Preparation method of graphene

Abstract

The invention discloses a preparation method of graphene, and belongs to the field of graphite material production. The invention relates to a graphene preparation method, which comprises: S1, dispersing an oxidizing agent in water, adding graphite powder, uniformly dispersing, adding a bubble stabilizer, and uniformly dispersing to obtain a pre-dispersion liquid; s2, stirring and carrying out ultrasonic oscillation on the pre-dispersion liquid to generate bubbles, and carrying out oxidation stripping on the graphite; s3, finishing ultrasonic oscillation to obtain a graphene dispersion liquid, neutralizing the graphene dispersion liquid, filtering, cleaning and drying to obtain graphene. The method has the advantages that the graphene with uniform size is obtained, and the conductive performance of the graphene is exerted.

Description

Technical Field

[0001] This application relates to the field of graphite material production, and particularly to a method for preparing graphene. Background Art

[0002] Graphite is an allotrope of carbon. The graphite lattice has a hexagonal structure. In flake graphite, atoms are bonded by covalent bonds. After graphite is exfoliated into graphene flakes with micro-nano scale sizes by physical or chemical methods, it has the characteristics of being ultra-thin, ultra-light, ultra-high strength, excellent thermal conductivity and electrical conductivity, and can be used for the preparation of batteries, supercapacitors, electronic components, solar cells and various high-performance composite materials.

[0003] Existing graphene exfoliation technologies, such as the mechanical exfoliation method of peeling graphene from the surface of graphite using tape, have the disadvantage of low yield and difficulty in achieving large-scale preparation. Another example is using the kinetic energy of ultrasonic oscillation to break the graphite sheet layers, but the graphene sheets obtained in this way are fragmented and uneven, affecting the performance such as the electrical conductivity of graphene. Summary of the Invention

[0004] In order to obtain graphene with uniform size and give full play to the electrical conductivity of graphene, this application provides a method for preparing graphene.

[0005] The method for preparing graphene provided by this application adopts the following technical solutions: A method for preparing graphene, comprising the following steps: S1. Disperse an oxidant in water, add graphite powder, and after uniform dispersion, add a bubble stabilizer, and obtain a pre-dispersion liquid after uniform dispersion; S2. Stir and ultrasonically oscillate the pre-dispersion liquid to generate bubbles and oxidatively exfoliate the graphite; S3. End the ultrasonic oscillation, obtain a graphene dispersion liquid, neutralize the graphene dispersion liquid, filter, wash, and dry to obtain graphene.

[0006] By adopting the above technical solutions, ultrasonic oscillation is used to generate bubbles by cavitation inside the graphite powder, and during the ultrasonic oscillation process, the oxidant is introduced into the bubbles inside the graphite powder. The oxidant penetrates into the interlayers of the graphite powder along with the bubbles. The bubble stabilizer can maintain the stability of the cavitation bubbles inside the graphite powder and control the size and density of the bubbles by adjusting the surface tension. The oxidant causes an oxidation reaction between the interlayers of the graphite powder inside the bubbles, breaking the covalent bonds between the interlayers of the graphite powder and the intermolecular external hydrogen bonds between the graphite powder and water molecules, thereby oxidatively exfoliating the graphite inside the bubbles to obtain graphene sheets with the size of the bubbles. The graphene sheets have uniform size and the hexagonal structure of carbon atoms is neat. On this plane, the outer electrons of carbon atoms can transition between different electron energy levels to form an electron flow, having excellent electrical conductivity.

[0007] Optionally, in step S2, the surface tension of the pre-dispersion liquid is controlled to be 45 - 55 mN / m.

[0008] By adopting the above technical solution, controlling the surface tension of the pre-dispersion liquid enables the control of the size and density of the bubbles in the pre-dispersion liquid, which not only helps the oxidant to introduce bubbles into the graphite powder body, but also enables the bubbles to be maintained, thus contributing to the occurrence of oxidation reactions between the graphite layers, breaking the covalent bonds between the graphite layers, and obtaining graphene sheets with uniform sizes.

[0009] Optionally, the frequency of the ultrasonic oscillation is 20 - 80 KHz, and the power is 1000 w - 3000 w.

[0010] By adopting the above technical solution, the size and stability of the bubbles generated by the ultrasonic cavitation effect can be effectively controlled.

[0011] Preferably, the frequency of the ultrasonic oscillation is 40 - 50 KHz.

[0012] By adopting the above technical solution, the ultrasonic frequency within the above range helps to optimize the bubble generation process and ensure the uniform exfoliation of graphite by the oxidant inside the bubbles.

[0013] Optionally, in step S2, the stirring rate is 200 - 350 r / min.

[0014] By adopting the above technical solution, the combination of stirring and ultrasonic oscillation generates bubbles with sufficient density, controls the stirring rate to control the bubble size, and maintains the stability of the bubbles.

[0015] Optionally, the treatment time of the ultrasonic oscillation is 18 - 36 h.

[0016] By adopting the above technical solution, the oxidation reaction between the graphite layers proceeds orderly, improving the size uniformity of the exfoliated graphene sheets.

[0017] Optionally, the treatment time of the ultrasonic oscillation is 28 - 36 h.

[0018] Optionally, the diameter of the generated bubbles is controlled within 100 μm - 600 nm.

[0019] By adopting the above technical solution, under the control of the above oxidant, bubble stabilizer, ultrasonic oscillation frequency and stirring rate, the bubble diameter is maintained within the range of 100 μm - 600 nm, which can effectively improve the size uniformity of graphene. The bubble size within this range is moderate, which helps the oxidant to be evenly and stably distributed inside the graphite powder body, thereby realizing more precise and efficient exfoliation of the graphite powder. Finally, the obtained graphene sheet layers have consistent sizes and are neatly arranged, which is beneficial to improving the performance such as the electrical conductivity of graphene.

[0020] Optionally, the mass ratio of water to the oxidant is 1:(3.5 - 4.5), the mass ratio of the graphite powder to the oxidant is 1:(3.5 - 4.5), and the mass ratio of the bubble stabilizer to the oxidant is (0.5 - 1.5):(30 - 50).

[0021] By adopting the above technical solution, balancing the oxidant concentration, the oxidant content, and the bubble stabilizer helps to enhance the stability of the bubbles generated during the ultrasonic oscillation and the consistency of their sizes, thereby ensuring a more uniform graphene exfoliation process and ultimately obtaining high-quality graphene with uniform size and stable properties.

[0022] Optionally, the oxidant includes an oxidizing substance with a redox electrode potential ≥ 1.5 V.

[0023] By adopting the above technical solution, the covalent bonds between the layers of the graphite powder and the intermolecular hydrogen bonds formed between the graphite powder and the oxidant are broken, and graphene sheets are exfoliated.

[0024] Optionally, the oxidizing substance includes one or more of concentrated sulfuric acid, concentrated nitric acid, potassium permanganate, perchloric acid, potassium dichromate, and hydrogen peroxide.

[0025] Preferably, the oxidizing substance includes one or more of concentrated sulfuric acid, concentrated nitric acid, and hydrogen peroxide.

[0026] Optionally, the bubble stabilizer includes one or more of alkylolamide, alkylamine oxide, Tween, and polyether-modified silicone.

[0027] Preferably, the surfactant includes one or more of coconut diethanolamide, lauric diethanolamide, cetyl hydroxyethyl ammonium oxide, octadecyl hydroxyethyl ammonium oxide, Tween 20, Tween 21, and polyether-modified silicone.

[0028] Preferably, the bubble stabilizer includes a combination of coconut diethanolamide and polyether-modified silicone, or the bubble stabilizer includes a combination of Tween 21 and polyether-modified silicone.

[0029] By adopting the above technical solution and using the above combination of bubble stabilizers, it helps to introduce the oxidant into the bubbles and promote the penetration of the oxidant into the layers of the graphite powder, accelerating the exfoliation of the graphene sheets, thereby shortening the ultrasonic oscillation treatment time. For example, the original treatment time of 32 h can be compressed to 24 h, saving the preparation cost.

[0030] Optionally, the size of the graphite powder is 2000 - 10000 mesh.

[0031] Optionally, in step S3, the graphene dispersion is neutralized using one or two of an alkaline substance and a reducing substance.

[0032] By adopting the above technical solution, after the stripping is completed, the oxidant in the pre-dispersion liquid is neutralized, and according to the needs of the product, the graphene oxide obtained after oxidative stripping can be reduced to obtain graphene.

[0033] Optionally, the alkaline substance includes one or more of water-soluble hydroxides and ammonia.

[0034] Optionally, the reducing substance includes one or more of hydrazine hydrate, sodium borohydride, and glucose.

[0035] In summary, the present application has the following beneficial effects: 1. In the present application, ultrasonic oscillation is used to generate cavitation bubbles inside the graphite powder, and during the ultrasonic oscillation process, the oxidant is introduced into the bubbles inside the graphite powder. The oxidant penetrates into the interlayers of the graphite powder along with the bubbles. The bubble stabilizer can maintain the stability of the cavitation bubbles inside the graphite powder and control the size and density of the bubbles by adjusting the surface tension. The oxidant in the bubbles causes an oxidation reaction between the interlayers of the graphite powder, breaking the covalent bonds between the interlayers of the graphite powder and the intermolecular external hydrogen bonds formed between the graphite powder and the oxidant aqueous solution, thereby oxidatively stripping the graphite inside the bubbles to obtain graphene sheets of bubble size. The graphene sheets are uniformly arranged in size, forming a neat structure of carbon atom hexagonal planes. On this plane, the outer electrons of the graphene form an electron flow that transitions between different electron energy levels, generating a visible spectrum. The formation of the electron flow confirms the excellent electrical conductivity of graphene.

[0036] 2. By controlling the surface tension of the pre-dispersion liquid to control the size and density of the bubbles in the pre-dispersion liquid, it not only helps the oxidant to be introduced into the bubbles inside the graphite powder, but also enables the bubbles to be maintained, thus contributing to the occurrence of an oxidation reaction between the interlayers of the graphite, breaking the covalent bonds between the graphite layers, and obtaining graphene sheets with uniform size. Description of the Drawings

[0037] Figure 1 is the scanning electron microscope image of the graphene sheets prepared in Example 1.

[0038] Figure 2 is the scanning electron microscope image of the graphene sheets prepared in Example 2.

[0039] Figure 3 is the scanning electron microscope image of the graphene sheets prepared in Example 3.

[0040] Figure 4 is the scanning electron microscope image of the graphene sheets prepared in Example 4.

[0041] Figure 5 is the scanning electron microscope image of the graphene sheets prepared in Comparative Example 1.

[0042] Figure 6It is a scanning electron microscope image of the graphene sheets prepared in Comparative Example 2. Detailed implementation manners

[0043] For the existing graphene exfoliation technology, taking the method of ultrasonic vibration exfoliation as an example, ultrasonic waves with different frequencies generate high-frequency vibrations on the graphite slurry to obtain graphene. This type of method generates bubbles through ultrasonic vibration, and uses the high pressure generated when the bubbles rupture and expand to impact the graphite to obtain graphene.

[0044] In actual verification, it is found that the graphene obtained by the above method has an uneven structure because the high-pressure kinetic energy generated by the bubble rupture will damage the graphite structure, and the graphene breaks from the graphite surface rather than exfoliates. Coupled with the stable covalent bonds between the graphite layers, it is difficult to break the covalent bonds through ultrasonic vibration. What can ultimately be obtained are graphene fragments with different sizes, and the arrangement and size are difficult to meet the requirements of the neat graphene with a hexagonal structure of carbon atoms, and it is even more difficult to exert the advantage of graphene's conductivity.

[0045] This application uses ultrasonic vibration to cavitate and generate bubbles inside the graphite powder, and maintains the stable size of the bubbles. An oxidant is introduced into the bubbles to break the covalent bonds between the graphite powder layers under the oxidation reaction, and to break the intermolecular hydrogen bonds formed between graphene and water molecules during the infiltration process, realizing the exfoliation of graphene to form graphene with uniform bubble size and good performance in terms of conductivity and other aspects.

[0046] The following further elaborates on this application in conjunction with the attached Figure 1-6 Make a further detailed description of this application.

[0047] Example 1 A method for preparing graphene, comprising the following steps: S1. Disperse the oxidant in water, stir evenly, add the graphite powder, and after stirring and dispersing evenly, add the bubble stabilizer, and stir and disperse evenly to obtain a pre-dispersion liquid.

[0048] Among them, the mass ratio of deionized water to the oxidant is 1:3.5, the mass ratio of the graphite powder to the oxidant is 1:4.5, and the mass ratio of the bubble stabilizer to the oxidant is 0.5:30.

[0049] Specifically, the average size of the graphite powder is 2000 mesh, the oxidant is concentrated sulfuric acid with a mass concentration of 98%, and the bubble stabilizer is coconut diethanolamide.

[0050] S2. Pour the pre-dispersion liquid into an ultrasonic oscillator, stir while performing ultrasonic oscillation. The frequency of ultrasonic oscillation is 20 KHz, the power is 1000 w, the stirring rate is 350 r / min, to generate bubbles. The diameter of the generated bubbles is controlled within 100 μm - 600 nm. The oxidant oxidizes and exfoliates the graphite in the bubbles. The ultrasonic oscillation treatment time is 36 h. During this period, a surface tension tester is used to measure the surface tension of the pre-dispersion liquid. In this step, the average surface tension of the pre-dispersion liquid is 45 mN / m.

[0051] S3. End the ultrasonic oscillation to obtain a graphene dispersion liquid, add an alkaline substance to neutralize the graphene dispersion liquid to pH 7, perform centrifugal separation, filtration, washing, and vacuum drying to obtain graphene.

[0052] Specifically, the alkaline substance is sodium hydroxide.

[0053] The scanning electron microscope image of the obtained graphene is as Figure 1 shown, and the place pointed by the arrow is the visible spectrum.

[0054] Example 2 A method for preparing graphene, comprising the following steps: S1. Disperse the oxidant in water, stir evenly, add graphite powder, and after stirring and dispersing evenly, add a bubble stabilizer, and stir and disperse evenly to obtain a pre-dispersion liquid.

[0055] Among them, the mass ratio of deionized water to the oxidant is 1:4.5, the mass ratio of the graphite powder to the oxidant is 1:3.5, and the mass ratio of the bubble stabilizer to the oxidant is 1.5:50.

[0056] Specifically, the average size of the graphite powder is 10000 mesh, the oxidant is a 30% hydrogen peroxide solution by mass concentration, and the bubble stabilizer is Tween 21.

[0057] S2. Pour the pre-dispersion liquid into an ultrasonic oscillator, stir while performing ultrasonic oscillation. The frequency of ultrasonic oscillation is 80 KHz, the power is 3000 w, the stirring rate is 200 r / min, to generate bubbles. The diameter of the generated bubbles is controlled within 100 μm - 600 nm. The oxidant oxidizes and exfoliates the graphite in the bubbles. The ultrasonic oscillation treatment time is 28 h. During this period, a surface tension tester is used to measure the surface tension of the pre-dispersion liquid. In this step, the average surface tension of the pre-dispersion liquid is 55 mN / m.

[0058] S3. End the ultrasonic oscillation to obtain a graphene dispersion liquid, add an alkaline substance to neutralize the graphene dispersion liquid to pH 7, perform centrifugal separation, filtration, washing, and vacuum drying to obtain graphene.

[0059] Specifically, the alkaline substance is sodium hydroxide.

[0060] The SEM images of the obtained graphene are as Figure 2 shown, where the area pointed by the arrow is the visible spectrum.

[0061] Example 3 A method for preparing graphene, comprising the following steps: S1. Disperse the oxidant in water, stir evenly, add graphite powder, and after stirring and dispersing evenly, add a bubble stabilizer, and stir and disperse evenly to obtain a pre-dispersed liquid.

[0062] Wherein, the mass ratio of deionized water to the oxidant is 1:4, the mass ratio of the graphite powder to the oxidant is 1:4, and the mass ratio of the bubble stabilizer to the oxidant is 1:35.

[0063] Specifically, the average size of the graphite powder is 5000 mesh, the oxidant is concentrated nitric acid with a mass concentration of 68%, and the bubble stabilizer is coconut diethanolamide.

[0064] S2. Pour the pre-dispersed liquid into an ultrasonic oscillator, stir while performing ultrasonic oscillation, the frequency of the ultrasonic oscillation is 45KHz, the power is 2000w, the stirring rate is 300r / min, generate bubbles, and control the diameter of the generated bubbles to be 100μm - 600nm. The oxidant oxidizes and exfoliates the graphite in the bubbles. The ultrasonic oscillation treatment time is 32h. During this period, a surface tension tester is used to measure the surface tension of the pre-dispersed liquid. In this step, the average surface tension of the pre-dispersed liquid is 48mN / m.

[0065] S3. End the ultrasonic oscillation to obtain a graphene dispersion liquid, add an alkaline substance to neutralize the graphene dispersion liquid to pH 7, perform centrifugal separation, filtration, washing, and vacuum drying to obtain graphene.

[0066] Specifically, the alkaline substance is ammonia water.

[0067] The SEM images of the obtained graphene are as Figure 3 shown.

[0068] Example 4 A method for preparing graphene, the difference between this example and Example 1 lies in the S3 step.

[0069] S3. End the ultrasonic oscillation to obtain a graphene dispersion liquid, add an alkaline substance to neutralize the graphene dispersion liquid to pH 7, then add a reducing substance, continuously stir for 0.5h, perform centrifugal separation, filtration, washing, and vacuum drying to obtain graphene.

[0070] Specifically, the alkaline substance is sodium hydroxide; the reducing substance is hydrazine hydrate, and the mass ratio of the graphite powder to hydrazine hydrate is 1:0.5.

[0071] The scanning electron microscope image of the obtained graphene is as Figure 4 shown.

[0072] Comparative Example 1 A method for preparing graphene, comprising the following steps: S1. Disperse the graphite powder in water and stir evenly. After stirring and dispersing evenly, add a bubble stabilizer, and obtain a pre-dispersed liquid after stirring and dispersing evenly.

[0073] Among them, the mass ratio of deionized water to the graphite powder is 1:1, and the mass ratio of the graphite powder to the bubble stabilizer is 10:1.

[0074] Specifically, the average size of the graphite powder is 2000 mesh, and the bubble stabilizer is coconut diethanolamide.

[0075] S2. Pour the pre-dispersed liquid into an ultrasonic oscillator, stir while performing ultrasonic oscillation. The frequency of ultrasonic oscillation is 20 KHz, the power is 1000 w, the stirring rate is 350 r / min, generate bubbles, and control the diameter of the generated bubbles to be 100 μm - 600 nm. The ultrasonic oscillation treatment time is 36 h. During this period, use a surface tension tester to measure the surface tension of the pre-dispersed liquid. In this step, the average surface tension of the pre-dispersed liquid is 45 mN / m.

[0076] S3. End the ultrasonic oscillation, obtain a graphene dispersion liquid, perform centrifugal separation, filtration, cleaning, and vacuum drying to obtain graphene.

[0077] The scanning electron microscope image of the obtained graphene is as Figure 5 shown.

[0078] Comparative Example 2 A method for preparing graphene, comprising the following steps: S1. Disperse the oxidant in water, stir evenly, add the graphite powder, and obtain a pre-dispersed liquid after stirring and dispersing evenly.

[0079] Among them, the mass ratio of deionized water to the oxidant is 1:4, and the mass ratio of the graphite powder to the oxidant is 1:4.

[0080] Specifically, the average size of the graphite powder is 2000 mesh, and the oxidant is concentrated sulfuric acid with a mass concentration of 98%.

[0081] S2. Pour the pre-dispersed liquid into an ultrasonic oscillator, stir while performing ultrasonic oscillation. The frequency of ultrasonic oscillation is 20 KHz, the power is 1000 w, the stirring rate is 350 r / min, and the ultrasonic oscillation treatment time is 36 h.

[0082] S3. End the ultrasonic oscillation to obtain a graphene dispersion. Add an alkaline substance to neutralize the graphene dispersion to pH 7, followed by centrifugation, filtration, washing, and vacuum drying to obtain graphene.

[0083] Specifically, the alkaline substance is sodium hydroxide.

[0084] The scanning electron microscope image of the obtained graphene is as Figure 6 shown.

[0085] Preparation results The scanning electron microscope images of the graphene flakes prepared in Examples 1-4 and Comparative Examples 1-2 are shown in Figures 1-6.

[0086] As Figure 1 - Figure 4 shown, the graphene flakes prepared in Examples 1-4 have uniform sizes, and the carbon atom structures of the graphene flakes are neat. Moreover, a visible spectrum can be seen under the electron microscope electric field. The visible spectrum is formed by the transition of electron flows at different energy levels, further confirming the uniformity of the sizes of the graphene flakes prepared in Examples 1-4.

[0087] As Figure 5 and Figure 6 shown, since the graphene flakes in Comparative Example 1 were not oxidized and exfoliated by an oxidant, and the graphene flakes in Comparative Example 2 did not form stable bubbles during the preparation process, the sizes of the graphene flakes seen under the electron microscope electric field are uneven, resulting in the failure to achieve electron transition and thus the inability to generate a visible spectrum.

[0088] Application results Conductivity test: Disperse the graphene flakes prepared in Examples 1-4 and Comparative Examples 1-2 in the same water-based resin, stir and disperse evenly to prepare conductive paste samples. The addition amount of graphene flakes in the conductive paste is 9 g, the addition amount of the water-based resin is 50 g, and the solid content of the water-based resin is 36%.

[0089] Coat the conductive paste samples on a tempered glass plate with a 25 coating rod, bake and cure in an oven at 120 °C for 30 min, and measure the surface resistance after cooling. The results are shown in Table 1.

[0090] Table 1 Combined with Table 1, it can be seen that the conductive pastes prepared using the graphene flakes of Examples 1-4 have good conductivity.

[0091] This specific implementation manner is only an interpretation of the present application and does not limit the present application. After reading this specification, those skilled in the art can make modifications without creative contributions to this specific implementation manner as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A method for preparing graphene, characterized in that: The following steps are involved: S1. Dispersing the oxidant in water, adding graphite powder, adding a bubble stabilizer after uniform dispersion, and obtaining a pre-dispersion liquid after uniform dispersion; S2. Stirring and ultrasonically vibrating the pre-dispersed liquid to generate bubbles and oxidatively exfoliate the graphite; S3. End the ultrasonic oscillation to obtain a graphene dispersion, neutralize the graphene dispersion, filter, wash, and dry to obtain graphene.

2. A method for preparing graphene according to claim 1, characterized in that: In step S2, the surface tension of the pre-dispersion liquid is controlled to be 45-55 mN / m.

3. A method for preparing graphene according to claim 1, characterized in that: In step S2, the frequency of ultrasonic oscillation is 20~80KHz, and the power is 1000w-3000w.

4. The method for preparing graphene according to claim 1, characterized in that: In step S2, the stirring rate is 200~350r / min.

5. The method for preparing graphene according to claim 1, characterized in that: The diameter of the bubbles produced is controlled between 100μm and 600nm.

6. The method for preparing graphene according to claim 1, characterized in that: The mass ratio of water to the oxidant is 1:(3.5-4.5), the mass ratio of the graphite powder to the oxidant is 1:(3.5-4.5), and the mass ratio of the bubble stabilizer to the oxidant is (0.5-1.5):(30-50).

7. A method for preparing graphene according to any one of claims 1 to 6, characterized in that: The oxidant includes an oxidizing substance with a redox electrode potential of ≥1.5 volts.

8. A method for preparing graphene according to claim 7, characterized in that: The oxidizing substance includes one or more of concentrated sulfuric acid, concentrated nitric acid, potassium permanganate, perchloric acid, potassium dichromate and hydrogen peroxide.

9. A method for preparing graphene according to any one of claims 1 to 6, characterized in that: The bubble stabilizer includes one or more of alkyl alcohol amide, alkyl amine oxide, Tween and polyether modified silicone.

10. The method for preparing graphene according to claim 1, characterized in that: In step S3, the graphene dispersion is neutralized by using one or both of an alkaline substance and a reducing substance.

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