Highly selective gas-sensitive element for NO2 gas detection at room temperature and its preparation method

Abstract

The application discloses a high-selectivity gas sensor for NO2 gas detection at room temperature and a preparation method thereof, which comprises an electrode sheet and a black titanium dioxide sensing film uniformly loaded on the surface of the electrode sheet. TiO2 is added into a solvent to form a slurry, the slurry is uniformly drop-coated on the electrode sheet, then the electrode sheet is uniformly and slowly heated to remove the solvent, and the operation is repeated for multiple times, so that a TiO2 coating with a required thickness is formed on the surface of the electrode sheet; and the electrode sheet coated with the TiO2 coating is annealed in vacuum to form a black titanium dioxide sensing film on the surface of the electrode sheet. The black titanium dioxide sensing film has oxygen vacancies, and can realize detection of NO2 at room temperature, has high detection sensitivity, low detection limit and high selectivity, realizes rapid and efficient detection of NO2, has low detection cost, and is suitable for popularization and application.

Description

Technical Field

[0001] This invention relates to the field of gas sensor technology, specifically to a highly selective gas-sensitive element for NO2 gas detection at room temperature and its preparation method. Background Technology

[0002] Nitrogen dioxide (NO2) is a common harmful gas, mainly originating from the combustion of fossil fuels, vehicle exhaust emissions, and industrial production processes. In the atmosphere, it not only contributes to acid rain formation but also undergoes photochemical reactions with volatile organic compounds (VOCs) under sunlight, producing ozone and fine particulate matter (PM2.5). 2.5 NO2, through its high concentrations, exacerbates air pollution and reduces air quality. More seriously, NO2 poses significant health risks. Long-term exposure to high concentrations of NO2 can lead to respiratory and cardiovascular diseases, and even increase the risk of cancer. Furthermore, NO2 negatively impacts plant growth, inhibiting crop yield and quality, and damaging ecosystems. Monitoring Needs and Technological Challenges: As public awareness of environmental protection and health continues to rise, real-time and accurate monitoring of airborne NO2 concentrations has become crucial. Traditional NO2 detection methods, such as chemiluminescence and spectrophotometry, while offering high sensitivity and accuracy, suffer from drawbacks such as complex equipment, cumbersome operation, high cost, and difficulty in achieving rapid on-site detection. Therefore, developing a highly efficient, sensitive, and selective sensor for NO2 gas at room temperature is of great significance for environmental monitoring, industrial safety, and health protection.

[0003] Traditional metal-oxide-semiconductor (MOS) gas sensors, while offering advantages such as fast response and easy integration, typically require high-temperature operation, leading to increased energy consumption and device complexity. Furthermore, existing sensors suffer from a lack of gas selectivity and moisture resistance, preventing effective NO2 detection in mixed gases and high-humidity environments. Some studies have attempted to achieve room-temperature NO2 response and improve NO2 gas selectivity to some extent through composite fabrication or doping, but these methods still fail to provide NO2 gas identification and lack moisture resistance; moreover, composite fabrication increases device manufacturing costs. This invention addresses this need by proposing a novel room-temperature NO2 gas detection technology. Through innovative material design, it aims to overcome the shortcomings of existing technologies, achieving high sensitivity, high selectivity, and low detection limit for NO2 gas detection, and provides a method to improve the response sensitivity, selectivity, and moisture resistance of NO2. Summary of the Invention

[0004] The purpose of this invention is to provide a highly selective gas-sensitive element for NO2 gas detection at room temperature, a method for preparing the same, and a method for improving the response sensitivity, selectivity, and moisture resistance of NO2 detection. The technical problem to be solved is the low selectivity of existing metal oxide gas-sensitive elements for NO2 gas.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A highly selective gas-sensitive element for NO2 gas detection at room temperature includes an electrode sheet and a black TiO2 sensing film uniformly loaded on the surface of the electrode sheet. The black TiO2 sensing film is prepared by annealing a TiO2 coating under vacuum conditions.

[0007] A method for preparing a highly selective gas-sensitive element for NO2 gas detection at room temperature, specifically including the following steps:

[0008] (1) Add TiO2 to the solvent to form a slurry, and uniformly drop the slurry onto the electrode sheet. Then, slowly heat the electrode sheet on a hot plate to remove the solvent. Repeat this process multiple times to form a TiO2 coating of the required thickness on the surface of the electrode sheet.

[0009] (2) The electrode sheet coated with TiO2 is annealed in a vacuum to form a black TiO2 sensing film on the surface of the electrode sheet.

[0010] Preferably, the annealing temperature in step (2) is 450-550℃ and the annealing time is 2-6 hours. More preferably, the annealing temperature is 500℃ and the annealing time is 4 hours.

[0011] Preferably, the TiO2 in step (1) is nano-TiO2 with a burr structure on the surface. The specific preparation method is as follows: first, (NH4)2TiF6 and H3BO3 are added to water to form a mixed solution, and then ZnO is immersed in the above solution at room temperature until a white product appears at the bottom of the solution. After centrifugation and washing, nano-TiO2 with a burr structure on the surface is obtained. The molar ratio of (NH4)2TiF6, H3BO3 and ZnO is 1:(2.8-3.3):(0.2-0.25).

[0012] The solvents mentioned in step (1) include, but are not limited to, deionized water and ethanol.

[0013] In step (1), the electrode sheet is heated on the hot plate at a temperature 20-40°C lower than the boiling point of the solvent used. At this temperature, the electrode sheet can be heated slowly, avoiding excessively fast or high heating temperatures, which can easily cause defects such as cracks in the sensing film.

[0014] Preferably, the number of repetitions in step (1) is 2-8 times.

[0015] Compared with the prior art, the present invention has the following advantages: (1) The preparation method is simple, and the black TiO2 sensing film can be obtained by annealing under vacuum conditions; (2) The black TiO2 sensing film has more oxygen vacancies, realizes the detection of NO2 at room temperature, and has high detection sensitivity and low detection limit, with the detection limit as low as subppb level; (3) It exhibits excellent selectivity for NO2 gas and can effectively distinguish other common gases; (4) It realizes rapid and efficient detection of NO2, with low detection cost, and is suitable for widespread application. Attached Figure Description

[0016] Figure 1 X-ray diffraction (XRD) patterns of W-TiO2 and B-TiO2.

[0017] Figure 2 SEM images of W-TiO2 and B-TiO2.

[0018] Figure 3 The electron paramagnetic resonance (EPR) spectra of W-TiO2 and B-TiO2 are shown.

[0019] Figure 4 (a) is a comparison of the selectivity of W-TiO2 and B-TiO2 for NO2 and other gases; (b) is the response of W-TiO2 to 0.5 ppm NO2 under different humidity conditions; (c) is the response of B-TiO2 to 10 ppm NO2 under different humidity conditions. Detailed Implementation

[0020] The following description, in conjunction with the accompanying drawings and specific embodiments, provides further details.

[0021] Example 1

[0022] A method for preparing a highly selective gas-sensitive element for NO2 gas detection at room temperature, comprising the following steps:

[0023] (1) First, (NH4)2TiF6 and H3BO3 were added to water to form a mixed solution. Then, ZnO was immersed in the above solution at room temperature for 20-50 hours. A white product appeared at the bottom of the solution. The molar ratio of (NH4)2TiF6, H3BO3 and ZnO was 1:3:0.2. The product was separated from the reaction solution by centrifugation and washed three times with deionized water (DI) to finally obtain nano-TiO2 with a burr structure on the surface.

[0024] (2) TiO2 is mixed with deionized water to form a slurry. 3 μL of the slurry is uniformly drop-coated onto an electrode sheet (such as an alumina ceramic substrate). After drop-coating, the electrode sheet is heated on a hot plate at 70°C for 5 minutes to remove moisture. This process is repeated three times to form a TiO2 coating on the surface of the electrode sheet.

[0025] (3) The electrode sheet coated with TiO2 was annealed in air at 500°C for 4 hours to obtain white TiO2, which is denoted as W-TiO2.

[0026] Example 2

[0027] Except for step (3), all other steps in this embodiment are the same as in embodiment 1.

[0028] (3) The electrode sheet coated with TiO2 was annealed in a vacuum at 500°C for 4 hours to obtain black TiO2, which is denoted as B-TiO2.

[0029] The X-ray diffraction (XRD) patterns of W-TiO2 and B-TiO2 are as follows: Figure 1 As shown. All diffraction peaks in the XRD patterns of both samples can be clearly attributed to the anatase structure of TiO2 (JCPDS card number 21-1272), and no additional peaks or phases were observed. Compared to the other sample, the diffraction peaks of B-TiO2 are more pronounced, indicating its better crystallinity.

[0030] Figure 2 SEM images of W-TiO2 and B-TiO2 were obtained after annealing under different conditions. The SEM images of the products were basically the same. Both W-TiO2 and B-TiO2 retained the burr-like structure of TiO2 after annealing, which improved the specific surface area of ​​the gas-sensitive element.

[0031] Electron paramagnetic resonance (EPR) spectroscopy was performed on W-TiO2 and B-TiO2. Figure 3 As shown, B-TiO2 exhibits a strong EPR signal at g = 2.004, which was identified as electrons being trapped in oxygen vacancies, while this signal was almost unobservable in W-TiO2, confirming that B-TiO2 has more oxygen vacancies than W-TiO2.

[0032] The sensing performance of W-TiO2 and B-TiO2-based sensors for NO2 and several common interfering gases was tested at room temperature. The prepared W-TiO2 or B-TiO2 surface-loaded electrode sheets were placed in a sealed space filled with the gas to be measured, and the sensor response was measured. The gas to be measured was ethanol, isopropanol, acetone, carbon dioxide (CO2), hydrogen (H2), formaldehyde, and NO2. The sensor response was defined as follows: when R... a >R g When, response = (R a -R g ) / R g ×100%; when R a <R g When, response = (R g -R a ) / Ra ×100% (R) a and R g (These represent the sensor output resistance before and after gas exposure, respectively).

[0033] Figure 4 A radar chart comparing the selectivity of W-TiO2 and B-TiO2 for NO2 and other gases summarizes their responses to ethanol, isopropanol, acetone, carbon dioxide (CO2), hydrogen (H2), formaldehyde, and NO2. The chart shows that W-TiO2 and B-TiO2 have responses of 20.9% and 250%, respectively, to 3 ppm NO2. The response of B-TiO2 is 12 times that of W-TiO2. In addition to the improved response, B-TiO2 also shows significantly enhanced selectivity for NO2. B-TiO2 suppresses the responses to ethanol, isopropanol, acetone, carbon dioxide (CO2), hydrogen (H2), and formaldehyde, and shows almost no response to these gases. Compared to W-TiO2, the B-TiO2 sensor exhibits ultra-high selectivity for NO2, enabling the identification of NO2 in a mixed atmosphere of seven gases.

[0034] Furthermore, the sensing performance of W-TiO2 and B-TiO2 for NO2 under different humidity conditions ( Figure 4 In studies b and c), it was found that the response of W-TiO2 to NO2 increased with increasing humidity. Figure 4 b). In contrast, the response of B-TiO2 to NO2 in the range of relative humidity from 30% to 80% is not affected by atmospheric moisture. Figure 4 c). Compared to W-TiO2, B-TiO2 exhibits a significant resistance to humidity interference when detecting NO2.

Claims

1. A method for preparing a highly selective gas-sensitive element for NO2 gas detection at room temperature, characterized in that, Specifically, the following steps are included: (1) Add TiO2 to the solvent to form a slurry, uniformly drop the slurry onto the electrode sheet, and then uniformly and slowly heat the electrode sheet to remove the solvent. Repeat this process multiple times to form a TiO2 coating of the required thickness on the surface of the electrode sheet; In step (1), TiO2 is nano-TiO2 with a burr structure on the surface. (2) The electrode sheet coated with TiO2 is annealed in a vacuum to form a black TiO2 sensing film on the surface of the electrode sheet. The annealing temperature in step (2) is 450-550°C.

2. The method for preparing a highly selective gas-sensitive element for NO2 gas detection at room temperature according to claim 1, characterized in that, Annealing time is 2-6 hours.

3. The method for preparing a highly selective gas-sensitive element for NO2 gas detection at room temperature according to claim 1, characterized in that, The annealing temperature was 500°C and the annealing time was 4 hours.

4. The method for preparing a highly selective gas-sensitive element for NO2 gas detection at room temperature according to claim 1, characterized in that, The preparation method of nano-TiO2 with burr structure is as follows: First, (NH4)2TiF6 and H3BO3 are added to water to form a mixed solution. Then, ZnO is immersed in the above solution at room temperature until a white product appears at the bottom of the solution. After centrifugation and washing, nano-TiO2 with burr structure on the surface is obtained. The molar ratio of (NH4)2TiF6, H3BO3 and ZnO is 1:(2.8-3.3):(0.2-0.25).

5. The method for preparing a highly selective gas-sensitive element for NO2 gas detection at room temperature according to claim 1, characterized in that, The solvents mentioned in step (1) are deionized water and ethanol.

6. The method for preparing a highly selective gas-sensitive element for NO2 gas detection at room temperature according to claim 1, characterized in that, In step (1), the electrode sheet is heated on the hot plate at a temperature 20-40°C lower than the boiling point of the solvent used.

7. The method for preparing a highly selective gas-sensitive element for NO2 gas detection at room temperature according to claim 1, characterized in that, The oxygen vacancy content of TiO2 can be increased by controlling the annealing conditions.

8. A highly selective gas-sensitive element for NO2 gas detection at room temperature, prepared by the preparation method according to any one of claims 1-7, characterized in that, It includes an electrode sheet and a black titanium dioxide sensing film uniformly loaded on the surface of the electrode sheet. The black titanium dioxide sensing film is prepared by annealing a TiO2 coating under vacuum conditions.

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