Preparation method of layered Co3O4 / YFeO3 inverse opal heterojunction gas-sensitive material

Abstract

The invention relates to a preparation method of a layered Co3O4 / YFeO3 inverse opal heterojunction gas sensitive material for acetone detection in the technical field of gas sensing. The method comprises the following steps: dipping a precursor solution containing a yttrium source, an iron source and a complexing agent into a PI-PS composite template, and carrying out gradient heat treatment and primary calcination in a reducing atmosphere to obtain a YFO-600 sample; a YFO-600 sample, a cobalt source and a complexing agent are dissolved in ethylene glycol, calcination is conducted again in air to obtain the material, the material is of a three-dimensional ordered macroporous structure, and the molar ratio of Co3O4 to YFeO3 is (1-3): 3. The material is synthesized by adopting a hard template method and a two-step calcination process, and the concentration of active oxygen species can be remarkably improved by introducing a proper amount of Co3O4, so that excellent acetone sensing performance is obtained, namely ultralow theoretical / experimental detection limit (1.2 / 20 ppb), ultrahigh selectivity (response ratio is 14), excellent reproducibility and high sensitivity are achieved. Excellent long-term stability (a response retention rate of 98% over 30 days) and robust moisture resistance are achieved.

Description

Technical Field

[0001] This invention belongs to the field of gas sensing technology, specifically relating to a method for preparing a layered Co3O4 / YFeO3 inverse opal heterojunction gas-sensitive material for acetone detection, a method for preparing an acetone gas-sensitive element using the above method, an acetone gas-sensitive element prepared using the above method, and a portable device using the above acetone gas-sensitive element. Background Technology

[0002] Currently, acetone gas-sensitive materials based on resistive sensing principles mainly fall into three categories: traditional metal oxide semiconductors (such as ZnO, SnO2, WO3, etc.), spinel-type oxides (such as ferrites, cobalt-based spinels), and perovskite-type oxides (ABO3-type ferrites and stannates, etc.). However, these materials still have significant limitations in practical applications. Traditional metal oxide semiconductors generally exhibit broad-spectrum responses to various VOCs, but their surface reaction mechanisms lack specificity, resulting in poor selectivity in mixed atmospheres. Although spinel materials possess a certain degree of structural stability, their gas-sensing performance is still limited by insufficient sensitivity and slow response recovery. Perovskite oxides, due to their tunable crystal structure and electronic properties, show great potential in gas-sensing material design, but their intrinsic gas-sensing properties (such as sensitivity, selectivity, and stability) are often difficult to simultaneously meet practical application requirements, often requiring optimization through doping, recombination, or morphology manipulation.

[0003] Perovskite ferrites are a class of gas-sensitive materials that have attracted much attention due to their good thermal stability and chemical inertness, which are beneficial for maintaining stable performance of devices during long-term operation. The d-band center of YFeO3 is closer to the Fermi level than other perovskite ferrites. This favorable electronic structure is related to optimal gas molecule adsorption and minimized activation barriers for electron transfer at the gas-solid interface. For example, the literature "Liu et al., A novel ethanol sensor with high response based on one-dimensional YFeO3 nanorods" shows that the one-dimensional YFeO3 nanorod structure exposes more active sites on the material surface, which can effectively promote the adsorption process of the test gas by the YFeO3 nanorods, thereby improving gas-sensing performance. At 350℃, the response value of YFeO3 to 100 ppm ethanol is 18. Nevertheless, it is still difficult to simultaneously optimize key indicators such as response value, operating temperature, and selectivity using a single rare-earth ferrite. Constructing heterojunctions allows for the synergistic regulation of gas-sensing behavior by utilizing effects such as band matching and charge transfer at the interface, which is an effective way to improve overall performance. The well-matched work function between p-type Co3O4 and YFeO3 promotes favorable interfacial band alignment and facilitates effective support regulation. The inherent Co in Co3O4...3+ / Co 2+ Redox reactions further contribute to the catalytic activity of the upper stage. On the other hand, the microstructure of the sensing material has a significant impact on its gas-sensing performance. Three-dimensional ordered macroporous structures are considered an ideal morphology for simultaneously improving material sensitivity, response speed, and mechanical stability due to their high specific surface area, interconnected channels that facilitate gas diffusion, and stable framework structure. However, integrating heterojunctions with ordered macroporous structures in traditional one-step synthesis methods faces many challenges: differences in crystallization kinetics between different components can easily lead to phase separation, unclear interfaces, or pore structure collapse, making it difficult to achieve synergistic optimization of structure and interface. Summary of the Invention

[0004] (1) Technical problems to be solved Based on the above background, the present invention aims to provide a method for preparing a layered Co3O4 / YFeO3 inverse opal heterojunction gas-sensitive material for acetone detection, a method for preparing an acetone gas-sensitive element using the above method, an acetone gas-sensitive element prepared using the above method, and a portable device using the above acetone gas-sensitive element, so as to solve the shortcomings of existing acetone sensors in terms of selectivity, stability and low concentration detection capability, and meet the urgent need for high-performance acetone sensing technology in fields such as biomedical detection and industrial safety monitoring.

[0005] (2) Technical solution The first aspect of this invention provides a method for preparing a layered Co3O4 / YFeO3 inverse opal heterojunction gas-sensitive material for acetone detection, comprising the following steps: The polyimide substrate was vertically immersed in the polystyrene template solution, so that the PS self-assembled on the PI surface to form a PI-PS composite template; the precursor solution containing yttrium source, iron source and complexing agent was immersed in the PI-PS composite template, and after gradient heat treatment and initial calcination in a reducing atmosphere, the YFO-600 sample was obtained. YFO-600 sample, cobalt source and complexing agent were dissolved in ethylene glycol and then calcined again in air to obtain Co3O4 / YFeO3 inverse opal heterojunction gas-sensitive material, which is a composite material with a three-dimensional ordered macroporous structure, wherein the molar ratio of Co3O4 to YFeO3 is (1~3):3.

[0006] As a further improvement to the above scheme, the concentration of the polystyrene template solution is 0.15 wt%.

[0007] As a further improvement to the above scheme, the yttrium source is yttrium nitrate hexahydrate, the iron source is ferric nitrate nonahydrate, and the complexing agent is citric acid monohydrate; the ratio of yttrium nitrate hexahydrate, ferric nitrate nonahydrate, and citric acid monohydrate is 1.915 g: 2.02 g: 1.05 g.

[0008] As a further improvement to the above scheme, the gradient heat treatment is to first maintain a constant temperature of 350 °C for 4 hours at a heating rate of 1 °C / min, and then heat to 750 °C and hold for 3 hours at a heating rate of 2 °C / min.

[0009] As a further improvement to the above scheme, the reducing atmosphere is a mixed gas with a volume ratio of 5% H2 / Ar and a flow rate of 200 sccm; the initial calcination temperature is 600 ℃, the time is 2 hours, and the heating rate is 2 ℃ / min.

[0010] As a further improvement to the above scheme, the mass ratio of YFO-600 sample, cobalt source, complexing agent and ethylene glycol is 0.195 g:0.291 / 0.582 / 0.873 g:0.315 g:10 mL, and the molar ratio of Co3O4 to YFeO3 in the resulting composite material is 2:3.

[0011] As a further improvement to the above scheme, the hot condensation of the solution in ethylene glycol is carried out at 80°C; the heating rate for the second calcination is 15°C / min, and the calcination time is 0.5 hours.

[0012] A second aspect of the present invention also provides a method for preparing an acetone gas-sensitive element, the acetone gas-sensitive element comprising a ceramic substrate, interdigitated electrodes disposed on the surface of the substrate, and a sensitive material layer covering the interdigitated electrodes, the method for preparing the sensitive material layer comprising: The layered Co3O4 / YFeO3 inverse opal heterojunction gas-sensitive material prepared by the above-mentioned preparation method of arbitrary layered Co3O4 / YFeO3 inverse opal heterojunction gas-sensitive material is uniformly dispersed in anhydrous ethanol by ultrasonic treatment and grinding to form a suspension. The suspension was then deposited onto a ceramic substrate with interdigitated electrodes; Subsequently, it is thermosetting under vacuum conditions at 60-70°C to form a thin film, namely the sensitive material layer.

[0013] As a further improvement to the above scheme, the mass-to-volume ratio of layered Co3O4 / YFeO3 inverse opal heterojunction gas-sensitive material powder to anhydrous ethanol is 5 mg:10 μL, and the temperature is controlled at 180±2 ℃.

[0014] A third aspect of the present invention also provides an acetone gas-sensitive element, which is prepared by any of the above-described methods for preparing acetone gas-sensitive elements.

[0015] The fourth aspect of the present invention also provides a portable device, which includes a wearable face mask and a platform embedded in the wearable face mask. The platform is used for continuous exhaled acetone monitoring. The core of the platform is an MCU and integrates an intelligent sensing platform that controls temperature regulation through the MCU, acquires signals through sensors, and communicates via Wi-Fi. The platform is embedded in the wearable face mask, and the sensor is the acetone gas-sensitive element.

[0016] (3) Beneficial effects The method for preparing the layered Co3O4 / YFeO3 inverse opal heterostructure gas-sensitive material of this invention employs a hard template method and a two-step calcination process to synthesize the Co3O4 / YFeO3 inverse opal heterostructure. By introducing an appropriate amount of Co3O4, the concentration of reactive oxygen species can be significantly increased, thereby obtaining excellent acetone sensing performance: ultra-low theoretical / experimental detection limit (1.2 / 20 ppb), ultra-high selectivity (response ratio of 14), excellent reproducibility, excellent long-term stability (98% response retention rate for more than 30 days), and robust moisture resistance. This invention solves the shortcomings of existing acetone sensors in terms of selectivity, stability, and low-concentration detection capability, meeting the urgent need for high-performance acetone sensing technology in fields such as biomedical detection and industrial safety monitoring.

[0017] The heterojunction gas-sensitive material exhibits a theoretical detection limit of 1.2 ppb and an experimental detection limit of 20 ppb for acetone at 180 °C. It also demonstrates a response ratio of at least 14 for acetone at a concentration of 100 ppm, and a response retention rate of at least 98% after 30 days. The ordered porous structure and high interfacial dislocation density of the Co3O4 / YFeO3 inverse opal heterojunction gas-sensitive material synergistically promote the adsorption of the target gas. Simultaneously, the charge transfer effect at the heterojunction interface increases the concentration of chemically adsorbed oxygen species, significantly enhancing the gas-sensing performance. The acetone gas-sensitive element exhibits ultra-high sensitivity to acetone at 180 °C, characterized by an ultra-low theoretical / experimental detection limit (1.2 / 20 ppb), ultra-high selectivity (response ratio of 14), excellent reproducibility, excellent long-term stability (98% response retention rate after more than 30 days), and robust moisture resistance. This acetone sensing material and element possesses both excellent comprehensive gas-sensing performance and practical application potential, providing a novel and efficient technical solution for the accurate and rapid detection of trace amounts of acetone. The preparation process of this invention is simple and controllable, low in cost, and easy to scale up for mass production and practical application. Attached Figure Description

[0018] Figure 1 This is a flowchart illustrating the preparation method of the layered Co3O4 / YFeO3 inverse opal heterojunction gas-sensitive material for acetone detection provided in Example 1 of the present invention.

[0019] Figure 2This is a flowchart of a method for preparing a portable device according to Embodiment 2 of the present invention.

[0020] Figure 3 The images shown are SEM images of Experiment 1 and Experiment 2 of this invention. Region a is the SEM image of YFO-600 in Experiment 1, and region b is the SEM image of YC-2 sample in Experiment 2.

[0021] Figure 4 The diagram shows the curves, where region a represents the response curves of YFO-600 and YC-1, YC-2 and YC-3 gas-sensitive materials corresponding to Experimental Examples 1-4 to different concentrations of acetone, and region b represents the response curve of YC-2 gas-sensitive material in Experimental Example 3 to low concentrations of acetone and its fitted curve.

[0022] Figure 5 The graph shows the selectivity of the YFO-600 gas-sensitive materials in Experimental Example 1 and the YC-2 gas-sensitive materials in Experimental Example 3 to different gases at a concentration of 100 ppm.

[0023] Figure 6 The graph shows the long-term stability of the YC-2 gas-sensitive material in Experimental Example 3 to 100 ppm acetone in region a, and the response and recovery curves of the YC-2 gas-sensitive material in Experimental Example 3 to 100 ppm acetone under different humidity conditions.

[0024] Figure 7 This is a schematic diagram illustrating the practical application of the wearable face mask of the portable device of the present invention in alarm and normal states. Detailed Implementation

[0025] The technical solutions in the embodiments of the present invention will be clearly and completely described below. 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.

[0026] It should be noted that when a component is said to be "installed on" another component, it can be directly on the other component or it may be in a component that is centered on it. When a component is said to be "set on" another component, it can be directly set on the other component or it may also be in a component that is centered on it. When a component is said to be "fixed to" another component, it can be directly fixed to the other component or it may also be in a component that is centered on it.

[0027] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "or / and" as used herein includes any and all combinations of one or more of the associated listed items.

[0028] Example 1 This embodiment introduces a portable device comprising a wearable face mask and a platform embedded within the wearable face mask. The platform is used for continuous exhaled acetone monitoring. The platform's core is an MCU (Microcontroller Unit), which integrates temperature regulation control via the MCU, signal acquisition via a sensor, and Wi-Fi communication into a smart sensing platform. The platform is embedded in the wearable face mask. The sensor is an acetone gas-sensitive element. In this embodiment, the portable device is assembled as follows: its core is an ESP32C3 microcontroller unit (MCU), which integrates precise temperature regulation control, analog-to-digital conversion (ADC) output of signals acquired by the acetone gas-sensitive element, and Wi-Fi connectivity, forming a compact smart sensing platform. The platform is embedded in the wearable face mask for continuous exhaled acetone monitoring.

[0029] The acetone gas-sensitive element comprises a ceramic substrate, interdigitated electrodes disposed on the surface of the substrate, and a sensitive material layer covering the interdigitated electrodes. The preparation method of the sensitive material layer includes: uniformly dispersing a layered Co3O4 / YFeO3 inverse opal heterojunction gas-sensitive material in anhydrous ethanol through ultrasonic treatment and grinding to form a suspension; then depositing the suspension onto the ceramic substrate with interdigitated electrodes; and subsequently thermosetting it under vacuum conditions at 60-70℃ to form a thin film, i.e., the sensitive material layer. The mass-to-volume ratio of the layered Co3O4 / YFeO3 inverse opal heterojunction gas-sensitive material powder to anhydrous ethanol is 5 mg:10 μL, and the temperature is controlled at 180±2℃.

[0030] Please see Figure 1 The preparation method of the layered Co3O4 / YFeO3 inverse opal heterojunction gas-sensitive material for acetone detection includes: (1) preparation of YFO-600; (2) preparation of Co3O4 / YFeO3 inverse opal heterojunction gas-sensitive material. Therefore, the preparation method of acetone gas-sensitive element mainly includes: (1) preparation of YFO-600; (2) preparation of Co3O4 / YFeO3 inverse opal heterojunction gas-sensitive material; (3) fabrication of acetone gas-sensitive element. The fabricated acetone gas-sensitive element needs to be tested: the element substrate coated with gas-sensitive material is exposed in a gas test chamber, and the response and recovery characteristics of the gas-sensitive element to the target gas are recorded by a four-channel gas-sensitive test system (SD101) at a certain temperature. The gas response is given by the formula S = R g / Ra Calculate, where R g The operating resistance, R, is recorded when the target analyte reaches a steady state in the presence of the target analyte. a The sensor was stabilized in atmospheric conditions (25 °C, ± 15%RH) to establish a baseline resistance. The tested acetone gas-sensitive element was used for integrated assembly of portable devices.

[0031] (1) Preparation of YFO-600: A polyimide (PI) substrate is vertically immersed in a polystyrene (PS) template solution, so that the PS self-assembles on the PI surface to form a PI-PS composite template; a precursor solution containing yttrium source, iron source and complexing agent is immersed in the PI-PS composite template, and after gradient heat treatment and calcination in a reducing atmosphere, a YFO-600 sample is obtained.

[0032] The polystyrene template solution concentration can be 0.15 wt%, the yttrium source can be yttrium nitrate hexahydrate, the iron source can be ferric nitrate nonahydrate, and the complexing agent can be citric acid monohydrate. The ratio of yttrium nitrate hexahydrate, ferric nitrate nonahydrate, and citric acid monohydrate can be 1.915 g:2.02 g:1.05 g, respectively. The gradient heat treatment can be a first isothermal treatment at 350 ℃ for 4 hours at a heating rate of 1 ℃ / min, followed by heating to 750 ℃ ​​and holding for 3 hours at a heating rate of 2 ℃ / min. The reducing atmosphere can be a mixed gas with a volume ratio of 5% H2 / Ar at a flow rate of 200 sccm; the initial calcination temperature can be 600 ℃ for 2 hours at a heating rate of 2 ℃ / min.

[0033] (2) Preparation of Co3O4 / YFeO3 composite material: YFO-600 sample, cobalt source and complexing agent were dissolved in ethylene glycol and then calcined in air to obtain Co3O4 / YFeO3 inverse opal heterostructure material.

[0034] The mass ratio of YFO-600 sample, cobalt source, complexing agent, and ethylene glycol can be 0.195 g:0.291 / 0.582 / 0.873 g:0.315 g:10 mL, resulting in a composite material with a Co3O4 to YFeO3 molar ratio of 2:3. Thermal condensation of the solution in ethylene glycol can be carried out at 80℃; the heating rate for recalcination can be 15℃ / min, and the calcination time can be 0.5 hours.

[0035] (3) Fabrication of the gas-sensitive element: YFO-600 or YC composite was uniformly dispersed in anhydrous ethanol by ultrasonic treatment and grinding. The suspension was then deposited onto an alumina ceramic substrate using a pipette. Subsequently, the film was thermo-cured under vacuum to ensure solvent evaporation.

[0036] The Co3O4 / YFeO3 inverse opal heterojunction gas-sensitive material possesses a three-dimensional ordered macroporous structure, with a molar ratio of Co3O4 to YFeO3 of (1~3):3. The theoretical detection limit for acetone at 180℃ is 1.2 ppb, and the experimental detection limit is 20 ppb. At a concentration of 100 ppm, the response ratio to acetone is no less than 14, and the response retention rate to acetone after 30 days is no less than 98%. The ordered porous structure and high interfacial dislocation density of the Co3O4 / YFeO3 inverse opal heterojunction gas-sensitive material synergistically promote the adsorption of the target gas. Simultaneously, the charge transfer effect at the heterojunction interface increases the concentration of chemically adsorbed oxygen species, significantly enhancing the gas-sensing performance. The acetone gas-sensitive element exhibits ultra-high sensitivity to acetone at 180℃, characterized by an ultra-low theoretical / experimental detection limit (1.2 / 20 ppb), ultra-high selectivity (response ratio of 14), excellent reproducibility, excellent long-term stability (98% response retention rate for over 30 days), and robust moisture resistance. This acetone sensing material and element combine excellent comprehensive gas-sensing performance with practical application potential, providing a novel and efficient technical solution for the accurate and rapid detection of trace amounts of acetone. The preparation process of this invention is simple and controllable, low in cost, and easy to scale up for mass production and practical application.

[0037] In summary, the preparation method of the layered Co3O4 / YFeO3 inverse opal heterostructure gas-sensitive material of the present invention synthesizes the Co3O4 / YFeO3 inverse opal heterostructure using a hard template method and a two-step calcination process. By introducing an appropriate amount of Co3O4, the concentration of reactive oxygen species can be significantly increased, thereby obtaining excellent acetone sensing performance: ultra-low theoretical / experimental detection limit (1.2 / 20 ppb), ultra-high selectivity (response ratio of 14), excellent reproducibility, excellent long-term stability (98% response retention rate for more than 30 days), and robust moisture resistance.

[0038] Example 2 This embodiment illustrates in detail the method for preparing the portable device of Example 1. Please refer to [link / reference]. Figure 2 The preparation method of portable devices mainly includes five steps.

[0039] (1) Preparation of YFO-600: First, a PI substrate was vertically immersed in a PS solution (PS solution concentration 0.15wt%, volume 5 mL, temperature 42 °C) and heated to promote the self-assembly of PS on the PI surface, thereby forming a PI-PS complex. Next, yttrium nitrate hexahydrate, ferric nitrate nonahydrate, and citric acid monohydrate were dissolved in ethanol (masses of yttrium nitrate hexahydrate, ferric nitrate nonahydrate, and citric acid monohydrate were 0.582 g, 2.02 g, and 1.05 g, respectively, and the volume of ethanol was 10 mL), and a transparent solution was formed by ultrasonic stirring. Subsequently, the prepared PI-PS complex was immersed in the precursor solution, allowing yttrium nitrate and ferric nitrate to penetrate into the pores of PS through capillary action. The composite was subjected to controlled-temperature heat treatment (first, a constant temperature treatment at 350 °C for 4 hours (heating rate: 1 °C / min), followed by heating to 750 °C and holding for 3 hours (heating rate: 2 °C / min)) to obtain pure-phase YFeO3. Finally, the obtained YFO precursor was placed in a horizontal tube furnace and calcined in a reducing atmosphere (calcination at 600 °C for 2 hours, heating rate: 2 °C / min). Through a gradient heating calcination process, the YFO-600 sample was finally obtained.

[0040] (2) Preparation of Co3O4 / YFeO3 inverse opal: YFO-600 perovskite, cobalt nitrate hexahydrate, and citric acid monohydrate were homogenized in ethylene glycol by ultrasonication (the masses of YFO perovskite, cobalt nitrate hexahydrate, and citric acid monohydrate could be 0.195 g, 0.582 g, and 0.315 g, respectively, and the volume of ethylene glycol was 10 mL, i.e., the molar ratio of Co3O4 to YFeO3 was approximately 2:3). The resulting precursor solution was thermally condensed under continuous magnetic stirring (the magnetic stirring temperature could be 80 °C) until the solvent was completely evaporated. After the sol-gel transition, the obtained dry gel was calcined in static air (the calcination temperature could be 380 °C, the time could be 0.5 h, and the heating rate could be 15 °C / min) to prepare the Co3O4 / YFeO3 composite material.

[0041] (3) Fabrication of the gas-sensitive element: Based on the layered Co3O4 / YFeO3 composite gas-sensitive material, this invention constructs a resistive ammonia gas-sensitive element. The gas-sensitive element includes an alumina ceramic substrate, Pt interdigitated electrodes disposed on the substrate surface, and a Co3O4 / YFeO3 coating covering the electrodes. Specifically, YFO-600 or the YC composite is uniformly dispersed in anhydrous ethanol by ultrasonic treatment and grinding. Then, the suspension is deposited onto the alumina ceramic substrate using a pipette. Subsequently, the film is thermo-cured under vacuum (the temperature required for thermo-curing under vacuum is 70 °C) to ensure solvent evaporation.

[0042] (4) Testing of the gas-sensitive element: The element substrate coated with the gas-sensitive material is exposed in a gas test chamber. At a specific temperature (optimal test temperature is 180 °C), the response and recovery characteristics of the gas-sensitive element to the target gas are recorded using a four-channel gas-sensitive testing system (SD101). The gas response is expressed by the formula S = R g / R a Calculate, where R g The operating resistance, R, is recorded when the target analyte reaches a steady state in the presence of the target analyte. a The sensor is stabilized in atmospheric conditions (25 °C, ± 15%RH) to establish a baseline resistance.

[0043] (5) Portable device integration and assembly: Its core is the ESP 32 C3 microcontroller unit (MCU), which can integrate precise temperature regulation, signal acquisition through analog-to-digital conversion (ADC), and Wi-Fi connection to form a compact intelligent sensing platform. The platform is embedded in a wearable mask for continuous exhaled acetone monitoring.

[0044] The Co3O4 / YFeO3 composite material prepared by this invention exhibits excellent acetone detection performance at 180℃, with a theoretical / experimental detection limit of 1.2 / 20 ppb. It also shows high sensitivity, ultra-high selectivity (response ratio of 14), excellent reproducibility, excellent long-term stability (98% response retention rate within 30 days), and strong moisture resistance over a wide concentration range from 20 ppb to 100 ppm.

[0045] The beneficial effects of the present invention are as follows: (1) The preparation process is simple and the key parameters are highly controllable, making it suitable for large-scale production; (2) The obtained nanostructure has a high specific surface area, which can promote the efficient diffusion of gas molecules and surface adsorption reaction; (3) The synergistic combination of its ordered porous structure and high interfacial dislocation density promotes the enhanced adsorption of the target gas; (4) The transfer of charge at the heterojunction interface increases the concentration of chemically adsorbed oxygen and improves the gas-sensitive response.

[0046] To demonstrate the feasibility of this invention, this embodiment presents four experimental examples for illustration.

[0047] Experimental Example 1 The preparation of YFO-600 gas-sensitive materials and components and the testing of their gas-sensitive performance are illustrated in the following steps of this experimental example.

[0048] (1) Preparation of YFO-600: First, a PI substrate was vertically immersed in a PS solution (concentration 0.15 wt%, volume 5 mL) and heated to 42 °C to promote the self-assembly of PS on the PI surface, thereby forming a PI-PS complex. Next, 1.915 g of yttrium nitrate hexahydrate, 2.02 g of ferric nitrate nonahydrate, and 1.05 g of citric acid monohydrate were dissolved in 10 mL of ethanol and ultrasonically stirred to form a transparent solution. Subsequently, the prepared PI-PS complex was immersed in the precursor solution, allowing yttrium nitrate and ferric nitrate to penetrate into the pores of PS through capillary action. The complex was subjected to temperature-controlled heat treatment: first, it was kept at 350 °C for 4 hours (heating rate: 1 °C / min), then the temperature was programmed to rise to 750 °C and held for 3 hours (heating rate: 2 °C / min) to obtain pure phase YFeO3. Finally, the obtained YFO precursor YFeO3 was placed in a horizontal tube furnace and calcined in a reducing atmosphere (5% H2 / Ar, flow rate 200 sccm). Through a gradient heating calcination process (600 °C for 2 hours, heating rate: 2 °C / min), the YFO-600 sample was finally obtained.

[0049] (2) Fabrication of the gas-sensitive element: 5 mg of YFO-600 was uniformly dispersed in 10 μL of anhydrous ethanol by ultrasonic treatment and grinding. The suspension was then deposited onto an alumina ceramic substrate using a pipette. Subsequently, the film was thermo-cured under vacuum at 60 °C to ensure solvent evaporation.

[0050] (3) Testing of the gas-sensitive element: The element substrate coated with gas-sensitive material is exposed in a gas test chamber, and the response and recovery characteristics of the gas-sensitive element to the target gas are recorded using a four-channel gas-sensitive testing system (SD101) at a certain temperature. The gas response is expressed by the formula S = R g / R a Calculate, where R g The operating resistance, R, is recorded when the target analyte reaches a steady state in the presence of the target analyte. a The sensor is stabilized in atmospheric conditions (25 °C, ± 15%RH) to establish a baseline resistance.

[0051] To analyze the morphology and performance of YFO-600, such as Figure 3 In region a shown, YFO-600 exhibits a three-dimensional ordered macroporous morphology. For example... Figure 4 In region b shown, the response of YFO-600 to 100 ppm NO2 was 9.1 when tested at 180°C.

[0052] Experimental Example 2 The preparation of YC-1 gas-sensitive materials and components and the testing of their gas-sensitive performance are illustrated in the following steps of this experimental example.

[0053] (1) Preparation of YFO-600: YFO-600 perovskite powder was synthesized by referring to step (1) of Experimental Example 1.

[0054] (2) Preparation of Co3O4 / YFeO3 inverse opal YC-1: 0.195 g YFO-600 perovskite, 0.291 g cobalt nitrate hexahydrate, and 0.315 g citric acid monohydrate were homogenized in 10 mL ethylene glycol by ultrasonication. The resulting precursor solution was thermally cooled at 80 °C with continuous magnetic stirring until the solvent was completely evaporated. After the sol-gel transition, the obtained dry gel was calcined in static air at 380 °C for 0.5 h (heating rate: 15 °C / min) to obtain the Co3O4 / YFeO3 composite material, named YC-1.

[0055] (3) Fabrication of the gas-sensitive element: 5 mg YC-1 was uniformly dispersed in 10 μL of anhydrous ethanol by ultrasonic treatment and grinding. The suspension was then deposited onto an alumina ceramic substrate using a pipette. Subsequently, the film was thermo-cured under vacuum at 60 °C to ensure solvent evaporation.

[0056] (4) Testing of the gas-sensitive element: The element substrate coated with gas-sensitive material is exposed in a gas test chamber, and the response and recovery characteristics of the gas-sensitive element to the target gas are recorded using a four-channel gas-sensitive testing system (SD101) at a certain temperature. The gas response is expressed by the formula S = R g / R a Calculate, where R g The operating resistance, R, is recorded when the target analyte reaches a steady state in the presence of the target analyte. a The sensor is stabilized in atmospheric conditions (25 °C, ± 15%RH) to establish a baseline resistance.

[0057] Figure 4 In region a shown, one of the curves, YC-2, showed responses of 2.7 and 20.5 to 1 and 100 ppm NO2, respectively, when tested at 180 °C.

[0058] Experimental Example 3 The preparation of YC-2 gas-sensitive materials and components and the testing of their gas-sensitive performance are illustrated in the following steps of this experimental example.

[0059] (1) Preparation of YFO-600: YFO-600 perovskite powder was synthesized by referring to step (1) of Experimental Example 1.

[0060] (2) Preparation of Co3O4 / YFeO3 inverse opal YC-2: 0.195 g YFO-600 perovskite, 0.582 g cobalt nitrate hexahydrate, and 0.315 g citric acid monohydrate were homogenized in 10 mL ethylene glycol by ultrasonication. The resulting precursor solution was thermally cooled at 80 °C with continuous magnetic stirring until the solvent was completely evaporated. After the sol-gel transition, the obtained dry gel was calcined in static air at 380 °C for 0.5 h (heating rate: 15 °C / min) to obtain the Co3O4 / YFeO3 composite material, named YC-2.

[0061] (3) Fabrication of the gas-sensitive element: 5 mg YC-2 was uniformly dispersed in 10 μL of anhydrous ethanol by ultrasonic treatment and grinding. The suspension was then deposited onto an alumina ceramic substrate using a pipette. Subsequently, the film was thermo-cured under vacuum at 60 °C to ensure solvent evaporation.

[0062] (4) Testing of the gas-sensitive element: The element substrate coated with gas-sensitive material is exposed in a gas test chamber, and the response and recovery characteristics of the gas-sensitive element to the target gas are recorded using a four-channel gas-sensitive testing system (SD101) at a certain temperature. The gas response is expressed by the formula S = R g / R a Calculate, where R g The operating resistance, R, is recorded when the target analyte reaches a steady state in the presence of the target analyte. a The sensor is stabilized in atmospheric conditions (25 °C, ± 15%RH) to establish a baseline resistance.

[0063] (5) Portable device integration and assembly: Its core is the ESP 32 C3 microcontroller unit (MCU), which can integrate precise temperature regulation, signal acquisition through analog-to-digital conversion (ADC), and Wi-Fi connection to form a compact intelligent sensing platform. The platform is embedded in a wearable mask for continuous exhaled acetone monitoring.

[0064] To analyze the morphology and performance of YC-2, such as Figure 3 In region b shown, the YC-2 composite material retains a three-dimensional ordered macroporous morphology, and increased surface roughness can be observed within the pore network. For example... Figure 4 In region a shown, the responses of YC-2 to 1 ppm NO2 and 100 ppm NO2 at 180 °C were 8.7 and 55, respectively. Figure 4 In region b, the YC-2 composite material exhibits quantitative detection capability for acetone ranging from 20 to 500 ppb under optimal operating conditions, maintaining a detectable signal (1.18) at 20 ppb acetone and showing a theoretical detection limit of 1.2 ppb. The R-value is related to the response value and acetone concentration.2 =0.997 further verifies the operational reliability of trace detection. For example... Figure 5 As shown, the YC-2 composite material exhibits a significantly stronger response to acetone than that to ethanol, formaldehyde, ethylene glycol, isopropanol, triethylamine, NH3, and CO2 at 100 ppm concentrations. The YC-2 composite material's response to acetone is 14 times higher than that to its primary solvent (ethanol), demonstrating extremely high selectivity. Furthermore, as... Figure 6 Region a, under dynamic response monitoring for over 30 days, maintained approximately 98% of its initial response amplitude, confirming exceptional operational stability. Figure 6 The dynamic response of the YC-2 composite material to 100 ppm acetone in region b, within a relative humidity (RH) range of 15%–67%, shows that the YC-2 composite material exhibits only an 8.1% attenuation with increasing humidity. When the sensor is placed inside a mask and worn by a healthy individual (…),… Figure 7 In area a), the system remains in low-power standby mode. When acetone concentration is detected to be above a set threshold, the mask triggers a continuous visual alarm via an indicator light. Figure 7 As shown in area b), the sensor data is wirelessly transmitted to a cloud server, enabling remote real-time tracking of acetone levels via a dedicated mobile or desktop interface. Figure 7 The area shown is c).

[0065] Experiment Example 4 The preparation of YC-3 gas-sensitive materials and elements and the testing of their gas-sensitive performance are illustrated in this experimental example, which includes the following steps: (1) Preparation of YFO-600: YFO-600 perovskite powder was synthesized by referring to step (1) of Experimental Example 1.

[0066] (2) Preparation of Co3O4 / YFeO3 inverse opal YC-3: 0.195 g YFO-600 perovskite, 0.873 g cobalt nitrate hexahydrate, and 0.315 g citric acid monohydrate were homogenized in 10 mL ethylene glycol by ultrasonication. The resulting precursor solution was thermally condensed at 80 °C with continuous magnetic stirring until the solvent was completely evaporated. After the sol-gel transition, the obtained dry gel was calcined in static air at 380 °C for 0.5 h (heating rate: 15 °C / min) to obtain the Co3O4 / YFeO3 composite material, named YC-3.

[0067] (3) Fabrication of the gas-sensitive element: 5 mg YC-3 was uniformly dispersed in 10 μL of anhydrous ethanol by ultrasonic treatment and grinding. The suspension was then deposited onto an alumina ceramic substrate using a pipette. Subsequently, the film was thermo-cured under vacuum at 60 °C to ensure solvent evaporation.

[0068] (4) Testing of the gas-sensitive element: The element substrate coated with gas-sensitive material is exposed in a gas test chamber, and the response and recovery characteristics of the gas-sensitive element to the target gas are recorded using a four-channel gas-sensitive testing system (SD101) at a certain temperature. The gas response is expressed by the formula S = R g / R a Calculate, where R g The operating resistance, R, is recorded when the target analyte reaches a steady state in the presence of the target analyte. a The sensor is stabilized in atmospheric conditions (25 °C, ± 15%RH) to establish a baseline resistance.

[0069] Figure 4 In region a shown, the response of YC-2 to 1 and 100 ppm NO2 at 180 °C was 5 and 33.1, respectively.

[0070] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0071] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for preparing a layered Co3O4 / YFeO3 inverse opal heterojunction gas-sensitive material for acetone detection, characterized in that, It includes the following steps: The polyimide substrate was vertically immersed in the polystyrene template solution, so that the PS self-assembled on the PI surface to form a PI-PS composite template; the precursor solution containing yttrium source, iron source and complexing agent was immersed in the PI-PS composite template, and after gradient heat treatment and initial calcination in a reducing atmosphere, the YFO-600 sample was obtained. YFO-600 sample, cobalt source and complexing agent were dissolved in ethylene glycol and then calcined again in air to obtain Co3O4 / YFeO3 inverse opal heterojunction gas-sensitive material, which is a composite material with a three-dimensional ordered macroporous structure, wherein the molar ratio of Co3O4 to YFeO3 is (1~3):

3.

2. The preparation method of the layered Co3O4 / YFeO3 inverse opal heterojunction gas-sensitive material for acetone detection according to claim 1, characterized in that, The polystyrene template solution concentration is 0.15 wt%.

3. The method for preparing the layered Co3O4 / YFeO3 inverse opal heterojunction gas-sensitive material for acetone detection according to claim 1, characterized in that, The yttrium source is yttrium nitrate hexahydrate, the iron source is ferric nitrate nonahydrate, and the complexing agent is citric acid monohydrate; the ratio of yttrium nitrate hexahydrate, ferric nitrate nonahydrate, and citric acid monohydrate is 1.915 g: 2.02 g: 1.05 g.

4. The preparation method of the layered Co3O4 / YFeO3 inverse opal heterojunction gas-sensitive material for acetone detection according to claim 1, characterized in that, The gradient heat treatment consisted of first being kept at 350 °C for 4 hours with a heating rate of 1 °C / min, and then being heated to 750 °C and held for 3 hours with a heating rate of 2 °C / min.

5. The method for preparing the layered Co3O4 / YFeO3 inverse opal heterojunction gas-sensitive material for acetone detection according to claim 1, characterized in that, The reducing atmosphere was a mixture of 5% H2 / Ar by volume, with a flow rate of 200 sccm; the initial calcination temperature was 600 ℃, the time was 2 hours, and the heating rate was 2 ℃ / min.

6. The method for preparing the layered Co3O4 / YFeO3 inverse opal heterojunction gas-sensitive material for acetone detection according to claim 1, characterized in that, The mass ratio of YFO-600 sample, cobalt source, complexing agent, and ethylene glycol was 0.195 g:0.291 / 0.582 / 0.873 g:0.315 g:10 mL, and the molar ratio of Co3O4 to YFeO3 in the resulting composite material was 2:

3. And / or, the hot condensation of the solution in ethylene glycol is carried out at 80°C; the heating rate for the second calcination is 15°C / min, and the calcination time is 0.5 hours.

7. A method for preparing an acetone gas-sensitive element, the acetone gas-sensitive element comprising a ceramic substrate, interdigitated electrodes disposed on the surface of the substrate, and a sensitive material layer covering the interdigitated electrodes, characterized in that, The method for preparing the sensitive material layer includes: The layered Co3O4 / YFeO3 inverse opal heterojunction gas-sensitive material for acetone detection prepared by the preparation method of the layered Co3O4 / YFeO3 inverse opal heterojunction gas-sensitive material for acetone detection according to any one of claims 1 to 6 is uniformly dispersed in anhydrous ethanol by ultrasonic treatment and grinding to form a suspension. The suspension was then deposited onto a ceramic substrate with interdigitated electrodes; Subsequently, it is thermosetting under vacuum conditions at 60-70°C to form a thin film, namely the sensitive material layer.

8. The method for preparing the acetone gas-sensitive element according to claim 7, characterized in that, The mass-to-volume ratio of layered Co3O4 / YFeO3 inverse opal heterojunction gas-sensitive material powder to anhydrous ethanol was 5 mg:10 μL, and the temperature was controlled at 180±2 ℃.

9. An acetone gas-sensitive element, characterized in that, It is prepared using the method for preparing acetone gas-sensitive elements as described in claim 7 or 8.

10. A portable device comprising a wearable face mask and a platform embedded in the wearable face mask, the platform being used for continuous exhaled acetone monitoring, the platform being a core MCU and integrating an intelligent sensing platform that controls temperature regulation via the MCU, acquires signals via sensors, and communicates via Wi-Fi, wherein the platform is embedded in the wearable face mask, characterized in that... The sensor is the acetone gas-sensitive element as described in claim 9.

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