A heteroporous fluorine-doped cation covalent organic framework material, a preparation method and application thereof

Abstract

The application relates to the technical field of functional materials, in particular to a heteroporous fluorine-doped cationic covalent organic framework material and a preparation method and application thereof. 2h Symmetric monomers and C2 symmetric monomers, D 2h The symmetric monomer is tetra-(4-aminophenyl) ethylene, the C2 symmetric monomer is a side functional monomer, the side functional monomer comprises one or both of a fluorine-containing monomer and a cationic monomer, the fluorine-containing monomer is 2', 3', 5', 6'-tetrafluoro-[1,1':4',1"-terphenyl]-4,4"-dimethylformaldehyde, and the cationic monomer is 4,7-bis(4-formylphenyl)-1,3-dimethyl-1H-benzo[d]imidazol-3-bromonium. The application solves the problems that the existing COF material has poor PFAS adsorption performance and single adsorption type, and realizes simultaneous and efficient adsorption of long-chain and short-chain PFAS.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of functional materials, in particular to a heteroporous fluorine-doped cationic covalent organic framework material and a preparation method and application thereof. BACKGROUND

[0002] Perfluoro or polyfluoroalkyl substances (PFAS) are a class of artificially synthesized compounds in which part or all of the hydrogen atoms on the carbon chain are replaced by fluorine atoms, which are widely used in various consumer and industrial products. However, PFAS are carcinogenic, biotoxic, persistent and bioaccumulative in the environment. This makes them widely present in environmental media, food, etc., threatening human health.

[0003] Covalent organic framework (COF) materials, as a new type of porous organic nanomaterial, have the advantages of ordered porosity, good stability and customizable functionality, and have attracted widespread attention in the field of PFAS pollutant adsorption treatment. However, the lack of highly integrated functional groups and suitable pore size adjustment limits their adsorption performance for PFAS. For example, some conventional COF materials have low adsorption capacity for specific PFAS when treating PFAS-containing wastewater, which cannot meet the demand for high adsorption efficiency in practical applications.

[0004] Although some studies have reported that the integration of functional groups into COF nanomaterials improves the adsorption performance for PFAS, these studies are mostly implemented in single-pore COFs and only target a single PFAS. If different structures and lengths of PFAS coexist in the environment, the existing materials cannot meet the demand for adsorbing multiple PFAS, greatly hindering their application expansion in complex environments. SUMMARY

[0005] The purpose of the present application is to provide a heteroporous fluorine-doped cationic covalent organic framework material and a preparation method and application thereof, which solves the problems of poor adsorption performance and single adsorption type of existing COF materials for PFAS, and realizes simultaneous and efficient adsorption of long-chain and short-chain PFAS.

[0006] To achieve the above-mentioned purpose, the present application provides a heteroporous fluorine-doped cationic covalent organic framework material, which comprises D 2h symmetric monomers and C2 symmetric monomers, D 2h The symmetric monomer is tetra-(4-aminophenyl) ethylene (ETTA), and the C2 symmetric monomer is a side functional monomer, which comprises one or both of a fluorine-containing monomer and a cationic monomer. The fluorine-containing monomer is 2', 3', 5', 6'-tetrafluoro-[1, 1': 4', 1"-terphenyl]-4, 4"-diformaldehyde (TFTDA), and the cationic monomer is 4, 7-bis(4-formylphenyl)-1, 3-dimethyl-1H-benzo[d]imidazol-3-bromonium (BFBlM).

[0007] Preferably, the molar ratio of the tetra-(4-aminophenyl)ethylene and the side functional monomer is 1:2.

[0008] Preferably, when the side functional monomer is both a fluorine-containing monomer and a cationic monomer, the molar ratio of the fluorine-containing monomer and the cationic monomer is 1:1 to 1:6.

[0009] A preparation method of a heteroporous fluorine-doped cationic covalent organic framework material, which is prepared by Schiff base reaction of tetra-(4-aminophenyl)ethylene and a side functional monomer.

[0010] Preferably, the method comprises the following steps,

[0011] S1, tetra-(4-aminophenyl)ethylene and a side functional monomer are added to a glass tube, then o-dichlorobenzene / n-butanol solvent is added, and the mixture is ultrasonically treated;

[0012] S2, a catalyst is added to the glass tube of S1 to obtain a reaction system, and the reaction system is ultrasonically treated, then subjected to cyclic degassing and sealed;

[0013] S3, after the reaction system of S2 returns to room temperature, it is transferred to a muffle furnace for heating reaction, and after the reaction is completed, the product is washed and dried overnight to obtain a heteroporous fluorine-doped cationic covalent organic framework material.

[0014] Preferably, in S1, the volume ratio of o-dichlorobenzene to n-butanol is 1:1, and the ultrasonic treatment time is 15 min.

[0015] Preferably, in S2, the catalyst is acetic acid, and the ultrasonic treatment time is 10 min.

[0016] Preferably, in S2, the cyclic degassing is a cycle of freezing-pumping-air-defrosting, the freezing is to place the glass tube in liquid nitrogen for freezing, the pumping-air is to use a vacuum pump to pump air to the glass tube, and the defrosting is to take the frozen glass tube out of the low-temperature environment, and let it naturally defrost at room temperature or defrost through a warm water bath.

[0017] Preferably, in S3, the heating reaction temperature is 120 DEG C, the reaction time is 72 h, the washing is to use super-dry tetrahydrofuran to wash and filter 5 times, then use anhydrous ethanol to wash and filter 3 times, and the drying is to vacuum dry at 80 DEG C.

[0018] Application of a heteroporous fluorine-doped cationic covalent organic framework material, the heteroporous fluorine-doped cationic covalent organic framework material is applied to adsorb perfluoro or polyfluoro alkyl substances.

[0019] Mechanism of the present application:

[0020] The present application selects ETTA as D based on the structure, molecular length, chemical group and adsorption mechanism of PFAS 2h The symmetrical monomer builds an ordered basic framework for the material, and the symmetrical structure thereof can guide the regular arrangement between monomers and guarantee the order of the whole material. The fluorine-containing monomer TFTDA and the cationic monomer BFBIM are cooperatively used as the C2 symmetrical monomer in different proportions to form a covalent organic framework material with a heteroporous structure. The heteroporous structure provides a hierarchical porous network and rich adsorption sites, and realizes efficient adsorption of PFAS. Meanwhile, the positive charges introduced by the cationic monomer and the negative charges of the PFAS molecule produce electrostatic adsorption; the fluorine atoms of the fluorine-containing monomer and the fluorine atoms in the PFAS exist F-F mutual attraction and hydrogen bond donors, which provide specific adsorption; and the hydrophobicity of the covalent organic framework material and the hydrophobicity of the PFAS interact with each other, further promoting the adsorption capacity of the PFAS.

[0021] The present application has the following beneficial effects:

[0022] (1) The present application adopts the above-mentioned heteroporous fluorine-doped cationic covalent organic framework material and its preparation method and application. The fluorine-doped cationic covalent organic framework material with a heteroporous structure is prepared by the cooperation of the cationic monomer and the fluorine-containing monomer, and can integrate electrostatic adsorption, F-F mutual attraction and hydrophobic interaction in the framework material with mesopores and micropores, realizing simultaneous and efficient adsorption of long-chain and short-chain PFAS.

[0023] (2) The present application adopts the above-mentioned heteroporous fluorine-doped cationic covalent organic framework material and its preparation method and application. The synthesized heteroporous fluorine-doped cationic covalent organic framework material has good crystal diffraction peaks, some of which have obvious diffraction peaks at 1.8°-1.9°, and has hierarchical porosity, providing more adsorption sites and diffusion channels for PFAS molecules.

[0024] (3) The present application adopts the above-mentioned heteroporous fluorine-doped cationic covalent organic framework material and its preparation method and application. In the field of environmental remediation, especially in the treatment of PFAS-polluted water, soil and the like, it has great application potential and can be used for industrial wastewater treatment, drinking water purification and the like. Moreover, the synthesis method is convenient for large-scale production and application promotion.

[0025] The technical solutions of the present application will be further described in detail below with reference to the drawings and examples. DESCRIPTION OF DRAWINGS

[0026] Figure 1 is the XRD graph of the COF material prepared in Examples 1-5 and Comparative Example 1 of the present application; Figure 1 a in the above is the XRD graph of COF-C, Figure 1 b in the above is the XRD graph of COF-F, Figure 1c is the XRD pattern of COF-F1N1 in FIG. Figure 1 d is the XRD pattern of COF-F1N2 in FIG. Figure 1 e is the XRD pattern of COF-F1N5 in FIG. Figure 1 f is the XRD pattern of COF-N in FIG.

[0027] Figure 2 is the SEM image of COF-F1N5 of Example 4 of the present application;

[0028] Figure 3 is the TEM image of COF-F1N5 of Example 4 of the present application; Figure 3 a is the TEM image of COF-F1N5 at 200 nm in FIG. Figure 3 b is the TEM image of COF-F1N5 at 100 nm in FIG. Figure 3 c is the TEM image of COF-F1N5 at 50 nm in FIG.

[0029] Figure 4 is the N2 adsorption isotherm and surface area of the COF materials prepared in Examples 1-4 and Comparative Example 1 of the present application;

[0030] Figure 5 is the pore size distribution of the COF materials prepared in Examples 1-4 and Comparative Example 1 of the present application; Figure 5 a is the pore size distribution of COF-C in FIG. Figure 5 b is the pore size distribution of COF-F in FIG. Figure 5 c is the pore size distribution of COF-F1N1 in FIG. Figure 5 d is the pore size distribution of COF-F1N2 in FIG. Figure 5 e is the pore size distribution of COF-F1N5 in FIG.

[0031] Figure 6 is the adsorption performance of the COF materials prepared in Examples 1-5 of the present application against PFOA and GenX;

[0032] Figure 7 is the nonlinear fitting graph of the isothermal adsorption of the COF materials prepared in Examples 2-4 and Comparative Example 1 of the present application against PFOA;

[0033] Figure 8 is the nonlinear fitting graph of the isothermal adsorption of the COF materials prepared in Examples 2-4 and Comparative Example 1 of the present application against GenX;

[0034] Figure 9 is the graph of the removal rate of the COF materials prepared in Examples 2-4 and Comparative Example 1 of the present application against PFOA;

[0035] Figure 10is a schematic diagram of the Gen X removal rate of the COF material prepared in Examples 2-4 and Comparative Example 1 of the present application. DETAILED DESCRIPTION

[0036] The present application is further described below in conjunction with the accompanying drawings and examples. Unless otherwise defined, technical or scientific terms used in the present application shall have the same meaning as commonly understood by one of ordinary skill in the art to which the present application pertains. The features or characteristics mentioned in the present application or the features or characteristics mentioned in the specific examples can be combined in any manner, and these specific examples are only used to illustrate the present application and not to limit the scope of the present application.

[0037] Example 1

[0038] The present application provides a heteroporous fluorine-doped cationic covalent organic framework material, and a preparation method thereof comprises the following steps:

[0039] S1, 0.0764 mmol ETTA and 0.1528 mmol TFTDA are added to a glass tube, then 3 mL of o-dichlorobenzene / n-butanol solvent (1:1, v / v) is added, and they are fully mixed by ultrasonic treatment for 15 min.

[0040] S2, 0.3 mL of acetic acid (concentration of 6 mol / L) is added to the glass tube of S1 as a catalyst to obtain a reaction system, the reaction system is immediately treated by ultrasonic treatment for 10 min, and then is quickly placed in liquid nitrogen for cyclic freezing-pumping-dewaxing three steps for cyclic degassing and sealing. Freezing is to freeze the glass tube in liquid nitrogen, pumping is to use a vacuum pump to pump the glass tube, and dewaxing is to take the frozen glass tube out of the low temperature environment, and naturally dewax at room temperature or through a warm water bath.

[0041] S3, after the reaction system of S2 returns to room temperature, it is transferred to a muffle furnace, and is reacted at 120℃ for 72h, after the reaction is completed, the product is washed with super-dry tetrahydrofuran for 5 times, then is washed with anhydrous ethanol for 3 times, and finally the washed material is vacuum dried at 80℃ overnight to obtain a heteroporous fluorine-doped cationic covalent organic framework material, which is named as COF-F.

[0042] Example 2

[0043] The present application provides a heteroporous fluorine-doped cationic covalent organic framework material, and a preparation method thereof comprises the following steps:

[0044] S1, 0.0764 mmol ETTA, 0.0764 mmol TFTDA and 0.0764 mmol BFBIM are added to a glass tube, then 3 mL of o-dichlorobenzene / n-butanol solvent (1:1, v / v) is added, and they are fully mixed by ultrasonic treatment for 15 min.

[0045] S2, 0.3 mL of acetic acid (concentration of 6 mol / L) was added to the glass tube of S1 as a catalyst to obtain a reaction system, the reaction system was immediately subjected to ultrasonic treatment for 10 min, and then was quickly placed in liquid nitrogen to perform a cycle of freezing-pumping-dewetting for three steps to perform cyclic degassing and then sealing. Freezing is to place the glass tube in liquid nitrogen for freezing, pumping is to use a vacuum pump to pump the glass tube, and dewetting is to take the frozen glass tube out of the low-temperature environment, so that it is naturally thawed at room temperature or thawed through a warm water bath.

[0046] S3, after the reaction system of S2 returned to room temperature, it was transferred to a muffle furnace and reacted at 120 DEG C for 72 h, after the reaction was completed, the product was washed with super-dry tetrahydrofuran for 5 times, then washed with anhydrous ethanol for 3 times, finally, the washed material was vacuum dried at 80 DEG C overnight, to obtain a heteroporous fluorine-doped cationic covalent organic framework material, named COF-F1N1.

[0047] Example 3

[0048] The application provides a heteroporous fluorine-doped cationic covalent organic framework material, and a preparation method thereof.

[0049] S1, 0.0764 mmol of ETTA, 0.051 mmol of TFTDA and 0.1018 mmol of BFB1M were added to a glass tube, then 3 mL of o-dichlorobenzene / n-butanol solvent (1:1, v / v) was added, and they were fully mixed through ultrasonic treatment for 15 min.

[0050] S2, 0.3 mL of acetic acid (concentration of 6 mol / L) was added to the glass tube of S1 as a catalyst to obtain a reaction system, the reaction system was immediately subjected to ultrasonic treatment for 10 min, and then was quickly placed in liquid nitrogen to perform a cycle of freezing-pumping-dewetting for three steps to perform cyclic degassing and then sealing. Freezing is to place the glass tube in liquid nitrogen for freezing, pumping is to use a vacuum pump to pump the glass tube, and dewetting is to take the frozen glass tube out of the low-temperature environment, so that it is naturally thawed at room temperature or thawed through a warm water bath.

[0051] S3, after the reaction system of S2 returned to room temperature, it was transferred to a muffle furnace and reacted at 120 DEG C for 72 h, after the reaction was completed, the product was washed with super-dry tetrahydrofuran for 5 times, then washed with anhydrous ethanol for 3 times, finally, the washed material was vacuum dried at 80 DEG C overnight, to obtain a heteroporous fluorine-doped cationic covalent organic framework material, named COF-F1N2.

[0052] Example 4

[0053] The application provides a heteroporous fluorine-doped cationic covalent organic framework material, and a preparation method thereof.

[0054] S1, 0.0764mmol ETTA, 0.025mmol TFTDA and 0.127mmol BFBIM are added into a glass tube, then 3mL of o-dichlorobenzene / n-butanol solvent (1:1, v / v) is added, and they are fully mixed by ultrasonic treatment for 15min.

[0055] S2, 0.3mL of acetic acid (concentration of 6mol / L) is added into the glass tube of S1 as a catalyst to obtain a reaction system, the reaction system is immediately subjected to ultrasonic treatment for 10min, and then is rapidly placed into liquid nitrogen to perform a cycle of freezing-pumping-dewarming for cyclic degassing and sealing.

[0056] S3, after the reaction system of S2 is restored to room temperature, it is transferred into a muffle furnace, and is reacted at 120 DEG C for 72h, after the reaction is completed, the product is washed and filtered with super-dry tetrahydrofuran for 5 times, then is washed and filtered with anhydrous ethanol for 3 times, finally, the washed material is vacuum dried at 80 DEG C overnight to obtain a heteroporous fluorine-doped cationic covalent organic framework material, which is named as COF-F1N5.

[0057] Example 5

[0058] The application provides a heteroporous cationic covalent organic framework material, and a preparation method thereof.

[0059] S1, 0.0764mmol ETTA, 0.025mmol TFTDA and 0.127mmol BFBIM are added into a glass tube, then 3mL of o-dichlorobenzene / n-butanol solvent (1:1, v / v) is added, and they are fully mixed by ultrasonic treatment for 15min.

[0060] S2, 0.3mL of acetic acid (concentration of 6mol / L) is added into the glass tube of S1 as a catalyst to obtain a reaction system, the reaction system is immediately subjected to ultrasonic treatment for 10min, and then is rapidly placed into liquid nitrogen to perform a cycle of freezing-pumping-dewarming for cyclic degassing and sealing.

[0061] S3, after the reaction system of S2 is restored to room temperature, it is transferred to a muffle furnace, and reacted at 120°C for 72h, after the reaction is completed, the product is washed with super-dry tetrahydrofuran for 5 times, then washed with anhydrous ethanol for 3 times, and finally, the washed material is dried at 80°C under vacuum overnight to obtain a heteroporous fluorine-doped cationic covalent organic framework material, named COF-N.

[0062] Comparative Example 1

[0063] The present application provides a heteroporous covalent organic framework material, and a preparation method thereof, comprising the following steps:

[0064] S1, 0.0764mmol ETTA, 0.1528mmol 1,4-bis(4-formylphenyl)benzene are added to a glass tube, then 3mL of o-dichlorobenzene / n-butanol solvent (1:1, v / v) is added, and they are mixed by ultrasonic treatment for 15min.

[0065] S2, 0.3mL of acetic acid (concentration of 6mol / L) is added to the glass tube of S1 as a catalyst to obtain a reaction system, the reaction system is immediately treated by ultrasonic treatment for 10min, and then quickly placed in liquid nitrogen for cyclic freezing-pumping-dewaxing to perform cyclic degassing and sealing. Freezing is to place the glass tube in liquid nitrogen for freezing, pumping is to use a vacuum pump to pump the glass tube, and dewaxing is to take the frozen glass tube out of the low-temperature environment, and naturally dewax at room temperature or through a warm water bath.

[0066] S3, after the reaction system of S2 is restored to room temperature, it is transferred to a muffle furnace, and reacted at 120°C for 72h, after the reaction is completed, the product is washed with super-dry tetrahydrofuran for 5 times, then washed with anhydrous ethanol for 3 times, and finally, the washed material is dried at 80°C under vacuum overnight to obtain a heteroporous covalent organic framework material, named COF-N.

[0067] Performance test

[0068] The COF materials prepared by Examples 1-5 and Comparative Example 1 are characterized by an X-ray diffractometer (XRD, Rigaku) with CuKα radiation.

[0069] Figure 1The XRD patterns of the COF materials prepared in Examples 1-5 and Comparative Example 1 of the present application are shown in the figure, and COF-C has a clear XRD diffraction peak at about 1.8°, indicating that COF-C has a hexagonal uniform distribution and crystallinity. COF-F, COF-F1N1, COF-F1N2, and COF-F1N5 have clear XRD diffraction peaks at 1.8°-1.9°, and weaker diffraction peaks at 3.7°-3.8°, 5.6°-5.7, and 7.5-7.6°. COF-N has a weak diffraction peak at about 3.9°, which may be due to the full proportion of cationic monomers weakening the COF crystallinity. However, overall, the COF materials prepared by the present application using fluorine-containing monomers and cationic monomers also have good crystal structures.

[0070] The surface morphology of COF-F1N5 prepared in Example 4 was characterized by scanning electron microscopy (SEM, JEOL) and transmission electron microscopy (TEM).

[0071] Figure 2 The SEM image of COF-F1N5 prepared in Example 4 of the present application is shown in the figure, and COF-F1N5 exhibits smooth, rhombic plate-like and flower-like amorphous nanostructures. Figure 3 The TEM image of COF-F1N5 prepared in Example 4 of the present application is shown in the figure, and under transmission electron microscopy, it can be clearly observed that most of the regions of COF-F1N5 have rich ordered lattice structures, and the particles show a flaky stacking morphology, indicating the formation of a two-dimensional structure with high crystallinity.

[0072] The COF materials prepared in Examples 1-4 and Comparative Example 1 of the present application were evaluated for whether they are heteroporous COF materials by nitrogen adsorption-desorption isotherms. The specific surface area was calculated using the Brunauer-Emmett-Teller method (BET). By using non-local density functional theory (DFT), the results such as pore size distribution and specific surface area were obtained from the adsorption data. The nitrogen adsorption-desorption measurement results further verified the hierarchical porosity of the COF materials.

[0073] Figure 4are the N2 adsorption isotherms and surface area of the COF materials prepared in Examples 1-4 and Comparative Example 1 of the present application, as shown in the figure, the N2 adsorption isotherms of the COF materials prepared in Examples 1-4 and Comparative Example 1 show gradual adsorption, sharp rise in adsorption before P / P0=0.01, slower adsorption between P / P0=0.05-0.15, and the N2 adsorption isotherms of all of them show type IV adsorption isotherm, which clearly proves that the synthesized COF materials have both micropores and mesopores, belong to heteroporous materials, which means that the two functional monomers are successfully integrated into the heteroporous COF framework, and a complex pore structure is constructed, which provides abundant space and diverse adsorption sites for PFAS adsorption. And in different pressure intervals, the adsorption capacity of COF-F1N1, COF-F1N2 and COF-F1N5 is better than that of COF-C and COF-F, which shows that the micropores and mesopores of COF-F1N1, COF-F1N2 and COF-F1N5 work well in the adsorption process, can quickly adsorb and maintain a high adsorption capacity. While the pore synergy of COF-C and COF-F is insufficient, which affects the overall adsorption efficiency.

[0074] The Brunauer-Emmett-Teller method (BET) method was used to calculate the specific surface area of COF-C, COF-F, COF-F1N1, COF-F1N2 and COF-F1N5, which were 217.26 m 2 / g, 218 m 2 / g, 446.73 m 2 / g, 500.88 m 2 / g, 410.94 m 2 / g, respectively. The larger the specific surface area, the more sites on the surface of the material that can be used for adsorption. The significantly higher specific surface area of COF-F1N1, COF-F1N2 and COF-F1N5 means that they can provide more interfaces for contact with PFAS molecules, thereby increasing the ability to adsorb PFAS. In contrast, the specific surface area of COF-C and COF-F is smaller, and the available adsorption sites are limited, so their adsorption performance is relatively weak.

[0075] Figure 5is a schematic diagram of the pore size distribution of the COF materials prepared in Examples 1-4 and Comparative Example 1 of the present application, as shown in the figure, the COF materials prepared in Examples 1-4 and Comparative Example 1 of the present application all have both mesopores (>2 nm) and micropores (<2 nm) in the pore size distribution, but COF-F1N1, COF-F1N2 and COF-F1N5 have more advantages in the rationality and adaptability of the pore size distribution. PFAS molecules of different lengths and structures have different sizes, micropores can provide physical confinement for smaller PFAS molecules, and mesopores can help larger size PFAS molecules to diffuse and enter the interior of the material for adsorption. COF-F1N1, COF-F1N2 and COF-F1N5 have similar contents of both types of pores, which can better match the sizes of different PFAS molecules, provide more suitable adsorption space for various PFAS, and improve the adsorption efficiency. In contrast, COF-C and COF-F have significantly less micropore content than mesopore content, meaning that there are limited adsorption sites for small molecule PFAS, making it difficult to efficiently adsorb small size PFAS molecules, and more critically, lacking cationic monomers and being unable to adsorb PFAS through electrostatic adsorption, which limits the overall adsorption efficiency. This concept is also verified in the results of the PFAS adsorption experiments of different chain lengths, and the adsorption effect of these two materials is poor.

[0076] Isothermal adsorption test was used to preliminarily screen the COF materials. The COF materials prepared in Examples 1-5 (250 mg / L) were added to 30 mL of 100 μmol / L standard solution of PFOA (perfluorooctanoic acid) and GenX (hexafluoropropylene oxide dimer acid ammonium salt), mixed thoroughly, then the mixture was shaken on a shaking table at room temperature for 24 hours, then centrifuged to obtain the supernatant, filtered through a 0.2 μm membrane filter, and then the filtrate was analyzed by UHPLC-MS / MS (ultra-high performance liquid chromatography-tandem mass spectrometry) to determine the remaining PFOA and GenX contents.

[0077] Figure 6 is a schematic diagram of the adsorption performance of the COF materials prepared in Examples 1-5 of the present application on PFOA and GenX, as shown in the figure, COF-F1N1, COF-F1N2 and COF-F1N5 all show better performance than COF-F and COF-N in adsorbing PFOA and GenX.

[0078] Further, the adsorption performance of COF-F1N1, COF-F1N2 and COF-F1N5 was evaluated by isothermal adsorption test and adsorption kinetics test, and COF-C was used as a control. The adsorption capacity and adsorption rate were calculated using the following formula:

[0079]

[0080] In the formula, C0(mg / L) is the initial concentration of PFAS;

[0081] C e (mg / L) is the equilibrium concentration of PFAS;

[0082] C t (mg / L) is the concentration of PFAS at time t;

[0083] m (mg) and V (mL) represent the mass of adsorbent and the volume of solution, respectively.

[0084] Meanwhile, the Langmuir and Freundlich adsorption isotherm models were used to fit the adsorption of two PFAS by the heteroporous COF materials to describe the adsorption processes of COF-F1N1, COF-F1N2 and COF-F1N5.

[0085] The Langmuir adsorption isotherm equation is as follows:

[0086]

[0087] The Freundlich adsorption isotherm equation is as follows:

[0088]

[0089] In the formula, q m (mg / g) is the maximum adsorption capacity;

[0090] K L is the Langmuir constant;

[0091] K F is the Freundlich constant;

[0092] C e (mg / L) is the concentration of PFAS at adsorption equilibrium.

[0093] Figure 7 Figure 2-4 is a nonlinear fitting graph of the isothermal adsorption of the COF materials prepared in Examples 2-4 and Comparative Example 1 to PFOA, as shown in the figure, the equilibrium adsorption capacity of COF-F1N1, COF-F1N2 and COF-F1N5 to PFOA is obviously better than that of COF-C, and increases with the increase of the proportion of cationic monomer incorporation.

[0094] Figure 8 Figure 2-4 is a nonlinear fitting graph of the isothermal adsorption of the COF materials prepared in Examples 2-4 and Comparative Example 1 to PFOA, as shown in the figure, the equilibrium adsorption capacity of COF-F1N1, COF-F1N2 and COF-F1N5 to PFOA is obviously better than that of COF-C, and increases with the increase of the proportion of cationic monomer incorporation.

[0095] Adsorption kinetics test: 30 mL of a 1 mg / L aqueous solution of PFOA or Gen X was added to the bottle. Then 3 mg of COF material (COF-F1N1, COF-F1N2, COF-F1N5 and COF-C) was added and mixed thoroughly. Subsequently, different time intervals (2 min, 5 min, 10 min, 15 min, 30 min, 1 h, 2 h) were given at room temperature and treated on a shaker at 250 rpm. The mixture of all samples was filtered through a 0.2 μm membrane filter, and the filtrate was analyzed using UHPLC-MS / MS to determine the remaining PFOA and GenX content. All batch tests were repeated three times. The removal rate, pseudo-first-order kinetic model and pseudo-second-order kinetic model were used to fit the process of the kinetic adsorption test to describe the adsorption process of the COF material in this study. The calculation formulas of the pseudo-first-order kinetic model and pseudo-second-order kinetic model are as follows:

[0096] ln(q e -q t )=ln q e -k1t

[0097]

[0098] Where q t (mg / g) is the adsorption loading of the adsorbent at time t;

[0099] q e (mg / g) is the adsorption capacity of the adsorbent at equilibrium;

[0100] k1(min -1 ) is the pseudo-first-order rate constant;

[0101] k2 (g / mg·min) is the pseudo-second-order rate constant.

[0102] Figure 9 This is a schematic diagram showing the PFOA removal rates of COF materials produced in Examples 2-4 and Comparative Example 1. As shown, COF-F1N1, COF-F1N2, and COF-F1N5 all achieved over 90% PFOA removal rates within 15 minutes, and over 95% within 20 minutes. COF-F1N5 had the fastest PFOA adsorption rate, reaching 90% removal in just 10 minutes. In contrast, COF-C, which lacks functional integration, achieved a 50% removal rate within 30 minutes and over 90% removal after 120 minutes.

[0103] Figure 10The COF material prepared in Examples 2-4 and Comparative Example 1 of the present application is shown in the figure, and the removal rate of Gen X by COF-F1N1 and COF-F1N2 is more than 90% in 20 min. COF-F1N5 reaches more than 90% in only 2 min. COF-C needs 120 min to reach 90%. This shows that the adsorption performance of the functionalized integrated COF-F1N1, COF-F1N2 and COF-F1N5 is greatly improved, and the pollutants can be removed more quickly and efficiently.

[0104] Therefore, the present application uses cationic monomers and fluorine-containing monomers to cooperatively prepare fluorine-doped cationic covalent organic framework materials with heteroporous structures, which have good crystal structures, high crystallinity and hierarchical porosity, provide more active sites and diffusion channels for PFAS adsorption, and achieve efficient adsorption of long-chain and short-chain PFAS.

[0105] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application but not to limit it, although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that: the technical solutions of the present application can still be modified or replaced by equivalents, and these modifications or equivalent replacements cannot make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present application.

Claims

1. A heteroporous fluorine-doped cationic covalent organic framework material, characterized by: By D 2h Symmetric monomers and C2 symmetric monomers are prepared by Schiff base reaction, D 2h The symmetrical monomer is tetrakis-(4-aminophenyl)ethylene, the C2 symmetrical monomer is a side functional monomer, the molar ratio of tetrakis-(4-aminophenyl)ethylene to the side functional monomer is 1:2, the side functional monomer is one or both of a fluorine-containing monomer and a cationic monomer, the fluorine-containing monomer is 2',3',5',6'-tetrafluoro-[1,1':4',1"-terphenyl]-4,4"-dicarbaldehyde, and the cationic monomer is 4,7-bis(4-formylphenyl)-1,3-dimethyl-1H-benzo[d]imidazol-3-ium bromide.

2. The heteroporous fluorine-doped cationic covalent organic framework material according to claim 1, characterized in that: When the side functional monomers are a fluorine-containing monomer and a cationic monomer, the molar ratio of the fluorine-containing monomer to the cationic monomer is 1:1 to 1:

6.

3. A method for preparing a heteroporous fluorine-doped cationic covalent organic framework material, characterized by: The heteroporous fluorine-doped cationic covalent organic framework material according to any one of claims 1 to 2 is prepared by a Schiff base reaction between tetrakis-(4-aminophenyl)ethylene and a side functional monomer, wherein the molar ratio of tetrakis-(4-aminophenyl)ethylene to the side functional monomer is 1:

2.

4. The method for preparing a heteroporous fluorine-doped cationic covalent organic framework material according to claim 3, characterized in that: The following steps are included: S1. Tetrakis-(4-aminophenyl)ethylene and pendant functional monomers are added to a glass tube, followed by addition of o-dichlorobenzene / n-butanol solvent, and ultrasonic treatment is performed to mix. S2. Add a catalyst to the glass tube of S1 to obtain a reaction system, subject the reaction system to ultrasonic treatment, and then perform cyclic degassing and sealing; S3. After the reaction system of S2 returns to room temperature, it is transferred to a muffle furnace for heating reaction. After the reaction is completed, the product is washed and dried overnight to obtain a heteroporous fluorine-doped cationic covalent organic framework material.

5. The method for preparing a heteroporous fluorine-doped cationic covalent organic framework material according to claim 4, characterized in that: The volume ratio of o-dichlorobenzene to n-butanol in S1 was 1:1, and the ultrasonic treatment time was 15 min.

6. The method for preparing a heteroporous fluorine-doped cationic covalent organic framework material according to claim 4, characterized in that: In S2, the catalyst is acetic acid, and the ultrasonic treatment time is 10 min.

7. The method for preparing a heteroporous fluorine-doped cationic covalent organic framework material according to claim 4, characterized in that: The cyclic degassing in S2 consists of three steps: cyclic freezing-pumping-thawing. Freezing is to put the glass tube into liquid nitrogen for freezing, pumping is to use a vacuum pump to evacuate the glass tube, and thawing is to take the frozen glass tube out of the low-temperature environment and thaw it naturally at room temperature or thaw it in a warm water bath.

8. The method for preparing a heteroporous fluorine-doped cationic covalent organic framework material according to claim 4, characterized in that: The heating reaction temperature in S3 is 120° C., the reaction time is 72 h, washing is performed by using ultra-dry tetrahydrofuran for washing and filtering 5 times, then washing and filtering 3 times with anhydrous ethanol, and drying is performed by vacuum drying at 80° C.

9. Application of a heteroporous fluorine-doped cationic covalent organic framework material, characterized by: The heteroporous fluorine-doped cationic covalent organic framework material according to any one of claims 1 to 2 is used for adsorbing perfluorinated or polyfluorinated alkyl substances.

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