Aza-crown ether functionalized polyacrylonitrile fiber as well as preparation method and application thereof

Abstract

The invention is applicable to the technical field of materials, and provides an aza-crown ether functional polyacrylonitrile fiber and a preparation method and application thereof.The preparation method comprises the steps that polyacrylonitrile fiber, amine compounds and water are subjected to heating reflux for 3.5 h, and amino functional fiber is prepared; under the nitrogen atmosphere, heating and refluxing the fiber, an acylation reagent and an anhydrous organic solvent for 4 hours to obtain acylation modified fiber; and heating and refluxing the acylated modified fiber, 1, 10-diaza-18-crown ether-6, alkali, water and an alcohol solvent for 15 hours, and carrying out post-treatment to obtain the target fiber. The process is mild and controllable, the obtained fiber is good in mechanical strength and has efficient and specific adsorption on Ca < 2 + > under the neutral or alkaline condition, the saturated adsorption capacity reaches 1.049 mmolg <-1 >, adsorption equilibrium can be achieved within 30 min, the adsorption capacity on other metal ions such as Mg < 2 + > and Cu < 2 + > is extremely low, the raw materials are easy to obtain and recycle, and the method can be widely applied to the field of hard water treatment.

Description

Technical Field

[0001] This application belongs to the field of materials technology, and in particular relates to a nitrogen crown ether functionalized polyacrylonitrile fiber, its preparation method and application. Background Technology

[0002] Water hardness is mainly determined by Ca 2+ and Mg 2+ The total concentration of calcium and magnesium determines the water hardness. In plateau regions, due to scarce rainfall and abundant calcium and magnesium minerals, and in coastal regions, due to rising sea levels, water hardness is generally increasing. Higher water hardness not only shortens the lifespan of industrial equipment and increases safety hazards, but also raises the probability of related diseases in humans. Among these, calcium... 2+ Its effect on water hardness is far greater than that on Mg. 2+ Therefore, reducing the Ca content in the water body 2+ The content has important practical significance.

[0003] Currently reducing Ca in water bodies 2+ The main methods include membrane filtration, fractionation, and adsorption complexation. Membrane filtration requires significant external force to pass water through the filter membrane, resulting in high energy consumption and treatment costs, and leaving high-hardness water residue after filtration. Fractionation consumes extremely high energy and produces a large amount of scale at the bottom of the fractionation tower, reducing boiler efficiency and even clogging pipes.

[0004] The adsorption-complexation method can be carried out at room temperature, has low energy consumption, is highly efficient and stable, allows for reusable adsorbents, and is easy to operate. Loading functional groups of small-molecule adsorbents onto a support to create shaped, easily recyclable adsorbents represents a green and environmentally friendly development direction. Existing technologies have already explored supported adsorbent materials such as natural rubber-supported α-Fe₂O₃ and mordenized cellulose-supported ethylenediaminetetraacetic anhydride, demonstrating the application potential of polymer-supported small-molecule adsorbents in the field of hardening reduction.

[0005] Polyacrylonitrile fiber (PANF) boasts excellent chemical stability and low cost. Its surface contains highly reactive cyano and ester groups, allowing for deep, high-density surface modification, and it is easily recyclable, making it an ideal adsorbent carrier. Crown ethers, with their cyclic polyether structures, can complex with alkali metal ions; modified azacrown ethers can effectively complex alkaline earth metal ions. However, current technologies do not chemically modify azacrown ethers for grafting onto polyacrylonitrile fibers to achieve adsorption of Ca in water. 2+ Selective adsorption technology is rarely reported; at the same time, improper control during the preparation of azacrown ether functionalized fibers can lead to problems such as decreased fiber mechanical strength and limited adsorption volume, making it difficult to balance adsorption performance and practical application performance. Summary of the Invention

[0006] The purpose of this application is to provide a method for preparing azacrown ether functionalized polyacrylonitrile fiber, aiming to solve the technical problems of high energy consumption and poor applicability of existing water hardening methods, as well as the lack of selectivity of immobilized calcium adsorbent materials and the difficulty in preparing fiber-based adsorbent materials that balance the degree of modification and mechanical strength.

[0007] The embodiments of this application are implemented as follows: a method for preparing azacrown ether functionalized polyacrylonitrile fiber includes: Polyacrylonitrile fiber, amine compound, and water were added to a reaction vessel and heated under reflux for 3.5 h. After washing and drying, amino-functionalized fiber was obtained. Under a nitrogen atmosphere, amino-functionalized fibers, acylation reagents, and anhydrous organic solvents were added to a reaction vessel and heated under reflux for 4 h. After impurity removal, washing, and drying, acylated modified fibers were obtained. Acylated modified fibers, 1,10-diaza-18-crown ether-6, alkali, water, and alcohol solvent were added to a reaction vessel and heated under reflux for 15 h. After filtration, washing, extraction, and drying, diaza-crown ether-functionalized polyacrylonitrile fibers were obtained. Another objective of this application is to provide a nitrogen crown ether functionalized polyacrylonitrile fiber obtained by the above preparation method.

[0008] Another objective of this application is the application of the above-described azacrown ether-functionalized polyacrylonitrile fiber in the selective adsorption of calcium ions in water.

[0009] This application provides a method for preparing aza-crown ether-functionalized polyacrylonitrile fibers. The aza-crown ether functionalization of polyacrylonitrile fibers is achieved through a three-step chemical modification process, sequentially performing amino functionalization, acylation modification, and aza-crown ether grafting. Simultaneously, the reaction time of each step is precisely controlled to effectively balance the degree of fiber surface modification and the mechanical strength of the matrix. The resulting functionalized fibers exhibit good performance under neutral and alkaline conditions regarding Ca... 2+ It possesses highly efficient and specific adsorption properties, with a saturated adsorption capacity of 1.049 mmol·g. -1 Adsorption equilibrium can be reached within 30 minutes for Mg. 2+ Cu 2+ The adsorption capacity of coexisting metal ions is extremely low, and the adsorption selectivity is excellent. The preparation process is mild and highly controllable, resulting in fibers with good mechanical properties. The raw materials are readily available and easy to recycle, making it suitable for a wide range of applications in hard water treatment. It meets the needs of large-scale water treatment in my country and effectively enhances the economic and practical value of water treatment functional materials. Attached Figure Description

[0010] Figure 1 (a) PANF and (b) PAN provided in the embodiments of this application EF, (c)PANF-Cl and (d)PAN O Infrared spectrum of F; Figure 2 (a) PANF and (b) PAN provided in the embodiments of this application E F, (c)PANF-Cl and (d)PAN O Electron scan of F; Figure 3 This is a graph showing the change in calcium ion adsorption capacity of azacrown ether-functionalized polyacrylonitrile fibers as a function of solution pH, provided in the embodiments of this application. Figure 4 The graph shows the change in calcium ion adsorption capacity of the azacrown ether-functionalized polyacrylonitrile fiber as a function of adsorption time, as provided in the embodiments of this application. Detailed Implementation

[0011] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0012] To address the shortcomings of existing water hardening methods, such as high energy consumption, poor applicability, lack of selectivity in immobilized calcium adsorbents, and difficulty in balancing performance and practicality in the preparation of fiber-based adsorbents, this application provides a method for preparing nitrogen-crown ether-functionalized polyacrylonitrile fibers. This method includes the following core chemical modification steps, with process parameters for each step optimized through systematic experiments to balance the degree of modification and mechanical strength: Polyacrylonitrile fiber, amine compound, and water were added to a reaction vessel and heated under reflux for 3.5 h. After washing and drying, amino-functionalized fiber was obtained. Under a nitrogen atmosphere, amino-functionalized fibers, acylation reagents, and anhydrous organic solvents were added to a reaction vessel and heated under reflux for 4 h. After impurity removal, washing, and drying, acylated modified fibers were obtained. Acylated modified fibers, 1,10-diaza-18-crown ether-6, alkali, water, and alcohol solvent were added to a reaction vessel and heated under reflux for 15 h. After filtration, washing, extraction, and drying, diaza-crown ether-functionalized polyacrylonitrile fibers were obtained.

[0013] Preferably, the amine compound is one or more of ethylenediamine, 1,3-propanediamine, N-methyl-1,3-propanediamine, N,N-dimethyl-1,3-propanediamine, and hydrazine hydrate.

[0014] Preferably, the acylation reagent is chloroacetyl chloride; the anhydrous organic solvent is one of anhydrous acetonitrile and anhydrous ethanol.

[0015] Preferably, the alkali is sodium carbonate; the alcohol solvent is one or more of ethylene glycol, ethanol, and 1,4-dioxane.

[0016] Preferably, the mass-to-volume ratio of polyacrylonitrile fiber, amine compound, and water is 1.00 g: 4~6 mL: 8~10 mL.

[0017] Preferably, the mass-to-volume ratio of amino-functionalized fiber, acylation reagent, and anhydrous organic solvent is 1.00 g: 4~6 mL: 18~22 mL.

[0018] Preferably, the mass molar ratio of the acylated modified fiber, 1,10-diaza-18-crown ether-6, and the base is 1 g : 0.018~0.020 mol : 0.001~0.003 mol.

[0019] Preferably, the method for preparing the azacrown ether functionalized polyacrylonitrile fiber includes: Polyacrylonitrile fiber, ethylenediamine, and double-distilled water were added to a reaction vessel at a mass-volume ratio of 1.00 g: 5 mL: 9 mL. The mixture was heated under reflux for 3.5 h, washed with distilled water at 60-70 °C until the filtrate was neutral, and then dried under vacuum to obtain amino-functionalized fiber. Under a nitrogen atmosphere, amino-functionalized fibers, chloroacetyl chloride, and anhydrous acetonitrile were added to a reaction vessel at a mass-to-volume ratio of 1.00 g: 5 mL: 20 mL. The mixture was heated under reflux for 4 h, washed with distilled water at 60-70 °C, and tested with AgNO3 solution until no Cl was detected. - Vacuum drying yields acylated modified fibers; Acylated modified fibers, 1,10-diaza-18-crown ether-6, sodium carbonate, deionized water, and ethylene glycol were added to a reaction vessel at a ratio of 1 g: 0.019 mol: 0.002 mol: 5 mL: 10 mL. The mixture was stirred and heated under reflux for 15 h. After filtration and washing, the mixture was extracted by Soxhlet extraction, washed again, and dried under vacuum to obtain diaza-crown ether-functionalized polyacrylonitrile fibers.

[0020] This application also provides azirconium crown ether functionalized polyacrylonitrile fibers prepared by the above method. After three-step modification, the surface of these fibers is grafted with azirconium crown ether functional groups, and the mechanical strength retention rate reaches over 89%. Under neutral and alkaline conditions, the fibers exhibit resistance to Ca2+. 2+ It has specific recognition and complexation capabilities.

[0021] This application also provides the application of the aforementioned nitrogen-crown ether-functionalized polyacrylonitrile fiber in the selective adsorption of calcium ions in water. This fiber can be directly immersed in the hard water system to be treated to achieve Ca... 2+ It exhibits highly efficient and selective adsorption, and the adsorbed material is easily separated, recovered, and reused, making it suitable for the practical application needs of large-scale water treatment.

[0022] The specific adsorption operation is as follows: Dry azacrown ether-functionalized polyacrylonitrile fibers are immersed in a calcium ion aqueous solution prepared from soluble calcium salts for adsorption treatment; wherein the ratio of fiber to calcium ion aqueous solution is 20 mg: 28~32 mL, and the initial concentration of the calcium ion aqueous solution is 1 × 10⁻⁶. -3 mol・L -1 The soluble calcium salt is one or more of calcium nitrate and calcium chloride, and the optimal ratio of fiber to calcium ion aqueous solution is 20 mg: 30 mL. This adsorption process needs to be carried out under neutral or alkaline pH conditions, and adsorption equilibrium can be reached after an adsorption time of ≥30 min. After adsorption, the fiber is removed and washed, and the washing solution is combined with the remaining solution to be treated. The concentration of remaining calcium ions in the solution is determined by inductively coupled plasma mass spectrometry (ICP-MS) to calculate the actual adsorption amount. The adsorbed aza-crown ether functionalized polyacrylonitrile fiber can be recovered after simple treatment, and the recovered fiber still maintains good selective adsorption performance for calcium ions, allowing for multiple cycles for calcium ion adsorption treatment in water, effectively reducing the operating cost of water treatment.

[0023] The following detailed description of the azacrown ether-functionalized polyacrylonitrile fibers, their preparation methods, and applications, using specific embodiments, is provided. Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods; and the materials and reagents used are commercially available unless otherwise specified.

[0024] The following examples illustrate in detail the optimization of process parameters for each reaction step and the modification effects of different raw material selections. Unless otherwise specified, all experimental methods used in the examples are conventional methods; and all materials and reagents used are commercially available unless otherwise specified.

[0025] Example 1: Optimization Experiment of Amino Functionalization Reaction Time This embodiment investigates the effect of different reaction times during the amino functionalization stage on the modification effect and mechanical properties of polyacrylonitrile fibers. The experimental method is as follows: Multiple 1.00g portions of polyacrylonitrile fiber (PANF, tensile strength 8.63cN) were taken and added to 50mL three-necked flasks with 5mL ethylenediamine and 9mL double-distilled water, respectively. The mixtures were heated under reflux for 3h, 3.5h, and 3.75h, respectively. After the reaction was complete, the filtrate was washed with distilled water at 60-70℃ until neutral, and then vacuum dried to obtain amino-functionalized fibers (PANF) with different reaction times. E F), the weight gain, acid exchange capacity and mechanical properties of each fiber were determined, and the results are shown in serial numbers 2-4 in Table 1. At the same time, unmodified polyacrylonitrile fiber was used as a blank control (serial number 1 in Table 1).

[0026] Table 1. Effects of different reaction times on the weight gain, acid exchange capacity, and mechanical properties of functionalized fibers at each step. Note: The tensile strength retention rate is based on unmodified polyacrylonitrile fiber; PAN E F represents amino-functionalized fiber, PANF-Cl represents acylated modified fiber, and PAN represents... O F represents azacrown ether-functionalized polyacrylonitrile fiber.

[0027] As shown in Table 1, the optimal reaction time for amino functionalization is 3.5 h. When the reaction time is less than 3.5 h, the degree of cellulose amination is insufficient, resulting in low weight gain and poor functionality. Reflux for 3 h only achieves a 7% weight gain, and the acid exchange capacity is only 1.01 mmol·g. -1 When the reaction time exceeds 3.5 hours, although the fiber weight gain increases rapidly (reaching 16.8% after 3.75 hours of reflux), excessive swelling of the fiber occurs, the internal polymer cross-linking structure is destroyed, and a macroscopic "melting" phenomenon appears. Mechanical strength decreases significantly, with a breaking strength retention rate of only 91%, rendering it unsuitable for practical application. Reflux for 3.5 hours results in a fiber weight gain of 10.8% and an acid exchange capacity of 1.60 mmol·g. -1 The fracture strength retention rate reaches 97%, achieving the optimal balance between the degree of modification and mechanical strength.

[0028] Example 2: Optimization experiment of acylation modification reaction time This embodiment investigates the effect of different reaction times during the acylation modification stage on the modification effect and mechanical properties of amino-functionalized fibers. The experimental method is as follows: The amino-functionalized fiber (PAN) prepared by reflux for 3.5 hours in Example 1 was used. E F) Multiple portions, each 1.00 g, were added to a 100 mL three-necked round-bottom flask under a nitrogen atmosphere with 5 mL of chloroacetyl chloride and 20 mL of anhydrous acetonitrile. The mixtures were heated under reflux for 3.5 h, 4 h, and 4.5 h, respectively. After the reaction was complete, the flask was washed with distilled water at 60-70 °C and the solution was checked with AgNO3 solution until no Cl was detected. - Vacuum drying was performed to obtain acylated modified fibers (PANF-Cl) with different reaction times. The weight gain, acid exchange capacity and mechanical properties of each fiber were measured, and the results are shown in Table 1, numbers 5-7.

[0029] As shown in Table 1, controlling the acylation modification reaction time to 4 hours is a balanced choice between the degree of modification and mechanical strength: 4 hours of reflux can increase the fiber weight by 20% and the acid exchange capacity by 2.18 mmol·g. -1 The fracture strength retention rate was 92%, indicating a good modification effect and mechanical properties that met practical application requirements. However, at a reaction time of 3.5 h, the acylation reaction was incomplete, achieving only a 13.7% weight gain, with an acid exchange capacity of 1.58 mmol·g. -1If the reaction time is extended to 4.5 hours, the fiber weight increases by 28%, and the acid exchange capacity increases to 2.86 mmol·g. -1 However, the fracture strength retention rate is only 84%, and the mechanical strength is greatly reduced, which cannot meet the needs of practical applications.

[0030] In this embodiment, the acylation reagent chloroacetyl chloride is easily hydrolyzed by water, so all organic solvents used are dehydrated. Compared with anhydrous ethanol and anhydrous acetonitrile, anhydrous acetonitrile can make the fiber achieve a higher weight gain in a shorter time, making it the preferred solvent. At the same time, the nitrogen atmosphere can effectively prevent the acylation reagent from deteriorating when exposed to oxygen. The impurity removal washing needs to be done by detecting the absence of chloride ions with silver nitrate solution to ensure that there is no residual reagent on the fiber surface.

[0031] Example 3: Optimization of reaction time for azacrown ether grafting This embodiment investigates the effect of different reaction times during the azacrown ether grafting stage on the modification effect and mechanical properties of acylated modified fibers. The experimental method is as follows: Multiple portions (1 g each) of the acylated modified fiber (PANF-Cl) obtained by reflux for 4 hours in Example 2 were added to a 50 mL three-necked flask with 0.019 mol 1,10-diaza-18-crown ether-6, 0.002 mol sodium carbonate, 5 mL deionized water, and 10 mL ethylene glycol. The mixture was heated under reflux for 10 h, 15 h, and 20 h under electromagnetic stirring, respectively. After the reaction was completed, the mixture was filtered, washed, extracted using a Soxhlet extract, washed again, and dried under vacuum to obtain diaza-crown ether-functionalized polyacrylonitrile fibers (PANF-Cl) with different reaction times. O F), the weight gain, acid exchange capacity and mechanical properties of each fiber were determined, and the results are shown in serial numbers 8-10 in Table 1.

[0032] The data in Table 1 show that the optimal grafting time for the azacrown ether was 15 h: reflux for 15 h achieved a 10% weight gain and an acid exchange capacity of 0.40 mmol·g. -1 The fracture strength retention rate was 89%, representing the optimal combination of grafting efficiency and mechanical strength. However, at a reaction time of 10 hours, the grafting reaction was incomplete, achieving only a 2.5% weight gain, and the acid exchange capacity was only 0.10 mmol·g⁻¹. -1 The grafting amount of azacrown ether was low; when the reaction time was extended to 20 h, the fiber weight gain reached 14.1%, and the acid exchange capacity was 0.54 mmol·g. -1 However, the mechanical strength of the fiber further decreased, and the breaking strength retention rate was only 79%, which is difficult to meet the mechanical performance requirements for actual use.

[0033] In this embodiment, sodium carbonate is used as an acid-binding agent to promote the grafting reaction; 1,10-diaza-18-crown ether-6 has good solubility in ethanol, 1,4-dioxane, and ethylene glycol. After comparison and optimization, ethylene glycol was selected as the alcohol solvent: when ethanol is used as the solvent, the fiber weight gain after heating and refluxing for 48 hours is only 4.8%; when 1,4-dioxane is used as the solvent, the weight gain reaches 7.8%, both of which are far lower than the modification effect when ethylene glycol is used as the solvent; the extraction step adopts Soxhlet extraction, which can fully remove ungrafted small molecule impurities on the fiber surface and ensure the purity of the functionalized fiber.

[0034] Example 4 Experimental study on the effects of amino-functionalization modification of different amine compounds This embodiment investigates the effects of different amine compounds on the amino-functionalization modification of polyacrylonitrile fibers. The experimental method is as follows: Multiple 1.00 g portions of polyacrylonitrile fiber (PANF, tensile strength 8.63 cN) were taken and mixed with amine compounds such as ethylenediamine, 1,3-propanediamine, N-methyl-1,3-propanediamine, N,N-dimethyl-1,3-propanediamine, hydrazine hydrate, aminourea hydrochloride, and carbazide at a mass-to-volume ratio of 1.00 g: 5 mL: 9 mL. The mixtures were then added to 50 mL three-necked flasks. The reflux time was adjusted according to the reactivity of the different amine compounds to ensure that each system achieved a similar functionality (0.5 mmol·g⁻¹). -1 After the reaction, the fibers were washed with distilled water at 60-70℃ until the filtrate was neutral, and then dried under vacuum to obtain amino-functionalized fibers modified with different amine compounds. The weight gain, acid exchange capacity, mechanical properties, and reaction time required to reach the target functionality of each fiber were determined. The results are shown in Table 2.

[0035] Table 2. Weight gain, acid exchange capacity and mechanical properties of fibers modified with different amine compounds Note: 1. The tensile strength retention rates for items 1-11 are based on unmodified polyacrylonitrile fibers, and the tensile strength retention rates for items 12-15 are based on chloroacetyl chloride modified fibers; 2. PAN H F, PAN A F, PANPF, PAN S F, PAN T F represents amino-functionalized fibers modified with different primary amine compounds, PAN C F represents alkyl hydrazine modified fiber, PAN J F is a hydrazine hydrate modified fiber.

[0036] As shown in Table 2, ethylenediamine, 1,3-propanediamine, N-methyl-1,3-propanediamine, and N,N-dimethyl-1,3-propanediamine, among other reagents containing primary amine groups, are preferred amine compounds for amino functionalization. Ethylenediamine is the optimal choice, exhibiting high reactivity with the cyano group of polyacrylonitrile fibers, reaching 0.5 mmol·g. -1 Functionality can be achieved in just 3.5 hours, with good amination effect. The modified fiber has a weight gain of 6.3% and an acid exchange capacity of 0.47 mmol·g. -1 The tensile strength retention rate reached 99.7%, with almost no loss of mechanical properties; 1,3-propanediamine showed the highest reactivity, reaching the target functionality in just 0.7 hours, but the fiber weight gain after modification was low; while reagents containing hydrazide groups, such as aminourea hydrochloride and carbazide, reacted slowly with cyano groups, with aminourea hydrochloride reaching a reaction rate of 0.44 mmol·g. -1 Functionality requires 36 hours, and carbazide reaches 0.55 mmol·g. -1 Functionality requires 40 hours, and the mechanical strength of carbonyl hydrazine modified fibers gradually decreases with increasing reaction time, resulting in poor practicality.

[0037] All amine compounds exhibited varying degrees of crosslinking when reacting with polyacrylonitrile fibers. Except for fibers directly modified with carbazide, the fibers modified with the other functionalized molecules achieved greater weight gain and functionality over longer periods and at higher temperatures, with a modification degree of 0.5 mmol·g. -1 At that time, the mechanical strength retention rate of all fibers except those directly modified with carbazide was over 92%.

[0038] The two parameters used in this application, weight gain and functionality, are calculated using the following formulas: Weight gain (%) = [(Fiber mass after modification - Fiber mass before modification) / Fiber mass before modification] × 100%; Functionality (mmol・g -1 = 1000 × [(Fiber mass after modification - fiber mass before modification) / (Fiber mass after modification × increase in molecular formula mass)] × 100%.

[0039] Example 5: Preferred preparation process of azacrown ether functionalized polyacrylonitrile fibers Based on the process parameter optimization results of Examples 1-4 above, this example provides a preferred preparation process for azira-crown ether functionalized polyacrylonitrile fibers, and simultaneously completes the preparation of 1,10-diaza-18-crown ether-6. The specific steps are as follows: 5.1 Preparation of 1,10-diaza-18-crown ether-6 Step 1: Add acetone (50 mL), sodium iodide (0.044 mol, 6.66 g), and triethylene diiodide (0.02 mol, 3.8 g) to a 100 mL three-necked flask and heat under reflux for 70 h. Cool to room temperature, filter, and rotary evaporate. Remove the precipitated sodium iodide by filtration. Dissolve the filtrate in ether (100 mL) to obtain a reddish-brown solution. Wash the ether layer with saturated sodium thiosulfate solution (150 mL), and then remove the ether by rotary evaporation to obtain diiodotriethylene diiodide, a pale yellow liquid.

[0040] Step 2: Diiodotriethylene glycol (0.045 mol, 6.66 g) was dissolved in 20 mL of anhydrous acetonitrile and slowly added dropwise to a mixed solution of diaminotriethylene glycol (0.044 mol, 6.5 g), anhydrous sodium carbonate (0.237 mol, 25.08 g), and anhydrous acetonitrile. The mixture was heated under reflux for 18 h, filtered, and rotary evaporated. The residue was then dissolved in 20 mL of a mixed solvent (V:V dioxane = 1:1), refluxed for 30 min, cooled overnight, and the resulting large amount of white crystals was dissolved in a small amount of water and extracted with chloroform (100 mL) for 18 h. Finally, the mixture was recrystallized three times with n-heptane to obtain white crystals.

[0041] 5.2 Preparation of azacrown ether functionalized fibers, the preparation route is shown below: Aminofunctionalization: 1.00 g of polyacrylonitrile fiber (tensile strength 8.63 cN), 5 mL of ethylenediamine, and 9 mL of double-distilled water were added to a 50 mL three-necked flask and heated under reflux for 3.5 h. The filtrate was repeatedly washed with distilled water at 60-70 °C until neutral. The fiber was then dried overnight in a vacuum drying oven at 60 °C to obtain ethylenediamine-functionalized fiber (PAN). E (F), the fiber gained 10.8% weight and had an acid exchange capacity of 1.60 mmol·g. -1 The fracture strength is 8.43 cN, and the retention rate is 97% (corresponding to serial number 3 in Table 1).

[0042] Acylation modification: Under a nitrogen atmosphere, 1.00 g of the above ethylenediamine functionalized fiber, 5 mL of chloroacetyl chloride, and 20 mL of anhydrous acetonitrile were added to a 100 mL three-necked round-bottom flask. The mixture was heated under reflux for 4 h, washed with distilled water at 60-70 °C, and tested with silver nitrate solution until no white precipitate (no chloride ions) was found. The fiber was then vacuum dried overnight at 60 °C to obtain chloroacetyl chloride modified fiber (PANF-Cl). This fiber had a weight gain of 20% and an acid exchange capacity of 2.18 mmol·g. -1 The fracture strength is 7.94 cN, and the retention rate is 92% (corresponding to serial number 6 in Table 1).

[0043] Azacrown ether grafting: 1 g of the above-mentioned chloroacetyl chloride-modified fiber, 0.019 mol of 1,10-diaza-18-crown ether-6, 0.002 mol of sodium carbonate, 5 mL of deionized water, and 10 mL of ethylene glycol were added to a 50 mL three-necked flask. The mixture was heated under reflux for 15 h with electromagnetic stirring. After filtration, the fiber was washed with deionized water. The fiber was then extracted with ethanol in a Soxhlet extractor for 48 h. After filtration and ethanol washing, the fiber was dried overnight in a vacuum drying oven at 60 °C to obtain brownish-yellow azacrown ether-functionalized polyacrylonitrile fiber (PAN). O (F), the fiber has a 10% weight gain and an acid exchange capacity of 0.40 mmol·g. -1 The fracture strength is 7.64 cN, and the retention rate is 89% (corresponding to serial number 9 in Table 1).

[0044] 5.3 Characterization of fiber structure For polyacrylonitrile fiber (PANF) and amino-functionalized fiber (PAN) E F), acylated modified fibers (PANF-Cl) and nitrogen crown ether functionalized polyacrylonitrile fibers (PANF-Cl) O F) Infrared spectroscopy and scanning electron microscopy characterization were performed, and the results are as follows: Infrared spectra of four fibers (KBr compression method) are as follows: Figure 1 As shown in the infrared spectrum of the PANF fibrils, 2242 cm⁻¹ -1 The absorption peak at 1737 cm⁻¹ represents the stretching vibration absorption peak of -CN. -1 The peak represents the C=O stretching vibration absorption peak of methyl acrylate. (This refers to the absorption peak of PAN fibers after ethylenediamine amination.) E In the infrared spectrum of F, 3200-3500 cm⁻¹ -1 The new peak appearing at 1650 cm⁻¹ is the absorption peak of the stretching vibration of NH₃; -1 The absorption band at 1563 cm⁻¹ is the amide I band, attributed to the stretching vibration absorption peak of the carbonyl group in the amide; -1 The absorption band at this point is the amide II band, which is the result of the superposition of CN stretching vibration and NH bending vibration, proving the success of amino functionalization modification. The infrared spectrum of the functionalized fiber PANF-Cl modified with chloroacetyl chloride is compared with that of PAN. E The absence of a distinct new peak compared to F may be due to the presence of amide bonds and carbonyl groups in PANF-Cl, which overlap with the characteristic peaks of the functional groups introduced by acylation. (Note: The last sentence appears to be incomplete and possibly refers to a different topic. It likely refers to a specific type of PAN fiber, possibly related to a crown ether-functionalized fiber.) O In the infrared spectrum of F, compared with PANF-Cl, 1106 cm⁻¹ -1 The newly emerging peak corresponds to the symmetric stretching vibration of COC, indicating that the azacrown ether was successfully loaded onto the fiber. The three-step modification process achieved precise grafting of the target functional group.

[0045] Scanning electron microscope images of the four fibers are shown below. Figure 4 As shown. Under 200x magnification, the surface of polyacrylonitrile (PANF) pre-fibers is relatively smooth, and a small number of small cracks can be clearly observed on the fiber surface under high magnification; PAN after ethylenediamine amination treatment... E F, the fiber surface becomes rough and the cracks deepen, indicating that the amination treatment slightly damages the fiber structure, but the overall morphology remains good; PANF-Cl treated with chloroacetyl chloride further increases the surface roughness; the final prepared PAN O The surface roughness of F is further increased compared to PANF-Cl, but the overall fiber structure has not changed significantly. Combined with the mechanical strength test results, it is proved that this functionalized fiber can meet the requirements for subsequent calcium ion adsorption tests.

[0046] Example 6: Test of calcium ion adsorption performance of azacrown ether functionalized polyacrylonitrile fibers The azacrown ether functionalized polyacrylonitrile fiber (PAN) obtained in Example 5 O F) A comprehensive test of calcium ion adsorption performance was conducted. Inductively coupled plasma mass spectrometry (ICP-MS) was used to determine the concentration of metal ions in the solution during the test. Based on this, key indicators such as saturated adsorption capacity and adsorption rate were calculated. Specific test methods and results are as follows: 6.1 Adsorption Selectivity Test Weigh 20 mg of dried azacrown ether-functionalized polyacrylonitrile fiber and immerse it in 30 mL of water with an initial concentration of 1×10⁻⁶. - 3 mol・L -1 The fiber was stirred in an aqueous solution of lead, copper, calcium, chromium, cobalt, cadmium, magnesium, iron, and silver ions at room temperature for 24 hours. The fiber was then removed and washed. The washing solution was combined with the remaining solution, and the equilibrium concentration of each ion was determined and the saturated adsorption capacity was calculated. The results are shown in Table 3.

[0047] Table 3. Saturated adsorption capacity of azacrown ether functionalized polyacrylonitrile fibers for different metal ions As shown in Table 3, the saturated adsorption capacity of this fiber for calcium ions reaches 1.049 mmol·g. -1 Its adsorption capacity is much higher than that of other metal ions; the saturated adsorption capacity for magnesium and copper ions is only 0.003 mmol·g. -1 0.004 mmol·g -1 The adsorption capacity is almost negligible, and the adsorption capacity for other metal ions is also at a low level, indicating that the fiber has excellent specific adsorption and selective performance for calcium ions, and can achieve selective removal of calcium ions in water.

[0048] 6.2 Effect of pH on calcium ion adsorption performance test Weigh 20 mg of dried azacrown ether-functionalized polyacrylonitrile fiber and immerse it in 30 mL of water with an initial concentration of 1×10⁻⁶. -3 mol・L -1 In a calcium ion aqueous solution with a pH of 2-9, after stirring at room temperature for 12 hours, the equilibrium concentration of calcium ions in the solution was measured and the adsorption capacity was calculated. The results are as follows: Figure 3 As shown. Figure 3 The graph shows the change in calcium ion adsorption capacity as a function of solution pH. As can be seen, solution pH significantly affects the calcium ion adsorption performance of this fiber: under acidic conditions (pH=2~4), the fiber's adsorption capacity for calcium ions is extremely low; as the solution pH increases to the neutral and alkaline range (pH=5~9), the fiber's adsorption capacity for calcium ions shows a significant upward trend and remains at a high level. This phenomenon is because under acidic conditions, the nitrogen atoms on the fiber undergo protonation, reducing their complexation ability with calcium ions, while the complexation reaction can proceed efficiently under neutral and alkaline conditions. This adsorption characteristic is well-suited to the weakly alkaline environment of hard water, seawater, and other water bodies requiring treatment, and thus has practical application value.

[0049] 6.3 Calcium ion adsorption kinetics test At room temperature (298 K), 20 mg of dried azacrown ether-functionalized polyacrylonitrile fiber was weighed and immersed in 30 mL of solution with an initial concentration of 1×10⁻⁶. -3 mol・L -1 The solution was continuously stirred in an aqueous solution containing calcium ions, and samples were taken at 1, 5, 10, 15, 20, 25, 30, 45, and 60 min. The residual concentration of calcium ions in the solution at each time point was measured, and the adsorption capacity was calculated. The results are as follows: Figure 4 As shown. Figure 4 The graph shows the change in calcium ion adsorption capacity over time. As can be seen, the adsorption process of calcium ions by the fiber can be divided into a rapid adsorption stage and an equilibrium stage: in the rapid adsorption stage (first 5 minutes), the adsorption capacity of the fiber for calcium ions rapidly increases to 29 mg / g. -1 After 5 minutes, the adsorption rate slowed down, and the adsorption capacity showed a slow upward trend. By 30 minutes, the adsorption capacity no longer changed, reaching adsorption equilibrium. At this point, the maximum adsorption capacity of the fiber for calcium ions was 41.95 mg·g⁻¹. -1 The results indicate that the fiber has a fast adsorption rate for calcium ions, reaching adsorption equilibrium in 30 minutes, which meets the efficiency requirements for large-scale water treatment.

[0050] 6.4 Cyclic Use Performance Test After desorption, washing, and drying, the nitrogen-crown ether-functionalized polyacrylonitrile fibers that had undergone calcium ion adsorption were subjected to the same calcium ion adsorption test. After five consecutive cycles, the saturated adsorption capacity of the fibers for calcium ions was measured. The test results showed that after five cycles, the saturated adsorption capacity of the fibers for calcium ions remained at 0.95 mmol·g. -1 The above results show no significant decrease in adsorption performance, indicating that the fiber has good recyclability and can be recycled multiple times, effectively reducing the raw material and operating costs of water treatment.

[0051] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of this patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method for preparing azacrown ether-functionalized polyacrylonitrile fiber, characterized in that, include: Polyacrylonitrile fiber, amine compound, and water were added to a reaction vessel and heated under reflux for 3.5 h. After washing and drying, amino-functionalized fiber was obtained. Under a nitrogen atmosphere, amino-functionalized fibers, acylation reagents, and anhydrous organic solvents were added to a reaction vessel and heated under reflux for 4 h. After impurity removal, washing, and drying, acylated modified fibers were obtained. Acylated modified fibers, 1,10-diaza-18-crown ether-6, alkali, water, and alcohol solvent were added to a reaction vessel and heated under reflux for 15 h. After filtration, washing, extraction, and drying, diaza-crown ether-functionalized polyacrylonitrile fibers were obtained.

2. The method for preparing azacrown ether functionalized polyacrylonitrile fiber according to claim 1, characterized in that, The amine compound is one or more of ethylenediamine, 1,3-propanediamine, N-methyl-1,3-propanediamine, N,N-dimethyl-1,3-propanediamine, and hydrazine hydrate.

3. The method for preparing azacrown ether functionalized polyacrylonitrile fiber according to claim 1, characterized in that, The acylation reagent is chloroacetyl chloride; the anhydrous organic solvent is one of anhydrous acetonitrile and anhydrous ethanol.

4. The method for preparing azacrown ether functionalized polyacrylonitrile fiber according to claim 1, characterized in that, The alkali is sodium carbonate; the alcohol solvent is one or more of ethylene glycol, ethanol, and 1,4-dioxane.

5. The method for preparing azacrown ether functionalized polyacrylonitrile fiber according to claim 1, characterized in that, The mass-volume ratio of polyacrylonitrile fiber, amine compounds, and water is 1.00 g: 4~6 mL: 8~10 mL.

6. The method for preparing azacrown ether functionalized polyacrylonitrile fiber according to claim 1, characterized in that, The mass-to-volume ratio of amino-functionalized fiber, acylation reagent, and anhydrous organic solvent is 1.00 g: 4~6 mL: 18~22 mL.

7. The method for preparing azacrown ether functionalized polyacrylonitrile fiber according to claim 1, characterized in that, The mass molar ratio of acylated modified fiber, 1,10-diaza-18-crown ether-6, and base is 1 g : 0.018~0.020 mol : 0.001~0.003 mol.

8. The method for preparing azacrown ether functionalized polyacrylonitrile fiber according to claim 1, characterized in that, include: Polyacrylonitrile fiber, ethylenediamine, and double-distilled water were added to a reaction vessel at a mass-volume ratio of 1.00 g: 5 mL: 9 mL. The mixture was heated under reflux for 3.5 h, washed with distilled water at 60-70 °C until the filtrate was neutral, and then dried under vacuum to obtain amino-functionalized fiber. Under a nitrogen atmosphere, amino-functionalized fibers, chloroacetyl chloride, and anhydrous acetonitrile were added to a reaction vessel at a mass-to-volume ratio of 1.00 g: 5 mL: 20 mL. The mixture was heated under reflux for 4 h, washed with distilled water at 60-70 °C, and tested with AgNO3 solution until no Cl was detected. - Vacuum drying yields acylated modified fibers; Acylated modified fibers, 1,10-diaza-18-crown ether-6, sodium carbonate, deionized water, and ethylene glycol were added to a reaction vessel at a ratio of 1 g: 0.019 mol: 0.002 mol: 5 mL: 10 mL. The mixture was stirred and heated under reflux for 15 h. After filtration and washing, the mixture was extracted by Soxhlet extraction, washed again, and dried under vacuum to obtain diaza-crown ether-functionalized polyacrylonitrile fibers.

9. A nitrogen-crown ether-functionalized polyacrylonitrile fiber obtained by any one of the preparation methods described in claims 1 to 8.

10. The application of the azacrown ether-functionalized polyacrylonitrile fiber as described in claim 9 in the selective adsorption of calcium ions in water.

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