NO2 gas sensing material, NO2 gas sensor and preparation method and application thereof

Abstract

The invention discloses an NO2 gas sensing material, an NO2 gas sensor and a preparation method and application of the NO2 gas sensing material and the NO2 gas sensor. The NO2 gas sensing material is a semiconductor substrate material doped with variable-valence metal elements; the material of the semiconductor substrate is BiOX, and the element X is at least one of Cl, Br and I; the variable-valence metal element is a variable-valence transition metal element. The invention provides a design and preparation method of a gas sensor capable of rapidly detecting NO2 at room temperature. The method can realize reversible detection of NO2 at room temperature.

Description

Technical Field

[0001] This application relates to an NO2 gas sensing material, an NO2 gas sensor, its preparation method and application, belonging to the field of nanomaterials and environmental monitoring technology. Background Technology

[0002] Continuous human activities are the main culprit behind the release of nitrogen dioxide (NO2) into the atmosphere. Nitrogen dioxide is an unhealthy gas with an acidic taste and a pungent odor. Therefore, rapid and efficient detection of NO2 is essential. Gas sensors, as a new type of intelligent and miniaturized device, can achieve highly sensitive detection of gas molecules in the environment.

[0003] The core of gas sensors lies in the design and fabrication of gas-sensitive materials. Semiconductor nanostructures have attracted widespread attention from researchers due to their low cost, simple fabrication methods, and high detection sensitivity. However, single semiconductor nanostructures present several problems, such as low stability, poor selectivity, and high operating temperatures. These issues limit the application of semiconductor gas sensors. Therefore, modifying the original semiconductor nanostructure is crucial for improving the performance of semiconductor gas sensors.

[0004] BiOX has emerged as a potential competitor in the development of novel NO2 gas sensors. Considering its ease of integration with other materials, compatibility with various devices, and controllable morphology, BiOX possesses a sufficient surface area to adsorb NO2 molecules. However, at room temperature, BiOX sensors still suffer from low sensitivity and slow response recovery, thus requiring modification to achieve efficient and highly sensitive detection. Summary of the Invention

[0005] The mechanism by which semiconductor resistive gas sensors detect target gas molecules relies on the reaction between the absorbed target gas molecules and chemically adsorbed oxygen species on the surface of the sensing material, which changes the sensor's resistance. The concentration of the target gas is detected by measuring the change in resistance under conditions of presence or absence of the target gas. By establishing the relationship between gas concentration and resistance change, the gas concentration can be determined.

[0006] Modifying the original semiconductor is one of the powerful means to improve the performance of gas sensors. By doping to create vacancies, the accessibility of the material to the target gas molecules can be improved, thereby enhancing its gas sensing performance. In addition, using variable valence metals as dopants can achieve rapid electron transfer and redox reactions at room temperature, thereby improving the sensor's response recovery time and durability at room temperature.

[0007] This invention provides a design and fabrication method for a sensor capable of reversibly detecting NO2 at room temperature. We employ a transition metal with a variable valence state as a dopant to control the vacancy concentration in the original material, thereby achieving a highly sensitive detection process. The advantage of the variable valence state lies in its ability to achieve rapid response recovery kinetics for NO2, a highly reactive gas, providing technical guidance for the rapid detection of NO2 at room temperature.

[0008] One aspect of this application provides an NO2 gas sensing material, wherein the NO2 gas sensing material is a semiconductor substrate material doped with a variable valence metal element;

[0009] The semiconductor substrate material is BiOX, wherein the X element is at least one of Cl, Br, and I;

[0010] The variable-valence metal element is a variable-valence transition metal element.

[0011] Optionally, the variable valence transition metal element is at least one selected from Fe, Co, Ni, Cu, and Sn.

[0012] Optionally, the content of variable valence metal elements in the NO2 gas sensing material is 0.01 to 0.05 mol / g, expressed as molar amount of variable valence metal elements.

[0013] Optionally, in the NO2 gas sensing material, the content of the variable valence metal element is independently selected from any value in the range of 0.01 to 0.05 mol / g or any value between the two.

[0014] Another aspect of this application provides a method for preparing the above-mentioned NO2 gas sensing material, the method comprising:

[0015] (1) Mix the Bi-containing precursor and the variable-valence transition metal precursor with an organic solvent to obtain mixed solution I;

[0016] (2) Add the precursor containing element X to mixed solution I to dissolve, obtain mixed solution II, react, and dry under vacuum to obtain the NO2 gas sensing material.

[0017] Optionally, the Bi-containing precursor is selected from at least one of bismuth chloride, bismuth nitrate, and organobismuth compounds.

[0018] Optionally, in the precursor containing a variable-valence transition metal element, the variable-valence transition metal element is at least one selected from Fe, Co, Ni, Cu, and Sn.

[0019] The Fe-containing precursor is selected from at least one of ferric chloride, ferric nitrate, and organoferric compounds.

[0020] The Co-containing precursor is selected from at least one of cobalt chloride, cobalt nitrate, and organocobalt compounds.

[0021] The Ni-containing precursor is at least one of nickel chloride, nickel nitrate, or organonickel compounds.

[0022] The Cu-containing precursor is at least one of copper chloride, copper nitrate, or an organocopper compound.

[0023] The Sn-containing precursor is at least one of tin chloride or organotin compounds.

[0024] Optionally, the X-containing precursor is at least one of NaX and KX, wherein X is at least one of Cl, Br, and I.

[0025] Optionally, the organic solvent is at least one of ethylene glycol, ethanol, and water.

[0026] Optionally, in the mixed solution I, the concentration of the Bi-containing precursor is 0.1 to 0.5 mol / L, expressed as molar amounts of Bi.

[0027] Optionally, in the mixed solution I, the concentration of the Bi-containing precursor is independently selected from any value in the range of 0.1 to 0.5 mol or any value between the two.

[0028] Optionally, the mass ratio of the Bi-containing precursor: the X-containing precursor: the variable-valence transition metal precursor is 0.5-1: 0.1-0.5: 0.01-0.05.

[0029] Optionally, the reaction temperature is 120–160°C, and the reaction time is 8–16 h.

[0030] Optionally, the vacuum drying temperature is 50–85°C, and the vacuum drying time is 6–12 hours.

[0031] Optionally, the temperature of the reaction (2) is 160-200℃ and the reaction time is 16-24h.

[0032] Optionally, in step (2), the reaction is further followed by centrifugation and washing with a polar solvent;

[0033] The polar solvent is at least one of ethanol, water, and methanol;

[0034] The number of centrifugations is 3 to 7.

[0035] Preparation of BiOX using conventional methods: BiOX is prepared using a one-pot hydrothermal method. The specific procedure is as follows: A certain amount of Bi precursor is weighed and added to a certain amount of ethylene glycol mixed solution, and dissolved under magnetic stirring. Then, a certain amount of X (X = Cl, Br, I) precursor is added to the mixture, and dissolved again under magnetic stirring. The solution is then transferred to a 100 mL polytetrafluoroethylene-lined high-temperature reactor and heated to 120-160℃ for 8-16 hours. The resulting product is washed several times by centrifugation with a polar solvent, dried in a vacuum drying oven, and ground into a uniform powder using an agate mortar.

[0036] In this application, the preparation of Fe-BiOX is similar to that of BiOX, employing a one-pot hydrothermal method. The specific procedure is as follows: A certain amount of Bi precursor and Fe precursor are weighed and added to a certain amount of ethylene glycol mixed solution, and dissolved under magnetic stirring. Then, a certain amount of X (X = Cl, Br, I) precursor is added to the mixture, and dissolved again under magnetic stirring. The solution is then transferred to a 100 mL polytetrafluoroethylene-lined high-temperature reactor and heated to 120-160 °C for 8-16 h. The resulting product is washed several times by centrifugation with a polar solvent, dried in a vacuum drying oven, and ground into a uniform powder using an agate mortar.

[0037] Preparation of other metal ions (Co, Ni, Cu, Sn)-BiOX: The preparation of other metal ions (Co, Ni, Cu, Sn)-BiOX also adopts a one-pot hydrothermal method. The specific scheme is as follows: A certain amount of Bi precursor and Co, Ni, Cu, Sn precursors are weighed and added to a certain amount of ethylene glycol mixed solution, and dissolved under magnetic stirring. Then, a certain amount of X (X = Cl, Br, I) precursor is added to the mixed system, and dissolved again under magnetic stirring. The above solution is then transferred to a 100 mL polytetrafluoroethylene-lined high-temperature reactor and heated to 120-160℃ for 8-16 h. The obtained product is washed several times by centrifugation with a polar solvent, dried in a vacuum drying oven, and ground into a uniform powder in an agate mortar.

[0038] In another aspect, this application provides an NO2 gas sensor, the NO2 gas sensor comprising the above-described NO2 gas sensing material.

[0039] In another aspect, this application provides a method for preparing the above-mentioned NO2 gas sensor, the method comprising:

[0040] A slurry containing the NO2 gas sensing material is drop-coated onto the surface of an interdigitated electrode, dried, and aged to obtain a NO2 gas sensing electrode. The NO2 gas sensing electrode is then connected to a testing instrument to obtain the NO2 gas sensor.

[0041] Optionally, the slurry further includes a solvent, which is at least one of water, ethanol, and acetone;

[0042] The mass concentration of the NO2 gas sensing material in the slurry is 0.1g.

[0043] Optionally, the drying temperature is 65–100°C, and the drying time is 12–48 hours.

[0044] Optionally, the aging temperature is 180–200°C, and the aging time is 12–24 hours.

[0045] Another aspect of this application provides an application of the above-described NO2 gas sensing material or the above-described NO2 gas sensor in detecting NO2, wherein the detection temperature is room temperature.

[0046] As one specific implementation method, the technical solution includes:

[0047] 1. Preparation of Fe-BiOX

[0048] Similar to the preparation method of BiOX, Fe-BiOX is also prepared using a one-pot hydrothermal method. The specific procedure is as follows: A certain amount of Bi precursor and Fe precursor are weighed and added to a certain amount of ethylene glycol mixed solution, and dissolved under magnetic stirring. Then, a certain amount of X (X = Cl, Br, I) precursor is added to the mixture, and dissolved again under magnetic stirring. The solution is then transferred to a 100 mL polytetrafluoroethylene-lined high-temperature reactor and heated to 120-160℃ for 8-16 hours. The resulting product is washed several times by centrifugation with a polar solvent, dried in a vacuum drying oven, and ground into a uniform powder using an agate mortar.

[0049] 2. Fabrication of NO2 Gas Sensor

[0050] (1) Using interdigitated electrodes as gas sensing electrodes, the prepared sample was added to an appropriate amount of solvent and mixed to form a uniform slurry. The slurry was then uniformly drop-coated onto the electrode surface to form a film. The interdigitated electrodes were dried in an oven to evaporate the solvent, resulting in a sensing film.

[0051] (2) Then, the electrode obtained in step (1) is aged in an oven to remove the organic solvent remaining on the electrode, resulting in a gas sensing electrode with stable resistance. The gas sensing electrode is then connected to a testing instrument to obtain a NO2 gas sensor. Optionally, in step (1), the solvent is selected from at least one of ultrapure water, anhydrous ethanol, and acetone.

[0052] 3. NO2 gas detection methods

[0053] (1) Using interdigitated electrodes as gas sensing electrodes, 5-10 μL of slurry was dropped onto the surface of a substrate with Ag-Pd printed interdigitated electrodes. The electrodes were dried at 65-100 °C to form a sensing film.

[0054] (2) The modified interdigitated electrode is heated in an oven to 180-200°C for 12-24 hours to remove residual organic solvents and obtain the NO2 gas sensor to be tested.

[0055] (3) The gas sensing test adopts the dynamic gas mixing method. A flow controller is used to mix a certain concentration of NO2 with air to obtain a quantitative concentration of NO2 gas. The gas is introduced into the test gas box, and the NO2 gas molecules are detected by recording the resistance change of the sensor before and after the gas is introduced.

[0056] (4) Record the initial resistance of the sensor in air as Ra. Introduce different concentrations of trihydroxydibutyl ketone into the test chamber and record the resistance when the gas is introduced as Rg. Plot the working curve based on the relationship between the ratio of Rg to Ra and the concentration of trihydroxydibutyl ketone gas molecules.

[0057] The sensor detects NO2, and the gas sensor operates at room temperature.

[0058] This application enables highly sensitive and selective detection of NO2 at room temperature. The gas sensing material of the sensor is Fe-doped BiOCl.

[0059] This application proposes a design and fabrication method for a NO2 gas sensor capable of rapid detection at room temperature, enabling reversible detection of NO2 gas. The high selectivity and rapid response recovery are attributed to the doping of the variable-valence metal Fe, utilizing the rapid transition between the +2 and +3 valence states of Fe to enhance the adsorption-desorption kinetics of NO2 at room temperature. Simultaneously, the abundant vacancies generated by Fe doping provide rich active sites for NO2 adsorption and reaction, significantly improving its gas sensing performance. The successful design of this material and the fabrication of the sensor offer a new approach and strategy for the detection of toxic and harmful gases at room temperature. Furthermore, the use of variable-valence metals can be extended to fields such as catalysis and energy, making it a valuable reference.

[0060] The beneficial effects that this application can produce include:

[0061] (1) The NO2 gas sensor described in this application is simple to prepare and easy to operate. It achieves rapid, sensitive and highly selective detection of NO2 gas molecules and is low in cost. In addition, the test conditions close to room temperature provide conditions for portable detection of the sensor and has market development prospects.

[0062] (2) This application provides a novel method for preparing nanoelectrode materials. The preparation method is simple and provides a new strategy for regulating the electronic effects caused by doping.

[0063] (3) This application provides technical guidance for the control of response recovery time in the field of gas sensing. Attached Figure Description

[0064] Figure 1 This is the XRD pattern of the NO2 gas sensing material obtained in Example 1 of this application.

[0065] Figure 2 This is a SEM image of the NO2 gas sensing material obtained in Example 1 of this application, where the scale bar is 1 μm.

[0066] Figure 3 This is a gas sensing response diagram of the NO2 gas sensing material obtained in Example 1 of this application. Figure 4 The operating curve of the NO2 gas sensor of Example 10 is plotted for Example 11. Detailed Implementation

[0067] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0068] Unless otherwise specified, all raw materials used in the embodiments of this application were purchased through commercial channels.

[0069] In the embodiments of this application, the following instruments are used to characterize a novel quantum dot-sensitized nanoelectrode gas sensing material:

[0070] Instrument Model Manufacturer RX I Fourier Transform Infrared Spectrometer Perkin Elmer, USA TGA55 Thermogravimetric Analyzer TA Company, USA Model Smart Lab SE XRD Nippon Rigaku Co., Ltd. Gemini 300 Field Emission Scanning Electron Microscope Carl Zeiss AG Optoelectronic Integrated Test Platform CGS-MT KQ3200DB CNC Ultrasonic Cleaner Kunshan Ultrasonic Instruments Co., Ltd.

[0071] Example 1

[0072] Preparation of Fe-BiOCl:

[0073] 0.5 g of bismuth nitrate and 0.1 g of ferric nitrate were weighed and added to 30 mL of a mixed solution of ethylene glycol, and dissolved under magnetic stirring. Then, 0.5 g of NaCl was added to the mixture, and dissolved again under magnetic stirring. The solution was then transferred to a 100 mL polytetrafluoroethylene-lined high-temperature reactor and heated to 120 °C for 8 h. The resulting product was washed five times by centrifugation with ethanol and water, dried in a vacuum drying oven at 50 °C for 24 h, and then ground into a uniform powder using an agate mortar.

[0074] Example 2

[0075] Preparation of Fe-BiOBr:

[0076] 0.5 g of bismuth nitrate and 0.1 g of ferric nitrate were weighed and added to 30 mL of a mixed solution of ethylene glycol, and dissolved under magnetic stirring. Then, 0.5 g of NaBr was added to the mixture, and dissolved again under magnetic stirring. The solution was then transferred to a 100 mL polytetrafluoroethylene-lined high-temperature reactor and heated to 140 °C for 10 h. The resulting product was washed six times by centrifugation with ethanol and water, dried in a vacuum drying oven at 50 °C for 24 h, and then ground into a uniform powder using an agate mortar.

[0077] Example 3

[0078] Preparation of Fe-BiOI:

[0079] 0.5 g of bismuth nitrate and 0.1 g of ferric nitrate were weighed and added to 30 mL of a ethylene glycol mixture, and dissolved under magnetic stirring. Then, 0.5 g of NaI was added to the mixture, and dissolved again under magnetic stirring. The solution was then transferred to a 100 mL polytetrafluoroethylene-lined high-temperature reactor and heated to 160 °C for 12 h. The resulting product was washed six times by centrifugation with ethanol and water, dried in a vacuum drying oven at 40 °C for 12 h, and then ground into a uniform powder using an agate mortar.

[0080] Example 4

[0081] Preparation of Cu-BiOCl:

[0082] 0.5 g of bismuth nitrate and 0.1 g of copper nitrate were weighed and added to 30 mL of a ethylene glycol mixture, and dissolved under magnetic stirring. Then, 0.5 g of NaCl was added to the mixture, and dissolved again under magnetic stirring. The solution was then transferred to a 100 mL polytetrafluoroethylene-lined high-temperature reactor and heated to 120 °C for 10 h. The resulting product was washed five times by centrifugation with ethanol and water, dried in a vacuum drying oven at 45 °C for 12 h, and then ground into a uniform powder using an agate mortar.

[0083] Example 5

[0084] Preparation of Cu-BiOBr:

[0085] 0.5 g of bismuth nitrate and 0.1 g of copper nitrate were weighed and added to 30 mL of a ethylene glycol mixture, and dissolved under magnetic stirring. Then, 0.5 g of NaBr was added to the mixture, and dissolved again under magnetic stirring. The solution was then transferred to a 100 mL polytetrafluoroethylene-lined high-temperature reactor and heated to 140 °C for 10 h. The resulting product was washed five times by centrifugation with ethanol and water, dried in a vacuum drying oven at 60 °C for 12 h, and then ground into a uniform powder using an agate mortar.

[0086] Example 6

[0087] Preparation of Cu-BiOI:

[0088] 0.5 g of bismuth nitrate and 0.1 g of copper nitrate were weighed and added to 30 mL of a ethylene glycol mixture, and dissolved under magnetic stirring. Then, 0.5 g of NaI was added to the mixture, and dissolved again under magnetic stirring. The solution was then transferred to a 100 mL polytetrafluoroethylene-lined high-temperature reactor and heated to 140 °C for 12 h. The resulting product was washed five times by centrifugation with ethanol and water, dried in a vacuum drying oven at 60 °C for 12 h, and then ground into a uniform powder using an agate mortar.

[0089] Example 7

[0090] Preparation of Ni-BiOCl:

[0091] 0.5 g of bismuth nitrate and 0.1 g of nickel nitrate were weighed and added to 30 mL of a ethylene glycol mixture, and dissolved under magnetic stirring. Then, 0.5 g of NaCl was added to the mixture, and dissolved again under magnetic stirring. The solution was then transferred to a 100 mL polytetrafluoroethylene-lined high-temperature reactor and heated to 100 °C for 10 h. The resulting product was washed five times by centrifugation with ethanol and water, dried in a vacuum drying oven at 50 °C for 12 h, and then ground into a uniform powder using an agate mortar.

[0092] Example 8

[0093] Preparation of Co-BiOCl:

[0094] 0.5 g of bismuth nitrate and 0.1 g of cobalt nitrate were weighed and added to 30 mL of a ethylene glycol mixture, and dissolved under magnetic stirring. Then, 0.5 g of NaCl was added to the mixture, and dissolved again under magnetic stirring. The solution was then transferred to a 100 mL polytetrafluoroethylene-lined high-temperature reactor and heated to 160 °C for 10 h. The resulting product was washed five times by centrifugation with ethanol and water, dried in a vacuum drying oven at 60 °C for 24 h, and then ground into a uniform powder using an agate mortar.

[0095] Example 9

[0096] Preparation of Sn-BiOCl:

[0097] 0.5 g of bismuth nitrate and 0.1 g of tin chloride were weighed and added to 30 mL of a ethylene glycol mixture, and dissolved under magnetic stirring. Then, 0.5 g of NaCl was added to the mixture, and dissolved again under magnetic stirring. The solution was then transferred to a 100 mL polytetrafluoroethylene-lined high-temperature reactor and heated to 120 °C for 10 h. The resulting product was washed seven times by centrifugation with ethanol and water, dried in a vacuum drying oven at 60 °C for 24 h, and then ground into a uniform powder using an agate mortar.

[0098] Example 10

[0099] Construction of a NO2 gas sensor:

[0100] (1) Using interdigitated electrodes as gas sensing electrodes, 0.1 g of the novel quantum dot-sensitized nanoelectrode gas sensing material prepared in Example 1 was added to 10 ml of water and mixed to form a homogeneous slurry. Then, 10 μL of the slurry was dropped onto the surface of the Ag-Pd printed interdigitated electrode substrate. The electrode was dried at 80 °C for 24 h to form a sensing film.

[0101] (2) Then the electrode obtained in step (1) is heated to 200°C in an oven for 5 hours to remove the residual organic solvent, thus obtaining the NO2 gas sensor.

[0102] Example 11

[0103] The NO2 gas sensor prepared in Example 10 was applied to the detection of NO2 gas molecules. The steps are as follows:

[0104] (1) Preparation of gas sensing electrode: The NO2 gas sensor constructed in Example 10 was used as the working electrode;

[0105] (2) Preparation of standard gas: In order to obtain the required gas, liquid NO2 is added to the test chamber using a micro-syringe and evaporated directly;

[0106] (3) Plotting the working curve: Connect the electrode described in (1) to the gas sensor detection device, and perform gas mixing in the gas chamber using the method described in (2); test the resistance of the sensor before and after gas flow in a chamber with constant relative humidity and temperature; plot the working curve based on the relationship between the obtained resistance change and NO2 concentration; the resistance change is represented by Rg / Ra, where Ra refers to the resistance in ambient air, and Rg is the resistance in the gas being measured; the working curve is plotted with NO2 gas molecule concentration as the abscissa and Rg / Ra as the ordinate. Figure 4 It can be seen from this that the sensor exhibits a good linear range for NO2.

[0107] Test case

[0108] The NO2 gas sensing material obtained in Example X was tested, wherein XRD was performed as follows: Figure 1 As shown, by Figure 1 As can be seen, the material was successfully synthesized; the SEM image is as follows. Figure 2 As shown, by Figure 2 It can be seen that the material has a hollow nanoflower structure; the gas sensing response diagram is as follows. Figure 3 As shown, by Figure 3 It can be seen that the material responds well to NO2.

[0109] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A NO2 gas sensing material, characterized in that, The NO2 gas sensing material is a semiconductor substrate material doped with variable valence metal elements; The semiconductor substrate material is BiOX, wherein the X element is at least one of Cl, Br, and I; The variable-valence metal element is a variable-valence transition metal element.

2. The NO2 gas sensing material according to claim 1, characterized in that, The variable valence transition metal element is at least one of Fe, Co, Ni, Cu, and Sn; Preferably, the content of variable valence metal elements in the NO2 gas sensing material is 0.01 to 0.05 mol / g, expressed as the molar amount of variable valence metal elements.

3. A method for preparing the NO2 gas sensing material according to any one of claims 1 to 2, characterized in that, The method includes: (1) Mix the Bi-containing precursor and the variable-valence transition metal precursor with an organic solvent to obtain mixed solution I; (2) Add the precursor containing element X to mixed solution I to dissolve, obtain mixed solution II, react, and dry under vacuum to obtain the NO2 gas sensing material.

4. The method according to claim 3, characterized in that, The Bi-containing precursor is selected from at least one of bismuth chloride, bismuth nitrate, and organobismuth compounds. Preferably, in the precursor containing a variable-valence transition metal element, the variable-valence transition metal element is at least one selected from Fe, Co, Ni, Cu, and Sn. The Fe-containing precursor is selected from at least one of ferric chloride, ferric nitrate, and organoferric compounds. The Co-containing precursor is selected from at least one of cobalt chloride, cobalt nitrate, and organocobalt compounds. The Ni-containing precursor is at least one of nickel chloride, nickel nitrate, or organonickel compounds. The Cu-containing precursor is at least one of copper chloride, copper nitrate, or an organocopper compound. The Sn-containing precursor is at least one of tin chloride or organotin compounds.

5. The method according to claim 3, characterized in that, The X-containing precursor is at least one of NaX and KX, wherein X is at least one of Cl, Br, and I; Preferably, the organic solvent is at least one of ethylene glycol, ethanol, and water; Preferably, in the mixed solution I, the concentration of the Bi element precursor is 0.1–0.5 mol / L, calculated as the molar amount of Bi element; Preferably, the mass ratio of the Bi-containing precursor: the X-containing precursor: the variable-valence transition metal precursor is 0.5-1: 0.1-0.5: 0.01-0.

05.

6. The method according to claim 3, characterized in that, The reaction temperature is 120–160°C, and the reaction time is 8–16 hours. Preferably, the vacuum drying temperature is 50–85°C, and the vacuum drying time is 6–12 hours; The reaction temperature in (2) is 160-200℃ and the reaction time is 16-24h. Preferably, in step (2), the reaction is further followed by centrifugal washing with a polar solvent; The polar solvent is at least one of ethanol, water, and methanol; The number of centrifugations is 3 to 7.

7. A NO2 gas sensor, characterized in that, The NO2 gas sensor includes the NO2 gas sensing material as described in any one of claims 1 to 2.

8. A method for preparing the NO2 gas sensor according to claim 7, characterized in that, The preparation method includes: A slurry containing the NO2 gas sensing material is drop-coated onto the surface of an interdigitated electrode, dried, and aged to obtain a NO2 gas sensing electrode. The NO2 gas sensing electrode is then connected to a testing instrument to obtain the NO2 gas sensor.

9. The preparation method according to claim 8, characterized in that, The slurry also includes a solvent, which is at least one of water, ethanol, and acetone; The mass concentration of the NO2 gas sensing material in the slurry is 0.1g. Preferably, the drying temperature is 65–100°C, and the drying time is 12–48 hours; Preferably, the aging temperature is 180–200°C, and the aging time is 12–24 hours.

10. The application of the NO2 gas sensing material according to any one of claims 1 to 3 or the NO2 gas sensor according to claim 7 in the detection of NO2, characterized in that, The temperature measured was room temperature.

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