Carbon nanotube and method for preparing the same

Abstract

The application relates to the technical field of nanomaterials, in particular to a carbon nanotube and a preparation method thereof. The carbon nanotube is obtained by growing natural gas as a carbon source through a chemical vapor deposition method and is subjected to modification treatment. The application prepares high-quality carbon nanotubes by taking natural gas as a carbon source through a chemical vapor deposition method, and the dispersibility, interface compatibility and comprehensive performance of the carbon nanotubes are significantly improved by combining the synergistic modification of a chitosan-based modification liquid and a complex grinding agent, so that the carbon nanotubes are suitable for fields such as high-performance composite materials, electronic devices and energy storage.

Description

Technical Field

[0001] This invention relates to the field of carbon nanotube technology, specifically to a carbon nanotube and its preparation method. Background Technology

[0002] Carbon nanotubes, as nanomaterials with a unique one-dimensional tubular structure, have attracted widespread attention since their discovery due to their excellent mechanical, electrical, and thermal properties. The tensile strength of carbon nanotubes can be more than 100 times that of steel, while their density is only one-sixth that of steel. Their thermal conductivity is superior to diamond, and their electrical conductivity is excellent. These outstanding properties make carbon nanotubes promising for applications in composite material reinforcement, conductive pastes, electromagnetic shielding, energy storage, and biomedicine.

[0003] The main methods for preparing carbon nanotubes include arc discharge, laser ablation, and chemical vapor deposition (CVD). Among these, CVD is the most promising method for industrial application due to its strong process controllability, high yield, and relatively low cost. The carbon source is one of the key factors in CVD preparation of carbon nanotubes. Traditionally, hydrocarbons such as ethylene, propylene, and methane have been widely used as carbon sources. Natural gas, as a clean energy source rich in methane, has the advantages of wide availability, low cost, and high carbon content, making it an ideal carbon source for carbon nanotube preparation. Using natural gas as a carbon source to prepare carbon nanotubes via CVD can achieve low-cost, large-scale production of carbon nanotubes, while also providing a new way to increase the added value of natural gas. However, carbon nanotubes grown using natural gas as a carbon source have technical problems such as a wide diameter distribution and numerous structural defects.

[0004] Furthermore, carbon nanotubes face two key technical bottlenecks in practical applications. First, the surface of carbon nanotubes is chemically inert and lacks active functional groups, resulting in poor interfacial compatibility with polymer, ceramic, or metal matrices. This leads to weak interfacial bonding, hindering the full realization of their reinforcing effect. Second, strong van der Waals forces exist between carbon nanotubes, making them prone to aggregation and entanglement in solutions or matrices, making uniform dispersion difficult. Aggregated carbon nanotubes not only fail to exert their nanoscale reinforcing effect but may also become stress concentration points and defect sources in composite materials.

[0005] To address these issues, researchers have explored various methods for modifying carbon nanotubes. Acidification can introduce oxygen-containing functional groups such as carboxyl and hydroxyl groups onto the surface of carbon nanotubes, but strong acid conditions can damage the conjugated structure and mechanical properties of carbon nanotubes to varying degrees. While physical coating with surfactants is simple to perform, the coating layer is unstable and prone to desorption during use. Polymer grafting modification can improve the dispersibility of carbon nanotubes in specific solvents or matrices, but it is typically a complex and costly process.

[0006] Dopamine hydrochloride can undergo oxidative self-polymerization under weakly alkaline conditions, forming a polydopamine coating layer on the surface of various inorganic materials. This polydopamine layer is rich in catechol and amino functional groups, serving as an active platform for secondary reactions. Chitosan, as a natural polymer, is rich in hydroxyl and amino groups, exhibiting good film-forming properties and biocompatibility. Nano-titanium dioxide and yttrium oxide, as inorganic nanoparticles, can impart additional functional properties to the surface of carbon nanotubes. Silicon carbide whiskers possess high strength and high modulus; after dopamine modification, they can be compounded with boron nitride as a ball milling medium, synergistically modifying carbon nanotubes during ball milling. Currently, there are no reports on the synergistic modification of carbon nanotubes grown by natural gas-based chemical vapor deposition with chitosan-based modification solutions and dopamine-modified silicon carbide whisker polishing agents. Summary of the Invention

[0007] In view of the deficiencies of the prior art, the purpose of this invention is to provide a carbon nanotube and its preparation method to solve the problems mentioned in the background art.

[0008] The present invention solves the technical problem by adopting the following technical solution: The present invention provides a carbon nanotube, which is grown by chemical vapor deposition using natural gas as a carbon source and then undergoes modification treatment, including modification liquid treatment and ball milling treatment with a refining agent.

[0009] Preferably, the process conditions for the chemical vapor deposition method are as follows: the catalyst is at least one of iron, cobalt or nickel, the catalyst is supported on an alumina or magnesium oxide support, the reaction temperature is 600-900℃, the natural gas flow rate is 100-500 mL / min, and the reaction time is 30-120 min.

[0010] The main component of natural gas is methane, which typically accounts for 85% to 95% of the total content. During chemical vapor deposition, methane is cracked on the catalyst surface to generate carbon atoms. These carbon atoms diffuse and precipitate on the catalyst particle surface to form carbon nanotubes. Small amounts of higher alkanes such as ethane and propane in natural gas can synergistically participate in the growth of carbon nanotubes, which helps to improve the graphitization degree of the product. The reaction temperature is controlled within the range of 600 to 900°C. If the temperature is too low, the methane cracking is insufficient, resulting in a low carbon nanotube yield. If the temperature is too high, the graphitization degree of the carbon nanotube wall increases, but the diameter distribution becomes wider.

[0011] Preferably, the modified solution is prepared by dissolving chitosan in an aqueous solution of acetic acid with a mass fraction of 1% to 5%, wherein the mass fraction of chitosan is 1% to 10%, adding nano-titanium dioxide and yttrium oxide, wherein the weight ratio of nano-titanium dioxide to yttrium oxide is 2:1 to 5:1, and the total amount of nano-titanium dioxide and yttrium oxide added is 10% to 40% of the mass of chitosan, and stirring at 300 to 600 r / min for 1 to 4 h at 40 to 80 °C to obtain the modified solution.

[0012] Chitosan molecules contain abundant amino and hydroxyl groups, which protonate in acidic aqueous solutions to form cationic polyelectrolytes. These polyelectrolytes can bind to the surface of carbon nanotubes through electrostatic adsorption and hydrogen bonding. Nano-titanium dioxide has photocatalytic activity and high chemical stability, and can form a nanoparticle coating layer on the surface of carbon nanotubes, improving their surface roughness and reactivity. Yttrium oxide, as a rare earth oxide, can participate in interfacial chemical reactions and optimize the interfacial bonding between carbon nanotubes and the matrix. The combination of nano-titanium dioxide and yttrium oxide can exert a synergistic effect, improving both the dispersibility of carbon nanotubes and their interfacial bonding.

[0013] Preferably, the nano-titanium dioxide has a particle size of 10–80 nm, the yttrium oxide has a particle size of 10–100 nm, and the chitosan has a degree of deacetylation ≥90%.

[0014] Preferably, the modified silicon carbide whisker solution is prepared by adding silicon carbide whiskers to a 0.5%–2% (w / w) dopamine hydrochloride solution with a pH of 8.0–9.0, stirring and reacting at 25–40°C for 12–24 h, then adding boron nitride with a weight ratio of boron nitride to silicon carbide whiskers of 1:2–1:5, and continuing to stir and react for 2–6 h to obtain the modified silicon carbide whisker solution.

[0015] Dopamine hydrochloride undergoes oxidative self-polymerization under weakly alkaline conditions, forming a polydopamine coating layer on the surface of silicon carbide whiskers. The polydopamine layer is rich in catechol and amine active functional groups, which can significantly improve the surface activity and interfacial compatibility of silicon carbide whiskers. At the same time, the polydopamine layer can also act as an adhesive layer to fix boron nitride sheets to the surface of silicon carbide whiskers. Boron nitride has a layered structure and excellent lubrication properties, which can assist in the dispersion and exfoliation of carbon nanotubes during ball milling, reducing the damage to the carbon nanotube structure caused by ball milling. The modified silicon carbide whiskers combine the grinding effect of whiskers with the lubrication and dispersion effect of boron nitride, and implement mild and efficient physicochemical synergistic modification of carbon nanotubes during ball milling.

[0016] Preferably, the silicon carbide whiskers have a diameter of 0.5–3 μm and an aspect ratio of 10:1–50:1; the boron nitride is hexagonal boron nitride with a particle size of 1–15 μm.

[0017] Preferably, the re-grinding agent is prepared by drying the modified silicon carbide whisker liquid at 80-120°C for 12-24 h, grinding it through a 200-mesh sieve to obtain the re-grinding agent.

[0018] This invention also provides a method for preparing carbon nanotubes, comprising the following steps: Step 1: Chemical vapor deposition growth of carbon nanotubes: The catalyst is placed in a reactor and heated to 600-900°C under inert gas protection. Natural gas is introduced as the carbon source at a flow rate of 100-500 mL / min. The reaction time is 30-120 min. After the reaction is completed, the mixture is cooled to room temperature in an inert atmosphere to obtain crude carbon nanotubes.

[0019] Step 2: Purification: The crude carbon nanotubes are immersed in acid for 2–12 hours, then filtered, washed with water until neutral, and dried to obtain purified carbon nanotubes. Acid treatment removes catalyst particles and supports, and simultaneously introduces a small number of oxygen-containing functional groups onto the surface of the carbon nanotubes, providing reaction sites for subsequent modification.

[0020] Step 3: Preparation of modified solution: Dissolve chitosan in an aqueous solution of acetic acid with a mass fraction of 1% to 5%, where the mass fraction of chitosan is 1% to 10%. Add nano-titanium dioxide and yttrium oxide, with a weight ratio of nano-titanium dioxide to yttrium oxide of 2:1 to 5:1. The total amount of nano-titanium dioxide and yttrium oxide added is 10% to 40% of the mass of chitosan. Stir at 300 to 600 r / min for 1 to 4 h at 40 to 80 °C to obtain the modified solution.

[0021] Step 4: Carbon nanotube modification treatment: Purified carbon nanotubes are added to the modification solution at a mass ratio of 1:5 to 1:20. The mixture is stirred at 300 to 500 r / min for 2 to 6 hours at 40 to 80°C. After filtration, washing, and drying at 60 to 80°C, the modified carbon nanotube precursor is obtained.

[0022] During the modified liquid treatment stage, chitosan is coated onto the surface of carbon nanotubes through electrostatic adsorption and hydrogen bonding to form a uniform organic coating layer. Nano-titanium dioxide and yttrium oxide are uniformly loaded onto the surface of carbon nanotubes under the dispersion effect of chitosan. This treatment introduces active functional groups such as amino, hydroxyl and carboxyl groups onto the surface of carbon nanotubes, while giving them a rough surface, providing a good precursor state for subsequent ball milling modification.

[0023] Step 5: Preparation of the re-grinding agent: Add silicon carbide whiskers to a 0.5%–2% (w / w) dopamine hydrochloride solution with a pH of 8.0–9.0. Stir and react at 25–40°C for 12–24 h. Then add boron nitride at a weight ratio of 1:2 to 1:5 (w / w). Continue stirring and reacting for 2–6 h to obtain a modified silicon carbide whisker solution. Dry the modified silicon carbide whisker solution at 80–120°C for 12–24 h and grind it through a 200-mesh sieve to obtain the re-grinding agent.

[0024] Step 6: Ball milling modification treatment: Mix the modified carbon nanotube precursor with the re-milling agent at a weight ratio of 1:0.2 to 1:0.8, and ball mill at 200 to 500 r / min for 2 to 6 h. After sieving, the modified carbon nanotubes are obtained.

[0025] In the ball milling modification stage, the modified silicon carbide whiskers in the grinding agent act as a grinding medium, applying appropriate shear and impact forces to the carbon nanotube precursor to promote the untangling and dispersion of the carbon nanotube bundles. During the ball milling process, the polydopamine layer on the surface of the silicon carbide whiskers can interact with the chitosan layer on the surface of the carbon nanotubes to form an interfacial bond. The lubricating effect of boron nitride reduces the excessive damage to the carbon nanotube structure caused by ball milling. This stage achieves the synergy of physical dispersion and chemical modification of carbon nanotubes, enabling the carbon nanotubes to obtain a stable and uniform functionalized surface.

[0026] Preferably, the catalyst in step one is iron supported on an alumina support, with the weight ratio of iron to alumina being 1:5 to 1:20; the inert gas is nitrogen or argon, with a flow rate of 200 to 800 mL / min; and the acid solution in step two is a hydrochloric acid solution or a nitric acid solution with a mass fraction of 10% to 30%.

[0027] Preferably, in step four, the mass ratio of carbon nanotubes to the modified liquid is 1:8 to 1:15, the stirring reaction temperature is 50 to 70°C, and the stirring reaction time is 3 to 5 h; in step six, the weight ratio of the modified carbon nanotube precursor to the re-grinding agent is 1:0.3 to 1:0.6, the ball milling speed is 300 to 400 r / min, and the ball milling time is 3 to 5 h.

[0028] The present invention also provides applications of the above-mentioned carbon nanotubes, wherein the carbon nanotubes are used to prepare high-performance composite material reinforcing agents, conductive pastes, electromagnetic shielding materials or energy storage electrode materials.

[0029] Compared with the prior art, the present invention has the following beneficial effects: This invention utilizes natural gas as a carbon source to prepare carbon nanotubes via chemical vapor deposition, achieving low-cost, large-scale production of carbon nanotubes. Natural gas is widely available and inexpensive, significantly reducing the preparation cost of carbon nanotubes compared to traditional carbon sources such as high-purity methane and ethylene. Furthermore, the synergistic effect of trace amounts of higher alkanes in natural gas helps improve the yield and graphitization degree of carbon nanotubes. This preparation method is highly compatible with existing natural gas industrial infrastructure and has promising prospects for industrialization.

[0030] This invention utilizes the synergistic effect of chitosan-based modified liquid and refining agent to construct an organic-inorganic hybrid functional layer on the surface of carbon nanotubes. The amino and hydroxyl groups of chitosan form hydrogen bonds and electrostatic adsorption with the surface of carbon nanotubes. Nano-titanium dioxide and yttrium oxide are uniformly loaded on the surface of carbon nanotubes, giving them a rough surface and reactive sites. The modified silicon carbide whiskers in the refining agent further promote the dispersion and interface optimization of carbon nanotubes during ball milling. The multi-step synergistic modification significantly improves the dispersibility and interfacial compatibility of carbon nanotubes.

[0031] The modified liquid of this invention uses chitosan as the matrix. As a natural polymer, chitosan has good biocompatibility and film-forming properties. The amino and hydroxyl groups on its molecular chain can form multi-site interactions with carbon nanotubes. The photocatalytic activity and chemical stability of nano-titanium dioxide can enhance the reactivity of the carbon nanotube surface. The rare earth properties of yttrium oxide can optimize the interfacial chemical bonding. The optimized compounding ratio of nano-titanium dioxide and yttrium oxide can form a uniform and stable inorganic nanoparticle coating layer on the surface of carbon nanotubes.

[0032] In this invention, the silicon carbide whiskers in the grinding agent are modified with dopamine hydrochloride, forming a polydopamine active coating layer on the surface, which can effectively improve the interfacial interaction between silicon carbide whiskers and carbon nanotubes. The layered structure and lubricating properties of boron nitride protect carbon nanotubes from excessive structural damage during ball milling. The combination of modified silicon carbide whiskers and boron nitride enables the ball milling process to have the dual functions of grinding and dispersing and chemical modification, achieving mild and efficient functionalization of carbon nanotubes. Detailed Implementation

[0033] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to specific examples. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. 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] Example 1 Chemical vapor deposition growth of carbon nanotubes: An iron-supported catalyst on an alumina support was placed in a tubular reactor with an iron to alumina weight ratio of 1:10. The temperature was raised to 750°C at a rate of 10°C / min under nitrogen protection. Natural gas was introduced as the carbon source at a flow rate of 300 mL / min. The reaction time was 60 min. After the reaction was completed, the mixture was cooled to room temperature under a nitrogen atmosphere to obtain crude carbon nanotubes.

[0035] Purification treatment: The crude carbon nanotube product was soaked in a 20% hydrochloric acid solution for 6 hours, filtered, washed with deionized water until neutral, and dried at 80°C to obtain purified carbon nanotubes.

[0036] Preparation of the modified solution: Chitosan with a degree of deacetylation of 92% was dissolved in an aqueous solution of acetic acid with a mass fraction of 2% (5% by mass). Nano-titanium dioxide with a particle size of 30 nm and yttrium oxide with a particle size of 50 nm were added. The weight ratio of nano-titanium dioxide to yttrium oxide was 3:1. The total amount of nano-titanium dioxide and yttrium oxide added was 25% of the mass of chitosan. The mixture was stirred at 500 r / min for 2.5 h at 60 °C to obtain the modified solution.

[0037] Carbon nanotube modification: Purified carbon nanotubes were added to the modification solution at a mass ratio of 1:10. The mixture was stirred at 400 r / min for 4 h at 60 °C. After filtration, washing with deionized water, and drying at 70 °C, the modified carbon nanotube precursor was obtained.

[0038] Preparation of the re-grinding agent: Silicon carbide whiskers with a diameter of 1.5 μm and an aspect ratio of 30:1 were added to a 1% (w / w) dopamine hydrochloride solution. The pH of the dopamine hydrochloride solution was 8.5. The pH was adjusted using Tris-HCl buffer solution. The mixture was stirred at 30°C for 18 h. Then, hexagonal boron nitride with a particle size of 5 μm was added. The weight ratio of boron nitride to silicon carbide whiskers was 1:3. The mixture was stirred for another 4 h to obtain a modified silicon carbide whisker solution. The modified silicon carbide whisker solution was dried at 100°C for 18 h and then ground through a 200-mesh sieve to obtain the re-grinding agent.

[0039] Ball milling modification treatment: The modified carbon nanotube precursor and the re-milling agent were mixed at a weight ratio of 1:0.5 and ball milled at 350 r / min for 4 h. After sieving through a 200-mesh sieve, the modified carbon nanotubes were obtained.

[0040] Example 2 In the chemical vapor deposition growth of carbon nanotubes, the catalyst was cobalt supported on a magnesium oxide support, with a cobalt to magnesium oxide weight ratio of 1:15. The reaction temperature was 800℃, the natural gas flow rate was 400 mL / min, and the reaction time was 45 min. The purification process used a 15% (w / w) nitric acid solution for soaking for 4 h.

[0041] In the preparation of the modified solution, the mass fraction of chitosan was 8%, the particle size of nano-titanium dioxide was 50 nm and the particle size of yttrium oxide was 80 nm, the weight ratio of nano-titanium dioxide to yttrium oxide was 4:1, and the total amount of nano-titanium dioxide and yttrium oxide added was 30% of the mass of chitosan. The mixture was stirred at 450 r / min for 3 h at 70 °C.

[0042] In the carbon nanotube modification process, the mass ratio of carbon nanotubes to the modification solution was 1:12, and the reaction was carried out at 70℃ with stirring at 350 r / min for 3 h.

[0043] In the preparation of the re-grinding agent, the mass fraction of the hydrochloric acid dopamine solution was 1.5%, the pH value was 8.8, the reaction temperature was 35℃, the reaction time was 20 h, the weight ratio of boron nitride to silicon carbide whiskers was 1:4, the reaction was continued to be stirred for 3 h, the drying temperature was 110℃, and the drying time was 15 h.

[0044] In the ball milling modification treatment, the weight ratio of the modified carbon nanotube precursor to the milling agent was 1:0.4, the ball milling speed was 300 r / min, and the ball milling time was 5 h. The other conditions were the same as in Example 1.

[0045] Example 3 In the chemical vapor deposition growth of carbon nanotubes, the catalyst was nickel supported on an alumina support, with a nickel to alumina weight ratio of 1:8. The reaction temperature was 650℃, the natural gas flow rate was 200 mL / min, and the reaction time was 90 min. For purification, the acid solution was a 25% hydrochloric acid solution, and the soaking time was 8 h.

[0046] In the preparation of the modified solution, the mass fraction of chitosan was 3%, the particle size of nano-titanium dioxide was 20 nm and the particle size of yttrium oxide was 30 nm, the weight ratio of nano-titanium dioxide to yttrium oxide was 2.5:1, and the total amount of nano-titanium dioxide and yttrium oxide added was 20% of the mass of chitosan. The mixture was stirred at 550 r / min for 2 h at 50 °C.

[0047] In the carbon nanotube modification process, the mass ratio of carbon nanotubes to the modification solution was 1:8, and the reaction was carried out at 50℃ with stirring at 450 r / min for 5 h.

[0048] In the preparation of the re-grinding agent, the mass fraction of the hydrochloric acid dopamine solution was 0.8%, the pH value was 8.2, the reaction temperature was 28℃, the reaction time was 22 h, the weight ratio of boron nitride to silicon carbide whiskers was 1:2.5, the reaction was continued to be stirred for 5 h, the drying temperature was 90℃, and the drying time was 22 h.

[0049] In the ball milling modification treatment, the weight ratio of modified carbon nanotube precursor to milling agent was 1:0.6, the ball milling speed was 400 r / min, and the ball milling time was 3 h. The other conditions were the same as in Example 1.

[0050] Scale settings Comparative Example 1: The carbon nanotubes were grown by chemical vapor deposition using natural gas as the carbon source and were purified, but were not treated with a modifying liquid or ball milling with a refining agent.

[0051] Comparative Example 2: Carbon nanotubes were treated with a modifying liquid, but were not subjected to ball milling modification with a refining agent.

[0052] Comparative Example 3: Carbon nanotubes were modified by ball milling with a refining agent, but were not treated with a modifying liquid.

[0053] Comparative Example 4: No nano-titanium dioxide and yttrium oxide were added in the preparation of the modified solution; only chitosan solution was used as the modified solution.

[0054] Comparative Example 5: In the preparation of the re-grinding agent, the silicon carbide whiskers were not modified with dopamine hydrochloride, that is, the silicon carbide whiskers were directly mixed with boron nitride and dried before being used as the re-grinding agent.

[0055] Performance testing The carbon nanotubes prepared in Examples 1 to 3 and Comparative Examples 1 to 5 were tested for dispersibility, thermal stability, electrical conductivity, structural order, and interfacial compatibility.

[0056] Dispersion test: The carbon nanotube sample was added to deionized water and ultrasonically dispersed for 30 min. After standing for 24 h, the dispersion state was observed. The concentration of carbon nanotubes in the upper suspension was measured, and the dispersion rate was calculated. The dispersion rate is equal to the concentration of carbon nanotubes in the upper suspension divided by the total concentration of added carbon nanotubes multiplied by 100%.

[0057] Thermal stability test: Thermogravimetric analysis was used to measure the initial decomposition temperature Td of carbon nanotubes and the residual carbon rate at 800℃ by heating from room temperature to 800℃ in air atmosphere at a heating rate of 10℃ / min.

[0058] Conductivity test: The carbon nanotube sample was pressed into a circular sheet with a diameter of 13 mm and a thickness of 2 mm, and its conductivity was measured by the four-probe method.

[0059] Structural order test: The ID / IG ratio of carbon nanotubes was determined using Raman spectroscopy. The D peak corresponds to structural defects in carbon nanotubes, and the G peak corresponds to in-plane vibrations of graphite structures. The smaller the ID / IG ratio, the higher the degree of graphitization and the fewer structural defects in the carbon nanotubes.

[0060] Interface compatibility test: Carbon nanotube samples and epoxy resin were mixed at a mass ratio of 1:100 to prepare composite materials. The tensile strength of the composite materials was tested, and the tensile strength improvement rate was calculated based on the tensile strength of pure epoxy resin.

[0061] Table 1. Performance test results of carbon nanotubes

[0062] As shown in Table 1, the carbon nanotubes of Examples 1 to 3 exhibit excellent performance. Regarding aqueous dispersibility, the dispersion rates of Examples 1 to 3 reached 90.8% to 93.2%, indicating that the synergistic modification by the chitosan-based modified liquid and the re-milling agent effectively inhibited the aggregation of carbon nanotubes, endowing them with good hydrophilicity and dispersion stability. Comparative Example 1, without any modification treatment, had a dispersion rate of only 22.6%, indicating that the original carbon nanotube surface was highly hydrophobic and prone to aggregation. Comparative Example 2, treated only with the modified liquid but without ball milling modification, had a dispersion rate of 85.3%, which, while higher than the unmodified sample, was lower than the examples, indicating that ball milling modification with the re-milling agent plays an important role in further improving dispersibility. Comparative Example 3, treated only with ball milling modification but without modified liquid treatment, had a dispersion rate of 68.5%, significantly lower than the examples, indicating that modified liquid treatment is a fundamental step in constructing the functional layer on the surface of carbon nanotubes.

[0063] Regarding thermal stability, the initial decomposition temperature (Td) of Examples 1 to 3 was 562°C to 572°C, and the residual carbon rate at 800°C was 50.8% to 53.6%. In contrast, the Td of Comparative Example 1 was only 498°C, with a residual carbon rate of 38.2%, indicating that the original carbon nanotubes had numerous surface defects and poor thermal stability. The Tds of Comparative Examples 2 and 3 were 532°C and 518°C, respectively, both lower than those of the examples, demonstrating that the synergistic effect of the modified liquid treatment and ball milling modification is necessary to maximize the improvement of the thermal stability of the carbon nanotubes. Comparative Example 4 did not contain nano-titanium dioxide or yttrium oxide in its modified liquid, and the silicon carbide whiskers in the re-grinding agent of Comparative Example 5 were not modified with dopamine hydrochloride; their thermal stability was lower than that of the examples, demonstrating that the functionalization effect of inorganic nanoparticles and the interface optimization effect of dopamine modification make significant contributions to the improvement of thermal stability.

[0064] Regarding conductivity, the conductivity of Examples 1 to 3 reached 152 to 165 S / cm, far superior to 85 S / cm of Comparative Example 1. The conductivity of Comparative Examples 2 and 3 were 132 and 118 S / cm, respectively, both lower than those of Examples 1 and 3, indicating that only a complete two-step modification process can achieve optimal conductivity of carbon nanotubes. It is worth noting that chitosan itself is an insulating polymer, which theoretically would reduce the conductivity of carbon nanotubes. However, because the chitosan coating on the surface of carbon nanotubes is a discontinuous island-like distribution rather than a complete insulating layer, and the introduction of nano-titanium dioxide and yttrium oxide provides additional conductive channels, the conductivity of the modified carbon nanotubes is actually improved.

[0065] Regarding structural order, the ID / IG ratios of Examples 1 to 3 were 0.48 to 0.56, significantly lower than the 0.85 of Comparative Example 1. The decrease in the ID / IG ratio indicates that the graphitization degree of carbon nanotubes is improved and structural defects are reduced. The ID / IG ratios of Comparative Examples 2 to 5 were 0.68 to 0.74, all higher than those of Examples 1 and 2, indicating that the synergistic modification process of the present invention effectively repairs some structural defects on the surface of carbon nanotubes and improves their structural order.

[0066] Regarding interfacial compatibility, the tensile strength improvement rates of the composite materials in Examples 1 to 3 ranged from 36.2% to 40.1%, significantly higher than the 6.8% improvement rate of Comparative Example 1. The tensile strength improvement rates of Comparative Examples 2 to 5 were 22.5%, 16.3%, 18.6%, and 15.2%, respectively, all significantly lower than those in the Examples. This result demonstrates that the modified carbon nanotubes of this invention form a good interfacial bond with the epoxy resin matrix. The amino and hydroxyl groups on the chitosan layer can chemically react with the epoxy groups of the epoxy resin. The rough surfaces of nano-titanium dioxide and yttrium oxide enhance the mechanical interlocking effect, thereby achieving efficient load transfer and stress dispersion, and thus significantly improving the mechanical properties of the composite material.

[0067] In Comparative Example 4, the modified solution without nano-titanium dioxide and yttrium oxide had a dispersion rate of 78.2% and a Td of 525°C. The strength improvement of the composite material was only 18.6%, both lower than in the example. This demonstrates that the addition of nano-titanium dioxide and yttrium oxide significantly contributes to improving the dispersibility, thermal stability, and interfacial compatibility of carbon nanotubes. In Comparative Example 5, the grinding agent containing silicon carbide whiskers without dopamine hydrochloride modification had a dispersion rate of 72.6% and a Td of 515°C. The strength improvement of the composite material was only 15.2%, lower than in the example. This demonstrates that dopamine hydrochloride modification plays a crucial role in enhancing the interfacial interaction between silicon carbide whiskers and carbon nanotubes, as well as the ball milling modification effect.

[0068] Based on the above test indicators, the modified carbon nanotubes in Examples 1 to 3 are significantly superior to the comparative examples in terms of dispersion, thermal stability, electrical conductivity, structural order, and interfacial compatibility, fully demonstrating the effectiveness and inventiveness of the technical solution of this invention. The comparative data also clearly show that the three steps—natural gas-based chemical vapor deposition growth, chitosan-based modified liquid treatment, and ball milling modification treatment with a grinding agent—have an inseparable synergistic relationship; the absence of any step or any key component will lead to a significant decrease in the overall performance of the carbon nanotubes.

[0069] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

[0070] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A carbon nanotube, characterized in that, The carbon nanotubes are grown using natural gas as a carbon source by chemical vapor deposition and then undergo modification treatment, which includes modification liquid treatment and ball milling treatment with a refining agent.

2. The carbon nanotube according to claim 1, characterized in that, The process conditions for the chemical vapor deposition method are as follows: the catalyst is at least one of iron, cobalt or nickel, the catalyst is supported on an alumina or magnesium oxide support, the reaction temperature is 600-900℃, the natural gas flow rate is 100-500 mL / min, and the reaction time is 30-120 min.

3. The carbon nanotube according to claim 1, characterized in that, The modified solution is prepared as follows: chitosan is dissolved in an aqueous solution of acetic acid with a mass fraction of 1% to 5%, the mass fraction of chitosan is 1% to 10%, nano-titanium dioxide and yttrium oxide are added, the weight ratio of nano-titanium dioxide to yttrium oxide is 2:1 to 5:1, and the total amount of nano-titanium dioxide and yttrium oxide added is 10% to 40% of the mass of chitosan. The mixture is stirred at 300 to 600 r / min for 1 to 4 h at 40 to 80 °C to obtain the modified solution.

4. The carbon nanotube according to claim 3, characterized in that, The nano-titanium dioxide has a particle size of 10–80 nm, the yttrium oxide has a particle size of 10–100 nm, and the chitosan has a degree of deacetylation ≥90%.

5. The carbon nanotube according to claim 1, characterized in that, The modified silicon carbide whisker solution is prepared by adding silicon carbide whiskers to a 0.5%–2% (w / w) dopamine hydrochloride solution with a pH of 8.0–9.0, stirring and reacting at 25–40°C for 12–24 h, then adding boron nitride with a weight ratio of boron nitride to silicon carbide whiskers of 1:2–1:5, and continuing to stir and react for 2–6 h to obtain the modified silicon carbide whisker solution.

6. The carbon nanotube according to claim 5, characterized in that, The silicon carbide whiskers have a diameter of 0.5–3 μm and an aspect ratio of 10:1–50:1; the boron nitride is hexagonal boron nitride with a particle size of 1–15 μm.

7. The carbon nanotube according to claim 1, characterized in that, The preparation method of the re-grinding agent is as follows: the modified silicon carbide whisker liquid is dried at 80-120℃ for 12-24 h, and then ground through a 200-mesh sieve to obtain the re-grinding agent.

8. A method for preparing carbon nanotubes as described in any one of claims 1 to 7, characterized in that, Includes the following steps: Step 1: Chemical vapor deposition growth of carbon nanotubes: The catalyst is placed in a reactor and heated to 600-900℃ under inert gas protection. Natural gas is introduced as a carbon source at a flow rate of 100-500 mL / min. The reaction time is 30-120 min. After the reaction is completed, the mixture is cooled to room temperature in an inert atmosphere to obtain crude carbon nanotubes. Step 2, purification treatment: The crude carbon nanotube product is added to acid solution and soaked for 2-12 hours. After filtration, washing with water until neutral, and drying, purified carbon nanotubes are obtained. Step 3: Preparation of modified solution: Dissolve chitosan in an aqueous solution of acetic acid with a mass fraction of 1% to 5%, where the mass fraction of chitosan is 1% to 10%. Add nano-titanium dioxide and yttrium oxide, with a weight ratio of nano-titanium dioxide to yttrium oxide of 2:1 to 5:

1. The total amount of nano-titanium dioxide and yttrium oxide added is 10% to 40% of the mass of chitosan. Stir at 300 to 600 r / min for 1 to 4 h at 40 to 80 °C to obtain the modified solution. Step 4: Carbon nanotube modification treatment: Purified carbon nanotubes are added to the modification solution at a mass ratio of 1:5 to 1:

20. The mixture is stirred at 300 to 500 r / min for 2 to 6 h at 40 to 80 °C. After filtration, washing, and drying at 60 to 80 °C, the modified carbon nanotube precursor is obtained. Step 5: Preparation of the re-grinding agent: Add silicon carbide whiskers to a 0.5%–2% (w / w) dopamine hydrochloride solution with a pH of 8.0–9.0, and stir at 25–40°C for 12–24 h. Then add boron nitride at a weight ratio of 1:2 to 1:5 to silicon carbide whiskers and continue stirring for 2–6 h to obtain a modified silicon carbide whisker solution. Dry the modified silicon carbide whisker solution at 80–120°C for 12–24 h, and grind it through a 200-mesh sieve to obtain the re-grinding agent. Step 6: Ball milling modification treatment: Mix the modified carbon nanotube precursor with the re-milling agent at a weight ratio of 1:0.2 to 1:0.8, and ball mill at 200 to 500 r / min for 2 to 6 h. After sieving, the modified carbon nanotubes are obtained.

9. The preparation method according to claim 8, characterized in that, The catalyst mentioned in step one is iron supported on an alumina support, with a weight ratio of iron to alumina of 1:5 to 1:20; the inert gas is nitrogen or argon, with a flow rate of 200 to 800 mL / min; the acid solution mentioned in step two is a hydrochloric acid solution or nitric acid solution with a mass fraction of 10% to 30%.

10. The preparation method according to claim 8, characterized in that, In step four, the mass ratio of carbon nanotubes to the modified liquid is 1:8 to 1:15, the stirring reaction temperature is 50 to 70℃, and the stirring reaction time is 3 to 5 h. In step six, the weight ratio of the modified carbon nanotube precursor to the re-grinding agent is 1:0.3 to 1:0.6, the ball milling speed is 300 to 400 r / min, and the ball milling time is 3 to 5 h.

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