Nitrogen dioxide gas sensitive material based on vte2 and application thereof

Abstract

The application relates to the technical field of gas sensor gas-sensitive materials, in particular to a nitrogen dioxide gas-sensitive material based on VTe2 and a preparation method and application thereof. The gas-sensitive material comprises VTe2, the VTe2 is in a hollow spherical structure composed of two-dimensional nanometer thin sheets, the thickness of the two-dimensional nanometer thin sheets is 40-60 nm, and the gas-sensitive material is prepared by one-step hydrothermal method or solvothermal method. The gas-sensitive material provided by the application has good gas sensitivity and selectivity to NO2 gas, can be used for detecting trace NO2 in the environment, the gas-sensitive sensing element prepared by using the gas-sensitive material has good selectivity to NO2 gas, excellent gas-sensitive performance, small influence by environmental humidity, good long-term stability, and good adsorption and desorption to NO2 gas, and can be used for multiple gas detections in a short time.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of gas sensor gas sensitive material, in particular to a nitrogen dioxide gas sensitive material based on VTe2 and a preparation method and application thereof. BACKGROUND

[0002] Nitrogen dioxide (NO2) is a toxic gas with irritant and volatile, showing brown-red in the air. Nitrogen dioxide is easily soluble in water, and can react with water to generate nitric acid. Nitrogen dioxide gas produced by natural factors or industrial production and discharged into the atmosphere will produce acid rain, which will fall to the ground on rainy days, causing harm to human living environment and health.

[0003] The sources of NO2 mainly include the following aspects: on the one hand, it is naturally produced from nature, through lightning to combine N2 and O2 in the air in a free state and microbial decomposition, on the other hand, it mainly comes from industrial production process, motor vehicle emissions and combustion of fossil fuels. Industrial production and combustion of natural gas, coal and other fossil fuels will release NO2, which will pollute the air and cause serious harm to people's health and living environment if not treated systematically and directly discharged into the air; and when it rains or it is foggy, it will react to form acid rain and fall to the environment of people's life with rainwater, causing damage to human living environment, such as acidification of lakes and soil, damage to crops on land, death of organisms in river water, etc. NO2 can also react with hydrocarbons, oxygen and other substances to generate aerosols, which can form photochemical smog, causing serious harm to people's health and living environment. When people accidentally inhale NO2 gas, they will feel dizzy, cough and have throat discomfort, and if they inhale it for a long time, they will induce bronchial diseases and even lung cancer. Based on the above reasons, it is of great significance to manufacture a high-performance, reliable sensor for detecting NO2 to protect human health and social public safety.

[0004] Transition metal dichalcogenide (TMDs) is a two-dimensional semiconductor material with a layered structure, which has a wide potential application prospect in the fields of nanoelectronics, nanodevices, magnetic materials, optoelectronics, catalysis, etc. due to its special electrical, magnetic, optical and other properties. Transition metal dichalcogenide (TMDs) contains many two-dimensional materials, among which vanadium ditelluride (VTe2) is one of the members of the TMDs family that has not been developed for gas sensing applications, mainly because of the lack of a simple and reliable synthesis method. Common preparation methods of TMDs materials include chemical vapor deposition, mechanical exfoliation and molecular beam epitaxial growth, etc. Therefore, it is of great significance to provide a simple VTe2 synthesis method and make the prepared VTe2 have good gas sensitivity to NO2 for use in NO2 gas sensors.

[0005] In view of the above, the present application is proposed. SUMMARY

[0006] The first object of the present application is to provide a VTe2-based nitrogen dioxide gas sensitive material, which has a hollow spherical micro-morphology, a large specific surface area and a large number of active sites, and has good gas sensitivity and selectivity to NO2 gas.

[0007] The second object of the present application is to provide a preparation method of the VTe2-based nitrogen dioxide gas sensitive material as described above, which has a simple preparation process and a high yield, and the prepared VTe2 has a two-dimensional nanosheet composed of a hollow spherical morphology, and has good gas sensitivity and selectivity to NO2.

[0008] The third object of the present application is to provide the application of the VTe2-based nitrogen dioxide gas sensitive material as described above in the detection of NO2 gas.

[0009] In order to achieve the above objects of the present application, the following technical solutions are adopted:

[0010] A VTe2-based nitrogen dioxide gas sensitive material, comprising VTe2, wherein the VTe2 has a hollow spherical structure composed of two-dimensional nanosheets, and the thickness of the two-dimensional nanosheets is 40-60 nm.

[0011] A preparation method of the VTe2-based nitrogen dioxide gas sensitive material as described above, comprising the following steps:

[0012] Mixing a vanadium source, a tellurium source and a solvent, and synthesizing a VTe2 nanometer gas sensitive material through a hydrothermal reaction or a solvothermal reaction.

[0013] The application of the VTe2-based nitrogen dioxide gas sensitive material as described above in the detection of NO2 gas.

[0014] Compared with the prior art, the present application has the following beneficial effects:

[0015] (1) The VTe2-based nitrogen dioxide gas sensitive material provided by the present application has a hollow micro-nano spherical morphology composed of two-dimensional nanosheets, and the morphology of the micro-nano spheres makes it have a higher specific surface area, provides more active sites, and has good gas sensitivity and selective adsorption to NO2 gas.

[0016] (2) The present application successfully synthesizes a VTe2 nanometer gas sensitive material by one-step hydrothermal or solvothermal method, and has a simple synthesis process, a high yield of VTe2, a large specific surface area of VTe2, a large number of active sites, good gas sensitivity and selective adsorption to NO2 gas, and can be used for detecting trace amounts of NO2 in the environment.

[0017] (3) The VTe2 nano gas sensitive material prepared by the method has good selectivity to NO2 gas, excellent gas sensitive performance, good adsorption and desorption to NO2 gas, can detect gas for multiple times in a short time, and has excellent long-term stability. BRIEF DESCRIPTION OF DRAWINGS

[0018] In order to more clearly illustrate the specific embodiments of the present application or the technical solutions in the prior art, the drawings needed to be used in the specific embodiments or the prior art description will be briefly introduced. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0019] Figure 1 The synthesis process schematic diagram of the VTe2 nano gas sensitive material provided by the embodiment of the present application is shown in the figure.

[0020] Figure 2 The WS-30B gas sensitive test system principle diagram is shown in the figure.

[0021] Figure 3 The XRD diagram of the VTe2 nano gas sensitive material prepared by the embodiment 1 of the present application is shown in the figure.

[0022] Figure 4 The SEM morphology diagram of different multiples of the VTe2 nano gas sensitive material prepared by the embodiment 1 of the present application is shown in the figure.

[0023] Figure 5 The EDS element analysis diagram of the VTe2 nano gas sensitive material prepared by the embodiment 1 of the present application is shown in the figure.

[0024] Figure 6 The (a) XPS total spectrum, (b) local enlarged diagram of the XPS total spectrum, (c) V2p XPS spectrum and (d) Te3d XPS diagram of the VTe2 nano gas sensitive material prepared by the embodiment 1 of the present application are shown in the figure.

[0025] Figure 7 The response curve of the sensitivity of the sensor prepared by the VTe2 nano gas sensitive material prepared by the embodiment 1 of the present application to 50ppm NO2 with temperature change is shown in the figure.

[0026] Figure 8 The response curve of the sensor prepared by the VTe2 nano gas sensitive material prepared by the embodiment 1 of the present application to different concentrations of NO2 at 140℃ is shown in the figure.

[0027] Figure 9 The response recovery curve of the sensor prepared by the VTe2 nano gas sensitive material prepared by the embodiment 1 of the present application to 50ppm NO2 at 140℃ is shown in the figure.

[0028] Figure 10 Response value of the sensor prepared by using the VTe2 nano-gas sensitive material prepared in Example 1 of the present application to 50ppm different gases at 140℃;

[0029] Figure 11 Response curve of the sensor prepared by using the VTe2 nano-gas sensitive material prepared in Example 1 of the present application to different gases at different concentrations at 140℃;

[0030] Figure 12 Response value of the sensor prepared by using the VTe2 nano-gas sensitive material prepared in Example 1 of the present application to NO2 at different humidities at 140℃;

[0031] Figure 13 Response curve of the sensor prepared by using the VTe2 nano-gas sensitive material prepared in Example 1 of the present application to 50ppm NO2 for 5 times of continuous testing at 140℃;

[0032] Figure 14 Long-term stability test results of the response of the sensor prepared by using the VTe2 nano-gas sensitive material prepared in Example 1 of the present application to 50ppm NO2 at 140℃;

[0033] Figure 15 Response mechanism diagram of the sensor based on the VTe2 nano-gas sensitive material provided by the present application. DETAILED DESCRIPTION

[0034] The technical solutions of the present application will be described clearly and completely in combination with the drawings and specific embodiments, but those skilled in the art will understand that the following described embodiments are part of the embodiments of the present application, not all the embodiments, and should not be regarded as limiting the scope of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application. The specific conditions are not specified in the embodiments, and the conventional conditions or the conditions recommended by the manufacturer are used. The reagents or instruments used are not specified by the manufacturer, and are conventional products that can be purchased on the market.

[0035] The first aspect of the present application provides a VTe2-based nitrogen dioxide gas sensitive material, comprising VTe2, wherein the VTe2 is in a hollow spherical structure composed of two-dimensional nanosheets, the thickness of the two-dimensional nanosheets is 40-60nm, for example, 40nm, 45nm, 50nm, 55nm, 60nm, or a range value composed of any two point values.

[0036] The VTe2 gas-sensitive material provided by the application has a hollow spherical morphology composed of two-dimensional nanosheet, and the morphology of the micro-nanosphere can provide higher specific surface area and more active sites, thereby improving the gas sensitivity of the VTe2 gas-sensitive material.

[0037] The VTe2-based nitrogen dioxide gas-sensitive material provided by the application can selectively adsorb NO2 gas and has excellent gas sensitivity to NO2 gas, and also has good adsorption and desorption performance, short response time and recovery time for NO2 gas, can perform gas detection for multiple times in a short time, is less affected by environmental humidity, has strong adaptability, and has good long-term stability.

[0038] As shown in Figure 1 The second aspect of the application provides a preparation method of the VTe2-based nitrogen dioxide gas-sensitive material described in the foregoing embodiments, and the preparation method comprises the following steps:

[0039] The vanadium source, the tellurium source and the solvent are mixed, and the VTe2 nano gas-sensitive material is synthesized through a hydrothermal reaction or a solvothermal reaction.

[0040] The VTe2 nano gas-sensitive material is successfully synthesized through a one-step hydrothermal or solvothermal method, the synthesis process is simple and has high yield, which facilitates the application research of the VTe2 material in different fields, and the VTe2 material synthesized by the method has a hollow micro-nanosphere morphology formed by two-dimensional nanosheet, has large specific surface area and many active sites, has good gas sensitivity and selectivity to NO2 gas, and can be used for detection of trace NO2 gas, thereby expanding the application field of the VTe2 material.

[0041] In some specific embodiments of the application, the vanadium source comprises vanadic acid and / or a vanadic acid salt, and the vanadic acid salt used is a soluble salt, for example, can be ammonium metavanadate.

[0042] In some specific embodiments of the application, the tellurium source comprises an oxide of tellurium, for example, tellurium dioxide.

[0043] In some specific embodiments of the application, the molar ratio of V and Te in the vanadium source and the tellurium source is 10-15:1, for example, any one value or a range value composed of any two point values in 10:1, 11:1, 12:1, 13:1, 14:1 and 15:1.

[0044] In some specific embodiments of the application, the solvent comprises hydrazine hydrate and water, and to avoid impurities, the water is preferably deionized water, and the hydrazine hydrate participates in the reaction as a reducing agent in addition to being a solvent in the preparation process.

[0045] In some embodiments of the present application, the reaction temperature for the synthesis is 180-220℃, for example, any one of 180℃, 190℃, 200℃, 210℃, 220℃ or a range formed by any two of them; the reaction time for the synthesis is 18-30h, for example, any one of 18h, 21h, 24h, 27h, 30h or a range formed by any two of them.

[0046] In some embodiments of the present application, after the reaction is completed, the steps of solid-liquid separation, washing and drying are further included.

[0047] In some embodiments of the present application, the solid-liquid separation can be performed by centrifugal separation, filtration, suction filtration, etc.

[0048] In some embodiments of the present application, the washing includes: washing by alternately using ethanol and water, to avoid impurities, the ethanol is preferably anhydrous ethanol, and the water is preferably deionized water.

[0049] In some embodiments of the present application, the drying temperature is 60-100℃, for example, any one of 60℃, 70℃, 80℃, 90℃, 100℃ or a range formed by any two of them; the drying time is 8-12h, for example, any one of 8h, 9h, 10h, 11h, 12h or a range formed by any two of them.

[0050] In some embodiments of the present application, the vanadium source includes metavanadic acid and ammonium metavanadate, the tellurium source includes tellurium dioxide, and the mass ratio of the metavanadic acid, the ammonium metavanadate and the tellurium dioxide is 6-8:0.3-1:1, for example, any one of 6:0.3:1, 6:0.5:1, 6:1:1, 7:0.3:1, 7:0.5:1, 7:1:1, 8:0.3:1, 8:0.5:1, 8:1:1 or a range formed by any two of them.

[0051] The metavanadic acid serves as a vanadium source on one hand and provides an acidic environment for the system on the other hand, so that the synthesis process is carried out in an acidic environment.

[0052] In some embodiments of the present application, the mass of the metavanadic acid to the volume of the hydrazine hydrate is 25-30mg / mL, for example, any one of 25mg / mL, 26mg / mL, 27mg / mL, 28mg / mL, 29mg / mL, 30mg / mL or a range formed by any two of them; the mass of the tellurium dioxide to the volume of the water is 0.3-0.5mg / mL, for example, any one of 0.3mg / mL, 0.33mg / mL, 0.4mg / mL, 0.5mg / mL or a range formed by any two of them.

[0053] In some embodiments of the present application, the preparation method of the VTe2 nano gas sensitive material comprises the following steps:

[0054] Mixing vanadyl sulfate, tellurium dioxide and hydrazine hydrate to obtain material A; mixing ammonium metavanadate and water to obtain material B; mixing material A and material B to obtain material C; transferring material C to a reaction kettle and heating to react, thereby obtaining the product.

[0055] In some embodiments of the present application, the stirring speed during the preparation of material A is 400-600 r / min, for example, any one value or a range value formed by any two values selected from 400 r / min, 450 r / min, 500 r / min, 550 r / min and 600 r / min, and the stirring time is 10-15 h, for example, any one value or a range value formed by any two values selected from 10 h, 11 h, 12 h, 13 h, 14 h and 15 h.

[0056] The third aspect of the present application provides a VTe2-based nitrogen dioxide gas sensitive material according to any one of the preceding embodiments, or an application of the gas sensitive material prepared by the preparation method according to any one of the preceding embodiments in NO2 gas detection.

[0057] In some embodiments of the present application, the application of the gas sensitive material in an NO2 gas sensitive sensing element, for example, includes but is not limited to a sensor comprising the gas sensitive sensing element.

[0058] In some embodiments of the present application, the detection temperature when the gas sensitive material is used for NO2 gas detection is 120-160℃, for example, any one value or a range value formed by any two values selected from 120℃, 130℃, 140℃ and 160℃.

[0059] In some preferred embodiments of the present application, the detection temperature when the gas sensitive material is used for NO2 gas detection is 140℃.

[0060] In some embodiments of the present application, the response time of the gas sensitive material to 50 ppm of NO2 gas is less than 25 s, and the recovery time is less than 35 s.

[0061] Some embodiments of the present application will be described in detail below in combination with specific application examples. The raw materials used in the examples, such as the materials without special instructions, can be purchased on the market.

[0062] Example 1

[0063] Preparation Example

[0064] The preparation method of the VTe2 gas sensitive material comprises the following steps:

[0065] First, 140 mg of metavanadic acid and 20 mg of tellurium dioxide are added to a beaker containing 5 mL of hydrazine hydrate, and stirred in a magnetic stirrer at a speed of 500 r / min for 12 hours to obtain material A.

[0066] Then, 10 mg of ammonium metavanadate is added to a beaker containing 30 mL of deionized water to obtain material B, and the uniformly stirred material A is poured into the material B, and stirred until a uniform material C is formed.

[0067] Finally, the material C is transferred to a 100 mL vacuum reactor, and heated at 200 °C for 24 hours. After the reaction is completed, centrifugal operation is performed, and the precipitate is collected and dried in a vacuum drying oven at 80 °C for 10 hours, to obtain the VTe2 gas sensitive material.

[0068] Sample characterization:

[0069] 1) X-ray powder diffraction (XRD)

[0070] In this study, the X'Pert PRO X-ray diffractometer manufactured by the Netherlands PANalytical Company is used to accurately detect and analyze the prepared VTe2 gas sensitive material. The device uses Cu Kα as its radiation source; at the same time, the related technical parameters are: wavelength λ = 1.5442 Å, current density 40 mA, tube pressure value 40 kV, and the scanning angle range is from 5° to 90°, and the scanning rate per minute is set to 10°.

[0071] Figure 3 The XRD pattern of the VTe2 gas sensitive material prepared in Example 1 is consistent with the VTe2 original pattern standard card (ICSD: 01-077-0309). The main diffraction peaks of VTe2 correspond to the 2θ angles 13.7°, 27.6°, 31.8°, 38.4°, 40°, 41.9°, 50.1°, 51.4°, 52.9°, 56.8° on the standard card, and the corresponding crystal face characteristic diffraction peaks (001), (002), (310), (202), (600), (003), (-913), (-314), (203) and (-715). These clear peaks indicate that the synthesized vanadium ditelluride has good crystallinity. The blue line in the figure represents the standard card, and the XRD pattern proves that the VTe2 material is successfully synthesized in this experiment.

[0072] 2) Scanning electron microscope (SEM)

[0073] The microstructure of the sample was studied in depth using a JSM-6700F scanning electron microscope manufactured by JEOL. First, a small amount of sample was applied to a conductive film, and excess residue was removed with a cotton ball. Next, in order to improve its conductivity, the sample was subjected to a gold spray treatment. Subsequently, the completed sample was placed in the sample chamber, and after the vacuum was drawn, the shape and appearance of the sample were observed.

[0074] Figure 4 The partial surface microstructure of the VTe2 gas-sensitive material prepared in Example 1 was observed, and it was found that the morphology of VTe2 was a hollow spherical morphology composed of two-dimensional nanosheets, and the thickness of the two-dimensional nanosheets was about 50 nm. From the figure, it can be observed that the VTe2 nanospheres grow to form a multi-dimensional microstructure, and this micro-nanosphere morphology provides a higher surface area, allowing it to have more active sites, thereby improving the gas sensitivity of the VTe2 material.

[0075] 3) EDS analysis

[0076] In order to better prove the synthesis of the VTe2 material, EDS testing was performed on the VTe2 gas-sensitive material prepared in Example 1 using the energy spectrometer in the SEM testing equipment. From the EDS figure Figure 5 , it can be observed that there are V and Te elements in the sample. The uniform distribution of V and Te elements in the characterization area can be clearly observed, and the V element is more obvious in the characterization area, while the Te element is not very obvious. This may be because during the synthesis process, part of the tellurium dioxide was reduced to elemental tellurium to provide a substrate for the growth of VTe2, so the V element is clear and on the outer surface, and the tellurium element is wrapped inside by the V element.

[0077] 4) X-ray photoelectron spectroscopy (XPS)

[0078] In this study, the PHI-5300 X-ray photoelectron spectrometer manufactured by the American Perkin Elmer Company was used to analyze the valence state of the compounds in the composite material in depth. The instrument uses Al, Kα (1486.6 eV) as the excitation light source to ensure the accuracy and reliability of the analysis process. The device power is set to 250 W, and the voltage is 12.5 kV to ensure stable and efficient operation. During the analysis process, the gas pressure in the analysis chamber was maintained at 10 -9 Torr to reduce the interference of environmental factors. In addition, the reference binding energy of carbon C1s (284.8 eV) was used to correct the data to ensure the accuracy and consistency of the analysis results, and the results are shown in Figure 6 .

[0079] Figure 6In the figure, (a) is the XPS spectrum of the VTe2 gas-sensitive material prepared in Example 1. As can be seen from the spectrum, the VTe2 gas-sensitive material is composed of V and Te elements. The C element may come from the polluting carbon components adsorbed on the surface of the gas-sensitive material when it comes into contact with air, but it will not affect the properties of the VTe2 gas-sensitive material. Moreover, it can be seen that the energy spectrum of C is relatively weak, which is the same as the results of XRD and SEM tests.

[0080] (b) is a magnified view of the XPS total spectrum of the VTe2 gas-sensitive material, which clearly shows the location of each element.

[0081] (c) is the fine XPS spectrum of V 2p, where the V 2p spectrum has two peaks at 517.4 eV and 524.4 eV, representing V 2p and V 2p, respectively. (4+) 2p 3 / 2 and V (4+) 2p 1 / 2 The presence of vanadium in its tetravalent oxidation state confirms the existence of VTe2 material. The figure also shows the presence of V... (5+) The valence state indicates that vanadium oxide formed on the surface of the VTe2 material during hydrothermal synthesis. During the synthesis of vanadium ditelluride, some vanadium is easily oxidized, resulting in the formation of trace amounts of vanadium oxide on the surface of the vanadium ditelluride.

[0082] (d) is the fine XPS plot of Te 3d, with peaks at 573.1 eV and 583.5 eV, corresponding to V-Te bonds formed by 3d... 5 / 2 and 3D 3 / 2 The oxidation state indicates the successful formation of VTe2. The figure also shows the presence of the Te-O state at 576.5 eV and 586.7 eV, which can be attributed to the small amount of metallic tellurium formed during the hydrothermal synthesis of vanadium telluride when hydrazine hydrate reduced tellurium dioxide; this metallic tellurium was then oxidized to tellurium dioxide during the hydrothermal process.

[0083] As can be seen from the XRD, SEM, EDS and XPS test results above, the present invention successfully synthesized VTe2 gas-sensitive material, which has a hollow spherical morphology composed of two-dimensional nanosheets.

[0084] Example 2

[0085] Application Examples:

[0086] To facilitate material testing, the prepared gas-sensitive material was fabricated into a uniform gas-sensitive sensing element. The fabrication process is as follows:

[0087] The VTe2 gas sensitive material prepared in Example 1 was added into ethanol, and ultrasonic treatment was carried out for 3-5 min to obtain a uniform slurry with a concentration of 10 mg / mL. Then, the slurry was uniformly applied to an Al2O3 ceramic tube with Au electrode. In the experiment, the slurry should uniformly cover the Au electrode, and the thickness should be consistent with the Al2O3 ceramic tube. After coating, the ceramic tube was dried at 80 DEG C in vacuum for 10 hours. After drying, the ceramic tube with the gas sensitive material was taken out, four Pt wires were welded to the base pins, and the Ni-Cr alloy coil inside the ceramic tube was welded to the corresponding pins. The Ni-Cr alloy coil served as a heating element to realize the heating function of the ceramic tube. After the preparation of the gas sensor, aging treatment was carried out to ensure stability and reliability. In order to obtain the aged device, a WS-30B gas sensitive tester was used in the experiment under the condition of a power supply voltage of 5 V, and the device was aged for 6 hours.

[0088] The WS-30B gas sensitive tester was used for detection, and its working principle was as follows:

[0089] The WS-30B gas sensitive detection device using voltage measurement method could detect the current resistance value of the gas sensor and record it, and its working principle was as shown in FIG. 1. Figure 2 In the figure, V h represents the heating voltage in the gas sensitive detection device, V c represents the test voltage of the gas sensitive detection device, and V out is the voltage of the load resistor R1 connected in series. In the experiment, the test voltage of the WS-30B gas sensitive test system was 5 V, and the resistance calculation formula of the gas sensor was R= (V c -V out ) / (V out / R1). In the test, the real-time resistance change of the gas sensor was recorded by indirectly recording the voltage division of the gas sensor through real-time monitoring of the voltage division V out of the load resistor R1.

[0090] Gas configuration in the test process:

[0091] In the present application, the gas to be tested has two states at room temperature, namely the gas state represented by nitrogen dioxide and the liquid state represented by acetone, ethanol, formaldehyde and ammonia (gas precursor solution to be tested). The liquid state at room temperature volatilizes very slowly during the test, so a micro-sampler is used to take an appropriate amount of gas precursor solution to be tested from the solution bottle and inject it into the test chamber of the gas sensitive tester with an evaporation table to heat the gas solution and accelerate the volatilization of the gas solution in the test chamber. The concentration of the gas to be tested is determined by formula 2.1, and the calculation formula is as follows:

[0092] V x = V x C x M x 10 -9 / (22.4 x d x p) (2.1)

[0093] In formula 2.1, V x represents the volume of the precursor liquid of the gas to be tested, in milliliters (mL). V represents the volume of the closed chamber of the gas test box, in milliliters (mL). C represents the concentration of the gas to be tested, in ppm (parts per million). M represents the molar mass of the precursor liquid of the gas to be tested, in grams per mole (g·mol -1 ). d represents the density of the precursor liquid of the gas to be tested, in grams per cubic centimeter (g·cm -3 ). p represents the purity of the precursor liquid of the gas to be tested, in percentage (wt%). In the experiments of the present application, the volume of the test chamber of the WS-30B gas sensitive tester is set to 18 liters.

[0094] Gas sensitivity test:

[0095] (1) Gas sensitivity test at different temperatures

[0096] The response of the VTe2 gas sensitive sensing element prepared in the present application to 50 ppm nitrogen dioxide was tested at room temperature to 180 °C, Figure 7 is the response value of the VTe2 gas sensitive sensing element at 100-180 °C. It can be seen from the figure that the response of the VTe2 gas sensitive sensing element is best at 140 °C;

[0097] From the response curve of the VTe2 gas sensitive sensing element at different temperatures to 50 ppm nitrogen dioxide in Figure 7 It can be seen that in the process of temperature rising, the gas sensitivity first increases and then decreases, and when the test temperature reaches 140 °C, the gas sensitive response value reaches the maximum. In the range of 100-140 °C, the adsorption oxygen activation ability of the VTe2 gas sensitive material to nitrogen dioxide is weak, but with the increase of temperature, the gas sensitivity is enhanced; however, when the temperature exceeds 140 °C, the adsorption oxygen energy escapes, which weakens the adsorption effect and reduces the active sites, resulting in the decrease of the gas sensitive performance. Therefore, the best working temperature of the VTe2 gas sensitive sensing element is 140 °C.

[0098] (2) Gas sensitivity test at different concentrations of NO2

[0099] At the best working temperature of 140 °C, the sensitivity of the VTe2 gas sensitive sensing element to nitrogen dioxide gas with different concentrations was tested, Figure 8The response curve of the VTe2 gas sensitive sensing element to different concentrations of nitrogen dioxide gas is shown in the figure. It can be seen from the figure that the VTe2 gas sensitive sensing element has a good response to nitrogen dioxide gas regardless of the concentration, which indicates that it has excellent gas sensitivity to NO2. As the concentration of nitrogen dioxide gas gradually increases in the test, the response value of the VTe2 gas sensitive sensing element also gradually increases and then slowly tends to a saturated state. This is because the hollow spherical microstructure of VTe2 increases the specific surface area of the material, thereby improving the adsorption sites of the VTe2 material for nitrogen dioxide gas. As can be clearly seen from the figure, after stopping the introduction of nitrogen dioxide gas, the resistance of the gas sensitive sensing element can be restored to the initial value in a short time, which indicates that the VTe2 material prepared by the present application has good desorption properties for nitrogen dioxide gas at a working temperature of 140 DEG C.

[0100] (3) Test of response time and desorption time

[0101] In actual application process, the gas sensor often has high requirements for its own response time and recovery time. Figure 9 is the response curve of the VTe2 gas sensitive sensing element to 50 ppm nitrogen dioxide gas at 140 DEG C. As can be seen from the figure, as soon as the VTe2 gas sensitive sensing element contacts nitrogen dioxide gas, the resistance value of the gas sensitive material on the gas sensitive sensing element will change rapidly and slowly tend to a saturated state. When the nitrogen dioxide gas is discharged from the test chamber, the resistance of the gas sensitive element will quickly recover to the initial value, and Figure 9 It can be seen that the response time of the VTe2 gas sensitive sensing element to 50 ppm nitrogen dioxide gas is 24 s, and the recovery time is 33 s, which is short in response and recovery time and high in detection efficiency.

[0102] (4) Selectivity test

[0103] Selectivity is an important performance index of a gas sensor, which measures its anti-interference ability to gases other than the target gas in a complex environment. A sensor with high selectivity can accurately detect the target gas and resist interference from other gases. In order to study the selectivity of the VTe2 gas sensitive sensing element, 50 ppm concentrations of nitrogen dioxide (NO2), ammonia (NH3), formaldehyde (HCHO), ethanol (C2H5OH) and acetone (CH3COCH3) were tested at 140 DEG C and the response values were calculated. Figure 10 is the response column chart of the VTe2 gas sensitive sensing element to 50 ppm different gases at 140 DEG C. As can be seen from the figure, the response value of the VTe2 gas sensitive sensing element prepared by the present application to NO2 gas is much higher than that to other gases, which indicates that the VTe2 gas sensitive sensing element prepared by the present application has excellent selectivity to NO2 gas.

[0104] After the selectivity of 50 ppm gas was tested, the response of the VTe2 gas sensing element to five kinds of gases at different concentrations was tested at a working temperature of 140 ℃. Figure 11 It can be seen that the selectivity of the VTe2 gas sensing element to nitrogen dioxide gas is the highest regardless of the concentration of the gas, and the response is not reduced by the interference of other gases, and the order of selectivity is nitrogen dioxide > ammonia > ethanol > acetone > formaldehyde.

[0105] (5) Influence of humidity on gas sensing performance

[0106] In actual application scenarios, the gas sensing performance of a gas sensor can be affected by different humidity conditions. In order to study the moisture resistance of the gas sensor, the gas sensing performance of the VTe2 gas sensing element under different humidity conditions was tested. Generally, the environmental humidity fluctuates within a certain range, but the humidity in the closed environment of the test chamber is relatively stable. By adding an appropriate amount of deionized water on the evaporation table in the test chamber of the WS-30B test instrument, the deionized water is quickly volatilized by heating, and the humidity in the test chamber gradually increases to the required humidity test condition. When it is necessary to reduce the humidity in the test chamber, a moisture-proof desiccant is usually added to the test chamber to reduce the humidity in the test chamber.

[0107] Figure 12 is a column chart of the response value of the VTe2 gas sensing element to 50 ppm nitrogen dioxide gas at a humidity of 40%-80% at the best working temperature of 140 ℃. The experimental results show that the response value is the highest when the working humidity is 40%, and as the environmental humidity increases, the response of the VTe2 gas sensing element to nitrogen dioxide gas gradually decreases, but the overall response of the gas sensing element to nitrogen dioxide gas does not change much.

[0108] (6) Stability test of VTe2 gas sensing element

[0109] Stability is closely related to the service life of a gas sensor. Excellent stability not only saves material resources, but also prolongs the service life and reduces maintenance costs, which is in line with China's sustainable development strategy. The VTe2 gas sensing element prepared by the present application is continuously tested for multiple repetitions at a working temperature of 140 ℃, Figure 13 is the response curve of the VTe2 gas sensing element after 5 continuous tests. After testing, the VTe2 gas sensing element has good stability, which is closely related to the adsorption and desorption performance of the VTe2 gas sensing material to nitrogen dioxide gas.

[0110] The present application also studies the long-term stability of the VTe2 gas sensing element. The response change of the VTe2 sensor to 50 ppm nitrogen dioxide gas within 30 days was tested, as shown in Figure 14As shown, the experimental results show that with the increase of days, the gas sensing performance presents a slight up and down trend, which may be related to the change of the environmental humidity in the test chamber of the test instrument, but the gas sensing response of the VTe2 gas sensitive sensing element has no obvious change as a whole, and has good long-term stability.

[0111] (7) Adsorption mechanism

[0112] From the above experimental test results, it can be concluded that the gas sensing performance of the VTe2 material has good selectivity to nitrogen dioxide gas at 140 DEG C. The gas sensing mechanism diagram is as shown in Figure 15 , wherein the gas sensing mechanism of the VTe2 sensor is mainly that the target gas is adsorbed on the active site on the surface of the VTe2 nanomaterial, the charge moves and desorbs, so as to cause the resistance of the material to change, when the VTe2 nanomaterial is in the air, its micro-surface is adsorbed by oxygen molecules, since the oxygen molecules have electronegativity, they will extract the electrons on the surface of the VTe2 nanomaterial, and exist in the form of adsorbed oxygen molecules, as shown in formula 2.2, and according to different temperatures, it is converted into three different oxygen ions, respectively O2 - , O - , O 2- , as shown in formulas 2.3-2.5, when the temperature environment is less than 100 DEG C, O2 - is generated, when the temperature environment is greater than 100 DEG C and less than 300 DEG C, O - is generated, and when the temperature environment is greater than 300 DEG C, O 2- is generated. At the best working temperature 140 DEG C of the present application, O 2(ads) exists in the form of capturing electrons on the surface of the nanomaterial.

[0113] O 2(gas) →O 2(ads) #(2.2)

[0114] O 2(ads) + e - →O2 - (ads) #(2.3)

[0115] O 2(ads) + 2e - →2O - (ads) #(2.4)

[0116] O 2(ads) + 4e - →2O 2- (ads) #(2.5)

[0117] ​From the above analysis, the electrons in the conduction band of VTe2 gas sensitive material are captured by oxygen molecules, thus reducing, while the surface layer of the material is depleted of electrons, resulting in an increase in the resistance of VTe2 gas sensitive material. O - The state of high ionic activity and binding energy is relatively weak, when the gas sensitive material monitors different gases, O - The state of the ion will be easily separated from the surface of VTe2 gas sensitive material. When monitoring nitrogen dioxide gas, nitrogen dioxide gas has strong oxidizing properties, NO2 molecules and oxygen molecules have the same properties, first is converted to the adsorbed state of NO 2（ads） Molecule, as shown in equation 2.6, and has a larger affinity potential than oxygen molecules, and has a higher electrophilic property, which results in more electrons on the surface of VTe2 gas sensitive material being captured by NO2 molecules, and also can extract O2 - State of ion electrons, converted into chemical state NO2 - Ion, as shown in equations 2.7-2.8:

[0118] NO 2(gas) →NO 2(ads) #(2.6)

[0119] NO 2(ads) + e - →NO2 - (ads) #(2.7)

[0120] NO 2(ads) +O2 - (ads) →NO2 - (ads) +O 2(gas) #(2.8)

[0121] After a series of reactions, the number of conduction band electrons of VTe2 gas sensor is reduced, resulting in the widening of the electron depletion layer on the surface of the material, and the resistance of the gas sensitive material is increased.

[0122] Although the present application has been illustrated and described with reference to specific embodiments, it is realized that the above examples are only used to illustrate the technical solutions of the present application, and are not limited thereto; those skilled in the art should understand that the technical solutions recorded in the above embodiments can be modified, or some or all of the technical features can be replaced by equivalents, without departing from the spirit and scope of the present application; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application; therefore, this means that all these replacements and modifications within the scope of the present application are included in the appended claims.

Claims

1. A VTe2-based nitrogen dioxide gas sensitive material, characterized in that, The VTe2 comprises a hollow spherical structure composed of two-dimensional nanosheets, and the thickness of the two-dimensional nanosheets is 40-60 nm. The preparation method of the VTe2-based nitrogen dioxide gas-sensitive material comprises the following steps: Mixing vanadic acid, tellurium dioxide and hydrazine hydrate to obtain material A; mixing ammonium metavanadate and water to obtain material B; mixing the material A and the material B to obtain material C; transferring the material C to a reaction kettle and heating at 180-220 ℃ for 18-30 h to obtain the VTe2-based nitrogen dioxide gas-sensitive material. The molar ratio of V in the vanadic acid and the ammonium metavanadate to Te in the tellurium dioxide is 10-15:

1. The hydrazine hydrate is used as a reducing agent in addition to a solvent in the preparation process.

2. The VTe2-based nitrogen dioxide gas sensing material of claim 1, wherein, The mass ratio of the vanadic acid, the ammonium metavanadate and the tellurium dioxide is 6-8:0.3-1:

1.

3. The VTe2-based nitrogen dioxide gas sensing material of claim 2, wherein, The mass of the vanadic acid to the volume of the hydrazine hydrate is 25-30 mg / mL, and the mass of the tellurium dioxide to the volume of the water is 0.3-0.5 mg / mL.

4. The application of the VTe2-based nitrogen dioxide gas-sensitive material in claim 1-3 in NO2 gas detection.

5. Use according to claim 4, characterized in that, The application of the gas-sensitive material in a NO2 gas-sensitive sensing element.

6. Use according to claim 4, characterized in that, The detection temperature of the gas-sensitive material in NO2 gas detection is 120-160 ℃.

7. Use according to claim 4, characterized in that, The response time of the gas-sensitive material to 50 ppm NO2 gas is less than 25 s, and the recovery time is less than 35 s.

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