NO gas-sensitive material, preparation method thereof and application of NO gas-sensitive material in sensor

Abstract

The invention relates to an NO gas-sensitive material, a preparation method thereof and application of the NO gas-sensitive material in a sensor, and belongs to the technical field of gas sensing. The NO gas sensitive material is metal-doped tungsten trioxide, and the metal doping amount in the NO gas sensitive material is 1-5 mol%; the metal is In, Nb, V and Ta. Tungsten hexachloride, n-heptane and metal chloride are mixed to prepare a mixed solution; carrying out heating reaction on the mixed solution to obtain a coarse precipitate, and centrifuging and washing the coarse precipitate to obtain a fine precipitate; and drying, grinding and calcining the fine precipitate to obtain the NO gas-sensitive material. The preparation method of the NO gas-sensitive material is simple and has controllability and repeatability, the NO gas-sensitive material shows excellent response sensitivity when being used for the NO gas sensor, and the NO gas-sensitive material has the advantages of accurate response sensitivity, gas interference resistance, long-term use stability and the like when being applied to the NO gas sensor based on a temperature modulation detection method; the device is especially suitable for detecting NO gas exhaled by a human body.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of gas sensing, and particularly relates to a NO gas-sensitive material, a preparation method thereof and application thereof in a sensor. BACKGROUND

[0002] Nitric oxide (NO) is a colorless and odorless gas, which can pose a serious threat to human health at high concentrations. In industrial and agricultural activities, the emission of NO is one of the important environmental problems. NO also has important physiological functions in living organisms. Exhaled NO is an important biomarker of asthma. A NO sensor is a device for detecting the concentration of nitric oxide in the environment, which is widely used in industrial emission monitoring, environmental monitoring, laboratory research, and medical health fields. However, due to different application scenarios, the performance requirements of NO sensors, such as detection range, sensitivity, response time, etc., are also significantly different.

[0003] Metal oxide semiconductors (MOS) play an important role in detecting various volatile organic compound gases, such as zinc oxide, tin oxide, tungsten oxide, titanium oxide, etc. Gas-sensitive materials can be used for detecting gases such as ethanol, methane, nitrogen dioxide, carbon monoxide, nitric oxide, and hydrogen. However, it is still a challenge to obtain a gas sensor with high selectivity, sensitivity, fast response, and stability, as well as the best response working temperature matching the gas sensor. SUMMARY

[0004] In view of the problems in the prior art, the application provides a NO gas-sensitive material, a preparation method thereof, and application thereof in a sensor.

[0005] To achieve the above-mentioned purpose, the technical solution adopted by the application is as follows: In a first aspect, the application provides a NO gas-sensitive material, which is metal-doped tungsten trioxide (WO3), wherein the metal doping amount is 1-5 mol%; the metal is any one of In, Nb, V, and Ta; the preparation method of the NO gas-sensitive material comprises the following steps: mixing tungsten hexachloride, n-heptane, and metal chloride to prepare a mixed solution; heating and reacting the mixed solution to obtain a coarse precipitate, and then centrifuging and washing the coarse precipitate to obtain a fine precipitate; drying, grinding, and calcining the fine precipitate to obtain metal-doped tungsten trioxide, which is the NO gas-sensitive material; and the molar ratio of the tungsten hexachloride to the metal chloride is 10: (0.101-0.526).

[0006] Preferably, the metal is Ta.

[0007] Preferably, the metal doping amount is 2 mol%.

[0008] Further, the amount of the tungsten hexachloride used in 1 mL of n-heptane is 0.2-0.25 mmol.

[0009] For example, the amount ratio of the tungsten hexachloride, n-heptane and metal chloride is 10 mmol: (40-50) mL: (0.101-0.526) mmol. Preferably, the amount ratio of the tungsten hexachloride, n-heptane and metal chloride is 10 mmol: 50 mL: (0.101-0.526) mmol.

[0010] Further, the metal chloride is TaCl5, InCl3, VCl3, NbCl5.

[0011] Further, the heating reaction condition is 140-180℃ for 10-14h; preferably, the heating reaction condition is 160℃ for 12h.

[0012] Further, the centrifugation and washing of the crude precipitate to obtain fine precipitate comprises: adding the crude precipitate into anhydrous ethanol and centrifuging at a speed of 5000-7000 r / min for 3-6 min, repeating 3-5 times, and then replacing the anhydrous ethanol with deionized water and repeating the above centrifugation operation to collect the fine precipitate. Preferably, the crude precipitate is added into anhydrous ethanol and centrifuged at a speed of 6000 r / min for 5 min, repeating 5 times, and then replacing the anhydrous ethanol with deionized water and centrifuging at a speed of 7000 r / min for 3 min, repeating 3 times.

[0013] Further, the drying condition is 55-80℃ for 12-24h; preferably, the drying condition is 60℃ for 12h.

[0014] Further, the calcination condition is 420-480℃ for 2-4h, and the heating rate is 2-5℃ / min; preferably, the calcination condition is 450℃ for 2h, and the heating rate is 2℃ / min.

[0015] In a second aspect, the present application provides a NO gas sensor, which comprises a sensing element, and the sensing element comprises the NO gas-sensitive material.

[0016] Further, the response temperature of the NO gas sensor at constant temperature is 100-300℃, and preferably, the response temperature at constant temperature is 175℃.

[0017] Further, the gas-sensitive response detection limit of the NO gas sensor is 5ppb.

[0018] In a third aspect, the present application provides a NO detection method based on temperature modulation, which is implemented by using the NO gas sensor and comprises the following steps: In a first stage, the sensing unit is desorbed according to a target desorption temperature in an air environment, and the resistance fluctuation error in t seconds is determined every t seconds until the resistance fluctuation error in t seconds is less than or equal to 5%; In a second stage, the resistance change of the sensing unit at a response temperature is recorded in an air environment, and the duration is m seconds; In a third stage, the first stage is performed after the second stage is completed, that is, the sensing unit is desorbed according to a target desorption temperature in an air environment, and the resistance fluctuation error in t seconds is determined every t seconds until the resistance fluctuation error in t seconds is less than or equal to 5%; In a fourth stage, the resistance of the sensing unit at a response temperature is recorded in an NO environment, and the gas-sensitive response of the sensor to NO is obtained based on a sensitivity calculation method; After the fourth stage is completed, a detection cycle is ended, and the NO gas sensor enters the first stage or the second stage.

[0019] Preferably, the temperature range of the temperature modulation is 175-350℃.

[0020] Further, the NO gas sensor based on the detection method of temperature modulation is used for the NO gas sensitivity detection in human exhaled gas; and the concentration detection range of NO is 5-200 ppb.

[0021] The present application has the following beneficial effects: The NO gas-sensitive material provided by the present application has simple preparation method, controllability and repeatability, exhibits excellent response sensitivity when used in the NO gas sensor, and has accurate response sensitivity, gas interference resistance and long-term use stability when applied in the NO gas sensor based on the detection method of temperature modulation, and is especially suitable for the detection of human exhaled NO gas.

[0022] Other features and advantages of the present application will be illustrated in the following description, and some will become apparent from the description, or will be understood by those skilled in the art through implementation of the present application. The purposes and other advantages of the present application can be achieved and obtained by the specific embodiments indicated in the description. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 XRD patterns of the NO gas-sensitive materials prepared in Examples 1-4; Figure 2 SEM images of the NO gas-sensitive materials prepared in Examples 1-4; Figure 3Gas sensing response of NO gas sensor of Example 1-4 to 50 ppb NO at 100-300 °C constant temperature working condition; Figure 4 Detection limit of gas sensing response of NO gas sensor of Example 1 to NO at constant temperature working condition; Figure 5 Gas sensing response of NO gas sensor of Example 1 to 50 ppb NO at constant temperature working condition with 50 ppb interfering gas NO2; Figure 6 Response time and recovery time of NO gas sensor of Example 1 to 50 ppb NO at constant temperature 175 °C working condition; Figure 7 Working flow chart of detection method based on temperature modulation for NO gas sensor; Figure 8 Response and recovery of NO gas sensor of Example 1 to 50 ppb NO based on detection method of temperature modulation; Figure 9 Gas sensing response of NO gas sensor of Example 1 to 5-200 ppb NO under temperature modulation; Figure 10 Response curve and gas sensing response of NO gas sensor of Example 1 to various test gases under temperature modulation; Figure 11 Dry gas interference test of NO gas sensor of Example 1 under temperature modulation; Figure 12 Repeatability and long-term stability test of NO gas sensor of Example 1 under temperature modulation; Figure 13 Concentration response curve of NO gas sensor of Example 1 to different concentrations of NO under temperature modulation at different humidity; Figure 14 Accuracy test curve of NO gas sensor of Example 1 to different concentrations of NO under temperature modulation; Figure 15 Accuracy test curve of NO gas sensor of Example 1 to NO in mixed gas environment under temperature modulation. DETAILED DESCRIPTION

[0024] In order to make the purposes, technical solutions and advantages of the present application clearer, the embodiments of the present application will be described in detail below with specific examples. The technical terms and scientific terms used in the present application have the meanings commonly understood by those skilled in the art of the present application, unless otherwise defined. Those skilled in the art can make various improvements and changes to the specific embodiments of the present application without departing from the concept of the present application, and these all fall within the scope of protection of the present application. The raw materials used in the present application are all commercially available unless otherwise specified.

[0025] Example 1 The NO gas sensitive material is 2 mol%Ta-WO3, and the preparation method of the NO gas sensitive material comprises the following steps: mixing tungsten hexachloride, n-heptane and metal chloride TaCl5 (99.99%, purchased from Merck) according to WCl6:TaCl5:n-heptane=10.00 mmol:0.204 mmol:50.0 mL and fully stirring for 4 hours to prepare a mixed solution with a concentration of 0.2 M and a volume of 50 mL; transferring the mixed solution into a 100 mL stainless steel polytetrafluoroethylene reaction kettle, heating and reacting at 160°C for 12 hours to obtain a coarse precipitate, centrifuging the coarse precipitate in anhydrous ethanol at a speed of 6000 r / min for 5 minutes, repeating 5 times, replacing the anhydrous ethanol with deionized water, and centrifuging at a speed of 7000 r / min for 3 minutes, repeating 3 times to obtain a fine precipitate; drying the fine precipitate in a 60°C oven for 12 hours, grinding, heating at a rate of 2°C / min, calcining at 450°C for 2 hours to obtain 2 mol%Ta-WO3.

[0026] Preparation of the NO gas sensor: The NO gas sensor comprises 16 sensing elements, and each sensing element is composed of a zirconia micro-hotplate chip, a gas sensitive film, a pin electrode, a heating electrode and a temperature measuring electrode. The gas sensitive film is formed by spraying and coating the 2 mol%Ta-WO3 gas sensitive material on the pin electrode, the materials of the heating electrode and the temperature measuring electrode are Pt, the material of the pin electrode is Au, the heating electrode is used for heating the gas sensitive film, the temperature measuring electrode can feedback the temperature of the gas sensitive film, and the pin electrode is used for collecting the resistance signal of the gas sensitive film.

[0027] The spraying and coating of the gas sensitive film comprises the following steps: adding 2 g of 2 mol%Ta-WO3 gas sensitive material into 10 g of organic slurry with a certain ratio, grinding for 10 minutes, adjusting the slurry viscosity to 4500 mPa·s, transferring the prepared initial slurry into a ball mill tank, and ball milling at a speed of 300 r / min for 4 hours to prepare the gas sensitive slurry.

[0028] The organic slurry is prepared from organic solvent and additives in a mass ratio of 10:0.5; the solvent is prepared from terpineol, butyl carbitol acetate, dibutyl phthalate in a mass ratio of 5:3.5:1.5; the additives are ethyl cellulose, sorbitan trioleate, 1,4 butyrolactone, hydrogenated castor oil in a mass ratio of 12:8:2:1.

[0029] The gas sensitive slurry is prepared by electrostatic micro-jet (electrostatic voltage 1000V, slurry flow 1 ul / min) using a 60 micron diameter needle to spray the pin electrode part of the zirconia micro-hotplate chip, forming a gas sensitive film, followed by calcination at 350°C for 2 hours, gold ball wire bonding packaging and aging, and the NO gas sensor is completed.

[0030] Example 2 Different from Example 1, the NO gas sensitive material is 2 mol% In-WO3, and the metal chloride is InCl3 (99.99%, purchased from Merck).

[0031] Example 3 Different from Example 1, the NO gas sensitive material is 2 mol% Nb-WO3, and the metal chloride is NbCl5 (99.99%, purchased from Merck).

[0032] Example 4 Different from Example 1, the NO gas sensitive material is 2 mol% V-WO3, and the metal chloride is VCl3 (>99%, purchased from Merck).

[0033] Figure 1 The XRD analysis of the NO gas sensitive materials prepared in Examples 1-4 shows that WO3 can be accurately matched to the corresponding standard card (PDF #20-1324), and all the doped modified WO3 materials show excellent crystallinity and purity, with almost no additional impurity peaks, proving that the sample materials are successfully synthesized.

[0034] Figure 2 The SEM images of the NO gas sensitive materials prepared in Examples 1-4 show that the particles of all the materials are tightly packed, and all the materials do not show special morphology structure, and compared with the method of controlling the morphology structure and material composition, this preparation method has better controllability and repeatability.

[0035] The gas response test of the NO gas sensor prepared in Examples 1-4 is as follows: (1) Constant temperature NO response test: In the constant temperature working mode, the NO gas sensor prepared by Example 1-4 was passed with air at a constant point temperature in the temperature range of 100-300°C, and after the resistance value of the NO gas sensor was stable, the target gas 50 ppb of NO was passed to record the resistance value. According to the standard definition of gas sensitive response, the resistance of the sensor in air and NO environment is represented as R Air and R NO (Air and NO as subscripts). The calculation method for evaluating the NO response in this constant temperature working mode is as follows: Response (constant temperature mode) = R NO / R Air . Referring to Figure 3 , in the constant temperature working mode, in the temperature range of 100-300°C, the response of the NO gas sensor of Example 1-4 to 50 ppb of NO increases first and then decreases with the increase of working temperature, and the maximum response is observed at 175°C, wherein 2 mol% Ta-WO3 shows obvious advantages.

[0036] In addition, referring to Figure 4 , the NO gas sensor of 2 mol% Ta-WO3 prepared by Example 1 has a detection limit of at least 5 ppb for the gas sensitive response of NO, which has excellent detection sensitivity compared with the detection limit of ppm order.

[0037] (2) For NO, NO2 is the most recognized interfering gas, and constant temperature NO response test containing interfering gas NO2 is carried out: the difference from (1) test is that the NO gas sensor prepared by Example 1 is passed with target gas 50 ppb of NO and 50 ppb of interfering gas NO2. Referring to Figure 5 , the gas sensitive response value (t 90%Res time) of 2 mol% Ta-WO3 to 50 ppb of NO2 is compared with the gas sensitive response value of NO at the same temperature, and it is found that at 175°C in constant temperature mode, 2 mol% Ta-WO3 meets the requirement of NO sensitivity, and the NO response interference rate is the smallest, and the best NO response temperature is determined as 175°C.

[0038] (3) Constant temperature NO response and recovery time test: Since the NO gas sensor of Example 1-4 shows the maximum response at 175°C, and the NO2 response interference rate is the smallest, Example 1 is selected for response and recovery time test.

[0039] Referring to Figure 6 , under the condition of 175°C constant temperature, the response time and recovery time of 2 mol% Ta-WO3 sensor unit of Example 1 exposed to 50 ppb of NO are 64.10 s (t90%Res ) and 78.10 s (t 90%Rec ).

[0040] Example 5 In order to further optimize the response and recovery time of the NO gas sensor, the inventors propose a temperature modulation based detection method for the NO gas sensor, which performs detection in the following manner after the detection instruction reaches the NO gas sensor: Specifically, the NO gas sensor based on the temperature modulation detection method of Example 1 is used for gas sensitive response to 50 ppb NO, which includes: The first stage, the sensing unit performs desorption at the target desorption temperature of 350°C in the air environment, and judges the resistance fluctuation error every 5 seconds, and when the resistance fluctuation error is less than or equal to 5%, it enters the second stage; The second stage, record the resistance change of the sensing unit at the response temperature of 175°C in the air environment, the duration is 30 seconds, and calculate the change amplitude C Air = R Air-2 / R Air-1 ; The purpose of obtaining the resistance change amplitude of the sensor in the air is threefold: first, by comparing R Air after each high-temperature exposure, it is verified whether the impurity gas (including NO) on the surface of the sensor has been completely desorbed. Second, due to the influence of oxygen accumulation, rapid temperature modulation can cause the R Air of the sensor to drift. In addition, it is used to collect the environmental background, and obtain the interference of the current environment to the sensor resistance.

[0041] The third stage, after completing the second stage, execute the first stage (i.e. desorption in air at 350°C), the determination method of the duration is the same as the first stage, and when the execution is passed, it enters the fourth stage; The fourth stage, record the resistance of the sensing unit at the response temperature in the 50 ppb NO environment, and obtain the gas sensitive response of the sensor to NO based on the sensitivity calculation method (C NO = R NO-2 / R NO-1 ); After the completion of the fourth stage, a detection cycle ends, and the sensor enters the first stage or the second stage. Finally, by differentiating, the interference caused by the environment and oxygen accumulation effect is eliminated, and the characteristic response is calculated using C Air and C NO : Response (temperature modulation mode) = C NO / C Air .

[0042] Figure 7 The working flowchart of the temperature modulation based detection method for the NO gas sensor. Figure 7Note: Initial state: sensor temperature is 175℃, environment is NO or air; Desorption completion: the resistance of sensor fluctuates less than or equal to 5% before and after 5s in air; Waiting for detection state: NO is off, sensor is in air.

[0043] Figure 8 For the temperature modulation based detection method, the response time of the 2 mol% Ta-WO3 sensor of Example 1 to 50 ppb NO is about 30 s, and the recovery time is less than 15 s, which is significantly better than the performance in the constant temperature response mode. In addition, the gas sensitive response amplitude is further enhanced due to the oxygen accumulation effect, and the gas sensitive response of the sensor to 50 ppb NO is increased from 1.52 to 1.90 in the same response time (30 s), and multiple accurate NO detections can be performed in a short time.

[0044] Example 6 Performance of the NO gas sensor based on the temperature modulation detection method of Example 5 and actual application situation: (1) Sensitivity: The sensitivity of the 2 mol% Ta-WO3 sensor of Example 1 to different concentrations of NO based on temperature modulation was tested, and according to the concentration range of NO in human exhaled air, the test was performed in the range of 5-200 ppb, and the test method was replaced by the concentration of NO as in Example 5. As shown in Figure 9 , it shows a clear resistance response trend in the whole concentration range, and the response value of the sensor to 5 ppb NO is 1.12, showing better sensitivity than in the constant temperature working mode (response value is 1.08). The sensitivity can meet the detection requirements of the concentration of NO in exhaled air (the concentration of NO exhaled by normal personnel is 5-25 ppb, and the concentration of NO exhaled by asthma personnel is 25-100 ppb or higher).

[0045] (2) Selectivity: Based on temperature modulation, the selectivity of the sensor of Example 1 was evaluated, and the test method was replaced by the type of test gas as in Example 5, and the types and concentrations of interference gases tested are shown in Table 1. Referring to Figure 10 , the response curve of the sensor to the test gas and the gas sensitive response table, the response value of the sensor of Example 1 to all gases in Table 1 (except NO and NO2) is less than 10%, which is lower than the response value to 5 ppb NO.

[0046] Table 1: Typical types and concentrations of human exhaled air

[0047] (3) Gas interference resistance: The anti-interference of the sensor of Example 1 was tested based on temperature modulation, and the test method was different from that of Example 5, in which the test gas was replaced by an interference environment, and the interference environment was a mixture of 50 ppb NO and a fixed concentration of interference gas selected in the selective test. The response to 12 different mixed gases was tested, and the response curve and the corresponding response value are shown in Figure 11 In all mixed gas scenarios, the fluctuation error of the gas sensitive response value of 50 ppb NO was less than 10%.

[0048] (4) Repeatability and long-term stability: Based on temperature modulation, the repeatability and long-term stability of the sensor of Example 1 were evaluated, and the NO concentrations tested were 15 ppb, 75 ppb and 200 ppb. The NO response of the 2 mol% Ta-WO3 sensor unit was tested 900 times to evaluate its repeatability. Within a period of three months, the NO response of the 2 mol% Ta-WO3 sensor unit was evaluated once every two months to verify its long-term stability. Referring to Figure 12 , the results show that the response fluctuation error of the 2 mol% Ta-WO3 sensor is less than 10% throughout the test process, showing excellent repeatability and long-term stability.

[0049] (5) Humidity interference test: Humidity is an inevitable interference factor in human exhaled gas, so the degree of humidity influence under temperature modulation working conditions was evaluated. The response of the sensor of Example 1 to NO with a concentration of 5-200 ppb was evaluated in a relative humidity (RH) range of 0-90%, and the results are shown in Figure 13 As shown, the increase in humidity will weaken the response value, but the detection limit of the 2 mol% Ta-WO3 sensor unit for NO is still less than 5 ppb.

[0050] (6) Single-component NO recognition detection accuracy and applicability verification: The detection accuracy and applicability of the sensor of Example 1 were evaluated under laboratory simulation conditions based on temperature modulation to determine its actual application value. The accuracy of the single-component NO sensor was verified by testing NO concentrations in the range of 5 ppb to 200 ppb, and each concentration was repeated three times. The results are shown in Figure 14 and Table 2, which shows that the average recognition error of the 2 mol% Ta-WO3 sensor unit for various NO concentrations is less than 5%.

[0051] Table 2: NO accuracy test recognition results

[0052] (7) Verification of NO recognition accuracy in mixed gas environment: Based on temperature modulation, the accuracy of the sensor of Example 1 in a mixed gas environment was evaluated, the test method was consistent with (3) gas interference resistance, divided into twelve groups, each group was repeated three times, the original response curve was as shown in Figure 15 The results are shown in Table 3 as NO concentration values, the average concentration output error of the 2 mol% Ta-WO3 sensor unit is less than 10%, slightly higher in the ethanol mixed gas scene, 12.45%, overall the comprehensive performance of the application is good.

[0053] Table 3: NO anti-interference test identification results

[0054] Finally, it should be noted that: the above only for the preferred embodiments of the present application, and not for limiting the present application, although the foregoing detailed description of the present application is made with reference to the foregoing examples, for those skilled in the art, it still can be modified, or part of the technical features of the equivalent replacement, within the spirit and principles of the present application, any modification, equivalent replacement, improvement, etc., should be included within the scope of the present application.

Claims

1. A NO gas-sensitive material, characterized in that: The NO gas-sensitive material is metal-doped tungsten trioxide, wherein the metal doping amount is 1-5 mol%. The metal is any one of In, Nb, V, and Ta. The preparation method of the NO gas-sensitive material comprises the following steps: mixing tungsten hexachloride, n-heptane, and metal chloride to prepare a mixed solution; heating the mixed solution to react to obtain a coarse precipitate, centrifuging and washing the coarse precipitate to obtain a fine precipitate; drying, grinding, and calcining the fine precipitate to obtain metal-doped tungsten trioxide, namely the NO gas-sensitive material; the molar ratio of the tungsten hexachloride to the metal chloride is 10:(0.101-0.526).

2. The NO gas-sensitive material according to claim 1, characterized in that: The metal is Ta.

3. The NO gas-sensitive material according to claim 1, characterized in that: The metal doping amount is 2 mol%.

4. The NO gas-sensitive material according to claim 1, characterized in that: The amount of tungsten hexachloride used in 1 mL of n-heptane is 0.2-0.25 mmol.

5. The NO gas-sensitive material according to claim 1, characterized in that: The metal chlorides are TaCl5, InCl3, VCl3, and NbCl5.

6. The NO gas-sensitive material according to claim 1, characterized in that: The heating reaction condition is to react at 140-180° C. for 10-14 hours.

7. The NO gas-sensitive material according to claim 1, characterized in that: The drying condition is drying at 55-80° C. for 12-24 hours.

8. The NO gas-sensitive material according to claim 1, characterized in that: The calcination conditions are: calcination at 420-480° C. for 2-4 hours, and a heating rate of 2-5° C. / min.

9. A NO gas sensor, characterized in that: The NO gas sensor comprises a sensing element, and the sensing element comprises the NO gas-sensitive material according to any one of claims 1 to 8.

10. A NO detection method based on temperature modulation, characterized in that: The detection method is implemented using the NO gas sensor according to claim 9, comprising the following steps: In the first stage, the sensor unit desorbs the sensor according to the target desorption temperature in the air environment, and determines the resistance fluctuation error within t seconds every t seconds until the resistance fluctuation error within t seconds is ≤5%; In the second stage, the resistance change of the sensing unit at the response temperature is recorded in the air environment for a duration of m seconds; The third phase is to be carried out in accordance with the first phase after the second phase is completed; In the fourth stage, the resistance of the sensor unit at the response temperature is recorded in the NO environment, and the gas-sensitive response of the sensor to NO is obtained based on the sensitivity calculation method.

11. The detection method according to claim 10, characterized in that: The temperature range of temperature modulation is 175-350℃.

12. The detection method according to claim 10, characterized in that The detection method is used for detecting the sensitivity of NO gas in human exhaled gas.

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