Indium-doped tin dioxide nanofiber material, preparation method and application thereof, gas sensor and preparation method and application thereof

Abstract

The invention relates to the technical field of gas detection, and discloses an indium-doped tin dioxide nanofiber material and a preparation method and application thereof, and a gas sensor and a preparation method and application thereof. The indium-doped tin dioxide nanofiber material is of a tubular structure, the surface of the indium-doped tin dioxide nanofiber material is of a porous structure, and pores in the porous structure are micropores and mesopores. The indium-doped tin dioxide nanofiber material has excellent sensing performance on ethylene, and a sensor containing the indium-doped tin dioxide nanofiber material as a gas sensitive material has a high response value and a low detection lower limit on low-concentration ethylene, and is high in detection sensitivity.

Description

Technical Field

[0001] The present invention relates to the technical field of gas detection, and in particular to an indium-doped tin dioxide nanofiber material, a preparation method and application thereof, and a gas sensor, a preparation method and application thereof. Background Art

[0002] Detecting dissolved ethylene in power transformer oil is a key indicator for assessing the insulation condition of equipment and predicting early thermal failures. Traditional detection methods, such as gas chromatography, rely on a complex oil-gas separation process, typically taking more than 50 minutes, requiring bulky equipment, and incurring high maintenance costs. While infrared spectroscopy or electrochemical sensors can achieve rapid detection, they lack sensitivity for low concentrations of ethylene (<10 ppm), with detection limits typically exceeding 5 ppm. This makes it difficult to meet the stringent real-time online monitoring requirements of the power industry standard, "QGDW 10536-2021 - Technical Specifications for Online Monitoring of Dissolved Gases in Transformer Oil."

[0003] In the field of semiconductor gas sensors, tin dioxide (SnO2)-based materials have been widely studied due to their high sensitivity, but pure SnO2 sensors have significant defects: their optimal operating temperature is as high as 300-400°C, resulting in excessive device power consumption (>500mW). Summary of the Invention

[0004] The purpose of the present invention is to overcome the problem of excessively high operating temperature of gas sensors in the prior art, resulting in excessive power consumption of the device. The present invention provides an indium-doped tin dioxide nanofiber material, a preparation method and application thereof, a gas sensor, a preparation method and application thereof. The indium-doped tin dioxide nanofiber material has excellent sensing performance for ethylene. The sensor containing the indium-doped tin dioxide nanofiber material as a gas-sensitive material operates at a lower temperature and not only has a higher response value and a lower detection limit for low-concentration ethylene, but also has a higher detection sensitivity and saves energy.

[0005] To achieve the above objectives, the present invention provides an indium-doped tin dioxide nanofiber material in a first aspect. The indium-doped tin dioxide nanofiber material has a tubular structure and a porous structure on the surface. The pores in the porous structure are micropores and mesopores.

[0006] Preferably, the doping amount of indium in the indium-doped tin dioxide nanofiber material is 0.5-1 at %.

[0007] Preferably, the specific surface area of the indium-doped tin dioxide nanofiber material is 90-100 m 2 / g.

[0008] Preferably, the diameter of the indium-doped tin dioxide nanofiber material is 110-130 nm.

[0009] Preferably, the pores in the porous structure have a diameter of 1 to 50 nm.

[0010] A second aspect of the present invention provides a method for preparing an indium-doped tin dioxide nanofiber material, the method comprising the following steps: mixing indium salt, tin salt, morphology control agent and solvent to obtain spinning solution; electrospinning the spinning solution to obtain a precursor fiber membrane; The precursor fiber membrane is allowed to stand and calcined to obtain indium-doped tin dioxide nanofibers.

[0011] Preferably, the indium salt is calculated as indium element, and the tin salt is calculated as tin element, and the weight ratio of the indium salt to the tin salt is 0.5-2:100.

[0012] Preferably, the usage ratio of the tin salt, the morphology control agent and the solvent is 1 g: 3-8 g: 20-30 mL.

[0013] Preferably, the indium salt is selected from at least one of indium chloride, indium nitrate and indium acetylacetonate.

[0014] Preferably, the tin salt is selected from at least one of tin dichloride, tin acetate and tin tetrachloride.

[0015] Preferably, the morphology control agent is selected from at least one of polyvinyl pyrrolidone, polyethylene oxide and cetyltrimethylammonium bromide.

[0016] Preferably, the solvent is selected from at least one of ethanol, N,N-dimethylformamide and ethylene glycol.

[0017] Preferably, the process of mixing the indium salt, the tin salt, the morphology control agent and the solvent comprises: dissolving the indium salt and the tin salt in the solvent, stirring, and then adding the morphology control agent and mixing.

[0018] Preferably, the mixing conditions include: a temperature of 30-50° C. and a time of 4-6 hours.

[0019] Preferably, the process of electrospinning the spinning solution includes: injecting the spinning solution into an injection pump and squeezing the spinning solution out of a spinneret through a needle to form droplets; then applying an electric field, the droplets form a jet, and the jet is deposited on a receiving plate to form a precursor fiber membrane.

[0020] Preferably, the propulsion flow rate of the syringe pump is 0.5-0.7 mL / h.

[0021] Preferably, the voltage of the applied electric field is 18-22 kV.

[0022] Preferably, the distance between the needle and the receiving plate is 15-20 cm.

[0023] Preferably, the electrospinning time is 5-8 hours.

[0024] Preferably, the standing conditions include: a temperature of 50-70° C. and a time of 8-12 hours.

[0025] Preferably, the calcination process comprises: heating to 500-700° C. at a heating rate of 4-6° C. / min and keeping the temperature for 4-6 hours.

[0026] The third aspect of the present invention provides an indium-doped tin dioxide nanofiber material prepared by the method described above.

[0027] A fourth aspect of the present invention provides a use of the indium-doped tin dioxide nanofiber material as a gas-sensitive material.

[0028] A fifth aspect of the present invention provides a gas sensor, comprising an upper substrate, a lower substrate, and a composite permeable material layer, wherein the upper substrate, the lower substrate, and the composite permeable material layer constitute a three-dimensional structure having an inner cavity, and the composite permeable material layer is located on a side of the three-dimensional structure, and a plurality of interdigital electrodes are provided on each of the upper substrate and the lower substrate, the interdigital electrodes on the upper substrate and the interdigital electrodes on the lower substrate are arranged opposite to each other in the inner cavity, and the interdigital electrodes on the upper substrate and the interdigital electrodes on the lower substrate are staggered in the inner cavity; Each interdigital electrode is coated with a sensitive layer, and the sensitive layer fills the gaps in the inner cavity, wherein the sensitive layer contains the indium-doped tin dioxide nanofiber material mentioned above.

[0029] Preferably, the upper substrate and the lower substrate are both ceramic substrates.

[0030] Preferably, the length and width of the upper substrate and the lower substrate are respectively (2.5-3.5) mm×(2.5-3.5) mm.

[0031] Preferably, the interdigital electrodes are gold interdigital electrodes.

[0032] Preferably, the distance between two adjacent interdigital electrodes is 30-80 μm.

[0033] Preferably, the outer surface of the interdigital electrode has a porous structure, and the diameter of the pores in the porous structure is 80-120 nm.

[0034] Preferably, the composite permeable material layer comprises a polytetrafluoroethylene layer and an aluminum oxide layer from the outside to the inside, the pore size of the polytetrafluoroethylene layer is larger than the pore size of the aluminum oxide layer, and the aluminum oxide layer is close to the inner cavity of the three-dimensional structure.

[0035] Preferably, the pore size of the polytetrafluoroethylene layer is 0.1-0.3 μm, and the pore size of the aluminum oxide layer is 2-10 nm.

[0036] Preferably, the thickness ratio of the polytetrafluoroethylene layer to the aluminum oxide layer is 1:0.01-0.1.

[0037] Preferably, the composite permeable material layer has a thickness of 3-8 mm.

[0038] Preferably, the outer surfaces of the upper substrate and the lower substrate have a ruthenium oxide heating layer, a K-type thermocouple is provided on the ruthenium oxide heating layer, and the ruthenium oxide heating layer and the K-type thermocouple form a closed-loop temperature control module.

[0039] A sixth aspect of the present invention provides a method for preparing the gas sensor described above, the method comprising: Carving a plurality of interdigital electrodes on the upper substrate and the lower substrate respectively, so that the interdigital electrodes on the upper substrate and the interdigital electrodes on the lower substrate are relatively distributed and staggered; Coating a slurry containing the indium-doped tin dioxide nanofiber material described above on the surface of each interdigital electrode, and then curing the slurry into a sensitive layer on the surface of the interdigital electrode by annealing, so that the sensitive layer fills the space between the upper substrate and the lower substrate; The composite permeable material layer is coated on the outside of the sensitive layer, and then the composite permeable material layer and the sensitive layer are compounded by hot pressing.

[0040] Preferably, the method further comprises: before coating the slurry containing indium-doped tin dioxide nanofiber material on the surface of each interdigital electrode, forming a pore structure on the outer surface of the interdigital electrode by plasma treatment.

[0041] Preferably, the method further comprises: screen printing a ruthenium oxide heating layer on the outer surfaces of the upper substrate and the lower substrate, and installing a K-type thermocouple on the ruthenium oxide heating layer.

[0042] Preferably, the preparation process of the slurry containing the indium-doped tin dioxide nanofiber material comprises: mixing the indium-doped tin dioxide nanofiber material with anhydrous ethanol by ball milling.

[0043] Preferably, the mass ratio of the indium-doped tin dioxide nanofiber material to anhydrous ethanol is 1:3-8.

[0044] Preferably, the annealing conditions include: a temperature of 300-500° C. and a time of 2-5 hours.

[0045] A seventh aspect of the present invention provides an application of the aforementioned gas sensor in detecting ethylene.

[0046] Compared with the prior art, the present invention has at least the following beneficial effects: (1) Lowering the operating temperature: The indium-doped tin dioxide nanofiber material provided by the present invention has excellent gas-sensing performance to ethylene dissolved in power transformer oil at a relatively low operating temperature because the tin dioxide is doped with indium and is a nanofiber material. The gas sensor using the material as a gas-sensitive material can operate at a low temperature of 200°C, which not only saves energy but also prevents material aging.

[0047] The reasons why the indium-doped tin dioxide nanofiber material provided by the present invention can have excellent gas-sensing performance at a lower operating temperature mainly include the following aspects: First, from the perspective of micromorphology, the grains of indium-doped tin dioxide nanofibers are smaller, and the small size effect is obvious, which increases the specific surface area of the material, making the contact area between the target gas and the gas-sensitive material larger, and making the redox reaction easier to proceed; Secondly, indium-doped tin dioxide nanofibers exhibit a microscopically porous structure with pores distributed across the surface. According to gas diffusion theory, this microstructure accelerates the diffusion of test gases, facilitates the adsorption of gas molecules on the material surface, and promotes interaction between the material and gas molecules, thereby effectively improving gas sensing performance. Thirdly, from the perspective of oxygen vacancies, compared with pure tin dioxide nanofibers, indium-doped tin dioxide nanofibers have more oxygen vacancies (the addition of In causes lattice defects, destroying the original lattice structure), which will produce more chemically adsorbed oxygen when air comes into contact with the material (oxygen vacancies attract oxygen molecules in the air, forming active oxygen groups that adsorb on the surface of the material). Oxygen vacancies have higher chemical reactivity and stronger oxidizing ability. This is because they can serve as storage and release sites for oxygen atoms, enhancing the material's oxygen storage and release capacity (mainly the redox reaction between active oxygen groups and the target gas (ethylene) to produce electron interaction, which is the principle of gas-sensitive response), thereby effectively promoting the interaction between gas-sensitive materials and gas molecules.

[0048] Fourthly, oxygen vacancies can provide unpaired electrons, thereby enhancing catalytic activity.

[0049] Due to the above four reasons, the indium-doped tin dioxide nanofiber material provided by the present invention is used as a gas-sensitive material, which does not require high temperature to provide the energy required for reaction and activation, and can achieve optimal gas-sensitive performance at low temperature.

[0050] (2) Improved sensitivity: The surface of the indium-doped tin dioxide nanofiber material provided by the present invention has a porous structure and a large specific surface area, thereby increasing the effective contact area of the material. Applying it to a gas sensor can improve the response value of the gas sensor to low-concentration ethylene, reduce the detection limit, and improve the detection sensitivity.

[0051] Preferably, when the surface of the material has a porous structure, the surface oxygen vacancy concentration is high and the indium doping amount is within a specific range, the response value of the gas sensor using this material as the sensitive material to low concentration ethylene (for example, 5ppm) can be increased to 4.8, which is 220% higher than that of traditional SnO2-based sensors. The detection limit can be as low as 100ppb, which can accurately capture trace amounts of ethylene generated by early failures.

[0052] (3) Reducing the volume of the sensor: The entire preparation process of the gas sensor of the present invention is compatible with MEMS manufacturing technology. After the indium-doped tin dioxide nanofiber material forms a sensitive layer in the sensor, the thickness of the sensitive layer can be controlled within 10 μm. Therefore, the volume of the gas sensor prepared can be reduced by 60% compared with the traditional sensor. It can be directly integrated into the transformer oil circuit system to realize in-situ online monitoring.

[0053] (4) Improved stability: The gas sensor provided by the present invention has a response attenuation rate of <5% after continuous operation for 1000 hours at low operating temperature, and has high stability, meeting the reliability requirement of five-year maintenance-free substation equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 It is a structural schematic diagram of the gas sensor provided by the present invention.

[0055] Figure 2 It is a schematic structural diagram of the composite permeable material layer provided by the present invention.

[0056] Figure 3 It is a working schematic diagram of the composite permeable material layer provided by the present invention.

[0057] Figure 4 These are SEM images of tin dioxide nanofiber materials with different indium doping amounts prepared in Examples 1-3 and Comparative Example 1.

[0058] Figure 5 TEM images of the nanofiber materials prepared in Example 1 and Comparative Example 1.

[0059] Figure 6 HRTEM images of the nanofiber materials prepared in Example 1 and Comparative Example 1.

[0060] Figure 7 3 and 4 are XRD patterns of tin dioxide nanofiber materials with different indium doping amounts prepared in Examples 1-3 and Comparative Example 1.

[0061] Figure 8 This is the XPS graph of the 8at% indium-doped tin dioxide nanofiber material prepared in Example 1.

[0062] Figure 9 It is a gas-sensing performance test chart of the gas sensors prepared in Examples 4-6 and Comparative Example 2.

[0063] Description of Reference Numerals 1 Upper substrate; 2 Lower substrate; 3 Composite permeable material layer; 4 Interdigitated electrodes; 5 Sensitive layer; 31 Polytetrafluoroethylene layer; 32 Alumina layer. DETAILED DESCRIPTION

[0064] The following describes the specific embodiments of the present invention in detail with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention and are not intended to limit the present invention.

[0065] The endpoints of the ranges and any values disclosed herein are not limited to the precise ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0066] In addition to the high optimal operating temperature of existing gas sensors, which leads to excessive device power consumption, long-term high-temperature operation can easily cause material aging. In addition, existing gas sensors also have a traditional planar electrode structure design, which means that the effective reaction area only accounts for 35-40% of the substrate surface, resulting in low utilization rate. It is relatively difficult for gas to contact the effective sensing area, which seriously restricts the improvement of sensitivity.

[0067] To meet the demand for precise detection of dissolved gases, particularly dissolved ethylene, in transformer oil, this invention combines a specific indium-doped tin dioxide (In-SnO2) nanofiber material with a novel sensor structure to develop a highly sensitive, stable, compact, and low-temperature gas sensor. A key element of this technology lies in optimizing the gas-sensing material and its preparation process, leveraging the inherent advantages of the nanofiber material: its large surface area, which increases the contact area between the target gas and the gas-sensing material and facilitates redox reactions.

[0068] As previously mentioned, the surface of the indium-doped tin dioxide nanofiber material provided by the present invention has a porous structure and a tubular structure. Due to the presence of the porous structure, the specific surface area of the indium-doped tin dioxide nanofiber material is greatly increased, so that the effective contact area between the material and the target gas is greatly increased. Using it as a sensitive material in a gas sensor can improve the response value of the gas sensor to low-concentration ethylene, reduce the detection limit, and improve the detection sensitivity of the target gas. In addition, doping indium into tin dioxide and forming a nanofiber material can refine the grains, with a significant small size effect, and also increase the specific surface area of the material, so that the contact area between the target gas and the gas-sensitive material is larger, and the redox reaction is easier to proceed; and In-doped SnO2 nanofibers have more oxygen vacancies, so that more chemically adsorbed oxygen is generated when air comes into contact with the material. Since oxygen vacancies can serve as storage and release sites for oxygen atoms, enhancing the material's oxygen storage and release capacity, oxygen vacancies have higher chemical reactivity and stronger oxidation ability, thereby effectively promoting the interaction between gas-sensitive materials and gas molecules. This allows indium-doped tin dioxide nanofiber materials to be used as gas-sensitive materials. This material does not require high temperatures to provide the energy required for reaction and activation, and can achieve optimal gas-sensing performance at low temperatures.

[0069] In some embodiments, the specific surface area of the indium-doped tin dioxide nanofiber material can be 90-100 m 2 / g. Specifically, when the specific surface area of the nanofiber material is too large, it means that the material has too many defects and vacancies, which, on the one hand, leads to instability of the material structure and affects the reliability of the detection results. On the other hand, the response recovery time will be prolonged. Among them, the response recovery time refers to the need to purge the material after one test is completed to blow away the gas to be tested so that the material response value returns to the standard value before the next test can be carried out. If the specific surface area of the nanofiber material is too large, the gas to be tested will be adsorbed and stuck in the material, which is not conducive to purge; when the specific surface area of the nanofiber material is too small, the effective contact area between the material and the target gas is too small, resulting in a decrease in detection sensitivity. Therefore, when the specific surface area of the nanofiber material is within this range, the detection sensitivity of the gas sensor can be further improved while ensuring the accuracy of the detection results.

[0070] In the present invention, the indium-doped tin dioxide nanofiber material has a high surface oxygen vacancy concentration, which is 3.2 times higher than that of pure SnO2. A higher surface oxygen vacancy concentration increases the availability of oxygen-active groups, making it easier for target gases to react with these groups, causing changes in the material's resistance and generating a gas-sensitive response.

[0071] In some preferred embodiments, the indium doping level in the indium-doped tin dioxide nanofiber material is 0.5-1 at%, preferably 0.7-0.9 at%, where at% represents atomic percentage, representing the percentage of atoms of a particular element relative to the total atomic number of the material. When this material has a porous surface structure, a high surface oxygen vacancy concentration, and the indium doping level is within this range, it exhibits excellent gas-sensing properties. A gas sensor using this material as a sensitive material can achieve a response value of 4.8 to low concentrations of ethylene (e.g., 5 ppm), a 220% improvement over conventional SnO2-based sensors. The detection limit can be as low as 100 ppb, enabling accurate capture of trace amounts of ethylene generated by early-stage failures.

[0072] Furthermore, the porous structure on the surface of the indium-doped tin dioxide nanofiber material can be a three-dimensional interconnected through-pore structure, and the pores in the porous structure are micropores and mesopores. In some embodiments, the pores in the porous structure have a pore size of 1 to 50 nm.

[0073] Preferably, the diameter of the indium-doped tin dioxide nanofiber material can be 110-130 nm. When the diameter of the nanofiber material is within this range, it can ensure that it has a larger specific surface area and improve the gas sensing performance.

[0074] Experiments have shown that a sensor using the indium-doped tin dioxide nanofiber material described herein as the sensitive material exhibits a response value (Ra / Rg) of 4.8 to 5 ppm ethylene at an operating temperature of 200°C. Even when exposed to 100 ppb ethylene gas, the sensor maintains a significant response, with a response time of 80 seconds. Using electrospinning technology, the inventors successfully produced indium-doped tin dioxide nanofibers with a porous surface structure, a high concentration of surface oxygen vacancies, and an appropriate indium doping level.

[0075] Specifically, the method for preparing indium-doped tin dioxide nanofiber material comprises the following steps: mixing indium salt, tin salt, morphology control agent and solvent to obtain spinning solution; electrospinning the spinning solution to obtain a precursor fiber membrane; The precursor fiber membrane is allowed to stand and calcined to obtain indium-doped tin dioxide nanofibers.

[0076] In the present invention, the dosage ratio of the indium salt and the tin salt needs to be controlled within an appropriate range. In some preferred embodiments, the weight ratio of the indium salt to the tin salt is 0.5~1:100, wherein the indium salt is calculated as indium element and the tin salt is calculated as tin element, that is, the weight ratio of the indium element in the indium salt to the tin element in the tin salt is 0.5~1:100. When the weight ratio of the indium salt to the tin salt is greater than this range, the indium doping in the material is excessive, resulting in the failure of the indium quantum dot effect, and the obtained material becomes an ordinary mixture of the two materials of indium salt and tin salt, and the gas-sensing effect is greatly reduced; when the weight ratio of the indium salt to the tin salt is less than this range, the indium doping in the material is too little, resulting in insufficient introduction of oxygen vacancy defects in the material and insufficient gas-sensing effect.

[0077] In some embodiments, the indium salt, the morphology-controlling agent, and the solvent can be used in a ratio of 1 g: 3-8 g: 20-30 mL. Controlling the ratio of the indium salt, the morphology-controlling agent, and the solvent within this range can produce a nanofiber material with an optimal morphology, sufficient oxygen vacancies, and optimal gas-sensing performance.

[0078] In the method described in the present invention, the indium salt, the tin salt, the morphology control agent and the solvent can all be conventionally selected in the art, as long as the purpose of the present invention can be achieved.

[0079] In some embodiments, the indium salt is selected from at least one of indium chloride (InCl3), indium nitrate (In(NO3)3), and indium acetylacetonate (In(acac)3), preferably indium chloride. The indium chloride and indium nitrate may be in the form of crystalline hydrates, for example, indium chloride is InCl3·4H2O, and indium nitrate is In(NO3)3·xH2O.

[0080] In some embodiments, the tin salt is selected from at least one of tin dichloride (SnCl2), tin acetate Sn(CH3COO)4 and tin tetrachloride (SnCl4), preferably tin dichloride; wherein the tin salt can be in the form of a crystalline hydrate, for example, tin dichloride is SnCl2·2H2O.

[0081] In some embodiments, the morphology control agent is selected from at least one of polyvinyl pyrrolidone (PVP), polyethylene oxide (PEO) and cetyltrimethylammonium bromide (CTAB), preferably polyvinyl pyrrolidone.

[0082] In some embodiments, the solvent is selected from at least one of ethanol, N,N-dimethylformamide, and ethylene glycol. Preferably, the solvent is a mixture of ethanol and N,N-dimethylformamide, and the volume ratio of ethanol to N,N-dimethylformamide can be 1:1.

[0083] In the present invention, the process of mixing the indium salt, tin salt, morphology control agent, and solvent is not particularly limited, as long as these components can be mixed uniformly. In order to improve the uniformity of the mixing of the indium salt, tin salt, morphology control agent, and solvent and obtain a uniform spinning solution, in a preferred embodiment, the process of mixing the indium salt, tin salt, morphology control agent, and solvent includes: dissolving the indium salt and tin salt in the solvent, stirring, and then adding the morphology control agent to mix.

[0084] In some preferred embodiments, the mixing conditions include: a temperature of 30-50° C. and a time of 4-6 hours. Controlling the mixing conditions within this range can further improve the uniformity of the spinning solution.

[0085] In the present invention, the electrospinning process can be performed according to conventional procedures in the art. In one embodiment, the electrospinning process of the spinning solution includes: injecting the spinning solution into a syringe pump and extruding the spinning solution through a needle through a spinneret to form droplets; then applying an electric field, causing the droplets to form a jet, which is deposited on a receiving plate to form a precursor fiber film. Typically, the syringe pump used for electrospinning is equipped with a needle, such as a 22-gauge stainless steel needle.

[0086] In some preferred embodiments, the injection pump can have a propulsion flow rate of 0.5-0.7 mL / h. If the injection pump propulsion flow rate is too high, it may lead to jet breakage, uneven fiber diameters, and insufficient solvent volatilization. If the injection pump propulsion flow rate is too low, it may lead to jet discontinuity and fiber breakage.

[0087] In some preferred embodiments, the applied electric field voltage can be 18-22 kV. Furthermore, the electric field is applied in a closed humidity-controlled chamber (relative humidity <30%). Furthermore, the distance between the needle and the receiving plate can be 15-20 cm.

[0088] In the present invention, the electrospinning time can be determined according to the amount of product to be prepared. In some embodiments, the electrospinning time can be 5-8 hours. It should be noted that the electrospinning time here refers to the time used for the entire electrospinning process.

[0089] In order to make the obtained precursor fiber membrane more stable, the precursor fiber membrane can be allowed to stand before calcination. In order to further improve the stability of the precursor fiber membrane, in some preferred embodiments, the standing conditions include: a temperature of 50-70°C and a time of 8-12 hours.

[0090] In the present invention, the purpose of calcination is to form a porous structure and surface oxygen vacancies in the material. To increase the specific surface area and surface oxygen vacancies, the present invention utilizes a suitable gradient temperature calcination process to prepare indium-doped tin dioxide nanofiber materials. In some preferred embodiments, the calcination process includes heating to 500-700°C at a heating rate of 4-6°C / min and holding the temperature for 4-6 hours. Furthermore, the resulting material after calcination is a powder.

[0091] Furthermore, the present invention also provides an indium-doped tin dioxide nanofiber material prepared by the method described above.

[0092] In some preferred embodiments, the indium-doped tin dioxide nanofiber material has a tubular structure and a porous structure on the surface, and the pores in the porous structure are micropores and mesopores.

[0093] In some preferred embodiments, the doping amount of indium in the indium-doped tin dioxide nanofiber material is 0.5-1 at %.

[0094] In some preferred embodiments, the specific surface area of the indium-doped tin dioxide nanofiber material is 90-100 m 2 / g.

[0095] In some preferred embodiments, the diameter of the indium-doped tin dioxide nanofiber material is 110-130 nm.

[0096] In some preferred embodiments, the pores in the porous structure have a pore diameter of 1 to 50 nm.

[0097] The present invention also provides a use of the indium-doped tin dioxide nanofiber material as a gas-sensitive material.

[0098] Since the indium-doped tin dioxide nanofiber material has a porous structure, a high surface oxygen vacancy concentration, and is doped with an appropriate amount of indium, it has excellent gas-sensing properties to gases, especially ethylene.

[0099] Furthermore, the present invention also provides a gas sensor containing the aforementioned indium-doped tin dioxide nanofiber material. Figure 1As shown, the gas sensor includes an upper substrate 1, a lower substrate 2, and a composite permeable material layer 3. The upper substrate 1, the lower substrate 2, and the composite permeable material layer 3 form a three-dimensional structure with an inner cavity, with the composite permeable material layer 3 located on the side of the three-dimensional structure. Multiple interdigital electrodes 4 are provided on each of the upper and lower substrates 1 and 2. The interdigital electrodes 4 on the upper and lower substrates 2 are arranged opposite each other within the inner cavity, and the interdigital electrodes 4 on the upper and lower substrates 1 and 2 are staggered within the inner cavity. Each interdigital electrode 4 is coated with a sensitive layer 5, which fills the gaps within the inner cavity. The sensitive layer 5 contains the indium-doped tin dioxide nanofiber material described above. A gas sensor with this structure is not only compact but also increases the contact area between the gas-sensitive material and the dissolved gas in the oil, and improves the transmission efficiency of carriers (electrons) in the gas-sensitive material.

[0100] It needs to be further explained that the gas sensor provided by the present invention is a three-dimensional structure, with the top and bottom being the upper substrate 1 and the lower substrate 2 respectively, and the lower part of the upper substrate 1 and the upper part of the lower substrate 2 both having a plurality of interdigitated electrodes 4 (i.e., an interdigitated electrode array), and there is a certain gap between two adjacent interdigitated electrodes 4 on the upper substrate 1 and two adjacent interdigitated electrodes on the lower substrate 2; the interdigitated electrodes 4 on the upper substrate 1 face downward, and the interdigitated electrodes 4 on the lower substrate 2 face upward, and are arranged in an alternating manner; a sensitive layer 5 of a certain thickness is provided on the outer surface of each interdigitated electrode 4 to fill the space between the upper substrate 1 and the lower substrate 2, and the composite permeable material layer 3 is located outside the sensitive layer 5, that is, located on the four sides of the front, back, left and right of the three-dimensional structure.

[0101] Generally, the upper substrate 1 and the lower substrate 2 can be conventionally selected in the art, as long as they have a flat surface, stable chemical properties, and high physical strength. In a preferred embodiment, the upper substrate 1 and the lower substrate 2 are both ceramic substrates, which not only have a flat surface, stable chemical properties, high physical strength, but also are low in cost.

[0102] In the present invention, the dimensions of the upper substrate 1 and the lower substrate 2 can be determined based on actual needs. Generally, the upper substrate 1 and the lower substrate 2 are thin plates, and their thickness is not significant. Their dimensions typically consist of length and width. In one embodiment, the length and width of the upper substrate 1 and the length and width of the lower substrate 2 are each independently (2.5-3.5) mm × (2.5-3.5) mm, preferably 3 mm × 3 mm.

[0103] The interdigitated electrodes referred to in the present invention are those conventionally understood by those skilled in the art. In the present invention, compared to other electrodes, the use of interdigitated electrodes can transform a planar sensor into a three-dimensional sensor, significantly increasing the contact area between the target gas and the gas-sensitive material. Furthermore, it is easier to arrange more electrode rods in a three-dimensional space, facilitating carrier transmission. In a preferred embodiment, the interdigitated electrodes 4 can be gold, which can improve conductivity and stability.

[0104] By combining the three-dimensional interdigitated electrodes with indium-doped tin dioxide nanofiber materials with a porous surface structure, the effective contact area of the indium-doped tin dioxide nanofiber materials can be expanded 2.8 times compared to conventional sensors, the signal transmission efficiency can be increased 6.5 times, and the response time can be shortened to 80 seconds, fully meeting the real-time monitoring needs on site.

[0105] In some preferred embodiments, the spacing between two adjacent interdigital electrodes 4 is 30-80 μm. If the spacing between two adjacent interdigital electrodes 4 is too large, the carrier migration path in the gas-sensitive material will be lengthened, reducing the gas-sensitive response value; if the spacing between two adjacent interdigital electrodes 4 is too small, there is a risk of accidental contact between the interdigital electrodes 4 on the upper substrate 1 and the lower substrate 2, causing sensor failure.

[0106] Preferably, the outer surface of the interdigital electrodes 4 has a porous structure, and the pores in the porous structure may have a diameter of 80-120 nm, thereby increasing the contact area between the gas-sensitive material in the sensitive layer 5 and the interdigital electrodes 4, thereby improving the sensitivity of the sensor.

[0107] In the present invention, there is no particular limitation on the thickness of the sensitive layer 5 covering the interdigital electrodes 4 , as long as it can fill the internal space of the sensor. In actual operation, the thickness of the sensitive layer 5 is determined by the size of the sensor and the spacing between the interdigital electrodes 4 .

[0108] The composite permeable material layer 3 adopts gradient densification permeable membrane technology, such as Figure 2 As shown, the composite permeable material layer 3 includes a polytetrafluoroethylene layer 31 and an aluminum oxide layer 32 from the outside to the inside. The pore size of the polytetrafluoroethylene layer 31 is larger than that of the aluminum oxide layer 32 and is close to the inner cavity side of the three-dimensional structure. Figure 3 As shown, the large-pore polytetrafluoroethylene layer 31 can block the colloidal particles in the oil, and the small-pore alumina layer 32 can selectively pass ethylene molecules, achieving an ethylene molecule permeability of more than 95%, while completely blocking oil-phase pollutants, making the C2H4 / C2H2 selectivity ratio reach 12:1, and significantly improving the anti-interference ability.

[0109] In a preferred embodiment, the pore size of the polytetrafluoroethylene layer 31 is 0.1-0.3 μm, and the pore size of the aluminum oxide layer 32 is 2-10 nm. Limiting the pore size of the polytetrafluoroethylene layer 31 and the pore size of the aluminum oxide layer 32 to this range can further improve the selectivity of ethylene.

[0110] In some embodiments, the composite permeable material layer 3 has a thickness of 3-8 mm. Furthermore, the thickness ratio of the polytetrafluoroethylene layer 31 to the alumina layer 32 can be 1:0.01-0.1. Controlling the thickness of the composite permeable material layer 3, as well as the thickness of the polytetrafluoroethylene layer 31 and the alumina layer 32 within this range ensures efficient oil filtration by the polytetrafluoroethylene layer and selective ethylene filtration by the alumina layer 32, while minimizing the power loss of ethylene permeating the membrane.

[0111] Furthermore, the outer surfaces of the upper substrate 1 and the lower substrate 2 have a ruthenium oxide heating layer, and a K-type thermocouple is provided on the ruthenium oxide heating layer. The ruthenium oxide heating layer and the K-type thermocouple constitute a closed-loop temperature control module, and the PID algorithm is used to stabilize the operating temperature at 200±1°C, thus obtaining an assembled sensor. Thereafter, the sensor is aged for 48 hours in a dry air environment containing 5% C2H4 to improve stability before being put into use.

[0112] The gas sensor provided by the present invention has a response value (Ra / Rg) of 4.8 to 5ppm ethylene at an operating temperature of 200°C. Even when exposed to 100ppb ethylene gas, the sensor still has a significant response with a response time of 80s. The selectivity ratio for C2H4 / C2H2 can be increased to 12:1. After 1000 hours of continuous operation in an oil phase environment, the response attenuation rate is <5%, fully meeting the reliability requirements of five-year maintenance-free for power equipment.

[0113] In order to further explain the aforementioned gas sensor, the present invention also provides a method for preparing the aforementioned gas sensor, the method comprising: A plurality of interdigital electrodes 4 are respectively engraved on the upper substrate 1 and the lower substrate 2, so that the interdigital electrodes 4 on the upper substrate 1 and the interdigital electrodes 4 on the lower substrate 2 are distributed relative to each other, and the interdigital electrodes 4 on the upper substrate 1 and the interdigital electrodes 4 on the lower substrate 2 are staggered; A slurry containing the aforementioned indium-doped tin dioxide nanofiber material is coated on the surface of each interdigital electrode 4, and then the slurry is solidified into a sensitive layer 5 on the surface of the interdigital electrode 4 by annealing, so that the sensitive layer 5 fills the space between the upper substrate 1 and the lower substrate 2; The composite permeable material layer 3 is coated on the outside of the sensitive layer 5, and then the composite permeable material layer 3 and the sensitive layer 5 are firmly compounded by hot pressing.

[0114] In the present invention, preferably, the interdigital electrodes 4 are respectively etched on the upper substrate 1 and the lower substrate 2 by a photolithography process, wherein the photolithography process can be performed according to conventional operations in the art. Specifically, the operation process of the photolithography process includes: (1) Substrate pretreatment: The ceramic substrate was ultrasonically cleaned with acetone and isopropyl alcohol for 10 minutes to remove organic pollutants, then dried with nitrogen and baked at 120°C for dehydration; (2) Coating photoresist (spin coating negative photoresist, such as SU-8 2000 series). The specific process includes: low speed coating for 5 seconds → high speed coating at 3000 rpm for 30 seconds → soft baking (95°C, 3 minutes). The thickness of the coating is about 1.5 μm. (3) Mask exposure: Use a chromium mask (50 μm interdigital gap pattern) close to the substrate, 365 nm UV exposure (energy 100 mJ / cm²) → post-bake (65 ° C / 1 minute + 95 ° C / 2 minutes) to promote crosslinking; (4) Development and etching: Soak in a special developer (SU-8 Developer) for 60 seconds → rinse with deionized water → ion beam etching (Ar⁺, 200eV) to expose the gold layer → electroplating to thicken the gold electrode to 300nm; (5) Degumming and cleaning: Oxygen plasma ashing for 10 minutes to remove the residual glue layer → secondary cleaning to ensure the cleanliness of the electrode surface.

[0115] In a preferred embodiment, the preparation process of the slurry containing indium-doped tin dioxide nanofiber material includes: mixing the indium-doped tin dioxide nanofiber material with anhydrous ethanol by ball milling; adopting this preparation process can improve the uniformity of the slurry.

[0116] Furthermore, the mass ratio of the indium-doped tin dioxide nanofiber material to anhydrous ethanol can be 1:3-8, preferably 1:5.

[0117] In the present invention, preferably, a micro-dispensing process can be used to apply a slurry containing indium-doped tin dioxide nanofiber material to the surface of each interdigital electrode 4, wherein the micro-dispensing process can be performed according to conventional operations in the art. Specifically, the operation process of the micro-dispensing process includes: Step S1, slurry preparation: Indium-doped tin dioxide nanofibers and anhydrous ethanol were ball-milled at a mass ratio of 1:5 (300 rpm, 2 hours) → sieved (400 mesh) to remove agglomerates, and the viscosity was controlled at 800-1200 cP; Step S2, dispensing parameter setting: Equipment: Piezoelectric micro-dispenser (such as Nordson EFD Ultra); Needle: 150μm inner diameter tapered needle; Parameters: Air pressure 0.2 Bar → Dispensing speed 5 mm / s → Single dispensing volume 3 nL (accuracy ±0.1 nL); Step S3, positioning coating: the visual positioning system calibrates the position of the interdigitated electrodes → continuously dispenses glue along the electrode direction (with a spacing of 100 μm) → covers the entire electrode surface and gaps; Step S3, annealing and curing (step heating process): Room temperature → 100℃ (30 minutes) to remove solvent → 100 → 400℃ (2℃ / min) → keep at 400℃ for 3 hours → cool naturally to form a sensitive layer.

[0118] In order to increase the contact area between the gas-sensitive material in the sensitive layer 5 and the interdigital electrodes 4, and thereby improve the sensitivity of the sensor, the method further includes: before coating the surface of each interdigital electrode 4 with a slurry containing indium-doped tin dioxide nanofiber material, forming a porous structure on the outer surface of the interdigital electrode 4 through plasma treatment.

[0119] In the present invention, the method for coating the composite permeable material layer 3 on the sensitive layer 5 is not limited. For example, the composite permeable material layer 3 can be coated on the sensitive layer 5 using a vapor deposition method. Specifically, the process of coating the composite permeable material layer 3 on the sensitive layer 5 using a vapor deposition method includes: ① placing a polytetrafluoroethylene / alumina composite membrane in the target position of a vacuum chamber; ② securing the substrate to a rotating support (rotating speed of 5 rpm); ③ sputtering: Ar⁺ ion bombardment (power of 300 W), film deposition rate of 0.5 nm / s; ④ endpoint control: stopping when the film thickness reaches 15 μm on the film thickness monitor. The composite permeable material layer 3 is a pre-prepared composite permeable membrane.

[0120] In order to make the indium-doped tin dioxide nanofiber material slurry bond more tightly to the substrate, in a preferred embodiment, the annealing conditions include: a temperature of 300-500° C. and a time of 2-5 hours.

[0121] In order to prepare a complete gas sensor, the method also includes: screen-printing a ruthenium oxide heating layer on the outer surfaces of the upper substrate 1 and the lower substrate 2, and installing a K-type thermocouple on the ruthenium oxide heating layer to construct a closed-loop temperature control module; using a PID algorithm to stabilize the operating temperature at 200±1°C. After the sensor is assembled, it is aged in a dry air environment containing 5% C2H4 for 48 hours to improve stability.

[0122] The present invention also provides an application of the aforementioned gas sensor for ethylene detection. When the gas sensor provided by the present invention is used for ethylene detection, the sensor achieves a response value (Ra / Rg) of 4.8 to 5 ppm ethylene at a low operating temperature (200°C). Even when exposed to 100 ppb ethylene gas, the sensor maintains a significant response with a response time of 80 seconds. The selectivity for C2H4 / C2H2 can be increased to 12:1. After 1000 hours of continuous operation in an oil-phase environment, the response decay rate is less than 5%, fully meeting the five-year maintenance-free reliability requirements for power equipment. This demonstrates the advantages of the gas sensor provided by the present invention, including low operating temperature, high detection sensitivity, high selectivity for ethylene, and high stability.

[0123] The present invention will be described in detail below through examples, but the scope of protection of the present invention is not limited thereto. In the following examples, unless otherwise specified, the methods used are conventional methods; and the raw materials used are common commercial products.

[0124] Examples 1 to 3 are used to illustrate the preparation process of indium-doped tin dioxide nanofiber materials.

[0125] Example 1 The preparation method of indium-doped tin dioxide nanofiber material comprises: (1) 0.8 g of SnCl2·2H2O (tin salt) and 0.012 g of InCl3·4H2O (indium salt) were dissolved in a mixed solvent consisting of 10 mL of ethanol and 10 mL of DMF (N,N-dimethylformamide). After stirring until completely dissolved, 4 g of polyvinylpyrrolidone (PVP) was added and stirred at 40°C for 5 hours to form a uniform spinning solution. The weight ratio of indium in the indium salt to tin in the tin salt was 1.1:100.

[0126] (2) The spinning solution was injected into a syringe pump equipped with a 22-gauge stainless steel needle and squeezed out of the spinneret through the needle to form droplets. The propulsion flow rate of the syringe pump was set to 0.6 mL / h. Then, a 20 kV high voltage electric field was applied in a closed humidity control room (relative humidity < 30%). The droplets formed a jet, which was deposited on the receiving plate to form a precursor fiber membrane. The distance between the needle and the receiving plate was 18 cm, and the spinning was continued for 6 hours. (3) The precursor fiber membrane was placed in a 60°C oven for 10 h and then transferred to a muffle furnace. The temperature was raised to 600°C at a rate of 5°C / min and kept at this temperature for 5 h to obtain an indium-doped tin dioxide nanofiber material, wherein the indium doping amount was 0.8 at%.

[0127] Example 2 Indium-doped tin dioxide nanofiber material was prepared according to the method of Example 1, except that the amounts of tin salt and indium salt used were different from those in Example 1.

[0128] Specifically, in step (1), 0.8 g SnCl2·2H2O (tin salt) and 0.0075 g InCl3·4H2O (indium salt) are dissolved in a mixed solvent, and the indium doping amount of the finally obtained indium-doped tin dioxide nanofiber material is 0.5 at%.

[0129] Example 3 Indium-doped tin dioxide nanofiber material was prepared according to the method of Example 1, except that the amounts of tin salt and indium salt used were different from those in Example 1.

[0130] Specifically, in step (1), 0.8 g SnCl2·2H2O (tin salt) and 0.015 g InCl3·4H2O (indium salt) are dissolved in a mixed solvent, and the indium doping amount of the finally obtained indium-doped tin dioxide nanofiber material is 1 at%.

[0131] Comparative Example 1 The method of Example 1 was followed, except that no indium salt was added in step (1), that is, the indium doping amount was 0 at %.

[0132] The specific operation process includes: (1) Dissolve 0.8 g of SnCl2·2H2O (tin salt) in a mixed solvent consisting of 10 mL of ethanol and 10 mL of DMF (N,N-dimethylformamide). Stir until completely dissolved, then add 4 g of polyvinylpyrrolidone (PVP). Stir continuously at 40 °C for 5 h to form a uniform spinning solution.

[0133] (2) The spinning solution was injected into a syringe pump equipped with a 22-gauge stainless steel needle and squeezed out of the spinneret through the needle to form droplets. The propulsion flow rate of the syringe pump was set to 0.6 mL / h. Then, a 20 kV high voltage electric field was applied in a closed humidity control room (relative humidity < 30%). The droplets formed a jet, which was deposited on the receiving plate to form a precursor fiber membrane. The distance between the needle and the receiving plate was 18 cm, and the spinning was continued for 6 hours. (3) The precursor fiber membrane was placed in a 60°C oven for 10 h and then transferred to a muffle furnace, heated to 600°C at a rate of 5°C / min and kept at this temperature for 5 h.

[0134] Test Example 1 Figure 4 These are SEM images of tin dioxide nanofiber materials with different indium doping amounts prepared in Examples 1-3 and Comparative Example 1. Figure 4 (a)-(d) are respectively 0 at% indium doping amount (Comparative Example 1), 0.5 at% indium doping amount (Example 2), 0.8 at% indium doping amount (Example 1), and 1.0 at% indium doping amount (Example 3).

[0135] from Figure 4 As can be seen in the figure, the surfaces of tin dioxide nanofiber materials with different indium doping levels exhibit a porous and tubular structure. The tube diameters of pure SnO2 nanofiber materials and In-doped SnO2 nanofiber materials do not change significantly. Furthermore, pure SnO2 nanofiber materials exhibit densely packed grains. Unlike pure SnO2 nanofiber materials, the grains of 0.8at% In-SnO2 nanofiber materials and 1.0at% In-SnO2 nanofiber materials are dispersed and stacked, with numerous tiny pores distributed on the nanofiber surface. This facilitates the adsorption of gas molecules and promotes the response of the gas-sensitive material. Further observation revealed that the 0.8at% In-SnO2 nanofiber material has a distinct hollow structure with well-developed internal hollow spaces, which facilitate the flow of gas molecules and promote the interaction between gas and the SnO2 surface, thereby improving the material's gas-sensing performance.

[0136] Comprehensive analysis reveals that both pure and In-doped SnO2 nanofiber materials exhibit tubular structures. The 0.8at% In-SnO2 nanofiber material exhibits the smallest grain size, the loosest grain packing, fine pores on the surface, and the most developed hollow interior space. These characteristics suggest that the 0.8at% In-SnO2 nanofiber material should possess a higher specific surface area, which facilitates the adsorption of gas molecules on the material surface, increases the contact area between the material surface and gas molecules, and promotes redox reactions. Therefore, it is preliminarily determined that the 0.8at% In-SnO2 nanofiber material possesses the most favorable microstructural features for gas sensing.

[0137] Test Example 2 Figure 5 TEM images of the nanofiber materials prepared in Example 1 and Comparative Example 1, wherein: Figure 5 (a) is the TEM micrograph of pure SnO2 nanofiber material. Figure 5 (b) TEM micrograph of 0.8at% In-SnO2 nanofiber material.

[0138] from Figure 5 As can be seen from the figure, the pure SnO2 nanofiber material has large grains and densely packed grains, consistent with the SEM test results mentioned above. Compared to the pure SnO2 nanofiber material, the 0.8at% In-SnO2 nanofiber material has finer grains and looser packing. Furthermore, the 0.8at% In-SnO2 nanofiber material exhibits a distinct hollow tube structure and pores on the nanofiber surface.

[0139] Test Example 3 Figure 6 HRTEM images of the nanofiber materials prepared in Example 1 and Comparative Example 1, wherein: Figure 6(c) is the HRTEM image of pure SnO2 nanofiber material. Figure 6 (d) HRTEM image of 0.8at% In-SnO2 nanofiber material.

[0140] from Figure 6 It can be seen that the lattice spacing of the (110) crystal plane of pure SnO2 nanofiber material is 0.33 nm, and the lattice spacing of the (110) crystal plane of 0.8at%In-SnO2 nanofiber material is 0.32 nm. The lattice spacing of the (110) crystal plane of SnO2 nanofiber material decreases after indium doping, which is consistent with the XRD test results.

[0141] Test Example 4 Figure 7 The XRD patterns of the tin dioxide nanofiber materials with different indium doping amounts prepared in Examples 1-3 and Comparative Example 1 are as follows: Figure 7 (a) is the XRD pattern of SnO2 nanofiber material samples with different In doping amounts. Figure 7 (b) is an enlarged view of the (110) diffraction peak at 25.8°~27.3°.

[0142] from Figure 7 It can be seen that pure SnO2 nanofiber materials and SnO2 nanofiber materials doped with different proportions of In are both typical rutile structures (PDF#71-0652). Each sample shows all the characteristic diffraction peaks of SnO2, indicating that the SnO2 nanomaterials were successfully prepared and still have a stable crystal structure after calcination at 600°C. The characteristic peak intensity of the sample is high and sharp, which shows that the prepared SnO2 nanomaterials have high purity and crystallinity. In the XRD patterns of SnO2 nanomaterials doped with In at different proportions, due to the low content of introduced In, no characteristic peaks of indium oxide are shown. In addition, at 2 The three strong characteristic peaks at =26.5°, 33.9° and 51.7° correspond to the (110), (101) and (211) crystal planes of SnO2, respectively.

[0143] Figure 7 (b) shows the enlarged view of the (110) diffraction peak of SnO2 nanofiber materials doped with different ratios of In (25.8°~27.3°). It can be clearly seen that with the increase of In doping ratio, the (110) diffraction peak shifts to the high angle direction. This is because the covalent radius of In is smaller than that of Sn. When In 3+ Replaced by Sn 4+ Monkey will cause lattice distortion, which will reduce the interplanar spacing of doped SnO2. According to the Bragg formula nλ = 2dsinθ (in, drepresents the interplanar spacing, θ It is expressed as the angle between the incident X-ray and the corresponding crystal plane, λ Indicates the wavelength of X-rays during testing, n represents the diffraction order), due to the interplanar spacing d Decrease the incident angle θ will increase, resulting in a shift of the (110) peak, again confirming the successful incorporation of In.

[0144] Test Example 5 Figure 8 This is the XPS graph of the 8at% indium-doped tin dioxide nanofiber material prepared in Example 1, wherein: Figure 8 (a) is the full XPS spectrum, Figure 8 (b) is the In 3d XPS spectrum, Figure 8 (c) is the O 1s XPS spectrum, Figure 8 (d) is the Sn 3d XPS spectrum.

[0145] from Figure 8 It can be seen that Sn, In, O, and C elements exist in the sample, among which the reference standard peak of C 1s is 284.8 eV. Figure 8 (b) is the 3d XPS spectrum of In element. After peak fitting, the characteristic peak of In element In 3d 3 / 2 and characteristic peak In 3d 5 / 2 The peak positions are shifted, indicating that Sn ions interact with the doped In ions. This also indicates that the valence of In is +3. Figure 8 (c) is the 1s XPS spectrum of O element. The two asymmetric peaks can be deconvoluted into symmetric peaks of three types of oxygen, corresponding to lattice oxygen (O L ), oxygen vacancies (O V ) and adsorbed oxygen (O C The increase of chemically adsorbed oxygen and oxygen vacancies on the surface of the material will cause a significant change in conductivity, thereby improving the gas-sensitive material response value of the material. Figure 8 (d) is the 3d XPS spectrum of Sn element, the characteristic peak of Sn element Sn 3d 3 / 2 and characteristic peaks Sn 3d 5 / 2 They are located at 492.9 eV and 484.4 eV respectively, with a binding energy difference of 8.5 eV, which confirms the composition of SnO2.

[0146] Examples 4-6 are used to illustrate the preparation process of the gas sensor.

[0147] Example 4 The preparation process of the gas sensor includes: S1. Using a 3×3 mm ceramic substrate as an upper substrate 1 and a lower substrate 2, a plurality of gold interdigital electrodes (gold interdigital electrode arrays) are etched on the upper substrate 1 and the lower substrate 2 respectively by photolithography, so that the interdigital electrodes 4 on the upper substrate 1 and the interdigital electrodes 4 on the lower substrate 2 are arranged relative to each other, and the interdigital electrodes 4 on the upper substrate 1 and the interdigital electrodes 4 on the lower substrate 2 are staggered, and the spacing between adjacent interdigital electrodes 4 on the upper substrate 1 and the lower substrate 2 is 50 μm; S2, forming a pore with a diameter of about 100 nm on the surface of each interdigital electrode 4 under oxygen plasma treatment; S3. The indium-doped tin dioxide nanofiber material prepared in Example 1 (doping amount of indium is 0.8 at %) is ball-milled with anhydrous ethanol at a mass ratio of 1:5 to form a uniform slurry. The slurry is then coated on the surface of each interdigital electrode 4 using a micro-dispensing process. The slurry is then annealed at 400° C. for 3 hours to solidify the slurry into a sensitive layer 5 on the surface of the interdigital electrode 4, completing interfacial bonding and ensuring that the sensitive layer 5 fills the space between the upper substrate 1 and the lower substrate 2. S4. A 15 μm thick composite permeable material layer 3 is coated on the outside of the sensitive layer 5 by a vapor deposition method, so that the upper substrate 1, the lower substrate 2 and the composite permeable material layer 3 form a three-dimensional structure with an inner cavity, and the composite permeable material layer 3 is located on the side of the three-dimensional structure, wherein the composite permeable material layer 3 includes a polytetrafluoroethylene layer 31 and an aluminum oxide layer 32, the pore size of the polytetrafluoroethylene layer 31 is 0.2 μm, the pore size of the aluminum oxide layer 32 is 5 nm, and the thickness of the polytetrafluoroethylene layer 31 and the aluminum oxide layer 32 can be 1:0.05. Then, the composite permeable material layer 3 and the sensitive layer 5 are firmly compounded by hot pressing; S5. Screen-print a ruthenium oxide heating layer on the outer surface of the upper substrate 1 and the lower substrate 2, and install a K-type thermocouple on the ruthenium oxide heating layer to construct a closed-loop temperature control module; use a PID algorithm to stabilize the operating temperature at 200±1°C. After the sensor is assembled, age it in a dry air environment containing 5% C2H4 for 48 hours for standby use.

[0148] Example 5 A gas sensor was prepared according to the method of Example 4, except that in step S3, the indium-doped tin dioxide nanofiber material prepared in Example 1 was replaced by the indium-doped tin dioxide nanofiber material prepared in Example 2 (the indium doping amount was 0.5 at %).

[0149] Example 6 A gas sensor was prepared according to the method of Example 4, except that in step S3, the indium-doped tin dioxide nanofiber material prepared in Example 1 was replaced by the indium-doped tin dioxide nanofiber material prepared in Example 3 (the indium doping amount was 1 at %).

[0150] Comparative Example 2 A gas sensor was prepared according to the method of Example 4, except that in step S3, the indium-doped tin dioxide nanofiber material prepared in Example 1 was replaced by the material prepared in Comparative Example 1 (the indium doping amount was 0 at %).

[0151] Test Example 6 The gas sensing performance of the gas sensors prepared in Examples 4-6 and Comparative Example 2 to ethylene at different concentrations was tested.

[0152] Figure 9 This is the gas-sensing performance test diagram of the gas sensor, where: Figure 9 (a) Shows the response values of each gas sensor to C2H4 at different operating temperatures; Figure 9 (b) shows the response of 0.8at% In-SnO2 sensor to C2H4 at 200℃ and the change of C2H4 concentration; Figure 9 (c) shows the relationship between the response value of 0.8at% In-SnO2 sensor to C2H4 and the change of C2H4 gas concentration at 200℃; Figure 9 (d) shows that selectivity is one of the important indicators for evaluating the gas-sensing performance of materials. Figure 9 (d) shows the response values of the 0.8 at% In-SnO2 sensor to C2H4 in the presence of various interfering gases at 200°C, with the concentration of each interfering gas and C2H4 being 5 ppm.

[0153] In order to explore the optimal working temperature of the gas sensor, the gas sensors prepared in Examples 4-6 and Comparative Example 6 were tested for their gas sensing performance in the temperature range of 100-250°C. Figure 9 As can be seen in (a), the operating temperature has a significant effect on the gas-sensing properties of the material. Figure 9(a) shows the response values of the gas sensors prepared in Examples 4-6 and Comparative Example 6 to 5 ppm C2H4 gas at different operating temperatures. It can be seen that the introduction of In improves the response values of the SnO2 sensors to C2H4 to varying degrees, with the 0.8 at% In-SnO2 sensor showing the most significant improvement. Combined with the FESEM test results, it can be inferred that 0.8 at% is the optimal In doping level. Increasing the In doping level to 1.0 at% decreases the sensor's response to C2H4 gas, demonstrating that appropriate element doping can improve the response value of gas-sensitive materials. Further increasing the doping ratio actually reduces gas-sensing performance. Furthermore, with increasing temperature, the response value of the 0.8 at% In-SnO2 to 5 ppm C2H4 gas increases first and then decreases, with the optimal operating temperature being 200°C. The response value of the 0.8 at% In-SnO2 to 5 ppm C2H4 at 200°C is 4.8, a significant improvement compared to the pure SnO2 sensor.

[0154] Figure 9 (b) shows the variation of the response value of the 0.8at% In-SnO2 sensor to C2H4 with C2H4 concentration at 200°C. It can be seen that the response values of the 0.8at% In-SnO2 sensor to 5 ppm, 10 ppm, 20 ppm, 30 ppm, and 40 ppm C2H4 are 4.8, 8.5, 10.7, 11.8, and 12.4, respectively, and the growth rate of the gas response value gradually decreases with increasing gas concentration.

[0155] Figure 9 (c) shows the relationship between the C2H4 response of the 0.8at% In-SnO2 sensor and the C2H4 gas concentration at low C2H4 concentrations at 200°C. Data fitting reveals that when the C2H4 concentration is less than 8 ppm, the C2H4 response of the 0.8at% In-SnO2 sensor exhibits a linear relationship with increasing C2H4 concentration: y = 0.8284x + 0.0028, demonstrating good linearity, where x is the C2H4 concentration (ppm) and y is the C2H4 response.

[0156] Selectivity is one of the important indicators for evaluating the gas-sensing performance of materials. Figure 9(d) shows the response of the 0.8 at% In-SnO2 sensor to 5 ppm C2H4 at 200°C in the presence of interfering gases. The interfering gases are gases that may be present in transformer environments (including CH4, C2H6, C2H2, CO, CO2, and H2), with each gas concentration at 5 ppm. The test results show that the 0.8 at% In-SnO2 sensor has a significantly greater response to C2H4 than to the other interfering gases, particularly CH4, C2H6, CO, and CO2. This demonstrates that the 0.8 at% In-SnO2 sensor has good gas selectivity and strong anti-interference capabilities for transformer detection.

[0157] It should be understood that parts not elaborated in detail in this specification belong to the prior art.

[0158] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. An indium-doped tin dioxide nanofiber material, characterized in that: The indium-doped tin dioxide nanofiber material has a tubular structure and a porous structure on the surface, wherein the pores in the porous structure are micropores and mesopores.

2. The indium-doped tin dioxide nanofiber material according to claim 1, characterized in that: The doping amount of indium in the indium-doped tin dioxide nanofiber material is 0.5-1 at %.

3. The indium-doped tin dioxide nanofiber material according to claim 1 or 2, characterized in that: The specific surface area of the indium-doped tin dioxide nanofiber material is 90-100 m 2 / g; And / or, the diameter of the indium-doped tin dioxide nanofiber material is 110-130 nm; And / or, the pores in the porous structure have a pore diameter of 1 to 50 nm.

4. A method for preparing indium-doped tin dioxide nanofiber material, characterized in that: The method comprises the following steps: mixing indium salt, tin salt, morphology control agent and solvent to obtain spinning solution; electrospinning the spinning solution to obtain a precursor fiber membrane; The precursor fiber membrane is allowed to stand and calcined to obtain indium-doped tin dioxide nanofibers.

5. The method according to claim 4, characterized in that The indium salt is calculated as indium element, and the tin salt is calculated as tin element, and the weight ratio of the indium salt to the tin salt is 0.5-2:100; and / or, the tin salt, the morphology control agent, and the solvent are used in a ratio of 1 g: 3-8 g: 20-30 mL; And / or, the indium salt is selected from at least one of indium chloride, indium nitrate and indium acetylacetonate; and / or, the tin salt is selected from at least one of tin dichloride, tin acetate and tin tetrachloride; and / or, the morphology control agent is selected from at least one of polyvinyl pyrrolidone, polyethylene oxide and cetyltrimethylammonium bromide; And / or, the solvent is selected from at least one of ethanol, N,N-dimethylformamide and ethylene glycol.

6. The method according to claim 4 or 5, characterized in that The process of mixing the indium salt, the tin salt, the morphology control agent and the solvent comprises: dissolving the indium salt and the tin salt in the solvent, stirring, and then adding the morphology control agent to mix; And / or, the mixing conditions include: a temperature of 30-50° C. and a time of 4-6 hours.

7. The method according to claim 4, characterized in that The process of electrospinning the spinning solution comprises: injecting the spinning solution into a syringe pump and squeezing the spinning solution out of a spinneret through a needle to form droplets; then applying an electric field to form a jet from the droplets, and the jet is deposited on a receiving plate to form a precursor fiber membrane; and / or, the propulsion flow rate of the syringe pump is 0.5-0.7 mL / h; and / or, the voltage of the applied electric field is 18-22 kV; and / or, the distance between the needle and the receiving plate is 15-20 cm; And / or, the electrospinning time is 5-8 hours.

8. The method according to claim 4, characterized in that The standing conditions include: a temperature of 50-70°C and a time of 8-12 hours; And / or, the calcination process includes: heating to 500-700° C. at a heating rate of 4-6° C. / min and keeping the temperature for 4-6 hours.

9. Indium-doped tin dioxide nanofiber material prepared by the method according to any one of claims 4 to 8.

10. Use of the indium-doped tin dioxide nanofiber material according to any one of claims 1 to 3 and 9 as a gas-sensitive material.

11. A gas sensor, characterized in that: The gas sensor comprises an upper substrate (1), a lower substrate (2) and a composite permeable material layer (3); the upper substrate (1), the lower substrate (2) and the composite permeable material layer (3) constitute a three-dimensional structure having an inner cavity, and the composite permeable material layer (3) is located on the side of the three-dimensional structure; a plurality of interdigitated electrodes (4) are provided on both the upper substrate (1) and the lower substrate (2); the interdigitated electrodes (4) on the upper substrate (1) and the interdigitated electrodes (4) on the lower substrate (2) are arranged relative to each other in the inner cavity, and the interdigitated electrodes (4) on the upper substrate (1) and the interdigitated electrodes (4) on the lower substrate (2) are staggered in the inner cavity; Each interdigital electrode (4) is coated with a sensitive layer (5), and the sensitive layer (5) fills the gaps in the inner cavity, wherein the sensitive layer (5) contains the indium-doped tin dioxide nanofiber material according to any one of claims 1 to 3 and 9.

12. The gas sensor according to claim 11, characterized in that: The upper substrate (1) and the lower substrate (2) are both ceramic substrates; And / or, the length and width of the upper substrate (1) and the lower substrate (2) are respectively (2.5-3.5) mm × (2.5-3.5) mm; And / or, the interdigital electrodes (4) are gold interdigital electrodes; and / or, the spacing between two adjacent interdigital electrodes (4) is 30-80 μm; And / or, the outer surface of the interdigitated electrode (4) has a porous structure, and the pores in the porous structure have a pore diameter of 80-120 nm.

13. The gas sensor according to claim 11, characterized in that: The composite permeable material layer (3) comprises, from the outside to the inside, a polytetrafluoroethylene layer (31) and an aluminum oxide layer (32); the pore size of the polytetrafluoroethylene layer (31) is larger than the pore size of the aluminum oxide layer (32); and the aluminum oxide layer (32) is close to the inner cavity of the three-dimensional structure; and / or, the pore size of the polytetrafluoroethylene layer (31) is 0.1-0.3 μm, and the pore size of the aluminum oxide layer (32) is 2-10 nm; and / or, the thickness ratio of the polytetrafluoroethylene layer (31) to the aluminum oxide layer (32) is 1:0.01-0.1; And / or, the thickness of the composite permeable material layer (3) is 3-8 mm.

14. The gas sensor according to claim 11, characterized in that: The outer surfaces of the upper substrate (1) and the lower substrate (2) are provided with ruthenium oxide heating layers, and K-type thermocouples are arranged on the ruthenium oxide heating layers. The ruthenium oxide heating layers and the K-type thermocouples form a closed-loop temperature control module.

15. A method for preparing the gas sensor according to any one of claims 11 to 14, characterized in that: The method includes: A plurality of interdigital electrodes (4) are respectively engraved on the upper substrate (1) and the lower substrate (2), so that the interdigital electrodes (4) on the upper substrate (1) and the interdigital electrodes (4) on the lower substrate (2) are relatively distributed, and the interdigital electrodes (4) on the upper substrate (1) and the interdigital electrodes (4) on the lower substrate (2) are staggered; A slurry containing the indium-doped tin dioxide nanofiber material according to any one of claims 1 to 3 and 9 is applied to the surface of each interdigital electrode (4), and then the slurry is solidified into a sensitive layer (5) on the surface of the interdigital electrode (4) by annealing, and the sensitive layer (5) fills the space between the upper substrate (1) and the lower substrate (2); The composite permeable material layer (3) is coated on the outside of the sensitive layer (5), and then the composite permeable material layer (3) and the sensitive layer (5) are composited by hot pressing.

16. The method according to claim 15, characterized in that The method further comprises: before coating a slurry containing an indium-doped tin dioxide nanofiber material on the surface of each interdigital electrode (4), forming a pore structure on the outer surface of the interdigital electrode (4) by plasma treatment; And / or, the method further comprises: screen-printing a ruthenium oxide heating layer on the outer surfaces of the upper substrate (1) and the lower substrate (2), and installing a K-type thermocouple on the ruthenium oxide heating layer.

17. The method according to claim 15, characterized in that The preparation process of the slurry containing indium-doped tin dioxide nanofiber material comprises: mixing the indium-doped tin dioxide nanofiber material with anhydrous ethanol by ball milling; And / or, the mass ratio of the indium-doped tin dioxide nanofiber material to anhydrous ethanol is 1:3-8; And / or, the annealing conditions include: a temperature of 300-500° C. and a time of 2-5 hours.

18. Use of the gas sensor according to any one of claims 11 to 14 in detecting ethylene.

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