Plasma discharge system and application thereof, and synthesis method of temperature-sensitive substance
By introducing ion exchange membranes and temperature control components into the plasma discharge system, the decomposition and side reaction problems in the synthesis of temperature-sensitive substances were solved, and efficient synthesis of ammonia and hydrogen peroxide was achieved.
Patent Information
- Application Number
- CN202510872103.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-06-26
- Publication Date
- 2025-10-14
AI Technical Summary
Existing plasma technology easily causes decomposition, isomerization or side reactions of the target substances when synthesizing temperature-sensitive substances such as ammonia and hydrogen peroxide, limiting its application.
An ion exchange membrane is introduced into the plasma discharge system and combined with temperature control components to control the reaction temperature and solution temperature, forming an isolated reaction chamber to reduce the loss of active species.
Effectively control the synthesis process of temperature-sensitive substances, improve synthesis efficiency, reduce decomposition and side reactions, and significantly enhance the synthesis effect of ammonia and hydrogen peroxide.
Smart Images
Figure CN120771813A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application belongs to the technical field of plasma electrochemistry, and particularly relates to a plasma discharge system, application thereof and a synthesis method of temperature-sensitive substances. BACKGROUND
[0002] Plasma refers to a quasi-neutral gas state composed of ions, electrons, atoms and molecules, which is called the "fourth state of matter". When plasma is in contact with a liquid, a plasma electrochemical system is formed. The active components in the plasma and the physical and chemical processes they undergo make the plasma-liquid interface become a reaction region with multiple physical processes, in which there is exchange of matter, charge and energy. The plasma reaction activity can be transferred to the liquid through the interface to become the reaction activity of the liquid, which has the ability to synthesize many materials that need special treatment or are difficult to synthesize under general conditions. Therefore, it is widely used in the fields of semiconductor industry, material processing, surface modification and waste gas purification. However, the heat effect generated by plasma and electrochemical processes can cause the decomposition, isomerization or side reactions of target substances, which limits its application in the synthesis of temperature-sensitive substances such as ammonia and hydrogen peroxide, and has certain limitations. SUMMARY
[0003] The first object of the present application is to solve the problems of decomposition, isomerization or side reactions of target substances in the synthesis of temperature-sensitive substances in the existing plasma technology, and to provide a plasma discharge system.
[0004] The second object of the present application is to provide the application of the above-mentioned plasma discharge system in the preparation of temperature-sensitive substances.
[0005] The third object of the present application is to provide a synthesis method of temperature-sensitive substances.
[0006] Specifically, the plasma discharge system comprises: a gas source configured to provide a reaction-required gas; a liquid storage part configured to store a plasma reaction solution; a plasma electrochemistry part comprising a plasma reactor structured to form a reaction chamber for performing a plasma electrochemistry reaction, and a plasma generation assembly, the gas source and the reaction chamber being communicated through a capillary tube; an ion exchange membrane arranged in the reaction chamber to divide the reaction chamber into a first chamber and a second chamber, the first chamber being communicated with the liquid storage part; the plasma generation assembly comprising a plasma electrode, a plasma power supply and a counter electrode connected in sequence, the plasma electrode being inserted into the first chamber, and the counter electrode being inserted into the second chamber; a temperature control part comprising a first water bath temperature controller configured to regulate a temperature of the plasma reaction solution in the liquid storage part, and a second water bath temperature controller configured to regulate a reaction temperature of the plasma electrochemistry reaction in the plasma reactor; and a product collection part configured to collect a reaction product of the plasma electrochemistry part.
[0007] Further, the liquid storage part comprises at least one liquid storage tank, and a peristaltic pump is arranged between the liquid storage tank and the first chamber.
[0008] Further, a peristaltic pump is arranged between the gas source and the reaction chamber.
[0009] Further, a measurement resistor is arranged between the plasma electrode and the plasma power supply, and a current-limiting resistor is arranged between the plasma power supply and the counter electrode.
[0010] The application further provides an application of the above plasma discharge system in preparation of a temperature-sensitive substance.
[0011] Further, the temperature-sensitive substance is hydrogen peroxide and / or ammonia.
[0012] The application provides a synthesis method of the temperature-sensitive substance, which adopts the above plasma discharge system to synthesize the temperature-sensitive substance.
[0013] Further, the synthesis method comprises: preparing the plasma reaction solution and storing the plasma reaction solution in the liquid storage part, adjusting the temperature of the plasma reaction solution by the first water bath temperature controller; introducing the plasma reaction solution into the plasma reactor, opening the gas source to introduce the reaction gas, opening the plasma power supply to apply a voltage to the plasma electrode and the counter electrode to generate a discharge plasma, and controlling the reaction temperature of the plasma electrochemistry reaction in the plasma reactor by the first water bath temperature controller; and collecting the temperature-sensitive substance by the product collection part.
[0014] Further, when the temperature-sensitive substance is ammonia, the plasma reaction solution is a sodium sulfate solution, the concentration of the sodium sulfate solution is 0.001 mol / L-0.05 mol / L, and the pH value is 3.5-4.5; and the reaction gas is nitrogen.
[0015] Further, when the temperature-sensitive substance is ammonia, the flow rate of the plasma reaction solution into the plasma reactor is 0.01 mL / min-4 mL / min, the flow rate of the reaction gas is 25 sccm-75 sccm, the discharge current of the plasma power supply is 20 mA-30 mA, and the reaction temperature is 0°C-10°C.
[0016] Beneficial effects:
[0017] The plasma discharge system provided by the application effectively controls the reaction temperature during the synthesis of the temperature-sensitive substance, improves the utilization efficiency of active species in the plasma electrochemical reaction, and reduces the decomposition, isomerization or side reaction of the temperature-sensitive substance, thereby significantly improving the synthesis efficiency of the temperature-sensitive substance, and having a wide application prospect in the synthesis of temperature-sensitive substances such as ammonia and hydrogen peroxide. BRIEF DESCRIPTION OF DRAWINGS
[0018] Figure 1 A structure schematic diagram of the plasma discharge system for preparing ammonia provided by the embodiment in the application is shown in the figure;
[0019] Figure 2 A sectional view of the plasma reactor provided by the embodiment in the application is shown in the figure (A-A in the figure); Figure 1
[0020] Figure 3 The concentration change graph of ammonia in the second collection tank when the temperature of the sodium sulfate solution (0.01 mol / L, pH=4.0) in the liquid storage tank and the plasma reactor is controlled to be 5°C is shown in the figure;
[0021] Figure 4 The concentration change graph of ammonia in the second collection tank when the temperature of the sodium sulfate solution (0.01 mol / L, pH=4.0) in the liquid storage tank and the plasma reactor is controlled to be 25°C is shown in the figure;
[0022] Figure 5 The concentration change graph of ammonia in the second collection tank when the temperature of the sodium sulfate solution (0.01 mol / L, pH=4.0) in the liquid storage tank and the plasma reactor is controlled to be room temperature is shown in the figure;
[0023] Figure 6 The control of the temperature of the sodium sulfate solution (0.01 mol / L, pH = 4.0) in the storage tank and the plasma reactor in the examples of the present application is kept at different temperatures, and the comparison chart of the concentration of ammonia in the second collection tank is measured.
[0024] The figure mark: 1, the storage part; 2, the plasma electrochemistry part; 21, the plasma reactor; 22, the plasma generating assembly; 3, the temperature control part; 31, the first water bath temperature controller; 32, the second water bath temperature controller; 4, the product collection part; 41, the first collection tank; 42, the second collection tank; 5, the ion exchange membrane; 6, the first chamber; 7, the second chamber; 8, the plasma electrode; 9, the measurement resistance; 10, the plasma power supply; 11, the current-limiting resistance; 12, the counter electrode. DETAILED DESCRIPTION
[0025] The inventor of the present application based on the existing problems of the decomposition, isomerization or side reaction of the target substance in the synthesis of temperature-sensitive substances, after extensive and in-depth research and a large number of experiments, creatively found that: introducing an ion exchange membrane with ion selectivity in the plasma discharge system and cooperating with the control of the reaction solution and the reaction temperature can effectively reduce the loss of active species and the decomposition, isomerization and side reaction of temperature-sensitive substances, thereby realizing the effect of efficient preparation of temperature-sensitive substances. Based on this, the technical scheme of the present application is obtained.
[0026] In the present application, the plasma discharge system specifically comprises: a gas source, a storage part, a plasma electrochemistry part, a temperature control part and a product collection part. Among them, the plasma electrochemistry part comprises a plasma reactor and a plasma generating assembly, the plasma reactor is structured to form a reaction chamber for carrying out plasma electrochemistry reaction, and the gas source and the reaction chamber are communicated through a capillary tube; an ion exchange membrane is arranged in the reaction chamber to separate the reaction chamber into a first chamber and a second chamber, and the first chamber and the storage part are communicated; the plasma generating assembly comprises a plasma electrode, a plasma power supply and a counter electrode which are electrically connected in sequence, the plasma electrode is inserted into the first chamber, and the counter electrode is inserted into the second chamber. The temperature control part comprises a first water bath temperature controller and a second water bath temperature controller, the first water bath temperature controller is used to regulate the temperature of the plasma reaction solution in the storage part, and the second water bath temperature controller is used to regulate the reaction temperature of the plasma electrochemistry reaction in the plasma reactor.
[0027] In the present application, the gas source is used to provide reaction gas for the synthesis of temperature-sensitive substances, which is a kind of instrument commonly used in the prior art, and the person skilled in the art can make adaptive selection according to the actual needs, and the present application does not particularly limit it.
[0028] In the present application, the liquid storage part is used to hold the plasma reaction solution, which specifically includes a liquid storage tank, and the number of liquid storage tanks is determined according to the plasma reaction solution required in the synthesis of temperature-sensitive substances, and the number can be 1, 2, 3, 4, 5 or other integer values.
[0029] In some specific embodiments, a peristaltic pump is preferably arranged between the liquid storage tank and the first chamber. At this time, the arrangement of the peristaltic pump can realize the control of the flow rate of the plasma reaction solution entering the plasma reactor, so as to further improve the synthesis efficiency of the temperature-sensitive substances.
[0030] In some specific embodiments, a peristaltic pump is preferably arranged between the gas source and the reaction chamber. At this time, the arrangement of the peristaltic pump can realize the control of the flow rate of the gas entering the plasma reactor, so as to generate micro-bubbles in the plasma reaction solution, reduce the loss of the plasma, and ultimately improve the synthesis efficiency of the temperature-sensitive substances.
[0031] In some specific embodiments, a measuring resistor is preferably arranged between the plasma electrode and the plasma power source, and a current-limiting resistor is preferably arranged between the plasma power source and the counter electrode. At this time, the voltage applied to the plasma electrode and the counter electrode can be more accurately controlled, and the controllability of the synthesis process of the temperature-sensitive substances is improved.
[0032] In the present application, the plasma electrode, the measuring resistor, the plasma power source, the current-limiting resistor and the counter electrode are conventional technical means used in plasma electrochemistry technology. Those skilled in the art can make adaptive selection according to actual needs, and the present application does not particularly limit them.
[0033] In the present application, the first water bath temperature controller and the second water bath temperature controller are a kind of instruments commonly used in the prior art to realize temperature control. Those skilled in the art can make adaptive selection according to needs, and the present application does not particularly limit them.
[0034] In the present application, the product collection part is used to collect the reaction products generated by the plasma electrochemistry part, which specifically includes a collection tank, and the number of collection tanks is determined according to the temperature-sensitive substances to be obtained, and the number can be 1, 2, 3, 4, 5 or other integer values.
[0035] Based on the potential of the above-mentioned plasma discharge system in realizing low active species loss and high synthesis efficiency of temperature-sensitive substances, the present application also provides the application of the plasma discharge system in the preparation of temperature-sensitive substances.
[0036] In the present application, specific examples of the temperature-sensitive substance that can be synthesized by the plasma discharge system include, but are not limited to, hydrogen peroxide and / or ammonia.
[0037] The present application also provides a synthesis method for synthesizing a temperature-sensitive substance by using the above-mentioned plasma discharge system. The synthesis method specifically comprises: preparing a plasma reaction solution and loading it into the liquid storage part, adjusting the temperature of the plasma reaction solution by the first water bath temperature controller; taking the plasma reaction solution into the plasma reactor, opening the gas source to introduce the reaction gas, and opening the plasma power supply to apply voltage to the plasma electrode and the counter electrode to generate discharge plasma, and controlling the reaction temperature of the plasma electrochemical reaction in the plasma reactor by the first water bath temperature controller; and collecting the temperature-sensitive substance by the product collection part.
[0038] In the present application, when the temperature-sensitive substance to be synthesized is ammonia, the plasma reaction solution is specifically a sodium sulfate solution, and the concentration of the sodium sulfate solution is preferably 0.001 mol / L to 0.05 mol / L, specifically 0.001 mol / L, 0.005 mol / L, 0.01 mol / L, 0.02 mol / L, 0.04 mol / L, 0.05 mol / L or any value therebetween; the pH value of the sodium sulfate solution is preferably 3.5 to 4.5, specifically 3.5, 3.8, 3.9, 4, 4.1, 4.3, 4.5 or any value therebetween; and the reaction gas is specifically nitrogen.
[0039] In the present application, when the temperature-sensitive substance to be synthesized is ammonia, the synthesis conditions specifically include: the flow rate of the plasma reaction solution into the plasma reactor is preferably 0.01 mL / min to 4 mL / min, specifically 0.01 mL / min, 0.05 mL / min, 0.08 mL / min, 0.1 mL / min, 0.5 mL / min, 1 mL / min, 1.5 mL / min, 2 mL / min, 3 mL / min, 4 mL / min, or any value therebetween; the flow rate of the reaction gas is preferably 25 seem to 75 seem, specifically 25 seem, 28 seem, 30 seem, 35 seem, 40 seem, 45 seem, 50 seem, 60 seem, 70 seem, 75 seem, or any value therebetween; the discharge current of the plasma power supply is preferably 20 mA to 30 mA, specifically 20 mA, 21 mA, 23 mA, 25 mA, 28 mA, 29 mA, 30 mA, or any value therebetween; and the reaction temperature is preferably 0°C to 10°C, specifically 0°C, 3°C, 4°C, 5°C, 8°C, 10°C, or any value therebetween. At this time, compared with the reaction temperature of 25°C commonly used in the synthesis of ammonia by low-temperature plasma method, the ultra-low temperature of 0°C to 10°C can unexpectedly significantly improve the concentration of the synthesized ammonia under the condition of low flow rate of the plasma reaction solution.
[0040] The embodiments of the present application are described in detail below, and the examples thereof are intended to explain the present application and cannot be understood as limiting the present application. The specific techniques or conditions not mentioned in the embodiments are performed according to the techniques or conditions described in the literature in the art or according to the product instructions. The reagents or instruments not mentioned by the manufacturer are all conventional products that can be obtained by purchase.
[0041] Embodiment
[0042] The present embodiment is used to illustrate a plasma discharge system for preparing ammonia and a synthesis method of ammonia. Figure 1 The structural schematic diagram of the plasma discharge device provided for the present embodiment is shown in Figure 1 The plasma discharge system includes a gas source (not shown in the figure), a liquid storage part 1, a plasma electrochemical part 2, a temperature control part 3, and a product collection part 4. The liquid storage part 1 includes at least one liquid storage tank, which contains sodium sulfate solution (0.01 mol / L, pH=4.0) as the plasma reaction solution. The plasma electrochemical part 2 includes a plasma reactor 21 and a plasma generation assembly 22.
[0043] Figure 2 The cross-sectional view of the plasma reactor 21 is shown in Figure 1 and2 The plasma reactor 21 is structured to form a reaction chamber for conducting plasma electrochemical reaction, and a detachable ion exchange membrane 5 (Suzhou Shengernuo Technology Co., Ltd., proton exchange membrane N117) is arranged in the reaction chamber to divide the reaction chamber into a first chamber 6 and a second chamber 7. A water inlet (not shown in the figure) is formed in the side wall of the plasma reactor 21 and communicates with the first chamber 6. A liquid storage tank and the water inlet in the side wall of the plasma reactor 21 are connected by a pipeline, and a peristaltic pump is arranged between the liquid storage tank and the plasma reactor 21 to drive the reaction solution in the liquid storage tank into the first chamber 6. A gas source is connected to the first chamber 6 and the second chamber 7 of the plasma reactor 21 by a stainless steel capillary, and a peristaltic pump is arranged between the gas source and the plasma reactor 21 to drive nitrogen gas into the first chamber 6 and the second chamber 7 through the stainless steel capillary to generate micro-bubbles.
[0044] Referring to Figure 1 and 2 The plasma generating assembly 22 specifically includes a plasma electrode 8, a measurement resistance 9, a plasma power supply 10, a current-limiting resistance 11 and a counter electrode 12 connected in sequence. The plasma electrode 8 includes a tungsten wire and a quartz tube, the tungsten wire is completely covered by the quartz tube and the end of the tungsten wire is recessed into the cavity of the quartz tube by a certain distance, the plasma electrode 8 is inserted into the first chamber 6, and the end of the plasma electrode 8 is immersed in the plasma reaction solution. The counter electrode 12 includes a tungsten wire and a quartz tube, the tungsten wire is covered by the quartz tube and the end of the tungsten wire extends outward from the end of the quartz, the counter electrode 12 is inserted into the second chamber 7, and the end of the counter electrode 12 is immersed in the plasma reaction solution.
[0045] The temperature control part 3 includes a first water bath temperature controller 31 and a second water bath temperature controller 32; the first water bath temperature controller 31 is used to regulate the temperature of the plasma reaction solution in the liquid storage tank; the second water bath controller 32 is used to control the temperature of the plasma reaction solution in the plasma reactor 21.
[0046] The product collection part 4 includes a first collection tank 41 and a second collection tank 42. The first collection tank 41 is connected to the first chamber 6 by a pipeline to collect the product solution obtained by the reaction of the first chamber 6; the second collection tank 42 is connected to the second chamber 7 by a pipeline to collect the product solution obtained by the reaction of the second chamber 7.
[0047] Among them, the above-mentioned gas source, first water bath temperature controller 31, second water bath temperature controller 32, measurement resistance 9, plasma power supply 10 and current-limiting resistance 11 are a kind of instruments commonly used in existing plasma electrochemical technology, and those skilled in the art can make adaptive selection from existing technology according to actual needs, and do not particularly limit them.
[0048] The synthesis method of ammonia provided by the embodiment uses the plasma discharge system provided above as a reaction device, and the synthesis method specifically comprises the following steps:
[0049] Take sodium sulfate solution (0.01 mol / L, pH = 4.0) and pass it into the plasma reactor 21 at a flow rate of 2-16 mL / min to make the first chamber 6 and the second chamber 7 contain a certain amount of sodium sulfate solution (0.01 mol / L, pH = 4.0), and keep the solution flow rate unchanged in the subsequent process;
[0050] Pass nitrogen into the first chamber 6 at a flow rate of 50 sccm, and at this time, the sodium sulfate solution in the first chamber 6 generates tiny bubbles;
[0051] Turn on the first water bath temperature controller 31 and the second water bath temperature controller 32 to keep the temperature of the sodium sulfate solution (0.01 mol / L, pH = 4.0) in the liquid storage tank and the plasma reactor 21 constant;
[0052] Turn on the plasma power supply 10 and set the discharge current to 25 mA, apply voltage to the plasma electrode 8 and the counter electrode 12 to generate discharge plasma at the quartz tube opening, and synthesize ammonia. After 20 min of reaction, detect the concentration of ammonia in the second collection tank 42.
[0053] Figure 3 To control the temperature of the sodium sulfate solution (0.01 mol / L, pH = 4.0) in the liquid storage tank and the plasma reactor 21 to be 5°C, the concentration change graph of ammonia in the second collection tank 42 is measured. Figure 4 To control the temperature of the sodium sulfate solution (0.01 mol / L, pH = 4.0) in the liquid storage tank and the plasma reactor 21 to be 25°C, the concentration change graph of ammonia in the second collection tank 42 is measured. Figure 5 To control the temperature of the sodium sulfate solution (0.01 mol / L, pH = 4.0) in the liquid storage tank and the plasma reactor 21 to be room temperature (the room temperature during the reaction is 25°C, and the reaction solution and reaction temperature are not controlled during the reaction, that is, the synthesis of ammonia is carried out under non-constant temperature conditions), the concentration change graph of ammonia in the second collection tank 42 is measured. Figure 6 To control the temperature of the sodium sulfate solution (0.01 mol / L, pH = 4.0) in the liquid storage tank and the plasma reactor 21 to be room temperature (the room temperature during the reaction is 25°C, and the reaction solution and reaction temperature are not controlled during the reaction, that is, the synthesis of ammonia is carried out under non-constant temperature conditions), the concentration change graph of ammonia in the second collection tank 42 is measured.
[0054] From the above, it can be seen that the temperature of the sodium sulfate solution (0.01 mol / L, pH = 4.0) in the liquid storage tank and the plasma reactor 21 has a great influence on the synthesis of ammonia. Figures 3-6The results show that the ion exchange membrane provided by the embodiment of the application and the low-temperature control (5 DEG C) of the reaction solution are matched with each other, the decomposition, isomerization or side reaction of the target substance in the process of the plasma electrochemical reaction can be effectively reduced, and the ammonia concentration prepared at a low solution flow rate is significantly improved.
[0055] Although the embodiments of the present application have been shown and described above, it should be understood by those skilled in the art that the above embodiments are exemplary and cannot be understood as limiting the present application, and those skilled in the art can make changes, modifications, replacements and variations to the above embodiments within the scope of the present application without departing from the principles and purposes of the present application.
Claims
1. A plasma discharge system, characterized in that: The plasma discharge system comprises: A gas source, which is used to provide the gas required for the reaction; a liquid storage portion for containing a plasma reaction solution; The plasma electrochemical unit includes a plasma reactor and a plasma generating assembly. The plasma reactor is structured to form a reaction chamber for performing a plasma electrochemical reaction. The gas source and the reaction chamber are connected by a capillary. An ion exchange membrane is provided in the reaction chamber to separate the reaction chamber into a first chamber and a second chamber. The first chamber is connected to the liquid storage unit. The plasma generating assembly includes a plasma electrode, a plasma power supply, and a counter electrode electrically connected in sequence. The plasma electrode is inserted in the first chamber, and the counter electrode is inserted in the second chamber. a temperature control unit comprising a first water bath temperature controller and a second water bath temperature controller, wherein the first water bath temperature controller is used to control the temperature of the plasma reaction solution in the liquid storage unit, and the second water bath temperature controller is used to control the reaction temperature of the plasma electrochemical reaction in the plasma reactor; The product collecting section is used to collect the reaction products of the plasma electrochemical section.
2. The plasma discharge system according to claim 1, characterized in that: The liquid storage portion includes at least one liquid storage tank, and a peristaltic pump is provided between the liquid storage tank and the first chamber.
3. The plasma discharge system according to claim 1, wherein: A peristaltic pump is provided between the gas source and the reaction chamber.
4. The plasma discharge system according to claim 1, wherein: A measuring resistor is provided between the plasma electrode and the plasma power supply, and a current-limiting resistor is provided between the plasma power supply and the counter electrode.
5. Use of the plasma discharge system according to any one of claims 1 to 4 in the preparation of temperature-sensitive materials.
6. The use according to claim 5, characterized in that The temperature sensitive substance is hydrogen peroxide and / or ammonia.
7. A method for synthesizing a temperature-sensitive substance, characterized in that: The synthesis method adopts the plasma discharge system described in any one of claims 1 to 4 to synthesize the temperature sensitive material.
8. The method for synthesizing a temperature-sensitive substance according to claim 7, wherein: The synthesis method comprises: preparing a plasma reaction solution and placing it in the liquid storage portion, and adjusting the temperature of the plasma reaction solution by the first water bath temperature controller; The plasma reaction solution is introduced into a plasma reactor, the gas source is opened to introduce a reaction gas, the plasma power supply is turned on to apply voltage to the plasma electrode and the counter electrode to generate a discharge plasma, and the reaction temperature of the plasma electrochemical reaction in the plasma reactor is controlled by the first water bath temperature controller; The temperature-sensitive substance is collected and obtained through the product collection part.
9. The method for synthesizing a temperature-sensitive substance according to claim 8, wherein: When the temperature-sensitive substance is ammonia, the plasma reaction solution is a sodium sulfate solution, the concentration of the sodium sulfate solution is 0.001 mol / L to 0.05 mol / L, and the pH value is 3.5 to 4.5; and the reaction gas is nitrogen.
10. The method for synthesizing a temperature-sensitive substance according to claim 9, wherein: When the temperature-sensitive substance is ammonia, the flow rate of the plasma reaction solution into the plasma reactor is 0.01 mL / min to 4 mL / min, the flow rate of the reaction gas is 25 sccm to 75 sccm, the discharge current of the plasma power supply is 20 mA to 30 mA, and the reaction temperature is 0°C to 10°C.