Preparation method and application of functionalized covalent organic framework materials

Abstract

The invention discloses a preparation method and application of a functionalized covalent organic framework material, the preparation method is to obtain a covalent organic framework using diurea primary amine and trialdehyde phloroglucinol as monomers, successively denitrify, decarbonate and bromine to obtain a brominated polymer, and finally react the brominated polymer with trimethylamine or imidazole to obtain a functionalized covalent organic framework material. The present invention can obtain a variety of functionalized covalent organic framework materials by changing the monomers, and the preparation method has good universality; in addition, the functionalized covalent organic framework material prepared by the present invention can have strong electrostatic interaction, hydrophobic interaction, hydrogen bonding and p-π interaction forces with perfluoroalkyl, polyfluoroalkyl compounds and their salts, and shows fast adsorption rate, high adsorption capacity and good anti-matrix effect to PFASs, and has broad application prospects for the adsorption of perfluoroalkyl and polyfluoroalkyl compounds and their salts in actual environmental water samples.

Description

Technical Field

[0001] The present invention relates to new materials in the field of environmental analysis, and in particular to a preparation method of a functionalized covalent organic framework material and applications thereof. Background Art

[0002] Perfluoroalkyl and polyfluoroalkyl substances (PFASs) are a class of synthetic organic compounds in which all or some of the hydrogen atoms in their carbon chains are replaced by fluorine atoms. Since their development in the 1950s, PFASs, due to their strong hydrophobicity and excellent chemical stability, have flourished in the preparation of chemical intermediates and other daily necessities. The continued and widespread use of PFASs has led to their ubiquitous presence in the environment and biota, raising significant concerns about their adverse health effects. Physiological and epidemiological studies have confirmed that PFASs exhibit hepatotoxicity, immunotoxicity, reproductive toxicity, and carcinogenicity. Furthermore, their presence in the human body can lead to chronic diseases such as uricemia and, more seriously, can be transmitted through breastfeeding. Currently, many countries and regions have implemented mandatory regulations or restrictions on the production and use of perfluorooctane sulfonic acid (PFOS), perfluorooctanoic acid (PFOA) and its salts, and C11-C14 perfluorocarboxylates (PFCAs).

[0003] Compared to previously reported organic polymers, cationic and imidazole-functionalized organic polymers (TAGX-Cl) exhibit superior electrostatic adsorption, hydrogen bonding, and P-π synergistic effects, as well as high adsorption capacity, rapid adsorption, strong tolerance, and excellent regeneration. However, due to their limited surface area, their adsorption capacity is still very limited compared to covalent organic framework adsorbents. Therefore, the design and development of cationic or imidazole-functionalized organic framework materials as adsorbents for PFASs is an effective approach to address the challenges of PFAS adsorption and capacity enhancement. Summary of the Invention

[0004] In view of this, the first object of the present invention is to provide a method for preparing a functionalized covalent organic framework material, and the second object is to provide an application of a covalent organic framework material functionalized with a quaternary ammonium salt cation.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] The method for preparing the functionalized covalent organic framework material of the present invention comprises the following steps:

[0007] In the first step, diurea primary amine and trialdehyde phloroglucinol were used as monomers to prepare the covalent organic framework Urea-COF or DT-Urea-COF by a solvothermal method. The structural formulas are as follows:

[0008] ;

[0009] Wherein, when the diurea primary amine is 1,1'-(3,3'-dimethyl-[1,1'-biphenyl]-4,4'-diyl) diurea, the diurea primary amine and the trialdehyde phloroglucinol are copolymerized to obtain the Urea-COF; when the diurea primary amine is N,N'-(2-methyl-1,4-phenylene) diurea, the diurea primary amine and the trialdehyde phloroglucinol are copolymerized to obtain the DT-Urea-COF;

[0010] In the second step, Urea-COF or DT-Urea-COF is subjected to denitrification and decarbonation treatment to obtain RC-COF or DT-RC-COF, the structural formulas of which are as follows:

[0011] ;

[0012] In the third step, the RC-COF or DT-RC-COF synthesized in the second step is reacted with N-bromosuccinimide to obtain RC-COF-Br or DT-RC-COF-Br, the structural formulas of which are as follows:

[0013] ;

[0014] In the fourth step, RC-COF-Br or DT-RC-COF-Br is dispersed in a trimethylamine aqueous solution or a 6-methylimidazole solution to obtain a cation-functionalized covalent organic framework material or an imidazole-functionalized covalent organic framework material.

[0015] The beneficial effects are as follows: the present invention can obtain a variety of functionalized covalent organic framework materials by changing the monomers. The preparation method has good universality and important promotion value. In addition, the functionalized covalent organic framework material prepared by the preparation method of the present invention can have strong electrostatic, hydrophobic, hydrogen bonding and p-π interactions with perfluoroalkyl and polyfluoroalkyl compounds and their salts, and exhibits fast adsorption rate, high adsorption capacity and good anti-matrix effect on PFASs. The material also has regeneration ability and has broad application prospects for the adsorption of perfluoroalkyl and polyfluoroalkyl compounds and their salts in actual environmental water samples.

[0016] Preferably, in the fourth step, RC-COF-Br or DT-RC-COF-Br is dispersed in a trimethylamine aqueous solution to obtain a quaternary ammonium salt cation functionalized covalent organic framework material, the structural formula of which is as follows:

[0017] .

[0018] In another preferred embodiment, in the fourth step, RC-COF-Br is dispersed in N-methylimidazole to obtain an N-methylimidazole functionalized covalent organic framework material, the structural formula of which is as follows:

[0019] .

[0020] Preferably, the denitrification and decarbonation treatment in the second step includes the following: first washing with a solvent, dispersing it in water after washing, and heating it in a sealed state for 48 h to 72 h at a heating temperature of 150° C. to 160° C.;

[0021] In the third step, RC-COF or DT-RC-COF reacts with N-bromosuccinimide, which includes the following steps: adding RC-COF or DT-RC-COF powder to 1,1,2,2-tetrachloroethane, then adding NBS and BPO, stirring the reaction in an inert environment, cooling to room temperature, washing with dichloromethane, and vacuum drying to obtain RC-COF-Br or DT-RC-COF-Br.

[0022] The present invention also provides the use of quaternary ammonium salt cation functionalized covalent organic framework materials or N-methylimidazole functionalized covalent organic framework materials in the quantitative detection of perfluoroalkyl and polyfluoroalkyl substances and their salts.

[0023] Preferably, the application involves using a functionalized covalent organic framework material as an adsorbent to adsorb perfluoroalkyl and polyfluoroalkyl substances and their salts from a liquid. The adsorption conditions are as follows: a pH of 2.0 to 9.0; 5 mg of the functionalized covalent organic framework material added to 50 mL of a perfluoroalkyl solution; and adsorption under room temperature oscillation for 60 minutes. More preferably, the pH is 3.0, and the adsorbent achieves a removal rate of >95% for the analyte.

[0024] Preferably, after adsorption, the adsorbed sample is detected by UPLC-MS / MS, and the liquid chromatography conditions are: mobile phase A is 0.1% formic acid aqueous solution; mobile phase B is 0.1% formic acid acetonitrile solution.

[0025] Compared with the prior art, the advantages of the present invention are:

[0026] The present invention can produce a variety of functionalized covalent organic framework materials by modifying monomers. This preparation method has excellent universality and significant promotional value. Furthermore, the preparation method of the present invention can be used to post-modify the metal-organic framework with quaternary ammonium salts or imidazoles. The modified materials not only have ultra-high crystallinity and stability, but also have a large specific surface area, providing a larger adsorption space for the target compound.

[0027] There is not only a strong electrostatic interaction between the post-modification material of the present invention and the target object, but also intermolecular interaction forces (such as P-π interaction force, OHN hydrogen bond and FFN hydrogen bond). The adsorbent adsorbs perfluoroalkyl and polyfluoroalkyl substances through the combined action of electrostatic interaction and intermolecular interaction forces, with good adsorption effect, reusability, good anti-interference ability, and practical application value.

[0028] Experiments have shown that the RC-COF-Br of the present invention can reach adsorption equilibrium for the target PFASs within 40 minutes at the fastest, with a fast adsorption rate and an adsorption capacity generally above 850 mg / g (among which, the adsorption capacity for potassium perfluorobutanesulfonic acid is as high as 1831.3 mg / g), which is 2 to 40 times the adsorption capacity of existing metal-organic frameworks. It has broad application prospects for the adsorption of perfluoroalkyl and polyfluoroalkyl compounds and their salts in actual environmental water samples. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 These are the SEM, TEM and EDS characterization results of RC-COF-N-Br of the present invention.

[0030] Figure 2 These are the infrared and solid-state carbon nuclear magnetic resonance spectroscopy characterization results of the RC-COF-N-Br of the present invention.

[0031] Figure 3 This is the XPS characterization result of RC-COF-N-Br of the present invention.

[0032] Figure 4 This is the XRD characterization result of RC-COF-N-Br of the present invention.

[0033] Figure 5 This is the nitrogen adsorption characterization result of RC-COF-N-Br of the present invention.

[0034] Figure 6 is the contact angle of the intermediate product of the present invention and RC-COF-N-Br.

[0035] Figure 7 Figure a shows the effect of pH on the adsorption of RC-COF-N-Br, and figure b shows the Zeta potential test results of RC-COF-N-Br at different pH values.

[0036] Figure 8 This is the adsorption kinetics result of RC-COF-N-Br of the present invention.

[0037] Figure 9 is the adsorption capacity of RC-COF-N-Br of the present invention for PFASs.

[0038] Figure 10This is a result of the reproducibility of the RC-COF-N-Br of the present invention.

[0039] Figure 11 It is the surface electrostatic formula of RC-COF-N-Br and PFASs in the present invention.

[0040] Figure 12 This is the XPS comparison chart before and after RC-COF-N-Br adsorption.

[0041] Figure 13 This is the EDS comparison chart before and after RC-COF-N-Br adsorption.

[0042] Figure 14 It is an analysis of the non-covalent interaction between RC-COF-N-Br and PFASs.

[0043] Figure 15 This is the application of the RC-COF-N-Br of the present invention in actual environmental water samples.

[0044] Figure 16 The effect of humic acid and sodium chloride in water on the adsorption performance of RC-COF-N-Br.

[0045] Figure 17 This is the XRD characterization result of the N-methylimidazole-COF of the present invention.

[0046] Figure 18 This is the nitrogen adsorption characterization result of the N-methylimidazole-COF of the present invention. DETAILED DESCRIPTION

[0047] The embodiments of the present invention are described in detail below with reference to the accompanying drawings. It should be noted that the abbreviations of the reagents used in the present invention are as follows: NMP is N-methyl-2-pyrrolidone, o -DCB is o-dichlorobenzene, DMF is N,N-dimethylformamide, NBS is N-bromosuccinimide, BPO is benzoyl peroxide; PFBA is perfluorobutyric acid, PFPeA is perfluoropentanoic acid, PFHxA is perfluorohexanoic acid, PFHpA is perfluoroheptanoic acid, PFOA is perfluorooctanoic acid, PFNA is perfluorononanoic acid, PFDA is perfluorodecanoic acid, PFUnDA is perfluoroundecanoic acid, PFPeS is perfluoropentanesulfonic acid, PFHpS is perfluoroheptanesulfonic acid, GenX is perfluoro(2-methyl-3-oxahexanoic acid), PFBSK is perfluorobutanesulfonic acid potassium salt, PFHxSK is perfluorohexanesulfonic acid potassium salt, and PFOSK is perfluorooctanesulfonic acid potassium salt.

[0048] Example 1 Preparation of RC-COF-N-Br according to the present invention

[0049] The preparation method of RC-COF-N-Br of the present invention comprises the following contents:

[0050] In the first step, 4,4'-diisocyanato-3,3'-dimethylbiphenyl (2.0 g, 7.57 mmol) was added to aqueous ammonia (28% NH3·H2O) at 0°C. The mixture was stirred at 0°C for 30 min, then warmed to room temperature and stirred overnight. The solid product was collected, washed with water and THF, and then dried in vacuo to obtain 1,1'-(3,3'-dimethyl-[1,1'-biphenyl]-4,4'-diyl)diurea as a white powder.

[0051] ;

[0052] In the second step, trialdehyde phloroglucinol (21.0 mg, 0.10 mmol), 1,1'-(3,3'-dimethyl-[1,1'-biphenyl]-4,4'-diyl) diurea (44.8 mg, 0.15 mmol), NMP (1.2 mL), o -DCB (0.3 mL) and glacial acetic acid (6 M, 0.1 mL) were added, and the tube was sealed after ultrasonication for 10 seconds. The reaction was heated at 90 °C for 72 h. The precipitate was washed with DMF and acetone in sequence, and then dried under vacuum at 60 °C for 12 h to obtain brown Urea-COF.

[0053]

[0054] In the third step, the powder washed in the second step was directly transferred to a heat-resistant tube, ultrasonicated with water for 2 minutes, sealed, and heated at 160°C for 72 hours to remove nitrogen and carbon dioxide. The sample was then briefly washed with DMF and acetone to obtain a solvated sample. To activate the sample, solvent exchange was performed with DMF, methanol, THF, and n-hexane, respectively. Finally, the sample was dried under vacuum at 60°C for 12 hours to obtain a dark red solid RC-COF.

[0055] ;

[0056] In the fourth step, 200 mg of RC-COF powder was added to 12.5 mL of 1,1,2,2-tetrachloroethane, followed by the addition of NBS (61.3 mg, 0.34 mmol) and BPO (2.75 mg). The mixture was stirred at 120 °C in an inert atmosphere for 5 h, cooled to room temperature, washed with dichloromethane, and dried in vacuo at 80 °C for 24 h to obtain RC-COF-Br.

[0057] ;

[0058] In the fifth step, RC-COF-Br was dispersed in a 38% trimethylamine aqueous solution (TMA) at room temperature for 48 h, and then washed with deionized water several times to obtain RC-COF-N-Br;

[0059] .

[0060] Example 2 Preparation of the N-methylimidazole functionalized covalent organic framework material of the present invention

[0061] The difference between this embodiment and embodiment 1 is that the fifth step is different: this embodiment is to disperse RC-COF-Br in N-methylimidazole, specifically including the following contents:

[0062] 50 mg of RC-COF-Br was dissolved in 20 mL of CH2Cl2 and transferred to 6 mL of N-methylimidazole. The mixture was stirred at room temperature for 48 h, filtered, and the precipitate was washed with CH2Cl2 to remove unreacted RC-COF-Br. The mixture was then vacuum dried at 60°C for 12 h. After drying, the mixture was dispersed in methanol and then transferred to a dialysis bag with a cutoff of 3 kDa and dialyzed for 24 h to remove low molecular weight polymers. Finally, the product was vacuum dried to obtain N-methylimidazole-COF.

[0063] .

[0064] Example 3 Preparation of DT-RC-COF-N-Br according to the present invention

[0065] The difference between this embodiment and embodiment 1 is that this embodiment uses N,N'-(2-methyl-1,4-phenylene) diurea instead of 1,1'-(3,3'-dimethyl-[1,1'-biphenyl]-4,4'-diyl) diurea in embodiment 1.

[0066] The synthesis of N,N'-(2-methyl-1,4-phenylene) diurea in this example comprises the following steps: adding 2,5-diisocyanatotoluene (7.57 mmol) to aqueous ammonia (28% NH3·H2O) at 0°C, stirring at 0°C for 30 minutes, then warming to room temperature and stirring overnight, collecting the solid product, washing with water and THF, and drying in vacuo to obtain the product;

[0067] ;

[0068] The structural formulas of DT-Urea-COF, DT-RC-COF, DT-RC-COF-Br and DT-RC-COF-N-Br in this embodiment are as follows:

[0069] 、

[0070] .

[0071] Example 4 Characterization of the Functionalized Covalent Organic Framework of the Present Invention

[0072] 1. Characterization of quaternary ammonium cation-functionalized covalent organic framework material RC-COF-N-Br

[0073] 1. The SEM, TEM and EDS characterization results of RC-COF-N-Br of the present invention are shown in Figure 1 .Depend on Figure 1 a It can be seen that RC-COF-N-Br presents a fluffy flake morphology and a loose and porous spatial structure. Figure 1 As shown in Figure 2, RC-COF-N-Br exhibits excellent crystallinity and a honeycomb-like hexagonal pore structure. EDS spectra reveal uniform distribution of C, N, O, and Br elements throughout the material, providing preliminary evidence for the successful introduction of the quaternary ammonium salt.

[0074] 2. Infrared characterization of RC-COF-N-Br of the present invention is shown in Figure 2 a. By Figure 2 a It can be seen that in RC-COF-N-Br, 601 cm -1 The peak at 804 cm in RC-COF is attributed to the C-Br bond, indicating that the NBS was successfully brominated. -1 The CH peak at RC-COF-N-Br shifted to 815 cm -1 At 1263 cm -1 The CN peak at (RC-COF) shifts to 1267 cm -1 (RC-COF-N-Br), indicating that the quaternary ammonium salt modification was successful and part of the CN bond here comes from the quaternary ammonium salt; 2914 cm -1 The peak at is attributed to the CH stretching vibration in (-CH3), which once again proves the successful introduction of quaternary ammonium salt.

[0075] 3. The solid-state NMR carbon spectroscopy characterization results of RC-COF-N-Br are shown in Figure 2 b. By Figure 2 b It can be seen that the characteristic peaks at 212 ppm, 207 ppm, and 184 ppm can be attributed to the carbon in the C=O bond of the enol interconversion, the peaks at 142-128 ppm can be attributed to the carbon on the benzene ring, the peaks at 113 ppm and 105 ppm can be attributed to the carbon in C=C, and the characteristic peaks at 53 ppm, 45 ppm, 33 ppm, 24 ppm, and 17 ppm can be attributed to the carbon in -CH-, the carbon in -CH2, and the carbon in -CH3 in the quaternary ammonium salt, respectively, further proving the successful preparation of RC-COF-N-Br.

[0076] 4. XPS characterization results of RC-COF-N-Br are shown in Figure 3 .Depend on Figure 3 It can be seen that an obvious Br 3p characteristic signal peak appears in the full spectrum of RC-COF-Br, indicating that NBS is successfully brominated; compared with the C1s high-resolution spectrum of RC-COF-Br, the quaternary ammonium salt CN (288.97 eV) peak appears in the C1s high-resolution spectrum of RC-COF-N-Br, indicating that the quaternary ammonium salt cation is successfully introduced through chemical bonding.

[0077] 5. XRD characterization results of RC-COF-N-Br are shown in Figure 4 .Depend on Figure 4 As can be seen from a, the Urea-COF low-angle peak is at 2.9°, which is a characteristic low-angle peak of the covalent organic framework; the RC-COF low-angle peak shifts to the right to 3.3°; the RC-COF-N-Br low-angle peak appears at 3.2°, and the peak intensity of the material remains very high, which indicates that the ultra-high crystallinity of the material is retained. RC-COF-N-Br was immersed in water, 1 M hydrochloric acid, 1 M sodium hydroxide, methanol, N, N-dimethylformamide, tetrahydrofuran, dichloromethane, n-hexane, and perfluorinated compounds for a certain period of time, and then taken out and dried for XRD testing. The results are shown in Figure 2. Figure 4 b. By Figure 4 As shown in Figure b, RC-COF-N-Br still maintains high crystallinity after being immersed in different solvents, indicating that the material has strong stability. Figure 4 c, whose cell parameters are: a=b=29.81Å, c=3.45Å, α=β=90° and γ=120°. Figure 4 d shows that the unit cell of RC-COF-N-Br is composed of 7 minimum units and is hexagonal as a whole; Figure 4 e and 4f show that there are van der Waals forces, π-π forces and other interactions in RC-COF-N-Br.

[0078] 6. Nitrogen adsorption characterization results of RC-COF-N-Br are shown in Figure 5 .Depend on Figure 5 It can be seen that the surface area of ​​RC-COF-N-Br is 1134 cm 3 ·g -1 The pore sizes of micropores and mesopores are 0.64 nm and 4.7 nm respectively, and the volume ratio of mesopores to micropores is 1:1, indicating that it still has a large surface area after modification, and the combination of mesopores and micropores also provides a larger adsorption space.

[0079] 7. Contact angles of four materials Figure 6 .Depend on Figure 6It can be seen that the contact angle of Urea-COF is 107°, the contact angle of RC-COF with better crystallinity is 110°, the contact angle of RC-COF-Br is 102°, and the contact angle of the final product quaternary ammonium salt modified RC-COF-N-Br is 92°, indicating that RC-COF-N-Br can be well dispersed in water.

[0080] 2. Characterization of N-methylimidazole-COF of the present invention

[0081] 1. XRD characterization results of N-methylimidazole-COF (see Figure 17 ) It can be seen that the small-angle peak appears at 3.3°, indicating that the high crystallinity of the material is still retained after modification with N-methylimidazole.

[0082] 2. Characterization results of nitrogen adsorption of N-methylimidazole-CO (see Figure 18 ) It can be seen that the pore size of the metal organic framework after N-methylimidazole modification is 2.3nm and the specific surface area is 1728.6m 2 / g.

[0083] Example 4 Application of RC-COF-N-Br of the present invention

[0084] Based on the RC-COF-N-Br prepared in Example 1, the present invention constructs a strategy for removing perfluoroalkyl and polyfluoroalkyl compounds from environmental water samples. The strategy includes the following:

[0085] In the first step, 5 mg of RC-COF-N-Br was added to 50 mL of sample, and the pH of the mixture was adjusted to 2.0-9.0 (preferably 3.0). The mixture was then sonicated for 30 seconds to completely disperse the RC-COF-N-Br. The mixture was then shaken at room temperature for 2 hours to allow the RC-COF-N-Br to adsorb the analytes (i.e., PFASs) in the sample or standard solution.

[0086] In the second step, UPLC-MS / MS was used to detect the pre-adsorption sample and a mixed standard solution of PFASs (with a certain concentration gradient), and the post-adsorption sample was detected using UPLC-MS / MS. The UPLC-MS / MS liquid chromatography conditions were as follows: gradient elution was used to separate the target analytes, mobile phase A was 0.1% formic acid in water, mobile phase B was 0.1% formic acid in acetonitrile, and the gradient elution was shown in Table 1. The flow rate was 0.3 mL / min, the column temperature was 40°C, and the injection volume was 2 µL.

[0087] Table 1 Gradient elution of liquid chromatography mobile phase

[0088]

[0089] The mass spectrometry analysis conditions were as follows: electrospray ionization (ESI) and multiple reaction monitoring (MRM) mode were used for the qualitative and quantitative analysis of PFASs; curtain gas pressure: 35.0 psi; spray voltage: -4500 V; nebulization temperature: 550°C; nebulization gas pressure: 55 psi; auxiliary gas pressure: 60 psi;

[0090] Determine the standard curve for each target compound based on the concentration and peak area of ​​the mixed standard solution, and determine the concentration of the analyte before adsorption based on the standard curve. C i (in mg / L) and the concentration of the analyte after adsorption C e (Unit is mg / L), and then determine the adsorption capacity and removal rate. Among them, the adsorption capacity Qe= ( C i ﹣ C e ) v / m , removal rate R% =( C i ﹣ C e ) / C i ; Where v is the volume of the sample, mL ；m is the amount of adsorbent used, g .

[0091] Example 5 Adsorption performance of RC-COF-N-Br of the present invention for per / polyfluorinated compounds

[0092] It should be pointed out that the PFASs mixed solution in this embodiment is a mixed solution prepared from PFBA, PFPeA, PFHxA, PFHpA, PFOA, PFNA, PFDA, PFUnDA, PFPeS, PFHpS, GenX, PFBSK, PFHxSK and PFOSK, and the concentration of each target substance is 10 mg / L.

[0093] 1. Effect of pH on the adsorption of RC-COF-N-Br

[0094] To evaluate the effect of pH, 50 mL of PFASs mixed solution was taken and the pH was adjusted to 2-9. 5 mg of RC-COF-N-Br was added to each mixed solution as an adsorbent. The mixture was shaken at 25°C and 120 rpm for 2 h. The adsorbed solution was sampled and analyzed. The results are shown in Table 2. Figure 7 a.

[0095] Depend on Figure 7It can be seen that the removal rate of perfluorosulfonic acid compounds of the RC-COF-N-Br of the present invention as an adsorbent is generally greater than that of perfluorocarboxylic acid compounds and perfluorocarboxylic acid substitutes. This is because when adsorption is performed based on electrostatic forces, the electronegativity of the sulfonic acid compound is stronger and the adsorption effect is better. When the pH is 3, the degree of protonation of the quaternary ammonium salt cation in the solution is high and PFASs also exist in the form of anions, and there is a strong electrostatic attraction between the two. Therefore, the adsorption removal rate is the highest at this time, and its removal rate for each target is above 95%. When the pH of the adsorption system is greater than 3, the removal rate of the adsorbent for the target gradually decreases with the increase of pH; it reaches the lowest when pH = 9. This is because as the acidity of the solution decreases, the protonation state of the quaternary ammonium salt cation is significantly weakened, and the electrostatic force between RC-COF-N-Br and PFASs decreases, resulting in a decrease in adsorption efficiency.

[0096] The present invention has carried out the Zeta potential test on RC-COF-N-Br, and the result is shown in FIG. Figure 7 b. By Figure 7 b It can be seen that the potential of RC-COF-N-Br is higher under acidic conditions, and the positive potential of RC-COF-N-Br is the highest when pH=3, which further verifies that the adsorption effect of RC-COF-N-Br on PFASs is best at pH=3.

[0097] 2. Adsorption kinetics of PFASs on RC-COF-N-Br

[0098] Prepare standard solutions of PFBA, PFPeA, PFHxA, PFHpA, PFOA, PFNA, PFDA, PFUnDA, PFPeS, PFHpS, GenX, PFBSK, PFHxSK, and PFOSK, with a concentration of 50 mg / L for each target compound. Take 50 mL of the standard solution (three parallel preparations for each target compound), add 5 mg of RC-COF-N-Br, adjust the pH to 3.0, shake at room temperature, and take samples regularly for analysis. The results are shown in the table. Figure 8 .

[0099] Depend on Figure 8 It can be seen that the adsorption of 14 perfluorinated compounds by RC-COF-N-Br of the present invention generally reaches adsorption equilibrium in 40 to 60 minutes, and the removal rate of each perfluorinated compound is above 95% when the adsorption equilibrium is reached, indicating that RC-COF-N-Br of the present invention can quickly adsorb short-chain perfluorinated compounds.

[0100] 3. Adsorption capacity of RC-COF-N-Br for PFASs

[0101] First, a standard solution of each compound was prepared, with a concentration gradient of 1 mg / L-200 mg / L for each perfluorinated compound. Second, 50 mL (three replicates for each standard solution) was added, 5 mg of RC-COF-N-Br was added, the pH was adjusted to 3.0, and the mixture was shaken at room temperature for 60 min. The supernatant was centrifuged and analyzed. The results are shown in Table 1. Figure 9 and Table 2.

[0102] Table 2 Adsorption capacity of RC-COF-N-Br for PFASs

[0103]

[0104] Depend on Figure 9 It can be seen that for perfluorocarboxylic acid compounds, the hydrophobic effect becomes stronger as the carbon chain grows, resulting in a continuous increase in adsorption capacity. For perfluorosulfonic acid, the sulfonate group has a stronger electronegativity than the carboxylic acid, and electrostatic attraction plays a major role in the entire adsorption process. As the carbon chain grows, the electrostatic effect is affected and the electronegativity weakens, so the adsorption capacity of perfluorosulfonic acid substances gradually decreases with the increase in carbon chain. Furthermore, the RC-COF-N-Br of the present invention exhibits high adsorption capacity for all 14 perfluorochemicals, with an adsorption capacity of up to 1831.3 mg / g for PFBSK and 1193.7 mg / g for the perfluoro substitute GenX.

[0105] 4. Influence of matrix on adsorption of RC-COF-N-Br

[0106] This study used common co-pollutants, humic acid (HA) and sodium chloride (NaCl), as interfering substances to investigate their effects on adsorption. Specifically, HA or NaCl was added to a mixed solution of perfluorinated compounds to prepare a 10-50 mg / L humic acid solution or a 10-200 mg / L sodium chloride solution. 50 mL of each humic acid solution and sodium chloride solution were added to 5 mg of adsorbent, ultrasonically dispersed, and shaken at room temperature for 2 hours. The supernatant was centrifuged and analyzed by UPLC-MS / MS. The removal rate of perfluorinated compounds was calculated. The results are shown in Table 1. Figure 16 .Depend on Figure 16 As shown, when the humic acid concentration was 10 mg / L, the removal efficiency of RC-COF-N-Br for the fourteen perfluorinated compounds remained above 90%. When the sodium chloride concentration was 10 mg / L, the removal efficiency of RC-COF-N-Br for the fourteen perfluorinated compounds was also above 90%. However, the concentrations of humic acid and sodium chloride in actual environmental water samples are generally less than 10 mg / L. These results indicate that RC-COF-N-Br has the potential to effectively remove PFASs in real-world water samples.

[0107] 5. Regeneration of RC-COF-N-Br as adsorbent

[0108] 5 mg of RC-COF-N-Br was added to 50 mL of a mixed solution of fourteen perfluorinated compounds (the concentration of each perfluorinated compound was 10 mg / L), the pH was adjusted to 3.0, and adsorption was carried out under oscillation at room temperature for 60 min. After the adsorption was completed, the removal rate of each target compound was calculated and determined; after adsorption, the adsorbent was desorbed with methanol and adsorption was repeated under the above conditions. This cycle was repeated five times. The results are shown in Figure 2. Figure 10 .

[0109] Depend on Figure 10 It can be seen that the RC-COF-N-Br of the present invention still maintains a high removal rate for fourteen perfluorinated compounds after being recycled five times, indicating that RC-COF-N-Br can be efficiently regenerated and reused.

[0110] 6. Verification of the adsorption mechanism of PFASs by RC-COF-N-Br as an adsorbent

[0111] 1) Using DFT, we studied the surface electrostatic potential (ESP) distribution of PFASs and RC-COF-N-Br ions. The results are shown in Figure 11 .Depend on Figure 11 It can be seen that RC-COF-N-Br is electropositive in aqueous solvent, the acid ions of PFASs are electronegative, and the CF chains are electronegative. The results show that the positive ammonium ions in RC-COF-N-Br and the electronegative acid ions in PFASs in aqueous solution are bound by electrostatic interactions.

[0112] 2) XPS analysis of RC-COF-N-Br adsorbed with PFASs was performed, and the results are shown in Figure 12 .Depend on Figure 12 It can be seen that after RC-COF-N-Br adsorbed PFASs, CN in the quaternary ammonium salt moved from (286.91 eV) to (287.92 eV), CC moved from (284.38 eV) to (284.53 eV), CN moved from (285.27 eV) to (286.35 eV), and C=O moved from (288.97 eV) to (290.43 eV); F appeared in the full spectrum after RC-COF-N-Br adsorbed PFASs, while the Br content decreased, indicating that PFASs were successfully adsorbed on RC-COF-N-Br.

[0113] 3) EDS analysis of RC-COF-N-Br adsorbed with PFASs was performed, and the results are shown in Figure 13 .Depend on Figure 13 It can be seen that before adsorption, C, N, O, and Br elements are evenly distributed, and there is no F element. After adsorption, F element appears and the Br element content decreases, which is consistent with the results of XPS full spectrum analysis.

[0114] 4) NCI analysis results between RC-COF-N-Br and PFASs (see Figure 14 ) indicates that the RC-COF-N-Br of the present invention possesses electron donor sites and a large conjugated system, which can bind to PFAS ions through P-π interactions and hydrogen bonding (OHN, FHN). Therefore, the adsorption of PFASs by RC-COF-N-Br of the present invention is primarily attributed to the synergistic interaction between electrostatic attraction and intermolecular interactions.

[0115] Example 6 Application of the RC-COF-N-Br of the Present Invention in Adsorbing PFASs in Actual Water Samples

[0116] PFASs were first detected in actual water samples using the chromatography and mass spectrometry analysis conditions described in Example 2. None of the four actual water samples contained PFASs. To assess the performance of RC-COF-N-Br in these water samples, 1 μg / L of a PFASs mixed solution was added to each actual water sample. The details are as follows:

[0117] Take 50 mL of actual water sample (added with PFASs mixed solution), add 5 mg RC-COF-N-Br and adjust the pH to 3.0. After oscillation adsorption at room temperature for 60 minutes, the water sample was tested on the instrument. The results are shown in the table. Figure 15 .

[0118] Depend on Figure 15 As shown, RC-COF-N-Br, as an adsorbent, achieved removal rates exceeding 99% for all 14 perfluorinated compounds in real water samples, unaffected by the matrix in the water. These results demonstrate that the RC-COF-N-Br adsorbent has great potential for highly efficient removal of PFASs in real water samples.

Claims

1. A method for preparing a functionalized covalent organic framework material, characterized in that: The following steps are involved: In the first step, diurea primary amine and trialdehyde phloroglucinol were used as monomers to prepare the covalent organic framework Urea-COF or DT-Urea-COF by a solvothermal method. The structural formulas are as follows: 、 ； Wherein, when the diurea primary amine is 1,1'-(3,3'-dimethyl-[1,1'-biphenyl]-4,4'-diyl) diurea, the diurea primary amine and the trialdehyde phloroglucinol are copolymerized to obtain the Urea-COF; when the diurea primary amine is N,N'-(2-methyl-1,4-phenylene) diurea, the diurea primary amine and the trialdehyde phloroglucinol are copolymerized to obtain the DT-Urea-COF; In the second step, Urea-COF or DT-Urea-COF is subjected to denitrification and decarbonation treatment to obtain RC-COF or DT-RC-COF, the structural formulas of which are as follows: 、 ； In the third step, the RC-COF or DT-RC-COF synthesized in the second step is reacted with N-bromosuccinimide to obtain RC-COF-Br or DT-RC-COF-Br, the structural formulas of which are as follows: 、 ； In the fourth step, RC-COF-Br or DT-RC-COF-Br is dispersed in a trimethylamine aqueous solution or a 6-methylimidazole solution to obtain a functionalized covalent organic framework material.

2. The method for preparing a functionalized covalent organic framework material according to claim 1, wherein: In the fourth step, RC-COF-Br or DT-RC-COF-Br is dispersed in a trimethylamine aqueous solution to obtain a quaternary ammonium salt cation functionalized covalent organic framework material, the structural formula of which is as follows: or .

3. The method for preparing a functionalized covalent organic framework material according to claim 1, wherein: In the fourth step, RC-COF-Br is dispersed in N-methylimidazole to obtain an N-methylimidazole functionalized covalent organic framework material, the structural formula of which is as follows: 。 4. The method for preparing a functionalized covalent organic framework material according to claim 1, wherein: The denitrification and decarbonation treatment in the second step includes the following: washing with a solvent, dispersing the washed product in water, and heating the product in a sealed container for 48 to 72 hours at a temperature of 150 to 160°C; In the third step, RC-COF or DT-RC-COF is reacted with N-bromosuccinimide, comprising the following steps: adding RC-COF or DT-RC-COF powder to 1,1,2,2-tetrachloroethane, then adding NBS and BPO, stirring the reaction in an inert atmosphere, cooling to room temperature, washing with dichloromethane, and vacuum drying to obtain RC-COF-Br or DT-RC-COF-Br.

5. Use of the functionalized covalent organic framework material prepared according to any one of claims 1 to 4 in the adsorption of perfluoroalkyl and polyfluoroalkyl substances and their salts.

6. The use according to claim 5, characterized in that: The application is to use functionalized covalent organic framework materials as adsorption materials to adsorb perfluoroalkyl and polyfluoroalkyl substances and their salts in liquids, and the adsorption conditions are as follows: pH 2.0-9.0; the amount of adsorbent added is 5 mg of functionalized covalent organic framework materials added to 50 mL of perfluoro solution, and adsorption is carried out by oscillation at room temperature for 60 minutes.

7. The use according to claim 6, characterized in that: The pH was 3.

0.

8. The use according to claim 6, characterized in that: After adsorption, the adsorbed sample was detected by UPLC-MS / MS; the liquid chromatography conditions of UPLC-MS / MS were as follows: mobile phase A was 0.1% formic acid in water; mobile phase B was 0.1% formic acid in acetonitrile.

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