A NiO / Bi2MoO6 heterojunction array, its preparation method and application

Abstract

The present invention belongs to the field of preparation of gas sensing materials, and discloses a NiO / Bi2MoO6 heterojunction array and its preparation method and application. First, the present invention uses a hydrothermal method to in-situ grow a Ni(OH)2 nanosheet array on the surface of a commercial flat Al2O3 gas-sensitive substrate, then converts the Ni(OH)2 nanosheet array into a porous NiO nanosheet array through oxidation annealing treatment, and finally uses a solvothermal method to further in-situ deposit Bi2MoO6 nanoparticles on the surface of the NiO nanosheet array to obtain a NiO / Bi2MoO6 heterojunction array. The preparation process of the present invention is simple, low in cost and low in risk. The NiO / Bi2MoO6 heterojunction array prepared by the present invention has a porous structure and a large specific surface area, and has good heterojunction interface contact, and can realize high-selectivity detection of ethyl ether gas at room temperature under visible light excitation.

Description

Technical Field

[0001] The present invention belongs to the field of preparation of gas sensing materials, and particularly relates to a NiO / Bi2MoO6 heterojunction array, a preparation method thereof, and an application thereof. Background Art

[0002] In recent years, the effective monitoring of harmful, toxic, flammable, and explosive gases based on resistive semiconductor gas sensors has attracted great attention. However, current semiconductor sensors usually need to work at high temperatures (200 °C - 400 °C), which not only greatly increases the power consumption and manufacturing cost of the sensors, but also limits the possibility of their use in flammable and explosive environments. Developing semiconductor gas sensors that can work effectively at room temperature has become one of the current research hotspots.

[0003] Recently, it has been reported that photoexcitation can be used to improve the sensing performance of semiconductor gas sensors, especially to reduce the working temperature of the sensors. However, there are still two key problems to be solved for current photoexcitation-type room-temperature gas sensors. First, in the vast majority of semiconductor gas-sensitive materials, the recombination rate of photo-generated electron / hole pairs is extremely high, and the lifetime is short (10 ns - 100 ns), resulting in a very small number of carriers that can truly participate in the gas-sensitive reaction. In this case, the charge signal of the gas-solid reaction cannot be effectively converted into a resistance signal, which seriously hinders the further improvement of room-temperature gas sensing performance under light illumination. Second, commonly used semiconductor gas-sensitive materials are all typical wide-bandgap semiconductors (such as SnO2, ZnO, TiO2, etc.), and they usually only have good absorption and response to ultraviolet light, resulting in that most reported photoexcitation-type room-temperature gas sensors can only work under ultraviolet light excitation. Ultraviolet light excitation not only greatly increases the manufacturing cost and energy consumption of the sensors, but also increases the risk of eye damage.

[0004] Constructing semiconductor gas-sensitive materials into heterojunctions is expected to be an effective means to solve the above problems. First, the unique charge transfer mechanism of heterojunctions has been proven to greatly improve the separation efficiency of photo-generated carriers and extend their lifetime. In addition, by reasonably selecting semiconductor materials with both gas-sensitive activity and excellent visible light absorption characteristics in the heterojunction, it is expected to further achieve the response of semiconductor gas-sensitive materials to visible light, thereby comprehensively improving the room-temperature gas sensing performance under visible light excitation. Therefore, how to reasonably select semiconductor components with both matched lattice structure and energy band structure to construct heterojunctions with excellent high gas-sensitive activity and visible light response has become a key problem. Summary of the Invention

[0005] The purpose of the present invention is to solve the deficiencies of the prior art and provide a NiO / Bi2MoO6 heterojunction array, a preparation method thereof, and an application thereof. The following technical solutions are specifically adopted:

[0006] According to a first aspect of the present invention, there is provided a NiO / Bi2MoO6 heterojunction array, which includes a substrate and a NiO / Bi2MoO6 heterojunction array grown in situ on the surface of the substrate; the substrate used is an Al2O3 gas-sensing substrate; the NiO / Bi2MoO6 heterojunction array is composed of NiO nanosheets and Bi2MoO6 nanoparticles. Among them, the NiO nanosheets are in an array structure of vertical interlaced growth, the lateral size of the nanosheets is 5 μm - 10 μm, the thickness is 20 nm - 50 nm, the nanosheets have abundant mesopores, and the size of the mesopores is mainly concentrated at 3.5 nm; the Bi2MoO6 nanoparticles are evenly dispersed on the surface of the NiO nanosheets, and their size is about 20 nm - 50 nm.

[0007] According to a second aspect of the present invention, there is also provided a method for preparing the above-mentioned NiO / Bi2MoO6 heterojunction array, including the following steps:

[0008] (a) Mix nickel nitrate, ammonium fluoride, urea and water evenly and stir for 0.2 h - 1 h to obtain a reaction solution;

[0009] (b) Add the Al2O3 gas-sensing substrate into the reaction solution obtained in step (a) for hydrothermal reaction; after the reaction is completed, wash, dry and anneal to obtain the Al2O3 gas-sensing substrate grown with a NiO nanosheet array.

[0010] (c) Add bismuth nitrate and sodium molybdate into a mixed solution of ethylene glycol and absolute ethanol, mix evenly to obtain solution A; immerse the Al2O3 gas-sensing substrate grown with a NiO nanosheet array obtained in step (b) into solution A for thermal reaction; after the reaction is completed, wash and dry to obtain the NiO / Bi2MoO6 heterojunction array.

[0011] The present invention uses the hydrothermal method to in-situ grow a Ni(OH)2 nanosheet array on the surface of the Al2O3 gas-sensing substrate, converts the Ni(OH)2 nanosheet array into a porous NiO nanosheet array through oxidation annealing treatment, and finally uses the solvothermal method to further in-situ deposit Bi2MoO6 nanoparticles on the surface of the NiO nanosheet array to prepare the NiO / Bi2MoO6 heterojunction array. This preparation method is simple in operation, the raw materials used are cheap and easy to obtain, and the risk is low. Only hydrothermal / solvothermal reaction combined with annealing treatment is required to prepare the product. The NiO / Bi2MoO6 heterojunction array prepared by this method has a porous structure and a large specific surface area, and has good heterojunction interface contact, and can realize high-selectivity detection of ethyl ether gas at room temperature under visible light excitation.

[0012] Preferably, before step (b), pre-treatment of the Al2O3 gas-sensitive substrate is also included, specifically: immersing the Al2O3 gas-sensitive substrate in water and absolute ethanol in sequence, washing three times, and drying.

[0013] Preferably, the molar ratio of nickel nitrate, ammonium fluoride, and urea is 1:(3 - 5):(4 - 6). Among them, urea, as a base source, its decomposition can produce OH - (CO(NH2)2 → NH3↑ + HCNO), the metal Ni ions in nickel nitrate and OH - combine to form Ni(OH)2. And ammonium fluoride, as a salt of strong acid and weak base, can effectively regulate the pH value of the reaction system, thereby realizing the control of the nucleation and growth of Ni(OH)2, and then forming an ultrathin nanosheet morphology. More preferably, the molar ratio of nickel nitrate, ammonium fluoride, and urea is 1:4:5. When the amount of urea and ammonium fluoride is too much or too little, it is not conducive to the formation of the best nanosheet structure.

[0014] Preferably, in step (b), the conditions of the hydrothermal reaction are: the temperature is 100 °C - 120 °C, and the time is 5 hours - 10 hours. Within this temperature range, the base source urea begins to decompose slowly. When the temperature is too low, urea cannot decompose to produce OH - , and Ni(OH)2 cannot nucleate and grow; when the temperature is too high, urea decomposes too fast, and ammonium fluoride cannot regulate the pH value of the reaction system through buffering.

[0015] Preferably, in step (b), the treatment conditions of the annealing are: the temperature is 450 °C - 600 °C, and the time is 1 hour - 3 hours. The annealing treatment converts Ni(OH)2 into NiO through decomposition and dehydration reactions. When the temperature is too low, Ni(OH)2 cannot be completely decomposed and dehydrated into NiO; when the temperature is too high, the NiO nanosheets will further continue to grow, resulting in the thickening and adhesion of the nanosheets.

[0016] Preferably, the molar ratio of bismuth nitrate and the sodium molybdate is 2:1.

[0017] Preferably, in the mixed solution, the volume ratio of ethylene glycol and absolute ethanol is 5 mL:(30 mL - 50 mL). Ethylene glycol and absolute ethanol, as two common organic solvents, have different viscosities and polarities. The addition of a small amount of ethylene glycol can regulate the viscosity and polarity of the reaction solvent, thus facilitating the growth of Bi2MoO6 nanoparticles. More preferably, the volume ratio of ethylene glycol and absolute ethanol is 5 mL:40 mL.

[0018] Preferably, in step (c), the conditions for the thermal reaction are as follows: the temperature is 140 °C - 180 °C, and the time is 10 hours - 15 hours. Bi2MoO6 nanoparticles are more likely to nucleate and grow within this temperature range. When the temperature is too high, the nanoparticles are prone to overgrowth; when the temperature is too low, the yield of the product is low.

[0019] According to the third aspect of the present invention, there is also provided the application of the above-mentioned NiO / Bi2MoO6 heterojunction array material in room-temperature gas sensing. The NiO / Bi2MoO6 heterojunction array prepared by the present invention can achieve high-selectivity detection of ethyl ether gas at room temperature under visible light excitation.

[0020] The beneficial effects of the present invention are as follows: (1) The preparation process of the present invention is simple and low-cost, only requiring hydrothermal / solvothermal reaction combined with annealing treatment; (2) The NiO / Bi2MoO6 heterojunction array prepared by the present invention has a porous structure and a large specific surface area; (3) The NiO / Bi2MoO6 heterojunction array prepared by the present invention has good heterojunction interface contact; (4) The NiO / Bi2MoO6 heterojunction array prepared by the present invention can achieve high-selectivity detection of ethyl ether gas at room temperature under visible light excitation. Description of the Drawings

[0021] Figure 1 Shown are photos of the commercial flat Al2O3 gas-sensitive substrate (produced by Huachuang Ruike Technology Co., Ltd.) used in the present invention and the gas sensor grown with the NiO / Bi2MoO6 heterojunction array;

[0022] Figure 2 Shown is a schematic diagram of the preparation process of the NiO / Bi2MoO6 heterojunction array gas sensor in the present invention;

[0023] Figure 3 Shown are the X-ray diffraction (XRD) patterns of the NiO / Bi2MoO6 heterojunction array and the comparative sample in the present invention;

[0024] Figure 4 Shown are the scanning electron microscope (SEM) images, transmission electron microscope (TEM) images, and elemental distribution maps of the NiO / Bi2MoO6 heterojunction array and the comparative sample NiO in the present invention;

[0025] Figure 5 Shown is the scanning electron microscope (SEM) image of the comparative sample Bi2MoO6 in the present invention;

[0026] Figure 6 Shown are the nitrogen adsorption / desorption isotherms and the corresponding pore size distribution curves of the NiO / Bi2MoO6 heterojunction array and the comparative sample in the present invention;

[0027] Figure 7 The figure shows the kinetic gas-sensing response diagrams of the NiO / Bi2MoO6 heterojunction array sensor and the comparative sensor in the present invention to 100 ppm of ethyl ether at room temperature without light illumination;

[0028] Figure 8 The figure shows the gas-sensing performance test diagrams of the NiO / Bi2MoO6 heterojunction array sensor and the comparative sensor in the present invention to ethyl ether under visible light excitation at room temperature;

[0029] Figure 9 The figure shows the comparative diagrams of the gas-sensing responses of the NiO / Bi2MoO6 heterojunction array sensor in the present invention to various common gases at 100 ppm under visible light excitation at room temperature;

[0030] Figure 10 The figure shows the stability test diagram of the gas-sensing performance of the NiO / Bi2MoO6 heterojunction array sensor in the present invention after long-term use. Detailed implementation manners

[0031] The following will clearly and completely describe the concept of the present invention and the technical effects produced in combination with the embodiments and the drawings, so as to fully understand the purpose, scheme and effects of the present invention. It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments can be combined with each other.

[0032] Embodiment 1

[0033] A NiO / Bi2MoO6 heterojunction array, the preparation method thereof includes the following steps (the specific schematic diagram is as shown in Figure 2 ):

[0034] Nickel nitrate (Ni(NO3)2·6H2O), ammonium fluoride (NH4F) and urea (CH4N2O) are added to a polytetrafluoroethylene autoclave according to a molar ratio of 1:4:5, and then deionized water is added until the inner liner filling degree is 72%, and magnetic stirring is continued for 0.5 hours to obtain a reaction solution; the commercial flat Al2O3 gas-sensing substrate is repeatedly washed in deionized water and absolute ethanol and then dried for standby. After adding the washed commercial flat Al2O3 gas-sensing substrate to the reaction solution, hydrothermal reaction is carried out, the reaction temperature is set at 100 °C, and the reaction time is 8 hours; after the reaction is completed, the commercial flat Al2O3 gas-sensing substrate is washed and dried, and then annealed in a muffle furnace, the annealing temperature is set at 500 °C, and the annealing time is 2 hours to obtain a NiO nanosheet array (as shown in Figure 1As shown in the figure, the results show that there are two pairs of Pt interdigital electrodes on the surface of the Al2O3 gas-sensitive substrate. One pair is the heating electrode, and the other pair is the resistance signal collection electrode. After growing the NiO / Bi2MoO6 heterojunction array, a black film is obviously formed on its surface. Bismuth nitrate (Bi(NO3)3·5H2O) and sodium molybdate (Na2MoO4·2H2O) are dissolved in 5 mL of ethylene glycol respectively according to the molar ratio of 2:1. Under magnetic stirring, these two solutions are successively added to 40 mL of absolute ethanol. After complete mixing, the reaction solution is transferred to a 100 mL polytetrafluoroethylene autoclave. The commercial flat Al2O3 gas-sensitive substrate with grown NiO nanosheet arrays is immersed in the solution for solvothermal reaction. The reaction temperature is set at 160 °C and the reaction time is 12 hours. After the reaction, the commercial flat Al2O3 gas-sensitive substrate is washed and dried to obtain the final product NiO / Bi2MoO6 heterojunction array.

[0035] Example 2

[0036] A NiO / Bi2MoO6 heterojunction array, the preparation method of which (only adjusting the hydrothermal reaction conditions compared with Example 1) includes the following steps:

[0037] Nickel nitrate (Ni(NO3)2·6H2O), ammonium fluoride (NH4F) and urea (CH4N2O) are added to a polytetrafluoroethylene autoclave according to the molar ratio of 1:4:5, and then deionized water is added until the inner liner filling degree is 80%. Magnetic stirring is continued for 0.5 hours to obtain a reaction solution; the commercial flat Al2O3 gas-sensitive substrate is washed repeatedly in deionized water and absolute ethanol and then dried for standby. After adding the washed commercial flat Al2O3 gas-sensitive substrate to the reaction solution, hydrothermal reaction is carried out. The reaction temperature is set at 110 °C and the reaction time is 10 hours; after the reaction, the commercial flat Al2O3 gas-sensitive substrate is washed and dried, and then annealed in a muffle furnace. The annealing temperature is set at 500 °C and the annealing time is 2 hours to obtain a NiO nanosheet array. Bismuth nitrate (Bi(NO3)3·5H2O) and sodium molybdate (Na2MoO4·2H2O) are dissolved in 5 mL of ethylene glycol respectively according to the molar ratio of 2:1. Under magnetic stirring, these two solutions are successively added to 50 mL of absolute ethanol. After complete mixing, the reaction solution is transferred to a 100 mL polytetrafluoroethylene autoclave. The commercial flat Al2O3 gas-sensitive substrate with grown NiO nanosheet arrays is immersed in the solution for solvothermal reaction. The reaction temperature is set at 160 °C and the reaction time is 12 hours. After the reaction, the commercial flat Al2O3 gas-sensitive substrate is washed and dried to obtain the final product NiO / Bi2MoO6 heterojunction array.

[0038] Example 3

[0039] A NiO / Bi2MoO6 heterojunction array and its preparation method (compared with Example 1, only the addition amounts of nickel nitrate (Ni(NO3)2·6H2O), ammonium fluoride (NH4F) and urea (CH4N2O) are adjusted, and the specific reaction conditions are adjusted according to the addition amounts) include the following steps:

[0040] Add nickel nitrate (Ni(NO3)2·6H2O), ammonium fluoride (NH4F) and urea (CH4N2O) into a polytetrafluoroethylene autoclave according to a molar ratio of 1:5:6, then add deionized water until the inner liner filling degree is 72%, and continuously stir magnetically for 0.2 hours to obtain a reaction solution; repeatedly wash a commercial flat Al2O3 gas-sensing substrate in deionized water and absolute ethanol and then dry it for standby. After adding the washed commercial flat Al2O3 gas-sensing substrate into the reaction solution, carry out a hydrothermal reaction, set the reaction temperature to 100 °C and the reaction time to 10 hours; after the reaction is completed, wash and dry the commercial flat Al2O3 gas-sensing substrate, and then carry out annealing treatment in a muffle furnace, set the annealing temperature to 450 °C and the annealing time to 2 hours to obtain a NiO nanosheet array. Dissolve bismuth nitrate (Bi(NO3)3·5H2O) and sodium molybdate (Na2MoO4·2H2O) in 5 mL of ethylene glycol respectively according to a molar ratio of 2:1. Under magnetic stirring, add these two solutions into 45 mL of absolute ethanol in sequence. After complete mixing, transfer the reaction solution to a polytetrafluoroethylene autoclave with a volume of 100 mL, immerse the commercial flat Al2O3 gas-sensing substrate with the grown NiO nanosheet array into the solution for a solvothermal reaction, set the reaction temperature to 170 °C and the reaction time to 10 hours. After the reaction is completed, wash and dry the commercial flat Al2O3 gas-sensing substrate to obtain the final product NiO / Bi2MoO6 heterojunction array.

[0041] The NiO / Bi2MoO6 heterojunction arrays prepared in Preparation Examples 1-3 are composed of NiO nanosheets and Bi2MoO6 nanoparticles. Among them, the NiO nanosheets are in an array structure of vertical and staggered growth, the lateral size of the nanosheets is about 5 μm - 10 μm, the thickness is about 20 nm - 50 nm, the nanosheets have abundant mesopores, and the size of the mesopores mainly concentrates on 3.5 nm; the Bi2MoO6 nanoparticles are evenly dispersed on the surface of the NiO nanosheets, and their size is about 20 nm - 50 nm.

[0042] Comparative Example 1

[0043] A method for preparing Bi2MoO6 nanoparticles includes the following steps:

[0044] Bismuth nitrate (Bi(NO3)3·5H2O) and sodium molybdate (Na2MoO4·2H2O) were dissolved in 5 mL of ethylene glycol respectively according to a molar ratio of 2:1. Under magnetic stirring, these two solutions were successively added to 45 mL of absolute ethanol. After complete mixing, the reaction solution was transferred to a 100 mL polytetrafluoroethylene autoclave for solvothermal reaction. The reaction temperature was set at 170 °C and the reaction time was 10 hours. After the reaction, the Bi2MoO6 nanoparticles were washed and dried to obtain the final product (as Figure 5 shown in the scanning electron microscope image. It can be seen that the Bi2MoO6 nanoparticles exhibited an aggregated shape composed of nanorod-like particles).

[0045] Subsequently, the products prepared in Examples 1-3 and Comparative Example 1 were tested, and the test results are as follows:

[0046] Figure 3 This is the X-ray diffraction (XRD) pattern of the NiO / Bi2MoO6 heterojunction array and the comparative sample in the present invention. It can be seen that the NiO nanosheet array is a pure phase of NiO, the comparative sample Bi2MoO6 has a pure phase of Bi2MoO6, and the obtained NiO / Bi2MoO6 heterojunction array after combination has the phases of both NiO and Bi2MoO6, verifying the synthesis of the heterojunction.

[0047] Figure 4 This is the scanning electron microscope (SEM) photograph, transmission electron microscope (TEM) photograph and elemental distribution map of the NiO / Bi2MoO6 heterojunction array and the comparative sample NiO in the present invention. Figure 4 a-4e are individual NiO nanosheets. It can be seen that a large-scale, dense NiO nanosheet array grows uniformly and vertically in an interlaced manner on the surface of a commercial flat Al2O3 gas-sensing substrate ( Figure 4 a and 4b), and there are a large number of uniformly distributed mesopores on the surface of the nanosheets ( Figure 4 c). The selected area electron diffraction (SAED) pattern obtained from a single nanosheet shows obvious single-crystal signals ( Figure 4 d). All the diffraction spots can perfectly correspond to face-centered cubic NiO, which is consistent with the XRD results. The high-resolution TEM (HRTEM) image shows clear lattice fringes with an interplanar spacing of 0.24 nm ( Figure 4 e), which can be attributed to the (111) crystal plane of cubic NiO. After solvothermal reaction, high-density Bi2MoO6 nanoparticles grow uniformly on the NiO nanosheets ( Figure 4 f-4h), forming a hierarchical NiO / Bi2MoO6 heterostructure array. In the SAED pattern ( Figure 4i), In addition to the single-crystal diffraction spots of NiO, polycrystalline diffraction rings attributed to Bi2MoO6 nanoparticles can be clearly seen. The HRTEM image shows that the interplanar spacing of 0.24 nm is consistent with the (111) plane of cubic NiO, and the interplanar spacing of 0.32 nm matches the (131) plane of Bi2MoO6 ( Figure 4 j). The above results indicate that a good heterojunction interface is formed between NiO and Bi2MoO6. In addition, the EDS elemental mapping images show that the spatial distributions of Ni, O, Bi, and Mo are uniform ( Figure 4 k-4o).

[0048] Figure 6 This is the nitrogen adsorption / desorption isotherms and the corresponding pore size distribution curves of the NiO / Bi2MoO6 heterojunction arrays and the control samples in the present invention. By calculation, the BET specific surface areas of NiO, NiO / Bi2MoO6, and Bi2MoO6 are 60.07, 47.42, and 39.75 m 2 / g, respectively. It can be inferred from the shape of the nitrogen adsorption-desorption isotherms that the samples have abundant pores, and the average pore sizes of NiO, NiO / Bi2MoO6, and Bi2MoO6 are 3.54, 7.95, and 18.54 nm, respectively. The high surface area and porosity are expected to promote the absorption and penetration of the target gas, thus facilitating the gas-sensing reaction.

[0049] As a volatile organic compound, ethyl ether is widely used in agriculture, food, biology, and medical industries. Excessive inhalation can cause headache, proteinuria, inhibition of red blood cell growth, and even death. There have been some reports on the detection of ethyl ether by semiconductor gas sensors. However, these sensors usually need to work at high temperatures (>100 °C). To our knowledge, there is no report on the detection of ethyl ether by semiconductor gas sensors at room temperature. Considering that ethyl ether is flammable and explosive, the operation of sensors at high temperatures poses a safety hazard. Therefore, the development of semiconductor gas sensors capable of effectively detecting ethyl ether at room temperature is of great significance to human health and safety.

[0050] On this basis, the prepared array sensors are used in the present invention to detect ethyl ether gas at room temperature. It can be seen that in the absence of light excitation at room temperature, the responses of the three sensors based on NiO, NiO / Bi2MoO6, and Bi2MoO6 to ethyl ether (100 ppm) are all very limited (<1.5) ( Figure 7 ). However, based on the NiO / Bi2MoO6 heterojunction array sensor, under the excitation of a low-power (0.06 W) white LED light at room temperature, it shows excellent gas sensitivity to ethyl ether, can immediately respond to different concentrations of ethyl ether (5 - 500 ppm), and recover when exposed to air ( Figure 8). Even at a low ether concentration of 10 ppm, the sensor still showed a response value of 4.87. Figure 8 Figure d-8f shows the responses of different sensors to several consecutive gas in-and-out cycles, which confirms the reproducibility of the sensor's response to ether at room temperature. After each gas in-and-out cycle, the resistance can basically return to the original value. It is worth noting that the enhancement effect of photoexcitation on the gas-sensing response of NiO / Bi2MoO6 is very obvious, but the enhancement effect on NiO and Bi2MoO6 is not very obvious.

[0051] Figure 9 Figure shows the sensing selectivity of the NiO / Bi2MoO6 heterojunction array sensor to ether. It can be seen that among various volatile organic compounds (ammonia, triethylamine, acetone, ethyl acetate, etc.), NiO / Bi2MoO6 shows an obvious response to ether, indicating its excellent selectivity.

[0052] To test the long-term stability of the NiO / Bi2MoO6 heterojunction array sensor, its responses to 100 ppm ether were recorded after 15 days and 65 days respectively ( Figure 10 ). It was found that even after 65 days of use, the response value could still reach about 6, indicating that the attenuation of the sensor performance is acceptable.

[0053] Although the description of the present invention has been quite detailed and particularly describes several of the described embodiments, it is not intended to be limited to any of these details or embodiments or any particular embodiment, but rather should be regarded as providing a broad possible interpretation of these claims in light of the prior art by reference to the appended claims, so as to effectively cover the intended scope of the present invention. In addition, the present invention is described above in terms of embodiments foreseeable by the inventors for the purpose of providing a useful description, and those non-substantive modifications to the present invention that are not currently foreseeable may still represent equivalent modifications of the present invention.

Claims

1. A NiO / Bi2MoO6 heterojunction array, characterized in that, It includes a substrate and a NiO / Bi2MoO6 heterojunction array grown in-situ on the surface of the substrate; the substrate is an Al2O3 gas-sensing substrate, and the NiO / Bi2MoO6 heterojunction array is composed of NiO nanosheets and Bi2MoO6 nanoparticles; The preparation method of the NiO / Bi2MoO6 heterojunction array includes the following steps: (a)Mix nickel nitrate, ammonium fluoride, urea and water evenly and stir for 0.2 hours - 1 hour to obtain a reaction solution; (b)Add the Al2O3 gas-sensing substrate into the reaction solution obtained in step (a) for hydrothermal reaction; after the reaction is completed, wash, dry and anneal to obtain an Al2O3 gas-sensing substrate grown with a NiO nanosheet array; (c)Add bismuth nitrate and sodium molybdate into a mixed solution of ethylene glycol and absolute ethanol, mix evenly to obtain solution A; immerse the Al2O3 gas-sensing substrate grown with a NiO nanosheet array obtained in step (b) into solution A for solvothermal reaction; after the reaction is completed, wash and dry to obtain a NiO / Bi2MoO6 heterojunction array.

2. The NiO / Bi2MoO6 heterojunction array according to claim 1, characterized in that, Before step (b), it also includes pre-treating the Al2O3 gas-sensing substrate, specifically: immersing the Al2O3 gas-sensing substrate into water and absolute ethanol in sequence, washing three times and drying.

3. The NiO / Bi2MoO6 heterojunction array according to claim 1, characterized in that, The molar ratio of the nickel nitrate, the ammonium fluoride and the urea is 1:(3 - 5):(4 - 6).

4. The NiO / Bi2MoO6 heterojunction array according to claim 1, characterized in that, In step (b), the conditions of the hydrothermal reaction are: the temperature is 100 °C - 120 °C and the time is 5 hours - 10 hours.

5. The NiO / Bi2MoO6 heterojunction array according to claim 1, characterized in that, In step (b), the treatment conditions of the annealing are: the temperature is 450 °C - 600 °C and the time is 1 hour - 3 hours.

6. The NiO / Bi2MoO6 heterojunction array according to claim 1, characterized in that, The molar ratio of the bismuth nitrate and the sodium molybdate is 2:

1.

7. The NiO / Bi2MoO6 heterojunction array according to claim 1, characterized in that, In the mixed solution, the volume ratio of ethylene glycol and absolute ethanol is 5 mL:(30 mL - 50 mL).

8. The NiO / Bi2MoO6 heterojunction array according to claim 1, characterized in that, In step (c), the conditions of the solvothermal reaction are: the temperature is 140 °C - 180 °C and the time is 10 hours - 15 hours.

9. Application of the NiO / Bi2MoO6 heterojunction array according to claim 1 in room temperature gas sensing.

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