CN111592377B

CN111592377B - Electromagnetic shielding foam composite material and preparation method and application thereof

Info

Publication number: CN111592377B
Application number: CN202010402368.6A
Authority: CN
Inventors: 胡友根; 沈友康; 赵涛; 田锭坤; 王勇; 许亚东; 孙蓉
Original assignee: Shenzhen Institute of Advanced Electronic Materials
Current assignee: Shenzhen Institute of Advanced Electronic Materials
Priority date: 2020-05-13
Filing date: 2020-05-13
Publication date: 2022-04-19
Anticipated expiration: 2040-05-13
Also published as: CN111592377A

Abstract

The invention discloses an electromagnetic shielding foam composite material, a preparation method and application thereof. The electromagnetic shielding foam composite material comprises a foam-shaped carbonized material matrix, wherein a conductive reinforcing substance is attached to the foam-shaped carbonized material matrix, and the conductive reinforcing substance is a combination of metal particles and reduced graphene oxide; the metal particles are nano silver. It is prepared by the following method: 1) sequentially soaking the foam base material in a precursor solution of a conductive reinforcing substance, and then sequentially drying; 2) heating the soaked foam base material obtained in the step 1), and carrying out pyrolysis carbonization to obtain the foam composite material. The preparation method is simple and has good mechanical and electrical properties.

Description

Electromagnetic shielding foam composite material and preparation method and application thereof

Technical Field

The invention relates to the field of materials, in particular to electromagnetic shielding foam and a preparation method thereof.

Background

The development of modern science and technology promotes the continuous increase of national economy, and more refined electronic devices require electromagnetic shielding materials to be developed in the direction of lighter weight and more excellent performance. Foams such as Melamine (MF), Polyurethane (PU) and the like are light polymer foam materials with high porosity which can reach 99% and fully-open-cell three-dimensional grid structure systems, and have the characteristics of light weight, low density and the like. For example: the melamine foam is a flexible and flexible open foam prepared by high-temperature foaming of safe melamine resin, and has unique chemical and physical stability due to a stable chemical structure and a three-dimensional reticular cross-linking system in the melamine foam, and can not be aged or decomposed in a weak acid and weak base environment, has no residual free formaldehyde, and has sanitary performance reaching national standards. Besides excellent sound absorption, heat insulation and fire resistance, the composite material has the advantages of high flame resistance, environmental protection, sanitation and safety, especially when compared with similar products such as glass wool, polyurethane foam and the like.

The polymer foam matrix has no conductive capability and extremely high resistivity, so that the foam has no good shielding effect and cannot meet the commercial requirement. If the macromolecule foam is pyrolyzed and carbonized at high temperature to form carbonized foam with certain conductive capability, the foam framework is calcined at high temperature (hundreds of DEG to 2000 ℃) to form carbonized porous foam, and a porous foam sample has strong conductive capability, thereby having certain electromagnetic shielding capability. However, the conductivity of the amorphous carbon foam material obtained after high-temperature carbonization is still not very high, so that the shielding performance of the amorphous carbon foam material cannot achieve the expected effect.

Graphene Oxide (GO) is a layered material obtained by oxidizing graphite, and is a separated graphene oxide lamellar structure which is easily formed by the steps of oxidizing a graphene layer into hydrophilic graphene oxide after bulk phase graphite is treated by fuming concentrated acid solution and heating or ultrasonic stripping in water. Graphene oxide contains a large number of oxygen-containing functional groups including hydroxyl, epoxy functional groups, carbonyl, carboxyl, and the like. The hydroxyl and epoxy functional groups are located primarily on the basal plane of the graphite, while the carbonyl and carboxyl groups are located at the edges of the graphene. The aqueous solution of GO exhibits a significant negative charge characteristic due to the presence of its surface functional groups.

Silver is a noble metal, has very beneficial conductive performance, and has very good electromagnetic shielding effect. Silver nitrate is used as the most common silver salt for preparing silver and is widely applied to the preparation of nano silver particles, dendritic silver and flaky silver. Most of the current protocols use chemical reduction methods, i.e. reducing silver nitrate to silver using reducing agents (hydrazine hydrate, hydroxylamine, glucose, potassium sodium tartrate, hydrogen, etc.). The chemical reduction method has the defects of complex preparation method, waste liquid treatment and the like.

At present, foam shielding materials are mainly prepared by adopting methods such as freeze drying, dipping, orientation mixing and the like in the prior patent, but the problems of low electromagnetic shielding efficiency, poor electromagnetic radiation resistance, easy foam dispersion, low absorption shielding efficiency, poor mechanical property, complex preparation process and the like exist.

Disclosure of Invention

In order to solve the above problems, an aspect of the present invention provides a foam composite material comprising a foam-like carbonized material substrate having a conductive reinforcing material attached thereto, the conductive reinforcing material being selected from the group consisting of metal particles, reduced graphene oxide, and a combination of metal particles and reduced graphene oxide.

In the technical scheme of the invention, the foam-like carbonized material matrix is obtained by calcining an open-cell type polymer foam substrate selected from Melamine (MF) foam, Polyurethane (PU) foam, polyvinyl chloride (PVC) foam, ethylene-vinyl acetate copolymer (EVA) foam, polystyrene-poly (4-vinylpyridine) (PS-b-P4VP) foam, poly (4-methylstyrene) -poly (4-vinylpyridine) (P4mS-b-P4VP) foam, polylactic acid (PLA) -based polybutylene succinate (PBS) foam, preferably, the foam substrate is selected from melamine foam and polyurethane foam.

In the technical scheme of the invention, the metal particles and the reduced graphene oxide attached to the foam-shaped carbonized material matrix are obtained by soaking the foam base material in a metal salt solution and a graphene oxide solution to attach the foam base material to a foam precursor and then calcining the foam precursor.

In the technical scheme of the invention, the metal particles are nano silver.

In the technical scheme of the invention, the metal salt solution is silver nitrate, a silver carbonate solution, a silver acetate solution and a silver trifluoroacetate solution.

In the technical scheme of the invention, the conductive reinforcing substance accounts for 40-50% of the mass of the foam composite material.

In another aspect, the present invention provides a method for preparing a foam composite, comprising the steps of:

1) sequentially soaking the foam base material in a precursor solution of a conductive reinforcing substance, and then sequentially drying;

2) heating the soaked foam base material obtained in the step 1), and carrying out pyrolysis carbonization to obtain the foam composite material.

In the technical scheme of the invention, in the step 1), the conductive enhancing substance is metal particles and reduced graphene oxide.

In the technical scheme of the invention, in the step 1), the precursor of the conductive enhancing substance is metal salt and graphene oxide, and the step 1) comprises the steps of soaking the foam base material in a graphene oxide solution, drying after soaking, then adding the foam base material into a metal salt solution, and drying after soaking.

In the technical scheme of the invention, the metal particles are nano silver particles.

In the technical scheme of the invention, the metal salt solution is silver nitrate solution, silver carbonate solution, silver acetate solution and silver trifluoroacetate solution.

In the technical scheme of the invention, the concentration of the graphene oxide solution is 0.1-0.5mg/mL, preferably 0.15-0.4mg/mL, and more preferably 0.2mg/mL

In the solution according to the invention, the concentration of the metal salt solution is 0.5 to 5 wt.%, preferably 0.8 to 2 wt.%, more preferably 1 wt.%.

In the technical scheme of the invention, the heating temperature in the step 2) is more than 800 ℃, preferably more than 1000 ℃.

In the technical scheme of the invention, the heating in the step 2) is performed under an inert atmosphere, preferably, the inert atmosphere is argon or nitrogen.

In the present invention, the fillers used are Graphene Oxide (GO) and silver nitrate.

In the technical scheme of the invention, the mass percentage of the carbon foam in the composite foam is 50-60%.

In the technical scheme of the invention, the density of the foam substrate is 0.01-0.07g cm^-1Preferably 0.03 to 0.06g cm^-1. When the density of the foam composite material is higher than 0.08g cm^-1If the filler content is too high, the foam composite material has poor resilience and is easily pulverized under pressure.

In the technical scheme of the invention, the used foam base material is porous foam which is directly pyrolyzed by adopting foam with larger porosity. The pore size of the MF foam before carbonization in the examples was 150-200. mu.m. The pore diameter of Carbonized MF Foam (CMF) after pyrolysis and carbonization is 50-100 μm. The pore size of the foam after pyrolysis is relatively uniform, and the conductive filler is relatively uniformly distributed on the carbon skeleton.

In the invention, GO is attached to the surface of the polymer foam skeleton in a physical adsorption mode.

In the technical scheme of the invention, the nano silver is attached to the surface of the substrate by the following method: soaking a foam sample containing graphene oxide in a silver salt solution, placing the foam sample in an oven for drying, depositing a layer of silver nitrate inside and outside a matrix, performing one-step pyrolysis through high-temperature carbonization reaction under inert atmosphere to form a carbon foam framework, and forming a foam composite material containing Reduced Graphene Oxide (RGO) and nano silver on the carbon foam framework;

preferably, the metal salt solution takes water as a solvent;

preferably, the metal salt is selected from the group consisting of silver nitrate, silver carbonate and silver acetate.

According to the scheme of the invention, GO can be attached to the surface of a high molecular polymer foam framework through physical adsorption, meanwhile, after GO is deposited, negative electricity is contained in foam, the foam is soaked in a silver salt water solution, a shallow layer of silver ions can be adsorbed at the place where GO exists on the foam, the silver ions cannot be dissociated in the foam, then pyrolysis reduction is carried out, and the composite foam is directly converted into the final composite foam through one-step conversion. The electromagnetic shielding foam prepared by the method has the advantages of excellent compressibility and cycling stability, high conductivity, extremely light weight and stronger electromagnetic shielding performance.

In the technical scheme of the invention, the CMF foam, the RGO filler and the nano silver are not unique in proportion, the preferable carbon content is 60%, the two fillers are regulated and controlled in 40%, and the proportion of GO and silver nitrate is mainly controlled in experiments. The adsorption amount of GO is controlled by controlling the time and the times of adsorbing GO solution, and the adsorption amount of silver is controlled by controlling the time and the times of adsorbing silver salt.

In the present invention, CMF/RGO/Ag refers to a foam composite material using melamine as a foam base material and reduced graphene oxide and nano silver as a conductive reinforcing material.

In the present invention, CMF/Ag refers to a foam composite material using melamine as a foam base material and nano silver as a conductive reinforcing material.

In the present invention, CMF/RGO refers to a foam composite material using melamine as a foam base material and reduced graphene oxide as a conductive reinforcing material.

The invention takes RGO and Ag as the conductive enhancing substances on the foam porous reticular structure made of the carbon skeleton, so that the carbon skeleton, the RGO and the Ag are tightly combined to form a stable conductive loop.

In the scheme of the invention, the used foam raw material is a polymer foam material which is common in life, is light, soft and has extremely excellent resilience, and can be carbonized into porous carbon foam under the high-temperature condition.

In still another aspect, the invention provides a foam composite material prepared by the above preparation method.

In the technical scheme of the invention, the density of the foam composite material CMF/RGO/Ag is 0.02-0.06g cm^-1。

In the technical scheme of the invention, the EMI SE value of the foam composite material CMF/RGO/Ag is 50-70 dB.

In the technical scheme of the invention, the foam composite material CMF/RGO takes melamine as a foam base material and reduced graphene oxide as a conductive reinforcing substance, and the shielding value is 30-35 dB.

In the technical scheme of the invention, the foam composite material CMF/RGO/Ag is prepared by taking melamine as a foam base material and reducing graphene oxide and nano silver as conductive reinforcing substances, and the shielding value is 55-65 dB.

In a further aspect of the invention there is provided the use of the foam composite of the invention as an electromagnetic shielding material.

The invention adopts a high-temperature pyrolysis carbonization method, prepares the high-efficiency electromagnetic shielding foam in a very simple mode, and has the advantages of stable foam structure, excellent mechanical property, extremely light weight and the like. Compared with pure macromolecule foam carbonized materials, the scheme of the invention can obtain electromagnetic shielding foam materials with higher conductivity and higher efficiency under the same condition. Compared with pure metal foam, the high-strength high-corrosion-resistance high-density high-strength foam material has the advantages of strong corrosion resistance, extremely low density and extremely light weight, and is particularly applied to the fields of precision electronics, aerospace and the like. Compared with the chemical plating of the surface of the high polymer foam, the preparation process is simple and environment-friendly, the bonding capacity between the foam framework and the metal is stronger, the foam framework is not easy to fall off, and the mechanical stability is greatly improved.

According to the invention, firstly, a simple physical adsorption method is adopted, open-cell type high-molecular polymer foam is taken as a raw material, and the high porosity and capillary characteristics of the foam material are utilized to be sequentially soaked in a graphene oxide aqueous solution and a silver nitrate aqueous solution for adsorption, so that the graphene oxide is attached to the surface of a polymer foam framework. The principle that silver ions (positive charges) in a silver salt aqueous solution and opposite charges of a graphene oxide aqueous solution (negative charges) are attracted mutually is utilized to realize uniform adsorption of the silver ions on the surface of the graphene oxide, and the foam is dried and then placed in an inert atmosphere for high-temperature carbonization to prepare the high-conductivity type foam material with the reduced graphene oxide and metal silver particles attached to the surface of a carbon foam framework. The final adjustment of the mechanical property, the electrical property and the electromagnetic shielding property of the electromagnetic shielding foam can be realized by regulating and controlling the concentration, the adsorption times, the carbonization temperature and other parameters of the graphene oxide solution and the silver salt solution. The foam material prepared by the invention has the advantages of high conductivity, excellent mechanical compression cycle stability, light weight and the like.

According to the invention, by utilizing the characteristics of high-temperature carbonized polymer foam, after the high-molecular foam physically adsorbs GO, the GO is reduced into Reduced Graphene Oxide (RGO) while pyrolysis is carried out, so that the conductive capability of the foam is remarkably improved.

The invention adopts a high-temperature pyrolysis mode to directly reduce silver salt into metallic silver, and the prepared silver has uniform particle size and extremely stable performance. Compared with chemical reduction silver, the method has the advantages of uniform particle size, difficult agglomeration, uniform distribution and the like.

Advantageous effects

1. Compared with the traditional conductive composite metal material, the composite conductive foam material has the following advantages: the preparation is simple and economic, the molding processing is more convenient, and the electrical property and the mechanical property of the material can be adjusted under certain conditions.

2. By utilizing the positive and negative relation between GO and silver ions, the two fillers can uniformly grow on the carbon skeleton, and the mechanical property and the electrical property of the foam are improved.

3. The experiment aims to prepare an electromagnetic shielding material, and the foam prepared by the method is light in weight, extremely low in density and capable of keeping a shielding value of 50dB at the low density.

4. The electromagnetic shielding effect of the conductive composite foam is mainly absorption efficiency, and the carbon foam framework not only can play a role of supporting the filler, but also can absorb electromagnetic waves and enhance the shielding performance. The RGO is used as a carbon-based filler, has the characteristics of the carbon-based filler, absorbs electromagnetic waves, improves the overall shielding performance of the foam composite material together through the absorption effect of the carbon skeleton on the electromagnetic waves and the superposition shielding of the RGO on the electromagnetic waves, and finally, the dense nano silver layer of the foam enables the shielding performance to be further improved, so that the EMI value of the conductive foam composite material reaches a higher value.

5. The experimental method is extremely simple, three materials are subjected to heat treatment simultaneously in a one-step pyrolysis mode, time and steps are saved, and the prepared foam has excellent performance.

Drawings

FIG. 1 is a flow chart of the experimental preparation.

FIG. 2 is an SEM image of a polymer foam.

FIG. 3 is SEM images of MF/GO and MF/RGO.

FIG. 4 is an SEM image of CMF/RGO/Ag.

FIG. 5 shows EMI shielding performance results.

Detailed Description

In order to make the aforementioned objects, features and advantages of the present invention comprehensible, specific embodiments accompanied with figures are described in detail below, but the present invention is not to be construed as limiting the implementable range thereof.

EXAMPLE 1 preparation of electromagnetic shielding foam

Melamine Foam (MF) is selected as a foam base material, the aperture of the base material is 150-200 mu m, and the base material is dried for later use after being washed by water. And ultrasonically dispersing the GO aqueous solution with the concentration of 2mg/mL for 2h to improve the dispersion uniformity, and then diluting with ultrapure water to the concentration of 0.2mg/mL for later use. The MF with the size of 90mm multiplied by 60mm multiplied by 30mm is soaked in 250mL of 0.2mg/mL GO water solution, the GO is taken out after 10min and is placed in a 70 ℃ blast oven for drying for 24h, and the moisture in the GO is removed to form MF/GO foam. Preparing a silver nitrate aqueous solution with the concentration of 1 wt%, soaking the MF/GO foam in 250mL of silver nitrate aqueous solution, transferring the silver nitrate aqueous solution to an oven at 80 ℃ for drying for 12h after 10min to obtain MF/GO/AgNO₃Foam of MF/GO/AgNO₃And pyrolyzing the foam by adopting a tubular furnace, heating to 1000 ℃ at a speed of 10 ℃/min, keeping the temperature for 2 hours, and then naturally cooling to room temperature. By a one-step high-temperature method, the carbonization of MF foam, the reduction of GO into RGO and the synchronous acquisition of metal silver particles can be realized, and the CMF/RGO/Ag foam is prepared. Silver nitrate is reduced to metallic silver at high temperature, and the reaction chemical formula is 2AgNO₃＝2Ag+2NO₂+O₂. The prepared CMF/RGO/Ag foam can keep stable appearance, excellent conductivity and high-efficiency electromagnetic shielding performance under 1000-time cyclic compression test, and the density of the foam is 0.05g cm^-1And the shielding performance can reach 65 dB.

Meanwhile, directly pyrolyzing MF foams with the same slice size by using a tube furnace, heating to 1000 ℃ at the speed of 10 ℃/min, keeping the temperature for 2 hours, and then naturally cooling to room temperature. The prepared CMF foam has the mass of about 40-50% of CMF/RGO/Ag foam and the shielding property of 22 dB.

Example 2 preparation experiment of electromagnetic shielding foam

The experimental process was similar to example 1, the same samples were used, the amount of adsorbed GO was controlled by adjusting the GO concentration, the experiment was performed with 0.1mg/ml GO aqueous solution, and the other experimental parts were the same as example 1. The density of the CMF/RGO/Ag foam material is 0.04g cm^-1The shielding effectiveness is 45 dB.

Example 3 preparation experiment of electromagnetic shielding foam

The experimental process was similar to example 1, the same samples were used, the amount of adsorbed GO was controlled by adjusting the GO concentration, the experiment was performed with 0.5mg/ml GO aqueous solution, and the other experimental parts were the same as example 1. The density of the CMF/RGO/Ag foam material is 0.05g cm^-1The shielding effectiveness is 60 dB.

Example 4 preparation experiment of electromagnetic shielding foam

The experimental procedure was similar to that of example 1, using the same sample, controlling the content of adsorbed silver by adjusting the concentration of silver nitrate, using silver nitrate: water 5: 95, i.e., at a concentration of 5 wt%, was tested, and the other experimental parts were the same as in example 1. The density of the CMF/RGO/Ag foam material prepared is 0.1g cm^-1The shielding effectiveness is 50 dB.

Example 5 preparation experiment of electromagnetic shielding foam

The experimental procedure was similar to that of example 1, using the same sample, controlling the amount of adsorbed silver by adjusting the concentration of silver nitrate, using silver nitrate: water ═ 0.5: 99.5, i.e. a concentration of 0.5% by weight, the rest of the experiment was identical to example 1. The density of the CMF/RGO/Ag foam material is 0.03g cm^-1The shielding effectiveness is 40 dB.

EXAMPLE 6 preparation experiment of electromagnetic shielding foam

The experimental procedure was similar to that of example 1, the same sample was used, the reduction was carried out by adjusting the pyrolysis temperature of the tube furnace, the reduction was carried out at 500 ℃, and the other experimental portions were the same as those of example 1. The density of the CMF/RGO/Ag foam material is 0.08g cm^-1Shielding effectiveness of 30dB

Example 7 preparation experiment of electromagnetic shielding foam

The experimental procedure was similar to that of example 1, the same sample was used, the reduction was carried out by adjusting the pyrolysis temperature of the tube furnace, the reduction was carried out at 800 ℃, and the other experimental portions were the same as those of example 1. The density of the CMF/RGO/Ag foam material is 0.07g cm^-1The shielding effectiveness is 50 dB.

EXAMPLE 8 preparation experiment of electromagnetic shielding foam

The experimental procedure was similar to that of example 1, the polymer matrix was replaced with polyurethane foam, and the reduction was carried out at 1000 ℃ in the same manner as in example 1. The density of the obtained carbonized polyurethane/RGO/Ag foam material is 0.04g cm^-1The shielding effectiveness is 40 dB. Example 9 preparation experiment of electromagnetic shielding foam

The experimental procedure was similar to example 1, except that the reduction was carried out at 1000 ℃ except for the step of adsorbing GO, and the other experimental parts were the same as in example 1. The density of the prepared CMF/Ag foam material is 0.07g cm^-1The shielding effectiveness is 37 dB.

EXAMPLE 10 preparation experiment of electromagnetic shielding foam

The procedure was analogous to example 1, except that the reduction was carried out at 1000 ℃ except for the step in which the nitrate was adsorbed, and the other experimental parts were identical to example 1. The density of the CMF/RGO foam obtained was 0.04g cm^-1The shielding effectiveness is 30 dB.

EXAMPLE 11 Effect of the order of preparation of electromagnetic shielding foams

The experimental procedure was similar to that of example 1, using the same sample except that MF was immersed in 250mL of 1 wt% aqueous silver nitrate solution, and after 10min, it was transferred to 80 ℃ oven for drying for 12h to obtain MF/AgNO₃Foaming, adding 250mL of 0.2mg/mL GO aqueous solution, taking out after 10min, placing in a 70 ℃ blast oven for drying for 24h, removing water to obtain MF/AgNO₃(ii) GO foams. The poor silver distribution was found by SEM and for the product of example 1, the silver distribution was found to be uniform for the product of example 1. Although not wishing to be bound by theory, it is possible that the ag layer is made uniform by the negative charge of GO, followed by the adsorption of the ag graded ions by GO. This example illustrates the effect of the preparation sequence of the present invention on the experimental results.

The comparison of example 1, example 2 and example 3 shows that the electromagnetic shielding composite foam can be prepared in all three ways, and the foam prepared in example 3 can achieve the electromagnetic shielding capability similar to that of example 1, but the prepared foam has more powder slag and the performance of the prepared foam is influenced in the aspect of commercial application, so that the shielding performance can be achieved when the GO concentration is 0.15-0.4mg/mL, but the effect of example 1 is the best. At the same time, the foam prepared in example 2 had inferior electrical properties, and thus the electromagnetic shielding properties were also much inferior to those of example 1.

Comparing examples 1, 4 and 5, it is found that the content of adsorbed silver nitrate directly affects the electrical and electromagnetic shielding properties of the foam, and when the concentration of silver nitrate is too high, the foam can maintain the skeleton of the foam after the re-pyrolysis is finished, but when the foam is pressed, the foam is immediately changed into powder and cannot be used for commercial application; meanwhile, when the concentration of silver nitrate is reduced, the composite foam prepared by the experiment has fewer nano silver particles on the surface and does not have a shielding layer with more compact performance on a foam framework, and a foam sample adopts a vector analyzer to test the electromagnetic shielding performance of the foam sample, and the result proves that the shielding performance of the foam is far inferior to that of the foam in the embodiment 1.

By comparing example 1, example 6 and example 7, it was found that the use of different carbonization pyrolysis temperatures has a strong influence on various properties of the foam. If the carbonization temperature is reduced, the foam can be carbonized, but the carbonization degree is not high, the foam is not carbonized sufficiently, and the conductivity and the electromagnetic shielding performance of the foam are directly influenced, and tests on the foams prepared in the three experiments of example 1, example 6 and example 7 prove that the higher the pyrolysis temperature is, the better the electromagnetic shielding performance of the foam is.

Through comparison between examples 1 and 8, it is found that the shielding performance is greatly affected by using different base foams, the foam framework of polyurethane is not stable, the framework is easy to loosen after carbonization, the foam cannot be compressed, the electrical property is poor, and therefore, the selection of the foam is also important.

The comparison of example 1, example 9 and example 10 shows that different fillers have a greater influence on the shielding capability of the electromagnetic shielding foam, and specifically, as shown in fig. 5, the use of two conductive fillers RGO and Ag can greatly improve the shielding effectiveness under the same density condition compared with the use of a single filler (RGO or Ag), thereby producing an unexpected technical effect.

Claims

1. A method of preparing a foam composite comprising the steps of:

2) heating the soaked foam base material obtained in the step 1), and performing pyrolysis carbonization to obtain a foam composite material;

in the step 1), the conductive reinforcing substance is metal particles and reduced graphene oxide, the precursor of the conductive reinforcing substance is metal salt and graphene oxide, and the step 1) is to soak the foam base material in a graphene oxide solution, dry the foam base material after soaking, then add the foam base material in a metal salt solution, and dry the foam base material after soaking;

the metal salt solution is silver nitrate solution, silver acetate solution and silver trifluoroacetate solution; the metal particles are nano silver particles;

the foam substrate is selected from melamine foam, Polyurethane (PU) foam, polyvinyl chloride foam, ethylene-vinyl acetate copolymer foam, polystyrene-poly (4-vinylpyridine) foam, poly (4-methylstyrene) -poly (4-vinylpyridine) foam and polylactic acid-based polybutylene succinate foam.

2. The method of claim 1, wherein the metal salt solution has a concentration of 0.5 to 5 wt%.

3. The method according to claim 2, wherein the concentration of the metal salt solution is 0.8 to 2 wt%.

4. The method according to claim 1, wherein the concentration of the graphene oxide solution is 0.1-0.5 mg/mL.

5. The method according to claim 1, wherein the graphene oxide solution has a concentration of 0.15-0.4 mg/mL.

6. The process according to claim 1, wherein the heating temperature in the step 2) is 800 ℃ or higher.

7. The method according to claim 6, wherein the heating temperature in the step 2) is 1000 ℃ or higher.

8. The method according to claim 1, wherein the density of the foam substrate is 0.03 to 0.7g cm^-1。

9. A foam composite comprising a foamed carbonized material matrix having a conductivity enhancing substance attached thereto, the conductivity enhancing substance being a combination of metal particles and reduced graphene oxide; the metal particles are nano silver;

the foamed composite material is obtained by the production method according to any one of claims 1 to 8.

10. The foam composite of claim 9, the conductivity enhancing substance comprising 40% to 50% by mass of the foam composite.

11. The foam composite according to claim 9, having a foam cell size of 50-100 μm and a density of 0.01-0.1g cm^-1The shielding effectiveness is more than 40 dB.

12. Use of the foam composite according to any one of claims 9 to 11 as an electromagnetic shielding material.