NixFe2-xO semiconductor gas sensitive material with asymmetric defect, preparation method and application

Abstract

The invention belongs to the field of metal oxide semiconductor-gas sensing, and particularly relates to a Ni < x > Fe < 2-x > O semiconductor gas-sensitive material with asymmetric defects, a preparation method and application, the sensing material is characterized in that Ni is doped in a Fe2O3 framework to form a Ni < x > Fe < 2-x > O bimetallic oxide rich in Ni-Ov-Fe asymmetric defects, Ni is used as a main active site for adsorbing and catalyzing NO2, and the Ni is used as a main active site for adsorbing and catalyzing NO2. And with the mutual reaction with active oxygen on asymmetric defects on the surface of the material, the sensing performance on NO2 is improved. The Ni < x > Fe < 2-x > O sensing material is prepared through a hydrothermal-calcination method, the interaction between Ni element and other atoms in a Fe2O3 frame is remarkable, and the electron transmission capacity is improved. The material is clear in labor division in the NO2 sensing process, NO2 and O2 have respective adsorption activation sites, then reaction is carried out, excellent NO2 sensing response performance and extremely low detection limit (200 ppb) are shown, and a good foundation is laid for development of novel metal oxide semiconductors.

Description

Technical Field

[0001] This invention belongs to the field of metal-oxide-semiconductor gas sensing, and particularly relates to Ni with asymmetric defects. x Fe 2-x O-semiconductor gas-sensitive materials, preparation methods and applications. Background Technology

[0002] Nitrogen dioxide (NO2) is a toxic gas with a strong, pungent odor and is a common air pollutant, primarily originating from vehicle exhaust emissions, fossil fuel combustion, and industrial production processes. NO2 not only poses serious health risks to the human respiratory and nervous systems but also reacts with moisture and oxygen in the air to form nitric acid, causing environmental problems such as acid rain and photochemical smog. Studies have shown that the environmental safety exposure limit for NO2 is relatively low; long-term exposure to even low concentrations of NO2 can have adverse effects on human health. Therefore, highly sensitive, rapid, and stable detection of NO2 in the environment is of great significance for protecting human health and the ecological environment.

[0003] Currently, commonly used NO2 detection methods include chemiluminescence, ultraviolet spectroscopy, Fourier transform infrared spectroscopy, and electrochemical analysis. While these methods offer high detection accuracy, most of the detection equipment is bulky, expensive, and requires complex sample pretreatment processes, hindering real-time, portable monitoring. In contrast, gas sensors based on metal oxide semiconductors (MOS) have become a research hotspot in recent years due to their advantages such as simple fabrication, low cost, fast response speed, and integrability.

[0004] Among numerous metal oxide sensing materials, α-Fe₂O₃ (hematite-type iron oxide) is widely used for NO₂ gas detection due to its good chemical stability, abundant resources, and environmental friendliness. However, pure Fe₂O₃ materials suffer from problems such as small specific surface area, low carrier concentration, and insufficient response sensitivity and selectivity, which limit its application in the detection of low-concentration NO₂. To improve the gas-sensing performance of Fe₂O₃, researchers have proposed various modification strategies, including nanostructure modulation, noble metal loading, and metal ion doping.

[0005] Transition metal ion doping is considered an effective way to improve the gas-sensing performance of Fe2O3. Doping ions can alter the band structure and carrier concentration of Fe2O3, regulating oxygen adsorption and surface reactivity, thereby significantly improving the material's conductivity and gas response characteristics. Nickel (Ni), as a common transition metal, has a stable valence state and strong electronic modulation capabilities. The introduction of Ni ions can not only induce changes in the band structure of the Fe2O3 lattice and promote electron migration, but also increase the density of surface active sites, enhancing the ability to adsorb NO2 molecules, thus achieving a highly sensitive response to NO2 gas.

[0006] Several studies have reported the application of Fe2O3-based metal oxide composites, such as Se-doped Fe2O3 and Ag nanoparticle-modified Fe2O3@MoS2 core-shell structures, in NO2 gas detection, demonstrating advantages such as enhanced response and shortened response / recovery time. However, existing materials still suffer from high detection limits (typically in the ppm range), insufficient selectivity, and poor long-term stability, making it difficult to meet the demand for high-precision real-time detection of low-concentration NO2 (e.g., ppb level). Therefore, developing a gas sensing material with high sensitivity, low detection limit, excellent stability, and selectivity is of significant research and application value for achieving efficient NO2 monitoring. Summary of the Invention

[0007] To address the problems existing in the prior art, this invention provides a Ni with asymmetric defects. x Fe 2-x O-semiconductor gas-sensitive materials, preparation methods and applications, denoted as Ni x Fe 2-x O.

[0008] This invention is achieved by using a Ni material with asymmetric defects. x Fe 2-x The O-semiconductor gas-sensitive material is a bimetallic oxide rich in Ni-Ov-Fe asymmetric defects, formed by replacing Fe atoms in Fe2O3 with a small amount of Ni atoms. The preferred molar fraction x of the doping is 0.01–0.2. During NO2 sensing, Ni acts as an active site to promote NO2 conversion.

[0009] Furthermore, the molar ratio of Ni to Fe is 1:99 to 1:9.

[0010] Furthermore, the Ni produced x Fe 2-x All O-type components must be aged for 24 hours before use.

[0011] The present invention provides a Ni with asymmetric defects x Fe 2-xThe preparation method of O semiconductor gas-sensitive material includes the following steps: Step 1: Prepare the precursor solution: Dissolve a certain proportion of nickel chloride and ferric chloride in a certain amount of deionized water, add an appropriate amount of urea, and stir thoroughly.

[0012] Step 2, Material Preparation: After hydrothermal treatment of the above precursors, centrifugation, washing, drying, and grinding into powder are carried out, followed by high-temperature calcination to obtain Ni. x Fe 2-x O.

[0013] Step 3, Sensor chip preparation: Take an appropriate amount of Ni x Fe 2-x O powder is dissolved in deionized water and ultrasonically mixed to form a homogeneous suspension. An appropriate amount of the suspension is then pipetted onto the electrode plate and allowed to air dry.

[0014] Furthermore, in step one, the molar ratio of nickel chloride to ferric chloride is 1:99 to 1:9, the solution concentration is 0.1-1M, and the molar ratio of the precursor to urea is 1:1-1:5. Urea acts as a precipitant during the hydrothermal process, slowly decomposing to release OH-. - This promotes the uniform precipitation of precursors.

[0015] Furthermore, in step one, the solution needs to be stirred for 0.5-1 hour until the solution is mixed evenly and becomes clear.

[0016] Furthermore, in the hydrothermal treatment in step two, the heat treatment is carried out at 100~180℃ for 10~20h. The high temperature and high pressure provided by the hydrothermal process are to accelerate the reaction process.

[0017] Furthermore, the washing process in step two includes deionized water washing and alcohol washing, three times each, with a drying temperature of 60-90℃ and a time of 6-12 hours. The deionized water washing is to remove excess soluble impurities from the surface, while the alcohol washing process is to wash away residual organic components on the catalyst surface.

[0018] Furthermore, in step two, the hydrothermal temperature is 100~180℃ and the hydrothermal time is 10~20h; calcination is carried out at 100~150℃ for 10~16h, and after the calcination treatment is completed, it is naturally cooled to room temperature.

[0019] Furthermore, in step two, the calcination atmosphere is one or more of hydrogen, ammonia, air, and helium; the calcination temperature is 200~800℃, the calcination time is 2~8h, the heating rate is 2~5℃ / min, and the calcination process is completed and then naturally cooled to room temperature.

[0020] Furthermore, in step three, Ni x Fe 2-x The preparation method of the O sensor sheet is as follows: Nix Fe 2-x Prepare a solution of O with a concentration of 0.01~0.5 g / mL. After thorough mixing, take 1~5 μL of the mixture and coat it onto the electrode sheet, then air dry or bake it. Ni is preferred. x Fe 2-x O The concentration of the solution is 0.05~0.2%. g / mL, preferably the volume of solution obtained is 1~2μL, using water or ethanol as solvent.

[0021] Another object of the present invention is to provide a method utilizing the Ni x Fe 2-x Application of O semiconductor gas-sensitive materials in NO2 gas sensing.

[0022] Based on the above technical solutions and the technical problems solved, the advantages and positive effects of the technical solution to be protected by this invention are as follows: First, to address the problems of poor stability and detection limits that fail to meet practical requirements in traditional metal oxide sensors, this invention prepares Ni with asymmetric defects via a hydrothermal method. x Fe 2-x In Ni-doped sensing materials, significant interactions enhance electron transport capabilities. Ni acts as an active site, promoting NO2 adsorption and conversion. The resulting asymmetric defects induce local electron rearrangement, adsorbing large amounts of reactive oxygen species as reactants for NO2. Ni doping significantly improves the material's NO2 sensing response and lowers the detection limit (10 ppb), while also reducing the optimal operating temperature (approximately 50°C). This indicates that the asymmetric defects in Ni... x Fe 2-x O materials possess superior catalytic performance, laying a solid foundation for the development of novel metal oxide semiconductors and providing new possibilities for the development of high-precision integrated sensors.

[0023] The Ni with asymmetric defects provided by this invention x Fe 2-x The preparation method of O nanoparticle metal oxide semiconductor sensing materials is convenient, low-cost, highly operable, and easy to realize industrial production.

[0024] This invention provides a method for detecting NO2 in bimetallic oxide semiconductor materials. Ni specifically adsorbs NO2 molecules, which then react fully with reactive oxygen species on the material surface, resulting in a significant change in electrical resistance even at extremely low concentrations. Furthermore, the incorporation of Ni facilitates smoother electron transfer within the material, leading to a faster response recovery time. Simultaneously, surface asymmetric defects enhance oxygen activation, increasing surface activity and optimizing the reaction temperature for NO2 sensing. This invention overcomes the current limitations of insufficient detection limits and high operating temperatures in NO2 sensing, providing an optimized approach for the development of other high-performance gas-sensitive materials.

[0025] Secondly, as supplementary evidence of the inventiveness of the claims of this invention, it is also reflected in the following important aspects.

[0026] (1) The expected benefits of the technical solution of the present invention after transformation are: Since the sensing material is inexpensive and easy to synthesize, it is suitable for mass production and can be used to combine MEMS technology with integrated circuits to make an integrated sensing microsystem, which provides a foundation and possibility for the development of portable, fast and compact new gas sensing devices.

[0027] (2) The technical solution of this invention fills a technical gap in the industry both domestically and internationally: there have been no reports on metal oxide gas sensing materials with extremely low experimental detection limits (<100ppb) for detecting NO2 gas under dynamic gas mixing conditions. The technical solution proposed in this invention realizes the preparation of ultrasensitive sensing materials, which have low operating temperature and excellent selectivity, as well as strong moisture resistance, and can be used for practical detection.

[0028] (3) The technical solution of the present invention solves a technical problem that people have long desired to solve but have never been able to solve successfully: The present invention provides a method to solve the problem that the detection limit of metal oxide sensors for detecting NO2 gas is not low enough. In the NO2 gas sensing process, Ni specifically adsorbs NO2 molecules and reacts with the surface active oxygen phase adsorbed by the asymmetric defects around it, and can continuously adsorb new NO2 gas molecules, showing a strong attraction to low concentrations of NO2. Therefore, the sensor exhibits an extremely low detection limit. Attached Figure Description

[0029] Figure 1 The present invention relates to Ni with asymmetric defects. x Fe 2-x Flowchart of the preparation process of O semiconductor gas-sensitive materials. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0031] This invention provides a Ni with asymmetric defects. x Fe 2-x The O-semiconductor gas-sensitive material comprises: a small amount of Ni atoms replacing Fe atoms in Fe2O3 to form a bimetallic oxide rich in Ni-Ov-Fe asymmetric defects, wherein the doping molar fraction x is preferably 0.01–0.20. During NO2 sensing, Ni acts as an active site to promote NO2 conversion, while the asymmetric defects serve as activation sites for O2.

[0032] The molar ratio of Ni to Fe is 1:99 to 1:9.

[0033] The asymmetric defect Ni x Fe 2-x The working principle of O-semiconductor gas-sensitive materials is based on the synergistic effect of Ni and Fe, as well as their contained asymmetric defects. First, Fe2O3 provides a good conductive substrate with a high specific surface area and abundant defects that can adsorb oxygen species. This structure allows Fe2O3 nanoparticles to effectively participate in gas adsorption and reaction processes, while Ni atoms act as adsorbents and catalyzers for NO2, thereby enhancing the overall gas-sensing performance of the material.

[0034] In the NO2 gas sensing process, Ni x Fe 2-x Defects on the surface of O nanoparticles play a crucial role. These defects primarily refer to the structural asymmetric vacancies formed after Ni doping due to the absence of oxygen atoms and the difference in atomic size between the two metals. These asymmetric defects provide adsorption sites for O2 molecules, forming oxygen-active species (O2). 2- O - and O 2- These oxygen-reactive species react with NO2, resulting in electron transfer, a change that can be detected, thus enabling NO2 gas sensing.

[0035] The molar ratio of Ni to Fe is controlled between 1:99 and 1:9. Adjusting this ratio can further optimize the material's sensing performance. Changes in this ratio affect the distribution of Ni atoms within the Fe₂O₃ framework and the formation of oxygen vacancies, thus influencing the material's overall gas-sensing properties. In practical applications, this ratio can be adjusted according to specific needs to achieve optimal NO₂ sensing performance.

[0036] like Figure 1 As shown, an embodiment of the present invention provides a Ni with asymmetric defects. x Fe 2-x The preparation method of O semiconductor gas-sensitive material includes the following steps: Step 1: Prepare the precursor solution: Dissolve a certain proportion of nickel chloride and ferric chloride in a certain amount of deionized water, add an appropriate amount of urea, and stir thoroughly.

[0037] Step 2, Material Preparation: After hydrothermal treatment of the above precursors, centrifugation, washing, drying, and grinding into powder are carried out, followed by high-temperature calcination to obtain Ni. x Fe 2-x O.

[0038] Step 3, Sensor chip preparation: Take an appropriate amount of Ni x Fe 2-x O powder is dissolved in deionized water and ultrasonically mixed to form a homogeneous suspension. An appropriate amount of the suspension is then pipetted onto the electrode plate and allowed to air dry.

[0039] In step one, the molar ratio of nickel chloride to ferric chloride is 1:99 to 1:9, preferably 1:50 to 1:9; the solution concentration is 0.1 to 1 M, preferably 0.1 to 0.5 M; and the molar ratio of the precursor to urea is 1:1 to 1:5, preferably 1:3 to 1:5. Urea acts as a precipitant during the hydrothermal process, slowly decomposing to release OH-. - This promotes the uniform precipitation of precursors.

[0040] In step one, the solution needs to be stirred for 0.5 to 1 hour until the solution is mixed evenly and becomes clear.

[0041] In step two, the hydrothermal treatment involves heat treatment at 100-180°C for 10-20 hours, preferably at 100-150°C for 10-16 hours. The high temperature and pressure provided by the hydrothermal process are to accelerate the reaction process.

[0042] The washing process in step two includes deionized water washing and alcohol washing, three times each, with a drying temperature of 60-90℃ and a time of 6-12 hours. The deionized water washing is to remove excess soluble impurities from the surface, while the alcohol washing process is to wash away residual organic components on the catalyst surface.

[0043] In step two, the calcination atmosphere is one of hydrogen, ammonia, air, or helium; the calcination temperature is 200~800℃, the calcination time is 2~8h, and the heating rate is 2~5℃ / min; preferably 400~600℃, calcination time is 2~4h. After calcination, the mixture is allowed to cool naturally to room temperature.

[0044] In step three, Ni x Fe 2-x The preparation method of the O sensor sheet is as follows: Ni x Fe 2-x Prepare a solution of O with a concentration of 0.01~0.5 g / mL. After thorough mixing, take 1~5 μL of the mixture and coat it onto the electrode sheet, then air dry or bake it. Ni is preferred.x Fe 2-x The concentration of the O solution is 0.05~0.2g / mL, and the volume of the solution obtained is preferably 1~2μL, using water or ethanol as the solvent.

[0045] This invention provides a method for utilizing the Ni x Fe 2-x Application of O semiconductor gas-sensitive materials in NO2 gas sensing.

[0046] To make the present invention more fully disclosed, more specific embodiments are described below.

[0047] Example 1: Ni x Fe 2-x Preparation of O: First, a precursor solution of FeCl3·6H2O and NiCl2·6H2O in a certain proportion was prepared according to relevant data, and then a certain amount of urea was added. The molar ratio of Ni to Fe was 1:19, and the solution concentration was controlled at 0.1M. Then, a hydrothermal reaction was carried out in an oven at 120℃ for 10 hours. After natural cooling, the mixture was washed three times with water and ethanol respectively, dried, and ground into powder. The powder was then calcined at 500℃ for 2 hours in a tube furnace under hydrogen conditions. After calcination, it was ground again to obtain Ni. 0.1 Fe 1.9 O3 powder. Can be directly fabricated for use in NO2 sensing.

[0048] NO2 gas sensing performance test: Ni 0.1 Fe 1.9 O3 powder was mixed with water to a concentration of 0.1 mg / μL. 2 μL of the suspension was pipetted onto an electrode plate, allowed to air dry, and then connected to a resistance monitoring device for NO2 detection. The dynamic gas detection flow rate was 3 L / min, simulating the gaseous composition of NO2 in the air, consisting of a mixture of NO2, N2, and O2, with O2 maintaining a 21% concentration. First, the sensor resistance was stabilized at 150°C in air. By varying the ratio of NO2 and N2 while keeping O2 constant, the target concentration was achieved. Then, simulated NO2 gas was introduced into the reaction chamber, triggering a sensor response. After reaching peak response, the simulated NO2 gas was cut off, and air was introduced, allowing the sensor response to recover.

[0049] At 150°C, this Ni 0.05 Fe 1.95The O sensor has a response value of Ra / Rg=21 for detecting 10ppm NO2 gas, a response time of 26s, and a recovery time of 41s; it exhibits different progressive response values ​​for different concentrations of NO2 gas; the detection limit is as low as 200ppb; it has excellent selectivity, short-term cycling performance (relative standard deviation of only 0.9% for 10 response values) and long-term stability (it can still maintain a response value of Ra / Rg=21 during a test of up to 60 days).

[0050] Example 2: Ni x Fe 2-x Preparation of O: First, a precursor solution of FeCl3·6H2O and NiCl2·6H2O in a certain proportion was prepared according to relevant data, and then a certain amount of urea was added. The molar ratio of Ni to Fe was 1:9, and the solution concentration was controlled at 0.1M. Then, a hydrothermal reaction was carried out in an oven at 120℃ for 10 hours. After natural cooling, the mixture was washed three times with water and ethanol respectively, dried, and ground into powder. The powder was then calcined at 500℃ for 2 hours in a tube furnace under ammonia conditions. After calcination, it was ground again to obtain Ni. 0.2 Fe 1.8 O3 powder. Can be directly fabricated for use in NO2 sensing.

[0051] NO2 gas sensing performance test: Ni 0.2 Fe 1.8 O3 powder was mixed with water to a concentration of 0.1 mg / μL. 2 μL of the suspension was pipetted onto an electrode plate, allowed to air dry, and then connected to a resistance monitoring device for NO2 detection. The dynamic gas detection flow rate was 3 L / min, simulating the gaseous composition of NO2 in the air, consisting of a mixture of NO2, N2, and O2, with O2 maintaining a 21% concentration. First, the sensor resistance was stabilized at 150°C in air. By varying the ratio of NO2 and N2 while keeping O2 constant, the target concentration was achieved. Then, simulated NO2 gas was introduced into the reaction chamber, triggering a sensor response. After reaching peak response, the simulated NO2 gas was cut off, and air was introduced, allowing the sensor response to recover.

[0052] At 150°C, this Ni 0.2 Fe 1.8 The O3 sensor has a response value of Ra / Rg=10 for detecting 10ppm NO2 gas, a response time of 43s, and a recovery time of 66s. It exhibits different progressive response values ​​for different concentrations of NO2 gas. The detection limit is as low as 500ppb. It has excellent selectivity, short-term cycling performance (relative standard deviation of only 0.9% for 10 response values) and long-term stability (it can still maintain a response value of Ra / Rg=10 during a test of up to 60 days).

[0053] Example 3: Ni x Fe 2-x Preparation of O: First, a precursor solution of FeCl3·6H2O and NiCl2·6H2O in a certain proportion was prepared according to relevant data, and then a certain amount of urea was added. The molar ratio of Ni to Fe was 1:39, and the solution concentration was controlled at 0.1M. Then, a hydrothermal reaction was carried out in an oven at 120℃ for 10 hours. After natural cooling, the mixture was washed three times with water and ethanol respectively, dried, and ground into powder. The powder was then calcined in a muffle furnace at 500℃ under air conditions for 2 hours. After calcination, it was ground again to obtain Ni. 0.05 Fe 1.95 O3 powder. Can be directly fabricated for use in NO2 sensing.

[0054] NO2 gas sensing performance test: Ni 0.05 Fe 1.95 O3 powder was mixed with water to a concentration of 0.1 mg / μL. 2 μL of the suspension was pipetted onto an electrode plate, allowed to air dry, and then connected to a resistance monitoring device for NO2 detection. The dynamic gas detection flow rate was 3 L / min, simulating the gaseous composition of NO2 in the air, consisting of a mixture of NO2, N2, and O2, with O2 maintaining a 21% concentration. First, the sensor resistance was stabilized at 150°C in air. By varying the ratio of NO2 and N2 while keeping O2 constant, the target concentration was achieved. Then, simulated NO2 gas was introduced into the reaction chamber, triggering a sensor response. After reaching peak response, the simulated NO2 gas was cut off, and air was introduced, allowing the sensor response to recover.

[0055] At 150°C, this Ni 0.05 Fe 1.95 The O3 sensor has a response value of Ra / Rg=15 for detecting 10ppm NO2 gas, a response time of 78s, and a recovery time of 112s. It exhibits different progressive response values ​​for different concentrations of NO2 gas. The detection limit is as low as 500ppb. It has excellent selectivity, short-term cycling performance (relative standard deviation of only 0.9% for 10 response values) and long-term stability (it can still maintain a response value of Ra / Rg=15 during a test of up to 60 days).

[0056] Example 4: Ni x Fe 2-xPreparation of O: First, a precursor solution of FeCl3·6H2O and NiCl2·6H2O in a certain proportion was prepared according to relevant data, and then a certain amount of urea was added. The molar ratio of Ni to Fe was 1:49, and the solution concentration was controlled at 0.1M. Then, a hydrothermal reaction was carried out in an oven at 120℃ for 10 hours. After natural cooling, the mixture was washed three times with water and ethanol respectively, dried, and ground into powder. The powder was then calcined at 500℃ for 2 hours in a tube furnace under hydrogen conditions. After calcination, it was ground again to obtain Ni. 0.2 Fe 1.8 O3 powder. Can be directly fabricated for use in NO2 sensing.

[0057] NO2 gas sensing performance test: Ni 0.04 Fe 1.96 O3 powder was mixed with water to a concentration of 0.1 mg / μL. 2 μL of the suspension was pipetted onto an electrode plate, allowed to air dry, and then connected to a resistance monitoring device for NO2 detection. The dynamic gas detection flow rate was 3 L / min, simulating the gaseous composition of NO2 in the air, consisting of a mixture of NO2, N2, and O2, with O2 maintaining a 21% concentration. First, the sensor resistance was stabilized at 150°C in air. By varying the ratio of NO2 and N2 while keeping O2 constant, the target concentration was achieved. Then, simulated NO2 gas was introduced into the reaction chamber, triggering a sensor response. After reaching peak response, the simulated NO2 gas was cut off, and air was introduced, allowing the sensor response to recover.

[0058] At 150°C, this Ni 0.04 Fe 1.96 The O3 sensor has a response value of Ra / Rg=8 for detecting 10ppm NO2 gas, a response time of 92s, and a recovery time of 150s. It exhibits different progressive response values ​​for different concentrations of NO2 gas. The detection limit is as low as 1ppm. It has excellent selectivity, short-term cycling performance (the relative standard deviation of 10 response values ​​is only 0.9%), and long-term stability (it can still maintain a response value of Ra / Rg=8 during a test of up to 60 days).

Claims

1. A Ni with asymmetric defects x Fe 2-x O-semiconductor gas-sensitive material, characterized in that... A small number of Ni atoms replace Fe atoms in Fe2O3 to form a bimetallic oxide rich in Ni-Ov-Fe asymmetric defects. Ni acts as the main active site for adsorbing and catalyzing NO2, and reacts with active oxygen on the asymmetric defects to improve the sensing performance of NO2.

2. A Ni having asymmetric defects according to claim 1 x Fe 2-x The method for preparing O semiconductor gas-sensitive materials is characterized by... Includes the following steps: S101: Preparation of precursor solution: Dissolve a certain proportion of nickel nitrate and ferric nitrate in a certain amount of deionized water, add an appropriate amount of urea, and stir thoroughly. S102: Material preparation: After hydrothermal treatment of the above precursors, centrifugation, washing, drying, and grinding into powder are carried out, followed by calcination to obtain Ni. x Fe 2-x O; S103: Sensor sheet preparation: Take an appropriate amount of Ni x Fe 2-x O powder is dissolved in deionized water and ultrasonically mixed to form a uniform suspension. An appropriate amount of the suspension is then added to the electrode plate using a pipette and allowed to air dry.

3. The Ni with asymmetric defects as described in claim 1 x Fe 2-x The method for preparing O semiconductor gas-sensitive materials is characterized by... The Ni element in S101 comes from one or more of nickel chloride, nickel nitrate, nickel acetate, nickel sulfate, and nickel phosphate.

4. The Ni with asymmetric defects as described in claim 1 x Fe 2-x The method for preparing O semiconductor gas-sensitive materials is characterized by... The Fe metal salt solution in S101 includes one or more of ferric chloride, ferric acetate, ferric chloride, ferric sulfate, and ferric phosphate.

5. The Ni with asymmetric defects as described in claim 1 x Fe 2-x The method for preparing O semiconductor gas-sensitive materials is characterized by... The molar ratio of Ni metal salt to Fe metal salt in S101 is 1:99 to 1:9; The stirring time in S101 is 0.5~1h until the solution is mixed evenly and clear; The hydrothermal temperature in S102 is 100~180℃, and the hydrothermal time is 10~20h; it is calcined at 100~150℃ for 10~16h, and then naturally cooled to room temperature after the calcination treatment is completed.

6. The Ni with asymmetric defects as described in claim 1 x Fe 2-x The method for preparing O semiconductor gas-sensitive materials is characterized by... In S102, the calcination atmosphere is one or more of hydrogen, ammonia, air, and helium; the calcination temperature is 200~800℃, the calcination time is 2~8h, and the calcination process is completed and then naturally cooled to room temperature.

7. The Ni with asymmetric defects as described in claim 1 x Fe 2-x The method for preparing O semiconductor gas-sensitive materials is characterized by... Ni in S103 x Fe 2-x The preparation method of the O sensor sheet is as follows: Ni x Fe 2-x Prepare a solution of O with a concentration of 0.01~0.5g / mL. After mixing evenly, take 1~5μL of the mixed solution and coat it onto the electrode sheet. Let it air dry or bake dry, using water or ethanol as the solvent.

8. A Ni with asymmetric defects prepared by the preparation method according to any one of claims 2 to 7 x Fe 2-x Application of O semiconductor gas-sensitive materials in NO2 gas sensing.

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