Preparation method of ultra-sensitive nitrogen dioxide room temperature gas sensor

Abstract

The invention relates to a preparation method of a room-temperature nitrogen dioxide sensor. According to the invention, heteropolyacid hydrate is used as a gas-sensitive material, and heteropolyacid solid powder is dried, washed and heated to obtain the final sensing material. The defects in the prior art are overcome. The material has the characteristics of high sensitivity, high response speed, no need of an external heat source, response at room temperature and the like, a traditional gas sensitive element heating part is not needed, and the material can show ultra-sensitive property to low-concentration nitrogen dioxide gas at room temperature. And the economical efficiency and the stability of the sensor are improved.

Description

Technical Field

[0001] The present invention relates to gas sensor technology, and in particular to an ultrasensitive heteropoly acid room-temperature nitrogen dioxide gas sensor. Background Art

[0002] With the development of industry and the increase in the number of cars on the road, a large amount of toxic and harmful gases are emitted, affecting people's physical health and environmental quality. Gases such as nitrogen oxides and carbon dioxide are common air pollutants. Gas sensors play an important role in achieving efficient detection of toxic and harmful gases.

[0003] Nitrogen dioxide is a highly toxic gas that widely exists in automobile exhaust and industrial emissions and is one of the main gases forming acid rain. When NO 2 reacts with water vapor in the air, nitric acid will be generated, and then acidic substances will fall to the ground, causing damage to organisms and the environmental ecosystem. In addition, NO 2 reacts with volatile organic compounds (VOCs) to form secondary organic aerosols (SOA), which will lead to hazy weather, affecting people's lives and causing danger. Long-term exposure to excessive nitrogen dioxide atmosphere will cause serious damage to the human respiratory system, trigger airway inflammation, significantly decline lung function, and significantly increase the risk of respiratory tract infections. In view of the above effects, developing a more sensitive, safe and reliable gas sensor that can effectively monitor the concentration of nitrogen dioxide and provide early warning signals is of extremely important practical significance for protecting the environment and ensuring personal health.

[0004] Currently, the sensing materials for monitoring nitrogen dioxide mainly include tin dioxide, zinc oxide, tungsten oxide, etc., but they also face some challenges in practical applications, including poor stability, long response and recovery times, poor selectivity, low response values, etc. Therefore, it is of important practical significance to develop a nitrogen dioxide gas sensor that has good stability, high sensitivity, fast response and recovery times, and low production cost at room temperature. Summary of the Invention

[0005] The object of the present invention is to overcome the shortcomings of the nitrogen dioxide gas sensor in the above background art and establish a room-temperature gas sensor with sensitive response, good stability and selectivity, and short response and recovery times.

[0006] To achieve the above object, the technical solution of the present invention is as follows:

[0007] A preparation method of a room-temperature nitrogen dioxide gas sensor, the main technical features of which include the following steps:

[0008] (1) Dissolve the heteropoly acid hydrate powder in an ethanol solution; use an ultrasonic disperser to disperse the solution in an environment of 45°C for 60 minutes to obtain a heteropoly acid dispersion;

[0009] (2) Take a certain amount of the heteropoly acid dispersion obtained in step (1), let it stand for a period of time, then pour off the upper clear liquid, and add ethanol solution for washing;

[0010] (3) Put the product after washing in step (2) into a vacuum oven for drying to form a heteropoly acid dry powder;

[0011] (4) Put the solid powder obtained in step (3) in a tubular furnace, and calcine it at 100°C for 6 hours in a hydrogen-nitrogen mixed atmosphere to obtain a calcined heteropoly acid gas-sensitive material;

[0012] (5) Grind the gas-sensitive material obtained in step (4), according to the mass ratio of the gas-sensitive material to ethanol of 1:4, gradually add ethanol dropwise while grinding until a uniform slurry is obtained. Take an appropriate amount of the slurry and coat it on the surface of the ceramic tube with gold electrodes on the ceramic substrate, and then heat it at 80 - 110°C for more than 24 hours to obtain an ultrasensitive room-temperature hydrogen sensor;

[0013] Preferably, the temperature of the vacuum oven in step (3) should be set at 50 - 80°C, and dry the heteropoly acid solid powder at this temperature overnight;

[0014] Through the above technical solution, the present invention provides a method for using a heteropoly acid sensing material to detect nitrogen dioxide at room temperature. The heteropoly acid has a high ability to recognize gas molecules. The present invention utilizes the special structure, good catalytic activity, large specific surface area and good recognition effect on gas molecules of the heteropoly acid to prepare a sensing material for detecting nitrogen dioxide gas at room temperature. This sensing material can achieve sensitive detection of gas molecules. In addition, the preparation method is simple, the raw material cost is low and easy to obtain.

[0015] The advantages and effects of the present invention are as follows:

[0016] It can realize the response of quasi-semiconductor materials to low-concentration nitrogen dioxide gas at room temperature, and has the characteristics of high sensitivity and fast response speed;

[0017] This invention does not require the heating components of traditional gas-sensitive elements, improving the economy and stability of the gas-sensitive sensor;

[0018] The following describes the present invention in detail with reference to the accompanying drawings and specific embodiments, but it is not a limitation to the present invention. Brief Description of the Drawings

[0019] Figure 1 It is a schematic diagram of the room-temperature nitrogen dioxide gas sensor in the present invention;

[0020] Figure 2 Response / recovery curves of the sensor for detecting low-concentration nitrogen dioxide in Example 1;

[0021] Figure 3 Response / recovery curves of the sensor for detecting low-concentration nitrogen dioxide in Example 2;

[0022] Figure 4 Response / recovery curves of the sensor for detecting low-concentration nitrogen dioxide in Example 3; Detailed implementation manners

[0023] The present invention will be described below in conjunction with the accompanying drawings and specific examples, and the present invention can be better understood according to the described examples.

[0024] A heteropolyacid gas sensor is prepared using phosphotungstic acid hydrate as a raw material and its application, and the specific preparation method is as follows:

[0025] Example 1:

[0026] 1. 0.2 g of H 3 PW 12 O 40 ·x H 2 O powder is mixed into 10 ml of ethanol solution, and the mixed solution is dispersed in an environment of 45 °C for 60 min using an ultrasonic disperser to completely dissolve it, obtaining a uniformly dispersed phosphotungstic acid solution;

[0027] 2. Take a certain amount of phosphotungstic acid dispersion, let it stand at room temperature, remove the upper clear liquid, then add ethanol to dissolve and let it stand, repeat several times to obtain phosphotungstic acid solid;

[0028] 3. The obtained phosphotungstic acid solid is placed in a vacuum oven set at 60 °C and dried overnight to form phosphotungstic acid dry powder;

[0029] 4. The obtained phosphotungstic acid precursor dry powder is placed in a tube furnace, and under a hydrogen-nitrogen mixed atmosphere, it is heated from room temperature to 80 °C at a rate of 1 °C / min and maintained for 200 min to obtain the calcined phosphotungstic acid material;

[0030] 5. Take 0.05 mg of the gas-sensitive material obtained in step 4, add 2 μl of ethanol solution dropwise while grinding until a uniform slurry is obtained, take an appropriate amount of the slurry and coat it on the surface of the ceramic tube with gold electrodes on the ceramic substrate, and then heat it at 80 - 110 °C for more than 24 h to obtain an ultrasensitive room-temperature hydrogen sensor.

[0031] The room-temperature nitrogen dioxide gas sensor prepared in Example 1 is as Figure 1 shown, with a ceramic as the substrate and only a pair of gold electrodes for the output of the sensor electrical signal.

[0032] The response / recovery changes of the nitrogen dioxide gas sensor prepared in Example 1 to nitrogen dioxide at 10 - 50 ppb at room temperature and its sensitivity to nitrogen dioxide at different concentrations are as Figure 2 shown. The response value to 10 ppb nitrogen dioxide gas is 0.88%, the response time to nitrogen dioxide at different concentrations is 5 - 20 s, and the recovery time is 10 - 20 s.

[0033] Example 2:

[0034] This example is similar to Example 1, except that the calcination temperature in Step 1 is 80 °C, and the calcination temperature in this example is 100 °C.

[0035] The response / recovery changes of the resistance value of the nitrogen dioxide gas sensor prepared in Example 2 to nitrogen dioxide at 10 - 50 ppb at room temperature and its sensitivity to nitrogen dioxide at different concentrations are as Figure 3 shown. The results show that the performance of the nitrogen dioxide gas sensor after calcination at 100 °C has increased by 92%.

[0036] Example 3:

[0037] This example is similar to Example 2, except that the calcination temperature is 180 °C.

[0038] The response / recovery changes of the resistance value of the nitrogen dioxide gas sensor prepared in Example 3 to nitrogen dioxide at 10 - 50 ppb at room temperature and its sensitivity to nitrogen dioxide at different concentrations are as Figure 4 shown. The results show that the response degree of the nitrogen dioxide gas sensor has decreased by 96% compared with that of Example 2.

[0039] The present invention uses the static gas distribution method to measure the sensitive characteristics of the hydrogen sensor, directly detecting the change in the resistance value of the sensor under different environments. The sensor sensitivity is defined as

[0040]

[0041] where ΔR is R 1 - R 2 , R 1 is the resistance value of the nitrogen dioxide gas sensor in ambient air, and R 2 is the resistance value of the nitrogen dioxide gas sensor in the gas to be measured. The concentration unit of the gas to be measured is ppm.

[0042] The above shows and describes the main features and advantages of the present invention.

[0043] The above embodiments are illustrative rather than restrictive. Several embodiments can be listed within the defined scope. Therefore, changes and modifications within the overall concept of the present invention should fall within the protection scope of the present invention.

Claims

1. A method for preparing a room temperature nitrogen dioxide sensor, characterized in that: The following steps are involved: (1) Heteropoly acid hydrate is used as the basic material, and no other materials need to be added; (2) Weighing the solid particles of the heteropolyacid hydrate, dissolving them in an organic solvent or deionized water, using an ultrasonic disperser or other stirring device to obtain a uniform solution, leaving it to stand for a period of time, discarding the supernatant, and then washing it with ethanol several times to leave the remaining solid material; (3) drying the remaining solid material and baking it under a certain atmosphere to obtain the desired sensing material; (4) According to different preparation processes, the drying temperature is set at 50-80°C, the drying time is set at 4-10 hours, the baking temperature is set at 60-300°C, and the baking time is set at 7-16 hours; (5) Heteropolyacid as the basic material, heteropolyacid salts can also be selected as gas-sensitive materials; (6) using immersion treatment to treat the surface of the semiconductor coating with a dye solution; (7) Drying the impregnated sample at room temperature; (8) The prepared heteropolyacid sensing material exhibits ultrasensitive gas sensing properties to NO2 at room temperature. The resistance of the gas-sensitive layer decreases with the adsorption of NO2. When 10 ppb and 50 ppm NO2 are introduced, the sensitivity of the sensor is 11.94 and 19.77, respectively.

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