Polyethyleneimine modified magnetic polymer microsphere, preparation method and adsorption characteristic method

Abstract

The invention provides a polyethyleneimine modified magnetic polymer microsphere, a preparation method and an adsorption decolorization method. The polyethyleneimine modified magnetic polymer microsphere takes superparamagnetic Fe3O4 as a core and a surface amino-functionalized styrene and glycidyl methacrylate copolymer as a shell, the superparamagnetic Fe3O4 is obtained by using a coprecipitation method, and the magnetic polymer microsphere is obtained by using a dispersion polymerization method; wherein the average particle size of the polyethyleneimine modified magnetic polymer microspheres is 200 to 300 [mu] m, and the magnetization intensity of the polyethyleneimine modified magnetic polymer microspheres is 18.5 to 35.85 emu / g; and the superparamagnetic Fe3O4 accounts for 10.6-25.2% of the mass of the whole polyethyleneimine modified magnetic polymer microsphere. The polyethyleneimine modified magnetic polymer microspheres are amino-functionalized magnetic particles with a core-shell structure obtained through a dispersion polymerization method, the technical problems that a magnetic adsorbent prepared through an existing technology is low in magnetic responsiveness and uneven in particle size distribution are solved, and efficiency improvement and cost control of dye molecule wastewater treatment are facilitated.

Description

Technical Field

[0001] The present invention relates to the field of preparation of magnetic adsorbents, and particularly relates to a polyethyleneimine-modified magnetic polymer microsphere, a preparation method thereof, and an adsorption and decolorization method thereof. Background Art

[0002] With the rapid development of industries such as textile and printing and dyeing, a large amount of wastewater containing dye molecules is discharged into the environment, causing serious pollution to water bodies, soil, and ecosystems. Dye molecules not only make the water body show high chromaticity, affecting the beauty and transparency of the water body, but also pose a threat to the survival and reproduction of aquatic organisms due to their complex chemical structures and potential toxicity. Even through the transfer of the food chain, it may ultimately endanger human health. Therefore, developing efficient, economical, and environmentally friendly dye molecule decolorization technologies is of crucial significance for protecting the environment, maintaining ecological balance, and ensuring human health.

[0003] Common dye molecule decolorization technologies include physical decolorization methods (such as adsorption method and membrane separation method), chemical decolorization methods (such as oxidation-reduction method and photocatalysis method), and biological decolorization methods (microbial degradation method and plant purification method). However, due to the existence of inherent defects such as low treatment efficiency, the need for other expensive reagents, incomplete removal of pollutants, high energy consumption, and the generation of unpredictable toxic by-products, their applications in the treatment of dye molecule wastewater are greatly restricted. The adsorption method is considered the most promising water purification and restoration method due to its advantages such as simple operation, high treatment efficiency, wide application range, economic feasibility, and no secondary pollution. The adsorption method utilizes the selective adsorption performance of the adsorbent for dye molecules to enrich the dye molecules on its surface, and its adsorption mechanism mainly includes many chemical and physical processes such as electrostatic interaction, ion exchange, metal chelation, complexation, hydrolysis precipitation, etc. The core of the adsorption method is the adsorbent, and various adsorbents for treating dye molecule pollutants have been developed, such as activated carbon, minerals, biomass, and composite materials. However, in sewage treatment, traditional adsorption materials have disadvantages such as low adsorption capacity, low adsorption efficiency, low adsorption selectivity, and inability to be reused, which restricts the application of these adsorbents and cannot meet the needs of current social development. Therefore, developing new adsorbents with low cost, simple operation process, reusable, and environmentally friendly is a current research hotspot.

[0004] In recent years, magnetic polymer microspheres have received extensive attention as a new type of adsorbent. Magnetic polymer microspheres are microspheres formed by combining inorganic magnetic particles and organic polymer materials in a certain way. They not only have a large specific surface area, low cost, simple preparation, and easy functionalization, but also have the characteristics of solid-phase carriers such as easy separation and purification, and can adjust biocompatibility. Preparing functional magnetic polymer microspheres through surface modification plays a supplementary role in their functions and applications. The purpose of surface functionalization is to introduce some specific active functional groups (such as amino groups, carboxyl groups, hydroxyl groups, aldehyde groups, etc.) on the surface of magnetic polymer microspheres to increase their interaction with the separated substances or the substances to be immobilized. Therefore, magnetic microspheres have shown great advantages in the fields of environment, biomedicine, and food industry and are currently widely used.

[0005] CN111468049A discloses a preparation and application method of carboxylated magnetic polymer microspheres, which includes the following steps: performing a carboxylation reaction on the pretreated (coating the magnetic nanoparticles with polydopamine) magnetic nanoparticles and 2,3-dimercaptosuccinic acid to obtain magnetic composite particles; dispersing the magnetic composite particles in an alkaline buffer solution and stirring and reacting with 2,3-dimercaptosuccinic acid at room temperature; separating the product obtained from the stirring reaction under the action of a magnetic field to obtain a solid product; removing impurities from the solid product and drying it to obtain carboxylated magnetic polymer microspheres. The carboxylated magnetic polymer microspheres prepared by this method have good adsorption effect and high adsorption efficiency, can be recycled multiple times after desorption, are environmentally friendly and economical, and save production costs. However, coating magnetic nanoparticles with polydopamine usually has operational complexity, poor controllability of surface functional groups, and easy aggregation between magnetic nanoparticles, which limits large-scale applications. CN104587977B discloses a preparation method of agarose magnetic microspheres with surface carboxylation modification and the application of the agarose magnetic microspheres with surface carboxylation modification to adsorb methyl orange dye in printing and dyeing waste liquid. Its preparation method includes: one, preparing non-magnetic core agarose microspheres; two, activating and crosslinking the non-magnetic core agarose microspheres; three, preparing a mixed solution of agarose microspheres and iron ions; four, preparing agarose magnetic microspheres; five, amino group modification on the microsphere surface; six, carboxyl group modification on the microsphere surface to obtain agarose magnetic microspheres with surface carboxylation modification. However, the preparation process of this patent includes multiple steps, from the preparation of non-magnetic core agarose microspheres to multiple crosslinkings and modifications, etc. The steps are cumbersome, increasing the operation difficulty and time cost in the production process, and the condition control of each step is relatively strict, prone to errors, affecting the quality and performance consistency of the final product.

[0006] CN114192079B discloses a magnetic hollow polymer microsphere, its preparation method and application. The magnetic hollow polymer microsphere includes a hollow polymer microsphere, magnetic nanoparticles and a hydrophilic modification layer. The magnetic nanoparticles are located in the inner cavity of the hollow polymer microsphere, and the hydrophilic modification layer covers the outer wall of the hollow polymer microsphere. Its preparation method includes the preparation of uniformly sized hollow polymer microspheres, the composite of hollow microspheres and superparamagnetic nanoparticles, and the surface functionalization modification of hollow microspheres. The magnetic hollow polymer microsphere has good surface hydrophilicity, a relatively small reduced density, high magnetic responsiveness, a fast magnetic reaction speed, and a long suspension time in the aqueous dispersion, and is suitable for the detection field. However, during the preparation of magnetic polymer microspheres by emulsion polymerization, it is difficult to completely remove impurities such as emulsifiers on the surface of the microspheres, resulting in impure products, affecting the performance and application effect of the microspheres, and may interfere with the adsorption of target substances. At present, there is little research on the adsorption and decolorization technology of magnetic polymer microspheres used in dyes. This is mainly because the polymer microspheres obtained by the existing preparation process of magnetic adsorbents have poor particle size uniformity and low magnetic responsiveness, which limit their large-scale application in the field of dye decolorization. Therefore, it is an urgent problem to be solved. Summary of the Invention

[0007] Aiming at the defects in the prior art, the purpose of the present invention is to provide a polyethyleneimine-modified magnetic polymer microsphere. The polyethyleneimine-modified magnetic polymer microsphere is an amino-functionalized magnetic particle with a core-shell structure obtained by dispersion polymerization, which solves the technical problems of low magnetic responsiveness and uneven particle size distribution of the magnetic adsorbent prepared by the existing process, and is beneficial to improving the efficiency and cost control of dye molecule wastewater treatment.

[0008] The technical solution of the present invention is as follows: The present invention provides a polyethyleneimine-modified magnetic polymer microsphere, which uses superparamagnetic Fe3O4 as the core and a copolymer of styrene and glycidyl methacrylate with surface amino-functionalization as the shell. Among them, the superparamagnetic Fe3O4 is obtained by the coprecipitation method, and the magnetic polymer microsphere is obtained by the dispersion polymerization method; Among them, the average particle size of the polyethyleneimine-modified magnetic polymer microsphere is 200-300 μm, and the magnetization intensity is 18.5-35.85 emu / g; The superparamagnetic Fe3O4 accounts for 10.6-25.2% of the mass of the entire polyethyleneimine-modified magnetic polymer microsphere.

[0009] Further, the polyethyleneimine-modified magnetic polymer microsphere is at 2024 cm -1 、1087 cm -1 、990 cm -1The peaks at [specific position] are respectively the stretching vibration absorption peak of the carbon-carbon unsaturated bond, the stretching vibration absorption peak of the carbon-oxygen bond, and the characteristic absorption peak of the epoxy bond. At 1579 cm -1 The peak at [specific position] is the N-H deformation vibration absorption peak.

[0010] Furthermore, the polyethyleneimine-modified magnetic polymer microspheres are obtained by the ring-opening addition reaction of polyethyleneimine with the epoxy groups on the surface of the magnetic polymer microspheres.

[0011] Furthermore, the average particle size of the superparamagnetic Fe3O4 is 8 - 20 nm.

[0012] Furthermore, the molecular weight of the polyethyleneimine (PEI) is 10000 - 70000.

[0013] Furthermore, in the polyethyleneimine-modified magnetic polymer microspheres, the molar number of amino groups per gram of microspheres is 80 - 260 μmol / g.

[0014] Furthermore, the polyethyleneimine-modified magnetic polymer microspheres are obtained by the free radical polymerization of styrene and glycidyl methacrylate on the surface of superparamagnetic Fe3O4 particles and the cross-linking between polymer chains to form a core-shell structure, and then introducing amino groups on the surface of the magnetic polymer microspheres.

[0015] The present invention also provides a preparation method of the aforementioned polyethyleneimine-modified magnetic polymer microspheres, which includes the following steps: Step S1: Prepare Fe3O4 magnetic fluid by the co-precipitation method Step S1-1: Oxidation reaction: Dissolve a part of FeCl2·4H2O in distilled water and concentrated hydrochloric acid, then add the mixed solution into a three-necked flask and heat it to 50 - 55 °C. Adjust the rotation speed of the constant-speed stirrer to 200 - 300 r / min and dropwise add hydrogen peroxide until the solution changes color. Pass N2 into the three-necked flask and raise the temperature to 80 - 95 °C to remove the excess hydrogen peroxide; Step S1-2: When the reaction solution obtained in step 1-1 is cooled to 55 - 65 °C, dissolve the remaining FeCl2·4H2O in concentrated hydrochloric acid and distilled water and then add it to the three-necked flask; Step S1-3: Co-precipitation reaction: Adjust the rotation speed of the constant-speed stirrer to 300 - 600 r / min, and quickly dropwise add NaOH solution using a separatory funnel to make the divalent iron ions and trivalent iron ions undergo a co-precipitation reaction under alkaline conditions to generate Fe3O4 nanoparticles; Step S1-4: When the rotational speed of the constant-speed stirrer is adjusted to 150 - 200 r / min, slowly add the surfactant solution dropwise using a separating funnel. After the addition is complete, introduce N2 into the three-necked flask, stir, and wash the reaction solution alternately with distilled water and solvent until it is neutral to obtain Fe3O4 magnetic fluid (i.e., superparamagnetic Fe3O4). Step S2: Prepare magnetic polymer microspheres by dispersion polymerization Step S2-1: Uniformly disperse the above-mentioned Fe3O4 magnetic fluid in a dispersant and a solvent at 55 - 65 °C, and raise the temperature of the mixture to 72 - 88 °C. Step S2-2: Free radical polymerization and crosslinking reaction Slowly add the mixed solution containing the polymerization monomer, functional monomer, initiator, and crosslinking agent to the mixture of the above-mentioned Fe3O4 magnetic fluid. Under stirring conditions, the initiator decomposes thermally to generate free radicals, which initiate the free radical polymerization reaction of the polymerization monomer on the surface of the magnetic fluid; as the polymerization reaction proceeds, the polymer chains grow continuously, and crosslinking reactions occur between the polymer chains, finally forming magnetic polymer microspheres with a magnetic fluid core and a polymer shell. Step S3: Prepare amino-functionalized magnetic polymer microspheres Dissolve polyethyleneimine in a mixed solvent of at least one of 1,4-dioxane, tetrahydrofuran, dimethylformamide, ethylene glycol dimethyl ether and water, and then place the magnetic polymer microspheres in step 2 into the obtained mixed solution for sufficient swelling, and then carry out a grafting reaction at 80 - 90 °C for 6 - 15 h. After the reaction is completed, filter out the microspheres and wash them with distilled water multiple times, and dry them under vacuum at 50 - 60 °C to obtain amino-functionalized magnetic polymer microspheres.

[0016] Furthermore, the mass ratio of FeCl2·4H2O in step S1-1 and step S1-2 is (1 : 0.4) - (1 : 0.75).

[0017] Furthermore, in step S1-1 and step S1-2, in the oxidation reaction, the mass ratio of concentrated hydrochloric acid, FeCl2·4H2O and distilled water is (1 : 2 : 20) - (1 : 4 : 40). Adding hydrochloric acid during the dissolution of ferrous chloride mainly plays the roles of inhibiting hydrolysis, preventing oxidation, increasing solubility, and stabilizing the solution.

[0018] Furthermore, in step S1-1, the mass ratio of FeCl2·4H2O to hydrogen peroxide is (1 : 0.1) - (1 : 0.3).

[0019] Furthermore, in step S1-2, the concentration of the concentrated hydrochloric acid is 12 mol / L.

[0020] Further, the mass ratio of FeCl2·4H2O in step S1-1 to NaOH in step 1-3 is (1:1) to (1:1.5).

[0021] Further, in step S1-3, the concentration of the NaOH solution is 5 to 7.5 mol / L.

[0022] Further, in step S1-4, the surfactant includes any one or both of sodium dodecyl sulfonate and polyethylene glycol.

[0023] Further, in step S1-4, the mass ratio of sodium dodecyl sulfonate to polyethylene glycol is (1:2) to (1:4).

[0024] Further, in step S1-4, the surfactant solution is a solution formed by dissolving sodium dodecyl sulfonate and polyethylene glycol (6000) in water and ethanol.

[0025] Further, in step S1-4, the solvent is at least one of ethanol, propanol, or n-butanol.

[0026] Further, in step S1-4, the mass ratio of sodium dodecyl sulfonate, polyethylene glycol (6000), water, and ethanol is (1:2:10:20) to (1:4:40:60).

[0027] Further, in step S1-4, the stirring time is 3 to 5 h.

[0028] In the present invention, in step S1, first, hydrogen peroxide is dropped into the solution containing iron chloride tetrahydrate, and an oxidation reaction occurs to oxidize part of the ferrous ions to ferric ions, facilitating the subsequent formation of magnetite; subsequently, when the ferrous chloride solution and the sodium hydroxide solution are added, the ferrous ions and ferric ions in the solution undergo a coprecipitation reaction under alkaline conditions to form magnetite nanoparticles; finally, the surfactant can adsorb on the surface of the generated magnetite particles to prevent particle aggregation, enabling them to be stably dispersed in the solution to form a ferrofluid.

[0029] Further, in step S2-1, the dispersant is at least one of polyethylene glycol (6000), polyethylene glycol (4000), polyvinylpyrrolidone, or polyvinyl alcohol.

[0030] Further, in step S2-1, the solvent is at least one of ethanol, propanol, or n-butanol.

[0031] Further, in step S2-1, the mass ratio of the dispersant, the Fe3O4 magnetic fluid, and the solvent is (1:4:40) to (1:15:100).

[0032] Further, in step S2-1, dissolve polyethylene glycol (6000) in ethanol and place it in a three-necked flask. At the same time, add water. When the temperature rises to 45-60 °C, add the Fe3O4 magnetic fluid prepared in step 1 to the three-necked flask, introduce N2, and stir at 55-65 °C and 300-400 r / min for 20-40 min, and then heat the temperature to 70-88 °C.

[0033] Further, in step S2-2, the polymerization monomer is styrene.

[0034] Further, in step S2-2, the functional monomer is glycidyl methacrylate (GMA).

[0035] Further, in step S2-2, the initiator is at least one of benzoyl peroxide (BPO), di-tert-butyl peroxide (DTBP), and azobisisobutyronitrile (AIBN).

[0036] Further, in step S2-2, the crosslinking agent is at least one of divinylbenzene (DVB) and N,N'-methylenebisacrylamide (MBA).

[0037] Further, in step S2-2, the mass ratio of the crosslinking agent, the functional monomer, the initiator, and the polymerization monomer is (1:1:1.5:5) to (1:2:3:12).

[0038] Further, in step S2-2, the total time of the free radical polymerization reaction and the crosslinking reaction is 4-8 h.

[0039] Further, in step S2-2, the stirring rate is 150-300 rpm.

[0040] Further, in step S2-2, weigh benzoyl peroxide, dissolve it in styrene, then add glycidyl methacrylate and divinylbenzene, and slowly add the obtained mixture to the three-necked flask using a separatory funnel, and stir at 150-300 rpm for 4-8 h.

[0041] Further, step S2-2 further includes washing the magnetic polymer microspheres with distilled water and vacuum drying at 50-70 °C after the free radical polymerization and crosslinking reactions are completed.

[0042] In the present invention, in step S2, when preparing magnetic polymer microspheres by dispersion polymerization, glycidyl methacrylate is used as a functional monomer. Among them, the molecular structure of glycidyl methacrylate contains epoxy groups (glycidyl ester groups). During the polymerization reaction, these epoxy groups will be introduced into the structure of the magnetic polymer microspheres, providing active sites for subsequent reactions with PEI.

[0043] In the present invention, in step S3, the magnetic polymer microspheres will absorb the solvent and swell, causing the polymer chain segments to stretch, which facilitates the grafting reaction between the PEI molecules and the active groups on the surface of the microspheres. Under the temperature condition of 80 - 90 °C and after a reaction time of 6 - 15 h, the amino groups in the PEI molecules react chemically with the active groups (such as epoxy groups, etc.) on the surface of the magnetic polymer microspheres, thereby introducing amino groups onto the surface of the magnetic polymer microspheres and realizing the amino-functionalization of the magnetic polymer microspheres.

[0044] The present invention also provides an adsorption and decolorization method for the aforementioned polyethyleneimine-modified magnetic polymer microspheres, which is used to adsorb dye molecules in wastewater, and the dye molecules carry at least one of functional groups such as sulfonic acid groups, mercapto groups, and carboxyl groups.

[0045] Furthermore, the concentration of the dye molecules in the wastewater is 50 - 500 mg / L.

[0046] Furthermore, the pH of the wastewater is 2 - 7, preferably 5.

[0047] Furthermore, when the concentration of the dye molecules in the wastewater is 50 - 500 mg / L and the pH of the wastewater is 4 - 6, the polyethyleneimine-modified magnetic polymer microspheres adsorb the dye molecules with sulfonic acid groups through electrostatic interaction, and its adsorption capacity is 130 - 240 mg / g, preferably 135 - 220 mg / g.

[0048] In the present invention, the adsorption capacity of the polyethyleneimine-modified magnetic polymer microspheres is expressed as the mass of the dye molecules adsorbed per unit mass of the polyethyleneimine-modified magnetic polymer microspheres.

[0049] Furthermore, when the dosage of the polyethyleneimine-modified magnetic polymer microspheres is reduced from 3.0 g / L to 0.5 g / L, the adsorption capacity of the polyethyleneimine-modified magnetic polymer microspheres for the dye molecules increases from 50 mg / g to 250 mg / g.

[0050] Furthermore, when the dosage of the polyethyleneimine-modified magnetic polymer microspheres is increased from 0.5 g / L to 3.0 g / L, the removal rate of the polyethyleneimine-modified magnetic polymer microspheres for the dye molecules increases from 70% to 95%.

[0051] Further preferably, the dosage of the polyethyleneimine-modified magnetic polymer microspheres is 1.0 g / L.

[0052] Further, when the concentration of dye molecules in the wastewater is 100 mg / L and the adsorption time is 30 min to 120 min, the adsorption capacity of the polyethyleneimine-modified magnetic polymer microspheres for dye molecules is 80 mg / g to 100 mg / g.

[0053] Further, when the concentration of dye molecules in the wastewater is 200 mg / L and the adsorption time is 30 min to 120 min, the adsorption capacity of the polyethyleneimine-modified magnetic polymer microspheres for dye molecules is 130 mg / g to 175 mg / g.

[0054] Further, at a temperature of 25°C to 45°C, the adsorption capacity of the polyethyleneimine-modified magnetic polymer microspheres for dye molecules is 173.121 mg / g to 240.365 mg / g.

[0055] The beneficial technical effects of the present invention are reflected in the following aspects: (1) The polyethyleneimine-modified magnetic polymer microspheres of the present invention have a unique and optimized structure. Different from the microspheres prepared by the embedding method, emulsion polymerization method and suspension polymerization method in the prior art, on the one hand, the polyethyleneimine-modified magnetic polymer microspheres use superparamagnetic Fe3O4 as the core, ensuring good magnetic responsiveness and enabling rapid and efficient separation under the action of an external magnetic field, effectively solving the problem of poor magnetic responsiveness of microspheres prepared by traditional methods. The magnetization intensity reaches 18.5 - 35.85 emu / g, greatly improving the operation convenience and treatment efficiency in practical applications; on the other hand, the copolymer of styrene with glycidyl methacrylate with surface amino-functionalization is used as the shell. This core-shell structure not only provides a stable physical form but also enables the microspheres to have good dispersibility in the solution, avoiding the phenomenon of easy adhesion of microspheres in the prior art. At the same time, the amino-functionalized shell layer increases the active sites on the surface of the microspheres, which is conducive to specific or non-specific interactions with the target substances, expanding the application prospects of the microspheres in the field of wastewater containing dyes and heavy metal ions.

[0056] (2) The present invention selects polyethyleneimine molecules as the amino-modified compound, which contains a large number of primary, secondary, and tertiary amine groups. These groups generate electrostatic adsorption with the dye. At the same time, the polyethyleneimine molecular chain contains a large number of amino groups, making it highly hydrophilic and capable of improving the hydrophilicity of the magnetic polymer microspheres. In addition, the polyethyleneimine molecules can bind to the magnetic microspheres, enhancing their mechanical properties. The present invention selects styrene as the polymerization monomer, which has many advantages such as low cost, easy copolymerization, good thermal stability, and no easy explosive polymerization, which is conducive to improving the rigidity and chemical resistance of the final microsphere product and is not easily corroded by strong acids or strong bases.

[0057] (3) In terms of the preparation process, the present invention avoids the inherent defects of the existing emulsion polymerization and suspension polymerization methods. Compared with emulsion polymerization, the preparation process of the present invention does not introduce emulsifier impurities that are difficult to remove, thus ensuring the purity and performance stability of the product and reducing the performance fluctuations and uncertainties of the microspheres caused by impurities. Compared with suspension polymerization, the present invention realizes precise control of the microdroplet size through precise dispersion polymerization technology. The prepared magnetic polymer microspheres have uniform particle size and controllable size, with an average particle size of 200 - 300 μm, improving the consistency and repeatability of the product, reducing the scrap rate in the production process, effectively saving production costs and resources; at the same time, it also avoids the problems such as the difficulty in quickly and effectively separating the magnetic microspheres from the solution, low utilization rate of magnetic particles, and weak magnetic responsiveness in the actual application of the magnetic microspheres obtained by the suspension polymerization process.

[0058] (4) The present invention uses polyethyleneimine to modify magnetic polymer microspheres and utilizes functional group surface modification technology to increase the distribution density and quantity of amino functional groups on the surface of magnetic polymer microspheres, so that the molar number of amino groups per gram of microspheres reaches 80 - 260 μmol / g. The modification process of the present invention is simple to operate and the conditions are easy to control, and it can achieve efficient functional modification under mild reaction conditions, which is conducive to large-scale industrial production.

[0059] (5) When the present invention prepares superparamagnetic Fe3O4 magnetic fluid by the coprecipitation method, hydrogen peroxide is first added dropwise to the divalent iron solution to undergo an oxidation reaction to oxidize some ferrous ions to ferric ions. Then, after adding ferrous chloride solution and sodium hydroxide solution, the divalent iron ions and ferric ions in the solution undergo a coprecipitation reaction under alkaline conditions. The generated Fe3O4 nanoparticles have a magnetic responsiveness increased by more than 10% compared with the traditional coprecipitation method (directly using ferric ions and ferrous ions to undergo coprecipitation under alkaline conditions), and have uniform particle size and good dispersion.

[0060] (6) When the present invention prepares superparamagnetic Fe3O4 magnetic fluid by the coprecipitation method, it is unexpectedly found that adding a small amount of hydrochloric acid during the dissolution process of FeCl2·4H2O in Step 1-2 helps to inhibit hydrolysis, prevent oxidation, increase solubility and stabilize the solution.

[0061] (7) The polyethyleneimine-modified magnetic polymer microspheres of the present invention exhibit excellent adsorption performance. The abundant amino functional groups on the surface and the optimized structure endow them with extremely strong adsorption capacity for pollutants such as dyes. The present invention has tested the influence laws of pH value, microsphere dosage, adsorption time and adsorption temperature on the adsorption amount through a large number of experiments, screened out the better treatment conditions for dye wastewater, provided a guiding basis for scientific researchers to effectively reduce the concentration of pollutants in wastewater and achieve higher purification standards in practice, expanded the application prospects of polyethyleneimine-modified magnetic polymer microspheres in the purification field of industrial dye wastewater (such as textile printing and dyeing, leather processing, papermaking, etc.), and provided a solid environmental protection technical support for industrial sustainable development.

[0062] (8) The adsorption process of the polyethyleneimine-modified magnetic polymer microspheres of the present invention has good selectivity and reversibility. In a complex pollutant system, it can preferentially adsorb target pollutants. At the same time, under suitable elution conditions, the regeneration and repeated use of the microspheres can be realized. After multiple cycles of use, it can still maintain high adsorption performance, further reducing the treatment cost and improving the resource utilization rate, providing strong technical support for environmental protection and resource recycling. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] Figure 1 It is a transmission electron microscope image of the Fe3O4 magnetic fluid prepared in Step S1 of the embodiment.

[0064] Figure 2 It is the XRD analysis of the Fe3O4 magnetic fluid prepared in Step 1 of the embodiment.

[0065] Figure 3 It is the FI-IR spectrum of the Fe3O4 particles without surface active coating (a) and the FI-IR spectrum of the Fe3O4 with surface active coating in Step S1-4 of the embodiment (b).

[0066] Figure 4 It is the hysteresis regression line of the Fe3O4 magnetic fluid prepared in the embodiment.

[0067] Figure 5 It is the optical microscope photo of the polyethyleneimine-modified magnetic polymer microspheres of the embodiment.

[0068] Figure 6Infrared spectra of the polyethyleneimine-modified magnetic polymer microspheres (PEI-[P(St-GMA)] magnetic polymer microspheres) and unmodified magnetic polymer microspheres (P(St-GMA) magnetic polymer microspheres) (control) of the examples.

[0069] Figure 7 To test the hysteresis regression lines of P(St-GMA) magnetic polymer microspheres and PEI-[P(St-GMA)] magnetic polymer microspheres using VSM at room temperature.

[0070] Figure 8 Optical microscope photographs of the polyethyleneimine-modified magnetic polymer microspheres of Comparative Example 1.

[0071] Figure 9 Hysteresis regression lines of the polyethyleneimine-modified magnetic polymer microspheres of Comparative Example 1.

[0072] Figure 10 Optical microscope photographs of the PEI-[P(St-GMA)] magnetic polymer microspheres of Comparative Example 2.

[0073] Figure 11 Hysteresis regression lines of the PEI-[P(St-GMA)] magnetic polymer microspheres of Comparative Example 2.

[0074] Figure 12 Transmission electron microscope images of Fe3O4 magnetic fluid prepared by the unimproved coprecipitation method of Comparative Example 2.

[0075] Figure 13 To test the effect of pH value on the adsorption performance of the PEI-[P(St-GMA)] magnetic polymer microspheres prepared in the examples.

[0076] Figure 14 To test the effect of the dosage of the PEI-[P(St-GMA)] magnetic polymer microspheres prepared in the examples on the adsorption performance.

[0077] Figure 15 To test the effect of adsorption time on the adsorption performance of the PEI-[P(St-GMA)] magnetic polymer prepared in the examples.

[0078] Figure 16 To test the effect of temperature on the adsorption performance of the PEI-[P(St-GMA)] magnetic polymer microspheres prepared in the examples. The left and right figures are Langmuir and Freundlich adsorption isotherms.

[0079] Figure 17 To test the effect of adsorption time on the adsorption performance of the hexamethylenediamine-modified magnetic polymer microspheres prepared in Comparative Example 3. Specific embodiments

[0080] The preferred embodiments of the present invention will be described in more detail below. Although the preferred embodiments of the present invention are described below, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to make the present invention more thorough and complete, and to fully convey the scope of the present invention to those skilled in the art.

[0081] Example This example provides a polyethyleneimine-modified magnetic polymer microsphere. The polyethyleneimine-modified magnetic polymer microsphere has a superparamagnetic Fe3O4 core and a shell of a copolymer of styrene and glycidyl methacrylate with surface amino-functionalization. Among them, the superparamagnetic Fe3O4 is obtained by the coprecipitation method, and the magnetic polymer microsphere is obtained by the dispersion polymerization method; Among them, the average particle size of the polyethyleneimine-modified magnetic polymer microsphere is 240 μm, and the magnetization intensity is 28.11 emu / g; The superparamagnetic Fe3O4 accounts for 24.82% of the mass of the entire polyethyleneimine-modified magnetic polymer microsphere; The polyethyleneimine-modified magnetic polymer microsphere has peaks at 2024 cm -1 , 1087 cm -1 , 990 cm -1 which are the stretching vibration absorption peaks of carbon-carbon unsaturated bonds, the stretching vibration absorption peaks of carbon-oxygen bonds, and the characteristic absorption peaks of epoxy bonds respectively. The peak at 1579 cm -1 is the N-H deformation vibration absorption peak; The average particle size of the superparamagnetic Fe3O4 is 12 nm; The molecular weight of polyethyleneimine (PEI) is 20,000; In the polyethyleneimine-modified magnetic polymer microsphere, the number of moles of amino groups per gram of microspheres is 140 μmol / g.

[0082] Among them, the number of moles of amino groups per gram of microspheres is determined by the conductometric titration method. The specific process is as follows: Place the prepared magnetic polymer microsphere dispersion solution in a beaker, and immerse the electrode (the measuring electrode of the conductivity meter) in the solution. Start slowly dropping the titrant hydrochloric acid. After each drop of a certain volume (such as V1 milliliters), record the conductivity value of the solution. As the titrant is added, the amino groups in the solution gradually react with hydrochloric acid, and the conductivity will gradually change; Continue the titration. When the conductivity changes abruptly, the corresponding point is the titration end point. The end point is determined by plotting the conductivity-titrant volume curve; According to the volume (V2 mL) and concentration (C mol / L) of the titrant (hydrochloric acid) consumed at the titration endpoint, the amount of substance of hydrochloric acid reacting with the amino group (n = C×V2) can be calculated. Since the reaction between hydrochloric acid and the amino group is 1:1, the amount of substance of the amino group is also n. Then the number of moles of amino groups per gram of microspheres = n / m.

[0083] The preparation method of polyethyleneimine-modified magnetic polymer microspheres is as follows: Step S1: Prepare Fe3O4 magnetic fluid by coprecipitation method Step S1-1: Oxidation reaction: Weigh 4.2 g of FeCl2·4H2O in a beaker, dissolve it with 80 mL of distilled water, put it into a 250 mL three-necked flask, add 2 mL of concentrated hydrochloric acid, heat it to 50 °C using a water bath, adjust the speed of the constant-speed stirrer to 200 rpm, add 0.8 g of hydrogen peroxide dropwise until the solution changes color, then introduce N2 into the three-necked flask, raise the temperature to 80 °C, and remove the excess hydrogen peroxide; Step S1-2: When the reaction solution obtained in step 1-1 is cooled to 60 °C, dissolve 2.5 g of FeCl2·4H2O in 1 mL of hydrochloric acid solution (the concentration of the hydrochloric acid solution is 12 mol / L), add distilled water to 30 mL and then add it to the above three-necked flask; Step S1-3: Coprecipitation reaction: When the speed of the constant-speed stirrer is adjusted to 300 r / min, quickly add 25 mL of 5 mol / L NaOH solution dropwise using a separatory funnel, so that ferrous ions and ferric ions undergo a coprecipitation reaction under alkaline conditions to form Fe3O4 nanoparticles; Step S1-4: Weigh 0.5 g of sodium dodecyl sulfate and 1.5 g of polyethylene glycol (6000), dissolve them with 10 mL of water and add 20 mL of ethanol to obtain a surfactant solution. Then, when the speed of the constant-speed stirrer is adjusted to 200 r / min, slowly add the above surfactant solution dropwise using a separatory funnel. After the addition is complete, introduce N2 into the three-necked flask for 10 min, stir for 3 h, and alternately wash the reaction solution with distilled water and at least one of ethanol, propanol, or n-butanol until it is neutral to obtain Fe3O4 magnetic fluid with an average particle size of 8 - 20 nm; Step S2: Prepare magnetic polymer microspheres by dispersion polymerization Step S2-1: Weigh 2 g of polyethylene glycol (6000), dissolve it with a mixed solvent of 50 mL of ethanol and 50 mL of water, put it into a three-necked flask. When the temperature rises to 60 °C, add 12 g of the prepared Fe3O4 magnetic fluid to the three-necked flask, introduce N2, stir at 60 °C at 350 rpm for 20 min, and then heat the temperature to 75 °C; Step S2-2: Free radical polymerization and crosslinking reaction Weigh 3.5 g of benzoyl peroxide (BPO), dissolve it in 15 mL of styrene, then add 3 mL of glycidyl methacrylate (GMA) and 2 mL of divinylbenzene (DVB). Slowly add the above-mentioned mixed solution into a three-necked flask using a separatory funnel. After dropping, stir at 200 rpm for 4 h to form magnetic polymer microspheres with Fe3O4 magnetic fluid as the core and polymer as the shell. After the reaction, wash the microspheres with distilled water 4 - 5 times, and place them in an electrothermal blast drying oven at 70 °C for drying for later use; Step S3: Prepare amino-functionalized magnetic polymer microspheres Dissolve polyethyleneimine in a mixed solvent of 1,4-dioxane and water. Then place the magnetic polymer microspheres from Step 2 in the obtained mixed solution for sufficient swelling, and carry out a grafting reaction at 88 °C for 8 h. After the reaction, filter out the microspheres and wash them with distilled water multiple times, and dry them under vacuum at 50 °C to obtain amino-functionalized magnetic polymer microspheres.

[0084] Figure 1 It is the transmission electron microscope image of the Fe3O4 magnetic fluid prepared in Step 1 of the example.

[0085] From Figure 1 it can be seen that the middle color of the prepared Fe3O4 magnetic fluid is darker, which is the Fe3O4 magnetic particles. The edge is relatively clear, basically presenting an irregular quadrilateral and in a crystalline form; the outer layer has a lighter color, indicating that a layer of polyethylene glycol (PEG) and sodium dodecyl sulfate (SDS) is adsorbed on the surface; there is a relatively slight agglomeration phenomenon, which has no impact on the stability. The particle size distribution is relatively uniform, and the average particle size is about 12 nm. It can be considered that PEG and SDS are wound around the surface of Fe3O4 particles through coordination bonds or hydrogen bonds to form a solvation layer, preventing the mutual aggregation of small particles, thus being uniformly dispersed in the aqueous solution to form a magnetic fluid with good stability, and at the same time enhancing the affinity with polymer materials.

[0086] Figure 2 It is the XRD pattern of the Fe3O4 magnetic fluid prepared in Step 1 of the example. From Figure 2 it can be seen that 31°, 36°, 43°, 53°, 57°, and 62° are respectively the characteristic diffraction peaks of the 6 crystal planes of Fe3O4 crystal (220), (311), (400), (422), (511), and (440). The characteristic diffraction peaks of the Fe3O4 crystal are very obvious, and there are basically no impurity peaks. It can be seen that the Fe3O4 nanoparticles belong to the cubic spinel structure, and it can be determined that the prepared sample is composed of single-phase Fe3O4.

[0087] Figure 3FI-IR spectra of Fe3O4 particles without surface active coating (a) and FI-IR spectra of Fe3O4 particles with surface active coating in step S1-4 of the example (b).

[0088] From Figure 3 Figure (a), it can be seen that the Fe3O4 particles without surface active coating have absorption peaks near 580 cm -1 and 3422 cm -1 , corresponding to the characteristic absorption of Fe3O4 particles and hydroxyl groups in Fe(OH)2 or Fe(OH)3 respectively.

[0089] From Figure 3 Figure (b), it can be seen that on the infrared spectrum of the Fe3O4 particles after surface active modification, the absorption peak at 588 cm -1 (bending vibration absorption peak of Fe-O) is the characteristic absorption peak of Fe3O4. The characteristic absorption peaks of polyethylene glycol are at 1387 cm -1 (C-O-C stretching vibration), 3410 cm -1 (-OH stretching vibration), 2850 cm -1 (CH2CH2 stretching vibration). The characteristic absorption peaks of sulfonate groups are at 1160 - 1220 cm -1 and 1030 - 1070 cm -1 . The characteristic absorption peaks at 2922 cm -1 , 2840 cm -1 , 1380 cm -1 , 1460 cm -1 are the characteristic absorption peaks of -CH3 and -CH2-. These characteristic absorption peaks indicate that a layer of polyethylene glycol and sodium dodecyl sulfonate is coated on the surface of Fe3O4, and no new absorption peaks are generated (the characteristic absorption peak at 1718 cm -1 is formed by the oxidation of the -OH part of the polyethylene glycol end group into a carbonyl group), indicating that polyethylene glycol does not chemically react with Fe3O4 but is physically adsorbed on its surface.

[0090] Figure 4 is the hysteresis regression line of the Fe3O4 magnetic fluid prepared in the example. It can be seen from Figure 4 that the two hysteresis regression lines basically coincide, indicating that the remanence of the obtained Fe3O4 magnetic fluid is very low, with good superparamagnetism. The saturation magnetization intensity of Fe3O4 is 53.56 emu / g, indicating strong magnetic responsiveness of the magnetic fluid.

[0091] Figure 5 is the optical microscope photograph of the polyethyleneimine-modified magnetic polymer microspheres in the example. It can be seen from Figure 5 that the average particle size of the microspheres is between 200 - 300 μm, and the particle size is uniform, with regular spherical shapes and no agglomeration phenomenon.

[0092] Figure 6 FT-IR spectra of the polyethyleneimine-modified magnetic polymer microspheres (PEI-[P(St-GMA)] magnetic polymer microspheres) and unmodified magnetic polymer microspheres (P(St-GMA) magnetic polymer microspheres) (control) for the examples. It can be seen that there are the same peaks at 2024 cm -1 , 1087 cm -1 , and 990 cm -1 , which are the stretching vibration absorption peaks of carbon-carbon unsaturated bonds, the stretching vibration absorption peaks of carbon-oxygen bonds, and the characteristic absorption peaks of epoxy bonds, respectively. However, it can be clearly seen from Figure 6 that the peak heights at 1087 cm -1 and 990 cm -1 in the PEI-[P(St-GMA)] magnetic polymer microspheres are lower than those in the P(St-GMA) magnetic polymer microspheres, indicating that the ring-opening reaction of the epoxy bond has occurred; 1579 cm -1 is the N-H deformation vibration absorption peak of the PEI-[P(St-GMA)] magnetic polymer microspheres. By comparing the FT-IR spectra of the PEI-[P(St-GMA)] magnetic polymer microspheres and the P(St-GMA) magnetic polymer microspheres, it can be known that the P(St-GMA) magnetic polymer microspheres have been successfully modified by polyethyleneimine to obtain PEI-[P(St-GMA)] magnetic polymer microspheres with amino groups on the surface.

[0093] Figure 7 Hysteresis regression curves of the P(St-GMA) magnetic polymer microspheres and the PEI-[P(St-GMA)] magnetic polymer microspheres were measured by VSM at room temperature. The hysteresis regression curves show that both the P(St-GMA) magnetic polymer microspheres and the PEI-[P(St-GMA)] magnetic polymer microspheres have superparamagnetism, and the saturation magnetization intensities are 33.74 emu / g and 28.11 emu / g, respectively. This result indicates that during the process of the Fe3O4 particles being encapsulated in the reaction of the P(St-GMA) magnetic polymer microspheres and PEI, some of the Fe3O4 particles in the magnetic microspheres have been oxidized, so the saturation magnetization intensity of the PEI-[P(St-GMA)] magnetic polymer microspheres has decreased to a certain extent compared with that of the P(St-GMA) magnetic polymer microspheres. However, they can be separated from water under the action of an external magnetic field, and the adsorbent can be reused.

[0094] Comparative Example 1 Comparative Example 1 provides a polyethyleneimine-modified magnetic polymer microsphere with superparamagnetic Fe3O4 as the core and a copolymer of styrene and glycidyl methacrylate functionalized with surface amino groups as the shell. Among them, the superparamagnetic Fe3O4 is obtained by the coprecipitation method, and the magnetic polymer microspheres are obtained by the suspension polymerization method; Among them, the average particle size of the polyethyleneimine-modified magnetic polymer microspheres is 300 μm, and the magnetization intensity is 9.43 emu / g; The superparamagnetic Fe3O4 accounts for 10.24% of the mass of the entire polyethyleneimine-modified magnetic polymer microspheres.

[0095] The average particle size of the superparamagnetic Fe3O4 is 12 nm; The molecular weight of polyethyleneimine (PEI) is 20,000; In the polyethyleneimine-modified magnetic polymer microspheres, the number of moles of amino groups per gram of microspheres is 83 μmol / g.

[0096] The preparation method of the polyethyleneimine-modified magnetic polymer microspheres is as follows: Step S1: Prepare Fe3O4 magnetic fluid by the same coprecipitation method as in Example 1 Step S1-1: Oxidation reaction: Weigh 4 g of FeCl2·4H2O in a beaker, dissolve it with 50 mL of distilled water, put it into a 250 mL three-necked flask, add 2 mL of concentrated hydrochloric acid (the concentration of the hydrochloric acid solution is 12 mol / L), heat it to 50 °C using a water bath, adjust the speed of the constant-speed stirrer to 200 rpm, dropwise add 0.5 g of hydrogen peroxide until the solution changes color, then introduce N2 into the three-necked flask, raise the temperature to 80 °C, and remove the excess hydrogen peroxide; Step S1-2: When the reaction solution obtained in Step 1-1 is cooled to 60 °C, dissolve 2.5 g of FeCl2·4H2O in 1 mL of hydrochloric acid solution (the concentration of the hydrochloric acid solution is 12 mol / L), add distilled water to 30 mL, and then add it to the above three-necked flask; Step S1-3: Coprecipitation reaction: When the speed of the constant-speed stirrer is adjusted to 300 r / min, quickly dropwise add 20 mL of a 5 mol / L NaOH solution using a separatory funnel to cause the divalent iron ions and trivalent iron ions to undergo a coprecipitation reaction under alkaline conditions to form Fe3O4 nanoparticles; Step S1-4: Weigh 0.5 g of sodium dodecyl sulfate and 1 g of polyethylene glycol (6000), dissolve them with 10 mL of water and add 25 mL of ethanol to obtain a surfactant solution. Then, when the speed of the constant-speed stirrer is adjusted to 200 r / min, slowly dropwise add the above surfactant solution using a separatory funnel. After the addition is complete, introduce N2 into the three-necked flask for 10 min, stir for 3 h, and alternately wash the reaction solution with distilled water and at least one of ethanol, propanol, or n-butanol until it is neutral to obtain Fe3O4 magnetic fluid with an average particle size of 8 - 20 nm; Step P2: Prepare magnetic polymer microspheres by suspension polymerization Step P2-1: Weigh 2 g of polyethylene glycol (6000) and add it to a three-necked flask. At the same time, add 100 mL of water. When the temperature rises to 60 °C, add 10 g of the Fe3O4 magnetic fluid prepared in Step 1 to the three-necked flask, and introduce N2. Stir at 350 rpm for 20 min at 60 °C, and then heat the temperature to 75 °C. Step P2-2: Weigh 3.5 g of benzoyl peroxide (BPO), dissolve it in 15 mL of styrene, then add 2 mL of glycidyl methacrylate (GMA) and 2 mL of divinylbenzene (DVB). Use a separatory funnel to slowly add the above mixture to the three-necked flask. After dropping, stir at 200 rpm for 4 h to form magnetic polymer microspheres with Fe3O4 magnetic fluid as the core and polymer as the shell. After the reaction is completed, wash the microspheres 4-5 times with distilled water, and place them in an electrothermal blast drying oven at 70 °C for drying for later use. Step 3: Prepare amino-functionalized magnetic polymer microspheres Dissolve polyethyleneimine in a mixed solvent of 1,4-dioxane and water. Then place the magnetic polymer microspheres in Step T2 into the obtained mixed solution and fully swell them. Then carry out a grafting reaction at 88 °C for 8 h. After the reaction is completed, filter out the microspheres and wash them many times with distilled water, and dry them under vacuum at 50 °C to obtain amino-functionalized magnetic polymer microspheres.

[0097] Figure 8 It is the optical microscope photograph of the polyethyleneimine-modified magnetic polymer microspheres of Comparative Example 1. It can be seen from Figure 8 that the average particle size of the amino-functionalized magnetic microspheres prepared by suspension polymerization is between 150-300 μm, and the particle size of the magnetic microspheres is uneven.

[0098] Figure 9 It is the hysteresis regression line of the polyethyleneimine-modified magnetic polymer microspheres of Comparative Example 1. It can be seen from Figure 9 that although the PEI-[P(St-GMA)] magnetic polymer microspheres of Comparative Example 1 have superparamagnetism, their saturation magnetization intensity is weak, only 9.43 emu / g, and they cannot be separated from water under the action of an external magnetic field.

[0099] Comparative Example 2 Comparative Example 2 provides a polyethyleneimine-modified magnetic polymer microsphere with superparamagnetic Fe3O4 as the core and a copolymer of styrene and glycidyl methacrylate with surface amino-functionalization as the shell. Among them, the superparamagnetic Fe3O4 is obtained by an unimproved coprecipitation method, and the magnetic polymer microspheres are obtained by dispersion polymerization. Among them, the average particle size of the polyethyleneimine-modified magnetic polymer microspheres is 220 μm, and the magnetization intensity is 13.39 emu / g. The superparamagnetic Fe3O4 accounts for 15.4% of the mass of the entire polyethyleneimine-modified magnetic polymer microspheres. The average particle size of superparamagnetic Fe3O4 is 12.6 nm.

[0100] The molecular weight of polyethyleneimine (PEI) is 20,000; In the polyethyleneimine-modified magnetic polymer microspheres, the molar number of amino groups per gram of microspheres is 108 μmol / g.

[0101] The preparation method is as follows: Step T1: Prepare Fe3O4 magnetic fluid by using the unmodified co-precipitation method Weigh 4 g of FeCl3·4H2O and 2.2 g of FeCl2·6H2O and add them to a three-necked flask equipped with a thermometer and a condenser. Add 100 mL of distilled water and simultaneously introduce N2; when the temperature of the obtained mixed solution is maintained at 70 °C, slowly add 25% concentrated ammonia water under rapid stirring, adjust the pH to 7 - 9, control the reaction time within 2 min. After the co-precipitation reaction ends, stir at a low speed at 60 °C for 20 min, slowly add the sodium dodecylbenzenesulfonate surfactant solution, and the resulting black precipitate is aged in a water bath for 1 h; separate Fe3O4 with a magnet, wash it with deionized water multiple times until the solution pH = 7, and prepare the magnetic fluid for later use; Step S2: Prepare magnetic polymer microspheres by using dispersion polymerization Step S2-1: Weigh 2 g of polyethylene glycol (6000), dissolve it in 150 mL of ethanol and put it into a three-necked flask. At the same time, add 50 mL of water. When the temperature rises to 60 °C, add 12 g of the prepared Fe3O4 magnetic fluid to the three-necked flask, and introduce N2. After stirring at 350 rpm for 20 min at 60 °C, heat the temperature to 75 °C; Step S2-2: Free radical polymerization and cross-linking reaction Weigh 3.5 g of benzoyl peroxide (BPO), dissolve it in 15 mL of styrene, then add 2.4 mL of glycidyl methacrylate (GMA) and 2 mL of divinylbenzene (DVB). Use a separatory funnel to slowly add the above mixed solution to the three-necked flask. After dropping, stir at 200 rpm for 4 h to form magnetic polymer microspheres with the magnetic fluid as the core and the polymer as the shell. After the reaction ends, wash the microspheres 4 - 5 times with distilled water, and place them in a 70 °C electrothermal blast drying oven for drying, and keep for later use; Step S3: Prepare amino-functionalized magnetic polymer microspheres Dissolve polyethyleneimine in a mixed solvent of 1,4-dioxane and water. Then place the magnetic polymer microspheres in step S2 into the obtained mixed solution for sufficient swelling, and carry out a grafting reaction at 88 °C for 8 h. After the reaction ends, filter out the microspheres, wash them with distilled water multiple times, and dry them under vacuum at 50 °C to obtain amino-functionalized magnetic polymer microspheres.

[0102] Figure 10 Optical microscope photograph of the PEI-[P(St-GMA)] magnetic polymer microspheres of Comparative Example 2. It can be seen from Figure 10 that the particle size of the amino-functionalized magnetic microspheres is between 180 - 300 μm. The particle size of the magnetic microspheres is uneven, and the magnetic responsiveness is poor.

[0103] Figure 11 Hysteresis regression line of the PEI-[P(St-GMA)] magnetic polymer microspheres of Comparative Example 2. It can be seen from Figure 11 that although the PEI-[P(St-GMA)] magnetic polymer microspheres have superparamagnetism, the saturation magnetization intensity is relatively weak, only 13.39 emu / g. Under the action of an external magnetic field, the separation speed from water is slow, and recycling is difficult.

[0104] Figure 12 Transmission electron microscope image of the Fe3O4 magnetic fluid prepared by the unimproved coprecipitation method of Comparative Example 2. It can be seen from Figure 12 that the edge of the magnetic fluid of Comparative Example 2 is relatively blurred, showing an irregular shape; the outer layer has a darker color and more serious agglomeration phenomenon, and the particle size distribution is uneven.

[0105] Comparative Example 3 Comparative Example 3 is an ethylenediamine-modified magnetic polymer microsphere. The ethylenediamine-modified magnetic polymer microsphere has a superparamagnetic Fe3O4 core and a shell of a copolymer of styrene and glycidyl methacrylate with surface amino-functionalization. Among them, the superparamagnetic Fe3O4 is obtained by the coprecipitation method, and the magnetic polymer microsphere is obtained by the dispersion polymerization method; Among them, the average particle size of the ethylenediamine-modified magnetic polymer microsphere is 220 μm, and the magnetization intensity is 23.22 emu / g; The superparamagnetic Fe3O4 accounts for 22.34% of the mass of the entire ethylenediamine-modified magnetic polymer microsphere; The peak height ratio of the ethylenediamine-modified magnetic polymer microsphere at 972 cm -1 and 885 cm -1 is lower than that of the unmodified magnetic polymer microsphere magnetic P(St-GMA), indicating that the epoxy bond has undergone a ring-opening reaction; 1570 cm -1 is the N-H deformation vibration absorption peak of the ethylenediamine-modified magnetic microsphere.

[0106] The average particle size of the superparamagnetic Fe3O4 is 12 nm; The molecular weight of ethylenediamine is 146.24; In the ethylenediamine-modified magnetic polymer microsphere, the molar number of amino groups per gram of microsphere is 60.2 μmol / g; The equilibrium adsorption capacity for Acid Fuchsin (AF) with an initial concentration of 200 mg / L is 134 mg / g.

[0107] The preparation method of ethylenediamine-modified magnetic polymer microspheres is as follows: Step S1: Prepare Fe3O4 magnetic fluid by coprecipitation method Step S1-1: Oxidation reaction: Weigh 4.2 g of FeCl2·4H2O in a beaker, dissolve it with 80 mL of distilled water, put it into a 250 mL three-necked flask, add 2 mL of concentrated hydrochloric acid, heat it to 50 °C using a water bath, adjust the speed of the constant-speed stirrer to 200 rpm, dropwise add 0.8 g of hydrogen peroxide until the solution changes color, then introduce N2 into the three-necked flask, raise the temperature to 80 °C, and remove the excess hydrogen peroxide; Step S1-2: When the reaction solution obtained in step 1-1 is cooled to 60 °C, dissolve 2.5 g of FeCl2·4H2O in 1 mL of hydrochloric acid solution (the concentration of the hydrochloric acid solution is 12 mol / L), add distilled water to 30 mL, and then add it to the above three-necked flask; Step S1-3: Coprecipitation reaction: When the speed of the constant-speed stirrer is adjusted to 300 r / min, quickly dropwise add 25 mL of 5 mol / L NaOH solution using a separatory funnel, so that divalent iron ions and trivalent iron ions undergo coprecipitation reaction under alkaline conditions to form Fe3O4 nanoparticles; Step S1-4: Weigh 0.5 g of sodium dodecyl sulfate and 1.5 g of polyethylene glycol (6000), dissolve them with 10 mL of water and add 20 mL of ethanol to obtain a surfactant solution. Then, when the speed of the constant-speed stirrer is adjusted to 200 r / min, slowly dropwise add the above surfactant solution using a separatory funnel. After the addition is complete, introduce N2 into the three-necked flask for 10 min, stir for 3 h, and alternately wash the reaction solution with distilled water and at least one of ethanol, propanol, or n-butanol until it is neutral to obtain Fe3O4 magnetic fluid with an average particle size of 8 - 20 nm; Step S2: Prepare magnetic polymer microspheres by dispersion polymerization Step S2-1: Weigh 2 g of polyethylene glycol (6000), dissolve it with a mixed solvent of 50 mL of ethanol and 50 mL of water, and put it into a three-necked flask. When the temperature rises to 60 °C, add 12 g of the prepared Fe3O4 magnetic fluid to the three-necked flask, introduce N2, stir at 350 rpm at 60 °C for 20 min, and then heat the temperature to 75 °C; Step S2-2: Free radical polymerization and cross-linking reaction Weigh 3.5 g of benzoyl peroxide (BPO), dissolve it in 15 mL of styrene, then add 3 mL of glycidyl methacrylate (GMA) and 2 mL of divinylbenzene (DVB). Slowly add the above mixture into a three-necked flask using a separatory funnel. After dropping, stir at 200 rpm for 4 h to form magnetic polymer microspheres with Fe3O4 magnetic fluid as the core and polymer as the shell. After the reaction, wash the microspheres with distilled water 4 - 5 times, and place them in an electric blast drying oven at 70 °C for drying for later use; Step S3: Prepare amino-functionalized magnetic polymer microspheres Dissolve ethylenediamine in N,N-dimethylformamide solvent, then place the magnetic polymer microspheres from Step 2 in the obtained mixed solution for sufficient swelling, and carry out grafting reaction at 75 °C for 8 h. After the reaction, filter out the microspheres and wash them with distilled water multiple times, and dry them under vacuum at 50 °C to obtain amino-functionalized magnetic polymer microspheres.

[0108] Test example Test example 1 Effect of pH value on the adsorption capacity of magnetic polymer microspheres

[0109] Test the effect of pH value on the adsorption of acid fuchsin (AF) by the PEI-[P(St-GMA)] magnetic polymer microspheres prepared in the example. At room temperature, prepare a 50 mL 200 mg / L AF solution, the dosage of PEI-[P(St-GMA)] magnetic polymer microspheres is 0.05 g, carry out oscillating adsorption at a speed of 150 r / min, and make the pH value vary in the range of 2 - 7. The adsorption time is 120 min, measure the concentration of AF, and calculate the adsorption capacity.

[0110] As Figure 13 It can be seen that when pH = 4, the adsorption capacity is the largest. This is because at a lower pH value, the amino groups on the PEI-[P(St-GMA)] magnetic polymer microspheres are protonated, which can increase the electrostatic interaction force of the adsorbent on the -SO3H on the dye molecule AF. However, when the acidity of the solution is too strong, the amino groups (-NH2) in the AF molecule will also be protonated. At the same time, the dissociation of -SO3H is inhibited, and the electrostatic attraction is transformed into electrostatic repulsion, resulting in a decrease in the adsorption capacity. Although acidic conditions are beneficial to improving the adsorption decolorization rate, the treatment of acidic wastewater is complex and troublesome. Considering the adsorption effect and the impact on water bodies during adsorption applications, it is therefore chosen to carry out the adsorption treatment of PEI-[P(St-GMA)] magnetic polymer microspheres under near-neutral conditions, that is, at pH = 5.

[0111] From Figure 13It can be seen that when the concentration of dye molecules in the wastewater is 50 - 500 mg / L and the pH of the wastewater is 4 - 6, the polyethyleneimine-modified magnetic polymer microspheres adsorb the dye molecule AF with sulfonic groups through electrostatic interaction, and the adsorption capacity is 135 - 220 mg / g.

[0112] Test Example 2 Effect of the dosage of PEI-[P(St-GMA)] magnetic polymer microspheres on the adsorption performance.

[0113] To study the effect of the dosage of PEI-[P(St-GMA)] magnetic polymer microspheres on the adsorption capacity, take the PEI-[P(St-GMA)] magnetic polymer microspheres of known different masses in the examples respectively, adjust the initial pH value to 5.0, configure an AF solution with V = 50 mL and a concentration of 200 mg / L in a conical flask, and after oscillating at a speed of 150 r / min for 120 min at room temperature, measure the concentration of the remaining AF in the solution and calculate the adsorption capacity. The effect of the dosage of PEI-[P(St-GMA)] magnetic polymer microspheres on the adsorption capacity is as Figure 14 shown. As the dosage of the adsorbent increases from 0.5 g / L to 3.0 g / L, the adsorption capacity of the PEI-[P(St-GMA)] magnetic polymer microspheres for AF gradually decreases. This is because when the concentration of AF in the solution is constant, when the dosage of the PEI-[P(St-GMA)] magnetic polymer microspheres is less, the more AF molecules are surrounded by the PEI-[P(St-GMA)] magnetic polymer microspheres per unit mass, so the more AF is adsorbed by the magnetic microsphere adsorbent per unit mass and the adsorption capacity is greater.

[0114] At the same time, the removal rate of AF in the solution by the PEI-[P(St-GMA)] magnetic polymer microspheres gradually increases and can be as high as over 94%. This is because the more PEI-[P(St-GMA)] magnetic polymer microspheres there are, the more adsorption sites are provided, which is beneficial to the adsorption of AF, so the removal rate is higher. When the dosage of the PEI-[P(St-GMA)] magnetic polymer microspheres increases to 1.0 g / L and then continues to increase, the increase range of the removal rate changes little. Considering saving the PEI-[P(St-GMA)] magnetic polymer microspheres and ensuring the removal effect of AF in the solution at the same time, the dosage of the adsorbent at the intersection of the removal rate curve and the adsorption capacity curve is selected as the most suitable dosage of the PEI-[P(St-GMA)] magnetic polymer microspheres for adsorbing AF.

[0115] From Figure 14It can be seen that when the dosage of polyethyleneimine-modified magnetic polymer microspheres is reduced from 3.0 g / L to 0.5 g / L, the adsorption capacity of polyethyleneimine-modified magnetic polymer microspheres for dye molecules increases from 50 mg / g to 250 mg / g; when the dosage of polyethyleneimine-modified magnetic polymer microspheres is increased from 0.5 g / L to 3.0 g / L, the removal rate of polyethyleneimine-modified magnetic polymer microspheres for dye molecules increases from 70% to 95%.

[0116] Test Example 3 Effect of adsorption time on the adsorption performance of PEI-[P(St-GMA)] magnetic polymer microspheres (prepared in the example) and ethylenediamine-modified magnetic polymer microspheres (prepared in Comparative Example 3).

[0117] Study the effect of adsorption time on the adsorption of AF by the PEI-[P(St-GMA)] magnetic microspheres prepared in the example to determine the time required to reach adsorption equilibrium. Prepare 100 mg / L and 200 mg / L AF solutions in a conical flask, adjust the pH to 5, add 0.1 g of PEI-[P(St-GMA)] magnetic polymer microspheres, and perform oscillating adsorption at 298 K. Take the supernatant at certain time intervals to measure the concentration of AF in the solution after adsorption, and calculate the adsorption capacity q of the PEI-[P(St-GMA)] magnetic microspheres at different adsorption times t . The experimental results are as Figure 15 shown. Within the initial 30 min, as the adsorption time t increases, the adsorption capacity of the PEI-[P(St-GMA)] magnetic polymer microspheres for AF increases rapidly, and the adsorption is in the rapid stage; after 30 min, as the adsorption time increases, the adsorption curve becomes flat, the increase in adsorption capacity is slow, and the adsorption gradually reaches equilibrium. This is because there are relatively many adsorption vacancies on the surface of the PEI-[P(St-GMA)] magnetic polymer microspheres in the initial stage of adsorption, and the AF ions in the aqueous solution are quickly captured by the abundant amino active adsorption sites on the particle surface, resulting in a relatively fast increase in the adsorption capacity. As the number of active sites of the PEI-[P(St-GMA)] magnetic polymer microspheres gradually decreases and the electrostatic interaction weakens, the acid fuchsin ions are not easily close to the surface of the PEI-[P(St-GMA)] magnetic polymer microspheres, thereby slowing down the increase rate of the adsorption capacity until adsorption equilibrium is reached.

[0118] As Figure 15 shown, when the concentration of dye molecules in the wastewater is 100 mg / L and the adsorption time is 30 min to 120 min, the adsorption capacity of the polyethyleneimine-modified magnetic polymer microspheres for dye molecules is 80 mg / g to 100 mg / g.

[0119] When the concentration of dye molecules in the wastewater is 200 mg / L and the adsorption time is from 30 min to 120 min, the adsorption capacity of polyethyleneimine-modified magnetic polymer microspheres for dye molecules is from 130 mg / g to 175 mg / g.

[0120] As Figure 17 shown, when the concentration of dye molecules in the wastewater is 200 mg / L and the adsorption time is from 30 min to 120 min, the adsorption capacity of ethylenediamine-modified magnetic polymer microspheres for dye molecules is from 90 mg / g to 135 mg / g. The adsorption performance of polyethyleneimine-modified magnetic polymer microspheres is stronger than that of ethylenediamine-modified magnetic polymer microspheres.

[0121] Test Example 4 Effect of temperature on the adsorption performance of PEI-[P(St-GMA)] magnetic polymer microspheres.

[0122] Experimental study on the equilibrium adsorption of dye AF by PEI-[P(St-GMA)] magnetic polymer microspheres prepared in the examples at different temperatures. The experimental data were fitted using the Langmuir and Freundlich adsorption isotherm models to illustrate the adsorption mechanism of PEI-[P(St-GMA)] magnetic polymer microspheres for dye AF. The results are shown in Table 1.

[0123] Langmuir isothermal adsorption equation:

[0124] Freundlich isothermal adsorption equation:

[0125] In the formula: q e is the equilibrium adsorption capacity (mg / g); q m is the maximum adsorption capacity of monolayer adsorption (mg / g); C 0 and C e are the concentrations of fuchsine acid solution at the initial and equilibrium times (mg / L), respectively; b is the adsorption equilibrium constant of the Langmuir model (L / g); K F is an empirical constant (L / g), related to the magnitude of the adsorption capacity; n is related to the interaction strength between the adsorbed molecules and the adsorbent surface.

[0126] Table 1 Langmuir and Freundlich parameters of AF on the magnetic PEI-[P(St-GMA)] polymer microspheres of the examples at different temperatures

[0127] Figure 16 and Table 1 respectively show the isothermal fitting diagrams of the adsorption of AF dye by PEI-[P(St-GMA)] magnetic polymer microspheres and their related parameters. From the R 2 value, it can be seen that both the Langmuir and Freundlich equations well fit the data of the dye AF by PEI-[P(St-GMA)] magnetic polymer microspheres. As can be seen from Table 1, the saturated adsorption capacities of PEI-[P(St-GMA)] magnetic polymer microspheres for the dye AF at 25 °C, 35 °C, and 45 °C are 173.121 mg / g, 208.341 mg / g, and 240.365 mg / g respectively, which are relatively close to the experimental values and the correlation coefficients are relatively high (R 2 > 0.99). The adsorption of the dye AF by PEI-[P(St-GMA)] magnetic polymer microspheres conforms to the Langmuir adsorption isotherm model, which is monolayer adsorption.

[0128] The above is only the preferred embodiment of the present invention, and it is not any other form of limitation to the present invention. Any modification or equivalent change made according to the technical essence of the present invention still belongs to the scope protected by the present invention.

Claims

1. A polyethyleneimine modified magnetic polymer microsphere, characterized in that: The polyethyleneimine modified magnetic polymer microspheres have superparamagnetic Fe3O4 as the core and surface amino functionalized styrene and glycidyl methacrylate copolymer as the shell, wherein the superparamagnetic Fe3O4 is obtained by coprecipitation method and the magnetic polymer microspheres are obtained by dispersion polymerization method; The average particle size of the polyethyleneimine modified magnetic polymer microspheres is 200 to 300 μm, and the magnetization intensity is 18.5 to 35.85 emu / g; The superparamagnetic Fe3O4 accounts for 10.6-25.2% of the mass of the entire polyethyleneimine modified magnetic polymer microspheres.

2. The polyethyleneimine modified magnetic polymer microspheres according to claim 1, characterized in that: The polyethyleneimine modified magnetic polymer microspheres have a -1 , 1087 cm -1 、990 cm -1 The peaks at 1579 cm-1 are the stretching vibration absorption peak of the carbon-carbon unsaturated bond, the stretching vibration absorption peak of the carbon-oxygen bond, and the characteristic absorption peak of the epoxy bond. -1 The peak is the NH deformation vibration absorption peak.

3. The polyethyleneimine modified magnetic polymer microspheres according to claim 1 or 2, characterized in that: In the polyethyleneimine modified magnetic polymer microspheres, the molar number of amino groups in each gram of microspheres is 80 to 260 μmol / g.

4. A method for preparing polyethyleneimine modified magnetic polymer microspheres according to any one of claims 1 to 3, characterized in that: The steps include: Step S1: Preparation of Fe3O4 magnetic fluid by coprecipitation method Step S1-1: Oxidation reaction: a portion of FeCl2·4H2O is dissolved in distilled water and concentrated hydrochloric acid, and then the mixed solution is added to a three-necked flask and heated to 50-55°C. When the speed of the constant speed stirrer is adjusted to 200-300 r / min, hydrogen peroxide is added dropwise until the solution changes color, N2 is introduced into the three-necked flask, and the temperature is increased to 80-95°C to remove excess hydrogen peroxide; Step S1-2: When the reaction solution obtained in step 1-1 is cooled to 55-65°C, the remaining FeCl2·4H2O is dissolved in concentrated hydrochloric acid and distilled water and then added to a three-necked flask; Step S1-3: coprecipitation reaction: when the speed of the constant speed stirrer is adjusted to 300-600 r / min, a NaOH solution is rapidly added dropwise using a separatory funnel to cause a coprecipitation reaction between the divalent iron ions and the trivalent iron ions under alkaline conditions to generate Fe3O4 nanoparticles; Step S1-4: When the speed of the constant speed stirrer is adjusted to 150-200 r / min, the surfactant solution is slowly added dropwise using a separatory funnel. After the addition is completed, N2 is introduced into the three-necked flask, stirred, and the reaction solution is alternately washed with distilled water and a solvent until it is neutral to obtain Fe3O4 magnetic fluid (i.e., superparamagnetic Fe3O4); Step S2: Preparation of magnetic polymer microspheres by dispersion polymerization Step S2-1: uniformly dispersing the Fe3O4 magnetic fluid in a dispersant and a solvent at 55-65°C, and raising the temperature of the mixture to 72-88°C; Step S2-2: Free radical polymerization and cross-linking reaction Slowly adding a mixed solution containing a polymerization monomer, a functional monomer, an initiator, and a cross-linking agent into the mixture of the above-mentioned Fe3O4 magnetic fluid, under stirring conditions, the initiator is thermally decomposed to generate free radicals, which initiate a free radical polymerization reaction of the polymerization monomer on the surface of the magnetic fluid; as the polymerization reaction proceeds, the polymer chain continues to grow, and a cross-linking reaction occurs between the polymer chains, and finally a magnetic polymer microsphere with the magnetic fluid as the core and the polymer as the shell is formed; Step S3: Preparation of amino-functionalized magnetic polymer microspheres Dissolve polyethyleneimine in a mixed solvent of at least one of 1,4-dioxane, tetrahydrofuran, dimethylformamide, ethylene glycol dimethyl ether and water, then place the magnetic polymer microspheres in the obtained mixed solution to fully swell, and then carry out a grafting reaction at 80-90° C. for 6-15 h. After the reaction, filter out the microspheres, wash them with distilled water for multiple times, and vacuum dry them at 50-60° C. to obtain amino-functionalized magnetic polymer microspheres.

5. The preparation method according to claim 4, characterized in that: The mass ratio of FeCl2·4H2O in step S1-1 and step S1-2 is (1:0.4) to (1:0.75).

6. The preparation method according to claim 5, characterized in that: In step S1-1 and step S1-2, in the oxidation reaction, the mass ratio of concentrated hydrochloric acid, FeCl2·4H2O and distilled water is (1:2:20) to (1:4:40).

7. The preparation method according to claim 5, characterized in that: In step S1-4, the mass ratio of sodium dodecyl sulfate, polyethylene glycol (6000), water and ethanol is (1:2:10:20) to (1:4:40:60).

8. The preparation method according to claim 5, characterized in that: In step S2-1, the mass ratio of the dispersant, the Fe3O4 magnetic fluid and the solvent is (1:4:40) to (1:15:100).

9. The preparation method according to claim 5, characterized in that: In step S2-2, the mass ratio of the cross-linking agent, the functional monomer, the initiator and the polymerization monomer is (1:1:1.5:5) to (1:2:3:12).

10. A method for adsorption decolorization of polyethyleneimine modified magnetic polymer microspheres according to any one of claims 1 to 3, characterized in that: The polyethyleneimine modified magnetic polymer microspheres are used to adsorb dye molecules in wastewater, and the dye molecules have at least one of the functional groups such as sulfonic acid group, mercapto group, carboxyl group and the like.

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