ZnSnO3 / SnO2 microtube materials, preparation methods and applications

Abstract

This invention relates to composite materials formed from ZnSnO3 and SnO2, specifically to ZnSnO3 / SnO2 microtube materials, their preparation methods, and applications. The method involves pretreating waste poplar catkins, followed by readily and fully adsorbing them with a metal salt to obtain a Zn / Sn poplar catkin precursor; calcining and cooling this precursor yields the ZnSnO3 / SnO2 microtube material. This preparation method is simple, uses low-cost raw materials, and is environmentally friendly, achieving the resource utilization of waste poplar catkins. Sensors based on this composite material exhibit high sensitivity, low detection limit, high selectivity, and excellent long-term stability for gases such as triethylamine. Furthermore, this composite material can be widely applied in various fields such as gas sensing, photocatalysis, and energy storage, showing promising industrialization prospects.

Description

Technical Field

[0001] This invention relates to composite materials formed from ZnSnO3 and SnO2, specifically to ZnSnO3 / SnO2 microtube materials, preparation methods, and applications. Background Technology

[0002] ZnSnO3, a typical ternary perovskite oxide semiconductor, and SnO2, a common n-type wide-bandgap oxide semiconductor, both possess excellent semiconductor properties and have broad application prospects in gas sensing, photocatalysis, lithium-ion batteries, and supercapacitors. Combining ZnSnO3 and SnO2 to form a composite material allows for the formation of an n-type heterojunction through their bandgap matching, effectively promoting the separation and transport of photogenerated carriers and reducing carrier recombination rates. Compared to single ZnSnO3 or SnO2 materials, the composite material exhibits significantly improved semiconductor performance, gas-sensing response characteristics, and catalytic activity.

[0003] Currently, the main methods for preparing ZnSnO3 / SnO2 composite materials include the sol-gel method, hydrothermal method, coprecipitation method, and vapor deposition method. The sol-gel method is complex, has a long reaction cycle, and uses large amounts of organic solvents, resulting in poor environmental friendliness. Composite materials prepared by the hydrothermal and coprecipitation methods are prone to particle agglomeration, making morphology control difficult and resulting in low specific surface area, which affects the material's gas adsorption and charge transport properties. The vapor deposition method requires sophisticated equipment, has high production costs, and is difficult to scale up. Furthermore, existing preparation methods often use chemical reagents as templates or are template-free, failing to fully utilize the unique morphology of natural biomass and hindering the resource utilization of solid waste, thus contradicting the development concept of green chemistry.

[0004] In gas-sensitive detection applications, gas sensors based on ZnSnO3 / SnO2 composite materials are core devices for detecting volatile organic compounds. Triethylamine, a common raw material in the chemical and pharmaceutical industries, poses significant practical risks due to trace leaks of toxicity, flammability, and explosiveness. Therefore, achieving high sensitivity, low detection limit, and high selectivity in its detection is crucial. However, existing ZnSnO3 / SnO2-based gas sensors still suffer from several problems: First, the composite material has an irregular morphology, small specific surface area, and few gas adsorption sites, resulting in low sensor sensitivity and a relatively high detection limit. Second, the heterojunction interface has poor bonding and low charge separation efficiency, leading to slow sensor response / recovery speeds. Third, the sensor has poor selectivity for target gases and weak anti-interference capabilities in complex gas environments. Fourth, the sensor exhibits poor long-term stability, with response values ​​prone to drift during use, necessitating frequent calibration.

[0005] Furthermore, the application scenarios for ZnSnO3 / SnO2 composite materials remain relatively limited, with existing research mainly focusing on gas sensing. There is insufficient development of their applications in photocatalysis, energy storage, and other fields, failing to fully leverage the performance advantages brought by their heterojunction and unique morphology. Therefore, developing a simple, environmentally friendly, and scalable method for preparing ZnSnO3 / SnO2 composite materials, producing composites with regular morphology, large specific surface area, and good heterojunction bonding, and expanding their application areas, while simultaneously developing high-performance ZnSnO3 / SnO2-based sensors to address the technical shortcomings of existing sensors, has become an urgent technical problem to be solved in this field. Summary of the Invention

[0006] This invention utilizes discarded poplar catkins as a natural biological template to prepare ZnSnO3 / SnO2 microtubule materials through purification, metal salt impregnation, and calcination. This composite material inherits the microtubule structure of poplar catkins, exhibiting a large specific surface area and abundant pores. Furthermore, ZnSnO3 and SnO2 form a stable n-type heterojunction, resulting in excellent semiconductor properties. The preparation method is simple, uses low-cost raw materials, and is environmentally friendly, achieving the resource utilization of solid waste. Sensors based on this composite material exhibit high sensitivity, low detection limit, high selectivity, and excellent long-term stability for gases such as triethylamine. Moreover, this composite material can be widely applied in various fields such as gas sensing, photocatalysis, and energy storage, showing promising industrialization prospects.

[0007] In a first aspect, the present invention provides a method for preparing ZnSnO3 / SnO2 microtube material, comprising the following steps: washing waste poplar catkins with deionized water to remove water-soluble impurities, then soaking them in an acid solution for ultrasonic treatment, filtering and washing with water until neutral to obtain a purified poplar catkin template; immersing the purified poplar catkin template in a metal salt solution containing zinc ions, tin ions, nitrate ions and chloride ions, filtering after full adsorption to obtain a Zn / Sn poplar catkin precursor; drying the Zn / Sn poplar catkin precursor and calcining it, then naturally cooling it to room temperature to obtain the ZnSnO3 / SnO2 microtube material.

[0008] This invention utilizes the biological template function of discarded poplar catkins, taking advantage of their natural one-dimensional microtubule structure to allow metal ions to be uniformly adsorbed on the template surface and pores. After calcination, the poplar catkin template undergoes pyrolysis, and the composite material inherits the microtubule structure, solving the problems of irregular morphology and small specific surface area of ​​existing composite materials. At the same time, by controlling the ion ratio of the metal salt solution and the calcination process, a stable heterojunction between ZnSnO3 and SnO2 is ensured, thereby improving the semiconductor performance of the material.

[0009] In some technical solutions, the acid solution is a 0.1mM~1M hydrochloric acid solution, specifically 0.1mM, 0.5mM, 1.0mM, 5.0mM, 10.0mM, 20.0mM, 30.0mM, 40.0mM, 50.0mM, 60.0mM, 70.0mM, 80.0mM, 90.0mM, 0.1M, 0.2M, 0.3M, 0.4M, 0.5M, 0.6M, 0.7M, 0.82M, 0.9M, or 1M hydrochloric acid solution; the hydrochloric acid solution can effectively remove impurities such as lignin, pectin, and ash from poplar catkins, while avoiding damage to the microtubule structure of poplar catkins by strong acid.

[0010] In some technical solutions, the waste poplar catkins are cut before washing, with the length of the cut catkins being 0.5~2cm. This facilitates the uniformity of subsequent impregnation operations, prevents excessively long catkins from tangling and clumping, and ensures sufficient contact between the template and the metal salt solution. The ultrasonic treatment time is 10~60min, and the ultrasonic power is 100~500W. These ultrasonic parameters can maintain the integrity of the microtubular structure of the poplar catkins while removing impurities. If the ultrasonic power is too low, the impurities will not be completely removed, and if the power is too high, the template structure may collapse.

[0011] In some technical solutions, the metal salt solution is a mixed aqueous solution of water-soluble zinc salt and water-soluble tin salt, wherein zinc ions are derived from zinc nitrate hexahydrate, tin ions are derived from tin tetrachloride pentahydrate, nitrate ions are provided by zinc nitrate, and chloride ions are provided by tin tetrachloride. No additional reagents are needed, simplifying the process. When preparing the metal salt solution, tin tetrachloride pentahydrate is first dissolved in a small amount of dilute hydrochloric acid, and then deionized water and zinc nitrate hexahydrate are added, which can effectively inhibit Sn. 4 Hydrolysis of ⁺ ensures the clarity and stability of the metal salt solution.

[0012] In some technical solutions, the molar ratio of zinc ions to tin ions in the metal salt solution is (0.1~2):10, specifically 0.1:10, 0.2:10, 0.3:10, 0.4:10, 0.5:10, 0.6:10, 0.7:10, 0.8:10, 0.9:10, 1.0:10, 1.1:10, 1.2:10, 1.3:10, 1.4:10, 1.5:10, 1.6:10, 1.7:10, 1.8:10, 1.9:10, or 2.0:10. This molar ratio is crucial for ensuring the formation of a stable heterojunction between ZnSnO3 and SnO2. If the zinc ion ratio is too low, the amount of ZnSnO3 generated will be insufficient, and an effective heterojunction cannot be formed. If the ratio is too high, it will cause ZnSnO3 to agglomerate in the composite material, destroying the heterojunction interface.

[0013] In some technical solutions, the molar ratio of nitrate ions to chloride ions in the metal salt solution is (0.2~4):40, specifically 0.2:40, 0.3:40, 0.4:40, 0.5:40, 0.6:40, 0.7:40, 0.8:40, 0.9:40, 1.0:40, 1.1:40, 1.2:40, 1.3:40, 1.4:40, 1.5:40, 1.6:40, 1.7:40, 1.8:40, 1.9:40, 2.0:40, and 2.1:40. 0, 2.2:40, 2.3:40, 2.4:40, 2.5:40, 2.6:40, 2.7:40, 2.8:40, 2.9:40, 3.0:40, 3.1:40, 3.2:40, 3.3:40, 3.4:40, 3.5:40, 3.6:40, 3.7:40, 3.8:40, 3.9:40, 4.0:40; The ratio of nitrate ions to chloride ions can regulate the adsorption rate and distribution uniformity of metal ions on the poplar fluff template, ensuring the uniform composition of the composite material after calcination.

[0014] In some technical solutions, the impregnation time is 2~24h, the impregnation temperature is 20~60℃, and continuous stirring is carried out during the impregnation process at a stirring rate of 100~500rpm. These impregnation conditions can ensure that zinc and tin ions are fully and uniformly adsorbed on the surface and inside the pores of the poplar catkin template, laying the foundation for the subsequent preparation of a composite material with uniform composition. If the impregnation time is too short or the temperature is too low, the adsorption of metal ions will be insufficient, and if the stirring rate is too low, the contact between the template and the solution will be uneven.

[0015] In some technical solutions, the Zn / Sn poplar fluff precursor is vacuum dried before calcination at a temperature of 60-100℃ for 4-12 hours. Vacuum drying prevents the precursor from clumping during drying and also prevents metal ions from segregating due to excessive moisture evaporation, ensuring a uniform distribution of metal ions in the precursor. The calcination process involves heating to 500-800℃ at a rate of 5-10℃ / min and holding for 2-4 hours. Slow heating ensures that the poplar fluff template is fully pyrolyzed into CO2 and H2O, avoiding the gas impact that damages the microtubule structure caused by rapid heating. The calcination temperature and holding time ensure that the metal salt is completely decomposed into ZnSnO3 and SnO2, forming a well-crystallized heterojunction. If the temperature is too low, the decomposition will be incomplete; if the temperature is too high, the composite material grains will grow, reducing the specific surface area.

[0016] Secondly, the present invention provides a ZnSnO3 / SnO2 microtube material obtained by the above preparation method. The composite material has a microtube structure, which is formed by uniformly stacking nanoparticles. The average observed tube diameter is 3-9 micrometers, the specific surface area is 10-100 m² / g, and the pore size distribution is 2-80 nm. In the composite material, ZnSnO3 and SnO2 form a stable n-n heterojunction. SnO2 has (211), (101) and (110) crystal planes, with corresponding lattice fringes of 0.176 nm, 0.264 nm and 0.335 nm, respectively. ZnSnO3 has (220) and (006) crystal planes, with corresponding lattice fringes of 0.132 nm and 0.235 nm, respectively.

[0017] The microtubule structure of this composite material provides a large specific surface area and abundant pore structure, which can provide a large number of active sites for gas molecule adsorption and catalytic reaction, while accelerating gas mass transfer and charge transport rates. The formation of heterojunction causes the energy bands of the two materials to bend, forming a built-in electric field, which effectively promotes the separation and transport of photogenerated carriers, reduces the carrier recombination rate, and significantly improves the semiconductor, gas-sensing and catalytic performance of the composite material.

[0018] Thirdly, this invention provides a semiconductor material obtained by the above-described preparation method. This semiconductor material is an n-type semiconductor, composed of the aforementioned ZnSnO3 / SnO2 microtube material. Under a reducing gas atmosphere, adsorbed oxygen on the material surface reacts with the reducing gas, releasing free electrons and causing a decrease in material resistance. Under an oxidizing gas atmosphere, the oxidizing gas injects holes into the material surface, capturing free electrons and causing an increase in material resistance. This semiconductor characteristic provides a core theoretical basis for its use as a gas-sensitive material, enabling qualitative and quantitative detection of gases by detecting changes in material resistance.

[0019] Fourthly, the present invention provides a sensor comprising a ceramic component, a heat-generating component, a gas detection layer, a resistance detection electrode, a resistance acquisition module, and a heating and temperature control module; the ceramic component has a heating cavity, the heat-generating component is disposed in the heating cavity, the gas detection layer is loaded on the surface of the ceramic component and located outside the heating cavity, and is composed of the aforementioned ZnSnO3 / SnO2 microtube material; the resistance detection electrode is a pair, extending from the gas detection layer; the resistance acquisition module, together with the ZnSnO3 / SnO2 microtube material and the pair of resistance detection electrodes, forms a signal acquisition circuit for acquiring resistance change signals of the material; the heating and temperature control module is electrically connected to the heat-generating component, for supplying power to the heat-generating component and regulating the temperature of the heat-generating component, and providing a stable operating temperature for the gas detection layer through thermal conduction of the ceramic component.

[0020] In some technical solutions, the ceramic component is an Al2O3 ceramic tube, which has good electrical insulation, high temperature resistance, and thermal conductivity, ensuring the structural stability and uniform temperature conduction of the sensor under high-temperature operating conditions. The heat-generating component is a nickel-chromium (Ni-Cr) alloy resistance wire, which can generate stable heat after being energized, and has good high temperature resistance, oxidation resistance, and chemical stability, meeting the long-term operating requirements of the sensor. The resistance detection electrode is a gold (Au) electrode, which is prepared on the surface of the ceramic component by sputtering. The gold electrode has excellent conductivity and chemical inertness, and the sputtering process can ensure a tight bond between the electrode and the ceramic component and the gas detection layer, reducing contact resistance and ensuring the accuracy of resistance signal acquisition.

[0021] In some technical solutions, the sensor also includes a breathable and dustproof shell, which wraps around the ceramic component and the gas detection layer. The pore size of the shell is 0.1 to 1 micrometer, which can effectively prevent dust, particulate matter and other contaminants from polluting the gas detection layer, while not affecting the diffusion and adsorption of gas molecules. It may also include an explosion-proof encapsulation structure to meet the usage requirements of chemical explosion-hazardous environments and improve the safety of the sensor in flammable and explosive environments. It may also include a wireless transmission module, which is electrically connected to the resistance acquisition module to transmit the acquired resistance data to a remote terminal in real time, so as to realize remote monitoring and early warning of gas.

[0022] In some technical solutions, the resistance acquisition module is a high-precision, high-resistance acquisition module with an acquisition accuracy of ≤0.01Ω, which can accurately acquire minute resistance changes of ZnSnO3 / SnO2 microtube materials to ensure the accuracy of gas detection results; the heating and temperature control module has a precise temperature control function with a temperature control accuracy of ±1℃, which can ensure the stable working temperature of the gas detection layer and avoid temperature fluctuations affecting the gas-sensitive response performance.

[0023] Fifthly, the present invention provides a method for detecting gas, implemented using the aforementioned sensor, comprising the following steps: connecting the sensor to a power supply and a data processing module, stabilizing the temperature of the gas detection layer to a preset operating temperature using a heating and temperature control module; introducing a carrier gas into the sensor detection area, and after the sensor resistance stabilizes, acquiring the reference resistance value Ra of the sensor in the carrier gas using a resistance acquisition module; mixing the gas to be tested with the carrier gas and introducing it into the sensor detection area, and after the sensor resistance change stabilizes, acquiring the resistance value Rg of the sensor in the gas to be tested using a resistance acquisition module; calculating the response value according to a preset formula using a data processing module, and achieving qualitative and quantitative detection of the gas to be tested based on the magnitude and trend of the response value and the selectivity characteristics of the sensor.

[0024] In some technical solutions, when the gas to be tested is triethylamine, the preset operating temperature is 217℃. This temperature is the optimal operating temperature for the sensor to detect triethylamine, ensuring that the triethylamine gas reacts efficiently with the adsorbed oxygen on the surface of the composite material, achieving maximum gas-sensitive response. When the gas to be tested is formaldehyde, the preset operating temperature is adjusted to 180~200℃; when the gas to be tested is ammonia, the preset operating temperature is adjusted to 230~250℃. Adjusting the optimal operating temperature for different gases can optimize the sensor's detection performance for each gas.

[0025] In some technical solutions, the carrier gas is air, but inert gases such as nitrogen and argon can also be used. The carrier gas flow rate is 50~200 sccm. Using air as the carrier gas can make the detection conditions consistent with the actual atmospheric environment, improve the practicality of the detection results, and ensure that the gas molecules are in uniform and stable contact with the gas detection layer, avoiding the influence of airflow fluctuations on the detection results.

[0026] In some technical solutions, the gas to be tested is selected from at least one of ethanol, acetone, benzene, formaldehyde, ammonia and triethylamine; the mixing method of the gas to be tested and the carrier gas is dynamic gas mixing, with a mixing accuracy of ≤±2%, which can accurately control the concentration of the gas to be tested and ensure the accuracy and repeatability of the quantitative detection results.

[0027] In some technical solutions, when the gas to be tested is a reducing gas (triethylamine, formaldehyde, ethanol, etc.), the response value is calculated using the formula S=Ra / Rg; when the gas to be tested is an oxidizing gas (ammonia, etc.), the response value is calculated using the formula S=Rg / Ra. The response time and recovery time are defined as the time required for the total resistance change of the sensor to reach 90% after exposure to the target gas and carrier gas. This is an industry-standard for evaluating the performance of gas sensors and ensures the comparability of the detection results.

[0028] In some technical solutions, the sensor's response value to 100 ppm triethylamine is 58.15, with a response time of 3.8 s and a recovery time of 469 s. The detection limit for triethylamine is as low as 0.1 ppb, and the detection range is 0.1 ppb to 100 ppm. The response value to triethylamine shows a good linear relationship with concentration, with a linear fitting equation of y = 0.56x + 1.74 and a coefficient of determination R² = 0.999. This linear equation enables accurate quantitative detection of triethylamine concentration. The sensor's response value to 10 ppm triethylamine shows no significant fluctuation over 60 days, demonstrating excellent long-term stability. Furthermore, the sensor's selectivity coefficient for triethylamine is significantly higher than that for ethanol, acetone, benzene, formaldehyde, and NH3, and it still exhibits good anti-interference capabilities in mixed systems of triethylamine and the aforementioned gases.

[0029] Sixthly, this invention provides applications for the aforementioned ZnSnO3 / SnO2 microtube material. This composite material can be applied to the field of triethylamine gas detection, specifically including real-time monitoring of triethylamine leaks in chemical production workshops, online detection of triethylamine residues in pharmaceutical reaction systems, and dynamic monitoring of triethylamine release during food fermentation. It can also be applied to gas-sensitive detection fields such as rapid detection of total volatile organic compounds (VOCs), selective detection of benzene series compounds (benzene, toluene, xylene) in industrial waste gas, trace formaldehyde detection in indoor air, and monitoring of ammonia concentration in livestock farming environments. Furthermore, based on its heterojunction and microtube structure characteristics, it can also be applied to the field of photocatalytic degradation of organic pollutants in water (methyl orange, rhodamine B, etc.), the field of active materials for supercapacitor electrodes, and the field of negative electrode materials for lithium-ion batteries. It can also be used as the core detection element of portable gas detectors or applied to gas sensor arrays to achieve simultaneous differentiation and quantitative detection of multiple gases.

[0030] The ZnSnO3 / SnO2 microtube material preparation method of this invention uses waste poplar catkins as a biological template, realizing the resource utilization of solid waste. The process is simple, environmentally friendly, low in raw material cost, and highly reproducible, making it suitable for large-scale production. The prepared composite material has a microtube structure, a large specific surface area, and abundant pores. Furthermore, ZnSnO3 and SnO2 form a stable n-type heterojunction, exhibiting excellent semiconductor performance. The sensor prepared based on this composite material has a stable structure and is easy to test. It exhibits high sensitivity, low detection limit, high selectivity, fast response speed, and excellent long-term stability for gases such as triethylamine, with strong anti-interference ability. At the same time, this composite material has a wide range of applications, covering multiple fields such as gas sensing, photocatalysis, and energy storage, and has good industrialization prospects and practical application value. Attached Figure Description

[0031] Figure 1 The XRD patterns of three ZnSnO3 / SnO2 microtube materials (S1, S2, S3) are shown. Figure 1 a is in the range of 10~80° 2θ. Figure 1 b is in the range of 20~32° 2θ.

[0032] Figure 2 FTIR images of three ZnSnO3 / SnO2 microtube materials (S1, S2, S3) are shown.

[0033] Figure 3 XPS plots of three ZnSnO3 / SnO2 microtube materials (S1, S2, S3) are shown.

[0034] Figure 4The Tauc plots of the UV-Vis diffuse reflectance spectra of ZnSnO3 / SnO2 microtube materials S1(a), S2(b), and S3(c) are shown. In the figure, α is the absorption coefficient, obtained from the diffuse reflectance data; hν is the photon energy; and au represents arbitrary units.

[0035] Figure 5 Electron paramagnetic resonance spectra of three ZnSnO3 / SnO2 microtube materials (S1, S2, S3) are shown.

[0036] Figure 6 The O 1s high-resolution XPS spectra of ZnSnO3 / SnO2 microtube materials S1(a), S2(b), and S3(c) are shown.

[0037] Figure 7 Low-magnification SEM images of ZnSnO3 / SnO2 microtubule materials S1(a, d), S2(b, e), and S3(c, f) are shown, as well as a TEM image of ZnSnO3 / SnO2 microtubule material S2(g, h, i).

[0038] Figure 8 The ammonia adsorption-desorption curves (a) and pore size distribution curves (b) of three ZnSnO3 / SnO2 microtube materials are shown.

[0039] Figure 9 The TG test results of the poplar fluff precursor impregnated with Zn / Sn salt (molar ratio of 1 / 10) in air atmosphere are shown.

[0040] Figure 10 The results of detecting 100 ppm triethylamine are shown using three sensors made of ZnSnO3 / SnO2.

[0041] Figure 11 The resistance change curves of three sensors for TEA gas are shown.

[0042] Figure 12 The linear fitting equations and stability test results for TEA gas from three sensors are shown.

[0043] Figure 13 The results show the S2 sensor continuously testing TEA gas for 60 days and observing the changes in response values.

[0044] Figure 14The full XPS spectrum of the S2 sensor before and after contact with TEA gas is shown.

[0045] Figure 15 The graph shows the amount of oxygen adsorbed on the surface of the S2 sensor, and the dynamic response results to 10 ppm TEA in high-purity N2 and air atmospheres, respectively.

[0046] Figure 16 A diagram illustrating the sensing mechanism of the microtubular S2 sensor with triethylamine gas was drawn.

[0047] Figure 17 The image shows the sensor's detection results of the egg liquid spoilage process over 48 hours. Detailed Implementation

[0048] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application. Reagents not specifically described in detail herein are all conventional reagents and are commercially available; methods not specifically described in detail are all conventional experimental methods and can be learned from the prior art.

[0049] Example 1: Preparation of ZnSnO3 / SnO2 microtube material (zinc-tin molar ratio 0.5:10, nitrate-chlorine molar ratio 1:40)

[0050] Purification of poplar catkin template: Waste poplar catkins were cut to a length of 0.5 cm, washed three times with deionized water, soaked in 0.5 M hydrochloric acid solution, sonicated at 400 W for 20 min, filtered and washed with water until neutral, and dried at 60 °C for 12 h to obtain purified poplar catkin template.

[0051] Preparation of metal salt solution: First, dissolve tin tetrachloride pentahydrate in a small amount of deionized water, then add deionized water and zinc nitrate hexahydrate to prepare a metal salt solution with the concentration of tin tetrachloride pentahydrate being 0.08M. Prepare a metal salt solution with a molar ratio of zinc ion to tin ion of 0.5:10 and a molar ratio of nitrate ion to chloride ion of 1:40.

[0052] Metal salt impregnation: 1g of purified poplar catkin template was impregnated in 50mL of metal salt solution at an impregnation temperature of 40℃ and a stirring rate of 300rpm for 8h. After filtration, it was vacuum dried at 90℃ for 6h to obtain Zn / Sn poplar catkin precursor.

[0053] Calcination preparation: The precursor was heated to 700℃ at a heating rate of 5℃ / min, held at that temperature for 2h, and then naturally cooled to room temperature to obtain ZnSnO3 / SnO2 microtube material S1.

[0054] The resulting composite material S1 has a microtubular structure with an average observed tube diameter of 3.26 μm. It is composed of uniformly packed 13 nm particles, has a specific surface area of ​​33 m² / g, and a pore size distribution of 7.3 nm. ZnSnO3 and SnO2 form a stable heterojunction. The lattice fringe sizes corresponding to the (211), (101), and (110) crystal planes of SnO2 are 0.176 nm, 0.264 nm, and 0.335 nm, respectively. The lattice fringe sizes corresponding to the (220) and (006) crystal planes of ZnSnO3 are 0.132 nm and 0.235 nm, respectively.

[0055] Example 2: Preparation of ZnSnO3 / SnO2 microtube materials (zinc-tin molar ratio 1:10, nitrate-chlorine molar ratio 2:40)

[0056] Purification of poplar catkin template: Waste poplar catkins were cut to a length of 1 cm and washed repeatedly with deionized water 3 times to remove water-soluble impurities; the washed poplar catkins were soaked in 0.1M hydrochloric acid solution and ultrasonically treated under ultrasonic power of 300W and ultrasonic time of 30min. After filtration, the catkins were washed with deionized water until neutral and dried in an oven at 60℃ for 12h to obtain purified poplar catkin template.

[0057] Preparation of metal salt solution: First, dissolve tin tetrachloride pentahydrate in a small amount of deionized water, then add deionized water and zinc nitrate hexahydrate to prepare a metal salt solution, wherein the concentration of tin tetrachloride pentahydrate is 0.08M, the concentration of zinc nitrate hexahydrate is 0.008M, the molar ratio of zinc ions to tin ions is 1:10, and the molar ratio of nitrate ions to chloride ions is 2:40.

[0058] Metal salt impregnation: Take 1g of purified poplar catkin template and immerse it in 50mL of the above metal salt solution. Impregnate for 12h at an impregnation temperature of 30℃ and a stirring rate of 200rpm. After sufficient adsorption, filter to obtain Zn / Sn poplar catkin precursor. Place the precursor in an 80℃ vacuum drying oven and dry for 8h.

[0059] Calcination preparation: The dried Zn / Sn poplar fluff precursor was placed in a muffle furnace and heated to 600℃ at a heating rate of 8℃ / min. The temperature was held for 2 hours and then naturally cooled to room temperature to obtain ZnSnO3 / SnO2 microtube material S2.

[0060] The resulting composite material S2 has a microtubular structure with an average observed tube diameter of 3.1 μm. It is composed of uniformly packed 10 nm particles, has a specific surface area of ​​39.6 m² / g, and a pore size distribution of 5.7 nm. ZnSnO3 and SnO2 form a heterojunction. The lattice fringe sizes corresponding to the (211), (101), and (110) crystal planes of SnO2 are 0.176 nm, 0.264 nm, and 0.335 nm, respectively. The lattice fringe sizes corresponding to the (220) and (006) crystal planes of ZnSnO3 are 0.132 nm and 0.235 nm, respectively.

[0061] Example 3: Preparation of ZnSnO3 / SnO2 microtube materials (zinc-tin molar ratio 2:10, nitrate-chlorine molar ratio 4:40)

[0062] Purification of poplar catkin template: Waste poplar catkins were cut to a length of 2cm, washed three times with deionized water, soaked in 0.01M hydrochloric acid solution, sonicated at 200W for 40min, filtered and washed with water until neutral, and dried at 60℃ for 12h to obtain purified poplar catkin template.

[0063] Preparation of metal salt solutions: Prepare metal salt solutions with a zinc ion to tin ion molar ratio of 2:10 and a nitrate ion to chloride ion molar ratio of 4:40, using the same method as in Example 1.

[0064] Metal salt impregnation: 1g of purified poplar catkin template was impregnated in 50mL of metal salt solution at 25℃ and 100rpm for 24h. After filtration, it was vacuum dried at 70℃ for 10h to obtain Zn / Sn poplar catkin precursor.

[0065] Calcination preparation: The precursor was heated to 500℃ at a heating rate of 10℃ / min, held at that temperature for 4h, and then naturally cooled to room temperature to obtain ZnSnO3 / SnO2 microtube material S3.

[0066] The resulting composite material S3 has a microtubular structure with an average observed tube diameter of approximately 5.85 μm. It is composed of uniformly packed ~19 nm particles, has a specific surface area of ​​16.1 m² / g, and a pore size distribution of 13.1 nm. ZnSnO3 and SnO2 form a stable heterojunction. The lattice fringe sizes corresponding to the (211), (101), and (110) crystal planes of SnO2 are 0.176 nm, 0.264 nm, and 0.335 nm, respectively. The lattice fringe sizes corresponding to the (220) and (006) crystal planes of ZnSnO3 are 0.132 nm and 0.235 nm, respectively.

[0067] Test Example 1: Spectral Analysis

[0068] Depend on Figure 1 As can be seen from a, the material composition and the diffraction peaks in the figure are consistent with those of the standard crystal card SnO2 (JCPDS No. 41-1445), and also correspond to the (110), (116), and (220) crystal planes of ZnSnO3 (JCPDS No. 52-1381), respectively. However, it should be noted that due to the low proportion of Zn and the low calcination temperature of the material, no obvious rhombohedral ZnSnO3 diffraction peaks were observed in the spectra of S1, S2, and S3. Figure 1 b can be clearly seen that, with Zn 2+ With increasing Zn content, the (110) peak of materials S1, S2, and S3 shifts to a smaller angle, which is attributed to Zn 2+ The ionic radius of Sn4+ (74 pm) is greater than that of Sn4+ (69 pm), which confirms the presence of lattice doping in the composite material.

[0069] Figure 2 It can be seen that 1628 and 3445 cm -1 The nearby absorption peaks represent the bending and stretching vibrations of HOH and OH adsorbed on the material surface, at 652 and 512 cm⁻¹, respectively. -1 The strong absorption peaks at the point can be attributed to the bending vibration of the O-Sn-O bond and the stretching vibration of Zn-O, respectively, proving that the ZnSnO3 / SnO2 composite material was successfully obtained [10.1016 / j.cej.2025.162681].

[0070] Figure 3 It can be seen that all three types of ZnSnO3 / SnO2 are composed of three elements: Zn, Sn, and O.

[0071] Figure 4 The UV-Vis diffuse reflectance spectra of three ZnSnO3 / SnO2 materials are shown. The optical band gap of S2 (Eg = 2.92) is significantly lower than that of S1 (Eg = 3.01) and S3 (Eg = 3.48). This is likely due to the presence of electron donor oxygen vacancy defects, which leads to the formation of interstitial states or donor-level bands between the valence and conduction bands of the sensing material, thus reducing the band gap of S2. The reduction in band gap not only significantly increases the concentration of free electrons in the conduction band but also accelerates the migration rate of electrons from the bulk phase to the material surface, thereby increasing the content and reactivity of adsorbed oxygen species on the surface.

[0072] Figure 5 Electron paramagnetic resonance (EPR) spectra of three ZnSnO3 / SnO2 samples are shown. The EPR signal intensity of sample S2 at g = 2.001 is significantly higher than that of S1 and S3, demonstrating that the appropriate content of ZnSnO3 composite can significantly increase the concentration of VO in the material.

[0073] Figure 6 The O 1s high-resolution XPS spectra of three ZnSnO3 / SnO2 are shown. Figure 6 It can be seen that the O 1s spectra of the three materials can be fitted with three characteristic peaks, corresponding to hydroxyl oxygen (OH), surface adsorbed oxygen (OA), and lattice oxygen (OL), respectively. The OA contents on the surface of materials S1, S2, and S3 are 23.72%, 27.38%, and 18.97%, respectively, with material S2 having the highest OA content, further confirming the above analysis. That is, the increase in oxygen vacancy concentration significantly promotes the chemical adsorption and activation of oxygen molecules in the air, thereby increasing the content of surface active oxygen species. Therefore, compared with S1 and S3, material S2, with its oxygen-rich vacancy defects and high OA content, will have more surface adsorption and active sites, thus effectively improving its gas-sensing performance.

[0074] Test Example 2: Microscopic Observation

[0075] Figure 7 Low-magnification SEM and TEM images of three ZnSnO3 / SnO2 materials are shown. All three materials exhibit microtubule structures. Figure 7 The af images show that materials S1, S2, and S3 are uniformly packed with small nanoparticles of 13 nm, 10 nm, and 19 nm, respectively, while larger nanoparticle spheres are non-uniformly distributed on the tube walls. The size distribution of the three materials reveals that when the molar ratio increases from 0.5 / 10 to 1.0 / 10, the particle size of S2 is smaller than that of S1. However, when it increases to 1.5 / 10, the particle size of S3 is larger than that of S2. This indicates that an appropriate doping amount helps suppress particle size growth, resulting in S2 having a richer mesoporous structure and a larger specific surface area, which significantly increases its gas adsorption capacity and the content of chemical reaction sites. Simultaneously, the uniform packing of small particles also significantly improves the electron transfer efficiency of the material, enhancing its gas-sensing performance.

[0076] like Figure 7 As can be seen from g, there are abundant pores between the grains. Figure 7 The lattice fringes at 0.176, 0.264, and 0.335 nm are labeled, corresponding to the (211), (101), and (110) crystal planes of SnO2, respectively. Meanwhile, the lattice fringes at 0.132 and 0.235 nm correspond to the (220) and (006) crystal planes of ZnSnO3, respectively. Furthermore, from the selected electron diffraction pattern ( Figure 7 Multiple bright diffraction rings can be seen in i), which belong to the (211), (101), and (110) crystal planes of SnO2 and the (220) and (006) crystal planes of ZnSnO3, respectively, further confirming that S2 is a composite material composed of ZnSnO3 and SnO2.

[0077] Test Example 3: N2 Adsorption-Desorption Experiment

[0078] Figure 8 The graph shows the statistical changes in specific surface area and pore structure of three ZnSnO3 / SnO2 N2 adsorption-desorption experiments.

[0079] like Figure 8 It can be seen that the specific surface area of ​​material S1 is 33.0 m². 2 ·g -1 The pore size with the highest distribution rate is 7.3 nm; the specific surface area of ​​the S2 material is 39.6 m². 2 ·g -1 The pore size with the highest distribution rate is 5.7 nm; the specific surface area of ​​the S3 material is 16.1 m². 2 ·g -1The pore size with the highest distribution rate is 13.1 nm. It can be seen that the S2 material has a larger specific surface area and a smaller mesopore size, which not only provides sufficient space for the adsorption of gas molecules, but also facilitates the rapid diffusion / transport and sieving process of the target gas in the sensitive layer, thereby improving the material's selectivity for the target gas.

[0080] Example 4: Preparation of ZnSnO3 / SnO2 microtubule materials (hydrochloric acid concentration 1M, ultrasonic power 500W)

[0081] The only difference between this embodiment and Example 1 is that the acid solution in step 1 is a 1M hydrochloric acid solution, the ultrasonic power is 500W, and the ultrasonic time is 10min. All other steps and parameters are the same, resulting in ZnSnO3 / SnO2 microtube material S4. The obtained composite material S4 has a microtube structure with an average observed tube diameter of 4μm, a specific surface area of ​​110m² / g, and good heterojunction crystallinity.

[0082] Test Example 4: Calcination Temperature Test

[0083] Figure 9 The image shows a TG (thermal conductivity) chart of poplar fluff precursors impregnated with Zn / Sn salt (molar ratio 1 / 10) under air atmosphere. Figure 9 It can be known that the precursor of poplar catkins is at 600 o At temperature C, weight loss was complete, with a residual amount of 8.6%. This result demonstrates that the poplar fluff precursor impregnated with the mixed salt solution successfully adsorbed Zn. 2+ and Sn 4+ and in 600 o At C, it is completely converted into ZnSnO3 and SnO2.

[0084] Example 6: Preparation of n-type semiconductor materials

[0085] The ZnSnO3 / SnO2 microtube materials S1-S5 prepared in Examples 1-5 were pressed and shaped to obtain the n-type semiconductor material of the present invention. The semiconductor material exhibits significant semiconductor characteristics, with reduced resistance in a reducing gas (triethylamine) atmosphere and increased resistance in an oxidizing gas (ammonia) atmosphere.

[0086] Example 7: Fabrication of ZnSnO3 / SnO2-based Sensors (Basic Model)

[0087] Slurry preparation: Take 10 mg of the composite materials S1, S2 and S3 from Example 1 to prepare basic sensors in parallel, mix with 15 μL of terpineol, and grind thoroughly into a uniform slurry.

[0088] Coating and drying: The slurry is uniformly coated on the surface of an Al2O3 ceramic tube with a pair of Au sputtering electrodes and four Pt wires, and then dried in an oven at 80°C.

[0089] Calcination to remove gumming: Place the dried ceramic tube in a muffle furnace and calcine at 350℃ for 1 hour to remove terpineol.

[0090] Assemble the heating element: Weld four Pt wires to the four terminals of the hexagonal base, with two Pt wires connected to the Au electrode as signal leads and the other two as heating leads; insert a Ni-Cr alloy resistance wire into the ceramic tube heating chamber as a heater.

[0091] Aging stability: The assembled device was inserted into an aging platform at 217℃ and aged for 24 hours to improve the resistance stability of the sensor and obtain a basic ZnSnO3 / SnO2-based sensor.

[0092] Example 8: Fabrication of ZnSnO3 / SnO2-based sensor (with breathable and dustproof housing + wireless transmission)

[0093] The difference between this embodiment and embodiment 7 is that after step 5, a breathable and dustproof shell with a ventilated pore diameter of 0.5μm is added to the ceramic tube, and a high-precision high-resistivity acquisition module (acquisition accuracy 0.01Ω), a heating and temperature control module (temperature control accuracy ±1℃) and a wireless transmission module are integrated on the hexagonal base to obtain an upgraded ZnSnO3 / SnO2-based sensor.

[0094] Example 9: Fabrication of ZnSnO3 / SnO2-based sensor (explosion-proof encapsulation)

[0095] The difference between this embodiment and embodiment 8 is that an explosion-proof encapsulation structure is added to the outside of the breathable and dustproof shell to adapt to the hazardous environment of chemical explosion, resulting in an explosion-proof ZnSnO3 / SnO2-based sensor.

[0096] Example 10: Triethylamine Gas Detection Method

[0097] The sensor from Example 8 was used to detect triethylamine gas. The ambient temperature was 20-25°C and the humidity was 20-30%RH. The steps are as follows:

[0098] Sensor debugging: Connect the sensor to the power supply and data processing module, and stabilize the temperature of the gas detection layer at 217℃ through the heating and temperature control module.

[0099] Reference resistance acquisition: Using air as the carrier gas, with a flow rate of 100 sccm, air is introduced into the sensor detection area. After the resistance stabilizes, the reference resistance value Ra is acquired.

[0100] Detection of the gas to be tested: The dynamic gas mixing method (gas mixing accuracy ±1%) is adopted. Triethylamine is mixed with air to prepare gas of different concentrations, which is then introduced into the detection area. After the resistance stabilizes, the resistance value Rg is collected.

[0101] Response value calculation and detection: The response value is calculated according to Ra / Rg, and the quantitative detection of triethylamine is achieved by linear fitting equation; after the detection is completed, air is introduced, and the detection is completed when the resistance recovers to more than 90% of Ra.

[0102] Test Example 5: Gas Sensing Performance Test

[0103] Referring to the method of Example 10, three sensors made of ZnSnO3 / SnO2 were used to detect 100 ppm of triethylamine.

[0104] Figure 10 As shown in Figure a, within the operating temperature range of 92-252 °C, the response values ​​of the three sensors initially increase gradually with increasing operating temperature, reaching a maximum at 217 °C, and then decrease. This is because at low temperatures, triethylamine (TEA) molecules are in an inert state and cannot overcome the activation energy barrier to react with adsorbed oxygen; as the temperature increases, the entire reaction process accelerates. However, at higher temperatures, gas molecules gain sufficient energy to rapidly detach from the material surface without affecting the conductivity of the sensor, leading to a decrease in its response value. Therefore, the optimal operating temperature for all three sensors is 217 °C, with response values ​​for 100 ppm TEA of S1 (13.67), S2 (58.15), and S3 (6.95), respectively. The response value of S2 is 4.25 and 8.37 times that of S1 and S3, respectively.

[0105] like Figure 10 b, Response time of sensor S1 (t) res The recovery time is 2.5s, and the recovery time is t. rec The value is 190.8 s. For example... Figure 10 c. The response time of the S2 sensor is 3.8s, and the recovery time is 469s. For example... Figure 10 d, The response time of the S2 sensor is 4.2s and the recovery time is 198s.

[0106] like Figure 10 As shown in the figure, the S2 sensor has a response time of 54 s and a recovery time of 103.6 s for trace amounts of 0.1 ppb TEA. This means that the S2 sensor also exhibits rapid response and recovery capabilities for trace amounts of TEA, indicating its extremely high sensitivity.

[0107] Figure 10 f represents the three sensors at 217 o Radar graph of C's response to 100 ppm triethylamine, ethanol, acetone, benzene, formaldehyde, and NH3. (See image) Figure 10 As can be seen from f, the S1, S2 and S3 sensors all showed the highest response values ​​to triethylamine, with the S2 sensor showing significantly higher values ​​than the other two sensors.

[0108] Selectivity is a key parameter for evaluating the accuracy of conductivity sensors in detecting target gases. Poor selectivity can lead to false alarms or missed alarms, and may even render the sensor unusable in practice. Figure 10 By analyzing the response value of the S2 sensor to triethylamine gas, the selectivity coefficients of the S2 sensor for other gases can be calculated. The ratio of the S2 sensor's response value to triethylamine gas to its response values ​​for other gases is used as the selectivity coefficient. The results show that the selectivity coefficient for the S2 sensor in detecting triethylamine and ethanol is 2.58, for triethylamine and acetone it is 7.94, for triethylamine and benzene it is 9.52, for triethylamine and formaldehyde it is 9.3, and for triethylamine and ammonia it is 29.08.

[0109] Figure 11 Three sensors are shown in 217 o The resistance change curve of the sensor under operating temperature C for TEA gas shows that as the TEA gas concentration increases, the degree of resistance reduction gradually increases, and the resistance can be completely restored to the initial resistance Ra after the TEA gas is removed, demonstrating excellent continuous detection capability. This trend is consistent with the detection law of n-type semiconductors for reducing gases. Specifically, at 217°C, the S1 sensor has a TEA concentration detection range of 8 ~ 100 ppm, and the response value increases from 1.79 to 13.67. At 217°C, the S3 sensor has a TEA concentration range of 5 ~ 100 ppm, and the response value increases from 1.84 to 6.95. In comparison, the S2 sensor ( Figure 11 b and Figure 11 e) offers a wider detection range of 0.1 ppb to 100 ppm, with the response value increasing from 1.24 to 58.15. This wider detection range and the practical detection limit of 0.1 ppb make it more advantageous in practical applications.

[0110] Table 1 shows the detection performance of existing SnO2-based materials for detecting TEA gas. As can be seen from Table 1, this sensor has the lowest detection limit compared to previously reported SnO2-based materials.

[0111] Table 1

[0112]

[0113] Figure 12 a~c show the linear fitting equations for TEA gas from the three sensors. (From...) Figure 12 As can be seen from a to c, all three have a good linear relationship.

[0114] Figure 12 Figures d to f show the response-recovery curves of the resistance and response values ​​of the three sensors after five cycles of testing with TEA gas. Figure 12 As shown in d~f, the sensor exhibits a highly consistent signal response in multiple repeated tests, and no significant signal attenuation or baseline drift was observed in the response curves.

[0115] Figure 13 The results show the S2 sensor continuously testing TEA gas for 60 days and observing the changes in the response values. Figure 13 It can be seen that the S2 sensor did not show significant fluctuation in response value to 10 ppm TEA gas at 217℃ within 60 days, indicating that the material has excellent reproducibility and long-term stability.

[0116] like Figure 13 As shown in Figure a, the S2 sensor's response value to 10 ppm TEA gas only decreased from 7.22 to 6.65 within a humidity environment of 54-94% RH. Compared to the normal test environment (Rg / Ra = 7.38@10 ppm), humidity had almost no effect. This is because oxygen vacancies readily adsorb water molecules, thereby weakening the competition between water molecules and TEA for active sites, protecting the redox reaction between chemisorbed oxygen and the target gas, and preventing a decrease in response value due to increased humidity. Furthermore, in actual detection environments, the types of gases are diverse; therefore, good anti-interference capability is crucial.

[0117] Mixtures of 10 ppm TEA with 10 ppm ethanol, acetone, benzene, formaldehyde, and ammonia were prepared and detected using an S2 sensor. The results are as follows: Figure 13 As can be seen from b, the S2 sensor has relatively high anti-interference ability and sensitivity, thus demonstrating that the ZnSnO3 / SnO2 microtube material provided in this application shows great potential in the quality detection of high-protein foods.

[0118] Analysis example: Gas-sensitive mechanism

[0119] According to the conduction model of metal-oxide-semiconductor (MOS) sensors, the gas-sensitive response is determined by the interaction between surface-adsorbed oxygen species and the target gas on the surface of the sensing material. When the sensor is exposed to air, O2 in the air adsorbs on the material surface and removes electrons from the conduction band to form surface-adsorbed oxygen (O2). - (ads) (Eq. 1, 2), simultaneously, the resistance increases with the formation of an electron depletion layer. Subsequently, upon contact with reducing TEA gas, TEA molecules react with O on the material surface. - (ads) The reaction produces CO2, H2O and NO2 (Eq. 3), and electrons are released and return to the material, increasing the carrier concentration, which leads to a smaller electron depletion layer and a lower resistance.

[0120] O2(gas) → O 2(ads) (1)

[0121] O 2(ads) + 2e − → 2O − (ads) (100 < T < 300 o C) (2)

[0122] 2(C2H5)3N + 43O − (ads) →12CO2 + 15H2O + 2NO2 + 43e − (3)

[0123] Based on this, this analysis first performed XPS analysis on the elemental composition and valence state of the S2 material surface before and after exposure to TEA gas. The XPS full spectrum of the S2 sensor before and after contact with TEA gas was obtained. Figure 14 As can be seen, an N 1s peak appeared on the surface of the material after contact. (O 1s spectrum) Figure 6 and Figure 15 a) It can be seen that the surface adsorbed oxygen content decreased from 27.38% to 19.60%, confirming that TEA molecules and the O on the material surface... - (ads) A redox reaction occurred. To further explore whether the S2 sensor's response to TEA gas originates entirely from O... A To further illustrate the contribution of this analysis example, the S2 sensor was also tested at 217. o Dynamic response of C to 10 ppm TEA in high-purity N2 and air atmosphere ( Figure 15 (b) After placing the S2 sensor in a high-purity N2 environment, the initial Ra value gradually decreased and stabilized at Rn (resistance stable in a nitrogen environment). This is related to the increase in electrons in the conduction band caused by the desorption of adsorbed oxygen on the sensor layer surface. After injecting 10 ppm of TEA gas into the N2 atmosphere, the sensor resistance rapidly decreased to a stable Rg(N2). However, in the N2 atmosphere, the response value of TEA gas (S = 6.26) was lower than that of the same concentration of gas in air (S = 7.36). This is because the material O in the N2 atmosphere... A The significantly reduced content leads to a noticeably lower Rn value compared to the Ra value in air. Notably, the S2 sensor cannot recover to Rn in an N2 atmosphere, primarily due to the O2 consumed by the TEA. AThis is related to the lack of replenishment in this oxygen-deficient environment. After subsequent exposure to air, the sensor's resistance fully recovers to the Ra value, and it exhibits reversible response / recovery capability to 10 ppm TEA gas. Therefore, these results indicate that the S2 sensor's response to reducing TEA originates from electron transfer induced by a chemical reaction between surface oxygen species and TEA gas. This confirms the presence of O... − (ads) It plays an important role in the sensing process. Meanwhile, the N 1s high-resolution XPS spectrum after contact with TEA gas ( Figure 15 c) A binding energy peak near 399.6 eV can be detected, which can be attributed to adsorbed NO3. - (ads), further confirming the occurrence of the reaction in formula (3).

[0124] Figure 16 A diagram illustrating the sensing mechanism of the microtubular S2 sensor with triethylamine gas was drawn. (For example...) Figure 16 As shown in Figure a, when the ZnSnO3 / SnO2 microtube material provided in this application comes into contact with O2 in the air, the O2 molecules will abstract electrons from the conduction band of the material and form highly reactive O2 molecules. − (ads) leads to an increase in the material's resistance, and the reaction process is O 2(gas) → 2O 2(ads) ;O 2(ads) + 2e − → 2O − (ads) (100 < T < 300 o C) When triethylamine gas is introduced, it will react with highly reactive O2. − (ads) undergoes the following redox reaction: 2(C2H5)3N + 43O − (ads) →12CO2 + 15H2O + 2NO2 + 43e − During this process, oxygen species release electrons back into the material, causing the material to shrink, which in turn results in a change in electrical signal.

[0125] Depend on Figure 16 As shown in b, in the ZnSnO3 / SnO2 heterojunction material, the work functions of ZnSnO3 and SnO2 are 5.65 eV and 4.9 eV, respectively. Electrons flow from SnO2 to ZnSnO3 until the Fermi level reaches equilibrium, causing the band structures of SnO2 and ZnSnO3 to bend upwards and downwards, and electron depletion layers and electron accumulation layers to form on the surfaces of SnO2 and ZnSnO3, respectively. This high concentration of electron transfer at the heterojunction allows adsorbed O2 molecules to quickly capture electrons and form more O2. − (ads) Species (T=217) o(C) To improve sensing performance. Furthermore, the presence of oxygen vacancy defects in the ZnSnO3 / SnO2 microtube material provides numerous active sites for O2 molecule adsorption on the material surface, further improving the oxygen species formation process and thus providing sufficient active oxygen species for the redox reaction during sensing. When the ZnSnO3 / SnO2 microtube material is exposed to TEA gas, TEA molecules react with O... − (ads) Redox reactions occur between species, generating CO2, H2O, and NO2, and releasing electrons. This process reduces the thickness of the electron depletion layer and electron accumulation layer at the heterogeneous interface, thereby reducing the resistance. Furthermore, the ZnSnO3 / SnO2 microtube material provided in this application possesses abundant mesopores and a large specific surface area, which also effectively improves its response recovery speed as a gas sensor. Figure 10 c and Figure 10 e).

[0126] Application Example 1: Detection of Triethylamine in Food

[0127] The spoilage process of high-protein eggs, crabs, and oysters is mainly due to decarboxylation and deamination reactions caused by the degradation of amino acids by endogenous and microbial enzymes, accompanied by the production of large amounts of volatile amines (ammonia, trimethylamine, and triethylamine, etc.). Among these, TEA gas is an important component and evaluation indicator of the spoilage process, and reports indicate that a TEA concentration of 5 ppm can be used as a threshold for indicating spoilage.

[0128] Based on the superior TEA sensitivity of the S2 sensor, this application example is performed at room temperature (25°C). o C) The changes in TEA gas concentration released from 100 mL of egg liquid, 100 g of crab and oyster stored in 2.5 L sealed narrow-mouth bottles over a certain period of time were measured.

[0129] Figure 17 a and Figure 17 b shows the sensor's detection of the egg liquid spoilage process over 48 hours. With increasing storage time, the sensor's response continuously increased and showed good reversibility. Simultaneously, it can be seen that the TEA gas concentration produced by the egg liquid was less than 5 ppm from 0 to 28 hours, not reaching the spoilage threshold. However, with the continuous accumulation of endogenous and microbial enzymes, the spoilage rate of the egg liquid increased sharply between 28 and 32 hours, and the TEA concentration reached 5.6 ppm, indicating that the egg liquid had begun to spoil and was no longer edible.

[0130] In comparison, crabs rot much faster. Figure 17 c and Figure 17d represents the change in TEA gas concentration released by crabs over 12 hours. Notably, the TEA gas concentration increased 7.1-fold from 4 to 6 hours (9.75 ppm), indicating a sharp increase in spoilage rate. This suggests that crabs are no longer suitable for consumption 6 hours after death to avoid food poisoning. Oysters, on the other hand, produce TEA much more slowly at room temperature. Figure 17 e and Figure 17 As can be seen from f, the TEA gas concentration released by oysters at 12 hours was only 2.3 ppm, which did not reach the spoilage threshold. However, the TEA gas concentration released within 24 hours was only 9.89 ppm (> 5 ppm), making them inedible. This is due to the rapid increase in endogenous enzymes and microbial enzymes during the 12-24 hour period, which led to a significant increase in their spoilage rate. Egg liquid should be stored at room temperature for no more than 28 hours, swimming crab for no more than 6 hours, and oysters for no more than 12 hours, or even less, for optimal cooking. Simultaneously, it was confirmed that using discarded poplar catkins as a sacrificial template at 600... o The S2 sensor obtained by C has a very promising application prospect in food quality detection.

[0131] Application Example 2: Application of ZnSnO3 / SnO2 microtube materials in photocatalysis

[0132] The composite material S2 from Example 2 was used as a photocatalyst and added to a 10 mg / L methyl orange aqueous solution. The solution was irradiated under simulated sunlight, and the methyl orange concentration was measured every 30 minutes. The results showed that after 120 minutes of irradiation, the methyl orange degradation rate reached 98.5%, significantly higher than that of single ZnSnO3 (65.2%) and SnO2 (58.7%), indicating that the heterojunction of the composite material significantly improved the photocatalytic performance.

[0133] Application Example 3: Application of ZnSnO3 / SnO2 microtube materials in supercapacitors

[0134] Using the composite material S2 from Example 2 as the electrode active material, a supercapacitor electrode was prepared, and its electrochemical performance was tested. The results showed that the electrode had a specific capacitance of 320 F / g, and after 5000 charge-discharge cycles, the specific capacitance retention rate still reached 92%, demonstrating excellent capacitance performance and cycle stability.

[0135] Comparative Example 1: Template-free preparation of ZnSnO3 / SnO2 microtube materials

[0136] Without using poplar catkin templates, the metal salt solution from Example 1 was directly co-precipitated, dried, and calcined to obtain ZnSnO3 / SnO2 material. The resulting material consisted of irregular particles with a specific surface area of ​​only 35 m² / g and poor heterojunction interfacial bonding. The sensor prepared based on this material showed a response value of only 12.3 to 100 ppm triethylamine, a detection limit of 1 ppb, and a 25% decrease in response value after 30 days, demonstrating performance far inferior to the product of this invention.

[0137] Comparative Example 2: Preparation of ZnSnO3 / SnO2 microtube materials with a zinc-tin molar ratio of 3:10

[0138] The only difference between this comparative example and Example 1 is that the molar ratio of zinc ions to tin ions in the metal salt solution is 3:10. In the resulting composite material, ZnSnO3 agglomerates, and the heterojunction structure is destroyed. The sensor prepared based on this material has a response value of only 21.5 to 100ppm triethylamine and a response time of 12.3s, which significantly reduces its performance.

[0139] The ZnSnO3 / SnO2 microtube material preparation method of the present invention uses waste poplar catkins as a biological template, realizing the resource utilization of agricultural and forestry solid waste. The process is simple, convenient to operate, and has low raw material cost. It does not require the use of organic solvents, is green and environmentally friendly, has high reproducibility, and is suitable for large-scale production. By controlling the template purification, metal salt impregnation and calcination process, the integrity of the microtube structure of the composite material and the stability of the heterojunction are ensured.

[0140] The ZnSnO3 / SnO2 microtube material of this invention uses waste poplar fluff as a biological template to obtain a unique microtube structure. It is composed of uniformly stacked nanoparticles, with a large specific surface area and abundant pore structure, which can provide a large number of active sites for gas adsorption and catalytic reactions. At the same time, ZnSnO3 and SnO2 form a stable n-n heterojunction, which effectively promotes carrier separation and transport, reduces recombination rate, and the semiconductor performance, gas-sensing characteristics and catalytic activity are significantly better than those of single materials and template-free composite materials.

[0141] The ZnSnO3 / SnO2-based sensor of this invention has a reasonable structural design and can be configured with a breathable and dustproof shell, explosion-proof packaging, wireless transmission and other modules according to the usage requirements to adapt to different application scenarios. The sensor has ultra-high sensitivity to triethylamine (100ppm response value 58.15), ultra-low detection limit (0.1ppb), wide detection range (0.1ppb~100ppm), fast response speed (3.8s) and excellent long-term stability (no fluctuation in response value after 60 days). It also has high selectivity for target gases and strong anti-interference ability in complex gas systems.

[0142] The gas detection method of the present invention is simple to operate, accurate in detection, and highly practical. The optimal working temperature and response value calculation formula can be adjusted according to different gases to be tested, so as to realize the qualitative and quantitative detection of various gases such as triethylamine, formaldehyde, and ammonia. The detection conditions are consistent with the actual atmospheric environment, and the detection results are reliable.

[0143] The ZnSnO3 / SnO2 microtube material of this invention has a wide range of applications. It can be used not only for gas-sensitive detection in chemical, pharmaceutical, food, and indoor air fields, but also for photocatalytic degradation of organic pollutants, supercapacitors, and lithium-ion batteries. It fully leverages the performance advantages of its microtube structure and n-heterojunction, and has good industrialization prospects and practical application value.

[0144] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application 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 therein. Such 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 this application.

Claims

1. A method for preparing ZnSnO3 / SnO2 microtube material, characterized in that, include: Waste poplar catkins were washed with deionized water to remove water-soluble impurities, then soaked in an acid solution and sonicated. After filtration and washing with water, purified poplar catkin template was obtained. The purified poplar catkin template was immersed in a metal salt solution containing zinc and tin ions. After full adsorption, it was filtered and dried to obtain the Zn / Sn poplar catkin precursor. The Zn / Sn poplar fluff precursor was then calcined and cooled to obtain ZnSnO3 / SnO2 microtube material.

2. The preparation method according to claim 1, characterized in that, The acid solution is a 0.1 mM to 1 M hydrochloric acid solution.

3. The preparation method according to claim 1, characterized in that, The metal salt solution is an aqueous solution containing zinc ions, nitrate ions, tin ions and chloride ions.

4. The preparation method according to claim 1, characterized in that, In the metal salt solution, the molar ratio of zinc ions to tin ions is (0.1~2):10; In the metal salt solution, the molar ratio of nitrate ions to chloride ions is (0.2~4):

40.

5. A ZnSnO3 / SnO2 microtube material obtained by the preparation method according to any one of claims 1 to 4.

6. The ZnSnO3 / SnO2 microtube material according to claim 1, characterized in that, The microtube material is a microtube structure, which is formed by uniformly stacking nanoparticles, and the average observed diameter of the microtube structure is 1~10 micrometers. The microtube material is formed by ZnSnO3 and SnO2 to form a heterojunction; The SnO2 has (211), (101) and (110) crystal planes, with corresponding lattice fringes of 0.176 nm, 0.264 nm and 0.335 nm, respectively; The ZnSnO3 has (220) and (006) crystal planes, with corresponding lattice stripes of 0.132 nm and 0.235 nm, respectively.

7. A semiconductor material obtained by the preparation method according to any one of claims 1 to 4, wherein the semiconductor material is an n-type semiconductor, and its resistance decreases in a reducing gas atmosphere and increases in an oxidizing gas atmosphere.

8. A sensor, characterized in that, include: Ceramic components with heating chambers; Heat-generating components are installed in the heating chamber; A ZnSnO3 / SnO2 microtube material prepared by any one of claims 1 to 4 is loaded onto the surface of a ceramic part and outside the heating cavity, wherein the ZnSnO3 / SnO2 microtube material forms a gas detection layer. A pair of resistive detection electrodes extending from the gas detection layer; as well as The resistance acquisition module, together with the ZnSnO3 / SnO2 microtube material and the pair of resistance detection electrodes, forms a signal acquisition circuit; The heating and temperature control module inputs an external voltage to the heat-generating element, causing the heat-generating element to generate heat in the heating chamber, and then conducts the heat to the gas detection layer through the ceramic component, so that the gas detection layer can detect the gas.

9. A method for detecting a gas, characterized in that, Includes the following steps: Connect the sensor as described in claim 8 to the power supply and data processing module; The temperature of the gas detection layer is controlled by the heating and temperature control module. Air is introduced into the sensor detection area as a carrier gas. After the sensor resistance stabilizes, the reference resistance value Ra of the sensor in the air is acquired by the resistance signal acquisition module. The gas to be tested is mixed with the air carrier gas and then introduced into the sensor detection area. After the sensor resistance changes steadily, the resistance value Rg of the sensor in the gas to be tested is collected. The data processing module calculates the response value according to the formula Ra / Rg; The gas is detected based on the response value.

10. An application of a ZnSnO3 / SnO2 microtube material, characterized in that, The ZnSnO3 / SnO2 microtube material obtained by the preparation method according to any one of claims 1 to 4 is applied to the detection of triethylamine gas.

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