Flexible ammonia gas sensor based on covalent organic framework as well as preparation method and application of flexible ammonia gas sensor
The preparation of covalent organic framework material COF-1 by a solvent-free method solves the environmental protection and flexibility problems of traditional ammonia gas sensors, realizing efficient and sensitive ammonia detection, which is suitable for complex application scenarios.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-18
- Publication Date
- 2026-04-03
AI Technical Summary
Existing ammonia gas sensors have environmental problems, are difficult to synthesize, take a long time to prepare, and have poor flexibility, making them difficult to adapt to complex application scenarios. Traditional materials also have shortcomings in performance, such as high energy consumption and poor selectivity.
The covalent organic framework material COF-1 was synthesized using a solvent-free method. Trimethylbenzaldehyde and p-phenylenediamine were used as monomers, and strong Lewis acid salts were added as salt templates. COF-1 was prepared by solid-state milling and then formed into an ammonia-sensitive material on interdigitated electrodes using polyimide as a flexible substrate to enhance structural stability and sensitivity.
It achieves green and environmentally friendly efficient preparation, improves the synthesis efficiency of covalent organic framework materials, and the sensor exhibits short response time and high sensitivity at room temperature, making it suitable for complex application scenarios.
Smart Images
Figure CN121784098A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of gas sensors, and more particularly to a flexible ammonia gas sensor based on a covalent organic framework, its preparation method, and its application. Background Technology
[0002] Ammonia, a common toxic and harmful gas, is widely present in industrial production, agriculture, and daily life. Excessive ammonia leaks can cause serious harm to human health and the ecological environment. Therefore, rapid, accurate, and sensitive detection of ammonia is of great significance. Currently, there are many types of ammonia gas sensors, including semiconductor, electrochemical, and optical types. However, traditional ammonia gas sensors have certain shortcomings in performance. For example, semiconductor sensors typically operate at high temperatures, consume a lot of energy, and have limited selectivity; electrochemical sensors have relatively short lifespans and are susceptible to environmental interference; optical sensors are expensive, have complex structures, and are not conducive to large-scale application.
[0003] Covalent organic frameworks (COF-1), as a novel type of porous organic material, possess advantages such as large specific surface area, tunable pore size, and good chemical stability, showing great application potential in the field of gas sensing. Applying COF-1 materials to ammonia sensors is expected to improve the sensor's sensitivity and selectivity. However, current COF-1-based ammonia sensors often employ organic solvents in their synthesis, posing environmental concerns. Furthermore, the synthesis process is difficult and time-consuming, hindering mass production. Additionally, the sensors exhibit poor flexibility, making them unsuitable for complex application scenarios.
[0004] It is evident that the preparation of highly crystalline covalent organic frameworks remains a significant challenge, limiting their practical applications. Therefore, there is an urgent need to develop a gas sensor based on covalent organic framework materials that is environmentally friendly and suitable for large-scale production. Summary of the Invention
[0005] To address the problems existing in the prior art, this invention provides a flexible ammonia gas sensor based on a covalent organic framework, its preparation method, and its application. Trimethylbenzaldehyde and p-phenylenediamine are selected as monomers, and small-pore COF-1 is constructed through solid-state grinding to enhance structural stability and improve the synthesis efficiency of the covalent organic framework material COF-1. Furthermore, COF-1 ammonia-sensitive material is formed on interdigitated electrodes using PI as a flexible substrate, resulting in a sensor with good flexibility and sensitivity.
[0006] The first objective of this invention is to provide a flexible ammonia gas sensor based on a covalent organic framework, the gas sensor comprising: a flexible polyimide substrate, interdigitated electrodes attached to the flexible polyimide substrate, and a covalent organic framework material coated on the interdigitated electrodes.
[0007] The second objective of this invention is to provide a method for fabricating a flexible ammonia gas sensor based on a covalent organic framework, the method comprising: S1 uses pyromellitic aldehyde and p-phenylenediamine as reactants, adds a strong Lewis acid salt as a salt template, mixes them evenly, and then reacts by grinding to obtain an intermediate product. S2 After placing the intermediate product in a high-temperature oven for heat preservation, it is then filtered and washed to obtain the covalent organic framework material COF-1. S3. The covalent organic framework material COF-1 is dispersed in an ethanol solution and subjected to ultrasonic treatment to prepare a COF-1 suspension; S4. The COF-1 suspension is directly drop-coated onto the interdigitated electrodes attached to the polyimide flexible substrate using a drop-coating method. After drying, the COF-1 ammonia-sensitive material is formed, resulting in a flexible ammonia gas sensor based on a covalent organic framework.
[0008] Specifically, in step S1, the mass ratio of pyromellitic aldehyde to p-phenylenediamine is approximately 1:0.77; the mass ratio of pyromellitic aldehyde to strong Lewis acid salt is 1:1 to 1:3; and the strong Lewis acid salt is zinc trifluoromethanesulfonate or zinc chloride.
[0009] Specifically, the grinding reaction time in step S1 is 5 to 10 minutes.
[0010] Specifically, the structural formula of the covalent organic framework material COF-1 mentioned in step S1 is: ; Specifically, the heat preservation time in step S2 is 10~100s, and the temperature is 100~120℃.
[0011] Specifically, the ultrasonic treatment time in step S3 is 40 min; the concentration of the COF-1 suspension is 5 mg / mL.
[0012] Specifically, the interdigitated electrode mentioned in step S4 is a copper interdigitated electrode with a finger width of 50~100μm, an interdigital spacing of 50~100μm, and 10~20 pairs of interdigitated fingers.
[0013] Specifically, the polyimide flexible substrate has a thickness of 25 μm and a size of 10 mm × 10 mm.
[0014] A third objective of this invention is the application of the same flexible ammonia gas sensor described above in the detection of ammonia at room temperature.
[0015] Compared with the prior art, the beneficial effects of the present invention include: (1) The present invention uses a solvent-free method to synthesize covalent organic framework material COF-1, which is prepared by adding strong Lewis salts such as zinc trifluoromethanesulfonate or zinc chloride as monomers and grinding them thoroughly. The preparation method using solid-state grinding and Lewis salt catalysis does not require the use of organic solvents, which solves the problems of toxicity and pollution caused by the reliance on organic solvents in traditional synthesis methods. At the same time, it also solves the problems of difficult synthesis, long preparation time and difficulty in large-scale production, which is in line with the principles of green chemistry. (2) In this invention, pyromellitic methyl ether (aldehyde monomer) and p-phenylenediamine (amine monomer) are selected as monomers. Due to the small pore size of the above two monomers, zinc ions can easily enter the pores during the reaction. By constructing small-pore COF-1, it is beneficial for zinc ion insertion and enhances structural stability. Zinc trifluoromethanesulfonate or zinc chloride are selected as strong Lewis salts, which have the functions of catalytic condensation reaction and salt template. Due to the presence of metallic zinc ions in strong Lewis salts, the synthesis time of COF-1 is greatly shortened. It also catalyzes the reaction between amine and aldehyde groups, and zinc ions are inserted into the COF-1 pores, which enhances crystallinity and structural stability and improves the synthesis efficiency of covalent organic framework material COF-1. (3) The present invention uses polyimide (PI) as a flexible substrate and forms COF-1 ammonia sensitive material on the flexible interdigitated electrode, which makes the sensor have good flexibility and sensitivity and can adapt to more complex application scenarios. At room temperature and ammonia concentration of 100ppm, the Rt test shows that the response time is short and the sensitivity is high, with excellent detection performance and broad application prospects and market potential. Attached Figure Description
[0016] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings in the following description are merely exemplary, and those skilled in the art can derive other embodiments based on the provided drawings without creative effort.
[0017] Figure 1 This is a flowchart illustrating the fabrication process of the flexible ammonia gas sensor prepared according to an embodiment of the present invention. Figure 2 This is a schematic diagram of the structure of the flexible ammonia gas sensor prepared according to an embodiment of the present invention; Figure 3 The chemical structure diagram of COF-1, a covalent organic framework material prepared in an embodiment of the present invention; Figure 4 The XRD pattern of COF-1, a covalent organic framework material prepared in Example 1 of this invention; Figure 5(ab) are SEM images of the covalent organic framework material COF-1 prepared in Example 1 of the present invention at different magnifications; Figure 6 The infrared spectrum of COF-1, a covalent organic framework material prepared in Example 1 of this invention; Figure 7 The XRD pattern of the reactants prepared in Comparative Example 1 of this invention; Figure 8 The image shows the recovery curves of the flexible ammonia gas sensor prepared in Example 1 of this invention for five consecutive dynamic responses to 100 ppm ammonia at room temperature. Figure 9 The image shows the dynamic response recovery curves of the flexible ammonia gas sensor prepared in Example 1 of this invention for different concentrations of ammonia at room temperature. Detailed Implementation
[0018] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Unless otherwise defined, all technical and scientific terms used in this specification have the same meaning as commonly understood by those skilled in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing specific embodiments only and is not intended to limit the present invention.
[0019] Please see Figure 1-3 , Figure 1 This is a flowchart illustrating the fabrication process of the flexible ammonia gas sensor prepared according to an embodiment of the present invention. Figure 2 This is a schematic diagram of the structure of the flexible ammonia gas sensor prepared according to an embodiment of the present invention; wherein, 1 is a flexible substrate, 2 is an interdigitated electrode, and 3 is a COF-1 ammonia gas sensitive material; Figure 3 for Figure 3 The chemical structure diagram of the covalent organic framework material COF-1 prepared in this embodiment of the invention is shown below; the specific steps are as follows: Example
[0020] S1 uses 1g of pyromellitic aldehyde and 0.77g of p-phenylenediamine as reaction monomers, adds 1g of zinc trifluoromethanesulfonate as a salt template, mixes evenly, and then reacts by grinding at room temperature for 10 minutes to obtain the intermediate product. S2 The intermediate product was placed in a high-temperature oven and kept at 120 °C for 80 seconds, and then washed by vacuum filtration with deionized water to obtain the covalent organic framework material COF-1. S3 The covalent organic framework material COF-1 was dispersed in an ethanol solution and ultrasonically treated for 40 min to prepare a COF-1 suspension with a concentration of 5 mg / mL; S4. The COF-1 suspension was directly drop-coated onto the interdigitated electrodes (12 interdigitated fingers, 50 μm finger width, and 50 μm interdigitated distance) attached to the polyimide flexible substrate (25 μm thick, 10 mm × 10 mm in size) using a drop-coating method. The electrodes were then dried at 70 °C to form the COF-1 ammonia-sensitive material, thus obtaining the flexible ammonia gas sensor based on a covalent organic framework prepared in Example 1.
[0021] Example 2 S1 uses 1g of pyromellitic aldehyde and 0.77g of p-phenylenediamine as reaction monomers, adds 1.5g of zinc trifluoromethanesulfonate as a salt template, mixes evenly, and then reacts by grinding at room temperature for 10 minutes to obtain the intermediate product. S2 The intermediate product was placed in a high-temperature oven and kept at 120 °C for 80 seconds, and then washed by vacuum filtration with deionized water to obtain the covalent organic framework material COF-1. S3 The covalent organic framework material COF-1 was dispersed in an ethanol solution and ultrasonically treated for 40 min to prepare a COF-1 suspension with a concentration of 5 mg / mL; S4. The COF-1 suspension was directly drop-coated onto the interdigitated electrodes (12 interdigitated fingers, 50 μm finger width, and 50 μm interdigitated spacing) attached to the polyimide flexible substrate (25 μm thick, 10 mm × 10 mm in size) using a drop-coating method. The electrodes were then dried at 70 °C to form the COF-1 ammonia gas sensitive material, thus obtaining the flexible ammonia gas sensor based on a covalent organic framework prepared in Example 2. Example
[0022] S1 uses 1g of pyromellitic aldehyde and 0.77g of p-phenylenediamine as reaction monomers, adds 2g of zinc trifluoromethanesulfonate as a salt template, mixes evenly, and then reacts by grinding at room temperature for 10 minutes to obtain the intermediate product. S2 The intermediate product was placed in a high-temperature oven and kept at 120 °C for 80 seconds, and then washed by vacuum filtration with deionized water to obtain the covalent organic framework material COF-1. S3 The covalent organic framework material COF-1 was dispersed in an ethanol solution and ultrasonically treated for 40 min to prepare a COF-1 suspension with a concentration of 5 mg / mL; S4. The COF-1 suspension was directly drop-coated onto the interdigitated electrodes (12 interdigitated fingers, 50 μm finger width, and 50 μm interdigitated distance) attached to the polyimide flexible substrate (25 μm thick, 10 mm × 10 mm in size) using a drop-coating method. The electrodes were then dried at 70 °C to form the COF-1 ammonia-sensitive material, thus obtaining the flexible ammonia gas sensor based on a covalent organic framework prepared in Example 3. Example
[0023] S1 uses 1g of pyromellitic aldehyde and 0.77g of p-phenylenediamine as reaction monomers, adds 2.5g of zinc trifluoromethanesulfonate as a salt template, mixes evenly, and then reacts by grinding at room temperature for 10 minutes to obtain the intermediate product. S2 The intermediate product was placed in a high-temperature oven and kept at 120 °C for 80 seconds, and then washed by vacuum filtration with deionized water to obtain the covalent organic framework material COF-1. S3 The covalent organic framework material COF-1 was dispersed in an ethanol solution and ultrasonically treated for 40 min to prepare a COF-1 suspension with a concentration of 5 mg / mL; S4. The COF-1 suspension was directly drop-coated onto the interdigitated electrodes (12 interdigitated fingers, 50 μm finger width, and 50 μm interdigitated distance) attached to the polyimide flexible substrate (25 μm thick, 10 mm × 10 mm in size) using a drop-coating method. The electrodes were then dried at 70 °C to form the COF-1 ammonia-sensitive material, thus obtaining the flexible ammonia gas sensor based on a covalent organic framework prepared in Example 4.
[0024] Example 5 S1 uses 1g of pyromellitic aldehyde and 0.77g of p-phenylenediamine as reaction monomers, adds 3g of zinc trifluoromethanesulfonate as a salt template, mixes evenly, and then reacts by grinding at room temperature for 10 minutes to obtain the intermediate product. S2 The intermediate product was placed in a high-temperature oven and kept at 120 °C for 80 seconds, and then washed by vacuum filtration with deionized water to obtain the covalent organic framework material COF-1. S3 The covalent organic framework material COF-1 was dispersed in an ethanol solution and ultrasonically treated for 40 min to prepare a COF-1 suspension with a concentration of 5 mg / mL; S4. The COF-1 suspension was directly drop-coated onto the interdigitated electrodes (12 interdigitated pairs, 50 μm finger width, and 50 μm interdigitated spacing) attached to the polyimide flexible substrate (25 μm thick, 10 mm × 10 mm in size) using a drop-coating method. The electrodes were then dried at 70 °C to form the COF-1 ammonia-sensitive material, thus obtaining the flexible ammonia gas sensor based on a covalent organic framework prepared in Example 5.
[0025] Example 6 S1 uses 1g of pyromellitic aldehyde and 0.77g of p-phenylenediamine as reaction monomers, adds 1g of zinc chloride as a salt template, mixes evenly, and then reacts by grinding at room temperature for 8 minutes to obtain the intermediate product. S2 The intermediate product was placed in a high-temperature oven and kept at 110 °C for 50 seconds, and then washed by vacuum filtration with deionized water to obtain the covalent organic framework material COF-1. S3 The covalent organic framework material COF-1 was dispersed in an ethanol solution and ultrasonically treated for 40 min to prepare a COF-1 suspension with a concentration of 5 mg / mL; S4. The COF-1 suspension was directly drop-coated onto the interdigitated electrodes (14 interdigitated pairs, 80 μm finger width, and 80 μm interdigitated spacing) attached to the polyimide flexible substrate (25 μm thick, 10 mm × 10 mm in size) using a drop-coating method. The electrodes were then dried at 70 °C to form the COF-1 ammonia-sensitive material, thus obtaining the flexible ammonia gas sensor based on a covalent organic framework prepared in Example 6.
[0026] Example 7 S1 uses 1g of pyromellitic aldehyde and 0.77g of p-phenylenediamine as reactants, adds 1.3g of zinc chloride as a salt template, mixes evenly, and then reacts by grinding at room temperature for 5 minutes to obtain the intermediate product. S2 The intermediate product was placed in a high-temperature oven and kept at 100 °C for 100 s, and then washed by vacuum filtration with deionized water to obtain the covalent organic framework material COF-1. S3 The covalent organic framework material COF-1 was dispersed in an ethanol solution and ultrasonically treated for 40 min to prepare a COF-1 suspension with a concentration of 5 mg / mL; S4. The COF-1 suspension was directly drop-coated onto the interdigitated electrodes (14 interdigitated pairs, 100 μm finger width, and 100 μm interdigitated distance) attached to the polyimide flexible substrate (25 μm thick, 10 mm × 10 mm in size) using a drop-coating method. The electrodes were then dried at 70 °C to form the COF-1 ammonia gas sensitive material, thus obtaining the flexible ammonia gas sensor based on a covalent organic framework prepared in Example 7.
[0027] Example 8 S1 uses 1g of pyromellitic aldehyde and 0.77g of p-phenylenediamine as reactants, adds 2.7g of zinc chloride as a salt template, mixes evenly, and then reacts by grinding at room temperature for 10 minutes to obtain the intermediate product. S2 The intermediate product was placed in a high-temperature oven and kept at 110 °C for 40 seconds, and then washed by vacuum filtration with deionized water to obtain the covalent organic framework material COF-1. S3 The covalent organic framework material COF-1 was dispersed in an ethanol solution and ultrasonically treated for 40 min to prepare a COF-1 suspension with a concentration of 5 mg / mL; S4. The COF-1 suspension was directly drop-coated onto the interdigitated electrodes (12 interdigitated fingers, 50 μm finger width, and 50 μm interdigitated distance) attached to the polyimide flexible substrate (25 μm thick, 10 mm × 10 mm in size) using a drop-coating method. The electrodes were then dried at 70 °C to form the COF-1 ammonia-sensitive material, thus obtaining the flexible ammonia gas sensor based on a covalent organic framework prepared in Example 8.
[0028] Comparative Example 1 The difference from Example 1 is that no strong Lewis acid salt is added.
[0029] S1 uses 1g of pyromellitic methyl ether and 0.77g of p-phenylenediamine as the monomers. After mixing them evenly, the mixture is ground and reacted at room temperature for 10 minutes to obtain the intermediate product. S2 The intermediate product was placed in a high-temperature oven and kept at 120 °C for 80 s, and then washed by vacuum filtration with deionized water to obtain covalent organic framework COF-1. S3 The reactants were dispersed in an ethanol solution and sonicated for 40 min to prepare a COF-1 suspension with a concentration of 5 mg / mL; S4. The COF-1 suspension was directly drop-coated onto the interdigitated electrodes (12 interdigitated pairs, 50 μm finger width, and 50 μm interdigitated spacing) attached to the polyimide flexible substrate (25 μm thick, 10 mm × 10 mm in size) using a drop-coating method. The electrodes were then dried at 70 °C to form the COF-1 ammonia gas sensing material, thus obtaining the flexible ammonia gas sensor based on a covalent organic framework prepared in Comparative Example 1.
[0030] Comparative Example 2 The difference from Example 1 lies in the amount of strong Lewis acid salt added.
[0031] S1 uses 1g of pyromellitic aldehyde and 0.77g of p-phenylenediamine as reaction monomers, and adds 0.5g of zinc trifluoromethanesulfonate as a salt template. After mixing evenly, the reaction is carried out by grinding at room temperature for 10 minutes to obtain the intermediate product. S2 The intermediate product was placed in a high-temperature oven and kept at 120 °C for 80 s, and then washed by vacuum filtration with deionized water to obtain covalent organic framework COF-1. S3. COF-1 based on covalent organic framework was dispersed in ethanol solution and sonicated for 40 min to prepare a COF-1 suspension with a concentration of 5 mg / mL. S4. The COF-1 suspension was directly drop-coated onto the interdigitated electrodes (12 interdigitated pairs, 50 μm finger width, and 50 μm interdigitated spacing) attached to the polyimide flexible substrate (25 μm thick, 10 mm × 10 mm in size) using a drop-coating method. The electrodes were then dried at 70 °C to form the COF-1 ammonia gas sensitive material, thus obtaining the flexible ammonia gas sensor based on the reactants prepared in Comparative Example 2.
[0032] Comparative Example 3 The difference from Example 1 lies in the amount of strong Lewis acid salt added.
[0033] S1 uses 1g of pyromellitic aldehyde and 0.77g of p-phenylenediamine as reaction monomers, adds 3.5g of zinc trifluoromethanesulfonate as a salt template, mixes evenly, and then reacts by grinding at room temperature for 10 minutes to obtain the intermediate product. S2 The intermediate product was placed in a high-temperature oven and kept at 120 °C for 80 s, and then washed by vacuum filtration with deionized water to obtain covalent organic framework COF-1. S3. The covalent organic framework COF-1 was dispersed in an ethanol solution and sonicated for 40 min to prepare a COF-1 suspension with a concentration of 5 mg / mL. S4. The COF-1 suspension was directly drop-coated onto the interdigitated electrodes (12 interdigitated pairs, 50 μm finger width, and 50 μm interdigitated spacing) attached to the polyimide flexible substrate (25 μm thick, 10 mm × 10 mm in size) using a drop-coating method. The electrodes were then dried at 70 °C to form the COF-1 ammonia gas sensitive material, thus obtaining the flexible ammonia gas sensor based on the reactants prepared in Comparative Example 3.
[0034] Comparative Example 4 The difference from Example 1 is that the reaction monomers are different.
[0035] S1 uses 1g of 1,3,5-tris(4'-aldehyde phenyl)benzene and 0.77g of p-phenylenediamine as the monomers, adds 1g of zinc trifluoromethanesulfonate as the salt template, mixes evenly, and then reacts by grinding at room temperature for 10min to obtain the intermediate product. S2 The intermediate product is placed in a high-temperature oven and kept at 120 °C for 80 s, and then washed by vacuum filtration with deionized water to obtain the reactant. S3 The reactants were dispersed in an ethanol solution and sonicated for 40 min to prepare a reactant suspension with a concentration of 5 mg / mL; S4 The reactant suspension was directly drop-coated onto the interdigitated electrodes (12 interdigitated pairs, 50 μm finger width, and 50 μm interdigitated spacing) attached to the polyimide flexible substrate (25 μm thick, 10 mm × 10 mm in size) using a drop-coating method. The electrodes were then dried at 70 °C to form a reactant film, thus obtaining the reactant-based flexible ammonia gas sensor prepared in Comparative Example 4.
[0036] Structural characterization Figure 4 The image shows the XRD pattern of COF-1, a covalent organic framework material prepared in Example 1 of this invention; from Figure 4 As can be seen from the image, the covalent organic framework material COF-1 prepared in Example 1 exhibits layered structure characteristic peaks and secondary short-range ordered characteristic peaks. The characteristic peaks are distinct at various locations. The (100) crystal plane is located at approximately 5°, and its half-peak width is only about 1°, which proves the high crystallinity of the crystal formed. At the same time, the (001) crystal plane at approximately 25° corresponds to a layer spacing of 0.3 nm between the layers of the two-dimensional structure. In summary, this proves that the preparation of COF-1 was successful. Figure 5 (ab) are SEM images of the covalent organic framework material COF-1 prepared in Example 1 of this invention at different magnifications; from Figure 5 As shown in (ab), the covalent organic framework material COF-1 is composed of stacked two-dimensional materials, exhibiting clear signs of layer-by-layer stacking, proving the successful preparation of the two-dimensional material and further demonstrating the successful preparation of COF-1. At different magnifications, a uniform fibrous structure is clearly visible on the surface of the formed film, creating interconnected channels. This morphology provides a large specific surface area for the sensor's sensitive layer, exposing more active sites to interact with ammonia gas and improving the sensor's response capability. Simultaneously, the uniform surface morphology helps reduce electronic defects at grain boundaries, increasing the resistance change of the sensitive layer when ammonia gas is adsorbed, further enhancing the sensor's sensitivity. Figure 6 The infrared spectrum of COF-1, a covalent organic framework material prepared in Example 1 of this invention; from Figure 6 It can be seen from this that 1618 cm -1 The presence of a distinct characteristic peak of C=N stretching vibration at this point proves the successful preparation of COF-1. Figure 7 The XRD pattern of the reactants prepared in Comparative Example 1 of this invention is shown below. Figure 7 No obvious characteristic peaks were observed, indicating that the use of other monomers did not form a covalent organic framework material COF-1.
[0037] In the embodiments of this invention, the dosage of strong Lewis acids was optimized and screened. Strong Lewis acid catalysts act as salt templates, and their dosage needs to be more precisely matched to the potential coordination sites in the COF-1 structure. For this hypothetical structure of COF-1-1, which consists of six imine nitrogen atoms coordinated to a single Zn²⁺ atom, the dosage will be close to stoichiometry. A commonly used and safe dosage range is 30–60% of the molar ratio (relative to the trimesin monomer), which translates to a mass ratio of 1:0.6–1:1. In the embodiments of this invention, it was found that highly crystalline COF-1 could still be prepared by adding different proportions, possibly related to the rapid reaction of the material. Table 1 compares the crystallinity of the final COF-1 obtained by adding different mass ratios of trimesin and strong Lewis acid salts during the preparation process of Examples 1–5 and Comparative Examples 1–3.
[0038] Table 1
[0039] The results are shown in Table 1. According to the principle of optimal crystallinity, the covalent organic framework material COF-1 prepared when the mass ratio of pyromellitic aldehyde to strong Lewis acid salt is 1:1 to 1:3 has good crystallinity.
[0040] Performance testing In this embodiment of the invention, the detection of ammonia is preferably performed in a gas-sensitive testing device. The flexible ammonia gas sensor based on a covalent organic framework is placed on the sample holder of the gas-sensitive testing device, and the gas to be tested is preferably injected into the cavity of the gas-sensitive testing device.
[0041] The two electrodes of the interdigitated electrodes in the flexible ammonia gas sensor based on a covalent organic framework prepared in Example 1 are connected to two terminals of an electrochemical workstation via copper wires. A voltage of 1V is applied to the electrochemical workstation, and the current of the circuit consisting of the sensor, wires, and electrochemical workstation is collected. The chemiluminescence resistive ammonia sensor is placed on the sample holder of the gas-sensitive testing device. Ammonia gas of different concentrations is injected into the cavity of the gas-sensitive testing device, and the circuit current is collected at different times. The current is converted into an R-resistance-T-time curve. The sensing response value of the chemiluminescence resistive ammonia sensor is calculated based on the resistance-time curve. The sensing response value is calculated as follows: Sensing response value = (Rammonia - Rair) ÷ Rair × 100%, where the unit of sensing response value is %; a standard curve of sensing response value-ammonia concentration is obtained, where the concentrations of ammonia are 5ppm, 10ppm, 25ppm, 50ppm, 75ppm, and 100ppm. The linear relationship between the sensor response value and the ammonia concentration is shown in the following formula: y = (0.09297 ± 0.0057)x + (14.68 ± 0.3234), where x is the ammonia concentration (ppm) and y is the sensor response value (%). Then, based on the sensor response value-ammonia concentration curve, the ammonia concentration is calculated as follows: Ammonia concentration = (sensor response value - 14.68%) ÷ 0.0009297; where the ammonia concentration is in ppm and the sensor response value is in %. In this embodiment of the invention, the data consists of the SA3102 electrical testing system and the in-situ test cell, used to record and analyze the sensor's response data, such as resistance changes and response time.
[0042] Please see Figure 8-9 , Figure 8 This is a five-times continuous dynamic response recovery curve of the flexible ammonia gas sensor prepared in Example 1 of this invention to 100 ppm ammonia at room temperature. Upon contact with ammonia molecules, the resistance changes rapidly in one direction, reaching equilibrium before a relatively flat plateau appears. The chemiluminescence resistivity ammonia sensor exhibits maximum response to ammonia. As the ammonia is removed, the sensing signal rapidly decreases and returns to near the baseline before adsorption. The response is significant, with a response ratio of 60%, and high sensitivity across five consecutive tests, demonstrating good response stability. Calculations based on the formula show that its response value to ammonia at 100 ppm reaches approximately 60%, exhibiting excellent performance compared to existing reports. This superior performance stems from the specifically designed structure of the COF itself. Figure 9This is a dynamic response recovery curve of the flexible ammonia gas sensor prepared in Example 1 of the present invention to different concentrations of ammonia gas at room temperature; as the ammonia gas concentration increases, its response also increases. Analysis shows that the response value to ammonia gas exhibits a linear relationship with increasing ppm, which is in line with our expectations. Test results indicate that the flexible ammonia gas sensor prepared in Example 1 has the advantages of short response time and high sensitivity at a room temperature and an ammonia concentration of 100 ppm.
[0043] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.
Claims
1. A flexible ammonia gas sensor based on a covalent organic framework, characterized in that, The gas sensor includes: a polyimide flexible substrate, interdigitated electrodes attached to the polyimide flexible substrate, and a covalent organic framework material coated on the interdigitated electrodes.
2. A method for fabricating a flexible ammonia gas sensor based on a covalent organic framework as described in claim 1, characterized in that, The preparation method includes: S1 uses pyromellitic aldehyde and p-phenylenediamine as reactants, adds a strong Lewis acid salt as a salt template, mixes them evenly, and then reacts by grinding to obtain an intermediate product. S2 After placing the intermediate product in a high-temperature oven for heat preservation, it is then filtered and washed to obtain the covalent organic framework material COF-1. S3. The covalent organic framework material COF-1 is dispersed in an ethanol solution and subjected to ultrasonic treatment to prepare a COF-1 suspension; S4. The COF-1 suspension is coated onto the interdigitated electrodes attached to the polyimide flexible substrate by drop coating. After drying, the COF-1 ammonia gas sensitive material is formed, resulting in a flexible ammonia gas sensor based on a covalent organic framework.
3. The preparation method according to claim 2, characterized in that, In step S1, the mass ratio of pyromellitic methyl ether to p-phenylenediamine is approximately 1:0.77; the mass ratio of pyromellitic methyl ether to strong Lewis acid salt is 1:1 to 1:3; the strong Lewis acid salt is zinc trifluoromethanesulfonate or zinc chloride.
4. The preparation method according to claim 2, characterized in that, The grinding reaction time in step S1 is 5-10 min.
5. The preparation method according to claim 2, characterized in that, The structural formula of the covalent organic framework material COF-1 mentioned in step S1 is:
6. The preparation method according to claim 2, characterized in that, The heat preservation time in step S2 is 10~100s, and the temperature is 100~120℃.
7. The preparation method according to claim 2, characterized in that, The ultrasonic treatment time in step S3 is 40 min; the concentration of the COF-1 suspension is 5 mg / mL.
8. The preparation method according to claim 2, characterized in that, The interdigitated electrodes mentioned in step S4 are copper interdigitated electrodes with a finger width of 50~100μm, an interdigital spacing of 50~100μm, and 10~20 pairs of interdigitated fingers.
9. The preparation method according to claim 2, characterized in that, The polyimide flexible substrate has a thickness of 25 μm and a size of 10 mm × 10 mm.
10. The application of the flexible ammonia gas sensor as described in claim 1 in detecting ammonia at room temperature.