Preparation method and application of gas-sensitive material for detecting methane

Abstract

The invention relates to a preparation method and application of a gas-sensitive material for detecting methane. The preparation method comprises the following steps: stirring indium trichloride tetrahydrate, urea and deionized water to form a mixed solution; transferring the mixed solution into a stainless steel high-pressure reaction kettle with a polytetrafluoroethylene lining for reaction and sealing, and after the reaction is finished, naturally cooling the mixture to room temperature to obtain a precursor; centrifuging and washing the precursor, drying, and grinding to obtain a precursor material; calcining the precursor material in air to obtain a pure In2O3 material; the preparation method comprises the following steps: adding chloroauric acid and an In2O3 material into deionized water, and stirring to obtain a mixed solution; carrying out solid-liquid separation on the mixed solution, and washing the solid to obtain a precipitate; and drying the precipitate, calcining in air, cooling to room temperature, and grinding to obtain the Au / In2O3 gas sensitive material. The Au / In2O3 gas-sensitive material is prepared by doping metal Au into In2O3, and the specific surface area of the gas-sensitive material is increased, so that the sensitivity of the gas-sensitive material in practical application is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of gas sensors, and relates to a preparation method and application of a gas-sensitive material for detecting methane; in particular, it relates to a preparation method of an Au / In2O3 gas-sensitive material and the preparation of a gas sensor. Background Art

[0002] Methane is the second most abundant anthropogenic greenhouse gas after carbon dioxide (CO2), accounting for approximately 20% of global emissions. The global warming potential (GWP) of CH4 is approximately 28 times that of CO2 (according to EPA data). Furthermore, methane is an important readout for various diseases, including protection against myocardial ischemia. In clinical practice, methane saline (a methane-enriched aqueous solution) can alleviate myocardial ischemia. In animal models, methane can reduce myocardial infarction volume, improve cardiac function, and inhibit oxidative stress and inflammatory responses. The mechanisms may involve reducing the levels of inflammatory factors (e.g., IL-1β, IL-6, TNF-α), enhancing antioxidant capacity (e.g., increasing SOD activity), and reducing cell apoptosis (e.g., inhibiting caspase-3 and the Bax / Bcl-2 ratio). Therefore, the development of new methane sensors with high sensitivity and low detection limits is of great significance for both environmental monitoring and clinical diagnosis.

[0003] Metal oxide semiconductor (MOS) gas sensors, with their numerous advantages, such as high cost-effectiveness, high reproducibility, wide detection range, and ease of system integration, are suitable for detecting explosive gases. Indium oxide (In2O3) is a widely used semiconductor material with excellent physical and chemical properties. Currently, there are numerous reports on sensors for detecting methane. For example, the invention patent "Method for Fabricating a Gas Sensor for Methane Gas Detection" (CN 107449798 A) overcomes the drawbacks of existing catalytic methane sensors fabricated using a bridge circuit detection principle, such as high reference element resistance matching requirements and increased power consumption and shortened device lifespan due to prolonged operation at high temperatures. However, these sensors exhibit complex structures, hindering industry development. The invention patent "A ZnO-based Gas-Sensing Material for MEMS Methane Sensors and Its Preparation Method" demonstrates a ZnO-based gas-sensing material that reduces the sensor's detection limit and significantly improves resistance linearity and sensitivity, promoting the practical application of sensors for methane concentration detection in mines and everyday life. At present, it is necessary to study low-concentration methane sensors for the medical purpose of preventing myocardial blood damage.

[0004] Existing In2O3 sensors still cannot meet the needs of practical applications due to problems such as low response, high operating temperature and poor stability. In order to improve the gas sensing performance of In2O3, various methods have been tried, including morphology regulation, noble metal modification, element doping and heterostructure construction. The In2O3 crystal structure can accommodate a variety of noble metals such as platinum, gold, palladium and ruthenium. These metals can improve sensing performance through electronic sensitization effects and chemical sensitization effects (such as spillover effect). In particular, gold modification can not only change the electronic properties of the material, but also provide catalytic activity, thereby significantly enhancing the sensing performance. Summary of the Invention

[0005] The technical task of the present invention is to provide a methane gas-sensitive material and its preparation method, application and gas-sensitive components to address the low response and poor stability of sensing materials. By doping metal Au into In2O3 to prepare Au / In2O3 gas-sensitive material, the sensitivity of the gas-sensitive material is improved, thereby solving the above problems.

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

[0007] The present invention provides a method for preparing a gas-sensitive material for detecting methane, comprising the following steps:

[0008] Step 1: Stir indium trichloride tetrahydrate, urea and deionized water to form a mixed solution;

[0009] Step 2: Transfer the mixed solution to a stainless steel autoclave lined with polytetrafluoroethylene for reaction, seal it, and after the reaction is completed, cool the mixture naturally to room temperature to obtain a precursor;

[0010] Step 3: centrifuging and washing the precursor, drying it, and then grinding it to obtain the precursor material;

[0011] Step 4: calcining the precursor material in air to obtain pure In2O3 material;

[0012] Step 5: Add chloroauric acid and In2O3 material into deionized water and stir to obtain a mixed solution;

[0013] Step 6: separating the mixed solution into solid and liquid, and washing the solid to obtain a precipitate;

[0014] Step 7: Dry the precipitate, calcine it in air, cool it to room temperature and grind it to obtain Au / In2O3 gas-sensitive material.

[0015] The preparation method of the methane gas sensitive material comprises the following steps: in step 1, indium chloride tetrahydrate and urea are mixed in a mass ratio of 1:1.5 to 1:3, and deionized water is added to make the concentration of indium chloride tetrahydrate in the reaction system 0.05 to 0.15 mol / L.

[0016] In the preparation method of the methane gas-sensitive material, in step 2, the reaction temperature is 130-140°C.

[0017] In the preparation method of the methane gas-sensitive material, in step 2, the reaction time is 9-10 hours.

[0018] In the preparation method of the methane gas-sensitive material, in step three, the solid-liquid separation is centrifugal separation, the centrifugal speed is 10,000-12,000 r / min, and the centrifugal time is 1-2 min.

[0019] In the preparation method of the methane gas-sensitive material, in step 4, the calcination temperature is 500° C.; the calcination time is 2-3 hours, and the heating rate is 3-5° C. / min.

[0020] In the preparation method of the methane gas-sensitive material, in step 5, the mass ratio of In to Au is 100:1.0-3.0; and stirring is performed for 3-5 hours.

[0021] In the preparation method of the methane gas-sensitive material, in step 7, the drying temperature is 60-80° C.

[0022] The calcination reaction temperature is 350-400° C.; the calcination reaction time is 1-2 hours.

[0023] The method for preparing a gas-sensitive component from the Au / In2O3 gas-sensitive material prepared by the present invention comprises the following steps: welding an Al2O3 ceramic tube and a heating resistance wire to a base; dissolving the gas-sensitive material Au / In2O3 in anhydrous ethanol and stirring the mixture with a brush until the mixture becomes a paste to obtain a paste; uniformly coating the paste on the surface of the Al2O3 ceramic tube, drying the mixture in an oven at 60°C for 2 minutes, and repeating the coating and drying operations three times to obtain the gas-sensitive component.

[0024] The sensitive component of the present invention can be used as a gas-sensitive component for environmental monitoring and clinical diagnosis.

[0025] Preferably, indium trichloride tetrahydrate (InCl3·4H2O) and urea (CO(NH2)2) are mixed in a mass ratio of 1:1.5 to 1:3 (e.g., 733 mg:1100 to 2200 mg), and 20 to 50 mL of deionized water are added to make the concentration of InCl3·4H2O in the reaction system 0.05 to 0.15 mol / L.

[0026] Preferably, in step 5, the ratio is: the mass percentage of Au and Zn is

[0027] 0.03 or less, the mass ratio of In and Au (gold) is (100:1.0-3.0), and stirring is (3-5) hours.

[0028] Beneficial effects:

[0029] The present application uses metal Au to modify In2O3, which can increase the specific surface area of ​​the gas-sensitive material, thereby improving the sensitivity of the gas-sensitive material in practical applications.

[0030] Furthermore, the present application dopes In2O3 with the noble metal Au. Since the noble metal Au has catalytic activity, it can reduce the activation energy of chemical adsorption of the measured gas, promote the reaction between gas molecules and the surface of the gas-sensitive material, and thus further improve the sensitivity of the gas-sensitive material.

[0031] Furthermore, by doping In2O3 with the precious metal Au and selecting different doping levels, this application can more accurately detect methane gas. Experimental results show that compared to pure In2O3, the 1.0wt% Au / In2O3 sensor has a response value (Rg / Ra) of 44.6 to 100ppm methane, with response / recovery times of 32 seconds and 3 seconds, respectively. This sensor exhibits both excellent selectivity and long-term stability, showing great potential for practical application. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0033] Figure 1 X-ray diffraction patterns of the gas-sensitive materials in Examples 1-3 and the comparative example of the present application.

[0034] Figure 2 Scanning electron microscope images and transmission electron microscope images of the gas-sensitive material in Example 1 of the present application.

[0035] Figure 3 A graph showing the test results of the temperature sensitivity of gas-sensitive components prepared from the gas-sensitive materials in Examples 1-3 of the present application and the comparative example.

[0036] Figure 4 A graph showing the test results of the sensitivity of gas-sensitive components prepared from the gas-sensitive materials in Examples 1-3 of the present application and the comparative example to methane concentration.

[0037] Figure 5 Graph showing the repeatability test results of the gas-sensitive component prepared using the gas-sensitive material in Example 1 of the present application.

[0038] Figure 6 Graph showing the selectivity test results of gas-sensitive components prepared using sensitive materials in Examples 1-3 of the present application and the comparative example. DETAILED DESCRIPTION

[0039] The present invention is described below using specific embodiments so that those skilled in the art can easily understand the feasibility of the present invention after studying this specification. The present invention can be implemented through various specific embodiments, and the details in this specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. The following examples all achieve the purpose of the present invention.

[0040] Example 1:

[0041] (1) At room temperature, 733 mg of indium trichloride tetrahydrate and 1100 mg of urea were added to 20 ml of deionized water and magnetically stirred for 30 min.

[0042] (2) The mixed solution was transferred to a stainless steel autoclave lined with polytetrafluoroethylene, sealed, and subjected to hydrothermal reaction at 130°C for 10 hours. After the reaction, the mixture was naturally cooled to room temperature;

[0043] (3) centrifugation (rotation speed of 12000 r / min) and washing 5 times, drying at 70 °C overnight, and grinding to obtain the precursor material;

[0044] (4) calcining the precursor material in air and then naturally cooling it to room temperature to obtain the pure In2O3 gas-sensitive material, wherein the heat treatment temperature is 500°C, the holding time is 2h, and the heating rate is 5°C / min;

[0045] (5) 100 mg of the prepared pure In2O3 material was added to 20 ml of deionized water, and 442 μL of HAuCl4·4H2O solution (1.0 wt% Au / In2O3) was added. The above solutions were gradually added and gently stirred for 4 h to obtain a mixed solution.

[0046] (6) centrifuging and washing the mixed solution to obtain a precipitate;

[0047] (7) The mixture was dried at 60 °C overnight and finally calcined at 350 °C in a muffle furnace for 1 h to obtain 1.0 wt% Au / In2O3 nanorod material, which was named 1.0 wt% Au / In2O3.

[0048] Example 2:

[0049] (1) At room temperature, 733 mg of indium trichloride tetrahydrate and 1446 mg of urea were added to 30 ml of deionized water and magnetically stirred for 30 min.

[0050] (2) The mixed solution was transferred to a stainless steel autoclave lined with polytetrafluoroethylene, sealed, and subjected to hydrothermal reaction at 140°C for 9 hours. After the reaction, the mixture was naturally cooled to room temperature.

[0051] (3) centrifugation (rotation speed of 10000 r / min) and washing 5 times, drying at 60 ° C overnight, and grinding to obtain the precursor material;

[0052] (4) calcining the precursor material in air and then naturally cooling it to room temperature to obtain the pure In2O3 gas-sensitive material, wherein the heat treatment temperature is 500°C, the holding time is 3h, and the heating rate is 5°C / min;

[0053] (5) 100 mg of the prepared pure In2O3 material was added to 20 ml of deionized water, and 884 μL of HAuCl4·4H2O solution (2.0 wt% Au / In2O3) was added. The above solutions were gradually added and gently stirred for 4 h to obtain a mixed solution.

[0054] (6) centrifuging and washing the mixed solution to obtain a precipitate;

[0055] (7) The mixture was dried at 70 °C overnight and finally calcined at 400 °C in a muffle furnace for 2 h to obtain 2.0 wt% Au / In2O3 nanorod material, named 2.0 wt% Au / In2O3.

[0056] Example 3:

[0057] (1) At room temperature, 733 mg of indium trichloride tetrahydrate and 2200 mg of urea were added to 40 ml of deionized water and magnetically stirred for 30 min.

[0058] (2) The mixed solution was transferred to a stainless steel autoclave lined with polytetrafluoroethylene, sealed, and subjected to hydrothermal reaction at 130°C for 10 hours. After the reaction, the mixture was naturally cooled to room temperature;

[0059] (3) centrifugation (rotation speed of 12000 r / min) and washing 5 times, drying at 70 °C overnight, and grinding to obtain the precursor material;

[0060] (4) calcining the precursor material in air and then naturally cooling it to room temperature to obtain the pure In2O3 gas-sensitive material, wherein the heat treatment temperature is 500°C, the holding time is 2h, and the heating rate is 3°C / min;

[0061] (5) 100 mg of the prepared pure In2O3 material was added to 20 ml of deionized water, and 1326 μL of HAuCl4·4H2O solution (3.0 wt% Au / In2O3) was added. The above solutions were gradually added and gently stirred for 4 h to obtain a mixed solution.

[0062] (6) centrifuging and washing the mixed solution to obtain a precipitate;

[0063] (7) The mixture was dried at 80 °C overnight and finally calcined at 380 °C in a muffle furnace for 1 h to obtain 3.0 wt% Au / In2O3 nanorod material, named 3.0 wt% Au / In2O3.

[0064] Comparative Example:

[0065] 733 mg of indium trichloride tetrahydrate and 1441 mg of urea were added to 50 ml of deionized water and stirred to form a mixed solution; the mixed solution was subjected to a hydrothermal reaction at a temperature of 130°C and a time of 10 hours. After the reaction was completed, the solution was cooled to obtain a hydrothermal product; the hydrothermal product was centrifuged and washed 5 times at a centrifugal speed of 12000 r / min and a centrifugal time of 2 minutes. The obtained solid was washed to obtain a precipitate; the precipitate was dried in an oven at 60°C overnight, calcined at 500°C for 2 hours, and cooled to room temperature to obtain an In2O3 gas-sensitive material.

[0066] The gas-sensitive materials prepared in Examples 1-3 and the comparative example were subjected to X-ray diffraction, and the results are shown in Figure 1 , Figure 1 The XRD patterns of In2O3 gas-sensitive materials, 1.0wt% Au / In2O3 gas-sensitive materials, 2.0wt% Au / In2O3 gas-sensitive materials and 3.0wt% Au / In2O3 gas-sensitive materials are included. The prepared samples have four main diffraction peaks at diffraction angles of 30.6°, 35.4°, 51.2° and 60.7°, which correspond to the (222), (400), (440) and (622) crystal planes of the cubic In2O3 structure (JCPDS card No.06–0416). Figure 1 As shown in Figure 3, a significant peak shift is observed at low angles, which is caused by the incorporation of Au noble metal.

[0067] The gas-sensitive material prepared in Example 1 was observed using a scanning electron microscope. The results are shown in Figure 2 (ab), as shown in the figure, the prepared 1.0wt% Au / In2O3 gas-sensitive material is in a rod shape, and many rough pores appear on the surface. After being doped with metal Au, the gas-sensitive material maintains the rod shape with small protrusions on the surface. The specific surface area of ​​the 1.0wt% Au / In2O3 gas-sensitive material increases, which is more conducive to the adsorption of methane gas on its surface, thereby improving the sensitivity of the gas-sensitive material in practical applications. The gas-sensitive material prepared in Example 1 was observed using a transmission electron microscope, and the results are detailed in Figure 2(ce), as shown in the figure, the interplanar spacing of the (222) crystal planes of the In2O3 crystal plane is 0.290nm, and the interplanar spacing of Au is measured to be 0.250nm, corresponding to the (111) plane of the cubic phase Au, thus proving that it is successfully loaded on the surface of the In2O3 nanorods. At the same time, Figure 2 (fi) Mapping tests were also performed on gas-sensitive materials, and the experimental results showed that O, Au, and In elements were evenly distributed on the surface of the material.

[0068] Example 4: Preparation of gas-sensing components

[0069] First, an Al2O3 ceramic tube and a heating resistor wire were welded to a base. Then, 5 mg each of the aforementioned In2O3, 1.0 wt% Au / In2O3, 2.0 wt% Au / In2O3, and 3.0 wt% Au / In2O3 gas-sensing materials were dissolved in one drop of anhydrous ethanol and stirred with a brush until a paste formed. Finally, the paste was evenly coated on the surface of the Al2O3 ceramic tube and placed in a 60°C oven for 2 minutes. This operation was repeated three times. After drying, the In2O3, 1.0 wt% Au / In2O3, 2.0 wt% Au / In2O3, and 3.0 wt% Au / In2O3 gas-sensing components were obtained.

[0070] The methane sensing performance of the In2O3 gas sensor, 1.0wt% Au / In2O3 gas sensor, 2.0wt% Au / In2O3 gas sensor and 3.0wt% Au / In2O3 gas sensor prepared in Example 4 was tested. The gas sensor includes an Au electrode, an Al2O3 ceramic tube, a nickel-chromium heating resistor wire and a bakelite base. The test was carried out using a dynamic gas distribution analysis system, and the gas flow rate was controlled by a precision gas flow controller (MFC) to make the test results more reliable. The adjustment of different concentrations of the test target gas can be achieved by controlling the flow rate of the target gas and air. The test chamber is connected to a heating device to change the operating temperature of the gas sensor (100-400°C). The sensor response (S) to the target gas is defined as S=Ra / Rg, where Ra and Rg are the sensor resistance in air and target gas, respectively. The response time (τres) and recovery time (τrecov) are defined as the time required to reach 90% of the total difference in resistance before and after. During the test, the ambient temperature was 25° C. to 30° C., and the relative humidity (RH) was 15% to 30%.

[0071] The test results of gas sensitive materials for methane sensing performance are detailed in Figure 3-4 .

[0072] See Figure 3, gas sensing curves of In2O3 gas sensing element, 1.0wt% Au / In2O3 gas sensing element, 2.0wt% Au / In2O3 gas sensing element and 3.0wt% Au / In2O3 gas sensing element to methane gas with a concentration of 100ppm at different temperatures. Figure 3 The 1.0wt% Au / In2O3 and 3.0wt% Au / In2O3 gas-sensitive materials exhibited high methane gas response values ​​of 44.6 and 9.32, respectively, at 260°C. This sensor, which detects low concentrations, has the potential to be used for the prevention and protection of myocardial blood damage, providing real-time patient monitoring.

[0073] See Figure 4 , using different concentrations (1ppm, 5ppm, 10ppm, 15ppm, 20ppm, 30ppm) of methane (260℃) to test the response of In2O3 gas sensors, 1.0wt% Au / In2O3 gas sensors, 2.0wt% Au / In2O3 gas sensors and 3.0wt% Au / In2O3 gas sensors to investigate the response performance of gas-sensitive materials to different concentrations of methane. Figure 4 It can be seen that the response values ​​of In2O3 gas-sensitive material, 1.0wt% Au / In2O3 gas-sensitive material, 2.0wt% Au / In2O3 gas-sensitive material and 3.0wt% Au / In2O3 gas-sensitive material to methane increase with the increase of methane concentration, and have a good linear relationship.

[0074] See Figure 5 , the repeatability test of 100ppm methane (260℃) was conducted using 1.0wt% Au / In2O3 gas sensing elements to examine the repeatability performance of gas sensing materials. Figure 5 It can be seen that the 1.0wt% Au / In2O3 gas-sensitive material has good stability to methane. Figure 6 At the same time, the selectivity performance tests of In2O3 gas-sensitive components, 1.0wt% Au / In2O3 gas-sensitive components, 2.0wt% Au / In2O3 gas-sensitive components and 3.0wt% Au / In2O3 gas-sensitive components to methane (260℃) were investigated to investigate the selectivity performance of gas-sensitive materials to methane. Figure 6 It can be seen that the response performance of In2O3 gas-sensitive elements, 1.0wt% Au / In2O3 gas-sensitive materials, 2.0wt% Au / In2O3 gas-sensitive materials and 3.0wt% Au / In2O3 gas-sensitive materials to four different gases of 100ppm 100ppm NO, 100ppm CO, 100ppm H2S and 100ppm NH3 shows that 1.0wt% Au / In2O3 gas-sensitive material has good selectivity for methane.

[0075] The technical solutions disclosed and proposed by the present invention can be implemented by those skilled in the art by drawing on the content of this document and appropriately changing the conditions, routes, and other aspects. Although the methods and preparation techniques of the present invention have been described through preferred embodiments, it is obvious that those skilled in the art can modify or recombine the methods and technical routes described herein without departing from the content, spirit, and scope of the present invention to achieve the ultimate preparation technology. It is particularly important to point out that all similar substitutions and modifications that are obvious to those skilled in the art are considered to be included in the spirit, scope, and content of the present invention.

Claims

1. A method for preparing a gas-sensitive material for detecting methane, characterized in that: The steps include: Step 1: Stir indium trichloride tetrahydrate, urea and deionized water to form a mixed solution; Step 2: Transfer the mixed solution to a stainless steel autoclave lined with polytetrafluoroethylene for reaction, seal it, and after the reaction is completed, cool the mixture naturally to room temperature to obtain a precursor; Step 3: centrifuging and washing the precursor, drying it, and then grinding it to obtain the precursor material; Step 4: calcining the precursor material in air to obtain pure In2O3 material; Step 5: Add chloroauric acid and In2O3 material into deionized water and stir to obtain a mixed solution; Step 6: separating the mixed solution into solid and liquid, and washing the solid to obtain a precipitate; Step 7: Dry the precipitate, calcine it in air, cool it to room temperature and grind it to obtain Au / In2O3 gas-sensitive material.

2. The method for preparing a methane gas-sensitive material according to claim 1, wherein: In step 1, indium chloride tetrahydrate and urea are mixed in a mass ratio of 1:1.5 to 1:3, and deionized water is added to make the concentration of indium chloride tetrahydrate in the reaction system 0.05 to 0.15 mol / L.

3. The method for preparing a methane gas-sensitive material according to claim 1, wherein: In step 2, the reaction temperature is 130-140°C.

4. The method for preparing a methane gas-sensitive material according to claim 1, wherein: In step 2, the reaction time is 9-10 hours.

5. The method for preparing a methane gas-sensitive material according to claim 1, wherein: In step 3, the solid-liquid separation is centrifugal separation, the rotation speed of the centrifugal separation is 10000-12000 r / min, and the time of the centrifugal separation is 1-2 min.

6. The method for preparing a methane gas-sensitive material according to claim 1, wherein: In step 4, the calcination temperature is 500° C.; the calcination time is 2-3 h, and the heating rate is 3-5° C. / min.

7. The method for preparing a methane gas-sensitive material as claimed in claim 1, wherein: In step 5, the mass ratio of In to Au is 100:1.0-3.0; stirring is carried out for 3-5 hours.

8. The method for preparing a methane gas-sensitive material according to claim 1, wherein: In step 7, the drying temperature is 60-80°C; The calcination reaction temperature is 350-400° C.; the calcination reaction time is 1-2 hours.

9. A method for preparing a gas-sensitive component from the gas-sensitive material prepared according to claim 1, characterized in that: An Al2O3 ceramic tube and a heating resistance wire were welded to a base; the gas-sensitive material Au / In2O3 was dissolved in anhydrous ethanol and stirred with a brush until it became a paste to obtain a paste; the paste was evenly coated on the surface of the Al2O3 ceramic tube and dried in an oven at 60°C for 2 minutes. The coating and drying operations were repeated three times to obtain a gas-sensitive component.

10. The sensitive component of claim 9 should be used as a gas-sensitive component for environmental monitoring and clinical diagnosis.

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