ε-MnO2 / WO3 Heterojunction Material and Its Application in Detection of H2S Gas

Abstract

The invention discloses an ε-MnO2 / WO3 heterojunction material, which is a mixture of ε-MnO2 nanosheets and WO3 nanoparticles, on which flaky ε-MnO2 nanosheets are adhered, and the mass ratio of WO3 nanoparticles to the ε-MnO2 / WO3 heterojunction material is 5-15%. Also disclosed are a preparation method of the heterojunction material and an application of the heterojunction material in detecting H2S gas, as well as an ε-MnO2 / WO3 heterojunction H2S gas sensor made of the heterojunction material. The ε-MnO2 / WO3 heterojunction material has a high sensitivity and responsiveness to H2S gas, and can be used to prepare a sensor for detecting H2S gas at room temperature.

Description

Technical Field

[0001] The invention relates to an ε-MnO2 / WO3 heterojunction material and application thereof in detecting H2S gas, belonging to the technical field of semiconductor devices. Background Art

[0002] The Occupational Safety and Health Administration (OSHA) considers hydrogen sulfide (H2S) to be the second most toxic gas in the workplace after carbon monoxide (CO). H2S is a toxic, colorless gas with the smell of rotten eggs that can damage the respiratory and nervous systems. H2S in the environment mainly comes from the petroleum, industrial processing, coal, and natural gas processing industries. Long-term exposure to low concentrations (50ppm) of H2S can irritate the eyes and respiratory system, while exposure to high concentrations (250ppm) of the gas can cause cardiac arrest and death. Therefore, it is of great significance to develop an economical, convenient, and fast-responding H2S gas sensor.

[0003] So far, traditional metal oxide semiconductor materials represented by In2O3, ZnO, SnO2, WO3 and CuO have the advantages of low cost, unique structure, easy manufacturing, excellent physical and chemical properties, etc. However, there are still disadvantages such as the sensor must work at high temperature, the preparation process of gas-sensitive materials is complicated, and the long-term stability is poor. In this case, MnO2, as a common metal oxide semiconductor, has strong oxidizing properties, abundant oxygen vacancies and controllable morphology, and is usually used to deal with environmental problems related to sulfide pollution. In the field of gas sensors, they are usually used as H2 sensors or NH3 sensors, but there is also little research on H2S gas sensors. Therefore, from the perspective of reducing energy consumption and improving stability, it is necessary to design a MnO2-based H2S gas sensor that can work at room temperature. Summary of the invention

[0004] The object of the present invention is to provide an ε-MnO2 / WO3 heterojunction material having a high degree of responsiveness to H2S gas.

[0005] The purpose of the present invention is achieved through the following technical solutions:

[0006] An ε-MnO2 / WO3 heterojunction material is a mixture of ε-MnO2 nanosheets and WO3 nanoparticles. The WO3 nanoparticles are adhered with flaky ε-MnO2 nanosheets. The mass ratio of the WO3 nanoparticles to the ε-MnO2 / WO3 heterojunction material is 5-15%.

[0007] The present invention also discloses a method for preparing the above-mentioned ε-MnO2 / WO3 heterojunction material, which comprises dissolving ε-MnO2 nanosheets in a solvent to obtain an ε-MnO2 nanosheet solution, dissolving WO3 nanoparticles in a solvent to obtain a WO3 nanosolution, uniformly mixing the ε-MnO2 nanosheet solution and the WO3 nanosolution and then drying to obtain the ε-MnO2 / WO3 heterojunction material, wherein the mass ratio of the WO3 nanoparticles to the ε-MnO2 / WO3 heterojunction material is 5-15%.

[0008] Preferably, the solvent is anhydrous ethanol.

[0009] Preferably, the preparation method of ε-MnO2 nanosheets is:

[0010] (1) preparing a Mn(NO3)2 solution, a urea solution and a citric acid solution respectively, and mixing the three solutions after ultrasonic treatment to obtain a premixed solution;

[0011] (2) preparing an aqueous potassium permanganate solution, slowly dripping it into the premixed solution prepared previously, and then ultrasonically treating the resulting solution;

[0012] (3) adding the NH3·H2O aqueous solution dropwise to the mixed solution obtained in step (2) while stirring until the pH value becomes weakly acidic;

[0013] (4) placing the dissolved solution obtained in step (3) in a stainless steel high-pressure reactor for high-temperature reaction;

[0014] (5) After the reaction is completed, filter the precipitate, wash it to neutrality, dry the precipitate, and calcine it at 350±5°C;

[0015] (6) Add the calcined product into HNO3 solution, stir, and dry to obtain ε-MnO2 nanosheet material.

[0016] Preferably, in step (1), the concentration of Mn(NO3)2 solution is 50wt.%, and the dosage is 1.61g; the urea solution is 1.22g urea dissolved in 6.8mL deionized water; and the citric acid solution is 3.89g citric acid dissolved in 6.8mL deionized water.

[0017] Preferably, in step (2), the potassium permanganate aqueous solution is 1.42 g potassium permanganate dissolved in 30 mL deionized water.

[0018] Preferably, the pH value in step (3) is about 6.5.

[0019] Preferably, the reaction temperature in step (4) is 180°C and the reaction time is 12 hours; the calcination time in step (5) is 12 hours and the calcination temperature is 350±5°C.

[0020] The preparation method of ε-MnO2 nanosheets is an existing method, and other methods can also be used to prepare ε-MnO2 nanosheets or purchase commercial ε-MnO2 nanosheets.

[0021] The invention also discloses the application of the above-mentioned ε-MnO2 / WO3 heterojunction material in detecting H2S gas.

[0022] The present invention also discloses an ε-MnO2 / WO3 heterojunction H2S gas sensor, which is characterized in that the ε-MnO2 / WO3 heterojunction material described in claim 1 is coated on a SiO2 substrate or an interdigital electrode of a Si substrate.

[0023] The present invention adopts ε-MnO2 nanosheets and compounds WO3 nanoparticles in different proportions to obtain ε-MnO2 / WO3 heterojunction materials. The ε-MnO2 / WO3 heterojunction H2S gas sensor is prepared using the material. From the experimental results, it can be seen that the ε-MnO2 / WO3 heterojunction material has a high response to H2S gas. At room temperature, the response is 177-100ppm H2S. It can be used to prepare a sensor for detecting H2S gas at room temperature, and has shown excellent long-term stability in a stability test of up to 40 days. In addition, selectivity tests for different interfering gases (CO, H2, NH3) also show high selectivity for H2S gas. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 (a) Schematic diagram of the synthesis of ε-MnO2 nanosheets and the preparation of ε-MnO2 / WO3 heterojunction. (b) Schematic diagram of the gas sensor device.

[0025] Figure 2 Illustration of interdigitated electrodes on a substrate.

[0026] Figure 3 SEM images: (a) F-01: ε-MnO2 / 5wt.%WO3, (b) F-02: ε-MnO2 / 10wt.%WO3, (c) F-03: ε-MnO2 / 15wt.%WO3. (c) F-03: ε-MnO2 / 15wt.%WO3.

[0027] Figure 4 TEM, HRTEM and TEM mapping images of the prepared products: (a)-(d) F-01: MnO2 / 5wt.%WO3. (e)-(h) F-02: MnO2 / 10wt.%WO3, (i)-(l) F-03: MnO2 / 15wt.%WO3.

[0028] Figure 5Nitrogen adsorption and desorption test diagram: (a) F-01; (b) F-02; (c) F-03. (Inset: pore size distribution).

[0029] Figure 6 (a) and (b) Dynamic resistance and dynamic response curves of F-01 gas sensor for different H2S gas concentrations. (c) and (d) Dynamic resistance and dynamic response curves of F-02 gas sensor for different H2S gas concentrations. (e) and (f) Dynamic resistance and dynamic response curves of F-03 gas sensor for different H2S gas concentrations.

[0030] Figure 7 Comparison of the responses of F-01, F-02, and F-03 gas sensors to different H2S gas concentrations at room temperature.

[0031] Figure 8 Response time of F-01, F-02 and F-03 gas sensors to 100ppm H2S gas at room temperature.

[0032] Fig. 9 (a) Responsiveness of F-01, F-02 and F-03 gas sensors to different interfering gases at 100 ppm at room temperature; (b) Long-term stability of F-01, F-02 and F-03 gas sensors at room temperature; (c) Dynamic response of F-01, F-02 and F-03 gas sensors to 100 ppm H2S at different humidity.

[0033] Fig.10 (a) ε-MnO2 gas sensing mechanism, (b) ε-MnO2 / WO3 heterojunction gas sensing mechanism. DETAILED DESCRIPTION

[0034] The following is a clear and complete description of the technical solutions in the embodiments of the present invention in combination with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians without creative work are within the scope of protection of the present invention.

[0035] Example 1

[0036] like Figure 1 As shown in (a), the preparation process of the ε-MnO2 material is as follows:

[0037] 1.61 g of Mn(NO3)2 solution (50 wt.%) was diluted with deionized water to obtain 1.5 mL of solution. In addition, 1.22 g of urea and 3.89 g of citric acid were dissolved in 6.8 mL of deionized water, respectively. The three solutions were ultrasonically treated and mixed for further use. Then, 1.42 g of potassium permanganate was dissolved in 30 mL of deionized water and stirred for 1 h until completely dissolved, and the formed potassium permanganate aqueous solution was slowly dripped into the premixed solution prepared previously under stirring and the resulting solution was ultrasonicated for 1 h. Subsequently, NH3·H2O (25%) aqueous solution was added dropwise to the above mixed solution under stirring until the pH value was about 6.5. Thereafter, the dissolved solution was transferred to a stainless steel autoclave lined with polytetrafluoroethylene, and the autoclave was kept at 180°C for 12 h. After the reaction was completed, the precipitate produced was filtered and washed several times with anhydrous ethanol and deionized water until pH = 7. The precipitate was obtained by drying at 80 °C in air for 12 h and calcined at 350 °C for 4 h. Thereafter, 1.5 g of the obtained precipitate was added to 15 mL of HNO3 (65–68 wt.%) and stirred for 12 h. Finally, it was washed with deionized water and thoroughly dried at 110 °C to obtain the final ε-MnO2 nanosheet material.

[0038] Example 2

[0039] The preparation process of the ε-MnO2 / WO3 heterojunction is as follows:

[0040] ε-MnO2 nanosheets and WO3 nanoparticles were combined to prepare ε-MnO2 / WO3 heterojunctions. The specific experimental steps are as follows: 0.3g of the prepared ε-MnO2 nanosheets were taken and dissolved in 30mL of anhydrous ethanol respectively; in addition, 0.016g, 0.033g and 0.053g of WO3 nanoparticles were taken and dissolved in 10mL of anhydrous ethanol respectively. After ultrasonicating the prepared solution for 2h, the three contents of WO3 solution were added to the three prepared ε-MnO2 solutions while stirring, and then the three solutions were strongly magnetically stirred for 3h to fully mix and disperse evenly. In order to prevent agglomeration during the stirring process, the three mixed solutions were ultrasonicated for another 1h. Finally, the solutions of the three components were placed in a drying oven and dried at 100℃ for two days and nights to make them fully dry. The dried materials were fully ground and set aside. The obtained heterojunction materials ε-MnO2 / 5wt.% WO3, ε-MnO2 / 10wt.% WO3 and ε-MnO2 / 15wt.% WO3 were marked as F-01, F-02 and F-03 respectively.

[0041] Example 3

[0042] like Figure 1As shown in b, the preparation process of the ε-MnO2 / WO3 heterojunction gas sensor is as follows: take 0.05g of the powder prepared above, add it to 0.5mL of ethanol, ultrasonicate for 1h to obtain a uniform dispersion, take out a certain amount of the dispersion with a pipette, and evenly drop it on the interdigital electrodes of the Si substrate. After heating on a heating table for 1h, the ε-MnO2 / WO3 heterojunction H2S gas sensor is obtained. During the gas sensing experiment, a gas-sensitive measurement system of the sensor was established at an ambient air relative humidity (RH) of 25% and room temperature (25°C). The gas concentration was adjusted by MF2600, and the gas-sensitive performance was evaluated by measuring the recorded resistance change under a DC bias voltage of 0.1V using a semiconductor parameter analyzer (Keithley2400). The gas responsiveness in this study is defined as

[0043] S(%)=|R a -R g | / R g ×100%. In the formula, R a is the resistance in air, R g is the resistance value in the target gas. The response time refers to the time it takes for the resistance value of the gas sensor to change from Ra to R a -(R a -R g )×90% of the time required.

[0044] Figure 2 The figure below is a structural diagram of the interdigital electrodes on the substrate. The basic structure of the sensor is to bond or evaporate the interdigital electrodes on the Si substrate, and there are no specific requirements for the size and spacing.

[0045] Figure 3 The SEM images in the figure can preliminarily confirm the formation of the three heterojunction materials. The finely fragmented flake particles in this result are ε-MnO2, and the larger particles are WO3 nanoparticles. In addition, it can be seen from the results that the composite WO3 nanoparticles are all adhered with flake ε-MnO2 materials, which can explain the formation of ε-MnO2 / WO3 heterojunction from the perspective of physical morphology.

[0046] Figure 4 As shown, the microstructure and lattice fringes of the material can be observed more clearly. From the three sets of TEM images, it can be seen that the WO3 nanoparticles increase significantly with the doping concentration, and from the HRTEM, it can be seen that there is no obvious gap between ε-MnO2 and WO3, indicating that the two materials are in good contact and a heterojunction is formed. In addition, from the three sets of TEM mapping, the distribution of the three elements Mn, O, and W can be obtained, and it can be found that both materials are dispersed and have no impurities.

[0047] according to Figure 5As a result, the specific surface area is also an important parameter affecting the gas sensing performance. Therefore, the BET and BJH methods were used to study the structural characteristics of the three materials. The specific surface area data are shown as follows: F-01: 166.32m 2 / g, F-02: 165.57m 2 / g and F-03: 145.27m 2 / g. In addition, their average pore sizes are 5.791nm (F-01), 5.173nm (F-02) and 5.813nm (F-03) in order. The results show that the specific surface areas of the three materials are in the following order: F-01>F-02>F-03, that is, F-01 material has the highest specific surface area. The results of relevant literature have proved that suitable pore size and large specific surface area are conducive to the adsorption and diffusion of gas on the surface of the material, thereby improving the gas-sensitive performance of the gas sensor. However, the subsequent gas-sensitive test results show that the gas sensor prepared by F-03 has the best H2S gas response. The reason for this result may be the existence of the heterojunction, which provides a better redox reaction environment between the gas-sensitive material and the gas.

[0048] Figure 6 The gas sensing detection performance of the gas sensor prepared by the heterojunction material prepared above is presented and discussed in the figure. First, as can be seen from the figure, the H2S gas sensing experiment was carried out on the F-01, F-02 and F-03 sensors at room temperature, and the gas concentration range was 10ppm to 100ppm. It can be intuitively observed that the sensors with three composite ratios showed different degrees of resistance change. In general, the resistance change of sensors F-01, F-02 and F-03 is that the resistance gradually decreases with the increase of H2S gas concentration. However, it can be seen from the response curves (b)(d)(f) that the responsivity has different degrees of change. After calculation, it is found that under the condition of 100ppmH2S, the responses are: F-01 is 118.28; F-02 is 166.22 and F-03 is 177.13. F-03, as a sensor composited with 15wt.% WO3, showed the best response performance. This result proves that the gas sensing performance of ε-MnO2 gas sensor can be improved by composited with a certain amount of WO3 nanoparticles.

[0049] Figure 7As shown in the figure, the F-01, F-02 and F-03 sensors were subjected to H2S gas sensing experiments at room temperature. The response comparison of the gas concentration range from 10ppm to 100ppm showed two results: (1) Although the response degree of the F-01 sensor is better than that of the pure ε-MnO2-based sensor, it is not significantly enhanced like the F-02 sensor. Although the F-03 sensor has the best performance among the three heterojunction sensors, it can still be seen from the comparison curve that the increase in response is not significant compared with the F-02 sensor, indicating that the 10wt.% WO3 composite ratio is a dividing point that affects the response performance of the ε-MnO2-based sensor. (2) In fact, it can be seen from the comparison chart that at lower concentrations (10ppm), the improvement in response is not very obvious, and the difference in response between different sensors is not large. Therefore, it can be seen that the presence of the heterojunction will have a greater impact on the response in slightly higher concentrations of H2S gas.

[0050] Figure 8 As shown, H2S gas sensitivity experiments were carried out on F-01, F-02 and F-03 sensors at room temperature with a gas concentration of 100 ppm. The response times of F-01, F-02 and F-03 sensors were 118.9 s, 119.9 s and 106 s, respectively.

[0051] Fig. 9 As shown in the figure, the F-01, F-02 and F-03 sensors were subjected to gas sensing experiments with different interfering gases (including NH3, CO and H2) at room temperature, and the gas concentration was 100ppm. Fig. 9From the results in a, we can see that at room temperature, for different gases of 100ppm, the responsivity of the F-01 gas sensor to NH3, CO, H2 and H2S is 40, 38, 39.04 and 118.28 respectively; the responsivity of the F-02 gas sensor to NH3, CO, H2 and H2S is 45.36, 38.46, 31.85 and 166.22 respectively; the responsivity of the F-03 gas sensor to NH3, CO, H2 and H2S is 61.4, 39.6, 37.8 and 177.13 respectively. This result proves that the presence of the heterojunction improves the gas-sensing performance of the sensor. Subsequently, the long-term stability of the three sensors was also explored in this experiment. Under the test conditions of forty days and a cycle of ten days, it was found that the sensor would have a significant decrease in response performance after use, but as time goes by, the response performance can be restored to the initial state, ensuring that the sensor can be recycled. In addition, the responsiveness of the three sensors was tested and calculated under different relative humidity, and it was found that the responsiveness would decrease with the increase of relative humidity. This result shows that relative humidity has a negative impact on gas sensors, and this change is consistent with the gas response state of metal oxide sensors facing a high water molecule environment. The main reason is: in a high humidity environment, water molecules will be adsorbed on the surface of the gas-sensitive material, blocking the adsorption of the target gas and its interaction with the gas-sensitive material, so the responsiveness of the sensor will be reduced.

[0052] Fig.10 As shown, the inherent gas-sensing mechanism of heterojunction gas sensors is much more complicated than the sensing mechanism of ordinary nanomaterials, and further in-depth analysis is needed. Therefore, the gas-sensing mechanism of the ε-MnO2 / WO3 heterojunction sensor will be analyzed and explained to explain why the existence of the heterojunction improves the gas-sensing performance of the ε-MnO2 nanosheets to H2S gas. It is well known that in real-time gas monitoring, metal oxide semiconductor sensors mainly rely on gas adsorption / desorption to cause resistance changes in gas-sensitive materials. Therefore, revealing the inherent mechanism of resistance change can directly explain the gas-sensing mechanism of the sensor. It can be roughly divided into two situations for discussion:

[0053] First, when in air:

[0054] It can be explained that: ① Whether it is for ε-MnO2 gas sensor or heterojunction gas sensor, the gas adsorption / analysis model is equally applicable. When the sensor is exposed to air, the oxygen molecules in the air will diffuse along the surface of the material. Because the oxygen molecules in the air have strong electronegativity, they will be adsorbed on the surface of the material. Subsequently, the adsorbed oxygen molecules will extract electrons from the conduction band of the gas-sensitive material and be ionized into oxygen ions O δ- (For example, 2- , O - and O 2-). Through the space charge model analysis, it can be seen that through the above oxygen adsorption reaction, electrons will be consumed inside the gas-sensitive material, so its electron depletion layer will become wider, thereby generating a high potential barrier and a high resistance value. Therefore, the oxygen adsorption (Equation 4-1 to Equation 4-4) reaction process can be explained as follows:

[0055] O 2(gas) →O 2(ads) (4-1)

[0056]

[0057]

[0058]

[0059] ② When there is an ε-MnO2 / WO3 heterojunction, since the conduction band of WO3 is about 0.74eV and the conduction band of MnO2 is about 1.33eV, during the process of Fermi level balance, the carriers at the contact surface of the two will flow from WO3 to MnO2, causing the energy band at the WO3 interface to bend upward and the energy band at the ε-MnO2 contact surface to bend downward due to electron aggregation. The Fermi level effect will accelerate the movement of carriers at the interface, causing more oxygen to be adsorbed on the surface of the gas-sensitive material, thereby generating a higher potential barrier on the surface of the MnO2 / WO3 heterojunction and increasing the resistance value. Therefore, the dual effects of oxygen adsorption in the air and the heterojunction will increase the barrier width of the gas-sensitive material and increase the material resistance value.

[0060] Secondly, in the target gas H2S:

[0061] ①H2S molecules will also diffuse along the surface of ε-MnO2 and WO3 and can be adsorbed on the surface of the material. Afterwards, the adsorbed H2S will dissociate with the oxygen adsorbed on the surface of the gas-sensitive material to form oxygen ions O δ- The electrons captured by oxygen adsorption will be released back to the material conduction band, making its depletion layer narrower, the potential barrier lowered, and the resistance lowered.

[0062]

[0063] In addition, for ε-MnO2, H2S adsorbed on the oxygen vacancies of ε-MnO2 will still ionize to form HS-, and then the adsorbed HS - With the surface Mn 4+ , Lattice oxygen O L and adsorbed oxygen O ads interact to form Mn 3+ 、V O , S and H2O.

[0064] ② In addition, from the perspective of energy band theory, when the ε-MnO2 / WO3 heterojunction exists, due to the presence of more oxygen adsorption, the redox reaction between H2S and adsorbed oxygen will intensify, causing the adsorbed oxygen to desorb rapidly and the electrons to be quickly released back to the conduction band of the material, causing the potential barrier to drop sharply and the resistance to drop sharply.

[0065] Therefore, the sensor's responsiveness to H2S gas is effectively improved by preparing the ε-MnO2 / WO3 heterojunction, and the presence of the heterojunction also makes up for the lack of specific surface area reduction caused by the composite WO3 nanoparticles. However, due to the intensification of the redox reaction between the gas-sensitive material and the target gas, its performance recovery becomes slow.

Claims

1. Application of ε-MnO2 / WO3 heterojunction material in detecting H2S gas, characterized by: The ε-MnO2 / WO3 heterojunction material is a mixture of ε-MnO2 nanosheets and WO3 nanoparticles, on which flaky ε-MnO2 nanosheets adhere, and the mass ratio of WO3 nanoparticles to the ε-MnO2 / WO3 heterojunction material is 5-15%.

2. A method for preparing an ε-MnO2 / WO3 heterojunction material, characterized in that The ε-MnO2 nanosheets are dissolved in a solvent to obtain an ε-MnO2 nanosheet solution, WO3 nanoparticles are dissolved in a solvent to obtain a WO3 nanosolution, the ε-MnO2 nanosheet solution and the WO3 nanosolution are uniformly mixed and then dried to obtain an ε-MnO2 / WO3 heterojunction material, wherein the mass ratio of the WO3 nanoparticles to the ε-MnO2 / WO3 heterojunction material is 5-15%.

3. The method for preparing the ε-MnO2 / WO3 heterojunction material according to claim 2, characterized in that The solvent is anhydrous ethanol.

4. The method for preparing the ε-MnO2 / WO3 heterojunction material according to claim 2, characterized in that: The preparation method of ε-MnO2 nanosheets is as follows: (1) preparing a Mn(NO3)2 solution, a urea solution and a citric acid solution respectively, and mixing the three solutions after ultrasonic treatment to obtain a premixed solution; (2) preparing an aqueous solution of potassium permanganate, slowly dripping it into the premixed solution prepared previously, and then ultrasonically treating the resulting solution; (3) Adding the NH3·H2O aqueous solution dropwise to the mixed solution obtained in step (2) while stirring until the pH value becomes weakly acidic; (4) placing the dissolved solution obtained in step (3) in a stainless steel high-pressure reactor for high-temperature reaction; (5) After the reaction is completed, the precipitate is filtered, washed to neutrality, dried, and calcined; (6) The calcined product is added to a HNO3 solution and stirred, and then dried to obtain ε-MnO2 nanosheet material.

5. The method for preparing the ε-MnO2 / WO3 heterojunction material according to claim 4, characterized in that: In step (1), the concentration of Mn(NO3)2 solution is 50wt.%, and the amount used is 1.61g; the urea solution is 1.22g urea dissolved in 6.8mL deionized water; and the citric acid solution is 3.89g citric acid dissolved in 6.8mL deionized water.

6. The method for preparing the ε-MnO2 / WO3 heterojunction material according to claim 5, characterized in that: In step (2), the potassium permanganate aqueous solution is 1.42 g potassium permanganate dissolved in 30 mL deionized water.

7. The method for preparing the ε-MnO2 / WO3 heterojunction material according to claim 4, characterized in that: In step (4), the reaction temperature is 180°C and the reaction time is 12 h; in step (5), the calcination time is 12 h and the calcination temperature is 350±5°C.

8. An ε-MnO2 / WO3 heterojunction H2S gas sensor, characterized in that The ε-MnO2 / WO3 heterojunction material is coated on the interdigital electrodes of the SiO2 substrate, wherein the ε-MnO2 / WO3 heterojunction material is a mixture of ε-MnO2 nanosheets and WO3 nanoparticles, and flaky ε-MnO2 nanosheets are adhered to the WO3 nanoparticles, and the mass ratio of WO3 nanoparticles to the ε-MnO2 / WO3 heterojunction material is 5-15%.

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