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

Abstract

The application relates to the technical field of semiconductor gas sensors for gas detection, and particularly relates to an in-situ construction method and application of a gas sensor for volatile aroma substance detection, which comprises the following steps: a zinc nitrate hexahydrate aqueous solution and a 2-methyl imidazole aqueous solution are mixed according to different molar ratios to obtain a precursor solution; a plane electrode is fixed on the surface of a glass slide with the plane electrode facing upwards, and then the glass slide is transferred into the precursor solution; the precursor solution is subjected to a hydrothermal reaction at 90 DEG C for 4h; after the hydrothermal reaction is completed, the glass slide is cooled to room temperature, the electrode surface is washed with deionized water, and the electrode is subjected to drying treatment after impurities are removed; the obtained dry electrode is calcined at 500 DEG C in an air atmosphere for 2h to construct an in-situ grown semiconductor sensor; the application realizes rapid sensing response to nine volatile aroma substances, and in the gas-sensitive research of volatile substances such as the volatile substance of ocimene in volatile aroma substances, the application shows excellent gas-sensitive characteristics.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of semiconductor gas sensors for gas detection, in particular to a method for in-situ construction of a gas sensor for volatile aroma substance detection and applications thereof. BACKGROUND

[0002] In the process of tea production and identification, volatile substances in tea aroma are key indicators of tea quality, which cannot be ignored. It is an important consideration factor for consumers when selecting tea, and it can also reflect the quality status of tea growth and production process. Generally, the more unique and rich the volatile aroma substances are, the higher the quality of tea is. Therefore, accurate evaluation of volatile aroma substances is crucial for the development of the tea industry. In addition, tea trees and the tea produced are susceptible to various pests and diseases, which can adversely affect the yield and quality of tea, and thus harm the economic interests of tea farmers. When tea trees are attacked by pests and diseases, they will release a series of volatile organic compounds, including linalool. The change in the content of linalool can directly reflect the growth environment of tea, and is one of the important bases for judging the health of tea trees and the quality of tea. In the past, the evaluation of volatile aroma substances often relied on the tasting and identification of experienced professionals. This method not only consumes time and effort, but also is easily affected by subjective factors. Therefore, developing a sensor technology that can quickly, accurately and reliably detect volatile aroma substances is of great significance for judging the degree of tea tree infestation and tea quality.

[0003] Zinc oxide as a semiconductor material has great application potential in the field of gas sensors. Its excellent electrical properties, good chemical stability, and high sensitivity to volatile organic compounds make it a popular gas sensing material. It is worth mentioning that zinc oxide sensors have achieved remarkable results in the detection of aliphatic and aromatic compounds, which is attributed to the special affinity of its surface to adsorbed molecules. In recent years, thanks to the continuous advancement of zinc oxide material preparation processes and the continuous improvement of sensor performance, zinc oxide-based gas sensors are expected to be applied to the detection and early warning of plant pests and diseases.

[0004] In-situ growth technology has many advantages in the preparation of sensor materials. It can make the sensor material grow directly on the surface of the sensing substrate, form an atomic-level close connection, enhance the bonding force between the material and the substrate, and improve the stability and life of the sensor. Among them, the material can be grown in a specific location and its growth morphology can be precisely controlled, such as growing different morphologies of zinc oxide nanostructures to enhance the selectivity and response performance of the target gas. In addition, this technology can simplify the preparation process, combine material synthesis and fixation into one step, reduce steps, avoid material transfer loss and pollution, improve preparation efficiency and reduce cost, which is conducive to large-scale production and application of sensors. Therefore, by using in-situ growth method, it is expected to realize rapid and accurate detection of volatile aroma substances by constructing a zinc oxide semiconductor gas sensor, which can be used as a real-time and accurate monitoring tool in tea tree cultivation and tea production process, and give strong support to the sustainable development of tea industry. Therefore, the volatile aroma substance sensor based on in-situ growth of zinc oxide has a very promising market application prospect. It can not only carry out real-time pest monitoring work on tea trees and evaluate tea quality, but also play an important supporting role in quality control and brand shaping of tea market. SUMMARY

[0005] The purpose of the present application is to provide a method for constructing an in-situ growth semiconductor gas sensor for detecting nine volatile aroma substances such as linaloe, geraniol, linalool, leaf alcohol, decanal, farnesene, methyl salicylate, n-octanol and phenethyl alcohol, and its application, which realizes rapid sensing response to nine volatile aroma substances. In the gas-sensitive research of volatile aroma substance linaloe, it shows excellent gas-sensitive characteristics.

[0006] The purpose of the present application can be achieved by the following technical solutions:

[0007] The in-situ construction method of the gas sensor for volatile aroma substance detection comprises the following steps:

[0008] Mix the aqueous solution of zinc nitrate hexahydrate and the aqueous solution of 2-methyl imidazole according to different molar ratios to obtain a precursor solution;

[0009] Fix the plane electrode upward on the surface of the glass slide, and then transfer it into the precursor solution;

[0010] The precursor solution is hydrothermally reacted at 90 DEG C for 4h, and after the hydrothermal reaction is completed, it is cooled to room temperature, the glass slide is taken out, the electrode surface is washed with deionized water, and after the impurities are removed, it is dried;

[0011] The obtained dry electrode is calcined at 500 DEG C in air atmosphere for 2h to construct an in-situ growth semiconductor sensor;

[0012] The in-situ growth zinc oxide gas sensitive material has a sheet shape and a shuttle shape, and the response of the in-situ growth zinc oxide gas sensitive material to 5ppm of a linaloe gas reaches 200 at 375 DEG C, the response time is between 23-26s, and the recovery time is 1-2s.

[0013] As a further scheme of the present application: the molar ratio of zinc nitrate hexahydrate to 2-methylimidazole is 1: (2.5-7.5).

[0014] As a further scheme of the present application: the mass fraction of the aqueous solution of zinc nitrate hexahydrate is 0.3-0.8%.

[0015] As a further scheme of the present application: the mass fraction of the aqueous solution of 2-methylimidazole is 0.5-2%.

[0016] As a further scheme of the present application: the size specification of the planar electrode is 1*1.5mm, the thickness is 0.26mm, and the sensing layer is vertically placed on the surface of the glass slide.

[0017] As a further scheme of the present application: the temperature for drying the electrode is 30-60 DEG C, and the drying time is 4-12h.

[0018] As a further scheme of the present application: the heating rate of the dried electrode in the calcination process is 5 DEG C·min -1 .

[0019] As a further scheme of the present application: the thickness of the in-situ growth zinc oxide gas sensitive material grown on the surface of the electrode is 0.52-1.48um.

[0020] The application of the in-situ growth semiconductor gas sensor is used for testing nine kinds of volatile aroma substances, including linaloe, geraniol, linalool, leaf alcohol, decanal, farnesene, methyl salicylate, n-octanol and phenethyl alcohol.

[0021] The present application has the following beneficial effects:

[0022] The preparation method of the in-situ growth zinc oxide gas sensitive material is simple and easy to operate, and the sensor based on the obtained in-situ growth zinc oxide gas sensitive material shows excellent sensing characteristics, such as high sensitivity and high stability, for volatile aroma substances.

[0023] In the process of using the in-situ growth zinc oxide gas sensitive material for constructing a sensor for nine kinds of volatile aroma substances, a zinc oxide sensitive film is self-grown on the surface of the electrode through an in-situ growth process, so that the sensor is constructed, and rapid sensing response to the nine kinds of volatile aroma substances can be realized. BRIEF DESCRIPTION OF DRAWINGS

[0024] In order to make the technical solutions in the embodiments of the present application clearer, the accompanying drawings needed in the embodiment description will be briefly introduced. Obviously, the accompanying drawings in the following description are only some embodiments of the present application, and all other embodiments obtained by those of ordinary skill in the art without any creative effort based on these accompanying drawings should belong to the protection scope of the present application.

[0025] Figure 1 are SEM pictures of four kinds of in-situ grown zinc oxide material samples prepared by the present application, wherein, Figure 1 a-d are respectively cross-sectional SEM images of Sensor_1-Sensor_4 in-situ grown zinc oxide gas sensitive material, Figure 1 e-h are respectively surface SEM images of Sensor_1-Sensor_4 in-situ grown zinc oxide gas sensitive material (after annealing);

[0026] Figure 2 are XRD pictures of four kinds of in-situ grown zinc oxide nano gas sensitive material provided by the present application;

[0027] Figure 3 are Response (Rgas / Rair)-Time (s) curves of the gas sensitive performance of four kinds of in-situ grown zinc oxide material prepared by the present application under the working temperature of 375℃ and the response value of 5ppm of linalooxide, geraniol, linalool, leaf alcohol, decanal, farnesene, methyl salicylate, n-octanol, phenethyl alcohol under the calcination of air atmosphere at 500℃.

[0028] Figure 4 are bar graphs of the response value of four kinds of in-situ grown zinc oxide gas sensitive material prepared by the present application under the working temperature of 375℃ and the response value of 5ppm of linalooxide, geraniol, linalool, leaf alcohol, decanal, farnesene, methyl salicylate, n-octanol, phenethyl alcohol under the calcination of air atmosphere at 500℃. DETAILED DESCRIPTION

[0029] In order to make the technical solutions in the embodiments of the present application clearer, the accompanying drawings needed in the embodiment description will be briefly introduced. Obviously, the accompanying drawings in the following description are only some embodiments of the present application, and all other embodiments obtained by those of ordinary skill in the art without any creative effort based on these accompanying drawings should belong to the protection scope of the present application.

[0030] Embodiment 1

[0031] The in-situ construction method of the volatile aroma substance detection gas sensor provided by the embodiments of the present application specifically comprises the following steps:

[0032] Step 1: weigh zinc nitrate hexahydrate, dissolve in deionized water, and magnetically stir uniformly for 10 min to obtain a first transparent solution; weigh 2-methylimidazole, dissolve in deionized water, and magnetically stir uniformly for 10 min 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;

[0033] Step 2: place the planar electrode sensing layer upward on the surface of a glass slide, place the inner liner at the bottom of a 50 mL polytetrafluoroethylene inner liner, slowly transfer the precursor solution to the inner liner, seal the inner liner in a reaction kettle, and then place the reaction kettle in a 90℃ oven for hydrothermal reaction for 4 h;

[0034] 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;

[0035] The mass fraction of the zinc nitrate hexahydrate aqueous solution is 0.3%, and the mass fraction of the 2-methylimidazole aqueous solution is 0.5%;

[0036] Step 3: After the hydrothermal reaction is completed, the reaction kettle is naturally cooled to room temperature, the inner liner is taken out, the glass slide in the inner liner is taken out, and the glass slide and the electrode surface are slowly washed with deionized water to remove surface impurities, and then dried in an oven;

[0037] The temperature for drying the electrode is 60℃, and the drying time is 6 h, so as to remove the moisture on the surface of the electrode;

[0038] Step 4: the obtained dried electrode is calcined at 500℃ in an air atmosphere for 2 h to obtain a 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 is sheet-shaped and shuttle-shaped, and the thicknesses are 0.98 μm;

[0039] The heating rate of the dried electrode during the calcination process is 5℃·min -1 .

[0040] Example 2

[0041] The in-situ construction method of the volatile aroma substance detection gas sensor provided by the embodiments of the present application specifically comprises the following steps:

[0042] Step 1: weigh zinc nitrate hexahydrate, dissolve in deionized water, and magnetically stir uniformly for 10 min to obtain a first transparent solution; weigh 2-methylimidazole, dissolve in deionized water, and magnetically stir uniformly for 10 min 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;

[0043] Step 2: Place the planar electrode sensing layer upwards and fix it on the surface of a glass slide, and then place it at the bottom of a 50 mL polytetrafluoroethylene inner liner, slowly transfer the precursor solution to the inner liner, seal the inner liner in a reaction kettle, and then place the reaction kettle in an oven at 90 DEG C for hydrothermal reaction for 4 h;

[0044] 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;

[0045] The mass fraction of the zinc nitrate hexahydrate aqueous solution is 0.5%, and the mass fraction of the 2-methylimidazole aqueous solution is 1%;

[0046] Step 3: After the hydrothermal reaction is completed, the reaction kettle is naturally cooled to room temperature, the inner liner is taken out, the glass slide in the inner liner is taken out, and the glass slide and the electrode surface are slowly washed with deionized water to remove surface impurities, and then dried in an oven;

[0047] The temperature for drying the electrode is 60 DEG C, and the drying time is 6 h, so as to remove the moisture on the surface of the electrode;

[0048] Step 4: The obtained dried electrode is calcined at 500 DEG C in an air atmosphere for 2 h to obtain a 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 is a porous laminated shape, and the thickness is 1.48 μm;

[0049] The heating rate of the dried electrode during the calcination process is 5 DEG C·min -1 .

[0050] Example 3

[0051] The in-situ construction method of the volatile aroma substance detection gas sensor provided by the embodiment of the application specifically comprises the following steps:

[0052] Step 1: Weigh zinc nitrate hexahydrate, dissolve it in deionized water, and magnetically stir for 10 min to obtain a first transparent solution; weigh 2-methylimidazole, dissolve it in deionized water, and magnetically stir for 10 min 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;

[0053] Step 2: Place the planar electrode sensing layer upwards and fix it on the surface of a glass slide, and then place it at the bottom of a 50 mL polytetrafluoroethylene inner liner, slowly transfer the precursor solution to the inner liner, seal the inner liner in a reaction kettle, and then place the reaction kettle in an oven at 90 DEG C for hydrothermal reaction for 4 h;

[0054] 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;

[0055] The mass fraction of the zinc nitrate hexahydrate aqueous solution is 0.7%, and the mass fraction of the 2-methylimidazole aqueous solution is 1.5%;

[0056] Step 3: After the hydrothermal reaction is completed, the reaction kettle is naturally cooled to room temperature, the inner liner is taken out, the glass slide in the inner liner is taken out, and the glass slide and the electrode surface are slowly washed with deionized water to remove surface impurities, and then dried in an oven;

[0057] The temperature for drying the electrode is 60 DEG C, and the drying time is 6 h, so as to remove the moisture on the surface of the electrode;

[0058] Step 4: The obtained dried electrode is calcined at 500 DEG C in an air atmosphere for 2 h to obtain a 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 shuttle-shaped, and the thickness is 0.98 mu m;

[0059] The temperature rising rate of the dried electrode in the calcination process is 5 DEG C per minute -1 .

[0060] Example 4

[0061] The in-situ construction method of the volatile aroma substance detection gas sensor provided by the embodiment of the application specifically comprises the following steps:

[0062] Step 1: Weigh zinc nitrate hexahydrate, dissolve it in deionized water, and magnetically stir uniformly for 10 min to obtain a first transparent solution; weigh 2-methylimidazole, dissolve it in deionized water, and magnetically stir uniformly for 10 min 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;

[0063] Step 2: Place the planar electrode sensing layer upward on the surface of a glass slide, place it at the bottom of a 50 mL polytetrafluoroethylene inner liner, slowly transfer the precursor solution to the inner liner, seal the inner liner in a reaction kettle, and then place the reaction kettle in a 90 DEG C oven for hydrothermal reaction for 4 h;

[0064] 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;

[0065] The mass fraction of the zinc nitrate hexahydrate aqueous solution is 0.8%, and the mass fraction of the 2-methylimidazole aqueous solution is 2%.

[0066] 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;

[0067] The electrode was dried at a temperature of 60°C for 6 hours to remove moisture from the electrode surface.

[0068] 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;

[0069] The heating rate of the dry electrode during the calcination process is 5℃·min -1 .

[0070] Example 5

[0071] The application of the gas sensor for detecting volatile aroma substances provided in an embodiment of the present invention includes the following steps:

[0072] After calcination, the electrodes are welded to the sensor base and further constructed into a gas sensor for performance testing of volatile aroma substances;

[0073] 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.

[0074] Among them, the nine volatile aroma substances include ocimene, geraniol, linalool, leaf alcohol, decanal, farnesene, methyl salicylate, n-octanol, and phenylethyl alcohol.

[0075] Performance Testing

[0076] 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:

[0077] 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.

[0078] 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;

[0079] 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.

[0080] 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;

[0081] like Figure 4As shown, the bar chart shows the response values of four sensors prepared based on the in-situ growth of zinc oxide gas sensitive material to 5ppm of myrcene, geraniol, linalool, leaf alcohol, decanal, farnesene, methyl salicylate, n-octanol, phenethyl alcohol at a working temperature of 375℃. As can be seen from the figure, the tea leaf sensor based on the in-situ growth of zinc oxide gas sensitive material shows good response to the above volatile aroma substances.

[0082] As can be seen from the above, the in-situ growth of zinc oxide gas sensitive material in the embodiment of the present application has a great improvement in performance, with a response of 200 to 5ppm of myrcene gas at 375℃, and a great improvement in response recovery time, specifically, the response time is between 23-26s, and the recovery time is only 1-2s.

[0083] 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 to limit 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 in-situ construction of a gas sensor for volatile aroma substance detection, characterized by, The method comprises the following steps: Mixing an aqueous solution of zinc nitrate hexahydrate with an aqueous solution of 2-methylimidazole according to different molar ratios to obtain a precursor solution; Fixing a planar electrode upward on the surface of a glass slide, and then transferring it into the precursor solution; Hydrothermally reacting the precursor solution at 90℃ for 4h, cooling to room temperature after the hydrothermal reaction, taking out the glass slide, washing the electrode surface with deionized water, and drying after removing impurities; Calcining the obtained dry electrode at 500℃ in an air atmosphere for 2h to construct an in-situ grown semiconductor sensor; The in-situ grown zinc oxide gas-sensitive material has a sheet-like and shuttle-like morphology, and has a response of 200 to 5ppm of ocimene gas at 70% humidity and 375℃, a response time of 23-26s, and a recovery time of 1-2s; The in-situ grown zinc oxide gas-sensitive material has a thickness of 0.52-1.48μm on the electrode surface; The sensor is used to test nine volatile aroma substances, including ocimene, geraniol, linalool, leaf alcohol, decanal, farnesene, methyl salicylate, n-octanol, and phenethyl alcohol.

2. The method according to claim 1, wherein The molar ratio of zinc nitrate hexahydrate to 2-methylimidazole is 1: (2.5-7.5).

3. The method according to claim 1, wherein the gas sensor is constructed in situ. The mass fraction of the aqueous solution of zinc nitrate hexahydrate is 0.3-0.8%.

4. The method according to claim 1, wherein The mass fraction of the aqueous solution of 2-methylimidazole is 0.5-2%.

5. The method according to claim 1, wherein the gas sensor is constructed in situ. The size specification of the planar electrode is 1*1.5mm, and the thickness is 0.26mm, and the sensing layer is placed vertically upward on the surface of the glass slide.

6. The method according to claim 1, wherein the gas sensor is constructed in situ. The drying temperature of the electrode is 30-60℃, and the drying time is 4-12h.

7. The method according to claim 1, wherein the gas sensor is constructed in situ. The heating rate of the dry electrode during calcination is 5℃·min-1.

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