Flexible ammonia sensor, preparation method and application thereof

Abstract

This invention relates to a flexible ammonia sensor, its preparation method, and its application. The preparation method includes: S1: reacting Ti3C2T... x Calcination yields TiO2@Ti3C2T x S2: Apply TiO2@Ti3C2T x A first mixed solution is prepared by mixing aniline monomer with HCl; a second mixed solution is prepared by mixing aniline monomer with HCl; and a third mixed solution is prepared by mixing ammonium persulfate with HCl. S3: A polyimide film is immersed in the first mixed solution, and the third mixed solution is added to the second mixed solution to prepare a fourth mixed solution. S4: The fourth mixed solution is added to the first mixed solution to react and obtain a flexible ammonia sensor. The flexible ammonia sensor is prepared using the above method. The application is in real-time monitoring of ammonia emissions from high-humidity agricultural soils. The flexible ammonia sensor of this invention has high sensitivity at room temperature and excellent resistance to moisture interference and mechanical bending resistance.

Description

Technical Field

[0001] This invention relates to a flexible ammonia sensor, its preparation method, and its application, belonging to the field of gas detection sensor technology based on new materials. Background Technology

[0002] Ammonia (NH3), a common colorless gas with a strong, pungent odor, is not only an important raw material in industrial production but also a significant air pollutant. Beyond traditional industrial and atmospheric environmental monitoring, real-time detection of ammonia in agricultural soil environments is equally crucial for economic and ecological guidance. During agricultural fertilization, ammonia release from the soil is a relevant indicator of soil nutrient loss. Higher ammonia volatilization rates indicate lower effective nitrogen absorption by crops. Therefore, real-time monitoring of dynamically released ammonia in the soil environment is central to establishing a quantitative model of the relationship between fertilizer absorption and crop growth, and is also a key prerequisite for assessing soil fertilizer absorption efficiency and guiding modern "precision agriculture" and "smart fertilization." Currently, traditional monitoring methods (such as spectroscopic analysis or ammonia nitrogen detection in water) are not only cumbersome and time-consuming but also cannot achieve in-situ real-time monitoring, failing to meet the immediate data feedback requirements of smart agricultural production. Even more challenging is that the actual farmland soil environment is extremely complex, often accompanied by persistent high humidity (relative humidity is often above 40%-90%), and conventional room temperature gas sensors are prone to signal drift or even failure due to water molecule interference in humid environments. Summary of the Invention

[0003] To overcome the above-mentioned defects of the prior art, the present invention provides a flexible ammonia sensor, its preparation method and application. The flexible ammonia sensor has high sensitivity when operating at room temperature, excellent resistance to moisture interference and mechanical bending resistance, and is especially suitable for real-time monitoring of ammonia emissions from high-humidity agricultural soils.

[0004] The technical solution adopted in this invention is: a method for preparing a flexible ammonia gas sensor, comprising the following steps: S1: For Ti3C2T x The powder was calcined at a constant temperature to obtain TiO2@Ti3C2T x ; S2: The TiO2@Ti3C2T x A first mixed solution was prepared by mixing with HCl solution; a second mixed solution was prepared by mixing aniline monomer solution and HCl solution; and a third mixed solution was prepared by mixing ammonium persulfate and HCl solution. S3: Immerse the polyimide film (or polyimide substrate) in the first mixed solution, and add the third mixed solution dropwise to the second mixed solution to prepare the fourth mixed solution; S4: The fourth mixed solution is added dropwise to the first mixed solution that submerges the polyimide film to react, and TiO2@Ti3C2T is grown in situ on the surface of the polyimide film. x A flexible ammonia gas sensor was obtained by using PANI composite sensitive material.

[0005] Preferably, in S1, the calcination temperature is 500℃, the time is 18h~20h, and the heating rate is 1℃ / min~2℃ / min.

[0006] Preferably, in step S2, the concentration and amount of HCl solution used to prepare the first mixed solution, the second mixed solution, and the third mixed solution are the same.

[0007] Furthermore, in step S2, the concentration of the HCl solution used to prepare the first mixed solution, the second mixed solution, and the third mixed solution is 1M.

[0008] Preferably, when preparing the first mixed solution, the TiO2@Ti3C2T x The ratio of TiO2@Ti3C2T to the HCl solution is 10mg~30mg per 5mL of HCl solution. x .

[0009] Furthermore, in preparing the first mixed solution, the TiO2@Ti3C2T x The ratio of TiO2@Ti3C2T to the HCl solution is 20 mg per 5 mL of HCl solution. x .

[0010] Preferably, when preparing the second mixed solution, the ratio of the aniline monomer solution to the HCl solution is 26 μL of the aniline monomer solution added to every 5 mL of the HCl solution.

[0011] Preferably, when preparing the third mixed solution, the ratio of ammonium persulfate to HCl solution is 28 mg of ammonium persulfate added to every 5 mL of HCl solution.

[0012] Preferably, in step S2, the prepared first mixed solution, second mixed solution and third mixed solution are subjected to ultrasonic dispersion treatment, and then transferred to an ice-water bath after ultrasonic dispersion treatment. Steps S3 and S4 are both carried out in an ice-water bath.

[0013] Preferably, the ultrasonic dispersion treatment time in S2 is 20 min to 40 min.

[0014] Preferably, in step S3, the polyimide film is cleaned and air-dried before being immersed in the first mixed solution.

[0015] Furthermore, the polyimide film is cleaned by immersing it in acetone for ultrasonic cleaning.

[0016] A flexible ammonia sensor is prepared using any of the flexible ammonia sensor preparation methods disclosed in this invention.

[0017] Preferably, the flexible sensor comprises a flexible polyimide substrate and a composite sensitive film in situ impregnated and grown on the surface of the flexible polyimide substrate, wherein the composite sensitive film is TiO2@Ti3C2T x / PANI composite sensitive material.

[0018] Preferably, the flexible sensor further includes two test electrodes, which are respectively connected to both sides of the upper surface of the flexible polyimide substrate and respectively in ohmic contact with the composite sensitive film.

[0019] The application of flexible ammonia sensors prepared by any of the methods disclosed in this invention, or any of the flexible ammonia sensors disclosed in this invention, in real-time monitoring of ammonia emissions in high-humidity agricultural soils.

[0020] Furthermore, applications in real-time monitoring of ammonia emissions from high-humidity agricultural soils include applications in monitoring nitrogen fertilizer volatilization, assessing nitrogen fertilizer utilization, applying precision fertilization in agriculture, and monitoring the atmospheric environment of agricultural production.

[0021] The beneficial effects of this invention are: (1) The flexible ammonia sensor of the present invention is constructed on a flexible polyimide substrate by in-situ impregnation growth method to form TiO2@Ti3C2T x / PANI composite material sensitive film layer, utilizing partially oxidized two-dimensional Ti3C2T x The layered framework effectively inhibited the aggregation of PANI nanofibers, constructing a continuous mesoporous network that facilitates rapid diffusion and desorption of ammonia. Simultaneously, relying on Ti3C2T... x The high conductivity and the strong interfacial heterojunction formed between TiO2 and PANI generated in situ significantly broaden the specific electrical response signal to ammonia. This in-situ interfacial anchoring effect not only endows the flexible ammonia sensor with excellent bending mechanical stability, but also significantly improves the overall protonation degree of the material, effectively shielding the intrusion and interference of water molecules. It is especially suitable for the application needs of long-term, stable and real-time monitoring of trace ammonia in complex high humidity (relative humidity of 40%-90%) environments such as agricultural soil. (2) The flexible ammonia sensor of the present invention uses TiO2@Ti3C2T x / PANI composite sensing material has excellent room temperature gas sensing activity and resistance to humidity interference, and can achieve highly sensitive and accurate detection of ultra-low concentration ammonia (as low as 0.3ppm) in complex environments with normal temperature and high humidity. (3) The flexible ammonia sensor of the present invention forms a strong interface bond between the sensitive material and the substrate, which completely overcomes the problem of thin film peeling and delamination that easily occurs in ammonia sensors prepared by traditional physical coating method. The preparation method of the flexible ammonia sensor of the present invention is simple, the reaction conditions are mild and easy to control, and it is suitable for mass industrial production. (4) The flexible ammonia sensor of the present invention adopts a flexible sensing structure based on polyimide film. The device is small in size, has strong resistance to mechanical bending fatigue, and is easy to miniaturize and integrate into the system. It is not only suitable for mass production, but also perfectly adapted to complex terrain scenarios such as actual farmland. It is especially suitable for real-time monitoring of ammonia emissions in high-humidity agricultural soil, providing strong hardware technical support for smart agriculture fertilization monitoring. Attached Figure Description

[0022] Figure 1 This is a flowchart of the preparation method of the flexible ammonia sensor of the present invention; Figure 2 This is a schematic diagram of the structure of the flexible ammonia sensor of the present invention; Figure 3 These are SEM images of each individual component in the preparation process of the flexible ammonia sensor of the present invention and the obtained flexible ammonia sensor. Figure 4 This refers to the precursor material used in the fabrication process of the flexible ammonia sensor of the present invention and the prepared TiO2@Ti3C2T. x XRD test images of the PANI composite sensitive material; Figure 5 This is the TiO2@Ti3C2T of Embodiment 1 of the present invention. x / PANI composite sensitive material for dynamic gas-sensing response-recovery curves at room temperature under different ammonia concentrations; Figure 6 This is the TiO2@Ti3C2T of Embodiment 1 of the present invention. x / Comparison curves of dynamic gas-sensitive response-recovery of PANI composite sensitive material and PANI material to ammonia under ambient temperature and humidity conditions; Figure 7 This is a dynamic response curve of a pure PANI sensor to different concentrations of ammonia (ammonia concentration range of 0.3ppm~400ppm) at room temperature; Figure 8This is a dynamic response curve of the flexible ammonia sensor of Embodiment 1 of the present invention to different concentrations of ammonia (ammonia concentration range of 0.3ppm to 1000ppm) at room temperature. Figure 9 This is a comparison graph showing the gas-sensing response values ​​of a pure PANI sensor and the flexible ammonia sensor of Embodiment 1 of the present invention as a function of ammonia concentration. Figure 10 This is a comparison chart of the gas-sensing response of the flexible ammonia sensor of Embodiment 1 of the present invention to ammonia under room temperature and different relative humidity conditions. Figure 11 This is a comparison chart of the long-term stability of the flexible ammonia sensor in Embodiment 1 of the present invention. Detailed Implementation

[0023] See Figure 1 This invention discloses a method for preparing a flexible ammonia sensor, comprising the following steps: S1: For Ti3C2T x The powder was calcined at a constant temperature and then naturally cooled to room temperature to obtain partially oxidized TiO2@Ti3C2T. x (Powdered form).

[0024] For the Ti3C2T x The calcination of the powder is preferably carried out in a tube furnace. The calcination temperature is preferably 500℃, and the time can be 18h to 20h, for example, 18h, 19h or 20h, preferably 20h. The heating rate is preferably 1℃ / min to 2℃ / min, for example, 1℃ / min, 1.5℃ / min or 2℃ / min.

[0025] The Ti3C2T x The purity of the powder is preferably 98%, and the particle size is preferably 200 mesh.

[0026] S2: The TiO2@Ti3C2T x A first mixed solution was prepared by mixing with HCl solution, a second mixed solution was prepared by mixing aniline monomer (ANI) solution and HCl solution, and a third mixed solution was prepared by mixing ammonium persulfate (APS, powder) and HCl solution.

[0027] The concentration and amount of HCl solution used in preparing the first mixed solution, the second mixed solution and the third mixed solution are preferably the same, and the concentration of the HCl solution used is preferably 1M, which can be prepared by mixing concentrated hydrochloric acid and deionized water in a suitable ratio.

[0028] In preparing the first mixed solution, the TiO2@Ti3C2T xThe ratio of TiO2@Ti3C2T to the HCl solution can be 10mg~30mg per 5mL of the HCl solution. x For example, 10 mg, 20 mg, or 30 mg of TiO2@Ti3C2T can be added to every 5 mL of the HCl solution. x Preferably, 20 mg of TiO2@Ti3C2T is added to every 5 mL of the HCl solution. x In preparing the second mixed solution, the preferred ratio of the aniline monomer solution to the HCl solution is 26 μL of the aniline monomer solution per 5 mL of the HCl solution; in preparing the third mixed solution, the preferred ratio of the ammonium persulfate to the HCl solution is 28 mg of the ammonium persulfate per 5 mL of the HCl solution. The preparation of the first, second, and third mixed solutions can be carried out in containers, such as beakers or flasks.

[0029] The first, second, and third mixed solutions obtained are preferably subjected to ultrasonic dispersion treatment to ensure thorough mixing and dispersion. The ultrasonic dispersion treatment time is preferably 20 to 40 minutes, for example, 20, 30, or 40 minutes. After ultrasonic dispersion treatment, each solution is preferably transferred to a pre-cooled ice-water bath for cooling.

[0030] S3: Immerse the polyimide film (PI film, or polyimide substrate, PI substrate) in the first mixed solution, and add the third mixed solution dropwise to the second mixed solution to prepare the fourth mixed solution.

[0031] Before immersing the polyimide film in the first mixed solution, it is preferable to clean the polyimide film and let it air dry. The preferred method for cleaning the polyimide film is to immerse it in acetone for ultrasonic cleaning. The ultrasonic cleaning time is preferably 15 minutes to remove oil and impurities from the surface.

[0032] In practical applications, the polyimide film can be cut into 1cm×1cm squares as the polyimide substrate.

[0033] S4: The fourth mixed solution is slowly added dropwise to the first mixed solution that submerges the polyimide film, and TiO2@Ti3C2T is grown in situ on the surface of the polyimide film. x / PANI composite sensitive material, after the reaction is completed, a flexible ammonia sensor (substrate) is obtained, which is then removed from the solution and allowed to air dry naturally.

[0034] Both S3 and S4 are carried out in an ice-water bath, and the reaction time in S4 is usually 3h to 5h, for example 3h, 4h or 5h.

[0035] See Figure 2 The present invention also discloses a flexible ammonia sensor, which is prepared using any of the methods disclosed herein. The flexible sensor comprises a flexible polyimide substrate 1 and a composite sensitive film 2 in situ impregnated and grown on the surface of the flexible polyimide substrate. The composite sensitive film is TiO2@Ti3C2T. x The flexible sensor also includes two test electrodes, which are respectively connected to both sides of the upper surface of the flexible polyimide substrate and are in ohmic contact with the composite sensing film.

[0036] The flexible ammonia sensor uses highly conductive TiO2@Ti3C2T x As the supporting framework layer, two-dimensional Ti3C2T that has undergone high-temperature partial oxidation is used. x As a highly conductive transmission network and heterojunction control layer, polyaniline (PANI) nanofibers with high specificity response to ammonia are used as the sensitive host (the main material for specific ammonia recognition and deprotonation response). In-situ composite effectively suppresses the spontaneous aggregation of polyaniline, increases the continuous mesopore volume and specific surface area of ​​the sensitive layer, and increases the overall protonation degree of the composite sensitive material through in-situ interface anchoring, thereby effectively improving the response speed and gas-sensing characteristics of the flexible ammonia sensor.

[0037] The sensing mechanism of the flexible ammonia sensor is as follows: ammonia molecules diffuse into the material interior and at the interface through the rich mesoporous network of the composite sensitive film layer. During this process, ammonia interacts specifically with polyaniline (PANI). As a strong Lewis base, ammonia preferentially binds to protons on the PANI molecular chain, undergoing a reversible deprotonation reaction. In this process, PANI transforms from a highly conductive emerald green imine salt (ES) state to a low-conductivity emerald green imine base (EB) state, resulting in a sharp decrease in the hole carrier concentration within its bulk phase. Simultaneously, a heterojunction barrier and space charge region are formed between the in-situ generated n-type TiO2 and p-type PANI due to the Fermi level difference. When electrons released from the deprotonation reaction are injected into the recombination system, they recombine with holes at the interface, leading to a further significant increase in the width of the heterojunction depletion layer. Ultimately, this results in a significant increase in the overall resistance of the flexible ammonia sensor, and the rate of change of this resistance serves as the detection signal of the flexible ammonia sensor. The magnitude of the detection signal is determined by the adsorption / desorption rate of ammonia at the interface and the amount of charge transfer, while the reaction rate and signal amplification depend on the initial protonation degree of the sensitive layer material, the band structure (heterojunction barrier difference), and the microstructure of the electrode material (such as the porosity, specific surface area, morphology, etc. of the material).

[0038] The reaction formula is as follows: ; The formula for calculating the gas-sensitive response is as follows: .

[0039] The individual components in the fabrication process of the flexible ammonia sensor and the SEM images of the resulting flexible ammonia sensor are shown below. Figure 3 As shown, (a) is a SEM image of polyaniline material, which shows that it is mostly composed of fibrous clusters; (b) is a Ti3C2T x SEM images of the material show a clear interlayer structure, which can provide more growth sites for subsequent polyaniline materials; (c) The figure shows the TiO2@Ti3C2T obtained after calcination. x The SEM image of the material shows surface noise, which is TiO2 material generated in situ after calcination; (d) The image shows the SEM image of the flexible ammonia sensor, from which it can be clearly seen that TiO2@Ti3C2T x The application of this material can greatly improve the polyaniline clustering phenomenon, enabling it to be better exposed to the target gas and thus produce a superior gas-sensitive response.

[0040] The precursor material and TiO2@Ti3C2T used in the fabrication of the flexible ammonia sensor x The XRD pattern of the PANI composite sensitive material is shown below. Figure 4 As shown. By comparing with the standard spectrum, TiO2@Ti3C2T x The distinct sharp diffraction peaks (marked with ★) appearing in the curve are consistent with the rutile TiO2 standard card (JCPDS#21-1276) and the anatase TiO2 standard card (JCPDS#21-1272), indicating that Ti3C2T x TiO2 material with a rutile and anatase mixed-phase structure was successfully generated in situ after high-temperature oxidation treatment. The pure PANI curve showed a broad diffraction band (marked with *) between 20° and 30°, exhibiting typical characteristics of a semi-crystalline polymer. This indicates that the TiO2@Ti3C2T material prepared in this invention… x The spectrum of the / PANI composite sensitive material simultaneously contains the characteristic crystal plane diffraction peaks (★) of TiO2 and the characteristic broad peaks (*) of PANI, proving that TiO2@Ti3C2T x The framework and polyaniline were successfully composited in situ, and the composite process did not damage the basic crystal structure of the original material.

[0041] The present invention also discloses the application of the flexible ammonia sensor in real-time monitoring of ammonia emissions in high-humidity agricultural soil.

[0042] The application of the flexible ammonia sensor in the real-time monitoring of ammonia emissions in high-humidity agricultural soil includes its application in nitrogen fertilizer volatilization monitoring, nitrogen fertilizer utilization rate evaluation, precise agricultural fertilization, and atmospheric environment monitoring in agricultural production.

[0043] The following are the preparation examples of the flexible ammonia sensor: Example 1: Step 1. Pretreatment of the flexible substrate: Cut a polyimide (PI) film with a size of 1 cm × 1 cm as the substrate of the flexible ammonia sensor, immerse it in a beaker containing acetone and ultrasonically clean it for 15 min to remove surface oil stains and impurities. After cleaning, take it out and let it dry naturally for later use.

[0044] Step 2. Preparation of TiO2@Ti3C2T x / PANI two-dimensional framework material: Take multi-layer clay-like Ti3C2T x powder (purity 98%, 200 mesh) and place it in a tube furnace. Calcinate it at a constant temperature of 500 °C for 20 h in an air atmosphere to cause a partial oxidation reaction. After naturally cooling to room temperature, obtain TiO2@Ti3C2T x composite material powder for later use.

[0045] Step 3. Prepare the precursor solution: Measure 3 mL of concentrated hydrochloric acid (mass fraction 36%) and add it to 30 mL of deionized water to prepare a 1 M HCl solution for later use.

[0046] Step 4. Preparation of the precursor material: Take three beakers A, B, and C. Add 20 mg of the TiO2@Ti3C2T x powder prepared in Step 2 and 5 mL of 1 M HCl solution to beaker A; add 26 μL of aniline monomer (ANI) and 5 mL of 1 M HCl solution to beaker B; weigh 28 mg of ammonium persulfate (APS) powder in beaker C and completely dissolve it in 5 mL of 1 M HCl solution. Place the above three beakers A, B, and C in an ultrasonic cleaner and ultrasonically treat them for 30 min to make them fully mixed and dispersed.

[0047] Step 5. In-situ impregnation growth of the sensitive material: After ultrasonic treatment, beakers A, B, and C were transferred to a pre-cooled ice-water bath for cooling. First, the PI film substrate, cleaned in step one, was completely immersed in the suspension in beaker A. Then, the mixed solution in beaker C was added dropwise to beaker B and mixed thoroughly. Next, the mixed solution was slowly and dropwise added to beaker A. The entire reaction system was kept in the ice-water bath for 4 hours. After the reaction was completed, the PI substrate with the composite sensitive material attached to its surface was removed and allowed to air dry naturally, thus obtaining the flexible ammonia sensor (a PI substrate with a composite sensitive film grown on its surface).

[0048] Example 2: The difference between this embodiment and Embodiment 1 is that: In step four, TiO2@Ti3C2T is added to beaker A. x The amount of powder was changed to 10mg.

[0049] Apart from the differences mentioned above, the other implementation steps and methods are the same as in Example 1.

[0050] Example 3: The difference between this embodiment and Embodiment 1 is that: In step four, TiO2@Ti3C2T is added to beaker A. x The amount of powder was changed to 30mg.

[0051] The flexible ammonia sensors prepared in Examples 1, 2, and 3 were subjected to gas-sensing performance tests. The leads of the packaged flexible ammonia sensors were connected to a digital multimeter (Fluke 8846A), and the gas sensitivity was evaluated using a static gas mixing method at room temperature (25°C, 40% relative humidity). First, a predetermined concentration of ammonia gas was injected into a sealed test chamber and allowed to diffuse uniformly. Then, the flexible ammonia sensor was placed in the chamber, and its dynamic resistance change during ammonia adsorption was monitored and recorded in real time. After the response test was completed, the flexible ammonia sensor was removed and exposed to clean air for desorption until its resistance value completely recovered to the initial stable baseline state. This completed a closed-loop test of the sensitivity, response, and recovery time of the flexible ammonia sensor.

[0052] The response values ​​of the flexible ammonia sensors prepared in each embodiment to 50 ppm ammonia are compared in Table 1.

[0053] Table 1. Comparison of the response values ​​of the flexible ammonia sensors prepared in Examples 1, 2, and 3 to 50 ppm ammonia gas.

[0054] As shown in Table 1, the flexible ammonia sensors prepared in the three embodiments do not exhibit the same response characteristics to ammonia. The flexible ammonia sensor prepared in Example 1 shows the largest change in gas-sensing response, with a response value of 325% in the ammonia gas being tested, significantly greater than the 180% of the flexible ammonia sensor prepared in Example 2 and the 169% of the flexible ammonia sensor prepared in Example 3. This indicates that the flexible ammonia sensor prepared in Example 1 exhibits the best gas-sensing characteristics, suggesting that during the preparation of the first mixed solution, the TiO2@Ti3C2T... x The ratio of TiO2@Ti3C2T to the HCl solution (1M concentration) is 20mg per 5mL of the HCl solution. x The optimal dosage ratio is [the ratio of the dosage ratio of the two methods].

[0055] Table 2 shows the gas-sensing response values ​​of the flexible ammonia sensor prepared in Example 1 to 50 ppm ammonia at different bending radii.

[0056] Table 2. Comparison of gas-sensing response values ​​of the flexible ammonia sensor prepared in Example 1 to 50 ppm ammonia at different bending radii.

[0057] As shown in Table 2, the flexible ammonia sensor prepared in Example 1 maintained a consistent response to ammonia gas despite undergoing varying degrees of mechanical deformation. Even when the sensor was bent from a flat state to a minimum radius of 25 mm, its response value in the target gas remained as high as 292%, with the overall response value consistently maintained within the high range of 275% to 313%, without significant attenuation. This demonstrates that the flexible ammonia sensor prepared in Example 1 not only exhibits excellent gas-sensing performance but also demonstrates exceptional mechanical flexibility and resistance to bending deformation.

[0058] The flexible ammonia sensor prepared in Example 1 using TiO2@Ti3C2T x Gas-sensing performance of PANI composite sensing material was tested at different ammonia concentrations (0.3ppm~1000ppm): The gas-sensing performance was tested using a static method in a 1L sealed glass gas chamber. A measured amount of ammonia gas was injected into the chamber using a syringe, and the chamber was allowed to stand for 1 minute to allow the gas to diffuse and mix thoroughly. Then, the flexible ammonia gas sensor prepared in Example 1 was placed in the chamber, and the resistance change of the flexible ammonia gas sensor was recorded in real time using a digital multimeter (Fluke 8846A). After each sensing test cycle, the flexible ammonia gas sensor was placed in ambient air until the resistance returned to a stable baseline value. During the test, the ammonia gas concentration gradually increased to 1000 ppm in a stepwise manner.

[0059] The flexible ammonia sensor prepared in Example 1 using TiO2@Ti3C2T x The dynamic gas-sensing response-recovery comparison of the PANI composite sensing material at room temperature under different ammonia concentrations from 0.3ppm to 1000ppm is as follows: Figure 5 As shown in the figure, with the continuous increase of ammonia concentration, the sensor's response value (%) exhibits a significant and regular stepwise increase. Simultaneously, within each intake and exhaust cycle, the flexible ammonia sensor achieves a rapid resistance response and quickly recovers to the initial baseline after the introduction of clean air, demonstrating extremely excellent continuous detection capability and signal reversibility. Furthermore, the inset in the upper left corner of the figure shows a magnified curve of the flexible ammonia sensor in the low ammonia concentration range (0.3ppm~50ppm). It is clearly visible from the inset that even under extremely low ammonia concentration conditions, the sensor can still generate a clear, stable response signal without significant baseline drift. Therefore, the flexible ammonia sensor prepared in Example 1 not only possesses an extremely wide detection range but also exhibits ultra-high sensitivity, excellent repeatability, and superior room temperature operating stability, demonstrating outstanding ammonia sensing characteristics.

[0060] The flexible ammonia sensor prepared in Example 1 using TiO2@Ti3C2T x Comparative testing of the gas-sensing performance of PANI composite sensing material and PANI material under ambient temperature and humidity conditions: Under room temperature (25°C) and relative humidity (RH) of 40%, the flexible ammonia sensor and the PANI material sensor prepared in Example 1 were placed in the test chamber. After the baseline resistance of the devices stabilized, 50 ppm NH3 was introduced for gas-sensing testing. The real-time resistance changes of the two sensors during the NH3 introduction process were recorded. After the response reached stability, the target gas was stopped, and the environment was restored to air. The resistance changes during the recovery process were then recorded to obtain complete dynamic response-recovery curves. Subsequently, the response values, response times, and recovery times of the two materials were extracted from the dynamic curves. The response time was defined as the time required for the device to reach 90% of the total response change, and the recovery time was defined as the time required for the device to recover to 90% of its initial state after the NH3 was removed.

[0061] The flexible ammonia sensor prepared in Example 1 using TiO2@Ti3C2T x The dynamic gas-sensing response-recovery of the PANI composite sensing material (left area in the figure) and the pure PANI material (right area in the figure) to 50 ppm ammonia gas under room temperature and humidity (RT&RH) conditions is compared as follows: Figure 6 As shown in the figure, it can be clearly seen that when the target gas is introduced, the response value of the pure PANI sensor is only about 150%, and the response time ( τres The response time was 20s; in contrast, the flexible ammonia sensor prepared in Example 1 showed extremely high sensitivity to the same concentration of ammonia, with its response value rising sharply to approximately 325%, achieving an absolute increase of up to ΔR=174% compared to the pure PANI sensor, more than doubling the signal strength, and further shortening the response time to 17s. After the ammonia was cut off and clean air was introduced, both could recover within approximately 75s~76s. τ rec Complete desorption was achieved within the range, and the ammonia gas returned to a stable initial baseline level. Comparative results show that the composite sensitive material in the flexible ammonia sensor prepared in Example 1 successfully overcame the bottleneck of low sensitivity and slow response of single polyaniline materials, demonstrating excellent room-temperature ammonia detection performance and extremely high practical application value.

[0062] Figure 7 The graph shows the gas-sensitive dynamic response curves of a pure PANI sensor to different concentrations of ammonia (ammonia concentration range of 0.3ppm to 400ppm) at room temperature. Figure 8 The image shows the dynamic response curves of the flexible ammonia sensor of Example 1 to different concentrations of ammonia (ammonia concentration range of 0.3ppm to 1000ppm) at room temperature. Figure 9 This is a comparison graph showing the gas-sensing response values ​​of a pure PANI sensor and the flexible ammonia sensor of Embodiment 1 of the present invention as a function of ammonia concentration. Figure 7 , Figure 8 and Figure 9 It can be seen that as the ammonia concentration increases, the response values ​​of both the pure PANI sensor and the flexible ammonia sensor prepared in Example 1 gradually increase. Compared with the pure PANI sensor, the flexible ammonia sensor prepared in Example 1 exhibits a higher response value and a wider detection range throughout the entire test range, indicating that the introduction of composite materials effectively improves the sensor's ammonia detection performance. Therefore, the flexible ammonia sensor prepared in Example 1 not only has an extremely low detection limit and an extremely wide detection range, but also exhibits a highly reliable linear mapping relationship between its output signal and the gas concentration. This excellent linear response characteristic greatly simplifies the algorithm design of the subsequent signal acquisition and data calibration system, proving that the flexible ammonia sensor is fully capable of accurately and quantitatively detecting ammonia, perfectly meeting the wide-range, high-precision, real-time dynamic monitoring needs of soil ammonia volatilization concentration during actual agricultural fertilization.

[0063] The gas-sensing performance of the flexible ammonia gas sensor prepared in Example 1 was tested at room temperature and under different relative humidity conditions: First, the gas cylinder was placed open in environments with different relative humidity conditions for 3 minutes to allow its interior to fully contact and adapt to the corresponding humidity environments. Then, the flexible ammonia sensor prepared in Example 1 was placed inside, and 50 ppm NH3 was immediately introduced into the cylinder for gas sensitivity testing. The remaining testing procedures were the same as conventional gas sensitivity testing procedures, namely, recording the dynamic response-recovery curve of the flexible ammonia sensor under the action of NH3, and extracting parameters such as the corresponding response value, response time, and recovery time to evaluate the impact of different humidity conditions on sensor performance.

[0064] The gas-sensing response of the flexible ammonia sensor prepared in Example 1 to 50 ppm ammonia at room temperature and different relative humidity (RH = 40%~90%) is compared as follows: Figure 10 As shown in the figure, it can be clearly observed that when the relative humidity gradually increases from 40% to an extremely humid 90%, the gas-sensing response value of the flexible ammonia sensor prepared in Example 1 to 50 ppm ammonia remains at a high level of approximately 325%. Throughout the wide humidity range test interval, the height of the response signal bars under each humidity gradient remains almost completely consistent, without any obvious signal attenuation, fluctuation, or baseline drift. This fully demonstrates that the composite sensitive material of the flexible ammonia sensor prepared in Example 1 has extremely excellent anti-humidity interference capability. This characteristic ensures that the flexible ammonia sensor can still output a highly stable and accurate ammonia concentration detection signal when facing complex and variable real farmland soil environments that are constantly under high humidity.

[0065] Long-term stability testing was conducted on the flexible ammonia sensor prepared in Example 1: Long-term stability testing was conducted using the same methods as conventional gas-sensitive testing. The flexible ammonia sensor prepared in Example 1 was placed under fixed test conditions, and its NH3 response was tested once a day for 21 consecutive days. The changes in the response values ​​for each day were recorded. By comparing the changing trends of the sensor's response signal over the 21 days, the stability of the device during long-term storage and repeated use was evaluated.

[0066] The stability test results of the flexible ammonia sensor prepared in Example 1 over 21 days are compared with those of... Figure 11 As shown in the figure, the flexible ammonia sensor prepared in Example 1 exhibits a small fluctuation range in response value over 21 days, indicating that the flexible ammonia sensor has good stability.

[0067] The flexible ammonia sensor of the present invention has the characteristics of extremely high sensitivity, extremely low detection limit (0.3ppm), excellent mechanical bending resistance and excellent stability in high humidity environment (no signal drift occurs under relative humidity of 40%~90%). It is especially suitable for real-time monitoring of ammonia emissions in high humidity agricultural soil, and is also suitable for conventional ammonia detection.

[0068] Unless otherwise specified or further limited to one preferred or optional technical means being another, the preferred and optional technical means disclosed in this invention can be arbitrarily combined to form several different technical solutions.

Claims

1. A method for preparing a flexible ammonia gas sensor, characterized in that... Includes the following steps: S1: For Ti3C2T x The powder was calcined at a constant temperature to obtain TiO2@Ti3C2T x ; S2: The TiO2@Ti3C2T x A first mixed solution was prepared by mixing with HCl solution; a second mixed solution was prepared by mixing aniline monomer solution and HCl solution; and a third mixed solution was prepared by mixing ammonium persulfate and HCl solution. S3: Immerse the polyimide film in the first mixed solution, and add the third mixed solution dropwise to the second mixed solution to prepare a fourth mixed solution; S4: The fourth mixed solution is added dropwise to the first mixed solution that submerges the polyimide film to react, and TiO2@Ti3C2T is grown in situ on the surface of the polyimide film. x A flexible ammonia gas sensor was obtained by using PANI composite sensitive material.

2. The method for preparing the flexible ammonia sensor according to claim 1, characterized in that... In step S2, the concentration and amount of HCl solution used in preparing the first mixed solution, the second mixed solution, and the third mixed solution are the same.

3. The method for preparing the flexible ammonia sensor according to claim 2, characterized in that... The concentration of the HCl solution is 1M.

4. The method for preparing the flexible ammonia sensor according to claim 3, characterized in that... In preparing the first mixed solution, the TiO2@Ti3C2T x The ratio of TiO2@Ti3C2T to the HCl solution is 10mg~30mg per 5mL of HCl solution. x .

5. The method for preparing the flexible ammonia sensor according to claim 3, characterized in that... In preparing the second mixed solution, the ratio of the aniline monomer solution to the HCl solution is 26 μL of the aniline monomer solution added to every 5 mL of the HCl solution.

6. The method for preparing the flexible ammonia sensor according to claim 3, characterized in that... In preparing the third mixed solution, the ratio of ammonium persulfate to HCl solution is 28 mg of ammonium persulfate per 5 mL of HCl solution.

7. The method for preparing the flexible ammonia sensor according to claim 1, characterized in that... In step S2, the prepared first mixed solution, second mixed solution, and third mixed solution are subjected to ultrasonic dispersion treatment, and then transferred to an ice-water bath after ultrasonic dispersion treatment. Steps S3 and S4 are both carried out in an ice-water bath.

8. The method for preparing the flexible ammonia sensor according to claim 1, characterized in that... In S1, the calcination temperature is 500℃, the time is 18h~20h, and the heating rate is 1℃ / min~2℃ / min.

9. A flexible ammonia gas sensor, characterized in that... The flexible ammonia sensor was prepared using the method described in any one of claims 1-8.

10. The application of the flexible ammonia sensor prepared by the method of any one of claims 1-8 or the flexible ammonia sensor of claim 9 in real-time monitoring of ammonia emissions in high-humidity agricultural soil.

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