Trifluoromethyl / quaternary ammonium bifunctional COF material as well as preparation method and application thereof

Abstract

The invention discloses a preparation method of a trifluoromethyl / quaternary ammonium bifunctional COF material, which specifically comprises the following steps: mixing trialdehyde phloroglucinol, 2, 2-bis (3-amino-4-hydroxyphenyl) hexafluoropropane and a solvent, carrying out ultrasonic treatment, adding scandium trifluoromethanesulfonate, reacting, filtering, washing, drying, and carrying out bromination modification on the obtained COF (-CF3 / -OH); and finally, mixing the brominated COF (-CF3 / -OH), N, N-dimethyl butylamine and absolute ethyl alcohol, stirring, filtering, washing and drying to obtain the trifluoromethyl / quaternary ammonium bifunctional COF material. The invention also discloses an application of the trifluoromethyl / quaternary ammonium bifunctional COF material in adsorption of perfluoroalkyl substances in wastewater. According to the method, the periodic pore structure and the high specific surface area of the COFs are maintained, the amino content and the adsorption capacity are improved, the cycling stability of the material is enhanced, and after the material is repeatedly used for 10 times, the adsorption efficiency is still maintained to be 85% or above.

Description

Technical Field

[0001] This invention belongs to the field of covalent organic framework material preparation technology, specifically relating to a method for preparing trifluoromethyl / quaternary ammonium bifunctional COF materials, and also to the trifluoromethyl / quaternary ammonium bifunctional COF materials and their applications. Background Technology

[0002] Per- and polyfluoroalkyl substances (PFASs) are a class of organic synthetic compounds with a strong and stable CF bond as their core structure. They possess unique properties such as high chemical inertness, thermal stability, low molecular polarity, and amphiphilicity. In recent decades, PFASs have been widely used in consumer and industrial fields, such as cookware (e.g., Teflon coatings), disposable food packaging (e.g., fast food containers), furniture / carpet coatings, fire-fighting foams (e.g., AFFF), and paint surfactants, due to their ability to significantly improve the oil, water, and stain resistance of products. However, the environmental persistence and bioaccumulation of PFASs have become their fatal flaws: the strong electronegativity (3.98) and low polarizability (0.55 × 10⁻⁶) of the fluorine atom... -24 cm 3 The CF bond energy is as high as 485 kJ / mol (far higher than the 347 kJ / mol of the C-C bond), making PFASs difficult to be naturally degraded; at the same time, its amphiphilic nature (hydrophobic CF chain and hydrophilic functional group) makes it easy for it to accumulate in organisms.

[0003] Currently, the main technologies for removing PFASs from water include oxidation (such as advanced oxidation), ultraviolet irradiation, sonochemistry, electrochemistry, and adsorption. Among these, adsorption is one of the most promising technologies due to its advantages such as simple operation, no secondary pollution, and wide applicability (it can treat wastewater with low concentrations of PFASs). Although traditional adsorbents such as activated carbon, zeolite, and resins are widely used, they suffer from problems such as low adsorption capacity (e.g., activated carbon's adsorption capacity for PFOA is only 50-100 mg / g), poor selectivity (easily adsorbing impurities such as organic matter and heavy metals in water), and short cycle life (adsorption efficiency drops below 50% after 3-5 uses), making it difficult to meet practical engineering needs.

[0004] In recent years, covalent organic frameworks (COFs) have emerged as a novel type of porous material due to their periodic pore structure (pore size adjustable from 0.5 to 5 nm) and high specific surface area (up to 3000-5000 m²). 2With its abundant functional groups (such as amino, cyano, and fluorine groups) and designability, COFs have shown great potential in the adsorption of PFASs. Compared with traditional adsorbents, COFs have the following advantages: by controlling the pore size, precise separation of PFASs with different chain lengths (such as short-chain PFOA and long-chain PFOS) can be achieved; by introducing functional groups such as amino and fluorine groups, electrostatic interactions can be formed with the hydrophilic anionic groups of PFASs (such as -COOH), or fluorine affinity interactions can be formed with CF chains (FF bond energy is about 155 kJ / mol), significantly improving the adsorption capacity; the covalent bond structure of COFs gives it good chemical stability, and it can be reused after simple regeneration (such as ethanol washing and thermal desorption).

[0005] Although COFs exhibit advantages in PFAS adsorption, the stability of functionalized COF preparation remains a key bottleneck for their industrial application. Currently, COFs targeting PFAS adsorption are mainly amino-functionalized COFs (such as NH2-COF) and fluorinated COFs (such as F-COF). Among them, amino-functionalized COFs can efficiently capture the anionic groups of PFASs (such as -COO) through electrostatic interactions. - ), becoming a research hotspot. There are two main methods for preparing amino-functionalized COFs: (1) Reduction of azide-functionalized COFs: Azide groups (-N3) are reduced to amino groups (-NH2) by reducing agents such as sodium sulfite. The reaction conditions are mild (room temperature, aqueous solution), but the reaction efficiency is low (only 60-70%), resulting in insufficient amino content (usually <5 wt%), which is difficult to meet the high capacity adsorption requirements; (2) Reduction of cyano-functionalized vinyl COFs: Cyano groups (-CN) are reduced to amino groups (-NH2) by strong reducing agents such as lithium aluminum hydride (LiAlH4). The reaction efficiency is high (>90%), but strong reducing agents will destroy the framework structure of COFs: LiAlH4 will attack the C=C double bond (vinyl) or ether bond (-O-) in COFs, causing the framework to collapse, and its specific surface area will drop from 3500 m². 2 / g decreased to 1200m 2 Below a certain value (mg / g), the adsorption capacity decreases significantly. For example, the adsorption capacity for PFOA drops from 250 mg / g to 90 mg / g, and the cycle stability is poor; after five cycles, the adsorption efficiency drops from 95% to 60%. Furthermore, some amino-functionalized COFs face challenges in actual wastewater treatment, such as weak resistance to interference (susceptible to impurities like humic acid and sulfates in water) and difficulty in regeneration (requiring high temperature or strong acid / alkali treatment), further limiting their application. Summary of the Invention

[0006] The primary objective of this invention is to provide a method for preparing trifluoromethyl / quaternary ammonium bifunctional COF materials, utilizing bifunctional groups (-CF3 / -N). +The synergistic effect of these factors significantly improves the adsorption efficiency of the material for PFASs.

[0007] A second objective of this invention is to provide the above-mentioned trifluoromethyl / quaternary ammonium bifunctional COF material.

[0008] A third objective of this invention is to provide the application of trifluoromethyl / quaternary ammonium bifunctional COF materials in the adsorption of perfluoroalkyl substances in wastewater.

[0009] The first technical solution adopted in this invention is a method for preparing trifluoromethyl / quaternary ammonium bifunctional COF materials, which is implemented according to the following steps: Step 1: Prepare the precursor COF(-CF3 / -OH); Step 2: Modify COF(-CF3 / -OH) by bromination: Step 3: Mix the brominated COF (-CF3 / -OH), N,N-dimethylbutylamine, and anhydrous ethanol, stir, filter, wash several times with methanol, and vacuum dry to obtain the trifluoromethyl / quaternary ammonium bifunctional COF material.

[0010] The invention is further characterized in that, Step 1 specifically involves: Trialdehyde pyrogallol, 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane and solvent were mixed and dissolved by sonication. Scandium trifluoromethanesulfonate was added and reacted at room temperature for 3-24 h. The precipitate was filtered, washed several times with the mixed solution, extracted by Soxhlet extraction, and freeze-dried to obtain COF(-CF3 / -OH).

[0011] Both the solvent and the mixed solution are composed of 1,4-dioxane and mesitylene; the molar ratio of trialdehyde phloroglucinol, 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane, and scandium trifluoromethanesulfonate is 2-3:3-4:0.5-2.

[0012] The drying temperature is 50-80℃, the drying time is 12-24h; the ultrasonic time is 5-30min, the ultrasonic power is 80-250W, and the ultrasonic frequency is 20-40KHz.

[0013] Step 2 specifically involves: COF(-CF3 / -OH) was dispersed in THF and stirred for 10-60 min at an ice bath temperature of 0-10℃. Then, triethylamine and 1,4-dibromobutane were added, and the mixture was reacted at 0-10℃ for 1-5 h. The mixture was filtered, washed three times each with THF, methanol, and water, and dried under vacuum at 50-80℃ for 12-24 h to obtain brominated COF(-CF3 / -OH). The mass ratio of COF(-CF3 / -OH), triethylamine, and 1,4-dibromobutane was 3-4:1-2:1-2.

[0014] In step 3, the stirring temperature is 70-100℃ and the stirring time is 1-5 days; the vacuum drying temperature is 50-80℃ and the vacuum drying time is 12-24 hours; the molar ratio of the brominated COF(-CF3 / -OH) to N,N-dimethylbutylamine is 3-4:0.5-2.

[0015] The second technical solution adopted in this invention is a trifluoromethyl / quaternary ammonium bifunctional COF material prepared by a method for preparing trifluoromethyl / quaternary ammonium bifunctional COF materials.

[0016] The third technical solution adopted in this invention is the application of the trifluoromethyl / quaternary ammonium bifunctional COF material prepared by the preparation method of trifluoromethyl / quaternary ammonium bifunctional COF material in the adsorption of perfluoroalkyl substances in wastewater.

[0017] The beneficial effects of the present invention are as follows: The method of the present invention, by optimizing the functionalization path (such as using novel reducing agents and controlling reaction parameters), improves the amino content (>10wt%) and adsorption capacity (adsorption capacity for PFOA ≥200mg / g) while maintaining the periodic pore structure and high specific surface area of ​​COFs, and enhances the cycling stability of the material. After being reused 10 times, the adsorption efficiency is still maintained at more than 85%. Attached Figure Description

[0018] Figure 1 This invention is COF(-CF3 / -N) + Br - Synthesis route diagram; Figure 2 This is a scanning electron microscope (SEM) image of COF(-CF3 / -OH) of the present invention; Figure 3 These are different materials (COF(-CF3 / -OH), COF(-CF3 / -Br), COF(-CF3 / -N) + Br - A comparison chart of the adsorption performance of ( ); Figure 4 It is pH's effect on COF(-CF3 / -N) + Br - The effect curve of adsorption performance; Figure 5 It is the ionic strength (NaCl) versus COF (-CF3 / -N) + Br - The effect curve of adsorption performance; Figure 6 It is humic acid (HA) that affects COF(-CF3 / -N) + Br - The effect curve of adsorption performance; Figure 7 This is a comparison chart of the adsorption performance of different types of PFASs (anions, cations, and zwitterions); Figure 8 It is COF(-CF3 / -N) + Br - Reusability test curve (5 cycles); Figure 9 It is COF(-CF3 / -N) + Br - Comparison of PFASs removal performance in actual water samples between PFASs removal materials (PAC, IRA67, IRA900) and commercially available materials (PAC, IRA67, IRA900). Detailed Implementation

[0019] The present invention will now be described in detail with reference to specific embodiments and accompanying drawings.

[0020] The preparation method of the trifluoromethyl / quaternary ammonium bifunctional COF material of the present invention is specifically implemented according to the following steps: Step 1: Prepare the precursor COF(-CF3 / -OH); Trialdehyde phloroglucinol (TP), 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (AHPHF) and a solvent (the solvent being a mixture of 1,4-dioxane and mesitylene in a volume ratio of 4:1) were mixed and sonicated for 5-30 min at a power of 80-250 W and a frequency of 20-40 kHz. Scandium trifluoromethanesulfonate (Ш) (Sc(OTf)3) was added and reacted at room temperature for 3-24 h. The precipitate was filtered and washed several times with a mixed solution (a mixture of 1,4-dioxane and mesitylene in a volume ratio of 4:1), extracted with Soxhlet (methanol for 12 h, water for 12 h), and freeze-dried at 50-80 °C for 12-24 h to obtain COF(-CF3 / -OH). The molar ratio of trialdehyde phloroglucinol, 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane, and scandium trifluoromethanesulfonate is 2-3:3-4:0.5-2; Step 2: Modify COF(-CF3 / -OH) by bromination: COF(-CF3 / -OH) was dispersed in THF and stirred in an ice bath at 0-10℃ for 10-60 min; then triethylamine and 1,4-dibromobutane were added, and the mixture was reacted at 0-10℃ for 1-5 h; the mixture was filtered, washed three times each with THF, methanol, and water, and dried under vacuum at 50-80℃ for 12-24 h to obtain the brominated COF(-CF3 / -OH); The mass ratio of COF(-CF3 / -OH), triethylamine, and 1,4-dibromobutane is 3-4:1-2:1-2; Step 3, Preparation of trifluoromethyl / quaternary ammonium bifunctional COF materials: The brominated COF(-CF3 / -OH), N,N-dimethylbutylamine (NDMB), and anhydrous ethanol were mixed and stirred at 70-100℃ for 1-5 days; the mixture was filtered, washed several times with methanol, and dried under vacuum at 50-80℃ for 12-24 hours to obtain the target material (COF(-CF3 / -N...). + Br - This refers to a trifluoromethyl / quaternary ammonium bifunctional COF material; The molar ratio of brominated COF(-CF3 / -OH) to N,N-dimethylbutylamine is 3-4:0.5-2.

[0021] The reaction process of the trifluoromethyl / quaternary ammonium bifunctional COF material of the present invention is as follows: Figure 1 As shown, a trifluoromethyl-containing amino monomer (AHPHF) was condensed with trialdehyde phloroglucinol (TP) to synthesize a hydroxyl-containing COF precursor (COF(-CF3 / -OH)); bromine atoms were introduced into the hydroxyl site via bromination, followed by reaction with a tertiary amine (NDMB) to form a quaternary ammonium group, thus obtaining the bifunctional material COF(-CF3 / -N). + Br - The post-modification strategy avoids the harsh conditions (such as high temperature and strong reducing agents) required for the direct synthesis of bifunctional COFs, resulting in a simpler and more reproducible process. Simultaneously, the synergistic effect of the bifunctional groups (-CF3 enhances fluorine affinity, -N...) further enhances the synthesis. + Enhanced electrostatic effect gives the material high adsorption capacity, strong selectivity, resistance to interference (small impact of ionic strength and humic acid) and good reusability (removal rate is still >85% after 5 cycles).

[0022] Example 1 The preparation method of the trifluoromethyl / quaternary ammonium bifunctional COF material of the present invention is as follows: (1) Synthesis of precursor COF(-CF3 / -OH) Raw materials and proportions: 42 mg trialdehyde phloroglucinol (TP, CAS: 3164-55-4, 0.225 mmol); 110 mg 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (AHPHF, CAS: 75503-50-7, 0.30 mmol); 8.0 mL of 1,4-dioxane / trimethylbenzene mixed solvent (V / V=4:1); 6 mg scandium trifluoromethanesulfonate (Sc(OTf)3, 0.012 mmol, catalyst).

[0023] TP and AHPHF were added to a 25 mL reaction flask with a PTFE stopper, and a mixed solvent was added. The mixture was sonicated for 10 min (200 W, 40 kHz) until completely dissolved. Sc(OTf)3 was added, and the mixture was stirred at 25±2℃ for 1 h (the reaction system changed from clear to turbid). The precipitate was obtained by filtration through a 0.22 μm microporous membrane and washed three times (5 mL each time) with a mixed solvent. The precipitate was placed in a Soxhlet extractor and extracted successively with methanol (100 mL, 12 h) and deionized water (100 mL, 12 h) to remove unreacted raw materials. The mixture was freeze-dried at -50℃ and 10 Pa for 24 h to obtain a light brown powder COF(-CF3 / -OH), with a yield of 85% (based on TP).

[0024] Characterization data: SEM (accelerating voltage 10 kV, working distance 5 mm): densely packed irregular particles (particle size approximately 500 nm) with a rough surface; BET specific surface area (Micromeritics ASAP 2460): 100 m² 2 / g; Average pore size (BJH model): 2.2 nm (meets the size matching requirements of PFASs hydrophobic chains).

[0025] Example 2 The preparation method of the trifluoromethyl / quaternary ammonium bifunctional COF material of the present invention comprises the following steps: (1) Synthesis of COF(-CF3 / -OH): Add 42 mg of trialdehyde phloroglucinol (TP, 0.225 mmol) and 110 mg of 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (AHPHF, 0.30 mmol) to a 25 mL reaction flask, and then add 8.0 mL of a 1,4-dioxane / trimethylbenzene mixture. V / V =4:1), dissolved by sonication; 6 mg scandium trifluoromethanesulfonate (Ш) (Sc(OTf)3, 0.012 mmol) was added, and the mixture was reacted at room temperature for 1 h; the precipitate was filtered, washed with the mixed solution, extracted by Soxhlet (methanol 12 h, water 12 h), and freeze-dried (yield: 85%).

[0026] (2) Bromination modification: 0.5 g COF(-CF3 / -OH) was dispersed in 20 mL THF and stirred in an ice bath for 30 min; 1.0 mL triethylamine and 1.0 mL 1,4-dibromobutane were added, and the mixture was reacted at 35 °C for 12 h; the mixture was filtered, washed three times each with THF, methanol, and water, and dried under vacuum at 50 °C to obtain the brominated material (yield: 90%).

[0027] (3) Quaternary ammonium salt functionalization: 300 mg of the brominated material and 6.2 g of N,N-dimethylbutylamine (NDMB, 0.061 mol) were added to a 150 mL reaction flask, followed by 70 mL of anhydrous ethanol. The mixture was stirred at 90 °C for 3 days. After filtration, the mixture was washed with methanol and dried under vacuum at 100 °C to obtain the target material COF(-CF3 / -N + Br - Yield: 80%.

[0028] COF(-CF3 / -N + Br - Morphological characterization of materials: The morphology of COF(-CF3 / -OH) was characterized using scanning electron microscopy (SEM). Figure 2 It can be seen that COF(-CF3 / -OH) is a densely packed, irregular shape with a rough surface.

[0029] Example 3 The adsorption performance of the material in Example 2 was tested for PFASs. (1) Experimental conditions: initial concentration 10 mg / L (PFOA, PFOS), material dosage 0.1 g / L, 25℃, pH=7, adsorption time 24 h.

[0030] (2) Results: COF(-CF3 / -N + Br - The removal rates for PFOA and PFOS were 92.1% and 95.3%, respectively, far exceeding those of single-function COF, such as COF(-CF3 / -OH) with a removal rate of 62% and COF(-N) with a removal rate of 95.3%. + Br - The removal rate was 78%.

[0031] Designing adsorbents with corresponding active sites based on the structural characteristics of the analytes is an effective method. Both PFOA and PFOS contain anionic groups and CF chains, so amino monomers containing -CF3 and -OH groups and trialdehyde phloroglucinol (TP) were selected to synthesize trifluoromethyl-functionalized COFs. The hydroxyl groups on the COF backbone facilitate post-modification; after bromination, alkyl chains containing quaternary ammonium salts were modified onto the COF surface. The final synthesis yielded (-CF3 / -N... + Br - Bifunctional COFs.

[0032] By comparing COF(-CF3 / -OH), COF(-CF3 / -Br), and COF(-CF3 / -N) + Br -The adsorption properties of the three materials for PFOA and PFOS. Figure 3 It can be seen that COF(-CF3 / -OH) only achieved a removal rate of 62% for PFOA and PFOS. After functionalization with quaternary ammonium salts, the removal rate significantly increased to 90%; ultimately, COF(-CF3 / -N) was selected. + Br - To conduct subsequent experiments.

[0033] Example 4 COF(-CF3 / -N) prepared in Example 2 + Br - As an adsorbent, the removal performance of the material of the present invention for perfluoroalkyl carboxylic acids was studied, and the steps are as follows: Effect of pH on adsorption performance (1) Experimental conditions: pH=2-10, other conditions are the same as in Example 3.

[0034] (2) Results: When pH=2-7, the removal rate is >90%; when pH=10, the PFOA removal rate drops to 75% (electrostatic repulsion is enhanced), but the PFOS removal rate is still >80% (fluorine affinity is dominant).

[0035] Given that the pKa values ​​of PFOA and PFOS are 0.5 and -3.27, respectively, it is clear that under the experimental conditions, both analytes exist primarily in anionic form. The effect of solution pH on adsorption performance is as follows: Figure 4 As shown, the results indicate that as pH increases, COF(-CF3 / -N + Br - The removal rates of the two PFASs showed varying degrees of decrease, similar to the adsorption characteristics of most anionic pollutants. For PFOA, the removal rate of the material decreased significantly with increasing pH, especially when the pH was greater than 7. This is because at high pH, ​​hydroxide ions can compete with anionic PFAS for quaternary ammonium salt sites. In addition to the effect of electrostatic repulsion, hydrophobic interactions also played a role. When the pH decreased, H+ ions... + Increased concentration inhibits the ionization process of PFASs. The hydrophobicity of PFAS molecules is higher than that of their anionic forms. Therefore, increasing pH enhances the ionization of PFASs, leading to an increase in COF(-CF3 / -N) concentration. + Br - The hydrophobic interaction between COF(-CF3 / -N) and PFASs is weakened. The results indicate that COF(-CF3 / -N) + Br - The adsorption behavior of COF(-CF3 / -N) on PFOA was inhibited. Notably, the adsorption behavior of COF(-CF3 / -N) on PFOA was inhibited. + Br -The removal efficiency of PFOS is higher than 91.3% over a wide pH range (2~7), and the material still maintains high adsorption performance for PFOS at pH 10, with a removal rate greater than 79%.

[0036] The above results indicate that COF(-CF3 / -N) + Br - Although negatively affected by electrostatic repulsion and reduced hydrophobicity, it still exhibits good adsorption performance for PFOS.

[0037] Effect of NaCl on Adsorption Performance (1) Experimental conditions: pH=2-10, other conditions are the same as in Example 3.

[0038] (2) Results: When pH=2-7, the removal rate is >90%; when pH=10, the PFOA removal rate drops to 75% (electrostatic repulsion is enhanced), but the PFOS removal rate is still >80% (fluorine affinity is dominant).

[0039] The ionic strength of actual wastewater often varies significantly, therefore, this study investigates COF(-CF3 / -N) under different ionic strengths. + Br - The differences in the adsorption performance of PFASs are of great significance. For example... Figure 5 As shown, the effect of ionic strength on COF(-CF3 / -N) was investigated. + Br - The effect of COF(-CF3 / -N) adsorption on two PFASs. Within the studied sodium chloride concentration range, COF(-CF3 / -N + Br - The adsorption performance of the two PFASs is basically unaffected by changes in salt concentration.

[0040] The effect of humic acid (HA) on the removal performance of materials (1) Experimental conditions: pH=2-10, other conditions are the same as in Example 3.

[0041] (2) Results: When pH=2-7, the removal rate is >90%; when pH=10, the PFOA removal rate drops to 75% (electrostatic repulsion is enhanced), but the PFOS removal rate is still >80% (fluorine affinity is dominant).

[0042] The effect of humic acid (HA) on the adsorption of two PFAS was further investigated. Within the studied HA concentration range, COF(-CF3 / -N + Br - The PFOS removal rate remained basically stable, such as Figure 6 As shown, the removal rate of PFOA decreased slightly. This may be due to the difference in the concentration of HA and PFOA in COF(-CF3 / -N).+ Br - This is due to competitive adsorption on the surface of COF(-CF3 / -N). + Br - As some adsorption sites on the COF (-CF3 / -N) surface are gradually occupied by HA molecules, the number of available adsorption sites for PFOA decreases. Furthermore, HA does not exist solely as a single ion; the presence of hydrophobic groups in its structure can lead to the formation of aggregates through hydrophobic interactions. These relatively large aggregates can easily block COF (-CF3 / -N) adsorption sites. + Br - The porous structure of HA hinders the contact between some adsorption active sites and PFOA, thus reducing the overall adsorption efficiency. Furthermore, HA contains many functional groups, such as carboxyl and hydroxyl groups, which cause some adsorption sites attached to COF(-CF3 / -N) to become trapped. + Br - The HA molecules on COF(-CF3 / -N) serve as additional adsorption sites for PFOA. In competitive adsorption systems, COF(-CF3 / -N) + Br - The adsorption capacity of COF(-CF3 / -N) for both PFASs did not decrease significantly. Meanwhile, the concentration of HA in natural water bodies is generally lower than that in this study, therefore COF(-CF3 / -N) adsorption capacity was not significantly reduced. + Br - It has certain potential in practical applications.

[0043] Example 5 COF(-CF3 / -N) prepared in Example 2 + Br - As an adsorbent, the adsorption performance of the material of this invention on anionic, cationic and zwitterionic perfluoroalkyl substances was compared. With the expansion of the range of PFASs, in addition to typical anionic PFASs, cationic PFASs and zwitterionic PFASs have also been discovered and have attracted worldwide attention. To study COF(-CF3 / -N) + Br - The adsorption performance of anionic, cationic, and zwitterionic PFASs was investigated using Genx, PFOA, PFOS, PFOAAAmS, PFOSAAmS, and PFOSB. PFOAAAmS and PFOSAAmS are cationic PFASs, while PFOSB is a zwitterionic PFAS. Figure 7 It can be seen that, apart from GenX, COF(-CF3 / -N) + Br - It exhibits good removal efficiency for the other five PFASs. COF(-CF3 / -N) + Br -COF(-CF3 / -N) exhibits good removal efficiency for anionic, cationic, and zwitterionic PFASs, indicating that COF(-CF3 / -N) + Br - Fluorine-fluorine interactions and hydrophobic interactions play a dominant role in the adsorption of cations and zwitterionic PFASs. COF(-CF3 / -N) + Br - The adsorption capacity of anionic PFASs is better than that of cationic PFASs, which is due to the electrostatic repulsion between the quaternary ammonium salt and cationic PFASs in the material structure.

[0044] Example 6 COF(-CF3 / -N) prepared in Example 2 + Br - As an adsorbent, the reusability of the material of this invention for perfluoroalkyl carboxylic acids was studied, and the steps are as follows: (1) Regeneration conditions: Use a mixed solution of 70% (90% MeOH + 25% NH3·H2O) + 1% NaCl and regenerate by ultrasonication for 30 min.

[0045] (2) Results: After 5 cycles, the removal rates of PFOA and PFOS remained at 88.2% and 92.1% respectively, indicating that the material has good reusability.

[0046] The regeneration and reusability of adsorbents are crucial for their application in practical wastewater treatment. Therefore, different solutions are selected to regenerate the COF(-CF3 / -N) after PFAS adsorption. + Br - Methanol solution is ineffective at regenerating adsorbents, but adding 1% sodium chloride solution to methanol improves the regeneration efficiency, especially for PFOS. This is because Cl- promotes the desorption of PFASs from the quaternary ammonium salt groups and their redissolution in methanol. Simultaneously, regeneration of the adsorbed material using 90% MeOH + 25% NH3·H2O significantly improves the regeneration efficiency of PFOA. To achieve even higher regeneration efficiencies for both PFOA and PFOS, a mixed solution of 70% (90% MeOH + 25% NH3·H2O) + 1% NaCl was ultimately chosen for adsorbent regeneration. Figure 8 As shown, COF(-CF3 / -N + Br - Even after five adsorption-desorption cycles, it still exhibits good adsorption performance for PFOA and PFOS.

[0047] Example 7 The following uses the COF(-CF3 / -N) prepared in Example 2 as an example. + Br -As an adsorbent, the application of the material of this invention in actual samples was studied, and the steps are as follows: (1) Experimental materials: Wastewater from an electronics factory (containing GenX, PFOA and PFOS, with concentrations of 5.2 mg / L, 3.1 mg / L and 1.8 mg / L, respectively).

[0048] (2) Results: COF(-CF3 / -N + Br - The removal rates of GenX, PFOA and PFOS were 85.7%, 91.3% and 98.9% respectively, which were better than those of commercial materials (PAC removal rate <70%, IRA67 removal rate <80%).

[0049] The COF(-CF3 / -N) was evaluated. + Br - The effectiveness of removing PFASs from actual industrial wastewater was studied and compared with powdered activated carbon (PAC) and two anion exchange resins (IRA67 and IRA900). IRA67 and IRA900 have been proven to effectively remove PFASs from water. Figure 9 As shown, all four materials exhibited good adsorption performance for PFOS, with removal rates approaching 100%. However, COF(-CF3 / -N) showed the following effect: + Br - The COF(-CF3 / -N) exhibits superior removal performance for GenX and PFOA compared to the other three materials. This indicates that the prepared COF(-CF3 / -N) + Br - It has certain application prospects in the removal of PFASs in actual wastewater.

[0050] The trifluoromethyl / quaternary ammonium bifunctional COF material of the present invention has the following advantages: (1) Functional synergy: Bifunctional group (-CF3 / -N) + The synergistic effect significantly improves the adsorption efficiency of PFASs (removal rate > 90%), which is superior to single-function COFs (such as those containing only -N). + COF removal rate <70%) (2) Mild synthesis: The post-modification process does not require strong reducing agents or high temperatures (<100℃), which avoids damage to the COF framework and improves the stability of the material; (3) Anti-interference: It is not sensitive to ionic strength (NaCl concentration 0-0.5 mol / L) and humic acid (HA concentration 0-100 mg / L), and is suitable for actual wastewater; (4) Reusability: Regenerated by a mixed solution of 70% (90% MeOH + 25% NH3·H2O) + 1% NaCl, the adsorption capacity retention rate is >80% after 5 cycles, which reduces the cost of use; (5) Good selectivity: preferentially adsorbs PFASs on other organic pollutants such as quinolones and alkylphenols (removal rate difference > 30%).

Claims

1. A method for preparing trifluoromethyl / quaternary ammonium bifunctional COF materials, characterized in that, The specific steps are as follows: Step 1: Prepare the precursor COF(-CF3 / -OH); Step 2: Modify COF(-CF3 / -OH) by bromination: Step 3: Mix the brominated COF (-CF3 / -OH), N,N-dimethylbutylamine, and anhydrous ethanol, stir, filter, wash several times with methanol, and vacuum dry to obtain the trifluoromethyl / quaternary ammonium bifunctional COF material.

2. The preparation method of the trifluoromethyl / quaternary ammonium bifunctional COF material as described in claim 1, characterized in that, In step 1, specifically: Trialdehyde pyrogallol, 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane and solvent were mixed and dissolved by sonication. Scandium trifluoromethanesulfonate was added and reacted at room temperature for 3-24 h. The precipitate was filtered, washed several times with the mixed solution, extracted by Soxhlet extraction, and freeze-dried to obtain COF(-CF3 / -OH).

3. The preparation method of the trifluoromethyl / quaternary ammonium bifunctional COF material as described in claim 2, characterized in that, Both the solvent and the mixed solution are composed of 1,4-dioxane and mesitylene; the molar ratio of trialdehyde phloroglucinol, 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane, and scandium trifluoromethanesulfonate is 2-3:3-4:0.5-2.

4. The preparation method of the trifluoromethyl / quaternary ammonium bifunctional COF material as described in claim 2, characterized in that, The drying temperature is 50-80℃, the drying time is 12-24h; the ultrasonic time is 5-30min, the ultrasonic power is 80-250W, and the ultrasonic frequency is 20-40KHz.

5. The preparation method of the trifluoromethyl / quaternary ammonium bifunctional COF material as described in claim 1, characterized in that, Step 2 specifically involves: COF(-CF3 / -OH) was dispersed in THF and stirred for 10-60 min at an ice bath temperature of 0-10℃. Then, triethylamine and 1,4-dibromobutane were added, and the mixture was reacted at 0-10℃ for 1-5 h. The mixture was filtered, washed three times each with THF, methanol, and water, and dried under vacuum at 50-80℃ for 12-24 h to obtain brominated COF(-CF3 / -OH). The mass ratio of COF(-CF3 / -OH), triethylamine, and 1,4-dibromobutane was 3-4:1-2:1-2.

6. The method for preparing the trifluoromethyl / quaternary ammonium bifunctional COF material as described in claim 1, characterized in that, In step 3, the stirring temperature is 70-100℃ and the stirring time is 1-5 days; the vacuum drying temperature is 50-80℃ and the vacuum drying time is 12-24 hours; the molar ratio of the brominated COF(-CF3 / -OH) to N,N-dimethylbutylamine is 3-4:0.5-2.

7. The trifluoromethyl / quaternary ammonium bifunctional COF material prepared by the method for preparing trifluoromethyl / quaternary ammonium bifunctional COF material according to any one of claims 1-6.

8. The application of the trifluoromethyl / quaternary ammonium bifunctional COF material prepared by the method of any one of claims 1-6 in the adsorption of perfluoroalkyl substances in wastewater.

Images