Graphene powder, preparation method thereof and application thereof

Abstract

The application provides a graphene powder and a preparation method and application thereof, and the preparation method of the graphene powder comprises the following steps: under a high vacuum degree, a uniform and stable glow plasma is spontaneously generated in a microwave plasma device with inert gas as background gas under the action of microwaves; the flow of the inert gas is increased and the pressure of the system is increased to a low vacuum degree state, so that the glow plasma is changed into a state of coexistence of glow plasma and electric arc; the saturated steam of a liquid carbon source is brought into a reaction cavity of the microwave plasma device through negative pressure of the system, under the action of the glow plasma and the electric arc, the carbon source molecules are impacted by high-energy particles to be cracked, and the active carbon components after the cracking are nucleated and grown to obtain the graphene powder. The graphene powder is prepared by using the microwave plasma technology, and the nanoscale graphene powder with excellent dispersity can be continuously and efficiently prepared.

Description

Technical Field

[0001] This invention relates to a graphene powder, its preparation method and application, belonging to the field of graphene material technology. Background Technology

[0002] Graphene, with its excellent properties in acoustics, optics, electricity, and heat, has attracted widespread attention from researchers and has broad application prospects. In most applications, graphene needs to be thoroughly and uniformly mixed with other materials to form composite materials, which requires graphene powder to have specific dimensions and good dispersion characteristics in various systems. Currently, the mainstream graphene preparation methods are divided into two main categories: top-down and bottom-up methods. The top-down method mainly prepares graphene powder by exfoliating graphite raw materials; however, the size of the graphene powder obtained by this method is difficult to control uniformly, and untreated graphene powder is difficult to disperse stably in various dispersion systems. The bottom-up method mainly refers to chemical vapor deposition (CVD), which generally requires high energy to achieve carbon source pyrolysis and high temperatures to obtain high-quality graphene. This method has more demanding growth conditions and correspondingly higher costs.

[0003] In addition, graphene powder can also be prepared directly using microwave plasma technology without the need for additional heat sources, templates, or other conditions.

[0004] The following section will introduce some existing technologies for preparing graphene powder to enable those skilled in the art to better understand the current state of the technology.

[0005] CN110451496A discloses a method for continuous production of graphene powder, but the type of carbon source and reaction conditions used in this method differ from those of the present invention. Specifically, it uses high-purity hydrocarbons, alcohols, ethers, ketones, phenols, etc., as carbon sources. However, under low carbon source supply conditions, a large amount of carbon deposits are generated in the reactor within a short time, affecting the reaction. Oxygen etching treatment is required to remove the carbon deposits, making it impossible to achieve a long-term reaction. Furthermore, the quartz tube is easily damaged, leading to impure products. It is difficult to balance yield and quality, severely impacting the subsequent applications of the graphene powder.

[0006] CN107161987A discloses a method for preparing powdered graphene, but the type of carbon source and reaction conditions used in this method differ from those of the present invention. Specifically, it also uses high-purity hydrocarbons, alcohols, ethers, ketones, phenols, etc., as carbon sources, and requires the use of conductors or semiconductor materials as initiators for plasma initiation. During the reaction, the initiator remains in the reaction system. Due to the intense tip discharge, the plasma state is difficult to stabilize, making it difficult to control the state of the reaction system.

[0007] Therefore, providing a novel graphene powder, its preparation method, and its application has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0008] To address the aforementioned shortcomings and deficiencies, the present invention aims to provide a graphene powder, its preparation method, and its applications. This invention utilizes microwave plasma technology to prepare graphene powder, enabling continuous and efficient preparation of nanoscale graphene powder with excellent dispersibility.

[0009] To achieve the above objectives, on the one hand, the present invention provides a method for preparing graphene powder, wherein the method for preparing graphene powder includes:

[0010] Step (1): Under high vacuum, in an inert gas background in a microwave plasma device, a uniform and stable glow plasma is spontaneously generated under microwave action.

[0011] Step (2): Increase the flow rate of the inert gas and increase the system pressure to a low vacuum state so that the glow plasma is transformed into a state in which glow plasma and electric arc coexist;

[0012] Step (3): The saturated vapor of the liquid carbon source is brought into the reaction chamber of the microwave plasma device by the negative pressure of the system. Under the action of glow plasma and electric arc, the carbon source molecules are bombarded by high-energy particles and decomposed. The decomposed activated carbon components nucleate and grow to obtain graphene powder.

[0013] As a specific embodiment of the preparation method described above in this invention, in step (1), the inert gas includes one or a combination of argon, nitrogen and helium.

[0014] As a specific embodiment of the preparation method described above in this invention, in step (1), the pressure of the high vacuum state is less than or equal to -0.1 MPa.

[0015] As a specific embodiment of the preparation method described above in this invention, in step (1), the flow rate of the inert gas is 300-500 sccm.

[0016] As a specific embodiment of the preparation method described above in this invention, in step (1), the output power of the microwave is 700-1500W.

[0017] As a specific embodiment of the preparation method described above in this invention, in step (2), the flow rate of the inert gas is increased to 800-1600 sccm, at which point the system pressure is increased to -0.08 to -0.06 MPa.

[0018] As a specific embodiment of the preparation method described above in this invention, in step (2), while maintaining the original opening of the vacuum pump valve (i.e., the opening of the vacuum pump valve corresponding to the vacuum pump valve when the reaction chamber in the microwave plasma device is evacuated to a gauge pressure less than or equal to -0.1 MPa), increasing the flow rate of the inert gas will cause a change in the system pressure, resulting in a slight increase in system pressure. Under the high vacuum condition in step (1), the plasma exhibits a uniform and stable glow plasma state, while under normal pressure, the plasma exhibits a complete arc discharge state. In step (2), the system pressure is controlled between normal pressure and high vacuum, resulting in a low vacuum state. At this time, the plasma is not a single arc discharge or glow plasma state, but rather has a relatively intense arc discharge against a glow background, i.e., the plasma of the system is in a state where glow plasma and arc coexist. This invention can achieve continuous and rapid cracking, nucleation, and growth of carbon sources under the state where glow plasma and arc coexist, and rapidly detach from the reaction core region, reducing the nucleation time, thereby enabling the preparation of nanoscale graphene powder.

[0019] As a specific embodiment of the preparation method described above in this invention, step (3) specifically includes: bringing the saturated vapor of the liquid carbon source into the reaction chamber of the microwave plasma device through the negative pressure of the system. At this time, the plasma color changes from the plasma color of the inert gas to the plasma color of the carbon-containing active component, i.e., a bright green.

[0020] After the reaction has proceeded for a period of time, the saturated vapor of the liquid carbon source is cut off. Once the plasma color returns to the plasma color of the inert gas, the microwave output power is turned off. After the system returns to room temperature, the vacuum pump is turned off. Once the system returns to atmospheric pressure, the inert gas supply is stopped, and the graphene powder is collected.

[0021] As a specific embodiment of the preparation method described above in this invention, in step (3), the liquid carbon source includes one or a combination of several liquid alkanes and their derivatives, such as n-hexane, cyclohexane, and chloroform.

[0022] As a specific embodiment of the preparation method described above in this invention, in step (3), the reaction time is 2-4 hours.

[0023] This invention does not specify the system used in the graphene powder preparation method; a suitable system can be selected as needed. For example, in some embodiments of this invention, the graphene powder preparation method is implemented using a graphene powder preparation system. The graphene powder preparation system includes a microwave plasma device, a liquid carbon source storage tank, a vacuum pump, and an inert gas cylinder. The microwave plasma device includes a microwave generator equipped with a microwave output power supply and a reaction chamber disposed within the microwave generator. The outlet of the liquid carbon source storage tank is connected to the inlet of the reaction chamber via a pipeline and its outlet valve. The outlet of the inert gas cylinder is also connected to the inlet of the reaction chamber via a pipeline and its outlet valve. The vacuum pump is connected to the reaction chamber via a pipeline to evacuate the reaction chamber.

[0024] In some embodiments of the present invention, the reaction chamber is a quartz tube. In some specific embodiments of the present invention, the outer diameter of the quartz tube may be 3 cm and the wall thickness may be 4 mm.

[0025] As a specific embodiment of the preparation method described above in this invention, the method for preparing graphene powder using the graphene powder preparation system described above includes the following specific steps:

[0026] S1: Add the liquid carbon source to the liquid carbon source storage tank for later use, and close its outlet valve to ensure that the liquid carbon source does not enter the gas path before the graphene growth reaction.

[0027] S2: Turn on the vacuum pump to continuously evacuate the reaction chamber until the vacuum level reaches the required level, i.e., the gauge pressure is less than or equal to -0.1 MPa. Then, open the outlet valve of the inert gas cylinder and introduce inert gas at a flow rate of 300-500 sccm into the reaction chamber as the plasma working gas to create an inert gas atmosphere. After introducing the inert gas, the vacuum level of the system does not change significantly and can maintain a gauge pressure of approximately -0.1 MPa. Turn on the microwave output power to 700-1500W. After the plasma is generated, it will exhibit a uniform and stable glow plasma state, and the plasma color will be the same as that of inert gas plasma.

[0028] S3: While maintaining the original opening of the vacuum pump valve, increase the flow rate of the inert gas to 800-1600 sccm. At this time, the system pressure increases to -0.08 to -0.06 MPa, and the system is in a low vacuum state. At this time, the plasma state changes from a uniform / stable glow plasma state to a state in which glow plasma and electric arc coexist.

[0029] S4: Open the outlet valve of the liquid carbon source storage tank. Under negative pressure, due to the influence of the liquid's own saturated vapor pressure, the empty space of the liquid carbon source storage tank is filled with the saturated vapor of the liquid carbon source. The saturated vapor of the liquid carbon source is brought into the reaction chamber by the negative pressure of the system. After reaching the plasma core region, under the action of glow plasma and electric arc, the carbon source molecules are bombarded by high-energy particles and decompose. The decomposed activated carbon components nucleate and grow. At this time, the plasma color also changes from the plasma color of inert gas to the plasma color of carbon-containing active components, that is, bright green.

[0030] S5: After reacting for a period of time, such as 2-4 hours, close the outlet valve of the liquid carbon source storage tank. After the plasma color returns to the plasma color of the inert gas (e.g., if the inert gas is argon, the plasma color is pink), it indicates that there are no more activated carbon components such as carbon free radicals in the core region of the plasma. Turn off the microwave output power supply. After the system returns to room temperature, turn off the vacuum pump. After the system returns to normal pressure, close the outlet valve of the inert gas cylinder. Then the collector can be opened and graphene powder can be obtained.

[0031] In some embodiments of the present invention, after closing the outlet valve of the liquid carbon source storage tank and the microwave output power supply in S5, the system cooling and pressure recovery can be accelerated by means of air cooling and inert gas purging.

[0032] The method for preparing graphene powder provided by this invention can precisely control the size of graphene powder and obtain nanoscale graphene powder with excellent dispersibility by adjusting conditions such as plasma state and growth parameters.

[0033] On the other hand, the present invention also provides a graphene powder, wherein the graphene powder is prepared by the above-described method for preparing graphene powder.

[0034] As a specific embodiment of the graphene powder described above in this invention, wherein the graphene powder I D / I G The value is 0.3-1.3, I 2D / I G It is 0.3-0.7.

[0035] In another aspect, the present invention also provides the application of the above-described graphene powder as a reinforcing material.

[0036] Compared with the prior art, the beneficial technical effects achieved by the present invention include:

[0037] The method for preparing graphene powder provided by this invention is a continuous method for preparing nanoscale graphene powder. This method uses a micro-negative pressure (i.e., the system is in a low vacuum state) microwave plasma chemical vapor deposition method to achieve a plasma state in which glow discharge and electric arc coexist. This enables continuous and rapid pyrolysis, nucleation and growth of carbon source, and rapid detachment from the reaction core region, reducing the nucleation time. Thus, it is possible to prepare nanoscale graphene powder. Furthermore, the nanoscale graphene powder prepared by this invention has excellent solubility and can be well dispersed in various systems.

[0038] In summary, this invention utilizes microwave plasma technology to prepare graphene powder, enabling continuous and efficient preparation of nanoscale graphene powder with excellent dispersibility. Attached Figure Description

[0039] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0040] Figure 1 This is a simplified structural diagram of the graphene powder preparation system used in a specific embodiment of the present invention.

[0041] Figure 2 This is a transmission electron microscope (TEM) image of the graphene powder obtained in Example 1 of the present invention.

[0042] Figure 3 This is the Raman spectrum of the graphene powder obtained in Example 1 of the present invention.

[0043] Figure 4 This is the X-ray photoelectron spectrum of the graphene powder obtained in Example 1 of the present invention.

[0044] Figure 5 This is the Raman spectrum of the graphene powder obtained in Example 2 of the present invention.

[0045] Figure 6 This is the Raman spectrum of the graphene powder obtained in Example 3 of the present invention.

[0046] Explanation of key figure labels:

[0047] 1. Microwave plasma device;

[0048] 10. Microwave generator;

[0049] 11. Reaction chamber;

[0050] 2. Liquid carbon source storage tank;

[0051] 3. Vacuum pump;

[0052] 4. Inert gas cylinders. Detailed Implementation

[0053] It should be noted that the term "comprising" and any variations thereof in the specification, claims, and accompanying drawings of this invention are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or devices.

[0054] The "range" disclosed in this invention is given in the form of a lower limit and an upper limit. It can be one or more lower limits and one or more upper limits, respectively. A given range is defined by selecting a lower limit and an upper limit. The selected lower and upper limits define the boundaries of the particular range. All ranges defined in this way are composable, meaning that any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for specific parameters, it is also expected that ranges of 60-110 and 80-120 are also expected. Furthermore, if the listed minimum range values ​​are 1 and 2, and the listed maximum range values ​​are 3, 4, and 5, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5.

[0055] In this invention, unless otherwise specified, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this invention, and "0-5" is simply a shortened representation of these numerical combinations.

[0056] In this invention, unless otherwise specified, all embodiments and preferred embodiments mentioned in this invention can be combined with each other to form new technical solutions.

[0057] In this invention, unless otherwise specified, all technical features and preferred features mentioned in this invention can be combined with each other to form new technical solutions.

[0058] In this invention, unless otherwise specified, all steps mentioned herein may be performed sequentially or randomly, but are preferably performed sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0059] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. The embodiments described below are some, but not all, embodiments of this invention, and are only used to illustrate the invention, and should not be considered as limiting the scope of the invention. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0060] A simplified structural diagram of the graphene powder preparation system used in a specific embodiment of the present invention is shown below. Figure 1 As shown. From Figure 1 As can be seen, the graphene powder preparation system includes:

[0061] The system comprises a microwave plasma device 1, a liquid carbon source storage tank 2, a vacuum pump 3, and an inert gas cylinder 4. The microwave plasma device 1 includes a microwave generator 10 equipped with a microwave output power supply and a reaction chamber 11 vertically arranged within the microwave generator 10. The outlet of the liquid carbon source storage tank 2 is connected to the inlet of the reaction chamber 11 via a pipeline and its outlet valve. The outlet of the inert gas cylinder 4 is also connected to the inlet of the reaction chamber 11 via a pipeline and its outlet valve. The vacuum pump 3 is also connected to the reaction chamber 11 via a pipeline to evacuate the reaction chamber 11.

[0062] The reaction chamber 11 is a quartz tube with an outer diameter of 3 cm and a wall thickness of 4 mm.

[0063] Example 1

[0064] This embodiment provides a method for the continuous microwave plasma preparation of nanoscale graphene powder using n-hexane as a carbon source. The method employs, for example... Figure 1The graphene powder preparation system shown includes the following specific steps:

[0065] Step 1): Add n-hexane to the liquid carbon source storage tank for later use, and close its outlet valve to ensure that n-hexane does not enter the gas path before the graphene growth reaction;

[0066] Step 2): Turn on the vacuum pump and draw the pressure inside the quartz tube to below -0.1 MPa on the gauge. Then, introduce 300 sccm of argon gas into the quartz tube. After introducing argon gas, the vacuum level of the system does not change significantly, and the gauge pressure is approximately -0.1 MPa.

[0067] Step 3): Turn on the microwave output power and set the microwave output power to 700W. After a few seconds, glow plasma is generated. After the plasma is uniform and stable, adjust the argon flow rate to 800sccm. The plasma gradually changes from uniform and stable glow to a state where glow and electric arc coexist. At this time, the system pressure gradually increases to -0.08MPa and tends to stabilize.

[0068] Step 4): Open the outlet valve of the liquid carbon source tank to allow hexane to enter the quartz tube under negative pressure. The plasma color will change to a bright green. After reacting for 2 hours, close the outlet valve of the liquid carbon source tank. After the plasma color returns to the color of argon plasma, i.e., pink, turn off the microwave output power supply. After the system returns to room temperature, turn off the vacuum pump. After the system returns to atmospheric pressure, close the outlet valve of the inert gas cylinder. Then the collector can be opened to obtain graphene powder.

[0069] The transmission electron microscope (TEM) image and Raman spectrum of the graphene powder obtained in this embodiment are shown below. Figure 2 and Figure 3 As shown. Figure 2 The transmission electron microscope (TEM) images shown reveal that the sheet sizes of the graphene powder range from tens to hundreds of nanometers, as indicated by... Figure 3 The Raman spectrum shown clearly indicates that the graphene powder exhibits three peaks: D, G, and 2D, and I... D / I G A value of 1.24 indicates that the graphene powder has numerous defects. These defects primarily stem from its extremely small size and insufficient growth dwell time, preventing complete repair of the graphene sheet structure. However, these sufficient defects provide the graphene powder with more active sites, allowing it to bind oxygen-containing functional groups. This, in turn, can improve its dispersion performance in various dispersion systems and enhance its Ig content. 2D / I G The value of 0.34 indicates that the quality of the graphene powder is acceptable.

[0070] Additionally, the X-ray photoelectron spectrum of the graphene powder obtained in this embodiment is as follows: Figure 4As shown, the elemental composition of the graphene powder is mainly composed of C and O, with proportions of 93.93 at% and 6.07 at%, respectively. Compared with other existing graphene powders, the graphene powder obtained in Example 1 of this invention has a significantly increased oxygen content, thus possessing more oxygen-containing functional groups, which in turn brings excellent dispersibility to the graphene powder.

[0071] Example 2

[0072] This embodiment provides a method for the continuous microwave plasma preparation of nanoscale graphene powder using cyclohexane as a carbon source. The method employs, for example... Figure 1 The graphene powder preparation system shown includes the following specific steps:

[0073] Step 1): Add cyclohexane to the liquid carbon source storage tank for later use, and close its outlet valve to ensure that cyclohexane does not enter the gas path before the graphene growth reaction.

[0074] Step 2): Turn on the vacuum pump and draw the pressure inside the quartz tube to below -0.1 MPa on the gauge. Then, introduce 400 sccm of argon gas into the quartz tube. After introducing argon gas, the vacuum level of the system does not change significantly, and the gauge pressure is approximately -0.1 MPa.

[0075] Step 3): Turn on the microwave output power and set the microwave output power to 1100W. After a few seconds, glow plasma is generated. After the plasma is uniform and stable, adjust the argon flow rate to 1200sccm. The plasma gradually changes from uniform and stable glow to a state where glow and electric arc coexist. At this time, the system pressure gradually increases to -0.07MPa and tends to stabilize.

[0076] Step 4): Open the outlet valve of the liquid carbon source tank to allow cyclohexane to enter the quartz tube under negative pressure. The plasma color will change to a bright green. After reacting for 3 hours, close the outlet valve of the liquid carbon source tank. After the plasma color returns to the color of argon plasma, i.e., pink, turn off the microwave output power supply. After the system returns to room temperature, turn off the vacuum pump. After the system returns to atmospheric pressure, close the outlet valve of the inert gas cylinder. Then the collector can be opened to obtain graphene powder.

[0077] The Raman spectrum of the graphene powder obtained in this embodiment is as follows: Figure 5 As shown. Figure 5 The Raman spectrum shown clearly indicates that the graphene powder exhibits three peaks: D, G, and 2D, and I... D / I GThe Ig value reaching 0.91 indicates that the graphene powder also possesses numerous defects. These defects primarily stem from extremely small size and insufficient growth dwell time, preventing complete repair of the graphene sheet structure. However, these sufficient defects provide the graphene with more active sites, allowing it to bind oxygen-containing functional groups, thereby improving its dispersion performance in various dispersion systems and increasing Ig. 2D / I G A value of 0.50 indicates that the quality of the graphene powder is acceptable.

[0078] Example 3

[0079] This embodiment provides a method for the continuous microwave plasma preparation of nanoscale graphene powder using chloroform as a carbon source. The method employs, for example... Figure 1 The graphene powder preparation system shown includes the following specific steps:

[0080] Step 1): Add chloroform to the liquid carbon source storage tank for later use, and close its outlet valve to ensure that chloroform does not enter the gas path before the graphene growth reaction;

[0081] Step 2): Turn on the vacuum pump and draw the pressure inside the quartz tube to below -0.1 MPa on the gauge. Then, introduce 500 sccm of argon gas into the quartz tube. After introducing argon gas, the vacuum level of the system does not change significantly, and the gauge pressure is approximately -0.1 MPa.

[0082] Step 3): Turn on the microwave output power and set the microwave output power to 1500W. After a few seconds, glow plasma is generated. After the plasma is uniform and stable, adjust the argon flow rate to 1600sccm. The plasma gradually changes from uniform and stable glow to a state where glow and electric arc coexist. At this time, the system pressure gradually increases to -0.06MPa and tends to stabilize.

[0083] Step 4): Open the outlet valve of the liquid carbon source tank to allow chloroform to enter the quartz tube under negative pressure. The plasma color will change to a bright green. After reacting for 4 hours, close the outlet valve of the liquid carbon source tank. After the plasma color returns to the color of argon plasma, i.e., pink, turn off the microwave output power supply. After the system returns to room temperature, turn off the vacuum pump. After the system returns to atmospheric pressure, close the outlet valve of the inert gas cylinder. Then the collector can be opened to obtain graphene powder.

[0084] The Raman spectrum of the graphene powder obtained in this embodiment is as follows: Figure 6 As shown. Figure 6 The Raman spectrum shown clearly indicates that the graphene powder exhibits three peaks: D, G, and 2D, and I... D / I GA value of 0.34 indicates that the graphene powder also has relatively few defects. These defects mainly stem from their extremely small size and short growth dwell time, preventing complete repair of the graphene sheet structure. However, sufficient defects result in more active sites for the graphene, allowing it to bind oxygen-containing functional groups, thereby improving its dispersion performance in various dispersion systems and increasing Ig. 2D / I G A value of 0.69 indicates that the graphene powder is of superior quality.

[0085] Comparative Example 1

[0086] This comparative example provides a method for the continuous preparation of nanoscale graphene powder using n-hexane as a carbon source via microwave plasma. It is achieved using a microwave plasma deposition system without a vacuum device, and relates to atmospheric pressure microwave plasma technology for preparing graphene powder, including the following specific steps:

[0087] S1: Introduce 1200 sccm of argon gas into the system to purge the residual air in the system;

[0088] S2: Place n-hexane in a liquid carbon source storage tank and set up an argon bypass to bring the liquid carbon source into the reaction system by bubbling. Set the flow rate of the bypass argon to 200 sccm. Before the liquid carbon source is introduced, close the argon bypass and outlet valve of the liquid carbon source storage tank.

[0089] S3: Adjust the microwave power to 700W and initiate the generation of argon plasma in the system. After the plasma stabilizes, open the outlet valve of the liquid carbon source tank and open the argon bypass. Set the flow rate of the bypass argon to 200 sccm. At the same time, adjust the flow rate of the main argon so that the total flow rate of the main argon and the bypass argon is 1200 sccm.

[0090] S4: After the n-hexane vapor enters the reaction system, the plasma color changes from pink to green and becomes bright. At the same time, black flocculent material can be seen continuously drifting away from the system at the end of the quartz tube. Collect the black flocculent material.

[0091] S5: After about 20 minutes of reaction, the quartz tube in the plasma core area is red-hot. Close the outlet valves of the bypass argon gas and liquid carbon source storage tank, and adjust the flow rate of the main argon gas to 1200 sccm. It can be seen that a lot of black material remains on the quartz tube wall in the microwave reaction chamber area, i.e. the plasma core area.

[0092] S6: Under the condition of microwave power of 700W, oxygen of 20sccm is introduced into the system. The black substance can be seen to gradually decrease through the opening of the reaction chamber. After about 2-3 minutes, the quartz tube wall in the microwave reaction chamber area can be seen to have no obvious black substance residue, indicating that the residual carbon material in this area has been completely etched.

[0093] S7: Repeat the S3-S6 reaction for 4 hours to obtain graphene powder. When the quartz tube was removed, irreversible damage was found to have occurred on the inner wall of the microwave-irradiated area of ​​the quartz tube.

[0094] Comparative Example 1 is related to the methods for preparing powdered graphene mentioned in CN110451496A and CN107161987A in the background section. Both methods utilize a microwave plasma deposition system without a vacuum device to prepare powdered graphene. In a microwave plasma without a vacuum device, a completely arc discharge plasma is formed. Even if glow discharge plasma exists, its proportion is extremely small and its impact is negligible. Therefore, Comparative Example 1 can be considered as preparing powdered graphene using a completely arc discharge plasma.

[0095] Since Comparative Example 1 uses a microwave plasma deposition system without a vacuum device to prepare graphene powder, it is necessary to set an additional Faraday coil or metal wire in the microwave irradiation area to discharge and initiate plasma. However, the graphene powder preparation system used in this embodiment of the invention is equipped with a vacuum device, and in step (2), the flow rate of inert gas is increased and the system pressure is increased to a low vacuum state, thereby enabling the self-initiation of plasma.

[0096] In Example 1 of this invention, the flow rate of inert gas is increased and the system pressure is increased to a low vacuum state in step (2) of the graphene powder preparation method, so that the glow plasma is transformed into a state in which glow plasma and electric arc coexist. That is, Example 1 of this invention uses low-pressure assisted microwave plasma to prepare graphene powder, which can achieve long-term non-replacement of quartz tube and no external conditions are required for plasma initiation. The low-pressure environment quickly carries the product graphene out of the reaction system, which is conducive to promoting the chemical reaction and improving the graphene production efficiency. Compared with Comparative Example 1, it has significant advantages in terms of continuity and efficiency.

[0097] The dispersibility of graphene powder is determined by its nanoscale size and oxygen-containing functional groups. The graphene powder obtained in Example 1 of this invention has a nanoscale size and contains a certain amount of oxygen in the form of oxygen-containing functional groups, which promotes its dispersion in various solvents. In contrast, the graphene powder obtained in Comparative Example 1 has an extremely low oxygen content (O content <0.6%), and it can bind very few oxygen-containing functional groups. Therefore, its dispersion performance in various solvents is poor, significantly worse than that of the graphene powder provided in Example 1 of this invention.

[0098] Comparative Example 2

[0099] This comparative example provides a method for preparing powdered graphene using gas-phase plasma with n-hexane as the carbon source, including the following specific steps:

[0100] S1: Evacuate the quartz tube to 50Pa (absolute pressure);

[0101] S2: Place n-hexane into the liquid carbon source storage tank and close the outlet valve of the liquid carbon source storage tank;

[0102] S3: Hexane vapor is introduced into the quartz tube by argon bubbling;

[0103] S4: The argon flow rate was set to 200 sccm, the pressure inside the quartz tube was controlled to 120 Pa (absolute pressure), and the microwave output power was set to 500 W before starting the plasma reaction. The plasma exhibited a uniform glow state and remained pink in color. The reason why the plasma color remained pink in S4 is that under high vacuum conditions, the concentration of carbon source in the reaction system was extremely low, and the plasma state was relatively uniform. The activated carbon component produced by the decomposition of the extremely low concentration of carbon source did not cause a change in plasma color. In addition, under high vacuum conditions and with a small gas flow rate, the plasma state would not change from glow to discharge. This can be regarded as a process of preparing graphene using a completely glow plasma.

[0104] S5: A filter screen is set at the tail end for receiving. After the reaction lasts for 20 minutes, the microwave output power supply and the outlet valve of the inert gas cylinder are turned off. After the temperature of the quartz tube returns to room temperature, the reaction system is opened. No black powder is found on the filter screen set at the tail end, but black powder is found attached to the inner wall of the quartz tube in the microwave irradiation area. This indicates that graphene or carbon materials need to have an attachment substrate in the reaction system. However, the preparation method provided in this embodiment of the invention can achieve the preparation of graphene powder with excellent dispersion performance and high quality without setting an attachment substrate.

[0105] Comparing the experimental results of the embodiments of the present invention and the comparative examples, it can be seen that in step (2) of the graphene powder preparation method of the present invention, increasing the flow rate of inert gas and increasing the system pressure to a low vacuum state, so as to transform the glow plasma into a state where glow plasma and electric arc coexist, can achieve at least the following four beneficial technical effects: Firstly, it can extend the microwave plasma discharge region, and the extended reaction region can prolong the process of carbon source decomposition and nucleation growth. Specifically, in a low-pressure environment, the gas particle spacing is large, the electron acceleration path is longer, and it is easier to accumulate high energy to induce ionization; while in a normal pressure environment, the high-frequency electric field oscillates rapidly, so that electrons can repeatedly collide with particles in a short distance to achieve efficient ionization. Generally, the range of action of the high-frequency electric field is small. Therefore, in a normal pressure environment, the plasma can only be generated and maintained violently within the range of action of the high-frequency electric field, while in a low-pressure environment, the activity range of the ionized particles can be separated from the range of action of the high-frequency electric field, so the plasma region will be wider.

[0106] Secondly, the use of low pressure, i.e. low vacuum, allows the graphene powder product to leave the reaction system quickly, reducing the product concentration and promoting the shift of chemical equilibrium to the positive direction.

[0107] Thirdly, low voltage can be used to achieve plasma self-excitation, eliminating the need for metal wires or Faraday coils to induce plasma, thus avoiding the introduction of unnecessary impurities;

[0108] Furthermore, it enables the direct vapor deposition of graphene powder without a substrate, and the graphene powder exhibits excellent dispersion performance and superior quality.

[0109] The above description is merely a specific embodiment of the present invention and should not be construed as limiting the scope of the invention. Therefore, substitutions of equivalent components, or equivalent changes and modifications made within the scope of protection of this patent, should still fall within the scope of this patent. Furthermore, the technical features, technical features and technical inventions, and technical inventions in this invention can be freely combined and used.

Claims

1. A method for preparing graphene powder, characterized in that, The method for preparing the graphene powder includes: Step (1): Under high vacuum conditions, in an inert gas as the background gas in a microwave plasma device, a uniform and stable glow plasma is spontaneously generated under the action of microwaves; wherein, the pressure of the high vacuum condition is less than or equal to -0.1 MPa, the flow rate of the inert gas is 300-500 sccm, and the output power of the microwave is 700-1500 W. Step (2): While maintaining the original opening of the vacuum pump valve used in step (1), increase the flow rate of the inert gas to 800-1600 sccm and increase the system pressure to a low vacuum state of -0.08 to -0.06 MPa, so that the glow plasma is transformed into a state in which glow plasma and electric arc coexist. Step (3): The saturated vapor of the liquid carbon source is brought into the reaction chamber of the microwave plasma device by the negative pressure of the system. Under the action of glow plasma and electric arc, the carbon source molecules are bombarded by high-energy particles and decomposed. The decomposed activated carbon components nucleate and grow to obtain graphene powder.

2. The preparation method according to claim 1, characterized in that, In step (1), the inert gas includes one or a combination of argon, nitrogen and helium.

3. The preparation method according to claim 1, characterized in that, Step (3) specifically includes: using the negative pressure of the system to bring the saturated vapor of the liquid carbon source into the reaction chamber of the microwave plasma device. At this time, the plasma color changes from the plasma color of the inert gas to the plasma color of the carbon-containing active component, i.e., bright green. After the reaction has proceeded for a period of time, the saturated vapor of the liquid carbon source is cut off. Once the plasma color returns to the plasma color of the inert gas, the microwave output power is turned off. Once the system returns to room temperature, the vacuum pump is turned off. Once the system returns to atmospheric pressure, the inert gas supply is stopped, and the graphene powder is collected.

4. The preparation method according to claim 1 or 3, characterized in that, In step (3), the liquid carbon source includes one or a combination of several of n-hexane, cyclohexane and chloroform.

5. The preparation method according to claim 1 or 3, characterized in that, In step (3), the reaction time is 2-4 hours.

6. A graphene powder, characterized in that, The graphene powder is prepared by the method for preparing graphene powder according to any one of claims 1-5.

7. The graphene powder according to claim 6, characterized in that, The graphene powder I D / I G The value is 0.3-1.

3. I 2D / I G It is 0.3-0.

7.

8. The application of the graphene powder according to claim 6 or 7 as a reinforcing material.

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