A transition metal-doped ZnIn2S4 gas sensor, its fabrication method and application

Abstract

The application belongs to the field of new materials and electronic information technology, and particularly relates to a transition metal doped ZnIn2S4 gas sensor and a preparation method and application thereof. The gas sensor comprises a substrate and a transition metal doped ZnIn2S4 nanoarray in situ grown on the surface of the substrate, the nanoarray is composed of a plurality of two-dimensional nanosheet layers, the two-dimensional nanosheet layers are arranged in an interlaced stacking mode and extend at an angle of ±5° relative to the normal direction of the substrate surface, and the two-dimensional nanosheet layers are combined into a network assembly with a three-dimensional flower-like topological structure through physical or chemical connection. The preparation method is simple, the energy band structure of the material is effectively controlled and the band gap is reduced, on the other hand, the specific surface area of the material is significantly increased and the pore size distribution is optimized. The gas sensor prepared by the method has excellent gas selectivity to triethylamine, high response value and fast recovery speed, and is expected to be applied to the fields of environmental monitoring and food safety.

Description

Technical Field

[0001] This invention relates to the fields of new materials and electronic information technology, specifically to a transition metal-doped ZnIn2S4 gas sensor, its preparation method, and its application. Background Technology

[0002] With the acceleration of modern industrialization and the increasing frequency of human activities, air pollution has become a global concern. Among numerous pollutants, volatile organic compounds (VOCs) have received considerable attention due to their wide range of sources, complex composition, and significant hazards. Triethylamine, a typical aliphatic amine VOC, is widely used in chemical synthesis, preservative manufacturing, and seafood processing. However, triethylamine has a strong pungent odor and significant biotoxicity. Short-term exposure to low concentrations of triethylamine can cause severe irritation to the conjunctiva and respiratory system, while long-term exposure may even lead to pulmonary edema and corneal damage. Furthermore, triethylamine is also a significant component of the volatile basic nitrogen released during the spoilage of protein-rich foods (such as seafood and meat). Therefore, developing a real-time, rapid, highly sensitive, and highly selective triethylamine gas sensor is of paramount practical importance, whether for ambient air quality monitoring, industrial production safety early warning, or food freshness assessment.

[0003] Currently, gas sensor technology for detecting triethylamine primarily utilizes metal-oxide-semiconductor (MOS) materials, such as tin dioxide, zinc oxide, and tungsten oxide. These sensors dominate commercial applications due to their low production cost and simple circuit design. However, traditional MOS sensors often face bottlenecks such as high operating temperature, high power consumption, sensitivity to ambient humidity, and poor selectivity. High-temperature operating environments not only increase energy consumption but also pose safety hazards related to flammable and explosive gases, and accelerate grain growth and aging of sensitive materials, thereby reducing the long-term stability of the sensor. In contrast, ternary metal sulfides (such as ZnIn2S4), as a narrow-bandgap semiconductor material with visible light response, have attracted widespread attention in the field of gas sensing due to their unique layered crystal structure, abundant surface active sites, and good chemical stability.

[0004] Although pure ZnIn2S4 material has shown some potential for gas sensing, several bottlenecks limit its practical application performance. First, pure ZnIn2S4 has a low intrinsic carrier concentration and a wide bandgap, resulting in poor conductivity and high baseline resistance at low temperatures. Second, the insufficient density of active sites on the unmodified material surface leads to low adsorption energy for target gas molecules, limiting the improvement of sensitivity. Furthermore, traditional gas sensor fabrication processes typically involve powder synthesis, slurry preparation, and coating. This non-in-situ preparation method results in loose contact between the sensitive film and the substrate, high interfacial contact resistance, and the film is prone to peeling off during use, leading to poor device consistency and long-term stability.

[0005] To overcome the aforementioned shortcomings, elemental doping and device structure modulation are considered effective modification strategies. Cu, as an important transition metal element, has an ionic radius similar to that of zinc ions, making it easy to achieve lattice substitution doping. Theory and experiments show that Cu doping can introduce impurity energy levels into ZnIn2S4, modulate the band structure, reduce the band gap, and thus improve the material's conductivity. Simultaneously, the lattice distortion caused by doping generates abundant sulfur vacancies and other defects, which are expected to become active centers for gas adsorption. Furthermore, in-situ growth technology enables the sensitive material to nucleate and grow directly on the electrode surface, forming a well-organized and firmly bonded nanoarray structure, effectively solving the problem of poor interfacial contact and providing a three-dimensional porous network structure with a large specific surface area conducive to gas diffusion. However, there are currently no reports on the in-situ growth of Cu-doped ZnIn2S4 nanosheet arrays and their application in triethylamine detection, especially in-depth research combining band structure evolution and gas-sensing mechanisms. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing ZnIn2S4-based gas sensors, such as low sensitivity, poor conductivity, and poor selectivity, as well as a series of problems caused by traditional non-in-situ thick-film fabrication processes. This invention provides a transition metal-doped ZnIn2S4 gas sensor, its fabrication method, and its applications. The gas sensor features an open, three-dimensional flower-like network structure with abundant pores. This structure not only ensures stable mechanical adhesion and good electrical contact between the sensitive material and the substrate but also creates unobstructed gas diffusion channels.

[0007] In this invention, the transition metal-doped ZnIn2S4 gas sensor exhibits a crystal structure in which transition metals, such as Cu, successfully enter the ZnIn2S4 lattice in ionic form, replacing some Zn atom sites or occupying interstitial spaces. Cu doping significantly increases the specific surface area of ​​the material; the 3 wt% doped sample achieves a specific surface area of ​​168.98 m² / g and a pore volume of 0.49 cm³ / g.

[0008] To achieve the above objectives, the present invention provides a transition metal-doped ZnIn2S4 gas sensor, comprising a substrate and a transition metal-doped ZnIn2S4 nanoarray grown in situ on the surface of the substrate. The nanoarray is composed of multiple two-dimensional nanosheets arranged in an alternating stacked manner and extending at an angle of ±5° relative to the normal direction of the substrate surface, forming a network assembly with a three-dimensional flower-like topology through physical or chemical bonding; the transition metal is embedded in the lattice structure of the ZnIn2S4 in the form of atomic doping.

[0009] Preferably, the transition metal is selected from Cu or Cd, and the doping amount is from 1 wt% to 5 wt%.

[0010] Preferably, the transition metal-doped ZnIn2S4 nanoarray has a specific surface area of ​​140 m² / g to 170 m² / g and a pore volume of 0.30 cm³ / g to 0.50 cm³ / g.

[0011] Preferably, the thickness of the two-dimensional nanosheets is 5 nm to 20 nm, the lateral dimension is 0.5 μm to 2 μm, and the stagger angle between adjacent sheets is 60° or 80°.

[0012] Preferably, the substrate is an insulating substrate or a conductive substrate, wherein the insulating substrate is selected from Al2O3, SiO2 or quartz, and the conductive substrate is selected from doped silicon, graphene or metal foil.

[0013] A second aspect of this invention provides a method for fabricating a transition metal-doped ZnIn2S4 gas sensor, comprising a one-step hydrothermal method for in-situ growth of a transition metal-doped ZnIn2S4 nanoarray on a substrate surface; the method includes:

[0014] A mixed solution containing a transition metal precursor and a ZnIn2S4 precursor is placed in a sealed reactor, and a surface-cleaned substrate is added. The reaction is carried out at 60°C to 100°C for 1 to 4 hours by water bath heating. After the reaction is completed, the substrate is naturally cooled, removed, washed and dried to obtain the transition metal-doped ZnIn2S4 gas sensor as described in this invention.

[0015] Preferably, the preparation process of the mixed solution includes:

[0016] S1. Mix deionized water and glycerin at a volume ratio of 15~25:2~5 until homogeneous, add nitric acid to adjust the pH of the system to 2.0~3.0, and then ultrasonically disperse for 0.5 to 2 hours;

[0017] S2. Add zinc source, indium source, sulfur source and transition metal source in sequence, and stir until completely dissolved and a homogeneous system is formed.

[0018] Preferably, the zinc source is selected from zinc chloride or zinc nitrate.

[0019] Preferably, the indium source is selected from indium chloride or indium nitrate.

[0020] Preferably, the sulfur source is selected from thioacetamide or sodium thiosulfate.

[0021] Preferably, the transition metal source is selected from copper or cadmium sources, including copper chloride, copper nitrate, or cadmium chloride and cadmium acetate.

[0022] Preferably, the concentration of the nitric acid is 0.5 mol / L to 2 mol / L.

[0023] Preferably, the concentration of the zinc source is 6.65 mmol / L to 11.74 mmol / L.

[0024] Preferably, the concentration of the indium source is 6.7 mmol / L to 11.8 mmol / L.

[0025] Preferably, the concentration of the sulfur source is 13.3 mmol / L to 23.5 mmol / L.

[0026] Preferably, the concentration of the transition metal source is 0.043 mmol / L to 0.22 mmol / L.

[0027] Preferably, the substrate is selected from Al2O3, SiO2 or quartz.

[0028] Preferably, the washing process includes washing with deionized water and anhydrous ethanol in sequence.

[0029] Preferably, the drying temperature is 60°C to 80°C, and the drying time is 4 to 12 hours.

[0030] A third aspect of the present invention provides the application of the transition metal-doped ZnIn2S4 gas sensor described herein in catalytic oxidation, catalytic degradation of VOCs, photocatalytic water splitting, or detection of volatile organic compounds.

[0031] Preferably, the detection of volatile organic compounds includes a highly sensitive detection method for triethylamine at temperatures ranging from room temperature to 350°C, with a detection response value ≥85 and a detection limit ≤2000ppm.

[0032] Compared with the prior art, the present invention has at least the following beneficial effects:

[0033] 1. In-situ growth creates a stable interface, significantly improving device stability. The in-situ growth technology enables the nanosheet array to nucleate and grow directly on the ceramic substrate and electrode surface, forming atomic-level close contact. This effectively eliminates the microcracks and high interfacial resistance present in traditional coated films, prevents film peeling, and significantly improves the long-term stability of the sensor.

[0034] 2. Transition metal doping modulates band structure for electronic sensitization. Characterization techniques such as UV-Vis and UPS confirm that the introduction of Cu deeply modulates the electronic structure of ZnIn2S4. Cu doping not only alters the surface chemical environment but also introduces impurity energy levels, changing the valence band position and significantly reducing the band gap. A narrower band gap lowers the energy barrier for electronic excitation, increasing the intrinsic conductivity of the material at operating temperatures, thereby enhancing the sensor's electrical response to the target gas.

[0035] 3. The three-dimensional hierarchical porous structure and increased active sites enhance the gas-sensing performance. BET tests show that appropriate Cu doping (especially 3 wt%) induces nanosheet refinement, constructing a three-dimensional hierarchical porous structure with an ultra-high specific surface area (168.98 m² / g). Benefiting from the gas diffusion advantages brought by the three-dimensional open flower-like array structure and the electronic and chemical sensitization effects brought by Cu doping, this sensor exhibits specific adsorption and catalytic oxidation capabilities for triethylamine molecules, demonstrating ultra-high sensitivity, a response value as high as 95 for 100 ppm triethylamine, rapid response and recovery times of only 33 seconds and 326 seconds, and excellent selectivity under interference backgrounds such as ethanol and ammonia. Attached Figure Description

[0036] Figure 1 The images show (a): X-ray diffraction (XRD) patterns and (b): magnified X-ray diffraction (XRD) profiles of pure ZnIn2S4, 1% Cu-ZnIn2S4, 3% Cu-ZnIn2S4, and 5% Cu-ZnIn2S4 nanoarrays.

[0037] Figure 2The images show the microstructure and elemental distribution of the 3% Cu-doped ZnIn2S4 nanosheets prepared in Example 1 and the comparative undoped pure ZnIn2S4 nanosheet arrays. (a) to (c) are SEM images of the undoped pure ZnIn2S4 nanosheets: (a) is a low-magnification scanning electron microscope (SEM) image showing a large-area uniformly grown array; (b) is a medium-magnification SEM image clearly showing a three-dimensional flower-like network structure; (c) is a high-magnification SEM image showing the ultrathin two-dimensional nanosheets supporting each other; (d) to (f) are SEM images of the 3% Cu-doped ZnIn2S4 nanosheet array; (g) to (h) are TEM images of the 3% Cu-doped ZnIn2S4 nanosheet array; (i) to (j) are HRTEM images of the 3% Cu-doped ZnIn2S4 nanosheet array; and (k) to (o) are EDS elemental distribution images of the 3% Cu-doped ZnIn2S4 nanosheet array.

[0038] Figure 3 The images shown are scanning electron microscope images (a) to (c) and (d) to (h) of the 1% Cu-doped ZnIn2S4 nanosheet array prepared in Example 2: elemental distribution diagrams.

[0039] Figure 4 The images shown are scanning electron microscope images (a) to (c) and (d) to (h) of the 5% Cu-doped ZnIn2S4 nanosheet array prepared in Example 3: elemental distribution maps.

[0040] Figure 5 The images shown are scanning electron microscope images (a) to (c) and (d) to (h) of the 3% Cd-doped ZnIn2S4 nanosheet array prepared in Example 4: elemental distribution maps.

[0041] Figure 6 The image shows the X-ray photoelectron spectroscopy (XPS) analysis of the samples prepared in this invention; where (a) is the XPS spectrum of Zn 2p, (b) is the XPS spectrum of In 3d, (c) is the XPS spectrum of S 2p, and (d) is the XPS spectrum of Cu 2p, demonstrating the surface chemical states and electronic interactions between elements.

[0042] Figure 7 The figures show nitrogen adsorption-desorption isotherms and pore size distributions of different samples prepared in this invention, used to characterize the specific surface area and pore structure of the materials. (a) is pure ZnIn2S4; (b) is 1% Cu-ZnIn2S4; (c) is 3% Cu-ZnIn2S4; and (d) is 5% Cu-ZnIn2S4.

[0043] Figure 8The table shown is a statistical table of specific surface area, pore volume and average pore diameter of different samples prepared in this invention.

[0044] Figure 9 The images show the ultraviolet photoelectron spectra (UPS) of different samples; where (a), (b), (c), and (d) are the UPS of pure ZnIn2S4, 1% Cu-ZnIn2S4, 3% Cu-ZnIn2S4, and 5% Cu-ZnIn2S4, respectively.

[0045] Figure 10 The Kubelka-Munk transform reflectance spectra of different samples derived from ultraviolet-visible (UV-Vis) absorption spectra are shown; where (a), (b), (c), and (d) are the Kubelka-Munk transform reflectance spectra of pure ZnIn2S4, 1% Cu-ZnIn2S4, 3% Cu-ZnIn2S4, and 5% Cu-ZnIn2S4, respectively.

[0046] Figure 11 The figures show the response curves of pure ZnIn2S4, 1% Cu-ZnIn2S4, 3% Cu-ZnIn2S4, and 5% Cu-ZnIn2S4 to triethylamine at a concentration of 100 ppm at different temperatures; where (a) represents pure ZnIn2S4, 1% Cu-ZnIn2S4, 3% Cu-ZnIn2S4, and 5% Cu-ZnIn2S4; and (b) represents pure ZnIn2S4, 1% Cu-ZnIn2S4, and 5% Cu-ZnIn2S4.

[0047] Figure 12 The diagram shows the repeatability of different samples for 100 ppm triethylamine over several cycles at 250 °C; where (a) is pure ZnIn2S4; (b) is 1% Cu-ZnIn2S4; (c) is 3% Cu-ZnIn2S4; and (d) is 5% Cu-ZnIn2S4.

[0048] Figure 13 The results show the dynamic sensing characteristics of different samples at 250℃ for different concentrations (20 to 2000 ppm) of triethylamine; where (a) is pure ZnIn2S4; (b) is 1% Cu-ZnIn2S4; (c) is 3% Cu-ZnIn2S4; and (d) is 5% Cu-ZnIn2S4.

[0049] Figure 14The results show the dynamic sensing characteristics of different samples at 250℃ for different concentrations (1 to 20 ppm) of triethylamine; where (a) is pure ZnIn2S4; (b) is 1% Cu-ZnIn2S4; (c) is 3% Cu-ZnIn2S4; and (d) is 5% Cu-ZnIn2S4.

[0050] Figure 15 The results include: (a) the detection limit of the gas-sensitive reaction of 5% Cu-ZnIn2S4 with triethylamine; and (b) the response-recovery time curve of 5% Cu-ZnIn2S4 with triethylamine.

[0051] Figure 16 The figure shows the response of 5% Cu-ZnIn2S4 to different types of volatile organic compound gases (100 ppm). Detailed Implementation

[0052] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0053] According to a first aspect of the present invention, a transition metal-doped ZnIn2S4 gas sensor is provided, comprising a substrate and a transition metal-doped ZnIn2S4 nanoarray grown in situ on the surface of the substrate. The nanoarray is composed of multiple two-dimensional nanosheets arranged in an alternating stacked manner and extending at an angle of ±5° relative to the normal direction of the substrate surface, forming a network assembly with a three-dimensional flower-like topology through physical or chemical bonding; the transition metal is embedded in the lattice structure of the ZnIn2S4 in the form of atomic doping.

[0054] In this invention, the transition metal-doped ZnIn2S4 nanosheet array gas sensor comprises a high-temperature resistant gas-sensitive substrate and a transition metal, such as Cu-doped ZnIn2S4 nanosheet array sensitive layer, in situ attached and grown on its surface. The gas-sensitive substrate is preferably a planar alumina ceramic substrate with gold or platinum interdigitated electrodes. The nanosheet array is an open, three-dimensional flower-like network structure with abundant pores, formed by numerous two-dimensional ultrathin nanosheets, only 5 to 20 nanometers thick, interlaced at angles of 60° or 80°, supported, and grown approximately perpendicularly on the substrate surface. This structure not only ensures stable mechanical adhesion and good electrical contact between the sensitive material and the substrate but also constructs unobstructed gas diffusion channels. In terms of crystal structure, Cu elements successfully enter the ZnIn2S4 lattice in ionic form, replacing some Zn atom sites or occupying lattice interstices. Through Cu doping, the specific surface area of ​​the material is significantly increased; the specific surface area of ​​a 3 wt% doped sample can reach 168.98 m². 2 / g, with a pore volume of 0.49 cm³. 3 / g.

[0055] As a further preferred embodiment, in the transition metal-doped ZnIn2S4 nanosheet array, the doping amount of transition metal, such as Cu, is 1 wt% to 5 wt%, preferably 3 wt%.

[0056] As a further preferred embodiment, the transition metal-doped ZnIn2S4 nanoarray has a specific surface area of ​​140 m² / g to 170 m² / g and a pore volume of 0.30 cm³ / g to 0.50 cm³ / g.

[0057] As a further preferred embodiment, the substrate is an insulating substrate or a conductive substrate, wherein the insulating substrate is selected from Al2O3, SiO2 or quartz, and the conductive substrate is selected from doped silicon, graphene or metal foil.

[0058] The preparation method of the above-mentioned transition metal-doped ZnIn2S4 gas sensor is disclosed in detail in a second aspect of the present invention. This method employs a one-step water bath method, and the process flow is simple.

[0059] As a further preferred embodiment, the specific steps include: First, substrate pretreatment is performed by ultrasonically cleaning the commercial alumina gas-sensitive substrate sequentially in anhydrous ethanol and deionized water to remove surface contaminants; second, a precursor solution is prepared by mixing deionized water and glycerol in a certain proportion, adjusting the pH value to an acidic environment with acid, ultrasonically dispersing the mixture, and then sequentially adding sulfur source, indium source, zinc source, and copper source, stirring to dissolve and obtain a uniform and transparent precursor solution; third, in-situ growth in a water bath is performed by immersing the cleaned gas-sensitive substrate in the precursor solution and reacting at a constant temperature of 60°C to 100°C for a certain time, allowing Cu-doped ZnIn2S4 nanocrystals to heterogeneously nucleate on the substrate surface and grow into a two-dimensional nanosheet array; finally, post-treatment is performed by removing the substrate, washing and drying it to obtain the sensor.

[0060] As a further preferred embodiment, the volume ratio of deionized water to glycerol is 15-25:2-5, preferably 20 mL:3 mL; the pH adjustment using acid specifically involves using nitric acid to adjust the pH of the solution to 2.0-3.0, preferably 2.5. The acidic environment and the addition of glycerol are crucial for regulating the crystal nucleation rate and inducing anisotropic growth of nanosheets.

[0061] As a further preferred embodiment, for the optimal embodiment with a 3% Cu doping amount, the formulation of the reaction precursor solution specifically comprises 20 mL of deionized water, 3 mL of glycerol, zinc chloride, indium chloride, and thioacetamide copper chloride in a molar ratio of 1:1:2, and copper chloride corresponding to a 3% Cu doping amount. The preferred reaction conditions are a water bath reaction at 80°C for 2 hours.

[0062] According to a third aspect of the present invention, the application of the transition metal-doped ZnIn2S4 gas sensor described herein is provided in catalytic oxidation, catalytic degradation of VOCs, photocatalytic water splitting, or detection of volatile organic compounds.

[0063] As a further preferred embodiment, the detection of volatile organic compounds includes a highly sensitive detection method for triethylamine at temperatures ranging from room temperature to 350°C, with a detection response value ≥85 and a detection limit ≤2000ppm.

[0064] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0065] Unless otherwise specified, the raw materials used in the following embodiments are all disclosed in the prior art, such as those that can be directly purchased or prepared according to the preparation methods disclosed in the prior art.

[0066] Example 1

[0067] A Cu-doped ZnIn2S4 nanosheet array gas sensor, wherein the Cu doping amount is 3 wt%, is prepared as follows:

[0068] First, select a commercial flat Al2O3 gas-sensitive substrate, and place it in anhydrous ethanol and deionized water in sequence. Clean it in an ultrasonic cleaner for 15 minutes each time to thoroughly remove surface oil and impurities. After removal, place it in an oven to dry for later use.

[0069] Next, the reaction precursor solution was prepared: 20 mL of deionized water and 3 mL of glycerol were added to a clean 25 mL beaker, and the pH of the mixed solution was adjusted dropwise to 2.5 using 1 mol / L dilute nitric acid (HNO3). The solution was ultrasonically treated in an ultrasonic cleaner for 1 hour to form a homogeneous solvent system. Subsequently, thioacetamide (TAA), indium chloride tetrahydrate (InCl3·4H2O), and zinc chloride (ZnCl2) were added to the above solution in a molar ratio of 2:1:1, along with 3 wt% copper chloride (CuCl2) doping. A magnetic stir bar was placed in the solution, and the mixture was magnetically stirred at room temperature for 30 minutes until all solids were completely dissolved, yielding a clear and homogeneous reaction precursor solution.

[0070] Then, in-situ growth is performed: the cleaned Al2O3 gas-sensitive substrate is fixed vertically or at an angle and completely immersed in the above-mentioned reaction precursor solution. The mouth of the beaker is sealed to prevent solvent evaporation, and then the beaker is placed in a water bath preheated to 80 °C and the reaction is maintained at a constant temperature for 2 hours. During this process, the solution gradually becomes turbid, and Cu-doped ZnIn2S4 nanocrystals undergo heterogeneous nucleation on the surface of the gas-sensitive substrate, gradually growing into two-dimensional nanosheets, and then assembling into a brown thin film array.

[0071] Finally, post-processing was performed: After the reaction was completed, the gas-sensitive substrate was removed from the solution and its surface was slowly rinsed alternately with deionized water and anhydrous ethanol to remove loosely attached precipitates and residual ions. The cleaned substrate was then placed in an oven and dried at 60°C for 8 hours to obtain a 3% Cu-doped ZnIn2S4 nanosheet array gas sensor.

[0072] Example 2

[0073] A Cu-doped ZnIn2S4 nanosheet array gas sensor, wherein the Cu doping amount is 1 wt%, is prepared as follows:

[0074] First, select a commercial flat Al2O3 gas-sensitive substrate, and place it in anhydrous ethanol and deionized water in sequence. Clean it in an ultrasonic cleaner for 15 minutes each time to thoroughly remove surface oil and impurities. After removal, place it in an oven to dry for later use.

[0075] Next, the reaction precursor solution was prepared: 15 mL of deionized water and 2 mL of glycerol were added to a clean 25 mL beaker, and the pH of the mixed solution was adjusted dropwise to 3 using 1 mol / L dilute nitric acid (HNO3). The solution was ultrasonically treated in an ultrasonic cleaner for 0.5 hours to form a homogeneous solvent system. Subsequently, thioacetamide (TAA), indium chloride tetrahydrate (InCl3·4H2O), and zinc chloride (ZnCl2) were added to the above solution in a molar ratio of 2:2:1, along with 1 wt% copper chloride (CuCl2) doping. A magnetic stir bar was placed in the solution, and the mixture was magnetically stirred at room temperature for 30 minutes until all solids were completely dissolved, yielding a clear and homogeneous reaction precursor solution.

[0076] Then, in-situ growth is performed: the cleaned Al2O3 gas-sensitive substrate is fixed vertically or at an angle and completely immersed in the above-mentioned reaction precursor solution. The mouth of the beaker is sealed to prevent solvent evaporation, and then the beaker is placed in a water bath preheated to 80 °C and the reaction is maintained at a constant temperature for 2 hours. During this process, the solution gradually becomes turbid, and Cu-doped ZnIn2S4 nanocrystals undergo heterogeneous nucleation on the surface of the gas-sensitive substrate, gradually growing into two-dimensional nanosheets, and then assembling into a brown thin film array.

[0077] Finally, post-processing was performed: After the reaction was completed, the gas-sensitive substrate was removed from the solution and its surface was slowly rinsed alternately with deionized water and anhydrous ethanol to remove loosely attached precipitates and residual ions. The cleaned substrate was then placed in an oven and dried at 60°C for 8 hours to obtain a 1% Cu-doped ZnIn2S4 nanosheet array gas sensor.

[0078] Example 3

[0079] A Cu-doped ZnIn2S4 nanosheet array gas sensor, wherein the Cu doping amount is 5 wt%, is prepared as follows:

[0080] First, select a commercial flat Al2O3 gas-sensitive substrate, and place it in anhydrous ethanol and deionized water in sequence. Clean it in an ultrasonic cleaner for 15 minutes each time to thoroughly remove surface oil and impurities. After removal, place it in an oven to dry for later use.

[0081] Next, the reaction precursor solution was prepared: 25 mL of deionized water and 5 mL of glycerol were added to a clean 30 mL beaker, and the pH of the mixed solution was adjusted dropwise to 2 using 1 mol / L dilute nitric acid (HNO3). The solution was ultrasonically treated in an ultrasonic cleaner for 1 hour to form a homogeneous solvent system. Subsequently, thioacetamide (TAA), indium chloride tetrahydrate (InCl3·4H2O), and zinc chloride (ZnCl2) were added to the above solution in a molar ratio of 4:3:1, along with 5 wt% copper chloride (CuCl2) doping. A magnetic stir bar was placed in the solution, and the mixture was magnetically stirred at room temperature for 30 minutes until all solids were completely dissolved, yielding a clear and homogeneous reaction precursor solution.

[0082] Then, in-situ growth is performed: the cleaned Al2O3 gas-sensitive substrate is fixed vertically or at an angle and completely immersed in the above-mentioned reaction precursor solution. The mouth of the beaker is sealed to prevent solvent evaporation, and then the beaker is placed in a water bath preheated to 80 °C and the reaction is maintained at a constant temperature for 2 hours. During this process, the solution gradually becomes turbid, and Cu-doped ZnIn2S4 nanocrystals undergo heterogeneous nucleation on the surface of the gas-sensitive substrate, gradually growing into two-dimensional nanosheets, and then assembling into a brown thin film array.

[0083] Finally, post-processing was performed: After the reaction was complete, the gas-sensitive substrate was removed from the solution and its surface was slowly rinsed alternately with deionized water and anhydrous ethanol to remove loosely attached precipitates and residual ions. The cleaned substrate was then placed in an oven and dried at 60°C for 8 hours to obtain a 5% Cu-doped ZnIn2S4 nanosheet array gas sensor.

[0084] Example 4

[0085] Unlike Example 1, the Cu source was replaced with a Cd source.

[0086] A Cd-doped ZnIn2S4 nanosheet array gas sensor, wherein the Cd doping amount is 3wt%, is fabricated as follows:

[0087] First, select a commercial flat Al2O3 gas-sensitive substrate, and place it in anhydrous ethanol and deionized water in sequence. Clean it in an ultrasonic cleaner for 15 minutes each time to thoroughly remove surface oil and impurities. After removal, place it in an oven to dry for later use.

[0088] Next, the reaction precursor solution was prepared: 15 mL of deionized water and 2 mL of glycerol were added to a clean 25 mL beaker, and the pH of the mixed solution was adjusted dropwise to 2 using 1 mol / L dilute nitric acid (HNO3). The solution was ultrasonically treated in an ultrasonic cleaner for 1 hour to form a homogeneous solvent system. Subsequently, thioacetamide (TAA), indium chloride tetrahydrate (InCl3·4H2O), and zinc chloride (ZnCl2) were added to the above solution in a molar ratio of 2:2:1, along with cadmium chloride (CdCl2) at a corresponding 5 wt% doping amount. A magnetic stir bar was placed in the solution, and the mixture was magnetically stirred at room temperature for 30 minutes until all solids were completely dissolved, yielding a clear and homogeneous reaction precursor solution.

[0089] Then, in-situ growth is performed: the cleaned Al2O3 gas-sensitive substrate is fixed vertically or tilted and completely immersed in the above-mentioned reaction precursor solution. The mouth of the beaker is sealed to prevent solvent evaporation, and then the beaker is placed in a water bath preheated to 80 °C and the reaction is maintained at a constant temperature for 2 hours. During this process, the solution gradually becomes turbid, and Cd-doped ZnIn2S4 nanocrystals undergo heterogeneous nucleation on the surface of the gas-sensitive substrate, gradually growing into two-dimensional nanosheets, and then assembling into a brown thin film array.

[0090] Comparative Example 1

[0091] A pure ZnIn2S4 nanosheet array gas sensor is fabricated as follows:

[0092] First, select a commercial flat Al2O3 gas-sensitive substrate, and place it in anhydrous ethanol and deionized water in sequence. Clean it in an ultrasonic cleaner for 15 minutes each time to thoroughly remove surface oil and impurities. After removal, place it in an oven to dry for later use.

[0093] Next, the reaction precursor solution was prepared: 16 mL of deionized water and 4 mL of glycerol were added to a clean 25 mL beaker, and the pH of the mixed solution was adjusted dropwise to 3 using 1 mol / L dilute nitric acid (HNO3). The solution was ultrasonically treated in an ultrasonic cleaner for 0.5 hours to form a homogeneous solvent system. Subsequently, thioacetamide (TAA), indium chloride tetrahydrate (InCl3·4H2O), and zinc chloride (ZnCl2) were added to the above solution in a molar ratio of 5:3:1, without adding copper chloride. A magnetic stir bar was placed in the solution and the mixture was magnetically stirred at room temperature for 30 minutes until all solids were completely dissolved, resulting in a clear and homogeneous reaction precursor solution.

[0094] Then, in-situ growth is performed: the cleaned Al2O3 gas-sensitive substrate is fixed vertically or at an angle and completely immersed in the above-mentioned reaction precursor solution. The mouth of the beaker is sealed to prevent solvent evaporation, and then the beaker is placed in a water bath preheated to 80 °C and the reaction is maintained at a constant temperature for 2 hours. During this process, the solution gradually becomes turbid, and ZnIn2S4 nanocrystals undergo heterogeneous nucleation on the surface of the gas-sensitive substrate, gradually growing into two-dimensional nanosheets, which then assemble into a yellow thin film array.

[0095] Finally, post-processing was performed: After the reaction was complete, the gas-sensitive substrate was removed from the solution and its surface was slowly rinsed alternately with deionized water and anhydrous ethanol to remove loosely attached precipitates and residual ions. The cleaned substrate was then placed in an oven and dried at 60°C for 8 hours to obtain a pure ZnIn2S4 nanosheet array gas sensor.

[0096] The sensors prepared in Examples 1 to 3 and Comparative Example 1 were characterized and their performance was tested. The specific results are as follows:

[0097] like Figure 1 As shown, the crystal structure of the obtained sample was analyzed using X-ray diffraction (XRD) technology. Figure 1 As shown in (a), both pure ZnIn2S4 (comparative example) and samples doped with different proportions of Cu (Examples 1 to 3) exhibit clear and sharp diffraction peaks within a scanning range of 20 to 60 degrees. The positions of all diffraction peaks closely match the standard card of hexagonal ZnIn2S4, and no diffraction peaks of oxides, copper sulfide, or other impurity phases were detected. This indicates that the in-situ water bath growth method of the present invention successfully prepared a high-purity, well-crystallized ZnIn2S4 structure. Notably, through fine scanning and magnified comparison of the diffraction peaks of characteristic crystal planes such as (006), it was found that with the increase of Cu doping, the positions of the characteristic diffraction peaks shifted slightly but regularly to higher angles, such as... Figure 1 As shown in (b), according to Bragg's equation, the shift in peak position corresponds to the contraction of the interplanar spacing. Since the ionic radius of Cu ions (approximately 0.73 Å) is slightly smaller than that of Zn ions (approximately 0.74 Å), when Cu ions successfully enter the ZnIn2S4 lattice and replace some Zn sites, it inevitably causes a contraction of the cell parameters, resulting in lattice distortion. This regular lattice distortion effect strongly proves that Cu elements are successfully doped into the lattice to form a solid solution, rather than simply adhering to the surface in the form of oxide or sulfide particles.

[0098] like Figure 2 As shown, the microstructure of the samples was characterized in detail using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). SEM and TEM allow for the observation of the morphology and microstructure of the prepared samples. Figure 2Middle (a) to Figure 2 Image (c) shows the morphology in a comparative proportion. Figure 2 Middle (d) to Figure 2 Image (f) shows the morphology of the sample from Example 1, which exhibits an extremely uniform and continuous growth state across the entire alumina substrate, completely covering the interdigitated electrode region. High-magnification SEM images clearly show that the material is composed of numerous ultrathin two-dimensional nanosheets interlaced and supported, assembling into an open three-dimensional porous flower-like array structure. Morphologically, Cu doping did not alter the original morphology of the comparative example, and this unique sheet-array hierarchical structure has dual advantages: firstly, the ultrathin nanosheets greatly increase the geometric specific surface area of ​​the material, exposing more surface atoms; secondly, the interlaced layers construct a rich network of macropores and mesopores, which connect directly to the substrate, providing channels for the rapid diffusion and transport of gas molecules. Figure 2 (g) to Figure 2 Image (j) shows TEM and HRTEM characterization. The bright-field TEM image reveals that the nanosheets exhibit a translucent, veil-like appearance with clear edges and no obvious curling, directly confirming their extremely thin thickness, allowing the electron beam to easily penetrate. Further magnified HRTEM images clearly show neatly arranged, high-contrast lattice fringes, indicating extremely high crystallinity and the absence of obvious amorphous regions. The image clearly shows two sets of lattice fringes with different orientations and high contrast, indicating good crystallinity of the synthesized nanosheets. Precise measurements show that the interplanar spacing of the first set of lattice fringes is approximately 0.324 nm, corresponding to the (102) crystal plane of the hexagonal ZnIn2S4 system; the adjacent second set of lattice fringes has an interplanar spacing of approximately 0.308 nm, corresponding to the (013) crystal plane of ZnIn2S4. This coexistence of multiple crystal planes confirms that the nanosheets are a polycrystalline structure assembled from multiple oriented microcrystalline domains, rich in active grain boundaries. Crucially, comparison with standard PDF data revealed a slight shift in the measured interplanar spacing compared to the standard value. This microscopic change in lattice parameters, after ruling out measurement errors, is directly attributed to the lattice distortion effect caused by Cu ion doping. As Cu ions successfully enter the lattice, replacing some Zn sites or occupying interstitial sites, the cell parameters change, manifesting as a fine adjustment in interplanar spacing in HRTEM. Notably, while clear ZnIn2S4 bulk lattice fringes were observed in the HRTEM images, no lattice fringes belonging to second phases such as copper oxide or copper sulfide were found at grain boundaries or on the surface, nor were any obvious phase interfaces observed. This microscopic evidence strongly supports the XRD results, indicating that Cu did not precipitate as an impurity phase but successfully entered the ZnIn2S4 lattice, forming a uniform solid solution structure. Figure 2 middle (k) to Figure 2 The image (o) shows the elemental mapping of the EDS spectrum. The four elements Zn, In, S, and Cu are distributed very uniformly within the scanning area, without localized enrichment or segregation. In contrast, while the pure ZnIn₂S₄ in the comparative example also exhibits a sheet-like structure, its nanosheets are thicker and more tightly stacked. The sample in Example 2, due to its lower doping concentration, showed little effect on morphological control and had slightly lower porosity; while the sample in Example 3, due to its rapid growth, exhibited significant agglomeration, resulting in insufficient exposure of active sites.

[0099] like Figure 3 The image shows the morphology and elemental distribution of the sample from Example 2. Figure 3 Middle (a) to Figure 3 As can be seen from the SEM image in (c), due to the low doping amount, its microstructure is similar to that of pure ZnIn2S4. The nanosheets are relatively tightly packed, and although the porosity is improved compared to the pure sample, it is not as rich as that of the 3% doped sample. Figure 3 Middle (d) to Figure 3 The EDS mapping in (h) clearly detected the presence of Cu signal. Although the signal intensity was weaker than that of the 3% sample (corresponding to a lower doping concentration), the distribution of Cu elements still maintained a high degree of uniformity, and no local agglomeration points appeared. This proves that even at low concentrations, the one-step water bath method can achieve uniform ion doping.

[0100] like Figure 4 The image shows the morphology and elemental distribution of the sample from Example 3. Figure 4 Middle (a) to Figure 4 In the SEM image in (c), obvious morphological degradation can be observed. The excessive introduction of Cu ions may have acted as too many nucleation centers or changed the crystal growth kinetics, resulting in an excessively fast crystal growth rate. In some areas, obvious nanosheet agglomeration and disordered stacking appeared. This dense agglomeration structure closed some mesoporous channels, which is not conducive to gas adsorption and desorption. Figure 4 Middle (d) to Figure 4 The EDS mapping in (h) shows a significant increase in Cu signal intensity, while maintaining a uniform distribution. This indicates that high-concentration doping did not lead to macroscopic segregation of Cu; the performance degradation is mainly attributed to the reduction in effective specific surface area caused by microscopic agglomeration. (Comprehensive comparison) Figure 2 to Figure 3 It is known that a Cu doping amount of 3% is the optimal balance point for controlling the microstructure, which is most conducive to forming a smooth, uniform and ultrathin three-dimensional nanosheet array structure.

[0101] like Figure 5 As shown, the morphology and elemental distribution of Example 4 are illustrated. It can be observed that there are no significant changes compared to Examples 1 to 3.

[0102] To further investigate the evolution of the surface chemical state, elemental valence state, and local electronic environment of ZnIn2S4 materials under different Cu doping concentrations, this invention performed high-resolution X-ray photoelectron spectroscopy (XPS) analysis on the samples prepared in Example 1 and Comparative Examples 1-3. Figure 6 As shown, the high-resolution energy spectrum of Zn 2p was first analyzed ( Figure 6 (a)). For the undoped pure ZnIn2S4 sample (Comparative Example 1), its Zn 2p 3 / 2 and Zn 2p 1 / 2 The characteristic peak positions correspond to typical Zn 2+ Oxidation state. When 1% Cu doping was introduced (Example 2), the positions of these two characteristic peaks shifted slightly towards the high binding energy direction. As the doping amount increased to 3% (Example 1), this positive shift became more significant, reaching approximately 0.4 eV. When the doping amount was further increased to 5% (Example 3), the peak positions remained at the high binding energy position. This trend of increasing binding energy with increasing doping amount has a clear physical meaning: since the electronegativity of the dopant element Cu (1.90) is significantly higher than that of the matrix element Zn (1.65), when Cu ions enter the lattice and replace Zn sites, the attraction of Cu atoms to the surrounding electron cloud is stronger, resulting in a decrease in the electron density around the adjacent Zn atoms, a weakening of the shielding effect, and thus an increase in the inner-shell electron binding energy of Zn atoms. This regular shift confirms that Cu was successfully incorporated and caused a change in the lattice electronic environment. Next, the high-resolution energy spectrum of In 3d was analyzed ( Figure 6 (b)). In 3d of pure ZnIn2S4 sample. 5 / 2 and In 3d 3 / 2 The peak positions indicate that In exists in the +3 valence form. In Comparative Example 2, the In 3d peak position remained almost unchanged. However, in Example 1 and Comparative Example 3, the In 3d peak position showed a significant synchronous shift towards higher energies. Although Cu mainly substitutes for Zn sites, since ZnIn2S4 has a layered structure, the local electronic perturbations of Zn sites will inevitably be transferred to In atoms through S-bridge bonds, leading to a linked change in the chemical environment of In. Further analysis of the high-resolution energy dispersive spectroscopy of S 2p was then conducted. Figure 6 (c) This is key to revealing the defect formation mechanism. The S 2p spectrum of pure ZnIn2S4 exhibits standard S 2p... 3 / 2 and S 2p 1 / 2The sample exhibits a double peak, with symmetrical and sharp peak shapes. For the 3% Cu-doped sample in Example 1, the S 2p peak not only shifts significantly towards higher binding energy, indicating a decrease in S electron cloud density, but more importantly, its full width at half maximum (FWHM) is significantly broadened. Peak fitting analysis reveals that this broadening originates from the contribution of low-coordinate sulfur species on the surface (i.e., sulfur near sulfur vacancies). This is due to the substitution of Zn by Cu ions (+1 or +2 valence). 2+ This disrupts the original charge balance, and the lattice spontaneously generates sulfur vacancies (Vs) to maintain electroneutrality. In the 5% Cu-doped sample of Comparative Example 3, the S 2p peak width further increases, indicating that the sulfur vacancy concentration increases with increasing doping concentration. However, excessively high vacancy concentrations may lead to defect aggregation, forming non-radiative recombination centers, which is detrimental to carrier transport. Finally, the high-resolution energy dispersive spectroscopy of Cu 2p was analyzed (…). Figure 6 (d) No Cu signal was detected in the pure ZnIn2S4 spectrum, serving as a baseline control. In Comparative Example 2, an extremely weak signal peak appeared. As the doping concentration increased to 3% (Example 1), the characteristic peak intensity of Cu 2p significantly increased, the signal-to-noise ratio improved substantially, and the peak position stabilized, without any corresponding Cu 2p peak appearing. 2+ The satellite peaks indicate that Cu mainly enters the lattice in the +1 valence state, forming stable Cu-S bonds. In Comparative Example 3, the Cu 2p peak reaches its maximum intensity, further confirming the positive correlation between doping concentration and feed amount. Combined XPS analysis of the four elements shows that a 3% Cu doping concentration, while achieving effective electronic structure control, induces an appropriate amount of sulfur vacancy defects, providing the optimal chemical basis for excellent gas-sensing performance.

[0103] To quantitatively analyze the pore structure characteristics of the material, nitrogen adsorption-desorption tests were performed on different samples. For example... Figure 7 As shown, the nitrogen adsorption-desorption isotherms and pore size distribution of each sample are displayed. All samples exhibit type IV isotherm characteristics, accompanied by H3 type hysteresis loops, indicating the presence of abundant interlamellar slit-like mesopores within the material. Figure 8As shown in the table, the specific surface area, pore volume, and average pore size parameters of each sample are detailed. The data shows that the specific surface area of ​​the comparative example is 127.40 m² / g, and the pore volume is 0.42 cm³ / g. In contrast, the specific surface area of ​​Example 1 is significantly increased to 168.98 m² / g, and the pore volume increases to 0.49 cm³ / g. This result indicates that 3% Cu doping most effectively induces the refinement and thinning of the nanosheets, constructing a microstructure with the largest specific surface area. The large specific surface area means that a unit mass of material can provide more gas adsorption active sites, which is the key geometric factor for the optimal gas-sensing performance of this sample. The specific surface areas of Examples 2 and 3 are 140.23 m² / g and 117.53 m² / g, respectively, which are lower than the optimal example. This is consistent with the morphological patterns observed by SEM, indicating that excessively high or low doping levels cannot achieve optimal structural characteristics.

[0104] To reveal the physical mechanism by which Cu doping enhances gas-sensing performance at the band structure level, this invention combines ultraviolet-visible absorption spectroscopy (UV-Vis) and ultraviolet photoelectron spectroscopy (UPS) for in-depth analysis. Figure 9 The figures show test data for the UPS of Examples 1 to 3 and the comparative example, from which the distance from the Fermi level to the vacuum level in Examples 1 to 3 and the comparative example can be obtained. The work function of the comparative example is 4.52 eV. Figure 9 In Example 2 (a), the work function is 4.18 eV. Figure 9 In Example (b), the work function of Example 1 is 4.08 eV ( Figure 9 In Example 3 (c), the work function is 3.82 eV. Figure 9 (d)). For example Figure 10 As shown, the results of ultraviolet-visible absorption spectroscopy (UV-Vis) are presented, with a comparative band gap of 2.50 eV ( Figure 10 In Example 2 (a), the band gap is 2.39 eV. Figure 10 In Example 1 (b), the band gap is 2.21 eV. Figure 10 In Example 3 (c), the band gap is 2.18 eV. Figure 10 (d) A comprehensive analysis combining UV-Vis and UPS data reveals that the introduction of Cu ions introduces new impurity energy levels into the band gap of ZnIn2S4. These levels undergo orbital hybridization with the valence band apex, leading to an upward shift in the valence band position and thus effectively reducing the band gap. This optimization of the band structure not only improves the material's conductivity but may also modulate the charge transfer barrier of surface adsorbed species, promoting rapid electron transfer at the gas-solid interface and laying a solid electronic foundation for highly sensitive gas-sensitive responses.

[0105] Based on this, the inventors used the prepared nanoarray to detect triethylamine gas. Nine test points were selected within a temperature range of 25°C to 400°C, and the tests were repeated several times at each temperature. The response values ​​of four samples to triethylamine at different temperatures are as follows: Figure 11 As shown. In an environment with a triethylamine concentration of 100 ppm, the response values ​​of the four samples gradually increased as the operating temperature increased within the range of 150°C to 200°C. When the operating temperature was within the range of 25°C to 250°C, the response values ​​of the comparative examples, Examples 1 to 3, gradually increased. The response values ​​first increased and then decreased, exhibiting an overall mountain-like shape, reaching their maximum value at an operating temperature of 250°C. Specifically, the average response value of the comparative example to 100 ppm triethylamine was 2.24. The average response value of Example 2 to 100 ppm triethylamine increased to 9.73. The average response value of Example 3 was 3.65, which was 1.63 times that of the comparative example. The highest response value of Example 1 was 95.24, which was 43.86 times that of the comparative example, 9.79 times that of Example 2, and 26.09 times that of Example 3. Therefore, by doping with Cu, the gas-sensing performance of triethylamine was significantly improved, and 250°C was selected as the optimal operating temperature in the subsequent gas-sensing tests.

[0106] like Figure 12 As shown, the dynamic response of different samples to triethylamine was recorded in continuous and repeated tests under a triethylamine atmosphere of 100 ppm. Each sample was tested repeatedly for 12 cycles under the same conditions. In any cycle, it was observed that the introduction of triethylamine gas immediately caused a change in the material's resistivity, which then tended to stabilize at a certain value. With the release of triethylamine and the introduction of air, the resistance value eventually returned to its original value. After repeated testing over multiple cycles, the data showed high stability. The construction of the heterostructure has a significant impact on the response to triethylamine gas. Compared with the comparative example ( Figure 12 (a) , Example 2 ( Figure 12 Example 3 (b) Figure 12 Compared to the response value of Example 1 (d), Example 1 (d) Figure 12 The average response value of (c) increased significantly. Changing the doping amount of Cu is an important means to improve the gas-sensing performance. The average response value was further improved when the doping amount reached 3%.

[0107] Dynamic sensing characteristics of different samples for different concentrations of triethylamine, such as Figure 13As shown. Within a certain concentration range, the response value is directly proportional to the triethylamine concentration. That is, as the triethylamine concentration increases, the response value of each sample also increases. However, when the triethylamine concentration reaches a certain value, the response value will stabilize within a certain range and reach saturation. Importantly, Cu-doped ZnIn2S4 exhibits significant advantages compared to various previously reported ZnIn2S4-related trimethylamine sensors, especially in terms of response value and operating temperature. When the triethylamine concentration is below 20 ppm, the changes in resistance values ​​detected in Examples 1 to 3 and the comparative example are shown below. Figure 14 As shown.

[0108] like Figure 15 As shown in Figure (a), Example 1 demonstrates the linear fit of triethylamine gas at 300°C for different concentrations (from 10 ppm to 500 ppm). According to the formula LOD = κσ / S (where κ is typically set to 3, σ represents the standard deviation of the measurement, and S represents the slope), the limit of detection (LOD) is approximately 900 ppb. Considering that the permissible safe emission limit for triethylamine in practical applications is 10 ppm, the obtained LOD fully meets the requirements of actual monitoring. Figure 15 As shown in (b), the response / recovery curves are data from one period extracted from the stability test data of Example 1. Response time is defined as the time required for the sensor to reach 90% of its maximum resistance after exposure to gas, while recovery time is the time required for the sensor to recover to 90% of its initial resistance after exposure to air. The test results show that the response time and recovery time are 33 seconds and 326 seconds, respectively.

[0109] Furthermore, selectivity is another key parameter for evaluating gas sensors. Under the same test conditions, the response of Example 1 was tested by introducing 100 ppm of different common ambient gases (including methanol, ethanol, formaldehyde, acetaldehyde, benzene, toluene, acetic acid, formic acid, acetone, and ethyl acetate). Figure 16 As shown, Example 1 exhibits significant selectivity for triethylamine.

[0110] The embodiments of the present invention have been described above with reference to the accompanying drawings. Specific examples have been used to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only for the purpose of helping to understand the core idea of ​​the present invention. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims, and all of these forms are within the protection scope of the present invention.

Claims

1. A transition metal-doped ZnIn2S4 gas sensor, comprising an Al2O3 substrate and a Cu-doped ZnIn2S4 nanoarray grown in situ on the surface of the substrate via a one-step water bath method, characterized in that: The Cu-doped ZnIn2S4 nanoarray forms an atomically close interface with the Al2O3 substrate, eliminating microcracks and interfacial contact resistance present in the coating film. The nanoarray is composed of multiple two-dimensional nanosheets arranged in an alternating stack and extending at an angle of ±5° relative to the normal direction of the substrate surface. The stagger angle between adjacent sheets is 60° or 80°, and they are connected by physical or chemical means to form a network assembly with a three-dimensional flower-like topology. The thickness of the two-dimensional nanosheets is 5 nm to 20 nm, and the lateral dimension is 0.5 μm to 2 μm. The Cu doping amount is 3 wt%, and it is embedded in the ZnIn2S4 lattice structure in the form of atomic doping. The Cu-doped ZnIn2S4 nanoarray has a specific surface area of ​​168.98 m² / g and a pore volume of 0.49 cm³ / g. The gas sensor, operating at 250°C, has a response value ≥85 for triethylamine gas at a concentration of 100 ppm, a response time ≤35 seconds, and a detection limit ≤1 ppm.

2. A method for preparing the transition metal-doped ZnIn2S4 gas sensor of claim 1, characterized in that, A 3 wt% Cu-doped ZnIn2S4 nanoarray was grown in situ on a substrate surface using a one-step hydrothermal method. The method includes: S1. Mix deionized water and glycerol at a volume ratio of 20:3 until homogeneous, and add 1 mol / L nitric acid to adjust the pH of the system to 2.

5. Then, treat the mixture with ultrasonic dispersion for 1 hour. S2. Zinc chloride, indium chloride, and thioacetamide are added sequentially, along with a copper source of 3 wt% doping amount. The mixture is stirred until completely dissolved and a homogeneous system is formed. The molar ratio of zinc chloride, indium chloride, and thioacetamide is 1:2:2; the concentration of zinc chloride is 6.65 mmol / L ~ 11.74 mmol / L; the concentration of indium chloride is 6.7 mmol / L ~ 11.8 mmol / L; and the concentration of thioacetamide is 13.3 mmol / L ~ 23.5 mmol / L. S3. The solutions obtained in steps S1 and S2 are mixed and placed in a sealed reaction vessel. An Al2O3 substrate with a cleaned surface is added, and the reaction is carried out at 80°C for 2 hours by water bath heating. After the reaction is completed, the substrate is naturally cooled, removed, and washed with deionized water and anhydrous ethanol in sequence. It is then dried at 60°C to 80°C for 4 to 12 hours to obtain the transition metal doped ZnIn2S4 gas sensor.

3. The method according to claim 2, characterized in that, The copper source is selected from copper chloride or copper nitrate.

4. The application of the transition metal-doped ZnIn2S4 gas sensor of claim 1 in the detection of triethylamine gas.

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