Qcm based on hydroxyl-functionalized covalent organic framework materials, methods of preparation and applications

Abstract

The application provides a QCM based on a hydroxyl-functionalized covalent organic framework material, a preparation method and application, the QCM comprising a quartz crystal wafer with a silver electrode, and the surface of the quartz crystal wafer is provided with a hydroxyl-functionalized covalent organic framework material; the hydroxyl-functionalized covalent organic framework material is a covalent organic framework film or a covalent organic framework nanoparticle prepared by reacting 1,3,5-tri(4-aminophenyl)benzene with 2,5-dihydroxyterephthaldehyde. The skeleton of the hydroxyl-functionalized covalent organic framework material contains a large number of uniformly distributed hydroxyl functional groups, can produce specific recognition effect on H2S through hydrogen bond and acid-base interaction, and has extremely high selectivity to H2S. The covalent organic framework material has an ordered mesoporous structure and a high specific surface area, can effectively enrich H2S molecules, and improves the detection sensitivity. The QCM based on the material can work at room temperature, the response and recovery times are both not more than 14s, the detection limit is as low as 5 ppm, and the real-time requirement of industrial safety and environmental monitoring can be met.

Description

Technical Field

[0001] This invention belongs to the field of gas detection technology, specifically, it relates to a QCM based on hydroxyl-functionalized covalent organic framework material, its preparation method, and its application in hydrogen sulfide detection. Background Technology

[0002] Hydrogen sulfide (H2S) is a widespread toxic and harmful gas, primarily originating from industrial activities such as petroleum refining, natural gas extraction, and wastewater treatment, as well as natural processes like volcanic eruptions and anaerobic decomposition of organic matter. H2S is highly corrosive and toxic; even at low concentrations, it can cause serious damage to the human respiratory and nervous systems. Long-term exposure to H2S can also lead to chronic diseases. Oil refineries, wastewater treatment plants, and confined spaces pose acute occupational hazards, while industrial sites and areas near geothermal zones present potential risks of chronic diseases. Therefore, rapid and highly selective detection of H2S is of great significance for ensuring industrial production safety, environmental monitoring, and public health.

[0003] Currently, commonly used H2S detection technologies mainly include metal oxide semiconductor (MOS) sensors, electrochemical sensors, and optical detection methods. Among these, MOS sensors typically operate at high temperatures, consume high power, and are susceptible to environmental humidity; while electrochemical sensors offer high sensitivity, they suffer from cross-sensitivity, short lifespan, and complex maintenance; and although optical detection methods offer high accuracy, the instruments are expensive, making portability and real-time online monitoring difficult. Therefore, developing an H2S sensor that can operate stably at room temperature, has a rapid response, excellent selectivity, and is cost-effective has become a current research hotspot.

[0004] Quartz crystal microbalance (QCM) sensors, based on the piezoelectric effect, can convert nanogram-level mass changes into measurable frequency signals. They offer advantages such as real-time response, ease of operation, low power consumption, easy integration, low cost, and room-temperature operation, and have garnered significant attention in recent years. QCM sensors are widely applicable to sensitive materials; by coating their surfaces with materials possessing specific recognition capabilities, highly selective detection of target gases can be achieved. Therefore, developing high-performance sensitive materials suitable for QCM platforms is crucial for improving the performance of gas sensors.

[0005] In recent years, covalent organic frameworks (COFs) have shown great promise in the field of gas sensing due to their highly ordered pore structure, high specific surface area, good thermal and chemical stability, and strong structural designability. Compared with amorphous polymers or disordered porous carbon, the crystallinity of COFs ensures the repeatability of sensor responses; compared with traditional metal oxides, COFs can operate efficiently at room temperature, avoiding the energy consumption and safety hazards associated with high-temperature operation. More importantly, through molecular design, specific functional groups (such as hydroxyl, amino, and heterocyclic groups) can be introduced into the COF backbone, thereby providing abundant and accessible recognition sites for target gas molecules.

[0006] For H2S detection, hydroxyl (-OH) functional groups are considered a highly promising recognition unit due to their hydrogen bonding and acid-base interactions with H2S molecules. However, current research on using hydroxyl-functionalized COFs in QCM sensors to achieve highly selective and rapid H2S detection is still limited. Further research on the design of related sensitive materials and sensor performance is needed; in other words, existing H2S detection technologies still have shortcomings in terms of selectivity, response speed, and room-temperature operability.

[0007] In view of this, developing a QCM sensor based on hydroxyl-functionalized covalent organic framework materials to achieve high selectivity, rapid response and stable detection of H2S has become an urgent technical problem to be solved. Summary of the Invention

[0008] Therefore, the technical problem to be solved by this invention is that traditional H2S detection technology has shortcomings in terms of selectivity, response speed, cost, and operating conditions. Thus, this invention proposes a QCM based on hydroxyl-functionalized covalent organic framework material, which has strong selectivity, fast response speed, low cost, and long-term stability, as well as its preparation method and its application in H2S gas detection.

[0009] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows: The first aspect of this invention provides a QCM based on a hydroxyl-functionalized covalent organic framework material, comprising a quartz wafer with a silver electrode, wherein the quartz wafer with the silver electrode is provided with a hydroxyl-functionalized covalent organic framework material; wherein the hydroxyl-functionalized covalent organic framework material is a covalent organic framework film prepared by reacting 1,3,5-tris(4-aminophenyl)benzene with 2,5-dihydroxy-terephthalaldehyde; or the hydroxyl-functionalized covalent organic framework material is a covalent organic framework nanoparticle prepared by reacting 1,3,5-tris(4-aminophenyl)benzene with 2,5-dihydroxy-terephthalaldehyde.

[0010] Preferably, the hydroxyl-functionalized covalent organic framework material is the covalent organic framework film, and the thickness of the covalent organic framework film is 50-1500 nm.

[0011] Alternatively, as a preferred embodiment, the hydroxyl-functionalized covalent organic framework material is the covalent organic framework nanoparticle, and the average particle size of the covalent organic framework nanoparticle is 200-600 nm.

[0012] Preferably, the quartz crystal has a frequency of 5-10MHz and a diameter of 8-14mm.

[0013] A second aspect of this invention provides a method for preparing the QCM based on hydroxyl-functionalized covalent organic frameworks, comprising the following steps: To prepare an aqueous solution, glacial acetic acid was added to 1,3,5-tris(4-aminophenyl)benzene. After the 1,3,5-tris(4-aminophenyl)benzene dissolved, ultrapure water was added to obtain an aqueous solution. In the aqueous solution, the mass concentration of 1,3,5-tris(4-aminophenyl)benzene was 0.01-0.2 wt%, and the mass concentration of glacial acetic acid was 0.05-0.5 wt%. An organic phase solution is prepared by adding a first organic solvent to 2,5-dihydroxyterephthalaldehyde, dispersing the solution, and then forming an organic phase solution. The mass concentration of 2,5-dihydroxyterephthalaldehyde in the organic phase solution is 0.005-0.1 wt%. Interfacial polymerization involves placing the aqueous solution in a reaction vessel, then adding the organic solution dropwise, and reacting at 15-30°C for 10-180 min to form the covalent organic framework film at the interface separation point. The covalent organic framework film is attached to the surface of the quartz wafer with silver electrodes.

[0014] Preferably, the first organic solvent is one of ethyl acetate, n-hexane, or toluene.

[0015] Alternatively, a second aspect of the present invention provides a method for preparing the QCM based on hydroxyl-functionalized covalent organic framework material, comprising the following steps: S1. Mix 1,3,5-tris(4-aminophenyl)benzene and 2,5-dihydroxyterephthalaldehyde, and add a second organic solvent to obtain a premixed solution, wherein the molar ratio of 1,3,5-tris(4-aminophenyl)benzene to 2,5-dihydroxyterephthalaldehyde is 1:1-1:2. S2. Add glacial acetic acid to the premixed solution, react at room temperature for 10-60 min, and collect the reaction product by centrifugation. S3. Wash and dry the reaction product to obtain the covalent organic framework nanoparticles. S4. Coat the covalent organic framework nanoparticles onto the surface of the quartz wafer with silver electrodes.

[0016] Preferably, the second organic solvent is one of acetonitrile, tetrahydrofuran, or N,N-dimethylformamide.

[0017] Preferably, in step S2, during the centrifugation collection of the reaction product, the centrifugation speed is 5000-10000 rpm and the centrifugation time is 10-20 min; in step S3, the drying temperature is 60-100℃ and the drying time is 8-24 h.

[0018] A third aspect of this invention provides an application of the aforementioned QCM based on hydroxyl-functionalized covalent organic framework material in hydrogen sulfide detection.

[0019] The technical solution of the present invention has the following advantages compared with the prior art: This invention provides a QCM based on hydroxyl-functionalized covalent organic framework materials, comprising a quartz wafer with silver electrodes, the surface of which is coated with the hydroxyl-functionalized covalent organic framework material. The hydroxyl-functionalized covalent organic framework material is a covalent organic framework film prepared by reacting 1,3,5-tris(4-aminophenyl)benzene with 2,5-dihydroxy-terephthalaldehyde; or it is covalent organic framework nanoparticles prepared by reacting 1,3,5-tris(4-aminophenyl)benzene with 2,5-dihydroxy-terephthalaldehyde. In the QCM based on hydroxyl-functionalized covalent organic framework materials provided by this invention, the framework of the hydroxyl-functionalized covalent organic framework material contains a large number of uniformly distributed hydroxyl functional groups, which can specifically recognize H2S through hydrogen bonding and Brønsted acid-base interactions, thus exhibiting extremely high selectivity for H2S. Meanwhile, this covalent organic framework material possesses an ordered mesoporous structure and high specific surface area, enabling it to effectively enrich H2S molecules and improve detection sensitivity. Its crystallinity and chemical stability ensure the repeatability and long-term stability of the sensor response. The synthesis conditions for this covalent organic framework material are mild, the operation is simple, and no complex equipment is required. QCM gas sensors based on this material can operate at room temperature, with response and recovery times both not exceeding 14 seconds and detection limits as low as 5 ppm, meeting the real-time requirements of industrial safety and environmental monitoring. Attached Figure Description

[0020] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings, wherein... Figure 1 This is a chemical structure diagram of the hydroxyl-functionalized covalent organic framework material in the QCM based on hydroxyl-functionalized covalent organic framework material provided in Embodiment 1 of the present invention; Figure 2 This is a scanning electron microscope (SEM) image of the hydroxyl-functionalized covalent organic framework material in the QCM based on hydroxyl-functionalized covalent organic framework material provided in Example 1 of this invention; Figure 3 This is an atomic force microscopy (AFM) image of the hydroxyl-functionalized covalent organic framework material in the QCM based on hydroxyl-functionalized covalent organic framework material provided in Embodiment 1 of the present invention. Figure 4 This is the Fourier transform infrared spectrum of the hydroxyl-functionalized covalent organic framework material in the QCM based on hydroxyl-functionalized covalent organic framework material provided in Embodiment 1 of the present invention; Figure 5 This is the Raman spectrum of the hydroxyl-functionalized covalent organic framework material in the QCM based on hydroxyl-functionalized covalent organic framework material provided in Example 1 of the present invention; Figure 6 This is the N2 adsorption-desorption isotherm test diagram of the hydroxyl-functionalized covalent organic framework material in the QCM based on the hydroxyl-functionalized covalent organic framework material provided in Example 1 of the present invention; Figure 7 This is a pore size distribution diagram of the hydroxyl-functionalized covalent organic framework material in the QCM based on hydroxyl-functionalized covalent organic framework material provided in Embodiment 1 of the present invention; Figure 8 This is a water contact angle test diagram of the hydroxyl-functionalized covalent organic framework material in the QCM based on hydroxyl-functionalized covalent organic framework material provided in Embodiment 1 of the present invention; Figure 9 This is a high-resolution N 1s XPS spectrum of the hydroxyl-functionalized covalent organic framework material in the QCM based on hydroxyl-functionalized covalent organic framework material provided in Example 1 of this invention; Figure 10 This is the EDS elemental distribution map of the hydroxyl-functionalized covalent organic framework material in the QCM based on hydroxyl-functionalized covalent organic framework material provided in Embodiment 1 of the present invention; Figure 11 This is a test graph of the response of the QCM gas sensor based on hydroxyl-functionalized covalent organic framework material provided in Embodiment 1 of the present invention to 20 ppm H2S and interfering gases. Figure 12 This is a real-time response test graph of the QCM gas sensor based on hydroxyl-functionalized covalent organic framework material provided in Embodiment 1 of the present invention to a gradually increasing H2S concentration at room temperature; Figure 13 This is a dynamic response test diagram of the QCM gas sensor based on hydroxyl-functionalized covalent organic framework material provided in Example 1 of the present invention when repeatedly exposed to 20-100 ppm H2S; Figure 14 This is a cycle stability test chart of the QCM gas sensor based on hydroxyl-functionalized covalent organic framework material provided in Embodiment 1 of the present invention under five consecutive cycles of 80, 50 and 20 ppm H2S. Figure 15 This is a test chart of the long-term stability of the QCM gas sensor based on hydroxyl-functionalized covalent organic framework material provided in Example 1 of the present invention at H2S concentrations of 20-100 ppm over 30 days. Figure 16 It is a linear calibration plot of frequency shift as a function of H2S concentration; Figure 17 This is a schematic diagram of the gas sensing mechanism of H2S by the QCM gas sensor based on hydroxyl-functionalized covalent organic framework material provided in Embodiment 1 of the present invention; Figure 18 This is a scanning electron microscope (SEM) image of the hydroxyl-functionalized covalent organic framework material in the QCM based on hydroxyl-functionalized covalent organic framework material provided in Example 4 of the present invention. Detailed Implementation

[0021] Example 1 This embodiment provides a QCM based on a hydroxyl-functionalized covalent organic framework material, including a quartz wafer with a silver electrode. The surface of the quartz wafer with the silver electrode is provided with a hydroxyl-functionalized covalent organic framework material. In this embodiment, the hydroxyl-functionalized covalent organic framework material is a covalent organic framework film prepared by reacting 1,3,5-tris(4-aminophenyl)benzene (TAPB) with 2,5-dihydroxyterephthalaldehyde (DHTP). In this embodiment, the thickness of the covalent organic framework film is 1100 nm.

[0022] The QCM based on hydroxyl-functionalized covalent organic framework material provided in this embodiment is prepared through the following steps: a. To prepare an aqueous solution, add glacial acetic acid to 1,3,5-tris(4-aminophenyl)benzene (TAPB). After TAPB is completely dissolved, add ultrapure water to form an aqueous phase. The aqueous solution contains 0.05 wt% TAPB and 0.1 wt% glacial acetic acid.

[0023] b. Prepare an organic phase solution by adding ethyl acetate as the first organic solvent to 2,5-dihydroxyterephthalaldehyde (DHTP), dispersing it ultrasonically to form an organic phase solution with a DHTP mass concentration of 0.015 wt%.

[0024] c. Interfacial polymerization: After placing the aqueous phase solution in the reaction vessel, the organic phase solution is added dropwise to the reaction vessel to form a water-oil two-phase system. The interfacial polymerization reaction is carried out at 20°C for 120 min, and a covalent organic framework film is formed at the interface separation point.

[0025] d. Attach a covalent organic framework thin film to the surface of a quartz wafer with silver electrodes.

[0026] Alternatively, a quartz wafer with silver electrodes is placed in a reaction vessel. Then, following the preparation method for hydroxyl-functionalized covalent organic framework films described above, an aqueous phase solution and an organic phase solution are prepared separately. These are then added dropwise sequentially. After the interfacial polymerization reaction is complete, the QCM is removed, and then annealed and cleaned to complete the preparation of the QCM. In this embodiment, the QCM has a wafer frequency of 10MHz and a wafer diameter of 14mm, exhibiting a small size and high integration.

[0027] The QCM based on hydroxyl-functionalized covalent organic frameworks (COMs) provided in this embodiment contains a large number of uniformly distributed hydroxyl functional groups in its framework. These functional groups can specifically recognize H2S through hydrogen bonding and Brønsted acid-base interactions, thus exhibiting extremely high selectivity for H2S. Simultaneously, this COM material possesses an ordered mesoporous structure and high specific surface area, effectively enriching H2S molecules and improving detection sensitivity. Its crystallinity and chemical stability ensure the repeatability and long-term stability of the sensor response. The synthesis conditions of this COM material are mild, the operation is simple, and no complex equipment is required. The COM film can be directly transferred onto the quartz wafer of the QCM, avoiding the aggregation and uneven thickness problems that may occur with traditional coating methods. The QCM gas sensor based on this COM film can operate at room temperature, with response and recovery times not exceeding 14 seconds and a detection limit as low as 5 ppm, far below the 20 ppm exposure limit specified by occupational safety standards such as OSHA, meeting the real-time requirements of industrial safety and environmental monitoring. Furthermore, the QCM gas sensor exhibits excellent repeatability and stability in both continuous cyclic testing and 30-day long-term testing, with a relative standard deviation (RSD) of ≤4.38%, demonstrating promising prospects for practical application.

[0028] Example 2 This embodiment provides a QCM based on a hydroxyl-functionalized covalent organic framework material, including a quartz wafer with a silver electrode. The surface of the quartz wafer with the silver electrode is provided with a hydroxyl-functionalized covalent organic framework material. In this embodiment, the hydroxyl-functionalized covalent organic framework material is a covalent organic framework film prepared by reacting 1,3,5-tris(4-aminophenyl)benzene (TAPB) with 2,5-dihydroxyterephthalaldehyde (DHTP). In this embodiment, the thickness of the covalent organic framework film is 50 nm.

[0029] The QCM based on hydroxyl-functionalized covalent organic framework material provided in this embodiment is prepared through the following steps: a. To prepare an aqueous solution, add glacial acetic acid to 1,3,5-tris(4-aminophenyl)benzene (TAPB). After TAPB is completely dissolved, add ultrapure water to form an aqueous phase. The aqueous solution contains 0.01 wt% TAPB and 0.05 wt% glacial acetic acid.

[0030] b. Prepare an organic phase solution by adding n-hexane as the first organic solvent to 2,5-dihydroxyterephthalaldehyde (DHTP), dispersing it by ultrasonication to form an organic phase solution. The mass concentration of DHTP in the organic phase solution is 0.005 wt%.

[0031] c. Interfacial polymerization: After placing the aqueous phase solution in the reaction vessel, the organic phase solution is added dropwise to the reaction vessel to form a water-oil two-phase system. The interfacial polymerization reaction is carried out at 15°C for 180 min, and a covalent organic framework film is formed at the interface separation point.

[0032] d. Attach a covalent organic framework thin film to the surface of a quartz wafer with silver electrodes.

[0033] Alternatively, a quartz wafer with silver electrodes is placed in a reaction vessel, and then, following the preparation method for hydroxyl-functionalized covalent organic framework films described above, an aqueous phase solution and an organic phase solution are prepared separately. These are then added dropwise sequentially. After the interfacial polymerization reaction is complete, the QCM is removed, and then annealed and cleaned to complete the preparation of the QCM. In this embodiment, the QCM has a wafer frequency of 5 MHz and a wafer diameter of 8 mm.

[0034] Example 3 This embodiment provides a QCM based on a hydroxyl-functionalized covalent organic framework material, including a quartz wafer with a silver electrode. The surface of the quartz wafer with the silver electrode is provided with a hydroxyl-functionalized covalent organic framework material. In this embodiment, the hydroxyl-functionalized covalent organic framework material is a covalent organic framework film prepared by reacting 1,3,5-tris(4-aminophenyl)benzene (TAPB) with 2,5-dihydroxyterephthalaldehyde (DHTP). In this embodiment, the thickness of the covalent organic framework film is 1500 nm.

[0035] The QCM based on hydroxyl-functionalized covalent organic framework material provided in this embodiment is prepared through the following steps: a. To prepare an aqueous solution, add glacial acetic acid to 1,3,5-tris(4-aminophenyl)benzene (TAPB). After TAPB is completely dissolved, add ultrapure water to form an aqueous phase. The aqueous solution contains 0.2 wt% TAPB and 0.5 wt% glacial acetic acid.

[0036] b. Prepare an organic phase solution by adding toluene, the first organic solvent, to 2,5-dihydroxyterephthalaldehyde (DHTP), and dispersing it by ultrasonication to form an organic phase solution. The mass concentration of DHTP in the organic phase solution is 0.1 wt%.

[0037] c. Interfacial polymerization: After placing the aqueous phase solution in the reaction vessel, the organic phase solution is added dropwise to the reaction vessel to form a water-oil two-phase system. The interfacial polymerization reaction is carried out at 30°C for 10 minutes, and a covalent organic framework film is formed at the interface separation point.

[0038] d. Attach a covalent organic framework thin film to the surface of a quartz wafer with silver electrodes.

[0039] Alternatively, a quartz wafer with silver electrodes is placed in a reaction vessel, and then, following the preparation method for hydroxyl-functionalized covalent organic framework films described above, an aqueous phase solution and an organic phase solution are prepared separately. These are then added dropwise sequentially. After the interfacial polymerization reaction is complete, the QCM is removed, and then annealed and cleaned to complete the preparation of the QCM. In this embodiment, the QCM has a wafer frequency of 7 MHz and a wafer diameter of 11 mm.

[0040] Example 4 This embodiment provides a QCM based on hydroxyl-functionalized covalent organic framework material, including a quartz wafer with silver electrodes. The surface of the quartz wafer with silver electrodes is provided with hydroxyl-functionalized covalent organic framework material. In this embodiment, the hydroxyl-functionalized covalent organic framework material is a covalent organic framework nanoparticle prepared by reacting 1,3,5-tris(4-aminophenyl)benzene (TAPB) with 2,5-dihydroxyterephthalaldehyde (DHTP). In this embodiment, the average particle size of the covalent organic framework nanoparticle is 200-600 nm.

[0041] The QCM based on hydroxyl-functionalized covalent organic framework material provided in this embodiment is prepared through the following steps: S1. Mix 1,3,5-tris(4-aminophenyl)benzene (TAPB) and 2,5-dihydroxyterephthalaldehyde (DHTP), add acetonitrile as a second organic solvent, and sonicate until completely dissolved to obtain a premixed solution. In the premixed solution, the molar ratio of TAPB to DHTP is 1:1.5. Specifically, in this example, the amount of TAPB is 0.02 mmol, the amount of DHTP is 0.03 mmol, and the volume of acetonitrile is 10 ml.

[0042] S2. Add 1 ml of glacial acetic acid to the premixed solution, react at room temperature for 30 min under magnetic stirring, centrifuge at 8000 rpm for 15 min, and collect the reaction product.

[0043] S3. The reaction product was washed three times by centrifugation with ethanol, and the washed reaction product was dried at 80°C for 12 hours to obtain covalent organic framework nanoparticles.

[0044] S4. Coating hydroxyl-functionalized covalent organic framework nanoparticles onto the surface of a quartz wafer with a silver electrode: The prepared dried covalent organic framework nanoparticles are mixed with anhydrous ethanol to prepare a suspension with a concentration of 1-5 mg / mL. In this embodiment, the concentration of the suspension is 3 mg / mL. The suspension is ultrasonically treated until the covalent organic framework nanoparticles are fully dispersed to avoid agglomeration. Then, the suspension is added dropwise to the central area of ​​the quartz wafer with the silver electrode, so that the liquid spreads and coats the electrode surface. After drop coating, the quartz wafer is placed in a clean environment and left to stand at room temperature for 10-30 min. In this embodiment, the standing time is 20 min. The frequency of the quartz wafer is 7 MHz and the diameter is 10 mm. After the coating is initially dried, it is annealed at 60-100℃ for 10-30 min. In this embodiment, the annealing temperature is 80℃ and the treatment time is 20 min.

[0045] Example 5 This embodiment provides a QCM based on hydroxyl-functionalized covalent organic framework material, including a quartz wafer with silver electrodes. The surface of the quartz wafer with silver electrodes is provided with hydroxyl-functionalized covalent organic framework material. In this embodiment, the hydroxyl-functionalized covalent organic framework material is a covalent organic framework nanoparticle prepared by reacting 1,3,5-tris(4-aminophenyl)benzene (TAPB) with 2,5-dihydroxyterephthalaldehyde (DHTP). In this embodiment, the average particle size of the covalent organic framework nanoparticle is 200-600 nm.

[0046] The QCM based on hydroxyl-functionalized covalent organic framework material provided in this embodiment is prepared through the following steps: S1. Mix 1,3,5-tris(4-aminophenyl)benzene (TAPB) and 2,5-dihydroxyterephthalaldehyde (DHTP), add a second organic solvent tetrahydrofuran, and sonicate until completely dissolved to obtain a premixed solution. In the premixed solution, the molar ratio of TAPB to DHTP is 1:1. Specifically, in this example, the amount of TAPB is 0.01 mmol, the amount of DHTP is 0.01 mmol, and the volume of tetrahydrofuran is 8 ml.

[0047] S2. Add 0.5 ml of glacial acetic acid to the premixed solution, react at room temperature for 10 min under magnetic stirring, centrifuge at 5000 rpm for 20 min, and collect the reaction product.

[0048] S3. The reaction product was washed three times by centrifugation with ethanol and dried at 60°C. In this example, the drying time was 24 hours to obtain covalent organic framework nanoparticles.

[0049] S4. Coating hydroxyl-functionalized covalent organic framework nanoparticles onto the surface of a quartz wafer with a silver electrode: The prepared dry covalent organic framework nanoparticles are mixed with anhydrous ethanol to prepare a suspension with a concentration of 1-5 mg / mL. In this embodiment, the concentration of the suspension is 1 mg / mL. The suspension is ultrasonically treated until the covalent organic framework nanoparticles are fully dispersed to avoid agglomeration. Then, the suspension is added dropwise to the central area of ​​the quartz wafer with the silver electrode, so that the liquid spreads and coats the electrode surface. After drop coating, the quartz wafer is placed in a clean environment and left to stand at room temperature for 10-30 min. In this embodiment, the standing time is 10 min. The frequency of the quartz wafer is 9 MHz and the diameter is 12 mm. After the coating is initially dried, it is annealed at 60-100℃ for 10-30 min. In this embodiment, the annealing temperature is 60℃ and the treatment time is 30 min.

[0050] Example 6 This embodiment provides a QCM based on hydroxyl-functionalized covalent organic framework material, including a quartz wafer with silver electrodes. The surface of the quartz wafer with silver electrodes is provided with hydroxyl-functionalized covalent organic framework material. In this embodiment, the hydroxyl-functionalized covalent organic framework material is a covalent organic framework nanoparticle prepared by reacting 1,3,5-tris(4-aminophenyl)benzene (TAPB) with 2,5-dihydroxyterephthalaldehyde (DHTP). In this embodiment, the average particle size of the covalent organic framework nanoparticle is 200-600 nm.

[0051] The QCM based on hydroxyl-functionalized covalent organic framework material provided in this embodiment is prepared through the following steps: S1. Mix 1,3,5-tris(4-aminophenyl)benzene (TAPB) and 2,5-dihydroxyterephthalaldehyde (DHTP), add the second organic solvent N,N-dimethylformamide, and sonicate until completely dissolved to obtain a premix. In the premix, the molar ratio of TAPB to DHTP is 1:2. Specifically, in this example, the amount of TAPB is 0.02 mmol, the amount of DHTP is 0.04 mmol, and the volume of N,N-dimethylformamide is 10 ml.

[0052] S2. Add 6 ml of glacial acetic acid to the premixed solution, react at room temperature for 10 min under magnetic stirring, centrifuge at 10000 rpm for 10 min, and collect the reaction product.

[0053] S3. The reaction product was washed three times by centrifugation with ethanol and dried at 100°C. In this example, the drying time was 8 hours to obtain covalent organic framework nanoparticles.

[0054] S4. Coating hydroxyl-functionalized covalent organic framework nanoparticles onto the surface of a quartz wafer with a silver electrode: The prepared dried covalent organic framework nanoparticles are mixed with anhydrous ethanol to prepare a suspension with a concentration of 1-5 mg / mL. In this embodiment, the concentration of the suspension is 5 mg / mL. The suspension is ultrasonically treated until the covalent organic framework nanoparticles are fully dispersed to avoid agglomeration. Then, the suspension is added dropwise to the central area of ​​the quartz wafer with the silver electrode, so that the liquid spreads and coats the electrode surface. After drop coating, the quartz wafer is placed in a clean environment and left to stand at room temperature for 10-30 min. In this embodiment, the standing time is 30 min. The frequency of the quartz wafer is 6 MHz and the diameter is 13 mm. After the coating is initially dried, it is annealed at 60-100℃ for 10-30 min. In this embodiment, the annealing temperature is 100℃ and the treatment time is 10 min.

[0055] Experimental Example 1. Characterization of structure and chemical properties To clarify the structural characteristics of the hydroxyl-functionalized covalent organic framework material in the QCM based on hydroxyl-functionalized covalent organic framework materials provided in the embodiments of this application, the covalent organic framework film provided in Embodiment 1 of this application was comprehensively characterized. For ease of description, in the following experimental examples, the covalent organic framework film is written as COF-TAPB / DHTP, and its structural formula is as follows: Figure 1 As shown.

[0056] (1) The surface morphology of COF-TAPB / DHTP was observed by scanning electron microscopy (SEM), and the test results are as follows: Figure 2 As shown in the figure, the COF-TAPB / DHTP provided in Embodiment 1 of this application is a continuous and uniform thin film with a smooth surface and no obvious defects.

[0057] (2) The thickness of COF-TAPB / DHTP was measured by atomic force microscopy (AFM), and the test results are as follows: Figure 3 As shown in the AFM image, the thickness of the hydroxyl-functionalized covalent organic framework film is 1100 nm.

[0058] (3) The chemical structure of COF-TAPB / DHTP was tested by Fourier transform infrared spectroscopy (FTIR). Vibrational spectroscopy confirmed the successful formation of the COF-TAPB / DHTP framework. The specific test results are as follows: Figure 4 As shown, the FTIR test results reveal the characteristic signals of imine bond formation: at 1586 cm⁻¹ -1A new absorption peak appears at [location], along with the C=O stretching vibration peak of the aldehyde group (1662 cm⁻¹). -1 ) and amino-NH stretching vibration bands (3420, 3344 cm) -1 The complete disappearance of the precursor functional group confirms its depletion.

[0059] (4) Raman spectroscopy test results are as follows Figure 5 As shown, the test results are displayed at 1597 cm. -1 A new C=N stretching vibration peak appeared at 1354 cm⁻¹. -1 NH2 band and 1673 cm -1 The disappearance of the C=O band further confirms that the Schiff base condensation reaction between the aldehyde monomer and the amine monomer has been completed.

[0060] The porosity and surface properties of the synthesized COF-TAPB / DHTP were further investigated using various characterization techniques: (5) The porous structure of COF-TAPB / DHTP was evaluated by nitrogen adsorption-desorption measurement, and the test results are as follows: Figure 6 As shown, Brunauer-Emmett-Teller (BET, gas adsorption method) analysis revealed that the specific surface area of ​​COF-TAPB / DHTP was 204.443 m². 2 / g.

[0061] (6) The pore size distribution diagram derived from the adsorption isotherm using the Barrett-Joyner-Halenda (BJH) model is shown below. Figure 7 As shown, the calculated average pore size is 2.850 nm, therefore this material is classified as mesoporous.

[0062] (7) The surface wettability of COF-TAPB / DHTP was evaluated by contact angle measurement, and the test results are as follows: Figure 8 As shown, the COF-TAPB / DHTP surface is a hydrophilic surface with a contact angle of 60.1°, which is consistent with the expected effect of the hydroxyl functional groups present in the structure.

[0063] (8) The chemical composition and bonding state of COF-TAPB / DHTP were analyzed by X-ray photoelectron spectroscopy (XPS), and the test results are as follows: Figure 9 As shown, the high-resolution N 1s XPS spectrum shows two peaks at 399.9 eV and 397.9 eV, corresponding to C=N and CN respectively, confirming the imine bond-linked framework structure.

[0064] (9) Energy-dispersive X-ray (EDX) surface distribution analysis was used to test the elemental distribution within the COF framework. The test results are as follows: Figure 10 As shown, the test results demonstrate the uniform distribution of carbon (C), nitrogen (N), and oxygen (O) throughout the sample, confirming the structural integrity and homogeneity of the covalent organic framework.

[0065] The above characterization results collectively confirm the successful synthesis of hydroxyl-functionalized COF-TAPB / DHTP, which possesses high specific surface area and ideal chemical properties, making it suitable for H2S gas detection.

[0066] 2. Sensing performance testing of the COF-TAPB / DHTP-based QCM gas sensor (1) The selectivity of the QCM gas sensor provided in Embodiment 1 of this application was evaluated by interference testing. The test results are as follows: Figure 11 As shown in (a), compared to four common interfering gases: NH3, H2, NO2, and C2H5OH (all at a concentration of 20 ppm), this QCM gas sensor exhibits superior selectivity for H2S. Exposure to H2S caused a significant frequency shift of 26 Hz in the QCM gas sensor, while the shifts caused by the other four interfering gas analytes were all below 10 Hz. Furthermore, the dynamic response characteristics of the gas QCM were investigated using time-resolved measurements, which is crucial for practical applications. Figure 11 As shown in (b) (transient response test diagram for 20 ppm H2S), the sensor achieved a rapid response time of 11 seconds when exposed to 20 ppm H2S and fully recovered to baseline within 14 seconds under N2 purging. This rapid response-recovery behavior, coupled with its excellent selectivity, meets the stringent requirements of industrial safety monitoring.

[0067] (2) The real-time response of the QCM gas sensor provided in Example 1 of this application under different concentrations of H2S was tested, and the test results are as follows: Figure 12 As shown, when the sensor was exposed to different concentrations of H2S from 5 to 100 ppm, the frequency shift gradually increased with the increase of H2S analyte concentration, showing a direct and quantitative correlation.

[0068] (3) A cumulative exposure test was performed on the QCM gas sensor provided in Example 1 of this application to determine its quantitative detection capability. The sensor was continuously exposed to 20 ppm of H2S without any recovery. The test results are as follows: Figure 13 As shown in the figure, the frequency shift exhibits a clear progressive relationship: 21 Hz after the first exposure, 48 Hz after the second exposure, 70 Hz after the third exposure, and 88 Hz after the fourth exposure, corresponding to cumulative concentrations of 20, 40, 60, and 80 ppm, respectively. This linear response behavior confirms that the sensor is suitable for quantitative analysis of ppm-level concentrations.

[0069] (4) A repeatability test was performed on the QCM gas sensor provided in Example 1 of this application to evaluate its reliability and long-term stability. The test results are as follows: Figure 14 As shown in the figure, the QCM gas sensor was exposed to H2S at 80 ppm, 50 ppm, and 20 ppm for five consecutive cycles, and the results showed significant consistency. The frequency shifts in each cycle were 77±3 Hz (RSD = 2.73%), 45±2 Hz (RSD = 4.38%), and 23±1 Hz (RSD = 2.99%), respectively, which confirms the sensor's excellent reversibility and operational stability.

[0070] (5) Further test and calculate the long-term stability and minimum detection limit of the QCM gas sensor provided in Example 1 of this application, and evaluate the sensor's response over 30 days. The test results are as follows: Figures 15-16 As shown, the test and calculation results indicate that the sensor's response remained almost constant throughout the entire test period (e.g., Figure 15 As shown), this indicates its suitability for long-term monitoring applications. Meanwhile, the sensor's limit of detection (LOD) for H2S is 5 ppm (signal-to-noise ratio > 3), based on the 3σ / S method (σ = 2.1, S = 0.98, from y = 0.98x + 5.67, R² = 0.997 (as shown)). Figure 16 The calculated LOD (Level of Exposure) is 6 ppm, which confirms this detection limit. This detection capability is far below critical occupational safety thresholds, including the OSHA Permissible Exposure Limit (PEL) of 20 ppm and the EU-adopted limit of 10 ppm.

[0071] The test results above demonstrate that the COF-TAPB / DHTP-based QCM sensor is a highly selective, fast-response, and reliable platform suitable for real-time H2S detection in industrial and environmental monitoring applications.

[0072] 3. SEM images of the covalent organic framework nanoparticles provided in Example 4 of this application were tested, and the test results are as follows: Figure 18 As shown in the figure, the covalent organic framework nanoparticles prepared by the method provided in this application are spherical with uniform morphology and no obvious defects. Their uniform morphology is suitable for coating on a quartz wafer with a silver electrode, thereby obtaining a quartz crystal microbalance (QCM) gas sensor.

[0073] In summary, this application successfully synthesized a hydroxyl-functionalized covalent organic framework (COF-TAPB / DHTP) material and applied it to a QCM gas sensor, specifically for H2S detection. Because the hydroxyl-functionalized COF-TAPB / DHTP material contains abundant hydroxyl groups, it can undergo double hydrogen bonding and acid-base interactions with H2S molecules (e.g., ...). Figure 17 As shown in the figure, the QCM gas sensor possesses excellent selectivity (26 Hz for H2S, <10 Hz for interfering gases), extremely short response-recovery time (<14s), and excellent repeatability (RSD ≤ 4.38%). These characteristics, along with its room temperature operation and long-term stability, make the QCM gas sensor a promising candidate for H2S monitoring, particularly suitable for industrial safety and environmental protection.

[0074] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. Use of a QCM based on a hydroxyl-functionalized covalent organic framework material, characterized in that, The QCM based on hydroxyl-functionalized covalent organic framework material is applied to hydrogen sulfide detection. The QCM based on hydroxyl-functionalized covalent organic framework material includes a quartz wafer with a silver electrode, and the surface of the quartz wafer with the silver electrode is provided with hydroxyl-functionalized covalent organic framework material. The hydroxyl-functionalized covalent organic framework material is a covalent organic framework film prepared by reacting 1,3,5-tris(4-aminophenyl)benzene with 2,5-dihydroxyterephthalaldehyde; or the hydroxyl-functionalized covalent organic framework material is a covalent organic framework nanoparticle prepared by reacting 1,3,5-tris(4-aminophenyl)benzene with 2,5-dihydroxyterephthalaldehyde.

2. The application of QCM based on hydroxyl-functionalized covalent organic framework materials according to claim 1, characterized in that, The hydroxyl-functionalized covalent organic framework material is the covalent organic framework film, and the thickness of the covalent organic framework film is 50-1500 nm.

3. Use of a QCM based on a hydroxyl-functionalized covalent organic framework material according to claim 1, characterized in that, The hydroxyl-functionalized covalent organic framework material is the covalent organic framework nanoparticle, and the average particle size of the covalent organic framework nanoparticle is 200-600 nm.

4. The application of QCM based on hydroxyl-functionalized covalent organic framework materials according to any one of claims 1-3, characterized in that, The quartz wafer has a frequency of 5-10MHz and a diameter of 8-14mm.

5. The application of QCM based on hydroxyl-functionalized covalent organic framework materials according to claim 4, characterized in that, The QCM based on hydroxyl-functionalized covalent organic framework material is prepared through the following steps: To prepare an aqueous solution, glacial acetic acid was added to 1,3,5-tris(4-aminophenyl)benzene. After the 1,3,5-tris(4-aminophenyl)benzene dissolved, ultrapure water was added to obtain an aqueous solution. In the aqueous solution, the mass concentration of 1,3,5-tris(4-aminophenyl)benzene was 0.01-0.2 wt%, and the mass concentration of glacial acetic acid was 0.05-0.5 wt%. An organic phase solution is prepared by adding a first organic solvent to 2,5-dihydroxyterephthalaldehyde, dispersing the solution, and then forming an organic phase solution. The mass concentration of 2,5-dihydroxyterephthalaldehyde in the organic phase solution is 0.005-0.1 wt%. Interfacial polymerization involves placing the aqueous solution in a reaction vessel, then adding the organic solution dropwise, and reacting at 15-30°C for 10-180 min to form the covalent organic framework film at the interface separation point. The covalent organic framework film is attached to the surface of the quartz wafer with silver electrodes.

6. The application of QCM based on hydroxyl-functionalized covalent organic framework materials according to claim 5, characterized in that, The first organic solvent is one of ethyl acetate, n-hexane, or toluene.

7. The application of QCM based on hydroxyl-functionalized covalent organic framework materials according to claim 4, characterized in that, The QCM based on hydroxyl-functionalized covalent organic framework material is prepared through the following steps: S1. Mix 1,3,5-tris(4-aminophenyl)benzene and 2,5-dihydroxyterephthalaldehyde, and add a second organic solvent to obtain a premixed solution, wherein the molar ratio of 1,3,5-tris(4-aminophenyl)benzene to 2,5-dihydroxyterephthalaldehyde is 1:1-1:

2. S2. Add glacial acetic acid to the premixed solution, react at room temperature for 10-60 min, and collect the reaction product by centrifugation. S3. Wash and dry the reaction product to obtain the covalent organic framework nanoparticles. S4. Coat the covalent organic framework nanoparticles onto the surface of the quartz wafer with silver electrodes.

8. The application of QCM based on hydroxyl-functionalized covalent organic framework materials according to claim 7, characterized in that, The second organic solvent is one of acetonitrile, tetrahydrofuran, or N,N-dimethylformamide.

9. The application of QCM based on hydroxyl-functionalized covalent organic framework materials according to claim 8, characterized in that, In step S2, during the centrifugation collection of reaction products, the centrifugation speed is 5000-10000 rpm and the centrifugation time is 10-20 min; in step S3, the drying temperature is 60-100℃ and the drying time is 8-24 h.

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