Method for gas-phase synthesis of graphene

Abstract

According to the method, a chemical vapor deposition system comprises a cracking zone and a nucleation growth zone, inert gas is introduced into the chemical vapor deposition system, then carbon source gas is introduced for a cracking reaction, the nucleation growth zone is heated and cooled, and then graphene powder is collected in tail gas; wherein the reaction temperature of the cracking zone is 800-1000 DEG C, the flow rate of the inert gas is 1-10 SLM, and the flow rate of the carbon source gas is 10-30 sccm; the reaction temperature of the nucleation growth area is 900-1200 DEG C and is higher than that of the cracking area, and the length of the nucleation growth area is larger than or equal to 50 cm. The heating mode of the nucleation growth area comprises infrared radiation, laser heating or inductive coupling. According to the method disclosed by the invention, large-scale size regulation and control of the graphene powder can be realized, the size range of the graphene powder prepared in the prior art is expanded, and the requirements of the industry on the graphene powder with different sizes can be met.

Description

Technical Field

[0001] The present invention relates to the field of graphene preparation, and in particular to a method for gas-phase synthesis of graphene. Background Art

[0002] Graphene is a two-dimensional sp 2 An allotrope of hybrid carbon with excellent electrical, optical, thermal, and mechanical properties. The industrial application of graphene requires it to be large in size and have uniform properties. Currently, chemical vapor deposition is a typical method for preparing large-scale, high-quality, high-purity, low-oxygen-content, and few-layer graphene powders, but it also has disadvantages such as complex processes. We developed a method for the vapor growth of graphene in the early stages and achieved continuous preparation of graphene (Chinese Patent Application No.: 201910875607.7). We also developed a method for preparing graphene powder with adjustable size (Chinese Patent Application No.: 202010167294.2), which achieved the adjustable size of vapor-synthesized graphene powder within 300nm.

[0003] However, with the increasing application of graphene powder, there is an urgent demand for other sizes of powder, such as 500nm, 800nm, and even micron-level high-quality graphene powder. Therefore, it is necessary to achieve wider size adjustment in the graphene gas phase preparation process. Summary of the Invention

[0004] The purpose of this application is to provide a method for gas-phase synthesis of graphene to solve the problems existing in the prior art and meet the industry's needs for high-quality graphene powders of different sizes.

[0005] To achieve the above objectives, the preparation method provided in this application is as follows:

[0006] A method for gas-phase synthesis of graphene, wherein a chemical vapor deposition system includes a cracking zone and a nucleation and growth zone, an inert gas is introduced into the chemical vapor deposition system, and then a carbon source gas is introduced to perform a cracking reaction, the nucleation and growth zone is heated, and after cooling, graphene powder is collected in the tail gas;

[0007] The reaction temperature of the cracking zone is 800-1000°C, the flow rate of the inert gas is 1-10 SLM, and the flow rate of the carbon source gas is 10-30 sccm;

[0008] The reaction temperature of the nucleation growth zone is 900-1200° C., which is higher than the reaction temperature of the cracking zone, and the length is ≥50 cm.

[0009] In the above method, the heating method of the nucleation and growth zone includes infrared radiation, laser heating or inductive coupling.

[0010] In the above method, the length of the nucleation and growth zone is 50 to 150 cm.

[0011] In the above method, the time for the gas to flow through the nucleation and growth zone is 1.5 to 60 seconds.

[0012] In the above method, the cooling process is natural cooling.

[0013] In the above method, the tail gas is collected by a filter membrane.

[0014] In the above method, the carbon source includes one or more of methane, ethylene, acetylene, ethanol or acetone.

[0015] In the above method, the chemical vapor deposition system is a microwave plasma chemical vapor deposition system.

[0016] In the above method, the nucleation and growth zone adopts an infrared radiation heater.

[0017] The application of the method of the present application in the production of products related to graphene powders of different sizes also falls within the scope of protection of the present application.

[0018] The present application proposes a method for gas-phase synthesis of graphene, which achieves size adjustment of gas-phase synthesized graphene powder by appropriate factors such as nucleation growth zone length, gas flow rate and time.

[0019] The reaction of gas phase synthesis of graphene powder is completed by the cracking of carbon source and the recombination of carbon radicals. The reaction zone of this application can be divided into two parts: cracking zone and nucleation growth zone. Figure 1 As shown, adjusting the length of the nucleation and growth zone can control the time it takes for carbon radicals to recombine, thereby achieving a wide range of size adjustment for vapor-phase graphene powders. This differs from previous synthesis schemes. Furthermore, extending the length of the nucleation and growth zone increases the reaction time, allowing for more complete reactions at each stage and consequently increasing the size of the resulting graphene powder.

[0020] Existing technologies can adjust the size of graphene powder within 300nm, mainly by controlling the growth time by controlling the gas flow rate, etc. However, there is no regulation on the length of the graphene growth zone. The temperature of the synthesis zone is completely dependent on the residual temperature of the cracking nucleation zone for growth. The growth interval is too short and the gas residence time is less than 1 second, so it is impossible to prepare larger powders. The present application increases the length of the nucleation growth zone and controls the appropriate temperature and gas flow rate to achieve the synthesis of graphene powders of different sizes. The temperature of the nucleation growth zone is different from the temperature of the cracking zone, which helps to synthesize high-quality graphene powders of different sizes.

[0021] Compared with existing technologies, the advantages of this application are as follows: 1. The method of this application can achieve a wide range of graphene powder size control, expanding the size range of graphene powders produced by existing technologies and meeting the industry's demand for graphene powders of different sizes. 2. The method of this application adjusts the length of the nucleation and growth zone and controls the time for carbon radical recombination, enabling better control of the synthesis process, an orderly reaction process, high material purity, and more conducive to the production of high-quality graphene powders of different sizes. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of the reaction zone for gas-phase synthesis of graphene.

[0023] Figure 2 This is a schematic diagram of the gas-phase graphene synthesis process for this application.

[0024] Figure 3 Schematic diagram of the device for the preparation method of this application.

[0025] Figure 4 This is a statistical diagram of the size of the graphene powder obtained in Example 1.

[0026] Figure 5 This is a statistical diagram of the size of the graphene powder obtained in Example 2.

[0027] Figure 6 This is a statistical diagram of the size of the graphene powder obtained in Example 3.

[0028] Figure 7 This is a statistical diagram of the size of the graphene powder obtained in Example 4.

[0029] Figure 8 This is a statistical diagram of the size of the graphene powder obtained in Example 5.

[0030] Figure 9 This is a statistical diagram of the size of the graphene powder obtained in Comparative Example 1. DETAILED DESCRIPTION

[0031] The method of the present application is described in detail below through specific examples, but the present application is not limited thereto. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present application shall be included within the scope of protection of the present application. It should be understood that the specific examples are merely used to explain the present application and are not intended to limit the present application.

[0032] It should be understood that the experimental methods used in the following examples of this application are conventional methods unless otherwise specified. The materials, reagents, etc. used in the following examples of this application are all commercially available unless otherwise specified.

[0033] A method for synthesizing graphene in the gas phase, such as Figure 2As shown, first, an inert gas, such as a mixture of one or more of argon, krypton, xenon, nitrogen, etc., is introduced into the chemical vapor deposition system, wherein high-purity argon is preferred, and the inert gas flow rate is 1 to 10 SLM (SLM, liters per minute under standard conditions), preferably about 5 SLM. Then, a carbon source gas, such as one or more of methane, ethylene, acetylene, ethanol, acetone, etc., wherein methane is preferred, and the purity of methane is preferably not less than 99.999%, is introduced, and the flow rate of the carbon source gas is 10 to 30 sccm (sccm, milliliters per minute under standard conditions), preferably about 20 sccm, to carry out a cracking reaction. The reaction temperature in the cracking zone is 800 to 1000°C, preferably about 900°C.

[0034] The nucleation and growth zone is then heated, cooled naturally, and the graphene powder is collected from the tail gas. The reaction temperature of the nucleation and growth zone is 900-1200°C, which is higher than the reaction temperature of the cracking zone. The length is ≥50 cm, and can be 50-150 cm or longer. The gas flows through the nucleation and growth zone for 1.5-60 seconds.

[0035] When the temperature of the nucleation growth zone is lower than that of the cracking zone, the rate of nucleation growth slows down until it stops, and the synthesized graphene powder is small in size. Even if the reaction is carried out in the nucleation growth zone for a certain period of time, large-sized graphene powder cannot be synthesized due to the limitations of the reaction conditions.

[0036] When the microwave plasma system has no heating zone after the cracking zone, or the temperature of the nucleation and growth zone is lower than 900°C, the free ions after cracking stay in the nucleation and growth zone for less than 1 second, and graphene powder with a size of less than 300nm is obtained.

[0037] When the temperature of the nucleation growth zone is set to 900-1200° C., the length is 50-150 cm, and the residence time of the free ions after cracking in the nucleation growth zone is 1-3 seconds, the graphene powder with a size of 300-1000 nm can be obtained.

[0038] When the temperature of the nucleation growth zone is set to 900-1200° C., the length is greater than 150 cm, and the residence time of the free ions after cracking in the nucleation growth zone is greater than 3 seconds, the graphene powder with a size of more than 1 μm can be obtained.

[0039] like Figure 3 As shown, the chemical vapor deposition system described in the method of the present application is a microwave plasma system, and the nucleation and growth zone adopts an infrared radiation heater.

[0040] Example 1

[0041] To synthesize graphene in the gas phase, inert gas Ar is introduced, and then carbon source gas CH4 is introduced for cracking reaction, the nucleation growth zone is heated, the temperature of the infrared radiation heater is set to 950°C, the length of the nucleation growth zone is 50cm, and after reaching the set temperature and stabilizing for half an hour, the microwave plasma system is turned on and the microwave plasma system power is set to 1.5KW, and the cracking zone reaction temperature is 900°C. The flow rate of Ar is controlled to 5SLM, and the flow rate of CH4 is 20sccm, initiating the system to produce a stable plasma. The gas flows through the nucleation growth zone for 1s. At this time, it can be seen that the system produces obvious luminescence and heating phenomena, and a large amount of powdered graphene floats out of the outlet of the device. After collecting the powder, the size is counted by a laser particle size analyzer, and it is found that the size of the powdered graphene is D90~494nm, that is, the largest size is 494nm, such as Figure 4 shown.

[0042] Example 2

[0043] Graphene was synthesized in the gas phase using the same method as in Example 1, except that the length of the nucleation and growth zone was 100 cm. The gas flowed through the nucleation and growth zone for 2 seconds.

[0044] It can be seen that the system produces obvious luminescence and heating phenomenon, and a large amount of powdered graphene floats out of the device outlet. After collecting the powder and performing size statistics using a laser particle size analyzer, it is found that the size of the powdered graphene is D90~722nm, that is, the largest size is 722nm. Figure 5 shown.

[0045] Example 3

[0046] Graphene was synthesized in the gas phase using the same method as in Example 1, except that the length of the nucleation and growth zone was 150 cm. The gas flowed through the nucleation and growth zone for 3 seconds.

[0047] It can be seen that the system produces obvious luminescence and heating phenomena, and a large amount of graphene powder floats out of the device outlet. After collecting the powder and performing size statistics using a laser particle size analyzer, it is found that the size of the graphene powder is D90~930nm. The powder size includes 1μm and above, and the largest size is 930nm. Figure 6 shown.

[0048] Example 4

[0049] To synthesize graphene in the gas phase, inert gas Ar is introduced, and then carbon source gas CH4 is introduced for cracking reaction, the nucleation growth zone is heated, the temperature of the infrared radiation heater is set to 900°C, the length of the nucleation growth zone is 50cm, and after reaching the set temperature and stabilizing for half an hour, the microwave plasma system is turned on and the microwave plasma system power is set to 1.5KW, and the cracking zone reaction temperature is 800°C. The flow rate of Ar is controlled to 5SLM, and the flow rate of CH4 is 20sccm, initiating the system to produce a stable plasma. The gas flows through the nucleation growth zone for 1s. At this time, it can be seen that the system produces obvious luminescence and heating phenomena, and a large amount of powdered graphene floats out of the device outlet. After collecting the powder, the size is counted by a laser particle size analyzer, and it is found that the size of the powdered graphene is D90~508nm, that is, the largest size is 508nm, such as Figure 7 shown.

[0050] Example 5

[0051] To synthesize graphene in the gas phase, inert gas Ar is introduced, and then carbon source gas CH4 is introduced for cracking reaction, the nucleation growth zone is heated, the temperature of the infrared radiation heater is set to 1150°C, the length of the nucleation growth zone is 50cm, and after reaching the set temperature and stabilizing for half an hour, the microwave plasma system is turned on and the microwave plasma system power is set to 1.5KW, and the cracking zone reaction temperature is 900°C. The flow rate of Ar is controlled to 5SLM, and the flow rate of CH4 is 20sccm, initiating the system to produce a stable plasma. The gas flows through the nucleation growth zone for 1s. At this time, it can be seen that the system produces obvious luminescence and heating phenomena, and a large amount of powdered graphene floats out of the device outlet. After collecting the powder, the size is counted by a laser particle size analyzer, and it is found that the size of the powdered graphene is D90~537nm, that is, the largest size is 537nm, such as Figure 8 shown.

[0052] Comparative Example 1

[0053] The infrared radiation heater was turned off, the microwave plasma system power was set to 1.5KW, and the reaction temperature in the cracking zone was set to 900°C. The Ar flow rate was controlled to 5SLM and the CH4 flow rate was 20sccm to generate a stable plasma. At this time, a large amount of graphene powder floated out of the device outlet. After collecting the powder, the size was counted by a laser particle size analyzer. It was found that the size of the graphene powder was D90~236nm, that is, the largest size was 236nm. Figure 9 shown.

[0054] Comparative Example 2

[0055] The method for gas phase synthesis of graphene is the same as that in Example 1, except that the reaction temperature in the pyrolysis zone is 1000°C.

[0056] The rate of nucleation growth slows down until it stops, and the synthesized graphene powder is small in size, ranging from D90 to 236 nm, that is, the largest size is 236 nm; it is impossible to synthesize graphene powder of larger size.

[0057] The above examples and comparative examples demonstrate that, as the length of the nucleation and growth zone of the present invention increases, the reaction time increases, the reactions at each stage become more complete, and the size of the resulting graphene powder increases accordingly. Increasing the temperature of the nucleation and growth zone results in higher purity graphene. The reaction temperature of the nucleation and growth zone of the present invention should be higher than that of the cracking zone; otherwise, a wider range of size control will be impossible.

[0058] The above are only preferred embodiments of the present application and do not limit the patent scope of the present application. Any equivalent structure or equivalent process transformation made using the contents of the present application specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A method for gas phase synthesis of graphene, characterized in that, The chemical vapor deposition system includes a cracking zone and a nucleation and growth zone. An inert gas is introduced into the chemical vapor deposition system, and then a carbon source gas is introduced to perform a cracking reaction. The nucleation and growth zone is heated, and after cooling, graphene powder is collected in the tail gas. The reaction temperature of the cracking zone is 800-1000°C, the flow rate of the inert gas is 1-10 SLM, and the flow rate of the carbon source gas is 10-30 sccm; The reaction temperature of the nucleation growth zone is 900-1200° C., which is higher than the reaction temperature of the cracking zone. The length of the nucleation growth zone is ≥50 cm.

2. The method for gas-phase synthesis of graphene according to claim 1, wherein: The heating method of the nucleation growth zone includes infrared radiation, laser heating or inductive coupling.

3. The method for gas-phase synthesis of graphene according to claim 1, wherein: The length of the nucleation growth zone is 50 to 150 cm.

4. The method for gas-phase synthesis of graphene according to claim 1, wherein: The gas flows through the nucleation and growth zone for 1.5 to 60 seconds.

5. The method for gas-phase synthesis of graphene according to claim 1, wherein: The cooling process is natural cooling.

6. The method for gas-phase synthesis of graphene according to claim 1, wherein: The exhaust gas is collected through a filter membrane.

7. The method for gas-phase synthesis of graphene according to claim 1, wherein: The carbon source includes one or more of methane, ethylene, acetylene, ethanol or acetone.

8. A method for gas-phase synthesis of graphene according to any one of claims 1 to 7, characterized in that: The chemical vapor deposition system is a microwave plasma chemical vapor deposition system.

9. A method for gas-phase synthesis of graphene according to any one of claims 1 to 7, characterized in that: The nucleation and growth zone adopts an infrared radiation heater.

10. Use of the method according to any one of claims 1 to 9 in the production of graphene powder-related products.

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