Tin dioxide-based ammonia gas sensor as well as preparation method and application thereof

Abstract

The invention discloses a stannic oxide-based ammonia gas sensor as well as a preparation method and application thereof, relates to the technical field of gas sensors, and solves the problems of high detection lower limit, poor gas selectivity and low sensitivity of a traditional semiconductor ammonia gas sensor. A sensitive material based on oxygen vacancy regulation and control SnO2 / ZIF-67 is prepared on the surface of an interdigital gold electrode by adopting a chemical vapor deposition method, a planar electrode, an aluminum oxide ceramic substrate, a heater and a Pt wire are welded and packaged according to a general indirectly-heated gas sensitive element, and the SnO2 / ZIF-67 semiconductor ammonia gas sensor is prepared. The lower detection limit of the SnO2 / ZIF-67 semiconductor ammonia gas sensor is 1 ppm; meanwhile, the NH3 selectivity and sensitivity of the sensor are improved through the synergistic effect of SnO2 and ZIF-67, and the sensor can be used for detecting ammonia gas leakage and can be applied to judging the safety of ammonia gas in chemical production operation, environmental gas detection and other applications.

Description

Technical Field

[0001] The present invention relates to the technical field of gas sensors, and particularly relates to a tin dioxide-based ammonia sensor, a preparation method thereof, and an application thereof. Background Art

[0002] As an important chemical raw material, ammonia is widely used in industrial production, such as fertilizer manufacturing, refrigeration, the electronics industry, etc. However, ammonia is highly harmful to human health and the environment. It can irritate organs such as the respiratory tract and eyes. Exposure to an environment with a concentration of 500 ppm for 15 minutes can cause acute injuries such as burns of the respiratory mucosa. When the concentration exceeds 1700 ppm, it will cause fatal injuries such as bronchospasm and acute pulmonary edema, and the fatality rate is as high as 80% after 30 minutes of exposure. At the same time, a large amount of ammonia is released in agricultural activities, affecting the atmospheric environment. Ammonia molecules in the atmosphere generate ammonium nitrate fine particles (PM2.5) through photochemical reactions. During its sedimentation process, it causes soil acidification (the pH value drops by 0.5 - 1.5 units), resulting in a 15% - 30% reduction in crop yields, and disrupting the nitrogen cycle balance in water bodies, leading to an increase in the eutrophication degree in coastal areas and forming an ecological chain destruction effect. Therefore, in order to detect the concentration of ammonia in the environment, ammonia sensors have become one of the key research directions in the current sensor technology field.

[0003] Traditional semiconductor ammonia sensors (such as tin dioxide, zinc oxide, iron oxide, etc.) are based on the interaction between gases and the semiconductor surface, and detect the ammonia concentration by the change in the semiconductor resistance caused by ammonia adsorption. Semiconductor ammonia sensors have been widely studied and applied due to their low cost and simple preparation process. However, traditional semiconductor ammonia sensors respond to multiple gases and are easily interfered by volatile organic compounds, hydrogen sulfide, etc., and it is difficult to accurately detect the ammonia concentration in a complex environment. At the same time, the lower detection limit of traditional semiconductor ammonia sensors is high (greater than 100 ppm), the resistance change is small when detecting low-concentration ammonia, and it cannot meet the high-precision air quality monitoring requirements. Moreover, when traditional semiconductor ammonia sensors are used for real-time monitoring, the response and recovery times are long, and they cannot quickly detect changes in the ammonia concentration.

[0004] To improve the above-mentioned defects of traditional semiconductor ammonia sensors, developing a semiconductor ammonia sensor for detecting low-concentration ammonia is of great significance for promoting the refined development of air quality monitoring in the environmental monitoring industry and promoting green development in the industrial manufacturing field. Summary of the Invention

[0005] In order to solve the problems of high lower detection limit, poor gas selectivity, and low sensitivity of traditional semiconductor ammonia sensors, the present invention proposes a tin dioxide-based ammonia sensor, a preparation method thereof, and an application thereof. The technical solution of the present invention is as follows:

[0006] A preparation method of a tin dioxide-based ammonia sensor, comprising the following preparation steps:

[0007] S1: Add the aqueous citric acid solution and the aqueous thioacetamide solution to the aqueous stannous chloride dihydrate solution to obtain a mixed solution. Immerse the planar electrode in the mixed solution, and add the aqueous sodium hydroxide solution dropwise to the mixed solution for a water bath reaction. After the reaction is completed, rinse the planar electrode, and then dry the planar electrode.

[0008] S2: Add the aqueous citric acid solution and the aqueous thioacetamide solution to the aqueous stannous chloride dihydrate solution to obtain a mixed solution. Immerse the dried planar electrode in S1 in the mixed solution, and add the aqueous sodium hydroxide solution dropwise to the mixed solution for a water bath reaction. After the reaction is completed, rinse the planar electrode, and then dry the planar electrode. Calcinate the dried planar electrode. Immerse the calcined planar electrode in the dimethylimidazole methanol solution, and continue to add the cobalt nitrate hexahydrate methanol solution to the dimethylimidazole methanol solution for stirring to prepare a planar electrode surface-modified with the SnO2 / ZIF-67 semiconductor sensitive material.

[0009] S3: Transfer the planar electrode surface-modified with the SnO2 / ZIF-67 semiconductor sensitive material to a tube furnace, heat it up under a nitrogen atmosphere, and then carry out a reaction under a mixed atmosphere of nitrogen and oxygen. After the reaction is completed, cool the tube furnace to room temperature. Finally, transfer the planar electrode to a muffle furnace for calcination to prepare a planar electrode based on oxygen vacancy-regulated SnO2 / ZIF-67. Weld and package the planar electrode, the alumina ceramic substrate, the heater, and the Pt wire according to the general indirectly heated gas sensor element to prepare the SnO2 / ZIF-67 semiconductor ammonia sensor.

[0010] Further, the planar electrode is an interdigital gold electrode.

[0011] Further, the molar ratio of citric acid, thioacetamide, stannous chloride dihydrate, and sodium hydroxide in S1 is 25:4:16:20.

[0012] Further, the dosages of citric acid and sodium hydroxide in S2 are the same as those in S1, the dosage of thioacetamide is twice that in S1, and the dosage of stannous chloride dihydrate is twice that in S1.

[0013] Further, the temperature of the water bath reaction is 65°C, and the time of the water bath reaction is 3 h; the temperature of the drying is 40°C.

[0014] Further, the temperature of the calcination in S2 is 500°C, and the time of the calcination is 2 h; the stirring time is 1 h.

[0015] Further, the heating rate in S3 is 10 °C / min, and the temperature is raised from 20 °C to 500 °C; the reaction temperature is 500 °C, and the reaction time is 1 h; the volume ratio of nitrogen to oxygen is 1-3:1-3;

[0016] Further, the calcination temperature in S3 is 500 °C, and the calcination time is 2 h.

[0017] A tin dioxide-based ammonia sensor is prepared by the above preparation method.

[0018] An application of the above tin dioxide-based ammonia sensor is applied to chemical production operations or environmental gas detection.

[0019] Compared with the prior art, the present invention solves the problems of high detection limit, poor gas selectivity and low sensitivity of traditional semiconductor ammonia sensors. The specific beneficial effects are as follows:

[0020] 1. Low detection limit: The present invention uses chemical vapor deposition to prepare a sensitive material based on oxygen vacancy-regulated SnO2 / ZIF-67 on the surface of interdigital gold electrodes, which changes the catalytic ability of the pure SnO2 / ZIF-67 material, provides more hole oxygen on the surface of the semiconductor sensitive material, and thus provides more reactive sites, improves the gas-sensing performance of the sensor, and reduces the detection limit of the SnO2 / ZIF-67 semiconductor ammonia sensor. At 370 °C, the sensor still has a response value of 14% to a NH3 concentration of 1 ppm, which can be used for the detection of ammonia leakage, and then to judge the safety of ammonia in applications such as chemical production operations and environmental gas detection, and has practicality.

[0021] 2. The synergistic effect of SnO2 and ZIF-67 improves gas selectivity and sensitivity: The present invention utilizes the regular pore topology structure of ZIF-67 to provide rich adsorption sites for gas molecules. At the same time, there is a specific coordination effect between the coordinatively unsaturated cobalt active sites in ZIF-67 and NH3 molecules. The synergistic effect of this bifunctional property promotes the efficient adsorption and directional diffusion of NH3 molecules, significantly increases the contact probability between NH3 and the SnO2 active interface, and improves the NH3 selectivity of the SnO2 / ZIF-67 semiconductor ammonia sensor; the work function difference between SnO2 and ZIF-67 can induce electron migration at the heterojunction interface, and electrons transfer directionally from ZIF-67 to SnO2 until the Fermi level is balanced. This process triggers interface energy band reconstruction and forms a space charge layer; when the sensor is exposed to an NH3 environment, the electrons released by the redox reaction of NH3 and adsorbed oxygen are injected into the heterojunction space charge region, and the interface barrier modulation effect is triggered through carrier concentration rearrangement, which is finally converted into a detectable change in resistance signal, improving the sensitivity of the SnO2 / ZIF-67 semiconductor ammonia sensor.

[0022] 3. Achieving large-scale industrial applications: The SnO2 / ZIF-67 semiconductor ammonia sensor prepared by the present invention has excellent conductivity and chemical stability. The preparation process is simple, efficient, and low-cost, which is conducive to realizing batch industrial production. Description of the Drawings

[0023] Figure 1 is a schematic structural diagram of the SnO2 / ZIF-67 semiconductor ammonia sensor;

[0024] Figure 2 is the standard working curve of the operating temperature-response value of the SnO2 / ZIF-67 semiconductor ammonia sensor;

[0025] Figure 3 is the standard working curve of the ammonia concentration-response value of the SnO2 / ZIF-67 semiconductor ammonia sensor prepared in Example 2. Detailed Embodiments

[0026] To make the technical solutions of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the present invention. It should be noted that the following embodiments are only used to better understand the technical solutions of the present invention and should not be construed as a limitation of the present invention.

[0027] Example 1.

[0028] S1: Add 25 mL of 0.3 mol / L citric acid aqueous solution and 15 mL of 0.08 mol / L thioacetamide aqueous solution to 30 mL of 0.16 mol / L stannous chloride dihydrate aqueous solution and stir to obtain a mixed solution. Transfer the prepared mixed solution to a 65°C constant temperature water bath, and immerse the pre-cleaned interdigital gold electrode in the mixed solution. Under continuous stirring, add 1.5 mL of 160 g / L sodium hydroxide solution to the mixed solution and maintain the water bath reaction for 3 h; after the reaction is completed, take out the interdigital gold electrode, repeatedly rinse it with deionized water to remove the residues, and then place the interdigital gold electrode in a vacuum drying oven and dry it at 40°C;

[0029] S2: Add 25 mL of 0.3 mol / L citric acid aqueous solution and 15 mL of 0.16 mol / L thioacetamide aqueous solution to 30 mL of 0.32 mol / L stannous chloride dihydrate aqueous solution, stir to obtain a mixed solution, transfer the prepared mixed solution to a 65 °C constant temperature water bath, immerse the dried interdigital gold electrode in S1 into the mixed solution, under the condition of continuous stirring, add 1.5 mL of 160 g / L sodium hydroxide solution to the mixed solution, and keep the water bath reaction for 3 h; after the reaction is completed, take out the interdigital gold electrode, repeatedly rinse it with deionized water to remove residues, then place the interdigital gold electrode in a vacuum drying oven and dry it at 40 °C; finally, place the dried interdigital gold electrode in a muffle furnace and calcine it at 500 °C for 2 h; immerse the calcined interdigital gold electrode in 10 mL of 32.5 g / L dimethylimidazole methanol solution, and continue to add 10 mL of 14.5 g / L cobalt nitrate hexahydrate methanol solution to the dimethylimidazole methanol solution, stir continuously at room temperature for 1 h to self-assemble the SnO2 / ZIF-67 sensitive material on the surface of the interdigital gold electrode, and prepare an interdigital gold electrode with a SnO2 / ZIF-67 semiconductor sensitive material modified on the surface;

[0030] S3: Transfer the interdigital gold electrode with a SnO2 / ZIF-67 semiconductor sensitive material modified on the surface to a tubular furnace, use a vacuum pump to evacuate the air in the tubular furnace to make the tubular furnace in a vacuum state; then, fill the tubular furnace with nitrogen to standard atmospheric pressure, and repeat the operations of evacuating and filling nitrogen three times to establish a stable nitrogen environment; under a nitrogen atmosphere, heat the tubular furnace from 20 °C to 500 °C at a heating rate of 10 °C / min; when the temperature reaches 500 °C, carry out a chemical vapor deposition reaction, switch the carrier gas to a mixed gas of nitrogen (37.5 sccm) and oxygen (12.5 sccm) (oxygen concentration is 25%), and keep it at 500 °C for 1 h to achieve oxygen vacancy regulation; after the reaction is completed, turn off the heating system, wait for the tubular furnace to cool naturally to room temperature, then transfer the interdigital gold electrode to a muffle furnace and calcine it at 500 °C for 2 hours to prepare an interdigital gold electrode based on oxygen vacancy-regulated SnO2 / ZIF-67; weld and package the interdigital electrode, Al2O3 ceramic substrate, heater and Pt wire according to a general indirectly heated gas sensor to prepare a SnO2 / ZIF-67 semiconductor ammonia sensor.

[0031] As Figure 1Schematic diagram of the structure of an oxygen vacancy-regulated SnO2 / ZIF-67 semiconductor ammonia sensor. As can be seen from the figure, the ammonia sensor uses an Al2O3 ceramic substrate (3mm×3mm×0.25mm) as the base. Interdigitated gold electrodes and nickel-cadmium alloy heating electrodes based on oxygen vacancy-regulated SnO2 / ZIF-67 are respectively installed on the upper and lower surfaces of the Al2O3 insulating ceramic substrate, and a Pt wire for measurement is also installed. The working principle of the SnO2 / ZIF-67 semiconductor ammonia sensor is as follows: When the sensitive material based on oxygen vacancy-regulated SnO2 / ZIF-67 on the surface of the interdigitated gold electrode is exposed to an air environment, a chemisorption reaction of oxygen molecules occurs on the surface of the sensitive material, and O 2- / O - adsorbed oxygen species are formed by capturing free electrons on the surface layer of the material, thereby forming an electron depletion layer at the semiconductor interface, resulting in a significant increase in the matrix resistance of the ammonia sensor. When the environmental medium is switched to ammonia, NH3 molecules with strong reducing properties undergo an oxidation-reduction reaction with the adsorbed oxygen on the surface of the SnO2 / ZIF-67 sensitive material. During the reaction process, the captured electrons are re-injected into the semiconductor conduction band, causing the thickness of the depletion layer to decrease, and ultimately resulting in a characteristic decrease in the resistance value of the sensor; at the same time, the work function difference between SnO2 and ZIF-67 will induce electron migration at the heterojunction interface, and electrons will transfer directionally from ZIF-67 to SnO2 until the Fermi level is balanced. This process triggers interface energy band reconstruction and forms a space charge layer; when the system is exposed to an ammonia environment, the electrons released by the oxidation-reduction reaction of NH3 and adsorbed oxygen are injected into the heterojunction space charge region, and the interface barrier modulation effect is triggered through the rearrangement of carrier concentration, which is ultimately converted into a detectable change in resistance signal, improving the sensitivity of the sensor.

[0032] Example 2.

[0033] The difference between this example and Example 1 is that in S3, the carrier gas is a mixed gas of nitrogen (25 sccm) and oxygen (25 sccm) (oxygen concentration is 50%). The remaining preparation steps and conditions are the same as those in Example 1, and an SnO2 / ZIF-67 semiconductor ammonia sensor is prepared.

[0034] Example 3.

[0035] The difference between this example and Example 1 is that in S3, the carrier gas is a mixed gas of nitrogen (12.5 sccm) and oxygen (37.5 sccm) (oxygen concentration is 75%). The remaining preparation steps and conditions are the same as those in Example 1, and an SnO2 / ZIF-67 semiconductor ammonia sensor is prepared.

[0036] As Figure 2Standard working curves of the operating temperature-response values of the ammonia sensors based on SnO2 / ZIF-67 prepared in Examples 1-3. As can be seen from the figure, the ammonia sensor based on SnO2 / ZIF-67 prepared in Example 2 has a response value of 281% to 100 ppm NH3 at 370 °C, which is higher than that of the sensors prepared in the other two examples. Thus, it can be seen that by regulating the SnO2 / ZIF-67 semiconductor sensitive material through chemical vapor deposition, more hole oxygen and reactive sites are provided on the surface of the semiconductor sensitive material, which can greatly improve the gas-sensing performance of the sensor.

[0037] Put the SnO2 / ZIF-67 semiconductor ammonia sensor prepared in Example 2 into the gas chamber and measure the resistance value R of the sensor in air. a , Use a micro syringe to inject 1 ppm to 100 ppm of ammonia into the gas chamber and measure the resistance value of the sensor in ammonia with different concentrations, namely R g , According to the definition formula of sensitivity S = (R a / R g - 1) × 100%, calculate the sensitivity of the sensor at different concentrations. For example Figure 3 Standard working curves of the ammonia concentration-response values of the SnO2 / ZIF-67 semiconductor ammonia sensor prepared in Example 2. As can be seen from the figure, when the operating temperature is 370 °C, the response value of the SnO2 / ZIF-67 semiconductor ammonia sensor to NH3 increases with the increase of NH3 concentration. When the NH3 concentration is 1 ppm, the sensor still has a response value of 14%. Thus, it can be seen that this sensor has excellent characteristics of high sensitivity and low detection limit.

[0038] The present invention uses chemical vapor deposition to prepare a sensitive material based on oxygen vacancy-regulated SnO2 / ZIF-67 on the surface of interdigital gold electrodes, providing more hole oxygen on the surface of the semiconductor sensitive material, improving the gas-sensing performance of the sensor, and reducing the detection limit of the SnO2 / ZIF-67 semiconductor ammonia sensor; at the same time, the synergistic effect of SnO2 and ZIF-67 is used to improve the NH3 selectivity and sensitivity of the SnO2 / ZIF-67 semiconductor ammonia sensor, which can be used for the detection of ammonia leakage, and then judge the safety of ammonia in applications such as chemical production operations and environmental gas detection, and can achieve large-scale industrial production.

[0039] The descriptions of the above embodiments are only used to help understand the method and its core idea of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

[0040] The foregoing description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A preparation method of a tin dioxide-based ammonia sensor, characterized in that, It includes the following preparation steps: S1: Add an aqueous solution of citric acid and an aqueous solution of thioacetamide to an aqueous solution of stannous chloride dihydrate to obtain a mixed solution. Immerse a planar electrode in the mixed solution, and add an aqueous solution of sodium hydroxide dropwise to the mixed solution for a water bath reaction. After the reaction is completed, rinse the planar electrode, and then dry the planar electrode; S2: Add an aqueous solution of citric acid and an aqueous solution of thioacetamide to an aqueous solution of stannous chloride dihydrate to obtain a mixed solution. Immerse the dried planar electrode in S1 in the mixed solution, and add an aqueous solution of sodium hydroxide dropwise to the mixed solution for a water bath reaction. After the reaction is completed, rinse the planar electrode, and then dry the planar electrode; Calcinate the dried planar electrode; Immerse the calcined planar electrode in a dimethylimidazole methanol solution, and continue to add a cobalt nitrate hexahydrate methanol solution to the dimethylimidazole methanol solution for stirring to prepare a planar electrode with a SnO2 / ZIF-67 semiconductor sensitive material modified on its surface; S3: Transfer the planar electrode with a SnO2 / ZIF-67 semiconductor sensitive material modified on its surface to a tubular furnace, heat it up under a nitrogen atmosphere, and then react under a mixed atmosphere of nitrogen and oxygen. After the reaction is completed, cool the tubular furnace to room temperature. Finally, transfer the planar electrode to a muffle furnace for calcination to prepare a planar electrode based on oxygen vacancy-regulated SnO2 / ZIF-67; Weld and package the planar electrode, an alumina ceramic substrate, a heater, and a Pt wire according to a general side-heated gas sensor element to prepare a SnO2 / ZIF-67 semiconductor ammonia sensor.

2. The preparation method of the tin dioxide-based ammonia sensor according to claim 1, characterized in that The planar electrode is an interdigital gold electrode.

3. The preparation method of the tin dioxide-based ammonia sensor according to claim 1, characterized in that, In S1, the molar ratio of citric acid, thioacetamide, stannous chloride dihydrate, and sodium hydroxide is 25:4:16:

20.

4. The preparation method of the tin dioxide-based ammonia sensor according to claim 1, characterized in that, In S2, the dosages of citric acid and sodium hydroxide are the same as those in S1, the dosage of thioacetamide is twice that in S1, and the dosage of stannous chloride dihydrate is twice that in S1.

5. The preparation method of the tin dioxide-based ammonia sensor according to claim 1, characterized in that, The temperature of the water bath reaction is 65 °C, and the time of the water bath reaction is 3 h; the drying temperature is 40 °C.

6. The preparation method of the tin dioxide-based ammonia sensor according to claim 1, wherein, In S2, the calcination temperature is 500 °C, and the calcination time is 2 h; the stirring time is 1 h.

7. The preparation method of the tin dioxide-based ammonia sensor according to claim 1, wherein, In S3, the heating rate is 10 °C / min, and it is heated from 20 °C to 500 °C; the reaction temperature is 500 °C, and the reaction time is 1 h; the volume ratio of nitrogen to oxygen is 1-3:1-3.

8. The preparation method of the tin dioxide-based ammonia sensor according to claim 1, characterized in that, In S3, the calcination temperature is 500 °C, and the calcination time is 2 h.

9. A tin dioxide-based ammonia sensor, characterized in that, Prepared by the preparation method according to any one of claims 1-8.

10. An application of the tin dioxide-based ammonia sensor according to claim 9, characterized in that, Applied to chemical production operations or environmental gas detection.

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