Preparation method of SnO2 / SnS2 composite material formaldehyde gas sensor

Abstract

The application relates to a preparation method of a SnO2 / SnS2 composite formaldehyde gas sensor, and relates to a formaldehyde gas sensor preparation method.The preparation process comprises SnO2 preparation and sulfidation treatment, and a subsequent washing and drying step is combined to prepare a SnO2 / SnS2 porous hollow spherical composite structure.The material is a hollow spherical structure, the surface is loose and porous, has a high specific surface area and a large number of active sites; in addition, an n-n heterostructure is formed between the SnO2 hollow sphere and SnS2 nanoparticles, and excellent detection performance is exhibited on formaldehyde gas. The sensor device prepared by the application has the advantages of small size, high sensitivity, high sensitivity on formaldehyde gas at room temperature, good selectivity, long-term stability, and an ultralow detection limit. In addition, the SnO2 / SnS2 hollow sphere composite structure sensor material preparation process is simple and stable, and has a wide application prospect in formaldehyde detection.

Description

Technical Field

[0001] This invention relates to a method for preparing a formaldehyde gas sensor, and more particularly to a method for preparing a formaldehyde gas sensor made of SnO2 / SnS2 composite material. Background Technology

[0002] Formaldehyde (HCHO) is a common volatile organic compound widely used in many aspects of daily life, including medical, textile, and chemical industries. It is also a major indoor air pollutant. Long-term exposure to formaldehyde can cause various diseases, and in severe cases, disability and cancer. According to the World Health Organization's (WHO) "Guidelines for Indoor Air Quality," the maximum safe concentration of formaldehyde for human exposure in indoor air is 8.0 ppb. Real-time and accurate detection of low concentrations of formaldehyde in the air is crucial; therefore, designing gas sensors with excellent sensing performance is essential for early warning detection.

[0003] Metal-oxide-semiconductor (MOS) gas sensors have attracted widespread attention due to their portability, high sensitivity, low manufacturing cost, and stable performance. SnO2, as a typical n-type semiconductor, possesses good thermal stability and high electron mobility, making it a typical low-cost gas-sensitive material. However, SnO2 also suffers from drawbacks such as high operating temperature, low sensitivity, and poor selectivity, hindering the effective detection of formaldehyde at room temperature.

[0004] Therefore, to address the aforementioned issues, performance can be improved through modification, such as doping with noble metals, altering its morphology, or constructing heterojunctions. In recent years, methods to enhance the sensitivity of SnO2 by constructing heterojunctions have been widely applied. Two-dimensional metal sulfides (SnS2, ZnS, WS2, MoS2, etc.) possess advantages such as exposed active sites and low operating temperatures, leading to their widespread use in gas sensors. Among these, SnS2, as an n-type semiconductor gas-sensitive material, exhibits more gas adsorption sites and higher conductivity, making it highly attractive for regulating electron transport characteristics. Therefore, constructing SnO2 / SnS2 composite materials with n-type heterojunctions can help improve the detection sensitivity for formaldehyde. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing a SnO2 / SnS2 composite material formaldehyde gas sensor. This invention uses a sulfidation process to synthesize SnO2 / SnS2 hollow sphere composite material and uses it to detect formaldehyde gas, thereby improving the problems of high operating temperature and poor sensitivity to low concentrations of gas in existing SnO2 gas sensors.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] A method for preparing a formaldehyde gas sensor made of SnO2 / SnS2 composite material, the steps of which are as follows:

[0008] First, SnO2 / SnS2 hollow sphere composite material was prepared, following these steps:

[0009] 1) Weigh out tin chloride pentahydrate (SnCl4·5H2O) and sodium hydroxide (NaOH) and dissolve them in deionized water. Stir magnetically for 30 min at room temperature to ensure complete dissolution and dispersion.

[0010] 2) The obtained transparent solution was transferred into a 50 mL polytetrafluoroethylene-lined stainless steel high-pressure reactor and placed in an oven at 200 °C for 24 hours, and then allowed to cool naturally to room temperature.

[0011] 3) Centrifuge the solution after the reaction to obtain the reaction product, and then wash it repeatedly with deionized water and anhydrous ethanol alternately;

[0012] 4) Place the washed reaction product in a drying oven at a constant temperature and dry it overnight at 60 °C. After drying, cool it to obtain tin dioxide (SnO2).

[0013] 5) Weigh out tin dioxide (SnO2) and dissolve it in a mixed solution of deionized water and glacial acetic acid. Stir magnetically for 30 min at room temperature to ensure complete dissolution and dispersion. This solution is denoted as solution A.

[0014] 6) Weigh out thiourea, dissolve it in deionized water, and stir magnetically for 30 minutes at room temperature to ensure complete dissolution and dispersion. This solution is designated as solution B.

[0015] 7) Mix solution A and solution B and stir magnetically for 30 minutes at room temperature to ensure thorough mixing;

[0016] 8) The obtained solution was transferred into a polytetrafluoroethylene-lined stainless steel high-pressure reactor and placed in an oven at 150°C for 2 hours, and then allowed to cool naturally to room temperature.

[0017] 9) Centrifuge the solution after the reaction to obtain the reaction product, and then wash it repeatedly with deionized water and anhydrous ethanol alternately;

[0018] 10) Place the washed reaction product in a drying oven at a constant temperature and dry it overnight at 60 °C. After drying, cool it to obtain SnO2 / SnS2 hollow sphere composite material.

[0019] 2) Prepare a gas sensor for formaldehyde detection, the steps are as follows:

[0020] (1) Take SnO2 / SnS2 hollow sphere composite material and ethanol solution and grind them thoroughly in an agate mortar. Coat it on the surface of Al2O3 ceramic tube so that it completely covers Al2O3 ceramic tube and gold electrode. Dry it at 80 °C.

[0021] (2) Pass the heating wire through the Al2O3 ceramic tube and weld its two ends to the heating electrode of the base. Then, weld the platinum wire connected to the gold electrode on the surface of the ceramic tube to the measuring electrode of the base to obtain the gas sensor element.

[0022] (3) Place the prepared components on a benchtop gas-sensitive element aging table and age them at 150 °C for 24 hours;

[0023] (4) Use the WS-30A gas sensitivity tester to test the gas sensitivity characteristics of the sensor.

[0024] The method for preparing a formaldehyde gas sensor made of SnO2 / SnS2 composite material, wherein the test temperature for testing the gas sensitivity characteristics of the sensor is from room temperature to 250 °C.

[0025] The advantages and effects of this invention are:

[0026] (1) The present invention prepares SnO2 / SnS2 hollow sphere composite material by hydrothermal method combined with subsequent washing and drying treatment. The raw materials are easy to obtain and the preparation process is simple, making it suitable for large-scale production.

[0027] (2) The unique 3D structure of the SnO2 / SnS2 hollow sphere composite material prepared by this invention can effectively promote gas adsorption and electron transfer, thereby enhancing the gas sensing performance of the material. The nanocomposite material can exhibit good detection performance for formaldehyde gas at room temperature, and also has good reproducibility, high selectivity and good long-term stability.

[0028] (3) The formaldehyde gas sensor based on SnO2 / SnS2 hollow sphere composite material prepared by the present invention has a simple manufacturing process, small size and high sensitivity, and is suitable for industrial mass production. Attached Figure Description

[0029] Figure 1 The XRD pattern of the product;

[0030] Figure 2 Scanning electron microscope (SEM) images of the product prepared in Example 1;

[0031] Figure 3 Scanning electron microscope image of the product prepared in Example 2;

[0032] Figure 4 Scanning electron microscope image of the product prepared in Example 3;

[0033] Figure 5 Scanning electron microscope image of the product prepared in Example 4;

[0034] Figure 6 The dynamic response recovery curves of Examples 1, 2, 3, and 4 to 0.1 ppm formaldehyde at room temperature are shown.

[0035] Figure 7 The following are bar graphs showing the effects of 0.1 ppm formaldehyde on Examples 1, 2, 3, and 4 at room temperature;

[0036] Figure 8 Examples 1, 2, 3, and 4 show the dynamic response recovery curves to 10 ppm formaldehyde at room temperature.

[0037] Figure 9 The bar graphs for Examples 1, 2, 3, and 4 at room temperature against 10 ppm formaldehyde are shown.

[0038] Figure 10 Example 3 shows the dynamic response recovery curve to formaldehyde (0.1-1 ppm) at room temperature;

[0039] Figure 11 The fitted curves for the response of Example 3 to formaldehyde content (0.1-1 ppm) are shown.

[0040] Figure 12 The response curves of Example 3 to formaldehyde content (10-100 ppm) are shown.

[0041] Figure 13 Example 3 shows the dynamic response recovery curves to formaldehyde (10-100 ppm) at room temperature;

[0042] Figure 14 The bar chart shows the response values ​​of Examples 1, 2, 3, and 4 to six different gases (0.1 ppm) at room temperature.

[0043] Figure 15 The bar chart shows the response values ​​of Examples 1, 2, 3, and 4 to six different gases (10 ppm) at room temperature;

[0044] Figure 16 Example 1: Long-term stability test of formaldehyde gas at 0.1 ppm and 10 ppm at room temperature;

[0045] Figure 17 Example 3 is a long-term stability test of formaldehyde gas at 0.1 ppm and 10 ppm at room temperature. Implementation

[0046] The present invention will be further described below with reference to the embodiments shown in the accompanying drawings.

[0047] The preparation method of SnO2 / SnS2 hollow sphere composite material includes the following steps:

[0048] Step 1: Weigh an appropriate amount of tin chloride pentahydrate (SnCl4·5H2O) and an appropriate amount of sodium hydroxide (NaOH) and dissolve them in deionized water. Stir magnetically for 30 minutes at room temperature to ensure complete dissolution and dispersion.

[0049] Step 2: The obtained transparent solution is transferred into a 50 mL stainless steel high-pressure reactor lined with polytetrafluoroethylene and placed in an oven at 200 °C for 24 hours, and then allowed to cool naturally to room temperature.

[0050] Step 3: Centrifuge the solution after the reaction to obtain the reaction product, and then wash it repeatedly with deionized water and anhydrous ethanol alternately.

[0051] Step 4: Place the washed reaction product in a drying oven at a constant temperature and dry it overnight at 60 °C. After drying, cool it to obtain tin dioxide (SnO2).

[0052] Step 5: Weigh an appropriate amount of tin dioxide (SnO2) and dissolve it in a mixed solution of deionized water and glacial acetic acid. Stir magnetically for 30 minutes at room temperature to ensure complete dissolution and dispersion. This solution is referred to as solution A.

[0053] Step 6: Weigh an appropriate amount of thiourea, dissolve it in 20 mL of deionized water, and stir magnetically for 30 min at room temperature to ensure complete dissolution and dispersion. This solution is designated as solution B.

[0054] Step 7: Mix solution A and solution B and stir magnetically for 30 minutes at room temperature to ensure thorough mixing;

[0055] Step 8: The obtained solution is transferred into a 50 mL polytetrafluoroethylene-lined stainless steel high-pressure reactor and placed in an oven at 150 °C for 2 hours, and then allowed to cool naturally to room temperature.

[0056] Step 9: Centrifuge the solution after the reaction to obtain the reaction product, and then wash it repeatedly with deionized water and anhydrous ethanol alternately.

[0057] Step 10: Place the washed reaction product in a drying oven at a constant temperature and dry it overnight at 60 °C. After drying, cool it to obtain the SnO2 / SnS2 hollow spherical composite material.

[0058] The steps of this invention for preparing a gas sensor using a hollow spherical nanocomposite material of SnO2 / SnS2 are as follows:

[0059] Step 1: Take a certain amount of SnO2 / SnS2 composite material and a small amount of ethanol solution and grind it thoroughly in an agate mortar. Coat it on the surface of the Al2O3 ceramic tube so that it completely covers the Al2O3 ceramic tube and the gold electrode. Dry it at 80 °C.

[0060] Step 2: Pass the heating wire through the Al2O3 ceramic tube and weld its two ends to the heating electrode of the base. Then, weld the platinum wire connected to the gold electrode on the surface of the ceramic tube to the measuring electrode of the base to obtain the gas sensor element.

[0061] Step 3: Place the prepared components on a benchtop gas-sensitive element aging table and age at 150 °C for 24 hours;

[0062] Step 4: Use the WS-30A gas sensitivity tester to test the gas sensitivity characteristics of the sensor. The test temperature is room temperature - 250 °C. Example 1

[0063] Preparation of SnO2 hollow sphere materials

[0064] Step 1: Weigh out an appropriate amount of 1.73 g of tin chloride pentahydrate (SnCl4·5H2O) and 1.25 g of sodium hydroxide (NaOH) and dissolve them in deionized water. Stir magnetically for 30 min at room temperature to ensure complete dissolution and dispersion.

[0065] Step 2: The obtained transparent solution is transferred into a 50 mL stainless steel high-pressure reactor lined with polytetrafluoroethylene and placed in an oven at 200 °C for 24 hours, and then allowed to cool naturally to room temperature.

[0066] Step 3: Centrifuge the solution after the reaction to obtain the reaction product, and then wash it repeatedly with deionized water and anhydrous ethanol alternately.

[0067] Step 4: Place the washed reaction product in a drying oven at a constant temperature and dry it overnight at 60 °C. After drying, cool it to obtain SnO2 hollow spherical material.

[0068] Structural characterization of SnO2 hollow sphere materials

[0069] The crystal structure of the product was characterized using an XRD powder diffractometer (XRD, Shimadzu XRD-600). Figure 1 The XRD pattern of the product shows that its diffraction peaks are consistent with those of the SnO2 standard card PDF#41-1445. The diffraction peaks are sharp and have high intensity, and no other impurity peaks are present, indicating that it has high purity and good crystallinity.

[0070] The morphology of the product was characterized using scanning electron microscopy (FESEM, ZEISS Ultra Plus). Figure 2 As shown in (a)-(b), the pure SnO2 sample in the product exhibits a hollow spherical structure with a loose and porous surface and a diameter of approximately 2-4 μm. Example 2

[0071] (1) Preparation of SnO2 / SnS2 hollow sphere composite material

[0072] Step 1: Weigh an appropriate amount of 0.25 g of tin dioxide (SnO2) and dissolve it in a mixed solution of 18 mL of deionized water and 2 mL of glacial acetic acid. Stir magnetically for 30 min at room temperature to ensure complete dissolution and dispersion. This solution is referred to as solution A.

[0073] Step 2: Weigh an appropriate amount of thiourea (Sn:S=3:1), dissolve it in 20mL of deionized water, and stir magnetically for 30 minutes at room temperature to ensure complete dissolution and dispersion. This solution is referred to as solution B.

[0074] Step 3: Mix solution A and solution B, and stir magnetically for 30 minutes at room temperature to ensure thorough mixing;

[0075] Step 4: The obtained solution is transferred into a 50 mL stainless steel high-pressure reactor lined with polytetrafluoroethylene and placed in an oven at 150 °C for 2 hours, and then allowed to cool naturally to room temperature.

[0076] Step 5: Centrifuge the solution after the reaction to obtain the reaction product, and then wash it repeatedly with deionized water and anhydrous ethanol alternately.

[0077] Step 6: Place the washed reaction product in a drying oven at a constant temperature and dry it overnight at 60 °C. After drying, cool it to obtain the SnO2 / SnS2 hollow sphere composite material.

[0078] (2) Structural characterization of SnO2 / SnS2 hollow sphere composite material

[0079] The crystal structure of the product was characterized using an XRD powder diffractometer (Shimadzu XRD-6100). The XRD pattern of the hollow spherical SnO2 / SnS2 structure showed that the small diffraction peaks near 28.2, 32.1, and 49.9° corresponded to the (100), (101), and (110) crystal planes of the hexagonal SnS2. The synthesized sample showed no extraneous impurity peaks, indicating good purity and crystallinity.

[0080] The morphology of the product was characterized using scanning electron microscopy (FESEM, ZEISS Ultra Plus). Figure 3As shown, the product retains its hollow spherical structure with almost no significant change in size. However, compared to the pure SnO2 sample, the surface of the nanosheets in the sample with the introduction of SnS2 gradually becomes rougher, which may be due to the formation of SnS2 nanoparticles on the surface of the SnO2 hollow spheres. Example 3

[0081] (1) Preparation of SnO2 / SnS2 hollow sphere composite material

[0082] The steps are the same as in Example 2.

[0083] Step 2: Weigh an appropriate amount of thiourea (Sn:S=3:2), dissolve it in 20 mL of deionized water, and stir magnetically for 30 min at room temperature to ensure complete dissolution and dispersion. This solution is denoted as solution B.

[0084] Steps three, four, and five are the same as in Example 2.

[0085] (2) Structural characterization of SnO2 / SnS2 hollow sphere composite material

[0086] The crystal structure of the product was characterized using an XRD powder diffractometer (XRD, Shimadzu XRD-6100). Figure 1 The XRD pattern of the product shows diffraction peaks that match those on the standard SnS2 card PDF#23-0677.

[0087] The morphology of the product was characterized using scanning electron microscopy (FESEM, ZEISS Ultra Plus). Figure 4 As shown, the product still exhibits a hollow spherical structure with little change in size, and the surface of the nanosheets gradually becomes rougher. Example 4

[0088] (1) SnO2 / SnS2 hollow spherical nanocomposite material

[0089] The steps are the same as in Example 2.

[0090] Step 2: Weigh an appropriate amount of thiourea (Sn:S=3:5), dissolve it in 20 mL of deionized water, and stir magnetically for 30 min at room temperature to ensure complete dissolution and dispersion. This solution is denoted as solution B.

[0091] Steps three, four, and five are the same as in Example 2.

[0092] (2) Structural characterization of SnO2 / SnS2 hollow sphere composite material

[0093] The crystal structure of the product was characterized using an XRD powder diffractometer (XRD, Shimadzu XRD-6100). Figure 1The XRD pattern of the product shows that the diffraction peaks of SnO2 are slightly enhanced, while the diffraction peaks of SnS2 disappear. The peaks are sharp and there are no impurity peaks.

[0094] The morphology of the product was characterized using scanning electron microscopy (FESEM, ZEISS Ultra Plus). Figure 5 As shown, the product still exhibits a hollow spherical structure, but the surface roughness of the nanosheets increases and the edges become smoother, while the pores become larger.

[0095] A gas sensor was fabricated using the prepared SnO2 / SnS2 hollow sphere composite material, and its gas-sensing performance for formaldehyde gas was tested.

[0096] To evaluate the effect of operating temperature on the gas sensor and obtain its optimal operating parameters, the gas-sensing performance of the sample was studied in the range of room temperature to 250°C. Figure 6 The figure shows the dynamic response recovery curves of four gas sensors to 0.1 ppm formaldehyde at room temperature. As can be seen from the figure, Example 1 shows almost no response to 0.1 ppm formaldehyde at room temperature, mainly due to the high operating temperature of SnO2. The other three gas sensors exhibit typical n-type semiconductor characteristics after the introduction of formaldehyde at room temperature. This demonstrates that the gas-sensing performance of the gas sensors changes with the sulfur content. Figure 7 The response values ​​of four gas sensors to 0.1 ppm formaldehyde at room temperature are shown. The study found that, except for Example 1, the other three examples exhibited good sensing performance. Figure 8-9 The dynamic response recovery curves and response value histograms of four gas sensors at room temperature for 10 ppm formaldehyde are shown. It can be seen that Example 1 still shows no response, while Example 3 still has a maximum response value of 17.51. Example 3 exhibits the best performance in response to formaldehyde at room temperature, while Example 4 responds to 0.1 ppm formaldehyde at room temperature. We know that Example 1 has almost no response to formaldehyde at room temperature, and Example 3 shows the best response. Figure 10 The figure shows the dynamic response recovery curves of Example 3 at room temperature for low concentrations of formaldehyde (0.1-1 ppm). As can be seen from the figure, when Example 3 is exposed to formaldehyde, the resistance drops rapidly. Upon exposure to air, the resistance gradually increases again, almost recovering to the initial resistance value, which is entirely consistent with the characteristics of an n-type semiconductor gas sensor. With increasing formaldehyde concentration, the sensitivity gradually increases from 1.93 (0.1 ppm) to 9.11 (1 ppm). Figure 11-12The figures show the dynamic response recovery curves for high concentrations of formaldehyde (10-100 ppm) at room temperature and the response to high concentrations of formaldehyde at room temperature in Example 3. As can be seen from the figures, the gas sensor exhibits no significant response hysteresis during repeated exposure cycles, demonstrating good repeatability. The response value of the gas sensor increases rapidly with increasing formaldehyde concentration. When the formaldehyde concentration exceeds 10 ppm, the increase in response value slows down, and the sensitivity increases slowly from 17.51 ​​(10 ppm) to 54.04 (100 ppm), indicating that the gas sensor gradually approaches saturation with increasing formaldehyde concentration. Figure 13-14 This is a stereoscopic diagram showing the response values ​​of the four gas sensors of the embodiments to six different gases at temperatures of 0.1 ppm and 10 ppm formaldehyde, ethanol, ammonia, methanol, TMA, and acetone. It can be seen that the four gas sensors have almost no response to gases other than formaldehyde, while Example 3 shows the best response to 0.1 ppm and 10 ppm formaldehyde at room temperature, indicating the sensor's excellent formaldehyde selectivity. To examine the long-term stability of the performance of the two formaldehyde gas sensors of Examples 1 and 3, the responses of the two gas sensors to 0.1 ppm and 10 ppm formaldehyde at room temperature were recorded periodically. Figure 15-16 As can be seen, the response to formaldehyde hardly decreased, indicating that the sensor has good long-term stability against formaldehyde at room temperature.

Claims

1. A method for preparing a SnO2 / SnS2 composite material formaldehyde gas sensor, characterized in that, The preparation method comprises the following steps: First, SnO2 / SnS2 hollow sphere composite material is prepared, and the steps are as follows: 1) SnCl4.5H2O and NaOH are weighed and dissolved in deionized water, and magnetically stirred at room temperature for 30 min to make them completely dissolved and dispersed; 2) The obtained transparent solution is transferred into a 50 mL polytetrafluoroethylene-lined stainless steel high-pressure reaction kettle, and placed in an oven at 200 °C for 24 hours, and then naturally cooled to room temperature; 3) The reaction solution is centrifuged to obtain the reaction product, which is then washed repeatedly with deionized water and anhydrous ethanol alternately; 4) The washed reaction product is placed in a constant-temperature drying box and dried at 60 °C overnight, and then cooled after drying to obtain SnO2; 5) SnO2 is weighed and dissolved in a mixed solution of deionized water and glacial acetic acid, and magnetically stirred at room temperature for 30 min to make it completely dissolved and dispersed, which is recorded as solution A; 6) Thiourea is weighed and dissolved in deionized water, and magnetically stirred at room temperature for 30 min to make it completely dissolved and dispersed, which is recorded as solution B; 7) Solution A and solution B are mixed and magnetically stirred at room temperature for 30 min to make them completely mixed; 8) The obtained solution is transferred into a polytetrafluoroethylene-lined stainless steel high-pressure reaction kettle, and placed in an oven at 150 °C for 2 hours, and then naturally cooled to room temperature; 9) The reaction solution is centrifuged to obtain the reaction product, which is then washed repeatedly with deionized water and anhydrous ethanol alternately; 10) The washed reaction product is placed in a constant-temperature drying box and dried at 60 °C overnight, and then cooled after drying to obtain SnO2 / SnS2 hollow sphere composite material; 2) A gas sensor for detecting formaldehyde is prepared, and the steps are as follows: (1) SnO2 / SnS2 hollow sphere composite material and ethanol solution are taken and ground in a agate mortar to coat the surface of an Al2O3 ceramic tube, so that the Al2O3 ceramic tube and gold electrode are completely covered, and the mixture is dried at 80 °C; (2) A heating wire is passed through the Al2O3 ceramic tube and welded at both ends to the heating electrode of the base, and then the platinum wire connected to the gold electrode on the surface of the ceramic tube is welded to the measuring electrode of the base to prepare a gas sensor element; (3) The prepared element is placed on a table-type gas sensitive element aging table and aged at 150 °C for 24 hours; (4) WS-30A gas sensitive tester is used to test the gas sensitive properties of the sensor.

2. The method for preparing a Sn02 / SnS2 composite material formaldehyde gas sensor according to claim 1, characterized in that, The test temperature for testing the gas sensitive properties of the sensor is room temperature to 250 °C.

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