A method for preparing and applying ultrathin, large-size hexagonal boron nitride nanosheets that can be mass-produced.

Abstract

A method for preparing and applying ultrathin, large-size hexagonal boron nitride nanosheets capable of large-scale production is disclosed, belonging to the field of two-dimensional material preparation technology. The method includes: 1. Preparing a boron nitride dispersion solution; 2. Sonicating the boron nitride dispersion solution using an ultrasonic processor; 3. High-speed stirring the ultrasonically pretreated boron nitride dispersion solution using a high-speed mixer; 4. Centrifuging the stirred boron nitride solution, collecting the supernatant, washing and drying it to obtain ultrathin, large-size boron nitride nanosheets. This invention's preparation method is simple, efficient, economical, environmentally friendly, has high yield, high reliability, and can be mass-produced. The prepared boron nitride nanosheets have advantages such as large sheet diameter, small thickness, uniform particle size, and high lattice integrity, and can be applied in the fields of electronic device thermal management, energy storage, and photoelectrochemistry.

Description

Technical Field

[0001] This invention belongs to the field of two-dimensional material preparation technology, specifically relating to a method for preparing and applying ultrathin, large-size hexagonal boron nitride nanosheets that can be mass-produced. Background Technology

[0002] Hexagonal boron nitride nanosheets (BNNS) are two-dimensional (2D) layered nanomaterials with high thermal conductivity, high insulation, excellent mechanical properties, and chemical stability, making them widely used in fields such as thermal management of electronic devices, high-voltage insulation, energy storage, and photoelectrochemistry. However, the excellent physical properties of 2D boron nitride nanosheets mainly depend on the sheet thickness and lateral dimensions. Compared to conventional boron nitride (BN), thin and large boron nitride nanosheets exhibit higher thermal conductivity, better mechanical strength, and lower flexural modulus (good flexibility), thus displaying some ideal assembly properties. Leveraging this advantage, large-size thin boron nitride nanosheets have been used to manufacture advanced composite materials such as films / fibers with high thermal conductivity, high strength, and high flexibility. However, despite high demand, high-quality BNNS is limited by low production efficiency, making it difficult to achieve large-scale industrial production.

[0003] Currently, BNNS synthesis methods are mainly divided into two categories: bottom-up growth methods and top-down exfoliation methods. Bottom-up growth methods typically use chemical vapor deposition, epitaxial growth, and direct organic synthesis to grow BNNS on a substrate. While these methods can yield high-quality few-layer BNNS, the preparation process is cumbersome, time-consuming, and requires complex infrastructure and harsh process environments (e.g., Chinese patents 202311544643.8, 202311417197.4), resulting in high production costs and extremely low yields. In contrast, top-down exfoliation methods are simpler to operate and have lower costs. Top-down exfoliation methods use external forces such as mechanical impact or chemical reactions to peel BNNS from the bulk BN stack. Typical methods include liquid-phase ultrasonication, mechanical ball milling, ion intercalation, supercritical fluid exfoliation, and electrochemical exfoliation (e.g., Chinese patents 202311390084.X, 202310669027.9). However, most of these methods still suffer from low yields and outputs (typically <20% yield, typically <0.3g), and the resulting BNNS have small lateral dimensions (hundreds of nanometers and below) and are prone to numerous lattice defects. Furthermore, the preparation process is affected by long peeling cycles, high energy consumption, and toxic organic solvents, failing to meet the requirements of large-scale industrial production. Therefore, there is an urgent need to develop a simple, efficient, low-cost, high-yield, highly reliable, and environmentally friendly method for the large-scale production of ultrathin, large-size BNNS to address the manufacturing needs of various advanced materials applications. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a method for preparing and applying ultrathin, large-size hexagonal boron nitride nanosheets that can be mass-produced.

[0005] This invention provides a highly efficient method for preparing boron nitride nanosheets (BNNS) based on a combination of ultrasound and ultra-high-speed stirring. The method first utilizes ultrasonic impact to create defects on the surface and edges of boron nitride and graft hydroxyl groups, initially weakening the interlayer forces of boron nitride. Then, through ultra-high-speed stirring in a blender, the interaction of hydrogen bonds at the defects and the shearing, cavitation, and impact forces generated by the ultra-high speed synergistically induce tearing and slipping behavior in the boron nitride, continuously and efficiently exfoliating ultrathin, large-size BNNS. The preparation method of this invention is simple, efficient, economical, environmentally friendly, has high yield, high reliability, and can be mass-produced. The prepared boron nitride nanosheets have advantages such as large sheet diameter, small thickness, uniform particle size, and high lattice integrity. The final yield of this method reaches 83.1%, and the average particle size of the generated boron nitride nanosheets is 4.20 μm, the average thickness is 1.45 nm, and the aspect ratio is as high as 2896, meeting the technical requirements for large-scale preparation of ultrathin, large-size hexagonal boron nitride nanosheets.

[0006] A method for preparing ultrathin, large-size hexagonal boron nitride nanosheets that can be mass-produced is specifically carried out according to 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, the boron nitride dispersion is first ultrasonically vibrated using an ultrasonic processor, and then the hexagonal boron nitride is bombarded by a micro-jet generated by ultrasonic cavitation, which causes defects to be generated on the surface and edges of the hexagonal boron nitride and grafted with hydroxyl groups to obtain a hydroxyl-functionalized BN-OH solution.

[0009] 3. Pour the hydroxyl-functionalized BN-OH solution into a blender and stir for a period of time. Boron nitride will be stripped off. After stirring, centrifuge the BN-OH solution at low speed and take the supernatant to obtain a stable and dispersed BNNS suspension. At the same time, collect the centrifuged precipitate as the raw material for the next stripping.

[0010] 4. The BNNS suspension was vacuum filtered, washed, and then dispersed in pure water. The solution was then freeze-dried to obtain ultrathin, large-size hexagonal boron nitride nanosheets.

[0011] The significant advantages of this invention compared to existing technologies are:

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

[0013] (2) This invention successfully achieved the exfoliation of ultrathin, large-size hexagonal boron nitride nanosheets. The exfoliated boron nitride nanosheets have advantages such as large sheet diameter, thin thickness, uniform structure, and high lattice quality; for example... Figure 6 and Figure 7 As shown, the exfoliated boron nitride nanosheets have an average particle size of 4.2 μm and an average thickness of only 1.45 nm, with an aspect ratio as high as 2896, which is a significant advantage in the cutting-edge research on boron nitride exfoliation in recent years.

[0014] (3) This 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 inexpensive but also environmentally friendly, non-toxic, and pollution-free. In addition, this solvent will not remain on BNNS, eliminating the need for a complicated washing process; at the same time, the excess solvent remaining after stripping can be reused after filtering to remove small BN particles, making it recyclable.

[0015] (4) The blender and ultrasonic processor used in this invention are inexpensive, widely available and have a mature industrial design foundation, which can support large-scale mass production of products and effectively solve the problems of high price, high energy consumption and high noise of other traditional stripping equipment (such as ball mills, high pressure homogenizers, ultrafine grinders, etc.).

[0016] (5) The high-quality ultrathin large-size hexagonal boron nitride nanosheets prepared by this invention can be used in the fields of thermal management of electronic devices, energy storage and photoelectrochemistry. Attached Figure Description

[0017] Figure 1 The graph shows the change in BNNS yield with peeling time when using the peeling method in Examples 1-4 of the present invention, the ultrasonic peeling method in Comparative Examples 1-4, and the mixing method in Comparative Examples 5-8.

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

[0019] Figure 3 The infrared spectra of BN, BN-OH and BNNS in Example 1 are shown below.

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

[0021] Figure 5This is a SEM image of the precipitate centrifuged at low speed in step three of Example 1;

[0022] Figure 6 The AFM diagram of BNNS in Example 1;

[0023] Figure 7 The images show the statistical distribution of the average thickness of BNNS, the statistical distribution of the average particle size, and the comparison of the diameter-to-thickness ratio in Example 1. Detailed Implementation

[0024] Specific Implementation Method 1: This implementation method describes a method for preparing ultrathin, large-size hexagonal boron nitride nanosheets that can be mass-produced. The method is specifically completed according to 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, the boron nitride dispersion is first ultrasonically vibrated using an ultrasonic processor, and then the hexagonal boron nitride is bombarded by a micro-jet generated by ultrasonic cavitation, which causes defects to be generated on the surface and edges of the hexagonal boron nitride and grafted with hydroxyl groups to obtain a hydroxyl-functionalized BN-OH solution.

[0027] 3. Pour the hydroxyl-functionalized BN-OH solution into a blender and stir for a period of time. Boron nitride will be stripped off. After stirring, centrifuge the BN-OH solution at low speed and take the supernatant to obtain a stable and dispersed BNNS suspension. At the same time, collect the centrifuged precipitate as the raw material for the next stripping.

[0028] 4. The BNNS suspension was vacuum filtered, washed, and then dispersed in pure water. The solution was then freeze-dried to obtain ultrathin, large-size hexagonal boron nitride nanosheets.

[0029] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the particle size of the hexagonal boron nitride mentioned in step one is 10μm to 30μm; the volume ratio of isopropanol to water in the mixed solvent of isopropanol and water mentioned in step one is 1:(1 to 2). Other steps are the same as in Specific Implementation Method One.

[0030] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that: the concentration of the boron nitride dispersion in step one is 1 mg / mL to 10 mg / mL; the magnetic stirring speed in step one is 300 r / min, and the magnetic stirring time is 20 min to 40 min. Other steps are the same as in Specific Implementation Method One or Two.

[0031] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that the power of the ultrasonic oscillation in step two is 200W to 400W, and the ultrasonic oscillation time is 0.5h to 1h. The other steps are the same as in Specific Implementation Methods One to Three.

[0032] Specific Implementation Method Five: This implementation method differs from Specific Implementation Methods One to Four in that: the speed of the blender in step three is 30,000 r / min to 40,000 r / min; the number of blades in the blender is 2 to 8; and the capacity of the blender is 1L to 8L; the mixing time is 0.5h to 1.5h. Other steps are the same as in Specific Implementation Methods One to Four.

[0033] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that the speed of low-speed centrifugation in step three is 1000 rpm to 2500 rpm, and the low-speed centrifugation time is 10 min to 20 min. The other steps are the same as in Specific Implementation Methods One to Five.

[0034] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods One to Six in that the centrifuged precipitate described in step two undergoes the stripping process of steps two and three repeatedly, from 1 to 20 times. The other steps are the same as in Specific Implementation Methods One to Six.

[0035] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Methods One to Seven in that: the pore size of the filter membrane used for vacuum filtration in step four is 0.22 μm; the washing in step four involves washing the solid material obtained from vacuum filtration with pure water, and the washing is performed 2 to 3 times. Other steps are the same as in Specific Implementation Methods One to Seven.

[0036] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One to Eight in the following ways: the mass ratio of the washed BNNS to the volume of purified water in step four is (1g~1.5g):(100mL~200mL); the freeze-drying temperature program in step four is set to -35℃~35℃, and the drying time is 36h~40h; the lateral dimension of the ultrathin large-size hexagonal boron nitride nanosheets in step four is 2μm~7μm, and the thickness is 1nm~2nm. Other steps are the same as in Specific Implementation Methods One to Eight.

[0037] Specific Implementation Method 10: This implementation method is the application of ultrathin, large-size hexagonal boron nitride nanosheets in the fields of thermal management, energy storage, and photoelectrochemistry of electronic devices.

[0038] The beneficial effects of the present invention are verified using the following embodiments:

[0039] Example 1: A method for preparing ultrathin, large-size hexagonal boron nitride nanosheets that can be mass-produced, specifically comprising the following steps:

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

[0041] In step one, the volume ratio of isopropanol to water in the mixed solvent of isopropanol and water is 2:3.

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

[0043] 2. The boron nitride dispersion was ultrasonically vibrated using an ultrasonic processor. The micro-jet generated by ultrasonic cavitation bombarded the hexagonal boron nitride, causing defects to be generated on the surface and edges of the boron nitride and grafting hydroxyl groups, thus obtaining a hydroxyl-functionalized BN-OH solution.

[0044] The ultrasonic processor mentioned in step two has a power of 300W and an ultrasonic oscillation time of 0.5h.

[0045] 3. Pour the hydroxyl-functionalized BN-OH solution into a high-speed blender and stir at ultra-high speed for 1 hour. The interaction of hydrogen bonds at the defects and the shearing, cavitation and impact of the high speed of the blender will synergistically induce the exfoliation of boron nitride. Centrifuge the stirred boron nitride solution at low speed and take the supernatant to obtain a stable and dispersed BNNS suspension. At the same time, collect the centrifuged precipitate and disperse it in the original solvent. Repeat the exfoliation process of steps 2 to 3, repeating the cycle 3 times (0.5 hours of ultrasonic combined with 1 hour of ultra-high speed stirring is counted as 1 exfoliation). The total number of exfoliation cycles of the collected centrifuged precipitate is 4, which is equivalent to an exfoliation time of 6 hours.

[0046] The blender mentioned in step three has a rotation speed of 32,000 r / min, 4 blades, and a capacity of 1.2L.

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

[0048] 4. The stable and dispersed BNNS suspension obtained in step 3 is vacuum filtered, then washed to remove small particles of BNNS. The washed BNNS is then dispersed in pure water and freeze-dried to obtain ultrathin, large-size hexagonal boron nitride nanosheets (finished BNNS). The finished BNNS is then weighed, and the BNNS yield is calculated based on the ratio of the finished product's mass to the original boron nitride mass. The yield is calculated every two exfoliation cycles (i.e., 3 hours of exfoliation time).

[0049] The filter membrane used for vacuum filtration in step four has a pore size of 0.22 μm;

[0050] The washing solution mentioned in step four is purified water, and the washing is performed three times.

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

[0052] Example 2: The difference between this example and Example 1 is that in step three, the centrifuged precipitate is collected simultaneously and dispersed in the original solvent. The stripping process from step two to step three is repeated, cycled 7 times (0.5 hours of ultrasonic combined with 1 hour of ultra-high-speed stirring is counted as one stripping cycle). The total number of stripping cycles for the collected centrifuged precipitate is 8, which translates to a stripping time of 12 hours. Other steps and parameters are the same as in Example 1.

[0053] Example 3: The difference between this example and Example 1 is that, in step three, the centrifuged precipitate is collected and dispersed in the original solvent. The stripping process from step two to step three is repeated 11 times (0.5 hours of ultrasonic combined with 1 hour of ultra-high-speed stirring is counted as one stripping cycle). The total number of stripping cycles for the collected centrifuged precipitate is 12, which translates to a stripping time of 18 hours. Other steps and parameters are the same as in Example 1.

[0054] Example 4: The difference between this example and Example 1 is that, in step three, the centrifuged precipitate is collected and dispersed in the original solvent. The stripping process from step two to step three is repeated 15 times (0.5 hours of ultrasonic combined with 1 hour of ultra-high-speed stirring is counted as one stripping cycle). The total number of stripping cycles for the collected centrifuged precipitate is 16, which translates to a stripping time of 24 hours. Other steps and parameters are the same as in Example 1.

[0055] Comparative Example 1: The preparation of hexagonal boron nitride nanosheets by ultrasonic exfoliation was carried out according to the following steps:

[0056] 5g of hexagonal boron nitride (BN) with a particle size of 25μm was added to a 1L mixture of isopropanol and water and stirred magnetically to obtain a boron nitride dispersion. The boron nitride dispersion was ultrasonically vibrated for 3 hours using an ultrasonic processor. The ultrasonically vibrated boron nitride solution was centrifuged at low speed, and the supernatant was collected. The supernatant was then vacuum filtered, washed, freeze-dried, and weighed to obtain the final BNNS product. Meanwhile, the centrifuged precipitate was collected, and the ultrasonic exfoliation process was repeated once. The number of ultrasonic cycles in Control Example 1 was 2, which translates to a total ultrasonic time of 6 hours. Finally, the BNNS yield was calculated based on the ratio of the mass of the finished product to the mass of the original boron nitride. The BNNS yield was calculated every 3 hours of ultrasonic exfoliation.

[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 300 r / min, and the stirring time is 20 min;

[0059] The ultrasonic processor has a power of 300W;

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

[0061] The filter membrane used in the vacuum filtration process has a pore size of 0.22 μm.

[0062] The solvent used for washing is purified water, and the washing process is repeated three times.

[0063] The freeze-drying temperature is -35℃ to 35℃, 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 ultrasound cycles in Comparative Example 2 is 4, which translates to a total ultrasound time of 12 hours. All other steps and parameters are the same as in Example 1.

[0065] Comparative Example 3: The difference between this comparative example and Comparative Example 1 is that the number of ultrasound cycles in Comparative Example 3 was 6, which translates to a total ultrasound time of 18 hours. All other steps and parameters were the same as in Example 1.

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

[0067] Comparative Example 5: The preparation of hexagonal boron nitride nanosheets by a high-speed blender stirring method was carried out according to the following steps:

[0068] 5g of hexagonal boron nitride (BN) with a particle size of 25μm was added to 1L of a mixed solvent of isopropanol and water, and magnetically stirred until homogeneous to obtain a boron nitride dispersion. The boron nitride dispersion was then subjected to ultra-high-speed stirring using a high-speed mixer for 3 hours. The stirred boron nitride solution was centrifuged at low speed, and the supernatant was collected. The supernatant was then vacuum filtered, washed, freeze-dried, and weighed to obtain the final BNNS product. Simultaneously, the centrifuged precipitate was collected, and the above stirring and stripping process was repeated once. In Comparative Example 5, the stirring was repeated twice, translating to a total stirring time of 6 hours. Finally, the BNNS yield was calculated based on the ratio of the finished product's mass to the original boron nitride mass, with ultrasonic stripping used to calculate the BNNS yield every 3 hours.

[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 300 r / min, and the stirring time is 20 min;

[0071] The blender has a speed of 32,000 r / min, 4 blades, and a capacity of 1.2 L.

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

[0073] The filter membrane used in the vacuum filtration process has a pore size of 0.22 μm.

[0074] The solvent used for washing is purified water, and the washing process is repeated three times.

[0075] The freeze-drying temperature is -35℃ to 35℃, 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 was performed 4 times in Comparative Example 6, which translates to a total stirring time of 12 hours. All other steps and parameters are the same as in Example 5.

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

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

[0079] Figure 1The graph shows the change in BNNS yield with peeling time when using the peeling method in Examples 1-4 of the present invention, the ultrasonic peeling method in Comparative Examples 1-4, and the mixing method in Comparative Examples 5-8.

[0080] from Figure 1 It is evident that the peeling method of this invention significantly improves the yield compared to the ultrasonic peeling method and the blender mixing method alone. Within the same peeling time (24h), the peeling method provided by this invention achieves a final yield of up to 83.1%, which is 3.07 times that of the ultrasonic method alone (27.1%) and 3.54 times that of the blender mixing method alone (23.5%).

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

[0082] from Figure 2 As can be seen, the peak intensity of the (002) characteristic peak of BNNS is significantly reduced compared with the original BN, indicating that there is less stacking of ultrathin BNNS. At the same time, the position of the (002) characteristic peak in the figure shifts slightly to the left from 26.81° to 26.73°. According to the Bragg equation (2dsinθ=n*λ), the interlayer distance of the BNNS plane increases, indicating that the stripped BNNS is more "fluffy".

[0083] Figure 3 The infrared spectra of BN, BN-OH and BNNS in Example 1 are shown below.

[0084] from Figure 3 It can be seen that, compared to the original BN sample, BN-OH and BNNS show differences at ~3380 cm⁻¹. -1 The presence of a broad peak with a distinct B-OH group indicates that the ultrasonic pretreatment successfully grafted hydroxyl groups onto boron nitride.

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

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

[0087] Figure 5 This is a SEM image of the precipitate centrifuged at low speed in step three of Example 1;

[0088] from Figure 5 It is evident that after synergistic treatment with ultrasonic oscillation and ultra-high-speed stirring, the original BN underwent various exfoliation behaviors, including edge wrinkling and expansion. 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 hydrodynamic behaviors of cavitation, shearing, and impact generated by ultrasonic treatment and ultra-high-speed stirring, the high-speed impact and shear forces applied to the edges of BN can overcome the interaction between BN sheets, causing BN to wrinkle and slip. In addition, Figure 5 (c) and (d) show that the boron nitride surface is covered with stripes of varying directions. This phenomenon mainly originates from the three-dimensional dynamic behavior of surface tearing caused by the synergistic effect of ultrasound and ultra-high-speed stirring. Firstly, the cavitation effect of ultrasound in the liquid generates a localized high-temperature microjets. The impact of these microjets causes defects on the boron nitride surface and grafts hydroxyl groups. Secondly, the rapid turbulence caused by ultra-high-speed stirring continuously scours the defects. In a hydrogen-rich solvent environment, the interaction of hydrogen bonds accelerates the tearing and breakage of the boron nitride nanosheets at the defects. This dynamic behavior is similar to "tearing tape," with the boron nitride nanosheets at the defects being continuously torn off. Therefore, after one peeling cycle, the boron nitride surface is left with striped marks from the tearing. In recent research papers or patents on boron nitride peeling, edge wrinkling and lamellar slippage have occasionally appeared. However... Figure 5 The surface tearing dynamics exhibited in (c) and 5(d) have not been found in studies using physical exfoliation methods. These multi-type, multi-dimensional exfoliation behaviors are key factors in improving boron nitride nanosheet yield and maintaining their shape and structure.

[0089] Figure 6 The AFM diagram of BNNS in Example 1;

[0090] The surface morphology of the large-sized ultrathin boron nitride nanosheets obtained in Example 1 was measured using an atomic force microscope (AFM) from Bruker Dimension Icon, Germany. Before testing, the large-sized ultrathin boron nitride nanosheets were dispersed in pure water. After uniform dispersion, the BNNS dispersion was dropped onto a clean silicon wafer and dried at 60°C to remove the solvent. During testing, random locations were selected, and AFM morphology images were scanned. The results are shown below. Figure 6 As shown. From Figure 6 It can be seen that the lateral dimensions of boron nitride nanosheets are 3–4 μm, and the thickness of the nanosheets is 1.4–1.6 nm. The surface of the boron nitride nanosheets is undulating and the thickness is uniform, exhibiting typical two-dimensional sheet-like characteristics.

[0091] Figure 7 The above are statistical distribution diagrams of average thickness, average particle size, and aspect ratio of BNNS in Example 1.

[0092] from Figure 7It can be seen that the average thickness of the ultrathin boron nitride nanosheets is 1.45 nm, and the average particle size is 4.2 μm. The thickness meets the requirement of being "ultrathin," while the lateral dimensions meet the requirement of being "large." The aspect ratio was calculated by comparing the particle size to the thickness. The calculated aspect ratio of BNNS in Example 1 is as high as 2896, demonstrating a significant advantage in recent years' cutting-edge research on boron nitride exfoliation.

[0093] The above description is merely a preferred embodiment of the present invention. These specific embodiments are different implementations based on the overall concept of the present invention, and the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing ultrathin, large-size hexagonal boron nitride nanosheets that can be mass-produced, characterized in that... The preparation method is specifically carried out 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, the boron nitride dispersion is first ultrasonically vibrated using an ultrasonic processor, and then the hexagonal boron nitride is bombarded by a micro-jet generated by ultrasonic cavitation, which causes defects to be generated on the surface and edges of the hexagonal boron nitride and grafted with hydroxyl groups to obtain a hydroxyl-functionalized BN-OH solution.

3. Pour the hydroxyl-functionalized BN-OH solution into a blender and stir for a period of time. Boron nitride will be stripped off. After stirring, centrifuge the BN-OH solution at low speed and take the supernatant to obtain a stable and dispersed BNNS suspension. At the same time, collect the centrifuged precipitate as the raw material for the next stripping.

4. The BNNS suspension was vacuum filtered, washed, and then dispersed in pure water. The solution was then freeze-dried to obtain ultrathin, large-size hexagonal boron nitride nanosheets.

2. The method for preparing mass-producible ultrathin large-size hexagonal boron nitride nanosheets according to claim 1, characterized in that... The particle size of the hexagonal boron nitride mentioned in step one is 10μm~30μm; the volume ratio of isopropanol to water in the mixed solvent of isopropanol and water mentioned in step one is 1:(1~2).

3. The method for preparing ultrathin, 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 in step one is 1 mg / mL to 10 mg / mL; the magnetic stirring speed in step one is 300 r / min, and the magnetic stirring time is 20 min to 40 min.

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

5. The method for preparing ultrathin, large-size hexagonal boron nitride nanosheets that can be mass-produced according to claim 1, characterized in that... The speed of the blender mentioned in step three is 30,000 r / min to 40,000 r / min, the number of blending blades in the blender is 2 to 8, and the capacity of the blender is 1L to 8L; the stirring time is 0.5h to 1.5h.

6. The method for preparing a mass-producible ultrathin large-size hexagonal boron nitride nanosheet according to claim 1, characterized in that... The speed of the low-speed centrifugation in step three is 1000 rpm to 2500 rpm, and the low-speed centrifugation time is 10 min to 20 min.

7. The method for preparing ultrathin, large-size hexagonal boron nitride nanosheets that can be mass-produced according to claim 1, characterized in that... The centrifuged precipitate described in step three is subjected to the stripping process of steps two and three, repeated 1 to 20 times.

8. The method for preparing a mass-producible ultrathin large-size hexagonal boron nitride nanosheet according to claim 1, characterized in that... The pore size of the filter membrane used in step four is 0.22 μm; the washing process in step four involves washing the solid material obtained by vacuum filtration with pure water, and the washing is performed 2 to 3 times.

9. The method for preparing a mass-producible ultrathin large-size hexagonal boron nitride nanosheet according to claim 1, characterized in that... The mass ratio of the washed BNNS to the volume of purified water in step four is (1g~1.5g):(100mL~200mL); the freeze-drying temperature program in step four is set to -35℃~35℃, and the drying time is 36h~40h; the lateral dimension of the ultrathin large-size hexagonal boron nitride nanosheets in step four is 2μm~7μm, and the thickness is 1nm~2nm.

10. The application of the ultrathin, 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 for electronic devices.

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