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

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 nanoparticles and their preparation methods and applications

Technical field

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

Background technique

Carbon-coated metal materials have optoelectronic, magnetic and mechanical properties. Depending on the metal particles, the material can be used in electromagnetic materials, energy storage materials, catalysts, biomedicine and other aspects.

Carbon-coated metal materials are particles with an ordered core-shell structure, in which nanometal particles are the core and the carbon layer closely surrounds the core. Since the shell of the nanometal particles is surrounded by a carbon layer, the nanometal particles are confined in a small space by the carbon layer. The carbon layer has a series of advantages such as high temperature resistance, oxidation resistance, and corrosion resistance. As a coating shell, it can avoid the impact of the environment on nanometal particles and solve the problem that nanometal particles cannot exist stably in the air. In addition, due to the existence of the shell, the compatibility and stability between certain nanometal particles and other systems can also be improved.

CN105375031A discloses a method for preparing cathode materials for lithium ion batteries, including: 1) mixing a carbon source and microorganisms and stirring in an aerobic environment to promote the growth of microorganisms. The carbon source includes one of glucose, sucrose and starch. One or more; 2) Mix the product obtained in the above steps with an iron source, a phosphorus source, and a lithium source; 3) Leave to age; 4) Dry; 5) Grind the dried product for the first time; 6) The first heat treatment ;7) Second grinding; 8) Second heat treatment, the temperature of the second heat treatment is higher than the temperature of the first heat treatment. The lithium-ion battery cathode material is carbon-coated nanostructured lithium iron phosphate, with a particle size range of 100-200 nm. The process is complicated, and the resulting coating layer is an ordinary carbon layer.

CN105185999A discloses a negative electrode material for lithium-ion power batteries, which has a core-shell structure. The shell of the core-shell structure is a carbon coating layer. The core of the core-shell structure is a carbon core material. 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 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 When ; The carbon core material is one of natural graphite, artificial graphite, mesophase carbon microspheres, and organic pyrolytic carbon. The specific preparation method includes: 1) adding the carbon core material into the transition metal aqueous salt solution, immersing it at 50°C for 1 hour, and continuing to raise the temperature to 100°C until the solvent is evaporated to dryness to obtain a carbon core material doped with transition metal elements; 2) adding The carbon core material doped with transition metal elements is added to the lithium compound aqueous solution, mixed, immersed at 50°C for 1 hour, and then heated to 100°C until the solvent evaporates to dryness to obtain the carbon core material doped with lithium element; 3) Add the lithium element doped carbon core material Mix the carbon core material and pyrolyzed carbon source, stir for 2 hours, and keep at 800-2800°C for 2-20 hours under nitrogen protection to obtain a composite material, which can be obtained after cooling to room temperature. However, the process is complex and energy-consuming, and the resulting carbon coating layer has a network structure and poor mechanical properties.

Therefore, improved carbon-coated metal nanoparticles are needed.

Contents of the invention

The purpose of the present invention is to overcome the defects of the existing carbon-coated metal nanoparticle structures and provide carbon-coated metal nanoparticles and their preparation methods and applications.

In order to achieve the above object, the first aspect of the present invention provides a carbon-coated metal nanoparticle, including: metal particles and a coating layer covering the metal particles, wherein the average particle size of the metal particles is 10-50 nm. , 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.

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

(1) Dissolve the metal salt in water, stir and dissolve to obtain a metal salt solution;

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

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

(4) Subjecting the carbon-metal solid powder to optional pre-oxidation and then carbonization to obtain carbon-coated metal nanoparticles;

The carbon source is sulfonated pitch.

A third aspect of the present invention provides carbon-coated metal nanoparticles prepared by the preparation method of the present invention.

The fourth aspect of the present invention provides an application of the carbon-coated metal nanoparticles of the present invention in electromagnetic materials.

Through the above technical solution, the present invention can provide carbon-coated metal nanoparticles whose coating layer is a graphitized carbon layer, and the particles have an average particle diameter of 10-50 nm. The invention provides the use of sulfonated pitch to prepare a coating layer. The coating layer that can be obtained has a graphitized structure, which can provide better electromagnetic properties for carbon-coated metal nanoparticles, and the saturation magnetization value can be higher than 30emu/g.

Description of the drawings

Figure 1 is an XRD spectrum of carbon-coated nanoparticles provided in Example 1 of the present invention;

Figure 2 is an SEM spectrum of the carbon-coated nanoparticles provided in Example 1 of the present invention;

Figure 3 is a TEM spectrum of the carbon-coated nanoparticles provided in Example 1 of the present invention;

Figure 4 is an SEM spectrum of the carbon-coated nanoparticles provided in Comparative Example 2 and Comparative Example 3 of the present invention, wherein Figure a is the spectrum of Comparative Example 2, and Figure b is the spectrum of Comparative Example 3;

Figure 5 is an SEM spectrum provided by Comparative Example 6 of the present invention.

Detailed ways

The endpoints of ranges and any values disclosed herein are not limited to the precise range or value, but these ranges or values are to be understood to include values approaching such ranges or values. For numerical ranges, the endpoint values of each range, the endpoint values of each range and individual point values, and the individual point values can be combined with each other to obtain one or more new numerical ranges. These values The scope shall be deemed to be specifically disclosed herein.

A first aspect of the present invention provides carbon-coated metal nanoparticles, including: metal particles and a coating layer coating the metal particles, wherein the average particle size of the metal particles is 10-50 nm, and the coating layer The 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 nanoparticles provided by the invention have a core-shell structure. The core is a metal particle with a smaller average particle size; the shell is a coating layer of graphitized carbon. Among them, the average particle size of the metal particles provided in some embodiments is preferably 15-40 nm. The average particle size of the finally formed carbon-coated metal nanoparticles can be in the range of 45-500 nm.

In the carbon-coated metal nanoparticles provided by the present invention, the composition of the coating layer is mainly carbon, and the structure of the coating layer is a graphitized carbon layer. Through the XRD method, it can be determined from the crystal plane spacing results that the structure of the carbon constituting the coating layer is a layered structure like graphite, and the carbon layer spacing is 0.335-0.345nm. As mentioned above, the carbon-coated metal nanoparticles have this structure, and the graphitized carbon layer can help provide better stability of the metal particles, as well as compatibility and stability with other systems.

In some embodiments of the present invention, the composition of the carbon-coated metal nanoparticles, preferably, the weight ratio of the metal particles to the coating layer is 1:3-1:99, preferably 1:20- 1:60, for example, any one value and any two values among 1:20, 1:25, 1:30, 1:35, 1:40, 1:45, 1:50, 1:55, 1:60 A range of values. More preferably, it is 1:31-1:52. For example, the amount of the coating layer described above can provide the carbon-coated metal nanoparticles with better electromagnetic properties.

In some embodiments of the present invention, the metal particles may be particles containing multiple metal elements. Preferably, the metal particles contain Group VIII metal elements; preferably, they contain at least one of Fe, Co and Ni. Further, the metal particles may be at least one of nickel nanoparticles, iron nanoparticles, and cobalt nanoparticles.

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

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

(1) Dissolve the metal salt in water, stir and dissolve to obtain a metal salt solution;

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

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

(4) Subjecting the carbon-metal solid powder to optional pre-oxidation and then carbonization to obtain carbon-coated metal nanoparticles;

Wherein, the carbon source is sulfonated pitch.

In some embodiments of the present invention, by selecting a water-soluble carbon source and a metal salt solution, the carbon-coated metal nanoparticles provided by the present invention can be obtained using simple preparation steps. 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 nickel nitrate, cobalt chloride, nitric acid At least one of cobalt.

In some embodiments of the present invention, the inventor found that selecting a water-soluble substance as the carbon source can be beneficial in providing the obtained coating layer with a graphitized carbon layer. Preferably, the water solubility rate of the sulfonated asphalt is above 65%. For example, it is a range consisting of any one value of 65%, 70%, 75%, 80%, 85%, 90%, 95%, 99% and any two values, more preferably 87-93%, and 87% , 88%, 89%, 90%, 91%, 92%, 93%, any one value and the range composed of any two values.

In some embodiments of the present invention, sulfonated pitch is preferred as the carbon source. Although it may contain miscellaneous elements, such as oxygen, sulfur, and sodium, it has a relatively high content of carbon and hydrogen elements. Preferably, the sum of carbon and hydrogen content in the sulfonated pitch is above 70% by weight, preferably 70% by weight, 75% by weight, 80% by weight, 85% by weight, 90% by weight, or 95% by weight. %, 99% by weight, and the range consisting of any two values, more preferably 72-82% by weight, and 72% by weight, 73% by weight, 74% by weight, 75% by weight, 76% by weight, 77% by weight A range consisting of any one value among weight%, 78% by weight, 79% by weight, 80% by weight, 81% by weight, and 82% by weight, and any two values. The coating layer that enables the obtained carbon-coated metal nanoparticles to have a graphitized carbon layer provides better electromagnetic properties. The sulfonated asphalt is commercially available, such as the series of sulfonated asphalt products produced by Liaocheng Hualong Chemical Co., Ltd. Or made in the laboratory.

In some embodiments of the present invention, preferably, the weight ratio of the metal salt to the carbon source is 1:5-1:20. For example, the weight ratio is 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1: Any one value among 16, 1:17, 1:18, 1:19, 1:20 and the range composed of any two values. Preferably it is 1:9-1:12. The ratio and size relationship between the core and shell structures of the prepared carbon-coated metal nanoparticles can be controlled.

In some embodiments of the present invention, preferably, in step (3), the evaporation drying rate is 30 mL/h-70 mL/h. By controlling the evaporation drying process within the above rate range, the obtained carbon-metal solid powder can withstand the process of step (4), and obtain carbon-coated metal nanoparticles with better wrapping effect.

In some embodiments of the present invention, preferably, the pre-oxidation conditions include: pre-oxidation temperature is 250-300°C, and pre-oxidation time is 3-7 hours. It can be beneficial to achieve the effect or function of uniformly coating the metal with the carbon layer.

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

A third aspect of the present invention provides carbon-coated metal nanoparticles prepared by the preparation method of the present invention. Wherein, the carbon-coated metal nanoparticles include: metal particles as cores, with an average particle diameter of 10-50nm, preferably 15-40nm; and a coating layer of graphitized carbon layer as shell, in which carbon The layer-to-layer spacing 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 Group VIII metal elements, preferably at least one of Fe, Co, and Ni. More preferably, the metal particles can be at least one of nickel nanoparticles, iron nanoparticles, and cobalt nanoparticles. kind.

The fourth aspect of the present invention provides an application of the carbon-coated metal nanoparticles of the present invention in electromagnetic materials. The saturation magnetization value of the carbon-coated metal nanoparticles can be higher than 30 emu/g.

The present invention will be described in detail below through examples. In the following examples, the average particle size of metal particles was measured by the XRD method. The X-ray diffraction analysis instrument used was D8AX from Bruker AXS Co., Ltd. of Germany. Cu-Kα target X-rays were used. The wavelength λ was 0.1541nm. The operating voltage of the instrument was 40kV. , current 100mA, scanning range 10-80°, 2θ/θ continuous scanning mode, step size 0.02°. Calculated using Scherrer's formula. D=kλ/(βcosθ), k is constant temperature, λ is X-ray wavelength, β is the half-width of the diffraction peak, and θ is the diffraction angle. Among them, k is taken as 0.89.

The interlayer spacing of carbon-coated carbon layers was measured using monochromatic rays. The interlayer spacing of the carbon-coated carbon layer of the sample can be obtained from the Bragg equation and formula. The Bragg equation nλ = 2d sinθ; where d is the interlayer spacing, θ is the angle between the incident X-ray and the corresponding layer, and λ is the wavelength of the X-ray. , n is the diffraction order.

The morphology and structure analysis of carbon-coated metal nanoparticles were observed with a scanning electron microscope (SEM), using a Nova NanoSEM450 from the Czech Republic;

The saturation magnetization of carbon-coated metal nanoparticles was measured by a vibrating sample magnetometer (VSM), and the instrument was Lake Shore 7410, USA. Saturation magnetization is a physical quantity that characterizes the magnetic strength of a magnet. When the size of the nanomagnet is reduced, the saturation magnetization will decrease and the magnetism will increase. Show whether carbon-coated metal nanoparticles have electromagnetic properties.

Example 1

1) Dissolve 0.50g of nickel nitrate hexahydrate in water (stir and dissolve at 50°C for 20 minutes) to become a nickel nitrate solution; then add 4.55g of sulfonated asphalt-1 (Liaocheng Hualong Chemical Co., Ltd., water solubility rate is 87%, carbon and the hydrogen content is 76wt%) (the weight ratio of nickel nitrate hexahydrate: sulfonated asphalt is 1:9.1), dissolve for 2 hours until fully dissolved, and obtain a carbon-containing nickel salt solution;

2) Evaporate and dry the carbon-containing nickel salt solution at a rate of 50 mL/h, and evaporate the water to obtain carbon-nickel solid powder;

3) Pre-oxidize the carbon-nickel solid powder at 280°C for 5 hours, and then vacuum carbonize it at 850°C for 5 hours to obtain carbon-coated nickel nanoparticles.

The obtained carbon-coated nickel nanoparticles were tested by XRD, SEM and TEM. In the XRD spectrum in Figure 1, three significant peaks appearing at 2θ positions of 44.50°, 51.85° and 76.38° correspond to the diffraction peaks of the (111), (200) and (220) planes of elemental nickel respectively. The average particle size of the nickel particles is 38.1nm, and the coating layer is a graphitized carbon layer (the carbon layer spacing is 0.34nm).

SEM and TEM photos show that the obtained carbon-coated nickel nanoparticles have a core-shell structure (as shown in Figures 2 and 3, with metallic nickel grains inside and layered graphitic carbon outside). The nickel particles have fine grains. The surface is smooth and covered with layered graphitized carbon. The weight ratio of nickel nanoparticles to coating layer is 1:35. The saturation magnetization value of carbon-coated nickel nanoparticles is higher than 30emu/g.

Example 2

1) Dissolve 0.50g of ferric nitrate hexahydrate in water (stir and dissolve at 50°C for 20 minutes) to become ferric nitrate solution; then add 4.55g of sulfonated asphalt-1 (Liaocheng Hualong Chemical Co., Ltd., water solubility rate is 87%, carbon and the hydrogen content is 76wt%) (the weight ratio of iron nitrate hexahydrate: sulfonated asphalt is 1:9.1), dissolve for 2 hours until fully dissolved, and obtain a carbon-containing iron salt solution;

2) Evaporate and dry the carbon-containing iron salt solution at a rate of 30 mL/h, and evaporate the water to obtain carbon-iron solid powder;

3) Pre-oxidize the carbon-iron solid powder at 280°C for 5 hours, and then vacuum carbonize it at 1000°C for 2 hours to obtain carbon-coated iron nanoparticles.

The obtained carbon-coated nickel nanoparticles were tested by XRD, SEM and TEM. XRD shows the diffraction peaks of elemental iron. The average particle size of the iron particles is 15.7nm, and the coating layer is a graphitized carbon layer (the carbon layer spacing is 0.34nm).

SEM and TEM photos are similar to those obtained in Example 1, showing that the obtained carbon-coated iron nanoparticles have a core-shell structure. The iron particles have fine grains, smooth surfaces, and are coated with layered graphitized carbon on the outside. The weight ratio of iron nanoparticles to coating layer is 1:31. The saturation magnetization value of carbon-coated iron nanoparticles is higher than 30 emu/g.

Example 3

1) Dissolve 1g of cobalt chloride in water (stir and dissolve at 50°C for 20 minutes) to become a cobalt chloride solution; then add 9g of sulfonated asphalt-2 (Liaocheng Hualong Chemical Co., Ltd., water solubility rate is 93%, carbon and hydrogen The sum of the element contents is 72wt%) (the weight ratio of cobalt chloride: sulfonated asphalt is 1:9), and is dissolved for 2 hours until fully dissolved; a carbon-containing cobalt salt solution is obtained;

2) Evaporate and dry the carbon-containing cobalt salt solution at a rate of 70 mL/h, and evaporate the water to obtain carbon-cobalt solid powder;

3) Pre-oxidize the carbon-cobalt solid powder at 250°C for 5 hours, and then vacuum carbonize it at 900°C for 3 hours to obtain carbon-coated cobalt nanoparticles.

The obtained carbon-coated cobalt nanoparticles were tested by XRD, SEM and TEM. XRD shows the diffraction peak of elemental cobalt. The average particle size of the cobalt particles is 26.9nm, and the coating layer is a graphitized carbon layer (the carbon layer spacing is 0.34nm).

The SEM and TEM photos are similar to those obtained in Example 1. The obtained carbon-coated cobalt nanoparticles have a core-shell structure. The cobalt particles have fine grains and smooth surfaces, and are coated with layered graphitized carbon on the outside. The weight ratio of cobalt nanoparticles to coating layer is 1:37. The saturation magnetization value of carbon-coated cobalt nanoparticles is higher than 30emu/g.

Example 4

1) Dissolve 1g of nickel nitrate hexahydrate in water (stir and dissolve at 50°C for 20 minutes) to become a nickel nitrate solution; then add 12g of sulfonated asphalt-2 (Liaocheng Hualong Chemical Co., Ltd., water solubility rate is 93%, carbon and hydrogen The sum of the element contents is 72wt%) (the weight ratio of nickel nitrate hexahydrate: sulfonated asphalt is 1:12), dissolve for 2 hours until fully dissolved; obtain a carbon-containing nickel salt solution;

2) Evaporate and dry the carbon-containing nickel salt solution at a rate of 50 mL/h, and evaporate the water to obtain carbon-nickel solid powder;

3) Carbonize the carbon-nickel solid powder in vacuum at 1000°C for 2 hours to obtain carbon-coated nickel nanoparticles.

The obtained carbon-coated nickel nanoparticles were tested by XRD, SEM and TEM. XRD shows the diffraction peaks of elemental nickel. The average particle size of the nickel particles is 28.9nm, and the coating layer is a graphitized carbon layer (the carbon layer spacing is 0.34nm).

The SEM and TEM photos are similar to those obtained in Example 1. The obtained carbon-coated nickel nanoparticles have a core-shell structure. The nickel particles have fine grains and smooth surfaces, and are coated with layered graphitized carbon on the outside. The weight ratio of nickel nanoparticles to coating layer is 1:52. The saturation magnetization value of carbon-coated nickel nanoparticles is higher than 30emu/g.

Comparative example 1

Follow the method of Example 1, except that the carbonization condition is 700°C for 5 hours.

The obtained carbon-coated nickel nanoparticles were tested by XRD, SEM and TEM. The average particle size of nickel nanoparticles is 75nm, and the interlayer spacing of the carbon layers in the coating layer is 0.65nm. Photos of SEM tests show that the coating layer of the obtained carbon-coated nickel nanoparticles is not a graphitized layer. The saturation magnetization value of carbon-coated nickel nanoparticles is lower than 30 emu/g.

Comparative example 2

According to the method of Example 1, the difference is that the evaporation rate in step (3) is 10 mL/h.

The obtained carbon-coated nickel nanoparticles were tested by XRD, SEM and TEM. The average particle size of nickel nanoparticles is 67nm. The SEM test photos show that the obtained nickel nanoparticles are elongated and the carbon coating layer has a tailing phenomenon, indicating that the evaporation rate of water affects the shape of the metal, and the tailing of the carbon coating layer will affect the practical interface effect. , as shown in Figure 4a. The cladding layer does not form a graphitized carbon layer. The saturation magnetization value of carbon-coated nickel nanoparticles is lower than 30 emu/g.

Comparative example 3

Follow the method of Example 3, except that the carbonization condition is 1200°C for 5 hours.

The obtained carbon-coated cobalt nanoparticles were tested by XRD, SEM and TEM. The average particle size of cobalt nanoparticles is 87nm, and the SEM test photos show agglomeration, as shown in Figure 4b. The cladding layer does not form a graphitized carbon layer. The saturation magnetization value of carbon-coated cobalt nanoparticles is lower than 30 emu/g.

Comparative example 4

Follow the method of Example 1, except that 4.55g of sulfonated asphalt-3 (homemade, water solubility rate is 52%, and the sum of carbon and hydrogen content is 82wt%) is used to replace 4.55g of sulfonated asphalt-1. , to prepare carbon-coated nickel nanoparticles.

The obtained carbon-coated nickel nanoparticles were tested by XRD, SEM and TEM. The average particle size of nickel nanoparticles is 123nm. The SEM test photos show that the carbon layer spacing of the outer coating layer is 0.47nm, which is not a graphitized carbon layer. The saturation magnetization value of carbon-coated nickel nanoparticles is lower than 30 emu/g.

Comparative example 5

Follow the method of Example 1, except that 4.55g of sulfonated asphalt-4 (self-made, water solubility rate is 65%, and the sum of carbon and hydrogen content is 68wt%) is used to replace 4.55g of sulfonated asphalt-1. , to prepare carbon-coated nickel nanoparticles.

The obtained carbon-coated nickel nanoparticles were tested by XRD, SEM and TEM. The average particle size of nickel nanoparticles is 122nm. The SEM test photos show that the carbon layer spacing of the outer coating layer is 0.49nm, which is not a graphitized carbon layer. The saturation magnetization value of carbon-coated nickel nanoparticles is lower than 30 emu/g.

Comparative example 6

Follow the method of Example 1, except that 4.55g of petroleum asphalt is used to replace 4.55g of sulfonated asphalt-1. However, SEM test photos show that carbon-coated nickel nanoparticles cannot be produced.

It can be seen from the above examples and comparative examples that implementing the method provided by the present invention can obtain carbon-coated metal nanoparticles with a graphitized structure in the coating layer, which 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 concept of the present invention, many simple modifications can be made to the technical solution of the present invention, including the combination of various technical features in any other suitable manner. These simple modifications and combinations should also be regarded as the disclosed content of the present invention. All belong to the protection scope of the present invention.

Claims (15)

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

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.