A method for preparing metal-coated lignin microspheres for electromagnetic shielding

Abstract

This invention discloses a method for preparing metal-coated lignin microspheres for electromagnetic shielding, relating to the field of electromagnetic shielding materials technology; comprising: Step 1: preparing raw materials, preparing MXene dispersion, preparing modified lignin microspheres, and preparing a metal salt solution; Step 2: performing self-assembly and loading: slowly adding the MXene aqueous dispersion dropwise to the cationic lignin microsphere solution, adding deionized water to the mixture and stirring, in which positively charged cationic lignin microspheres and negatively charged MXene undergo electrostatic self-assembly to form QLMs@M Xene microspheres were prepared by adding metal salt solution dropwise to the aqueous dispersion of MXene microspheres at a concentration of 40%-80% of the total volume, along with hydrazine hydrate, and stirring continuously to ensure that the metal was fully adsorbed onto the active sites of the QLMs@MXene microspheres. Step 3: The mixture was subjected to a hydrothermal reaction to allow the adsorbed metal ions to grow in situ into nanoparticles and be reduced and loaded onto the surface of QLMs@MXene. Step 4: The solid product from the hydrothermal reaction was centrifuged, washed, and freeze-dried to obtain QLMs@MXene@M composite microspheres.

Description

Technical Field

[0001] This invention discloses a method for preparing metal-coated lignin microspheres for electromagnetic shielding, relating to the field of electromagnetic shielding materials technology. Background Technology

[0002] In recent years, novel shielding materials such as carbon-based materials, graphene, carbon nanotubes, and conductive polymers have been extensively studied. However, in terms of achieving a green shielding mechanism that is "primarily absorption and secondarily reflection," single materials often struggle to achieve the synergistic effect of dielectric loss and magnetic loss.

[0003] Two-dimensional transition metal carbides / nitrides (MXenes), as an emerging two-dimensional layered material, have shown great application potential in the field of electromagnetic shielding due to their metallic-level conductivity, abundant surface functional groups, and unique layered structure. Especially T... i3 C2T x MXene, with its multilayered structure, can induce multiple reflections and scatterings of electromagnetic waves within the material, thereby achieving efficient electromagnetic wave attenuation. However, pure MXene materials still face challenges in practical applications: firstly, its shielding mechanism is still mainly based on dielectric loss, lacking magnetic loss components, which limits further improvement in shielding effectiveness; secondly, MXene nanosheets are prone to self-stacking and structural degradation in high humidity or oxidizing environments, severely affecting their long-term stability. To address these issues, attempts have been made to combine magnetic nanoparticles with MXene, introducing magnetic loss to optimize impedance matching and achieve dual attenuation of electromagnetic waves through both electrical and magnetic means. However, it is currently not possible to uniformly anchor magnetic particles on the MXene surface and construct a stable multilayered structure to prevent nanoparticle aggregation and MXene oxidation. Summary of the Invention

[0004] This invention addresses the problems of existing technologies by providing a method for preparing metal-coated lignin microspheres for electromagnetic shielding. The specific solution proposed in this invention is as follows: This invention provides a method for preparing metal-coated lignin microspheres for electromagnetic shielding, comprising: Step 1: Prepare the raw materials: Step 11: Preparation of MXene dispersion: Few-layer MXene nanosheets were prepared into an MXene aqueous dispersion of 3-30 mg / mL. Step 12: Preparation of modified lignin microspheres: Dissolve modified cationic lignin (QLMs) in an organic solvent, add the cationic lignin solution dropwise to water under stirring, and then collect the modified lignin microspheres by centrifugation and filtration to prepare an aqueous solution with a concentration of 10-50 mg / mL. Step 13: Prepare metal salt solutions: Prepare a 0.1-10 mol / L nickel chloride hexahydrate solution, a 0.1-2 mol / L cobalt chloride hexahydrate solution, or a 0.1-3 mol / L ferric chloride hexahydrate solution; Step 2: Self-assembly and loading: The MXene aqueous dispersion is slowly added dropwise to the cationic lignin microsphere solution at a volume ratio of 1:10-6:10. Deionized water is added to the mixture and the mixture is stirred. In the mixture, the positively charged cationic lignin microspheres and the negatively charged MXene self-assemble electrostatically to form QLMs@MXene microspheres. The metal salt solution is added dropwise at a volume of 40%-80% of the MXene aqueous dispersion volume. Hydrazine hydrate is added and the mixture is stirred continuously to allow the metal to be fully adsorbed on the active sites of the QLMs@MXene microspheres. Step 3: Perform a hydrothermal reaction on the mixture to allow the adsorbed metal ions to grow in situ into nanoparticles, which are then reduced and loaded onto the surface of QLMs@MXene. Step 4: The solid product of the hydrothermal reaction is centrifuged, washed, and freeze-dried to obtain QLMs@MXene@M composite microspheres, with QLMs as the core, MXene as the dielectric loss intermediate layer, and metal microparticles M as the magnetic loss shell.

[0005] Preferably, in step 11 of the method for preparing metal-coated lignin microspheres for electromagnetic shielding, the MAX phase ceramic powder is treated by hydrochloric acid / lithium fluoride etching, and after washing and centrifugation, it is ultrasonically exfoliated to obtain few-layer MXene nanosheets.

[0006] Preferably, in step 12 of the method for preparing metal-coated lignin microspheres for electromagnetic shielding, alkaline lignin is taken, and the cationic modifying reagent used includes quaternary ammonium salts or amination polymers. Cationic groups are introduced through Mannich reaction, ring-opening polymerization reaction or free radical reaction to obtain modified cationic lignin (QLMs).

[0007] Preferably, in step 3 of the method for preparing metal-coated lignin microspheres for electromagnetic shielding, the mixture is transferred to a high-pressure reactor and subjected to a hydrothermal reaction at 155-180°C for 10-20 hours.

[0008] Preferably, in step 4 of the method for preparing metal-coated lignin microspheres for electromagnetic shielding, after the hydrothermal reaction is completed, the solid product is allowed to cool naturally to room temperature, the fixed product is centrifuged, and washed 3-5 times with deionized water and anhydrous ethanol in sequence. The washed solid product is placed in a freeze dryer and freeze-dried at -50°C for 15-24 hours to obtain QLMs@MXene@M composite microspheres.

[0009] The present invention also provides metal-coated lignin microspheres for electromagnetic shielding, wherein the microspheres have a core-shell structure and include: The core is a modified cationic lignin microsphere (QLMs); A dielectric loss intermediate layer covering the surface of the core, wherein the intermediate layer is made of MXene material; The outer shell layer covering the surface of the intermediate layer is composed of metal particles, including iron, cobalt, or nickel.

[0010] Cationic lignin microspheres can be spherical or irregularly shaped near spherical, with a particle size of approximately 2-5 micrometers.

[0011] MXene materials are two-dimensional transition metal carbides, nitrides, or carbonitrides, preferably T. i3 C2T x MXene, where T x Represents surface functional groups, including one or more of -O, -OH, and -F.

[0012] The present invention also provides a method for applying metal-coated lignin microspheres for electromagnetic shielding, wherein the metal-coated lignin microspheres for electromagnetic shielding are applied to the manufacture of electromagnetic shielding materials.

[0013] Preferably, the application method involves fabricating a metal-coated lignin microsphere for electromagnetic shielding into an electromagnetic shielding film, an electromagnetic shielding coating, an electromagnetic shielding foam, or an electromagnetic shielding composite material with a polymer matrix.

[0014] The advantages of this invention are: (1) The present invention uses low-density cationic lignin (QLMs) as the core, which greatly reduces the weight of the overall microspheres.

[0015] (2) The structure forms two heterogeneous interfaces: QLMs@MXene and MXene@M.

[0016] (3) The outer M-shell provides a rich magnetic loss mechanism (eddy current loss, natural resonance).

[0017] (4) Cationic lignin (QLMs) serve as the core material, giving the entire microsphere system the characteristics of being renewable and biodegradable.

[0018] (5) The numerous functional groups (hydroxyl, amino, etc.) on the lignin molecular chain help to form hydrogen bonds or electrostatic bonds with MXene, enhance interfacial bonding, and improve the structural stability of the composite microspheres. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, some simple figures will be drawn below to describe the sample data characterization process in the implementation of the present invention.

[0020] Figure 1 The images show the infrared absorption spectra and elemental comparison diagrams of the lignin microspheres before and after modification in Example 1. The modified lignin exhibits a significant -N group. + (CH3)3 peak. The content of each element can be seen in the bar chart in the figure.

[0021] Figure 2 The images show scanning electron microscope (SEM) images of QLMs, QLMs@MXene, and QLMs@MXene@Ni microspheres from Example 1. a) shows QLMs microspheres, exhibiting a three-dimensional microsphere structure with a diameter of approximately 5 μm; b) shows QLMs@MXene microspheres; and c) shows QLMs@MXene@Ni microspheres, with Ni nanoparticles of approximately 50-100 nm in diameter uniformly dispersed on the QLMs@MXene surface.

[0022] Figure 3 The image shows the electromagnetic shielding performance test analysis of the QLMs@MXene@Ni microspheres in Example 1. The obtained QLMs@MXene@Ni microspheres were mixed with paraffin wax, pressed into a ring sample, and tested using a vector network analyzer. In the X-band, the electromagnetic shielding effectiveness (EMISE) of this material reached an average of 41 dB, with absorption loss being the dominant factor, indicating that the material has excellent absorption-type electromagnetic shielding performance. Detailed Implementation

[0023] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0024] Lignin is the second most abundant aromatic polymer in nature after cellulose, and it has the advantages of being widely available, inexpensive, and renewable. Cationic lignins (QLMs) obtained through chemical modification not only retain the three-dimensional network structure and abundant active functional groups of lignin, but also endow it with good water solubility and positive charge. Example

[0025] The preparation process for QLMs@MXene@Ni microspheres is as follows: Step 1: Prepare the raw materials: Step 11: Preparation of MXene dispersion: The MAX phase ceramic powder was treated with hydrochloric acid / lithium fluoride etching. After washing and centrifugation, few-layer MXene nanosheets were obtained by ultrasonic exfoliation. The few-layer MXene nanosheets were then prepared into a 10 mg / mL MXene aqueous dispersion. Step 12: Preparation of modified lignin microspheres: Cationic lignin solution was added dropwise to water under stirring. 1.0 g of alkali lignin (AL) was added to 50 mL of deionized water, followed by 0.5 g of NaOH and 0.5 g of EPTAC. The mixture was heated and stirred at 50 °C for 2 h. After cooling, the pH was adjusted to 2, and the mixture was centrifuged. The precipitate was washed twice with anhydrous ethanol to obtain quaternized lignin (QAL). 0.25 g of QAL was dissolved in 10 mL of DMSO solvent and added dropwise to 50 mL of ultrapure water under stirring. The mixture was centrifuged to remove residual DMSO, and then vacuum dried at 50 °C to obtain lignin-based microspheres (QLMs). A 10 mg / mL aqueous solution of QLMs was prepared. Step 13: Prepare metal salt solution: Prepare a 1 mol / L nickel chloride hexahydrate solution; Step 2: Self-assembly and loading: The QLMs solution was lightly sonicated. 10 mL (10 mg / mL) of MXene aqueous dispersion was slowly added dropwise to 12 mL (20 mg / mL) of QLMs solution. 40 mL of deionized water was added to the above solution and stirred for 30 min. In the mixture, positively charged cationic lignin microspheres and negatively charged MXene self-assembled electrostatically to form QLMs@MXene microspheres. 2 mL of NiCl2·6H2O was added and stirred to form a homogeneous solution. Then, 10 mL of N2H4·H2O was slowly added dropwise and stirred for 30 min to allow the metal to be fully adsorbed on the active sites of the QLMs@MXene microspheres.

[0026] Step 3: Transfer the mixture to a 100mL stainless steel high-pressure reactor and carry out a hydrothermal reaction at 160℃ for 15h to allow the adsorbed metal ions to grow in situ into nanoparticles and be reduced and loaded onto the QLMs@MXene surface. Step 4: The solid product from the hydrothermal reaction was centrifuged, washed five times with deionized water and ethanol, and freeze-dried for 15 hours to obtain QLMs@MXene@Ni microspheres. QLMs served as the core, MXene as the dielectric loss interlayer, and Ni microparticles as the magnetic loss shell. Example

[0027] The preparation process for QLMs@MXene@Ni microspheres is as follows: Step 1: Prepare the raw materials: Step 11: Preparation of MXene dispersion: The MAX phase ceramic powder was treated with hydrochloric acid / lithium fluoride etching. After washing and centrifugation, few-layer MXene nanosheets were obtained by ultrasonic exfoliation. The few-layer MXene nanosheets were then prepared into a 20 mg / mL MXene aqueous dispersion. Step 12: Preparation of modified lignin microspheres: Cationic lignin solution was added dropwise to water under stirring. 3.0 g of alkali lignin (AL) was added to 30 mL of deionized water, followed by 5 mL of DETA added dropwise. The pH of the solution was adjusted to 10-11 using 0.1 mol / L sodium hydroxide solution. Subsequently, 3.5 mL of formaldehyde solution was added dropwise, and the temperature was raised to 50 °C. The reaction was continued for 4 h. The reaction solution was then transferred to 150 mL of ethanol and washed three times with ethanol. Finally, the product was placed in a 40 °C oven to obtain QAL. 0.25 g of QAL was dissolved in 10 mL of DMSO solvent and added dropwise to 50 mL of ultrapure water under stirring. The solution was centrifuged to remove residual DMSO, and then vacuum dried at 50 °C to obtain lignin-based microspheres (QLMs). A 20 mg / mL aqueous solution of QLMs was prepared. Step 13: Prepare the metal salt solution: Prepare a 0.1 mol / L nickel chloride hexahydrate solution; Step 2: Self-assembly and loading: The QLMs solution was lightly sonicated. 10 mL (3 mg / mL) of MXene aqueous dispersion was slowly added dropwise to 12 mL (10 mg / mL) of QLMs solution. 40 mL of deionized water was added to the above solution and stirred for 30 min. In the mixture, positively charged cationic lignin microspheres and negatively charged MXene self-assembled electrostatically to form QLMs@MXene microspheres. 2 mL of NiCl2·6H2O was added and stirred to form a homogeneous solution. Then, 8 mL of N2H4·H2O was slowly added dropwise and stirred for 30 min to allow the metal to be fully adsorbed on the active sites of QLMs@MXene microspheres.

[0028] Step 3: Transfer the mixture to a 100mL stainless steel high-pressure reactor and carry out a hydrothermal reaction at 165℃ for 20h to allow the adsorbed metal ions to grow in situ into nanoparticles and be reduced and loaded onto the QLMs@MXene surface. Step 4: The solid product from the hydrothermal reaction was centrifuged, washed five times with deionized water and ethanol, and freeze-dried for 20 hours to obtain QLMs@MXene@Ni microspheres. QLMs served as the core, MXene as the dielectric loss interlayer, and Ni microparticles as the magnetic loss shell. Example

[0029] The preparation of QLMs@MXene@Fe microspheres follows the procedure below: Step 1: Prepare the raw materials: Step 11: Preparation of MXene dispersion: The MAX phase ceramic powder was treated with hydrochloric acid / lithium fluoride etching. After washing and centrifugation, few-layer MXene nanosheets were obtained by ultrasonic exfoliation. The few-layer MXene nanosheets were then prepared into an MXene aqueous dispersion of 15 mg / mL. Step 12: Preparation of modified lignin microspheres: Cationic lignin solution was added dropwise to water under stirring. 1.0 g of alkali lignin (AL) was added to 50 mL of deionized water, followed by 0.5 g of NaOH and 0.5 g of EPTAC. The mixture was heated and stirred at 50 °C for 2 h. After cooling, the pH was adjusted to 2, and the mixture was centrifuged. The precipitate was washed twice with anhydrous ethanol to obtain quaternized lignin (QAL). 0.25 g of QAL was dissolved in 10 mL of DMSO solvent and added dropwise to 50 mL of ultrapure water under stirring. The mixture was centrifuged to remove residual DMSO, and then vacuum dried at 50 °C to obtain lignin-based microspheres (QLMs). A 15 mg / mL aqueous solution of QLMs was prepared. Step 13: Prepare the metal salt solution: Prepare a 0.1 mol / L ferric chloride hexahydrate solution; Step 2: Self-assembly and loading: The QLMs solution was lightly sonicated. 10 mL (3 mg / mL) of MXene aqueous dispersion was slowly added dropwise to 12 mL (10 mg / mL) of QLMs solution. 40 mL of deionized water was added to the above solution and stirred for 30 min. In the mixture, positively charged cationic lignin microspheres and negatively charged MXene self-assembled electrostatically to form QLMs@MXene microspheres. 2.5 mL of ferric chloride hexahydrate solution was added and stirred to form a homogeneous solution. Then, 10 mL of N2H4·H2O was slowly added dropwise and stirred for 30 min to allow the metal to be fully adsorbed on the active sites of the QLMs@MXene microspheres.

[0030] Step 3: Transfer the mixture to a 100mL stainless steel high-pressure reactor and carry out a hydrothermal reaction at 175℃ for 12h to allow the adsorbed metal ions to grow in situ into nanoparticles and be reduced and loaded onto the surface of QLMs@MXene. Step 4: The solid product from the hydrothermal reaction was centrifuged, washed five times with deionized water and ethanol, and freeze-dried for 15 hours to obtain QLMs@MXene@Fe microspheres. QLMs served as the core, MXene as the dielectric loss interlayer, and Fe microparticles as the magnetic loss shell. Example

[0031] The preparation of QLMs@MXene@Co microspheres follows the procedure below: Step 1: Prepare the raw materials: Step 11: Preparation of MXene dispersion: The MAX phase ceramic powder was treated with hydrochloric acid / lithium fluoride etching. After washing and centrifugation, few-layer MXene nanosheets were obtained by ultrasonic exfoliation. The few-layer MXene nanosheets were then prepared into an MXene aqueous dispersion of 15 mg / mL. Step 12: Preparation of modified lignin microspheres: Cationic lignin solution was added dropwise to water under stirring. 1.0 g of alkali lignin (AL) was added to 50 mL of deionized water, followed by 0.5 g of NaOH and 0.5 g of EPTAC. The mixture was heated and stirred at 50 °C for 2 h. After cooling, the pH was adjusted to 2, and the mixture was centrifuged. The precipitate was washed twice with anhydrous ethanol to obtain quaternized lignin (QAL). 0.25 g of QAL was dissolved in 10 mL of DMSO solvent and added dropwise to 50 mL of ultrapure water under stirring. The mixture was centrifuged to remove residual DMSO, and then vacuum dried at 50 °C to obtain lignin-based microspheres (QLMs). A 3 mg / mL aqueous solution of QLMs was prepared. Step 13: Prepare the metal salt solution: Prepare a 0.1 mol / L cobalt chloride hexahydrate solution; Step 2: Self-assembly and loading: The QLMs solution was lightly sonicated. 10 mL (3 mg / mL) of MXene aqueous dispersion was slowly added dropwise to 12 mL (10 mg / mL) of QLMs solution. 40 mL of deionized water was added to the above solution and stirred for 30 min. In the mixture, positively charged cationic lignin microspheres and negatively charged MXene self-assembled electrostatically to form QLMs@MXene microspheres. 2 mL of cobalt chloride hexahydrate solution was added and stirred to form a homogeneous solution. Then, 8 mL of N2H4·H2O was slowly added dropwise and stirred for 2 h to allow the metal to be fully adsorbed on the active sites of QLMs@MXene microspheres.

[0032] Step 3: Transfer the mixture to a 100mL stainless steel high-pressure reactor and carry out a hydrothermal reaction at 180℃ for 6 hours to allow the adsorbed metal ions to grow in situ into nanoparticles and be reduced and loaded onto the surface of QLMs@MXene. Step 4: The solid product from the hydrothermal reaction was centrifuged, washed five times with deionized water and ethanol, and freeze-dried for 15 hours to obtain QLMs@MXene@Co microspheres. QLMs served as the core, MXene as the dielectric loss interlayer, and Co microparticles as the magnetic loss shell. Example

[0033] The preparation process for QLMs@MXene@Ni microspheres is as follows: Step 1: Prepare the raw materials: Step 11: Preparation of MXene dispersion: The MAX phase ceramic powder was treated with hydrochloric acid / lithium fluoride etching. After washing and centrifugation, few-layer MXene nanosheets were obtained by ultrasonic exfoliation. The few-layer MXene nanosheets were then prepared into a 30 mg / mL MXene aqueous dispersion. Step 12: Preparation of modified lignin microspheres: Cationic lignin solution was added dropwise to water under stirring. 1.0 g of alkali lignin (AL) was added to 50 mL of deionized water, followed by 0.5 g of NaOH and 0.5 g of EPTAC. The mixture was heated and stirred at 50 °C for 2 h. After cooling, the pH was adjusted to 2, and the mixture was centrifuged. The precipitate was washed twice with anhydrous ethanol to obtain quaternized lignin (QAL). 0.25 g of QAL was dissolved in 10 mL of DMSO solvent and added dropwise to 50 mL of ultrapure water under stirring. The mixture was centrifuged to remove residual DMSO, and then vacuum dried at 50 °C to obtain lignin-based microspheres (QLMs). A 50 mg / mL aqueous solution of QLMs was prepared. Step 13: Prepare the metal salt solution: Prepare a 5 mol / L nickel chloride hexahydrate solution; Step 2: Self-assembly and loading: The QLMs solution was lightly sonicated. 10 mL (30 mg / mL) of MXene aqueous dispersion was slowly added dropwise to 12 mL (50 mg / mL) of QLMs solution. 40 mL of deionized water was added to the above solution and stirred for 30 min. In the mixture, positively charged cationic lignin microspheres and negatively charged MXene self-assembled electrostatically to form QLMs@MXene microspheres. 2 mL of nickel chloride hexahydrate solution was added and stirred to form a homogeneous solution. Then, 8 mL of N2H4·H2O was slowly added dropwise and stirred for 1 h to allow the metal to be fully adsorbed on the active sites of QLMs@MXene microspheres.

[0034] Step 3: Transfer the mixture to a 100mL stainless steel high-pressure reactor and carry out a hydrothermal reaction at 160℃ for 6 hours to allow the adsorbed metal ions to grow in situ into nanoparticles and be reduced and loaded onto the surface of QLMs@MXene. Step 4: The solid product from the hydrothermal reaction was centrifuged, washed five times with deionized water and ethanol, and freeze-dried for 15 hours to obtain QLMs@MXene@Ni microspheres. QLMs served as the core, MXene as the dielectric loss interlayer, and Ni microparticles as the magnetic loss shell.

[0035] The above are preferred embodiments of the method of the present invention, and all embodiments of the present invention achieve the corresponding technical effects, as shown in Embodiment 1. Within the scope of the technical solution of the present invention, the type and amount of reagents used can be adjusted according to actual conditions. Unless otherwise specified, all reagents involved in the method of the present invention are purchased through legitimate channels or obtained as gifts.

[0036] The present invention provides a metal-coated lignin microsphere for electromagnetic shielding, which has a core-shell structure and comprises: The core is a modified cationic lignin microsphere (QLMs); A dielectric loss intermediate layer covering the surface of the core, wherein the intermediate layer is made of MXene material; The outer shell layer covering the surface of the intermediate layer is composed of metal particles, including iron, cobalt, or nickel.

[0037] It can be applied to the production of electromagnetic shielding materials. For example, a metal-coated lignin microsphere for electromagnetic shielding can be blended with a polymer matrix such as PVA, and then the solution can be cast or sprayed to form an electromagnetic shielding film or coating; or the microspheres can be added to a foaming system such as polyurethane, and then foamed and cured to prepare electromagnetic shielding foam.

[0038] The above-described embodiments are merely preferred embodiments provided to fully illustrate the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are all within the scope of protection of the present invention. The scope of protection of the present invention is defined by the claims.

Claims

1. A method for preparing metal-coated lignin microspheres for electromagnetic shielding, characterized in that: include: Step 1: Prepare the raw materials: Step 11: Preparation of MXene dispersion: Few-layer MXene nanosheets were prepared into an MXene aqueous dispersion of 3-30 mg / mL. Step 12: Preparation of modified lignin microspheres: Dissolve modified cationic lignin (QLMs) in an organic solvent, add the cationic lignin solution dropwise to water under stirring, and then collect the modified lignin microspheres by centrifugation and filtration to prepare an aqueous solution with a concentration of 10-50 mg / mL. Step 13: Prepare metal salt solutions: Prepare a 0.1-10 mol / L nickel chloride hexahydrate solution, a 0.1-2 mol / L cobalt chloride hexahydrate solution, or a 0.1-3 mol / L ferric chloride hexahydrate solution; Step 2: Self-assembly and loading: The MXene aqueous dispersion is slowly added dropwise to the cationic lignin microsphere solution at a volume ratio of 1:10-6:

10. Deionized water is added to the mixture and the mixture is stirred. In the mixture, the positively charged cationic lignin microspheres and the negatively charged MXene self-assemble electrostatically to form QLMs@MXene microspheres. The metal salt solution is added dropwise at a volume of 40%-80% of the MXene aqueous dispersion volume. Hydrazine hydrate is added and the mixture is stirred continuously to allow the metal to be fully adsorbed on the active sites of the QLMs@MXene microspheres. Step 3: Perform a hydrothermal reaction on the mixture to allow the adsorbed metal ions to grow in situ into nanoparticles, which are then reduced and loaded onto the surface of QLMs@MXene. Step 4: The solid product of the hydrothermal reaction is centrifuged, washed, and freeze-dried to obtain QLMs@MXene@M composite microspheres, with QLMs as the core, MXene as the dielectric loss intermediate layer, and metal microparticles M as the magnetic loss shell.

2. The method for preparing metal-coated lignin microspheres for electromagnetic shielding according to claim 1, characterized in that in step 11, the MAX phase ceramic powder is treated by hydrochloric acid / lithium fluoride etching, and after washing and centrifugation, it is ultrasonically exfoliated to obtain few-layer MXene nanosheets.

3. The method for preparing metal-coated lignin microspheres for electromagnetic shielding according to claim 1, characterized in that: In step 12, alkaline lignin is taken, and the cationic modifying reagents used include quaternary ammonium salts or amination polymers. Cationic groups are introduced through Mannich reaction, ring-opening polymerization reaction or free radical reaction to obtain modified cationic lignin (QLMs).

4. The method for preparing metal-coated lignin microspheres for electromagnetic shielding according to claim 1, characterized in that: In step 3, the mixture is transferred to a high-pressure reactor and subjected to a hydrothermal reaction at 155-180℃ for 10-20 hours.

5. The method for preparing metal-coated lignin microspheres for electromagnetic shielding according to claim 1, characterized in that in step 4, after the hydrothermal reaction is completed, the solid product is allowed to cool naturally to room temperature, the fixed product is centrifuged, washed 3-5 times with deionized water and anhydrous ethanol, and the washed solid product is placed in a freeze dryer and freeze-dried at -50℃ for 15-24h to obtain QLMs@MXene@M composite microspheres.

6. A metal-coated lignin microsphere for electromagnetic shielding, characterized in that... The microspheres have a core-shell structure and include: The core is a modified cationic lignin microsphere (QLMs); A dielectric loss intermediate layer covering the surface of the core, wherein the intermediate layer is made of MXene material; The outer shell layer covering the surface of the intermediate layer is composed of metal particles, including iron, cobalt, or nickel.

7. A method for applying metal-coated lignin microspheres for electromagnetic shielding, characterized in that: The metal-coated lignin microspheres for electromagnetic shielding described in claim 6 are used to manufacture electromagnetic shielding materials.

8. The application method according to claim 7, characterized in that: A metal-coated lignin microsphere for electromagnetic shielding is fabricated into an electromagnetic shielding film, an electromagnetic shielding coating, an electromagnetic shielding foam, or an electromagnetic shielding composite material with a polymer matrix.

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