Deuterium labeled polyethylene nanoplastics, methods of making and uses

Abstract

The present application belongs to the field of environmental analytical chemistry and isotope tracing technology, and discloses a kind of deuterium-labeled polyethylene nano-plastic, preparation method and application.The preparation method comprises: using polyethylene as raw material, and carrying out hydrogen-deuterium catalytic exchange reaction with deuterium gas under the action of catalyst;The reaction product is purified by dissolution and precipitation to obtain deuterium-labeled polyethylene;Then, after being dissolved in aromatic hydrocarbon solvent, it is quickly injected into pre-cooled ethanol, and a nanoparticle suspension is prepared by precipitation;After filtration, washing and dispersant stabilization treatment, a deuterium-labeled polyethylene nano-plastic aqueous dispersion is obtained.The method can realize controllable adjustment of deuterium substitution rate of 10%-60%, and the synthesis scale is significantly improved.The deuterium-labeled polyethylene nano-plastic prepared by the present application is stable in water dispersion, and can be applied to isotope quantitative tracing in scenes such as soil-plant system absorption and transport, environmental medium migration and biological enrichment, and provides a reliable technical means for ecological environment and health risk assessment of polyethylene nano-plastic.

Description

Technical Field

[0001] This invention relates to the fields of environmental analytical chemistry and isotope tracing technology, specifically to a deuterium-labeled polyethylene nanoplastic, its preparation method, and its application. Background Technology

[0002] Polyethylene (PE) is the world's most produced synthetic polymer, widely used in agricultural mulch films, packaging materials, and daily necessities. During use and disposal, PE products gradually degrade into micron- and nano-sized particles (i.e., microplastics and nanoplastics) through mechanical wear, photodegradation, and biodegradation, accumulating in large quantities in soil and water. Nanoplastics (particle size <1 μm), due to their small size, can penetrate the biological barrier of plant roots, be absorbed and transported to the above-ground parts, and thus pose a potential health risk through the food chain. Therefore, accurately quantifying PE nanoplastics in plants is a crucial prerequisite for assessing their ecological and health risks.

[0003] Currently, methods for tracking the fate of nanoplastics in organisms have the following shortcomings: (1) Fluorescent labeling method: tracers are formed by doping nanoplastics with fluorescent dyes, but the dyes are prone to leakage and photobleaching, and will change the surface properties of the particles, leading to false positive or false negative signals; (2) Metal doping method: nanoplastics are doped with metal elements such as palladium, gold, and lanthanides, and highly sensitive detection is performed by inductively coupled plasma mass spectrometry (ICP-MS), but the introduction of metal elements irreversibly changes the density, surface charge and aggregation behavior of the particles, making them unable to represent the environmental behavior of the original plastic; (3) Radioactive isotope labeling method (such as... 14 C) Extremely high sensitivity, but requires specialized synthesis facilities, and is subject to safety and regulatory restrictions, making it difficult to promote and apply on a large scale; (4) Conventional spectroscopic methods such as infrared spectroscopy (FTIR) and Raman spectroscopy do not require external labeling, but the CH stretching vibration peak of polyethylene (3100-2800 cm⁻¹) is not readily apparent. -1 The signals of polyethylene (PE) overlap significantly with those of lipids, carbohydrates, and proteins in biological tissues, resulting in substantial matrix interference. Furthermore, PE has a weak Raman scattering cross section, leading to insufficient sensitivity.

[0004] Stable isotope labeling, especially deuterium ( 2 H) labeling offers unique advantages for accurate quantitative tracing of micron or nanoplastics. First, deuterium has extremely low natural abundance, resulting in low analytical background and high detection sensitivity. Second, deuterium is covalently embedded in the polymer backbone, making it difficult to detach during accumulation in organisms, and its structural stability is far superior to exogenous labeling such as fluorescent dyes or metal doping. Third, the physicochemical properties of deuterated compounds are highly consistent with their hydrogen counterparts, and the tracing results better reflect the true environmental behavior of the original plastic.

[0005] However, the preparation of existing deuterium-labeled polymers mainly relies on polymerization routes containing deuterium monomers, facing dual bottlenecks of cost and scale. For example, invention patent CN115594782A discloses a deuterated polystyrene nanoparticle, its preparation method, and its application in the quantitative detection of nanoplastic concentrations in plants. Deuterium-labeled polystyrene nanoparticles were prepared via emulsion polymerization using deuterated styrene-d8 as the monomer. However, the deuterium-containing monomers used in this method are extremely expensive, resulting in a single synthesis scale typically only reaching milligrams, which is insufficient to meet the needs of large-scale environmental exposure experiments.

[0006] Hydrogen-deuterium (H / D) catalytic exchange technology offers another pathway to overcome the aforementioned bottlenecks. This route starts directly from commercially available polymers, replacing some CH bonds with CD bonds in the main chain through catalytic exchange while preserving the polymer backbone structure. This bypasses expensive deuterium-containing monomers, significantly reducing raw material costs and enabling gram-scale production. For example, Reference 1 (Solvent selective hydrogen-deuterium exchange on saturated polyolefins, Macromolecules 2012, 45, 7778-7782) used Pt / C as a catalyst for hydrogen exchange reactions of linear saturated polyolefins (ethylene), polyethylene-substituted propylene, and isotactic polyolefins (propylene), achieving gram-scale H / D exchange of saturated polyolefins. However, this H / D catalytic exchange work only completed the synthesis of deuterated polyethylene and has not yet involved the controllable preparation and tracer application of nanoplastics.

[0007] Transforming macroscopic bulk polymers into monodisperse nanoparticles requires precise control of nucleation and growth kinetics during the high-temperature dissolution-rapid precipitation process, while maintaining the integrity of the deuteration labeling at each stage of purification, solvent replacement, and surface stabilization. The mass production of this deuterated polyethylene nanoplastic makes it feasible to conduct statistically sound quantitative studies on the absorption and translocation of nanoplastics in plants based on environmentally relevant doses, a field currently lacking. Summary of the Invention

[0008] Existing stable isotope labeling methods utilize deuterium-containing monomer polymerization routes with low synthesis scale, failing to meet the sample quantity requirements of large-scale environmental exposure experiments. Furthermore, catalytic hydrogen-deuterium exchange technology is limited to macroscopic polymer synthesis, failing to convert it into monodisperse nanoparticles and establish stable aqueous dispersion and biological quantitative tracing methods, thus hindering the quantitative analysis of plant absorption and translocation of polyethylene nanoplastics. This invention provides a method for preparing deuterium-labeled polyethylene nanoplastics with large synthesis scale, controllable deuteration rate, and good stability. The deuterium-labeled polyethylene nanoplastics prepared by this method enable statistically sound quantitative studies of nanoplastic absorption and translocation in plants and animals, and significantly improve the tracking accuracy of nanoplastics in environmental media and within plants and animals.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing deuterium-labeled polyethylene nanoplastics includes the following steps: Step 1: Using polyethylene, saturated hydrocarbon solvent and catalyst as raw materials, deuterium gas is introduced under an inert atmosphere to carry out the reaction to obtain a reaction mixture; Step 2: Dissolve the reaction mixture in a haloaromatic solvent and filter. Add an alcohol solvent to the filtrate to precipitate and dry to obtain deuterium-labeled polyethylene. Step 3: Dissolve the deuterium-labeled polyethylene in an aromatic solvent, heat and reflux, then inject it into pre-cooled ethanol and stir to obtain a suspension of deuterium-labeled polyethylene nanoparticles. After filtration, obtain deuterium-labeled polyethylene nanoplastics.

[0010] This invention, based on hydrogen-deuterium catalytic exchange technology, directly utilizes inexpensive commercially available polyethylene, providing sufficient and customizable labeling materials for large-scale environmental exposure experiments. Furthermore, by leveraging the difference in solubility of deuterated polyethylene in halogenated aromatics and its precipitation in alcohols, repeated precipitation removes catalyst residues and unreacted oligomers, avoiding interference from residual catalysts or byproducts with subsequent isotope ratio mass spectrometry detection signals, fundamentally ensuring the reliability of quantitative results. Subsequently, it is dissolved in aromatic solvents and then rapidly injected into pre-cooled alcohols. The temperature difference and solvent displacement cause instantaneous supersaturation of the polymer chain solubility, inducing homogeneous nucleation to obtain nanoscale particles. Finally, particle size separation through filtration yields deuterium-labeled polyethylene nanoplastics in nanoparticle form.

[0011] Preferably, the polyethylene in step 1 is selected from one or more of low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, and high-density polyethylene; The saturated hydrocarbon solvent is selected from one or more of C5-C8 saturated hydrocarbon solvents, specifically one or more of n-pentane and isooctane.

[0012] When C5-C8 saturated hydrocarbon solvents are used as solvents in the H / D catalytic exchange reaction, deuterium gas can selectively react with polyethylene polymers and undergo isotope exchange. Furthermore, the saturated hydrocarbon solvents themselves are chemically stable with few side reactions, ensuring that the deuteration reaction occurs only on the target product, polyethylene.

[0013] More preferably, the ratio of polyethylene to saturated hydrocarbon solvent is 1 g: 50-200 mL.

[0014] Preferably, the catalyst described in step 1 is selected from one or more of palladium on carbon, platinum on carbon, rhodium on carbon, and ruthenium on carbon; The mass fraction of precious metals in the catalyst is 5%-10%.

[0015] More preferably, the catalyst is palladium on carbon.

[0016] Preferably, the mass ratio of polyethylene to catalyst is 2-10:1.

[0017] Preferably, the inert atmosphere is either argon or nitrogen.

[0018] Preferably, in step 1, the pressure of introducing deuterium gas for the reaction is 1.5-3.0 MPa, the reaction temperature is 160℃-180℃, and the reaction time is 0.5-24 h.

[0019] By using the deuterium gas pressure, reaction temperature, and reaction time within the above range, polyethylene with different deuteration rates can be prepared within a wide range, flexibly meeting different detection sensitivity requirements.

[0020] Preferably, the halogenated aromatic solvent in step 2 is selected from one or more of 1,2,4-trichlorobenzene and o-dichlorobenzene; The alcohol solvent is selected from one or more C1-C3 alcohol solvents, specifically one or more of methanol and ethanol; The volume ratio of polyethylene to halogenated aromatic solvent is 1 g: 20-50 mL; the volume ratio of alcohol solvent to halogenated aromatic solvent is 5-1:1.

[0021] Choosing halogenated aromatic hydrocarbon solvents allows for the complete dissolution of polyethylene at high temperatures, utilizing the difference in solubility parameters—the extension of molecular chains in halogenated aromatic hydrocarbon solvents and the collapse of chain segments in alcohol solvents—to achieve this. During precipitation, unreacted catalyst particles, unable to be encapsulated by the polymer chains, remain in the liquid phase and are filtered out. Using these solvents for dissolution and precipitation effectively eliminates residual metal catalysts, preventing interference with the accuracy of isotope ratio determination in subsequent detection methods due to sensitivity to trace impurities, thus ensuring the accuracy of quantitative results.

[0022] Preferably, the drying in step 2 is carried out by vacuum drying, with a drying temperature of 50℃-100℃ and a drying time of 12-24 h.

[0023] Preferably, the deuteration rate of the deuterated polyethylene obtained in step 2 is 10%-60%.

[0024] Preferably, the aromatic solvent in step 3 is selected from one or more of xylene and toluene; The concentration of deuterium-labeled polyethylene in aromatic solvents is 1-5 mg / mL.

[0025] More preferably, the concentration of deuterium-labeled polyethylene in an aromatic solvent is 2 mg / mL.

[0026] Preferably, the temperature of the heating reflux in step 3 is 140℃-200℃, and the time is 1-4 h.

[0027] Preferably, the volume ratio of ethanol to aromatic solvent is 1-5:1.

[0028] More preferably, the pre-cooling temperature in step 3 is 0℃-8℃.

[0029] Heating and refluxing within the above conditions causes the polymer chains to be in a disordered coil state. Then, rapidly injecting ethanol at the pre-cooled temperature can achieve extremely high supersaturation in a very short time. The thermodynamic driving force promotes the formation of a large number of crystal nuclei. At the same time, the low temperature rapidly freezes the chain segment movement, kinetically locking the particle size at the nanoscale. The prepared nanoparticles have a surface roughness and defect sites that are closer to those of real-world nanoplastics.

[0030] Preferably, the stirring speed in step 3 is 500-1500 rpm.

[0031] Preferably, the filter membrane used for filtration in step 3 is an organic polymer microporous filter membrane with a pore size of 0.8-5.0 μm.

[0032] More preferably, the filter membrane is a polytetrafluoroethylene membrane or a polyvinylidene fluoride membrane.

[0033] On the other hand, the present invention also provides deuterium-labeled polyethylene nanoplastics prepared by the aforementioned preparation method.

[0034] Furthermore, the present invention also provides the application of the aforementioned deuterium-labeled polyethylene nanoplastics in environmental and biological tracer applications of polyethylene nanoplastics, wherein the applications include one or more of the following: The deuterium-labeled polyethylene nanoplastics are used as isotope tracers in the study of absorption and translocation in soil and plant systems. The deuterium-labeled polyethylene nanoplastics serve as quantitative probes for studying migration, transformation, and fate in environmental media. The deuterium-labeled polyethylene nanoplastics serve as quantitative standard substances required for studies on bioaccumulation and food chain transmission.

[0035] Preferably, the method for quantitative tracing of plant uptake using deuterium-labeled polyethylene nanoplastics includes the following steps: Deuterium-labeled polyethylene nanoplastics were transferred to an aqueous dispersion containing a dispersant to obtain a deuterium-labeled polyethylene nanoplastic aqueous dispersion. Add the deuterium-labeled polyethylene nanoplastic aqueous dispersion to the plant hydroponic system, and let the plants grow in the nutrient solution containing the deuterium-labeled polyethylene nanoplastic for 7-21 days. After exposure, root and aboveground tissues were collected separately, washed, dried, and ground, and the δ-values ​​in the plant tissues were measured. 2 H value was calculated, and the content of deuterium-labeled polyethylene nanoplastics in plant tissues was determined.

[0036] Deuterium-labeled polyethylene nanoplastics are transferred to an aqueous dispersion containing a dispersant to break up the aggregates. At the same time, the dispersant is physically adsorbed onto the surface of the nanoparticles through hydrophobic interactions, forming steric hindrance or electrostatic repulsion. This solves the problem of easy aggregation and sedimentation of nanoparticles in the aqueous phase, allowing them to be used directly in a stable suspension for real-world environmental simulations such as hydroponics. This significantly improves the ease of operation and the accuracy of exposure dosage.

[0037] Among them, elemental analysis-isotope ratio mass spectrometry was used to determine the δ in the tissue. 2 The H value was used to calculate the content of deuterium-labeled polyethylene nanoplastics in the tissue using the isotope mass balance method.

[0038] More preferably, the detection limit of the quantitative tracer is calculated based on three times the standard deviation of the deuterium content in blank plant tissue, and the quantification limit is calculated based on ten times the standard deviation.

[0039] Preferably, the dispersant is selected from one or more of protein-based, polyvinyl alcohol-based, nonionic surfactant-based, and anionic surfactant-based dispersants; The mass fraction of the dispersant in the aqueous dispersion of deuterium-labeled polyethylene nanoplastics is 0.01%-0.1%.

[0040] The above-mentioned types of dispersants have good biocompatibility and long stability time, and can prevent aggregation.

[0041] More preferably, the dispersant is one or more of bovine serum albumin, polyvinyl alcohol, Tween 80, and sodium dodecylbenzene sulfonate.

[0042] More preferably, the dispersant is one or more of bovine serum albumin and Tween 80.

[0043] Compared with the prior art, the present invention has the following beneficial effects: (1) The preparation method provided by the present invention is based on the heterogeneous catalytic H / D exchange route and combined with purification and nanoprecipitation technology, bypassing the expensive deuterated monomer, significantly improving the synthesis scale of deuterated polyethylene, fundamentally solving the urgent need for large-scale, high-dose labeling materials in environmental exposure experiments; transforming macroscopic deuterated polyethylene into nanoscale particles with controllable particle size and good dispersibility, and achieving long-term stable dispersion in the aqueous phase, the preparation method is simple and controllable.

[0044] (2) The deuteration rate of the prepared deuterated polyethylene nanoplastic is precisely controllable and can be flexibly adapted to the sensitivity requirements of different detection instruments. Furthermore, there is no significant difference in the molecular weight distribution, thermal stability and surface chemical properties of polyethylene before and after deuteration. Moreover, there is no statistical difference in the root absorption and stem transport behavior of the two types of particles by plants, thus realizing the true tracking and high-precision tracking of the original polyethylene nanoplastic.

[0045] (3) Polyethylene nanoplastics that can be prepared on a large scale, have precise control over deuteration rate, be stored for a long time, and be truly traced can be widely used in research on the environmental health risks of micro / nanoplastics. Attached Figure Description

[0046] Figure 1 This is a comparison of the infrared spectra of the deuterium-labeled polyethylene prepared in Example 1 and the original polyethylene.

[0047] Figure 2 This is a scanning electron microscope image of the deuterated polyethylene nanoplastic prepared in Example 1.

[0048] Figure 3 This is a comparison chart showing the absorption of polyethylene nanoplastics with different deuteration rates in the roots and stems of pea seedlings in Examples 1-3.

[0049] Figure 4 This figure shows the absorption of different concentrations of deuterium-labeled polyethylene nanoplastics by pea seedling roots.

[0050] Figure 5 The infrared spectrum of the deuterated polyethylene prepared in Comparative Example 2 is shown. Detailed Implementation

[0051] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Modifications or equivalent substitutions made by those skilled in the art based on their understanding of the technical solutions of this invention, without departing from the spirit and scope of the invention, should be covered within the protection scope of this invention.

[0052] All raw materials used in the following specific implementation methods were purchased from the market.

[0053] In this embodiment, a Fourier transform infrared spectrometer was used to test the samples, and the test conditions were within the range of 4000-400 cm⁻¹. -1 Step length 4 cm -1 The number of scans should be no less than 64. The characteristic absorption peaks of the CH bond are located in the range of 3100-2800 cm⁻¹. -1 The characteristic absorption peaks of the CD bond are located in the 2300-2000 cm⁻¹ range. -1 The deuteration rate of deuterated polyethylene (DPE) x D The calculation can be performed according to the following formula: Deuteration rate ( x D )= , in, The integral area of ​​the CD stretching vibration peak. The integral area of ​​the CH stretching vibration peak. The relative absorbance correction factor for the CD and CH bonds is taken as... =0.63.

[0054] Quantitative analysis of deuterium-labeled polyethylene nanoplastics in plant tissues: Dried plant tissue powder (particle size less than 100 mesh) was sealed in silver capsules, and the δ¹⁸O₂ content was determined by elemental analysis-isotope ratio mass spectrometry (EA-IRMS). 2 The H value was used to calculate the content of nanoplastics in the tissue using the hydrogen isotope mass balance method.

[0055] Stability test of deuterium-labeled polyethylene nanoplastics: The aqueous dispersion of deuterium-labeled polyethylene nanoplastics was stored at 4°C in the dark for 6 months. Samples were taken at regular intervals, and particle size changes were monitored by dynamic light scattering (DLS). Sedimentation was recorded by visual observation and photography.

[0056] Example 1 The method for preparing deuterium-labeled polyethylene nanoplastics provided in this embodiment includes the following steps: (1) Polyethylene (5.0 g), isooctane (500 mL) and 10 wt% palladium on carbon catalyst (2.5 g) were added to a high-pressure reactor, sealed, and purged with argon gas. Deuterium gas (D2) was introduced and pressurized to 3.0 MPa. The reactor was stirred at 170 °C for 12 h. After cooling, the residual gas was released to obtain the deuterated polyethylene reaction mixture.

[0057] (2) The deuterated polyethylene reaction mixture was dissolved in 250 mL of 1,2,4-trichlorobenzene, filtered to remove the catalyst, and the filtrate was added dropwise to 500 mL of cold methanol to precipitate. After filtration, the mixture was dried under vacuum at 80 °C for 18 h to obtain deuterated labeled polyethylene 1. The deuteration rate was confirmed to be 56.4% by Fourier transform infrared spectroscopy (FTIR).

[0058] (3) Dissolve 160 mg of the above-mentioned deuterium-labeled polyethylene polymer in 80 mL of xylene (concentration 2 mg / mL) and reflux at 145 °C for 2 h until completely dissolved. Inject the hot solution into 100 mL of pre-cooled (4 °C) anhydrous ethanol and stir to room temperature to obtain a nanoparticle suspension. After filtration through a polytetrafluoroethylene (PTFE) membrane (pore size 1.0 μm), washing with ethanol, ultrasonic recovery, and centrifugation purification, deuterium-labeled polyethylene nanoplastic 1 is obtained.

[0059] Deuterium-labeled polyethylene nanoplastic 1 was dispersed in 200 mL of deionized water containing 0.05 wt% bovine serum albumin (BSA) to obtain deuterium-labeled polyethylene nanoplastic aqueous dispersion 1.

[0060] Figure 1 The image shows a comparison of the infrared spectra of the deuterium-labeled polyethylene nanoplastic 1 prepared in Example 1 and the original polyethylene. Compared with the original polyethylene, after the H / D exchange reaction, the CH stretching vibration peak (3100-2800 cm⁻¹) is significantly higher. -1 The strength decreases, and at approximately 2300-2000 cm -1 Characteristic absorption peaks attributable to the CD stretching vibration were observed. The original polyethylene showed no detectable signal in the CD region, confirming that the CD signal originated entirely from the H / D exchange reaction.

[0061] Figure 2 This is a scanning electron microscope image of the deuterium-labeled polyethylene nanoplastic 1 prepared in Example 1. Figure 2 The deuterium-labeled polyethylene nanoplastic 1 was observed to be spherical nanoparticles with a uniform particle size distribution. The average hydrodynamic diameter measured by dynamic light scattering (DLS) was 266 nm. Stability tests showed that the deuterium-labeled polyethylene nanoplastic aqueous dispersion 1 prepared in this embodiment showed no visible sedimentation and no significant change in particle size after being stored at 4°C in the dark for 6 months.

[0062] Example 2 The method for preparing deuterium-labeled polyethylene nanoplastics provided in this embodiment includes the following steps: (1) Polyethylene (10 g), n-heptane (500 mL) and 10 wt% palladium on carbon catalyst (2.0 g) were added to a high-pressure reactor, sealed, and purged with argon gas. D2 was introduced to pressurize to 2.0 MPa, and the reaction was stirred at 165 °C for 1 h. After cooling, the residual gas was released to obtain the deuterated polyethylene reaction mixture.

[0063] (2) The reaction mixture was dissolved in 400 mL of o-dichlorobenzene, filtered to remove the catalyst, and the filtrate was added dropwise to 100 mL of excess cold methanol to precipitate. After filtration, the mixture was dried under vacuum at 60 °C for 24 h to obtain deuterated polyethylene 2. FTIR confirmed that the deuteration rate was 10.8%.

[0064] (3) Dissolve 625 mg of the above-mentioned deuterium-labeled polyethylene polymer in 250 mL of xylene (concentration 2.5 mg / mL) and reflux at 145 °C for 2 h until completely dissolved. Inject the hot solution into 500 mL of pre-cooled (0 °C) anhydrous ethanol and stir to room temperature to obtain a nanoparticle suspension. After filtration through a PTFE membrane (0.8 μm), washing with ethanol, ultrasonic recovery, and centrifugation purification, deuterium-labeled polyethylene nanoplastic 2 is obtained.

[0065] Deuterium-labeled polyethylene nanoplastic 2 was dispersed in 500 mL of deionized water containing 0.10 wt% BSA to obtain deuterium-labeled polyethylene nanoplastic aqueous dispersion 2.

[0066] Example 3 The method for preparing deuterium-labeled polyethylene nanoplastics provided in this embodiment includes the following steps: (1) Polyethylene (10 g), n-hexane (600 mL) and 10 wt% palladium on carbon catalyst (2.0 g) were added to a high-pressure reactor, sealed, and purged with argon gas. D2 was introduced to pressurize to 2.8 MPa, and the reaction was stirred at 170 °C for 4 h. After cooling, the residual gas was released to obtain the deuterated polyethylene reaction mixture.

[0067] (2) The deuterated polyethylene reaction mixture was dissolved in 400 mL of 1,2,4-trichlorobenzene, filtered to remove the catalyst, and the filtrate was added dropwise to 800 mL of cold methanol to precipitate. After filtration, the mixture was dried under vacuum at 100 °C for 12 h to obtain deuterated labeled polyethylene 3. FTIR confirmed that the deuteration rate was 31.2%.

[0068] (3) Dissolve 320 mg of the above polymer in 200 mL of xylene (1.6 mg / mL) and reflux at 185 °C for 2 h until completely dissolved. Pour the hot solution into 200 mL of pre-cooled (4 °C) anhydrous ethanol and stir to room temperature to obtain a nanoparticle suspension. After filtration through a PTFE membrane (5.0 μm), washing with ethanol, ultrasonic recovery, and centrifugation purification, deuterium-labeled polyethylene nanoplastic 3 is obtained.

[0069] Deuterium-labeled polyethylene nanoplastic 3 was dispersed in 500 mL of deionized water containing 0.05 wt% BSA to obtain deuterium-labeled polyethylene nanoplastic aqueous dispersion 3.

[0070] Example 4 The method for preparing deuterium-labeled polyethylene nanoplastics provided in this embodiment includes the following steps: (1) Polyethylene (20 g), n-pentane (500 mL) and 5 wt% platinum-carbon catalyst (2.0 g) were added to a high-pressure reactor, sealed, and purged with argon gas. D2 was introduced to pressurize to 2.5 MPa, and the reaction was stirred at 170 °C for 10 h. After cooling, the residual gas was released to obtain the deuterated polyethylene reaction mixture.

[0071] (2) The deuterated polyethylene reaction mixture was dissolved in 600 mL of 1,2,4-trichlorobenzene, filtered to remove the catalyst, and the filtrate was added dropwise to 1500 mL of cold methanol to precipitate. After filtration, the mixture was dried under vacuum at 80 °C for 18 h to obtain deuterated labeled polyethylene 4. FTIR confirmed that the deuteration rate was 22.5%.

[0072] (3) Dissolve 500 mg of the above polymer in 250 mL of xylene (2.0 mg / mL) and reflux at 165 °C for 4 h until completely dissolved. Pour the hot solution into 250 mL of pre-cooled (4 °C) anhydrous ethanol and stir to room temperature to obtain a nanoparticle suspension. After filtration through a PTFE membrane (5.0 μm), washing with ethanol, ultrasonic recovery, and centrifugation purification, deuterium-labeled polyethylene nanoplastic 4 is obtained.

[0073] Deuterium-labeled polyethylene nanoplastic 4 was dispersed in 500 mL of deionized water containing Tween 80 to obtain deuterium-labeled polyethylene nanoplastic aqueous dispersion 4.

[0074] Example 5 A hydroponic exposure experiment was conducted using peas as a model plant. Pea seedlings were cultured for 14 days in modified Hoagland nutrient solutions containing different deuterated polyethylene nanoplastics as described in Examples 1-3. A control group with the original polyethylene nanoplastics and treatment groups with different deuteration rates were set up, with an exposure concentration of 50 mg / L.

[0075] After exposure, root and stem tissues were collected separately, washed, dried, and ground, and then δ-ray diffraction (δ) was measured using EA-IRMS. 2 The H value was used to calculate the content of polyethylene nanoplastics in the tissue using the isotope mass balance method.

[0076] Figure 3 This is a comparison of the absorption of polyethylene nanoplastics with different deuteration rates in the roots and stems of pea seedlings in Examples 1-3. The results showed that the absorption of polyethylene nanoplastics with different deuteration rates in the roots was basically the same, with no statistically significant difference between groups (p>0.05); no significant difference was also observed in the translocation amount in the stems. This indicates that under the experimental conditions, a deuteration rate within the range of 10%-60% did not significantly affect the plant absorption and translocation behavior of polyethylene nanoplastics.

[0077] Example 6 Pea was used as a model plant in a hydroponic exposure experiment. Pea seedlings were cultured for 14 days in modified Hoagland nutrient solutions containing deuterated polyethylene nanoplastics with deuteration rates of 56.4% and 10.8% prepared in Examples 1 and 2. A control group containing the original polyethylene nanoplastics and treatment groups containing polyethylene nanoplastics with different deuteration rates were set up at exposure concentrations of 0.1, 1, 10, 100, 1000, and 10000 μg / L. Other conditions were the same as in Example 5.

[0078] Figure 4 This figure shows the uptake of deuterium-labeled polyethylene nanoplastics at different concentrations by pea seedling roots. The results showed that the limits of detection (LOD) and quantitation (LOQ) of polyethylene nanoplastics with a deuteration rate of 56.4% in pea seedling roots were 0.75 and 2.46 μg NP / g dry weight, respectively, while those of polyethylene nanoplastics with a deuteration rate of 10.8% were 3.67 and 12.67 μg NP / g dry weight, respectively. No deuterium signals above the LOD were detected in the root tissues of the 0.1 μg / L and 1 μg / L exposure groups, and quantification was stable within the exposure range of 10–10000 μg / L.

[0079] Comparative Example 1 (using platinum oxide catalyst) Polyethylene (5.0 g), isooctane (500 mL), and platinum oxide catalyst (2.5 g) were added to a high-pressure reactor, and the reaction and post-treatment were carried out according to the conditions of Example 1. After the reaction was completed, FTIR detection showed no identifiable absorption peak in the CD region, indicating that platinum oxide has no significant catalytic activity for the H / D exchange reaction of polyethylene.

[0080] Comparative Example 2 (low reaction temperature) The preparation process of Comparative Example 2 is the same as that of Example 1, except that the reaction temperature is 130°C.

[0081] Figure 5 The image shows the infrared spectrum after the reaction is complete. The results show that an extremely weak absorption peak appears in the CD region after the reaction is complete, and FTIR confirms that the deuteration rate is only 3.9%, indicating that the lower reaction temperature is unfavorable for the H / D exchange reaction of polyethylene.

[0082] The above results show that the deuterium-labeled polyethylene nanoplastics of the present invention have the characteristics of large-scale synthesis, adjustable deuteration rate, and long-term stable storage, which can meet the needs of precise quantitative research on polyethylene nanoplastics in environmental media and in animals and plants, and have broad application prospects in the fields of nanoplastic detection, ecological environment assessment and human health risk assessment.

Claims

1. A method for preparing deuterium-labeled polyethylene nanoplastics, characterized in that, Includes the following steps: Step 1: Using polyethylene, saturated hydrocarbon solvent and catalyst as raw materials, deuterium gas is introduced under an inert atmosphere to carry out the reaction to obtain a reaction mixture; the catalyst is selected from one or more of palladium on carbon, platinum on carbon, rhodium on carbon and ruthenium on carbon; Step 2: Dissolve the reaction mixture in a haloaromatic solvent and filter. Add an alcohol solvent to the filtrate to precipitate and dry to obtain deuterium-labeled polyethylene. Step 3: Dissolve the deuterium-labeled polyethylene in an aromatic solvent, heat and reflux, then inject it into pre-cooled ethanol and stir to obtain a suspension of deuterium-labeled polyethylene nanoparticles. After filtration, obtain deuterium-labeled polyethylene nanoplastics.

2. The method for preparing deuterium-labeled polyethylene nanoplastics according to claim 1, characterized in that, The saturated hydrocarbon solvent in step 1 is selected from one or more of C5-C8 saturated hydrocarbon solvents; the ratio of polyethylene to saturated hydrocarbon solvent is 1 g: 50-200 mL; In step 2, the halogenated aromatic solvent is selected from one or more of 1,2,4-trichlorobenzene and o-dichlorobenzene; the alcohol solvent is selected from one or more of C1-C3 alcohol solvents; the volume ratio of alcohol solvent to halogenated aromatic solvent is 5-1:

1. The aromatic solvent in step 3 is selected from one or more of xylene and toluene; the volume ratio of ethanol to aromatic solvent is 1-5:

1.

3. The method for preparing deuterium-labeled polyethylene nanoplastics according to claim 1, characterized in that, The mass ratio of polyethylene to catalyst is 2-10:

1.

4. The method for preparing deuterium-labeled polyethylene nanoplastics according to claim 1, characterized in that, In step 1, the pressure of the deuterium gas introduced for the reaction is 1.5-3.0 MPa, the reaction temperature is 160℃-180℃, and the reaction time is 0.5-24 h.

5. The method for preparing deuterium-labeled polyethylene nanoplastics according to claim 1, characterized in that, In step 2, the ratio of polyethylene to halogenated aromatic solvent is 1 g: 20-50 mL; The deuteration rate of the obtained deuterated polyethylene was 10%-60%; In step 3, the concentration of deuterium-labeled polyethylene in aromatic solvents is 1-5 mg / mL.

6. The method for preparing deuterium-labeled polyethylene nanoplastics according to claim 1, characterized in that, In step 3, the reflux temperature is 140℃-200℃, and the time is 1-4 h; The pre-cooling temperature is 0℃-8℃.

7. The deuterium-labeled polyethylene nanoplastic prepared by the preparation method according to any one of claims 1-6.

8. The application of the deuterium-labeled polyethylene nanoplastics according to claim 7 in environmental and biological tracer applications of polyethylene nanoplastics.

9. The application according to claim 8, characterized in that, A method for quantitative tracing of plant uptake using deuterium-labeled polyethylene nanoplastics includes the following steps: Deuterium-labeled polyethylene nanoplastics were transferred to an aqueous solution containing a dispersant and dispersed to obtain a deuterium-labeled polyethylene nanoplastic aqueous dispersion. Add the deuterium-labeled polyethylene nanoplastic aqueous dispersion to the plant hydroponic system, and let the plants grow in the nutrient solution containing the deuterium-labeled polyethylene nanoplastic for 7-21 days. After exposure, root and aboveground tissues were collected separately, and the δ-values ​​in the plant tissues were measured. 2 The H value was calculated, and the content of deuterium-labeled polyethylene nanoplastics in plant tissues was determined.

10. The application according to claim 9, characterized in that, The dispersant is selected from one or more of the following: protein-based, polyvinyl alcohol-based, nonionic surfactant-based, and anionic surfactant-based dispersants. The mass fraction of the dispersant in the aqueous dispersion of deuterium-labeled polyethylene nanoplastics is 0.01%-0.1%.

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