Co3O4 / ZnIn2S4 / Pt heterojunction array, preparation method thereof and gas sensor

Abstract

The invention belongs to the technical field of nano material heterojunctions, and particularly relates to a Co3O4 / ZnIn2S4 / Pt heterojunction array, a preparation method thereof and a gas sensor. The Co3O4 / ZnIn2S4 / Pt heterojunction solar cell comprises a substrate and a Co3O4 / ZnIn2S4 / Pt heterojunction array which grows on the surface of the substrate in situ, and the Co3O4 / ZnIn2S4 / Pt heterojunction array is composed of a Co3O4 nanowire, a ZnIn2S4 nanosheet and Pt nanoparticles. The Co3O4 / ZnIn2S4 / Pt heterojunction array is formed by a Co3O4 nanowire, a ZnIn2S4 nanosheet and Pt nanoparticles. The Co3O4 / ZnIn2S4 / Pt heterojunction array disclosed by the invention has good heterogeneous interface contact, and an efficient multi-interface charge transfer characteristic is realized. Due to abundant S vacancy active sites on the surface of ZnIn2S4 and the chemical sensitization effect of Pt nanoparticles, the adsorption activity of the heterojunction array to molecules is enhanced. The Co3O4 / ZnIn2S4 / Pt heterojunction array can be applied to gas sensing, and high-selectivity detection of triethylamine at the temperature of 200 DEG C is realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of nanomaterial heterojunctions, and in particular relates to a Co3O4 / ZnIn2S4 / Pt heterojunction array, a preparation method thereof, and a gas sensor. Background Art

[0002] As one of the most common and widely used gas sensors, resistive gas sensors based on semiconductor gas-sensing materials hold great promise for VOC (Volatile Organic Compound) gas detection. However, their gas-sensing performance still lags far behind theoretical values and practical requirements. The development of efficient VOC gas-sensing materials has become a research hotspot in recent years.

[0003] In principle, the performance of resistive gas sensors depends primarily on the surface adsorption reaction and accompanying interfacial charge transfer that occurs when semiconductor gas-sensing materials come into contact with gases, resulting in changes in resistance. Therefore, the key to improving the gas-sensing performance of semiconductor gas-sensing materials lies in enhancing their surface gas adsorption activity and improving interfacial charge transfer efficiency. From the perspective of improving surface gas adsorption activity, the most common strategy is to design micro- / nanoporous structures with large specific surface areas and abundant surface active sites. From the perspective of improving interfacial charge transfer efficiency, constructing heterostructures (including semiconductor heterostructures and semiconductor-metal heterostructures) is an important strategy. However, overall, among these strategies for improving gas sensing performance, two key issues remain to be addressed.

[0004] First, in terms of device structure, the current manufacturing of resistive gas sensors typically involves preparing semiconductor gas-sensing materials in powder form, dispersing them into a slurry through methods such as ultrasonication or ball milling, and finally assembling the slurry onto a prefabricated substrate (usually Al2O3) by brushing or screen printing to obtain a thick-film device. During this process, gas-sensing materials, especially those with micro- / nanoporous structures, are prone to agglomeration, structural damage, or poor electrical contact with the substrate, resulting in a significant reduction in specific surface area and the number of surface active sites, thereby significantly reducing gas-sensing activity.

[0005] Secondly, in terms of heterostructure construction, it is generally believed that due to the difference in work function, heterojunctions can effectively enhance charge transfer between interfaces, thereby improving gas sensing performance. However, in reality, due to the mismatch of lattice structure or band structure, it is difficult to form a strong and tight heterostructure interface between semiconductor elements or between semiconductors and metals in many cases. This makes it difficult to achieve effective charge transfer between components, resulting in the inability to effectively convert the charge signal of the gas-solid reaction into a resistance signal, which greatly hinders the further improvement of gas sensing performance. In particular, compared with common binary semiconductor heterostructures or semiconductor-metal heterostructures, designing a ternary heterostructure with a tight and strong multi-interface is still a huge challenge. Summary of the Invention

[0006] The purpose of the present invention is to solve at least one of the technical problems existing in the prior art and provide a Co3O4 / ZnIn2S4 / Pt heterojunction array and its preparation method and application, specifically a sandwich structure Co3O4 / ZnIn2S4 / Pt heterojunction array and its preparation method and gas sensor.

[0007] The applicants discovered that the adsorption activity of the heterostructure array for both oxygen and triethylamine molecules is enhanced due to the abundant S vacancy active sites on the ZnIn2S4 surface and the chemical sensitization effect of Pt nanoparticles. Crucially, robust pn heterointerfaces (Co3O4 / ZnIn2S4) and semiconductor-metal heterointerfaces (Co3O4 / Pt and ZnIn2S4 / Pt) are formed within the ternary heterostructure, enabling efficient multi-interface charge transfer, enabling the effective conversion of charge signals from gas-solid reactions into resistance signals. Furthermore, due to the 1D / 2D / 0D porous array design and in-situ growth strategy, the ternary Co3O4 / ZnIn2S4 / Pt heterostructure array not only exhibits a large specific surface area for gas adsorption and reaction, but also avoids a series of issues associated with traditional powdered gas-sensing materials during device fabrication.

[0008] In this invention, the applicant designed a ternary Co3O4 / ZnIn2S4 / Pt heterostructure array gas sensor. This sensor consists of a Co3O4 nanowire array grown in situ on a flat alumina substrate as a framework, ultrathin ZnIn2S4 nanosheets wrapped around the surface of the Co3O4 nanowire array, and a highly dispersed outer layer of Pt nanoparticles. It provides excellent sensing performance for the detection of the volatile organic compound triethylamine, exhibiting a relative high sensitivity (R) of approximately 118.97 for 100 ppm of triethylamine at a relatively low operating temperature of 200°C. a / R g) with remarkable response, excellent response / recovery speed and selectivity, and long-lasting stability (over three months). Based on first-principles calculations and a series of spectroscopic characterizations (including in situ spectroscopy), the heterostructure arrays exhibited enhanced adsorption activity for both oxygen and triethylamine molecules. Crucially, robust pn heterointerfaces (Co3O4 / ZnIn2S4) and semiconductor-metal heterointerfaces (Co3O4 / Pt and ZnIn2S4 / Pt) were formed within the ternary heterostructures, enabling efficient multi-interface charge transfer. Furthermore, due to the in situ 1D / 2D / 0D porous array design, the ternary Co3O4 / ZnIn2S4 / Pt heterostructure arrays not only possessed a large specific surface area for gas adsorption and reaction, but also avoided a number of issues associated with conventional powdered gas-sensing materials during device fabrication. This invention, through the comprehensive design of ternary heterostructures with multiple interfaces, provides a new perspective for improving the gas-sensing performance of semiconductor materials.

[0009] The technical solutions of the present invention are as follows: A first aspect of the present invention provides a Co3O4 / ZnIn2S4 / Pt heterojunction array, comprising a substrate and a Co3O4 / ZnIn2S4 / Pt heterojunction array in situ grown on the surface of the substrate, wherein the Co3O4 / ZnIn2S4 / Pt heterojunction array is composed of a Co3O4 nanowire array, ZnIn2S4 nanosheets, and Pt nanoparticles; Among them, the Co3O4 nanowire array is an array structure grown vertically on a planar substrate, the ZnIn2S4 nanosheets wrap the Co3O4 nanowire array, and the Pt nanoparticles are evenly dispersed on the ZnIn2S4 nanosheets; the Co3O4 nanowire array and the ZnIn2S4 nanosheets form a pn heterointerface, and the Pt nanoparticles form semiconductor-metal heterointerfaces on the surfaces of the Co3O4 nanowire array and the ZnIn2S4 nanosheets, respectively.

[0010] The Co3O4 / ZnIn2S4 / Pt heterojunction array fabricated in this invention forms robust pn heterointerfaces (Co3O4 / ZnIn2S4) and semiconductor-metal heterointerfaces (Co3O4 / Pt and ZnIn2S4 / Pt), enabling efficient multi-interface charge transfer and effectively converting the charge signal from the gas-solid reaction into a resistance signal. Furthermore, the Co3O4 nanowire arrays of this invention possess a large specific surface area, significantly enhancing the material's surface gas adsorption activity compared to regular dodecahedral cobalt oxides such as CoO and CoO2, and NiO nanosheet arrays. Consequently, at relatively low operating temperatures, the Co3O4 / ZnIn2S4 / Pt heterojunction arrays exhibit excellent gas selectivity for triethylamine, with a high response value and rapid recovery rate.

[0011] The present invention constructs a semiconductor gas sensor array in situ on a gas-sensitive substrate. As a further preferred embodiment, the substrate is an Al2O3 gas-sensitive substrate.

[0012] The aforementioned Al2O3 gas-sensing substrate is a commercially available flat-plate Al2O3 gas-sensing substrate. Composed of inexpensive and readily available Al2O3, the substrate features two pairs of Pt interdigital electrodes on its surface: one pair for heating and the other for collecting resistance signals. Both substrate heating and resistance signal collection are highly convenient, and the two pairs of electrodes do not interfere with each other. A Co3O4 / ZnIn2S4 / Pt heterojunction array serves as a novel gas-sensing layer, enabling surface gas adsorption and gas-sensing reactions.

[0013] As a further preferred embodiment, the longitudinal size of the Co3O4 nanowire is 2 μm to 10 μm, the thickness of the ZnIn2S4 nanosheet wrapping is 10 nm to 50 nm, and the size of the Pt nanoparticles is 1 nm to 3 nm.

[0014] As a further preferred embodiment, the loading amount of the Pt nanoparticles is 1 wt% to 3 wt%; The specific surface area of the Co3O4 / ZnIn2S4 / Pt is 90m 2 / g~100m 2 / g.

[0015] The second aspect of the present invention provides a method for preparing the Co3O4 / ZnIn2S4 / Pt heterojunction array, comprising the following steps: Co3O4 nanowires were grown on the surface of a planar substrate using a hydrothermal method combined with annealing treatment to obtain a Co3O4 nanowire array grown vertically on the planar substrate. growing ZnIn2S4 nanosheets on the surface of the Co3O4 nanowire array by a water bath method to obtain an intermediate product, a Co3O4 / ZnIn2S4 heterostructure array; Pt nanoparticles are deposited on the surface of the Co3O4 / ZnIn2S4 heterostructure array by a photodeposition method to obtain a final product, a Co3O4 / ZnIn2S4 / Pt heterojunction array.

[0016] As a further preferred embodiment, the steps of growing Co3O4 nanowires on the substrate surface by a hydrothermal method combined with annealing treatment specifically include: Cobalt nitrate, ammonium fluoride and urea are dissolved in deionized water and stirred to obtain a reaction solution. A flat substrate is then added to the reaction solution for a hydrothermal reaction. The reaction time is 4 h to 8 h and the reaction temperature is 90 ℃ to 130 ℃. After the reaction, the flat substrate is washed and dried, and then annealed at 300 ℃ to 500 ℃ for 1 h to 3 h. After the annealing treatment, Co3O4 nanowire arrays are obtained.

[0017] As a further preferred embodiment, the molar ratio of cobalt nitrate, ammonium fluoride and urea is 1:1~4:3~7. Urea is an alkali source, and its decomposition can produce OH - (CO(NH2)2→NH3↑+HCNO), metal Co ions and OH in cobalt nitrate - Combined, they form Co(OH)2. Ammonium fluoride, as a strong acid and weak base salt, can effectively regulate the pH of the reaction system, thereby controlling the nucleation and growth of Co(OH)2 and ultimately forming the nanowire morphology. Extensive experimental research has revealed that the optimal molar ratio of cobalt nitrate, ammonium fluoride, and urea is 1:2:5. Excessive or insufficient amounts of urea and ammonium fluoride are not conducive to the formation of an optimal nanowire structure.

[0018] As a further preferred embodiment, the specific steps of growing ZnIn2S4 nanosheets on the surface of the Co3O4 nanowires by a water bath method include: Adjust the pH of water to 1-3 with nitric acid, add glycerol, and sonicate to obtain a solution; Zinc chloride, indium chloride and thioacetamide are dissolved in the solution, mixed and stirred to obtain a reaction solution, and then the Co3O4 nanowire array is immersed in the reaction solution for a water bath reaction, the temperature is maintained at 60°C to 100°C, and the reaction is carried out for 1 hour to 3 hours. After the reaction is completed, the product is washed and dried to finally obtain a Co3O4 / ZnIn2S4 heterostructure array.

[0019] As a further preferred embodiment, the concentration of the nitric acid is 0.5 mol / L to 2 mol / L; The molar ratio of the zinc chloride, indium chloride and thioacetamide is 1:1-3:1-4.

[0020] As a further preferred embodiment, the specific steps of depositing Pt nanoparticles on the surface of the Co3O4 / ZnIn2S4 heterostructure array by photodeposition include: Pour methanol and chloroplatinic acid solution into water and mix well to obtain a mixed solution; The Co3O4 / ZnIn2S4 heterostructure array is immersed in the mixed solution to perform a photodeposition reaction, and the alumina flat substrate is irradiated with a mercury lamp. After the reaction is completed, the alumina flat substrate is washed and dried to obtain a Co3O4 / ZnIn2S4 / Pt heterojunction array.

[0021] As a further preferred embodiment, the addition ratio of the methanol and chloroplatinic acid solution is 4-6 mL: 0.008-0.012 mmol.

[0022] As a further preferred embodiment, the power of the mercury lamp is 600 W to 1200 W, and the irradiation time is 0.3 h to 1.0 h; A third aspect of the present invention provides a gas sensor comprising the above-mentioned Co3O4 / ZnIn2S4 / Pt heterojunction array.

[0023] As a further preferred embodiment, the gas sensor is a gas sensor for detecting triethylamine.

[0024] The Co3O4 / ZnIn2S4 / Pt heterojunction nanosheet array of the present invention is applied to a gas sensor as a gas-sensitive sensing layer for surface gas adsorption and gas-sensitive reaction, and has a highly selective detection characteristic for triethylamine.

[0025] The present invention has at least one of the following beneficial effects: 1. The Co3O4 / ZnIn2S4 / Pt heterojunction array of the present invention is composed of a Co3O4 nanowire array grown in situ on a flat alumina substrate as a framework, ultrathin ZnIn2S4 nanosheets wrapped around the surface of the Co3O4 nanowire array, and a highly dispersed outer layer of Pt nanoparticles. On the one hand, the use of the Co3O4 nanowire array as a framework is different from the prior art, which uses NiO, CoO, CoO2, and other oxide arrays. The Co3O4 nanorod array prepared by the hydrothermal method is composed of nanoparticles with a large number of pores between the particles. Therefore, the Co3O4 has a larger specific surface area, greatly improving the material's surface gas adsorption activity, and has a structural advantage over regular dodecahedral cobalt oxides such as CoO and CoO2, and NiO nanosheet arrays. On the other hand, the prior art disperses noble metals on the surface of the oxide array, enhancing the semiconductor material's absorption capacity of visible light through the noble metal surface plasmon resonance effect, promoting the generation of photogenerated carriers. The present invention, however, disperses noble metals on the surface of ZnIn2S4 nanosheets. The chemical sensitization of the noble metal nanoparticles not only significantly enhances the adsorption activity of the Co3O4 / ZnIn2S4 heterojunction array for molecules, but also the large surface area of ZnIn2S4 itself, forming a heterojunction with Pt nanoparticles, provides abundant surface active sites. Therefore, compared to prior heterojunction nanosheet arrays, the Co3O4 / ZnIn2S4 / Pt heterojunction array prepared in the present invention features Pt nanoparticles forming semiconductor-metal heterointerfaces (Co3O4 / Pt and ZnIn2S4 / Pt) on the surfaces of Co3O4 and ZnIn2S4, respectively. The gradual establishment of these interfaces ultimately achieves efficient multi-interface charge transfer characteristics. Under low operating temperature conditions, the Co3O4 / ZnIn2S4 / Pt heterojunction array exhibits excellent gas selectivity for triethylamine, with high response values and fast recovery speed. The present invention exhibits excellent long-term stability and humidity resistance, promising broad application prospects in practical production. 2. The preparation process of the present invention is simple and low-cost. The Co3O4 / ZnIn2S4 / Pt heterojunction array prepared by the present invention has good heterogeneous interface contact and realizes efficient multi-interface charge transfer characteristics. Due to the design of the in-situ 1D / 2D / 0D porous array structure, the ternary Co3O4 / ZnIn2S4 / Pt heterojunction array not only has a large gas adsorption and reaction specific surface area, but also avoids a series of problems of traditional powder gas-sensitive materials in the device manufacturing process. In addition, the Co3O4 / ZnIn2S4 / Pt heterojunction array can be used in gas sensors, specifically for the highly selective detection of triethylamine at a relatively low operating temperature of 200°C. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1Shown are the XRD patterns of Co3O4, ZnIn2S4, Co3O4 / ZnIn2S4 and Co3O4 / ZnIn2S4 / Pt; Figure 2 (a) and (b) are SEM images of Co3O4 nanowire arrays; (c) and (d) are SEM images of pure ZnIn2S4; (e) and (f) are SEM images of Co3O4 / ZnIn2S4 heterojunction arrays; (g) -(t) are SEM images, TEM images, HRTEM images and EDS element distribution images of Co3O4 / ZnIn2S4 / Pt heterojunction arrays, respectively; (u) is a schematic diagram of the preparation process of Co3O4 / ZnIn2S4 / Pt heterojunction arrays.

[0027] Figure 3 XPS spectra of Co₃O₄, ZnIn₂S₄, Co₃O₄ / ZnIn₂S₄, and Co₃O₄ / ZnIn₂S₄ / Pt. (a) Co 2p XPS spectrum; (b) O 1s XPS spectrum; (c) Zn 2p XPS spectrum; (d) In 3d XPS spectrum; (e) S 2p XPS spectrum; (f) Pt 4f XPS spectrum.

[0028] Figure 4 Nitrogen adsorption-desorption isotherms and pore size distribution curves of different samples. (a) Co3O4; (b) ZnIn2S4; (c) Co3O4 / ZnIn2S4; (d) Co3O4 / ZnIn2S4 / Pt.

[0029] Figure 5 The response curves of Co3O4, ZnIn2S4, Co3O4 / ZnIn2S4, and Co3O4 / ZnIn2S4 / Pt to 100 ppm triethylamine at different temperatures are shown in Figure 2. (a) Co3O4, ZnIn2S4, Co3O4 / ZnIn2S4, and Co3O4 / ZnIn2S4 / Pt; (b) Co3O4, ZnIn2S4, and Co3O4 / ZnIn2S4.

[0030] Figure 6 Figure 2 shows the repeatability of different samples for 100 ppm triethylamine over several cycles at 200°C. (a) Co3O4; (b) ZnIn2S4; (c) Co3O4 / ZnIn2S4; (d) Co3O4 / ZnIn2S4 / Pt.

[0031] Figure 7The following table shows the dynamic sensing characteristics of different samples to different concentrations of triethylamine at 200°C. (a) Co3O4; (b) ZnIn2S4; (c) Co3O4 / ZnIn2S4; (d) Co3O4 / ZnIn2S4 / Pt.

[0032] Figure 8 (a) Response curves of four samples with triethylamine concentrations in the range of 20-2000 ppm; (b) Detection limit of Co3O4 / ZnIn2S4 / Pt for triethylamine gas sensitivity; (c) Response-recovery time curve of Co3O4 / ZnIn2S4 / Pt to 100 ppm triethylamine; (d) Response of Co3O4 / ZnIn2S4 / Pt to different types of volatile organic compound gases.

[0033] Figure 9 (a) Response curve of Co3O4 / ZnIn2S4 / Pt to 100 ppm triethylamine at 200°C and 90% high humidity; (b) Long-term stability of the response value and baseline resistance of Co3O4 / ZnIn2S4 / Pt.

[0034] Figure 10 Ultraviolet photoelectron spectra (UPS), Kubelka-Munk transform reflectance spectra derived from UV-visible (UV-Vis) absorption spectra, and Mott-Schottky plots of different samples. (a), (b), and (c) are the UPS, Kubelka-Munk transform reflectance spectrum, and Mott-Schottky plot of Co₃O₄, respectively; (d), (e), and (f) are the UPS, Kubelka-Munk transform reflectance spectrum, and Mott-Schottky plot of ZnIn₂S₄, respectively.

[0035] Figure 11 In situ Fourier transform infrared spectra of Co3O4 / ZnIn2S4 / Pt heterostructure nanoarrays in triethylamine atmosphere. (a) is the total in situ Fourier transform infrared spectrum; (b) is the peak at 1250-1540 cm -1 In situ Fourier transform infrared spectra in the range of 2230–2454 cm -1 In situ Fourier transform infrared spectra in the range of 2500-3400 cm -1 In situ Fourier transform infrared spectroscopy in the range. DETAILED DESCRIPTION

[0036] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0037] Example 1 A Co3O4 / ZnIn2S4 / Pt heterojunction array, the preparation process of the Co3O4 / ZnIn2S4 / Pt heterostructure array is as follows Figure 2 As shown in u. First, a Co(OH)2 nanowire array is in situ grown on a commercial alumina flat substrate using a hydrothermal reaction. The Co(OH)2 nanowires are then converted into a Co3O4 nanowire array by calcination. Using the Co3O4 nanowire array as a substrate, ultrathin ZnIn2S4 nanosheets are uniformly coated on its surface by a water bath method to obtain a Co3O4 / ZnIn2S4 heterostructure array. Finally, Pt nanoparticles are uniformly deposited by photochemical reduction to obtain a Co3O4 / ZnIn2S4 / Pt heterostructure array. The specific preparation method includes the following steps: Step 1: First, wash the commercial flat-plate Al2O3 gas-sensitive substrate (produced by Wuhan Huachuang Ruike Technology Co., Ltd.) repeatedly in deionized water and anhydrous ethanol and then dry it for use; Step 2: Cobalt nitrate (Co(NO3)2·6H2O), ammonium fluoride (NH4F), and urea (CH4N2O) were added to a polytetrafluoroethylene autoclave in a molar ratio of 1:2:5. Deionized water was then added until the inner volume filling degree was 40%, and magnetic stirring was continued for 1.0 hour to obtain a reaction solution. A washed commercial flat-plate Al2O3 gas-sensing substrate was added to the reaction solution and a hydrothermal reaction was carried out at a temperature of 110°C for 6 hours. After the reaction, the commercial flat-plate Al2O3 gas-sensing substrate was washed and dried, and then annealed in a muffle furnace at a temperature of 400°C for 2 hours to obtain a Co3O4 nanowire array. Step 3: Dissolve zinc chloride, indium chloride, and thioacetamide in deionized water at a molar ratio of 1:1:2, mix thoroughly, and stir for 0.5 hours to obtain a reaction solution. Adjust the pH of the solution to 2.5 with 0.5 mol / L nitric acid. Then, immerse the Co3O4 nanowire array in the reaction solution for a water bath reaction. Maintain the reaction solution at 80°C in a water bath for 2 hours. After the reaction, wash and dry the product to obtain a Co3O4 / ZnIn2S4 heterostructure array.

[0038] Step 4: Pour methanol (5 mL) and chloroplatinic acid (H2PtCl6) solution (0.01024 mmol) into 40 mL of deionized water and mix well to obtain a mixed solution; then immerse the Co3O4 / ZnIn2S4 heterostructure array in the mixed solution for photodeposition reaction. Set the power of the mercury lamp to 1000 W to irradiate the Co3O4 / ZnIn2S4 heterostructure array for 30 minutes. After the reaction, wash and dry the product to obtain a Co3O4 / ZnIn2S4 / Pt heterojunction array.

[0039] Example 2 A Co3O4 / ZnIn2S4 / Pt heterojunction array, the preparation method of which comprises the following steps: Step 1: First, wash the commercial flat-plate Al2O3 gas-sensitive substrate (produced by Wuhan Huachuang Ruike Technology Co., Ltd.) repeatedly in deionized water and anhydrous ethanol and then dry it for use; Step 2: Cobalt nitrate (Co(NO3)2·6H2O), ammonium fluoride (NH4F), and urea (CH4N2O) were added to a polytetrafluoroethylene autoclave in a molar ratio of 1:4:5. Deionized water was then added until the inner volume was filled to 50%, and magnetic stirring was continued for 0.5 hours to obtain a reaction solution. A washed commercial flat-plate Al2O3 gas-sensing substrate was added to the reaction solution and a hydrothermal reaction was carried out at a temperature of 130°C for 4 hours. After the reaction, the commercial flat-plate Al2O3 gas-sensing substrate was washed and dried, and then annealed in a muffle furnace at a temperature of 400°C for 2 hours to obtain a Co3O4 nanowire array. Step 3: Dissolve zinc chloride, indium chloride, and thioacetamide in deionized water at a molar ratio of 1:2:3, mix thoroughly, and stir for 0.5 hours to obtain a reaction solution. Adjust the pH of the solution to 2.5 with 1 mol / L nitric acid. Then, immerse the Co3O4 nanowire array in the reaction solution for a water bath reaction. Maintain the reaction solution at 100°C in a water bath for 2 hours. After the reaction, wash and dry the product to obtain a Co3O4 / ZnIn2S4 heterostructure array.

[0040] Step 4: Pour methanol (5 mL) and chloroplatinic acid (H2PtCl6) solution (0.01024 mmol) into 40 mL of deionized water and mix well to obtain a mixed solution; then immerse the Co3O4 / ZnIn2S4 heterostructure array in the mixed solution for photodeposition reaction. Set the power of the mercury lamp to 1000 W to irradiate the Co3O4 / ZnIn2S4 heterostructure array for 30 minutes. After the reaction, wash and dry the product to obtain a Co3O4 / ZnIn2S4 / Pt heterojunction array.

[0041] Example 3 A Co3O4 / ZnIn2S4 / Pt heterojunction array, the preparation method of which comprises the following steps: Step 1: First, wash the commercial flat-plate Al2O3 gas-sensitive substrate (produced by Wuhan Huachuang Ruike Technology Co., Ltd.) repeatedly in deionized water and anhydrous ethanol and then dry it for use; Step 2: Cobalt nitrate (Co(NO3)2·6H2O), ammonium fluoride (NH4F), and urea (CH4N2O) were added to a polytetrafluoroethylene autoclave in a molar ratio of 1:2:3. Deionized water was then added until the inner volume was filled to 60%, and magnetic stirring was continued for 0.5 hours to obtain a reaction solution. A washed commercial flat-plate Al2O3 gas-sensing substrate was added to the reaction solution and a hydrothermal reaction was carried out at a temperature of 100°C for 8 hours. After the reaction, the commercial flat-plate Al2O3 gas-sensing substrate was washed and dried, and then annealed in a muffle furnace at a temperature of 400°C for 2 hours to obtain a Co3O4 nanowire array. Step 3: Dissolve zinc chloride, indium chloride, and thioacetamide in deionized water at a molar ratio of 1:1:4, mix thoroughly, and stir for 0.5 hours to obtain a reaction solution. Adjust the pH of the solution to 2.5 with 1 mol / L nitric acid. Then, immerse the Co3O4 nanowire array in the reaction solution for a water bath reaction. Maintain the reaction solution at 60°C in a water bath for 3 hours. After the reaction, wash and dry the product to obtain a Co3O4 / ZnIn2S4 heterostructure array.

[0042] Step 4: Pour methanol (5 mL) and chloroplatinic acid (H2PtCl6) solution (0.01024 mmol) into 40 mL of deionized water and mix well to obtain a mixed solution; then immerse the Co3O4 / ZnIn2S4 heterostructure array in the mixed solution for photodeposition reaction. Set the power of the mercury lamp to 1000 W to irradiate the Co3O4 / ZnIn2S4 heterostructure array for 30 minutes. After the reaction, wash and dry the product to obtain a Co3O4 / ZnIn2S4 / Pt heterojunction array.

[0043] Comparative Example 1 Only Co3O4 nanowire arrays were prepared, and the preparation method was as follows: Cobalt nitrate (Co(NO₃)₂·6H₂O), ammonium fluoride (NH₄F), and urea (CH₄N₂O) were added to a polytetrafluoroethylene autoclave in a molar ratio of 1:2:5. Deionized water was then added to a 40% filling degree of the autoclave, and magnetic stirring was continued for 0.5 h to obtain a reaction solution. A washed commercial flat-plate Al₂O₃ gas-sensing substrate was added to the reaction solution, followed by a hydrothermal reaction at 110°C for 6 h. After the reaction, the commercial flat-plate Al₂O₃ gas-sensing substrate was washed and dried, and then annealed in a muffle furnace at 400°C for 2 h to obtain Co₃O₄ nanowire arrays.

[0044] Comparative Example 2 Only ZnIn2S4 powder was prepared, and the preparation method was as follows: Dissolve zinc chloride, indium chloride, and thioacetamide in deionized water at a molar ratio of 1:1:2, mix well, and stir for 0.5 hours to obtain a reaction solution. Adjust the pH of the solution to 2.5 with 1 mol / L nitric acid. The reaction solution is then placed in a water bath, maintained at 80°C, for 2 hours. After the reaction, the product is washed and dried to obtain ZnIn2S4 powder.

[0045] Comparative Example 3 Only Co3O4 / ZnIn2S4 heterostructure arrays were prepared, and the preparation method was as follows: Cobalt nitrate (Co(NO₃)₂·6H₂O), ammonium fluoride (NH₄F), and urea (CH₄N₂O) were added to a polytetrafluoroethylene autoclave in a molar ratio of 1:2:5. Deionized water was then added to a 40% filling level, and magnetic stirring was continued for 0.5 hours to obtain a reaction solution. A washed commercial flat-plate Al₂O₃ gas-sensing substrate was added to the reaction solution, followed by a hydrothermal reaction at 110°C for 6 hours. After the reaction, the commercial flat-plate Al₂O₃ gas-sensing substrate was washed and dried, and then annealed in a muffle furnace at 400°C for 2 hours to obtain Co₃O₄ nanowire arrays. Zinc chloride, indium chloride, and thioacetamide were dissolved in deionized water at a molar ratio of 1:1:2, mixed, and stirred for 0.5 hours to obtain a reaction solution. The pH of the solution was adjusted to 2.5 with 1 mol / L nitric acid. Co₃O₄ nanowire arrays were then immersed in the reaction solution for a water bath reaction, maintained at 80°C in a water bath, for 2 hours. After the reaction, the product was washed and dried to obtain a Co₃O₄ / ZnIn₂S₄ heterostructure array.

[0046] The specific results of characterization and performance testing of the sensors prepared in Example 1 and Comparative Examples 1-3 are as follows: The crystal structure of the samples was studied by XRD. Figure 1 As shown, the eight characteristic peaks of the Co3O4 nanowire array at 19.09°, 31.28°, 36.82°, 38.54°, 44.79°, 55.64°, 59.36°, and 65.23° are in good agreement with the standard chart for cubic Co3O4 (JCPDS No. 43-1003), indicating that the Co3O4 nanowire (NW) array is a pure phase structure. For ZnIn2S4, the three characteristic peaks at 21.94°, 27.98°, and 47.56° are highly consistent with the standard chart for hexagonal ZnIn2S4 (JCPDS No. 65-2023). Comparison of the characteristic peak positions reveals that no additional peaks appear in the Co3O4 / ZnIn2S4 heterostructure array, indicating that the sample is composed of cubic Co3O4 and hexagonal ZnIn2S4. The XRD pattern of the Co3O4 / ZnIn2S4 / Pt heterostructure array prepared in Example 1 is similar to that of the Co3O4 / ZnIn2S4 heterostructure array. Due to the low loading rate and small size of the Pt nanoparticles, the characteristic peaks of Pt cannot be clearly observed in the XRD pattern of the Co3O4 / ZnIn2S4 / Pt heterostructure array.

[0047] The morphology of the prepared materials was characterized by SEM and TEM. Figure 2 a and 2b are SEM images of Co3O4 nanowire (NW) arrays. It can be visually observed that the sample consists of a large number of nearly upright and smooth surface nanowire arrays. Figure 2 c and 2d are the morphological characteristics of pure ZnIn2S4. The sample is composed of large nanosheets, and a large number of nanosheets are aggregated into spheres. Figure 2 Figures 2e and 2f are low- and high-magnification morphological features of the Co3O4 / ZnIn2S4 heterostructure array. It can be seen that, in stark contrast to the smooth surface of pure Co3O4 nanowires, a thin layer of flaky ZnIn2S4 is uniformly coated on the surface of the Co3O4 nanowires. For the Co3O4 / ZnIn2S4 / Pt heterostructure array prepared in Example 1, the Pt nanoparticles could not be directly observed by SEM due to their small size. Figure 2 Therefore, TEM was used to further characterize the samples. Figure 2 i-2k shows a TEM image of a Co3O4 / ZnIn2S4 / Pt heterostructure array. It was found that ultrathin ZnIn2S4 nanosheets were uniformly coated on the Co3O4 nanowires, and Pt nanoparticles with an average particle size of 1-3 nm were densely dispersed on the surface. HRTEM characterization ( Figure 2l and 2m), three different lattice fringes can be clearly observed. After measurement and data comparison, the three different lattice fringes correspond to the (220) crystal plane of Co3O4, the (102) crystal plane of ZnIn2S4 and the (111) crystal plane of Pt. These data further confirm the existence of Pt nanoparticles and the successful formation of a robust heterogeneous interface between the three components in the Co3O4 / ZnIn2S4 / Pt heterostructure array. Through the element energy spectrum distribution diagram ( Figure 2 n-2t), it can be seen intuitively that Co, O, Zn, In, S and Pt elements are evenly distributed in the corresponding areas.

[0048] In order to further analyze the chemical state of the samples, X-ray photoelectron spectroscopy (XPS) of Co3O4, ZnIn2S4, Co3O4 / ZnIn2S4 and Co3O4 / ZnIn2S4 / Pt was detected. By fitting the XPS data of Co element in Co3O4 sample, a pair of spin-orbit doublets and a pair of satellite peaks were observed. The satellite peaks at the binding energies of 781.06 eV and 796.11 eV are respectively from Co 2+ 2p 3 / 2 Track and Co 2+ 2p 1 / 2 orbitals, the characteristic peaks at 779.75 eV and 794.77 eV are from Co 3+ 2p 3 / 2 Track and Co 3+ 2p 1 / 2 By comparing the characteristic peak positions of Co element in Co3O4 / ZnIn2S4 and Co3O4 / ZnIn2S4 / Pt with those in pure Co3O4 samples, no significant changes were found ( Figure 3 a). In addition, the peaks of O element in pure Co3O4 at binding energies of 530.04eV and 531.14eV represent lattice oxygen and chemically adsorbed oxygen, respectively. After the formation of the heterostructure, the lattice oxygen moves slightly toward the lower binding energy direction. Most obviously, the ratio of chemically adsorbed oxygen to lattice oxygen increases significantly. According to previous reports, the surface of ZnIn2S4 is rich in S vacancies, which can greatly promote the adsorption of oxygen. The precious metal Pt has excellent catalytic properties, which can further promote the dissociation of oxygen molecules on the surface of the material and produce more reactive chemically adsorbed oxygen. This may be an important reason for the improvement of gas-sensing performance. For the Zn element in the ZnIn2S4 sample ( Figure 3 c), the binding energies of 1021.1 eV and 1044.2 eV represent the Zn 2+ 2p 3 / 2 Orbital and Zn 2+ 2p 1 / 2 Orbit. In element ( Figure 3 d) Peaks appear at binding energies of 444.71 eV and 452.42 eV, which are attributed to In 3+ In 3D 5 / 2 Orbital and In3d 3 / 2 track. Figure 3 e shows the high-resolution spectrum of the element S. 161.77eV and 163.00eV are the electrons from S 2- Valence S2p 3 / 2 Orbitals and S 2p 1 / 2 The energy required for orbital escape and transition to the vacuum level. Figure 3 As shown in c-3e, compared with the pure ZnIn2S4 sample, the Zn in the Co3O4 / ZnIn2S4 sample 2+ 2p 3 / 2 (1021.93eV), Zn 2+ 2p 1 / 2 (1044.99eV), In 3+ 3d 5 / 2 (445.06eV), In 3+ 3d 3 / 2 (452.61eV), S 2- 2p 3 / 2 (161.73 eV) and S 2- 2p 1 / 2 Characteristic peaks and In in Co3O4 / ZnIn2S4 / Pt sample 3+ 3d 5 / 2 (445.02 eV), In 3+ 3d 3 / 2 (452.57 eV), S 2- 2p 3 / 2 (161.69 eV) and S 2- 2p 1 / 2 (162.88 eV) characteristic peaks all shift to higher binding energies. By analyzing the changes in the binding energy of each element in XPS, the binding energy of the O element in the binary sample decreases, while the binding energy of the Zn, In and S elements increases. Since the binding energy is inversely proportional to the change in electron density, the above results show that the electron density of Co3O4 decreases after the formation of the heterostructure, while the electron density of ZnIn2S4 increases. The results show that the built-in electric field promotes the transfer of electrons from ZnIn2S4 to Co3O4, and also confirms that a robust heterostructure is formed between Co3O4 and ZnIn2S4, which promotes strong interfacial electronic interactions. The XPS characteristic peaks of Pt are located at 72.32eV and 73.56eV (corresponding to the Pt 4f of metallic Pt) 7 / 2 ), and 75.57eV and 76.59eV (corresponding to the Pt 4f 5 / 2The splitting of these peaks is caused by spin-orbit coupling ( Figure 3 f).

[0049] In order to further analyze the microstructure of the sample, including specific surface area, pore volume and average pore size, nitrogen adsorption-desorption isotherms and pore size distribution curves are shown in Figure 2. Figure 4 As shown. Pure Co3O4 ( Figure 4 a) exhibited a relatively low specific surface area (21.4263 m 2 / g), low pore volume and large pore width, indicating that the number of active sites is limited. In contrast, ZnIn2S4 ( Figure 4 b) has a specific surface area of 42.0258 m 2 / g, the pore volume is larger and the pore width is slightly smaller, which indicates that its structure is more suitable for gas molecule adsorption and diffusion. Figure 4 c) The specific surface area and pore volume increased significantly by 76.4981 m 2 / g, while the pore width decreased, indicating that the composite synthesis process effectively optimized the microstructure. Figure 4 d is the nitrogen adsorption-desorption isotherm and pore size distribution curve of Co3O4 / ZnIn2S4 / Pt. Although the addition of Pt leads to a slight decrease in the specific surface area and pore volume, it leads to a slight increase in the pore width.

[0050] On this basis, the applicant used the prepared nanoarray to detect triethylamine gas. Five test points were selected in the temperature range of 150°C to 250°C, and each temperature test point was tested several times. The response values of the four samples to triethylamine at different temperatures are as follows: Figure 5 As shown in Figures 5a and 5b, in an environment with a triethylamine concentration of 100 ppm, the response values of the four samples gradually increased as the operating temperature increased from 150°C to 200°C. When the operating temperature ranged from 200°C to 250°C, the response values of Co₃O₄, Co₃O₄ / ZnIn₂S₄, and Co₃O₄ / ZnIn₂S₄ / Pt gradually decreased, while the response value of ZnIn₂S₄ continued to increase. Generally, the response values first increased and then decreased, exhibiting an overall mountain-like shape, reaching a maximum value at an operating temperature of 200°C. Specifically, the average response value of Co₃O₄ to 100 ppm triethylamine was 5.24. The average response value of Co₃O₄ / ZnIn₂S₄ was significantly higher (19.43), 3.71 times that of Co₃O₄. The highest response value of Co3O4 / ZnIn2S4 / Pt was 118.97, 22.7 times that of Co3O4 and 6.12 times that of Co2O4 / ZnIn2S4. Therefore, the gas-sensing performance of triethylamine was significantly improved by constructing a heterostructure. In subsequent gas-sensing tests, 200°C was selected as the optimal operating temperature.

[0051] In a triethylamine atmosphere with a concentration of 100 ppm, the dynamic responses of different samples to triethylamine were recorded in continuous and repeated tests ( Figure 6 ). Each sample was tested repeatedly for 10 cycles under the same conditions. In any cycle, it can be observed that the introduction of triethylamine gas immediately causes a change in the material resistance, which then tends to stabilize at a certain value. With the release of triethylamine and the introduction of air, the resistance value will eventually return to its original value. After repeated testing for many cycles, the data showed high stability. The construction of the heterogeneous structure has a non-negligible effect on the response of triethylamine gas. Compared with pure Co3O4 ( Figure 6 a) and pure ZnIn2S4 ( Figure 6 b) compared with the response value of Co3O4 / ZnIn2S4 ( Figure 6 c) The mean response value increased significantly. Figure 6 d is Co3O4 / ZnIn2S4 / Pt. Modification of precious metal platinum nanoparticles is also an important means to improve gas sensing performance. By loading Pt nanoparticles on Co3O4 / ZnIn2S4, the average response value is further improved.

[0052] The dynamic sensing characteristics of different samples to different concentrations of triethylamine are as follows: Figure 7 As shown. Within a certain concentration range, the response value is proportional to the concentration of triethylamine. That is, as the concentration of triethylamine increases, the response value of each sample will also increase. However, when the concentration of triethylamine reaches a certain value, the response value will stabilize within a certain range and reach a saturated state. When the concentration of triethylamine is lower than 20ppm, it is difficult to detect Co3O4 ( Figure 7 a) and ZnIn2S4 ( Figure 7 b) Changes in resistance. However, Co3O4 / ZnIn2S4 ( Figure 7 c) and Co3O4 / ZnIn2S4 / Pt ( Figure 7 d) It can still respond to lower concentrations of gas. Importantly, compared with various previously reported Co3O4-related trimethylamine sensors, Co3O4 / ZnIn2S4 / Pt shows obvious advantages, especially in terms of response value and operating temperature.

[0053] from Figure 8 a can more systematically compare the response differences of the four samples with triethylamine concentrations ranging from 20 to 2000 ppm. It is not difficult to see that the response value of Co3O4 / ZnIn2S4 / Pt is the highest, followed by Co3O4 / ZnIn2S4. By processing the data, the detection limit (LOD) of triethylamine using Co3O4 / ZnIn2S4 / Pt can be obtained ( Figure 8 b). Through formula fitting, it can be seen that its detection limit can reach 633.7 ppb, which is much lower than the safe leakage value of triethylamine. Figure 8 As shown in Figure c, when 100ppm triethylamine gas is injected, the resistance response value changes rapidly, with a response time of about 185 seconds. It takes about 452 seconds for the resistance value to recover to 90% of the initial resistance. In addition, the responses of Co3O4 / ZnIn2S4 / Pt to 100ppm triethylamine, ethanol, ammonia, n-propanol, methanol, formaldehyde, acetic acid, ethyl acetate, acetaldehyde, acetone and trimethylamine gas were recorded and compared. By comparing the response values of Co3O4 / ZnIn2S4 / Pt to different gases at the same operating temperature and gas concentration ( Figure 8 d), the results showed that it has excellent gas-sensitive selectivity for triethylamine.

[0054] In addition, Co3O4 / ZnIn2S4 / Pt also exhibits excellent resistance to humidity interference and long-term stability to triethylamine. Figure 9 As shown in Figure a, under high humidity of 200 ppm and 90% humidity, it can still maintain a response value of about 120 to triethylamine (100 ppm). To investigate whether it has a long-term stable response to triethylamine, data were collected four times over three months. Under the same conditions, the response value of Co3O4 / ZnIn2S4 / Pt to triethylamine decreased by about 11.21% after 90 days, showing high stability ( Figure 9 b).

[0055] To further elucidate the band structure arrangement of Co3O4 and ZnIn2S4 in the formed heterostructure, a series of characterizations (including UPS, UV-visible absorption spectroscopy, and Mott Schottky test) were performed ( Figure 10 ). Figure 10 a and Figure 10 The UPS test data of d can be used to obtain the distance from the Fermi level to the vacuum level of Co3O4 and ZnIn2S4, that is, the work function is 11.5eV and 10.52eV respectively. According to the results of UV-visible absorption spectrum, the energy band gap of Co3O4 and ZnIn2S4 is 1.35eV ( Figure 10 b) and 2.28 eV ( Figure 10 e). According to the Mott Schottky test, the conduction band of Co3O4 is about 1.039eV ( Figure 10 c), while the valence band of ZnIn2S4 is about -0.483eV ( Figure 10 f).

[0056] Finally, in order to elucidate the real-time gas-sensing reaction of triethylamine on the heterojunction surface, in situ infrared spectroscopy measurements were performed ( Figure 11 ). At 2881.129 cm -1 、2940.91 cm -1 and 2977.55 cm -1The decrease in peak intensity at the characteristic peak of triethylamine is attributed to the participation of the -CH2 and -CH3 groups in triethylamine during the surface reaction. This attenuation indicates that the C-H bonds in triethylamine are gradually adsorbed and oxidized at the surface active sites. Oxygen (O2), acting as an oxidant in the reaction atmosphere, may first be activated and then react with triethylamine, breaking its -CH2 and -CH3 bonds and thus reducing its vibrational signal. During the reaction, triethylamine decomposes into intermediates (such as amine compounds or oxygen-containing species), the properties of which may also lead to changes in the characteristic peaks. Low-frequency region 1294.03 cm -1 and 1384.63 cm -1 The peaks at 1473.32 cm may correspond to -NH or other functional groups. Over time, further oxidation leads to the decomposition of these intermediates, causing these peaks to gradually weaken. -1 The vibration peak at may be derived from the bending vibration of the CN bond, which weakens over time, indicating that the CN bond is partially broken and a nitrogen-containing small molecule intermediate (such as NO) is subsequently formed. x or NH3). 2350.80 cm -1 and 2373.94 cm -1 The new peak intensity at is clearly attributed to the production of carbon dioxide. Symmetrical and asymmetric stretching vibrations of CO2 are responsible for the characteristic peaks in this wavenumber range. During the decomposition of triethylamine, the cleavage of the CH and CN bonds releases small molecular fragments (such as CO or H2O), which are further oxidized to form CO2 on the catalyst surface. The pn heterojunction effect at the Co3O4 and ZnIn2S4 interface promotes electron-hole separation and improves the oxidation efficiency. Furthermore, Pt modification reduces the activation energy of the reaction, further accelerating the conversion of the oxidation products. In summary, the gas-sensing reaction of triethylamine on the heterojunction surface can lead to its mineralization and decomposition under catalysis.

[0057] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A Co3O4 / ZnIn2S4 / Pt heterojunction array, characterized in that: The invention comprises a substrate and a Co3O4 / ZnIn2S4 / Pt heterojunction array in situ grown on the surface of the substrate, wherein the Co3O4 / ZnIn2S4 / Pt heterojunction array is composed of a Co3O4 nanowire array, ZnIn2S4 nanosheets and Pt nanoparticles; Among them, the Co3O4 nanowire array is an array structure grown vertically on a planar substrate, the ZnIn2S4 nanosheets wrap the Co3O4 nanowire array, and the Pt nanoparticles are evenly dispersed on the ZnIn2S4 nanosheets; the Co3O4 nanowire array and the ZnIn2S4 nanosheets form a pn heterointerface, and the Pt nanoparticles form semiconductor-metal heterointerfaces on the surfaces of the Co3O4 nanowire array and the ZnIn2S4 nanosheets, respectively.

2. The Co3O4 / ZnIn2S4 / Pt heterojunction array according to claim 1, characterized in that The longitudinal size of the Co3O4 nanowire array is 2 μm to 10 μm, the thickness of the ZnIn2S4 nanosheet wrapping is 10 nm to 50 nm, and the size of the Pt nanoparticles is 1 nm to 3 nm; The substrate is an Al2O3 gas-sensitive substrate.

3. The Co3O4 / ZnIn2S4 / Pt heterojunction nanowire array according to claim 1, characterized in that: The loading amount of the Pt nanoparticles is 1 wt% to 3 wt%; The specific surface area of Co3O4 / ZnIn2S4 / Pt is 90 m 2 / g~100 m 2 / g.

4. The method for preparing the Co3O4 / ZnIn2S4 / Pt heterojunction array according to any one of claims 1 to 3, characterized in that: The following steps are involved: Co3O4 nanowire arrays were grown on the surface of a planar substrate using a hydrothermal method combined with post-annealing treatment to obtain Co3O4 nanowire arrays grown vertically on the planar substrate. growing ZnIn2S4 nanosheets on the surface of the Co3O4 nanowire array by a water bath method to obtain an intermediate product, a Co3O4 / ZnIn2S4 heterostructure array; Pt nanoparticles are deposited on the surface of the Co3O4 / ZnIn2S4 heterostructure array by a photodeposition method to obtain a final product, a Co3O4 / ZnIn2S4 / Pt heterojunction array.

5. The preparation method according to claim 4, characterized in that The steps of growing Co3O4 nanowire arrays on the substrate surface using a hydrothermal method specifically include: Cobalt nitrate, ammonium fluoride, and urea were dissolved in deionized water and stirred to obtain a reaction solution. A flat substrate was then added to the reaction solution for a hydrothermal reaction. The reaction time was 4 h to 8 h and the reaction temperature was 90°C to 130°C. After the reaction, the flat substrate was washed and dried, and then annealed at 300°C to 500°C for 1 h to 3 h. After the annealing treatment, Co3O4 nanowire arrays were obtained.

6. The preparation method according to claim 5, characterized in that The molar ratio of the cobalt nitrate, ammonium fluoride and urea is 1:1-4:3-7; The planar substrate is a flat Al2O3 gas-sensitive substrate.

7. The preparation method according to claim 4, characterized in that The specific steps of growing ZnIn2S4 nanosheets on the surface of the Co3O4 nanowire array by the water bath method include: Dissolving zinc chloride, indium chloride, and thioacetamide in the solution, mixing and stirring to obtain a reaction solution, adjusting the pH value of the water to 1-3 with nitric acid, and then immersing the Co3O4 nanowire array in the mixed solution for a water bath reaction at a temperature maintained at 60°C to 100°C for 1 h to 3 h. After the reaction, washing and drying the product to obtain a Co3O4 / ZnIn2S4 heterostructure array; The concentration of the nitric acid is 0.5 mol / L to 2 mol / L; The molar ratio of the zinc chloride, indium chloride and thioacetamide is 1:1-3:1-4.

8. The preparation method according to claim 4, characterized in that The specific steps of depositing Pt nanoparticles on the surface of the Co3O4 / ZnIn2S4 heterostructure array by using the photodeposition method include: Pour methanol and chloroplatinic acid solution into water and mix well to obtain a mixed solution; The Co3O4 / ZnIn2S4 heterostructure array is immersed in the mixed solution to perform a photodeposition reaction, and the alumina flat substrate is irradiated with a mercury lamp. After the reaction is completed, the product is washed and dried to obtain a Co3O4 / ZnIn2S4 / Pt heterojunction array.

9. The preparation method according to claim 7, characterized in that The ratio of methanol and chloroplatinic acid solution added is 4-6 mL: 0.008-0.012 mmol; The power of the mercury lamp is 600 W to 1200 W, and the irradiation time is 0.3 h to 1.0 h.

10. A gas sensor, characterized in that: Comprising the Co3O4 / ZnIn2S4 / Pt heterojunction array according to any one of claims 1 to 3.

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