SnSe / In2O3 nano composite material and gas sensor based on SnSe / In2O3 nano composite material

Abstract

The invention discloses a SnSe / In2O3 nano composite material and a gas sensor based on the SnSe / In2O3 nano composite material. A two-dimensional material SnSe and a metal oxide In2O3 are combined through a chemical vapor deposition and spin coating method and are used for a NO2 gas sensor. The sensor disclosed by the invention has a relatively high response value and a relatively low detection limit to 1ppm of NO2 at room temperature, and has relatively good moisture resistance and stability, so that a new scheme and path are provided for the NO2 gas sensor in the aspects of crop growth monitoring and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of composite material preparation, and particularly relates to an SnSe / In2O3 nanocomposite material and its application in a gas sensor. Background Art

[0002] There may be several nitrogen oxides in the atmosphere, including NO2, NO, N2O, and N2O3. Plants absorb gaseous NO2 faster, and NO2 is more toxic than other NO x and has a more toxic effect. NO2 deposits in plants or indirectly affects through chemical reactions in the atmosphere. For example, it dissolves in cells to produce nitrite ions and nitrate ions, acidifying the cells and causing large, irregular brown or black spots on the leaves. Moreover, high concentrations of NO2 can cause obvious damage to most crops, reducing the plant's resistance to pests and diseases, thereby affecting the yield and quality of crops.

[0003] Among these sensing materials for manufacturing semiconductor gas sensors, metal oxides such as zinc oxide (ZnO), indium oxide (In2O3), tin oxide (SnO2), and tungsten oxide (WO3) have proven to be the best candidate materials for manufacturing resistive gas sensors due to their advantages of simple manufacturing, low cost, easy portability, and high sensitivity. However, high working temperature, high power consumption, and low selectivity limit their rapid development. Among two-dimensional (2D) nanomaterials, graphene, transition metal sulfides, layered metal oxides, black phosphorus, etc., due to their unique single-atom layer structure, high specific surface area, and many surface active sites, show great potential in gas sensors. And 2D material gas sensors have the advantages of high sensitivity, fast response speed, low energy consumption, and can work at room temperature. However, since 2D nanomaterials often form a dense stacked structure during the formation of the conductive network, it is not conducive to the full contact between the thin flakes inside the conductive network and gas molecules, resulting in relatively low sensitivity and response recovery speed at room temperature. However, combining metal oxides with 2D nanomaterials to construct heterostructures can combine the advantages of each other and overcome their respective deficiencies, thereby improving the sensing performance of the prepared gas sensor.

[0004] Therefore, developing a nitrogen dioxide gas sensor with high responsiveness, low detection limit, and high selectivity for rapid detection of NO2 for agriculture is one of the important measures to improve crop yields. In addition, the gas sensor based on the SnSe / In2O3 heterojunction also has good moisture resistance and can be used in greenhouse environments to provide good environmental monitoring for studying crop growth. Summary of the Invention

[0005] The object of the present invention is to provide a preparation method of SnSe / In2O3 nanocomposite and its application in a gas sensor, so as to solve the disadvantages of high operating temperature, poor selectivity and stability existing in the prior art for nitrogen dioxide gas sensors based on simple oxides.

[0006] To achieve the object, the present invention adopts the following technical solutions:

[0007] The present invention first discloses a preparation method of SnSe / In2O3 nanocomposite, including the following steps:

[0008] Step 1: Prepare SnSe thin film by chemical vapor deposition method using Sn powder and Se powder as precursors.

[0009] Step 2: Coat the dispersion of In2O3 nanosheets on the surface of the SnSe thin film to obtain SnSe / In2O3 nanocomposite.

[0010] Further, the specific method of step 1 is: Place the Sn powder at the heating center position of the tubular furnace, place the Se powder upstream of the Sn powder, place the mica substrate downstream of the Sn powder, heat up to 800 - 900 °C in an argon atmosphere, keep warm for 10 - 20 min, and then cool naturally to obtain the SnSe thin film.

[0011] Preferably: The Se powder is placed 25 - 30 cm upstream of the Sn powder, and the mica substrate is placed 16 - 18 cm downstream of the Sn powder; during the heating-up, heat preservation and cooling processes, the argon flow rate is 60 - 80 sccm, and the furnace pressure is 70 - 80 Pa.

[0012] Preferably, the mass ratio of Sn powder to Se powder is 0.8 - 1:1.

[0013] Further, the specific method of step 2 is: Disperse the In2O3 nanosheets in absolute ethanol, and then use a pipette to drop this dispersion on the SnSe thin film to obtain SnSe / In2O3 nanocomposite.

[0014] The present invention also discloses the application of the SnSe / In2O3 nanocomposite prepared according to the above preparation method in a gas sensor. This gas sensor uses the SnSe / In2O3 nanocomposite as a gas-sensitive material to realize the detection of nitrogen dioxide gas at room temperature.

[0015] Compared with the prior art, the beneficial effect of the present invention is to obtain a sensor with good stability, selectivity and moisture resistance and capable of detecting low-concentration nitrogen dioxide gas at room temperature, specifically reflected in:

[0016] (1) The present invention first synthesizes a SnSe / In2O3 composite material with a p-n heterostructure by using the methods of CVD and spin coating, and fabricates it into a gas sensor element for the detection of nitrogen dioxide gas. This synthesis method is simple in operation, low in cost, and the prepared nano-composite materials are relatively uniformly combined, with a compact structure and excellent performance.

[0017] (2) Due to the formation of the p-n heterojunction, the performance of the gas sensor based on this composite material is significantly improved.

[0018] (3) Aiming at the problems that gas sensors based on metal oxides require a relatively high operating temperature to provide sufficient performance and gas sensors based on two-dimensional materials have a low response, the present invention adopts a gas sensor based on the heterojunction of metal oxides and two-dimensional materials, providing new materials and new methods for room-temperature nitrogen dioxide gas sensors, and having great potential in developing room-temperature detection of low-concentration nitrogen dioxide gas.

[0019] (4) For the research on the growth of greenhouse crops, the sensor of the present invention has the performance of moisture resistance and can effectively detect NO2 gas in the greenhouse, providing good conditions for the growth of crops. Description of the Drawings

[0020] Figure 1 It is a schematic diagram of the preparation method of the SnSe / In2O3 nano-composite material and the gas sensor based on it in the embodiment of the present invention.

[0021] Figure 2 It is the structural characterization of the SnSe / In2O3 nano-composite material in Example 1 of the present invention, where: (a) is the Raman spectrum analysis diagram of SnSe, In2O3 and the SnSe / In2O3 heterojunction; (b) is the X-ray diffraction analysis diagram of the SnSe / In2O3 heterojunction.

[0022] Figure 3 It is a schematic diagram of the device of the gas sensor based on the SnSe / In2O3 heterostructure in Example 1 of the present invention.

[0023] Figure 4 It is the gas-sensing performance analysis of the gas sensor based on the SnSe / In2O3 heterostructure in Example 1 of the present invention, where: (a) is the response of the gas sensor based on SnSe to 100 ppm NO2 at room temperature, the response of the gas sensor based on In2O3 to 1 ppm NO2 at 100 °C, and the response diagram of the gas sensor based on SnSe / In2O3 to 1 ppm NO2 at room temperature; (b) is the response and recovery time diagram of the gas sensor based on the SnSe / In2O3 heterojunction to 1 ppm NO2 at room temperature.

[0024] Figure 5 Response performance analysis of the gas sensor based on the SnSe / In2O3 heterostructure in Example 1 of the present invention, where: (a) is the dynamic response graph of 100 ppb - 1 ppm NO2 at room temperature; (b) is the room temperature dynamic gas response graph of 1 ppm NO2.

[0025] Figure 6 Gas sensing performance analysis of the gas sensor based on the SnSe / In2O3 heterostructure in Example 1 of the present invention, where: (a) is the selectivity schematic diagram for different gases at room temperature; (b) is the long-term stability test for 1 ppm NO2 at room temperature.

[0026] Figure 7 Gas sensing performance analysis of the gas sensor based on the SnSe / In2O3 heterostructure in Example 1 of the present invention, where: (a) is the detection limit test curve graph; (b) is the humidity performance test for 1 ppm NO2 at room temperature. Detailed implementation manners

[0027] In order to more clearly elaborate the purpose, features and advantages of the present invention, the synthesis method of the SnSe / In2O3 nanocomposite material in the present invention and the manufacture and gas sensing test of the gas sensor based on this material will be described in detail below with reference to the drawings and implementation cases. The following content is only an example and explanation of the innovative idea of the present invention. Any professional in the technical field makes various forms of modifications, supplements or adopts similar alternative solutions to the specific implementation manners described, as long as it does not deviate from the innovative idea or exceed the boundaries defined by the claims of this patent, it should be regarded as the protection scope of this innovation.

[0028] Example 1

[0029] As Figure 1 shown, the SnSe / In2O3 nanocomposite material is prepared according to the following steps in this example:

[0030] 1. Preparation of SnSe thin film

[0031] The experiment was carried out in a tube furnace equipped with a quartz tube (diameter 26 mm), and this tube furnace includes three heating zones. 50 mg of Sn powder (99.9%, Macklin) was loaded into an alumina boat and placed at the center of the second heating zone. Another alumina boat filled with 50 mg of Se powder (>99%, Macklin) was placed about 28 cm upstream of the Sn powder (calculated by the distance between the centers of the two alumina boats), and the alumina boat equipped with a mica substrate was placed about -16 cm downstream of the Sn powder (calculated by the distance between the centers of the two alumina boats).

[0032] Before growth, the tubular furnace was flushed with Ar gas: the quartz tube was evacuated to ~0.6 Torr, then filled with argon gas (Ar, purity 99.995%) to ambient pressure, and then evacuated to ~0.6 Torr again. This process was repeated 3 times.

[0033] After flushing, the Ar gas flow rate was controlled at 80 sccm and the furnace pressure was 80 Pa: heated to 800 °C at a rate of 10 °C / min, held for growth for 20 min, and after natural cooling, a SnSe thin film was obtained.

[0034] 2. Preparation of SnSe / In2O3 heterojunction

[0035] The In2O3 nanosheets were added to anhydrous ethanol to obtain a dispersion. Then, this dispersion was dropped onto a partial area of the SnSe thin film surface using a pipette, and a heterojunction was formed between SnSe and In2O3, thereby obtaining a SnSe / In2O3 nanocomposite.

[0036] Figure 2 For the SnSe / In2O3 nanocomposite obtained in this example, the Raman spectrum ( Figure 2 (a) therein) and the X-ray diffraction pattern ( Figure 2 (b) therein). As Figure 2 (a) shows, the Raman spectrum characterized the structures of SnSe, In2O3, and SnSe / In2O3. The analysis indicated that both SnSe and In2O3 formed good crystal structures, and the characteristic peaks of SnSe / In2O3 hardly shifted compared with the Raman peaks of single SnSe and In2O3, which demonstrated that the crystal structure remained unchanged after the formation of the SnSe / In2O3 heterojunction. Figure 2 In (b), corresponding diffraction peaks appeared for SnSe / In2O3 through X-ray diffraction analysis.

[0037] 3. Fabrication of gas sensors

[0038] Using the thermal evaporation method, a gold electrode (thickness 50 nm) was set in each of the separate SnSe region and the region coated with In2O3 of the SnSe / In2O3 heterojunction to construct a gas sensor as shown in Figure 3 .

[0039] For comparison, this example also constructed a gas sensor based on a single SnSe thin film (directly evaporating two gold electrodes on the SnSe thin film prepared in step 1) and a gas sensor based on a single In2O3 thin film (directly dropping the dispersion of In2O3 nanosheets onto the surface of a mica substrate to form an In2O3 thin film, and then evaporating two gold electrodes thereon).

[0040] 4. Gas sensing performance testing

[0041] The gas-sensing performance was tested using a multi-channel dynamic gas detector. The dynamic gas distribution system is equipped with five mass flow meters with different ranges. Using high-purity dry air as the background gas, different concentrations of gas mixtures can be achieved by automatically adjusting the flow ratio of each gas path. Then, the Keithley 2612B source meter is used to collect the resistance changes of the gas-sensing element in the test chamber in real time. The response of the tested sensor is defined as S = R g / R a , where R a and R g are the room temperature resistances of the gas sensor exposed to high-purity dry air and the target gas, respectively. The response time / recovery time is the time consumed for the sensor to change 90% of the total resistance from the initial / saturated state during the response / recovery process. When testing the gas-sensing performance, the target gas is dry gas at room temperature of 25 ± 2 °C.

[0042] The gas-sensing performance test results of the SnSe / In2O3 nanocomposite obtained in this example are as Figures 4 to 7 shown, where:

[0043] Figure 4 (a) in is the response of the SnSe-based gas sensor to 100 ppm NO2 at room temperature, the response of the In2O3-based gas sensor to 1 ppm NO2 at 100 °C, and the response diagram of the SnSe / In2O3-based gas sensor to 1 ppm NO2 at room temperature. It can be seen from the figure that the response of the SnSe-based gas sensor to 100 ppm NO2 at room temperature is 1.6, the response of the In2O3-based gas sensor to 1 ppm NO2 at 100 °C is 10.3, while the response of the SnSe / In2O3-based gas sensor to 1 ppm NO2 at room temperature is 17.33, which is much higher than the response of single materials to NO2

[0044] Figure 4 (b) in is the response and recovery time diagram of the SnSe / In2O3 heterojunction-based gas sensor to 1 ppm NO2 at room temperature. It can be seen from the figure that the SnSe / In2O3 heterojunction-based gas sensor has a fast response to 1 ppm NO2 at room temperature, only 72 s.

[0045] Figure 5 (a) in is the dynamic response diagram of the SnSe / In2O3 heterojunction-based gas sensor to 100 ppb - 1 ppm NO2 at room temperature. It can be seen from the figure that the response of the SnSe / In2O3 heterojunction-based gas sensor to NO2 at room temperature increases with the increase of concentration, and it still has a good response to ppb-level NO2.

[0046] Figure 5 In (b), it is the room-temperature dynamic gas response graph of the gas sensor based on the SnSe / In2O3 heterojunction to 1 ppm NO2. It can be seen from the graph that the gas sensor based on the SnSe / In2O3 heterojunction still maintains good response and recovery characteristics in five cyclic tests, indicating that the gas sensor has good repeatability.

[0047] Figure 6 In (a), it is the selectivity test graph of the gas sensor based on the SnSe / In2O3 heterojunction. At room temperature, 100 ppm of H2, NH3, C3H6O, C2H5OH, and 1 ppm of NO2 are tested. It can be seen from the graph that the response of the gas sensor based on the SnSe / In2O3 heterojunction to NO2 is much higher than that of other gases, indicating that this sensor has good selectivity to NO2 gas.

[0048] Figure 6 In (b), it is the long-term stability test graph of the gas sensor based on the SnSe / In2O3 heterojunction. The sensor is tested once every week, and it is found that its response value fluctuates very little, indicating that the sensor has good stability.

[0049] Figure 7 In (a), it is the detection limit test curve graph of the gas sensor based on the SnSe / In2O3 heterojunction. It can be seen from the graph that the relationship between the response of the gas sensor based on the SnSe / In2O3 heterojunction to NO2 and the gas concentration can be fitted to a linear function. According to the linear fitting result, the lower detection limit of the sensor can be obtained as 19.8 ppb.

[0050] Figure 7 In (b), it is the humidity performance test of the gas sensor based on the SnSe / In2O3 heterojunction to 1 ppm NO2 at room temperature. It can be seen from the graph that at different humidities, the response of the gas sensor based on the SnSe / In2O3 heterojunction to 1 ppm NO2 fluctuates very little, and it can be concluded that this sensor has good moisture resistance.

[0051] Therefore, the gas sensor based on the SnSe / In2O3 heterojunction has a response value of 17.33 to 1 ppm of NO2 at room temperature, a response time of only 72 s, good dynamic response, good repeatability, a low detection limit (19.8 ppb), and excellent moisture resistance.

[0052] As can be seen from the above, the SnSe / In2O3 gas sensor is known for its excellent responsiveness, low detection limit, and remarkable moisture resistance. For low-concentration nitrogen dioxide at room temperature, it also exhibits fast response and recovery performance. These characteristics demonstrate the great potential of the SnSe / In2O3 composite heterojunction material in the development of gas detection for low-concentration nitrogen dioxide at room temperature.

[0053] The above-described content is merely a preferred embodiment of the present invention and does not mean a limitation to the present invention. Without departing from the spirit and principle of the present invention, those skilled in the art can make various modifications and improvements to the present invention, and these modifications and improvements should be included in the protection scope of the present invention.

Claims

1. A preparation method of SnSe / In2O3 nanocomposite, characterized in that, It includes the following steps: Step 1: Prepare a SnSe thin film by chemical vapor deposition method using Sn powder and Se powder as precursors; Step 2: Coat the dispersion of In2O3 nanosheets on the surface of the SnSe thin film to obtain the SnSe / In2O3 nanocomposite.

2. The preparation method of the SnSe / In2O3 nanocomposite according to claim 1, characterized in that, The specific method of Step 1 is: Place the Sn powder at the heating center position of the tube furnace, place the Se powder upstream of the Sn powder, and place the mica substrate downstream of the Sn powder. Heat to 800 - 900 °C in an argon atmosphere, keep the temperature for growth for 10 - 20 min, and then cool naturally to obtain the SnSe thin film.

3. The preparation method of the SnSe / In2O3 nanocomposite according to claim 2, characterized in that: The Se powder is placed 25 - 30 cm upstream of the Sn powder, and the mica substrate is placed 16 - 18 cm downstream of the Sn powder; during the heating, temperature-keeping and cooling processes, the argon flow rate is 60 - 80 sccm, and the furnace pressure is 70 - 80 Pa.

4. The preparation method of the SnSe / In2O3 nanocomposite according to claim 2, characterized in that: The mass ratio of Sn powder to Se powder is 0.8 - 1:

1.

5. A SnSe / In2O3 nanocomposite prepared by the preparation method according to any one of claims 1 - 4.

6. An application of the SnSe / In2O3 nanocomposite according to claim 5 in a gas sensor.

7. A gas sensor, characterized in that, The gas sensor uses the SnSe / In2O3 nanocomposite according to claim 5 as the gas-sensitive material.

8. The gas sensor according to claim 7, characterized in that, The gas sensor is used to detect nitrogen dioxide gas at room temperature.

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