A metal organic framework-based humidity sensor, and a preparation method and application thereof

Abstract

This invention discloses a metal-organic framework-based humidity sensor, its preparation method, and its application, belonging to the field of humidity sensor technology. The sensor includes an alumina ceramic substrate, interdigitated electrodes, and a humidity-sensitive thin film. The sensitive material is MOF-303 modified with single-atom Fe, where Fe atoms are dispersed in single-atom form and coordinated with four N atoms in the MOF-303 framework to form a Fe-N4 configuration. This invention enhances the dissociation ability of water molecules by anchoring single-atom Fe to form Fe-N4 hydrophilic active centers, resulting in excellent performance of the sensor across the entire humidity range of 5%-98%RH, with a detection limit as low as 5%RH, a response value of 10387, a resolution of 0.1%RH, and a response time of only 6 seconds. It is prepared using a low-temperature coordination-driven strategy, with mild reaction conditions, a simple process, compatibility with existing microfabrication technologies, good process repeatability, and potential for large-scale production.

Description

Technical Field

[0001] This invention belongs to the field of humidity sensor technology, specifically relating to a metal-organic framework-based humidity sensor, its preparation method, and its application. Background Technology

[0002] Real-time, high-precision humidity monitoring plays an indispensable role in cutting-edge fields such as wearable health devices, non-contact human-computer interaction, precision electronic manufacturing, and national defense security. Among various sensor designs such as resistive, current-type, and voltage-type sensors, impedance-based humidity sensors show broad application prospects due to their fast response speed, low cost, and ease of integration.

[0003] Currently, traditional porous materials (such as activated carbon and mesoporous silica) and some metal oxides have inherent limitations in humidity detection: they have insufficient affinity for water molecules and cannot capture enough moisture in low humidity environments to form a continuous proton transport network. This results in weak sensor response and poor stability under low humidity conditions, and even the generation of sensing dead zones, making it impossible to achieve high sensitivity and high resolution detection across the entire humidity range.

[0004] Metal-organic frameworks (MOFs) have become candidate materials for humidity sensing due to their highly tunable pore structure, high specific surface area, and rich surface chemistry. Among them, MOF-303 has attracted attention for its excellent water collection ability, mainly due to the uncoordinated nitrogen atom sites within its framework. However, the proton conduction process of pristine MOF-303 is severely limited by the high water dissociation energy barrier, resulting in low free proton generation efficiency, making it difficult to directly use it to construct high-sensitivity, high-resolution impedance humidity sensors.

[0005] To overcome the aforementioned technical bottlenecks, this invention proposes a single-atom modification strategy. Inspired by the outstanding efficiency of single-atom catalysis in the adsorption and dissociation activation of water molecules, this invention constructs a stable Fe-N4 hydrophilic active center by anchoring atomically dispersed Fe atoms onto uncoordinated N atoms in the MOF-303 framework, thereby providing a novel humidity sensor and its preparation method. Summary of the Invention

[0006] The purpose of this invention is to provide a metal-organic framework-based humidity sensor, its preparation method, and its application, in order to solve the problems mentioned in the background art.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A metal-organic framework-based humidity sensor has a planar structure and includes a substrate with alumina ceramic as the substrate, interdigitated electrodes printed on the upper surface of the substrate, and a humidity-sensitive film coated on the surface of the interdigitated electrodes. The humidity-sensitive film is a single-atom Fe-modified MOF-303 (Fe-MOF-303) sensitive material. In the Fe-MOF-303 sensitive material, Fe atoms are dispersed in the form of single atoms on the MOF-303 support and coordinate with four N atoms in the MOF-303 framework to form a Fe-N4 coordination configuration.

[0008] In a preferred embodiment, the thickness of the humidity-sensitive film is 10~50μm.

[0009] In a preferred embodiment, the interdigitated electrode comprises 15 to 20 pairs of electrode fingers, which are formed by sputtering etching process, and its metal layer structure consists of titanium layer, copper layer, nickel layer and gold layer from the inside to the outside.

[0010] In a preferred embodiment, the titanium layer has a thickness of 0.1~0.3μm, the copper layer has a thickness of 5~10μm, the nickel layer has a thickness of 4~6μm, and the gold layer has a thickness of 1~3μm.

[0011] In a preferred embodiment, the linewidth of the interdigitated electrode is 100~200μm and the line spacing is 50~100μm.

[0012] A method for fabricating a metal-organic framework-based humidity sensor, comprising the following steps: S1 preparation of Fe-MOF-303 sensitive material; S2 is used to prepare an alumina ceramic substrate with interdigitated electrodes; S3 prepared a dispersion by dispersing Fe-MOF-303 sensitive material in deionized water, then drop-coated it onto the surface of the interdigitated electrode, and obtained a humidity sensor after heat treatment.

[0013] As a preferred embodiment, the preparation of the Fe-MOF-303 sensitive material in step S1 includes the following sub-steps: S11 Dissolve 2.08 g of aluminum chloride hexahydrate and 1.5-2.5 g of 3,5-pyrazole dicarboxylic acid monohydrate in 144 mL of deionized water and stir magnetically at room temperature for 0.5 h to obtain a homogeneous mixed solution. S12 dissolves 0.52g of sodium hydroxide in 5.48mL of deionized water and stirs magnetically at room temperature for 0.5h to obtain a homogeneous sodium hydroxide solution; S13 Sodium hydroxide solution is added dropwise to the mixed solution at a rate of 0.25~0.35 mL / min, transferred to a reflux reflux device, and reacted under constant temperature magnetic stirring at 120~140℃ for 2 hours; The S14 reaction system was naturally cooled to room temperature. The precipitate was washed by alternating centrifugation with deionized water and ethanol, and then dried to obtain MOF-303 powder. S15 involves dispersing 20-60 mg of ferric chloride and 0.2 g of MOF-303 powder together in 40-60 mL of acetonitrile to form a suspension, and then heating the mixture at 70-90 °C for 12-24 h. The S16 reaction solution was cooled to room temperature, and the precipitate was washed by alternating centrifugation with deionized water and ethanol. The precipitate was then dried to obtain the Fe-MOF-303 sensitive material.

[0014] As a preferred embodiment, step S2 specifically involves: selecting an alumina ceramic sheet with a length of 10-20 mm and a width of 10-20 mm as a substrate, depositing 15-20 pairs of interdigitated electrodes as described in any one of claims 3 to 5 on the surface of the ceramic sheet using a sputtering etching process, and then ultrasonically cleaning the surface of the ceramic sheet with anhydrous ethanol and deionized water in sequence, and drying it for later use.

[0015] In a preferred embodiment, the concentration of the dispersion in step S3 is 30-50 mg / mL, and the heat treatment is heating under an infrared lamp for 6-12 hours.

[0016] The aforementioned metal-organic framework-based humidity sensor can be used in the field of humidity detection.

[0017] The working principle of the humidity sensor described in this invention is as follows: when the ambient humidity changes, the sensitive film efficiently captures and dissociates water molecules through the Fe-N4 active sites, generating protons (H). + ) and hydrated hydrogen ions (H3O) + This leads to a significant change in the impedance of the thin film. Accurate detection of ambient humidity can be achieved by monitoring the impedance change across the interdigitated electrodes. The sensor's response (S) is defined as: S = Z L / Z H Z L and Z H These are the impedance values ​​of the sensor under low humidity (e.g., 0%RH) and high humidity (e.g., 98%RH), respectively.

[0018] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention innovatively anchors atomically dispersed Fe sites within the MOF-303 framework, and synchrotron radiation (XAFS) analysis confirms the formation of a stable Fe-N4 coordination structure. This single-atom dispersion not only greatly improves the utilization efficiency of metallic Fe and reduces the raw material cost of the sensitive material, but also regulates the electronic structure of the material through strong metal-carrier interactions, significantly enhancing the chemical activity of the sensitive material, thereby greatly improving the sensing performance of the humidity sensor. 2. The Fe-MOF-303-based humidity sensor developed in this invention exhibits excellent performance across the entire humidity range (5%-98%RH); its detection limit is as low as 5%RH, and its response value to 98%RH humidity is as high as 10387; at the same time, the sensor has an ultra-high resolution of 0.1%RH and a fast response time of 6 seconds. 3. The core mechanism for improving humidity sensitivity in this invention lies in the introduction of Fe-N4 active sites; self-driven water dissociation experiments demonstrate that the Fe-N4 sites, as highly efficient catalytic centers, can significantly enhance the chemisorption of water molecules and effectively reduce the dissociation energy barrier of water molecules, promoting the dissociation of protons (H+). + The generation and migration of protons enable the sensor to generate significant electrical signal responses even in extremely low humidity conditions, solving the problem of low proton conduction efficiency of traditional materials in low humidity environments. 4. This invention employs a low-temperature coordination-driven strategy (solvent-thermal reaction at 70~90℃) to achieve stable formation of single atoms, avoiding the high-temperature pyrolysis process typically required in the preparation of traditional single-atom catalysts. The reaction conditions are mild and the process is simple. At the same time, the preparation method of this sensor has good compatibility with existing microfabrication technologies, possesses excellent process repeatability and large-scale production potential, and can meet the needs of industrial mass production. Attached Figure Description

[0019] Figure 1 These are the X-ray diffraction patterns of the MOF-303 and Fe-MOF-303 sensitive materials prepared in Example 1; Figure 2 These are transmission electron microscope images and corresponding elemental mapping diagrams of the Fe-MOF-303 sensitive material prepared in Example 1. Figure 3 These are the structural and electronic configuration characterization diagrams of the Fe-MOF-303 sensitive material prepared in Example 1. Sub-figure a shows the normalized FeK-edge X-ray absorption near-edge structure (XANES) spectrum of the Fe series reference sample and the Fe-MOF-303 sensitive material, sub-figure b shows the normalized FeK-edge extended X-ray absorption fine structure (EXAFS) spectrum of the Fe series reference sample and the Fe-MOF-303 sensitive material, and sub-figure c shows the fitting curve of the EXAFS spectrum of the Fe-MOF-303 sensitive material. Figure 4 This is a schematic diagram of the structure of the self-actuated device used to verify the water molecule dissociation mechanism in Example 1 and a comparison diagram of its voltage response. Sub-figure a is a structural and working principle diagram of the Fe-MOF-303 self-actuated device, and sub-figure b is a bar chart comparing the output voltage of the self-actuated devices based on the original MOF-303 and Fe-MOF-303 at 33% and 98% RH. Figure 5This is the real-time impedance response curve of the Fe-MOF-303 sensor in Example 1 at 11-98% RH. Figure 6 These are the real-time impedance response curves of the Fe-MOF-303 sensor in Example 1 at 5% and 7% RH. Figure 7 This is the continuous monitoring curve of minute humidity changes based on the Fe-MOF-303 sensor in Example 1 at a 48.9% RH standard; Figure 8 This is the repeatability test curve of the Fe-MOF-303 sensor in Example 1 at 85% RH; Figure 9 These are the response and recovery curves of the Fe-MOF-303 sensor in Example 1 at 85% RH; Figure 10 These are the response and recovery curves of the Fe-MOF-303 sensor in Example 2 at 85% RH. Detailed Implementation

[0020] The following is a combination of appendices Figure 1-10 The present invention will be further described in conjunction with the embodiments.

[0021] The following embodiments are used to illustrate the present invention, but should not be used to limit the scope of protection of the present invention. The conditions in the embodiments can be further adjusted according to specific conditions, and simple improvements to the method of the present invention under the premise of the concept of the present invention are all within the scope of protection claimed by the present invention.

[0022] Example 1 (1) Dissolve 2.08 g of aluminum chloride hexahydrate and 1.5 g of 3,5-pyrazole dicarboxylic acid monohydrate in 144 mL of deionized water and stir magnetically for 0.5 h at room temperature to obtain a homogeneous mixed solution; (2) Dissolve 0.52g of sodium hydroxide in 5.48mL of deionized water and stir magnetically for 0.5h at room temperature to obtain a homogeneous sodium hydroxide solution; (3) The sodium hydroxide solution obtained in step (2) is added dropwise to the mixed solution obtained in step (1) at a rate of 0.25 mL / min, and the mixed solution is transferred to a reflux device and reacted under constant temperature magnetic stirring at 120 °C for 2 h. (4) After the reaction system of step (3) is naturally cooled to room temperature, the precipitate is washed by alternating centrifugation with deionized water and ethanol, and then dried to obtain MOF-303 powder; (5) Disperse 20 mg of ferric chloride and 0.2 g of MOF-303 powder obtained in step (4) in 40 mL of acetonitrile to form a suspension, and heat at 70 °C for 12 h. (6) After cooling the solution from step (5) to room temperature, the precipitate was washed by alternating centrifugation with deionized water and ethanol, and then dried to obtain the Fe-MOF-303 sensitive material.

[0023] (7) Using an alumina ceramic sheet as a substrate, the alumina ceramic sheet is 10 mm long and 10 mm wide; 15 pairs of interdigitated electrodes with metal layer structures are deposited on the upper surface of the ceramic sheet by sputtering etching process. The metal layer structure consists of titanium, copper, nickel and gold layers from the inside to the outside, with thicknesses of 0.1 μm, 5 μm, 4 μm and 1 μm, respectively; the line width of the interdigitated electrode is 100 μm and the line spacing is 50 μm. (8) The upper surface of the alumina ceramic sheet obtained in step (7) was ultrasonically cleaned and dried in sequence with anhydrous ethanol and deionized water. (9) Disperse the prepared Fe-MOF-303 sensitive material in deionized water to prepare a uniform dispersion with a concentration of 30 mg / mL; drop the above solution onto the surface of the alumina ceramic sheet interdigitated electrode after drying in step (8), and then heat-treat it under an infrared lamp for 6 hours to obtain a humidity sensor based on Fe-MOF-303 with a film thickness of 10 μm.

[0024] Example 2 (1) Dissolve 2.08 g of aluminum chloride hexahydrate and 2.0 g of 3,5-pyrazole dicarboxylic acid monohydrate in 144 mL of deionized water and stir magnetically for 0.5 h at room temperature to obtain a homogeneous mixed solution; (2) Dissolve 0.52g of sodium hydroxide in 5.48mL of deionized water and stir magnetically for 0.5h at room temperature to obtain a homogeneous sodium hydroxide solution; (3) The sodium hydroxide solution obtained in step (2) is added dropwise to the mixed solution obtained in step (1) at a rate of 0.25 mL / min, and the mixed solution is transferred to a reflux device and reacted under constant temperature magnetic stirring at 120 °C for 2 h. (4) After the reaction system of step (3) is naturally cooled to room temperature, the precipitate is washed by alternating centrifugation with deionized water and ethanol, and then dried to obtain MOF-303 powder; (5) Disperse 40 mg of ferric chloride and 0.2 g of MOF-303 powder obtained in step (4) together in 50 mL of acetonitrile to form a suspension, and heat at 80 °C for 12 h. (6) After cooling the solution from step (5) to room temperature, the precipitate was washed by alternating centrifugation with deionized water and ethanol, and then dried to obtain the Fe-MOF-303 sensitive material.

[0025] (7) Using an alumina ceramic sheet as a substrate, the alumina ceramic sheet is 20 mm long and 20 mm wide; 15 pairs of interdigitated electrodes with metal layer structures are deposited on the upper surface of the ceramic sheet by sputtering etching process. The metal layer structure consists of titanium, copper, nickel and gold layers from the inside to the outside, with thicknesses of 0.1 μm, 5 μm, 4 μm and 1 μm, respectively; the line width of the interdigitated electrode is 100 μm and the line spacing is 50 μm. (8) The upper surface of the alumina ceramic sheet obtained in step (7) was ultrasonically cleaned and dried in sequence with anhydrous ethanol and deionized water. (9) Disperse the prepared Fe-MOF-303 sensitive material in deionized water to prepare a uniform dispersion with a concentration of 30 mg / mL; drop the above solution onto the surface of the alumina ceramic sheet interdigitated electrode after drying in step (8), and then heat-treat it under an infrared lamp for 6 hours to obtain a humidity sensor based on Fe-MOF-303 with a film thickness of 10 μm.

[0026] Example 3 (1) Dissolve 2.08 g of aluminum chloride hexahydrate and 2.5 g of 3,5-pyrazole dicarboxylic acid monohydrate in 144 mL of deionized water and stir magnetically for 0.5 h at room temperature to obtain a homogeneous mixed solution; (2) Dissolve 0.52g of sodium hydroxide in 5.48mL of deionized water and stir magnetically for 0.5h at room temperature to obtain a homogeneous sodium hydroxide solution; (3) The sodium hydroxide solution obtained in step (2) is added dropwise to the mixed solution obtained in step (1) at a rate of 0.3 mL / min, and the mixed solution is transferred to a reflux device and reacted under constant temperature magnetic stirring at 130 °C for 2 h. (4) After the reaction system of step (3) is naturally cooled to room temperature, the precipitate is washed by alternating centrifugation with deionized water and ethanol, and then dried to obtain MOF-303 powder; (5) Disperse 60 mg of ferric chloride and 0.2 g of MOF-303 powder obtained in step (4) together in 60 mL of acetonitrile to form a suspension, and heat at 90 °C for 24 h. (6) After cooling the solution from step (5) to room temperature, the precipitate was washed by alternating centrifugation with deionized water and ethanol, and then dried to obtain the Fe-MOF-303 sensitive material.

[0027] (7) Using an alumina ceramic sheet as a substrate, the alumina ceramic sheet is 10 mm long and 10 mm wide; 20 pairs of interdigitated electrodes with metal layer structures are deposited on the upper surface of the ceramic sheet by sputtering etching process. The metal layer structure consists of titanium, copper, nickel and gold layers from the inside to the outside, with thicknesses of 0.3 μm, 10 μm, 6 μm and 3 μm, respectively; the linewidth of the interdigitated electrode is 200 μm and the line spacing is 100 μm; (8) The upper surface of the alumina ceramic sheet obtained in step (7) was ultrasonically cleaned and dried in sequence with anhydrous ethanol and deionized water. (9) Disperse the prepared Fe-MOF-303 sensitive material in deionized water to prepare a uniform dispersion with a concentration of 40 mg / mL; drop the above solution onto the surface of the alumina ceramic sheet interdigitated electrode after drying in step (8), and then heat-treat it under an infrared lamp for 6 hours to obtain a humidity sensor based on Fe-MOF-303 with a film thickness of 30 μm.

[0028] Example 4 (1) Dissolve 2.08 g of aluminum chloride hexahydrate and 1.5 g of 3,5-pyrazole dicarboxylic acid monohydrate in 144 mL of deionized water and stir magnetically for 0.5 h at room temperature to obtain a homogeneous mixed solution; (2) Dissolve 0.52g of sodium hydroxide in 5.48mL of deionized water and stir magnetically for 0.5h at room temperature to obtain a homogeneous sodium hydroxide solution; (3) The sodium hydroxide solution obtained in step (2) is added dropwise to the mixed solution obtained in step (1) at a rate of 0.35 mL / min, and the mixed solution is transferred to a reflux device and reacted under constant temperature magnetic stirring at 140 °C for 2 h. (4) After the reaction system of step (3) is naturally cooled to room temperature, the precipitate is washed by alternating centrifugation with deionized water and ethanol, and then dried to obtain MOF-303 powder; (5) Disperse 60 mg of ferric chloride and 0.2 g of MOF-303 powder obtained in step (4) together in 60 mL of acetonitrile to form a suspension, and heat at 80 °C for 12 h. (6) After cooling the solution from step (5) to room temperature, the precipitate was washed by alternating centrifugation with deionized water and ethanol, and then dried to obtain the Fe-MOF-303 sensitive material.

[0029] (7) Using an alumina ceramic sheet as a substrate, the alumina ceramic sheet is 20 mm long and 20 mm wide; 20 pairs of interdigitated electrodes with metal layer structures are deposited on the upper surface of the ceramic sheet by sputtering etching process. The metal layer structure consists of titanium, copper, nickel and gold layers from the inside to the outside, with thicknesses of 0.3 μm, 10 μm, 6 μm and 3 μm, respectively; the line width of the interdigitated electrode is 200 μm and the line spacing is 100 μm. (8) The upper surface of the alumina ceramic sheet obtained in step (7) was ultrasonically cleaned and dried in sequence with anhydrous ethanol and deionized water. (9) Disperse the prepared Fe-MOF-303 sensitive material in deionized water to prepare a uniform dispersion with a concentration of 50 mg / mL; drop the above solution onto the surface of the alumina ceramic sheet interdigitated electrode after drying in step (8), and then heat-treat it under an infrared lamp for 12 hours to obtain a humidity sensor based on Fe-MOF-303 with a film thickness of 50 μm.

[0030] Performance testing and characterization The Fe-MOF-303 sensitive material prepared in Example 1 and the humidity sensor based on this material were systematically characterized and their performance tested. The results are as follows: 1. X-ray diffraction (XRD) The X-ray diffraction patterns of the MOF-303 and Fe-MOF-303 sensitive materials prepared in Example 1 are as follows: Figure 1 As shown; by Figure 1 It can be seen that a series of diffraction peaks appearing at 2θ of 8.76° and 17.54° correspond to the (011) and (022) crystal planes of MOF-303, respectively. All diffraction peaks match the standard spectrum of MOF-303. No impurity phases related to iron oxide or elemental iron were detected, confirming that the introduction of Fe does not destroy the crystal structure of MOF-303 and does not form iron-based nanoparticles or clusters.

[0031] 2. Transmission electron microscopy (TEM) and elemental mapping characterization Transmission electron microscope images and corresponding elemental mapping diagrams of the Fe-MOF-303 sensitive material prepared in Example 1 are shown below. Figure 2 As shown, the Fe-MOF-303 sensitive material exhibits a regular cubic morphology, and C, Al, O, N, and Fe elements are uniformly distributed on the surface of the sensitive material. In addition, no nanoparticles or nanoclusters related to Fe species were observed in the TEM image, which preliminarily indicates that Fe was successfully introduced into the surface of MOF-303 in the form of single atoms.

[0032] 3. Synchrotron X-ray Absorption Fine Structure (XAFS) Characterization The structural and electronic configuration characterization diagrams of the Fe-MOF-303 sensitive material prepared in Example 1 are shown below. Figure 3 As shown; sub-figure a is the normalized FeK edge X-ray absorption near-edge structure (XANES) spectrum of Fe series reference sample and Fe-MOF-303 sensitive material. It can be seen that the absorption edge position of Fe-MOF-303 is located between the absorption edges of FeO and Fe2O3, indicating that the oxidation state of Fe in Fe-MOF-303 is between +2 and +3 valence.

[0033] Sub-figure b shows the normalized FeK edge extended X-ray absorption fine structure (EXAFS) spectra of the Fe series reference sample and the Fe-MOF-303 sensitive material. It can be seen that a distinct characteristic peak is observed at 1.44 Å, which is attributed to the coordination interaction of the Fe-N bond. No characteristic peaks corresponding to the Fe-Fe bond (2.18 Å) or the Fe-O bond (1.41 Å) were observed, further indicating that the Fe element in Fe-MOF-303 is dispersed in the form of single atoms on the MOF-303 support.

[0034] Sub-figure c shows the fitting curve of the above EXAFS spectrum. The fitting results show that the Fe-N bond length is 2.01 Å and the coordination number is about 4.1, indicating that the central Fe atom is coordinated with four N atoms, forming a stable Fe-N4 coordination configuration in the MOF-303 framework.

[0035] 4. Experiment to verify the mechanism of water molecule dissociation To verify the catalytic effect of the Fe-N4 active site on water molecule dissociation, a self-actuated device based on the original MOF-303 and Fe-MOF-303 was constructed. Its structural schematic diagram and voltage response comparison are shown below. Figure 4 As shown.

[0036] Sub-figure a shows the structure and working principle of the Fe-MOF-303 self-driven humidity sensor. It can be seen that Fe-MOF-303, as a catalytic solid electrolyte, actively dissociates adsorbed water molecules into protons (H+). + ) and hydroxide ions (OH) - Protons migrate to the cathode to participate in the hydrogen evolution reduction reaction, while the aluminum anode undergoes continuous oxidation, thereby generating a detectable voltage signal at both ends of the device.

[0037] Subfigure b is a bar chart comparing the output voltage of the self-driven humidity sensor based on the original MOF-303 and Fe-MOF-303 at 33% and 98% RH. It can be seen that within the tested humidity range, the output voltage of the Fe-MOF-303 sensor is much higher than that of the original MOF-303 sensor. This directly proves that the single-atom Fe-N4 site can effectively catalyze and significantly reduce the dissociation energy barrier of water molecules, thereby generating more free protons to participate in the conduction process.

[0038] 5. Impedance response performance across the entire humidity range The real-time impedance response curves of the Fe-MOF-303-based sensor prepared in Example 1 at 11-98% RH are shown below. Figure 5 As shown, the Fe-MOF-303 sensor exhibits excellent response performance across the entire humidity range. With increasing ambient humidity, its impedance value decreases significantly by four orders of magnitude (from 10 MΩ to 10 MΩ). -3(MΩ), and when the sensor is exposed to switch back to 0%RH, the sensor can quickly recover to its initial state, indicating that it has good reversibility.

[0039] 6. Low humidity detection limit The real-time impedance response curves of the Fe-MOF-303-based sensor prepared in Example 1 at 5% and 7% RH are shown below. Figure 6 As shown, the Fe-MOF-303 sensor still exhibits extremely high sensitivity in extremely low humidity environments, accurately and clearly distinguishing the minute humidity difference between 5%RH and 7%RH. The sensor's detection limit is as low as 5%RH, solving the problem of the sensing "blind zone" of traditional humidity sensors in low humidity environments.

[0040] 7. High-resolution detection performance The continuous monitoring curve of minute humidity changes by the Fe-MOF-303 sensor prepared in Example 1 at a 48.9% RH standard is shown below. Figure 7 As shown, the sensor can stably and continuously capture extremely small fluctuations in ambient humidity, achieving ultra-high resolution detection of up to 0.1%RH, demonstrating its great potential in complex environmental monitoring that requires high-precision humidity differentiation.

[0041] 8. Cyclic stability and repeatability The repeatability test curve of the Fe-MOF-3O3 sensor prepared in Example 1 at 85% RH is shown below. Figure 8 As shown, the impedance response curve and baseline of the sensor remain almost unchanged during the cyclic dynamic test of being exposed to the target humidity of 85%RH and then restored to the initial dry state. This indicates that the adsorption and dissociation process of water molecules based on the Fe-N4 active site has extremely high reversibility, which gives the sensor excellent cyclic stability and repeatability.

[0042] 9. Response and recovery time The response and recovery curves of the Fe-MOF-303-based sensor prepared in Example 1 at 85% RH are shown below. Figure 9 As shown, the sensor has an extremely fast response speed to sudden changes in ambient humidity, with a response time of only 6 seconds. This rapid response characteristic is due to the efficient chemical adsorption and dissociation mechanism of water molecules by the Fe-N4 active center.

[0043] The response and recovery curves of the Fe-MOF-303-based sensor prepared in Example 2 at 85% RH are shown below. Figure 10As shown, even with changes in preparation parameters such as precursor concentration and heat treatment process, the sensor still exhibits rapid response and recovery characteristics and stable sensing electrical signal to humidity changes; this further confirms the reliability of the preparation method described in this invention and the excellent process repeatability of the Fe-MOF-3O3 sensitive material.

[0044] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A metal-organic framework-based humidity sensor, having a planar structure, characterized in that: It includes a substrate based on alumina ceramic, interdigitated electrodes printed on the upper surface of the substrate, and a humidity-sensitive film coated on the surface of the interdigitated electrodes; The humidity-sensitive film is a single-atom Fe-modified MOF-303 (Fe-MOF-303) sensitive material. In the Fe-MOF-303 sensitive material, Fe atoms are dispersed in the form of single atoms on the MOF-303 support and coordinate with four N atoms in the MOF-303 framework to form a Fe-N4 coordination configuration.

2. The metal-organic framework-based humidity sensor according to claim 1, characterized in that: The thickness of the humidity-sensitive film is 10~50μm.

3. The metal-organic framework-based humidity sensor according to claim 1, characterized in that: The interdigitated electrode comprises 15 to 20 pairs of electrode fingers and is formed by sputtering etching. Its metal layer structure consists of a titanium layer, a copper layer, a nickel layer, and a gold layer from the inside out.

4. A metal-organic framework-based humidity sensor according to claim 3, characterized in that: The titanium layer has a thickness of 0.1~0.3μm, the copper layer has a thickness of 5~10μm, the nickel layer has a thickness of 4~6μm, and the gold layer has a thickness of 1~3μm.

5. A metal-organic framework-based humidity sensor according to claim 3, characterized in that: The linewidth of the interdigitated electrode is 100~200μm, and the line spacing is 50~100μm.

6. A method for preparing a metal-organic framework-based humidity sensor, characterized in that, When applied to a metal-organic framework-based humidity sensor as described in any one of claims 1 to 5, the method includes the following steps: S1 preparation of Fe-MOF-303 sensitive material; S2 is used to prepare an alumina ceramic substrate with interdigitated electrodes; S3 prepared a dispersion by dispersing Fe-MOF-303 sensitive material in deionized water, then drop-coated it onto the surface of the interdigitated electrode, and obtained a humidity sensor after heat treatment.

7. The method for preparing a metal-organic framework-based humidity sensor according to claim 6, characterized in that, The preparation of the Fe-MOF-303 sensitive material in step S1 includes the following sub-steps: S11 Dissolve 2.08 g of aluminum chloride hexahydrate and 1.5-2.5 g of 3,5-pyrazole dicarboxylic acid monohydrate in 144 mL of deionized water and stir magnetically at room temperature for 0.5 h to obtain a homogeneous mixed solution. S12 dissolves 0.52g of sodium hydroxide in 5.48mL of deionized water and stirs magnetically at room temperature for 0.5h to obtain a homogeneous sodium hydroxide solution; S13 Sodium hydroxide solution is added dropwise to the mixed solution at a rate of 0.25~0.35 mL / min, transferred to a reflux reflux device, and reacted under constant temperature magnetic stirring at 120~140℃ for 2 hours; The S14 reaction system was naturally cooled to room temperature. The precipitate was washed by alternating centrifugation with deionized water and ethanol, and then dried to obtain MOF-303 powder. S15 involves dispersing 20-60 mg of ferric chloride and 0.2 g of MOF-303 powder together in 40-60 mL of acetonitrile to form a suspension, and then heating the mixture at 70-90 °C for 12-24 h. The S16 reaction solution was cooled to room temperature, and the precipitate was washed by alternating centrifugation with deionized water and ethanol. The precipitate was then dried to obtain the Fe-MOF-303 sensitive material.

8. The method for preparing a metal-organic framework-based humidity sensor according to claim 6, characterized in that, Step S2 specifically involves: selecting an alumina ceramic sheet with a length of 10-20 mm and a width of 10-20 mm as a substrate, using a sputtering etching process to deposit 15-20 pairs of interdigitated electrodes as described in any one of claims 3 to 5 on the surface of the ceramic sheet, and then sequentially ultrasonically cleaning the surface of the ceramic sheet with anhydrous ethanol and deionized water, and drying it for later use.

9. The method for preparing a metal-organic framework-based humidity sensor according to claim 6, characterized in that, The concentration of the dispersion in step S3 is 30~50 mg / mL, and the heat treatment is heating under an infrared lamp for 6~12 hours.

10. An application of a metal-organic framework-based humidity sensor in humidity detection, characterized in that, The metal-organic framework-based humidity sensor is the metal-organic framework-based humidity sensor as described in any one of claims 1 to 5.

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