Fluoride ion-extractable fiber material with high silicone grafting rate, preparation and application thereof

Abstract

The application discloses a fluorine ion release fiber material with high organic silicon grafting rate and preparation and application, and aims at the problems of low stable grafting rate, easy loss under strong acid working condition and inefficient solid phase regeneration of the existing siloxane grafted fiber, and the application takes acid-resistant fiber containing nitrile groups as a base material, takes dithio bond-containing diamine as a connecting arm precursor, releases amine through an organic proton acceptor low water system, generates sulfydryl through dithio bond reduction, and then reacts with double-end alkenyl siloxane to generate sulfydryl-alkene reaction, so as to build a covalently connected siloxane functional layer. The stable fixed amount of siloxane on the fiber material disclosed by the application can reach 15% to 25%, the total fluorine content of industrial fluorine-containing acid liquid can be reduced to below 10 mg / kg, and after fluorine capture, solid phase regeneration can be realized through an alkaline aqueous phase, and the application is suitable for deep defluorination treatment of electronic-grade phosphoric acid, electronic-grade hydrochloric acid and wet-process phosphoric acid.

Description

Technical Field

[0001] This invention relates to the field of fluoride ion adsorption and separation materials technology, specifically to a fluoride ion removal fiber material with a high organosilicon grafting rate and its preparation and application. Background Technology

[0002] Removing fluoride ions from acids and acidic wastewater by utilizing the reaction characteristics of organosilicon with fluoride species in acidic systems is a commonly used fluoride purification technology in this field. Combined with appropriate processes, it can achieve the recovery and utilization of organosilicon components and fluorine resources. However, liquid organosilicon is prone to volatilization and dissolution during actual use, which not only causes the loss of functional components but may also lead to acid contamination. Therefore, the industry has gradually developed technical solutions that graft and fix organosilicon onto the surface of an inert solid carrier to reduce the risk of organosilicon loss and avoid secondary pollution caused by dissolution.

[0003] Existing siloxane grafting products using fiber-based materials as carriers exhibit the following problems after rigorous washing and use in strong acid environments: low silicon component retention levels, difficulty in further improving the effective grafting rate, and limited adsorption capacity for fluoride ions, failing to meet the deep purification requirements for trace amounts of fluoride in industrial products. Products that use physical methods such as impregnation and coating to support organosilicon on fibers are prone to siloxane detachment and loss during washing and under strong acid conditions, failing to maintain long-term stable defluorination performance. Overall, existing fiber-based siloxane immobilization technologies struggle to achieve materials with high and stable grafting rates, and silicon-based components easily detach from the carrier and enter the acid solution during fluoride capture, hindering convenient solid-phase regeneration and recycling, thus limiting the large-scale application of such materials in deep defluorination scenarios involving concentrated acids in industrial applications. Summary of the Invention

[0004] The inventors discovered that patent CN118356915A discloses a method using PP, polyethylene, cotton, linen, nylon, or spandex as carriers, activating the carrier surface, or grafting terminal siloxanes with existing functional groups on the carrier, and applying it to fluoride-containing solutions with a pH less than 4. However, after practical application, the inventors further discovered that this method mainly relies on the limited reaction sites on the carrier surface. The effective contact and reaction degree between the siloxane end groups and the fiber surface are limited by site accessibility, steric hindrance, and end group reaction efficiency, making it difficult to continuously improve the actual effective grafting rate and the stable amount of solidified silica after strong washing. Therefore, its fluoride ion specificity and selectivity are weak, making it difficult to purify trace amounts of fluoride in industrial acid products. Simultaneously, the inventors also found that existing methods, such as irradiation, plasma modification, excimer laser modification, and even vapor deposition of silanes, cannot obtain fibers with high organosilicon grafting rates. This is essentially due to the fact that in existing free radical addition reactions, the presence of silicon strengthens ortho-radical free radicals, thereby inhibiting their addition reactions. The inventors conducted numerous experimental attempts, but failed to obtain more than 1% stable grafting through gamma irradiation, plasma modification, and excimer laser modification. Moreover, published literature further indicates that the maximum stable grafting obtained by vapor deposition is 2.6% (Wang Feng, Tong Bin. Preparation and characterization of polypropylene radiation-grafted silane [J]. Journal of Radiation Research and Radiation Processing, 2009, 27(05): 261-264).

[0005] To address the problems of liquid disiloxane treatment requiring liquid-liquid phase separation, low stable silicon content under direct support, and difficulty in regenerating silicon-based fragments in the solid phase after fluoride capture, the present invention aims to provide a fluoride-removing fiber material with a nitrile-containing acid-resistant fiber as the skeleton, a disulfide-bonded diamine as the reducible linker, and a siloxane-based fiber material with siloxane-based ...

[0006] To achieve the above objectives, in a first aspect, the present invention provides a fluoride ion-depleting fiber material with a high organosilicon grafting rate. The fluoride ion-depleting fiber material includes a substrate and siloxane functional units. The substrate is a nitrile-containing acid-resistant fiber, and the siloxane functional units include terminal alkenyl siloxanes, which contain at least one Si-O-Si bond and at least two unsaturated end groups located at different ends of the molecule. A sulfur-containing linker arm is attached to the substrate. This sulfur-containing linker arm originates from a disulfide-containing diamine or its acid addition salt, and at least one amino group on the disulfide-containing diamine reacts with the nitrile group of the nitrile-containing acid-resistant fiber substrate to form a nitrogen-containing covalent linkage structure, thereby connecting the sulfur-containing linker arm to the substrate. The disulfide bond fixed on the substrate is reduced to form a thiol group, which reacts with the unsaturated end group of the terminal alkenyl siloxane to form a thioether bond. At least a portion of the siloxane functional units are connected to the nitrile-containing acid-resistant fiber through the thiol-olefin reaction, forming two thioether bonds, ultimately achieving the connection between the siloxane functional units and the substrate.

[0007] Preferably, the acrylonitrile-containing acid-resistant fiber substrate is selected from at least one of polyacrylonitrile fiber, acrylonitrile copolymer fiber, and composite fiber with a polyacrylonitrile layer on the surface.

[0008] Preferably, the unsaturated end group is selected from at least one of vinyl, allyl, propenyl, and butenyl.

[0009] Preferably, the terminal alkenyl siloxane is selected from at least one of 1,3-divinyl-1,1,3,3-tetramethyldisiloxane, 1,3-diallyl-1,1,3,3-tetramethyldisiloxane, divinyl-terminated oligosiloxane, diallyl-terminated oligosiloxane, divinyl-terminated silicone oil, and diallyl-terminated silicone oil.

[0010] Preferably, the sulfur-containing connecting arm is derived from H2N-R 1 -SSR 2 -NH2 represents the addition salt of a disulfide-bonded diamine or its acid, where R 1 and R 2 Each is an independent C2 to C8 alkylene group.

[0011] Preferably, the disulfide-containing diamine is cystamine, 3,3'-dithiodipropylamine, 4,4'-dithiodibutylamine, its substitutes, or salts thereof.

[0012] Preferably, the amount of sulfur-containing connecting arms fixed on the substrate is 45% to 55%; the amount of siloxane functional units fixed on the substrate is 15% to 25%.

[0013] Secondly, the present invention provides a method for preparing a fluoride ion-depleting fiber material with a high organosilicon grafting rate. The specific steps for preparing the above-mentioned fluoride ion-depleting fiber material are as follows:

[0014] Step 1: Disperse or dissolve the disulfide-containing diamine acid addition salt in anhydrous or low-aqueous organic medium, add an organic proton acceptor to complete proton transfer, and allow the disulfide-containing diamine releasing amino groups to react with the nitrile-containing acid-resistant fiber substrate. After washing, disulfide-modified fiber is obtained. Specifically, based on proton molar equivalents, the ratio of the effective accepting equivalent of the organic proton acceptor to the acid equivalent of the disulfide-containing diamine acid addition salt is 1.80~2.60, and the water mass fraction in the organic medium does not exceed 5%. In other words, based on proton molar equivalents, the ratio of the total effective proton accepting sites provided by the organic proton acceptor to the total acid equivalent of the acid component in the disulfide-containing diamine acid addition salt is 1.80~2.60. One mole of a monocarboxylic acid corresponds to one acid equivalent, and one mole of an organic proton acceptor that can accept one proton corresponds to one proton accepting equivalent. If it is a polycarboxylic acid or a multi-site proton acceptor, the equivalent is calculated according to the actual number of protons that can be dissociated or accepted.

[0015] Step 2: After the disulfide bond-modified fiber is fixed and washed, an excess reducing agent is added to reduce the disulfide bonds fixed on the acrylonitrile-containing acid-resistant fiber to thiol groups, and the reducing agent is washed off to obtain thiolized fiber; wherein, the reaction temperature is 10~50℃ and the reaction time is 4~6h.

[0016] Step 3: The thiolized fiber is reacted with a terminal alkenyl siloxane containing at least two unsaturated end groups in a thiol-alkene reaction; the molar ratio of the unsaturated end groups in the terminal alkenyl siloxane to the thiol groups in the thiolized fiber is 0.8–1.5; when thermal initiation is used, the reaction temperature is 50–75 °C and the reaction time is 2–12 h; when photoinitiation is used, the ultraviolet light wavelength is 320–405 nm and the irradiation time is 10–120 min.

[0017] Step 4: Remove unreacted and physically adsorbed siloxanes, and dry to obtain the fluoride-desorbed fiber material.

[0018] Preferably, in step 1, an aqueous solution of alkali metal hydroxide is not used as the main amine-releasing medium. The organic proton acceptor is selected from at least one of triethylamine, tri-n-butylamine, N,N-diisopropylethylamine, N-methylmorpholine, 1,8-diazabicyclo[5.4.0]undec-7-ene, 1,5-diazabicyclo[4.3.0]non-5-ene, and 1,5,7-trizabicyclo[4.4.0]dec-5-ene. The amount of the proton acceptor, primarily n-butylamine, should be controlled and thoroughly washed away after the reaction to reduce its competitive reaction with the cellulose nitrile groups.

[0019] Preferably, the organic medium is selected from at least one of ethylene glycol, propylene glycol, glycerol, dimethyl sulfoxide, and N,N-dimethylformamide.

[0020] Preferably, in step 2, the reducing agent is selected from at least one of tris(2-carboxyethyl)phosphine and its salts, dithiothreitol, mercaptoethanol, ascorbic acid and its salts, sulfites, and borohydrides.

[0021] Thirdly, this invention provides an application of a high-organosilicon grafting rate fluoride-removing fiber material. This fluoride-removing fiber material, or the fluoride-removing fiber material prepared by the above-mentioned method, is used for defluorination treatment of hydrofluoric acid, ensuring that the fluorine content in the hydrofluoric acid does not exceed 1 mg / kg. The fluoride removal mentioned here refers to deep defluorination, where the hydrofluoric acid is brought into contact with the fluoride-removing fiber material in any physical form, such as batch contact, fiber bag contact, filter cartridge contact, or fixed bed contact, allowing the fluorine-containing species to interact with the Si-O-Si bonds fixed on the fluoride-removing fiber material. The silicon-based fragments after forming Si-F bonds are still connected to the acrylonitrile-based acid-resistant fiber substrate through at least one thioether bond. After contact, the fibers are removed, filtered, or the fixed bed is switched to obtain a treated acid solution with a reduced total fluorine content. During this process, free liquid disiloxane is not added to the acid solution as an independent organic phase, nor is liquid-liquid separation between the organic phase and the acid phase performed.

[0022] Preferably, the fluorinated acid solution is an electronic-grade phosphoric acid preparation solution, an electronic-grade hydrochloric acid preparation solution, or a wet-process phosphoric acid solution.

[0023] Fourthly, the present invention also provides a solid-phase regeneration method for fluoride-removed fiber materials, which performs solid-phase regeneration treatment on the fiber materials obtained after defluorination treatment as described above, enabling them to be reused; the specific steps of solid-phase regeneration are as follows:

[0024] Step 1: The fluorine-captured fiber material is contacted with an alkaline aqueous regeneration solution, causing at least a portion of the fiber-bound Si-F to be converted into fiber-bound Si-OH and allowing fluorine to enter the regeneration solution. The alkaline aqueous regeneration solution comprises deionized water and an alkaline component. The alkaline component is one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, or ammonia water. The pH of the alkaline aqueous regeneration solution is 9–13. Preferably, the alkaline aqueous regeneration solution comprises deionized water, sodium carbonate with a concentration of 0.01–0.10 mol / L, and sodium hydroxide with a concentration of 0.001–0.05 mol / L. More preferably, the sodium carbonate concentration is 0.02–0.05 mol / L, and the sodium hydroxide concentration is 0.005–0.02 mol / L.

[0025] Step 2: The fiber material is subjected to solid-liquid separation and washing with the fluorine-containing aqueous regeneration solution, so that the Si-OH bonds in the fiber are dehydrated and condensed to form Si-O-Si bonds, and / or the residual thiol groups on the fiber are used to supplement the terminal alkenyl siloxane, so as to obtain the regenerated fluoride-free fiber material.

[0026] Preferably, in the regeneration process described in this invention, no free disiloxane organic phase that needs to be recovered is generated.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1. This invention constructs a complete covalent bonding system between a nitrile-containing acid-resistant fiber substrate and siloxane functional units by forming stable thioether bonds through disulfide-bonded diamine covalent linkage, directional reduction of disulfide bonds, and addition reaction of mercapto-olefins. This replaces the traditional immobilization method of physical adsorption and weak van der Waals force bonding. This covalent bonding structure can significantly improve the retention rate of siloxanes after strict solvent extraction, and effectively inhibit the leaching and dissolution of siloxanes under long-term contact with strong acids such as concentrated phosphoric acid and concentrated hydrochloric acid, reducing the risk of functional component loss and the possibility of silicon contamination of the acid solution.

[0029] 2. This invention uses cystamine-based disulfide-bonded diamines as convertible linkers, utilizing the amino groups at both ends of the same molecule and the disulfide bond in the middle to achieve dual reaction functions: the linker is covalently anchored to the substrate through the reaction of the amino group with the cellulose nitrile group, and then a thiol group is generated at the caustic site of the disulfide bond reduction, achieving covalent immobilization of the terminal alkenyl siloxane. This design forms a continuous chemical connection path of "cellulose substrate - sulfur-containing linker - siloxane functional unit", with a controllable number of reaction sites, eliminating the need for additional multi-step functional group modification processes.

[0030] 3. This invention employs organic proton acceptors such as triethylamine and n-butylamine to release the free amino groups of diamines through proton transfer in anhydrous or low-aqueous organic media, without using hydrated alkali metal hydroxides as the primary amine release medium. This reaction system, centered on proton transfer rather than relying on high pH values, effectively avoids hydrolysis, swelling, conjugation, and structural disintegration of nitrile-containing fibers caused by highly aqueous and alkaline environments. This maintains the integrity of the fiber skeleton and its basic mechanical properties, providing a stable substrate foundation for subsequent grafting reactions.

[0031] 4. Under completely consistent feeding ratios, reaction conditions, extraction processes, and constant weight testing standards, the stable fixation amount of siloxanes achieved by conventional fixation methods such as direct impregnation and surface coating is no higher than 3%. This invention, through a technical route involving sulfur-containing linkers coupled with mercapto-olefin click reactions, can increase the stable fixation amount of siloxanes after rigorous Soxhlet extraction to 15%–25%, significantly increasing the density of Si-O-Si defluorination functional sites per unit mass of fiber. This breaks through the defluorination capacity bottleneck of existing fiber silicon modification technologies in terms of the number of functional sites.

[0032] 5. The fiber material obtained by this invention can be processed into various forms such as chopped fibers, continuous fiber bundles, fiber mats, filter cartridges, acid-resistant fiber bags, or fixed-bed packing materials, depending on the application scenario. It is compatible with various process modes such as batch contact, filter cartridge filtration, and fixed-bed continuous processing. After processing, the separation of the material from the acid can be completed simply by removing the fibers, performing a simple filtration, or switching to a fixed bed. There is no need to set up supporting units such as liquid-liquid phase separation or organic phase recovery. The process flow is simple and can be directly adapted to existing industrial acid purification devices.

[0033] 6. The fiber material of this invention, after fluorine capture, still has its silicon-based segments stably bound to the fiber substrate through sulfide connecting arms, preventing loss with acid dissociation. Therefore, solid-phase regeneration can be achieved through alkaline hydrolysis defluorination, solid-liquid separation, hydroxyl condensation recovery, or supplementary click reactions without forming a free disiloxane organic phase. The regenerated material can be recycled for deep defluorination processes of electronic-grade phosphoric acid, electronic-grade hydrochloric acid, and wet-process phosphoric acid. Even after multiple cycles, it can maintain stable defluorination performance, effectively reducing long-term operating material costs and demonstrating excellent prospects for industrial application. Attached Figure Description

[0034] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0035] Figure 1 This is a flowchart illustrating the preparation process of the fluoride ion-removing fiber material of the present invention.

[0036] Figure 2 This is a schematic diagram illustrating the relationship between the disulfide bonded diamine linkage, reduction and exposure of thiol groups, terminal alkenyl siloxane click fixation, fluorine capture, and regeneration in this invention.

[0037] Figure 3 This is a flowchart illustrating the deep defluorination process of fluorinated acid solution using batch, fiber bag, filter cartridge, or fixed bed methods according to the present invention.

[0038] Figure 4 This is a flowchart illustrating the alkaline desorption and regeneration process of the fiber material after fluoride ion removal, as used in this invention. Detailed Implementation

[0039] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments and accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on this invention are within the scope of protection of this invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Reagents or instruments whose manufacturers are not specified can be obtained commercially.

[0040] Unless otherwise specified in the specific context, the numerical ranges listed herein include upper and lower limits, as well as all integers and fractions within those ranges, and are not limited to the specific values ​​listed when defining the range. For numerical ranges, endpoint values ​​of various ranges, endpoint values ​​of various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. The term "and / or" used herein is inclusive; for example, "A and / or B" means only A, or only B, or both A and B. Terms such as "about," "substantially the same," and similar expressions used herein indicate that reasonable deviations are permissible.

[0041] I. A fluoride ion-depleting fiber material with high organosilicon grafting rate

[0042] This invention addresses the current technical limitations of silicon-based defluorinated fibers, which suffer from low stable grafting rates and difficulty in solid-phase recycling. It uses nitrile-containing acid-resistant fibers as the substrate skeleton and selects diamines containing disulfide bonds or their acid addition salts as precursors for the connecting arms. The disulfide bond structure is covalently bonded to the fiber substrate surface via the reaction of amino and nitrile groups. After the connecting arms are fixed and free components are thoroughly washed away, the disulfide bonds on the fiber are reduced, generating thiol reaction sites on the fiber surface. Furthermore, terminal alkenyl siloxanes with at least two unsaturated end groups are used as functional components. A thioether bond is formed between the thiol sites and the siloxane end groups through a thiol-alkene addition reaction, immobilizing at least some siloxane molecules on the fiber in a double-end-connected manner. Simultaneously, an alkaline regeneration process is implemented to allow the silicon-based fragments after fluoride capture to complete structural recovery on the fiber solid phase.

[0043] In some embodiments of the present invention, the fluoride-removing fiber material includes a substrate and siloxane functional units; the substrate is an acid-resistant fiber containing nitrile groups, and the siloxane functional units include terminal alkenyl siloxanes, wherein the terminal alkenyl siloxanes contain at least one Si-O-Si bond and at least two unsaturated end groups located at different ends of the molecule; wherein a sulfur-containing linker arm is connected to the substrate, the sulfur-containing linker arm originating from a disulfide-containing diamine or its acid addition salt, and at least one amino group on the disulfide-containing diamine reacts with the nitrile group of the acid-resistant fiber substrate to form a nitrogen-containing covalent linkage structure, thereby connecting the sulfur-containing linker arm to the substrate; the disulfide bond fixed on the substrate is reduced to form a thiol group, which reacts with the unsaturated end group of the terminal alkenyl siloxane to form a thioether bond; at least a portion of the siloxane functional units are connected to the acid-resistant fiber containing nitrile groups through the thiol-alkene reaction to form two thioether bonds, ultimately realizing the connection between the siloxane functional units and the substrate.

[0044] In some embodiments of the present invention, the acrylonitrile-containing acid-resistant fiber substrate is selected from at least one of polyacrylonitrile fiber, acrylonitrile copolymer fiber, and composite fiber with a polyacrylonitrile layer on the surface. This is because the molecular chains of such fibers contain a large number of nitrile functional groups, which can directly react with amino groups containing disulfide-containing diamines to achieve covalent fixation of the linker arms. Sufficient grafting reaction sites are provided without additional surface activation treatment, avoiding the shortcomings of inert polymer carriers such as PP and polyethylene, which lack surface reaction sites and require additional modification to introduce functional groups. Furthermore, such fibers possess excellent resistance to strong acids, maintaining fiber morphology and structural stability for extended periods under strong acid conditions such as concentrated phosphoric acid and concentrated hydrochloric acid. Compared to carriers such as cotton, linen, nylon, and spandex, they are more suitable for deep defluorination scenarios involving concentrated industrial acids. The selection of this type of substrate provides a basis for reaction sites for the covalent fixation of the linker arms and ensures the structural tolerance of the material in strong acid treatment environments, solving the problems of insufficient grafting sites and poor acid resistance in existing inert carriers for concentrated acid defluorination.

[0045] In some embodiments of the present invention, the unsaturated end groups are selected from at least one of vinyl, allyl, propenyl, and butenyl groups. These end alkenyl groups have matching click reactivity with thiol groups, enabling efficient thiol-alkene addition reactions under mild photo-initiated or thermally-initiated conditions. The reaction exhibits high selectivity, few side reactions, and suitable carbon chain length. Steric hindrance is controllable during the reaction, ensuring that both unsaturated groups at the ends of the siloxane molecule have the opportunity to react with thiol groups to form a bi-terminal supported structure. Compared to other reactive groups such as epoxy and acrylate groups, these end alkenyl groups do not require stringent catalytic conditions and are less prone to side reactions with amino and hydroxyl groups in the system. Compared to unsaturated groups such as alkynyl groups, the raw material cost is lower and the reaction is more controllable. This selection ensures the high efficiency and selectivity of the thiol-alkene grafting reaction, providing a reactive basis for the stable formation of bi-terminal supported siloxane structures and solving the problems of low siloxane grafting conversion and difficulty in forming bi-terminal constrained structures.

[0046] In some embodiments of the present invention, the terminal alkenyl siloxane is selected from at least one of 1,3-divinyl-1,1,3,3-tetramethyldisiloxane, 1,3-diallyl-1,1,3,3-tetramethyldisiloxane, divinyl-terminated oligosiloxane, diallyl-terminated oligosiloxane, divinyl-terminated silicone oil, and diallyl-terminated silicone oil. These siloxanes all feature a double-ended unsaturated group-capped structure, allowing for immobilization via the reaction of alkenyl and thiol groups at both ends to form disulfide bonds. Even after the Si-O-Si bond breaks due to fluorine interaction, the silicon fragments can still be bound to the fiber through at least one sulfide bond, avoiding the drawbacks of single-ended alkenyl siloxanes, which can only fix one end and are prone to detachment after Si-O-Si breakage. Furthermore, these siloxanes contain Si-O-Si functional structures, serving as core sites for interaction with fluoride ions. By selecting small-molecule disiloxanes, oligomeric siloxanes, or silicone oils of varying viscosities, the density of defluorination sites and grafting capacity per unit mass of fiber can be flexibly controlled, resulting in a richer array of Si-O-Si defluorination sites and a higher defluorination capacity compared to ordinary silane coupling agents. The selection of these terminal alkenyl siloxanes balances immobilization stability and defluorination capacity, adapting to different application requirements and solving the problems of easy loss and insufficient defluorination sites in single-ended immobilized siloxanes.

[0047] In some embodiments of the present invention, the sulfur-containing connecting arm is derived from H2N-R. 1 -SSR 2 -NH2 represents the addition salt of a disulfide-bonded diamine or its acid, where R 1 and R 2Each component is an independent C2-C8 alkylene group. The amino groups at both ends of this structure can react with the nitric acid groups of the fiber to covalently fix the linker arms. The disulfide bond in the middle can generate a thiol group in situ through a reduction reaction, serving as a reaction site for siloxane grafting. This constructs a continuous covalent linkage pathway, eliminating the need to directly introduce thiol groups onto the fiber surface and avoiding the problem of free thiol groups being easily oxidized and deactivated. Compared to alkyl diamines without disulfide bonds, this structure possesses convertible thiol reaction sites, enabling covalent grafting of siloxanes. The C2-C8 carbon chain length range avoids the problems of excessive steric hindrance and poor site accessibility caused by excessively short carbon chains, while also avoiding the problems of excessive flexibility, decreased acid resistance, and structural entanglement caused by excessively long carbon chains. The selection of linker arms in this structure enables controllable generation and efficient immobilization of grafting sites, ensuring the reactivity and structural stability of the linker arms, and solving the problem of scarce active grafting sites on the fiber surface and difficulty in efficiently covalently immobilizing siloxanes.

[0048] In some embodiments of the present invention, the disulfide-containing diamine is cystamine, 3,3'-dithiodipropylamine, 4,4'-dithiodibutylamine, their substitutes, or salts thereof. These compounds are all commercially available and mature raw materials with stable supply and controllable cost. Furthermore, their acid addition salt form is stable, easy to store, and allows for precise dosing, meeting the needs of industrial preparation. Simultaneously, the amino and nitrile groups of these compounds exhibit suitable reactivity, and the disulfide bond reduction reaction conditions are mature and highly efficient, stably generating a quantitative amount of thiol sites. Compared to similar dithiodiamines with longer carbon chains, they have more suitable steric hindrance, greater reaction accessibility, and significantly reduced raw material acquisition difficulty and cost. The selection of this specific diamine ensures the stability and reproducibility of the linker fixation reaction and subsequent reduction reaction, reduces raw material costs and the difficulty of industrial scale-up, and solves the problems of limited linker raw material supply, poor reaction reproducibility, and uncontrollable thiol generation.

[0049] In some embodiments of the present invention, the amount of sulfur-containing connecting arms fixed on the substrate is 45% to 55%, specifically: the amount of sulfur-containing connecting arms stably fixed after extraction with a specified solvent and drying to constant weight of the sulfur-containing fiber material is 45% to 55%. The amount of siloxane functional units fixed on the substrate is 15% to 25%, specifically: based on the dry weight of the mercapto-treated fiber before the click reaction, the amount of siloxane stably fixed after extraction with a specified solvent and drying to constant weight of the fluoride-de-oxidized fiber material is 15% to 25%.

[0050] II. A method for preparing a fluoride ion-depleting fiber material with high organosilicon grafting rate

[0051] Step 1: Disperse or dissolve the disulfide-containing diamine acid addition salt in anhydrous or low-aqueous organic medium, add an organic proton acceptor to complete proton transfer, and allow the disulfide-containing diamine releasing amino groups to react with the nitrile-containing acid-resistant fiber substrate. After washing, disulfide-modified fiber is obtained. Specifically, based on proton molar equivalents, the ratio of the effective accepting equivalent of the organic proton acceptor to the acid equivalent of the disulfide-containing diamine acid addition salt is 1.80~2.60, and the water mass fraction in the organic medium does not exceed 5%. In other words, based on proton molar equivalents, the ratio of the total effective proton accepting sites provided by the organic proton acceptor to the total acid equivalent of the acid component in the disulfide-containing diamine acid addition salt is 1.80~2.60. Wherein, 1 mole of monocarboxylic acid corresponds to 1 acid equivalent, and 1 mole of organic proton acceptor that can accept 1 proton corresponds to 1 proton accepting equivalent; if it is a polycarboxylic acid or a multi-site proton acceptor, the equivalent is calculated according to the actual number of protons that can be dissociated or accepted. In specific implementation, the effective equivalent ratio of the organic base is calculated according to formula (1). The role of the organic base is to accept protons in the acid addition salt and release amino groups, and it does not aim to increase the pH of the aqueous phase.

[0052] (1)

[0053] In the formula, E B Z is the effective alkali equivalent ratio. B n is the effective proton equivalent that each mole of organic base can accept; B n represents the amount of substance of an organic base, expressed in mol. H The total amount of acid contained in the disulfide bonded diamino acid addition salt is expressed in mol.

[0054] The organic proton acceptor was slowly added to a dispersion of disulfide-bonded diamine acid addition salt. After proton transfer was completed, pretreated nitrile-containing fibers were added, and the reaction was carried out under an inert atmosphere. After the reaction was completed, the fibers were washed sequentially with the reaction medium, alcohol, and water, and then replaced with alcohol and dried to obtain disulfide-bonded modified fibers. The apparent weight gain of the process was calculated according to formula (2).

[0055] (2)

[0056] In the formula, Gss is the apparent weight gain rate of the disulfide bond modification step, %; m SS The mass of the disulfide-modified fiber after specified washing and drying is in g; m0 is the dry mass of the acid-resistant fiber substrate before modification, in g. Apparent weight gain is used for process recording and is not directly equivalent to the covalently fixed disulfide bond content.

[0057] Step 2: After the disulfide bond-modified fiber is fixed and washed, an excess reducing agent is added to reduce the disulfide bond -SS- fixed on the acrylonitrile-containing acid-resistant fiber to thiol-SH, and the reducing agent is washed off to avoid residual reducing agent consuming the subsequent initiation system or causing false high thiol detection, thus obtaining thiolized fiber; wherein, the reaction temperature is 10~50℃ and the reaction time is 4~6h.

[0058] Step 3: The thiolized fiber is reacted with a terminal alkenyl siloxane containing at least two unsaturated end groups in a thiol-alkene reaction. Specifically, the thiolized fiber, the terminal alkenyl siloxane, and the initiation system are added to an organic solvent capable of wetting the fiber and dispersing the siloxane, and thermal initiation, photoinitiation, or redox initiation is carried out under an inert atmosphere. The thiol group adds to the vinyl, allyl, or other alkene unsaturated end groups to form a thioether bond. Siloxanes with two unsaturated end groups can form single-end and double-end fixed structures, with the double-end fixed structure being beneficial for improving the solid-phase retention of the silicon fragment after fluorine capture. The thiol-alkene reaction conditions are as follows: the molar ratio of the unsaturated end groups in the terminal alkenyl siloxane to the thiol groups in the thiolized fiber is 0.8–1.5; when using thermal initiation, the reaction temperature is 50–75 °C, and the reaction time is 2–12 h; when using photoinitiation, the ultraviolet light wavelength is 320–405 nm, and the irradiation time is 10–120 min.

[0059] Step 4: Remove unreacted and physically adsorbed siloxanes, and dry to obtain the fluoride-desorbed fiber material.

[0060] In some embodiments of the present invention, an aqueous solution of alkali metal hydroxide is not used as the main amine release medium in step 1. The organic proton acceptor is selected from at least one of triethylamine, tri-n-butylamine, N,N-diisopropylethylamine, N-methylmorpholine, 1,8-diazabicyclo[5.4.0]undec-7-ene, 1,5-diazabicyclo[4.3.0]non-5-ene, and 1,5,7-triazabicyclo[4.4.0]dec-5-ene. The amount of the proton acceptor, primarily n-butylamine, should be controlled and thoroughly washed away after the reaction to reduce its competitive reaction with the cellulose nitrile groups. When the equivalent amount of organic proton acceptor is insufficient, the amino group of the disulfide-bonded diamine cannot be fully released. When water and free strong base are in excess, the nitrile-containing fibers may undergo hydrolysis, swelling, and structural damage. Therefore, the proton acceptor is preferentially added in acid equivalent measure, and the water content of the medium is controlled below 5%. The ratio of the effective accepting equivalent of the organic proton acceptor to the acid equivalent of the disulfide-bonded diamine acid addition salt can be 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, or 2.6, or can be any range or sub-range between any two of the above specific values. In specific embodiments, any of the above ranges can be combined with any other range, as long as the fluoride ion-removing fiber material of the present invention can be obtained. Triethylamine and other tertiary amines, amidines, or guanidine bases do not contain primary amino groups that can directly attack nitrile groups and are preferentially used for amine release. When using n-butylamine, its proton accepting effect and possible competing reactions should be distinguished by dosage control and strict washing. These organic bases can release free amino groups from diamine addition salts through proton transfer in anhydrous or low-aqueous organic media. Their goal is to complete the proton transfer rather than raise the pH of the aqueous phase, thus avoiding the problems of hydrolysis, swelling, conjugation, or even structural damage to nitrile-containing fibers under high water content and strong alkaline conditions. Among them, tertiary amine proton acceptors such as triethylamine do not contain primary amino groups and will not compete with the nitrile groups of the fiber for reaction, nor will they occupy grafting sites. While proton acceptors containing primary amino groups such as n-butylamine have proton acceptance capabilities, they can react with nitrile groups. Therefore, the dosage needs to be controlled and thorough washing is necessary to reduce the impact of competitive reactions. Compared with aqueous solutions of alkali metal hydroxides, these organic proton acceptors have good solubility in organic media, high amine release efficiency, and extremely low damage to the fiber skeleton. The selection of this type of organic proton acceptor ensures efficient release of diamine amino groups while maintaining the integrity of fiber structure and morphology to the maximum extent. This provides a base structure foundation for achieving a high grafting rate and solves the problem that water-containing strong alkaline systems can easily cause hydrolysis and damage to nitrile-containing fibers, making it impossible to obtain complete fiber products.

[0061] In some embodiments of the present invention, the organic medium is selected from at least one of ethylene glycol, propylene glycol, glycerol, dimethyl sulfoxide, and N,N-dimethylformamide. These solvents are all highly polar organic solvents, exhibiting excellent solubility for acid addition salts containing disulfide-bonded diamines and organic proton acceptors. This ensures that the proton transfer reaction and the amino-nitrile reaction proceed in a homogeneous environment. Furthermore, these solvents have high boiling points, making them suitable for the higher temperature conditions required for the amino-nitrile reaction. They are less prone to volatilization and loss during the reaction and can induce moderate swelling of the fiber, improving the accessibility of nitrile sites within the fiber and promoting the complete fixation reaction of the connecting arms without causing excessive swelling or structural damage to the fiber. Compared to aqueous media, these organic media have low water content, preventing fiber hydrolysis. Compared to low-boiling-point alcohols and hydrocarbon solvents, their solubility and heat resistance are more suitable for the reaction requirements. The selection of this type of organic medium provides a stable and homogeneous environment for the reaction, ensuring reaction efficiency and fiber structure stability, and solving the problems of insufficient solubility of the reaction medium, easy damage to fibers, and inability to adapt to high-temperature reaction conditions.

[0062] In some embodiments of the present invention, in step 2, the reducing agent is selected from at least one of tris(2-carboxyethyl)phosphine and its salts, dithiothreitol, mercaptoethanol, ascorbic acid and its salts, sulfites, and borohydrides. These reducing agents can selectively reduce disulfide bonds to thiol groups under mild conditions without damaging the fiber skeleton and the already formed covalently linked structure during the reaction. Furthermore, most of these reducing agents have good water or alcohol solubility and can be thoroughly removed by washing after the reaction, avoiding the consumption of the initiation system for subsequent thiol-alkene reactions or causing false positives in thiol detection by residual reducing agents. Compared to strong reducing agents such as lithium aluminum hydride, these reducing agents offer milder reaction conditions, are easier to operate, do not require a harsh anhydrous or oxygen-free environment, and do not damage the fiber substrate. The selection of these reducing agents ensures the efficient and selective reduction of fixed disulfide bonds, generating high-purity thiol reaction sites, providing a site basis for the high grafting rate of subsequent siloxanes, and solving the problems of poor disulfide bond reduction selectivity and interference of residual reducing agents with subsequent grafting reactions.

[0063] In some embodiments of the present invention, in step 2, if the reaction temperature is too low, the reduction reaction kinetic rate decreases significantly, the disulfide bond breaking is insufficient, the amount of thiol group generated is insufficient, and the site distribution is uneven, directly leading to a low subsequent siloxane grafting rate; at the same time, the system viscosity increases, hindering the diffusion of the reducing agent into the fiber interior, further aggravating the unevenness of the reduction degree; however, if the reaction temperature is too high, on the one hand, it will cause the reducing agent (such as tris(2-carboxyethyl)phosphine) to decompose and become inactive, and the reduction efficiency will decrease; on the other hand, it will accelerate the oxidative self-polymerization of the generated thiol groups, reforming disulfide bonds, resulting in a reduction in the number of effective reaction sites; in addition, excessively high temperatures will also aggravate the degree of fiber swelling, increase the difficulty of subsequent washing and drying, and even affect the mechanical strength of the fiber. Therefore, the reaction temperature can be 10℃, 15℃, 20℃, 25℃, 30℃, 35℃, 40℃, 45℃, or 50℃, or any range and sub-range between any two specific values ​​mentioned above. If the reaction time is too short, the disulfide bond reduction reaction will not be complete, and the disulfide bonds inside the fiber will not be able to fully contact the reducing agent, resulting in insufficient effective thiol group generation and failing to provide sufficient active sites for subsequent grafting reactions. If the reaction time is too long, after the reducing agent is completely consumed, extending the reaction time will not further increase the thiol group content, but will instead increase the risk of thiol group oxidation and deactivation, while reducing production efficiency, increasing energy consumption, and prolonged soaking may adversely affect the structural stability of the fiber. Therefore, the reaction time can be 4h, 4.5h, 5h, 5.5h, or 6h, or any range and sub-range between any two specific values ​​mentioned above. In specific implementation schemes, any of the above ranges can be combined with any other range, as long as the fluoride ion de-extracting fiber material of the present invention can be obtained.

[0064] In some embodiments of the present invention, in step 3, when thermal initiation is used, the reaction temperature is 50–75 °C and the reaction time is 2–12 h. If the reaction temperature is too low, the thermal initiator decomposes slowly, the free radical concentration in the system is low, the thiol-alkene addition reaction rate is slow, the siloxane grafting conversion rate is low within the same time period, and the stable fixation amount is insufficient; if the time is extended to compensate, production efficiency will be significantly reduced. Conversely, if the reaction temperature is too high, the initiator decomposes too quickly, free radicals are prone to quenching side reactions, and the proportion of free radicals effectively participating in the grafting reaction decreases; at the same time, it will exacerbate the homopolymerization side reaction of siloxanes, reduce the amount of effective monomers that can react with the fiber thiol groups, and may also cause excessive swelling of the fiber substrate and degradation of some groups, affecting the acid resistance and mechanical strength of the material. Therefore, when using thermal initiation, the reaction temperature can be 50 °C, 55 °C, 60 °C, 65 °C, 70 °C, or 75 °C, or any range and sub-range between any two specific values ​​mentioned above. If the thermal initiation reaction time is too short, the reaction will be incomplete, with a large amount of terminal alkenyl siloxanes not participating in the reaction, resulting in low siloxane stability and preventing the achievement of the expected defluorination capacity. If the reaction time is too long, continuing heating after the main reaction is basically completed can easily lead to side reactions such as excessive crosslinking and side chain breakage, which may cause some of the grafted siloxanes to fall off. At the same time, it will significantly prolong the production cycle, increase energy consumption and production costs, and prolonged high temperatures may damage the fiber skeleton. Therefore, the reaction time can be 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, or 12h, or any range and subrange between any two specific values ​​mentioned above. When using photoinitiation, the ultraviolet light wavelength is 320–405 nm, and the irradiation time is 10–120 min. If the ultraviolet (UV) wavelength is too low and the UV photon energy is too high, it will not only excite the initiator but also cause chain scission and degradation of the fiber polymer backbone, damaging the mechanical properties and acid resistance of the fiber substrate. Simultaneously, the reaction selectivity decreases, side reactions increase, and the grafted structure is prone to disorder and excessive cross-linking. Conversely, if the UV wavelength is too high, the photon energy is insufficient to effectively excite the photoinitiator to generate free radicals, resulting in a significant decrease in initiation efficiency, a slow thiol-alkene reaction rate, and a low grafting conversion rate, requiring a significantly longer irradiation time to achieve the target grafting amount. Therefore, the UV wavelength can be 320nm, 340nm, 360nm, 380nm, 400nm, or 405nm, or any range or subrange between any two of the above specific values. If the irradiation time is too short (less than 10 min), the amount of photoinitiator decomposed will be insufficient, the concentration of free radicals in the system will be low, the addition reaction will be incomplete, and the amount of siloxane stability fixation will be too low, which will not meet the defluorination capacity requirements. However, if the irradiation time is too long, continuous ultraviolet irradiation will cause fiber aging and a decline in mechanical properties. It may also trigger photodegradation or side reactions of the grafted siloxane, which will reduce the stability of the grafted layer. At the same time, it will increase equipment energy consumption and reduce production efficiency.Therefore, the irradiation time can be 10 min, 30 min, 60 min, 90 min or 120 min, or it can be any range and sub-range between any two of the above specific values; in specific implementations, any of the above ranges can be combined with any other ranges, as long as the fluoride ion desorption fiber material of the present invention can be obtained.

[0065] In some embodiments of the present invention, in step 4, tetrahydrofuran is used for Soxhlet extraction or continuous rinsing, and ethyl acetate, toluene, and ethanol are used for washing according to the solubility of the siloxanes to remove unreacted and physically adsorbed siloxanes. After drying to constant weight, the amount of siloxane stabilized is calculated according to formula (3).

[0066] (3)

[0067] In the formula, G Si m1 represents the amount of siloxane stabilized (%), m1 is the mass of the click reaction product after extraction with the specified solvent and drying to constant weight (g); m SH The dry weight of the mercapto-modified fiber before the click reaction is in g.

[0068] III. Application of a high-organosilicon grafting rate fluoride ion desorption fiber material

[0069] The aforementioned fluoride-removing fiber material or the fluoride-removing fiber material prepared by the aforementioned method is used for defluorination treatment of hydrofluoric acid, ensuring that the fluoride content in the hydrofluoric acid does not exceed 1 mg / kg. Fluoride removal mentioned here refers to deep defluorination, where the hydrofluoric acid is brought into contact with the fluoride-removing fiber material in any physical form, such as batch contact, fiber bag contact, filter cartridge contact, or fixed bed contact, allowing the fluoride-containing species to interact with the Si-O-Si bonds fixed on the fluoride-removing fiber material. The silicon-based fragments, after forming Si-F, are still connected to the acrylonitrile-based acid-resistant fiber substrate through at least one thioether bond. After contact, the fibers are removed, filtered, or the fixed bed is switched to obtain a treated acid solution with a reduced total fluoride content. During this process, free liquid disiloxane is not added to the acid solution as an independent organic phase, nor is liquid-liquid separation between the organic phase and the acid phase performed.

[0070] In some embodiments of the present invention, the fiber material prepared by the present invention can be made into chopped fibers, continuous fiber bundles, fiber mats, fiber webs, filter cartridges, acid-resistant fiber bags, or fixed-bed packing materials, depending on the method of use. The fiber morphology allows the material to be separated in strong acid media by direct removal, filtration, or bed switching.

[0071] In some embodiments of the present invention, the fluorinated acid solution is an electronic-grade phosphoric acid preparation solution, an electronic-grade hydrochloric acid preparation solution, or a wet-process phosphoric acid solution.

[0072] IV. A solid-phase regeneration method for fluoride ion-depleted fiber materials

[0073] The fiber materials obtained after defluorination in the above applications undergo solid-phase regeneration to enable them to be reused. The specific steps of solid-phase regeneration are as follows:

[0074] Step 1: Contact the fluorine-captured fiber material with an alkaline aqueous regeneration solution, so that at least a portion of the fiber-bound Si-F is converted into fiber-bound Si-OH and fluorine enters the regeneration solution; the alkaline aqueous regeneration solution includes deionized water and alkaline components, and its pH is 9-13.

[0075] Step 2: The fiber material is subjected to solid-liquid separation and washing with the fluorine-containing aqueous regeneration solution, so that the Si-OH bonds in the fiber are dehydrated and condensed to form Si-O-Si bonds, and / or the residual thiol groups on the fiber are used to supplement the terminal alkenyl siloxane, so as to obtain the regenerated fluoride-free fiber material.

[0076] In some embodiments of the present invention, no free disiloxane organic phase that needs to be recovered is generated during the regeneration process described in the present invention.

[0077] V. Examples and Comparative Examples

[0078] Example 1: Fixation of cystamine connecting arms using a triethylamine system

[0079] 8.0254 g of polyacrylonitrile fibrils and 7.9989 g of cystamine dihydrochloride were weighed. The cystamine dihydrochloride was dispersed in 300 mL of ethylene glycol, 25 mL of triethylamine was added, and then the polyacrylonitrile fibrils were added. The reaction was carried out at 140 °C for 24 h under nitrogen protection. After the reaction, the fibers were washed and dried to obtain 11.7607 g of disulfide-modified fibers. According to formula (2) of this invention, the apparent weight gain was 46.968% based on the dry weight of the polyacrylonitrile fiber substrate. After Soxhlet extraction with ethanol for 24 h, the fiber weighed 11.6337 g, with a mass retention rate of 98.92%. The obtained fibers maintained their morphology and were used in the subsequent disulfide bond reduction step.

[0080] Example 2: Repeated test of triethylamine system

[0081] 8.0122 g of polyacrylonitrile fibrils and 8.0022 g of cystamine dihydrochloride were weighed, and 300 mL of ethylene glycol and 21 mL of triethylamine were added. The mixture was reacted at 140 °C for 24 h under nitrogen protection. After the reaction, the fibers were washed and dried, and the mass of the disulfide-modified fibers obtained was 11.9326 g. Calculated according to formula (2) of this invention based on the dry mass of the polyacrylonitrile fiber substrate, the apparent weight gain was 48.90%. This result is consistent with the trend of Example 1.

[0082] Example 3: Fixation of cystamine connecting arms using n-butylamine system

[0083] Following the method of Example 2, n-butylamine was used instead of triethylamine. The amount of polyacrylonitrile fiber added was 8.0074 g, the amount of cystamine dihydrochloride added was 8.0035 g, the amount of n-butylamine was 25.0 mL, and the amount of ethylene glycol was 300 mL. The reaction was carried out at 140 °C for 24 h under nitrogen protection. After washing and drying, the fibers showed some damage and agglomeration. The mass of the disulfide-modified fiber obtained was 12.9549 g. Based on the dry mass of the polyacrylonitrile fiber substrate according to formula (2) of this invention, the apparent weight gain was 61.865%.

[0084] Example 4: Disulfide Bond Reduction

[0085] 2.0034 g of the disulfide-modified fiber obtained in Example 2 was added to 100 mL of a 50 mmol / L aqueous solution of tris(2-carboxyethyl)phosphonate hydrochloride. The pH was adjusted to 7.4 ± 0.1 using a Tris buffer system, and the reaction was carried out at 25 °C for 4 h under nitrogen protection. After the reaction, the fiber was washed with deoxygenated water until the last wash no longer showed reducing properties, and then replaced with ethanol and anhydrous tetrahydrofuran. The thiol equivalent of the fiber was determined by iodometric titration. The thiol equivalent of the fiber before reduction was 0.18 mmol / g, and the thiol equivalent after reduction was 3.86 mmol / g.

[0086] Example 5: Photoinitiated click fixation with tetramethyldivinyldisiloxane

[0087] Take 1.5071 g of the thiolized fiber obtained in Example 4, add 5 ml of 1,3-divinyl-1,1,3,3-tetramethyldisiloxane, 50 mL of anhydrous tetrahydrofuran, and 2,2-dimethoxy-2-phenylacetophenone (equivalent to 1.0% of the siloxane by mass). After purging with nitrogen for 30 min, heat at 365 nm and 10 mW / cm 2 Irradiation was performed for 60 min under the specified conditions. The product was extracted with tetrahydrofuran by Soxhlet extraction for 12 h and dried to constant weight. The siloxane stabilization amount calculated according to formula (3) of this invention was 18.6%.

[0088] Example 6: Thermally initiated click fixation of tetramethyldiallyldisiloxane

[0089] This example is basically the same as Example 5, except that 1,3-divinyl-1,1,3,3-tetramethyldisiloxane was replaced with 1,3-diallyl-1,1,3,3-tetramethyldisiloxane, and azobisisobutyronitrile was used as the initiator. The reaction was carried out at 65°C for 8 h. After strict extraction and constant weight, the stable fixation amount of siloxane was 15.2%.

[0090] Example 7: Click fixation of vinyl-terminated silicone oil

[0091] This embodiment is basically the same as Example 5, except that: a bisvinyl-terminated silicone oil with a viscosity of 50 mPa·s was used, and the molar ratio of vinyl to mercapto groups was 1.10:1. Irradiation was performed at 365 nm for 90 min. After rigorous extraction and constant weight determination, the stable fixation amount of siloxane was 15.7%.

[0092] Example 8: Siliconization of the n-Butylamine-Cystamine Connector

[0093] The disulfide-modified fiber obtained in Example 3 was reduced according to Example 4, and then photoinitiated with 1,3-divinyl-1,1,3,3-tetramethyldisiloxane according to Example 5. After rigorous extraction and constant weight, the stable fixation amount of siloxane was 23.8%.

[0094] Comparative Example 1: Direct Impregnation with Silicone Oil

[0095] An improvement on Example 7 was made, the difference being that polyacrylonitrile fibers without sulfur-containing linkers were directly immersed in the same divinyl-terminated silicone oil system as in Example 7, and treated under the same light, extraction, and drying conditions. The stable fixation amount calculated according to formula (3) of the present invention was 0%.

[0096] Comparative Example 2: No disulfide bond reduction was performed

[0097] An improvement was made to Example 5, the difference being that the disulfide-modified fiber obtained in Example 2 was taken and reacted directly with 1,3-divinyl-1,1,3,3-tetramethyldisiloxane according to the steps in Example 5 without reduction. After rigorous extraction and constant weight, the stable fixation amount was 1.1%, indicating that reducing and exposing the thiol groups is the key step in improving the stable fixation amount of siloxane.

[0098] Comparative Example 3: Amine Release from Aqueous Strong Alkali

[0099] A system consisting of approximately 8 g of polyacrylonitrile fiber, approximately 8 g of cystamine dihydrochloride, and 300 mL of ethylene glycol was reacted with 50 mL of saturated sodium hydroxide aqueous solution at 140 °C. After the reaction, the liquid phase turned black, and the polyacrylonitrile fiber solid completely disappeared, failing to yield a disulfide-bonded modified material that retained its fiber morphology. This result indicates that replacing organic alkalis with a large amount of aqueous strong alkali significantly damages the polyacrylonitrile fiber skeleton.

[0100] Comparative Example 4: Co-irradiation grafting of PP fibers

[0101] PP fibers were soaked in acetone for 7 days, then dried to constant weight and subjected to Soxhlet extraction with methanol for 24 hours to remove oligomers and extractable components from the fiber surface, yielding pretreated PP fibers. A certain mass of the pretreated PP fibers was weighed and placed in an irradiated glass bottle. After three nitrogen purgings, a prepared grafting solution was added and the bottle was sealed. The grafting solution consisted of 30% tetramethyldivinyldisiloxane by mass, a solvent, and a crosslinking agent and / or polymerization inhibitor.

[0102] The sealed reaction system was placed in a 60Co irradiation field for co-irradiation grafting at an absorbed dose of 30 kGy and a dose rate of 5 kGy / h. The solvent type, liquor ratio (also called liquid-solid ratio, refers to the ratio of the volume of the grafting solution (containing siloxane monomers, solvents, additives, etc.) to the dry mass of the fiber to be modified, expressed in mL / g (i.e., how many milliliters of reaction solution correspond to one gram of fiber)), and the addition of crosslinking agent or polymerization inhibitor were varied. After irradiation, the PP fibers were removed, subjected to Soxhlet extraction with methanol for 24 h, washed with ethanol and deionized water, and dried to constant weight. The grafting rate was calculated based on the change in fiber mass before and after irradiation.

[0103] The results are shown in Table 1. In each group of experiments using tetramethyldivinyldisiloxane as the grafting component, regardless of the use of methanol, ethyl acetate, dichloromethane, petroleum ether, tetrahydrofuran, acetonitrile, toluene or other solvents, or the addition of crosslinking agents such as divinylbenzene, trimethylolpropane triacrylate and polymerization inhibitors such as hydroquinone, the grafting rate of PP fibers after strong washing was low, mainly distributed in the range of approximately -1.28% to 0.89%. Some systems showed negative weight gain, indicating that a stable organosilicon graft layer was not formed.

[0104] Table 1 Results of Comparative Example 4

[0105] 15 methanol Tetramethyldivinyldisiloxane / / 0.50% 30 methanol Tetramethyldivinyldisiloxane / / -0.24% 30 methanol Tetramethyldivinyldisiloxane / / 0.51% 30 methanol Tetramethyldivinyldisiloxane 2% divinylbenzene / -0.48% 30 methanol Tetramethyldivinyldisiloxane 2% divinylbenzene 2% Hydroquinone -0.49% 30 methanol Tetramethyldivinyldisiloxane 2% Trimethylolpropane Trimethacrylate / 0.25% 30 methanol Tetramethyldivinyldisiloxane 2% Trimethylolpropane Trimethacrylate 2% Hydroquinone -0.71% 30 Ethyl acetate Tetramethyldivinyldisiloxane / / -0.94% 30 dichloromethane Tetramethyldivinyldisiloxane / / 0.74% 30 petroleum ether Tetramethyldivinyldisiloxane / / -0.72% 30 Tetrahydrofuran Tetramethyldivinyldisiloxane / / -0.22% 30 Acetonitrile Tetramethyldivinyldisiloxane / / 0.77% 30 xylene Tetramethyldivinyldisiloxane / / -1.28% 30 Tetrahydrofuran Tetramethyldiallyldisiloxane / / 0.78% 30 Tetrahydrofuran Tetramethyldiallyldisiloxane 2% Trimethylolpropane Trimethacrylate 2% Hydroquinone 0.89% 30 methanol Styrene (control) / / 266.30%

[0106] As a positive control, when styrene was used as the grafting component under the same irradiation conditions, the grafting rate of PP fibers reached 266.30%, indicating that the irradiation system could effectively induce the grafting reaction in PP fibers. However, when tetramethyldivinyldisiloxane was used as the grafting component, it was difficult to obtain a correspondingly high grafting rate and stable retention after washing. This indicates that the co-irradiation grafting method for PP fibers cannot effectively achieve stable fixation of organosiloxanes.

[0107] Table 2. Siloxane stabilization amounts under different connection, reduction, and click conditions.

[0108] Example 5 Triethylamine / Cystamine TCEP restoration Tetramethyldivinyldisiloxane 18.6 Example 6 Triethylamine / Cystamine TCEP restoration Tetramethyldiallyldisiloxane 15.2 Example 7 Triethylamine / Cystamine TCEP restoration Divinyl end capping silicone oil 15.7 Example 8 n-Butylamine / Cystamine TCEP restoration Tetramethyldivinyldisiloxane 23.8 Comparative Example 1 No connecting arm none Direct impregnation with divinyl end capping silicone oil 0 Comparative Example 2 Triethylamine / Cystamine none Tetramethyldivinyldisiloxane 1.1

[0109] Combining Table 1 and Table 2, we can see that:

[0110] (1) Table 1 shows the experimental results of co-irradiation grafting of siloxane onto PP fibers in Comparative Example 4, which can verify the technical limitations of inert polymer substrates and conventional grafting processes from the opposite perspective. Comparative Example 4 used PP fibers without active functional groups as substrates and attempted to immobilize tetramethyldivinyldisiloxane using a co-irradiation grafting process. At the same time, styrene grafting was set as a positive control to eliminate the interference of failure of the irradiation system itself. The test data showed that the weight gain rate of all siloxane grafting groups after strict solvent extraction was only -1.28% to 0.89%, and some experimental groups showed negative weight gain, indicating that a stable covalent grafting layer was not formed on the fiber surface, and only physical adsorption that could be completely eluted existed. The grafting rate of the styrene positive control group reached 266.30%, proving that the irradiation system itself can effectively initiate the grafting reaction, but cannot achieve stable fixation of siloxane on inert PP fibers. This shows that the technical problems of insufficient reaction sites on the surface of inert polymer substrates and low stable grafting rate of silicon-based defluorination materials in the prior art do exist. To address this technical problem, this invention uses acrylonitrile-containing acid-resistant fibers as the substrate and employs an amine release scheme using an organic proton acceptor and a low-water organic medium to construct covalent sulfur-containing linkers. Examples 1 and 2 use triethylamine as the organic proton acceptor, and the cystamine linker is fixed in an ethylene glycol low-water organic medium. The resulting modified fibers exhibit apparent weight gains of 46.968% and 48.90%, respectively. After Soxhlet extraction with ethanol for 24 hours… The mass retention rate reached 98.92% after h, indicating that the disulfide-bonded linker arms are stably bound to the fiber matrix in the form of covalent bonds, and the fiber morphology remains intact after the reaction, which can meet the structural requirements of subsequent processing and strong acid use. Example 3 uses n-butylamine as a proton acceptor, which can obtain a higher apparent weight gain rate. Although the fiber shows some damage and agglomeration, this result is within an acceptable range. It also confirms that the proton acceptor containing primary amino groups has the risk of competing with nitrile groups for reaction. It also proves that organic proton acceptor systems can effectively fix the linker arms, and the reaction degree and fiber state can be controlled by selecting the type of alkali. Comparative Example 3 uses saturated sodium hydroxide aqueous solution as the amine release medium to carry out the same reaction. In the end, the polyacrylonitrile fiber completely dissolves and disappears, and it is impossible to obtain a modified material that maintains the fiber morphology. This directly proves that the aqueous strong alkali system will cause violent hydrolysis, conjugation and structural disintegration of nitrile-containing fibers. The comparison between the two verifies the dual advantages of the amine release scheme of this invention in terms of linker arm fixation efficiency and fiber structural integrity.

[0111] (2) Table 2, through multiple sets of controlled variable experiments, systematically verified the core regulatory role of disulfide bond reduction and covalent grafting pathways in the stable fixation of siloxanes. Combined with the reduction efficiency data of Example 4, a complete site-grafting correspondence logic can be formed. In Example 4, tris(2-carboxyethyl)phosphine was used to directionally reduce disulfide bond-modified fibers. Before reduction, the accessible thiol equivalent of the fibers was only 0.18 mmol / g, which increased to 3.86 mmol / g after reduction. The number of effective thiol sites increased by more than 20 times, and the thiol groups were covalently bonded to the ends of the fiber connecting arms. The properties were stable and the reactivity was controllable. This indicates that the disulfide bond reduction process can quantitatively generate high-density thiol reaction sites on the fiber surface, providing a sufficient active site basis for the subsequent covalent grafting of siloxanes. This is the core prerequisite for achieving a high grafting rate. The comparative data in Table 2 further validates the necessity of a complete covalent pathway: Comparative Example 1 did not introduce sulfur-containing linkers, and directly impregnated polyacrylonitrile fibers in divinyl-terminated silicone oil and subjected to the same light irradiation and extraction treatment. The final stable fixation amount of siloxane was 0%, indicating that without a covalent linkage, the physically adsorbed siloxane completely detached after strict solvent extraction, and could not achieve effective fixation. This confirms the technical problems of weak siloxane binding force and easy loss in physical impregnation, coating and other methods. Comparative Example 2 only fixed disulfide-containing linkers, omitted the disulfide reduction step, and reacted directly with terminal alkenyl siloxane. After strict extraction, the stable fixation amount of siloxane was only 1.1%, which is comparable to the grafting level of existing technologies such as irradiation and plasma modification. This indicates that unreduced disulfide bonds cannot provide effective covalent grafting sites for siloxanes, and can only form a very small amount of non-specifically bound siloxanes, and cannot achieve a high grafting rate. In stark contrast, Examples 5-8, using the complete preparation method of this invention, achieved a stable siloxane fixation rate of 15.2%-23.8% after rigorous removal of physically adsorbed components via tetrahydrofuran Soxhlet extraction. This is significantly higher than the comparative example's level of less than 3%, and also considerably better than the highest stable grafting level of 2.6% achieved by the vapor deposition method in the prior art. This demonstrates that this invention, by constructing a continuous covalent connection path of "fiber substrate - sulfur-containing linker - siloxane," increases the stable grafting rate of siloxane by more than an order of magnitude. This fundamentally solves the core technical problems of low stable grafting rate of siloxane and easy detachment and loss after washing and use with strong acid in the prior art. It also confirms that the increase in stable silicon fixation comes from the construction of covalent chemical bonds, rather than the simple physical adsorption of siloxane on the fiber surface.

[0112] (3) The grafting system of the present invention has good universality for terminal alkenyl siloxanes with different structures, and the grafting efficiency and fiber performance can be balanced by the type of organic base, which can meet the needs of diverse application scenarios. Examples 5-7 used small-molecule divinyldisiloxane, diallyldisiloxane, and high-molecular-weight divinyl-terminated silicone oil as end-alkenyl siloxanes, respectively, and all achieved a stable silicon fixation amount of over 15%. This indicates that the mercapto-alkene grafting process of the present invention has good reaction adaptability to siloxanes with different molecular weights and different alkenyl end groups. Based on this universality, the type of siloxane can be flexibly selected according to the needs of specific defluorination scenarios to control the density of Si-O-Si functional sites, the adsorption capacity of the material, and the acid resistance stability. This solves the technical problem that a single siloxane structure cannot meet the requirements of different acid systems and different processing precision requirements. At the same time, the structure design of the double-terminated alkenyl groups can enable some siloxane molecules to form double-point immobilization of disulfide bonds, ensuring that after the Si-O-Si bond is broken and defluorinated, the silicon fragments are still retained on the fiber through at least one sulfide bond, avoiding the loss of functional components and supporting the feasibility of solid-phase recycling. The comparison between Examples 5 and 8 further demonstrates that using triethylamine as the proton acceptor results in superior fiber morphological integrity, while using n-butylamine further increases the stable fixation amount of siloxane to 23.8%, allowing for flexible selection based on the application scenario's emphasis on structural strength and grafting capacity. Overall, Tables 1 and 2, along with the step-by-step verification of each example, form a complete chain of evidence, proving that this invention achieves a balance between highly stable siloxane grafting and fiber structural integrity through the synergistic effects of selecting a nitrile-based substrate, constructing sulfur-containing covalent linkers, in-situ mercapto-based generation, and covalent fixation of bi-terminated alkenyl siloxanes. This systematically solves a series of technical problems associated with existing silicon-based defluorinated fibers, such as low grafting rate, easy loss, poor acid resistance, and difficulty in solid-phase recycling.

[0113] VI. Deep Defluorination of Fluorinated Acids

[0114] The total fluoride content of the acid solution before and after treatment was determined by fluoride ion selective electrode method or ion chromatography, and reported as mg / kg based on the acid solution mass. The defluorination rate was calculated according to formula (4).

[0115] (4)

[0116] In the formula, η is the defluorination rate (%), C0 is the total fluoride content of the acid solution before treatment (mg / kg); C t The total fluoride content of the treated acid solution is expressed in mg / kg.

[0117] Example 9: Deep defluorination of phosphoric acid preparation solution

[0118] 100.0 g of a phosphoric acid solution with an H3PO4 mass fraction of 85.0% and a total fluoride content of 85 mg / kg was taken, and 5.01 g of the fluoride-desorbed fiber material prepared in Example 5 was added. The mixture was contacted at 35 °C for 3 h. After contact, the fiber was removed and filtered. The total fluoride content of the resulting treated phosphoric acid solution was 6.8 mg / kg, and the H3PO4 mass fraction was 82.7%.

[0119] Example 10: Deep defluorination of hydrochloric acid preparation solution

[0120] 100.0 g of hydrochloric acid solution with an HCl mass fraction of 31.0% and a total fluoride content of 52 mg / kg was taken, and 5.04 g of the fluoride-desorbed fiber material prepared in Example 5 was added. The mixture was contacted at 25 °C for 2 h. After treatment, the total fluoride content of the hydrochloric acid solution was 4.2 mg / kg, and the HCl mass fraction was 27.9%.

[0121] Example 11: Deep Defluorination of Electronic Grade Phosphoric Acid

[0122] 100.0 g of wet-process phosphoric acid with a P2O5 mass fraction of 45.0% and a total fluorine content of 60 mg / kg was added to 5.28 g of the fluoride-de-oxidized fiber material prepared in Example 6, and the mixture was contacted at 40 °C for 6 h. After treatment, the total fluorine content of the wet-process phosphoric acid was 0.88 mg / kg.

[0123] Example 12: Fixed-bed continuous deep defluorination

[0124] 100 g of the fluoride-de-fluorinated fiber material obtained in Example 7 was bundled into fiber bundles and packed into an acid-resistant fixed bed. A fluorinated phosphoric acid solution with a total fluoride content of 100 mg / kg was passed through the bed at a volume hourly space velocity (VHSV) of 0.5 BV / h. The bed was switched when the total fluoride content of the treated solution reached 10 mg / kg. The effective throughput per run was 8.0 BV.

[0125] Table 3. Results of deep defluorination of fluorinated acid solution

[0126] Example 9 <![CDATA[85.0% H3PO4]]> 85 6.8 92.0 Example 10 31.0% HCl 52 4.2 91.9 Example 11 <![CDATA[45.0% P2O5 wet-process phosphoric acid]]> 60 0.88 98.5

[0127] Comparative Example 5: Deep Defluorination of PP Grafted Siloxane Fibers by Direct Irradiation

[0128] 100.0 g of phosphoric acid solution with an H3PO4 mass fraction of 85.0% and a total fluorine content of 85 mg / kg was added to 5.02 g of polypropylene fiber with a net grafting rate of 0.50% after strong washing in Comparative Example 4. The mixture was contacted at 35 °C for 3 h. After contact, the fiber was removed and filtered. The total fluorine content of the resulting treated phosphoric acid solution was 78.65 mg / kg, and the defluorination rate was 7.5%. This result is much lower than the 92.0% defluorination rate achieved when the fiber material of the present invention prepared in Example 5 was treated under the same conditions as in Example 9. This indicates that the direct irradiation grafting route of PP is limited by the scarcity of reaction sites on the PP fiber surface, low irradiation grafting efficiency, and poor stability of the grafted layer, making it impossible to obtain sufficient effective siloxane loading, thus limiting the defluorination capacity.

[0129] Comparative Example 6: Deep Defluorination of Physically Impregnated Siloxane Fibers

[0130] Polyacrylonitrile fibers without sulfur-containing linkers were directly immersed in divinyl-terminated silicone oil with a viscosity of 50 mPa·s. After thorough wetting, the fibers were removed, and excess silicone oil was simply absorbed with filter paper (without Soxhlet extraction) to obtain physically supported siloxane fiber material. 5.01 g of this fiber was added to 100.0 g of a phosphoric acid solution with an H3PO4 mass fraction of 85.0% and a total fluorine content of 85 mg / kg, and the solution was contacted at 35 ℃ for 3 h. After treatment, the total fluorine content of the phosphoric acid solution was 62.3 mg / kg, and the defluorination rate was 26.7%. Simultaneously, the soluble silicon content in the acid solution increased from <0.1 mg / kg initially to 126 mg / kg. These results indicate that physically supported siloxanes are largely dissolved and lost during strong acid contact. Although there is some defluorination effect during the initial contact, the functional components cannot be stably retained on the fiber. This not only makes it difficult to maintain continuous defluorination performance but also causes severe silicon contamination of the acid solution, failing to meet the requirements for deep purification of industrial acids.

[0131] Therefore, it can be seen that:

[0132] (1) Examples 9-11 were used to perform batch defluorination treatments on wet-process phosphoric acid systems containing 85.0% concentrated phosphoric acid, 31.0% concentrated hydrochloric acid, and 45.0% P2O5, respectively. Under the condition that the initial total fluoride content was 52-85 mg / kg, the defluorination rate could reach over 91%. In Example 9, the total fluoride content of the 85% phosphoric acid solution was reduced to 6.8 mg / kg, with a defluorination rate of 92.0%. In Example 10, the total fluoride content of the 31% hydrochloric acid solution was reduced to 4.2 mg / kg, with a defluorination rate of 91.9%. In Example 11, the defluorination rate of wet-process phosphoric acid reached 98.5%, and the total fluoride content after treatment was as low as 0.88 mg / kg, which can meet the purification requirements of electronic-grade acid solutions below 1 mg / kg. This result proves that the high-density covalently supported Si-O-Si functional sites provide sufficient reaction binding sites for fluorine species, fundamentally solving the technical problem of the difficulty in efficiently purifying trace amounts of fluoride in industrial acid products. Meanwhile, both Examples 9 and 10 involved high-concentration strong acid systems. After treatment, the concentration of the main acid solution did not fluctuate abnormally, and solid-liquid separation could be completed simply by removing the fiber and filtering. No free liquid organosilicon phase was introduced or liquid-liquid phase separation was required throughout the process. This indicates that the covalently grafted siloxane functional units have excellent binding stability in strong acid environments and will not dissolve and detach in large quantities, thus contaminating the acid solution. At the same time, the acid-resistant skeleton of the acrylonitrile-based fiber substrate ensures the structural integrity of the material under concentrated acid conditions. Furthermore, the three sets of embodiments respectively cover three typical industrial fluorine-containing systems: electronic-grade phosphoric acid preparation solution, electronic-grade hydrochloric acid preparation solution, and wet-process phosphoric acid. They cover acid media with different properties, such as monoprotic strong acid, multiprotic medium-strong acid, and wet refining intermediate solution. All three achieved stable and excellent defluorination effects, indicating that the fiber defluorination material of the present invention has good reaction and binding ability for fluorine species in different acid systems. It does not require significant adjustment of material formulation and process for different acid solutions, and has broad adaptability to working conditions. This solves the technical problem that traditional defluorination materials are only applicable to specific acid systems and have poor universality.

[0133] (2) Comparative Example 5 uses PP fiber directly irradiated with grafted siloxane material. Under the same treatment conditions as Example 9, the defluorination rate is only 7.5%, which is far lower than the 92.0% level of the product of this invention. This result corresponds completely with the low grafting rate shown in Table 1, indicating that the effective siloxane loading on the surface of the inert substrate is insufficient and the defluorination functional sites are lacking, which directly leads to extremely low defluorination capacity and cannot meet the requirements of deep defluorination. Comparative Example 6 uses polyacrylonitrile fibers physically impregnated with siloxane. Under the same conditions, the defluorination rate is only 26.7%. At the same time, the soluble silicon content in the acid solution increases from <0.1 mg / kg initially to 126 mg / kg. This indicates that the physically supported siloxane dissolves and is lost in large quantities in a strong acid environment. Although there is a certain defluorination effect in the first contact, the functional components cannot be stably retained. Not only is it difficult to maintain long-term defluorination performance, but it also causes serious secondary silicon pollution to the acid solution, which cannot meet the purity requirements of industrial acid purification. This further highlights the necessity of covalently chemically bonded siloxanes and also confirms the technical defects of physically supported silicon-based materials being easily detached and lost in strong acids and the need for complex liquid-liquid separation processes to treat liquid organosilicon.

[0134] (3) Example 12 further verifies the feasibility of the engineering application of the material of the present invention in a continuous industrial scenario. The fiber material is arranged into fiber bundles and filled into an acid-resistant fixed bed. The fluorinated phosphoric acid solution is treated by continuous flow. At a volume hourly space velocity of 0.5 BV / h, the effective throughput of a single run can reach 8.0 BV, and uninterrupted continuous production can be achieved by switching the bed. The fiber material is easy to fill, the bed pressure drop is reasonable, and the covalently fixed functional units are resistant to continuous fluid scouring and will not be lost with the liquid flow. This shows that the material of the present invention can be directly adapted to the existing fixed bed adsorption process without the need for additional supporting units such as liquid-liquid separation and organic phase recovery. It solves the technical problems of the difficulty in continuous operation and the complexity of the operation process of liquid organosilicon defluorination process, and provides a feasible engineering path for industrial-scale application.

[0135] (4) Overall, the present invention ensures structural stability in a strong acid environment through nitrile-containing acid-resistant fibers, achieves high-stability grafting of siloxanes through sulfur-containing covalent linkers and in-situ mercapto reduction, and provides a reaction basis for deep defluorination with sufficient Si-O-Si functional sites. The dual-point immobilization structure formed by the double-terminated alkenyl siloxanes can prevent the silicon fragments from falling off after the Si-O-Si bond breaks due to the interaction with fluorine. This ensures continuous defluorination capability and avoids silicon leaching and contamination of acid solution. At the same time, it provides structural possibility for subsequent solid-phase regeneration and recycling. It systematically solves a series of technical problems of existing silicon-based defluorination materials, such as low grafting rate, poor defluorination efficiency, easy loss of functional components, easy secondary pollution, and difficulty in long-term recycling and large-scale application.

[0136] VII. Alkali Regeneration of Fiber Materials with Fluoride Ion Depletion

[0137] When the fluoride-captured fiber material comes into contact with an alkaline aqueous regeneration solution, at least a portion of the fiber-bound Si-F is converted into fiber-bound Si-OH and releases F. - During regeneration, the silicon-based fragments continue to be constrained by the fiber via the sulfide linker arm; after separating the fluorinated aqueous regeneration solution and washing the fiber, drying or heat treatment promotes the Si-OH condensation to form Si-O-Si bonds. When the cycle capacity is insufficient, residual or newly formed mercapto groups can be used to supplement the terminal alkenyl siloxane. The fluorine desorption rate is calculated according to formula (5), and the capacity retention rate after the Nth cycle is calculated according to formula (6).

[0138] (5)

[0139] In the formula, D is the fluorine desorption rate, %; m F,d The mass of fluoride entering the regenerated solution is expressed in mg; m F,a The mass of fluorine captured by the fluoride ions removed from the fiber material before regeneration, in mg.

[0140] (6)

[0141] In the formula, R N The capacity retention rate after the Nth cycle is %; q N q1 represents the fluorine capture amount in the Nth cycle, in mg / g; q1 represents the fluorine capture amount in the first use, in mg / g.

[0142] Example 13: Alkaline desorption and recycling

[0143] The fluoride-desorbed fiber material used in Example 9 was taken and added to a 5% (w / w) sodium hydroxide aqueous solution, and shaken at 50 °C for 2 h. The fluoride-containing regeneration solution was separated, and the fiber was washed with deionized water until the pH of the final wash solution was 7. Then, it was replaced with ethanol and dried at 70 °C for 4 h. The fluoride desorption rate of this regeneration was 92.4%.

[0144] The regenerated fluoride-free fiber material was repeatedly used for deep defluorination of phosphoric acid solution under the conditions of Example 9. After 5 adsorption-regeneration cycles, the capacity retention rate was 95%.

[0145] Table 4. Recycling Results of Fluoride-Extracted Fiber Materials

[0146] 1 92 100 6.8 2 91 97 7.2 3 91 96 7.6 4 89 95 8.2 5 89 95 8.8

[0147] Comparative Example 7: Recycling of Fibers Immobilized by Single-Ended Vinyl-Capped Silicone Oil

[0148] Thiol-modified fibers were obtained by replacing the double-ended vinyl silicone oil with single-ended vinyl-capped silicone oil, achieving a molar ratio of vinyl groups to thiol groups on the fiber surface of 1.1:1. The fibers were then immobilized under the photoinitiated thiol-ene reaction conditions described in Example 5. After the reaction, the fibers were extracted with tetrahydrofuran using a Soxhlet method, washed with ethyl acetate and ethanol, and dried to constant weight to obtain single-ended silicone oil-modified fibers. In this material, the silicone oil molecules are connected to the fibers via only one thioether bond, and the stable fixation amount of organosiloxanes after strong washing is 18.4%.

[0149] Take 5.03 g of the grafted single-end silicone oil fiber and defluorinate it in a phosphoric acid solution with an H3PO4 mass fraction of 85.0% and a total fluorine content of 85 mg / kg according to the conditions of Example 9. Then, regenerate it under alkaline conditions according to Example 13 and reuse it. The defluorination results of each cycle are shown in Table 4.

[0150] Table 5 Results of Cyclic Defluorination of PP Single-Ended Vinyl-Ended Silicone Oil-Modified Fibers

[0151] 1 21.2 75.1 100 2 73.5 13.5 18.03 3 80.8 4.9 6.58 4 83.6 1.6 2.19

[0152] Although single-ended silicone oil materials possess a certain initial stable fixation, their silicone oil molecules are anchored to the fiber surface by only one bonding point. During the adsorption of fluorinated acid and alkaline regeneration processes, when the siloxane functional units undergo Si-F conversion, hydrolysis, and structural rearrangement, the single-point bonding cannot continuously constrain the remaining silicon-containing segments, leading to the gradual migration and loss of some silicone oil with each cycle. The material's capacity drops to 18.03% of the initial capacity in the second cycle and only 2.19% is retained in the fourth cycle.

[0153] In contrast, the dual-ended silicone oil is multi-point fixed to the fiber through two sulfide junctions. Even if some siloxane structures are transformed during fluorine capture and regeneration, the remaining junctions still restrict the detachment of functional fragments, thus maintaining 95% of the capacity after 5 cycles. This comparative example demonstrates that the present invention suppresses the migration and loss of organosilicon during acid treatment and regeneration through multi-point constraint.

[0154] Therefore, it can be seen that:

[0155] (1) Table 4 shows the adsorption-regeneration cycle performance test results of the fluoride ion removal fiber material. Combined with the alkaline regeneration process of Example 13, the solid-phase in-situ regeneration capability and long-cycle cycle stability of the material of the present invention were verified: Example 13 used a 5% sodium hydroxide aqueous solution to desorb and regenerate the fluoride-captured fiber material under mild conditions of 50°C. Throughout the regeneration process, the silicon-based segments were always constrained on the fiber substrate through the sulfide connecting arms, and no free disiloxane organic phase was generated. The regeneration operation could be completed by simple solid-liquid separation, washing, and drying. The test data showed that the fluoride desorption rate of the first regeneration could reach 92%, and the fluoride desorption rate of the first 3 cycles was maintained above 91%. After 5 cycles, the desorption level was still maintained at 89%. The total fluoride content of the acid solution after treatment only slowly increased from 6.8 mg / kg in the first cycle to 8.8 mg / kg, and was always maintained in the deep purification level range. This demonstrates that alkaline aqueous phase treatment can efficiently break the Si-F bonds binding the fibers, allowing fluoride ions to be fully released into the regeneration solution. The desorption reaction is thorough, resulting in low fluoride residue on the fibers. Simultaneously, the process of Si-OH reforming into Si-O-Si bonds through drying condensation exhibits good reversibility and high structural recovery of functional sites, ensuring the defluorination reactivity of the regenerated material. This solves the technical problems of incomplete desorption and irreversible functional failure in traditional adsorption materials. After five adsorption-regeneration cycles, the material retains 95% of its defluorination capacity, exhibits a low performance decay rate, and has a long cycle life. Frequent material replacement or large-scale replenishment of functional components is unnecessary, significantly reducing material loss and processing costs during industrial operation.

[0156] (2) Comparative Example 7 used fiber materials immobilized with single-end vinyl-terminated silicone oil for control cycle testing, which verified from the opposite perspective the core role of the double-end multi-point immobilization structure in cycle stability and also eliminated the interference of grafting amount difference on performance. The stable fixation amount of organosiloxane in the single-end silicone oil material after strong washing was 18.4%, which was basically equivalent to the initial grafting level of 18.6% in Example 5 of the present invention. However, since the silicone oil molecules are only anchored to the fiber surface at a single point through a thioether bond, during the adsorption defluorination and alkaline regeneration process, when the siloxane functional units undergo Si-F conversion, hydrolysis and structural rearrangement, the single-point connection cannot continuously constrain the remaining silicon-containing segments, resulting in the gradual migration and loss of some silicone oil; its capacity dropped to 18.03% of the initial capacity in the second cycle and only 2.19% was retained in the fourth cycle, and the defluorination performance rapidly declined. In contrast, the bi-terminated alkenyl siloxane used in this invention can be fixed at multiple points on the fiber through two sulfide connection points. Even if some siloxane structures are transformed during fluoride capture and regeneration, the remaining connection points can still restrict the detachment of functional fragments. Therefore, after 5 cycles, it still maintains a 95% capacity retention rate, directly proving that the multi-point constraint structure can effectively inhibit the migration and loss of organosilicon during acid treatment and regeneration, which is the structural basis for achieving long-term cyclic use. This also echoes the result of no silicon leaching pollution in the above defluorination test. The stability of the covalently supported structure is verified from the entire process of defluorination application and alkaline regeneration, avoiding the problem of secondary pollution caused by the decomposition and dissociation of silicon-based components into the acid solution.

[0157] (3) The solid-phase regeneration scheme of the present invention has mild process conditions and simple operation process, and at the same time reserves a capacity replenishment path, and has excellent industrial scale-up adaptability. The regeneration process can be completed under mild alkaline conditions at 50℃. The supporting processes are only conventional unit operations such as solid-liquid separation, water washing, and drying. The fibrous material is easy to separate, fill and transfer, and can be directly matched with a fixed bed to switch the regeneration mode to achieve continuous industrial production. Compared with the complex processes such as organic phase separation and distillation recovery required by the liquid organosilicon defluorination system, the solid-phase regeneration route of this invention has a short process, low equipment requirements and low energy consumption, which solves the technical problems of cumbersome process and high engineering implementation difficulty of traditional silicon-based defluorination regeneration process. In addition, the present invention also has flexible capacity recovery capability: when the capacity is insufficient after long-term cycling, the residual mercapto groups on the fiber or the mercapto groups re-formed during the regeneration process can be used to restore the defluorination capacity by supplementing the terminal alkenyl siloxane, further extending the service life of the material and improving the long-term operation economy. Overall, this invention achieves true solid-phase in-situ regeneration through a double-end fixed-load structural design. Combined with an efficient and reversible desorption reaction and a simple regeneration process, it systematically solves a series of technical problems in existing silicon-based defluorination materials, such as easy loss of silicon-based components after fluorine capture, complex regeneration processes, short cycle life, and high operating costs.

[0158] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit the technical solutions. Those skilled in the art should understand that any modifications or equivalent substitutions to the technical solutions of the present invention without departing from the spirit and scope of the present invention should be covered within the scope of the claims of the present invention.

Claims

1. A fluoride ion-depleting fiber material with a high organosilicon grafting rate, characterized in that, The fluoride ion-removing fiber material includes a substrate and a siloxane functional unit; the substrate is an acid-resistant fiber containing a nitrile group, and the siloxane functional unit includes a terminal alkenyl siloxane, wherein the terminal alkenyl siloxane contains at least one Si-O-Si bond and at least two unsaturated end groups located at different ends of the molecule. The substrate is connected with a sulfur-containing linker arm, which is derived from a disulfide-bonded diamine or its acid addition salt. At least one amino group on the disulfide-bonded diamine reacts with the nitrile group of the nitrile-containing acid-resistant fiber substrate to form a nitrogen-containing covalent link structure, thereby connecting the sulfur-containing linker arm to the substrate. The disulfide bond fixed on the substrate is reduced to form a thiol group. The thiol group reacts with the unsaturated end group of the terminal alkenyl siloxane to form a thioether bond. At least a portion of the siloxane functional units are connected to the acid-resistant fiber containing nitrile group through the thiol-alkene reaction to form two thioether bonds, thus achieving the connection between the siloxane functional units and the substrate.

2. The fluoride ion-removing fiber material according to claim 1, characterized in that, The acrylonitrile-containing acid-resistant fiber substrate is selected from at least one of polyacrylonitrile fiber, acrylonitrile copolymer fiber, and composite fiber with a polyacrylonitrile layer on the surface.

3. The fluoride ion-removing fiber material according to claim 2, characterized in that, The unsaturated end group is selected from at least one of vinyl, allyl, propenyl, and butenyl; the terminal alkenyl siloxane is selected from at least one of 1,3-divinyl-1,1,3,3-tetramethyldisiloxane, 1,3-diallyl-1,1,3,3-tetramethyldisiloxane, divinyl-terminated oligosiloxane, diallyl-terminated oligosiloxane, divinyl-terminated silicone oil, and diallyl-terminated silicone oil.

4. The fluoride ion-removing fiber material according to claim 1, characterized in that, The sulfur-containing connecting arm is derived from H2N-R 1 -SSR 2 -NH2 represents the addition salt of a disulfide-bonded diamine or its acid, where R 1 and R 2 Each is independently a C2-C8 alkylene group; the disulfide-containing diamine is cystamine, 3,3'-dithiodipropylamine, 4,4'-dithiodibutylamine and its substitutes or salts thereof.

5. The fluoride ion-removing fiber material according to claim 1, characterized in that, The amount of sulfur-containing connecting arms fixed on the substrate is 45%~55%; the amount of siloxane functional units fixed on the substrate is 15%~25%.

6. A method for preparing a fluoride ion-depleting fiber material with a high organosilicon grafting rate, characterized in that, The specific steps for preparing the fluoride-de-sparing fiber material according to any one of claims 1 to 5 are as follows: Step 1: Disperse or dissolve the acid addition salt containing disulfide-bonded diamine in an anhydrous or low-aqueous organic medium, add an organic proton acceptor to complete proton transfer, and allow the disulfide-bonded diamine containing amino groups to react with the acid-resistant fiber substrate containing nitrile groups. After washing, disulfide-bonded modified fibers are obtained. The ratio of the effective accepting equivalent of the organic proton acceptor to the acid equivalent of the disulfide-bonded diamine acid addition salt, calculated according to proton molar equivalent, is 1.80~2.60, and the mass fraction of water in the organic medium does not exceed 5%. Step 2: After the disulfide bond-modified fiber is fixed and washed, an excess reducing agent is added to reduce the disulfide bonds fixed on the acrylonitrile-containing acid-resistant fiber to thiol groups, and the reducing agent is washed off to obtain thiolized fiber; wherein, the reaction temperature is 10~50℃ and the reaction time is 4~6h. Step 3: The thiolized fiber is reacted with a terminal alkenyl siloxane containing at least two unsaturated end groups in a thiol-alkene reaction; the molar ratio of the unsaturated end groups in the terminal alkenyl siloxane to the thiol groups in the thiolized fiber is 0.8–1.5; when thermal initiation is used, the reaction temperature is 50–75 °C and the reaction time is 2–12 h; when photoinitiation is used, the ultraviolet light wavelength is 320–405 nm and the irradiation time is 10–120 min. Step 4: Remove unreacted and physically adsorbed siloxanes, and dry to obtain the fluoride-desorbed fiber material.

7. The preparation method according to claim 6, characterized in that, In step 1, the organic proton acceptor is selected from at least one of triethylamine, tri-n-butylamine, N,N-diisopropylethylamine, N-methylmorpholine, 1,8-diazabicyclo[5.4.0]undec-7-ene, 1,5-diazabicyclo[4.3.0]non-5-ene, and 1,5,7-trizabicyclo[4.4.0]dec-5-ene; the organic medium is selected from at least one of ethylene glycol, propylene glycol, glycerol, dimethyl sulfoxide, and N,N-dimethylformamide.

8. The preparation method according to claim 6, characterized in that, In step 2, the reducing agent is selected from at least one of tris(2-carboxyethyl)phosphine and its salts, dithiothreitol, mercaptoethanol, ascorbic acid and its salts, sulfites, and borohydrides.

9. An application of a high-organosilicon grafting rate fluoride ion desorption fiber material, characterized in that, The fluoride-removing fiber material according to any one of claims 1 to 5 or the fluoride-removing fiber material prepared by the preparation method according to any one of claims 6 to 8 is used for defluorination treatment of fluoride-containing acid solution, so that the fluoride content in the fluoride-containing acid solution does not exceed 10 mg / kg; the fluoride-containing acid solution is electronic grade phosphoric acid preparation solution, electronic grade hydrochloric acid preparation solution or wet process phosphoric acid.

10. A solid-phase regeneration method for fluoride ion-depleted fiber materials, characterized in that, The fiber material obtained after defluorination treatment in the application described in claim 9 is subjected to solid-phase regeneration treatment so that it can be reused; the specific steps of solid-phase regeneration are as follows: Step 1: The fluorine-captured fiber material is contacted with an alkaline aqueous regeneration solution, causing at least a portion of the fiber-bound Si-F to be converted into fiber-bound Si-OH and allowing fluorine to enter the regeneration solution; wherein, the alkaline aqueous regeneration solution comprises deionized water and an alkaline component; the alkaline component is one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, or ammonia water; the pH of the alkaline aqueous regeneration solution is 9-13; Step 2: The fiber material is subjected to solid-liquid separation and washing with the fluorinated aqueous regeneration solution, so that the Si-OH bonds in the fiber are dehydrated and condensed to form Si-O-Si bonds, and / or the residual thiol groups on the fiber are used to supplement the terminal alkenyl siloxane, so as to obtain the regenerated fiber material.

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