CN112919431B - Hexagonal boron nitride nano-sheet with high yield and high crystallinity and preparation method thereof - Google Patents
Hexagonal boron nitride nano-sheet with high yield and high crystallinity and preparation method thereof Download PDFInfo
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- C01B21/064—Binary compounds of nitrogen with metals, with silicon, or with boron, or with carbon, i.e. nitrides; Compounds of nitrogen with more than one metal, silicon or boron with boron
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Abstract
The invention provides a hexagonal boron nitride nanosheet with high yield and high crystallinity and a preparation method thereof, which are used for solving the technical problems of low yield, high cost and difficulty in realizing large scale of nano boron nitride preparation. According to the invention, submicron boron nitride is prepared and is used as a ball milling raw material, and is effectively stripped by a mechanical ball milling method by utilizing the small particle size, the large specific surface area and the large active sites of submicron boron nitride, so that the stripping efficiency can be greatly increased, and the obtained boron nitride nanosheets are uniform in size, high in crystallinity and high in yield, and have high production and application values.
Description
Technical Field
The invention belongs to the field of material preparation, and particularly relates to a hexagonal boron nitride nano-sheet with high yield and high crystallinity and a preparation method thereof.
Background
Hexagonal boron nitride nano-sheets (BNSs), commonly called as 'Bai Danmo alkene', have similar heat conduction performance and mechanical property to those of graphene, and also have a cathode luminescence effect, electrical conductivity, thermal stability and high-temperature oxidation resistance, so that the BNSs have huge application market and prospect. However, hexagonal boron nitride (h-BN) is stronger in interlayer van der waals forces than graphene due to ionic bonding between adjacent layers, making intercalation and exfoliation of boron nitride more difficult than graphite.
The existing BNSS preparation method mainly comprises a 'bottom-up' vapor deposition method and a chemical stripping method, and a 'top-down' mechanical stripping method and an ultrasonic auxiliary solvent stripping method. The vapor deposition method has the advantages of high temperature, up to 1800 ℃, high equipment cost and difficult mass production. The chemical stripping method is to use chemical oxidation method for preparing graphene to realize effective stripping, namely adopting concentrated H 2 SO 4 、KMnO 4 And H 2 O 2 The h-BN is stripped by a chemical method, and the BNSS can be obtained by the method, but the yield is very low, and the raw materials are not green and environment-friendly. According to the mechanical ball milling method, the hard balls are utilized to strip the block h-BN into few layers or single-layer boron nitride nano sheets under the action of high shearing force and impact force, and practice shows that if the ball milling time is short, the stripping efficiency is low, and if the ball milling time is too long, the h-BN structure is damaged, so that the crystallinity of the hard balls is seriously reduced, and the crystal defects are more.
Chinese patent CN111137866a discloses a method for preparing boron nitride nanosheets by stripping h-BN, which uses sodium citrate surfactant to provide ions for intercalation, and strips h-BN by high temperature and high pressure reaction and repeated liquid phase ultrasonic dispersion, so as to prepare BNNS. The method combines high-temperature high-pressure reaction and ultrasonic assisted solvent stripping, has unsatisfactory stripping effect and lower yield. Chinese patent CN111320149a discloses a method for preparing hexagonal boron nitride nano-sheet dispersion, which uses boric acid and industrial grade h-BN as raw materials, and performs mechanical ball milling, and performs graded gradient centrifugal treatment to obtain h-BN dispersion with different nano-sheet sizes. The product obtained by the method has different sizes, and can be obtained by carrying out centrifugal separation for multiple times in a grading way, so that the BNs with smaller sizes can be obtained, and the yield of the BNs with smaller sizes is lower. Song Xiaoling et al (supercritical CO 2 Preparation of h-BN nanosheets and cobalt-loaded catalytic performance study [ J ]]NowSubstitution, 2018 (38): 9,164-167) adopts h-BN as precursor, adopts ultrasonic auxiliary supercritical CO 2 The stripping process produces BNSs with a thickness of less than 50 layers using supercritical CO 2 Stripping is performed, and the equipment cost is high. Chen Anhui et al (discussed in the scale preparation process of boron nitride nanosheets, zhang Pingji, university of major company's Shuoshi paper, 2016) combined with a ball milling method and an ultrasonic assisted stripping method, and using urea as a dry powder ball milling reagent, the ratio of boron nitride to urea is 1:20, ball milling time is 10h, ultrasonic dispersion is carried out for 2h, the boron nitride nanosheets are prepared, the stripping efficiency is 43%, the concentration of dispersion liquid is up to 2.7mg/mL, and the ball milled product is required to be placed into a dialysis belt for dialysis treatment to remove urea. In the above-mentioned "top-down" peeling methods, BNNs can be obtained, but the peeling effect is not high, the yield of BNNs is low, and the size is not uniform, so that it is difficult to realize large-scale production.
Disclosure of Invention
In order to solve the technical problems of low yield, high cost and difficult realization of scale of the preparation of the nano boron nitride, the invention utilizes the characteristics of small particle size, large specific surface area and more active sites of submicron boron nitride, and effectively strips the submicron boron nitride by a mechanical ball milling method, thereby greatly increasing the stripping efficiency, and the obtained boron nitride (h-BN) nanosheets have uniform size, high crystallinity and high yield and have very high production and application values.
The invention aims to provide a preparation method of hexagonal boron nitride nano-sheets with high yield and high crystallinity, which comprises the steps of preparing submicron-sized boron nitride from a carbon-nitrogen compound and a boron-containing compound through a solid phase method, and then ball-milling the obtained submicron-sized boron nitride to obtain the hexagonal boron nitride nano-sheets. The preparation method specifically comprises the following steps:
step one, uniformly mixing a carbon nitrogen compound and a boron-containing compound, and heating and preserving heat;
step two, cooling to room temperature, and then heating to perform high-temperature roasting;
step three, washing and drying the product obtained after the high-temperature roasting in the step two to obtain submicron boron nitride;
and step four, stripping the submicron boron nitride obtained in the step three through mechanical ball milling to obtain the hexagonal boron nitride nano-sheet.
In the first step of the above-mentioned preparation method,
the carbon nitrogen compound is selected from small molecule carbon nitrogen compounds containing amino, preferably at least one of urea and melamine;
the boron-containing compound is at least one selected from boric acid, metaboric acid and ammonium borate;
the mass ratio of the carbon-nitrogen compound to the boron-containing compound is 1: (1.5-5); too small a proportion increases the smoke amount and subsequent treatment amount during roasting, and wastes the raw material of the boron-containing compound; excessive proportion can lead to failure to form submicron boron nitride, and the requirement of the subsequent process is not met;
the heating temperature rising rate is more than 600 ℃/h, the faster temperature rising rate is beneficial to the improvement of the yield of boron nitride, meanwhile, the fast temperature rising is beneficial to the formation of a large number of seed crystals of boron nitride in a short time, and the product with submicron granularity is easier to form in the subsequent reaction process;
the heating and heat preserving temperature is 700-900 ℃, the reaction speed is slow when the temperature is lower than the temperature range, the boron nitride crystal is easier to grow into micron-sized with larger granularity when the temperature is higher than the temperature range, and an agglomeration product with irregular shape is formed; the heating and heat preserving time is 2-4 h, the shorter time can lead to incomplete reaction, and the longer heat preserving time can lead to the growth of boron nitride particles.
In the first step, no addition of reaction auxiliary agent such as alkali metal (NaCl, naF, etc.) or alkali earth metal halide such as (CaCl) is required 2 Etc.), thereby avoiding corrosion of the high temperature reaction furnace by the inorganic salt added in the prior art.
In the second step of the preparation method, the heating rate is more than 600 ℃/h; the high-temperature roasting temperature is 1100-1300 ℃, and oxygen elements as impurities exist in the h-BN product under the temperature range, and larger (> 1 μm) product particles are formed under the temperature range; the high-temperature roasting time is 2-6 h, the deoxidization is incomplete in a shorter time, and the boron nitride particles grow up in a longer roasting time. And step two, the raw materials in the step one are cooled to room temperature after being reacted, and the annealing and cooling treatment is carried out, so as to avoid the rapid and continuous growth of h-BN crystal particles caused by continuously heating to 1100-1300 ℃ in the reaction process.
In the third step of the preparation method, washing and acid washing are adopted, wherein the washing is carried out by adopting hot water with the temperature of 80-100 ℃, and the acid washing solution is sulfuric acid solution with the mass percentage concentration of 0.5-1.0%; and step two, washing the product obtained after high-temperature roasting by water, washing by acid, filtering, washing by distilled water for multiple times, drying at the drying temperature of 40-80 ℃, and drying to obtain the submicron boron nitride, wherein the particle size of the obtained submicron boron nitride is 0.1-2 mu m, preferably 0.2-0.8 mu m.
In the fourth step of the preparation method, water is also added in the ball milling operation, the dosage of the added water is not particularly required, the mixture is preferably mixed by ball milling, and the dosage ratio of submicron boron nitride to water is preferably 1: (5 to 20), more preferably 1: (10-15);
in the ball milling operation, the ball milling time is 3-10 hours, preferably 4-6 hours; the ball milling time is too short, the generated h-BN nano-sheets are fewer, and the yield is low; the ball milling time is too long, so that the product BNs is disordered, in addition, the ball milling time is long, the abrasion degree of the ball mill and the grinding ball is increased, and the energy consumption is increased;
the ball milling can be realized by adopting common ball milling equipment and ball milling technology, and the ball milling mode can adopt planetary rotation and revolution rotation (Z-axis rotation) and positive and negative alternate operation, wherein the planetary rotation speed can be 250-400 rpm, preferably 300-380 rpm, and more preferably 320-370 rpm; the revolution speed may be 5 to 12 rpm, preferably 8 to 12 rpm, and more preferably 10 to 11 rpm. The planetary rotation speed is an important factor influencing the stripping effect, and low rotation speed can lead to low stripping efficiency and low yield; however, the rotating speed is too high, the loss of the ball mill and the grinding ball is increased, the ammonia gas amount generated in the ball milling process is large, the crystallinity of the formed h-BN product BNs is reduced, and the phenomenon of disorder layer is easily generated.
In the ball milling operation, the grinding ball medium used is selected from grinding balls with higher hardness and strength, preferably at least one selected from stainless steel, ceramics and zirconia, more preferably zirconia; in the ball milling operation, the mass ratio of the submicron boron nitride to the grinding balls is 1: (60 to 100), preferably 1: (75-85); the grinding balls comprise grinding ball particles with different sizes, the preferable size range of the grinding balls is 0.5-15 mm, the more preferable size range is 1-10 mm, the particularly preferable sizes of the grinding balls are 10mm, 5mm, 3mm and 1mm, and the mass ratio of the grinding balls with corresponding sizes is 1 (2-5): 3-8, preferably 1 (2-4): 3-6;
washing, suction filtering, washing and drying the hexagonal boron nitride nano-sheets obtained after ball milling to obtain hexagonal boron nitride nano-sheet powder with high yield and high crystallinity; wherein the drying temperature is 40-80 ℃, and the drying process is finished by adopting drying equipment commonly used in the field, such as vacuum drying equipment; the vacuum filtration is carried out by adopting a microporous filter membrane, the aperture of the microporous filter membrane is 0.22-1.2 mu m, preferably 0.22-0.45 mu m, distilled water is used for washing for multiple times after the suction filtration, and then a filter cake is dried to obtain a BNs product with good dispersion, or hexagonal boron nitride nano-sheets obtained by ball milling can be directly dispersed into a solvent after water washing, suction filtration and washing to prepare BNs dispersion liquid with certain concentration, and the solvent is at least one selected from ethanol, water, acetone, chloroform, benzene, toluene and N, N-dimethylformamide.
The second object of the present invention is to provide a hexagonal boron nitride nanosheet with high yield and high crystallinity, which is prepared by the preparation method.
The preparation method comprises the steps of synthesizing submicron-level boron nitride (h-BN), and then stripping by a ball milling method to obtain BNs nano sheets with uniform size. The h-BN nano-sheets are synthesized by the two-step synthesis method, so that the problems that the h-BN nano-sheets (or nano-particles) prepared by the solid-phase synthesis method are low in crystallinity, the nano-sheets with fewer layers are difficult to synthesize and the like are avoided, the defects of low stripping efficiency, low BNs yield, poor crystallinity and the like of a direct mechanical stripping method are avoided, the stripping time and the stripping strength are reduced, and the stripping efficiency is improved. The BNs obtained by the method has uniform size, avoids the centrifugal separation and washing processes carried out for multiple times in the subsequent classification, improves the separation and washing efficiency, does not need to add ball milling auxiliary agents or intercalators in the ball milling process, and improves the purity of products.
Compared with the prior art, the invention has the following beneficial effects:
1. the preparation method comprises the steps of preparing submicron-level h-BN through a segmented high-temperature solid-phase reaction, and then performing ball milling mechanical stripping by taking the submicron-level h-BN as a raw material to prepare the hexagonal boron nitride nanosheets; the BNs obtained by the method has uniform size and high yield, and compared with the prior art, the BNs are prevented from being subjected to centrifugal separation and washing for multiple times in a grading way, and the subsequent separation and washing efficiency is greatly improved;
2. in the preparation method provided by the invention, no ball milling auxiliary agent such as urea, boric acid, L-amino acid and the like are required to be added in the ball milling process, and the submicron h-BN flake is directly and effectively stripped by utilizing the lower layer number, larger specific surface area and higher activity of the submicron h-BN flake, so that the purity and crystallinity of the h-BN nano-flake are prevented from being reduced due to the surface reaction of the added auxiliary agent with h-BN in high shear force and high-speed impact, and the difficulty of subsequent impurity removal and washing is avoided, and the production efficiency and the product purity are improved;
3. according to the invention, grinding balls with different sizes and proportions are added in the ball milling operation, the planetary rotation speed and the Z-axis rotation speed are regulated, and the planetary rotation speed and the Z-axis rotation speed are alternately operated in the forward and reverse directions, so that the ball milling efficiency is increased and the ball milling time is greatly shortened (lower than 10 h) due to lower number of layers of submicron h-BN sheets in the ball milling process; compared with the prior art, the defects of disorder layer phenomenon, crystallinity reduction and the like caused by long-time ball milling are avoided, and the crystallinity of BNs is improved;
4. the preparation method provided by the invention is simple and feasible, is environment-friendly, has higher crystallinity and yield of the obtained BNs, is more uniform in morphology and size, and has wide application prospect.
Drawings
FIG. 1 is a Scanning Electron Microscope (SEM) photograph of submicron boron nitride obtained from boric acid and melamine in example 1. As can be seen from FIG. 1, submicron boron nitride obtained in example 1 has regular shape and uniform size, and the size is 0.3-0.6. Mu.m.
Fig. 2 is a Transmission Electron Microscope (TEM) photograph of BNNs obtained after ball milling of example 1.
FIG. 3 is an X-ray diffraction (XRD) pattern of BNs prepared in example 1 (a), comparative example 1 (b) and comparative example 3 (c), with the (100), (101), (102) of the BNs products corresponding to diffraction angles of 41.5 °,43.8 ° and 50.1 °, respectively.
FIG. 4 is a Transmission Electron Microscope (TEM) photograph of BNs prepared in comparative example 1.
FIG. 5 is a comparative photograph showing the uniform dispersions obtained in example 1 (a) and comparative example 1 (b) after 15 days of standing and settling.
FIG. 6 is a Transmission Electron Microscope (TEM) photograph of BNs prepared in comparative example 3.
Detailed Description
The present invention is described in detail below with reference to specific embodiments, and it should be noted that the following embodiments are only for further description of the present invention and should not be construed as limiting the scope of the present invention, and some insubstantial modifications and adjustments of the present invention by those skilled in the art from the present disclosure are still within the scope of the present invention.
The test apparatus and test method used in the examples were as follows:
SEM: a scanning electron microscope;
XRD: an X-ray diffractometer;
BNs dispersion concentration determination method after standing the treated boron nitride nano-sheet dispersion for a period of time, taking out a certain volume of upper layer liquid by a liquid-transferring gun, and transferring the upper layer liquid into a clean small bottle with known quality. The vials were placed in a forced air drying oven, the solvent evaporated and dried at 90℃for 24h. The total mass of the vial and the solid dry matter was weighed and the concentration of the nanoplatelets was calculated by differential methods as follows.
In the formula, the concentration (mg/mL) of the C-boron nitride nanosheet dispersion, the total mass (mg) of the M-vial and the solid dry matter, the mass (mg) of the M-vial, and the volume (mL) of the upper liquid taken out.
The raw materials and sources used in the examples are as follows:
melamine (Shandong Heli Tai), boric acid (Russian BORMCC), ethanol (Zhongtian Fine)
Zirconia ball (Changsha Miqi instrument limited company)
Microporous filter membrane (Shanghai Xinya)
Dopamine (Shanghai Miclin Biochemical Co., ltd.)
Example 1
(1) Weighing 200g of melamine and 600g of boric acid, uniformly mixing in a mixer, placing in a high-frequency induction furnace for roasting, rapidly heating to 900 ℃ at the speed of 600 ℃/h, and preserving heat for 4 hours;
(2) Annealing, cooling to room temperature, then rapidly heating to 1200 ℃ at a heating rate of 600 ℃/h, and continuously roasting for 4 hours to generate submicron h-BN (shown in figure 1);
(3) Collecting a product, crushing, sieving with a 40-mesh sieve, boiling with hot water for half an hour, filtering and separating to obtain a filter cake, pickling with a sulfuric acid solution with the concentration of 0.8% and the mass of the sulfuric acid solution being 10 times that of the wet filter cake, washing with water to obtain a neutral product, drying the filter cake obtained by filtering and separating at 150 ℃ to obtain submicron-level h-BN powder with the particle size of 0.3-0.6 mu m and the median particle size D50 of about 350nm;
(4) Weighing 20g of submicron-level h-BN powder, placing the powder into an omnibearing planetary ball mill, adding 200ml of distilled water, adding 1500g of zirconia balls with different sizes and proportions, wherein the zirconia balls have the size and mass ratio of 10mm to 5mm to 3mm to 1 mm=1 to 2.6 to 3.3, regulating the planetary rotation speed to 350 revolutions per minute, regulating the Z-axis rotation speed to 10 revolutions per minute, performing ball milling in a positive-negative alternating mode, stopping for 5min every 30min, and performing ball milling for 4h.
(5) After the ball milling is finished, the ball milling tank is opened, and the gas with pungent smell can be smelled. Taking out the materials, washing the zirconia balls with distilled water, collecting washing liquid, carrying out vacuum suction filtration by using a microporous filter membrane, washing the filter membrane with the pore diameter (0.22 mu m) for multiple times by using distilled water, and drying a filter cake in a 50 ℃ oven for 24 hours to obtain BNs powder.
And dispersing the filter cake obtained by suction filtration in ethanol or distilled water to obtain BNs dispersion liquid. The peeled BNs can be well dispersed in an aqueous solution to form a uniform dispersion liquid, and the whole BNs is milky white. A uniform and stable dispersion with a concentration of up to 100mg/mL (0.1 g/L) was obtained. The obtained BNs nano-sheets are transparent and uniformly distributed, have a fold structure similar to the edge of graphene, have a small amount of aggregation phenomenon, have the thickness of about 4-10 nm, and have the BNs layer number range of about 5-15 (shown in figure 2).
In example 1, 350nm D50 h-BN is used as a raw material for ball milling, and the collected product solution is placed for 72 hours, so that almost no sedimentation phenomenon exists, the suspension is thick white emulsion, and the lower layer is not precipitated and layered.
Example 2
The preparation method is characterized in that 200g of melamine and 300g of boric acid are used as raw materials, other preparation processes and conditions are the same as those of the example 1, submicron-level h-BN powder is obtained in the step (3), the median particle diameter D50 is about 600nm and is larger than that of the example 1, and the sizes and thicknesses of BNs nanosheets obtained after ball milling are basically the same as those of the example 1.
Example 3
The preparation method is characterized in that 200g of melamine and 1000g of boric acid are used as raw materials, other preparation processes and conditions are the same as those of the example 1, submicron-level h-BN powder is obtained in the step (3), the median particle diameter D50 is about 350nm, and the sizes and thicknesses of BNs nano sheets obtained after ball milling are basically the same as those of the example 1.
Example 4
The preparation method is the same as in example 1, only in the step (4), the ball milling time is regulated to 6 hours, other conditions are unchanged, and the product is not obviously changed from example 1, which indicates that the ball milling time is 4 hours, so that h-BN can be effectively stripped, and BNs with good dispersibility and uniform size can be obtained.
Example 5
The preparation method is the same as in example 1, and only in the step (4), the Z-axis rotation is adjusted to 5 rpm, the planetary rotation speed is 255 rpm, and other conditions are unchanged. Washing the ball-milled material with distilled water, collecting the material in a beaker, standing for 24 hours, wherein the upper suspension is light milky white, and the lower suspension is white precipitated, which indicates that the formed h-BN particles are larger, sedimentation is easy to occur, the BNs yield is lower, and the particle size is uneven.
Comparative example 1
BNs were prepared in comparative example 1 using commercially available h-BN (23. Mu.mD 50, large particle h-BN obtained by one firing at high temperature) by the procedures of steps (4) to (5) in example 1. In the step (4), the ball milling raw material adopts commercial h-BN with the size of 23 mu m D, in order to increase the impact force of large particles h-BN and grinding balls, the mass of the added zirconia is 1600g, the mass ratio of the zirconia to the grinding balls is 10mm to 5mm to 3mm to 1 mm=1 to 1.5 to 2.7, and other conditions are unchanged. Washing the ball-milled material with distilled water, collecting the material in a beaker, standing for 12 hours, wherein the upper suspension is light milky, and the lower precipitation phenomenon is obvious, which indicates that the formed h-BN particles are larger, sedimentation is easy to occur, the BNs yield is lower, the particle size is uneven, and multistage and repeated centrifugal separation and washing are needed to obtain h-BN with different sizes. As can be seen from fig. 4, the TEM image of the product obtained in comparative example 1 shows that the BNNs nanosheets obtained in comparative example 1 have a non-uniform thickness, the sheet-like structure h-BN has a low transparency, no obvious graphene-like fold structure is shown, the edge defects are more, the thickness is about 7-25 nm, and the number of BNNs layers is about 10-25 (fig. 4 d).
FIG. 5 is a comparative graph showing the uniform dispersions obtained in example 1 (a) and comparative example 1 (b) after 15 days of standing and sedimentation. As shown in FIG. 5, the dispersion obtained by ball milling stripping of large particles h-BN (23. Mu.mD 50) in comparative example 1 was significantly higher in sedimentation rate than example 1. Since the sedimentation rate of the particles in the suspension is proportional to the size of the particle, it is shown that the BNNs obtained from large particles have a non-uniform thickness distribution and a poor stripping effect.
Comparative example 2
Into a 500ml three-necked flask, 1.5g of hexagonal boron nitride (h-BN, 23. Mu.mD 50) and 9g of KMnO were charged 4 And 200mL 98% H 2 Placing the three-neck flask into a water bath kettle with constant temperature of 60 ℃ for magnetically stirring for 12 hours, taking a 1L beaker, adding about 200g of ice and 40ml of H after the reaction is finished 2 O 2 Slowly pouring the reactant into a beaker to obtain a dispersion liquid, standing for 1 hour, and finding that the chemical stripping is performed by a potassium permanganate method, so that the effect is poor, the product particles are large, uniformly dispersed white sol-like liquid cannot be formed, the delamination in the beaker is obvious, the bottom of the beaker has obvious white precipitation, and the upper layer is transparent colorless clear liquid.
Comparative example 3
The preparation method is the same as in example 1, and only in the step (4), a certain amount of hydrophilic and lipophilic amine molecules dopamine is added to serve as a ball milling auxiliary agent, the mass ratio of h-BN to dopamine is 10:1, and other conditions are unchanged. The product is off-white, other phenomena are similar to those of the example 1, obvious sedimentation phenomenon hardly occurs within 72 hours, and the dispersion liquid is uniform and stable, so that the addition of a proper amount of ball milling auxiliary agent can be helpful for effective stripping of h-BN to a certain extent, because dopamine molecules interact with the h-BN in the ball milling process, and the stripping effect is promoted. As shown in fig. 6, the obtained BNNs are transparent, the distribution is more uniform than that of example 1, but the edge angles of the nano sheets are smaller, most of the nano sheets are round, as shown in fig. 6b, the thickness of the nano sheets is about 2-10 nm, the layer number range of the BNNs is about 3-15, which indicates that the interaction of amine molecules and atoms of the h-BN edge structure promotes the effective stripping of h-BN, but the addition of dopamine brings impurities into the product, and the difficulty in separating and washing subsequent products is increased.
Claims (11)
1. A preparation method of hexagonal boron nitride nano-sheet with high yield and high crystallinity comprises the steps of preparing submicron boron nitride from carbon nitride and boron-containing compound through a solid phase method, and then ball-milling the obtained submicron boron nitride to obtain the hexagonal boron nitride nano-sheet; the preparation method specifically comprises the following steps:
step one, uniformly mixing a carbon nitrogen compound and a boron-containing compound, and heating and preserving heat; the heating and heat preserving temperature is 700-900 ℃, and the heating and heat preserving time is 2-4 hours;
step two, cooling to room temperature, and then heating to perform high-temperature roasting; the high-temperature roasting temperature is 1100-1300 ℃, and the high-temperature roasting time is 2-6 hours;
step three, washing and drying the product obtained after roasting in the step two to obtain submicron boron nitride;
step four, stripping the submicron boron nitride obtained in the step three through mechanical ball milling to obtain the hexagonal boron nitride nanosheets, wherein the grinding ball size in the ball milling operation is 10mm, 5mm, 3mm and 1mm, the mass ratio of the grinding balls with corresponding sizes is 1 (2-5): (3-8), and the ball milling time is 3-10 h; the ball milling mode adopts planetary rotation and revolution rotation, positive and negative alternate operation is carried out, the planetary rotation speed is 250-400 rpm, and the revolution rotation speed is 5-12 rpm.
2. The method according to claim 1, wherein in the first step,
the carbon nitrogen compound is selected from small molecule carbon nitrogen compounds containing amino; and/or the number of the groups of groups,
the boron-containing compound is at least one selected from boric acid, metaboric acid and ammonium borate; and/or the number of the groups of groups,
the mass ratio of the carbon-nitrogen compound to the boron-containing compound is 1: (1.5-5); and/or the number of the groups of groups,
the heating temperature rising rate is more than 600 ℃/h.
3. The method according to claim 2, wherein in the first step,
the carbon nitrogen compound is at least one selected from urea and melamine.
4. The method according to claim 1, wherein in the second step,
the heating rate is more than 600 ℃/h.
5. The method according to claim 1, wherein in the third step,
the washing adopts water washing and acid washing; and/or the number of the groups of groups,
the drying temperature is 40-80 ℃; and/or the number of the groups of groups,
the particle size of the submicron-level boron nitride is 0.1-2 mu m.
6. The method according to claim 5, wherein,
the particle size of the submicron-level boron nitride is 0.2-0.8 mu m; and/or the number of the groups of groups,
the water washing is carried out by adopting hot water with the temperature of 80-100 ℃; and/or the number of the groups of groups,
the acid washing solution is sulfuric acid solution with the mass percentage concentration of 0.5-1.0%.
7. The method according to claim 1, wherein in the fourth step,
water is also added in the ball milling operation; and/or the number of the groups of groups,
the ball milling time is 4-6 hours; and/or the number of the groups of groups,
and washing, suction filtering, washing and drying the hexagonal boron nitride nano-sheets obtained by ball milling to obtain the hexagonal boron nitride nano-sheet powder with high yield and high crystallinity.
8. The method according to claim 7, wherein,
in the ball milling operation, the dosage ratio of submicron boron nitride to water is 1 (5-20); and/or the number of the groups of groups,
the grinding balls adopted in the ball milling operation are at least one selected from stainless steel, ceramic and zirconia; and/or the number of the groups of groups,
in the ball milling operation, the mass ratio of the submicron boron nitride to the grinding balls is 1 (60-100); and/or the number of the groups of groups,
the suction filtration adopts a microporous filter membrane to carry out vacuum filtration; and/or the number of the groups of groups,
the drying temperature is 40-80 ℃; and/or the number of the groups of groups,
and washing, suction filtering and washing the hexagonal boron nitride nano-sheets obtained by ball milling, and dispersing the hexagonal boron nitride nano-sheets in a solvent to obtain hexagonal boron nitride nano-sheet dispersion liquid.
9. The method according to claim 8, wherein,
in the ball milling operation, the dosage ratio of submicron boron nitride to water is 1 (10-15); and/or the number of the groups of groups,
the grinding balls adopted in the ball milling operation are selected from zirconium oxide; and/or the number of the groups of groups,
in the ball milling operation, the mass ratio of the submicron boron nitride to the grinding balls is 1 (75-85).
10. The method according to claim 8, wherein,
the grinding balls are 10mm, 5mm, 3mm and 1mm in size, and the mass ratio of the grinding balls with corresponding sizes is 1 (2-4): (3-6); and/or the number of the groups of groups,
the aperture of the microporous filter membrane adopted by the suction filtration is 0.22-1.2 mu m; and/or the number of the groups of groups,
the solvent of the hexagonal boron nitride nanosheet dispersion liquid is at least one selected from ethanol, water, acetone, chloroform, benzene, toluene and N, N-dimethylformamide.
11. The method according to claim 10, wherein,
the aperture of the microporous filter membrane adopted by the suction filtration is 0.22-0.45 mu m.
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