A method for highly selective growth of single-walled carbon nanotubes on a carbon fiber matrix

Abstract

This invention discloses a method for highly selectively growing single-walled carbon nanotubes on a carbon fiber matrix, belonging to the field of carbon nanocomposite material preparation technology. The invention introduces oxygen-containing functional groups into the carbon fiber surface through hydrogen peroxide surface activation treatment to enhance catalyst anchoring ability. Simultaneously, a citric acid-assisted iron-nickel bimetallic catalytic system is employed to regulate the size and dispersion state of the metal catalytic particles through complexation and confinement, thereby forming nanoscale catalytic active centers suitable for single-walled carbon nanotube nucleation. During chemical vapor deposition, highly selective growth of single-walled carbon nanotubes on the carbon fiber surface is achieved through synergistic regulation of hydrogen reduction and methane carbon source pyrolysis conditions, while effectively suppressing the formation of multi-walled carbon nanotubes and amorphous carbon.

Description

Technical Field

[0001] This invention belongs to the field of carbon nanocomposite material preparation technology, and relates to the modification of carbon fiber composite materials, specifically to a method for highly selectively growing single-walled carbon nanotubes on a carbon fiber matrix. Background Technology

[0002] Carbon fibers possess high specific strength, high specific modulus, and excellent fatigue resistance, making them widely used in high-performance structural composite materials. However, carbon fiber surfaces typically exhibit a highly graphitized structure with low surface energy and strong chemical inertness, lacking active sites that can effectively interact with matrix materials or functional components. This results in limited interfacial bonding between carbon fibers and resins or other functional phases, significantly restricting interfacial shear strength and load transfer efficiency. Therefore, structural and chemical regulation of carbon fiber surfaces to construct micro- and nano-scale hierarchical structures is an important approach to improving their interfacial properties.

[0003] The in-situ growth of carbon nanotubes on carbon fiber surfaces using chemical vapor deposition (CVD) to construct multi-scale hierarchical "carbon fiber-carbon nanotube" reinforced structures has become a widely studied technique in recent years. This method can introduce nanoscale reinforcing units while maintaining the continuous structure of carbon fibers, significantly improving interfacial bonding performance through mechanical interlocking and interfacial bridging, and endowing the composite material with excellent electrical conductivity and multifunctional properties. However, existing techniques still have significant shortcomings in the growth of carbon nanotubes on carbon fiber surfaces. First, existing methods more readily generate multi-walled carbon nanotubes (MWCNTs) on carbon fiber surfaces, but these catalyst particles are larger and unevenly distributed, resulting in more structural defects in the obtained carbon nanotubes and making it difficult to achieve selective growth of single-walled carbon nanotubes (SWCNTs). In contrast, single-walled carbon nanotubes have superior electrical properties, higher specific surface area, and stronger interfacial interaction capabilities, but their growth process is more sensitive to the size and distribution of catalyst particles. Typically, the preferential growth of single-walled carbon nanotubes (SHU) is only favorable when the catalyst particles are at the nanoscale (usually a few nanometers or even smaller) and uniformly distributed; larger catalyst particles are more likely to induce the formation of multi-walled carbon nanotubes or amorphous carbon. Therefore, achieving precise control over the size and distribution of catalyst particles is crucial for the selective growth of SHU. Secondly, due to the lack of polar functional groups on the carbon fiber surface, its wettability and adsorption capacity for metal salt catalyst precursors are poor, resulting in catalyst loading on its surface mainly relying on physical adsorption, with limited binding force. During subsequent drying, calcination, or high-temperature growth, the catalyst precursor is prone to migration, aggregation, or even detachment, forming catalyst particles with uneven size distribution, further reducing the nucleation density and growth selectivity of SHU. Thirdly, although bimetallic catalytic systems have potential advantages in regulating carbon nanotube structure, without effective control methods on the carbon fiber surface, bimetallic components are prone to aggregation or uneven distribution, leading to increased catalyst particle size or uncontrolled distribution, which is detrimental to the stable growth of SHU. In addition, some existing technologies often use high growth temperatures or strong acid or strong oxidant treatments to improve catalytic activity or promote carbon nanotube growth. These methods can easily damage the graphite layer structure on the surface of carbon fibers, reduce their bulk mechanical properties, and hinder their application in high-performance structural composite materials. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a method for highly selectively growing single-walled carbon nanotubes on a carbon fiber matrix. This method solves the technical problems in existing technologies, such as uneven catalyst particle size distribution, difficulty in achieving selective growth of single-walled carbon nanotubes on the carbon fiber surface, weak adsorption of catalyst precursors leading to easy aggregation and detachment, difficulty in controlling bimetallic components, and easy damage to the mechanical properties of carbon fiber by high-temperature / strong activation treatment.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: A method for highly selectively growing single-walled carbon nanotubes on a carbon fiber matrix, the method comprising the following steps: Step 1, carbon fiber pretreatment: The carbon fiber bundle is separated and cut into short carbon fibers, which are then subjected to heat treatment and activation treatment in sequence; after the activation treatment is completed, they are washed and dried in sequence to obtain the carbon fiber carrier.

[0006] Step 2, prepare the catalyst solution: Weigh iron salt, nickel salt and organic acid and add solvent to them, stir and prepare the catalyst solution.

[0007] Step 3, Impregnation and curing: The carbon fiber support obtained in Step 1 is impregnated in the catalyst solution prepared in Step 2 under ultrasonic assistance to obtain a carbon fiber support loaded with catalyst; the carbon fiber support loaded with catalyst is dried and calcined in sequence to obtain a carbon fiber matrix.

[0008] Step 4, Chemical Vapor Deposition: The carbon fiber matrix obtained in Step 3 is placed in a protective atmosphere and heated until the growth temperature is reached. Hydrogen gas is first introduced, followed by a carbon source, so that carbon nanotubes grow on the surface of the carbon fiber matrix. Then, it is cooled in a protective atmosphere to obtain a carbon fiber material with single-walled carbon nanotubes grown on it.

[0009] The present invention also has the following technical features: Specifically, in step one, the length of the short carbon fiber is 1 cm.

[0010] Specifically, in step one, the heat treatment conditions are as follows: in a protective atmosphere, the temperature is increased to 450-550°C at a heating rate of 5-10°C / min, and the holding time is 60-120min.

[0011] Specifically, in step one, the protective atmosphere used during the heat treatment is argon, and the flow rate of the protective atmosphere is 200-500 sccm.

[0012] Specifically, in step one, the activation treatment conditions are as follows: the heat-treated short carbon fibers are placed in a 10-20 wt% hydrogen peroxide solution and treated at 60-90°C for 30-90 min.

[0013] Specifically, in step one, the heating method used during the activation treatment is a water bath.

[0014] Specifically, in step one, the drying conditions are as follows: drying at 60–120°C for 12–24 hours.

[0015] Specifically, in step two, the iron salt is selected from one or more of ferric nitrate, ferric acetate, and ferric sulfate; the nickel salt is selected from one or more of nickel nitrate, nickel acetate, and nickel sulfate; the organic acid is selected from one or more of citric acid, succinic acid, and acetic acid; and the solvent is ethanol.

[0016] Specifically, in step two, the molar ratio of the iron salt, nickel salt, and organic acid is 1:1:(1-10).

[0017] Specifically, in step three, the ultrasonic power is 100W and the immersion time is 10-30 minutes.

[0018] Specifically, in step three, the drying conditions are as follows: drying at 60–120°C for 12–24 hours.

[0019] Specifically, in step three, the calcination conditions are as follows: calcination is carried out in an air atmosphere at a temperature of 150–250°C for 2–6 hours.

[0020] Specifically, in step four, the protective atmosphere is argon, and the flow rate of the protective atmosphere is 100-300 sccm.

[0021] Specifically, in step four, the flow rate of the hydrogen gas is 50–200 sccm.

[0022] Specifically, in step four, the carbon source is methane, and the flow rate of the carbon source is 20–70 sccm.

[0023] Specifically, in step four, the heating rate is 5-10℃ / min, the growth temperature is 800-1000℃, and the growth time of single-walled carbon nanotubes is 30-120 min.

[0024] Compared with the prior art, the present invention has the following technical effects: (I) This invention enhances the catalyst anchoring ability by introducing oxygen-containing functional groups into the surface of carbon fibers through hydrogen peroxide surface activation treatment. Simultaneously, a citric acid-assisted iron-nickel bimetallic catalytic system is employed to regulate the size and dispersion state of the metal catalytic particles through complexation and confinement, thereby forming nanoscale catalytic active centers suitable for the nucleation of single-walled carbon nanotubes. During chemical vapor deposition (CVD), the highly selective growth of single-walled carbon nanotubes on the carbon fiber surface is achieved through the synergistic regulation of hydrogen reduction and methane carbon source pyrolysis conditions, while effectively suppressing the formation of multi-walled carbon nanotubes and amorphous carbon.

[0025] (II) The single-walled carbon nanotubes obtained by the present invention are grown in situ on the surface of carbon fibers by catalytic growth to form a uniformly distributed nanostructure. Only single-walled carbon nanotubes are present on the surface of carbon fibers, and no multi-walled carbon nanotubes appear. Their diameter distribution is relatively narrow and they are closely attached to the surface of carbon fibers. They have the characteristics of high structural uniformity and few defects, and form a stable interface bond with the carbon fiber matrix.

[0026] (III) This invention improves the electrical conductivity and interfacial interaction capabilities of the composite material without significantly reducing the mechanical properties of carbon fibers, and achieves the controllable growth of single-walled carbon nanotubes. Therefore, the composite material prepared by this invention has good application prospects in high-performance structure-function integrated composite materials, conductive materials, and related advanced application fields.

[0027] (IV) The uniformity of the catalyst particle size and distribution used in this invention directly determines the structural type of carbon nanotubes. Small and uniformly distributed catalyst particles are conducive to the nucleation and stable growth of single-walled carbon nanotubes, while larger particles are more likely to induce the formation of multi-walled structures. At the same time, through the synergistic effect of organic acid complexation and the active sites on the carbon fiber surface, the catalyst particle size can be effectively controlled, thereby improving the growth selectivity of single-walled carbon nanotubes. Attached Figure Description

[0028] Figure 1 Carbon nanotubes grown on the surface of carbon fibers under the conditions described in Examples 1(c), 2(a), 3(b), and 4(d).

[0029] Figure 2 SEM images of Comparative Example 1 without added citric acid (a) and SEM images of the untreated carbon fiber surface in Comparative Example 1 (b).

[0030] Figure 3 SEM image of single-walled carbon nanotubes (CNT-850) grown in situ on the surface of carbon fiber.

[0031] Figure 4The images show transmission electron microscopy (TEM) images of the obtained carbon nanotubes (CNT-850) and the corresponding diameter distribution statistics.

[0032] Figure 5 This is the Raman spectrum of single-walled carbon nanotubes (CNT-850) on carbon fibers.

[0033] Figure 6 The peaks are RBM characteristic peaks in the Raman spectrum of single-walled carbon nanotubes (CNT-850) on carbon fibers.

[0034] Figure 7 The images are Raman spectra at different temperatures in Examples 5, 6 and 7.

[0035] Figure 8 yes Figure 7 100-300 cm - ¹ Enlarged view.

[0036] The specific content of the present invention will be further explained in detail below with reference to the embodiments. Detailed Implementation

[0037] It should be noted that, unless otherwise specified, all raw materials used in this invention are those known in the art.

[0038] The following are specific embodiments of the present invention. It should be noted that the present invention is not limited to the following specific embodiments. All equivalent modifications made based on the technical solutions of this application fall within the protection scope of the present invention.

[0039] Example 1 This embodiment provides a method for highly selectively growing single-walled carbon nanotubes on a carbon fiber matrix, which specifically includes the following steps: Step 1, Carbon Fiber Pretreatment: The carbon fiber bundle was separated and cut into short carbon fibers approximately 1 cm in length. These were then placed in a quartz tube of a tube furnace and heated to 450°C at a rate of 10°C / min under argon protection at 300 sccm, and held for 120 minutes. The heat-treated short carbon fibers were then placed in a 20 wt% hydrogen peroxide solution and activated at 60°C using a water bath for 90 minutes. Activation was performed to introduce oxygen-containing functional groups such as hydroxyl and carboxyl groups onto the carbon fiber surface, thereby improving its surface energy and adsorption capacity for catalyst precursors, and providing stable anchoring points for uniform catalyst loading. After activation, the carbon fibers were rinsed three times with deionized water and then dried in a forced-air drying oven at 60°C for 24 hours to obtain the carbon fiber support.

[0040] Step 2: Prepare the catalyst solution: Weigh 0.606g of ferric nitrate, 0.436g of nickel nitrate, and 2.52g of citric acid (the molar ratio of ferric nitrate, nickel nitrate, and citric acid is 1:1:8). Place the above raw materials in a beaker, add 20mL of ethanol, and then stir with a magnetic stirrer for 30min to obtain the catalyst solution. The organic acid in the catalyst solution is used to complex the metal ions, which will regulate the dispersion state of the catalyst precursor on the carbon fiber surface in subsequent steps and inhibit catalyst particle agglomeration.

[0041] Step 3, Impregnation and Curing: The carbon fibers obtained in Step 1 are impregnated in the catalyst solution prepared in Step 2 for 30 minutes under ultrasonic assistance (ultrasonic power 100W, impregnation time 10-30 minutes) to ensure uniform distribution and loading of the catalyst precursor onto the carbon fiber support surface, resulting in a catalyst-loaded carbon fiber support. The catalyst-loaded carbon fiber support is then dried in a forced-air drying oven at 60°C for 24 hours. Subsequently, it is calcined in air using a muffle furnace at 200°C for 2 hours to obtain the carbon fiber matrix. In this step, the catalyst precursor is gradually decomposed and transformed into nanoscale bimetallic catalytic particles through heat treatment. The size distribution of these particles is synergistically regulated by organic acid complexation and the active sites on the carbon fiber surface.

[0042] Step four, chemical vapor deposition: The carbon fiber matrix obtained in step three is placed in a tube furnace. First, inert argon gas is introduced into the furnace to purge the air from the tubes. Then, the argon flow rate is adjusted to 200 sccm, and the temperature is increased at a rate of 5℃ / min until the growth temperature of 850℃ is reached. Next, reducing gas hydrogen is introduced at a flow rate of 50 sccm, followed by methane at a flow rate of 25 sccm. This allows for the selective growth of single-walled carbon nanotubes (SUVs) on the carbon fiber matrix surface. The growth time for SUVs is 60 min. The furnace is then cooled to room temperature under argon protection to obtain carbon fiber material with SUVs grown on it. This product is designated CNT-850. This step achieves preferential growth of SUVs by controlling the catalyst particle size to a nanoscale range suitable for SUV nucleation, combined with the synergistic regulation of the reaction atmosphere and carbon source supply conditions, while effectively suppressing the formation of multi-walled carbon nanotubes and amorphous carbon.

[0043] Example 2 This embodiment provides a method for highly selectively growing single-walled carbon nanotubes on a carbon fiber matrix. The method is basically the same as that in Embodiment 1, except that in step two of this embodiment, the molar ratio of ferric nitrate, nickel nitrate and citric acid is 1:1:0.

[0044] Example 3 This embodiment provides a method for highly selectively growing single-walled carbon nanotubes on a carbon fiber matrix. The method is basically the same as that in Embodiment 1, except that in step two of this embodiment, the molar ratio of ferric nitrate, nickel nitrate and citric acid is 1:1:1.

[0045] Example 4 This embodiment provides a method for highly selectively growing single-walled carbon nanotubes on a carbon fiber matrix. The method is basically the same as that in Embodiment 1, except that in step two of this embodiment, the molar ratio of ferric nitrate, nickel nitrate and citric acid is 1:1:10.

[0046] Example 5 This embodiment provides a method for highly selectively growing single-walled carbon nanotubes on a carbon fiber matrix. The method is basically the same as that in Embodiment 1, except that in step four of this embodiment, the temperature for CVD growth of single-walled carbon nanotubes is 800℃.

[0047] Example 6 This embodiment provides a method for highly selectively growing single-walled carbon nanotubes on a carbon fiber matrix. The method is basically the same as that in Embodiment 1, except that in step four of this embodiment, the temperature for CVD growth of single-walled carbon nanotubes is 900℃.

[0048] Example 7 This embodiment provides a method for highly selectively growing single-walled carbon nanotubes on a carbon fiber matrix. The method is basically the same as that in Embodiment 1, except that in step four of this embodiment, the temperature for CVD growth of single-walled carbon nanotubes is 1000℃.

[0049] Comparative Example 1 This comparative example provides a method for highly selectively growing single-walled carbon nanotubes on a carbon fiber matrix. The method is basically the same as that in Example 1, except that citric acid is not added when preparing the catalyst solution in step two of this comparative example.

[0050] In this comparative example, step two is as follows: Weigh 0.606 g of ferric nitrate and 0.436 g of nickel nitrate, place the above raw materials in a beaker, add 20 mL of ethanol, and then stir with a magnetic stirrer for 30 min to obtain a catalyst solution. The molar ratio of ferric nitrate to nickel nitrate is 1:1.

[0051] Comparative Example 2 This comparative example provides a method for highly selectively growing single-walled carbon nanotubes on a carbon fiber matrix. The method is basically the same as that in Example 1, except that the short carbon fibers were not activated in step one of this comparative example.

[0052] The product characterization and performance of the embodiments are as follows: (1) Analysis of microscopic morphology and structural evolution (see Figure 1 , Figure 2 , Figure 3 ): Figure 1 These are carbon nanotubes grown on the surface of carbon fibers under the conditions described in Examples 1, 2, 3, and 4. Figure 1 (a) is an SEM image of the sample from Example 2. It can be seen that, due to the absence of citric acid, the carbon nanotubes on the carbon fiber are multi-walled carbon nanotubes. Figure 1 (b) is an SEM image of the sample from Example 3. It can be seen that when the amount of citric acid added is small, the catalyst distribution is uneven and there are very few single-walled carbon nanotubes. Figure 1 (c) is an SEM image of the sample from Example 1. It can be seen that only single-walled carbon nanotubes grew on the carbon fibers in Example 1, demonstrating the high selectivity of the method. Furthermore, the diameter distribution is uniform, approximately 1–2 nm. Figure 1 (d) is a SEM image of the sample in Example 4. Due to excessive citric acid, the catalyst is difficult to adhere to the carbon fiber surface, resulting in sparse growth of single-walled carbon nanotubes.

[0053] Figure 2 (a) is a SEM image of Comparative Example 1 without the addition of citric acid. It can be seen that the catalyst is severely enriched and the particle size is large in the sample without the addition of citric acid. Figure 2 (b) is a SEM image of the untreated carbon fiber surface in Comparative Example 1, which shows that the surface is smooth.

[0054] Figure 3 The surface morphology of the treated carbon fibers is shown. The treated carbon fiber surface forms a certain degree of roughness, and the surface activity is significantly improved, which is conducive to the adsorption and fixation of catalyst precursors; while the untreated carbon fiber surface is relatively smooth, its adsorption capacity for catalyst precursors is weak, and the distribution of the supported layer is uneven.

[0055] (2) Internal structure and interface analysis (see Figure 4 ): Combination Figure 4 TEM images further confirmed that under these conditions, the formation of numerous tubular nanostructures on the carbon fiber surface exhibits single-walled structure characteristics, with small diameters and concentrated distribution. Under suitable temperature and atmosphere conditions, small-sized and uniformly distributed catalytic particles can preferentially induce the nucleation and growth of single-walled carbon nanotubes; when the temperature is too high, the catalytic particles are prone to agglomeration, leading to the formation of multi-walled carbon nanotubes or amorphous carbon, thus reducing the selectivity of single-walled carbon nanotubes.

[0056] (3) Phase composition and defect analysis (see Figure 5 , Figure 6 , Figure 7 , Figure 8 ): Figure 5 The Raman spectra in the sample showed that the CNT-850 sample had obvious RBM characteristic peaks of single-walled carbon nanotubes, which also proved the successful synthesis of single-walled carbon nanotubes. Figure 6 The magnified Raman spectrum in the image shows that the Raman spectrum is located at 100-300 cm⁻¹. - A distinct RBM characteristic peak appeared between ¹ and 233 cm⁻¹, with the peak position at 233 cm⁻¹. -1 The empirical formula ωRBM = A / d + B is used, where A is a constant (commonly 227–248 cm in the literature). - ¹·nm), B≈0~15cm -1 It is known that the diameter of carbon nanotubes is approximately 1 nm. And... Figure 7 These are the Raman spectra at different temperatures in Examples 5, 6, and 7. Figure 8 yes Figure 7 100-300cm - The magnified image¹ shows that changing the growth temperature of single-walled carbon nanotubes alters the RBM peak position. At lower temperatures, the RBM peak position is in the low wavenumber region, indicating a larger single-walled tube diameter. In the high-temperature region, the RBM peak position exhibits a red shift, indicating a decrease in the single-walled tube diameter. This is compared to the optimal temperature of 850℃. Figure 5 For the medium-sized sample, the RBM peaks at other temperatures were broader and had lower intensities, indicating that 850℃ is the optimal growth temperature.

Claims

1. A method for highly selectively growing single-walled carbon nanotubes on a carbon fiber matrix, characterized in that, The method includes the following steps: Step 1, carbon fiber pretreatment: The carbon fiber bundle is separated and cut into short carbon fibers, which are then subjected to heat treatment and activation treatment in sequence; after activation treatment, they are washed and dried in sequence to obtain carbon fiber carrier; Step 2, preparing the catalyst solution: Weigh out iron salt, nickel salt and organic acid, add solvent to them, and stir to obtain the catalyst solution; Step 3, Impregnation and curing: The carbon fiber support obtained in Step 1 is impregnated in the catalyst solution prepared in Step 2 under ultrasonic assistance to obtain a carbon fiber support loaded with catalyst; the carbon fiber support loaded with catalyst is dried and calcined in sequence to obtain a carbon fiber matrix. Step 4, Chemical Vapor Deposition: The carbon fiber matrix obtained in Step 3 is placed in a protective atmosphere and heated until the growth temperature is reached. Hydrogen gas is first introduced, followed by a carbon source, so that carbon nanotubes grow on the surface of the carbon fiber matrix. Then, it is cooled in a protective atmosphere to obtain a carbon fiber material with single-walled carbon nanotubes grown on it.

2. The method for highly selectively growing single-walled carbon nanotubes on a carbon fiber matrix as described in claim 1, characterized in that, In step one, the heat treatment conditions are as follows: in a protective atmosphere, the temperature is increased to 450-550°C at a heating rate of 5-10°C / min, and the holding time is 60-120min.

3. The method for highly selectively growing single-walled carbon nanotubes on a carbon fiber matrix as described in claim 1, characterized in that, In step one, the activation treatment conditions are as follows: the heat-treated short carbon fibers are placed in a 10-20 wt% hydrogen peroxide solution and treated at 60-90°C for 30-90 min.

4. The method for highly selectively growing single-walled carbon nanotubes on a carbon fiber matrix as described in claim 1, characterized in that, In step two, the iron salt is selected from one or more of ferric nitrate, ferric acetate, and ferric sulfate; the nickel salt is selected from one or more of nickel nitrate, nickel acetate, and nickel sulfate; the organic acid is selected from one or more of citric acid, succinic acid, and acetic acid; and the solvent is ethanol.

5. The method for highly selectively growing single-walled carbon nanotubes on a carbon fiber matrix as described in claim 1, characterized in that, In step two, the molar ratio of the iron salt, nickel salt and organic acid is 1:1:(1-10).

6. The method for highly selectively growing single-walled carbon nanotubes on a carbon fiber matrix as described in claim 1, characterized in that, In step three, the ultrasonic power is 100W and the immersion time is 10-30 minutes.

7. The method for highly selectively growing single-walled carbon nanotubes on a carbon fiber matrix as described in claim 1, characterized in that, In step three, the calcination conditions are as follows: calcination is carried out in an air atmosphere at a temperature of 150–250°C for 2–6 hours.

8. The method for highly selectively growing single-walled carbon nanotubes on a carbon fiber matrix as described in claim 1, characterized in that, In step four, the carbon source is methane, and the flow rate of the carbon source is 20–70 sccm.

9. The method for highly selectively growing single-walled carbon nanotubes on a carbon fiber matrix as described in claim 1, characterized in that, In step four, the heating rate is 5–10 °C / min, the growth temperature is 800–1000 °C, and the growth time of the single-walled carbon nanotubes is 30–120 min.

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