CN108529573B - Method for preparing hexagonal boron nitride nanosheets by using molten alkali and ultrasonic stripping technology - Google Patents
Method for preparing hexagonal boron nitride nanosheets by using molten alkali and ultrasonic stripping technology Download PDFInfo
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Abstract
The invention relates to a method for preparing hexagonal boron nitride nanosheets by using molten alkali and ultrasonic stripping technology. Specifically, the method adopts a molten alkali pretreatment technology combined with an ultrasonic stripping technology to prepare the hexagonal boron nitride nanosheet. The invention also discloses a hexagonal boron nitride nanosheet prepared by the method. The method has the characteristics of simple process, low cost, safety, no pollution and capability of quickly and efficiently preparing the hexagonal boron nitride nanosheet.
Description
Technical Field
The invention relates to the field of materials, in particular to a method for preparing hexagonal boron nitride nanosheets by using molten alkali and ultrasonic stripping technology.
Background
Two-dimensional layered materials (material thickness between 1nm and 100 nm) in nano materials have special physicochemical characteristics and numerous potential applications, and are considered to be more and more important by more people. Among the two-dimensional layered nanomaterials, hexagonal boron nitride nanosheets (h-BNNs) have attracted extensive attention because of their structural similarity to graphene, and their chemical stability, thermal stability and other properties are particularly excellent, so that h-BNNs have more excellent performance than graphene in some fields, such as the preparation of high thermal conductivity ceramic devices, thermal conductivity insulating composite materials and recyclable adsorbents.
To date, the methods for preparing h-BNNs are not numerous, and mainly include chemical vapor deposition, mechanical stripping, and liquid phase stripping, wherein the liquid phase stripping is theoretically high in yield. However, the yield of h-BNNs prepared by the traditional liquid phase stripping technology is actually very low due to the strong ionic bonding effect between layers of hexagonal boron nitride.
Therefore, there is a strong need in the art for a new technique for exfoliation of hexagonal boron nitride nanoplates.
Disclosure of Invention
The invention aims to provide a novel technology for stripping hexagonal boron nitride nanosheets.
In a first aspect of the present invention, there is provided a method of preparing hexagonal boron nitride nanoplates, the method comprising the steps of:
1) providing a first mixed solution comprising a first solvent and hexagonal boron nitride powder pretreated with molten alkali dispersed in the first solvent;
2) ultrasonically treating the first mixed solution to obtain a second mixed solution;
3) optionally filtering the second mixed solution, washing the obtained precipitate, and re-dispersing the obtained product in a second solvent to obtain a third mixed solution;
4) and centrifuging the product obtained in the previous step, collecting the upper-layer dispersion liquid, and drying to obtain the hexagonal boron nitride nanosheet.
In another preferred embodiment, the first solvent and the second solvent are water, preferably deionized water.
In another preferred embodiment, after step 4), the following steps are optionally included:
5) re-dispersing the precipitate obtained by centrifuging in the step 4) in a second solvent, and adding an alkaline substance to obtain a fourth mixed solution;
6) repeating steps 2) -4) except that: and replacing the first mixed solution with the fourth mixed solution.
In another preferred embodiment, steps 5) -6) are repeated, preferably 1-5 times.
In another preferred embodiment, the hexagonal boron nitride powder pretreated with molten alkali is prepared as follows:
a-1) providing a basic substance and hexagonal boron nitride powder;
a-2) mixing the basic substance and the hexagonal boron nitride powder to obtain a first mixture;
a-3) treating the first mixture at high temperature to obtain the hexagonal boron nitride powder pretreated by the molten alkali.
In another preferred embodiment, the hexagonal boron nitride powder has a particle size of 1-20 μm, preferably 3-18 μm, more preferably 4-15 μm.
In another preferred embodiment, the alkaline substance is selected from the group consisting of: sodium hydroxide, potassium hydroxide, or a combination thereof.
In another preferred embodiment, the alkaline substance is a mixture of sodium hydroxide and potassium hydroxide.
In another preferred example, the mixing ratio of the sodium hydroxide and the potassium hydroxide in the alkaline substance is 0.1 to 5, preferably 0.3 to 3, more preferably 0.5 to 2.5 by mass.
In another preferred example, the mass ratio of the basic substance to the hexagonal boron nitride powder in the first mixture is 1 to 20, preferably 1 to 10, more preferably 1 to 6.
In another preferred embodiment, the treatment temperature of the high-temperature treatment is 100-; and/or
The treatment time of the high-temperature treatment is 0.1-6h, preferably 0.3-4.5h, and more preferably 0.5-4 h.
In another preferred embodiment, in the step 2), the processing power of the ultrasonic treatment is 80-320W, preferably 100-; and/or
The treatment time of the ultrasonic treatment is 0.1 to 10 hours, preferably 0.3 to 6 hours, and more preferably 0.5 to 3 hours.
In another preferred embodiment, the pore size of the filter screen used in the filtering treatment is 0.22-5 um, preferably 0.4-1 um.
In another preferred embodiment, the washing treatment is carried out with a third solvent.
In another preferred embodiment, the third solvent is water, preferably deionized water.
In another preferred embodiment, in step 4), the centrifugation speed of the centrifugation treatment is 500-; and/or
The centrifugation time of the centrifugation treatment is 1-60min, preferably 3-30min, more preferably 5-20 min.
In another preferred embodiment, in step 4), the treatment temperature of the drying treatment is 50-120 ℃, preferably 60-90 ℃, and more preferably 80 ℃; and/or
The treatment time of the drying treatment is 0.5 to 4 hours, preferably 1 to 3 hours, and more preferably 2 hours.
In another preferred embodiment, the process has a yield of 10% or more, preferably 13% or more, more preferably 16% or more, most preferably 18% or more.
In a second aspect of the invention, there is provided a hexagonal boron nitride nanosheet prepared using the method of the first aspect of the invention.
In another preferred embodiment, the hexagonal boron nitride nanoplates have one or more characteristics selected from the group consisting of:
1) the particle size of the hexagonal boron nitride nanosheet is 0.5-2.5 um;
2) the thickness of the hexagonal boron nitride nanosheet is 0.5-7 nm;
3) the surface of the hexagonal boron nitride nanosheet is modified with hydroxyl;
4) the thermal conductivity of the uniform heating sheet prepared by the extraction rate of the hexagonal boron nitride nanosheet is as high as 58W/mK.
It is to be understood that within the scope of the present invention, the above-described features of the present invention and those specifically described below (e.g., in the examples) may be combined with each other to form new or preferred embodiments. Not to be reiterated herein, but to the extent of space.
Drawings
Fig. 1 is SEM results of hexagonal boron nitride nanoplates obtained in example 1.
Fig. 2 is TEM results of hexagonal boron nitride nanoplates obtained in example 1.
FIG. 3 shows FT-IR results for hexagonal boron nitride powder as a starting material and hexagonal boron nitride nanoplates obtained in example 1.
Fig. 4 shows the dispersibility test results of the hexagonal boron nitride nanosheets obtained in example 1.
Detailed Description
Through long-term and intensive research, the inventor can prepare the hexagonal boron nitride nanosheet in a short time and high efficiency by adopting the molten alkali intercalation pretreatment hexagonal boron nitride powder and combining the ultrasonic stripping technology. On this basis, the inventors have completed the present invention.
Term(s) for
As used herein, the term "molten alkali" refers to an alkali melted by a high temperature treatment, the treatment temperature of the high temperature treatment being generally 100-: sodium hydroxide, potassium hydroxide, or a combination thereof.
As used herein, the term "ultrasonic exfoliation" means that the exfoliation is achieved by ultrasonic treatment.
Preparation method
The invention provides a method for preparing hexagonal boron nitride nanosheets, which comprises the following steps:
1) providing a first mixed solution comprising a first solvent and hexagonal boron nitride powder pretreated with molten alkali dispersed in the first solvent;
2) ultrasonically treating the first mixed solution to obtain a second mixed solution;
3) optionally filtering the second mixed solution, washing the obtained precipitate, and re-dispersing the obtained product in a second solvent to obtain a third mixed solution;
4) and centrifuging the product obtained in the previous step, collecting the upper-layer dispersion liquid, and drying to obtain the hexagonal boron nitride nanosheet.
In another preferred embodiment, the first solvent and the second solvent are water, preferably deionized water.
In another preferred embodiment, after step 4), the following steps are optionally included:
5) re-dispersing the precipitate obtained by centrifuging in the step 4) in a second solvent, and adding an alkaline substance to obtain a fourth mixed solution;
6) repeating steps 2) -4) except that: and replacing the first mixed solution with the fourth mixed solution.
In another preferred embodiment, steps 5) -6) are repeated, preferably 1-5 times.
In the present invention, the hexagonal boron nitride powder pretreated with molten alkali is prepared as follows:
a-1) providing a basic substance and hexagonal boron nitride powder;
a-2) mixing the basic substance and the hexagonal boron nitride powder to obtain a first mixture;
a-3) treating the first mixture at high temperature to obtain the hexagonal boron nitride powder pretreated by the molten alkali.
In another preferred embodiment, the hexagonal boron nitride powder has a particle size of 1-20 μm, preferably 3-18 μm, more preferably 4-15 μm.
In the present invention, the alkaline substance includes (but is not limited to): sodium hydroxide, potassium hydroxide, or a combination thereof.
In another preferred embodiment, the alkaline substance is a mixture of sodium hydroxide and potassium hydroxide.
In another preferred example, the mixing ratio of the sodium hydroxide and the potassium hydroxide in the alkaline substance is 0.1 to 5, preferably 0.3 to 3, more preferably 0.5 to 2.5 by mass.
In the present invention, the mass ratio of the basic substance to the hexagonal boron nitride powder in the first mixture is 1 to 20, preferably 1 to 10, more preferably 1 to 6.
In the invention, the treatment temperature of the high-temperature treatment is 100-300 ℃, preferably 120-260 ℃, and more preferably 140-240 ℃; and/or
The treatment time of the high-temperature treatment is 0.1-6h, preferably 0.3-4.5h, and more preferably 0.5-4 h.
In the invention, in the step 2), the processing power of the ultrasonic treatment is 80-320W, preferably 100-; and/or
The treatment time of the ultrasonic treatment is 0.1 to 10 hours, preferably 0.3 to 6 hours, and more preferably 0.5 to 3 hours.
In another preferred embodiment, the pore size of the filter screen used in the filtering treatment is 0.22-5 um, preferably 0.4-1 um.
In another preferred embodiment, the washing treatment is carried out with a third solvent.
In another preferred embodiment, the third solvent is water, preferably deionized water.
In the present invention, in step 4), the centrifugation speed of the centrifugation treatment is 500-; and/or
The centrifugation time of the centrifugation treatment is 1-60min, preferably 3-30min, more preferably 5-20 min.
In the invention, in the step 4), the drying treatment temperature is 50-120 ℃, preferably 60-90 ℃, and more preferably 80 ℃; and/or
The treatment time of the drying treatment is 0.5 to 4 hours, preferably 1 to 3 hours, and more preferably 2 hours.
In another preferred embodiment, the process has a yield of 10% or more, preferably 13% or more, more preferably 16% or more, most preferably 18% or more.
Typically, the preparation method comprises the following steps:
1) grinding and stirring sodium hydroxide and potassium hydroxide uniformly to obtain mixed alkali, and then uniformly mixing the mixed alkali and hexagonal boron nitride powder to obtain a mixture;
2) transferring the prepared mixture to a polytetrafluoroethylene crucible, putting the polytetrafluoroethylene crucible into an autoclave, reacting at a high temperature for 1-5h, and naturally cooling to room temperature;
3) dispersing the obtained reactant in deionized water, ultrasonically stripping, filtering the obtained product, washing with the deionized water, dispersing in the deionized water again, centrifuging, collecting the upper-layer dispersion liquid, and drying to obtain the hexagonal boron nitride nanosheet;
4) dispersing the centrifugal precipitate obtained in the step into deionized water, adding sodium hydroxide and potassium hydroxide for ultrasonic stripping, filtering the obtained product, washing with deionized water, dispersing again, centrifuging, collecting the upper-layer dispersion liquid, and drying to obtain the hexagonal boron nitride nanosheet;
5) optionally repeating step 4) further increases the strip yield.
The average diameter of the hexagonal boron nitride powder adopted by the invention is 3-15 μm. The optimized time for the reaction of the hexagonal boron nitride powder and the molten alkali is 1-5 h.
In the invention, the hexagonal boron nitride powder is pretreated by utilizing molten alkali intercalation, and then the pretreated boron nitride powder is subjected to ultrasonic stripping in an alkali solution, so that higher yield of hexagonal boron nitride nanosheets (h-BNNs) can be obtained in a shorter time.
The method is used for stripping hexagonal boron nitride nanosheets (h-BNNs) and simultaneously functionalizing the surface of the lamella of the hexagonal boron nitride nanosheets, so that the dispersibility of the h-BNNs in a solvent is greatly improved, and a favorable platform is provided for further surface functionalization.
Hexagonal boron nitride nanosheet
The invention provides a hexagonal boron nitride nanosheet, which is prepared by adopting the method.
In the present invention, the hexagonal boron nitride nanoplates have one or more characteristics selected from the group consisting of:
1) the particle size of the hexagonal boron nitride nanosheet is 0.5-2.5 um;
2) the thickness of the hexagonal boron nitride nanosheet is 0.5-7 nm;
3) the surface of the hexagonal boron nitride nanosheet is modified with hydroxyl;
4) the thermal conductivity of the uniform heating sheet prepared by the extraction rate of the hexagonal boron nitride nanosheet is as high as 58W/mK.
Compared with the prior art, the invention has the following main advantages:
(1) the preparation method has the characteristics of simple process, cheap and easily obtained treatment raw materials, low requirement on equipment, low toxicity to the environment and convenience for large-scale production, and can greatly reduce the cost of the product;
(2) the preparation method has the characteristics of high speed and high efficiency, and the yield is as high as 19%;
(3) the size of the hexagonal boron nitride nanosheet is 0.5-2.5 um, and the thickness of the hexagonal boron nitride nanosheet is 0.5-7 nm.
(4) The surface of the hexagonal boron nitride nanosheet is modified by hydroxyl, so that the hexagonal boron nitride nanosheet is easy to disperse in deionized water for the second time;
(5) the in-plane thermal conductivity of the boron nitride uniform heating sheet prepared by the extraction rate of the hexagonal boron nitride nanosheet is as high as 58W/mK.
The invention will be further illustrated with reference to the following specific examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. The experimental procedures, in which specific conditions are not noted in the following examples, are generally carried out according to conventional conditions or according to conditions recommended by the manufacturers. Unless otherwise indicated, percentages and parts are by weight.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. In addition, any methods and materials similar or equivalent to those described herein can be used in the methods of the present invention. The preferred embodiments and materials described herein are intended to be exemplary only.
Example 1
(1) Respectively weighing 2.5g of sodium hydroxide and 2.5g of potassium hydroxide, fully grinding and uniformly mixing to obtain mixed alkali, and uniformly mixing the mixed alkali and 5g of hexagonal boron nitride powder (the particle size is about 3-18 um).
(2) The obtained mixture was transferred to a polytetrafluoroethylene crucible and placed in an autoclave, reacted at 180 ℃ for 1 hour, and then naturally cooled to room temperature.
(3) Dispersing reaction products in a reaction kettle in deionized water, carrying out 160W ultrasonic stripping on the obtained mixed solution for 1h, filtering the obtained mixture (the aperture of a filter screen is 0.4um) after the ultrasonic treatment is finished, and repeatedly washing the mixture for a plurality of times by using 90 ℃ ionic water at room temperature so as to clean alkali liquor and boric acid (such as a mixture of sodium borate and potassium borate). After washing the product, the product was redispersed in deionized water and centrifuged (centrifugation speed 1700 rpm, centrifugation time 30min), and the upper dispersion was collected and dried (drying temperature 80 ℃ C., treatment time 2 h).
(4) The precipitate obtained by the centrifugation in the above step was redispersed in deionized water, and 2.5g each of sodium hydroxide and potassium hydroxide was added. The mixed solution is ultrasonically stripped for 1h at 160W. After the ultrasound was completed, the resulting mixture was filtered and washed repeatedly with 90 ℃ ionized water several times at room temperature to wash out the alkali solution and borate. And (3) after cleaning the product, re-dispersing the product, centrifuging, collecting the upper-layer dispersion liquid, and drying to obtain the hexagonal boron nitride nanosheet with the yield of 13%.
Results
SEM, TEM, FT-IR and dispersibility tests are respectively carried out on the hexagonal boron nitride nanosheets obtained in example 1.
Fig. 1 is SEM results of hexagonal boron nitride nanoplates obtained in example 1.
As can be seen from fig. 1: the size of the obtained hexagonal boron nitride nanosheet is 0.5-2.5 um, and the thickness is about 0.5-7 nm.
Fig. 2 is TEM results of hexagonal boron nitride nanoplates obtained in example 1.
As can be seen from fig. 2: hexagonal boron nitride powder has been successfully exfoliated into hexagonal boron nitride nanoplates.
FIG. 3 shows FT-IR results of hexagonal boron nitride powder (h-BN) as a starting material and hexagonal boron nitride nanosheets (h-BNNS) obtained in example 1.
As can be seen from fig. 3: the surface of the obtained hexagonal boron nitride nanosheet is modified with hydroxyl.
Fig. 4 shows the dispersibility test results of the hexagonal boron nitride nanosheets obtained in example 1.
As can be seen from fig. 4: and ultrasonically dispersing the obtained hexagonal boron nitride nanosheet in deionized water again, and standing for 16h without obvious sedimentation.
Example 2
The difference from example 1 is that: the addition amounts of sodium hydroxide and potassium hydroxide in steps (1) and (4) were 3g and 2g, respectively.
Example 3
The difference from example 1 is that: the addition amounts of sodium hydroxide and potassium hydroxide in steps (1) and (4) were 3.33g and 1.67g, respectively.
Example 4
The difference from example 1 is that: the addition amount of the hexagonal boron nitride powder in the step (1) is 2 g.
Example 5
The difference from example 1 is that: the addition amount of the hexagonal boron nitride powder in the step (1) is 1 g.
Example 6
The difference from example 1 is that: the reaction temperature in step (2) was 150 ℃.
Example 7
The difference from example 1 is that: the reaction temperature in step (2) was 200 ℃.
Example 8
The difference from example 1 is that: the reaction in the step (2) is carried out at 180 ℃ for 2 h.
Example 9
The difference from example 1 is that: the reaction in the step (2) is carried out at 180 ℃ for 4 h.
Example 10
The difference from example 1 is that: after step (4), the precipitate obtained by centrifugation was redispersed in deionized water, and 2.16g of sodium hydroxide and 2.84g of potassium hydroxide were added. And carrying out ultrasonic stripping on the obtained mixed solution for 2 h. After the ultrasound was completed, the resulting mixture was filtered and washed repeatedly with 90 ℃ ionized water several times at room temperature to wash out the alkali solution and borate. And (3) after cleaning the product, re-dispersing the product, centrifuging, collecting the upper-layer dispersion liquid, and drying to obtain the hexagonal boron nitride nanosheet, wherein the yield of the hexagonal boron nitride nanosheet is 16.5% (adding up the product in example 1).
Example 11
The difference from example 10 is that: after example 10, the precipitate from the centrifugation was redispersed in 250mL of deionized water and 2.156g of sodium hydroxide and 2.844g of potassium hydroxide were added. And carrying out ultrasonic stripping on the obtained mixed solution for 2 h. After the ultrasound was completed, the resulting mixture was filtered and washed repeatedly with 90 ℃ ionized water several times at room temperature to wash out the alkali solution and borate. After cleaning the product, the obtained product was redispersed in deionized water, centrifuged, collected as the upper dispersion, and dried, to obtain hexagonal boron nitride nanosheet with a yield of 18.2% (cumulatively with the product of example 10).
Example 12
The difference from example 11 is that: after example 11, the precipitate from the centrifugation was redispersed in 250mL of deionized water and 2.156g of sodium hydroxide and 2.844g of potassium hydroxide were added. And carrying out ultrasonic stripping on the obtained mixed solution for 2 h. After the ultrasound was completed, the resulting mixture was filtered and washed repeatedly with 90 ℃ ionized water several times at room temperature to wash out the alkali solution and borate. After washing the product, the product was redispersed and centrifuged, and the upper dispersion was collected and dried to give hexagonal boron nitride nanosheets in 19% yield (cumulative example 11 product).
The detection results of the hexagonal boron nitride nanosheets obtained in examples 2-12 were similar to that of the hexagonal boron nitride nanosheets obtained in example 1.
Example 13
The hexagonal boron nitride nanosheet obtained in any one of embodiments 1 to 12 of the invention is used for preparing a homothermal sheet by a conventional method, and the thermal conductivity of the obtained homothermal sheet is as high as 58W/mK.
All documents referred to herein are incorporated by reference into this application as if each were individually incorporated by reference. Furthermore, it should be understood that various changes and modifications of the present invention can be made by those skilled in the art after reading the above teachings of the present invention, and these equivalents also fall within the scope of the present invention as defined by the appended claims.
Claims (10)
1. A method of making hexagonal boron nitride nanoplates, the method comprising the steps of:
1) providing a first mixed solution comprising a first solvent and hexagonal boron nitride powder pretreated with molten alkali dispersed in the first solvent; the first solvent is water;
wherein the molten base pre-treated hexagonal boron nitride powder is prepared by:
a-1) providing a basic substance and hexagonal boron nitride powder; wherein the alkaline substance is selected from the group consisting of: sodium hydroxide, potassium hydroxide, or a combination thereof; the particle size of the hexagonal boron nitride powder is 3-18 μm;
a-2) mixing the basic substance and the hexagonal boron nitride powder to obtain a first mixture; wherein, in the first mixture, the mass ratio of the alkaline substance to the hexagonal boron nitride powder is 1-6;
a-3) treating the first mixture at high temperature to obtain the hexagonal boron nitride powder pretreated by the molten alkali; wherein the treatment temperature of the high-temperature treatment is 120-260 ℃;
2) ultrasonically treating the first mixed solution to obtain a second mixed solution; wherein the processing power of the ultrasonic treatment is 100-250W; and the treatment time of the ultrasonic treatment is 0.5-3 h;
3) filtering the second mixed solution, washing the obtained precipitate, and re-dispersing the obtained product in a second solvent to obtain a third mixed solution; wherein the second solvent is water; in the step 3), the aperture of the filter screen used for the filtration treatment is 0.4-1 um;
4) centrifuging the product obtained in the previous step, collecting upper-layer dispersion liquid, and drying to obtain hexagonal boron nitride nanosheets;
after the step 4), the following steps are also included:
5) re-dispersing the precipitate obtained by centrifuging in the step 4) in a second solvent, and adding an alkaline substance to obtain a fourth mixed solution;
6) repeating steps 2) -4) except that: replacing the first mixed solution with the fourth mixed solution;
the hexagonal boron nitride nanosheet has the following characteristics:
1) the particle size of the hexagonal boron nitride nanosheet is 0.5-2.5 um;
2) the thickness of the hexagonal boron nitride nanosheet is 0.5-7 nm;
3) the surface of the hexagonal boron nitride nanosheet is modified with hydroxyl; and
4) the thermal conductivity of the even heating plate prepared by pumping filtration of the hexagonal boron nitride nanosheet is as high as 58W/mK.
2. The method of claim 1,
the particle size of the hexagonal boron nitride powder is 4-15 μm; or
a-2) the mass ratio of the basic substance to the hexagonal boron nitride powder in the first mixture is 1; or
In the step 2), the processing power of the ultrasonic treatment is 120-200W.
3. The method according to claim 2, wherein the alkaline substance is a mixture of sodium hydroxide and potassium hydroxide, and the mixing ratio of sodium hydroxide to potassium hydroxide in the alkaline substance is 0.1 to 5 by mass.
4. The method of claim 2, wherein the first mixture comprises the basic substance and the hexagonal boron nitride powder in a mass ratio of 1.
5. The method as claimed in claim 2, wherein the treatment temperature of the high temperature treatment is 140-240 ℃; and/or
The treatment time of the high-temperature treatment is 0.5-4 h.
6. The method as claimed in claim 1, wherein in step 2), the processing power of the ultrasonic treatment is 120-200W; and
the processing time of the ultrasonic treatment is 0.5-3 h.
7. The method as claimed in claim 1, wherein, in the step 4), the centrifugation speed of the centrifugation treatment is 500-8000 rpm; and/or
The centrifugation time of the centrifugation treatment is 1-60 min.
8. The method according to claim 1, wherein in the step 4), the drying treatment is performed at a treatment temperature of 50-120 ℃; and/or
The processing time of the drying treatment is 0.5-4 h.
9. Hexagonal boron nitride nanoplates produced by the method of claim 1.
10. Hexagonal boron nitride nanoplates as in claim 9, wherein the hexagonal boron nitride nanoplates have the following characteristics:
1) the particle size of the hexagonal boron nitride nanosheet is 0.5-2.5 um;
2) the thickness of the hexagonal boron nitride nanosheet is 0.5-7 nm;
3) the surface of the hexagonal boron nitride nanosheet is modified with hydroxyl; and
4) the thermal conductivity of the even heating plate prepared by pumping filtration of the hexagonal boron nitride nanosheet is as high as 58W/mK.
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