Construction method and application of gas sensor for detecting aroma of six kinds of tea leaves

Abstract

The application relates to the technical field of semiconductor gas sensors, in particular to a construction method and application of a gas sensor for detecting six kinds of tea aroma, which comprises the following steps: mixing a zinc nitrate hexahydrate aqueous solution and a 2-methyl imidazole aqueous solution to obtain a precursor solution; controlling the precursor solution to be hydrothermally reacted at 90 DEG C for 4h; after the hydrothermal reaction is completed, the suspension is cooled to room temperature, centrifuged, washed and dried to obtain white precipitates; the obtained dry sample is calcined at 500 DEG C under an air atmosphere for 2h to obtain a zinc oxide gas-sensitive material; the zinc oxide gas-sensitive material is dissolved in ethanol, forms a suspension after ultrasonic treatment, is drop-coated onto the surface of a plane electrode, and is constructed into a semiconductor sensor; the application realizes rapid sensing response of leaf alcohol, and in the gas-sensitive research of the volatile substance leaf alcohol in tea aroma, the application shows excellent gas-sensitive characteristics.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of semiconductor gas sensors, specifically to a method for constructing a gas sensor for detecting the aroma of six kinds of tea and its application. BACKGROUND

[0002] Tea aroma, as an important indicator of tea quality, plays an indispensable role in tea production and identification. It is not only one of the key factors for consumers to choose tea, but also an important reflection of the state of plants during tea growth and production. The richness and uniqueness of tea aroma often directly reflect the quality of tea, so accurate evaluation is crucial for the development of the tea industry. Tea trees and the tea they produce are often affected by various pests and diseases, which not only affects the yield and quality of tea, but also directly affects the economic benefits of tea farmers. Under the attack of pests and diseases, tea trees produce a series of volatile organic compounds, such as leaf alcohol. Changes in the content of leaf alcohol can directly reflect the environmental conditions of tea trees, and it is one of the important indicators of the health of tea trees and the quality of tea. Traditionally, the evaluation of tea aroma often requires experienced professionals to taste and identify, which is not only time-consuming and labor-intensive, but also greatly influenced by subjective factors. Therefore, developing a fast, accurate and reliable sensor technology to detect the content of leaf alcohol in tea aroma is of great significance for judging the degree of tea tree infestation by pests and the quality of tea.

[0003] Zinc oxide, as a semiconductor material, has a wide application prospect in the field of gas sensors. Its excellent electrical properties, chemical stability, and high sensitivity to volatile organic compounds make it an ideal gas sensing material. In particular, zinc oxide sensors perform well in detecting aliphatic and aromatic compounds, which is related to their special affinity for adsorbed molecules. In recent years, with the continuous development of zinc oxide material preparation technology and the continuous optimization of sensor performance, it is possible to apply zinc oxide-based gas sensors in the field of tea pest and disease detection. By using zinc oxide-based gas sensors, it is expected to achieve rapid and accurate detection of the content of leaf alcohol in tea aroma, thereby providing real-time and accurate monitoring means for tea tree cultivation, tea production and other processes, and providing strong support for the sustainable development of the tea industry.

[0004] Therefore, the tea aroma sensor based on zinc oxide proposed by us has great market application potential, not only can provide real-time pest and disease monitoring and tea quality evaluation services for tea trees, but also

[0005] provide strong support for the quality control and brand building of the tea market. SUMMARY

[0006] The application aims to provide a construction method and application of a gas sensor for six tea aroma detections, realize a rapid sensing response to leaf alcohol, and show excellent gas-sensitive characteristics in the gas-sensitive research of the volatile leaf alcohol in tea aroma.

[0007] The application aims to provide a construction method and application of a gas sensor for six tea aroma detections, realize a rapid sensing response to leaf alcohol, and show excellent gas-sensitive characteristics in the gas-sensitive research of the volatile leaf alcohol in tea aroma.

[0008] The construction method of the gas sensor for six tea aroma detections comprises the following steps:

[0009] Step 1: mix a zinc nitrate hexahydrate aqueous solution and a 2-methylimidazole aqueous solution to obtain a precursor solution; control the precursor solution to undergo a hydrothermal reaction at 90 DEG C for 4h;

[0010] Step 2: after the hydrothermal reaction, cool to room temperature, centrifugal wash and dry the suspension to obtain a white precipitate;

[0011] Step 3: calcine the obtained dry sample at 500 DEG C in an air atmosphere for 2h to obtain a zinc oxide gas-sensitive material;

[0012] Step 4: dissolve the zinc oxide gas-sensitive material in ethanol, form a suspension after ultrasonic treatment, drop coat onto the surface of a planar electrode, and construct a semiconductor sensor.

[0013] As a further scheme of the application, the molar ratio of the zinc nitrate hexahydrate to the 2-methylimidazole is 1:8-10.

[0014] As a further scheme of the application, the mass fraction of the zinc nitrate hexahydrate aqueous solution is 1-3%.

[0015] As a further scheme of the application, the mass fraction of the 2-methylimidazole aqueous solution is 3-9%.

[0016] As a further scheme of the application, the centrifugal washing is performed for 3 times, the centrifugal rotation speed is 6000-10000rpm, and the centrifugal time is 5-10min.

[0017] As a further scheme of the application, the temperature for drying the precipitate is 60-80 DEG C, and the drying time is 6-48h.

[0018] As a further scheme of the application, the heating rate of the dry sample in the calcination process is 5 DEG C·min -1 .

[0019] As a further scheme of the application, the morphology of the zinc oxide gas-sensitive material is granular.

[0020] As a further scheme of the application, the particle size of the zinc oxide gas-sensitive material is 45-55nm.

[0021] Application of the semiconductor gas sensor, the semiconductor sensor prepared by the method is used for testing leaf alcohol, geraniol, decanal, n-octanol, phenethyl alcohol and methyl salicylate.

[0022] Advantages of the present application:

[0023] In the present application, the preparation method of the whole zinc oxide gas sensitive material is simple and easy to operate, and the sensor constructed based on the obtained zinc oxide gas sensitive material exhibits excellent sensing characteristics such as high sensitivity and high stability for tea aroma;

[0024] In the process of using the zinc oxide gas sensitive material for constructing a tea aroma sensor, the prepared zinc oxide gas sensitive material is subjected to a sensor sensitive film process to construct a tea aroma sensor, which can realize rapid sensing response to leaf alcohol, and exhibits excellent gas sensitive characteristics in the gas sensitive research of volatile substances leaf alcohol in tea aroma. BRIEF DESCRIPTION OF DRAWINGS

[0025] The present application will be further described below with reference to the accompanying drawings.

[0026] Figure 1 is the SEM picture of the zinc oxide material sample prepared in the present application;

[0027] Figure 2 is the XRD picture of the zinc oxide nano gas sensitive material provided by the present application;

[0028] Figure 3 is the gas sensitive performance test Response (Rgas / Rair)-Time (s) curve of the zinc oxide material prepared by calcining at 500 DEG C in air atmosphere at a working temperature of 325 DEG C for leaf alcohol;

[0029] Figure 4 is the gas sensitive test response value bar chart of the zinc oxide gas sensitive material prepared by calcining at 400 DEG C in air atmosphere at a working temperature of 325 DEG C for three different concentrations of leaf alcohol, geraniol, decanal, n-octanol, phenethyl alcohol and methyl salicylate. DETAILED DESCRIPTION

[0030] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0031] Example 1

[0032] Please refer to Figure 1As shown, the application is a construction method of a gas sensor for detecting six tea leaf aromas, comprising:

[0033] Step 1: weigh zinc nitrate hexahydrate, dissolve in deionized water, and magnetically stir uniformly for 5 min to obtain a first transparent solution; weigh 2-methylimidazole and dissolve in deionized solution to obtain a second transparent solution; slowly add the first transparent solution to the second transparent solution under magnetic stirring to obtain a mixed precursor solution; transfer the precursor solution to a 50 mL polytetrafluoroethylene liner, seal the liner, and place it in a reaction kettle; then place the reaction kettle in an oven at 90℃ for hydrothermal reaction for 4 h;

[0034] The molar ratio of zinc nitrate hexahydrate to 2-methylimidazole is 1:8.

[0035] The mass fraction of the zinc nitrate hexahydrate aqueous solution is 1-3%, and the mass fraction of the 2-methylimidazole aqueous solution is 3%.

[0036] Step 2: After the hydrothermal reaction is completed, the reaction kettle is naturally cooled to room temperature, the liner is removed, the suspension in the liner is transferred to a 50 mL centrifuge tube, the white precipitate in the liner is washed and centrifuged with deionized water, and the collected white precipitate is dried.

[0037] The white precipitate is washed and centrifuged 3 times at a centrifugal speed of 6000 rpm for 5 min; the precipitate is dried at a temperature of 60℃ for 6 h to remove the water in the precipitate.

[0038] Step 3: The obtained dried sample is calcined at 500℃ in air for 2 h to obtain a zinc oxide gas sensitive material; the morphology of the zinc oxide gas sensitive material is granular, and the particle size is 45 nm.

[0039] The temperature rising rate of the dried sample during calcination is 5℃·min -1 ;

[0040] Step 4: 0.25 mg of the zinc oxide gas sensitive material is dissolved in 10 μL of ethanol to form a suspension, which is further drop-coated onto the surface of a planar electrode to construct a semiconductor sensor for detecting tea leaf aroma.

[0041] Example 2

[0042] Please refer to Figure 1 As shown, the application is a construction method of a gas sensor for detecting six tea leaf aromas, comprising:

[0043] Step 1: weigh the zinc nitrate hexahydrate, dissolve in deionized water, and magnetically stir for 5 min to obtain a first transparent solution; weigh the 2-methylimidazole and dissolve in deionized solution to obtain a second transparent solution; slowly add the first transparent solution to the second transparent solution under magnetic stirring to obtain a mixed precursor solution, transfer the precursor solution to a 50mL polytetrafluoroethylene liner, seal the liner in a reaction kettle, and then place the reaction kettle in an oven at 90℃ for hydrothermal reaction for 4h;

[0044] The molar ratio of zinc nitrate hexahydrate to 2-methylimidazole is 1:9.

[0045] The mass fraction of the zinc nitrate hexahydrate aqueous solution is 2%, and the mass fraction of the 2-methylimidazole aqueous solution is 6%.

[0046] Step 2: After the hydrothermal reaction is completed, the reaction kettle is naturally cooled to room temperature, the liner is taken out, the suspension in the liner is transferred to a 50mL centrifuge tube, the white precipitate in the liner is washed and centrifuged with deionized water, and the collected white precipitate is dried.

[0047] The centrifugal washing is performed 3 times, the centrifugal speed is 80000rpm, and the centrifugal time is 8min; the temperature for drying the precipitate is 70℃, and the drying time is 25h to remove the water in the precipitate.

[0048] Step 3: The obtained dried sample is calcined at 500℃ in air for 2h to obtain a zinc oxide gas sensitive material; the morphology of the zinc oxide gas sensitive material is granular, and the particle size is 50nm.

[0049] The heating rate of the dried sample during calcination is 5℃·min -1 ;

[0050] Step 4: 0.25mg of the zinc oxide gas sensitive material is dissolved in 10μL of ethanol to form a suspension after ultrasonic treatment, which is further drop-coated on the surface of a planar electrode to construct a semiconductor sensor for detecting tea aroma.

[0051] Example 3

[0052] Please refer to Figure 1 The application is a construction method of a gas sensor for detecting six kinds of tea aroma, which comprises:

[0053] Step 1: weigh the zinc nitrate hexahydrate, dissolve in deionized water, and stir uniformly under magnetic force for 5 min to obtain a first transparent solution; weigh the 2-methylimidazole and dissolve in deionized solution to obtain a second transparent solution; slowly add the first transparent solution to the second transparent solution under magnetic stirring to obtain a mixed precursor solution, transfer the precursor solution to a 50 mL polytetrafluoroethylene liner, seal the liner in a reaction kettle, and then place the reaction kettle in an oven at 90℃ for hydrothermal reaction for 4 h;

[0054] The molar ratio of zinc nitrate hexahydrate to 2-methylimidazole is 1:10.

[0055] The mass fraction of the zinc nitrate hexahydrate aqueous solution is 3%, and the mass fraction of the 2-methylimidazole aqueous solution is 9%.

[0056] Step 2: After the hydrothermal reaction is completed, the reaction kettle is naturally cooled to room temperature, the liner is taken out, the suspension in the liner is transferred to a 50 mL centrifuge tube, the white precipitate in the liner is washed and centrifuged with deionized water, and the collected white precipitate is dried.

[0057] The centrifugation is performed 3 times at a centrifugal speed of 6000-10000 rpm for 5-10 min, and the precipitate is dried at a temperature of 60-80℃ for 6-48 h to remove the water in the precipitate.

[0058] Step 3: The obtained dried sample is calcined at 500℃ in air for 2 h to obtain a zinc oxide gas sensitive material. The morphology of the zinc oxide gas sensitive material is granular, and the particle size is 45-55 nm.

[0059] The heating rate of the dried sample during calcination is 5℃·min -1 ;

[0060] Step 4: 0.25 mg of the zinc oxide gas sensitive material is dissolved in 10 μL of ethanol to form a suspension after ultrasonic treatment, which is further drop-coated on the surface of a planar electrode to construct a semiconductor sensor for detecting tea aroma.

[0061] Example 4

[0062] The application of the semiconductor gas sensor includes that the gas sensitive material can be used for rapid detection of tea aroma substances, specifically:

[0063] The zinc oxide gas sensitive material is dispersed in anhydrous ethanol and drop-coated on the surface of a planar electrode by a pipette, and a gas sensor is further constructed after natural drying for performance testing of tea aroma;

[0064] In the production process of the zinc oxide gas sensitive material for tea aroma sensor, the zinc oxide gas sensitive material prepared in the above examples is subjected to a sensor sensitive film process to construct a tea aroma sensor, so that rapid sensing response to leaf alcohol can be realized.

[0065] In the morphology observation and performance detection of the zinc oxide gas sensitive material sample prepared in the above examples, the following results can be obtained:

[0066] (1) As shown in Figure 1 , the SEM image of the zinc oxide prepared in Example 1 can be seen from Figure 1 that the synthesized zinc oxide is composed of nanoparticles with an average particle size of about 50 nm. From the SEM characterization results, it can be found that the nanoparticles have uniform size distribution and have a certain degree of concave-convex surface. This structure makes the zinc oxide particles have a high ratio between surface area and volume, which is beneficial to enhance the sensitivity of the gas response. At the same time, the surface structure with a certain degree of concave-convex surface helps to improve the surface reactivity of the material and can provide more active sites, thereby enhancing the sensing performance. In addition, the uniformly distributed irregular cubic particles ensure the stability and repeatability of the material in application.

[0067] (2) As shown in Figure 2 , from the X-ray diffraction (XRD) pattern of the zinc oxide sample, it can be seen that there are obvious diffraction peaks at 2θ angles of 31.8, 34.5, 36.3, 56.7 and 63.1°, respectively corresponding to the (100), (002), (101), (110) and (103) crystal planes of zinc oxide, indicating that the sample is hexagonal zinc oxide, and the peak shape is sharp, indicating that the product has complete crystallization.

[0068] The gas sensitive application of the above-mentioned zinc oxide nanomaterial of the present application is that the zinc oxide nanosensitive material is dispersed in a small amount of ethanol, then is dropped and coated on the surface of a plane electrode by a pipette gun, is naturally dried, is further constructed into a gas sensor, is aged on an aging table for three days, and then is subjected to gas sensitive detection; the sensor is subjected to gas sensitive test on leaf alcohol at a working temperature of 325℃;

[0069] (3) As shown in Figure 3Figure 6 shows the dynamic response curve of the sensor based on the zinc oxide gas sensitive material to different concentrations (10 to 100 ppm) of leaf alcohol at a humidity of 38% and a working temperature of 325°C. As can be seen from the figure, the response value of the sensor based on the zinc oxide gas sensitive material is 60 at a concentration of 10 ppm, and the response value reaches 130 at a concentration of 100 ppm, highlighting excellent sensing performance. In addition, the sensitivity of the gas sensitive sensor increases with the increase of the concentration of leaf alcohol gas, indicating that the prepared sensor has good reversibility;

[0070] (4) as Figure 4 Figure 5 shows the response value bar chart of the sensor based on the zinc oxide gas sensitive material to three concentrations (0.5 ppm, 5 ppm, 10 ppm) of six gases (leaf alcohol, geraniol, decanal, n-octanol, phenethyl alcohol, methyl salicylate) at a humidity of 30% and a working temperature of 325°C. As can be seen from the figure, the tea leaf sensor based on the zinc oxide gas sensitive material shows good response to the above tea aroma.

[0071] As can be seen from the above, the zinc oxide gas sensitive material of the embodiment of the present application has excellent gas sensing performance at 325°C.

[0072] The above has described one embodiment of the present application in detail, but the content described is only the preferred embodiment of the present application, and cannot be considered as used for limiting the implementation range of the present application. Any equivalent changes and improvements made according to the scope of the present application should still belong to the patent coverage range of the present application.

Claims

1. A method for constructing a gas sensor for detecting the aroma of six types of tea, characterized in that, Includes the following steps: Step 1: Mix the aqueous solution of zinc nitrate hexahydrate with the aqueous solution of 2-methylimidazole to obtain the precursor solution; control the hydrothermal reaction of the precursor solution at 90 °C for 4 h; Step 2: After the hydrothermal reaction is complete, cool to room temperature, centrifuge, wash, and dry the suspension to obtain a white precipitate; Step 3: Calcine the obtained dried sample in air at 500℃ for 2 hours to obtain zinc oxide gas-sensitive material; Step 4: Dissolve the zinc oxide gas-sensitive material in ethanol, sonicate it to form a suspension, and drop it onto the surface of the planar electrode to construct a semiconductor sensor; The zinc oxide gas-sensitive material has a granular morphology. The particle size of the zinc oxide gas-sensitive material is 45-55 nm; This semiconductor sensor is used to test leaf alcohol, geraniol, decanal, n-octanol, phenethyl alcohol, and methyl salicylate; The molar ratio of zinc nitrate hexahydrate to 2-methylimidazole is 1:8-10; The mass fraction of zinc nitrate hexahydrate aqueous solution is 1-3%; The mass fraction of 2-methylimidazole aqueous solution is 3-9%; The semiconductor sensor operates at a temperature of 325°C.

2. The method for constructing a gas sensor for detecting six types of tea aromas according to claim 1, characterized in that, Centrifuge and wash 3 times, centrifuge at 6000-10000 rpm for 5-10 min.

3. The method for constructing a gas sensor for detecting six types of tea aromas according to claim 1, characterized in that, The precipitate is dried at a temperature of 60-80℃ for a duration of 6-48 hours.

4. The method for constructing a gas sensor for detecting six types of tea aromas according to claim 1, characterized in that, The heating rate of the dried sample during calcination was 5 °C·min. -1 .

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