Graphene powder, method for preparing same by using synthesis gas as raw material and application thereof

Abstract

The application provides a graphene powder and a method for preparing the graphene powder from a synthesis gas and application of the graphene powder, and the method comprises the following steps: under high vacuum conditions, a 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, the output power of the microwaves is increased, and the pressure of the system is increased to a micro-negative pressure state, so that the glow plasma is transformed, and the system is in a state where the glow plasma and the electric arc coexist; the synthesis gas is introduced into the microwave plasma device, and under the action of the glow plasma and the electric arc, the molecules of the synthesis gas are impacted by high-energy particles to be cracked, and the carbon species after cracking is nucleated and grown to obtain the graphene powder. The application synchronously provides the energy required for carbon source cracking and graphene nucleation and growth through microwave plasma discharge, and does not need additional heat source, template and other conditions, and the prepared graphene has high purity and high quality.

Description

Technical Field

[0001] This invention relates to a graphene powder and a method for preparing it using syngas as a raw material, as well as its application, belonging to the field of graphene material technology. Background Technology

[0002] Graphene, with its superior properties in sound, light, electricity, and heat, has attracted widespread attention from researchers and has broad application prospects. Currently, the mainstream methods for graphene preparation are divided into two main categories: top-down and bottom-up methods. The top-down method mainly involves exfoliating graphite raw materials to prepare graphene powder, a process involving solution handling that can lead to the retention of more contaminants in the graphene powder. The bottom-up method generally requires higher energy to achieve carbon source pyrolysis to obtain high-quality graphene, and its growth conditions are harsh, resulting in higher production costs. Both contaminant retention and high production costs can affect the application of graphene.

[0003] Currently, the raw materials used to prepare high-quality graphene are mainly high-purity small-molecule substances such as hydrocarbons (methane, ethylene, acetylene, etc.) and alcohols (methanol, ethanol, etc.), which are relatively expensive. In petroleum processing, syngas, as an important feedstock gas, has a wide range of sources (for example, it can be produced by gasifying solid fuels such as coal or coke, or by producing light hydrocarbons such as natural gas and naphtha, or by partially oxidizing heavy oil), diverse uses, and its main components are CO and H2. Furthermore, its composition ratio can be adjusted according to requirements.

[0004] In addition, most existing bottom-up preparation methods for graphene powders focus on chemical vapor deposition technology, but this technology requires the combination of high-temperature pyrolysis, plasma, templates and other conditions, and requires additional heat sources, templates and other materials, resulting in high production costs and complex processes.

[0005] Therefore, providing a novel method for preparing graphene powder using syngas as a raw material, as well as the resulting graphene powder and its applications, has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] To address the aforementioned shortcomings and deficiencies, one objective of this invention is to provide a method for preparing graphene powder using syngas as a raw material. The method provided by this invention uses syngas, commonly used in the petrochemical industry, as a carbon source. Through microwave plasma technology, it achieves carbon source decomposition, nucleation, and growth processes within a reaction region, in a reactor (such as...). Figure 1 The graphene powder can be collected at the end of the quartz tube, eliminating the need for post-processing and achieving the preparation of high-quality graphene powder.

[0007] Another object of the present invention is to provide a graphene powder, which is prepared by the above-described method of preparing graphene powder using syngas as a raw material.

[0008] Another object of the present invention is the application of the above-described graphene powder as a reinforcing material.

[0009] To achieve the above objectives, the present invention provides a method for preparing graphene powder using syngas as a raw material, wherein the method includes the following steps:

[0010] Step (1): Under high vacuum conditions, a stable glow plasma is spontaneously generated in a microwave plasma device with an inert gas as the background gas under the action of microwaves.

[0011] Step (2): Increase the flow rate of the inert gas, increase the output power of the microwave, and increase the system pressure to a slightly negative pressure state so that the glow plasma will change and the system will be in a state where glow plasma and electric arc coexist.

[0012] Step (3): Synthesis gas is introduced into the microwave plasma device. Under the action of glow plasma and electric arc, the synthesis gas molecules are bombarded by high-energy particles, namely electrons and ions formed in the process of generating stable glow plasma in step (1), and the carbon species after decomposition nucleate and grow to obtain graphene powder.

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

[0014] As a specific embodiment of the method described above in this invention, in step (1), the high vacuum condition includes a pressure of -0.05 to -0.1 MPa.

[0015] In a specific embodiment of the method described above in this invention, in step (1), the flow rate of the inert gas is 200-500 sccm, and the output power of the microwave is 300-600W.

[0016] In step (1) of the method described above in this invention, under high vacuum conditions, the working gas (i.e., the inert gas) is accelerated by a small number of free electrons in the microwave high-frequency electric field to have kinetic energy and to force them to collide with other unionized inert gas molecules, thereby generating enough secondary electrons. When the number of generated electrons is greater than or equal to the number of lost electrons, inert gas breakdown will occur and trigger discharge, at which time a uniform and stable glow plasma can be generated.

[0017] In a specific embodiment of the method described above in this invention, in step (2), the flow rate of the inert gas is 1000-5000 sccm, and the output power of the microwave is 1000-2000W.

[0018] As a specific embodiment of the method described above in this invention, in step (2), the pressure corresponding to the micro-negative pressure state is greater than or equal to -0.02 MPa and less than 0 MPa, that is, the range of pressure (P) is -0.02 ≤ P < 0.

[0019] This invention uses syngas as a carbon source to prepare graphene powder. Syngas is an important raw material used in chemical production, and its sources include, but are not limited to, syngas obtained by methods such as partial oxidation of heavy oil, steam reforming of light oil, and steam reforming of coal.

[0020] In a specific embodiment of the method described above in this invention, in step (3), the volume fraction of CO in the synthesis gas is 40% or more, and the volume fraction of H2 is 40% or more.

[0021] As a specific embodiment of the method described above in this invention, in step (3), the volume fraction of CO in the synthesis gas is 45% or more, and the volume fraction of H2 is 45% or more.

[0022] In a specific embodiment of the method described above in this invention, in step (3), the volume fraction of CO in the synthesis gas is 45-55%, and the volume fraction of H2 is 55-45%. At this time, the synthesis gas is composed of CO and H2, which can avoid the adverse effects of impurities contained in the synthesis gas on the quality of graphene powder.

[0023] In a specific embodiment of the method described above in this invention, in step (3), the flow rate of the synthesis gas is 5-200 sccm.

[0024] In one specific embodiment of the method described above in this invention, the reaction time in step (3) is more than 1 hour.

[0025] In steps (2) and (3) of the method described above, the system pressure is in a slightly negative pressure state, which is conducive to the reaction products leaving the reaction system. From the perspective of reaction equilibrium, it can promote the reaction. In step (1), the plasma can be self-initiated under high vacuum conditions, that is, under negative pressure conditions. Then, adjusting the system pressure to a slightly negative pressure state helps the plasma to maintain the excited state for a long time, and it will not become chaotic or even extinguished over time. The microwave power fed back by the system can remain at zero for a long time, that is, all microwave energy is applied to the working gas, avoiding energy waste. In addition, under the slightly negative pressure state, glow plasma and electric arc coexist, presenting a dynamic balance, which can effectively expand the range of electric arc, that is, expand the nucleation range of carbon source cracking, which is conducive to the occurrence of carbon source cracking nucleation process. Furthermore, glow plasma and electric arc local (mainly the electric arc part) have ultra-high temperature, which can reach several thousand K, and the range of action is small. It presents a large temperature gradient with the edge of the reactor in the microwave plasma device. The temperature of several thousand K is also sufficient to provide energy for carbon source cracking. And with the change of temperature gradient, the cracked components gradually undergo nucleation growth process to obtain graphene powder. In addition, the slight negative pressure state is conducive to maintaining the stability of the plasma state for a long time, which can last for more than 1 hour. As a result, the growth time in step (3) is significantly increased, thereby reducing the difficulty of operation.

[0026] On the other hand, the present invention also provides a graphene powder, which is prepared by the method described above for preparing graphene powder using syngas as a raw material.

[0027] As a specific embodiment of the graphene powder described above in this invention, the specific surface area of ​​the graphene powder is >250m². 2 / g, Raman results showed I D / I G <0.4, I 2D / I G >0.6, the percentage of carbon and oxygen atoms, i.e., C / O>40, and the impurity content is ~0%.

[0028] In another aspect, the present invention also provides the application of the above-described graphene powder as a reinforcing material.

[0029] Compared with the prior art, the beneficial technical effects achieved by the present invention include:

[0030] 1) The method for preparing graphene powder using syngas as raw material provided by the present invention obtains graphene powder with low impurity content and high graphitization degree after treating syngas with microwave plasma discharge. During the preparation process, the energy required for carbon source cracking and graphene nucleation and growth is provided simultaneously by microwave plasma discharge, without the need for additional heat sources, templates, or other conditions. Moreover, the prepared graphene has high purity and high quality, and has great market competitiveness in the fields of reinforcing materials and biomedicine.

[0031] 2) The method provided by this invention uses widely available syngas as a carbon source, providing an effective way for its high-value-added applications.

[0032] 3) The method for preparing graphene powder using syngas, a material commonly used in the petrochemical industry, provided by this invention is simple to operate, easy to achieve batch preparation, and suitable for industrial production. Attached Figure Description

[0033] 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.

[0034] Figure 1 This is a schematic diagram of the structure of the microwave plasma device used in an embodiment of the present invention.

[0035] Figure 2 This is a schematic diagram of the microwave plasma device used in Comparative Example 1.

[0036] Figure 3 The N2 adsorption-desorption isotherm diagram of graphene powder provided in Example 1 of the present invention.

[0037] Figure 4 The image shows the Raman spectrum of the graphene powder provided in Example 2 of this invention.

[0038] Figure 5 Thermogravimetric curve of graphene powder provided in Example 3 of the present invention.

[0039] Figure 6 The X-ray photoelectron spectrum of the graphene powder provided in Example 3 of this invention.

[0040] Figure 7 This is a scanning electron microscope image of the graphene powder provided in Example 3 of the present invention.

[0041] Figure 8 The image shows a scanning electron microscope image (top view of the substrate surface) of the product obtained in Comparative Example 2.

[0042] Figure 9 The image shows a scanning electron microscope image (top view of the substrate surface) of the product obtained in Comparative Example 3.

[0043] Figure 10 This is a scanning electron microscope image (front view, also known as a cross-sectional view of the substrate surface) of the product obtained in Comparative Example 2.

[0044] Figure 11 This is a scanning electron microscope image (front view, also known as a cross-sectional view of the substrate surface) of the product obtained in Comparative Example 3.

[0045] Figure 12 This is a transmission electron microscope image of graphene powder provided in Embodiment 3 of the present invention.

[0046] Figure 13 This is a comparison chart of the tensile properties of the graphene-aramid composite film and the tensile properties of the aramid film in Application Example 1 of the present invention.

[0047] Explanation of main icon numbers:

[0048] 1-Short-circuit piston, 2-Microwave irradiation area, 3-Quartz tube, 4-Three-pin regulator, 5-Circulator, 6-Microwave generator (magnetic head), 7-High voltage power supply, 8-Graphene powder collection tank, 9-Vacuum pump, 10-Exhaust gas pipeline. Detailed Implementation

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] In this invention, unless otherwise specified, the term "two kinds" as used in this specification means "at least two kinds".

[0055] 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.

[0056] 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.

[0057] Example 1

[0058] This embodiment provides a method for preparing graphene powder using syngas as a raw material, which employs a structural schematic diagram as shown below. Figure 1The microwave plasma device shown includes a short-circuit piston 1, a microwave irradiation area 2, a quartz tube 3, a three-pin regulator 4, a circulator 5, a microwave generator (magnetic head) 6, a high-voltage power supply 7, a graphene powder collection tank 8, a vacuum pump 9, and an exhaust gas pipeline 10. The short-circuit piston 1 and the three-pin regulator 4 are located on both sides of the microwave irradiation area 2. The quartz tube 3 is located in the microwave irradiation area 2 and is connected to the microwave generator (magnetic head) 6 through the three-pin regulator 4 and the circulator 5. The microwave generator (magnetic head) 6 is powered by the high-voltage power supply 7. The outlet of the quartz tube 3 is connected to the first opening of the graphene powder collection tank 8 through a pipeline. The second opening of the graphene powder collection tank 8 is connected to the exhaust gas pipeline 10 through a pipeline via the vacuum pump 9.

[0059] The method includes the following specific steps:

[0060] Step 1): Check the airtightness of the device;

[0061] Step 2): Turn on vacuum pump 9. When the system pressure drops to the lowest gauge pressure (generally, a pointer vacuum gauge with a range of -0.1 to 0.15 MPa is used, and the lowest gauge pressure is -0.1 MPa), turn off vacuum pump 9 and introduce argon gas for gas replacement. Repeat this several times to remove residual air in the device.

[0062] Step 3): Keep the vacuum pump on. At this time, the system pressure drops to the gauge pressure of -0.1MPa. Introduce 300sccm of argon gas, turn on the high-voltage power supply 7 and set the output power to 500W. After the microwave output stabilizes, the argon gas is broken down to produce glow plasma. The plasma is uniformly light purple. It can be observed that the glow plasma coverage area has exceeded the microwave irradiation range.

[0063] Step 4): After the glow plasma stabilizes, increase the argon flow rate to 1000 sccm and adjust the output power of the high-voltage power supply 7 to 1200W. At this time, the system pressure gradually increases to a slightly negative pressure state (the system pressure rises to approximately -0.01 MPa as indicated by the gauge pressure). The glow plasma state changes, gradually changing from a uniform glow state to a state of mixed glow and arc, that is, arc discharge is generated in a large glow area, and it can be observed that the plasma coverage area shrinks to slightly larger than the microwave irradiation range. In addition, the stability of the plasma can also be determined by the microwave feedback power. When the microwave feedback power is zero, it indicates that the microwave energy is used to generate plasma and there is no energy waste.

[0064] Step 5): After the plasma stabilizes, 20 sccm of syngas (CO and H2 volume ratio of 55:45) is introduced. After the gas flow stabilizes, the plasma color changes to a bright green. Since the end of the system is closer to the vacuum pump at this time, the vacuum level is high, and no black powder is seen falling. As the reaction time increases, a large amount of black powder can be seen adhering to the tube wall at the end of the quartz tube. Throughout the reaction process, the high voltage power supply shows that the microwave feedback power remains at zero.

[0065] Step 6): After the reaction lasted approximately 60 minutes, the syngas flow meter was turned off. Once the plasma color returned to a pale purple, observation revealed only a small amount of carbon buildup in the microwave-irradiated area, with an area of ​​approximately 1-2 cm². 2 Adjust the output power of the high voltage power supply 7 to 800W, introduce 20sccm of oxygen to etch the carbon deposits on the tube wall. The carbon deposits on the tube wall can be eliminated in about 5 minutes. Stop the oxygen supply. During the entire etching process, the microwave feedback power displayed by the high voltage power supply remains at zero.

[0066] Step 7): Repeat steps 5) and 6) multiple times to obtain a large amount of graphene powder.

[0067] Example 2

[0068] This embodiment provides a method for preparing graphene powder using syngas as a raw material, which employs a structural schematic diagram as shown below. Figure 1 The microwave plasma device shown includes a short-circuit piston 1, a microwave irradiation area 2, a quartz tube 3, a three-pin regulator 4, a circulator 5, a microwave generator (magnetic head) 6, a high-voltage power supply 7, a graphene powder collection tank 8, a vacuum pump 9, and an exhaust gas pipeline 10. The short-circuit piston 1 and the three-pin regulator 4 are located on both sides of the microwave irradiation area 2. The quartz tube 3 is located in the microwave irradiation area 2 and is connected to the microwave generator (magnetic head) 6 through the three-pin regulator 4 and the circulator 5. The microwave generator (magnetic head) 6 is powered by the high-voltage power supply 7. The outlet of the quartz tube 3 is connected to the first opening of the graphene powder collection tank 8 through a pipeline. The second opening of the graphene powder collection tank 8 is connected to the exhaust gas pipeline 10 through a pipeline via the vacuum pump 9.

[0069] The method includes the following specific steps:

[0070] Step 1): Check the airtightness of the device;

[0071] Step 2): Turn on vacuum pump 9. When the system pressure drops to the lowest gauge pressure (-0.1MPa), turn off vacuum pump 9 and introduce argon gas for gas replacement. Repeat this several times to remove residual air from the device.

[0072] Step 3): Keep the vacuum pump on (-0.1MPa), introduce 200sccm of argon gas, turn on the high-voltage power supply 7 and set the output power to 300W. After the microwave output stabilizes, the argon gas will be broken down to produce glow plasma. The plasma is uniformly light purple and it can be observed that the glow plasma coverage area has exceeded the microwave irradiation range.

[0073] Step 4): After the glow plasma stabilizes, increase the argon flow rate to 3000 sccm and adjust the output power of the high-voltage power supply 7 to 1500W. At this time, the system pressure gradually increases to a slightly negative pressure state (the system pressure rises to approximately -0.01 MPa as indicated by the gauge pressure). The glow plasma state changes, gradually changing from a uniform glow state to a state of mixed glow and arc, that is, arc discharge is generated in a large glow area, and the plasma coverage area can be observed to shrink to slightly larger than the microwave irradiation range. In addition, the stability of the plasma can also be determined by the microwave feedback power. When the microwave feedback power is zero, it indicates that the microwave energy is used to generate plasma and there is no energy waste.

[0074] Step 5): After the plasma stabilizes, 40 sccm of synthesis gas (the volume ratio of CO to H2 is 50:50) is introduced. After the gas flow stabilizes, the plasma color changes and turns bright green. Since the end of the system is closer to the vacuum pump at this time, the vacuum level is high and no black powder is seen falling. As the reaction time increases, a large amount of black powder can be seen adhering to the tube wall at the end of the quartz tube. Throughout the reaction process, the microwave feedback power of the high voltage power supply remains at zero.

[0075] Step 6): After the reaction lasted approximately 90 minutes, the syngas flow meter was turned off. Once the plasma color returned to a pale purple, observation revealed only a small amount of carbon buildup in the microwave-irradiated area, with an area of ​​approximately 2 cm². 2 Adjust the output power of the high voltage power supply 7 to 800W, introduce 30sccm of oxygen to etch the carbon deposits on the tube wall. The carbon deposits on the tube wall can be eliminated in about 5 minutes. Stop the oxygen supply. During the entire etching process, the microwave feedback power displayed by the high voltage power supply remains at zero.

[0076] Step 7): Repeat steps 5) and 6) multiple times to obtain a large amount of graphene powder.

[0077] Example 3

[0078] This embodiment provides a method for preparing graphene powder using syngas as a raw material, which employs a structural schematic diagram as shown below. Figure 1The microwave plasma device shown includes a short-circuit piston 1, a microwave irradiation area 2, a quartz tube 3, a three-pin regulator 4, a circulator 5, a microwave generator (magnetic head) 6, a high-voltage power supply 7, a graphene powder collection tank 8, a vacuum pump 9, and an exhaust gas pipeline 10. The short-circuit piston 1 and the three-pin regulator 4 are located on both sides of the microwave irradiation area 2. The quartz tube 3 is located in the microwave irradiation area 2 and is connected to the microwave generator (magnetic head) 6 through the three-pin regulator 4 and the circulator 5. The microwave generator (magnetic head) 6 is powered by the high-voltage power supply 7. The outlet of the quartz tube 3 is connected to the first opening of the graphene powder collection tank 8 through a pipeline. The second opening of the graphene powder collection tank 8 is connected to the exhaust gas pipeline 10 through a pipeline via the vacuum pump 9.

[0079] The method includes the following specific steps:

[0080] Step 1): Check the airtightness of the device;

[0081] Step 2): Turn on vacuum pump 9. When the system pressure drops to the lowest gauge pressure (-0.1MPa), turn off vacuum pump 9 and introduce argon gas for gas replacement. Repeat this several times to remove residual air from the device.

[0082] Step 3): Keep the vacuum pump on (-0.1MPa), introduce 500sccm of argon gas, turn on the high-voltage power supply 7 and set the output power to 600W. After the microwave output stabilizes, the argon gas will be broken down to produce glow plasma. The plasma is uniformly light purple and it can be observed that the glow plasma coverage area has exceeded the microwave irradiation range.

[0083] Step 4): After the glow plasma stabilizes, increase the argon flow rate to 5000 sccm and adjust the output power of the high-voltage power supply 7 to 1600W. At this time, the system pressure gradually increases to a slightly negative pressure state (the system pressure rises to approximately -0.01 MPa as indicated by the gauge pressure). The glow plasma state changes, gradually changing from a uniform glow state to a state of mixed glow and arc, that is, arc discharge is generated in a large glow area, and the plasma coverage area can be observed to shrink to slightly larger than the microwave irradiation range. In addition, the stability of the plasma can also be determined by the microwave feedback power. When the microwave feedback power is zero, it means that the microwave energy is used to generate plasma and there is no energy waste.

[0084] Step 5): After the plasma stabilizes, 50 sccm of syngas (CO and H2 volume ratio of 45:55) is introduced. After the gas flow stabilizes, the plasma color changes to a bright green. Since the end of the system is closer to the vacuum pump at this time, the vacuum level is high, and no black powder is seen falling. As the reaction time increases, a large amount of black powder can be seen adhering to the tube wall at the end of the quartz tube. Throughout the reaction process, the high voltage power supply shows that the microwave feedback power remains at zero.

[0085] Step 6): After the reaction lasted approximately 120 minutes, the syngas flow meter was turned off. Once the plasma color returned to a pale purple, observation revealed only a small amount of carbon buildup in the microwave-irradiated area, with an area of ​​approximately 2-3 cm². 2 Adjust the output power of the high voltage power supply 7 to 800W, introduce 50sccm of oxygen to etch the carbon deposits on the tube wall. The carbon deposits on the tube wall can be eliminated in about 8 minutes. Stop the oxygen supply. During the entire etching process, the microwave feedback power displayed by the high voltage power supply remains at zero.

[0086] Step 7): Repeat steps 5) and 6) multiple times to obtain a large amount of graphene powder.

[0087] Comparative Example 1

[0088] This comparative example provides a method for preparing graphene powder using syngas as a raw material, which employs a structural schematic diagram as shown below. Figure 2 The microwave plasma device shown includes a short-circuit piston 1, a microwave irradiation area 2, a quartz tube 3, a three-pin regulator 4, a circulator 5, a microwave generator (magnetic head) 6, a high-voltage power supply 7, and a graphene powder collection tank 8. The short-circuit piston 1 and the three-pin regulator 4 are located on both sides of the microwave irradiation area 2. The quartz tube 3 is located in the microwave irradiation area 2 and is connected to the microwave generator (magnetic head) 6 through the three-pin regulator 4 and the circulator 5. The microwave generator (magnetic head) 6 is powered by the high-voltage power supply 7. The outlet of the quartz tube 3 is connected to the inlet of the graphene powder collection tank 8 through a pipeline.

[0089] The method includes the following specific steps:

[0090] Step 1): Check the airtightness of the device;

[0091] Step 2): Purge the reaction system with 1200 sccm of argon gas to purge any residual air from the system;

[0092] Step 3): Keep 1200 sccm of argon gas flowing in, turn on the high voltage power supply 7 and set the output power to 700W. After the microwave output is stable, place the Faraday coil in the microwave irradiation area to initiate plasma, which will then generate plasma arc discharge. The plasma coverage area almost overlaps with the microwave irradiation area and the color is light purple.

[0093] Step 4): After the arc plasma stabilizes, 20 sccm of syngas (CO and H2 volume ratio of 55:45) is introduced into the system. After the syngas flow stabilizes, the color of the arc plasma changes from light purple to green. Only a very small amount of powder can be seen falling at the end of the quartz tube. As the reaction time increases, the microwave feedback power begins to fluctuate. After 20 minutes of reaction, the microwave feedback power gradually increases from the initial 0W to 15W. It is necessary to adjust the three-pin regulator 4 to control the microwave feedback power. As the time continues to extend, it is no longer possible to simply adjust the three-pin regulator 4 to control the microwave feedback power. The microwave feedback power continues to deviate from the normal state (0W), and the plasma state becomes unstable. Black substances remain on the quartz tube wall in the microwave irradiation area, and local red-hot phenomena are observed.

[0094] Step 5): If the reaction continues, after 28 minutes, the plasma state will fluctuate violently and will be unable to maintain the plasma initiation state, resulting in plasma extinction.

[0095] Step 6): Based on step 5), after the reaction has proceeded for 25 minutes, turn off the synthesis gas flow meter. After the plasma color returns to light purple, introduce 20 sccm of oxygen into the system. The carbon deposits on the tube wall can be eliminated in about 5 minutes. Then stop the oxygen supply. During the etching process, the microwave feedback power gradually returns to 0W.

[0096] Step 7): Repeat steps 4) and 6) for about 5 hours. The amount of graphene powder obtained at the tail end is small, and there is obvious local damage to the quartz tube wall (caused by local high temperature due to carbon accumulation on the quartz tube wall, and carbon reacts with the SiO2 material of the quartz tube). White particles are found in the powder collected at the tail end.

[0097] Comparative Example 2

[0098] This comparative example provides a method for preparing graphene using syngas as a raw material, which includes the following specific steps:

[0099] Step 1): Check the airtightness of the device;

[0100] Step 2): Place the SiC substrate in the center of the microwave irradiation area, turn on the vacuum pump, and when the system pressure drops to the lowest gauge pressure (-0.1MPa), turn off the vacuum pump and introduce argon gas for gas replacement. Repeat this several times to remove the residual air in the device.

[0101] Step 3): Keep the vacuum pump on (-0.1MPa), introduce 200sccm of argon gas, turn on the high voltage power supply and set the output power to 300W. After the microwave output stabilizes, the argon gas will be broken down to produce glow plasma. The plasma is uniformly light purple and it can be observed that the glow plasma coverage area has exceeded the microwave irradiation range.

[0102] Step 4): After the glow plasma stabilizes, introduce 20 sccm of syngas (CO and H2 volume ratio of 55:45). After the gas flow stabilizes, start timing. As time goes on, the SiC substrate gradually shows a red-hot state.

[0103] Step 5): After the reaction has lasted for about 60 minutes, the synthesis gas flow meter is turned off. By observing that a large amount of carbon has been deposited on the quartz tube wall near the SiC substrate, the SiC substrate is almost impossible to observe. The vacuum pump is turned off. When the system pressure returns to normal pressure, the argon gas is turned off. After the system temperature drops to room temperature, the SiC substrate is taken out and it is found that it is covered with black material, while no black powder is collected at the tail end.

[0104] Comparing the embodiments of the present invention with Comparative Example 2, it can be seen that the method provided by the present invention uses microwave plasma as the main generation means, requiring no external heat source, no temperature control, and no substrate to obtain graphene powder. Comparative Example 2, however, uses low-pressure plasma-assisted chemical vapor deposition of graphene on a substrate surface. It uses a SiC substrate and mainly utilizes a carbon source to generate a carbon buffer layer at high plasma temperature. Under the action of the plasma electric field, the carbon source continues to grow graphene on the buffer layer. The resulting product is not graphene powder, but rather tends to be vertically aligned graphene sheets, such as... Figure 8 and Figure 10 As shown.

[0105] Comparative Example 3

[0106] This comparative example provides a method for preparing graphene using syngas as a raw material, which includes the following specific steps:

[0107] Step 1): Check the airtightness of the device;

[0108] Step 2): Place the copper substrate in the center of the microwave irradiation area, turn on the vacuum pump, and when the system pressure drops to the lowest gauge pressure (-0.1MPa), turn off the vacuum pump and introduce argon gas for gas replacement. Repeat this several times to remove the residual air in the device.

[0109] Step 3): Keep the vacuum pump on (-0.1MPa), introduce 200sccm of argon gas, turn on the high-voltage power supply and set the output power to 300W. After the microwave output stabilizes, the argon gas will be broken down to produce glow plasma. The plasma is uniformly light purple and the coverage of the glow plasma has exceeded the microwave irradiation range.

[0110] Step 4): After the glow plasma stabilizes, introduce 20 sccm of syngas (CO and H2 volume ratio of 55:45). After the gas flow stabilizes, start timing. As time goes on, the copper substrate gradually shows a red-hot state.

[0111] Step 5): After the reaction has lasted for about 60 minutes, the synthesis gas flow meter is turned off. By observing that a large amount of carbon deposits are attached to the quartz tube wall near the copper substrate, the copper substrate can hardly be observed. The vacuum pump is turned off. When the system pressure returns to normal pressure, the argon gas is turned off. After the system temperature drops to room temperature, the copper substrate is taken out and it is found that it is covered with black material, while no black powder is collected at the tail end.

[0112] Comparing the embodiments of the present invention with Comparative Example 3, it can be seen that the method provided by the present invention uses microwave plasma as the main generation means, requiring no external heat source, no temperature control, and no substrate to obtain graphene powder. Comparative Example 3, however, uses low-pressure plasma-assisted chemical vapor deposition of graphene on a substrate surface, employing a copper substrate. It primarily utilizes a carbon source to generate a carbon buffer layer at high plasma temperatures, and under the influence of the plasma electric field, graphene is subsequently grown on the buffer layer. The resulting product is not graphene powder, but rather tends to be vertically aligned graphene sheets, such as... Figure 9 and Figure 11 As shown.

[0113] Test Example 1

[0114] This test example uses the graphene powder provided in Example 1 to conduct N2 adsorption-desorption experiments, and measures the specific surface area of ​​the graphene powder using the BET method. The obtained N2 adsorption-desorption isotherms are shown below. Figure 3 As shown, calculations show that the specific surface area of ​​the graphene powder provided in Example 1 is ~260m². 2 / g.

[0115] Test Example 2

[0116] This test example uses Raman spectroscopy to characterize the graphene powder provided in Example 2. The obtained Raman spectrum is shown below. Figure 4 As shown. From Figure 4 As can be seen from this, it mainly exhibits three distinct peaks, namely the one located at 1350 cm⁻¹. -1 The D peak is located at 1580 cm. -1 The G peak and located at 2700cm -1The 2D peak, determined by the intensity ratio of the D peak to the G peak (I D / I G The defect situation of graphene powder can be obtained by measuring the intensity ratio of the 2D peak to the G peak (I). 2D / I G This can give a rough idea of ​​the number of layers in the graphene powder. For example... Figure 4 As shown, the graphene powder I provided in Example 2 D / I G =0.31, indicating that the defect degree of this graphene powder is relatively low. 2D / I G =0.81, indicating that the graphene powder has a relatively small number of layers, generally less than 4 layers.

[0117] Test Example 3

[0118] This test example involves thermogravimetric analysis (at an oxygen atmosphere) of the graphene powder provided in Example 3. The heating range is 100-900℃, and the resulting thermogravimetric curves are shown below. Figure 5 As shown. From Figure 5 As can be seen, after the temperature reaches 780℃, the graphene powder provided in Example 3 is completely burned off with almost no residue, indicating that the graphene powder does not contain impurities that cannot be decomposed in an oxygen environment.

[0119] Test Example 4

[0120] This test example uses X-ray photoelectron spectroscopy to characterize the graphene powder provided in Example 3 to analyze its elemental composition. The obtained X-ray photoelectron spectrum is shown below. Figure 6 As shown. According to Figure 6 It can be seen that in the graphene powder provided in Example 3, the proportions of C and O elements are 97.68 at% and 2.32 at%, respectively, and its C / O ratio reaches 42.1, indicating that the graphene powder has a high carbon content.

[0121] Test Example 5

[0122] In this test example, the graphene powder provided in Example 3 and the products obtained from Comparative Examples 2-3 were characterized by scanning electron microscopy to obtain their surface morphology. The obtained scanning electron micrographs are shown below. Figure 7 , Figure 8 and Figure 9 As shown. Figure 7 The image shown is a scanning electron microscope image of the graphene powder provided in Embodiment 3 of the present invention. The testing method is to directly coat the graphene powder onto the conductive adhesive and then perform SEM testing. Since there is no substrate present during the growth of the graphene powder, the graphene sheets tend to form wrinkled and clustered graphene spherical particles. Therefore, the SEM image mostly shows this wrinkled particle shape.

[0123] Both Comparative Examples 2 and 3 used substrates in the preparation of graphene. Generally speaking, it is easier to obtain graphene sheets perpendicular to the substrate when growing graphene on a substrate under plasma irradiation. Figure 8 and Figure 9 This is a top view obtained from SEM testing of graphene on a substrate. It is a flower-like shape when viewed from a height perpendicular to the substrate surface. This is a representative top view of vertically arranged graphene.

[0124] Figure 10 and Figure 11 Representative SEM front views (also known as substrate surface cross-sectional views) of graphene obtained in Comparative Examples 2 and 3 are shown below. Figure 10 and Figure 11 As can be seen, the graphene obtained in Comparative Examples 2 and 3 mainly exhibits as vertically arranged graphene sheets perpendicular to the substrate surface, with the area above the white line being the graphene sheet and the area below the white line being the substrate. This type of graphene is not free-living; it requires attachment to a substrate to exhibit this state. Without a substrate, it is merely a self-supporting graphene sheet. In summary, from... Figures 8-11 As can be seen, the products obtained from Comparative Examples 2 and 3 are graphene sheets that tend to be vertically aligned.

[0125] Test Example 6

[0126] This test example uses transmission electron microscopy (TEM) to characterize the graphene powder provided in Example 3 to obtain its sheet morphology. The obtained TEM images are shown below. Figure 12 As shown. When characterizing graphene powder using transmission electron microscopy, it is often necessary to ultrasonically disperse the graphene powder in anhydrous ethanol. Under the action of ultrasound, the graphene powder sheets open up, forming individual sheets, thus allowing for... Figure 12 The transmission electron microscope image shown indicates that the graphene powder provided in Example 3 of this invention is in the form of thin sheets.

[0127] Application Example 1

[0128] In this application example, the graphene powder obtained in Example 1 of the present invention is added to aramid to prepare a graphene composite aramid film to reinforce the aramid. The specific steps are as follows:

[0129] Step 1): Add 1 wt% graphene powder to the aramid polymerization solution and mix thoroughly using a three-roll mill to obtain a graphene composite aramid polymerization solution.

[0130] Step 2): Use a coating machine to coat the PI film surface with graphene composite aramid polymer solution to obtain a graphene composite aramid film (uncured and demolded);

[0131] Step 3): Immerse the PI film with graphene composite aramid film in clean water for curing and demolding. After demolding, place the graphene composite aramid film in an oven for drying.

[0132] Step 4): After drying, the graphene composite aramid film is cut into the required test size, i.e., 5mm×100mm. Its thickness is measured and a tensile test is performed using a mechanical testing instrument to obtain the tensile performance data of the graphene composite aramid film.

[0133] Step 5): Repeat steps 2), 3), and 4) with pure aramid polymer solution to obtain aramid film tensile property data.

[0134] The tensile property data of graphene-aramid composite film and aramid film were plotted on... Figure 13 Comparing China and Israel, from Figure 13 As can be seen, the composite aramid film with added graphene powder exhibits improvements in both stress and strain. The tensile strength increases from 282.6 MPa to 378.5 MPa (an increase of approximately 33.9%), and the elongation at break increases from 16.4% to 23.1% (an increase of approximately 40.9%). These data demonstrate that the composite aramid film with added graphene powder shows significant improvements in both strength and toughness.

[0135] 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 using syngas as a raw material, characterized in that, The method includes the following steps: Step (1): Under high vacuum conditions, a stable glow plasma is spontaneously generated in a microwave plasma device with an inert gas as the background gas under the action of microwaves; in step (1), the flow rate of the inert gas is 200-500 sccm, the output power of the microwave is 300-600 W, and the high vacuum conditions include: pressure of -0.05 to -0.1 MPa; Step (2): Increase the flow rate of the inert gas, increase the output power of the microwave, and increase the system pressure to a slightly negative pressure state so that the glow plasma will transform and the system will be in a state where glow plasma and electric arc coexist; In step (2), the flow rate of the inert gas is 1000-5000 sccm, the output power of the microwave is 1000-2000 W, and the pressure corresponding to the slightly negative pressure state is greater than or equal to -0.02 MPa and less than 0 MPa; Step (3): Under the condition of maintaining the system pressure at a slightly negative pressure state, syngas is introduced into the microwave plasma device. Under the action of glow plasma and electric arc, the syngas molecules are bombarded by high-energy particles and decomposed. The decomposed carbon species nucleate and grow to obtain graphene powder. In the synthesis gas, the volume fraction of CO is 45-55% and the volume fraction of H2 is 55-45%.

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

3. The method according to claim 1 or 2, characterized in that, In step (3), the flow rate of the synthesis gas is 5-200 sccm.

4. The method according to claim 1 or 2, characterized in that, In step (3), the reaction time is more than 1 hour.

5. A graphene powder, characterized in that, The graphene powder is prepared by the method for preparing graphene powder using syngas as a raw material as described in any one of claims 1-4, wherein the specific surface area of ​​the graphene powder is >250 m². 2 / g, Raman results showed I D / I G <0.4, I 2D / I G >0.6, the percentage of carbon and oxygen atoms is >40.

6. The application of the graphene powder according to claim 5 as a reinforcing material.

Images