A method for preparing functionalized graphene

Abstract

The application belongs to the technical field of graphene preparation, and particularly relates to a preparation method of functionalized graphene. The application provides a preparation method of functionalized graphene, which comprises the following steps: performing first-stage ball milling on graphite raw materials under vacuum conditions to obtain first mixed materials; performing second-stage ball milling on the first mixed materials under supercritical carbon dioxide conditions to obtain second mixed materials; and performing natural oxidation on the second mixed materials under oxygen-containing conditions to obtain the functionalized graphene. In the application, the initial stage of ball milling needs to be performed under vacuum conditions to obtain maximum ball milling bead collision energy and manufacture certain defects on the edges of graphite sheet layers; then, ball milling is performed under supercritical CO2 conditions, and the high-density supercritical CO2 state greatly enhances the penetration-intercalation effect of CO2 molecules, that is, the peeling effect is greatly improved. Under the combined action of the two, a graphene product with high conductivity and high dispersibility can be prepared.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of graphene preparation, and particularly relates to a preparation method of functionalized graphene. BACKGROUND

[0002] Graphene has a wide application prospect in the fields of energy, health, environment and the like due to its excellent electrical, thermal, mechanical and other properties, and is one of the new materials that are focused on. So far, a variety of graphene preparation methods have been reported. Among them, the "top-down" exfoliation process taking layered graphite as raw material is the main method for mass production of graphene. Chemical oxidation exfoliation and mechanical exfoliation are typical two kinds of processes. Among them, the Hummer or improved Hummer method is a typical chemical oxidation exfoliation method, which can obtain hydrophilic graphene oxide, but this method uses a large amount of harmful chemicals such as strong oxidants and strong acids. In addition, even through reduction, the damage of the graphene lattice by the oxidation process cannot be completely restored, so this method damages the excellent electrical properties of graphene.

[0003] The mechanical exfoliation method is to take graphite as raw material and obtain graphene by mechanical shearing or ball milling method. In particular, the ball milling method combined with supercritical CO2 (for example, Chinese patents with publication numbers CN102107869A, CN106044764A and CN102115078A) can scale up the preparation of high-quality graphene. However, the graphene prepared by this method is hydrophobic and is difficult to disperse in polar solvents such as water, thereby limiting its application field. In addition, Song et al. (Chemical Engineering Journal, 298, 198 (2016).) and Chen et al. (Industrial & Engineering Chemistry Research. 2017, 56, 6939-6944) prepared hydrophilic graphene nanosheets by introducing surfactants and polymers PVP through mechanical exfoliation of graphite, which improved the dispersibility of graphene. However, the use of surfactants and polymers greatly reduces the electrical properties of graphene, which will have an adverse effect on subsequent applications. Therefore, how to greenly and scale up the preparation of graphene with high dispersibility and high conductivity while maintaining the integrity of the intrinsic structure is a problem to be solved. SUMMARY

[0004] The purpose of the present application is to provide a preparation method of functionalized graphene. The method provided by the present application can obtain graphene with high dispersibility and high conductivity.

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

[0006] The present application provides a preparation method of functionalized graphene, comprising the following steps:

[0007] ball-milling the graphite raw material under vacuum condition to obtain a first mixture;

[0008] ball-milling the first mixture under supercritical carbon dioxide condition to obtain a second mixture;

[0009] naturally oxidizing the second mixture under oxygen-containing condition to obtain the functionalized graphene.

[0010] Preferably, the graphite raw material comprises one or more of natural graphite, expanded graphite and flake graphite.

[0011] Preferably, the mass ratio of the graphite raw material to the ball-milling beads in the first stage ball-milling and the second stage ball-milling is independently 1:10-100.

[0012] Preferably, the vacuum degree of the vacuum condition is -0.05- -0.1 MPa.

[0013] Preferably, the rotation speed of the first stage ball-milling is 150-500 rpm, and the time is 4-12 h.

[0014] Preferably, the temperature of the first stage ball-milling is 20-50℃.

[0015] Preferably, the density of the supercritical carbon dioxide is 0.10-0.90 g / cm 3 .

[0016] Preferably, the rotation speed of the second stage ball-milling is 250-450 rpm, and the time is 10-50 h.

[0017] Preferably, the temperature of the second stage ball-milling is 35-50℃.

[0018] Preferably, the time of the natural oxidation is 30-300 min.

[0019] The application provides a preparation method of functionalized graphene, comprising the following steps: ball-milling a graphite raw material under vacuum condition to obtain a first mixture; ball-milling the first mixture under supercritical carbon dioxide condition to obtain a second mixture; and naturally oxidizing the second mixture under oxygen-containing condition to obtain the functionalized graphene.

[0020] Compared with the prior art, the application has the following beneficial effects:

[0021] In the present application, the graphite raw material is first ball milled in a vacuum state. In the above state, the ball milling beads have high collision energy, which can quickly and efficiently break large pieces of graphite into small pieces of graphite, and can activate the edges of the layers to create certain defects, so that they can be naturally oxidized in an oxygen-containing atmosphere without using any oxidizing agent. This selective oxidation strategy of the edges is fundamentally different from the traditional Hummer method, that is, the oxidation area is only at the edges of the layers, while most of the layers can still maintain the intrinsic crystal structure, thereby maintaining excellent electrical properties.

[0022] Next, under high CO2 density, supercritical CO2 molecules can efficiently penetrate and intercalate through the defects in the edges of the layers, and the kinetic structure of the ball milling beads also changes from breaking to shearing due to the high density of CO2. Under the combination of the two, graphite can be mass-exfoliated into few-layer graphene. Compared with the prior art, the present application also reveals the effect of CO2 density on the kinetic structure of the ball milling beads through computer simulation, that is, the exfoliation and functionalization of graphite can be realized simultaneously by utilizing the kinetic characteristics of the ball milling beads under different CO2 densities.

[0023] On the other hand, the existing liquid-assisted ball milling or solution ball milling functionalization method involves the use of a large amount of organic solvent. These organic solvents not only have high toxicity, but also have the problem of difficult separation from the ball milling products. The supercritical CO2 used in the present application is an extremely special solvent, which not only maintains the fluid behavior like a liquid during ball milling, but also has high diffusivity and high permeability of a gas, and its diffusion capacity is generally tens of times that of a liquid. More importantly, the solvation ability of supercritical CO2 changes with density, which means that its effect on graphite exfoliation and functionalization can be realized by adjusting the density, which is impossible in traditional liquid-phase ball milling. In addition, the supercritical CO2 solvent used in the present application is a gas at room temperature, which has almost no toxicity compared with organic solvents and is easy to separate from the sample efficiently. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 The flowchart of the preparation method provided by the present application;

[0025] Figure 2 The burning diagram caused by the severe oxidation of the sample in the air during the natural oxidation process in Example 1;

[0026] Figure 3 The ball milling bead collision energy distribution diagram of the computer simulation in Example 1;

[0027] Figure 4 The Raman diagram of the functionalized graphene prepared in Example 1;

[0028] Figure 5TEM image of the functionalized graphene prepared in Example 1;

[0029] Figure 6 The Zeta potential diagram of the functionalized graphene prepared in Example 1 in water;

[0030] Figure 7 This is a photograph of the functionalized graphene prepared in Example 1 dispersed in water.

[0031] Figure 8 The image shows a TEM image of the functionalized graphene prepared in Comparative Example 1. Detailed Implementation

[0032] This invention provides a method for preparing functionalized graphene, comprising the following steps:

[0033] The graphite raw material was ball-milled under vacuum conditions to obtain the first mixture.

[0034] The first mixture was subjected to a second-stage ball milling under supercritical carbon dioxide conditions to obtain a second mixture.

[0035] The second mixture is subjected to natural oxidation under oxygen-containing conditions to obtain the functionalized graphene.

[0036] In this invention, unless otherwise specified, all raw materials used in the preparation are commercially available products well known to those skilled in the art.

[0037] The present invention involves ball milling graphite raw materials under vacuum conditions in the first stage to obtain a first mixture.

[0038] In this invention, the graphite raw material preferably includes one or more of natural graphite, expanded graphite, and flake graphite, more preferably flake graphite; the particle size of the graphite raw material is preferably 50-500 mesh, more preferably 200 mesh. In this invention, the grinding balls used in the first stage of ball milling are preferably zirconia grinding balls, and the diameter of the grinding balls is preferably 0.1-30 mm, more preferably 5-15 mm. In this invention, the mass ratio of the graphite raw material to the grinding balls is preferably 1:10-100, more preferably 1:20-90, and more preferably 1:30-80.

[0039] In the present application, the vacuum degree of the vacuum condition is preferably -0.05 to -0.1 MPa, further preferably -0.06 to -0.09 MPa, and more preferably -0.07 to -0.08 MPa. In the present application, the rotation speed of the first-stage ball milling is preferably 150 to 500 rpm, further preferably 200 to 400 rpm, and more preferably 250 to 300 rpm; and the time is preferably 4 to 12 h, further preferably 5 to 10 h, and more preferably 6 to 8 h. In the present application, the temperature of the first-stage ball milling is preferably 20 to 50℃, further preferably 25 to 45℃, and more preferably 40℃.

[0040] The equipment for ball milling in the present application is not particularly limited, and any equipment known to those skilled in the art can be used. In the specific embodiments of the present application, the first-stage ball milling and the second-stage ball milling are both preferably performed in a planetary ball mill. In the present application, the first-stage ball milling is directly followed by the second-stage ball milling without discharging, i.e., the first-stage ball milling and the second-stage ball milling are performed in the same ball milling equipment, and the ratio of the graphite raw material to the ball milling beads is the same during the ball milling process.

[0041] After obtaining the first mixture, the present application performs second-stage ball milling on the first mixture under supercritical carbon dioxide condition to obtain a second mixture.

[0042] In the present application, the density of carbon dioxide under the supercritical carbon dioxide condition is preferably 0.10 to 0.90 g / cm 3 , further preferably 0.3 to 0.8 g / cm 3 , and more preferably 0.5 to 0.6 g / cm 3 . In the present application, the rotation speed of the second-stage ball milling is preferably 250 to 450 rpm, further preferably 280 to 420 rpm, and more preferably 300 to 400 rpm; and the time is preferably 10 to 50 h, further preferably 20 to 40 h. In the present application, the temperature of the second-stage ball milling is preferably 35 to 50℃, and further preferably 40 to 45℃.

[0043] After the second-stage ball milling, the present application further preferably includes separating the material obtained by ball milling from the ball milling beads. The method for separation in the present application is not particularly limited, and any method known to those skilled in the art can be used.

[0044] After obtaining the second mixture, the present application performs natural oxidation on the second mixture under an oxygen-containing condition to obtain the functionalized graphene.

[0045] In the present application, the oxygen-containing condition preferably comprises air. In the present application, the time of the natural oxidation is preferably 30-300 min, further preferably 50-250 min, and more preferably 100-200 min.

[0046] The flowchart of the preparation method provided by the present application is shown in Figure 1

[0047] The specific flow of the preparation method provided by the present application is preferably as follows: the graphite raw material and the ball milling beads are put into a high-pressure stainless steel ball mill, the cover is screwed tightly, and then the ball mill is fixed on a ball milling device. A certain amount of CO2 is pumped into the ball mill through a high-pressure pump to exhaust the air, and then the vacuum pump is used to pump the gas in the ball mill to a near-vacuum state. The ball mill is started, and the ball milling temperature is set; then, the first-stage ball milling is carried out at the set speed, and the machine is stopped after completion. Then, CO2 is pumped into the ball mill through the high-pressure pump to make the CO2 density in the ball mill reach the required density. The ball mill is started, the ball milling temperature is set, and the second-stage ball milling is carried out at the set speed, and the machine is stopped after completion. The CO2 is released through the valve on the ball mill until the pressure in the ball mill drops to atmospheric pressure, the cover of the ball mill is opened, the material is taken out, and the ball milling beads and the sample are separated, the sample is naturally oxidized under the oxygen-containing condition, and the functionalized graphene is obtained.

[0048] In order to further illustrate the present application, the preparation method of the functionalized graphene provided by the present application is described in detail below in combination with the drawings and examples, but they should not be understood as limiting the protection scope of the present application.

[0049] Example 1

[0050] 15 g of 100-mesh natural flake graphite and 400 g of ball milling beads (zirconia ball milling beads with a diameter of 5-15 mm) are put into a 300 mL high-pressure stainless steel ball mill, the cover is screwed tightly, and then the ball mill is fixed on a planetary ball mill. A certain amount of CO2 is pumped into the ball mill through a high-pressure pump to exhaust the air, and then the vacuum pump is used to pump the gas in the ball mill to a near-vacuum state (-0.1 MPa). The ball mill is started, and the temperature of the ball mill temperature controller is set to 40℃; then, the machine is run at a speed of 450 rpm for 8 h, and the machine is stopped after completion. Then, CO2 is pumped into the ball mill through the high-pressure pump to make the CO2 density in the ball mill reach 0.70 g / cm 3 The ball mill is started, and the temperature of the ball mill temperature controller is set to 40℃, and the machine is run at a speed of 400 rpm for 24 h, and the machine is stopped after completion. The CO2 is released through the valve on the ball mill until the pressure in the ball mill drops to atmospheric pressure, the cover of the ball mill is opened, the material is taken out, and the ball milling beads and the sample are separated through a screen, the sample is naturally oxidized in air for 3 h, and the functionalized graphene is obtained.

[0051] wherein, Figure 2 ​The combustion caused by the severe oxidation of the sample in air during the autoxidation process in Example 1 can be clearly observed from the combustion graph.

[0052] For the ball milling process at different stages in Example 1, the collision energy distribution of the ball milling beads was calculated using computer simulation; the structure and morphology of the sample were analyzed using Raman spectroscopy and transmission electron microscopy; and the dispersion performance of the sample in water was analyzed using a Zeta potential instrument. Meanwhile, to further illustrate the electrical properties of the obtained graphene, the obtained functionalized graphene powder was dissolved in water, and a film was prepared through filtration-drying-pressing and the conductivity was measured.

[0053] Figure 3 For the ball milling bead collision energy distribution graph simulated by the computer in Example 1, it can be seen that the collision energy corresponding to the maximum collision frequency of the ball milling beads is quite different in the vacuum and supercritical states. Therefore, the state of vacuum can rapidly activate the edges of the graphite sheet layer in a short time, and the activated carbon species can combine with oxygen and water in air to form oxygen-containing functional groups. In addition, the high collision energy in near-vacuum can effectively break large graphite sheet layers into small pieces and form certain defects at the edges of the sheet layers, which are helpful for the subsequent CO2 penetration-intercalation-exfoliation process.

[0054] Figure 4 For the Raman graph of the functionalized graphene prepared in Example 1, it can be seen from Figure 4 that after ball milling, the 2D peak of the graphite itself is normalized and shifted from 2719 cm -1 to 2676 cm -1 , indicating that the graphite sheet layer has been effectively exfoliated.

[0055] Figure 5 For the TEM graph of the functionalized graphene prepared in Example 1, it can be seen from Figure 5 that after ball milling, the natural flake graphite is exfoliated into translucent single-layer graphene with complete crystal structure.

[0056] Further through the filtration-drying-pressing process, it is made into a graphene film with a thickness of 15 μm, and the conductivity is measured to be 1.92×10 5 S / m, which has good electrical conductivity.

[0057] In addition to good electrical conductivity, the above graphene also has excellent dispersibility in water. Figure 6 For the Zeta potential graph of the functionalized graphene prepared in Example 1 in water, as Figure 6 shown, the Zeta potential of the 0.1 mg / mL graphene aqueous dispersion is -72.4, -68.2 and -55.4 mV after standing for 0, 30 and 270 days, respectively, which has stable water dispersibility.

[0058] Figure 7 A photograph of the dispersion of the functionalized graphene prepared in Example 1 in water is shown in Figure 1. Figure 7 It can be seen that the graphene aqueous dispersion did not show any layering phenomenon even after standing for 270 days, and had excellent dispersion stability.

[0059] Example 2

[0060] A 10 g of 100 mesh natural flake graphite and 400 g of ball milling beads (zirconia milling beads with a diameter of 5-15 mm) were placed in a 300 mL high-pressure stainless steel ball mill, the cover was tightened, and the mill was then fixed on a planetary ball mill. A certain amount of CO2 was pumped into the ball mill through a high-pressure pump to remove the air, and then the ball mill was pumped to a near vacuum state (-0.1 MPa) using a vacuum pump. The ball mill was started, and the temperature of the ball mill temperature controller was set to 40°C; then, after running at a speed of 450 rpm for 4 h, the ball mill was stopped. Then, CO2 was pumped into the ball mill through a high-pressure pump to make the CO2 density in the ball mill reach 0.70 g / cm3. The ball mill was started, and the temperature of the ball mill temperature controller was set to 40°C, and the ball mill was run at a speed of 400 rpm for 28 h and then stopped. The CO2 was released through the valve on the ball mill until the pressure in the ball mill dropped to atmospheric pressure, the cover of the ball mill was opened, the material was taken out, and the ball milling beads and the sample were separated by a screen, and the sample was naturally oxidized in air for 3 h to obtain the functionalized graphene. 3 The ball mill was started, and the temperature of the ball mill temperature controller was set to 40°C, and the ball mill was run at a speed of 400 rpm for 28 h and then stopped. The CO2 was released through the valve on the ball mill until the pressure in the ball mill dropped to atmospheric pressure, the cover of the ball mill was opened, the material was taken out, and the ball milling beads and the sample were separated by a screen, and the sample was naturally oxidized in air for 3 h to obtain the functionalized graphene.

[0061] The conductivity and dispersion of the functionalized graphene obtained were tested in the manner of Example 1.

[0062] The functionalized graphene obtained was made into a graphene film with a thickness of 12 μm, and the conductivity was measured to be 2.37 x 10 5 S / m, which had good conductivity. In addition to having good conductivity, the graphene had excellent dispersion in water, and the Zeta potential of the aqueous dispersion was -35.4 mV after standing for 30 days, which had good dispersion stability.

[0063] Example 3

[0064] A 300 mL high-pressure stainless steel ball mill pot was charged with 10 g of 200 mesh natural flake graphite and 400 g of ball milling beads (zirconia ball milling beads with a diameter of 5-15 mm), the pot lid was tightened, and the pot was then fixed on a planetary ball mill. A certain amount of CO2 was pumped into the ball mill pot to remove the air by a high-pressure pump, and then the pot was evacuated to a near vacuum state (-0.1 MPa) by a vacuum pump. The ball mill was started, and the temperature of the ball mill temperature controller was set to 40°C; then, the ball mill was run at a speed of 450 rpm for 2 h and stopped. Then, CO2 was pumped into the ball mill pot by a high-pressure pump to make the CO2 density in the pot reach 0.84 g / cm3 3 . The ball mill was started, and the temperature of the ball mill temperature controller was set to 40°C; then, the ball mill was run at a speed of 400 rpm for 30 h and stopped. The CO2 was released through the valve on the ball mill pot until the pressure in the ball mill pot decreased to atmospheric pressure, the ball mill pot lid was opened, the material was taken out, and the ball milling beads and the sample were separated by a screen, the sample was placed in air for natural oxidation for 3 h, and the functionalized graphene was obtained.

[0065] The conductivity and dispersibility of the obtained functionalized graphene were tested in the same manner as in Example 1.

[0066] The obtained functionalized graphene was made into a graphene film with a thickness of 17 μm, and the conductivity was measured to be 3.40 x 10 5 S / m, which had good conductivity. In addition to having good conductivity, the graphene had excellent dispersibility in water, and the Zeta potential of the aqueous dispersion of the graphene was -20.7 mV after standing for 30 days, which had good dispersion stability.

[0067] Comparative Example 1

[0068] A 300 mL high-pressure stainless steel ball mill pot was charged with 10 g of 200 mesh natural flake graphite and 400 g of ball milling beads (zirconia ball milling beads with a diameter of 5-15 mm), the pot lid was tightened, and the pot was then fixed on a planetary ball mill. A certain amount of CO2 was pumped into the ball mill pot to remove the air by a high-pressure pump, and then the pot was evacuated to a near vacuum state (-0.1 MPa) by a vacuum pump. The ball mill was started, and the temperature of the ball mill temperature controller was set to 40°C; then, the ball mill was run at a speed of 450 rpm for 2 h and stopped. Then, CO2 was pumped into the ball mill pot by a high-pressure pump to make the CO2 density in the pot reach 0.84 g / cm3

[0069] The properties of the obtained functionalized graphene were tested in the same manner as in Example 1.

[0070] The graphene sheets prepared in Comparative Example 1 were smaller (about 50-500 nm) and thicker (about 30-100 nm), and maintained the water dispersibility consistent with Example 1 but the conductivity was greatly reduced to 7.89 x 10 3 S / m. This shows that the near-vacuum ball milling process can only simply break up the bulk graphite and does not have the ability to exfoliate. Figure 8 The TEM image of the functionalized graphene prepared in Comparative Example 1 is shown in FIG. 2B. As shown in FIG. 2B, the graphene prepared in Comparative Example 1 had a poor crystal structure compared to the graphene prepared in Example 1 (FIG. 2A), and thus the graphene film prepared after ball milling had poor conductivity. However, the graphene sheets had a high number of oxygen-containing functional groups at the edges due to the high collision energy during the near-vacuum ball milling stage, and thus maintained high water dispersibility, with a Zeta potential of -59.4 mV for the dispersion after 30 days of standing. Figure 8 Figure 5 The TEM image of the functionalized graphene prepared in Comparative Example 1 is shown in FIG. 2B. As shown in FIG. 2B, the graphene prepared in Comparative Example 1 had a poor crystal structure compared to the graphene prepared in Example 1 (FIG. 2A), and thus the graphene film prepared after ball milling had poor conductivity. However, the graphene sheets had a high number of oxygen-containing functional groups at the edges due to the high collision energy during the near-vacuum ball milling stage, and thus maintained high water dispersibility, with a Zeta potential of -59.4 mV for the dispersion after 30 days of standing.

[0071] Comparative Example 2

[0072] A 15 g sample of 100 mesh natural flake graphite and 400 g of ball milling beads (zirconium oxide ball milling beads with a diameter of 5-15 mm) were placed in a 300 mL high-pressure stainless steel ball mill, the lid was tightened, and the ball mill was then fixed on a planetary ball mill. CO2 was pumped into the ball mill through a high-pressure pump until the CO2 density in the ball mill reached 0.70 g / cm 3 The ball mill was started, and the temperature of the ball mill temperature controller was set to 40°C. After 32 h of operation at a rotation speed of 400 rpm, the ball mill was stopped. The CO2 was released through the valve on the ball mill until the pressure in the ball mill dropped to atmospheric pressure, the lid of the ball mill was opened, the material was removed, and the ball milling beads and the sample were separated through a screen. The sample was left to naturally oxidize in air for 3 h to obtain the functionalized graphene.

[0073] The sample was separated and analyzed for structure, morphology, dispersibility, and conductivity using the method of Example 1. Compared to Example 1, the graphene prepared in Comparative Example 2 had larger sheets (about 1-3 pm) and smaller thickness (about 1-5 nm), and the conductivity was greatly increased to 5.23 x 10 5 S / m, but had essentially no water dispersibility.

[0074] This shows that simply using CO2 ball milling has a strong exfoliation effect and can effectively exfoliate bulk graphite into few-layer graphene. However, the collision energy during the CO2 ball milling stage is low, and it is difficult to efficiently activate the edges of the graphene sheets on a large scale, so there are fewer oxygen-containing functional groups and the water dispersibility is very poor.

[0075] Comparative Example 3

[0076] ​A 300 mL high-pressure stainless steel ball mill pot was charged with 15 g of 100 mesh natural flake graphite and 400 g of ball milling beads (zirconia ball milling beads with a diameter of 5-15 mm), the pot lid was tightened, and the pot was then fixed on a planetary ball mill. CO2 was pumped into the ball mill pot through a high-pressure pump until the CO2 density in the pot reached 0.10 g / cm3. The ball mill was started, and the temperature of the ball mill temperature controller was set to 40 °C; then, the ball mill was stopped after running at a speed of 450 rpm for 8 h. Then, CO2 was pumped into the ball mill pot through the high-pressure pump until the CO2 density in the pot reached 0.70 g / cm3. 3 The ball mill was started, and the temperature of the ball mill temperature controller was set to 40 °C; then, the ball mill was stopped after running at a speed of 400 rpm for 24 h. The CO2 was released through the valve on the ball mill pot until the pressure in the ball mill pot dropped to atmospheric pressure, the ball mill pot lid was opened, the material was taken out, and the ball milling beads and the sample were separated through a screen, the sample was left to naturally oxidize in air for 3 h, and the functionalized graphene was obtained. 3 The ball mill was started, and the temperature of the ball mill temperature controller was set to 40 °C; then, the ball mill was stopped after running at a speed of 400 rpm for 24 h. The CO2 was released through the valve on the ball mill pot until the pressure in the ball mill pot dropped to atmospheric pressure, the ball mill pot lid was opened, the material was taken out, and the ball milling beads and the sample were separated through a screen, the sample was left to naturally oxidize in air for 3 h, and the functionalized graphene was obtained.

[0077] The sample was separated and analyzed for structure, morphology, dispersion performance, and electrical conductivity using the method of Example 1. Compared with Example 1, the graphene sheets prepared in Comparative Example 3 were larger (about 1-2 pm) and thinner (about 1-8 nm), and the electrical conductivity increased to 4.17 x 10 5 S / m, but the water dispersion performance was poor, and the water dispersion liquid was stratified and precipitated.

[0078] Comparative Example 4

[0079] A 300 mL high-pressure stainless steel ball mill pot was charged with 15 g of 100 mesh natural flake graphite and 400 g of ball milling beads (zirconia ball milling beads with a diameter of 5-15 mm), the pot lid was tightened, and the pot was then fixed on a planetary ball mill. A certain amount of CO2 was pumped into the ball mill pot through a high-pressure pump to remove air, and then the pot was pumped to a near vacuum state (-0.1 MPa) using a vacuum pump. The ball mill was started, and the temperature of the ball mill temperature controller was set to 40 °C; then, the ball mill was stopped after running at a speed of 450 rpm for 8 h. Then, CO2 was pumped into the ball mill pot through the high-pressure pump until the CO2 density in the pot reached 0.70 g / cm3. 3 The ball mill was started, and the temperature of the ball mill temperature controller was set to 40 °C; then, the ball mill was stopped after running at a speed of 400 rpm for 24 h. The CO2 was released through the valve on the ball mill pot until the pressure in the ball mill pot dropped to atmospheric pressure, the ball mill pot lid was opened, the material was taken out, and the ball milling beads and the sample were separated through a screen, the sample was left to naturally oxidize in air for 3 h, and the functionalized graphene was obtained.

[0080] The sample structure, morphology, dispersion performance and conductive performance were separated and analyzed by the method of Example 1. Compared with Example 1, the conductivity of the graphene film prepared in Comparative Example 4 increased to 2.19 x 10 5 S / m, but the water dispersion performance was poor, and the water dispersion liquid showed stratification and precipitation. This is because the oxygen was isolated when the ball mill was opened, so the activated edge of the sheet layer cannot be effectively oxidized during the ball milling process. At the same time, the increasing conductivity also indicates that the sheet edge does not introduce oxygen-containing functional groups, and the intrinsic structure is good. This shows that the atmosphere state when the ball mill is opened will significantly affect the degree of oxidation of graphene, and the edge of the graphene sheet activated by ball milling must be effectively oxidized in an oxygen-containing atmosphere.

[0081] Comparative Examples 3 and 4 show that whether the state of the sample when the ball mill is opened contains oxygen will significantly affect whether functionalized graphene can be obtained; and the CO2 density in the ball mill will significantly affect the collision energy of the ball mill beads. With the increase of CO2 density, its collision energy will be greatly reduced Figure 3 ). Therefore, reasonable control of the CO2 density at different ball milling stages and the oxygen-containing conditions when the ball mill is opened will help to prepare graphene products with high conductivity and high dispersion.

[0082] As can be seen from the above, in the initial stage of ball milling, vacuum state should be adopted for ball milling to obtain the maximum ball milling bead collision energy, and to quickly create certain defects in the edge of the graphite sheet in a shorter time; then, the CO2 density needs to be increased to reduce the collision energy of the ball milling beads, and the high-density supercritical CO2 state greatly enhances the penetration-intercalation effect of CO2 molecules, that is, the stripping effect is greatly improved. In the last stage of stripping, the sample is kept in an oxygen-free environment for a certain time, and the operation of contacting with oxygen-containing conditions has a decisive influence on the preparation of graphene products with high conductivity and high dispersion.

[0083] Although the above examples have made a detailed description of the present application, it is only a part of the embodiments of the present application, not all embodiments, and other embodiments can be obtained according to the present embodiments without creativity, which are within the protection scope of the present application.

Claims

1. A method for preparing functionalized graphene, characterized in that, Includes the following steps: The graphite raw material was ball-milled under vacuum conditions to obtain the first mixture. The first mixture was subjected to a second-stage ball milling under supercritical carbon dioxide conditions to obtain a second mixture. The second mixture is subjected to natural oxidation under oxygen-containing conditions to obtain the functionalized graphene.

2. The preparation method according to claim 1, characterized in that, The graphite raw material includes one or more of natural graphite, expanded graphite, and flake graphite.

3. The preparation method according to claim 1, characterized in that, During the first and second stage ball milling processes, the mass ratio of the graphite raw material to the milling beads is independently 1:10 to 100.

4. The preparation method according to claim 1, characterized in that, The vacuum level of the vacuum condition is -0.05 to -0.1 MPa.

5. The preparation method according to claim 1, characterized in that, The first stage of ball milling involves a rotation speed of 150–500 rpm and a time of 4–12 hours.

6. The preparation method according to claim 1, characterized in that, The temperature of the first stage of ball milling is 20-50℃.

7. The preparation method according to claim 1, characterized in that, The density of carbon dioxide under the supercritical carbon dioxide conditions is 0.10–0.90 g / cm³. 3 .

8. The preparation method according to claim 1, characterized in that, The second stage of ball milling involves a rotation speed of 250–450 rpm and a time of 10–50 h.

9. The preparation method according to claim 1, characterized in that, The temperature of the second stage of ball milling is 35-50℃.

10. The preparation method according to claim 1, characterized in that, The natural oxidation time is 30 to 300 minutes.

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