Method for detecting trimethylamine gas by RuO2 / ZnMoO4 / MoO3 gas-sensitive material

Abstract

The invention discloses a method for detecting trimethylamine gas by using a RuO2 / ZnMoO4 / MoO3 gas sensitive material, and relates to a method for detecting trimethylamine gas, RuO2 / ZnMoO4 / MoO3 is of a nanosheet structure, ZnMoO4 and RuO2 are uniformly loaded on MoO3, and more active sites are provided for gas adsorption. The RuO2 / ZnMoO4 / MoO3 gas sensor prepared by the invention is simple in manufacturing method, has good response and selectivity when detecting trimethylamine, is not influenced by other interference gases, meets the requirement of on-site rapid detection, has good stability, can be repeatedly used, and has a wide application prospect in the field of food safety monitoring.

Description

Technical Field

[0001] The present invention relates to a method for detecting trimethylamine gas, and particularly to a method for detecting trimethylamine gas by using a RuO2 / ZnMoO4 / MoO3 gas-sensitive material. Background Art

[0002] Trimethylamine (TMA) is a unique volatile organic amine and is the most abundant amine in the atmosphere. It has a wide range of sources, and the generation and emission of trimethylamine accompany livestock farming, food processing, and the treatment of domestic wastewater. Trimethylamine is related to the process of food spoilage and degradation. A large amount of trimethylamine will be released during the spoilage of fish, shrimp, meat, etc., resulting in a foul smell. Secondly, in real life and work, trimethylamine often enters the human body through respiration, causing harm to human health. The nasal cavity, bronchus, lungs and other parts of the human body will be damaged due to the stimulating effect of trimethylamine. Due to the toxicity of trimethylamine, respiratory diseases such as pneumonia and lung cancer will occur. In addition, trimethylamine is considered an important biomarker for disease diagnosis and human health monitoring. For example, the concentration of trimethylamine exhaled by individuals with chronic kidney disease exceeds 0.2 ppm, indicating its potential utility as a biomarker for monitoring chronic kidney disease. Therefore, the detection and quantification of trimethylamine levels have become crucial in environmental monitoring, ensuring food safety, medical diagnosis, etc.

[0003] With the development of the Internet of Things, sensors have become key enablers for enhancing personal safety and environmental sustainability. Among them, metal oxide semiconductor sensors are well-known for their high sensitivity, direct fabrication, cost efficiency, and seamless integration with modern control systems, which have attracted the interest of many researchers. Among the various metal oxides used to prepare metal oxide semiconductor sensors, molybdenum trioxide (MoO3) exhibits obvious advantages. MoO3 has a unique special structure of octahedra sharing corners and edges, which endows it with broad ion channels and embedding sites. This characteristic makes it show great potential in detecting oxidizing and reducing properties. However, in practical applications, further improvement and optimization are needed for the sensing response, selectivity, stability, and response / recovery time of MoO3 sensors at low temperatures. The gas-sensing properties of metal oxide semiconductor gas sensors can be improved by constructing heterojunctions with compounds having different Fermi levels. Such a composite system can not only retain the original physical and chemical properties of the metal oxide semiconductor but also exhibit superior performance beyond single-component materials. In addition, loading noble metals is an effective way to improve the sensing performance through the catalytic activity and electron interaction of metals. Ruthenium (Ru) is a corrosion-resistant and stable light gray polyvalent rare metal with excellent corrosion resistance and stability. In the natural environment, ruthenium usually exists in the form of ruthenium dioxide (RuO2). Due to its excellent catalytic activity and chemical stability, it is often used as a catalyst in catalytic reactions and electrochemical processes. In recent years, numerous studies have shown that Ru and its oxides have shown remarkable effects in improving the gas-sensing performance of metal oxide semiconductor (MOS) materials. Existing gas sensors for detecting trimethylamine gas have a relatively high operating temperature, poor stability, and selectivity. Summary of the Invention

[0004] The object of the present invention is to propose a method for detecting trimethylamine gas using a RuO2 / ZnMoO4 / MoO3 gas-sensitive material. This method designs and synthesizes a gas-sensitive material with a RuO2 / ZnMoO4 / MoO3 nanosheet structure for detecting trimethylamine gas through a solvothermal technique. The whole production process uses easily available raw materials, has a simple process, a controllable process flow, and the obtained material reduces the optimal operating temperature, has a good response to trimethylamine, significant selectivity, and excellent long-term stability.

[0005] The object of the present invention is achieved through the following technical solutions: A method for detecting trimethylamine gas using a RuO2 / ZnMoO4 / MoO3 gas-sensitive material, the method having the following processes and steps: I. Preparation of the RuO2 / ZnMoO4 / MoO3 gas-sensitive material: First, ammonium heptamolybdate tetrahydrate ((NH4)6Mo7O 24·4H2O) was calcined at 500 °C for 2 h to obtain the MoO3 precursor; subsequently, the MoO3 precursor was dissolved in H2O2 and stirred for 30 min; then, methanol was added to the above solution and stirred for 24 h; then the solution was transferred to a stainless-steel autoclave with a polytetrafluoroethylene liner and reacted at 180 °C for 12 h; after cooling to room temperature, the precipitate was washed 6 times with ethanol and then dried overnight at 60 °C. Finally, the product was calcined in a muffle furnace at 400 °C for 2 h to obtain MoO3 nanosheets; The MoO3 nanosheets were added to methanol and ultrasonically dispersed, then zinc nitrate hexahydrate (Zn(NO3)2·6H2O) and dimethylimidazole (C4H6N2) were added and stirred for 12 h. After that, the precipitate was washed 6 times with absolute ethanol and then dried overnight at 60 °C; finally, the product was calcined in a muffle furnace at 500 °C for 2 h to obtain the ZnMoO4 / MoO3 composite material; The synthesis of the RuO2 / ZnMoO4 / MoO3 composite material was the same as that of ZnMoO4 / MoO3, except that ruthenium(III) chloride hydrate (RuCl3·H2O) in different proportions was added in the above step (2); II. Detection of trimethylamine gas using the above materials as gas-sensitive materials to fabricate a gas sensor: The powder prepared above was ground and mixed with ethanol to form a uniform slurry; then this slurry was used as a coating and applied to the outer surface of the ceramic tube. The electrodes of the ceramic tube consisted of four platinum wires and two gold electrodes spaced 6 nm apart; when ethanol evaporated to form the sensing film, a Ni-Cr heating wire passed through the ceramic tube; subsequently, the Ni-Cr heating wire and the Pt wires were welded to a hexagonal base to assemble the gas sensor, as shown in Figure 1 (a); finally, the gas sensor was placed on a WS-30A and aged at 400 °C for 48 h to make it stable.

[0006] Advantages and beneficial effects of the present invention: (1) The RuO2 / ZnMoO4 / MoO3 composite material prepared by the present invention effectively reduces the working temperature of the sensor; (2) The sensor prepared by the present invention has high response, excellent selectivity and long-term stability; (3) The RuO2 / ZnMoO4 / MoO3 trimethylamine sensor prepared by the present invention has a simple preparation method and convenient assembly, is suitable for large-scale industrial production, and has broad application prospects in the field of food monitoring. Description of the drawings

[0007] Figure 1 (a) is a schematic structural diagram of the trimethylamine sensor; Figure 1 (b) is the sensitivity of the gas sensor to 10 ppm trimethylamine gas at a test temperature of 50 - 300 °C; Figure 1(c) shows the selectivity of the gas sensor to 10 ppm gas at 150 °C; Figure 1(d) shows the relationship between the response of the gas sensor and the trimethylamine concentration (0.05 - 500 ppm) at 150 °C; Figure 1(e) shows the response of the gas sensor of Example 4 to 10 ppm trimethylamine within 40 days; Figure 1(f) shows the repeatability curve of the gas sensor of Example 4 to 10 ppm trimethylamine gas at 150 °C. Detailed implementation mode

[0008] The present invention will be described in detail below with reference to the embodiments shown in the drawings.

[0009] The preparation method of RuO2 / ZnMoO4 / MoO3 nanosheets includes the following steps: Example 1

[0010] Preparation of MoO3 nanosheets Step 1: Calcinate 5 g of (NH4)6Mo7O 24 ·4H2O at 500 °C for 2 h to obtain a MoO3 precursor. After cooling to room temperature, the obtained precipitate is washed 6 times with ethanol and then dried overnight at 60 °C.

[0011] Step 2: Dissolve 0.72 g of the MoO3 precursor in 5 mL of H2O2 and stir for 30 min. Then, add methanol (30 mL) to the above solution and stir for 24 h. Then transfer this solution to a 50 mL stainless steel autoclave with a polytetrafluoroethylene lining and react at 180 °C for 12 h.

[0012] Step 3: Calcinate the product of Step 2 in a muffle furnace at 400 °C for 2 h to obtain MoO3 nanosheets; Example 2

[0013] Preparation of ZnMoO4 / MoO3 nanosheets Steps 1, 2, and 3 are the same as in Example 1; Step 4: Add 50 mg of MoO3 nanosheets to 30 mL of methanol, ultrasonically disperse for 30 min, then add 9 mg of Zn(NO3)2·6H2O and 24 mg of C4H6N2, stir for 12 h, wash the precipitate 6 times with absolute ethanol, and then dry overnight at 60 °C.

[0014] Step 5: Calcinate the product of Step 4 in a muffle furnace at 500 °C for 2 h to obtain a ZnMoO4 / MoO3 composite material. Example 3

[0015] Preparation of 1-RuO2 / ZnMoO4 / MoO3 Nanosheets Steps 1, 2, and 3 are the same as in Example 1; Step 4: Add 50 mg of MoO3 precursor to 30 mL of methanol and ultrasonically disperse for 30 min. Then add 9 mg of Zn(NO3)2·6H2O, 24 mg of C4H6N2, and 1 mg of RuCl3·H2O, and stir magnetically for 12 h. Wash the resulting precipitate with absolute ethanol 6 times, and then dry overnight at 60 °C; Step 5: Calcinate the product of Step 4 in a muffle furnace at 500 °C for 2 h to obtain the 1-RuO2 / ZnMoO4 / MoO3 composite material. Example 4

[0016] Preparation of 3-RuO2 / ZnMoO4 / MoO3 Nanosheets Steps 1, 2, and 3 are the same as in Example 1 Step 4: Add 50 mg of MoO3 precursor to 30 mL of methanol and ultrasonically disperse for 30 min. Then add 9 mg of Zn(NO3)2·6H2O, 24 mg of C4H6N2, and 3 mg of RuCl3·H2O, and stir magnetically for 12 h. Wash the resulting precipitate with absolute ethanol 6 times, and then dry overnight at 60 °C; Step 5: Calcinate the product of Step 4 in a muffle furnace at 500 °C for 2 h to obtain the 3-RuO2 / ZnMoO4 / MoO3 composite material. Example 5

[0017] Preparation of 5-RuO2 / ZnMoO4 / MoO3 Nanosheets. Steps 1, 2, and 3 are the same as in Example 1 Step 4: Add 50 mg of MoO3 precursor to 30 mL of methanol and ultrasonically disperse for 30 min. Then add 9 mg of Zn(NO3)2·6H2O, 24 mg of C4H6N2, and 5 mg of RuCl3·H2O, and stir magnetically for 12 h. Wash the resulting precipitate with absolute ethanol 6 times, and then dry overnight at 60 °C; Step 5: Calcinate the product of Step 4 in a muffle furnace at 500 °C for 2 h to obtain the 5-RuO2 / ZnMoO4 / MoO3 composite material.

[0018] Gas Sensitivity Test of RuO2 / ZnMoO4 / MoO3 Composite Material The RuO2 / ZnMoO4 / MoO3 composite material was added to anhydrous ethanol and mixed to form a uniform slurry, which was coated on an Al2O3 ceramic tube. There were two gold electrodes and four platinum wires on the Al2O3 ceramic tube, and a nickel-chromium heating wire was inside the tube. The ceramic tube was welded to a six-pin base to obtain the gas sensor element as shown in Fig. 1 (a). Among them, the material obtained in Example 4 was analyzed by scanning electron microscopy for its microstructure, and it can be seen that the sample presented a two-dimensional nanosheet structure with a thickness ranging from 10 to 30 nm. Fig. 1 (b) shows the sensing response of the sensor to 10 ppm trimethylamine at different working temperatures. The response of all the sensors in the examples initially increased with the increase of the working temperature until it reached the maximum value, and then decreased with the continuous increase of the temperature, thus presenting an "increase-maximum-decrease" pattern. It is worth noting that ZnMoO4 improved the response of the sensor, and the addition of RuO2 reduced the optimal working temperature of the sensor, thus enhancing the reliability and stability of practical applications. Among all the sensors, the sensor in Example 4 showed the highest trimethylamine sensing response (121.1 / 150 °C). Fig. 1 (c) shows the selectivity test of the sensor in Example 4 to 10 ppm of various gases. It can be seen that the response of the sensor to other interfering gases (methanol, ethanol, ammonia, formaldehyde, and acetone) can be ignored, indicating that the sensor has good selectivity to trimethylamine. Fig. 1 (d) shows the sensing response to different concentrations of trimethylamine at 150 °C. With the increase of the trimethylamine concentration (0.05 - 50 ppm), the response of all the sensors increased rapidly. Subsequently, when the trimethylamine concentration further increased, this upward trend gradually slowed down, which may be due to the adsorption saturation of high-concentration trimethylamine. In addition, it is worth noting that at the same trimethylamine concentration, the sensor in Example 4 always showed the highest response and was able to detect trimethylamine as low as 0.05 ppm (response about 1.38), highlighting its excellent ability to detect trace TMA in the atmosphere. Fig. 1 (e) shows that under the condition of 150 °C, the response of the sensor in Example 4 to trimethylamine remained at a high level for 40 days, indicating its good long-term stability. As shown in Fig. 1 (f), under the condition of 150 °C, a five-cycle test was carried out on 10 ppm trimethylamine, and Example 4 showed excellent response and recovery trends, with no obvious attenuation compared with the initial response, indicating that the sensor in Example 4 has good reproducibility.

Claims

1. A method for detecting trimethylamine gas using RuO2 / ZnMoO4 / MoO3 gas-sensitive material, characterized in that: The method has the following processes and steps:

1. Preparation of RuO2 / ZnMoO4 / MoO3 gas-sensitive materials: (1) First, ammonium molybdate tetrahydrate ((NH4)6Mo7O 24 ·4H2O) was calcined at 500℃ for 2 h to obtain a MoO3 precursor; then, the MoO3 precursor was dissolved in H2O2 and stirred for 30 min; then, methanol was added to the above solution and stirred for 24 h; then the solution was transferred to a polytetrafluoroethylene-lined stainless steel autoclave and reacted at 180℃ for 12 h; after cooling to room temperature, the precipitate was washed with ethanol 6 times and then dried at 60℃ overnight. Finally, the product was calcined at 400℃ in a muffle furnace for 2 h to obtain MoO3 nanosheets; (2) MoO3 nanosheets were added to methanol for ultrasonic dispersion, and then zinc nitrate hexahydrate (Zn(NO3)2·6H2O) and dimethylimidazole (C4H6N2) were added and stirred for 12 h. The precipitate was washed with anhydrous ethanol for 6 times and then dried at 60 °C overnight. Finally, the product was calcined at 500 °C in a muffle furnace for 2 h to obtain a ZnMoO4 / MoO3 composite material. (3) The synthesis of RuO2 / ZnMoO4 / MoO3 composite materials and ZnMoO4 / MoO3 is achieved by adding different proportions of ruthenium (III) chloride hydrate (RuCl3·H2O) in the above step (2); 2. The above materials are used as gas sensitive materials to make gas sensors for the detection of trimethylamine gas: The powder prepared above was ground and mixed with ethanol to make a uniform slurry; this slurry was then applied as a coating on the outer surface of a ceramic tube, and the ceramic tube electrode consisted of four platinum wires and two gold electrodes spaced 6 nm apart; when the ethanol evaporated to form a sensing film, a Ni-Cr heating wire passed through the ceramic tube; subsequently, the Ni-Cr heating wire and the Pt wire were welded to a hexagonal base to assemble the gas sensor, as shown in Figure 1 (a); finally, the gas sensor was placed on a WS-30A and aged at 400°C for 48 h to make it stable.

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