A method for separating microplastics in food or environment based on sustainable magnetic nanoparticles

Abstract

The present application relates to a kind of methods for separating microplastics in food or environment based on sustainable magnetic nanoparticles, the method for separating microplastics in food or environment based on sustainable magnetic nanoparticles, comprising the following steps: Fe3O4@OA magnetic nanoparticles are added to the food sample solution or environmental sample solution containing microplastics, after ultrasonic mixing, magnetic separation treatment is carried out, and the magnetic separation time is not less than 5 min;Wherein, the ratio of the amount of Fe3O4@OA magnetic nanoparticles and the mass of microplastics is not less than 4, and in Fe3O4@OA magnetic nanoparticles, at least 3.5 μL oleic acid is modified per gram Fe3O4.The method has the advantages of simple adsorption separation process, low energy consumption, low cost, high separation efficiency, fast separation speed, can be applied to a variety of complex matrixes, etc.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of microplastic separation, and in particular to a method for separating microplastics in food or environment based on sustainable magnetic nanoparticles. BACKGROUND

[0002] Under the current social environment, the increasing amount of plastic waste has become an undeniable fact. These discarded plastic waste will gradually break down over time to form smaller particles, i.e. MPs (microplastics). MPs, due to their high specific surface area and strong hydrophobicity, have strong adsorption capacity for other pollutants, and have become a new type of pollutant, so it is urgent to explore how to effectively remove MPs from food and environmental systems. Current research on methods for removing MPs mainly focuses on coagulation, membrane separation, advanced oxidation, biodegradation and adsorption methods. Among them, coagulation method needs to use a large amount of coagulant and has low removal efficiency; membrane filtration method is prone to cause membrane damage and form secondary pollution; advanced oxidation method has high cost and high energy consumption; and the biodegradation method is not yet mature. Adsorption method is widely used to remove pollutants in water environment due to its simple operation, low energy consumption and environmental friendliness.

[0003] In recent years, Fe3O4 magnetic nanoparticles with low cost, environmental safety and unique magnetic response performance have attracted widespread attention. Magnetic separation method has been reported to be used for adsorption and separation of MPs in water. The hydrophobic surface of MPs can be "magnetized" by combining magnetic nanoparticles, and the "magnetized" MPs can be adsorbed and removed due to the action of the magnetic field. Therefore, the magnetic separation method shows potential advantages of high efficiency and environmental protection in removing MPs. However, Fe3O4 nanoparticles tend to aggregate to reduce their surface energy due to their large surface-to-volume ratio. Therefore, the magnetic nanoparticles need to be coated with surfactants to produce spatial repulsion when two particles approach each other.

[0004] Patent No. CN116272878B discloses a method for removing microplastics in food based on magnetic metal organic framework materials, which mainly modifies Fe3O4 magnetic nanoparticles with silicon oxides and aluminum salts. The resulting product has high removal efficiency for PVC, but low removal efficiency for PS, PP and other microplastics. SUMMARY

[0005] The present application provides a method for separating microplastics in food or environment based on sustainable magnetic nanoparticles, which has the advantages of high microplastic separation efficiency, fast separation speed, and multiple separation types.

[0006] The technical scheme adopted by the present application to solve the above technical problems is:

[0007] A method for separating microplastics in food or environment based on sustainable magnetic nanoparticles, characterized in that it comprises the following steps: adding Fe3O4@OA magnetic nanoparticles to a food or environment sample solution containing microplastics, ultrasonic mixing, and then performing magnetic separation treatment for not less than 5 minutes; wherein the ratio of the amount of Fe3O4@OA magnetic nanoparticles added to the mass of microplastics is not less than 4, and in the Fe3O4@OA magnetic nanoparticles, at least 3.5 μL of oleic acid is modified per gram of Fe3O4.

[0008] In one example, the mass ratio of Fe3O4@OA magnetic nanoparticles added to microplastics is not less than 40.

[0009] In one example, the types of separated microplastics include at least one of PP, PE, PS, PVC, PET, and PA.

[0010] In one example, the preparation method of Fe3O4@OA magnetic nanoparticles is as follows:

[0011] S1: Take ferrous sulfate heptahydrate and ferric chloride hexahydrate with a molar ratio of 0.02:0.043, respectively, and dissolve them in deionized water to obtain solution A;

[0012] S2: Place solution A in a magnetic stirring water bath and heat to 70-95°C, then add ammonia water to adjust the pH to not less than 11, and stir vigorously for not less than 7 minutes to obtain solution B;

[0013] S3: Adjust the pH of solution B to 7 with 1 mol / L hydrochloric acid solution, then add oleic acid and stir evenly, then keep at 65-95°C for not less than 40 minutes, and then cool to room temperature to obtain solution C;

[0014] S4: Collect the magnetic nanoparticles with a magnet, then wash them repeatedly with ethanol and deionized water to remove excess oleic acid, vacuum dry the washed magnetic nanoparticles at not less than 50°C for not less than 6 hours, then grind into powder, and obtain.

[0015] In one example, the recovery method of Fe3O4@OA magnetic nanoparticles after magnetic separation treatment is: adding DMSO desorption solvent to the system to be separated, the amount of which is 50% of the total volume of the system after addition, ultrasonic mixing in an ultrasonic cleaner to desorb Fe3O4@OA magnetic nanoparticles from the surface of microplastics, then collecting Fe3O4@OA magnetic nanoparticles with a strong magnet, and drying to obtain.

[0016] In one example, the drying conditions are: drying in a vacuum freeze dryer overnight for at least 12 hours.

[0017] In one example, the sample solution is at least one of a seawater sample, a soil sample, a toothpaste sample, a tea sample, a honey sample, a kelp sample, and a fish sample.

[0018] The present application has the advantages of the above-mentioned method:

[0019] 1. The adsorption separation process is simple, low in energy consumption and cost.

[0020] 2. The adsorption separation efficiency is high, which can be up to 100%.

[0021] 3. The adsorption separation speed is fast, specifically not only the mixing is fast, but also the magnetic separation treatment is fast, and a high adsorption separation efficiency can be achieved in 5 minutes.

[0022] 4. It can show good separation effect in various complex matrices, and has scalability and practicality. It is expected to be applied to the removal of MPs in water body systems such as mariculture farms and wastewater treatment plants, which can not only reduce the potential harm to aquatic organisms, but also improve water quality, which is conducive to environmental protection and sustainable development.

[0023] 5. The oleic acid modified Fe3O4 magnetic nanoparticles synthesized in the present application are safe and non-toxic, and have high biocompatibility, which lays a foundation for their wide application in food and environmental fields. On the other hand, they can be recycled, and their recycling efficiency can still reach 88% under the condition of low concentration of microplastics, meeting the demand of sustainable development. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 is the Fourier infrared spectrum of Fe3O4@OA magnetic nanoparticles;

[0025] Figure 2 is the particle size distribution graph (a) and TEM electron microscope graph (b) of Fe3O4@OA magnetic nanoparticles;

[0026] Figure 3 is the contact angle determination result of Fe3O4@OA magnetic nanoparticles;

[0027] Figure 4 is the modification principle diagram of Fe3O4@OA magnetic nanoparticles;

[0028] Figure 5 is the separation efficiency result graph of Fe3O4@OA magnetic nanoparticles on PS MPs under different magnetic adsorption times;

[0029] Figure 6 is the separation efficiency result graph of Fe3O4 magnetic nanoparticles with different amounts of oleic acid modification on PS MPs;

[0030] Figure 7 The results of the separation efficiency of PS MPs by different concentrations of Fe3O4@OA magnetic nanoparticles;

[0031] Figure 8 The fluorescence spectrum of PS MPs under 488 nm excitation wavelength (a) and the fluorescence intensity under 518 nm wavelength (b) of PS MPs with surface-adsorbed magnetic nanoparticles under different solvent conditions;

[0032] Figure 9 The results of the separation efficiency of PS MPs by different surface-modified Fe3O4 magnetic nanoparticles;

[0033] Figure 10 The epifluorescence microscope images of self-made fluorescent PE (a) and PP (b) MPs;

[0034] Figure 11 The results of the separation efficiency of self-made fluorescent PE and PP MPs by Fe3O4@OA magnetic nanoparticles;

[0035] Figure 12 The fluorescence spectrum and actual image of self-made fluorescent PE and PP MPs before and after adsorption by Fe3O4@OA magnetic nanoparticles;

[0036] Figure 13 The results of the separation efficiency of MPs by recycled Fe3O4@OA magnetic nanoparticles;

[0037] Figure 14 The results of the separation efficiency of MPs by Fe3O4@OA magnetic nanoparticles in seven simulated actual samples;

[0038] Figure 15 The fluorescence spectrum of MPs before and after separation by Fe3O4@OA magnetic nanoparticles in simulated actual samples;

[0039] Figure 16 The cell activity results of Fe3O4@OA magnetic nanoparticles. DETAILED DESCRIPTION

[0040] In order to make the technical features of the present solution clear, the present application will be described in detail below through specific embodiments, and in conjunction with the accompanying drawings.

[0041] (I) Instruments and materials

[0042] 1.1 Instruments: Magnetic stirring water bath (Model HCJ-4E) purchased from Wuxi Zhanhai Technology Co., Ltd.; electronic balance (Model CAVZ14C) purchased from OHAUS, USA; UV / O cleaner (Model ProCleaner 220) purchased from Bioforce Nanosciences, USA; nanoparticle size and potential analyzer (Model Zetasizer Nano ZS90) purchased from Malvern, UK; Fourier infrared spectrometer (NICOLET iS10) purchased from Thermo Fisher, USA; ultrasonic cleaner (Model SB-5200D) purchased from Ningbo Xinzhi Biotechnology Co., Ltd.; magnetic stirrer (Model AMM-6T) purchased from Tianjin Autesen Co., Ltd.; fluorescence spectrophotometer (Model RF-6000) purchased from Shimadzu, Japan; Sartorius water purification system (Model Arium Pro VF) purchased from Sartorius, Germany; ultrasonic cell disruptor (Model 92-IIDN) purchased from Ningbo Xinzhi Biotechnology Co., Ltd.; constant temperature shaker (Model HY-4B) purchased from Shaoxing Super Instrument Co., Ltd.; electric fluorescence microscope (Model Ni-E) purchased from NIKON, Japan; constant temperature water bath (Model HH-2) purchased from Guohua Electrical Appliance Co., Ltd.; microplate reader (Model Varioskan Flash) purchased from Thermo Fisher, USA.

[0043] 1.2 Materials: Pharmaceutical iron trichloride hexahydrate, ferrous sulfate heptahydrate, ammonia water, oleic acid, hydrochloric acid, anhydrous ethanol, potassium bromide, sodium chloride, bovine serum albumin, tetrahydrofuran, ferrous chloride tetrahydrate, citric acid monohydrate, dextran 40, tetraethyl orthosilicate, gelatin, sodium hydroxide, urea, dimethyl sulfoxide, all purchased from Sinopharm Group. Green fluorescent polystyrene microspheres purchased from Tianjin Baisi Chromatography Technology Development Center. PE plastic powder and PP plastic powder purchased from Dongguan Huachuang Plasticizing Co., Ltd. Nile red purchased from Beijing Solaybao Technology Co., Ltd. Tea (Hangzhou Tea Factory Co., Ltd.); toothpaste (Unilever (China) Co., Ltd.); kelp (Fujian Yuyuan Marine Food Co., Ltd.); honey (Beijing Baihua Bee Industry); large yellow croaker (Ningbo Lulin Market).

[0044] (II) Preparation of Fe3O4@OA magnetic nanoparticles

[0045] 2.1 Preparation method of Fe3O4@OA magnetic nanoparticles

[0046] One specific method is to accurately weigh 5.56 g (0.020 mol) of ferrous sulfate heptahydrate (FeS04-7H20) and 11.60 g (0.043 mol) of ferric chloride hexahydrate (FeCl3-6H20), and make them completely dissolved in 350 mL of deionized water. The mixed solution is placed in a magnetic stirring water bath and heated to about 80°C, and then 20 mL of ammonia water (NH3-H20) is quickly added to maintain the pH at about 11.0-12.0, and stirred vigorously for about 10 min. The pH of the system is adjusted to about 7.0 with 1 M (1 mol / L) hydrochloric acid (HC1) solution, and then 0.35 mL of oleic acid is added and stirred uniformly. The above reaction system is maintained at 80°C for 1 h and then cooled to room temperature. The magnetic nanoparticles are collected by a magnet and washed repeatedly with ethanol and deionized water for several times to remove excess oleic acid. The washed magnetic nanoparticles are dried under vacuum at 60°C for 12 h, and the dried magnetic nanoparticles are ground into powder for use. In the following experimental process, the "Fe304@OA magnetic nanoparticles" can also be referred to as "oleic acid-modified Fe304 magnetic nanoparticles".

[0047] The preparation method of the Fe304 magnetic nanoparticles without oleic acid modification is the same as that of the Fe304@OA magnetic nanoparticles, except that the step of adding oleic acid is not included: the pH of the system is adjusted to about 7.0 with 1 mol / L hydrochloric acid solution, and then 0.35 mL of oleic acid is added and stirred uniformly.

[0048] 2.2 Determination of the synthesis of Fe304@OA magnetic nanoparticles

[0049] 2.2.1 Infrared determination

[0050] The determination method is to use the tabletting method to prepare samples of Fe304@OA magnetic nanoparticles and unmodified Fe304 magnetic nanoparticles, respectively. Specifically, the completely dried magnetic nanoparticles are ground in an agate mortar, and then potassium bromide powder dried in an oven at 125°C for 4 h is added. The magnetic nanoparticles and potassium bromide powder are mixed uniformly at a ratio of 1:20 (v / v) and then transferred to a tablet mold, vacuumized and pressed for 2 min. The mixture forms a translucent small disc under the action of pressure, which is placed in a Fourier infrared spectrometer for testing. The test results are shown in Figure 1

[0051] The results are shown in Table 1. Figure 1 ​From the analysis, it can be seen that the band at 580 cm-1 is attributed to the Fe-O bending in the Fe3O4 lattice for the unmodified Fe3O4 MNPs. The bands at 1630 cm-1 and 3405 cm-1 are attributed to the characteristic peaks of -OH on the surface of Fe3O4. After the esterification reaction, some new bands appear in the spectrum of the synthesized Fe3O4@OA MNPs, which can be attributed to the various vibrational modes of the functional groups of the oleic acid molecules, including the -CH3 umbrella mode (1413 cm-1), -C=O- stretching vibration (1714 cm-1), asymmetric (2852 cm-1) and symmetric (2922 cm-1) -CH2- stretching, and asymmetric stretching vibration of -COO- (1457 cm-1). The above results show that the oleic acid is successfully modified on the surface of the Fe3O4 MNPs.

[0052] 2.2.2 Particle size distribution determination

[0053] The determination method is as follows: the particle size of the Fe3O4@OA MNPs is determined by a nanoparticle size potential analyzer. Specifically, the Fe3O4@OA MNPs are dissolved in water by ultrasonic to form a liquid sample of 1 mg / L, and 1 mL thereof is taken into a particle size sample cell. After removing the bubbles, the determination is performed in the nanoparticle size potential analyzer, and the determination results are shown in Table 2. Figure 2 a. Wherein the refractive indexes of the Fe3O4@OA and water are 3.04 and 1.33, respectively.

[0054] Figure 2 a. The dynamic light scattering results of the Fe3O4 MNPs before and after modification with oleic acid are shown, which show that the average particle sizes of the magnetic nanoparticle aggregates are 350 nm and 255 nm, respectively. The decrease in the DLS particle size indicates that the successful modification of the oleic acid increases the dispersibility of the Fe3O4 MNPs, and the magnetic aggregation effect is reduced.

[0055] 2.2.3 TEM electron microscope characterization

[0056] The characterization method is as follows: first, place the copper mesh in a UV / O cleaner, and irradiate it with an ultraviolet lamp for 5 min to hydrophilize the surface of the copper mesh. Hold the copper mesh with tweezers and place it horizontally. Dissolve the Fe3O4@OA MNPs in water by ultrasonic to prepare a liquid sample of 1 mg / L, and drop 4 μL thereof onto the copper mesh. Absorb the excess liquid drops with a paper towel and place it in a dark place at room temperature. After the water is completely dried, place it in a TEM electron microscope for observation. The observation results are shown in Table 3. Figure 2 b.

[0057] Figure 2b is the TEM transmission electron microscope image of Fe3O4@OA magnetic nanoparticles. The Fe3O4@OA magnetic nanoparticles prepared in the present study have a single particle size of about 20 nm, and due to the magnetic effect, they are in a state of aggregation with each other. The upper right corner of the figure is an insert showing that the magnetic nanoparticles rapidly aggregate to the side close to the magnet within 1 min under the attraction of a strong magnet, and the solution changes from turbidity to clarity, indicating that the Fe3O4@OA magnetic nanoparticles have good magnetism.

[0058] 2.2.4 Contact angle measurement

[0059] Measurement method: The completely dried Fe3O4@OA magnetic nanoparticles were ground into a solid powder in a mortar. In order to prevent roughness effect, an appropriate amount of solid powder was spread on an adhesive-coated glass slide, and then flattened with another glass slide, leaving no excess powder, and then placed in a contact angle measuring instrument for contact angle measurement. The measurement results are shown in Figure 3 .

[0060] In general, materials with a contact angle less than 90° are considered hydrophilic, and materials with a contact angle greater than 90° are considered hydrophobic. The contact angle experimental results of Fe3O4@OA magnetic nanoparticles are shown in Figure 3 . The contact angle of unmodified Fe3O4 magnetic nanoparticles is less than 90°, indicating that it has strong hydrophilicity, because the surface of the magnetic nanoparticles contains hydrophilic groups -OH. The contact angle θ of Fe3O4@OA magnetic nanoparticles is 136.4° (greater than 90°), indicating that it has strong hydrophobicity. The enhancement of hydrophobicity is due to the long-chain alkane branched to the surface of the magnetic nanoparticles, which further verifies the successful modification of oleic acid.

[0061] In summary, the present application successfully prepared Fe3O4@OA magnetic nanoparticles with hydrophobic properties, and the modification principle is as follows: the Fe3O4@OA magnetic nanoparticles prepared in the present application use the esterification reaction between the carboxyl group (-COOH) in the oleic acid molecule and the hydroxyl group (-OH) on the surface of Fe3O4 to firmly combine, and at the same time, the long-chain alkane with hydrophobic properties at the end of the oleic acid molecule is exposed on the surface of the magnetic nanoparticles, providing effective hydrophobic sites for the adsorption of MPs. This modification method not only theoretically enhances the adsorption of Fe3O4 magnetic nanoparticles to MPs, but also makes it more sustainable in environmental governance applications due to the biocompatibility and environmental friendliness of oleic acid. The specific modification principle is shown in Figure 4 .

[0062] (Three) Adsorption and separation experiment of Fe3O4@OA magnetic nanoparticles on microplastics in deionized water samples

[0063] 3.1 Involved method

[0064] 3.1.1 Method for preparing fluorescent microplastic standard solution: Deionized water and fluorescent polystyrene microspheres are used to prepare a fluorescent MP standard solution with a certain microplastic concentration.

[0065] 3.1.2 Adsorption separation method: Fe3O4@OA magnetic nanoparticles are added to the fluorescent MP standard solution to maintain a concentration of 1 g / L, and then placed in an ultrasonic cleaner for 2 min to promote the adsorption of Fe3O4@OA magnetic nanoparticles to the surface of MPs. Under the magnetic action of a strong magnet, MPs with Fe3O4@OA magnetic nanoparticles adsorbed on their surface are attracted to the side close to the magnet, thereby realizing the adsorption separation of MPs in a liquid environment.

[0066] 3.1.3 Desorption method: Desorption solvent is added to the solution containing adsorbed microplastics, and the mixture is ultrasonically mixed for 3 min in an ultrasonic cleaner to desorb Fe3O4@OA magnetic nanoparticles from the surface of PS MPs. The higher the fluorescence intensity in the solution, the more desorption occurs.

[0067] 3.1.4 Adsorption separation efficiency calculation method: First, the concentration of residual microplastics in the system is calculated by the standard curve of microplastic fluorescence intensity and concentration, and then the adsorption separation efficiency of magnetic nanoparticles for microplastics is calculated by the separation efficiency formula.

[0068] wherein the standard curve is Y = 129.06x - 19.58 (wherein Y is the fluorescence intensity of plastics, x is the concentration of MPs, R2 = 0.999), and the above formula is the standard curve of fluorescence intensity at 518 nm wavelength and microplastic concentration under excitation light at 488 nm wavelength.

[0069] Separation efficiency = [1 - (C1V1 / C0V0)] * 100%, wherein C0 and C1 represent the concentrations of residual MPs in the system before and after adsorption separation by Fe3O4@OA magnetic nanoparticles, and V0 and V1 represent the volumes of liquid phases.

[0070] 3.2 Effect of magnetic adsorption time on the adsorption separation of microplastics by Fe3O4@OA magnetic nanoparticles

[0071] A 25 mg / L PS fluorescent microplastic standard solution is prepared according to the method in 3.1.1. The microplastics are adsorbed and separated according to the method in 3.1.2, wherein the amount of oleic acid modification of Fe3O4@OA magnetic nanoparticles is 3.5 μL / g, and the fluorescence intensity of residual MPs at 518 nm is measured when the magnet adsorption time is 1 min, 3 min, 5 min, 10 min and 30 min, respectively. Then the adsorption separation efficiency under different magnet adsorption times is calculated according to the method in 3.1.4, and the results are shown in Figure 5 .

[0072] By Figure 5 It can be seen that after 1 min of magnetic separation, PS fluorescent MPs are adsorbed and separated in a very short time, and the separation efficiency reaches 95%. After 3 min of separation, the removal rate of MPs from the solution is more than 98%. The removal rate reaches saturation at 5 min, and the removal efficiency hardly changes with the increase of time, and only a small amount of MPs remains in the system. Shi et al. reported that the separation efficiency of commercially available magnetic nanoparticles for MPs was only 80% within 150 min, while the Fe3O4@OA magnetic nanoparticles prepared in this study can achieve high-efficiency separation of MPs within 5 min.

[0073] 3.3 Explore the effect of the amount of oleic acid modification on the adsorption and separation of microplastics by Fe3O4@OA magnetic nanoparticles

[0074] Prepare a 25 mg / L PS fluorescent microplastic standard solution according to the method in 3.1.1. Perform microplastic adsorption and separation according to the method in 3.1.2. During the separation process, the magnet adsorption time is 5 min, and 1 g of Fe3O4 magnetic nanoparticles modified with 0, 2 μL / g, 3.5 μL / g, 5 μL / g, and 10 μL / g of oleic acid are added, respectively. The residual MPs fluorescence value after adsorption and separation of MPs in the system by Fe3O4 magnetic nanoparticles with different amounts of oleic acid modification is measured. Calculate the adsorption and separation efficiency under different amounts of oleic acid modification according to the method in 3.1.4, and the results are shown in Figure 6 .

[0075] By Figure 6 It can be seen that after 1 min of magnetic separation, PS fluorescent MPs are adsorbed and separated in a very short time, and the separation efficiency reaches 95%. After 3 min of separation, the removal rate of MPs from the solution is more than 98%. The removal rate reaches saturation at 5 min, and the removal efficiency hardly changes with the increase of time, and only a small amount of MPs remains in the system. Shi et al. reported that the separation efficiency of commercially available magnetic nanoparticles for MPs was only 80% within 150 min, while the Fe3O4@OA magnetic nanoparticles prepared in this study can achieve high-efficiency separation of MPs within 5 min.

[0076] 3.4 Explore the effect of the amount of Fe3O4@OA magnetic nanoparticles on the adsorption and separation of microplastics

[0077] Prepare a PS fluorescent microplastic standard solution of 25 mg / L according to the method in 3.1.1. Perform microplastic adsorption separation according to the method in 3.1.2, in the process, add Fe3O4 magnetic nanoparticles with a modification amount of 3.5 μL / g, and control the ratio of the amount of addition to the mass of PS MPs (g / g) to be 4, 20, 40, 120 and 200 respectively, and measure the fluorescence value (518 nm) of the residual MPs after the adsorption separation of MPs in the system by the Fe3O4@OA magnetic nanoparticles of different concentrations when the magnet adsorption time is 5 min, and calculate the separation efficiency under different concentrations according to the method in 3.1.4, and the results are shown in Figure 7 .

[0078] It can be seen from Figure 7 that as the ratio of Fe3O4@OA magnetic nanoparticles to MPs increases from 4 to 200 (g / g), the separation efficiency of PS MPs gradually increases. This can be attributed to the increase in adsorption density of Fe3O4@OA magnetic nanoparticles on PS MPs with the increase in concentration, thereby causing more MPs to be adsorbed and separated by the strong magnet. When the ratio of Fe3O4@OA magnetic nanoparticles to MPs is 4 (g / g), the separation efficiency reaches 90%; when the ratio is 20 (g / g), the separation efficiency of magnetic nanoparticles on MPs significantly increases to 95%; when the concentration of magnetic nanoparticles continues to increase, and the ratio is greater than or equal to 40 (g / g), the separation efficiency is as high as 98%, and there is no significant increase in the separation results of 120 and 200 (g / g).

[0079] 3.5 Explore the force of Fe3O4@OA magnetic nanoparticles on microplastic adsorption

[0080] Prepare a PS fluorescent MP standard solution with a concentration of 25 mg / L according to the method in 3.1.1; perform microplastic adsorption separation according to the method in 3.1.2; and perform microplastic desorption operation according to the method in 3.1.3. In the desorption process, the desorption solvents added are 50% (v / v) dimethyl sulfoxide (DMSO), 5 mol / L urea (Urea), 10 mmol / L sodium hydroxide (NaOH), 10 mmol / L hydrogen chloride (HCl) and 3 mol / L sodium chloride (NaCl). The adsorption force between Fe3O4@OA magnetic nanoparticles and MPs is inferred by measuring the fluorescence intensity of the residual MPs in the solution after desorption, and the fluorescence spectrum of PS MPs with surface adsorbed magnetic nanoparticles under different solvent conditions at an excitation wavelength of 488 nm is shown in Figure 8 a, the fluorescence intensity at a wavelength of 518 nm is shown in Figure 8 b. Among them, in Figure 8 a, the inset is the corresponding real picture under dark field.

[0081] It can be seen from the above that the desorption of PS MPs from the surface of Fe3O4@OA magnetic nanoparticles is the weakest in 50% (v / v) DMSO, and the desorption of PS MPs from the surface of Fe3O4@OA magnetic nanoparticles is the strongest in 5 mol / L Urea.Figure 8 From Figs. 8a and 8b, it can be seen that the fluorescence intensity of the system increased significantly after the introduction of DMSO, which clearly indicated that the hydrophobic interaction force made a major contribution to the effective adsorption. The fluorescence enhancement effect in the system was weak when urea, sodium hydroxide and hydrochloric acid were added, that is, the desorption of MPs was not obvious, indicating that the hydrogen bond and electrostatic interaction force were weak. It is worth noting that the fluorescence intensity of the system added with sodium hydroxide was higher than that of the system added with hydrochloric acid, because after the addition of sodium hydroxide, the high pH caused the Fe3O4@OA magnetic nanoparticles to produce negative charges, and the electrostatic repulsion with the negatively charged PS MPs led to desorption. In addition, by adding sodium chloride to screen the charge interaction, the obtained fluorescence intensity was obviously lower, indicating that the electrostatic interaction contributed less to the adsorption. In summary, we speculate that the main force between the MPs with strong hydrophobic properties and the Fe3O4@OA magnetic nanoparticles is the hydrophobic interaction.

[0082] 3.6 Exploration of the effects of different surface modified Fe3O4 magnetic nanoparticles on adsorption and separation of microplastics

[0083] 3.6.1 Preparation of SiO2, gelatin and dextran modified Fe3O4 magnetic nanoparticles

[0084] (1) Preparation of SiO2 modified Fe3O4 magnetic nanoparticles

[0085] The SiO2 modified Fe3O4 magnetic nanoparticles were prepared by Stöber method. 1 g of the above dried and ground Fe3O4 magnetic nanoparticle sample was dispersed in a solution composed of 20 mL of deionized water and 60 mL of ethanol, and ultrasonically dispersed for 30 min. Then, it was placed in a magnetic stirrer and stirred while adding 1 mL of ammonia water dropwise, and continued to stir for 30 min, and 6 mL of TEOS (mass ratio of TEOS to Fe3O4 was 11.2) was added in batches, and stirred at room temperature for 24 h. After the reaction was completed, the sample was washed with ethanol for 3-5 times to remove the remaining reactants, and then washed with deionized water for 3-5 times. The sample was vacuum dried at a temperature of 60 °C for 12 h to obtain the SiO2 modified Fe3O4 magnetic nanoparticles.

[0086] (2) Preparation of gelatin modified Fe3O4 magnetic nanoparticles

[0087] Fe3O4 magnetic nanoparticles were synthesized by co-precipitation of ferrous and ferric ions with ammonia. First, 1.22 g of FeCl3-6H2O and 2.38 g of FeSO4-7H2O were dissolved in 40 mL of deionized water under nitrogen atmosphere and placed in a magnetic stirring water bath at 80°C and stirred vigorously for 10 min. 5 mL of ammonia was added and the mixture was stirred vigorously for 30 min to allow the Fe3O4 magnetic nanoparticles to precipitate fully. Then, 2 mL of a 2.38 M aqueous solution of citric acid monohydrate was added to the Fe3O4 magnetic nanoparticle system and the reaction was continued at 95°C for 90 min. Next, 1 g of gelatin solid powder was accurately weighed and dissolved in 100 mL of water and stirred at 60°C for 30 min to obtain a gelatin aqueous solution. 6 mL of the gelatin aqueous solution was added to the prepared citric acid-modified Fe3O4 solution and the reaction was carried out in a 95°C water bath for 30 min to obtain a gelatin-modified Fe3O4 magnetic nanoparticle solution. Finally, the system was cooled to room temperature and the gelatin-modified Fe3O4 magnetic nanoparticles were collected from the solution using a strong magnet, washed several times with ultrapure water and vacuum dried in an oven at 60°C for 12 h. The dried magnetic nanoparticles were ground into powder for use.

[0088] (2) Preparation of dextran-modified Fe3O4 magnetic nanoparticles

[0089] Dextran-modified Fe3O4 magnetic nanoparticles were prepared by co-precipitation. The specific method is as follows: 4 g of dextran 40 and 2 g of FeCl3-6H2O were dissolved in 30 mL of deionized water, then 0.8 g of ferrous chloride tetrahydrate was added. After the solid was completely dissolved, the mixture was stirred vigorously under nitrogen atmosphere and 5 mL of ammonia was quickly added to the system. The mixture immediately turned black. The reaction system was kept at 60°C for 1 h and then cooled to room temperature. The product was washed several times with ethanol and deionized water and collected using a strong magnet. The product was placed in a 60°C oven and vacuum dried for 12 h for use.

[0090] 3.6.2 Comparison of adsorption effects of Fe3O4 magnetic nanoparticles with different surface modifications

[0091] Fluorescent PS MPs standard solutions were diluted to 25 mg / L, 50 mg / L, 100 mg / L, and 200 mg / L, respectively. Five different modified Fe3O4 magnetic nanoparticles (unmodified, oleic acid-modified, SiO2-modified, gelatin-modified, and dextran-modified) were added to each solution, maintaining a concentration of 1 g / L in the system. The mixture was then ultrasonicated for 2 min to promote the adsorption of the modified Fe3O4 magnetic nanoparticles onto the MPs surface. After 5 min of adsorption with a strong magnet, the fluorescence intensity (at 518 nm) of the remaining MPs after adsorption and separation by the five modified Fe3O4 magnetic nanoparticles was measured at 488 nm excitation wavelength. The remaining MPs were calculated using the corresponding standard curve, and the separation efficiency of Fe3O4 modified by different methods for MPs was calculated according to the separation efficiency formula. The results are shown in [Figure number missing]. Figure 9 .

[0092] pass Figure 9 It is evident that Fe3O4@OA magnetic nanoparticles exhibit good separation effects for MPs of varying concentrations, with separation efficiencies exceeding 95%. This may be attributed to the hydrophobic interaction between the long-chain alkanes on oleic acid molecules and MPs. The adsorption and separation efficiency of gelatin-modified Fe3O4 magnetic nanoparticles for MPs decreases with increasing MP concentration, likely due to the increased electrostatic repulsion between the two molecules as MP concentration rises, leading to a decrease in adsorption efficiency. Unmodified Fe3O4 magnetic nanoparticles show moderate separation effects for MPs of various concentrations, which can be attributed to the weak hydrogen bonding between the -OH groups on the Fe3O4 surface prepared by co-precipitation and the CH and OH groups on MPs. Dextran and silica-modified Fe3O4 magnetic nanoparticles show moderate separation effects for low concentrations but poor effects for high concentrations, possibly because these two hydrophilic modifications do not significantly alter the hydrophobic properties of the magnetic nanoparticles. In summary, hydrophobic Fe3O4@OA magnetic nanoparticles can achieve efficient adsorption and separation of both low and high concentrations of MPs, which further confirms that hydrophobic interaction forces are the key forces that enhance the adsorption and separation performance of magnetic nanoparticles for MPs.

[0093] (iv) Adsorption and separation of self-made fluorescent microplastics in BSA aqueous solution by Fe3O4@OA magnetic nanoparticles

[0094] Since MPs have the property of interacting with biomolecules in the environment (such as proteins), this part uses an aqueous solution containing bovine serum albumin (BSA) to disperse and stabilize MPs in order to more closely resemble their state in the real environment.

[0095] 4.1 Preparation of self-made fluorescent microplastics and their standard curves and characterization

[0096] 4.1.1 Preparation method

[0097] First, weigh 200 mg of plastic powder (PE or PP) and add it to 100 mL of 0.001 wt% BSA solution. Mix the powder in a constant-temperature shaker for 30 min. Then, add 1 mL of 1 g / L Nile Red dye solution and stain in the dark for 2 h. Wash away excess Nile Red dye solution using a vacuum filter. Redisperse the stained plastic powder in the BSA solution using ultrasound for later use. The concentration of MPs is determined by weighing the dried solid powder.

[0098] 4.1.2 Standard Curve

[0099] Self-made fluorescent PE and PP MPs were diluted with different concentration gradients (10 mg / L, 50 mg / L, 100 mg / L, 200 mg / L, 500 mg / L, 800 mg / L, 1000 mg / L), and the fluorescence intensity of PE and PP MPs at different concentrations was measured at 630 nm under an excitation wavelength of 530 nm. The R² values ​​of the fitted standard curves were all greater than 0.99, indicating good fit. The standard curves corresponding to the self-made fluorescent microplastics are as follows: Y = 10.26x + 81.47 (PE); Y = 13.77x + 134.92 (PP); where Y is the fluorescence intensity of the plastic and x is the concentration of MPs.

[0100] 4.1.3 Characterization Results

[0101] Figure 10 a and Figure 10 b shows images of PEMPs (approximately 800 nm in diameter) and PPMPs (approximately 2 μm in diameter) microplastics stained with Nile Red against a BSA background, observed under a motorized fluorescence microscope. The results indicate that they emit distinct orange-red fluorescence in dark-field conditions. The MPs exhibit various morphologies of real plastic fragments, with relatively uniform particle size, and can be used in the following experiments.

[0102] 4.2 Adsorption and separation of self-made fluorescent microplastics

[0103] PE and PP MPs standard solutions were diluted to 25 mg / L, 50 mg / L, 100 mg / L, and 200 mg / L, respectively. For these concentrations, adsorption separation was performed according to the method in 3.1.2 (magnetic adsorption time 5 min, oleic acid modification amount of Fe3O4@OA magnetic nanoparticles 3.5 μL / g, mass ratio 40). The separation efficiency was calculated using the method in 3.1.4, where the standard curve was replaced with the standard curve corresponding to the self-made fluorescent microplastic. Figure 11The figure shows the separation efficiency of Fe3O4@OA magnetic nanoparticles for self-made fluorescent PE(a) and PP(b) MPs. Figure 12 The images show the fluorescence spectra and physical images of Fe3O4@OA magnetic nanoparticles before and after adsorption of self-made fluorescent PP MPs. In the images, a, b, c, and d are the spectra corresponding to 25 mg / L, 50 mg / L, 100 mg / L, and 200 mg / L, respectively.

[0104] pass Figure 11 It can be seen that the adsorption and separation efficiencies of Fe3O4@OA magnetic nanoparticles for PE and PP MPs at four different concentrations are all higher than 95%, indicating good separation effect. Furthermore, there are no significant differences between the groups, suggesting that the separation efficiency is not significantly affected by the different plastic components. Therefore, it can be proven that the separation effect of Fe3O4@OA magnetic nanoparticles for MPs mainly depends on the hydrophobic properties of the MPs and is independent of the type and composition of the plastics.

[0105] pass Figure 12 It can be seen that after the PP MPs of different concentrations are separated by Fe3O4@OA magnetic nanoparticle adsorption, the high-concentration PP MPs solution changes from a distinct purplish-red color to clear and transparent. Furthermore, the detectable fluorescence intensity at all four concentrations is significantly reduced. This result further and intuitively reflects the good effect of this method on MPs separation.

[0106] 4.3 Investigation into the recyclability of self-made fluorescent microplastics

[0107] Taking PP MPs as an example, two MPs solutions with concentrations of 25 mg / L and 50 mg / L were prepared, and adsorption separation experiments were conducted according to the adsorption separation conditions in section 4.2. 50% (v / v) DMSO was added to the system to allow Fe3O4@OA magnetic nanoparticles to detach from the MPs surface. The Fe3O4@OA magnetic nanoparticles were collected using a strong magnet and dried overnight in a vacuum freeze dryer for 12 h. The freeze-dried magnetic nanoparticles were then ultrasonically mixed back into the MPs solution for magnetic separation. The fluorescence value of the remaining MPs in the solution was measured, and the concentration of the remaining MPs in the system was calculated based on the corresponding standard curve. The adsorption separation efficiency of Fe3O4@OA magnetic nanoparticles for MPs was calculated using the separation efficiency formula. The results are shown in [Figure 1]. Figure 13 The results for 25 mg / L and 50 mg / L are shown in the figure, where a and b correspond to the results for 25 mg / L and 50 mg / L, respectively.

[0108] pass Figure 13It can be seen that the magnetic nanoparticles adsorbed on the surface of MPs can be desorbed under the action of DMSO and can continue to be used for the adsorption and separation of MPs, that is, the recycling of magnetic nanoparticles is realized. There is a significant difference in the adsorption and separation of MPs of different concentrations by Fe3O4@OA magnetic nanoparticles in the second use, and the separation efficiency decreases significantly with the increase of the concentration of MPs, which may be because part of the oleic acid attached to the surface of Fe3O4 magnetic nanoparticles is lost after desorption by DMSO, resulting in a decrease in the adsorption effect of MPs. However, under the condition of low concentration (25 mg / L), the adsorption and separation efficiency of Fe3O4@OA magnetic nanoparticles to MPs can still reach about 88%, which shows that this method of recycling is more feasible in the range of low concentration of MPs and can effectively reduce the cost of actual application.

[0109] (Five) Adsorption and separation of self-made fluorescent microplastics in actual samples by Fe3O4@OA magnetic nanoparticles

[0110] The types, sizes and proportions of MPs existing in nature are complex and diverse. In order to more realistically simulate the actual situation, PE and PP MPs mixed at a ratio of 1:1 (c / c) were used to simulate the addition of MPs in the actual sample according to the types and proportions of MPs in the freshwater environment in China.

[0111] 5.1 Preparation of actual sample solution and its standard curve

[0112] 5.1.1 Seawater sample

[0113] (1) Sample solution preparation: The seawater sample used in this study was collected at Qingdao Huangdao Seaside. After standing at room temperature of 20℃ for 2h, 50mL of supernatant was taken and mixed with PE and PP MPs to obtain seawater containing MPs with a final concentration of 20 mg / L. It was stored at 20℃ for subsequent use. The seawater sample without the addition of MPs under the same conditions was used as a blank control.

[0114] (2) Standard curve preparation: 10 mg / L, 50 mg / L, 100 mg / L, 200 mg / L, 500 mg / L, 1000 mg / L and 2000 mg / L of MPs solution were prepared respectively. Under the excitation wavelength of 530 nm, the fluorescence intensity at 630 nm was measured, and the standard curve was prepared according to the relationship between fluorescence intensity and concentration. The standard curve formula obtained is: Y= 10.82x + 185.45 (where: Y is the fluorescence intensity of plastic, x is the concentration of MPs, R2=0.999).

[0115] 5.1.2 Soil sample

[0116] (1) Sample solution preparation: 5 g of soil from the green belt of Ocean University of China was randomly weighed, and the organic matter in the soil was digested by Fenton method. 50 mL of H2O2 (10%), 5 mL of FeSO4·7H2O (2 mM) and 25 mL of H2O were added to the soil, and the pH was adjusted to 3.0. After stirring, it was placed for 1 h. Then, the solution was heated at 90°C for 2 h until the liquid was completely evaporated. Finally, 20 mL of deionized water was added to the soil, mixed thoroughly, and 15 mL of the supernatant was taken and added to the PE and PP MPs mixture to obtain a soil water containing MPs with a final concentration of 50 mg / L, which was stored at 20°C for subsequent use. The soil water without adding MPs under the same conditions was used as a blank control.

[0117] (2) Standard curve preparation: The standard curve formula was obtained according to the same method in 5.1.1 (2): Y = 12.22x - 86.67 (where: Y is the fluorescence intensity of plastic, x is the concentration of MPs, R2=0.999)

[0118] 5.1.3 Toothpaste sample

[0119] (1) Sample solution preparation: 2 g of commercially available toothpaste was weighed and dissolved in 100 mL of deionized water, and the solution was heated at 50°C for 10 min to ensure dissolution of the toothpaste. Then, the solution was placed at 20°C for 30 min, and the supernatant was taken and added to the PE and PP MPs mixture to obtain a toothpaste water containing MPs with a final concentration of 125 mg / L, which was stored at 20°C for subsequent use. The toothpaste water without adding MPs under the same conditions was used as a blank control.

[0120] (2) Standard curve preparation: The standard curve formula was obtained according to the same method in 5.1.1 (2): Y = 10.03x +2073.51 (where: Y is the fluorescence intensity of plastic, x is the concentration of MPs, R2=0.989)

[0121] 5.1.4 Tea sample

[0122] (1) Sample solution preparation: 2 g of tea purchased from the market was added to 100 mL of deionized water and heated at 90°C for 60 min. Then, the solution was placed at 20°C for 3 d, and 50 mL of the supernatant was taken and added to the PE and PP MPs mixture to obtain a tea water containing MPs with a final concentration of 10 mg / L, which was stored at 20°C for subsequent use. The tea water without adding MPs under the same conditions was used as a blank control.

[0123] (2) Standard curve preparation: The standard curve equation was obtained according to the same method in 5.1.1(2): Y = 8.94x + 642.75 (where: Y is the fluorescence intensity of plastic, x is the concentration of MPs, R2= 0.991)

[0124] 5.1.5 Honey sample

[0125] (1) Sample solution preparation: 2 g of commercially available honey was weighed and dissolved in 100 mL of deionized water. Then, it was placed at 20°C for 2 h, and the supernatant was taken and mixed with PE and PP MPs mixture to obtain a final concentration of 16 mg / L of honey water containing MPs, which was stored at 20°C for subsequent use. The entire experiment was blank controlled by honey supernatant without adding MPs under the same conditions.

[0126] (2) Standard curve preparation: The standard curve equation was obtained according to the same method in 5.1.1(2): Y = 11.86x + 659.23 (where: Y is the fluorescence intensity of plastic, x is the concentration of MPs, R2= 0.999)

[0127] 5.1.6 Kelp sample

[0128] (1) Sample solution preparation: 10 g of kelp sample was taken, cut and soaked in 100 mL of deionized water. Then, the mixture was placed at 20°C for 2 h, and the supernatant was taken and mixed with PE and PP MPs mixture to obtain a final concentration of 25 mg / L of kelp supernatant containing MPs, which was stored at 20°C for subsequent use. The entire experiment was blank controlled by kelp supernatant without adding MPs under the same conditions.

[0129] (2) Standard curve preparation: The standard curve equation was obtained according to the same method in 5.1.1(2): Y = 15.03x + 806.44 (where: Y is the fluorescence intensity of plastic, x is the concentration of MPs, R2= 0.999)

[0130] 5.1.7 Fish meat sample

[0131] (1) Sample solution preparation: 50 g of peeled large yellow croaker fish meat was weighed, crushed into a paste and 0.01wt% of PBS buffer was added to maintain the quality of the fish meat. 5 g of fish meat paste was dissolved in 100 mL of deionized water and mixed uniformly by using an ultrasonic crusher. Then, the mixture was placed at 20°C for 12 h, and the supernatant was taken and mixed with PE and PP MPs mixture to obtain a final concentration of 1 mg / L of fish meat supernatant containing MPs, which was stored at 20°C for subsequent use. The entire experiment was blank controlled by fish meat supernatant without adding MPs under the same conditions.

[0132] (2) Standard curve: The standard curve formula was obtained according to the same method in 5.1.1 (2): Y = 15.10x + 7902.42 (where: Y is the fluorescence intensity of plastic, x is the concentration of MPs, R2=0.923)

[0133] 5.2 Adsorption separation experiment of actual samples

[0134] According to the method in 3.1.2, microplastic adsorption separation was carried out (magnetic adsorption time was 5 min, the amount of Fe3O4@OA magnetic nanoparticle oil modification was 3.5 μL / g, and the mass ratio was 40); after replacing the standard curve of self-made fluorescent microplastic, the separation efficiency was calculated according to the method in 3.1.4, and the results were shown in Figure 14 . It can be seen from Figure 14 that the adsorption separation efficiency of Fe3O4@OA magnetic nanoparticles on MPs in 7 kinds of actual environment and food samples was more than 91%, and it had good separation effect in different systems. It was proved that the hydrophobic interaction between oleic acid molecules and MPs was firm and reliable, and the method of using Fe3O4@OA magnetic nanoparticles to remove MPs from complex real samples was effective and feasible.

[0135] In order to more intuitively illustrate the adsorption separation effect of MPs, the fluorescence spectra of MPs in 7 kinds of actual samples before and after separation by Fe3O4@OA magnetic nanoparticles were analyzed, and the results were shown in Figure 15 . Before adding Fe3O4@OA magnetic nanoparticles, different standard fluorescent MPs in actual samples showed strong fluorescence signal at 630 nm; after adsorption separation by magnetic nanoparticles, the fluorescence intensity decreased obviously. This showed that most of the fluorescent MPs were attached with Fe3O4@OA magnetic nanoparticles, and realized the separation from the system with the magnetic action of strong magnet. In addition, in the relatively simple matrix (seawater, soil), the difference of fluorescence intensity before and after adsorption separation by Fe3O4@OA magnetic nanoparticles was relatively large; on the contrary, in other relatively complex matrix (toothpaste, tea, fish, honey, kelp), the difference of fluorescence intensity before and after separation was relatively small. This can be explained as the establishment of standard curve in complex matrix is affected by many factors, when the content of standard fluorescent MPs is 0, the relatively strong fluorescence intensity can be detected in the relatively complex matrix, which leads to the larger vertical intercept in the standard curve, and thus the comparison of fluorescence spectrum before and after adsorption is not as strong as in the simple matrix. Even so, through the comparison of fluorescence spectrum before and after adsorption, it can be found that the fluorescence intensity in different actual sample systems before and after adsorption of magnetic nanoparticles has changed obviously, which further proves the feasibility of the application of this adsorption separation method in actual samples.

[0136] (VI) Cell toxicity analysis of Fe3O4@OA magnetic nanoparticles

[0137] From 5.2, Fe3O4@OA magnetic nanoparticles have good adsorption and separation effect in actual samples, however, the influence of residual magnetic nanoparticles on human health after separating MPs is not clear, therefore, whether Fe3O4@OA magnetic nanoparticles have cytotoxicity is explored by adding Fe3O4@OA magnetic nanoparticles to HepG2 cell suspension. As shown in the results Figure 16 The cell activity under 5 different concentrations is greater than 95%, which has no significant difference with the control group, secondly, the cell activity does not decrease with the increase of the concentration of Fe3O4@OA magnetic nanoparticles, and the cell activity can still reach about 99% under the high concentration of 1000 mg / L, which indicates that Fe3O4@OA magnetic nanoparticles have no effect on cell activity. In conclusion, it can be proved that after the surface of Fe3O4 magnetic nanoparticles is modified with oleic acid, the cytotoxicity is not increased, Fe3O4@OA magnetic nanoparticles are safe and non-toxic, and have high biocompatibility, which lays a foundation for its wide application in food and environmental fields.

[0138] In conclusion, Fe3O4@OA magnetic nanoparticles exhibit superior feasibility in adsorption and separation of MPs. The adsorption and separation method of the present application is compared with other existing separation methods, and the results are shown in Table 1. The advantages of the method proposed in the present application are as follows: first, the method can achieve efficient separation (removal rate greater than 91%) in various complex matrices, which means that the hydrophobic interaction relied on by the method is firm and reliable, and is expected to be applied to actual scenes. Secondly, the method shows good separation effect on various MPs of different particle sizes and different types, which proves the universal applicability of the method, and further provides the possibility for the separation of MPs in actual environment and complex matrix. Finally, the raw materials of the method are easy to obtain, the preparation process is simple and low in energy consumption, and the cost is low, which meets the needs of safety, environmental protection and sustainability.

[0139] Table 1 Comparison of different adsorption and separation methods for MPs

[0140]

[0141] In conclusion, the method for separating microplastics of the present application not only has the advantages of simplicity, easy preparation, high efficiency and low cost, but also shows good separation effect in various complex matrices, and has scalability and practicability. The method of the present application is expected to be applied to the removal of MPs in water body systems such as mariculture farms and wastewater treatment plants, which not only can reduce the potential harm to aquatic organisms, but also can improve water quality, which is conducive to environmental protection and sustainable development.

[0142] The above detailed description does not limit the scope of the application, and any alternative improvements or changes made by those skilled in the art to the embodiments of the application fall within the scope of the application. The application is not limited by the details described above, but is limited only by the claims.

Claims

1. A method for separating microplastics in food or the environment based on sustainable magnetic nanoparticles, characterized in that, The steps include: adding Fe3O4@OA magnetic nanoparticles to a food or environmental sample solution containing microplastics, ultrasonically mixing, and then performing magnetic separation treatment for a time of not less than 5 minutes. The ratio of the amount of Fe3O4@OA magnetic nanoparticles added to the mass of the microplastics is not less than 4, and each gram of Fe3O4 in the Fe3O4@OA magnetic nanoparticles is modified with at least 3.5 μL of oleic acid. The preparation method of Fe3O4@OA magnetic nanoparticles is as follows: S1 Weigh ferrous sulfate heptahydrate and ferric chloride hexahydrate in a molar ratio of 0.02:0.043 and dissolve them in deionized water to obtain solution A; S2 Place solution A in a magnetically stirred water bath and heat it to 70-95℃, then quickly add ammonia to adjust the pH to not less than 11, and stir vigorously to obtain solution B. The stirring time is not less than 7 min; S3 Adjust the pH of solution B to 7 with 1 mol / L hydrochloric acid solution, then add oleic acid and stir evenly, then maintain at 65-95℃ for not less than 40 min, and then cool to room temperature to obtain solution C; S4 Collect the magnetic nanoparticles with a magnet, then wash them repeatedly with ethanol and deionized water to remove excess oleic acid, and then vacuum dry the washed magnetic nanoparticles at not less than 50°C for not less than 6 h, and then grind them into powder to obtain the final product; The method for recovering Fe3O4@OA magnetic nanoparticles after magnetic separation is as follows: DMSO desorption solvent is added to the system to be separated, with the amount added accounting for 50% of the total volume of the system after addition. The mixture is ultrasonically mixed in an ultrasonic cleaner to desorb the Fe3O4@OA magnetic nanoparticles from the microplastic surface. Then, the Fe3O4@OA magnetic nanoparticles are collected using a strong magnet and dried to obtain the final product.

2. The method for separating microplastics in food or the environment based on sustainable magnetic nanoparticles according to claim 1, characterized in that, The mass ratio of the added Fe3O4@OA magnetic nanoparticles to microplastics is not less than 40.

3. The method for separating microplastics in food or the environment based on sustainable magnetic nanoparticles according to claim 1, characterized in that, The separated microplastics include at least one of the following: PP, PE, PS, PVC, PET, and PA.

4. The method for separating microplastics in food or the environment based on sustainable magnetic nanoparticles according to claim 1, characterized in that, The drying conditions in the recovery method are: overnight drying in a vacuum freeze dryer for at least 12 hours.

5. The method for separating microplastics in food or the environment based on sustainable magnetic nanoparticles according to claim 1, characterized in that, The sample solution must be at least one of the following: seawater sample, soil sample, tea sample, honey sample, kelp sample, or fish sample.

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