Three-dimensional hollow network structure boron nitride and preparation method thereof

Abstract

The application relates to a three-dimensional hollow network structure boron nitride, and a main process of a preparation method thereof is as follows: taking citric acid, sodium borate and strontium carbonate as raw materials, a boron-containing precursor is obtained through a sol-gel method; then, the boron-containing precursor is pre-nitridated under a nitrogen-containing atmosphere to obtain a pre-nitridation product; next, the pre-nitridation product is uniformly mixed with ammonium borate and ammonium chloride through ball milling, and then is placed into a high-pressure reaction kettle to react, so that the three-dimensional hollow network structure boron nitride is obtained. The three-dimensional hollow network structure boron nitride prepared by the application has a connected network structure formed by multiple cavity units, has high purity, provides a new idea for preparation of a hollow boron nitride structure, and has a good application prospect in the fields of gas adsorption, water pollution treatment, hydrogen storage and a drug carrier.

Description

Technical Field

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

[0002] Hexagonal boron nitride (h-BN) is a compound belonging to the III-V group. It is a white, lubricating hexagonal crystalline material with a structure and properties similar to graphite, hence it is also known as "white graphite." BN materials possess advantages such as good chemical stability, thermal stability, and biocompatibility, low dielectric constant, high electric field breakdown strength, and good processability, making them a promising new functional material with significant application value. Hollow h-BN materials further exhibit characteristics such as large hollow cavities, high specific surface area, large pore volume, abundant structural defects, partial ionic BN bonds, and slight surface buckling. This material shows great potential for applications in water pollution treatment, hydrogen storage, and toxic gas adsorption.

[0003] Currently, there are many methods for preparing hierarchical boron nitride structures with different structures, such as the high-pressure phenylthermal method, the high-temperature molten salt method, and chemical vapor deposition. Reports of such hierarchical structures include: Wang Jilin et al. prepared hollow boron nitride tubes with oriented layering forming the tube wall using boric acid, magnesium nitrate, and ammonia as raw materials through a high-temperature nitriding and high-pressure synthesis process. Chen Wenzhuo et al. prepared a precursor using magnesium chloride hexahydrate and boric acid as raw materials, and then carried out a nitriding reaction in a tube furnace using the precursor as a boron source, thus obtaining for the first time a one-dimensional hierarchical thin-walled BN micron-sized square tube with a special morphology. Yin Hong et al. synthesized a sea urchin-shaped nanotube-sphere hierarchical structure by assembling boron nitride nanospheres and boron nitride nanotubes using a simple process; furthermore, by controlling the morphology and size, their specific surface area, catalytic activity, and adsorption activity can be improved. Zhang et al. synthesized a BN nanocarpet composed of nanosheets and nanorods using a modified hot-press phenylthermal method, which has a large specific surface area and high-density structural defects, exhibiting rapid adsorption capacity for methylene blue solution in aqueous solution. Wang et al. prepared a sea urchin-like boron nitride (BN) layered structure assembled from nanotubes and nanosheets using a two-step method. They proposed gas-liquid-solid and gas-solid composite growth mechanisms to control the formation of the BN layered structure, which showed significant progress in the adsorption of heavy metal ions. However, the reaction temperature of this preparation process reached 1400℃, and the process was complex.

[0004] To date, most of the reported hierarchical structures of hollow boron nuclei (BN) are one-dimensional, and there are very few reports on three-dimensional hierarchical structures of hollow boron nuclei. Summary of the Invention

[0005] The technical problem to be solved by this invention is to provide a three-dimensional hollow network structure boron nitride and its preparation method, addressing the shortcomings of existing technologies. This invention utilizes citric acid, sodium borate, and strontium carbonate as raw materials, obtaining a boron-containing precursor via a sol-gel method. Then, a BN-encapsulated [Sr-O-Na] precursor is formed through high-temperature pre-nitridation, followed by a high-pressure reaction with ammonium borate and ammonium chloride to obtain a three-dimensional hollow network structure boron nitride.

[0006] The technical solution adopted by the present invention to solve the above-mentioned problems is as follows:

[0007] A three-dimensional hollow network structure of boron nitride has a microstructure consisting of multiple interconnected network units. The size of each cavity unit is in the range of 0.3-1 μm, and the wall thickness of the cavity is in the range of 30-100 nm (generally, the wall thickness of the cavity is in the range of 30-50 nm). The cavity surface is loaded with boron nitride nanosheets.

[0008] The preparation method of the above-mentioned three-dimensional hollow network structure boron nitride includes the following steps:

[0009] (1) Strontium carbonate, sodium borate and citric acid are mixed and dissolved in pure water, then stirred evenly to carry out sol-gel reaction to obtain gel;

[0010] (2) The gel obtained in step (1) is placed in a muffle furnace and calcined to obtain a boron-containing precursor;

[0011] (3) The boron-containing precursor obtained in step (2) is pre-nitrided in a nitrogen atmosphere to obtain the pre-nitrided product;

[0012] (4) The pre-nitrided product obtained in step (3) is ball-milled and mixed with ammonium borate and ammonium chloride, and then placed in a high-pressure reactor to react and obtain crude product;

[0013] (5) After acid washing and drying of the crude product obtained in step (4), boron nitride with a three-dimensional hollow network structure is obtained.

[0014] According to the above scheme, in step (1), the molar ratio of strontium carbonate and sodium borate is 1:1 to 1:5; the amount of citric acid added accounts for 20 to 40% of the total molar amount of strontium carbonate and sodium borate.

[0015] According to the above scheme, in step (1), the concentration of sodium borate in the solvent water is 3-5 mol / L, and the concentration of strontium carbonate in the solvent water is 1-4 mol / L.

[0016] According to the above scheme, in step (1), the stirring is carried out by water bath heating, the heating temperature is 50-100℃, and the time is 6-18h.

[0017] According to the above scheme, in step (2), the calcination temperature is 800-950℃ and the holding time is 3-8h.

[0018] According to the above scheme, in step (3), the nitrogen-containing atmosphere is NH3 atmosphere, the flow rate is 50-200 mL / min; the pre-nitriding temperature is 850-1000℃, and the holding time is 2-6 h.

[0019] According to the above scheme, in step (4), the mass ratio of the pre-nitrided product to ammonium borate and ammonium chloride is (5-11):1:1.

[0020] According to the above scheme, in step (4), the reaction time in the high-pressure reactor is 4 to 8 hours and the reaction temperature is 500 to 600°C.

[0021] According to the above scheme, in step (5), the acid washing involves dispersing the crude product in 4-10 mol / L hydrochloric acid and heating and stirring for 4-8 hours; after the acid washing is completed, the drying temperature is 50-70℃ and the time is 8-12 hours.

[0022] In the synthesis process of the three-dimensional hollow network structure boron nitride of this invention, the following chemical reactions may occur:

[0023] SrCO3 (l) + Na2B4O7 (l) + C6H8O7 (l) →[Sr-BO-Na] (s) (1)

[0024] [Sr-BO-Na] (s) + NH3 (g) → [B-Sr-ON-Na] (s) (2)

[0025] [B-Sr-ON-Na] (s) → [Sr-O-Na] / BN Layer (3)

[0026] NH4HB4O7·3H2O (s) → NH3 (g) +B* (g) +H2O (g) (4)

[0027] NH3 (g) → N* (g) + H2 (g) (5)

[0028] NH4Cl (s) → N* (g) + H2 (g) + HCl (g) (6)

[0029] [Sr-O-Na] / BN Layer(s)+N*(g)+B*(g)+HCl(g)+H2(g)→3D-BN(s)+[Sr-Cl](s)+NaCl(s)+H2O(l)(7)

[0030] The possible reaction mechanism of the above synthesis process is as follows: A boron-containing precursor [Sr-BO-Na] is synthesized via a sol-gel method, followed by pre-nitridation in a tube furnace. During nitridation, as the temperature gradually increases, the [Sr-BO-Na] precursor gradually becomes liquid, and boron is precipitated from the precursor surface to form gaseous boron oxide. Due to the concentration difference, the boron inside diffuses continuously to the outside, reacting with the external nitrogen-reactive gas using the precursor as a template to form a [Sr-O-Na] / BN Layer (cavity unit). Under high temperature and high pressure conditions, NH4HB4O7·3H2O and NH4Cl decompose to form a highly reactive mixed gas containing B*, N*, NH3, and H2. B* further reacts with the newly generated highly reactive N-containing mixed gas and combines with the [Sr-O-Na] / BN Layer surface to form BN crystal nuclei. According to the gas-solid (VS) growth mechanism, BN crystal nuclei gradually grow to form BN nanosheets. After the reaction is completed, the obtained product is washed with hydrochloric acid and nitric acid water, thus finally generating boron nitride with a unique three-dimensional hollow mesh hierarchical structure.

[0031] Compared with the prior art, the beneficial effects of the present invention are:

[0032] 1. This invention uses citric acid, sodium borate and strontium carbonate as raw materials to obtain a boron-containing precursor through a sol-gel method. Then, a preliminary pre-nitriding reaction is carried out in a tube furnace to form a BN / [Sr-O-Na] precursor, which is then reacted with ammonium borate and ammonium chloride under high temperature and high pressure to obtain a three-dimensional hollow network structure boron nitride.

[0033] 2. The three-dimensional hollow network structure boron nitride prepared by this invention has a connected network structure composed of multiple cavity units, high purity, regular morphology, and boron nitride nanosheets loaded on the surface, providing a new approach for the preparation of hollow BN structures. At the same time, it has good application prospects in the fields of gas adsorption, water pollution treatment, hydrogen storage and drug carrier. Attached Figure Description

[0034] Figure 1 The image shows the scanning electron microscope (SEM) image of the BN sample obtained in Comparative Example 1.

[0035] Figure 2 The image shown is a scanning electron microscope (SEM) image of the BN sample obtained in Example 1.

[0036] Figure 3 The image shows the X-ray diffraction (XRD) pattern of the BN sample obtained in Example 1.

[0037] Figure 4 The image shows the infrared (FTIR) spectrum of the BN sample obtained in Example 1.

[0038] Figure 5The image shows the Raman spectrum of the BN sample obtained in Example 1. Detailed Implementation

[0039] 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.

[0040] In the following examples, the morphology of the obtained products was observed using a GeminiSEM300 (Carl Zeiss) scanning electron microscope (SEM); X-ray diffraction analysis (XRD) was performed using a Rigaku D / MAX-LLIA X-ray powder diffractometer. 2θ ranges from 5 to 80°; Fourier transform infrared (FTIR) spectroscopy was performed using a Thermo Nexus 470 Fourier transform infrared spectrometer (ThermoNicol); Raman spectroscopy was performed using a Thermo Fisher DXR Raman spectrometer (Thermo Fisher, USA).

[0041] Comparative Example 1

[0042] A method for preparing boron nitride, comprising the following steps:

[0043] (1) Strontium carbonate, sodium borate, and citric acid were mixed and dissolved in 200 mL of deionized water under magnetic stirring at room temperature, so that the concentrations of sodium borate, strontium carbonate, and citric acid were 4 mol / L, 2 mol / L, and 2.4 mol / L, respectively. The mixture was then stirred until homogeneous to obtain a precursor solution. Subsequently, the solution was heated in a water bath with stirring (80 °C, 12 h) until a gel was formed. The gel was then calcined in a muffle furnace at 800 °C for 6 h to obtain a boron-containing precursor.

[0044] (2) The above boron-containing precursor was placed in a tube furnace, and ammonia gas was introduced after vacuuming. The ammonia gas flow rate was 150 ml / min. The furnace was kept at 950°C for 120 min, cooled to 200°C, the gas valve was closed, and the furnace was allowed to cool naturally to room temperature to obtain the pre-nitrided product.

[0045] (3) Disperse the pre-nitrided product in 20 ml of distilled water, add 50 ml of 12 mol / L hydrochloric acid, heat and stir at 50 °C for 4 h, then wash with deionized water and centrifuge three times, wash with ethanol three times, and finally vacuum dry at 70 °C for 10 h to obtain a boron nitride, denoted as BN sample.

[0046] like Figure 1 As shown in the SEM image of the BN sample prepared in this comparative example, it can be seen that the cavity surface of the BN sample is relatively smooth, without boron nitride nanosheet loading, and the network structure is not interconnected or intertwined.

[0047] Example 1

[0048] A method for preparing a three-dimensional hollow network structure of boron nitride includes the following steps:

[0049] (1) Strontium carbonate, sodium borate, and citric acid were mixed and dissolved in 200 mL of deionized water under magnetic stirring at room temperature, so that the concentrations of sodium borate, strontium carbonate, and citric acid were 4 mol / L, 2 mol / L, and 2.4 mol / L, respectively. The mixture was then stirred until homogeneous to obtain a precursor solution. Subsequently, the solution was heated in a water bath with stirring (80 °C, 12 h) until a gel was formed. The gel was then calcined in a muffle furnace at 800 °C for 6 h to obtain a boron-containing precursor.

[0050] (2) The above boron-containing precursor was placed in a tube furnace, and ammonia gas was introduced after vacuuming. The ammonia gas flow rate was 150 ml / min. The furnace was kept at 950°C for 120 min, cooled to 200°C, the gas valve was closed, and the furnace was allowed to cool naturally to room temperature to obtain the pre-nitrided product.

[0051] (3) The pre-nitrided product was ball-milled with ammonium borate and ammonium chloride at a mass ratio of 8:1:1 and then placed in a high-pressure reactor to react for 4 hours at a reaction temperature of 500℃ to obtain the crude product.

[0052] (4) Disperse the crude product in 20 ml of distilled water, add 50 ml of 12 mol / L hydrochloric acid, heat and stir at 50 °C for 4 h, then wash with deionized water and centrifuge three times, wash with ethanol three times, and finally vacuum dry at 70 °C for 10 h to obtain a three-dimensional hollow grid hierarchical boron nitride, denoted as 3D-BN sample.

[0053] like Figure 2 As shown in the SEM image of the 3D-BN sample prepared in this embodiment, the microstructure of the 3D-BN sample is a connected network structure composed of multiple cavity units. The size of each cavity unit is in the range of 0.3-1μm, the wall thickness of the cavity is in the range of 30-50nm, and the cavity surface is loaded with boron nitride nanosheets.

[0054] like Figure 3 As shown, the XRD pattern of the 3D-BN sample prepared in this embodiment has five obvious diffraction peaks, located at 2θ = 26.75°, 41.59°, 43.40°, 54.94°, and 76.08°, respectively. The peaks correspond to the (002), (100), (101), (004), and (110) crystal planes of the h-BN crystal (JCPDF No. 34-0421), indicating that the sample has no impurity phase and has high purity.

[0055] like Figure 4The image shows the FTIR spectrum of the 3D-BN sample prepared in this embodiment. The spectrum reveals three distinct characteristic absorption peaks, located at 810 cm⁻¹. -1 1380cm -1 and 3440cm -1 Among them, at 810cm -1 and 1380cm -1 The absorption peaks at 3440 cm⁻¹ correspond to the out-of-plane and in-plane stretching vibrations of the h-BN crystal, respectively. -1 The absorption peak at that point is usually due to the stretching vibration of the OH bonds in the adsorbed water.

[0056] like Figure 5 As shown in the Raman spectrum of the 3D-BN sample prepared in this embodiment, the value is located at 1430 cm⁻¹. -1 The diffraction peak at that location is the E of h-BN. 2g Caused by in-plane tensile vibration.

[0057] Example 2

[0058] A method for preparing a three-dimensional hollow network structure of boron nitride includes the following steps:

[0059] (1) Strontium carbonate, boric acid, and citric acid were mixed and dissolved in 200 mL of deionized water under magnetic stirring at room temperature, so that the concentrations of sodium borate, strontium carbonate, and citric acid were 4 mol / L, 2 mol / L, and 2.4 mol / L, respectively. The mixture was then stirred until homogeneous to obtain a precursor solution. Subsequently, the solution was heated in a water bath with stirring (80 °C, 12 h) until a gel was formed. The gel was then calcined in a high-temperature furnace at 800 °C for 6 h. The gel was then removed and ground to obtain a boron-containing precursor.

[0060] (2) Place the above boron-containing precursor in a tube furnace, evacuate the furnace and then introduce ammonia gas at a flow rate of 200 ml / min. Keep the furnace at 950°C for 120 min, cool it down to 200°C, close the gas valve, and let it cool naturally to room temperature to obtain the pre-nitrided product.

[0061] (3) The pre-nitrided product was ball-milled with ammonium borate and ammonium chloride at a mass ratio of 8:1:1 and then placed in a high-pressure reactor to react for 4 hours at a reaction temperature of 500℃ to obtain the crude product.

[0062] (4) Disperse the crude product in 20 ml of distilled water, add 50 ml of 12 mol / L hydrochloric acid, heat and stir at 50 °C for 4 h, then wash with deionized water and centrifuge three times, wash with ethanol three times, and finally vacuum dry at 70 °C for 10 h to obtain a three-dimensional hollow grid hierarchical boron nitride, denoted as 3D-BN sample.

[0063] Example 3

[0064] A method for preparing a three-dimensional hollow network structure of boron nitride includes the following steps:

[0065] (1) Strontium carbonate, sodium borate, and citric acid were mixed and dissolved in 200 mL of deionized water under magnetic stirring at room temperature, so that the concentrations of sodium borate, strontium carbonate, and citric acid were 4 mol / L, 2 mol / L, and 2.4 mol / L, respectively. The mixture was then stirred until homogeneous to obtain a precursor solution. Subsequently, the solution was heated in a water bath with stirring (80 °C, 12 h) until a gel was formed. The gel was then calcined in a high-temperature furnace at 800 °C for 6 h. The gel was then removed and ground to obtain a boron-containing precursor.

[0066] (2) Place the above boron-containing precursor in a tube furnace, evacuate the furnace and then introduce ammonia gas at a flow rate of 100 ml / min. Keep the furnace at 950°C for 120 min, cool it down to 200°C, close the gas valve, and let it cool naturally to room temperature to obtain the pre-nitrided product.

[0067] (3) The pre-nitrided product was ball-milled with ammonium borate and ammonium chloride at a mass ratio of 8:1:1 and then placed in a high-pressure reactor to react for 4 hours at a reaction temperature of 500℃ to obtain the crude product.

[0068] (4) Disperse the crude product in 20 ml of distilled water, add 50 ml of 12 mol / L hydrochloric acid, heat and stir at 50 °C for 4 h, then wash with deionized water and centrifuge three times, wash with ethanol three times, and finally vacuum dry at 70 °C for 10 h to obtain a three-dimensional hollow grid hierarchical boron nitride, denoted as 3D-BN sample.

[0069] Example 4

[0070] A method for preparing a three-dimensional hollow network structure of boron nitride includes the following steps:

[0071] (1) Strontium carbonate, sodium borate, and citric acid were mixed and dissolved in 200 mL of deionized water under magnetic stirring at room temperature, so that the concentrations of sodium borate, strontium carbonate, and citric acid were 4 mol / L, 2 mol / L, and 2.4 mol / L, respectively. The mixture was then stirred until homogeneous to obtain a precursor solution. Subsequently, the solution was heated in a water bath with stirring (80 °C, 12 h) until a gel was formed. The gel was then calcined in a high-temperature furnace at 800 °C for 4 h. The gel was then removed and ground to obtain a boron-containing precursor.

[0072] (2) Place the above boron-containing precursor in a tube furnace, evacuate the furnace and then introduce ammonia gas at a flow rate of 200 ml / min. Keep the furnace at 1000℃ for 120 min, cool it down to 200℃ with the furnace, close the gas valve, and let it cool naturally to room temperature to obtain the pre-nitrided product.

[0073] (3) The pre-nitrided product was ball-milled with ammonium borate and ammonium chloride at a mass ratio of 8:1:1 and then placed in a high-pressure reactor to react for 4 hours at a reaction temperature of 500℃ to obtain the crude product.

[0074] (4) Disperse the crude product in 20 ml of distilled water, add 50 ml of 12 mol / L hydrochloric acid, heat and stir at 50 °C for 4 h, then wash with deionized water and centrifuge three times, wash with ethanol three times, and finally vacuum dry at 70 °C for 10 h to obtain a three-dimensional hollow grid hierarchical boron nitride, denoted as 3D-BN sample.

[0075] Example 5

[0076] A method for preparing a three-dimensional hollow network structure of boron nitride includes the following steps:

[0077] (1) Strontium carbonate, sodium borate, and citric acid were mixed and dissolved in 200 mL of deionized water under magnetic stirring at room temperature, resulting in concentrations of 4 mol / L, 2 mol / L, and 2.4 mol / L for sodium borate, strontium carbonate, and citric acid, respectively. The mixture was then stirred until homogeneous to obtain a precursor solution. Subsequently, the solution was heated in a water bath with stirring (80 °C, 12 h) until a gel formed. The gel was then calcined in a high-temperature furnace at 900 °C for 6 h. The gel was then removed and ground to obtain a boron-containing precursor.

[0078] (2) Place the above boron-containing precursor in a tube furnace, evacuate the furnace and then introduce ammonia gas at a flow rate of 200 ml / min. Keep the furnace at 950°C for 120 min, cool it down to 200°C, close the gas valve, and let it cool naturally to room temperature to obtain the nitrided product.

[0079] (3) The pre-nitrided product was ball-milled with ammonium borate and ammonium chloride at a mass ratio of 8:1:1 and then placed in a high-pressure reactor to react for 4 hours at a reaction temperature of 500℃ to obtain the crude product.

[0080] (4) Disperse the crude product in 20 ml of distilled water, add 50 ml of 12 mol / L hydrochloric acid, heat and stir at 50 °C for 4 h, then wash with deionized water and centrifuge three times, wash with ethanol three times, and finally vacuum dry at 70 °C for 10 h to obtain a three-dimensional hollow grid hierarchical boron nitride, denoted as 3D-BN sample.

[0081] 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 three-dimensional hollow network structure of boron nitride, characterized in that... Its microstructure is a connected network structure composed of multiple cavity units. The size of each cavity unit is in the range of 0.3-1μm, the wall thickness of the cavity is in the range of 30-100nm, and the cavity surface is loaded with boron nitride nanosheets.

2. A method for preparing a three-dimensional hollow network structure of boron nitride, characterized in that... The main steps are as follows: (1) Strontium carbonate, sodium borate and citric acid are mixed and dissolved in water, stirred evenly, and then a sol-gel reaction is carried out to obtain a gel; (2) The gel obtained in step (1) is placed in a muffle furnace and calcined to obtain a boron-containing precursor; (3) The boron-containing precursor obtained in step (2) is pre-nitrided in a nitrogen atmosphere to obtain the pre-nitrided product; (4) The pre-nitrided product obtained in step (3) is ball-milled and mixed with ammonium borate and ammonium chloride and then placed into a reaction vessel to react and obtain a crude product; (5) After acid washing and drying of the crude product obtained in step (4), boron nitride with a three-dimensional hollow network structure is obtained.

3. The method for preparing a three-dimensional hollow network structure of boron nitride according to claim 2, characterized in that... In step (1), the molar ratio of strontium carbonate to sodium borate is 1:1 to 1:5; the amount of citric acid added accounts for 20 to 40% of the total molar amount of strontium carbonate and sodium borate.

4. The method for preparing a three-dimensional hollow network structure boron nitride according to claim 2, characterized in that... In step (1), the concentration of sodium borate in the solvent water is 3-5 mol / L, and the concentration of strontium carbonate in the solvent water is 1-4 mol / L.

5. The method for preparing a three-dimensional hollow network structured boron nitride according to claim 2, characterized in that... In step (1), stirring is carried out by water bath heating, with a heating temperature of 50-100℃ and a time of 6-18h.

6. The method for preparing a three-dimensional hollow network structure boron nitride according to claim 2, characterized in that... In step (2), the calcination temperature is 800-950℃ and the holding time is 3-8h.

7. The method for preparing a three-dimensional hollow network structured boron nitride according to claim 2, characterized in that... In step (3), the nitrogen atmosphere is NH3 atmosphere, the flow rate is 50-200 mL / min; the pre-nitriding temperature is 850-1000℃, and the holding time is 2-6 h.

8. The method for preparing a three-dimensional hollow network structure boron nitride according to claim 2, characterized in that... In step (4), the mass ratio of the pre-nitrided product to ammonium borate and ammonium chloride is (5-11):1:

1.

9. The method for preparing a three-dimensional hollow network structure boron nitride according to claim 2, characterized in that... In step (4), the reaction time in the reactor is 4 to 8 hours, the reaction temperature is 500 to 600°C, and the reactor is sealed to form a high pressure.

10. The method for preparing a three-dimensional hollow network structure boron nitride according to claim 2, characterized in that... In step (5), the acid washing involves dispersing the crude product in 4-7 mol / L hydrochloric acid and heating and stirring for 4-8 hours; after the acid washing is completed, the drying temperature is 50-70℃ and the time is 8-12 hours.

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