Hexagonal boron nitride flake derived with boron nitride nanotube structure and preparation method and application thereof

Abstract

The application discloses a kind of hexagonal boron nitride flake derived with boron nitride nanotube structure and its preparation method and application, the method includes the following steps: (1) preparation ZIF-67 modified hexagonal boron nitride flake;(2) preparation MgCo-ZIF modified hexagonal boron nitride flake;(3) preparation hexagonal boron nitride flake-boron nitride nanotube precursor;(4) hexagonal boron nitride flake-boron nitride nanotube precursor ammoniation: hexagonal boron nitride flake-boron nitride nanotube precursor is heated to 1100~1600 ℃ in inert atmosphere, then ammonia gas is introduced to ammoniation treatment, reaction is carried out, then it is naturally cooled to room temperature, and the hexagonal boron nitride flake derived with boron nitride nanotube structure is obtained.The method of the application does not need to add additional external boron source as catalyst, the preparation process is simple, the requirement to equipment is low, easy to realize industrialization, greatly saves equipment cost.

Description

TECHNICAL FIELD

[0001] The present application relates to a hexagonal boron nitride flake, in particular to a hexagonal boron nitride flake derived with a boron nitride nanotube structure and a preparation method and application thereof. BACKGROUND

[0002] With the rapid development of electronic devices, nanomaterials are also increasingly widely used in smart phones, wearable devices, tablet computers and battery packaging. Boron nitride nanomaterials exhibit unique physical and chemical properties, such as electrical insulation, high specific surface area, low dielectric constant, good thermal and chemical stability, and excellent thermal conductivity. Boron nitride nanomaterials not only impart high thermal conductivity to polymers, but also enable the filled composite material to still maintain electrical insulation, and have been widely used in the fields of electronics / optoelectronics, catalysis, energy storage and conversion, sensors and electronic product development, nanocomposites, etc.

[0003] Like carbon nanomaterials such as graphene and carbon nanotubes, boron nitride also has structures of different dimensions, and a series of boron nitride nanostructures have been synthesized, including: zero-dimensional boron nitride nanospheres; one-dimensional boron nitride nanostructures, mainly including boron nitride nanowires, boron nitride nanorods, and boron nitride nanofibers; two-dimensional boron nitride nanostructures, mainly including boron nitride nanosheets (BNNSs), boron nitride nanoribbons (BNNRs), boron nitride nanotubes (BNNTs), and three-dimensional nanostructure porous boron nitride fullerenes, etc. Different dimensional boron nitride structures have different properties. Due to the similar size and morphology of single-dimensional fillers, there are a large number of voids between the fillers, leading to serious interface phonon scattering. The use of the synergistic effect between multi-dimensional fillers can improve the overall filling density of the composite material, thereby building a bridge between the fillers to form a large thermal conduction network and improve the thermal conductivity.

[0004] According to the existing chemical synthesis method, i.e. annealing a boron-containing and nitrogen-containing precursor at normal pressure and high temperature in a tube furnace, the surface of the prepared hexagonal boron nitride flake is smooth, and when applied in a composite material, the contact area with the matrix material is small, thereby leading to limited enhancement of thermal conductivity.

[0005] In addition, the traditional chemical vapor deposition method for growing boron nitride nanotubes requires the addition of a catalyst and a boron source from the outside, and many factors such as the boron source and the catalyst have a great influence on the structure, morphology and yield of BNNTs, and the growth is difficult, and the uniformity of the product is difficult to control. SUMMARY

[0006] The purpose of the present application is to provide a hexagonal boron nitride flake derived with a boron nitride nanotube structure and a preparation method and application thereof, which does not require the additional addition of an external boron source as a catalyst, has a simple preparation process, low equipment requirements, is easy to realize industrialization, and greatly saves equipment costs.

[0007] To achieve the above object, the present application provides a preparation method of hexagonal boron nitride flakes derived with boron nitride nanotube structure, which comprises the following steps:

[0008] (1) Preparation of ZIF-67 modified hexagonal boron nitride flakes

[0009] The hexagonal boron nitride flakes are soaked in methanol and mixed with 2-methyl imidazole methanol solution to obtain a mixed solution A;

[0010] The mixed solution A is mixed with a cobalt nitrate hexahydrate methanol solution, fully stirred and reacted to obtain a mixed solution B, which is left to stand;

[0011] The mixed solution B is separated and dried to obtain a ZIF-67 modified hexagonal boron nitride flakes precursor, denoted as ZIF-67@BNFs;

[0012] (2) Preparation of MgCo-ZIF modified hexagonal boron nitride flakes

[0013] The ZIF-67@BNFs and a magnesium chloride hexahydrate methanol solution are mixed, fully stirred and reacted to obtain a mixed solution C, which is left to stand;

[0014] The mixed solution C is separated and dried to obtain a MgCo-ZIF modified hexagonal boron nitride flakes precursor, denoted as MgCo-ZIF@BNFs;

[0015] (3) Preparation of hexagonal boron nitride flakes-boron nitride nanotube precursor

[0016] The MgCo-ZIF@BNFs are added to an aqueous boric acid solution, heated and stirred at 30-100°C to obtain a slurry precursor;

[0017] The slurry precursor is dried to obtain a hexagonal boron nitride flakes-boron nitride nanotube precursor;

[0018] (4) Ammoniation of hexagonal boron nitride flakes-boron nitride nanotube precursor

[0019] The hexagonal boron nitride flakes-boron nitride nanotube precursor is heated to 1100-1600°C in an inert atmosphere and then subjected to ammonia treatment by introducing ammonia gas, reacted, and then naturally cooled to room temperature to obtain hexagonal boron nitride flakes derived with boron nitride nanotube structure.

[0020] Preferably, in step (1), the molar ratio of the hexagonal boron nitride flakes to 2-methyl imidazole is (1-5):(2-1).

[0021] More preferably, in step (1), the molar ratio of the hexagonal boron nitride flakes to 2-methylimidazole is 2:1.5.

[0022] Preferably, in step (1), the molar ratio of the cobalt nitrate hexahydrate to 2-methylimidazole is 1:(2-50).

[0023] More preferably, in step (1), the molar ratio of the cobalt nitrate hexahydrate to 2-methylimidazole is 1:5.0-5.2.

[0024] Preferably, in any one or both of steps (1)-(2), the standing time is 2-48 h; or / and,

[0025] In any one or more than two of steps (1)-(3), the drying temperature is 40-200℃.

[0026] Preferably, in step (2), the mass ratio of the magnesium chloride hexahydrate to ZIF-67@BNFs is (1-10):(0.1-5).

[0027] More preferably, in step (2), the mass ratio of the magnesium chloride hexahydrate to ZIF-67@BNFs is 6-7:5.

[0028] Preferably, in step (1), the concentration of the methanol solution of the hexagonal boron nitride flakes is 1-20 mol / L; the concentration of the methanol solution of 2-methylimidazole is 1-20 mol / L; or / and, in step (1), the concentration of the methanol solution of the cobalt nitrate hexahydrate is 0.1-10 mol / L; or / and, in step (2), the concentration of the methanol solution of the magnesium chloride hexahydrate is 0.1-10 mol / L; or / and, in step (3), the concentration of the aqueous boric acid solution is 0.1-10 mol / L.

[0029] More preferably, in step (1), the concentration of the methanol solution of the hexagonal boron nitride flakes is 2 mol / L; the concentration of the methanol solution of 2-methylimidazole is 3 mol / L; or / and, in step (1), the concentration of the methanol solution of the cobalt nitrate hexahydrate is 0.58 mol / L; or / and, in step (2), the concentration of the methanol solution of the magnesium chloride hexahydrate is 0.3 mol / L; or / and, in step (3), the concentration of the aqueous boric acid solution is 0.5 mol / L.

[0030] Preferably, in step (4), heating to 1300-1400℃ is followed by ammonia treatment by introducing ammonia gas.

[0031] Preferably, in step (4), the gas of the inert atmosphere is selected from any one or more than two of nitrogen, argon, helium, neon and radon; or / and, the heating is at a rate of 1-15℃ / min to 1100-1600℃; or / and, the time of the ammoniation treatment is 1-10h. The present application controls the ammoniation conditions to obtain the hexagonal boron nitride flakes derived with the boron nitride nanotube structure.

[0032] More preferably, in step (4), the heating is at a rate of 1-2℃ / min to 1300-1400℃; or / and, the time of the ammoniation treatment is 1-3h.

[0033] More preferably, in step (4), the hexagonal boron nitride flake-boron nitride nanotube precursor is heated to 1100-1600℃ in 100sccm inert atmosphere, then ammoniation treatment is carried out by introducing 100sccm ammonia, the ammonia is switched to 100sccm inert atmosphere, and the hexagonal boron nitride flakes derived with the boron nitride nanotube structure are obtained by natural cooling to room temperature.

[0034] Preferably, in step (4), the precursor is placed in a crucible, and the crucible used can be but not limited to an alumina crucible, a silicon nitride crucible or a boron nitride crucible.

[0035] Another object of the present application is to provide the hexagonal boron nitride flakes derived with the boron nitride nanotube structure obtained by the preparation method.

[0036] Another object of the present application is to provide the hexagonal boron nitride flakes derived with the boron nitride nanotube structure in the field of heat conduction.

[0037] The hexagonal boron nitride flakes derived with the boron nitride nanotube structure of the present application, the preparation method and the application thereof have the following advantages:

[0038] Compared with the traditional hexagonal boron nitride flakes and BNNTs nanofillers, the boron nitride flake-boron nitride nanotube structure prepared by the present application can fully exert the synergistic effect of flakes and tubes, improve the interface properties, significantly increase the contact area, and form a bridging structure between the BNNTs and the boron nitride flakes, which makes it easier to be connected, improves the conduction efficiency of phonons, and builds a complete and continuous heat conduction network in the polymer matrix at a lower filling amount, thereby increasing the contact area of the nanofiller / matrix, reducing the interface thermal resistance, and effectively widening the application of boron nitride in the field of functional composites.

[0039] Compared with the prior art, the application does not need to add an external boron source as a catalyst, the traditional chemical vapor deposition method for growing boron nitride nanotubes needs to add a catalyst and a boron source from outside, and the growth is difficult, and the uniformity of the product is difficult to control. Compared with the common method, the preparation process of the application is simple, the problems of expensive equipment and complex process are solved, the requirement for equipment is low, industrialization is easy to realize, the equipment cost is greatly saved, the chemical raw materials used are cheap and easy to obtain, and the prepared hexagonal boron nitride flake-boron nitride nanotube structure has important application prospect in the heat conduction field, and provides a basis for realizing large-scale preparation of high-quality and high-purity boron nitride nanotubes. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 SEM photos of samples prepared in Example 1 of the application.

[0041] Figure 2 X-ray diffraction (XRD) spectrum of samples prepared in Example 1 of the application.

[0042] Figure 3 SEM photos of samples prepared in Example 2 of the application.

[0043] Figure 4 SEM photos of samples prepared in Example 3 of the application.

[0044] Figure 5 SEM photos of samples prepared in Comparative Example 1 of the application. DETAILED DESCRIPTION

[0045] The technical solutions in the embodiments of the application will be described below in a clear and complete manner. Obviously, the described embodiments are only a part of the embodiments of the application, rather than all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the application.

[0046] A hexagonal boron nitride flake derived with a boron nitride nanotube structure, and a preparation method thereof, comprises the following steps:

[0047] (1) preparing a ZIF-67 modified hexagonal boron nitride flake

[0048] The hexagonal boron nitride flake powder is soaked in methanol and mixed with a 2-methyl imidazole methanol solution to ensure complete adsorption and assembly on the surface. Then, the mixed solution is further mixed with a cobalt nitrate hexahydrate methanol solution, and fully stirred to achieve sufficient reaction, to obtain a mixed solution, which is left to stand. The mixed solution is centrifuged and dried to obtain a ZIF-67 modified hexagonal boron nitride flake precursor powder, denoted as ZIF-67@BNFs.

[0049] (2) Preparation of MgCo-ZIF modified hexagonal boron nitride flakes

[0050] The obtained ZIF-67@BNFs powder and magnesium chloride hexahydrate methanol solution are mixed, and uniform dispersion and sufficient reaction between the components are achieved by sufficient stirring to obtain a mixed solution, which is left to stand. The mixed solution is centrifuged and dried to obtain a MgCo-ZIF modified hexagonal boron nitride flake precursor powder, denoted as MgCo-ZIF@BNFs.

[0051] (3) Preparation of hexagonal boron nitride flake-boron nitride nanotube precursor

[0052] Boric acid is dissolved in deionized water, and the obtained MgCo-ZIF@BNFs powder is added to the boric acid aqueous solution, which is heated and stirred in a water bath to obtain a slurry precursor. The precursor solution is dried to obtain a hexagonal boron nitride flake-boron nitride nanotube precursor powder.

[0053] (4) Ammoniation of the precursor powder

[0054] The hexagonal boron nitride flake-boron nitride nanotube precursor powder is placed in a crucible and heated to a certain temperature in an inert atmosphere, and then ammonia gas is introduced for ammoniation treatment for a period of time to react, and then naturally cooled to room temperature to obtain a hexagonal boron nitride flake-boron nitride nanotube structure powder, with boron nitride nanotube structures derived on the hexagonal boron nitride flakes.

[0055] Compared with the prior art, the present application does not need to add an external boron source as a catalyst, and the traditional chemical vapor deposition method for growing boron nitride nanotubes needs to add a catalyst and a boron source from the outside, which is difficult to grow and the uniformity of the product is difficult to control. Moreover, compared with the prior art, the prior art usually needs multiple temperature zone heating equipment to heat the external boron source to form active B reactants by forming gaseous B or decomposing a precursor containing solid B, but this will cause the synthesis of BNNTs to be dispersed in the entire container, resulting in a decrease in the efficiency of collecting BNNTs. However, the preparation process of the present application is simple, and only needs to heat and ammoniate the treated sample to obtain hexagonal boron nitride flakes loaded with boron nitride nanotubes, solving the problems of complex process, low efficiency of collecting BNNTs, etc. The present application has low requirements for equipment and is easy to realize industrialization, greatly saving equipment costs. The chemical raw materials used are low in price and easy to obtain. The prepared hexagonal boron nitride flake-boron nitride nanotube structure has important application prospects in the field of heat conduction, providing a basis for large-scale preparation of high-quality and high-purity boron nitride nanotubes. Moreover, hexagonal boron nitride flakes loaded with boron nitride nanotubes have not been reported in the literature.

[0056] The prepared hexagonal boron nitride flake is derived with boron nitride nanotube structure, when the structure is applied to a composite material, the synergy of the flake and the tube can be fully played, the interface characteristics are improved, the contact area is significantly increased, the bridging structure formed by the BNNTs and the hexagonal boron nitride flake makes it easier to be lapped and improves the phonon conduction efficiency, and a complete and continuous heat conduction network can be constructed in the polymer matrix at a lower filling amount, so that the heat conduction performance is improved.

[0057] Further, in the preparation step of the ZIF-67 modified hexagonal boron nitride flake, the concentration of the methanol solution of the hexagonal boron nitride flake is 1-20 mol / L.

[0058] Further, in the preparation step of the ZIF-67 modified hexagonal boron nitride flake, the concentration of the methanol solution of the hexagonal boron nitride flake is 1-20 mol / L.

[0059] Further, in the preparation step of the ZIF-67 modified hexagonal boron nitride flake, the concentration of the methanol solution of the 2-methyl imidazole is 1-20 mol / L.

[0060] Further, in the preparation step of the ZIF-67 modified hexagonal boron nitride flake, the concentration of the methanol solution of the 2-methyl imidazole is 1-20 mol / L.

[0061] Further, in the preparation step of the ZIF-67 modified hexagonal boron nitride flake, the molar ratio of the hexagonal boron nitride flake to the 2-methyl imidazole is (1-5):(2-1).

[0062] Further, in the preparation step of the ZIF-67 modified hexagonal boron nitride flake, the concentration of the methanol solution of the cobalt nitrate hexahydrate is 0.1-10 mol / L.

[0063] Further, in the preparation step of the ZIF-67 modified hexagonal boron nitride flake, the concentration of the methanol solution of the cobalt nitrate hexahydrate is 0.1-10 mol / L.

[0064] Further, in the preparation step of the ZIF-67 modified hexagonal boron nitride flake, the molar ratio of the cobalt nitrate hexahydrate to the 2-methyl imidazole is 1:(2-50).

[0065] Further, in the preparation step of the ZIF-67 modified hexagonal boron nitride flake, the standing time is 2-48 h, and the drying temperature is 40-200 DEG C.

[0066] Further, in the preparation step of the MgCo-ZIF modified hexagonal boron nitride flake, the mass ratio of the magnesium chloride hexahydrate to the ZIF-67@BNFs is (1-10):(0.1-5).

[0067] Further, in the step of preparing the MgCo-ZIF modified hexagonal boron nitride flakes, the concentration of the methanol solution of magnesium chloride hexahydrate is 0.1-10 mol / L.

[0068] Further, in the step of preparing the MgCo-ZIF modified hexagonal boron nitride flakes, the concentration of the methanol solution of magnesium chloride hexahydrate is 0.1-10 mol / L.

[0069] Further, in the step of preparing the MgCo-ZIF modified hexagonal boron nitride flakes, the concentration of the methanol solution of magnesium chloride hexahydrate is 0.1-10 mol / L.

[0070] Further, in the step of preparing the MgCo-ZIF modified hexagonal boron nitride flakes, the concentration of the methanol solution of magnesium chloride hexahydrate is 0.1-10 mol / L.

[0071] Further, in the step of preparing the MgCo-ZIF modified hexagonal boron nitride flakes, the concentration of the methanol solution of magnesium chloride hexahydrate is 0.1-10 mol / L.

[0072] Further, in the step of preparing the MgCo-ZIF modified hexagonal boron nitride flakes, the concentration of the methanol solution of magnesium chloride hexahydrate is 0.1-10 mol / L.

[0073] Further, in the step of preparing the MgCo-ZIF modified hexagonal boron nitride flakes, the concentration of the methanol solution of magnesium chloride hexahydrate is 0.1-10 mol / L.

[0074] Further, in the step of preparing the MgCo-ZIF modified hexagonal boron nitride flakes, the concentration of the methanol solution of magnesium chloride hexahydrate is 0.1-10 mol / L.

[0075] Further, in the step of preparing the MgCo-ZIF modified hexagonal boron nitride flakes, the concentration of the methanol solution of magnesium chloride hexahydrate is 0.1-10 mol / L.

[0076] Further, in the step of preparing the MgCo-ZIF modified hexagonal boron nitride flakes, the concentration of the methanol solution of magnesium chloride hexahydrate is 0.1-10 mol / L.

[0077] In order to better illustrate the technical solutions of the present application, the present application will be further described below in combination with the following Example 1. It should be noted that the examples are only used to illustrate the technical solutions in detail and will not limit the protection scope of the present application.

[0078] Example 1

[0079] A boron nitride nanotube structure derived on a hexagonal boron nitride flake, and a preparation method thereof is as follows:

[0080] (1) Preparation of ZIF-67 modified hexagonal boron nitride flakes (ZIF-67@BNFs)

[0081] 0.50 g (0.02 mol) of hexagonal boron nitride flakes were immersed in 10 mL of methanol. Then, 5 mL of a methanol solution containing 1.23 g (0.015 mol) of 2-methylimidazole was added to ensure complete adsorption and assembly on the surface of the boron nitride flakes. Then, 5 mL of a methanol solution containing 0.83 g (0.0029 mol) of cobalt nitrate hexahydrate was added, and after sufficient stirring, a mixed solution was obtained. The mixed solution was left to stand for 12 hours. Then, the mixed solution was centrifuged at 5000 rpm for 5 min, and the obtained precipitate was washed with methanol for 3 times and dried at 65°C for 12 h to obtain ZIF-67@BNFs.

[0082] (2) Preparation of MgCo-ZIF modified hexagonal boron nitride flakes (MgCo-ZIF / BNFs)

[0083] 0.5 g of ZIF-67@BNFs was placed in 10 mL of a 0.3 mol / L magnesium chloride hexahydrate methanol solution, and the mixture was stirred thoroughly and left to stand for 12 h. Then, the mixed solution was centrifuged at 5000 rpm for 5 min, washed with methanol for 3 times, and dried at 65°C for 12 h to obtain MgCo-ZIF / BNFs.

[0084] (3) Preparation of hexagonal boron nitride flake-boron nitride nanotube precursor powder

[0085] 0.5 g of MgCo-ZIF / BNFs was placed in 5 mL of a 0.5 mol / L boric acid aqueous solution, and a slurry precursor was obtained by stirring in a water bath at 80°C. The slurry precursor was dried at 65°C for 12 h to obtain a hexagonal boron nitride flake-boron nitride nanotube precursor powder.

[0086] (4) Ammoniation of the precursor powder

[0087] The prepared hexagonal boron nitride flake-boron nitride nanotube precursor powder was placed in an alumina crucible, heated to 1300℃ at a heating rate of 2℃ / min in a nitrogen atmosphere of 100sccm, then the nitrogen was switched to 100sccm of ammonia for ammonia treatment for 1h, after the reaction, the ammonia was switched to 100sccm of nitrogen to cool to room temperature, and then taken out, to obtain the hexagonal boron nitride flake-boron nitride nanotube powder.

[0088] As shown in the SEM photograph of Figure 1 As shown in the SEM photograph of

[0089] As shown in the XRD pattern of Figure 2 As shown in the XRD pattern of the hexagonal boron nitride flake-boron nitride nanotube obtained in Example 1, the peaks at 26.7°, 41.7°, 55.2° and 75.9° correspond to the (002), (100), (004) and (110) planes of h-BN, respectively, proving that the product prepared is a high-purity h-BN structure.

[0090] Example 2

[0091] In this example, the ammonia treatment temperature in step (4) is 1400℃, and the other steps are the same as in Example 1.

[0092] As shown in the SEM photograph of Figure 3 As shown in the SEM photograph of the product obtained in Example 2 of the application, a large number of boron nitride nanotubes are loaded on the obtained hexagonal boron nitride flake, and the diameter of the boron nitride nanotubes obtained due to the increase in temperature is larger and the length is longer.

[0093] Example 3

[0094] In this example, the ammonia treatment time in step (4) is 3h, and the other steps are the same as in Example 1.

[0095] As shown in the SEM photograph of Figure 4 As shown in the SEM photograph of the product obtained in Example 3 of the application, a large number of boron nitride nanotubes are loaded on the obtained hexagonal boron nitride flake, and the diameter of the boron nitride nanotubes obtained due to the extension of the ammonia treatment time is larger.

[0096] Comparative Example 1

[0097] In this comparative example, step (2) in Example 1 is not performed, and step (3) is directly performed on ZIF-67@BNFs, and the other steps are the same as in Example 1.

[0098] As shown in the SEM photograph of Figure 5Fig. 6 is a SEM photograph of the boron nitride nanotubes obtained in Example 1 of the present application, and it is shown that the boron nitride nanotubes are loaded on the hexagonal boron nitride flakes.

[0099] While the application has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope of the application. It is therefore intended that whatever is described herein is to be included within the scope of the application.

Claims

1. A method for preparing hexagonal boron nitride thin films with derived boron nitride nanotube structures, characterized in that, The method includes the following steps: (1) Preparation of ZIF-67 modified hexagonal boron nitride thin films Hexagonal boron nitride sheets were soaked in methanol and then mixed with a 2-methylimidazolium methanol solution to obtain mixed solution A. Mix the aforementioned mixed solution A with a cobalt nitrate hexahydrate methanol solution, stir thoroughly to react, and then let it stand. The mixed solution B was separated and dried to obtain the ZIF-67 modified hexagonal boron nitride sheet precursor, denoted as ZIF-67@BNFs; (2) Preparation of MgCo-ZIF modified hexagonal boron nitride sheets The ZIF-67@BNFs and magnesium chloride hexahydrate methanol solution were mixed and stirred thoroughly to obtain mixed solution C, which was then allowed to stand. The mixed solution C was separated and dried to obtain the MgCo-ZIF modified hexagonal boron nitride sheet precursor, denoted as MgCo-ZIF@BNFs; (3) Preparation of hexagonal boron nitride sheet-boron nitride nanotube precursor The MgCo-ZIF@BNFs were added to an aqueous boric acid solution and heated and stirred at 30–100 °C to obtain a slurry precursor. The slurry precursor was dried to obtain a hexagonal boron nitride sheet-boron nitride nanotube precursor. (4) Ammoniation of hexagonal boron nitride sheet-boron nitride nanotube precursor The hexagonal boron nitride sheet-boron nitride nanotube precursor was heated to 1100-1600°C in an inert atmosphere and then ammonified with ammonia gas to carry out the reaction. Afterward, it was naturally cooled to room temperature to obtain a hexagonal boron nitride sheet with a derived boron nitride nanotube structure.

2. The preparation method according to claim 1, characterized in that, In step (1), the molar ratio of the hexagonal boron nitride sheet to 2-methylimidazole is (1-5):(2-1).

3. The preparation method according to claim 1, characterized in that, In step (1), the molar ratio of cobalt nitrate hexahydrate to 2-methylimidazole is 1:(2-50).

4. The preparation method according to claim 1, characterized in that, In any one or both of steps (1) to (2), the settling time is 2 to 48 hours; Or / and, in any one or more of steps (1) to (3), the drying temperature is 40 to 200°C.

5. The preparation method according to claim 1, characterized in that, In step (2), the mass ratio of magnesium chloride hexahydrate to ZIF-67@BNFs is (1-10):(0.1-5).

6. The preparation method according to claim 1, characterized in that, In step (1), the concentration of the methanol solution of the hexagonal boron nitride sheet is 1-20 mol / L; Or / and, in step (1), the concentration of the methanol solution of 2-methylimidazole is 1 to 20 mol / L; Or / and, in step (1), the concentration of the methanol solution of cobalt nitrate hexahydrate is 0.1 to 10 mol / L; Or / and, in step (2), the concentration of the methanol solution of magnesium chloride hexahydrate is 0.1 to 10 mol / L; Or / and, in step (3), the concentration of the boric acid aqueous solution is 0.1 to 10 mol / L.

7. The preparation method according to claim 1, characterized in that, In step (4), the inert atmosphere gas is selected from any one or more of nitrogen, argon, helium, neon and radon; Or / and, the heating is performed at a rate of 1 to 15 °C / min to 1100 to 1600 °C; Or / and, the ammoniation treatment time is 1 to 10 hours.

8. The preparation method according to claim 1, characterized in that, In step (4), the hexagonal boron nitride flake-boron nitride nanotube precursor powder is placed in a crucible, wherein the crucible is selected from an alumina crucible, a silicon nitride crucible, or a boron nitride crucible.

9. Hexagonal boron nitride sheets with derived boron nitride nanotube structures obtained by the preparation method according to any one of claims 1 to 8.

10. The application of the hexagonal boron nitride sheet with a boron nitride nanotube structure as described in claim 9 in the field of thermal conductivity.

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