A NO2 room temperature gas sensor based on a Pt-Sn3O4 / SnO2 sensitive material and a preparation method thereof

Abstract

A room-temperature NO2 gas sensor based on Pt-Sn3O4 / SnO2 sensitive material and its fabrication method are disclosed, belonging to the technical field of metal oxide semiconductor gas sensors. The gas sensor consists of an Al2O3 planar ceramic substrate with a heating electrode at the bottom and a pair of interdigitated gold electrodes on the upper surface, and a Pt-Sn3O4 / SnO2 sensitive material coated on the gold electrodes and the ceramic substrate. This invention uses a simple hydrothermal and impregnation method, utilizing stannous chloride dihydrate, trisodium citrate dihydrate, and sodium hydroxide as precursors, to hydrothermally and calcinate and synthesize the Sn3O4 / SnO2 composite material. Platinum-supported Sn3O4 / SnO2 sensitive material is then prepared using the impregnation method. This sensor exhibits excellent selectivity and high sensitivity (78–1 ppm) for NO2 gas at room temperature (30°C). The device of this invention has a simple fabrication process, small size, and is suitable for mass production.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor metal oxide gas sensor technology, specifically relating to a NO2 room temperature gas sensor based on Pt-Sn3O4 / SnO2 sensitive material and its preparation method. Background Technology

[0002] Nitrogen dioxide (NO2), primarily produced by vehicle exhaust emissions in urban areas, is one of the most harmful air pollutants and a major contributor to acid rain, smog, and ozone formation. Furthermore, NO2 has a significant impact on human health; inhalation can lead to lung inflammation, eye burns, and difficulty breathing. In China's ambient air quality standards (GB3095-2012), the annual, daily, and hourly safe concentration limits for NO2 are approximately 21.2 ppb, 42.4 ppb, and 106.0 ppb, respectively. Therefore, to better monitor ambient air quality and protect human health, it is necessary to develop high-performance NO2 gas sensors.

[0003] Among the many types of gas sensors, resistive gas sensors using semiconductor metal oxides as the sensing material have advantages such as low cost, simple manufacturing process, good stability and high sensitivity, and are currently one of the most widely used gas sensors.

[0004] Tin dioxide (SnO2) is a typical N-type semiconductor gas-sensitive material, widely used for detecting toxic and harmful gases. In recent years, the gas-sensitive properties of other tin oxides (such as SnO, Sn2O3, and Sn3O4) have also been reported. Among them, Sn3O4 has attracted much attention due to its unique gas-sensitive properties, as its surface possesses lone pairs of electrons, which are active sites for oxidizing gases. Therefore, Sn3O4 is also a potential sensitive material for oxidizing gases.

[0005] Metal oxide gas sensors primarily enhance their sensitivity through methods such as heterojunction construction, metal ion doping, and noble metal loading. For different types of tin oxide, due to their different band structures, heterojunctions can be constructed to achieve better performance. Surface loading with noble metals (Au, Ag, Pt, Pd, etc.) increases the active sites on the material surface due to chemical and electronic sensitization mechanisms, further improving the material's gas-sensitizing performance. Therefore, to prepare a high-performance NO2 gas sensor, this invention utilizes a simple hydrothermal and impregnation method to obtain a Pt-Sn3O4 / SnO2 sensitive material, and confirms that this material exhibits high response (78–1 ppm) and good selectivity to low concentrations of NO2 at room temperature (30°C). Summary of the Invention

[0006] The purpose of this invention is to provide an NO2 gas sensor based on Pt-Sn3O4 / SnO2 sensitive material and its preparation method.

[0007] This invention utilizes a simple hydrothermal and impregnation method to hydrothermally synthesize Sn3O4 sensing materials using stannous chloride dihydrate, trisodium citrate dihydrate, and sodium hydroxide. Sn3O4 / SnO2 composite materials are obtained through sintering, and platinum-supported Sn3O4 / SnO2 sensing materials are prepared using the impregnation method. Using Pt-Sn3O4 / SnO2 as the sensing material provides a heterogeneous structure and, more importantly, the noble metal support, offers more reactive sites, improving the detection of target gases through both electronic and chemical sensitization. Due to the synergistic effect of these two aspects, the reaction efficiency of the gas-sensitive material is significantly improved, thereby enhancing the gas-sensitizing characteristics of the sensor. The commercially available planar chip sensor used in this invention has a simple manufacturing process, small size, and is suitable for mass production in industry, thus possessing significant application value and broad application prospects in detecting NO2 in specific environments.

[0008] The present invention discloses an NO2 gas sensor based on Pt-Sn3O4 / SnO2 sensitive material, comprising an Al2O3 flat ceramic substrate with a pair of interdigitated gold electrodes on the upper surface and a serpentine platinum heating electrode on the bottom, and a sensitive material coated on the upper surface of the Al2O3 flat ceramic substrate and the interdigitated gold electrodes; characterized in that: the sensitive material is Pt-Sn3O4 / SnO2, and the sensitive material is prepared by the following steps.

[0009] (1) Add 3.5-4.0g of stannous chloride dihydrate (SnCl2·2H2O) and 11-12g of trisodium citrate dihydrate (Na3C6H5O7·2H2O) to 30-50mL of deionized water and stir continuously for 20-30 minutes;

[0010] (2) Add 0.6-0.8g of sodium hydroxide (NaOH) to 30-50mL of deionized water and stir continuously for 10-20 minutes;

[0011] (3) Add the solution obtained in step (2) dropwise to the solution obtained in step (1) and stir continuously for 20 to 30 minutes;

[0012] (4) Transfer the solution obtained in step (3) to a hydrothermal reactor, keep it at 160-180°C for 12-14 hours, take it out, let it cool naturally to room temperature, wash the precipitate with deionized water and ethanol by centrifugation several times, and then dry it at 60-80°C; calcine the obtained powder in air at 400-450°C for 1.5-2.5 hours, cool it to room temperature and take it out to obtain Sn3O4 / SnO2 sensitive material powder;

[0013] (5) Take 100 mg of the Sn3O4 / SnO2 sensitive material powder prepared in step (4), place it in 60-80 mL of deionized water and stir until the powder is completely dispersed. Then add 0.0004-0.0006 mmol H2PtCl6 and 0.02-0.05 g sodium borohydride (NaBH4) and continue stirring for 1-2 hours. Then wash the precipitate with deionized water and ethanol by centrifugation several times, and then dry it at 60-80℃ to obtain Pt-Sn3O4 / SnO2 sensitive material powder.

[0014] The method for fabricating an NO2 gas sensor based on Pt-Sn3O4 / SnO2 sensitive material according to the present invention, wherein the sensor adopts a planar chip structure, and the steps are as follows:

[0015] (1) Take an appropriate amount of Pt-Sn3O4 / SnO2 sensitive material powder and mix it with anhydrous ethanol at a mass ratio of 0.25 to 0.5:1 to form a paste. Then, use a brush to apply a small amount of the paste evenly to the surface of an Al2O3 flat ceramic sheet with a platinum heating electrode at the bottom and a pair of interdigitated gold electrodes on the upper surface, so that it completely covers the Al2O3 flat ceramic sheet and the interdigitated gold electrodes and forms a sensitive material film with a thickness of 20 to 30 μm. The Al2O3 flat ceramic sheet is square with a side length of 3 to 4 mm and a thickness of 0.2 to 0.3 mm. The width of a single gold electrode is 0.4 to 0.5 mm, the spacing between interdigitated electrodes is 1 to 2 mm, and the gap between adjacent interdigitated electrodes is 0.2 to 0.3 mm. A platinum wire is led out from the gold electrode with a length of 4 to 6 mm.

[0016] (2) The Al2O3 flat ceramic sheet coated with the sensitive material film is baked under an infrared lamp for 5 to 10 minutes. After the sensitive material is dry, the Al2O3 flat ceramic sheet is welded onto a hexagonal base and then encapsulated to obtain a NO2 gas sensor based on Pt-Sn3O4 / SnO2 sensitive material.

[0017] The NO2 gas sensor based on Pt-Sn3O4 / SnO2 sensitive material prepared in this invention has the following advantages:

[0018] 1. Pt-Sn3O4 / SnO2 sensitive materials were successfully prepared using a simple hydrothermal method and impregnation method. The synthesis method is simple and low in cost.

[0019] 2. By loading trace amounts of precious metal Pt onto the surface of Sn3O4 / SnO2 composite material, the sensitivity of Sn3O4 / SnO2-based sensor to NO2 at room temperature (78-1 ppm) was significantly improved and the recovery speed of NO2 gas was accelerated, thus improving the selectivity of the sensor. It has broad application prospects in detecting NO2 content in microenvironments.

[0020] 3. It adopts commercially available planar chip sensors, which have simple manufacturing processes, small size, and are suitable for mass production. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the sensor device;

[0022] Figure 2 XRD patterns of Sn3O4 / SnO2 and Pt-Sn3O4 / SnO2 sensitive materials;

[0023] Figure 3 a and Figure 3 b represents the SEM morphology of the Sn3O4 / SnO2 sensitive material at different magnification ratios. Figure 3 c and Figure 3 d represents the SEM morphology of the Pt-Sn3O4 / SnO2 sensitive material at different magnification ratios;

[0024] Figure 4 a and Figure 4 b is a TEM image of the Pt-Sn3O4 / SnO2 sensitive material; Figure 4 c is Figure 4 The linear EDS plot corresponding to b;

[0025] Figure 5 HRTEM image of Pt-Sn3O4 / SnO2 sensitive material;

[0026] Figure 6 Selectivity of the sensor for seven analyte gases at 30°C in the comparative and example embodiments;

[0027] Figure 7 a and Figure 7 b is the response recovery curve of the sensor in the comparative example and the embodiment to 1ppm NO2 gas at 30°C; Figure 7 c and Figure 7 d represents the response recovery curve of the sensor in the comparative example and the embodiment to 1 ppm NO2 gas at 50°C;

[0028] Figure 8 a and Figure 8 b is the response recovery curve of the sensor in the embodiment to 20-5000 ppb NO2 gas at 30°C; Figure 8 c and Figure 8 d shows the response recovery curve of the sensor in the embodiment to 20-5000 ppb NO2 gas at 50°C;

[0029] Figure 9 a represents the sensitivity-NO2 concentration characteristic curves of the sensors in the comparative and example embodiments at 30°C; Figure 9b shows the sensitivity-NO2 concentration characteristic curves of the sensors in the comparative and example embodiments at 50°C. Figure 9 c is the sensitivity-NO2 concentration characteristic curve of the sensor in the comparative example at 30℃ and 50℃; Figure 9 d shows the sensitivity-NO2 concentration characteristic curves of the sensor in the example at 30℃ and 50℃;

[0030] Figure 10 The embodiment shows the long-term stability curve of the sensor's sensitivity to 1ppm NO2 gas at 30℃.

[0031] like Figure 1 As shown, the Al2O3 square flat ceramic sheet has a side length of 3mm and a thickness of 0.25mm; the width of a single gold electrode is 0.45mm, the interdigital spacing is 1mm, and the gap between adjacent interdigitals is 0.3mm; the platinum wire leading out from the gold electrode has a length of 5mm; and there is a serpentine platinum electrode at the bottom as a heating electrode.

[0032] like Figure 2 As shown, the XRD patterns of the sensitive materials Sn3O4 / SnO2 and Pt-Sn3O4 / SnO2 reveal that both Sn3O4 / SnO2 and Pt-Sn3O4 / SnO2 exhibit characteristic peaks of both Sn3O4 (standard card 16-737) and SnO2 (standard card 41-1445), confirming that the host material is a composite material of Sn3O4 and SnO2. For Pt-Sn3O4 / SnO2, due to the low Pt loading, it is difficult to find the Pt peak in the XRD pattern.

[0033] like Figure 3 As shown in the SEM image, the morphology of the Sn3O4 / SnO2 composite sensitive material is nanosheets, and the morphology of Pt-Sn3O4 / SnO2 is almost indistinguishable from that of Sn3O4 / SnO2, indicating that the loading of the noble metal Pt is relatively small and not obvious in the SEM image.

[0034] like Figure 4 The TEM image of the Pt-Sn3O4 / SnO2 sensitive material shows that there are clusters with a radius of about 2 nm distributed on the material surface. The elemental analysis of the clusters in linear EDS confirmed that they are Pt clusters, thus proving the successful loading of Pt on the material surface.

[0035] like Figure 5 As shown, two lattice spacings of 0.329 nm and 0.264 nm can be found in the HRTEM image of the Pt-Sn3O4 / SnO2 sensitive material, which correspond to the (101) crystal plane of Sn3O4 and the (111) crystal plane of SnO2, respectively. This further confirms that there is a Sn3O4 and SnO2 heterojunction in the sensitive material.

[0036] like Figure 6 As shown, the sensors in the comparative example and the embodiment both showed the highest response to NO2 at an operating temperature of room temperature (30°C). The sensor in the embodiment showed much better selectivity for NO2 than the sensor in the comparative example.

[0037] like Figure 7 As shown, the response recovery curves of the sensors in the comparative and examples to 1 ppm NO2 gas are relatively smooth at an operating temperature of 30°C, with response / recovery times of 525 / 9068s and 942 / 4558s, respectively. At a low operating temperature (50°C), the response recovery times of the sensors in the comparative and examples to 1 ppm NO2 gas are 508 / 5379s and 662 / 420s, respectively, which are significantly improved compared to their operating temperature of 30°C. At the same time, the recovery speed of the sensors in the examples to NO2 gas at operating temperatures of 30°C and 50°C is much higher than that of the sensors in the comparative examples.

[0038] like Figure 8 As shown, the sensor in the embodiment exhibits excellent response and recovery characteristics to different concentrations (20-5000 ppb) of NO2 under operating temperature conditions of 30°C and 50°C.

[0039] like Figure 9 As shown, the sensor in the embodiment exhibits superior sensitivity to different concentrations of NO2 (20-5000 ppb) compared to the sensor in the comparative example at operating temperatures of 30°C and 50°C. Furthermore, both the sensor in the comparative example and the sensor in the embodiment demonstrate higher sensitivity to different concentrations of NO2 (20-5000 ppb) at an operating temperature of 30°C compared to 50°C.

[0040] like Figure 10 As shown, during the 30-day testing period, the sensor in the embodiment operating at 30°C showed minimal fluctuations in response to 1 ppm NO2 gas and maintained high sensitivity.

[0041] Note: In this patent, the sensitivity of the device (N-type semiconductor) in the reducing gas test is defined as the ratio of resistance (R0). a / R g ), where R a Represents the resistance (R) between two gold electrodes in air. a ), while R g The resistance value (R) between the two gold electrodes in the gas being tested. gDuring the testing process, a static testing system was used. The device was placed in a 1L gas cylinder, a certain amount of the organic gas to be tested was injected, and the change in resistance was observed and recorded. The corresponding sensitivity value was then calculated. Detailed Implementation

[0042] Comparative Example 1

[0043] The specific fabrication process of the NO2 gas sensor using Sn3O4 / SnO2 composite sensing material is as follows:

[0044] (1) Add 3.6g of stannous chloride dihydrate (SnCl2·2H2O) and 11.8g of trisodium citrate dihydrate (Na3C6H5O7·2H2O) to 40mL of deionized water and stir continuously for 30 minutes;

[0045] (2) Add 0.8g of sodium hydroxide (NaOH) to 40mL of deionized water and stir continuously for 20 minutes;

[0046] (3) Add the solution obtained in step (2) dropwise to the solution obtained in step (1) and stir continuously for 30 minutes;

[0047] (4) Transfer the solution obtained in step (3) to a hydrothermal reactor, keep it at 180°C for 12 hours, take it out, let it cool naturally to room temperature, wash the precipitate with deionized water and ethanol by centrifugation several times, and then dry it at 60°C; calcine the obtained powder in air at 400°C for 2 hours, cool it to room temperature and take it out, thereby obtaining 1.5g of Sn3O4 / SnO2 sensitive material powder.

[0048] (5) Take Sn3O4 / SnO2 sensitive material powder and mix it with anhydrous ethanol at a mass ratio of 0.3:1 to form a paste. Then, use a brush to dip a small amount of paste and evenly coat it on the surface of an Al2O3 flat ceramic sheet with a heating electrode at the bottom and a pair of interdigitated gold electrodes on the upper surface, so that it completely covers the Al2O3 flat ceramic sheet and the gold electrodes and forms a 25μm thick sensitive material film.

[0049] (6) The coated flat ceramic sheet is baked under an infrared lamp for 8 minutes. After the sensitive material is dry, the above device is soldered onto a hexagonal base and then packaged to obtain a NO2 gas sensor based on Sn3O4 / SnO2 sensitive material.

[0050] The Al2O3 square flat ceramic sheet has a side length of 3 mm and a thickness of 0.25 mm; the width of a single gold electrode is 0.45 mm, the interdigital spacing is 1 mm, and the gap between adjacent interdigitals is 0.3 mm; the platinum wires leading out from the gold electrodes are 5 mm long.

[0051] Example 1

[0052] The specific fabrication process of the NO2 gas sensor using Pt-Sn3O4 / SnO2 sensing material is as follows:

[0053] (1) Add 3.6g of stannous chloride dihydrate (SnCl2·2H2O) and 11.8g of trisodium citrate dihydrate (Na3C6H5O7·2H2O) to 40mL of deionized water and stir continuously for 30 minutes;

[0054] (2) Add 0.8g of sodium hydroxide (NaOH) to 40mL of deionized water and stir continuously for 20 minutes;

[0055] (3) Add the solution obtained in step (2) dropwise to the solution obtained in step (1) and stir continuously for 30 minutes;

[0056] (4) Transfer the solution obtained in step (3) to a hydrothermal reactor, keep it at 180°C for 12 hours, take it out, let it cool naturally to room temperature, wash the precipitate with deionized water and ethanol by centrifugation several times, and then dry it at 60°C; calcine the obtained powder in air at 400°C for 2 hours, cool it to room temperature and take it out, thereby obtaining 1.5g of Sn3O4 / SnO2 sensitive material powder;

[0057] (5) Take 100 mg of the Sn3O4 / SnO2 sensitive material powder prepared in step (4), place it in 70 mL of deionized water and stir until the powder is completely dispersed. Then add 0.0005 mmol H2PtCl6 and 0.02 g sodium borohydride (NaBH4) and continue stirring for 1.5 hours. Then wash the precipitate with deionized water and ethanol by centrifugation several times, and then dry it at 60 °C to obtain 90 mg of Pt-Sn3O4 / SnO2 sensitive material powder.

[0058] (6) Take an appropriate amount of material powder from step (5) and mix it with ethanol at a mass ratio of 0.3:1 to form a paste. Then, use a brush to dip a small amount of paste and evenly coat it on the surface of an Al2O3 flat ceramic sheet with a heating electrode at the bottom and a pair of interdigitated gold electrodes on the upper surface, so that it completely covers the Al2O3 flat ceramic sheet and the gold electrodes and forms a 25μm thick sensitive material film.

[0059] (7) The coated flat ceramic sheet is baked under an infrared lamp for 8 minutes. After the sensitive material is dry, the above device is soldered onto a hexagonal base and then packaged to obtain a NO2 gas sensor based on Pt-Sn3O4 / SnO2 sensitive material.

[0060] The Al2O3 square flat ceramic sheet has a side length of 3 mm and a thickness of 0.25 mm; the width of a single gold electrode is 0.45 mm, the interdigital spacing is 1 mm, and the gap between adjacent interdigitals is 0.3 mm; the platinum wires leading out from the gold electrodes are 5 mm long.

Claims

1. A NO2 room temperature gas sensor based on Pt-Sn3O4 / SnO2 sensitive material, comprising an Al2O3 planar ceramic substrate with a heating electrode at the bottom and a pair of interdigitated gold electrodes on the upper surface, and a sensitive material coated on the upper surface of the Al2O3 planar ceramic substrate and the interdigitated gold electrodes; characterized in that: The sensitive material is a Pt-Sn3O4 / SnO2 material, and it is prepared by the following steps. (1) Add 3.5-4.0g of stannous chloride dihydrate and 11-12g of trisodium citrate dihydrate to 30-50mL of deionized water and stir continuously for 20-30 minutes; (2) Add 0.6-0.8g of sodium hydroxide to 30-50mL of deionized water and stir continuously for 10-20 minutes; (3) Add the solution obtained in step (2) dropwise to the solution obtained in step (1) and stir continuously for 20 to 30 minutes; (4) Transfer the solution obtained in step (3) to a hydrothermal reactor, keep it at 160-180°C for 12-14 hours, take it out, let it cool naturally to room temperature, wash the precipitate with deionized water and ethanol by centrifugation several times, and then dry it at 60-80°C; calcine the obtained powder in air at 400-450°C for 1.5-2.5 hours, cool it to room temperature and take it out to obtain Sn3O4 / SnO2 sensitive material powder; (5) Take 100 mg of the Sn3O4 / SnO2 sensitive material powder prepared in step (4), place it in 60-80 mL of deionized water and stir until the powder is completely dispersed. Then add 0.0004-0.0006 mmol H2PtCl6 and 0.02-0.05 g sodium borohydride and continue stirring for 1-2 hours. Then wash the precipitate with deionized water and ethanol by centrifugation several times, and then dry it at 60-80℃ to obtain Pt-Sn3O4 / SnO2 sensitive material powder.

2. The NO2 room temperature gas sensor based on Pt-Sn3O4 / SnO2 sensitive material as described in claim 1, characterized in that: The Al2O3 planar ceramic sheet is square, with a side length of 3-4 mm and a thickness of 0.2-0.3 mm; the width of a single gold electrode is 0.4-0.5 mm, the spacing between interdigitated electrodes is 1-2 mm, and the gap between adjacent interdigitated electrodes is 0.2-0.3 mm; platinum wires with a length of 4-6 mm are led out from the gold electrodes.

3. The method for preparing a NO2 gas sensor based on Pt-Sn3O4 / SnO2 sensitive material as described in claim 1 or 2, comprising the following steps: (1) Take an appropriate amount of Pt-Sn3O4 / SnO2 material powder and mix it with anhydrous ethanol at a mass ratio of 0.25 to 0.5:1 to form a paste. Then, use a brush to dip the paste and evenly coat it on the surface of an Al2O3 flat ceramic sheet with a heating electrode at the bottom and a pair of interdigitated gold electrodes on the upper surface, so that it completely covers the Al2O3 flat ceramic sheet and the gold electrodes and forms a sensitive material film with a thickness of 20 to 30 μm. (2) The coated flat ceramic sheet is baked under an infrared lamp for 5 to 10 minutes. After the sensitive material is dry, the above device is welded onto a hexagonal base and then packaged to obtain a NO2 room temperature gas sensor based on Pt-Sn3O4 / SnO2 sensitive material.

Images