A MOF-derived SnO2@MOx composite semiconductor gas-sensitive material, its preparation method and application

Abstract

The application provides a MOF derived SnO2@MOx composite semiconductor gas sensitive material, a preparation method and application, and belongs to the technical field of novel functional materials and gas sensors. The method comprises the following steps: preparing a Sn-MOF precursor and a compounded impregnation solution; and preparing the SnO2@MOx composite semiconductor gas sensitive material by using the Sn-MOF precursor and the compounded impregnation solution. The application also provides a SnO2@MOx composite semiconductor gas sensitive material prepared by the above method, which is composed of a SnO2 core and an outer MOx shell layer, and application of the SnO2@MOx composite semiconductor gas sensitive material in H2S gas sensing. The SnO2@MOx composite semiconductor gas sensitive material prepared by the application shows tens of thousands of gas sensitive responses and an extremely low detection limit to H2S gas, greatly widens the gas detection range, simultaneously shows excellent selectivity and stability, has practical values in industrial fields and medical fields, and lays a good foundation for accurate monitoring of gas sensors.

Description

Technical Field

[0001] This invention belongs to the field of novel functional materials and gas sensor technology, and particularly relates to a MOF-derived SnO2@MOx composite semiconductor gas-sensitive material, its preparation method and application. Background Technology

[0002] Hydrogen sulfide (H2S) is a highly toxic acidic gas widely present in work environments such as oil and gas extraction, wastewater treatment, landfill, and livestock farming. my country's "Occupational Exposure Limits for Hazardous Factors in the Workplace" (GBZ2.1-2019) stipulates that the permissible concentration limit for H2S is 10 mg / m³ (approximately 7 ppm). When the concentration of H2S in the air reaches 1 ppm, it can irritate the eyes and respiratory tract. Exposure to high concentrations can lead to olfactory paralysis or even death within minutes. Furthermore, H2S is corrosive to metal equipment, easily causing secondary accidents. Therefore, continuous and reliable on-site monitoring of H2S is crucial for ensuring human health and production safety.

[0003] Among various H2S detection technologies, metal oxide semiconductor sensors have become the preferred solution for portable on-site monitoring due to their advantages such as small size, low cost, ease of integration, and fast response. Commonly used gas-sensitive materials include ZnO, In2O3, SnO2, and WO3. However, existing metal oxide-based gas-sensitive materials for H2S detection still have the following key problems: First, poor selectivity, as the materials respond to a variety of reducing gases, making it difficult to accurately identify H2S in complex atmospheres; second, insufficient stability, as the strong reducing properties of H2S cause the sulfide compounds generated in the reaction to deposit on the material surface, resulting in poisoning of active sites and making it difficult for the material to return to its initial state; third, insufficient sensitivity and detection limit, with most sensors having a detection limit higher than 1 ppm, which is insufficient to meet the needs of ultra-low concentration applications such as early leak warning and breathalyzer detection.

[0004] To address the aforementioned issues, researchers have attempted improvements through strategies such as heterostructure construction and elemental doping. One scholar prepared hollow CuO-SnO2 nanotubes using electrospinning, leveraging the pn heterojunction effect to enhance the response of pure SnO2 to 10 ppm H2S from unresponsive to 4.7, achieving a detection limit of 2.5 ppm. This study confirms the effectiveness of heterostructures in improving the H2S sensitivity of SnO2-based materials. However, this approach employs a stepwise composite process, with physical contact between CuO and SnO2, resulting in limited interfacial bonding strength and failing to address the long-term stability issues caused by sulfur poisoning. Furthermore, its 2.5 ppm detection limit still falls short of the requirements for ppb-level trace detection.

[0005] Therefore, how to improve H2S sensitivity and selectivity while enhancing the material's resistance to sulfur poisoning and long-term stability through refined interface structure design is a technical challenge that urgently needs to be solved in this field. Summary of the Invention

[0006] The purpose of this invention is to provide a MOF-derived SnO2@MOx composite semiconductor gas-sensitive material, its preparation method, and its application, in order to solve the technical problems of poor selectivity, insufficient stability, and insufficient sensitivity and detection limit of metal oxide-based gas-sensitive materials used for H2S detection in the prior art.

[0007] To solve the above-mentioned technical problems, the specific technical solution of the present invention is as follows:

[0008] A method for preparing MOF-derived SnO2@MOx composite semiconductor gas-sensitive material, the method comprising the following steps:

[0009] Step S1: Prepare Sn-MOF precursor;

[0010] Step S2: Mix MOx-corresponding nitrate, water, glycerol, citric acid and / or urea, F127 and / or P123 evenly to prepare a compound impregnation solution;

[0011] Step S3: Using Sn-MOF precursor and composite impregnation solution, prepare hierarchical porous SnO2@MOx composite semiconductor gas-sensitive material.

[0012] Further, step S1 includes the following steps:

[0013] Step S11: Dissolve 0.576 g NaOH and 1.014 g C9H6O6 (H3BTC) in 84 mL of deionized water to obtain solution A.

[0014] Step S12: Dissolve 7.014 g SnCl4·5H2O in a mixed solution of 60 mL deionized water and 36 mL N,N-dimethylformamide (DMF) to obtain solution B.

[0015] Step S13: After solutions A and B have fully dissolved, mix solutions A and B into a beaker. Place the beaker in a 50 ºC water bath and react for 12 h. After the reaction is complete, collect the product.

[0016] Step S14: Wash the product three times with deionized water and ethanol alternately, and dry it overnight in an oven at 80 °C to obtain Sn-MOF precursor powder.

[0017] Further, step S3 includes the following steps:

[0018] Step S31: Mix the Sn-MOF precursor with the compound impregnation solution and impregnate it quantitatively through the pore volume to form a uniform suspension;

[0019] Step S32: Dry the suspension to obtain Sn-MOF gel modified with the compound solution;

[0020] Step S33: The Sn-MOF gel modified with the compound solution is transferred to a tube furnace and subjected to segmented calcination in different atmospheres. This causes the Sn-MOF precursor to undergo self-sacrificial pyrolysis and simultaneously triggers the local reduction reaction of the nitrates of the corresponding MOx metals, generating a MOx shell in situ on the SnO2 surface and forming a semi-coherent epitaxial heterostructure. After the calcination is completed, the material is naturally cooled to room temperature to obtain a hierarchical porous SnO2@MOx composite semiconductor gas-sensitive material.

[0021] Furthermore, the M in MOx corresponding to nitrate is one or more of Cu, Fe, Ni, Mn, and Co.

[0022] Furthermore, the molar ratio of Sn-MOF precursor to MOx corresponding nitrate is 100:1-1:1;

[0023] The molar ratio of MOx to nitrate:citric acid and / or urea:F127 and / or P123 is 1:0.5-3:0.005-0.03.

[0024] Furthermore, the first stage of calcination is carried out at a temperature of 150-300℃, with an atmosphere of either Ar / N2 or low oxygen, and a calcination time of 2-6 h; the second stage of calcination is carried out at a temperature of 300-800℃, with an atmosphere of either low oxygen or air, and a calcination time of 2-4 h.

[0025] This invention also proposes a MOF-derived SnO2@MOx composite semiconductor gas-sensitive material prepared by the above method. The SnO2@MOx composite semiconductor gas-sensitive material consists of a SnO2 core and an outer MOx shell. The MOx is generated in situ on the SnO2 surface through a simultaneous self-sacrificial pyrolysis-local reduction reaction of the Sn-MOF precursor complex, and forms a semi-coherent epitaxial heterointerface with SnO2.

[0026] Furthermore, M can be one or more of Cu, Fe, Ni, Mn, and Co.

[0027] Furthermore, the Sn-MOF precursor and the MOx-corresponding nitrate complex solution are constructed in situ through a self-sacrificial pyrolysis-local reduction synchronous process, which causes the near-surface layer of SnO2 close to the interface to undergo M element doping / enrichment, and synergistically forms the epitaxial heterostructure interface and defect gradient coupling body with the outer MOx shell, so that the SnO2 and MOx components are uniformly and tightly combined.

[0028] This invention also proposes an application of SnO2@MOx composite semiconductor gas-sensitive material in H2S gas sensing.

[0029] Compared with the prior art, the present invention has the following beneficial technical effects:

[0030] This invention utilizes a simultaneous reaction mechanism of self-sacrificing pyrolysis and local reduction of MOF precursors to generate a MOx shell in situ on the SnO2 surface, forming a semi-coherent epitaxial heterostructure with strong interfacial coupling. This feature not only relates to the interfacial structure type (semi-coherent epitaxy) but also to the formation mechanism (simultaneous pyrolysis-reduction) and the regulation of strong interfacial interactions, significantly distinguishing it from heterostructures obtained through conventional physical composites or simple calcination.

[0031] 1. Ultra-high sensitivity and low detection limit: Excellent sensing performance: To address the problems of low sensitivity, high detection limit, and poor stability of traditional metal oxide sensors, which make them unsuitable for practical applications, this invention prepares SnO2@MOx composite materials through a simultaneous self-sacrificing pyrolysis-local reduction reaction of MOF precursors. The composite material forms a semi-coherent epitaxial heterostructure coupled with a defect gradient, resulting in more oxygen vacancies on its surface, which is conducive to the formation of surface reactive oxygen species and enhances the adsorption capacity of the target gas H2S. The SnO2 and MOx components are tightly bound together and interact significantly, enhancing electron transport capabilities and exhibiting excellent H2S sensing response and an extremely low detection limit (ppt).

[0032] 2. High dynamic response and stability: The SnO2 in the gas-sensitive material is MOF-derived SnO2, which has a larger specific surface area and abundant gas diffusion channels compared with other synthesis methods. After material composite, the particle size is further reduced and the gas channels are enlarged, which is beneficial to the adsorption / desorption process of H2S gas.

[0033] 3. Strong stability: Through the synergistic effect between components, the composite material significantly increases the formation of surface reactive oxygen species. By regulating the reaction pathway, in experiments involving dynamic detection of H2S gas, the material guides the conversion of H2S to SO2, rather than to toxic sulfates, thus enhancing its stability.

[0034] 4. Simple preparation method and low cost: The raw materials used in this gas-sensitive material are readily available, inexpensive, highly operable, and suitable for industrial production.

[0035] The SnO2@MOx composite material developed in this invention significantly improves the H2S gas sensing performance through component synergy and structural optimization. It exhibits ultra-high sensitivity, a detection limit as low as ppt, high dynamic response, and excellent stability, thanks to abundant oxygen vacancies, efficient electron transport, and controllable reaction pathways. The material preparation method is simple and low-cost, possessing promising prospects for industrial application and providing a precise sensing foundation for the Internet of Things, smart healthcare, and environmental monitoring. The resulting SnO2@MOx composite semiconductor gas-sensitive material exhibits a gas-sensing response of tens of thousands of ppt and an extremely low detection limit (ppt level) for H2S gas, greatly expanding the gas detection range; it also demonstrates excellent selectivity and stability, possessing practical value in both industrial and medical fields, laying a solid foundation for precise gas sensor monitoring.

[0036] As further supporting evidence of the inventiveness of this invention, the following important aspects are also reflected:

[0037] (1) The expected benefits and commercial value of the technical solution of this invention after transformation are as follows:

[0038] Because of its low cost, simple processing, and ability to be mass-produced, this gas-sensitive material can be integrated with MEMS technology to manufacture high-performance integrated sensing microsystems, providing a key technological foundation for the development of portable, fast, and miniaturized gas sensing devices.

[0039] (2) The technical solution of this invention fills a technical gap in the industry both domestically and internationally:

[0040] As of the date of this invention, no metal oxide gas sensing materials with extremely low experimental detection limits (ppt) for detecting H2S gas under dynamic gas mixing conditions have been reported. The technical solution proposed in this invention enables the preparation of ultrasensitive sensing materials with extremely high sensitivity (100 ppm, Ra / Rg≈27000) and excellent selectivity, as well as high dynamic response and stability, making it suitable for practical detection.

[0041] (3) The technical solution of the present invention solves a technical problem that people have long wanted to solve but have never been able to solve successfully:

[0042] Metal oxide semiconductor gas-sensitive materials have long been limited by problems such as low sensitivity, poor selectivity, and low reusability. This invention achieves ultra-high response values ​​and a detection limit at the ppt level, greatly expanding the gas detection range and accuracy. Furthermore, this invention also features high selectivity and superior stability. Attached Figure Description

[0043] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0044] Figure 1 This is a flowchart of the preparation method of MOF-derived SnO2@Mox composite semiconductor gas-sensitive material provided in the embodiments of the present invention;

[0045] Figure 2 This is the XRD pattern of the SnO2@CuO composite gas-sensitive material synthesized in Example 1 of the present invention (XRD is an abbreviation for X-ray diffraction). The preceding number represents the molar percentage of Cu in Sn. For example, 5SnO2@CuO means Cu:Sn = 5%:1.

[0046] Figure 3 This is a microscopic morphology image (TEM image, TEM is an abbreviation for Transmission Electron Microscope) of the SnO2@CuO composite gas-sensitive material synthesized in Example 1 of this invention.

[0047] Figure 4 This is a microscopic morphology image (SEM image, SEM is an abbreviation for Scanning Electron Microscope) of the SnO2@CuO composite gas-sensitive material synthesized in Example 1 of this invention.

[0048] Figure 5 This is an XPS image of the SnO2@CuO composite gas-sensitive material synthesized in Example 1 of this invention;

[0049] Figure 6 This is a single-response curve of the SnO2@CuO composite gas-sensitive material synthesized in Example 1 of this invention for detecting 100 ppm H2S gas.

[0050] Figure 7 This is the response diagram of the SnO2@CuO composite gas-sensitive material synthesized in Example 1 of the present invention in detecting the H2S gas concentration gradient from 660 ppt to 100 ppm.

[0051] Figure 8 This is a long-term stability response diagram of the SnO2@CuO composite gas-sensitive material synthesized in Example 1 of the present invention in detecting 100 ppm H2S gas;

[0052] Figure 9This is a comparison chart of the SnO2@CuO composite gas-sensitive material synthesized in Example 1 of this invention when detecting different gases. Detailed Implementation

[0053] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. 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.

[0054] This invention proposes a method for preparing MOF (metal-organic framework) derived SnO2@MOx composite semiconductor gas-sensitive materials, such as... Figure 1 As shown, the method includes the following steps:

[0055] Step S1: Prepare Sn-MOF precursor, i.e. tin-containing metal-organic framework precursor.

[0056] Step S11: Dissolve 0.576 g NaOH and 1.014 g C9H6O6 (H3BTC) in 84 mL of deionized water to obtain solution A.

[0057] Step S12: Dissolve 7.014 g SnCl4·5H2O in a mixed solution of 60 mL deionized water and 36 mL N,N-dimethylformamide (DMF) to obtain solution B.

[0058] Step S13: After solutions A and B have fully dissolved, mix solutions A and B into a beaker. Place the beaker in a 50 ºC water bath and react for 12 h. After the reaction is complete, collect the product.

[0059] Step S14: Wash the product three times with deionized water and ethanol alternately, and dry it overnight in an oven at 80 °C to obtain Sn-MOF precursor powder.

[0060] Step S2: Mix MOx-corresponding nitrate, water, glycerol, citric acid and / or urea, F127 and / or P123 evenly to prepare a compound impregnation solution.

[0061] Specifically, the compound impregnation solution consists of different proportions of MOx-corresponding nitrates (M(NO3)n), water, glycerol, citric acid and / or urea, F127 and / or P123. M is one or more of Cu, Fe, Ni, Mn, and Co.

[0062] The amount of MOx-corresponding nitrate (M(NO3)n) added is determined by the ratio of Sn-MOF precursor to MOx-corresponding nitrate, and the molar ratio of Sn-MOF precursor to MOx-corresponding nitrate is 100:1-1:1; preferably 30:1-10:1.

[0063] In the compound impregnation solution, the molar ratio of M(NO3)n: citric acid and / or urea: F127 and / or P123 is 1:0.5-3:0.005-0.03, preferably 1:1-2:0.01-0.02.

[0064] The addition of citric acid is to transform M(NO3)n into a complex state, reducing instantaneous supersaturation and allowing it to form a metal-organic network on the surface after drying, which is then calcined into a uniform nanoparticle shell. The addition of urea is to achieve a slow deposition process. Citric acid and urea can be added simultaneously or one of them can be added at a time. When added simultaneously, the molar ratio of citric acid to urea is 1:0.5 to 1:2.

[0065] The addition of glycerol is to increase viscosity, limit salt migration, and prevent salt from migrating outward and forming large particles during drying. The glycerol addition ratio is water:glycerol = 9:1 to 7:3 (volume ratio).

[0066] F127 and P123 serve as soft template agents, enabling the shell to be both continuous and granular, naturally forming interconnected mesopores of 2–20 nm. F127 and P123 can be added simultaneously or one of them can be added separately. When added simultaneously, the molar ratio of F127 to P123 is 1:0.5 to 1:3.

[0067] Step S3: Using Sn-MOF precursor and composite impregnation solution, prepare hierarchical porous SnO2@MOx composite semiconductor gas-sensitive material.

[0068] Step S31: Mix the Sn-MOF precursor with the compound impregnation solution and impregnate it quantitatively through the pore volume to form a uniform suspension.

[0069] Specifically, the shell thickness can be controlled by quantitative impregnation based on pore volume, forming a uniform suspension. The shell thickness can be controlled by multiple equivalent depositions and repeated cycles, with the number of cycles being 2-5.

[0070] Step S32: Dry the suspension to obtain Sn-MOF gel modified with the compound solution.

[0071] Step S33: The Sn-MOF gel modified with the compound solution is transferred to a tube furnace and subjected to segmented calcination in different atmospheres. This causes the Sn-MOF precursor to undergo self-sacrificial pyrolysis and simultaneously triggers the local reduction reaction of the nitrates of the corresponding MOx metals, generating a MOx shell in situ on the SnO2 surface and forming a semi-coherent epitaxial heterostructure. After the calcination is completed, the material is naturally cooled to room temperature to obtain a hierarchical porous SnO2@MOx composite semiconductor gas-sensitive material.

[0072] Specifically, the purpose of segmented calcination is to prevent MOx from sintering into islands and to achieve continuous coverage.

[0073] The first stage calcination temperature is 150-300℃, preferably 180-260℃; the second stage calcination temperature is 300-800℃, preferably 400-600℃, and the total calcination time is 4-10 h.

[0074] Each stage of the atmosphere is one of Ar / N2, low oxygen, or air. The first stage atmosphere is preferably one of Ar / N2 or low oxygen, and the calcination time is 2-6 h; the second stage atmosphere is preferably one of low oxygen or air, and the calcination time is 2-4 h.

[0075] The purpose of segmented calcination is to first create a localized reducing environment in an inert / reducing atmosphere by utilizing the self-sacrifice of the Sn-MOF precursor, thereby promoting directional nucleation at the interface, element doping / enrichment, and the establishment of defect gradients such as oxygen vacancies. Then, oxidation and crystallization are carried out to remove residual carbon and stabilize the continuous MOx shell and epitaxial heterostructure.

[0076] Furthermore, the products obtained in steps S1 and S3 both need to be ground. Grinding the product in S1 helps to make the annealing more thorough, and grinding the product in S3 helps to dissolve and prepare the sensor sheet for H2S sensing testing.

[0077] This invention provides a MOF-derived SnO2@MOx composite semiconductor gas-sensitive material, prepared by the above method. The material consists of a SnO2 core and an outer MOx shell, wherein M is one or more of Cu, Fe, Ni, Mn, and Co. The MOx is generated in situ on the SnO2 surface through a simultaneous self-sacrificing pyrolysis-local reduction reaction of the Sn-MOF precursor complex, and forms a semi-coherent epitaxial heterointerface with SnO2, exhibiting strong interaction.

[0078] Transition metal oxides (MOx) are loaded onto the surface of SnO2 using a pore volume quantitative impregnation-segmented calcination method. The SnO2@MOx composite semiconductor gas-sensitive material is constructed in situ from a Sn-MOF precursor and a MOx-corresponding nitrate compound solution through a self-sacrificial pyrolysis-local reduction synchronous process. This process causes M element doping / enrichment to occur in the near-surface layer of SnO2 near the interface, which, together with the outer MOx shell, forms the epitaxial heterostructure interface and defect gradient coupling body. This allows the SnO2 and MOx components to be uniformly and tightly bonded together, and enhances the sensing performance through rapid electron transport during the reaction process.

[0079] The working principle of this SnO2@MOx semiconductor gas-sensitive material is based on the synergistic effect of SnO2 and MOx components. First, the MOF-derived SnO2 perfectly inherits the high specific surface area and porous structure of the MOF template, providing abundant active sites for gas adsorption and reaction, effectively suppressing the aggregation phenomenon caused by MOx loading, and improving the material's thermal stability. Second, the semi-coherent epitaxial heterostructure formed by the composite material increases the synergistic effect between components, optimizing adsorption sites and reaction pathways. In experiments dynamically detecting H2S gas, it guides the transformation of H2S to SO2, rather than toxic sulfates, etc., and the gas-sensing performance of the material can be maintained at a high level even after long-term exposure to H2S atmosphere. Third, the MOx loading directly determines the particle size of the gas-sensitive material, optimizing the SnO2@MOx pores. The MOx shell is a continuous particle with a thickness of 1–8 nm, covering 70–100% of the SnO2 outer surface, forming interconnected mesoporous mass transfer channels in the 2–20 nm range, regulating the gas diffusion rate, and optimizing sensing performance.

[0080] This invention provides an application of MOF-derived SnO2@MOx composite semiconductor gas-sensitive material in H2S gas sensing.

[0081] Example 1:

[0082] Preparation of SnO2@CuO: First, Sn-MOF precursor powder was prepared. A composite impregnation solution was prepared with the following composition: Cu(NO3)2·3H2O (molar ratio of Cu(NO3)2·3H2O to Sn-MOF precursor is 1:20), water: glycerol = 9:1, Cu(NO3)2·3H2O: citric acid: P123 = 1:1.5:0.01. The Sn-MOF precursor and the composite impregnation solution were mixed, and the impregnation cycle was performed 4 times with a pore volume quantitative method. After drying, the sample was ground into powder. The material was transferred to a tube furnace and annealed at 220℃ for 3 hours under Ar atmosphere with a continuous heating rate of 5℃ / min; the atmosphere was then switched to air, and the temperature was further increased to 400℃ for 2 hours with a continuous heating rate of 5℃ / min. After natural cooling, the product was collected and ground with agate to obtain the SnO2@CuO composite semiconductor gas-sensitive material. The SnO2@CuO composite semiconductor gas-sensitive material synthesized in Example 1 of this invention was characterized, as follows: Figure 2-5 The images shown are XRD patterns, TEM images, SEM images, and XPS analysis.

[0083] H2S gas-sensing performance test: 0.015 g of the synthesized SnO2@CuO composite semiconductor gas-sensing material was dissolved in 400 μL of deionized water. The sample was placed in an ultrasonic machine and sonicated for 5 min to disperse it evenly in the water. Then, 2.5 μL of the dispersed sample solution was taken with a pipette and evenly coated onto the electrode plate. After the solution was allowed to air dry naturally, a layer of composite gas-sensing material was coated on the surface of the electrode plate, forming a SnO2@CuO sensor. The SnO2@CuO sensor was transferred to a heating stage and connected to a resistance monitoring device for H2S detection. The entire monitoring process adopted the dynamic gas mixing principle to simulate the air flow in the environment. The dynamic gas flow rate was 3 L / min, simulating the gas composition of hydrogen sulfide in the air environment, which was a mixture of H2S, N2, and O2, with O2 maintaining a proportion of 20%, i.e., 600 ml / min. First, the heating stage was controlled to 250°C, and air, 100 ppm H2S gas, and air were sequentially introduced at a rate of 3 L / min. The resistance changes during gas switching were collected to obtain the response value change curve. The gas-sensitive properties of the SnO2@CuO synthesized in this invention are as follows: Figure 6-9 As shown, this SnO2@CuO composite semiconductor gas-sensitive material exhibits excellent sensing performance in detecting H2S gas. At 250℃, the SnO2@CuO sensor has a response value of approximately 27,000 for detecting 100 ppm H2S gas, with a response time of 75 s and an ultrafast recovery time of less than 10 s. It shows different progressive response values ​​for different concentrations of H2S gas; the detection limit reaches the ppt level; it has excellent selectivity, and is basically unaffected by interference from other gases in H2S detection; it also exhibits good stability, maintaining a response value of approximately 25,000 even after 54 consecutive days of testing.

[0084] Example 2:

[0085] Preparation of SnO2@Fe2O3: First, Sn-MOF precursor powder was prepared. A composite impregnation solution was prepared with the following composition: Fe(NO3)2·6H2O (molar ratio of Fe(NO3)2·6H2O to SnO2 1:15), water: glycerol = 8:1, Fe(NO3)2·6H2O: citric acid: P123 = 1:1.5:0.01. The Sn-MOF precursor and composite impregnation solution were mixed, and the impregnation cycle was performed 4 times with a pore volume-controlled amount. After drying, the sample was ground into powder. The material was transferred to a tube furnace and annealed at 220℃ for 3 hours under Ar atmosphere with a continuous heating rate of 5℃ / min; the atmosphere was then switched to air, and annealed again at 400℃ for 2 hours with a continuous heating rate of 5℃ / min. After natural cooling, the product was collected and ground with agate to obtain the SnO2@Fe2O3 composite semiconductor gas-sensitive material.

[0086] H2S gas-sensing performance test: 0.015 g of the synthesized SnO2@Fe2O3 composite semiconductor gas-sensing material was dissolved in 400 μL of deionized water. The sample was placed in an ultrasonic machine and sonicated for 5 min to disperse it evenly in the water. Then, 2.5 μL of the dispersed sample solution was taken with a pipette and evenly coated onto the electrode plate. After the solution was allowed to air dry naturally, a layer of composite gas-sensing material was coated on the surface of the electrode plate, forming a SnO2@Fe2O3 sensor. The SnO2@Fe2O3 sensor was transferred to a heating stage and connected to a resistance monitoring device for H2S detection. The entire monitoring process adopted the dynamic gas mixing principle to simulate the air flow in the environment. The dynamic gas flow rate was 3 L / min, simulating the gas composition of hydrogen sulfide in the air environment, which was a mixture of H2S, N2, and O2, with O2 maintaining a proportion of 20%, i.e., 600 ml / min. First, the heating stage was controlled to 250°C, and air, 100 ppm H2S gas, and air were sequentially introduced at a rate of 3 L / min. The resistance changes during gas switching were collected to obtain the response value change curve. At 250°C, the SnO2@Fe2O3 sensor had a response value of approximately 6000 for detecting 100 ppm H2S gas, and exhibited different progressive response values ​​for different concentrations of H2S gas; the detection limit reached the ppb level; the sensing performance was slightly inferior to the SnO2@CuO material in Example 1.

[0087] Example 3:

[0088] Preparation of SnO2@CuO: First, Sn-MOF precursor powder was prepared. A composite impregnation solution was prepared with the following composition: Cu(NO3)2·3H2O (molar ratio of Cu(NO3)2·3H2O to SnO2 is 1:15), water: glycerol = 8:3, Cu(NO3)2·3H2O: urea: F127 = 1:2:0.02. The Sn-MOF precursor and composite impregnation solution were mixed, and the impregnation cycle was performed 5 times with a pore volume-controlled amount. After drying, the sample was ground into powder. The material was transferred to a tube furnace and annealed at 200℃ for 2 hours under Ar atmosphere with a continuous heating rate of 5℃ / min; the atmosphere was then switched to air, and the temperature was further increased to 450℃ for 1 hour with a continuous heating rate of 5℃ / min. After natural cooling, the product was collected and ground with agate to obtain the SnO2@CuO composite semiconductor gas-sensitive material.

[0089] H2S gas-sensing performance test: 0.015 g of the synthesized SnO2@CuO composite semiconductor gas-sensing material was dissolved in 400 μL of deionized water. The sample was placed in an ultrasonic machine and sonicated for 5 min to disperse it evenly in the water. Then, 2.5 μL of the dispersed sample solution was taken with a pipette and evenly coated onto the electrode plate. After the solution was allowed to air dry naturally, a layer of composite gas-sensing material was coated on the surface of the electrode plate, forming a SnO2@CuO sensor. The SnO2@CuO sensor was transferred to a heating stage and connected to a resistance monitoring device for H2S detection. The entire monitoring process adopted the dynamic gas mixing principle to simulate the air flow in the environment. The dynamic gas flow rate was 3 L / min, simulating the gas composition of hydrogen sulfide in the air environment, which was a mixture of H2S, N2, and O2, with O2 maintaining a proportion of 20%, i.e., 600 ml / min. First, the heating stage was controlled to reach 250°C, and air, 100 ppm H2S gas, and air were sequentially introduced at a rate of 3 L / min. The resistance changes during gas switching were collected to obtain the response value change curve. At 250°C, the SnO2@CuO sensor had a response value of approximately 63 for detecting 100 ppm H2S gas, and exhibited different progressive response values ​​for different concentrations of H2S gas; the detection limit reached the ppm level; the sensing performance was slightly inferior to the SnO2@CuO material in Example 1.

[0090] Example 4:

[0091] Preparation of SnO2@CuO: First, Sn-MOF precursor powder was prepared. A composite impregnation solution was prepared with the following composition: Cu(NO3)2·3H2O (molar ratio of Cu(NO3)2·3H2O to SnO2 is 1:15), water: glycerol = 8:1, Cu(NO3)2·3H2O: urea / citric acid: F127 = 1:1.5:0.01. The Sn-MOF precursor and composite impregnation solution were mixed, and the impregnation cycle was performed 5 times with a pore volume-controlled amount. After drying, the sample was ground into powder. The material was transferred to a tube furnace and annealed at 220℃ for 3 hours under N2 atmosphere with a continuous heating rate of 5℃ / min; the atmosphere was then switched to air, and the temperature was further increased to 350℃ for 2 hours with a continuous heating rate of 5℃ / min. After natural cooling, the product was collected and ground with agate to obtain the SnO2@CuO composite semiconductor gas-sensitive material.

[0092] H2S gas-sensing performance test: 0.015 g of the synthesized SnO2@CuO composite semiconductor gas-sensing material was dissolved in 400 μL of deionized water. The sample was placed in an ultrasonic machine and sonicated for 5 min to disperse it evenly in the water. Then, 2.5 μL of the dispersed sample solution was taken with a pipette and evenly coated onto the electrode plate. After the solution was allowed to air dry naturally, a layer of composite gas-sensing material was coated on the surface of the electrode plate, forming a SnO2@CuO sensor. The SnO2@CuO sensor was transferred to a heating stage and connected to a resistance monitoring device for H2S detection. The entire monitoring process adopted the dynamic gas mixing principle to simulate the air flow in the environment. The dynamic gas flow rate was 3 L / min, simulating the gas composition of hydrogen sulfide in the air environment, which was a mixture of H2S, N2, and O2, with O2 maintaining a proportion of 20%, i.e., 600 ml / min. First, the heating stage was controlled to reach 250°C, and air, 100 ppm H2S gas, and air were sequentially introduced at a rate of 3 L / min. The resistance changes during gas switching were collected to obtain the response value change curve. This SnO2@CuO sensor showed a response value of approximately 3900 for detecting 100 ppm H2S gas, exhibiting different progressive response values ​​for different H2S concentrations. The detection limit reached the ppb level; however, its sensing performance was slightly inferior to the SnO2@CuO material in Example 1.

[0093] Example 5:

[0094] Preparation of SnO2@CuO: First, Sn-MOF precursor powder was prepared. A composite impregnation solution was prepared with the following composition: Cu(NO3)2·3H2O (molar ratio of Cu(NO3)2·3H2O to SnO2 is 1:15), water: glycerol = 9:1, Cu(NO3)2·3H2O: urea: F127 = 1:1:0.01. The number of impregnation cycles was 5 times for quantitative pore volume measurement. After drying, the sample was ground into powder. The material was transferred to a tube furnace and annealed at 180℃ for 4 hours under N2 atmosphere with a continuous heating rate of 5℃ / min; the atmosphere was then switched to air, and annealed again at 350℃ for 1.5 hours with a continuous heating rate of 5℃ / min. After natural cooling, the product was collected and ground with agate to obtain the SnO2@CuO composite semiconductor gas-sensitive material.

[0095] H2S gas-sensing performance test: 0.015 g of the synthesized SnO2@CuO composite semiconductor gas-sensing material was dissolved in 400 μL of deionized water. The sample was ultrasonicated for 5 min to disperse it evenly in the water. Then, 2.5 μL of the dispersed sample solution was evenly coated onto the electrode plate using a pipette. After the solution was allowed to air dry naturally, a layer of composite gas-sensing material was coated onto the surface of the electrode plate. The electrode plate was transferred to the heating stage and connected to a resistance monitoring device for H2S detection. The entire monitoring process adopted the dynamic gas mixing principle to simulate the air flow in the environment. The dynamic gas flow rate was 3 L / min, simulating the gas composition of hydrogen sulfide in the air environment, which was a mixture of H2S, N2, and O2, with O2 maintaining a proportion of 20%, i.e., 600 ml / min. First, the heating stage was programmed to reach 250°C, and air, 100 ppm H2S gas, and air were sequentially introduced at a rate of 3 L / min. The resistance change results during the gas change were collected to obtain the response value change curve. At 250℃, the SnO2@CuO sensor has a response value of about 1030 when detecting 100ppm H2S gas, and has different progressive response values ​​for different concentrations of H2S gas; the detection limit reaches the ppb level; the sensing performance is slightly worse than the SnO2@CuO material in Example 1.

[0096] Evidence related to the technical effects obtained by the embodiments of the present invention

[0097] Figure 2 The image shows the XRD pattern of the SnO2@CuO metal oxide semiconductor sensing material synthesized in Example 1. Compared with the PDF standard card, the presence of SnO2 is clearly visible. When the CuO content is low, there are no obvious diffraction peaks in the XRD pattern. Only when CuO:SnO2≥3:10 does the SnO2@CuO material show a weak CuO diffraction peak.

[0098] Figure 3This is a TEM image of the SnO2@CuO gas-sensitive material synthesized in Example 1. It demonstrates that a semi-coherent epitaxial heterostructure is formed between the two components of the material of this invention.

[0099] Figure 4 This is a microscopic morphology image of the SnO2@CuO gas-sensitive material synthesized in Example 1.

[0100] Figure 5 The image shows the XPS plot of the SnO2@CuO gas-sensitive material synthesized in Example 1, which proves that Cu has both +1 and +2 valence states.

[0101] Figure 6 This is a single-response curve of the SnO2@CuO gas-sensitive material synthesized in Example 1 detecting 100 ppm H2S gas. It can be seen that the response value of this invention to 100 ppm H2S gas is approximately 27000, reaching a relatively stable state, with a response time of 75 s and a recovery time of 9 s.

[0102] Figure 7 This is the response graph of the SnO2@CuO gas-sensitive material synthesized in Example 1 to the detection of H2S gas concentration gradients from 660 ppt to 100 ppm. It can be seen that the response of this invention to different hydrogen sulfide gases exhibits a certain regularity, providing strong support for the accurate detection of H2S concentration.

[0103] Figure 8 This is a long-term stability response diagram of the SnO2@CuO gas-sensitive material synthesized in Example 1 for detecting 100 ppm H2S gas. It can be seen that the present invention exhibits excellent stability in long-term testing against H2S, meeting the requirements of practical applications.

[0104] Figure 9 This is a response graph of the SnO2@CuO gas-sensitive material synthesized in Example 1 for detecting various gases. It can be seen that the present invention exhibits excellent selectivity for H2S gas, strong anti-interference ability, and can be well used as an H2S sensor.

[0105] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing MOF-derived SnO2@MOx composite semiconductor gas-sensitive material, characterized in that, The method includes the following steps: Step S1: Prepare Sn-MOF precursor; Step S2: Mix MOx-nitrate-water-glycerol-citric acid and / or urea-F127 and / or P123 evenly to prepare a compound impregnation solution; Step S3: Prepare hierarchical porous SnO2@MOx composite semiconductor gas-sensitive material using Sn-MOF precursor and composite impregnation solution; Step S3 includes the following steps: Step S31: Mix the Sn-MOF precursor with the compound impregnation solution and impregnate it quantitatively through the pore volume to form a uniform suspension; Step S32: Dry the suspension to obtain Sn-MOF gel modified with the compound solution; Step S33: The Sn-MOF gel modified with the compound solution is transferred to a tube furnace and subjected to segmented calcination in different atmospheres. This causes the Sn-MOF precursor to undergo self-sacrificial pyrolysis and simultaneously triggers the local reduction reaction of the nitrates of the corresponding MOx metals, generating a MOx shell in situ on the SnO2 surface and forming a semi-coherent epitaxial heterostructure. After the calcination is completed, the material is naturally cooled to room temperature to obtain a hierarchical porous SnO2@MOx composite semiconductor gas-sensitive material.

2. The method for preparing MOF-derived SnO2@MOx composite semiconductor gas-sensitive material according to claim 1, characterized in that, Step S1 includes the following steps: Step S11: Dissolve 0.576 g NaOH and 1.014 g C9H6O6 (H3BTC) in 84 mL of deionized water to obtain solution A; Step S12: Dissolve 7.014 g SnCl4·5H2O in a mixed solution of 60 mL deionized water and 36 mL N,N-dimethylformamide (DMF) to obtain solution B; Step S13: After solutions A and B have fully dissolved, mix solutions A and B into a beaker; place it in a 50 ºC water bath and react for 12 h; after the reaction is complete, collect the product; Step S14: Wash the product three times with deionized water and ethanol alternately, and dry it overnight in an oven at 80 °C to obtain Sn-MOF precursor powder.

3. The method for preparing MOF-derived SnO2@MOx composite semiconductor gas-sensitive material according to claim 1, characterized in that, MOx corresponds to nitrates in which M is one or more of Cu, Fe, Ni, Mn, and Co.

4. The method for preparing MOF-derived SnO2@MOx composite semiconductor gas-sensitive material according to claim 1, characterized in that, The molar ratio of Sn-MOF precursor to MOx corresponding nitrate is 100:1-1:1; The molar ratio of MOx to nitrate:citric acid and / or urea:F127 and / or P123 is 1:0.5-3:0.005-0.

03.

5. The method for preparing MOF-derived SnO2@MOx composite semiconductor gas-sensitive material according to claim 1, characterized in that, The first stage of calcination is carried out at a temperature of 150-300℃, with an atmosphere of either Ar / N2 or low oxygen, and a calcination time of 2-6 h. The second stage of calcination is carried out at a temperature of 300-800℃, with an atmosphere of either low oxygen or air, and a calcination time of 2-4 h.

6. A MOF-derived SnO2@MOx composite semiconductor gas-sensitive material, characterized in that, Prepared by the method described in any one of claims 1-5, the SnO2@MOx composite semiconductor gas-sensitive material consists of a SnO2 core and an outer MOx shell. The MOx is generated in situ on the SnO2 surface through a simultaneous self-sacrificing pyrolysis-local reduction reaction of the Sn-MOF precursor complexing agent, and forms a semi-coherent epitaxial heterointerface with SnO2.

7. The MOF-derived SnO2@MOx composite semiconductor gas-sensitive material according to claim 6, characterized in that, M can be one or more of Cu, Fe, Ni, Mn, and Co.

8. The MOF-derived SnO2@MOx composite semiconductor gas-sensitive material according to claim 6, characterized in that, Sn-MOF precursor and MOx-corresponding nitrate complex solution are constructed in situ through a self-sacrificing pyrolysis-local reduction synchronous process, which causes M element doping / enrichment to occur in the near-surface layer of SnO2 near the interface, and synergistically forms the epitaxial heterostructure and defect gradient coupling body with the outer MOx shell, so that the SnO2 and MOx components are uniformly and tightly combined.

9. A SnO2@MOx composite semiconductor gas-sensitive material prepared by any one of the methods described in claims 1-5, or the application of the SnO2@MOx composite semiconductor gas-sensitive material described in any one of claims 6-8 in H2S gas sensing.

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