Surface-carbonized hexagonal boron nitride nanosheets, and preparation method and application thereof

Abstract

The present application belongs to the technical field of lubricating materials, and particularly relates to surface carbonized hexagonal boron nitride nanosheets, a preparation method and application thereof, and a water-based lubricant. The present application focuses on solving the problem of difficulty in large-scale production of hexagonal boron nitride nanosheets. The method is simple to prepare and suitable for large-scale production. In the present application, the water-soluble polysaccharide modifier used is a green and environmentally friendly reagent, and the cost is relatively low. The method is safe and does not involve toxic chemical reagents, and is free of environmental pollution. The surface carbonized hexagonal boron nitride nanosheets provided by the present application have excellent dispersibility and stability in a lubricating medium, can be directly used as a lubricating additive, do not need to be treated for multiple times, can exhibit excellent friction-reducing and wear-resistant performance, and are suitable for various water-based lubricating liquid systems.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of lubricating materials, and particularly relates to a surface carbonized hexagonal boron nitride nanosheet, a preparation method and application thereof, and a water-based lubricant. BACKGROUND

[0002] Friction and wear is the main cause of energy loss and workpiece failure of mechanical equipment in operation, and the most effective and convenient method to control or reduce such wear is to use lubricants. The role of lubricants here is to reduce the friction generated by two or more surfaces in motion, and even to achieve the effects of rapid cooling, corrosion prevention and system contamination removal, thus requiring some specific additives to achieve the above effects. Many documents at home and abroad have confirmed that two-dimensional nanomaterials can play a role in reducing friction and wear as lubricating additives. Among the two-dimensional nanomaterials, hexagonal boron nitride nanosheets (h-BNNSs) with the name of white graphene, due to its similar physicochemical properties to graphene and its typical two-dimensional layered structure, has shown great potential in the field of tribology. In recent years, h-BNNSs as a lubricating oil additive has been proved to have excellent lubricating performance, mainly playing a role in friction film protection, as well as playing a role in repairing and polishing effect. Different from graphene, the B atoms and N atoms of boron nitride show different electronegativity, so the B atoms and N atoms between adjacent layers show the characteristics of partial ionic bond and the ability of mutual attraction, which increases the sliding resistance between the layers, thus becoming a very competitive material to replace traditional lubricating additives containing sulfur salts and phosphates.

[0003] However, due to the large particle size of the original hexagonal boron nitride (h-BN) itself and the disadvantage of poor dispersion in the lubricating medium, its application to the green lubrication direction is seriously restricted. The atoms inside the same layer of h-BN are connected by sigma bond, the layers interact with each other by van der Waals force, and also have the characteristics of ionic bond, that is, the "lip-lip" interaction between adjacent layers, the interlayer interaction force is very strong, which makes it relatively difficult to peel off h-BN. In order to obtain few-layer or even single-layer h-BN NSs, people have studied various technologies, such as chemical vapor deposition, chemical oxidation or intercalation, micro-mechanical peeling, solvent ultrasonic peeling and so on. Related reports point out that hydroxyl functionalized boron nitride nanosheets (OH-BNNSs) can be prepared by reacting with water at high temperature, hydrothermal reaction with NaOH or ball milling shear with NaOH, or by using plasma treatment. In addition, Lei et al. successfully prepared amino-functionalized boron nitride nanosheets (NH2-BNNSs) by adding urea in the process of ball milling peeling, and the concentration of which dispersed in aqueous solution can reach 30 mg / mL, and the colloidal solution can still remain stable at room temperature for several weeks. Unfortunately, many methods of peeling off hexagonal boron nitride still have some shortcomings, such as high cost, the inevitable use of corrosive chemicals or volatile organic solvents, relatively complex post-processing (such as the addition of urea up to 60 times of h-BN, which makes the post-processing step cumbersome), harsh process conditions such as high temperature and high pressure, and difficult large-scale preparation. More importantly, due to the surface inertness (few surface functional groups of the peeled h-BNNSs), it is difficult to stably disperse in the lubricating medium, therefore, how to simply and efficiently peel off the layered material to prepare green and environmentally friendly, low-cost, high-yield h-BNNSs and apply them to the lubrication field is a hot topic with certain significance. SUMMARY

[0004] The purpose of the present application is to provide a surface carbonized hexagonal boron nitride nanosheet and a preparation method and application thereof, and a water-based lubricant. The preparation method provided by the present application can simply and efficiently prepare green and environmentally friendly, low-cost, high-yield surface carbonized hexagonal boron nitride nanosheets.

[0005] In order to achieve the above purpose, the present application provides the following technical solutions:

[0006] The present application provides a preparation method of a surface carbonized hexagonal boron nitride nanosheet, comprising the following steps:

[0007] Mixing hexagonal boron nitride, water-soluble polysaccharide modifier and water for wet ball milling to obtain a ball milling material;

[0008] After washing out the ball milling material, performing first centrifugal separation to obtain a suspension;

[0009] carburizing the modified hexagonal boron nitride solid to obtain the surface-carburized hexagonal boron nitride nanosheet.

[0010] carburizing the modified hexagonal boron nitride solid to obtain the surface-carburized hexagonal boron nitride nanosheet.

[0011] The rotation speed of the first centrifugal separation is 2000-3000 rpm, and the rotation speed of the second centrifugal separation is 6000-10000 rpm.

[0012] Preferably, the water-soluble polysaccharide modifier comprises one or more of hydroxypropyl cellulose, hydroxypropyl methyl cellulose, sodium carboxymethyl cellulose and carboxymethyl chitosan.

[0013] Preferably, the mass ratio of the hexagonal boron nitride, the water-soluble polysaccharide modifier and the water is 1:1-3:30, and the time of the wet ball milling is 10-24 h.

[0014] Preferably, after the washing, the obtained slurry is subjected to stirring and ultrasonic dispersion in sequence; the time of the stirring is 2-4 h, and the time of the ultrasonic dispersion is 2-4 h.

[0015] Preferably, the temperature of the carburization is 200-250℃, and the time is 4-8 h.

[0016] The application further provides the surface-carburized hexagonal boron nitride nanosheet prepared by the preparation method.

[0017] The application further provides the application of the surface-carburized hexagonal boron nitride nanosheet as a lubricating additive.

[0018] The application further provides a water-based lubricant comprising the surface-carburized hexagonal boron nitride nanosheet and a water-alcohol solution.

[0019] The surface-carburized hexagonal boron nitride nanosheet is the surface-carburized hexagonal boron nitride nanosheet as described above.

[0020] Preferably, the content of the surface-carburized hexagonal boron nitride nanosheet in the water-based lubricant is 0.1-1 wt%.

[0021] Preferably, the water-alcohol solution comprises water and ethylene glycol, and the volume ratio of the water to the ethylene glycol is 1:1-1.5.

[0022] The application provides a preparation method of surface carbonized hexagonal boron nitride nanosheets, comprising the following steps: mixing hexagonal boron nitride, a water-soluble polysaccharide modifier and water to perform wet ball milling to obtain a ball milling material; performing first centrifugal separation on the ball milling material after washing to obtain a suspension; performing second centrifugal separation on the suspension to obtain modified hexagonal boron nitride solids; and performing carbonization on the modified hexagonal boron nitride solids to obtain the surface carbonized hexagonal boron nitride nanosheets; the rotating speed of the first centrifugal separation is 2000-3000 rpm; and the rotating speed of the second centrifugal separation is 6000-10000 rpm. The surface carbonized hexagonal boron nitride nanosheets prepared by combining wet ball milling and heat treatment are used as a green and environmentally-friendly two-dimensional sheet material. The application focuses on solving the problem that the hexagonal boron nitride nanosheets are difficult to be produced on a large scale, and the method is simple and suitable for mass production. In the application, the water-soluble polysaccharide modifier used is a green and environmentally-friendly reagent, and the cost is relatively low, the method is safe, and no toxic and harmful chemical reagents are involved, and the environment is not polluted.

[0023] The application also provides a water-based lubricant comprising the surface carbonized hexagonal boron nitride nanosheets and a water-alcohol solution; the surface carbonized hexagonal boron nitride nanosheets are the surface carbonized hexagonal boron nitride nanosheets in the above technical solution. The surface carbonized hexagonal boron nitride nanosheets provided by the application have excellent dispersibility and stability in a lubricating medium, can be directly used as a lubricating additive, do not need to be treated for multiple times, can exhibit excellent friction-reducing and wear-resistant performance, and are suitable for various water-based lubricating liquid systems. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 Optical photos of hexagonal boron nitride and surface carbonized hexagonal boron nitride nanosheets obtained in Examples 1-4 dispersed in a water-alcohol solution on the first day;

[0025] Figure 2 Optical photos of hexagonal boron nitride and surface carbonized hexagonal boron nitride nanosheets obtained in Examples 1-4 dispersed in a water-alcohol solution on the seventh day;

[0026] Figure 3 Optical photos of hexagonal boron nitride and surface carbonized hexagonal boron nitride nanosheets obtained in Examples 1-4 dispersed in a water-alcohol solution on the thirtieth day;

[0027] (1) is hexagonal boron nitride, (2) is Example 1, (3) is Example 2, (4) is Example 3, and (5) is Example 4;

[0028] Figure 4 An infrared spectrum of the surface carbonized hexagonal boron nitride nanosheets prepared in Example 1;

[0029] Figure 5The infrared spectrum of the surface carbonized hexagonal boron nitride nanosheet prepared for Example 2 is shown in the following figure:

[0030] Figure 6 The infrared spectrum of the surface carbonized hexagonal boron nitride nanosheet prepared for Example 3 is shown in the following figure:

[0031] Figure 7 The infrared spectrum of the surface carbonized hexagonal boron nitride nanosheet prepared for Example 4 is shown in the following figure:

[0032] Figure 8 The transmission electron microscope image of the surface carbonized hexagonal boron nitride nanosheet prepared for Example 1 is shown in the following figure:

[0033] Figure 9 The friction test result diagram of the surface carbonized hexagonal boron nitride nanosheet prepared for Example 1 as a lubricating additive added into the water-alcohol solution under different concentrations is shown in the following figure:

[0034] Figure 10 The friction test result diagram of the surface carbonized hexagonal boron nitride nanosheet prepared for Example 1 and Comparative Example 2 as a lubricating additive added into the water-alcohol solution is shown in the following figure:

[0035] Figure 11 The friction test result diagram of the surface carbonized hexagonal boron nitride nanosheet prepared for Examples 1-4 as a lubricating additive added into the water-alcohol solution is shown in the following figure:

[0036] Figure 12 The average friction coefficient and wear scar diameter data diagram of the surface carbonized hexagonal boron nitride nanosheet prepared for Example 1 and Comparative Example 2 as well as the modified hexagonal boron nitride solid prepared for Comparative Example 1 as a lubricating additive added into the water-alcohol solution is shown in the following figure. DETAILED DESCRIPTION

[0037] The present application provides a preparation method of surface carbonized hexagonal boron nitride nanosheet, comprising the following steps:

[0038] Mixing hexagonal boron nitride, water-soluble polysaccharide modifier and water for wet ball milling to obtain a ball milling material;

[0039] After washing out the ball milling material, performing first centrifugal separation to obtain a suspension;

[0040] Performing second centrifugal separation on the suspension to obtain a modified hexagonal boron nitride solid;

[0041] Performing carbonization on the modified hexagonal boron nitride solid to obtain the surface carbonized hexagonal boron nitride nanosheet;

[0042] The rotation speed of the first centrifugal separation is 2000-3000 rpm; and the rotation speed of the second centrifugal separation is 6000-10000 rpm.

[0043] In the present application, all the raw materials for preparation are commercially available products well known to those skilled in the art, unless otherwise specified.

[0044] In the present application, the hexagonal boron nitride, the water-soluble polysaccharide modifier and water are mixed to perform wet ball milling to obtain a ball milling material.

[0045] In the present application, the purity of the hexagonal boron nitride is preferably 99.8%, and the particle size is preferably 5-15 μm.

[0046] In the present application, the water-soluble polysaccharide modifier preferably includes one or more of hydroxypropyl cellulose, hydroxypropyl methyl cellulose, sodium carboxymethyl cellulose and carboxymethyl chitosan.

[0047] In the present application, the water is preferably deionized water, unless otherwise specified.

[0048] In the present application, the mixing is preferably performed by dissolving the water-soluble polysaccharide modifier into water to form a mucilage, and then adding the hexagonal boron nitride into the mucilage.

[0049] In the present application, the mass ratio of the hexagonal boron nitride, the water-soluble polysaccharide modifier and water is preferably 1:1-3:30, and further preferably 1:2:30.

[0050] In the present application, the time for wet ball milling is preferably 10-24 h, and further preferably 12-16 h; the rotation speed for wet ball milling is preferably 500-800 rpm; the wet ball milling is preferably performed in a ball milling jar; the ball milling jar is preferably an agate jar; the size of the agate jar is preferably 100 mL; the ball milling beads used in the wet ball milling are preferably agate beads, and further preferably first agate beads with a diameter of 5 mm and second agate beads with a diameter of 10 mm, and the mass ratio of the first agate beads to the second agate beads is preferably 30:20.

[0051] In the present application, the wet ball milling preferably includes sequentially and alternately performing forward rotation ball milling and reverse rotation ball milling, and the time for a single forward rotation ball milling and reverse rotation ball milling is independently preferably 30 min; the interval between the forward rotation ball milling and the reverse rotation ball milling is preferably 10 min. In the present application, the interval between the forward rotation ball milling and the reverse rotation ball milling can protect the instrument on the basis of ensuring sufficient ball milling time. The present application utilizes the mechanical shearing force and impact force between the ball milling beads to exfoliate the thick-layer h-BN into few-layer h-BNNSs, and the collision of the ball milling beads will generate active sites at the edge position and the surface of the nanosheet, and the active hydroxyl groups on the surface of the modifier will react with the active sites to form new boron-oxygen chemical bonds, thereby realizing exfoliation and covalent grafting at the same time.

[0052] After obtaining the ball mill material, the ball mill material is washed out, and then subjected to first centrifugal separation to obtain a suspension.

[0053] The washing process is not particularly limited in the present application, and any method known to those skilled in the art can be used.

[0054] In the present application, the obtained slurry is preferably subjected to stirring and ultrasonic dispersion in sequence after being washed out; the stirring time is preferably 2-4 h, and the ultrasonic dispersion time is preferably 2-4 h.

[0055] In the present application, the rotation speed of the first centrifugal separation is 2000-3000 rpm. In the present application, the number of the first centrifugal separation is preferably 1, and the time is preferably 20-30 min. In the present application, the first centrifugal separation can remove large pieces of boron nitride that have not been exfoliated. In the present application, the suspension is preferably the upper three-quarters of the volume of slurry in the system obtained after the first centrifugal separation.

[0056] After obtaining the suspension, the suspension is subjected to second centrifugal separation to obtain modified hexagonal boron nitride solid.

[0057] In the present application, the rotation speed of the second centrifugal separation is 6000-10000 rpm, preferably 7000-8000 rpm. In the present application, the number of the second centrifugal separation is preferably 3, and the single time is preferably 20-30 min. In the present application, the second centrifugal separation can remove excess grinding aids and boron nitride fragments with severely damaged structures.

[0058] After the second centrifugal separation is completed, the obtained precipitate is preferably subjected to drying; the drying process is not particularly limited in the present application, and any method known to those skilled in the art can be used; after the drying is completed, the present application can obtain modified hexagonal boron nitride solid; the particle size of the modified hexagonal boron nitride solid is preferably 100-300 nm.

[0059] After obtaining the modified hexagonal boron nitride solid, the modified hexagonal boron nitride solid is subjected to carbonization to obtain the surface-carbonized hexagonal boron nitride nanosheet.

[0060] In the present application, the carbonization temperature is preferably 200-250℃, further preferably 220-230℃; the time is preferably 4-8 h, further preferably 5-6 h; the carbonization is preferably carried out in a nitrogen atmosphere; and the carbonization is preferably carried out in a tube furnace. In order to prevent the surface macromolecular chain segment from breaking down and failing during repeated friction tests, the present application performs carbonization treatment to form a carbon film on the surface, which plays a reinforcing role.

[0061] After the carbonization is completed, the application also preferably comprises naturally cooling the obtained brown product, and collecting the brown product to obtain the surface-carbonized hexagonal boron nitride nanosheet.

[0062] The application also provides the surface-carbonized hexagonal boron nitride nanosheet prepared by the preparation method described in the above technical solution, wherein the particle size of the surface-carbonized hexagonal boron nitride nanosheet is 100-300 nm.

[0063] The application also provides the application of the surface-carbonized hexagonal boron nitride nanosheet described in the above technical solution as a lubricating additive. The surface-carbonized hexagonal boron nitride nanosheet provided by the application can play the effect of reducing friction and wear under the simulation of real working conditions by a four-ball friction and wear tester.

[0064] The application also provides a water-based lubricant comprising the surface-carbonized hexagonal boron nitride nanosheet and a water-alcohol solution, wherein the surface-carbonized hexagonal boron nitride nanosheet is the surface-carbonized hexagonal boron nitride nanosheet described in the above technical solution.

[0065] In the application, the content of the surface-carbonized hexagonal boron nitride nanosheet in the water-based lubricant is preferably 0.1-1 wt%, the water-alcohol solution preferably comprises water and ethylene glycol, and the volume ratio of the water and the ethylene glycol is preferably 1:1-1.5.

[0066] In the application, the surface-carbonized hexagonal boron nitride nanosheet can be stably dispersed in water and the water-alcohol solution for a long time.

[0067] In order to further illustrate the application, the application of a surface-carbonized hexagonal boron nitride nanosheet, a preparation method and application thereof, and a water-based lubricant are described in detail below in combination with the drawings and examples, but they should not be understood as limiting the protection scope of the application.

[0068] Example 1

[0069] 3 g of hydroxypropyl cellulose was dissolved in 30 g of deionized water to form a mucilage, 1 g of original hexagonal boron nitride powder with an average diameter of 10 μm was dispersed therein, and then two kinds of agate beads with diameters of 5 mm (30 g) and 10 mm (20 g) were loaded into an agate ball mill tank with a volume of 100 mL, the ball mill tank was installed on a ball mill, the rotation speed of the ball mill was set to 550 rpm, and the ball mill was set to rotate forward for 30 min, reverse for 30 min, and the interval was 10 min, the total time was 18 h, and the sample was collected after the ball milling was completed, and a milky white viscous ball mill was obtained.

[0070] The ball mill was washed out with about 200 mL of deionized water from the ball mill tank, and was subjected to 2 h magnetic stirring, 2 h ultrasonic dispersion, and then was moved into a centrifuge, and was subjected to first centrifugation at 2000 rpm for 30 min to remove unexfoliated large pieces of boron nitride, and about three fourths of the upper layer of the suspension was collected.

[0071] Then, second centrifugation was performed at 8000 rpm for 20 min, and was performed for a total of 3 times to remove excess hydroxypropyl cellulose and boron nitride fragments with severely damaged structure, and the precipitate was dried to obtain hydroxypropyl cellulose modified boron nitride nanosheets (HPC-BNNSs).

[0072] The hydroxypropyl cellulose modified boron nitride nanosheets were loaded into a crucible, and were placed in the middle of a quartz tube, and were subjected to heat treatment in a tube furnace under nitrogen atmosphere purging, and the furnace temperature was set to 220°C, and the heating time was 6 h, and then was naturally cooled, and the product was collected to obtain surface carbonized hexagonal boron nitride nanosheets (C-HPC-BNNSs), and a transmission electron microscope image thereof is shown in FIG. 2. Figure 8

[0073] Example 2

[0074] 3 g of hydroxypropyl methyl cellulose was dissolved in 30 g of deionized water to form a mucilage, and 1 g of original hexagonal boron nitride powder with an average diameter of 10 μm was dispersed therein, and then was loaded into a 100 mL agate ball mill tank together with two kinds of agate beads with diameters of 5 mm (30 g) and 10 mm (20 g). The ball mill tank was installed on a ball mill, and the rotation speed of the ball mill was set to 650 rpm, and in order to protect the instrument and ensure sufficient ball milling time, it was set to forward rotation for 30 min, reverse rotation for 30 min, and interval of 10 min, and the total time was 20 h. After the ball milling was completed, the sample was collected to obtain a milky white viscous ball mill.

[0075] The ball mill was washed out with about 200 mL of deionized water from the ball mill tank, and was subjected to 2 h magnetic stirring, 2 h ultrasonic dispersion, and then was moved into a centrifuge, and was subjected to first centrifugation at 2000 rpm for 30 min to remove unexfoliated large pieces of boron nitride, and about three fourths of the upper layer of the suspension was collected.

[0076] Then, second centrifugation was performed at 8000 rpm for 20 min, and was performed for a total of 3 times to remove excess hydroxypropyl methyl cellulose and boron nitride with damaged structure, and the precipitate was dried to obtain hydroxypropyl methyl cellulose modified boron nitride nanosheets (HPMC-BNNSs).

[0077] The hydroxypropyl methyl cellulose modified boron nitride nanosheets were loaded into a crucible, and were placed in the middle of a quartz tube, and were subjected to heat treatment in a tube furnace under nitrogen atmosphere purging, and the furnace temperature was set to 230°C, and the heating time was 6 h, and then was naturally cooled, and the product was collected to obtain surface carbonized hexagonal boron nitride nanosheets (C-HPMC-BNNSs).​

[0078] Example 3

[0079] The 3 g of sodium carboxymethyl cellulose was dissolved in 30 g of deionized water to form a viscous liquid, and then 1 g of raw hexagonal boron nitride powder with an average diameter of 10 μm was dispersed therein, and then the two kinds of agate balls with diameters of 5 mm (30 g) and 10 mm (20 g) were loaded into a 100 mL agate ball mill tank. The ball mill tank was installed on the ball mill, and the rotation speed of the ball mill was set to 650 rpm, and in order to protect the instrument and ensure sufficient ball milling time, it was set to forward rotation for 30 min, reverse rotation for 30 min, and interval for 10 min, and the total time was 20 h. After the ball milling was completed, the ball milling sample was collected, and a milky white viscous ball milling material was obtained.

[0080] The ball milling material was washed out of the ball mill tank with about 200 mL of deionized water, and was subjected to 2 h magnetic stirring, 2 h ultrasonic dispersion, and then was moved into a centrifuge, and was subjected to first centrifugation at a rotation speed of 2000 rpm for 30 min to screen out un-exfoliated large-size boron nitride, and about three-quarters of the upper layer suspension was collected.

[0081] Then, second centrifugation was carried out at a rotation speed of 8000 rpm for 20 min, and a total of 3 times were carried out to remove excess sodium carboxymethyl cellulose and structurally damaged boron nitride, and the precipitate was dried to obtain sodium carboxymethyl cellulose modified boron nitride nanosheets (CMC-Na-BNNSs).

[0082] The sodium carboxymethyl cellulose modified boron nitride nanosheets were loaded into a crucible and placed in the middle of a quartz tube, and were subjected to heat treatment in a tube furnace under nitrogen atmosphere purging, and the furnace temperature was set to 210 ℃, and the heating time was 6 h, and then the product was collected after natural cooling, and the surface carbonized hexagonal boron nitride nanosheets (C-CMC-Na-BNNSs) were obtained.

[0083] Example 4

[0084] The 2 g of carboxymethyl chitosan was dissolved in 30 g of deionized water to form a viscous liquid, and then 1 g of raw hexagonal boron nitride powder with an average diameter of 5 μm was dispersed therein, and then the two kinds of agate balls with diameters of 5 mm (30 g) and 10 mm (20 g) were loaded into a 100 mL agate ball mill tank. The ball mill tank was installed on the ball mill, and the rotation speed of the ball mill was set to 500 rpm, and in order to protect the instrument and ensure sufficient ball milling time, it was set to forward rotation for 30 min, reverse rotation for 30 min, and interval for 10 min, and the total time was 16 h. After the ball milling was completed, a milky white viscous ball milling material was obtained.

[0085] The ball mill was washed out with about 200 mL of deionized water, and was subjected to 2 h magnetic stirring, 2 h ultrasonic dispersion, and then was moved into a centrifuge, which was subjected to a first centrifugation at a speed of 2500 rpm for 30 min to remove unexfoliated large-size boron nitride, and about three-fourths of the supernatant was collected.

[0086] Then, a second centrifugation was performed at a speed of 7000 rpm for 20 min, and this was repeated three times to remove excess carboxymethyl chitosan and damaged boron nitride, and the precipitate was collected to obtain carboxymethyl chitosan-modified boron nitride nanosheets (CMCS-BNNSs).

[0087] The carboxymethyl chitosan-modified boron nitride nanosheets were loaded into a crucible, which was placed in the middle of a quartz tube, and was subjected to heat treatment in a tube furnace under nitrogen atmosphere purging, and the furnace temperature was set to 200°C, and the heating time was 5 h, and then the product was collected after natural cooling, which was surface-carbonized hexagonal boron nitride nanosheets (C-CMCS-BNNSs).

[0088] Comparative Example 1

[0089] 3 g of hydroxypropyl cellulose was dissolved in 30 g of deionized water to form a viscous liquid, and 1 g of raw hexagonal boron nitride powder with an average diameter of 10 μm was dispersed therein, and then was loaded into a 100 mL agate ball mill tank together with two agate beads with diameters of 5 mm (30 g) and 10 mm (20 g), respectively. The ball mill tank was installed on a ball mill, and the rotation speed of the ball mill was set to 550 rpm, and in order to protect the instrument and ensure sufficient ball milling time, it was set to forward rotation for 30 min, reverse rotation for 30 min, and interval for 10 min, and the total time was 18 h. After the ball milling was completed, the ball mill sample was collected, and a milky white viscous ball mill material was obtained.

[0090] The ball mill sample was washed out with about 200 mL of deionized water, and was subjected to 2 h magnetic stirring, and then was subjected to 2 h ultrasonic dispersion, and then was moved into a centrifuge, which was subjected to a first centrifugation at a speed of 2000 rpm for 30 min to remove unexfoliated large-size boron nitride, and about three-fourths of the supernatant was collected.

[0091] Then, a second centrifugation was performed at a speed of 8000 rpm for 20 min, and this was repeated three times to remove excess hydroxypropyl cellulose and damaged boron nitride fragments, and the precipitate was dried to obtain hydroxypropyl cellulose-modified boron nitride nanosheets (HPC-BNNSs). As a comparison, no subsequent tube furnace heating treatment was performed.

[0092] Comparative Example 2

[0093] The 3 g of hydroxypropyl cellulose was dissolved in 30 g of deionized water to form a mucilage, and 1 g of raw hexagonal boron nitride powder with an average diameter of 10 μm was dispersed therein, and then the two kinds of agate beads with diameters of 5 mm (30 g) and 10 mm (20 g) were loaded into a 100 mL agate ball mill jar. The ball mill jar was installed on a ball mill, and the rotation speed of the ball mill was set to 550 rpm. In order to protect the instrument and ensure sufficient ball milling time, it was set to forward rotation for 30 min, reverse rotation for 30 min, and interval for 10 min, and the total time was 18 h. After the ball milling was completed, a milky white viscous ball mill material was obtained.

[0094] The ball mill sample was washed out of the ball mill with about 200 mL of deionized water, and was subjected to 2 h magnetic stirring and 2 h ultrasonic dispersion, and then was transferred into a centrifuge, and was subjected to first centrifugation at a rotation speed of 2000 rpm for 30 min to screen and remove un-exfoliated large pieces of boron nitride, and about three-quarters of the upper layer of the suspension was collected.

[0095] Then, the second centrifugation was performed at a rotation speed of 8000 rpm for 20 min, and was performed for a total of 3 times to remove excess hydroxypropyl cellulose and damaged boron nitride, and the precipitate was dried to obtain hydroxypropyl cellulose modified boron nitride nanosheets (HPC-BNNSs).

[0096] The hydroxypropyl cellulose modified boron nitride nanosheets were loaded into a crucible and placed in the middle of a quartz tube, and were subjected to heat treatment in a tube furnace under nitrogen atmosphere purging, and the furnace temperature was set to 220 ℃, and the heating time was 3 h, and then the product was collected after natural cooling, and was surface carbonized hexagonal boron nitride nanosheets (C-HPC-BNNSs-3h).

[0097] Performance test

[0098] (1) Figure 1 The optical photographs of hexagonal boron nitride (h-BN) and surface carbonized hexagonal boron nitride nanosheets obtained in Examples 1-4 dispersed in a water-alcohol solution on the first day; Figure 2 The optical photographs of hexagonal boron nitride (h-BN) and surface carbonized hexagonal boron nitride nanosheets obtained in Examples 1-4 dispersed in a water-alcohol solution on the seventh day; Figure 3 The optical photographs of hexagonal boron nitride (h-BN) and surface carbonized hexagonal boron nitride nanosheets obtained in Examples 1-4 dispersed in a water-alcohol solution on the thirtieth day; wherein (1) is hexagonal boron nitride, (2) is Example 1, (3) is Example 2, (4) is Example 3, and (5) is Example 4;

[0099] As Figures 1 to 3As shown, the dispersion degree of C-HPC-BNNSs, C-HPMC-BNNSs, C-CMC-Na-BNNSs and C-CMCS-BNNSs is significantly different from that of h-BN. It can be preliminarily judged that after modification, they have good dispersibility in aqueous alcohol solution and can be stably dispersed for a long time.

[0100] (2) To verify the success of surface grafting, infrared spectral analysis was performed on the surface-carbide hexagonal boron nitride nanosheets prepared in Examples 1-4, such as... Figures 4 to 7 As shown, compared to the original unmodified hexagonal boron nitride:

[0101] The introduction of the hydroxyl peak in Example 1 and the 1060 cm⁻¹ peak -1 The obvious absorption peak at the point corresponds to the BO stretching vibration, indicating that the hydroxyl group on hydroxypropyl cellulose and the B atom on boron nitride have achieved covalent grafting.

[0102] The introduction of the hydroxyl peak in Example 2 and the 1067 cm⁻¹ peak -1 The obvious absorption peak at the point corresponds to the BO stretching vibration, indicating that the hydroxyl group on hydroxypropyl methylcellulose and the B atom on boron nitride have achieved covalent grafting.

[0103] The introduction of the hydroxyl peak in Example 3 and the 1063 cm⁻¹ peak -1 The obvious absorption peak at the point corresponds to the BO stretching vibration, indicating that the hydroxyl group on sodium carboxymethyl cellulose and the B atom on boron nitride have achieved covalent grafting.

[0104] The introduction of the hydroxyl peak in Example 4 and the 1066 cm⁻¹ peak -1 The obvious absorption peak at this point corresponds to the BO stretching vibration, indicating that the hydroxyl groups on carboxymethyl chitosan and the B atoms on boron nitride have achieved covalent grafting.

[0105] (3) The surface-carved hexagonal boron nitride nanosheets prepared in Example 1 were directly added as lubricating additives to an aqueous alcohol solution with a water-to-ethylene glycol volume ratio of 1:1. The additive mass fractions were 0.1 wt%, 0.3 wt%, 0.5 wt%, and 1.0 wt%, respectively. The mixture was ultrasonicated for 30 min to ensure uniform dispersion, thus obtaining lubricating system samples with different concentrations of surface-carved hexagonal boron nitride nanosheets. Friction and wear performance tests were conducted using an MS-10A four-ball friction tester, employing GCr15 steel balls with a diameter of 12.7 mm. The test temperature was 25℃, the loading force was 196 N, the rotation speed was 1450 rpm, and the test time was 1800 s. The friction test curves of different concentrations of surface-carved hexagonal boron nitride nanosheet lubricating additives acting on the aqueous alcohol system are shown below. Figure 9 As shown, the measured data are organized into Table 1.

[0106] Table 1 Anti-friction and anti-wear performance of surface carbonized hexagonal boron nitride nanosheets of Example 1 as water-based lubricant additives

[0107] Sample name Average coefficient of friction Average wear scar diameter (mm) Aqueous alcoholic solution 0.196 0.777 0.1 wt% C-HPC-BNNSs 0.101 0.496 0.3 wt% C-HPC-BNNSs 0.103 0.438 0.5 wt% C-HPC-BNNSs 0.095 0.402 1.0 wt% C-HPC-BNNSs 0.116 0.503

[0108] As can be seen in Table 1, compared with the water-alcohol system without adding additives, the average friction coefficient of the water-alcohol system with the surface carbonized hexagonal boron nitride nanosheets of Example 1 as lubricating additives is reduced by 52% at most, and the wear scar diameter is reduced by 48% at most. The experiment proves that the addition of the surface carbonized hexagonal boron nitride nanosheets can indeed improve the anti-friction and anti-wear performance of the water-alcohol solution.

[0109] (4) The surface carbonized hexagonal boron nitride nanosheets prepared in Example 2, Example 3, Example 4, and Comparative Example 2 and the modified boron nitride nanosheets prepared in Comparative Example 1 were directly added to a water-alcohol solution with a volume ratio of water to ethylene glycol of 1:1 as lubricating additives, and the additive mass fraction was 0.5wt%. The additives were uniformly dispersed by ultrasonic treatment for 30 min to obtain lubricant samples. The friction and wear performance experiment was carried out by using an MS-10A four-ball friction tester, and a GCr15 steel ball with a diameter of 12.7 mm was used for testing. The test temperature was 25°C, the load was 196N, the rotation speed was 1450 rpm, and the test time was 1800 s. The test results are shown in Table 2, Figures 10 to 12

[0110] Table 2 Performance of surface carbonized hexagonal boron nitride nanosheets of examples and comparative examples as water-based lubricant additives

[0111] Average coefficient of friction Average wear scar diameter (mm) Example 2 0.106 0.460 Example 3 0.119 0.491 Example 4 0.113 0.483 Comparative Example 1 0.100 0.587 Comparative Example 2 0.115 0.534

[0112] As can be seen from Table 2:

[0113] The C-HPMC-BNNSs prepared in Example 2 as additives can reduce the average friction coefficient of the water-alcohol system to 0.106 and the wear scar diameter to 0.460 mm.

[0114] The C-CMC-Na-BNNSs prepared in Example 3 as additives can reduce the average friction coefficient of the water-alcohol system to 0.119 and the wear scar diameter to 0.491 mm.

[0115] The C-CMCS-BNNSs prepared in Example 4 as additives can reduce the average friction coefficient of the water-alcohol system to 0.113 and the wear scar diameter to 0.483 mm.

[0116] The HPC-BNNSs prepared in Comparative Example 1 as additives can reduce the average friction coefficient of the water-alcohol system to 0.100, but the wear scar diameter is 0.587 mm, and the oil cup is obviously heated after the test is completed. In combination with the friction test curve​Figure 10 It is found that HPC-BNNSs without tube furnace heating show good performance in a short time, but with the increase of friction time, the surface grafted segments are broken, which causes the internal agglomeration of boron nitride nanosheets, affecting the lubricating effect. It is necessary to ensure that the tube furnace heating treatment is essential to ensure that BNNSs play a lubricating role.

[0117] The C-HPC-BNNSs-3h prepared by Comparative Example 2 can make the average friction coefficient of the water-alcohol system decrease to 0.115, and the wear scar diameter decrease to 0.534 mm. Compared with the sample heated in the tube furnace for 6h under the same conditions, the lubricating effect is slightly worse, which shows that the carbonization conditions are different, and the lubricating effect of the obtained product is also different. Figure 10

[0118] Although the above examples make a detailed description of the present application, it is only a part of the embodiments of the present application, not all the embodiments, and other embodiments can be obtained under the premise of no creativity according to the present embodiments, which belong to the protection scope of the present application.​

Claims

1. A method for preparing surface-carbonized hexagonal boron nitride nanosheets, characterized by, The method comprises the following steps: mixing hexagonal boron nitride, water-soluble polysaccharide modifier and water to perform wet ball milling to obtain a ball milling material; the water-soluble polysaccharide modifier is hydroxypropyl cellulose; the mass ratio of the hexagonal boron nitride, the water-soluble polysaccharide modifier and the water is 1:3:30; the wet ball milling comprises sequentially and alternately performing forward rotation ball milling and reverse rotation ball milling, and the time of a single forward rotation ball milling and a single reverse rotation ball milling is independently 30 min; the forward rotation ball milling and the reverse rotation ball milling are separated by 10 min; the time of the wet ball milling is 18 h; and the rotation speed of the wet ball milling is 550 rpm; performing first centrifugal separation on the ball milling material after washing to obtain a suspension; performing second centrifugal separation on the suspension to obtain modified hexagonal boron nitride solid; performing carbonization on the modified hexagonal boron nitride solid to obtain the surface-carbonized hexagonal boron nitride nanosheet; the temperature of the carbonization is 220 DEG C, and the time of the carbonization is 6 h; the rotation speed of the first centrifugal separation is 2000 rpm; and the rotation speed of the second centrifugal separation is 8000 rpm.

2. The production method according to claim 1, characterized by, the washing further comprises sequentially performing stirring and ultrasonic dispersion on the obtained material liquid; the time of the stirring is 2-4 h, and the time of the ultrasonic dispersion is 2-4 h.

3. The surface-carbonized hexagonal boron nitride nanoplatelets produced by the production method of claim 1 or 2, characterized in that, the particle size of the surface-carbonized hexagonal boron nitride nanosheet is 100-300 nm.

4. Application of the surface-carbonized hexagonal boron nitride nanosheet of claim 3 as a lubricating additive.

5. A water-based lubricant characterized by, The water-based lubricant comprises surface-carbonized hexagonal boron nitride nanosheet and water-alcohol solution; the surface-carbonized hexagonal boron nitride nanosheet is the surface-carbonized hexagonal boron nitride nanosheet of claim 3.

6. The water-based lubricant according to claim 5, characterized in that, the content of the surface-carbonized hexagonal boron nitride nanosheet in the water-based lubricant is 0.1-1 wt%.

7. The water-based lubricant of claim 5, wherein the water-alcohol solution comprises water and ethylene glycol; and the volume ratio of the water to the ethylene glycol is 1:1-1.5.

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