Divalent lanthanide series metal marked yellow-green fluorescent plastic microspheres as well as preparation method and application of bivalent lanthanide series metal marked yellow-green fluorescent plastic microspheres

Abstract

The invention discloses a divalent lanthanide series metal marked yellow-green fluorescent plastic microsphere as well as a preparation method and application thereof, and relates to the technical field of high-molecular polymer preparation. The preparation method of the plastic microspheres comprises the following steps: preparing a nitrogen heterocyclic ligand N8 in an argon atmosphere; the preparation method comprises the following steps: in a nitrogen atmosphere, dropwise adding a mixed solution of a nitrogen heterocyclic ligand N8 and methanol into a mixed solution of EuBr2 and methanol, and reacting to prepare Eu-N8; the preparation method comprises the following steps: dissolving Eu-N8 in a solvent containing polyvinylpyrrolidone, and carrying out first embedding treatment through a hydrothermal method to obtain PVP-coated Eu-N8; in the process of synthesizing the polystyrene micro-nano plastic, PVP-coated Eu-N8 is added for secondary hydrothermal coating treatment, and the plastic microspheres are obtained. The plastic microsphere particles prepared by the method disclosed by the invention are uniform and consistent in particle size, have high-brightness yellow-green fluorescence and high stability, and can be directly added into various environmental samples to realize fluorescent tracing and quantitative detection of micro-plastics.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high molecular polymer preparation, and particularly relates to a divalent lanthanide metal labeled yellow-green fluorescent plastic microsphere and a preparation method and application thereof. BACKGROUND

[0002] As a new pollutant, micro-nano plastic has complex structure, various types and wide distribution, and at present, there is still a lack of in-depth research on various micro-nano plastics. The detection method of micro-nano plastic is insufficient, and some researchers propose to mark the plastic microsphere by metal, and to calculate the amount of micro-nano plastic by determining the metal content coated after the digestion of micro-nano plastic. In the existing research, the coated metal is mainly palladium and trivalent europium, and the plastic microsphere labeled with europium has the red fluorescence of trivalent europium, and the plastic microsphere labeled with palladium cannot be traced by fluorescence to its migration path. The commercially available plastic microsphere labeled with lanthanide metal mainly has red fluorescence, which is the same as the fluorescence of the spontaneous light of the biological body, such as chlorophyll, and is not conducive to observing the migration and conversion process in the biological body. Divalent europium also has fluorescence characteristics, and can be considered to be developed for labeling plastic microspheres, but the fluorescence complex of divalent europium is easily oxidized to trivalent europium in air, which causes the fluorescence characteristics to change, and the initiator with oxidation property is also added in the synthesis process of the plastic microsphere, which also causes the divalent europium to be oxidized to trivalent europium, thereby losing the fluorescence characteristics. At the same time, the metal binding stability of the plastic microsphere labeled with divalent europium is also a key problem to be solved, and the metal in the plastic microsphere is easy to leak if the preparation method is improper, which is not conducive to long-term use. SUMMARY

[0003] In view of the above problems, the present application provides a divalent lanthanide metal labeled yellow-green fluorescent plastic microsphere and a preparation method and application thereof. The plastic microsphere particles prepared by the method have uniform particle size, high-brightness yellow-green fluorescence and high stability, and can be directly added to various environmental samples to realize fluorescence tracing and quantitative detection of microplastics. The specific technical scheme is as follows: A preparation method of a divalent lanthanide metal labeled yellow-green fluorescent plastic microsphere, comprising the following steps: (1) preparing an azacyclic ligand N8 under an argon atmosphere; the azacyclic ligand N8 is a simple name of 1,4,7,10,13,16,21,24-octazabicyclo[8.8.8]hexacosane; (2) slowly adding a mixture of the azacyclic ligand N8 and methanol to a mixed solution of EuBr2 and methanol under a nitrogen atmosphere to react, removing the methanol, and purifying by reduced pressure sublimation to obtain Eu-N8; (3) dissolving the Eu-N8 in a solvent containing polyvinylpyrrolidone, and performing a first embedding treatment by a hydrothermal method to obtain PVP@Eu-N8; (4) adding the PVP@Eu-N8 in the process of synthesizing the polystyrene micro-nano plastic to perform a second hydrothermal coating treatment, so as to obtain the divalent lanthanide metal labeled yellow-green fluorescent plastic microspheres.

[0004] Further, in step (1), the preparation method of the nitrogen heterocyclic ligand N8 is as follows: Step A, under an argon atmosphere, 10-15 mL of triethylamine and 200-250 mL of isopropyl alcohol are first added to a three-necked flask, and the temperature is reduced to -78 to -70°C; then 5-10 mL of tris(2-aminoethyl)amine is added, and 7-8 mL of glyoxal solution is added dropwise at a speed of 0.08-0.16 mL / min while stirring, and the reaction is carried out for 16-24 h, and isopropyl alcohol is removed by drying under reduced pressure; then 250-300 mL of chloroform is added and stirred for 1-2 h, and then filtered to remove yellow solid impurities; finally, the chloroform in the solution is removed under reduced pressure to obtain an intermediate product; Step B, the intermediate product is dissolved in 200-300 mL of dichloroethane, 30-42 g of sodium triacetoxyborohydride is added at room temperature, and the reaction is carried out for 3-4 h, the dichloroethane is removed under reduced pressure, the product is extracted with dichloromethane for 2-3 times, the combined extract is dried under reduced pressure to remove the dichloromethane, the obtained product is added with water under stirring until it is completely dissolved, and the half of the aqueous solution is removed under heating in a nitrogen atmosphere, and the product is recrystallized by cooling with ice water, and the liquid is removed by filtration to obtain a white solid, and the white solid is dried under reduced pressure to obtain the nitrogen heterocyclic ligand N8.

[0005] Further, in step (2), the mixture of EuBr2 and methanol is prepared by mixing 0.1-0.3 mol of EuBr2 with 20-40 mL of methanol; and the mixture of the nitrogen heterocyclic ligand N8 and methanol is prepared by dissolving 0.1-0.2 mol of the nitrogen heterocyclic ligand N8 in 20-30 mL of methanol.

[0006] Further, in step (2), the dropping speed of the mixture of the nitrogen heterocyclic ligand N8 and methanol is 1-4 mL / min.

[0007] Further, in step (2), the pressure of the reduced pressure is 10 -5 Pa, and the temperature is 150-250°C.

[0008] Further, in step (3), the temperature of the first embedding treatment is 65-85°C, and the time is 1-3 h.

[0009] Further, in step (3), the mass of the polyvinylpyrrolidone is greater than or equal to the mass of Eu-N8.

[0010] Further, the specific method of step (4) is: first, add 40-50 mL of 50-60% volume concentration of ethanol aqueous solution or water as a dispersion medium into a three-necked flask, continue to add Tris-HCl solution to adjust the pH to 7-8, then pass nitrogen and warm to 65-85 DEG C, then add 0.5-2.5 mL of styrene, 100 muL-500 muL of divinylbenzene and / or 0.5-2.5 mL of acrylonitrile, then continue to add 0.05-0.1 g of potassium persulfate dissolved in 5-10 mL of water, react for 20-60 min, then add 5-10 mL of PVP@Eu-N8 to the reaction system, and continue to react for 12-24 h, to obtain the divalent lanthanide metal labeled yellow-green fluorescent plastic microspheres.

[0011] The application further provides the divalent lanthanide metal labeled yellow-green fluorescent plastic microspheres prepared by the preparation method.

[0012] The application further provides the divalent lanthanide metal labeled yellow-green fluorescent plastic microspheres prepared by the preparation method.

[0013] Compared with the prior art, the application has the following beneficial effects: 1. The divalent lanthanide metal labeled yellow-green fluorescent plastic microspheres synthesized by the application have the divalent europium coated in the core-shell structure, avoid oxidation of the divalent europium by free radicals in the environment, have stable yellow-green fluorescence, and the fluorescence intensity of the finished product does not change after being placed for several months, which indicates that the coated divalent europium is not oxidized and is combined stably.

[0014] 2. The divalent lanthanide metal labeled yellow-green fluorescent plastic microspheres synthesized by the application are different from the red fluorescent commercially available lanthanide metal labeled plastic microspheres, are a new type of metal labeled fluorescent plastic microspheres, have both fluorescent properties and metal labeling functions, can track the migration behavior in the environment through a fluorescence microscope, and can be quantitatively detected based on metal labeling, and have significant commercial application value.

[0015] 3. The lanthanide metal in the divalent lanthanide metal labeled yellow-green fluorescent plastic microspheres prepared by the application is combined stably, and long-term stability experiments show that the metal leakage amount of the synthesized yellow-green fluorescent plastic microspheres is about 0.01 mu g / L per week, which can be ignored compared with the coated amount, proving that the lanthanide metal coated by the fluorescent plastic microspheres prepared by the method almost does not leak from the plastic microspheres, and can be used for quantitative analysis of micro-nano plastic migration and fate in complex environments. BRIEF DESCRIPTION OF DRAWINGS

[0016] In order to more clearly illustrate the technical solutions of the embodiments of the application, the following will briefly introduce the drawings needed to be used in the embodiment description.

[0017] Figure 1Scanning electron microscope image of the yellow-green fluorescent plastic microspheres labeled with divalent lanthanide metal prepared in Example 3; Figure 2 Excitation and emission spectra of the yellow-green fluorescent plastic microspheres labeled with divalent lanthanide metal prepared in Example 1; Figure 3 Fluorescence intensity change diagram of the yellow-green fluorescent plastic microspheres labeled with divalent lanthanide metal prepared in Example 1; Figure 4 The content of microplastics in Arabidopsis thaliana after the yellow-green fluorescent plastic microspheres labeled with divalent lanthanide metal prepared in Example 3 as micro-nano plastic pollutants entered the Arabidopsis thaliana plants was detected.

[0018] Figure 5 The yellow-green fluorescent characteristic was shown after the yellow-green fluorescent plastic microspheres labeled with divalent lanthanide metal prepared in Example 3 as a model of micro-nano plastic pollutants entered the plant root system. DETAILED DESCRIPTION

[0019] The specific embodiments of the present application are described in detail below, but it should be understood that the protection scope of the present application is not limited by the specific embodiments.

[0020] Example 1 The preparation method of the yellow-green fluorescent plastic microspheres labeled with divalent lanthanide metal in this embodiment is as follows: (1) 12 mL of triethylamine and 250 mL of isopropyl alcohol were added to a 1 L three-necked flask under an argon atmosphere, and the temperature was lowered to -78°C. 5 mL of tris(2-aminoethyl)amine was added, and 7.5 mL of glyoxal solution was added dropwise at a speed of 0.08 ml / min through a syringe peristaltic pump under stirring of the stirring paddle. The reaction was carried out for 24 h. The isopropyl alcohol was removed by drying under reduced pressure at 40°C, and 300 mL of chloroform was added and stirred for 2 h, and then filtered to remove yellow solid impurities. The chloroform in the solution was removed under reduced pressure to obtain an intermediate product; The intermediate product was dissolved in 200 mL of dichloroethane, and 42 g of sodium triacetoxyborohydride was added at room temperature and reacted for 4 h. The dichloroethane was removed under reduced pressure, and the product was extracted twice with 300 ml of dichloromethane, and the combined extract was dried under reduced pressure to remove the dichloromethane. The obtained product was dissolved in water under stirring, and half of the aqueous solution was removed under reduced pressure in a nitrogen atmosphere. The product was recrystallized by ice water cooling, and the liquid was removed by filtration to obtain a white solid. The white solid was dried under reduced pressure to obtain the nitrogen heterocyclic ligand; (2) 0.1 mol of EuBr2 and 20 mL of methanol were added to a 100 mL flask under a nitrogen atmosphere, and 0.1 mol of the nitrogen heterocyclic ligand was dissolved in 20 mL of methanol. The nitrogen heterocyclic ligand solution was slowly added to the flask, and Eu-N8 was obtained by removing the methanol. The obtained Eu-N8 was purified by sublimation under reduced pressure to obtain pure Eu-N8; (3) 0.1 g Eu-N8 and 0.1 g polyvinylpyrrolidone were added into a solution containing 10 ml water, and embedding treatment was carried out by a hydrothermal method under magnetic stirring, the solution was heated to 70°C, and reaction was carried out for 1 h, and PVP@Eu-N8 powder was obtained by drying under reduced pressure; (4) 20 ml water and 25 ml alcohol were added into a three-necked flask, 5 ml Tris-HCl solution with a concentration of 1 mol / L was continuously added, pH was adjusted to about 7, nitrogen was blown, and the temperature was increased to 70°C, 1 ml styrene was added, 100 μl crosslinking agent divinylbenzene was continuously added, 0.05 g potassium persulfate solution dissolved in 5 ml water was continuously added, reaction was carried out for 30 min, the solution was translucent, 5 ml PVP@Eu-N8 solution was added into the reaction system, and reaction was continuously carried out for 24 h, and light yellow divalent lanthanide metal labeled yellow-green fluorescent plastic microspheres suspension was obtained. The particle size of the nanometer plastic microspheres synthesized in the embodiment was 200 nm, which was measured by a potential particle size analyzer.

[0021] Figure 2 The excitation and emission spectra of the plastic microspheres prepared in the embodiment were basically the same as those of the plastic microspheres prepared in other embodiments, and the excitation and emission spectra of the plastic microspheres prepared in the embodiment were as shown in FIG. 1. Figure 2 It can be known that the plastic microspheres prepared in the embodiment have an excitation wavelength of 386 nm and an emission wavelength of 567 nm.

[0022] Figure 3 The change graph of the fluorescence intensity at 567 nm of the plastic microspheres prepared in the embodiment was measured for 4 h in an air atmosphere when the excitation wavelength was 386 nm, and it can be found that the fluorescence intensity basically did not change, which indicates that the plastic microspheres prepared in the embodiment tightly coat the divalent europium and are not easily oxidized, and the fluorescent plastic microspheres prepared by the method have air stability.

[0023] Embodiment 2 The preparation method of the divalent lanthanide metal labeled yellow-green fluorescent plastic microspheres in the embodiment is as follows: (1) 12 ml triethylamine and 250 ml isopropyl alcohol were added into a 1 L three-necked flask under an argon atmosphere, the temperature was decreased to -78°C, 5 ml tris(2-aminoethyl)amine was added, 7.5 ml glyoxal solution was added into the stirring paddle by a syringe peristaltic pump at a speed of 0.10 ml / min under stirring, reaction was carried out for 24 h. Isopropyl alcohol was removed by drying under reduced pressure at 40°C, 300 ml chloroform was added, stirring was carried out for 2 h, and then yellow solid impurities were removed by filtration. Chloroform in the solution was removed by drying under reduced pressure, and an intermediate product was obtained. The intermediate product was dissolved in 300 mL of dichloroethane, 42 g of sodium triacetoxyborohydride was added at room temperature, and the reaction was carried out for 4 h. Dichloroethane was removed under reduced pressure, and the product was extracted with 300 mL of dichloromethane for 3 times. The combined extract was dried under reduced pressure to remove dichloromethane. The obtained product was dissolved in water under stirring, and half of the aqueous solution was removed under reduced pressure in a nitrogen atmosphere. The product was recrystallized by ice water cooling, and the liquid was removed by filtration to obtain a white solid. The white solid was dried under reduced pressure to obtain the nitrogen heterocyclic ligand; (2) 0.1 mol of EuBr2 was added to a 100 mL flask containing 20 mL of methanol under a nitrogen atmosphere, and 0.1 mol of the nitrogen heterocyclic ligand was dissolved in 20 mL of methanol. The nitrogen heterocyclic ligand solution was gradually added to the flask, and Eu-N8 was obtained by removing the methanol. The obtained Eu-N8 was purified by sublimation under reduced pressure to obtain pure Eu-N8; (3) 0.3 g of Eu-N8 and 0.5 g of polyvinylpyrrolidone were added to a solution containing 50 mL of water, and embedding treatment was carried out by a hydrothermal method under magnetic stirring. The solution was heated to 70°C, and the reaction was carried out for 3 h. PVP@Eu-N8 powder was obtained by drying under reduced pressure; (4) 20 mL of water and 25 mL of alcohol were added to a three-necked flask, and 5 mL of Tris-HCl solution with a concentration of 1 mol / L was further added to adjust the pH to about 7. After being warmed to 70°C under nitrogen atmosphere, 0.5 mL of styrene, 0.5 mL of acrylonitrile, 100 μL of crosslinking agent divinylbenzene, and 0.05 g of potassium persulfate solution dissolved in 5 mL of water were added. The solution was translucent, and 5 mL of PVP@Eu-N8 solution was added to the reaction system. After being reacted for 24 h, a light yellow divalent lanthanide metal labeled yellow-green fluorescent plastic microsphere suspension was obtained. The particle size of the nanometer plastic microspheres synthesized in this example was 240 nm, and the plastic microspheres had higher fluorescence intensity and heat resistance compared with those of Example 1.

[0024] Example 3 (1) 12 mL of triethylamine and 250 mL of isopropyl alcohol were added to a 1 L three-necked flask under an argon atmosphere, and the temperature was lowered to -78°C. 5 mL of tris(2-aminoethyl)amine was added, and 7.5 mL of glyoxal solution was added at a rate of 0.12 mL / min by a syringe peristaltic pump under stirring of the stirring paddle. The reaction was carried out for 24 h. Isopropyl alcohol was removed under reduced pressure at 40°C, 300 mL of chloroform was added, and the yellow solid impurities were removed by filtration after stirring for 2 h. Chloroform in the solution was removed under reduced pressure to obtain an intermediate product; The intermediate product was dissolved in 250 mL of dichloroethane, 42 g of sodium triacetoxyborohydride was added at room temperature, and the reaction was carried out for 4 h. Dichloroethane was removed under reduced pressure, and the product was extracted with 300 mL of dichloromethane for 3 times. The combined extract was dried under reduced pressure to remove dichloromethane. The obtained product was dissolved in water under stirring, and half of the aqueous solution was removed under reduced pressure in a nitrogen atmosphere. The product was recrystallized by ice water cooling, and the liquid was removed by filtration to obtain a white solid. The white solid was dried under reduced pressure to obtain the nitrogen heterocyclic ligand; (2) 0.1 mol of EuBr2 was added to a 100 mL flask with 20 mL of methanol under a nitrogen atmosphere, and 0.1 mol of the nitrogen heterocyclic ligand was dissolved in 20 mL of methanol. The nitrogen heterocyclic ligand solution was gradually added to the flask, and Eu-N8 was obtained by removing the methanol. The obtained Eu-N8 was purified by sublimation under reduced pressure to obtain pure Eu-N8; (3) 0.3 g of Eu-N8 and 0.5 g of polyvinylpyrrolidone were added to a solution containing 50 mL of water, and embedding treatment was carried out by a hydrothermal method under magnetic stirring. The solution was heated to 70°C, and the reaction was carried out for 3 h. PVP@Eu-N8 powder was obtained by drying under reduced pressure; (4) 45 mL of water was added to a three-necked flask, and 5 mL of Tris-HCl solution with a concentration of 1 mol / L was continuously added to adjust the pH to about 7. After being warmed to 70°C under nitrogen atmosphere, 2.5 mL of styrene, 2.5 mL of acrylonitrile, and 500 μL of crosslinking agent divinylbenzene were added. Then, 0.03 g of potassium persulfate solution dissolved in 5 mL of water was continuously added to react for 20 min, and the solution was milky white. 0.3 g of PVP@Eu-N8 was prepared into a 5 mL aqueous solution, which was added to the reaction system. After 1 h of reaction, the solution was light yellow, and after 24 h of continuous reaction, a light yellow divalent lanthanide metal-labeled yellow-green fluorescent plastic microsphere suspension was obtained. The scanning electron microscope image of the plastic microspheres synthesized in this example is shown in Figure 1 , and it can be seen from Figure 1 that the microspheres have regular morphology and uniform particle size, and the average particle size is 52.78 ± 7.142 nm.

[0025] Example 4 To verify that the divalent europium is tightly coated by the core-shell and will not leak, the nanometer plastic microsphere suspension synthesized in Example 3 was dialyzed with a dialysis bag for one week to remove impurities therein. The dialyzed suspension was used as a subsequent experimental or commercial use solution. The use solution was dialyzed with a dialysis bag, and the leakage of europium element was detected by taking a sample once a week. The content of europium element in the sample was detected by inductively coupled plasma mass spectrometry. The detection results of the continuous sampling for 7 weeks showed that the leakage amount was about 0.01 μg per week, which was negligible compared with the coated amount, indicating that the plastic microspheres synthesized by the method had good stability, and the coated europium hardly leaked. At the same time, a certain amount of nanometer plastic microspheres prepared in Example 3 was taken, and the Eu content was detected after digestion with mixed acid. The detection results showed that the Eu accounted for 0.26% of the mass of the nanometer plastic microspheres in Example 3.

[0026] Example 5 The nanometer plastic microspheres synthesized in Example 3 are used as a model of pollutants for studying the stress of microplastic pollution on plant growth. Specifically, after the Arabidopsis thaliana is cultured for 21 days, a nanometer plastic suspension is added to the culture solution of the Arabidopsis thaliana, configured as a solution of 10 mg / L, 1 mg / L and 0.1 mg / L. The prepared solution is poured into the flowerpot in which the Arabidopsis thaliana is cultured, and the pouring is performed once every 3 days, for a treatment of one month, and a total of 10 times of pouring. The stems, leaves and root systems of the Arabidopsis thaliana subjected to the stress treatment are harvested, dried and weighed, and after digestion with mixed acid, the content of Eu is detected by inductively coupled plasma mass spectrometry. The mass of the nanometer plastic microspheres absorbed by the Arabidopsis thaliana is calculated in combination with the proportion of Eu in the mass of the nanometer plastic microspheres, and the absorption amounts of the Arabidopsis thaliana to the nanometer plastic suspensions with different concentrations are compared and analyzed, as shown in Figure 4 The content of the plastic microspheres can be calculated by the content of the coated Eu, which indicates that the plastic microspheres prepared by the method can be used for quantitative detection of micro-nano plastics in a complex environment. Further, the yellow-green fluorescent plastic microspheres prepared by the method can be observed to be enriched in the plant (Arabidopsis thaliana) in a fluorescence microscope, as shown in Figure 5 The yellow-green fluorescent plastic microspheres prepared by the method can be detected by fluorescence labeling.

[0027] In summary, the plastic microspheres prepared by the method have uniform and consistent particle sizes, high-brightness yellow-green fluorescence, high stability, and can be directly added to various environmental samples to realize fluorescence tracing and quantitative detection of microplastics.

[0028] The foregoing description of specific exemplary embodiments of the application is intended to be illustrative only and is not intended to limit the application to the precise forms described. Many modifications and variations are possible in light of the above teachings without departing from the spirit or essential characteristics of the application. The exemplary embodiments were chosen and described in order to explain the principles of the application and its practical application to thereby enable others skilled in the art to best utilize the application and various embodiments with various modifications as are suited to the particular use contemplated. It is intended that the scope of the application be defined by the claims and their equivalents.

Claims

1. A method for the preparation of divalent lanthanide metal labeled yellow-green fluorescent plastic microspheres, characterized in that, The method comprises the following steps: (1) preparing an azacyclic ligand N8 under an argon atmosphere; (2) slowly adding a mixture of the azacyclic ligand N8 and methanol to a mixture of EuBr2 and methanol under a nitrogen atmosphere, and then removing the methanol and purifying the mixture by sublimation under reduced pressure to obtain Eu-N8; (3) dissolving the Eu-N8 in a solvent containing polyvinylpyrrolidone, and performing a first embedding treatment by a hydrothermal method to obtain PVP@Eu-N8; (4) adding the PVP@Eu-N8 to a process of synthesizing polystyrene micro-nano plastic to perform a second hydrothermal coating treatment, so that the yellow-green fluorescent plastic microspheres labeled by the divalent lanthanide metal are obtained.

2. A process for the preparation of divalent lanthanide metal labeled greenish yellow fluorescent plastic microspheres according to claim 1, characterized in that, In step (1), the azacyclic ligand N8 is prepared by the following method: Step A: under an argon atmosphere, 10-15 mL of triethylamine and 200-250 mL of isopropyl alcohol are added to a three-necked flask, and the temperature is reduced to -78 to -70 °C; then 5-10 mL of tris(2-aminoethyl)amine is added, and 7-8 mL of glyoxal solution is added at a speed of 0.08-0.16 mL / min while stirring, and the reaction is carried out for 16-24 h; isopropyl alcohol is removed by drying under reduced pressure; then 250-300 mL of chloroform is added and stirred for 1-2 h, and then filtered to remove yellow solid impurities; finally, the chloroform in the solution is removed under reduced pressure to obtain an intermediate product; Step B: the intermediate product is dissolved in 200-300 mL of dichloroethane, 30-42 g of sodium triacetoxyborohydride is added at room temperature, and the reaction is carried out for 3-4 h; dichloroethane is removed under reduced pressure, the product is extracted with dichloromethane for 2-3 times, the combined extract is dried under reduced pressure to remove dichloromethane, and the obtained product is added with water under stirring until it is completely dissolved; under a nitrogen atmosphere, half of the aqueous solution is removed by heating, and the product is recrystallized by cooling with ice water; the liquid is removed by filtration to obtain a white solid, and the white solid is dried under reduced pressure to obtain the azacyclic ligand N8.

3. A process for the preparation of divalent lanthanide metal labeled greenish yellow fluorescent plastic microspheres as claimed in claim 1, wherein, In step (2), the mixture of EuBr2 and methanol is prepared by mixing 0.1-0.3 mol of EuBr2 with 20-40 mL of methanol; and the mixture of the azacyclic ligand N8 and methanol is prepared by dissolving 0.1-0.2 mol of the azacyclic ligand N8 in 20-30 mL of methanol.

4. A process for the preparation of divalent lanthanide metal labeled greenish yellow fluorescent plastic microspheres as claimed in claim 1, wherein, In step (2), the dropping speed of the mixture of the azacyclic ligand N8 and methanol is 1-4 mL / min.

5. The method of claim 1, wherein the method is characterized by, In step (2), the pressure of the reduced pressure is 10 -5 Pa, and the temperature is 150-250°C.

6. A process for the preparation of divalent lanthanide metal labeled greenish yellow fluorescent plastic microspheres as claimed in claim 1, wherein, In step (3), the temperature of the first embedding treatment is 65-85 °C, and the time is 1-3 h.

7. A process for the preparation of divalent lanthanide metal labeled greenish yellow fluorescent plastic microspheres as claimed in claim 1, wherein, In step (3), the mass of the polyvinylpyrrolidone added is greater than or equal to the mass of the Eu-N8.

8. A process for the preparation of divalent lanthanide metal labeled greenish yellow fluorescent plastic microspheres as claimed in claim 1, wherein, The specific method of step (4) is: first, add 40-50 mL of 50-60% volume concentration of ethanol aqueous solution or water as dispersion medium into a three-necked flask, continue to add Tris-HCl solution to adjust pH to 7-8, then pass nitrogen and heat to 65-80℃, add 1-2.5 mL of styrene, 100 μL-500 μL of divinylbenzene and / or 0.5-2.5 mL of acrylonitrile, then continue to add 0.05-0.1 g of potassium persulfate dissolved in 5-10 mL of water, react for 20-60 min, then add 5-10 mL of PVP@Eu-N8 to the reaction system, continue to react for 12-24 h, to obtain the divalent lanthanide metal labeled yellow-green fluorescent plastic microspheres.

9. The divalent lanthanide metal labeled yellow-green fluorescent plastic microspheres prepared by the preparation method of any one of claims 1 to 8.

10. The application of the divalent lanthanide metal labeled yellow-green fluorescent plastic microspheres of claim 9 in micro-nano plastic detection.

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