Accordion-shaped graphene-magnetic metal nanoparticle composite wave-absorbing material and preparation method thereof

Abstract

A preparation method of an accordion-shaped graphene-magnetic metal M nanoparticle composite wave-absorbing material comprises the following steps: (1) oxidizing crystalline flake graphite to obtain an oxidized mixture, (2) reacting the mixture with hydrogen peroxide and washing to obtain a precursor product A, and (3) adding the precursor product A into an aqueous solution of polyether amine to obtain a mixture, and carrying out heat treatment and washing to obtain the accordion-shaped graphene-magnetic metal M nanoparticle composite wave-absorbing material. The preparation method comprises the following steps: (1) preparing a graphene / magnetic metal M nano-particle composite material, (2) mixing the graphene / magnetic metal M nano-particle composite material with the graphene / magnetic metal M nano-particle composite material to obtain a mixture, and freeze-drying the mixture to obtain a precursor product B, (4) adding the precursor product B into a magnetic metal M ion solution for standing and freeze-drying to obtain a magnetic metal M ion / GOF system, and (5) annealing the magnetic metal M ion / GOF system under the protection of inert gas to obtain the accordion-shaped graphene / magnetic metal M nano-particle composite material. The maximum value of reflection loss of a uniform mixture of the wave-absorbing material with the metal content of 10wt% and paraffin is-46.3 dB at 17.92 GHz, and the wave-absorbing bandwidth is 6.8 GHz under the condition that the thickness is 2.2 mm.

Description

Technical Field

[0001] The invention relates to an accordion-shaped graphene / magnetic metal (such as iron) nanoparticle composite wave absorbing material and a preparation method thereof, and belongs to the field of electromagnetic wave absorption. Background Art

[0002] With the rapid development of communication equipment and electronic technology in modern society, the use of electromagnetic waves has brought great convenience to human life. However, electromagnetic radiation and interference not only affect the operation of wireless communication and electronic equipment, but also threaten human health. Electromagnetic wave absorbing materials are a type of material that effectively attenuates and absorbs interfering electromagnetic waves and reduces the reflection of electromagnetic waves on the surface of the material. They play an increasingly important role in communications, electronics, aerospace, military industry, medical care, environmental protection and other fields. Traditional absorbers, such as typical ferrite powders, metal powders and carbonyl iron, have their disadvantages such as high density, easy corrosion, difficult processing and single performance, which greatly limit their application in practical scenarios. New graphene composite absorbers have been reported to be potential high-performance electromagnetic wave functional materials.

[0003] Graphene has become one of the hot spots for studying new wave-absorbing materials due to its excellent physical and chemical properties, but the high electrical conductivity and single loss mechanism of graphene make its impedance matching performance poor, resulting in unsatisfactory wave-absorbing performance of graphene. Chinese patents CN116634754A, CN116456707A, CN116355589A, etc. all use electromagnetic wave absorbing composite materials with graphene as the main body, showing good wave-absorbing ability, and have the advantages of light weight, environmental protection, and high efficiency. However, most of the graphene electromagnetic shielding materials reported at present are limited by the preparation cost, complex process, and long cycle of graphene, making it difficult to have excellent wave-absorbing performance at low thickness and low filling amount, which greatly limits its application in aerospace, communications, mobile phones, computers and other electronic devices. In order to solve this problem, Chinese patent CN116510630A uses hydrothermal self-assembly and freeze-drying technology to obtain a ternary composite aerogel formed by stacking graphene sheets, which has high absorption intensity, wide absorption bandwidth, thin matching thickness and low filling ratio. However, the preparation process is complicated and the structure is difficult to maintain. Chinese patent CN115955833A obtains a composite absorber made of layered compounds and magnetic graphite. The layered structure gives it good absorbency, but its absorbency and effective absorption width cannot meet actual requirements. Therefore, it is urgent to have an efficient graphene absorber that has a simple preparation process, good absorbency and can be industrially produced.

[0004] US2020276797A1 discloses a shielding filler, a shielding coating containing the shielding filler, a preparation method and uses thereof. The shielding filler uses melamine sponge as a carrier, and its surface is covered with FeOx / graphene.

[0005] KR20160137415A discloses a method for preparing a graphene-magnetic particle composite, which can provide the composite under mild conditions and can prepare the composite without using a reducing agent and a surfactant that affect the morphology of the magnetic particles.

[0006] WO2022262479A1 discloses a skin-core structure fiber with infrared and radar stealth, and its preparation method and use. The core material of the skin-core structure fiber includes 10 parts of paraffin wax, 0.7-1.5 parts of electromagnetic wave absorber, and 1 part of high molecular polymer, wherein the electromagnetic wave absorber is one or more ferrous oxide intercalated graphene oxide, nano ferrous oxide and carbon black, and the skin-core structure fiber is obtained by spinning the core material and the skin material.

[0007] WO2018021648A1 discloses a composition for an electromagnetic wave shielding sheet, the composition comprising: a binder resin; magnetic particles; and carbon-based inorganic particles, wherein the binder resin comprises a styrene-butadiene-based rubber resin containing anhydride groups, and the content of the magnetic particles is 80 parts by weight or more and less than 100 parts by weight relative to 100 parts by weight of solid content. In addition, an electromagnetic wave shielding sheet made of the composition for an electromagnetic wave shielding sheet is provided.

[0008] US2018206367A1 discloses a polymer-based broadband electromagnetic wave shielding film, which improves electromagnetic wave shielding and absorption performance by applying a multilayer graphene-nanotube-metal oxide nanostructure in which a conductive material and a magnetic material are compositely combined as a filler of the polymer.

[0009] KR20140102480A discloses a graphene-magnetic metal composite for absorbing electromagnetic waves and a method for manufacturing the same, and specifically, relates to a graphene-magnetic metal composite in which plate-like crystalline magnetic metal particles are bonded to the surface of reduced graphene oxide (RGO) to absorb electromagnetic waves and a method for manufacturing the same. The graphene-magnetic metal composite for absorbing electromagnetic waves can maintain magnetic permeability in a wide band from low frequency to high frequency by bonding nanoscale plate-like magnetic metal particles to RGO, and has excellent electromagnetic wave absorption capability by controlling the dielectric constant through hybridization with graphene.

[0010] KR102011800B1 discloses a method for separating and obtaining a magnetic graphene nanopowder composite from a reducing composite, wherein the reducing composite is formed by reducing the oxygen of the graphene oxide and the nanomagnetic powder by drying and heat treatment after mixing the nanomagnetic powder with a graphene oxide dispersion, and then magnetically separating the nanomagnetic powder.

[0011] KR20160115012A discloses an electromagnetic wave shielding material and a method for manufacturing the same. The electromagnetic wave shielding material includes a polymer in which a composite nanopowder is dispersed. The composite nanopowder includes: graphene; and a metal oxide reduced from the crystal structure of the graphene.

[0012] KR101401542B1 discloses an electromagnetic wave absorbing film containing graphene oxide and a method for manufacturing the same, and more specifically, discloses an electromagnetic wave absorbing film comprising: magnetic metal fibers; graphene oxide combined with crystalline magnetic metal particles; and a polymer resin in which the magnetic metal fibers and the graphene oxide are dispersed by being oriented in an in-plane direction. The electromagnetic wave absorbing film comprises magnetic metal fibers and graphene oxide for electromagnetic wave absorption, thereby performing more effective electromagnetic wave absorption compared to a film comprising only the electromagnetic wave absorbing film. In addition, the graphene oxide comprises crystalline magnetic metal particles or crystalline TiO2 particles to improve the electromagnetic wave absorption efficiency.

[0013] KR20200121088A discloses a method for producing a graphene-metal oxide nanoparticle composite material, which produces a mixed solution by mixing a solution containing graphite oxide and a metal precursor containing neutral metal atoms in a solvent having a boiling point of 150°C or higher, and performs heat treatment by heating the mixed solution with an infrared emission heater inside the mixed solution, thereby providing a graphene composite material in which nanoparticles are uniformly produced by minimizing the temperature difference between the wall surface and the center of the mixed solution during the reaction.

[0014] WO2021094836A1 discloses a low-density EMI shielding composition comprising a soft elastomer, a conductive nanostructure, and metal ferrite-doped reduced graphene oxide (RGO), and a method for preparing the composition.

[0015] KR20160025987A discloses a method for preparing a graphene-metal oxide nanoparticle hybrid material, which comprises the following steps: (a) preparing a solution containing graphite oxide; (b) mixing a metal precursor containing neutral metal atoms into the solution; and (c) heating the solution. A graphene composite material having uniform nanoparticles can be provided.

[0016] KR20170124347A discloses an electromagnetic shielding material, in which a metal surface dispersed in a carbon substrate is coated with a carbon layer. The electromagnetic (EMI) shielding material comprises: a carbon substrate (A); metal particles (B) dispersed inside, outside, or inside and outside the carbon substrate (A); and a carbon layer (C) with a thickness of 2-10 nm formed on the surface of the metal particles (B).

[0017] KR20190115399A discloses an electromagnetic wave shielding composite material, which includes a porous graphene structure, an organic polymer layer and magnetic material particles. The porous graphene structure may include a graphene film and holes surrounded by the graphene film. The organic polymer layer may cover the porous graphene structure. A magnetic material may be provided between the porous graphene structure and the organic polymer layer. The magnetic material particles may be selectively arranged on the graphene film.

[0018] JP2020072209A discloses an electromagnetic wave absorber and a method for manufacturing the same, which can have an excellent absorption effect on electromagnetic waves in the high frequency range of the GHz band and has high heat resistance. Resin 2 contains flat metal soft magnetic powder 3. The flat metal soft magnetic powder is arranged in a certain direction in the resin. In addition, graphene 4 is added to the resin. The resin is a polyimide resin. In addition, it is in the form of a film or a sheet. The flat metal soft magnetic powder and the graphene are arranged in a planar direction.

[0019] AU2021103725A4 discloses a method for preparing a composite absorber based on magnetic nanoparticles / graphene / carbon fiber. Graphene grows uniformly on the surface of carbon fiber, and then magnetic nanoparticles are introduced between the gaps of graphene to form a magnetic loss layer, so that the composite material has both dielectric loss and magnetic loss, which helps to achieve impedance matching by adjusting the electromagnetic parameters of the material. The prepared absorbing material is a multidimensional, cross-scale composite material composed of zero-dimensional, one-dimensional and two-dimensional materials, which can adapt to the multidimensional absorption characteristics of electromagnetic waves.

[0020] CN107922210A discloses a method for preparing a magnetic iron oxide-graphene composite material, wherein magnetic particles in the form of FeOx are naturally formed on the surface of graphene. In addition, a magnetic material is formed on the surface of graphene while the defects of the graphene are minimized, so that the magnetic iron oxide-graphene composite material can be effectively used as an electromagnetic wave absorber.

[0021] US2012168383A1 discloses a graphene-iron oxide composite, which consists of graphene and needle-shaped iron oxide nanoparticles grown on the surface of the graphene, and its manufacturing method includes (a) preparing a reduced graphene dispersion solution, (B) mixing the dispersion solution with a solution containing an iron oxide precursor to prepare a mixture, (C) stirring the mixture to prepare a graphene-iron oxide dispersion solution containing a graphene-iron oxide composite having needle-shaped iron oxide nanoparticles grown on the surface of the graphene, and (D) separating the graphene-iron oxide composite from the graphene-iron oxide composite dispersion solution.

[0022] KR20190138189A discloses graphene with ferromagnetism and a method for manufacturing the same. The ferromagnetic graphene can stably exhibit ferromagnetism for a long time, does not change its properties even under harsh conditions, and can be used as a magnetic storage device or a drug carrier.

[0023] At present, most graphene absorbing materials use single-layer or few-layer graphene oxide and other materials to compound and reduce to graphene-based composite materials. In this process, the orderly arrangement of graphene requires precise control, and the process is relatively complicated. However, the single attenuation mechanism of graphene makes its impedance matching poor, making it difficult for electromagnetic waves to enter the absorber, so compounding with soft magnetic materials such as iron, cobalt, and nickel can adjust the impedance matching of the material and improve the wave absorption ability. However, such materials are easy to agglomerate, and it is difficult to obtain small and uniform magnetic nanoparticles and compound with graphene. Although the special structure can promote the attenuation of electromagnetic waves to a large extent, the process of obtaining a specially arranged graphene composite material is relatively complicated and costly.

[0024] In order to solve the above problems, the existing technical solutions usually select hydrothermal, high-temperature reduction and other methods to obtain graphene composite materials, and at the same time, graphene needs to be loaded with uniform and well-dispersed nanoparticles. Whether it is synthesizing nanoparticles first or growing nanoparticles on graphene, the reaction conditions need to be well regulated when preparing nanoparticles. At present, the performance of most graphene absorbing materials cannot meet the actual requirements, the preparation process is complicated, the cycle is long, the production cost is high, and the structure is difficult to control. In addition, organic solvents may be required in the preparation process, and a large amount of harmful gases may be generated during use, which is not green and environmentally friendly.

[0025] At present, the preparation process of graphene absorbing materials is complicated and costly, and the absorbing materials also have problems such as low absorption intensity, narrow effective bandwidth, high thickness and high density when used. Summary of the invention

[0026] In order to solve the above problems, the present invention provides an accordion-shaped (or called "cross-layered" or "stacked") graphene / magnetic metal nanoparticle composite absorbing material and its preparation method and application. The composite absorbing material provided by the present invention can effectively solve the problems of low absorbing intensity, high density, high thickness and narrow absorption frequency band existing in existing absorbing materials.

[0027] In the present application, the “magnetic metal M” refers to one, two (eg, iron-cobalt, iron-nickel or nickel-cobalt) or three (ie, iron-cobalt-nickel) selected from iron, cobalt and nickel.

[0028] According to a first embodiment of the present invention, a method for preparing an accordion-shaped graphene / magnetic metal M (e.g., iron, cobalt and / or nickel) nanoparticle composite wave absorbing material is provided, wherein the "magnetic metal M" refers to one, two (e.g., iron-cobalt, iron-nickel or nickel-cobalt) or three (i.e., iron-cobalt-nickel) selected from iron, cobalt and nickel. The method comprises:

[0029] (1) adding flake graphite to a concentrated sulfuric acid solution of potassium permanganate, stirring, and then standing for oxidation to obtain an oxidized mixture;

[0030] (2) pouring the mixture obtained in step (1) into ice water to cool, then slowly adding H2O2 (hydrogen peroxide) until no bubbles are generated, and after the solid (when M is iron, it is a golden solid) in the mixed solution settles, washing with water (i.e., pouring off the supernatant, and then slowly adding deionized water for washing) for multiple times (e.g., 3-10 times, preferably 4-8 times, more preferably 5-6 times, i.e., repeatedly washing multiple times) to obtain a precursor product A;

[0031] (3) adding the precursor product A obtained in step (2) to an aqueous solution of polyetheramine (e.g., polyetheramine ED2003, Huntsman) to obtain a mixture, slowly stirring and then standing (or slightly stirring and then standing) (e.g., 1-3 days), then heating at a (heat treatment) temperature of 80-100°C (preferably 85-100°C, more preferably 90-100°C, 95-100°C, such as 97, 98 or 99°C) (for preferably 4-30h, more preferably 6-20h, more preferably 8-12h, such as 10 hours), washing the mixture with deionized water for multiple times (e.g., 3-10 times, preferably 4-8 times, more preferably 5-6 times) until the pH of the washing water is ≈ 7, and freeze-drying the mixture to obtain a precursor product B;

[0032] (4) adding the precursor product B obtained in step (3) to a magnetic metal M ion solution and allowing the solution to stand; filtering the resulting mixture and freeze-drying the mixture to obtain a (magnetic metal) M ion / GOF system (e.g., Fe 3+ / GOF system);

[0033] (5) The (magnetic metal) M ion / GOF system (e.g., Fe 3+ / GOF system), and annealing is performed under the protection of an inert gas (such as argon) to obtain a M / LrGO absorbing material, that is, an accordion-shaped graphene / magnetic metal M nanoparticle composite material, such as an accordion-shaped graphene / iron nanoparticle composite material.

[0034] Preferably, in (4), the precursor product B obtained in step (3) is added to one of the following magnetic metal ion solutions and allowed to stand: (a1) iron ion solution, (b1) cobalt ion solution, (c1) nickel ion solution, (d1) iron ion / cobalt ion solution, (e1) iron ion / nickel ion solution, (f1) cobalt ion / nickel ion solution or (g1) iron ion / cobalt ion / nickel ion solution; the obtained mixture is filtered and freeze-dried to obtain (a2) an iron ion / GOF system (e.g., Fe 3+ / GOF system), (b2) cobalt ion / GOF system (e.g. Co 2+ / GOF system), (c2) nickel ion / GOF system (e.g. Ni 2+ / GOF system), (d2) iron ion / cobalt ion / GOF system (e.g. Fe 3+ / Co 2+ / GOF system), (e2) iron ion / nickel ion / GOF system (e.g. Fe 3 + / Ni 2+ / GOF system), (f2) nickel ion / cobalt ion / GOF system (e.g. Ni 2+ / Co 2+ / GOF system) or (g2) iron ion / cobalt ion / nickel ion / GOF system (e.g. Fe 3+ / Co 2+ / Ni 2+ / GOF system);

[0035] Preferably, in step (5), (a2), (b2), (c2), (d2), (e2), (f2) or (g2), such as Fe 3+ / GOF, and annealing treatment is carried out under the protection of an inert gas (such as argon) to obtain (a3) ​​Fe / LrGO absorbing material, (b3) Co / LrGO absorbing material, (c3) Ni / LrGO absorbing material, (d3) Fe / Co / LrGO absorbing material, (e3) Fe / Ni / LrGO absorbing material, (f3) Ni / Co / LrGO absorbing material or (g3) Fe / Ni / Co / LrGO absorbing material, that is, accordion-shaped graphene / magnetic metal M nanoparticle composite materials, such as accordion-shaped graphene / iron nanoparticle composite materials.

[0036] Preferably, the size of the flake graphite in step (1) is 60-500 mesh, preferably 100-325 mesh; more preferably 130-290 mesh.

[0037] Preferably, in step (1), the mass ratio of flake graphite to potassium permanganate is 1:(1.5-8), preferably 1:(1.8-6), preferably 1:(2-4), and more preferably 1:(2.5-3.5).

[0038] Preferably, the temperature of the oxidation reaction in step (1) is 0-45° C., preferably 0-35° C., preferably 0-30° C. The time of the oxidation reaction is 6-50 hours, preferably 8-40 hours, preferably 12-24 hours.

[0039] Preferably, the sedimentation time in step (2) is 5 minutes to 5 hours, preferably 8 minutes to 2 hours, preferably 10 to 60 minutes.

[0040] The polyetheramine is a polyetheramine having a number average molecular weight of 400-3000, preferably 700-2700, more preferably 900-2500, preferably 1000-2300, more preferably 1500-2200, and more preferably 1800-2003, such as Huntsman's polyetheramine ED2003.

[0041] Preferably, the concentration of the aqueous solution of polyetheramine (number average molecular weight is 400-3000, preferably 700-2700, more preferably 900-2500, for example 1000-2003) in step (3) (for example, the concentration of polyetheramine ED2003) is 0.004-0.06 mol / L, preferably 0.005-0.05 mol / L, preferably 0.008-0.04 mol / L, preferably 0.01-0.03 mol / L, preferably 0.015-0.025 mol / L.

[0042] Preferably, in step (3), the weight ratio of the precursor product A to the polyetheramine in the aqueous solution of polyetheramine (eg polyetheramine ED2003, Huntsman) is 1:10-1:50, preferably 1:20-1:45, preferably 1:30-1:40.

[0043] Preferably, the concentration of the (magnetic) metal M ion (e.g., iron ion, nickel ion and / or cobalt ion) solution (e.g., a1, b1, c1, d1, e1, f1 or g1 solution) in step (4) is 0.3-2.5 mol / L, preferably 0.5-2 mol / L, preferably 0.7-1.8 mol / L, preferably 0.9-1.7 mol / L, preferably 1-1.5 mol / L. The standing time in step (4) is 12-70 hours, preferably 18-60 hours, more preferably 24-48 hours.

[0044] Preferably, in step (4), the relative amounts of the precursor product B and the magnetic metal M ion solution should be such that: in the M / LrGO (e.g., Fe / LrGO) absorber obtained in step (5), the content (or loading) of the metal M is 5-60wt%, preferably 10-55wt%, more preferably 20-50wt%, more preferably 30-45wt%, such as 35 or 40wt%, based on the weight of the M / LrGO absorber. Generally, in step (4), the mass ratio of the precursor product B to the metal M ions in the magnetic metal M ion solution is 10:1-1:10 (i.e., 10-0.1:1), preferably 7:1-1:7 (i.e., 7-0.14:1), preferably 5:1-1:5 (i.e., 5-0.2:1), preferably 4:1-1:4 (i.e., 4-0.25:1), preferably 1:1-1:2 (i.e., 1-0.5:1).

[0045] Preferably, the annealing temperature in step (5) is 700-1000° C., preferably 750-900° C., preferably 780-870° C., preferably 800-850° C. The annealing time is 0.5-4 hours, preferably 1-2 hours.

[0046] According to a second embodiment of the present invention, there is also provided an accordion-shaped graphene composite absorbing material prepared by the above method, wherein the microstructure of the M / LrGO (e.g., Fe / LrGO) absorbing material is an accordion-like structure composed of layered reduced graphene oxide and magnetic metal M (e.g., Fe) nanoparticles uniformly distributed between the layers.

[0047] Wherein in the M / LrGO (e.g., Fe / LrGO) absorbing material, the content (or loading amount) of metal M is 5-60wt%, preferably 10-55wt%, more preferably 20-50wt%, more preferably 30-45wt%, such as 35 or 40wt%, based on the weight of the M / LrGO absorbing material.

[0048] According to the third embodiment of the present invention, a composite absorbing material is provided, which is formed by mixing the absorbing material described in the second embodiment with paraffin wax. Alternatively, the composite absorbing material is formed by mixing the absorbing material described in the second embodiment with silicone resin.

[0049] Preferably, the silicone resin is any one or a combination of methylphenyl silicone resin, methyl silicone resin, low-phenylmethyl silicone resin, silicone resin emulsion, self-drying silicone resin, high-temperature silicone resin, epoxy-modified silicone resin, silicone polyester-modified resin, self-drying environmentally friendly silicone resin, environmentally friendly silicone resin, non-stick coating silicone resin, high-gloss silicone resin, benzyl transparent silicone resin, methyl transparent silicone resin, mica bonding silicone resin, polymethyl silicone resin, amino silicone resin, fluorosilicone resin, silicone resin solution, silicone-epoxy resin, silicone polyester resin, solvent-resistant silicone resin, silicone resin adhesive, fluorosilicone resin silicone resin sealant, high-temperature resistant methyl silicone resin, self-drying silicone insulating varnish, methyl MQ silicone resin, vinyl MQ silicone resin, and silicone-acrylic resin coating.

[0050] Preferably, the maximum reflection loss of a uniform mixture of 10 wt% of the material and paraffin is -46.3 dB at 17.92 GHz, and the absorption bandwidth is 6.8 GHz at a thickness of 2.2 mm, and the wt% content is based on the weight of the uniform mixture (formed by the material and paraffin).

[0051] According to a fourth embodiment of the present invention, there is also provided the use of the composite absorbing material described in the above technical solution in improving the electromagnetic wave absorption performance of the material, or the use of the composite absorbing material in an absorbing device.

[0052] More specifically, the present invention provides:

[0053] A composite wave-absorbing material is obtained by fixing iron nanoparticles in situ between accordion-shaped graphene layers.

[0054] An accordion-shaped graphene / iron nanoparticle composite absorbing material and a preparation method thereof, comprising the following steps:

[0055] (1) Add flake graphite to a concentrated sulfuric acid solution of potassium permanganate, stir, and then allow to stand for oxidation;

[0056] (2) pouring the mixed solution obtained in step (1) into ice water to cool it down, then slowly adding H2O2 until no bubbles are generated, after the golden yellow solid in the mixed solution settles, pouring off the supernatant, and then slowly adding deionized water, repeating 5-6 times to obtain a precursor product A;

[0057] (3) adding the precursor product A obtained in step (2) to the polyetheramine 2003 solution, stirring slightly and standing for 1-3 days, then heating at 98° C. for 8-12 hours, washing with deionized water until the pH is about 7, and freeze-drying to obtain the precursor product B;

[0058] (4) Add the precursor product B obtained in step (3) to the Fe(NO3)3 solution and let it stand, filter and freeze-dry to obtain Fe 3+ / GOF;

[0059] (5) The Fe obtained in step (4) 3+ / GOF was annealed under argon protection to obtain Fe / LrGO absorbing material.

[0060] In the present invention, the size of the flake graphite in step (1) is 100-325 mesh, and the mass ratio of flake graphite to potassium permanganate is 1:(2-4).

[0061] In the present invention, the reaction temperature of step (1) is 0-35°C and the reaction time is 12-24h.

[0062] In the present invention, the sedimentation time in step (2) is 10-60 min.

[0063] In the present invention, the concentration of the polyetheramine 2003 in step (3) is 0.01-0.03 mol / L.

[0064] In the present invention, the concentration of the Fe(NO3)3 solution in step (4) is 0.5-2 mol / L, and the standing time is 24-48h.

[0065] In the present invention, the annealing temperature in step (5) is 700-1000° C., and the annealing time is 1-2 h.

[0066] In the present invention, the Fe / LrGO absorbing material prepared by the method has a microstructure similar to an accordion-like structure composed of layered reduced graphene oxide and Fe nanoparticles uniformly distributed between the layers, wherein the maximum reflection loss of a uniform mixture of 10% of the material and paraffin is -46.3dB at 17.92GHz, and the absorbing bandwidth is 6.8GHz under the condition of a thickness of 2.2mm.

[0067] An accordion-shaped graphene / iron nanoparticle composite wave-absorbing material and a preparation method thereof are prepared by the above method.

[0068] According to another embodiment provided by the present invention, the accordion-shaped graphene / iron nanoparticle composite absorbing material is used as an electromagnetic absorbing material.

[0069] The accordion-shaped graphene / magnetic metal M (such as iron) nanoparticle composite wave absorbing material of the present invention can be applied in the fields of communications, electronics, aerospace, military industry, navigation, automobiles, medical treatment, environmental protection and many precision electronic instruments.

[0070] Advantages of the present invention

[0071] Compared with the prior art, the technical effects of the present invention are:

[0072] (a) The present invention compounds graphene and Fe nanoparticles to enhance the material's magnetic loss capacity to enhance impedance matching and improve the material's absorption and loss performance of electromagnetic waves; in addition, the Fe nanoparticles distributed between the layers can effectively reduce the agglomeration of particles and the stacking of graphene, forming a unique accordion-shaped structure.

[0073] (b) A large number of heterogeneous interfaces are formed between the graphene sheets and the Fe nanoparticles, which can form a strong interface relaxation polarization. The defects and oxygen-containing functional groups in the reduced graphene oxide can form dipole polarization. The smaller Fe nanoparticles enhance the exchange resonance performance of the composite material to electromagnetic waves. In addition, the layered space of graphene can cause electromagnetic waves to form multiple reflections inside the material, which greatly improves the electromagnetic wave absorption and loss capacity.

[0074] (c) The present invention has outstanding wave absorbing properties such as strong electromagnetic wave reflection loss, wide effective absorption band, low filler amount and thickness, and the preparation method of the present invention is simple, and has good application prospects in the field of wave absorbing.

[0075] (d) The finished product prepared by the present invention has good uniformity, controllable size, simple process, low cost, and meets the requirements of industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0076] Figure 1 It is a SEM image of the Fe / LrGO composite wave absorbing material prepared in Example 1 of the present invention.

[0077] Figure 2 It is a reflection loss curve diagram of the Fe / LrGO complex wave absorbing material prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0078] The specific implementation of the present invention is described in detail below with reference to examples. It should be understood that the specific implementation described herein is only used to illustrate and explain the present invention, and is not used to limit the present invention. Other non-essential changes made according to the above invention content all belong to the protection scope of the present invention.

[0079] The invention provides a wave absorbing material, which fixes iron nanoparticles in situ between layers of accordion-shaped graphene to obtain a composite material.

[0080] A method for preparing an accordion-shaped graphene / iron nanoparticle composite absorbing material, the method comprising:

[0081] (1) Add flake graphite to a concentrated sulfuric acid solution of potassium permanganate, stir, and then allow to stand for oxidation;

[0082] (2) pouring the mixture obtained in step (1) into ice water to cool, then slowly adding H2O2 until no bubbles are generated, after the golden yellow solid in the mixed solution settles, pouring out the supernatant, then slowly adding deionized water, repeating 5-6 times until the pH of the supernatant is ≈ 7, to obtain a precursor product A;

[0083] (3) adding the precursor product A obtained in step (2) to the polyetheramine 2003 solution, stirring slightly and standing for 1-3 days, then heating at 98° C. for 8-12 hours, washing with deionized water until the pH is about 7, and freeze-drying to obtain the precursor product B;

[0084] (4) Add the precursor product B obtained in step (3) to the iron ion solution and let it stand, filter and freeze-dry to obtain Fe 3+ / GOF;

[0085] (5) The Fe obtained in step (4) 3+ / GOF was annealed under argon protection to obtain Fe / LrGO absorbing material.

[0086] The present invention adds flake graphite to a concentrated sulfuric acid solution of potassium permanganate for static oxidation, and stirs the obtained dispersion to obtain graphite oxide. In the present invention, the size of the flake graphite is 100-325 mesh, more preferably 100 mesh; the mass ratio of flake graphite to potassium permanganate in the step is 1: (2-4), more preferably 1: 4; the reaction temperature is 0-35°C, more preferably 35°C; the reaction time is 12-24h, more preferably 16h. In the present invention, the role of this step is to introduce oxygen-containing functional groups between graphite layers, which helps to increase the interlayer spacing.

[0087] In the present invention, the sedimentation time is preferably 10-60 min, more preferably 30 min. In the present invention, this step is to obtain layered graphene oxide.

[0088] In the present invention, the concentration of the polyetheramine 2003 is preferably 0.01-0.03 mol / L, more preferably 0.02 mol / L. In the present invention, the iron ion reagent preferably includes ferric chloride, ferric sulfate or ferric nitrate, and the concentration of the iron ion solution is 0.5-2 mol / L, more preferably 1 mol / L. In the present invention, the standing time of the precursor B in the iron ion solution is preferably 24-48 h, more preferably 48 h.

[0089] In the present invention, the annealing temperature is preferably 700-1000° C., more preferably 800° C.; the annealing time is preferably 1-2 h, more preferably 2 h.

[0090] Example 1

[0091] (1) Add 100-mesh flake graphite into a concentrated sulfuric acid solution of potassium permanganate, with the mass ratio of flake graphite to potassium permanganate being 1:4, stir for 30 minutes, and then allow to oxidize at 35°C for 12 hours;

[0092] (2) After the reaction is completed, the mixture is poured into ice water to cool down, and H2O2 is slowly added until no bubbles are generated. After the golden yellow solid in the mixture settles for 30 minutes, the supernatant is poured out, and deionized water is slowly added. This is repeated 5-6 times until the pH of the supernatant is ≈ 7 to obtain the precursor product A;

[0093] (3) 0.5 g of the precursor product A was added to 50 mL of a 0.02 mol / L aqueous solution of polyetheramine 2003, stirred slightly and allowed to stand for 3 days, then heated at 98 °C for 12 h, washed with deionized water until the pH was ≈ 7, and freeze-dried to obtain the precursor product B;

[0094] (4) Add 0.5 g of precursor product B to 50 mL of 1 mol / L Fe(NO3)3 solution and let stand for 24 h. Filter and freeze-dry to obtain Fe 3+ / GOF.

[0095] (5) Fe 3+ / GOF is annealed at 800° C. for 2 hours under argon protection to finally obtain a Fe / LrGO composite absorbing material; wherein the Fe content is 50wt%, and the wt% content is based on the weight of the Fe / LrGO composite absorbing material.

[0096] Figure 1 This is a SEM image of the Fe / LrGO composite absorbing material prepared in Example 1 of the present invention. It can be seen that rGO has a layered structure and Fe is in the form of particles interspersed between the layers of rGO.

[0097] Figure 2 The absorption reflection loss curve of the Fe / LrGO composite absorber prepared in Example 1 of the present invention measured by the coaxial method, the maximum reflection loss of a uniform mixture of the material with a content of 10wt% and paraffin is -46.3dB at 17.92GHz, and the absorption bandwidth reaches 6.8GHz under the condition of a thickness of 2.2mm. The wt% content is based on the weight of the uniform mixture.

[0098] Example 2

[0099] (1) Add 100-mesh flake graphite into a concentrated sulfuric acid solution of potassium permanganate, with the mass ratio of flake graphite to potassium permanganate being 1:4, stir for 30 minutes, and then allow to oxidize at 35°C for 12 hours;

[0100] (2) After the reaction is completed, the mixture is poured into ice water to cool down, and H2O2 is slowly added until no bubbles are generated. After the golden yellow solid in the mixture settles for 30 minutes, the supernatant is poured out, and deionized water is slowly added. This is repeated 5-6 times until the pH of the supernatant is ≈ 7 to obtain the precursor product A;

[0101] (3) 0.5 g of the precursor product A was added to 50 mL of a 0.02 mol / L aqueous solution of polyetheramine 2003, stirred slightly and allowed to stand for 3 days, then heated at 98 °C for 8 h, washed with deionized water until the pH was ≈ 7, and freeze-dried to obtain the precursor product B;

[0102] (4) Step 4: Add 0.5 g of precursor product B to 50 mL of 0.5 mol / L Fe(NO3)3 solution and let stand for 24 h. Filter and freeze-dry to obtain Fe 3+ / GOF;

[0103] (5) Fe 3+ / GOF was annealed at 800℃ for 2h under argon protection to finally obtain a composite absorbing material.

[0104] Example 3

[0105] (1) Add 100-mesh flake graphite into a concentrated sulfuric acid solution of potassium permanganate, with the mass ratio of flake graphite to potassium permanganate being 1:2. Stir for 30 minutes and then allow to oxidize at 35°C for 12 hours.

[0106] (2) After the reaction is completed, the mixture is poured into ice water to cool down, and H2O2 is slowly added until no bubbles are generated. After the golden yellow solid in the mixture settles for 30 minutes, the supernatant is poured out, and deionized water is slowly added. This is repeated 5-6 times until the pH of the supernatant is ≈ 7 to obtain the precursor product A;

[0107] (3) 0.5 g of the precursor product A was added to 50 mL of a 0.02 mol / L aqueous solution of polyetheramine 2003, stirred slightly and allowed to stand for 3 days, then heated at 98 °C for 12 h, washed with deionized water until the pH was ≈ 7, and freeze-dried to obtain the precursor product B;

[0108] (4) Add 0.5 g of precursor product B to 50 mL of 1 mol / L Fe(NO3)3 solution and let stand for 24 h. Filter and freeze-dry to obtain Fe 3+ / GOF;

[0109] (5) Fe 3+ / GOF was annealed at 800℃ for 1h under argon protection to finally obtain a composite absorbing material.

[0110] Example 4

[0111] (1) Add 200-mesh flake graphite into a concentrated sulfuric acid solution of potassium permanganate, with the mass ratio of flake graphite to potassium permanganate being 1:4, stir for 30 minutes, and then stand for oxidation at 35°C for 12 hours;

[0112] (2) After the reaction is completed, the mixture is poured into ice water to cool down, and H2O2 is slowly added until no bubbles are generated. After the golden yellow solid in the mixture settles for 30 minutes, the supernatant is poured out, and deionized water is slowly added. This is repeated 5-6 times until the pH of the supernatant is ≈ 7 to obtain the precursor product A;

[0113] (3) 0.5 g of the precursor product A was added to 50 mL of a 0.02 mol / L polyetheramine 2003 solution, stirred slightly and allowed to stand for 3 days, then heated at 98 °C for 10 h, washed with deionized water until the pH was ≈ 7, and freeze-dried to obtain the precursor product B;

[0114] (4) Add 0.5 g of precursor product B to 50 mL of 0.5 mol / L Fe(NO3)3 solution and let stand for 2 days. Filter and freeze-dry to obtain Fe 3+ / GOF;

[0115] (5) Fe 3+ / GOF was annealed at 800℃ for 2h under argon protection to finally obtain a composite absorbing material.

[0116] Example 5 (containing nickel)

[0117] (1) Add 100-mesh flake graphite into a concentrated sulfuric acid solution of potassium permanganate, with the mass ratio of flake graphite to potassium permanganate being 1:4, stir for 30 minutes, and then allow to oxidize at 35°C for 12 hours;

[0118] (2) After the reaction is completed, the mixture is poured into ice water to cool down, and H2O2 is slowly added until no bubbles are generated. After the golden yellow solid in the mixture settles for 30 minutes, the supernatant is poured out, and deionized water is slowly added. This is repeated 5-6 times until the pH of the supernatant is ≈ 7 to obtain the precursor product A;

[0119] (3) 0.5 g of the precursor product A was added to 50 mL of a 0.02 mol / L aqueous solution of polyetheramine 2003, stirred slightly and allowed to stand for 3 days, then heated at 98 °C for 12 h, washed with deionized water until the pH was ≈ 7, and freeze-dried to obtain the precursor product B;

[0120] (4) Add 0.5 g of precursor product B to 50 mL of 1 mol / L Ni(NO3)2 solution and let stand for 24 h. Filter and freeze-dry to obtain Ni 2+ / GOF;

[0121] (5) Ni 2+ / GOF was annealed at 800℃ for 2h under argon protection to finally obtain Ni / LrGO composite absorbing material.

[0122] Example 6

[0123] Example 1 was repeated, except that the Fe / LrGO absorbing material prepared in Example 1 was uniformly mixed with methyl silicone resin to obtain a composite absorbing material.

[0124] Comparative Example 1

[0125] (1) Add 100-mesh flake graphite into a concentrated sulfuric acid solution of potassium permanganate, with the mass ratio of flake graphite to potassium permanganate being 1:4, stir for 30 minutes, and then allow to oxidize at 35°C for 12 hours;

[0126] (2) After the reaction is completed, the mixture is poured into ice water to cool down, and H2O2 is slowly added until no bubbles are generated. After the golden yellow solid in the mixture settles for 30 minutes, the supernatant is poured out, and deionized water is slowly added. This is repeated 5-6 times until the pH of the supernatant is ≈ 7 to obtain the precursor product A;

[0127] (3) 0.5 g of the precursor product A was added to 50 mL of a 0.02 mol / L polyetheramine 2003 solution, stirred slightly and allowed to stand for 3 days, then heated at 98 °C for 12 h, washed with deionized water until the pH was ≈ 7, and freeze-dried to obtain the precursor product B;

[0128] (4) Add 0.5 g of precursor product B to 50 mL of 1 mol / L Fe(NO3)3 solution and let stand for 24 h. Filter and freeze-dry to obtain Fe 3+ / GOF.

[0129] (5) Fe 3+ / GOF was annealed at 600 °C for 2 h under argon protection to finally obtain a composite absorbing material.

[0130] Comparative Example 2

[0131] (1) Add 100-mesh flake graphite into a concentrated sulfuric acid solution of potassium permanganate, with the mass ratio of flake graphite to potassium permanganate being 1:4, stir for 30 minutes, and then allow to oxidize at 35°C for 12 hours;

[0132] (2) After the reaction is completed, the mixture is poured into ice water to cool down, and H2O2 is slowly added until no bubbles are generated. After the golden yellow solid in the mixture settles for 30 minutes, the supernatant is poured out, and deionized water is slowly added. This is repeated 5-6 times until the pH of the supernatant is ≈ 7 to obtain the precursor product A;

[0133] (3) 0.5 g of the precursor product A was added to 50 mL of a 0.02 mol / L polyetheramine 2003 solution, stirred slightly and allowed to stand for 3 days, then heated at 98 °C for 12 h, washed with deionized water until the pH was ≈ 7, and freeze-dried to obtain the precursor product B;

[0134] (4) The precursor product B is annealed at 800°C for 2 h under argon protection to finally obtain a composite absorbing material.

[0135] Comparative Example 3

[0136] (1) Add 100-mesh flake graphite into a concentrated sulfuric acid solution of potassium permanganate, with the mass ratio of flake graphite to potassium permanganate being 1:4, stir for 30 minutes, and then allow to oxidize at 35°C for 12 hours;

[0137] (2) After the reaction is completed, the mixture is poured into ice water to cool down, and H2O2 is slowly added until no bubbles are generated. After the golden yellow solid in the mixture settles for 30 minutes, the supernatant is poured out, and deionized water is slowly added. This is repeated 5-6 times until the pH of the supernatant is ≈ 7 to obtain the precursor product A;

[0138] (3) 0.5 g of the precursor product A was added to a 0.02 mol / L polyetheramine 2003 solution, ultrasonicated for 10 min, gently stirred and allowed to stand for 3 days, then heated at 98 °C for 12 h, washed with deionized water until the pH was ≈ 7, and freeze-dried to obtain the precursor product B;

[0139] (4) Add 0.5 g of precursor product B to 50 mL of 1 mol / L Fe(NO3)3 solution and let stand for 2 days. Filter and freeze-dry to obtain Fe 3+ / GOF.

[0140] (5) Fe 3+ / GOF was annealed at 800℃ for 2h under argon protection to finally obtain a composite absorbing material.

[0141] Performance Testing

[0142] In order to measure the absorbing performance of the material, the accordion-shaped graphene absorbing material was mixed with paraffin to form a coaxial ring with an inner diameter of 7 mm, an outer diameter of 3.04 mm, and a thickness of 2 mm (i.e., a uniform mixture in the form of a ring). The complex dielectric constant ε in the 2-18 GHz band was tested at room temperature using an Agilent E5071C vector network analyzer using a coaxial method. r and complex magnetic permeability μ r .

[0143] According to the measured ε r and μ r Calculate the absorption performance:

[0144]

[0145]

[0146] Among them, Z0, Z in , ε r and μ r are free impedance, input space impedance, complex permittivity and complex permeability. f, d and c represent the test frequency, material thickness and the speed of electromagnetic waves in free space, respectively.

[0147] The test results are shown in Table 1. The microwave absorbing sheet sold by Hanhong Fucheng Company was used as the control group.

[0148] Table 1 - Wave absorption performance test results

[0149] Minimum reflection loss RL(dB) Filler content (wt%) Thickness(mm) Example 1 -46.3 10 1.8 Example 2 -24.0 10 2.5 Example 3 -20.5 10 2.2 Example 4 -41.2 10 2.9 Example 5 -39.4 10 1.6 Control group 18 - 2.0 Comparative Example 1 -13.0 10 2.0 Comparative Example 2 -7.3 10 1.5 Comparative Example 3 -15.9 10 2.5

[0150] As can be seen from Table 1, the conductivity, thickness and electromagnetic shielding effectiveness of the expanded graphite electromagnetic shielding film prepared by the present invention are much higher than those of the commercially available graphene electromagnetic shielding film, and after design adjustment, compared with the comparative expanded graphite electromagnetic shielding film, it is more conducive to promotion and use in high-performance electromagnetic shielding materials.

[0151] In summary, the present invention does not involve any organic solvent in the preparation process, and has a simple process and strong operability, and can realize the large-scale, green and low-cost preparation of graphene absorbing materials, which is suitable for industrial production; the present invention uses the graphene framework obtained after the layered graphene oxide is fixed to realize the uniform dispersion of metal nanoparticles in the graphene interlayer and prevent the mutual agglomeration of graphene and nanoparticles, thereby improving the impedance matching between the material and the air; the present invention combines the advantages of graphene and magnetic nanoparticles, combines a variety of loss mechanisms such as conductive loss, magnetic loss, interface polarization and multiple reflections, increases and enhances the absorbing performance of the material, reduces the thickness and filling amount of the absorbing material, and can also reduce the material density. The obtained material can well meet the requirements of modern absorbing materials of "thin, light, wide and strong".

Claims

1. A method for preparing an accordion-shaped graphene-magnetic metal M nanoparticle composite wave absorbing material, wherein the "magnetic metal M" is one, two or three selected from iron, cobalt and nickel, the method comprising: (1) adding flake graphite to a concentrated sulfuric acid solution of potassium permanganate, stirring, and then standing for oxidation to obtain an oxidized mixture; (2) pouring the mixture obtained in step (1) into ice water to cool, then slowly adding H2O2 until no bubbles are generated, and after the solid in the mixed solution is settled, washing with water for multiple times (e.g., 3-10 times, preferably 4-8 times, more preferably 5-6 times, i.e., repeatedly washing for multiple times) to obtain a precursor product A; (3) adding the precursor product A obtained in step (2) to an aqueous solution of polyetheramine to obtain a mixture, slowly stirring and then standing, then heating at a heat treatment temperature of 80-100° C., washing the mixture with deionized water for multiple times until the pH of the washing water is 5.5-7.0, preferably 6.0-7.0, more preferably 6.5-7.0, and freeze-drying the mixture to obtain a precursor product B; (4) adding the precursor product B obtained in step (3) to the magnetic metal M ion solution and allowing the solution to stand; filtering the obtained mixture and freeze-drying it to obtain a magnetic metal M ion / GOF system (e.g., Fe 3+ / GOF); (5) The magnetic metal M ion / GOF system (e.g., Fe 3+ / GOF), and annealing treatment is performed under the protection of an inert gas (such as argon) to obtain a M / LrGO absorbing material, that is, an accordion-shaped graphene / magnetic metal M nanoparticle composite material.

2. The preparation method according to claim 1, wherein in step (3), the heat treatment temperature is 85-100°C, preferably 90-100°C, preferably 95-100°C, for example 97, 98 or 99°C; and / or In step (1), the size of the flake graphite is 60-500 mesh, preferably 100-325 mesh; more preferably 130-290 mesh; and / or In the step (1), the mass ratio of flake graphite to potassium permanganate is 1:(1.5-8), preferably 1:(1.8-6), preferably 1:(2-4), more preferably 1:(2.5-3.5); and / or In step (1), the temperature of the oxidation reaction is 0-45°C, preferably 0-35°C, preferably 0-30°C, and the time of the oxidation reaction is 6-50 hours, preferably 8-40 hours, preferably 12-24 hours; and / or In step (2), the settling time is 5 minutes to 5 hours, preferably 8 minutes to 2 hours, preferably 10 to 60 minutes; and / or In step (3), the polyetheramine is a polyetheramine having a number average molecular weight of 400-3000, preferably 700-2700, more preferably 900-2500, preferably 1000-2300, more preferably 1500-2200, and more preferably 1800-2003; and / or In step (3), the concentration of the aqueous solution of the polyetheramine is 0.004-0.06 mol / L, preferably 0.005-0.05 mol / L, preferably 0.008-0.04 mol / L, preferably 0.01-0.03 mol / L, preferably 0.015-0.025 mol / L; and / or In step (3), the weight ratio of the precursor product A to the polyetheramine in the aqueous solution of the polyetheramine (eg, polyetheramine ED2003) is 1:10-1:50, preferably 1:20-1:45, preferably 1:30-1:

40.

3. The preparation method according to claim 1 or 2, wherein In (4), the precursor product B obtained in step (3) is added to one of the following metal ion solutions and allowed to stand: (a1) iron ion solution, (b1) cobalt ion solution, (c1) nickel ion solution, (d1) iron ion / cobalt ion solution, (e1) iron ion / nickel ion solution, (f1) cobalt ion / nickel ion solution or (g1) iron ion / cobalt ion / nickel ion solution; the obtained mixture is filtered and freeze-dried to obtain (a2) an iron ion / GOF system (e.g., Fe 3+ / GOF system), (b2) cobalt ion / GOF system (e.g. Co 2+ / GOF system), (c2) nickel ion / GOF system (e.g. Ni 2+ / GOF system), (d2) iron ion / cobalt ion / GOF system (e.g. Fe 3+ / Co 2+ / GOF system), (e2) iron ion / nickel ion / GOF system (e.g. Fe 3+ / Ni 2+ / GOF system), (f2) nickel ion / cobalt ion / GOF system (e.g. Ni 2+ / Co 2+ / GOF system) or (g2) iron ion / cobalt ion / nickel ion / GOF system (e.g. Fe 3+ / Co 2+ / Ni 2+ / GOF system); In step (5), (a2), (b2), (c2), (d2), (e2), (f2) or (g2), such as Fe 3 + / GOF, and annealing treatment is carried out under the protection of an inert gas (such as argon) to obtain (a3) ​​Fe / LrGO absorbing material, (b3) Co / LrGO absorbing material, (c3) Ni / LrGO absorbing material, (d3) Fe / Co / LrGO absorbing material, (e3) Fe / Ni / LrGO absorbing material, (f3) Ni / Co / LrGO absorbing material or (g3) Fe / Ni / Co / LrGO absorbing material, that is, accordion-shaped graphene / magnetic metal M nanoparticle composite material.

4. The preparation method according to any one of claims 1 to 3, wherein The concentration of the magnetic metal M ion solution in step (4) is 0.3-2.5 mol / L, preferably 0.5-2 mol / L, preferably 0.7-1.8 mol / L, preferably 0.9-1.7 mol / L, preferably 1-1.5 mol / L The standing time in step (4) is 12-70 hours, preferably 18-60 hours, more preferably 24-48 hours.

5. The preparation method according to any one of claims 1 to 4, wherein The temperature of the annealing treatment in step (5) is 700-1000° C., preferably 750-900° C., preferably 780-870° C., preferably 800-850° C.; and / or, The annealing time in step (5) is 0.5-4 hours, preferably 1-2 hours.

6. The preparation method according to any one of claims 1 to 5, wherein in step (4), the relative amounts of the precursor product B and the magnetic metal M ion solution are such that: in the obtained M / LrGO (e.g., Fe / LrGO) absorbing material, the content (or loading) of the metal M is 5-60wt%, preferably 10-55wt%, more preferably 20-50wt%, more preferably 30-45wt%, such as 35 or 40wt%, based on the weight of the M / LrGO absorbing material; and / or In step (4), the mass ratio of the precursor product B to the metal M ions in the magnetic metal M ion solution is 10:1-1:10 (i.e., 10-0.1:1), preferably 7:1-1:7 (i.e., 7-0.14:1), preferably 5:1-1:5 (i.e., 5-0.2:1), preferably 4:1-1:4 (i.e., 4-0.25:1), preferably 1:1-1:2 (i.e., 1-0.5:1).

7. An accordion-shaped graphene composite absorbing material prepared by the method according to any one of claims 1 to 6, wherein the microstructure of the M / LrGO (e.g., Fe / LrGO) absorbing material is an accordion-like structure composed of layered reduced graphene oxide and magnetic metal M (e.g., Fe) nanoparticles uniformly distributed between the layers.

8. The absorbing material according to claim 7, wherein in the M / LrGO (e.g., Fe / LrGO) absorbing material, the content (or loading amount) of metal M is 5-60wt%, preferably 10-55wt%, more preferably 20-50wt%, more preferably 30-45wt%, such as 35 or 40wt%, based on the weight of the M / LrGO absorbing material.

9. A composite absorbing material, characterized in that: The composite absorbing material is formed by mixing the absorbing material according to claim 7 or 8 with paraffin or silicone resin; Preferably, a uniform mixture of 10 wt % absorbing material and paraffin or silicone resin has a maximum reflection loss of -46.3 dB at 17.92 GHz and an absorbing bandwidth of 6.8 GHz at a thickness of 2.2 mm, and the wt % content is based on the weight of the uniform mixture formed by the material and paraffin or silicone resin.

10. Use of the absorbing material according to any one of claims 7 to 9, wherein the composite absorbing material is used in absorbing equipment.

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