N-Zn / Co-NO gas sensitive material and preparation method and application thereof, gas sensitive sensor and preparation method and application thereof

Abstract

The invention relates to the field of gas sensing, and discloses an N-Zn / Co-NO gas sensitive material and a preparation method and application thereof, a gas sensitive sensor and a preparation method and application thereof, the N-Zn / Co-NO gas sensitive material comprises a Zn / Co-MOF material, and nitrogen is loaded in pores and on the surface of the Zn / Co-MOF material. The N-Zn / Co-NO gas sensitive material has a special porous structure and chemical properties, the original structure is optimized through nitrogen doping treatment, more active sites are formed, and the catalytic activity of the surface of the material is enhanced, so that the sensitivity to transformer oil dissolved gases such as hydrogen and methane is improved.

Description

Technical Field

[0001] The present invention relates to the field of gas sensing, and particularly to an N-Zn / Co-NO gas-sensitive material and its preparation method and application, a gas sensor and its preparation method and application. Background Art

[0002] As a core device of the power grid, it is difficult to directly monitor the internal defects of power transformers through external means. However, internal faults of transformers will cause chemical reactions in transformer oil and insulating materials, generating and dissolving different types of fault characteristic gases such as hydrogen, methane, ethylene, etc. Therefore, the detection of dissolved gases in transformer oil is particularly important. It can timely detect most of the hidden dangers and defects inside the transformer, and is of great significance for ensuring the safe and stable operation of the power grid.

[0003] In the field of detecting dissolved gases in transformer oil, although traditional methods such as gas chromatography do play a certain role, they have obvious deficiencies in terms of real-time performance, operation convenience, and cost-effectiveness. In contrast, metal oxide semiconductor nanomaterials have shown broad application prospects in the detection of toxic, harmful, and flammable gases due to their high sensitivity, low cost, miniaturized design, and excellent compatibility with modern electronic systems. However, when faced with the detection of low-concentration gases (such as H 2 , CH 4 ), single metal oxide semiconductor materials have encountered a series of challenges such as insufficient sensitivity, poor selectivity, and high operating temperature, which seriously hinder their application and popularization in actual detection. Summary of the Invention

[0004] The purpose of the present invention is to overcome a series of problems existing in the detection of low-concentration gases by existing single metal oxide semiconductor materials, such as insufficient sensitivity, poor selectivity, and high operating temperature, and to provide an N-Zn / Co-NO gas-sensitive material and its preparation method and application, a gas sensor and its preparation method and application. The N-Zn / Co-NO gas-sensitive material exhibits excellent gas-sensing performance, including high sensitivity to the dissolved gases H 2 , CH 4 in transformer oil at low temperature.

[0005] To achieve the above object, on the one hand, the present invention provides an N-Zn / Co-NO gas-sensitive material, and the N-Zn / Co-NO gas-sensitive material includes a Zn / Co-MOF material, and nitrogen elements are loaded in the pores and on the surface of the Zn / Co-MOF material.

[0006] Preferably, the N-Zn / Co-NO gas-sensitive material of the present invention is a nitrogen-doped porous nano double metal oxide, belonging to nano-porous materials; the particle size of the N-Zn / Co-NO gas-sensitive material is 100-500 nm.

[0007] The second aspect of the present invention provides a preparation method of the above N-Zn / Co-NO gas-sensitive material, which is characterized by comprising the following steps:

[0008] Mix a zinc salt, a cobalt salt and a surfactant with a solvent, and stir to obtain solution A;

[0009] Mix isophthalic acid with DMF, and stir to obtain solution B;

[0010] Mix solution A and solution B, then carry out a hydrothermal reaction, cool after the hydrothermal reaction ends, carry out solid-liquid separation on the obtained material after cooling to obtain a solid product, wash and dry the solid product to obtain a Zn / Co-MOF material;

[0011] Mix the Zn / Co-MOF material with formalin, ammonia water and urea, then stir and carry out solid-liquid separation to obtain a solid phase material, wash the solid phase material, then immerse the washed solid phase material in ammonia water, and then carry out drying to obtain a solid complex, and subject the solid complex to heat treatment to obtain the N-Zn / Co-NO gas-sensitive material.

[0012] Further, mix a zinc salt, a cobalt salt and a surfactant with a solvent, wherein the weight ratio of the zinc salt, the cobalt salt and the surfactant is 1:1:15-20. Controlling the ratio of each substance within this range helps to form a stable and uniformly structured Zn / Co-MOF material subsequently.

[0013] Preferably, the ratio of the total weight of the zinc salt, the cobalt salt and the surfactant to the volume of the solvent is 1 g:15-30 mL. Controlling the amount of the solvent within this range can control the concentration of the reaction system, which is beneficial to the growth and dispersion of MOF crystals.

[0014] Further, the zinc salt is selected from one or more of zinc nitrate, zinc chloride, zinc sulfate and zinc carbonate; in a specific embodiment, the zinc salt is selected from zinc nitrate.

[0015] Preferably, the cobalt salt is selected from one or more of cobalt nitrate, cobalt chloride, cobalt acetate and cobalt sulfate; in a specific embodiment, the cobalt salt is selected from cobalt nitrate.

[0016] The surfactant used in the present invention is to enhance the dispersibility and stability of the material, and the surfactant is selected from one or more of polyvinyl pyrrolidone (PVP), polyethylene glycol, sodium lauryl sulfate and polysorbate; in a specific embodiment, the surfactant is polyvinyl pyrrolidone.

[0017] In a preferred embodiment, the solvent contains water and anhydrous alcohol, and the volume ratio of water to anhydrous alcohol is 1:1-2.

[0018] In the present invention, the anhydrous alcohol is anhydrous methanol and / or anhydrous ethanol; in a specific case, the anhydrous alcohol is anhydrous ethanol.

[0019] In the present invention, zinc salt, cobalt salt and surfactant are mixed with a solvent. In order to further ensure that all solutes can be fully dissolved and mixed evenly, it is also necessary to stir for a certain time at an appropriate stirring speed. Therefore, it is preferred to stir at a stirring speed of 300 to 500 rpm for 15 to 30 minutes to obtain a uniform and transparent solution A.

[0020] In the present invention, isophthalic acid is mixed with DMF (N, N-dimethylformamide). In order to ensure that the solute can be fully dissolved and mixed evenly, stirring is also required under appropriate conditions, preferably stirring at a stirring speed of 300 to 800 rpm for 15 to 20 minutes to obtain a clear solution B (through sufficient stirring, ensure that the isophthalic acid is completely dissolved in DMF); wherein, phthalic acid, as an organic ligand, plays a key role in the construction of MOF materials, so the amount of phthalic acid needs to be reasonably controlled. In a preferred case, the solid-liquid ratio of isophthalic acid to DMF is 0.1 g: 20 to 30 mL.

[0021] Furthermore, in order to avoid precipitation caused by excessive local concentration when solution A and solution B are mixed, solution B is preferably poured slowly and continuously into solution A while gently stirring to obtain a uniformly mixed solution, and then the mixed solution is subjected to a hydrothermal reaction.

[0022] Preferably, the volume ratio of solution A to solution B is 1:1-2.

[0023] The conditions of the hydrothermal reaction include: a temperature of 120 to 180° C. and a time of 12 to 18 hours. Controlling the amounts of solution A and solution B and the conditions of the hydrothermal reaction within the above range is helpful in forming a stable and structurally uniform Zn / Co-MOF material.

[0024] In the present invention, after the hydrothermal reaction is completed, it is preferably cooled naturally to room temperature to avoid material structure damage caused by a sudden drop in temperature.

[0025] In the present invention, the room temperature refers to 20-30°C.

[0026] In the present invention, when the material obtained after cooling is subjected to solid-liquid separation, the solid-liquid separation operation may be filtration or centrifugation, further filtration.

[0027] In order to further remove unreacted raw materials, solvent residues and possible impurities, the specific operations of washing and drying the solid product include: using anhydrous ethanol to centrifugally wash the solid product three times (the speed of each centrifugal washing of the solid product is 10,000 to 12,000 rpm, and the time is 10 to 20 minutes. After each centrifugal washing, the precipitate after centrifugation is retained and the supernatant is poured out), and then the solid product after centrifugal washing is dried to ensure that the solvent in the solid product after centrifugal washing is completely volatilized to obtain a pure Zn / Co-MOF material, wherein the drying conditions include: a temperature of 60 to 80°C and a time of 12 to 24 hours.

[0028] In order to increase the nitrogen content of the N-Zn / Co-NO gas-sensitive material as much as possible, the present invention uses formalin (FA), ammonia (NH 4 OH) and urea, among which FA can form new chemical bonds with MOF functional groups, ammonia can adjust the pH value, and urea is used to control crystal growth, making it easier to enhance the embedding of nitrogen elements.

[0029] Preferably, the weight ratio of the Zn / Co-MOF material to formalin, ammonia water and urea is 1-2:50:5:5.

[0030] Furthermore, the Zn / Co-MOF material is mixed with formalin, ammonia water and urea, and then stirred and solid-liquid separated, wherein the stirring time is 12 to 24 hours, and the stirring speed is 300 to 800 rpm; controlling the amount of the above raw materials and the stirring operation conditions within the corresponding range is conducive to the full adsorption of the porous Zn / Co-MOF material; wherein the solid-liquid separation method can be centrifugation.

[0031] In the present invention, the solid phase material is preferably washed multiple times with ethanol to remove FA and urea residues attached to the surface of the solid phase material (Zn / Co-NO).

[0032] In the present invention, the washed solid phase material is immersed in ammonia water in order to further enhance the embedding of nitrogen elements, so as to increase the nitrogen doping amount, wherein the weight ratio of the washed solid phase material to ammonia water is 1:1-2.

[0033] In the present invention, the washed solid material is immersed in ammonia water, and then the washed solid material together with the ammonia water is directly placed at room temperature for natural drying until the ammonia water completely volatilizes. Since ammonia water itself has strong volatility, natural drying and volatilization at room temperature can result in more nitrogen elements remaining in the pores of the solid material. If the heating drying method is adopted, the ammonia water will volatilize completely, and less nitrogen elements will remain in the pores of the solid material, thereby affecting the final performance of the finished N-Zn / Co-NO gas-sensitive material.

[0034] Among them, the specific operation of heat-treating the solid composite in the present invention includes: heating the solid composite at a heating rate of 3-6 °C / minute to 80-120 °C and holding for 20-24 h, then heating at a heating rate of 3-6 °C / minute to 150-180 °C and holding for 7-9 h, and finally heating at a heating rate of 3-6 °C / minute to 700-800 °C and holding for 8-12 h. The method of holding at different stages here is to ensure the full progress of heat treatment, control the crystal growth and morphology, and can improve the stability and performance of the material.

[0035] Furthermore, the present invention heat-treats the solid composite under a protective gas; the protective gas is selected from one or more of nitrogen, helium, neon, argon, krypton, and xenon, and preferably nitrogen.

[0036] The reason why the N-Zn / Co-NO gas-sensitive material in the present invention has high sensitivity to transformer oil dissolved gases such as hydrogen and methane mainly lies in its special porous structure and chemical properties of the material. Through nitrogen doping treatment, the original structure of Zn / Co-MOF is optimized, forming more active sites, and these active sites can more effectively adsorb and desorb gas molecules such as hydrogen and methane. In addition, the catalytic activity on the surface of the N-Zn / Co-NO porous structure material is also enhanced, promoting the interaction between gas molecules and the material surface, thereby improving the sensitivity to hydrogen and methane. Specifically, when hydrogen or methane transformer oil dissolved gas molecules contact the surface of the N-Zn / Co-NO material, they will interact with the active sites on the material surface, resulting in a change in the resistance of the material. This resistance change can be captured by the gas sensor and converted into a corresponding electrical signal output, thereby realizing the detection and measurement of transformer oil dissolved gases such as hydrogen and methane.

[0037] The third aspect of the present invention provides an application of the above N-Zn / Co-NO gas-sensitive material in a gas sensor.

[0038] The fourth aspect of the present invention provides a gas sensor, and the surface of the ceramic tube electrode of the gas sensor is coated with the above N-Zn / Co-NO gas-sensitive material.

[0039] The fifth aspect of the present invention provides a method for preparing the above gas sensor, comprising the following steps:

[0040] Mix terpineol and a polymer binder to obtain a mixed binder. After grinding the N-Zn / Co-NO gas-sensitive material, mix it with the mixed binder to obtain a gas-sensitive paste.

[0041] Clean the ceramic tube electrode, then dry it. Then apply the gas-sensitive paste on the surface of the cleaned ceramic tube electrode to obtain a ceramic tube electrode coated with the gas-sensitive paste. Calcinate the ceramic tube electrode coated with the gas-sensitive paste, then insert a nickel-chromium heating wire into the calcined ceramic tube electrode. Then weld the platinum wire and the nickel-chromium heating wire on the calcined ceramic tube electrode to a six-pin socket, and then age it to obtain the gas sensor.

[0042] In a preferred case, the polymer binder is selected from one or more of ethyl cellulose, polyurethane, and polystyrene.

[0043] In a preferred embodiment, the weight ratio of terpineol to the polymer binder is 95-99:1. This ratio ensures that the binder system has good volatility and coating properties. Among them, terpineol, as the main component, provides appropriate volatility and solubility; while the polymer binder, as a small additive, mainly plays the role of enhancing the adhesion and improving the mechanical strength of the film.

[0044] Preferably, the grinding time is 10-15 min.

[0045] Further, the weight ratio of the N-Zn / Co-NO gas-sensitive material to the mixed binder is 1:20-50.

[0046] In the present invention, preferably, anhydrous ethanol is used to ultrasonically clean the ceramic tube electrode to remove surface impurities.

[0047] In a preferred embodiment, the drying conditions include: temperature 60-80 °C, time 12-24 h.

[0048] Among them, the amount of the gas-sensitive paste applied only needs to ensure that the thickness of the N-Zn / Co-NO gas-sensitive material coated on the surface of the ceramic tube electrode in the finished gas sensor is 100-300 nm.

[0049] In the present invention, the purpose of calcining the ceramic tube electrode coated with the gas-sensitive paste is to remove the mixed binder in the gas-sensitive paste and improve the mechanical strength of the N-Zn / Co-NO gas-sensitive material on the ceramic tube electrode. To achieve better results, the calcination conditions need to be controlled within a reasonable range. Therefore, preferably, the calcination conditions include: temperature 300-500 °C, time 1-3 h.

[0050] Further, the four platinum wires on the calcined ceramic tube electrode are welded to four pins of a six-pin socket, and then the nickel-chromium heating wire is welded to the other two pins of the six-pin socket. Finally, aging is carried out on an aging platform to ensure the stability of the circuit during the test.

[0051] In a specific embodiment, the conditions for aging include: a voltage of 5V and a time of 7 days.

[0052] The sixth aspect of the present invention provides an application of the above gas sensor in the detection of hydrogen and methane.

[0053] The present invention adopts an improved hydrothermal synthesis method to successfully react and generate Zn / Co-MOF material, and introduces nitrogen element through subsequent treatment to form a porous high-nitrogen-doped Zn / Co bimetallic oxide material N-Zn / Co-NO gas-sensitive material. This material has a special porous structure and chemical properties. Through nitrogen doping treatment, the original structure is optimized, more active sites are formed, and the catalytic activity on the material surface is enhanced, thereby improving the sensitivity to transformer oil dissolved gases such as hydrogen and methane. This innovative material synthesis method not only increases the nitrogen content of the material, but also optimizes its porous structure and enhances the gas-sensing performance.

[0054] In the process of preparing the N-Zn / Co-NO gas-sensitive material, the present invention further adopts a multiple calcination method to introduce N-containing small molecule materials into the MOF pores to achieve high-nitrogen doping. This technology not only increases the nitrogen content of the material, but also enhances the catalytic activity of the material, further improving the sensitivity to transformer oil dissolved gases.

[0055] The preparation process of the gas sensor of the present invention includes steps such as slurry preparation, coating, calcination, welding, and aging. This process is not only simple to operate and easy to implement, but also can ensure the stability and reliability of the gas-sensitive material, improving the service life and performance of the sensor. The sensor can timely detect most of the hidden dangers and defects inside the transformer, which is of great significance for ensuring the safe and stable operation of the power grid.

[0056] Compared with the prior art, the present invention has the following beneficial effects:

[0057] Improve sensitivity: The N-Zn / Co-NO gas-sensitive material has a special porous structure and chemical properties. Applying it to the gas sensor can more effectively adsorb and desorb transformer oil dissolved gas molecules such as hydrogen and methane, thereby improving the sensitivity of the sensor.

[0058] Enhanced stability: By optimizing the material synthesis and sensor preparation processes, the present invention improves the stability and reliability of the gas-sensitive material. When used in gas sensors, it can reduce the failure rate of the sensors and extend their service life.

[0059] Cost reduction: Compared with the traditional gas chromatography method, the gas sensor preparation method provided by the present invention has lower costs and is more easily applicable to large-scale production and applications.

[0060] Real-time monitoring: This sensor can monitor the gas changes inside the transformer in real time, promptly detect potential faults and hidden dangers, and provide strong guarantees for the safe and stable operation of the power grid. Description of the Drawings

[0061] Figure 1 is a schematic diagram of the preparation of the N-Zn / Co-NO gas-sensitive material of the present invention;

[0062] Figure 2 is the N element EDS diagram of the N-Zn / Co-NO gas-sensitive material obtained in Example 1;

[0063] Figure 3 is the XRD diagram of the N-Zn / Co-NO gas-sensitive material obtained in Example 1;

[0064] Figure 4 is the N 2 adsorption-desorption curve of the N-Zn / Co-NO gas-sensitive material obtained in Example 1;

[0065] Figure 5 is the response curve of the gas sensor obtained in Example 1 to 5 ppm H 2 at different operating temperatures;

[0066] Figure 6 is the response curve of the gas sensor obtained in Example 1 to 5 ppm CH 4 at different operating temperatures. Detailed Embodiments

[0067] The following detailed description of the specific embodiments of the present invention is provided in conjunction with the accompanying drawings and examples. It should be understood that the specific embodiments described herein are only for the purpose of illustration and explanation of the present invention, and are not intended to limit the present invention.

[0068] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values of each range, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0069] In addition, the technical solutions between the various embodiments provided by the present invention can be combined with each other, but it must be based on the ability of those of ordinary skill in the art to implement. When the combination of technical solutions results in contradictions or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0070] The preparation schematic diagram of the N-Zn / Co-NO gas-sensitive material of the present invention is as Figure 1 shown.

[0071] The room temperature in the following examples all refers to 25 °C.

[0072] Example 1

[0073] (1) Mix 30 mL of deionized water and 30 mL of absolute ethanol evenly in a beaker to obtain a solvent. Weigh 0.175 g of zinc salt (Zn(NO 3 ) 2 ·6H 2 O), 0.175 g of cobalt salt (Co(NO 3 ) 2 ·6H 2 O) and 2.625 g of surfactant (PVP) and add them one by one to the beaker containing the solvent. Mix the zinc salt, cobalt salt and surfactant with the solvent, where the weight ratio of the zinc salt, cobalt salt and surfactant is 1:1:15, and the ratio of the total weight of the zinc salt, cobalt salt and surfactant to the volume of the solvent is 1 g:20 mL; continue to stir at a stirring speed of 300 revolutions per minute for 30 min to obtain a uniformly transparent solution A;

[0074] (2) Mix 0.1 g of isophthalic acid with 20 mL of DMF and stir well at a stirring speed of 300 revolutions per minute for 15 min to obtain a clear solution B;

[0075] (3) Slowly and continuously pour Solution B into Solution A while gently stirring to obtain a uniformly mixed mixture (the volume ratio of Solution A to Solution B is 1:1). Then transfer the mixture to a 100 mL polytetrafluoroethylene-lined autoclave, seal it, and place it in an oven preheated to 150 °C for hydrothermal reaction. The conditions of the hydrothermal reaction include: temperature of 150 °C, time of 18 h, and keep the oven temperature constant during this period. After the hydrothermal reaction, let the autoclave cool naturally to room temperature to obtain the cooled material. Filter the cooled material to obtain a solid product. Wash the solid product by centrifugation with anhydrous ethanol three times (the rotation speed for each centrifugal washing of the solid product is 11,000 revolutions per minute, and the time is 10 min). Then place the centrifugally washed solid product in a vacuum drying oven for drying. The drying conditions include: temperature of 60 °C, time of 24 h, to obtain the Zn / Co-MOF material;

[0076] (4) Take 500 mg of the Zn / Co-MOF material obtained in step (3) and mix it with 25 g of formalin, 2.5 g of ammonia water, and 2.5 g of urea (the weight ratio of the Zn / Co-MOF material to formalin, ammonia water, and urea is 1:50:5:5). Then continuously stir at a stirring speed of 500 revolutions per minute for 12 h. Then perform centrifugation to obtain a solid phase material. Wash the solid phase material with anhydrous ethanol multiple times. Then completely immerse the washed solid phase material in ammonia water, and the weight ratio of the washed solid phase material to ammonia water is 1:1. Then place the washed solid phase material together with ammonia water at room temperature for natural drying to obtain a solid complex. Place the solid complex in a tube furnace and perform heat treatment on the solid complex under a protective gas (nitrogen). The specific operation of heat treatment of the solid complex includes: heat the solid complex at a heating rate of 5 °C per minute to 80 °C and hold for 24 h, then heat at a heating rate of 5 °C per minute to 150 °C and hold for 7 h, and finally heat at a heating rate of 5 °C per minute to 800 °C and hold for 8 h to obtain the N-Zn / Co-NO gas-sensitive material.

[0077] Example 2

[0078] Implemented according to the method of Example 1, except that in step (1), weigh 0.175 g of zinc salt (Zn(NO 3 ) 2 ·6H 2 O), 0.175 g of cobalt salt (Co(NO 3 ) 2 ·6H 2 O) and 3.15 g of surfactant (PVP) and add them one by one to a beaker containing a solvent, that is, the weight ratio of the zinc salt, cobalt salt, and surfactant is 1:1:18, to prepare the N-Zn / Co-NO gas-sensitive material.

[0079] Example 3

[0080] It was carried out according to the method of Example 1, except that in step (4), 1000 mg of the Zn / Co-MOF material obtained in step (3) was mixed with 25 g of formalin, 2.5 g of ammonia water and 2.5 g of urea (the weight ratio of the Zn / Co-MOF material to formalin, ammonia water and urea was 2:50:5:5) to prepare the N-Zn / Co-NO gas-sensitive material.

[0081] Example 4

[0082] A kind of N-Zn / Co-NO gas-sensitive material, which includes the Zn / Co-MOF material, and nitrogen element is loaded in the pores and on the surface of the Zn / Co-MOF material; this N-Zn / Co-NO gas-sensitive material is prepared by the method of Example 1.

[0083] Example 5

[0084] A kind of N-Zn / Co-NO gas-sensitive material, which includes the Zn / Co-MOF material, and nitrogen element is loaded in the pores and on the surface of the Zn / Co-MOF material; this N-Zn / Co-NO gas-sensitive material is prepared by the method of Example 2.

[0085] Example 6

[0086] A kind of N-Zn / Co-NO gas-sensitive material, which includes the Zn / Co-MOF material, and nitrogen element is loaded in the pores and on the surface of the Zn / Co-MOF material; this N-Zn / Co-NO gas-sensitive material is prepared by the method of Example 3.

[0087] Example 7

[0088] The N-Zn / Co-NO gas-sensitive materials in Examples 4 to 6 all have a special porous structure and can be applied to gas sensors, further improving the sensitivity of the gas sensors.

[0089] Example 8

[0090] A kind of gas sensor, on the surface of the ceramic tube electrode of this gas sensor, the N-Zn / Co-NO gas-sensitive material of Example 4 is coated.

[0091] Example 9

[0092] A kind of gas sensor, on the surface of the ceramic tube electrode of this gas sensor, the N-Zn / Co-NO gas-sensitive material of Example 5 is coated.

[0093] Example 10

[0094] A gas sensor, on the surface of the ceramic tube electrode of which is coated with the N-Zn / Co-NO gas-sensitive material of Example 6.

[0095] Example 11

[0096] The preparation method of the gas sensor of Example 8 specifically comprises the following steps:

[0097] S1. Mix terpineol and a polymer binder (ethyl cellulose) evenly at a weight ratio of 99:1 to obtain a mixed binder. After grinding the N-Zn / Co-NO gas-sensitive material of Example 4 in an agate mortar for 10 min, uniformly mix it with the mixed binder to form a gas-sensitive paste with a consistent concentration; the weight ratio of the N-Zn / Co-NO gas-sensitive material to the mixed binder is 1:20.

[0098] S2. Ultrasonically clean the ceramic tube electrode with absolute ethanol to remove surface impurities, then place it in a drying oven at 60 °C for 24 h. Then, uniformly coat the gas-sensitive paste obtained in step S1 on the surface of the dried ceramic tube electrode to obtain a ceramic tube electrode coated with the gas-sensitive paste. Place the ceramic tube electrode coated with the gas-sensitive paste in a muffle furnace and calcine it in air at 400 °C for 2 h. Then, insert a nickel-chromium heating wire into the calcined ceramic tube electrode. Next, weld the four platinum wires on the calcined ceramic tube electrode to four feet of a six-pin socket with a soldering iron, and then weld the nickel-chromium heating wire to the other two feet of the six-pin socket with a soldering iron. Finally, perform aging on an aging platform. The aging conditions include: voltage of 5 V and time of 7 days to obtain a gas sensor, and the thickness of the N-Zn / Co-NO gas-sensitive material coated on the surface of the ceramic tube electrode in this gas sensor is 100 nm.

[0099] Example 12

[0100] The preparation method of the gas sensor of Example 9 is implemented according to the method of Example 11. The difference is that in step S1, the N-Zn / Co-NO gas-sensitive material of Example 5 is used to prepare a gas sensor.

[0101] Example 13

[0102] The preparation method of the gas sensor of Example 10 is implemented according to the method of Example 11. The difference is that in step S1, the N-Zn / Co-NO gas-sensitive material of Example 6 is used to prepare a gas sensor.

[0103] Example 14

[0104] The gas sensors in Examples 8 to 10 all have good sensitivity and can all be used to detect hydrogen and methane.

[0105] Comparative Example 1

[0106] Implemented according to the method of Example 1, except that in step (1), no cobalt salt is used to obtain a Zn-MOF material, and in step (4), the Zn-MOF material is used to replace the Zn / Co-MOF material to obtain a gas-sensitive material D1.

[0107] Comparative Example 2

[0108] Implemented according to the method of Example 11, except that in step S1, the gas-sensitive material D1 is used to replace the N-Zn / Co-NO gas-sensitive material of Example 4 to obtain a gas sensor.

[0109] Comparative Example 3

[0110] Implemented according to the method of Example 1, except that in step (1), no zinc salt is used to obtain a Co-MOF material, and in step (4), the Co-MOF material is used to replace the Zn / Co-MOF material to obtain a gas-sensitive material D2.

[0111] Comparative Example 4

[0112] Implemented according to the method of Example 11, except that in step S1, the gas-sensitive material D2 is used to replace the N-Zn / Co-NO gas-sensitive material of Example 4 to obtain a gas sensor.

[0113] Comparative Example 5

[0114] Implemented according to the method of Example 1, except that the Zn / Co-MOF material is directly heat-treated to obtain a gas-sensitive material D3.

[0115] Comparative Example 6

[0116] Implemented according to the method of Example 11, except that in step S1, the gas-sensitive material D3 is used to replace the N-Zn / Co-NO gas-sensitive material of Example 4 to obtain a gas sensor.

[0117] Test Example 1

[0118] Perform N element EDS detection on the N-Zn / Co-NO gas-sensitive material obtained in step (4) of Example 1. The EDS diagram is as Figure 2 shown. From Figure 2It can be seen that in the prepared N-Zn / Co-NO gas-sensitive material, nitrogen elements are loaded in the pores and on the surface of the Zn / Co-MOF gas-sensitive material. The particle size of the N-Zn / Co-NO gas-sensitive material is in the range of 100-200 nm. A smaller particle size means a shorter diffusion path of gas molecules inside the material, which helps to accelerate the interaction rate between gas molecules and the sensing material. Therefore, the sensor can respond faster to changes in gas concentration and shorten the response time.

[0119] Test Example 2

[0120] The Zn / Co-MOF material obtained in step (3) of Example 1 and the N-Zn / Co-NO gas-sensitive material obtained in step (4) were subjected to XRD detection. The XRD pattern is as Figure 3 shown. From Figure 3 it can be seen that compared with the Zn / Co-MOF material, the XRD diffraction peaks of the N-Zn / Co-NO gas-sensitive material are significantly weakened, indicating that the original crystal structure of Zn / Co-MOF has been partially damaged or reconstructed under high-temperature treatment, and then transformed into an N-Zn / Co-NO gas-sensitive material with a new metal oxide crystal structure. The newly formed metal oxide crystal structure has more active sites, which can more effectively adsorb and desorb target gas molecules (such as hydrogen, methane, etc.), thereby improving the detection sensitivity and response speed of the gas sensor to dissolved gases in transformer oil.

[0121] Test Example 3

[0122] The N 2 adsorption-desorption isotherm of the N-Zn / Co-NO gas-sensitive material obtained in step (4) of Example 1 was detected. The specific operation is as follows: First, the N-Zn / Co-NO gas-sensitive material obtained in step (4) of Example 1 was placed in a specific surface area and porosity analyzer test device. Subsequently, the N-Zn / Co-NO gas-sensitive material was degassed at 120 °C to remove the impurity gases adsorbed on the surface of the N-Zn / Co-NO gas-sensitive material. Then, nitrogen was introduced as the adsorbate into the test system. By precisely controlling the partial pressure of nitrogen, the nitrogen concentration was gradually increased, and the adsorption amount of nitrogen by the N-Zn / Co-NO gas-sensitive material at different nitrogen concentrations was recorded. After completing the measurement of the adsorption process, the nitrogen concentration was gradually decreased to conduct the measurement of the desorption process, and the release amount of nitrogen during the desorption process was recorded. By plotting the relationship curve between the adsorption amount and the nitrogen partial pressure, the N 2 adsorption-desorption isotherm of the N-Zn / Co-NO gas-sensitive material was obtained.

[0123] The N2 adsorption-desorption isotherm is as Figure 4 shown. From Figure 4 it can be seen that the specific surface area of the N-Zn / Co-NO gas-sensitive material is as high as 824 m2 / g, which is much higher than the specific surface area of conventional metal oxide materials. In the adsorption - desorption isotherm, it can be observed that before the relative pressure P / P0 = 0.4, the adsorption amount continuously increases, and there is a slight hysteresis phenomenon in the desorption process. This phenomenon indicates that there are some mesoporous and macroporous structures in the N - Zn / Co - NO material. These pore structures not only provide more adsorption sites for gas molecules but also facilitate the diffusion and transport of gas molecules inside the material.

[0124] Test Example 4

[0125] With the adsorption of target gas molecules on the surface of the gas - sensitive sensor, electrons transfer from the sensor material to the target molecules, resulting in a change in the resistance of the gas - sensitive sensor. This change can be converted into an electrical signal for output, thereby realizing the detection of the target gas. This test example evaluates the gas - sensitive performance of the gas - sensitive sensor for dissolved gases H 2 and CH 4 in transformer oil.

[0126] Response curve of the gas - sensitive sensor in Detection Example 8 to 5 ppm H 2 : First, place the gas - sensitive sensor in Detection Example 8 in a test chamber with a controllable atmosphere. Subsequently, inject a mixed gas with a hydrogen concentration of 5 ppm (usually using nitrogen or air as the balance gas) into the test chamber through an accurate gas flow controller. At the same time, use a high - precision temperature and humidity control system to maintain the stability and consistency of the test environment. Detect the response values of the gas - sensitive sensor in Detection Example 8 to 5 ppm H 2 at different temperatures respectively, and obtain the response curve, as shown in Figure 5 below.

[0127] Response curve of the gas - sensitive sensor in Detection Example 8 to 5 ppm CH 4 : First, place the gas - sensitive sensor in Detection Example 8 in a test chamber with a controllable atmosphere. Subsequently, inject a mixed gas with a methane concentration of 5 ppm (usually using nitrogen or air as the balance gas) into the test chamber through an accurate gas flow controller. At the same time, use a high - precision temperature and humidity control system to maintain the stability and consistency of the test environment. Detect the response values of the gas - sensitive sensor in Detection Example 8 to 5 ppm CH 4 at different temperatures respectively, and obtain the response curve, as shown in Figure 6 below.

[0128] It can be seen from Figure 5 and Figure 6 that as the temperature increases, the response values of the gas - sensitive sensor in Detection Example 8 show a trend of first increasing and then decreasing. The gas - sensitive sensor in Detection Example 8 has the highest response to H 2 and CH at the operating temperature of 80 °C.4 The response values reached maximum values of 56 and 37 respectively;

[0129] Among them, the response value is calculated using the calculation formula of the n-type semiconductor gas sensor: S = R g / R a , where S is the response value, R g is the resistance value of the gas sensor in air, and R a is the resistance value of the gas sensor in the gas to be measured;

[0130] According to the same method, the gas sensors of Examples 9-10, and the gas sensors of Comparative Examples 2, 4, and 6 were respectively detected for their response curves to 5 ppm H 2 and 5 ppm CH 4 . It was detected that the response curves of the gas sensors of Examples 9-10, and the gas sensors of Comparative Examples 2, 4, and 6 to 5 ppm H 2 and 5 ppm CH 4 were similar to the response curves of the gas sensor of Example 8 to 5 ppm H 2 and 5 ppm CH 4 . That is, as the temperature increased, the response value of the gas sensor showed a trend of first increasing and then decreasing, and when the working temperature was 80 °C, the response value reached the maximum. The specific maximum response values are shown in Table 1.

[0131] Table 1

[0132]

[0133] As can be seen from Table 1, the response values of the bimetal oxide gas sensors (such as Examples 8-10) to hydrogen (H 2 ) and methane (CH 4 ) are significantly higher than those of the single metal oxide gas sensors (such as Comparative Examples 2 and 4). Taking Example 8 and Comparative Example 2 as an example, the response value of the gas sensor of Example 8 to H 2 is 56, while the gas sensor of Comparative Example 2 is only 37, and there is a similar significant increase in the response value to CH 4 . This indicates that the bimetal oxide sensor can detect the dissolved gases in transformer oil more sensitively, improving the sensitivity and accuracy of detection.

[0134] By combining the characteristics of two different metal elements, bimetallic oxides can form more complex crystal structures and more active sites, thereby enhancing the adsorption and catalytic capabilities for target gases. In addition, the doping of N element significantly changes the electronic structure of Zn / Co bimetallic oxides. This change not only improves the conductivity of the material but also increases the number of active sites, thus significantly enhancing the adsorption and response capabilities of the material to hydrogen or methane molecules.

[0135] It should be understood that the parts not elaborated in detail in this specification all belong to the prior art.

[0136] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A N-Zn / Co-NO gas-sensitive material, characterized in that: The N-Zn / Co-NO gas-sensitive material comprises a Zn / Co-MOF material, and nitrogen elements are loaded in the pores and on the surface of the Zn / Co-MOF material.

2. The N-Zn / Co-NO gas-sensitive material according to claim 1, characterized in that: The particle size of the N-Zn / Co-NO gas-sensitive material is 100-500 nm.

3. A method for preparing the N-Zn / Co-NO gas-sensitive material according to claim 1 or 2, characterized in that: The following steps are involved: The zinc salt, the cobalt salt and the surfactant are mixed with a solvent and stirred to obtain a solution A; Mix isophthalic acid and DMF, and stir to obtain solution B; The solution A is mixed with the solution B, and then a hydrothermal reaction is carried out. After the hydrothermal reaction is completed, the solution is cooled, and the material obtained after cooling is subjected to solid-liquid separation to obtain a solid product. The solid product is washed and dried to obtain a Zn / Co-MOF material; The Zn / Co-MOF material is mixed with formalin, ammonia water and urea, and then stirred and solid-liquid separated to obtain a solid phase material, the solid phase material is washed, and then the washed solid phase material is immersed in ammonia water, followed by drying to obtain a solid composite, and the solid composite is heat-treated to obtain a N-Zn / Co-NO gas-sensitive material.

4. The preparation method according to claim 3, characterized in that: Mixing a zinc salt, a cobalt salt and a surfactant with a solvent, wherein the weight ratio of the zinc salt, the cobalt salt and the surfactant is 1:1:15-20; and / or The ratio of the total weight of the zinc salt, the cobalt salt and the surfactant to the volume of the solvent is 1 g: 15 to 30 mL.

5. The preparation method according to claim 3 or 4, characterized in that: The zinc salt is selected from one or more of zinc nitrate, zinc chloride, zinc sulfate and zinc carbonate; and / or The cobalt salt is selected from one or more of cobalt nitrate, cobalt chloride, cobalt acetate and cobalt sulfate; and / or The surfactant is selected from one or more of polyvinyl pyrrolidone, polyethylene glycol, sodium lauryl sulfate and polysorbate; and / or The solvent contains water and anhydrous alcohol, and the volume ratio of water to anhydrous alcohol is 1:1-2; and / or The anhydrous alcohol is anhydrous methanol and / or anhydrous ethanol.

6. The preparation method according to claim 3 or 4, characterized in that: The zinc salt, the cobalt salt and the surfactant are mixed with the solvent, and stirred at a stirring speed of 300 to 500 rpm for 15 to 30 minutes to obtain a solution A.

7. The preparation method according to claim 3, characterized in that: Mixing isophthalic acid and DMF, stirring at a stirring speed of 300 to 800 rpm for 15 to 20 min to obtain a solution B; and / or The solid-liquid ratio of isophthalic acid to DMF is 0.1 g: 20-30 mL.

8. The preparation method according to claim 3, characterized in that: The volume ratio of solution A to solution B is 1:1-2; and / or The conditions of the hydrothermal reaction include: a temperature of 120 to 180° C. and a time of 12 to 18 hours; and / or The solid product is washed and dried, and the drying conditions include: a temperature of 60 to 80° C. and a time of 12 to 24 hours.

9. The preparation method according to claim 3, characterized in that: The weight ratio of the Zn / Co-MOF material to formalin, ammonia water and urea is 1-2:50:5:5; and / or The Zn / Co-MOF material is mixed with formalin, ammonia water and urea, and then stirred and solid-liquid separated, wherein the stirring time is 12 to 24 hours and the stirring speed is 300 to 800 revolutions per minute.

10. The preparation method according to claim 3, characterized in that: Immersing the washed solid phase material in ammonia water, wherein the weight ratio of the washed solid phase material to the ammonia water is 1:1-2; and / or The specific operation of heat treating the solid composite comprises: heating the solid composite to 80-120° C. at a heating rate of 3-6° C. / min and keeping the temperature for 20-24 h, then heating the solid composite to 150-180° C. at a heating rate of 3-6° C. / min and keeping the temperature for 7-9 h, and finally heating the solid composite to 700-800° C. at a heating rate of 3-6° C. / min and keeping the temperature for 8-12 h; and / or The solid composite is heat treated under a protective gas.

11. Use of the N-Zn / Co-NO gas-sensitive material according to claim 1 or 2 in a gas sensor.

12. A gas sensor, characterized in that: The surface of the ceramic tube electrode of the gas sensor is coated with the N-Zn / Co-NO gas-sensitive material according to claim 1 or 2.

13. A method for preparing the gas sensor according to claim 12, characterized in that: The following steps are involved: Mixing pineol and a polymer binder to obtain a mixed binder, grinding an N-Zn / Co-NO gas-sensitive material, and mixing the mixed binder with the N-Zn / Co-NO gas-sensitive material to obtain a gas-sensitive slurry; The ceramic tube electrode is cleaned and then dried, and then the gas-sensitive slurry is coated on the surface of the cleaned ceramic tube electrode to obtain a ceramic tube electrode coated with the gas-sensitive slurry. The ceramic tube electrode coated with the gas-sensitive slurry is calcined, and then a nickel-chromium heating wire is inserted into the calcined ceramic tube electrode. Then, the platinum wire and the nickel-chromium heating wire on the calcined ceramic tube electrode are welded to a six-pin socket, and then aged to obtain a gas sensor.

14. The preparation method according to claim 13, characterized in that: The polymer binder is selected from one or more of ethyl cellulose, polyurethane and polystyrene; and / or The weight ratio of terpineol to polymer adhesive is 95-99:1; and / or The grinding time is 10 to 15 minutes; and / or The weight ratio of the N-Zn / Co-NO gas-sensitive material to the mixed adhesive is 1:20-50; and / or The drying conditions include: a temperature of 60 to 80° C. and a time of 12 to 24 hours; and / or The calcination conditions include: a temperature of 300 to 500° C. and a time of 1 to 3 hours.

15. Use of the gas sensor according to claim 12 in hydrogen and methane detection.

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