Magnetic imidazolyl composite material, preparation method thereof and application thereof in enrichment and degradation of pet microplastics
By modifying the surface of composite materials with Fe3O4 as the magnetic core and grafting imidazole functional groups, we have achieved efficient enrichment and in-situ catalytic degradation of PET microplastics, solving the problems of secondary pollution and resource waste in the treatment of microplastics in water bodies, and realizing efficient and environmentally friendly resource-based treatment.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- NANJING NORMAL UNIVERSITY
- Filing Date
- 2026-03-27
- Publication Date
- 2026-06-26
AI Technical Summary
Existing technologies are insufficient for efficiently enriching and degrading PET microplastics in water, posing risks of secondary pollution and resource waste. Furthermore, existing magnetic separation technologies are difficult to recycle.
Using Fe3O4 as the magnetic core, double bond anchors are introduced by surface modification with silane coupling agent KH-570, and 1-vinylimidazolium is grafted and polymerized to form a magnetic composite material with surface rich in imidazolium functional groups, thereby achieving magnetic response enrichment and in-situ catalytic degradation.
It achieves efficient capture and rapid separation of PET microplastics, with a removal rate of over 90%. The catalyst can be recycled and reused, and the degradation product is the high-value monomer BHETA. The degradation process is green and environmentally friendly.
Smart Images
Figure CN122277829A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of environmental functional materials and the resource utilization technology of polymeric waste, specifically to a magnetic imidazole-based composite material, its preparation method, and its application in enriching and degrading PET microplastics. Background Technology
[0002] The mass production and use of plastic products has led to serious environmental pollution problems. Polyethylene terephthalate (PET), one of the most widely used plastics, is broken down into microplastics (particles smaller than 5 mm) through physical, chemical, and biological processes in the environment, which are now widely distributed in water bodies, soil, and other environmental media. Studies have shown that microplastics can adsorb organic pollutants such as heavy metals, polycyclic aromatic hydrocarbons (PAHs), and polychlorinated biphenyls (PCBs). Plastic fragments containing additives, when ingested by organisms, can have fatal impacts on ecosystems. Due to their tiny size, microplastics are easily ingested by aquatic organisms and transferred through the food chain at the trophic level, ultimately threatening human health.
[0003] Currently, technologies for removing microplastics from water bodies mainly include agglomeration sedimentation, filtration, membrane separation, and adsorption, with the goal of concentrating and removing microplastics from the dispersed medium. Among these, magnetic separation technology, due to its simple operation, high processing capacity, and low sludge production, can be functionalized to endow magnetic nanoparticles with the specific capture ability of target pollutants, thus enriching microplastics from water bodies. However, most existing technologies only achieve phase transfer of pollutants; the enriched microplastics still require subsequent treatment such as landfilling, incineration, or catalytic degradation, posing risks of secondary pollution or resource waste. Therefore, developing an integrated technology that couples efficient microplastic capture with in-situ resource conversion is an ideal approach to achieving sustainable governance of microplastics.
[0004] While existing technologies utilize imidazole compounds to catalyze the depolymerization of PET, these are mostly homogeneous catalytic systems, making catalyst recovery difficult. Furthermore, they are primarily applicable to macroscopic PET waste with regular morphology, and cannot be directly applied to microplastics that are highly dispersed, low in concentration, and difficult to collect. Therefore, there is an urgent need to develop a recyclable material that combines enrichment and catalysis functions to achieve integrated enrichment, degradation, and recycling of PET microplastics in water. Summary of the Invention
[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a magnetic imidazole-based composite material, its preparation method, and its applications. The composite material uses iron(III) oxide (Fe3O4) as the magnetic core, and introduces double bond anchors through surface modification with a silane coupling agent KH-570, followed by graft polymerization of 1-vinylimidazolium to form a magnetic composite material with a surface rich in imidazole functional groups. This composite material possesses both magnetic response enrichment and in-situ catalytic degradation functions, enabling efficient capture, rapid separation, and green depolymerization of PET microplastics in water.
[0006] To achieve the above objectives, the present invention provides the following technical solution:
[0007] This invention provides a magnetic imidazole-based composite material, wherein the material has Fe3O4 as a magnetic core, and the surface is sequentially coated with a KH-570 coupling layer and a polyvinyl imidazole functional layer, and the surface is rich in imidazole functional groups.
[0008] Furthermore, the saturation magnetization of the composite material is 90-110 emu / g; the removal rate of PET microplastics reaches over 90%.
[0009] This invention also provides a method for preparing a magnetic imidazole-based composite material, comprising the following steps:
[0010] (1) Hydroxylation treatment of magnetic core: Fe3O4 is dispersed in an alkaline solution for hydroxylation treatment to obtain Fe3O4 with hydroxyl-rich surface;
[0011] (2) KH-570 modification: The hydroxylated Fe3O4 obtained in step (1) is dispersed in an organic solvent, and silane coupling agent KH-570 is added to react to obtain Fe3O4@KH-570;
[0012] (3) 1-Vinylimidazol graft polymerization: Fe3O4@KH-570 obtained in step (2) is dispersed in an organic solvent, 1-vinylimidazol monomer and initiator are added, and graft polymerization reaction is carried out under an inert atmosphere to obtain Fe3O4@KH-570@VIM composite material.
[0013] Further, in step (1), the alkaline solution is a sodium hydroxide solution or a potassium hydroxide solution with a concentration of 0.5-2 mol / L; the hydroxylation treatment time is 12-24 hours and the treatment temperature is 20-60℃.
[0014] Further, in step (2), the organic solvent is toluene, ethanol or isopropanol; the mass ratio of KH-570 to Fe3O4 is 1:5-1:20; the reaction temperature is 70-90℃ and the reaction time is 12-24 hours.
[0015] Further, in step (3), the organic solvent is acetonitrile, toluene, or N,N-dimethylformamide; the initiator is azobisisobutyronitrile (AIBN) or benzoyl peroxide (BPO); the mass ratio of 1-vinylimidazolium to Fe3O4@KH-570 is 1:1-10:1; the amount of initiator is 1%-5% of the mass of 1-vinylimidazolium; the graft polymerization reaction temperature is 60-80℃, and the reaction time is 2-8 hours.
[0016] Furthermore, the mass ratio of 1-vinylimidazole to Fe3O4@KH-570 is 5:1; the reaction temperature is 70℃; and the reaction time is 4 hours.
[0017] This invention also provides an application of a magnetic imidazole-based composite material in the enrichment and degradation of PET microplastics, the application comprising the following steps:
[0018] (1) Enrichment of PET microplastics: The magnetic imidazole composite material is added to water containing PET microplastics, the pH value is adjusted to a non-alkaline range, and the aggregates are allowed to settle. The composite material containing PET microplastics is separated and enriched by a magnetic field.
[0019] (2) In-situ catalytic degradation: The composite material enriched with PET microplastics obtained in step (1) is used as a catalyst, ethanolamine is added, and the mixture is heated to carry out an aminolysis reaction, so that the PET microplastics are degraded into bis(2-hydroxyethyl) terephthalate (BHETA).
[0020] (3) Catalyst recovery: After the reaction is completed, the composite material is recovered by magnetic field separation for use in the next cycle.
[0021] Further, in step (1), the particle size of the PET microplastics is 10-500 μm; the pH value of the water is controlled at 3-7; and the aggregation and settling time is 3-8 hours.
[0022] Furthermore, in step (1), before the enrichment of the PET microplastics, the water containing the PET microplastics is subjected to ultraviolet activation treatment for 1-3 hours.
[0023] Furthermore, in step (2), the aminolysis reaction temperature is 80-120℃ and the reaction time is 30-120 minutes.
[0024] Furthermore, in step (2), the aminolysis reaction temperature is 100°C and the reaction time is 60 minutes.
[0025] This invention uses Fe3O4 as a magnetic core, coupled with KH-570 silane and grafted with 1-vinylimidazolium to construct a Fe3O4@KH-570@VIM composite material with magnetic response, enrichment, and catalytic functions. The design principle is as follows: the protonated imidazole cations on the material surface generate electrostatic attraction with PET microplastics, and the imidazole ring and the PET benzene ring form π-π conjugation, realizing efficient aggregation and magnetic separation of microplastics; at the same time, the surface imidazole acts as a catalytic active center, activating ethanolamine and breaking the PET ester bond, completing the in-situ catalytic degradation to generate the high-value monomer BHETA, thereby realizing the integrated treatment of enrichment, separation, degradation, and resource utilization.
[0026] Beneficial effects: Compared with the prior art, the present invention has significant advantages:
[0027] (1) The magnetic imidazole-based composite material prepared by this invention has high enrichment efficiency. This invention achieves high-efficiency enrichment of PET microplastics by grafting imidazole functional groups onto the surface and utilizing the π-π conjugation effect and electrostatic attraction between the imidazole ring and the PET benzene ring, with a removal rate of over 92.3%. This invention uses Fe3O4 as the magnetic core, and the saturation magnetization of the composite material reaches 100 emu / g, which remains at 90 emu / g after enriching PET. It has excellent magnetic response performance and can achieve rapid magnetic separation without the need for traditional filtration or centrifugation, making it convenient for material recovery and recycling. After fixing the imidazole group on the surface of the magnetic support, the nature of the catalytic active site does not change, and the catalytic activity is stable. It has high catalytic activity and selectivity for the aminolysis reaction of PET, and the product is high-purity BHETA. The performance of the catalyst does not decrease significantly after being recycled three times.
[0028] (2) The preparation process of the present invention is simple and the cost is low, and it has good environmental and economic benefits.
[0029] (3) The magnetic imidazole-based composite material prepared by this invention has broad application prospects and is suitable for PET microplastics of different particle sizes. It can be directly used for the treatment of polluted water bodies. It integrates the magnetic response enrichment function with the in-situ catalytic degradation function, realizing the whole process of efficient capture, rapid separation and green depolymerization of PET microplastics from water bodies, and solving the problem that traditional technologies only achieve phase transfer but have difficulty in subsequent disposal. Attached Figure Description
[0030] Figure 1 The figure shows the effect of the synthesis conditions of Fe3O4@KH-570@VIM on the PET removal rate; where (a) is the 1-vinylimidazol grafting time; (b) is the grafting temperature; (c) is the amount of 1-vinylimidazol; and (d) is the amount of crosslinking agent.
[0031] Figure 2The image shows VSM test results before and after Fe3O4@KH-570@VIM enrichment of PET according to this invention.
[0032] Figure 3 The figure shows the effect of agglomeration and sedimentation conditions on PET removal rate in this invention; where (a) is the effect of UV activation time on PET removal rate; (b) is the effect of pH value on PET removal rate; and (c) is the PET conversion rate and BHETA yield for different cycles.
[0033] Figure 4 This is a comparison chart showing the effect of magnetic materials at different modification stages of the present invention on the removal of PET agglomerates and sedimentation.
[0034] Figure 5 The infrared spectra of the Fe3O4@KH-570@VIM degradation product prepared in this invention are compared with those of the degradation product of Comparative Example 4. Detailed Implementation
[0035] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0036] Experimental methods not specified in the examples are generally performed under standard conditions or as recommended by the manufacturer. Unless otherwise specified, all raw materials and reagents used are commercially available products.
[0037] Example 1
[0038] Hydroxylation treatment of Fe3O4 magnetic core
[0039] Weigh 5 g of Fe3O4 powder and disperse it in 100 mL of 1 mol / L NaOH solution. Stir the mixture at 40 °C for 18 hours. After the reaction is complete, wash with deionized water until neutral, then wash three times with anhydrous ethanol, and dry under vacuum at 60 °C for 12 hours to obtain hydroxylated Fe3O4.
[0040] Preparation of Fe3O4@KH-570
[0041] Weigh 2 g of the prepared hydroxylated Fe3O4 and disperse it in 100 mL of anhydrous toluene, then sonicate for 30 minutes. Add 0.4 g of KH-570 and stir the mixture at 80 °C under nitrogen protection for 18 hours. After the reaction is complete, wash three times with anhydrous toluene to remove unreacted KH-570, then wash three times with anhydrous ethanol, and dry under vacuum at 60 °C for 12 hours to obtain Fe3O4@KH-570.
[0042] Preparation of Fe3O4@KH-570@VIM
[0043] Weigh 0.5 g of the prepared Fe3O4@KH-570 and disperse it in 50 mL of acetonitrile, then sonicate for 30 minutes. Add 2.5 g of 1-vinylimidazolium and 0.05 g of AIBN, purge with nitrogen for 30 minutes to remove oxygen, and then stir the reaction at 70°C under nitrogen protection for 4 hours. After the reaction is complete, wash three times with anhydrous ethanol to remove unreacted monomers and homopolymers, and then vacuum dry at 60°C for 12 hours to obtain the Fe3O4@KH-570@VIM composite material of the present invention.
[0044] Example 2
[0045] To investigate the effects of different grafting reaction times, different grafting reaction temperatures, different amounts of 1-vinylimidazole, and different amounts of crosslinking agent on the removal rate of PET microplastics during the preparation of Fe3O4@KH-570@VIM composite materials, the following series of experiments were designed.
[0046] 1. To investigate the effect of different grafting reaction times on the removal rate of PET microplastics.
[0047] The preparation steps were the same as in Example 1, except that the grafting reaction time was set to 2 h, 4 h, 6 h, and 8 h, while all other conditions remained unchanged. Using PET microplastics with a particle size of 50 μm as a model pollutant, the removal rate of PET microplastics by the prepared Fe3O4@KH-570@VIM composite material was tested. Figure 1 As shown in (a), when the grafting reaction time is 4 h, the removal rate of PET microplastics by the Fe3O4@KH-570@VIM composite material reaches its peak; with further extension of the reaction time, the removal rate tends to stabilize.
[0048] 2. To investigate the effect of different grafting reaction temperatures on the removal rate of PET microplastics.
[0049] The preparation steps were the same as in Example 1, except that the grafting reaction temperatures were set to 50℃, 60℃, 70℃, and 80℃, while all other conditions remained unchanged. Using PET microplastics with a particle size of 50 μm as a model pollutant, the removal rate of the prepared Fe3O4@KH-570@VIM composite material was tested. Figure 1 As shown in (b), the Fe3O4@KH-570@VIM composite material achieved the highest removal rate of PET microplastics when the grafting reaction temperature was 70℃.
[0050] 3. To investigate the effect of different 1-vinylimidazole dosages on PET removal rate.
[0051] The preparation steps were the same as in Example 1, except that the mass ratio of 1-vinylimidazole to Fe3O4@KH-570 was 1:1, 3:1, 5:1, 7:1, and 10:1, while all other conditions remained unchanged. Using PET microplastics with a particle size of 50 μm as a model pollutant, the removal rate of PET microplastics by the prepared Fe3O4@KH-570@VIM composite materials was tested. Figure 1 As shown in (c), the PET microplastic removal rate reaches a maximum of 92.3% when the mass ratio is 5:1.
[0052] 4. To investigate the effect of different crosslinking agent dosages on the removal rate of PET microplastics.
[0053] The preparation steps were the same as in Example 1, except that different amounts of the crosslinking agent EGDMA (ethylene glycol dimethacrylate) were added, and the molar ratio of EGDMA to 1-vinylimidazole was set to 0:1, 0.05:1, 0.1:1, and 0.2:1, while all other conditions remained unchanged. Using PET microplastics with a particle size of 50 μm as a model pollutant, the removal rate of PET microplastics by the prepared Fe3O4@KH-570@VIM composite material was tested. Figure 1 As shown in (d), the removal rate of PET microplastics was the highest when no crosslinking agent was added; after adding the crosslinking agent, the removal rate dropped to 78.59%.
[0054] Example 3
[0055] To investigate the enrichment effect of the prepared Fe3O4@KH-570@VIM composite material on PET microplastics, the effects of UV activation time and water pH on the enrichment effect of PET microplastics, the in-situ catalytic degradation effect of supported PET microplastics, and the recycling performance of the Fe3O4@KH-570@VIM composite catalyst, the following series of experiments were designed.
[0056] 1. Enrichment of PET microplastics
[0057] Take 100 mL of water containing 50 mg / L PET microplastics (particle size 50 μm), add 0.02 g of the Fe3O4@KH-570@VIM composite material prepared in Example 1, adjust the pH to 5, and stir the reaction at room temperature for 5 hours. After the reaction, use an external magnetic field to separate and enrich the PET-containing composite material, and measure the concentration of residual PET in the supernatant. The removal rate is calculated to be 92.3%. Figure 2As shown, the saturation magnetization of the composite material before enrichment is about 100 emu / g, exhibiting excellent magnetic response performance and enabling rapid solid-liquid separation under an applied magnetic field. After enrichment of PET microplastics, the saturation magnetization decreases slightly to 90 emu / g, but still maintains a sufficiently high magnetic separation capability, ensuring efficient separation of the composite material from the water after agglomeration and sedimentation, and supporting the stable PET microplastic enrichment and recycling effect of this system.
[0058] 2. Effect of UV activation treatment time on the enrichment effect of PET microplastics
[0059] PET microplastics were enriched according to the method in Example 3-1, except that the water containing PET microplastics was subjected to ultraviolet activation treatment before enrichment, with activation times set to 0 h, 1 h, 2 h, and 3 h, respectively. Figure 3 As shown in (a), the PET removal rate increased significantly after 2 hours of UV activation; with further extension of the activation time, the removal rate tended to saturate.
[0060] 3. The effect of water pH on the enrichment effect of PET microplastics
[0061] PET microplastic enrichment was performed according to the method in Example 3-1, the difference being that the pH of the water was adjusted to 3, 5, 7, 9, and 11 respectively. Figure 3 As shown in (b), under non-alkaline conditions (pH 3-7), the PET removal rate remained above 85%; under alkaline conditions, the removal rate decreased significantly.
[0062] 4. In-situ catalytic degradation effect of supported PET microplastics
[0063] The Fe3O4@KH-570@VIM composite material enriched with PET microplastics from Example 3-1 (containing approximately 4.6 mg of PET) was mixed with 5 mL of ethanolamine and stirred at 100°C for 60 minutes. After the reaction was complete, the mixture was cooled to room temperature, diluted with an appropriate amount of deionized water, and the catalyst was recovered by magnetic field separation. The degradation solution was then treated and analyzed by high-performance liquid chromatography (HPLC). The PET conversion rate was calculated to be 100%, and the BHETA yield was 81.76%.
[0064] 5. Recycling performance of Fe3O4@KH-570@VIM composite catalyst
[0065] In-situ catalytic degradation of supported PET was carried out according to the methods in Examples 3-4. After the reaction, the catalyst was recovered by magnetic separation, washed three times with anhydrous ethanol, and then directly used in the next round of reaction. Figure 3 As shown in (c), after the catalyst was recycled 3 times, the conversion rate of PET microplastics and the yield of BHETA did not decrease significantly; however, the performance began to decline after the 4th use.
[0066] Comparative Example 1
[0067] The effect of unmodified Fe3O4 composite material on the removal of PET microplastics
[0068] PET microplastic enrichment was performed according to the method in Example 3-1, except that unmodified Fe3O4 was used instead of the Fe3O4@KH-570@VIM composite material.
[0069] Comparative Example 2
[0070] The effect of Fe3O4@KH-570 composite material on the removal of PET microplastics
[0071] The enrichment of PET microplastics was carried out according to the method of Example 3-1, except that Fe3O4@KH-570 prepared in Example 1 was used instead of Fe3O4@KH-570@VIM composite material.
[0072] Comparative Example 3
[0073] Effect of cross-linked Fe3O4@KH-570@PVIM composite material on the removal of PET microplastics
[0074] Crosslinked Fe3O4@KH-570@PVIM (EGDMA:1-vinylimidazol molar ratio = 0.1:1) was prepared according to the methods of Examples 2-4, and PET microplastics were enriched according to the methods of Examples 3-1.
[0075] like Figure 4 As shown, the unmodified Fe3O4 composite material in Comparative Example 1 only achieved a removal rate of 9.7% for PET microplastics; the Fe3O4@KH-570 composite material in Comparative Example 2 achieved a removal rate of 23.58% for PET microplastics; and the cross-linked material in Comparative Example 3 achieved a removal rate of 78.59% for PET microplastics. This demonstrates that the imidazole functional group is key to improving the enrichment efficiency of PET microplastics. The non-cross-linked Fe3O4@KH-570@VIM prepared in this invention can fully expose active sites and achieve efficient capture through electrostatic interaction and π-π conjugation, significantly outperforming unmodified, coupled, and cross-linked materials, resulting in the optimal enrichment effect.
[0076] Comparative Example 4
[0077] Comparison of products from different degradation systems
[0078] PET bottle flakes were catalytically degraded using a MEIM:MEA eutectic solvent system (1-methylimidazole:ethanolamine molar ratio = 1:2) as reported in the literature, at 100℃ for 60 minutes. The degradation products were collected and analyzed by infrared spectroscopy. The results are as follows: Figure 5 As shown in (a) of the diagram. Figure 5 (b) shows the infrared results of the products obtained in Examples 3-4. Comparing the two, the infrared characteristic peak positions and relative intensities of the products obtained in the MEIM:MEA eutectic solvent system are completely consistent with those of the products obtained in Examples 3-4, confirming that they are both BHETA.
Claims
1. A magnetic imidazole-based composite material, characterized in that, The composite material uses Fe3O4 as a magnetic core, and its surface is sequentially coated with a KH-570 coupling layer and a polyvinyl imidazole functional layer, and its surface is rich in imidazole functional groups.
2. The magnetic imidazole-based composite material according to claim 1, characterized in that, The composite material has a saturation magnetization of 90-110 emu / g and a removal rate of over 90% for PET microplastics.
3. The method for preparing the magnetic imidazole-based composite material as described in claim 1, characterized in that: Includes the following steps: (1) Hydroxylation treatment of magnetic core: Fe3O4 is dispersed in an alkaline solution for hydroxylation treatment to obtain Fe3O4 with hydroxyl-rich surface; (2) KH-570 modification: The hydroxylated Fe3O4 obtained in step (1) was dispersed in an organic solvent, and silane coupling agent KH-570 was added to react to obtain Fe3O4@KH-570; (3) 1-Vinylimidazol graft polymerization: Fe3O4@KH-570 obtained in step (2) is dispersed in an organic solvent, 1-vinylimidazol monomer and initiator are added, and graft polymerization reaction is carried out under an inert atmosphere to obtain Fe3O4@KH-570@VIM composite material.
4. The method for preparing the magnetic imidazole-based composite material according to claim 3, characterized in that, In step (1), the hydroxylation treatment time is 12-24 hours and the treatment temperature is 20-60℃.
5. The method for preparing the magnetic imidazole-based composite material according to claim 3, characterized in that, In step (2), the mass ratio of KH-570 to Fe3O4 is 1:5-1:20; the reaction temperature is 70-90℃; and the reaction time is 12-24 hours.
6. The method for preparing the magnetic imidazole-based composite material according to claim 3, characterized in that, In step (3), the mass ratio of 1-vinylimidazolium to Fe3O4@KH-570 is 1:1-10:1; the amount of initiator is 1%-5% of the mass of 1-vinylimidazolium; the graft polymerization reaction temperature is 60-80℃, and the reaction time is 2-8 hours.
7. The method for preparing the magnetic imidazole-based composite material according to claim 3, characterized in that, The mass ratio of 1-vinylimidazole to Fe3O4@KH-570 is 5:1; the reaction temperature is 70℃ and the reaction time is 4 hours.
8. The application of the magnetic imidazole-based composite material as described in claim 1 in the enrichment and degradation of PET microplastics, characterized in that, The application includes the following steps: (1) Enrichment of PET microplastics: The magnetic imidazole composite material is added to water containing PET microplastics, the pH value is adjusted to a non-alkaline range, and the aggregates are allowed to settle. The composite material containing PET microplastics is separated and enriched by magnetic field. (2) In-situ catalytic degradation: The composite material enriched with PET microplastics obtained in step (1) is used as a catalyst, ethanolamine is added, and the mixture is heated to carry out an aminolysis reaction, so that the PET microplastics are degraded into bis(2-hydroxyethyl) terephthalate (BHETA). (3) Catalyst recovery: After the reaction is completed, the composite material is recovered by magnetic field separation for use in the next cycle.
9. The application according to claim 8, characterized in that, In step (1), the particle size of the PET microplastics is 10-500 μm; the pH value of the water is 3-7; and the aggregation and settling time is 3-8 hours.
10. The application according to claim 8, characterized in that, In step (1), before enrichment, the water containing PET microplastics is subjected to ultraviolet activation treatment for 1-3 hours.