Two-dimensional material exfoliation method based on the synergistic effect of resonance crushing and crystal growth

Abstract

The present invention discloses a method for exfoliating two-dimensional materials based on the synergistic effect of resonance crushing and crystal growth, comprising: crushing a bulk material and uniformly dispersing it in a solvent to form a dispersion; freezing the dispersion to form a solid material; placing the solid material in a low-temperature environment where the temperature is lower than or equal to the freezing point of the solvent, and subjecting the solid material to ultrasonic treatment to resonate the solvent crystallized between layers, so that at least part of the crystallized solvent is crushed, and at the same time enabling the liquid solvent in the surrounding environment to enter the broken gaps and continue to solidify and crystallize in this low-temperature environment. With the continuous crushing and growth of the crystals between the material layers, two-dimensional materials are finally exfoliated from the bulk material; the surface tension of the solvent matches the surface energy of the two-dimensional material. The method for exfoliating two-dimensional materials of the present invention is convenient to operate, has a small solvent usage amount, high exfoliation efficiency, good quality of the exfoliated two-dimensional materials, is suitable for large-scale production, and has potential industrialization value.

Description

Technical Field

[0001] The present invention relates to a method for exfoliating two-dimensional materials, specifically to a method for exfoliating two-dimensional materials based on the synergistic effect of resonance crushing and crystal growth, belonging to the field of materials science. Background Art

[0002] Two-dimensional (2D) materials are a new type of nanomaterial, which are widely used in many basic and applied research fields such as electronics, optics, optoelectronics, energy storage and power generation, catalysis, sensing detection, biomedicine, etc. Two-dimensional materials are sheet-like structures with a thickness of only a single atom or a few atoms, and the lateral size ranges from a few nanometers to several hundred nanometers and above. This special structure endows two-dimensional materials with good anisotropy, but at the same time greatly increases the preparation difficulty of two-dimensional materials, and its low exfoliation efficiency further limits the application of two-dimensional materials in various fields.

[0003] The existing two-dimensional material exfoliation techniques mainly include mechanical exfoliation, liquid-phase exfoliation, electrochemical intercalation exfoliation techniques, etc. However, the above exfoliation techniques all have some deficiencies to varying degrees. For example, although the mechanical exfoliation technique has a low cost, its yield is low, the size is small, and it is difficult to control the number of layers of the exfoliated material; electrochemical intercalation exfoliation can prepare 2D materials with few layers or even single layers, but the process is complex, time-consuming, and oxidation, insufficient intercalation, and some electrochemical side reactions will inevitably occur during the intercalation process, so that there are often some defects in the exfoliated product, which will affect the physical and chemical properties of the material; although the liquid-phase exfoliation technique is simple and fast, it requires the use of a large amount of toxic and harmful solvents, and during the exfoliation process, the long-term and intense ultrasonic force will reduce the lateral size of the product, and it is difficult to obtain large-size two-dimensional materials.

[0004] In order to solve the problems such as low efficiency of the existing two-dimensional material exfoliation techniques, the present application proposes a method for exfoliating two-dimensional materials based on the synergistic effect of resonance crushing and crystal growth. Summary of the Invention

[0005] Aiming at the deficiencies of the prior art, the main purpose of the present invention is to provide a method for exfoliating two-dimensional materials based on the synergistic effect of resonance crushing and crystal growth, so as to improve the efficiency of exfoliating two-dimensional materials and provide the possibility for the industrial production of two-dimensional materials.

[0006] To achieve the foregoing invention purpose, the technical solutions adopted by the present invention include:

[0007] Some embodiments of the present invention provide a method for exfoliating two-dimensional materials based on the synergistic effect of resonance crushing and crystal growth, which includes:

[0008] Crush the bulk material and then uniformly disperse it in a solvent to obtain a dispersion;

[0009] Freeze the dispersion liquid to form a solid material;

[0010] Place the solid material in a low-temperature environment where the temperature is lower than or equal to the freezing point of the solvent, and perform ultrasonic treatment on the solid material to resonate the crystallized solvent therein, so that at least part of the solidified solvent is broken, and at the same time, the liquid solvent in the surrounding environment enters the broken gaps and continues to solidify and crystallize in the low-temperature environment. As the crystals between the material layers are continuously broken and grown, the growth of solvent crystals between the two-dimensional material layers is realized, and finally the two-dimensional material is peeled off from the bulk material;

[0011] Wherein, the surface tension of the solvent matches the surface energy of the two-dimensional material.

[0012] In one embodiment, the fragmentation treatment can be achieved by various known methods in the art, such as grinding, ball milling, etc., and is not limited thereto.

[0013] Exemplarily, the bulk material can be ground into particles with a particle size of 1-1000 μm and then uniformly dispersed in a solvent to form a dispersion liquid.

[0014] In one embodiment, the method for peeling the two-dimensional material further includes: adding a surfactant to the solvent to adjust the surface tension of the solvent to match the surface energy of the two-dimensional material.

[0015] Wherein, the surfactant can adopt various surfactants known in the art, such as sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB), etc., and is not limited thereto.

[0016] In one embodiment, the material of the bulk material includes black phosphorus, graphite, transition metal dichalcogenides (TMDs), boron nitride, transition metal carbonitrides (MAX), metal phosphotrisulfide materials, etc., and is not limited thereto.

[0017] In one embodiment, the two-dimensional material includes black phosphorus nanosheets, graphene, transition metal dichalcogenide nanosheets, boron nitride nanosheets, transition metal carbonitride nanosheets (MXene), metal phosphotrisulfide nanosheets, etc., and is not limited thereto.

[0018] In one embodiment, the freezing point of the solvent is -30°C to 20°C.

[0019] Furthermore, the solvent includes one or more combinations of water, organic solvents, etc.

[0020] Exemplarily, the organic solvent is selected from organic protonic solvents with a freezing point in the range of -40°C to 20°C, such as N-methylpyrrolidone (NMP), dimethyl sulfoxide (DMSO), etc., and is not limited thereto.

[0021] Exemplarily, the solvent includes a mixture of water and an organic solvent, wherein the volume ratio of water to the organic solvent is 1:99 to 99:1.

[0022] In one embodiment, the content of the solid phase in the dispersion is 0.1 to 99.0 Wt%, preferably 10 to 90 Wt%.

[0023] In one embodiment, the low-temperature environment can be achieved by using a cold trap or other devices with refrigeration functions.

[0024] In one embodiment, the frequency of the ultrasonic treatment is 20 to 100 kHz, the power is 100 to 2000 W, preferably 300 to 800 W. In one embodiment, the time of the ultrasonic treatment is 1 to 1000 min, preferably 300 to 800 min.

[0025] In addition, according to the material of the bulk material and the selected solvent, etc., the frequency, power, ultrasonic time, etc. of the ultrasonic wave can be adjusted accordingly to obtain the best two-dimensional material exfoliation effect.

[0026] In one embodiment, before the ultrasonic treatment, some liquid solvents or solvents with coexistence of liquid and solid states can be added and mixed with the solid material, and then the ultrasonic treatment is carried out, so that there is sufficient liquid solvent in the surrounding environment during the ultrasonic process to enter the broken gaps and continue to solidify and crystallize in the low-temperature environment.

[0027] In one embodiment, the two-dimensional material exfoliation method specifically includes: after the ultrasonic treatment is completed, the solid material undergoes a phase change and the two-dimensional material therein is separated.

[0028] Exemplarily, the ultrasonic action can be used to cause the solid material to undergo a phase change, and then the two-dimensional material therein is separated by centrifugation, wherein the centrifugation speed used is 1000 to 20000 rpm / min.

[0029] Of course, heating or other methods can also be used to cause the solid material to undergo a phase change, and filtration, freeze-drying or other separation methods are used to separate and obtain the two-dimensional material.

[0030] In one embodiment, the method for exfoliating two-dimensional materials further includes: cleaning and drying the exfoliated two-dimensional materials. Exemplarily, the two-dimensional materials can be cleaned one or more times using various cleaning solvents known in the art, such as deionized water, organic solvents, or mixtures thereof. After that, the two-dimensional materials can be dried using various methods known in the art, such as natural drying, vacuum drying, freeze drying, etc.

[0031] Compared with the prior art, the method for exfoliating two-dimensional materials proposed by the present invention utilizes high-energy ultrasonic waves to cause the solidified solvent to resonate and thus crush it, creating certain crystal defects or microcracks, enabling more external liquid solvent to enter the crystal defects and continue to solidify and crystallize under the action of low temperature. As the interlayer crystals of the material continuously break and grow, the volume further expands until the van der Waals force between the layers of the two-dimensional material is destroyed, that is, the exfoliation of the two-dimensional material is achieved based on the synergistic effect of resonance crushing and crystal growth. It is not only convenient to operate, has a small amount of solvent used, high exfoliation efficiency, but also is not limited by the solvent expansion rate. As long as the conditions permit, it can be applied to any solvent, is suitable for large-scale production, and has potential industrialization value. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0033] Figure 1 is the schematic diagram of a method for exfoliating two-dimensional materials based on the synergistic effect of resonance crushing and crystal growth in the present invention;

[0034] Figure 2 is the transmission electron microscope photograph of the black phosphorus nanosheets exfoliated in Example 1;

[0035] Figure 3a is the atomic force microscope image of the black phosphorus nanosheets after exfoliation in Example 1;

[0036] Figure 3b is the thickness distribution diagram of the black phosphorus nanosheets after exfoliation in Example 1;

[0037] Figure 3c is the average thickness distribution diagram of the black phosphorus nanosheets after exfoliation in Example 1;

[0038] Figure 4a is the relationship diagram between the number of layers of black phosphorus exfoliated in Example 1 and its Raman shift;

[0039] Figure 4bLinear relationship diagram between black phosphorus with different number of layers exfoliated in Example 1 and its Raman shift;

[0040] Figure 4c Relationship diagram between black phosphorus with different number of layers exfoliated in Example 1 and its Raman shift;

[0041] Figure 5 Transmission electron microscope of black phosphorus nanosheets exfoliated in Example 2;

[0042] Figure 6 Transmission electron microscope of black phosphorus nanosheets exfoliated in Example 3;

[0043] Figure 7 Transmission electron microscope of black phosphorus nanosheets exfoliated in Example 8;

[0044] Figure 8a Atomic force microscope image of black phosphorus nanosheets exfoliated in Example 8;

[0045] Figure 8b Thickness distribution diagram of black phosphorus nanosheets after exfoliation in Example 8;

[0046] Figure 8c Average thickness distribution diagram of black phosphorus nanosheets after exfoliation in Example 8;

[0047] Figure 9 Transmission electron microscope of black phosphorus nanosheets exfoliated in Example 9;

[0048] Figure 10a Atomic force microscope image of black phosphorus nanosheets exfoliated in Example 9;

[0049] Figure 10b Thickness distribution diagram of black phosphorus nanosheets after exfoliation in Example 9;

[0050] Figure 10c Average thickness distribution diagram of black phosphorus nanosheets after exfoliation in Example 9;

[0051] Figure 11 Transmission electron microscope of black phosphorus nanosheets exfoliated in Example 16;

[0052] Figure 12 Transmission electron microscope of black phosphorus nanosheets exfoliated in Example 17;

[0053] Figure 13 Transmission electron microscope image of FePS3 nanosheets exfoliated in Example 18;

[0054] Figure 14 XRD image of FePS3 nanosheets exfoliated in Example 18;

[0055] Figure 15 TEM image of the MXene nanosheets exfoliated in Example 19;

[0056] Figure 16 TEM image of the BN nanosheets exfoliated in Example 20;

[0057] Figure 17 TEM image of the black phosphorus nanosheets exfoliated in Comparative Example 2. Detailed implementation manners

[0058] As mentioned above, in the existing exfoliation methods, some researchers have proposed to use the violent action of ultrasonic waves to break the van der Waals forces between the layers of two-dimensional materials. The main principle is as follows: after the bulk material is dispersed in the solvent, the solvent molecules will uniformly intercalate into the layers of the two-dimensional material, and the ultrasonic action uses the instantaneous high pressure generated by the cavitation of the solvent to break the van der Waals forces between the layers of the two-dimensional material. However, long-term ultrasonic action will cause the lateral size distribution of the material to be non-uniform. And the applicant also noticed that the liquid will solidify and crystallize near the freezing point, and the crystal lattice will vibrate under the action of ultrasonic waves, resulting in the phenomenon of lattice defects.

[0059] In view of this, the present application proposes a two-dimensional material exfoliation method based on the synergistic effect of resonance crushing and crystal growth, and its implementation process and principle can be referred to Figure 1 , specifically as follows:

[0060] First, the bulk material is preliminarily crushed (such as grinding, ball milling, etc.) and then uniformly dispersed in a solvent to form a dispersion liquid. Then, the dispersion liquid is frozen to form a solid material. After that, the solid material is placed in an environment where the temperature is near the freezing point of the solvent, and ultrasonic treatment is performed on the solid material. Before the ultrasonic treatment, the solvent between the two-dimensional material layers in the crushed bulk material is still in a crystalline state. During the ultrasonic treatment, the solvent crystal lattice resonates under the strong forced vibration of the ultrasonic wave, and the crystal structure is broken, and a large number of defects may exist around and inside the crystal. Then, the liquid-phase solvent in the surrounding environment will flow into the crystal between the two-dimensional material layers with defects due to its excellent fluidity and continue to grow along the original direction to form crystals. Since the amount of solvent molecules entering is much larger than the amount of solvent molecules present before the ultrasonic treatment, the volume change of the regenerated crystal is greater than that before the ultrasonic treatment. This process is the synergistic effect of resonance crushing and crystal growth. Since the time of the crystal crushing process and the crystal growth process caused by this ultrasonic wave is approximately the same as the working / interval time of the ultrasonic instrument, this process is very rapid and can be continuously cycled until the crystal between the two-dimensional material layers grows to a state where it can break the van der Waals force between the layers of the two-dimensional material, that is, the exfoliation of the two-dimensional material is achieved. After that, the solid material is thawed, and few-layer two-dimensional materials can be separated. The applicable separation methods include gradient centrifugation, freeze-drying, etc., and are not limited thereto.

[0061] The content of the present invention will be more detailedly explained below in conjunction with the accompanying drawings and several embodiments. However, it should be understood that the embodiments disclosed herein are only exemplary of the present invention, and the present invention can be embodied in various forms. Therefore, the specific functional details disclosed herein should not be construed as restrictive, but only as the basis of the claims and as a representative basis for teaching those skilled in the art to adopt the present invention in any appropriate detailed embodiment in different ways.

[0062] Unless otherwise specifically stated, the use of the terms "comprising", "having" should generally be understood as open and non-restrictive.

[0063] Example 1 A method for exfoliating black phosphorus, comprising the following steps:

[0064] 1. Weigh a certain amount of bulk black phosphorus material, place it in a crucible and preliminarily grind it into a powder with a particle size of about 500 μm, and add deoxygenated water dissolved with sodium dodecyl sulfate with a concentration of about 0.5 g / L as a solvent. Disperse it in an ultrasonic cleaner for about 30 min to obtain a colloidal solution.

[0065] 2. Place the dispersed colloidal solution in liquid nitrogen (-196 °C) for rapid freezing.

[0066] 3. Take out the frozen solid material from the mold and place it in an ultrasonic device for preparation of exfoliation.

[0067] 4. Add a certain amount of solvent in a solid-liquid mixed state to the ultrasonic device, where the content of the solid phase is 50 Wt%. Set the ultrasonic frequency to about 20 kHz, the power to about 500 W, and the total ultrasonic time to about 600 min. Set the cold trap temperature near 0 °C, and start the ultrasonic device and the cold trap device.

[0068] 5. Collect the colloidal solution after exfoliation and perform centrifugal separation. First, centrifuge at a speed of about 3000 rpm / min for about 30 min to remove the unexfoliated bulk materials; then centrifuge at a speed of about 12,000 rpm / min for about 30 min. The lower layer precipitate is the two-dimensional material with fewer layers. After washing the separated two-dimensional material several times with ethanol and deionized water, perform freeze-drying at about -80 °C and under vacuum conditions.

[0069] 6. Weigh after freeze-drying, compare with the initial added amount to calculate the exfoliation efficiency, and the calculated exfoliation efficiency is 11.7%.

[0070] Figure 2 This is a transmission electron microscope image of the black phosphorus nanosheets obtained by exfoliation in this example. It can be seen that the exfoliated black phosphorus nanosheets have a good lamellar structure.

[0071] Figures 3a - 3c Shows the atomic force microscope image of the black phosphorus nanosheets obtained by exfoliation in this example, as well as the average thickness of the nanosheets. It can be seen that the thickness of the exfoliated black phosphorus nanosheets is about 2.6 nm, and the number of layers is about 3 - 4 layers, indicating that the method of this example can obtain black phosphorus nanosheets with a lower number of layers.

[0072] Figures 4a - 4c Shows the relationship diagram between the black phosphorus with different numbers of layers obtained by exfoliation in this example and its Raman shift. It can be seen that as the number of layers continuously decreases, the Raman shift continuously moves towards lower wavenumbers.

[0073] Example 2 A method for exfoliating black phosphorus, comprising the following steps:

[0074] 1. Weigh a certain amount of bulk black phosphorus material, place it in a crucible and preliminarily grind it into a powder with a particle size of about 800 μm, add it to N-methylpyrrolidone dissolved with sodium dodecyl sulfate at a concentration of about 0.45 g / L, and disperse it in an ultrasonic cleaner for 30 min to obtain a colloidal solution.

[0075] 2. Place the dispersed colloidal solution in liquid nitrogen (-196 °C) for rapid freezing.

[0076] 3. Take out the frozen solid material from the mold and place it in an ultrasonic device for preparation of exfoliation.

[0077] 4. Add a certain amount of solvent in a solid-liquid mixed state to the ultrasonic device, where the content of the solid phase is 10 Wt%, and set the ultrasonic frequency to about 20 kHz, the power to about 500 W, and the total ultrasonic time to about 600 min. Set the cold trap temperature to about -25 °C, and start the ultrasonic device and the cold trap device.

[0078] 5. Collect the colloidal solution after exfoliation and perform centrifugal separation. First, centrifuge at a speed of about 3000 rpm / min for about 30 min to remove the unexfoliated blocky materials; then centrifuge at a speed of about 12000 rpm / min for about 30 min. The lower layer precipitate is the two-dimensional material with fewer layers. After washing the separated two-dimensional material several times with ethanol and deionized water, perform freeze-drying at -80 °C and under vacuum conditions.

[0079] 6. Weigh after freeze-drying, compare with the initial addition amount to calculate the exfoliation efficiency, and the calculated exfoliation efficiency is 12.8%.

[0080] Figure 5 This is the transmission electron microscope image of the black phosphorus nanosheets exfoliated in this example. It can be seen that using N-methylpyrrolidone as the solvent, the exfoliated black phosphorus nanosheets have a good lamellar structure.

[0081] In this example, N-methylpyrrolidone can also be replaced by ultrapure water, which has a higher freezing point than N-methylpyrrolidone and the system is easier to maintain.

[0082] Example 3 A method for exfoliating black phosphorus, comprising the following steps:

[0083] A method for exfoliating black phosphorus, comprising the following steps:

[0084] 1. Weigh a certain amount of bulk black phosphorus material, place it in a crucible and preliminarily grind it into a powder with a particle size of about 300 μm, add dimethyl sulfoxide dissolved with sodium dodecyl sulfate at a concentration of about 0.4 g / L as the solvent, and disperse it in an ultrasonic cleaner for 30 min to obtain a colloidal solution.

[0085] 2. Place the dispersed colloidal solution in liquid nitrogen (-196 °C) for rapid freezing.

[0086] 3. Take out the frozen solid material from the mold and put it into the ultrasonic device for exfoliation preparation.

[0087] 4. Add a certain amount of solvent in a solid-liquid mixed state to the ultrasonic device, where the content of the solid phase is 25 wt%, and set the ultrasonic frequency to about 20 kHz, the power to about 500 W, and the total ultrasonic time to about 600 min. Set the cold trap temperature to around 18 °C, and start the ultrasonic device and the cold trap device.

[0088] 5. Collect the colloidal solution after exfoliation and perform centrifugal separation. First, centrifuge at a speed of about 3000 rpm for about 30 min to remove the unexfoliated bulk materials; then centrifuge at a speed of about 12000 rpm for about 30 min. The lower precipitate is the two-dimensional material with fewer layers. After washing the separated two-dimensional material several times with ethanol and deionized water, perform freeze-drying under -80 °C and vacuum conditions.

[0089] 6. Weigh after freeze-drying and calculate the exfoliation efficiency by comparing with the initial addition amount. The calculated exfoliation efficiency is 10.2%. Figure 6 This is the transmission electron microscope of the black phosphorus nanosheets exfoliated in this example. It can be seen that under the condition of DMSO as the solvent, the number of layers of the exfoliated black phosphorus nanosheets is relatively large.

[0090] Example 4 A method for exfoliating black phosphorus, comprising the following steps:

[0091] 1. Weigh a certain amount of bulk black phosphorus material, place it in a crucible and preliminarily grind it into a powder with a particle size of about 100 μm, and add it to a deoxygenated aqueous solution containing about 0.35 g / L sodium dodecyl sulfate as the solvent. Disperse it in an ultrasonic cleaner for about 30 min to obtain a colloidal solution.

[0092] 2. Place the dispersed colloidal solution in liquid nitrogen (-196 °C) for rapid freezing.

[0093] 3. Take out the frozen solid material from the mold and put it into an ultrasonic device for exfoliation preparation.

[0094] 4. Add a certain amount of solvent in the solid-liquid mixed state to the ultrasonic device, where the content of the solid phase is 55 wt%, and set the ultrasonic frequency to about 20 kHz, the power to about 100 W, and the total ultrasonic time to about 600 min. Set the cold trap temperature near 0 °C, and start the ultrasonic device and the cold trap device.

[0095] 5. Collect the colloidal solution after exfoliation and perform centrifugal separation. First, centrifuge at a speed of about 3000 rpm for about 30 min to remove the unexfoliated bulk materials; then centrifuge at a speed of about 12000 rpm for about 30 min. The lower precipitate is the two-dimensional material with fewer layers. After washing the separated two-dimensional material several times with ethanol and deionized water, perform freeze-drying under -80 °C and vacuum conditions.

[0096] 6. Weigh after freeze-drying and calculate the exfoliation efficiency by comparing with the initial addition amount. The calculated exfoliation efficiency is 4.8%.

[0097] Example 5 A method for exfoliating black phosphorus, comprising the following steps:

[0098] 1. Weigh a certain amount of bulk black phosphorus material, place it in a crucible and preliminarily grind it into powder with a particle size of about 250 μm, and add it to a deoxygenated aqueous solution containing about 0.45 g / L sodium dodecyl sulfate as a solvent. Disperse it in an ultrasonic cleaner for about 30 min to obtain a colloidal solution.

[0099] 2. Place the dispersed colloidal solution in liquid nitrogen (-196 °C) for rapid freezing.

[0100] 3. Take out the frozen solid material from the mold and put it into an ultrasonic device for exfoliation preparation.

[0101] 4. Add a certain amount of solvent in a solid-liquid mixed state to the ultrasonic device, where the content of the solid phase is 45 wt%, and set the ultrasonic frequency to about 20 kHz, the power to about 300 W, and the total ultrasonic time to about 600 min. Set the cold trap temperature near 0 °C, and start the ultrasonic device and the cold trap device.

[0102] 5. Collect the exfoliated colloidal solution and perform centrifugal separation. First, centrifuge at a speed of about 3000 rpm for about 30 min to remove the unexfoliated bulk material; then centrifuge at a speed of about 12000 rpm for about 30 min. The lower layer precipitate is the two-dimensional material with fewer layers. After washing the separated two-dimensional material several times with ethanol and deionized water, perform freeze-drying at -80 °C and under vacuum conditions.

[0103] 6. Weigh after freeze-drying, compare with the initial added amount to calculate the exfoliation efficiency, and the calculated exfoliation efficiency is 7.9%.

[0104] Example 6 A method for exfoliating black phosphorus, comprising the following steps:

[0105] 1. Weigh a certain amount of bulk black phosphorus material, place it in a crucible and preliminarily grind it into powder with a particle size of about 300 μm, and add it to a deoxygenated aqueous solution containing about 0.65 g / L sodium dodecyl sulfate as a solvent. Disperse it in an ultrasonic cleaner for about 30 min to obtain a colloidal solution.

[0106] 2. Place the dispersed colloidal solution in liquid nitrogen (-196 °C) for rapid freezing.

[0107] 3. Take out the frozen solid material from the mold and put it into an ultrasonic device for exfoliation preparation.

[0108] 4. Add a certain amount of solvent in a solid-liquid mixed state to the ultrasonic device, where the content of the solid phase is 35 wt%, and set the ultrasonic frequency to about 20 kHz, the power to about 800 W, and the total ultrasonic time to about 600 min. Set the cold trap temperature near 0 °C, and start the ultrasonic device and the cold trap device.

[0109] 5. Collect the colloidal solution after exfoliation and perform centrifugal separation. First, centrifuge at a speed of about 3000 rpm for about 30 min to remove the unexfoliated bulk materials; then centrifuge at a speed of about 12000 rpm for about 30 min. The lower precipitate is the two-dimensional material with fewer layers. After washing the separated two-dimensional material several times with ethanol and deionized water, perform freeze-drying under -80 °C and vacuum conditions.

[0110] 6. Weigh after freeze-drying and calculate the exfoliation efficiency by comparing with the initial addition amount. The calculated exfoliation efficiency is 12.4%.

[0111] Example 7 A method for exfoliating black phosphorus, comprising the following steps:

[0112] 1. Weigh a certain amount of bulk black phosphorus material, place it in a crucible and preliminarily grind it into a powder with a particle size of about 250 μm, and add it to a deoxygenated aqueous solution containing sodium dodecyl sulfate with a concentration of about 0.75 g / L as the solvent. Disperse in an ultrasonic cleaner for about 30 min to obtain a colloidal solution.

[0113] 2. Place the dispersed colloidal solution in liquid nitrogen (-196 °C) for rapid freezing.

[0114] 3. Take out the frozen solid material from the mold and put it into an ultrasonic device for exfoliation preparation.

[0115] 4. Start the ultrasonic device and the cold trap device, set the ultrasonic frequency to about 20 kHz, the power to about 1500 W, the total ultrasonic time to about 600 min, set the cold trap temperature near 0 °C, and add a certain amount of solvent in a solid-liquid mixed state to the ultrasonic device, where the content of the solid phase is 35 wt%.

[0116] 5. Collect the colloidal solution after exfoliation and perform centrifugal separation. First, centrifuge at a speed of about 3000 rpm for about 30 min to remove the unexfoliated bulk materials; then centrifuge at a speed of about 12000 rpm for about 30 min. The lower precipitate is the two-dimensional material with fewer layers. After washing the separated two-dimensional material several times with ethanol and deionized water, perform freeze-drying under -80 °C and vacuum conditions.

[0117] 6. Weigh after freeze-drying and calculate the exfoliation efficiency by comparing with the initial addition amount. The calculated exfoliation efficiency is 15.2%.

[0118] Example 8 A method for exfoliating black phosphorus, comprising the following steps:

[0119] 1. Weigh a certain amount of bulk black phosphorus material, place it in a crucible and preliminarily grind it into a powder with a particle size of about 250 μm, and add it to a deoxygenated aqueous solution containing about 0.6 g / L sodium dodecyl sulfate as a solvent. Disperse it in an ultrasonic cleaner for about 30 min to obtain a colloidal solution.

[0120] 2. Place the dispersed colloidal solution in liquid nitrogen (-196 °C) for rapid freezing.

[0121] 3. Take out the frozen solid material from the mold and put it into an ultrasonic device for exfoliation preparation.

[0122] 4. Add a certain amount of solvent in the solid-liquid mixed state to the ultrasonic device, where the content of the solid phase is 15 wt%, and set the ultrasonic frequency to about 20 kHz, the power to about 2000 W, and the total ultrasonic time to about 600 min. Set the cold trap temperature near 0 °C, and start the ultrasonic device and the cold trap device.

[0123] 5. Collect the colloidal solution after exfoliation and perform centrifugal separation. First, centrifuge at a speed of about 3000 rpm / min for about 30 min to remove the unexfoliated bulk material; then centrifuge at a speed of about 12000 rpm / min for about 30 min. The lower layer precipitate is the two-dimensional material with fewer layers. After washing the separated two-dimensional material several times with ethanol and deionized water, perform freeze-drying at -80 °C and under vacuum conditions.

[0124] 6. Weigh after freeze-drying, compare with the initial addition amount to calculate the exfoliation efficiency, and the calculated exfoliation efficiency is 15.8%.

[0125] Figure 7 This is the transmission electron microscope of the black phosphorus nanosheets exfoliated in this example. It can be seen that the ultrasonic power is one of the main factors affecting the exfoliation effect. As the ultrasonic power increases, the exfoliation effect becomes better, but due to too high power, it is difficult to maintain the environment of resonance crushing and crystal growth. Therefore, 500 W is selected as the optimal condition.

[0126] Figures 8a - 8c The atomic force microscope images of the black phosphorus nanosheets exfoliated in this example are shown. It can be seen that the thickness of the exfoliated black phosphorus nanosheets is about 1.3 nm, and the number of layers is about 1 - 2 layers, indicating that the ultrasonic power has an impact on the number of layers of the nanosheets.

[0127] Example 9 A method for exfoliating black phosphorus, including the following steps:

[0128] 1. Weigh a certain amount of bulk black phosphorus material, place it in a crucible and initially grind it into a powder with a particle size of about 700 μm. Add it to a deoxygenated aqueous solution containing sodium dodecyl sulfate with a concentration of about 0.35 g / L as the solvent, and disperse it in an ultrasonic cleaner for 30 min to obtain a colloidal solution.

[0129] 2. Place the dispersed colloidal solution in liquid nitrogen (-196 °C) for rapid freezing.

[0130] 3. Take out the frozen solid material from the mold and put it into an ultrasonic device for exfoliation preparation.

[0131] 4. Add a certain amount of solvent in a solid-liquid mixed state to the ultrasonic device, where the content of the solid phase is 50 wt%, set the ultrasonic frequency to about 20 kHz, the power to about 500 W, and the total ultrasonic time to about 60 min. Set the cold trap temperature near 0 °C, and start the ultrasonic device and the cold trap device.

[0132] 5. Collect the colloidal solution after exfoliation and perform centrifugal separation. First, centrifuge at a speed of about 3000 rpm / min for about 30 min to remove the unexfoliated bulk material; then centrifuge at a speed of about 120000 rpm / min for about 30 min. The lower layer precipitate is the two-dimensional material with fewer layers. After washing the separated two-dimensional material several times with ethanol and deionized water, perform freeze-drying at -80 °C and under vacuum conditions.

[0133] 6. Weigh after freeze-drying, compare with the initial addition amount to calculate the exfoliation efficiency, and the calculated exfoliation efficiency is 6.3%.

[0134] Figure 9 This is the transmission electron microscope photo of the black phosphorus nanosheets exfoliated in this example. It can be seen that time is also one of the main factors affecting the exfoliation effect. As time decreases, the exfoliation effect weakens.

[0135] Figure 10a This is the atomic force microscope image of the black phosphorus nanosheets exfoliated in this example. It can be seen from Figure 10b , c that the thickness of the exfoliated black phosphorus nanosheets is mostly about 4.8 nm, and the number of layers is about 7 - 8 layers, indicating that the total ultrasonic time has an impact on the number of layers of black phosphorus obtained by exfoliation.

[0136] Example 10 A method for exfoliating black phosphorus, including the following steps:

[0137] 1. Weigh a certain amount of bulk black phosphorus material, place it in a crucible and initially grind it into a powder with a particle size of about 650 μm. Add it to a deoxygenated aqueous solution containing sodium dodecyl sulfate with a concentration of about 0.30 g / L as the solvent, and disperse it in an ultrasonic cleaner for 30 min to obtain a colloidal solution.

[0138] 2. Place the dispersed colloidal solution in liquid nitrogen (-196 °C) for rapid freezing.

[0139] 3. Take out the frozen solid material from the mold and put it into an ultrasonic device for preparation of exfoliation.

[0140] 4. Add a certain amount of solvent in a solid-liquid mixed state to the ultrasonic device, where the content of the solid phase is 45 wt%, and set the ultrasonic frequency to about 20 kHz, the power to about 500 W, and the total ultrasonic time to about 100 min. Set the cold trap temperature near 0 °C, and start the ultrasonic device and the cold trap device.

[0141] 5. Collect the exfoliated colloidal solution and perform centrifugal separation. First, centrifuge at a speed of about 3000 rpm / min for about 30 min to remove the unexfoliated blocky materials; then centrifuge at a speed of about 120000 rpm / min for about 30 min. The lower layer precipitate is the two-dimensional material with fewer layers. After washing the separated two-dimensional material several times with ethanol and deionized water, perform freeze-drying under -80 °C and vacuum conditions.

[0142] 6. Weigh after freeze-drying, compare with the initial addition amount to calculate the exfoliation efficiency, and the calculated exfoliation efficiency is 8.2%.

[0143] Example 11 A method for exfoliating black phosphorus, comprising the following steps:

[0144] 1. Weigh a certain amount of blocky black phosphorus material, place it in a crucible and preliminarily grind it into powder with a particle size of about 700 μm, add a deoxygenated aqueous solution containing sodium dodecyl sulfate with a concentration of about 0.35 g / L as the solvent, and disperse it in an ultrasonic cleaner for 30 min to obtain a colloidal solution.

[0145] 2. Place the dispersed colloidal solution in liquid nitrogen (-196 °C) for rapid freezing.

[0146] 3. Take out the frozen solid material from the mold and put it into an ultrasonic device for preparation of exfoliation.

[0147] 4. Add a certain amount of solvent in a solid-liquid mixed state to the ultrasonic device, where the content of the solid phase is 50 wt%, and set the ultrasonic frequency to about 20 kHz, the power to about 500 W, and the total ultrasonic time to about 300 min. Set the cold trap temperature near 0 °C, and start the ultrasonic device and the cold trap device.

[0148] 5. Collect the colloidal solution after exfoliation and perform centrifugal separation. First, centrifuge at a speed of about 3000 rpm / min for about 30 min to remove the unexfoliated bulk materials; then centrifuge at a speed of about 120000 rpm / min for about 30 min. The lower-layer precipitate is the two-dimensional material with fewer layers. After washing the separated two-dimensional material several times with ethanol and deionized water, perform freeze-drying under -80 °C and vacuum conditions.

[0149] 6. Weigh after freeze-drying and calculate the exfoliation efficiency by comparing with the initial addition amount. The calculated exfoliation efficiency is 9.7%.

[0150] Example 12 A method for exfoliating black phosphorus, comprising the following steps:

[0151] 1. Weigh a certain amount of bulk black phosphorus material, place it in a crucible and preliminarily grind it into a powder with a particle size of about 700 μm, add it to a deoxygenated aqueous solution containing sodium dodecyl sulfate with a concentration of about 0.45 g / L as a solvent, and disperse it in an ultrasonic cleaner for 30 min to obtain a colloidal solution.

[0152] 2. Place the dispersed colloidal solution in liquid nitrogen (-196 °C) for rapid freezing.

[0153] 3. Take out the frozen solid material from the mold and put it into an ultrasonic device for exfoliation preparation.

[0154] 4. Add a certain amount of solvent in a solid-liquid mixed state to the ultrasonic device, where the content of the solid phase is 50 wt%, set the ultrasonic frequency to about 20 kHz, the power to about 500 W, and the total ultrasonic time to about 1000 min, set the cold trap temperature near 0 °C, and start the ultrasonic device and the cold trap device.

[0155] 5. Collect the colloidal solution after exfoliation and perform centrifugal separation. First, centrifuge at a speed of about 3000 rpm / min for about 30 min to remove the unexfoliated bulk materials; then centrifuge at a speed of about 120000 rpm / min for about 30 min. The lower-layer precipitate is the two-dimensional material with fewer layers. After washing the separated two-dimensional material several times with ethanol and deionized water, perform freeze-drying under -80 °C and vacuum conditions.

[0156] 6. Weigh after freeze-drying and calculate the exfoliation efficiency by comparing with the initial addition amount. The calculated exfoliation efficiency is 13.1%.

[0157] Example 13 A method for exfoliating black phosphorus, comprising the following steps:

[0158] 1. Weigh a certain amount of bulk black phosphorus material, place it in a crucible and preliminarily grind it into powder with a particle size of about 450 μm. Add it to a deoxygenated aqueous solution containing sodium dodecyl sulfate with a concentration of about 0.5 g / L as the solvent, and disperse it in an ultrasonic cleaner for 30 min to obtain a colloidal solution.

[0159] 2. Place the dispersed colloidal solution in liquid nitrogen (-196 °C) for rapid freezing.

[0160] 3. Take out the frozen solid material from the mold and put it into an ultrasonic device for exfoliation preparation.

[0161] 4. Add a certain amount of solvent in the solid-liquid mixed state to the ultrasonic device, where the content of the solid phase is 90 wt%, and set the ultrasonic frequency to about 40 kHz, the power to about 500 W, and the total ultrasonic time to about 600 min. Set the cold trap temperature near 0 °C, and start the ultrasonic device and the cold trap device.

[0162] 5. Collect the colloidal solution after exfoliation and perform centrifugal separation. First, centrifuge at a speed of about 3000 rpm for about 30 min to remove the unexfoliated bulk material; then centrifuge at a speed of about 120000 rpm for about 30 min. The lower layer precipitate is the two-dimensional material with fewer layers. After washing the separated two-dimensional material several times with ethanol and deionized water, perform freeze-drying at -80 °C and under vacuum conditions.

[0163] 6. Weigh after freeze-drying, compare with the initial addition amount to calculate the exfoliation efficiency, and the calculated exfoliation efficiency is 7.3%.

[0164] Example 14 A method for exfoliating black phosphorus, comprising the following steps:

[0165] 1. Weigh a certain amount of bulk black phosphorus material, place it in a crucible and preliminarily grind it into powder with a particle size of about 450 μm. Add it to a deoxygenated aqueous solution containing sodium dodecyl sulfate with a concentration of about 0.35 g / L as the solvent, and disperse it in an ultrasonic cleaner for 30 min to obtain a colloidal solution.

[0166] 2. Place the dispersed colloidal solution in liquid nitrogen (-196 °C) for rapid freezing.

[0167] 3. Take out the frozen solid material from the mold and put it into an ultrasonic device for exfoliation preparation.

[0168] 4. Add a certain amount of solvent in the solid-liquid mixed state to the ultrasonic device, where the content of the solid phase is 20 wt%, and set the ultrasonic frequency to about 60 kHz, the power to about 500 W, and the total ultrasonic time to about 600 min. Set the cold trap temperature near 0 °C, and start the ultrasonic device and the cold trap device.

[0169] 5. Collect the colloidal solution after exfoliation and perform centrifugal separation. First, centrifuge at a speed of about 3000 rpm / min for about 30 min to remove the unexfoliated bulk materials; then centrifuge at a speed of about 120000 rpm / min for about 30 min. The lower layer precipitate is the two-dimensional material with fewer layers. After washing the separated two-dimensional material several times with ethanol and deionized water, perform freeze-drying under -80°C and vacuum conditions.

[0170] 6. Weigh after freeze-drying and calculate the exfoliation efficiency by comparing with the initial addition amount. The calculated exfoliation efficiency is 6.7%.

[0171] Example 15 A method for exfoliating black phosphorus, comprising the following steps:

[0172] 1. Weigh a certain amount of bulk black phosphorus material, place it in a crucible and preliminarily grind it into a powder with a particle size of about 450 μm, add it to a deoxygenated aqueous solution containing sodium dodecyl sulfate with a concentration of about 0.45 g / L as a solvent, and disperse it in an ultrasonic cleaner for 30 min to obtain a colloidal solution.

[0173] 2. Place the dispersed colloidal solution in liquid nitrogen (-196°C) for rapid freezing.

[0174] 3. Take out the frozen solid material from the mold and put it into an ultrasonic device for exfoliation preparation.

[0175] 4. Add a certain amount of solvent in a solid-liquid mixed state to the ultrasonic device, where the content of the solid phase is 40 wt%, set the ultrasonic frequency to about 80 kHz, the power to about 500 W, and the total ultrasonic time to about 600 min, set the cold trap temperature near 0°C, and start the ultrasonic device and the cold trap device.

[0176] 5. Collect the colloidal solution after exfoliation and perform centrifugal separation. First, centrifuge at a speed of about 3000 rpm / min for about 30 min to remove the unexfoliated bulk materials; then centrifuge at a speed of about 120000 rpm / min for about 30 min. The lower layer precipitate is the two-dimensional material with fewer layers. After washing the separated two-dimensional material several times with ethanol and deionized water, perform freeze-drying under -80°C and vacuum conditions.

[0177] 6. Weigh after freeze-drying and calculate the exfoliation efficiency by comparing with the initial addition amount. The calculated exfoliation efficiency is 5.9%.

[0178] Example 16 A method for exfoliating black phosphorus, comprising the following steps:

[0179] 1. Weigh a certain amount of bulk black phosphorus material, place it in a crucible and preliminarily grind it into a powder with a particle size of about 450 μm. Add it to a deoxygenated aqueous solution containing sodium dodecyl sulfate with a concentration of about 0.55 g / L as the solvent, and disperse it in an ultrasonic cleaner for 30 min to obtain a colloidal solution.

[0180] 2. Place the dispersed colloidal solution in liquid nitrogen (-196 °C) for rapid freezing.

[0181] 3. Take out the frozen solid material from the mold and put it into an ultrasonic device for exfoliation preparation.

[0182] 4. Add a certain amount of solvent in a solid-liquid mixed state to the ultrasonic device, where the content of the solid phase is 50 wt%. Set the ultrasonic frequency to about 100 kHz, the power to about 500 W, and the total ultrasonic time to about 600 min. Set the cold trap temperature near 0 °C, and start the ultrasonic device and the cold trap device.

[0183] 5. Collect the colloidal solution after exfoliation and perform centrifugal separation. First, centrifuge at a speed of about 3000 rpm for about 30 min to remove the unexfoliated bulk material; then centrifuge at a speed of about 120000 rpm for about 30 min. The lower layer precipitate is the two-dimensional material with fewer layers. After washing the separated two-dimensional material several times with ethanol and deionized water, perform freeze-drying at -80 °C and under vacuum conditions.

[0184] 6. Weigh after freeze-drying, compare with the initial addition amount to calculate the exfoliation efficiency, and the calculated exfoliation efficiency is 7.2%.

[0185] Figure 11 This is the transmission electron microscope photo of the black phosphorus nanosheets exfoliated in this example. It can be seen that the change of ultrasonic frequency has a certain influence on the exfoliation effect, indicating that the change of ultrasonic frequency has an impact on the resonance comminution effect of the crystal. From the perspective of exfoliation efficiency, the ultrasonic frequency is also one of the factors affecting the exfoliation efficiency. It can be seen that when the ultrasonic frequency increases, the exfoliation efficiency decreases rapidly. Therefore, it can be judged that an appropriate ultrasonic frequency has a great influence on the comminution degree of the solid solvent. Therefore, 20 kHz with better effect is selected as the optimal ultrasonic frequency.

[0186] Example 17 A method for exfoliating black phosphorus, comprising the following steps:

[0187] 1. Weigh a certain amount of bulk black phosphorus material, place it in a crucible and preliminarily grind it into a powder with a particle size of about 250 μm. Add it to a deoxygenated aqueous solution containing cetyltrimethylammonium bromide with a concentration of about 0.5 g / L as the solvent, and disperse it in an ultrasonic cleaner for 30 min to obtain a colloidal solution.

[0188] 2. Place the dispersed colloidal solution in liquid nitrogen (-196 °C) for rapid freezing.

[0189] 3. Take out the frozen solid material from the mold and put it into an ultrasonic device for preparation of exfoliation.

[0190] 4. Add a certain amount of solvent in a solid-liquid mixed state to the ultrasonic device, where the content of the solid phase is 30%, set the ultrasonic frequency to about 20 kHz, the power to about 500 W, and the total ultrasonic time to about 600 min. Set the cold trap temperature at 0 °C, and start the ultrasonic device and the cold trap device nearby.

[0191] 5. Collect the colloidal solution after exfoliation and perform centrifugal separation. First, centrifuge at a speed of about 3000 rpm for about 30 min to remove the unexfoliated bulk materials; then centrifuge at a speed of about 120000 rpm for about 30 min. The lower layer precipitate is the two-dimensional material with fewer layers. After washing the separated two-dimensional material several times with ethanol and deionized water, perform freeze-drying under -80 °C and vacuum conditions.

[0192] 6. Weigh after freeze-drying, compare with the initial addition amount to calculate the exfoliation efficiency, and the calculated exfoliation efficiency is 10.9%.

[0193] Figure 12 This is the transmission electron microscope image of the black phosphorus nanosheets exfoliated in this example. It can be seen that the exfoliated nanosheets have a good lamellar structure, uniform lamellar size, and fewer layers. At the same time, it is found that although the surfactant has an impact on the exfoliation efficiency, it is not a decisive factor.

[0194] Example 18 A method for exfoliating metal phosphotrithioate (FePS 3 ) nanosheets, comprising the following steps:

[0195] 1. Weigh a certain amount of bulk FePS 3 material, place it in a crucible, preliminarily grind it to a powder with a particle size of about 750 μm, then add a deoxygenated water solvent containing sodium dodecyl sulfate with a concentration of 0.1 g / L as the solvent, and disperse it in an ultrasonic cleaner for 30 min to obtain a colloidal solution.

[0196] 2. Place the dispersed colloidal solution in liquid nitrogen (-196 °C) for rapid freezing.

[0197] 3. Take out the frozen solid material from the mold and put it into an ultrasonic device for preparation of exfoliation.

[0198] 4. Add a certain amount of solvent in a solid-liquid mixed state to the ultrasonic device, where the content of the solid phase is 10 wt%, and set the ultrasonic frequency to about 20 kHz, the power to about 500 W, and the total ultrasonic time to about 600 min. Set the cold trap temperature near 0 °C, and start the ultrasonic device and the cold trap device.

[0199] 5. Collect the colloidal solution after peeling and perform centrifugal separation. First, centrifuge at a speed of about 3000 rpm / min for about 30 min to remove the unpeeled blocky materials; then centrifuge at a speed of about 12000 rpm / min for about 30 min. The lower layer precipitate is the two-dimensional material with fewer layers. After washing the separated two-dimensional material several times with ethanol and deionized water, perform freeze-drying at -80 °C and under vacuum conditions.

[0200] 6. Weigh after freeze-drying, compare with the initial addition amount to calculate the peeling efficiency, and the calculated peeling efficiency is 45.4%.

[0201] Figure 13 For the FePS 3 nanosheets peeled in this example, it can be seen that the peeled FePS 3 nanosheets have a good lamellar structure, with uniform lamellar size and fewer layers.

[0202] Figure 14 For the FePS 3 XRD analysis picture of the nanosheets peeled in this example, it can be seen that the FePS 3 nanosheets obtained after peeling by the method of this example have a good crystal structure.

[0203] Example 19 A method for peeling transition metal carbonitride (MXene) nanosheets, comprising the following steps:

[0204] 1. Weigh a certain amount of bulk transition metal carbonitride material (MAX), place it in a crucible, and after preliminary grinding to a powder with a particle size of about 1000 μm, add a deoxygenated water solvent containing sodium dodecyl sulfate with a concentration of 0.05 g / L as the solvent, and disperse it in an ultrasonic cleaner for 30 min to obtain a colloidal solution.

[0205] 2. Place the dispersed colloidal solution in liquid nitrogen (-196 °C) for rapid freezing.

[0206] 3. Take out the frozen solid material from the mold and put it into the ultrasonic device for peeling preparation.

[0207] 4. Add a certain amount of solvent in a solid-liquid mixed state to the ultrasonic device, where the content of the solid phase is 15 wt%, and set the ultrasonic frequency to about 50 kHz, the power to about 500 W, and the total ultrasonic time to about 600 min. Set the cold trap temperature near 0 °C, and start the ultrasonic device and the cold trap device.

[0208] 5. Collect the colloidal solution after delamination and perform centrifugal separation. First, centrifuge at a speed of about 3000 rpm / min for about 30 min to remove the unpeeled bulk materials; then centrifuge at a speed of about 12000 rpm / min for about 30 min. The lower layer precipitate is the two-dimensional material with fewer layers. After washing the separated two-dimensional material several times with ethanol and deionized water, perform freeze-drying at -80 °C and under vacuum conditions.

[0209] 6. Weigh after freeze-drying, compare with the initial addition amount to calculate the delamination efficiency, and the calculated delamination efficiency is 58.3%.

[0210] Figure 15 This is the transmission electron microscopy image of the MXene nanosheets obtained by delamination in this example. It can be seen that the delaminated MXene nanosheets have a good lamellar structure, with uniform lamellar sizes and fewer layers.

[0211] Example 20 A method for delaminating hexagonal boron nitride nanosheets, comprising the following steps:

[0212] 1. Weigh a certain amount of bulk hexagonal boron nitride material, place it in a crucible, and after preliminary grinding to a powder with a particle size of about 50 μm, add a deoxygenated water solvent containing sodium dodecyl sulfate with a concentration of 0.01 g / L as the solvent, and disperse it in an ultrasonic cleaner for 30 min to obtain a colloidal solution.

[0213] 2. Place the dispersed colloidal solution in liquid nitrogen (-196 °C) for rapid freezing.

[0214] 3. Take out the frozen solid material from the mold and put it into the ultrasonic device for delamination preparation.

[0215] 4. Add a certain amount of solvent in a solid-liquid mixed state to the ultrasonic device, where the content of the solid phase is 70 wt%, and set the ultrasonic frequency to about 20 kHz, the power to about 500 W, and the total ultrasonic time to about 600 min. Set the cold trap temperature near 0 °C, and start the ultrasonic device and the cold trap device.

[0216] 5. Collect the colloidal solution after peeling and perform centrifugal separation. First, centrifuge at a speed of about 3000 rpm / min for about 30 min to remove the unpeeled bulk materials; then centrifuge at a speed of about 12000 rpm / min for about 30 min. The lower layer precipitate is the two-dimensional material with fewer layers. After washing the separated two-dimensional material several times with ethanol and deionized water, perform freeze-drying under -80 °C and vacuum conditions.

[0217] 6. Weigh after freeze-drying and calculate the peeling efficiency by comparing with the initial addition amount. The calculated peeling efficiency is 34.5%. Figure 16 It is the transmission electron microscope image of the BN nanosheets peeled in this example. It can be seen from the figure that the peeled BN nanosheets have a good lamellar structure, uniform lamellar size, and fewer layers.

[0218] Comparative Example 1 A method for peeling black phosphorus provided in this comparative example includes:

[0219] (1) Weigh a certain amount of bulk black phosphorus material, place it in a crucible, and after preliminary grinding to a powder with a particle size of about 1000 μm, add it to deoxygenated water and disperse it in an ultrasonic cleaner for about 30 min to obtain a colloidal solution.

[0220] (2) Place the dispersed colloidal solution in liquid nitrogen (-196 °C) for rapid freezing.

[0221] (3) After freezing, place the solid material in the refrigerator and freeze it for about 4 hours.

[0222] (4) After taking out the solid material from the refrigerator, let it thaw naturally. After thawing, ultrasonically disperse it in an ultrasonic cleaner for 5 min to obtain a colloidal solution.

[0223] (5) Repeat steps (2) to (4) 10 times.

[0224] (5) The same as step (5) of Example 1.

[0225] (6) Weigh after freeze-drying and calculate the peeling efficiency by comparing with the initial addition amount. The calculated peeling effect is almost negligible. Therefore, the ordinary freeze-thaw method that only relies on solidification expansion to apply longitudinal shear force has almost no effect in peeling black phosphorus nanosheets.

[0226] Comparative Example 2 A method for peeling black phosphorus provided in this comparative example includes:

[0227] (1) Weigh a certain amount of bulk black phosphorus material, place it in a crucible, and after preliminary grinding to a powder with a particle size of about 1000 μm, add it to N-methylpyrrolidone and disperse it in an ultrasonic cleaner for about 30 min to obtain a colloidal solution.

[0228] (2) Place the colloidal solution into an ultrasonic device, start the ultrasonic device and the cold trap device, set the ultrasonic frequency to about 20 kHz, the power to about 500 W, the time to about 360 min, and set the cold trap temperature to 10 °C.

[0229] (3) The same as step (5) of Example 1.

[0230] (4) Weigh after freeze-drying, calculate the exfoliation efficiency by comparing with the initial addition amount, and the calculated exfoliation efficiency is 9.5%.

[0231] Figure 17 It is a transmission electron microscope image of the black phosphorus nanosheets exfoliated in this comparative example. It can be seen that the exfoliated black phosphorus nanosheets have a good lamellar structure, but the degree of exfoliation is not high and the number of layers is relatively large.

[0232] Although the present invention has been described with reference to illustrative embodiments, those skilled in the art will understand that various other changes, omissions and / or additions can be made without departing from the spirit and scope of the present invention and elements of the embodiments can be replaced with substantial equivalents. Additionally, many modifications can be made to adapt a particular situation or material to the teachings of the present invention without departing from the scope of the present invention. Therefore, it is not intended that the present invention be limited to the particular embodiments disclosed for carrying out the present invention, but rather that the present invention will include all embodiments falling within the scope of the appended claims.

Claims

1. A method for exfoliating two-dimensional materials based on the synergistic effect of resonance crushing and crystal growth, characterized in that, it includes: After grinding the bulk material into particles with a particle size of 1-1000 μm, uniformly disperse it in a solvent to form a dispersion; Freeze the dispersion to form a solid material; Place the solid material in a low-temperature environment, the temperature of the low-temperature environment is maintained at or below the freezing point of the solvent, and ultrasonically treat the solid material. The frequency of the ultrasonic treatment is 20~100 kHz and the power is 100~2000 W, so that the crystallized solvent in the solid material resonates, causing at least part of the crystallized solvent to break, and at the same time allowing the liquid solvent in the surrounding environment to enter the broken gaps and continue to solidify and crystallize in the low-temperature environment. As the crystals between the material layers continue to break and grow, the growth of solvent crystals between the two-dimensional material layers is realized, and finally the two-dimensional material is exfoliated from the bulk material; wherein, the surface tension of the solvent matches the surface energy of the two-dimensional material, and the freezing point of the solvent is -30°C to 20°C; The material of the bulk material includes one or a combination of black phosphorus, graphite, transition metal dichalcogenides, boron nitride, transition metal carbonitrides, metal phosphotrisulfides, etc., and the two-dimensional material includes one or a combination of black phosphorus nanosheets, graphene, transition metal dichalcogenide nanosheets, boron nitride nanosheets, transition metal carbonitride nanosheets, metal phosphotrisulfide nanosheets, etc.

2. The method for exfoliating two-dimensional materials according to claim 1, characterized in that: The solvent includes any one or a combination of water and organic solvents.

3. The method for exfoliating two-dimensional materials according to claim 2, characterized in that: The organic solvent includes organic protonic solvents.

4. The method for exfoliating two-dimensional materials according to claim 1, characterized in that it further includes: Adding a surfactant to the solvent to adjust the surface tension of the solvent.

5. The method for exfoliating two-dimensional materials according to claim 1, characterized in that: The time of the ultrasonic treatment is 1~1000 min.

6. The method for exfoliating two-dimensional materials according to claim 1, characterized in that: The content of the solid phase in the dispersion is 0.1~99.9 Wt%.

7. The method for exfoliating two-dimensional materials according to claim 1, characterized in that, specifically includes: After completing the ultrasonic treatment, thaw and uniformly disperse the solid material, and then separate the two-dimensional material therein.

8. The method for exfoliating two-dimensional materials according to claim 7, characterized in that, specifically includes: Thaw the solid material by ultrasonic action, and then centrifuge to separate the two-dimensional material therein, and the centrifugation speed used is 1000~20000 rpm / min.

9. The method for exfoliating two-dimensional materials according to any one of claims 7-8, characterized in that, it further includes: Cleaning and drying the separated two-dimensional material.

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