A preparation method and application of Co@PA6-PEI / GO heavy metal adsorbent material

Abstract

This invention relates to the field of water treatment technology and adsorption materials, and discloses a method for preparing and applying a Co@PA6-PEI / GO heavy metal adsorption material. Magnetic Co@PA6 microspheres are prepared using a reaction-induced phase inversion method. The surface carboxyl group density is increased through alkaline hydrolysis. Branched polyethyleneimine (PEI) is covalently grafted onto the microsphere surface using EDC / NHS coupling chemistry, achieving surface amination modification. This method organically combines the magnetic separation performance of Co@PA6 microspheres, the chelating adsorption performance of PEI, and the high specific surface area advantage of GO, resulting in a material with uniform particle size, stable structure, magnetic recyclability, and adjustable heavy metal adsorption capacity, particularly for Pb. 2+ Cu 2+ Cd 2+ Zn 2+ Cr 6+ It exhibits excellent adsorption performance for heavy metal ions, with adsorption capacity adjustable in the range of 290-348 mg / g, and also has good recycling performance.

Description

Technical Field

[0001] This invention belongs to the field of environmental remediation materials and water treatment technology, specifically relating to a method for preparing and applying a novel Co@PA6-PEI / GO heavy metal adsorption material. This composite material can be used for the efficient adsorption and removal of heavy metal ions in water. Background Technology

[0002] Heavy metal pollution is a serious environmental problem today, especially the accumulation of heavy metal ions (such as Cu²⁺, Pb²⁺, Cd²⁺, Zn²⁺, etc.) in water bodies. These ions are highly toxic, non-degradable, and bioaccumulative, posing a serious threat to ecosystems and human health. Therefore, developing efficient, economical, and environmentally friendly heavy metal adsorbents is of great significance.

[0003] Among existing adsorption technologies, adsorption is considered the most promising method due to its advantages such as simple operation, low cost, high efficiency, and no secondary pollution. Single materials (such as activated carbon and zeolite) often face problems such as limited adsorption capacity, insufficient selectivity, and separation difficulties. Magnetic polymer microspheres combine the advantages of traditional polymer microspheres (large specific surface area and highly designable surface functional groups) with the magnetic response characteristics of magnetic nanoparticles, achieving rapid magnetic separation and recovery of adsorbents. PA6 microspheres, due to their excellent mechanical properties, chemical stability, and surface chemical activity, have been applied in catalysis, drug carriers, and other fields, and can be used in environmental remediation. However, PA6 microspheres have a relatively low specific surface area, limited adsorption capacity for metal ions, and insufficient selectivity, which restricts their application in complex systems.

[0004] Carbon materials are widely used in the treatment of wastewater containing heavy metal ions due to their high adsorption capacity, high chemical stability, relatively low cost, and ease of modification. Graphene oxide (GO), as a carbon material with great adsorption potential, is highly favored due to its oxygen-containing functional groups on the surface and its good hydrophilicity. Literature reports that GO can adsorb heavy metal ions at a capacity of 150-300 mg / g. However, GO as an adsorbent suffers from problems such as difficulty in recovery due to its powdered form and the limited variety of surface functional groups. These issues, to some extent, limit its adsorption performance.

[0005] In recent years, researchers have attempted to combine different materials to leverage their synergistic advantages. Patent CN201710150745.6 discloses a magnetic adsorption material and its preparation method, which combines magnetic particles with porous materials to form a magnetic adsorbent. However, this method has the following shortcomings: (1) the material structure is simple and the types of adsorption sites are limited; (2) there is still room for improvement in adsorption capacity and selectivity; (3) the density of surface functional groups cannot be controlled, which limits its applicability in different application scenarios. Patent WO2014094130A1 discloses a method for using magnetic GO to remove heavy metals, but this material is only a binary composite structure and does not achieve controllability of adsorption capacity.

[0006] Polyethyleneimine (PEI) is a polymer rich in amino groups. Its primary, secondary, and tertiary amino groups can form chelates with heavy metal ions, making them ideal functional groups for heavy metal adsorption. However, direct application of PEI suffers from high water solubility and difficulty in recovery. Immobilizing PEI on a solid support can solve this problem, but existing methods mostly employ physical adsorption, resulting in poor stability and easy detachment. EDC / NHS coupling chemistry is a mature covalent bonding method widely used in biomolecule immobilization, but its application in the surface modification of magnetic polymer microspheres is less studied. Summary of the Invention

[0007] This invention aims to overcome the shortcomings of existing technologies and provide a method for preparing and applying Co@PA6-PEI / GO heavy metal adsorbent materials. It combines magnetic fillers with polymer microspheres, immobilizes PEI through covalent grafting, and then composites it with GO. Through rational material and structural design, a highly efficient, environmentally friendly, magnetically recyclable heavy metal ion adsorbent material with adjustable surface amino density is obtained. Specifically, branched polyethyleneimine (PEI) of different molecular weights is covalently grafted onto the surface of Co@PA6 microspheres using an EDC / NHS coupling chemical method, achieving surface amino modification. PEI molecules contain abundant primary (-NH2), secondary (-NH-), and tertiary (-N-) amino groups, which readily protonate and acquire a positive charge in aqueous solution. By selecting different molecular weights of PEI (e.g., 600, 1800, 10000 Da), the number and density of amino groups on the PA6 microsphere surface can be precisely controlled. The modified Co@PA6-PEI microspheres have a positively charged surface and are firmly bonded to the negatively charged GO through electrostatic attraction, forming a Co@PA6-PEI / GO composite material. Amino groups can bind to heavy metal ions through mechanisms such as complexation, electrostatic attraction, and ion exchange; therefore, the final amount of heavy metal ion adsorption can be controlled by adjusting the molecular weight of PEI.

[0008] The key innovations of this invention are: (1) Co powder is encapsulated in situ inside PA6 microspheres by reaction-induced phase inversion method to obtain a highly magnetic carrier; (2) PEI is covalently grafted by EDC / NHS coupling chemistry, which is more stable than physical adsorption; (3) A ternary composite structure is constructed, which organically combines magnetic separation performance, chelate adsorption performance and high specific surface area advantages; (4) The adsorption capacity is controllable by the molecular weight of PEI.

[0009] The technical solution of the present invention is as follows: A method for preparing a Co@PA6-PEI / GO heavy metal adsorbent material includes the following steps: Co@PA6 microspheres are prepared by in-situ polymerization-induced phase inversion method, alkaline hydrolysis is performed on them to increase the surface carboxyl group density, the surface carboxyl groups are activated by EDC / NHS, and the surface of Co@PA6 microspheres is modified by amino-containing PEI through covalent bonding, and then combined with GO through electrostatic adsorption to obtain the Co@PA6-PEI / GO composite material.

[0010] The preparation method includes the following steps: (1) Disperse nano-magnetic Co powder in caprolactam monomer by ultrasonication to obtain Co / CL suspension; add polyethylene glycol to Co / CL suspension under vacuum or protective atmosphere, and stir at 120~140℃ for 2~4h to obtain mixed solution; add initiator to mixed solution, then remove water under vacuum at 130~160℃ for 20~40min, then add activator, and polymerize at 150~200℃ for 20~60min. The system undergoes phase inversion to obtain Co@PA6 / PEG alloy. After crushing the alloy, wash with water for 24~48h, filter under vacuum, and dry to obtain Co@PA6 microspheres.

[0011] (2) Co@PA6 microspheres were subjected to mild hydrolysis in alkaline solution for 15-60 min. After washing until neutral, Co@PA6 microspheres were dispersed in MES buffer, and EDC and NHS were added and reacted for 1-4 h to convert the surface carboxyl groups into NHS activated esters to obtain Co@PA6-COO-NHS. (3) The Co@PA6-COO-NHS microspheres obtained in step (2) were immediately dispersed in PBS buffer, and branched polyethyleneimine (PEI) was added. PEI was covalently grafted onto the surface of PA6 microspheres via amide bonds through a nucleophilic substitution reaction to obtain Co@PA6-PEI. After washing and drying, the Co@PA6-PEI aqueous dispersion was obtained by dispersing it in deionized water. (4) Disperse GO in deionized water and stir ultrasonically to form a uniform dispersion. Slowly add the Co@PA6-PEI aqueous dispersion from step (3) to the GO aqueous dispersion. Stir so that the positively charged Co@PA6-PEI microspheres and the negatively charged GO are combined by electrostatic attraction. After filtration and drying, Co@PA6-PEI / GO composite microspheres are obtained.

[0012] In a further embodiment, the nano-magnetic Co powder has a particle size of 50-200 nm and a purity of ≥99%; the polyethylene glycol has a molecular weight of at least one of PEG2000, PEG4000, PEG6000, and PEG8000, preferably PEG4000; the amounts of polyethylene glycol and caprolactam are 15-25% and 75-85% of the total mass of polyethylene glycol and caprolactam, respectively, preferably 20% and 80%, respectively.

[0013] In a further embodiment, the initiator is an alkali metal hydride, alkali metal hydroxide, alkali metal alkoxide, or alkali metal carbonate, preferably sodium hydroxide. The preferred amount added is 0.1-1 wt% of the total mass of caprolactam and polyethylene glycol; the activator is an isocyanate, acyl chloride, acid anhydride, or acylcaprolactam, preferably toluene diisocyanate. The preferred amount added is 0.1-1 wt% of the total mass of caprolactam and polyethylene glycol.

[0014] In a further embodiment, the alkaline solution is a 0.05~0.2wt% NaOH solution or a 0.05~0.2wt% KOH solution; the alkaline hydrolysis temperature is 40~80℃, preferably 60℃; and the alkaline hydrolysis time is 15~60 min, preferably 30 min.

[0015] In a further embodiment, the concentration of EDC is 0.1~0.5wt%, and the concentration of NHS is 0.025~0.1wt%; the pH value of the MES buffer is preferably 5.5; the molar ratio of EDC to NHS is preferably 4:1; the reaction temperature is preferably 25℃; and the reaction time is preferably 2h.

[0016] In a further embodiment, the amount of PEI added is preferably 10-20 wt% of the mass of PA6 microspheres; the pH value of the PBS buffer is 7.4; the reaction temperature is preferably 25-30℃; and the reaction time is preferably 10-16 h.

[0017] In a further embodiment, the preferred mass ratio of Co@PA6-PEI to GO is 1:10; the preferred stirring speed is 1000~2000 r / min; and the preferred stirring time is 2~3h.

[0018] In a further embodiment, the GO aqueous dispersion is preferably at a concentration of 2 mg / mL.

[0019] The technical solution of this invention is further detailed as follows: (1) Nano-magnetic Co powder is ultrasonically dispersed in caprolactam (CL) monomer to obtain Co / CL suspension, with the mass ratio of Co powder to CL being 1:5~1:15; under vacuum or protective atmosphere, polyethylene glycol is added to Co / CL suspension and stirred at 120~140℃ for 2~4h; after adding initiator, water is removed under vacuum at 130~160℃ for 20~40min; then an activator is added and polymerized at 150~200℃ for 20~60min, and the system undergoes phase inversion to obtain Co@PA6 / PEG alloy; after high-speed pulverization and washing, micron-sized Co@PA6 microspheres with a particle size of 20-25μm are obtained, and the saturation magnetization of the Co@PA6 microspheres is 15~35 emu / g; (2) The Co@PA6 microspheres were subjected to mild hydrolysis in an alkaline solution to increase the surface carboxyl group density to 0.3~0.8 mmol / g, and washed until neutral before use; (3) Disperse the Co@PA6 microspheres obtained in step (2) in MES buffer, add 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS), and react to convert the surface carboxyl groups into NHS activated esters to obtain Co@PA6-COO-NHS. (4) The Co@PA6-COO-NHS microspheres obtained in step (3) were immediately dispersed in PBS buffer, and branched polyethyleneimine (PEI) was added. PEI was covalently grafted onto the surface of PA6 microspheres through amide bonds via a nucleophilic substitution reaction to obtain Co@PA6-PEI. After washing and drying, the Co@PA6-PEI aqueous dispersion was obtained by dispersing it in deionized water. (5) Disperse graphene oxide (GO) in deionized water and stir ultrasonically to form a uniform dispersion (1~3 mg / mL). Slowly add the Co@PA6-PEI aqueous dispersion from step (4) to the GO aqueous dispersion. Stir so that the positively charged Co@PA6-PEI microspheres and the negatively charged GO are combined by electrostatic attraction. After filtration and drying, Co@PA6-PEI / GO composite microspheres are obtained.

[0020] In step (3), the concentration of EDC is 0.1~0.5wt%, the concentration of NHS is 0.025~0.1wt%, the pH of MES buffer is 4.5~6.0, the reaction temperature is 20~30℃, the reaction time is 1~4 h, the molar ratio of EDC to NHS is 2:1~5:1, and the molar ratio of EDC to carboxyl groups on the surface of PA6 microspheres is 3:1~10:1. The molecular weight of the branched PEI mentioned in step (4) is selected from one or more combinations of 600 Da, 1800 Da, and 10000 Da. By adjusting the molecular weight of PEI, the adsorption capacity of the composite material for heavy metal ions can be precisely controlled. The amount of PEI added is 5~30 wt% of the mass of PA6 microspheres. The pH value of PBS buffer is 7.0~8.0. The reaction temperature is 20~40℃ and the reaction time is 8~24 h. After the reaction in step (4) is completed, it is necessary to wash with deionized water until neutral, wash with EDTA solution to remove trace metal ions, and then wash with deionized water. The number of washings is not less than 5 times. In step (5), the mass ratio of Co@PA6-PEI to GO is 1:5 to 1:15; the stirring speed is 500 to 3000 r / min and the stirring time is 1 to 3 h; the GO is prepared by the Hummers method, washed until neutral and then sonicated in deionized water for 1 to 3 h to form a dispersion with a concentration of 1 to 3 mg / mL.

[0021] This invention further protects a PEI-grafted modified Co@PA6-PEI / GO composite microsphere prepared using the method described above. This composite microsphere has the following characteristics: (1) Particle size range 20-25μm, with uniform particle size distribution; (2) The saturation magnetization is 10~30 emu / g, and it can be quickly separated by an external magnetic field; (3) The surface amino density is 1.5~5.0 mmol / g, which can be controlled by the molecular weight of PEI; (4) The specific surface area of ​​BET is 80~150 m² / g.

[0022] The application of the composite microspheres in removing heavy metals from wastewater containing heavy metal ions.

[0023] The heavy metal ions include Pb. 2+ Cu 2+ Cd 2+ Zn 2+ Cr 6+ One or more of the following; the adsorption conditions are: pH 4~7, temperature 15~40℃, adsorbent dosage 0.3~1.0 g / L, and adsorption time 0.5~4h.

[0024] The adsorption capacity of this composite microsphere for different heavy metal ions can be controlled by the molecular weight of PEI, and for Pb... 2+ The adsorption capacity is 290~348 mg / g, for Cu 2+ The adsorption capacity is 215~330 mg / g, for Cd 2+ The adsorption capacity is 185~235 mg / g, for Cr 6+The adsorption capacity is 120~165 mg / g; it can be reused after elution with 0.1~0.5wt% HCl solution, and the adsorption efficiency remains above 85% after 5 cycles.

[0025] The advantages of this invention compared to the prior art are as follows: 1. Application Innovation: This invention is the first to propose the organic combination of PA6 microspheres with magnetic Co powder, PEI, and GO for the adsorption of heavy metal ions. Compared with single PA6 microspheres, the adsorption capacity is increased by 5-8 times. Compared with pure magnetic GO materials, the composite material of this invention has higher mechanical strength and chemical stability, filling the gap in the application of magnetic PA6 microspheres in water treatment. Furthermore, through reasonable material and structural design, a Co@PA6-PEI / GO composite material with excellent adsorption performance was prepared.

[0026] 2. Methodological Innovation: This invention employs anion reaction-induced phase inversion, where the presence of PEG induces phase inversion of Cl, encapsulating Co powder to obtain uniformly sized, highly magnetic Co@PA6 microspheres. The highly magnetic Co@PA6-PEI / GO composite material is more easily and rapidly recovered via magnetic force after adsorbing heavy metal ions (solid-liquid separation completed within 1-2 minutes), avoiding the secondary pollution problems of traditional adsorption materials and significantly reducing operating costs.

[0027] 3. Structural Innovation: This invention innovatively combines two-dimensional sheet-like GO with three-dimensional Co@PA6 microspheres, effectively preventing GO aggregation and fully leveraging the high specific surface area advantage of GO (the composite material's specific surface area can reach 80-150 m² / g), thereby improving the adsorption efficiency for heavy metal ions. The combination of Co@PA6 microspheres with excellent mechanical properties and chemical corrosion resistance with GO provides mechanical support for the GO, improving the aggregation problem when GO is used alone and further enhancing the chemical stability of the composite material during adsorption. This makes it suitable for treating heavy metal pollution in complex water bodies (maintaining stability within the pH range of 2-10).

[0028] 4. Adjustable Performance: This invention utilizes PEI of different molecular weights to modify Co@PA6 microspheres, enabling precise control of the adsorption capacity of different heavy metal ions by altering the amino group density in the Co@PA6-PEI / GO composite material. By modifying Co@PA6 microspheres with PEI of different molecular weights and then combining them with GO, Co@PA6-PEI / GO composite materials with different amino group densities are prepared. Amino groups can form complexes with heavy metal ions; therefore, the final heavy metal ion adsorption content can be continuously and precisely controlled by adjusting the amino group density on the surface of the Co@PA6 microspheres.

[0029] 5. Innovative Covalent Grafting Technology: This invention innovatively employs EDC / NHS coupling chemistry to achieve covalent bonding between PEI and the surface of Co@PA6 microspheres, forming stable amide bonds. Compared to physical adsorption or electrostatic adsorption, covalent bonding results in a robust PEI bonding layer (PEI detachment rate <5% after 5 cycles). Furthermore, both the EDC / NHS activation and PEI grafting reactions are carried out entirely in aqueous solution, offering advantages such as no need for organic solvents, mild reaction conditions, low energy consumption, and no VOC emissions. This aligns with green chemistry principles and significantly reduces environmental burden and production costs. Attached Figure Description

[0030] Figure 1 Adsorption mechanism diagram of Co@PA6-PEI / GO composite material.

[0031] Figure 2 Scanning electron microscope image of Co@PA6 microspheres Figure 3 The image shows the adsorption effect of the Co@PA6-PEI(1.8k) / GO composite material prepared in Example 2 on Cu2+ within a reaction time of 0-240 min.

[0032] Figure 4 The graph shows the magnetic adsorption efficiency and cyclic regeneration performance of the Co@PA6-PEI(600) / GO composite material prepared in Example 3. Detailed Implementation

[0033] The present invention is further described below through specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0034] Example 1 Step 1: Preparation of carboxylated Co@PA6 microspheres 8g of nano-Co powder was added to 80g of caprolactam monomer, and the mixture was ultrasonically treated in a water bath at 85℃ for 45min to obtain a suspension. Under a nitrogen atmosphere, 20g of PEG4000 was added to the suspension, and the mixture was stirred at 120℃ for 3h to obtain a mixed solution. This mixed solution was placed in a heating mantle at 150℃ for vacuum dehydration for 30min. Zeolite and 0.4g of NaOH were added, and dehydration was continued for another 30min. 0.6g of TDI was added, and the mixture was rapidly and vigorously shaken before being poured into a mold at 180℃ for polymerization for 30min. The Co@PA6 / PEG alloy was pulverized using a high-speed pulverizer and then soaked in water for 48h to etch the PEG phase. The dissolved PEG in the water was removed by vacuum filtration, and the mixture was dried in an oven at 120℃ for 48h to obtain Co@PA6 microspheres (average particle size 22.5μm, saturation magnetization 25 emu / g). 10 g of Co@PA6 microspheres were dispersed in 200 mL of 0.1 wt% NaOH solution and stirred at 60 °C for 30 min for alkaline hydrolysis. The microspheres were washed with deionized water until neutral and then vacuum filtered to obtain Co@PA6-COOH microspheres. The Co@PA6-COOH microspheres were dispersed in MES buffer (pH 5.5, 100 mL) and sonicated for 30 min to ensure complete dispersion. EDC (0.2 wt%, 20 mmol) and NHS (0.05 wt%, 5 mmol) were added, and the mixture was magnetically stirred at 25 °C for 2 h, converting the surface carboxyl groups to NHS-activated esters. After multiple washes and filtrations, Co@PA6-COO-NHS microspheres were obtained.

[0035] Step 2: PEI grafting reaction (PEI 10000) 2 g of PEI 10000 (equivalent to 20 wt% of the PA6 microspheres) was dissolved in 20 mL of PBS buffer (pH 7.4). Co@PA6-COO-NHS microspheres were dispersed in 100 mL of PBS, and the PEI solution was added dropwise. The mixture was stirred at 25 °C for 12 h. After centrifugation and washing, the microspheres were washed with EDTA (0.01 wt%) solution and finally washed with deionized water until neutral. The microspheres were then vacuum dried to obtain Co@PA6-PEI(10k) powder.

[0036] Step 3: Combining with GO Co@PA6-PEI(10k) powder was dispersed in deionized water (solid content 2wt%) and ultrasonically dispersed for 1 h to obtain a uniform milky white dispersion. A 2 mg / mL GO aqueous dispersion was prepared, controlling the mass ratio of GO to Co@PA6-PEI(10k) to be 10:1. The Co@PA6-PEI(10k) aqueous dispersion was slowly added dropwise to the GO aqueous dispersion, and the mixture was stirred for 3 h. After washing and drying, a black Co@PA6-PEI(10k) / GO composite material was obtained.

[0037] Step 4: Adsorption performance test The Co@PA6-PEI(10k) / GO composite material obtained in this embodiment was used for the treatment of heavy metals in sewage / wastewater. 50 mg of the Co@PA6-PEI(10k) / GO composite material was added to 100 ml of 100 mg / L Pb solution at pH 6. 2+ In ionized wastewater, adsorption was performed at 25℃ and an oscillation rate of 180 r / min for 24 h. ICP-MS analysis showed the residual concentration reached a maximum adsorption capacity of 345 mg / g ± 10 mg / g. The adsorbed material could be completely separated within 1.5 minutes using an external magnetic field. After elution with 0.2 wt% HCl solution, the material could be reused, maintaining 92% of its adsorption capacity after 5 cycles.

[0038] Example 2 Step 1 is the same as in Example 1.

[0039] Step 2: PEI grafting reaction (PEI 1800) 1.5 g of PEI 1800 (equivalent to 15 wt% of the PA6 microspheres) was dissolved in 20 mL of PBS buffer (pH 7.4). Co@PA6-COO-NHS microspheres were dispersed in 100 mL of PBS, and the PEI solution was added dropwise. The mixture was stirred at 30 °C for 16 h. After centrifugation and washing, the microspheres were washed with EDTA (0.01 wt%) solution and finally washed with deionized water until neutral. The microspheres were then vacuum dried to obtain Co@PA6-PEI(1.8k) powder.

[0040] Step 3: Same as Example 1 Step 4: Adsorption kinetics test The Co@PA6-PEI(1.8k) / GO composite material obtained in this embodiment was used to treat heavy metals in wastewater / sewage with different contact times. A Cu concentration of 200 mg / L was prepared. 2+ The solution was adjusted to pH 6, and 50 mg of the composite material was added to 100 mL of Cu. 2+ In solution, adsorption was performed with shaking at 25℃ and 180 r / min. The adsorption effect of Co@PA6-PEI(1.8k) / GO composite material on Cu(II) was compared within the reaction time range of 0-240 min. Figure 3 As shown in the figure. The results indicate that adsorption proceeds rapidly in the first 60 minutes, reaches equilibrium after 120 minutes, and has a maximum adsorption capacity of 321 ± 12 mg / g, conforming to a pseudo-second-order kinetic model. Pb adsorption was performed. 2+ Adsorption tests, under the same conditions as in Example 1, showed an adsorption capacity of 318 ± 12 mg / g.

[0041] Example 3 Step 1 is the same as in Example 1.

[0042] Step 2: PEI grafting reaction (PEI 600) 1 g of PEI 600 (equivalent to 10 wt% of the PA6 microspheres) was dissolved in 20 mL of PBS buffer (pH 7.4). Co@PA6-COO-NHS microspheres were dispersed in 100 mL of PBS, and the PEI solution was added dropwise. The mixture was stirred at 25 °C for 10 h. After centrifugation and washing, the mixture was washed with EDTA (0.01 wt%) solution and finally washed with deionized water until neutral. The mixture was then vacuum dried to obtain Co@PA6-PEI(600) powder.

[0043] Step 3: Same as Example 1 Step 4: Cyclic Regeneration Performance Test The magnetic separation cycle stability performance of the Co@PA6-PEI(600) / GO composite material obtained in this embodiment was determined.

[0044] At pH=6, the initial Cr 6+ At a concentration of 200 mg / L and an experimental temperature of 25 °C, Co@PA6-PEI(600) / GO microspheres were used to adsorb Cr. 6+ The microspheres were then recovered using an external magnetic field (magnetic separation time approximately 1.5 minutes). After desorption of the collected composite microspheres using a 0.2 wt% HCl aqueous solution for 30 minutes, the microspheres were cycled for adsorption five times. Figure 4 As shown in the figure. The results indicate that the adsorption capacity was maintained at 99%–95% of the initial adsorption capacity during the first and second cycles. After five cycles, the adsorption capacity decreased, gradually decreasing from 100% to 89.7%, demonstrating good cycling stability. (The last sentence appears to be incomplete and possibly refers to a separate process involving Pb.) 2+ Adsorption test: Under the same conditions as in Example 1, the adsorption capacity was 290±15 mg / g. Example 4

[0045] Step 1 is the same as in Example 1. Step 2: PEI grafting reaction (mixing PEI 1800 and PEI 10000) Co@PA6-COO-NHS microspheres were dispersed in PBS buffer, and a mixture of PEI 1800 (1.0 g) and PEI 10000 (0.5 g) was added, with a total amount equivalent to 15 wt% of the PA6 microspheres. The mixture was stirred at 30 °C for 14 h. After centrifugation and washing, the mixture was washed with EDTA (0.01 wt%) solution and finally washed with deionized water until neutral. The mixture was then vacuum dried to obtain Co@PA6-PEI (1.8 kJ / 10 kJ) powder.

[0046] Step 3 is the same as in Example 1. Step 4: Adsorption performance test The Co@PA6-PEI(1.8k / 10k) / GO composite material obtained in this example was used for the treatment of heavy metals in wastewater. Under the same experimental conditions as in Example 1, the adsorption capacity of the Co@PA6-PEI(1.8k / 10k) / GO composite material for Pb²⁺ was 335±8 mg / g, which is between that of Example 1 and Example 2, verifying the continuous adjustability of the adsorption capacity.

[0047] Comparative Example 1 Pb was carried out using unmodified pure Co@PA6 microspheres. 2+ Adsorption tests, under the same conditions as in Example 1, showed an adsorption capacity of only 45 mg / g, demonstrating that the introduction of PEI and GO significantly improved the adsorption performance.

[0048] Comparative Example 2 A Co@PA6-PEI (physical adsorption) / GO composite material was prepared by loading PEI onto the surface of Co@PA6 microspheres using a physical adsorption method (without EDC / NHS coupling). The initial adsorption capacity was similar to that of Example 1 (340 mg / g), but after 5 cycles, the adsorption capacity decreased to 210 mg / g, with a retention rate of only 61.8%, which was much lower than that of the covalent grafting method (92%), demonstrating the superiority of covalent grafting.

[0049] Comparative Example 3 Pb using pure GO 2+ Adsorption tests showed an adsorption capacity of 182 mg / g, but recovery was difficult due to centrifugation time exceeding 15 minutes, and magnetic separation was unsuccessful. This demonstrates the necessity of introducing a magnetic Co@PA6 support.

[0050] Table 1. Effects of different materials on Pb 2+ Adsorption performance comparison Material Adsorption capacity (mg / g) Magnetic separation time (min) Retention rate (%) after 5 cycles Example 1 345±10 1.5 92.0 Example 2 318±12 1.5 89.7 Example 3 290±15 1.5 87.2 Example 4 335±8 1.5 90.6 Comparative Example 1 45 1.5 95 Comparative Example 2 340 1.8 61.8 Comparative Example 3 182 - - As can be seen from Table 1, the Co@PA6-PEI / GO composite material prepared in this invention has the advantages of high adsorption capacity, rapid magnetic separation and good cycling stability, and its overall performance is better than that of the comparative materials.

[0051] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing a Co@PA6-PEI / GO heavy metal adsorbent material, comprising the following steps: (1) The nano-magnetic Co powder was ultrasonically dispersed in caprolactam (CL) monomer to obtain Co / CL suspension. Polyethylene glycol was added to Co / CL suspension, and initiator and activator were added. Polymerization was carried out for 20~60 min, and the system underwent phase inversion to obtain Co@PA6 / PEG alloy. Micron-sized Co@PA6 microspheres were obtained by pulverization; (2) The Co@PA6 microspheres were hydrolyzed in an alkaline solution to increase the surface carboxyl group density to 0.3~0.8 mmol / g; (3) Disperse the Co@PA6 microspheres obtained in step (2) in MES buffer, add 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS) to obtain Co@PA6-COO-NHS microspheres; (4) Disperse the Co@PA6-COO-NHS microspheres obtained in step (3) in PBS buffer, add branched polyethyleneimine (PEI), and undergo nucleophilic substitution reaction to obtain Co@PA6-PEI aqueous dispersion; (5) Co@PA6-PEI aqueous dispersion was added dropwise to graphene oxide (GO) aqueous dispersion and stirred so that the positively charged Co@PA6-PEI microspheres and the negatively charged GO were combined by electrostatic attraction to obtain Co@PA6-PEI / GO composite microspheres.

2. The preparation method according to claim 1, characterized in that, The nano-magnetic Co powder mentioned in step (1) has a particle size of 50~200nm and a purity of ≥99%; the molecular weight of polyethylene glycol is at least one or a combination of PEG2000, PEG4000, PEG6000, and PEG8000. The amounts of polyethylene glycol and caprolactam used are 15-25% and 75-85% of the total mass of polyethylene glycol and caprolactam, respectively.

3. The preparation method according to claim 1, characterized in that, The initiator mentioned in step (1) is an alkali metal hydride, alkali metal hydroxide, alkali metal alkoxide, or alkali metal carbonate; the amount of initiator added is 0.1 to 1 wt% of the total mass of polyethylene glycol and caprolactam; the activator is an isocyanate, acyl chloride, acid anhydride, or acylcaprolactam; the amount of activator added is 0.1 to 1 wt% of the total mass of polyethylene glycol and caprolactam.

4. The preparation method according to claim 1, characterized in that, The alkaline solution mentioned in step (2) is a 0.05~0.2wt% NaOH solution or a 0.05~0.2wt% KOH solution; the alkaline hydrolysis temperature is 40~80℃ and the time is 15~60 min; In step (3), the concentration of EDC is 0.1~0.5wt%, the concentration of NHS is 0.025~0.1wt%, the pH of MES buffer is 4.5~6.0, the reaction temperature is 20~30℃, the reaction time is 1~4 h, the molar ratio of EDC to NHS is 2:1~5:1, and the molar ratio of EDC to carboxyl groups on the surface of PA6 microspheres is 3:1~10:

1. The molecular weight of the branched PEI mentioned in step (4) is selected from one or more combinations of 600 Da, 1800 Da, and 10000 Da. By adjusting the molecular weight of PEI, the adsorption capacity of the composite material for heavy metal ions can be precisely controlled. The amount of PEI added is 5~30 wt% of the mass of PA6 microspheres. The pH value of PBS buffer is 7.0~8.

0. The reaction temperature is 20~40℃ and the reaction time is 8~24 h. After the reaction in step (4) is completed, it is necessary to wash with deionized water until neutral, wash with EDTA solution to remove trace metal ions, and then wash with deionized water. The number of washings is not less than 5 times. In step (5), the mass ratio of Co@PA6-PEI to GO is 1:5 to 1:15; the stirring speed is 500 to 3000 r / min and the stirring time is 1 to 3 h; the GO is prepared by the Hummers method, washed until neutral and then sonicated in deionized water for 1 to 3 h to form a dispersion with a concentration of 1 to 3 mg / mL.

5. A Co@PA6-PEI / GO composite microsphere prepared by the method described in any one of claims 1 to 4.

6. The composite microspheres according to claim 5, characterized in that, The composite microspheres have a particle size range of 20-25 μm and a uniform particle size distribution; the saturation magnetization is 10-30 emu / g, and they can be rapidly separated by an external magnetic field; the surface amino density is 1.5-5.0 mmol / g, which can be controlled by the molecular weight of PEI; and the BET specific surface area is 80-150 m² / g.

7. The application of the composite microspheres according to claim 5 or 6 in the removal of heavy metals from wastewater containing heavy metal ions.

8. The application according to claim 7, characterized in that, The heavy metal ions include one or more of Pb 2+ , Cu 2+ , Cd 2+ , Zn 2+ , Cr 6+ ; the adsorption conditions are: pH 4~7, temperature 15~40℃, adsorbent dosage 0.3~1.0 g / L, adsorption time 0.5~4h.

9. The application according to claim 7, characterized in that, The adsorption capacity of this composite microsphere for different heavy metal ions can be controlled by the molecular weight of PEI, and for Pb... 2+ The adsorption capacity is 290~348 mg / g, for Cu 2+ The adsorption capacity is 215~330 mg / g, for Cd 2+ The adsorption capacity is 185~235 mg / g, for Cr 6+ The adsorption capacity is 120~165 mg / g; it can be reused after elution with 0.1~0.5wt% HCl solution, and the adsorption efficiency remains above 85% after 5 cycles.

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