One-dimensional boron nitride tertiary hierarchical structure and preparation method thereof

Abstract

The application relates to a one-dimensional boron nitride three-level hierarchical structure, and a main process of a preparation method thereof is as follows: a boron-containing precursor is prepared by using a magnesium-containing source, a boron-containing source, a cosolvent, a nickel source and a strong base as raw materials through a molten salt method; the boron-containing precursor, a nickel salt and a strong base are placed in solvent water, are uniformly dispersed through ultrasonic dispersion, and are subjected to heating and stirring; the obtained suspension liquid is filtered and dried to obtain a [B-O-Mg-Ni] precursor; the [B-O-Mg-Ni] precursor is calcined in a nitrogen-containing atmosphere to obtain a nitrided crude product; and finally, the nitrided crude product is subjected to acid washing, centrifugal drying and the like to obtain a boron nitride micro hollow tube hierarchical structure with nanotube-loaded surfaces. The application does not need to use a substrate, has a simple preparation process, is low in price, and has high purity of the obtained boron nitride product.

Description

Technical Field

[0001] This invention belongs to the field of inorganic materials, specifically relating to a one-dimensional boron nitride three-level hierarchical structure and its preparation method. Background Technology

[0002] Faced with market demands for portability, high performance, and cost-effectiveness, electronic products are increasingly becoming more multifunctional, miniaturized, lightweight, and highly integrated. The heat generated during device operation has a significant impact on device lifespan, safety, and efficiency. Achieving efficient heat dissipation has become a highly challenging yet very real problem in future electronic packaging technology. Hexagonal boron nitride (h-BN) nanomaterials, such as boron nitride nanoparticles (BNNPs), boron nitride nanotubes (BNNTs), boron nitride microtubes (BNMTs), and boron nitride nanosheets (BNNSs), are considered among the most promising high thermal conductivity inorganic nanomaterials in recent years. They possess unique physicochemical properties, including an ultrawide bandwidth (5.0–6.0 eV) and high thermal conductivity (50–600 W / m²). -1 K -1 Boron nitride (hBN) exhibits high mechanical strength and other advantages, making it a promising candidate for applications in copper clad laminates (CCLs), electronic packaging (EMC), thermal interface materials (TIMS), light-emitting diodes (LEDs), and phase-change energy storage (PCMs). By constructing hierarchical boron nitride (hBN) filler units, a multi-layered, multi-scale material composed of one or more low-dimensional hBN units can significantly reduce the number of building blocks in the composite material with the same filler content. This reduces the overlap between building blocks, lowers interfacial thermal resistance, and improves the thermal conductivity of the composite material. Therefore, developing high specific surface area multidimensional hBN hierarchical structures has significant research value and application prospects in the field of high thermal conductivity electronic packaging materials.

[0003] Several hierarchical structures of boron nitride have been reported. For example, Ji Yuchun et al. prepared a bouquet-shaped BN nanocapsule secondary hierarchical structure material using magnesium powder and boron oxide powder as raw materials via a self-propagating high-temperature synthesis-assisted annealing method. The average diameter of the bouquet was about 1 μm, and the BN nanocones that make up the bouquet structure were hollow structures with an average length and wall thickness of about 500 nm and 40 nm, respectively. The hollow boron nitride structure prepared by this method has a small size, low purity, small specific surface area, and contains a high content of magnesium oxide impurities, making it unsuitable as a high thermal conductivity filler. Xiao et al. first prepared a hollow microsphere secondary hierarchical structure assembled from hBN microsheets using the salt template method, then molded it into an hBN three-dimensional network structure, and finally prepared an hBN / EP composite material with a unique filler isolation structure by the impregnation method. Cui et al. prepared a nanoflower secondary hierarchical structure composed of hBN nanosheets by a pressure-switching one-step chemical synthesis method. This structure has a high specific surface area, and a filling amount of 3 wt% can increase the thermal conductivity of polyvinyl alcohol (PVA) film to 3.44 times that of pure PVA. However, to date, research on boron nitride hierarchical structures has mainly focused on the preparation and application of second-order hierarchical structures, while reports on higher-level multi-level hierarchical structures are scarce. It is well known that the physicochemical properties of inorganic materials are closely related to their morphology and structure. Therefore, conducting research on the synthesis and application of multi-level boron nitride structures has significant theoretical and practical implications. Summary of the Invention

[0004] The technical problem to be solved by this invention is to provide a one-dimensional boron nitride tertiary hierarchical structure and its preparation method, addressing the shortcomings of the existing technology. This invention is the first to prepare a one-dimensional boron nitride tertiary hierarchical structure with a unique morphology, consisting of boron nitride micron-sized hollow tubes, boron nitride nanosheets loaded on the surface of the hollow tubes, and bamboo-like boron nitride nanotubes. The preparation process does not require the use of alumina, silicon oxide, metal sheets, or other materials as a collection substrate for BN samples, and does not require high-end equipment, thus facilitating the mass production of high-purity, unique one-dimensional boron nitride tertiary hierarchical structure powder.

[0005] The technical solution adopted by the present invention to solve the above-mentioned problems is as follows:

[0006] A method for preparing a one-dimensional boron nitride tertiary hierarchical structure powder mainly includes the following steps:

[0007] (1) Using magnesium source and boron source as reaction raw materials, adding flux, and reacting by molten salt method to obtain boron-containing precursor; wherein, the flux is a mixture of any one or more of lithium chloride, sodium chloride, potassium chloride, etc. in any proportion;

[0008] (2) The boron-containing precursor and water-soluble nickel salt were added to the solvent water and ultrasonically dispersed evenly. Then, a certain concentration of sodium hydroxide solution was added dropwise, heated and stirred, filtered, washed with water and dried to obtain the [BO-Mg-Ni] precursor.

[0009] (3) The [BO-Mg-Ni] precursor was annealed in a nitrogen-containing atmosphere to obtain the crude nitrided product;

[0010] (4) The crude nitriding product is purified to obtain white boron nitride powder, which is the one-dimensional boron nitride three-level hierarchical structure powder.

[0011] According to the above scheme, the magnesium source is one or more of magnesium oxide, magnesium chloride, magnesium nitrate, magnesium hydroxide, etc., mixed in any proportion; the boron source is one or more of boric acid, boron oxide, borax, etc., mixed in any proportion.

[0012] According to the above scheme, in step (1), the molten salt reaction is calcined at 700-1000℃ for 4-6 hours, and the optimal calcination temperature is 1000℃ for 6 hours.

[0013] According to the above scheme, the molar ratio of magnesium source, boron source and water-soluble nickel salt is 1:(2~7):(0.05~0.2) of Mg:B:Ni, and the flux is 0.1 to 1 times the total mass of boron source and magnesium source.

[0014] According to the above scheme, in step (2), the stirring temperature during the heating and stirring process is 60-100℃, and the stirring time is 5-7h; the OH- concentration in the strong alkali solution is 1-10mol / L, and the OH- concentration is controlled. — The amount added is adjusted to bring the pH of the system to 9–11; the amount of water-soluble nickel salt added in the solvent water is 1–8 mg / mL.

[0015] According to the above scheme, in step (3), the nitrogen-containing atmosphere is one of N2 atmosphere, NH3 atmosphere, or a mixed atmosphere of N2 and H2, and the flow rate is 50ml / min to 200ml / min.

[0016] According to the above scheme, in step (3), the temperature is raised to 1000-1200℃ for annealing and held for 2-6 hours; among which, the optimal holding temperature is 1200℃ and the holding time is 5 hours.

[0017] According to the above scheme, the annealing process in step (3) uses a three-temperature zone tube furnace, which can form a stable temperature field and provide a stable reaction environment for the precursor nitriding process, which is conducive to improving the purity, content and stability of the product. In contrast, the traditional annealing process generally uses a single-temperature zone tube furnace, which has an unstable temperature field.

[0018] According to the above scheme, in step (4), the purification method is as follows: disperse the crude nitrided product in deionized water, add acid (such as 12mol / L concentrated hydrochloric acid) to adjust the pH of the system to about 1, heat and stir at 50-80℃ for 6-12h, then wash with deionized water and ethanol and centrifuge, and dry to complete the purification.

[0019] The one-dimensional boron nitride tertiary hierarchical structure powder prepared by the above method has a microstructure that shows it mainly consists of boron nitride micro-hollow tubes, boron nitride nanosheets and bamboo-like boron nitride nanotubes loaded on the surface of the boron nitride micro-hollow tubes. Specifically, the outer diameter of the boron nitride micro-hollow tubes ranges from 0.4 to 5 μm, the wall thickness ranges from 10 to 30 nm, and the tube length ranges from 4 to 30 μm; the diameter of the surface-loaded boron nitride nanosheets ranges from 50 to 150 nm, and the thickness ranges from 2 to 5 nm; the tube length of the surface-loaded bamboo-like boron nitride nanotubes ranges from 0.3 to 10 μm, and the diameter ranges from 50 to 150 nm.

[0020] In the synthesis of a one-dimensional boron nitride tertiary structure, the following chemical reactions may occur, taking the following example: MgCl2 as the magnesium source, H3BO3 as the boron source, NaCl as the flux, NiCl2 as the nickel salt, NaOH as the strong base, and NH3 as the atmosphere:

[0021] MgCl2+H3BO3+NaCl→ [B-Mg-O-Cl-Na] (1)

[0022] [B-Mg-O-Cl -Na]+ NiCl2+ NaOH→ [B-Mg-O-Ni-H] (2)

[0023] [B-Mg-O- Ni-H] + NH3 → BNNSs-BNNTs / BNMTs + MgO + H2O + Ni (3)

[0024] BNNSs-BNNTs / BNMTs + MgO+Ni+HCl→BNNSs-BNNTs / BNMTs +MgCl2+ NiCl2 +H2O(4)

[0025] In this invention, the possible reaction mechanism for preparing a one-dimensional boron nitride tertiary structure is as follows: the boron source originates from a solid [B-Mg-O-Ni] precursor. During the nitriding process, as the temperature gradually increases, the [B-Mg-O-Ni] precursor gradually becomes liquid. Some boron diffuses from the precursor to the surface and combines with the surrounding nitrogen-containing active gas to form BN crystal nuclei. According to the gas-liquid-solid catalytic growth mechanism, the [B-Mg-O-Ni] precursor also generates some [Mg-Ni] alloy droplets during the reaction, which act as a composite low-melting-point high-efficiency catalyst, promoting the formation of boron nitride microtubes. The formation process of the nanosheet structure on the surface of the microtube follows the VS growth mechanism. Simultaneously, after the formation of the BN microtube, another portion of the boron in the precursor forms a gaseous boron source at high temperature. Ni(OH)2 on the surface of the microtube in the precursor is reduced to Ni droplets as a catalyst. The gaseous boron source and the nitrogen-containing gas formed by the decomposition of ammonia form the initial BN crystal nuclei on the surface of the Ni droplets. Following the Ni-catalyzed top growth mechanism on the surface of boron nitride microtubes, a large number of BN nanotubes are eventually formed on the surface of boron nitride microtubes.

[0026] Compared with the prior art, the beneficial effects of the present invention are:

[0027] 1. This invention is the first to prepare a one-dimensional boron nitride tertiary hierarchical structure with a special morphology, which is mainly composed of boron nitride micron hollow tubes, boron nitride nanosheets and bamboo-shaped boron nitride nanotubes loaded on the surface of the boron nitride micron hollow tubes. The sample has a high specific surface area and has potential application prospects in the fields of adsorption, surface modification, functionalization, thermal conductivity and material reinforcement and toughening.

[0028] 2. This invention eliminates the need for alumina, silicon dioxide, or metal sheets as a collection substrate for BN samples, facilitating the mass production of high-purity, unique one-dimensional boron nitride powder with a three-level hierarchical structure. Furthermore, this invention utilizes common, traditional commercial raw materials and reagents, eliminating the need for high-end equipment, resulting in a simple process, low production costs, and significant industrialization potential.

[0029] 3. This invention utilizes a highly active [Mg-Ni-] composite metal as a catalyst. Compared with single metal catalysts, it has a lower eutectic point and can improve the activity of the catalyst at relatively low temperatures, which is beneficial for the efficient preparation of one-dimensional boron nitride three-level hierarchical structures, thereby improving yield and purity. Attached Figure Description

[0030] Figure 1 The image shown is a scanning electron microscope (SEM) image of BN obtained in Example 1.

[0031] Figure 2 Here is a scanning electron microscope (SEM) image of BN obtained for comparison, where Figure 2 a is the graph obtained from Comparative Example 1. Figure 2 b is the graph obtained from Comparative Example 2.

[0032] Figure 3 This is a transmission electron microscope (TEM) image of BN obtained in Example 1.

[0033] Figure 4 The image shows the X-ray diffraction (XRD) pattern of BN obtained in Example 1.

[0034] Figure 5 The image shows the infrared (FT-IR) spectrum of BN obtained in Example 1. Detailed Implementation

[0035] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0036] In the following embodiments, the tube furnace is a 3-temperature zone tube furnace with a stable temperature zone length of 30cm.

[0037] In the following examples, the morphology was observed using a Gemini SEM 300 scanning electron microscope (FSEM) (Carl Zeiss); the internal microstructure of the samples was studied using a JEM2100-F transmission electron microscope (TEM); the products were ultrasonically dispersed in anhydrous ethanol and dropped onto a copper grid; the X-ray diffraction (XRD) analysis of the obtained products was performed using an Empyrean X-ray powder diffractometer. 2θ was 10-90°; Infrared analysis was performed using a Thermo Nexus 670 Fourier transform infrared spectrometer (Thermo Fisher, USA); Raman analysis was performed using a Thermo Fisher DXR laser confocal micro Raman spectrometer (Thermo Fisher, USA).

[0038] Comparative Example 1

[0039] A method for preparing a one-dimensional boron nitride secondary hierarchical structure includes the following steps:

[0040] (1) According to the molar ratio of MgCl2·6H2O and H3BO3 of 1:4, and the flux of MgCl2·6H2O and H3BO3 of 0.5, weigh 11.13g H3BO3, 9.16g MgCl2·6H2O, and 10.14g NaCl, mix them and grind them thoroughly for 15min. Then put them into a muffle furnace and heat them to 1000℃ at a heating rate of 5℃ / min. Hold them at this temperature for 6 hours and cool them to room temperature with the furnace to obtain the boron-containing precursor.

[0041] (2) Add 300 ml of deionized water to a beaker, add the precursor obtained in step (1), and sonicate for 15 min. Then add 4 mol / L NaOH solution to the beaker until the pH is 10. Then heat to 80 °C in a water bath crucible and stir at 300 r / min for 10 h. After filtration, wash three times with deionized water and dry to obtain the [BO-Mg] precursor.

[0042] (3) The [BO-Mg] precursor prepared above is evenly dispersed in a crucible, placed in a tube furnace, and after vacuuming, ammonia gas is introduced at a flow rate of 100 ml / min. The furnace is kept at 1150℃ for 5 h, cooled to 200℃ with the furnace, the gas valve is closed, and the furnace is allowed to cool naturally to room temperature to obtain the crude product.

[0043] (3) Disperse the crude product in 150ml of distilled water, add 100ml of 12mol / L hydrochloric acid, heat and stir at 80℃ for 12h, then wash with deionized water and centrifuge three times, wash with ethanol twice, and finally vacuum dry at 60℃ for 12h to obtain boron nitride microtube hierarchical structure powder with surface-loaded nanosheets, denoted as BN sample.

[0044] like Figure 2 The image shows the SEM spectrum of the BN sample prepared in this comparative example. Figure 2 (a) It can be seen that the BN sample is a boron nitride microtube with a diameter ranging from 1 to 3 μm, and the surface is loaded with boron nitride nanosheets with an average thickness of about 3 nm. The main reason for the difference between Comparative Example 1 and the Example is the lack of the process of Ni salt precipitation to coat the surface of the boron-containing precursor, which resulted in the Example only obtaining a conventional one-dimensional microtube secondary hierarchical structure with surface-coated nanosheets.

[0045] Example 1

[0046] A method for preparing a one-dimensional boron nitride tertiary hierarchical structure includes the following steps:

[0047] (1) According to the molar ratio of MgCl2·6H2O and H3BO3 of 1:4, and the flux of MgCl2·6H2O and H3BO3 of 0.5, weigh 11.13g H3BO3, 9.15g MgCl2·6H2O, and 10.14g NaCl, mix them and grind them thoroughly for 15min. Then put them into a muffle furnace and heat them to 1000℃ at a heating rate of 5℃ / min. Hold them at this temperature for 6 hours and cool them to room temperature with the furnace to obtain the boron-containing precursor.

[0048] (2) Add 300 ml of deionized water to a beaker, add the boron-containing precursor obtained in step (1) and 1.07 g of NiCl2·6H2O (the molar ratio of MgCl2·6H2O and NiCl2·6H2O is 1:0.1), disperse by ultrasonication for 15 min, add 4 mol / L NaOH solution to the beaker until the pH is 10, then heat to 80 °C in a water bath crucible, stir at 300 r / min for 10 h, filter, wash three times with deionized water and dry to obtain the [BO-Mg-Ni] precursor;

[0049] (3) The [BO-Mg-Ni] precursor prepared above is evenly dispersed in a crucible, placed in a tube furnace, and after vacuuming, ammonia gas is introduced at a flow rate of 150 ml / min. The furnace is kept at 1150℃ for 5 h, cooled to 200℃ with the furnace, the gas valve is closed, and the furnace is allowed to cool naturally to room temperature to obtain the crude product.

[0050] (3) Disperse the crude product in 150ml of distilled water, add 100ml of 12mol / L hydrochloric acid, heat and stir at 80℃ for 12h, then wash with deionized water and centrifuge three times, wash with ethanol twice, and finally vacuum dry at 60℃ for 12h to obtain silvery-white one-dimensional three-level hierarchical boron nitride powder, denoted as BN sample.

[0051] like Figure 1 The image shows the SEM spectrum of the BN sample prepared in this embodiment. Figure 1 (a, b, c, d) indicates that the BN sample is a one-dimensional boron nitride tertiary structure (i.e., BNNTs / BNMTs sample) consisting of boron nitride micro-hollow tubes, boron nitride nanosheets and bamboo-like boron nitride nanotubes loaded on the surface of the boron nitride micro-hollow tubes; the outer diameter of the boron nitride micro-hollow tubes ranges from 0.5 to 3.5 μm, the tube length from 5 to 30 μm, and the wall thickness from 10 to 30 nm; the surface of the micro-hollow tubes has a large number of boron nitride nanosheets and bamboo-like boron nitride nanotubes; the tube length of the nanotubes is mainly concentrated in the range of 0.5 to 8 μm, the diameter is mainly concentrated in the range of 75 to 150 nm, and the average diameter is about 100 nm; the average diameter of the nanosheets is about 120 nm, and the thickness is about 2 to 4 nm.

[0052] like Figure 3 The image shows a TEM image of the BNNSs-BNNTs / BNMTs sample prepared in this embodiment. As can be seen from the figure, the microtube sample has a micron-sized hollow tube morphology, and the tube is loaded with a large number of bamboo-like nanotubes. The average diameter of the nanotubes is about 80-100 nm, and clear lattice fringes can be observed. The lattice spacing is about 0.33 nm, which is consistent with the lattice constant of the (002) crystal plane of hBN, indicating that it is an hBN material.

[0053] like Figure 4 As shown, the XRD pattern of the BN sample prepared in this embodiment has five obvious diffraction peaks, located at 2θ = 26.63°, 42.16°, 42.91°, 54.96°, and 76.42°, respectively. The peaks correspond to the (002), (100), (101), (004), and (110) crystal planes of h-BN crystal (JCPDF No. 45-1171), indicating that the sample has no impurity phase and high crystallinity.

[0054] like Figure 5 As shown in the FTIR spectrum of the BN sample prepared in this embodiment, there are three obvious characteristic absorption peaks, located at 802 cm⁻¹. -1 1380cm -1 3417cm -1 Location. Among them, 1380cm -1 and 802cm -1 The absorption peaks at these locations correspond to the in-plane stretching vibration and out-of-plane bending vibration of the BN bond in the h-BN material, respectively, while the peak at 3417 cm⁻¹ corresponds to these vibrations. -1 The absorption peak at that point is usually due to the stretching vibration of OH bonds in adsorbed water or slight surface oxidation.

[0055] Example 2

[0056] A method for preparing a one-dimensional boron nitride tertiary hierarchical structure includes the following steps:

[0057] (1) According to the molar ratio of MgCl2·6H2O and H3BO3 of 1:2, and the flux of MgCl2·6H2O and H3BO3 of 0.8, weigh 5.57g H3BO3, 9.17g MgCl2·6H2O, and 11.78g NaCl, mix them and grind them thoroughly for 15min. Then put them into a muffle furnace and heat them to 950℃ at a heating rate of 5℃ / min. Hold them at that temperature for 6 hours and cool them to room temperature with the furnace to obtain the boron-containing precursor.

[0058] (2) Add 300 ml of deionized water to a beaker, add the boron-containing precursor obtained in step (1) and 0.54 g of NiCl2·6H2O (the molar ratio of MgCl2·6H2O and NiCl2·6H2O is 1:0.05), disperse by ultrasonication for 15 min, add 4 mol / L NaOH solution to the beaker until the pH is 10, then heat to 80 °C in a water bath crucible, stir at 300 r / min for 10 h, filter, wash three times with deionized water and dry to obtain the [BO-Mg-Ni] precursor;

[0059] (3) The [BO-Mg-Ni] precursor prepared above is evenly dispersed in a crucible, placed in a tube furnace, and after vacuuming, ammonia gas is introduced at a flow rate of 50 ml / min. The furnace is kept at 1200℃ for 5 h, cooled to 200℃ with the furnace, the gas valve is closed, and the furnace is allowed to cool naturally to room temperature to obtain the crude product.

[0060] (3) Disperse the crude product in 150ml of distilled water, add 100ml of 12mol / L hydrochloric acid, heat and stir at 80℃ for 12h, then wash with deionized water and centrifuge three times, wash with ethanol twice, and finally vacuum dry at 60℃ for 12h to obtain silver-white surface-loaded nanotube hierarchical boron nitride powder, denoted as BN sample.

[0061] The BN sample obtained in Example 2 is a one-dimensional boron nitride tertiary structure consisting of boron nitride micro-hollow tubes, boron nitride nanosheets loaded on the surface of the boron nitride micro-hollow tubes, and bamboo-shaped boron nitride nanotubes. The micro-tubes are hollow short tubes with a length ranging from 1 to 10 μm. The surface of the micro-tubes is loaded with a small amount of boron nitride nanotubes with a length of 1 to 10 μm and an average diameter of about 120 nm.

[0062] Comparative Example 2

[0063] A method for preparing a hierarchical boron nitride structure with surface-loaded nanosheets, comprising the following steps:

[0064] (1) According to the molar ratio of MgCl2·6H2O and H3BO3 1:1, the flux is 0.6 of the sum of the masses of MgCl2·6H2O and H3BO3. Weigh 1.87g H3BO3, 6.11g MgCl2·6H2O, and 4.77g NaCl, mix them and grind them thoroughly for 15min. Heat them in a muffle furnace to 850℃ and keep them at that temperature for 6 hours. Then cool them to room temperature with the furnace to obtain the precursor.

[0065] (2) Add 300 ml of deionized water to a beaker, add the precursor obtained in step (1) and 0.71 g of NiCl2·6H2O (the molar ratio of MgCl2·6H2O and NiCl2·6H2O is 1:0.1), disperse by ultrasonication for 15 min, add 4 mol / L NaOH solution to the beaker until the pH is 10, then heat to 80 °C in a water bath crucible and stir at 300 r / min for 10 h, then filter, wash three times with deionized water and dry.

[0066] (3) The above-prepared precursor is evenly dispersed in a crucible, placed in a tube furnace, and after vacuuming, ammonia gas is introduced at a flow rate of 100 ml / min. The furnace is kept at 1200℃ for 5 hours, then cooled to 200℃ with the furnace. The gas valve is closed, and the furnace is allowed to cool naturally to room temperature to obtain the crude product.

[0067] (3) Disperse the crude product in 150ml of distilled water, add 100ml of 12mol / L hydrochloric acid, heat and stir at 80℃ for 12h, then wash with deionized water and centrifuge three times, wash with ethanol twice, and finally vacuum dry at 60℃ for 12h to obtain boron nitride powder, which is recorded as BN sample.

[0068] like Figure 2 As shown in (b), the BN sample obtained in Comparative Example 2 is an elliptical hollow sphere with a large number of nanosheets loaded on its surface. It is severely aggregated, and the diameter of the elliptical hollow sphere is between 1 and 10 μm.

[0069] Example 3

[0070] A method for preparing a one-dimensional boron nitride tertiary hierarchical structure includes the following steps:

[0071] (1) According to the molar ratio of MgCl2·6H2O and H3BO3 of 1:7, and the flux of MgCl2·6H2O and H3BO3 of 1.0, weigh 19.49g H3BO3, 9.18g MgCl2·6H2O, and 28.62g NaCl, mix them and grind them thoroughly for 15min. Then put them into a muffle furnace and heat them to 950℃ at a heating rate of 5℃ / min. Hold them at that temperature for 6 hours and cool them to room temperature with the furnace to obtain the boron-containing precursor.

[0072] (2) Add 300 ml of deionized water to a beaker, add the boron-containing precursor obtained in step (1) and 1.18 g of NiCl2·6H2O (the molar ratio of MgCl2·6H2O and NiCl2·6H2O is 1:0.11), disperse by ultrasonication for 15 min, add 4 mol / L NaOH solution to the beaker until the pH is 10, then heat to 80 °C in a water bath crucible, stir at 300 r / min for 10 h, filter, wash three times with deionized water and dry to obtain the [BO-Mg-Ni] precursor;

[0073] (3) The [BO-Mg-Ni] precursor prepared above is evenly dispersed in a crucible, placed in a tube furnace, and after vacuuming, ammonia gas is introduced at a flow rate of 200 ml / min. The furnace is kept at 1200℃ for 5 h, cooled to 200℃ with the furnace, the gas valve is closed, and the furnace is allowed to cool naturally to room temperature to obtain the crude product.

[0074] (3) Disperse the crude product in 150ml of distilled water, add 100ml of 12mol / L hydrochloric acid, heat and stir at 80℃ for 12h, then wash with deionized water and centrifuge three times, wash with ethanol twice, and finally vacuum dry at 60℃ for 12h to obtain boron nitride powder, which is recorded as BN sample.

[0075] The BN sample obtained in Example 3 is a one-dimensional boron nitride tertiary structure consisting of boron nitride micro-hollow tubes, boron nitride nanosheets loaded on the surface of the hollow tubes, and bamboo-like boron nitride nanotubes. The micro-tubes are hollow tubes with a diameter of 2-4 μm and a length of 10-30 μm. The surface of the micro-tubes is loaded with boron nitride nanotubes with an average diameter of 80 nm. The nanosheets on the surface of the micro-tubes have an average diameter of about 120 nm and an average thickness of about 4 nm.

[0076] Example 4

[0077] A method for preparing a one-dimensional boron nitride tertiary hierarchical structure includes the following steps:

[0078] (1) According to the molar ratio of MgCl2·6H2O and H3BO3 of 1:4, and the flux of 0.4 times the mass of MgCl2·6H2O and H3BO3, weigh 8.36g of H3BO3, 9.20g of MgCl2·6H2O, and 8.76g of NaCl, mix them and grind them thoroughly for 15min. Then put them into a muffle furnace and heat them to 950℃ at a heating rate of 5℃ / min. Hold them at that temperature for 6 hours and cool them to room temperature with the furnace to obtain the boron-containing precursor.

[0079] (2) Add 300 ml of deionized water to a beaker, add the boron-containing precursor obtained in step (1) and 0.73 g of NiCl2·6H2O (the molar ratio of MgCl2·6H2O and NiCl2·6H2O is 1:0.067), disperse by ultrasonication for 15 min, add 4 mol / L NaOH solution to the beaker until the pH is 10, then heat to 80 °C in a water bath crucible, stir at 300 r / min for 10 h, filter, wash three times with deionized water and dry to obtain the [BO-Mg-Ni] precursor;

[0080] (3) The [BO-Mg-Ni] precursor prepared above is evenly dispersed in a crucible, placed in a tube furnace, and after vacuuming, ammonia gas is introduced. The furnace is kept at 1200℃ for 5 hours, cooled to 200℃ with the furnace, the gas valve is closed, and the furnace is allowed to cool naturally to room temperature to obtain the crude product.

[0081] (3) Disperse the crude product in 150ml of distilled water, add 100ml of 12mol / L hydrochloric acid, heat and stir at 80℃ for 12h, then wash with deionized water and centrifuge three times, wash with ethanol twice, and finally vacuum dry at 60℃ for 12h to obtain boron nitride powder, which is recorded as BN sample.

[0082] The BN sample obtained in Example 4 is a one-dimensional boron nitride tertiary structure consisting of boron nitride micro-hollow tubes, boron nitride nanosheets loaded on the surface of the hollow tubes, and bamboo-like boron nitride nanotubes. The micro-tubes are hollow tubes with a diameter of 1 to 4 μm and a length of 5 to 25 μm. A small number of nanotubes are loaded on the surface of the micro-tubes, with a length of 1 to 4 μm and an average diameter of about 100 nm.

[0083] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements and modifications without departing from the inventive concept of the present invention, and these all fall within the protection scope of the present invention.

Claims

1. A method for preparing a one-dimensional boron nitride tertiary hierarchical structure, characterized in that, The main steps are as follows: (1) Using magnesium source and boron source as reaction raw materials, a flux is added and calcined at 700~1000℃ to obtain a boron-containing precursor; wherein, the flux is any one or more of lithium chloride, sodium chloride and potassium chloride in any proportion; wherein, the magnesium source and boron source are fed in a molar ratio of Mg to B of 1:2~7, and the flux is 0.1~1 times the total mass of boron source and magnesium source; (2) Add the boron-containing precursor and nickel salt to the solvent water and ultrasonically disperse them evenly. Then add a strong alkali solution, heat and stir, then filter, wash with water and dry to obtain the [BO-Mg-Ni] precursor. The ratio between the amount of water-soluble nickel salt and the magnesium source in step (1) is calculated as the molar ratio of Mg to Ni, and is in the range of 1: (0.05~0.2). (3) The [BO-Mg-Ni] precursor is heated to 1000~1200℃ in a nitrogen-containing atmosphere and held for a period of time to obtain the crude nitrided product; (4) The crude nitriding product was purified to obtain white boron nitride powder, which is a one-dimensional boron nitride three-level hierarchical structure; The one-dimensional boron nitride three-level hierarchical structure is formed by loading boron nitride nanosheets and bamboo-like boron nitride nanotubes onto the surface of boron nitride micro-hollow tubes; wherein, the outer diameter of the boron nitride micro-hollow tubes is in the range of 0.4~5μm, the wall thickness is in the range of 10~30nm, and the tube length is in the range of 1~30μm; the boron nitride nanotubes have a tube length of 0.3~10μm and a diameter in the range of 50~150nm.

2. The method for preparing a one-dimensional boron nitride three-level hierarchical structure according to claim 1, wherein the calcination time in step (1) is 4~6h.

3. The method for preparing a one-dimensional boron nitride three-level hierarchical structure according to claim 1, wherein in step (1), the magnesium source is one or more of magnesium oxide, magnesium chloride, magnesium nitrate, and magnesium hydroxide in any proportion; and the boron source is one or more of boric acid, boron oxide, and borax in any proportion.

4. According to the method for preparing a one-dimensional boron nitride tertiary hierarchical structure as described in claim 1, in step (2), the stirring temperature during the heating and stirring process is 40~60℃, and the stirring time is 5~7h; the OH in the strong alkaline solution — The concentration is 1~10 mol / L, and the OH content is controlled. — The amount added should be adjusted to bring the pH of the system to 9-11; the amount of water-soluble nickel salt added to the solvent water should be 1-8 mg / mL.

5. The method for preparing a one-dimensional boron nitride three-level hierarchical structure according to claim 1, wherein in step (3), the nitrogen-containing atmosphere is one of N2 atmosphere, NH3 atmosphere, or a mixed atmosphere of N2 and H2, and the flow rate is 50 ml / min to 200 ml / min.

6. In the preparation method of a one-dimensional boron nitride three-level hierarchical structure according to claim 1, in step (3), the annealing temperature is 1000~1200℃ and the holding time is 2~6h.

7. The method for preparing a one-dimensional boron nitride three-level hierarchical structure according to claim 1, characterized in that... In step (4), the purification method is as follows: the crude nitrided product is dispersed in solvent water, acid is added to adjust the pH to 0.5~1.5, heated and stirred at 50~80℃ for 6~12h, then washed with water and ethanol and centrifuged, and dried to complete the purification.

Images