CN111943182A

CN111943182A - Graphene powder and method for improving graphene defects

Info

Publication number: CN111943182A
Application number: CN201910403412.2A
Authority: CN
Inventors: 李镇宇; 涂博闵; 陈家荣; 黄宇文
Original assignee: Xsense Technology Corp
Current assignee: Agson Technology Co ltd
Priority date: 2019-05-15
Filing date: 2019-05-15
Publication date: 2020-11-17

Abstract

A method of ameliorating graphene defects, comprising: introducing and leading mixed fluid with reaction compound and supercritical fluid to infiltrate the graphene powder in the reaction tank in which the graphene powder is contained and which accords with the supercritical fluid environment, wherein the reaction compound comprises compound of carbon, hydrogen, nitrogen, silicon or oxygen element so as to passivate and repair the graphene structure defect of the graphene powder; and separating the mixed fluid from the graphene powder, and adsorbing the graphene powder remaining in the mixed fluid by using a molecular sieve. The invention also provides graphene powder prepared by the method. According to the invention, the structural defect proportion of graphene can be effectively reduced, the composition content of graphene can be increased, the number of layers of graphene can be reduced, and graphene powder with good heat conduction and electric conduction performance can be provided.

Description

Graphene powder and method for improving graphene defects

Technical Field

The present invention relates to a method for improving graphene defects, and more particularly, to a method for improving graphene defects using a mixed fluid containing a reactive compound and a supercritical fluid.

Background

Graphene (Graphene), which is one of the thinnest and strongest nanomaterials, is a two-dimensional honeycomb-like carbonaceous material having a single layer of carbon atoms, and has excellent electrical conductivity, thermal conductivity, mechanical and barrier properties, thermal stability, light transmittance, and corrosion resistance, and thus can be used as a functional filler in various fields such as electronic components, light-emitting components, electromagnetic wave shielding, lithium battery electrodes, solar cells, conductive coatings, heat dissipation materials, conductive inks, and biosensors.

At present, the main methods for preparing graphene include: physical peeling, oxidation reduction, deep frying and acetylene burning, but the above methods all are liable to cause graphene to generate many defects (defects) which are formed by breaking covalent bonds of grain boundaries to form dangling bonds (dangling bonds); if the defect is not treated, the electrical property, physical property and chemical property of the graphene are affected, and the application field of the graphene is further limited. Therefore, repairing the graphene defect is a problem to be solved in the art.

However, in the prior art, a wet chemical reaction method is mainly adopted to repair the graphene defect by bonding elements such as hydrogen or oxygen, but the wet chemical reaction is performed at room temperature, so that the effect of passivating the defect is limited, and the characteristics of the graphene cannot be completely recovered; moreover, elements of the wet chemical reaction process are difficult to permeate into the multi-layer graphene layer and the interior of the multi-layer graphene layer, and the graphene layer above the double layers cannot be completely repaired; in addition, the wet chemical reaction process is complex and expensive, and the waste liquid formed by the process is a serious concern for the future environment, which is one of the obstacles for the quantitative production of graphene.

In view of the above, a method for improving graphene defects, which can effectively reduce graphene defects, improve graphene performance and reduce process cost, is needed to solve the problems in the prior art.

Disclosure of Invention

In order to solve the above problems, the present invention provides a method for improving graphene defects, comprising: introducing and leading mixed fluid with reaction compound and supercritical fluid to infiltrate the graphene powder in the reaction tank in which the graphene powder is contained and which accords with the supercritical fluid environment, wherein the reaction compound comprises compound of carbon, hydrogen, nitrogen, silicon or oxygen element so as to passivate and repair the graphene structure defect of the graphene powder; and separating the mixed fluid from the graphene powder, and adsorbing the graphene powder remaining in the mixed fluid by using a molecular sieve.

The present invention also provides a graphene powder comprising: graphene having at least one chemical bond selected from the group consisting of N-H, C-H, C-O, C-N and C-Si, the number of graphene layers being 20 or less; wherein the 2D/G value of the graphene powder is 0.3 to 0.6, and the G/D value of the graphene powder is 2.0 to 4.0, and the 2D/G value and the G/D value are obtained from intensity ratios of Raman shift 1351 wavenumber (D band), Raman shift 1587 wavenumber (G band), and Raman shift 2687 wavenumber (2D band) of Raman spectroscopy.

The method for improving the defects of the graphene can effectively reduce the proportion of the structural defects of the graphene, increase the composition content of the graphene and reduce the number of layers of the graphene, can provide the graphene powder with good heat conduction and electric conduction properties, has the advantages of simple process, no pollution problem and low process cost, and has wide application prospect.

Drawings

Embodiments of the invention are described by way of example with reference to the accompanying drawings:

fig. 1 is a flowchart of a first embodiment of a defect-amelioration processing apparatus for graphene;

FIG. 2 is a schematic view of the apparatus of the reaction tank;

fig. 3 is a flowchart of a second embodiment of a defect-amelioration processing apparatus for graphene;

fig. 4 is a flowchart of a third embodiment of a defect improvement processing apparatus for graphene;

fig. 5 is a flowchart of a fourth embodiment of a defect improvement processing apparatus for graphene;

fig. 6 is a flowchart of a fifth embodiment of a defect improvement processing apparatus for graphene;

fig. 7 is a raman spectrum of the graphene powder according to an embodiment;

fig. 8 is a raman spectrum of unrepaired graphene powder; and

fig. 9 is a raman spectrum of the graphene powder repaired by the wet chemical reaction method.

Wherein the reference numerals are as follows:

1 mixing tank

2 reaction tank

3 separating tank

10 graphite material

11 graphene powder (unrepaired)

11' repaired graphene powder

12 supercritical fluid storage tank

13 reaction compound storage tank

14 pump

15 Filter device

20 preparation tank

21 molecular sieve

22 container

23 stirring device

24 grinding device

25 pipeline

31 molecular sieve.

Detailed Description

The embodiments of the present invention are described below with reference to specific embodiments, and those skilled in the art can easily understand the advantages and effects of the present invention from the disclosure of the present specification. The invention is capable of other and different embodiments and its several details are capable of modification in various other respects, all without departing from the spirit and scope of the present disclosure. Moreover, all ranges and values herein are inclusive and combinable. Any number or point within the ranges set forth herein, e.g., any integer, may be treated as the minimum or maximum value to derive a lower range, etc.

According to the invention, a method for improving graphene defects comprises the following steps: introducing and leading mixed fluid with reaction compound and supercritical fluid to infiltrate the graphene powder in the reaction tank in which the graphene powder is contained and which accords with the supercritical fluid environment, wherein the reaction compound comprises compound of carbon, hydrogen, nitrogen, silicon or oxygen element so as to passivate and repair the graphene structure defect of the graphene powder; and separating the mixed fluid from the graphene powder, and adsorbing the graphene powder remaining in the mixed fluid by using a molecular sieve.

The graphene powder refers to graphene having 30 or less layers, particularly 20 or less layers or 10 or less layers, without any repair treatment.

According to the invention, the supercritical fluid is used as a carrier or a solvent of a reaction compound by utilizing the solubility and the diffusion capacity of the supercritical fluid, when the supercritical fluid permeates into the layered structure of the graphene, the reaction compound is passivated and repaired at the position of the structural defect of the graphene, and after the repair is finished, the solvent can be completely separated. In addition, by means of the permeation of the supercritical fluid, the acting force between the graphene layer and the layer can be effectively reduced, the graphene is further stripped and separated, the number of layers of the graphene is reduced, the yield of the graphene is improved, and the performance of the graphene powder is improved. Wherein the supercritical fluid comprises carbon dioxide, nitrogen, ethylene, propane, propylene or water. In one embodiment, the supercritical fluid is carbon dioxide or water.

The reaction compound comprises a compound of carbon, hydrogen, nitrogen, silicon or oxygen elements, and the reaction compound can be converted into an ionic state under the supercritical fluid environment, so that the ionic state reacts with dangling bonds of the structure in the graphene layer to form bonding with the elements such as carbon, hydrogen, nitrogen, silicon or oxygen, and the purpose of the bonding is to passivate and change the surface functional groups of the graphene and improve the processability of subsequent application. The reactant compound selected as the solute may be in any form and includes solid, liquid or gaseous, wherein the reactant compound is particularly preferably in gaseous form, and consideration is given to compounds that do not react with and have good solubility in the supercritical fluid. To reduce the reaction energy barrier of the reaction compound, the molecular weight of the reaction compound is preferably not more than 200 grams per mole (g/mol), and the adsorption force between the reaction compound and the graphene dangling bond is also important. In one embodiment, the reaction compound includes at least one selected from the group consisting of an organosilicon compound, an alkane, an alkene, an alkyne, an ammonia molecule and its derivatives, a hydroxide, and an organic base.

In another embodiment, when the supercritical fluid is carbon dioxide, the reaction compound comprises one selected from the group consisting of silane compounds, ethylene, methane, acetylene, ammonia, and water. Wherein the silane compound comprises monosilane, methylsilane or dimethylsilane.

In yet another embodiment, when the supercritical fluid is carbon dioxide, the reaction compound is water, ammonia, or a silane compound.

Before introducing the mixed fluid containing the reaction compound and the supercritical fluid, the method uses a high-pressure injection pump and a heater to enable the fluid in the mixing tank to reach a preset temperature and pressure value and to be in a supercritical state, and then the reaction compound is injected into the mixing tank to be mixed for 5 to 10 minutes so as to be dissolved in the supercritical fluid to form the mixed fluid containing the reaction compound and the supercritical fluid.

In one embodiment, the volume ratio of the reaction compound to the supercritical fluid is from 1:1 to 1: 10.

In another embodiment, the volume ratio of the reaction compound to the supercritical fluid is from 1:1 to 1: 2.

Referring to fig. 1, the defect-improving graphene processing apparatus according to the present invention includes a supercritical fluid storage tank 12, a reaction compound storage tank 13, a mixing tank 1, a reaction tank 2, and a pump 14 in this order. Wherein, the reaction tank 2 comprises a container 22 and a molecular sieve 21, and the molecular sieve 21 can be a layer body. The operation process comprises the following steps: placing the graphene powder 11 in a container 22 in a high pressure resistant reaction tank 2, when the reaction tank reaches a preset temperature and pressure value and meets the supercritical fluid environment, introducing a mixed fluid which is fully dissolved in a mixing tank 1 and has a reaction compound and a supercritical fluid, and infiltrating the graphene powder in the reaction tank 2 at high pressure for a preset time to passivate and repair the structural defects of the graphene; finally, after the mixed fluid and the repaired graphene powder are completely separated by the pump 14, the reaction tank is returned to normal temperature and normal pressure, the repaired graphene powder 11' is taken out, the molecular sieve 21 can adsorb the remaining graphene powder in the mixed fluid in the separation process, and the graphene powder retained on the molecular sieve can also be used as a rear end.

In one embodiment, referring to fig. 2, a stirring device 23 is further disposed in the reaction tank 2, and is used to stir the graphene powder 11 in the container 22 in a mechanical control or magnetic control manner, which is helpful for improving the impregnation efficiency of the mixed fluid containing the reaction compound and the supercritical fluid in the graphene powder.

In another embodiment, the graphene powder is directly contained in a reaction tank without a container.

In one embodiment, the pressure of the reaction tank is 50 to 100 atm, and the temperature of the reaction tank is 25 to 400 ℃.

In another embodiment, when the supercritical fluid is carbon dioxide, the pressure of the reaction vessel is 62 to 82 atm and the temperature of the reaction vessel is 28 to 40 ℃.

In one embodiment, the infiltration time is from 2 to 60 minutes.

In another embodiment, the infiltration time is from 10 to 30 minutes.

In one embodiment, the volume ratio of the graphene powder to the mixed fluid in the reaction tank is 0.01 to 1000.

On the other hand, since the supercritical fluid has an effect of extracting impurities such as sulfide, phosphide, and iron-containing substances in the graphene, the separation process after the impregnation treatment requires complete separation of the mixed fluid of the reactant compound and the supercritical fluid, so as to prevent the impurities from remaining on the surface of the graphene and affecting the product effect.

The pore size of the molecular sieve is mainly less than 50 microns, and the pore size of the molecular sieve is selected according to the subsequent application of graphene: if the subsequent application is in the field of heat dissipation, selecting a molecular sieve with the pore diameter of 30-50 microns; if the subsequent application is in the field of batteries, the molecular sieve with the pore diameter less than 5 microns is selected.

In one embodiment, the step of separating the mixed fluid from the graphene powder includes feeding the mixed fluid into a separation tank independent of the reaction tank.

In addition, in an embodiment, the method for improving graphene defects further includes forming a graphite material into graphene powder before or while introducing the mixed fluid.

Referring to fig. 3, an embodiment of a method for improving graphene defects is described, in which a graphite material is made into graphene powder in a preparation tank 20 independent from a reaction tank before the mixed fluid is introduced into the reaction tank 2, the preparation method of the graphene powder includes a physical layer preparation method, a redox method, a frying method or an acetylene combustion method; after the production, the graphene powder is transferred to the container 22 in the reaction tank 2 and subjected to a high-pressure impregnation treatment. The operation process comprises the following steps: preparing a graphite material 10 into graphene powder in a preparation tank 20, transferring the graphene powder to a container 22 of a reaction tank 2, introducing a mixed fluid which is fully dissolved in a mixing tank 1 and contains a reaction compound and a supercritical fluid after the reaction tank 2 reaches a preset temperature and pressure value, and infiltrating the graphene powder in the reaction tank 2 at high pressure for a preset time to passivate and repair the structural defects of the graphene; finally, after the mixed fluid and the repaired graphene powder are completely separated by the pump 14, the reaction tank is returned to normal temperature and normal pressure, the repaired graphene powder 11' is taken out, the residual graphene powder in the mixed fluid can be adsorbed by the molecular sieve 21 in the separation process, and the graphene powder remained on the molecular sieve can also be used for subsequent application.

In one embodiment, the graphite material with a particle size of less than 10 microns and a graphite content of greater than 95% is selected.

In another embodiment, the method for improving graphene defects is to make a graphite material into graphene powder in the reaction tank while introducing the mixed fluid.

Referring to fig. 4, a specific embodiment of introducing the mixed fluid and preparing graphene powder is described, wherein a grinding device 24 is further disposed in the reaction tank 2, and the graphene powder is prepared from the graphite material 10 by physical delamination, and is impregnated with the mixed fluid of the reactive compound and the supercritical fluid at a high pressure for a predetermined time in a supercritical fluid environment at a predetermined temperature and pressure value, so as to passivate and repair the defects; after impregnating the graphene powder, standing for at least 30 minutes to settle the repaired graphene powder in the grinding device 24; then, after the mixed fluid and the repaired graphene powder are completely separated, the reaction tank is returned to normal temperature and normal pressure, and the repaired graphene powder 11' is taken out, wherein the separation process further comprises the step of introducing the mixed fluid separated from the reaction tank into a separation tank 3 by a pump 14, in addition, the temperature and the pressure of the separation tank 3 also accord with the supercritical fluid environment so as to maintain the solvent in a supercritical state, a molecular sieve 31 is arranged in the separation tank 3, the graphene powder remained in the mixed fluid can be adsorbed by the molecular sieve 21, and the graphene powder remained on the molecular sieve can also be used for subsequent application.

Referring to fig. 5, in an embodiment, the method for improving graphene defects of the present invention further includes separating the mixed fluid from the graphene powder, filtering the mixed fluid with the reaction compound and the supercritical fluid in the separation tank 3 through the filtering device 15, and then refluxing the mixed fluid to the reaction tank 2 for recycling.

In another embodiment, the ratio of the mixture of the refluxed reactant compound and the supercritical fluid in the reaction tank is 5 to 20%

Referring to fig. 6, in an embodiment, the method for improving Graphene defects of the present invention further includes connecting the reaction tank 2 and the separation tank 3 by a pipeline 25 having a pipe diameter of less than 1 mm, wherein a flow velocity of a mixed fluid in the pipeline 25 is at least 400 m/s, which is different from a general connecting pipeline having a pipe diameter of at least 2 to 3 cm, and preparing a repaired Graphene powder 11' having a particle diameter of less than 10 nm by using a pressure difference between the reaction tank and the separation tank and an impact force of the mixed fluid on a narrow pipe wall, even the particle diameter of the Graphene powder can be less than 5 nm, which is a Graphene Quantum Dot (Graphene Quantum Dot) having a Quantum confinement effect and a boundary effect, and which can be used in the fields of solar photovoltaic devices, biomedicines, light emitting diodes, sensors, and the like.

The invention also provides graphene powder prepared by the method, which comprises the following steps: graphene having at least one chemical bond selected from the group consisting of N-H, C-H, C-O, C-N and C-Si, the number of graphene layers being 20 or less; wherein the 2D/G value of the graphene powder is 0.3 to 0.6, and the G/D value of the graphene powder is 2.0 to 4.0, and the 2D/G value and the G/D value are obtained by raman spectroscopy analysis, as shown in fig. 7, which is a raman spectrum of the graphene powder of an embodiment, the laser wavelength used by the Raman spectrometer is 400-550 nanometers, the wave number of Raman shift 1351 is a D frequency band, the G band at a Raman shift of 1587 wavenumbers, and the 2D band at a Raman shift of 2687 wavenumbers, the 2D/G value and the G/D value are ratios obtained from intensities of the respective frequency bands, wherein, the value of the 2D/G value represents the number of graphene layers of the graphene powder, and a low 2D/G value means that the number of graphene layers is more, and the 2D/G value of the graphene powder represents that the number of graphene layers of the graphene powder is less than 15; the G/D value represents a defect ratio in graphene, and a high G/D value means that the defect ratio in graphene is lower.

The graphene powder prepared by the method for improving the graphene defects has the resistivity of 1.0-10.0 x10^-6Ohm-cm (ohm-cm) and thermal conductivity of 1500-4000W/(meter. Kelvin) (W/m.K), which can greatly improve the electrical conductivity and thermal conductivity of the graphene powder.

In one embodiment, the content of graphene in the graphene powder repaired by the method can be increased from less than 80.0% to 99.95%.

The graphene powder provided by the method can be applied to the field of coatings and adhesive films, and the repaired graphene powder has carbon, hydrogen, nitrogen, silicon or oxygen elements which are beneficial to dispersing graphene in polar or non-polar solvents, so that the stability of the formula of the coatings and adhesive films can be improved, wherein the compatible solvents of the repaired graphene powder comprise: water, formamide, trifluoroacetic acid, dimethyl sulfoxide, acetonitrile, dimethylformamide, hexamethylphosphoramide, methanol, ethanol, acetic acid, isopropanol, pyridine, tetramethylethylenediamine, acetone, triethylamine, n-butanol, dioxane, tetrahydrofuran, methyl formate, tributylamine, butanone, ethyl acetate, trioctylamine, dimethyl carbonate, diethyl ether, isopropyl ether, n-butyl ether, trichloroethylene, diphenyl ether, dichloromethane, chloroform, dichloroethane, toluene, benzene, carbon tetrachloride, carbon disulfide, cyclohexane, hexane, or kerosene. The coating and the adhesive film have the effects of heat dissipation, electromagnetic wave shielding and electric conduction, and can be used for products such as temperature equalizing films of mobile phones, functional clothes, energy storage devices, motor modules, coatings of automobile industry or military equipment and the like.

The present invention is further illustrated in detail by examples.

Example 1:

firstly, a mixed fluid which takes water as a reaction compound and supercritical carbon dioxide as a solvent is configured in a mixing tank, wherein the volume ratio of the water to the carbon dioxide is 1: injecting carbon dioxide into a mixing tank by a high-pressure injection pump, enabling the temperature in the mixing tank to reach 31 ℃ and the pressure in the mixing tank to reach 80 standard atmospheric pressure by a heater, enabling the carbon dioxide fluid to be in a supercritical state, then injecting water into the mixing tank, mixing for 5-10 minutes, and enabling the water and the supercritical carbon dioxide to be fully dissolved to form a mixed fluid.

Placing graphene powder to be treated in a container in a reaction tank, wherein the number of graphene layers of the graphene powder is about 15 to 20; when the temperature of the reaction tank reaches 31 ℃, the pressure reaches 80 standard atmospheric pressure and meets the supercritical fluid environment, introducing a mixed fluid which is fully dissolved in the mixing tank, wherein the volume ratio of the graphene powder in the reaction tank to the mixed fluid is 100, and infiltrating the graphene powder in the reaction tank for about 30 minutes under high pressure to passivate and repair the structural defects of the graphene; finally, the mixed fluid and the repaired graphene powder are completely separated by a pump, the graphene powder remaining in the mixed fluid is adsorbed by the molecular sieve, after separation, the reaction tank is returned to normal temperature and normal pressure, the repaired graphene powder is taken out, and the 2D/G value and the G/D value of the graphene powder are analyzed by a raman spectrometer, and the analysis results are shown in fig. 7 and table 1.

The details of the test methods relating to raman spectroscopy analysis are as follows:

1. raman spectrometer instrument

2. Analysis method using Raman spectrometer

The Raman spectrometer uses a laser wavelength of 532 nanometers, a Raman shift of 1351 wave number as a D band, a Raman shift of 1587 wave number as a G band, and a Raman shift of 2687 wave number as a 2D band, wherein the 2D/G value and the G/D value are ratios obtained by the intensity of each band, the 2D/G value represents the number of graphene layers of numerical graphene powder, and the lower 2D/G value means that the number of graphene layers is more; the numerical value of the G/D value represents the defect ratio of the graphene, and the high G/D value means that the defect ratio of the graphene is lower.

Example 2:

the method for improving defects of graphene and the method for testing the defects of graphene are the same as those of example 1 except that the graphene powder to be treated in example 1 is replaced with a graphene powder containing about 6 to 10 layers of graphene.

Comparative example 1:

the raman spectrometer analysis was performed on the graphene powder prepared by the physical delamination method and not repaired, the test method is the same as that of example 1, and the analysis results are shown in fig. 8 and table 1.

Comparative example 2:

graphene powder repaired in a wet chemical reaction manner, wherein the graphene powder to be treated contains about 10 to 15 layers of graphene; next, the graphene powder after wet chemical repair was analyzed by raman spectroscopy in the same manner as in example 1, and the analysis results are shown in fig. 9 and table 1.

TABLE 1

As can be seen from the results in table 1, compared to comparative example 1, the graphene powder prepared by the method for improving graphene defects of the present invention significantly improves the 2D/G value and the G/D value, and indeed has the effects of reducing the number of layers of graphene and reducing the structural defect ratio of graphene; in addition, compared with comparative example 2, although the graphene powder prepared by the present invention cannot provide a very low defect ratio of the graphene prepared by the wet chemical reaction method, the graphene powder prepared by the present invention can effectively reduce the number of graphene layers, and can also improve the electrical property, chemical property and physical property of the graphene product.

In conclusion, the method for improving the graphene defects can effectively reduce the structural defect proportion of the graphene, increase the composition content of the graphene and reduce the number of layers of the graphene, can provide the graphene powder with good heat conduction and electric conduction properties, has the advantages of simple process, no pollution problem and low process cost, and has wide application prospect.

The above embodiments are merely illustrative, and not restrictive, of the invention. Modifications and variations can be made to the above-described embodiments by those skilled in the art without departing from the spirit and scope of the present invention. Therefore, the scope of the invention is defined by the appended claims, and is covered by the disclosure unless it does not affect the effect and the implementation of the invention.

Claims

1. A method of ameliorating graphene defects, comprising:

introducing and leading mixed fluid with reaction compound and supercritical fluid to infiltrate the graphene powder in a reaction tank which contains the graphene powder and accords with the supercritical fluid environment, wherein the reaction compound comprises a compound of carbon, hydrogen, nitrogen, silicon or oxygen element so as to passivate and repair the graphene structure defect of the graphene powder; and

and separating the mixed fluid from the graphene powder, and adsorbing the graphene powder remained in the mixed fluid by using a molecular sieve.

2. The method of claim 1, wherein the reaction compound is converted to an ionic state in the supercritical fluid environment to react with the structural defects of the graphene to form bonds, wherein the reaction compound has a molecular weight of no more than 200 g/mol.

3. The method of claim 2, wherein the reaction compound comprises at least one selected from the group consisting of organosilicon compounds, alkanes, alkenes, alkynes, ammonia molecules and derivatives thereof, hydroxides, and organic bases.

4. The method of claim 1, wherein the supercritical fluid comprises carbon dioxide, nitrogen, ethylene, propane, propylene, or water.

5. The method according to claim 1, wherein when the supercritical fluid is carbon dioxide, the reaction compound comprises at least one selected from the group consisting of a silane compound, ethylene, methane, acetylene, ammonia gas, and water, wherein the silane compound comprises monosilane, methylsilane, or dimethylsilane.

6. The method according to claim 1, wherein the volume ratio of the reaction compound to the supercritical fluid is 1:1 to 1:10, and the volume ratio of the graphene powder to the mixed fluid in the reaction tank is 0.01 to 1000.

7. The method of claim 1, wherein the pressure of the reaction tank is 50 to 100 atm, the temperature of the reaction tank is 25 to 400 ℃, and the impregnation time is 2 to 60 minutes.

8. The method of claim 1, further comprising forming a graphite material into graphene powder prior to or while introducing the mixed fluid.

9. The method of claim 8, wherein the graphene powder is prepared by forming the graphite material into graphene powder in a preparation tank separate from the reaction tank before introducing the mixed fluid, and transferring the graphene powder into the reaction tank.

10. The method according to claim 8, wherein the graphene powder is prepared by preparing the graphite material into graphene powder in the reaction tank while introducing the mixed fluid, wherein a grinding device is further arranged in the reaction tank, and the graphene powder is prepared in a physical delamination manner.

11. The method of claim 10, further comprising standing the graphene powder and mixed fluid for at least 30 minutes after impregnating the graphene powder to settle the graphene powder.

12. The method of claim 1, wherein the molecular sieve is disposed in a layer within the reaction tank, wherein the molecular sieve has a pore size of less than 50 microns.

13. The method of claim 1, wherein the step of separating the mixed fluid from the graphene powder comprises feeding the mixed fluid into a separation tank independent of a reaction tank, wherein a molecular sieve is further disposed in the separation tank.

14. A method according to claim 13, further comprising connecting the reaction tank and the separation tank with a pipeline having a pipe diameter of less than 1 mm, and controlling a flow velocity of the mixed fluid in the pipeline to be at least 400 m/s.

15. The method of claim 1, further comprising filtering the mixed fluid after separating the mixed fluid from the graphene powder; and refluxing the mixed fluid into the reaction tank at a reflux ratio of 5 to 20%.

16. A graphene powder comprising:

graphene having at least one chemical bond selected from the group consisting of N-H, C-H, C-O, C-N and C-Si, wherein the number of graphene layers is 20 or less;

characterized in that the graphene powder has a 2D/G value of 0.3 to 0.6, the graphene powder has a G/D value of 2.0 to 4.0, and the 2D/G value and the G/D value are obtained from intensity ratios of Raman shift 1351 wavenumber (D band), Raman shift 1587 wavenumber (G band), and Raman shift 2687 wavenumber (2D band) by Raman spectroscopy.

17. The graphene powder according to claim 16, wherein the graphene content is 80.0% to 99.95%.

18. The graphene powder of claim 16, wherein the graphene powder has a thermal conductivity of 1500 to 4000 watts/(meter-kelvin) (W/m-K) and an electrical resistivity of 1.0 to 10.0x10^-6Ohm-centimeters (ohm-cm).