Chain-shaped anisometric fe3o4@si o2@c core-shell material, preparation method and application thereof

Abstract

This invention belongs to the field of microwave absorbing materials technology, specifically relating to chain-like irregular Fe3O4@SiO2@C core-shell materials, their preparation methods, and applications. The chain-like irregular core-shell materials of this invention are assembled from irregularly shaped monomers chained together by carbon layers. Each irregularly shaped monomer has a core-shell structure formed by a core of iron(III) oxide coated with rod-shaped silica. This invention uses ellipsoidal or cubic iron(III) oxide as a template, growing rod-shaped silica on its surface to obtain hammer-shaped or hexagonal nanocomposite units. These units are then reduced and annealed to obtain magnetic particles, which are then coated with epoxy resin under a magnetic field to forcibly assemble into chains. Finally, calcination forms a carbon shell, resulting in two types of chain-like irregular Fe3O4@SiO2@C core-shell materials. This invention employs an external magnetic field forced assembly method and controls the morphology of the core-shell material units, thereby regulating the dielectric and magnetic properties. The materials of this invention have novel morphology and excellent performance, showing broad application prospects in microwave absorption, catalysis, and other fields.

Description

Technical Field

[0001] This invention belongs to the field of microwave absorbing materials technology, specifically relating to chain-like irregular Fe3O4@SiO2@C core-shell materials and their preparation and application. Background Technology

[0002] Electromagnetic wave absorbing materials are crucial for addressing electromagnetic pollution and have therefore attracted widespread attention. Constructing high-performance electromagnetic composite material systems is a research hotspot in the field of electromagnetic wave absorption. Utilizing electromagnetic synergy to achieve matching of electromagnetic wave magnetoresistance and electrical impedance can broaden the absorption bandwidth of electromagnetic waves. The multiple heterogeneous interfaces formed by material composites induce interfacial polarization, further improving the electromagnetic wave loss capability of the materials. One-dimensional nanomagnets possess strong shape anisotropy, thus exhibiting a higher Snoek's threshold frequency compared to zero-dimensional structures. At microwave frequencies, one-dimensional magnetic nanostructures such as FeNi3 nanochains, Fe3O4, and ZnFe2O4 nanofibers all exhibit natural resonance peaks and high μ" values. Furthermore, similar to carbon nanotubes, the high aspect ratio of one-dimensional magnetic nanostructures enables them to form conductive networks. However, the morphology of current chain-like magnetic absorbing materials is limited by the uniformity of magnetic unit morphology, making it impossible to fully explore the relationship between one-dimensional magnetic structures and absorption performance in complex chain-like structures. Therefore, the synthesis and performance research of irregularly shaped nanochain-like magnetic absorbing materials are urgently needed. Summary of the Invention

[0003] The purpose of this invention is to provide a novel morphological and high-performance chain-like irregular unit Fe3O4@SiO2@C core-shell material, as well as its preparation and application.

[0004] The chain-like irregularly shaped Fe3O4@SiO2@C core-shell material provided by this invention is assembled from irregularly shaped monomers chained together by carbon layers. The irregularly shaped monomers form a core-shell structure with a core of iron oxide (Fe3O4) and a coating of rod-shaped silica. Changing the morphology of the iron oxide core to ellipsoidal or cubic shapes can alter the amount of rod-shaped silica coating. This invention uses ellipsoidal and cubic iron oxide as templates, respectively, to grow rod-shaped silica on their surfaces, obtaining hammer-shaped and hexagonal nanocomposite units, respectively. Annealing under a reducing atmosphere yields magnetic particles, which are then coated with epoxy resin under a magnetic field, forcibly assembled into chains, and finally calcined to form a carbon shell, resulting in two types of chain-like irregularly shaped Fe3O4@SiO2@C core-shell materials.

[0005] This invention employs a novel external magnetic field forced assembly method and controls the morphology of the core-shell material units, thereby modulating the dielectric and magnetic properties. The material exhibits novel morphology and excellent performance, showing broad application prospects in microwave absorption, catalysis, and other fields.

[0006] The method for preparing the chain-like irregular unit Fe3O4@SiO2@C core-shell material provided by this invention includes the following specific steps:

[0007] S1. Dissolve polyvinylpyrrolidone in pentanol, then add iron oxide aqueous dispersion, sodium citrate aqueous solution, ammonia, anhydrous ethanol and tetraethyl orthosilicate in sequence. Shake well and let stand in an oven. Then centrifuge, wash and dry to obtain irregular Fe2O3@SiO2 powder.

[0008] S2. Anneal the Fe2O3@SiO2 powder obtained in step S1 under a hydrogen-argon atmosphere to obtain Fe3O4@SiO2 powder.

[0009] S3. Place the Fe3O4@SiO2 powder obtained in step S2 into a mixed solution of water and anhydrous ethanol, then add ammonia, resorcinol and formaldehyde, place in a magnetic field environment, heat in a water bath, centrifuge, wash and dry after reaction to obtain chain Fe3O4@SiO2@PR powder.

[0010] S4. The Fe3O4@SiO2@PR powder obtained in step S3 is sintered under nitrogen to obtain a chain-like irregular Fe3O4@SiO2@C core-shell material.

[0011] Further, in step S1, the ratio of polyvinylpyrrolidone to pentanol is 1:(8-12)g / mL.

[0012] Furthermore, in step S1, the iron oxide can be in the form of an ellipsoid or a cube.

[0013] Furthermore, in step S1, the mass fraction of the iron oxide aqueous dispersion is 0.05-0.15 g / mL, and the volume ratio of the iron oxide aqueous dispersion to pentanol is 3:(800-1200).

[0014] Furthermore, in step S1, the concentration of the sodium citrate aqueous solution is 0.15–0.25 mol / L, and the volume ratio of the sodium citrate aqueous solution to pentanol is 1:(80–120).

[0015] Furthermore, in step S1, the concentration of the ammonia water is 25-28 wt%, the purity of the anhydrous ethanol is ≥99.7%, and the volume ratios of the ammonia water, anhydrous ethanol, and tetraethyl orthosilicate to pentanol are 2:(95-105), 1:(9.5-10.5), and 1:(95-105), respectively.

[0016] Furthermore, in step S1, the temperature of the oven is 58-62°C, and the settling time is 0.5-3 hours.

[0017] Furthermore, in step S2, the hydrogen concentration (i.e., hydrogen volume percentage) of the hydrogen-argon atmosphere is 4% to 6%, the annealing temperature is 380 to 420°C, the heating rate is 1.5 to 2.5°C / min, and the holding time is 3.5 to 4.5 hours.

[0018] Furthermore, in step S3, the purity of the anhydrous ethanol is ≥99.7%, and the volume ratio of anhydrous ethanol to water is 2:(0.8~1.2).

[0019] Furthermore, in step S3, the concentration of the ammonia water is 25-28 wt%, and the mass ratio of ammonia water, resorcinol, and formaldehyde is 5:(0.8-1.2):(0.8-1.2).

[0020] Furthermore, in step S3, the water bath temperature is 28–32°C, and the stirring time is 1–3 hours.

[0021] Furthermore, in step S4, the sintering temperature is 740–760°C, the heating rate is 4.5–5.5°C / min, and the holding time is 1.2–2 hours.

[0022] This invention also provides a chain-like irregularly shaped Fe3O4@SiO2@C core-shell material obtained by the above preparation method. The iron oxide core is selected to be ellipsoidal or cubic. Correspondingly, the irregularly shaped core-shell monomers are hammer-shaped and hexagonal, respectively.

[0023] The present invention also provides applications of the above-mentioned chain-shaped irregular unit Fe3O4@SiO2@C core-shell material, specifically in the field of microwave absorption.

[0024] Compared with the prior art, the present invention has the following advantages:

[0025] (1) The synthesis method of this invention is novel. By forcibly assembling under a magnetic field, irregular units are strung together into a chain, and an assembly with a special morphology is successfully synthesized.

[0026] (2) The chain structure assembly and synthesis method provided by the present invention has a certain degree of universality. Different shapes and materials of cores can be replaced to construct units with different morphologies and assemble them into chains.

[0027] (3) The micron tube material provided by the invention is applied in the field of microwave absorption and has the advantages of high absorption rate, thin coating and wide bandwidth. Attached Figure Description

[0028] Figure 1Scanning electron microscope (SEM) images of (a) hexagonal Fe2O3@SiO2 core-shell material; (b) chain-like hexagonal Fe3O4@SiO2@PR core-shell material; (c) chain-like hexagonal Fe3O4@SiO2@C core-shell material; (d) hammer-shaped Fe2O3@SiO2 core-shell material; (e) chain-like hammer-shaped Fe3O4@SiO2@PR core-shell material; and (f) hammer-shaped Fe3O4@SiO2@C core-shell material.

[0029] Figure 2 Scanning electron microscope (SEM) images of (a) cubic Fe2O3@SiO2 core-shell material; (b) chain-like cubic Fe3O4@SiO2@PR core-shell material; (c) chain-like cubic Fe3O4@SiO2@C core-shell material; (d) ellipsoidal Fe2O3@SiO2 core-shell material; (e) chain-like ellipsoidal Fe3O4@SiO2@PR core-shell material; and (f) chain-like ellipsoidal Fe3O4@SiO2@C core-shell material.

[0030] Figure 3 The X-ray diffraction pattern of the chain-like hexagonal Fe3O4@SiO2@C core-shell material.

[0031] Figure 4 The graphs show the relative complex permittivity and relative complex permeability of (a) chain-like hexagonal Fe3O4@SiO2@C core-shell materials in the frequency range of 2–18 GHz; (c) chain-like hammer-shaped Fe3O4@SiO2@C core-shell materials in the frequency range of 2–18 GHz; and (e) chain-like monogonal Fe3O4@SiO2@C core-shell materials in the frequency range of 2–18 GHz.

[0032] Figure 5 (a) Reflection loss of chain-like hexagonal Fe3O4@SiO2@C core-shell material in the frequency range of 2–18 GHz; (b) Reflection loss of chain-like hammer-shaped Fe3O4@SiO2@C core-shell material in the frequency range of 2–18 GHz; (c) Reflection loss of chain-like monogonal unit Fe3O4@SiO2@C core-shell material in the frequency range of 2–18 GHz.

[0033] Figure 6Morphological characterization and reconstructed magnetic field distribution of the chain-like hexagonal Fe3O4@SiO2@C core-shell material; (a) Scanning electron microscope (SEM) image of the chain-like hexagonal Fe3O4@SiO2@C core-shell material; (b) Transmission electron microscope (TEM) image of the chain-like hexagonal Fe3O4@SiO2@C core-shell material; (c) Local TEM image of the chain-like hexagonal Fe3O4@SiO2@C core-shell material; (d) Local reconstructed magnetic field distribution of the chain-like hexagonal Fe3O4@SiO2@C core-shell material. Detailed Implementation

[0034] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0035] The preparation of cubic iron oxide used in each embodiment is based on the literature (Colloids and Surfaces A: Physicochemical and Engineering Aspect 1998, 134, 265-279).

[0036] Unless otherwise specified, all other raw materials or processing technologies involved are conventional commercially available products or conventional processing technologies in this field.

[0037] Example 1: Preparation of chain-like hexagonal unit Fe3O4@SiO2@C core-shell material:

[0038] (1) 30 μL of cubic iron oxide aqueous dispersion with a concentration of 0.1 g / mL was injected into 10 mL of n-pentanol solution with a concentration of 0.1 g / mL polyvinylpyrrolidone (PVP, Mw = ~55,000), and 240 μL of deionized water, 100 μL of sodium citrate aqueous solution with a concentration of 0.2 mol / L, 200 μL of ammonia water, 1 mL of anhydrous ethanol and 100 μL of tetraethyl orthosilicate were added in sequence. After each addition, the mixture was stirred vigorously and reacted at 60 °C for 2 h. After centrifugation, washing and drying, hexagonal Fe2O3@SiO2 powder with six silicon rods was obtained.

[0039] (2) The hexagonal Fe2O3@SiO2 powder prepared in step (1) was placed in H2 / Ar (5% H2) atmosphere and reduced at 400℃ for 4 hours with a heating rate of 2℃ / min to obtain hexagonal Fe3O4@SiO2 powder;

[0040] (3) Weigh 5 mg of the hexagonal Fe3O4@SiO2 powder prepared in step (2), disperse it in a mixed solution of 10 mL anhydrous ethanol and 5 mL deionized water, and disperse it evenly by ultrasonication; then add 0.25 g ammonia, 0.05 g resorcinol and 0.05 g formaldehyde; then place the solution in a magnetic field environment and stir it in a 30 °C water bath for 1 hour. Centrifuge, wash and dry to obtain chain Fe3O4@SiO2@PR powder coated with phenolic resin;

[0041] (4) The chain-like Fe3O4@SiO2@PR powder prepared in step (3) was carbonized at 750°C for 1.5 hours under N2 atmosphere with a heating rate of 5°C / min to obtain the target product chain-like hexagonal unit Fe3O4@SiO2@C core-shell material.

[0042] Example 2, Preparation of chain-like hammer-shaped unit Fe3O4@SiO2@C core-shell material:

[0043] The majority of the results are the same as in Example 1, except that the morphology of the iron oxide is changed to an ellipsoid.

[0044] Example 3, Preparation of chain-like unicornuate unit Fe3O4@SiO2@C core-shell material:

[0045] The process is largely the same as in Example 1, except that in the preparation of Fe2O3@SiO2 powder, the amount of ammonia added is 150-200 μL and the amount of deionized water added is 200 μL.

[0046] Comparative Example 1: Preparation of chain-like cubic unit Fe3O4@SiO2@C core-shell material using magnetic field:

[0047] Compared with Example 1, most of the process is the same, except that the preparation process of Fe2O3@SiO2 powder is changed to: 0.1g Fe2O3 and 2ml ammonia water are added to 20ml deionized water and 140ml anhydrous ethanol solution, and then 200μL tetraethyl orthosilicate is added dropwise. After stirring for 6h, the mixture is centrifuged, washed, and dried to obtain Fe2O3@SiO2 powder.

[0048] Comparative Example 2: Preparation of chain-like ellipsoidal unit Fe3O4@SiO2@C core-shell material:

[0049] Compared with Example 2, most of the process is the same, except that the preparation process of Fe2O3@SiO2 powder is changed as follows: 0.1g Fe2O3 and 2ml ammonia water are added to 20ml deionized water and 140ml anhydrous ethanol solution, and then 200μL tetraethyl orthosilicate is added dropwise. After stirring for 6h, the mixture is centrifuged, washed, and dried to obtain Fe2O3@SiO2 powder.

[0050] The microstructure of the materials in the above embodiments was characterized using scanning electron microscopy (SEM, Hitachi SEM S-4800). Sample preparation method: the powder sample was ultrasonically dispersed in ethanol, then dropped onto a conductive silicon wafer and dried for testing. The microstructure of a series of composite materials was characterized using transmission electron microscopy (TEM, JEOL JEM-2100F). Sample preparation method: the powder sample was ultrasonically dispersed in ethanol, then dropped onto a carbon-supported copper mesh and dried for testing. X-ray diffraction patterns were obtained using a Bruker D8 Advance instrument. The complex relative permittivity and permeability in the 2.0–18.0 GHz range were measured using a vector network analyzer (model N5230C).

[0051] Figure 1 Scanning electron microscope image of a chain-like anisomorphic Fe3O4@SiO2@C core-shell material. Figure 1 and Figure 2 The scale bar in the figures is 1 micrometer. Here, a represents the microstructure of the hexagonal Fe2O3@SiO2 core-shell structure unit, b represents the microstructure of the chain-like hexagonal Fe3O4@SiO2@PR core-shell material, c represents the microstructure of the chain-like hexagonal Fe3O4@SiO2@C core-shell material in Example 1, d represents the microstructure of the hammer-shaped Fe2O3@SiO2 core-shell structure unit, e represents the microstructure of the chain-like hammer-shaped Fe3O4@SiO2@PR core-shell material, and f represents the microstructure of the chain-like hammer-shaped Fe3O4@SiO2@C core-shell material in Example 2. It can be observed that cubic seeds coated with silica synthesize a hexagonal magnetic core-shell structure; ellipsoidal seeds result in a hammer-shaped magnetic core-shell structure. Under the influence of a magnetic field, the magnetic units are forcibly assembled, as shown in Figures b and e. After forming a chain, each magnetic unit retains its original morphology, and a distinct epoxy resin coating layer can be seen on the outside. The unit morphology and chain structure remain intact after nitrogen sintering.

[0052] Figure 2 These are scanning electron microscope (SEM) images of the chain-like non-irregular Fe3O4@SiO2@C core-shell material. In the images, a represents the microstructure of a cubic Fe2O3@SiO2 core-shell structural unit; b represents the microstructure of the chain-like cubic Fe3O4@SiO2@C core-shell material in Example 1; c represents the microstructure of the chain-like cubic Fe3O4@SiO2@C core-shell material; d represents the microstructure of an ellipsoidal Fe2O3@SiO2 core-shell structural unit; e represents the microstructure of the chain-like ellipsoidal Fe3O4@SiO2@PR core-shell material; and f represents the microstructure of the chain-like ellipsoidal Fe3O4@SiO2@C core-shell material in Example 2. After high-temperature sintering, the magnetic forces between the non-irregular units increase, making aggregation more likely.

[0053] Figure 3The figure shows the X-ray diffraction (XRD) analysis of Example 1. In the figure, the (311), (400) and (440) crystal planes (JCPDS No. 72-2303) corresponding to the iron oxide component and the (002) crystal plane corresponding to the carbon component were detected in Example 1, confirming the compositional integrity of the synthesized structure.

[0054] Figure 4 (a) shows the real and imaginary parts (ε', ε”) of the complex permittivity of the chain-like hexagonal unit Fe3O4@SiO2@C core-shell material in Example 1, and (b) shows the real and imaginary parts (μ', μ”) of the complex permeability, used to reveal the mechanism of its excellent microwave absorption performance. The microwave absorption performance of the composite material mainly originates from polarization loss capability and magnetic loss. It can be found that the real part of the dielectric parameter of the chain-like hexagonal unit Fe3O4@SiO2@C core-shell material is relatively high, and the value decreases rapidly with increasing frequency, decreasing by about 1.2 from 19.8 in the range of 2.0 to 18.0 GHz; while the imaginary part of the dielectric decreases from 16.0 to 6.6. This is because the one-dimensional structure improves the conductivity of the material, and the multi-shell design constructs multiple interfaces, which can dissipate electromagnetic waves entering the material. Due to the one-dimensional linear magnetic assembly, the overall magnetism of the chain-like hexagonal unit Fe3O4@SiO2@C core-shell material is greatly increased, thereby increasing magnetic loss. The real part of the magnetic permeability of the chain-like hexagonal unit Fe3O4@SiO2@C core-shell material reaches 1.7, and the imaginary part reaches 0.3. (c) shows the real and imaginary parts (ε', ε”) of the complex permittivity of the Fe3O4@SiO2@C core-shell material with chain-shaped hammer-shaped units in Example 2. (d) shows the real and imaginary parts (μ', μ”) of the complex permeability. The real and imaginary parts of the dielectric parameters of the Fe3O4@SiO2@C core-shell material with chain-shaped hammer-shaped units are both low and change relatively slowly with frequency. There is a small peak in the imaginary part of the dielectric between 10 and 12 GHz, which may be a polarization peak caused by the abundant polarization relaxation phenomenon in the material. There is also a small peak in the imaginary part of the permeability of the Fe3O4@SiO2@C core-shell material with chain-shaped hammer-shaped units between 10 and 12 GHz, which may be caused by natural resonance. (e) shows the real and imaginary parts (ε', ε”) of the complex dielectric constant of the chain-like monogonal Fe3O4@SiO2@C core-shell material in Example 3, and (f) shows the real and imaginary parts (μ', μ”) of the complex permeability. The real and imaginary parts of the dielectric parameters of the chain-like monogonal Fe3O4@SiO2@C core-shell material are both low and change relatively slowly with frequency. There is a polarization relaxation peak in the imaginary part of the dielectric between approximately 12 GHz and 16 GHz. The imaginary part of the permeability of the chain-like monogonal Fe3O4@SiO2@C core-shell material also has two magnetic resonance peaks between approximately 12 GHz and 16 GHz, which may be caused by natural resonance.

[0055] Figure 5 They are respectively:

[0056] (a) The reflection loss of the chain-like hexagonal unit Fe3O4@SiO2@C core-shell material in Example 1 in the frequency range of 2.0-18.0 GHz was found to be -12.4 dB at 14.4 GHz when the thickness is 1.5 mm; when the thickness is 3 mm, the effective absorption efficiency at low frequency reaches 68.4%, which can cover 74% of the S-C band.

[0057] (b) The reflection loss of the chain-shaped hammer-shaped unit Fe3O4@SiO2@C core-shell material in Example 2 in the frequency range of 2.0-18.0GHz was found to be -11.6dB at 17.9GHz at a thickness of 1.5mm and -37.4dB at 16.8GHz at a thickness of 5.0mm.

[0058] (c) The reflection loss of the chain-like monoangular Fe3O4@SiO2@C core-shell material in Example 3 in the frequency range of 2.0-18.0 GHz was found to be -8.3 dB at 17.9 GHz at a thickness of 1.5 mm and -26.8 dB at 17.6 GHz at a thickness of 4.5 mm.

[0059] In summary, the chain-like Fe3O4@SiO2@C core-shell material of this invention exhibits excellent electromagnetic wave loss capability in the low-frequency range of electromagnetic waves. This invention employs an external magnetic field to assemble the chain, controlling the morphology of the chain units to modulate the dielectric and magnetic properties. With a thickness of 3 mm, an absorption efficiency of over 68.4% can be achieved in the 3.54-8.0 GHz frequency range. Therefore, it has promising application prospects in the field of low-frequency absorption.

Claims

1. A method for preparing a chain-like irregular Fe3O4@SiO2@C core-shell material, characterized in that, The specific steps are as follows: S1. Dissolve polyvinylpyrrolidone in pentanol, then add iron oxide aqueous dispersion, sodium citrate aqueous solution, ammonia, anhydrous ethanol, and tetraethyl orthosilicate in sequence. Shake well and let stand in an oven. Then centrifuge, wash, and dry to obtain irregular Fe2O3@SiO2 powder. The ratio of polyvinylpyrrolidone to pentanol is 1:(8~12) g / mL. The iron oxide is ellipsoidal and cubic in shape. The temperature of the oven is 58~62 ℃, and the standing time is 0.5~3 hours. S2. Anneal the Fe2O3@SiO2 powder obtained in step S1 under a hydrogen-argon atmosphere at a temperature of 380~420 ℃, a heating rate of 1.5~2.5 ℃ / min, and a holding time of 3.5~4.5 hours to obtain Fe3O4@SiO2 powder. S3. Place the Fe3O4@SiO2 powder obtained in step S2 into a mixed solution of water and anhydrous ethanol, then add ammonia, resorcinol, and formaldehyde, and place it in a magnetic field environment. Heat it in a water bath at a temperature of 28-32 °C for 1-3 hours. After the reaction, separate, wash, and dry to obtain chain-like Fe3O4@SiO2@PR powder coated with phenolic resin PR. S4. The Fe3O4@SiO2@PR powder obtained in step S3 is sintered under a nitrogen atmosphere to obtain a chain-like irregular Fe3O4@SiO2@C core-shell material; wherein the sintering temperature is 740~760 ℃, the heating rate is 4.5~5.5 ℃ / min, and the sintering time is 1.2~2 hours.

2. The preparation method according to claim 1, characterized in that, In step S1: The mass fraction of the iron oxide aqueous dispersion is 0.05~0.15 g / mL, and the volume ratio of the iron oxide aqueous dispersion to pentanol is 3:(800~1200). The concentration of the sodium citrate aqueous solution is (0.15~0.25) mol / L, and the volume ratio of sodium citrate aqueous solution to pentanol is 1: (80~120). The concentration of the ammonia water is 25~28 wt%, the purity of the anhydrous ethanol is ≥ 99.7%, and the volume ratios of ammonia water, anhydrous ethanol, and tetraethyl orthosilicate to pentanol are 2: (95~105), 1: (9.5~10.5), and 1: (95~105), respectively.

3. The preparation method according to claim 1, characterized in that, The hydrogen concentration in the hydrogen-argon atmosphere described in step S2 is 4% to 6%.

4. The preparation method according to claim 1, characterized in that, In step S3: The purity of the anhydrous ethanol is ≥ 99.7%, and the volume ratio of anhydrous ethanol to water is 2:(0.8~1.2). The concentration of the ammonia water is 25-28 wt%, and the mass ratio of ammonia water, resorcinol, and formaldehyde is 5:(0.8~1.2):(0.8~1.2).

5. A chain-like irregular Fe3O4@SiO2@C core-shell material obtained by the preparation method according to any one of claims 1-4, the chain-like material comprising a core-shell structural unit composed of a core of iron oxide and a rod-shaped shell of silicon dioxide and a chain-like outer carbon coating layer; The iron oxide core is ellipsoidal and cubic; the heteromorphic core-shell monomers are hammer-shaped and hexagonal, respectively.

6. The application of the chain-like irregular Fe3O4@SiO2@C core-shell material as described in claim 5 in the field of microwave absorption.

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