity methane (CH4, 99.99%) and high-purity hydrogen (H2, 99.999%). The total flow rate of the mixed gas is 50 sccm, where the volume ratio of CH4 to H2 is approximately 1:1 (specifically, CH4: 25 sccm, H2: 25 sccm).

[0091] A mixed gas stream carries gaseous ferrocene-sulfur molecular clusters into the subsequent heating zone. In the high-temperature zone (Zones 2-5), ferrocene pyrolyzes to generate iron nanoparticles, with sulfur playing a regulating role, and methane catalytically cracking on the surface of the iron particles to provide a carbon source. The growth reaction is carried out for 20 minutes at a constant temperature of 1000°C in Zone 4. The product is discharged from the reaction tube with the gas stream, and a large amount of fluffy black flocculent material is collected in the quartz wool filter (or cold trap) at the end of the reaction tube. This is the main target product of this invention—high-quality single-walled carbon nanotubes.

[0092] (4) Reaction termination: After 20 minutes, first shut off the methane and hydrogen gas lines, then switch back to pure argon (200 sccm) to purge and protect the system.

[0093] Stop heating in all heating zones and allow the entire system to cool naturally to room temperature under an argon atmosphere (approximately 4-6 hours). After growth, a small amount of black, dense layer can be observed adhering to the inner wall of the middle section of the reaction tube (Zone 2 to Zone 4). This layer mainly consists of carbonaceous byproducts generated under non-ideal conditions and some deactivated catalyst particles, which can be physically scraped off and treated separately.

[0094] 4. Acid washing and purification: Steps (1)-(4) are the same as in Example 1.

[0095] (5) Final product: After drying, purified black, fluffy powder of SWNTs was obtained, labeled as SWNTs-1000 constant. Transmission electron microscopy (TEM) characterization revealed that it consisted of multiple carbon nanotube bundles with residual large metal nanoparticles. Raman spectroscopy analysis showed that... G / I D =16.

[0096] The foregoing embodiments have provided a detailed description of the inventive intent and implementation of the present invention. However, those skilled in the art will understand that the above embodiments are merely preferred embodiments of the present invention. Due to space limitations, not all embodiments can be listed here. Any implementation that embodies the technical solution of the claims of the present invention is within the protection scope of the present invention.

[0097] It should be noted that the above content is a further detailed description of the present invention in conjunction with specific embodiments, and it should not be considered that the specific embodiments of the present invention are limited to this. Under the guidance of the above embodiments, those skilled in the art can make various improvements and modifications based on the above embodiments, and these improvements or modifications fall within the protection scope of the present invention.

Claims

1. A method for preparing single-walled carbon nanotubes, characterized in that, The floating catalyst chemical vapor deposition method includes the following steps: S1. Ferrocene and sublimed sulfur are mixed at a mass ratio of 85:1 to 115:1, and the resulting catalyst precursor is placed in the preheating zone of a tube furnace. The tubular furnace is provided with at least three independently temperature-controlled zones along the airflow direction, which are, in order, a preheating zone for the sublimation of catalyst precursors, at least one transition reaction zone for the formation and activation of catalyst nanoparticles, and a main growth zone for the growth of single-walled carbon nanotubes. S2. The main growth zone is heated to a growth temperature of 950℃~1050℃ and kept stable, and the transition reaction zone is heated to a set temperature of 500℃~850℃; then, the preheating zone is heated to 160℃~220℃ at a rate of not less than 15℃ / min to sublimate the catalyst precursor. S3. A mixed reaction gas containing methane and hydrogen is introduced, carrying the gaseous catalyst precursor through the transition reaction zone and the main growth zone in sequence. By controlling the flow rate of the mixed reaction gas and the length of each temperature zone, the average passage time of the gaseous catalyst precursor in the transition reaction zone is 1.5-3 minutes, and the average passage time in the main growth zone is 5-10 minutes. The crude product of single-walled carbon nanotubes is then collected in the product collection unit and separated to obtain single-walled carbon nanotubes.

2. The method according to claim 1, characterized in that, In step S2, the target heating temperature of the main growth temperature zone is 1000℃±10℃.

3. The method according to claim 1 or 2, characterized in that, In step S2, the target heating temperature of the preheating zone is 190°C.

4. The method according to claim 1, characterized in that, The tubular furnace has five independently controlled temperature zones, which are sequentially designated as the first temperature zone, the second temperature zone, the third temperature zone, the fourth temperature zone, and the fifth temperature zone along the airflow direction; wherein, the first temperature zone is the preheating zone, the second and third temperature zones are the transition reaction zones, and the fourth temperature zone is the main growth temperature zone.

5. The method according to claim 4, characterized in that, Step S2 is as follows: First, the fourth temperature zone is heated to a growth temperature of 950℃~1050℃, the second temperature zone is heated to 500℃, and the third and fifth temperature zones are heated to 800℃; then, the first temperature zone is heated to 160℃-220℃.

6. The method according to claim 5, characterized in that, The temperature of the fourth temperature zone is 1000℃±10℃.

7. The method according to claim 4, characterized in that, In step S3: The average passage time of the gaseous catalyst precursor in the second temperature zone is 30–60 seconds; The average passage time of the gaseous catalyst precursor in the third temperature zone is 60–120 seconds; The average passage time of the gaseous catalyst precursor in the fourth temperature zone is 5-10 minutes. The average passage time of the gaseous catalyst precursor in the fifth temperature zone is 60–120 seconds.

8. The method according to claim 1, characterized in that, The separation method in step S3 is as follows: the crude product of single-walled carbon nanotubes is purified by acid washing to obtain purified single-walled carbon nanotubes.

9. A single-walled carbon nanotube, characterized in that, Prepared by the method according to any one of claims 1 to 8.

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