Preparation method and application of ultrathin large-size hexagonal boron nitride nanosheet capable of being produced in large scale

Abstract

The invention discloses a preparation method and application of an ultrathin large-size hexagonal boron nitride nanosheet capable of being produced on a large scale, and belongs to the technical field of two-dimensional material preparation. The method comprises the following steps: 1, preparing a boron nitride dispersion solution; 2, performing ultrasonic oscillation on the boron nitride dispersion liquid by using an ultrasonic processor; 3, stirring the boron nitride dispersion liquid subjected to ultrasonic pretreatment at an ultra-high speed by using a wall breaking machine; and 4, centrifuging the stirred boron nitride, taking supernate, washing and drying to obtain the ultrathin large-size boron nitride nanosheet. The preparation method disclosed by the invention has the characteristics of simplicity, high efficiency, economy, environmental protection, high yield, high reliability, large-scale preparation and the like, and the prepared boron nitride nanosheet has the advantages of large sheet diameter, small thickness, uniform particles, high lattice integrity and the like, and can be applied to the fields of thermal management, energy storage and photoelectrochemistry of electronic devices.

Description

Technical Field

[0001] The present invention belongs to the technical field of two-dimensional material preparation, and specifically relates to a preparation method and application of ultra-thin large-size hexagonal boron nitride nanosheets that can be mass-produced. Background Art

[0002] Hexagonal boron nitride nanosheets (BNNS) are two-dimensional (2D) lamellar nanomaterials that are widely used in electronic device thermal management, high voltage insulation, energy storage, and photoelectrochemistry due to their advantages such as high thermal conductivity, high insulation, excellent mechanical properties, and chemical stability. However, the excellent physical properties of 2D BNNS depend mainly on the thickness and lateral size of the sheets. Compared with conventional BN, thin and large BNNS have higher thermal conductivity, better mechanical strength, and lower bending modulus (good flexibility), thus showing some ideal assembly properties. With this advantage, large-sized thin BNNS have been used to manufacture advanced composite materials such as films / fibers with high thermal conductivity, high strength, and high flexibility. However, despite the high demand, high-quality BNNS are limited by low production efficiency and are difficult to achieve large-scale industrial production requirements.

[0003] At present, the synthesis methods of BNNS are mainly divided into two categories: bottom-up growth method and top-down stripping method. The bottom-up growth method usually uses chemical vapor deposition, epitaxial growth and direct organic synthesis to grow BNNS on a substrate. Although these methods can obtain high-quality few-layer BNNS, the preparation process is cumbersome and time-consuming and requires complex infrastructure and harsh process environment (for example, Chinese patents 202311544643.8, 202311417197.4), which makes the production cost high and the yield extremely low. In contrast, the top-down stripping method is simple to operate and has low cost. The top-down stripping method is to peel BNNS from the bulk BN stacking layer through external forces such as mechanical impact or chemical reaction. Typical methods include liquid phase ultrasound, mechanical ball milling, ion intercalation, supercritical fluid stripping and electrochemical stripping (for example, Chinese patents 202311390084.X, 202310669027.9). However, the yield and output of most of these methods are still low (yield is usually <20%, output is usually <0.3g), and the resulting BNNS are small in lateral size (hundreds of nanometers and below) and prone to a large number of lattice defects. In addition, the preparation process is also affected by long stripping cycles, high energy consumption, and toxic organic solvents, which cannot meet the requirements of large-scale industrial production. Therefore, it is urgent to develop a simple, efficient, low-cost, high-yield, highly reliable, economical and environmentally friendly method for large-scale production of ultra-thin large-size BNNS to meet the manufacturing needs of different advanced material application fields. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a preparation method and application of ultra-thin large-size hexagonal boron nitride nanosheets that can be mass-produced.

[0005] The present invention provides a method for efficiently preparing BNNS based on the combination of ultrasound and ultra-high-speed stirring. The method first uses ultrasonic impact to produce defects on the surface and edge of boron nitride and graft hydroxyl groups, preliminarily weakening the interlayer force of boron nitride, and then through the ultra-high-speed stirring of a wall-breaking machine, the interaction of hydrogen bonds at the defects and the shear, cavitation and impact generated by ultra-high speeds are used to synergistically induce the tearing and sliding behavior of boron nitride, and continuously and efficiently peel off ultra-thin large-size BNNS. The preparation method of the present invention has the characteristics of being simple and efficient, economical and environmentally friendly, high yield, high reliability and large-scale preparation. The prepared boron nitride nanosheets have the advantages of large sheet diameter, small thickness, uniform particles and high lattice integrity. The final yield of the method is as high as 83.1%, and the average particle size of the generated boron nitride nanosheets is 4.20μm, the average thickness is 1.45nm, and the diameter-to-thickness ratio is as high as 2896, which meets the technical requirements for large-scale preparation of ultra-thin large-size hexagonal boron nitride nanosheets.

[0006] A method for preparing ultra-thin large-size hexagonal boron nitride nanosheets that can be mass-produced is specifically completed in the following steps:

[0007] 1. Add hexagonal boron nitride to a mixed solvent of isopropanol and water, and stir magnetically to obtain a boron nitride dispersion;

[0008] Second, firstly, an ultrasonic processor is used to ultrasonically vibrate the boron nitride dispersion, and then the micro jet generated by ultrasonic cavitation bombards the hexagonal boron nitride to produce defects on the surface and edge of the hexagonal boron nitride and graft hydroxyl groups to obtain a hydroxyl-functionalized BN-OH solution;

[0009] 3. Pour the hydroxyl-functionalized BN-OH solution into a wall-breaking machine and stir for a period of time to allow the boron nitride to be exfoliated. After the stirring is completed, centrifuge the BN-OH solution at a low speed and take the supernatant to obtain a stably dispersed BNNS suspension. At the same time, collect the centrifugal precipitate as the raw material for the next exfoliation.

[0010] Fourth, the BNNS suspension is vacuum filtered and then washed, the washed BNNS is dispersed in pure water, and then freeze-dried to obtain ultra-thin large-sized hexagonal boron nitride nanosheets.

[0011] Compared with the prior art, the present invention has the following significant effects:

[0012] (1) The present invention provides a multi-dimensional boron nitride exfoliation method based on the coordinated design of ultrasound and ultra-high-speed stirring. Compared with the traditional liquid phase ultrasound method, this method significantly improves the exfoliation efficiency;Figure 1 As shown, within the same stripping time (24h), the yield of the stripping method provided by the present invention reaches up to 83.1%, which is 3.07 times that of the traditional ultrasonic method (27.1%);

[0013] (2) The present invention successfully realizes the exfoliation of ultra-thin large-sized hexagonal boron nitride nanosheets. The exfoliated boron nitride nanosheets have the advantages of large sheet diameter, thin thickness, uniform structure and high lattice quality; Figure 6 and Figure 7 As shown, the average particle size of the exfoliated boron nitride nanosheets is 4.2μm, the average thickness is only 1.45nm, and the aspect ratio is as high as 2896, which has outstanding advantages in the frontier research work of boron nitride exfoliation in recent years;

[0014] (3) The present invention selects a mixed solution of water and isopropanol as the stripping auxiliary solvent. Compared with other stripping auxiliary solvents (N,N-dimethylformamide, N-methylpyrrolidone and glucose, etc.), this solvent is not only low-cost, but also environmentally friendly, non-toxic and pollution-free. In addition, the solvent will not remain on the BNNS, eliminating the complicated washing process; at the same time, the excess solvent left after stripping can be reused after filtering to remove small particles of BN, which is recyclable;

[0015] (4) The wall breaking machine and ultrasonic processor used in the present invention are low-cost, widely available and have a mature industrial design foundation. They can support large-scale mass production of products and effectively solve the problems of high price, high energy consumption and high noise existing in other traditional peeling equipment (such as ball mills, high-pressure homogenizers, ultrafine grinders, etc.).

[0016] (5) The high-quality, ultra-thin, large-size hexagonal boron nitride nanosheets prepared by the present invention can be used in the fields of thermal management of electronic devices, energy storage, and photoelectrochemistry. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a graph showing the change in BNNS yield over the peeling time when the peeling method is used in Examples 1-4 of the present invention, the ultrasonic peeling method is used in Comparative Examples 1-4, and the wall breaking machine stirring method is used in Comparative Examples 5-8;

[0018] Figure 2 XRD comparison diagram of BNNS prepared in Example 1 and original BN;

[0019] Figure 3 is the infrared spectra of BN, BN-OH and BNNS in Example 1;

[0020] Figure 4 This is a SEM comparison of the original BN and BNNS in Example 1;

[0021] Figure 5This is a SEM image of the centrifugal precipitate under low-speed centrifugation in step 3 of Example 1;

[0022] Figure 6 is the AFM image of BNNS in Example 1;

[0023] Figure 7 The graphs are the statistical distribution graph of the average thickness, the statistical distribution graph of the average particle size, and the comparison graph of the diameter-to-thickness ratio of BNNS in Example 1. DETAILED DESCRIPTION

[0024] Specific implementation method 1: This implementation method is a method for preparing ultra-thin large-size hexagonal boron nitride nanosheets that can be mass-produced, which is specifically completed in the following steps:

[0025] 1. Add hexagonal boron nitride to a mixed solvent of isopropanol and water, and stir magnetically to obtain a boron nitride dispersion;

[0026] Second, firstly, an ultrasonic processor is used to ultrasonically vibrate the boron nitride dispersion, and then the micro jet generated by ultrasonic cavitation bombards the hexagonal boron nitride to produce defects on the surface and edge of the hexagonal boron nitride and graft hydroxyl groups to obtain a hydroxyl-functionalized BN-OH solution;

[0027] 3. Pour the hydroxyl-functionalized BN-OH solution into a wall-breaking machine and stir for a period of time to allow the boron nitride to be exfoliated. After the stirring is completed, centrifuge the BN-OH solution at a low speed and take the supernatant to obtain a stably dispersed BNNS suspension. At the same time, collect the centrifugal precipitate as the raw material for the next exfoliation.

[0028] Fourth, the BNNS suspension is vacuum filtered and then washed, the washed BNNS is dispersed in pure water, and then freeze-dried to obtain ultra-thin large-sized hexagonal boron nitride nanosheets.

[0029] Specific embodiment 2: This embodiment differs from specific embodiment 1 in that: the particle size of the hexagonal boron nitride described in step 1 is 10 μm to 30 μm; the volume ratio of isopropanol to water in the mixed solvent of isopropanol and water described in step 1 is 1:(1 to 2). The other steps are the same as those in specific embodiment 1.

[0030] Specific embodiment 3: This embodiment differs from specific embodiment 1 or 2 in that: the concentration of the boron nitride dispersion described in step 1 is 1 mg / mL to 10 mg / mL; the speed of the magnetic stirring described in step 1 is 300 r / min, and the time of the magnetic stirring is 20 min to 40 min. The other steps are the same as those of specific embodiment 1 or 2.

[0031] Specific embodiment 4: This embodiment differs from specific embodiments 1 to 3 in that the power of the ultrasonic oscillation in step 2 is 200W to 400W, and the time of the ultrasonic oscillation is 0.5h to 1h. The other steps are the same as those of specific embodiments 1 to 3.

[0032] Specific implementation method 5: This implementation method is different from specific implementation methods 1 to 4 in that the speed of the wall-breaking machine described in step 3 is 30000r / min to 40000r / min, the number of wall-breaking blades in the wall-breaking machine is 2 to 8 pages, and the capacity of the wall-breaking machine is 1L to 8L; the stirring time is 0.5h to 1.5h. The other steps are the same as those of specific implementation methods 1 to 4.

[0033] Specific embodiment 6: This embodiment differs from specific embodiments 1 to 5 in that the rotation speed of the low-speed centrifugation in step 3 is 1000 rpm to 2500 rpm, and the time of the low-speed centrifugation is 10 min to 20 min. The other steps are the same as those of specific embodiments 1 to 5.

[0034] Specific embodiment 7: This embodiment differs from specific embodiments 1 to 6 in that the centrifugal precipitate in step 2 is subjected to the stripping process of steps 2 and 3 repeatedly, and the number of repetitions is 1 to 20. The other steps are the same as those of specific embodiments 1 to 6.

[0035] Specific embodiment 8: This embodiment differs from specific embodiments 1 to 7 in that: the pore size of the filter membrane for vacuum filtration in step 4 is 0.22 μm; the washing in step 4 is to use pure water to wash the solid matter obtained by filtration, and the number of washing times is 2 to 3 times. The other steps are the same as those of specific embodiments 1 to 7.

[0036] Specific embodiment 9: The difference between this embodiment and specific embodiments 1 to 8 is that the mass ratio of the washed BNNS described in step 4 to the volume of pure water is (1g to 1.5g): (100mL to 200mL); the temperature program of the freeze drying described in step 4 is set to -35℃ to 35℃, and the drying time is 36h to 40h; the lateral size of the ultra-thin large-size hexagonal boron nitride nanosheets described in step 4 is 2μm to 7μm, and the thickness is 1nm to 2nm. The other steps are the same as specific embodiments 1 to 8.

[0037] Specific embodiment ten: This embodiment is the application of ultra-thin large-size hexagonal boron nitride nanosheets in the fields of thermal management, energy storage and photoelectrochemistry of electronic devices.

[0038] The following examples are used to verify the beneficial effects of the present invention:

[0039] Example 1: A method for preparing ultra-thin large-size hexagonal boron nitride nanosheets that can be mass-produced is specifically completed by the following steps:

[0040] 1. Add 5 g of hexagonal boron nitride with a particle size of 25 μm into 1 L of a mixed solvent of isopropanol and water, and stir magnetically until uniform to form a boron nitride dispersion;

[0041] The volume ratio of isopropanol to water in the mixed solvent of isopropanol and water in step 1 is 2:3;

[0042] In step 1, the speed of magnetic stirring is 300 r / min, and the stirring time is 20 min;

[0043] Second, an ultrasonic processor is used to ultrasonically vibrate the boron nitride dispersion, and the micro-jets generated by ultrasonic cavitation bombard the hexagonal boron nitride, so that defects are generated on the surface and edge of the boron nitride and hydroxyl groups are grafted to obtain a hydroxyl-functionalized BN-OH solution;

[0044] The power of the ultrasonic processor described in step 2 is 300W, and the ultrasonic oscillation time is 0.5h;

[0045] 3. Pour the hydroxyl-functionalized BN-OH solution into a wall breaker and stir it at ultra-high speed for 1 hour. The interaction of hydrogen bonds at the defects and the fluid mechanics such as shear, cavitation and impact generated by the ultra-high speed of the wall breaker are synergistically induced to induce the exfoliation of boron nitride. The stirred boron nitride solution is centrifuged at low speed, and the supernatant is taken to obtain a stably dispersed BNNS suspension; at the same time, the centrifugal precipitate is collected, and the collected centrifugal precipitate is dispersed in the original solvent, and the exfoliation process from step 2 to step 3 is repeated 3 times (0.5h ultrasound and 1h ultra-high speed stirring are recorded as 1 exfoliation), and the total number of cyclic exfoliation of the collected centrifugal precipitate is 4 times, which is converted into a exfoliation time of 6 hours;

[0046] The speed of the wall-breaking machine described in step 3 is 32000r / min, the number of wall-breaking blades is 4, and the capacity of the wall-breaking machine is 1.2L;

[0047] The speed of the low-speed centrifugation in step 3 is 1500 r / min, and the time of the low-speed centrifugation is 10 min;

[0048] Fourth, the stably dispersed BNNS suspension obtained in step 3 is vacuum filtered, washed, and small particles of BNNS are removed, and then the washed BNNS are dispersed in pure water, followed by freeze drying, to finally obtain ultra-thin large-sized hexagonal boron nitride nanosheets (BNNS finished product); the BNNS finished product is then weighed, and the BNNS yield is calculated based on the mass ratio of the finished product to the mass of the original boron nitride; the yield is calculated once every 2 peeling cycles (i.e., 3 hours of peeling time);

[0049] The pore size of the filter membrane for vacuum filtration described in step 4 is 0.22 μm;

[0050] The washing solution described in step 4 is pure water, and the washing times are 3 times;

[0051] The freeze drying temperature program described in step 4 is set to -35°C to 35°C, and the drying time is 36 hours.

[0052] Example 2: The difference between this example and Example 1 is that in step 3, the centrifugal precipitate is collected, the collected centrifugal precipitate is dispersed in the original solvent, and the stripping process from step 2 to step 3 is repeated 7 times (0.5h ultrasound and 1h ultra-high-speed stirring are recorded as 1 stripping), and the total number of stripping cycles of the collected centrifugal precipitate is 8 times, which is converted into a stripping time of 12 hours. The other steps and parameters are the same as those in Example 1.

[0053] Example 3: The difference between this example and Example 1 is that in step 3, the centrifugal precipitate is collected, the collected centrifugal precipitate is dispersed in the original solvent, and the stripping process from step 2 to step 3 is repeated 11 times (0.5h ultrasound and 1h ultra-high-speed stirring are recorded as 1 stripping), and the total number of stripping cycles of the collected centrifugal precipitate is 12 times, which is converted into a stripping time of 18 hours. The other steps and parameters are the same as those in Example 1.

[0054] Example 4: The difference between this example and Example 1 is that in step 3, the centrifugal precipitate is collected, the collected centrifugal precipitate is dispersed in the original solvent, and the stripping process from step 2 to step 3 is repeated 15 times (0.5h ultrasound and 1h ultra-high-speed stirring are recorded as 1 stripping), and the total number of stripping cycles of the collected centrifugal precipitate is 16 times, which is converted into a stripping time of 24 hours. The other steps and parameters are the same as those in Example 1.

[0055] Comparative Example 1: Preparation of hexagonal boron nitride nanosheets by ultrasonic exfoliation, specifically completed in the following steps:

[0056] 5 g of hexagonal boron nitride (BN) with a particle size of 25 μm was added to a mixed solvent of 1 L of isopropanol and water, and magnetic stirring was performed to obtain a boron nitride dispersion; the boron nitride dispersion was ultrasonically oscillated by an ultrasonic processor for 3 hours, and the sonicated boron nitride solution was centrifuged at a low speed to obtain the supernatant; the supernatant was then vacuum filtered, washed, freeze-dried and weighed to finally obtain a BNNS finished product; at the same time, the centrifugal precipitate was collected, and the above-mentioned ultrasonic stripping process was repeated for 1 cycle; the number of cyclic ultrasonic cycles in Control Example 1 was 2 times, which was converted to a total ultrasonic time of 6 hours; finally, the BNNS yield was calculated based on the mass ratio of the finished product to the mass of the original boron nitride, and the BNNS yield was calculated once every 3 hours of ultrasonic stripping;

[0057] The volume ratio of isopropanol to water in the mixed solvent of isopropanol and water is 2:3;

[0058] The magnetic stirring speed is 300r / min, and the stirring time is 20min;

[0059] The power of the ultrasonic processor is 300W;

[0060] The speed of the low-speed centrifugation is 1500 r / min, and the time of the low-speed centrifugation is 10 min;

[0061] The pore size of the vacuum filtration membrane is 0.22 μm;

[0062] The solvent used in the washing is pure water, and the washing times are 3 times.

[0063] The freeze-drying temperature is -35°C to 35°C, and the drying time is 36 hours.

[0064] Comparative Example 2: The difference between this comparative example and comparative example 1 is that the number of ultrasonic cycles in comparative example 2 is 4 times, which is converted into a total ultrasonic time of 12 hours. The other steps and parameters are the same as those in Example 1.

[0065] Comparative Example 3: The difference between this comparative example and comparative example 1 is that the number of cyclic ultrasound in comparative example 3 is 6 times, which is converted into a total ultrasound time of 18 hours. The other steps and parameters are the same as those in Example 1.

[0066] Comparative Example 4: The difference between this comparative example and comparative example 1 is that the number of cyclic ultrasound in comparative example 4 is 8 times, which is converted into a total ultrasound time of 24 hours. The other steps and parameters are the same as those in Example 1.

[0067] Comparative Example 5: Preparation of hexagonal boron nitride nanosheets by a wall breaking machine stirring method, which is specifically completed in the following steps:

[0068] Add 5 g of hexagonal boron nitride (BN) with a particle size of 25 μm to a mixed solvent of 1 L of isopropanol and water, stir evenly with a magnetic stirrer to obtain a boron nitride dispersion; use a wall breaker to stir the boron nitride dispersion at ultra-high speed for 3 hours, centrifuge the stirred boron nitride solution at low speed, and take the supernatant; then vacuum filter the supernatant, wash it again, freeze-dry it, and weigh it to finally obtain the BNNS finished product. At the same time, collect the centrifugal precipitate, repeat the above stirring and stripping process, and repeat it once. The number of stirring times for Control Example 5 is 2 times, which is equivalent to a total stirring time of 6 hours. Finally, the BNNS yield is calculated based on the mass ratio of the finished product to the mass of the original boron nitride, and the BNNS yield is calculated every 3 hours of ultrasonic stripping;

[0069] The volume ratio of isopropanol to water in the mixed solvent of isopropanol and water is 2:3;

[0070] The magnetic stirring speed is 300r / min, and the stirring time is 20min;

[0071] The speed of the wall breaking machine is 32000r / min, the number of wall breaking knives is 4 pages, and the capacity of the wall breaking machine is 1.2L;

[0072] The speed of the low-speed centrifugation is 1500 r / min, and the time of the low-speed centrifugation is 10 min;

[0073] The pore size of the vacuum filtration membrane is 0.22 μm;

[0074] The solvent used in the washing is pure water, and the washing times are 3 times.

[0075] The freeze-drying temperature is -35°C to 35°C, and the drying time is 36 hours.

[0076] Comparative Example 6: The difference between this comparative example and comparative example 5 is that the stirring times in comparative example 6 are 4 times, which is converted into a total stirring time of 12 hours. The other steps and parameters are the same as those in Example 5.

[0077] Comparative Example 7: The difference between this comparative example and comparative example 5 is that the stirring times in comparative example 7 are 6 times, which is converted into a total stirring time of 18 hours. The other steps and parameters are the same as those in Example 5.

[0078] Comparative Example 8: The difference between this comparative example and comparative example 5 is that the stirring times in comparative example 8 are 8 times, which is converted into a total stirring time of 24 hours. The other steps and parameters are the same as those in Example 5.

[0079] Figure 1This is a graph showing the change in BNNS yield over the peeling time when the peeling method is used in Examples 1-4 of the present invention, the ultrasonic peeling method is used in Comparative Examples 1-4, and the wall breaking machine stirring method is used in Comparative Examples 5-8;

[0080] from Figure 1 It can be seen that the yield of the exfoliation method of the present invention is significantly improved compared with the single ultrasonic exfoliation method and the single wall-breaking machine stirring method. Within the same exfoliation time (24h), the final yield of the exfoliation method provided by the present invention is as high as 83.1%, which is 3.07 times that of the single ultrasonic method (27.1%) and 3.54 times that of the single wall-breaking machine stirring method (23.5%).

[0081] Figure 2 XRD comparison diagram of BNNS prepared in Example 1 and original BN;

[0082] from Figure 2 It can be seen that compared with the original BN, the peak intensity of the BNNS (002) characteristic peak is significantly reduced, indicating that the ultra-thin BNNS is less stacked. At the same time, the position of the (002) characteristic peak in the figure slightly shifts left from 26.81° to 26.73°. According to the Bragg equation (2dsinθ=n*λ), the distance between the BNNS plane layers becomes larger, indicating that the peeled BNNS is more "fluffy".

[0083] Figure 3 is the infrared spectra of BN, BN-OH and BNNS in Example 1;

[0084] from Figure 3 It can be seen that compared with the original BN sample, BN-OH and BNNS have a -1 There is an obvious broad peak of B-OH group at the bottom, indicating that the ultrasonic vibration pretreatment operation successfully grafted hydroxyl groups onto boron nitride.

[0085] Figure 4 This is a SEM comparison of the original BN and BNNS in Example 1;

[0086] from Figure 4 It can be seen that the lateral size of the original boron nitride is about 25μm, and the thickness of the layer is about 2μm; the peeled BNNS presents a smooth and nearly transparent surface morphology, with a lateral size of about 4μm, and the lateral diameter and thickness of the layer are significantly reduced compared with the original BN.

[0087] Figure 5 This is a SEM image of the centrifugal precipitate under low-speed centrifugation in step 3 of Example 1;

[0088] from Figure 5 It can be seen that after the synergistic treatment of ultrasonic vibration and ultra-high-speed stirring, the original BN underwent a variety of exfoliation behaviors, including the expansion behavior of edge wrinkling ( Figure 5(a)), dislocation behavior of lamellar slip ( Figure 5 (b)), and the three-dimensional dynamic behavior of surface tearing ( Figure 5 (c), 5(d)). Under the influence of fluid mechanics such as cavitation, shear and impact generated by ultrasonic treatment and ultra-high-speed stirring, the high-speed impact and shear force applied to the edge of BN can overcome the interaction between BN sheets, causing BN to wrinkle and slip. In addition, Figure 5 (c), 5(d) show that the surface of boron nitride is covered with stripes in different directions. This phenomenon is mainly caused by the three-dimensional dynamic behavior of surface tearing caused by the synergistic effect of ultrasound and ultra-high-speed stirring. First, the cavitation effect of ultrasound in the liquid will produce a local high-temperature micro-jets phenomenon. The impact of the micro-jets causes defects on the surface of boron nitride and grafts hydroxyl groups. On this basis, the rapid turbulence caused by ultra-high-speed stirring continuously flushes the defects. In the hydrogen-rich solvent environment, the interaction of hydrogen bonds accelerates the tearing and breaking of boron nitride nanosheets at the defects. Its dynamic behavior is similar to "tearing tape". The boron nitride nanosheets at the defects are constantly torn off. Therefore, after a peeling cycle, the surface of the boron nitride has traces of torn stripes. In recent research papers or patents on boron nitride peeling, edge wrinkling and sheet sliding behavior occasionally appear. However Figure 5 (c) and 5(d) exhibited dynamic surface tearing behaviors, which have not been found in the physical peeling method research. The above multi-type and multi-dimensional peeling behaviors are the key factors to improve the yield of boron nitride nanosheets and maintain the shape and structure of boron nitride nanosheets.

[0089] Figure 6 is the AFM image of BNNS in Example 1;

[0090] The surface morphology of the large-sized ultra-thin boron nitride nanosheets obtained in Example 1 was tested using an atomic force microscope (AFM) from Bruker Dimension Icon, Germany. Before the test, the large-sized ultra-thin boron nitride nanosheets were dispersed in pure water. After the dispersion was uniform, the BNNS dispersion was dropped on a clean silicon wafer and dried at 60°C to remove the solvent. During the test, a random position was selected and the AFM morphology image was scanned. The results are shown in Figure 2. Figure 6 As shown. Figure 6 It can be seen that the lateral size of BNNS is 3-4 μm, and the thickness of the nanosheet is 1.4-1.6 nm. The surface of the boron nitride nanosheet is small and the thickness is uniform, showing typical two-dimensional sheet characteristics.

[0091] Figure 7 The statistical distribution diagram of the average thickness, the statistical distribution diagram of the average particle size and the comparison diagram of the diameter-to-thickness ratio of BNNS in Example 1;

[0092] from Figure 7It can be seen that the average thickness of the ultra-thin boron nitride nanosheets is 1.45nm, and the average particle size is 4.2μm. Its thickness meets the requirement of "ultra-thin", and its lateral size meets the requirement of "large size". The diameter-to-thickness ratio is calculated by the ratio of particle size to thickness. After calculation, the diameter-to-thickness ratio of BNNS in Example 1 is as high as 2896, which has outstanding advantages in the frontier research work of boron nitride exfoliation in recent years.

[0093] The above are only preferred specific embodiments of the present invention, which are all different implementations based on the overall concept of the present invention, and the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for preparing ultra-thin large-size hexagonal boron nitride nanosheets that can be mass-produced, characterized in that The preparation method is specifically completed according to the following steps:

1. Add hexagonal boron nitride to a mixed solvent of isopropanol and water, and stir magnetically to obtain a boron nitride dispersion; Second, firstly, an ultrasonic processor is used to ultrasonically vibrate the boron nitride dispersion, and then the micro jet generated by ultrasonic cavitation bombards the hexagonal boron nitride to produce defects on the surface and edge of the hexagonal boron nitride and graft hydroxyl groups to obtain a hydroxyl-functionalized BN-OH solution; 3. Pour the hydroxyl-functionalized BN-OH solution into a wall-breaking machine and stir for a period of time to allow the boron nitride to be exfoliated. After the stirring is completed, centrifuge the BN-OH solution at a low speed and take the supernatant to obtain a stably dispersed BNNS suspension. At the same time, collect the centrifugal precipitate as the raw material for the next exfoliation. Fourth, the BNNS suspension is vacuum filtered and then washed, the washed BNNS is dispersed in pure water, and then freeze-dried to obtain ultra-thin large-sized hexagonal boron nitride nanosheets.

2. The method for preparing ultra-thin large-size hexagonal boron nitride nanosheets that can be mass-produced according to claim 1, characterized in that The particle size of the hexagonal boron nitride described in step 1 is 10 μm to 30 μm; the volume ratio of isopropanol to water in the mixed solvent of isopropanol and water described in step 1 is 1:(1 to 2).

3. The method for preparing ultra-thin large-size hexagonal boron nitride nanosheets that can be mass-produced according to claim 1, characterized in that The concentration of the boron nitride dispersion described in step 1 is 1 mg / mL to 10 mg / mL; the rotation speed of the magnetic stirring described in step 1 is 300 r / min, and the time of the magnetic stirring is 20 min to 40 min.

4. The method for preparing ultra-thin large-size hexagonal boron nitride nanosheets that can be mass-produced according to claim 1, characterized in that The power of the ultrasonic oscillation in step 2 is 200W to 400W, and the time of the ultrasonic oscillation is 0.5h to 1h.

5. The method for preparing ultra-thin large-size hexagonal boron nitride nanosheets that can be mass-produced according to claim 1, characterized in that The rotation speed of the wall breaking machine described in step three is 30000r / min~40000r / min, the number of wall breaking blades in the wall breaking machine is 2 pages~8 pages, and the capacity of the wall breaking machine is 1L~8L; the stirring treatment time is 0.5h~1.5h.

6. The method for preparing ultra-thin large-size hexagonal boron nitride nanosheets that can be mass-produced according to claim 1, characterized in that The rotation speed of the low-speed centrifugation in step 3 is 1000 rpm to 2500 rpm, and the time of the low-speed centrifugation is 10 min to 20 min.

7. The method for preparing ultra-thin large-size hexagonal boron nitride nanosheets that can be mass-produced according to claim 1, characterized in that The centrifugal precipitate in step 2 is subjected to the stripping process of steps 2 and 3 repeatedly, and the number of repetitions is 1 to 20 times.

8. The method for preparing ultra-thin large-size hexagonal boron nitride nanosheets that can be mass-produced according to claim 1, characterized in that The pore size of the filter membrane for vacuum filtration described in step 4 is 0.22 μm; the washing described in step 4 is to use pure water to wash the solid matter obtained by filtration, and the number of washing times is 2 to 3 times.

9. The method for preparing ultra-thin large-size hexagonal boron nitride nanosheets that can be mass-produced according to claim 1, characterized in that The mass ratio of the washed BNNS described in step 4 to the volume of pure water is (1g~1.5g):(100mL~200mL); the temperature program of the freeze-drying described in step 4 is set to -35℃~35℃, and the drying time is 36h~40h; the lateral size of the ultra-thin large-size hexagonal boron nitride nanosheets described in step 4 is 2μm~7μm, and the thickness is 1nm~2nm.

10. Use of the ultra-thin large-size hexagonal boron nitride nanosheets prepared by the preparation method according to any one of claims 1 to 9, characterized in that Ultrathin large-size hexagonal boron nitride nanosheets are used in the fields of thermal management, energy storage and photoelectrochemistry of electronic devices.

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