A gas sensitive element based on SnO2@MoS2 nanocomposite and a preparation method thereof

Abstract

The application belongs to the technical field of semiconductor nanomaterials, and specifically discloses a xylene gas-sensitive material based on hierarchical three-dimensional SnO2@MoS2 nanocomposites and a gas-sensitive element manufacturing method. The gas-sensitive material takes SnO2 nanofibers as a framework, grows uniform MoS2 nanosheets on the surface of the SnO2 nanofibers through a simple hydrothermal method, and then obtains three-dimensional hierarchical SnO2@MoS2 nanocomposites through heat treatment. The obtained hierarchical SnO2@MoS2 nanocomposites are mixed with anhydrous ethanol at a ratio of 4:1 to form a paste, which is uniformly coated on the surface of a ceramic tube electrode, an electric heating wire is added inside, and the semiconductor gas-sensitive element is welded, aged and packaged to prepare a xylene gas-sensitive element. The gas-sensitive element has the characteristics of strong humidity interference resistance, high sensitivity, good selectivity to target gas and good stability in xylene gas detection, and can be used for detecting xylene gas in the environment.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor nanomaterials technology, and relates to novel xylene gas detection materials and gas-sensitive elements, specifically to a hierarchical three-dimensional SnO2@MoS2 nanocomposite gas-sensitive material for xylene gas detection and a gas-sensitive element prepared therefrom. Background Technology

[0002] Xylene, a volatile organic compound, is extremely harmful to the human body. It irritates the eyes and upper respiratory tract, and chronic poisoning can lead to neurasthenia syndrome. In practical applications, the detection limit (LOD) and sensitivity of sensors play a crucial role in detecting toxic and harmful gases. Although the human olfactory system can detect malodorous gases, in some cases, the concentration of these gases or VOCs is too low for the human nose to detect. Therefore, it is necessary to develop devices for detecting trace amounts of toxic gases. Semiconductor gas sensors effectively overcome these shortcomings in the sensor field. Furthermore, the movement of electrons and holes in semiconductor nanomaterials is also influenced by the material's size and geometry. Some metal oxide semiconductors and their derived composite structures (such as Co3O4, CuO, NiO, WO3, ZnO, MoO3) have been used for xylene gas sensing.

[0003] SnO2, as an N-type sensitive material with a wide bandgap, has been widely used in gas sensors due to its high sensitivity. MoS2, as a novel two-dimensional semiconductor material, possesses advantages such as an inherent bandgap and a stable band structure. It has been reported that many MoS2-based hierarchical heterostructures can be used for gas sensing enhancement, photocatalysis, energy storage, and supercapacitors. While hierarchical structures based on SnO2 and MoS2 have also been reported, no research has yet been found on their application for xylene detection. Therefore, this invention develops a low-cost, high-sensitivity xylene gas sensor with excellent humidity resistance, which helps solve related practical application problems. Summary of the Invention

[0004] The technical problem solved by this invention is to address the shortcomings of existing xylene gas sensors, such as insufficient sensitivity to xylene gas, insufficient detection limit, poor selectivity, and excessively high operating temperature.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0006] The first aspect of the present invention discloses a three-dimensional hierarchical SnO2@MoS2 nanocomposite material, which is composed of SnO2 nanofibers as a framework and a uniform array of MoS2 nanosheets assembled and grown on their surface.

[0007] Preferably, the SnO2 nanofiber has uniform morphology and rough surface, and has a diameter of 210-230 nm; the MoS2 nanosheet self-assembles to form a flower shape, and has a highly ordered array, and has a sheet thickness of 140-150 nm; and the SnO2@MoS2 composite material has an outer diameter of 240-260 nm.

[0008] The second aspect of the present application discloses a preparation method of the SnO2@MoS2 nanocomposite material, comprising the following steps:

[0009] S1: under stirring at 800-1000 rpm, 1.2 g of PVP is slowly added into a beaker containing 8 mL of ethanol to obtain solution 1; meanwhile, 0.15 g / mL of SnCl2·2H2O is added into N,N-dimethylformamide under stirring at 800-1000 rpm to obtain solution 2, and the solution 1 and the solution 2 are mixed and magnetically stirred to form a uniform viscous transparent solution; the viscous transparent solution is collected after electrospinning to obtain a spinning precursor, and the spinning precursor is calcined to obtain SnO2 nanofiber;

[0010] S2: 0.2 mmol of (NH4)6Mo7O 24 ·4H2O and 6.1 mmol of CH4N2S are dissolved in a beaker containing 40 mL of deionized water under vigorous stirring to obtain a solution, which is placed in a container, and then the SnO2 nanofiber in S1 is added into the container and soaked in the container overnight at room temperature, and then the sample is collected after drying in a drying box;

[0011] S3: 0.2 mmol of (NH4)6Mo7O 24 ·4H2O and 6.1 mmol of CH4N2S are dissolved in deionized water under vigorous stirring, and after stirring for 10 minutes, a mixed solution is obtained, which is transferred into a sealed autoclave with a polytetrafluoroethylene liner, and finally the sample in S2 is added into the sealed autoclave for heating, and heated at 210℃ for 12 h, and after heating, cooled to room temperature and the supernatant is poured out, and the black precipitate is collected by centrifugation, washed and dried, and dried in a drying box at 60℃ overnight to obtain the SnO2@MoS2 nanocomposite material.

[0012] Preferably, the electrospinning process in S1 is that the relative humidity of the environment is 10%-50%, the voltage between the collection plate and the needle tip of the syringe is 18 kV, and the distance between the collection plate and the needle tip of the syringe is 20 cm.

[0013] Preferably, the calcination process of the spinning precursor in S1 is that the temperature is increased to 600℃ at a temperature increasing rate of 1-3℃ / min, and then held for 5 h.

[0014] Preferably, the purity of the ammonium molybdate and thiourea is 99% and 99%, respectively.

[0015] The third aspect of the present application discloses a xylene gas sensitive element based on the above-mentioned three-dimensional hierarchical SnO2@MoS2 nanocomposite material, which is a semiconductor gas sensitive element made of a semiconductor type tube, a flat plate, and a micro-hot plate electrode.

[0016] Preferably, the gas sensitive element is a tube type semiconductor gas sensitive element, and the preparation method comprises the following steps: mixing the hierarchical SnO2@MoS2 nanocomposite material and ethanol in a certain proportion to form a paste, uniformly coating the paste on the surface of a ceramic tube, sequentially adding heating wires, welding, aging, and packaging to obtain the tube type semiconductor gas sensitive element.

[0017] Preferably, the technical indicators of the gas sensitive element include:

[0018] The working temperature is 160-260 DEG C.

[0019] The detection sensitivity R of the element to 100 ppm xylene is g / R a about 23.5.

[0020] The response time is 21.5 s, and the recovery time is 60.4 s.

[0021] The sensitivity of the element to 100 ppm xylene is higher than the sensitivity of any one of 100 ppm ammonia, acetone, ethanol, methanol, and formaldehyde.

[0022] Preferably, the lower limit of the concentration of xylene gas detected by the gas sensitive element is 0.5 ppm.

[0023] Compared with the prior art, the present application has the following advantages:

[0024] 1. The hierarchical SnO2@MoS2 nanocomposite material prepared by electrospinning combined with hydrothermal synthesis reaction has a three-dimensional core-shell nano-heterojunction structure with SnO2 nanofibers as the framework and uniform MoS2 nanosheet arrays grown on the fiber surface by the hydrothermal method, which can increase the specific surface area of the gas sensitive material, construct a three-dimensional hierarchical core-shell heterostructure, increase the number of active sites in the material, thereby increasing the adsorption of the gas sensitive material to the gas, effectively improving the sensitivity and selectivity of the material to xylene gas, and the preparation process of the above-mentioned material is simple and low in cost.

[0025] 2. The gas sensitive element prepared by the present application has high sensitivity to xylene gas, good selectivity and stability to interfering gases, low detection limit, and the lower limit of the concentration of xylene gas detected is 0.5 ppm. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1The X-ray diffraction pattern of the hierarchical SnO2@MoS2 nanocomposite in Example 1 has characteristic peaks of MoS2 in addition to the peaks of SnO2 fibers, proving that the MoS2 nanosheets are successfully grown on the SnO2 fibers, and no other peaks are observed in the figure, proving the purity of the product.

[0027] Figure 2 The SEM image of the three-dimensional SnO2@MoS2 core-shell nanocomposite in Example 1 shows that the MoS2 nanosheets are uniformly grown on the nanofibers, and there are no MoS2 nanosheets that are independently nucleated and grown.

[0028] Figure 3 The TEM image of the three-dimensional SnO2@MoS2 core-shell nanocomposite in Example 1 shows that the composite structure has a large number of pores.

[0029] Figure 4 The response of the gas sensing element in Example 1 to 100 ppm of xylene at different temperatures is shown in the figure, and it can be seen that the response of the gas sensing element to 100 ppm of xylene at 220°C is the highest, reaching 23.5.

[0030] Figure 5 The selectivity of the gas sensing element in Example 1 to eight different 100 ppm gases is shown in the figure, and it can be seen that the response of the gas sensing element to xylene is the highest, and the response to other interfering gases can be ignored, showing good anti-interference performance.

[0031] Figure 6 The continuous response recovery curve of the gas sensing element in Example 1 to different concentrations of xylene (0.125-100 ppm) shows that the gas sensing material has a low detection limit and the gas sensing element has a good linear relationship with different concentrations of xylene.

[0032] Figure 7 The principle flowchart of preparing a xylene gas sensing element using the three-dimensional hierarchical SnO2@MoS2 nanocomposite. DETAILED DESCRIPTION

[0033] The present application will be further described in the following examples, but the present application is not limited to the scope of the examples. The experimental methods in the following examples are not specified, and the methods are selected according to conventional methods and conditions, or according to the instructions of the products.

[0034] Example 1

[0035] The hierarchical SnO2@MoS2 nanocomposite was prepared, and the specific steps were as follows:

[0036] (1) 1.2 g PVP was slowly added into a beaker containing 8 mL ethanol under magnetic stirring, and 2.8 g SnCl2·2H2O was dissolved in 10 mL DMF under vigorous stirring. After 1 h stirring to become a homogeneous solution, the two solutions were mixed and magnetically stirred for 12 h to form a homogeneous viscous transparent solution, which was loaded into a syringe and ready for use.

[0037] (2) The syringe containing the prepared solution was placed into the electrospinning machine, and the relevant parameters were set as follows: the temperature in the electrospinning machine was 45℃, the relative humidity was 20%, the voltage between the collecting plate and the needle tip of the syringe was adjusted to 18 kV, and the distance between the collecting plate and the needle of the syringe was set to 20 cm. After the electrospinning was completed, the sample collected from the collecting plate was calcined at a heating rate of 1℃ / min to 600℃ and kept for 3 h, to obtain SnO2 nanofibers.

[0038] (3) A certain amount of (NH4)6Mo7O 24 ·4H2O and deionized water were mixed under gentle stirring to prepare a solution, which was then placed into a centrifuge tube, and the prepared SnO2 nanofibers (80 mg) were added and soaked in the centrifuge tube at room temperature overnight. After that, the sample was collected by drying in a drying oven.

[0039] (4) 0.2 mmol (NH4)6Mo7O 24 ·4H2O and 6.1 mmol CH4N2S were dissolved in a beaker containing 40 mL deionized water under vigorous stirring. After 10 min stirring, the mixture solution was transferred into a 50 mL stainless steel sealed autoclave with a polytetrafluoroethylene liner, and 80 mg of the pretreated SnO2 nanofibers were added to the above solution and heated at 210℃ in a high-temperature drying oven for 12 h. After the heating was completed, the black precipitate was collected by centrifugation after cooling to room temperature and pouring off the supernatant, and then washed repeatedly with water and ethanol. Finally, the sample was dried in a 60℃ drying oven overnight to obtain the final sample, which was named as SnO2@MoS2.

[0040] The specific steps for preparing a gas sensing element from the above hierarchical SnO2@MoS2 nanocomposite material are as follows:

[0041] An appropriate amount of ethanol was added to the obtained hierarchical SnO2@MoS2 nanocomposite material to make a paste, which was uniformly coated on the surface of a tubular electrode. After adding a heating wire, the gas sensing element was welded, aged, and packaged according to the tubular semiconductor gas sensing element manufacturing process to obtain the gas sensing element.

[0042] The hierarchical SnO2@MoS2 nanocomposite material obtained by the above preparation method was characterized as shown in Figures 1-3

[0043] ​Figure 1 For X-ray diffraction patterns, all diffraction peaks of SnO2@MoS2nanocomposites are indexed to hexagonal MoS2and tetragonal SnO2, which are consistent with JCPDS 37-1492 and JCPDS 41-1445, respectively. In addition, these diffraction peaks are consistent with those of pure fibers and pure nanosheets. It can be seen that all nanocomposites show characteristic peaks of SnO2with tetragonal rutile structure, which are consistent with the peak intensity of pure SnO2NFs, and no other impurity diffraction peaks are observed, indicating that the product has high purity. By Figure 2 SEM images and Figure 3 TEM characterization images can clearly see that the aspect ratio of SnO2NFs is large, with a diameter of about 222 nm. Moreover, these nanofibers are very uniform and the surface is relatively rough, which is conducive to the growth of nanosheets. In addition, pure MoS2nanosheets will self-assemble into flower shapes, which is also conducive to nucleation and growth on nanofibers. After further hydrothermal treatment, MoS2nanosheets grow uniformly on the surface of SnO2NFs, which strongly proves the successful preparation of hierarchical SnO2@MoS2nanocomposites.

[0044] The gas sensitive element obtained by the above preparation method was subjected to gas sensitive performance test, and the gas sensitive performance test was carried out on CGS-8 gas sensitive element test system by static gas distribution method, and the results are shown in Figures 4-6

[0045] Figure 4 The figure shows the optimal working temperature of hierarchical SnO2@MoS2heterostructure material for 100ppm xylene gas, and from the figure it can be seen that the optimal temperature is 220℃. Figure 5 The figure shows the selectivity of hierarchical SnO2@MoS2heterostructure material to 6 different gases, and it has good selectivity to xylene gas. Figure 6 The figure shows the continuous response and recovery of hierarchical SnO2@MoS2core-shell heterostructure material to different concentrations of xylene gas, and from the figure it can be seen that the gas sensitive element has good linear relationship to different concentrations of xylene.

[0046] Example 2

[0047] The hierarchical SnO2@MoS2nanocomposite was prepared, and the specific steps were as follows:

[0048] (1) The same as example 1.

[0049] (2) The same as example 1.

[0050] (3) 0.1 mmol (NH4)6Mo7O 24 ​• 4H2O and 6.1 mmol CH4N2S were dissolved in a beaker with 40 mL of deionized water under vigorous stirring. After stirring for 10 min, the mixture solution was transferred into a 50 mL stainless steel sealed autoclave with a polytetrafluoroethylene liner, and then 80 mg of pretreated SnO2nanofibers were added into the above solution and heated at 210 °C in a high-temperature drying oven for 12 h. After the heating was completed, the black precipitate was collected by centrifugation after cooling to room temperature and pouring out the supernatant, and then washed repeatedly with water and ethanol for several times. Finally, the sample was dried in a 60 °C drying oven overnight to obtain the final sample, which was named as SnO2@MoS2.

[0051] The specific steps for preparing the gas sensor from the above three-dimensional SnO2 / Co3O4core-shell nanocomposite are the same as those in Example 1.

[0052] Example 3

[0053] The specific steps for preparing the hierarchical SnO2@MoS2nanocomposite are as follows:

[0054] (1) The same as in Example 1.

[0055] (2) The same as in Example 1.

[0056] (3) 0.2 mmol (NH4)6Mo7O 24 • 4H2O and 6.1 mmol CH4N2S were dissolved in a beaker with 40 mL of deionized water under vigorous stirring. After stirring for 10 min, the mixture solution was transferred into a 50 mL stainless steel sealed autoclave with a polytetrafluoroethylene liner, and then 80 mg of pretreated SnO2nanofibers were added into the above solution and heated at 210 °C in a high-temperature drying oven for 12 h. After the heating was completed, the black precipitate was collected by centrifugation after cooling to room temperature and pouring out the supernatant, and then washed repeatedly with water and ethanol for several times. Finally, the sample was dried in a 60 °C drying oven overnight to obtain the final sample, which was named as SnO2@MoS2.

[0057] The specific steps for preparing the gas sensor from the above hierarchical SnO2@MoS2core-shell nanocomposite are the same as those in Example 1.

[0058] The above examples are the preferred embodiments of the present application, but the embodiments of the present application are not limited by the above examples, and any changes, modifications, substitutions, combinations, simplifications made without departing from the spirit and principles of the present application shall be equivalent replacement methods, which are all included in the protection scope of the present application.

Claims

1. A xylene gas-sensitive element based on a three-dimensional hierarchical SnO2@MoS2 nanocomposite material, characterized in that, It includes SnO2@MoS2 nanocomposite materials, and also includes semiconductor gas-sensitive elements made using semiconductor tubular, flat, and micro-hot plate electrodes; The three-dimensional hierarchical SnO2@MoS2 nanocomposite material is composed of a SnO2 nanofiber skeleton and a uniform array of MoS2 nanosheets assembled and grown on its surface. The SnO2 nanofiber skeleton has a uniform morphology and a rough surface, with a diameter of 210-230 nm; the MoS2 nanosheets self-assemble into flower shapes, with a highly ordered array and a sheet thickness of 140-150 nm; the outer diameter of the SnO2@MoS2 composite material is 240-260 nm. The preparation method of the SnO2@MoS2 nanocomposite material includes the following steps: S1: Under stirring at 800-1000 rpm, 1.2 g PVP was slowly added to a beaker containing 8 mL of ethanol and stirred until homogeneous to obtain solution 1; simultaneously, under stirring at 800-1000 rpm, 0.15 g / mL SnCl2·2H2O was added to N,N-dimethylformamide and stirred until homogeneous to obtain solution 2. Solutions 1 and 2 were mixed and magnetically stirred to form a homogeneous viscous transparent solution; the viscous transparent solution was electrospun and collected to obtain a spinning precursor, which was then calcined to obtain SnO2 nanofibers; S2: Add 0.2 mmol (NH4)6Mo7O 24 • 4H2O and 6.1 mmol CH4N2S were dissolved in a beaker containing 40 mL of deionized water under vigorous stirring to prepare a solution. The solution was then placed in a container, and SnO2 nanofibers from S1 were added to the container. The solution was soaked in the container overnight at room temperature, and then dried in a drying oven to collect the sample. S3: First add 0.2 mmol (NH4)6Mo7O 24 • 4H2O and 6.1 mmol CH4N2S were dissolved in deionized water under vigorous stirring. After stirring for 10 minutes, a mixed solution was obtained. The mixed solution was then transferred to a sealed autoclave with a polytetrafluoroethylene substrate. Finally, the sample from S2 was added to the sealed autoclave and heated at 210 °C for 12 h. After heating, the mixture was cooled to room temperature and the supernatant was poured off. The black precipitate was collected by centrifugation, washed, dried, and dried overnight in a drying oven at 60 °C to obtain SnO2@MoS2 nanocomposite material. The electrospinning process described in S1 is as follows: the relative humidity of the environment is 10% to 50%, the voltage between the collecting plate and the syringe needle tip is 18 kV, and the distance between the collecting plate and the syringe needle tip is 20 cm. The calcination process of the spinning precursor described in S1 is as follows: the temperature is raised to 600℃ at a heating rate of 1-3℃ / min and then held for 5 hours.

2. The xylene gas-sensitive element according to claim 1, characterized in that, The gas-sensitive element is a tubular semiconductor gas-sensitive element, which is prepared by mixing the graded SnO2@MoS2 nanocomposite material and ethanol in a certain proportion to form a paste, uniformly coating it on the surface of a ceramic tube, adding heating wires in sequence, welding, aging, and encapsulating to obtain the tubular semiconductor gas-sensitive element.

3. The xylene gas-sensitive element according to any one of claims 1 or 2, characterized in that, The technical specifications of the gas-sensitive element include: The operating temperature is 160–260℃; The detection sensitivity R of the element to 100 ppm xylene g / R a It is 23.5; The response time is 21.5s, and the recovery time is 60.4s. The sensitivity to 100 ppm xylene is higher than that to any one of 100 ppm ammonia, acetone, ethanol, methanol and formaldehyde.

4. The application of the xylene gas-sensitive element as described in any one of claims 1 to 3 in the detection of xylene gas, characterized in that, The gas-sensitive element has a detection limit of 0.5 ppm for xylene gas concentration.

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