A method for preparing highly branched carbon nanotubes

Abstract

This invention proposes a method for preparing highly branched carbon nanotubes. The specific steps are as follows: First, polydopamine is coated onto the surface of carbon nanotubes, then dispersed in an organic solvent. Next, a ligand-coated colloidal nanocrystal solution is added, and the nanocrystals are loaded onto the surface of the carbon nanotubes using ultrasonic loading. Finally, secondary carbon nanotubes are grown through high-temperature carbonization and chemical vapor deposition, completing the preparation of highly branched carbon nanotubes. This invention uses ligand-coated colloidal nanocrystals as a catalyst for the growth of secondary carbon nanotubes. Coating the carbon nanotube surface with polydopamine modifies its surface, utilizing the abundant functional groups of polydopamine to enhance its binding ability with the colloidal nanocrystals. High-temperature carbonization anchors the colloidal nanocrystals to the carbon nanotube surface. This method effectively improves catalyst efficiency and can be used for the mass production of densely branched carbon nanotubes with high structural uniformity.

Description

Technical Field

[0001] This invention belongs to the field of materials preparation and nanotechnology, and specifically relates to a method for preparing highly branched carbon nanotubes. Background Technology

[0002] Carbon nanotubes have attracted widespread attention in the field of nanotechnology due to their excellent electrical conductivity and superior mechanical strength. These properties enable their widespread application in energy storage, catalysis, and sensors. However, traditional carbon nanotubes also have some problems that limit their practical applications. One major problem is that carbon nanotubes tend to aggregate, reducing the effective surface area and making it difficult for electrolyte ions to enter the active sites. In addition, pristine carbon nanotubes often lack sufficient active sites for certain electrochemical reactions, thus limiting their catalytic activity.

[0003] To overcome these drawbacks, the development of branched carbon nanotubes has become a promising solution. Branched carbon nanotubes possess a multi-level structure, consisting of a basic carbon nanotube framework and numerous secondary branched carbon nanotubes. This unique structure offers the following advantages compared to traditional carbon nanotubes: First, the branched structure of branched carbon nanotubes helps alleviate the aggregation problem commonly found in virgin carbon nanotubes. This improves the dispersibility of carbon nanotubes and the accessibility of electrolyte ions. Second, the unique structure of branched carbon nanotubes provides a larger specific surface area, offering more active sites for electrochemical reactions.

[0004] Despite the numerous advantages of branched carbon nanotubes (CNTs), their fabrication and practical applications currently face several obstacles. A major challenge lies in the loading efficiency of catalysts for secondary carbon nanotube growth. For example, loading metal nanoparticles as catalysts using atomic layer deposition (ALD) often requires multiple repetitions to achieve the desired metal particle size. Furthermore, the inherent inert surface properties of virgin carbon nanotubes limit the loading density of metal nanoparticles, leading to a sparse distribution of branched carbon nanotubes. The irregular distribution and uneven diameter of secondary carbon nanotubes further reduce the material's uniformity and stability. Moreover, existing hydrothermal methods for introducing metal-organic frameworks as catalysts have limitations in scaling up production. Therefore, improving the inert surface of virgin carbon nanotubes to achieve efficient catalyst loading, and realizing highly branched and structurally uniform branched carbon nanotubes in mass production, remain significant challenges in this field. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing highly branched carbon nanotubes. The technical solution adopted by this invention is as follows: First, polydopamine is coated on the surface of carbon nanotubes, then dispersed in an organic solvent, and then a solution of ligand-coated metal oxide nanoparticles is added to it. Nanocrystals are loaded onto the surface of carbon nanotubes by ultrasonic loading. Finally, secondary carbon nanotubes are grown through high-temperature carbonization and chemical vapor deposition processes, thus completing the preparation of highly branched carbon nanotubes.

[0006] The present invention proposes a method for preparing highly branched carbon nanotubes, the specific steps of which are as follows:

[0007] (1) 20 mg-1 g of carbon nanotubes were dispersed in a mixed solution of water and ethanol, then dopamine hydrochloride was added and stirred for 5 minutes, followed by the addition of trihydroxyaminomethane buffer and stirring at room temperature for 12 hours. After the reaction was completed, the sample was washed with water and ethanol until the pH of the filtrate was neutral. After drying, polydopamine-coated carbon nanotube powder was obtained; the amount of dopamine hydrochloride added was 10 mg-0.5 g.

[0008] (2) Disperse 20 mg-1 g of polydopamine-coated carbon nanotubes in 10-100 mL of organic solvent and disperse by ultrasonication to obtain a dispersion system containing carbon nanotubes.

[0009] (3) Add 0.08-4 mL of 50 mg / mL ligand-coated metal oxide nanoparticle solution to the dispersion system containing carbon nanotubes in step (2), and sonicate for 10-30 minutes.

[0010] (4) Remove free nanoparticles by centrifugation, collect and dry the precipitate, and then place it in a tube furnace for heat treatment in an inert atmosphere (N2 / Ar) at a heating rate of 2 ℃ / min. The heat treatment temperature is 500℃.

[0011] (5) Place the product obtained in step (4) downstream of a tube furnace and place 0.1-5 g of carbon source upstream. Heat the furnace to 800°C at a heating rate of 10°C / min and hold for 3 hours before slowly cooling down.

[0012] In this invention, in step (1), tris(hydroxymethyl)aminomethane buffer is added to control the pH value of the solution to 8.5.

[0013] In this invention, the organic solvent mentioned in step (2) is n-hexane.

[0014] In this invention, the ligands in step (3) are oleic acid and oleylamine.

[0015] In this invention, the metal oxide nanoparticles in step (3) are NiFe2O4 nanoparticles.

[0016] In this invention, the carbon source mentioned in step (5) is dicyandiamide.

[0017] In this invention, during the process of heating to 800°C in step (5), an H2 / Ar mixed atmosphere is introduced before 700°C, and an inert atmosphere (N2 / Ar) is introduced after 700°C.

[0018] The beneficial effects of this invention are as follows: This invention uses ligand-coated colloidal nanocrystals as a catalyst for the growth of secondary carbon nanotubes. Polydopamine is coated onto the surface of the carbon nanotubes for surface modification. The abundant functional groups of polydopamine enhance the binding ability with the colloidal nanocrystals. High-temperature carbonization anchors the colloidal nanocrystals to the carbon nanotube surface. This invention effectively improves the inert surface of carbon nanotubes, increases the catalyst loading efficiency, and enables the mass production of branched carbon nanotubes with dense branching and high structural uniformity. Attached Figure Description

[0019] Figure 1 This is a scanning electron microscope image of the highly branched carbon nanotubes prepared in Example 1 of the present invention.

[0020] Figure 2 This is a scanning electron microscope image of the highly branched carbon nanotubes prepared in Example 2 of the present invention.

[0021] Figure 3 This is a scanning electron microscope image of the highly branched carbon nanotubes prepared in Example 3 of the present invention. Detailed Implementation Example 1

[0022] (1) 20 mg of carbon nanotubes were dispersed in a mixture of water and ethanol, followed by the addition of 10 mg of dopamine hydrochloride and stirring for 5 minutes. Then, trihydroxyaminomethane buffer was added and stirred at room temperature for 12 hours. After the reaction was completed, water and ethanol were added to wash until the pH was neutral. After drying, polydopamine-coated carbon nanotube powder was obtained.

[0023] (2) 20 mg of polydopamine-coated carbon nanotubes were dispersed in 10 mL of n-hexane by ultrasonic dispersion;

[0024] (3) Add 0.08 mL of 50 mg / mL NiFe2O4 nanoparticle solution coated with oleic acid and oleylamine to the dispersion system containing carbon nanotubes in step (2), and sonicate for 10 minutes;

[0025] (4) Remove free nanoparticles by centrifugation, collect and dry the precipitate, and then place it in a tube furnace for heat treatment in an inert atmosphere (N2 / Ar) at a heating rate of 2 ℃ / min. The heat treatment temperature is 500℃.

[0026] (5) Place the product obtained in step (4) downstream of a tube furnace, place 0.1 g of carbon source upstream, heat to 800°C at a heating rate of 10°C / min, hold for 3 hours and then slowly cool down.

[0027] Figure 1 This is a scanning electron microscope image of the highly branched carbon nanotubes prepared in Example 1 of the present invention. It can be seen that densely branched carbon nanotubes are grown on the surface of the initial carbon nanotubes, and the secondary carbon nanotubes are evenly distributed on the initial carbon nanotube framework with basically the same diameter and an average length of about 500 nm. Example 2

[0028] (1) 500 mg of carbon nanotubes were dispersed in a mixture of water and ethanol, followed by the addition of 250 mg of dopamine hydrochloride and stirring for 5 minutes. Then, trihydroxyaminomethane buffer was added and stirred at room temperature for 12 hours. After the reaction was completed, water and ethanol were added to wash until the pH was neutral. After drying, polydopamine-coated carbon nanotube powder was obtained.

[0029] (2) 500 mg of polydopamine-coated carbon nanotubes were dispersed in 50 mL of n-hexane by ultrasonic dispersion;

[0030] (3) Add 2 mL of 50 mg / mL NiFe2O4 nanoparticle solution coated with oleic acid and oleylamine to the dispersion system containing carbon nanotubes in step (2) and sonicate for 20 minutes.

[0031] (4) Remove free nanoparticles by centrifugation, collect and dry the precipitate, and then place it in a tube furnace for heat treatment in an inert atmosphere (N2 / Ar) at a heating rate of 2 ℃ / min. The heat treatment temperature is 500℃.

[0032] (5) Place the product obtained in step (4) downstream of a tube furnace, place 2.5 g of carbon source upstream, heat to 800°C at a heating rate of 10°C / min, hold for 3 hours and then slowly cool down.

[0033] Figure 2 This is a scanning electron microscope image of the highly branched carbon nanotubes prepared in Example 2 of the present invention. It can be seen that densely branched carbon nanotubes are grown on the surface of the initial carbon nanotubes, and the secondary carbon nanotubes are evenly distributed on the initial carbon nanotube framework with basically the same diameter and an average length of about 300 nm. Example 3

[0034] (1) 1 g of carbon nanotubes were dispersed in a mixture of water and ethanol, followed by the addition of 500 mg of dopamine hydrochloride and stirring for 5 minutes. Then, trihydroxyaminomethane buffer was added and stirred at room temperature for 12 hours. After the reaction was completed, water and ethanol were added to wash until the pH was neutral. After drying, polydopamine-coated carbon nanotube powder was obtained.

[0035] (2) 1 g of polydopamine-coated carbon nanotubes were dispersed in 100 mL of n-hexane by ultrasonic dispersion;

[0036] (3) Add 4 mL of 50 mg / mL NiFe2O4 nanoparticle solution coated with oleic acid and oleylamine to the dispersion system containing carbon nanotubes in step (2), and sonicate for 30 minutes.

[0037] (4) Remove free nanoparticles by centrifugation, collect and dry the precipitate, and then place it in a tube furnace for heat treatment in an inert atmosphere (N2 / Ar) at a heating rate of 2 ℃ / min. The heat treatment temperature is 500℃.

[0038] (5) Place the product obtained in step (4) downstream of a tube furnace, place 5 g of carbon source upstream, heat to 800°C at a heating rate of 10°C / min, hold for 3 hours and then slowly cool down.

[0039] Figure 3 This is a scanning electron microscope image of the highly branched carbon nanotubes prepared in Example 3 of the present invention. It can be seen that densely branched carbon nanotubes are grown on the surface of the initial carbon nanotubes, and the secondary carbon nanotubes are evenly distributed on the initial carbon nanotube framework with basically the same diameter and an average length of about 300 nm.

Claims

1. A method for preparing highly branched carbon nanotubes, characterized in that, The specific steps are as follows: (1) 20 mg-1 g of carbon nanotubes were dispersed in a mixed solution of water and ethanol, then dopamine hydrochloride was added and stirred for 5 minutes, followed by the addition of trihydroxyaminomethane buffer and stirring at room temperature for 12 hours. After the reaction was completed, the sample was washed with water and ethanol until the pH of the filtrate was neutral. After drying, polydopamine-coated carbon nanotube powder was obtained. The amount of dopamine hydrochloride added was 10 mg-0.5 g. (2) Disperse 20 mg-1 g of polydopamine-coated carbon nanotube powder into 10-100 mL of organic solvent and disperse by ultrasonication to obtain a dispersion system containing carbon nanotubes. (3) Add 0.08-4 mL of 50 mg / mL ligand-coated metal oxide nanoparticle solution to the dispersion system containing carbon nanotubes in step (2), and sonicate for 10-30 minutes; the ligand is oleic acid and oleylamine; the metal oxide nanoparticle is NiFe2O4 nanoparticle; (4) Remove free nanoparticles by centrifugation, collect and dry the precipitate, and then place it in a tube furnace for heat treatment in an inert N2 / Ar atmosphere at a heating rate of 2℃ / min. The heat treatment temperature is 500℃. (5) Place the product obtained in step (4) downstream of a tube furnace and place 0.1-5 g of carbon source upstream. Heat the furnace to 800°C at a heating rate of 10°C / min and hold for 3 hours before slowly cooling down.

2. The method for preparing highly branched carbon nanotubes according to claim 1, characterized in that, In step (1), add tris(hydroxymethyl)aminomethane buffer solution to control the pH of the solution to 8.

5.

3. The method for preparing highly branched carbon nanotubes according to claim 1, characterized in that, The organic solvent mentioned in step (2) is n-hexane.

4. The method for preparing highly branched carbon nanotubes according to claim 1, characterized in that, The carbon source mentioned in step (5) is dicyandiamide.

5. The method for preparing highly branched carbon nanotubes according to claim 1, characterized in that, During the process of raising the temperature to 800°C in step (5), an H2 / Ar mixed atmosphere is introduced before 700°C, and an N2 / Ar inert atmosphere is introduced after 700°C.

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