Heteroporous fluorine-doped cation covalent organic framework material as well as preparation method and application thereof

Abstract

The invention relates to the technical field of functional materials, in particular to a heteroporous fluorine-doped cation covalent organic framework material and a preparation method and application thereof.The heteroporous fluorine-doped cation covalent organic framework material comprises a D2h symmetric monomer and a C2 symmetric monomer, the D2h symmetric monomer is tetra-(4-aminobenzene) ethylene, the C2 symmetric monomer is a side functional monomer, and the side functional monomer is a fluorine-doped cation covalent organic framework material. The side functional monomer comprises one or two 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''-dicarboxaldehyde, and the cationic monomer is 4, 7-bis (4-formylphenyl)-1, 3-dimethyl-1H-benzo [d] imidazole-3-onium bromide. The problems that an existing COF material is poor in PFAS adsorption performance and single in adsorption type are solved, and long-chain PFAS and short-chain PFAS are efficiently adsorbed at the same time.

Description

Technical Field

[0001] The present invention relates to the technical field of functional materials, and particularly to a hetero-porous fluorine-doped cationic covalent organic framework material, a preparation method thereof, and an application thereof. Background Art

[0002] Per- and polyfluoroalkyl substances (PFAS) are a class of synthetic compounds in which some or all of the hydrogen atoms on the carbon chain are replaced by fluorine atoms, and are widely used in a variety of consumer and industrial products. However, PFAS are carcinogenic, biotoxic, persistent and bioaccumulative in the environment. This has led to their widespread presence in environmental media, food, etc., threatening human health.

[0003] As emerging porous organic nanomaterials, covalent organic framework (COF) materials have the advantages of ordered porosity, good stability, and customizable functions, and have received extensive attention in the field of PFAS pollutant adsorption and treatment. However, the lack of highly integrated functional groups and appropriate pore size regulation limits their adsorption performance for PFAS. For example, when some conventional COF materials are used to treat wastewater containing PFAS, the adsorption amount of specific PFAS is low, unable to meet the requirements of high adsorption efficiency in practical applications.

[0004] Although some studies have reported that partially functionalized and integrated COF nanomaterials have improved the adsorption performance for PFAS, most of these studies have been achieved in single-pore COF and only for the adsorption of a single PFAS. When different structures and lengths of PFAS coexist in the environment, existing materials cannot meet the requirement of adsorbing multiple PFAS, which greatly hinders their application expansion in actual complex environments. Summary of the Invention

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

[0006] To achieve the above object, the present invention provides a hetero-porous fluorine-doped cationic covalent organic framework material, including D 2h symmetric monomer and C 2 symmetric monomer, D 2h The symmetric monomer is tetra-(4-aminophenyl)ethylene (ETTA), C 2The symmetric monomer is a side-functional monomer, and the side-functional monomer includes one or two of a fluorinated monomer and a cationic monomer. The fluorinated monomer is 2',3',5',6'-tetrafluoro-[1,1':4',1”-terphenyl]-4,4”-dicarboxaldehyde (TFTDA), and the cationic monomer is 4,7-bis(4-formylphenyl)-1,3-dimethyl-1H-benzo[d]imidazol-3-ium bromide (BFBlM).

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

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

[0009] A preparation method of a porous fluorine-doped cationic covalent organic framework material is to prepare the above-mentioned porous fluorine-doped cationic covalent organic framework material by a Schiff base reaction of tetra-(4-aminophenyl)ethylene and a side-functional monomer.

[0010] Preferably, it includes the following steps

[0011] S1. Add tetra-(4-aminophenyl)ethylene and the side-functional monomer into a glass tube, then add o-dichlorobenzene / n-butyl alcohol solvent, and ultrasonically treat the mixture;

[0012] S2. Add a catalyst to the glass tube in S1 to obtain a reaction system, ultrasonically treat the reaction system and then perform cyclic degassing and sealing;

[0013] S3. After the reaction system in S2 returns to room temperature, transfer it to a muffle furnace for heating reaction. After the reaction is completed, wash and dry the product overnight to obtain the porous fluorine-doped cationic covalent organic framework material.

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

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

[0016] Preferably, the cyclic degassing in S2 includes three steps of cyclic freezing - pumping - thawing. Freezing is to freeze the glass tube in liquid nitrogen, pumping is to use a vacuum pump to pump air from the glass tube, and thawing is to take out the frozen glass tube from the low-temperature environment and let it thaw naturally at room temperature or by a warm water bath.

[0017] Preferably, in S3, the temperature of the heating reaction is 120 °C, the reaction time is 72 h, washing is to wash and filter 5 times with ultra-dry tetrahydrofuran, and then wash and filter 3 times with absolute ethanol, and drying is to dry in vacuum at 80 °C.

[0018] An application of an isoporous fluorine-doped cation covalent organic framework material. The isoporous fluorine-doped cation covalent organic framework material is used for adsorbing perfluoro or polyfluoroalkyl substances.

[0019] Mechanism of the present invention:

[0020] The present invention selects ETTA as the D according to the structure, molecular length, chemical group and adsorption mechanism of PFAS. 2h Symmetrical monomers build an orderly basic framework for the material. Their symmetrical structure can guide the regular arrangement of monomers and ensure the overall orderliness of the material. The fluorinated monomer TFTDA and the cationic monomer BFBlM work together as C 2 Symmetrical monomers form a covalent organic framework material with a heteroporous structure. The heteroporous structure provides a hierarchical porous network and abundant adsorption sites, achieving efficient adsorption of PFAS. At the same time, the positive charge introduced by the cationic monomer produces an electrostatic adsorption effect with the negative charge of the PFAS molecule; there is FF mutual attraction and hydrogen bond donor between the fluorine atoms of the fluorine-containing monomer and the fluorine atoms in PFAS, providing specific adsorption; at the same time, the hydrophobicity of the covalent organic framework material interacts with the hydrophobic characteristics of PFAS, further promoting the adsorption capacity of PFAS.

[0021] Beneficial effects of the present invention:

[0022] (1) The present invention adopts the above-mentioned heteroporous fluorine-doped cationic covalent organic framework material and its preparation method and application, and prepares a heteroporous fluorine-doped cationic covalent organic framework material by synergistically preparing a cationic monomer and a fluorine-containing monomer. The heteroporous structure of the fluorine-doped cationic covalent organic framework material can be integrated with electrostatic adsorption, FF mutual attraction and hydrophobic interaction in the framework material with both mesoporous and microporous pore sizes, thereby achieving simultaneous and efficient adsorption of long-chain and short-chain PFAS.

[0023] (2) The present invention 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 graded porosity, providing more adsorption sites and diffusion channels for PFAS molecules.

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

[0025] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. Description of the Drawings

[0026] Figure 1 is the XRD pattern of the COF materials prepared in Examples 1-5 and Comparative Example 1 of the present invention; Figure 1 where a in [the figure] is the XRD pattern of COF-C, Figure 1 where b in [the figure] is the XRD pattern of COF-F, Figure 1 where c in [the figure] is the XRD pattern of COF-F1N1, Figure 1 where d in [the figure] is the XRD pattern of COF-F1N2, Figure 1 where e in [the figure] is the XRD pattern of COF-F1N5, Figure 1 where f in [the figure] is the XRD pattern of COF-N;

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

[0028] Figure 3 is the TEM image of COF-F1N5 in Example 4 of the present invention; Figure 3 where a in [the figure] is the TEM image of COF-F1N5 at 200 nm, Figure 3 where b in [the figure] is the TEM image of COF-F1N5 at 100 nm, Figure 3 where c in [the figure] is the TEM image of COF-F1N5 at 50 nm;

[0029] Figure 4 is the schematic diagram of the N 2 adsorption isotherm and surface area of the COF materials prepared in Examples 1-4 and Comparative Example 1 of the present invention;

[0030] Figure 5 is the schematic diagram of the pore size distribution of the COF materials prepared in Examples 1-4 and Comparative Example 1 of the present invention; Figure 5 where a in [the figure] is the schematic diagram of the pore size distribution of COF-C, Figure 5 where b in [the figure] is the schematic diagram of the pore size distribution of COF-F, Figure 5 where c in [the figure] is the schematic diagram of the pore size distribution of COF-F1N1, Figure 5 where d in [the figure] is the schematic diagram of the pore size distribution of COF-F1N2, Figure 5 where e in [the figure] is the schematic diagram of the pore size distribution of COF-F1N5;

[0031] Figure 6 is the schematic diagram of the adsorption performance of the COF materials prepared in Examples 1-5 of the present invention for PFOA and GenX;

[0032] Figure 7 is the non-linear fitting graph of the isothermal adsorption of PFOA by the COF materials prepared in Examples 2-4 and Comparative Example 1 of the present invention;

[0033] Figure 8 It is a non-linear fitting graph of the isothermal adsorption of Gen X by the COF materials prepared in Examples 2-4 of the present invention and Comparative Example 1;

[0034] Figure 9 It is a schematic diagram of the removal rate of PFOA by the COF materials prepared in Examples 2-4 of the present invention and Comparative Example 1;

[0035] Figure 10 It is a schematic diagram of the removal rate of Gen X by the COF materials prepared in Examples 2-4 of the present invention and Comparative Example 1. Detailed implementation manners

[0036] The present invention will be further described below in conjunction with the drawings and embodiments. Unless otherwise defined, the technical terms or scientific terms used in the present invention should have the ordinary meanings understood by those with ordinary skills in the field to which the present invention belongs. The above-mentioned features mentioned in the present invention or the features mentioned in the specific examples can be combined arbitrarily. These specific embodiments are only used to illustrate the present invention and do not limit the scope of the present invention.

[0037] Example 1

[0038] The present invention provides a hetero-porous fluorine-doped covalent organic framework material, and its preparation method includes the following steps:

[0039] S1. Add 0.0764 mmol of ETTA and 0.1528 mmol of TFTDA into a glass tube, and then add 3 mL of o-dichlorobenzene / n-butanol solvent (1:1, v / v), and ultrasonically treat for 15 min to fully mix them.

[0040] S2. Add 0.3 mL of acetic acid (concentration: 6 mol / L) as a catalyst to the glass tube in S1 to obtain a reaction system. Immediately ultrasonically treat the reaction system for 10 min, and then quickly put it into liquid nitrogen for three steps of cyclic freezing-pump evacuation-thawing for cyclic degassing and then seal it. Freezing means putting the glass tube into liquid nitrogen for freezing, pump evacuation means using a vacuum pump to evacuate the glass tube, and thawing means taking out the frozen glass tube from the low-temperature environment and allowing it to thaw naturally at room temperature or by a warm water bath.

[0041] S3. After the reaction system in S2 returns to room temperature, transfer it to a muffle furnace and react at 120 °C for 72 h. After the reaction is completed, wash and filter the product 5 times with ultra-dry tetrahydrofuran, then wash and filter it 3 times with absolute ethanol, and finally vacuum-dry the washed material at 80 °C overnight to obtain a hetero-porous fluorine-doped cationic covalent organic framework material, named COF-F.

[0042] Example 2

[0043] The present invention provides a hetero-porous fluorine-doped cationic covalent organic framework material, and its preparation method includes the following steps:

[0044] S1. Add 0.0764 mmol of ETTA, 0.0764 mmol of TFTDA, and 0.0764 mmol of BFBlM into a glass tube, then add 3 mL of o-dichlorobenzene / n-butanol solvent (1:1, v / v), and ultrasonically treat for 15 min to fully mix them.

[0045] S2. Add 0.3 mL of acetic acid (concentration: 6 mol / L) into the glass tube of S1 as a catalyst to obtain a reaction system. Immediately ultrasonically treat the reaction system for 10 min, then quickly put it into liquid nitrogen for cyclic freezing - pumping - thawing three steps for cyclic degassing and then seal. Freezing means putting the glass tube into liquid nitrogen for freezing, pumping means using a vacuum pump to pump air from the glass tube, and thawing means taking out the frozen glass tube from the low-temperature environment and allowing it to thaw naturally at room temperature or by warm water bath thawing.

[0046] S3. After the reaction system of S2 returns to room temperature, transfer it to a muffle furnace and react at 120 °C for 72 h. After the reaction is completed, wash and filter the product 5 times with ultra-dry tetrahydrofuran, then wash and filter it 3 times with absolute ethanol. Finally, vacuum dry the washed material at 80 °C overnight to obtain the hetero-porous fluorine-doped cationic covalent organic framework material, named COF-F1N1.

[0047] Example 3

[0048] The present invention provides a hetero-porous fluorine-doped cationic covalent organic framework material, and its preparation method includes the following steps:

[0049] S1. Add 0.0764 mmol of ETTA, 0.051 mmol of TFTDA, and 0.1018 mmol of BFBlM into a glass tube, then add 3 mL of o-dichlorobenzene / n-butanol solvent (1:1, v / v), and ultrasonically treat for 15 min to fully mix them.

[0050] S2. Add 0.3 mL of acetic acid (concentration: 6 mol / L) into the glass tube of S1 as a catalyst to obtain a reaction system. Immediately ultrasonically treat the reaction system for 10 min, then quickly put it into liquid nitrogen for cyclic freezing - pumping - thawing three steps for cyclic degassing and then seal. Freezing means putting the glass tube into liquid nitrogen for freezing, pumping means using a vacuum pump to pump air from the glass tube, and thawing means taking out the frozen glass tube from the low-temperature environment and allowing it to thaw naturally at room temperature or by warm water bath thawing.

[0051] S3. After the reaction system of S2 returns to room temperature, transfer it to a muffle furnace and react at 120 °C for 72 h. After the reaction, wash the product thoroughly with ultra-dry tetrahydrofuran by filtration 5 times, then wash it thoroughly with absolute ethanol by filtration 3 times. Finally, dry the washed material under vacuum at 80 °C overnight to obtain a hetero-porous fluorine-doped cationic covalent organic framework material named COF-F1N2.

[0052] Example 4

[0053] The present invention provides a hetero-porous fluorine-doped cationic covalent organic framework material, and its preparation method includes the following steps:

[0054] S1. Add 0.0764 mmol of ETTA, 0.025 mmol of TFTDA and 0.127 mmol of BFBlM into a glass tube, then add 3 mL of o-dichlorobenzene / n-butanol solvent (1:1, v / v), and ultrasonically treat for 15 min to mix them thoroughly.

[0055] S2. Add 0.3 mL of acetic acid (concentration 6 mol / L) as a catalyst to the glass tube of S1 to obtain a reaction system. Immediately ultrasonically treat the reaction system for 10 min, then quickly put it into liquid nitrogen for cyclic freezing - pumping - thawing three steps for cyclic degassing and then seal it. Freezing means putting the glass tube into liquid nitrogen for freezing, pumping means using a vacuum pump to pump air from the glass tube, and thawing means taking out the frozen glass tube from the low-temperature environment and allowing it to thaw naturally at room temperature or by a warm water bath.

[0056] S3. After the reaction system of S2 returns to room temperature, transfer it to a muffle furnace and react at 120 °C for 72 h. After the reaction, wash the product thoroughly with ultra-dry tetrahydrofuran by filtration 5 times, then wash it thoroughly with absolute ethanol by filtration 3 times. Finally, dry the washed material under vacuum at 80 °C overnight to obtain a hetero-porous fluorine-doped cationic covalent organic framework material named COF-F1N5.

[0057] Example 5

[0058] The present invention provides a hetero-porous cationic covalent organic framework material, and its preparation method includes the following steps:

[0059] S1. Add 0.0764 mmol of ETTA and 0.1528 mmol of BFBlM into a glass tube, then add 3 mL of o-dichlorobenzene / n-butanol solvent (1:1, v / v), and ultrasonically treat for 15 min to mix them thoroughly.

[0060] S2, add 0.3mL of acetic acid (concentration of 6mol / L) as catalyst to the glass tube of S1 to obtain a reaction system, and immediately ultrasonicate the reaction system for 10min, and then quickly put it into liquid nitrogen for cyclic freezing-pumping-thawing three steps for cyclic degassing and sealing. 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 by a warm water bath.

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

[0062] Comparative Example 1

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

[0064] S1. Add 0.0764 mmol ETTA and 0.1528 mmol 1,4-di(4-formylphenyl)benzene into a glass tube, then add 3 mL o-dichlorobenzene / n-butanol solvent (1:1, v / v), and perform ultrasonic treatment for 15 min to mix them thoroughly.

[0065] S2, add 0.3mL of acetic acid (concentration of 6mol / L) as catalyst to the glass tube of S1 to obtain a reaction system, and immediately ultrasonicate the reaction system for 10min, and then quickly put it into liquid nitrogen for cyclic freezing-pumping-thawing three steps for cyclic degassing and sealing. 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 by a warm water bath.

[0066] S3. After the reaction system of S2 returns to room temperature, it is transferred to a muffle furnace and reacted at 120°C for 72 hours. After the reaction is completed, the product is thoroughly washed and filtered with ultra-dry tetrahydrofuran for 5 times, and then thoroughly washed and filtered with anhydrous ethanol for 3 times. Finally, the washed material is vacuum dried at 80°C overnight to obtain a heteroporous covalent organic framework material, named COF-C.

[0067] Performance Testing

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

[0069] Figure 1 XRD patterns of the COF materials prepared in Examples 1-5 and Comparative Example 1 of the present invention are shown as follows. As shown in the figure, COF-C has an obvious XRD diffraction peak at about 1.8°, indicating that COF-C has a hexagonal uniform distribution and crystallinity. Obvious XRD diffraction peaks of COF-F, COF-F1N1, COF-F1N2, and COF-F1N5 are found at 1.8° - 1.9°, and weak diffraction peaks are present at 3.7° - 3.8°, 5.6° - 5.7°, and 7.5 - 7.6°. A weak diffraction peak of COF-N is observed at about 3.9°, which may be due to the full proportion of cationic monomers weakening the crystallinity of COF. Generally speaking, however, the COF materials prepared by the present invention 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 SEM image of COF-F1N5 in Example 4 of the present invention is shown as follows. As shown in the figure, COF-F1N5 exhibits a smooth, rhombic plate-like and flower-like amorphous nanostructure. Figure 3 TEM image of COF-F1N5 in Example 4 of the present invention is shown as follows. As shown in the figure, under the transmission electron microscope, it can be clearly observed that most regions of COF-F1N5 have a rich ordered lattice structure, and the particles show a sheet-like stacking morphology, indicating the formation of a two-dimensional structure with high crystallinity.

[0072] The nitrogen adsorption-desorption isotherms were used to evaluate whether the COF materials prepared in Examples 1-4 and Comparative Example 1 were isoporous COF materials. The Brunauer-Emmett-Teller (BET) method was used to calculate the specific surface area. By using the non-local density functional theory (DFT), 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 4 Schematic diagrams of the N 2 adsorption isotherms and surface areas of the COF materials prepared in Examples 1-4 and Comparative Example 1 of the present invention are shown as follows. As shown in the figure, the N 2 adsorption isotherms of the COF materials prepared in Examples 1-4 and Comparative Example 1 show stepwise adsorption, with a sharp increase in adsorption before P / P 0 = 0.01 and a slower adsorption between P / P 0 = 0.05 - 0.15. Their N 2The adsorption isotherms all show type-IV adsorption isotherms, which clearly prove that the synthesized COF materials have both micropores and mesopores and belong to heteroporous materials. This means that the two functional monomers have been successfully integrated into the heteroporous COF framework, constructing a complex pore structure, providing abundant space and diverse adsorption sites for the adsorption of PFAS. Moreover, in different pressure ranges, the adsorption capacities of COF-F1N1, COF-F1N2, and COF-F1N5 are all better than those of COF-C and COF-F, indicating that the micropores and mesopores of COF-F1N1, COF-F1N2, and COF-F1N5 cooperate well during the adsorption process, can adsorb quickly and maintain a high adsorption capacity. However, the pore synergy of COF-C and COF-F is insufficient, affecting the overall adsorption efficiency.

[0074] Calculated by the Brunauer-Emmett-Teller (BET) method, the specific surface areas of COF-C, COF-F, COF-F1N1, COF-F1N2, and COF-F1N5 are 217.26 m 2 / g, 218 m 2 / g, 446.73 m 2 / g, 500.88 m 2 / g, and 410.94 m 2 / g, respectively. The larger the specific surface area, the more sites available for adsorption on the material surface. The significantly higher specific surface areas of COF-F1N1, COF-F1N2, and COF-F1N5 mean that they can provide more interfaces for contact with PFAS molecules, thus increasing the ability to adsorb PFAS. In contrast, the specific surface areas of COF-C and COF-F are smaller, and the available adsorption sites are limited, resulting in relatively weak adsorption performance.

[0075] Figure 5Schematic diagram of the pore size distribution of the COF materials prepared in Examples 1-4 and Comparative Example 1 of the present invention. As shown in the figure, the COF materials prepared in Examples 1-4 and Comparative Example 1 both have two pore size distributions of mesopores (>2 nm) and micropores (<2 nm), but COF-F1N1, COF-F1N2, and COF-F1N5 have more advantages in the rationality and adaptability of the pore size distribution. PFAS molecules with different lengths and structures have different sizes. Micropores can provide a physical confinement effect on smaller PFAS molecules, while mesopores help larger-sized PFAS molecules diffuse and enter the material interior for adsorption. The contents of the two pore sizes of COF-F1N1, COF-F1N2, and COF-F1N5 are similar, which can better match the sizes of different PFAS molecules, provide a more suitable adsorption space for various PFAS, and improve the adsorption efficiency. In contrast, the micropore content of COF-C and COF-F is significantly less than that of mesopores, meaning that the adsorption sites for small-molecule PFAS are limited, and it is difficult to efficiently adsorb small-sized PFAS molecules. More critically, the lack of cationic monomers makes it impossible to adsorb PFAS through electrostatic adsorption, and the overall adsorption efficiency is limited. This concept was also verified in the results of the adsorption experiments on PFAS with different chain lengths, and the adsorption effects of these two materials were poor.

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

[0077] Figure 6 Schematic diagram of the adsorption performance of the COF materials prepared in Examples 1-5 of the present invention for PFOA and GenX. As shown in the figure, COF-F1N1, COF-F1N2, and COF-F1N5 all showed better performance than COF-F and COF-N in adsorbing PFOA and GenX.

[0078] The adsorption performances of COF-F1N1, COF-F1N2, and COF-F1N5 were further evaluated by isothermal adsorption experiments and adsorption kinetics experiments, with COF-C as a control. The adsorption capacity and adsorption rate were calculated using the following formulas:

[0079]

[0080] In the formula, C 0 (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 PFAS concentration at time t;

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

[0084] Meanwhile, the Langmuir and Freundlich adsorption isotherm models were used to fit the adsorption processes of two PFASs by the porous 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 This is the non-linear fitting graph of the isothermal adsorption of PFOA by the COF materials prepared in Examples 2-4 and Comparative Example 1 of the present invention. As shown in the figure, the equilibrium adsorption amounts of COF-F1N1, COF-F1N2, and COF-F1N5 for PFOA are significantly better than those of COF-C, and increase with the increase of the incorporation ratio of the cationic monomer.

[0094] Figure 8 This is the non-linear fitting graph of the isothermal adsorption of Gen X by the COF materials prepared in Examples 2-4 and Comparative Example 1 of the present invention. As shown in the figure, the equilibrium adsorption amounts of COF-F1N1, COF-F1N2, and COF-F1N5 for Gen X are significantly better than those of COF-C, and increase with the increase of the incorporation ratio of the cationic monomer.

[0095] Adsorption kinetics experiment: Add 30 mL of an aqueous solution of 1 mg / L PFOA or Gen X into a bottle. Then add 3 mg of COF materials (COF-F1N1, COF-F1N2, COF-F1N5, and COF-C) and mix well. Subsequently, process at 250 rpm on a shaker at room temperature for different time intervals (2 min, 5 min, 10 min, 15 min, 30 min, 1 h, 2 h). Filter the mixture of all samples through a 0.2 μm membrane filter, and then analyze the filtrate using UHPLC-MS / MS to determine the remaining PFOA and Gen X contents. All batch experiments 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 experiment to describe the adsorption process of COF materials in this study. The calculation formulas of the pseudo-first-order kinetic model and the pseudo-second-order kinetic model are as follows:

[0096] ln(q e -q t ) = ln q e -k 1 t

[0097]

[0098] In the formula, q t (mg / g) is the adsorption capacity of the adsorbent at time t;

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

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

[0101] k 2 (g / mg·min) is the pseudo-second-order rate constant.

[0102] Figure 9 It is a schematic diagram of the removal rate of PFOA by the COF materials prepared in Examples 2-4 and Comparative Example 1 of the present invention. As shown in the figure, COF-F1N1, COF-F1N2, and COF-F1N5 can all achieve a removal rate of more than 90% for PFOA at 15 min and a removal rate of more than 95% at 20 min. COF-F1N5 has the fastest adsorption rate for PFOA and can reach a 90% removal rate at 10 min. For COF-C without functional integration, it reaches a 50% removal rate at 30 min and can reach a removal rate of more than 90% only at 120 min.

[0103] Figure 10It is a schematic diagram of the removal rate of Gen X by the COF materials prepared in Examples 2-4 and Comparative Example 1 of the present invention. As shown in the figure, the removal rates of Gen X by COF-F1N1 and COF-F1N2 reached over 90% in 20 minutes. COF-F1N5 reached over 90% in only 2 minutes. It took 120 minutes for COF-C to reach a removal rate of 90%. This indicates that the adsorption performance of the functionally integrated COF-F1N1, COF-F1N2, and COF-F1N5 has been significantly improved, and they can remove pollutants more quickly and efficiently.

[0104] Therefore, the present invention prepares a fluorine-doped cationic covalent organic framework material with a heterogeneous pore structure through the synergistic effect of a cationic monomer and a fluorine-containing monomer. It has a good crystal structure, high crystallinity, and hierarchical porosity, providing more active sites and diffusion channels for PFAS adsorption, and achieving efficient adsorption of long-chain and short-chain PFAS.

[0105] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that they can still modify or equivalently replace the technical solutions of the present invention, and these modifications or equivalent replacements do not make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A heteroporous fluorine-doped cationic covalent organic framework material, characterized in that: Including D 2h Symmetric monomer and C2 symmetric monomer, D 2h The symmetrical monomer is tetrakis-(4-aminophenyl)ethylene, the C2 symmetrical monomer is a side functional monomer, the side functional monomer includes one or two 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"-dicarboxaldehyde, and the cationic monomer is 4,7-bis(4-formylphenyl)-1,3-dimethyl-1H-benzo[d]imidazole-3-bromide.

2. The heteroporous fluorine-doped cationic covalent organic framework material according to claim 1, characterized in that: The molar ratio of tetrakis-(4-aminophenyl)ethylene to the side functional monomer is 1:

2.

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

6.

4. A method for preparing a heteroporous fluorine-doped cationic covalent organic framework material, characterized in that: The heteroporous fluorine-doped cationic covalent organic framework material as claimed in any one of claims 1 to 3 is prepared by Schiff base reaction of tetrakis-(4-aminophenyl)ethylene and side functional monomers.

5. The method for preparing a heteroporous fluorine-doped cationic covalent organic framework material according to claim 4, characterized in that: The following steps are included: S1, adding tetrakis-(4-aminophenyl)ethylene and side functional monomers into a glass tube, then adding o-dichlorobenzene / n-butanol solvent, and mixing by ultrasonic treatment; S2, adding a catalyst to the glass tube of S1 to obtain a reaction system, subjecting the reaction system to ultrasonic treatment, and then cyclically 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.

6. The method for preparing a heteroporous fluorine-doped cationic covalent organic framework material according to claim 5, 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.

7. The method for preparing a heteroporous fluorine-doped cationic covalent organic framework material according to claim 5, characterized in that: The catalyst in S2 is acetic acid, and the ultrasonic treatment time is 10 min.

8. The method for preparing a heteroporous fluorine-doped cationic covalent organic framework material according to claim 5, characterized in that: The cyclic degassing in S2 includes 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.

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

10. An application of a heteroporous fluorine-doped cationic covalent organic framework material, characterized in that: The heteroporous fluorine-doped cationic covalent organic framework material as described in any one of claims 1 to 3 is used for adsorbing perfluoro or polyfluoroalkyl substances.

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