CN110237821A - Preparation of a ferromagnetic nanoparticle and its application in the extraction and removal of microplastics - Google Patents

Abstract

The invention belongs to the technical field of environmental pollution research and the technical field of environmental protection, and specifically relates to a ferromagnetic nanoparticle, its preparation and the application of removing microplastics in the environment based on the nanoparticle. The surface of iron nanoparticles is modified with methoxysilane to generate siloxane bonds (‑Si‑O‑Si‑), and the alkyl chains face outwards to form hydrophobic iron nanoparticles. The application of the ferromagnetic nanomaterial in the extraction and removal of microplastics in environmental samples. The method of the present invention has wide applicability, reliable method, simple operation and low cost, and can be used not only for the extraction and identification of microplastics in environmental pollution (water, soil, sediment) research, but also for environmental water bodies, sewage, drinking water The removal of microplastics provides a new solution for research and environmental governance in the field of microplastic environmental pollution, which is suitable for further development and application.

Description

Preparation of a ferromagnetic nanoparticle and its application in the extraction and removal of microplastics

technical field

The invention belongs to the technical field of environmental pollution research and the technical field of environmental protection, and specifically relates to a ferromagnetic nanoparticle, its preparation and the application of removing microplastics in the environment based on the nanoparticle.

Background technique

Microplastics are a new type of environmental pollutants, which can absorb heavy metals and persistent organic pollutants and migrate and transform in the environment. Due to the small particle size, microplastics are easily ingested by animals, and can release toxic and harmful substances carried by them, which will affect the growth and development, reproduction, and gene expression of organisms. In 2014, the first United Nations Environment Assembly (UNEP1) listed microplastic pollution as one of the top ten global environmental problems to be solved for the first time. In 2015, UNEP2 listed marine microplastics as the second largest scientific issue in the field of environmental and ecological science research, and ranked it with global climate change, ozone depletion and ocean acidification as a major global environmental issue of common concern to scientists around the world.

In recent years, international research reports on microplastic pollution have increased rapidly, but there is no systematic and standardized method for the extraction and separation of microplastics. At present, commonly used extraction methods include flotation (density separation), chemical digestion (enzyme digestion, peroxide digestion, acid digestion), visual identification (manual sorting). Although the above methods are widely used, the extraction efficiency is relatively low and limited by the types of plastics. Among them, visual identification is only suitable for plastic particles with larger particle sizes; the density separation method is only suitable for polymers with a density lower than that of the density solution, and cannot separate polymers with higher densities; the chemical digestion method is affected by the type of chemicals used and the reaction temperature. There are different types of microplastics, some of which can degrade microplastics; the post-treatment of these methods mostly uses filtration to separate and extract, and these methods are only suitable for separating microplastics larger than a specific pore size (for example: 45 μm), and the fibers in the filter paper will bring Secondary pollution of microplastics. In addition, new methods, such as electrostatic separation and elution column optimization, are constantly being developed, but these methods have problems such as complex devices, cumbersome steps, and unsuitability for laboratory analysis, especially for collecting submicron or even nanoscale microplastics ( <20μm) is challenging, and such microplastics are more likely to enter the organism through ingestion or other mechanisms, which is one of the most concerned and urgent problems in the field of microplastics. Therefore, it is necessary to establish a suitable and effective method to extract and separate microplastics of various particle sizes in environmental samples, so as to provide technical support for subsequent accurate quantitative detection and removal of microplastics in the environment.

Contents of the invention

Aiming at the deficiencies in the prior art, the present invention provides a ferromagnetic nanoparticle, its preparation and the application of removing microplastics in the environment based on the nanoparticle.

To achieve the above object, the technical solution adopted in the present invention is:

A ferromagnetic nanoparticle, the surface of the iron nanoparticle is modified with methoxysilane to form a siloxane bond (-Si-O-Si-), and the alkyl chain faces outward to form a hydrophobic iron nanoparticle.

Preparation method of ferromagnetic nanoparticles:

1) Ferromagnetic particles: Dissolve ferric chloride (FeCl ₃ 6H ₂ O) in excess ethylene glycol (EG), add anhydrous sodium acetate (NaAC) and polyethylene glycol (PEG) and stir, Sonicate until dissolved; use mechanical stirring, heat in a water bath, collect the sample by centrifugation after the reaction, and wash repeatedly three times to obtain ferromagnetic particles;

2) Ferromagnetic nanoparticles: disperse the obtained ferromagnetic particles in methanol solution, then add hexadecyltrimethoxysilane to the obtained dispersion, and perform silanization modification treatment to obtain hydrophobic ferromagnetic nanoparticles .

Said step 1) dissolving ferric chloride (FeCl ₃ 6H ₂ O) in ethylene glycol (EG), sonicating until completely dissolved; adding anhydrous sodium acetate (NaAC) and polyethylene glycol (PEG) and stirring , sonicate until dissolved; add a stirring rod, heat in a water bath at 60-80°C, and stop the reaction after stirring for 30-90 minutes; after the solution is cooled to room temperature, pour the liquid into the reactor, and conduct a hydrothermal reaction at 150-220°C for 12-24h; Pour the black magnetic fluid to remove the supernatant, collect the naturally settled precipitate, wash, and dry to obtain ferromagnetic particles; among them, ferric chloride (FeCl ₃ 6H ₂ O), ethylene glycol (EG), anhydrous sodium acetate The molar ratio of (NaAC) to polyethylene glycol (PEG) is: 0.05～0.1:0.001～0.01:0.005～0.01:1.

The surface of the ferromagnetic nanoparticles is modified. After modification, the hydroxyl group (-OH) in the natural oxide layer of the iron nanoparticles reacts covalently with the methoxysilane (-Si-OCH ₃ ) in HDTMS to generate silicon Oxyalkylene bond (-Si-O-Si-). Si-O bonds have higher covalent bond energy (452kJ/mol), which is higher than CC bonds (345.6kJ/mol), and have strong chemical stability in environmental samples.

The naturally settled precipitate was repeatedly washed with distilled water and absolute ethanol, and then vacuum-dried at 60° C. to constant weight.

The step 2) adding the ferromagnetic nanoparticles obtained above into the methanol solution, ultrasonically until the ferromagnetic nanoparticles are uniformly dispersed in the methanol solution; adding hexadecyltrimethoxysilane (HDTMS, purity > 85%), ultrasonically 10-30min, placed in a shaking table at room temperature for 12-24h; use a magnet to separate the ferromagnetic nanoparticles to obtain ferromagnetic nanoparticles; wherein, ferromagnetic nanoparticles, methanol solution and hexadecyl trimethoxy Base silane 40-80mg: 40-80mL: 1-2mL.

The particles obtained from the separation are diluted with water to 2-5 g/L, and then uniformly dispersed by ultrasonic before use.

Application of ferromagnetic nanoparticles, the application of the ferromagnetic nanomaterials in the extraction and removal of microplastics in environmental samples.

Furthermore, the surface of the iron nanoparticles is modified with methoxysilane, and the silyl groups face outwards to form hydrophobic iron nanoparticles. Due to the hydrophobic effect, the modified iron nanoparticles can have a strong adsorption with microplastics, thereby realizing the extraction and removal of microplastics.

The microplastics are plastic particles, fibers or films with a diameter of less than 5mm; meanwhile, it also has a good effect on the extraction of submicron and nanoscale microplastics.

A method for extracting and removing microplastics by ferromagnetic nanomaterials, adding the obtained ferromagnetic nanomaterials to a sample to be removed, mixing and standing for 5-10 minutes, so that microplastics are adsorbed by iron nanoparticles, and then passed through a magnet The process of powering on and off can extract and remove it.

The process of energizing and de-energizing the magnet is to adopt a de-energized electromagnet that "powers on and demagnetizes, and powers off to have magnetism", so that the microplastics are adsorbed to the magnet in the power-off state; after powering on, the microplastics adsorbed on the magnet Easy to rinse off the magnet.

The beakers, petri dishes and other utensils used in the whole process of microplastic extraction and removal are all made of glass, so as to avoid cross-contamination of microplastic samples by using plastic products in the extraction process and improve the accuracy of sample extraction.

Compared with the prior art, the present invention has the advantages of:

The invention adopts nano adsorption technology to extract and remove microplastics. The preparation method of the nano-adsorption material is to firstly synthesize magnetic nanoparticles by a solvothermal method, and then use hexadecyltrimethoxysilane to chemically modify the surface to obtain hydrophobic iron nanoparticles. The hydrophobicity of the modified iron nanoparticles promotes the adsorption of the microplastics, so that the surface of the microplastics is coated with a layer of magnetic nanoparticles. Furthermore, the de-energized electromagnet is used to extract and separate the microplastics adsorbed with magnetic nanoparticles, the loss of plastic particles is small, and it will not interfere with subsequent identification and quantitative analysis. The magnetic particles prepared by the invention have a small particle size and a large specific surface area, and further have high adsorption performance for microplastics, are suitable for microplastic samples of different particle sizes, and can especially extract microplastics below 20 μm that are currently difficult to separate. The ferromagnetic nanoparticles prepared by the invention have the advantages of environmental friendliness, easy removal and the like.

The method of the present invention has wide applicability, reliable method, simple operation and low cost, and can be used not only for the extraction and identification of microplastics in environmental pollution (water, soil, sediment) research, but also for environmental water bodies, sewage, drinking water The removal of microplastics provides a new solution for research and environmental governance in the field of microplastic environmental pollution, which is suitable for further development and application.

Description of drawings

Fig. 1 is a schematic diagram of the synthesis method of the hydrophobic ferromagnetic nanoparticles provided by the embodiment of the present invention.

Fig. 2 is a schematic diagram of the structure of hydrophobic ferromagnetic nanoparticles provided by the embodiment of the present invention.

Fig. 3 is a transmission electron microscope image of hydrophobic ferromagnetic nanoparticles provided by the embodiment of the present invention (the particle diameter is about 300-400nm, and there is no agglomeration among the particles).

Fig. 4 is a schematic flow diagram of the hydrophobic ferromagnetic nanoparticles provided by the embodiment of the present invention used in the extraction of microplastics (the microplastics are circular as an example).

Fig. 5 is a diagram of the trajectory of submicron microplastics adsorbed with iron nanoparticles under the attraction force of a magnet provided by the embodiment of the present invention.

Fig. 6 is a fluorescent photogram of the submicron-sized microplastics adsorbed with iron nanoparticles provided by the embodiment of the present invention before and 20 minutes after the addition of the magnet.

Detailed ways

The present invention will be further described by specific examples below, but the protection scope of the present invention is not limited to the present embodiment, and all changes or modifications under the same principle and design conditions as the present invention are within the scope of protection disclosed by the present invention.

The following examples test the recovery rate of microplastics of different sizes and types (LDPE, HDPE, PP, PET, PVC, PE), among which the size of microplastics is divided into: large microplastics (1mm ~ 5mm), medium microplastics (333μm ~ 1mm), small microplastics (20 μm ~ 333 μm), submicron microplastics (<20 μm), among which the large and medium ranges represent the commonly measured microplastic sizes in the environment (usually collected by MANTA trawl nets with a grid size of 333 μm), Small and sub-micron microplastics are more harmful to organisms, but there is no better extraction method.

Embodiment 1: a kind of preparation method of hydrophobic ferromagnetic nanoparticles,

As shown in Figure 1, perform the following steps in sequence:

1), 1.35g iron trichloride (FeCl3 6H2O) is dissolved in 40ml ethylene glycol (EG), stirs and ultrasonic to dissolve completely; Add 3.6g anhydrous sodium acetate (NaAC) and 4g polyethylene glycol ( PEG) stirred, sonicated until dissolved; heated in a water bath at 60°C, mechanically stirred for 30 minutes, and then sonicated for 1 hour; after the solution was cooled to room temperature, pour the liquid into the reaction kettle, and blast at 200°C for 10 hours; pour off the supernatant from the black magnetic fluid solution, poured into a beaker and naturally settled; washed three times with distilled water and absolute ethanol, poured off the supernatant, and vacuum-dried at 60°C to constant weight to obtain ferromagnetic particles.

2), adding 0.08g of ferromagnetic nanoparticles to 50mL of methanol (purity>99.5%) solution, sonicating until the ferromagnetic nanoparticles are evenly dispersed in the methanol solution; adding 0.5ml of hexadecyltrimethoxysilane ( HDTMS, purity > 85%), ultrasonic 30S, placed in a shaker at room temperature for 12h; use a magnet to separate the ferromagnetic nanoparticles from the solution; pour off the supernatant, dilute to 20ml with water, and obtain a concentration of 4g /L hydrophobic ferromagnetic nanoparticle suspension.

3) Before use, disperse the hydrophobic ferromagnetic nanoparticle suspension evenly with ultrasound (see Figure 2 and Figure 3).

It can be seen from Figures 2 and 3 that the surface of ferromagnetic nanoparticles is modified. After modification, the hydroxyl group (-OH) in the natural oxide layer of iron nanoparticles and the methoxysilane (-Si-OCH ₃ ) in HDTMS undergo covalent The reaction forms a siloxane bond (-Si-O-Si-). The Si-O bond has a higher covalent bond energy (452kJ/mol), which is higher than the CC bond (345.6kJ/mol), and has strong chemical stability in environmental samples; the particle size is about 300-400nm, and the particle There is no reunion between.

Example 2: Extraction of microplastics in water using hydrophobic ferromagnetic nanoparticles obtained in the above examples

Add the microplastics to 50 mL of deionized water, add about 0.5 mL of the above-mentioned embodiment to obtain a suspension of hydrophobic iron nanoparticles, stir and mix with a glass rod for 2 min. Add the magnet into the beaker and stir slowly. After the magnetized microplastics are adsorbed on the magnet, take out the magnet. Apply 12V voltage to the magnet to demagnetize the magnet, rinse the magnet with a small amount of distilled water, rinse the microplastics on the magnet to a glass petri dish, and perform visual counting or stereoscopic microscope counting in the glass petri dish.

According to the method of the above steps, different sizes (large, medium and small) and different types (HDPE (high density polyethylene), LDPE (low density polyethylene), PP (polypropylene), PET (polyester), PVC (polyvinyl chloride) PE (polyethylene)) microplastics were added to 50mL deionized water for recovery experiments to verify the feasibility of the method. The average recovery rate is calculated according to the following formula:

in:

--The average recovery rate(%)

x _i -- the number of extracted microplastics (pieces)

y _i -- the number of microplastics added (pieces)

n--the number of experiments

The experimental results are shown in Table 1, Table 2 and Table 3.

Table 1 Recovery rate of large microplastics (1mm-5mm) in water by nano-adsorption technology

Table 2 Recovery rate of medium-sized microplastics (333 μm ~ 1 mm) in water by nano-adsorption technology

Table 3 Recovery rate of small microplastics (20 μm to 333 μm) in water bodies by nano-adsorption technology

It can be seen from the above Tables 1-3 that the hydrophobic ferromagnetic nanoparticles have a better extraction effect on microplastics in water bodies, and the recovery rates for different types of large microplastics are above 93.3%. For different types of medium and small microplastics The recoveries were all 100%.

Example 3: Extraction of Microplastics in Sediments Using Hydrophobic Ferromagnetic Nanoparticles Obtained in the Examples Above

In order to prevent the impact of microplastics in the sediment on the recovery rate of the experiment, the sieved 5mm sediment was placed in a muffle furnace and burned at 450°C for 3h. Weigh 100g of sediment into a beaker, add different types of microplastics, stir evenly with a glass rod, then add 200mL of saturated sodium chloride solution, stir, mix evenly, and settle for 5 minutes. The supernatant was transferred to another beaker, and the remaining small amount of supernatant was transferred with a glass glue tip dropper, and this process was repeated 3 times. Add 2 mL of the hydrophobic iron nanoparticle suspension obtained in the example to the transferred supernatant, and stir and mix with a glass rod for 2 min. Add the magnet into the beaker and stir slowly. After the magnetized microplastics are adsorbed on the magnet, take out the magnet. Apply 12V voltage to the magnet to demagnetize the magnet, rinse the magnet with distilled water, rinse the microplastics on the magnet to a glass petri dish, and perform visual counting or stereoscopic microscope counting in the glass petri dish.

According to the above steps, different sizes (large, medium and small), different types (HDPE (high-density polyethylene), LDPE (low-density polyethylene), PP (polypropylene), PET (polyester), PVC (polyvinyl chloride) PE (polyethylene)) microplastics were added to 100g of sediment for the recovery rate experiment, to verify the feasibility of the method, the results are shown in Table 4, Table 5 and Table 6.

Table 4 Recovery rate of large microplastics (1mm-5mm) in sediments by nano-adsorption technology

Table 5 Recovery rate of medium-sized microplastics (333 μm ~ 1 mm) in sediments by nano-adsorption technology

Table 6 Recovery rate of small and medium-sized microplastics (20 μm to 333 μm) in sediments by nano-adsorption technology

It can be seen from the above Tables 4-6 that the hydrophobic ferromagnetic nanoparticles have a better extraction effect on microplastics in sediments, and the recovery rates of different types of large microplastics mixed in sediments are all above 90%; The recovery rates of different types of medium-sized microplastics in sediments were all above 86.7%; the recovery rates of different types of medium-sized microplastics mixed in sediments were all above 83.3%.

Example 4: Extraction of submicron microplastics (<20 μm) by using the hydrophobic ferromagnetic nanoparticles obtained in the above examples

In this example, purchased 10 μm sub-micron microplastics were selected, and the microplastics were first fluorescently stained: add Nile Red to the microplastics, shake for 12 hours, centrifuge at 14000 r/min, pour off the supernatant, and wash with distilled water for 2 Once, distilled water was added and ultrasonically dispersed.

Dissolve the fluorescently dyed microplastics in 1.5mL saturated sodium chloride solution, then add 0.02mL hydrophobic iron nanoparticle suspension, stir and mix with a glass rod for 2min, put the magnet in a petri dish, and observe under the fluorescence microscope Observe the process of the microplastics being gradually adsorbed on the magnet (Figure 5). After about 20 minutes, the adsorption is complete (Figure 6). The magnet with adsorbed microplastics can be directly placed in the field of view of the fluorescence microscope to count the microplastics.

It can be seen from the above Figures 5 and 6 that after the submicron microplastics adsorb iron nanoparticles, the adsorption trajectory is obvious under the magnetic force of the magnet, and all the submicron microplastics in the sample can be extracted within 20 minutes.

Claims (10)

1. a kind of ferromagnetism nanometer particle, it is characterised in that: Fe nanometer particles surface is modified using methoxy silane, generates silicon oxygen Alkane key (- Si-O-Si-), and alkyl chain is outwardly, forms hydrophobic Fe nanometer particles.

2. the preparation method of ferromagnetism nanometer particle according to claim 1, it is characterised in that:

1) ferromagnetic particles: by ferric trichloride (FeCl₃·6H₂O it) is dissolved in excessive ethylene glycol (EG), then plus anhydrous acetic acid Sodium (NaAC) and polyethylene glycol (PEG) stirring, ultrasound to dissolution；Using mechanical stirring, heating water bath, centrifugation is received after reaction Collect sample, is washed repeatedly to get ferromagnetic particles；

2) it ferromagnetism nanometer particle: disperses above-mentioned acquisition ferromagnetic particles in methanol solution, then into the dispersion liquid of acquisition Hexadecyl trimethoxy silane is added, carries out silylation modification processing to get hydrophobicity ferromagnetism nanometer particle.

3. the preparation method of ferromagnetism nanometer particle as described in claim 2, it is characterised in that: the step 1) is by tri-chlorination Iron (FeCl₃·6H₂O it) is dissolved in ethylene glycol (EG), ultrasound is to being completely dissolved；Anhydrous sodium acetate (NaAC) and polyethylene glycol is added (PEG) it stirs, ultrasound to dissolution；In 60-80 DEG C of heating water bath under stirring condition, 30-90min is stirred, is stopped after ultrasonic 1h anti- It answers；After solution is cooled to room temperature, liquid is poured into reaction kettle, 150-220 DEG C of hydro-thermal reaction 12-24h, then by black magnetic Fluid inclines supernatant, collects the washing of precipitate of natural subsidence, is drying to obtain ferromagnetic particles；Wherein, ferric trichloride (FeCl₃·6H₂O), the molar ratio of ethylene glycol (EG), anhydrous sodium acetate (NaAC) and polyethylene glycol (PEG) are as follows: 0.05~0.1: 0.001~0.01:0.005~0.01:1.

4. the preparation method of ferromagnetism nanometer particle according to claim 3, it is characterised in that: the precipitating of the natural subsidence It is washed repeatedly with distilled water and dehydrated alcohol, is dried under vacuum to constant weight in 60 DEG C after washing.

5. the preparation method of ferromagnetism nanometer particle as described in claim 2, it is characterised in that: the step 2) is obtained above-mentioned It obtains ferromagnetism nanometer particle to be added in methanol solution, ultrasound to ferromagnetism nanometer particle is dispersed in methanol solution；Add Enter hexadecyl trimethoxy silane (HDTMS, purity > 85%), ultrasonic 10-30min is placed in shaking table shakes at room temperature 12-24h；Ferromagnetism nanometer particle is isolated to get ferromagnetism nanometer particle is arrived with magnet；Wherein, ferromagnetism nanometer particle, Methanol solution and hexadecyl trimethoxy silane 40~80mg:40~80mL:1-2mL.

6. the preparation method of ferromagnetism nanometer particle as described in claim 5, it is characterised in that: the separation obtains particle warp Water is diluted to 2-5g/L, then using preceding uniform through ultrasonic disperse.

7. the application of ferromagnetism nanometer particle according to claim 1, it is characterised in that: the ferromagnetic nano material is in ring Application in the sample of border in the extraction and removal of micro- plastics.

8. the application of ferromagnetism nanometer particle according to claim 7, it is characterised in that: micro- plastics are less than for diameter Plastic grain, fiber or the film of 5mm.

9. a kind of ferromagnetic nano material is to the method for extraction and the removal of micro- plastics, it is characterised in that: will be described in claim 1 It obtains ferromagnetic nano material and mixing standing 5-10min is added into sample to be removed, inhale micro- plastics by Fe nanometer particles It is attached, it is then powered by magnet, the process of power-off can be extracted and be removed.

10. ferromagnetic nano material according to claim 9 is to the method for extraction and the removal of micro- plastics, it is characterised in that: The magnet is powered, the process of power-off is to power off micro- plastics using the power loss type electromagnet of " energization demagnetization, power-off have magnetic " Magnet is adsorbed under state；After energization, the micro- plastics being adsorbed on magnet are easy to rinse from magnet.