Process for the preparation and purification of nanoparticles of plasmonic graphene- magnetic core structures

Abstract

The application provides a preparation and purification method of graphene oxide@magnetic core structure nanoparticles, which comprises the following steps: graphene@magnetic core structure nanoparticles are modified by plasma oxidation; the graphene@magnetic core structure nanoparticles treated by plasma are mixed with water, then the mixture is subjected to high-speed shearing dispersion, standing, removal of nanoparticles floating on the water surface, magnetic separation, removal of non-magnetic free graphene, and the obtained magnetic material is a crude product; the crude product is mixed with an ethanol aqueous solution, then the mixture is subjected to high-pressure homogenization, magnetic separation, and removal of non-magnetic free graphene, and the modified graphene oxide@magnetic core structure nanoparticles are obtained. The preparation and purification method is simple, mild, controllable, high in yield, and capable of preparing high-purity modified graphene oxide@magnetic core structure nanoparticles.

Description

Technical Field

[0001] This invention belongs to the field of nanomaterials technology, specifically relating to a method for preparing and purifying nanoparticles with a plasma-derived graphene oxide-magnetic core structure. Background Technology

[0002] Magnetic nanoparticles are magnetic materials located in the nanoscale (1-100 nm) and possess quantum size effects, surface effects, small size effects, and excellent soft magnetic properties. In practice, due to volume and surface effects, magnetic nanoparticles are usually special nanocomposite materials with a core-shell structure.

[0003] The surface of graphene-magnetic core structured nanoparticles is a structurally stable graphene shell. By modifying the surface of the graphene shell to generate different kinds of chemical groups, the surface physicochemical properties of the graphene-magnetic core structured nanoparticles can be further endowed, thus broadening their application range.

[0004] To date, traditional modification methods have all employed wet chemical methods to oxidize graphene. However, since graphene-magnetic core nanoparticles have a core-shell structure, wet chemical methods have many shortcomings, such as complex chemical reaction processes that require many intermediate steps to finally achieve oxidation modification, and the degree of oxidation is not high. Summary of the Invention

[0005] This invention provides a method for preparing and purifying nanoparticles with a plasma-derived graphene oxide-magnetic core structure.

[0006] Specifically, the present invention provides the following technical solution:

[0007] A method for preparing and purifying plasma-generated graphene oxide-magnetic core structured nanoparticles includes the following steps:

[0008] (1) Placing graphene-magnetic core structured nanoparticles in a processing chamber and allowing processing gas to flow into the processing chamber, wherein the processing gas includes oxygen-containing gas;

[0009] (2) The processing gas is excited by a plasma excitation source to form plasma, and the graphene-magnetic core structure nanoparticles are exposed to the plasma environment to oxidize and modify the graphene-magnetic core structure nanoparticles.

[0010] Plasma is a dry process with mild and controllable characteristics. Plasma discharge ionizes the gas, which generates active groups. In the plasma state, the active groups are linked to the graphene. The process is simple and can directly oxidize the surface of graphene-magnetic core structure nanoparticles.

[0011] (3) The plasma-treated graphene-magnetic core structure nanoparticles are mixed with water, and then the mixture is dispersed by high-speed shearing, allowed to stand, and the nanoparticles floating on the water surface are removed. The non-magnetic free graphene is removed by magnetic separation, and the resulting magnetic material is the crude product.

[0012] In the plasma-treated nanoparticles, on the one hand, some particles are not surface-modified due to nanoparticle aggregation, and their surfaces have no oxygen-containing groups; on the other hand, some particles have their shell-core structure destroyed due to excessive plasma etching, causing the graphene shell and magnetic core to separate and generate free graphene and free magnetic core. In step (3), the present invention first uses high-speed shear dispersion to eliminate the electrostatic force and van der Waals force (commonly known as soft aggregation) between particles, so that the soft aggregated particles are dispersed. Then, the difference in hydrophilicity between oxygen-containing groups such as hydroxyl, carboxyl, and aldehyde groups and graphene is used to separate the unmodified particles (the nanoparticles with oxidized graphene-magnetic core structure are hydrophilic and can be dispersed in deionized water, while the unmodified graphene-magnetic core structure nanoparticles and free magnetic core will float on the water surface). Then, the free graphene is removed by magnetic separation to obtain the crude product.

[0013] (4) The crude product is mixed with an ethanol aqueous solution, and then the mixture is subjected to high pressure homogenization and magnetic separation to remove non-magnetic free graphene, thereby obtaining oxidized graphene-magnetic core structure nanoparticles.

[0014] In step (4), the present invention found that dispersing the crude product in an ethanol aqueous solution and then subjecting it to high-pressure homogenization can effectively break the chemical bonds (commonly known as hard agglomeration) between the graphene-magnetic core structure nanoparticles and free graphene in the crude product, thereby dispersing the hard agglomerate particles. Then, the free graphene is removed by magnetic separation, thus finally obtaining high-purity oxidized modified graphene-magnetic core structure nanoparticles, which can be widely used in the fields of biomedicine, mechanical electronics, and functional materials development.

[0015] Preferably, in the above preparation and purification method, the pressure of the processing gas in the processing chamber is maintained at 100-90000 Pa, more preferably 300-500 Pa, under which the reaction gas is easily ionized.

[0016] Preferably, in the above preparation and purification methods, the processing gas is selected from any one of the following (1) to (5):

[0017] (1) Carbon dioxide, with a gas flow rate of 100-20000 sccm; it ionizes to form plasma, mainly through the following processes:

[0018] CO2→CO·+O·;

[0019] CO·→C·+O·;

[0020] CO· + O· → COO·;

[0021] C·+O·→CO·.

[0022] After carbon dioxide gas is ionized, it will add oxygen-containing groups, such as carboxyl groups, hydroxyl groups, aldehyde groups and oxygen atoms to the surface of graphene.

[0023] (2) Oxygen, with a gas flow rate of 100-20000 sccm; it is ionized to form plasma, mainly through the following processes:

[0024] O2→O·+O·;

[0025] C + O· → CO·;

[0026] CO·+O·→COO·.

[0027] After oxygen is ionized, oxygen-containing groups, such as carboxyl, hydroxyl, aldehyde groups, and oxygen atom doping, are added to the surface of graphene.

[0028] (3) Argon and carbon dioxide, wherein argon accounts for 5-15% of the total gas volume (volume percentage, the same below), and the gas flow rate is 100-20000 sccm; it is ionized to form plasma, mainly through the following processes:

[0029] Ar→Ar·;

[0030] CO2→CO·+O·;

[0031] CO·→C·+O·;

[0032] CO· + O· → COO·;

[0033] C·+O·→CO·.

[0034] Because argon has a low ionization potential, it can be ionized at low energy levels. At the same time, excited argon atoms can accelerate carbon dioxide ionization more quickly and completely through collisions. Therefore, argon can assist in the ionization of carbon dioxide gas, thereby increasing the oxidation degree of graphene-magnetic core structure nanoparticles.

[0035] (4) Argon and oxygen, wherein argon accounts for 5-15% of the total gas volume and the gas flow rate is 100-20000 sccm; it forms plasma through ionization, mainly through the following processes:

[0036] Ar→Ar·;

[0037] O2→O·+O·;

[0038] C + O· → CO·;

[0039] CO·+O·→COO·.

[0040] Because argon has a low ionization potential, it can be ionized at low energy levels. At the same time, excited argon atoms can accelerate oxygen ionization more quickly and thoroughly through collisions. Therefore, argon can assist in the ionization of oxygen, thereby increasing the oxidation degree of graphene-magnetic core structure nanoparticles.

[0041] (5) Oxygen and carbon dioxide, of which oxygen accounts for 10-35% of the total gas volume and has a flow rate of 100-20000 sccm; it is ionized to form plasma, mainly through the following processes:

[0042] Ar→Ar·;

[0043] O2→O·+O·;

[0044] CO2→CO·+O·;

[0045] CO·→C·+O·;

[0046] CO· + O· → COO·;

[0047] C·+O·→CO·.

[0048] The ionization of oxygen increases the number of excited-state oxygen atoms. These excited-state oxygen atoms combine with excited-state carbon atoms and excited-state CO to increase the number of carboxyl, hydroxyl, and aldehyde groups in the graphene-magnetic core nanoparticles. At the same time, the increase in the number of excited-state oxygen atoms increases the amount of oxygen atom doping, and the overall degree of oxidation of the surface graphene increases.

[0049] Preferably, in the above preparation and purification method, the plasma excitation source is a glow discharge plasma excitation source, and the oxidation modification time of the graphene-magnetic core structure nanoparticles is 5~25 min.

[0050] Preferably, in the above preparation and purification method, the graphene-magnetic core structured nanoparticles are core-shell particles with nanomagnetic particles as the core and multilayer graphene as the shell. The surface of the multilayer graphene can be linked with various functional groups, making it easy to modify without affecting the core properties of the particles.

[0051] Preferably, in the above preparation and purification method, in step (3), the plasma-treated graphene-magnetic core structure nanoparticles are mixed with water at a mass-volume ratio of 0.2-10 g / L.

[0052] Preferably, in the above preparation and purification method, the high-speed shear dispersion speed is 1500-3000 rpm, and the high-speed shear dispersion time is 20-50 min.

[0053] Preferably, in the above preparation and purification method, in step (4), the crude product is mixed with an ethanol aqueous solution at a mass-volume ratio of 0.2-10 g / L. Preferably, the volume fraction of ethanol in the ethanol aqueous solution is 30%~60%.

[0054] Preferably, in the above preparation and purification method, the pressure of high-pressure homogenization is 600-90 bar, and the high-pressure homogenization time is 10-60 min.

[0055] Preferably, in any of the above preparation and purification methods, the magnetic separation specifically involves: applying an external static magnetic field to the mixture in the container, causing the graphene-magnetic core structure nanoparticles to be adsorbed onto the inner wall of the container, while the non-magnetic free graphene remains in the suspension, and removing the suspension to achieve the separation of the non-magnetic free graphene.

[0056] The beneficial effects achieved by this invention are as follows:

[0057] The preparation and purification method provided by this invention is simple, mild and controllable, and has a high yield, enabling the preparation of high-purity oxidized graphene-magnetic core structure nanoparticles. Attached Figure Description

[0058] Figure 1 This is a TEM image of nanoparticles with a graphene-magnetic core structure according to an embodiment.

[0059] Figure 2 The hysteresis loop of the graphene-magnetic core structure nanoparticles according to the embodiment.

[0060] Figure 3 The image shows the Raman spectrum of the graphene-magnetic core structure nanoparticles according to the embodiment.

[0061] Figure 4 This is a process flow diagram of the preparation and purification method according to Example 1.

[0062] Figure 5 This is a schematic diagram of the structure of the graphene-magnetic core structure nanoparticles modified according to Example 1.

[0063] Figure 6 The image shows the infrared spectrum of the oxidized graphene-magnetic core structure nanoparticles according to Example 1.

[0064] Figure 7 XPS spectra of the oxidized graphene-magnetic core structure nanoparticles according to Example 1.

[0065] Figure 8 The images show a comparison of the soft agglomerates before and after dispersion in Example 1, with the left image showing the dispersion before dispersion and the right image showing the dispersion after dispersion.

[0066] Figure 9 The images show a comparison of the hard agglomerated particles before and after dispersion in Example 1, with the left image showing the particles before dispersion and the right image showing the particles after dispersion. Detailed Implementation

[0067] The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of the invention. Where specific techniques or conditions are not specified in the embodiments, they should be performed in accordance with the techniques or conditions described in the literature in the field, or in accordance with the product manual.

[0068] In the following embodiments, all instruments and equipment used, unless otherwise specified, are conventional products that can be purchased through legitimate channels. Unless otherwise stated, all methods described are conventional methods, and all raw materials are available from publicly available commercial sources.

[0069] The preparation methods of the graphene-magnetic core structure nanoparticles used in the following embodiments are based on the preparation methods described in Wei, ZQ. Liu, LG. Yang, H. Characterization of carbon encapsulated Fe-nanoparticles prepared by confined arc plasma [J]. Transactions of Nonferrous Metals Society of China. 2011, 2026-2030.

[0070] Figure 1 This is a TEM image of nanoparticles with a graphene-magnetic core structure according to an embodiment.

[0071] Figure 2 The image shows the hysteresis loop of the graphene-magnetic core structure nanoparticles according to the embodiment. It exhibits good magnetic properties, showing hysteresis at room temperature, and is ferromagnetic with almost zero hysteresis. This indicates that the composite material is superparamagnetic and can respond rapidly to applied external magnetic fields.

[0072] Figure 3The image shows the Raman spectrum of the graphene-magnetic core structure nanoparticles according to the embodiment. Raman spectroscopy revealed distinct peaks around 1330 cm⁻¹, 1585 cm⁻¹, and 2600 cm⁻¹, which are consistent with the characteristic peak positions of typical graphene (D band 1350 cm⁻¹, G band 1580 cm⁻¹, 2D band 2600 cm⁻¹). The surface of the graphene-magnetic core structure nanoparticles is graphene. Since the 2D peak width of monolayer graphene is approximately 30 cm⁻¹, and that of bilayer graphene is approximately 50 cm⁻¹, and even wider for three or more layers, the measured 2D peak width of the graphene-magnetic core structure nanoparticles is 67 cm⁻¹, proving that the surface of the graphene-magnetic core structure nanoparticles is multilayered graphene. Furthermore, the stronger G peak than the 2D peak also indicates that the surface of the graphene-magnetic core structure nanoparticles is multilayered graphene.

[0073] Example 1

[0074] This embodiment provides a method for purifying plasma-generated graphene oxide-magnetic core structured nanoparticles, such as... Figure 4 As shown, it includes the following steps:

[0075] (1) Place the graphene-magnetic core structure nanoparticles in a substrate and place them in a microwave plasma device;

[0076] (2) Turn on the vacuum pump and evacuate to 150 Pa. Introduce oxygen into the vacuum chamber at a flow rate of 3000 sccm. Adjust the vacuum pump to bring the pressure inside the chamber to 300 Pa. Adjust the power supply of the plasma device and slowly increase the power. When yellow oxygen plasma is observed to be generated, quickly adjust the power to 3000 W to modify the graphene-magnetic core structure nanoparticles.

[0077] (3) After 14 minutes of modification, turn off the vacuum pump, stop the gas output, and take out the sample.

[0078] (4) The modified magnetic nanoparticles were placed in a glass dish and allowed to stand at room temperature, then dispersed in deionized water at a concentration of 7 g / L.

[0079] (5) Place the solution in a high-speed shear dispersion homogenizer and shear disperse at 9000 rpm for 30 min. After standing for 3 min, remove the nanoparticles floating on the water surface, thereby removing the unoxidized particles.

[0080] (6) Magnetic separation is performed using the magnetic properties of the particles to remove non-magnetic free graphene and obtain pre-purified graphene oxide-magnetic core structure nanoparticles, i.e. crude product.

[0081] (7) Disperse the crude product in a 50% ethanol aqueous solution at a mass-volume ratio of 3 g / L.

[0082] (8) The solution obtained in step (7) was homogenized and dispersed at 650 bar for 30 min using a high-pressure dispersion homogenizer, and then magnetic separation was performed again to remove non-magnetic free graphene, so as to obtain high-purity graphene oxide-magnetic core structure nanoparticles with a purity of 97% and a yield of 74%.

[0083] Figure 5 This is a schematic diagram of the structure of the graphene-magnetic core structure nanoparticles modified according to Example 1.

[0084] Figure 6 The image shows the infrared spectrum of the oxidized graphene-magnetic core structure nanoparticles according to Example 1.

[0085] Figure 7 XPS spectra of the oxidized graphene-magnetic core structure nanoparticles according to Example 1.

[0086] Figure 8 The images show a comparison of the soft agglomerates before and after dispersion in Example 1, with the left image showing the dispersion before dispersion and the right image showing the dispersion after dispersion.

[0087] Figure 9 The images show a comparison of the hard agglomerated particles before and after dispersion in Example 1, with the left image showing the particles before dispersion and the right image showing the particles after dispersion.

[0088] Example 2

[0089] This embodiment provides a method for purifying plasma-generated graphene oxide-magnetic core structured nanoparticles, including the following steps:

[0090] (1) Graphene-magnetic core structure nanoparticles are placed on a substrate and placed in a microwave plasma device;

[0091] (2) Turn on the vacuum pump and evacuate to 150 Pa. Introduce oxygen into the vacuum chamber at a flow rate of 4500 sccm. Adjust the vacuum pump to bring the pressure inside the chamber to 500 Pa. Adjust the power supply of the plasma device and slowly increase the power. When a pale blue carbon dioxide plasma is observed to be generated, quickly adjust the power to 3500 W to modify the graphene-magnetic core structure nanoparticles.

[0092] (3) After 16 minutes of modification, turn off the vacuum pump, stop the gas output, and take out the sample.

[0093] (4) The modified magnetic nanoparticles were placed in a glass dish and allowed to stand at room temperature, then dispersed in deionized water at a concentration of 7 g / L.

[0094] (5) Place the solution in a high-speed shear dispersion homogenizer and shear disperse at 9000 rpm for 30 min. After standing for 3 min, remove the nanoparticles floating on the water surface, thereby removing the unoxidized particles.

[0095] (6) Magnetic separation is performed using the magnetic properties of the particles to remove non-magnetic free graphene and obtain pre-purified graphene oxide-magnetic core structure nanoparticles, i.e. crude product.

[0096] (7) Disperse the crude product in a 50% ethanol aqueous solution at a mass-volume ratio of 3 g / L.

[0097] (8) The solution obtained in step (7) was homogenized and dispersed at 650 bar for 30 min using a high-pressure dispersion homogenizer, and then magnetic separation was performed again to remove non-magnetic free graphene, so as to obtain high-purity graphene oxide-magnetic core structure nanoparticles with a purity of 98% and a yield of 74%.

[0098] Example 3

[0099] This embodiment provides a method for purifying plasma-generated graphene oxide-magnetic core structured nanoparticles, including the following steps:

[0100] (1) Place the graphene-magnetic core structure nanoparticles in a substrate and place them in a radio frequency plasma device;

[0101] (2) Turn on the vacuum pump and evacuate to 100 Pa. Introduce argon gas into the vacuum chamber at a flow rate of 1000 sccm. Adjust the vacuum pump to bring the pressure inside the chamber to 450 Pa. Adjust the power supply of the plasma device and slowly increase the power. When white argon plasma is observed to be generated, introduce carbon dioxide at a flow rate of 4000 sccm. When the white argon plasma turns into blue carbon dioxide plasma, increase the power to 3500 W to modify the graphene-magnetic core structure nanoparticles.

[0102] (3) After 16 minutes of modification, turn off the vacuum pump, stop the gas output, and take out the sample.

[0103] (4) The modified magnetic nanoparticles were placed in a glass dish and allowed to stand at room temperature, then dispersed in deionized water at a concentration of 7 g / L.

[0104] (5) Place the solution in a high-speed shear dispersion homogenizer and shear disperse at 9000 rpm for 30 min. After standing for 3 min, remove the nanoparticles floating on the water surface, thereby removing the unoxidized particles.

[0105] (6) Magnetic separation is performed using the magnetic properties of the particles to remove non-magnetic free graphene and obtain pre-purified graphene oxide-magnetic core structure nanoparticles, i.e. crude product.

[0106] (7) Disperse the crude product in a 50% ethanol aqueous solution at a mass-volume ratio of 3 g / L;

[0107] (8) The solution obtained in step (7) was homogenized and dispersed at 650 bar for 30 min using a high-pressure dispersion homogenizer, and then magnetic separation was performed again to remove non-magnetic free graphene, so as to obtain high-purity graphene oxide-magnetic core structure nanoparticles with a purity of 97% and a yield of 78%.

[0108] Comparative Example 1

[0109] This embodiment provides a method for purifying plasma-generated graphene oxide-magnetic core structured nanoparticles, including the following steps:

[0110] (1) Place the graphene-magnetic core structure nanoparticles in a substrate and place them in a microwave plasma device;

[0111] (2) Turn on the vacuum pump and evacuate to 150 Pa. Introduce oxygen into the vacuum chamber at a flow rate of 4500 sccm. Adjust the vacuum pump to bring the pressure inside the chamber to 500 Pa. Adjust the power supply of the plasma device and slowly increase the power. When a pale blue carbon dioxide plasma is observed to be generated, quickly adjust the power to 3500 W to modify the graphene-magnetic core structure nanoparticles.

[0112] (3) After 21 minutes of modification, turn off the vacuum pump, stop the gas output, and take out the sample.

[0113] It was found that the graphene shell on the sample surface was completely destroyed, and the core-shell structure no longer existed.

[0114] Comparative Example 2

[0115] This embodiment provides a method for purifying plasma-generated graphene oxide-magnetic core structured nanoparticles, including the following steps:

[0116] (1) Place the graphene-magnetic core structure nanoparticles in a substrate and place them in a microwave plasma device;

[0117] (2) Turn on the vacuum pump and evacuate to 150 Pa. Introduce oxygen into the vacuum chamber at a flow rate of 4500 sccm. Adjust the vacuum pump to bring the pressure inside the chamber to 500 Pa. Adjust the power supply of the plasma device and slowly increase the power. When a pale blue carbon dioxide plasma is observed to be generated, quickly adjust the power to 3500 W to modify the graphene-magnetic core structure nanoparticles.

[0118] (3) After 16 minutes of modification, turn off the vacuum pump, stop the gas output, and take out the sample.

[0119] (4) The modified magnetic nanoparticles were placed in a glass dish and allowed to stand at room temperature, then dispersed in deionized water at a concentration of 14 g / L.

[0120] (5) Place the solution in a high-speed shear dispersion homogenizer and shear disperse at 9000 rpm for 30 min. After standing for 3 min, remove the nanoparticles floating on the water surface, thereby removing the unoxidized particles.

[0121] It was found that when the solution concentration was too high, the magnetic nanoparticles could not be completely dispersed in the water, and the floating matter on the surface could not distinguish between the magnetic nanoparticles before and after modification, resulting in a significant decrease in yield.

[0122] Comparative Example 3

[0123] This embodiment provides a method for purifying plasma-generated graphene oxide-magnetic core structured nanoparticles, including the following steps:

[0124] (1) Place the graphene-magnetic core structure nanoparticles in a substrate and place them in a microwave plasma device;

[0125] (2) Turn on the vacuum pump and evacuate to 150 Pa. Introduce oxygen into the vacuum chamber at a flow rate of 4500 sccm. Adjust the vacuum pump to bring the pressure inside the chamber to 500 Pa. Adjust the power supply of the plasma device and slowly increase the power. When a pale blue carbon dioxide plasma is observed to be generated, quickly adjust the power to 3500 W to modify the graphene-magnetic core structure nanoparticles.

[0126] (3) After 16 minutes of modification, turn off the vacuum pump, stop the gas output, and take out the sample.

[0127] (4) The modified magnetic nanoparticles were placed in a glass dish and allowed to stand at room temperature, then dispersed in deionized water at a concentration of 7 g / L.

[0128] (5) Place the solution in a high-speed shear dispersion homogenizer and shear disperse at 9000 rpm for 30 min. After standing for 3 min, remove the nanoparticles floating on the water surface, thereby removing the unoxidized particles.

[0129] (6) Magnetic separation is performed using the magnetic properties of the particles to remove non-magnetic free graphene and obtain pre-purified graphene oxide-magnetic core structure nanoparticles, i.e. crude product.

[0130] (7) Disperse the crude product in water at a mass-volume ratio of 3 g / L.

[0131] (8) The solution obtained in step (7) was homogenized and dispersed at 650 bar for 30 min using a high-pressure dispersion homogenizer, and then magnetic separation was performed again to remove non-magnetic free graphene, so as to obtain high-purity graphene oxide-magnetic core structure nanoparticles with a purity of 78% and a yield of 59%.

[0132] Although the present invention has been described in detail above with general descriptions, specific embodiments, and experiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A method for preparing and purifying plasma-generated graphene oxide-magnetic core structured nanoparticles, characterized in that, Includes the following steps: (1) Placing graphene-magnetic core structured nanoparticles in a processing chamber and allowing processing gas to flow into the processing chamber, wherein the processing gas includes oxygen-containing gas; (2) The processing gas is excited by a plasma excitation source to form plasma, and the graphene-magnetic core structure nanoparticles are exposed to the plasma environment to oxidize and modify the graphene-magnetic core structure nanoparticles. (3) The plasma-treated graphene-magnetic core structure nanoparticles are mixed with water, and then the mixture is dispersed by high-speed shearing, allowed to stand, and the nanoparticles floating on the water surface are removed. The non-magnetic free graphene is removed by magnetic separation, and the resulting magnetic material is the crude product. (4) The crude product is mixed with an ethanol aqueous solution, and then the mixture is subjected to high pressure homogenization and magnetic separation to remove non-magnetic free graphene, thereby obtaining oxidized graphene-magnetic core structure nanoparticles. The processing gas is selected from any one of the following (1) to (5): (1) Carbon dioxide; (2) Oxygen; (3) Argon and carbon dioxide, of which argon accounts for 5-15% of the total gas volume; (4) Argon and oxygen, with argon accounting for 5-15% of the total gas volume; (5) Oxygen and carbon dioxide, of which oxygen accounts for 10 to 35% of the total gas volume.

2. The preparation and purification method according to claim 1, characterized in that, The processing gas pressure is maintained at 100-90000 Pa in the processing chamber.

3. The preparation and purification method according to claim 1, characterized in that, The plasma excitation source is a glow discharge plasma excitation source, and the oxidation modification time for the graphene-magnetic core structure nanoparticles is 5~25 min.

4. The preparation and purification method according to claim 1, characterized in that, The graphene-magnetic core structure nanoparticles are core-shell type particles with nanomagnetic particles as the core and multilayer graphene as the shell.

5. The preparation and purification method according to claim 1, characterized in that, In step (3), the plasma-treated graphene-magnetic core structure nanoparticles are mixed with water at a mass-volume ratio of 0.2-10 g / L.

6. The preparation and purification method according to claim 1, characterized in that, The high-speed shear dispersion is performed at a rotation speed of 3000-15000 rpm for a duration of 20-50 min.

7. The preparation and purification method according to any one of claims 1-6, characterized in that, In step (4), the crude product is mixed with an ethanol aqueous solution at a mass-volume ratio of 0.2-10 g / L.

8. The preparation and purification method according to claim 7, characterized in that, In step (4), the volume fraction of ethanol in the aqueous ethanol solution is 30%-60%.

9. The preparation and purification method according to claim 7, characterized in that, The high-pressure homogenization pressure is 600-900 bar, and the high-pressure homogenization time is 10-60 min.

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