In-situ construction method and application of gas sensor for detecting volatile aroma substances

Abstract

The invention relates to the technical field of semiconductor gas sensors for gas detection, in particular to an in-situ construction method and application of a gas sensor for volatile aroma substance detection, and the in-situ construction method comprises the following steps: mixing an aqueous solution of zinc nitrate hexahydrate and an aqueous solution of 2-methylimidazole according to different molar ratios to obtain a precursor solution; upwards fixing a planar electrode on the surface of a glass slide, and then transferring the planar electrode into the precursor solution; carrying out hydrothermal reaction on the precursor solution at 90 DEG C for 4 hours, after the hydrothermal reaction is finished, cooling to normal temperature, taking out the glass slide, washing the surface of an electrode by using deionized water, removing impurities, and then carrying out drying treatment; calcining the obtained dried electrode in an air atmosphere at 500 DEG C for 2 hours to construct an in-situ growth semiconductor sensor; according to the present invention, the rapid sensing response on nine volatile aroma substances is achieved, and the excellent gas sensitive characteristic is represented in the gas sensitive research on the volatile substance ocimene in the volatile aroma substances.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor gas sensors for gas detection, and in particular to an in-situ construction method and application of a gas sensor for detecting volatile aroma substances. Background Art

[0002] During tea production and identification, volatile compounds in tea aroma are key indicators of tea quality, and their importance cannot be underestimated. They are not only a crucial factor for consumers when selecting tea, but also reflect the quality of tea during its growth and production. Generally, the richer and more unique the volatile aroma compounds, the higher the quality of the tea. Therefore, accurate assessment of these compounds is crucial to the development of the tea industry. Furthermore, tea plants and the tea they produce are susceptible to various pests and diseases, which negatively impact tea yield and quality, and in turn harm the economic interests of tea growers. When tea plants are attacked by pests and diseases, they release a range of volatile organic compounds, including ocimene. Changes in ocimene content provide a direct indicator of the tea's growing environment and are a key indicator of tea plant health and tea quality. Traditionally, the assessment of volatile aroma compounds has relied on tasting and identification by experienced professionals. This method is not only time-consuming and labor-intensive, but also prone to subjective influences. Therefore, developing a sensor technology that can quickly, accurately and reliably detect volatile aroma substances is of vital importance for determining the extent of tea tree pests and the quality of tea leaves.

[0003] As a semiconductor material, zinc oxide (ZnO) holds great potential for application in gas sensors. Its exceptional electrical properties, chemical stability, and high sensitivity to volatile organic compounds make it a highly sought-after gas sensing material. Notably, ZnO sensors demonstrate remarkable success in detecting aliphatic and aromatic compounds, attributed to the unique affinity of their surface for adsorbed molecules. In recent years, thanks to continued advancements in ZnO material preparation and improvements in sensor performance, ZnO-based gas sensors are poised for application in the detection and early warning of plant pests and diseases.

[0004] In-situ growth technology has many significant advantages in the preparation of sensor materials. It can make the sensor material grow directly on the surface of the sensing substrate, forming a close connection at the atomic level, enhancing the bonding between the material and the substrate, and improving the stability and life of the sensor. Among them, the material can be grown in a specific location area and its growth morphology can be precisely controlled, such as growing zinc oxide nanostructures of different forms to enhance the selectivity and response performance to the target gas. In addition, this technology can simplify the preparation process, combine material synthesis and fixation into one, reduce the number of steps, avoid material transfer loss and pollution, improve preparation efficiency, reduce costs, and facilitate large-scale production and application of sensors. Therefore, by utilizing the in-situ growth method to construct a zinc oxide semiconductor gas sensor, it is expected to achieve rapid and accurate detection of volatile aroma substances. In the process of tea tree cultivation and tea production, it can be used as a real-time and accurate monitoring tool, providing strong support for the sustainable development of the tea industry. Therefore, the volatile aroma substance sensor based on in-situ grown zinc oxide proposed by us has extremely considerable market application prospects. It can not only carry out real-time pest and disease monitoring on tea trees and evaluate the quality of tea, but also play an extremely important supporting role in quality control and brand building in the tea market. Summary of the Invention

[0005] The purpose of the present invention is to provide a construction method and application of an in-situ grown semiconductor gas sensor for detecting nine volatile aroma substances, including ocimene, geraniol, linalool, leaf alcohol, decanal, farnesene, methyl salicylate, n-octanol, and phenylethyl alcohol, to achieve rapid sensing response to the nine volatile aroma substances. In the gas sensing research of ocimene, a volatile substance among volatile aroma substances, the sensor exhibits excellent gas sensing properties.

[0006] The purpose of the present invention can be achieved through the following technical solutions: The in-situ construction method of a gas sensor for detecting volatile aroma substances comprises the following steps: mixing an aqueous solution of zinc nitrate hexahydrate and an aqueous solution of 2-methylimidazole in different molar ratios to obtain a precursor solution; The flat electrode is fixed on the surface of a glass slide with the electrode facing upwards and then transferred into the precursor solution; The precursor solution was hydrothermally reacted at 90°C for 4 h. After the hydrothermal reaction was completed, it was cooled to room temperature, the glass slide was removed, and the electrode surface was rinsed with deionized water to remove impurities and then dried. The obtained dried electrode was calcined at 500°C in air atmosphere for 2 h to construct an in-situ grown semiconductor sensor. The in-situ grown zinc oxide gas-sensitive material has a flake-like and spindle-like morphology, and its response to 5 ppm ocimene gas at 375°C reaches 200, with a response time between 23-26 s and a recovery time of 1-2 s.

[0007] As a further embodiment of the present invention, the molar ratio of zinc nitrate hexahydrate to 2-methylimidazole is 1:(2.5-7.5).

[0008] As a further solution of the present invention: the mass fraction of the aqueous solution of zinc nitrate hexahydrate is 0.3-0.8%.

[0009] As a further solution of the present invention: the mass fraction of the aqueous solution of 2-methylimidazole is 0.5-2%.

[0010] As a further solution of the present invention: the planar electrode has a size of 1*1.5 mm and a thickness of 0.26 mm, and the sensing layer is placed vertically upward on the surface of the slide.

[0011] As a further solution of the present invention: the electrode is dried at a temperature of 30-60° C. and the drying time is 4-12 hours.

[0012] As a further solution of the present invention: the heating rate of the dry electrode during the calcination process is 5°C·min -1 .

[0013] As a further solution of the present invention: the in-situ grown zinc oxide gas-sensitive material is grown on the electrode surface with a thickness of 0.52-1.48 μm.

[0014] Application of in situ grown semiconductor gas sensor, which is used to test nine volatile aroma compounds including ocimene, geraniol, linalool, leaf alcohol, decanal, farnesene, methyl salicylate, n-octanol, and phenylethyl alcohol.

[0015] Beneficial effects of the present invention: The preparation method of the in-situ grown zinc oxide gas-sensitive material of the present invention is simple and easy to operate, and the sensor constructed based on the obtained in-situ grown zinc oxide gas-sensitive material exhibits excellent sensing properties such as high sensitivity and high stability to volatile aroma substances; When in-situ grown zinc oxide gas-sensitive materials are used to construct sensors for nine volatile aroma substances, a zinc oxide sensitive film is self-grown on the electrode surface through an in-situ growth process, thereby constructing a sensor, which can achieve rapid sensing response to nine volatile aroma substances. Among them, in the gas sensing research of ocimene, a volatile substance in tea aroma, it shows excellent gas-sensing properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0017] Figure 1 The following are SEM images of four in-situ grown zinc oxide material samples prepared by the present invention, wherein: Figure 1 ad are the cross-sectional SEM images of in-situ grown zinc oxide gas-sensitive materials of Sensor_1-Sensor_4, Figure 1 eh are the surface SEM images of in-situ grown zinc oxide gas-sensitive materials (after annealing) of Sensor_1-Sensor_4 respectively; Figure 2 This is the XRD picture of four in-situ grown zinc oxide nano gas-sensitive materials provided by the present invention; Figure 3 The gas-sensing performance test of four in-situ grown zinc oxide materials prepared by calcining in an air atmosphere at 500°C at a working temperature of 375°C to 5 ppm of ocimene is shown in the response (Rgas / Rair)-time (s) curves. Figure 4 This is a bar chart of the response values of four in-situ grown zinc oxide gas-sensitive materials prepared by calcining in an air atmosphere at 500°C to 5 ppm of ocimene, geraniol, linalool, leaf alcohol, decanal, farnesene, methyl salicylate, n-octanol, and phenylethanol at a working temperature of 375°C. DETAILED DESCRIPTION

[0018] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0019] Example 1 The in-situ construction method of a gas sensor for detecting volatile aroma substances provided by an embodiment of the present invention specifically includes the following steps: Step 1: Weigh zinc nitrate hexahydrate, dissolve it in deionized water, and stir it evenly under magnetic force for 10 minutes to obtain a first transparent solution; weigh 2-methylimidazole, dissolve it in deionized water, and stir it evenly under magnetic force for 10 minutes to obtain a second transparent solution; under magnetic stirring, slowly add the first transparent solution to the second transparent solution to obtain a mixed precursor solution; Step 2: With the planar electrode sensing layer facing upward, fix it on the surface of the glass slide and place it on the bottom of a 50mL polytetrafluoroethylene liner. Slowly transfer the precursor solution to the liner, seal the liner and place it in a reactor. Then place the reactor in a 90℃ oven for hydrothermal reaction for 4 hours. The molar ratio of zinc nitrate hexahydrate to 2-methylimidazole is 1:7.5; specifically, the mass of zinc nitrate hexahydrate is 0.148 g, and the mass of 2-methylimidazole is 0.308 g; The mass fraction of zinc nitrate hexahydrate aqueous solution is 0.3%, and the mass fraction of 2-methylimidazole aqueous solution is 0.5%; Step 3: After the hydrothermal reaction is completed, wait for the reactor to cool naturally to room temperature, open the reactor and remove the liner, take out the glass slide in the liner, slowly rinse the glass slide and electrode surface with deionized water to remove surface impurities, and then put it in an oven for drying; The electrode was dried at a temperature of 60°C for 6 hours to remove moisture from the electrode surface. Step 4: The obtained dried electrode was calcined at 500°C in air atmosphere for 2 hours to obtain Sensor_1 in situ grown zinc oxide gas sensitive material sensor; the morphology of the Sensor_1 in situ grown zinc oxide gas sensitive material sensor was flake-shaped and spindle-shaped, with a thickness of 0.98 μm respectively; The heating rate of the dry electrode during the calcination process is 5℃·min -1 .

[0020] Example 2 The in-situ construction method of a gas sensor for detecting volatile aroma substances provided by an embodiment of the present invention specifically includes the following steps: Step 1: Weigh zinc nitrate hexahydrate, dissolve it in deionized water, and stir it evenly under magnetic force for 10 minutes to obtain a first transparent solution; weigh 2-methylimidazole, dissolve it in deionized water, and stir it evenly under magnetic force for 10 minutes to obtain a second transparent solution; under magnetic stirring, slowly add the first transparent solution to the second transparent solution to obtain a mixed precursor solution; Step 2: With the planar electrode sensing layer facing upward, fix it on the surface of the glass slide and place it on the bottom of a 50mL polytetrafluoroethylene liner. Slowly transfer the precursor solution to the liner, seal the liner and place it in a reactor. Then place the reactor in a 90℃ oven for hydrothermal reaction for 4 hours. The molar ratio of zinc nitrate hexahydrate to 2-methylimidazole is 1:5; specifically, the mass of zinc nitrate hexahydrate is 0.148 g, and the mass of 2-methylimidazole is 0.205 g; The mass fraction of zinc nitrate hexahydrate aqueous solution is 0.5%, and the mass fraction of 2-methylimidazole aqueous solution is 1%; Step 3: After the hydrothermal reaction is completed, wait for the reactor to cool naturally to room temperature, open the reactor and remove the liner, take out the glass slide in the liner, slowly rinse the glass slide and electrode surface with deionized water to remove surface impurities, and then put it in an oven for drying; The electrode was dried at a temperature of 60°C for 6 hours to remove moisture from the electrode surface. Step 4: The obtained dried electrode was calcined at 500°C in air atmosphere for 2 hours to obtain Sensor_2 in situ grown zinc oxide gas sensitive material sensor; the morphology of the Sensor_2 in situ grown zinc oxide gas sensitive material sensor was porous laminated, and the thickness was 1.48 μm; The heating rate of the dry electrode during the calcination process is 5℃·min -1 .

[0021] Example 3 The in-situ construction method of a gas sensor for detecting volatile aroma substances provided by an embodiment of the present invention specifically includes the following steps: Step 1: Weigh zinc nitrate hexahydrate, dissolve it in deionized water, and stir it evenly under magnetic force for 10 minutes to obtain a first transparent solution; weigh 2-methylimidazole, dissolve it in deionized water, and stir it evenly under magnetic force for 10 minutes to obtain a second transparent solution; under magnetic stirring, slowly add the first transparent solution to the second transparent solution to obtain a mixed precursor solution; Step 2: With the planar electrode sensing layer facing upward, fix it on the surface of the glass slide and place it on the bottom of a 50mL polytetrafluoroethylene liner. Slowly transfer the precursor solution to the liner, seal the liner and place it in a reactor. Then place the reactor in a 90℃ oven for hydrothermal reaction for 4 hours. The molar ratio of zinc nitrate hexahydrate to 2-methylimidazole is 1:2.5; specifically, the mass of zinc nitrate hexahydrate is 0.148 g, and the mass of 2-methylimidazole is 0.103 g; The mass fraction of zinc nitrate hexahydrate aqueous solution is 0.7%, and the mass fraction of 2-methylimidazole aqueous solution is 1.5%; Step 3: After the hydrothermal reaction is completed, wait for the reactor to cool naturally to room temperature, open the reactor and remove the liner, take out the glass slide in the liner, slowly rinse the glass slide and electrode surface with deionized water to remove surface impurities, and then put it in an oven for drying; The electrode was dried at a temperature of 60°C for 6 hours to remove moisture from the electrode surface. Step 4: calcining the obtained dried electrode at 500°C in air atmosphere for 2 hours to obtain Sensor_3 in-situ grown zinc oxide gas sensitive material sensor; the morphology of the Sensor_3 in-situ grown zinc oxide gas sensitive material sensor is spindle-shaped and the thickness is 0.98 μm; The heating rate of the dry electrode during the calcination process is 5℃·min -1 .

[0022] Example 4 The in-situ construction method of a gas sensor for detecting volatile aroma substances provided by an embodiment of the present invention specifically includes the following steps: Step 1: Weigh zinc nitrate hexahydrate, dissolve it in deionized water, and stir it evenly under magnetic force for 10 minutes to obtain a first transparent solution; weigh 2-methylimidazole, dissolve it in deionized water, and stir it evenly under magnetic force for 10 minutes to obtain a second transparent solution; under magnetic stirring, slowly add the first transparent solution to the second transparent solution to obtain a mixed precursor solution; Step 2: With the planar electrode sensing layer facing upward, fix it on the surface of the glass slide and place it on the bottom of a 50mL polytetrafluoroethylene liner. Slowly transfer the precursor solution to the liner, seal the liner and place it in a reactor. Then place the reactor in a 90℃ oven for hydrothermal reaction for 4 hours. The molar ratio of zinc nitrate hexahydrate to 2-methylimidazole is 1:5; specifically, the mass of zinc nitrate hexahydrate is 0.074 g, and the mass of 2-methylimidazole is 0.102 g; The mass fraction of zinc nitrate hexahydrate aqueous solution is 0.8%, and the mass fraction of 2-methylimidazole aqueous solution is 2%; Step 3: After the hydrothermal reaction is completed, wait for the reactor to cool naturally to room temperature, open the reactor and remove the liner, take out the glass slide in the liner, slowly rinse the glass slide and electrode surface with deionized water to remove surface impurities, and then put it in an oven for drying; The electrode was dried at a temperature of 60°C for 6 hours to remove moisture from the electrode surface. Step 4: calcining the obtained dried electrode at 500°C in air atmosphere for 2 hours to obtain Sensor_4 in-situ grown zinc oxide gas sensitive material sensor; the morphology of the Sensor_4 in-situ grown zinc oxide gas sensitive material sensor is irregular spherical and the thickness is 0.52 μm; The heating rate of the dry electrode during the calcination process is 5℃·min -1 .

[0023] Example 5 The application of the gas sensor for detecting volatile aroma substances provided in an embodiment of the present invention includes the following steps: After calcination, the electrodes are welded to the sensor base and further constructed into a gas sensor for performance testing of volatile aroma substances; When the in-situ grown zinc oxide gas-sensitive material is used in the production process of nine tea aroma sensors, the in-situ grown zinc oxide gas-sensitive material that has undergone the in-situ growth process in the above embodiment is used to self-grow a zinc oxide sensitive film on the electrode surface to construct a volatile aroma substance sensor. This can achieve a rapid sensing response to the nine volatile aroma substances. In the gas sensing research of ocimene, a volatile substance among volatile aroma substances, it can quickly demonstrate excellent gas sensing properties. Among them, the nine volatile aroma substances include ocimene, geraniol, linalool, leaf alcohol, decanal, farnesene, methyl salicylate, n-octanol, and phenylethyl alcohol.

[0024] Performance Testing During the morphology observation and performance testing of the in-situ grown zinc oxide gas-sensitive material samples prepared in Examples 1-4 above, the following results were obtained: like Figure 1 As shown, from Figure 1 (a) It can be seen that the cross-sectional thickness of the in-situ grown zinc oxide gas-sensitive material of Sensor_1 is 0.98 μm, and its surface morphology ( Figure 1 (e)) is composed of stacked larger sheet structures; Figure 1 (b) The thickness of the in-situ grown zinc oxide gas-sensitive material of Sensor_2 is 1.48 μm, and the surface morphology is ( Figure 1 (f)) presents a flake-like aggregated structure. By comparison, it is found that Sensor_3 in-situ grown zinc oxide gas sensing material ( Figure 1 (c) Although the thickness of the in-situ grown zinc oxide gas sensing material is the same as that of Sensor_1, its surface morphology ( Figure 1 (g)) is a uniform spindle-shaped structure; while Sensor_4 in situ grows zinc oxide gas-sensitive material ( Figure 1 (d)) has the smallest thickness, which is 0.52 μm, and its surface morphology ( Figure 1 (h) Although it also exhibits the characteristics of a spindle-shaped structure, its surface roughness is significantly increased compared with the in-situ grown zinc oxide gas-sensitive material of Sensor_3.

[0025] like Figure 2 As shown in the X-ray diffraction (XRD) pattern of the in situ grown zinc oxide sample, it can be clearly seen that its 2θ angle has obvious diffraction peaks at 31.8°, 34.4°, 36.3°, 56.6° and 63.1°, corresponding to the (100), (002), (101), (110) and (103) crystal planes of zinc oxide, respectively, indicating that the sample is hexagonal zinc oxide, and the peaks are sharp, indicating that the product is completely crystallized; In the gas sensing application of the in-situ grown zinc oxide nanomaterial of the present invention, the electrodes are calcined and welded to the sensor base to further construct a gas sensor, which is then aged on an aging table for three days before gas sensing is performed. The sensor is tested for ocimene gas sensing at an operating temperature of 375°C. like Figure 3 The figure shows the dynamic response curves of four sensors prepared based on in-situ grown zinc oxide gas-sensitive materials to different concentrations (0.05 to 7.5 ppm) of ocimene at a humidity of 70% and an operating temperature of 375°C. It can be seen from the figure that the response value of the sensor based on in-situ grown zinc oxide gas-sensitive materials is 4.5 at a concentration of 0.05 ppm, and the response value reaches 240 when the concentration is 7.5 ppm, highlighting the excellent sensing performance. In addition, the sensitivity of the gas sensor increases with the increase of ocimene gas concentration, indicating that the prepared sensor has good reversibility; like Figure 4 The bar graph shows the response values of four sensors prepared based on in-situ grown zinc oxide gas-sensitive materials to 5 ppm of ocimene, geraniol, linalool, leaf alcohol, decanal, farnesene, methyl salicylate, n-octanol, and phenylethanol at an operating temperature of 375°C. The figure shows that the tea sensors based on in-situ grown zinc oxide gas-sensitive materials all exhibit good responses to these volatile aroma compounds.

[0026] In summary, the in-situ grown zinc oxide gas-sensitive material of the embodiment of the present invention has a response of 200 to 5 ppm of ocimene gas at 375°C, which greatly improves the performance, and its response recovery time is also greatly improved. Specifically, the response time is between 23-26s, and the recovery time is even shorter, only 1-2s.

[0027] The above is a detailed description of an embodiment of the present invention. However, the content described is only a preferred embodiment of the present invention and should not be considered to limit the scope of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the patent coverage of the present invention.

Claims

1. An in-situ construction method for a gas sensor for detecting volatile aroma substances, characterized in that: The following steps are involved: mixing an aqueous solution of zinc nitrate hexahydrate and an aqueous solution of 2-methylimidazole in different molar ratios to obtain a precursor solution; The flat electrode is fixed on the surface of a glass slide with the electrode facing upwards and then transferred into the precursor solution; The precursor solution was hydrothermally reacted at 90°C for 4 h. After the hydrothermal reaction was completed, it was cooled to room temperature, the glass slide was removed, and the electrode surface was rinsed with deionized water to remove impurities and then dried. The obtained dried electrode was calcined at 500°C in air atmosphere for 2 h to construct an in-situ grown semiconductor sensor. The in-situ grown zinc oxide gas-sensitive material has a flake-like and spindle-like morphology, and its response to 5 ppm ocimene gas at 375°C reaches 200, with a response time between 23-26 s and a recovery time of 1-2 s.

2. The in-situ construction method of a gas sensor for detecting volatile aroma substances according to claim 1, characterized in that: The molar ratio of zinc nitrate hexahydrate to 2-methylimidazole is 1:(2.5-7.5).

3. The in-situ construction method of a gas sensor for detecting volatile aroma substances according to claim 1, characterized in that: The mass fraction of the aqueous solution of zinc nitrate hexahydrate is 0.3-0.8%.

4. The in-situ construction method of a gas sensor for detecting volatile aroma substances according to claim 1, characterized in that: The mass fraction of the aqueous solution of 2-methylimidazole is 0.5-2%.

5. The in-situ construction method of a gas sensor for detecting volatile aroma substances according to claim 1, characterized in that: The planar electrode has a size of 1*1.5mm and a thickness of 0.26mm, and the sensing layer is placed vertically upward on the surface of the slide.

6. The in-situ construction method of a gas sensor for detecting volatile aroma substances according to claim 1, characterized in that: The electrode is dried at a temperature of 30-60°C and for a drying time of 4-12 hours.

7. The in-situ construction method of a gas sensor for detecting volatile aroma substances according to claim 1, characterized in that: The heating rate of the dry electrode during the calcination process is 5℃·min -1 .

8. The in-situ construction method of a gas sensor for detecting volatile aroma substances according to claim 1, characterized in that: The in-situ grown zinc oxide gas-sensitive material grows on the electrode surface with a thickness of 0.52-1.48 μm.

9. Application of in-situ grown semiconductor gas sensors, characterized in that: A zinc oxide semiconductor gas sensor prepared by the method according to any one of claims 1 to 8 is used to test nine volatile aroma substances: ocimene, geraniol, linalool, leaf alcohol, decanal, farnesene, methyl salicylate, n-octanol, and phenylethyl alcohol.

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