A graphene micron sieve, its preparation method and application in gas sensor

Abstract

The present invention discloses a graphene micron sieve, a preparation method thereof, and its application in a gas sensor. The present invention utilizes the condensation phenomenon to liquefy the introduced water vapor on the surface of the substrate to form water droplets. After high-temperature rapid heating treatment, the area in contact with the water droplets can form an oxygen-rich structure that inhibits the nucleation / growth of graphene, while other areas remain unchanged. During the CVD process, the oxygen-rich structure inhibits the nucleation / growth of graphene, so that the final grown graphene film has a sieve-like structure. Using the method described in the present invention, a graphene micron sieve film with controllable sieve diameter can be directly grown on a non-metallic substrate, avoiding the adverse effects of conventional template etching processes on device performance, and laying the foundation for the in-situ construction of patterned graphene in the field of electronic devices. The present invention also relates to the application of the graphene micron sieve in a gas sensor, utilizing the graphene micron sieve's adsorption capacity for gas molecules to detect the presence and concentration of gas by monitoring changes in resistance or conductivity.

Description

Technical Field

[0001] The present invention relates to graphene-derived materials and chemical vapor deposition (CVD) preparation technology thereof, and in particular to a graphene micron sieve, a preparation method thereof and application in a gas sensor. Background Art

[0002] Graphene is a carbon atom sp 2 This ultra-thin, two-dimensional material, composed of a single atomic layer of hybrids tightly packed into a hexagonal honeycomb lattice, possesses unique crystal structure that imparts excellent optical, electrical, thermal, and mechanical properties. This unique structure holds great promise for applications in transparent conductive films, flexible electronics, electrochemical energy storage, graphene composites, biomedicine, and sensing. Graphene sieves, a specialized structure consisting of a single or few layers of graphene with a high density of perforations, possess a greater surface area and more boundaries than conventional graphene films. This provides a large number of active sites for adsorption of molecules, giving them enormous potential for application in gas sensors.

[0003] Currently, there are two main methods for preparing graphene sieves. One is the top-down approach, which typically involves transferring graphene grown by mechanical exfoliation or metal CVD onto a non-metallic substrate such as SiO2 / Si and etching it into the graphene sieve using a porous mask. The other is the bottom-up approach, which uses porous metal templates or self-assembled metal spheres as catalysts to grow the graphene sieve on a SiO2 / Si substrate. However, both methods suffer from the prominent problem of contamination and doping of the graphene sieve by residues left when removing conventional "hard" templates. Furthermore, the pretreatment steps are numerous and the production cycle is long. Therefore, developing a method for directly growing graphene sieves on non-metallic substrates such as SiO2 / Si is of great significance. Summary of the Invention

[0004] The present invention aims to provide a method for preparing a graphene microsieve. This method offers the advantages of simple operation, good controllability, and environmental friendliness. It effectively addresses the current challenges of patterned graphene preparation, such as the proneness to contamination and damage at the edges, complex processes, and high production costs. It also lays the foundation for research into the in-situ construction of electronic devices using graphene microsieves without transfer. Another object of the present invention is to provide the use of graphene microsieves as sensitive materials in gas sensors for detecting gas molecules, detecting the presence and concentration of gases by monitoring changes in resistance or conductivity.

[0005] Based on the above purpose, the technical solution adopted by the present invention is:

[0006] A method for preparing a graphene micron sieve comprises the following steps:

[0007] 1) Place the cleaned non-metallic substrate in a quartz tube at room temperature, and fill it with heated carrier gas and water vapor in a non-oxidizing atmosphere to form water droplets on the non-metallic substrate;

[0008] 2) Heating the substrate pretreated in step 1) from room temperature to a growth temperature of 900-1200°C for at least 1 minute to form a reaction system;

[0009] 3) Maintaining the temperature in step 2) unchanged, turning off the carrier gas and water vapor, introducing a carbon source and hydrogen into the reaction system in step 2), and growing a graphene micromesh on the substrate treated in step 2) for a growth time of 20 to 180 minutes;

[0010] 4) After the reaction is completed, the carbon source and hydrogen are turned off, and the mixture is cooled to room temperature under the protection of a non-oxidizing atmosphere to obtain a graphene micron sieve.

[0011] Furthermore, in step 1), the non-metallic substrate used includes but is not limited to a silicon wafer, a quartz wafer, boron nitride, alumina, a mica wafer or a silicon wafer with a silicon dioxide coating.

[0012] Furthermore, in step 1) and step 4), the non-oxidizing atmosphere is nitrogen or an inert gas or a mixture of the two.

[0013] Furthermore, in step 1), the method of heating the carrier gas and water vapor includes but is not limited to a water bath, an alcohol bath, an oil bath, a sand bath, electric heating and microwave heating.

[0014] Furthermore, in step 1), water vapor is brought into the reaction system through a carrier gas, and the carrier gas used is at least one of nitrogen and an inert gas, and the volume purity of both is greater than 99.9%. The amount of water vapor added is adjusted by changing the carrier gas flow rate, and the carrier gas flow rate is greater than 0 to 100 ml / min.

[0015] Furthermore, in step 1), the time required for condensation to form water droplets on the substrate is 1 to 20 minutes.

[0016] Furthermore, in step 2), the time required for the substrate to be heated from room temperature to the growth temperature is 1 to 5 minutes. After reaching the growth temperature, the substrate is maintained for 1 to 10 minutes.

[0017] Furthermore, in step 3), the carbon source used is a hydrocarbon: at least one of methane, ethane, acetylene, ethylene, methanol, ethanol, benzene, toluene, and cyclohexane, the volume ratio of the carbon source to hydrogen is (0.1-10):1, and the flow rate of hydrogen is 1-500 ml / min.

[0018] Furthermore, when the carbon source is liquid, it is placed in a Mengniu washing bottle and brought into the reaction system by bubbling a carrier gas. The molar ratio of the carbon source to the carrier gas is (0.1~10):1, and the carrier gas is nitrogen or an inert gas or a mixture of the two.

[0019] Furthermore, in step 4), the cooling rate is not less than 1°C / s. The cooling rate is generally 1°C / s to 10°C / s.

[0020] The graphene micron sieve prepared by the above preparation method mainly has graphene nucleation points formed in a circle. As the growth time increases, the nucleation points grow and the inside of the spliced ​​film becomes sieve-shaped, and the average pore size ranges from submicron to tens of microns.

[0021] The above-mentioned graphene micron sieve is used as a sensitive material of a gas sensor in detecting gas molecules.

[0022] Furthermore, the gas molecules are nitrogen dioxide, hydrogen, carbon monoxide, ammonia, hydrogen sulfide, volatile organic compounds or other harmful gases.

[0023] The process of detecting gas molecules is as follows:

[0024] a. Connect electrodes at both ends of the graphene micron sieve to obtain a sensor, ensuring good contact between the electrodes and the graphene micron sieve in order to apply voltage and measure the conductivity change of the graphene micron sieve;

[0025] b. Calibrate the sensor using a series of standard gases of known concentration to establish the relationship between conductivity change and gas concentration;

[0026] c. Place the graphene microsieve in a test gas environment, apply a known voltage, measure the conductivity change of the graphene microsieve, and record the conductivity change data of the graphene microsieve under different gas concentrations;

[0027] d. Analyze the collected data, determine the relationship between gas concentration and resistivity change, and calculate the concentration of the gas to be measured;

[0028] e. After each test, clean the graphene micron sieve using clean gas or a vacuum system to remove adsorbed gas molecules to ensure the reusability and accuracy of the sensor.

[0029] The design concept of the present invention is:

[0030] The condensation phenomenon is used to liquefy the introduced water vapor on the substrate surface to form water droplets. After high-temperature rapid heating treatment, the area in contact with the water droplets on the growth substrate can form an oxygen-rich structure, while other areas remain unchanged. During the CVD process, the oxygen-rich structure will inhibit the nucleation / growth of graphene, so that the final grown graphene film has a sieve-like structure.

[0031] The characteristics and beneficial effects of the present invention are:

[0032] 1. The present invention proposes a green method for preparing graphene micron sieve. The water droplet mask formed by liquefaction of water vapor does not need to be removed. It has the advantages of simple operation, good controllability and no pollution.

[0033] 2. The graphene micron sieve prepared by the present invention can realize the in-situ construction of gas sensor devices on non-metallic substrates, avoiding problems such as graphene material contamination and damage caused by the transfer process. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 Schematic diagram of the experimental setup for growing graphene micro-sieves on non-metallic materials using the CVD method. In the figure, 11 is the gas inlet; 12 is the quartz tube; 13 is the substrate; 14 is the gas outlet; 15 is the horizontal reactor; 16 is the conical flask; and 17 is the mass flowmeter.

[0035] Figure 2 This is a scanning electron microscope image of a circular distribution of graphene nucleation sites grown on a SiO2 / Si substrate. The scale bar is 1 micron. The experimental conditions are as in Example 1.

[0036] Figure 3 This is an optical microscope photograph of a graphene micrometer mesh grown on a SiO2 / Si substrate. The scale bar in the figure is 10 microns. The experimental conditions are shown in Example 2.

[0037] Figure 4 This is a scanning electron microscope image of a graphene micrometer mesh grown on a SiO2 / Si substrate. The scale bar in the figure is 1 micron. The experimental conditions are shown in Example 3.

[0038] Figure 5 This is a transmission electron micrograph of a graphene microsieve grown on a SiO2 / Si substrate and transferred to a microgrid. The scale in the figure is 2 microns. The experimental conditions are shown in Example 3.

[0039] Figure 6 This is an optical microscope photograph of a graphene micrometer mesh grown on a SiO2 / Si substrate. The scale bar in the figure is 10 microns. The experimental conditions are shown in Example 3.

[0040] Figure 7 This is a Raman spectrum of a graphene micro-sieve grown on a SiO2 / Si substrate, with a laser wavelength of 532 nm. The experimental conditions are shown in Example 3.

[0041] Figure 8 This is an atomic force microscope image of a graphene micromesh grown on a SiO2 / Si substrate. The scale bar in the image is 10 microns. The experimental conditions are shown in Example 3.

[0042] Figure 9 This is the C1s X-ray photoelectron spectrum of a graphene microsieve grown on a SiO2 / Si substrate. The experimental conditions are shown in Example 3.

[0043] Figure 10 This is an optical microscope photograph of a graphene micrometer mesh grown on a SiO2 / Si substrate. The scale bar in the figure is 10 microns. The experimental conditions are shown in Example 4.

[0044] Figure 11 This is the C1s X-ray photoelectron spectrum of a graphene microsieve grown on a SiO2 / Si substrate. The experimental conditions are shown in Example 4.

[0045] Figure 12 The resistance dynamics of the graphene micrometer sieve under different nitrogen dioxide gas concentrations. The experimental conditions are shown in Example 5.

[0046] Figure 13 ] is the fitting curve of the graphene micro-sieve resistance response rate as a function of nitrogen dioxide concentration. The experimental conditions are shown in Example 5. DETAILED DESCRIPTION

[0047] Below, the present invention is further described in detail by examples.

[0048] like Figure 1 As shown, a horizontal reactor 15 is equipped with a quartz tube 12. One end of the tube 12 serves as a gas inlet 11, the outer end of which is connected to a mass flowmeter 17. The other end of the tube 12 serves as a gas outlet 14. A substrate 13 is placed at the front end of the tube 12. Water vapor from an Erlenmeyer flask 16 is introduced into the reaction system via a carrier gas (e.g., an inert gas such as argon, nitrogen, or a mixture thereof). Gas inlet 11 is equipped with multiple mass flowmeters 17, which selectively control the flow of gases such as hydrogen, methane, ethylene, acetylene, or argon. A liquid carbon source (e.g., ethanol, methanol, benzene, toluene, or cyclohexane) is placed in a Monterey bottle and introduced via bubbling with argon or a mixture of argon and nitrogen.

[0049] Example 1

[0050] A method for preparing a graphene micron sieve, such as Figure 1As shown, the present invention uses a horizontal reactor to grow graphene micron-sieves. A quartz tube 12 is located within the horizontal reactor 15. A gas inlet 11 and a gas outlet 14 are provided at either end of the quartz tube 12. The gas inlet 11 is provided with an air inlet pipe, which is connected to several branch pipes. Each branch pipe is equipped with a mass flowmeter 17, and one branch pipe is connected to an Erlenmeyer flask 16. First, a substrate 13 (in this embodiment, a SiO2 / Si substrate, i.e., a substrate formed by depositing 290 nm thick silicon dioxide on a silicon wafer) is ultrasonically cleaned in deionized water, acetone, and isopropyl alcohol for 30 minutes each. After cleaning, the SiO2 / Si substrate 13 is placed at the front end of the quartz tube 12 (room temperature environment, tube diameter 20 mm, length 1200 mm); first, argon gas is passed through a branch pipe (not through the conical flask 16) to exhaust the air in the quartz tube 12, and then 20 ml / min of argon gas (as a carrier gas) is passed into the conical flask 16, and the deionized water vapor heated in the water bath in the conical flask 16 is introduced into the reaction system, and the liquefied water droplets on the SiO2 / Si substrate are kept for 5 minutes; it is quickly placed in a horizontal reaction furnace (furnace tube diameter 22 mm, constant temperature zone length 20 mm) 15) was heat treated at 1100°C in the central area for 5 minutes; after the heat treatment, the argon carrier gas containing water vapor was turned off, and methane and hydrogen were introduced (the gas flow rates were 15 ml / min for methane and 60 ml / min for hydrogen, with hydrogen alone as a reducing gas), and the growth of graphene microsieve began for 30 minutes. After the growth was completed, the methane and hydrogen were turned off, and argon was introduced. The mixture was rapidly cooled to room temperature at a rate of 10°C / s, and the resulting graphene nucleation points were distributed in a circular pattern.

[0051] Scanning electron microscopy Figure 2 ,Depend on Figure 2 It can be seen that the obtained graphene nucleation points are mainly formed around a circle, there are very few graphene islands inside the circle, and there are a large number of graphene islands outside the circle that are not spliced ​​into a film.

[0052] Example 2

[0053] A method for preparing a graphene micron sieve, such as Figure 1As shown, the present invention uses a horizontal reactor to grow graphene micron-sieves. A quartz tube 12 is located within the horizontal reactor 15. A gas inlet 11 and a gas outlet 14 are provided at either end of the quartz tube 12. The gas inlet 11 is provided with an air inlet pipe, which is connected to several branch pipes. Each branch pipe is equipped with a mass flowmeter 17, and one branch pipe is connected to an Erlenmeyer flask 16. First, a substrate 13 (in this embodiment, a SiO2 / Si substrate, i.e., a substrate formed by depositing 290 nm thick silicon dioxide on a silicon wafer) is ultrasonically cleaned in deionized water, acetone, and isopropyl alcohol for 30 minutes each. After cleaning, the SiO2 / Si substrate 13 is placed at the front end of the quartz tube 12 (room temperature environment, tube diameter 20 mm, length 1200 mm); first, argon gas is passed through a branch pipe (not through the conical flask 16) to exhaust the air in the quartz tube 12, and then 20 ml / min of argon gas (as a carrier gas) is passed into the conical flask 16, and the deionized water vapor heated in the water bath in the conical flask 16 is introduced into the reaction system, and the liquefied water droplets on the SiO2 / Si substrate are kept for 2 minutes; it is quickly placed in a horizontal reaction furnace (furnace tube diameter 22 mm, constant temperature zone length 20 mm) 15) was heat treated at 1100°C in the central area for 5 minutes; after the heat treatment, the argon carrier gas containing water vapor was turned off, and methane and hydrogen were introduced (the gas flow rates were 15 ml / min for methane and 60 ml / min for hydrogen, with hydrogen alone as a reducing gas), and the growth of graphene microsieve began for 60 minutes. After the growth was completed, the methane and hydrogen were turned off, argon was introduced, and the film was rapidly cooled to room temperature at a rate of 10°C / s to obtain a graphene film with a sieve-like structure.

[0054] Optical microscope photos are shown in Figure 3 ,Depend on Figure 3 It can be seen that the interior of the obtained graphene film is in the shape of a sieve hole, and the diameter of the sieve hole is about 0.6 microns.

[0055] Example 3

[0056] A method for preparing a graphene micron sieve, such as Figure 1As shown, the present invention uses a horizontal reactor to grow graphene micron-sieves. A quartz tube 12 is located within the horizontal reactor 15. A gas inlet 11 and a gas outlet 14 are provided at either end of the quartz tube 12. The gas inlet 11 is provided with an air inlet pipe, which is connected to several branch pipes. Each branch pipe is equipped with a mass flowmeter 17, and one branch pipe is connected to an Erlenmeyer flask 16. First, a substrate 13 (in this embodiment, a SiO2 / Si substrate, i.e., a substrate formed by depositing 290 nm thick silicon dioxide on a silicon wafer) is ultrasonically cleaned in deionized water, acetone, and isopropyl alcohol for 30 minutes each. After cleaning, the SiO2 / Si substrate was placed at the front end of the quartz tube 12 (room temperature environment, tube diameter 20 mm, length 1200 mm); first, argon was passed through a branch pipe (not through the conical flask 16) to exhaust the air in the quartz tube 12, and then 20 ml / min of argon (as a carrier gas) was passed into the conical flask 16. The deionized water vapor heated in the water bath in the conical flask 16 was introduced into the reaction system, and the liquefied water droplets on the SiO2 / Si substrate were kept for 5 minutes; it was quickly placed in a horizontal reaction furnace (furnace tube diameter 2 2 mm, constant temperature zone length 20 mm) was heat treated at 1100°C in the central area of ​​15 for 5 minutes; after the heat treatment, the argon carrier gas containing water vapor was turned off, and methane and hydrogen were introduced (the gas flow rates were 15 ml / min for methane and 60 ml / min for hydrogen, and hydrogen was used alone as a reducing gas), and the growth of graphene microsieve began. The growth time was 60 minutes. After the growth was completed, the methane and hydrogen were turned off, argon was introduced, and the film was rapidly cooled to room temperature at a rate of 10°C / s to obtain a graphene film with a sieve-like structure.

[0057] The graphene film was analyzed and characterized using optical microscopy, Raman spectroscopy, atomic force microscopy, and transmission electron microscopy. The results are detailed in Figures 4 to 9 ,Depend on Figure 4 It can be seen that the interior of the graphene film obtained by this method is sieve-shaped, and there is a clear boundary between the graphene inside the pores and the graphene outside the pores. Figure 5 It can be seen from the transmission electron microscope photos that the graphene film obtained by this method has a sieve-like shape after being transferred to the microgrid. Figure 6 As shown in the optical microscope photo, it can be seen that the mesh structure array inside the graphene film obtained by this method has a pore size of about 3 microns. Figure 7 As shown in Figure 2, the Raman spectrum of the graphene micro-sieve shows that the quality of graphene crystals inside and outside the pores is different, and there is a significant difference in thickness. Figure 8 As shown in the AFM image, the graphene micro-sieve film obtained by this method has a thickness of about 0.86 nm and an average layer thickness of about three layers. Figure 9 As shown in the C1s X-ray photoelectron spectrum, the graphene film obtained by this method has sp2 and sp 3 Hybridized carbon-carbon bonds and carbon-oxygen bonds.

[0058] Example 4

[0059] A method for preparing a graphene micron sieve, such as Figure 1 As shown, the present invention uses a horizontal reactor to grow graphene micron-sieves. A quartz tube 12 is located within the horizontal reactor 15. A gas inlet 11 and a gas outlet 14 are provided at either end of the quartz tube 12. The gas inlet 11 is provided with an air inlet pipe, which is connected to several branch pipes. Each branch pipe is equipped with a mass flowmeter 17, and one branch pipe is connected to an Erlenmeyer flask 16. First, a substrate 13 (in this embodiment, a SiO2 / Si substrate, i.e., a substrate formed by depositing 290 nm thick silicon dioxide on a silicon wafer) is ultrasonically cleaned in deionized water, acetone, and isopropyl alcohol for 30 minutes each. After cleaning, the SiO2 / Si substrate was placed at the front end of the quartz tube 12 (room temperature environment, tube diameter 20 mm, length 1200 mm); first, argon gas was passed through a branch pipe (not passing through the conical flask 16) to exhaust the air in the quartz tube 12, and then 20 ml / min of argon gas (as a carrier gas) was passed into the conical flask 16. Deionized water vapor heated in the water bath in the conical flask 16 was introduced into the reaction system, and the liquefied water droplets on the SiO2 / Si substrate were kept for 10 minutes; it was quickly placed in a horizontal reaction furnace (furnace tube straight The central area of ​​the film (diameter 22 mm, constant temperature zone length 20 mm) was heat treated (temperature 1100°C) for 5 minutes; after the heat treatment was completed, the argon carrier gas containing water vapor was turned off, and methane and hydrogen were introduced (gas flow rates of methane 15 ml / min and hydrogen 60 ml / min, respectively, with hydrogen alone as a reducing gas), and the growth of graphene microsieve began. The growth time was 60 minutes. After the growth was completed, the methane and hydrogen were turned off, argon was introduced, and the film was rapidly cooled to room temperature at a rate of 10°C / s to obtain a graphene film with a sieve-like structure.

[0060] Optical microscope observation Figure 10 ,Depend on Figure 10 It can be seen that the interior of the obtained graphene film is sieve-shaped, and the sieve pore diameter is about 17 microns. Figure 11 As shown in the C1s X-ray photoelectron spectrum, the graphene film obtained by this method has sp 2 and sp 3 Hybridized carbon-carbon bonds and a more prominent carbon-oxygen bond.

[0061] Example 5

[0062] Gold electrodes with a width of 200 microns and a thickness of 50 nanometers were deposited on both ends of the graphene microsieve obtained in Example 3 to ensure good electrical contact between the electrodes and the graphene microsieve. The sensor was placed in a sealed test chamber at room temperature to ensure stable environmental conditions. Argon gas was introduced at a rate of 1000 ml / min to remove air from the chamber for 5 minutes. Gas molecules (nitrogen dioxide in this example) were introduced in concentrations of 1, 2, 4, 8, 12, 16, and 20 ppm via a precise mass flow controller. The duration of each gas introduction was controlled to achieve a response time of 3 minutes and a recovery time of 20 minutes. Finally, a curve was established showing the relationship between the resistance change of the graphene microsieve and the gas concentration. Figure 12 and 13 The dynamic change of the gas sensor's resistance to nitrogen dioxide gas concentrations ranging from 1 to 20 ppm, as well as the fitting curve of the response rate versus nitrogen dioxide concentration, are shown. The sensor sensitivity is as high as 7.25% ppm. -1 .

[0063] The results of the examples demonstrate that the present invention utilizes condensation to liquefy introduced water vapor on the substrate surface, forming water droplets. After rapid high-temperature heating, the areas in contact with the water droplets form oxygen-rich structures that inhibit graphene nucleation and growth. The method described herein enables the direct growth of graphene microsieve films with controllable pore diameters on non-metallic substrates, avoiding the adverse effects of conventional template etching on device performance and laying the foundation for the in-situ fabrication of patterned graphene in electronic devices. The present invention also utilizes the graphene microsieve's ability to adsorb gas molecules, detecting the presence and concentration of gases by monitoring changes in resistance or conductivity.

Claims

1. A method for preparing a graphene micron sieve, characterized in that: The following steps are involved: 1) Place the cleaned non-metallic substrate in a quartz tube at room temperature, and fill it with heated carrier gas and water vapor in a non-oxidizing atmosphere to form water droplets on the non-metallic substrate; 2) heating the substrate pretreated in step 1) from room temperature to a growth temperature of 900-1200° C. for at least 1 minute to form a reaction system; 3) Maintaining the temperature in step 2) unchanged, turning off the carrier gas and water vapor, introducing a carbon source and hydrogen into the reaction system in step 2), and growing a graphene micromesh on the substrate treated in step 2) for a growth time of 20 to 180 minutes; 4) After the reaction is completed, the carbon source and hydrogen are turned off, and the mixture is cooled to room temperature under the protection of a non-oxidizing atmosphere to obtain a graphene micron sieve.

2. The method for preparing the graphene micron sieve according to claim 1, wherein In step 1), the non-metallic substrate used is a silicon wafer, a quartz wafer, boron nitride, alumina, a mica wafer or a silicon wafer with a silicon dioxide coating.

3. The method for preparing the graphene micron sieve according to claim 1, wherein In step 1), the carrier gas and water vapor are heated in a water bath, an alcohol bath, an oil bath, a sand bath, electric heating, or microwave heating; the carrier gas is at least one of nitrogen and an inert gas, and the amount of water vapor added is adjusted by changing the carrier gas flow rate. The carrier gas flow rate is 20 ml / min to 100 ml / min, and the time required for condensation to form water droplets on the substrate is 1 to 20 minutes.

4. The method for preparing the graphene micron sieve according to claim 1, wherein In step 2), the time required to heat the substrate from room temperature to the growth temperature is 1 to 5 minutes.

5. The method for preparing the graphene micron sieve according to claim 1, wherein: In step 3), the carbon source used is at least one of methane, ethane, acetylene, ethylene, methanol, ethanol, benzene, toluene and cyclohexane, the volume ratio of the carbon source to hydrogen is (0.1-10):1, and the flow rate of hydrogen is 1-500 ml / min; when the carbon source is a liquid, it is placed in a container bottle and introduced into the reaction system by bubbling with a carrier gas, and the molar ratio of the carbon source to the carrier gas is (0.1-10):

1.

6. The method for preparing the graphene micron sieve according to claim 1, wherein: In step 1) and step 4), the non-oxidizing atmosphere is nitrogen or an inert gas or a mixture of the two; in step 4), the cooling rate is not less than 1°C / s.

7. The graphene micron sieve prepared by the preparation method according to any one of claims 1 to 6.

8. Use of the graphene microsieve according to claim 7 as a sensitive material of a gas sensor in detecting gas molecules.

9. The use according to claim 8, characterized in that The gas molecules are nitrogen dioxide, hydrogen, carbon monoxide, ammonia, hydrogen sulfide or volatile organic compounds.

10. The use according to claim 8, characterized in that The detection process is as follows: a. Connect electrodes at both ends of the graphene micron sieve to obtain a sensor; b. Calibrate the sensor using a series of standard gases of known concentration to establish the relationship between conductivity change and gas concentration; c. Place the graphene microsieve in a test gas environment, apply a known voltage, measure the conductivity change of the graphene microsieve, and record the conductivity change data of the graphene microsieve under different gas concentrations; d. Analyze the collected data, determine the relationship between gas concentration and conductivity change, and calculate the concentration of the gas to be measured; e. After each test, clean the graphene micron sieve using clean gas or a vacuum system to remove adsorbed gas molecules.

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