Fluorine-functionalized cationic covalent organic framework adsorbents and preparation and use thereof

Abstract

The fluorine-functionalized cationic covalent organic framework adsorbent and its preparation and application belong to the field of environmental functional materials. The adsorbent is an iCOF containing fluorine side chains, which is prepared by post-modification of an imine group COF containing pyridine nitrogen with a fluorine-containing halogenated alkane. The surface charge, specific surface area and hydrophilic / hydrophobic property of the adsorbent are regulated by post-modification of fluorine-containing halogenated alkanes with different lengths. Under the synergistic effect of electrostatic interaction, pore filling effect, hydrophobic interaction and fluorine-fluorine interaction, the adsorbent exhibits excellent adsorption performance for perfluoro and multi-fluoro alkyl compounds (PFASs), and has the advantages of rapid adsorption and high adsorption capacity. The adsorbent has high adsorption efficiency for low-concentration perfluorooctanoic acid (PFOA) in different water qualities, and can be widely used for adsorption of various PFASs. Through the strategy of constructing multiple interaction synergies, the dependence on single interaction of traditional porous adsorbents is broken, and the efficient adsorption of water-soluble PFASs is realized, which has application prospects in the field of new pollutant removal.

Description

Technical Field

[0001] This invention relates to the field of environmental functional materials technology, and particularly to a series of functional covalent organic frameworks (COFs) materials and their applications, especially a series of fluorinated functionalized cationic covalent organic frameworks (iCOFs) adsorbents and their preparation and application in the adsorption of perfluorinated and polyfluoroalkyl compounds (PFASs). Background Technology

[0002] Covalent organic frameworks (COFs) are a class of long-range ordered, structurally tunable crystalline porous materials composed of organic units linked by covalent bonds. With their high specific surface area, well-ordered pore structure, excellent chemical stability, and structural designability, COFs show great promise in adsorption, catalysis, detection, energy storage, and sensing. Through molecular design, by selecting or synthesizing monomers with specific functional groups, the microstructure and surface properties of COFs can be precisely controlled. In adsorption applications, COFs can not only construct abundant hierarchical channels to facilitate mass transfer, but also, through the functional groups introduced on their surface, specifically interact with target pollutants, thereby achieving highly efficient adsorption and separation.

[0003] Per- and polyfluoroalkyl substances (PFASs) are a class of highly persistent fluorinated organic pollutants. Their molecules contain hydrophobic fluorocarbon chains and high-energy CF bonds, making them extremely difficult to degrade in the natural environment. With their widespread use in industrial and consumer sectors, PFASs have entered aquatic and soil environments through various pathways, posing a serious threat to ecosystems and human health. Conventions have already included several PFASs, such as perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA), in their persistent organic pollutant control lists. Therefore, developing technologies for the efficient removal of PFASs from the environment is urgently needed.

[0004] Among existing removal technologies, adsorption is widely studied due to its simplicity and low cost. However, traditional adsorbents (such as activated carbon) generally suffer from limited capacity, slow rate, and low selectivity in the adsorption of PFASs. Although various interactions, including electrostatic interactions, pore-filling effects, hydrophobic interactions, and fluorine-fluorine interactions, have been reported as effective modes of PFASs adsorption, conventional adsorbents struggle to systematically regulate these interactions, hindering the development of highly efficient PFASs adsorbents.

[0005] Based on this, by utilizing the designability of covalent organic frameworks, ionic covalent organic framework adsorbents with both hydrophobic properties and fluoroalkyl chains can be synthesized in a targeted manner. It is expected that, based on the intrinsic pore filling effect, they can specifically recognize and efficiently capture PFASs molecules through enhanced electrostatic interactions, hydrophobic interactions, and fluorine-fluorine interactions, providing a new solution for the development of next-generation high-performance PFASs adsorbent materials. Summary of the Invention

[0006] The purpose of this invention is to solve the above-mentioned problems in the prior art and to provide a series of fluorinated functionalized cationic covalent organic framework adsorbents, their preparation, and their application in the adsorption of perfluorinated and polyfluoroalkyl compounds.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A fluorinated functionalized cationic covalent organic framework adsorbent is described, wherein the adsorbent uses a pyridine nitrogen-containing imine-based covalent organic framework as its matrix, and fluorinated side chains are introduced by modification of the pyridine nitrogen sites of the matrix with fluorinated haloalkanes, with bromide ions as the counterion; the adsorbent has a porous structure and a BET specific surface area of ​​744.9–1200.7 m². 2 / g, with an average pore size of 2.00–2.12 nm; the structural formula of the adsorbent is as follows:

[0009]

[0010] Where R is -C2H4C X-2 F 2X-3 X = 4, 6, or 8.

[0011] The post-modification is carried out in an alkaline environment, the fluorinated haloalkane is an iodofluoroalkane, and the reaction product replaces the counterion with a bromide ion through ion exchange.

[0012] In the iodofluoroalkane, the two carbon atoms closest to the pyridine nitrogen atom do not contain fluorine atoms, while the remaining carbon atoms are all fluorine atoms.

[0013] The water contact angle of the adsorbent is 60.5°~80.6°.

[0014] The preparation method of the fluorinated functionalized cationic covalent organic framework adsorbent includes the following steps:

[0015] 1) 4,4',4'',4'''-(pyrene-1,3,6,8-tetramethyl)tetraphenylamine and (2,2'-bipyridine)-5,5'-dicarboxaldehyde were condensed in a mixed solvent of mesitylene and dioxane, with acetic acid as a catalyst, via a Schiff base reaction to obtain an imine-based covalent organic framework matrix containing pyridine nitrogen;

[0016] 2) The matrix obtained in step 1) is dispersed in acetonitrile, iodofluoroalkanes and basic substances are added, and the reaction is carried out at 160-180℃ for 2-4 days to obtain fluorinated covalent organic frameworks containing iodide counterions.

[0017] 3) Mix the product obtained in step 2) with a saturated potassium bromide solution, shake to perform ion exchange, and replace the counterion with iodide ions to bromide ions. Wash and dry to obtain the fluorinated functionalized cationic covalent organic framework adsorbent.

[0018] Application of the fluorinated functionalized cationic covalent organic framework adsorbent in the adsorption of perfluorinated and polyfluoroalkyl compounds.

[0019] The perfluorinated and polyfluoroalkyl compounds are selected from any one or more of the following: perfluorohexanoic acid (PFHxA), perfluorooctanoic acid (PFOA), perfluorotetradecanoic acid (PFTeDA), perfluoro-1-butanesulfonic acid (PFBS), perfluorooctanesulfonic acid (PFOS), perfluorobutyric acid (PFBA), and hexafluoropropylene oxide dimer acid (GenX).

[0020] The adsorption process is carried out in pure water, seawater, lake water, groundwater, sewage, or water containing 6% aqueous film-forming foam extinguishing agent.

[0021] The initial concentration of the perfluorinated and polyfluoroalkyl compounds is from 1 ppb to 1000 ppm; the pseudo-second-order adsorption kinetic constant K2 of the adsorbent for PFOA is 0.137 to 0.180 g / (mg·min), and the maximum adsorption capacity of Langmuir is 2963.3 to 3594.5 mg / g.

[0022] Compared with the prior art, the beneficial effects achieved by the technical solution of this invention are:

[0023] 1. iCOF-XF has a rich pore structure, which is beneficial to accelerate the adsorption rate of PFOA. Its adsorption kinetic constant is significantly better than that of many existing adsorption materials.

[0024] 2. iCOF-XF utilizes multiple mechanisms such as pore filling effect, electrostatic interaction, hydrophobic interaction and fluorine-fluorine interaction during the adsorption process, which can efficiently adsorb PFOA and has a significantly higher adsorption capacity than other comparative adsorbents.

[0025] 3. iCOF-XF exhibits excellent performance in the adsorption of broad-spectrum PFASs and is suitable for the adsorption and removal of different types of PFASs. Attached Figure Description

[0026] Figure 1 PXRD pattern of iCOF-XF, a fluorine-functionalized cationic covalent organic framework adsorbent.

[0027] Figure 2 The FT-IR spectrum of the fluorine-functionalized cationic covalent organic framework adsorbent iCOF-XF.

[0028] Figure 3Nitrogen adsorption-desorption curves of iCOF-XF, a fluorine-functionalized cationic covalent organic framework adsorbent.

[0029] Figure 4 Pore ​​size distribution diagram of iCOF-XF, a fluorine-functionalized cationic covalent organic framework adsorbent.

[0030] Figure 5 Water contact angle and photograph of iCOF-XF, a fluorine-functionalized cationic covalent organic framework adsorbent.

[0031] Figure 6 The adsorption kinetics curves of PFOA by iCOF-XF, a fluorine-functionalized cationic covalent organic framework adsorbent.

[0032] Figure 7 The adsorption isotherm of PFOA for iCOF-XF, a fluorine-functionalized cationic covalent organic framework adsorbent.

[0033] Figure 8 The graph shows the removal efficiency of the fluorinated functionalized cationic covalent organic framework adsorbent iCOF-XF for broad-spectrum PFASs. Detailed Implementation

[0034] To make the technical problems, technical solutions and beneficial effects of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. However, the scope of protection of the present invention is not limited to the following embodiments.

[0035] The preparation of the fluorinated functionalized cationic covalent organic framework adsorbent iCOF-XF of this invention includes three steps:

[0036] First, a covalent organic framework matrix PY-BPY-COF containing pyridine nitrogen and imine group is synthesized via Schiff base reaction. Then, a fluorinated iodoalkane is subjected to a post-modification reaction with the matrix under alkaline conditions to obtain an intermediate iCOF-XF-I containing an iodine counterion. Finally, the counterion is replaced with bromide ions through bromide ion exchange to obtain the target adsorbent iCOF-XF.

[0037] The iCOF-XF series of adsorbents is prepared by introducing fluorinated iodoalkanes of different lengths into PY-BPY-COF, followed by bromide ion exchange, as shown in the following reaction formula:

[0038]

[0039] PY-BPY-COF iCOF-XF-I iCOF-XF

[0040] Where R is -C2H4C X-2 F 2X-3X represents the number of carbon atoms in the fluorine side chain, X=4, 6 or 8, corresponding to iCOF-4F, iCOF-6F and iCOF-8F respectively.

[0041] Preparation Example 1: Synthesis of Covalent Organic Framework Matrix PY-BPY-COF

[0042] First, the pyridine nitrogen-containing imine-based covalent organic framework matrix PY-BPY-COF (hereinafter referred to as the parent COF) was synthesized via Schiff base reaction. 113.0 mg of 4,4',4'',4'''-(pyrene-1,3,6,8-tetramethyl)tetraphenylamine (PY), 85 mg of (2,2'-bipyridine)-5,5'-dicarboxaldehyde (BPY), and 10 mL of a 1:1 mixture of mesitylene and dioxane solvent were added to a Schlenk tube. After sonication for 5 min and homogenization, 1 mL of 6 M acetic acid was added. The reaction system was then placed in liquid nitrogen for freezing while simultaneously evacuating the system under vacuum. After 5 min, the system was thawed. This freezing-vacuum-thawing cycle was repeated three times to remove oxygen from the system. The reaction tube was then sealed and the reaction was carried out at 120 °C for 3 days. After the reaction was completed, the product was extracted with tetrahydrofuran by Soxhlet for 12 h, washed three times with ethanol, and then collected by filtration. The product was dried under vacuum at 60 °C for 12 h to obtain an orange-yellow solid PY-BPY-COF with a yield of 86.3%.

[0043] Preparation Example 2: Synthesis of fluorine-functionalized covalent organic framework iCOF-XF-I containing iodide counterion

[0044] Taking iCOF-4F as an example: 50 mg of PY-BPY-COF was dispersed in 4 mL of acetonitrile, 1 mL of 1,1,1,2,2-pentafluoro-4-iodobutane and 2 mg of sodium bicarbonate were added, and the mixture was reacted in a hydrothermal reactor at 170 °C for 3 days. The product was extracted with tetrahydrofuran by Soxhlet for 12 h, washed three times with ethanol, and then collected by filtration. The product was dried at 60 °C for 12 h to obtain a brown solid iCOF-4F-I.

[0045] iCOF-6F-I and iCOF-8F-I were prepared according to the above method, the difference being that 1,1,1,2,2,3,3,4,4-nonafluoro-6-iodohexane and 1,1,1,2,2,3,3,4,4,5,5,6,6-tetrazofluoro-8-iodooctane were used instead of 1,1,1,2,2-pentafluoro-4-iodobutane, respectively, while the other conditions were the same.

[0046] Preparation Example 3: Synthesis of iCOF-XF, a fluorine-functionalized cationic covalent organic framework adsorbent

[0047] Under a nitrogen atmosphere, 50 mg of iCOF-XF-I and 20 mL of saturated potassium bromide solution were added to a Schlenk tube, and the reaction was carried out with shaking at room temperature for 12 h. The product was collected by filtration, and a fresh 20 mL of saturated potassium bromide solution was added again under a nitrogen atmosphere, and shaking was continued for another 12 h. After replacing the potassium bromide three times, the product was collected by filtration, washed three times with 50 mL of methanol, then three times with 50 mL of ultrapure water, and then washed with ultrapure water until no obvious precipitate was formed when 0.1 M dilute silver nitrate solution was added to the eluent. The product was dried under vacuum at 60 °C for 12 h to obtain a brown solid iCOF-XF.

[0048] Figure 1 The X-ray diffraction (PXRD) pattern of the iCOF-XF adsorbent is presented, and the crystallinity and periodic pore structure of the material are verified by the characteristic diffraction peaks. The figure shows sharp diffraction peaks of iCOF-XF at 2θ = ~5°, ~8°, and ~25°, corresponding to the (110), (200), and (001) crystal planes, indicating that it has a highly ordered two-dimensional layered stacking structure. The PXRD patterns of the functionalized (iCOF-4F / 6F / 8F) adsorbents show no significant peak shift compared to the parent COF, indicating that the side-chain modification did not destroy the crystal framework. However, the intensity of some peaks is slightly reduced, which may be related to the steric hindrance effect of the fluoroalkyl groups. This result provides crucial evidence for the structural stability of the material.

[0049] Figure 2 FT-IR spectra of the fluorine-functionalized cationic covalent organic framework adsorbent iCOF-XF. All samples were analyzed at 1627 cm⁻¹. -1 Strong characteristic peaks appeared at all locations, corresponding to the C = N stretching vibration, indicating the successful formation of imine bonds; simultaneously, the N–H and C = O characteristic peaks in the monomer disappeared, further confirming the formation of imine bonds. For fluorinated functionalized samples, at 1130 cm⁻¹... -1 and 1204 cm -1 C–F stretching vibration peaks appear at [location], and pyridine ring vibrations (1545, 1348 cm⁻¹) are also observed. -1 ) shifts to lower wavenumbers, at 2925 cm -1 The presence of methylene C–H stretching vibrations indicates that the fluorinated side chains have been successfully grafted onto the material.

[0050] Figure 3 Nitrogen adsorption-desorption curves of iCOF-XF, a fluorine-functionalized cationic covalent organic framework adsorbent, are shown. The results indicate that both the parent COF and iCOF-XF exhibit mesoporous characteristics. Calculations based on the BET model show that the specific surface area of ​​the parent COF is as high as 2070.7 m². 2 g -1Although the specific surface area decreased after functionalization due to the steric hindrance of the side chains, all iCOF-XF still maintained a high specific surface area, which fully demonstrates that the post-modification process did not destroy the porous structure of the material.

[0051] Figure 4 This is a pore size distribution diagram of the fluorine-functionalized cationic covalent organic framework adsorbent iCOF-XF. Analysis using the BJH model reveals a concentrated mesoporous pore size distribution. While the pore sizes of the parent COF and iCOF-XF are slightly reduced after functionalization, an ordered mesoporous environment is still maintained. This ordered mesoporous structure is beneficial for mass transfer of PFAS molecules and the occurrence of pore-filling effects.

[0052] Figure 5 The water contact angle test results and photographs of the fluorinated functionalized cationic covalent organic framework adsorbent iCOF-XF are presented. The tests show that the water contact angle of iCOF-XF ranges from 60.5° to 80.6°, and gradually increases with the growth of the fluorinated side chains. This indicates that the material has moderate surface hydrophobicity, and the fluorinated modification enhances the interfacial properties. The photographs visually demonstrate the solid-state morphology and wetting behavior of the sample, further supporting the material's suitability as a PFAS adsorbent in water.

[0053] Application Example 1: Adsorption performance of iCOF-XF on PFOA.

[0054] 1. Adsorption kinetics test: 10 mg of iCOF-XF sample was weighed and dispersed in 100 mL of 100 ppm PFOA standard solution. After thorough shaking and adsorption for different times at 25℃, the solution was collected for liquid chromatography-mass spectrometry (LC-MS) to determine the PFOA concentration. Adsorption kinetic curves of iCOF-XF to PFOA were plotted based on the adsorption amount and time at different times (see figure). Figure 6 The figure shows the change in the adsorption capacity of iCOF-XF for PFOA over time at different time points. By fitting these data, the corresponding adsorption kinetic parameters can be obtained, thus providing a deeper understanding of the adsorption rate and mechanism of PFOA by the material. The adsorption kinetic constants of iCOF-XF for PFOA at room temperature were obtained through fitting, and the specific data are shown in Table 1. The comparison results of the adsorption kinetic constants of iCOF-XF and other related adsorbents for PFOA are shown in Table 2.

[0055] Therefore, in terms of adsorption performance, iCOF-XF exhibits excellent adsorption rate and adsorption capacity for PFOA. At room temperature, the adsorption kinetic constant K2 of iCOF-XF for PFOA is 0.137~0.180 g / (mg×min).

[0056] Table 1 Kinetic fitting parameters of iCOF-XF adsorption process for PFOA

[0057]

[0058] Table 2 Comparison of adsorption kinetic fitting parameters for PFOA by reported adsorbents and iCOF-XF of the present invention

[0059]

[0060] 2. Adsorption isotherm test: Weigh 10 mg of iCOF-XF sample and disperse it in 100 mL of PFOA standard solution with a concentration of 50-1000 ppm. After adsorption by shaking for 12 h at 25℃, take the solution and test its PFOA concentration. Plot the adsorption isotherm of iCOF-XF for PFOA based on the equilibrium adsorption capacity and equilibrium concentration. Figure 7 The adsorption isotherm describes the relationship between the adsorption capacity and the PFOA concentration in the solution when adsorption reaches equilibrium at a certain temperature. Analysis of the adsorption isotherm yields important parameters such as the maximum adsorption capacity, providing a basis for evaluating the material's adsorption capacity for PFOA. The maximum adsorption capacity was found to be 2963.3–3594.5 mg / g, as shown in Table 3. This value is significantly higher than that of other common adsorbents, as shown in Table 4.

[0061] Table 3 shows the fitting results of the adsorption isotherms of PFOA by iCOF-XF.

[0062]

[0063] Table 4 Comparison of the reported adsorption capacities of adsorbents and iCOF-XF for PFOA

[0064]

[0065] 3. Adsorption performance test of low-concentration broad-spectrum PFASs in different water environments: 10 mg of iCOF-XF sample was weighed and dispersed in 100 mL of PFOA, PFTeDA, PFBS, PFOS, PFBA, and GenX solutions with a concentration of 1 ppb in different water environments (pure water, seawater, lake water, groundwater, sewage, and 6% AFFF). After adsorption by shaking at 25℃ for 12 h, the concentration of each PFASs was measured. The adsorption and removal efficiency of iCOF-XF for different types of PFASs in different water environments was calculated. The results are shown in [Figure number missing]. Figure 8 The results directly reflect the removal efficiency of the adsorbent for different types of PFASs, demonstrating the material's application potential in removing broad-spectrum PFASs. The results show that iCOF-XF exhibits high removal rates for low concentrations of broad-spectrum PFASs in various aquatic environments.

[0066] The above embodiments illustrate that the adsorbent developed in this invention has significant advantages in adsorbing PFASs, especially PFOA, and exhibits good performance, particularly in the adsorption of PFOA in low-concentration water environments. It also shows good performance in adsorbing broad-spectrum PFASs.

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[0089] It should be noted that the above description is only a preferred embodiment of the present invention. Any covalent organic framework materials prepared using other similar chain segments based on the technical solution of the present invention should be considered to fall within the protection scope of the present invention.

Claims

1. A fluorine-functionalized cationic covalent organic framework adsorbent, characterized in that: The adsorbent uses a pyridine nitrogen-containing imine covalent organic framework as its matrix. Fluorine-containing side chains are introduced by modifying the pyridine nitrogen sites of the matrix with fluorinated haloalkanes, and bromide ions are used as the counterion. The adsorbent has a porous structure with a BET specific surface area of ​​744.9–1200.7 m². 2 / g, with an average pore size of 2.00–2.12 nm; the structural formula of the adsorbent is as follows: Where R is -C2H4C X-2 F 2X-3 X = 4, 6, or 8.

2. The fluorinated functionalized cationic covalent organic framework adsorbent as described in claim 1, characterized in that: The post-modification is carried out in an alkaline environment, the fluorinated haloalkane is an iodofluoroalkane, and the reaction product replaces the counterion with a bromide ion through ion exchange.

3. The fluorinated functionalized cationic covalent organic framework adsorbent as described in claim 2, characterized in that: In the iodofluoroalkane, the two carbon atoms closest to the pyridine nitrogen atom do not contain fluorine atoms, while the remaining carbon atoms are all fluorine atoms.

4. The fluorinated functionalized cationic covalent organic framework adsorbent as described in claim 1, characterized in that: The water contact angle of the adsorbent is 60.5°~80.6°.

5. A method for preparing a fluorinated functionalized cationic covalent organic framework adsorbent as described in any one of claims 1 to 4, characterized in that, Includes the following steps: 1) 4,4',4'',4'''-(pyrene-1,3,6,8-tetramethyl)tetraphenylamine and (2,2'-bipyridine)-5,5'-dicarboxaldehyde were condensed in a mixed solvent of mesitylene and dioxane, with acetic acid as a catalyst, via a Schiff base reaction to obtain an imine-based covalent organic framework matrix containing pyridine nitrogen; 2) The matrix obtained in step 1) is dispersed in acetonitrile, iodofluoroalkanes and basic substances are added, and the reaction is carried out at 160-180℃ for 2-4 days to obtain fluorinated covalent organic frameworks containing iodide counterions. 3) Mix the product obtained in step 2) with a saturated potassium bromide solution, shake to perform ion exchange, and replace the counterion with iodide ions to bromide ions. Wash and dry to obtain the fluorinated functionalized cationic covalent organic framework adsorbent.

6. The application of the fluorinated functionalized cationic covalent organic framework adsorbent according to any one of claims 1 to 4 or the fluorinated functionalized cationic covalent organic framework adsorbent prepared by the preparation method according to claim 5 in the adsorption of perfluorinated and polyfluoroalkyl compounds.

7. The application as described in claim 6, characterized in that, The perfluorinated and polyfluoroalkyl compounds are selected from any one or more of the following: perfluorohexanoic acid, perfluorooctanoic acid, perfluorotetradecanoic acid, perfluoro-1-butanesulfonic acid, perfluorooctanesulfonic acid, perfluorobutyric acid, and hexafluoropropylene oxide dimer acid.

8. The application as described in claim 6, characterized in that: The adsorption process is carried out in pure water, seawater, lake water, groundwater, sewage, or water containing 6% aqueous film-forming foam extinguishing agent.

9. The application as described in claim 6, characterized in that: The initial concentration of the perfluorinated and polyfluoroalkyl compounds is from 1 ppb to 1000 ppm; the pseudo-second-order adsorption kinetic constant K2 of the adsorbent for perfluorooctanoic acid is 0.137 to 0.180 g / (mg·min), and the maximum adsorption capacity of Langmuir is 2963.3 to 3594.5 mg / g.

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