Pillararene-grafted covalent organic framework in-situ polymerization nanochannel membrane and application thereof

Abstract

The application provides a columnar aromatic grafting covalent organic framework in-situ polymerization nanochannel membrane and application thereof, and relates to the fields of water environment monitoring, covalent organic framework membrane functionalization and electrochemical sensing detection. The application takes a polyethylene terephthalate straight nanochannel membrane as a substrate, carries out benzidine modification through activation, in-situ polymerizes benzidine, 4,4'-diamino diphenyl-2,2'-dicarboxylic acid and tri-aldehyde phloroglucinol to form a COF three-dimensional network in the nanochannel, and then carries out amidation reaction to covalently graft amino columnar [5] aromatic on the surface of the COF membrane, so as to construct a nanochannel-COF nanopore-columnar aromatic sub-nanomolecular pore three-level structure synergistic membrane sensing system. The membrane uses columnar aromatic limited inclusion to provide specific recognition sites for perfluoro and polyfluoro alkyl substances, and combines with the electrochemical limited effect of the nanochannel to realize signal three-level amplification, so that pg / L level high-sensitivity detection of perfluoro and polyfluoro alkyl substances, especially perfluorooctanoic acid, in water can be realized.

Description

Technical Field

[0001] This invention relates to the fields of water environment monitoring, functionalization of covalent organic framework membranes and electrochemical sensing, and more specifically to a columnar aromatic hydrocarbon-grafted covalent organic framework in-situ polymerized nanochannel membrane and its applications. Background Technology

[0002] Perfluorinated and polyfluorinated alkyl substances (PFAS), due to their extremely strong carbon-fluorine bond structure, are persistent, bioaccumulative, and toxic, and are known as "permanent chemicals." They are widely present in the aquatic environment and pose a serious threat to aquatic ecosystems and human health. As the core water source area of ​​the South-to-North Water Diversion Project, the Danjiangkou Reservoir area currently lacks monitoring coverage for emerging persistent organic pollutants such as PFAS. Therefore, accurate monitoring of PFAS levels in the reservoir area is crucial for ensuring water quality safety.

[0003] Among existing PFAS detection technologies, liquid chromatography-mass spectrometry is the "gold standard," but it has drawbacks such as expensive equipment, complex pretreatment, and inability to conduct rapid on-site screening. Fluorescence spectroscopy is susceptible to matrix interference, and traditional electrochemical sensors have detection limits in the ng / L range, which is insufficient to meet the needs of trace detection.

[0004] Covalent organic framework (COF) membranes possess highly ordered pores, large specific surface area, and excellent stability, making them suitable for constructing sensing platforms. Columnar aromatic hydrocarbons, as a new generation of supramolecular hosts, have rigid columnar cavities and host-guest selective recognition capabilities, enabling them to specifically bind PFAS molecules. Combining columnar aromatic hydrocarbons with in-situ COF membranes to construct a three-level structure synergistic sensing system can overcome the bottlenecks of low detection sensitivity and severe matrix interference in existing methods, achieving ultrasensitive detection of PFAS. Summary of the Invention

[0005] In view of this, the present invention addresses the problems of insufficient trace sensitivity and severe interference from complex matrices in existing PFAS detection technologies by providing a method for preparing and applying a columnar aromatic hydrocarbon-grafted COF in-situ polymerized nanochannel membrane for highly sensitive detection and identification of PFAS. By constructing a three-level synergistic structure of "nanochannel-COF nanopore-column aromatic hydrocarbon sub-nano molecular pore", highly sensitive and selective detection of PFAS at the pg / L level is achieved.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A columnar aromatics-grafted covalent organic framework (COF) in-situ polymerized nanochannel membrane is based on polyethylene terephthalate (PET) straight nanochannel membrane. An imine-type COF three-dimensional network is grown in-situ within the nanochannel. Amino columnar aromatics are covalently grafted onto the surface of the COF three-dimensional network via amide bonds [5] to form a three-level pore structure of "nanochannel-COF nanopore-column aromatics sub-nano molecular pore". The membrane has specific recognition and electrochemical signal amplification capabilities for perfluorinated and polyfluoroalkyl substances (PFAS), and can achieve high sensitivity detection at the pg / L level.

[0007] Preferably, the COF three-dimensional network is generated by in-situ polymerization of benzidine (BD), 4,4'-diaminobiphenyl-2,2'-dicarboxylic acid (DCBD) and trialdehyde phloroglucinol (TP) in nanochannels via a Schiff base reaction, and the contained carboxyl active sites are used for subsequent grafting.

[0008] Preferably, the amino column[5] aromatic hydrocarbon is activated by 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide (EDC) and N-hydroxysuccinimide (NHS) to form amide bonds with the carboxyl groups on the COF three-dimensional network and is covalently fixed, taking p-aminobenzoic acid column[5] aromatic hydrocarbon as an example.

[0009] Another object of the present invention is to provide a method for preparing the above-mentioned columnar aromatic hydrocarbon-grafted COF in-situ polymerized nanochannel membrane, comprising the following steps: (1) Preparation of PET straight nanochannel membrane: PET membrane was subjected to ultraviolet irradiation and acid-base etching to obtain uniform straight nanochannels, and then soaked in deionized water for later use; (2) In-situ polymerization of COF: The nanochannel membrane was activated by EDC / NHS and modified with benzidine and then fixed in a U-shaped groove. BD, DCBD and PTSA aqueous solution were added to the positive electrode side and TP solution was added to the negative electrode side. The reaction was carried out at 1 V DC voltage and 60℃ for 12~48 h to generate carboxylated COF membrane in-situ polymerization in the nanochannel. (3) Amino column[5] aromatic grafting: The COF membrane was activated again by EDC / NHS and then immersed in an amino column[5] aromatic solution for 1~12 h at room temperature for covalent modification to obtain an in-situ polymerized COF nanochannel membrane with column aromatic grafting. (4) Clean, dry and store.

[0010] Preferably, in step (2), the solvent of the TP solution is DMF:H2O = 1~3:9~7 (volume ratio); the concentrations of BD, DCBD and TP are all 1~100 micromoles, and the reaction is carried out at a constant temperature with the addition of solvent.

[0011] Preferably, in step (3), the concentration of the amino column[5] aromatic solution is 1~10 mmol / L, and the solvent is a polar aprotic solvent.

[0012] Specifically, the above preparation method includes: (1) Preparation of straight nanochannel membranes: A porous polyethylene terephthalate (PET) membrane was placed under a UV lamp, with both the front and back sides irradiated for 1 hour each. After irradiation, it was placed in a dark environment for 12 hours. The irradiated PET membrane was then fixed in an electrolytic cell. A 9 mol / L NaOH etching solution was added to one end of the cell, and a 1 mol / L KCl and HCOOH mixed inhibitor solution was added to the other end. After removing air bubbles, etching was performed at 35°C. When the picoammeter reading reached 5 × 10⁻⁶, the etching was completed. -6 At step A, the etching solution was replaced with 2 mol / L NaOH, and etching continued until the current reached 5 × 10⁻⁶. -5 A; After etching, drain the liquid from the electrolytic cell, add blocking liquid to both ends, first use DC current to scan the field for 15 min, then use AC current to scan the field for 5 min; repeatedly wash the membrane with deionized water 3 times, add deionized water to both ends again after washing, repeat DC current scanning for 15 min and AC current scanning for 5 min; finally, completely immerse the etched PET membrane in deionized water for 12 h to complete the standard well and obtain a straight nanochannel PET membrane. In step (1), the UV irradiation time determines the latent track density and uniformity. Insufficient irradiation will lead to uneven etching channels. The etching temperature is 35℃. If the temperature is too low, the etching rate will be slow. If the temperature is too high, the channel aperture will be too large and the morphology will be damaged. Step-by-step etching can precisely control the aperture. The current threshold is the key parameter for aperture control. Alternating electro-etching can remove impurities in the channel and improve the stability of ion transport. Soaking in deionized water for 12 h can make the film fully swell and stabilize the channel structure.

[0013] (2) In-situ polymerization of covalent organic framework membranes: The straight nanochannel PET membrane prepared in step (1) was immersed in a mixture of 48 mmol / L EDC and 13 mmol / L NHS activator at room temperature for 1 h. After removal, the surface residual reagent was rinsed with deionized water and then immersed in 1 mmol / L benzidine solution and allowed to stand at room temperature overnight. The membrane after reaction was removed and rinsed with deionized water and fixed in a U-shaped mold. An aqueous solution containing 2~8 μmol / L benzidine, 1~4 μmol / L 4,4'-diaminobiphenyl-2,2'-dicarboxylic acid and 20~80 μmol / L p-toluenesulfonic acid was added to the positive electrode side of the U-shaped mold, and a mixed solution of 2~8 μmol / L trialdehyde phloroglucinol DMF and H2O was added to the negative electrode side, wherein the volume ratio of DMF to water was 1~3:9~7. A DC voltage of 1 V was applied and the reaction was continued at a constant temperature of 60 ℃ for 12~48 h. h, the above reaction solution is replenished to both ends of the membrane at regular intervals during the reaction; after the reaction is completed, the membrane surface is rinsed with deionized water to obtain COF-filled nanochannels; In step (2), an activation time of 1 h ensures that the carboxyl groups are fully activated, while an excessively long time can lead to over-modification of the membrane surface; overnight modification with benzidine can achieve uniform grafting of the monolayer, providing anchoring sites for COF growth; a DC voltage of 1 V can drive the directional migration of monomers, while an excessively high voltage will damage the membrane structure; a reaction temperature of 60 °C is the optimal Schiff base reaction temperature, while a temperature that is too low will result in incomplete reaction, and a temperature that is too high will lead to solvent evaporation and monomer decomposition, thus ensuring that COF grows fully in the nanochannels and forms a continuous three-dimensional network.

[0014] (3) Synthesis of amino-column[5] aromatics: In a 250 mL three-necked flask in anhydrous and oxygen-free environment, 3.24 g of 1,4-di-(2-bromoethyl)benzene and 0.9 g of paraformaldehyde were added. The air in the flask was removed, and 150 mL of 1,2-dichloroethane was injected into the flask. The mixture was stirred for 5 min until the solid was completely dissolved. 3.0 mL of boron trifluoride diethyl ether complex was added as a catalyst. The reaction temperature was controlled at 30 °C. The reaction was tracked by TLC. The developing solvent was petroleum ether:dichloromethane = 1:1. After the raw materials were completely reacted, 20 mL of methanol was added to terminate the reaction. The solvent was removed by rotary evaporation. The filter cake was washed with dichloromethane after filtration. The filtrates were combined and washed twice with saturated saline solution, twice with 5% NaHCO3 solution, and twice with saturated saline solution. The organic phase was dried with anhydrous sodium sulfate and the solvent was removed under reduced pressure. The crude product was separated and purified by silica gel column chromatography. The eluent was petroleum ether:dichloromethane = 2:1. White brominated aromatic powder was obtained. [5] 500 mg of bromine[5] aromatic hydrocarbon, 2064.1 mg of Boc-p-aminobenzoic acid, and 732 mg of NaHCO3 were added to 100 mL of DMSO. The mixture was reacted under nitrogen protection at 50 °C for 12 h. After the reaction was complete, 100 mL of deionized water was added and the mixture was extracted three times with 50 mL of ethyl acetate each time. The organic phase was washed three times with saturated NaHCO3 solution and once with saturated brine. The phase was dried over anhydrous Na2SO4 for 1 h and the solvent was removed by rotary evaporation. A small amount of ethyl acetate was added to dissolve the residue. 60 mL of petroleum ether was slowly added for recrystallization. The mixture was then filtered and dried to obtain the Boc protected intermediate. Take 400-500 mg of intermediate and add it to 25 mL of a mixture of dichloromethane and trifluoroacetic acid = 4:1. Stir overnight at room temperature under nitrogen protection. After the reaction is complete, remove the solvent by rotary evaporation, add a small amount of methanol to dissolve the residue, add 40 mL of dichloroethane, let stand for 12 h, pour out the solution, and dry under vacuum to obtain amino columnar aromatics [5]. In step (3), the synthesis of bromo-column [5] aromatics requires strict anhydrous and oxygen-free conditions to avoid side reactions; a reaction temperature of 30°C can ensure a stable reaction, while excessively high temperatures can easily produce polymers; the deprotection of Boc uses a mixture of dichloromethane and trifluoroacetic acid in a volume ratio of 4:1, and room temperature reaction can efficiently remove the protecting group without damaging the molecular skeleton; recrystallization can improve the purity of the product and ensure the efficiency of subsequent grafting reactions.

[0015] (4) Preparation of column aromatics-grafted COF membranes The COF-filled nanochannel membrane prepared in step (2) was placed in a mixture of 48 mmol / L EDC and 13 mmol / L NHS activator and soaked at room temperature for 1 h. After taking it out, it was rinsed with deionized water and immersed in 1~10 mmol / L p-amino columnar aromatic solution [5] and allowed to stand at room temperature overnight. After the reaction was completed, the membrane surface was rinsed alternately with deionized water and ethanol and air-dried naturally to obtain columnar aromatic grafted COF in situ polymerized nanochannel membrane.

[0016] In step (4), secondary activation can ensure that the carboxyl groups on the COF membrane react fully and improve the grafting rate of column aromatics; for amino columns [5], the concentration of aromatics is 1~10 mmol / L to achieve uniform grafting. If the concentration is too high, physical adsorption will easily occur, affecting the detection selectivity; overnight reaction can ensure that the amidation reaction is complete and enhance the stability of the membrane.

[0017] Another objective of this invention is to provide the application of the above-mentioned columnar aromatic hydrocarbon-grafted COF in-situ polymerized nanochannel membrane in the highly sensitive detection of PFAS, for the electrochemical sensing detection of trace PFAS in water, using IV curves and current responses as signal outputs to achieve pg / L-level quantitative and qualitative identification.

[0018] Preferably, the PFAS includes perfluorooctane sulfonic acid (PFOS) and short-chain perfluoroalkyl carboxylic acids; wherein the detection limit for PFOA is ≤130 pg / L, and the linear range covers ng / L~μg / L.

[0019] Preferably, the detection system uses 0.1 mol / L KCl as the electrolyte and a scanning voltage of -2 to 2 V to achieve convenient in-situ detection through changes in ion current.

[0020] As can be seen from the above technical solution, compared with the prior art, the present invention has the following technical effects: The membrane prepared by this invention is used for highly sensitive detection and identification of perfluorinated and polyfluoroalkyl substances (PFAS) in water. The core target for detection is perfluorooctanoic acid (PFOA). The detection system uses 0.1 mol / L KCl as electrolyte and employs the IV current testing method to achieve quantitative detection of PFAS by means of changes in ion current within the membrane channel. The membrane has a detection limit of 124.39 pg / L for PFOA and exhibits superior selectivity compared to other perfluorinated compounds. It can be used for in-situ, rapid, and ultrasensitive monitoring of PFAS in complex water bodies such as tributaries of the Danjiangkou Reservoir. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0022] Figure 1 Schematic diagram of the functionalization process of nanochannel membranes; Figure 2 p-Amino column[5] aromatic synthesis route; Figure 3 1H NMR spectrum of amino-column[5] aromatics; Figure 4 Carbon NMR spectra of amino-column[5] aromatics; Figure 5 Mass spectrum of amino-column[5] aromatic hydrocarbons; Figure 6 Planar SEM images of bare membrane, COF in-situ polymerized membrane, and columnar aromatic grafted COF membrane; Figure 7 SEM images of the cross-sections of bare membrane, COF in-situ polymerized membrane, and columnar aromatic grafted COF membrane; Figure 8 Elemental distribution of bare membrane and columnar aromatic grafted COF membrane; Figure 9 IV curves of nanochannels at different modification stages; Figure 10 Infrared characterization images of films at different modification stages; Figure 11 Contact angle diagrams of membranes at different modification stages; Figure 12 Selectivity of columnar aromatic hydrocarbon-grafted COF membranes for perfluorinated compounds; Figure 13 Performance test results of columnar aromatic hydrocarbon-grafted COF membrane on PFOA; Figure 14 UV titration curves of amino column[5] aromatic hydrocarbons with different perfluorocarboxylic acids. Detailed Implementation

[0023] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] Performance test calculation formula 1. Formula for calculating standard error:

[0025] In the formula: S — standard error; Cᵢ — measured concentration; C — average concentration; n — number of tests.

[0026] 2. Formula for calculating the detection limit:

[0027] Where: LOD — detection limit; S 截距 — Standard deviation of the standard curve intercept; S 斜率 — Slope of the standard curve.

[0028] 3. Ion current test: Using 0.1 mol / L KCl as the electrolyte, the IV curve was tested with a picoammeter in the voltage range of -2 ~ 2 V, and the current change was recorded.

[0029] The materials and reagents used in each of the embodiments 1 to 6 of this invention are as follows: polyethylene terephthalate (PET) porous membrane, formic acid, potassium chloride, sodium hydroxide, hydrochloric acid, NaHCO3, sodium chloride, 1-(3-diaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC), N-hydroxysuccinimide (NHS), p-aminobenzoic acid, dimethyl sulfoxide (DMSO), perfluorooctanoic acid (PFOA), trifluoroacetic acid, benzidine (BD), 4,4'-diaminobiphenyl-2,2'-dicarboxylic acid (DCBD), p-toluenesulfonic acid (PTSA), trialdehyde phloroglucinol (TP), N,N-dimethylformamide (DMF), ethyl acetate, dichloromethane, 1,4-di-(2-bromoethyl)benzene, paraformaldehyde, boron trifluoride diethyl ether complex, and Boc-p-aminobenzoic acid. Preparation of bare straight nanochannel PET membranes

[0030] 1. Place the PET porous membrane under a UV lamp, irradiating the front and back sides for 1 hour each, and then place it in the dark for 12 hours.

[0031] 2. Fix the membrane in the electrolytic cell, add 9 mol / L NaOH etching solution to one end and 1 mol / L KCl + HCOOH inhibitor solution to the other end, and etch at 35 ℃.

[0032] 3. When the current reaches 5×10 -6 At step A, the etching solution was replaced with 2 mol / L NaOH, and etching continued until the current reached 5 × 10⁻⁶. -5 A.

[0033] 4. Discard the liquid, add stop liquid to both ends, and perform DC field sweeping for 15 minutes → AC field sweeping for 5 minutes.

[0034] 5. Rinse three times with deionized water, add water again, and perform DC field sweeping for 15 minutes and AC field sweeping for 5 minutes.

[0035] 6. Immerse the membrane in deionized water for 12 h to obtain a bare straight nanochannel PET membrane. Preparation of benzidine-modified nanochannel membranes

[0036] The remaining steps are the same as in Example 1, except for the following additional steps: 1. Take the bare membrane from Example 1 and immerse it in a mixture of 48 mmol / L EDC + 13 mmol / L NHS for 1 hour at room temperature.

[0037] 2. Rinse thoroughly with deionized water, immerse in 1 mmol / L benzidine solution, and allow to stand at room temperature for 12 h.

[0038] 3. Remove the membrane and rinse the surface with deionized water to obtain a benzidine-modified nanochannel membrane. Preparation of COF in-situ polymerized nanochannel membranes

[0039] The remaining steps are the same as in Example 2, except for the following additional steps: 1. Take the benzidine-modified film from Example 2 and fix it in a U-shaped groove mold.

[0040] 2. Add the following to the positive electrode side: 8 μmol / L benzidine + 4 μmol / L DCBD + 80 μmol / L p-toluenesulfonic acid aqueous solution.

[0041] 3. Add the following solution to the negative electrode side: a 1:9 mixture of DMF and H2O in the form of 8 μmol / L trialdehyde phloroglucinol.

[0042] 4. Apply a 1 V DC voltage and react at a constant temperature of 60 °C for 48 h, adding reaction solution periodically.

[0043] 5. After the reaction is complete, rinse thoroughly with deionized water to obtain a COF-filled nanochannel membrane. Preparation of amino-coated[5] aromatic-grafted COF membranes

[0044] The remaining steps are the same as in Examples 1, 2, and 3, only the grafting conditions are changed: 1. Take the COF membrane from Example 3 and immerse it in a mixture of 48 mmol / L EDC + 13 mmol / L NHS for 1 hour at room temperature.

[0045] 2. Wash with deionized water, immerse in 10 mmol / L of amino[5] aromatic solution, and react at room temperature for 12 h.

[0046] 3. Rinse with deionized water and ethanol three times alternately, and air dry naturally to obtain an amino-column[5] aromatic hydrocarbon grafted COF in situ polymerized nanochannel membrane. Preparation of amino-coated[5] aromatic-grafted COF membranes

[0047] The remaining steps are the same as in Examples 1, 2, and 3, only the grafting conditions are changed: 1. Take the COF membrane from Example 3 and immerse it in a mixture of 36 mmol / L EDC + 9.7 mmol / L NHS for 1 h at room temperature.

[0048] 2. Wash with deionized water, immerse in 5 mmol / L of p-amino[5] aromatic hydrocarbon solution, and react at room temperature for 6 h.

[0049] 3. Rinse with deionized water and ethanol three times alternately, and air dry naturally to obtain an amino-column[5] aromatic hydrocarbon grafted COF in situ polymerized nanochannel membrane. Preparation of amino-coated[5] aromatic-grafted COF membranes

[0050] The remaining steps are the same as in Examples 1, 2, and 3, only the grafting conditions are changed: 1. Take the COF membrane from Example 3 and immerse it in a mixture of 24 mmol / L EDC + 6.5 mmol / L NHS for 1 h at room temperature.

[0051] 2. Rinse with deionized water, immerse in 1 mmol / L of amino[5] aromatic solution, and react at room temperature for 1 h.

[0052] 3. Rinse with deionized water and ethanol three times alternately, and air dry naturally to obtain an amino-column[5] aromatic hydrocarbon grafted COF in situ polymerized nanochannel membrane. Performance testing of amino column[5] aromatic grafted COF membrane

[0053] The remaining steps are the same as in Examples 1, 2, 3, and 4. The prepared amino-coated [5] aromatic-grafted COF membrane was used for perfluorooctanoic acid detection performance testing. 1. Take the COF membrane from Example 4 and place it in the middle of a specially made tetrafluoroethylene mold. Add perfluorocarboxylic acid buffer solution (1 μmol / L PBS, pH=7) with a concentration range of 1~1000 ng / L to both ends.

[0054] 2. The detection performance of amino-coated aromatic COF membrane for perfluorooctanoic acid was analyzed by monitoring the IV current change with a picoammeter[5].

[0055] 3. By measuring the IV current of perfluorooctanoic acid (PFOA) at different concentrations, a Langmuir adsorption isotherm equation and a standard deviation calculation formula were established based on the current response, thus determining the detection limit of PFOA (see [reference]). Figure 12 and Figure 13 ).

[0056] Figure 1 A schematic diagram of the functionalization process of nanochannel membranes: It shows the complete modification process from bare pore nanochannels, through EDC / NHS activation of carboxyl groups, covalent modification with benzidine, in-situ polymerization to generate COF three-dimensional network in nanochannels, and finally grafting amino column aromatics through amidation reaction [5]. It clearly presents the step-by-step functionalization process of Example 1 → Example 2 → Example 3 → Example 4, and intuitively reflects the construction path of the three-level structure of "nanochannel-COF nanopore-column aromatic subnanopore".

[0057] Figure 2 The synthetic route for p-amino columnar[5] aromatics is shown: using 1,4-di-(2-bromoethyl)benzene and paraformaldehyde as raw materials, catalytic cyclization is used to generate brominated columnar[5] aromatics, which are then nucleophilically substituted with Boc-p-aminobenzoic acid. Finally, the Boc protecting group is removed under acidic conditions to obtain p-amino columnar[5] aromatics. The synthetic steps of the functional monomers in Examples 4-6 are used to clarify the relationship between molecular skeleton construction and functional group transformation.

[0058] Figure 3 The 1H NMR spectrum of the p-amino column[5] aromatic hydrocarbon shows proton signals in the aromatic region at δ 6.50–8.00 ppm, where δ≈6.90 ppm represents the macrocyclic benzene ring proton of the column[5] aromatic hydrocarbon, and δ≈7.10 ppm and δ≈7.80 ppm represent the benzene ring proton of the side chain p-aminobenzoic acid ester; δ 3.00–4.50 ppm represents the methylene proton in the aliphatic region; and δ≈5.90 ppm represents the active hydrogen signal of -NH2. All signal positions, splits, and integrations are consistent with the structure of the p-amino column[5] aromatic hydrocarbon, proving that the synthesized product has a correct structure and high purity.

[0059] Figure 4The NMR carbon spectrum of the p-amino column[5] aromatic hydrocarbon is as follows: δ≈166 ppm is the carbonyl signal of the ester group (-COO-); δ≈150 ppm is the carbon signal of the benzene ring connected to the amino group; δ≈134 ppm is the carbon signal of the benzene ring connected to the oxygen group; δ 45–68 ppm is the carbon signal of the methylene chain of the alkyl chain. The number of peaks and chemical shifts are consistent with the molecular symmetry structure, which verifies that the synthesized product is the target p-amino column[5] aromatic hydrocarbon.

[0060] Figure 5 The mass spectrum of the p-amino column[5] aromatic hydrocarbon is shown: the mass spectrum shows that the molecular ion peak m / z = 2240.80, which is consistent with the theoretical molecular weight of the p-amino column[5] aromatic hydrocarbon, proving that the target product is accurately synthesized and the purity meets the grafting requirements.

[0061] Figure 6 SEM images of bare membrane, COF in-situ polymerized membrane, and columnar aromatics-grafted COF membrane: (ac) Example 1 bare membrane, the surface shows a straight nanopore structure with uniform pore size and regular distribution, without any modification layer; (df) Example 3 COF membrane, the nanopores are completely filled by COF, and a continuous and dense modification layer is formed on the surface, covering the pore structure; (gi) Example 5 columnar aromatics membrane, the surface roughness is significantly improved, and the pores are further blocked, indicating that both COF in-situ growth and columnar aromatics grafting were successfully completed.

[0062] Figure 7 SEM images of the cross-sections of the bare membrane, the COF in-situ polymerized membrane, and the columnar aromatic grafted COF membrane: (a) The bare membrane of Example 1 has a cross-section of a uniform columnar porous structure; (b) The COF membrane of Example 3 has pores that are fully filled with COF and a distinct functional layer is formed on the surface; (c) The columnar aromatic membrane of Example 5 has a thicker and rougher functional layer on the surface, confirming the stable construction of the three-level porous structure.

[0063] Figure 8 The elemental distribution diagram of bare membrane and columnar aromatic graft COF membrane: In Example 1, the weight percentage of N element in the bare membrane is 0.00%; in Example 5, the weight percentage of N element in the columnar aromatic membrane is 0.67%. The N comes from the amino group of the p-amino columnar aromatic [5] and is evenly distributed, proving that the columnar aromatic was successfully covalently grafted onto the surface of the COF membrane.

[0064] Figure 9 IV curves of nanochannels at different modification stages: In 0.1 mol / L KCl, the bare membrane current in Example 1 was relatively large, indicating ion rectification; the membrane current in Example 2 with benzidine decreased significantly, and rectification disappeared; the membrane current in Example 3 with COF showed a small change, indicating weak rectification; and the membrane current in Example 4 with columnar aromatics increased significantly, indicating a strong ion rectification effect. This demonstrates that each modification step successfully controlled the channel charge and transport performance.

[0065] Figure 10Infrared characterization images of films at different modification stages: Example 1 bare film shows PET ester group characteristic peaks at 1710 cm⁻¹ and 1240 / 1090 cm⁻¹; Example 3 COF film shows C=N imine bond peaks at 1620–1640 cm⁻¹ and NH stretching vibration peaks at 3300–3400 cm⁻¹; Example 4 columnar aromatic film retains COF characteristic peaks and the NH signal is significantly enhanced, confirming the successful in-situ growth of COF and grafting of columnar aromatics.

[0066] Figure 11 Contact angle diagrams for membranes at different modification stages: Example 1 bare membrane 71.2°; Example 2 benzidine membrane 68.5°; Example 3 COF membrane 45.3°, with significantly improved hydrophilicity; Example 4 columnar aromatic membrane 55.3°. Overall, the wettability is good, suitable for detection in an aqueous environment.

[0067] Figure 12 Selectivity of columnar aromatic hydrocarbon-grafted COF membranes for perfluorinated compounds: In Example 4, the membrane at a concentration of 1 μg / L showed a much higher current response to PFOA than that to perfluorobutyric acid, valeric acid, hexanoic acid, heptanoic acid, and decanoic acid, indicating that the membrane has a specific recognition ability for PFOA and excellent selectivity.

[0068] Figure 13 Performance testing of column-aromatic-grafted COF membranes for PFOA: (a) The IV curve of the membrane in Example 4 showed a regular change with concentration at PFOA concentrations of 1~1000 ng / L (1 μmol / L PBS, pH=7); (b) The current response showed good linearity with concentration; (c) Langmuir fitting yielded LOD=124.39 pg / L; (d) The step response was stable, with the signal increasing stepwise in the range of 1~1000 ng / L, showing good reproducibility.

[0069] Figure 14 The UV spectral titration curves of amino columnar aromatic hydrocarbons [5] with different perfluorocarboxylic acids are as follows: the UV characteristic peak changes most significantly when amino columnar aromatic hydrocarbons [5] react with PFOA, indicating the most stable inclusion; the changes are weak when reacting with other perfluorocarboxylic acids, proving that the high selectivity of the membrane in Example 4 to PFOA is due to the specific host-guest inclusion effect of columnar aromatic hydrocarbons and PFOA.

[0070] As can be seen from the comparison of Examples 1 to 6, Example 4 represents the optimal preparation conditions: 1. Nanochannel etching: 35℃, step-by-step etching up to a current of 5×10⁻ 5 A. Soak in deionized water for 12 hours; 2. Activation conditions: 48 mmol / L EDC + 13 mmol / L NHS, activation at room temperature for 1 h; 3. In-situ COF growth: 1 V DC voltage, 60 ℃ reaction for 48 h; 4. Column aromatic grafting: 1~10 mmol / L of amino column[5] aromatics, reacted at room temperature for 12 h.

[0071] The columnar aromatic hydrocarbon-grafted COF in-situ polymerized nanochannel membrane prepared under these conditions has the lowest detection limit for PFOA (124.39 pg / L), the largest binding constant, the best selectivity, and the most stable current response, meeting the practical application requirements for high-sensitivity PFAS detection.

[0072] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0073] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A columnar aromatic hydrocarbon-grafted covalent organic framework in-situ polymerized nanochannel membrane, characterized in that, Using polyethylene terephthalate straight nanochannel membrane as substrate, an imine-type COF three-dimensional network is grown in situ within its nanochannel. The surface of the COF three-dimensional network is covalently grafted with amino columnar aromatics via amide bonds [5] to form a three-level pore structure of nanochannel-COF nanopore-column aromatic sub-nano molecular pore.

2. The columnar aromatic hydrocarbon-grafted covalent organic framework in-situ polymerized nanochannel membrane according to claim 1, characterized in that, The COF three-dimensional network is generated by in-situ polymerization of benzidine, 4,4'-diaminobiphenyl-2,2'-dicarboxylic acid and trialdehyde phloroglucinol in nanochannels via Schiff base reaction, and the contained carboxyl active sites are used for subsequent grafting.

3. The columnar aromatic hydrocarbon-grafted covalent organic framework in-situ polymerized nanochannel membrane according to claim 1, characterized in that, The amino column[5] aromatic hydrocarbon is activated by 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide and N-hydroxysuccinimide to form amide bonds with carboxyl groups on the COF three-dimensional network and covalently fixed.

4. A method for preparing a columnar aromatic hydrocarbon-grafted covalent organic framework in-situ polymerized nanochannel membrane as described in any one of claims 1-3, characterized in that, Includes the following steps: (1) Preparation of polyethylene terephthalate straight nanochannel membrane: The polyethylene terephthalate membrane was subjected to ultraviolet irradiation and acid-base etching to obtain uniform straight nanochannels, which were then soaked in deionized water for later use. (2) In-situ polymerization of COF: The nanochannel membrane was activated with 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide and N-hydroxysuccinimide, modified with benzidine and fixed in a U-shaped groove. Benzidine, 4,4'-diaminobiphenyl-2,2'-dicarboxylic acid and p-toluenesulfonic acid aqueous solution were added to the positive electrode side, and trialdehyde phloroglucinol solution was added to the negative electrode side. The reaction was carried out at 1 V DC voltage and 60 °C for 12~48 h to generate carboxylated COF membranes in-situ within the nanochannel. (3) Amino column[5] aromatic grafting: The COF membrane was activated again by 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide and N-hydroxysuccinimide, and then covalently modified by immersing it in an amino column[5] aromatic solution at room temperature for 1~12 h to obtain a column aromatic grafted covalent organic framework in-situ polymerized nanochannel membrane. (4) Clean, dry and store.

5. The preparation method according to claim 4, characterized in that, In step (2), the solvents for the trialdehyde phloroglucinol solution are DMF and water, with a volume ratio of 1~3:9~7; the concentrations of benzidine, 4,4'-diaminobiphenyl-2,2'-dicarboxylic acid and trialdehyde phloroglucinol are all 1~100 μmol, and the reaction is carried out at a constant temperature with the addition of a mixed solvent of DMF and water.

6. The preparation method according to claim 4, characterized in that, In step (3), the concentration of the amino column[5] aromatic solution is 1~10 mmol / L, and the solvent is a polar aprotic solvent.

7. The application of the columnar aromatic hydrocarbon-grafted covalent organic framework in-situ polymerized nanochannel membrane as described in any one of claims 1-3 in high-sensitivity PFAS detection, characterized in that, This device is used for electrochemical sensing detection of trace PFAS in water, using IV curves and current response as signal outputs to achieve quantitative and qualitative identification at the pg / L level.

8. The application according to claim 7, characterized in that, The PFAS includes perfluorooctane sulfonic acid and short-chain perfluoroalkyl carboxylic acids; wherein the detection limit for perfluorooctane is ≤130 pg / L, and the linear range covers ng / L~μg / L.

9. The application according to claim 7, characterized in that, The detection system uses 1 μmol / L PBS as a buffer solution (pH=7) and employs a scanning voltage of -2 ~ 2 V to achieve convenient in-situ detection through changes in ion current.

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