A flexible MOFs-based gas sensor capable of identifying multi-component VOCs in real time and a preparation method and application thereof

Abstract

The present application relates to the technical fields of gas sensor and atmospheric environment monitoring, and particularly relates to a flexible MOFs-based gas sensor capable of real-time identification of multi-component VOCs, a preparation method and application thereof, wherein the preparation method uses a polyimide film as a substrate, after substrate pretreatment and electrode deposition, suspensions of three MOFs are respectively dropped into each independent sensing electrode area of the interdigital electrode, and vacuum drying is performed to form three MOF sensing layers, then hydrophobic modification is performed by using PFDTES, thereby obtaining the flexible MOFs-based gas sensor capable of real-time identification of multi-component VOCs. The preparation method is simple in operation and easy for industrialized production, and the flexible MOFs-based gas sensor prepared by the method has excellent mechanical flexibility, mechanical stability, humidity resistance, temperature stability, long-term stability, and can realize accurate real-time identification of multi-component VOCs. The gas sensor is applied to atmospheric environment monitoring, and has good application prospect.

Description

Technical Field

[0001] This invention relates to the field of gas sensor and atmospheric environment monitoring technology, specifically to a flexible MOFs-based gas sensor capable of real-time identification of multi-component VOCs, its preparation method, and its application. Background Technology

[0002] Volatile organic compounds (VOCs) are carbon-containing chemical substances that are volatile under environmental pressure. These substances originate from factory fumes, vehicle exhaust, interior decoration materials, and biological processes. Besides harming the environment, VOCs are also toxic, carcinogenic, or genotoxic, posing a significant risk to human health. Therefore, real-time, selective, and sensitive detection of multiple VOCs in urban atmospheres, especially monitoring the dynamic changes in VOC concentrations and distinguishing between different VOC types, is crucial for protecting and maintaining the physical environment for human survival.

[0003] Traditional VOCs detection methods, such as gas chromatography-mass spectrometry (GC-MS) and high-performance liquid chromatography (HPLC), while offering high precision and selectivity, suffer from drawbacks including large size, high cost, and complex sample preparation requiring thermal desorption and solid-phase extraction. Furthermore, real-time online detection is extremely difficult. On the other hand, chemiluminescence resistive gas sensors are an attractive option due to their miniaturization potential, low power consumption (microwatt to milliwatt range), and fast response time. However, individual gas sensors exhibit poor selectivity because they are cross-sensitive to many substances in the air, including humidity, temperature, and even other gases such as CO2, NOx, and SO2.

[0004] Currently, the development and improvement of nanomaterials have greatly promoted the development of gas sensor arrays. Carbon-based materials such as carbon nanotubes and graphene, as well as metal oxide semiconductors and two-dimensional materials such as MXenes and MoSe2, are often used as sensing layers due to their high specific surface area and good conductivity. However, these carbon-based materials may have stability issues when exposed to harsh atmospheric conditions such as high humidity and corrosiveness, and lack sufficient flexibility to be deployed without wear, and their response to ppb-level VOCs is insufficient.

[0005] MOFs, composed of metal cations / clusters and organic linkers, possess a very large specific surface area, adjustable cavities, and modifiable surfaces, making them ideal for sensors. MOF gas sensors become even more selective and sensitive due to unique host-guest interactions, such as hydrogen bonding, π-complexation, and hydrophobic attraction between VOC molecules and MOF cavities / functional sites.

[0006] However, most MOF-based sensors are based on rigid substrates such as SiO2 and Al2O3, making them difficult to use in flexible or wearable applications, such as dynamic atmospheric monitoring, as they need to be attached to building surfaces, vehicle surfaces, and drone platforms. Furthermore, existing MOF-based sensor arrays cannot effectively handle humidity resistance and long-term stability issues in real-world atmospheric environments where relative humidity varies between 30% and 90%, and intraday temperature fluctuations occur. For example, existing MOF sensors experience a 30% to 50% drop in response when relative humidity increases from 30% to 90%, making them unreliable in the field. Flexible gas sensors are particularly useful in atmospheric monitoring because they can adapt to irregular surfaces, withstand bending and stretching, and can be integrated into mobile devices. Recently, flexible devices based on sensing layers made of polyimide, polyethylene terephthalate, cellulose, and nanomaterials have been investigated. However, most current flexible MOF-based sensor arrays only identify single-component VOCs and have the following four main problems: (1) the stability of MOFs on flexible substrates is poor without damaging the structure and sensing performance of MOFs; (2) they are easily affected by humidity and temperature interference under complex atmospheric conditions; (3) it is difficult to achieve accurate identification of multi-component VOCs; and (4) it is difficult to meet the requirements of sufficient mechanical and environmental stability for more than six months for practical applications. Summary of the Invention

[0007] To overcome the shortcomings of the prior art, the first objective of this invention is to provide a method for preparing a flexible MOFs-based gas sensor capable of real-time identification of multi-component VOCs. This method is simple to operate, easy to industrialize, and the resulting flexible MOFs-based gas sensor capable of real-time identification of multi-component VOCs has excellent mechanical flexibility, mechanical stability, moisture resistance, temperature stability, and long-term stability, and can achieve accurate real-time identification of multi-component VOCs.

[0008] To overcome the shortcomings of the prior art, the second objective of this invention is to provide a flexible MOFs-based gas sensor capable of real-time identification of multi-component VOCs. This flexible MOFs-based gas sensor capable of real-time identification of multi-component VOCs has excellent mechanical flexibility, mechanical stability, moisture resistance, temperature stability, and long-term stability, and can achieve accurate real-time identification of multi-component VOCs.

[0009] The third objective of this invention is to provide an application of a flexible MOF-based gas sensor capable of real-time identification of multi-component VOCs in atmospheric environmental monitoring.

[0010] To achieve the first objective of the invention, the technical solution adopted by the present invention is as follows:

[0011] This invention provides a method for fabricating a flexible MOF-based gas sensor capable of real-time identification of multi-component VOCs, comprising the following steps:

[0012] S1. Synthesis of three MOFs: The amino-containing UiO-66 type metal-organic framework material, copper-based organometallic framework material-1 and zeolite imidazole ester framework material-8 were synthesized by solvothermal method.

[0013] S2. Substrate pretreatment: The polyimide film is subjected to ultrasonic cleaning, nitrogen gas drying and oxygen plasma treatment to obtain a pretreated PI substrate;

[0014] S3, Electrode deposition: Deposit interdigitated electrodes on the pretreated PI substrate;

[0015] S4. MOF sensing layer preparation: The three MOFs synthesized in step S1 are dispersed in a solvent and ultrasonically treated to obtain three suspensions. The three suspensions are dropped onto each independent sensing electrode region of the interdigitated electrode. After vacuum drying, the three MOF sensing layers are formed to obtain a gas sensor.

[0016] S5. Hydrophobic modification treatment: Immerse the sensor obtained in step S4 in a hydrophobic modifier, let it stand at room temperature, and then vacuum dry it to form a hydrophobic layer on the surface of the MOF sensing layer, thus obtaining the flexible MOFs-based gas sensor for real-time identification of multi-component VOCs.

[0017] The hydrophobic modifier is prepared by dissolving (1H,1H,2H,2H-perfluorodecyl)triethoxysilane in anhydrous ethanol to form a solution with a volume fraction of 0.5% to 1.5%.

[0018] Further, in step S1, the synthesis method of the amino-containing UiO-66 type metal-organic framework material is as follows: Zirconium tetrachloride and aminoterephthalic acid are dissolved in N,N-dimethylformamide, and the mixture is magnetically stirred for 20-30 minutes. The resulting mixture is transferred to a reaction vessel and heated at 115-125°C for 23-25 ​​hours. After naturally cooling to room temperature, the precipitate is collected by centrifugation, washed successively with N,N-dimethylformamide and anhydrous ethanol, and then vacuum dried at 75-85°C for 11-13 hours to obtain the amino-containing UiO-66 type metal-organic framework material; and / or

[0019] In the mixture, the molar volume ratio of zirconium tetrachloride, aminoterephthalic acid and N,N-dimethylformamide is (0.8~1.2) mmol:(0.8~1.2) mmol:(25~35) mL.

[0020] Further, in step S1, the synthesis method of the copper-based organometallic framework material-1 is as follows: copper nitrate trihydrate is dissolved in N,N-dimethylformamide to obtain a first solution; 1,3,5-pyromellitic acid is dissolved in anhydrous ethanol to obtain a second solution; the first and second solutions are mixed and transferred to a reaction vessel; the reaction is carried out at 95℃~105℃ for 11h~13h; the precipitate is collected by centrifugation; the precipitate is washed successively with N,N-dimethylformamide and anhydrous ethanol; and then vacuum dried at 55℃~65℃ for 7h~9h to obtain the copper-based organometallic framework material-1; and / or

[0021] In the first solution, the molar volume ratio of copper nitrate trihydrate to N,N-dimethylformamide is (3.5~4.5) mmol: (15~25) mL;

[0022] In the second solution, the molar volume ratio of 1,3,5-pyromellitic acid to anhydrous ethanol is (2.0~3.0) mmol: (5~15) mL;

[0023] The volume ratio of the first solution to the second solution is (20~30):(10~18).

[0024] Further, in step S1, the synthesis method of the zeolite imidazole ester framework material-8 is as follows: zinc nitrate hexahydrate and 2-methylimidazole are dissolved in methanol, magnetically stirred for 15 min to 25 min, then allowed to stand at room temperature for 23 h to 25 h, the precipitate is collected by centrifugation, the precipitate is washed with methanol, and then vacuum dried at 65 °C to 75 °C for 9 h to 11 h to obtain the zeolite imidazole ester framework material-8; and / or

[0025] The molar volume ratio of zinc nitrate hexahydrate, 2-methylimidazole and methanol is (1.0~2.0) mmol: (6.0~7.0) mmol: (35~45) mL.

[0026] Furthermore, in step S2, the ultrasonic cleaning is performed using a mixture of acetone, ethanol, and deionized water for 10 to 20 minutes; the purpose of ultrasonic cleaning is to remove organic impurities and dust from the surface of the polyimide film.

[0027] The nitrogen flow drying is performed by drying the cleaned polyimide film with a nitrogen flow rate of 5 L / min to 15 L / min at room temperature for 25 min to 35 min; and / or

[0028] The oxygen plasma activation treatment conditions are as follows: oxygen flow rate of 15 sccm~25 sccm, power of 90W~110W, and activation time of 3min~8min. The use of oxygen plasma to activate the surface of the polyimide film (PI substrate) is to improve the interfacial adhesion between the PI substrate and the subsequently deposited electrodes. After oxygen plasma activation, hydroxyl (–OH) functional groups are generated on the PI substrate surface, which can form chemical bonds with the subsequently deposited titanium adhesion layer.

[0029] Furthermore, in step S3, a titanium adhesion layer with a thickness of 4nm to 6nm is sputtered onto the pretreated PI substrate using a magnetron sputtering coating equipment under conditions of 45W to 55W sputtering power, 0.4Pa to 0.6Pa working pressure, and 3min to 8min deposition time. Then, under a light-shielding mask, a gold sensing layer with a thickness of 90nm to 110nm is sputtered and deposited under conditions of 75W to 85W sputtering power, 0.2Pa to 0.4Pa working pressure, and 15min to 25min deposition time to obtain interdigitated electrodes.

[0030] The interdigitated electrodes (IDEs) prepared have the following parameters: electrode width of 50 µm, electrode spacing of 50 µm, number of electrode pairs of 20, and effective sensing area of ​​1 cm × 1 cm. This electrode structure can simultaneously realize the electrical connection of four sensing elements, which include one reference electrode and three MOF sensing electrodes, and can effectively suppress signal crosstalk between sensing channels.

[0031] Further, in step S4, the solvent is anhydrous ethanol, the concentration of the three suspensions is 3 mg / mL to 7 mg / mL, and the particle size of the solid particles in the suspension is 100 nm to 500 nm; and / or

[0032] The ultrasonic treatment time is 25 min to 35 min; and / or

[0033] The vacuum drying is carried out at 55℃~65℃ and a vacuum degree of -0.10 MPa~-0.08 MPa for 25min~35min; the purpose of vacuum drying is to remove the solvent in the suspension and prevent MOF decomposition.

[0034] The thickness of the MOF sensing layer is 0.9µm to 1.1µm. The MOF sensing layer thickness is controlled to approximately 0.9µm to 1.1µm by repeatedly drop-casting the suspension 2 to 3 times, achieving a performance balance between sensitivity and response time. Increasing the thickness of the MOF sensing layer can improve detection sensitivity but will prolong the response time; therefore, selecting an appropriate thickness achieves optimal overall performance.

[0035] The specific operation of adding the three suspensions to the interdigitated electrodes is as follows: using a micropipette with an accuracy of ±0.1µL, the three suspensions are added to the surface of each independent interdigitated electrode (IDEs) in 10µL each.

[0036] Furthermore, in step S5, the time for standing at room temperature is 50 min to 70 min;

[0037] The vacuum drying temperature is 95℃~105℃, and the vacuum drying time is 25min~35min. The vacuum drying process promotes the silanization reaction of (1H,1H,2H,2H-perfluorodecyl)triethoxysilane (PFDTES) and the hydroxyl groups on the MOF surface. The water contact angle of the hydrophobically modified material surface is approximately 115°, indicating that the modified surface possesses good hydrophobic properties.

[0038] The thickness of the hydrophobic layer is 40nm~60nm.

[0039] To achieve the second objective of the invention, the technical solution adopted by the present invention is as follows:

[0040] This invention provides a flexible MOFs-based gas sensor capable of real-time identification of multi-component VOCs, which is prepared by the aforementioned method for preparing a flexible MOFs-based gas sensor capable of real-time identification of multi-component VOCs.

[0041] To achieve the third objective of the invention, the technical solution adopted by the present invention is as follows:

[0042] This invention provides a flexible MOFs-based gas sensor capable of real-time identification of multi-component VOCs, or the application of a flexible MOFs-based gas sensor capable of real-time identification of multi-component VOCs prepared by the above-described method for real-time identification of multi-component VOCs in atmospheric environmental monitoring.

[0043] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0044] (1) A method for preparing a flexible MOF-based gas sensor capable of real-time identification of multi-component VOCs according to the present invention involves using a polyimide film as a substrate. After substrate pretreatment and electrode deposition, suspensions of three MOFs are respectively dropped onto the independent sensing electrode regions of the interdigitated electrodes. After vacuum drying, three MOF sensing layers are formed. Then, the surface of the MOF sensing layers is hydrophobically modified using PFDTES to obtain a flexible MOF-based gas sensor capable of real-time identification of multi-component VOCs. This preparation method is simple to operate and easy to industrialize. The resulting flexible MOF-based gas sensor capable of real-time identification of multi-component VOCs has excellent mechanical flexibility, mechanical stability, moisture resistance, temperature stability, and long-term stability, and can achieve accurate real-time identification of multi-component VOCs.

[0045] (2) The present invention provides a flexible MOFs-based gas sensor that can identify multi-component VOCs in real time. It has excellent mechanical flexibility, mechanical stability, moisture resistance, temperature stability, and long-term stability, and can achieve accurate real-time identification of multi-component VOCs.

[0046] (3) Application of the flexible MOFs-based gas sensor of the present invention, which can identify multi-component VOCs in real time, is applied to atmospheric environmental monitoring and can achieve accurate real-time identification of multi-component VOCs. Therefore, the flexible MOFs-based gas sensor that can identify multi-component VOCs in real time has good application prospects. Attached Figure Description

[0047] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0048] Figure 1 The images show the SEM images of the three MOFs synthesized in step S1 of Embodiment 1 of the present invention.

[0049] Figure 2 The diagram shows the bending test results of the flexible MOFs-based gas sensor in Embodiment 1 of the present invention.

[0050] Figure 3 The bar chart shows the response values ​​of the flexible MOFs-based gas sensor prepared in Example 1 to six common atmospheric VOCs at a concentration of 50 ppm in an environment of 25°C and 50% relative humidity.

[0051] Figure 4The graph shows the curves of five consecutive response-recovery cycles of the flexible MOFs-based gas sensor prepared in Example 1 under 25°C and 50% RH conditions for 50 ppm ethanol.

[0052] Figure 5 The graph shows a comparison of the gas sensor responses of Example 1 and Comparative Example 1 to 50 ppm formaldehyde within a relative humidity range of 30% to 90%.

[0053] Figure 6 The graph shows the comparison between the detected values ​​and the VOC concentrations measured by GC-MS when the flexible MOFs-based gas sensor prepared in Example 1 continuously monitors the target VOCs for 72 hours. Detailed Implementation

[0054] To make the technical problem to be solved, the technical solution, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0055] The terminology used in the embodiments of this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. In this invention, the singular forms “a,” “the,” “first,” “second,” and “the” as used in the embodiments and appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0056] In this embodiment of the invention, a method for fabricating a flexible MOF-based gas sensor capable of real-time identification of multi-component VOCs includes the following steps:

[0057] S1. Synthesis of three MOFs: The amino-containing UiO-66 type metal-organic framework material, copper-based organometallic framework material-1 and zeolite imidazole ester framework material-8 were synthesized by solvothermal method.

[0058] S2. Substrate pretreatment: The polyimide film is subjected to ultrasonic cleaning, nitrogen gas drying and oxygen plasma activation treatment to obtain a pretreated PI substrate;

[0059] S3, Electrode deposition: Deposit interdigitated electrodes on the pretreated PI substrate;

[0060] S4. MOF sensing layer preparation: The three MOFs synthesized in step S1 are dispersed in a solvent and ultrasonically treated to obtain three suspensions. The three suspensions are dropped onto each independent sensing electrode region of the interdigitated electrode. After vacuum drying, the three MOF sensing layers are formed to obtain a gas sensor.

[0061] S5. Hydrophobic modification treatment: Immerse the sensor obtained in step S4 in a hydrophobic modifier, let it stand at room temperature, and then vacuum dry it to form a hydrophobic layer on the surface of the MOF sensing layer, thus obtaining the flexible MOFs-based gas sensor for real-time identification of multi-component VOCs.

[0062] The hydrophobic modifier is prepared by dissolving (1H,1H,2H,2H-perfluorodecyl)triethoxysilane in anhydrous ethanol to form a solution with a volume fraction of 0.5% to 1.5%.

[0063] In some embodiments, the synthesis method of the amino-containing UiO-66 type metal-organic framework material in step S1 is as follows: Zirconium tetrachloride and aminoterephthalic acid are dissolved in N,N-dimethylformamide, and the mixture is magnetically stirred for 20-30 minutes. The resulting mixture is transferred to a reaction vessel and heated at 115-125°C for 23-25 ​​hours. After natural cooling to room temperature, the precipitate is collected by centrifugation, washed sequentially with N,N-dimethylformamide and anhydrous ethanol, and then vacuum dried at 75-85°C for 11-13 hours to obtain the amino-containing UiO-66 type metal-organic framework material; and / or

[0064] In the mixture, the molar volume ratio of zirconium tetrachloride, aminoterephthalic acid and N,N-dimethylformamide is (0.8~1.2) mmol:(0.8~1.2) mmol:(25~35) mL.

[0065] In some embodiments, the synthesis method of the copper-based organometallic framework material-1 in step S1 is as follows: copper nitrate trihydrate is dissolved in N,N-dimethylformamide to obtain a first solution; 1,3,5-pyromellitic acid is dissolved in anhydrous ethanol to obtain a second solution; the first and second solutions are mixed and transferred to a reaction vessel; the reaction is carried out at 95℃~105℃ for 11h~13h; the precipitate is collected by centrifugation; the precipitate is washed successively with N,N-dimethylformamide and anhydrous ethanol; and then vacuum dried at 55℃~65℃ for 7h~9h to obtain the copper-based organometallic framework material-1; and / or

[0066] In the first solution, the molar volume ratio of copper nitrate trihydrate to N,N-dimethylformamide is (3.5~4.5) mmol: (15~25) mL;

[0067] In the second solution, the molar volume ratio of 1,3,5-pyromellitic acid to anhydrous ethanol is (2.0~3.0) mmol: (5~15) mL;

[0068] The volume ratio of the first solution to the second solution is (20~30):(10~18).

[0069] In some embodiments, the synthesis method of the zeolite imidazole ester framework material-8 in step S1 is as follows: zinc nitrate hexahydrate and 2-methylimidazole are dissolved in methanol, magnetically stirred for 15 min to 25 min, then allowed to stand at room temperature for 23 h to 25 h, the precipitate is collected by centrifugation, the precipitate is washed with methanol, and then vacuum dried at 65 °C to 75 °C for 9 h to 11 h to obtain the zeolite imidazole ester framework material-8; and / or

[0070] The molar volume ratio of zinc nitrate hexahydrate, 2-methylimidazole and methanol is (1.0~2.0) mmol: (6.0~7.0) mmol: (35~45) mL.

[0071] In some embodiments, in step S2, the ultrasonic cleaning is performed using a mixture of acetone, ethanol, and deionized water for 10 to 20 minutes; and / or

[0072] The nitrogen flow drying is performed by drying the cleaned polyimide film with a nitrogen flow rate of 5 L / min to 15 L / min at room temperature for 25 min to 35 min; and / or

[0073] The conditions for the oxygen plasma activation treatment are: oxygen flow rate of 15 sccm to 25 sccm, power of 90 W to 110 W, and activation treatment time of 3 min to 8 min.

[0074] In some embodiments, in step S3, a titanium adhesion layer with a thickness of 4nm to 6nm is sputtered on a pretreated PI substrate using a magnetron sputtering deposition equipment under conditions of 45W to 55W sputtering power, 0.4Pa to 0.6Pa working pressure, and 3min to 8min deposition time. Then, under a light-shielding mask, a gold sensing layer with a thickness of 90nm to 110nm is sputtered and deposited under conditions of 75W to 85W sputtering power, 0.2Pa to 0.4Pa working pressure, and 15min to 25min deposition time to obtain interdigitated electrodes.

[0075] In some embodiments, in step S4, the solvent is anhydrous ethanol, the concentration of the three suspensions is 3 mg / mL to 7 mg / mL, and the particle size of the solid particles in the suspension is 100 nm to 500 nm; and / or

[0076] The ultrasonic treatment time is 25 min to 35 min; and / or

[0077] The vacuum drying is performed at 55℃~65℃ and a vacuum degree of -0.10 MPa~-0.08 MPa for 25min~35min; and / or

[0078] The thickness of the MOF sensing layer is 0.9µm to 1.1µm.

[0079] In some embodiments, in step S5, the time for standing at room temperature is 50 min to 70 min; and / or

[0080] The vacuum drying temperature is 95℃~105℃, and the vacuum drying time is 25min~35min; and / or

[0081] The thickness of the hydrophobic layer is 40nm~60nm.

[0082] In this embodiment of the invention, a flexible MOFs-based gas sensor capable of real-time identification of multi-component VOCs is prepared by the aforementioned method for preparing a flexible MOFs-based gas sensor capable of real-time identification of multi-component VOCs.

[0083] In this embodiment of the invention, a flexible MOFs-based gas sensor capable of real-time identification of multi-component VOCs, or a flexible MOFs-based gas sensor capable of real-time identification of multi-component VOCs prepared by the above-described method, is applied in atmospheric environmental monitoring.

[0084] The following description is based on specific embodiments.

[0085] Example 1

[0086] A method for fabricating a flexible MOF-based gas sensor capable of real-time identification of multi-component VOCs includes the following steps:

[0087] S1. Synthesis of three MOFs: The amino-containing UiO-66 type metal-organic framework material, copper-based organometallic framework material-1 and zeolite imidazole ester framework material-8 were synthesized by solvothermal method.

[0088] The synthesis method of the amino-containing UiO-66 type metal-organic framework material is as follows: Zirconium tetrachloride and aminoterephthalic acid are dissolved in N,N-dimethylformamide. After magnetic stirring for 25 min, the resulting mixture is transferred to a reaction vessel and heated at 120°C for 24 h. After natural cooling to room temperature, the precipitate is collected by centrifugation and washed successively with N,N-dimethylformamide and anhydrous ethanol. Then, it is vacuum dried at 80°C for 12 h to obtain the amino-containing UiO-66 type metal-organic framework material (denoted as UiO-66-NH2). In this embodiment, the molar volume ratio of zirconium tetrachloride, aminoterephthalic acid, and N,N-dimethylformamide in the mixture is 1.0 mmol:1.0 mmol:30 mL. The specific surface area of ​​the UiO-66-NH2 synthesized in this embodiment is 1250 m² / g.

[0089] The synthesis method of copper-based organometallic framework material-1 is as follows: Copper nitrate trihydrate is dissolved in N,N-dimethylformamide to obtain a first solution, and 1,3,5-pyromellitic acid is dissolved in anhydrous ethanol to obtain a second solution. The first and second solutions are mixed and transferred to a reaction vessel, heated at 100°C for 12 hours, and then the precipitate is collected by centrifugation. The precipitate is washed successively with N,N-dimethylformamide and anhydrous ethanol, and then dried under vacuum at 60°C for 8 hours to obtain copper-based organometallic framework material-1 (denoted as HKUST-1). In this embodiment, the molar volume ratio of copper nitrate trihydrate to N,N-dimethylformamide in the first solution is 3.9 mmol:40 mL; the molar volume ratio of 1,3,5-pyromellitic acid to anhydrous ethanol in the second solution is 2.6 mmol:10 mL; and the volume ratio of the first solution to the second solution is 25:15. The specific surface area of ​​HKUST-1 synthesized in this embodiment is 1180 m² / g.

[0090] The synthesis method of zeolite imidazole ester framework material-8 is as follows: Zinc nitrate hexahydrate and 2-methylimidazole are dissolved in methanol, magnetically stirred for 20 min, then allowed to stand at room temperature for 24 h, centrifuged to collect the precipitate, washed with methanol, and then vacuum dried at 70 °C for 10 h to obtain zeolite imidazole ester framework material-8 (denoted as ZIF-8). In this embodiment, the molar volume ratio of zinc nitrate hexahydrate, 2-methylimidazole, and methanol is 1.6 mmol: 6.4 mmol: 40 mL. The specific surface area of ​​ZIF-8 synthesized in this embodiment is 1420 m² / g.

[0091] S2. Substrate pretreatment: The polyimide film was ultrasonically cleaned for 15 min using a mixture of acetone, ethanol and deionized water in a volume ratio of 1:1:1. Then, the cleaned polyimide film was dried with a nitrogen flow of 10 L / min at room temperature for 30 min. Finally, it was activated by oxygen plasma at an oxygen flow rate of 20 sccm, a power of 100 W and an activation time of 5 min to obtain the pretreated PI substrate.

[0092] S3. Electrode deposition: A titanium adhesion layer with a thickness of 5 nm is sputtered on the pretreated PI substrate using a magnetron sputtering deposition equipment under the conditions of 50 W sputtering power, 0.5 Pa working pressure and 5 min deposition time. Then, under a light-shielding mask, a gold sensing layer with a thickness of 100 nm is sputtered and deposited under the conditions of 80 W sputtering power, 0.3 Pa working pressure and 20 min deposition time to obtain interdigitated electrodes.

[0093] S4. Preparation of MOF sensing layer: The three MOFs synthesized in step S1 were dispersed in anhydrous ethanol and ultrasonically treated for 30 min to obtain three suspensions with a concentration of 5 mg / mL. The particle size of the solid particles in the suspensions was 100 nm to 500 nm. The three suspensions were added dropwise to the independent sensing electrode areas of the interdigitated electrodes (IDEs) using a micropipette with an accuracy of ±0.1 µL. The addition volume of each suspension was 10 µL. Then, the suspensions were vacuum dried at 60 °C and a vacuum degree of -0.09 MPa for 30 min to form three MOF sensing layers, thus obtaining a gas sensor. In this embodiment, the thickness of the MOF sensing layer was 1.0 µm.

[0094] S5. Hydrophobic modification treatment: The sensor obtained in step S4 is immersed in a hydrophobic modifier, left to stand at room temperature for 60 minutes, and then vacuum dried at 100°C for 30 minutes to form a hydrophobic layer on the surface of the MOF sensing layer, thus obtaining a flexible MOFs-based gas sensor for real-time identification of multi-component VOCs; in this embodiment, the thickness of the hydrophobic layer is 50 nm.

[0095] In this embodiment, the hydrophobic modifier is (1H,1H,2H,2H-perfluorodecyl)triethoxysilane dissolved in anhydrous ethanol to prepare a 1.0% (v / v) solution.

[0096] Example 2

[0097] A method for fabricating a flexible MOF-based gas sensor capable of real-time identification of multi-component VOCs includes the following steps:

[0098] S1. Synthesis of three MOFs: The amino-containing UiO-66 type metal-organic framework material, copper-based organometallic framework material-1 and zeolite imidazole ester framework material-8 were synthesized by solvothermal method.

[0099] The synthesis method of the amino-containing UiO-66 type metal-organic framework material is as follows: zirconium tetrachloride and aminoterephthalic acid are dissolved in N,N-dimethylformamide. After magnetic stirring for 20 min, the resulting mixture is transferred to a reaction vessel and heated at 115 °C for 25 h. After naturally cooling to room temperature, the precipitate is collected by centrifugation. The precipitate is washed successively with N,N-dimethylformamide and anhydrous ethanol, and then vacuum dried at 75 °C for 13 h to obtain the amino-containing UiO-66 type metal-organic framework material (denoted as UiO-66-NH2). In this embodiment, the molar volume ratio of zirconium tetrachloride, aminoterephthalic acid and N,N-dimethylformamide in the mixture is 0.8 mmol:0.8 mmol:25 mL.

[0100] The synthesis method of copper-based organometallic framework material-1 is as follows: copper nitrate trihydrate is dissolved in N,N-dimethylformamide to obtain a first solution, and 1,3,5-pyromellitic acid is dissolved in anhydrous ethanol to obtain a second solution. The first and second solutions are mixed and transferred to a reaction vessel, heated at 95°C for 13 hours, and the precipitate is collected by centrifugation. The precipitate is washed successively with N,N-dimethylformamide and anhydrous ethanol, and then dried under vacuum at 55°C for 9 hours to obtain copper-based organometallic framework material-1 (denoted as HKUST-1). In this embodiment, the molar volume ratio of copper nitrate trihydrate to N,N-dimethylformamide in the first solution is 3.5 mmol:15 mL; the molar volume ratio of 1,3,5-pyromellitic acid to anhydrous ethanol in the second solution is 2.0 mmol:5 mL; and the volume ratio of the first solution to the second solution is 20:10.

[0101] The synthesis method of zeolite imidazole ester framework material-8 is as follows: zinc nitrate hexahydrate and 2-methylimidazole are dissolved in methanol, magnetically stirred for 15 min, then allowed to stand at room temperature for 25 h, centrifuged to collect the precipitate, washed with methanol, and then vacuum dried at 65 °C for 11 h to obtain zeolite imidazole ester framework material-8 (denoted as ZIF-8); in this embodiment, the molar volume ratio of zinc nitrate hexahydrate, 2-methylimidazole and methanol is 1.0 mmol: 6.0 mmol: 35 mL.

[0102] S2. Substrate pretreatment: The polyimide film was ultrasonically cleaned for 10 min with a mixture of acetone, ethanol and deionized water in a volume ratio of 1:1:1. Then, the cleaned polyimide film was dried with a nitrogen flow of 5 L / min at room temperature for 35 min. Finally, it was activated by oxygen plasma with an oxygen flow rate of 15 scc mm, a power of 90 W and an activation time of 3 min to obtain the pretreated PI substrate.

[0103] S3. Electrode deposition: A titanium adhesion layer with a thickness of 4 nm is sputtered on the pretreated PI substrate using a magnetron sputtering coating equipment under the conditions of 45 W sputtering power, 0.4 Pa working pressure and 3 min deposition time. Then, under a light-shielding mask, a gold sensing layer with a thickness of 90 nm is sputtered and deposited under the conditions of 75 W sputtering power, 0.2 Pa working pressure and 15 min deposition time to obtain interdigitated electrodes.

[0104] S4. Preparation of MOF sensing layer: The three MOFs synthesized in step S1 were dispersed in anhydrous ethanol and ultrasonically treated for 25 min to obtain three suspensions with a concentration of 3 mg / mL. The particle size of the solid particles in the suspensions was 100 nm to 500 nm. The three suspensions were added dropwise to the independent sensing electrode areas of the interdigitated electrodes (IDEs) using a micropipette with an accuracy of ±0.1 µL. The addition volume of each suspension was 10 µL. Then, the suspensions were vacuum dried at 55 °C and a vacuum degree of -0.10 MPa for 35 min to form three MOF sensing layers, thus obtaining a gas sensor. In this embodiment, the thickness of the MOF sensing layer was 0.9 µm.

[0105] S5. Hydrophobic modification treatment: The sensor obtained in step S4 is immersed in a hydrophobic modifier, left to stand at room temperature for 50 minutes, and then vacuum dried at 95°C for 35 minutes to form a hydrophobic layer on the surface of the MOF sensing layer, thus obtaining a flexible MOFs-based gas sensor for real-time identification of multi-component VOCs; in this embodiment, the thickness of the hydrophobic layer is 40 nm.

[0106] In this embodiment, the hydrophobic modifier is (1H,1H,2H,2H-perfluorodecyl)triethoxysilane dissolved in anhydrous ethanol to prepare a 0.5% (v / v) solution.

[0107] Example 3

[0108] A method for fabricating a flexible MOF-based gas sensor capable of real-time identification of multi-component VOCs includes the following steps:

[0109] S1. Synthesis of three MOFs: The amino-containing UiO-66 type metal-organic framework material, copper-based organometallic framework material-1 and zeolite imidazole ester framework material-8 were synthesized by solvothermal method.

[0110] The synthesis method of the amino-containing UiO-66 type metal-organic framework material is as follows: Zirconium tetrachloride and aminoterephthalic acid are dissolved in N,N-dimethylformamide. After magnetic stirring for 30 min, the resulting mixture is transferred to a reaction vessel and heated at 125℃ for 23 h. After naturally cooling to room temperature, the precipitate is collected by centrifugation. The precipitate is washed successively with N,N-dimethylformamide and anhydrous ethanol, and then vacuum dried at 85℃ for 11 h to obtain the amino-containing UiO-66 type metal-organic framework material (denoted as UiO-66-NH2). In this embodiment, the molar volume ratio of zirconium tetrachloride, aminoterephthalic acid and N,N-dimethylformamide in the mixture is 1.2 mmol: 1.2 mmol: 35 mL.

[0111] The synthesis method of copper-based organometallic framework material-1 is as follows: copper nitrate trihydrate is dissolved in N,N-dimethylformamide to obtain a first solution, and 1,3,5-pyromellitic acid is dissolved in anhydrous ethanol to obtain a second solution. The first and second solutions are mixed and transferred to a reaction vessel, heated at 105°C for 11 hours, and the precipitate is collected by centrifugation. The precipitate is washed successively with N,N-dimethylformamide and anhydrous ethanol, and then dried under vacuum at 65°C for 7 hours to obtain copper-based organometallic framework material-1 (denoted as HKUST-1). In this embodiment, the molar volume ratio of copper nitrate trihydrate to N,N-dimethylformamide in the first solution is 4.5 mmol: 25 mL; the molar volume ratio of 1,3,5-pyromellitic acid to anhydrous ethanol in the second solution is 3.0 mmol: 15 mL; and the volume ratio of the first solution to the second solution is 30:18.

[0112] The synthesis method of zeolite imidazole ester framework material-8 is as follows: zinc nitrate hexahydrate and 2-methylimidazole are dissolved in methanol, magnetically stirred for 25 min, then allowed to stand at room temperature for 23 h, centrifuged to collect the precipitate, washed with methanol, and then vacuum dried at 75 °C for 9 h to obtain zeolite imidazole ester framework material-8 (denoted as ZIF-8); in this embodiment, the molar volume ratio of zinc nitrate hexahydrate, 2-methylimidazole and methanol is 2.0 mmol: 7.0 mmol: 45 mL.

[0113] S2. Substrate pretreatment: The polyimide film was ultrasonically cleaned for 20 min using a mixture of acetone, ethanol and deionized water in a volume ratio of 1:1:1. Then, the cleaned polyimide film was dried with a nitrogen flow of 15 L / min at room temperature for 25 min. Finally, it was activated by oxygen plasma at an oxygen flow rate of 25 sccm, a power of 110 W and an activation time of 8 min to obtain the pretreated PI substrate.

[0114] S3. Electrode deposition: A titanium adhesion layer with a thickness of 6 nm was sputtered on the pretreated PI substrate using a magnetron sputtering coating equipment under the conditions of 55 W sputtering power, 0.6 Pa working pressure and 8 min deposition time. Then, under a light-shielding mask, a gold sensing layer with a thickness of 110 nm was sputtered and deposited under the conditions of 85 W sputtering power, 0.4 Pa working pressure and 25 min deposition time to obtain interdigitated electrodes.

[0115] S4. Preparation of MOF sensing layer: The three MOFs synthesized in step S1 were dispersed in anhydrous ethanol and ultrasonically treated for 35 min to obtain three suspensions with a concentration of 7 mg / mL. The particle size of the solid particles in the suspensions was 100 nm to 500 nm. The three suspensions were added dropwise to the independent sensing electrode areas of the interdigitated electrodes (IDEs) using a micropipette with an accuracy of ±0.1 µL. The addition volume of each suspension was 10 µL. Then, the suspensions were vacuum dried at 65 °C and a vacuum degree of -0.08 MPa for 25 min to form three MOF sensing layers, thus obtaining a gas sensor. In this embodiment, the thickness of the MOF sensing layer was 1.1 µm.

[0116] S5. Hydrophobic modification treatment: The sensor obtained in step S4 is immersed in a hydrophobic modifier, left to stand at room temperature for 70 minutes, and then vacuum dried at 105°C for 25 minutes to form a hydrophobic layer on the surface of the MOF sensing layer, thus obtaining a flexible MOFs-based gas sensor for real-time identification of multi-component VOCs; in this embodiment, the thickness of the hydrophobic layer is 60 nm.

[0117] In this embodiment, the hydrophobic modifier is (1H,1H,2H,2H-perfluorodecyl)triethoxysilane dissolved in anhydrous ethanol to prepare a 1.5% (v / v) solution.

[0118] Example 4

[0119] A method for fabricating a flexible MOF-based gas sensor capable of real-time identification of multi-component VOCs includes the following steps:

[0120] S1. Synthesis of three MOFs: The amino-containing UiO-66 type metal-organic framework material, copper-based organometallic framework material-1 and zeolite imidazole ester framework material-8 were synthesized by solvothermal method.

[0121] The synthesis method of the amino-containing UiO-66 type metal-organic framework material is as follows: zirconium tetrachloride and aminoterephthalic acid are dissolved in N,N-dimethylformamide. After magnetic stirring for 22 min, the resulting mixture is transferred to a reaction vessel and heated at 118 °C for 24.5 h. After naturally cooling to room temperature, the precipitate is collected by centrifugation. The precipitate is washed successively with N,N-dimethylformamide and anhydrous ethanol, and then vacuum dried at 78 °C for 12.5 h to obtain the amino-containing UiO-66 type metal-organic framework material (denoted as UiO-66-NH2). In this embodiment, the molar volume ratio of zirconium tetrachloride, aminoterephthalic acid and N,N-dimethylformamide in the mixture is 0.9 mmol: 1.1 mmol: 28 mL.

[0122] The synthesis method of copper-based organometallic framework material-1 is as follows: copper nitrate trihydrate is dissolved in N,N-dimethylformamide to obtain a first solution, and 1,3,5-pyromellitic acid is dissolved in anhydrous ethanol to obtain a second solution. The first and second solutions are mixed and transferred to a reaction vessel, heated at 98°C for 12.5 h, and then centrifuged to collect the precipitate. The precipitate is washed successively with N,N-dimethylformamide and anhydrous ethanol, and then dried under vacuum at 58°C for 8.5 h to obtain copper-based organometallic framework material-1 (denoted as HKUST-1). In this embodiment, the molar volume ratio of copper nitrate trihydrate to N,N-dimethylformamide in the first solution is 3.7 mmol:18 mL; the molar volume ratio of 1,3,5-pyromellitic acid to anhydrous ethanol in the second solution is 2.3 mmol:8 mL; and the volume ratio of the first solution to the second solution is 22:13.

[0123] The synthesis method of zeolite imidazole ester framework material-8 is as follows: zinc nitrate hexahydrate and 2-methylimidazole are dissolved in methanol, magnetically stirred for 18 min, then allowed to stand at room temperature for 24.5 h, centrifuged to collect the precipitate, washed with methanol, and then vacuum dried at 68 °C for 10.5 h to obtain zeolite imidazole ester framework material-8 (denoted as ZIF-8); in this embodiment, the molar volume ratio of zinc nitrate hexahydrate, 2-methylimidazole and methanol is 1.2 mmol: 6.2 mmol: 38 mL.

[0124] S2. Substrate pretreatment: The polyimide film was ultrasonically cleaned for 12 min using a mixture of acetone, ethanol and deionized water in a volume ratio of 1:1:1. Then, the cleaned polyimide film was dried with a nitrogen flow of 8 L / min at room temperature for 33 min. Finally, it was activated by oxygen plasma at an oxygen flow rate of 18 sccm, a power of 95 W and an activation time of 4 min to obtain the pretreated PI substrate.

[0125] S3. Electrode deposition: A titanium adhesion layer with a thickness of 5 nm is sputtered on the pretreated PI substrate using a magnetron sputtering coating equipment under the conditions of 48 W sputtering power, 0.5 Pa working pressure and 4 min deposition time. Then, under a light-shielding mask, a gold sensing layer with a thickness of 95 nm is sputtered and deposited under the conditions of 78 W sputtering power, 0.3 Pa working pressure and 18 min deposition time to obtain interdigitated electrodes.

[0126] S4. Preparation of MOF sensing layer: The three MOFs synthesized in step S1 were dispersed in anhydrous ethanol and ultrasonically treated for 28 min to obtain three suspensions with a concentration of 4 mg / mL. The particle size of the solid particles in the suspensions was 100 nm to 500 nm. The three suspensions were added dropwise to the independent sensing electrode areas of the interdigitated electrodes (IDEs) using a micropipette with an accuracy of ±0.1 µL. The addition volume of each suspension was 10 µL. Then, the suspensions were vacuum dried at 58 °C and a vacuum degree of -0.09 MPa for 33 min to form three MOF sensing layers, thus obtaining a gas sensor. In this embodiment, the thickness of the MOF sensing layer was 1.0 µm.

[0127] S5. Hydrophobic modification treatment: The sensor obtained in step S4 is immersed in a hydrophobic modifier, left to stand at room temperature for 55 minutes, and then vacuum dried at 98°C for 33 minutes to form a hydrophobic layer on the surface of the MOF sensing layer, thus obtaining a flexible MOFs-based gas sensor for real-time identification of multi-component VOCs; in this embodiment, the thickness of the hydrophobic layer is 45 nm.

[0128] In this embodiment, the hydrophobic modifier is (1H,1H,2H,2H-perfluorodecyl)triethoxysilane dissolved in anhydrous ethanol to prepare a 0.8% (v / v) solution.

[0129] Example 5

[0130] A method for fabricating a flexible MOF-based gas sensor capable of real-time identification of multi-component VOCs includes the following steps:

[0131] S1. Synthesis of three MOFs: The amino-containing UiO-66 type metal-organic framework material, copper-based organometallic framework material-1 and zeolite imidazole ester framework material-8 were synthesized by solvothermal method.

[0132] The synthesis method of the amino-containing UiO-66 type metal-organic framework material is as follows: Zirconium tetrachloride and aminoterephthalic acid are dissolved in N,N-dimethylformamide. After magnetic stirring for 28 min, the resulting mixture is transferred to a reaction vessel and heated at 122℃ for 23.5 h. After naturally cooling to room temperature, the precipitate is collected by centrifugation. The precipitate is washed successively with N,N-dimethylformamide and anhydrous ethanol, and then vacuum dried at 82℃ for 11.5 h to obtain the amino-containing UiO-66 type metal-organic framework material (denoted as UiO-66-NH2). In this embodiment, the molar volume ratio of zirconium tetrachloride, aminoterephthalic acid and N,N-dimethylformamide in the mixture is 1.1 mmol: 0.9 mmol: 33 mL.

[0133] The synthesis method of copper-based organometallic framework material-1 is as follows: copper nitrate trihydrate is dissolved in N,N-dimethylformamide to obtain a first solution, and 1,3,5-pyromellitic acid is dissolved in anhydrous ethanol to obtain a second solution. The first and second solutions are mixed and transferred to a reaction vessel, heated at 102°C for 11.5 h, and then the precipitate is collected by centrifugation. The precipitate is washed successively with N,N-dimethylformamide and anhydrous ethanol, and then dried under vacuum at 62°C for 7.5 h to obtain copper-based organometallic framework material-1 (denoted as HKUST-1). In this embodiment, the molar volume ratio of copper nitrate trihydrate to N,N-dimethylformamide in the first solution is 4.2 mmol: 23 mL; the molar volume ratio of 1,3,5-pyromellitic acid to anhydrous ethanol in the second solution is 2.8 mmol: 13 mL; and the volume ratio of the first solution to the second solution is 28:16.

[0134] The synthesis method of zeolite imidazole ester framework material-8 is as follows: zinc nitrate hexahydrate and 2-methylimidazole are dissolved in methanol, magnetically stirred for 23 min, then allowed to stand at room temperature for 23.5 h, centrifuged to collect the precipitate, washed with methanol, and then vacuum dried at 72 °C for 9.5 h to obtain zeolite imidazole ester framework material-8 (denoted as ZIF-8); in this embodiment, the molar volume ratio of zinc nitrate hexahydrate, 2-methylimidazole and methanol is 1.8 mmol: 6.9 mmol: 43 mL.

[0135] S2. Substrate pretreatment: The polyimide film was ultrasonically cleaned for 18 min using a mixture of acetone, ethanol and deionized water in a volume ratio of 1:1:1. Then, the cleaned polyimide film was dried with a nitrogen flow of 12 L / min at room temperature for 28 min. Finally, it was activated by oxygen plasma at an oxygen flow rate of 23 sccm, a power of 105 W and an activation time of 7 min to obtain the pretreated PI substrate.

[0136] S3. Electrode deposition: A titanium adhesion layer with a thickness of 5 nm was sputtered onto the pretreated PI substrate using a magnetron sputtering coating equipment under the conditions of 52 W sputtering power, 0.6 Pa working pressure and 7 min deposition time. Then, under a light-shielding mask, a gold sensing layer with a thickness of 105 nm was sputtered and deposited under the conditions of 83 W sputtering power, 0.5 Pa working pressure and 22 min deposition time to obtain interdigitated electrodes.

[0137] S4. Preparation of MOF sensing layer: The three MOFs synthesized in step S1 were dispersed in anhydrous ethanol and ultrasonically treated for 33 min to obtain three suspensions with a concentration of 6 mg / mL. The particle size of the solid particles in the suspensions was 100 nm to 500 nm. The three suspensions were added dropwise to the independent sensing electrode areas of the interdigitated electrodes (IDEs) using a micropipette with an accuracy of ±0.1 µL. The addition volume of each suspension was 10 µL. Then, the suspensions were vacuum dried at 63 °C and a vacuum degree of -0.10 MPa for 28 min to form three MOF sensing layers, thus obtaining a gas sensor. In this embodiment, the thickness of the MOF sensing layer was 0.9 µm.

[0138] S5. Hydrophobic modification treatment: The sensor obtained in step S4 is immersed in a hydrophobic modifier, left to stand at room temperature for 65 minutes, and then vacuum dried at 102°C for 28 minutes to form a hydrophobic layer on the surface of the MOF sensing layer, thus obtaining a flexible MOFs-based gas sensor for real-time identification of multi-component VOCs; in this embodiment, the thickness of the hydrophobic layer is 55 nm.

[0139] In this embodiment, the hydrophobic modifier is (1H,1H,2H,2H-perfluorodecyl)triethoxysilane dissolved in anhydrous ethanol to prepare a 1.2% (v / v) solution.

[0140] Example 6

[0141] Application of any one of the preparation methods of flexible MOFs-based gas sensors capable of real-time identification of multi-component VOCs in atmospheric environmental monitoring in Examples 1 to 5.

[0142] Comparative Example 1

[0143] A method for fabricating a flexible MOF-based gas sensor capable of real-time identification of multi-component VOCs is disclosed. This method differs from Example 1 in that the hydrophobic modification treatment in step S5 is omitted. The remaining fabrication methods are the same as in Example 1, resulting in a gas sensor.

[0144] Structural morphology characterization

[0145] (I) Morphological characterization by scanning electron microscopy

[0146] The amino-containing UiO-66 type metal-organic framework material (UiO-66-NH2), copper-based organometallic framework material-1 (HKUST-1), and zeolite imidazole ester framework material-8 (ZIF-8) synthesized in step S1 of Example 1 were characterized by scanning electron microscopy (SEM). The SEM images are shown below. Figure 1 As shown.

[0147] Depend on Figure 1As can be seen, UiO-66-NH2 has a uniform cubic crystal structure with a particle size of approximately 200 nm; HKUST-1 has a clearly defined octahedral crystal structure with a size of approximately 500 nm; and ZIF-8 has a rhombic dodecahedral structure with a size of approximately 300 nm. The particles are uniformly distributed without obvious agglomeration, which is due to the suitable synthesis conditions.

[0148] Performance testing

[0149] (a) Hydrophobicity test

[0150] The water contact angle (WCA) of the three MOF sensing layers was measured before and after hydrophobic modification with PFDTES.

[0151] The hydrophobic layer surfaces formed by hydrophobic modification of the three MOF sensing layers in the flexible MOFs-based gas sensor for real-time identification of multi-component VOCs prepared in Example 1, and the three MOF sensing layer surfaces in the gas sensor prepared in Comparative Example 1, were tested using a contact angle meter. The test results are shown in Table 1 below.

[0152] Table 1. Water contact angle test results of three MOF sensing layers before and after hydrophobic modification.

[0153]

[0154] As shown in Table 1, all three MOF sensing layers exhibited high hydrophobicity after hydrophobic modification, indicating that the hydrophobic modifier was successfully applied to the surface of the three MOF sensing layers. Specifically, WCA > 90° indicates hydrophobicity, and WCA > 110° indicates high hydrophobicity.

[0155] (ii) Mechanical flexibility test

[0156] The mechanical flexibility of gas sensors must meet the application requirements in dynamic atmospheric environments, such as when they are fixed to the exterior walls of buildings, vehicle bodies, or drone bodies.

[0157] The flexibility of the flexible MOF-based gas sensor for real-time identification of multi-component VOCs prepared in Example 1 was evaluated using a self-made bending test tube. Bending tests were conducted with different bending radii (R) of 5 mm, 10 mm, and 15 mm. Furthermore, the relative resistance change was measured after 1000 bending cycles with a bending radius (R) of 5 mm. The test conditions and results are as follows: Figure 2 As shown.

[0158] Depend on Figure 2As can be seen, the flexible MOFs-based gas sensor for real-time identification of multi-component VOCs prepared in this invention maintains structural integrity in the flat state and in the bending states with bending radii R=5 mm, R=10 mm and R=15 mm, and no cracks or detachments were observed.

[0159] Depend on Figure 2 As shown in b, the flexible MOF-based gas sensor (R=5 mm) for real-time identification of multi-component VOCs prepared by this invention exhibits a relative resistance change of less than 2% after 1000 bending cycles. For bending radii of 10 mm and 15 mm, the relative resistance changes are less than 1.5% and 1%, respectively; the larger the bending radius, the better the resistance stability. Furthermore, after 1000 bending cycles (radius = 5 mm), the SEM image of this flexible MOF-based gas sensor shows no cracks or delamination between the MOF sensing layer and the PI substrate, indicating a strong adhesion between the two.

[0160] In addition, the mechanical stability test results under flat and different bending conditions are shown in Table 2.

[0161] Table 2. Mechanical stability test results under flat and different bending conditions.

[0162]

[0163] As shown in Table 2, the flexible MOF-based gas sensor for real-time identification of multi-component VOCs prepared in this invention exhibits excellent mechanical stability. This excellent mechanical stability is attributed to the following three factors: First, the flexible PI substrate has good tensile strength and toughness; second, the MOF sensing layer is prepared using a low-temperature solution process, thus avoiding thermal stress during manufacturing; and third, the PI substrate undergoes oxygen plasma pretreatment, which effectively enhances the adhesion between the substrate and the electrode layer.

[0164] (III) Sensor performance testing

[0165] The flexible MOFs-based gas sensor for real-time identification of multi-component VOCs prepared in Example 1 shows the following response to six common atmospheric VOCs (formaldehyde, benzene, toluene, xylene, acetone, and ethanol) at a concentration of 50 ppm (50% relative humidity, 25°C): Figure 3 As shown.

[0166] Depend on Figure 3 It is evident that the three MOF sensing layers respond differently to VOCsDE, which is precisely why they are able to distinguish between different VOCs.

[0167] Among them, the UiO-66-NH2 sensing layer, with its amino functionalization, exhibits the best response to polar VOCs. The formaldehyde response value S = 4.2 ± 0.3; the ethanol response value S = 4.8 ± 0.4. This is due to the interaction between the -NH2 group and the polar functional groups (-CHO, -OH) of VOCs.

[0168] HKUST-1 sensor layer contains Cu 2+ The center exhibits a good response to aromatic VOCs (benzene: S = 3.8 ± 0.3; toluene: S = 4.1 ± 0.3; xylene: S = 4.5 ± 0.4). This is due to the interaction of the aromatic ring with Cu. 2+ π-complexes were formed between the propeller units.

[0169] The ZIF-8 sensing layer has hydrophobic channels and exhibits good response to nonpolar VOCs, such as acetone (S = 3.8 ± 0.3) and benzene (S = 2.9 ± 0.2). This is attributed to the hydrophobic-hydrophobic interactions between its imidazole ring channels and the nonpolar portions of VOCs.

[0170] (iv) Response-Recovery Cycle Test

[0171] The flexible MOF-based gas sensor for real-time identification of multi-component VOCs prepared in Example 1 was subjected to five consecutive response-recovery cycles at 25°C and 50% RH to detect 50 ppm ethanol. Figure 4 As shown.

[0172] Depend on Figure 4 As can be seen, the flexible MOFs-based gas sensor for real-time identification of multi-component VOCs prepared in this invention exhibits good reproducibility.

[0173] Furthermore, the flexible MOF-based gas sensor prepared in this invention, capable of real-time identification of multi-component VOCs, exhibits excellent response and recovery rates. Specifically, it demonstrates the shortest response time for ethanol (18±2 s, recovery time 38±4 s); formaldehyde (22±3 s, recovery time 45±5 s); benzene (28±4 s, recovery time 52±6 s); toluene (25±3 s, recovery time 48±5 s); xylene (27±4 s, recovery time 55±7 s); and acetone (20±2 s, recovery time 42±47 s).

[0174] (v) Moisture resistance test

[0175] The flexible MOFs-based gas sensor from Example 1 and the gas sensor from Comparative Example 1 were selected, and a 50ppm formaldehyde gas sensitivity response test was conducted under different relative humidity environments ranging from 30% to 90%. The test results are as follows: Figure 5 As shown.

[0176] Depend on Figure 5 It can be seen that as the relative humidity increases from 30% to 90%, the response value of the sensor in Comparative Example 1 shows a significant decrease, with a response reduction of approximately 42% under 90% high humidity conditions; the sensor in Example 1 maintains stable detection performance across the entire humidity range, with a relative response change of less than 8%. This confirms that the flexible MOFs-based gas sensor modified with PFDTES hydrophobicity can effectively reduce humidity interference and significantly improve the anti-humidity performance of atmospheric VOCs detection.

[0177] (vi) Temperature stability test

[0178] The actual ambient temperature in cities usually fluctuates between 15℃ and 35℃. Therefore, the flexible MOFs-based gas sensor prepared in Example 1, which can identify multiple VOCs in real time, was placed in an environment with a relative humidity of 50% and temperatures of 15℃, 25℃, and 35℃, respectively. Gas-sensitive response tests were carried out on formaldehyde, toluene, and acetone at a concentration of 50 ppm. The test data under the condition of 15℃ was used as a reference. The relevant test results are shown in Table 3.

[0179] Table 3. Test results of the response of flexible MOFs-based gas sensors to VOCs at different temperatures.

[0180]

[0181] As shown in Table 3, the relative response change of the flexible MOFs-based gas sensor is less than 5% under various test temperature conditions, indicating that the flexible MOFs-based gas sensor of the present invention has excellent temperature anti-interference ability and temperature stability.

[0182] (vii) Long-term stability test

[0183] Long-term stability is a key performance indicator for practical applications of atmospheric monitoring, where sensors often need to operate continuously for months or even years. To evaluate the long-term performance of this sensor, the flexible MOF-based gas sensor prepared in Example 1 was placed in ambient air at 25°C and 50% relative humidity for 30 consecutive days, and its response signal to three types of VOCs (formaldehyde, toluene, and acetone) at a concentration of 50 ppm was measured weekly. After the test, the sensor's response value could still maintain 88% or more of the initial response value, confirming its excellent long-term stability.

[0184] (viii) Verification in a real atmospheric environment

[0185] Field tests were conducted in the urban area of ​​Beibei District, Chongqing, China (29°49′N, 106°26′E). The flexible MOF-based gas sensor prepared in Example 1 was compared with a gas chromatography-mass spectrometry (GC-MS) system to determine the coefficient of determination R. 2 A comparative analysis of relative error and detection reliability was conducted. To verify the real-time response capability of the flexible MOFs-based gas sensor of this invention to fluctuations in actual environmental pollutant concentrations, continuous real-time monitoring of target volatile organic compounds (VOCs) was carried out for 72 hours. The comparison results of the VOC concentration measured by the flexible MOFs-based gas sensor in Example 1 of this invention and GC-MS are detailed below. Figure 6 .

[0186] Depend on Figure 6 As can be seen, the coefficients of determination (R²) of the detection results from the flexible MOFs-based gas sensor and the GC-MS detection results of this invention are: formaldehyde 0.92; toluene 0.96; and acetone 0.94. This indicates that the detection data from both methods exhibit excellent linear correlation and high consistency. The relative errors of the three methods are 6.8±2.1%, 4.5±1.8%, and 5.3±2.0%, respectively, all below 10%, falling within a reasonable error range and meeting the practical application requirements for atmospheric environmental monitoring.

[0187] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for fabricating a flexible MOF-based gas sensor capable of real-time identification of multi-component VOCs, characterized in that, Includes the following steps: S1. Synthesis of three MOFs: The amino-containing UiO-66 type metal-organic framework material, copper-based organometallic framework material-1 and zeolite imidazole ester framework material-8 were synthesized by solvothermal method. S2. Substrate pretreatment: The polyimide film is subjected to ultrasonic cleaning, nitrogen gas drying and oxygen plasma activation treatment to obtain a pretreated PI substrate; S3, Electrode deposition: Deposit interdigitated electrodes on the pretreated PI substrate; S4. MOF sensing layer preparation: The three MOFs synthesized in step S1 are dispersed in a solvent and ultrasonically treated to obtain three suspensions. The three suspensions are dropped onto each independent sensing electrode region of the interdigitated electrode. After vacuum drying, the three MOF sensing layers are formed to obtain a gas sensor. S5. Hydrophobic modification treatment: Immerse the sensor obtained in step S4 in a hydrophobic modifier, let it stand at room temperature, and then vacuum dry it to form a hydrophobic layer on the surface of the MOF sensing layer, thus obtaining the flexible MOFs-based gas sensor for real-time identification of multi-component VOCs. The hydrophobic modifier is prepared by dissolving (1H,1H,2H,2H-perfluorodecyl)triethoxysilane in anhydrous ethanol to form a solution with a volume fraction of 0.5% to 1.5%.

2. The method for fabricating a flexible MOFs-based gas sensor capable of real-time identification of multi-component VOCs as described in claim 1, characterized in that, In step S1, the synthesis method of the amino-containing UiO-66 type metal-organic framework material is as follows: Zirconium tetrachloride and aminoterephthalic acid are dissolved in N,N-dimethylformamide, and the mixture is magnetically stirred for 20-30 minutes. The resulting mixture is transferred to a reaction vessel and heated at 115-125°C for 23-25 ​​hours. After naturally cooling to room temperature, the precipitate is collected by centrifugation, washed successively with N,N-dimethylformamide and anhydrous ethanol, and then vacuum dried at 75-85°C for 11-13 hours to obtain the amino-containing UiO-66 type metal-organic framework material; and / or In the mixture, the molar volume ratio of zirconium tetrachloride, aminoterephthalic acid and N,N-dimethylformamide is (0.8~1.2) mmol:(0.8~1.2) mmol:(25~35) mL.

3. The method for fabricating a flexible MOFs-based gas sensor capable of real-time identification of multi-component VOCs as described in claim 1, characterized in that, In step S1, the synthesis method of the copper-based organometallic framework material-1 is as follows: copper nitrate trihydrate is dissolved in N,N-dimethylformamide to obtain a first solution; 1,3,5-pyromellitic acid is dissolved in anhydrous ethanol to obtain a second solution; the first and second solutions are mixed and transferred to a reaction vessel; the reaction is carried out at 95℃~105℃ for 11h~13h; the precipitate is collected by centrifugation; the precipitate is washed successively with N,N-dimethylformamide and anhydrous ethanol; and then vacuum dried at 55℃~65℃ for 7h~9h to obtain the copper-based organometallic framework material-1; and / or In the first solution, the molar volume ratio of copper nitrate trihydrate to N,N-dimethylformamide is (3.5~4.5) mmol: (15~25) mL; In the second solution, the molar volume ratio of 1,3,5-pyromellitic acid to anhydrous ethanol is (2.0~3.0) mmol: (5~15) mL; The volume ratio of the first solution to the second solution is (20~30):(10~18).

4. The method for fabricating a flexible MOFs-based gas sensor capable of real-time identification of multi-component VOCs as described in claim 1, characterized in that, In step S1, the synthesis method of the zeolite imidazole ester framework material-8 is as follows: zinc nitrate hexahydrate and 2-methylimidazole are dissolved in methanol, magnetically stirred for 15-25 minutes, then allowed to stand at room temperature for 23-25 ​​hours, the precipitate is collected by centrifugation, the precipitate is washed with methanol, and then vacuum dried at 65-75°C for 9-11 hours to obtain the zeolite imidazole ester framework material-8; and / or The molar volume ratio of zinc nitrate hexahydrate, 2-methylimidazole and methanol is (1.0~2.0) mmol: (6.0~7.0) mmol: (35~45) mL.

5. The method for fabricating a flexible MOFs-based gas sensor capable of real-time identification of multi-component VOCs as described in claim 1, characterized in that, In step S2, the ultrasonic cleaning is performed using a mixture of acetone, ethanol, and deionized water for 10 to 20 minutes; and / or The nitrogen flow drying is performed by drying the cleaned polyimide film with a nitrogen flow rate of 5 L / min to 15 L / min at room temperature for 25 min to 35 min; and / or The conditions for the oxygen plasma activation treatment are: oxygen flow rate of 15 sccm to 25 sccm, power of 90 W to 110 W, and activation treatment time of 3 min to 8 min.

6. The method for fabricating a flexible MOFs-based gas sensor capable of real-time identification of multi-component VOCs as described in claim 1, characterized in that, In step S3, a titanium adhesion layer with a thickness of 4nm to 6nm is sputtered on the pretreated PI substrate using a magnetron sputtering coating equipment under conditions of 45W to 55W sputtering power, 0.4Pa to 0.6Pa working pressure, and 3min to 8min deposition time. Then, under a light-shielding mask, a gold sensing layer with a thickness of 90nm to 110nm is sputtered and deposited under conditions of 75W to 85W sputtering power, 0.2Pa to 0.4Pa working pressure, and 15min to 25min deposition time to obtain the interdigitated electrode.

7. The method for fabricating a flexible MOFs-based gas sensor capable of real-time identification of multi-component VOCs as described in claim 1, characterized in that, In step S4, the solvent is anhydrous ethanol, the concentration of the three suspensions is 3 mg / mL to 7 mg / mL, and the particle size of the solid particles in the suspension is 100 nm to 500 nm; and / or The ultrasonic treatment time is 25 min to 35 min; and / or The vacuum drying is performed at 55℃~65℃ and a vacuum degree of -0.10 MPa~-0.08 MPa for 25min~35min; and / or The thickness of the MOF sensing layer is 0.9µm to 1.1µm.

8. The method for fabricating a flexible MOFs-based gas sensor capable of real-time identification of multi-component VOCs as described in claim 1, characterized in that, In step S5, the time for standing at room temperature is 50 min to 70 min; and / or The vacuum drying temperature is 95℃~105℃, and the vacuum drying time is 25min~35min; and / or The thickness of the hydrophobic layer is 40nm~60nm.

9. A flexible MOF-based gas sensor capable of real-time identification of multi-component VOCs, characterized in that, It is prepared by the method described in claims 1 to 8 for a flexible MOFs-based gas sensor capable of real-time identification of multi-component VOCs.

10. The application of the flexible MOFs-based gas sensor capable of real-time identification of multi-component VOCs, prepared by the method of any one of claims 1 to 8, as described in claim 9, in atmospheric environmental monitoring.

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