Quaternary ammonium salt type cross-linked polymer xerogel adsorbent material, preparation method and application thereof

Abstract

The present disclosure provides a kind of quaternary ammonium salt type crosslinked polymer xerogel adsorption material and its preparation method and application.The adsorption material is the water-insoluble crosslinked polymer network formed by quaternary ammonium salt monomer and crosslinking agent through radical crosslinking copolymerization;The quaternary ammonium salt monomer has the structure of formula (I);The monomer constituting the crosslinked polymer network does not contain covalently bonded fluorine atom, and the adsorption material is in xerogel form and can be water-soluble in aqueous medium Swelling.The material provides electrostatic adsorption through quaternary ammonium salt positive potential point, and the medium-length chain alkyl adjacent to quaternary ammonium nitrogen forms a moderate hydrophobic microenvironment around the quaternary ammonium salt positive potential point, so as to give consideration to high load adsorption capacity and anti-competitive anion performance.The adsorption material provided by the present disclosure does not contain fluorine atom, avoids the environmental and cost problems that may be caused by fluorine-containing components and has simple preparation method, and has good water treatment application prospect.

Description

Technical Field

[0001] This disclosure relates to the field of water treatment adsorption materials technology, and in particular to quaternary ammonium salt type cross-linked polymer dry gel adsorption materials, their preparation methods and applications. Background Technology

[0002] Per- and polyfluoroalkyl substances (PFAS) are a class of organic compounds containing perfluorinated or polyfluorocarbon chains. Due to the high chemical stability of the CF bond, some PFAS exhibit strong persistence and migration capabilities in the environment. Perfluorocarboxylic acids such as perfluorooctanoic acid (PFOA) and perfluorovalerate (PFPeA) mainly exist in anionic form under normal aqueous conditions. Therefore, using positively charged adsorbent materials for electrostatic binding or ion exchange is an important technical approach for the adsorption and removal of PFAS in water.

[0003] Quaternary ammonium salt groups possess a positive charge unaffected by typical pH changes in water bodies, making them a commonly used functional group in anionic PFAS adsorbents. The ion-head groups of anionic PFAS can undergo electrostatic attraction or counter-ion exchange with the positive potential site of quaternary ammonium salts. Simultaneously, the fluorinated carbon chains inherent in PFAS can also generate additional interactions with hydrophobic or fluorine-containing structures in the adsorbent material. Therefore, the number of quaternary ammonium salt sites, site accessibility, the microenvironment adjacent to the sites, and the pore and swelling structure of the material can all influence the adsorption performance of PFAS.

[0004] Existing technologies have modified the alkyl substitution structure of quaternary ammonium salt functional sites in material systems such as anion exchange resins, porous polymers, metal-organic framework composites, and hydrogels. Some materials enhance the adsorption affinity or competitive adsorption capacity of PFAS with hydrophobic segments by introducing longer alkyl groups onto the quaternary ammonium nitrogen, thereby creating a hydrophobic microenvironment near the positive potential point of the quaternary ammonium salt. However, existing non-fluorinated quaternary ammonium salt porous adsorbent materials (such as monolithic blocks of polyHIPEs based on emulsion template solidification) rely on in-situ shaped micropores for mass transfer during synthesis; in non-emulsion three-dimensional cross-linked networks, they are prone to hydrophobic self-assembly, leading to localized dense pore blockage, burying active sites, and significantly reducing removal rates under high concentrations of inorganic competing anions.

[0005] Existing technologies also enhance PFAS adsorption performance by introducing fluorinated monomers, fluorinated segments, or fluorinated polymer domains into the adsorbent material, utilizing the synergistic effect of electrostatic and fluoride-affinity interactions. While this design strengthens the interaction between the material and the fluorinated segments of PFAS, it introduces additional stable organic fluorine structures into the adsorbent bulk and increases the factors that need to be considered in material composition, preparation, and post-use disposal.

[0006] However, the effect of alkyl substitution structure of quaternary ammonium salts on the adsorption performance of PFAS does not simply increase monotonically with increasing alkyl chain length. While elongating the alkyl chain can enhance local hydrophobicity, it may also increase steric shading around the positive potential point of the quaternary ammonium salt, reducing the number of charge sites per unit mass of material and affecting the material's hydrophilicity, pore structure, swelling properties, and aqueous mass transfer. Conversely, shorter alkyl groups are beneficial for increasing the density of positive potential points of the quaternary ammonium salt and site accessibility, but PFAS may face strong ionic competition when inorganic competing anions such as chloride, nitrate, and sulfate ions coexist.

[0007] Therefore, the equilibrium adsorption capacity of a material under high load conditions and its adsorption retention capacity under conditions of coexisting inorganic competing anions may be controlled by different structural factors. The former is usually closely related to the number of accessible quaternary ammonium salt positive potential sites per unit mass of material; the latter, in addition to being affected by electrostatic sites, may also be related to the hydrophobic microenvironment near the quaternary ammonium salt positive potential sites.

[0008] However, existing studies are typically based on rigid ion exchange resins, porous aromatic frameworks, surface-modified materials, or hydrogels containing multiple functional monomers. These different materials exhibit significant differences in polymer framework, functional site immobilization methods, pore structure, crosslinking density, and swelling behavior. Therefore, the quaternary ammonium salt alkyl chain length patterns obtained from one material system are difficult to directly use to determine suitable substitution structures in another crosslinked gel system.

[0009] Especially in cross-linked gels formed directly from polymerizable quaternary ammonium salt monomers, the alkyl substitution structure of the quaternary ammonium salt not only affects the interaction between individual functional sites and PFAS, but also simultaneously influences polymerization uniformity, cross-linked network structure, water absorption and swelling, effective site exposure, and the diffusion and mass transfer of PFAS within the network. Further research is needed to determine how to maintain a high number of positive potential sites for the quaternary ammonium salt while simultaneously creating a suitable non-fluorinated hydrophobic environment near these sites and achieving a reasonable match between the two within the cross-linked network. Summary of the Invention

[0010] The inventors unexpectedly discovered that the quaternary ammonium salt-type cross-linked polymer dry gel adsorbent material of the present invention, through free radical cross-linking copolymerization of quaternary ammonium salt monomers with the structure of formula (I) and cross-linking agents to form a specific dry gel morphology, can produce water absorption and swelling when in contact with water samples. It can maintain a high apparent ion exchange capacity while forming a moderate non-fluorinated hydrophobic microenvironment near the positive potential point of the quaternary ammonium salt, thereby taking into account both high loading adsorption capacity and anti-competitive anion performance. In particular, the above effect is particularly significant when the quaternary ammonium nitrogen adopts an asymmetric substitution structure of two short-chain alkyl groups and one medium-long-chain alkyl group. Among them, the effect is most excellent when the quaternary ammonium nitrogen is simultaneously connected to two methyl groups and one n-hexyl group (i.e., 2-(methacryloyloxy)ethyl dimethyl n-hexyl ammonium salt).

[0011] In a first aspect of this disclosure, a quaternary ammonium salt-type crosslinked polymer dry gel adsorbent material is provided, which is obtained by crosslinking and copolymerizing quaternary ammonium salt monomers and a crosslinking agent;

[0012] The quaternary ammonium salt monomer has the structure of the following formula (I):

[0013]

[0014] Wherein, R1 is H or methyl, R2 and R3 are each independently C1-C3 alkyl, R4 is C4-C7 alkyl, R5 is C2-C4 alkylene, and X - For Cl - ,Br - or I - .

[0015] In some embodiments, in the structure of formula (I), R2 and R3 are each independently methyl or ethyl, and R4 is a C4-C6 alkyl group.

[0016] In some embodiments, R1, R2, and R3 are methyl, and R4 is n-butyl, n-pentyl, or n-hexyl.

[0017] In some embodiments, the quaternary ammonium salt monomer is selected from one or more of 2-(methacryloyloxy)ethyl dimethyl n-hexyl ammonium salt, 2-(methacryloyloxy)ethyl dimethyl n-butyl ammonium salt, and 2-(methacryloyloxy)ethyl dimethyl n-pentyl ammonium salt.

[0018] In some embodiments, the crosslinking agent is selected from one or more of ethylene glycol dimethacrylate, 1,4-butanediol dimethacrylate, hexanediol dimethacrylate, trimethylolpropane trimethacrylate, and N,N'-methylenebisacrylamide.

[0019] In some embodiments, the ratio of the equilibrium adsorption capacity to the apparent ion exchange capacity of the quaternary ammonium salt crosslinked polymer dry gel adsorbent material for perfluorooctanoic acid is not less than 1.05, and / or the ratio for perfluorovalerate is not less than 0.9.

[0020] In some embodiments, under the conditions of an initial perfluorooctanoic acid concentration of 0.025 mmol / L and an inorganic competing anion concentration of 10 mmol / L, the quaternary ammonium salt crosslinked polymer dry gel adsorbent material achieves a perfluorooctanoic acid removal rate of not less than 90%.

[0021] In a second aspect of this disclosure, a method for preparing the above-mentioned quaternary ammonium salt-type crosslinked polymer dry gel adsorbent material is provided, comprising:

[0022] (1) In a solvent system, the above-mentioned quaternary ammonium salt monomer, crosslinking agent and thermal initiator are mixed and free radical crosslinking copolymerization is carried out at 40 to 90°C, preferably 50 to 70°C, to obtain crosslinked hydrogel;

[0023] (2) The obtained cross-linked hydrogel is crushed or shredded, swollen in a liquid medium, and then dried to obtain the quaternary ammonium salt type cross-linked polymer dry gel adsorbent material.

[0024] In some embodiments, in step (1), the molar ratio of the quaternary ammonium salt monomer to the crosslinking agent is 1:(0.20-0.40); the solvent system is an ethanol / water mixed solvent, wherein the mass ratio of ethanol to water is (0.1-2):1; and the amount of thermal initiator is 0.1 to 10 wt% of the total mass of the quaternary ammonium salt monomer and the crosslinking agent.

[0025] In some implementations, in step (2), the liquid medium is water, ethanol, or a mixture of ethanol and water, and the swelling time is 0.5 to 5 h; the drying is freeze drying, with a freeze drying temperature of -20 to -50°C and a freeze drying time of 12 to 72 h, preferably 12 to 36 h.

[0026] In a third aspect of this disclosure, a method for removing anionic perfluorinated and polyfluoroalkyl substances from a water sample is provided, comprising: contacting the aforementioned quaternary ammonium salt cross-linked polymer dry gel adsorbent material with a water sample containing anionic perfluorinated and polyfluoroalkyl substances, causing the quaternary ammonium salt cross-linked polymer dry gel adsorbent material to absorb water, swell, and adsorb the anionic perfluorinated and polyfluoroalkyl substances in the water sample; and performing solid-liquid separation between the adsorbed quaternary ammonium salt cross-linked polymer dry gel adsorbent material and the water sample.

[0027] Compared with the prior art, this disclosure has at least one of the following beneficial effects:

[0028] (1) Completely fluorine-free safety framework: The cross-linked network contains no covalently bonded fluorine atoms, eliminating the risk of secondary pollution from recalcitrant organic fluorine and significantly reducing the cost of material preparation and raw materials;

[0029] (2) Dynamic water absorption and swelling and rapid mass transfer: It abandons the rigid hard pore process that relies on emulsion template solidification. The unique dry gel state can swell when in contact with water samples. Through the adaptive stretching of chain segments, a three-dimensional hydration mass transfer channel is dynamically constructed. This solves the defects of the existing emulsion template solidification technology, such as the limited mass transfer of rigid hard pores and the easy occurrence of hydrophobic self-assembly and local dense pore blockage of long chain quaternary ammonium salts. It greatly improves the site utilization rate.

[0030] (3) Super strong anti-competitive performance brought about by specific spatial configuration: When the asymmetric substitution structure of two short-chain alkyl groups and one medium-long-chain alkyl group is adopted, the material of this disclosure achieves a removal rate of perfluorooctanoic acid of not less than 90% by utilizing the synergistic effect of "low steric hindrance exposure of the two short-chain alkyl groups" and "microscopic hydrophobic neighborhood of the single long-chain alkyl group". This has achieved significant and unexpected technical effects. Attached Figure Description

[0031] The accompanying drawings illustrate exemplary embodiments of the present disclosure and, together with the foregoing description, are intended to provide a better understanding of the technical aspects of the present disclosure; therefore, the present disclosure is not to be construed as limited to the drawings.

[0032] In this disclosure, C(abc) indicates that the number of carbon atoms of the three alkyl substituents on the quaternary ammonium nitrogen atom are a, b, and c, respectively. C(1-1-1) represents a trimethyl quaternary ammonium salt structure; C(1-1-4) represents a dimethyl n-butyl quaternary ammonium salt structure; C(1-1-6) represents a dimethyl n-hexyl quaternary ammonium salt structure; C(2-2-2) represents a triethyl quaternary ammonium salt structure; CF represents comparative materials with a fluorinated alkyl side chain attached to the quaternary ammonium nitrogen atom.

[0033] Figure 1 The structural diagrams are of C(1-1-6) quaternary ammonium salt monomer, C(1-1-4) quaternary ammonium salt monomer, C(1-1-1) quaternary ammonium salt monomer, C(2-2-2) quaternary ammonium salt monomer and CF quaternary ammonium salt monomer;

[0034] Figure 2 This is a schematic diagram of the preparation process of the adsorbent material disclosed herein;

[0035] Figure 3 Scanning electron microscope image of C(1-1-6) adsorbent material;

[0036] Figure 4 The apparent ion exchange capacity and adsorption performance of C(1-1-6), C(1-1-4) adsorbent materials, as well as C(1-1-1), C(2-2-2) and CF adsorbent materials, are presented.

[0037] Figure 5 The adsorption kinetics curves for PFOA and PFPeA are shown for each adsorbent material.

[0038] Figure 6 A comparison chart of PFOA removal rates of various adsorbent materials under coexisting inorganic competitive anion conditions;

[0039] Figure 7 The adsorption isotherms of PFOA and PFPeA for each adsorbent are shown, where (a) is the C(1-1-1) adsorbent, (b) is the C(1-1-4) adsorbent, (c) is the C(1-1-6) adsorbent, (d) is the CF adsorbent, and (e) is the C(2-2-2) adsorbent.

[0040] Figure 8 The effect of C(1-1-6) adsorbent material on PFOA removal efficiency under different pH conditions is shown in the figure.

[0041] Figure 9 The effect of C(1-1-6) adsorbent material on PFOA removal efficiency under conditions of coexistence with natural organic matter;

[0042] Figure 10 The elemental distribution diagram of the C(1-1-6) adsorbent material before and after adsorption of PFOA is shown. Detailed Implementation

[0043] This disclosure will be described in more detail below to aid in understanding it.

[0044] It should be understood that the terms or words used in this specification and the appended claims should not be construed as limited to their general or dictionary meanings, but rather interpreted based on their meanings and concepts corresponding to the technical aspects of this disclosure, on the basis of the principle that the inventors are allowed to define terms appropriately for the purpose of best illustration.

[0045] It should be further understood that, unless otherwise expressly stated, when used in the specification, "comprising" or "including" indicates the presence of the said element and does not exclude the presence or addition of one or more other elements.

[0046] As used herein, a range is used as a shorthand to describe the individual values ​​within the range and each value. Any value within the range can be chosen as an endpoint of the range. Thus, the ranges 1 to 5 specifically include 1, 2, 3, 4, and 5, as well as subranges such as 2 to 5, 3 to 5, 2 to 3, 2 to 4, 1 to 4, etc.

[0047] As used herein, the term "quaternary ammonium salt-type crosslinked polymer dry gel adsorbent material" (also referred to herein as adsorbent material) refers to a solid porous material obtained by drying (preferably freeze-drying) a water-insoluble crosslinked polymer network formed by free radical crosslinking copolymerization of quaternary ammonium salt monomers and crosslinking agents. In this material, the quaternary ammonium salt monomers provide positively charged adsorption sites, the crosslinking agent constructs a three-dimensional network framework, and the dry gel morphology formed after drying can reabsorb water and swell in an aqueous medium.

[0048] As used in this article, the term "quaternary ammonium salt monomer" refers to a compound whose molecular structure contains both a carbon-carbon double bond that can participate in free radical polymerization and a positive potential point of quaternary ammonium salt.

[0049] As used herein, the term "crosslinking agent" refers to a compound whose molecular structure contains two or more carbon-carbon double bonds that can participate in free radical polymerization.

[0050] As used in this article, the term "dry gel morphology" refers to the solid aggregate structure that maintains a stable macroscopic shape in the dry state after cross-linked hydrogels have been desolventized and dried. Specifically, it refers to the non-dense micromorphology with wrinkles and irregular skeletal gaps formed after being shaped by a specific freeze-drying process.

[0051] As used herein, the term "water absorption swelling" refers to the physical behavior in which water molecules spontaneously penetrate into the network under the drive of osmotic pressure and the positive potential point of the hydrophilic quaternary ammonium salt when the adsorbent material disclosed herein comes into contact with an aqueous medium, causing the polymer chain segments to adaptively stretch and expand, thereby significantly expanding the volume and three-dimensional mass transfer channels of the material.

[0052] As used herein, the term "free of covalently bonded fluorine atoms" means that the quaternary ammonium salt monomers, crosslinking agents, and any comonomers constituting the three-dimensional network do not have any covalent substitution of fluorine atoms (F) on the covalent backbone of their molecular structures.

[0053] As used herein, the term "liquid medium" refers to the liquid-phase fluid used to soak the bulk cross-linked hydrogel after the copolymerization reaction and induce its initial physical swelling. Specifically, it is selected from pure water, pure ethanol, or a mixture of ethanol and water, and is used to expand the network channels to facilitate the diffusion of residual small molecules.

[0054] As used in this article, the term "contact" refers to the spatial interface contact and bonding of dry adsorbent materials with water samples containing anionic perfluorinated and polyfluoroalkyl substances. In practical engineering, this includes all known water treatment process forms such as adding materials to wastewater and stirring (mixing) and packing materials into rigid columns to allow static flow of wastewater (fixed bed adsorption columns).

[0055] As used herein, the term “C1-C3 alkyl” refers to a straight-chain or branched alkyl group containing 1 to 3 carbon atoms, such as methyl, ethyl, n-propyl, isopropyl, etc.

[0056] As used herein, the term “C4-C7 alkyl” refers to a straight-chain or branched alkyl group containing 4 to 7 carbon atoms, such as n-butyl, isobutyl, tert-butyl, n-pentyl, n-hexyl, n-heptyl, etc.

[0057] As used herein, the term “C2-C4 alkylene” refers to a divalent straight-chain or branched alkylene containing 2 to 4 carbon atoms, such as ethylene, n-propylene, isopropylene, n-butylene, etc.

[0058] As used in this article, the term "ratio of equilibrium adsorption capacity to apparent ion exchange capacity" (i.e., q) e The / IEC is used to characterize the efficiency of each quaternary ammonium salt exchange site in actually capturing PFAS molecules.

[0059] This disclosure provides a quaternary ammonium salt-type crosslinked polymer dry gel adsorbent material, which is obtained by crosslinking and copolymerizing a quaternary ammonium salt monomer and a crosslinking agent; the quaternary ammonium salt monomer has the structure of the following formula (I):

[0060]

[0061] Wherein, R1 is H or methyl, R2 and R3 are each independently C1-C3 alkyl, R4 is C4-C7 alkyl, R5 is C2-C4 alkylene, and X - For Cl - ,Br - or I - .

[0062] In this disclosure, the cross-linked polymer network does not contain covalently bonded fluorine atoms, and the adsorbent material is in the form of a dry gel and is capable of absorbing water and swelling in an aqueous medium.

[0063] In some embodiments, the quaternary ammonium salt monomer having the structure of formula (I) in step (1) can be a commercially available polymerizable quaternary ammonium salt monomer, or it can be obtained by quaternizing an acrylate or methacrylate monomer containing a tertiary amine group with a C4-C7 alkyl halide. The C4-C7 alkyl halide can be one or more of bromobutane, bromopentane, and bromohexane. During the quaternization reaction, the molar ratio of the acrylate or methacrylate monomer containing the tertiary amine group to the C4-C7 alkyl halide is controlled at 1:(1.0-2.0).

[0064] In some embodiments, the quaternary ammonium salt-type crosslinked polymer dry gel adsorbent material comprises a functional structural unit formed by 2-(methacryloyloxy)ethyl dimethyl n-hexyl ammonium salt and a crosslinked structural unit formed by a crosslinking agent such as a polyfunctional olefin crosslinking agent, wherein the functional structural unit and the crosslinked structural unit together form a water-insoluble crosslinked polymer network.

[0065] In some embodiments, the quaternary ammonium nitrogen atom in the functional structural unit is attached to two methyl groups and one n-hexyl group; the monomers constituting the cross-linked polymer network do not contain covalently bonded fluorine atoms, except for the adsorbed perfluorinated and polyfluoroalkyl substances; the adsorbent material is prepared by washing and freeze-drying a cross-linked hydrogel and is capable of absorbing water and swelling in an aqueous medium.

[0066] In some embodiments, the crosslinking agent is ethylene glycol dimethacrylate. In some embodiments, the molar ratio of the 2-(methacryloyloxy)ethyl dimethyl n-hexylammonium salt to ethylene glycol dimethacrylate is 1:(0.20-0.40).

[0067] In some embodiments, the apparent ion exchange capacity of the quaternary ammonium salt-type crosslinked polymer dry gel adsorbent material of the present invention is 1.5-3.5 mmol / g; in some preferred embodiments, the apparent ion exchange capacity of the adsorbent material is 2.0-3.2 mmol / g; and in a further preferred embodiment, the apparent ion exchange capacity of the adsorbent material is 2.3-3.0 mmol / g.

[0068] In some preferred embodiments, under the conditions of an initial PFOA concentration of 0.025 mmol / L, an inorganic competing anion concentration such as sulfate ion concentration of 10 mmol / L, a water sample volume of 30 mL, an adsorbent material dosage of 5 mg, a temperature of 25°C, an oscillation speed of 180 rpm, and a contact time of 48 h, the removal rate of PFOA by the adsorbent material is not less than 90%.

[0069] The 2-(methacryloyloxy)ethyl dimethyl n-hexylammonium salt quaternary ammonium salt monomer, prepared or purchased above, a crosslinking agent, a thermal initiator, and an ethanol / water mixed solvent are mixed evenly. After deoxygenation by purging with nitrogen, a free radical crosslinking polymer reaction is carried out. After curing, a blocky crosslinked hydrogel is obtained. In some embodiments, the thermal initiator includes one or more of azobisisobutyronitrile, persulfate, and 2-hydroxy-2-methyl-1-phenyl-1-propanone.

[0070] In some embodiments, the mass ratio of ethanol to water in the ethanol / water mixed solvent is (0.1-2):1, preferably (0.3-0.8):1; the dosage of the quaternary ammonium salt monomer is 0.05-2.0 mol / L based on the volume of the reaction system.

[0071] In some preferred embodiments, the crosslinking agent is specifically ethylene glycol dimethacrylate (EGDMA), and the thermal initiator is specifically ammonium persulfate (APS).

[0072] To control the polymerization rate and aggregation morphology of the crosslinked network, the temperature of the free radical crosslinked polymer reaction is limited to 40 to 90°C, preferably 50 to 70°C, and the reaction time is 2 to 8 h.

[0073] After the polymerization reaction is completed, the resulting cross-linked hydrogel is macroscopically broken down or shredded, and then placed in a liquid medium for swelling. In some preferred embodiments, the liquid medium is specifically pure water (deionized water or distilled water), and the mass fraction of ethanol in the ethanol / water mixed solvent is controlled between 20% and 50%. The swelling time of the cross-linked hydrogel in the pure water medium is controlled between 0.5 and 3 hours.

[0074] The swollen and fully washed cross-linked hydrogel particles are collected and then dried. In some preferred embodiments, the drying process is specifically a freeze-drying process, with the freeze-drying time controlled between 12 and 36 hours. Moisture is removed by vacuum low-temperature freeze-drying, which, while removing ice crystals, also "locks in" the swollen and shaped non-dense micropolymer framework, ultimately yielding the quaternary ammonium salt-type cross-linked polymer dry gel adsorbent material.

[0075] The quaternary ammonium salt-type cross-linked polymer dry gel adsorbent material disclosed herein has extremely high application value in practical environmental water treatment engineering. In use, the dry adsorbent material is brought into spatial interface "contact" with a target water sample containing the target pollutant. Upon contact with the water sample, the material spontaneously absorbs water and swells instantly, opening three-dimensional mass transfer channels. Utilizing the synergistic effect of high-charge sites fixed within the cross-linked network and the microscopic non-fluorinated hydrophobic microenvironment, it efficiently captures anionic target pollutants in the water sample. Finally, solid-liquid separation is achieved through conventional methods such as sedimentation, filtration, or centrifugation.

[0076] In some preferred embodiments, the application method is specifically designed to remove anionic perfluorinated and polyfluoroalkyl substances (PFAS) from water samples. The anionic perfluorinated and polyfluoroalkyl substances include at least one of perfluorocarboxylic acid PFAS and perfluorosulfonic acid PFAS; more specifically, the anionic perfluorinated and polyfluoroalkyl substances include, but are not limited to, at least one of perfluorooctanoic acid and perfluorovalerate.

[0077] In some preferred embodiments, the materials disclosed herein exhibit exceptionally superior resistance to anion competition. The water samples containing perfluorinated and polyfluoroalkyl substances can be used not only in pure water systems but are also broadly compatible with complex aquatic environments. Specifically, the water samples may contain high concentrations of conventional inorganic competing anions, including at least one of chloride, nitrate, and sulfate ions, with an initial background molar concentration of these inorganic competing anions reaching 1 to 10 mmol / L. Under these high-concentration competing conditions, the preferred dimethyl hexyl adsorbent material of this disclosure, through hydrophobic interactions, can still maintain a stable removal rate of over 90% for organic fluorine pollutants such as perfluorooctanoic acid.

[0078] Example

[0079] The effects and functions of this disclosure will be described in more detail below through specific embodiments thereof. However, these embodiments are for illustrative purposes only, and the scope of the claims of this disclosure is not defined thereto.

[0080] Example 1: Preparation of C(1-1-6) quaternary ammonium salt monomer

[0081] 15 mmol of 2-(dimethylamino)ethyl methacrylate was dissolved in 15 mL of acetonitrile, and 22.5 mmol of 1-bromohexane was added. The resulting reaction system was stirred at 50 °C in the dark for 24 h to allow the tertiary amine group to undergo a quaternization reaction with 1-bromohexane.

[0082] After the reaction was complete, the reaction solution was cooled to room temperature and concentrated to approximately 1 / 10 of its original volume using rotary evaporation. Excess diethyl ether was added to the concentrate to precipitate the quaternary ammonium salt product. The precipitate was centrifuged at 10,000 rpm for 1 min, the supernatant was discarded, and the precipitate was washed three times with diethyl ether.

[0083] The washed product was dried under vacuum at 45°C to obtain 2-(methacryloyloxy)ethyl dimethyl n-hexyl ammonium bromide, namely the C(1-1-6) quaternary ammonium salt monomer.

[0084] Example 2: Preparation of C(1-1-6) adsorbent material

[0085] 1.5 mmol of the C(1-1-6) quaternary ammonium salt monomer prepared in Example 1 and 1.4 g of deionized water were added to a heat-resistant reaction tube and stirred until fully dissolved or uniformly dispersed to obtain the aqueous phase of the quaternary ammonium salt monomer.

[0086] Separately, 89.2 mg of ethylene glycol dimethacrylate was dissolved in 0.6 g of ethanol to obtain the ethanol phase of the crosslinking agent. The amount of ethylene glycol dimethacrylate added was approximately 0.45 mmol, and the molar ratio of the quaternary ammonium salt monomer to the crosslinking agent was approximately 1:0.30.

[0087] Under continuous stirring, the ethanol phase of the crosslinking agent was slowly added dropwise to the aqueous phase of the quaternary ammonium salt monomer; after the addition was complete, 3.4 mg of ammonium persulfate was added and mixed thoroughly. The resulting polymerization reaction system was reacted at 60 °C for 4 h to obtain a blocky crosslinked hydrogel.

[0088] The resulting cross-linked hydrogel was cut into small pieces, swollen in a liquid medium (deionized water) for 1 h, and repeatedly washed with deionized water to remove unreacted monomers, initiator residues and other soluble components.

[0089] The washed cross-linked hydrogel was freeze-dried for 24 h to obtain C(1-1-6) adsorbent material, which was then ground or crushed into particles suitable for adsorption experiments.

[0090] Thus, the positive potential point of the quaternary ammonium salt and the n-hexyl side chain connected to it are fixed in the water-insoluble crosslinking network through the same functional structural unit.

[0091] Example 3: Preparation of C(1-1-4) quaternary ammonium salt monomer and adsorbent material

[0092] 1-Bromobutane was used instead of 1-Bromohexane in Example 1. Other quaternization, concentration, precipitation, washing and drying conditions were the same as in Example 1 to obtain 2-(methacryloyloxy)ethyl dimethyl n-butylammonium bromide, i.e., C(1-1-4) quaternary ammonium salt monomer.

[0093] The C(1-1-6) quaternary ammonium salt monomer in Example 2 was replaced with this quaternary ammonium salt monomer, and other polymerization and post-treatment conditions were the same as in Example 2, to obtain C(1-1-4) adsorbent material.

[0094] The obtained C(1-1-4) adsorbent material was used to investigate the effects of medium and long chain alkyl length on apparent ion exchange capacity, PFAS adsorption capacity, adsorption kinetics, isothermal adsorption characteristics and resistance to competing anions.

[0095] Comparative Example 1: Preparation of C(1-1-1) adsorbent material

[0096] 2-(trimethylammonium) ethyl methacrylate halide was used as the C(1-1-1) quaternary ammonium salt monomer, and the amount of actual feed material was calculated based on the effective content of the product.

[0097] The C(1-1-1) quaternary ammonium salt monomer was used to replace the C(1-1-6) quaternary ammonium salt monomer in Example 2, and other polymerization and post-treatment conditions were the same as in Example 2 to obtain the C(1-1-1) adsorbent material.

[0098] When the quaternary ammonium salt monomer is used in the form of an aqueous solution, the water in the commercial solution is deducted accordingly to keep the amount of quaternary ammonium salt monomer and solvent composition of different polymerization systems comparable.

[0099] Comparative Example 2: Preparation of C(2-2-2) quaternary ammonium salt monomer and adsorption material

[0100] 15 mmol of 2-(diethylamino)ethyl methacrylate was dissolved in 15 mL of acetonitrile, and 22.5 mmol of bromoethane was added. The mixture was stirred at 50 °C in the dark for 24 h.

[0101] The reaction solution was concentrated, precipitated with diethyl ether, centrifuged, washed with diethyl ether, and dried under vacuum at 45°C to obtain 2-(methacryloyloxy)ethyltriethylammonium bromide, namely the C(2-2-2) quaternary ammonium salt monomer.

[0102] The C(1-1-6) quaternary ammonium salt monomer in Example 2 was replaced with this quaternary ammonium salt monomer, and the other polymerization and post-treatment conditions were the same as in Example 2, to obtain the C(2-2-2) adsorbent material.

[0103] Comparative Example 3: Preparation of CF Quaternary Ammonium Salt Monomer and Adsorption Material

[0104] 15 mmol of 2-(dimethylamino)ethyl methacrylate was dissolved in 15 mL of acetonitrile, and 22.5 mmol of 1,1,2,2-tetrahydroperfluorohexyl iodine was added. The mixture was stirred at 50 °C in the dark for 24 h.

[0105] The reaction solution was concentrated, precipitated with diethyl ether, centrifuged, washed with diethyl ether, and dried under vacuum at 45°C to obtain a CF quaternary ammonium salt monomer containing polymerizable double bonds.

[0106] The quaternary ammonium salt monomer was used to replace the C(1-1-6) quaternary ammonium salt monomer in Example 2. Other polymerization and post-treatment conditions were the same as in Example 2 to obtain the CF adsorbent material.

[0107] CF was used to compare the effects of non-fluorinated n-hexyl side chains and fluorinated side chains on the adsorption performance of PFAS.

[0108] Example 4: Microstructure characterization of C(1-1-6) adsorbent material

[0109] The C(1-1-6) adsorbent material prepared in Example 2 was used as the test sample. The dry sample was fixed on a conductive adhesive, sputtered with gold, and its microstructure was observed using a scanning electron microscope. The results are as follows. Figure 3 As shown. By Figure 3 It can be seen that the C(1-1-6) adsorbent material has a relatively rough, wrinkled surface with irregular pores and skeletal gaps, indicating that the freeze-dried material has a non-dense microstructure. This structure is beneficial for the material to absorb water and swell in water, and provides channels for PFAS to transfer mass into the cross-linked network and access quaternary ammonium salt functional sites.

[0110] Example 5: Apparent ion exchange capacity and high-load PFAS adsorption performance

[0111] Weigh 10 mg of the C(1-1-6) adsorbent material obtained in Example 2, the C(1-1-4) adsorbent material obtained in Example 3, and the adsorbent materials obtained in Comparative Examples 1-3, respectively, and add them to 25 mL of 0.2 mol / L sodium nitrate solution. Shake at 25 °C and 180 rpm for 48 h.

[0112] After oscillation, solid-liquid separation was performed, and the concentration of halide ions released in the liquid phase was determined by ion chromatography, and the apparent IEC was calculated.

[0113] Apparent ion exchange capacity is calculated according to the following formula:

[0114]

[0115] In the formula, Apparent ion exchange capacity, in mmol / g; The concentration of halide ions in the test solution is expressed in mmol / L. 1. Halogen ion concentration in blank test, in mmol / L; V is the volume of sodium nitrate solution, in L; f is the dilution factor; m is the mass of dry adsorbent material, in g.

[0116] Separately, prepare aqueous solutions of 1 mmol / L perfluorooctanoic acid (PFOA) and perfluoropentanoic acid (PFPeA). Take 30 mL of water sample, add 5 mg of the corresponding dry adsorbent, and shake at 25 °C and 180 rpm for 48 h. After adsorption is complete, determine the equilibrium concentration of PFAS in the aqueous phase and calculate the average equilibrium adsorption capacity. ) and site utilization efficiency ( / IEC), the result is as follows Figure 4 As shown.

[0117] Depend on Figure 4 It can be seen that the apparent ion exchange capacity of the C(1-1-1) adsorbent obtained in Comparative Example 1 is 3.438 mmol / g, which is the highest among all materials; the apparent ion exchange capacities of C(1-1-4) obtained in Example 3, C(2-2-2) obtained in Comparative Example 2, CF obtained in Comparative Example 3, and C(1-1-6) obtained in Example 2 are 2.969 mmol / g, 2.786 mmol / g, 2.759 mmol / g, and 2.532 mmol / g, respectively.

[0118] Under 1 mmol / L PFOA conditions, the average equilibrium adsorption capacities of C(1-1-1), C(1-1-4), C(1-1-6), CF, and C(2-2-2) were ( The average equilibrium adsorption capacities of the materials were 3.645 mmol / g, 2.886 mmol / g, 2.995 mmol / g, 2.840 mmol / g, and 2.801 mmol / g, respectively, under the condition of 1 mmol / L PFPeA. The average equilibrium adsorption capacities of the materials were 3.193 mmol / g, 2.794 mmol / g, 2.334 mmol / g, 2.362 mmol / g, and 2.358 mmol / g, respectively.

[0119] As can be seen from the above, the adsorption capacity and apparent ion exchange capacity of each material are not completely linearly related, indicating that the quaternary ammonium nitrogen substitution structure and its adjacent microenvironment also affect the actual adsorption performance of PFAS. C(1-1-1) has the highest apparent ion exchange capacity and the highest adsorption capacity per unit mass of PFOA and PFPeA, indicating that under the high loading conditions, the number of quaternary ammonium salt sites that can participate in adsorption per unit mass of material is an important factor affecting the adsorption capacity of PFAS.

[0120] After normalization of apparent ion exchange capacity, C(1-1-6) for PFOA The IEC value is 1.183, the highest among all materials, higher than C(1-1-1) (1.060), CF (1.029), C(2-2-2) (1.005), and C(1-1-4) (0.972). In particular, the apparent ion exchange capacity of C(2-2-2) is 2.786 mmol / g, higher than that of C(1-1-6) (2.532 mmol / g), but its PFOA equilibrium adsorption capacity and... The / IEC values ​​are all lower than those of C(1-1-6). This result indicates that the normalized adsorption advantage of C(1-1-6) for PFOA cannot be attributed to its greater number of apparent exchange sites, nor can it be obtained by simultaneously elongating all alkyl groups on the quaternary ammonium nitrogen, but is related to the specific asymmetric substitution structure of two methyl groups and one n-hexyl group.

[0121] For PFPeA, C(1-1-4) / IEC is 0.941, the highest among all materials; q of C(1-1-1), C(1-1-6), CF and C(2-2-2) e The / IEC values ​​were 0.929, 0.922, 0.856, and 0.846, respectively. C(1-1-4) showed a higher normalized adsorption capacity for PFPeA, while C(1-1-6) showed the highest normalized adsorption capacity for PFOA, indicating that the length of the medium-to-long chain alkyl group near the positive potential point of the quaternary ammonium salt may have different effects on the adsorption of PFAS with different chain lengths.

[0122] The above results indicate that the positive potential point of quaternary ammonium salts can bind anionic PFAS through electrostatic attraction or ion exchange; the medium-to-long-chain alkyl groups adjacent to the positive potential point of quaternary ammonium salts may provide additional hydrophobic stabilization to the PFAS segments. C(1-1-6) achieves an optimal balance between the number of sites, site utilization efficiency, and adsorption capacity. The n-hexyl side chain significantly promotes the normalized adsorption capacity of PFOA, while the n-butyl side chain exhibits a higher normalized adsorption capacity for the shorter-chain PFPeA. The q-value of C(1-1-6) for PFOA... e The / IEC value is 1.183, the highest among all materials, further verifying the advantage of this structure in terms of site utilization efficiency.

[0123] To further investigate whether this structure affects the rate at which PFAS reaches the effective site, adsorption kinetics experiments were conducted.

[0124] Example 6: PFAS Adsorption Kinetics

[0125] 50 mg / L aqueous solutions of PFOA and PFPeA were prepared, with a water sample volume of 30 mL and a dry adsorbent concentration of 0.1 g / L.

[0126] Each adsorbent was added to its corresponding solution, and the mixture was shaken at 25°C and 180 rpm. Samples were taken at preset time points to determine the PFAS concentration in the aqueous phase. / This indicates the proportion of the remaining concentration in the aqueous phase, and the results are as follows: Figure 5 As shown.

[0127] Depend on Figure 5 It can be seen that during the PFOA adsorption process, CF showed a faster concentration decrease in the initial stage of adsorption, and the adsorption rates of C(1-1-6) and C(1-1-4) were also faster than those of C(1-1-1); during the PFPeA adsorption process, C(1-1-6) showed a lower concentration decrease at 60 min. / .

[0128] Although C(1-1-1) has a high apparent IEC and high loading capacity, its initial adsorption is relatively slow, indicating that the number of sites cannot determine the mass transfer and binding rate of PFAS in the cross-linked network.

[0129] Both C(1-1-4) and C(1-1-6) have a medium-to-long-chain alkyl group near the positive potential point of the quaternary ammonium salt and exhibit a faster adsorption response than C(1-1-1). The faster initial adsorption of CF indicates that the fluorinated side chain can provide additional affinity, but C(1-1-6) also obtained faster kinetics without the introduction of a fluorinated structural domain.

[0130] Therefore, improving adsorption kinetics is not solely achieved by introducing fluorine-containing affinity domains.

[0131] To determine whether the structure could maintain PFAS adsorption under inorganic competitive anion conditions, a coexistence inorganic competitive anion experiment was further conducted.

[0132] Example 7: Effect of coexisting inorganic competing anions on PFOA adsorption

[0133] Prepare an aqueous solution of PFOA with an initial concentration of 0.025 mmol / L. Take 30 mL of water sample, add 5 mg of dry adsorbent, and add NaCl, NaNO3, or Na2SO4 respectively to make the corresponding anion concentration 1 mmol / L or 10 mmol / L; set up a blank group without adding the above anions.

[0134] Each system was shaken at 25℃ and 180 rpm for 48 h. After adsorption, the PFOA concentration in the aqueous phase was measured and the removal rate was calculated. The results are as follows: Figure 6 As shown.

[0135] Depend on Figure 6 It can be seen that, under the condition of no addition of competing anions, the PFOA removal rate of each material is relatively high; as the concentration of coexisting inorganic competing anions increases, the adsorption and retention capacity of different structural materials shows significant differences.

[0136] In the presence of 10 mmol / L chloride, nitrate and sulfate ions, the average PFOA removal rate of C(1-1-1) decreased to 71.27%, 44.96% and 10.32%, respectively.

[0137] This result combined Figure 4 This indicates that a higher number of positive potential points of quaternary ammonium salts can improve high loading capacity, but cannot guarantee the adsorption and retention of PFAS under strong inorganic competitive anion competition conditions on its own.

[0138] The average PFOA removal rates of C(1-1-6) obtained in Example 2 under the same three 10 mmol / L inorganic competitive anion conditions were 94.21%, 94.07% and 92.71%, respectively, showing strong resistance to competitive anions.

[0139] While conventional inorganic competing anions can compete for the positive potential point of quaternary ammonium salts, they lack the organic segments capable of acquiring the hydrophobic stabilizing effect of the adjacent n-hexyl group. Therefore, the non-fluorinated hydrophobic microenvironment near the positive potential point of the quaternary ammonium salt is beneficial for enhancing the competitive adsorption advantage of PFOA over inorganic competing anions.

[0140] Under 10 mmol / L sulfate ion conditions, the average PFOA removal rates of C(2-2-2) and CF were 63.59% and 86.90%, respectively, both lower than the 92.71% of C(1-1-6).

[0141] The fact that C(1-1-6) is superior to C(2-2-2) indicates that the anti-competitive performance is not obtained by simultaneously elongating the three alkyl groups, but is related to a specific asymmetric configuration of two methyl groups and one n-hexyl group.

[0142] The fact that C(1-1-6) outperformed the tested CF control indicates that, under the current cross-linking network and test conditions, achieving the aforementioned anti-competitive effect does not require the introduction of fluorine-containing affinity domains. These results demonstrate that the C(1-1-6) adsorbent maintains a high PFOA removal rate even under conditions where chloride, nitrate, and sulfate ions coexist, exhibiting universal anti-competitive ability against different types of inorganic competing anions.

[0143] To further differentiate between high-concentration capacity and low-concentration affinity, adsorption isotherm analysis was performed on each material.

[0144] Example 8: PFAS Adsorption Isotherm

[0145] PFOA and PFPeA aqueous solutions with different initial concentrations were prepared, with the initial PFAS concentration ranging from 10 to 500 mg / L. Adsorption tests were conducted using the C(1-1-6) adsorbent obtained in Example 2, the C(1-1-4) adsorbent obtained in Example 3, and the C(1-1-1), C(2-2-2), and CF adsorbents obtained in Comparative Examples 1-3, respectively.

[0146] Except for the initial PFAS concentration, the water sample volume, dry adsorbent amount, adsorption temperature, oscillation rate, and contact time for each group of experiments were 30 mL, 5 mg, 25℃, 180 rpm, and 48 h, respectively. After adsorption, the equilibrium concentration of PFAS in the aqueous phase was measured, the equilibrium adsorption capacity was calculated, and the isothermal adsorption data were fitted using the Langmuir model and the Freundlich model, respectively. The results are shown below. Figure 7 As shown.

[0147] The fitting results show that C(1-1-1) has the maximum fitted adsorption capacity for PFOA and PFPeA. The concentrations were 1733.1 mg / g and 963.9 mg / g, respectively, both the highest among all materials. (Combined) Figure 4 It can be seen that the apparent ion exchange capacity of C(1-1-1) is 3.438 mmol / g, which is also the highest among all materials. The above results corroborate each other, indicating that the number of accessible quaternary ammonium salt sites per unit mass of material is an important factor affecting the maximum adsorption capacity in the high concentration range.

[0148] The apparent ion exchange capacity of C(1-1-6) is 2.532 mmol / g, lower than that of CF (2.759 mmol / g) and C(2-2-2) (2.786 mmol / g), but its ion exchange capacity for PFOA is higher. The concentration was 1251.2 mg / g, higher than CF's 1163.9 mg / g and close to C(2-2-2)'s 1274.3 mg / g; its effect on PFPeA was... It was 686.6 mg / g, higher than CF's 641.9 mg / g and C(2-2-2)'s 648.4 mg / g.

[0149] The above results indicate that although C(1-1-6) has a relatively low apparent ion exchange capacity, it can still maintain a high fitted maximum adsorption capacity. Therefore, although the maximum adsorption capacity of different materials is generally affected by the number of positive potential points of the quaternary ammonium salt, it cannot be judged solely based on the apparent ion exchange capacity. The alkyl substitution structure near the positive potential point of the quaternary ammonium salt also affects the equilibrium adsorption performance of PFAS.

[0150] C(1-1-4) for PFOA and PFPeA The apparent ion exchange capacities were 1324.5 mg / g and 792.2 mg / g, respectively, both higher than those of C(1-1-6). Considering the difference in apparent ion exchange capacities between the two, it can be seen that as the adjacent medium-to-long-chain alkyl group extends from n-butyl to n-hexyl, the number of apparent sites per unit mass and the maximum adsorption capacity of the material change. This result indicates that side chain elongation does not monotonically increase the maximum adsorption capacity per unit mass, but rather requires a balance between the number of positively charged sites of the quaternary ammonium salt, site accessibility, and proximity hydrophobic interactions.

[0151] In summary, the adsorption isotherm results and Figure 4 The apparent ion exchange capacity and high-load adsorption results corroborate each other: the number of accessible quaternary ammonium salt sites mainly provides the basis for the adsorption capacity in the high concentration range, while the alkyl substitution mode on the quaternary ammonium nitrogen and its adjacent microenvironment further affect the actual equilibrium adsorption performance of the material. Although C(1-1-6) does not have the highest apparent ion exchange capacity and the maximum fitted adsorption capacity, it also exhibits fast adsorption kinetics and strong resistance to competing anions while maintaining a high adsorption capacity, reflecting a comprehensive balance between different adsorption properties.

[0152] Example 9: Effect of pH on PFOA adsorption performance

[0153] Prepare an initial concentration of 50 mg / L of PFOA aqueous solution, with a total volume of 20 mL for each group of water samples. Add the C(1-1-6) adsorbent material obtained in Example 2 to each group of water samples to make the dry adsorbent material concentration 0.2 g / L, that is, add 4 mg of dry adsorbent material to each group.

[0154] The initial pH of the water samples was adjusted to 3, 5, 7, 9, and 11 using either an acidic solution (sulfuric acid) or an alkaline solution (sodium hydroxide solution), respectively. Adsorption experiments were conducted under the same temperature, shaking speed, and contact time conditions. After adsorption, the PFOA concentration in the aqueous phase was measured, and the PFOA removal rate was calculated. The results are as follows: Figure 8 As shown.

[0155] Depend on Figure 8 It can be seen that the removal rate of PFOA by C(1-1-6) adsorbent material is higher than 90% in the pH range of 3-7, with the highest removal rate under neutral conditions, indicating that the material can maintain high and stable PFOA adsorption performance under acidic to neutral aqueous phase conditions.

[0156] PFOA removal rates decreased when the pH of the water sample increased to 9 and 11, but remained at a high level at pH 11. Since the quaternary ammonium groups in the material have a positive charge, this decrease should not be attributed to deprotonation of the quaternary ammonium sites. The decrease in adsorption performance under strongly alkaline conditions may be related to OH... - It is related to the competition for the positive potential point of quaternary ammonium salts and changes in the ionic environment of the solution.

[0157] The above results indicate that the C(1-1-6) adsorbent material can adsorb PFOA over a wide pH range, and exhibits high adsorption stability, especially in the pH range of 3-7, showing potential for application under different acid and alkaline conditions in water bodies.

[0158] Example 10: Adsorption performance under conditions of coexistence of natural organic matter

[0159] Prepare an initial concentration of 50 mg / L of PFOA aqueous solution, with a total volume of 20 mL for each group of water samples. Add the C(1-1-6) adsorbent material obtained in Example 2 to each group of water samples to make the dry adsorbent material concentration 0.2 g / L, that is, add 4 mg of dry adsorbent material to each group.

[0160] Sodium alginate, humic acid, and bovine serum albumin were selected as representatives of natural organic matter, namely polysaccharides, humic substances, and proteins, respectively. Sodium alginate is denoted as SA, humic acid as HA, and bovine serum albumin as BSA.

[0161] In the single natural organic matter interference test, SA, HA, or BSA were added to the PFOA water sample to make the corresponding natural organic matter concentration 7.5 mg / L. The experiment was carried out under the same adsorption conditions, and the PFOA concentration in the aqueous phase was measured and the removal rate was calculated after the adsorption was completed.

[0162] In the mixed natural organic matter interference experiment, SA, HA, and BSA were simultaneously added to the PFOA water sample, with each of the three at a concentration of 2.5 mg / L, resulting in a total mixed natural organic matter concentration of 7.5 mg / L. A blank control group without added natural organic matter was also set up. Samples were taken at 0, 5, 10, 20, 30, and 60 min to measure the PFOA concentration and calculate the corresponding removal rate. The results are as follows: Figure 9 As shown.

[0163] Depend on Figure 9 As shown in the left figure, when SA, HA or BSA are present at 7.5 mg / L, the removal rate of PFOA by the C(1-1-6) adsorbent material remains above 90%, indicating that at the natural organic matter concentration tested in this example, the three representative natural organic matter types did not significantly inhibit the PFOA removal effect of the material.

[0164] Depend on Figure 9 As shown in the right figure, in the mixed natural organic matter system with SA, HA, and BSA each at 2.5 mg / L, the removal rate of PFOA by C(1-1-6) increased rapidly with contact time, and its adsorption process was generally similar to that of the control group without added natural organic matter. At 60 min, both the mixed natural organic matter group and the control group achieved high PFOA removal rates, and no significant difference was observed between the two.

[0165] The above results indicate that, within the range of natural organic matter types, concentrations, and contact times tested in this embodiment, the C(1-1-6) adsorbent material can maintain a relatively fast PFOA adsorption response and a high endpoint removal rate, demonstrating a certain tolerance to natural organic matter interference.

[0166] Example 11: Material characterization before and after PFOA adsorption

[0167] The elemental distribution of the C(1-1-6) samples before and after PFOA adsorption obtained in Example 2 was characterized by SEM-EDS, and the results are as follows: Figure 10 As shown.

[0168] The fluorine signal in the sample before adsorption was weak; after PFOA adsorption, the fluorine signal in the detection area was significantly enhanced. This change is consistent with the enrichment of PFOA in the accessible area of ​​the C(1-1-6) adsorbent material, providing elemental distribution evidence for PFOA adsorption by the material.

[0169] Comprehensive Explanation of Implementation Results

[0170] The above examples and comparative examples show that the alkyl substitution structure on quaternary ammonium nitrogen can simultaneously affect the apparent ion exchange capacity, PFAS equilibrium adsorption capacity, adsorption kinetics, and competitive anion tolerance of the adsorbent material, but the different properties are not determined by the same structural factor alone.

[0171] C(1-1-1) exhibits the highest apparent ion exchange capacity among all materials and demonstrates high adsorption capacity per unit mass and fitted maximum adsorption capacity in both high-load adsorption and isothermal adsorption experiments. This result indicates that the number of accessible quaternary ammonium salt sites per unit mass of material is a crucial basis for the high-load PFAS adsorption capacity. As the alkyl substituent on the quaternary ammonium nitrogen increases, the overall number of apparent exchange sites per unit mass of material decreases; therefore, simply extending the alkyl chain cannot continuously improve the maximum adsorption capacity of the material.

[0172] However, the actual PFAS adsorption performance of the materials cannot be explained solely by the apparent ion exchange capacity. The apparent ion exchange capacity of C(1-1-6) is 2.532 mmol / g, lower than that of C(2-2-2) and CF, but its equilibrium adsorption capacity for PFOA is higher than that of C(2-2-2) and CF, respectively, and the PFOA... The / IEC value is 1.183, the highest among all materials. Adsorption isotherm results further indicate that although C(1-1-6) does not have the highest apparent ion exchange capacity, it still maintains a high fitted maximum adsorption capacity. These results suggest that the adsorption performance of C(1-1-6) for PFOA cannot be attributed solely to the number of positive potential points of the quaternary ammonium salt; the n-hexyl side chains adjacent to the positive potential points of the quaternary ammonium salt also affect the actual equilibrium adsorption behavior of PFAS.

[0173] A comparison between C(1-1-4) and C(1-1-6) shows that the length of the adjacent medium-to-long-chain alkyl group can affect the adsorption performance of PFAS with different chain lengths. C(1-1-4) has a higher normalized adsorption capacity for PFPeA, while C(1-1-6) has the highest normalized adsorption capacity for PFOA. This indicates that the effect of side chain length on PFAS adsorption is not simply a monotonic change with the length of the alkyl chain, but is related to the PFAS chain length, the number of positive potential sites of the quaternary ammonium salt, and the microenvironment adjacent to the site.

[0174] Adsorption kinetics results showed that the initial adsorption rates of PFAS by C(1-1-4) and C(1-1-6) were faster than those by C(1-1-1), indicating that a higher apparent ion exchange capacity does not necessarily correspond to a faster adsorption rate. Without being limited by a mechanistic explanation, the medium- to long-chain alkyl groups located near the positive potential point of the quaternary ammonium salt may facilitate the partitioning of PFAS from the aqueous phase to the cross-linked network and promote their proximity to the quaternary ammonium salt adsorption site.

[0175] The coexistence inorganic competitive anion assay further demonstrated the structural advantages of C(1-1-6). In the presence of 10 mmol / L chloride, nitrate, and sulfate ions, C(1-1-6) still achieved PFOA removal rates of 94.21%, 94.07%, and 92.71%, respectively; while C(1-1-1) showed removal rates decreasing to 71.27%, 44.96%, and 10.32% under the same conditions. These results indicate that while simply increasing the number of positive potential sites in the quaternary ammonium salt is beneficial for high adsorption capacity, it is insufficient to guarantee PFOA adsorption under conditions of strong inorganic competitive anion adsorption.

[0176] In the presence of 10 mmol / L sulfate ions, the removal rates of PFOA by C(2-2-2) and CF were 63.59% and 86.90%, respectively, both lower than the 92.71% of C(1-1-6). A comparison between C(1-1-6) and C(2-2-2) shows that simultaneously elongating the three alkyl groups on the quaternary ammonium nitrogen to ethyl groups does not achieve the same competitive anion tolerance as the structure with two methyl groups and one n-hexyl group, indicating that the technical effect does not stem from a simple simultaneous elongation of the alkyl chain or an overall increase in the hydrophobicity of the material. A comparison between C(1-1-6) and CF shows that, under the crosslinking network and test conditions of this disclosure, achieving strong competitive anion tolerance does not require the introduction of a fluorinated affinity domain.

[0177] Microscopic morphology characterization revealed that the C(1-1-6) adsorbent material possesses a rough, wrinkled framework with irregular pores and gaps, providing a morphological and structural basis for water absorption and mass transfer of PFAS into the cross-linked network. The fluorine signal in the material was significantly enhanced after PFOA adsorption, further indicating that PFOA can enter and accumulate in the accessible region of the material.

[0178] C(1-1-6) also exhibited good adaptability under different hydrochemical conditions. Within the pH range of 3-7, its PFOA removal rate remained above 90%. In the tested systems containing sodium alginate, humic acid, bovine serum albumin, and their mixtures, the material maintained a high PFOA removal rate and a fast adsorption response, indicating that the material possesses certain pH adaptability and tolerance to interference from natural organic matter.

[0179] Therefore, the technical contribution of this disclosure lies in employing a specific asymmetric substitution structure (particularly two methyl groups and one n-hexyl group) on the quaternary ammonium nitrogen atom, thereby covalently fixing the positive potential point of the quaternary ammonium salt and the adjacent non-fluorinated hydrophobic side chain to a water-absorbing crosslinked network using the same functional structural unit. The positive potential point of the quaternary ammonium salt provides a high-load adsorption capacity basis for anionic PFAS, while the adjacent n-hexyl side chain is beneficial for improving the actual adsorption performance, adsorption kinetics, and adsorption retention capacity relative to coexisting inorganic competing anions of PFAS, thereby achieving synergistic regulation of the adsorption capacity basis, adsorption rate, and tolerance to competing anions. The technical effect does not stem from simply increasing the charge density, simultaneously extending all alkyl groups, improving the overall hydrophobicity of the material, or introducing fluorinated affinity side chains, but is related to the specific asymmetric configuration of the two short-chain alkyl groups and the one medium-to-long-chain alkyl group and their fixation method in the adsorption material network.

[0180] Although several embodiments of this disclosure have been described and illustrated herein, those skilled in the art will readily contemplate a variety of other ways and / or structures for performing the functions described herein and / or obtaining the results described herein and / or one or more advantages, and each such variation and / or modification is considered to be within the scope of this disclosure.

Claims

1. A quaternary ammonium salt type crosslinked polymer dry gel adsorbent material, which is obtained by crosslinking and copolymerizing quaternary ammonium salt monomers and crosslinking agents; The quaternary ammonium salt monomer has the structure of the following formula (I): in, R1 is H or methyl, R2 and R3 are each independently C1-C3 alkyl, R4 is C4-C7 alkyl, R5 is C2-C4 alkylene, and X - For Cl - ,Br - or I - .

2. The quaternary ammonium salt type cross-linked polymer dry gel adsorbent material according to claim 1, characterized in that, In the structure of formula (I), R2 and R3 are each independently methyl or ethyl, and R4 is a C4-C6 alkyl group.

3. The quaternary ammonium salt type cross-linked polymer dry gel adsorbent material according to claim 2, characterized in that, In the structure of formula (I), R1, R2 and R3 are methyl groups, and R4 is n-butyl, n-pentyl or n-hexyl.

4. The quaternary ammonium salt type cross-linked polymer dry gel adsorbent material according to any one of claims 1 to 3, characterized in that, The quaternary ammonium salt monomer is selected from one or more of 2-(methacryloyloxy)ethyl dimethyl n-hexyl ammonium salt, 2-(methacryloyloxy)ethyl dimethyl n-butyl ammonium salt and 2-(methacryloyloxy)ethyl dimethyl n-pentyl ammonium salt.

5. The quaternary ammonium salt type cross-linked polymer dry gel adsorbent material according to claim 1, characterized in that, The crosslinking agent is selected from one or more of ethylene glycol dimethacrylate, 1,4-butanediol dimethacrylate, hexanediol dimethacrylate, trimethylolpropane trimethacrylate, and N,N'-methylenebisacrylamide.

6. The quaternary ammonium salt type cross-linked polymer dry gel adsorbent material according to claim 2 or 3, characterized in that, The ratio of the equilibrium adsorption capacity to the apparent ion exchange capacity of the quaternary ammonium salt crosslinked polymer dry gel adsorbent material for perfluorooctanoic acid is not less than 1.05, and / or the ratio for perfluorovalerate is not less than 0.

9.

7. The quaternary ammonium salt type cross-linked polymer dry gel adsorbent material according to claim 2 or 3, characterized in that, Under the conditions of an initial perfluorooctanoic acid (PFOA) concentration of 0.025 mmol / L and an inorganic competing anion concentration of 10 mmol / L, the quaternary ammonium salt-type cross-linked polymer dry gel adsorbent material achieves a PFOA removal rate of no less than 90%.

8. A method for preparing the quaternary ammonium salt type crosslinked polymer dry gel adsorbent material according to any one of claims 1-7, comprising: (1) In a solvent system, the quaternary ammonium salt monomer, the crosslinking agent and the thermal initiator of claim 1 are mixed and free radical crosslinking copolymerized at 40 to 90°C to obtain a crosslinked hydrogel; (2) The obtained cross-linked hydrogel is crushed or shredded, swollen in a liquid medium, and then dried to obtain the quaternary ammonium salt type cross-linked polymer dry gel adsorbent material.

9. The method according to claim 8, characterized in that, In step (1), the molar ratio of the quaternary ammonium salt monomer to the crosslinking agent is 1:(0.20-0.40); the solvent system is an ethanol / water mixture, wherein the mass ratio of ethanol to water is (0.1-2):1; the amount of thermal initiator is 0.1 to 10 wt% of the total mass of the quaternary ammonium salt monomer and the crosslinking agent. In step (2), the liquid medium is water, ethanol or a mixture of ethanol and water, and the swelling time is 0.5 to 5 h; the drying is freeze drying, the freeze drying temperature is -20 to -50℃, and the freeze drying time is 12 to 72 h.

10. A method for removing anionic perfluorinated and polyfluoroalkyl substances from a water sample, comprising: The quaternary ammonium salt type cross-linked polymer dry gel adsorbent material according to any one of claims 1-7 is brought into contact with a water sample containing anionic perfluorinated and polyfluoroalkyl substances, so that the quaternary ammonium salt type cross-linked polymer dry gel adsorbent material absorbs water, swells, and adsorbs anionic perfluorinated and polyfluoroalkyl substances in the water sample; And perform solid-liquid separation between the adsorbed quaternary ammonium salt cross-linked polymer dry gel adsorbent and the water sample.

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