Method for preparing room temperature ammonia sensor based on oxide sol-gel and sensor

Abstract

The application provides a preparation method of an oxide sol-gel-based room-temperature ammonia sensor and the sensor, and can be applied to the technical field of gas sensors and the technical field of micro-nano sensors. The preparation method comprises the following steps: irradiating a substrate by means of a laser to in-situ prepare at least two patterned laser-induced graphene electrodes on the surface of the substrate; dissolving a precursor of a multi-metal oxide in a target solvent to prepare a multi-oxide sol-gel mixed solution with a target concentration; coating the multi-oxide sol-gel mixed solution with the target concentration on the region where the at least two laser-induced graphene electrodes are formed to form a multi-oxide sol-gel film covering the at least two laser-induced graphene electrodes and the region between the electrodes; and irradiating the multi-oxide sol-gel film by means of a laser and adjusting the power of the laser irradiation in the process of irradiation to convert the multi-oxide sol-gel film into nanoparticles with ammonia sensitivity.

Description

Technical Field

[0001] This invention relates to the fields of gas sensor technology and micro / nano sensor technology, specifically to a method for preparing a room temperature ammonia sensor based on oxide sol-gel and the sensor itself. Background Technology

[0002] Currently, ammonia sensors face numerous challenges in their fabrication process. Traditional coating techniques and thin-film deposition processes have inherent limitations, leading not only to high fabrication costs but also to low specific surface area of ​​the ammonia-sensitive material, significantly suppressing the sensor's ammonia sensitivity. Summary of the Invention

[0003] In view of the above problems, the present invention provides a method for preparing a room temperature ammonia sensor based on oxide sol-gel and a sensor that reduces the preparation process cost and improves the ammonia sensitivity of the ammonia sensor.

[0004] One aspect of the present invention provides a method for fabricating a room-temperature ammonia sensor based on oxide sol-gel, comprising: irradiating a substrate with a laser to fabricate at least two patterned laser-induced graphene electrodes in situ on the substrate surface; dissolving a precursor of a multi-metal oxide in a target solvent to prepare a multi-oxide sol-gel mixture with a target concentration between 0.02 and 0.5 mol / L; coating the multi-oxide sol-gel mixture with the target concentration onto the region where the at least two laser-induced graphene electrodes are formed to form a multi-oxide sol-gel film covering the at least two laser-induced graphene electrodes and the region between the electrodes; irradiating the multi-oxide sol-gel film with the laser and adjusting the laser irradiation power during the irradiation process to transform the multi-oxide sol-gel film into nanoparticles with ammonia sensitivity, such that the pore size distribution of the mesoporous structure formed by the nanoparticles covering the laser-induced graphene electrodes and the region between the electrodes is in the range of 2 to 50 nm.

[0005] According to an embodiment of the present invention, the target concentration is determined as follows: an initial concentration of the multi-component oxide sol-gel mixture is determined, and an initial multi-component oxide sol-gel mixture is prepared based on the initial concentration; the initial multi-component oxide sol-gel mixture is coated on the region where at least two laser-induced graphene electrodes are formed to obtain an initial multi-component sol-gel film; the initial multi-component sol-gel film is converted into nanoparticles using the laser, and the first initial pore size of the mesoporous structure formed by the nanoparticles is detected; if the first initial pore size is less than 2 to 50 nm, the initial concentration is increased at a predetermined concentration change step between 0.02 and 0.5 mol / L; if the first initial pore size is greater than 2 to 50 nm, the initial concentration is decreased at a predetermined concentration change step between 0.02 and 0.5 mol / L.

[0006] According to an embodiment of the present invention, the irradiation power of the laser irradiation of the multi-component sol-gel film is between 0.05 and 8 W. During the irradiation of the multi-component sol-gel film using the laser, the laser irradiation power is adjusted as follows: an initial irradiation power of the laser irradiation of the multi-component sol-gel film is determined; the multi-component sol-gel film is converted into nanoparticles according to the initial irradiation power, and a second initial pore size of the mesoporous structure formed by the nanoparticles is detected; if the second initial pore size is lower than the range of 2 to 50 nm, the initial irradiation power is reduced in a predetermined power variation step between 0.05 and 8 W; if the second initial pore size is higher than the range of 2 to 50 nm, the initial irradiation power is increased in a predetermined power variation step between 0.05 and 8 W.

[0007] According to an embodiment of the present invention, the scanning speed of the laser irradiation of the multi-element sol-gel film is between 5 and 200 mm / s.

[0008] According to an embodiment of the present invention, the aforementioned multi-metal oxide includes at least tin oxide and zinc oxide; the preparation of a multi-metal oxide sol-gel mixture having a target concentration by dissolving the precursor of the multi-metal oxide in a target solvent includes: adding the precursor of the tin oxide to the target solvent to prepare a tin oxide precursor solution having the target concentration; adding the precursor of the zinc oxide to the target solvent to prepare a zinc oxide precursor solution having the target concentration; adding a sol-gel agent to the tin oxide precursor solution and the zinc oxide precursor solution respectively and stirring; and mixing the tin oxide precursor solution and the zinc oxide precursor solution after the sol-gel agent has been added for a predetermined time, according to a predetermined mixing volume ratio, to obtain the aforementioned multi-metal oxide sol-gel mixture.

[0009] According to an embodiment of the present invention, the molar ratio of the tin oxide precursor, the zinc oxide precursor, and the sol-gel aid is 1:(0.1~0.8):(0.01~0.3).

[0010] According to an embodiment of the present invention, the predetermined mixing volume ratio of the tin oxide precursor solution to the zinc oxide precursor solution includes (3~5):(1~2).

[0011] According to an embodiment of the present invention, the coating amount of the above-mentioned multi-component oxide sol-gel mixture is 10~25 μL / cm², and the thickness of the multi-component sol-gel film is 1~100 μm.

[0012] Another aspect of the present invention provides an ammonia sensor prepared by the above method, comprising: a substrate; at least two patterned laser-induced graphene electrodes formed in situ on the surface of the substrate by laser induction; and a nanoparticle layer having ammonia sensitivity, covering the at least two laser-induced graphene electrodes and the region between the electrodes.

[0013] According to an embodiment of the present invention, the at least two laser-induced graphene electrodes include a graphene positive electrode and a graphene negative electrode; the graphene positive electrode includes a plurality of first comb-like structures, the graphene negative electrode includes a plurality of second comb-like structures, the first comb-like structures and the second comb-like structures are arranged in an interleaved manner, and the distance between the first comb-like structures and the second comb-like structures is between 50 and 500 μm; the ammonia-sensitive nanoparticle layer completely covers the plurality of the first comb-like structures and the plurality of the second comb-like structures.

[0014] According to an embodiment of the present invention, at least two patterned laser-induced graphene electrodes are prepared in situ on the substrate surface by irradiating the substrate with a laser; a precursor of a multi-metal oxide is dissolved in a target solvent to prepare a multi-oxide sol-gel mixture with a target concentration; the multi-oxide sol-gel mixture is coated on the area where at least two laser-induced graphene electrodes are formed to form a multi-oxide sol-gel film covering at least two laser-induced graphene electrodes and the area between the electrodes; the multi-oxide sol-gel film is irradiated with a laser and the laser irradiation power is adjusted during the irradiation process to convert the multi-oxide sol-gel film into nanoparticles with ammonia sensitivity. In the fabrication of the ammonia sensor, a precursor of a multi-metal oxide is dissolved in a target solvent to prepare a multi-metal oxide sol-gel mixture with a concentration of 0.02–0.5 mol / L. This mixture can be coated onto the electrodes and the area between them, where hydrolysis and condensation reactions form a multi-metal oxide sol-gel film. This film, after laser irradiation, can be transformed into room-temperature gas-sensitive nanoparticles. These nanoparticles are not isolated but rather naturally construct mesoporous structures with pore sizes ranging from 2 to 50 nm through appropriate aggregation and stacking. In this sensor, the nanoparticles provide a high specific surface area and abundant surface active sites, forming the basis for the gas-sensitive reaction. The diverse and interconnected shapes of the mesoporous structures provide rapid diffusion channels for gas molecules, further increasing the specific surface area. Moreover, the mesoporous structure is positively correlated with the responsivity of the ammonia sensor, and the larger pore size effectively reduces the diffusion resistance of ammonia. The presence of nanoparticles and mesoporous structures maximizes active sites and optimizes mass transport. This unique structure not only increases gas adsorption capacity and accelerates gas diffusion rate, optimizing the reaction process, but also improves the thermal stability of the material, thereby significantly enhancing its gas-sensing performance. This enables the material to detect low-concentration gases quickly and sensitively. The combination of nanoparticles and mesoporous structures synergistically and significantly improves the sensor's adsorption capacity, reaction kinetics, and overall sensitivity to ammonia.

[0015] On the other hand, by employing laser direct writing technology, multi-component sol-gel films can be in situ converted into room-temperature gas-sensitive nanoparticles on a substrate. This process is simple and reduces processing costs. Moreover, by setting the concentration of the multi-component oxide sol-gel mixture between 0.02 and 0.5 mol / L, the pore size of the mesoporous structure can be ensured to be in the range of 2 to 50 nm. This pore size can provide a specific surface area, which can increase the gas adsorption capacity, accelerate the gas diffusion rate, and improve the ammonia sensitivity of the ammonia sensor. Attached Figure Description

[0016] The above-described features, other objects, and advantages of the present invention will become clearer from the following description of embodiments of the invention with reference to the accompanying drawings, in which:

[0017] Figure 1 A flowchart of a method for preparing a room temperature ammonia sensor based on an oxide sol-gel according to an embodiment of the present invention is shown.

[0018] Figure 2A A schematic diagram of a laser-induced graphene electrode according to an embodiment of the present invention is shown.

[0019] Figure 2B A laser-induced graphene electrode under an optical microscope is shown according to an embodiment of the present invention.

[0020] Figure 3 A flowchart of a method for preparing a room temperature ammonia sensor based on an oxide sol-gel according to another embodiment of the present invention is shown.

[0021] Figure 4 A schematic diagram of an ammonia sensor according to an embodiment of the present invention is shown.

[0022] Figure 5 A schematic diagram showing the change in gloss of the sol-gel in the laser direct-writing region according to an embodiment of the present invention is shown.

[0023] Figure 6 An image of a nanoparticle layer with ammonia sensitivity obtained by laser irradiation according to an embodiment of the present invention is shown under a scanning electron microscope.

[0024] Figure 7 The ammonia gas-sensitive response curve at room temperature according to an embodiment of the present invention is shown.

[0025] Figure 8 The cyclic test curve of 50 ppm ammonia at room temperature according to an embodiment of the present invention is shown.

[0026] Figure 9A The resistance response curves according to an embodiment of the present invention are shown as a function of ammonia concentration.

[0027] Figure 9B It shows Figure 9A Linear relationship between ammonia concentration and response amplitude.

[0028] Figure 10 The comparison of ammonia gas-sensitive response under different humidity levels according to an embodiment of the present invention is shown.

[0029] Figure 11 The gas-sensitive response of different gases at 100 ppm at room temperature is shown in the embodiment of the present invention.

[0030] Figure 12 The gas-sensitive response cycle test curve for 20 ppm ammonia at room temperature is shown according to an embodiment of the present invention. Detailed Implementation

[0031] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the invention. In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the embodiments of the invention for ease of explanation. However, it will be apparent that one or more embodiments may be practiced without these specific details. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0032] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. The terms “comprising,” “including,” etc., as used herein indicate the presence of the stated features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0033] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein are to be interpreted in a manner consistent with the context of this specification, and not in an idealized or overly rigid way.

[0034] When using expressions such as "at least one of A, B and C", they should generally be interpreted in accordance with the meaning that is commonly understood by those skilled in the art (e.g., "a system having at least one of A, B and C" should include, but is not limited to, a system having A alone, a system having B alone, a system having C alone, a system having A and B, a system having A and C, a system having B and C, and / or a system having A, B and C, etc.).

[0035] Currently, ammonia sensors face numerous technical challenges. Taking traditional metal oxide sensors as an example, their operation relies on high-temperature environments, requiring operation within a temperature range of 200-400 °C. This not only results in high energy consumption (exceeding 50 mW) but also makes them unsuitable for portable devices. Furthermore, these sensors exhibit poor sensitivity, with a response value below 90% when facing 100 ppm NH3. During adsorption and desorption processes, their speed is slow, resulting in a long response time.

[0036] In terms of fabrication processes, traditional coating techniques and thin-film deposition processes have inherent defects. Material agglomeration is difficult to avoid, resulting in a low specific surface area and significantly suppressing gas-sensitive activity (measured values ​​are usually 40%-60% lower than theoretical values). Furthermore, existing technologies lack precise control capabilities, which severely restricts the reliability of the devices.

[0037] The photolithography process also faces fundamental technological bottlenecks that are difficult to overcome. The process requires 12 complicated steps, including 4 photolithography exposures and 8 wet etching processes, resulting in high manufacturing costs per square centimeter. This undoubtedly forms an economic barrier that hinders large-scale industrial production.

[0038] To address the aforementioned issues, this invention utilizes laser direct writing technology to transform multi-component sol-gel films into room-temperature gas-sensitive nanoparticles on a flexible substrate. The sensor constructed using this technology exhibits high sensitivity at room temperature. Laser direct writing technology excels in creating high specific surface area nanostructures, significantly optimizing the gas-sensitive properties of sol-gels and accelerating response speed. At room temperature, this sensor achieves a response of 570% to 100 ppm gas, with typical adsorption / desorption times reduced to 130 s and 450 s, respectively. Its fabrication employs a one-step laser direct writing method, reducing costs by 90% compared to traditional processes, offering high flexibility and precision, and simplifying the process. This invention uses an inexpensive diode laser, abandoning expensive, complex, and difficult-to-maintain femtosecond lasers and other light sources, greatly reducing usage and maintenance costs.

[0039] Figure 1 A flowchart of a method for preparing a room temperature ammonia sensor based on an oxide sol-gel according to an embodiment of the present invention is shown.

[0040] like Figure 1 As shown, the method for preparing a room temperature ammonia sensor based on oxide sol-gel in this embodiment includes operations S110 to S140.

[0041] In operation S110, a laser is used to irradiate the substrate, and at least two patterned laser-induced graphene electrodes are fabricated in situ on the substrate surface.

[0042] In operation S120, the precursor of the multi-metal oxide is dissolved in the target solvent to prepare a multi-metal oxide sol-gel mixture with a target concentration between 0.02 and 0.5 mol / L.

[0043] In operation S130, a multi-component oxide sol-gel mixture with a target concentration is coated on the region where at least two laser-induced graphene electrodes are formed, forming a multi-component sol-gel film covering the at least two laser-induced graphene electrodes and the region between the electrodes.

[0044] In operation S140, a laser is used to irradiate the multi-component sol-gel film, and the power of the laser irradiation is adjusted during the irradiation process to transform the multi-component sol-gel film into nanoparticles with ammonia sensitivity, so that the pore size of the mesoporous structure formed by the nanoparticles covering the laser-induced graphene electrode and the area between the electrodes is in the range of 2~50 nm.

[0045] In some embodiments, the substrate may include a carbonaceous precursor material, such as polyimide (PI), graphene oxide, phenolic resin, polydimethylsiloxane, etc.

[0046] Figure 2A A schematic diagram of a laser-induced graphene electrode according to an embodiment of the present invention is shown; Figure 2B A laser-induced graphene electrode under an optical microscope is shown according to an embodiment of the present invention.

[0047] In some embodiments, at least two patterned laser-induced graphene electrodes can be formed by irradiating a substrate with a laser. For example... Figure 2A and Figure 2B As shown, Figure 2B yes Figure 2A The enlarged view shows that at least two laser-induced graphene electrodes may include a graphene positive electrode 201 and a graphene negative electrode 202. The graphene positive electrode 201 may include multiple first comb-like structures 2011, and the graphene negative electrode 202 may include multiple second comb-like structures 2021. The first comb-like structures 2011 and the second comb-like structures 2021 may be arranged in an interlaced pattern to form a cross-finger pattern. The distance between the first comb-like structures 2011 and the second comb-like structures 2021 may be between 50 and 500 μm.

[0048] The distance (interdigitation distance) between the first comb-like structure 2011 and the second comb-like structure 2021 is a key parameter affecting the resistivity and sensitivity of the sensitive material substrate. A smaller interdigitation distance proportionally increases the electrode index per unit area, expanding the total electrode surface area. This makes the interface between the sensitive material and gas molecules more compact, providing more adsorption sites and improving detection sensitivity. However, excessively small spacing presents structural stability issues: edge effects are prone to occur during microfabrication processes such as photolithography, reducing the strength of the electrode structure; the difference in thermal expansion coefficients between the sensitive material and the electrode substrate can cause material cracking, affecting the long-term performance of the sensor. Therefore, the interdigitation distance selected in this embodiment is approximately 200 μm, with a recommended range of 50–500 μm.

[0049] In some embodiments, the multi-metal oxide includes at least tin oxide (e.g., The target solvent can be at least one of a deionized aqueous solution or a volatile solvent, such as anhydrous ethanol.

[0050] Sol-gel solutions with concentrations of 0.02–0.5 mol / L can be prepared using anhydrous ethanol and tin oxide and zinc oxide precursors, respectively. Concentrated hydrochloric acid or acetic acid is then added dropwise as a sol-gel aid, and the mixture is stirred for a predetermined time until the solid components are completely dissolved, yielding tin oxide precursor solutions and zinc oxide precursor solutions. These solutions are then allowed to stand for a predetermined aging time. The tin oxide precursor solutions and zinc oxide precursor solutions, after standing for the predetermined aging time, are then mixed at a predetermined volume ratio to obtain a multi-component oxide sol-gel mixture.

[0051] The multi-component oxide sol-gel mixture can be coated onto the laser-induced graphene electrode and the area between the electrodes. The coating amount can be controlled. After the solution on the laser-induced graphene electrode and the area between the electrodes is naturally air-dried, the next coating operation can be performed to form a multi-component sol-gel film covering the laser-induced graphene electrode and the area between the electrodes.

[0052] For multi-component sol-gel films, drying at 70 °C for 20 min is possible. During drying, laser direct writing technology can be used to irradiate and process the dried multi-component sol-gel film, transforming it into ammonia-sensitive nanoparticles. This results in a mesoporous structure formed by the nanoparticles covering the laser-induced graphene electrode and the area between the electrodes, with pore sizes ranging from 2 to 50 nm. The pores exhibit diverse and interconnected shapes, along with a large specific surface area. This unique structure not only increases gas adsorption capacity, accelerates gas diffusion rate, and optimizes surface reaction processes, but also improves the material's thermal stability, thereby significantly enhancing its gas-sensing performance and enabling rapid and sensitive detection of low-concentration gases.

[0053] According to an embodiment of the present invention, at least two patterned laser-induced graphene electrodes are prepared in situ on the substrate surface by irradiating the substrate with a laser; a precursor of a multi-metal oxide is dissolved in a target solvent to prepare a multi-oxide sol-gel mixture with a target concentration; the multi-oxide sol-gel mixture is coated on the area where at least two laser-induced graphene electrodes are formed to form a multi-oxide sol-gel film covering at least two laser-induced graphene electrodes and the area between the electrodes; the multi-oxide sol-gel film is irradiated with a laser and the laser irradiation power is adjusted during the irradiation process to convert the multi-oxide sol-gel film into nanoparticles with ammonia sensitivity. In the fabrication of the ammonia sensor, a precursor of a multi-metal oxide is dissolved in a target solvent to prepare a multi-metal oxide sol-gel mixture with a concentration of 0.02–0.5 mol / L. This mixture can be coated onto the electrodes and the areas between them, where hydrolysis and condensation reactions form a multi-metal oxide sol-gel film. This film, after laser irradiation, can be transformed into room-temperature gas-sensitive nanoparticles. These nanoparticles form mesoporous structures with pore sizes ranging from 2 to 50 nm, exhibiting diverse and interconnected pore shapes and a large specific surface area. This unique structure not only increases gas adsorption and accelerates gas diffusion rates, optimizing surface reaction processes, but also improves the material's thermal stability, thereby significantly enhancing its gas-sensing performance and enabling rapid and sensitive detection of low-concentration gases. Furthermore, by employing laser direct writing technology, the multi-metal oxide sol-gel film can be in situ transformed into room-temperature gas-sensitive nanoparticles on a substrate, simplifying the process and reducing costs. On the other hand, setting the concentration of the multi-component oxide sol-gel mixture between 0.02 and 0.5 mol / L can ensure that the pore size of the mesoporous structure is in the range of 2 to 50 nm. This pore size can provide a specific surface area, which can increase the gas adsorption capacity, accelerate the gas diffusion rate, and improve the ammonia sensitivity of the ammonia sensor.

[0054] In some embodiments, the target concentration between 0.02 and 0.5 mol / L can be determined by: determining the initial concentration of the multi-component oxide sol-gel mixture and preparing the initial multi-component oxide sol-gel mixture based on the initial concentration; coating the initial multi-component oxide sol-gel mixture on the region forming at least two laser-induced graphene electrodes to obtain an initial multi-component sol-gel film; converting the initial multi-component sol-gel film into nanoparticles using a laser and detecting the first initial pore size of the mesoporous structure formed by the nanoparticles; increasing the initial concentration according to a predetermined concentration change step if the first initial pore size is below the range of 2 to 50 nm; and decreasing the initial concentration according to a predetermined concentration change step if the first initial pore size is above the range of 2 to 50 nm.

[0055] The target concentration can be continuously adjusted experimentally based on feedback from the mesopore size; in some cases, lower concentrations result in smaller pore sizes. Specifically, the initial concentration of the multi-component oxide sol-gel mixture (0.1 mol / L) can be determined first. An initial multi-component oxide sol-gel mixture is then prepared based on this initial concentration, coated with the mixture, and the resulting initial multi-component sol-gel film is irradiated with a laser to detect the initial pore size. For pore sizes below 2–50 nm, the initial concentration can be increased in predetermined steps (e.g., +0.02 mol / L); for pore sizes above 2–50 nm, the initial concentration can be decreased in predetermined steps (e.g., -0.02 mol / L).

[0056] In one embodiment, a target concentration between 0.02 and 0.5 mol / L allows for precise control of uniformity, porosity, density, and flexibility. Excessive concentration results in an overly thick multi-component sol-gel film, making it difficult for the laser to penetrate and affecting nanoparticle formation; conversely, insufficient concentration leads to a thinner multi-component sol-gel film, causing damage to the substrate and hindering nanoparticle formation.

[0057] In some embodiments, a multi-component oxide sol-gel mixture can be prepared according to a determined target concentration. Specifically, the process may include the following operations: adding a tin oxide precursor to a target solvent to prepare a tin oxide precursor solution with a target concentration; adding a zinc oxide precursor to a target solvent to prepare a zinc oxide precursor solution with a target concentration; adding a sol-gel agent (hydrochloric acid, acetic acid, etc., for adjusting pH) to the tin oxide precursor solution and the zinc oxide precursor solution, respectively, and stirring. In some embodiments, the molar ratio of the tin oxide precursor, the zinc oxide precursor, and the sol-gel agent may include 1:(0.1~0.8):(0.01~0.3). After the tin oxide precursor solution and the zinc oxide precursor solution with added sol-gel agent are both allowed to stand for a predetermined time, they are mixed according to a predetermined mixing volume ratio to obtain a multi-component oxide sol-gel mixture. In some embodiments, the predetermined mixing volume ratio includes (3~5):(1~2). By setting the molar ratio of tin oxide precursor, zinc oxide precursor, and sol-gel agent to 1:(0.1~0.8):(0.01~0.3), and the predetermined mixing volume ratio of tin oxide precursor solution to zinc oxide precursor solution to (3~5):(1~2), the resistance of the ammonia sensor, as well as the response amplitude and type of ammonia, can be controlled. For example, when the proportion of zinc oxide (ZnO) increases from 0.1 to 0.8, the resistance of the ammonia sensor may show a trend of first decreasing and then increasing, the ammonia response amplitude may show a trend of first increasing and then decreasing, and the response type may change from n-type dominant to np-synergistic. As another example, when the proportion of sol-gel agent increases from 0.01 to 0.3, the resistance of the ammonia sensor may decrease, the ammonia response amplitude may increase, and the response speed may accelerate. Furthermore, when the mixing ratio is adjusted from 3:2 to 5:1, the resistance of the ammonia sensor may decrease, the response amplitude may increase, but the response stability may slightly decrease.

[0058] In some embodiments, when coating a multi-component oxide sol-gel mixture with a target concentration, a drop-casting method can be used. The drop-casting amount of the multi-component oxide sol-gel mixture is 10-25 μL / cm² on the region where at least two laser-induced graphene electrodes are formed, and the thickness of the multi-component sol-gel film can be 1-100 μm. This thickness allows for precise control of uniformity, porosity, density, and flexibility. If the multi-component sol-gel film is too thick, the laser cannot penetrate it, affecting the formation of nanoparticles; if the multi-component sol-gel film is too thin, the laser will not only damage the substrate but also affect the formation of nanoparticles. Therefore, the thickness of the multi-component sol-gel film is controlled between 1-100 μm.

[0059] The coated multi-component sol-gel film can be irradiated with a laser, with the irradiation power ranging from 0.05 to 8 W. During laser irradiation, the irradiation power can be adjusted. For example, the initial irradiation power can be determined; the multi-component sol-gel film is then converted into nanoparticles according to the initial irradiation power, and the second initial pore size of the mesoporous structure formed by the nanoparticles is detected; if the second initial pore size is below 2–50 nm, the initial irradiation power is decreased in predetermined power increments between 0.05 and 8 W; if the second initial pore size is above 2–50 nm, the initial irradiation power is increased in predetermined power increments between 0.05 and 8 W.

[0060] The power used during laser irradiation can be continuously adjusted experimentally based on feedback from the aperture size; in some cases, higher power may result in a smaller aperture. Specifically, an initial irradiation power (e.g., 1 W) can be determined first, and the multi-element sol-gel film can be irradiated based on this initial power. The size of the second initial aperture can then be measured. For apertures smaller than 2–50 nm, the initial irradiation power can be decreased in predetermined power increments (e.g., -0.05 W). For apertures larger than 2–50 nm, the initial irradiation power can be increased in predetermined power increments (e.g., +0.05 W).

[0061] In one embodiment, the scanning speed for laser irradiation of the multi-component sol-gel film can be between 5 and 200 mm / s. The scanning speed allows for precise control of the size and distribution of the nanoparticles in the sensitive film. Too low a scanning speed may lead to substrate carbonization, which is not conducive to the formation of nanoparticles, while too high a scanning speed may make it difficult for the multi-component sol-gel film to be fully transformed into nanoparticles. Therefore, the scanning speed is set between 100 and 200 mm / s.

[0062] In some embodiments, when irradiating the substrate and the multi-component sol-gel film with a laser, a laser with a wavelength of 450 nm, a laser with a wavelength of 532 nm, or a laser with a wavelength of 1 μm can be used. The wavelength of the laser can precisely control the size and distribution of the nanoparticles in the sensitive film. For example, the shorter the wavelength, the higher the energy and the smaller the nanoparticle size; the longer the wavelength, the lower the energy and the larger the nanoparticle size. Therefore, a laser with a wavelength of 450 nm is preferred.

[0063] In some embodiments, when irradiating the substrate with a laser and when irradiating the multi-component sol-gel film with a laser, the power density used can be 0.1~5 KW / cm². 2Power density allows for precise control of the size and distribution of nanoparticles in the sensitive film. Excessive power density may damage the substrate, while insufficient power density may hinder nanoparticle formation. Therefore, the power density is set between 0.1 and 5 KW / cm². 2 between.

[0064] Figure 3 A flowchart of a method for preparing a room temperature ammonia sensor based on an oxide sol-gel according to another embodiment of the present invention is shown.

[0065] like Figure 3 As shown, the preparation method of this embodiment may include operations S301 to S303.

[0066] In operation S301, a fixed proportion of multi-component oxide sol-gel mixture is prepared.

[0067] This process may include precursor solution preparation, coating preparation, hydrolysis and condensation reaction, and gel drying.

[0068] S302 is in operation, laser irradiation.

[0069] This process may include designing electrode patterns, cleaning the substrate, setting parameters for laser irradiation, and controlling the atmosphere used for the laser, such as nitrogen or argon.

[0070] The ammonia sensor was tested using S303.

[0071] The process may include ammonia gas concentration adjustment, humidity adjustment, gas sensitivity measurement, and repeatability verification.

[0072] Figure 4 A schematic diagram of an ammonia sensor according to an embodiment of the present invention is shown.

[0073] like Figure 4 As shown, the ammonia sensor may include a substrate 401, at least two patterned laser-induced graphene electrodes formed in situ on the surface of the substrate 401 by laser induction, and a nanoparticle layer 402 with ammonia sensitivity covering the at least two laser-induced graphene electrodes and the area between the electrodes.

[0074] At least two laser-induced graphene electrodes include a graphene positive electrode 201 and a graphene negative electrode 202; the graphene positive electrode 201 includes multiple first comb-like structures 2011, and the graphene negative electrode 202 includes multiple second comb-like structures 2021. The first comb-like structures 2011 and the second comb-like structures 2021 are arranged in an interleaved manner, and the distance between the first comb-like structures 2011 and the second comb-like structures 2021 is between 50 and 500 μm; an ammonia-sensitive nanoparticle layer 402 completely covers the multiple first comb-like structures 2011 and the multiple second comb-like structures 2021.

[0075] Taking the MQ137 in traditional ammonia sensors as an example, the performance comparison between the ammonia sensor prepared in this embodiment and the traditional ammonia sensor can be shown in Table 1.

[0076] Table 1

[0077]

[0078] As shown in Table 1, the response value Rs / Ro represents the ratio of Rs to Ro, intuitively reflecting the change in resistance of the ammonia sensor due to contact with ammonia gas. Ro can be the resistance value of the ammonia sensor in a pure gas (such as dry, clean air), serving as the basic resistance of the ammonia sensor. Rs can be the resistance value of the ammonia sensor reaching a stable state in a test atmosphere containing ammonia gas; a higher response value is better. Typical response time (90%) is the time required for the signal change of the ammonia sensor to reach 90% of its final stable change value from the moment the ammonia sensor comes into contact with the gas. The shorter the better, indicating a faster response. The detection limit is the lowest gas concentration that the ammonia sensor can reliably detect, representing the limit of sensitivity; a lower limit is better. Operating temperature is the optimal operating temperature range for the ammonia sensor; the ammonia sensor in this embodiment can operate at room temperature. Power consumption is the power consumed by the ammonia sensor to maintain normal operation. Warm-up time is the time required from the cold start of the ammonia sensor to the output signal reaching a stable and reliable state.

[0079] According to the comparison results in Table 1, the ammonia sensor of the present invention can exhibit high ammonia sensitivity at room temperature. The ammonia-sensitive nanoparticle layer obtained by laser irradiation has a high specific surface area, which can significantly optimize the gas-sensitive properties of the sol-gel and accelerate the response speed to ammonia.

[0080] The following examples 1 to 6 further describe the preparation method of the room temperature ammonia sensor based on oxide sol-gel provided in the present invention and the ammonia sensor obtained therefrom.

[0081] Example 1

[0082] The laser-induced graphene electrode was fabricated using a 450 nm laser wavelength, 2.5 W laser power, 5 mm / s scanning speed, and 100 μm interdigitated spacing. The sol-gel was prepared by using anhydrous ethanol as a solvent to prepare 0.1 mol / L tin oxide and zinc oxide precursor solutions, with 38% concentrated hydrochloric acid added to each solution. The mixture was stirred for 4 h and aged for 24 h. The tin oxide and zinc oxide precursor solutions were then mixed at a 4:1 ratio to obtain a multi-component oxide sol-gel mixture, which was then drop-coated at a rate of 20 μL / cm² (corresponding to a multi-component sol-gel film thickness of approximately 20 μm). The final fabrication was completed by drying at 70 ℃ for 20 min and then laser direct writing at 0.25 W power and 5 mm / s scanning speed.

[0083] The ammonia sensor prepared in this embodiment has a response value of 590% to 100 ppm ammonia, a response time of 130 s, a detection limit of 0.6 ppm for ammonia, a power consumption of 25 nW, and a mesopore size of 10~50 nm.

[0084] Figure 5 A schematic diagram showing the change in gloss of the sol-gel in the laser direct-writing region according to an embodiment of the present invention is shown.

[0085] like Figure 5 As shown, the surface of the ammonia-sensitive nanoparticle layer 402 formed after laser irradiation is light-colored and has reduced gloss. This phenomenon indicates that the sol-gel was broken up during the laser direct writing process, thus forming tiny particles.

[0086] Figure 6 The SEM image of the sensitive layer in this embodiment is shown. The sol-gel nanoparticle system exhibits polydispersity characteristics, with uniform particle size distribution. Most particles are submicron-sized aggregates of 200-800 nm, and the interior is composed of a large number of nano-sized crystals. The particles are closely arranged to form a continuous sensitive layer.

[0087] Figure 7 The ammonia gas-sensitive response curve at room temperature according to an embodiment of the present invention is shown.

[0088] like Figure 7 As shown in the figure, the horizontal axis represents time, and the vertical axis represents the response amplitude. Under the conditions of ammonia flow rate of 100 ppm, 25 ℃, and 30% humidity, the resistance change of the device before and after ammonia flow is shown in the figure. Figure 7 As shown. When ammonia gas is introduced, the resistance increases, the response time is 130s, and the response value to ammonia gas reaches 590%. When air is introduced, the resistance decreases, and the recovery time is 450s.

[0089] Figure 8The cyclic test curve of 50 ppm ammonia at room temperature according to an embodiment of the present invention is shown.

[0090] like Figure 8 As shown, the horizontal axis represents time and the vertical axis represents the percentage of response. Under the conditions of 25 ℃ and 25% humidity, the ammonia sensor prepared in this embodiment of the invention has a relatively stable response to ammonia.

[0091] Figure 9A The resistivity response curves of the present invention as a function of ammonia concentration are shown. Figure 9B It shows Figure 9A Linear relationship between ammonia concentration and response amplitude.

[0092] like Figure 9A As shown, the horizontal axis represents time, which is the measurement time for a single continuous measurement of different ammonia concentrations. The vertical axis represents resistance. The resistance varies depending on the ammonia concentration; the higher the ammonia concentration, the greater the resistance, which in turn indicates a larger response amplitude.

[0093] according to Figure 9A The ammonia concentration and response amplitude can be obtained as follows: Figure 9B The linear relationship diagram shown is as follows. Figure 9B As shown, the horizontal axis represents the concentration of ammonia, and the vertical axis represents the response amplitude. There is a linear relationship between the ammonia concentration and the response amplitude.

[0094] Figure 10 The comparison of ammonia gas-sensitive response under different humidity levels according to an embodiment of the present invention is shown.

[0095] like Figure 10 As shown, the horizontal axis represents time, and the vertical axis represents resistance. The resistance in response to ammonia varies with different humidity levels; the higher the humidity, the lower the resistance. Furthermore, the ammonia sensor prepared in this embodiment exhibits excellent moisture resistance, displaying significant gas-sensitive response characteristics in environments with relative humidity not exceeding 50%.

[0096] Figure 11 The gas-sensitive response of different gases at 100 ppm at room temperature is shown in the embodiment of the present invention.

[0097] like Figure 11 As shown, the horizontal axis represents gas selectivity, and the vertical axis represents response amplitude. To comprehensively verify the gas selectivity characteristics of the sample, various different gases with consistent concentrations were selected during the experiment, such as ammonia, ethanol, methanol, isopropanol, acetone, and ethylene glycol, and gas-sensitive response tests were conducted. Figure 11The test results shown indicate that the ammonia sensor prepared in this embodiment of the invention can respond to ammonia and ethanol, and the response amplitude to ammonia is significantly greater than that to ethanol. It has almost no response to methanol, isopropanol, acetone and ethylene glycol. The ammonia sensor prepared in this embodiment of the invention exhibits excellent selectivity for ammonia.

[0098] Example 2

[0099] The laser-induced graphene electrode was prepared using a 4 W laser power, a power density of 0.5 kW / cm², a scanning speed of 200 mm / s, and an interdigital spacing of 300 μm. The sol-gel was prepared by using anhydrous ethanol as a solvent to prepare 0.02 mol / L tin oxide precursor and zinc oxide precursor solutions, with 38% concentrated hydrochloric acid added to each solution at a molar ratio of 1:0.1:0.01. The mixture was stirred for 5 h and aged for 24 h. The tin oxide and zinc oxide precursor solutions were then mixed at a 5:1 ratio and coated at a drop volume of 15 μL / cm², forming a thin multi-element sol-gel film of approximately 10 μm in a single coating. Drying conditions were 65 ℃ for 25 min. Laser direct writing was performed using a 0.05 W power and a scanning speed of 100 mm / s, with mesopore sizes of 2-5 nm.

[0100] The ammonia sensor prepared in this embodiment has a response value of 420% to 100 ppm ammonia, a response time of 150 s, and a power consumption of 6 nW.

[0101] Example 3

[0102] The laser-induced graphene electrode was prepared using a 4.8 W laser power, a power density of 3 kW / cm², a scanning speed of 150 mm / s, and an interdigital spacing of 200 μm. The sol-gel was prepared by using anhydrous ethanol as a solvent to prepare 0.2 mol / L tin oxide precursor and zinc oxide precursor solutions, with 25% acetic acid added to each solution at a molar ratio of 1:0.5:0.15. The mixture was stirred for 4.5 h and aged for 26 h. The tin oxide and zinc oxide precursor solutions were then mixed at a 3:1 ratio and coated at a drop volume of 20 μL / cm², forming a 30 μm thick multi-component sol-gel film. Drying conditions were 70 ℃ for 20 min, and laser direct writing was performed using a 0.05 W power and a scanning speed of 150 mm / s.

[0103] The ammonia sensor prepared in this embodiment has a mesopore size of 10-20 nm, a response value of 520% ​​to 100 ppm ammonia, and a detection limit of 0.8 ppm.

[0104] Example 4

[0105] The laser-induced graphene electrode was prepared using an 8 W laser power, a power density of 5 kW / cm², a scanning speed of 200 mm / s, and an interdigital spacing of 100 μm. The sol-gel was prepared by using anhydrous ethanol as a solvent to prepare 0.5 mol / L tin oxide precursor and zinc oxide precursor solutions, with 35% concentrated hydrochloric acid added to each solution at a molar ratio of 1:0.8:0.3 (tin oxide precursor: zinc oxide precursor: sol-gel additive). The mixture was stirred for 6 h and aged for 30 h. The tin oxide and zinc oxide precursor solutions were then mixed at a 4:1 ratio and coated at a drop volume of 25 μL / cm², with three coatings forming a 100 μm thick multi-element sol-gel film. Drying conditions were 75 ℃ for 15 min, and laser direct writing was performed using an 8 W power and a scanning speed of 200 mm / s.

[0106] The ammonia sensor prepared in this embodiment has a mesopore size of 10~50 nm, a response value of 280% to 100 ppm ammonia, and a power consumption of 45 nW.

[0107] Example 5

[0108] The laser-induced graphene electrode was prepared using a 2 W laser power, a power density of 1.25 kW / cm², a scanning speed of 100 mm / s, and an interdigital spacing of 250 μm. The sol-gel was prepared by using deionized water as a solvent to prepare 0.1 mol / L tin oxide precursor and zinc oxide precursor solutions, with 20% acetic acid added to each solution at a molar ratio of 1:0.3:0.05. The mixture was stirred for 4 h and aged for 22 h. The tin oxide and zinc oxide precursor solutions were then mixed in a 5:2 ratio and coated at a drop volume of 10 μL / cm², with repeated coating to form a multi-element sol-gel film of approximately 5 μm. Drying conditions were 68 ℃ for 22 min, and laser direct writing was performed using a 2 W power and a scanning speed of 100 mm / s.

[0109] The ammonia sensor prepared in this embodiment has a mesopore size of 10~50 nm, a response time of 100 s to 100 ppm ammonia, a response value of 250%, and a power consumption of 8 nW.

[0110] Example 6

[0111] The laser-induced graphene electrode was prepared using a 5 W laser power, a power density of 3.125 kW / cm², a scanning speed of 200 mm / s, and an interdigital spacing of 150 μm. The sol-gel was prepared by using anhydrous ethanol as a solvent to prepare 0.3 mol / L tin oxide precursor and zinc oxide precursor solutions, with 30% concentrated hydrochloric acid added to each solution at a molar ratio of 1:0.6:0.2. The mixture was stirred for 5 h and aged for 28 h. The tin oxide and zinc oxide precursor solutions were then mixed in a 3:2 ratio and coated at a drop volume of 22 μL / cm², with four coatings to form an 80 μm thick multi-element sol-gel film. Drying conditions were 80 ℃ for 18 min, and laser direct writing was performed using a 5 W power and a scanning speed of 200 mm / s.

[0112] The ammonia sensor prepared in this embodiment has a mesopore size of 10~50 nm, a response value of 550% to 100 ppm ammonia, a performance retention rate of 78% at 60% humidity, a 28-day attenuation rate of <5%, and a power consumption of 38 nW.

[0113] Figure 12 The gas-sensitive response cycle test curve for 20 ppm ammonia at room temperature is shown according to an embodiment of the present invention.

[0114] like Figure 12 As shown, the horizontal axis represents the number of days, and the vertical axis represents the daily average response amplitude. To verify the performance stability of the sample, a long-term, multi-repetition gas-sensitive cycle test was conducted on the ammonia sensor prepared in this embodiment of the invention. In the data processing, the average response amplitude of the ammonia sensor on each measurement day was first calculated, and then the obtained average values ​​were compared and analyzed. The test results show that the ammonia sensor prepared in this embodiment of the invention has excellent long-term repeatability and stability for ammonia.

[0115] Based on the mesopore size and ammonia response values ​​of Examples 1 to 6, it can be concluded that the mesopore size and ammonia responsiveness are generally positively correlated; that is, the larger the mesopore size, the higher the response value: when the pore size is in the range of 2 to 5 nm, the response value is 420%; when the pore size increases to 10 to 20 nm, the response value increases to 520%; and when the pore size further increases to 10 to 50 nm, the response value rises to 590%. The reason for this phenomenon is that a larger pore size can effectively reduce the diffusion resistance of ammonia. It is worth noting that mesopore size is not the only factor affecting ammonia response performance; process parameters also play a regulatory role. For example, in Example 5, the mesopore size was 10–50 nm, but the ammonia responsivity was only 250%. This may be due to the fact that the thickness of the multi-component sol-gel film was only 5 μm. Furthermore, the 1:0.3:0.05 ratio of tin oxide precursor: zinc oxide precursor: sol-gel agent may also result in the ammonia sensor prepared with this ratio not exhibiting optimal gas-sensing activity for ammonia, making it difficult to provide more active sites. In summary, a mesopore size of 10–50 nm offers better adaptability, ensuring both diffusion efficiency and material structural stability.

[0116] It should be noted that, unless it is explicitly stated that there is a sequential order of execution between different operations, or that there is a sequential order of execution between different operations in terms of technical implementation, the execution order between multiple operations may not be significant, and multiple operations may be executed simultaneously.

[0117] Those skilled in the art will understand that the features described in the various embodiments of the present invention can be combined and / or combined in various ways, even if such combinations or combinations are not explicitly described in the present invention. In particular, the features described in the various embodiments of the present invention can be combined and / or combined in various ways without departing from the spirit and teachings of the present invention. All such combinations and / or combinations fall within the scope of the present invention.

[0118] 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. 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 for preparing a room temperature ammonia sensor based on oxide sol-gel, characterized in that, The method includes: At least two patterned laser-induced graphene electrodes are fabricated in situ on the substrate surface by irradiating the substrate with a laser. A precursor of a multi-metal oxide is dissolved in a target solvent to prepare a multi-metal oxide sol-gel mixture with a target concentration between 0.02 and 0.5 mol / L. The multi-component oxide sol-gel mixture with a target concentration is coated on the region where the at least two laser-induced graphene electrodes are formed, to form a multi-component sol-gel film covering the at least two laser-induced graphene electrodes and the region between the electrodes; The multi-component sol-gel film is irradiated with the laser, and the power of the laser irradiation is adjusted during the irradiation process to transform the multi-component sol-gel film into nanoparticles with ammonia sensitivity, and to make the pore size distribution of the mesoporous structure formed by the nanoparticles covering the laser-induced graphene electrode and the area between the electrodes range from 2 to 50 nm. The target concentration is determined in the following manner: Determine the initial concentration of the multi-component oxide sol-gel mixture, and prepare an initial multi-component oxide sol-gel mixture based on the initial concentration; The initial multi-component oxide sol-gel mixture is coated on the region where the at least two laser-induced graphene electrodes are formed to obtain an initial multi-component sol-gel film; the initial multi-component sol-gel film is converted into nanoparticles using the laser, and the first initial pore size of the mesoporous structure formed by the nanoparticles is detected; When the initial pore size is less than 2 to 50 nm, the initial concentration is increased in increments of 0.02 to 0.5 mol / L according to a predetermined concentration change step. When the initial pore size is higher than 2~50 nm, the initial concentration is reduced in steps of 0.02~0.5 mol / L according to the predetermined concentration change step size; The power density used when irradiating the multi-component sol-gel film with laser is 0.1~5 KW / cm². 2 .

2. The method according to claim 1, characterized in that, The laser irradiation power of the multi-component sol-gel film is between 0.05 and 8 W; during the irradiation of the multi-component sol-gel film using the laser, the laser irradiation power is adjusted in the following manner: Determine the initial irradiation power of the laser irradiation on the multi-component sol-gel film; The multi-element sol-gel film is converted into nanoparticles according to the initial irradiation power, and the second initial pore size of the mesoporous structure formed by the nanoparticles is detected. When the second initial aperture is less than 2 to 50 nm, the initial irradiation power is reduced in predetermined power variation steps between 0.05 and 8 W. When the second initial aperture is higher than the range of 2 to 50 nm, the initial irradiation power is increased in steps of 0.05 to 8 W according to the predetermined power variation step.

3. The method according to claim 2, characterized in that, The scanning speed of the laser irradiation of the multi-element sol-gel film is between 5 and 200 mm / s.

4. The method according to claim 1, characterized in that, The multi-metal oxide includes at least tin oxide and zinc oxide; The step of dissolving the precursor of a multi-metal oxide in a target solvent to prepare a multi-metal oxide sol-gel mixture with a target concentration includes: The tin oxide precursor is added to the target solvent to prepare a tin oxide precursor solution with the target concentration; The zinc oxide precursor is added to the target solvent to prepare a zinc oxide precursor solution with the target concentration; Sol-gel additives were added to the tin oxide precursor solution and the zinc oxide precursor solution respectively, and the mixture was stirred. The tin oxide precursor solution and the zinc oxide precursor solution, after being added to the sol-gel additive and allowed to stand for a predetermined time, are mixed according to a predetermined mixing volume ratio to obtain the multi-element oxide sol-gel mixture.

5. The method according to claim 4, characterized in that, The molar ratio of the tin oxide precursor, the zinc oxide precursor, and the sol-gel aid is 1:(0.1~0.8):(0.01~0.3).

6. The method according to claim 4, characterized in that, The predetermined mixing volume ratio of the tin oxide precursor solution to the zinc oxide precursor solution is (3~5):(1~2).

7. The method according to claim 1, characterized in that, The coating amount of the multi-component oxide sol-gel mixture is 10~25 μL / cm², and the thickness of the multi-component sol-gel film is 1~100 μm.

8. An ammonia sensor prepared by the method according to any one of claims 1 to 7, characterized in that, The ammonia sensor includes: Substrate; At least two laser-induced graphene electrodes are patterned in situ and formed on the surface of the substrate by laser induction. A layer of ammonia-sensitive nanoparticles covers the at least two laser-induced graphene electrodes and the area between the electrodes.

9. The ammonia sensor according to claim 8, characterized in that, The at least two laser-induced graphene electrodes include a graphene positive electrode and a graphene negative electrode; The graphene positive electrode includes a plurality of first comb-shaped structures, and the graphene negative electrode includes a plurality of second comb-shaped structures. The first comb-shaped structures and the second comb-shaped structures are arranged in an alternating pattern, and the distance between the first comb-shaped structures and the second comb-shaped structures is between 50 and 500 μm. The ammonia-sensitive nanoparticle layer completely covers the plurality of first comb-like structures and the plurality of second comb-like structures.

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