A method for preparing a welded carbon nanotube@hexagonal boron nitride coaxial heterostructure

Abstract

The present application relates to controllable preparation of nanocarbon composite material, and particularly to a method for preparing a welded carbon nanotube@hexagonal boron nitride coaxial heterostructure. A carbon nanotube network is used as a template, and the volatilization amount of boron and nitrogen precursors is controlled during a normal pressure chemical vapor deposition process, so that an amorphous boron nitride welding structure is first grown at the network lap joint, and then hexagonal boron nitride is grown on the surface of the carbon nanotube and the amorphous welding structure, to obtain a welded carbon nanotube@hexagonal boron nitride coaxial hetero-network structure. By changing the volatilization temperature of the boron and nitrogen precursors and the chemical vapor deposition conditions, the microstructure (crystallinity, layer number, curling degree, etc.) of the amorphous welding structure and the coated hexagonal boron nitride is regulated. The welded coated structure can be directly used to construct a film, a fiber, a sponge and other macroscopic bodies, the welding structure at the lap joint in the network can enhance the binding force between carbon nanotube bundles, improve the mechanical properties of the film, and reduce the phonon scattering at the contact, thereby enhancing the heat conduction capacity of the network.

Description

Technical Field

[0001] This invention relates to the field of controllable preparation of nano-carbon composite materials, specifically a method for preparing welded carbon nanotube@hexagonal boron nitride coaxial heterostructures. Background Technology

[0002] Carbon nanotubes can be viewed as quasi-one-dimensional hollow tubular materials formed by rolling up graphene, possessing excellent physicochemical properties. Carbon nanotubes simultaneously exhibit chemical stability, lightweight, high electrical conductivity, and flexibility; in particular, the thermal conductivity of a single-walled carbon nanotube reaches as high as 3500 W·m. -1 K -1 Carbon nanotubes are an ideal candidate for next-generation thermal management materials, especially with broad application prospects in the field of heat dissipation for nanoelectronic devices. When applying nanoscale carbon nanotubes to the field of thermal management, they generally need to be constructed into macroscopic carbon nanotube bodies (such as thin films, vertical arrays, fibers, etc.). However, after being constructed into macroscopic bodies, their thermal conductivity decreases exponentially, which seriously restricts their application in thermal management.

[0003] Hexagonal boron nitride is a poly(phosphoric acid) compound with properties similar to graphene. 2 Materials with atomic hybrid structures also exhibit good thermal conductivity (400 W·m). -1 K -1 Furthermore, its thermal and chemical stability is superior to that of graphene. Previous studies have shown that combining hexagonal boron nitride with carbon nanotubes is an effective method for constructing high thermal conductivity composite materials. Researchers designed and synthesized a carbon nanotube@hexagonal boron nitride composite structure, in which hexagonal boron nitride serves as a thermally stable chemically inert protective layer at high temperatures and provides additional axial thermal conduction channels for the carbon nanotubes, thereby improving the thermal conductivity of the carbon nanotube composite structure.

[0004] Some progress has been made in the preparation methods and thermal conductivity studies of carbon nanotube@hexagonal boron nitride composite structures. For example, Jing et al. used boric acid and ammonia as boron and nitrogen sources, respectively, and a vertical carbon nanotube array as a template to grow coaxial heterogeneous carbon nanotube@boron nitride nanotube arrays in the gas phase. The compressive strength of the array was four times higher than that of the initial vertical carbon nanotube array, and the thermal conductivity was increased by 90%. Moreover, the array could still recover its original shape after being subjected to large strain. (Reference 1: L Jing, R Tay, H Li. et al. Nanoscale 2016, 8, 11114; Reference 2: L Jing, M Samani, B Liu. et al. ACS Appl. Mater. Interfaces) 2017, 9, 14555); Wang et al. used ammonia borane as boron and nitrogen precursors and single-walled carbon nanotube networks as templates to grow single-walled carbon nanotube@boron nitride nanotube heterostructures by low-pressure chemical vapor deposition, which improved the in-plane thermal conductivity of single-walled carbon nanotube films by 80%. (Reference 3: P Wang, Y Zheng, T Inoue. et.al ACS Nano 2020, 14, 4; Reference 4: P Wang, Y Feng, R Xiangg. et.al. Nanotechnology, 2021, 32, 205708)

[0005] However, the improvement in thermal conductivity brought about by the carbon nanotube@hexagonal boron nitride composite structure designed and prepared by the above methods is limited, and there is a significant gap compared with the theoretical thermal conductivity of carbon nanotubes. The reason for this is that when carbon nanotubes and their bundles are randomly arranged and overlapped to form a network structure or are arranged in a straight line, the overlaps are held together by van der Waals forces. During heat transfer, there will be severe phonon scattering, which increases the interfacial thermal resistance and seriously affects the thermal conductivity of the macroscopic carbon nanotube mass. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing a welded carbon nanotube@hexagonal boron nitride coaxial heterostructure. The welded structure at the overlap in the network can enhance the bonding force between carbon nanotube bundles, improve the mechanical properties of the film, reduce phonon scattering at the contact point, and enhance the thermal conductivity of the network.

[0007] The technical solution of this invention is:

[0008] A method for preparing a welded carbon nanotube@hexagonal boron nitride coaxial heterostructure involves using a carbon nanotube network as a template and employing atmospheric pressure chemical vapor deposition (CVD) to preferentially grow amorphous boron nitride at the network overlaps. The CVD conditions are then controlled to grow hexagonal boron nitride on the surfaces of the carbon nanotubes and the amorphous structure, resulting in a welded carbon nanotube@hexagonal boron nitride coaxial heterostructure. By adjusting the volatilization temperatures of the boron and nitrogen precursors and the CVD conditions, the crystallinity, number of layers, and curling degree of the microstructure of the amorphous structure and the hexagonal boron nitride coating are controlled to form a welded coating structure. This welded coating structure can then be used to directly construct thin films, fibers, or foam composites, thereby improving the thermal conductivity, mechanical strength, and chemical stability of the macrostructure.

[0009] The method for preparing a welded carbon nanotube@hexagonal boron nitride coaxial heterostructure uses a carbon nanotube network as a template. In an atmospheric pressure chemical vapor deposition system, the volatilization of boron and nitrogen precursors is first controlled to allow the amorphous structure to nucleate and grow at the network overlap. Then, the volatilization temperature of the boron and nitrogen sources is increased to allow hexagonal boron nitride to grow on the carbon nanotubes and the amorphous structure, thereby obtaining a carbon nanotube@hexagonal boron nitride coaxial heterostructure with a welded structure. The size of the welded structure and the thickness and crystallinity of the hexagonal boron nitride coating are controlled by changing the chemical composition of the precursor source, volatilization temperature, carrier gas flow rate, and time during the chemical vapor deposition process.

[0010] The method for preparing the welded carbon nanotube@hexagonal boron nitride coaxial heterostructure uses an irregularly overlapping carbon nanotube network as a template, wherein the carbon nanotube network is constructed from a single tube or a bundle of 2 to 30 small tubes, and the carbon nanotubes have high crystallinity and high surface cleanliness.

[0011] The method for preparing welded carbon nanotube@hexagonal boron nitride coaxial heterostructures uses boron and nitrogen precursors such as borane-tert-butylamine complex, ammoniaborane, borane trimethylamine complex, borane dimethylamine complex, 2-methylpyridineborane, or boron- and nitrogen-containing organic compounds. In the first step of atmospheric pressure chemical vapor deposition, the volatilization temperature of the precursor source is controlled at 45-85℃, and the chemical vapor deposition temperature is controlled at 600-1000℃ to obtain low partial pressure boron and nitrogen precursors, which preferentially nucleate and grow at the carbon nanotube overlap to form an amorphous boron nitride structure with welded carbon nanotube nodes.

[0012] In the method for preparing the welded carbon nanotube@hexagonal boron nitride coaxial heterostructure, in the second step of atmospheric pressure chemical vapor deposition, the volatilization temperature of the boron and nitrogen precursors is increased to 65-125℃, and the chemical vapor deposition temperature is 700-1200℃, so that layered hexagonal boron nitride is grown on the surface of the amorphous boron nitride structure and the carbon nanotube. The structure formed on the surface of the spherical welded structure is a closed spherical hexagonal boron nitride, and tubular hexagonal boron nitride with 2-10 layers is formed on the surface of the carbon nanotube.

[0013] The method for preparing welded carbon nanotube@hexagonal boron nitride coaxial heterostructure involves controlling the size and crystallinity of the grown welded structure and hexagonal boron nitride during both atmospheric pressure chemical vapor deposition growth processes by adjusting the partial pressure of boron and nitrogen precursors, as well as the chemical vapor deposition temperature, carrier gas flow rate, and time.

[0014] The method for preparing welded carbon nanotube@hexagonal boron nitride coaxial heterostructures uses, in addition to various boron and nitrogen-containing compounds, other volatile organic compounds containing carbon, silicon, and oxygen as precursors. The composition of the welded structure grown at the nodes of the carbon nanotube network is adjusted by controlling the amount of its volatilization.

[0015] The method for preparing welded carbon nanotube@hexagonal boron nitride coaxial heterostructure involves constructing a thin film, fiber, or foam composite macrostructure from the welded carbon nanotube@hexagonal boron nitride coaxial heterostructure through filtration, spinning, or freeze-drying.

[0016] The method for preparing a welded carbon nanotube@hexagonal boron nitride coaxial heterostructure has higher chemical and thermal stability. The welded structure enhances the interaction at the overlap of carbon nanotubes, reduces contact thermal resistance by decreasing phonon scattering at the overlap, and improves the mechanical and thermal conductivity of the carbon nanotube composite structure.

[0017] The design concept of this invention:

[0018] This invention provides a method for preparing a welded carbon nanotube@hexagonal boron nitride coaxial heterostructure. Using a carbon nanotube network as a template, the method controls the volatilization temperature of the precursor during atmospheric pressure chemical vapor deposition (CVD) to grow amorphous boron nitride structures at the network overlaps, thus achieving the welding of carbon nanotubes. Subsequently, hexagonal boron nitride is grown on the surfaces of the carbon nanotubes and the amorphous welded structure. Utilizing the similar atomic bonding structures of carbon nanotubes and hexagonal boron nitride, and using a random carbon nanotube network as a template, the nucleation sites and crystallization state of boron nitride are controlled by adjusting the partial pressures of boron and nitrogen sources during CVD, thereby obtaining the welded carbon nanotube@hexagonal boron nitride coaxial heterostructure.

[0019] This invention regulates the size, composition, number of hexagonal boron nitride (BN) coating layers, and crystallinity of amorphous welded structures by altering the composition, volatilization temperature, and chemical vapor deposition conditions of the boron and nitrogen precursors. The carbon nanotube@hexagonal boron nitride structure significantly improves the chemical stability and high-temperature thermal stability of carbon nanotubes. In particular, the BN-coated welded structure enhances the bonding force at the carbon nanotube network nodes and reduces phonon scattering at the contact points, thereby improving the mechanical properties and thermal conductivity of the composite structure.

[0020] The advantages and beneficial effects of this invention are:

[0021] 1. The preparation method of this invention achieves control over the chemical vapor deposition reaction kinetics by simply regulating the volatilization of the precursor source, enabling the nucleation and growth of boron nitride with different structures (crystallinity, number of layers, degree of curling, etc.) at different sites by precursor sources with different partial pressures. This provides a simple, controllable, and efficient method for synthesizing carbon nanotube@hexagonal boron nitride coaxial heterostructures with welded structures. Using a carbon nanotube network as a template, the volatilization of the precursor during atmospheric pressure chemical vapor deposition is controlled to grow amorphous boron nitride structures at the carbon nanotube overlaps, connecting the carbon nanotubes at the overlaps. Then, by increasing the volatilization of boron and nitrogen sources, layered hexagonal boron nitride-coated spherical structures and hexagonal boron nitride coaxial heterostructures are grown on the surfaces of amorphous boron nitride and carbon nanotubes.

[0022] 2. The structure prepared by this invention realizes the welding of carbon nanotubes at the overlap. By connecting the carbon nanotube network through the welding structure, it is expected to enhance the interaction force between carbon nanotubes, reduce phonon scattering, and make the macroscopic carbon nanotube network have better mechanical, thermal and chemical stability, which has broad application prospects in the field of nanoelectronic devices. Attached Figure Description

[0023] Figure 1 Transmission electron microscope image of a single-walled carbon nanotube network.

[0024] Figure 2 Transmission electron microscope image of amorphous boron nitride welded single-walled carbon nanotube films.

[0025] Figure 3 Morphological characterization of welded carbon nanotube@hexagonal boron nitride coaxial heterostructure composite films. (a) Scanning electron microscope image; (b) Transmission electron microscope image.

[0026] Figure 4 X-ray photoelectron spectroscopy analysis of welded carbon nanotube@hexagonal boron nitride coaxial heterostructure. In the figure, the horizontal axis represents binding energy (eV), and the vertical axis represents relative intensity (au).

[0027] Figure 5 Fourier transform infrared spectroscopy analysis of single-walled carbon nanotube films, amorphous boron nitride-welded single-walled carbon nanotube films, and welded carbon nanotube@hexagonal boron nitride coaxial heterostructure composite films. In the figure, the horizontal axis represents the wavenumber (cm²). -1 The vertical axis, Transmittance, represents the transmittance (au).

[0028] Figure 6 Optical microscope image of a sample of welded carbon nanotube@hexagonal boron nitride coaxial heterostructure thin film thermal conductivity measured by photothermal Raman spectroscopy.

[0029] Figure 7 Transmission electron microscope image of amorphous boron nitride-welded single-walled carbon nanotube films prepared using ammonia borane as a precursor.

[0030] Figure 8 Transmission electron microscope image of a welded carbon nanotube@hexagonal boron nitride coaxial heterostructure composite film prepared using ammonia borane as a precursor.

[0031] Figure 9 Transmission electron microscope image of a weld-free hexagonal boron nitride-coated single-walled carbon nanotube film. Detailed Implementation

[0032] To make the objectives, technical solutions and advantages of the present invention clearer, the present invention is described in detail below with reference to embodiments and accompanying drawings, but this is not intended to limit the scope of protection of this application.

[0033] Example 1

[0034] In this embodiment, the process for controllably preparing the coaxial heterostructure composite film of carbon nanotubes@hexagonal boron nitride is as follows:

[0035] (1) Transfer of carbon nanotube films. High-quality single-walled carbon nanotube films prepared by floating catalyst chemical vapor deposition were transferred by pressing to obtain a suspended self-supporting network. The thickness of the film was about 40 nm, and its microstructure consisted of irregularly overlapping small bundles of single-walled carbon nanotubes and a small number of single single-walled carbon nanotubes. Figure 1 The diameter of the single-walled carbon nanotubes is distributed between 5 and 50 nm. In the single-walled carbon nanotube film, the number of single single-walled carbon nanotubes accounts for about 40%, and the rest are small bundles of single-walled carbon nanotubes, each of which consists of 2 to 30 single-walled carbon nanotubes.

[0036] (2) Preparation of amorphous boron nitride welded single-walled carbon nanotube films by atmospheric pressure chemical vapor deposition. The self-supporting single-walled carbon nanotube film obtained in step (1) was placed in a tube furnace with a constant temperature zone of 1000℃. 300 sccm of high-purity (volume purity ≥99.999%) Ar gas was used as the carrier gas, and 30 mg of borane-tert-butylamine complex was placed at the inlet end of the tube furnace. The mixture was heated to 60℃ via a heating belt to allow it to volatilize into the constant temperature zone. After growth for 30 min, an amorphous boron nitride welded single-walled carbon nanotube network was obtained. Figure 2 ).

[0037] (3) Welded carbon nanotube@hexagonal boron nitride coaxial heterostructure composite film was prepared by atmospheric pressure chemical vapor deposition. After completing step (2), the temperature of the heating band was increased to 90℃ and the growth continued for 2.5h.

[0038] (4) Characterization of the welded carbon nanotube@hexagonal boron nitride coaxial heterostructure. Scanning electron microscopy images show that the carbon nanotubes are connected at the overlapping nodes by the grown amorphous boron nitride. Figure 3 a) Transmission electron microscopy images further confirmed that the amorphous boron nitride@hexagonal boron nitride core-shell structure at the nodes successfully welded and uniformly coated the carbon nanotube network, and that a certain number of hexagonal boron nitride nanotubes (1 to 10 layers in this embodiment) were also successfully epitaxially grown on the surface of the carbon nanotube bundles. Figure 3 b) Amorphous boron nitride@hexagonal boron nitride refers to a core-shell structure composed of preferentially grown amorphous boron nitride at the nodes and subsequently grown hexagonal boron nitride. This structure acts as a welder for the carbon nanotube film network. X-ray photoelectron spectroscopy analysis confirmed the presence of boron and nitrogen elements in this structure. Figure 4 Combined with Fourier transform infrared spectroscopy analysis ( Figure 5 It can be seen that, compared to the original single-walled carbon nanotube network, both the amorphous boron nitride welded single-walled carbon nanotube network and the welded carbon nanotube@hexagonal boron nitride coaxial heterostructure composite film have a thickness of 1384 cm⁻¹. -1 The presence of a distinct peak position corresponds to a typical BN bond-in-plane stretching mode, proving that boron nitride was successfully formed in both structures.

[0039] (5) Thermal conductivity testing of welded carbon nanotube@hexagonal boron nitride coaxial heterostructure. A self-supporting welded carbon nanotube@hexagonal boron nitride film was transferred to the surface of a single-pore molybdenum ring with a pore size of 200 μm. Figure 6 The photothermal Raman spectroscopy method was employed. A 633 nm Raman laser was used as the heat source to measure the rate of change of the G peak position of the carbon nanotubes with different Raman laser powers. A heating stage was used as the heat source to measure the rate of change of the G peak position of the carbon nanotubes with different heating temperatures. Based on this, the maximum temperature rise of the sample at a laser heating power of 2.4 mW was calculated to be approximately 160 °C. Therefore, the in-plane thermal conductivity of the film was calculated to be 30.5 W·m. -1 K -1 .

[0040] Example 2

[0041] In this embodiment, the process for controllably preparing the coaxial heterostructure composite film of carbon nanotubes@hexagonal boron nitride is as follows:

[0042] (1) Transfer of carbon nanotube films. Single-walled carbon nanotube films prepared by floating catalytic chemical vapor deposition were transferred by pressing to obtain suspended self-supporting network films. The thickness of the single-walled carbon nanotube films was about 100 nm. Its microstructure consisted of irregularly overlapping small bundles of single-walled carbon nanotubes and a small number of single single-walled carbon nanotubes. The diameter of the bundles was distributed in the range of 5 to 50 nm.

[0043] (2) Preparation of amorphous boron nitride welded single-walled carbon nanotube films by atmospheric pressure chemical vapor deposition. The self-supporting single-walled carbon nanotube film obtained in step (1) was placed in a tube furnace with a constant temperature zone of 1000℃. 300 sccm of high-purity (volume purity ≥99.999%) Ar gas was used as the carrier gas, and 30 mg of ammonia borane was placed at the gas inlet end of the tube furnace. The furnace was heated to 70℃ by a heating belt to allow it to volatilize into the constant temperature zone. After 10 min of growth, amorphous boron nitride welded single-walled carbon nanotube films were obtained. Figure 7 ).

[0044] (3) A welded carbon nanotube@hexagonal boron nitride coaxial heterostructure composite film was prepared by atmospheric pressure chemical vapor deposition. After completing step (2), the temperature of the heating band was increased to 95℃ and growth continued for 2 hours. The grown film has an amorphous boron nitride welded carbon nanotube@hexagonal boron nitride coaxial heterostructure. Figure 8 This embodiment demonstrates that the nucleation sites of boron nitride on the surface of carbon nanotubes can be controlled by adjusting the volatilization temperature of different types of boron and nitrogen precursors.

[0045] Example 3

[0046] In this embodiment, the process of controllably preparing and welding carbon nanotube@hexagonal boron nitride coaxial heterostructure composite fibers is as follows:

[0047] (1) Transfer of carbon nanotube films. Single-walled carbon nanotube films prepared by floating catalytic chemical vapor deposition were transferred by pressing to obtain suspended self-supporting network films. The thickness of the single-walled carbon nanotube films was 1 μm. Their microstructure consisted of irregularly overlapping small bundles of single-walled carbon nanotubes and a small number of single single-walled carbon nanotubes. The diameter of the bundles was distributed in the range of 5–50 nm.

[0048] (2) Preparation of amorphous boron nitride welded single-walled carbon nanotube films by atmospheric pressure chemical vapor deposition. The self-supporting single-walled carbon nanotube film obtained in step (1) was placed in a tube furnace with a constant temperature zone of 1000℃. 300 sccm of high-purity (volume purity ≥99.999%) Ar gas was used as the carrier gas. 60 mg of borane-tert-butylamine complex was placed at the gas inlet end of the tube furnace and heated to 60℃ by a heating belt to volatilize it into the constant temperature zone. After growing for 30 min, amorphous boron nitride welded single-walled carbon nanotube films were obtained.

[0049] (3) Welded carbon nanotube@hexagonal boron nitride coaxial heterostructure composite film was prepared by atmospheric pressure chemical vapor deposition. After completing step (2), the temperature of the heating band was increased to 90℃ and growth continued for 5 hours.

[0050] (4) Preparation of welded carbon nanotube@hexagonal boron nitride coaxial heterostructure composite fiber. The composite film obtained in step (3) was soaked in anhydrous ethanol for 1 hour, densified and dried, and then twisted under stretching force to obtain welded carbon nanotube@hexagonal boron nitride coaxial heterostructure composite fiber.

[0051] Comparative example

[0052] A coaxial heterostructure thin film of carbon nanotubes@hexagonal boron nitride without welded structure.

[0053] The preparation method in this comparative example is the same as that in Example 1, except that step (2) of preparing amorphous boron nitride welded single-walled carbon nanotube films by atmospheric pressure chemical vapor deposition in Example 1 is omitted. Instead, hexagonal boron nitride coated single-walled carbon nanotube films are directly obtained. Figure 9 Thermal conductivity tests were conducted on the thin film, and the maximum temperature rise of the sample under a laser heating power of 2.4 mW was measured to be approximately 360 °C. Based on this, the in-plane thermal conductivity of the thin film was calculated to be 12 W·m. -1 K -1 .

[0054] The comparative examples illustrate that, compared to direct coating with boron nitride, synthesizing and welding carbon nanotube@hexagonal boron nitride coaxial heterostructures can significantly improve the thermal conductivity of carbon nanotube films. Such films with nanometer-scale thickness are expected to be applied in thermal management fields such as heat dissipation of nanoelectronic devices.

[0055] The design concept and implementation scheme of this invention have been described in detail above. However, some modifications and improvements can still be made based on this invention. All such modifications or improvements made without departing from the spirit of this invention fall within the scope of protection claimed by this invention.

Claims

1. A method for preparing a welded carbon nanotube@hexagonal boron nitride coaxial heterostructure, characterized in that, Using carbon nanotube networks as templates, in an atmospheric pressure chemical vapor deposition system, the volatilization of boron and nitrogen precursors is first controlled, preferentially nucleating and growing amorphous boron nitride structures at the network overlaps. Then, the volatilization temperature of the boron and nitrogen precursors is increased, allowing hexagonal boron nitride to grow on the carbon nanotubes and amorphous boron nitride structures, resulting in a coaxial heterostructure of carbon nanotubes@hexagonal boron nitride with a welded structure. Specifically, in the first atmospheric pressure chemical vapor deposition process, the volatilization temperature of the precursor source is controlled at 45–85 °C; in the second atmospheric pressure chemical vapor deposition process, the volatilization temperature of the boron and nitrogen precursors is increased to 65–125 °C.

2. The method for preparing welded carbon nanotube@hexagonal boron nitride coaxial heterostructures according to claim 1, characterized in that, The size of the welded structure and the thickness and crystallinity of the hexagonal boron nitride coating were controlled by changing the chemical composition of the precursor source, volatilization temperature, carrier gas flow rate, and time during atmospheric pressure chemical vapor deposition.

3. The method for preparing welded carbon nanotube@hexagonal boron nitride coaxial heterostructures according to claim 1 or 2, characterized in that, Using an irregularly overlapping carbon nanotube network as a template, the carbon nanotube network is constructed from a single tube or a bundle of 2 to 30 small tubes, and the carbon nanotubes have high crystallinity and high surface cleanliness.

4. The method for preparing welded carbon nanotube@hexagonal boron nitride coaxial heterostructures according to claim 1 or 2, characterized in that, The boron and nitrogen precursors are borane-tert-butylamine complex, ammoniaborane, borane trimethylamine complex, borane dimethylamine complex, or 2-methylpyridineborane. In the first step of atmospheric pressure chemical vapor deposition, the chemical vapor deposition temperature is 600~1000℃. The low partial pressure boron and nitrogen precursors preferentially nucleate and grow at the carbon nanotube overlap to form an amorphous boron nitride structure with welded carbon nanotube nodes.

5. The method for preparing welded carbon nanotube@hexagonal boron nitride coaxial heterostructures according to claim 1 or 2, characterized in that, In the second step of atmospheric pressure chemical vapor deposition, the chemical vapor deposition temperature is 700~1200℃, which allows layered hexagonal boron nitride to grow on the surface of amorphous boron nitride structures and carbon nanotubes. The structure formed on the surface of the spherical welded structure is a closed spherical hexagonal boron nitride, and the number of tubular hexagonal boron nitride layers is 2~10 layers on the surface of carbon nanotubes.

6. The method for preparing welded carbon nanotube@hexagonal boron nitride coaxial heterostructures according to claim 1 or 2, characterized in that, In both atmospheric pressure chemical vapor deposition (CVD) growth processes, the size and crystallinity of the grown weld structure and hexagonal boron nitride are controlled by adjusting the partial pressure of boron and nitrogen precursors, as well as the CVD temperature, carrier gas flow rate, and time.

7. The method for preparing welded carbon nanotube@hexagonal boron nitride coaxial heterostructures according to claim 1 or 2, characterized in that, In addition to various boron and nitrogen-containing compounds, other volatile organic compounds containing carbon, silicon, and oxygen elements are selected as precursors, and the composition of the welded structure grown at the nodes of the carbon nanotube network is adjusted by regulating their volatilization.

8. The method for preparing welded carbon nanotube@hexagonal boron nitride coaxial heterostructures according to claim 1 or 2, characterized in that, Macroscopic composites of films, fibers, or foams are constructed from welded carbon nanotubes@hexagonal boron nitride coaxial heterostructures through methods such as filtration, spinning, or freeze-drying.

9. The method for preparing a welded carbon nanotube@hexagonal boron nitride coaxial heterostructure according to claim 1 or 2, characterized in that, The welded structure enhances the interaction at the overlap of carbon nanotubes, reduces contact thermal resistance by decreasing phonon scattering at the overlap location, and improves the mechanical and thermal conductivity of the carbon nanotube composite structure.

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