Method for preparing graphene

Abstract

The invention discloses a method for preparing graphene, and belongs to the field of nano materials. A method for preparing graphene comprises the following steps that graphite powder, water, acid and salt are evenly mixed, a mixed solution is obtained, and the salt can be dissolved in the water; placing the mixed solution in a low-temperature environment of-86 DEG C to 0 DEG C for cryopreservation, and freezing the mixed solution; after the cryopreservation is finished, unfreezing the frozen mixed solution until the mixed solution is dissolved; and after dissolving, dispersing the mixed solution, neutralizing the pH value of the mixed solution, filtering and drying to obtain the graphene. The preparation method has the advantages that the graphene with good quality is obtained, and the difficulty of the preparation process is reduced.

Description

Technical Field

[0001] This application relates to the field of nanomaterials, and in particular to a method for preparing graphene. Background Technology

[0002] Graphene, a two-dimensional honeycomb lattice material composed of a single layer of carbon atoms with sp² hybrid orbitals, has become a key research focus in the global new materials field due to its superior performance compared to traditional materials. Graphene has excellent electrical and thermal conductivity, high specific surface area, and excellent chemical stability and optical transmittance, making it outstanding in applications such as new energy, electronic information, aerospace, and biomedicine.

[0003] The raw material for preparing graphene is readily available graphite powder. The preparation method can be mechanical, which involves ball milling, high-speed shearing, or air jet milling of graphite powder to apply interlayer breaking forces and achieve graphene exfoliation; or it can be an oxidation-reduction method, which involves oxidizing graphite powder to form graphite oxide, weakening the interlayer forces, then ultrasonically exfoliating it, and finally reducing it to obtain graphene.

[0004] However, mechanical methods are prone to introducing structural defects, resulting in low yields of nanoscale graphene and high equipment requirements. On the other hand, the process conditions of the oxidation-reduction method need to be strictly controlled; otherwise, defects may easily appear in the graphene structure, leading to significant production difficulties. Summary of the Invention

[0005] In order to obtain high-quality graphene and reduce the difficulty of the preparation process, this application provides a method for preparing graphene.

[0006] The method for preparing graphene provided in this application adopts the following technical solution: A method for preparing graphene includes the following steps: Graphite powder, water, acid, and salt are mixed evenly to obtain a mixture, wherein the salt is soluble in water; The mixture is frozen in a low-temperature environment of -86℃ to 0℃. After freezing, the frozen mixture is thawed until dissolved; After dissolving, the mixture is dispersed, the pH of the mixture is neutralized, filtered, and dried to obtain graphene.

[0007] By employing the above technical solution, the mixed solution wets the graphite powder. With the aid of acid, the salt penetrates into the interlayer gaps of the graphite powder. When the mixed solution freezes in a low-temperature environment, the salt crystallizes within the interlayers of the graphite powder due to the low temperature, releasing a concentration higher than that of the graphite powder. 2 The energy of the covalent bond energy of the hybrid orbitals C and C atoms causes the interlayer bonds of the graphite powder to break, thus exfoliating graphene.

[0008] This method can obtain nanoscale graphene with a narrow particle size distribution. It not only has a simple process, but also effectively solves the application defects of graphene caused by over-oxidation or under-oxidation when preparing graphene with high-concentration oxidants in the traditional redox method.

[0009] Optionally, the mass ratio of the graphite powder, water, acid, and salt is 100:(500~2000):(300~700):(2~10).

[0010] By adopting the above technical solution, the proportion of each component in the mixture is controlled, so that the graphite powder can be fully dispersed and wetted in the mixture. With the cooperation of acid and salt, it can penetrate into the interlayer of graphite powder and crystallize at low temperature, release the heat of crystallization, break the C-C bonds between the graphite powder layers, and peel off the micron-sized graphite powder into nano-sized graphene.

[0011] Optionally, the acid includes one or more of sulfuric acid, nitric acid, perchloric acid, and phosphoric acid.

[0012] By adopting the above technical solution, the acid can be used to pickle the surface of graphite powder, and the oxidative etching effect of the acid helps the salt in the mixture to penetrate into the interlayer of graphite powder, thereby breaking the C-C bonds and obtaining nanoscale graphene.

[0013] Optionally, the concentration of sulfuric acid is 10-60 wt%; the concentration of nitric acid is 10-30 wt%.

[0014] Optionally, the salt includes one or both of inorganic salts and metal complex salts.

[0015] Optionally, the inorganic salt includes one or more of sodium chloride, potassium chloride, calcium chloride, magnesium chloride, sodium sulfate, potassium sulfate, and magnesium sulfate; the metal complex salt includes a complex of EDTA with calcium, iron, or magnesium.

[0016] By adopting the above technical solution, the salt can dissolve in water, enter the interlayer of graphite powder, and break the interlayer bonds of graphite powder by releasing energy through low-temperature crystallization, thereby achieving the exfoliation of graphene.

[0017] Optionally, the cryogenic environment in which the mixture is frozen is -55°C to -10°C.

[0018] By adopting the above technical solution, the optimal temperature of the low-temperature environment is selected, and the conditions for graphene exfoliation are optimized, resulting in a narrow particle size distribution of graphene.

[0019] Optionally, the mixture can be frozen for 3 to 10 hours.

[0020] Optionally, in the step of thawing the frozen mixture to dissolution, the thawing ambient temperature is 5°C to 40°C.

[0021] By adopting the above technical solution, the thawing temperature is controlled at a relatively low temperature of 5℃~40℃, avoiding the destruction of the sheet-like structure of the graphite layer due to rapid temperature rise, which helps the particle size distribution of graphene to be within a narrower range.

[0022] Optionally, the step of thawing the frozen mixture to thaw may further include ultrasonically vibrating the mixture.

[0023] By adopting the above technical solution, the kinetic energy of ultrasonic vibration helps to peel graphene from the interlayer of graphite powder.

[0024] Optionally, the frequency of ultrasonic oscillation is 40~80KHz.

[0025] Optionally, in the step of dispersing the mixture, the dispersion is carried out at a rate of ≥1000 rpm for 40~120 min.

[0026] By adopting the above technical solution, graphene is further fully exfoliated, allowing more micron-sized graphite powder to be exfoliated into nano-sized graphene.

[0027] Optionally, before freezing the mixture in a low-temperature environment of -86℃ to 0℃, the mixture should be continuously stirred for 40 to 120 minutes.

[0028] By adopting the above technical solution, the graphite powder is fully wetted, allowing the salt in the mixture to fully penetrate into the interlayer of the graphite powder, so that more graphene can be exfoliated during the subsequent low-temperature crystallization and breakage of C-C bonds.

[0029] Preferably, after dispersing the mixture, a portion of the mixture is extracted to test the graphene exfoliation. If the degree of graphene exfoliation does not meet expectations, the preparation method can be repeated multiple times.

[0030] In summary, this application has the following beneficial effects: 1. The mixture wets the graphite powder. With the aid of acid, the salt penetrates into the interlayer gaps of the graphite powder. When the mixture freezes at low temperatures, the salt crystallizes within the graphite powder layers due to the low temperature, releasing a higher concentration of phosphorus than the graphite powder. 2 The energy of the covalent bond energy of the C and C atoms in the hybrid orbitals breaks the interlayer bonds of the graphite powder, exfoliating graphene. This method can obtain nanoscale graphene with uniform number of graphene layers and narrow particle size distribution. It not only has a simple process flow, but also effectively solves the application defects of graphene prepared by high-concentration oxidants in the traditional redox method due to over-oxidation or under-oxidation.

[0031] 2. Control the proportion of each component in the mixture to ensure that the graphite powder can be fully dispersed and wetted in the mixture. With the cooperation of acid and salt, it can penetrate into the interlayer of graphite powder and crystallize at low temperature, releasing the heat of crystallization, breaking the C-C bonds between the graphite powder layers, and peeling the micron-sized graphite powder into nano-sized graphene. Attached Figure Description

[0032] Figure 1 This is a particle size distribution diagram of the graphene prepared in Example 3 of this application.

[0033] Figure 2 This is a particle size distribution diagram of the graphene prepared in Comparative Example 1 of this application.

[0034] Figure 3 This is a particle size distribution diagram of the graphene prepared in Comparative Example 2 of this application. Detailed Implementation

[0035] The following is in conjunction with the appendix Figure 1-3 This application will be described in further detail.

[0036] Among the existing methods for preparing graphene, the oxidation-reduction method is the mainstream method that can be used for industrial mass production. However, because excessive or insufficient oxidation can lead to structural defects in graphene, the oxidation-reduction method requires precise control of process conditions, which increases the difficulty and cost of production.

[0037] In recent years, an emerging method for preparing graphene has emerged: intercalation expansion. This method involves embedding an intercalating agent between graphite powder layers, followed by rapid heating to vaporize and expand the intercalating agent, thereby exfoliating the graphene. However, the inventors discovered in actual verification that, due to the need for rapid heating, the kinetic energy generated during the expansion of the intercalating agent is high, which easily destroys the sheet-like structure of graphite rather than exfoliates it. This results in graphene of varying sizes and a wide particle size distribution, making it difficult to meet the requirements for nanoscale graphene.

[0038] This application utilizes the combination of acid and salt. Under the oxidative etching action of acid, the salt in the mixture penetrates into the interlayer of graphite powder. The energy released by the salt crystallization in the interlayer of graphite powder due to low temperature causes the interlayer bonds of graphite powder to break, thus peeling off graphene. Furthermore, the mixture thaws from a frozen state, allowing the graphene to be peeled off gradually and gently, improving the peeling effect and narrowing the particle size distribution of graphene.

[0039]

Example 1

[0040] Mix graphite powder, water, acid and salt evenly, stir at 200 rpm for 40 minutes, then stop stirring to obtain a mixture.

[0041] S2. Freeze the mixture in a -55°C freezer for 4 hours to freeze the mixture.

[0042] S3. After freezing, remove the frozen mixture from the freezer to thaw and perform ultrasonic vibration. Control the ambient temperature during ultrasonic vibration at 20°C and the ultrasonic vibration frequency at 40KHz until it is thawed.

[0043] S4. After complete dissolution, disperse the mixture using a shear disperser at a rate of 1000 rpm for 120 min. Add ammonia water to neutralize the mixture until the pH is 7. Centrifuge, wash, filter, and dry to obtain graphene.

[0044]

Example 2

[0045] Mix graphite powder, water, acid, and salt thoroughly, and stir at 100 rpm for 120 minutes. Stop stirring to obtain a mixture.

[0046] S2. Place the mixture in a 0°C freezer for 10 hours to freeze the mixture.

[0047] S3. After freezing, remove the frozen mixture from the freezer to thaw and perform ultrasonic vibration. Control the ambient temperature during ultrasonic vibration at 40℃ and the ultrasonic vibration frequency at 80KHz until it is thawed and dissolved.

[0048] S4. After complete dissolution, disperse the mixture using a shear disperser at a rate of 1500 rpm for 40 min. Add ammonia water to neutralize the mixture until the pH is 7. Centrifuge, wash, filter, and dry to obtain graphene.

[0049]

Example 3

[0050] Mix graphite powder, water, acid and salt evenly, stir at 300 rpm for 40 minutes, then stop stirring to obtain a mixture.

[0051] S2. Freeze the mixture in a -86°C freezer for 3 hours to freeze the mixture.

[0052] S3. After freezing, remove the frozen mixture from the freezer to thaw and perform ultrasonic vibration. Control the ambient temperature during ultrasonic vibration at 5°C and the ultrasonic vibration frequency at 50KHz until it is thawed and dissolved.

[0053] S4. After complete dissolution, disperse the mixture using a shear disperser at a rate of 1200 rpm for 60 min. Add ammonia water to neutralize the mixture until the pH is 7. Centrifuge, wash, filter, and dry to obtain graphene.

[0054]

Example 4

[0055] Mix graphite powder, water, acid and salt evenly, stir at 300 rpm for 40 minutes, then stop stirring to obtain a mixture.

[0056] S2. Freeze the mixture in a -10°C freezer for 8 hours to freeze the mixture.

[0057] S3. After freezing, remove the frozen mixture from the freezer to thaw and perform ultrasonic vibration. Control the ambient temperature during ultrasonic vibration at 5°C and the ultrasonic vibration frequency at 50KHz until it is thawed and dissolved.

[0058] S4. After complete dissolution, disperse the mixture using a shear disperser at a rate of 1200 rpm for 60 min. Add ammonia water to neutralize the mixture until the pH is 7. Centrifuge, wash, filter, and dry to obtain graphene.

[0059] Comparative Example 1 A method for preparing graphene includes the following steps: S1. Weigh out graphite powder, water, acid, and salt in a mass ratio of 100:1000:600:7. The graphite powder is selected with a particle size of 2000 mesh; the acid is 60wt% sulfuric acid; and the salt is an inorganic salt soluble in water, specifically magnesium chloride.

[0060] Mix graphite powder, water, acid and salt evenly, stir at 300 rpm for 40 minutes, then stop stirring to obtain a mixture.

[0061] S2. Heat the mixture to 90°C and keep it warm for 20 minutes.

[0062] S3. After the heat preservation is completed, the mixture is naturally cooled to room temperature and subjected to ultrasonic vibration for 1 hour at a frequency of 50 kHz. The mixture is then dispersed using a shear disperser at a rate of 1200 rpm for 60 minutes. Ammonia water is added to neutralize the mixture until the pH reaches 7. The mixture is then centrifuged, washed, filtered, and dried to obtain graphene.

[0063] Comparative Example 2 A method for preparing graphene includes the following steps: S1. Weigh out graphite powder, water, and acid in a mass ratio of 100:1000:600. The graphite powder should have a particle size of 2000 mesh; the acid should be 60wt% sulfuric acid.

[0064] Mix graphite powder, water, and acid evenly, stir at 300 rpm for 40 minutes, then stop stirring to obtain a mixture.

[0065] S2. Freeze the mixture in a refrigerator at -86°C.

[0066] S3. After freezing, remove the frozen mixture from the freezer to thaw and perform ultrasonic vibration, controlling the ambient temperature during ultrasonic vibration at 5°C, until it is thawed and dissolved.

[0067] S4. After complete dissolution, disperse the mixture using a shear disperser at a rate of 1200 rpm for 60 min. Add ammonia water to neutralize the mixture until the pH is 7. Centrifuge, wash, filter, and dry to obtain graphene.

[0068] Comparative Example 3 A method for preparing graphene includes the following steps: S1. Weigh out graphite powder, water, and salt in a mass ratio of 100:1000:7. The graphite powder should have a particle size of 2000 mesh; the salt should be an inorganic salt, specifically magnesium chloride.

[0069] Mix graphite powder, water, and salt evenly, stir at 300 rpm for 40 minutes, then stop stirring to obtain a mixture.

[0070] S2. Freeze the mixture in a refrigerator at -86°C.

[0071] S3. After freezing, remove the frozen mixture from the freezer to thaw and perform ultrasonic vibration, controlling the ambient temperature during ultrasonic vibration at 5°C, until it is thawed and dissolved.

[0072] S4. After complete dissolution, disperse the mixture using a shear disperser at a rate of 1200 rpm for 60 min, then centrifuge, wash, filter, and dry to obtain graphene.

[0073] Effect detection Particle size analysis: The particle size of graphene prepared in different embodiments and comparative examples was measured using a laser particle size analyzer. The particle size distribution, cumulative percentage of 1.075 μm, D50, and weight-specific surface area were obtained. See the particle size distribution diagram below. Figure 1 , Figure 2 and Figure 3 The cumulative percentage at 1.075 μm, D50, and specific surface area are shown in Table 1. 1.075 μm is the dividing line; particles larger than 1.075 μm are in the micrometer range, and those smaller than 1.075 μm are in the nanometer range. Generally, a cumulative percentage at 1.075 μm greater than 20% can be considered as having produced nanoscale graphene. The breadth of the particle size distribution can be characterized by the range of particle sizes from the start to the end of particle size accumulation on the particle size distribution map.

[0074] Conductivity test: Graphene prepared in different examples and comparative examples was added to waterborne polyurethane at a dosage of 10 wt%. The resulting waterborne polyurethane was coated on the glass surface and dried to form a coating film. The resistance of the coating film was measured by a surface resistance meter. The results are shown in Table 2.

[0075] Table 1

[0076] Table 2

[0077] As shown in Table 1, the graphene prepared in Examples 1-4 has a cumulative percentage of 1.075 μm greater than 20%, which is nanoscale graphene. Moreover, the D50 particle size is small, the weight specific surface area is high, and the quality of graphene is high.

[0078] Comparing Example 3 with Comparative Examples 1, 2 and 3, it can be seen that the method of freezing the mixture at low temperature, and the use of acid and salt in the mixture, can effectively achieve the exfoliation of graphene.

[0079] Combination Figures 1-3 It can be seen that, compared with Comparative Example 1 and Comparative Example 2, the particle size distribution of Example 3 is narrower, with 1.075μm accumulating to more than 40%, indicating that the graphene exfoliation effect is good, the graphene sheet size is more consistent, and nanoscale graphene is obtained, which has stronger functional advantages.

[0080] Further analysis of Table 2 shows that, compared with Comparative Examples 1, 2, and 3, the graphene in Example 3 applied to the waterborne polyurethane coating has higher conductivity, which can effectively meet the requirements of scenarios with conductivity requirements.

[0081] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this specific embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for preparing graphene, characterized in that: Includes the following steps: Graphite powder, water, acid, and salt are mixed evenly to obtain a mixture, wherein the salt is soluble in water; The mixture is frozen in a low-temperature environment of -86℃ to 0℃. After freezing, the frozen mixture is thawed until dissolved; After dissolving, the mixture is dispersed, the pH of the mixture is neutralized, filtered, and dried to obtain graphene.

2. The method for preparing graphene according to claim 1, characterized in that: The mass ratio of the graphite powder, water, acid, and salt is 100:(500~2000):(300~700):(2~10).

3. The method for preparing graphene according to claim 1, characterized in that: The acid includes one or more of sulfuric acid, nitric acid, perchloric acid, and phosphoric acid.

4. The method for preparing graphene according to claim 1, characterized in that: The salt includes one or both of inorganic salts and metal complex salts.

5. The method for preparing graphene according to claim 4, characterized in that: The inorganic salts include one or more of sodium chloride, potassium chloride, calcium chloride, magnesium chloride, sodium sulfate, potassium sulfate, and magnesium sulfate; the metal complex salts include complexes of EDTA with calcium, iron, or magnesium.

6. The method for preparing graphene according to claim 1, characterized in that: The mixture is cryopreserved in a low-temperature environment of -55℃ to -10℃.

7. The method for preparing graphene according to claim 1, characterized in that: In the step of thawing the frozen mixture until it dissolves, the thawing ambient temperature is 5°C to 40°C.

8. The method for preparing graphene according to claim 1, characterized in that: The step of thawing the frozen mixture to thaw also includes ultrasonically vibrating the mixture.

9. The method for preparing graphene according to claim 1, characterized in that: In the step of dispersing the mixture, the dispersion is carried out at a rate of ≥1000 rpm for 40~120 min.

10. A method for preparing graphene according to claim 1, characterized in that: Before freezing the mixture in a low-temperature environment of -86℃ to 0℃, the mixture should be continuously stirred for 40 to 120 minutes.

Images