Fabrication of a Chemi-Resistivity Gas Sensor Based on Polyoxometalates and Its Application in Room Temperature Ammonia Detection

Abstract

This invention discloses a chemiluminescence gas sensor based on polyoxometalates (POMs), and relates to its fabrication method and application. The sensor is suitable for detecting ammonia at room temperature. The gas sensor includes an adapter base and a sensing element, wherein the sensing element consists of interdigitated electrodes and a sensitive material loaded on the electrode surface. This sensitive material is a composite material of POMs and SnO2. POMs, as excellent electron acceptors, possess good redox properties, thermal stability, and photosensitivity. When combined with SnO2, they can effectively suppress electron-hole recombination, thereby significantly improving the gas-sensing performance of the semiconductor material. Compared with existing technologies, the sensor provided by this invention exhibits high response characteristics to ammonia at room temperature, while also demonstrating excellent selectivity and repeatability.

Description

Technical Field

[0001] This invention belongs to the field of electronic component technology and relates to the preparation of a chemical resistance gas sensor based on polyoxometalates and its application in the detection of ammonia at room temperature. Background Technology

[0002] Ammonia (NH3), a toxic and harmful gas, is one of the major air pollutants and is widely used in chemical synthesis, nitrogen fertilizer production, and biomass combustion. Ammonia leakage and emissions pose significant health hazards. According to the regulations of the National Institute of Occupational Safety and Health, the maximum permissible concentration of ammonia in indoor air is 25 ppm (17 mg / cm³). 3 Long-term exposure to a concentration of 700 mg / m³ 3 An ammonia-rich environment can cause serious damage to the eyes, respiratory tract, and lungs. Furthermore, approximately 200 volatile compounds can be detected in human exhaled breath, with ammonia considered a key biomarker of health. For example, the ammonia concentration in the exhaled breath of patients with liver or kidney dysfunction can be several times higher than that of healthy individuals. Therefore, developing efficient and accurate ammonia detection sensors is of great significance for environmental monitoring and the development of smart healthcare.

[0003] Currently, various types of gas sensors have emerged in the market, such as carbon-based material sensors and organic polymer sensors, but they generally suffer from insufficient sensitivity and poor selectivity. Metal-oxide-semiconductor (MOS) gas sensors have become a research hotspot in recent years due to their advantages such as high sensitivity, fast response characteristics, and low cost. However, traditional MOS gas sensors generally face challenges such as high operating temperatures and poor environmental adaptability, making it difficult to achieve good sensitivity, fast response and recovery performance, and excellent selectivity at low temperatures or even room temperature. Therefore, developing ammonia sensing materials that can operate stably and with high performance at room temperature has become one of the key challenges that urgently need to be overcome in the field of gas sensing technology.

[0004] Tin dioxide (SnO2) is an n-type metal oxide semiconductor material that has attracted widespread attention in the field of gas sensors due to its advantages such as high carrier mobility, low cost, and simple preparation process. Polyoxometalates (POMs) are inorganic anion clusters formed by coordination and bridging of transition metals such as V, Mo, and W with oxygen atoms. Due to their excellent redox properties, good thermal stability, and photosensitivity, POMs have been widely used in catalysis, electrochromism, and biomedicine. Furthermore, POMs possess a semiconductor-like electronic structure, exhibiting strong electron acceptor properties. When combined with metal oxide semiconductors, they can effectively suppress electron-hole recombination, thereby significantly improving the gas-sensing performance of the semiconductor material. Therefore, POMs show great promise for applications in gas sensors. Summary of the Invention

[0005] This invention provides a chemiluminescence gas sensor based on polyoxometalates and its preparation and application methods. The sensor constructed using SnO2 / POMs composite material as the sensitive layer exhibits good selectivity and high sensitivity for ammonia at room temperature.

[0006] The technical solution is as follows:

[0007] A chemiluminescence resistivity gas sensor based on polyoxometalates comprises an adapter base and a sensing element. The sensing element includes a SnO2 / POMs sensitive layer and interdigitated electrode plates. The thickness of the sensitive layer is 1–150 μm, and the POMs are selected from H3PMo. 12 O 40 (PMo) 12 ), K 12.5 Na 1.5 [NaP5W 30 O 110 (P5W) 30 ), Na2[P2W 15 O 56 (P2W) 15 K7[La(H2O)] x (α2-P2W 17 O 61 )] (P2W 17 La), H6P2W 18 O 62 (P2W) 18 ) and H3PW 12 O 40 (PW) 12 Any one of them.

[0008] Furthermore, the SnO2 / POMs composite material achieves the coating of POMs on the surface of SnO2 nanosheets through an impregnation combined with liquid grinding method.

[0009] Furthermore, the interdigitated electrode sheet is gold-plated on a copper layer with a thickness of 5-15 μm and fixed to the substrate film by a hot pressing process; the number of interdigitated electrode pairs is 5 to 80 pairs, and the electrode spacing is 100-200 μm; the substrate material of the interdigitated electrode is PI or PET.

[0010] A method for fabricating a chemiluminescence gas sensor based on polyoxometalates includes cleaning interdigitated electrode sheets and assembling the sensor. The specific steps are as follows:

[0011] Step 1: Clean the interdigitated electrode pads sequentially with acetone, ethanol and deionized water using ultrasonic cleaning for 5-20 minutes, and then dry them under a nitrogen atmosphere;

[0012] Step 2: The cleaned interdigitated electrode sheets are subjected to vacuum ozone plasma treatment at a power of 50~80 W for 3~10 minutes.

[0013] Step 3: After thoroughly grinding the SnO2 / POMs composite material, disperse it in ethanol to prepare a suspension. Coat the suspension evenly on the surface of the interdigitated electrode using a drop-coating method and dry it at 50~80℃. Repeat the above drop-coating and drying process twice. Then place the device in a vacuum drying oven and age it at 100~180℃ for 6~12 hours. Finally, solder it to the adapter base to obtain the gas sensor.

[0014] In step one, the ultrasonic cleaning power is 200~350 W; in step three, the component mass ratio of the SnO2 / POMs composite material is 19:1~2:1, and the mass-volume ratio of the composite material to the ethanol solvent is 1 g : 20 mL~1 g : 50 mL.

[0015] The present invention also provides the application of the polyoxometalate-based gas sensor described in the above technical solution or the composite material sensor prepared by the above technical solution in ammonia detection.

[0016] All of the above gas sensors operate at room temperature.

[0017] This invention also provides a method for detecting ammonia. The operating temperature is controlled at 25 ± 2℃. The sensor is sequentially exposed to ammonia and other interfering gases until saturation is achieved, then air is introduced. After the sensor recovers, the initial resistance value R is recorded. a and the resistance value R in the gas g According to the formula S = R a / R g(n-type response) or S = R g / R a (p-type response) Calculate the sensitivity S.

[0018] The beneficial effects of this invention are as follows:

[0019] 1. This invention uses an impregnation combined with liquid grinding method to prepare a novel composite material and applies it to the field of gas sensing. This method is simple, has high yield and low cost, and has good repeatability and potential for large-scale application.

[0020] 2. By introducing POMs into the metal oxide, a synergistic effect between the two is achieved, significantly improving the gas-sensing performance and response rate of the sensor. The SnO2 used in this invention is obtained by calcination of a tin-based metal-organic framework material. As a wide-bandgap n-type semiconductor, it possesses excellent chemical and thermal stability, along with high-efficiency electron transport capabilities and abundant surface active sites. POMs have a semiconductor-like electronic structure and can act as excellent electron acceptors. Forming composite materials with the metal oxide semiconductor, they effectively promote electron-hole separation, improve charge carrier utilization, and thus enhance the sensor's response intensity.

[0021] 3. The sensor based on SnO2 / POMs composite material can achieve high response and rapid detection of ammonia at room temperature. Compared with traditional metal oxide sensors that need to operate at high temperatures and have poor selectivity, the sensor provided by this invention has high sensitivity, fast response and recovery time, and excellent selectivity, making it suitable for practical environmental monitoring and smart healthcare applications. Attached Figure Description

[0022] Figure 1 This is a scanning electron microscope image of the composite material.

[0023] Figure 2 The curves show the resistance changes over time for five ammonia gas sensors in Examples 1-4 and Comparative Example 1.

[0024] Figure 3 The bar chart shows the selectivity of the sensor prepared in Example 3 for ammonia. Detailed Implementation

[0025] The following non-limiting embodiments are intended to enable those skilled in the art to more fully understand the invention, but do not limit the invention in any way.

[0026] Unless otherwise specified, the test methods described in the embodiments are conventional methods. Unless otherwise specified, the raw materials used are all commercially available products. The specific embodiments of the present invention are further described below in conjunction with the accompanying drawings and technical solutions:

[0027] Example 1: This example provides a fabrication process for a room temperature ammonia sensor based on SnO2 / POMs composite material, including the following steps:

[0028] (1) Preparation of SnO2 nanosheets: The organic ligand 2,5-dihydroxyterephthalic acid was dissolved in 0.08 mol / L sodium hydroxide aqueous solution at a mass-volume ratio of 1 g:130 mL. The solution was stirred at room temperature to obtain a dispersion. Then, 20 mmol of stannous sulfate was added to the dispersion, and the mixture was heated in a water bath at 80°C for 10 hours. After the reaction was completed, the mixture was naturally cooled, washed 4 times with deionized water, and dried at 50°C for 10 hours to obtain Sn-based MOF powder. The powder was then calcined in a muffle furnace at 500°C for 5 hours in an air atmosphere to obtain SnO2 nanosheets.

[0029] (2) P5W 30 Synthesis: Sodium tungstate was dissolved in deionized water at a mass-to-volume ratio of 1 g: 1 mL. Concentrated phosphoric acid was slowly added and stirred until dissolved. The solution was then poured into a reaction vessel and reacted at 120°C for 12 hours. After the reaction vessel cooled, deionized water and potassium chloride were added to the solution, and the mixture was stirred until homogeneous. The solution was filtered, washed repeatedly with ethanol, and the precipitate was dissolved in water, recrystallized, and dried to obtain P5W. 30 powder;

[0030] (3) Preparation of SnO2 / P5W 30 Composite material: SnO2 nanosheets obtained in (1) and P5W nanosheets obtained in (2) 30 The powders were mixed and ground, in which the SnO2 nanosheets and P5W were selected. 30 The powders were mixed in a mass ratio of 19:1. Ethanol was then added at a mass-volume ratio of 1 g:25 mL for impregnation, followed by wet milling and drying in a 55°C forced-air drying oven for 6 hours to obtain the POMs-based composite material.

[0031] (4) The composite material was redispersed in ethanol to form a slurry, which was then uniformly coated onto the surface of the pretreated interdigitated electrode using a drop-coating method. After drying, the process was repeated twice. Subsequently, the device was placed in a vacuum drying oven and aged at 120°C for 10 hours. After aging, it was soldered to the adapter base to obtain SnO2 / P5W. 30 Ammonia gas sensor.

[0032] Example 2

[0033] The difference between this embodiment and Embodiment 1 is that, in step (3) when preparing the composite material, the SnO2 nanosheets and P5W are... 30 The mass ratio of the powders was 9:1. All other operating steps were the same as in Example 1, yielding SnO2 / P5W. 30 Ammonia gas sensor.

[0034] Example 3

[0035] The difference between this embodiment and Embodiment 1 is that, in step (3) when preparing the composite material, the SnO2 nanosheets and P5W are... 30 The mass ratio of the powders was 4:1. All other operating steps were the same as in Example 1, yielding SnO2 / P5W. 30 Ammonia gas sensor.

[0036] Figure 1 The SnO2 / P5W prepared in Example 3 is given. 30 The scanning electron microscope image of the composite material shows P5W. 30 Nanoparticles are clearly attached to the SnO2 surface.

[0037] Example 4

[0038] The difference between this embodiment and Embodiment 1 is that, in step (3), when preparing the composite material, the SnO2 nanosheets and P5W used are different. 30 The powder mass ratio was 2:1. All other operating steps were the same as in Example 1, ultimately yielding SnO2 / P5W. 30 Ammonia gas sensor.

[0039] Comparative Example 1

[0040] The SnO2 nanosheets prepared in step (1) of Example 1 were ground thoroughly in a mortar, and then ethanol was added at a mass-volume ratio of 1 g: 20 mL for impregnation, and wet grinding was performed until a uniform slurry was formed. The resulting slurry was coated onto the surface of the pretreated interdigitated electrode sheet by drop coating, and the process was repeated twice after drying. The device was then placed in a vacuum drying oven and aged at 120°C for 10 hours. After aging, it was welded to the adapter base to obtain the SnO2 ammonia sensor.

[0041] Performance testing: The five sensors prepared above were placed in the test chamber, and their initial resistance value R in air was recorded. a Different volumes of ammonia solution were injected into the chamber using a microsyringe, and then evaporated by heating on an evaporation platform to generate an ammonia atmosphere with a concentration of 10–50 ppm. The stable resistance value R of the sensor under each ammonia concentration was then measured. g And based on the sensitivity calculation formula S = R g / R a This allows us to obtain the sensitivity values ​​at the corresponding concentrations.

[0042] Table 1 shows Examples 1-4 and Comparative Example 1, illustrating the sensor sensitivity at ammonia concentrations of 10-50 ppm.

[0043] Table 1. Sensitivity of five gas sensors at ammonia concentrations of 10–50 ppm.

[0044] 10 ppm 20 ppm 30 ppm 40 ppm 50 ppm Comparative Example 1 1.56 1.60 1.65 1.77 1.80 Example 1 1.70 2.17 2.58 2.83 3.45 Example 2 1.97 2.77 3.51 3.87 4.83 Example 3 7.07 10.21 14.20 15.43 19.98 Example 4 4.02 5.80 7.99 8.26 9.17

[0045] like Figure 2 As shown, the SnO2 / P5W prepared in Examples 1 to 4 are examples of SnO2 / P5W. 30 The resistance change over time of the ammonia sensor and the SnO2 ammonia sensor prepared in Comparative Example 1 when exposed to 40 ppm ammonia at room temperature is shown in the figure. As can be seen from the figure, the sensor prepared in Example 3 exhibits superior gas-sensitive response performance. Figure 3 The response of the ammonia sensor prepared in Example 3 to 40 ppm NH3 and 500 ppm volatile organic gases such as ethanol, formaldehyde, toluene and acetone at room temperature is shown. The results show that the response value of the sensor to NH3 is significantly higher than that to other interfering gases, by several times.

[0046] The above descriptions of the embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles described in the present invention, and such improvements and modifications should all be considered to fall within the protection scope of the claims of the present invention.

Claims

1. A chemiluminescence resistivity gas sensor based on polyoxometalates, characterized in that: The gas sensor comprises an adapter base and a sensing element; the sensing element is a SnO2 / Polyoxometalates (POMs) sensitive layer and interdigitated electrode plates; the thickness of the sensitive layer is 1~150 μm, and the POMs are selected from H3PMo. 12 O 40 (PMo) 12 ), K 12.5 Na 1.5 [NaP5W 30 O 110 (P5W) 30 ), Na2[P2W 15 O 56 (P2W) 15 K7[La(H2O)] x (α2-P2W 17 O 61 )] (P2W 17 La), H6P2W 18 O 62 (P2W) 18 ) and H3PW 12 O 40 (PW) 12 Any one of them.

2. The gas sensor according to claim 1, characterized in that, The SnO2 / POMs composite material is obtained by coating POMs on the surface of SnO2 nanosheets through impregnation combined with liquid grinding.

3. The gas sensor according to claim 1, characterized in that, The interdigitated electrode sheet is gold-plated on a copper layer with a thickness of 5~15 μm and fixed to the base film by hot pressing process; Its interdigitated electrode pairs range from 5 to 80, and the electrode spacing is 100 to 200 μm; The interdigitated electrode substrate is PI or PET.

4. A method for fabricating a chemiluminescence gas sensor based on polyoxometalates, comprising cleaning interdigitated electrode sheets and assembling the sensor, characterized in that, The specific steps are as follows: Step 1: Clean the interdigitated electrode pads sequentially with acetone, ethanol and deionized water using ultrasonic cleaning for 5-20 minutes, and then dry them under a nitrogen atmosphere; Step 2: The cleaned interdigitated electrode sheets are subjected to vacuum ozone plasma treatment at a power of 50~80 W for 3~10 minutes. Step 3: After thoroughly grinding the SnO2 / POMs composite material, disperse it in ethanol to prepare a suspension. Coat the suspension evenly on the surface of the interdigitated electrode using a drop-coating method and dry it at 50~80℃. Repeat the above drop-coating and drying process twice. Then place the device in a vacuum drying oven and age it at 100~180℃ for 6~12 hours. Finally, solder it to the adapter base to obtain the gas sensor.

5. The preparation method according to claim 4, characterized in that, (1) The ultrasonic cleaning power described in step one is 200~350 W; (2) The mass ratio of the SnO2 / POMs composite material in step three is 19:1 to 2:1; the mass-volume ratio of the composite material to the ethanol solvent is 1 g : 20 mL to 1 g : 50 mL.

6. The application of a polyoxometalate-based gas sensor based on any one of claims 1 to 3, or a composite material sensor prepared by any one of claims 4 and 5, in ammonia detection.

7. The gas sensor according to any one of claims 1 to 6, characterized in that, The gas sensor operates at room temperature.

8. A method for detecting ammonia, characterized in that, Using the sensor described in claims 6 and 7, ammonia gas detection can be achieved at room temperature. Under conditions of 25 ± 2℃, the sensor is sequentially exposed to ammonia and other interfering gases until saturation, then air is introduced. After the sensor recovers, its resistance value R in the air is recorded. a and the resistance value R in the gas g According to the formula S = R a / R g (n-type response) or S = R g / R a (p-type response) Calculate sensitivity S.

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