CN114619025B

CN114619025B - Carbon-coated metal nanoparticle, and preparation method and application thereof

Info

Publication number: CN114619025B
Application number: CN202011460079.8A
Authority: CN
Inventors: 盛英; 文成玉; 张胜振
Original assignee: China Energy Investment Corp Ltd; National Institute of Clean and Low Carbon Energy
Current assignee: China Energy Investment Corp Ltd; National Institute of Clean and Low Carbon Energy
Priority date: 2020-12-11
Filing date: 2020-12-11
Publication date: 2023-09-29
Anticipated expiration: 2040-12-11
Also published as: CN114619025A

Abstract

The invention relates to the field of carbon-coated metal materials, and discloses carbon-coated metal nano particles and a preparation method thereof. The carbon-coated metal nanoparticle includes: the metal particles and the coating layer coating the metal particles, wherein the average particle size of the metal particles is 10-50nm, the coating layer is a graphitized carbon layer, and the carbon layer spacing in the graphitized carbon layer is 0.335-0.345nm. The obtained coating layer has a graphitized structure, and can provide better electromagnetic performance for the carbon-coated metal nano particles.

Description

Carbon-coated metal nanoparticle, and preparation method and application thereof

Technical Field

The invention relates to the field of carbon-coated metal materials, in particular to a core-shell carbon-coated metal nanoparticle, and a preparation method and application thereof.

Background

The carbon-coated metal material has photoelectric, magnetic and mechanical properties. According to different metal particles, the material can be used for various aspects such as electromagnetic materials, energy storage materials, catalysts, biomedicine and the like.

The carbon-coated metal material is a particle and has a core-shell structure which is orderly arranged, wherein nano metal particles are taken as a core, and a carbon layer tightly surrounds the core. Since the shell of the nano-metal particles is formed by surrounding the carbon layer, the nano-metal particles are confined in a small space by the carbon layer. The carbon layer has a series of advantages of high temperature resistance, oxidation resistance, corrosion resistance and the like, and can avoid the influence of the environment on the nano metal particles as a coating shell, thereby solving the problem that the nano metal particles cannot be stably in the air. In addition, due to the existence of the shell, the compatibility and stability between certain nano metal particles and other systems can be improved.

CN105375031a discloses a preparation method of a lithium ion battery anode material, which comprises the following steps: 1) A carbon source and microorganisms, the carbon source comprising one or more of glucose, sucrose and starch, and agitating in an aerobic environment to promote microbial growth; 2) Mixing the product obtained in the steps with an iron source, a phosphorus source and a lithium source; 3) Placing and aging; 4) Drying; 5) Grinding the dried product for the first time; 6) Performing first heat treatment; 7) Secondary grinding; 8) And a second heat treatment, wherein the temperature of the second heat treatment is higher than that of the first heat treatment. The lithium ion battery anode material is carbon-coated nano-structured lithium iron phosphate, and the particle size range is 100-200nm. The process is complex, and the obtained coating layer is a common carbon layer.

CN105185999a discloses a negative electrode material for a lithium ion power battery, which has a core-shell structure, wherein the shell of the core-shell structure is a carbon coating layer, the core of the core-shell structure is a carbon core material, and the carbon core material contains lithium element or lithium element and transition metal element; when the carbon core material contains lithium element, the molar ratio of the lithium element to carbon in the carbon core material is 0.004-0.15:8.3; when the carbon core material contains lithium element and transition metal element, the molar ratio of the lithium element to the transition metal element to the carbon element in the carbon core material is 0.004-0.15:0.001-0.04:8.3; the mass ratio of the carbon coating layer to the carbon core material is 0.1-3:100; the carbon core material is one of natural graphite, artificial graphite, mesophase carbon microspheres and organic pyrolytic carbon. The preparation method comprises the following steps: 1) Adding a carbon core material into a transition metal salt aqueous solution, soaking for 1h at 50 ℃, continuously heating to 100 ℃ until a solvent is evaporated to dryness to obtain a transition metal element doped carbon core material; 2) Adding the carbon core material doped with the transition metal element into a lithium compound aqueous solution, mixing, soaking for 1h at 50 ℃, and continuously heating to 100 ℃ until the solvent is evaporated to dryness to obtain the carbon core material doped with the lithium element; 3) Mixing the carbon core material doped with lithium element with pyrolytic carbon source, stirring for 2h, maintaining the temperature at 800-2800 ℃ under the protection of nitrogen for 2-20h to obtain a composite material, and cooling to room temperature to obtain the lithium-doped carbon core material. However, the process is complex and has high energy consumption, and the obtained carbon coating layer has a net structure and poor mechanical property.

Thus, there is a need for improved carbon-coated metal nanoparticles.

Disclosure of Invention

The invention aims to overcome the defect of the existing carbon-coated metal nanoparticle structure, and provides a carbon-coated metal nanoparticle, a preparation method and application thereof.

To achieve the above object, a first aspect of the present invention provides a carbon-coated metal nanoparticle comprising: the metal particles and the coating layer coating the metal particles, wherein the average particle size of the metal particles is 10-50nm, the coating layer is a graphitized carbon layer, and the carbon layer spacing in the graphitized carbon layer is 0.335-0.345nm.

Preferably, the weight ratio of the metal particles to the coating layer is 1:3-1:99.

The second aspect of the present invention provides a method for preparing carbon-coated metal nanoparticles, comprising:

(1) Dissolving metal salt in water, and stirring and dissolving to obtain a metal salt solution;

(2) Adding a carbon source into the metal salt solution to obtain a carbon-containing metal salt solution;

(3) Evaporating and drying the carbon-containing metal salt solution to obtain carbon-metal solid powder;

(4) Optionally pre-oxidizing the carbon-metal solid powder, and carbonizing to obtain carbon-coated metal nano particles;

the carbon source is sulfonated asphalt.

The third aspect of the present invention provides a carbon-coated metal nanoparticle prepared by the preparation method of the present invention.

In a fourth aspect, the present invention provides the use of the carbon-coated metal nanoparticle of the present invention in an electromagnetic material.

According to the technical scheme, the carbon-coated metal nano particle with the coating layer being the graphitized carbon layer can be provided, and the particle has an average particle size of 10-50 nm. The invention provides a coating prepared by using sulfonated asphalt, the obtained coating has a graphitized structure, better electromagnetic performance can be provided for carbon-coated metal nano particles, and the saturation magnetization value can be higher than 30emu/g.

Drawings

FIG. 1 is an XRD spectrum of carbon-coated nanoparticles according to example 1 of the present invention;

FIG. 2 is an SEM spectrum of carbon-coated nanoparticles according to example 1 of the present invention;

FIG. 3 is a TEM spectrum of the carbon-coated nanoparticle according to example 1 of the present invention;

FIG. 4 is a SEM spectra of carbon-coated nanoparticles according to comparative examples 2 and 3 of the present invention, wherein a is a spectrum of comparative example 2 and b is a spectrum of comparative example 3;

fig. 5 is an SEM spectrum provided in comparative example 6 of the present invention.

Detailed Description

The endpoints and any values of the ranges disclosed herein are not limited to the precise range or value, and are understood to encompass values approaching those ranges or values. For numerical ranges, one or more new numerical ranges may be found between the endpoints of each range, between the endpoint of each range and the individual point value, and between the individual point value, in combination with each other, and are to be considered as specifically disclosed herein.

The first aspect of the present invention provides a carbon-coated metal nanoparticle comprising: the metal particles and the coating layer coating the metal particles, wherein the average particle size of the metal particles is 10-50nm, the coating layer is a graphitized carbon layer, and the carbon layer spacing in the graphitized carbon layer is 0.335-0.345nm.

The carbon-coated metal nanoparticle provided by the invention has a core-shell structure. A core, which is a metal particle having a smaller average particle diameter; the shell is a coating layer of graphitized carbon. Wherein, the average particle diameter of the metal particles provided by some embodiments is preferably 15-40nm. The average particle size of the finally formed carbon-coated metal nanoparticles may be in the range of 45-500 nm.

In the carbon-coated metal nanoparticle provided by the invention, the composition of the coating layer is mainly carbon, and the structure of the coating layer is a graphitized carbon layer. The structure of the carbon constituting the coating layer can be judged from the interplanar spacing results by XRD measurement, and is a layered structure as that of graphite, and the carbon layer spacing is 0.335-0.345nm. The carbon-coated metal nanoparticles described above have this structure, and the graphitized carbon layer can help provide better stability of the metal particles, as well as compatibility with other systems and stability.

In some embodiments of the invention, the composition of the carbon-coated metal nanoparticle is preferably such that the weight ratio of the metal particle to the coating layer is from 1:3 to 1:99, preferably from 1:20 to 1:60, for example, in the range of any one of 1:20, 1:25, 1:30, 1:35, 1:40, 1:45, 1:50, 1:55, 1:60, and any two values. More preferably 1:31 to 1:52. For example, to the extent such coating is present, it is possible to provide the carbon-coated metal nanoparticles with better electromagnetic properties.

In some embodiments of the present invention, the metal particles may be particles containing a plurality of metal elements, preferably, the metal particles contain a group VIII metal element; preferably at least one of Fe, co and Ni. Further, the metal particles may be at least one of nickel nanoparticles, iron nanoparticles, cobalt nanoparticles.

In some embodiments of the present invention, carbon-coated metal nanoparticles are provided that can have better electromagnetic properties. Preferably, the carbon-coated metal nanoparticles can have a saturation magnetization value of greater than 30emu/g.

wherein the carbon source is sulfonated asphalt.

In some embodiments of the present invention, the carbon-coated metal nanoparticles provided herein can be obtained using simple preparation steps by selecting a water-soluble carbon source and a metal salt solution. Preferably, the metal salt is a metal salt of a group VIII element, preferably at least one of nickel nitrate, nickel acetate, cobalt chloride, iron nitrate and cobalt nitrate, more preferably at least one of nickel nitrate, cobalt chloride and cobalt nitrate.

In some embodiments of the invention, the inventors have found that the use of a water-soluble material for the carbon source can advantageously provide the resulting coating with a graphitized carbon layer. Preferably, the sulfonated asphalt has a water solubility of 65% or more. For example, the range is composed of any one value and any two values of 65%, 70%, 75%, 80%, 85%, 90%, 95%, 99%, more preferably 87 to 93%, and the range is composed of any one value and any two values of 87%, 88%, 89%, 90%, 91%, 92%, 93%.

In some embodiments of the present invention, sulfonated pitch is preferred as the carbon source, although it may contain heteroatoms such as oxygen, sulfur, sodium, but with higher levels of carbon and hydrogen elements. Preferably, the sum of the contents of the carbon element and the hydrogen element in the sulfonated asphalt is 70 wt% or more, preferably, for example, 70 wt%, 75 wt%, 80 wt%, 85 wt%, 90 wt%, 95 wt%, 99 wt% or any one value and any two value composition range, more preferably, 72 to 82wt%, and 72wt%, 73 wt%, 74 wt%, 75 wt%, 76wt%, 77 wt%, 78 wt%, 79 wt%, 80 wt%, 81 wt%, 82wt% or any two value composition range. The coating layer of the obtained carbon-coated metal nano particles is provided with a graphitized carbon layer, so that better electromagnetic performance is provided. The sulfonated asphalt is commercially available, for example, from Hualong chemical Co.Ltd. Or homemade in the laboratory.

In some embodiments of the invention, preferably, the weight ratio of the metal salt to the carbon source is 1:5-1:20. For example, the weight ratio is any one of the values and any two of the values of 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1:16, 1:17, 1:18, 1:19, 1:20. Preferably 1:9 to 1:12. The ratio and the size relation between the core and the shell structure of the prepared carbon-coated metal nano particles can be controlled.

In some embodiments of the invention, preferably, in step (3), the rate of evaporative drying is from 30mL/h to 70mL/h. And (3) controlling the evaporation drying process within the speed range, wherein the obtained carbon-metal solid powder can be subjected to the process of the step (4) to obtain the carbon-coated metal nano particles with better coating effect.

In some embodiments of the present invention, preferably, the pre-oxidizing conditions include: the pre-oxidation temperature is 250-300 ℃ and the pre-oxidation time is 3-7h. Can be beneficial to achieve the effect or function of uniformly coating the metal on the carbon layer.

In some embodiments of the present invention, preferably, the carbonization conditions include: the carbonization temperature is 750-1000 ℃, and the carbonization time is 1.5-5 h. The carbon source can be converted into a coating layer, and the coating layer becomes a carbon layer with a graphitized structure.

The third aspect of the present invention provides a carbon-coated metal nanoparticle prepared by the preparation method of the present invention. Wherein the carbon-coated metal nanoparticle comprises: the metal particles as nuclei have an average particle diameter of 10 to 50nm, preferably 15 to 40nm; and the coating layer is taken as a shell of the graphitized carbon layer, and the carbon layer-to-layer spacing in the graphitized carbon layer is 0.335-0.345nm. Wherein the weight ratio of the metal particles to the coating layer is 1:3-1:99, preferably 1:20-1:60. Preferably, the metal particles contain a group VIII metal element, preferably at least one of Fe, co, and Ni, and more preferably, the metal particles may be at least one of nickel nanoparticles, iron nanoparticles, cobalt nanoparticles.

In a fourth aspect, the present invention provides the use of the carbon-coated metal nanoparticle of the present invention in an electromagnetic material. The carbon-coated metal nanoparticles can have a saturation magnetization value of greater than 30emu/g.

The present invention will be described in detail by examples. In the following examples, the average particle diameter of the metal particles was measured by XRD, and the X-ray diffraction analyzer was operated in a 2 theta/theta continuous scanning mode with a step size of 0.02 DEG using D8AX from Bruce AXS, germany, using Cu-K alpha target X-rays, a wavelength lambda of 0.1541nm, an operating voltage of 40kV, a current of 100mA, and a scanning range of 10 to 80 ℃. The calculation was performed using the Scherrer formula. D=kλ/(βcos θ), k is the ordinary, λ is the X-ray wavelength, β is the half-width of the diffraction peak, and θ is the diffraction angle. Where k is taken to be 0.89.

The layer-to-layer spacing of the carbon-coated carbon was measured using monochromatic radiation. The carbon layer spacing of the coated carbon of the sample can be obtained by using a Bragg equation and a formula, wherein nλ=2dsin theta of the Bragg equation; where d is the interlayer spacing, θ is the angle between the incident X-ray and the corresponding layer, λ is the wavelength of the X-ray, and n is the diffraction order.

The morphology and structure analysis of the carbon-coated metal nano particles are observed by a Scanning Electron Microscope (SEM), and the instrument is a Nova NanoSEM450 of Czech;

the saturation magnetization of the carbon-coated metal nanoparticles was measured by a Vibrating Sample Magnetometer (VSM), the instrument being the Lake Shore 7410, usa. Saturation magnetization is a physical quantity representing the strong and weak current of the magnet, and when the size of the nano magnet is reduced, the saturation magnetization is reduced, and the magnetism is enhanced. Showing whether the carbon-coated metal nanoparticles have electromagnetic properties.

Example 1

1) 0.50g of nickel nitrate hexahydrate was dissolved in water (stirring dissolution at 50 ℃ C. For 20 minutes) to prepare a nickel nitrate solution; adding 4.55g of sulfonated asphalt-1 (water dissolution rate is 87%, and content sum of carbon and hydrogen elements is 76 wt%) (weight ratio of nickel nitrate hexahydrate to sulfonated asphalt is 1:9.1), dissolving for 2h to fully dissolve to obtain carbon-containing nickel salt solution;

2) Evaporating and drying the carbon-containing nickel salt solution at the rate of 50mL/h, and evaporating and drying water to obtain carbon-nickel solid powder;

3) Pre-oxidizing the carbon-nickel solid powder for 5 hours at 280 ℃, and carbonizing the carbon-nickel solid powder for 5 hours at 850 ℃ in vacuum to obtain the carbon-coated nickel nano particles.

The resulting carbon-coated nickel nanoparticles were subjected to XRD, SEM, TEM testing. The 3 distinct peaks in the XRD spectrum of fig. 1, which appear at positions 44.50 °, 51.85 ° and 76.38 ° in 2θ, correspond to the diffraction peaks of the (111), (200) and (220) planes of elemental nickel, respectively. The nickel particles had an average particle diameter of 38.1nm, and the coating layer was a graphitized carbon layer (carbon layer spacing of 0.34 nm).

SEM and TEM photographs show that the obtained carbon-coated nickel nano particles have a core-shell structure (as shown in figures 2 and 3, wherein the inner part is metal nickel grains, the outer part is lamellar graphite carbon), the grains of the nickel particles are fine, the surface is smooth, and the outer part is coated with lamellar graphitized carbon. The weight ratio of the nickel nano particles to the coating layer is 1:35. the saturated magnetization value of the carbon-coated nickel nano particles is higher than 30emu/g.

Example 2

1) 0.50g of ferric nitrate hexahydrate was dissolved in water (stirring dissolution at 50 ℃ C. For 20 minutes) to obtain a ferric nitrate solution; adding 4.55g of sulfonated asphalt-1 (water dissolution rate is 87% and content of carbon and hydrogen elements is 76 wt%) (weight ratio of ferric nitrate hexahydrate to sulfonated asphalt is 1:9.1), dissolving for 2h to fully dissolve to obtain carbon-containing ferric salt solution;

2) Evaporating and drying the carbon-containing ferric salt solution at the rate of 30mL/h, and evaporating and drying water to obtain carbon-iron solid powder;

3) Pre-oxidizing the carbon-iron solid powder for 5 hours at 280 ℃, and carbonizing the carbon-iron solid powder for 2 hours at 1000 ℃ in vacuum to obtain the carbon-coated iron nano particles.

The resulting carbon-coated nickel nanoparticles were subjected to XRD, SEM, TEM testing. XRD showed diffraction peaks of elemental iron. The average particle diameter of the iron particles was 15.7nm, and the coating layer was a graphitized carbon layer (carbon layer spacing was 0.34 nm).

SEM and TEM photographs were similar to those obtained in example 1, showing that the obtained carbon-coated iron nanoparticles had a core-shell structure, the iron particles had fine crystal grains, a smooth surface, and a lamellar graphitized carbon coating the outside. The weight ratio of the iron nano particles to the coating layer is 1:31. the saturated magnetization value of the carbon-coated iron nanoparticle is higher than 30emu/g.

Example 3

1) 1g of cobalt chloride is dissolved in water (stirring and dissolving for 20min at 50 ℃) to form cobalt chloride solution; adding 9g of sulfonated asphalt-2 (water dissolution rate is 93% and the sum of carbon and hydrogen element is 72 wt%) (cobalt chloride: sulfonated asphalt weight ratio is 1:9) into the mixture, and dissolving the mixture for 2 hours until the mixture is fully dissolved; obtaining a carbon-containing cobalt salt solution;

2) Evaporating and drying the carbon-containing cobalt salt solution at the rate of 70mL/h, and evaporating and drying water to obtain carbon-cobalt solid powder;

3) Pre-oxidizing the carbon-cobalt solid powder for 5 hours at 250 ℃, and carbonizing the carbon-cobalt solid powder for 3 hours at 900 ℃ in vacuum to obtain the carbon-coated cobalt nano particles.

The resulting carbon-coated cobalt nanoparticles were subjected to XRD, SEM, TEM testing. XRD showed diffraction peaks of elemental cobalt. The average particle diameter of the cobalt particles was 26.9nm, and the coating layer was a graphitized carbon layer (carbon layer spacing was 0.34 nm).

SEM and TEM photographs are similar to those of the example 1, the obtained carbon-coated cobalt nanoparticles have a core-shell structure, the cobalt particles have fine grains and smooth surfaces, and the outer surfaces of the cobalt particles are coated with lamellar graphitized carbon. The weight ratio of the cobalt nano particles to the coating layer is 1:37. the saturation magnetization value of the carbon-coated cobalt nanoparticle is higher than 30emu/g.

Example 4

1) 1g of nickel nitrate hexahydrate was dissolved in water (stirring dissolution at 50 ℃ C. For 20 minutes) to obtain a nickel nitrate solution; then adding 12g of sulfonated asphalt-2 (Hualong chemical Co., ltd., in chat, water dissolution rate is 93%, and the sum of carbon and hydrogen element is 72 wt%) (weight ratio of nickel nitrate hexahydrate to sulfonated asphalt is 1:12), dissolving for 2h to fully dissolve; obtaining a carbon-containing nickel salt solution;

3) And (3) carrying out vacuum carbonization on the carbon-nickel solid powder for 2 hours at the temperature of 1000 ℃ to obtain the carbon-coated nickel nano particles.

The resulting carbon-coated nickel nanoparticles were subjected to XRD, SEM, TEM testing. XRD showed diffraction peaks of elemental nickel. The nickel particles had an average particle diameter of 28.9nm, and the coating layer was a graphitized carbon layer (carbon layer spacing of 0.34 nm).

SEM and TEM photographs are similar to those of the example 1, the obtained carbon-coated nickel nanoparticles have a core-shell structure, the nickel particles have fine crystal grains and smooth surfaces, and the outer surfaces of the nickel particles are coated with lamellar graphitized carbon. The weight ratio of the nickel nano particles to the coating layer is 1:52. the saturated magnetization value of the carbon-coated nickel nano particles is higher than 30emu/g.

Comparative example 1

The procedure of example 1 was followed, except that the carbonization condition was 700℃for 5 hours.

The resulting carbon-coated nickel nanoparticles were subjected to XRD, SEM, TEM testing. The average particle diameter of the nickel nano particles is 75nm, and the carbon layer-to-layer spacing in the coating layer is 0.65nm. The photograph of SEM test shows that the resulting coating of carbon-coated nickel nanoparticles is not graphitized. The saturated magnetization value of the carbon-coated nickel nano particles is lower than 30emu/g.

Comparative example 2

The procedure of example 1 was followed, except that the evaporation rate in step (3) was 10mL/h.

The resulting carbon-coated nickel nanoparticles were subjected to XRD, SEM, TEM testing. The average particle size of the nickel nanoparticles was 67nm. The photograph of SEM test shows that the obtained nickel nanoparticle is elongated and the carbon coating layer has tailing phenomenon, which means that the evaporation rate of water affects the shape of metal, and the tailing of the carbon coating layer affects practical interface effect, as shown in fig. 4 a. The coating layer does not form a graphitized carbon layer. The saturated magnetization value of the carbon-coated nickel nano particles is lower than 30emu/g.

Comparative example 3

The procedure of example 3 was followed, except that the carbonization condition was 1200℃for 5 hours.

The resulting carbon-coated cobalt nanoparticles were subjected to XRD, SEM, TEM testing. The average particle size of the cobalt nanoparticles was 87nm and photographs from sem tests showed the appearance of agglomeration as shown in figure 4 b. The coating layer does not form a graphitized carbon layer. The saturation magnetization value of the carbon-coated cobalt nanoparticle is lower than 30emu/g.

Comparative example 4

Carbon-coated nickel nanoparticles were prepared by replacing 4.55g of sulfonated asphalt-1 with 4.55g of sulfonated asphalt-3 (homemade, water solubility of 52%, and carbon and hydrogen content of 82 wt%).

The resulting carbon-coated nickel nanoparticles were subjected to XRD, SEM, TEM testing. The nickel nanoparticles had an average particle diameter of 123nm and photographs from sem showed that the carbon layer spacing of the outer coating layer was 0.47nm, not the graphitized carbon layer. The saturated magnetization value of the carbon-coated nickel nano particles is lower than 30emu/g.

Comparative example 5

Carbon-coated nickel nanoparticles were prepared by replacing 4.55g of sulfonated asphalt-1 with 4.55g of sulfonated asphalt-4 (homemade, water solubility 65%, carbon and hydrogen content 68 wt%).

The resulting carbon-coated nickel nanoparticles were subjected to XRD, SEM, TEM testing. The average particle diameter of the nickel nanoparticles was 122nm, and photographs of sem tests showed that the carbon layer spacing of the outer coating layer was 0.49nm, not the graphitized carbon layer. The saturated magnetization value of the carbon-coated nickel nano particles is lower than 30emu/g.

Comparative example 6

The procedure of example 1 was followed except that 4.55g of sulfonated asphalt-1 was replaced with 4.55g of petroleum asphalt. Photographs from SEM testing showed that carbon-coated nickel nanoparticles could not be obtained.

From the above examples and comparative examples, it can be seen that the method provided by the invention can obtain carbon-coated metal nanoparticles with a coating layer having a graphitized structure, and has better electromagnetic properties.

The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the scope of the technical idea of the invention, a number of simple variants of the technical solution of the invention are possible, including combinations of the individual technical features in any other suitable way, which simple variants and combinations should likewise be regarded as being disclosed by the invention, all falling within the scope of protection of the invention.

Claims

1. A method for preparing carbon-coated metal nanoparticles, the method comprising:

wherein the carbon source is sulfonated asphalt;

wherein the carbon-coated metal nanoparticle comprises: a metal nanoparticle and a coating layer coating the metal nanoparticle;

wherein the average particle diameter of the metal nano particles is 10-50nm, the coating layer is a graphitized carbon layer, and the carbon layer-to-layer spacing in the graphitized carbon layer is 0.335-0.345nm.

2. The production method according to claim 1, wherein the metal salt is a metal salt of a group VIII element;

and/or the sulfonated asphalt has a water solubility of 65% or more;

and/or, the sum of the content of carbon element and hydrogen element in the sulfonated asphalt is more than 70 weight percent;

and/or the weight ratio of the metal salt to the carbon source is 1:5-1:20.

3. The production method according to claim 2, wherein the metal salt is at least one of nickel nitrate, nickel acetate, cobalt chloride, iron nitrate and cobalt nitrate.

4. A production method according to any one of claims 1 to 3, wherein in step (3), the rate of evaporation drying is 30mL/h to 70mL/h.

5. A production method according to any one of claims 1 to 3, wherein the pre-oxidation conditions include: the pre-oxidation temperature is 250-300 ℃ and the pre-oxidation time is 3-7h.

6. The production method according to claim 4, wherein the conditions of the pre-oxidation include: the pre-oxidation temperature is 250-300 ℃ and the pre-oxidation time is 3-7h.

7. The production method according to any one of claims 1 to 3, 6, wherein the carbonization conditions include: the carbonization temperature is 750-1000 ℃, and the carbonization time is 1.5-5 h.

8. The production method according to claim 4, wherein the carbonization conditions include: the carbonization temperature is 750-1000 ℃, and the carbonization time is 1.5-5 h.

9. The production method according to claim 5, wherein the carbonization conditions include: the carbonization temperature is 750-1000 ℃, and the carbonization time is 1.5-5 h.

10. A carbon-coated metal nanoparticle produced by the production method of any one of claims 1 to 9.

11. The carbon-coated metal nanoparticle of claim 10, wherein the metal nanoparticle has an average particle size of 15-40nm;

and/or the metal nanoparticles contain a group VIII metal element.

12. The carbon-coated metal nanoparticle of claim 11, wherein the metal nanoparticle comprises at least one of Fe, co, and Ni.

13. The carbon-coated metal nanoparticle of claim 10, wherein the weight ratio of the metal nanoparticle to the coating layer is 1:3-1:99.

14. The carbon-coated metal nanoparticle of claim 11 or 12, wherein the weight ratio of the metal nanoparticle to the coating layer is 1:3-1:99.

15. Use of carbon-coated metal nanoparticles according to any one of claims 10-14 in electromagnetic materials.