Gas sensor based on defect-state metal organic framework material, preparation method and application

Abstract

The invention belongs to the technical field of functional materials and gas sensing, and particularly relates to a gas sensor based on a defect-state metal organic framework material, a preparation method and application. In order to overcome the defects of the existing gas sensor in the aspects of sensitivity, selectivity, response speed and the like, a simple, convenient and efficient water treatment process is provided, the defect sites of two metal organic frameworks (ZIF-67 and MOF-74) are regulated and controlled, the specific surface area of the metal organic frameworks is increased, and the response of the ZIF-67 to ethylene gas and the response of the MOF-74 to acetone gas are remarkably improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of functional materials and gas sensing technology, and particularly relates to a gas sensor based on defective metal-organic framework materials, a preparation method and an application thereof. Background Art

[0002] In recent years, with the rapid development of the global economy, the problem of environmental pollution has become increasingly serious, posing a serious threat to human health and quality of life. Among various environmental pollutions, gas pollution is particularly prominent. In particular, the emissions of harmful gases not only damage the ecological environment but also pose a significant threat to human health. For example, the waste gas emitted by factories often contains toxic gases such as carbon monoxide (CO) and hydrogen sulfide (H 2 S), and these gases may trigger acute poisoning incidents. Man-made materials (such as plywood, paint, floor, etc.) widely used in indoor or enclosed places will also release volatile organic compounds (VOCs). Long-term exposure to these gases may lead to chronic respiratory diseases and even cancer. Facing these challenges, the research and application of gas detection technology are very important. By real-time and accurately monitoring the gas components in the environment, it can not only provide data support for the tracking and treatment of pollution sources but also prevent toxic gas leakage accidents in industrial production and improve safety.

[0003] Currently, the mainstream toxic gas detection technologies include electrochemistry, gas chromatography, mass spectrometry, and spectroscopy. Although they have good detection sensitivity and selectivity, the above technologies have disadvantages such as high cost, complex operation, and difficulty in miniaturization, making it difficult to achieve portability and real-time detection, which limits their wide popularization in actual scenarios. Therefore, developing new gas sensors with high sensitivity, high selectivity, low power consumption, and fast response has become the core research content in the field of gas detection. Among them, semiconductor gas sensors with low manufacturing cost and easy miniaturization just meet the above requirements and show great application potential. It can sensitively detect low-concentration gases in the environment and quickly convert the concentration change into an electrical signal, thereby realizing the efficient monitoring and alarm of toxic gases and providing a practical solution for portable and real-time gas detection.

[0004] According to the different sensing mechanisms of sensors, they can be divided into two major categories: resistance-controlled type and non-resistance-controlled type. Resistance-controlled gas sensors detect gas concentration by monitoring the change in conductivity caused by the reaction between the gas and the sensing material. Non-resistance-controlled gas sensors include field-effect transistor type, capacitance type, and diode type sensors, which calculate gas concentration by monitoring the change in threshold voltage, capacitance change, or diode rectification characteristics, respectively. Among them, resistive gas sensors can adapt to a variety of gases, and their output signals are convenient to integrate with other electronic components, making them suitable for real-time monitoring and control systems. Therefore, they are widely used in the fields of air quality monitoring, industrial waste gas detection, and environmental protection. Resistive gas sensors usually consist of a heating element, electrodes, a signal processing circuit, a protective housing, a substrate, and a sensing material. The heating element is used to provide the working temperature to enhance the reaction performance of the sensitive layer; the electrodes are responsible for detecting the resistance change of the material and transmitting signals; the signal processing circuit amplifies the output signal; the protective housing is used to prevent interference from the external environment; the substrate provides structural support for the entire sensor, and the sensing material is the core part, which detects gas concentration by causing a change in conductivity through reaction with gas molecules. Therefore, the detection performance of resistive gas sensors depends to a large extent on the gas adsorption rate or the reaction activity of the sensing material. Therefore, it is required that the sensing material has a large number of pores, a large specific surface area, and high catalytic activity. Therefore, how to select a suitable sensing material to meet the application requirements is the key to designing resistive gas sensors.

[0005] Currently, common sensing materials include metal oxides, metal sulfides, conductive polymers, carbon-based materials, and MXenes, etc. These materials have their own advantages and disadvantages. For example, metal oxides are widely used due to their high sensitivity and selectivity, but they have problems such as high working temperature and poor stability; metal sulfides have excellent mechanical properties and sensitivity, but toxic substances may be produced during the synthesis process; conductive polymers and carbon-based materials have good biocompatibility and plasticity, but their long-term stability is insufficient; although MXenes have excellent performance, their high production cost limits their applications. Against this background, metal-organic frameworks (MOFs), as a new type of porous crystalline material, stand out. MOFs are crystalline network structures formed by the coordination of metal ions or clusters with organic ligands. Due to their extremely high specific surface area, high porosity, biocompatibility, structural diversity, and tunable functionality, etc., they have developed rapidly and have been applied in multiple fields, such as electrochemical energy storage, catalysis, drug delivery and release, gas adsorption and separation, etc. In the field of gas detection, relying on their ultra-high specific surface area, porous structure, and tunable surface functional groups, MOFs can not only provide abundant adsorption sites and channels for gas molecules, significantly improving the sensitivity of the sensor, but also achieve highly selective detection of specific gases by precisely designing the pore size and regulating the surface properties. At the same time, MOFs have excellent chemical and thermal stability as well as the ability to dynamically adjust adsorption and desorption characteristics, ensuring their long-term stability and detection performance in complex environments, and becoming a current research hotspot and an important direction for future development.

[0006] As a crystalline material, MOFs also have properties similar to other solid materials, that is, there may be defects in their crystal lattices, and these defects will have a significant impact on their physical properties. The defects of MOFs will change their pore size, specific surface area, distribution of metal active sites, and functional groups, thus having a profound impact on the performance of the material. Compared with perfect crystals, although the existence of defects may reduce the stability of MOF materials, they can show more excellent performance than perfect crystals in aspects such as adsorption, separation, catalysis, and conductivity. During the preparation process of MOF materials, introducing defects is an effective strategy to improve their performance. To introduce defects into MOF materials, methods such as doping different metals or high-temperature annealing are often used to form some metal / ligand defects, but there are many external interference factors in such methods, and it is difficult to controllably adjust the defect concentration of MOFs.

[0007] Therefore, how to provide a sensor with low gas detection cost, high stability, and simple operation is a technical problem that needs to be solved urgently by those skilled in the art. Summary of the Invention

[0008] In view of this, the present invention discloses and provides a gas sensor, a preparation method, and an application based on a defect-state metal-organic framework material.

[0009] It should be noted that the present invention adopts a simple water treatment method to induce defects on two typical MOFs materials (ZIF-67 and MOF-74), precisely regulate their pore structures, and increase active sites. The gas sensor prepared thereby has achieved significant performance improvement during the detection of target gases. This method provides an innovative idea for designing high-performance gas sensors and demonstrates great application potential in fields such as air quality monitoring and industrial harmful gas detection.

[0010] To achieve the above object, the present invention adopts the following technical solutions:

[0011] The first technical object of the present invention is to provide a gas sensor based on a defective metal-organic framework material. The defective MOFs material with high active sites is uniformly dispersed in a solution, and is coated on an interdigital electrode by a drop coating method to form a flat and stable gas-sensitive film, thereby obtaining the gas sensor.

[0012] Furthermore, the defective MOFs material with high active sites is induced from the MOFs material by water treatment, and the MOFs material is ZIF-67 or MOF-74.

[0013] The second technical object of the present invention is to provide a preparation method of the gas sensor based on the defective metal-organic framework material as described above. The method specifically includes the following steps:

[0014] 1) Preparation of defective Def-MOFs

[0015] Respectively place 50 - 200 mg of ZIF-67 and MOF-74 statically in 20 - 50 mL of deionized water. The soaking time of ZIF-67 is 4 - 16 h, and the soaking time of MOF-74 is 4 - 48 h. The soaking process is carried out within the temperature range of 20 - 50 °C, and then freeze-dry at -40 to -80 °C for 12 - 72 h to obtain the gas-sensitive material Def-ZIF-67 or the gas-sensitive material Def-MOF-74;

[0016] 2) Preparation of the Def-MOFs gas sensor

[0017] Disperse the gas-sensitive material prepared in step 1) in a solvent to obtain a uniform gas-sensitive material slurry; uniformly coat the gas-sensitive material slurry on the surface of the interdigital electrode to form a gas-sensitive film, and heat-treat within the temperature range of 40 - 80 °C to remove the solvent, and finally obtain the Def-MOFs gas sensor.

[0018] It should be noted that in view of the problem that the performance of gas sensors depends on the reactivity of sensing materials, the present invention adopts a simple water treatment method. By inducing partial detachment of metal clusters or ligands by water molecules, defective MOF materials with high active sites are precisely generated, thereby significantly improving the adsorption capacity for target gases. Subsequently, the prepared defective MOFs are uniformly dispersed in a solution, and the solution is coated on interdigital electrodes by a drop-coating method to form a flat and stable gas-sensitive film. This method develops a new preparation process for defective MOFs, and based on this process, a new type of defective MOF-based gas sensor is successfully prepared, which has the characteristics of simplicity, low cost, and excellent sensing performance, providing an efficient and practical technical solution for the research and development of high-performance and low-cost gas sensors.

[0019] Further, the preparation operation of the ZIF-67 is as follows:

[0020] Take 0.29 - 0.58 g of cobalt(II) nitrate hexahydrate (Co(NO 3 ) 2 ·6H 2 O) and 0.74 - 2.63 g of 2-methylimidazole (2-MeIm) and dissolve them in 40 ml of anhydrous methanol respectively. Mix the two solutions so that the molar ratio of Co 2+ to 2-MeIm is 1:9 - 16; after stirring the mixture for 0.5 - 2 h, place it in the inner liner of a polytetrafluoroethylene reaction kettle, heat it to 100 - 150 °C, keep it for 24 h - 48 h and then cool it naturally; centrifuge to collect the obtained purple precipitate, wash it with anhydrous methanol 3 - 5 times, and finally vacuum dry it at 50 - 100 °C for 12 - 24 h to obtain ZIF-67 powder.

[0021] Further, the preparation operation of the MOF-74 is as follows:

[0022] Take 0.25 - 3.26 g of nickel(II) acetate tetrahydrate (Ni(CH 3 COO) 2 ·4H 2 O) and dissolve it in 30 - 60 ml of deionized water, and 0.19 - 0.52 g of 2,5-dihydroxyterephthalic acid (DHTPA) and dissolve it in 30 - 50 ml of tetrahydrofuran. Mix the two solutions so that the molar ratio of Ni 2+ to DHTPA is 2 - 5:1, stir evenly at room temperature, place it in the inner liner of a high-pressure reaction kettle, heat it at 100 - 150 °C and keep it for 24 - 48 h and then cool it naturally; centrifuge to collect the obtained precipitate, wash it with water and anhydrous ethanol 3 - 5 times, and vacuum dry it at 50 - 100 °C for 12 - 24 h to obtain MOF-74 powder.

[0023] Further, before coating the gas-sensitive material slurry on the surface of the interdigital electrode, the interdigital electrode sheet needs to be cleaned. The interdigital electrode sheet is placed in a mixed solution of deionized water and ethanol with a volume ratio of 1:2 to 10, ultrasonically cleaned for 0.5 to 2 h, and dried at a temperature in the range of 30 to 60 °C for 3 to 6 h to ensure the cleanliness of its surface.

[0024] Further, in order to improve the stability and repeatability of the gas-sensitive element, the gas-sensitive element is subjected to heat aging treatment.

[0025] The third technical object of the present invention is to provide an application of the gas sensor based on the defective metal-organic framework material as described above in the field of gas detection.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] (1) By introducing metal-organic framework (MOFs) materials, the present invention significantly improves the performance of the gas sensor by utilizing its many advantages. First of all, MOFs have a large specific surface area, an ultra-high porosity, and a rich and diverse topological structure, providing sufficient adsorption active sites for gas molecules and enhancing the interaction between the material and gas analytes. Secondly, its customizable pore cavities (pore size and geometric shape) not only accelerate the pre-concentration and enrichment of gases, but also achieve specific screening of gas molecules with different kinetic diameters through a unique molecular sieve effect. In addition, the organic ligands of MOFs can have reversible chemical interactions with specific gas molecules due to their rich functional groups, effectively improving the adsorption and desorption efficiency of gases and enhancing the reuse rate of the sensor. At the same time, its excellent structural stability ensures the reliability of the sensor during long-term use, providing strong support for the development of high-performance gas sensors.

[0028] (2) The present invention adopts a simple and efficient water treatment method to break the MOFs connection bonds through water molecules, resulting in the loss of metal clusters or ligands in the material. By controlling the water treatment time, a material with controllable defects is generated. This method not only has a simple process and easy regulation of the defect concentration, but also significantly increases the specific surface area of the sensing material, thereby enhancing its gas adsorption capacity and achieving the purpose of enhancing the sensitivity of the sensor.

[0029] (3) The defective MOFs gas sensor prepared by the present invention exhibits excellent sensitivity and selectivity in high humidity and complex gas environments due to the excellent chemical stability and dynamic adsorption capacity of the material, ensuring the accuracy and reliability of detection.

[0030] (4) The gas sensor designed by the present invention focuses on miniaturization and low energy consumption, meets the application requirements of portable devices, and can achieve real-time and efficient detection of target gases. Through a simplified preparation process and modular design, it not only effectively reduces the production cost, but also improves the stability and durability of the sensor. The sensor exhibits excellent performance in fields such as environmental monitoring and safety protection, providing a reliable solution for efficient and economical gas detection. Brief Description of the Drawings

[0031] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained according to the provided drawings.

[0032] Figure 1 It is the process flow chart of the preparation of the Def-ZIF-67 gas sensor based on the present invention.

[0033] Figure 2 It is the process flow chart of the preparation of the Def-MOF-74 gas sensor based on the present invention.

[0034] Figure 3 It is the physical diagram of the Def-ZIF-67 gas sensor and the Def-MOF-74 gas sensor based on the present invention.

[0035] Figure 4 It is the comparison of the morphological and elemental composition changes of MOFs (ZIF-67) before and after water treatment based on the present invention.

[0036] Figure 5 It is the comparison of the morphological and elemental composition changes of MOFs (MOF-74) before and after water treatment based on the present invention.

[0037] Figure 6 It is the real-time response curve of the Def-ZIF-67 gas sensor based on the present invention to different concentrations of ethylene (C 2 H 4 )(5 - 70 ppm).

[0038] Figure 7 It is the Def-ZIF-67 gas sensor of the present invention and the Def-ZIF-67 gas sensor after 16 hours of water treatment for different gases (ethylene (C 2 H 4 ), nitrogen dioxide (NO 2 ), ammonia (NH 3 ), acetone (C 3 H 6 O), carbon dioxide (CO 2Responsivity graph of ( )

[0039] Figure 8 This is the real-time response curve of the Def-MOF-74 gas sensor of the present invention to acetone (C 3 H 6 O) at different concentrations (15 - 100 ppm). Detailed implementation manners

[0040] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0041] The special term "embodiment" used here does not necessarily mean that any embodiment described as "exemplary" is better than or superior to other embodiments. For the performance index tests in the embodiments of this application, unless otherwise specified, conventional test methods in the art are adopted. It should be understood that the terms described in this application are only used to describe specific embodiments and are not intended to limit the content disclosed in this application.

[0042] Unless otherwise specified, the technical and scientific terms used herein have the same meanings as commonly understood by those of ordinary skill in the technical field to which this application belongs; other test methods and technical means not specifically noted in this application refer to the experimental methods and technical means commonly adopted by those of ordinary skill in the art.

[0043] In the description of the present invention, it should be understood that the orientation or positional relationships indicated by the terms "in", "on", "under", "rise", "fall", "vertical", "plane", "top", "bottom", "inside", "outside", etc. are based on the orientation or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus cannot be construed as a limitation of the present invention.

[0044] To better illustrate the content of this application, numerous specific details are given in the following specific embodiments. Those skilled in the art should understand that the application can be implemented without some specific details. In the embodiments, some methods, means, instruments, devices, etc. well known to those skilled in the art are not described in detail to highlight the gist of this application.

[0045] On the premise of no conflict, the technical features disclosed in the embodiments of this application can be combined arbitrarily, and the obtained technical solutions belong to the content disclosed in the embodiments of this application.

[0046] The present invention discloses a gas sensor based on defective metal-organic framework materials and a preparation method thereof. Through a simple and rapid water treatment method, the complex processes and high costs in traditional defect generation are avoided, and the limitations of traditional gas sensors in terms of sensitivity, selectivity, and cost control are successfully solved.

[0047] The technology of the present invention has the following advantages:

[0048] 1. The water treatment method is simple to operate, without the need for high temperature or complex equipment. This method is applicable to a variety of MOFs materials, and defects can be introduced only by soaking MOFs at room temperature. The preparation process is simple, efficient, environmentally friendly, and low-cost.

[0049] 2. The defective MOFs materials have a higher specific surface area and more active sites, significantly improving the sensitivity and selectivity of the gas sensor. It performs excellently especially in the detection of low-concentration target gases, and at the same time has long-term stability and can adapt to complex environmental conditions.

[0050] 3. The overall device design is reasonable, the sensor structure is compact, and at the same time, the low-power consumption characteristic is achieved through material optimization. The process flow has strong universality and is suitable for large-scale promotion in industrial production, providing an efficient and reliable technical solution for the development and practical application of high-performance gas sensors.

[0051] To better understand the present invention, the following further specifically elaborates the present invention through the following embodiments, but it should not be understood as a limitation of the present invention. For some non-essential improvements and adjustments made by those skilled in the art according to the above invention content, they are also considered to fall within the protection scope of the present invention.

[0052] Example 1

[0053] A preparation method of a gas sensor based on defective metal-organic framework materials includes the following steps:

[0054] 1) Preparation of ZIF-67

[0055] Take 0.58 g (2.4 mmol) of cobalt(II) nitrate hexahydrate (Co(NO 3 ) 2 ·6H 2 O) and 2.63 g (32.0 mmol) of 2-methylimidazole (2-MeIm) and dissolve them separately in 40 ml of anhydrous methanol. Mix the two solutions (the molar ratio of Co 2+ to 2-MeIm is 1:16). After the mixture is stirred evenly, place it in the inner liner of a polytetrafluoroethylene reaction kettle, heat it to 115 °C, keep it for 24 h and then cool it naturally. Centrifuge to collect the obtained purple precipitate, wash it 3 times with anhydrous methanol, and finally dry it under vacuum at 80 °C for 12 h to obtain ZIF-67 powder.

[0056] 2) Preparation of MOF-74

[0057] Take 1.31 g (5.26 mmol) of nickel acetate tetrahydrate (Ni(CH 3 COO) 2 ·4H 2 O) and dissolve it in 35 ml of deionized water, and dissolve 0.52 g (2.62 mmol) of 2,5-dihydroxyterephthalic acid (DHTPA) in 35 ml of tetrahydrofuran. Mix the two solutions (the molar ratio of Ni 2+ to DHTPA is 2:1), stir evenly at room temperature, place it in the inner liner of a high-pressure reactor, heat to 110 °C, keep it for 24 h and then cool naturally. Centrifuge to collect the obtained precipitate, wash it 3 times with water and absolute ethanol, and vacuum dry it at 80 °C for 12 h to obtain MOF-74 powder.

[0058] 3) Preparation of Defective Def-MOFs

[0059] Place the prepared ZIF-67 and MOF-74 separately in 30 mL of deionized water. The soaking time of ZIF-67 is 16 h, and the soaking time of MOF-74 is 48 h. The soaking process is carried out in the temperature range of 25 °C. Freeze-dry the samples at -45 °C for 48 h to obtain Def-ZIF-67 and Def-MOF-74 samples.

[0060] 4) Preparation of Def-MOFs Gas Sensors

[0061] Drop the gas-sensitive material onto the interdigital electrode by hand to form a uniform gas-sensitive film. The specific operation method is as follows: First, clean the interdigital electrode chip. Put the interdigital electrode chip into a mixed solution of deionized water and ethanol with a volume ratio of 1:2, ultrasonically clean it for 1 h and dry it at 60 °C for 6 h to ensure its surface is clean. Then, disperse the prepared gas-sensitive material (Def-ZIF-67 or Def-MOF-74) in a solvent, and after ultrasonic treatment, obtain a uniform gas-sensitive material slurry. Then connect the interdigital electrode to the tube socket, and evenly coat the gas-sensitive material slurry on the surface of the pretreated interdigital electrode to form a gas-sensitive film, and remove the solvent by heating treatment at 60 °C. In addition, in order to improve the stability and repeatability of the gas-sensitive element, heat-aging treatment is carried out on the gas-sensitive element, and finally a Def-MOFs gas sensor that can be used for gas-sensitive performance testing is obtained.

[0062] Example 2

[0063] A preparation method of a gas sensor based on defective metal-organic framework materials, comprising the following steps:

[0064] 1) Preparation of ZIF-67

[0065] Take 0.29 g (1.0 mmol) of cobalt(II) nitrate hexahydrate (Co(NO 3 ) 2 ·6H 2 O) and 0.99 g (12.0 mmol) of 2-methylimidazole (2-MeIm) and dissolve them separately in 40 ml of anhydrous methanol. Mix the two solutions (the molar ratio of Co 2+ to 2-MeIm is 1:12). After stirring the mixture evenly, place it in the inner liner of a polytetrafluoroethylene reaction kettle, heat it to 100 °C, keep it for 48 h and then cool it naturally. Centrifuge to collect the obtained purple precipitate, wash it 3 times with anhydrous methanol, and finally dry it in vacuum at 60 °C for 12 h to obtain ZIF-67 powder.

[0066] 2) Preparation of MOF-74

[0067] Take 1.31 g (5.26 mmol) of nickel(II) acetate tetrahydrate (Ni(CH 3 COO) 2 ·4H 2 O) and dissolve it in 35 ml of deionized water. Dissolve 0.52 g (2.62 mmol) of 2,5-dihydroxyterephthalic acid (DHTPA) in 35 ml of tetrahydrofuran. Mix the two solutions (the molar ratio of Ni 2+ to DHTPA is 2:1), stir evenly at room temperature, place it in the inner liner of a high-pressure reaction kettle, heat it to 110 °C, keep it for 24 h and then cool it naturally. Centrifuge to collect the obtained precipitate, wash it 3 times with water and anhydrous ethanol, and dry it in vacuum at 80 °C for 12 h to obtain MOF-74 powder.

[0068] 3) Preparation of defective Def-MOFs

[0069] Place the prepared ZIF-67 and MOF-74 separately in 30 mL of deionized water. The soaking time of ZIF-67 is 16 h, and the soaking time of MOF-74 is 48 h. The soaking process is carried out within the temperature range of 25 °C. Freeze-dry the samples at -45 °C for 48 h to obtain Def-ZIF-67 and Def-MOF-74 samples.

[0070] 4) Preparation of Def-MOFs gas sensors

[0071] The gas-sensitive material is drop-coated on the interdigital electrode by a manual method to form a uniform gas-sensitive film. The specific operation method is as follows: First, clean the interdigital electrode sheet. Put the interdigital electrode sheet into a mixed solution of deionized water and ethanol with a volume ratio of 1:2, ultrasonically clean it for 1 h and dry it at 60 °C for 6 h to ensure its surface is clean. Then, disperse the prepared gas-sensitive material (Def-ZIF-67 or Def-MOF-74) in a solvent, and after ultrasonic treatment, a uniform gas-sensitive material slurry is obtained. Next, connect the interdigital electrode to the tubular socket, and uniformly coat the gas-sensitive material slurry on the surface of the pretreated interdigital electrode to form a gas-sensitive film, and remove the solvent by heat treatment at 60 °C. In addition, to improve the stability and repeatability of the gas-sensitive element, the gas-sensitive element is subjected to heat aging treatment, and finally a Def-MOFs gas sensor that can be used for gas-sensing performance testing is obtained.

[0072] Example 3

[0073] A preparation method of a gas sensor based on a defective metal-organic framework material, comprising the following steps:

[0074] 1) Preparation of ZIF-67

[0075] Take 0.29 g (1.0 mmol) of cobalt nitrate hexahydrate (Co(NO 3 ) 2 ·6H 2 O) and 0.74 g (9.0 mmol) of 2-methylimidazole (2-MeIm) and dissolve them separately in 40 ml of anhydrous methanol. Mix the two solutions (the molar ratio of Co 2+ to 2-MeIm is 1:9). After the mixture is stirred evenly, place it in the inner liner of a polytetrafluoroethylene reaction kettle, heat it to 130 °C, keep it for 24 h and then cool it naturally. Centrifuge to collect the obtained purple precipitate, wash it 3 times with anhydrous methanol, and finally vacuum dry it at 60 °C for 12 h to obtain ZIF-67 powder.

[0076] 2) Preparation of MOF-74

[0077] Take 1.37 g (5.5 mmol) of nickel acetate tetrahydrate (Ni(CH 3 COO) 2 ·4H 2 O) and dissolve it in 35 ml of deionized water, and 0.19 g (1.1 mmol) of 2,5-dihydroxyterephthalic acid (DHTPA) and dissolve it in 35 ml of tetrahydrofuran. Mix the two solutions (Ni 2+The molar ratio with DHTPA was 5:1), and it was stirred evenly at room temperature, placed in the inner liner of a high-pressure reactor, heated to 110 °C, kept for 24 h and then naturally cooled. The obtained precipitate was collected by centrifugation, washed 3 times with water and absolute ethanol, and vacuum-dried at 80 °C for 12 h to obtain MOF-74 powder.

[0078] 3) Preparation of defective Def-MOFs

[0079] The prepared ZIF-67 and MOF-74 were respectively placed statically in 50 mL of deionized water. The soaking time of ZIF-67 was 4 h, and the soaking time of MOF-74 was 12 h. The soaking process was carried out within the temperature range of 25 °C. The samples were freeze-dried at -45 °C for 72 h to obtain Def-ZIF-67 and Def-MOF-74 samples.

[0080] 4) Preparation of Def-MOFs gas sensors

[0081] The gas-sensitive material was drop-coated on the interdigital electrode by a manual method to form a uniform gas-sensitive film. The specific operation method was as follows: First, the interdigital electrode sheet was cleaned. The interdigital electrode sheet was put into a mixed solution with a volume ratio of deionized water to ethanol of 1:5, ultrasonically cleaned for 2 h and dried at 60 °C for 6 h to ensure its surface was clean. Then, the prepared gas-sensitive material (Def-ZIF-67 or Def-MOF-74) was dispersed in a solvent, and after ultrasonic treatment, a uniform gas-sensitive material slurry was obtained. Then, the interdigital electrode was connected to the tube socket, and the gas-sensitive material slurry was evenly coated on the surface of the pretreated interdigital electrode to form a gas-sensitive film, and the solvent was removed by heat treatment at 60 °C. In addition, in order to improve the stability and repeatability of the gas-sensitive element, the gas-sensitive element was subjected to heat aging treatment, and finally, a Def-MOFs gas sensor that could be used for gas-sensing performance testing was obtained.

[0082] In order to further prove the beneficial effects of the present invention and better understand the present invention, the following comparative examples and test examples further illustrate the technical features disclosed in the present invention, but it should not be understood as a limitation to the present invention. For other improvements made by those skilled in the art based on the above-mentioned invention content without creative work, they are also considered to fall within the protection scope of the present invention.

[0083] Comparative Example 1

[0084] A preparation method of a gas sensor based on a metal-organic framework material, comprising the following steps:

[0085] 1) Preparation of ZIF-67

[0086] Take 0.58 g (2.4 mmol) of cobalt(II) nitrate hexahydrate (Co(NO 3 ) 2 ·6H2 O) and 2.63 g (32.0 mmol) of 2-methylimidazole (2-MeIm) were separately dissolved in 40 ml of anhydrous methanol. The two solutions were mixed (the molar ratio of Co 2+ to 2-MeIm was 1:16). After the mixture was stirred evenly, it was placed in the inner liner of a polytetrafluoroethylene reaction kettle, heated to 115 °C, kept for 24 h, and then naturally cooled. The purple precipitate obtained was collected by centrifugation, washed 3 times with anhydrous methanol, and finally dried in vacuo at 80 °C for 12 h to obtain ZIF-67 powder.

[0087] 2) Preparation of MOF-74

[0088] Take 1.31 g (5.26 mmol) of nickel acetate tetrahydrate (Ni(CH 3 COO) 2 ·4H 2 O) and dissolve it in 35 ml of deionized water, and dissolve 0.52 g (2.62 mmol) of 2,5-dihydroxyterephthalic acid (DHTPA) in 35 ml of tetrahydrofuran. The two solutions were mixed (the molar ratio of Ni 2+ to DHTPA was 2:1), stirred evenly at room temperature, placed in the inner liner of a high-pressure reaction kettle, heated to 110 °C, kept for 24 h, and then naturally cooled. The precipitate obtained was collected by centrifugation, washed 3 times with water and anhydrous ethanol, and dried in vacuo at 80 °C for 12 h to obtain MOF-74 powder.

[0089] 3) Preparation of MOFs gas sensors

[0090] The gas-sensitive material was drop-coated on the interdigital electrode by a manual method to form a uniform gas-sensitive film. The specific operation method is as follows: First, clean the interdigital electrode sheet, put the interdigital electrode sheet into a mixed solution of deionized water and ethanol with a volume ratio of 1:2, ultrasonically clean for 1 h and dry at 60 °C for 6 h to ensure its surface is clean. Then, disperse the prepared gas-sensitive material (ZIF-67 or MOF-74) in a solvent, and after ultrasonic treatment, a uniform gas-sensitive material slurry is obtained. Then connect the interdigital electrode to the tubular socket, and evenly coat the gas-sensitive material slurry on the surface of the pretreated interdigital electrode to form a gas-sensitive film, and remove the solvent by heating at 60 °C. In addition, in order to improve the stability and repeatability of the gas-sensitive element, the gas-sensitive element was subjected to heat aging treatment, and finally a MOFs gas sensor that can be used for gas-sensitive performance testing was obtained.

[0091] The test content is as follows:

[0092] As Figure 4, Morphological observation revealed that ZIF-67 presented a bright and smooth surface and a clear dodecahedral structure, while the Def-ZIF-67 sample treated with water showed a rough surface and an irregular shape. In addition, the elemental composition results showed that compared with ZIF-67, the atomic ratio of oxygen element (O) in Def-ZIF-67 increased from 22.4% to 36.4%, and the cobalt element (Co) increased from 5.0% to 17.5%. These results indicated the synthesis of defective ZIF-67.

[0093] As Figure 5 , compared with the original MOF-74 sample, the morphology of Def-MOF-74 showed significant morphological differences, and obvious changes also occurred in the atoms and mass percentages of the constituent elements, indicating that water treatment effectively induced the formation of defect sites, resulting in changes in its surface and structure.

[0094] As Figure 6 , as the concentration of ethylene (C 2 H 4 ) increased, the Def-ZIF-67 with an increasing number of water-induced defect sites showed a linear increase in its response degree, and compared with the ZIF-67 gas sensor, it could exhibit a higher response intensity. The response degree to 70 ppm ethylene was even as high as 3.71 times that of the ZIF-67 gas sensor.

[0095] As Figure 7 , the Def-ZIF-67 gas sensor showed that the response intensities to ethylene (C 2 H 4 ), nitrogen dioxide (NO 2 ), ammonia (NH 3 ), acetone (C 3 H 6 O), and carbon dioxide (CO 2 ) were enhanced by 2.3, 1.5, 1.3, 2.1, and 1.7 times respectively compared with the untreated ZIF-67. This indicated that the introduction of defects effectively improved the adsorption ability of ZIF-67 to ethylene and other gases, and the defective materials showed more superior performance in the detection of various gases.

[0096] As Figure 8 , under the action of water treatment, MOF-74 also showed a significant improvement in the response performance to acetone, presenting a linear growth trend, up to 2.97 times that of MOF-74 at most.

[0097] The foregoing description of the disclosed embodiments enables those skilled in the art to practice or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A gas sensor based on defective metal organic framework material, characterized in that: The defective MOFs material with high active sites is uniformly dispersed in a solution, and coated on the interdigital electrodes by a drop coating method to form a flat and stable gas-sensitive film, thereby preparing the gas sensor.

2. The gas sensor based on defective metal organic framework material according to claim 1, characterized in that: The defective MOFs material with high active sites is induced by water treatment of the MOFs material, and the MOFs material is ZIF-67 or MOF-74.

3. A method for preparing a gas sensor based on a defective metal organic framework material as claimed in claim 1, characterized in that: The method specifically comprises the following steps: 1) Preparation of defective Def-MOFs The ZIF-67 and MOF-74 are respectively placed in deionized water for immersion, and then freeze-dried to obtain the gas-sensitive material Def-ZIF-67 or the gas-sensitive material Def-MOF-74; 2) Preparation of Def-MOFs gas sensor The gas-sensitive material prepared in step 1) is dispersed in a solvent to obtain a uniform gas-sensitive material slurry; the gas-sensitive material slurry is uniformly coated on the surface of the interdigital electrode to form a gas-sensitive film, and the solvent is removed by heating to finally obtain the Def-MOFs gas sensor.

4. The method according to claim 3, characterized in that The preparation operation of ZIF-67 is as follows: Take 0.29-0.58g of cobalt nitrate hexahydrate (Co(NO3)2·6H2O) and 0.74-2.63g of 2-methylimidazole (2-MeIm) and dissolve them in 40ml of anhydrous methanol respectively. Mix the two solutions to make Co(NO3)2·6H2O. 2+ The molar ratio of ZIF-67 to 2-MeIm is 1:9-16; after the mixture is stirred for 0.5-2h, it is placed in a polytetrafluoroethylene reactor, heated to 100-150°C, maintained for 24h-48h and then naturally cooled; the purple precipitate is collected by centrifugation, washed with anhydrous methanol for 3-5 times, and finally vacuum dried at 50-100°C for 12-24h to obtain ZIF-67 powder.

5. The method according to claim 3, characterized in that: The preparation operation of MOF-74 is as follows: Take 0.25-3.26g of nickel acetate tetrahydrate (Ni(CH3COO)2·4H2O) and dissolve it in 30-60ml of deionized water. Dissolve 0.19-0.52g of 2,5-dihydroxyterephthalic acid (DHTPA) in 30-50ml of tetrahydrofuran. Mix the two solutions to make Ni 2+ The molar ratio of the precipitate to DHTPA is 2 to 5:1, stirred evenly at room temperature, placed in an inner tank of a high-pressure reactor, heated at 100 to 150° C. and maintained for 24 to 48 hours, and then naturally cooled; the precipitate obtained is collected by centrifugation, washed with water and anhydrous ethanol for 3 to 5 times, and vacuum dried at 50 to 100° C. for 12 to 24 hours to obtain MOF-74 powder.

6. The method according to claim 3, characterized in that Before applying the gas-sensitive material slurry to the surface of the interdigitated electrode, the interdigitated electrode sheet needs to be cleaned. The interdigitated electrode sheet is placed in a mixed solution of deionized water and ethanol in a volume ratio of 1:2 to 10, ultrasonically cleaned for 0.5 to 2 hours, and dried at a temperature range of 30 to 60°C for 3 to 6 hours to ensure that its surface is clean.

7. The method according to claim 3, characterized in that In step 1), the amount ratio of ZIF-67 or MOF-74 to water is 50-200 mg: 20-50 mL, the soaking temperature is 20-50° C., and the soaking time of ZIF-67 is 4-16 h, and the soaking time of MOF-74 is 4-48 h.

8. The method according to claim 3 or 7, characterized in that: The freeze-drying temperature in step 1) is -40 to -80°C, and the freeze-drying time is 12 to 72 hours.

9. The method according to claim 3, characterized in that: The heating treatment temperature in step 2) is 40 to 80°C.

10. Use of the gas sensor based on defective metal organic framework material as claimed in claim 1 or the gas sensor based on defective metal organic framework material prepared by the method as claimed in claim 3 in the field of gas detection.

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