A highly selective hydrogen sensor loaded sensitive material and its preparation method and application

Abstract

The present invention discloses a method for preparing a highly selective hydrogen sensor load-type sensitive material, comprising the following steps: S1: adding ferrocyanide and polyvinyl pyrrolidone to a hydrochloric acid solution and uniformly mixing to obtain a mixed solution A; S2: sealing the mixed solution A and then heating it at 88°C to 888°C for 28h to 823h; S3: centrifuging the material obtained in step S2 and washing it multiple times with a mixed solution of ethanol and deionized water, and then dispersing it in an ethanol solution to obtain a mixed solution B; S4: adding a weighed weak acid conjugate base to the mixed solution B, stirring it at room temperature for 98min, then centrifuging, washing, and drying to obtain a precursor material; S8: heating the precursor material obtained in S4 to 888°C under air conditions and keeping it warm for 188min to obtain a loaded α-Fe2O3-based composite sensitive material. The preparation method is simple in process, highly repeatable, and low in cost. The hydrogen sensor made of the sensitive material has obvious advantages in selectivity and response speed.

Description

Technical Field

[0001] The present invention belongs to the field of semiconductor metal oxide gas sensors, and in particular relates to a highly selective hydrogen sensor load-type sensitive material, a preparation method and an application thereof. Background Art

[0002] Hydrogen and carbon monoxide are two commonly used reducing agents in industrial production and have a wide range of applications. It is worth noting that carbon monoxide is a toxic gas that is flammable and explosive, while hydrogen is also a gas with high diffusion in air, high heat of combustion, and low explosive concentration. Therefore, real-time monitoring is necessary during industrial production to prevent leakage. Furthermore, carbon monoxide and hydrogen have similar physical and chemical properties, making it difficult to quickly identify the target gas in the event of a leak. Therefore, the development of a gas sensor with high sensitivity, fast response, high selectivity, and low concentration detection has always attracted much attention.

[0003] Semiconductor metal oxide gas sensors are widely used in the detection of toxic, flammable and explosive gases, and industrial waste gas due to their high stability, low cost, and simple manufacturing process. However, the sensitive materials used in semiconductor metal oxide gas sensors still face challenges such as low sensitivity, poor selectivity, and long response / recovery times that need to be addressed.

[0004] To develop highly sensitive and selective semiconductor metal oxide gas sensors, Chinese patent application number CN202110471022.6 discloses a method for preparing a SnO2-Pd@rGO sensitive material to improve the selectivity of hydrogen sensors. The porous, spherical SnO2-Pd@rGO composite material effectively forms a three-dimensional network structure during self-assembly, providing a larger surface area and providing more reaction sites for the adsorption of target gases, thereby improving the gas-sensing performance of small molecule gases. Chinese patent application number CN202111074941.6 discloses a method for preparing a precious metal-doped MOS@MOF sensitive material to improve the selectivity of hydrogen sensors. The synergistic effect of the MOS coating layer and the precious metal embedding layer regulates the size of the MOF pores, blocking most interfering gases and playing a key role in improving the selectivity of hydrogen sensors. The above sensitive materials all improve the sensitivity and selectivity of hydrogen sensors, but the preparation process of sensitive materials is relatively complicated, and the sensing type of the target gas and the interfering gas during the sensing process are both n-type, making it difficult to specifically detect the specific gas type that causes the sensor's n-type response. The literature reports the preparation of ZnO and Co3O4 composite gas-sensitive materials (Gas-sensing selectivity of n-ZnO / p-Co3O4 sensors for homogeneous reducing gas, Journal of Physics and Chemistry of Solids, 150(2021), 109864)) and the testing of H2 and CO sensing performance. The results show that when the composite material is mixed at a ratio of 1:0.61, at 350°C, the sensor exhibits an n-type response to H2 and a p-type response to CO, greatly improving the selectivity of the hydrogen sensor. However, the sensitive material exhibits severe agglomeration, resulting in a reduction in specific surface area and a reduction in active sites for adsorbing the target gas, resulting in low sensitivity to both H2 and CO.

[0005] To address the shortcomings of these sensitive materials during preparation, it is imperative to develop sensitive materials for hydrogen gas sensors with high selectivity, fast response, and low detection concentrations. Metal-organic frameworks (MOFs) are considered promising three-dimensional sensitive materials due to their high thermodynamic stability, large surface area, and low cost. However, their poor selectivity limits their widespread application in real life. Summary of the Invention

[0006] One object of the present invention is to provide a method for preparing a highly selective hydrogen sensor-loaded sensitive material in order to improve the selectivity and response speed of the hydrogen sensor in response to the above technical problems.

[0007] In order to achieve the above object of the invention, the present invention provides a method for preparing a highly selective hydrogen sensor loaded sensitive material, comprising the following steps:

[0008] S1: adding ferrocyanide and polyvinyl pyrrolidone to a hydrochloric acid solution and uniformly mixing to obtain a mixed solution A;

[0009] S2: Seal the mixed solution A and heat it at 80-85°C for 20-23 hours;

[0010] S3: centrifuging the material (Prussian blue, PB) obtained in step S2 and washing it multiple times with a mixed solution of ethanol and deionized water, and then dispersing it in an ethanol solution to obtain a mixed solution B;

[0011] S4: adding the weighed weak acid conjugate base to the mixed solution B, stirring at room temperature for 90 minutes, and then centrifuging, washing, and drying to obtain a precursor material;

[0012] S5: The precursor material obtained in S4 is heated to 550° C. under air conditions and kept warm for 180 minutes to obtain a supported three-dimensional α-Fe 2 O 3 -based composite sensitive material.

[0013] Compared to existing technologies, this invention uses high-surface-area Prussian blue as a precursor and, through chemical etching, produces a high-surface-area, porous, supported three-dimensional α-Fe₂O₃-based composite sensitive material. This composite material enables molecular contact and enhances stability. The preparation process is simple, highly reproducible, and low-cost.

[0014] Preferably, in step S1, the molar concentration of the ferrocyanide and polyvinyl pyrrolidone in the hydrochloric acid solution is 1:0.15-0.2.

[0015] Preferably, in step S1, the molar concentration of the hydrochloric acid is 0.01M to 0.1M.

[0016] Preferably, in step S1, the ferrocyanide is potassium ferrocyanide or potassium ferrocyanide.

[0017] Preferably, in step S4, the molar mass ratio of the alkali metal to the ferricyanide in the weak acid conjugate base is 1:1.4-2.5.

[0018] Preferably, in step S4, the weak acid conjugate base is any one of sodium molybdate, sodium silicate, sodium tungstate, potassium niobate, and potassium selenate.

[0019] Preferably, in step S3, the speed of the centrifuge during centrifugation is 8000 rpm / min.

[0020] Preferably, in step S5, the heating rate during heating is 0.5-2°C / min.

[0021] The present invention also provides a highly selective hydrogen sensor loaded sensitive material prepared by the above preparation method, wherein the loaded oxide accounts for 35% to 75% of the total mass of the sensitive material.

[0022] The present invention also provides the use of the above-mentioned supported α-Fe2O3-based sensitive material in a hydrogen sensor. Using the supported α-Fe2O3-based sensitive material as the gas-sensitive material of the hydrogen sensor can effectively improve the selectivity and response speed of the hydrogen sensor.

[0023] Compared to existing α-Fe2O3 sensitive materials, the present invention uses high-surface-area Prussian blue as a precursor and chemically etched to produce a high-surface-area, porous, loaded three-dimensional α-Fe2O3-based composite sensitive material. Because hydrogen adsorption energies, charge transfer quantities, and adsorption spacing differ on n-type and p-type oxide surfaces, loading the three-dimensional α-Fe2O3 gas-sensitive material with an n-type oxide changes the barrier height and interfacial charge layer thickness, thereby altering the hydrogen sensing type. This significantly improves selectivity and shortens response time. The loaded α-Fe2O3-based sensitive material of the present invention enables molecular contact, enhances stability, and features a simple, highly reproducible, and low-cost preparation method. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is the SEM image of the MoO3 / α-Fe2O3 sensitive material prepared in Example 1;

[0025] Figure 2 This is the SEM image of the WO3 / α-Fe2O3 sensitive material prepared in Example 2;

[0026] Figure 3 The dynamic response curve of the hydrogen sensor made of α-Fe2O3 sensitive material prepared in the comparative example at the optimal operating temperature, 5ppm hydrogen and 5ppm carbon monoxide conditions;

[0027] Figure 4 Dynamic response curve of the hydrogen sensor made of MoO3 / α-Fe2O3 sensitive material prepared in Example 1 under the conditions of 5ppm hydrogen and 5ppm carbon monoxide at the optimal operating temperature;

[0028] Figure 5 Dynamic response curve of the hydrogen sensor made of WO3 / α-Fe2O3 sensitive material prepared in Example 2 at the optimal operating temperature, 5ppm hydrogen and 5ppm carbon monoxide conditions;

[0029] Figure 6Stability curves of hydrogen sensors made from the MoO3 / α-Fe2O3 sensitive material prepared in Example 1 and the WO3 / α-Fe2O3 sensitive material prepared in Example 2 at the optimal operating temperature and 5 ppm hydrogen conditions. DETAILED DESCRIPTION

[0030] The present invention will be further described below in conjunction with specific embodiments. It should be understood that the implementation of the present invention is not limited to the following examples, and any pro forma modification or change based on the present invention will fall within the scope of the present invention. As the embodiments of the present invention only list two examples of support materials (MoO3 and WO3), they are not limited to these two support materials. Those skilled in the art can replace them with other metal oxide materials loaded in the α-Fe2O3 matrix, and can also adjust the dosage and experimental conditions of reagents and raw materials within the parameter range defined in the claims, or select other amide compounds as precipitants, all of which should be considered to fall within the scope of the present invention.

[0031] In the present invention, the equipment and raw materials used can be purchased from the market or commonly used in the field. The following are the main reagents used in the examples:

[0032]

[0033] Example 1:

[0034] Prepare MoO3 / α-Fe2O3 sensitive material according to the following steps:

[0035] 0.6585g of potassium ferricyanide and 16g of polyvinylpyrrolidone were sequentially added to 200mL of a 0.01M hydrochloric acid solution (the molar concentration ratio of potassium ferricyanide to polyvinylpyrrolidone in the hydrochloric acid solution was 1:0.2). The mixture was stirred under a magnetic stirrer for 60min to obtain a uniform mixed solution (at 400 rpm). The mixture was then placed in a sealed 250mL container and heated at 80°C for 22h. After natural cooling, the resulting material was centrifuged (8000 rpm) and washed several times with a mixture of ethanol and deionized water (the volume ratio of ethanol to deionized water was 1:3). The resulting precursor material was then dispersed in 100mL of an 80% ethanol solution to obtain a dispersion. 0.095 g of sodium molybdate was added to the above 30 mL dispersion and stirred for 90 min under a magnetic stirrer (400 rpm). The product was washed with a mixed solution of ethanol and deionized water (the volume ratio of ethanol to deionized water was 1:3), dried at 50 ° C for 12 h, and then calcined at 550 ° C in air for 3 h (heating rate of 2 ° C / min) to obtain a three-dimensional micro-nanoframe MoO3 / α-Fe2O3 sensitive material.

[0036] Example 2:

[0037] Prepare WO3 / α-Fe2O3 sensitive material according to the following steps:

[0038] 0.6585g of potassium ferricyanide and 12g of polyvinylpyrrolidone were added to 200mL of a 0.05M hydrochloric acid solution (the molar concentration ratio of potassium ferricyanide to polyvinylpyrrolidone in the hydrochloric acid solution was 1:0.15). The mixture was stirred for 60 minutes under a magnetic stirrer (at 400 rpm) to obtain a uniform mixed solution. The mixture was then placed in a sealed 250mL container and heated at 80°C for 22 hours. After natural cooling, the resulting material was centrifuged (8000 rpm) and washed several times with a mixture of ethanol and deionized water (the volume ratio of ethanol to deionized water was 1:3). The resulting precursor material was then dispersed in 100mL of an 80% ethanol solution to obtain a dispersion. 0.125 g of sodium tungstate was added to the above 30 mL dispersion and stirred for 90 min under a magnetic stirrer (the speed was 400 rpm). The product was washed with a mixed solution of ethanol and deionized water (the volume ratio of ethanol to deionized water was 1:3), dried at 50 ° C for 12 h, and then calcined in air at 550 ° C for 3 h (the heating rate was 2 ° C / min) to obtain a three-dimensional micro-nanoframe WO3 / α-Fe2O3 sensitive material.

[0039] Example 3:

[0040] Prepare SnO2 / α-Fe2O3 sensitive material according to the following steps:

[0041] 0.6585g of potassium ferricyanide and 15g of polyvinylpyrrolidone were added to 150mL of a 0.1M hydrochloric acid solution (the molar concentration ratio of potassium ferricyanide to polyvinylpyrrolidone in the hydrochloric acid solution was 1:0.18). The mixture was stirred under a magnetic stirrer for 60 minutes to obtain a uniform mixed solution (at 400 rpm). The mixture was then placed in a sealed 250mL container and heated at 80°C for 22 hours. After natural cooling, the resulting material was centrifuged (8000 rpm) and washed several times with a mixture of ethanol and deionized water (the volume ratio of ethanol to deionized water was 1:3). The resulting precursor material was then dispersed in 100mL of an 80% ethanol solution to obtain a dispersion. 0.506 g of potassium selenate was added to the above 30 mL dispersion and stirred for 90 min under a magnetic stirrer (the speed was 400 rpm). The product was washed with a mixed solution of ethanol and deionized water (the volume ratio of ethanol to deionized water was 1:3), dried at 50 ° C for 12 h, and then calcined in air at 550 ° C for 3 h (the heating rate was 2 ° C / min) to obtain a three-dimensional micro-nanoframe SnO2 / α-Fe2O3 sensitive material.

[0042] Example 4:

[0043] Prepare MoO3 / α-Fe2O3 sensitive material according to the following steps:

[0044] 0.85g of potassium ferrocyanide and 15g of polyvinylpyrrolidone were added to 150mL of a 0.1M hydrochloric acid solution (the molar concentration ratio of potassium ferrocyanide to polyvinylpyrrolidone in the hydrochloric acid solution was 1:0.18). The mixture was stirred for 60min under a magnetic stirrer (at 400 rpm) to obtain a uniform mixed solution. The mixture was then placed in a sealed 250mL container and heated at 80°C for 22h. After natural cooling, the resulting material was centrifuged (8000 rpm) and washed several times with a mixed solution of ethanol and deionized water (the volume ratio of ethanol to deionized water was 1:3). The precursor material was then dispersed in 100mL of an 80% ethanol solution to obtain a dispersion. 0.099 g of sodium molybdate was added to the above 30 mL dispersion and stirred for 90 min under a magnetic stirrer (400 rpm). The product was washed with a mixed solution of ethanol and deionized water (the volume ratio of ethanol to deionized water was 1:3), dried at 50 ° C for 12 h, and then calcined at 550 ° C in air for 3 h (heating rate of 2 ° C / min) to obtain a three-dimensional micro-nanoframe MoO3 / α-Fe2O3 sensitive material.

[0045] Comparative Example:

[0046] Prepare α-Fe2O3 sensitive material according to the following steps:

[0047] 0.6585g of potassium ferricyanide and 15g of polyvinylpyrrolidone were added to 200mL of 0.01M hydrochloric acid solution (the molar ratio of potassium ferricyanide to polyvinylpyrrolidone in the hydrochloric acid solution was 1:0.18). The mixture was stirred for 60 minutes on a magnetic stirrer (400 rpm) to obtain a homogeneous mixture. The mixture was then placed in a sealed 250mL container and heated at 80°C for 22 hours. After cooling naturally, the resulting material was centrifuged (8000 rpm) and washed several times with a mixture of ethanol and deionized water (1:3 by volume). The resulting precursor was then dispersed in 100mL of 80% ethanol. 30mL of the dispersion was added to 30mL of 0.2M sodium hydroxide solution and stirred for 2 minutes on a magnetic stirrer (400 rpm). The color of the mixture changed from blue to yellow. The product was then washed and dried and calcined in air at 400°C for 3 h (heating rate of 2°C / min) to obtain a three-dimensional micro-nanoframe α-Fe2O3 sensitive material.

[0048] Test result analysis:

[0049] from Figure 1 From the SEM image, it can be observed that the three-dimensional MoO3 / α-Fe2O3 sensitive material framework is uniform in size, highly dispersed and has a rough surface. Figure 2 The SEM image shows that the WO3 / α-Fe2O3 sensitive material framework is also highly dispersed and has a rough surface, indicating that the preparation method provided by the present invention can successfully prepare three-dimensional MoO3 / α-Fe2O3 sensitive materials and WO3 / α-Fe2O3 sensitive materials.

[0050] The MoO3 / α-Fe2O3 sensitive material prepared in Example 1, the WO3 / α-Fe2O3 sensitive material prepared in Example 2, and the α-Fe2O3 sensitive material prepared in the comparative example were mixed and stirred with a binder in a mortar to obtain a uniform mixed slurry, which was then evenly coated on the surface of the Al2O3 plate until the mixed slurry completely covered the electrode on the surface of the Al2O3 plate. The electrodes were calcined at 400°C for 3h to obtain MoO3 / α-Fe2O3 hydrogen sensors, WO3 / α-Fe2O3 hydrogen sensors, and α-Fe2O3 hydrogen sensors, respectively. The selectivity, response speed, and stability related performance tests were performed on them. The results are shown in FIG. Figures 3 to 6 shown.

[0051] from Figure 3It can be seen that the sensitivity of the α-Fe2O3 hydrogen sensor to 5ppm hydrogen and carbon monoxide at 300℃ is basically the same, and both are p-type sensors. Therefore, the selectivity of the α-Fe2O3 hydrogen sensor to hydrogen and carbon monoxide is poor. Figure 4 It can be seen that the MoO3 / α-Fe2O3 hydrogen sensor prepared in Example 1 exhibits a p-type response under 300°C and 5ppm carbon monoxide conditions, and an n-type response under 5ppm hydrogen conditions, with a fast response time. Figure 5 It can also be seen that the WO3 / α-Fe2O3 hydrogen sensor prepared in Example 2 exhibits a p-type response at 300°C and 5ppm carbon monoxide, and an n-type response with a fast response time at 5ppm hydrogen. Figure 6 It can be seen that the MoO3 / α-Fe2O3 hydrogen sensor prepared in Example 1 and the WO3 / α-Fe2O3 hydrogen sensor prepared in Example 2 both exhibit good stability under the conditions of 300°C and 5ppm hydrogen.

[0052] The above performance data show that using the loaded α-Fe2O3-based sensitive materials prepared in Example 1 and Example 2 as the gas-sensitive material of the hydrogen sensor changes the barrier height and interface charge layer thickness of the unloaded α-Fe2O3 sensitive material, and the prepared hydrogen sensor shows obvious advantages in selectivity.

[0053] The present invention is not limited to the applications listed in the specification and implementation methods, and can be fully applied to various fields suitable for the present invention. Without departing from the spirit and essence of the present invention, it is easy for those familiar with the art to implement additional modifications and variations, but these corresponding modifications and variations should all fall within the scope of protection required by the present invention.

[0054] The above descriptions are only some embodiments of the present invention and do not limit the implementation mode and protection scope of the present invention. Those skilled in the art should be aware that any solutions obtained by equivalent substitutions and obvious changes made using the contents of the present invention specification should be included in the protection scope of the present invention.

Claims

1. A highly selective hydrogen sensor loaded with three-dimensional The method for preparing a composite sensitive material is characterized by: The following steps are involved: S1: adding ferrocyanide and polyvinyl pyrrolidone to a hydrochloric acid solution and uniformly mixing to obtain a mixed solution A; the molar concentration of the ferrocyanide and polyvinyl pyrrolidone in the hydrochloric acid solution is 1:0.15-0.2; the molar concentration of the hydrochloric acid is 0.01 M-0.1 M; S2: Seal the mixed solution A and heat it at 80°C~85°C for 20 h~23 h; S3: centrifuging the material obtained in step S2 and washing it multiple times with a mixed solution of ethanol and deionized water, and then dispersing it in an ethanol solution to obtain a mixed solution B; S4: adding a weighed weak acid conjugate base to the mixed solution B, stirring at room temperature for 90 min, and then centrifuging, washing, and drying to obtain a precursor material; the molar mass of the alkali metal to ferrocyanide in the weak acid conjugate base is 1:1.4-2.5; the weak acid conjugate base is any one of sodium molybdate, sodium silicate, sodium tungstate, potassium niobate, and potassium selenate; S5: The precursor material obtained in S4 was heated to 550 °C under air conditions and kept warm for 180 min to obtain a supported three-dimensional Composite sensitive materials.

2. The preparation method according to claim 1, wherein: In step S1, the ferrocyanide is potassium ferrocyanide or potassium ferrocyanide.

3. The preparation method according to claim 1, wherein: In step S3, the centrifuge speed during centrifugation is 8000 rpm / min; the ethanol content in the ethanol solution is 80% by mass.

4. The preparation method according to claim 1, wherein: In step S5, the heating rate is 0.5-2°C / min.

5. A highly selective hydrogen sensor-loaded sensitive material, characterized by: The sensitive material is prepared by the preparation method according to any one of claims 1 to 4; wherein the loaded oxide accounts for 35% to 75% of the total mass of the sensitive material.

6. A highly selective loading type Based hydrogen sensor, characterized by: The gas-sensitive material is the highly selective hydrogen sensor-loaded sensitive material as claimed in claim 5 .

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