Method for preparing hexagonal boron nitride nano-materials with various morphologies and hexagonal boron nitride nano-materials prepared by method

Abstract

The method comprises the following steps: (1) uniformly mixing boric acid and a nitrogen source, then adding borax, uniformly mixing to obtain a mixture, and screening to obtain a mixture with the particle size of less than 180 microns; (2) treating the mixture of which the particle size is less than 180 microns at 85 DEG C for 4 hours to obtain a precursor; and (3) carrying out heating and heat preservation treatment on the precursor at normal pressure, then cooling to room temperature, and washing with water to obtain the hexagonal boron nitride nano material with various morphologies. According to the preparation method of the hexagonal boron nitride nano-materials with various morphologies, the preparation process is simple, the cost is low, the morphologies and the sizes are controllable, macro preparation can be achieved, and the prepared hexagonal boron nitride nano-materials have the characteristics of morphological diversity and uniform morphologies.

Description

Technical Field

[0001] The invention belongs to the technical field of inorganic non-metallic materials, and in particular relates to a method for preparing hexagonal boron nitride nanomaterials with various morphologies and the hexagonal boron nitride nanomaterials prepared thereby. Background Art

[0002] Hexagonal boron nitride has attracted much attention due to its graphite-like layered structure, high thermal stability, high mechanical strength, high thermal conductivity and low dielectric constant, and has good application prospects in many aspects, such as adsorption, hydrogen storage, catalysis, etc. In particular, in recent years, with the continuous deepening of research on h-BN materials, many novel boron nitride materials have been prepared, such as: three-dimensional nanoflowers, spheres, nanocarpets, nanonets, fibers, hollow spheres, microbelts, whiskers, etc. However, at present, most of the different morphologies of hexagonal boron nitride often require different preparation methods, such as three-dimensional nanoflowers using solid phase method and molten salt method, spheres using spray drying method and CVD method, and nanocarpets using hot pressing method. Therefore, it is of great practical significance to develop a simple, low-cost and controllable preparation process for hexagonal boron nitride nanomaterials with diverse morphologies and uniform morphology.

[0003] At present, the pyrolysis precursor method for synthesizing hexagonal boron nitride nanomaterials either produces hexagonal boron nitride with small morphological structures, which are often different in size in a certain morphology but relatively close in morphology, or with uneven morphological structures, which do not form a variety of uniform morphological structures in the true sense. In addition, the special dimensional morphological effects of hexagonal boron nitride nanomaterials with different morphological structures will give them unique physical and chemical properties, thereby broadening their application fields and giving full play to the application value of hexagonal boron nitride materials.

[0004] In summary, it is very necessary to provide a method for preparing hexagonal boron nitride nanomaterials with various morphologies and the hexagonal boron nitride nanomaterials prepared thereby. Summary of the invention

[0005] In order to solve one or more technical problems existing in the prior art, the present invention provides a method for preparing hexagonal boron nitride nanomaterials with various morphologies and the hexagonal boron nitride nanomaterials prepared thereby. The present invention provides a method for preparing a hexagonal boron nitride nanomaterial with the characteristics of simple operation (simple preparation process), low cost, green and efficient, controllable morphology and size, large-scale preparation, morphology diversity and uniformity of each morphology, and the hexagonal boron nitride nanomaterials prepared thereby.

[0006] In a first aspect, the present invention provides a method for preparing hexagonal boron nitride nanomaterials with various morphologies, the method comprising the following steps:

[0007] (1) mixing boric acid and a nitrogen source uniformly, then adding borax and mixing uniformly to obtain a mixture, and sieving to obtain a mixture with a particle size of less than 180 μm;

[0008] (2) treating the mixture with a particle size less than 180 μm at 85° C. for 4 h to obtain a precursor;

[0009] (3) The precursor is heated and kept at normal pressure, then cooled to room temperature, and washed with water to obtain hexagonal boron nitride nanomaterials with various morphologies.

[0010] Preferably, the nitrogen source is urea.

[0011] Preferably, the molar ratio of the urea to the boric acid is 1:(0.5-2).

[0012] Preferably, the molar ratio of the urea to the boric acid is 0.5:1, 1:1, 1.5:1 or 2:1.

[0013] Preferably, the borax is borax decahydrate; and / or the mass amount of the borax is 15% of the sum of the mass amounts of the nitrogen source and the boric acid.

[0014] Preferably, the heating and heat preservation treatment is carried out under a nitrogen atmosphere.

[0015] Preferably, the temperature of the heating and heat-insulating treatment is 900° C. to 1300° C., and the time of the heating and heat-insulating treatment is 3 h to 6 h.

[0016] Preferably, the temperature of the heating and heat preservation treatment is 1300° C., and the time of the heating and heat preservation treatment is 4 hours.

[0017] Preferably, the hexagonal boron nitride nanomaterial is in the shape of a small cylinder, a go piece, a few-layer nanosheet, or a "card house" structure composed of hexagonal sheets.

[0018] In a second aspect, the present invention provides a hexagonal boron nitride nanomaterial prepared by the method described in the first aspect of the present invention.

[0019] Compared with the prior art, the present invention has at least the following beneficial effects:

[0020] (1) The method for preparing hexagonal boron nitride nanomaterials with various morphologies provided by the present invention uses a low-temperature solvent-free and screening method to synthesize precursors, which is simple to operate, has fewer steps, and has fewer influencing factors. The low temperature of 85°C will not decompose the urea raw material, ensuring that there is sufficient nitrogen source in the process of synthesizing hexagonal boron nitride, so that more boron sources can be converted into boron nitride, thereby improving the yield, which can be as high as 95% or more; and, borax is added to the preparation method provided by the present invention, and the borax heating decomposition product is Na2O with a high melting point (melting point 1132°C), which is equivalent to an initial core and acts as a template, and at the same time, hexagonal boron nitride is formed on its surface. In the process of removing the template at the end, the hexagonal boron nitride is dispersed from the template, which increases the dispersibility of the hexagonal boron nitride nanomaterial and avoids the disadvantages of sintering and bonding into blocks. Each hexagonal boron nitride nanomaterial obtained has a uniform morphology and uniform size. At the same time, the method provided by the present invention is not only green and efficient, but also has a high yield and a high purity, and is easy to achieve large-scale production for promotion and application.

[0021] (2) The present invention successfully synthesized a variety of hexagonal boron nitride nanomaterials with different morphologies, including small cylindrical morphologies, go piece morphologies, few-layer nanosheet morphologies, and a "card house" structure morphology composed of hexagonal sheets, and each morphology is uniform; the hexagonal boron nitride nanomaterials with go piece morphologies, few-layer nanosheet morphologies, and a "card house" structure morphology composed of hexagonal sheets synthesized by the method of the present invention have not been reported in any prior art; and the hexagonal boron nitride nanomaterials with go piece morphologies, few-layer nanosheet morphologies, or hexagonal sheets synthesized by the present invention have no prior art reports. Compared with hexagonal boron nitride nanomaterials with solid spherical morphology, hexagonal boron nitride nanomaterials with "card room" structure usually have more obvious advantages in light, electricity, adsorption, thermal conductivity and / or functional applications. These characteristics make these hexagonal boron nitride nanomaterials in high-performance composite materials, catalyst carrier materials, water treatment and purification materials, high-efficiency thermal management materials and other applications show stronger competitiveness and application prospects; for example, hexagonal boron nitride nanomaterials with go piece morphology have better crystallinity (from the provided XRD diagram shows good crystallinity), which can improve the efficiency and quality of synthesized cubic boron nitride, and due to its lower defects, it can present better thermal conductivity when used as a thermal conductive filler; for example, hexagonal boron nitride nanomaterials with a few-layer nanosheet morphology usually have a larger specific surface area than spherical hexagonal boron nitride nanomaterials, and the layered structure exposes more reaction sites on the surface of each particle, thereby providing more physical and chemical active sites, especially in catalysis, adsorption, energy storage and other applications. It has significant advantages, and hexagonal boron nitride with a few-layer nanosheet structure has a wider bandgap and stronger insulation, making it widely used in the packaging and isolation layers of electronic devices; for example, hexagonal boron nitride nanomaterials with a "card room" structure morphology composed of hexagonal sheets have higher porosity and lower density due to their unique sheet and stacking characteristics, and can be used as a separator for batteries and capacitors and a solid electrolyte additive. It can show better effects, not only can it work in a high temperature environment, but also can improve the performance of electrochemical devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 These are XRD diagrams of hexagonal boron nitride nanomaterials with various morphologies prepared in Examples 1 to 4 of the present invention.

[0023] Figure 2 These are SEM images of hexagonal boron nitride nanomaterials with various morphologies prepared in Examples 1 to 4 of the present invention.

[0024] Figure 3 TEM images of hexagonal boron nitride nanomaterials with various morphologies prepared in Examples 1 to 4 of the present invention.

[0025] Figure 4This is a common optical image of the hexagonal boron nitride nanomaterial prepared by the present invention in a corundum crucible. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] In a first aspect, the present invention provides a method for preparing hexagonal boron nitride nanomaterials with various morphologies, the method comprising the following steps:

[0028] (1) mixing boric acid (H3BO3) and a nitrogen source uniformly, then adding borax (template) and mixing uniformly to obtain a mixture, and sieving to obtain a mixture with a particle size of less than 180 μm;

[0029] (2) treating the mixture with a particle size of less than 180 μm at 85° C. for 4 hours to obtain a precursor; in the present invention, no solvent is added when preparing the precursor, and after the raw materials are evenly mixed, the precursor can be obtained by treating at a low temperature of 85° C. Compared with the precursor obtained by adding a solvent to the mixture and heat treating at a relatively high temperature condition such as 200 to 550° C., the present invention adopts a method of treating a solvent-free mixture at a low temperature to obtain a precursor, which can more effectively control the reaction process and is conducive to the subsequent preparation of multi-morphological hexagonal boron nitride nanomaterials;

[0030] (3) The precursor is heated and insulated at normal pressure, then cooled to room temperature, and the template (borax) is removed by washing with water to obtain hexagonal boron nitride nanomaterials with various morphologies. In the present invention, it is preferred that the precursor is ball-milled (wet ball-milled) and dried before being heated and insulated at normal pressure. The present invention does not specifically limit the ball-milling and drying operations, and those skilled in the art can make conventional selections.

[0031] The method for preparing hexagonal boron nitride nanomaterials with various morphologies provided by the present invention utilizes a low-temperature solvent-free and screening method to synthesize a precursor, is simple to operate, has fewer steps, fewer influencing factors, and the low temperature of 85°C will not decompose the urea raw material, ensuring that there is sufficient nitrogen source in the process of synthesizing hexagonal boron nitride, so that more boron sources can be converted into boron nitride, thereby improving the yield, which can be as high as 95% or more; and, borax is added to the preparation method provided by the present invention, and the borax heating decomposition product is Na2O (melting point 1132°C) with a higher melting point, which is equivalent to an initial core that acts as a template, and at the same time, hexagonal boron nitride is formed on its surface, and in the process of removing the template at the end, the hexagonal boron nitride is dispersed from the template, increasing the dispersibility of the hexagonal boron nitride nanomaterial, avoiding the disadvantages of sintering and bonding into blocks, and each hexagonal boron nitride nanomaterial obtained has a uniform morphology and uniform size. At the same time, the method provided by the present invention is not only green and efficient, but also has a high yield, and the purity is also high, and it is easy to achieve large-scale production for promotion and application.

[0032] According to some preferred embodiments, the nitrogen source is urea (CO(NH2)2).

[0033] According to some preferred embodiments, the molar ratio of the urea to the boric acid is 1:(0.5-2).

[0034] The present invention provides a method for preparing hexagonal boron nitride nanomaterials with various morphologies, which utilizes the advantages of low-temperature treatment of precursors combined with template method to achieve high yield and large-scale preparation of hexagonal boron nitride nanomaterials with various uniform morphologies. The method mainly includes three processes: raw material preparation, low-temperature preparation of precursors, and template sintering synthesis. The specific steps are as follows:

[0035] (1) Raw material preparation: using boric acid as a boron source, urea as a nitrogen source, and borax decahydrate (Na2B4O7·10H2O) as a template, urea and boric acid are uniformly mixed with 15 wt% borax decahydrate in a molar ratio of 1:0.5 to 1:2, and sieved to obtain a mixture with a small and uniform particle size, specifically, sieved to obtain a mixture with a particle size of less than 180 μm;

[0036] (2) Low-temperature preparation of precursor: The obtained mixture with a particle size of less than 180 μm was treated in an oven at 85° C. for 4 h to obtain a white powder precursor;

[0037] (3) Template sintering synthesis: The white powder precursor is first ball-milled and dried, then heated and kept warm at normal pressure, then cooled to room temperature and washed with water to obtain hexagonal boron nitride nanomaterials with various morphologies. In some specific embodiments, for example, the white powder precursor is heated and kept warm at normal pressure by first spreading the white powder precursor in a corundum crucible and placing it in a horizontal tubular atmosphere furnace, heating it to 900°C to 1300°C in a nitrogen atmosphere and keeping it warm for 3h to 6h; then cooling it to room temperature and washing it with water to obtain the hexagonal boron nitride nanomaterials with various morphologies.

[0038] According to some preferred embodiments, the molar ratio of the urea to the boric acid is 0.5:1, 1:1, 1.5:1 or 2:1.

[0039] According to some preferred embodiments, the borax is borax decahydrate (Na2B4O7·10H2O); and / or the mass amount of the borax is 15% of the sum of the mass amounts of the nitrogen source and the boric acid.

[0040] According to some preferred embodiments, the heating and heat preservation treatment is carried out under a nitrogen atmosphere.

[0041] According to some preferred embodiments, the temperature of the heating and insulation treatment is 900°C to 1300°C (for example, 900°C, 1000°C, 1100°C, 1200°C or 1300°C), and the time of the heating and insulation treatment is 3h to 6h (for example, 3, 4, 5 or 6h); in the present invention, for example, the temperature can be increased to 900°C to 1300°C at a heating rate of 3 to 5°C / min and the heat treatment can be carried out at 900°C to 1300°C for 3h to 6h.

[0042] According to some preferred embodiments, the temperature of the heating and heat-insulating treatment is 1300° C., and the time of the heating and heat-insulating treatment is 4 hours.

[0043] According to some preferred embodiments, the hexagonal boron nitride nanomaterial is in the shape of a small cylinder, a go piece, a few-layer nanosheet, or a "card house" structure composed of hexagonal sheets.

[0044] The present invention successfully synthesizes a variety of hexagonal boron nitride nanomaterials with different morphologies, including small cylindrical morphologies, go piece morphologies, few-layer nanosheet morphologies, and "card house" morphologies composed of hexagonal sheets, and each morphology is uniform; the hexagonal boron nitride nanomaterials with go piece morphologies, few-layer nanosheet morphologies, and "card house" morphologies composed of hexagonal sheets synthesized by the method of the present invention have not been reported in any prior art; and the hexagonal boron nitride nanomaterials with go piece morphologies, few-layer nanosheet morphologies, or hexagonal sheets synthesized by the present invention are Compared with hexagonal boron nitride nanomaterials with solid spherical morphology, hexagonal boron nitride nanomaterials with "card room" structure usually have more obvious advantages in light, electricity, adsorption, thermal conductivity and / or functional applications. These characteristics make these hexagonal boron nitride nanomaterials have stronger competitiveness and application prospects in applications such as high-performance composite materials, catalyst carrier materials, water treatment and purification materials, and efficient thermal management materials. For example, hexagonal boron nitride nanomaterials with go piece morphology have better crystallinity (from the provided X RD graph shows good crystallinity), which can improve the efficiency and quality of synthesized cubic boron nitride, and due to its lower defects, it can exhibit better thermal conductivity when used as a thermal conductive filler; for example, hexagonal boron nitride nanomaterials with a few-layer nanosheet morphology usually have a larger specific surface area than spherical hexagonal boron nitride nanomaterials, and the layered structure exposes more reaction sites on the surface of each particle, thereby providing more physical and chemical active sites, especially in catalysis, adsorption, energy storage and other applications. It has significant advantages, and hexagonal boron nitride with a few-layer nanosheet structure has a wider bandgap and stronger insulation, making it widely used in the packaging and isolation layers of electronic devices; for example, hexagonal boron nitride nanomaterials with a "card room" structure morphology composed of hexagonal sheets have higher porosity and lower density due to their unique sheet and stacking characteristics, and can be used as a separator for batteries and capacitors and a solid electrolyte additive. It shows better effects, not only can it work in a high temperature environment, but also can improve the performance of electrochemical devices.

[0045] In some more preferred embodiments, by strictly controlling the mass amount of the borax to 15% of the sum of the mass amounts of the nitrogen source and the boric acid, controlling the temperature of the heating and heat preservation treatment to 1300°C, the heating and heat preservation treatment time to 4h, and controlling the molar ratio of the urea to the boric acid to 0.5:1, a hexagonal boron nitride nanomaterial with a small cylindrical morphology can be obtained, controlling the molar ratio of the urea to the boric acid to 1:1, a hexagonal boron nitride nanomaterial with a go piece morphology can be obtained, controlling the molar ratio of the urea to the boric acid to 1.5:1, a hexagonal boron nitride nanomaterial with a few-layer nanosheet morphology can be obtained, and controlling the molar ratio of the urea to the boric acid to 2:1, a hexagonal boron nitride nanomaterial with a "card room" structure morphology composed of hexagonal sheets can be obtained.

[0046] In a second aspect, the present invention provides a hexagonal boron nitride nanomaterial prepared by the method described in the first aspect of the present invention.

[0047] The present invention will be further described below by way of examples, but the protection scope of the present invention is not limited to these embodiments.

[0048] Example 1

[0049] ① Raw material preparation: urea CO(NH2)2 and boric acid H3BO3 are mixed uniformly in a molar ratio of 0.5:1 (denoted as U / B=0.5), and then borax decahydrate (Na2B4O7·10H2O) is added and mixed and ground for 1 hour to obtain a mixture, which is sieved to obtain a mixture with a particle size of less than 180 μm; wherein the mass amount of borax decahydrate is 15% of the sum of the mass amounts of urea and borax.

[0050] ② Low-temperature preparation of precursor: The obtained mixture with a particle size of less than 180 μm was treated in an oven at 85° C. for 4 h under air atmosphere to obtain a white powder precursor.

[0051] ③ Template sintering synthesis: The obtained white powder precursor was first placed in a ball mill with anhydrous ethanol as the ball milling medium, and ball milled at a speed of 300r / min for 3h under the condition of a ball-to-material ratio of 8:1, and then dried at 85°C. Then, it was spread flat in a corundum crucible and placed in a horizontal tubular atmosphere furnace and heated at 1300°C for 4h under a nitrogen atmosphere at normal pressure, and then cooled to room temperature. After washing with water, a small cylindrical hexagonal boron nitride nanomaterial was obtained with a yield of 95.2%. Its morphology is as follows Figure 2 a and Figure 3 (a) shown.

[0052] Example 2

[0053] ① Raw material preparation: urea CO(NH2)2 and boric acid H3BO3 are mixed uniformly in a molar ratio of 1:1 (denoted as U / B=1), and then borax decahydrate (Na2B4O7·10H2O) is added and mixed and ground for 1 hour to obtain a mixture, which is sieved to obtain a mixture with a particle size of less than 180 μm; wherein the mass amount of borax decahydrate is 15% of the sum of the mass amounts of urea and borax.

[0054] ② Low-temperature preparation of precursor: The obtained mixture with a particle size of less than 180 μm was treated in an oven at 85° C. for 4 h under air atmosphere to obtain a white powder precursor.

[0055] ③ Template sintering synthesis: The obtained white powder precursor was first placed in a ball mill with anhydrous ethanol as the ball milling medium, and ball milled at a speed of 300r / min for 3h under the condition of a ball-to-material ratio of 8:1, and then dried at 85°C. Then, it was spread flat in a corundum crucible and placed in a horizontal tubular atmosphere furnace and heated at 1300°C for 4h under a nitrogen atmosphere at normal pressure, and then cooled to room temperature. After washing with water, a hexagonal boron nitride nanomaterial with a go-piece morphology was obtained with a yield of 95.8%. Its morphology is as follows Figure 2 b and Figure 3 (b) as shown.

[0056] Example 3

[0057] ① Raw material preparation: urea CO(NH2)2 and boric acid H3BO3 are mixed uniformly in a molar ratio of 1.5:1 (denoted as U / B=1.5), and then borax decahydrate (Na2B4O7·10H2O) is added and mixed and ground for 1 hour to obtain a mixture, which is sieved to obtain a mixture with a particle size of less than 180 μm; wherein the mass amount of borax decahydrate is 15% of the sum of the mass amounts of urea and borax.

[0058] ② Low-temperature preparation of precursor: The obtained mixture with a particle size of less than 180 μm was treated in an oven at 85° C. for 4 h under air atmosphere to obtain a white powder precursor.

[0059] ③ Template sintering synthesis: The obtained white powder precursor was first placed in a ball mill with anhydrous ethanol as the ball milling medium, and ball milled at a speed of 300r / min for 3h under the condition of a ball-to-material ratio of 8:1, and then dried at 85°C, and then spread flat in a corundum crucible and placed in a horizontal tubular atmosphere furnace. It was heated and kept at 1300°C for 4h under a nitrogen atmosphere at normal pressure, and then cooled to room temperature. After washing with water, a hexagonal boron nitride nanomaterial with a few-layer nanosheet morphology was obtained, with a yield of 96.7%. Its morphology is as follows Figure 2 c and Figure 3 (c) as shown.

[0060] Example 4

[0061] ① Raw material preparation: urea CO(NH2)2 and boric acid H3BO3 are mixed uniformly in a molar ratio of 2:1 (denoted as U / B=2), and then borax decahydrate (Na2B4O7·10H2O) is added and mixed and ground for 1 hour to obtain a mixture, which is sieved to obtain a mixture with a particle size of less than 180 μm; wherein the mass amount of borax decahydrate is 15% of the sum of the mass amounts of urea and borax.

[0062] ② Low-temperature preparation of precursor: The obtained mixture with a particle size of less than 180 μm was treated in an oven at 85° C. for 4 h under air atmosphere to obtain a white powder precursor.

[0063] ③ Template sintering synthesis: The obtained white powder precursor is first placed in a ball mill with anhydrous ethanol as the ball milling medium, and ball milled at a speed of 300r / min for 3h under the condition of a ball-to-material ratio of 8:1, and then dried at 85°C, and then spread flat in a corundum crucible and placed in a horizontal tubular atmosphere furnace. It is heated and kept at 1300°C for 4h under a nitrogen atmosphere at normal pressure, and then cooled to room temperature. After washing with water, a hexagonal boron nitride nanomaterial with a "card room" structure morphology composed of hexagonal flakes is obtained, and the yield is 97.1%. Its morphology is as follows Figure 2 d and Figure 3 (d) as shown.

[0064] The XRD patterns of the hexagonal boron nitride nanomaterials with various morphologies prepared in Examples 1 to 4 of the present invention are as follows: Figure 1 As shown, see Figure 1 It can be seen that the products obtained in Examples 1 to 4 of the present invention are hexagonal boron nitride and no other obvious impurities are present. At the same time, it can be seen that as the ratio of urea to boric acid increases, the degree of graphitization of hexagonal boron nitride increases, indicating that the crystallinity is better.

[0065] The SEM images and TEM images of various morphologies of hexagonal boron nitride nanomaterials prepared in Examples 1 to 4 of the present invention are shown in FIG. Figure 2 and Figure 3 As shown, see Figure 2 and Figure 3 , it can be seen that the present invention provides a method for preparing hexagonal boron nitride nanomaterials with various morphologies. From these pictures, it can be seen that a variety of hexagonal boron nitride nanomaterials with different morphologies have been successfully synthesized, and each morphology is uniform (even), such as Figure 2 a and Figure 3 (a) is a small cylindrical morphology. Figure 2 b and Figure 3 (b) is a Go piece-shaped shape. Figure 2 c and Figure 3 (c) is a few-layer nanosheet morphology. Figure 2 d and Figure 3 (d) is the "card house" structure morphology composed of hexagonal sheets. These pictures further illustrate that the synthesized samples have morphological diversity and each morphology is uniform.

[0066] Parts of the present invention that are not described in detail are well known to those skilled in the art.

[0067] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing hexagonal boron nitride nanomaterials with various morphologies, characterized in that: The method comprises the following steps: (1) mixing boric acid and a nitrogen source uniformly, then adding borax and mixing uniformly to obtain a mixture, and sieving to obtain a mixture with a particle size of less than 180 μm; (2) treating the mixture with a particle size less than 180 μm at 85° C. for 4 h to obtain a precursor; (3) The precursor is heated and kept at normal pressure, then cooled to room temperature, and washed with water to obtain hexagonal boron nitride nanomaterials with various morphologies.

2. The method according to claim 1, characterized in that: The nitrogen source is urea.

3. The method according to claim 2, characterized in that: The molar ratio of the urea to the boric acid is 1:(0.5-2).

4. The method according to claim 2, characterized in that: The molar ratio of the urea to the boric acid is 0.5:1, 1:1, 1.5:1 or 2:

1.

5. The method according to claim 2, characterized in that: The borax is borax decahydrate; and / or The mass amount of the borax is 15% of the sum of the mass amounts of the nitrogen source and the boric acid.

6. The method according to claim 1, characterized in that: The heating and heat preservation treatment is carried out under a nitrogen atmosphere.

7. The method according to claim 1, characterized in that: The temperature of the heating and heat preservation treatment is 900° C. to 1300° C., and the time of the heating and heat preservation treatment is 3 h to 6 h.

8. The method according to claim 7, characterized in that: The temperature of the heating and heat preservation treatment is 1300° C., and the time of the heating and heat preservation treatment is 4 hours.

9. The method according to claim 1, characterized in that: The hexagonal boron nitride nanomaterial has a small cylindrical morphology, a go piece morphology, a few-layer nanosheet morphology, or a "card house" structure morphology composed of hexagonal sheets.

10. A hexagonal boron nitride nanomaterial prepared by the method according to any one of claims 1 to 9.

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