A molybdenum-based heterojunction gas-sensitive material, a preparation method and application thereof

Abstract

The application provides a molybdenum-based heterojunction gas-sensitive material and a preparation method and application thereof, and relates to the technical field of gas-sensitive materials.The molybdenum-based heterojunction gas-sensitive material is directly synthesized by a two-step hydrothermal method.The molybdenum-based heterojunction gas-sensitive material comprises nanorod MoO3 and nanoparticle NiWO4;and the nanoparticle NiWO4 and the nanorod MoO3 have a p-n heterostructure.The molybdenum-based heterojunction gas-sensitive material utilizes the heterojunction effect and the catalytic activation effect of NiWO4, effectively improves the gas-sensitive performance of MoO3, and significantly improves the response of the MoO3-NiWO4 gas-sensitive material to H2S gas, which is 2.78 times that of a single MoO3 gas-sensitive material under the same conditions, and the gas-sensitive material has excellent stability.In addition, the gas-sensitive material has a wide source of raw materials, is cheap and easy to obtain, has a simple preparation method, and has a wide industrial application potential.

Description

Technical Field

[0001] This invention relates to the field of gas-sensitive materials technology, and in particular to a molybdenum-based heterojunction gas-sensitive material, its preparation method, and its application. Background Technology

[0002] H2S is a colorless, flammable, and highly toxic gas with a rotten egg smell commonly found in human living environments. It can be used as a nerve agent, seriously harming the human respiratory and nervous systems. Short-term exposure to high concentrations of H2S gas can lead to acute poisoning or even death. Therefore, it is essential to develop a highly stable, selective, and sensitive H2S monitoring technology.

[0003] Currently, gas sensors, as a type of toxic and harmful gas monitoring device, have gas-sensitive materials as their core components. Different gases can be monitored by replacing different gas-sensitive materials, which has the advantages of being convenient, low-cost, and maintenance-free. Therefore, they have received widespread attention in the field of gas monitoring. In order to better monitor changes in H2S concentration, it is necessary to develop high-performance gas-sensitive materials.

[0004] MoO3, as an n-type metal oxide semiconductor material, exhibits highly stable physicochemical properties, enabling it to maintain excellent gas-sensing performance in various working environments. Furthermore, MoO3 possesses diverse and controllable microstructures and a surface rich in adsorbed oxygen, which not only increases the active sites for gas reactions but also promotes surface reactions. Therefore, MoO3 is a semiconductor material with superior gas-sensing performance in the field of gas sensing. However, single MoO3 gas-sensing materials still suffer from drawbacks in H2S gas monitoring, including high operating temperatures, low sensitivity, and poor selectivity, making it difficult to meet the practical requirements for H2S gas detection.

[0005] To improve the gas-sensing performance of MoO3 in H2S gas monitoring, various strategies have been employed in existing technologies. Chinese patent document CN105301061A discloses a self-assembled mesh-like α-MoO3 nanoribbon gas sensor, which fabricates mesh-like α-MoO3 nanoribbons using electron beam vapor deposition. While this invention improves the gas-sensing performance of α-MoO3 to some extent through morphology control, the gas-sensing material requires a high operating temperature. Even at the optimal operating temperature of 177℃, the response value for 10ppm H2S gas is only 13, indicating that sensitivity and energy consumption still need optimization. Furthermore, the electron beam vapor deposition method used to prepare this gas-sensing material involves expensive equipment, high preparation costs, and relatively slow deposition rates, severely limiting its industrial-scale application.

[0006] Chinese patent document CN103342388A discloses an α-type molybdenum oxide nanorod gas-sensitive material, its preparation method, and its application. This invention uses the prepared α-type molybdenum oxide nanorod gas-sensitive material for CO gas monitoring. Under the optimal operating temperature of 292℃, the response value for CO gas with a concentration of 40ppm is 239.6. However, this α-type molybdenum oxide nanorod gas-sensitive material can only achieve high sensitivity to the target gas under high temperature and high concentration conditions.

[0007] Therefore, providing an H2S gas-sensitive material with low operating temperature, high sensitivity, and good selectivity is of great technical significance and research value. Summary of the Invention

[0008] To address the technical problems existing in the prior art, this invention provides a molybdenum-based heterojunction gas-sensitive material, its preparation method, and its application. By specifically optimizing the morphology of MoO3 and introducing NiWO4 for synergistic cooperation, a MoO3-NiWO4 heterojunction is constructed, effectively solving the problems of high operating temperature, low sensitivity, and poor selectivity of existing MoO3 gas-sensitive materials for H2S gas detection.

[0009] To solve the above technical problems, the technical solution adopted by the present invention is as follows: A molybdenum-based heterojunction gas-sensitive material includes nanorod-shaped MoO3 and nanoparticle-shaped NiWO4; the nanoparticle-shaped NiWO4 is attached to the nanorod-shaped MoO3, and the nanoparticle-shaped NiWO4 and the nanorod-shaped MoO3 have a pn heterostructure. The molar ratio of the nanoparticle-shaped NiWO4 to the nanorod-shaped MoO3 is 1:3-15.

[0010] Preferably, the diameter of the nanorod-shaped MoO3 is 50-180 nm and the length is 500-2000 nm; The diameter of the nanoparticle-shaped NiWO4 is 30-150 nm.

[0011] A method for preparing the aforementioned molybdenum-based heterojunction gas-sensitive material includes the following steps: Step S01: Dissolve Na2MO4·2H2O in deionized water, adjust the pH to 1-4, stir continuously, place in a sealed container, carry out hydrothermal reaction at 180-220℃, separate and collect the precipitate and dry it to obtain nanorod-shaped MoO3 gas-sensitive material. Step S02: Place nanorod-shaped MoO3, Ni(NO3)2 and Na2WO4 in deionized water, then add ethylene glycol and mix evenly. Place the mixture in a sealed container and carry out a hydrothermal reaction at 150-200℃. After separating and collecting the precipitate and drying it, calcine it in an air atmosphere to obtain a molybdenum-based heterojunction gas-sensitive material.

[0012] Preferably, in step S01, the concentration of Na2MO4•2H2O dissolved in deionized water is controlled to be 0.08-0.15 mmol / mL.

[0013] Preferably, in step S01, the continuous stirring time is 2-4 hours; The hydrothermal reaction takes 20-26 hours.

[0014] Preferably, in step S02, the concentration of Ni(NO3)2 in deionized water is 0.02-0.04 mmol / mL; The molar ratio of Ni(NO3)2, Na2WO4 and nanorod-shaped MoO3 is 1:1:3-15; The volume ratio of deionized water to ethylene glycol is 1:1-1.5.

[0015] Preferably, in step S02, the hydrothermal reaction time is 10-15 hours; The calcination temperature is 300-500℃, and the calcination time is 2-5 hours.

[0016] Application of the aforementioned molybdenum-based heterojunction gas-sensitive material in H2S gas monitoring.

[0017] An H2S sensor was prepared using the aforementioned molybdenum-based heterojunction gas-sensitive material.

[0018] A method for preparing the aforementioned H2S sensor includes the following steps: mixing molybdenum-based heterojunction gas-sensitive material and anhydrous ethanol evenly at a molar ratio of 2-5:1, coating the mixture onto a sensor element, and then assembling it to obtain an H2S sensor. The dry coating amount of the molybdenum-based heterojunction gas-sensitive material on the sensor device is 8.2-10.2 mg / cm³. 2 .

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The molybdenum-based heterojunction gas-sensitive material of the present invention, namely MoO3-NiWO4 gas-sensitive material, uses nanorod-shaped MoO3 as the matrix, with a diameter of 50-180 nm and a length of 500-2000 nm. This structure not only provides a larger specific surface area for the gas-sensitive material, thereby increasing the active sites for gas reaction, but also provides a direct and unidirectional channel for electron transport, effectively avoiding grain boundary scattering, making the electrical signal caused by gas reaction clearer and easier to detect the target gas. On this basis, nanoparticle-shaped NiWO4 (diameter 30-150 nm) are uniformly attached to the nanorod-shaped MoO3, successfully constructing a MoO3-NiWO4 heterostructure, which is a pn heterostructure. This structure can not only accelerate the transport and separation of charge carriers in the gas-sensitive material, but also provide more highly active sites for the reaction, synergistically improving the gas-sensitive response capability of the material.

[0020] (2) The molybdenum-based heterojunction gas-sensitive material of the present invention, NiWO4 contains Ni 2+ It has a specific catalytic activation effect on H2S gas molecules. 2+ The sites preferentially chemisorb H2S molecules, weakening their SH bond energy and making them easier to dissociate and react with oxygen ions on the surface. This lowers the activation energy of the gas molecule reaction, promotes surface reactions, and consequently reduces the operating temperature and energy consumption of the MoO3-NiWO4 gas-sensitive material for H2S gas monitoring, thus improving its response to H2S gas. Experiments showed that, under the same conditions, the 7MoO3-NiWO4 gas-sensitive material exhibited the highest response value to 10 ppm H2S gas, significantly higher than its response to other gases, demonstrating excellent selectivity for H2S gas.

[0021] (3) The preparation method of the molybdenum-based heterojunction gas-sensitive material of the present invention directly synthesizes the MoO3-NiWO4 gas-sensitive material by a two-step hydrothermal method. The preparation method is simple and easy to operate. Compared with the existing methods of improving gas-sensitive performance by doping noble metal materials, the raw materials are cheap and readily available, the production cost is low, and it has greater potential for industrial-scale production.

[0022] (4) The molybdenum-based heterojunction gas-sensitive material of the present invention is applied to the monitoring of H2S gas, especially under the condition of temperature of 125-140℃, the response effect of H2S gas is better; according to the experiment, the response of 7MoO3-NiWO4 gas-sensitive material to 10ppm H2S gas at a temperature of 132℃ is 37.2, which is 2.78 times that of single MoO3 gas-sensitive material; at the same time, under the same conditions, the 7MoO3-NiWO4 gas-sensitive material was repeatedly tested 7 times for H2S gas at a concentration of 10ppm for 35 consecutive days, and the response value of the 7 times was around 37. The test results fluctuated little, indicating that the 7MoO3-NiWO4 gas-sensitive material has excellent long-term stability and repeatability. Attached Figure Description

[0023] Figure 1 The image shows a SEM image of the molybdenum-based heterojunction gas-sensitive material prepared in Example 3.

[0024] Figure 2 This is a TEM image of the molybdenum-based heterojunction gas-sensitive material prepared in Example 3.

[0025] Figure 3 The graph shows the selectivity of the gas-sensitive materials prepared in Example 3 and Comparative Example 1 for H2S gas.

[0026] Figure 4 The operating temperature diagrams are for the gas-sensitive materials prepared in Examples 1-5 and Comparative Examples 1-2.

[0027] Figure 5 The stability performance diagram is shown for the molybdenum-based heterojunction gas-sensitive material prepared in Example 3. Detailed Implementation

[0028] To provide a clearer understanding of the technical features, objectives, and effects of this invention, specific embodiments are now described. It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0029] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments of the present invention. As used herein, "first," "second," etc., are used to distinguish similar objects and are not used to describe a particular order or sequence. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0030] This invention provides a molybdenum-based heterojunction gas-sensitive material, comprising nanorod-shaped MoO3 and nanoparticle-shaped NiWO4; the nanoparticle-shaped NiWO4 is attached to the nanorod-shaped MoO3, and the nanoparticle-shaped NiWO4 and the nanorod-shaped MoO3 form a pn heterostructure. The molar ratio of the nanoparticle-shaped NiWO4 to the nanorod-shaped MoO3 is 1:3-15.

[0031] In this embodiment of the invention, the pn heterostructure formed by the nanoparticle-shaped NiWO4 and the nanorod-shaped MoO3 can not only accelerate the transport and separation of charge carriers in the gas-sensitive material, but also provide more highly active sites for the reaction; the supported NiWO4 acts as a co-catalyst, and the Ni in NiWO4... 2+ Ni has a specific catalytic activation effect on H2S gas molecules. 2+ The site can chemically adsorb H2S molecules, weaken their SH bond energy, make them more easily dissociated and react with oxygen ions on the surface, reduce the activation energy of gas molecule reactions, promote the occurrence of material surface reactions, and thus synergistically improve the gas-sensing performance of the material to H2S gas.

[0032] Preferably, in the molybdenum-based heterojunction gas-sensitive material, the molar ratio of the nanoparticle NiWO4 to the nanorod-shaped MoO3 is 1:5-7.

[0033] Preferably, in the molybdenum-based heterojunction gas-sensitive material, the diameter of the nanorod-shaped MoO3 is 50-180 nm and the length is 500-2000 nm; the diameter of the nanoparticle-shaped NiWO4 is 30-150 nm.

[0034] This invention also provides a method for preparing the molybdenum-based heterojunction gas-sensitive material, comprising the following steps: Step S01: Dissolve Na2MO4·2H2O in deionized water, adjust the pH to 1-4, stir continuously, place in a sealed container, carry out hydrothermal reaction at 180-220℃, separate and collect the precipitate and dry it to obtain nanorod-shaped MoO3 gas-sensitive material. Step S02: Place nanorod-shaped MoO3, Ni(NO3)2 and Na2WO4 in deionized water, then add ethylene glycol and mix evenly. Place the mixture in a sealed container and carry out a hydrothermal reaction at 150-200℃. After separating and collecting the precipitate and drying it, calcine it in an air atmosphere to obtain MoO3-NiWO4 gas-sensitive material, i.e., molybdenum-based heterojunction gas-sensitive material.

[0035] Preferably, in step S01, the concentration of Na2MO4•2H2O dissolved in deionized water is controlled to be 0.08-0.15 mmol / mL.

[0036] Preferably, in step S01, the continuous stirring time is 2-4 hours; the hydrothermal reaction time is 20-26 hours.

[0037] Preferably, in step S02, the concentration of Ni(NO3)2 in deionized water is 0.02-0.04 mmol / mL; the molar ratio of Ni(NO3)2, Na2WO4 and nanorod-shaped MoO3 is 1:1:3-15; and the volume ratio of deionized water to ethylene glycol is 1:1-1.5.

[0038] Preferably, in step S02, the hydrothermal reaction time is 10-15 h; the calcination temperature is 300-500 °C, and the calcination time is 2-5 h.

[0039] This invention also provides the application of the molybdenum-based heterojunction gas-sensitive material in H2S gas monitoring.

[0040] This invention also provides an H2S sensor, which is prepared using the molybdenum-based heterojunction gas-sensitive material.

[0041] Furthermore, the H2S sensor is prepared by uniformly mixing molybdenum-based heterojunction gas-sensitive material and anhydrous ethanol at a molar ratio of 2-5:1, and then coating the mixture onto the sensor element. The dry basis coating amount of the molybdenum-based heterojunction gas-sensitive material on the sensor element is controlled to be 8.2-10.2 mg / cm³. 2 Then, the electrodes of the sensor are fixed on the base, and the nickel-chromium resistance wire is assembled on the base. The sensor is aged at 80-100℃ for 2-5 days to obtain the H2S sensor.

[0042] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described below in conjunction with some specific embodiments.

[0043] Example 1 This embodiment provides a method for preparing a molybdenum-based heterojunction gas-sensitive material, the specific steps of which are as follows: (1) Dissolve 6.0 mmol of Na2MO4·2H2O in 60 mL of deionized water. After complete dissolution, adjust the pH to 1.0 with 68 wt% concentrated nitric acid. After stirring continuously for 4 h, place it in a sealed reaction vessel and carry out hydrothermal reaction at 180 °C for 26 h. Centrifuge to collect the precipitate and dry it to obtain nanorod-shaped MoO3 gas-sensitive material. (2) 3.0 mmol of nanorod-shaped MoO3, 1.0 mmol of Ni(NO3)2 and 1.0 mmol of Na2WO4 were placed in 30 mL of deionized water, and then 30 mL of ethylene glycol was added to the above solution. The mixture was stirred continuously for 60 min, placed in a sealed reaction vessel, and subjected to hydrothermal reaction at 150 °C for 15 h. The precipitate was collected by centrifugation and dried. The precipitate was calcined at 500 °C in air atmosphere for 2 h to obtain 3MoO3-NiWO4 gas-sensitive material.

[0044] This embodiment also provides a molybdenum-based heterojunction gas-sensitive material prepared by the aforementioned method; upon testing, in the 3MoO3-NiWO4 gas-sensitive material of this embodiment, the diameter distribution range of the nanorod-shaped MoO3 is 50-100 nm, the length distribution range is 500-900 nm, and the diameter distribution range of the nanoparticle-shaped NiWO4 is 100-150 nm; the nanoparticle-shaped NiWO4 and the nanorod-shaped MoO3 successfully constructed a pn heterostructure.

[0045] Example 2 This embodiment provides a method for preparing a molybdenum-based heterojunction gas-sensitive material, the specific steps of which are as follows: (1) Dissolve 4.8 mmol of Na2MO4·2H2O in 60 mL of deionized water. After complete dissolution, adjust the pH to 2.0 with 68 wt% concentrated nitric acid. After stirring continuously for 3 h, place it in a sealed reaction vessel and carry out hydrothermal reaction at 200 °C for 23 h. Centrifuge to collect the precipitate and dry it to obtain nanorod-shaped MoO3 gas-sensitive material. (2) 3.0 mmol of nanorod-shaped MoO3, 0.6 mmol of Ni(NO3)2 and 0.6 mmol of Na2WO4 were placed in 30 mL of deionized water, and then 35 mL of ethylene glycol was added to the above solution. The mixture was stirred continuously for 40 min and placed in a sealed reaction vessel. The hydrothermal reaction was carried out at 180 °C for 10 h. The precipitate was collected by centrifugation and dried. The precipitate was calcined at 400 °C in air atmosphere for 5 h to obtain 5MoO3-NiWO4 gas-sensitive material.

[0046] This embodiment also provides a molybdenum-based heterojunction gas-sensitive material prepared by the aforementioned method; upon testing, in the 5MoO3-NiWO4 gas-sensitive material of this embodiment, the diameter distribution range of the nanorod-shaped MoO3 is 80-120 nm, the length distribution range is 1000-1500 nm, and the diameter distribution range of the nanoparticle-shaped NiWO4 is 30-90 nm; the nanoparticle-shaped NiWO4 and the nanorod-shaped MoO3 successfully constructed a pn heterostructure.

[0047] Example 3 This embodiment provides a method for preparing a molybdenum-based heterojunction gas-sensitive material, the specific steps of which are as follows: (1) Dissolve 7.2 mmol of Na2MO4·2H2O in 60 mL of deionized water. After complete dissolution, adjust the pH to 3.0 with 68 wt% concentrated nitric acid. After stirring continuously for 2 h, place it in a sealed reaction vessel and carry out hydrothermal reaction at 190 °C for 24 h. Centrifuge to collect the precipitate and dry it to obtain nanorod-shaped MoO3 gas-sensitive material. (2) 5.6 mmol of nanorod-shaped MoO3, 0.8 mmol of Ni(NO3)2 and 0.8 mmol of Na2WO4 were placed in 30 mL of deionized water, and then 30 mL of ethylene glycol was added to the above solution. The mixture was stirred continuously for 30 min and placed in a sealed reaction vessel. The hydrothermal reaction was carried out at 180 °C for 12 h. The precipitate was collected by centrifugation and dried. The precipitate was calcined at 400 °C in air atmosphere for 3 h to obtain 7MoO3-NiWO4 gas-sensitive material.

[0048] This embodiment also provides a molybdenum-based heterojunction gas-sensitive material prepared by the aforementioned method; upon testing, in the 7MoO3-NiWO4 gas-sensitive material of this embodiment, the diameter distribution range of the nanorod-shaped MoO3 is 50-100 nm, the length distribution range is 800-1500 nm, and the diameter distribution range of the nanoparticle-shaped NiWO4 is 70-120 nm; the nanoparticle-shaped NiWO4 and the nanorod-shaped MoO3 successfully constructed a pn heterostructure.

[0049] Example 4 This embodiment provides a method for preparing a molybdenum-based heterojunction gas-sensitive material, the specific steps of which are as follows: (1) Dissolve 9.0 mmol of Na2MO4·2H2O in 60 mL of deionized water. After complete dissolution, adjust the pH to 4.0 with 68 wt% concentrated nitric acid. After stirring continuously for 3 h, place it in a sealed reaction vessel and carry out hydrothermal reaction at 220 °C for 20 h. Centrifuge to collect the precipitate and dry it to obtain nanorod-shaped MoO3 gas-sensitive material. (2) 10.0 mmol of nanorod-shaped MoO3, 1.0 mmol of Ni(NO3)2 and 1.0 mmol of Na2WO4 were placed in 30 mL of deionized water, and then 40 mL of ethylene glycol was added to the above solution. The mixture was stirred continuously for 50 min and placed in a sealed reaction vessel. The hydrothermal reaction was carried out at 160 °C for 14 h. The precipitate was collected by centrifugation and dried. The precipitate was calcined at 450 °C in air atmosphere for 3 h to obtain 10MoO3-NiWO4 gas-sensitive material.

[0050] This embodiment also provides a molybdenum-based heterojunction gas-sensitive material prepared by the aforementioned method; upon testing, in the 10MoO3-NiWO4 gas-sensitive material of this embodiment, the diameter distribution range of the nanorod-shaped MoO3 is 140-180 nm, the length distribution range is 1500-2000 nm, and the diameter distribution range of the nanoparticle-shaped NiWO4 is 80-130 nm; the nanoparticle-shaped NiWO4 and the nanorod-shaped MoO3 successfully constructed a pn heterostructure.

[0051] Example 5 This embodiment provides a method for preparing a molybdenum-based heterojunction gas-sensitive material, the specific steps of which are as follows: (1) Dissolve 6.0 mmol of Na2MO4·2H2O in 60 mL of deionized water. After complete dissolution, adjust the pH to 3.0 with 68 wt% concentrated nitric acid. After stirring continuously for 4 h, place it in a sealed reaction vessel and carry out hydrothermal reaction at 210 °C for 21 h. Centrifuge to collect the precipitate and dry it to obtain nanorod-shaped MoO3 gas-sensitive material. (2) 18.0 mmol of nanorod-shaped MoO3, 1.2 mmol of Ni(NO3)2 and 1.2 mmol of Na2WO4 were placed in 30 mL of deionized water, and 45 mL of ethylene glycol was added to the above solution. The mixture was stirred continuously for 30 min and placed in a sealed reaction vessel. The hydrothermal reaction was carried out at 170 °C for 13 h. The precipitate was collected by centrifugation and dried. The precipitate was calcined at 350 °C in air atmosphere for 4 h to obtain 15MoO3-NiWO4 gas-sensitive material.

[0052] This embodiment also provides a molybdenum-based heterojunction gas-sensitive material prepared by the aforementioned method; upon testing, in the 15MoO3-NiWO4 gas-sensitive material of this embodiment, the diameter distribution range of the nanorod-shaped MoO3 is 110-160 nm, the length distribution range is 1000-1800 nm, and the diameter distribution range of the nanoparticle-shaped NiWO4 is 50-110 nm; the nanoparticle-shaped NiWO4 and the nanorod-shaped MoO3 successfully constructed a pn heterostructure.

[0053] Example 6 The molybdenum-based heterojunction gas-sensitive materials of Examples 1-5 were mixed and ground evenly with anhydrous ethanol at a molar ratio of 5:1, and then coated onto the sensor device. The gold electrodes of the sensor device were then welded onto the base, and the nickel-chromium resistance wire was assembled on the base. The sensor was aged at 90°C for 5 days to obtain the H2S sensor of Examples 1-5.

[0054] In this case, the dry-base coating amount of the molybdenum-based heterojunction gas-sensitive material in Example 1 on the sensor device was controlled to be 8.2 mg / cm². 2The molybdenum-based heterojunction gas-sensitive material in Example 2 had a dry-base coating amount of 9.4 mg / cm² on the sensor device. 2 The molybdenum-based heterojunction gas-sensitive material in Example 3 had a dry-base coating amount of 9.2 mg / cm² on the sensor device. 2 The molybdenum-based heterojunction gas-sensitive material in Example 4 had a dry-base coating amount of 8.6 mg / cm² on the sensor device. 2 The molybdenum-based heterojunction gas-sensitive material in Example 5 had a dry-base coating amount of 10.2 mg / cm² on the sensor device. 2 .

[0055] Comparative Example 1 The preparation method of the gas-sensitive material in this comparative example is as follows: 7.2 mmol of Na2MO4·2H2O was dissolved in 60 mL of deionized water. After complete dissolution, the pH was adjusted to 3.0 with 68 wt% concentrated nitric acid. After continuous stirring for 2 h, the mixture was placed in a sealed reaction vessel and subjected to hydrothermal reaction at 190 °C for 24 h. The precipitate was collected by centrifugation and dried to obtain nanorod-shaped MoO3 gas-sensitive material.

[0056] Testing revealed that the diameter of the nanorod-shaped MoO3 in the gas-sensitive material prepared in Comparative Example 1 ranged from 50 to 100 nm, and the length ranged from 800 to 1500 nm.

[0057] Comparative Example 2 The preparation method of the gas-sensitive material in this comparative example is as follows: 0.8 mmol of Ni(NO3)2 and 0.8 mmol of Na2WO4 are dissolved in 30 mL of deionized water, and then 30 mL of ethylene glycol is added to the above solution. The mixture is stirred continuously for 30 min, placed in a sealed reaction vessel, and subjected to hydrothermal reaction at 180 °C for 12 h. The precipitate is collected by centrifugation and dried. The precipitate is then calcined at 450 °C in air atmosphere for 3 h to obtain NiWO4 gas-sensitive material.

[0058] Testing revealed that the diameter distribution of the nanoparticle-shaped NiWO4 in the gas-sensitive material prepared in Comparative Example 2 ranged from 70 to 120 nm.

[0059] Comparative Example 3 The preparation method of the gas-sensitive material in this comparative example is as follows: (1) Dissolve 7.2 mmol of Na2MO4·2H2O in 60 mL of deionized water. After complete dissolution, adjust the pH to 3.0 with 68 wt% concentrated nitric acid. After stirring continuously for 2 h, place it in a sealed reaction vessel and carry out hydrothermal reaction at 190 °C for 24 h. Centrifuge to collect the precipitate and dry it to obtain nanorod-shaped MoO3 gas-sensitive material. (2) 0.4 mmol of nanorod-shaped MoO3, 0.8 mmol of Ni(NO3)2 and 0.8 mmol of Na2WO4 were placed in 30 mL of deionized water, and then 30 mL of ethylene glycol was added to the above solution. The mixture was stirred continuously for 30 min and placed in a sealed reaction vessel. The mixture was subjected to hydrothermal reaction at 180 °C for 12 h. The precipitate was collected by centrifugation and dried. The precipitate was calcined at 400 °C in air atmosphere for 3 h to obtain 0.5 MoO3-NiWO4 gas-sensitive material.

[0060] Testing revealed that in the gas-sensitive materials prepared in Comparative Example 3, the diameter distribution range of the nanorod-shaped MoO3 was 50-100 nm, the length distribution range was 800-1500 nm, and the diameter distribution range of the nanoparticle-shaped NiWO4 was 70-120 nm.

[0061] Comparative Example 4 The preparation method of the gas-sensitive material in this comparative example is as follows: (1) Dissolve 7.2 mmol of Na2MO4·2H2O in 60 mL of deionized water. After complete dissolution, adjust the pH to 3.0 with 68 wt% concentrated nitric acid. After stirring continuously for 2 h, place it in a sealed reaction vessel and carry out hydrothermal reaction at 190 °C for 24 h. Centrifuge to collect the precipitate and dry it to obtain nanorod-shaped MoO3 gas-sensitive material. (2) 16.0 mmol of nanorod-shaped MoO3, 0.8 mmol of Ni(NO3)2 and 0.8 mmol of Na2WO4 were placed in 30 mL of deionized water, and then 30 mL of ethylene glycol was added to the above solution. The mixture was stirred continuously for 30 min and placed in a sealed reaction vessel. The hydrothermal reaction was carried out at 180 °C for 12 h. The precipitate was collected by centrifugation and dried. The precipitate was calcined at 400 °C in air atmosphere for 3 h to obtain 20MoO3-NiWO4 gas-sensitive material.

[0062] Testing revealed that in the gas-sensitive materials prepared in Comparative Example 4, the diameter distribution range of the nanorod-shaped MoO3 was 50-100 nm, the length distribution range was 800-1500 nm, and the diameter distribution range of the nanoparticle-shaped NiWO4 was 70-120 nm.

[0063] Following the method of Example 6, the gas-sensitive materials of Comparative Examples 1-4 were mixed and ground evenly with anhydrous ethanol and then coated onto the sensor device. The gold electrodes of the sensor device were then welded onto the base, and the nickel-chromium resistance wire was assembled onto the base. The sensor was aged at 90°C for 5 days to obtain the H2S sensor of Comparative Examples 1-4.

[0064] In this study, the dry coating amount of the gas-sensitive material in Comparative Example 1 on the sensor device was controlled to be 8.8 mg / cm³. 2The dry-base coating amount of the gas-sensitive material in Comparative Example 2 on the sensor device was 9.6 mg / cm³. 2 The dry-base coating amount of the gas-sensitive material in Comparative Example 3 on the sensor device was 9.3 mg / cm². 2 The dry-base coating amount of the gas-sensitive material in Comparative Example 4 on the sensor device was 8.5 mg / cm³. 2 .

[0065] Experimental Example 1 To test the H2S sensor response capability to H2S gas in each embodiment and comparative example, the gas-sensitive materials of Examples 1-5 and Comparative Examples 1-4 were tested and analyzed. The response performance of each gas-sensitive material to H2S gas at a concentration of 10 ppm at 132°C was tested. The specific results are shown in the table below:

[0066] It can be seen that the gas-sensitive materials prepared by single MoO3 and single NiWO4 in Comparative Examples 1 and 2 have low response values ​​to H2S gas, at 13.4 and 5.7 respectively. In contrast, the 3MoO3-NiWO4 gas-sensitive material prepared in Example 1 has a response value of 23.3 to H2S gas, which is significantly higher than that of single MoO3 and NiWO4 in Comparative Examples 1-2. This is mainly due to the limited surface catalytic activity and rapid electron-hole recombination of single MoO3 and single NiWO4, which greatly affects the response to H2S gas. However, when MoO3 and NiWO4 are combined to form a pn heterojunction, the gas-sensitive performance to H2S gas is significantly improved. The 3MoO3-NiWO4 prepared in Example 1 has a response value of 23.3 to H2S gas. This is because the prepared MoO3-NiWO4 heterojunction not only increases the electron migration rate and enhances the carrier transport and separation capabilities of the gas-sensitive material, but the supported NiWO4 also acts as a co-catalyst. 2+ Ni has a specific catalytic activation effect on H2S gas molecules. 2+ The sites can chemically adsorb H2S molecules, weaken their SH bond energy, further reduce the activation energy of gas molecule reactions, and promote the occurrence of surface reactions of gas-sensitive materials. Thus, the MoO3-NiWO4 heterojunction gas-sensitive material greatly enhances the response to H2S.

[0067] The response values ​​of 0.5MoO3-NiWO4 and 20MoO3-NiWO4 prepared in Comparative Examples 3 and 4 to H2S were 8.2 and 17.7, respectively, both lower than the response to H2S gas in Example 1. This demonstrates that both insufficient and excessive NiWO4 loading on MoO3 affect the gas-sensing performance to H2S gas. Analysis shows that insufficient NiWO4 loading on MoO3 leads to insignificant heterojunction and NiWO4 catalytic effects, resulting in reduced gas-sensing response to H2S gas. Conversely, excessive NiWO4 loading on MoO3 reduces the specific surface area, covering active sites and decreasing the number of active sites for gas adsorption and reaction on the material surface, ultimately leading to a decrease in gas-sensing performance. The 7MoO3-NiWO4 gas-sensing material prepared in Example 3 showed the highest response value to H2S gas, indicating that the optimal composite molar ratio of MoO3 to NiWO4 gas-sensing material is 7:1.

[0068] Experimental Example 2 The morphology of the 7MoO3-NiWO4 gas-sensitive material prepared in Example 3 was characterized, and the morphology image of the 7MoO3-NiWO4 gas-sensitive material is shown below. Figure 1 As shown. From Figure 1 It can be seen that, Figure 1 In the first part, MoO3 is in the form of nanorods with a diameter distribution range of 50-100 nm and a length distribution range of 800-1500 nm. The nanorod structure of MoO3 can provide a larger specific surface area and a direct, unidirectional channel for electron transport, avoiding grain boundary scattering, making the electrical signal caused by gas reaction clearer and facilitating H2S gas monitoring. Figure 1 In section 2, nanoparticle-shaped NiWO4 is attached to the surface of nanorod-shaped MoO3, with a diameter distribution ranging from 70-120 nm. The heterostructure formed by the nanorod-shaped MoO3 and nanoparticle-shaped NiWO4 enhances the conductivity of the gas-sensitive material, improves the transport and separation efficiency of charge carriers, and promotes gas reactions on the material surface. This enhances the monitoring capability of the MoO3-NiWO4 gas-sensitive material for H2S gas. Furthermore, the preparation of the heterostructure provides more highly active sites, lowers the activation energy of gas molecule reactions, and further promotes surface reactions. In addition, the nanoparticle-shaped NiWO4 can also act as a co-catalyst, attached to the nanorod-shaped MoO3. The Ni in NiWO4... 2+ Ni has a specific catalytic activation effect on H2S gas molecules. 2+ The sites can chemically adsorb H2S molecules, weaken their SH bond energy, make them easier to dissociate and react with oxygen ions on the surface, and directly improve the gas-sensing performance of MoO3-NiWO4 gas-sensitive material for H2S.

[0069] Based on the aforementioned response performance test results, the molybdenum-based heterojunction gas-sensitive material of the present invention exhibits a response value of 23.3-37.2 to 10 ppm H2S gas at a temperature of 132°C. Specifically, when the molar ratio of nanorod-shaped MoO3 to nanoparticle-shaped NiWO4 is 7:1, the response value to H2S gas reaches 37.2, which is 2.78 times that of the single MoO3 gas-sensitive material. Furthermore, under the same conditions, the gas sensor was repeatedly tested seven times over 35 consecutive days (tested once every five days) to 10 ppm H2S gas. The response values ​​to H2S gas were consistently around 37, with minimal fluctuations, indicating that the gas sensor based on the 7MoO3-NiWO4 gas-sensitive material possesses excellent long-term stability and repeatability for H2S gas monitoring.

[0070] Experimental Example 3 The 7MoO3-NiWO4 gas-sensitive material prepared in Example 3 was observed by transmission electron microscopy. The transmission electron microscopy image of the 7MoO3-NiWO4 gas-sensitive material is shown below. Figure 2 As shown. From Figure 2 Two different closely connected lattice stripes can be clearly seen in the figure. The stripe with a lattice spacing of 0.252 nm corresponds to the (041) crystal plane of the orthorhombic phase MoO3, and the stripe with a lattice spacing of 0.372 nm corresponds to the (320) crystal plane of the monoclinic phase NiWO4. The red curve in the figure is the lattice interface between MoO3 and NiWO4. The two crystals coexist and their crystal planes are in full contact, which shows the successful preparation of MoO3-NiWO4 gas-sensitive material. It also proves that the MoO3 crystal and NiWO4 crystal successfully constructed a pn heterojunction.

[0071] Test Example 4 The gas-sensitive selectivity of the gas-sensitive materials prepared in Example 3 and Comparative Example 1 were tested respectively, and the specific results are as follows: Figure 3 As shown. To test the selectivity of the gas sensor, different types of test gases with a concentration of 10 ppm were sequentially introduced into the testing instrument at a temperature of 132℃, and gas-sensing tests were conducted. The tests revealed that the 7MoO3-NiWO4 gas-sensing material exhibited the highest response value to H2S gas at a concentration of 10 ppm, significantly higher than the responses to other gases under the same testing conditions. This indicates that the 7MoO3-NiWO4 gas-sensing material demonstrates excellent selectivity for H2S gas. Analysis suggests that this is mainly due to the introduction of NiWO4, which optimizes the catalytic activity of the gas-sensing material surface, and the Ni... 2+These sites can serve as preferential adsorption and reaction sites for H2S molecules. Sulfur atoms in H2S molecules readily interact strongly with these metal sites, weakening their SH bond energy and further reducing the activation energy of H2S gas molecule reactions. This makes it easier for H2S to react with oxygen species adsorbed on the material surface, thereby significantly improving the selectivity of MoO3-NiWO4 gas-sensitive materials for H2S gas.

[0072] Experimental Example 5 The optimal operating temperature tests were conducted on the gas-sensitive materials prepared in Examples 1-5 and Comparative Examples 1-2, respectively, to test the response performance of each gas-sensitive material to 10 ppm H2S gas at different temperatures. Specific results are as follows: Figure 4 As shown. From Figure 4 The test results show that the MoO3-NiWO4 gas-sensitive materials with different composite ratios in Examples 1-5 exhibit better response to H2S gas at operating temperatures of 125-140℃, especially at 132℃ where the response reaches its peak. In contrast, the single MoO3 gas-sensitive material only reaches its peak response to H2S gas at 150℃. This indicates that the introduction of NiWO4 successfully constructs a heterojunction, improving electron transport efficiency and ensuring sufficient charge carriers for reaction even at lower temperatures. The preparation of the heterostructure also provides more highly active sites, lowers the activation energy of gas molecule reactions, and promotes surface reactions. Furthermore, NiWO4 can optimize the catalytic activity of the gas-sensitive material surface, and Ni... 2+ The site can also preferentially chemically adsorb H2S molecules, weakening their SH bond energy and further reducing the activation energy of the gas molecule reaction, allowing the reaction to occur at a lower temperature. This also shows that excessively high or low operating temperatures will affect the performance of gas-sensitive materials. Too low an operating temperature will cause oxygen molecules to lack sufficient energy to overcome the adsorption energy barrier, resulting in insufficient chemically adsorbed oxygen on the material surface. This will also cause H2S gas to lack sufficient energy to react with the adsorbed oxygen, leading to a decrease in gas-sensing performance. On the other hand, too high an operating temperature will cause the gas molecules adsorbed on the material surface to move faster and desorb, reducing the gas reaction on the material surface and also leading to a decrease in gas-sensing performance.

[0073] Experimental Example 6 Long-term stability tests were conducted on the 7MoO3-NiWO4 gas-sensitive material prepared in Example 3. Specifically, the test was repeated 7 times (once every 5 days) for 35 consecutive days at a temperature of 132°C with H2S gas at a concentration of 10 ppm. The specific results are as follows. Figure 5 As shown. By Figure 5As can be seen, the 7MoO3-NiWO4 gas-sensitive material in Example 3 showed a response of around 37 to H2S gas in 7 tests, with minimal fluctuation in the test results. This indicates that the gas sensor based on the 7MoO3-NiWO4 gas-sensitive material has excellent long-term stability and repeatability. This is mainly due to the excellent chemical stability of both MoO3 and NiWO4, and the rod-shaped structure of MoO3 having stronger structural rigidity and a stable electron transport channel. At the same time, the preparation of the heterojunction can provide a more stable electron transport path, making the response to H2S gas more stable.

[0074] Unless otherwise stated, all percentages used in this invention are mass percentages.

[0075] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A molybdenum-based heterojunction gas-sensitive material, characterized in that, It includes nanorod-shaped MoO3 and nanoparticle-shaped NiWO4; the nanoparticle-shaped NiWO4 is attached to the nanorod-shaped MoO3, and the nanoparticle-shaped NiWO4 and the nanorod-shaped MoO3 have a pn heterostructure. The molar ratio of the nanoparticle-shaped NiWO4 to the nanorod-shaped MoO3 is 1:3-15.

2. The molybdenum-based heterojunction gas-sensitive material according to claim 1, characterized in that, The diameter of the nanorod-shaped MoO3 is 50-180 nm, and the length is 500-2000 nm; The diameter of the nanoparticle-shaped NiWO4 is 30-150 nm.

3. A method for preparing a molybdenum-based heterojunction gas-sensitive material as described in claim 1 or 2, characterized in that, Includes the following steps: Step S01: Dissolve Na2MO4·2H2O in deionized water, adjust the pH to 1-4, stir continuously, place in a sealed container, carry out hydrothermal reaction at 180-220℃, separate and collect the precipitate and dry it to obtain nanorod-shaped MoO3 gas-sensitive material. Step S02: Place nanorod-shaped MoO3, Ni(NO3)2 and Na2WO4 in deionized water, then add ethylene glycol and mix evenly. Place the mixture in a sealed container and carry out a hydrothermal reaction at 150-200℃. After separating and collecting the precipitate and drying it, calcine it in an air atmosphere to obtain a molybdenum-based heterojunction gas-sensitive material.

4. The method for preparing the molybdenum-based heterojunction gas-sensitive material according to claim 3, characterized in that, In step S01, the concentration of Na2MO4•2H2O dissolved in deionized water is controlled to be 0.08-0.15 mmol / mL.

5. The method for preparing the molybdenum-based heterojunction gas-sensitive material according to claim 3, characterized in that, In step S01, the continuous stirring time is 2-4 hours; The hydrothermal reaction takes 20-26 hours.

6. The method for preparing the molybdenum-based heterojunction gas-sensitive material according to claim 3, characterized in that, In step S02, the concentration of Ni(NO3)2 in deionized water is 0.02-0.04 mmol / mL; The molar ratio of Ni(NO3)2, Na2WO4 and nanorod-shaped MoO3 is 1:1:3-15; The volume ratio of deionized water to ethylene glycol is 1:1-1.

5.

7. The method for preparing the molybdenum-based heterojunction gas-sensitive material according to claim 3, characterized in that, In step S02, the hydrothermal reaction time is 10-15 hours. The calcination temperature is 300-500℃, and the calcination time is 2-5 hours.

8. The application of a molybdenum-based heterojunction gas-sensitive material as described in claim 1 or 2 in H2S gas monitoring.

9. An H2S sensor, characterized in that, It is prepared using the molybdenum-based heterojunction gas-sensitive material as described in claim 1 or 2.

10. A method for preparing an H2S sensor as described in claim 9, characterized in that, The process includes the following steps: mixing molybdenum-based heterojunction gas-sensitive material and anhydrous ethanol evenly at a molar ratio of 2-5:1, coating the mixture onto the sensor, and then assembling it to obtain an H2S sensor. The dry coating amount of the molybdenum-based heterojunction gas-sensitive material on the sensor device is 8.2-10.2 mg / cm³. 2 .

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