Fluorinated cation difunctional magnetic COF superparticle material as well as preparation method and application thereof

Abstract

The invention discloses a fluorinated cation difunctional magnetic COF superparticle material as well as a preparation method and application thereof. The method comprises the following steps: S1, preparing carboxyl modified ferroferric oxide nanoparticles; s2, preparing a fluorine functional covalent organic framework microsphere F-COF; s3, carrying out cationization treatment on the F-COF, so as to obtain a cationized fluorine functional covalent organic framework microsphere QA-F-COF; and S4, assembling the QA-F-COF and the nanometer ferroferric oxide modified by the carboxyl group, so as to obtain the fluorinated cation difunctional magnetic COF superparticle material. Different from a common magnetic COF design concept, the fluorinated cation difunctional magnetic COF superparticle material is obtained by directly and electrostatically self-assembling and constructing ferriferrous oxide nanoparticles modified by fluorination, cation monodisperse COFs and carboxyl, and the fluorinated cation difunctional magnetic COF superparticle material has excellent stability and excellent PFAS adsorption performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of chemistry and nanomaterials, and particularly relates to a fluorinated cationic bifunctional magnetic COF superparticle material, a preparation method and applications thereof. BACKGROUND

[0002] Industrial production of fluorine-containing polymers (such as Teflon non-stick coating), waterproof and antifouling textiles, fire-fighting foams, etc. produce polyfluoroalkyl substances (PFAS). PFAS is chemically stable and difficult to degrade, and can exist in the environment for several years and be enriched through the food chain, threatening aquatic organisms and ecosystems. This can cause immune and endocrine system: reduced immunity, reproductive and developmental toxicity, organ damage, and carcinogenic risk, etc.

[0003] Due to the strong stability of PFAS and its trace presence in the environment, current removal methods such as photocatalysis, electrochemical oxidation, and biodegradation have low removal efficiency, complex equipment, and cumbersome operation. Adsorption technology is an important means for removing PFAS due to its low cost, simplicity, and high efficiency. Currently, activated carbon and ion exchange resins are the most commonly used PFAS adsorption materials. Despite this, they still have obvious limitations, such as long adsorption time, limited adsorption capacity, and difficulty in recycling, and as broad-spectrum adsorbents, their adsorption capacity is often affected by competitive adsorption of other substances. Increasing evidence shows that fluorine functionalization modification of adsorption materials can greatly improve the adsorption capacity and selectivity between adsorbents and PFAS through F-F interaction between adsorbents and PFAS. According to the structural characteristics of PFAS, there are a large number of C-F chains on the molecule, which have more obvious affinity for fluorinated alkanes than other functional groups, so PFAS can be selectively enriched through this "fluorophilicity". More importantly, fluorine-modified materials usually exhibit high hydrophobicity, which makes them difficult to disperse uniformly in aqueous media for effective adsorption of PFAS. Anion exchange resins with quaternary ammonium structures can improve the hydrophilicity of the material by forming hydrogen bonds between N atoms and water molecules. Therefore, developing adsorption materials with both C-F chains and quaternary ammonium cation structures is a promising high-efficiency adsorbent.

[0004] Covalent organic frameworks (COFs) are a new class of porous crystalline materials, which are mainly formed by different organic monomers through covalent bonds to form an ordered structure. Its characteristics are high specific surface area, microporous structure, customizable structure and easy modification. This special structure makes them widely studied in various fields such as adsorption separation, catalysis and biology. In recent years, a variety of functional COF materials for PFAS treatment and detection have been developed, and these COFs mainly achieve the recognition of PFAS through fluorine functionalization or cationization. In addition, magnetic COFs combine the advantages of magnetic nanoparticles and COFs, which can quickly separate and efficiently adsorb, and have great advantages in removing pollutants in water and simplifying mass spectrometry pretreatment processes. A variety of magnetic COF materials have been reported, and these materials are mainly grown on the surface of magnetite or deposited on the surface of COF. However, the limitations of these methods are obvious, such as serious agglomeration, poor morphology, poor crystallinity, or poor stability of the combination of magnetic particles and COF and pore blockage, and as a catalyst, acetic acid will corrode magnetite, not only reducing the magnetism but also introducing impurities. It is still a great challenge to develop high-performance magnetic COF materials. SUMMARY

[0005] The technical problem to be solved by the present application is to provide a fluorinated cationic bifunctional magnetic COF superparticle material, a preparation method and application thereof, which solves the problems in the prior art.

[0006] To achieve the above object, the technical scheme adopted by the present application is: the first aspect of the present application provides a preparation method of a fluorinated cationic bifunctional magnetic COF superparticle material, comprising the following steps:

[0007] S1, preparing carboxyl-modified magnetite nanoparticles;

[0008] S2, preparing fluorine-functionalized covalent organic framework microspheres F-COF;

[0009] S3, cationizing the F-COF to obtain cationized fluorine-functionalized covalent organic framework microspheres QA-F-COF;

[0010] S4, assembling the QA-F-COF and the carboxyl-modified nanometer magnetite to obtain the fluorinated cationic bifunctional magnetic COF superparticle material.

[0011] Preferably, step S1 is specifically:

[0012] FeCl3, trisodium citrate was dissolved in ethylene glycol, sodium acetate was added under stirring, stirring, the obtained mixture was transferred to a reaction kettle, heated reaction, after the reaction was completed, cooled to room temperature, washed with ethanol and deionized water in turn, vacuum dried, to obtain carboxyl modified ferroferric oxide nanoparticles.

[0013] Preferably, step S2 is specifically:

[0014] S2-1, preparing amorphous covalent organic polymer: monomer TFTA and monomer TAPB were ultrasonically dissolved in acetonitrile, acetic acid was added as a catalyst, mixed uniformly, placed at room temperature, the product was centrifuged and washed, vacuum dried to obtain amorphous covalent organic polymer;

[0015] S2-2, transformation of amorphous covalent organic polymer to crystalline covalent organic framework: the amorphous covalent organic polymer was dispersed in a mixed solution of mesitylene and 1,4-dioxane according to the volume composition, ultrasonically dispersed, added catalyst acetic acid and water, heated and reacted, cooled to room temperature, the solid product was collected by centrifugation and washed with tetrahydrofuran and ethanol in turn, vacuum dried, fluorine functional covalent organic framework microspheres, marked as F-COF.

[0016] Preferably, step S3 is specifically:

[0017] F-COF was dispersed in DMF, after ultrasonic, anhydrous potassium carbonate and iodomethane were added, stirred and reacted under heating, after the reaction was completed, cooled to room temperature, the solid product was collected by centrifugation and washed, vacuum dried, to obtain cationized fluorine functional covalent organic framework microspheres, marked as QA-F-COF.

[0018] Preferably, step S4 is specifically:

[0019] S4-1, QA-F-COF and magnetic particles were dispersed in ACN respectively to obtain aqueous phase 1 and aqueous phase 2 respectively; the aqueous phase 1 and the aqueous phase 2 were mixed to obtain a mixed aqueous phase;

[0020] S4-2, fluorinated electronic oil HFE 7500 was used as oil phase, the mixed aqueous phase was added to the fluorinated electronic oil HFE 7500, mixed uniformly under sealing, removed the sealing, evaporated overnight at room temperature to dry the aqueous phase, the precipitate was collected by centrifugation, washed, vacuum dried, to obtain the fluorinated cationic bifunctional magnetic COF super particle material, marked as COF SPs.

[0021] Preferably, the preparation method of the fluorinated cationic bifunctional magnetic COF super particle material comprises the following steps:

[0022] S1, preparing carboxyl modified ferroferric oxide nanoparticles:

[0023] FeCl3, trisodium citrate were dissolved in ethylene glycol, sodium acetate was added under stirring, the mixture was stirred for 15-60 min, and then transferred into a Teflon reactor, heated at 180-220℃ for 5-20 h, cooled to room temperature, washed with ethanol and deionized water in turn, and vacuum dried to obtain carboxyl-modified ferroferric oxide nanoparticles;

[0024] S2, preparation of fluorine-functionalized covalent organic framework microspheres:

[0025] S2-1, preparation of amorphous covalent organic polymer: 31.2-124.8 mg of monomer TFTA and 35.9-143.6 mg of monomer TAPB were ultrasonically dissolved in 12-50 mL of acetonitrile, 1.5-4.5 mL of acetic acid was added as a catalyst, the solution was mixed uniformly by vortexing for 10-40 s, and the product was obtained after centrifugation, and then washed with acetonitrile and ethanol in turn, and vacuum dried to obtain an amorphous covalent organic polymer;

[0026] S2-2, transformation of amorphous covalent organic polymer to crystalline covalent organic framework: 50-200 mg of amorphous covalent organic polymer was dispersed in a mixed solution of mesitylene and 1,4-dioxane, ultrasonically dispersed for 2-10 min, 7.5-15 mL of catalyst acetic acid and 0.5-5 mL of water were added, and the mixture was heated at 80-120℃ for 1-3 days, cooled to room temperature, and the solid product was collected by centrifugation and washed with tetrahydrofuran and ethanol in turn, and vacuum dried to obtain fluorine-functionalized covalent organic framework microspheres, denoted as F-COF;

[0027] S3, preparation of cationic fluorine-functionalized covalent organic framework microspheres:

[0028] 0.05-0.2 g of F-COF was dispersed in 10-40 mL of DMF, ultrasonically dispersed for 0.5-2 min, 0.05-0.2 g of anhydrous potassium carbonate and 0.5-2 mL of iodomethane were added, and the mixture was stirred at 40-60℃ for 12-48 h, cooled to room temperature, the solid product was collected by centrifugation and washed with ethanol, and vacuum dried to obtain cationic fluorine-functionalized covalent organic framework microspheres, denoted as QA-F-COF;

[0029] S4, assembly of QA-F-COF and carboxyl-modified nanometer ferroferric oxide:

[0030] S4-1, QA-F-COF and magnetic particles were dispersed in ACN respectively, and the concentration was 25-100 mg / mL, to obtain aqueous phase 1 and aqueous phase 2 respectively; aqueous phase 1 and aqueous phase 2 were mixed in a volume ratio of 5-15:1 to obtain a mixed aqueous phase;

[0031] S4-2, using fluorinated electronic oil HFE 7500 as the oil phase, 0.12-0.5 mL of the mixed water phase is added to 6-25 mL of fluorinated electronic oil HFE 7500, mixed uniformly under sealing, remove the sealing, open to the room temperature to evaporate overnight to dry the water phase, centrifugal collection of the precipitate, washed with ethanol, vacuum dried, to obtain the fluorinated cationic bifunctional magnetic COF super particle material, recorded as COF SPs.

[0032] In a second aspect of the present application, a fluorinated cationic bifunctional magnetic COF super particle material is provided, which is prepared by the method as described above.

[0033] In a third aspect of the present application, the use of the fluorinated cationic bifunctional magnetic COF super particle material as described above in the adsorption removal of PFAS is provided.

[0034] In a fourth aspect of the present application, a PFAS adsorbent is provided, characterized in that it comprises the fluorinated cationic bifunctional magnetic COF super particle material as described above.

[0035] In a fifth aspect of the present application, the use of the fluorinated cationic bifunctional magnetic COF super particle material as described above in the detection of PFAS is provided, and the application method is as follows:

[0036] First, the sample solution to be tested containing PFAS is mixed with the fluorinated cationic bifunctional magnetic COF super particle material to adsorb and enrich PFAS, and then magnetic separation is performed, the obtained solid product is added to an eluent, so that the adsorbed PFAS is desorbed into the eluent, the solid product is discarded after magnetic separation, and the eluent is collected and injected into LC-MS / MS (Liquid Chromatography-Tandem Mass Spectrometry) for analysis of the concentration of PFAS.

[0037] The present application has the following beneficial effects:

[0038] The present application is different from the general design concept of magnetic COF, and a fluorinated cationic bifunctional magnetic COF super particle material is constructed by a simple method of fluorination, cationic monodisperse COFs and carboxyl-modified ferroferric oxide nanoparticles directly electrostatic self-assembly, which has excellent stability and outstanding PFAS adsorption performance.

[0039] The fluorinated cationic bifunctional magnetic COF super particle material provided by the application can not only effectively remove PFAS, but also can perform trace analysis through the strong enrichment capacity thereof; wherein, the cationization is realized through simple post-modification by methyl iodide, and the reaction condition is simple and mild and can efficiently introduce strong positive charge, and the surface potential of the COF after cationization reaches +45.5 mV. Finally, the fluorinated cationic bifunctional magnetic COF super particle material: COF SPs is constructed through self-assembly with magnetic particles with negative surface potential;

[0040] Through the adsorption and detection experiment of PFAS, the results show that the COF SPs has super-high adsorption capacity, can reach adsorption equilibrium within 30 seconds, and the maximum adsorption capacity of perfluorooctanoic acid reaches 600 mg / g. In addition, this material greatly simplifies the process of mass spectrometric detection of PFAS, after elution of the PFAS adsorbed on the COF SPs, 18 kinds of PFAS can be ultra-trace detected within 10 minutes by combining LC-MS / MS, and the detection limit is as low as 0.0009-0.13 ng / L, and this material has great application prospect for the removal and detection of PFAS. BRIEF DESCRIPTION OF DRAWINGS

[0041] Figure 1 It is a preparation flowchart of the fluorinated cationic bifunctional magnetic COF super particle material of the application;

[0042] Figure 2 It is a SEM image of the carboxyl-modified ferroferric oxide nanoparticles prepared in Example 1;

[0043] Figure 3 It is a scanning electron microscope image and an EDS element scanning image of QA-F-COF prepared in Example 3

[0044] Figure 4 It is a SEM and a local magnification SEM of COF SPs prepared in Example 4;

[0045] Figure 5 It is a microscopic image of COF SPs prepared in Example 4 stored in water for different time;

[0046] Figure 6 It is an adsorption kinetics curve of COF SPs to PFOA (left figure) and an adsorption isotherm of QA-F-COF to PFOA at 25 DEG C (right figure);

[0047] Figure 7 It is a mass spectrometric TIC signal comparison result of 18 kinds of PFAS before and after adsorption treatment by COF SPs (blue line: before treatment; red line: after treatment);

[0048] Figure 8Standard curves of the 18 PFAS were established. DETAILED DESCRIPTION

[0049] The application will be further described in conjunction with the following examples, so that those skilled in the art can implement the application according to the description and the examples.

[0050] It should be understood that the terms such as "have", "contain" and "include" used herein do not exclude the presence or addition of one or more other elements or combinations thereof.

[0051] The test methods used in the following examples are conventional methods unless otherwise specified. The materials and reagents used in the following examples are commercially available unless otherwise specified. The specific conditions not specified in the following examples are carried out according to the conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments used are not specified by the manufacturer, and are conventional products that can be purchased on the market.

[0052] Example 1 Preparation of carboxyl-modified ferroferric oxide nanoparticles

[0053] Dissolve 0.65 g of FeCl3 and 0.22 g of trisodium citrate in 20 mL of ethylene glycol, add 1.2 g of sodium acetate under stirring, stir for 30 minutes, transfer the obtained mixture to a Teflon reactor, heat at 200°C for 10 h, cool to room temperature, and then sequentially wash with ethanol and deionized water, and vacuum dry to obtain carboxyl-modified ferroferric oxide nanoparticles.

[0054] Reference Figure 2 The SEM image of the carboxyl-modified ferroferric oxide nanoparticles prepared in this example shows the successful preparation of the carboxyl-modified ferroferric oxide nanoparticles, and the size thereof is about 500 nm.

[0055] Example 2 Preparation of fluorine-functionalized covalent organic framework microspheres

[0056] 1. Preparation of amorphous covalent organic polymer: dissolve 62.4 mg (0.3 mmol) of monomer TFTA (2,3,5,6-tetrafluoroterephthaldehyde) and 71.8 mg (0.2 mmol) of monomer TAPB [1,3,5-tris(4-aminophenyl)benzene] in 25 mL of acetonitrile under ultrasonic, add 1.5-4.5 mL of acetic acid as catalyst, vortex for 20 s to mix the solution uniformly, and then place at room temperature for 3 days. After centrifugation, the product is sequentially washed with acetonitrile and ethanol, and then vacuum dried to obtain the amorphous covalent organic polymer;

[0057] 2. Transformation of amorphous covalent organic polymer to crystalline covalent organic framework: take 100 mg of amorphous covalent organic polymer and disperse it in 20 mL of a mixed solution of mesitylene and 1,4-dioxane in a volume ratio of 1:1, ultrasonically disperse for 5 minutes, add 10 mL of catalyst acetic acid and 2.5 mL of water, heat and react at 100°C for 2 days, cool to room temperature, centrifugally collect the solid product, and sequentially wash with tetrahydrofuran and ethanol, vacuum dry, and obtain fluorine-functionalized covalent organic framework microspheres, denoted as F-COF.

[0058] Example 3: Preparation of cationized fluorine-functionalized covalent organic framework microspheres

[0059] Disperse 0.1 g of F-COF in 20 mL of DMF (N,N-dimethylformamide), after ultrasonic dispersion for 1 min, add 0.1 g of anhydrous potassium carbonate and 1 mL of iodomethane, stir and react at 50°C for 24 h, cool to room temperature, centrifugally collect the solid product and wash with ethanol, vacuum dry, and obtain cationized fluorine-functionalized covalent organic framework microspheres, denoted as QA-F-COF.

[0060] Reference Figure 3 The scanning electron microscope image and EDS element scan image of the QA-F-COF prepared in this example show that fluorinated, cationically monodisperse COF (QA-F-COF) is synthesized, with a size of 500 nm and uniform size and internal hollow structure.

[0061] Example 4: Assembly of QA-F-COF with carboxyl-modified nanometer-sized magnetite

[0062] S4-1, disperse QA-F-COF and magnetic particles in ACN (acetonitrile) respectively, with a concentration of 50 mg / mL, to obtain aqueous phase 1 and aqueous phase 2 respectively; mix aqueous phase 1 and aqueous phase 2 in a volume ratio of 9:1 to obtain a mixed aqueous phase;

[0063] S4-2, add 12.5 mL of fluorinated electronic oil HFE 7500 to a 50 mL centrifuge tube as an oil phase, take 0.25 mL of the mixed aqueous phase and add it to 12.5 mL of the fluorinated electronic oil HFE 7500, tightly cap the centrifuge tube and shake it vigorously by hand. After emulsification, remove the cap and place it in a fume hood at room temperature overnight to evaporate the water phase, and the solidified COF SPs are suspended in the remaining oil phase, centrifugally collect the precipitate, wash with ethanol, and vacuum dry to obtain the fluorinated cationic bifunctional magnetic COF superparticle material, denoted as COF SPs.

[0064] Reference Figure 4SEM and partial magnification SEM of COF SPs prepared for this example, which shows that the present application successfully constructed fluorinated, cationic double functional magnetic COF superparticles: COF SPs, by mixing fluorinated, cationic monodisperse COFs with carboxyl-modified ferroferric oxide nanoparticles through electrostatic self-assembly.

[0065] Referring to Figure 5 Microscopic images of COF SPs prepared for this example stored in water for different times, which shows that they can maintain stability in aqueous solution.

[0066] Example 6 Application of fluorinated cationic double functional magnetic COF superparticle material (COF SPs) to adsorption of PFOA

[0067] Batch adsorption experiments of PFOA (perfluorooctanoic acid) were carried out in 15 mL centrifuge tubes at 25°C using an orbital shaker. Before the adsorption experiment, 100 mg of COF SPs were pre-dispersed in a 1.5 mL EP tube, 1 mL of deionized water was added, and then ultrasonic treatment was carried out for 30 min. During the adsorption test, 5 mL of PFOA solution was first added to a 15 mL centrifuge tube, and then 25 μL (2 mg) of adsorbent suspension was added using a pipette.

[0068] Referring to Figure 6 , the left graph is the adsorption kinetics curve of COF SPs for PFOA (blue line: pseudo-first order; red line: pseudo-second order); the right graph is the adsorption isotherm of QA-F-COF on PFOA at 25°C. The specific test data are shown in Tables 1 and 2 below:

[0069] Table 1 Adsorption kinetics fitting of COF SPs adsorbing PFOA

[0070]

[0071] Table 2 Adsorption isotherm fitting of COF SPs adsorbing PFOA

[0072]

[0073] From the above test results, it can be seen that the COF SPs prepared by the present application have an ultra-high adsorption capacity, which can reach adsorption equilibrium within 30 seconds, and the maximum adsorption capacity for perfluorooctanoic acid reaches 600 mg / g.

[0074] Example 7 Application of fluorinated cationic double functional magnetic COF superparticle material (COF SPs) to PFAS detection

[0075] COF SPs adsorption treatment: 1 mL PFAS solution was added into a 1.5 mL EP tube, then 5 μL COF SPs suspension (0.5 mg COF SPs) was added, after oscillation at 25℃ for 2 min, the solution was removed by magnetic separation. Then 100 μL eluent (10% formic acid-methanol, volume concentration) was added, and continued to oscillate at 25℃ for 2 min, so that the PFAS adsorbed on the COF SPs was desorbed into the eluent.

[0076] LC-MS / MS analysis: The eluent was collected by magnetic separation and injected into LC-MS / MS for analysis.

[0077] Reference Figure 7 , the mass spectrum TIC signal comparison results of 18 kinds of PFAS before and after COF SPs adsorption treatment (blue line: before treatment; red line: after treatment);

[0078] Reference Figure 8 , the standard curve of 18 kinds of PFAS established by the above method (x axis: concentration; y axis: peak area).

[0079] The specific test data is shown in Table 3 as follows:

[0080] Table 3

[0081]

[0082]

[0083] Figure 7 、 Figure 8 and Table 3 shows that after the PFAS is first adsorbed and enriched by COF SPs, then separated and eluted, combined with LC-MS / MS detection, 18 kinds of PFAS can be detected at ultra-trace level within 10 minutes, and the detection limit is as low as 0.0009-0.13 ng / L.

[0084] Although the embodiments of the present application have been disclosed as above, it is not limited to the use listed in the specification and embodiments, and can be fully applied to various fields suitable for the present application, and additional modifications can be easily realized by those skilled in the art, therefore the present application is not limited to specific details, without departing from the general concept defined by the claims and equivalent scope.

Claims

1. A method for preparing a fluorinated cation bifunctional magnetic COF superparticle material, characterized in that: The following steps are involved: S1. Preparation of carboxyl-modified ferroferric oxide nanoparticles; S2, preparation of fluorine-functional covalent organic framework microspheres F-COF; S3, performing cationization treatment on F-COF to obtain cationic fluorine-functional covalent organic framework microspheres QA-F-COF; S4. Assemble QA-F-COF and carboxyl-modified nano-ferrosoferric oxide to obtain the fluorinated cation bifunctional magnetic COF superparticle material.

2. The method for preparing the fluorinated cationic bifunctional magnetic COF superparticle material according to claim 1, characterized in that: Step S1 is specifically as follows: FeCl3 and trisodium citrate were dissolved in ethylene glycol, and sodium acetate was added under stirring. The mixture was transferred to a reactor and heated for reaction. After the reaction was completed, the mixture was cooled to room temperature, washed with ethanol and deionized water in sequence, and vacuum dried to obtain carboxyl-modified ferrosoferric oxide nanoparticles.

3. The method for preparing the fluorinated cation bifunctional magnetic COF superparticle material according to claim 2, characterized in that: Step S2 is specifically as follows: S2-1. Preparation of an amorphous covalent organic polymer: dissolving monomers TFTA and TAPB in acetonitrile by ultrasonication, adding acetic acid as a catalyst, mixing well, and allowing to stand at room temperature. The product is centrifuged, washed with water, and vacuum-dried to obtain an amorphous covalent organic polymer; S2-2. Transformation of amorphous covalent organic polymers into crystalline covalent organic frameworks: The amorphous covalent organic polymer is dispersed in a mixed solution of mesitylene and 1,4-dioxane by volume, and ultrasonically dispersed. Catalytic acetic acid and water are added, and the reaction is heated. The reaction is cooled to room temperature, and the solid product is collected by centrifugation. The solid product is washed with tetrahydrofuran and ethanol in sequence, and vacuum dried to obtain fluorine-functionalized covalent organic framework microspheres, which are recorded as F-COF.

4. The method for preparing the fluorinated cation bifunctional magnetic COF superparticle material according to claim 3, characterized in that: Step S3 is specifically as follows: F-COF was dispersed in DMF. After sonication, anhydrous potassium carbonate and iodomethane were added. The mixture was stirred under heating and reacted. After the reaction was completed, the mixture was cooled to room temperature. The solid product was collected by centrifugation, washed, and vacuum-dried to obtain cationic fluorine-functional covalent organic framework microspheres, which were designated as QA-F-COF.

5. The method for preparing the fluorinated cation bifunctional magnetic COF superparticle material according to claim 4, characterized in that: Step S4 is specifically as follows: S4-1, dispersing QA-F-COF and magnetic particles in ACN to obtain aqueous phase 1 and aqueous phase 2, respectively; mixing aqueous phase 1 and aqueous phase 2 to obtain a mixed aqueous phase; S4-2. Using fluorinated electronic oil HFE 7500 as the oil phase, the mixed aqueous phase was added to the fluorinated electronic oil HFE 7500, and the mixture was mixed uniformly under a sealed state. The seal was removed, and the aqueous phase was evaporated overnight at room temperature to dryness. The precipitate was collected by centrifugation, washed, and vacuum-dried to obtain the fluorinated cationic bifunctional magnetic COF superparticle material, which was recorded as COF SPs.

6. The method for preparing the fluorinated cation bifunctional magnetic COF superparticle material according to claim 5, characterized in that: The following steps are involved: S1. Preparation of carboxyl-modified ferroferric oxide nanoparticles: Dissolve FeCl3 and trisodium citrate in ethylene glycol, add sodium acetate under stirring, and stir for 15-60 minutes. Transfer the resulting mixture to a Teflon reactor, heat and react at 180-220°C for 5-20 hours, cool to room temperature, wash with ethanol and deionized water in sequence, and vacuum dry to obtain carboxyl-modified ferrosoferric oxide nanoparticles; S2. Preparation of fluorine-functional covalent organic framework microspheres: S2-1. Preparation of an amorphous covalent organic polymer: 31.2-124.8 mg of TFTA monomer and 35.9-143.6 mg of TAPB monomer were ultrasonically dissolved in 12-50 mL of acetonitrile, 1.5-4.5 mL of acetic acid was added as a catalyst, and the solution was vortexed for 10-40 seconds to mix uniformly. The solution was allowed to stand at room temperature for 1-6 days. The product was centrifuged and washed with acetonitrile and ethanol, respectively, and vacuum dried to obtain an amorphous covalent organic polymer. S2-2. Transformation of amorphous covalent organic polymer into crystalline covalent organic framework: 50-200 mg of amorphous covalent organic polymer was dispersed in a mixed solution of mesitylene and 1,4-dioxane, and ultrasonically dispersed for 2-10 minutes. 7.5-15 mL of acetic acid and 0.5-5 mL of water were added, and the mixture was heated at 80-120° C. for 1-3 days. The mixture was cooled to room temperature, and the solid product was collected by centrifugation. The solid product was washed with tetrahydrofuran and ethanol in sequence, and dried under vacuum to obtain fluorine-functionalized covalent organic framework microspheres, which were recorded as F-COF. S3. Preparation of cationic fluorinated covalent organic framework microspheres: 0.05-0.2 g of F-COF was dispersed in 10-40 mL of DMF and ultrasonicated for 0.5-2 min. Then, 0.05-0.2 g of anhydrous potassium carbonate and 0.5-2 mL of iodomethane were added and stirred at 40-60 ° C for 12-48 h. The reaction was cooled to room temperature, and the solid product was collected by centrifugation, washed with ethanol, and vacuum dried to obtain cationic fluorine-functionalized covalent organic framework microspheres, which were recorded as QA-F-COF. S4. Assemble QA-F-COF with carboxyl-modified nano-ferroferric oxide: S4-1. Disperse QA-F-COF and magnetic particles in ACN at a concentration of 25-100 mg / mL to obtain aqueous phase 1 and aqueous phase 2, respectively; mix aqueous phase 1 and aqueous phase 2 at a volume ratio of 5-15:1 to obtain a mixed aqueous phase; S4-2. Using fluorinated electronic oil HFE 7500 as the oil phase, 0.12-0.5 mL of the mixed aqueous phase was added to 6-25 mL of fluorinated electronic oil HFE 7500, and the mixture was mixed uniformly under a sealed state. The seal was removed, and the aqueous phase was evaporated overnight at room temperature to dryness. The precipitate was collected by centrifugation, washed with ethanol, and vacuum dried to obtain the fluorinated cationic bifunctional magnetic COF superparticle material, which was recorded as COF SPs.

7. A fluorinated cation bifunctional magnetic COF superparticle material, characterized in that: It is prepared by the method according to any one of claims 1 to 7.

8. Use of the fluorinated cation bifunctional magnetic COF superparticle material as claimed in claim 8 in the adsorption and removal of polyfluoroalkyl substances.

9. A polyfluoroalkyl substance adsorbent, characterized in that: It comprises the fluorinated cation bifunctional magnetic COF superparticle material as claimed in claim 8.

10. Use of the fluorinated cationic bifunctional magnetic COF superparticle material according to claim 8 in detecting polyfluoroalkyl substances, wherein the method of use is: First, the sample solution containing polyfluoroalkyl substances to be tested is mixed with the fluorinated cation bifunctional magnetic COF superparticle material to adsorb and enrich the polyfluoroalkyl substances, and then magnetically separated. The obtained solid product is added to the eluent to desorb the adsorbed polyfluoroalkyl substances into the eluent. The solid product is magnetically separated and discarded, and the eluent is collected and injected into LC-MS / MS to analyze the concentration of polyfluoroalkyl substances.

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