Magnetic nano composite material, preparation method and application of magnetic nano composite material in fluorine-containing wastewater treatment

Abstract

The invention discloses a magnetic nano composite material, a preparation method and application of the magnetic nano composite material in fluorine-containing wastewater treatment. The preparation method of the magnetic nano composite material comprises the following steps: S1, preparing superparamagnetic Fe3O4 nano particles as magnetic cores; the surface of the magnetic core is coated with SiO2 to form a Fe3O4 coated SiO2 core-shell structure; s2, by taking the Fe3O4 coated SiO2 core-shell structure as a substrate, growing an MOF layer composed of zirconium (Zr) metal clusters on the surface of the Fe3O4 coated SiO2 core-shell structure to form an MOF composite material Fe3O4 coated SiO2 coated UiO-66 (Zr); and S3, carrying out amino functionalization treatment on the MOF, so as to form the ammonia modified MOF composite material Fe3O4 (at) SiO2 (at) UiO-66 (Zr)-NH2. The composite material is small in mass transfer resistance, can be recycled from water through magnetic separation after being used, can be repeatedly used after being regenerated, and solves the problems of limited adsorption capacity, difficulty in separation, high regeneration cost and the like in the existing low-concentration fluorine-containing wastewater treatment technology.

Description

Technical Field

[0001] The present invention relates to the treatment of fluorine-containing wastewater, and in particular to a magnetic nano-composite material, a preparation method and application thereof in the treatment of fluorine-containing wastewater. Background Art

[0002] In recent years, with the acceleration of industrialization, the discharge of fluoride-containing wastewater has continued to increase, causing serious pollution to the aquatic environment. Traditional fluoride-containing wastewater treatment methods, such as chemical precipitation, ion exchange, and adsorption, have many drawbacks, such as low adsorption capacity, difficult separation, and high regeneration costs, making it difficult to achieve deep purification and resource utilization of low-concentration fluoride-containing wastewater.

[0003] Currently, for the treatment of low-concentration fluoride-containing wastewater, there is an urgent need to develop a new, efficient, recyclable, and economical adsorption material and adsorption process to achieve resource utilization of fluorine. Existing adsorption materials, due to their large particle size, result in long adsorption and desorption times and complex regeneration processes, limiting their industrial application.

[0004] Therefore, designing and synthesizing a new adsorption material with high specific surface area, excellent adsorption performance, good selectivity, easy separation and recovery, and reusability, and developing a corresponding high-efficiency and low-cost fluorine-containing wastewater treatment process are of great significance for solving the problem of low-concentration fluorine-containing wastewater treatment and realizing the resource utilization of fluorine.

[0005] In terms of low-concentration fluorine-containing wastewater treatment, there are already some invention patents. For example, patent CN107029671A discloses a preparation method and application of a modified Fe3O4@MOF composite material. The composite material can be used to adsorb heavy metal mercury ions in industrial wastewater. The patent uses a solvent thermal method to prepare superparamagnetic ferroferric oxide nanoparticles, and adopts a layer-by-layer self-assembly method. With superparamagnetic ferroferric oxide as the core, metal central ions and organic ligands are deposited on its surface to synthesize MOF in situ to obtain Fe3O4@MOF composite material, and the Fe3O4@MOF composite material is surface modified. However, the patent still has the problem of how to further improve its adsorption of Hg 2+ Patent CN118403605A discloses a method for preparing and applying a lanthanum magnetic montmorillonite hydrogel adsorbent. By introducing iron and modifying it with the rare earth element lanthanum, this adsorbent exhibits a greater adsorption capacity and enhances its selectivity for fluoride ions. However, this patent still raises the question of how to optimize the adsorbent material to further increase its adsorption capacity and rate. Summary of the Invention

[0006] Existing technologies suffer from limited adsorption capacity, small specific surface area, poor selectivity, difficulty in separating from wastewater, difficulty in regeneration, and inability to realize resource utilization. To address these issues, the present invention provides a magnetic nanocomposite material, a preparation method, and its application in the treatment of low-concentration fluorine-containing wastewater.

[0007] The first aspect of the present invention provides a method for preparing a magnetic nanocomposite material, comprising the following steps:

[0008] S1, preparing superparamagnetic Fe3O4 nanoparticles as magnetic cores, and coating SiO2 on the surface of the magnetic cores to form a Fe3O4@SiO2 core-shell structure;

[0009] S2. Using the Fe3O4@SiO2 core-shell structure as a substrate, a MOF (metal organic framework) layer composed of zirconium (Zr) metal clusters is grown on its surface to form a MOF composite material: Fe3O4@SiO2@UiO-66(Zr);

[0010] S3. Performing amino functionalization treatment on the MOF composite material to form an ammonia-modified MOF composite material Fe3O4@SiO2@UiO-66(Zr)-NH2.

[0011] In one embodiment, in step S1, FeCl3·6H2O, sodium acetate and sodium citrate are dissolved in ethylene glycol to react to obtain Fe3O4 particles with a particle size of 5-50 nm, wherein the mass ratio of FeCl3·6H2O: sodium acetate: citric acid is 1:1.5-2.0:0.3-0.5.

[0012] The reaction equation is:

[0013]

[0014] Sodium citrate acts as a surfactant to control particle size, while sodium acetate provides an alkaline environment to promote Fe₃O₄ crystallization. The product is separated by a magnetic field and washed with ethanol and water before entering the next step of the synthesis process.

[0015] In one embodiment, the Fe3O4 particles are dispersed in an ethanol / water mixture; tetraethyl orthosilicate (TEOS) and ammonia water are added to react to form a SiO2 shell Fe3O4@SiO2 on the surface of the Fe3O4, wherein the mass ratio of tetraethyl orthosilicate: ethanol: water: ammonia water is 1:20-22:8-8.5:0.28-0.32; and the mass ratio of Fe3O4: TEOS is 1:0.93-1.87.

[0016] The reaction equation is:

[0017]

[0018] Si(OH)4→SiO2+2H2O

[0019] The SiO2 shell protects the magnetic core from oxidation and agglomeration and provides surface hydroxyl groups for subsequent MOF growth.

[0020] In one embodiment, in step S2, the Fe3O4@SiO2 is dispersed in an N,N-dimethylformamide (DMF) solution containing zirconium tetrachloride (ZrCl4) and phthalic acid (BDC) for reaction, and a UiO-66 type zirconium-based MOF layer is grown on the surface of the Fe3O4@SiO2 to obtain a Fe3O4@SiO2@UiO-66(Zr)MOF composite material, wherein the mass ratio of Fe3O4@SiO2:ZrCl4:BDC is 1:2.3-2.5:1.8-2.0.

[0021] The reaction equation is:

[0022] ZrCl4+H2BDC→Zr6O4(OH)4(BDC) 12 +HCl

[0023] ZrCl4 coordinates with BDC to form a UiO-66 framework, providing a high specific surface area and adsorption active sites.

[0024] In one embodiment, in step S3, an aminoterephthalic acid (NH2-BDC) ligand is added, and after the reaction, an ammonia-modified MOF composite material Fe3O4@SiO2@UiO-66(Zr)-NH2 is formed, and the mass ratio of Fe3O4@SiO2@UiO-66(Zr):NH2-BDC is 1:1.8-2.0.

[0025] The reaction equation is:

[0026] Zr6O4(OH)4(BDC) 12 +xNH2-BDC→Zr6O4(OH)4(BDC) 12-x (NH2-BDC) x +xBDC

[0027] The amino group enhances the selective adsorption capacity of fluoride ions.

[0028] In a second aspect of the present invention, the above-mentioned method for preparing a magnetic nanocomposite material is used to synthesize a magnetic nanocomposite material, which is applied to the treatment of low-concentration fluorine-containing wastewater.

[0029] In one embodiment, the adsorption, desorption and regeneration process of the magnetic nanocomposite material in treating low-concentration fluorine-containing wastewater includes the following steps:

[0030] Step 1: adding a magnetic nanocomposite material to a fluorine-containing wastewater solution to adsorb fluoride ions in the fluorine-containing wastewater solution;

[0031] Step 2, treating the adsorption-saturated magnetic nanocomposite material in a high gradient magnetic field;

[0032] Step 3, using NaOH solution and HCl solution to desorb and regenerate the adsorption saturated magnetic nanocomposite material;

[0033] Wherein, the pH value of the fluorine-containing wastewater solution in step 1 is 3-4, and the operating temperature is 50-60°C.

[0034] In one embodiment, in step 2, the high gradient magnetic field is generated by a high gradient magnetic field separator, and the magnetic field strength is not less than 1T.

[0035] In one embodiment, in step 3, the adsorption-saturated magnetic nanocomposite material is subjected to desorption and regeneration treatments in the following order: soaking in 4-5% NaOH solution, rinsing with raw water, soaking in 1-2% HCl solution, and rinsing with deionized water.

[0036] Because magnetic nanoparticle adsorbents can be used in the form of nanoparticles, they quickly reach equilibrium when in contact with fluorine-containing wastewater and can be separated from the water using a high-gradient magnetic field. This makes them reusable. In particular, they avoid clogging and the need for a fixed bed, making operation and maintenance very convenient.

[0037] Compared with the prior art, the magnetic nanocomposite material, preparation method and application in the treatment of fluorine-containing wastewater provided by the present invention have at least one of the following beneficial effects:

[0038] First, high adsorption capacity, suitable for deep purification of low-concentration fluoride-containing wastewater. The material has a high surface area (10-100m 2 / g), and can achieve efficient treatment of 10-30ppm fluoride-containing wastewater to a fluoride content below 1.0ppm.

[0039] Second, rapid adsorption kinetics improves treatment efficiency. The material has rapid mass transfer characteristics and can reach adsorption equilibrium within 1-5 minutes, greatly shortening the treatment time; it has excellent selective adsorption capacity for fluoride ions.

[0040] Third, by introducing amino functional groups into the MOF layer, the material's affinity and selectivity for fluoride ions are enhanced, effectively avoiding interference from other ions; no solid waste is generated during desorption, but ammonium fluoride or sodium fluoride is produced, which can realize the resource utilization of fluorine.

[0041] Fourth, it has good magnetic responsiveness and is easy to separate and recycle from wastewater. The Fe3O4 magnetic core in the material gives it superparamagnetism, which allows for rapid separation in high-gradient magnetic fields (greater than 1T). By adjusting the direction of the magnetic field, the adsorption and desorption transitions can be achieved, with a recovery rate of over 98%, solving the problem of difficult recycling of nanomaterials.

[0042] Fifth, it has excellent regeneration performance and can be reused. It adopts a simple alkali and acid washing regeneration process with high regeneration efficiency. After 20 cycles, the adsorption capacity can still be maintained at about 85%.

[0043] Sixth, the material has good stability and long service life. The core-shell structure formed by SiO2 coating enhances the chemical stability of the material under acidic conditions and prolongs its service life. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, without paying any creative work, other drawings obtained based on these drawings still fall within the scope of the present invention.

[0045] Figure 1 A flowchart of a method for preparing a magnetic nanocomposite material;

[0046] Figure 2 The flowchart of the adsorption and defluorination regeneration process of magnetic nanocomposites;

[0047] Figure 3 This is an electron microscope image of the MOF composite material nanoparticles in Example 1. DETAILED DESCRIPTION

[0048] The preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings so that the objects, features and advantages of the present invention can be more clearly understood. It should be understood that the embodiments shown in the accompanying drawings are not intended to limit the scope of the present invention, but are only intended to illustrate the essential spirit of the technical solution of the present invention.

[0049] In the following description, for the purpose of illustrating the various disclosed embodiments, certain specific details are set forth in order to provide a thorough understanding of the various disclosed embodiments. However, those skilled in the relevant art will recognize that the embodiments may be practiced without one or more of these specific details. In other cases, well-known devices, structures, and techniques associated with this application may not be shown or described in detail to avoid unnecessarily obscuring the description of the embodiments.

[0050] Reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any manner in one or more embodiments.

[0051] In the following description, in order to clearly show the structure and working mode of the present invention, many directional words will be used for description, but words such as "front", "back", "left", "right", "outside", "inside", "outward", "inward", "up", and "down" should be understood as convenient terms and should not be understood as restrictive terms.

[0052] It should be noted that the features shown in the drawings of this application may belong to one embodiment or to different embodiments, as long as there is no conflict between these features. To save space, this application may use the same drawing to illustrate different embodiments. In other words, the same drawing of this application can be used to illustrate features of different embodiments.

[0053] like Figure 1 As shown, this embodiment provides a method for preparing a superparamagnetic MOF nanocomposite material, comprising the following steps:

[0054] S1, preparing superparamagnetic Fe3O4 nanoparticles as magnetic cores; coating SiO2 on the surface of the magnetic cores to form a Fe3O4@SiO2 core-shell structure;

[0055] The method comprises dissolving FeCl3·6H2O, sodium acetate and sodium citrate in ethylene glycol, performing a thermal reaction at a temperature of 180°C for 8 hours to obtain Fe3O4 particles with a particle size of 5-50 nm, wherein the mass ratio of FeCl3·6H2O: sodium acetate: citric acid is 1:1.5-2.0:0.3-0.5.

[0056] The reaction equation is:

[0057]

[0058] Sodium citrate acts as a surfactant to control particle size, while sodium acetate provides an alkaline environment to promote Fe₃O₄ crystallization. The product is separated by a magnetic field and washed with ethanol and water before entering the next step of the synthesis process.

[0059] The Fe3O4 particles are dispersed in an ethanol / water mixture; tetraethyl orthosilicate (TEOS) and ammonia are added, and a hydrolysis reaction is carried out in a hydrothermal reactor at 60°C for 6 hours to form a SiO2 shell Fe3O4@SiO2 on the surface of the Fe3O4; wherein the mass ratio of tetraethyl orthosilicate: ethanol: water: ammonia is 1:20-22:8-8.5:0.28-0.32, and the mass ratio of Fe3O4: TEOS is 1:0.93-1.87, and the preferred ratio is Fe3O4: TEOS = 1:1.2-1.4.

[0060] The reaction equation is:

[0061]

[0062] Si(OH)4→SiO2+2H2O

[0063] The SiO2 shell protects the magnetic core from oxidation and agglomeration and provides surface hydroxyl groups for subsequent MOF growth.

[0064] S2. Using the Fe3O4@SiO2 core-shell structure as a substrate, a MOF layer composed of zirconium (Zr) metal clusters is grown on its surface to form a MOF (metal organic framework) composite material: Fe3O4@SiO2@UiO-66(Zr);

[0065] The Fe3O4@SiO2 is dispersed in an N,N-dimethylformamide (DMF) solution containing zirconium tetrachloride (ZrCl4) and phthalic acid (BDC); the reaction is carried out at 120°C in a hydrothermal reactor for 24 hours, and a UiO-66 type zirconium-based MOF layer is grown on the surface of the Fe3O4@SiO2 to obtain a Fe3O4@SiO2@UiO-66(Zr)MOF composite material, wherein the mass ratio of Fe3O4@SiO2:ZrCl4:BDC is in the range of 1:2.3-2.5:1.8-2.0, and the amount of DMF used is 300-450 mL of DMF per gram of Fe3O4@SiO2.

[0066] The reaction equation is:

[0067] ZrCl4+H2BDC→Zr6O4(OH)4(BDC) 12 +HCl

[0068] ZrCl4 coordinates with BDC to form a UiO-66 framework, providing a high specific surface area and adsorption active sites.

[0069] S3. Performing amino functionalization treatment on the MOF to form an ammonia-modified MOF composite material Fe3O4@SiO2@UiO-66(Zr)-NH2.

[0070] Aminoterephthalic acid (NH2-BDC) ligand was added and the reaction was carried out at 120°C in a hydrothermal reactor for 24 hours to introduce amino functional groups into the MOF layer to form an ammonia-modified MOF composite material: Fe3O4@SiO2@UiO-66(Zr)-NH2, with a mass ratio of Fe3O4@SiO2@UiO-66(Zr):NH2-BDC ranging from 1:1.8-2.0.

[0071] The reaction equation is:

[0072] Zr6O4(OH)4(BDC) 12 +xNH2-BDC→Zr6O4(OH)4(BDC) 12-x (NH2-BDC) x +xBDC

[0073] The structure of Fe3O4@SiO2@UiO-66(Zr)-NH2 can be described as a MOF composite material: Fe3O4 (core) → SiO2 (coating layer) → UiO-66(Zr).

[0074] Due to the inert magnetic core and SiO2 coating, the effective adsorption volume of MOF composite materials is relatively small. However, nanomaterials, relying on their large surface area, can achieve rapid adsorption and desorption, overcoming the problem of low effective adsorption volume. Assuming that the average radius of the MOF composite material is R, the calculation formula for the converted surface area A is:

[0075]

[0076] Where R is in μm, and ρ represents the density of the MOF composite material in g / cm 3 , the unit of A is m 2 / g.

[0077] This embodiment also provides a magnetic nanocomposite material, which is prepared using the above-mentioned method for preparing the magnetic nanocomposite material.

[0078] This embodiment also provides the application of the above magnetic nanocomposite material in the treatment of low-concentration fluorine-containing wastewater, including: Figure 2 The adsorption, desorption and regeneration process of the magnetic nanocomposite material in treating low-concentration fluorine-containing wastewater includes the following steps:

[0079] 1. Adding the above-mentioned ammonia-modified MOF composite material into an intermittent adsorption reactor filled with a fluorine-containing wastewater solution to adsorb fluoride ions in the fluorine-containing wastewater solution;

[0080] The pH of the fluorine-containing wastewater solution is adjusted to 3-4, and the operating temperature is 50-60°C.

[0081] The equilibrium adsorption capacity q of MOF composite material is calculated as follows:

[0082]

[0083] Where q is the equilibrium adsorption capacity (mg / g); C0 and C are the fluorine concentrations in the solution before and after adsorption (mg / L), respectively; V is the volume of the fluorine solution (L); and m is the mass of the adsorbent (g).

[0084] Based on a series of experimental data of q and C, the isothermal adsorption equilibrium equation is obtained by regression, and the Langmuir equation is:

[0085]

[0086] Among them, q m is the saturated adsorption capacity of the Langmuir adsorption equilibrium parameter under different adsorption temperatures and initial pH conditions; K is the adsorption equilibrium constant.

[0087] 2. treating the adsorption-saturated MOF composite material in a high gradient magnetic field, and quickly recovering the adsorption-saturated MOF composite material by the high gradient magnetic field;

[0088] The above operations can be performed in situ within a high-gradient magnetic field separator. The fixed permanent magnets in the high-gradient magnetic field separator have a distance of 0.5-5 cm between their north and south poles, a magnetic field strength of no less than 1 T, and a built-in magnetically conductive stainless steel wire 0.5-3 mm thick. This creates a high magnetic field gradient within a tiny space, enabling the efficient removal of superparamagnetic nanoparticles. By adjusting the magnetic field, the superparamagnetic MOF nanocomposite can be captured and separated.

[0089] 3. The adsorption-saturated MOF composite material is desorbed and regenerated by treating with dilute NaOH solution and dilute HCl solution.

[0090] The saturated superparamagnetic MOF nanocomposite material is soaked in a 4-5% dilute NaOH solution at 50° C. and then rinsed with deionized water; and then soaked in a 1-2% dilute HCl solution and then rinsed with deionized water.

[0091] Fe3O4@SiO2@UiO-66(Zr)-NH2 MOF composite material has a great potential in adsorbing fluoride ions (F - ) and regeneration and activation process, the changes in its surface functional groups can be divided into the following three stages:

[0092] 1. Adsorption stage: interaction between amino groups (-NH2) and fluoride ions

[0093] In acidic or neutral aqueous phase, the amino group (-NH2) of UiO-66-NH2 is easily protonated to -NH3 +, adsorbing negatively charged F through electrostatic attraction - ; Zirconium oxygen cluster (Zr-O) as Lewis acid site, with F - Form a coordination bond (Zr-F), and the amino group may assist in fixing F through hydrogen bonds - .

[0094] 2. NaOH regeneration stage: desorption and amino recovery

[0095] NaOH solution (pH>10) makes -NH3 + Deprotonation to -NH2 destroys the electrostatic adsorption and releases F - At this time, the amino group returns to a neutral state and the surface positive charge density decreases; the Zr-O bond may be partially hydrolyzed under strong alkaline conditions, but the high chemical stability of UiO-66-NH2 can inhibit structural collapse.

[0096] 3. HCl activation stage: amino group reprotonation and adsorption capacity recovery

[0097] HCl treatment (pH ≤ 4) reprotonates -NH2 to -NH3 + , restore the surface positive charge and enhance the - electrostatic adsorption capacity; HCl may partially dissolve the Zr-O bond, exposing more Zr4 + Active sites, but excessive acid treatment can damage the MOF framework. The HCl concentration needs to be controlled (e.g., 0.1-1 M) to balance the activation effect and structural stability.

[0098] 6g of a Fe3O4@SiO2@UiO-66(Zr)-NH2 MOF composite was weighed and placed in a 50mL Erlenmeyer flask. 30mL of a 10-20mg / L fluorine solution at pH 3.5 was added. After 10 minutes of adsorption reaction on a constant temperature shaker, high-gradient magnetic separation was performed, and the fluorine concentration in the supernatant was measured. 10mL of a 1mol / L NaOH solution was added to the particles obtained by magnetic separation. After 10 minutes of desorption, magnetic separation was performed again. The fluoride ion concentration in the supernatant was measured, and the desorption amount and desorption rate were calculated. To restore the protonated state of the hydroxyl groups on the adsorbent surface and regenerate the adsorbent, the material was washed with a pH 3.0 hydrochloric acid solution. After regeneration, a new cycle of adsorption-desorption-regeneration-transformation experiment was initiated and repeated until the fluoride ion concentration in the water was less than 1ppm.

[0099] After multiple adsorption-regeneration cycles, the amino groups may be partially lost due to oxidation or hydrolysis. The Zr-O bond of UiO-66-NH2 remains stable during multiple acid / base treatments, but extreme pH conditions (such as concentrated HCl or strong base) can lead to local structural defects. The surface functional group status is shown in Table 1:

[0100] Table 1

[0101]

[0102] Furthermore, the superparamagnetic MOF nano-adsorbent material's adsorption of fluoride in water decreases with increasing pH, reaching a maximum of 34.7 mg / g at pH 3.5 and 60°C. After adsorption reaches saturation, desorption using NaOH and regeneration with HCl achieves a desorption rate exceeding 97%, yielding a soluble, high-concentration fluoride solution that can be utilized. This adsorbent material has low mass transfer resistance and can be recovered from water through magnetic separation for repeated use. It is a promising defluorination material, potentially addressing the limited adsorption capacity, separation difficulties, and high regeneration costs of existing low-concentration fluoride wastewater treatment technologies.

[0103] The regeneration and activation are carried out in conjunction with a high gradient magnetic field separator. In the treatment of fluorine-containing wastewater, the pH of the fluorine-containing wastewater solution is first adjusted to 3-4, and the operating temperature is 50-60°C. The process of the present invention is simple and controllable, easy to operate, and easy to industrialize.

[0104] Example 1

[0105] Preparation of superparamagnetic Fe3O4 nanoparticles as magnetic cores, the specific steps are as follows:

[0106] 108 g of FeCl3·6H2O, 172.8 g of sodium acetate, and 37.8 g of sodium citrate were dissolved in 500 mL of ethylene glycol and stirred to form a homogeneous solution. The solution was transferred to a polytetrafluoroethylene-lined stainless steel reactor and heated to 180°C under nitrogen protection for 8 hours. After the reaction, the mixture was cooled to room temperature, separated by a high-gradient magnetic field, and repeatedly washed three times with anhydrous ethanol and deionized water to obtain 24.5 g (dry basis) of Fe3O4 nanoparticles with a particle size of approximately 5-50 nm.

[0107] SiO2 is coated on the surface of Fe3O4 to form a Fe3O4@SiO2 core-shell structure. The specific steps are as follows:

[0108] The above-mentioned Fe3O4 nanoparticles were dispersed in a mixed solution of 500mL of ethanol and 100mL of deionized water and ultrasonically dispersed for 30 minutes; 100mL of ammonia water and 50mL of tetraethyl orthosilicate (TEOS) were added and ultrasonic dispersion was continued for 30 minutes; the mixed solution was transferred to a three-necked flask and reacted at 60°C for 6 hours with continuous stirring; after the reaction, high-gradient magnetic field separation was performed and the mixture was repeatedly washed three times with anhydrous ethanol and deionized water to obtain about 32.4g (dry basis) of Fe3O4@SiO2 core-shell nanoparticles with a SiO2 shell thickness of about 10nm.

[0109] Taking Fe3O4@SiO2 as the substrate, a zirconium-based MOF layer is grown on its surface to form a Fe3O4@SiO2@UiO-66(Zr) composite material. The specific steps are as follows:

[0110] The Fe3O4@SiO2 was dispersed in an N,N-dimethylformamide (DMF) solution containing zirconium tetrachloride (ZrCl4) and phthalic acid (BDC); the reaction was carried out at 120°C in a hydrothermal reactor for 24 hours, and a UiO-66 type zirconium-based MOF layer was grown on the surface of the Fe3O4@SiO2 to obtain a Fe3O4@SiO2@UiO-66(Zr)MOF composite material. The mass ratio of Fe3O4@SiO2:ZrCl4:BDC was in the range of 1:2.3:1.8, and the amount of DMF used was 400 mL of DMF per gram of Fe3O4@SiO2.

[0111] After the reaction, the mixture was separated by a high gradient magnetic field and washed repeatedly with DMF and anhydrous ethanol three times to obtain 33.6 g (dry basis) of Fe3O4@SiO2@UiO-66(Zr) composite material.

[0112] The MOF surface is amino-functionalized. The specific steps are as follows:

[0113] During the above MOF synthesis process, 1 g of aminoterephthalic acid (NH2-BDC) ligand was added; the reaction was carried out for 24 h at a reaction temperature of 120°C, and amino functional groups were introduced into the UiO-66 layer through coordination bonds to form 33.8 g (dry basis) of amino-functionalized Fe3O4@SiO2@UiO-66(Zr)-NH2 composite material. The mass ratio of Fe3O4@SiO2@UiO-66(Zr):NH2-BDC was 1:1.8. Figure 3 This is the electron microscope image of Fe3O4@SiO2@UiO-66(Zr)-NH2 composite material nanoparticles.

[0114] The adsorption equilibrium was measured as shown in Table 2:

[0115] Table 2

[0116]

[0117] The composite material Fe3O4@SiO2@UiO-66(Zr)-NH2 was placed in a fully mixed reactor containing a fluorine-containing wastewater solution at a pH of 3-4 and an operating temperature of 60°C. Its high specific surface area and rapid mass transfer characteristics were utilized to achieve efficient adsorption of fluoride ions. The nanocomposite material was rapidly recovered using a high-gradient magnetic field (for small-scale batch experiments, a block permanent magnet was used for separation). The adsorbed material was desorbed using 10mL of a 4-5% dilute NaOH solution at 50°C. After rinsing with 10mL of raw water, it was partially converted with 10mL of 2% HCl and then rinsed with 10mL of deionized water to regenerate the adsorbent material. During the next adsorption, the pH of the wastewater was adjusted to 3.5-3.6. The experimental results are summarized in Table 3:

[0118] Table 3

[0119]

[0120] Other conditions remain unchanged, and the experiments are carried out in sequence. The experimental results are

[0121] The third time: the equilibrium concentration is C ∞3 =4.45mg / L;q ∞3 =21.4mg / g;

[0122] Fourth time: Equilibrium concentration is C ∞4 =1.76mg / L;q ∞4 =13.5mg / g;

[0123] Fifth time: Equilibrium concentration is C ∞5 =0.57mg / L;q ∞5 =5.93mg / g.

[0124] Adsorption 5 times meets the requirement (i.e., the emission concentration is less than 1.0 mg / L).

[0125] It should be pointed out that raw water refers to fluoride-containing wastewater or treated discharge water that meets the standards; NaOH solution, HCl solution and washing liquid are reused.

[0126] Example 2

[0127] Preparation of superparamagnetic Fe3O4 nanoparticles as magnetic cores, the specific steps are as follows:

[0128] 54 g of FeCl3·6H2O, 86.4 g of sodium acetate, and 21.6 g of sodium citrate were dissolved in 500 mL of ethylene glycol and stirred to form a homogeneous solution. The solution was transferred to a polytetrafluoroethylene-lined stainless steel reactor and heated to 180°C under nitrogen protection for 6 hours. After the reaction, the mixture was cooled to room temperature, separated by a high-gradient magnetic field, and repeatedly washed four times with anhydrous ethanol and deionized water to obtain 12.4 g (dry basis) of Fe3O4 nanoparticles with a particle size of approximately 5-50 nm.

[0129] SiO2 is coated on the surface of Fe3O4 to form a Fe3O4@SiO2 core-shell structure. The specific steps are as follows:

[0130] The above-mentioned Fe3O4 nanoparticles were dispersed in a mixed solution of 500mL of ethanol and 100mL of deionized water and ultrasonically dispersed for 20 minutes; 80mL of ammonia water and 40mL of tetraethyl orthosilicate (TEOS) were added and ultrasonic dispersion was continued for 20 minutes; the mixed solution was transferred to a three-necked flask and reacted at 65°C for 5 hours with continuous stirring; after the reaction, high-gradient magnetic field separation was performed and the mixture was repeatedly washed with anhydrous ethanol and deionized water 4 times to obtain 18.4g (dry basis) of Fe3O4@SiO2 core-shell nanoparticles with a SiO2 shell thickness of approximately 8nm.

[0131] Taking Fe3O4@SiO2 as the substrate, a zirconium-based MOF layer is grown on its surface to form a Fe3O4@SiO2@MIL-66(Zr) composite material. The specific steps are as follows:

[0132] The above-mentioned Fe3O4@SiO2 nanoparticles were dispersed in 250mL N,N-dimethylformamide (DMF) solution and ultrasonically dispersed for 25min; 1.5g zirconium tetrachloride (ZrCl4) and 2.5g phthalic acid (BDC) solutions were prepared separately, mixed and added to the ultrasonically dispersed solution; the mixed solution was transferred to a stainless steel reactor lined with polytetrafluoroethylene and reacted at 130℃ for 20h; after the reaction, high gradient magnetic field separation was carried out and the mixture was repeatedly washed with DMF and anhydrous ethanol four times to obtain approximately 19.2g (dry basis) of Fe3O4@SiO2:ZrCl4:BDC; the mass ratio of Fe3O4@SiO2:ZrCl4:BDC was 1:2.3:1.8.

[0133] The MOF surface was amino-functionalized to enhance fluoride ion adsorption selectivity. The specific steps are as follows: During the MOF synthesis process described above, 0.8 g of aminoterephthalic acid (NH2-BDC) ligand was added; the reaction was allowed to proceed for 24 hours at 120°C, introducing amino functional groups into the UiO-66 layer via coordination bonds, resulting in approximately 20.3 g (dry basis) of amino-functionalized Fe3O4@SiO2@UiO-66(Zr)-NH2 composite material. The mass ratio of Fe3O4@SiO2@UiO-66(Zr) to NH2-BDC was 1:1.8.

[0134] The adsorption equilibrium is measured as shown in Table 4:

[0135] Table 4

[0136]

[0137]

[0138] The resulting composite material, Fe3O4@SiO2@UiO-66(Zr)-NH2, was placed in a fully mixed reactor containing a fluorine-containing wastewater solution at a pH of 3-4 and an operating temperature of 60°C. Its high specific surface area and rapid mass transfer characteristics were utilized to achieve efficient adsorption of fluoride ions. Rapid recovery of the nanocomposite material was achieved through a high-gradient magnetic field (for small-scale batch experiments, block permanent magnet separation was used). The adsorbed material was desorbed using 10 mL of a 4-5% dilute NaOH solution at 50°C, then rinsed with 10 mL of raw water, partially transformed with 10 mL of 2% dilute HCl, and then rinsed with 10 mL of deionized water to regenerate the adsorbent material. During re-adsorption, the wastewater pH was adjusted to 3.5-3.6. The experimental results are summarized in Table 5:

[0139] Table 5

[0140]

[0141] Other conditions remain unchanged, and the experiments are carried out in sequence. The experimental results are

[0142] The third time: the equilibrium concentration is C ∞3 =9.1mg / L;q ∞3 =17.1mg / g;

[0143] Fourth time: Equilibrium concentration is C ∞4 =5.93mg / L;q ∞4 =15.8mg / g;

[0144] Fifth time: Equilibrium concentration is C ∞5 =3.24mg / L;q ∞5 =13.5mg / g;

[0145] Sixth time: Equilibrium concentration is C ∞6 =1.38mg / L;q ∞6 =9.3mg / g;

[0146] Seventh time: Equilibrium concentration is C ∞7 =0.47mg / L;q ∞7 =4.56mg / g;

[0147] Adsorption 7 times meets the requirements.

[0148] Example 3

[0149] Preparation of superparamagnetic Fe3O4 nanoparticles as magnetic cores, the specific steps are as follows:

[0150] 81 g of FeCl3·6H2O, 129.6 g of sodium acetate, and 32.4 g of sodium citrate were dissolved in 75 mL of ethylene glycol and stirred to form a homogeneous solution. The solution was transferred to a polytetrafluoroethylene-lined stainless steel reactor and heated to 190°C under nitrogen protection for 7 hours. After the reaction, the mixture was cooled to room temperature, separated by a high-gradient magnetic field, and repeatedly washed with anhydrous ethanol and deionized water five times to obtain 18.2 g (dry basis) of Fe3O4 nanoparticles with a particle size of approximately 5-50 nm.

[0151] SiO2 is coated on the surface of Fe3O4 to form a Fe3O4@SiO2 core-shell structure. The specific steps are as follows:

[0152] The above-mentioned Fe3O4 nanoparticles were dispersed in a mixed solution of 500mL of ethanol and 100mL of deionized water and ultrasonically dispersed for 35min; 100mL of ammonia water and 60mL of tetraethyl orthosilicate (TEOS) were added and ultrasonic dispersion was continued for 25min; the mixed solution was transferred to a three-necked flask and reacted at 55°C for 7h with continuous stirring; after the reaction, high-gradient magnetic field separation was performed and the mixture was repeatedly washed three times with anhydrous ethanol and deionized water to obtain 31.2g (dry basis) of Fe3O4@SiO2 core-shell nanoparticles with a SiO2 shell thickness of approximately 12nm.

[0153] Taking Fe3O4@SiO2 as the substrate, a zirconium-based MOF layer is grown on its surface to form a Fe3O4@SiO2@UiO-66(Zr) composite material. The specific steps are as follows:

[0154] The above-mentioned Fe3O4@SiO2 nanoparticles were dispersed in 250mL N,N-dimethylformamide (DMF) solution and ultrasonically dispersed for 40 minutes; 2.5g zirconium tetrachloride (ZrCl4) and 3.5g phthalic acid (BDC) solutions were prepared separately, and the two solutions were mixed and added to the ultrasonically dispersed solution; the mixed solution was transferred to a stainless steel reactor lined with polytetrafluoroethylene and reacted at 125℃ for 22h; after the reaction, high gradient magnetic field separation was carried out and the mixture was repeatedly washed with DMF and anhydrous ethanol five times to obtain approximately 31.5g (dry basis) of Fe3O4@SiO2:ZrCl4:BDC; the mass ratio of Fe3O4@SiO2:ZrCl4:BDC was 1:2.3:1.8.

[0155] The MOF surface is treated with amino functionalization to enhance the fluoride ion adsorption selectivity. The specific steps are as follows:

[0156] During the above-mentioned MOF synthesis process, 1.2 g of aminoterephthalic acid (NH2-BDC) ligand was additionally added; the reaction was carried out for 24 h at a reaction temperature of 120°C, and amino functional groups were introduced into the UiO-66 layer through coordination bonds to form 31.6 g (dry basis) of amino-functionalized Fe3O4@SiO2@UiO-66(Zr)-NH2 composite material.

[0157] The mass ratio of Fe3O4@SiO2@UiO-66(Zr):NH2-BDC is 1:1.8.

[0158] The adsorption equilibrium was measured as shown in Table 6:

[0159] Table 6

[0160]

[0161] The obtained composite material Fe3O4@SiO2@UiO-66(Zr)-NH2 was placed in a fully mixed reactor containing a fluorine-containing wastewater solution with a pH of 3-4 and an operating temperature of 60°C. Its high specific surface area and rapid mass transfer characteristics were used to achieve efficient adsorption of fluoride ions. The nanocomposite material was quickly recovered by a high gradient magnetic field (for small batch experiments, a block permanent magnet was used for separation). The adsorbed material was desorbed using 10mL of a 4-5% dilute NaOH solution at 50°C. After rinsing with 10mL of raw water, it was partially transformed with 10mL of 2% dilute HCl and then rinsed with 10mL of deionized water to regenerate the adsorbent material. During the second adsorption, the pH of the wastewater was adjusted to 3.5-3.6. The experimental results are summarized in Table 7:

[0162] Table 7

[0163]

[0164]

[0165] Other conditions remain unchanged, and the experiments are carried out in sequence. The experimental results are

[0166] The third time: the equilibrium concentration is C ∞3 =3.64mg / L;q ∞3 =23.8mg / g;

[0167] Fourth time: Equilibrium concentration is C ∞4 =0.91mg / L;q ∞4 =13.6mg / g;

[0168] Adsorption 4 times meets the requirements.

[0169] From Examples 1-3, it can be seen that to meet the emission standards (i.e., the emission concentration is less than 1.0 mg / L), the saturated adsorption capacity q m High (as q in Example 2 m Lower than q of Example 1 and Example 3 m , it takes 7 adsorptions to meet the emission standards), and it is also required that the adsorption equilibrium constant K is high (such as Example 3 is higher than Example 1, and the emission standards are met after 4 adsorptions).

[0170] In addition, Examples 1-3 reached the emission standards after adsorption 5, 7, and 4 times, respectively. The thickness of the SiO2 shell in Examples 1-3 was 10 nm, 8 nm, and 12 nm, respectively. It can be seen that the corresponding SiO2 shell thickness is large, the adsorbent loading is large, and the number of adsorption times is small.

[0171] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention.

[0172] The embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being defined by the appended claims rather than the foregoing description, and all changes that come within the meaning and range of equivalents of the claims are therefore intended to be embraced therein.

[0173] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, system or module that includes a series of elements includes not only those elements, but also other elements that are not explicitly listed, or elements that are inherent to such process, method, system or module. In the absence of further restrictions, an element defined by the sentence "comprises a..." does not exclude the presence of other identical elements in the process, method, system or module that includes the element.

[0174] The foregoing description is intended only to provide specific embodiments of the present invention, which will enable those skilled in the art to understand and implement the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not intended to be limited to the embodiments shown herein, but is to be construed in the widest possible manner consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a magnetic nanocomposite material, characterized in that: The following steps are included: S1, preparing superparamagnetic Fe3O4 nanoparticles as magnetic cores, and coating SiO2 on the surface of the magnetic cores to form a Fe3O4@SiO2 core-shell structure; S2. Using the Fe3O4@SiO2 core-shell structure as a substrate, a MOF (metal organic framework) layer composed of zirconium (Zr) metal clusters is grown on its surface to form a MOF composite material: Fe3O4@SiO2@UiO-66(Zr); S3. Performing amino functionalization treatment on the MOF composite material to form an ammonia-modified MOF composite material: Fe3O4@SiO2@UiO-66(Zr)-NH2.

2. The method for preparing the magnetic nanocomposite material according to claim 1, wherein: In step S1, FeCl3·6H2O, sodium acetate and sodium citrate are dissolved in ethylene glycol and reacted to obtain Fe3O4 particles; wherein the mass ratio of FeCl3·6H2O: sodium acetate: citric acid is 1:1.5-2.0:0.3-0.

5.

3. The method for preparing the magnetic nanocomposite material according to claim 2, wherein: The Fe3O4 particles are dispersed in an ethanol / water mixture; tetraethyl orthosilicate (TEOS) and ammonia are added to react to form a SiO2 shell Fe3O4@SiO2 on the surface of the Fe3O4; in, The mass ratio of ethyl orthosilicate: ethanol: water: ammonia water is 1:20-22:8-8.5:0.28-0.32; the mass ratio of Fe3O4: TEOS is 1:0.93-1.

87.

4. The method for preparing the magnetic nanocomposite material according to claim 1, wherein: In step S2, the Fe3O4@SiO2 is dispersed in an N,N-dimethylformamide (DMF) solution containing zirconium tetrachloride (ZrCl4) and phthalic acid (BDC); a reaction is carried out to grow a UiO-66 type zirconium-based MOF layer on the surface of the Fe3O4@SiO2 to obtain a Fe3O4@SiO2@UiO-66(Zr)MOF composite material; wherein the mass ratio of Fe3O4@SiO2:ZrCl4:BDC is 1:2.3-2.5:1.8-2.

0.

5. The method for preparing the magnetic nanocomposite material according to claim 1, wherein: In step S3, aminoterephthalic acid (NH2-BDC) ligand is added to form an ammonia-modified MOF composite material Fe3O4@SiO2@UiO-66(Zr)-NH2 after reaction; Among them, the mass ratio of Fe3O4@SiO2@UiO-66(Zr):NH2-BDC is 1:1.8-2.

0.

6. A magnetic nanocomposite material, characterized in that: The magnetic nanocomposite material is prepared by the preparation method according to any one of claims 1 to 5.

7. Use of the magnetic nanocomposite material according to claim 6 in the treatment of low-concentration fluorine-containing wastewater.

8. The use of the magnetic nanocomposite material in the treatment of low-concentration fluorine-containing wastewater according to claim 7, characterized in that: The adsorption, desorption and regeneration process of the magnetic nanocomposite material in the treatment of low-concentration fluorine-containing wastewater includes the following steps: Step 1: adding a magnetic nanocomposite material to a fluorine-containing wastewater solution to adsorb fluoride ions in the fluorine-containing wastewater solution; Step 2, treating the adsorption-saturated magnetic nanocomposite material in a high gradient magnetic field; Step 3: using NaOH solution and HCl solution to desorb and regenerate the adsorption-saturated magnetic nanocomposite material; Wherein, the pH value of the fluorine-containing wastewater solution in step 1 is 3-4, and the operating temperature is 50-60°C.

9. Use of the magnetic nanocomposite material according to claim 8 in the treatment of low-concentration fluorine-containing wastewater, characterized in that: In step 2, the high gradient magnetic field is generated by a high gradient magnetic field separator, and the magnetic field strength is not less than 1T.

10. Use of the magnetic nanocomposite material according to claim 8 in the treatment of low-concentration fluorine-containing wastewater, characterized in that: In step 3, the adsorption-saturated magnetic nanocomposite material is sequentially immersed in a 4-5% NaOH solution, rinsed with raw water, immersed in a 1-2% HCl solution, and rinsed with deionized water for desorption and regeneration.

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