A method for preparing graphene

Abstract

The application discloses a preparation method of graphene and belongs to the field of graphite material production. The preparation method of graphene comprises the following steps: S1, dispersing an oxidant in water, adding graphite powder, adding a bubble stabilizer after uniform dispersion, and obtaining a pre-dispersed solution after uniform dispersion; S2, stirring and ultrasonic oscillation of the pre-dispersed solution to generate bubbles and oxidize and peel the graphite; S3, ending the ultrasonic oscillation to obtain a graphene dispersion solution, neutralizing the graphene dispersion solution, filtering, cleaning, and drying to obtain graphene. The application has the effect of obtaining graphene with uniform size and exerting the conductive performance of the graphene.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of graphite material production, in particular to a preparation method of graphene. BACKGROUND

[0002] Graphite is a carbon allotrope, and the graphite crystal lattice is a hexagonal structure. The atoms in the flaky graphite are combined by covalent bonds. After the graphite is exfoliated into graphene sheets with micro-nano size by physical or chemical methods, the graphene has the properties of ultra-thinness, ultra-lightness, 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] The existing graphene exfoliation technologies have the following disadvantages. For example, the mechanical exfoliation method using adhesive tape to exfoliate graphene from the surface of graphite has the disadvantage of low yield and is difficult to realize macro-preparation. For another example, the kinetic energy of ultrasonic oscillation is used to break the graphite layers, but the graphene sheets prepared by this method are fragmented and non-uniform, which affects the electrical conductivity and other properties of the graphene. SUMMARY

[0004] In order to obtain graphene with uniform size and to exert the electrical conductivity of graphene, the present application provides a preparation method of graphene.

[0005] The preparation method of graphene provided by the present application adopts the following technical scheme:

[0006] The preparation method of graphene comprises the following steps:

[0007] S1. Disperse an oxidizing agent in water, add graphite powder, and then add a bubble stabilizer after uniform dispersion, to obtain a pre-dispersion liquid;

[0008] S2. Stir and ultrasonically oscillate the pre-dispersion liquid to generate bubbles and oxidize and exfoliate the graphite;

[0009] S3. Stop the ultrasonic oscillation, obtain a graphene dispersion liquid, neutralize the graphene dispersion liquid, filter and wash, and dry to obtain graphene.

[0010] By adopting the technical scheme, the cavitation bubbles are generated in the graphite powder by ultrasonic oscillation, and the oxidizing agent is introduced into the cavitation bubbles in the graphite powder during the ultrasonic oscillation, the oxidizing agent penetrates into the interlayer of the graphite powder along with the cavitation bubbles, the cavitation bubble stabilizer can maintain the stability of the cavitation bubbles in the graphite powder, and the size and density of the bubbles are controlled by adjusting the surface tension, the oxidizing agent in the bubbles causes oxidation reaction in the interlayer of the graphite powder, breaks the covalent bond in the interlayer of the graphite powder and the molecular outer hydrogen bond between the graphite powder and the water molecules, so that the graphite is oxidized and exfoliated in the bubbles to obtain the graphene sheets with the size of the bubbles. The graphene sheets are uniform in size, and the carbon atom hexagonal structure is neat. On the plane, the carbon atom outer electron can jump on different electron energy levels to form an electron flow, and the graphene sheets have excellent electrical conductivity.

[0011] Optionally, in the S2 step, the surface tension of the pre-dispersion liquid is controlled to be 45-55 mN / m.

[0012] By adopting the technical scheme, the surface tension of the pre-dispersion liquid is controlled to control the size and density of the bubbles in the pre-dispersion liquid, which not only helps the oxidizing agent to be introduced into the bubbles in the graphite powder, but also helps the bubbles to be maintained, so as to help the oxidation reaction to occur in the interlayer of the graphite, break the covalent bond in the interlayer of the graphite, and obtain the graphene sheets with uniform size.

[0013] Optionally, the frequency of the ultrasonic oscillation is 20-80 KHz, and the power is 1000 w-3000 w.

[0014] By adopting the technical scheme, the size of the bubbles generated by the ultrasonic cavitation effect can be effectively controlled.

[0015] Preferably, the frequency of the ultrasonic oscillation is 40-50 KHz.

[0016] By adopting the technical scheme, the ultrasonic frequency in the above range helps to optimize the bubble generation process and ensure that the oxidizing agent in the bubbles uniformly exfoliates the graphite.

[0017] Optionally, in the S2 step, the stirring rate is 200-350 r / min.

[0018] By adopting the technical scheme, the stirring and the ultrasonic oscillation are combined to generate bubbles with sufficient density, the stirring rate is controlled to control the size of the bubbles, and the stability of the bubbles is maintained.

[0019] Optionally, the processing time of the ultrasonic oscillation is 18-36 h.

[0020] By adopting the technical scheme, the oxidation reaction in the interlayer of the graphite is orderly carried out, and the size uniformity of the exfoliated graphene sheets is improved.

[0021] Optionally, the processing time of ultrasonic oscillation is 28-36 hours.

[0022] Optionally, the generated bubble diameter is controlled in the range of 100 μm-600 nm.

[0023] By adopting the above technical solutions, under the control of the oxidant, the bubble stabilizer, the ultrasonic oscillation frequency and the stirring rate, the bubble diameter is maintained in the range of 100 μm-600 nm, which can effectively improve the size uniformity of graphene. The bubble size in this range is moderate, which helps the oxidant to be uniformly and stably distributed inside the graphite powder, thereby realizing more accurate and efficient peeling of the graphite powder, and finally obtaining graphene sheets with consistent size and neat arrangement, which is beneficial to improving the conductivity and other performance of graphene.

[0024] Optionally, the mass ratio of water to oxidant is 1:(3.5-4.5), the mass ratio of graphite powder to oxidant is 1:(3.5-4.5), and the mass ratio of bubble stabilizer to oxidant is (0.5-1.5):(30-50).

[0025] By adopting the above technical solutions, the balance of oxidant concentration, oxidant content and bubble stabilizer helps to enhance the stability of the bubbles generated during ultrasonic oscillation and the consistency of their size, thereby ensuring that the graphene peeling process is more uniform, and finally obtaining high-quality graphene with uniform size and stable properties.

[0026] Optionally, the oxidant includes an oxidizing substance with a redox electrode potential ≥1.5 volts.

[0027] By adopting the above technical solutions, the covalent bond between the graphite powder layers and the intermolecular hydrogen bond between the graphite powder and the oxidant are broken, and graphene sheets are obtained by peeling.

[0028] Optionally, the oxidizing substance includes one or more of concentrated sulfuric acid, concentrated nitric acid, potassium permanganate, perchloric acid, potassium dichromate and hydrogen peroxide.

[0029] Preferably, the oxidizing substance includes one or more of concentrated sulfuric acid, concentrated nitric acid and hydrogen peroxide.

[0030] Optionally, the bubble stabilizer includes one or more of alkyl alcohol amide, alkyl amine oxide, Tween and polyether modified silicone.

[0031] Preferably, the bubble stabilizer includes one or more of cocodihydroxyethylamide, lauric acid diethanolamide, hexadecyl hydroxyethyl ammonium oxide, octadecyl hydroxyethyl ammonium oxide, Tween 20, Tween 21 and polyether modified silicone.

[0032] Preferably, the gas bubble stabilizer comprises oleic acid diethanolamide in combination with a polyether-modified silicone, or the gas bubble stabilizer comprises Tween 21 in combination with a polyether-modified silicone.

[0033] By using the above technical solution, the use of the above gas bubble stabilizer combination helps to introduce the oxidizing agent into the gas bubbles and promotes the penetration of the oxidizing agent into the interlayer of the graphite powder, accelerating the exfoliation of the graphene sheets, thereby shortening the time of ultrasonic oscillation treatment, for example, the original treatment time of 32h can be compressed to 24h, saving the preparation cost.

[0034] Optionally, the size of the graphite powder is 2000-10000 mesh.

[0035] Optionally, in the S3 step, the graphene dispersion liquid is neutralized by one or both of the alkaline substance and the reducing substance.

[0036] By using the above technical solution, the oxidizing agent in the pre-dispersion liquid is neutralized after exfoliation, and the graphene obtained by the oxidation and exfoliation can be reduced according to the product requirements.

[0037] Optionally, the alkaline substance includes one or more of water-soluble hydroxide and ammonia.

[0038] Optionally, the reducing substance includes one or more of hydrazine hydrate, sodium borohydride and glucose.

[0039] In summary, the present application has the following beneficial effects:

[0040] 1. The present application utilizes ultrasonic oscillation to generate bubbles in the graphite powder, and introduces the oxidizing agent into the bubbles in the graphite powder during ultrasonic oscillation. The oxidizing agent penetrates into the interlayer of the graphite powder along with the bubbles, the gas bubble stabilizer maintains the stability of the cavitation bubbles in the graphite powder, and adjusts the surface tension to control the size and density of the bubbles. The oxidizing agent in the bubbles causes oxidation reaction in the interlayer of the graphite powder, breaks the covalent bonds in the interlayer of the graphite powder and the molecular external hydrogen bonds generated between the graphite powder and the aqueous solution of the oxidizing agent, thereby exfoliating the graphite in the bubbles to obtain graphene sheets with uniform size. The graphene sheets are uniformly arranged to form a neat structure of carbon atom hexagonal plane. On this plane, the electrons outside the graphene nucleus form an electron flow that jumps between different energy levels, producing a visible spectrum. The formation of the electron flow confirms the excellent electrical conductivity of graphene.

[0041] 2. By controlling the surface tension of the pre-dispersion liquid, the size and density of the bubbles in the pre-dispersion liquid are controlled, which not only helps the oxidizing agent to enter the bubbles in the graphite powder, but also maintains the bubbles, thereby facilitating the oxidation reaction in the interlayer of the graphite, breaking the covalent bonds in the interlayer of the graphite, and obtaining graphene sheets with uniform size. BRIEF DESCRIPTION OF DRAWINGS

[0042] Figure 1 is a scanning electron microscope picture of the graphene sheet prepared in Example 1.

[0043] Figure 2 is a scanning electron microscope picture of the graphene sheet prepared in Example 2.

[0044] Figure 3 is a scanning electron microscope picture of the graphene sheet prepared in Example 3.

[0045] Figure 4 is a scanning electron microscope picture of the graphene sheet prepared in Example 4.

[0046] Figure 5 is a scanning electron microscope picture of the graphene sheet prepared in Comparative Example 1.

[0047] Figure 6 is a scanning electron microscope picture of the graphene sheet prepared in Comparative Example 2. DETAILED DESCRIPTION

[0048] The existing graphene exfoliation technology, for example, the method of exfoliating by ultrasonic oscillation, uses ultrasonic waves of different frequencies to produce high-frequency oscillation on the graphite slurry to obtain graphene. This kind of method produces bubbles by ultrasonic oscillation, and uses the high pressure generated when the bubbles burst and crack to impact the graphite to obtain graphene.

[0049] In actual verification, it is found that the graphene structure obtained by the above method is not uniform, because the high-pressure kinetic energy generated by the bubble burst will destroy the graphite structure, and the graphene is broken rather than exfoliated from the graphite surface. In addition, the covalent bond between the graphite layers is stable and difficult to break by ultrasonic oscillation, and the final product is a piece of graphene with different sizes, which is difficult to meet the requirements of the hexagonal structure of carbon atoms in the graphene, and it is more difficult to play the advantages of the conductivity of the graphene.

[0050] The present application uses ultrasonic oscillation to cavitate and produce bubbles inside the graphite powder body, and maintains the stability of the bubble size. Oxidizing agents are introduced into the bubbles to break the covalent bond between the graphite layers under the oxidation reaction, and destroy the molecular external hydrogen bond formed between the graphene and water molecules during the infiltration process, so as to realize the exfoliation of the graphene and form a graphene with uniform bubble size and good performance in conductivity and other aspects.

[0051] The following will be described in detail in combination with the accompanying drawings. Figures 1-6 The present application will be further described in detail.

[0052] Example 1

[0053] A method for preparing graphene, comprising the following steps:

[0054] S1. Disperse the oxidizing agent in water, stir until uniform, add graphite powder, stir until uniform, then add a bubble stabilizer, stir until uniform, to obtain a pre-dispersion.

[0055] The mass ratio of deionized water to oxidizing agent is 1:3.5, the mass ratio of graphite powder to oxidizing agent is 1:4.5, and the mass ratio of bubble stabilizer to oxidizing agent is 0.5:30.

[0056] Specifically, the average size of the graphite powder is 2000 mesh, the oxidizing agent is concentrated sulfuric acid with a mass concentration of 98%, and the bubble stabilizer is coconut oil diethanolamide.

[0057] S2. Pour the pre-dispersion into an ultrasonic oscillator, and stir while ultrasonically oscillating. The frequency of the ultrasonic oscillation is 20 KHz, the power is 1000 w, and the stirring rate is 350 r / min. The diameter of the generated bubbles is controlled to be between 100 μm and 600 nm. The oxidizing agent oxidizes and peels the graphite in the bubbles. The ultrasonic oscillation treatment time is 36 h. During this step, the average surface tension of the pre-dispersion is 45 mN / m.

[0058] S3. Stop the ultrasonic oscillation to obtain a graphene dispersion. Add a basic substance to neutralize the graphene dispersion to a pH of 7. Centrifuge, filter, and wash. Vacuum dry to obtain graphene.

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

[0060] The scanning electron microscope image of the obtained graphene is shown in FIG. 1, wherein the place indicated by the arrow is the visible spectrum. Figure 1

[0061] Example 2

[0062] A method for preparing graphene, comprising the following steps:

[0063] S1. Disperse the oxidizing agent in water, stir until uniform, add graphite powder, stir until uniform, then add a bubble stabilizer, stir until uniform, to obtain a pre-dispersion.

[0064] The mass ratio of deionized water to oxidizing agent is 1:4.5, the mass ratio of graphite powder to oxidizing agent is 1:3.5, and the mass ratio of bubble stabilizer to oxidizing agent is 1.5:50.

[0065] Specifically, the average size of the graphite powder is 10000 mesh, the oxidizing agent is a hydrogen peroxide solution with a mass concentration of 30%, and the bubble stabilizer is Tween 21.

[0066] ​S2. Pour the pre-dispersion liquid into an ultrasonic oscillator, and stir while ultrasonic oscillation is being carried out, the frequency of the ultrasonic oscillation being 80 KHz, the power being 3000 w, the stirring rate being 200 r / min, bubbles being generated, the diameter of the generated bubbles being controlled to be 100 μm-600 nm, the oxidant oxidizing and peeling off the graphite in the bubbles, the ultrasonic oscillation treatment time being 28 h, and the surface tension tester being used to measure the surface tension of the pre-dispersion liquid during the period, the average surface tension of the pre-dispersion liquid being 55 mN / m in this step.

[0067] S3. The ultrasonic oscillation is ended, a graphene dispersion liquid is obtained, an alkaline substance is added to neutralize the graphene dispersion liquid to pH 7, centrifugal separation, filtration, washing, and vacuum drying are carried out to obtain graphene.

[0068] Specifically, the alkaline substance is sodium hydroxide.

[0069] The scanning electron microscope picture of the obtained graphene is shown in FIG. 1, wherein the place indicated by the arrow is the visible light spectrum. Figure 2

[0070] Example 3

[0071] A method for preparing graphene, comprising the following steps:

[0072] S1. An oxidant is dispersed in water, stirred uniformly, graphite powder is added, and a bubble stabilizer is added after the graphite powder is stirred and dispersed uniformly, to obtain a pre-dispersion liquid.

[0073] 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 cocoyl diethanolamide.

[0074] 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 cocoyl diethanolamide.

[0075] S2. Pour the pre-dispersion liquid into an ultrasonic oscillator, and stir while ultrasonic oscillation is being carried out, the frequency of the ultrasonic oscillation being 80 KHz, the power being 3000 w, the stirring rate being 200 r / min, bubbles being generated, the diameter of the generated bubbles being controlled to be 100 μm-600 nm, the oxidant oxidizing and peeling off the graphite in the bubbles, the ultrasonic oscillation treatment time being 28 h, and the surface tension tester being used to measure the surface tension of the pre-dispersion liquid during the period, the average surface tension of the pre-dispersion liquid being 55 mN / m in this step.

[0076] S3. The ultrasonic oscillation is ended, a graphene dispersion liquid is obtained, an alkaline substance is added to neutralize the graphene dispersion liquid to pH 7, centrifugal separation, filtration, washing, and vacuum drying are carried out to obtain graphene.

[0077] ​Specifically, the alkaline substance is ammonia.

[0078] The scanning electron microscope picture of the obtained graphene is shown in Figure 3 .

[0079] Example 4

[0080] A method for preparing graphene, which is different from Example 1 in the S3 step.

[0081] S3. Stop 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 0.5 h, centrifugal separation, filtration, washing, and vacuum drying to obtain graphene.

[0082] Specifically, the alkaline substance is sodium hydroxide; and the reducing substance is hydrazine hydrate, and the mass ratio of the graphite powder to the hydrazine hydrate is 1:0.5.

[0083] The scanning electron microscope picture of the obtained graphene is shown in Figure 4 .

[0084] Comparative Example 1

[0085] A method for preparing graphene, which comprises the following steps:

[0086] S1. Disperse graphite powder in water and stir until uniform, then add a bubble stabilizer, and stir until uniform to obtain a pre-dispersion liquid.

[0087] The mass ratio of the deionized water to the graphite powder is 1:1, and the mass ratio of the graphite powder to the bubble stabilizer is 10:1.

[0088] Specifically, the average size of the graphite powder is 2000 mesh, and the bubble stabilizer is cocoyl diethanolamide.

[0089] S2. Pour the pre-dispersion liquid into an ultrasonic oscillator, and stir while ultrasonic oscillation, the frequency of the ultrasonic oscillation is 20 KHz, the power is 1000 w, the stirring rate is 350 r / min, bubbles are generated, the diameter of the generated bubbles is controlled to be 100 μm~600 nm, the ultrasonic oscillation treatment time is 36 h, and a surface tension tester is used to measure the surface tension of the pre-dispersion liquid during the treatment, and the average surface tension of the pre-dispersion liquid in this step is 45 mN / m.

[0090] S3. Stop the ultrasonic oscillation to obtain a graphene dispersion liquid, centrifugal separation, filtration, washing, and vacuum drying to obtain graphene.

[0091] The scanning electron microscope picture of the obtained graphene is shown in Figure 5 .

[0092] Comparative Example 2

[0093] A method for preparing graphene, comprising the following steps:

[0094] S1. Dispersing an oxidizing agent in water, stirring until uniform, adding graphite powder, and stirring until uniformly dispersed to obtain a pre-dispersion.

[0095] The mass ratio of deionized water to oxidizing agent is 1:4, and the mass ratio of graphite powder to oxidizing agent is 1:4.

[0096] Specifically, the average size of the graphite powder is 2000 mesh, and the oxidizing agent is concentrated sulfuric acid with a mass concentration of 98%.

[0097] S2. Pouring the pre-dispersion into an ultrasonic oscillator, stirring while ultrasonic oscillation, the frequency of ultrasonic oscillation is 20KHz, the power is 1000w, the stirring rate is 350r / min, and the ultrasonic oscillation treatment time is 36h.

[0098] S3. Stopping ultrasonic oscillation to obtain a graphene dispersion, adding a basic substance to neutralize the graphene dispersion to a pH of 7, centrifugal separation, filtration, washing, and vacuum drying to obtain graphene.

[0099] Specifically, the basic substance is sodium hydroxide.

[0100] The scanning electron microscope image of the obtained graphene is shown in Figure 6 .

[0101] Preparation results

[0102] The scanning electron microscope images of the graphene sheets prepared in Examples 1-4 and Comparative Examples 1-2 are shown in 1-6.

[0103] As shown in Figures 1-4 , the graphene sheets prepared in Examples 1-4 are uniform in size, and the carbon atom structure of the graphene sheets is neat, and visible spectrum can be seen under the electron microscope electric field, which is formed by the transition of electron flow at different energy levels, further confirming the uniformity of the size of the graphene sheets prepared in Examples 1-4.

[0104] As shown in Figure 5 and Figure 6 , the graphene sheets of Comparative Example 1 were not oxidized and peeled off by an oxidizing agent, and the graphene sheets of Comparative Example 2 did not form stable bubbles during preparation, so the size of the graphene sheets was not uniform under the electron microscope electric field, which resulted in failure to achieve electron transition, and thus no visible spectrum was generated.

[0105] Application results

[0106] Conductive test: the graphene sheets prepared by example 1-4 and comparative example 1-2 were dispersed in the same water-based resin, stirred to disperse uniformly, to prepare conductive paste samples. The graphene sheet addition amount in the conductive paste was 9g, the water-based resin addition amount was 50g, and the solid content of the water-based resin was 36%.

[0107] The conductive paste samples were coated on the tempered glass plate with a 25 coating rod, baked and cured in an oven at 120℃ for 30min, and the surface resistance was measured after cooling, and the results are shown in Table 1.

[0108] Table 1

[0109] Surface resistance (xlO3Ω-m) Example 1 6.6 Example 2 4.5 Example 3 8.2 Example 4 4.9 Comparative Example 1 77.0 Comparative Example 2 53.5

[0110] As can be seen from Table 1, the conductive paste prepared by the graphene sheets of examples 1-4 has good conductivity.

[0111] The specific embodiment is only an explanation of the present application, and is not a limitation of the present application, and those skilled in the art can make modifications to the specific embodiment without creative contribution after reading the present specification, but as long as it is within the scope of the claims of the present application, it is protected by the patent law.

Claims

1. A method for preparing graphene, characterized in that: The following steps are involved: S1. The oxidant is dispersed in water, graphite powder is added, and a bubble stabilizer is added after uniform dispersion to obtain a pre-dispersion solution; the mass ratio of the bubble stabilizer to the oxidant is (0.5~1.5):(30~50); the bubble stabilizer includes one or more of an alkylolamide, an alkylamine oxide, a Tween and a polyether-modified silicone; S2. Stirring and ultrasonically vibrating the pre-dispersed liquid to generate bubbles and oxidize and exfoliate the graphite; S3. End the ultrasonic oscillation to obtain a graphene dispersion, neutralize the graphene dispersion, filter, wash, and dry to obtain graphene; In step S2, the surface tension of the pre-dispersion liquid is controlled to be 45-55 mN / m.

2. The method for preparing graphene according to claim 1, wherein: In step S2, the frequency of ultrasonic oscillation is 20~80KHz, and the power is 1000w-3000w.

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

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

5. The method for preparing graphene according to claim 1, wherein: The mass ratio of water to the oxidant is 1:(3.5-4.5), and the mass ratio of the graphite powder to the oxidant is 1:(3.5-4.5).

6. A method for preparing graphene according to any one of claims 1 to 5, characterized in that: The oxidant includes an oxidizing substance with a redox electrode potential of ≥1.5 volts.

7. The method for preparing graphene according to claim 6, wherein: The oxidizing substance includes one or more of concentrated sulfuric acid, concentrated nitric acid, potassium permanganate, perchloric acid, potassium dichromate and hydrogen peroxide.

8. The method for preparing graphene according to claim 1, wherein: 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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