A QCM gas sensitive element based on electrostatic spinning Ce-MOF nanofiber and a preparation method thereof

Abstract

This invention discloses a QCM gas-sensitive element based on electrospun Ce-MOF nanofibers and its preparation method, belonging to the field of gas sensing materials technology. The gas-sensitive element includes a quartz crystal microbalance substrate and a sensitive coating disposed thereon, wherein the sensitive coating is Ce-UiO-66 nanofibers; the Ce-UiO-66 nanofibers are prepared by electrospinning, with a diameter of 300-500 nm, and the cerium element is represented by Ce. 3+ / Ce 4+ It exists in a mixed valence state. This invention combines the high specific surface area adsorption characteristics of MOF with the rapid mass transfer advantages of porous fibers. The QCM gas-sensitive element has high sensitivity and rapid response characteristics to borneol volatile gases. Moreover, the QCM gas-sensitive element provided by this invention has a simple preparation process, low cost, and can operate at room temperature.

Description

Technical Field

[0001] This invention belongs to the field of gas sensing materials technology, specifically a QCM gas sensing element based on electrospun Ce-MOF nanofibers and its preparation method. Background Technology

[0002] Borneol is a traditional Chinese medicine with effects such as refreshing the mind, clearing heat, and relieving pain. It is widely used in traditional Chinese medicine preparations and the fragrance industry. Borneol is highly volatile, and the concentration of its volatile gases directly affects the quality of the medicinal material, the stability of its efficacy, and the safety of its storage environment. Currently, the detection of borneol gases mostly relies on large-scale instruments such as gas chromatography-mass spectrometry, which suffers from high cost, complex operation, and difficulty in achieving real-time on-site monitoring. Therefore, developing a sensor that can rapidly and sensitively detect borneol volatile gases is of great significance for the quality control of traditional Chinese medicine.

[0003] In the field of gas sensors, quartz crystal microbalances (QCMs), as a mass-sensitive sensor, can operate at room temperature and has advantages such as real-time monitoring and rapid response, making them widely used for the detection of volatile organic compounds. The detection performance of QCMs is highly dependent on the properties of the sensing material.

[0004] Metal-organic frameworks (MOFs) are a class of porous crystalline materials formed by coordination bonds between metal ions or metal clusters and organic ligands, such as Ce-UiO-66. Due to their large specific surface area and abundant pore structure, they exhibit excellent adsorption and enrichment capabilities for volatile organic compounds. However, traditional MOF materials tend to aggregate and form poor films when coated on QCM electrodes, and their microporous structure restricts gas diffusion rates, significantly limiting the sensor's response speed and detection sensitivity. This makes it impossible to meet the practical requirements for rapid and sensitive detection of borneol volatile gases, thus limiting the application of MOF materials in QCM borneol sensors.

[0005] Electrospinning is a novel material preparation technology that can prepare one-dimensional MOF nanofiber structures. MOF nanofibers prepared by electrospinning can retain the high specific surface area adsorption characteristics of MOFs, provide rapid gas transport channels through the abundant pores on the fiber wall, and facilitate the formation of a uniform and stable sensitive film on the QCM electrode surface.

[0006] In summary, there are currently no technical solutions for applying electrospun MOF nanofibers to QCM borneol sensors, and the relevant technologies are still in the exploratory stage. Summary of the Invention

[0007] The purpose of this invention is to provide a QCM gas-sensitive element based on electrospun Ce-MOF nanofibers and its preparation method. The Ce-MOF nanofibers prepared by electrospinning technology are applied to the QCM gas sensor to achieve high sensitivity and rapid response detection of borneol volatile gases.

[0008] To achieve the above objectives, the technical solution of the present invention is as follows: A QCM gas-sensitive element based on electrospun Ce-MOF nanofibers includes a quartz crystal microbalance substrate and a sensitive coating disposed thereon, wherein the sensitive coating is Ce-UiO-66 nanofibers prepared by electrospinning technology.

[0009] Furthermore, in the Ce-UiO-66 nanofibers, cerium is simultaneously present as Ce 3+ and Ce 4+ It exists in mixed valence states.

[0010] Furthermore, the Ce-UiO-66 nanofibers have a diameter of 300–500 nm.

[0011] A method for preparing a QCM gas-sensitive element based on electrospun Ce-MOF nanofibers includes the following steps: S1: Using cerium oleate as the cerium source, it is formulated into a precursor sol together with terephthalic acid and a polymeric template agent; S2: Electrospin the precursor sol to obtain a composite fiber membrane; S3: Activate the composite fiber membrane; S4: The activated fiber membrane was placed in a mixed solvent of N,N-dimethylacetamide and N,N-dimethylformamide for a solvothermal reaction to remove the polymer template agent. After the reaction, it was washed with N,N-dimethylformamide and then vacuum dried to obtain Ce-UiO-66 nanofibers. S5: After dispersing the Ce-UiO-66 nanofibers obtained in step S4 in a solvent, they are coated onto the surface of a quartz crystal microbalance substrate and dried under vacuum to obtain a QCM gas-sensitive element.

[0012] Furthermore, in step S1, the polymeric template agent is polymethyl methacrylate.

[0013] Furthermore, the electrospinning process parameters in step S2 are as follows: feed speed 0.6-1.0 mL / h, voltage 15-20 kV, receiving distance 15-25 cm, ambient temperature 20-30 °C, and ambient relative humidity less than 30%.

[0014] Furthermore, the activation treatment in step S3 involves placing the composite fiber membrane in acetic acid vapor and treating it at 50–70°C for 4–8 hours.

[0015] Furthermore, in step S4, the temperature of the solvothermal reaction is 70–90°C, and the time is 3–6 hours.

[0016] Furthermore, the solvent in step S5 is deionized water. Ce-UiO-66 nanofibers are dispersed in deionized water to prepare a dispersion with a concentration of 0.5-2 mg / mL. 0.5-2 μL of the dispersion is coated onto a quartz crystal microbalance substrate and vacuum dried at 50-80°C for 1-3 hours to obtain the QCM gas-sensitive element.

[0017] Application of a QCM gas-sensitive element based on electrospun Ce-MOF nanofibers in the detection of volatile gases from borneol.

[0018] The beneficial effects of this invention are: This invention successfully prepared Ce-UiO-66 nanofiber material using electrospinning technology and applied it as a sensitive coating in a quality control membrane (QCM). This material combines the high specific surface area adsorption characteristics of MOFs with the rapid mass transfer advantages of porous fibers. Experimental results show that this QCM gas-sensitive element exhibits high sensitivity and rapid response characteristics to borneol volatile gases. The sensor prepared using this QCM gas-sensitive element shows a good linear relationship between the response value and the borneol concentration, with a detection limit down to the milligram level, and excellent repeatability and selectivity. The QCM gas-sensitive element provided by this invention has a simple preparation process, low cost, and can operate at room temperature, providing a novel and rapid detection method for the quality control of borneol. This QCM gas-sensitive element has broad application prospects in the fields of identification of genuine and counterfeit Chinese medicinal materials, quality grading, storage environment monitoring, and process control in the production of traditional Chinese medicine.

[0019] This invention does not require high-temperature calcination. Instead, it utilizes a mixed solvent of DMAc and DMF to dissolve PMMA under mild conditions, thereby completely preserving the crystalline structure and specific surface area of ​​Ce-UiO-66. Attached Figure Description

[0020] Figure 1 This is a scanning electron microscope image of the Ce-UiO-66 nanofiber material prepared in Example 1 of the present invention.

[0021] Figure 2 This is a transmission electron microscope (TEM) image of the Ce-UiO-66 nanofiber material prepared in Example 1 of this invention.

[0022] Figure 3 The image shows the response curve of the QCM gas-sensitive element prepared in Example 1 of this invention to the volatile gases of borneol.

[0023] Figure 4This is a bar chart showing the response / recovery time of the QCM gas-sensitive element prepared in Example 1 of the present invention to the volatile gases of borneol.

[0024] Figure 5 This is a test curve of the QCM gas-sensitive element prepared in Example 1 of the present invention for different masses of borneol volatile gases.

[0025] Figure 6 This is a repeatability test curve of the QCM gas-sensitive element prepared in Example 1 of the present invention for borneol volatile gases.

[0026] Figure 7 This is the XPS spectrum of Ce element in mixed valence state during the solvothermal reaction in Example 1 of the present invention.

[0027] Figure 8 This is a linear fitting graph showing the response of the QCM gas-sensitive element prepared in Example 1 of the present invention as a function of the concentration of borneol volatile gas.

[0028] Figure 9 This is a schematic diagram showing the selectivity of the QCM gas-sensitive element prepared in Example 1 of the present invention for volatile gases of borneol and peppermint in different proportions. Detailed Implementation

[0029] 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0030] Example 1 A method for preparing Ce-MOF nanofibers based on electrospinning includes the following: (1) Preparation of precursor solution: Add 1.8g of cerium oleate and 0.2g of oleic acid to 5mL of N,N-dimethylformamide (DMF), and sonicate for 30 minutes at an ultrasonic power of 120W to obtain a cerium source solution.

[0031] Add 0.474 g of terephthalic acid (H2BDC) to 5 mL of DMF and stir at 80 °C until fully dissolved to obtain a ligand solution.

[0032] Dissolve 2.0 g of polymethyl methacrylate (PMMA) in 7 mL of DMF and stir for 12 hours until the solution is completely transparent to obtain the PMMA template solution.

[0033] (2) Preparation of precursor sol for electrospinning: Under magnetic stirring, the cerium source solution was slowly added dropwise to the PMMA template solution, followed by the ligand solution being slowly added dropwise to the mixture. Stirring was continued for 12 hours to allow the components to fully mix and react, forming a uniform and stable precursor sol for electrospinning.

[0034] (3) Electrospinning: The obtained precursor sol was injected into a 10mL medical syringe. A stainless steel spinning needle was installed at the tip of the syringe. The syringe was fixed to the propulsion device of the electrospinning equipment. The propulsion device pushed the syringe, causing the sol to be extruded from the needle at a uniform speed. The extruded sol was placed in a high-voltage electric field environment set at 18kV (the high-voltage power supply was connected to the spinning needle, and the receiving plate was grounded to form a stable high-voltage electric field). Under the electrostatic attraction of the high-voltage electric field, the sol at the needle formed a Taylor cone, which was then stretched to form a continuous spinning jet and finally solidified into composite nanofibers. The composite fiber membrane was finally collected on the receiving plate.

[0035] The specific spinning parameters are set as follows: the syringe advance speed is 0.8 mL / h to ensure that the precursor sol is extruded from the spinning needle at a uniform and stable speed; the high-voltage power supply output voltage is adjusted to 18 kV; the receiving plate is a flat receiving plate covered with aluminum foil, and the vertical distance between the receiving plate and the spinning needle, i.e., the receiving distance, is controlled at 20 cm to ensure that the spinning jet can be fully stretched and solidified; the spinning environment needs to be strictly controlled, with the ambient temperature maintained at 25℃ and the relative humidity controlled at <30%RH to avoid excessive humidity causing bead-like defects on the fiber surface and temperature fluctuations affecting the uniformity of fiber diameter. The electrospinning process continues until the precursor sol in the syringe is completely extruded and uniformly collected on the aluminum foil-covered receiving plate to obtain a continuous and dense composite fiber membrane—PMMA@precursor composite nanofiber membrane.

[0036] (4) Formation of Ce-UiO-66 nanofibers: The composite fiber membrane was activated by immersion in acetic acid vapor at 60°C for 6 hours. After activation, the membrane was placed in a polytetrafluoroethylene-lined high-pressure reactor containing a mixed solvent of N,N-dimethylacetamide (DMAc) and DMF (volume ratio 1:1) and subjected to a solvothermal reaction at 80°C for 4 hours. During this process, the PMMA template was dissolved and removed, while cerium ions and H₂BDC nucleated, crystallized, and grew within the fiber wall to form a Ce-UiO-66 framework. After the reaction, the membrane was repeatedly washed five times with DMF to thoroughly remove residual template and solvent. Finally, the product was vacuum-dried at 60°C for 12 hours to obtain Ce-UiO-66 nanofibers.

[0037] In this invention, DMF is not only a solvent but also a proton acceptor and hydrolysis control agent. In the precursor sol, DMF can effectively inhibit premature coordination of metal ions with ligands, ensuring the stability of the sol, which is key to achieving electrospinning.

[0038] During the cleaning stage, DMAc and DMF are used due to their unique swelling properties. DMAc and DMF are strong solvents for PMMA but inert to the Ce-UiO-66 framework. The PMMA template can be dissolved at low temperatures, rather than through high-temperature calcination. If other solvents (such as acetone or chloroform) are used, it is difficult to completely remove PMMA; the residue can cause pore blockage and damage the formed MOF nanocrystals.

[0039] In this invention, PMMA functions as both a template agent and a spinning aid. During electrospinning, the polymer chain entanglement provided by PMMA is essential for forming continuous and uniform fibers. Without PMMA, electrospinning cannot be achieved using only low-molecular-weight MOF precursors. The combination of electrospinning technology and MOF materials offers a new approach to solving the problem of rapid detection of volatile gases from borneol.

[0040] A method for preparing a QCM gas-sensitive element based on electrospun Ce-MOF nanofibers includes the following steps: (1) The prepared Ce-UiO-66 nanofibers were dispersed in deionized water to prepare a uniform dispersion with a concentration of 1 mg / mL.

[0041] (2) Use a micropipette to evenly coat 1 mL of dispersion onto the center of the QCM substrate.

[0042] The QCM substrate is a circular quartz crystal sheet with a diameter of 8 mm and an initial fundamental frequency of 10 MHz. Electrodes are attached to both the top and bottom surfaces of the substrate, but they do not completely cover the top or bottom surface. The electrodes are circular with a radius of 2 mm (typically formed by silver plating on the substrate). In the experiment, drop-coating was performed only on the electrodes on one side of the QCM substrate. One mL of dispersion was dropped onto the center of the electrode on any side of the QCM substrate, and then allowed to air dry at room temperature. After drying, the sample coverage area was approximately 1 mm². 2 .

[0043] (3) The coated QCM substrate is placed in a vacuum oven at 60°C and dried for 2 hours to form a stable Ce-UiO-66 nanofiber sensitive coating on the surface of the QCM substrate, thus obtaining the QCM gas-sensitive element.

[0044] When the QCM gas-sensitive element of the present invention is used to detect borneol volatile gases, it achieves quantitative detection of the concentration of borneol volatile gases by real-time monitoring of the change in the resonant frequency of the element based on the mass sensitivity principle.

[0045] Performance test of borneol volatile gas detection: Different masses of borneol were placed in the same temperature environment with QCM gas-sensitive elements. Then, an electric current was applied to the electrodes on the QCM substrate, and the resonant frequency of each QCM gas-sensitive element was measured and recorded. Since different masses of borneol would produce different concentrations of target gas, the resonant frequency of each QCM gas-sensitive element would also be different. The frequency shift (QCM gas-sensitive element response) was calculated using the following formula: ΔF = f - f0; In the formula, f is the vibration frequency of the QCM gas sensor in the target gas, f0 represents the baseline frequency (i.e., the vibration frequency of the QCM gas sensor in the air), and ΔF is the frequency shift (response) of the QCM gas sensor.

[0046] According to the Sauerbrey equation, the mass m is proportional to the frequency shift ΔF, and thus the mass m of the target gas can be obtained.

[0047] Figure 1 and Figure 2 The prepared Ce-UiO-66 nanofibers exhibit a uniform and regular nanofiber structure with rough and porous fiber walls, which facilitates gas adsorption and diffusion.

[0048] Figure 1 It displays a regular one-dimensional nanofiber morphology, with uniform thickness and a diameter of approximately 420 nm.

[0049] Figure 3 This is the single-cycle response-recovery curve of the QCM gas sensor to the gas produced by the volatilization of 0.2g of borneol solid (i.e., saturated or constant-concentration vapor under these conditions). The gas sensor can adsorb the gas in the target gas environment, and can completely desorb the target gas when the gas sensor is in normal air without the target gas.

[0050] Figure 4 This is a bar graph showing the response and recovery time of the QCM gas sensor to the gas produced by the volatilization of 0.2g of borneol solid. The response time is approximately 58.4 seconds, and the recovery time is approximately 29.2 seconds, which is beneficial for achieving rapid detection.

[0051] Figure 5 The figure shows the dynamic response curves of the QCM gas sensor to volatile gases from borneol of different masses. As the mass of borneol increases, the frequency response value increases accordingly. Even at a low mass of 0.05g, the response signal can still be detected, indicating that the QCM gas sensor has high sensitivity and can meet the detection requirements for trace volatile gases from traditional Chinese medicine materials.

[0052] Figure 6The figure shows the repeatability test curve of the QCM gas sensor for the gas produced by the volatilization of 0.1g of borneol solid. After 6 cycles of testing, the response value of the QCM gas sensor remained stable, demonstrating good repeatability and reversibility, meeting the requirements of practical applications. The process of each cycle is as follows: The surface of the QCM gas-sensitive element is coated with a thin film of Ce-UiO-66. A background gas (usually dry air or nitrogen) is introduced into the test chamber. There are no borneol molecules. The QCM gas-sensitive element oscillates stably at a specific frequency under electric field excitation. This baseline frequency value is recorded as f0. At this time, the surface of the QCM gas-sensitive element is clean and there are no adsorbed borneol molecules.

[0053] Adsorption stage: The target gas is introduced into the test chamber. The target gas is a saturated vapor carrying 0.1g of borneol volatile molecules. The borneol molecules enter the test chamber and diffuse to the sensitive membrane surface of the QCM gas-sensitive element. The borneol molecules interact with the Ce-UiO-66 nanofiber sensitive coating. These forces capture and fix the borneol molecules to the membrane surface.

[0054] According to the formula above, as the mass of the QCM gas-sensitive element increases, the frequency decreases. The more borneol molecules are adsorbed, the greater the increase in the mass of the sensitive membrane, and the greater the decrease in the resonant frequency. Over time, the adsorption sites on the Ce-UiO-66 nanofiber sensitive coating surface are gradually occupied by borneol molecules, and the adsorption and desorption rates reach a dynamic equilibrium. The frequency no longer decreases and stabilizes at a minimum value f1. At this point, the response process ends.

[0055] The response time is the time it takes for the frequency to change from f0 to 90% of f1.

[0056] The response value ΔF reflects the sensor's sensitivity to camphor gas.

[0057] The gas was switched again, and once the frequency stabilized at f1, background gas was introduced into the test chamber. The background gas contained no borneol molecules, disrupting the adsorption-desorption equilibrium. Borneol molecules on the Ce-UiO-66 nanofiber sensitive coating surface began to desorb—detaching from the membrane surface, entering the gas flow, and being blown away. As the number of borneol molecules on the membrane surface decreased, the mass gradually returned to its initial state, and the resonant frequency gradually recovered. After a sufficiently long period, most of the borneol molecules were completely desorbed, and the frequency recovered to near the initial baseline frequency f0. At this point, the recovery process ended.

[0058] The recovery time is the time it takes for the frequency to rise from f1 to 90%ΔF.

[0059] Figure 7 The image shows the Ce3d orbital XPS spectrum of Ce-UiO-66 nanofibers, which shows that the Ce element exhibits Ce3d orbital characteristics. 3+ / Ce 4+ Mixed valence state.

[0060] Figure 8 The figure shows the linear fitting curve of the QCM gas-sensitive element response to the change in borneol volatile gas concentration. The fitting equation is ΔF=(-103.44)+(-1008.63)×m, where R 2 This represents the quality of the fit; it can be seen that there is a linear correlation in the concentration range of 0.05-0.3g.

[0061] Figure 9 The figure shows the selectivity test results of the QCM gas sensor for different proportions of borneol and peppermint. Analysis indicates that the QCM gas sensor exhibits good selectivity for borneol volatile gases.

[0062] The innovation of this invention lies in the use of electrospinning to prepare MOF materials. After the nanofibers are formed, PMMA is removed using the organic solvents DMAc and DMF. This avoids the structural collapse of the organic framework and the formation of oxides that occur after high-temperature calcination.

[0063] In this invention, Ce 3+ / Ce 4+ The redox pairs are key to constructing Ce-UiO-66 and maintaining its framework stability. The mixed valence states of Ce have been confirmed by XPS characterization. Figure 7 During solvothermal processes, Ce can undergo in-situ partial oxidation to form mixed-valence clusters, a property not possessed by other lanthanide elements (such as La, Nd, and Sm) that do not have stable tetravalent states.

[0064] If cerium is replaced with other rare earth elements, the following differences exist: 1. It is difficult to form a stable MOF structure that coordinates with terephthalic acid (H2BDC) because the UiO-66 topology itself is based on Ce element; 2. During the solvent reaction, the crystal growth is too fast or too slow due to the single valence state, making it impossible to achieve in-situ recrystallization on the PMMA fiber wall, thus making it difficult to maintain the fiber morphology.

[0065] 3. The ionic radius of rare earth elements tends to decrease with increasing atomic number. Ce is located at the beginning of the lanthanide series and has a specific ionic radius and coordination number (usually 8 or 12), which highly matches the coordination geometry of the H2BDC carboxylic acid group.

[0066] Therefore, the choice of cerium is based on its valence stability and precise matching with the reaction system, as other lanthanides or rare earth elements are difficult to achieve the same technical effect.

[0067] Those skilled in the art would, according to conventional thinking, choose calcination, but calcination inevitably leads to the carbonization of the organic ligands (H2BDC) in the MOF and the collapse of the framework, forming cerium oxide particles.

[0068] Example 2 Same as Example 1, except that: The composite fiber membrane was activated by placing it in acetic acid vapor and treating it at 50°C for 4 hours.

[0069] The activated fiber membrane underwent a solvothermal reaction at a temperature of 70°C for 3 hours.

[0070] Ce-UiO-66 nanofibers were dispersed in deionized water to prepare a dispersion with a concentration of 0.5 mg / mL. 0.5 μL of the dispersion was coated onto the center of a quartz crystal microbalance base and dried under vacuum at 50 °C for 1 hour to obtain a QCM gas-sensitive element.

[0071] Experiment on the volatility of borneol gas: The prepared QCM gas-sensitive element was tested using a conventional static measurement system (53220A, Keysight). The QCM substrate has a power-on port for powering the electrodes of the QCM substrate and reading their signals. It can be directly connected to the power-on port of the measurement system through a wire to form a closed loop, thereby energizing the electrodes of the QCM substrate and recording the vibration frequency of the QCM gas-sensitive element by the measurement system.

[0072] The test temperature was set at 25℃. At this temperature, multiple glass gas cylinders were used, and each cylinder contained a QCM gas-sensitive element and different masses of borneol. The wire connecting the QCM gas-sensitive element was passed through the cylinder stopper and connected to the power socket of the measurement system. The wire length was adjustable. Holes were drilled in the cylinder stoppers to allow the wires to pass through, and the stoppers were sealed with tape / Vaseline. Different masses of borneol would produce different concentrations of the target gas. The measurement system monitored and recorded the resonant frequency of the QCM gas-sensitive element in real time using a frequency counter, thereby obtaining the mass of the target gas adsorbed by the QCM gas-sensitive element.

[0073] Example 3 Same as Example 1, except that: The composite fiber membrane is activated by placing it in acetic acid vapor and treating it at 70°C for 8 hours.

[0074] The activated fiber membrane undergoes a solvothermal reaction at a temperature of 90°C for 6 hours.

[0075] Ce-UiO-66 nanofibers were dispersed in deionized water to prepare a dispersion with a concentration of 2 mg / mL. 2 μL of the dispersion was coated onto the center of a quartz crystal microbalance substrate and vacuum dried at 80°C for 3 hours to obtain a QCM gas-sensitive element.

[0076] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification.

Claims

1. A QCM gas-sensitive element based on electrospun Ce-MOF nanofibers, characterized in that, It includes a quartz crystal microbalance substrate and a sensitive coating disposed thereon, the sensitive coating being Ce-UiO-66 nanofibers prepared by electrospinning.

2. The gas-sensitive element according to claim 1, characterized in that, In the Ce-UiO-66 nanofibers, cerium is present in the form of Ce. 3+ and Ce 4+ It exists in mixed valence states.

3. The gas-sensitive element according to claim 1, characterized in that, The Ce-UiO-66 nanofibers have a diameter of 300–500 nm.

4. A method for preparing a QCM gas-sensitive element based on electrospun Ce-MOF nanofibers as described in any one of claims 1 to 3, characterized in that, Includes the following steps: S1: Using cerium oleate as the cerium source, it is formulated into a precursor sol together with terephthalic acid and a polymeric template agent; S2: Electrospin the precursor sol to obtain a composite fiber membrane; S3: Activate the composite fiber membrane; S4: The activated fiber membrane was placed in a mixed solvent of N,N-dimethylacetamide and N,N-dimethylformamide for a solvothermal reaction to remove the polymer template agent. After the reaction, it was washed with N,N-dimethylformamide and then vacuum dried to obtain Ce-UiO-66 nanofibers. S5: After dispersing the Ce-UiO-66 nanofibers obtained in step S4 in a solvent, they are coated onto the surface of a quartz crystal microbalance substrate and dried under vacuum to obtain a QCM gas-sensitive element.

5. The preparation method according to claim 4, characterized in that, The polymeric template agent in step S1 is polymethyl methacrylate.

6. The preparation method according to claim 4, characterized in that, The electrospinning process parameters in step S2 are as follows: feed speed 0.6-1.0 mL / h, voltage 15-20 kV, receiving distance 15-25 cm, ambient temperature 20-30℃, and ambient relative humidity less than 30%.

7. The preparation method according to claim 4, characterized in that, The activation treatment in step S3 involves placing the composite fiber membrane in acetic acid vapor and treating it at 50–70°C for 4–8 hours.

8. The preparation method according to claim 4, characterized in that, In step S4, the temperature of the solvothermal reaction is 70–90°C, and the time is 3–6 hours.

9. The preparation method according to claim 4, characterized in that, The solvent in step S5 is deionized water. Ce-UiO-66 nanofibers are dispersed in deionized water to prepare a dispersion with a concentration of 0.5-2 mg / mL. 0.5-2 μL of the dispersion is coated onto a quartz crystal microbalance substrate and vacuum dried at 50-80°C for 1-3 hours to obtain the QCM gas-sensitive element.

10. The application of a QCM gas-sensitive element based on electrospun Ce-MOF nanofibers as described in any one of claims 1 to 3 in the detection of borneol volatile gases.

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