Hexagonal boron nitride nanosheet and preparation method and application thereof

Abstract

This invention belongs to the field of hexagonal boron nitride technology, specifically relating to hexagonal boron nitride nanosheets, their preparation method, and applications. The method includes the following steps: determining the size of the hexagonal boron nitride nanosheets to be prepared; selecting template salts of different sizes according to the desired size of the hexagonal boron nitride nanosheets; mixing the template salt with a boron source and a nitrogen source using different methods according to the size of the template salt to obtain a reaction precursor; placing the reaction precursor in a reactor for reaction; after the reaction is completed, naturally cooling to room temperature and collecting the product; mixing and stirring the collected product with water, then filtering, washing, and drying to finally obtain the finished hexagonal boron nitride nanosheets. This invention fills a gap in related process fields, and the size of the prepared nanosheets is adjustable, with diameters ranging from hundreds of nanometers to tens of micrometers, adaptable to different application scenarios.

Description

Technical Field

[0001] This invention belongs to the field of hexagonal boron nitride technology, specifically relating to a hexagonal boron nitride nanosheet, its preparation method, and its application. Background Technology

[0002] Hexagonal boron nitride, also known as "white graphene," is a typical two-dimensional material composed of six-membered rings made up of nitrogen and boron atoms. Due to its various excellent physicochemical properties, it has outstanding application prospects in chip packaging, thermal conductivity, flame retardancy, and battery additives. To fully utilize the advantages of hexagonal boron nitride's two-dimensional properties, the high-quality, large-scale synthesis of hexagonal boron nitride nanosheets (rather than the synthesis of bulk boron nitride) is of great research value. Currently, there are two main synthetic routes for hexagonal boron nitride nanosheets: 1. "Top-down" method: This refers to obtaining hexagonal boron nitride nanosheets by exfoliating the obtained bulk boron nitride through external forces. The most mature methods in this approach are ultrasonic exfoliation (i.e., long-term ultrasonic treatment of a suspension of boron nitride powder using a high-power ultrasonic machine to collect nanosheets) and shear exfoliation (see reference material, i.e., dispersing boron nitride powder in a highly viscous liquid and exfoliating nanosheets through shear force generated by strong stirring). 2. "Bottom-up" method: This refers to the direct synthesis of boron nitride nanosheets from precursors. The most mature method in this approach is currently CVD (chemical vapor deposition), which uses gas flow to carry nitrogen and boron sources of precursors to react and grow on a growth substrate to obtain boron nitride nanosheets.

[0003] However, top-down methods such as ultrasonic exfoliation and shear exfoliation are generally time-consuming, have low yields, and are energy-intensive, typically yielding boron nitride dispersions. Collecting individual products is often cumbersome or impossible. Furthermore, the resulting nanosheets are generally relatively fragmented and small in size (diameter). Bottom-up methods such as CVD have high requirements for the growth substrate (usually single-crystal copper) and are costly. They also have extremely low yields per production run, are time-consuming, and energy-intensive. While the resulting nanosheets are relatively thin, their small size makes it difficult to obtain micron-sized nanosheets, and collection or transfer is challenging. Besides CVD, few methods have been reported that can synthesize hexagonal boron nitride nanosheets with high crystallinity, low defect density, and a large diameter-to-thickness ratio, even with few layers (<20 layers) or few layers (<=5 layers).

[0004] Furthermore, since most current synthesis methods produce nanosheets with fixed sizes, it is extremely important to provide a high-quality hexagonal boron nitride nanosheet that can adjust the size of the nanosheet to better meet the needs of different application scenarios. Summary of the Invention

[0005] The purpose of this invention is to provide a hexagonal boron nitride nanosheet, its preparation method and application. The prepared hexagonal boron nitride nanosheet has adjustable size, high crystallinity, low defect density, and large diameter / thickness ratio, and has the potential for large-scale production.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] This invention provides a method for large-scale preparation of hexagonal boron nitride nanosheets, comprising the following steps:

[0008] (1) Determine the size of the hexagonal boron nitride nanosheets to be prepared, and select template salts of different sizes according to the size of the hexagonal boron nitride nanosheets to be prepared;

[0009] (2) Depending on the size of the template salt, the template salt is mixed with boron source and nitrogen source using different methods to obtain the reaction precursor;

[0010] (3) The reaction precursor is placed in the reactor to react. After the reaction is completed, the product is collected after naturally cooling to room temperature. The collected product is mixed with water and stirred, then filtered, washed and dried to finally obtain the finished hexagonal boron nitride nanosheets.

[0011] In step (1), the size of the hexagonal boron nitride nanosheets includes boron nitride nanosheets of hundreds of nanometers, hexagonal boron nitride nanosheets of micrometers, and hexagonal boron nitride nanosheets of ten micrometers; the preparation of template salts of different sizes is to prepare lyophilized salts, precipitated salts, and crystalline salts, wherein the boron nitride nanosheets of hundreds of nanometers, the hexagonal boron nitride nanosheets of micrometers, and the hexagonal boron nitride nanosheets of ten micrometers correspond to lyophilized salts, precipitated salts, and crystalline salts, respectively.

[0012] Furthermore, the method for preparing the freeze-dried salt is as follows: the template salt and water are mixed in a mass ratio of 1:5 to 20, and the mixture is stirred continuously until the template salt is fully dissolved to form a clear and transparent liquid. The resulting liquid is frozen at -20 to -60°C until completely solidified, and then vacuum dried at -20 to 20°C and a pressure of 0 to 100 Pa until completely dry. The freeze-dried salt is collected, wherein the template salt includes sodium chloride.

[0013] Furthermore, the method for preparing the precipitated salt is as follows: prepare a saturated solution of template salt and water, ensuring that the template salt is completely dissolved, add ethanol at a mass ratio of 1:0.5-5, stir until the template salt is fully precipitated, filter, wash with ethanol, and dry by blowing air to obtain the precipitated salt, wherein the template salt includes sodium chloride.

[0014] Furthermore, the method for preparing the crystalline salt is as follows: a template salt with a particle size of 0.3μm to 2mm and a regular geometric shape and a purity of >98% is purchased directly, and the template salt includes sodium chloride.

[0015] Furthermore, in step (2), the specific steps for mixing the template salt with the boron source and the nitrogen source are as follows: the template salt is mixed with the boron source and the nitrogen source by mechanical stirring or grinding, and mixed at 60 to 1000 rpm for 1 to 10 hours until the template salt and the precursor are fully and uniformly mixed.

[0016] Furthermore, when the template salt is a lyophilized salt, the ratio of the lyophilized salt to the boron source in terms of the amount of Na atoms to B atoms is 5–150:1, and the ratio of the nitrogen source to the boron source in terms of the amount of N atoms to B atoms is 0.5–5:1; when the template salt is a precipitated salt, the ratio of the crystalline salt to the boron source in terms of the amount of Na atoms to B atoms is 30–150:1, and the ratio of the nitrogen source to the boron source in terms of the amount of N atoms to B atoms is 0.5–5:1; when the template salt is a crystalline salt, the ratio of the precipitated salt to the boron source in terms of the amount of Na atoms to B atoms is 20–150:1, and the ratio of the nitrogen source to the boron source in terms of the amount of N atoms to B atoms is 0.5–5:1.

[0017] Furthermore, the boron source includes one or more of boric acid and boron oxide, and the nitrogen source includes one or more of ammonia, dicyandiamide, melamine, and urea.

[0018] Furthermore, in step (3), the parameters of the reaction process are to raise the temperature to 1000℃ at a heating rate of 1 to 50℃ / min and keep it at that temperature for 0.5 to 5 hours; the mixing and stirring with water is to mix the collected product with 10 times the mass of water and stir at 0 to 1000 rpm for 1 to 10 hours until the soluble substances in the product are fully dissolved and the insoluble substances are fully dispersed.

[0019] The present invention also provides a method for preparing hexagonal boron nitride nanosheets, wherein the hexagonal boron nitride nanosheets include hundreds of nanometer-sized boron nitride nanosheets, micrometer-sized hexagonal boron nitride nanosheets, and tens of micrometer-sized hexagonal boron nitride nanosheets.

[0020] The present invention also provides an application of the hexagonal boron nitride nanosheets in the fields of chip packaging, thermal conductivity, flame retardancy and battery additives.

[0021] The beneficial effects of this invention are as follows:

[0022] This invention enables the bottom-up preparation of hexagonal boron nitride nanosheets with advantages such as high crystallinity, low defect density, and a large diameter-to-thickness ratio, resulting in excellent quality. Furthermore, this method fills a gap in related processing technologies. The nanosheets prepared by this invention have adjustable sizes, ranging from hundreds of nanometers to tens of micrometers, adaptable to various applications. The growth template used in this invention is a salt (such as sodium chloride), which is inexpensive, environmentally friendly, and reusable during the preparation process. This invention has the potential for large-scale production due to its readily available and affordable cost, simple and quick operation, relatively low requirements for production equipment, and high process tolerance, minimizing the likelihood of significant errors due to scale-up. Attached Figure Description

[0023] Figure 1 Scanning micrographs of freeze-dried salt at a 10 μm scale;

[0024] Figure 2 Scanning micrographs of the precipitated salt at a 50 μm scale;

[0025] Figure 3 This is a scanning micrograph of crystalline salt under a 20 μm scale.

[0026] Figure 4 Scanning electron micrographs of 100-nanometer-scale hexagonal boron nitride nanosheets on a 3μm scale;

[0027] Figure 5 Transmission electron microscopy images of hexagonal boron nitride nanosheets at the 200nm scale;

[0028] Figure 6 Transmission electron microscopy image of the edge of a hundred-nanometer-scale hexagonal boron nitride nanosheet at a 5nm scale.

[0029] Figure 7 Aberration-corrected scanning transmission electron microscope (STEM) images of hundred-nanometer-scale hexagonal boron nitride nanosheets on a 2nm scale;

[0030] Figure 8 X-ray diffraction pattern of hexagonal boron nitride nanosheets at the hundred-nanometer scale;

[0031] Figure 9 Scanning electron microscopy images of micron-sized hexagonal boron nitride nanosheets on a 10 μm scale;

[0032] Figure 10 Transmission electron microscopy images of micron-sized hexagonal boron nitride nanosheets on a 2μm scale;

[0033] Figure 11 Transmission electron microscopy image of the edge of a micron-sized hexagonal boron nitride nanosheet on a 5nm scale.

[0034] Figure 12 Aberration-corrected scanning transmission electron microscope (STEM) images of micron-sized hexagonal boron nitride nanosheets on a 3nm scale;

[0035] Figure 13 X-ray diffraction pattern of micron-sized hexagonal boron nitride nanosheets;

[0036] Figure 14 X-ray photoelectron spectroscopy of micron-sized hexagonal boron nitride nanosheets;

[0037] Figure 15 Scanning electron micrographs of 10-micrometer-scale hexagonal boron nitride nanosheets on a 50-μm scale;

[0038] Figure 16 The X-ray diffraction pattern of ten-micrometer-sized hexagonal boron nitride nanosheets. Detailed Implementation

[0039] This invention provides a method for preparing hexagonal boron nitride nanosheets, comprising the following steps:

[0040] I. Preparation of Salt Templates of Different Sizes

[0041] 1. Freeze-dried salt template (hereinafter referred to as freeze-dried salt): The template salt (commonly sodium chloride, but other common salts such as KCl can also be used, with a purity >98%, the same below) and water are mixed in a mass ratio of 1:5 to 20, preferably 1:9 to 12, and most preferably 1:10. After mixing, the mixture is stirred continuously until the template salt is fully dissolved to form a clear and transparent liquid. The resulting liquid is frozen at -20 to -60°C (preferably -40 to -55°C) until completely solidified, and then vacuum dried at -20 to 20°C (preferably -10 to 10°C) and a pressure of 0 to 100 Pa (preferably 0 to 10 Pa, most preferably 0 to 1 Pa) until completely dry. The freeze-dried salt is collected, and the scanning micrograph of the obtained freeze-dried salt under a 10 μm scale is shown below. Figure 1 As shown.

[0042] 2. Re-precipitation of salt template (hereinafter referred to as precipitated salt): Prepare a saturated solution of template salt and water, ensuring the template salt is completely dissolved. Add ethanol (purity >90%) at a mass ratio of solution to ethanol of 1:0.5–5 (preferably 1:0.9–1.5), stir until the template salt is fully precipitated, filter, wash with ethanol, and dry by forced air drying to obtain the precipitated salt. The scanning micrograph of the obtained precipitated salt under a 50 μm scale is shown below. Figure 2 As shown.

[0043] 3. Crystalline Salt: Purchase directly. Select a high-purity template salt (purity >98%) with a particle size of 0.3μm–2μm (preferably 0.9–1.2μm) and a regular geometric shape. The resulting crystalline salt should be visualized using a scanning electron microscope (SEM) at a 20μm scale, as shown below. Figure 3 As shown.

[0044] Scanned fiber images of different salt templates visually demonstrate that the sizes of salts differ depending on the template.

[0045] II. Mixing

[0046] The template salt of different sizes and the relative ratio of template salt to precursor are selected based on the required nanosheet size. The precursor includes a boron source and a nitrogen source. The boron source can be boric acid, boron oxide, or other common boron-containing compounds (purity >98%). The nitrogen source can be ammonia, dicyandiamide, melamine, urea, or other common nitrogen-containing compounds (purity >98%). Solid nitrogen sources need to be mixed with the salt template simultaneously with the boron source; gaseous nitrogen sources, such as ammonia, are only introduced during the high-temperature reaction. Details are as follows:

[0047] The mixing steps for preparing 100-nanometer-sized hexagonal boron nitride nanosheets are as follows: Lyophilized salt, boron source, and nitrogen source (solid) are mixed by mechanical stirring or grinding at 60–1000 rpm, preferably 100–300 rpm, for 1–10 hours, preferably 3–5 hours, until the template salt and precursor are fully and uniformly mixed. The molar ratio of Na atoms to B atoms between the lyophilized salt and the boron source is 5–150:1, preferably 10–50:1, and most preferably 10–20:1. If a solid nitrogen source is used, the molar ratio of N atoms to B atoms between the nitrogen source and the boron source is 1–5:1, preferably 1.5–2.5:1.

[0048] In addition, for the synthesis of boron nitride nanosheets at the hundred-nanometer scale, the boron source and nitrogen source (solid) can also be dissolved together with the template salt in water in the above proportion during the preparation of freeze-dried salt, and then subjected to the freeze-drying process. The collected product is used as a well-mixed precursor to participate in the next high-temperature reaction.

[0049] 2. Mixing steps for preparing micron-sized hexagonal boron nitride nanosheets: The precipitated salt, boron source, and nitrogen source (solid) are mixed by mechanical stirring or grinding at 60–1000 rpm, preferably 100–300 rpm, for 1–10 h, preferably 3–5 h, until the template salt and precursor are fully and uniformly mixed. The molar ratio of Na atoms to B atoms in the precipitated salt to boron source is 20–150:1, preferably 30–80:1, and most preferably 30–50:1. If a solid nitrogen source is used, the molar ratio of N atoms to B atoms in the nitrogen source to the boron source is 1–5:1, preferably 1.5–2.5:1.

[0050] 3. Mixing steps for preparing 10-micron-sized hexagonal boron nitride nanosheets: The crystalline salt, boron source, and nitrogen source (solid) are mixed by mechanical stirring or grinding at 60–1000 rpm, preferably 100–300 rpm, for 1–10 hours, preferably 3–5 hours, until the template salt and precursor are fully and uniformly mixed. The molar ratio of Na atoms to B atoms in the crystalline salt to boron source is 30–150:1, preferably 30–80:1, and most preferably 40–60:1. If a solid nitrogen source is used, the molar ratio of N atoms to B atoms in the nitrogen source to the boron source is 1–5:1, preferably 1.5–2.5:1.

[0051] After mixing, the reaction precursor is obtained.

[0052] III. High-Temperature Reaction

[0053] The mixed reaction precursors are placed in a reactor, and the temperature is increased to 1000°C at a heating rate of 1–50°C / min (preferably 5–20°C / min). The temperature is held for 0.5–5 hours (preferably 1–2 hours), and the product is collected after natural cooling to room temperature. If a gaseous nitrogen source such as ammonia is used, the reaction chamber must be filled with gaseous nitrogen at a temperature above 400°C. If a solid nitrogen source is used, the reaction can be carried out in air or under a common inert atmosphere (such as nitrogen or argon).

[0054] IV. Washing and Collection

[0055] The product from the high-temperature reaction is mixed with 10 times its weight of water and stirred (0–1000 rpm, preferably 100–300 rpm, 1–10 h, preferably 3–5 h) until the soluble components are fully dissolved and the insoluble components are fully dispersed. The mixture is then filtered and washed with water 1–3 times. The product is collected and dried to obtain the final product, hexagonal boron nitride nanosheets. Alternatively, freeze-drying or other methods can be used for drying without affecting the final product quality. The sodium chloride in the mother liquor obtained from the first washing can be recycled.

[0056] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0057] Example 1

[0058] A method for preparing 100-nanometer-sized hexagonal boron nitride nanosheets includes the following steps:

[0059] 1. Preparation of freeze-dried salt template:

[0060] Sodium chloride with a purity >98% and water were mixed at a mass ratio of 1:10. After mixing, the mixture was stirred continuously until the sodium chloride was fully dissolved to form a clear and transparent liquid. The resulting liquid was frozen at -50°C until completely solidified, and then vacuum dried at -5°C and 0.5 Pa until completely dry, and the freeze-dried salt was collected.

[0061] 2. Mixing:

[0062] The lyophilized salt, boric acid, and urea were mixed by mechanical stirring at 200 rpm for 5 hours until the lyophilized salt, boric acid, and urea were fully and uniformly mixed to obtain a well-mixed reaction precursor. The molar ratio of Na atoms to B atoms in the lyophilized salt to boric acid was 15:1; the molar ratio of N atoms to B atoms in the urea to boric acid was 2:1.

[0063] 3. High-temperature reaction:

[0064] The mixed reaction precursors were placed in a reactor and the temperature was increased to 1000℃ at a heating rate of 10℃ / min. The temperature was held for 1.5h and then naturally cooled to room temperature before the product was collected.

[0065] 4. Washing and collecting:

[0066] The product obtained in step 3 was mixed with 10 times its mass of water and stirred at 200 rpm for 4 hours until the soluble components were fully dissolved and the insoluble components were fully dispersed. The mixture was then filtered, washed twice with water, collected, and dried to obtain hexagonal boron nitride nanosheets of hundreds of nanometers in size. Scanning electron micrographs of the hundreds of nanometer-sized hexagonal boron nitride nanosheets at a 3 μm scale are shown below. Figure 4 As shown; transmission electron microscopy images of 100-nanometer-scale hexagonal boron nitride nanosheets at a 200 nm scale are shown below. Figure 5 As shown; transmission electron microscopy images of the edges of hundred-nanometer-scale hexagonal boron nitride nanosheets on a 5nm scale. Figure 6 As shown; aberration-corrected scanning transmission electron microscopy images of 100-nanometer-scale hexagonal boron nitride nanosheets on a 2nm scale are shown below. Figure 7 As shown; the X-ray diffraction pattern of the hundred-nanometer-sized hexagonal boron nitride nanosheets is as follows. Figure 8 As shown.

[0067] Example 2

[0068] A method for preparing micron-sized hexagonal boron nitride nanosheets includes the following steps:

[0069] 1. Preparation of precipitation salt template:

[0070] Prepare a saturated solution of sodium chloride with a purity >98% and water, ensuring that the sodium chloride is completely dissolved. Add ethanol with a purity >90% at a mass ratio of 1:1 and stir until sodium chloride is fully precipitated. Filter the solution, wash with ethanol, and dry it by blowing air to obtain the precipitated salt.

[0071] 2. Mixing:

[0072] The precipitated salt was mixed with boric acid and urea by mechanical stirring at 200 rpm for 5 hours until the precipitated salt, boric acid, and urea were fully and uniformly mixed to obtain a well-mixed reaction precursor. The ratio of Na atoms to B atoms in the freeze-dried salt to boric acid was 40:1; the ratio of N atoms to B atoms in the urea to boric acid was 2:1.

[0073] 3. High-temperature reaction:

[0074] The mixed reaction precursors were placed in a reactor and the temperature was increased to 1000℃ at a heating rate of 10℃ / min. The temperature was held for 1.5h and then naturally cooled to room temperature before the product was collected.

[0075] 4. Washing and collecting:

[0076] The product obtained in step 3 was mixed with 10 times its mass of water and stirred at 200 rpm for 4 hours until the soluble components were fully dissolved and the insoluble components were fully dispersed. The mixture was then filtered, washed twice with water, collected, and dried to obtain micron-sized hexagonal boron nitride nanosheets. Scanning electron micrographs of the micron-sized hexagonal boron nitride nanosheets at a 10 μm scale are shown below. Figure 9 As shown; transmission electron microscopy images of micron-sized hexagonal boron nitride nanosheets on a 2μm scale. Figure 10 As shown; transmission electron microscopy images of the edges of micron-sized hexagonal boron nitride nanosheets on a 5nm scale. Figure 11 As shown; aberration-corrected scanning transmission electron microscopy images of micron-sized hexagonal boron nitride nanosheets on a 3nm scale are shown below. Figure 12 As shown; the X-ray diffraction pattern of micron-sized hexagonal boron nitride nanosheets is as follows. Figure 13 As shown; the X-ray photoelectron spectrum of micron-sized hexagonal boron nitride nanosheets is as follows. Figure 14 As shown.

[0077] Example 3

[0078] A method for preparing 10-micron-sized hexagonal boron nitride nanosheets includes the following steps:

[0079] 1. Obtaining Crystallized Salt

[0080] Choose to purchase crystalline salts with a purity >98% that have a particle size of 0.3μm to 2mm and a regular geometric shape.

[0081] 2. Mixing:

[0082] The crystalline salt was mixed with boric acid and urea by mechanical stirring at 200 rpm for 5 hours until the crystalline salt, boric acid, and urea were fully and uniformly mixed to obtain a well-mixed reaction precursor. The ratio of Na atoms to B atoms in the freeze-dried salt to boric acid was 50:1; the ratio of N atoms to B atoms in the urea to boric acid was 2:1.

[0083] 3. High-temperature reaction:

[0084] The mixed reaction precursors were placed in a reactor and the temperature was increased to 1000℃ at a heating rate of 10℃ / min. The temperature was held for 1.5h and then naturally cooled to room temperature before the product was collected.

[0085] 4. Washing and collecting:

[0086] The product obtained in step 3 was mixed with 10 times its mass of water and stirred at 200 rpm for 4 hours until the soluble components were fully dissolved and the insoluble components were fully dispersed. The mixture was then filtered, washed twice with water, collected, and dried to obtain 10-micron-sized hexagonal boron nitride nanosheets. Scanning electron micrographs of the 10-micron-sized hexagonal boron nitride nanosheets at a 50 μm scale are shown below. Figure 15 As shown, the X-ray diffraction pattern of the 10-micron-sized hexagonal boron nitride nanosheets is as follows: Figure 16 As shown.

[0087] By referring to the methods in Examples 1-3 of this application combined with scanning electron microscopy images Figure 4 , Figure 9 , Figure 15 and transmission electron microscopy images Figure 5 , Figure 10 It is evident that the hexagonal boron nitride nanosheets obtained by different preparation processes have different sizes, conforming to their respective names and specifications of hundreds of nanometers, micrometers, and tens of micrometers. This proves that the method can successfully adjust the size of the prepared nanosheets, and also clearly demonstrates that the morphology of the prepared products is typical of sheets.

[0088] Meanwhile, transmission electron microscopy images of the edges of hexagonal boron nitride nanosheets were used as a reference. Figure 6 , Figure 11 It is evident that the hexagonal boron nitride nanosheets prepared by this method exhibit few-layer characteristics, typically consisting of 3-6 layers of hexagonal boron nitride, with a thickness of approximately 1-2 nm. This demonstrates the thinness of the nanosheets. Furthermore, combined with the micron-scale sheet diameter, it proves that the sheet diameter / thickness ratio of the nanosheets is relatively large, consistent with the advantages proposed by this method.

[0089] And through observation Figure 7 and Figure 12The study revealed the microstructure of the prepared hexagonal boron nitride nanosheets, which were generally ordered and free of obvious defects. Furthermore, the clear and independent electron diffraction patterns demonstrated the excellent single-crystal properties of the nanosheets within the indicated region. These conclusions fully demonstrate that the hexagonal boron nitride nanosheets prepared by this method have the advantages of fewer defects and higher quality.

[0090] And through Figure 8 , Figure 13 , Figure 14 , Figure 16 The X-ray diffraction pattern and X-ray photoelectron spectroscopy (XPS) revealed that the characteristic diffraction peaks in the X-ray diffraction pattern matched well with the standard hexagonal boron nitride diffraction peaks, and there were no extra impurity peaks, indicating that the prepared product is standard hexagonal boron nitride and does not contain other impurities. The diffraction peaks in the pattern are clear and sharp, indicating that the product has high crystallinity and good quality. Apart from the unavoidable contamination peaks of C and O elements during the testing process, the XPS showed only characteristic peaks of B and N elements, indicating that the prepared product contains only B and N elements and has high purity.

[0091] Finally, the aforementioned production process for hexagonal boron nitride nanosheets has achieved production at the 100-gram level. With equipment upgrades, achieving kilogram-level and ton-level production presents no theoretical challenge. This demonstrates the large-scale production potential of this process.

[0092] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for large-scale preparation of hexagonal boron nitride nanosheets, characterized in that, Includes the following steps: (1) Determine the size of the hexagonal boron nitride nanosheets to be prepared, and select template salts of different sizes according to the size of the hexagonal boron nitride nanosheets to be prepared; (2) The template salt is mixed with boron source and nitrogen source using different methods according to the size of the template salt to obtain the reaction precursor; (3) The reaction precursor is placed in the reactor to react. After the reaction is completed, the product is collected after naturally cooling to room temperature. The collected product is mixed with water and stirred, then filtered, washed and dried to finally obtain the finished hexagonal boron nitride nanosheets. In step (1), the size of the hexagonal boron nitride nanosheets includes boron nitride nanosheets of hundreds of nanometers, hexagonal boron nitride nanosheets of micrometers, and hexagonal boron nitride nanosheets of ten micrometers; the preparation of template salts of different sizes is to prepare lyophilized salts, precipitated salts, and crystalline salts, wherein the boron nitride nanosheets of hundreds of nanometers, the hexagonal boron nitride nanosheets of micrometers, and the hexagonal boron nitride nanosheets of ten micrometers correspond to lyophilized salts, precipitated salts, and crystalline salts, respectively; The method for preparing the freeze-dried salt is as follows: the template salt and water are mixed in a mass ratio of 1:5 to 20. After mixing, the mixture is stirred until the template salt is fully dissolved to form a clear and transparent liquid. The resulting liquid is frozen at -20 to -60°C until completely solidified, and then vacuum dried at -20 to 20°C and a pressure of 0 to 100 Pa until completely dry. The freeze-dried salt is collected. The template salt includes sodium chloride. The method for preparing the precipitated salt is as follows: prepare a saturated solution of template salt and water, ensuring that the template salt is completely dissolved, add ethanol at a mass ratio of 1:0.5-5, stir until the template salt is fully precipitated, filter, wash with ethanol, and dry by blowing air to obtain the precipitated salt, wherein the template salt includes sodium chloride; The method for preparing the crystalline salt is as follows: a template salt with a particle size of 0.3μm to 2μm and a regular geometric shape and a purity of >98% is purchased directly, and the template salt includes sodium chloride; In step (2), the specific steps for mixing the template salt with the boron source and the nitrogen source are as follows: the template salt is mixed with the boron source and the nitrogen source by mechanical stirring or grinding, and mixed at 60 to 1000 rpm for 1 to 10 hours until the template salt and the precursor are fully and uniformly mixed. When the template salt is a lyophilized salt, the ratio of the lyophilized salt to the boron source in terms of the amount of Na atoms to B atoms is 5–150:1; the ratio of the nitrogen source to the boron source in terms of the amount of N atoms to B atoms is 0.5–5:

1. When the template salt is a precipitated salt, the ratio of the crystalline salt to the boron source in terms of the amount of Na atoms to B atoms is 30–150:1; the ratio of the nitrogen source to the boron source in terms of the amount of N atoms to B atoms is 0.5–5:

1. When the template salt is a crystalline salt, the ratio of the precipitated salt to the boron source in terms of the amount of Na atoms to B atoms is 20–150:1; the ratio of the nitrogen source to the boron source in terms of the amount of N atoms to B atoms is 0.5–5:

1. The boron source includes one or more of boric acid and boron oxide, and the nitrogen source includes one or more of ammonia, dicyandiamide, melamine, and urea. In step (3), the parameters of the reaction process are to raise the temperature to 1000℃ at a heating rate of 1 to 50℃ / min and keep it at that temperature for 0.5 to 5 hours; the mixing and stirring with water is to mix the collected product with 10 times the mass of water and stir at 0 to 1000 rpm for 1 to 10 hours until the soluble substances in the product are fully dissolved and the insoluble substances are fully dispersed.

Images