Single-core dual-module graphene-based gas sensor and method of manufacturing the same

Abstract

The application provides a single-core double-module graphene-based gas sensor and a preparation method thereof, and relates to the technical field of gas sensors.The preparation method comprises the following steps: dividing the main surface of a wooden substrate into a first surface and a second surface which are arranged adjacently; coating a first metal salt solution on the first surface and a second metal salt solution on the second surface; irradiating the first surface and the second surface by using a laser beam, so that lignin and cellulose in the wooden substrate are cracked and restructured to form graphene, the first metal salt immersed in the first surface is decomposed to form first metal oxide nanoparticles, and the second metal salt immersed in the second surface is decomposed to form second metal oxide nanoparticles, so that a first sensitive layer and a second sensitive layer are obtained; and coating a conductive material on the wooden substrate and on the two sides of the first sensitive layer and the second sensitive layer respectively, so that a connecting electrode which is in contact with the first sensitive layer and the second sensitive layer respectively is formed, and a single-core double-module graphene-based gas sensor is obtained.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of gas sensors, and more particularly to a single-core dual-module graphene-based gas sensor and a preparation method thereof. BACKGROUND

[0002] With the aggravation of industrial emissions and urban air pollution, there are often multiple toxic gases (such as nitrogen dioxide (NO2) and hydrogen sulfide (H2S)) coexisting in the environment. The traditional single-module sensor has single selectivity, and multiple independent sensors need to be arranged when detecting mixed gas, resulting in bulky equipment, high cost, and cross interference of multi-sensor signals. Developing integrated dual-module gas sensors to realize the simultaneous identification of multiple target gases by a single device has become an urgent need to build an efficient and compact gas detection system. The mainstream gas sensors at present rely on metal oxide semiconductors (such as tin oxide (SnO2) and zinc oxide (ZnO)), and their core defects are reflected in three aspects: first, they need to work at a high temperature of 200℃ or above, resulting in high energy consumption and explosion hazards; second, they have poor selectivity, and it is difficult to distinguish gases with similar chemical properties (such as NO2 and sulfur dioxide (SO2)); third, the interface bonding force between the sensitive layer and the ceramic or silicon substrate is weak, and it is easy to peel off and fail after long-term use.

[0003] To address these problems, graphene materials stand out due to their unique two-dimensional structure, room-temperature sensitivity, and surface modifiability. Laser-induced graphene (LIG) technology further provides a solution for developing high-performance, low-power sensors by forming a three-dimensional porous graphene structure on a flexible substrate through laser direct writing process. Although research on graphene-based sensors has made progress, research on dual-module or multi-module devices is still in its early stages. Currently, graphene array sensors have low response to nitrogen dioxide and hydrogen sulfide, with detection concentrations generally in the ppm level, which is difficult to meet the needs of practical applications. In addition, the sensitive materials rely on noble metal (such as palladium and platinum) modification, which is costly, and the substrate is made of non-degradable polyimide or silica gel, which poses a risk of environmental pollution. More critically, the sensitive units of existing designs lack spatial resolution, and when detecting mixed gas, they are prone to signal superposition, making it impossible to accurately distinguish gases such as H2S and NO2. SUMMARY

[0004] To address at least one of the technical problems in the prior art, embodiments of the present application provide a single-core dual-module graphene-based gas sensor and a preparation method thereof. The prepared single-core dual-module graphene-based gas sensor can detect hydrogen sulfide and nitrogen dioxide in a mixed gas of hydrogen sulfide and nitrogen dioxide with high sensitivity and high selectivity.

[0005] The application provides a preparation method of a single-core double-module graphene-based gas sensor, which comprises the following steps: dividing a main surface of a wooden substrate into a first surface and a second surface arranged adjacently; coating a first metal salt solution on the first surface and a second metal salt solution on the second surface; irradiating the first surface and the second surface with a laser beam under the condition of no protective gas at room temperature, so that lignin and cellulose in the wooden substrate are cracked and restructured to form graphene, and the first metal salt immersed in the first surface is decomposed to form first metal oxide nanoparticles, and the second metal salt immersed in the second surface is decomposed to form second metal oxide nanoparticles, the first metal oxide nanoparticles and the second metal oxide nanoparticles are dispersed on the surface of each layer of graphene of the first surface and the second surface respectively, and a first sensitive layer and a second sensitive layer are obtained respectively, the first sensitive layer is suitable for detecting nitrogen dioxide gas, and the second sensitive layer is suitable for detecting hydrogen sulfide gas; a conductive material is coated on the wooden substrate and on both sides of the first sensitive layer and the second sensitive layer respectively, a connecting electrode in contact with the first sensitive layer and the second sensitive layer is formed respectively, and a single-core double-module graphene-based gas sensor is obtained.

[0006] Optionally, the wooden substrate is any one of linden wood, oak wood and pine wood.

[0007] Optionally, the wavelength of the laser beam is 256nm-760nm, and the power of the laser beam is 0.5W-10W.

[0008] Optionally, the irradiation of the first surface and the second surface with the laser beam under the condition of no protective gas at room temperature comprises the following steps: setting a target area on the first surface and the second surface respectively, and irradiating the target area with the laser beam under the condition of no protective gas at room temperature; wherein the target area is any one of a point, a line, a circle and a polygon.

[0009] Optionally, the first metal salt is any one of water-soluble salts of cobalt, iron and nickel; and the second metal salt is a water-soluble silver salt and a water-soluble transition metal salt.

[0010] Optionally, the first metal salt is any one of cobalt nitrate, iron nitrate and nickel nitrate; and the first metal oxide is any one of cobalt oxide, iron oxide and nickel oxide.

[0011] Optionally, the water-soluble silver salt comprises silver nitrate; the water-soluble transition metal salt is any one of cobalt nitrate, iron nitrate and nickel nitrate; and the second metal oxide nanoparticles are bimetallic oxide nanoparticles, the bimetallic oxide nanoparticles comprise silver oxide nanoparticles and transition metal oxide nanoparticles, the silver oxide comprises silver oxide, and the transition metal oxide is any one of cobalt oxide, iron oxide and nickel oxide.

[0012] Optionally, the size of the first metal oxide nanoparticles and the second metal oxide nanoparticles is 50nm-1000nm.

[0013] According to the embodiment of the application, the single-core double-module graphene-based gas sensor is prepared by the preparation method of the single-core double-module graphene-based gas sensor, and the single-core double-module graphene-based gas sensor comprises: a wooden substrate, a main surface of the wooden substrate is formed with a split line; a first sensitive layer and a second sensitive layer, which are formed on the main surface of the wooden substrate and are located on two sides of the split line, wherein the first sensitive layer is a composite material of graphene and first metal oxide nanoparticles, and the second sensitive layer is a composite material of graphene and second metal oxide nanoparticles; and two groups of connecting electrodes, which are arranged on the wooden substrate and are located on two sides of the first sensitive layer and the second sensitive layer respectively and are respectively overlapped with the first sensitive layer and the second sensitive layer.

[0014] Optionally, the detection range of the single-core double-module graphene-based gas sensor for the respective concentrations of hydrogen sulfide and nitrogen dioxide in a mixed gas of hydrogen sulfide and nitrogen dioxide is 50ppb-500ppb.

[0015] According to the single-core double-module graphene-based gas sensor and the preparation method thereof, the main surface of the wooden substrate is divided into the first surface and the second surface which are arranged adjacently, the first metal salt solution is coated on the first surface, and the second metal salt solution is coated on the second surface, the first surface and the second surface are irradiated by a laser beam at room temperature without a protective gas, so that the lignin and cellulose in the wooden substrate are cracked and restructured to form graphene, the first metal salt immersed in the first surface is decomposed to form first metal oxide nanoparticles, and the second metal salt immersed in the second surface is decomposed to form second metal oxide nanoparticles, the first metal oxide nanoparticles and the second metal oxide nanoparticles are respectively dispersed on the surface of each layer of graphene of the first surface and the second surface, the first sensitive layer and the second sensitive layer with high activity and high selectivity are obtained, the first sensitive layer is suitable for detecting nitrogen dioxide gas, the second sensitive layer is suitable for detecting hydrogen sulfide gas, the conductive material is coated on the wooden substrate and on two sides of the first sensitive layer and the second sensitive layer, the connecting electrodes which are in contact with the first sensitive layer and the second sensitive layer are formed, and the single-core double-module graphene-based gas sensor is obtained. The preparation process is simple and environmentally friendly, and the single-core double-module graphene-based gas sensor prepared by the preparation process can detect hydrogen sulfide and nitrogen dioxide in a mixed gas of hydrogen sulfide and nitrogen dioxide with high sensitivity and high selectivity. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 is a flowchart of the preparation method of the single-core double-module graphene-based gas sensor of the application;

[0017] Figure 2 This is an electron microscope image of the first metal oxide nanoparticles of the present invention dispersed on the surface of each layer of graphene on the first surface.

[0018] Figure 3 This is a top view of the single-core dual-module graphene-based gas sensor structure of the present invention;

[0019] Figure 4 This is a real-time response characteristic curve of the single-core dual-module graphene-based gas sensor in Embodiment 1 of the present invention to a mixed gas of 100ppb NO2 and 50ppb H2S.

[0020] Figure 5 This is a real-time response characteristic curve of the single-core dual-module graphene-based gas sensor in Embodiment 2 of the present invention to a mixed gas of 50ppb NO2 and 100ppb H2S.

[0021] Figure 6 This is a graph showing the real-time response characteristics of the single-core dual-module graphene-based gas sensor in Embodiment 3 of the present invention to 200ppb NO2 and 200ppb H2S.

[0022] Figure 7 These are selective histograms of the first and second sensitive layers of the single-core dual-module graphene-based gas sensor in Embodiment 3 of the present invention, wherein a) is a selective histogram of the second sensitive layer and b) is a selective histogram of the first sensitive layer;

[0023] Figure 8 This is a graph showing the real-time response characteristics of the single-core dual-module graphene-based gas sensor in Embodiment 4 of the present invention to 300ppb NO2 and 200ppb H2S.

[0024] Figure 9 This is a graph showing the real-time response characteristics of the single-core dual-module graphene-based gas sensor in Embodiment 5 of the present invention to 400ppb NO2 and 100ppb H2S.

[0025] Figure 10 This is a graph showing the real-time response characteristics of the single-core dual-module graphene-based gas sensor in Embodiment 6 of the present invention to 500ppb NO2 and 500ppb H2S.

[0026] Figure 11 This is a response-concentration line graph of the single-core dual-module graphene-based gas sensor in Embodiment 7 of the present invention to different concentrations of NO2 and H2S mixed gas combinations, wherein a) is the response-concentration line graph of the second sensitive layer to different concentrations of NO2 and H2S mixed gas combinations, and b) is the response-concentration line graph of the first sensitive layer to different concentrations of NO2 and H2S mixed gas combinations.

[0027] Figure 12 Figure 8 is a scanning electron microscope image of silver oxide and nickel oxide nanoparticle modified graphene in Example 8 of the present invention when the laser beam power is different;

[0028] Figure 13 Figure 9 is a scanning electron microscope image of iron oxide nanoparticle modified graphene in Example 9 of the present invention when the concentration of ferric nitrate solution is different;

[0029] Figure 14 Figure 10 is a real-time response characteristic curve of a single-core dual-module graphene-based gas sensor to 200 ppb of NO2 and 200 ppb of H2S in Example 10 of the present invention, wherein (a) is a real-time response characteristic curve of the first sensitive layer to a mixed gas of 200 ppb of NO2 and 200 ppb of H2S, and (b) is a real-time response characteristic curve of the second sensitive layer to a mixed gas of 200 ppb of NO2 and 200 ppb of H2S;

[0030] Figure 15 Figure 11 is a real-time response characteristic curve of a single-core dual-module graphene-based gas sensor to 200 ppb of NO2 and 200 ppb of H2S in Example 11 of the present invention, wherein (a) is a real-time response characteristic curve of the first sensitive layer to a mixed gas of 200 ppb of NO2 and 200 ppb of H2S, and (b) is a real-time response characteristic curve of the second sensitive layer to a mixed gas of 200 ppb of NO2 and 200 ppb of H2S;

[0031] Figure 16 Figure 12 is a real-time response characteristic curve of a single-core dual-module graphene-based gas sensor to 200 ppb of NO2 and 200 ppb of H2S in Example 12 of the present invention, wherein (a) is a real-time response characteristic curve of the first sensitive layer to a mixed gas of 200 ppb of NO2 and 200 ppb of H2S, and (b) is a real-time response characteristic curve of the second sensitive layer to a mixed gas of 200 ppb of NO2 and 200 ppb of H2S;

[0032] Figure 17 Figure 13 is a scanning electron microscope image of iron oxide nanoparticle modified graphene and silver oxide and cobalt oxide nanoparticle modified graphene in Example 13 of the present invention;

[0033] Figure 18 Figure 13 is a real-time response characteristic curve of a single-core dual-module graphene-based gas sensor to 200 ppb of NO2 and 200 ppb of H2S in Example 13 of the present invention, wherein (a) is a real-time response characteristic curve of the first sensitive layer to a mixed gas of 200 ppb of NO2 and 200 ppb of H2S, and (b) is a real-time response characteristic curve of the second sensitive layer to a mixed gas of 200 ppb of NO2 and 200 ppb of H2S.

[0034] In the drawings, the meaning of reference numerals is as follows:

[0035] 1. a split line;

[0036] 2. a wooden base;

[0037] 3. a first sensing layer;

[0038] 4. a second sensing layer;

[0039] 5. a connecting electrode. DETAILED DESCRIPTION

[0040] Hereinafter, embodiments of the present application will be described with reference to the accompanying drawings. It should be understood, however, that the description which follows is merely illustrative and is not intended to limit the scope of the present application. In the following detailed description of embodiments of the present application, numerous specific details are set forth in order to provide a thorough understanding of the present application. However, it will be apparent to one skilled in the art that one or more embodiments of the present application can be practiced without these specific details. In other instances, well-known structures and functions have not been described in detail in order to avoid obscuring aspects of the present application.

[0041] The terms used herein are merely used to describe specific embodiments and are not intended to limit the present application. The terms "include" and "have" and the like used herein indicate the presence of the described features, steps, operations, and / or components but do not preclude the presence or addition of one or more other features, steps, operations, or components.

[0042] All terms used herein, including technical and scientific terms, have the same meanings as those generally understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein should be interpreted as having meanings consistent with the context of the present description, and should not be interpreted in an idealized or overly formal way.

[0043] In the case of using expressions similar to "at least one of A, B, and C, etc.", it should generally be interpreted to include any of them alone, any combination of two or more of them, and the like in a manner that makes sense in the context of the present description (for example, "a system having at least one of A, B, and C" should include but not be limited to a system having A alone, a system having B alone, a system having C alone, a system having both A and B, a system having both A and C, a system having both B and C, and / or a system having A, B, and C together, etc.). In the case of using expressions similar to "at least one of A, B, or C, etc.", it should generally be interpreted to include any of them alone, any combination of two or more of them, and the like in a manner that makes sense in the context of the present description (for example, "a system having at least one of A, B, or C" should include but not be limited to a system having A alone, a system having B alone, a system having C alone, a system having both A and B, a system having both A and C, a system having both B and C, and / or a system having A, B, and C together, etc.).

[0044] With the increasing demand for gas detection in complex environments, the traditional single module gas sensor that can only detect a specific gas has been difficult to meet the requirements. With the development of sensor technology, especially the progress of nanomaterials and integrated circuit technology, gas sensors gradually develop towards integration and intelligence. As a product of multi-gas detection technology, in recent years, through combining different gas sensor modules in the same chip or the same system, the dual module sensor can detect multiple gases at the same time, improving the efficiency and accuracy of gas detection, especially in the monitoring of toxic gases, malodorous gases and common air pollutants, which has important application value. However, there are still some problems. If you want to integrate multiple types of gas sensors on the same chip, the process is very complex, because the modification steps of each type of metal or metal oxide nanoparticles are complicated and different, and the sensitivity and selectivity of multiple types of gas sensors integrated on the same chip are poor.

[0045] In order to solve the problems of complex preparation process and poor sensitivity and selectivity of the prepared gas sensor to low concentration (ppb level) nitrogen dioxide and hydrogen sulfide mixed gas, according to the inventive concept of one aspect of the present application, the main surface of the wood substrate is divided into first and second surfaces arranged adjacent to each other, the first metal salt solution is coated on the first surface, and the second metal salt solution is coated on the second surface. The first surface and the second surface are irradiated by a laser beam at room temperature without a protective gas to make lignin and cellulose in the wood substrate crack and reconfigure to form graphene, and the first metal salt immersed in the first surface decomposes to form first metal oxide nanoparticles, and the second metal salt immersed in the second surface decomposes to form second metal oxide nanoparticles. The first metal oxide nanoparticles and the second metal oxide nanoparticles are dispersed on the surface of each layer of graphene on the first surface and the second surface, respectively, to obtain a first sensitive layer and a second sensitive layer with high activity and high selectivity, respectively. The first sensitive layer is suitable for detecting nitrogen dioxide gas, and the second sensitive layer is suitable for detecting hydrogen sulfide gas. A conductive material is coated on the wood substrate and on both sides of the first sensitive layer and the second sensitive layer to form a connecting electrode in contact with the first sensitive layer and the second sensitive layer, respectively, to obtain a single-core dual module graphene-based gas sensor. The preparation process is simple and environmentally friendly, and the prepared single-core dual module graphene-based gas sensor can detect hydrogen sulfide and nitrogen dioxide in hydrogen sulfide and nitrogen dioxide mixed gas with high sensitivity and high selectivity.

[0046] Figure 1 It is a preparation method flowchart of the single-core dual module graphene-based gas sensor of the present application.

[0047] According to the preparation method of the single-core dual module graphene-based gas sensor provided by the embodiment of the present application, Figure 1As shown, the method comprises the following steps S1-S4.

[0048] Step S1: dividing a main surface of a wooden substrate into a first surface and a second surface arranged adjacently.

[0049] According to the embodiment of the present application, the main surface of the wooden substrate can be irradiated by the laser beam at room temperature without protective gas to divide the main surface of the wooden substrate into the first surface and the second surface arranged adjacently, and the power of the laser beam can be selected as 10 W.

[0050] According to the embodiment of the present application, the wooden substrate is any one of the following: basswood, oak and pine.

[0051] According to the embodiment of the present application, the wooden substrate is any size of wood block cut from natural wood.

[0052] In some specific embodiments, the wooden substrate is cut into wood blocks with a size of 1.5*4*5 cm.

[0053] Step S2: coating a first metal salt solution on the first surface and coating a second metal salt solution on the second surface.

[0054] According to the embodiment of the present application, the main surface of the wooden substrate is irradiated by the laser beam at room temperature without protective gas, and the surface layer of the main surface of the wooden substrate is carbonized to form a division line, and the wooden substrate has poor water absorption after carbonization, and the first metal salt solution coated on the first surface and the second metal salt solution coated on the second surface do not penetrate each other due to the small coating amount.

[0055] Step S3: irradiating the first surface and the second surface by the laser beam at room temperature without protective gas to cause lignin and cellulose in the wooden substrate to crack and reconfigure to form graphene, and cause the first metal salt immersed in the first surface to decompose to form first metal oxide nanoparticles and the second metal salt immersed in the second surface to decompose to form second metal oxide nanoparticles, the first metal oxide nanoparticles and the second metal oxide nanoparticles are dispersed on the surface of each layer of graphene of the first surface and the second surface respectively, and a first sensitive layer and a second sensitive layer are obtained respectively, the first sensitive layer is suitable for detecting nitrogen dioxide gas, and the second sensitive layer is suitable for detecting hydrogen sulfide gas.

[0056] According to the embodiment of the present application, the main surface of the wooden substrate is irradiated by the laser beam at room temperature without protective gas, and the surface layer of the main surface of the wooden substrate is carbonized to form a division line, and in step S3, the first surface and the second surface are simultaneously irradiated by the laser beam, and both are irradiated by the laser beam, but the power of the laser beam is different, which is beneficial to simplify the preparation process, facilitate operation and reduce cost.

[0057] According to the embodiment of the present application, the wood material is selected as the substrate for laser beam induced graphene formation for the following reasons. Firstly, the wood material is easy to handle, and the natural texture and structure of the wood material make it unnecessary to have complex processes when processing, and the cutting, polishing and other operations are convenient and efficient, which can effectively reduce the preparation cost and difficulty. Secondly, it is easy to combine with conductive materials (such as silver glue materials or metal materials), which is crucial for building high-performance electronic devices, can ensure the stability of the interface and promote charge transfer. Thirdly, the carbon content of the wood material is between 40% and 70%, which can stably provide enough carbon atoms to participate in the formation reaction of graphene when the laser beam is induced, ensuring the yield and quality of graphene. If the carbon content is too high (more than 70%), it is easy to cause excessive carbonization and defect generation, and if the carbon content is too low (less than 20%), it is not possible to form a complete graphene structure, and the wood material can effectively avoid these situations, and the whole process does not use strong acid or organic solvent, which is environmentally friendly and pollution-free, providing a solid foundation for laser beam induced high-quality graphene.

[0058] Step S4: coating a conductive material on the wood substrate and on both sides of the first sensitive layer and the second sensitive layer to form a connecting electrode in contact with the first sensitive layer and the second sensitive layer respectively, to obtain a single-core double-module graphene-based gas sensor.

[0059] Figure 2 is an electron microscope image of the first metal oxide nanoparticles dispersed on the surface of each layer of graphene on the first surface.

[0060] According to the embodiment of the present application, the wood substrate treated with different metal salt solutions is irradiated at room temperature without protective gas by using laser direct writing technology. When the laser beam irradiates the first surface of the wood substrate treated with the first metal salt solution, the wood substrate will absorb the energy of the laser beam, causing the lignin and cellulose in the wood substrate to crack, and the carbon atoms in the lignin and cellulose will rearrange to form graphene. At the same time, the energy of the laser beam can also decompose the first metal salt immersed in the wood substrate to form first metal oxide nanoparticles, as shown in Figure 2 Figure 2 ​The white small dots in the figure are the first metal oxide nanoparticles. The first metal oxide nanoparticles are uniformly distributed on the surface of each layer of graphene, obtaining a first sensitive layer which is a composite material of graphene and the first metal oxide nanoparticles, and the wooden substrate provides support for the composite material of graphene and the first metal oxide nanoparticles. When the laser beam irradiates the second surface, the wooden substrate treated by the second metal salt solution can absorb the energy of the laser beam, so that the lignin and cellulose in the wooden substrate can be cracked, and the carbon atoms in the lignin and cellulose can be rearranged to form graphene. At the same time, the energy of the laser beam can also decompose the second metal salt immersed in the wooden substrate to form second metal oxide nanoparticles, which are uniformly distributed on the surface of each layer of graphene, obtaining a second sensitive layer which is a composite material of graphene and the second metal oxide nanoparticles, and the wooden substrate provides support for the composite material of graphene and the second metal oxide nanoparticles.

[0061] According to the embodiment of the present application, the graphene has good electrical conductivity, which is beneficial to its response to the target gas at room temperature, and the graphene has a large specific surface area. The graphene modified by the first metal oxide nanoparticles and the second metal oxide nanoparticles respectively as the first sensitive layer and the second sensitive layer, wherein the first metal oxide nanoparticles can be used as adsorption sites for NO2 gas molecules, and the second metal oxide nanoparticles can be used as adsorption sites for H2S gas molecules, which significantly increases the number of active sites of NO2 and H2S gas molecules. When the NO2 gas molecules and the H2S gas molecules contact the first metal oxide nanoparticles and the second metal oxide nanoparticles respectively, they will react with the adsorbed oxygen to cause electron transfer. At the same time, the first metal oxide nanoparticles and the second metal oxide nanoparticles can be used as catalysts to make more NO2 and H2S gas molecules adsorbed on the surface of the graphene. The NO2 and H2S gas molecules and the graphene cause electron transfer due to the difference in Fermi level, thereby affecting the resistance of the first sensitive layer and the second sensitive layer. At the same time, the first sensitive layer and the second sensitive layer have strong selectivity to NO2 and H2S gas molecules respectively, and will produce different responses under different concentrations of NO2 and H2S mixed gas. Therefore, the single-core double-module graphene-based gas sensor has high response and good selectivity when detecting NO2 and H2S in ppb-level H2S and NO2 mixed gas.

[0062] According to the embodiment of the present application, for the first sensitive layer, transition metal oxides (cobalt oxide, iron oxide and nickel oxide) have d-d electron transition (electrons jump from a lower energy d orbital to a higher energy d orbital) and charge transfer, and there is strong absorption within the wavelength of 256nm-760nm of the laser beam, and the transition metal oxides (cobalt oxide, iron oxide and nickel oxide) have larger adsorption energy with NO2 gas compared with other transition metals, which is conducive to electron transfer between NO2 gas and the composite of graphene and the first metal oxide nanoparticles, so the transition metal oxides (cobalt oxide, iron oxide and nickel oxide) are selected to prepare the first sensitive layer for detecting NO2. For the second sensitive layer, based on the strong absorption of the transition metal oxides (cobalt oxide, iron oxide and nickel oxide) within the wavelength of 256nm-760nm of the laser beam, and the fact that Ag has larger adsorption energy with H2S molecules, H2S is more likely to adhere to the surface of the second sensitive layer and transfer electrons with the composite of graphene and the second metal oxide nanoparticles, so the silver oxide nanoparticles with good affinity and catalytic activity for H2S are selected as the sensing functional component, and the two are used together to prepare the second sensitive layer for detecting H2S.

[0063] According to the embodiment of the present application, the main surface of the wood substrate is divided into the first surface and the second surface arranged adjacently, the first metal salt solution is coated on the first surface, and the second metal salt solution is coated on the second surface, and the first surface and the second surface are irradiated by a laser beam at room temperature without a protective gas, so as to cause lignin and cellulose in the wood substrate to crack and reconfigure to form graphene (3D graphene), the first metal salt immersed in the first surface is decomposed to form first metal oxide nanoparticles, and the second metal salt immersed in the second surface is decomposed to form second metal oxide nanoparticles, the first metal oxide nanoparticles and the second metal oxide nanoparticles are dispersed on the surface of each layer of graphene of the first surface and the second surface respectively, and a first sensitive layer and a second sensitive layer with high activity and high selectivity are obtained respectively, the first sensitive layer is suitable for detecting nitrogen dioxide gas, and the second sensitive layer is suitable for detecting hydrogen sulfide gas. The process of carbonization and reconstruction of lignin and pyrolysis and oxidation of metal salt is completed synchronously by laser induction, and the graphene modified with the first metal oxide nanoparticles and the second metal oxide nanoparticles is synthesized in one step. Then, a conductive material is coated on the wood substrate and on both sides of the first sensitive layer and the second sensitive layer respectively to form a connection electrode in contact with the first sensitive layer and the second sensitive layer respectively, and a single-core double-module graphene-based gas sensor is obtained. The preparation process is simple and environmentally friendly, the material of the wood substrate is environmentally friendly, biodegradable and easy to recycle, the cost is low, and the single-core double-module graphene-based gas sensor prepared can detect H2S and NO2 in a mixed gas of H2S and NO2 with different concentrations with high sensitivity and high selectivity.

[0064] According to the embodiment of the present application, the wavelength of the laser beam is 256nm-760nm, and preferably the wavelength of the laser beam is 480nm-760nm. The power of the laser beam is 0.5W-10W.

[0065] According to the embodiment of the present application, the wavelength of the laser beam can be selected as 256nm, 480nm, 532nm, 760nm, etc. The power of the laser beam can be selected as 0.5W, 2W, 3W, 6W, 8W, 10W, etc. After a large number of tests, when the wavelength of the laser beam is 256nm and the power of the laser beam is 0.5W, after the single-core double-module graphene-based gas sensor is inputted with 100ppb NO2 and 50ppb H2S mixed gas, the resistance of the first sensitive layer decreases and the resistance of the second sensitive layer increases, and the response rates are-0.469% and 0.417% respectively. When the wavelength of the laser beam is 256nm and the power of the laser beam is 6W, after the single-core double-module graphene-based gas sensor is inputted with 50ppb NO2 and 100ppb H2S mixed gas, the resistance of the first sensitive layer decreases and the resistance of the second sensitive layer increases, and the response rates are-0.074% and 0.489% respectively. When the wavelength of the laser beam is 480nm and the power of the laser beam is 2W, after the single-core double-module graphene-based gas sensor is inputted with 200ppb NO2 and 200ppb H2S mixed gas, the resistance of the first sensitive layer decreases and the resistance of the second sensitive layer increases, and the response rates are-0.587% and 0.974% respectively. When the wavelength of the laser beam is 480nm and the power of the laser beam is 6W, after the single-core double-module graphene-based gas sensor is inputted with 300ppb NO2 and 200ppb H2S mixed gas, the resistance of the first sensitive layer decreases and the resistance of the second sensitive layer increases, and the response rates are-1.739% and 0.835% respectively. When the wavelength of the laser beam is 480nm and the power of the laser beam is 10W, after the single-core double-module graphene-based gas sensor is inputted with 400ppb NO2 and 100ppb H2S mixed gas, the resistance of the first sensitive layer decreases and the resistance of the second sensitive layer increases, and the response rates are-3.046% and 0.303% respectively. When the wavelength of the laser beam is 760nm and the power of the laser beam is 2W, after the single-core double-module graphene-based gas sensor is inputted with 500ppb NO2 and 500ppb H2S mixed gas, the resistance of the first sensitive layer decreases and the resistance of the second sensitive layer increases, and the response rates are-4.524% and 1.281% respectively.

[0066] According to the embodiment of the present application, after a large number of tests, with the increase of the power of the laser beam, the first metal oxide nanoparticles and the second metal oxide nanoparticles gradually tend to agglomerate from a uniform dispersion state, and when the power of the laser beam exceeds 10W, the first metal oxide nanoparticles and the second metal oxide nanoparticles are seriously agglomerated.

[0067] According to an embodiment of the present application, the irradiating the first surface and the second surface by the laser beam under the condition of no protective gas at room temperature comprises: setting a target region on the first surface and the second surface respectively, and irradiating the target region by the laser beam under the condition of no protective gas at room temperature. The target region is any one of a point, a line, a circle, and a polygon.

[0068] According to an embodiment of the present application, the target region set on the first surface and the second surface of the wood substrate treated by the different metal salt solutions is any one of a point, a line, a circle, a square, and a rectangle, and then the target region on the first surface and the second surface is respectively patterned by the laser beam.

[0069] According to an embodiment of the present application, the first metal salt is any one of water-soluble salts of cobalt, iron, and nickel. The second metal salt is a water-soluble silver salt and a water-soluble transition metal salt.

[0070] According to an embodiment of the present application, the water-soluble transition metal salt added in the second metal salt solution can assist in absorbing the energy of the laser beam, so that the lignin and cellulose in the wood substrate are cracked, the carbon atoms in the lignin and cellulose are rearranged to form graphene, and the second metal oxide nanoparticles are formed by the decomposition of the second metal salt immersed in the wood substrate under the action of the energy of the laser beam.

[0071] According to an embodiment of the present application, the first metal salt is any one of cobalt nitrate, iron nitrate, and nickel nitrate. The first metal oxide is any one of cobalt oxide, iron oxide, and nickel oxide.

[0072] According to an embodiment of the present application, the water-soluble silver salt includes silver nitrate, and the water-soluble transition metal salt is any one of cobalt nitrate, iron nitrate, and nickel nitrate. The second metal oxide nanoparticles are bimetallic oxide nanoparticles, and the bimetallic oxide nanoparticles include silver oxide nanoparticles and transition metal oxide nanoparticles. The silver oxide includes silver oxide, and the transition metal oxide is any one of cobalt oxide, iron oxide, and nickel oxide.

[0073] According to an embodiment of the present application, the cobalt nitrate solution can be coated on the first surface, and the mixed metal salt solution of silver nitrate and nickel nitrate can be coated on the second surface. The cobalt nitrate immersed in the first surface and the silver nitrate and nickel nitrate immersed in the second surface are respectively converted into cobalt oxide nanoparticles, silver oxide nanoparticles, and nickel oxide nanoparticles under the irradiation of the laser beam.

[0074] According to the embodiment of the present application, the ferric nitrate solution can be coated on the first surface, the mixed metal salt solution of silver nitrate and cobalt nitrate can be coated on the second surface, and the ferric nitrate immersed in the first surface and the silver nitrate and cobalt nitrate immersed in the second surface are converted into ferric oxide nanoparticles, silver oxide nanoparticles and cobalt oxide nanoparticles under the irradiation of the laser beam.

[0075] According to the embodiment of the present application, the ferric nitrate solution can be coated on the first surface, the mixed metal salt solution of silver nitrate and cobalt nitrate can be coated on the second surface, and the ferric nitrate immersed in the first surface and the silver nitrate and cobalt nitrate immersed in the second surface are converted into ferric oxide nanoparticles, silver oxide nanoparticles and cobalt oxide nanoparticles under the irradiation of the laser beam.

[0076] According to the embodiment of the present application, the ferric nitrate solution can be coated on the first surface, the mixed metal salt solution of silver nitrate and cobalt nitrate can be coated on the second surface, and the ferric nitrate immersed in the first surface and the silver nitrate and cobalt nitrate immersed in the second surface are converted into ferric oxide nanoparticles, silver oxide nanoparticles and cobalt oxide nanoparticles under the irradiation of the laser beam.

[0077] According to the embodiment of the present application, the concentration of the first metal salt solution is 0.5 mol / L to 2 mol / L.

[0078] According to the embodiment of the present application, the concentration of the first metal salt solution can be selected as 1 mol / L, 1.5 mol / L, 2 mol / L, etc. Through a large number of tests, as the concentration of the first metal salt solution continuously increases, the first metal oxide nanoparticles gradually tend to agglomerate from a uniformly dispersed state, and when the concentration of the first metal salt solution exceeds 2 mol / L, the first metal oxide nanoparticles have already agglomerated into blocks.

[0079] According to the embodiment of the present application, the concentration of the water-soluble silver salt and the water-soluble transition metal salt in the second metal salt solution is the same, and the concentration of the second metal salt solution is 0.5 mol / L to 2 mol / L.

[0080] According to the embodiment of the present application, the concentration of the second metal salt solution can be selected as 1 mol / L, 1.5 mol / L, 2 mol / L, etc. Through a large number of tests, as the concentration of the second metal salt solution continuously increases, the second metal oxide nanoparticles gradually tend to agglomerate from a uniformly dispersed state, and when the concentration of the second metal salt solution exceeds 2 mol / L, the second metal oxide nanoparticles have already agglomerated into blocks.

[0081] According to the embodiment of the present application, the size of the first metal oxide nanoparticles and the second metal oxide nanoparticles is 50 nm to 1000 nm.

[0082] According to an embodiment of the present application, the size of the first metal oxide nanoparticles and the second metal oxide nanoparticles is changed by the power of the laser beam, the concentration of the first metal salt solution and the concentration of the second metal salt solution. Through a large number of tests, with the increase of the power of the laser beam, the first metal oxide nanoparticles and the second metal oxide nanoparticles gradually tend to agglomerate from a uniformly dispersed state, and when the power of the laser beam exceeds 10 W, the first metal oxide nanoparticles and the second metal oxide nanoparticles are seriously agglomerated. With the continuous increase of the concentration of the first metal salt solution and the concentration of the second metal salt solution, the first metal oxide nanoparticles and the second metal oxide nanoparticles gradually tend to agglomerate from a uniformly dispersed state, respectively, and when the concentration of the first metal salt solution and the concentration of the second metal salt solution respectively exceed 2 mol / L, the first metal oxide nanoparticles and the second metal oxide nanoparticles are respectively agglomerated into blocks.

[0083] According to an embodiment of the present application, the conductive material includes silver glue material and metal material.

[0084] Figure 3 is a top view of a single-core double-module graphene-based gas sensor structure of the present application.

[0085] According to an embodiment of another aspect of the present application, as shown in Figure 3 A single-core double-module graphene-based gas sensor is provided, which is prepared by the above-mentioned preparation method of a single-core double-module graphene-based gas sensor, and includes a wooden substrate 2, a first sensitive layer 3, a second sensitive layer 4 and two groups of connecting electrodes 5. A division line 1 is formed on the main surface of the wooden substrate 2. The first sensitive layer 3 and the second sensitive layer 4 are formed on the main surface of the wooden substrate 2 and are located on both sides of the division line 1. The first sensitive layer 3 is a composite material of graphene and first metal oxide nanoparticles, and the second sensitive layer 4 is a composite material of graphene and second metal oxide nanoparticles. The two groups of connecting electrodes 5 are arranged on the wooden substrate 2 and are respectively located on both sides of the first sensitive layer 3 and the second sensitive layer 4 and are respectively overlapped with the first sensitive layer 3 and the second sensitive layer 4.

[0086] According to the embodiment of the present application, the external NO2 and H2S gas respectively contact the first sensitive layer 3 and the second sensitive layer 4, electron transfer occurs, the electrical conductivity of the first sensitive layer 3 and the second sensitive layer 4 changes, thereby affecting the resistance of the first sensitive layer 3 and the second sensitive layer 4, the connecting electrodes 5 on both sides of the first sensitive layer 3 and the connecting electrodes 5 on both sides of the second sensitive layer 4 facilitate the multimeter to test the resistance of the first sensitive layer 3 and the second sensitive layer 4 respectively, the first sensitive layer 3 and the second sensitive layer 4 have different selectivity to NO2 and H2S gas, thereby producing different responses to realize the detection of mixed gas, the single-core double-module graphene-based gas sensor prepared by the above method has superior performance, and has good sensitivity and high selectivity for the detection of different concentrations of NO2 and H2S in the NO2 and H2S mixed gas.

[0087] According to the embodiment of the present application, the single-core double-module graphene-based gas sensor has a detection range of 50ppb-500ppb for the concentration of hydrogen sulfide and nitrogen dioxide in the hydrogen sulfide and nitrogen dioxide mixed gas at room temperature.

[0088] According to the embodiment of the present application, the laser beam is used to etch the division line 1 to realize the double-zone isolation of the main surface of the wood substrate 2 under the condition of no protective gas at room temperature, and different metal salt solutions are respectively dropped and coated for laser induction under the condition of no protective gas at room temperature. Through single wood substrate division and partition metal salt loading, the construction of two gas sensing modules is realized. Breakthrough the single-function limitation of traditional sensors, the double-module collaborative work can eliminate cross interference, the detection limit reaches ppb level, and precise identification of double gas in complex environment is realized.

[0089] Embodiment 1

[0090] In this embodiment, oak wood is used as the wood substrate 2. First, a laser beam is used to irradiate the main surface of the wood substrate 2 at room temperature without a protective gas, forming a dividing line 1 to divide the main surface of the wood substrate 2 into an adjacent first surface and a second surface. The oak wood is cut into blocks of 1.5×9×5cm. A 1.5mol / L ferric nitrate solution is drop-coated onto the first surface of the wood substrate 2, and a 1mol / L mixed metal salt solution of silver nitrate and cobalt nitrate is drop-coated onto the second surface of the wood substrate 2. Then, it is placed in an oven and dried for 4 hours at a drying temperature of 60℃. Then, laser direct writing technology is used to pattern and induce the generation of graphene modified with iron oxide nanoparticles and graphene modified with silver oxide and cobalt oxide nanoparticles on the first and second surfaces respectively at room temperature without a protective gas, resulting in a first sensitive layer 3 and a second sensitive layer 4. The wavelength of the laser beam is 256nm, and the power of the laser beam is 0.5W. After the first sensitive layer 3 and the second sensitive layer 4 are prepared, the first sensitive layer 3 and the second sensitive layer 4 are connected to the printed circuit board (PCB) base using silver paste. The single-core dual-module graphene-based gas sensor based on oak one-step synthesis is then completed.

[0091] Subsequently, the prepared single-core dual-module graphene-based gas sensor was installed in a sealed cavity of known volume and tested at room temperature, connected to an external digital multimeter. First, air was introduced into the sealed cavity as a background gas at a constant flow rate until the resistance of the single-core dual-module graphene-based gas sensor stabilized. After the resistance stabilized, the air flow rate was kept constant, and the NO2 and H2S gas valves were opened to allow NO2 and H2S to mix thoroughly with the air before entering the sealed cavity and contacting the single-core dual-module graphene-based gas sensor. Timing was started simultaneously, and the change in resistance of the single-core dual-module graphene-based gas sensor was recorded within a specified time. After the reaction was complete, the NO2 and H2S gas valves were closed, allowing the single-core dual-module graphene-based gas sensor to re-expose itself to air. The resistance recovery process was observed, and after a certain recovery time, the next round of sensing tests was conducted.

[0092] Figure 4 This is a real-time response characteristic curve of the single-core dual-module graphene-based gas sensor in Embodiment 1 of the present invention to a mixed gas of 100ppb NO2 and 50ppb H2S.

[0093] like Figure 4 As shown, when the wavelength of the laser beam is 256nm and the power of the laser beam is 0.5W, after NO2 and H2S are introduced, the resistance of the first sensitive layer 3 of the single-core dual-module graphene-based gas sensor decreases and the resistance of the second sensitive layer 4 increases, with responsivity of -0.469% and 0.417%, respectively.

[0094] Example 2

[0095] Different from example 1, the wavelength of the laser beam used in this example is 256 nm, and the power of the laser beam is 6 W.

[0096] Figure 5 is a real-time response characteristic curve of the single-core double-module graphene-based gas sensor in example 2 to a mixed gas of 50 ppb NO2 and 100 ppb H2S.

[0097] As shown in Figure 5 , when the wavelength of the laser beam is 256 nm and the power of the laser beam is 6 W, the resistance of the first sensitive layer 3 of the single-core double-module graphene-based gas sensor decreases after the input of NO2 and H2S, and the resistance of the second sensitive layer 4 increases, with the response rates being -0.074% and 0.489%, respectively.

[0098] Example 3

[0099] In this example, basswood material is used as the wood substrate 2. First, the main surface of the wood substrate 2 is irradiated with a laser beam at room temperature without a protective gas to form a division line 1, so as to divide the main surface of the wood substrate 2 into a first surface and a second surface arranged adjacently. The basswood is cut into wood blocks with a size of 1.5×9×5 cm. A 1.5 mol / L nickel nitrate solution is drop-coated onto the first surface of the wood substrate 2, and a mixed metal salt solution of 1.5 mol / L silver nitrate and iron nitrate is drop-coated onto the second surface of the wood substrate 2. Then, the wood substrate 2 is placed in an oven for drying for 4 h, and the drying temperature is 60°C. Then, the laser direct writing technology is used to respectively patternize and induce the generation of nickel oxide nanoparticle modified graphene and silver oxide and iron oxide nanoparticle modified graphene on the first surface and the second surface at room temperature without a protective gas, to obtain the first sensitive layer 3 and the second sensitive layer 4, respectively. The wavelength of the laser beam is 480 nm, and the power of the laser beam is 2 W. After the preparation of the first sensitive layer 3 and the second sensitive layer 4, the silver glue is used to connect the first sensitive layer 3 and the second sensitive layer 4 to the PCB base, and the single-core double-module graphene-based gas sensor based on one-step synthesis of basswood is completed.

[0100] Subsequently, the prepared single-core double-module graphene-based gas sensor is installed in a closed cavity of a known volume, tested at room temperature, and connected with an external digital multimeter. First, air is used as the background gas, introduced into the closed cavity at a constant flow rate until the resistance of the single-core double-module graphene-based gas sensor stabilizes. After the resistance stabilizes, the air flow rate is kept constant, the NO2 and H2S gas valves are opened, and the NO2 and H2S are fully mixed with the air before entering the closed cavity and contacting the single-core double-module graphene-based gas sensor. At the same time, the timing starts, and the change in resistance of the single-core double-module graphene-based gas sensor within a specified time is recorded. After the reaction is completed, the NO2 and H2S gas valves are closed, the single-core double-module graphene-based gas sensor is reconnected with the air, and the resistance recovery process is observed. After a certain recovery time, the next round of sensing test is performed.

[0101] Figure 6 is a real-time response characteristic curve of the single-core double-module graphene-based gas sensor in Example 3 of the present application to 200 ppb NO2 and 200 ppb H2S.

[0102] As shown in Figure 6 , when the wavelength of the laser beam is 480 nm and the power of the laser beam is 2 W, the resistance of the first sensitive layer 3 of the single-core double-module graphene-based gas sensor decreases after the introduction of NO2 and H2S, and the resistance of the second sensitive layer 4 increases, with response rates of -0.587% and 0.974%, respectively.

[0103] Figure 7 is a selectivity column chart of the first sensitive layer and the second sensitive layer of the single-core double-module graphene-based gas sensor in Example 3 of the present application, wherein a) is a selectivity column chart of the second sensitive layer, and b) is a selectivity column chart of the first sensitive layer.

[0104] The laser direct writing technology is used to pattern the first surface and the second surface of the wooden substrate 2 to induce the generation of nickel oxide nanoparticle modified graphene and silver oxide and iron oxide nanoparticle modified graphene under room temperature without protective gas, to obtain the first sensitive layer 3 and the second sensitive layer 4, respectively. The wavelength of the laser beam is 480 nm, and the power of the laser beam is 2 W. After the preparation of the single-core double-module graphene-based gas sensor, the selectivity of the single-core double-module graphene-based gas sensor to different gases is tested. As shown in Figure 7 , the second sensitive layer 4 detects H2S as a reducing gas, and the resistance increases, with a positive response rate. It can be seen that the second sensitive layer 4 of the single-core double-module graphene-based gas sensor has higher selectivity to H2S. As shown in Figure 7As shown in the figure b) in the figure, the first sensitive layer 3 detects NO2 as an oxidizing gas, the resistance decreases, and the response degree is negative. It can be seen that the first sensitive layer 3 of the single-core double-module graphene-based gas sensor has higher selectivity to NO2, and the response degree to other gases (such as carbon monoxide (CO), methane (CH4)) is lower.

[0105] Embodiment 4

[0106] Different from embodiment 3, the wavelength of the laser beam used in this embodiment is 480 nm, and the power of the laser beam is 6 W.

[0107] Figure 8 is the real-time response characteristic curve of the single-core double-module graphene-based gas sensor in embodiment 4 of the present application to 300ppb NO2 and 200ppb H2S.

[0108] As shown in the figure b) in the figure, the first sensitive layer 3 detects NO2 as an oxidizing gas, the resistance decreases, and the response degree is negative. It can be seen that the first sensitive layer 3 of the single-core double-module graphene-based gas sensor has higher selectivity to NO2, and the response degree to other gases (such as carbon monoxide (CO), methane (CH4)) is lower. Figure 8 As shown in the figure b) in the figure, the first sensitive layer 3 detects NO2 as an oxidizing gas, the resistance decreases, and the response degree is negative. It can be seen that the first sensitive layer 3 of the single-core double-module graphene-based gas sensor has higher selectivity to NO2, and the response degree to other gases (such as carbon monoxide (CO), methane (CH4)) is lower.

[0109] Embodiment 5

[0110] Different from embodiment 3, the wavelength of the laser beam used in this embodiment is 480 nm, and the power of the laser beam is 6 W.

[0111] Figure 9 is the real-time response characteristic curve of the single-core double-module graphene-based gas sensor in embodiment 5 of the present application to 400ppb NO2 and 100ppb H2S.

[0112] As shown in the figure b) in the figure, the first sensitive layer 3 detects NO2 as an oxidizing gas, the resistance decreases, and the response degree is negative. It can be seen that the first sensitive layer 3 of the single-core double-module graphene-based gas sensor has higher selectivity to NO2, and the response degree to other gases (such as carbon monoxide (CO), methane (CH4)) is lower. Figure 9 As shown in the figure b) in the figure, the first sensitive layer 3 detects NO2 as an oxidizing gas, the resistance decreases, and the response degree is negative. It can be seen that the first sensitive layer 3 of the single-core double-module graphene-based gas sensor has higher selectivity to NO2, and the response degree to other gases (such as carbon monoxide (CO), methane (CH4)) is lower.

[0113] Embodiment 6

[0114] In this embodiment, pine wood is used as the wood substrate 2. First, a laser beam is used to irradiate the main surface of the wood substrate 2 at room temperature without a protective gas, forming a dividing line 1 to divide the main surface of the wood substrate 2 into an adjacent first surface and a second surface. The pine wood is cut into blocks of 1×9×5cm. A 2mol / L cobalt nitrate solution is drop-coated onto the first surface of the wood substrate 2, and a 1.5mol / L mixed metal salt solution of silver nitrate and nickel nitrate is drop-coated onto the second surface of the wood substrate 2. Then, it is placed in an oven and dried for 4 hours at a drying temperature of 60℃. Then, laser direct writing technology is used to pattern and induce the generation of graphene modified with cobalt oxide nanoparticles and graphene modified with silver oxide and nickel oxide nanoparticles on the first and second surfaces respectively at room temperature without a protective gas, resulting in a first sensitive layer 3 and a second sensitive layer 4. The wavelength of the laser beam is 760nm, and the power of the laser beam is 2W. After the first sensitive layer 3 and the second sensitive layer 4 are prepared, the first sensitive layer 3 and the second sensitive layer 4 are connected to the PCB base using silver paste. The single-core dual-module graphene-based gas sensor based on pine wood one-step synthesis is then completed.

[0115] Subsequently, the prepared single-core dual-module graphene-based gas sensor was installed in a sealed cavity of known volume and tested at room temperature, connected to an external digital multimeter. First, air was introduced into the sealed cavity as a background gas at a constant flow rate until the resistance of the single-core dual-module graphene-based gas sensor stabilized. After the resistance stabilized, the air flow rate was kept constant, and the NO2 and H2S gas valves were opened to allow NO2 and H2S to mix thoroughly with the air before entering the sealed cavity and contacting the single-core dual-module graphene-based gas sensor. Timing was started simultaneously, and the change in resistance of the single-core dual-module graphene-based gas sensor was recorded within a specified time. After the reaction was complete, the NO2 and H2S gas valves were closed, allowing the single-core dual-module graphene-based gas sensor to re-expose itself to air. The resistance recovery process was observed, and after a certain recovery time, the next round of sensing tests was conducted.

[0116] Figure 10 This is a graph showing the real-time response characteristics of the single-core dual-module graphene-based gas sensor in Embodiment 6 of the present invention to 500ppb NO2 and 500ppb H2S.

[0117] like Figure 10 As shown, when the wavelength of the laser beam is 760nm and the power of the laser beam is 2W, the resistance of the first sensitive layer 3 of the single-core dual-module graphene-based gas sensor decreases and the resistance of the second sensitive layer 4 increases after NO2 and H2S are introduced, with responsivity of -4.524% and 1.281%, respectively.

[0118] Example 7

[0119] Different from example 6, the wavelength of the laser beam used in this example is 760 nm, and the power of the laser beam is 6 W.

[0120] Figure 11 is a response-concentration line graph of the single-core double-module graphene-based gas sensor in example 7 to different concentrations of NO2 and H2S mixed gas combinations, wherein a) is a response-concentration line graph of the second sensitive layer to different concentrations of NO2 and H2S mixed gas combinations, and b) is a response-concentration line graph of the first sensitive layer to different concentrations of NO2 and H2S mixed gas combinations.

[0121] The laser direct writing technology is used to pattern the cobalt oxide nanoparticle modified graphene, and the silver oxide and nickel oxide nanoparticle modified graphene on the first surface and the second surface of the wooden substrate 2 at room temperature without a protective gas to obtain the first sensitive layer 3 and the second sensitive layer 4, respectively. The wavelength of the laser beam is 760 nm, and the power of the laser beam is 6 W. As shown in FIG. a) of Figure 11 , it can be seen that the second sensitive layer 4 prepared produces different responses to different concentrations of NO2 and H2S mixed gas. As shown in FIG. b) of Figure 11 , it can be seen that the first sensitive layer 3 prepared produces different responses to different concentrations of NO2 and H2S mixed gas, which indicates that the single-core double-module graphene-based gas sensor can detect NO2 and H2S in the mixed gas with high sensitivity and high selectivity.

[0122] Example 8

[0123] In this example, basswood material is used as the wooden substrate 2, and the second sensitive layer 4 synthesized in one step is tested by scanning electron microscopy (SEM).

[0124] First, the laser beam is used to irradiate the main surface of the wooden substrate 2 at room temperature without a protective gas to form a division line 1 to divide the main surface of the wooden substrate 2 into the first surface and the second surface arranged adjacent to each other. The basswood material is cut into a wood block with a size of 1.5×9×5 cm. A 2 mol / L iron nitrate solution is drop-coated to the first surface of the wooden substrate 2, and a 2 mol / L silver nitrate and nickel nitrate mixed metal salt solution is drop-coated to the second surface of the wooden substrate 2. Then, the wooden substrate 2 is placed in an oven for drying for 4 h at a drying temperature of 60°C. The laser direct writing technology is used to pattern the iron oxide nanoparticle modified graphene and the silver oxide and nickel oxide nanoparticle modified graphene on the first surface and the second surface at room temperature without a protective gas to obtain the first sensitive layer 3 and the second sensitive layer 4, respectively. The wavelength of the laser beam is 532 nm, and the power of the laser beam is 0.5 W, 3 W, 8 W, and 10 W, respectively. After the laser beam irradiation is completed, the sample is tested by SEM.

[0125] Figure 12 is a scanning electron microscope image of silver oxide and nickel oxide nanoparticle modified graphene in Example 8 when the laser beam power is different.

[0126] As shown in Figure (a) in Figure 12 , the wavelength of the laser beam is 532 nm, and the power of the laser beam is 0.5 W, the scanning electron microscope image of silver oxide and nickel oxide nanoparticle modified graphene. As shown in Figure (b) in Figure 12 , the wavelength of the laser beam is 532 nm, and the power of the laser beam is 3 W, the scanning electron microscope image of silver oxide and nickel oxide nanoparticle modified graphene. As shown in Figure (c) in Figure 12 , the wavelength of the laser beam is 532 nm, and the power of the laser beam is 8 W, the scanning electron microscope image of silver oxide and nickel oxide nanoparticle modified graphene. As shown in Figure (d) in Figure 12 , the wavelength of the laser beam is 532 nm, and the power of the laser beam is 10 W, the scanning electron microscope image of silver oxide and nickel oxide nanoparticle modified graphene. With the increase of the power of the laser beam, silver oxide and nickel oxide nanoparticles gradually tend to agglomeration from a uniform dispersed state, and when the power of the laser beam exceeds 10 W, silver oxide and nickel oxide nanoparticles are severely agglomerated.

[0127] Example 9

[0128] In this example, pine material is used as wood substrate 2, and one-step synthesized first sensitive layer 3 is subjected to scanning electron microscope (SEM) test.

[0129] First, the main surface of the wood substrate 2 is irradiated with a laser beam at room temperature without protective gas to form a division line 1 to divide the main surface of the wood substrate 2 into a first surface and a second surface arranged adjacent to each other, the pine material is cut into a wood block with a size of 1.5x9x5cm, an iron nitrate solution is drop-coated to the first surface of the wood substrate 2, a mixed metal salt solution of 2mol / L silver nitrate and nickel nitrate is drop-coated to the second surface of the wood substrate 2, the concentration of the iron nitrate solution is 0.5mol / L, 1mol / L, 1.5mol / L, 2mol / L respectively, and then placed in an oven for drying for 4h at a drying temperature of 60℃. Then, iron oxide nanoparticle modified graphene and silver oxide and nickel oxide nanoparticle modified graphene are respectively patterned and induced to generate on the first surface and the second surface under the condition of room temperature without protective gas by using laser direct writing technology, to obtain first sensitive layer 3 and second sensitive layer 4 respectively. The wavelength of the laser beam is 760 nm, and the power of the laser beam is 0.5 W. After the irradiation of the laser beam is completed, the sample is subjected to SEM test.

[0130] Figure 13This is a scanning electron microscope image of graphene modified with iron oxide nanoparticles in Example 9 of the present invention when the concentration of ferric nitrate solution is different.

[0131] like Figure 13 Figure (a) shows a scanning electron microscope image of graphene modified with iron oxide nanoparticles when the concentration of ferric nitrate solution is 0.5 mol / L. Figure 13 Figure (b) shows a scanning electron microscope image of graphene modified with iron oxide nanoparticles when the concentration of the ferric nitrate solution is 1 mol / L. Figure 13 Figure (c) shows a scanning electron microscope image of graphene modified with iron oxide nanoparticles when the concentration of the ferric nitrate solution is 1.5 mol / L. Figure 13 Figure (d) shows a scanning electron microscope image of graphene modified with iron oxide nanoparticles when the concentration of ferric nitrate solution is 2 mol / L. As the concentration of ferric nitrate solution increases, the iron oxide nanoparticles gradually tend to aggregate from a uniformly dispersed state. When the concentration of ferric nitrate solution exceeds 2 mol / L, the iron oxide nanoparticles have agglomerated into clumps.

[0132] Example 10

[0133] In this embodiment, pine wood is used as the wood substrate 2. First, a laser beam is used to irradiate the main surface of the wood substrate 2 at room temperature without a protective gas, forming a dividing line 1 to divide the main surface of the wood substrate 2 into an adjacent first surface and a second surface. The pine wood is cut into blocks of 1×9×5cm. A 1mol / L cobalt nitrate solution is drop-coated onto the first surface of the wood substrate 2, and a 2mol / L mixed metal salt solution of silver nitrate and nickel nitrate is drop-coated onto the second surface of the wood substrate 2. Then, it is placed in an oven and dried for 4 hours at a drying temperature of 60℃. Then, laser direct writing technology is used to pattern and induce the generation of graphene modified with cobalt oxide nanoparticles and graphene modified with silver oxide and nickel oxide nanoparticles on the first and second surfaces respectively at room temperature without a protective gas, resulting in a first sensitive layer 3 and a second sensitive layer 4. The wavelengths of the laser beam are 256nm, 480nm, 760nm, and 1064nm, and the power of the laser beam is 3W. After the first sensitive layer 3 and the second sensitive layer 4 are prepared, the first sensitive layer 3 and the second sensitive layer 4 are connected to the PCB base using silver paste. The single-core dual-module graphene-based gas sensor based on pine wood one-step synthesis is then completed.

[0134] Subsequently, the prepared single-core double-module graphene-based gas sensor is installed in a closed cavity with a known volume, tested at room temperature, and connected with an external digital multimeter. First, air is used as the background gas, introduced into the closed cavity at a constant flow rate until the resistance of the single-core double-module graphene-based gas sensor stabilizes. After the resistance stabilizes, the air flow rate remains unchanged, the valves of the NO2 and H2S gases are opened, the NO2 and H2S are fully mixed with the air, and then enter the closed cavity to contact the single-core double-module graphene-based gas sensor. At the same time, the timing starts, and the change in the resistance of the single-core double-module graphene-based gas sensor within a specified time is recorded. After the reaction is completed, the valves of the NO2 and H2S gases are closed, the single-core double-module graphene-based gas sensor is reconnected with the air, and the resistance recovery process is observed. After a certain recovery time, the next round of sensing test is performed.

[0135] Figure 14 Figure 7 is a real-time response characteristic curve of the single-core double-module graphene-based gas sensor in Example 10 to 200 ppb of NO2 and 200 ppb of H2S, wherein (a) is a real-time response characteristic curve of the first sensitive layer to 200 ppb of NO2 and 200 ppb of H2S mixed gas, and (b) is a real-time response characteristic curve of the second sensitive layer to 200 ppb of NO2 and 200 ppb of H2S mixed gas.

[0136] As shown in (a) of Figure 8, the response of the first sensitive layer 3 of the single-core double-module graphene-based gas sensor to NO2 first increases and then decreases as the wavelength of the laser beam increases. As shown in (b) of Figure 8, the response of the second sensitive layer 4 of the single-core double-module graphene-based gas sensor to NO2 first decreases and then increases as the wavelength of the laser beam increases. Figure 14 Figure 14 ​As shown in (b) in FIG. 6, the response of the second sensitive layer 4 to H2S increases first and then decreases with the increase of the wavelength of the laser beam. The reason may be that when the wavelength of the laser beam is short, the photon energy is high, which may cause local overheating or excessive carbonization of the material, and the generated graphene has more lattice defects, which will affect the charge transfer and adsorption between the gas molecules and the graphene. When the wavelength of the laser beam gradually increases, the photon energy becomes smaller, and it is more matched with the absorption peaks of the wood substrate 2 and the first metal salt (cobalt nitrate), the wood substrate 2 and the second metal salt (silver nitrate and nickel nitrate), which can provide sufficient time for carbon atoms to reconfigure at a suitable temperature, thereby generating high-quality composite materials of graphene and first metal oxide nanoparticles (cobalt oxide nanoparticles) and composite materials of graphene and second metal oxide nanoparticles (silver oxide and nickel oxide nanoparticles), reducing the lattice defects, and the number of layers of the growing graphene is also more uniform, thereby improving the gas sensing performance. The preferred wavelength range of the laser beam is 480 nm to 760 nm after testing. When the wavelength of the laser beam continues to increase, the laser energy may be insufficient, the degree of graphitization of the wood substrate 2 is weakened, and the defects are increased, so the response to the gas molecules is reduced. When the wavelength of the laser beam is 1064 nm, the photon energy is too low, and the induction process mainly depends on the thermal effect rather than the photoexcitation effect, the induction efficiency is poor, the generated graphene has many defects and low crystal quality, and the electrical conductivity and chemical activity are significantly reduced, which leads to the inability to respond to the gas molecules.

[0137] Example 11

[0138] In this embodiment, basswood material is used as the wood substrate 2. First, the main surface of the wood substrate 2 is irradiated by a laser beam at room temperature without a protective gas to form a division line 1, so as to divide the main surface of the wood substrate 2 into a first surface and a second surface arranged adjacent to each other. The basswood is cut into a wood block with a size of 1x9x5 cm. A 1.5 mol / L nickel nitrate solution is dropped and coated on the first surface of the wood substrate 2, and a mixed metal salt solution of 1.5 mol / L silver nitrate and iron nitrate is dropped and coated on the second surface of the wood substrate 2. Then, the wood substrate 2 is placed in an oven for drying for 4 h, and the drying temperature is 60°C. Then, the laser direct writing technology is used to respectively pattern the first surface and the second surface to induce the generation of nickel oxide nanoparticle modified graphene and silver oxide and iron oxide nanoparticle modified graphene at room temperature without a protective gas, so as to obtain a first sensitive layer 3 and a second sensitive layer 4. The wavelength of the laser beam is 760 nm, and the power of the laser beam is 18 W. After the first sensitive layer 3 and the second sensitive layer 4 are prepared, the silver glue is used to connect the first sensitive layer 3 and the second sensitive layer 4 on the PCB base, and the one-step synthesized single-core double-module graphene-based gas sensor based on basswood is completed.

[0139] Subsequently, the prepared single-core double-module graphene-based gas sensor is installed in a closed cavity with a known volume, tested at room temperature, and connected with an external digital multimeter. First, air is used as the background gas, introduced into the closed cavity at a constant flow rate until the resistance of the single-core double-module graphene-based gas sensor stabilizes. After the resistance stabilizes, the air flow rate is kept constant, the NO2 and H2S gas valves are opened, and the NO2 and H2S are fully mixed with the air before entering the closed cavity and contacting the single-core double-module graphene-based gas sensor. At the same time, the timing starts, and the change in resistance of the single-core double-module graphene-based gas sensor within a specified time is recorded. After the reaction is completed, the NO2 and H2S gas valves are closed, the single-core double-module graphene-based gas sensor is reconnected with the air, the resistance recovery process is observed, and after a certain recovery time, the next round of sensing test is performed.

[0140] Figure 15 is a real-time response characteristic curve of the single-core double-module graphene-based gas sensor in Example 11 to 200 ppb of NO2 and 200 ppb of H2S, wherein (a) is a real-time response characteristic curve of the first sensitive layer to a mixture of 200 ppb of NO2 and 200 ppb of H2S, and (b) is a real-time response characteristic curve of the second sensitive layer to a mixture of 200 ppb of NO2 and 200 ppb of H2S.

[0141] As shown in (a) of Figure 15 , the first sensitive layer 3 of the single-core double-module graphene-based gas sensor has failed to respond to NO2, and as shown in (b) of Figure 15 , the second sensitive layer 4 has failed to respond to H2S. The reason may be that when the power of the laser beam is too high (greater than 10 W), the higher temperature promotes the melting or sintering of the first metal oxide nanoparticles (nickel oxide nanoparticles) and the second metal oxide nanoparticles (silver oxide and iron oxide nanoparticles), resulting in an increase in particle size and a significant decrease in specific surface area, reducing the adsorption active sites of gas molecules, and thus causing the first sensitive layer 3 to fail to respond to NO2 and the second sensitive layer 4 to fail to respond to H2S.

[0142] Example 12

[0143] In this embodiment, basswood is used as the wood substrate 2. First, a laser beam is used to irradiate the main surface of the wood substrate 2 at room temperature without a protective gas to form a division line 1, thereby dividing the main surface of the wood substrate 2 into a first surface and a second surface arranged adjacent to each other. The basswood is cut into wood blocks with a size of 1×9×5 cm. A 5 mol / L iron nitrate solution is dropped onto the first surface of the wood substrate 2, and a mixed metal salt solution of 5 mol / L silver nitrate and nickel nitrate is dropped onto the second surface of the wood substrate 2. Then, the wood substrate 2 is placed in an oven for drying for 4 h at a drying temperature of 60°C. Then, the laser direct writing technology is used to respectively pattern the first surface and the second surface at room temperature without a protective gas to induce the generation of iron oxide nanoparticle-modified graphene and silver oxide and nickel oxide nanoparticle-modified graphene, thereby obtaining a first sensitive layer 3 and a second sensitive layer 4. The wavelength of the laser beam is 480 nm, and the power of the laser beam is 8 W. After the first sensitive layer 3 and the second sensitive layer 4 are prepared, the silver glue is used to connect the first sensitive layer 3 and the second sensitive layer 4 to the PCB base, and the one-step synthesized single-core dual-module graphene-based gas sensor made of basswood is completed.

[0144] Subsequently, the prepared single-core dual-module graphene-based gas sensor is installed in a closed cavity with a known volume, and tested at room temperature and connected with an external digital multimeter. First, air is used as the background gas, introduced into the closed cavity at a constant flow rate until the resistance of the single-core dual-module graphene-based gas sensor stabilizes. After the resistance stabilizes, the air flow rate is kept constant, the NO2 and H2S gas valves are opened, and the NO2 and H2S are fully mixed with the air before entering the closed cavity and contacting the single-core dual-module graphene-based gas sensor. At the same time, the timing starts, and the change of the resistance of the single-core dual-module graphene-based gas sensor within a specified time is recorded. After the reaction is completed, the NO2 and H2S gas valves are closed, the single-core dual-module graphene-based gas sensor is reconnected with the air, and the resistance recovery process is observed. After a certain recovery time, the next round of sensing test is performed.

[0145] Figure 16 FIG. 12 is a real-time response characteristic curve of the single-core dual-module graphene-based gas sensor of the embodiment 12 to 200 ppb NO2 and 200 ppb H2S, wherein (a) is a real-time response characteristic curve of the first sensitive layer to 200 ppb NO2 and 200 ppb H2S mixed gas, and (b) is a real-time response characteristic curve of the second sensitive layer to 200 ppb NO2 and 200 ppb H2S mixed gas.

[0146] As shown in (a) of FIG. 13, the first sensitive layer 3 of the single-core dual-module graphene-based gas sensor cannot respond to NO2, as shown in (b) of FIG. 13, the second sensitive layer 4 of the single-core dual-module graphene-based gas sensor can respond to H2S, and as shown in (c) of FIG. 13, the single-core dual-module graphene-based gas sensor can respond to NO2 and H2S. Figure 16 As shown in (a) of FIG. 13, the first sensitive layer 3 of the single-core dual-module graphene-based gas sensor cannot respond to NO2, as shown in (b) of FIG. 13, the second sensitive layer 4 of the single-core dual-module graphene-based gas sensor cannot respond to NO2, and as shown in (c) of FIG. 13, the single-core dual-module graphene-based gas sensor can respond to NO2 and H2S. Figure 16As shown in (b), the second sensitive layer 4 of the single-core dual-module graphene-based gas sensor can no longer respond to H2S. This may be because when the concentration is too high (greater than 2 mol / L), the first metal salt (ferric nitrate) and the second metal salt (silver nitrate and nickel nitrate) experience increased local heat accumulation during laser irradiation, leading to the melting and aggregation of the first metal oxide nanoparticles (iron oxide nanoparticles) and the second metal oxide nanoparticles (silver oxide and nickel oxide nanoparticles). This significantly reduces the specific surface area of ​​the first metal oxide nanoparticles (iron oxide nanoparticles) and the second metal oxide nanoparticles (silver oxide and nickel oxide nanoparticles), decreasing the adsorption active sites for gas molecules. Consequently, the first sensitive layer 3 cannot respond to NO2, and the second sensitive layer 4 cannot respond to H2S.

[0147] Example 13

[0148] In this embodiment, linden wood is used as the wood substrate 2. First, a laser beam is used to irradiate the main surface of the wood substrate 2 at room temperature without a protective gas, forming a dividing line 1 to divide the main surface of the wood substrate 2 into an adjacent first surface and a second surface. The linden wood is cut into blocks of 1×9×5cm. A 5mol / L ferric nitrate solution is drop-coated onto the first surface of the wood substrate 2, and a 5mol / L mixed metal salt solution of silver nitrate and cobalt nitrate is drop-coated onto the second surface of the wood substrate 2. Then, it is placed in an oven and dried for 4 hours at a drying temperature of 60℃. Then, laser direct writing technology is used to pattern and induce the formation of graphene modified with iron oxide nanoparticles and graphene modified with silver oxide and cobalt oxide nanoparticles on the first and second surfaces respectively at room temperature without a protective gas, resulting in a first sensitive layer 3 and a second sensitive layer 4. The wavelength of the laser beam is 1064nm, and the power of the laser beam is 18W. After the first sensitive layer 3 and the second sensitive layer 4 are prepared, SEM testing is performed.

[0149] Figure 17 These are scanning electron microscope images of graphene modified with iron oxide nanoparticles and graphene modified with silver oxide and cobalt oxide nanoparticles in Example 13 of this invention.

[0150] like Figure 17 As shown in (a), the iron oxide nanoparticles have agglomerated into clumps with a particle size exceeding 1000 nm, as... Figure 17 As shown in (b), silver oxide and cobalt oxide nanoparticles have agglomerated into clumps with a particle size exceeding 1000 nm.

[0151] Subsequently, the first sensitive layer 3 and the second sensitive layer 4 were connected to the PCB base using silver paste, and the single-core dual-module graphene-based gas sensor based on linden wood synthesis in one step was completed.

[0152] Subsequently, the prepared single-core dual-module graphene-based gas sensor was installed in a sealed cavity of known volume and tested at room temperature, connected to an external digital multimeter. First, air was introduced into the sealed cavity as a background gas at a constant flow rate until the resistance of the single-core dual-module graphene-based gas sensor stabilized. After the resistance stabilized, the air flow rate was kept constant, and the NO2 and H2S gas valves were opened to allow NO2 and H2S to mix thoroughly with the air before entering the sealed cavity and contacting the single-core dual-module graphene-based gas sensor. Timing was started simultaneously, and the change in resistance of the single-core dual-module graphene-based gas sensor was recorded within a specified time. After the reaction was complete, the NO2 and H2S gas valves were closed, allowing the single-core dual-module graphene-based gas sensor to re-expose itself to air. The resistance recovery process was observed, and after a certain recovery time, the next round of sensing tests was conducted.

[0153] Figure 18 This is a real-time response characteristic curve of the single-core dual-module graphene-based gas sensor in Embodiment 13 of the present invention to 200ppb NO2 and 200ppb H2S. Among them, (a) is the real-time response characteristic curve of the first sensitive layer to the mixed gas of 200ppb NO2 and 200ppb H2S, and (b) is the real-time response characteristic curve of the second sensitive layer to the mixed gas of 200ppb NO2 and 200ppb H2S.

[0154] like Figure 18 As shown in (a), the first sensitive layer 3 of the single-core dual-module graphene-based gas sensor can no longer respond to NO2, as... Figure 18 As shown in (b), the second sensitive layer 4 of the single-core dual-module graphene-based gas sensor can no longer respond to H2S. This may be because when the particle size of the first metal oxide nanoparticles (iron oxide nanoparticles) and the second metal oxide nanoparticles (silver oxide and cobalt oxide nanoparticles) is too large (greater than 1000 nm), the specific surface area decreases, reducing the number of exposed active sites. Simultaneously, the large particles have lower surface energy, reducing the adsorption of gas molecules, thus causing the first sensitive layer 3 to fail to respond to NO2 and the second sensitive layer 4 to fail to respond to H2S.

[0155] The embodiments of the present invention have been described above. However, these embodiments are merely illustrative and not intended to limit the scope of the invention. Although various embodiments have been described above, this does not mean that the measures in the various embodiments cannot be used advantageously in combination. The scope of the invention is defined by the appended claims and their equivalents. Various substitutions and modifications can be made by those skilled in the art without departing from the scope of the invention, and all such substitutions and modifications should fall within the scope of the invention.

Claims

1. A method of fabricating a single core dual module graphene based gas sensor, characterized in that, The method comprises the following steps: dividing a main surface of a wood substrate into a first surface and a second surface arranged adjacently; applying a first metal salt solution on the first surface and a second metal salt solution on the second surface; irradiating the first surface and the second surface with a laser beam at room temperature without a protective gas to cause lignin and cellulose in the wood substrate to crack and reconfigure into graphene, while causing the first metal salt immersed in the first surface to decompose into first metal oxide nanoparticles and the second metal salt immersed in the second surface to decompose into second metal oxide nanoparticles, the first metal oxide nanoparticles and the second metal oxide nanoparticles being dispersed on the surface of each layer of graphene of the first surface and the second surface respectively, to obtain a first sensitive layer and a second sensitive layer respectively, the first sensitive layer being suitable for detecting nitrogen dioxide gas and the second sensitive layer being suitable for detecting hydrogen sulfide gas, the power of the laser beam being 0.5 W-10 W, and the second metal salt being a water-soluble silver salt and a water-soluble transition metal salt; applying a conductive material on the wood substrate and on both sides of the first sensitive layer and the second sensitive layer to form a connecting electrode in contact with the first sensitive layer and the second sensitive layer respectively, to obtain the single-core double-module graphene-based gas sensor.

2. The production method according to claim 1, characterized by, The wood substrate is any one of lime wood, oak wood and pine wood.

3. The preparation method according to claim 1, characterized in that, The wavelength of the laser beam is 256 nm-760 nm.

4. The method of claim 1, wherein, The irradiation of the first surface and the second surface with the laser beam at room temperature without a protective gas comprises the following steps: setting a target area on the first surface and the second surface respectively, and irradiating the target area with the laser beam at room temperature without a protective gas; The target area is any one of a point, a line, a circle and a polygon.

5. The method of claim 1, wherein, The first metal salt is any one of a water-soluble salt of cobalt, iron and nickel.

6. The production method according to claim 5, wherein The first metal salt is any one of cobalt nitrate, iron nitrate and nickel nitrate. The first metal oxide is any one of cobalt oxide, iron oxide and nickel oxide.

7. The preparation method according to claim 5, characterized in that, The water-soluble silver salt includes silver nitrate, and the water-soluble transition metal salt is any one of cobalt nitrate, iron nitrate and nickel nitrate. The second metal oxide nanoparticles are bimetallic oxide nanoparticles, the bimetallic oxide nanoparticles include silver oxide nanoparticles and transition metal oxide nanoparticles, the silver oxide includes silver oxide, and the transition metal oxide is any one of cobalt oxide, iron oxide and nickel oxide.

8. The production method according to claim 7, wherein The size of the first metal oxide nanoparticles and the second metal oxide nanoparticles is 50 nm-1000 nm.

9. A single core dual module graphene based gas sensor prepared by the method of preparing a single core dual module graphene based gas sensor according to any one of claims 1-8, characterized in that, The single-core double-module graphene-based gas sensor comprises: a wood substrate, a main surface of the wood substrate being formed with a division line; a first sensitive layer and a second sensitive layer formed on the main surface of the wood substrate and located on both sides of the division line, wherein the first sensitive layer is a composite material of graphene and first metal oxide nanoparticles, and the second sensitive layer is a composite material of graphene and second metal oxide nanoparticles; Two groups of connecting electrodes are arranged on the wood substrate and are respectively located on two sides of the first sensitive layer and the second sensitive layer and are respectively overlapped with the first sensitive layer and the second sensitive layer.

10. The single-core dual module graphene-based gas sensor according to claim 9, wherein, The single-core double-module graphene-based gas sensor has a detection range of 50ppb-500ppb for the concentration of hydrogen sulfide and nitrogen dioxide in a mixed gas of hydrogen sulfide and nitrogen dioxide.

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