Precious metal doped SnO2 quantum dot gas sensitive material and sensor

Abstract

The invention provides a noble metal doped SnO2 quantum dot gas sensitive material and a sensor. The noble metal doped SnO2 quantum dot gas sensitive material comprises SnO2 quantum dots and noble metals uniformly dispersed on the SnO2 quantum dots, and is mainly prepared by the following steps: adding a noble metal source dispersion liquid into a tin tetrachloride oleic acid solution, and uniformly mixing to form a raw material mixed solution; and treating the raw material mixed solution by adopting a solvothermal method to prepare the noble metal doped SnO2 quantum dot gas sensitive material. Therefore, according to the noble metal doped SnO2 quantum dot gas-sensitive material, the noble metal is mainly introduced into the SnO2 quantum dot gas-sensitive material to improve the response and selectivity of ethylene gas detection, so that the noble metal doped SnO2 quantum dot gas-sensitive material as an ethylene-sensitive material has the characteristics of high sensitivity, selectivity, high response, low temperature resistance and the like aiming at ethylene; the gas sensor applying the sensitive material also has the characteristics of high sensitivity, good selectivity, low temperature resistance and the like on ethylene detection, and can be used in refrigeration monitoring of fruits and vegetables.

Description

Technical Field

[0001] The present invention relates to the field of gas-sensitive materials, and particularly to a noble metal-doped SnO2 quantum dot gas-sensitive material and a sensor. Background Art

[0002] Ethylene is an important plant hormone that plays a role at trace levels throughout the life cycle of plants by stimulating or regulating fruit ripening, flower opening, and leaf abscission (or shedding). Due to the long-distance transportation and long-term storage of fruits, they always need to be harvested in advance, and unripe fruits are also artificially ripened by ethylene. Ethylene molecules accumulated inside the packaging of fresh fruits can also stimulate physiological activities, thereby accelerating fruit spoilage, limiting its storage life, and causing product losses. In addition, fruit damage and spoilage can also induce ethylene biosynthesis. According to a report by the Food and Agriculture Organization of the United Nations (FAO), the reported food loss per year is 1.3 billion tons, accounting for 33% of the total food production, and the loss rate of fruits and vegetables is the highest (45%). Through ethylene monitoring, early fruit abnormalities can be detected in a timely manner, thus avoiding most of the losses. Therefore, continuous and accurate detection / monitoring of ethylene released by fruits is crucial for managing and controlling the harvesting, storage, packaging, transportation, and sales processes of climacteric fruits, which is particularly prominent in today's era of smart agriculture.

[0003] So far, various techniques for ethylene detection have been reported, including chromatography, spectroscopy, electrochemical sensors, chemical sensors, and fluorescent probes, among which chemical sensors stand out due to their timely response, high sensitivity, manual operation, and low cost. Recently, researchers have made many attempts to develop high-performance chemiresistive ethylene sensors. According to current research, although traditional metal oxide semiconductor (MOS) sensors (such as WO3, SnO2, and ZnO sensors) show high sensitivity to ethylene, the existing single-metal semiconductor oxide materials have poor selectivity, and the response and recovery times are very long, almost reaching hundreds of seconds, which greatly limits the application of such sensors in the field of ethylene gas detection. Therefore, researching sensitive and fast ethylene sensing materials remains a huge challenge.

[0004] Quantum dot gas-sensitive materials are a type of semiconductor nanocrystal with a size between 1 and 10 nanometers, which can be stably dispersed in solution. Due to their large specific surface area, they can achieve high and rapid responses to gases. Most of the reported quantum dot gas-sensitive material gas sensors respond to multiple gases, and improving the selectivity of quantum dot gas-sensitive materials for ethylene detection is one of the important research topics. Summary of the Invention

[0005] In view of this, the main object of the present invention is to provide a noble metal-doped SnO2 quantum dot gas-sensitive material (noble metal-SnO2 quantum dot gas-sensitive material), which is mainly prepared by introducing noble metals such as Pd (palladium), Au (gold), Ag (silver) and Pt (platinum) into the SnO2 quantum dot gas-sensitive material, so as to improve the response and selectivity to ethylene gas detection.

[0006] Another object of the present invention is to provide a gas sensor. The gas sensor uses the above-mentioned noble metal-SnO2 quantum dot gas-sensitive material as an ethylene-sensitive material, which can improve the selectivity to ethylene gas, shorten the response and reduce the detection limit. The gas sensor can be used to detect the ethylene release amount in fruits and vegetables.

[0007] Specifically, the technical solutions provided by the present invention are as follows: The present invention provides a noble metal-SnO2 quantum dot gas-sensitive material, which includes SnO2 quantum dots and noble metals uniformly dispersed on the SnO2 quantum dots. Among them, the noble metals are metals such as Pt, Au, Ag or Pd.

[0008] Furthermore, the SnO2 quantum dots have a particle size of 5-10 nm, and the proportion of the noble metal in the gas-sensitive material is 3-10 wt%.

[0009] The present invention also provides a preparation method of the above-mentioned noble metal-SnO2 quantum dot gas-sensitive material, which includes the steps of: first adding a noble metal source dispersion liquid to a tin tetrachloride oleic acid solution, uniformly mixing to form a raw material mixture; then treating the raw material mixture by a solvothermal method to obtain the noble metal-SnO2 quantum dot gas-sensitive material.

[0010] Among them, the noble metal source includes palladium chloride, chloroplatinic acid, chloroauric acid, silver nitrate, etc.

[0011] The step of forming the raw material mixture includes: dissolving the noble metal source in a first organic solvent and ultrasonically dispersing to obtain the noble metal source dispersion liquid; dropping the noble metal source dispersion liquid into the tin tetrachloride oleic acid solution according to a volume ratio of 1:3-5 and ultrasonically dispersing to obtain the raw material mixture. In this way, the metal source can be better dispersed in the oleic acid solution and is not easy to agglomerate.

[0012] In the noble metal source dispersion liquid, if the concentration of the noble metal source is too low, it is difficult to effectively improve the sensitivity of the SnO2 quantum dots; if the concentration is too high, the noble metal source dispersion liquid is prone to agglomeration. Therefore, the concentration of the noble metal source is 0.1-0.5 wt%, such as 0.1 wt%, 0.25 wt%, 0.5 wt%, etc. The first organic solvent can be anhydrous ethanol.

[0013] The preparation method of the tin tetrachloride oleic acid solution comprises: dissolving tin tetrachloride pentahydrate in an oleic acid solution and ultrasonically dispersing the tin tetrachloride oleic acid solution, wherein the concentration of the oleic acid solution is 80-95 wt %. The solid-to-liquid ratio of the tin tetrachloride pentahydrate to the oleic acid solution is 1:55-65 g / mL.

[0014] The steps of using the solvent thermal method for treatment include: placing the raw material mixture in a reactor, reacting at a high temperature of 150°C-200°C for 2-3.5 hours under an inert atmosphere, and naturally cooling to room temperature to obtain a product mixture; purifying the product mixture to obtain a noble metal-SnO2 quantum dot gas-sensitive material.

[0015] During the solvothermal treatment, tin tetrachloride is hydrolyzed to form SnO2 quantum dots, and the noble metal source is reduced to form the corresponding metal element, thereby realizing the in-situ synthesis of noble metal-SnO2 quantum dot gas-sensitive materials. In addition, during the solvothermal treatment, if the reaction temperature is too low or the reaction time is too short, the reaction conditions cannot be met, and the solvothermal reaction is likely to be incomplete and the yield is low; if the reaction temperature is too high or the reaction time is too long, the reaction product particles will be too small and difficult to purify. Therefore, the reaction temperature of the process is limited to 150°C-200°C, such as 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, etc.; the reaction time is limited to 2 h, 2.5 h, 3 h, 3.5 h, etc.

[0016] The purification step includes: centrifuging the product mixture to obtain a crude product; then using a second organic solvent to disperse and wash the crude product until the supernatant is clear and transparent, and naturally drying to obtain the noble metal-SnO2 quantum dot gas-sensitive material. The second organic solvent can be anhydrous ethanol.

[0017] The present invention provides a sensitive layer for a gas sensor, comprising the noble metal-SnO2 quantum dot gas sensitive material.

[0018] The present invention provides a method for preparing a sensitive layer for a gas sensor, comprising the steps of: dispersing the above-mentioned noble metal-SnO2 quantum dot gas-sensitive material in a third organic solvent to form a noble metal-doped SnO2 quantum dot dispersion; coating the noble metal-doped SnO2 quantum dot dispersion on a working electrode, and drying to form a sensitive layer on the working electrode.

[0019] If the concentration of the noble metal-doped SnO2 quantum dot dispersion is too low, the sensitivity of the sensitive layer will decrease; if the concentration of the dispersion is too high, the solution will precipitate and the dispersion will be uneven. Therefore, the concentration of the dispersion is preferably 45-55 mg / mL.

[0020] The main function of the third organic solvent is to disperse the noble metal-doped SnO2 quantum dots, and the solvents can be N,N-dimethylformamide, N-methyl-2-pyrrolidone, ethylene glycol, etc.

[0021] During the process of forming the sensitive layer, the drying temperature is preferably 70-90 °C, and the drying time is preferably 0.5-1.5 h.

[0022] The above preparation method further includes, after forming the sensitive material layer, welding the leads of the sensitive element on the base, and then the noble metal-doped SnO2 quantum dot gas sensor can be made after encapsulation and capping.

[0023] The present invention also provides a gas sensor, including the above-mentioned sensitive layer.

[0024] Preferably, the gas sensor is a resistive gas sensor.

[0025] The present invention also provides an application of the above gas sensor in detecting ethylene.

[0026] Furthermore, the above gas sensor is applied to detect the ethylene release amount in food substances such as fruits and vegetables.

[0027] Furthermore, the above gas sensor is applied to monitor the ethylene release amount of fruits and vegetables during the refrigeration process.

[0028] Therefore, compared with the prior art, the technical solution provided by the present invention has the following advantages: 1) The noble metal-SnO2 quantum dot gas-sensitive material provided by the present invention mainly uses tin tetrachloride and noble metal sources as raw materials, and is prepared by a solvothermal method. The preparation method is simple, low-cost, easy to integrate, and easy to mass-produce; 2) The noble metal-SnO2 quantum dot gas-sensitive material provided by the present invention has a large specific surface area and more reaction sites for detecting ethylene, thus greatly enhancing the sensitivity of the gas sensor; 3) The noble metal-SnO2 quantum dot gas-sensitive material provided by the present invention is doped with noble metals, so that the gas sensor using the noble metal-SnO2 quantum dot gas-sensitive material has high selectivity, high sensitivity, and fast response and recovery performance for ethylene gas; 4) Since the noble metal-SnO2 quantum dot gas-sensitive material is synthesized by an in-situ method and has good structural stability, the gas sensor using the noble metal-SnO2 quantum dot gas-sensitive material still has good gas-sensitive performance at low temperatures.

[0029] Therefore, since the noble metal-SnO2 quantum dot gas-sensitive material is used as an ethylene gas-sensitive material and has characteristics such as high sensitivity, selectivity, high response, and low-temperature resistance to ethylene, the gas sensor using the noble metal-SnO2 quantum dot gas-sensitive material also has characteristics such as high sensitivity, good selectivity, and low-temperature resistance for ethylene detection, and can be used for cold storage monitoring of fruits and vegetables. Description of the Drawings

[0030] Figure 1 It is a microstructural diagram for characterizing the Pd-SnO2 quantum dot gas-sensitive material C1 provided in Example 1 of the present invention; Figure 2 It is a schematic structural diagram (2a) of the gas chemoresistive sensor provided in the embodiment of the present invention and a specific structural diagram (2b) of the gas-sensitive element; Figure 3 It is a sensitivity comparison diagram of sensors S1-3 and DS1 to 10 ppm ethylene gas; Figure 4 It is a response curve of sensor S1 to 10 ppm ethylene gas; Figure 5 It is a sensitivity comparison diagram of sensor S1 to different gases and different concentrations; Figure 6 It is a response curve of sensor S1 to 50 ppm ethylene at -20°C.

[0031] Figure 7 It is a response curve of sensor S4 to 10 ppm ethylene gas. Detailed Embodiments

[0032] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention.

[0033] Unless otherwise specified, the terms used in the present invention are all common terms in the art. The technical means used in the embodiments, such as preparation processes, testing methods, etc., are all conventional means well known to those skilled in the art. The reagents and products used are also commercially available. The source, trade name of the reagents, and those that need to list their components are indicated when they first appear.

[0034] The present invention mainly uses tin tetrachloride and noble metal sources as raw materials, and combines the solvothermal method to in-situ form noble metal-SnO2 quantum dot gas-sensitive materials; since most current oxide quantum dot sensors have poor response performance to ethylene gas, the present invention further uses noble metal-SnO2 quantum dot gas-sensitive materials as the gas-sensitive layer to prepare ethylene sensors, making the ethylene sensors have characteristics such as high response, selectivity, low detection limit, and low-temperature resistance.

[0035] Example 1 This example provides a Pd-doped SnO2 quantum dot gas-sensitive material (Pd-SnO2 quantum dot gas-sensitive material) C1 and a preparation method. The preparation method includes the steps: (1) Dissolve 0.5 g of tin tetrachloride pentahydrate (SnCl4·5H2O) in 30 mL of oleic acid solution (concentration 90%), stir magnetically at about 30°C and ultrasonically disperse for more than 60 min until the solution is clear and free of particles and is fully mixed evenly to obtain a tin tetrachloride oleic acid solution.

[0036] (2) Dissolve 20 mg of palladium chloride in 10 ml of ethanol solution, and ultrasonically treat at room temperature for more than 30 min to obtain a uniform palladium chloride dispersion with a concentration of 0.25 wt%.

[0037] (3) Use a dropper to gradually add the uniform palladium chloride dispersion in step (2) drop by drop into the tin tetrachloride oleylamine solution in step (1), and ultrasonically treat at room temperature for more than 30 min to obtain a uniform raw material mixture.

[0038] (4) Transfer the raw material mixture in step (3) into a 50 ml reaction kettle, and react at a high temperature of 180°C for 3 h in an air environment to completely hydrolyze the tin tetrachloride to form SnO2 quantum dots, and at the same time completely reduce palladium chloride to form metallic elemental Pd, and then naturally cool to room temperature, filter to obtain a crude product; (5) Take out the crude product in step (4) and add it to a centrifuge tube, add ethanol for dispersion, centrifuge and wash until the supernatant is clear and transparent, and air-dry naturally in a dry and ventilated place to obtain 0.5 g of Pd-SnO2 quantum dot gas-sensitive material.

[0039] Structural characterization of Pd-SnO2 quantum dot gas-sensitive material: The structure of the Pd-SnO2 quantum dot gas-sensitive material was characterized by transmission electron microscopy technology, and the results are as Figure 1 shown. It can be seen from Figure 1 that the size of the Pd-doped SnO2 quantum dots is 5-10 nm, indicating that a uniform Pd-SnO2 quantum dot gas-sensitive material has been synthesized.

[0040] Examples 2-3 Examples 2-3 respectively provide a Pd-SnO2 quantum dot gas-sensitive material C2-3 and a preparation method. The main differences from Example 1 are that: in step (4) of this example, the reaction temperatures are 150°C and 200°C respectively, and the remaining steps are the same, and 0.47 g and 0.5 g of Pd-SnO2 quantum dot gas-sensitive materials are obtained respectively.

[0041] Comparative Examples 1-2 Comparative Examples 1-2 provide a Pd-SnO2 quantum dot gas-sensitive material DC1-2 and a preparation method. The main differences from Example 1 are as follows: In step (4) of this example, the reaction temperatures are 130 °C and 220 °C respectively, and the remaining steps are the same, obtaining 0.2 g and 0.3 g of Pd-SnO2 quantum dot gas-sensitive materials respectively.

[0042] Compared with Examples 1-3, the material DC1 provided by Comparative Example 1 is mainly due to the relatively low reaction temperature, resulting in incomplete reaction, and thus the yield of the Pd-SnO2 quantum dot gas-sensitive material is small; the material DC2 provided by Comparative Example 2 is mainly due to the relatively high reaction temperature, resulting in a relatively small particle size of the Pd-SnO2 quantum dots, which is not easy to purify, and thus the yield of the Pd-SnO2 quantum dot gas-sensitive material is small.

[0043] Examples 4-5 Examples 4-5 respectively provide a Pd-SnO2 quantum dot gas-sensitive material C4-5 and a preparation method. The main differences from the material C1 provided by Example 1 are as follows: In step (2) of this example, the concentrations of the palladium chloride dispersion are 0.1 wt% and 0.5 wt% respectively, and the remaining steps are the same.

[0044] Examples 6-8 Gas Chemical Resistance Sensors Examples 6-8 respectively provide a gas chemical resistance sensor S1-3. Each gas chemical resistance sensor includes three parts: a tube cap 1, a sensitive element 2, and a tube base 3, as Figure 2 shown in a. Among them, the sensitive element 2 is as Figure 2 shown in b, and includes a heating electrode, a heating resistor, an insulating material provided on the lower side of the ceramic substrate, and a working electrode (measurement electrode) and a sensitive layer provided on the upper side of the ceramic substrate. The heating resistor is provided on the heating electrode, the insulating material covers the heating resistor, the sensitive layer covers the working electrode, and the outer side of the sensitive layer is exposed to the air. The tube base 3 includes a base and a tube pin. Among them, the tube pin is fixed in the through hole of the base, both ends of the tube pin extend out of both side surfaces of the base, and the tube pin is connected to the sensitive element through a lead. The tube cap 1 is connected to the base 3 by interference fit, and the sensitive element 2 is encapsulated in the inner cavities of the tube cap and the base. Among them, the sensors S1-3 respectively use the Pd-SnO2 quantum dot gas-sensitive materials provided in Example 1 and Examples 4-5 as the sensitive layers C1 and C4-5 in the sensitive element 2. Specifically, S1-C1, S2-C4, S3-C5.

[0045] This example also provides a preparation method for the above gas chemical resistance sensor, including the steps: 1) Provide a sensitive element 2, where the sensitive element 2 includes a heating electrode, a heating resistor, an insulating material disposed on the lower side of the ceramic substrate, and a working electrode disposed on the upper side of the ceramic substrate. Clean the ceramic substrate with the above electrode structure and dry it; 2) Disperse the Pd-SnO₂ quantum dot gas-sensitive materials provided in Examples 1, 4 - 5 in N,N-dimethylformamide respectively to prepare a Pd-doped SnO₂ quantum dot dispersion with a concentration of 50 mg / mL; 3) Drop the Pd-doped SnO₂ quantum dot dispersion onto the working electrode on the upper side of the ceramic substrate, dry it at 80 °C for 1 h to form a sensitive layer, and the outer side of the sensitive layer is exposed to the air; 4) After encapsulation and capping 1, gas chemical resistance sensors containing Pd-SnO₂ quantum dot gas-sensitive materials as shown in Figure 2 can be respectively fabricated.

[0046] Comparative Examples 3 - 4 Comparative Example 3 provides a gas chemical resistance sensor DS1, whose structure and preparation method are basically the same as those of the gas chemical resistance sensor S1. The main difference is that the concentration of the palladium chloride dispersion used in the preparation of the Pd-SnO₂ quantum dot gas-sensitive material in DS1 is 0.05 wt%, and the rest of the steps are the same.

[0047] Comparative Example 4 provides a gas chemical resistance sensor DS2, whose structure and preparation method are basically the same as those of the gas chemical resistance sensor S2. The main difference is that the SnO₂ quantum dot gas-sensitive material is used as the sensitive layer in DS2, that is, Pd is not doped. The preparation method omits step (2) compared with Material C1, and in step (3), ethanol is directly dropped into the tin tetrachloride oleylamine solution, and the rest of the steps are the same.

[0048] Detect the sensitivities of sensors S1 - 3 and DS1, DS2. All tests are carried out at room temperature. The sensors are tested for gas-sensitive performance under a heating voltage of 4.5 V. The results are as shown in Figure 3 shown.

[0049] From Figure 3 it can be seen that: compared with the sensor DS2, the sensitivities of sensors S1 - 3 to ethylene gas are significantly improved, and the sensitivity change of the sensor DS1 to ethylene gas is not obvious. This is mainly because the concentration of the palladium chloride dispersion used in the preparation of the Pd-SnO₂ quantum dot gas-sensitive material in the sensor DS1 is relatively low, which cannot effectively improve the sensitivity of the SnO₂ quantum dot gas-sensitive material.

[0050] Figure 4Response curve of sensor S1 (using Pd-SnO2 quantum dot gas-sensitive material C1) to 10 ppm ethylene gas. It can be seen from this curve that the response time of the sensor to 10 ppm ethylene is 22 s and the recovery time is 66 s under the heating voltage of 4.5 V. Therefore, sensor S1 has fast response and recovery performance.

[0051] Sensitivity and selectivity test: Since the gases released by fruits and vegetables are commonly ethylene, ethanol, ammonia, hydrogen sulfide, nitrogen dioxide, etc., the following tests are carried out on sensors S1 and DS2 by simulating the gases released by fruits and vegetables. The results are as Figure 5 shown in Table 1.

[0052] Table 1 Comparison table of sensitivities (Ra / Rg) of sensors S1 and DS2 to different gases at different concentrations

[0053] Combined with Figure 5 and Table 1, it can be seen that under the same test environment and conditions, the response of sensor DS2 to ethylene gas is low, while the response to gases such as ethanol and hydrogen sulfide is high; while sensor S1 has high sensitivity to ethylene gas and can clearly identify ethylene gas among several common gases, indicating that the sensor S1 doped with noble metal Pd has better improved the selectivity of SnO2 sensor to ethylene gas.

[0054] Low-temperature stability test: Sensor S1 is placed in an environment with a humidity of 60% and a temperature of -20°C - 85°C, and is also tested under the heating voltage of 4.5 V. The sensitivities of sensor S1 at the temperatures shown in Table 2 are detected respectively. The results are shown in Table 2 and Figure 6 as follows.

[0055] Table 2 Sensitivity of sensor S1 to 50 ppm ethylene at different temperatures Temperature (°C) -20 0 20 40 60 85 Sensitivity (Ra / Rg) 8.383 6.232 6.661 4.926 2.982 2.638 It can be seen from Table 2 that sensor S1 has good sensitivity at -20°C to 85°C, especially excellent sensitivity in low-temperature environments, which makes the application range of this sensor relatively wide, and further indicates that the Pd-SnO2 quantum dot gas-sensitive material adopted in the embodiment of the present invention has characteristics such as low-temperature resistance, good structural stability and high sensitivity.

[0056] Example 9 This embodiment provides a Pt-doped SnO2 quantum dot gas-sensitive material (Pt-SnO2 quantum dot gas-sensitive material) C6 and a preparation method. The preparation method includes the steps: (1) Dissolve 1 g of tin(IV) chloride pentahydrate (SnCl4·5H2O) in 50 ml of oleic acid solution (concentration 90%). Stir magnetically and ultrasonically disperse for more than 60 min at about 30°C until the solution is clear and free of particles and is thoroughly mixed to obtain a tin(IV) chloride oleylamine solution.

[0057] (2) Dissolve 80 mg of chloroplatinic acid in 20 ml of ethanol solution. Ultrasonically treat for more than 30 min at room temperature to obtain a uniform chloroplatinic acid dispersion with a concentration of 0.5 wt%.

[0058] (3) Use a dropper to gradually add the uniform chloroplatinic acid dispersion in step (2) dropwise to the tin(IV) chloride oleylamine solution in step (1). Ultrasonically treat for more than 30 min at room temperature to obtain a uniform raw material mixture.

[0059] (4) Transfer the raw material mixture in step (3) into a 100 ml autoclave. Under a nitrogen atmosphere, react at a high temperature of 180°C for 3 h to completely hydrolyze the tin(IV) chloride therein to form SnO2 quantum dots, and at the same time completely reduce the chloroplatinic acid to form metallic elemental Pt. Then naturally cool to room temperature and filter to obtain a crude product; (5) Take out the crude product in step (4) and add it to a centrifuge tube. Add ethanol for dispersion, centrifuge and wash until the supernatant is clear and transparent. Place it in a dry and ventilated place to air dry naturally to obtain 0.8 g of Pt-SnO2 quantum dot gas-sensitive material C6.

[0060] This example also provides a gas sensor S4 including the above-mentioned Pt-SnO2 quantum dot gas-sensitive material C6 and its preparation method. The structure and preparation method of this gas sensor S4 are basically the same as those of the sensor S1 provided in Example 6. The main difference is that in this example, the Pt-SnO2 quantum dot gas-sensitive material C6 is used as the gas-sensitive material layer, and during the preparation of the sensor S4, the concentration of the Pt-SnO2 quantum dot dispersion is 50 mg / mL, and the rest is the same.

[0061] Detect the sensitivities of the sensor S4 to 50 ppm ethylene, 50 ppm ethanol, 50 ppm ammonia, 50 ppm hydrogen sulfide, and 10 ppm nitrogen dioxide. The results are shown in Table 3; the response curve of the sensor S4 to 50 ppm ethylene is shown in Table 3 and Figure 7 as shown.

[0062] Table 3 Sensitivities of the sensor S4 Item Ethylene Ethanol Ammonia Hydrogen sulfide Nitrogen dioxide Sensor S4 6.6 1.4 0.68 1.2 1.1

[0063] In summary, the noble metal-SnO2 quantum dot gas-sensitive material provided by the embodiments of the present invention has the characteristics of large specific surface area, stable structure, high selectivity, etc. Therefore, the gas sensor using the above noble metal-SnO2 quantum dot gas-sensitive material as the ethylene-sensitive layer has the characteristics of high detection sensitivity to ethylene, good selectivity, low-temperature resistance, good stability, wide application range, etc., and can be used for the refrigeration monitoring of fruits and vegetables.

[0064] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that it is still possible to modify the specific implementation manners of the present invention or perform equivalent replacements for some technical features; without departing from the spirit of the technical solutions of the present invention, they should all be covered within the scope of the technical solutions claimed by the present invention.

Claims

1. A noble metal doped SnO2 quantum dot gas-sensitive material, characterized in that: It comprises SnO2 quantum dots and noble metals uniformly dispersed on the SnO2 quantum dots, wherein the noble metal is Pt, Au, Ag or Pd.

2. The noble metal doped SnO2 quantum dot gas-sensitive material according to claim 1, characterized in that: The particle size of SnO2 quantum dots is 5-10 nm, and the proportion of the noble metal in the gas-sensitive material is 2-10 wt%.

3. A method for preparing the noble metal doped SnO2 quantum dot gas sensitive material according to claim 1, comprising the steps of: firstly adding a noble metal source dispersion into a tin tetrachloride oleic acid solution, uniformly mixing to form a raw material mixture; then treating the raw material mixture by a solvent thermal method to obtain the noble metal doped SnO2 quantum dot gas sensitive material; wherein, The noble metal source includes palladium chloride, chloroplatinic acid, chloroauric acid or silver nitrate.

4. The preparation method according to claim 3, characterized in that: The step of forming a raw material mixed solution comprises: dissolving the precious metal source in a first organic solvent and ultrasonically dispersing the solution to obtain the precious metal source dispersion, wherein the concentration of the precious metal source is 0.1-0.5 wt %; dropping the precious metal source dispersion into the tin tetrachloride oleic acid solution at a volume ratio of 1:3-5, and ultrasonically dispersing the solution to obtain the raw material mixed solution.

5. The preparation method according to claim 3 or 4, characterized in that: The steps of using the solvent thermal method for treatment include: placing the raw material mixture in a reactor, reacting at a high temperature of 150°C-200°C for 2-3.5 hours, and naturally cooling to room temperature to obtain a product mixture; purifying the product mixture to obtain the noble metal-doped SnO2 quantum dot gas-sensitive material.

6. The preparation method according to claim 5, characterized in that: The purification step includes: centrifuging the product mixture to obtain a crude product; then using a second organic solvent to disperse and wash the crude product until the supernatant is clear and transparent, and naturally drying to obtain the noble metal-doped SnO2 quantum dot gas-sensitive material.

7. A sensitive layer for a gas sensor, comprising the noble metal-doped SnO2 quantum dot gas-sensitive material according to claim 1 or 2.

8. A method for preparing the sensitive layer as claimed in claim 7, comprising the steps of: dispersing a noble metal-doped SnO2 quantum dot gas-sensitive material in a third organic solvent to form a noble metal-doped SnO2 quantum dot dispersion; coating the noble metal-doped SnO2 quantum dot dispersion on a working electrode, and drying to form a sensitive layer on the working electrode.

9. The preparation method according to claim 8, characterized in that: The concentration of the noble metal-doped SnO2 quantum dot dispersion is 45-55 mg / mL.

10. The preparation method according to claim 8 or 9, characterized in that: The third organic solvent includes at least one of N,N-dimethylformamide, N-methyl-2-pyrrolidone and ethylene glycol.

11. A gas sensor comprising the sensitive layer according to claim 7.

12. Use of the gas sensor according to claim 11 in detecting ethylene.

13. Use of the gas sensor according to claim 11 in detecting ethylene release from fruits and vegetables.

14. Use of the gas sensor according to claim 11 in monitoring the ethylene release of fruits and vegetables during refrigeration.

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