A gas-sensitive material based on a PVDF / ZIF-8 composite nanofiber membrane, a preparation method and application thereof

Abstract

The application relates to a PVDF / ZIF-8 composite nanofiber membrane-based gas-sensitive material and a preparation method and application thereof. β The PVDF / ZIF-8 composite nanofiber membrane material is composed of a PVDF hollow fiber matrix with a content of more than 80% and ZIF-8 which is in-situ grown in the inner cavity of the PVDF hollow fiber matrix, wherein the surface of the ZIF-8 is modified by perfluorooctyltriethoxysilane PFOTS, and the loading capacity is 8-12 wt%. Compared with the prior art, the PVDF / ZIF-8 composite nanofiber membrane material has specific adsorption capacity for the characteristic decomposition component CHF3 of the insulating gas C4F7N / CO2, and can be applied as a gas-sensitive material for detecting the characteristic decomposition component of the insulating gas C4F7N / CO2.

Description

Technical Field

[0001] This invention belongs to the field of gas sensor technology, and relates to a gas-sensitive material based on PVDF / ZIF-8 composite nanofiber membrane, its preparation method and application. Background Technology

[0002] Perfluoroisobutyronitrile (C4F7N) / CO2 mixed gas has become the preferred alternative to SF6 due to its superior insulation strength (35.45 kV higher than SF6 at a 20% concentration) and extremely low greenhouse effect (CO2 equivalent reduction >98%). As of 2024, over 200 C4F7N / CO2 insulated devices have been put into operation globally, covering 145 kV GIS switches and 110 kV gas-insulated transformers. However, during partial discharge or overheating faults (≥300℃), the C4F7N molecule's C-C bonds break, generating CF3 free radicals, which react with active hydrogen on the material surface to produce the characteristic marker trifluoromethane (CHF3). The concentration of CHF3 (50-500 ppm) is positively correlated with the severity of the fault. The accumulation of CHF3 not only significantly weakens insulation strength (breakdown voltage decrease >15% at a 10% concentration), but its weak toxicity (TLV 1000 ppm) also poses a potential threat to the health of maintenance personnel. While resistive gas sensors offer advantages such as compact structure, fast response, and low cost, current research focuses on detecting leaks in pure C4F7N, with a relative lack of development of sensitive materials for trace amounts of CHF3 in mixed gases. Furthermore, existing sensitive materials generally rely on high-temperature operation (>200℃) or ultraviolet excitation, which is insufficient to meet the low-power monitoring requirements of power equipment. Therefore, there is an urgent need to develop efficient online monitoring technologies for identifying CHF3.

[0003] While the composite nanofiber membrane provided by CN119711177A, which is used for the detection of C3F6, a component of C4F7N gas decomposition, can achieve highly sensitive and rapid identification of C3F6 gas, it is almost ineffective for CHF3 identification and monitoring because the properties of CHF3 are completely different from those of C3F6. Summary of the Invention

[0004] The purpose of this invention is to provide a gas-sensitive material based on PVDF / ZIF-8 composite nanofiber membrane, its preparation method and application, so as to achieve efficient identification and detection of CHF3, a characteristic decomposition component of C4F7N / CO2.

[0005] The objective of this invention can be achieved through the following technical solutions:

[0006] In a first aspect, the present invention provides a gas-sensitive material based on a PVDF / ZIF-8 composite nanofiber membrane, which is composed of... βThe product consists of a PVDF hollow fiber matrix with a phase content greater than 80% and ZIF-8 grown in situ within the cavity of the PVDF hollow fiber matrix, wherein the surface of the ZIF-8 is modified with perfluorooctyltriethoxysilane (PFOTS) and the loading is 8-12 wt%.

[0007] In a second aspect, the present invention provides a method for preparing a gas-sensitive material based on a PVDF / ZIF-8 composite nanofiber membrane, comprising the following steps:

[0008] S1. Prepare shell layer solution and core layer solution separately:

[0009] PVDF powder was dissolved in a mixed solvent of DMF and acetone, 2-methylimidazole and lithium chloride were added, and the mixture was stirred to obtain a shell solution.

[0010] Zinc nitrate was dissolved in glycerol to prepare a core layer solution;

[0011] S2, Coaxial electrospinning:

[0012] The shell solution and the core solution obtained in S1 were coaxially electrospun to obtain a nascent fiber membrane.

[0013] S3. Hollow structure formation and in-situ growth of ZIF-8:

[0014] The nascent fibrous membrane obtained from S2 was immersed in a methanol / water mixture containing benzimidazole. The reaction caused glycerol to dissolve and form a hollow cavity. Zinc ions diffused into the shell and reacted with 2-methylimidazole to generate ZIF-8.

[0015] S4. Critical point drying treatment:

[0016] The water content of the reaction product obtained in S3 was replaced successively with ethanol and tert-butanol, and then dried at the CO2 critical point.

[0017] S5, Fluorinated surface modification:

[0018] The dried fiber membrane obtained in S4 was immersed in an ethanol solution of PFOTS, then removed, purged with nitrogen, and annealed to obtain a PVDF / ZIF-8 composite nanofiber membrane, which is the target product.

[0019] Furthermore, in S1, the volume ratio of DMF to acetone in the shell solution is (6-8):(2-4), the mass concentration of PVDF is 16-20wt%, the amount of 2-methylimidazole added is 14-16% of the mass of PVDF, and the amount of lithium chloride added is 2-4% of the mass of PVDF.

[0020] Furthermore, in S1, the molar concentration of zinc nitrate in the core layer solution is 0.01~0.1 mol / L.

[0021] Furthermore, in S2, during the coaxial electrospinning process, the core needle size of the coaxial needle used is 27G and the shell needle size is 22G. The core flow rate is 0.7~0.9 mL / h, the shell flow rate is 1.3~1.7 mL / h, the applied voltage is 25kV, the receiving distance is 20cm, the relative humidity is 35~45%, and the temperature is 23~27℃.

[0022] Furthermore, in S2, the thickness of the resulting nascent fiber membrane is 140~160μm.

[0023] Furthermore, in S3, the concentration of benzimidazole is 0.008~0.012 mol / L;

[0024] The volume ratio of methanol to water is 3-5:1;

[0025] The reaction temperature is 60~70℃ and the time is 3~5h.

[0026] Furthermore, in S4, the drying process is carried out at a pressure of 7.4 MPa and a temperature of 31°C.

[0027] Furthermore, in S5, the mass concentration of PFOTS in the ethanol solution is 0.4~0.6 wt%;

[0028] The immersion treatment temperature is 55~65℃, and the time is 1~3h;

[0029] The annealing temperature is 110~130℃, and the time is 0.5~1.5h.

[0030] In a third aspect, the present invention provides an application of a gas-sensitive material based on a PVDF / ZIF-8 composite nanofiber membrane in the selective detection of CHF3, a characteristic decomposition component, in an environmentally friendly insulating gas C4F7N / CO2 mixture as a gas-sensitive sensor.

[0031] This invention reveals that C3F6 primarily interacts with gas-sensitive materials through van der Waals forces or π-electron interactions, with its detection mechanism based on changes in carrier concentration caused by the reaction of gas with surface oxygen adsorbed species. In contrast, CHF3, a saturated molecule lacking π bonds and exhibiting weak oxidizing properties, hardly reacts with surface oxygen species. Its interaction with the active sites on the gas-sensitive material surface is mainly through weak adsorption, hydrogen bonding, or dipole interactions. Based on this, this invention employs coaxial electrospinning to form a hollow PVDF structure and achieves a β-phase content >80% through LiCl induction. The strong polarity of the β-phase PVDF gives it a high dipole moment and dielectric response. When CHF3 molecules adsorb onto the interfacial ZIF-8 layer, it induces local dipole perturbations and interfacial charge transfer. Due to the high polarization sensitivity of the β-phase PVDF, these minute perturbations are amplified, improving sensitivity and the detection limit. Furthermore, CO2 critical point drying is used to avoid the reduction in sensitivity and response rate caused by local collapse or blockage of the MOF / pore structure, thereby effectively improving the high-efficiency identification and detection capability of CHF3.

[0032] Compared with the prior art, the present invention has the following advantages:

[0033] (1) β-phase PVDF enhances interfacial stability: A high-content β-phase (>80%) is formed by LiCl induction, and its -CH2 / CF2 dipole interacts with the Zn2 of ZIF-8. + It generates ion-dipole interactions, increasing the binding energy by 40%, which significantly enhances the stability and charge transport efficiency of the composite membrane.

[0034] (2) Shell premixed ligand: 2-methylimidazolium (2-mI) is dissolved in PVDF spinning solution at a concentration of 15±1 wt% to avoid subsequent diffusion steric hindrance and promote the uniform in-situ generation of ZIF-8 in the cavity. Attached Figure Description

[0035] Figure 1 This is a scanning electron microscope image of the PVDF / ZIF-8 composite nanofiber membrane of Example 1 of the present invention;

[0036] Figure 2 The XRD pattern of the PVDF / ZIF-8 composite nanofiber membrane in Example 1 is shown below.

[0037] Figure 3 The FTIR spectra of the PVDF / ZIF-8 composite nanofiber membranes of Example 1 and Comparative Example 1 are shown.

[0038] Figure 4 A comparison chart of the β-phase content of composite nanofiber membranes obtained with added LiCl (Example 1) and without added LiCl (Comparative Example 1);

[0039] Figure 5The resistivity variation diagram of the composite nanofiber membrane obtained in Example 1 is shown.

[0040] Figure 6 The resistivity variation of the composite nanofiber membrane obtained in Comparative Example 1 is shown in the graph.

[0041] Figure 7 The resistivity variation of the composite nanofiber membrane obtained in Comparative Example 2 is shown in the graph.

[0042] Figure 8 The resistivity variation of the composite nanofiber membrane obtained in Comparative Example 3 is shown in the graph.

[0043] Figure 9 The resistivity variation of the composite nanofiber membrane obtained in Comparative Example 4 is shown in the graph.

[0044] Figure 10 The resistivity variation of the composite nanofiber membrane obtained in Comparative Example 5 is shown in the graph.

[0045] Figure 11 The graph shows the response of the composite nanofiber membrane to different gases. Detailed Implementation

[0046] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0047] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0048] As used herein, the terms "and / or," "or / and," and "and / or" encompass any one of two or more of the related listed items, as well as any and all combinations of the related listed items. These arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. It should be noted that when at least three items are connected using at least two conjunctions selected from "and / or," "or / and," and "and / or," it should be understood that, in this application, the technical solution undoubtedly includes solutions connected by "logical AND," and also undoubtedly includes solutions connected by "logical OR."

[0049] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0050] In this application, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0051] This document only specifically discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, just as any upper limit can be combined with any other upper limit to form an unspecified range. Furthermore, each individually disclosed point or single value can itself serve as a lower or upper limit and be combined with any other point or single value or with other lower or upper limits to form an unspecified range.

[0052] Unless otherwise specified, the temperature parameters in this application may be either constant temperature processing or processing within a certain temperature range. The constant temperature processing allows temperature fluctuations within the precision range controlled by the instrument, such as ±5°C, ±4°C, ±3°C, ±2°C, or ±1°C.

[0053] In this document, the term "suitable" as used in phrases such as "suitable combination," "suitable method," and "any suitable method" refers to the ability to implement the technical solution of this application, solve the technical problem of this application, and achieve the expected technical effect of this application.

[0054] In this application, terms such as "further," "even further," and "particularly" are used to describe purposes and indicate differences in content, but should not be construed as limiting the scope of protection of this application.

[0055] In this application, "optionally," "optionally," and "optional" mean that something is optional, that is, it means that it is selected from either "with" or "without." If there are multiple "optional" entries in a technical solution, unless otherwise specified, and there are no contradictions or mutual constraints, each "optional" entry shall be independent.

[0056] In the description of the application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0057] Unless otherwise specified, all preparations and tests described herein took place at 25°C.

[0058] The terms “comprising,” “including,” “containing,” “having,” “comprising,” or other variations thereof are intended to cover non-closed inclusion, and no distinction is made between these terms. The term “comprising” means that other steps and ingredients may be added without affecting the final result. The compositions and methods / processes of the present invention comprise, consist of, and substantially consist of the essential elements and limitations described herein, as well as any additional or optional ingredients, components, steps, or limitations described herein. No distinction is made between the terms “efficacy,” “performance,” “effect,” and “potency” herein.

[0059] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions. Unless otherwise specified, all technical features and optional technical features of this application can be combined to form new technical solutions.

[0060] Unless otherwise specified, all steps of this application may be performed sequentially or randomly, but sequentially is preferred.

[0061] Example 1:

[0062] 3.6 g of PVDF (Mw=534000) was dissolved in 20 mL of a DMF / acetone mixed solvent (volume ratio 7:3), and 0.54 g of 2-methylimidazole and 0.12 g of LiCl were added. The mixture was stirred at 50 °C for 12 hours to form a shell layer solution. Simultaneously, 0.289 g of Zn(NO3)2·6H2O was dissolved in 10 mL of glycerol and ultrasonically dispersed to obtain a core layer spinning solution. A coaxial electrospinning apparatus (27G core layer needle, 22G shell layer needle) was used, with the core layer flow rate set to 0.8 mL / h and the shell layer flow rate to 1.5 mL / h. A voltage of 25 kV was applied, and the nascent fiber membrane was collected at a receiving distance of 20 cm and a humidity of 40%. The fiber membrane was then immersed in a methanol / water solution containing 0.15 g benzimidazole (methanol to water volume ratio 4:1, total volume 100 mL) and reacted at 65°C for 4 hours, allowing glycerol to dissolve and form hollow cavities. Simultaneously, zinc ions diffused to the shell and reacted with ligands to generate ZIF-8 crystals. The water in the fibers was successively replaced with ethanol and tert-butanol, followed by CO2 critical point drying (31°C, 7.4 MPa) to maintain the hollow structure. Finally, the membrane was immersed in a 0.5 wt% perfluorooctyltriethoxysilane (PFOTS) ethanol solution, treated at 60°C for 2 hours, purged with nitrogen, and annealed at 120°C for 1 hour to complete fluorination modification (resulting in fiber diameter 380±50 nm, hollow pore size 100±20 nm, and ZIF-8 loading 10.2 wt%), yielding a PVDF-ZIF-8 composite nanofiber membrane.

[0063] The PVDF-ZIF-8 composite nanofiber membrane prepared in Example 1 was tested as follows:

[0064] (1) The PVDF-ZIF-8 composite nanofiber membrane material prepared in Example 1 was characterized by scanning electron microscopy (SEM), combined with Figure 1 As shown in Figure (a), the PVDF nanofibers exhibit coarser nodules and a beaded morphology. Further analysis using the high-magnification electron microscope image in Figure (b) reveals that ZIF-8 crystal particles are dispersed and attached within the PVDF nanofiber network, forming a tight interfacial bond between the ZIF-8 particles and the PVDF fiber matrix. Furthermore, infrared spectroscopy and X-ray diffraction tests were performed on the prepared PVDF / ZIF-8 composite nanofiber membrane, and the results are as follows: Figure 2 and Figure 3 As shown, the FTIR spectrum indicates that 840 cm⁻¹ -1 The intensity of the β-phase characteristic peak at 763 cm⁻¹ is significantly higher than that at 763 cm⁻¹. -1 Based on the Gregorio formula, the relative content of the β phase crystal form is approximately 81.7%–84.1%. However, the XRD pattern shows that the PVDF material has a relatively broad peak with low intensity at 20.6°, while the β phase peak at 20.6° of the PVDF / ZIF-8 composite nanofiber membrane is sharper and has a greater intensity, indicating that the β phase content is the highest in this sample. Furthermore, the α phase of PVDF generally exhibits characteristic peaks at 17.7°, 18.3°, and 19.9°, but the XRD pattern shows that there are no obvious sharp peaks in these regions, and the α characteristic peak has basically disappeared.

[0065] (2) The composite nanofiber membrane prepared in Example 1 was fixed onto an interdigitated electrode substrate (using a gold-based interdigitated electrode IDE, with an alumina substrate and an electrode spacing of approximately 100 μm) to assemble a resistive gas sensor. During the test, the sensor was placed in a gas-sensitive testing system, and a C4F7N / CO2 mixed gas (i.e., 6% C4F7N / 94% CO2, volume fraction) was first introduced at room temperature to equilibrate for 30 min. Subsequently, the gas source was switched, and different concentrations of CHF3 gas were introduced. After the sensor response stabilized, C4F7N / CO2 gas was introduced again to achieve recovery. During this process, the resistance of the sensor changed, which allowed the detection of CHF3 gas. In the 50 ppm CHF3 test, as... Figure 5 As shown, the sensor exhibits a resistance change rate of 8.48% (ΔR / R0, where ΔR is the resistance difference before and after the target gas is introduced, and R0 is the resistance value before the target gas is introduced) and a response time of 112 s.

[0066] The results show that the PVDF / ZIF-8 composite hollow nanofiber membrane has good response characteristics to CHF3 gas and can meet the online detection requirements of fault markers in C4F7N / CO2 mixed media.

[0067] The sensor prepared in Example 1 was used to detect different gases using the same method. The background gas used for CO2 detection was a C4F7N / N2 mixture, with volume fractions of 10% and 90% for each component. The background gas for the other four gases was also a C4F7N / CO2 mixture. The concentration of all five gases was 50 ppm. Figure 11 It can be seen that, compared to CHF3, the sensor's response values ​​to other gas components are very low, which demonstrates the material's selective recognition of CHF3.

[0068] Comparative Example 1:

[0069] The results are largely the same as in Example 1, except that the addition of LiCl is omitted.

[0070] After testing, combined Figure 3 and Figure 4 It can be seen that the β-phase content of the obtained composite nanofiber membrane decreased from 84.1% to 63.4%. When it was fabricated into a gas sensor according to the method of Example 1 and tested, as... Figure 6 As shown, the corresponding resistance change rate ΔR / R0 decreased from 8.48% to 5.20%; the response time also slowed down (from 112s to 210s), and the baseline drift increased. The reason for this is that, due to the absence of LiCl-induced orientation, the β phase decreased significantly, leading to a reduction in polarization sensitivity, a weakening of the electrical amplification effect, and a decrease in both response sensitivity and rate.

[0071] Comparative Example 2:

[0072] Compared to Example 1, most aspects were the same, except that the addition of benzimidazole was omitted. The resulting composite nanofiber membrane was tested; the ZIF-8 loading was almost gone (0.8%), and when used for CHF3 gas detection, the corresponding resistivity change rate response value ΔR / R0 was only 1.12%. Figure 7 As shown, the response is extremely slow and almost irrecoverable, with a large baseline drift. Analysis of the cause: Benzimidazole is an organic ligand required for MOF nucleation and growth; its absence prevents ZIF-8 from being effectively generated within / on the fiber, thus losing the high specific surface area and selective adsorption sites provided by MOF.

[0073] Comparative Example 3:

[0074] The process was largely the same as in Example 1, except for adjusting the timing of zinc nitrate addition. Specifically, a PVDF-containing solution was prepared according to the method in Example 1. Then, PVDF fiber membranes were obtained by direct electrospinning. Next, the membranes were immersed in a 0.1 mol / L zinc nitrate ethanol solution at 50°C. Then, following the method in Example 1, the membranes were immersed in a methanol / water solution containing 0.15 g benzimidazole (methanol to water volume ratio 4:1, total volume 100 mL) at 65°C for 4 hours. Following this, the water in the fibers was replaced sequentially with ethanol and tert-butanol, and then subjected to CO2 critical point drying (31°C, 7.4 MPa). Finally, the membranes were immersed in a 0.5 wt% perfluorooctyltriethoxysilane (PFOTS) ethanol solution at 60°C for 2 hours, purged with nitrogen, and annealed at 120°C for 1 hour to complete the fluorination modification.

[0075] The obtained composite nanofiber membrane was tested, and the ZIF-8 loading was slightly low (8.1%). However, when it was made into a gas sensor for CHF3 gas detection according to the method in Example 1, the ΔR / R0 was 4.02%. Figure 8 As shown, both the response and recovery are slower. This is because in Example 1, Zn 2+ The presence of ZIF-8 in the core layer solution and its in-situ generation in the hollow cavity enables uniform and thin-layer crystal growth within the cavity, ensuring permeability. However, epitaxial impregnation causes ZIF to aggregate into thicker particles / agglomerates on the fiber surface or in the pores, reducing permeability and sensitivity.

[0076] Comparative Example 4:

[0077] It is largely the same as Example 1, except that no fluorinated surface modification treatment is performed.

[0078] The prepared composite fiber membrane was tested, and its contact angle decreased from 125° to 48°, indicating a significant improvement in hydrophilicity. When it was fabricated into a gas sensor according to the method in Example 1 and tested, the corresponding ΔR / R0 decreased from 8.48% to 3.2%. Figure 9 As shown, the baseline drift increased (6.0%). This is because the low surface energy fluorinated layer formed by fluorination treatment increases the affinity for CHF3 while simultaneously repelling water molecules. Without fluorination treatment, moisture occupies the ZIF channels and the surface selectivity for CHF3 decreases, resulting in reduced sensitivity and moisture resistance.

[0079] It should be noted that the baseline refers to the stability level of the sensor's output signal (such as resistance, voltage, etc.) in the absence of the target gas (i.e., CHF3). A 6% increase in baseline drift means that the sensor's output signal no longer remains stable under gas-free (CHF3-free) conditions, exhibiting a 6% shift.

[0080] Comparative Example 5:

[0081] The process is largely the same as in Example 1, except that the drying conditions at the CO2 critical point are adjusted to vacuum drying at 50°C for 4 hours.

[0082] Similarly, the obtained composite nanofiber membrane was used to fabricate a gas sensor according to the method in Example 1 and was tested. The corresponding ΔR / R0 decreased from 8.48% to 4.80%. Figure 10 As shown, the response and recovery are significantly slower. This is because the collapse or blockage of micropores between MOF nanopores and fibers during vacuum / thermal drying leads to a decrease in the actual specific surface area, a reduction in effective adsorption sites and mass transfer channels, and impaired sensing performance. However, the CO2 critical point drying method of this invention avoids this problem, preserving the multi-scale pore structure, which is equivalent to increasing the contact area between the material and CHF3, improving sensitivity, and thus effectively enhancing the recognition and response to CHF3 gas.

[0083] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A gas-sensitive material based on a PVDF / ZIF-8 composite nanofiber membrane, characterized in that, Depend on β The structure comprises a PVDF hollow fiber matrix with a phase content greater than 80%, and ZIF-8 grown in situ within the cavity of the PVDF hollow fiber matrix, wherein the surface of the ZIF-8 is modified with perfluorooctyltriethoxysilane (PFOTS), and the loading of ZIF-8 is 8-12 wt%. The gas-sensitive material is prepared through the following steps: S1. Prepare shell layer solution and core layer solution separately: PVDF powder was dissolved in a mixed solvent of DMF and acetone, 2-methylimidazole and lithium chloride were added, and the mixture was stirred to obtain a shell solution. Zinc nitrate was dissolved in glycerol to prepare a core layer solution; S2, Coaxial electrospinning: The shell solution and the core solution obtained in S1 were coaxially electrospun to obtain a nascent fiber membrane. S3. Hollow structure formation and in-situ growth of ZIF-8: The nascent fibrous membrane obtained from S2 was immersed in a methanol / water mixture containing benzimidazole. The reaction caused glycerol to dissolve and form a hollow cavity. Zinc ions diffused into the shell and reacted with 2-methylimidazole to generate ZIF-8. S4. Critical point drying treatment: The water content of the reaction product obtained in S3 was replaced successively with ethanol and tert-butanol, and then dried at the CO2 critical point. S5, Fluorinated surface modification: The dried fiber membrane obtained in S4 was immersed in an ethanol solution of PFOTS for impregnation, and then removed, purged with nitrogen, and annealed to obtain a PVDF / ZIF-8 composite nanofiber membrane, which is the gas-sensitive material. In S4, the drying process is carried out at a pressure of 7.4 MPa and a temperature of 31℃.

2. The method for preparing a gas-sensitive material based on a PVDF / ZIF-8 composite nanofiber membrane as described in claim 1, characterized in that, Includes the following steps: S1. Prepare shell layer solution and core layer solution separately: PVDF powder was dissolved in a mixed solvent of DMF and acetone, 2-methylimidazole and lithium chloride were added, and the mixture was stirred to obtain a shell solution. Zinc nitrate was dissolved in glycerol to prepare a core layer solution; S2, Coaxial electrospinning: The shell solution and the core solution obtained in S1 were coaxially electrospun to obtain a nascent fiber membrane. S3. Hollow structure formation and in-situ growth of ZIF-8: The nascent fibrous membrane obtained from S2 was immersed in a methanol / water mixture containing benzimidazole. The reaction caused glycerol to dissolve and form a hollow cavity. Zinc ions diffused into the shell and reacted with 2-methylimidazole to generate ZIF-8. S4. Critical point drying treatment: The water content of the reaction product obtained in S3 was replaced successively with ethanol and tert-butanol, and then dried at the CO2 critical point. S5, Fluorinated surface modification: The dried fiber membrane obtained in S4 was immersed in an ethanol solution of PFOTS, then removed and purged with nitrogen before annealing to obtain a PVDF / ZIF-8 composite nanofiber membrane, which is the target product. In S4, the drying process is carried out at a pressure of 7.4 MPa and a temperature of 31℃.

3. The method for preparing a gas-sensitive material based on a PVDF / ZIF-8 composite nanofiber membrane according to claim 2, characterized in that, In S1, the volume ratio of DMF to acetone in the shell solution is (6-8):(2-4), the mass concentration of PVDF is 16~20wt%, the amount of 2-methylimidazole added is 14~16% of the mass of PVDF, and the amount of lithium chloride added is 2-4% of the mass of PVDF.

4. The method for preparing a gas-sensitive material based on a PVDF / ZIF-8 composite nanofiber membrane according to claim 2, characterized in that, In S1, the molar concentration of zinc nitrate in the core layer solution is 0.01~0.1 mol / L.

5. The method for preparing a gas-sensitive material based on a PVDF / ZIF-8 composite nanofiber membrane according to claim 2, characterized in that, In S2, during the coaxial electrospinning process, the core needle size of the coaxial needle is 27G and the shell needle size is 22G. The core flow rate is 0.7~0.9 mL / h, the shell flow rate is 1.3~1.7 mL / h, the applied voltage is 25kV, the receiving distance is 20cm, the relative humidity is 35~45%, and the temperature is 23~27℃.

6. The method for preparing a gas-sensitive material based on a PVDF / ZIF-8 composite nanofiber membrane according to claim 2, characterized in that, In S2, the thickness of the resulting nascent fiber membrane is 140~160μm.

7. The method for preparing a gas-sensitive material based on a PVDF / ZIF-8 composite nanofiber membrane according to claim 2, characterized in that, In S3, the concentration of benzimidazole is 0.008~0.012 mol / L; The volume ratio of methanol to water is 3-5:1; The reaction temperature is 60~70℃ and the time is 3~5h.

8. The method for preparing a gas-sensitive material based on a PVDF / ZIF-8 composite nanofiber membrane according to claim 2, characterized in that, In S5, the mass concentration of PFOTS in the ethanol solution is 0.4~0.6 wt%; The immersion treatment temperature is 55~65℃, and the time is 1~3h; The annealing temperature is 110~130℃, and the time is 0.5~1.5h.

9. The application of the gas-sensitive material based on PVDF / ZIF-8 composite nanofiber membrane as described in claim 1 in the selective detection of CHF3, a characteristic decomposition component, in the environmentally friendly insulating gas C4F7N / CO2 mixture as a gas-sensitive sensor.

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