Room temperature ammonia gas sensor based on alpha-Fe2O3 / MoS2 composite film material and preparation method thereof

Abstract

The invention belongs to the technical field of semiconductor gas sensors, and particularly relates to a room-temperature ammonia gas sensor based on an alpha-Fe2O3 / MoS2 composite film material and a preparation method of the room-temperature ammonia gas sensor. In order to solve the problems that an existing ammonia gas sensor is low in sensitivity, high in working temperature, complex in preparation method and the like, the invention aims to provide the room-temperature ammonia gas sensor based on the alpha-Fe2O3 / MoS2 composite material, and the room-temperature ammonia gas sensor comprises an interdigital electrode and a sensitive material layer which are formed on the surface of a substrate; and the sensitive material layer is made of an alpha-Fe2O3 / MoS2 composite material. The agglomeration effect is reduced by compounding alpha-Fe2O3 and MoS2, the specific surface area is increased, and the room-temperature gas-sensitive response capability is improved.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor gas sensor technology, specifically relating to a room temperature ammonia gas sensor based on α-Fe2O3 and MoS2 composite materials and its preparation method. Background Technology

[0002] Ammonia is a key compound involved in the global biochemical nitrogen cycle, typically released from nitrogen-containing organic plant and animal matter, organic decomposition, industrial wastewater, and motor vehicles. It is an important industrial chemical widely used in the manufacture of pharmaceuticals, plastics, fertilizers, cleaning products, dyes, explosives, and synthetic fibers. However, it is undeniable that ammonia is also a harmful substance. On one hand, when the concentration of ammonia in the air exceeds normal levels, its corrosive and toxic properties can damage human organs such as the skin, eyes, and respiratory tract. China's "Indoor Air Quality Standard" GB / T18883-2002 stipulates that the concentration of ammonia in indoor air must not exceed 0.2635 ppm, and the "Hygienic Standard for Industrial Enterprise Design" TJ36-79 stipulates that the concentration of ammonia in workshop air must not exceed 39.53 ppm. On the other hand, highly reactive ammonia readily reacts with nitric acid and sulfuric acid in the air to form aerosols. The chemical fumes produced by these nanoscale aerosols contribute to the greenhouse effect, leading to a series of environmental problems. Therefore, developing an ammonia sensor with high response value, high selectivity, low detection limit, and long-term stability is of great significance for production safety and human health.

[0003] Currently, various techniques exist for the detection and monitoring of ammonia, including spectrometry, gas chromatography, electrochemical methods, and gas sensors. Among these, sensors are widely used in practical production and daily life due to their advantages such as high efficiency, sensitivity, and portability. Over the past few decades, various materials, including metal oxide semiconductors and carbon nanomaterials, have been developed for ammonia detection. However, most of these require high operating temperatures (>200℃), leading to complex manufacturing processes to integrate heaters into the devices and additional energy consumption. In recent years, gas sensors operating at room temperature have been extensively studied, and their gas-sensitive materials include noble metal-doped materials, heterojunction materials, composite materials, and some low-dimensional materials (such as MoS2, graphene oxide, and carbon nanotubes).

[0004] MoS2 is a two-dimensional transition metal chalcogenide. Its unique layered structure, high specific surface area, and tunable bandgap structure offer the possibility of fabricating low-power room-temperature ammonia sensors. However, due to the presence of van der Waals forces between the layers, MoS2 is prone to recombination, which often leads to poor sensing performance and significantly limits its practical applications. In recent years, some studies on the modification of MoS2 have been reported. For example, Jaeseo Park et al. prepared a Pt-modified MoS2 sensor using metal-organic gas vapor deposition, which showed a 5.58-fold and 4.25-fold increase in response values ​​to 70 ppm NH3 and H2S, respectively, compared to a pure MoS2 sensor prepared by the same method. Sukhwinder et al. proposed a sensor based on MoS2 / SWCNTs composite materials that can dually detect N, N-dimethylformamide, and ammonia at room temperature. However, the high response of these sensors to both gases simultaneously results in unsatisfactory selectivity. Ding et al. reported a simple and effective two-step hydrothermal method for preparing a Cu2O / MoS2 ammonia sensor, which achieved a 45% response to 20 ppm ammonia at an optimal operating temperature of 75 °C. Although the sensor's operating temperature is much lower than that of traditional metal oxide sensors (200-300 °C), it is still above room temperature. Summary of the Invention

[0005] To address the problems of low sensitivity, high operating temperature, and complex fabrication methods in existing ammonia sensors, this invention aims to provide a high-performance ammonia sensor based on α-Fe₂O₃ / MoS₂ composite thin film material and its fabrication method. The ammonia sensor provided by this invention exhibits excellent selectivity for ammonia, enabling highly sensitive and stable detection of ammonia under normal temperature and humidity conditions. Furthermore, the fabrication method of this invention is simple, has low production costs, and is easily applicable to large-scale production, making it highly promising for the market.

[0006] On one hand, the present invention provides a room temperature ammonia sensor based on α-Fe2O3 / MoS2 composite material, comprising: interdigitated electrodes formed on the surface of a substrate and a sensitive material layer; wherein the sensitive material layer is made of α-Fe2O3 / MoS2 composite material.

[0007] In this invention, an ammonia sensor is fabricated using an α-Fe₂O₃ / MoS₂ composite as the sensitive material. The ammonia sensor has a three-layer structure: a substrate at the bottom, interdigitated electrodes in the middle, and a sensitive layer based on the α-Fe₂O₃ / MoS₂ composite material at the top. MoS₂, as a transition metal dihalogenated compound, is a typical two-dimensional layered material with advantages such as high specific surface area and high electron mobility. Furthermore, when transformed from a bulk form to a nanostructure, it possesses the ability to transition from a 1.2 eV indirect bandgap to a 1.9 eV direct bandgap, exhibiting a tunable band structure. α-Fe₂O₃ has excellent ammonia response characteristics. The synergistic effect of the composite materials and the constructed pn junction structure enable the fabrication of an ammonia sensor with good selectivity, high sensitivity, and low power consumption.

[0008] Preferably, the thickness of the sensitive material layer does not exceed 30 μm; the α-Fe2O3 / MoS2 composite material includes: nano-flower-like MoS2 and α-Fe2O3 attached to the nano-flower-like MoS2; preferably, the particle size of the nano-flower-like MoS2 is 300-700 nm, and the particle size of the α-Fe2O3 is 10-30 nm.

[0009] Preferably, the loading of α-Fe2O3 in the α-Fe2O3 / MoS2 composite material is 1 to 10 wt%, more preferably 1 to 5 wt%.

[0010] Preferably, the interdigitated electrodes are made of a noble metal, preferably Au; and the substrate is an Al2O3 ceramic substrate.

[0011] Preferably, the ammonia sensor further includes a Pt electrode connected to the interdigital electrode.

[0012] In another aspect, the present invention provides a method for preparing a room temperature ammonia sensor based on α-Fe2O3 / MoS2 composite material, comprising: (1) Preparation of nanoflower-like MoS2; (2) Preparation of α-Fe2O3 / MoS2 composite material; (3) An α-Fe2O3 / MoS2 thin film was prepared on the surface of the interdigitated electrode by the drop method as a sensitive material layer, and a room temperature ammonia sensor based on the α-Fe2O3 / MoS2 composite material was obtained.

[0013] Preferably, the method for preparing the nanoflower-like MoS2 includes: 1) Mix and dissolve 1-3 mmol of molybdenum source and 7-11 mmol of sulfur source in 60-80 mL of deionized water. Stir on a magnetic stirrer for 20-40 min. Then add 1.5-3 mol of C6H8O7·H2O to the above solution and stir on a magnetic stirrer for 5-15 min to obtain a mixed solution. 2) The mixed solution was transferred to a reaction vessel and heated at 160-240℃ for 18-24 hours. Finally, after centrifugation, washing and drying, nano-flower-like MoS2 was obtained. Preferably, the molybdenum source is selected from at least one of Na2MoO4 and (NH4)2MoO4; the sulfur source is selected from at least one of CH4N2S, CH3CSNH2 and CH4N2O4S.

[0014] Preferably, the preparation method of the α-Fe2O3 / MoS2 composite material includes: 1) Dissolve 1-3 mmol of iron source in 60-80 mL of deionized water, then add 0.5-1.5 mmol of MoS2 powder to obtain a mixed solution; 2) Transfer the mixed solution to a reaction vessel and heat it at 160-200℃ for 8-16 hours. Then, centrifuge, wash and dry to obtain α-Fe2O3 / MoS2 composite material powder. Preferably, the iron source is selected from at least one of FeCl3, Fe(NO3)3, Fe2(SO4)3 and K4Fe(CN)6.

[0015] Preferably, the droplet method includes: taking 10-30 mg of α-Fe2O3 / MoS2 composite material powder and adding it to 0.5-1.5 mL of anhydrous ethanol and mixing to obtain an α-Fe2O3 / MoS2 dispersion; uniformly dropping the α-Fe2O3 / MoS2 dispersion onto an interdigitated electrode and then drying it to obtain an α-Fe2O3 / MoS2 film as a sensitive material layer.

[0016] The beneficial effects of this invention are: 1. This invention utilizes a secondary hydrothermal method to prepare a room temperature ammonia sensor based on α-Fe2O3 / MoS2 composite material. The preparation process is simple, low-cost, uses non-toxic materials, is small in size, and can be mass-produced. 2. This invention utilizes nano-flower-like MoS2 with excellent electrical properties and a large specific surface area to attach nano-α-Fe2O3 particles, increasing the number of active sites. Simultaneously, the attachment of α-Fe2O3 particles reduces MoS2 aggregation, further increasing the specific surface area and thus achieving room temperature response. Furthermore, α-Fe2O3 improves the ammonia-sensitivity of MoS2, enhancing its selectivity for ammonia. The composite of α-Fe2O3 and MoS2 forms a pn heterojunction, increasing the gas-sensing response capability and rate. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the ammonia sensor of the present invention. Figure 2 The images show SEM images of α-Fe₂O₃ / MoS₂, α-Fe₂O₃, and MoS₂, and XRD patterns of α-Fe₂O₃ / MoS₂ in Examples 1, 2, and 3 of this invention; wherein (a) is the SEM image of the α-Fe₂O₃ / MoS₂ composite prepared by the hydrothermal method, (b) is the SEM image of α-Fe₂O₃, (c) is the SEM image of MoS₂, and (d) is the XRD pattern of α-Fe₂O₃ / MoS₂; (modified here). Figure 3 The graph shows the gas-sensing response performance of the MoS2 sensor in Embodiment 2 of the present invention to 30 ppm ammonia gas at room temperature and 5% RH. Figure 4 The graph shows the gas-sensing response performance of the α-Fe2O3 / MoS2 sensor in Example 3 of the present invention to 30ppm ammonia at room temperature and 5%RH. Figure 5 This is a graph showing the long-term stability of the α-Fe2O3 / MoS2 sensor in Example 3 of the present invention; Figure 6 This is a selectivity assessment diagram of the α-Fe2O3 / MoS2 sensor in Example 3 of the present invention; Figure 7 The graph shows the gas-sensing response performance of α-Fe2O3 / MoS2 sensors with different α-Fe2O3 loadings in Examples 5 (1.5wt%), 3 (3.0wt%), 4 (6wt%), and 6 (9wt%) of the present invention to 30ppm ammonia at room temperature and 5%RH. Detailed Implementation

[0018] The present invention will be further illustrated by the following embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the present invention.

[0019] In this invention, the ammonia gas sensor based on the α-Fe2O3 / MoS2 composite material mainly uses an Al2O3 ceramic substrate as the substrate, on which Au-type interdigitated electrodes are deposited, and a sensitive material is loaded onto the interdigitated electrodes. The sensitive material is the α-Fe2O3 / MoS2 composite. The mechanism by which α-Fe2O3 / MoS2 improves the gas-sensing performance in this invention includes: on the one hand, the connection and composite of α-Fe2O3 and MoS2 forms a pn heterojunction, improving the carrier transfer capability; on the other hand, the incorporation of α-Fe2O3 can block direct contact between MoS2 particles, reducing MoS2 agglomeration and increasing the specific surface area. These two aspects work together to improve the gas-sensing response capability. Preferably, the optimal loading of α-Fe2O3 in the α-Fe2O3 / MoS2 composite material in this invention is 1–5 wt%. When the α-Fe2O3 content is low, the sensor is prone to incomplete recovery (in...). Figure 7 (As reflected in the text). Because α-Fe2O3 itself has a relatively high resistance, if the α-Fe2O3 content in the α-Fe2O3 / MoS2 composite is too high, it will lead to an increase in the initial resistance of the composite material and a decrease in the response performance.

[0020] In this invention, a simple secondary hydrothermal method is used to composite nano-α-Fe₂O₃ and nano-flower-like MoS₂, and a room-temperature ammonia sensor based on the α-Fe₂O₃ / MoS₂ composite thin film material is prepared. The compositing of α-Fe₂O₃ and MoS₂ reduces the agglomeration effect, increases the specific surface area, and improves the room-temperature gas-sensing response capability. The composite of the two materials forms a heterojunction, which increases the electron-hole pair transfer rate, thereby improving the response capability and response rate. The introduction of α-Fe₂O₃ also improves the ammonia-sensing performance of the material and enhances the selectivity of MoS₂ for ammonia. The following exemplarily illustrates the preparation method of the ammonia sensor based on the α-Fe₂O₃ / MoS₂ composite material.

[0021] 1–3 mmol of molybdenum source and 7–11 mmol of sulfur source were mixed and dissolved in 60–80 mL of deionized water. After stirring on a magnetic stirrer for 20–40 min, 1.5–3 mol of C6H8O7·H2O was added to the solution. After stirring on a magnetic stirrer for 5–15 min, the mixture was transferred to a 100 mL reactor and heated at 160–240 °C for 18–24 h. C6H8O7·H2O is a surfactant that controls the formation of flower-like structures in MoS2 nanoparticles.

[0022] After the reaction vessel cooled naturally to room temperature, the reaction vessel was opened, and the solution was filtered out to obtain a black substance. The black substance was washed sequentially by centrifugation in deionized water and anhydrous ethanol, centrifuged three times each at a rate of 5000–8000 r / min for 10–15 min each time, and then dried in a drying oven at 40–80℃ for 8–16 h to obtain MoS2 powder.

[0023] Dissolve 1–3 mmol of iron source in 60–80 mL of deionized water, stir on a magnetic stirrer for 20–40 min, add 0.5–1.5 mmol of MoS2 powder to the above solution, sonicate for 20–40 min, transfer the mixed solution to a 100 mL reactor, and heat at 160–200 °C for 8–16 h.

[0024] After the reaction vessel cooled naturally to room temperature, it was opened, and the solution was filtered out to obtain a black substance. The black substance was then washed sequentially by centrifugation in anhydrous ethanol and deionized water, three times each at a rate of 5000–8000 r / min for 10–15 min each time. Afterward, it was dried in a drying oven at 40–80℃ for 8–16 h to obtain α-Fe₂O₃ / MoS₂ powder. The adhesion of α-Fe₂O₃ to the flower-like MoS₂ alleviated the aggregation of MoS₂ particles, increasing the specific surface area and thus the response value. The introduction of α-Fe₂O₃ also specifically improved the ammonia-sensitive properties of MoS₂, giving it excellent selectivity for ammonia.

[0025] Take 10-30 mg of α-Fe2O3 / MoS2 and add it to 0.5-1.5 mL of anhydrous ethanol, and disperse it by ultrasonication for 20-40 min.

[0026] Use a pipette to take 10-30 μL of α-Fe2O3 / MoS2 dispersion and drop it evenly onto the interdigitated electrode. Then dry it in a drying oven at 40-80℃ for 8-16 h to obtain an ammonia sensor based on α-Fe2O3 / MoS2 composite material.

[0027] In this invention, the ammonia sensor comprises interdigitated electrodes formed on the upper surface of a substrate and a semiconductor sensing material deposited on the surface of the interdigitated electrodes. An α-Fe₂O₃ / MoS₂ composite prepared by a secondary hydrothermal method is used as the sensing material. A heterojunction is formed by the contact between n-type semiconductor α-Fe₂O₃ and p-type semiconductor MoS₂, thereby creating a depletion layer for electrons and holes. This increases the electron (hole) transfer rate and the carrier mobility, thus improving sensitivity. The attachment of α-Fe₂O₃ nanoparticles to MoS₂ nanoflowers effectively reduces the MoS₂ aggregation effect, increases the specific surface area, and improves the gas-sensing response. The introduction of α-Fe₂O₃ also improves the ammonia-sensing properties of MoS₂.

[0028] The following examples further illustrate the present invention in detail. It should also be understood that the following examples are only for further explanation of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention are within the scope of protection of the present invention. The specific process parameters, etc., in the following examples are merely examples within a suitable range; that is, those skilled in the art can make appropriate selections within the appropriate range based on the description herein, and are not intended to be limited to the specific values ​​in the examples below.

[0029] Example 1 The specific fabrication process of an ammonia gas sensor using pure α-Fe₂O₃ as the sensing material is as follows: (1) Dissolve 1.7 mmol of FeCl3·6H2O in 60 mL of deionized water and stir on a magnetic stirrer for 30 min. After it is completely dissolved and turns into a yellow transparent solution, transfer it to a 100 mL reaction vessel and heat it at 180 °C for 12 h. (2) After the reaction vessel has cooled to room temperature, open the reaction vessel and filter out the solution to obtain a black substance. Transfer the black substance to a centrifuge tube and wash it with anhydrous ethanol and deionized water in sequence. Centrifuge each tube three times at a speed of 8000 r / min for 15 min each time to remove impurities from the product. Then dry it in a drying oven at 60℃ for 12 h to obtain α-Fe2O3 powder. (3) Then, 0.5 mmol of α-Fe2O3 powder was dissolved in 0.5 mL of anhydrous ethanol and sonicated for 20 min to obtain α-Fe2O3 suspension. (4) The interdigitated electrode was ultrasonically cleaned in a mixed solution (ethanol:deionized water = 1:1) for 30 min, and then cleaned with deionized water and ethanol for 30 min each. Afterward, it was placed in a 60℃ oven to allow the surface water and anhydrous ethanol to evaporate completely. While ensuring the interdigitated electrode was clean, the prepared α-Fe2O3 suspension was dropped onto the interdigitated electrode and then dried in a 60℃ drying oven for 8 h to obtain an ammonia sensor based on α-Fe2O3. (5) By clamping the Au interdigitated electrode with the sensitive material between the Pt electrodes, the sensor based on α-Fe2O3 material described in this embodiment is obtained.

[0030] The response of the sensor prepared in Example 1 to 30 ppm ammonia was tested at room temperature. The sensor was placed in an air atmosphere, and after the sensor resistance stabilized, 30 ppm ammonia was injected, and the sensor resistance was allowed to stabilize further. After the resistance value stabilized, air was introduced to restore the resistance. The initial resistance of the α-Fe₂O₃ sensor exceeded 1 × 10⁻⁶. 6 Ω, unresponsive to 30 ppm ammonia at room temperature.

[0031] Example 2 The specific fabrication process of an ammonia gas sensor using pure MoS2 as the sensing material is as follows: (1) Mix 2 mmol of Na2MoO4·2H2O and 9 mmol of CH4N2S and dissolve them in 70 mL of deionized water. After stirring on a magnetic stirrer for 30 min, add 2.2 mol of C6H8O7·H2O to the above solution. After stirring on a magnetic stirrer for 10 min, transfer the mixed solution to a 100 mL reactor and heat it at 200 °C for 21 h. (2) After the reaction vessel has cooled to room temperature, open the reaction vessel and filter out the solution to obtain a black substance. Transfer the black substance to a centrifuge tube and wash it sequentially with anhydrous ethanol and deionized water, centrifuging three times at 8000 r / min for 15 min each time to remove impurities from the product. Then dry it in a drying oven at 60℃ for 12 h to obtain MoS2 powder. The subsequent preparation process of the MoS2 sensor is the same as in Example 1, except that MoS2 is used to replace α-Fe2O3. (3) The Au interdigitated electrode with sensitive material is clamped between the Pt electrodes to obtain the ammonia sensor based on MoS2 material described in this embodiment.

[0032] The response of the sensor prepared in Example 2 to 30 ppm ammonia was tested at room temperature. The sensor was placed in an air atmosphere, and after the sensor resistance stabilized, 30 ppm ammonia was injected, and the sensor resistance was allowed to stabilize. After the resistance value stabilized, air was introduced to restore the resistance. The MoS2 sensor only achieved a 5% response value to 30 ppm ammonia at room temperature and 5% RH, and could not fully recover to the initial resistance.

[0033] Example 3 The specific fabrication process of an ammonia gas sensor using α-Fe₂O₃ / MoS₂ as the sensing material and employing the dropping method is as follows: (1) Mix 2 mmol of Na2MoO4·2H2O and 9 mmol of CH4N2S and dissolve them in 70 mL of deionized water. After stirring on a magnetic stirrer for 30 min, add 2.2 mol of C6H8O7·H2O to the above solution. After stirring on a magnetic stirrer for 10 min, transfer the mixed solution to a 100 mL reactor and heat it at 200 °C for 21 h. (2) After the reaction vessel has cooled to room temperature, open the reaction vessel and filter out the solution to obtain the black substance. Transfer the black substance to a centrifuge tube and wash it with anhydrous ethanol and deionized water in sequence. Centrifuge each tube three times at a speed of 8000 r / min for 15 min each time to remove impurities from the product. Then dry it in a drying oven at 60℃ for 12 h to obtain MoS2 powder. (3) Dissolve 1.7 mmol of FeCl3·6H2O in 60 ml of deionized water and stir for 30 min. After it is completely dissolved and turns into a yellow transparent solution, dissolve 0.875 mmol of MoS2 in the above solution and then sonicate for 30 min. Then transfer it to a 100 ml reaction vessel and heat it at 180 °C for 12 h. (4) After the reactor has cooled to room temperature, open the reactor and filter out the solution to obtain a black substance. Transfer the black substance to a centrifuge tube and wash it sequentially with anhydrous ethanol and deionized water, centrifuging three times at 8000 r / min for 15 min each time to remove impurities from the product. Then dry it in a drying oven at 60℃ for 12 h to obtain α-Fe2O3 / MoS2 composite material powder; the loading of α-Fe2O3 in the α-Fe2O3 / MoS2 composite material is 3 wt%. (5) The subsequent preparation process of the α-Fe2O3 / MoS2 sensor is the same as that in Example 1, except that α-Fe2O3 / MoS2 is used to replace α-Fe2O3; (6) By clamping the Au interdigitated electrode with the sensitive material between the Pt electrodes, the ammonia sensor based on α-Fe2O3 / MoS2 material described in this embodiment is obtained.

[0034] The response of the sensor prepared in Example 3 to 30 ppm ammonia was tested at room temperature. The sensor was placed in an air atmosphere, and after the sensor resistance stabilized, 30 ppm ammonia was injected, and the sensor resistance was allowed to stabilize further. After the resistance value stabilized, air was introduced to restore the resistance. The α-Fe₂O₃ / MoS₂ sensor showed a response value of 15% to 30 ppm ammonia at room temperature and 5% RH, which is three times the response value of the pure MoS₂ sensor, with a response / recovery time of 250 s / 2100 s. After one month of storage, the α-Fe₂O₃ / MoS₂ sensor still retained 70% of its response capability, and its response value to ammonia was more than four times that of other volatile organic compound gases.

[0035] Figure 2The images show SEM images of α-Fe₂O₃, MoS₂, and α-Fe₂O₃ / MoS₂, as well as XRD patterns of α-Fe₂O₃ / MoS₂ in Examples 1, 2, and 3 of this invention. (a) is the SEM image of α-Fe₂O₃, showing that the average particle size of the α-Fe₂O₃ nanoparticles is approximately 100 nm, which is relatively small. (b) is the SEM image of MoS₂, showing that MoS₂ exhibits a flower-like structure with a diameter of approximately 500 nm. (c) is the SEM image of the α-Fe₂O₃ / MoS₂ composite prepared by the hydrothermal method, showing small α-Fe₂O₃ particles (10–30 nm) attached to the surface of the flower-like MoS₂ (300–700 nm). (d) is the XRD pattern of α-Fe₂O₃ / MoS₂, with peak positions corresponding to the standard PDF cards for α-Fe₂O₃ and MoS₂.

[0036] Figure 3 This is a graph showing the gas-sensing response performance of the MoS2 sensor in Embodiment 2 of the present invention to 30 ppm ammonia at room temperature and 5% RH. The response value only reaches 5%, and it cannot fully recover to the initial resistance.

[0037] Figure 4 This is a graph showing the gas-sensing response performance of the α-Fe₂O₃ / MoS₂ sensor in Example 3 of the present invention to 30 ppm ammonia at room temperature and 5% RH. Its response value is 15%, which is three times the response value of the pure MoS₂ sensor, and the response / recovery time is 250 s / 2100 s.

[0038] Figure 5 The graph shows the long-term stability of the α-Fe2O3 / MoS2 sensor in Example 3 of this invention. Its response performance was 15%, 14%, 12%, and 10% after 1, 2, 3, and 4 weeks of storage, respectively. The sensor retained 70% of its response capability after one month of storage.

[0039] Figure 6 This is a selectivity assessment diagram of the α-Fe₂O₃ / MoS₂ sensor in Example 3 of the present invention. The sensor's response to ammonia is more than four times that of other volatile organic compound gases.

[0040] Figure 7The graph shows the gas-sensing response performance of α-Fe₂O₃ / MoS₂ sensors with different α-Fe₂O₃ loadings to 30 ppm ammonia at room temperature and 5% RH in Examples 3, 4, 5, and 6 of this invention. The results show that the α-Fe₂O₃ / MoS₂ sensor with an α-Fe₂O₃ loading of 3.0 wt% exhibits the best response performance at 15%. Furthermore, 1.5 wt%, 6 wt%, and 9 wt% correspond to 14%, 12%, and 9%, respectively. Moreover, Examples 3, 5, and 6 recovered to their initial state within approximately 2000 s; while Example 4 did not recover to its initial state, only recovering 73% of its initial state.

[0041] Example 4 The preparation process of the room temperature ammonia sensor in Example 4 is the same as in Example 3, except that: 3.4 mmol of FeCl3·6H2O was dissolved in 60 ml of deionized water and stirred for 30 min until it was completely dissolved and turned into a yellow transparent solution. Then, 0.875 mmol of MoS2 was dissolved in the above solution, and then ultrasonically dispersed for 30 min. After that, it was transferred to a 100 ml reaction vessel and heated at 180 °C for 12 h. The loading of α-Fe2O3 in the α-Fe2O3 / MoS2 composite material is 6 wt%.

[0042] Example 5 The preparation process of the room temperature ammonia sensor in Example 5 is the same as in Example 3, except that: 0.85 mmol of FeCl3·6H2O was dissolved in 60 ml of deionized water and stirred for 30 min until it was completely dissolved and turned into a yellow transparent solution. Then, 0.875 mmol of MoS2 was dissolved in the above solution, and then ultrasonically dispersed for 30 min. After that, it was transferred to a 100 ml reaction vessel and heated at 180 °C for 12 h. The loading of α-Fe2O3 in the α-Fe2O3 / MoS2 composite material is 1.5 wt%.

[0043] Example 6 The preparation process of the room temperature ammonia sensor in Example 6 is the same as in Example 3, except that: 5.1 mmol of FeCl3·6H2O was dissolved in 60 ml of deionized water and stirred for 30 min until it was completely dissolved and turned into a yellow transparent solution. Then, 0.875 mmol of MoS2 was dissolved in the above solution, and then ultrasonically dispersed for 30 min. After that, it was transferred to a 100 ml reaction vessel and heated at 180 °C for 12 h. The loading of α-Fe2O3 in the α-Fe2O3 / MoS2 composite material is 9 wt%.

Claims

1. A room temperature ammonia gas sensor based on α-Fe2O3 / MoS2 composite material, characterized in that, include: Interdigitated electrodes and a sensitive material layer formed on the substrate surface; The sensitive material layer is made of α-Fe2O3 / MoS2 composite material.

2. The ammonia sensor according to claim 1, characterized in that, The thickness of the sensitive material layer does not exceed 30 μm; the α-Fe2O3 / MoS2 composite material includes: nano-flower-like MoS2 and α-Fe2O3 forming the nano-flower-like MoS2; preferably, the particle size of the nano-flower-like MoS2 is 300-700 nm, and the particle size of the α-Fe2O3 is 10-30 nm.

3. The ammonia sensor according to claim 1 or 2, characterized in that, The loading of α-Fe2O3 in the α-Fe2O3 / MoS2 composite material is 1 to 10 wt%, preferably 1 to 5 wt%.

4. The ammonia sensor according to any one of claims 1-3, characterized in that, The interdigitated electrodes are made of a precious metal, preferably Au; the substrate is an Al2O3 ceramic substrate.

5. The ammonia sensor according to any one of claims 1-4, characterized in that, The ammonia sensor also includes a Pt electrode connected to the interdigital electrode.

6. A method for preparing a room temperature ammonia sensor based on α-Fe2O3 / MoS2 composite material as described in any one of claims 1-5, characterized in that, include: (1) Preparation of nanoflower-like MoS2; (2) Preparation of α-Fe2O3 / MoS2 composite material; (3) An α-Fe2O3 / MoS2 thin film was prepared on the surface of the interdigitated electrode by the drop method as a sensitive material layer, and a room temperature ammonia sensor based on the α-Fe2O3 / MoS2 composite material was obtained.

7. The preparation method according to claim 6, characterized in that, The preparation method of the nanoflower-like MoS2 includes: 1) Mix and dissolve 1-3 mmol of molybdenum source and 7-11 mmol of sulfur source in 60-80 mL of deionized water. Stir on a magnetic stirrer for 20-40 min. Then add 1.5-3 mol of C6H8O7·H2O to the above solution and stir on a magnetic stirrer for 5-15 min to obtain a mixed solution. 2) The mixed solution was transferred to a reaction vessel and heated at 160-240℃ for 18-24 hours. Finally, after centrifugation, washing and drying, nano-flower-like MoS2 was obtained. Preferably, the molybdenum source is selected from at least one of Na2MoO4 and (NH4)2MoO4; the sulfur source is selected from at least one of CH4N2S, CH3CSNH2 and CH4N2O4S.

8. The preparation method according to claim 6, characterized in that, The preparation method of the α-Fe2O3 / MoS2 composite material includes: 1) Dissolve 1-3 mmol of iron source in 60-80 mL of deionized water, then add 0.5-1.5 mmol of MoS2 powder to obtain a mixed solution; 2) Transfer the mixed solution to a reaction vessel and heat it at 160-200℃ for 8-16 hours. Then, centrifuge, wash and dry to obtain α-Fe2O3 / MoS2 composite material powder. Preferably, the iron source is selected from at least one of FeCl3, Fe(NO3)3, Fe2(SO4)3 and K4Fe(CN)6.

9. The preparation method according to any one of claims 6-8, characterized in that, The droplet method includes: taking 10-30 mg of α-Fe2O3 / MoS2 composite material powder and adding it to 0.5-1.5 mL of anhydrous ethanol and mixing it to obtain an α-Fe2O3 / MoS2 dispersion; uniformly dropping the α-Fe2O3 / MoS2 dispersion onto an interdigitated electrode and then drying it to obtain an α-Fe2O3 / MoS2 film as a sensitive material layer.

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