Quartz crystal microbalance based on covalent organic framework material and ammonia gas sensor

Abstract

The invention provides a quartz crystal microbalance based on a covalent organic framework material and an ammonia sensor, the quartz crystal microbalance comprises a quartz crystal matrix, the quartz crystal matrix has a first surface and a second surface which are oppositely arranged, the first surface is provided with a sensing material film layer, and the second surface is provided with a covalent organic framework material. And the sensing material film layer is a ferrocene functionalized covalent organic framework nano film layer. The quartz crystal microbalance has excellent ammonia gas selectivity, the frequency shift can reach 65 Hz and far exceeds the condition that the frequency shift does not exceed 20 Hz when other gases are detected, the quartz crystal microbalance has a rapid response recovery behavior, and the response time is only 12 s. Therefore, the ammonia gas sensor with the quartz crystal microbalance based on the covalent organic framework material has good ammonia gas monitoring potential, and the sensitivity, selectivity and operation stability of ammonia gas monitoring are remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of gas detection technology, specifically relating to a quartz crystal microbalance and an ammonia sensor based on a covalent organic framework material. Background Technology

[0002] Ammonia is a colorless, alkaline gas with a strong, pungent odor. It is one of the most common gases in nature, present in air, water, and soil. It is also an important nitrogen source for plants and animals, primarily originating from animal excrement, plant humus, and human activities such as agriculture and industry. As a basic chemical raw material, ammonia is used in agriculture (e.g., agricultural fertilizers), the electronics industry (e.g., semiconductor industry), petrochemicals, and pest control. However, leaks or elevated concentrations of ammonia not only cause environmental pollution but also pose significant health risks to humans. Therefore, monitoring and preventing ammonia leaks in areas prone to occur can effectively reduce the occurrence of accidents and is of practical significance for environmental monitoring and public safety.

[0003] Currently, methods for monitoring ammonia in the air mainly include optical methods, calorimetry, gas chromatography, and acoustic methods. These methods require specific monitoring sensors, and conventional ammonia monitoring sensors suffer from low sensitivity, slow response, large equipment size, and high cost. Therefore, it is essential to develop ammonia sensors with high sensitivity, fast response speed, good stability, and low cost.

[0004] Among various types of sensors, the Quartz Crystal Microbalance (QCM) has attracted widespread attention from researchers in recent years due to its advantages such as high sensitivity, high response speed, simple structure, and low cost, and has been applied in various fields, including ammonia monitoring. The Quartz Crystal Microbalance is a mass-type gas sensor that utilizes the mass sensitivity of a piezoelectric quartz crystal wafer. Sensing materials modified on the surface of the quartz crystal wafer capture the analyte gas, and detection is achieved by measuring changes in the frequency of the quartz crystal, with accuracy down to the nanogram level. The performance of the Quartz Crystal Microbalance largely depends on the properties of the sensing material. Currently, various materials have been used to fabricate QCM-type ammonia sensors. Among them, porous materials have attracted considerable attention because they can provide high surface area, adjustable pore structure, and abundant adsorption sites, thereby improving sensor sensitivity. Among porous materials, covalent organic frameworks (COFs) are materials with locally highly ordered porous structures and tunable chemical properties, which help improve the performance of QCM-type sensors. However, although researchers are increasingly interested in applying COFs to gas sensors, their actual application in QCM-type sensors is still relatively limited. For example, the utilization rate of active sites in COFs is low, the structural tunability has not been fully developed, and COFs have not been fully applied to QCM-type sensors to improve performance such as selector sensitivity. In view of this, it is necessary to provide a novel quartz crystal microbalance based on covalent organic framework materials to achieve high-sensitivity monitoring of ammonia. Summary of the Invention

[0005] Therefore, the technical problem to be solved by the present invention is that the ammonia gas sensor in the prior art has low sensitivity and slow response speed. Thus, the present invention proposes a quartz crystal microbalance and ammonia gas sensor based on covalent organic framework material with high sensitivity, fast response speed and good operational stability.

[0006] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows:

[0007] The first aspect of the present invention provides a quartz crystal microbalance based on a covalent organic framework material. The quartz crystal microbalance includes a quartz crystal substrate. The quartz crystal has a first surface and a second surface disposed opposite to each other. A sensing material film layer is disposed on the first surface. The sensing material film layer is a ferrocene-functionalized covalent organic framework nanofilm layer.

[0008] Preferably, the thickness of the sensing material film is 40-60 nm.

[0009] Preferably, the ferrocene-functionalized covalent organic framework nanofilm has the following structural formula:

[0010]

[0011] In the above formula, for

[0012] Preferably, silver electrodes are respectively disposed on the first surface and the second surface, wherein the silver electrode is disposed between the quartz crystal substrate and the sensing material film layer on the first surface.

[0013] Preferably, the quartz crystal microbalance is prepared by the following steps:

[0014] S1. Add an aqueous solution containing 0.01wt%-0.1wt% 1,3,5-tris(4-aminophenyl)benzene and 0.1wt%-0.5wt% acetic acid to the reaction vessel;

[0015] S2. Add 0.001wt%-0.03wt% of n-hexaneferrocene-1,1′-diacetaldehyde to the reaction vessel. After the reaction, a ferrocene-functionalized covalent organic framework nanofilm is formed.

[0016] S3. A ferrocene-functionalized covalent organic framework nanofilm is deposited on the first surface of the quartz crystal substrate.

[0017] Preferably, in step S2, the reaction time is 5 min to 4 h and the reaction temperature is 20 to 30 °C.

[0018] Preferably, step S3 includes: placing the quartz crystal substrate at the bottom of the reaction vessel, and after the reaction in step S2 is completed, pulling the quartz crystal substrate out of the reaction vessel at a speed of 0.1-10 mm / s.

[0019] Preferably, step S3 includes a post-processing step: stabilizing the quartz crystal microbalance under vacuum at 40-60°C for 110-130 min.

[0020] A second aspect of the present invention provides an ammonia sensor comprising the aforementioned quartz crystal microbalance based on an organic framework material.

[0021] The technical solution of the present invention has the following advantages compared with the prior art:

[0022] The present invention provides a quartz crystal microbalance based on a covalent organic framework material, comprising a quartz crystal substrate having a first surface and a second surface disposed opposite to each other. A sensing material film layer is disposed on the first surface, and the sensing material film layer is a ferrocene-functionalized covalent organic framework nanofilm layer. This quartz crystal microbalance exhibits excellent ammonia selectivity, with a frequency shift of up to 65 Hz, far exceeding the frequency shift of no more than 20 Hz when detecting other gases, and also possesses rapid response and recovery behavior, with a response time of only 12 s. Therefore, the ammonia sensor with this covalent organic framework-based quartz crystal microbalance has excellent ammonia monitoring potential, significantly improving the sensitivity, selectivity, and operational stability of ammonia monitoring. Attached Figure Description

[0023] 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...

[0024] Figure 1 This is a cross-sectional schematic diagram of a quartz crystal microbalance based on a covalent organic framework material provided in an embodiment of the present invention;

[0025] Figure 2 These are the Raman spectra of TPB, FeDA, and COFs-TPB / FcDA;

[0026] Figure 3 These are the FTIR spectra of TPB, FeDA, and COFs-TPB / FcDA;

[0027] Figure 4 This is a high-resolution C1s spectrum of COFs-TPB / FcDA;

[0028] Figure 5 This is a high-resolution Fe2p spectrum of COFs-TPB / FcDA;

[0029] Figure 6 This is the N2 adsorption-desorption isotherm of COFs-TPB / FcDA;

[0030] Figure 7 This is a pore size distribution curve of COFs-TPB / FcDA;

[0031] Figure 8 These are SEM and EDS images of COFs-TPB / FcDA;

[0032] Figure 9 This is a response curve of the COFs-TPB / FcDA QCM sensor to NH3 in the range of 10-100ppm;

[0033] Figure 10This is a test graph showing the response of OFs-TPB / FcDAQCM to different gases at 10 ppm.

[0034] Figure 11 This is a real-time dynamic response curve of a COF sensor exposed to NH3 at room temperature as the concentration increases.

[0035] Figure 12 This is a dynamic response curve of COFs-TPB / FcDAQCM to 20-100ppm NH3 vapor;

[0036] Figure 13 This is a graph showing the cyclic stability test results of COFs-TPB / FcDAQCM against 5ppm NH3 gas.

[0037] Figure 14 It is a thermodynamic analysis curve.

[0038] The reference numerals in the figure are: 1-quartz crystal substrate; 101-first surface; 102-second surface; 2-sensing material film; 3-silver electrode. Detailed Implementation

[0039] Example 1

[0040] This embodiment provides a quartz crystal microbalance based on covalent organic framework materials, aiming to address the limited application of organometallic framework materials (COFs) in quartz crystal microbalance (QCM) sensors in existing technologies. In particular, the vast structural tunability of COFs has not been fully utilized; for example, the binding of redox active groups, metal ion coordination sites, or customized functional groups has not been adequately leveraged to improve sensor selectivity and other performance characteristics. To solve the above problems, this embodiment provides a quartz crystal microbalance based on covalent organic framework materials, such as... Figure 1 As shown, it includes a quartz crystal substrate 1. In this embodiment, the quartz crystal substrate 1 is in the shape of a flat cylinder and has a first surface 101 and a second surface 102 disposed opposite to each other. A sensing material film layer 2 is disposed on the first surface 101. Specifically, the sensing material film layer 2 is a ferrocene functionalized covalent organic framework nanofilm layer.

[0041] The quartz crystal microbalance based on covalent organic framework materials provided in this embodiment utilizes a ferrocene-functionalized covalent organic framework nanofilm as the sensing material layer. This results in excellent ammonia selectivity, with a frequency shift of up to 65 Hz, far exceeding the frequency shift of no more than 20 Hz when detecting other gases. Furthermore, it exhibits rapid response and recovery behavior, with a response time of only 12 seconds. Therefore, the ammonia sensor based on this covalent organic framework material quartz crystal microbalance possesses excellent ammonia monitoring potential, significantly improving the sensitivity, selectivity, and operational stability of ammonia monitoring.

[0042] In this embodiment, the thickness of the sensing material film 2 is 40-60 nm, and the sensing material film 2 covers the first surface 101. Furthermore, a silver electrode 3 is provided on the first surface 101 and the second surface 102 of the quartz crystal substrate 1. On the first surface, the silver electrode 3 is disposed between the quartz crystal substrate 1 and the sensing material film 2. In this embodiment, the thickness of the sensing material film 2 on the surface of the silver electrode 3 is preferably 50 nm.

[0043] Among them, the ferrocene-functionalized covalent organic framework nanofilm has the following structural formula:

[0044]

[0045] In the above formula, for

[0046] The quartz crystal microbalance with the above-mentioned ferrocene-functionalized covalent organic framework nanofilm was prepared by the following method:

[0047] S1. Add an aqueous solution containing 0.05 wt% 1,3,5-tris(4-aminophenyl)benzene (TPB) and 0.1 wt% acetic acid to a reaction vessel (such as a beaker).

[0048] S2. Ferrocene-functionalized covalent organic framework (COFs-TPB / FcDA) is synthesized by interfacial polymerization. 0.015 wt% of n-hexane-ferrocene-1,1′-diacetaldehyde (FeDA) solution is added to the reaction vessel in step S1, and the reaction is carried out at 25 °C for 2 h to obtain ferrocene-functionalized covalent organic framework nanofilm. The reaction solution of the nanofilm is collected.

[0049] S3. Place the quartz crystal substrate 1 with silver electrode 3 at the bottom of a culture container. Pour the nanofilm reaction solution obtained in step S2 into the culture container and pull the quartz crystal substrate 1 out of the culture container at a speed of 5 mm / s. When pulling, make the surface of the quartz substrate 1 vertically upward to ensure that the thickness of the formed nanofilm is uniform, thus obtaining the quartz crystal microbalance based on covalent organic framework material.

[0050] S4. Post-treatment: Before the ammonia test, the quartz crystal microbalance is thermally stabilized at 50°C under vacuum for 120 minutes.

[0051] This embodiment also provides an ammonia sensor, which includes the above-mentioned quartz crystal microbalance based on covalent organic framework material.

[0052] Example 2

[0053] This embodiment provides a quartz crystal microbalance based on a covalent organic framework material. Its structure is basically the same as that of Example 1, except that the quartz crystal microbalance is prepared by the following method:

[0054] S1. Add an aqueous solution containing 0.01 wt% 1,3,5-tris(4-aminophenyl)benzene (TPB) and 0.3 wt% acetic acid to a reaction vessel (such as a beaker).

[0055] S2. COFs-TPB / FcDA is synthesized by interfacial polymerization. 0.001 wt% of n-hexane-ferrocene-1,1′-diacetaldehyde (FeDA) solution is added to the reaction vessel in step S1 and reacted at 20 °C for 4 h to obtain ferrocene-functionalized covalent organic framework nanofilm. The reaction solution of the nanofilm is collected.

[0056] S3. Place the quartz crystal substrate 1 with the silver electrode 3 at the bottom of a culture container. Pour the nanofilm reaction solution obtained in step S2 into the culture container and then pull the quartz crystal substrate 1 out of the culture container at a speed of 0.1 mm / s. When pulling, make the surface of the quartz substrate 1 vertically upward to ensure that the thickness of the formed nanofilm is uniform, thus obtaining the quartz crystal microbalance based on covalent organic framework material.

[0057] S4. Post-treatment: Before the ammonia test, the quartz crystal microbalance is thermally stabilized at 40℃ under vacuum for 120 min.

[0058] This embodiment also provides an ammonia sensor, which includes the above-mentioned quartz crystal microbalance based on covalent organic framework material.

[0059] Example 3

[0060] This embodiment provides a quartz crystal microbalance based on a covalent organic framework material. Its structure is basically the same as that of Example 1, except that the quartz crystal microbalance is prepared by the following method:

[0061] S1. Add an aqueous solution containing 0.1 wt% 1,3,5-tris(4-aminophenyl)benzene (TPB) and 0.5 wt% acetic acid to a reaction vessel (such as a beaker).

[0062] S2. COFs-TPB / FcDA is synthesized by interfacial polymerization. 0.03 wt% of n-hexane-ferrocene-1,1′-diacetaldehyde (FeDA) solution is added to the reaction vessel in step S1 and reacted at 30 °C for 5 min to obtain ferrocene-functionalized covalent organic framework nanofilm. The reaction solution of the nanofilm is collected.

[0063] S3. Place the quartz crystal substrate 1 with silver electrode 3 at the bottom of a culture container. Pour the nanofilm reaction solution obtained in step S2 into the culture container and pull the quartz crystal substrate 1 out of the culture container at a speed of 10 mm / s. When pulling, make the surface of the quartz substrate 1 vertically upward to ensure that the thickness of the formed nanofilm is uniform, thus obtaining the quartz crystal microbalance based on covalent organic framework material.

[0064] S4. Post-treatment: Before the ammonia test, the quartz crystal microbalance is thermally stabilized at 60℃ under vacuum for 120 min.

[0065] This embodiment also provides an ammonia sensor, which includes the above-mentioned quartz crystal microbalance based on covalent organic framework material.

[0066] Experimental Example

[0067] 1. Structural and chemical characterization of ferrocene-functionalized organic frameworks (COFs-TPB / FcDA)

[0068] The Raman spectrum, Fourier transform infrared spectrum (FTIR), high-resolution C1s spectrum, and high-resolution Fe2p spectrum of the ferrocene functionalized organic framework prepared in Example 1 were tested. The test results are as follows: Figures 2-5 As shown.

[0069] from Figures 2-3 As can be seen, the formation of imine bonds was verified by Raman and FTIR spectroscopy. Raman spectroscopy shows that at 1590 cm⁻¹, the imine bond formation was confirmed. -1 The characteristic vibration of -C=N appeared at this point, and at the same time -NH2 (1342cm) -1 ) and -C=O(1660cm -1 The disappearance of the vibrational band confirms the completion of the Schiff base condensation between the aldehyde and amine precursors. FTIR spectroscopy further confirms these findings; in the COF structure, the vibrational band at 1586 cm⁻¹... -1 A new -C=N peak appeared at 1652 cm⁻¹, while no aldehyde -C=O peak was observed. -1 ) and amine-NH stretching strips (3420, 3344 and 3207cm) -1 This indicates that the framework was successfully formed.

[0070] XPS spectra of imine-linked cof as follows Figure 4As shown, the main components are CC / C=C (~284.8 eV), CN (~286.1 eV), C=N (~287.3 eV), and C=O (~288.7 eV). It is worth noting that, as... Figure 5 As shown, the Fe2p region of COFs-TPB / FcDA exhibits two well-resolved peaks, confirming the presence of Fe(II) in the diferric fragment within the COF framework.

[0071] 2. Nitrogen adsorption-desorption determination of porosity of COFs-TPB / FcDA

[0072] The nitrogen adsorption-desorption isotherms of COFs-TPB / FcDA were tested, and the test results are as follows: Figure 6 As shown in the figure, the measured surface area of ​​the Brunauer-Emmet-Teller (BET) is 280.347 m². 2 / g.

[0073] The pore size distribution of COFs-TPB / FcDA was calculated using the Barrett-Joyner-Halenda (BJH) model, and the test results are as follows. Figure 7 As shown in the figure, the average pore size is 2.375 nm, and the material is classified as a mesoporous material.

[0074] Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were performed on COFs-TPB / FcDA. The results are as follows: Figure 8 As shown, SEM images and corresponding EDS images confirm that the COF film has a uniform morphology and no defects were observed. These results confirm the successful synthesis of mesoporous ferrocene-functionalized COF with uniformly bound Fe sites, providing good surface area and chemical functionality for NH3 sensing.

[0075] 3. Testing the sensing performance of the quartz crystal microbalance (QCM) sensor based on ferrocene functionalized organic frameworks (COFs-TPB / FcDA).

[0076] The unique interaction between aldehyde groups and ammonia molecules in the ferrocene-functionalized organic framework provides a solid foundation for NH3 sensing applications. The sensing performance of a quartz crystal microbalance with ferrocene-functionalized covalent organic framework nanofilms of varying thicknesses was tested. The test results are as follows: Figure 9As shown, COFs-TPB / FcDA nanofilms were deposited for 2h, 3h, 4h, and 5h, respectively. The sensor with 4h deposition exhibited the highest response within the tested concentration range (10-100ppm NH3), achieving a balance between active site availability and gas diffusion efficiency. Therefore, this 4-hour deposition condition was selected for all subsequent gas-sensing performance evaluations to ensure consistent and optimal performance. This is because, under low COF loading, the sensor response is primarily controlled by dynamic processes, including the saturation adsorption capacity (Q) and the diffusion of the target gas across the accessible surface area. Increasing the COF loading can improve adsorption capacity and the number of active sites, thereby improving the sensor response. However, excessive loading ultimately degrades sensor performance because the increased diffusion limitation restricts gas access to the active sites.

[0077] The selective detection of NH3 by the above-mentioned COFs-TPB / FcDA-based QCM sensor was systematically evaluated by exposing it to six common interfering gases (HCHO, ethanol, H2S, acetone, NO2, and benzene) at a concentration of 10 ppm. The test results are as follows: Figure 10 As shown in the figure, the COF-based QCM sensor exhibits excellent NH3 selectivity, with a frequency shift of 65 Hz compared to <20 Hz for all other analytes. This significant selectivity is attributed to a synergistic dual interaction mechanism: (1) the formation of a Schiff base between the NH and aldehyde groups on the COF backbone; and (2) Lewis acid-base coordination at the Fe site (Fe(NH)x complex). The dynamic response characteristics of the sensor were also evaluated by time-resolved measurements, such as... Figure 10 As shown, the sensor achieved a fast response time of 12 seconds when exposed to 10 ppm NH3, and fully recovered the baseline within 13 seconds under N2 purging. This fast response-recovery behavior, coupled with the aforementioned selectability characteristics, meets the requirements of industrial safety monitoring.

[0078] The real-time NH3 sensing performance of the COFs-TPB / FcDA-based QCM sensor was evaluated at room temperature (25±1℃) and within a concentration range of 10-100 ppm. The test results are as follows: Figure 11 As shown, the sensor exhibits concentration-related frequency shifts of 65 Hz (10 ppm), 125 Hz (50 ppm), and 205 Hz (100 ppm), with a signal-to-noise ratio (SNR) exceeding 13:1 relative to baseline background noise (±5 Hz). This result demonstrates reliable detection capability down to 10 ppm NH3.

[0079] The cumulative response behavior of the sensor was examined by continuous exposure to 20 ppm NH3 without intermediate recovery, and the results are as follows: Figure 12As shown in the figure, there is a progressive frequency shift of 80Hz (20ppm), 115Hz (40ppm), 152Hz (60ppm), and 188Hz (80ppm), which confirms the sensor's linear recognition capability at ppm-level concentrations.

[0080] The cyclic stability of a COFs-TPB / FcDA-based QCM sensor on 5 ppm NH3 vapor was tested, and the test results are as follows: Figure 13 As shown, at 50 ppm NH3, the response was consistent across the three cycles (125 ± 4 Hz, RSD3 = 3.2%), meeting the industrial requirements for reliable monitoring.

[0081] Thermodynamic analysis was performed using a temperature-dependent microgravity method, and the analysis curves are as follows: Figure 14 As shown, the adsorption enthalpy (ΔH) calculated using the Clausius-Clapeyron equation is -45.22 kJ / mol. This value indicates weak chemisorption behavior, consistent with the reversible Schiff base formation between the aldehyde groups of NH3 and COFs. The detection limit (LOD) of the sensor was determined using two complementary methods: an experimental LOD of 10 ppm (SNR = bbbb3) and a calculated LOD of 4 ppm based on the 3σ / S method (σ = 2.1, S = 1.49, calibration curve y = 1.49x + 49.92, R0). 2 =0.98). Both values ​​are far below the major industrial safety standards (ACGIH: 25ppm; EU OEL: 20ppm; JSOH: 20ppm), fully demonstrating the potential of the QCM sensor provided in this application for practical NH monitoring applications. The above characteristics indicate that ferrocene-containing COF is highly effective in improving the performance of QCM sensors, providing an adjustable monitoring sensor with excellent sensitivity, selectivity, and operational stability for NH detection.

[0082] 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. A quartz crystal microbalance based on a covalent organic framework material, characterized in that, The quartz crystal microbalance comprises a quartz crystal substrate, the quartz crystal having oppositely arranged first and second surfaces, the first surface being provided with a sensing material film layer, the sensing material film layer being a ferrocene-functionalized covalent organic framework nanofilm layer.

2. The covalent organic framework material-based quartz crystal microbalance of claim 1, wherein, The sensing material film layer has a thickness of 40-60 nm.

3. The covalent organic framework material-based quartz crystal microbalance according to claim 1 or 2, characterized in that, The material of the ferrocene-functionalized covalent organic framework nanofilm layer has the following structural formula: In the above formulae, is 4. The covalent organic framework material-based quartz crystal microbalance of claim 3, wherein, The first and second surfaces are respectively provided with silver electrodes, and on the first surface, the silver electrode is arranged between the quartz crystal substrate and the sensing material film layer.

5. The covalent organic framework material-based quartz crystal microbalance of claim 4, wherein, The quartz crystal microbalance is prepared by the following steps: S1. adding an aqueous solution containing 0.01wt%-0.1wt% 1,3,5-tris(4-aminophenyl)benzene and 0.1wt%-0.5wt% acetic acid into a reaction vessel; S2. adding 0.001wt%-0.03wt% n-hexane ferrocene-1,1'-diacetaldehyde into the reaction vessel, and forming a ferrocene-functionalized covalent organic framework nanofilm after reaction; S3. depositing the ferrocene-functionalized covalent organic framework nanofilm on the first surface of the quartz crystal substrate.

6. The covalent organic framework material-based quartz crystal microbalance of claim 5, wherein, In the step S2, the reaction time is 5 min-4 h, and the reaction temperature is 20-30°C.

7. The covalent organic framework material-based quartz crystal microbalance of claim 6, wherein, The step S3 comprises: placing the quartz crystal substrate at the bottom of a culture vessel, pouring the reaction solution obtained in the step S2 into the culture vessel, and pulling the quartz crystal substrate out of the culture vessel at a speed of 0.1-10 mm / s.

8. The covalent organic framework material-based quartz crystal microbalance of claim 7, wherein, After the step S3, a post-treatment step is further included: vacuum heat stabilizing the quartz crystal microbalance at 40-60°C for 110-130 min.

9. An ammonia sensor characterized by comprising: An organic framework material-based quartz crystal microbalance as claimed in any one of claims 1-8.

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