A magnetic manganese dioxide tunable electromagnetic wave absorbing material and its preparation method

Abstract

The present invention discloses a magnetic manganese dioxide tunable electromagnetic wave absorption material and a preparation method thereof, and relates to the technical field of new material synthesis and preparation. KMnO4, a reducing agent and a potassium salt are weighed in sequence and added to a beaker filled with deionized water, and stirred thoroughly until mixed; a carbon material is weighed and added, and stirred thoroughly to mix evenly; manganese oxide nanowires are grown in situ using microwave-assisted hydrothermal method, and after the reaction is completed, washing and filtering are performed, and a composite material precursor is obtained by drying; the material is flash-heated and oxidized using a microwave tube furnace, and the material whose surface is not completely converted into manganese oxide is deeply oxidized to obtain a cage-shaped manganese dioxide nanowire / multilayer expanded graphite carbon-based composite material. By microwave hydrothermal irradiation oxidation method, the expanded graphite is morphologically modified during the preparation process to simultaneously tune the phase of magnetic manganese dioxide, so as to realize in-situ synthesis of magnetic manganese dioxide nanowires and efficient electromagnetic wave absorption and shielding, and the preparation process is simple and efficient.

Description

Technical Field

[0001] The present invention relates to the technical field of new material synthesis and preparation, and in particular to a magnetic manganese dioxide tunable electromagnetic wave absorbing material and a preparation method thereof. Background Art

[0002] The development of wireless communication technology has led to an increase in the use of electromagnetic waves, impacting both electronic devices and human safety. Consequently, the demand for high-performance electromagnetic wave absorbing and shielding materials has grown, becoming a research hotspot across multiple fields. However, traditional absorbing / shielding materials typically utilize two strategies: combining conductors such as graphene, MXene, and carbon nanotubes with semiconductors such as transition metal sulfides and oxides to increase dielectric loss; or utilizing the resonance and spatial matching properties of magnetic materials to increase magnetic loss. Both strategies attempt to manipulate either the composite's electromagnetic wave absorption or shielding properties, failing to simultaneously achieve materials with excellent electromagnetic wave absorption and shielding properties.

[0003] CN202411156855 discloses a preparation method and application of a core-sheath structured FeNi@(Co / CN)@ carbon fiber composite absorbing material. This method comprises mixing a mixed solution of polyacrylonitrile and ZIF-67 powder as an external phase solution, adding Fe powder and Ni powder as an internal phase solution, adopting a coaxial electrospinning process to manufacture coaxial fibers, and finally carbonizing the fibers under a reducing atmosphere to obtain a core-sheath structured FeNi@(Co / CN)@ carbon fiber. The prepared absorbing material has a minimum reflection loss (RL) of 3.07 mm when the thickness is matched. min ) is -61.84dB. When the matching thickness is 2.37mm, the effective absorption bandwidth (EAB) is 6.24GHz, but the operation is difficult and the matching thickness is large. CN202410650229 discloses a carbon-based composite material for electromagnetic shielding and its preparation method. Specifically, it uses carbonized nanocellulose as a matrix to load Fe3O4 magnetic nanoparticles. It is prepared by freeze-drying integrated casting, subsequent high-temperature heat treatment and coating treatment. The composite material has a total shielding effectiveness of more than 75dB in the range of 8-12GHz and a reflectivity of less than 0.06. However, the related process is time-consuming, the steps are complex, the reaction conditions are harsh, the shielding band is narrow, and the efficiency is low.

[0004] Therefore, it is crucial to develop a simple, efficient, and tunable electromagnetic wave absorbing and shielding composite material and its preparation method, which can meet the needs of mass production of high-quality and high-performance electromagnetic wave absorbing and shielding composite materials. Summary of the Invention

[0005] The purpose of the present invention is to provide a magnetic manganese dioxide tunable electromagnetic wave absorbing material and a preparation method thereof, so as to solve the problems that the preparation process of existing composite materials with electromagnetic wave absorption and shielding performance is complex and the shielding effect is poor.

[0006] To solve the above technical problems, the present invention adopts the following technical solutions: a magnetic manganese dioxide tunable electromagnetic wave absorbing material and a preparation method thereof, characterized by comprising the following steps: a magnetic manganese dioxide tunable electromagnetic wave absorbing material and a preparation method thereof, characterized by comprising the following steps:

[0007] S1. Sequentially weigh KMnO4, a reducing agent, and potassium salt and add them to a beaker filled with deionized water, stirring thoroughly until uniformly mixed to obtain material a;

[0008] S2. Weigh the carbon material, add it to material a, stir and mix thoroughly to obtain material b;

[0009] S3. Place material b in a Teflon crucible and use microwave-assisted hydrothermal in situ growth of manganese oxide nanowires. After the reaction is completed, rinse with deionized water to remove K + ions, washed and filtered, and then dried to obtain material c, i.e., a cage-like manganese dioxide nanowire / multilayer expanded graphite carbon-based composite material precursor;

[0010] S4. Place material c in a quartz crucible and perform flash heating oxidation in a microwave tube furnace to deeply oxidize the material on its surface that has not been completely converted into manganese oxide to obtain a cage-like manganese dioxide nanowire / multilayer expanded graphite carbon-based composite material.

[0011] A further technical solution is that the carbon material in step S2 is one or more of expanded graphite, carbon fiber, carbon nanotube, and carbon black.

[0012] A further technical solution is that in step S1, the reducing agent is one of urea and hydrazine hydrate, and the potassium salt is one of KCl, KNO3, and K2SO4.

[0013] A further technical solution is that the mass ratio of the carbon material, KMnO4, reducing agent, potassium salt and deionized water is 0.24:0.16:(1.60-3.28):(0.008-0.12):20.

[0014] A further technical solution is that the specific process of microwave-assisted hydrothermal in situ growth of manganese dioxide nanowires in step S3 is to place material b in a microwave hydrothermal synthesizer, with a microwave power of 500 to 3000 W, a microwave frequency of 2450±50 or 915±50 MHz, a reaction temperature of 180 to 200°C, and a reaction time of 30 to 180 min.

[0015] A further technical solution is that the drying in step S3 is performed using a household microwave oven with a microwave power of 180 to 900 W, a microwave frequency of 2450 ± 50 MHz, and a drying time of 10 to 60 s.

[0016] A further technical solution is that the specific process of the microwave tube furnace flash heating oxidation in step S4 is irradiation at a power of 500 to 6000 W, a microwave frequency of 2450±50 or 915±50 MHz, a microwave oxidation calcination temperature of 200 to 800°C, a calcination time of 8 to 12 seconds, and an atmosphere of air or oxygen.

[0017] A further technical solution is to prepare a magnetic manganese dioxide tunable electromagnetic wave absorbing material according to the above preparation method, which is applied in the field of electromagnetic wave absorption and shielding.

[0018] Reaction mechanism:

[0019] Preparation of manganese oxide nanowires:

[0020] 4KMnO4+2H2O→4MnO2+4KOH+3O2 (1)

[0021] 4KMnO4+2CH4N2O→2K2CO3+4MnO2+2NH3+2NO2+H2 (2)

[0022] 4MnO2+2H2O→4MnO(OH)+O2 (3)

[0023] 4MnO(OH)+O2→4MnO2+2H2O (4)

[0024] CH4N2O+H2O→NH2COO - +NH4 + (5)

[0025] 3MnO(OH)+2NH2COO - +3NH4 + →Mn3O4+5NH3+2H2O+2CO2 (6)

[0026] First, the carbon material is thoroughly stirred and mixed with a solution prepared with potassium permanganate, a reducing agent, and a potassium salt. The mixture is then placed in a Teflon crucible for microwave-assisted hydrothermal treatment. Potassium permanganate is reduced by urea to generate manganese dioxide. Under the guidance of potassium ions, a large number of nanowires are in situ grown on the surface of the carbon material to cover it. Water molecules not only accelerate the reduction of potassium permanganate but also convert part of the manganese dioxide into manganese oxyhydroxide. Upon completion of the microwave hydrothermal synthesis, a composite containing manganese dioxide nanowires and manganese oxyhydroxide is obtained.

[0027] The hydrothermal product is washed and dried, then flash-heated in a microwave tube furnace for oxidation. Microwave heating regulates the manganese dioxide / manganese oxyhydroxide / manganese trimanganese tetroxide phases, achieving phase homogeneity and coordinated electromagnetic wave absorption and shielding. Under microwave irradiation, the manganese oxyhydroxide rapidly oxidizes and dehydrates to manganese dioxide, and the resulting water molecules quickly escape, resulting in a homogeneous composite of manganese dioxide nanowires and carbon material. The microwave flash heating of the hydrothermal product results in a single product of manganese dioxide, resulting in the resulting manganese dioxide nanowire / carbon-based composite material achieving optimal electromagnetic wave absorption and shielding performance.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] The present invention utilizes a microwave hydrothermal-flash oxidation process to first produce a manganese dioxide-manganese oxyhydroxide nanowire / multilayer expanded graphite carbon-based composite. During the hydrothermal stage, the morphology of the manganese dioxide nanowires grown in situ on the carbon material surface is modified. Microwave flash oxidation is then used to regulate the phase composition, achieving a homogenized phase transition, thereby enhancing its magnetic properties and achieving the dual functions of electromagnetic wave absorption and shielding. This overcomes the shortcomings of conventional processes for preparing high-efficiency absorbing / shielding composite materials, such as complex, time-consuming, and inefficient steps. By achieving tunable phase and electromagnetic absorption and shielding properties of the manganese dioxide nanowire / carbon material composite, as well as morphology modification of the composite, the preparation process is simple, efficient, and easily industrialized. The prepared cage-like manganese dioxide nanowire / multi-layer expanded graphite carbon-based composite material has a reflection loss of -40.55 to -72.29 dB at a thickness of 1.4 to 4.0 mm, and an effective absorption bandwidth of 2.2 to 4.14 GHz. After being made into a 0.1 mm thin film, it has a strong electromagnetic wave shielding capability of up to 117 dB at 8 to 16 GHz. It has both thin and light characteristics and excellent electromagnetic wave absorption and shielding properties. It has excellent performance in the field of electromagnetic wave absorption and shielding and has good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 The XRD patterns of the precursors of the caged manganese dioxide nanowire / multilayer expanded graphite carbon-based composite materials synthesized by microwave hydrothermal method in Examples 1 and 2 are shown;

[0031] Figure 2 1 is the XRD pattern of the caged manganese dioxide nanowire / multilayer expanded graphite carbon-based composite material in Example 2 and Example 3;

[0032] Figure 3 : is the XED pattern of the caged manganese dioxide nanowire / multilayer expanded graphite carbon-based composite material in Example 3;

[0033] Figure 4This is an SEM image of the caged manganese dioxide nanowire / multilayer expanded graphite carbon-based composite material in Example 3;

[0034] Figure 5 This is the EDS spectrum of the caged manganese dioxide nanowire / multilayer expanded graphite carbon-based composite material in Example 3;

[0035] Figure 6 This is a graph showing the electromagnetic wave absorption performance of the caged manganese dioxide nanowire / multilayer expanded graphite carbon-based composite material in Example 3;

[0036] Figure 7 2 are XRD patterns of the composite materials in Example 3 and Comparative Example 2. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0038] Example 1

[0039] Raw materials were weighed according to the amounts of expanded graphite 0.24 g, KMnO4 0.16 g, urea 3.28 g, KCl 0.02 g, and deionized water 20 g.

[0040] (1) First, add 20g of deionized water into a beaker, then add KMnO4, urea, and KCl into the beaker in sequence and stir thoroughly to dissolve for 15 minutes.

[0041] (2) Add 0.24 g of expanded graphite to the mixed solution and stir thoroughly for 15 minutes.

[0042] (3) The material was placed in a Teflon beaker and transferred to a microwave hydrothermal synthesizer. The reaction temperature was 180 °C, the microwave power was 1200 W, the microwave frequency was 2450 ± 50 MHz, the heating rate was 10 °C / min, and the holding time was 60 min.

[0043] (4) Take out the material and wash it repeatedly with deionized water to remove K + ions, washed, filtered, and dried to obtain a caged manganese dioxide nanowire / multilayer expanded graphite carbon-based composite precursor. Drying was performed in a household microwave oven at a microwave power of 300 W, a microwave frequency of 2450 ± 50 MHz, and a drying time of 30 seconds to obtain the precursor material and investigate its properties.

[0044] (5) The dried precursor was transferred to a microwave tube furnace in an air atmosphere for reaction at a reaction temperature of 200°C, a microwave power of 1400 W, a microwave frequency of 2450 ± 50 MHz, and a holding time of 10 s.

[0045] (6) After the reaction is completed, the material is taken out to obtain a cage-like manganese dioxide nanowire / multilayer expanded graphite carbon-based composite material.

[0046] Example 2

[0047] Raw materials were weighed according to the amounts of expanded graphite 0.24 g, KMnO4 0.16 g, urea 3.28 g, KCl 0.02 g, and deionized water 20 g.

[0048] (1) First, add 20g of deionized water into a beaker, then add KMnO4, urea, and KCl into the beaker in sequence and stir thoroughly to dissolve for 15 minutes.

[0049] (2) Add 0.24 g of expanded graphite to the mixed solution and stir thoroughly for 15 minutes.

[0050] (3) The material was placed in a Teflon beaker and transferred to a microwave hydrothermal synthesizer. The reaction temperature was 180 °C, the microwave power was 1200 W, the microwave frequency was 2450 ± 50 MHz, the heating rate was 10 °C / min, and the holding time was 120 min.

[0051] (4) Take out the material and wash it repeatedly with deionized water to remove K + ions, washed, filtered, and dried to obtain a caged manganese dioxide nanowire / multilayer expanded graphite carbon-based composite precursor. Drying was performed using a household microwave oven with a microwave power of 300 W, a microwave frequency of 2450 ± 50 MHz, and a drying time of 30 seconds.

[0052] (5) The dried precursor was transferred to a microwave tube furnace in an air atmosphere for reaction at a reaction temperature of 200°C, a microwave power of 1400 W, a microwave frequency of 2450 ± 50 MHz, and a holding time of 10 s.

[0053] (6) After the reaction is completed, the material is taken out to obtain a cage-like manganese dioxide nanowire / multilayer expanded graphite carbon-based composite material.

[0054] Example 3

[0055] Raw materials were weighed according to the amounts of expanded graphite 0.24 g, KMnO4 0.16 g, urea 3.28 g, KCl 0.02 g, and deionized water 20 g.

[0056] (1) First, add 20g of deionized water into a beaker, then add KMnO4, urea, and KCl into the beaker in sequence and stir thoroughly to dissolve for 15 minutes.

[0057] (2) Add 0.24 g of expanded graphite to the mixed solution and stir thoroughly for 15 minutes.

[0058] (3) The material was placed in a Teflon beaker and transferred to a microwave hydrothermal synthesizer. The reaction temperature was 180 °C, the microwave power was 1200 W, the microwave frequency was 2450 ± 50 MHz, the heating rate was 10 °C / min, and the holding time was 120 min.

[0059] (4) Take out the material and wash it repeatedly with deionized water to remove K + ions, washed, filtered, and dried to obtain a caged manganese dioxide nanowire / multilayer expanded graphite carbon-based composite precursor. Drying was performed using a household microwave oven with a microwave power of 300 W, a microwave frequency of 2450 ± 50 MHz, and a drying time of 30 seconds.

[0060] (5) The dried precursor was transferred to a microwave tube furnace in an air atmosphere for reaction at a reaction temperature of 400°C, a microwave power of 3000W, a microwave frequency of 2450±50MHz, and a holding time of 10s.

[0061] (6) After the reaction is completed, the material is taken out to obtain a cage-like manganese dioxide nanowire / multilayer expanded graphite carbon-based composite material.

[0062] The XRD patterns of the cage-like manganese dioxide nanowire / multilayer expanded graphite carbon-based composite material precursor obtained by microwave hydrothermal treatment are shown in Figure 2. Figure 1 As shown in Figure 2, the crystallinity of the prepared cage-like manganese dioxide nanowire / multilayer expanded graphite carbon-based composite material is significantly improved under 120min microwave hydrothermal time compared to 60min. Figure 2 As shown by Figure 2 It can be seen that the prepared caged manganese dioxide nanowires all retain the characteristic diffraction peaks of the manganese oxide phase. The higher the temperature, the more pronounced these diffraction peaks become. This demonstrates that this method can rapidly and efficiently synthesize and prepare a uniform manganese dioxide phase. Furthermore, microwave radiation oxidation significantly adjusts the conversion of manganese oxyhydroxide to manganese dioxide, achieving a synergistic effect in both electromagnetic wave absorption and shielding.

[0063] The XED results of the cage-like manganese dioxide nanowire / multilayer expanded graphite carbon-based composite material prepared in Example 3 are as follows: Figure 3 As shown, the prepared composite material maintains the original phase of expanded graphite and exhibits the characteristic diffraction peaks of manganese dioxide. The SEM electron microscope images and EDS energy spectrum of the cage-like manganese dioxide nanowire / multilayer expanded graphite carbon-based composite material prepared in Example 3 are Figure 4 、 Figure 5 .from Figure 4 It can be seen that the morphology of expanded graphite is modified during the reaction process, and manganese dioxide nanowires grow on the surface of the material to form a cage-like multilayer three-dimensional structure; at the same time, Figure 5EDS energy spectrum analysis found that no new elements appeared. It can be seen that this method can be used to modify the surface of expanded graphite while realizing the in-situ growth synthesis of manganese dioxide nanowires, shortening the preparation steps of the composite material, making it simple, efficient, and easy to industrially apply.

[0064] The cage-like manganese dioxide nanowire multilayer expanded graphite composite material obtained in Example 3 was used to make a coaxial ring and tested in the range of 1-18 GHz. The prepared absorbing material had a RLmin of -75.56 dB and an EAB of 3.87 GHz for 15.16 GHz electromagnetic waves at a matching thickness of 1.48 mm. Figure 6 As shown in the figure, a caged manganese dioxide nanowire multilayer expanded graphite composite material was pressed into a 0.1 mm film at 20 MPa. Testing in the 12-19 GHz range revealed a strong electromagnetic wave shielding capability of 117 dB in the X and P bands. This material exhibits excellent electromagnetic wave absorption and shielding properties, and has promising applications in electromagnetic protection and stealth materials.

[0065] Example 4

[0066] Raw materials were weighed according to the amounts of expanded graphite 0.24 g, KMnO4 0.16 g, hydrazine hydrate 1.60 g, KCl 0.02 g, and deionized water 20 g.

[0067] (1) First, add 20g of deionized water into a beaker, then add KMnO4, hydrazine hydrate, and KCl into the beaker in sequence and stir thoroughly to dissolve for 15 minutes.

[0068] (2) Add 0.24 g of expanded graphite to the mixed solution and stir thoroughly for 15 minutes.

[0069] (3) The material was placed in a Teflon beaker and transferred to a microwave hydrothermal synthesizer. The reaction temperature was 180 °C, the microwave power was 1200 W, the microwave frequency was 2450 ± 50 MHz, the heating rate was 10 °C / min, and the holding time was 120 min.

[0070] (4) Take out the material and wash it repeatedly with deionized water to remove K + ions, washed, filtered, and dried to obtain a caged manganese dioxide nanowire / multilayer expanded graphite carbon-based composite precursor. Drying was performed using a household microwave oven with a microwave power of 300 W, a microwave frequency of 2450 ± 50 MHz, and a drying time of 30 seconds.

[0071] (5) The dried precursor was transferred to a microwave tube furnace in an air atmosphere for reaction at a reaction temperature of 400°C, a microwave power of 3000W, a microwave frequency of 2450±50MHz, and a holding time of 10s.

[0072] (6) After the reaction is completed, the material is taken out to obtain a cage-like manganese dioxide nanowire / multilayer expanded graphite carbon-based composite material.

[0073] Example 5

[0074] Raw materials were weighed according to the amounts of expanded graphite 0.24 g, KMnO4 0.16 g, urea 3.28 g, KNO3 0.008 g, and deionized water 20 g.

[0075] (1) First, add 20g of deionized water into a beaker, then add KMnO4, urea, and KNO3 into the beaker in sequence and stir thoroughly to dissolve for 15 minutes.

[0076] (2) Add 0.24 g of expanded graphite to the mixed solution and stir thoroughly for 15 minutes.

[0077] (3) The material was placed in a Teflon beaker and transferred to a microwave hydrothermal synthesizer. The reaction temperature was 180 °C, the microwave power was 1200 W, the microwave frequency was 2450 ± 50 MHz, the heating rate was 10 °C / min, and the holding time was 120 min.

[0078] (4) Take out the material and wash it repeatedly with deionized water to remove K + ions, washed, filtered, and dried to obtain a caged manganese dioxide nanowire / multilayer expanded graphite carbon-based composite precursor. Drying was performed using a household microwave oven with a microwave power of 300 W, a microwave frequency of 2450 ± 50 MHz, and a drying time of 30 seconds.

[0079] (5) The dried precursor was transferred to a microwave tube furnace in an air atmosphere for reaction at a reaction temperature of 400°C, a microwave power of 3000W, a microwave frequency of 2450±50MHz, and a holding time of 10s.

[0080] (6) After the reaction is completed, the material is taken out to obtain a cage-like manganese dioxide nanowire / multilayer expanded graphite carbon-based composite material.

[0081] Example 6

[0082] The raw materials were weighed according to the amounts of expanded graphite 0.24 g, KMnO4 0.16 g, urea 3.28 g, K2SO4 0.12 g, and deionized water 20 g.

[0083] (1) First, add 20g of deionized water into a beaker, then add KMnO4, urea, and K2SO4 into the beaker in sequence and stir thoroughly to dissolve for 15 minutes.

[0084] (2) Add 0.24 g of expanded graphite to the mixed solution and stir thoroughly for 15 minutes.

[0085] (3) The material was placed in a Teflon beaker and transferred to a microwave hydrothermal synthesizer. The reaction temperature was 180 °C, the microwave power was 1200 W, the microwave frequency was 2450 ± 50 MHz, the heating rate was 10 °C / min, and the holding time was 120 min.

[0086] (4) Take out the material and wash it repeatedly with deionized water to remove K + ions, washed, filtered, and dried to obtain a caged manganese dioxide nanowire / multilayer expanded graphite carbon-based composite precursor. Drying was performed using a household microwave oven with a microwave power of 300 W, a microwave frequency of 2450 ± 50 MHz, and a drying time of 30 seconds.

[0087] (5) The dried precursor was transferred to a microwave tube furnace in an air atmosphere for reaction at a reaction temperature of 400°C, a microwave power of 3000W, a microwave frequency of 2450±50MHz, and a holding time of 10s.

[0088] (6) After the reaction is completed, the material is taken out to obtain a cage-like manganese dioxide nanowire / multilayer expanded graphite carbon-based composite material.

[0089] Comparative Example 1

[0090] Raw materials were weighed according to the amounts of expanded graphite 0.24 g, KMnO4 0.16 g, urea 3.28 g, KCl 0.02 g, and deionized water 20 g.

[0091] (1) First, add 20g of deionized water into a beaker, then add KMnO4, urea, and KCl into the beaker in sequence and stir thoroughly to dissolve for 15 minutes.

[0092] (2) Add 0.24 g of expanded graphite to the mixed solution and stir thoroughly for 15 minutes.

[0093] (3) The material was placed in a hydrothermal reactor and transferred to a conventional hydrothermal synthesis reaction equipment for testing. The reaction temperature was 180°C and the holding time was 24 h.

[0094] (4) The material was removed and washed repeatedly with deionized water, and the solid product was removed and dried. Drying was performed using a household microwave oven with a microwave power of 300 W, a microwave frequency of 2450 ± 50 MHz, and a drying time of 30 s.

[0095] Comparing Comparative Example 1 with Example 1, it can be seen that microwave hydrothermal treatment greatly shortens the reaction time compared to conventional hydrothermal treatment.

[0096] Comparative Example 2

[0097] Raw materials were weighed according to the amounts of expanded graphite 0.24 g, KMnO4 0.16 g, urea 3.28 g, KCl 0.02 g, and deionized water 20 g.

[0098] (1) First, add 20g of deionized water into a beaker, then add KMnO4, urea, and KCl into the beaker in sequence and stir thoroughly to dissolve for 15 minutes.

[0099] (2) Add 0.24 g of expanded graphite to the mixed solution and stir thoroughly for 15 minutes.

[0100] (3) The material was placed in a Teflon beaker and transferred to a microwave hydrothermal synthesizer. The reaction temperature was 180 °C, the microwave power was 1200 W, the microwave frequency was 2450 ± 50 MHz, the heating rate was 10 °C / min, and the holding time was 120 min.

[0101] (4) Take out the material and wash it repeatedly with deionized water to remove K + ions, washed, filtered, and dried to obtain a caged manganese dioxide nanowire / multilayer expanded graphite carbon-based composite precursor. Drying was performed using a household microwave oven with a microwave power of 300 W, a microwave frequency of 2450 ± 50 MHz, and a drying time of 30 seconds.

[0102] (5) The dried precursor was transferred to a muffle furnace for reaction in an air atmosphere at a reaction temperature of 400°C, a heating rate of 10°C / min, and a holding time of 40 min.

[0103] (6) After the reaction is completed, the material is taken out to obtain a composite material.

[0104] XRD comparison of the composite materials of Example 3 and Comparative Example 2 Figure 7 As shown, microwave oxidation roasting not only greatly reduces the time, but also promotes the homogenization of the manganese dioxide phase. While microwaves are highly efficient and energy-saving, they also achieve a better microstructure, obtaining a homogeneous single material with efficient electromagnetic wave absorption.

[0105] Although the present invention has been described herein with reference to a number of illustrative embodiments thereof, it should be understood that numerous other modifications and implementations may be devised by those skilled in the art, and such modifications and implementations will fall within the scope of the present disclosure. More specifically, various variations and modifications may be made to the components or arrangements within the scope of the present disclosure, the drawings, and the claims. In addition to variations and modifications to the components or arrangements, other uses will also be apparent to those skilled in the art.

Claims

1. A method for preparing a magnetic manganese dioxide tunable electromagnetic wave absorbing material, characterized in that The steps include: S1. Sequentially weigh KMnO4, a reducing agent, and potassium salt and add them to a beaker filled with deionized water, stirring thoroughly until uniformly mixed to obtain material a; S2. Weigh the carbon material, add it to material a, stir and mix thoroughly to obtain material b; S3. Place material b in a Teflon crucible and use microwave-assisted hydrothermal in situ growth of manganese oxide nanowires. After the reaction is completed, rinse with deionized water to remove K + ions, washed and filtered, and then dried to obtain material c, i.e., a cage-like manganese dioxide nanowire / multilayer expanded graphite carbon-based composite material precursor; S4. The material c is placed in a quartz crucible and subjected to flash heating oxidation using a microwave tube furnace to deeply oxidize the surface of the material that is not completely converted into manganese oxide to obtain a cage-like manganese dioxide nanowire / multilayer expanded graphite carbon-based composite material; The reducing agent in step S1 is one of urea and hydrazine hydrate; the specific process of microwave-assisted hydrothermal in-situ growth of manganese dioxide nanowires in step S3 is to place material b in a microwave hydrothermal synthesizer, with a microwave power of 500-3000 W, a microwave frequency of 2450±50 or 915±50 MHz, a reaction temperature of 180-200° C., and a reaction time of 30-180 min; the specific process of microwave tube furnace flash heating oxidation in step S4 is to irradiate at a power of 500-6000 W, a microwave frequency of 2450±50 or 915±50 MHz, a microwave oxidation calcination temperature of 200-800° C., a calcination time of 8-12 s, and an atmosphere of air or oxygen.

2. The method for preparing a magnetic manganese dioxide tunable electromagnetic wave absorbing material according to claim 1, characterized in that: The carbon material in step S2 is one or more of expanded graphite, carbon fiber, carbon nanotube, and carbon black.

3. The method for preparing a magnetic manganese dioxide tunable electromagnetic wave absorbing material according to claim 1, characterized in that: The potassium salt in step S1 is one of KCl, KNO3, and K2SO4.

4. The method for preparing a magnetic manganese dioxide tunable electromagnetic wave absorbing material according to claim 1, characterized in that: The mass ratio of the carbon material, KMnO4, reducing agent, potassium salt and deionized water is 0.24:0.16:(1.60-3.28):(0.008-0.12):

20.

5. The method for preparing a magnetic manganese dioxide tunable electromagnetic wave absorbing material according to claim 1, characterized in that: In step S3, the drying is performed using a household microwave oven with a microwave power of 180 to 900 W, a microwave frequency of 2450 ± 50 MHz, and a drying time of 10 to 60 seconds.

6. A magnetic manganese dioxide tunable electromagnetic wave absorbing material, characterized in that: The material is prepared according to the preparation method of a magnetic manganese dioxide tunable electromagnetic wave absorbing material according to any one of claims 1 to 5, and is used in the field of electromagnetic wave absorption and shielding.

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