La-CPAN-PEI defluorination material as well as preparation method and application thereof

Abstract

The invention discloses a La-CPAN-PEI defluorination material as well as a preparation method and application thereof, and belongs to the technical field of water treatment. The preparation method of the material comprises the following steps: performing heat treatment on polyacrylonitrile fibers in protective gas to obtain cyclized polyacrylonitrile fibers; and dispersing the cyclized polyacrylonitrile fiber, an alkali catalyst, an organic lanthanum source and polyethyleneimine in a degassed alcoholic solution, and carrying out solvothermal reaction to obtain the La-CPAN-PEI defluorination material. According to the method, the pH response characteristic of the PEI chain is utilized, the fluorine ion adsorption process is precisely regulated and controlled, and the process shows the characteristics of acid adsorption and alkali removal and dynamic balance of an intermediate pH region. The material has high adsorption capacity, excellent selectivity and simple and convenient acid-base cyclic regeneration capacity through the synergistic effect of three mechanisms of electrostatic attraction, conformation mass transfer and precipitation immobilization, and has a good application prospect in deep treatment of fluorine-containing wastewater.

Description

Technical Field

[0001] This invention belongs to the field of water treatment technology, specifically relating to a La-CPAN-PEI defluorination material, its preparation method, and its application. Background Technology

[0002] Fluorine, an essential trace element for the human body, has an extremely narrow safe concentration window in drinking water. my country's "Standards for Drinking Water Quality" (GB5749-2022) clearly stipulates that the fluoride content in drinking water should be less than 1.0 mg / L, and the World Health Organization has set the limit for fluoride ions in drinking water at 1.5 mg / L. However, more than 200 million people worldwide are chronically exposed to water sources with excessive fluoride levels, particularly in vast areas of Asia and Africa. Long-term excessive intake of fluoride ions can irreversibly damage human hard tissues, leading to dental fluorosis and disabling skeletal fluorosis, posing a persistent threat to public health and socioeconomic development.

[0003] Among existing defluoridation technologies, adsorption is considered one of the most promising options due to its ease of operation, adaptability, and relatively low cost. However, traditional commercial adsorbents, such as activated alumina, generally suffer from limited adsorption capacity, slow kinetic rates, and the risk of secondary pollution caused by aluminum leaching under acidic conditions. Biomass materials such as bone char have problems with poor mechanical strength and unstable adsorption performance. Although other technologies, including coagulation sedimentation, membrane separation, and electroadsorption, are also used, they each face insurmountable bottlenecks: coagulation produces large amounts of fluoride-containing sludge and the residual fluoride concentration in the effluent is difficult to meet standards; membrane technology is costly, energy-intensive, and prone to fouling and clogging; and electroadsorption is limited by its effectiveness in treating low-salinity water and electrode lifespan.

[0004] In recent years, inorganic adsorbents based on the rare earth element lanthanum have attracted widespread attention due to their ability to form highly insoluble lanthanum fluoride precipitates with fluoride ions, exhibiting extremely high theoretical adsorption capacity and excellent selectivity. However, the industrial application of this technology faces two major challenges: First, the solid-liquid separation of nanoscale lanthanum-based materials is difficult and the preparation cost is high; second, and more severe, lies in the regeneration of the material after adsorption. Because LaF3 precipitates are extremely thermodynamically stable, traditional regeneration methods (such as using high-concentration strong bases for ion exchange) are often inefficient and incomplete, and the strong chemical environment can easily damage the material structure, leading to the loss of the active component lanthanum and a sharp decline in adsorption capacity, severely restricting its economic viability and sustainability.

[0005] Therefore, the water treatment field urgently needs to fundamentally solve the regeneration problem of lanthanum-based materials by maintaining their efficient defluorination properties through innovative material design concepts. This invention aims to construct a structurally stable lanthanum-based composite adsorbent that can achieve efficient regeneration and recycling in response to changes in environmental pH. Summary of the Invention

[0006] To address the shortcomings and deficiencies of existing technologies, this invention provides a La-CPAN-PEI defluorination material, its preparation method, and its applications, specifically addressing the slow adsorption kinetics at low concentrations, poor accessibility of active sites, and difficulty in recycling of existing defluorination materials. This material operates based on a triple sequential mechanism of "electrostatic attraction-conformational mass transfer-precipitation fixation." This unique property solves the key bottlenecks of traditional materials in deep purification and recycling.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] The first aspect of this invention is to provide a method for preparing a La-CPAN-PEI defluorination material, comprising the following steps; Step 1: Take a certain amount of polyacrylonitrile fiber (PAN), wash away surface impurities with alkali, wash with deionized water until neutral, and dry for later use; Step Two: The polyacrylonitrile fibers (PAN) obtained in Step One are heat-treated in a tube furnace at high temperature with a protective gas to activate them, transforming them into cyclized polyacrylonitrile fibers (CPAN) for later use. The core value of heat-treating and activating PAN lies in converting it into a highly reactive platform. This process induces cyclization of PAN molecules, generating abundant nitrogen-containing active sites that can form strong covalent bonds with PEI molecular chains, achieving stable grafting. This structure provides an ideal microenvironment for introducing organic lanthanum as an auxiliary ion, allowing lanthanum ions to synergistically interact with PEI amino groups to enhance the capture capacity of fluoride ions, ultimately significantly improving the overall adsorption performance of the material through a synergistic effect. Furthermore, the high-strength, rigid conjugated backbone formed after thermal cyclization of polyacrylonitrile fibers (PAN) allows the structure to exist stably in acidic and alkaline environments. This structural characteristic gives the material both good mechanical strength and recyclability. Step 3: Place the alcohol solution in an ultrasonic machine and sonicate to remove gas. The purpose is to remove dissolved oxygen from the alcohol solution, suppress solvothermal side reactions, reduce air bubbles adhering to the material surface, improve fiber wetting and dispersion, and ensure uniform grafting. Step 4: Cyclic polyacrylonitrile fiber (CPAN), alkaline catalyst, organic lanthanum source and polyethyleneimine (PEI) are dispersed in a degassed alcohol solution to obtain a solid-liquid mixture; Step 5: Place the solid-liquid mixture from Step 4 into a high-pressure reactor for solvothermal reaction; This invention uses a one-pot method to allow the reactants to react and obtain the target product, which can maintain a high content of polyethyleneimine grafted onto the surface of polyacrylonitrile fibers, thereby increasing the lanthanum content in the product and improving the adsorption effect of the product based on the adhesion of polyethyleneimine to organolanthanum.

[0009] Step 6: After completion, the precipitate is filtered and washed with polar organic solvent, alcohol and deionized water until the washing solution has no obvious color. The final product is obtained by freeze drying, which yields La-CPAN-PEI defluorination material, which is kept for later use.

[0010] As a preferred technical solution, in step one, the drying temperature is 60°C to 80°C, and the alkali is either KOH or NaOH.

[0011] As a preferred technical solution, in step two, the protective gas is nitrogen or an inert gas; the heat treatment time is 3 hours, the temperature is 200-220℃, the heating rate is 2-5℃ / min, and the gas flow rate is 50-100 mL / min.

[0012] As a preferred technical solution, the alcohol solution is methanol or ethanol. Methanol or ethanol has excellent solubility for PEI, which is beneficial for the uniform dispersion and bonding of grafted chains. Furthermore, their boiling points are much lower than 140 °C, allowing for the formation of suitable autogenous pressure in a closed reactor, promoting interfacial reactions and mass transfer. Using water or other solvents can have adverse effects. For example, when water is used as a solvent, CPAN fibers absorb water and swell at room temperature, and at 140 °C, they are prone to excessive swelling, leading to damage to the skeletal structure. When organic reagents such as DMF are used, DMF has high toxicity and a boiling point of 153 °C at normal pressure. At 140 °C and high pressure, vaporization is more difficult, resulting in insufficient autogenous pressure, which is detrimental to mass transfer and grafting. Additionally, it has high viscosity, is difficult to volatilize, and easily leaves residues; therefore, it is not used as a reaction solvent and is only used for post-reaction washing and impurity removal.

[0013] As a preferred technical solution, in step four, the alkaline catalyst is KOH or NaOH; the organic lanthanum source is lanthanum acetate or lanthanum acetylacetonate, with a mass ratio of lanthanum acetate to CPAN of 0.1:1 to 0.3:1, and a mass ratio of lanthanum acetylacetonate to CPAN of 0.138:1 to 0.414:1 (following molar ratios). Too little lanthanum source will result in poor adsorption of fluoride ions, while too much lanthanum source will not be fully attached to polyethyleneimine (PEI), leading to waste. Compared to inorganic lanthanum sources, the core advantage of using organic lanthanum sources in this invention lies in the fact that their organic ligands significantly improve the interfacial compatibility and binding ability between the lanthanum center and the organic substrate (CPAN-PEI). The hydrophobic ligands of organic lanthanum can tightly bind to the conjugated framework of CPAN and the hydrocarbon segments of PEI through hydrophobic interactions and π-π stacking, thereby promoting their uniform dispersion in the organic phase and avoiding aggregation problems caused by differences in hydrophilicity. Organic ligands can act as "molecular bridges," forming hydrogen bonds or van der Waals forces with CPAN / PEI surface functional groups through their oxygen, nitrogen, and other atoms, thus achieving a multi-anchoring mechanism that integrates "metal center-organic ligand-organic substrate" from single metal coordination.

[0014] As a preferred technical solution, the mass ratio of polyethyleneimine (PEI) to CPAN is 3:1 to 5:1. PEI is a white, viscous liquid with a high density, while CPAN is a brownish-red fiber with a low density. The combination of these two within the above-mentioned ratio range is optimal. The molecular weight of PEI is 10,000 to 100,000, preferably 100,000. PEI is a macromolecular organic compound; the higher the molecular weight, the larger the diameter and specific surface area of ​​the final synthesized material after grafting onto CPAN, allowing for the grafting of more organic lanthanum sources. Therefore, PEI with a molecular weight of 100,000 is preferred.

[0015] As a preferred technical solution, in step five, the temperature of the solvothermal reaction is 120°C to 160°C, and the time is 12h to 24h.

[0016] As a preferred technical solution, in step six, the polar organic solvent is N,N-dimethylformamide solution (DMF), and the freeze-drying temperature is set to -30℃ to -60℃ for 24 hours.

[0017] The second aspect of this invention is to provide a La-CPAN-PEI defluorination material, which is obtained by the preparation method described in the first aspect. Traditional high-efficiency adsorbents are mostly micro / nano powders, which are prone to loss and system clogging in actual water treatment, and solid-liquid separation is costly. The La-CPAN-PEI defluorination material prepared by this invention is an adsorbent material with a macroscopic linear morphology, its physical form resembling fibers or filter filaments. It can achieve rapid and thorough separation and recovery through simple filtration, sedimentation, or filling into a filter bed, significantly improving operational convenience and process stability.

[0018] A third aspect of the present invention is to provide the application of the La-CPAN-PEI defluorination material as described in the second aspect as an adsorbent for removing fluoride ions from water, comprising the following steps: The La-CPAN-PEI fluoride removal material is placed in a fluoride-containing aqueous solution. The pH of the fluoride-containing aqueous solution is adjusted to an acidic solution, and fluoride ions are adsorbed. After adsorption, the adsorbent is eluted and regenerated using an alkaline solution. Preferably, the pH of the acidic solution is 3-6, and the pH of the alkaline solution is 11-12. More preferably, dilute HNO3 or dilute HCl is used to adjust the solution to acidity; the alkaline solution is KOH or NaOH.

[0019] Using the La-CPAN-PEI defluorination material prepared according to this invention for the adsorption of fluoride ions, a clear adsorption-regeneration process is achieved: the material exhibits a clear "acid adsorption, alkali desorption" process with pH-based adsorption and desorption of fluoride ions in between. -The dynamic equilibrium characteristic. Under acidic conditions (pH < 7), the PEI chain protonates and becomes positively charged (NH2 → -NH3). + F is efficiently captured through "aminoprotonation electrostatic attraction". - Simultaneously, intramolecular hydrogen bonding leads to the aggregation of functional groups, weakening their interaction with water molecules and causing chain contraction, thus reducing Fo. - Transport to La 3+ The PEI chain undergoes deprotonation at specific sites, achieving efficient adsorption via a lanthanum precipitation-dominated mechanism. Under alkaline conditions (pH > 10), the PEI chain deprotonates, generating negatively charged sites. These sites form a tight hydrogen bond network with surrounding water molecules, promoting the complete expansion of functional groups. Strong PEI chain conformational regulation significantly exposes these sites and weakens electrostatic attraction, while high concentrations of OH-... - With F - Competition La 3+ The adsorption sites erode LaF3 precipitates, driving efficient desorption of fluoride ions. In the transitional pH range (pH 7-10), the material approaches its isoelectric point (pH 7-10), representing a critical state. At this point, the polymer chain's net charge is near zero, placing it in an intermediate conformation between contraction and extension. Chain-water interactions reach dynamic equilibrium, making it extremely sensitive to minute pH changes and representing a response switching window where adsorption and desorption coexist. At this point, the adsorption and desorption rates of fluoride ions are roughly equal.

[0020] Compared with the prior art, the beneficial effects of the present invention are: (1) This invention employs heat treatment of polyacrylonitrile fibers in a nitrogen or inert gas environment to construct a thermoplastic ladder polymer with a regular structure, rich in C=N active sites, and retaining molecular flexibility. This product serves as a functional substrate, providing a key structural basis for the subsequent pH-responsive conformational transition of the PEI chain and the efficient loading of organolanthanum. The principle is as follows: During cyclization in a nitrogen or inert gas atmosphere, the cyano groups (-C≡N) on the linear PAN chain undergo intramolecular cyclization, primarily transforming into a ladder-like framework containing numerous regular C=N structures (pyridine nitrogen). Simultaneously, a small number of uncyclized terminal cyano groups (-C≡N) and chain ends (-NH₂ / -NH) are generated. These nitrogen-containing sites work synergistically to achieve efficient and stable immobilization of the organolanthanum molecule. Specifically, the conjugated C=N framework stabilizes the aromatic structure of the organolanthanum ligand through π-π stacking, while the nitrogen atoms of the C=N and amine groups act as secondary coordination sites, undergoing weak coordination or hydrogen bonding with the organolanthanum center, thus providing a unique organic-inorganic hybrid active center for fluoride ion adsorption. Compared to traditional PAN fiber techniques that emphasize stabilization in an oxygen-containing atmosphere to construct a cross-linked structure and ensure the integrity of the carbonized morphology, this invention avoids the problem that the dense cross-linked network formed in an oxygen-containing atmosphere severely restricts the chain mobility and modifiability of the polymer.

[0021] (2) High efficiency and selectivity in defluorination: The material passes through La 3+ With F - A stable LaF3 precipitate is formed, and combined with the synergistic effect of PEI, a high adsorption capacity and excellent selectivity for fluoride ions are achieved.

[0022] (3) Controllable adsorption-regeneration process: Utilizing the pH-responsive characteristics of polyethyleneimine (PEI), the entire working cycle can be clearly and efficiently driven by simple external adjustment of "acid adsorption-alkali desorption". The regeneration cost is low and the operation and management are simple. (4) Excellent engineering applicability and cycle stability: The macroscopic linear structure overcomes the engineering bottlenecks of easy loss and difficult separation of powder materials, making them easy to recycle and reuse. At the same time, the robust cyclic polyacrylonitrile fiber (CPAN) skeleton and strong chemical bonding ensure that the material can maintain stable mechanical strength and adsorption performance after long-term use and multiple regenerations.

[0023] (5) Low overall cost and environmentally friendly: The raw material polyacrylonitrile fiber (PAN) used is inexpensive and readily available, and the preparation process is simple. The linear form and efficient regeneration capability further reduce operating and maintenance costs, and the entire system avoids the use of complex chemicals, making it more environmentally friendly. Attached Figure Description

[0024] Figure 1 This is a SEM image of a La-CPAN-PEI defluorination material prepared in Example 1.

[0025] Figure 2 The energy dispersive spectroscopy (EDS) elemental distribution diagram of a La-CPAN-PEI defluorination material prepared in Example 1 is shown below. Figure 3 The energy dispersive spectral density (EDS) distribution of N, C, La, and O elements in the La-CPAN-PEI defluorination material prepared in Example 1 is shown below. Detailed Implementation The present invention will be further described below with reference to embodiments. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention.

[0027] Example 1 A method for preparing and applying a La-CPAN-PEI defluorination material includes the following steps: Step 1: Wash the polyacrylonitrile fiber (PAN) with 0.01M NaOH to remove surface impurities, then wash with deionized water until neutral, and dry at 60℃ for 24 hours for later use. Step 2: The polyacrylonitrile fiber (PAN) obtained in Step 1 is calcined in a tube furnace at a high temperature of 210℃ for 3 hours under nitrogen, to convert it into cyclized polyacrylonitrile (CPAN) for later use. The heating rate is 5℃ / min and the gas flow rate is 50mL / min.

[0028] Step 3: Place the methanol solution in an ultrasonic machine and sonicate for 10 minutes to remove gas; set aside for later use. Step 4: Disperse 1g of dry cyclized polyacrylonitrile (CPAN), 0.6g (0.015mol) NaOH, 0.3g of lanthanum acetate and 4g of polyethyleneimine (PEI) (PEI has a molecular weight of 100,000) into the methanol solution treated in Step 3; Step 5: Place the liquid from Step 4 into a high-pressure reactor for a solvothermal reaction at 140°C for 12 hours. Step 6: After completion, the precipitate is filtered and washed with N,N-dimethylformamide solution (DMF), methanol and deionized water until the washing solution has no obvious color. The final product is obtained by drying at -60℃ for 24 hours and is kept for later use.

[0029] Figure 1 This is a SEM image of a La-CPAN-PEI defluorination material prepared in Example 1. Figure 1 It can be seen that the material has an ideal engineering morphology (easily recyclable fibers) and an optimized microstructure (a rough surface with a high specific surface area). Figure 2 This is an EDS elemental distribution overlay diagram of the material. The interwoven fiber network in the diagram represents the microstructure of the material, while the colored dotted distribution of N, La, O, and C visually demonstrates that lanthanum, as a key element, has been successfully and uniformly loaded onto the fiber skeleton, confirming the successful preparation of the fluorine removal material.

[0030] Figure 3 Figures A, B, C, and D are EDS surface distribution diagrams of N, C, La, and O elements in the material, respectively, showing that each element is uniformly distributed in the material in the form of a dotted network.

[0031] Detection Example 1 Prepare an initial sodium fluoride solution with a concentration of 10 mg / L, and adjust the pH to 5 with 0.1 M HCl. Place 0.1 g / L of the defluorination material into a 500 mL Erlenmeyer flask, and then add 500 mL of the prepared solution. Shake in a constant temperature shaker at 25°C for 1 hour. After filtration, measure the residual fluoride concentration using a fluoride ion electrode. Calculations show that the adsorption material of this invention reduces the fluoride ion concentration in the solution to below 1 mg / L (fluoride ion concentration 0.46 mg / L), which meets national standards. The adsorbed material can then be desorbed using an alkaline solution (prepared with NaOH) at pH 11 for recycling.

[0032] Cyclic performance test: Taking the product prepared in Example 1 as the object, after six adsorption-desorption cycle experiments, the fiber skeleton structure of the material remained basically intact, with only a small amount of local collapse or dissolution. The adsorption efficiency of fluoride ions decreased from the original 90.2% to 84.3%, indicating that it has good cyclic stability.

[0033] Example 2 A method for preparing and applying a La-CPAN-PEI defluorination material includes the following steps: Step 1: Wash the polyacrylonitrile fiber (PAN) with 0.01M KOH to remove surface impurities, then wash with deionized water until neutral, and dry at 60℃ for 24 hours for later use. Step 2: The polyacrylonitrile fiber (PAN) obtained in Step 1 is calcined in a tube furnace at a high temperature of 210℃ for 3 hours under nitrogen, to convert it into cyclized polyacrylonitrile (CPAN) for later use. The heating rate is 5℃ / min and the gas flow rate is 50mL / min.

[0034] Step 3: Place the ethanol solution in an ultrasonic machine and sonicate for 10 minutes to remove gas; set aside for later use. Step 4: Disperse 1g of dry cyclized polyacrylonitrile (CPAN), 0.84g (0.015mol) KOH, 0.3g of lanthanum acetate and 4g of polyethyleneimine (PEI) (PEI has a molecular weight of 100,000) into the ethanol solution treated in Step 3; Step 5: Place the liquid from Step 4 into a high-pressure reactor for a solvothermal reaction at 140°C for 12 hours. Step 6: After completion, the precipitate is filtered and washed with N,N-dimethylformamide solution (DMF), ethanol and deionized water until the washing solution has no obvious color. The final product is obtained by drying at -60℃ for 24 hours and is kept for later use.

[0035] Detection Example 2 Prepare an initial sodium fluoride solution with a concentration of 10 mg / L, and adjust the pH to 5 with 0.1 M HCl. Place 0.1 g / L of the defluorination material into a 500 mL Erlenmeyer flask, and then add 500 mL of the prepared solution. Shake in a constant temperature shaker at 25°C for 1 hour. After filtration, measure the residual fluoride concentration using a fluoride ion electrode. Calculations show that the adsorption material of this invention reduces the fluoride ion concentration in the solution to below 1 mg / L (fluoride ion concentration is 0.48 mg / L), which meets national standards. The adsorbed material can then be desorbed using an alkaline solution (prepared with KOH) at pH 11.

[0036] Example 3 A method for preparing and applying a La-CPAN-PEI defluorination material includes the following steps: Step 1: Wash the polyacrylonitrile fiber (PAN) with 0.01M NaOH to remove surface impurities, then wash with deionized water until neutral, and dry for later use. Step 2: The polyacrylonitrile fiber (PAN) obtained in Step 1 is calcined in a tube furnace at a high temperature of 210℃ for 3 hours under nitrogen, to convert it into cyclized polyacrylonitrile (CPAN) for later use. The heating rate is 5℃ / min and the gas flow rate is 50mL / min.

[0037] Step 3: Place the ethanol solution in an ultrasonic machine and sonicate for 10 minutes to remove gas; set aside for later use. Step 4: Disperse 1g of dry cyclized polyacrylonitrile (CPAN), 0.6g (0.015mol) NaOH, 0.414g of lanthanum acetylacetonate and 4g of polyethyleneimine (PEI) (PEI has a molecular weight of 100,000) into the ethanol solution treated in Step 3; Step 5: Place the liquid from Step 4 into a high-pressure reactor for a solvothermal reaction at 140°C for 12 hours. Step 6: After completion, the precipitate is filtered and washed with N,N-dimethylformamide solution (DMF), ethanol and deionized water until the washing solution has no obvious color. The final product is obtained by drying at -60℃ for 24 hours and is kept for later use.

[0038] Detection Example 3 Prepare an initial sodium fluoride solution with a concentration of 10 mg / L, and adjust the pH to 5 with 0.1 M HNO3. Place 0.1 g / L of the defluorination material into a 500 mL Erlenmeyer flask, and then add 500 mL of the prepared solution. Shake in a constant temperature shaker at 25°C for 1 hour. After filtration, measure the residual fluoride concentration using a fluoride ion electrode. Calculations show that the adsorption material of this invention reduces the fluoride ion concentration in the solution to below 1 mg / L (fluoride ion concentration is 0.52 mg / L), which meets national standards. The adsorbed material can then be desorbed using an alkaline solution (prepared with NaOH) at pH 11.

[0039] Example 4 A method for preparing and applying a La-CPAN-PEI defluorination material includes the following steps: Step 1: Wash the polyacrylonitrile fiber (PAN) with 0.01M KOH to remove surface impurities, then wash with deionized water until neutral, and dry for later use. Step 2: The polyacrylonitrile fiber (PAN) obtained in Step 1 is calcined in a tube furnace at a high temperature of 210℃ for 3 hours under nitrogen, to convert it into cyclized polyacrylonitrile (CPAN) for later use. The heating rate is 5℃ / min and the gas flow rate is 50mL / min.

[0040] Step 3: Place the methanol solution in an ultrasonic machine and sonicate for 10 minutes to remove gas; set aside for later use. Step 4: Disperse 1g of dry cyclized polyacrylonitrile (CPAN), 0.84g (0.015mol) KOH, 0.414g of lanthanum acetylacetonate and 4g of polyethyleneimine (PEI) (PEI has a molecular weight of 100,000) into the methanol solution treated in Step 3; Step 5: Place the liquid from Step 4 into a high-pressure reactor for a solvothermal reaction at 140°C for 12 hours. Step 6: After completion, the precipitate is filtered and washed with N,N-dimethylformamide solution (DMF), methanol and deionized water until the washing solution has no obvious color. The final product is obtained by drying at -60℃ for 24 hours and is kept for later use.

[0041] Detection Example 4 Prepare an initial sodium fluoride solution with a concentration of 10 mg / L, and adjust the pH to 5 with 0.1 M HNO3. Place 0.1 g / L of the defluorination material into a 500 mL Erlenmeyer flask, and then add 500 mL of the prepared solution. Shake in a constant temperature shaker at 25°C for 1 hour. After filtration, measure the residual fluoride concentration using a fluoride ion electrode. Calculations show that the adsorption material of this invention reduces the fluoride ion concentration in the solution to below 1 mg / L (fluoride ion concentration is 0.63 mg / L), which meets national standards. The adsorbed material can then be desorbed using an alkaline solution (prepared with KOH) at pH 11.

[0042] Comparative Example 1 Compared with Example 1, the only difference in Comparative Example 1 is that steps two, three, four, five, and six are omitted (only CPAN is used); all other processes are the same as in Example 1. The fluoride ion adsorption test was performed using the same test as in Detection Example 1, and the measured fluoride ion concentration decreased from 10 mg / L to 9.02 mg / L.

[0043] Comparative Example 2 Compared with Example 1, the only difference in Comparative Example 2 is that "0.3g of lanthanum acetate" was not added in step four; all other processes were the same as in Example 1. The fluoride ion adsorption test was conducted using the same method as in Detection Example 1, and the measured fluoride ion concentration decreased from 10 mg / L to 5.23 mg / L.

[0044] Comparative Example 3 Compared with Example 1, the only difference in Comparative Example 3 is that 4g of polyethyleneimine (PEI) was not added in step four; all other processes were the same as in Example 1. A fluoride ion adsorption test was performed using the same method as in Detection Example 1, and the measured fluoride ion concentration decreased from 10 mg / L to 8.72 mg / L.

[0045] Comparative Example 4 Compared with Example 1, the only difference in Comparative Example 4 is that step two is omitted, while all other processes are the same as in Example 1. The fluoride ion adsorption test was conducted using the same method as in Detection Example 1, and the measured fluoride ion concentration decreased from 10 mg / L to 6.73 mg / L.

[0046] Comparative Example 5 Compared with Example 1, the only difference in Comparative Example 5 is that N2 in step two is replaced with air; all other processes are the same as in Example 1. A fluoride ion adsorption test was conducted using the same method as in Detection Example 1, and the measured fluoride ion concentration decreased from 10 mg / L to 8.35 mg / L.

[0047] Comparative Example 6 Compared to Example 1, Comparative Example 6 differs only in that 4g of polyethyleneimine in step four is replaced with a small molecule amine compound (tetraethylenepentamine). The fluoride ion adsorption test was performed using the same method as in Detection Example 1, and the measured fluoride ion concentration decreased from 10 mg / L to 8.82 mg / L.

[0048] Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A method for preparing a La-CPAN-PEI defluorination material, characterized in that, Includes the following steps: Polyacrylonitrile fibers are heat-treated in a protective gas environment to obtain cyclized polyacrylonitrile fibers; Cyclic polyacrylonitrile fibers, an alkaline catalyst, an organic lanthanum source, and polyethyleneimine were dispersed in a degassed alcohol solution to obtain a solid-liquid mixture. After the solid-liquid mixture undergoes a solvothermal reaction, the resulting precipitate is separated and washed to obtain La-CPAN-PEI defluorination material.

2. The preparation method according to claim 1, characterized in that: The protective gas is nitrogen or an inert gas.

3. The preparation method according to claim 1, characterized in that: The heat treatment is performed at a temperature of 200-220℃ for 2-4 hours.

4. The preparation method according to claim 1, characterized in that: The alkaline catalyst is KOH or NaOH; the alcohol solution is methanol or ethanol; the degassing treatment method is ultrasonic degassing for 10-30 minutes.

5. The preparation method according to claim 1, characterized in that: The organic lanthanum source is lanthanum acetate or lanthanum acetylacetone; the mass ratio of the organic lanthanum source to the cyclized polyacrylonitrile fiber is (0.1-0.5):

1.

6. The preparation method according to claim 1, characterized in that: The molecular weight of the polyethyleneimine is 10,000 to 100,000; the mass ratio of the polyethyleneimine to the cyclized polyacrylonitrile fiber is (3-5):

1.

7. The preparation method according to claim 1, characterized in that: The solvothermal reaction is carried out at a temperature of 120-160℃ for 12-24 hours.

8. A La-CPAN-PEI fluoride removal material, characterized in that: It is obtained by the preparation method described in any one of claims 1 to 7.

9. The application of the La-CPAN-PEI defluorination material as described in claim 8 as an adsorbent for removing fluoride ions from water, characterized in that: Includes the following steps: The La-CPAN-PEI fluoride removal material is placed in a fluoride-containing aqueous solution. The pH of the fluoride-containing aqueous solution is adjusted to an acidic solution, and fluoride ions are adsorbed. After the adsorption is completed, the adsorbent is eluted and regenerated using an alkaline solution.

10. The application according to claim 9, characterized in that: The acidic solution has a pH of 3-6, and the alkaline solution has a pH of 11-12.

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