Cobalt ferrite-loaded nitrogen-sulfur-doped porous carbon composite material as well as preparation method and application thereof

Abstract

The invention discloses a cobalt ferrite-loaded nitrogen-sulfur-doped porous carbon composite material and a preparation method and application thereof, and belongs to the technical field of electromagnetic wave absorbing materials. Honeycomb nitrogen-sulfur-doped porous carbon is used as a lossy material matrix, and two-dimensional metal hydroxide containing FeCo metal cations is synthesized on the surface of the lossy material matrix through in-situ growth; and performing high-temperature pyrolysis in an inert atmosphere to synchronously obtain bimetallic nano magnetic particles formed by pyrolyzing the bimetallic hydroxide, thereby preparing the magnetic porous carbonaceous composite material of FeCo magnetic particle loaded honeycomb nitrogen-sulfur doped porous carbon. The micro / nano hierarchical structure formed by the bimetallic magnetic nanoparticles and the hierarchical porous structure ensures the lightweight characteristic of the composite material, and strong magnetic loss is introduced by adding the magnetic component. The invention provides a new design thought for preparing the broadband strong-loss electromagnetic wave absorbing material by combining the double-metal hydroxide derived magnetic nanoparticles and the porous carbon material.

Description

Technical Field

[0001] The present invention relates to the technical field of electromagnetic wave absorbing materials, and particularly relates to a cobalt ferrite supported nitrogen and sulfur doped porous carbon composite material, a preparation method thereof and an application thereof. Background Art

[0002] Electromagnetic wave pollution is a by-product of the rapid development of electronic devices and radio communication technologies. It not only threatens the security of the national defense system, but also threatens human life and health. In addition, it will interfere with the normal operation of precision instrument equipment. In addition to the requirement of broadband absorption effect, high-performance electromagnetic wave absorbing materials also put forward the requirements of light weight and strong loss. Therefore, it is necessary to precisely control the material system selection and microstructure design of the wave-absorbing material in multiple dimensions. Previously, the research group explored a porous carbon-based wave-absorbing material with ultra-light weight and multiple active sites in terms of material matrix selection. Its performance is superior to that of common magnetic metals, their oxides, ferrites and other traditional wave-absorbing materials. Due to the characteristics of low density and low-cost preparation, the aforementioned porous carbon-based wave-absorbing material has become a preferred material matrix for developing light-weight broadband wave-absorbing materials. In terms of material structure, screening or designing special microstructures such as hollow structures, core-shell structures, and porous structures has a significant effect on reducing the material density.

[0003] The loss types of electromagnetic waves mainly include dielectric loss, conductive loss and magnetic loss. At present, the common preparation strategy for wave-absorbing materials is to compound materials with different loss types, which can enable the wave-absorbing material to obtain a magnetic-electric synergistic loss mechanism at the heterogeneous interface, and greatly optimize the loss ability of the material internal to electromagnetic waves. Electric loss wave-absorbing materials are divided into two categories: resistive loss wave-absorbing materials and dielectric loss wave-absorbing materials, including carbon-based materials such as graphene, carbon nanotubes, and carbon fibers. Carbon-based composite materials have always been considered potential candidate materials for high-performance electromagnetic wave absorbing materials due to their synergistic loss mechanism and diverse composition and microstructure design. Carbon fibers, graphene and other carbon materials have become ideal candidate materials for microwave absorbing materials due to their tunable dielectric properties, good composite properties, low density and good chemical stability. Among them, porous carbon materials such as foam graphene, hierarchical porous carbon, and mesoporous carbon hollow spheres have also been studied due to their low density and large specific surface area.

[0004] Existing absorbing materials can often only show good absorption effects within a specific frequency band, and it is difficult to achieve broadband electromagnetic wave absorption, which limits the wide applicability of the materials in practical applications, especially in application scenarios that need to cover multiple frequency bands, such as 5G communications, radar stealth, etc. Although traditional magnetic materials, such as ferrites, have good magnetic loss performance, their density is high and it is difficult to meet the demand for lightweight materials in modern electronic devices. Although lightweight carbon-based materials have low density, their magnetic loss capacity is weak, making it difficult to achieve efficient electromagnetic wave absorption. The performance of electromagnetic wave absorbing materials depends not only on their loss capacity, but also on their impedance matching characteristics with free space. Existing materials often have deficiencies in impedance matching, which causes electromagnetic waves to be reflected on the surface of the material, reducing the absorption efficiency. Summary of the invention

[0005] The present invention provides a cobalt ferrite-loaded nitrogen-sulfur-doped porous carbon composite material, and a preparation method and application thereof. The present invention introduces layered double hydroxide (FeCo) magnetic nanoparticles into a nitrogen-sulfur-doped porous carbon matrix to achieve a synergistic effect of magnetic loss and dielectric loss, significantly improve the broadband absorption performance of the material, and effectively solve the technical problems of the existing materials that cannot balance light weight and strong magnetic loss and insufficient impedance matching.

[0006] The present invention provides a method for preparing a cobalt ferrite-loaded nitrogen-sulfur-doped porous carbon composite material, comprising the following steps:

[0007] With nitrogen-sulfur doped porous carbon as a matrix, soluble iron salt and soluble cobalt salt undergo hydrothermal reaction under the action of 2-methylimidazole, and iron-cobalt double hydroxide nanosheets are in situ grown on the surface of the nitrogen-sulfur doped porous carbon to obtain a composite precursor. Under a protective atmosphere, the composite precursor is heated to 700° C. to 900° C., annealed, and the iron-cobalt double hydroxide is converted into cobalt ferrite to obtain a cobalt ferrite-loaded nitrogen-sulfur doped porous carbon composite material.

[0008] As a preferred embodiment, based on the mass of the cobalt ferrite-loaded nitrogen-sulfur-doped porous carbon composite material, the loading amount of the cobalt ferrite is 4.5% to 6.5%.

[0009] As a preferred embodiment, the molar ratio of the soluble iron salt to the soluble cobalt salt is 1-3:1-3.

[0010] As a preferred implementation, the mass ratio of the nitrogen-sulfur doped porous carbon to 2-methylimidazole is 1:4-5.

[0011] As a preferred embodiment, the temperature of the hydrothermal reaction is 100°C to 120°C.

[0012] As a preferred implementation manner, the annealing time is 1.5h to 3h.

[0013] As a preferred embodiment, the preparation method of the nitrogen and sulfur co-doped porous carbon comprises the following steps: under a protective atmosphere, sodium citrate dihydrate and thioacetamide are heated to 550 °C - 650 °C at a heating rate of 2 °C / min to 5 °C / min, annealed for 1.5 h - 2.5 h, and cooled to room temperature to obtain a primary product. The primary product is etched in a hydrochloric acid solution and freeze-dried to obtain the nitrogen and sulfur co-doped porous carbon.

[0014] As a preferred embodiment, the heating rate is 3 °C / min to 5 °C / min, and the protective atmosphere is an argon atmosphere.

[0015] The second object of the present invention is to provide a cobalt ferrite supported nitrogen and sulfur co-doped porous carbon composite material prepared by the above preparation method.

[0016] The third object of the present invention is to provide an application of the above cobalt ferrite supported nitrogen and sulfur co-doped porous carbon composite material in the preparation of an electromagnetic wave absorbing material.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0018] The present invention provides a preparation method of a cobalt ferrite supported nitrogen and sulfur co-doped porous carbon composite material. Using the nitrogen and sulfur co-doped porous carbon as a matrix, cobalt-iron double metal hydroxide nanosheets are in-situ grown on the surface of the nitrogen and sulfur co-doped porous carbon to obtain a composite precursor. Under a protective atmosphere, the composite precursor is heated and annealed to obtain the cobalt ferrite supported nitrogen and sulfur co-doped porous carbon composite material. The present invention uses honeycomb-like nitrogen and sulfur co-doped porous carbon (NSC) as a lossy material matrix, and in-situ synthesizes two-dimensional metal hydroxides containing FeCo metal cations on its surface. Then, through high-temperature pyrolysis under an inert atmosphere, double metal nano-magnetic particles formed by the pyrolysis of the double metal hydroxide are simultaneously obtained, thereby preparing a magnetic porous carbonaceous composite material with FeCo magnetic particles supported on honeycomb-like nitrogen and sulfur co-doped porous carbon. The micro / nano hierarchical structure composed of double metal magnetic nanoparticles and multi-level pore structures ensures the light weight characteristics of the composite material, and the addition of magnetic components introduces strong magnetic loss, thereby improving the electromagnetic wave absorption performance of the composite material. The present invention provides a new design idea for the preparation of broadband and strong loss electromagnetic wave absorbing materials by combining double metal hydroxide-derived magnetic nanoparticles with porous carbon materials. The cobalt ferrite supported nitrogen and sulfur co-doped porous carbon composite material prepared by the present invention realizes efficient electromagnetic wave absorption in a wide frequency band, and at the same time has the characteristics of light weight, strong loss and good impedance matching.

[0019] The present invention introduces an interconnected porous structure into a carbon template through a simple etching technique. The pores generate a large number of carrier donors, thereby improving conductivity and enhancing the ability of the composite material to conduct electromagnetic wave losses, enabling the absorbing material to achieve strong broadband absorption in a thin layer state. Description of the Drawings

[0020] Figure 1 It is a scanning electron microscope image of the cobalt ferrite supported nitrogen and sulfur doped porous carbon composite material of Example 1 of the present invention. Among them, the scale of Figure (a) is 2μm, the scale of Figure (b) is 500nm, the scale of Figure (c) is 100nm, Figure (d) is, Figure (e) is, Figure (f) is the C element mapping diagram, Figure (g) is the O element mapping diagram, Figure (h) is the N element mapping diagram, Figure (i) is the S element mapping diagram, Figure (j) is the Fe element mapping diagram, and Figure (k) is the Co element mapping diagram.

[0021] Figure 2 It is a micrograph of the cobalt ferrite supported nitrogen and sulfur doped porous carbon composite material of Example 1 of the present invention. Among them, Figures (a) and (b) are transmission electron microscope images, Figures (c) to (e) are high-resolution transmission electron microscope images, and Figure (f) is a selected area electron diffraction image.

[0022] Figure 3 It is a scanning electron microscope image of the cobalt ferrite supported nitrogen and sulfur doped porous carbon composite material of Example 2 of the present invention. Among them, the scale of Figure (a) is 2μm, the scale of Figure (b) is 500nm, the scale of Figure (c) is 100nm, Figure (d) is, Figure (e) is, Figure (f) is the C element mapping diagram, Figure (g) is the O element mapping diagram, Figure (h) is the N element mapping diagram, Figure (i) is the S element mapping diagram, Figure (j) is the Fe element mapping diagram, and Figure (k) is the Co element mapping diagram.

[0023] Figure 4 It is a micrograph of the cobalt ferrite supported nitrogen and sulfur doped porous carbon composite material of Example 2 of the present invention. Among them, Figures (a) and (b) are transmission electron microscope images, Figures (c) to (e) are high-resolution transmission electron microscope images, and Figure (f) is a selected area electron diffraction image.

[0024] Figure 5 It is a scanning electron microscope image of the cobalt ferrite supported nitrogen and sulfur doped porous carbon composite material of Example 3 of the present invention. Among them, the scale of Figure (a) is 2μm, the scale of Figure (b) is 500nm, the scale of Figure (c) is 100nm, Figure (d) is, Figure (e) is, Figure (f) is the C element mapping diagram, Figure (g) is the O element mapping diagram, Figure (h) is the N element mapping diagram, Figure (i) is the S element mapping diagram, Figure (j) is the Fe element mapping diagram, and Figure (k) is the Co element mapping diagram.

[0025] Figure 6Micrograph of the cobalt ferrite supported nitrogen and sulfur doped porous carbon composite material of Embodiment 3 of the present invention, wherein, Figures (a) and (b) are transmission electron microscope images, Figures (c)-(e) are high-resolution transmission electron microscope images, and Figure (f) is a selected area electron diffraction image.

[0026] Figure 7 Spectra of the cobalt ferrite supported nitrogen and sulfur doped porous carbon composite materials of Embodiments 1-3 of the present invention, wherein, Figure (a) is an X-ray diffraction spectrum, Figure (b) is a Raman spectrum, Figure (c) is a nitrogen adsorption-desorption curve, and Figure (d) is a pore size distribution curve.

[0027] Figure 8 X-ray photoelectron spectroscopy (XPS) spectra of the cobalt ferrite supported nitrogen and sulfur doped porous carbon composite materials of Embodiments 1-3 of the present invention, wherein, Figure (a) is the full spectrum, Figure (b) is C1s, Figure (c) is N 1s, Figure (d) is S 2p, Figure (e) is Co2p, and Figure (f) is Fe 2p.

[0028] Figure 9 Hysteresis loop diagram of the cobalt ferrite supported nitrogen and sulfur doped porous carbon composite materials of Embodiments 1-3 of the present invention.

[0029] Figure 10 Dielectric and magnetic loss performance diagrams of the cobalt ferrite supported nitrogen and sulfur doped porous carbon composite materials of Embodiments 1-3 of the present invention, wherein, Figure (a) is a comparison diagram of the real part of the dielectric constant, Figure (b) is a comparison diagram of the imaginary part of the dielectric constant, Figure (c) is a dielectric loss tangent diagram, Figure (d) is a comparison diagram of the real part of the magnetic permeability, Figure (e) is a comparison diagram of the imaginary part of the magnetic permeability, and Figure (f) is a magnetic loss tangent diagram.

[0030] Figure 11 Corresponding relationship between the reflection loss (RL) curve and the matching thickness of the cobalt ferrite supported nitrogen and sulfur doped porous carbon composite material of Embodiment 1 of the present invention, wherein, Figure (a) is 5 wt%, Figure (b) is 10 wt%, and Figure (c) is 15 wt%.

[0031] Figure 12 Three-dimensional and corresponding two-dimensional reflection loss diagrams of the cobalt ferrite supported nitrogen and sulfur doped porous carbon composite material of Embodiment 1 of the present invention, wherein, Figures (a) and (d) are 5 wt%, Figures (b) and (e) are 10 wt%, and Figures (c) and (f) are 15 wt%.

[0032] Figure 13 Corresponding relationship between the reflection loss (RL) curve and the matching thickness of the cobalt ferrite supported nitrogen and sulfur doped porous carbon composite material of Embodiment 2 of the present invention, wherein, Figure (a) is 5 wt%, Figure (b) is 10 wt%, and Figure (c) is 15 wt%.

[0033] Figure 14 These are the three-dimensional and corresponding two-dimensional reflection loss diagrams of the cobalt ferrite supported nitrogen and sulfur co-doped porous carbon composite material of Embodiment 2 of the present invention. Among them, Figures (a) and (d) are for 5 wt%, Figures (b) and (e) are for 10 wt%, and Figures (c) and (f) are for 15 wt%.

[0034] Figure 15 This is the correspondence between the reflection loss (RL) curve and the matching thickness of the cobalt ferrite supported nitrogen and sulfur co-doped porous carbon composite material of Embodiment 3 of the present invention. Among them, Figure (a) is for a mass percentage of 5 wt%, Figure (b) is for a mass percentage of 10 wt%, and Figure (c) is for a mass percentage of 15 wt%.

[0035] Figure 16 These are the three-dimensional and corresponding two-dimensional reflection loss diagrams of the cobalt ferrite supported nitrogen and sulfur co-doped porous carbon composite material of Embodiment 3 of the present invention. Among them, Figures (a) and (d) are for 5 wt%, Figures (b) and (e) are for 10 wt%, and Figures (c) and (f) are for 15 wt%. Detailed implementation manners

[0036] In order to enable those skilled in the art to better understand and implement the technical solutions of the present invention, the present invention will be further described below in conjunction with specific embodiments and the accompanying drawings. However, the specific embodiments cited shall not be construed as limitations on the present invention. The following test methods and detection methods are all conventional methods unless otherwise specified; the reagents and raw materials are all commercially available unless otherwise specified.

[0037] Regarding the problems proposed in the background art of the present invention: First, existing microwave absorbing materials often can only exhibit good absorption effects within a specific frequency band and it is difficult to achieve broadband electromagnetic wave absorption. Second, traditional magnetic materials cannot balance light weight and strong magnetic loss performance. Third, existing electromagnetic wave absorbing materials often have deficiencies in impedance matching, resulting in reflection of electromagnetic waves on the material surface and reducing the absorption efficiency. Fourth, existing microwave absorbing materials are difficult to achieve the synergistic effect of multiple loss mechanisms, resulting in limited overall absorption performance. Based on the above problems, the present invention provides a cobalt ferrite supported nitrogen and sulfur co-doped porous carbon composite material and its preparation method and application.

[0038] The technical solutions of the present invention will be analyzed and described below.

[0039] The present invention provides a preparation method for a cobalt ferrite supported nitrogen and sulfur co-doped porous carbon composite material, comprising the following steps:

[0040] Preparation of nitrogen-sulfur doped porous carbon: Under a protective atmosphere, sodium citrate dihydrate and thioacetamide are heated to 550°C to 650°C at a heating rate of 2°C / min to 5°C / min, annealed for 1.5h to 2.5h, and cooled to room temperature to obtain a primary product. The primary product is etched in a hydrochloric acid solution, and freeze-dried to obtain nitrogen-sulfur doped porous carbon.

[0041] Preparation of cobalt ferrite-loaded nitrogen-sulfur-doped porous carbon composite material: dissolving soluble iron salt and soluble cobalt salt in anhydrous methanol and deionized water in a molar ratio of 1 to 3:1 to 3 to obtain solution A; adding the nitrogen-sulfur-doped porous carbon and 2-methylimidazole to a mixed solvent of anhydrous methanol and deionized water, and ultrasonically dispersing to obtain dispersion B; mixing solution A and dispersion B, mechanically stirring, and hydrothermally reacting at 100° C. to 120° C. to obtain a primary product, and using anhydrous methanol to heat the primary product The mixture is thoroughly washed three times with deionized water and dried to obtain a black powder, i.e., a composite precursor. The composite precursor is heated to 700-900°C in an argon atmosphere at a rate of 3°C / min-5°C / min, and annealed for 1.5h-3h to convert the iron-cobalt double hydroxide into cobalt ferrite to obtain a cobalt ferrite-loaded nitrogen-sulfur-doped porous carbon composite material. The loading amount of cobalt ferrite is 4.5%-6.5% based on the mass of the cobalt ferrite-loaded nitrogen-sulfur-doped porous carbon composite material.

[0042] In the above technical solution, by introducing layered double hydroxide (FeCo) magnetic nanoparticles into the nitrogen-sulfur doped porous carbon matrix, the synergistic effect of magnetic loss and dielectric loss is achieved, which significantly improves the wide-band absorption performance of the material and effectively solves the technical problems of existing materials that cannot balance light weight and strong magnetic loss and insufficient impedance matching.

[0043] The technical effects of the present invention are described below through specific embodiments.

[0044] Example 1

[0045] The preparation method of the cobalt ferrite-loaded nitrogen-sulfur-doped porous carbon composite material comprises the following steps:

[0046] S1, preparation of nitrogen-sulfur doped porous carbon: under a protective atmosphere, 5 g of sodium citrate dihydrate and 0.8 g of thioacetamide were heated to 600° C. at a heating rate of 5° C. / min, annealed for 2 h, and cooled to room temperature to obtain a primary product, which was etched in a hydrochloric acid solution and freeze-dried to obtain nitrogen-sulfur doped porous carbon.

[0047] S2. Preparation of cobalt ferrite supported nitrogen and sulfur co-doped porous carbon composite: Dissolve Fe(NO3)3·9H2O and Co(NO3)2·6H2O with a molar ratio of 1:1 in 30 mL of anhydrous methanol and 10 mL of deionized water to obtain solution A; according to a mass ratio of 1:5, add the nitrogen and sulfur co-doped porous carbon and 2-methylimidazole to a mixed solvent of 30 mL of anhydrous methanol and 10 mL of deionized water, and ultrasonically disperse for 30 min to obtain dispersion B; mix solution A and dispersion B, mechanically stir for 30 min, carry out hydrothermal reaction at 100 °C for 4 h to obtain a primary product, wash the primary product thoroughly three times with anhydrous methanol and deionized water, dry at 80 °C for 12 h to obtain a black powder, that is, obtain a composite precursor, in an argon atmosphere, heat the composite precursor to 800 °C at a rate of 5 °C / min, and anneal for 2 h to convert the iron-cobalt double metal hydroxide into cobalt ferrite, thereby obtaining the cobalt ferrite supported nitrogen and sulfur co-doped porous carbon composite.

[0048] Example 2

[0049] A preparation method of cobalt ferrite supported nitrogen and sulfur co-doped porous carbon composite, comprising the following steps:

[0050] S1. Preparation of nitrogen and sulfur co-doped porous carbon: Under a protective atmosphere, heat 5 g of sodium citrate dihydrate and 0.8 g of thioacetamide to 600 °C at a heating rate of 5 °C / min, carry out annealing treatment for 2 h, and cool to room temperature to obtain a primary product. Etch the primary product in a hydrochloric acid solution and freeze-dry to obtain the nitrogen and sulfur co-doped porous carbon.

[0051] S2. Preparation of cobalt ferrite supported nitrogen and sulfur co-doped porous carbon composite: Dissolve Fe(NO3)3·9H2O and Co(NO3)2·6H2O with a molar ratio of 1:3 in 30 mL of anhydrous methanol and 10 mL of deionized water to obtain solution A; according to a mass ratio of 1:5, add the nitrogen and sulfur co-doped porous carbon and 2-methylimidazole to a mixed solvent of 30 mL of anhydrous methanol and 10 mL of deionized water, and ultrasonically disperse for 30 min to obtain dispersion B; mix solution A and dispersion B, mechanically stir for 30 min, carry out hydrothermal reaction at 100 °C for 4 h to obtain a primary product, wash the primary product thoroughly three times with anhydrous methanol and deionized water, dry at 80 °C for 12 h to obtain a black powder, that is, obtain a composite precursor, in an argon atmosphere, heat the composite precursor to 800 °C at a rate of 5 °C / min, and anneal for 2 h to convert the iron-cobalt double metal hydroxide into cobalt ferrite, thereby obtaining the cobalt ferrite supported nitrogen and sulfur co-doped porous carbon composite.

[0052] Example 3

[0053] A preparation method of cobalt ferrite supported nitrogen and sulfur co-doped porous carbon composite, comprising the following steps:

[0054] S1. Preparation of nitrogen and sulfur co-doped porous carbon: Under a protective atmosphere, 5 g of sodium citrate dihydrate and 0.8 g of thioacetamide were heated to 600 °C at a heating rate of 5 °C / min, annealed for 2 h, and cooled to room temperature to obtain a primary product. The primary product was etched in a hydrochloric acid solution and freeze-dried to obtain nitrogen and sulfur co-doped porous carbon.

[0055] S2. Preparation of cobalt ferrite supported on nitrogen and sulfur co-doped porous carbon composite: Fe(NO3)3·9H2O and Co(NO3)2·6H2O with a molar ratio of 3:1 were dissolved in 30 mL of anhydrous methanol and 10 mL of deionized water to obtain solution A; according to a mass ratio of 1:5, the nitrogen and sulfur co-doped porous carbon and 2-methylimidazole were added to a mixed solvent of 30 mL of anhydrous methanol and 10 mL of deionized water, and ultrasonically dispersed for 30 min to obtain dispersion B; solution A and dispersion B were mixed, mechanically stirred for 30 min, and hydrothermally reacted at 100 °C for 4 h to obtain a primary product. The primary product was washed three times with anhydrous methanol and deionized water and dried at 80 °C for 12 h to obtain a black powder, i.e., a composite precursor. Under an argon atmosphere, the composite precursor was heated to 800 °C at a rate of 5 °C / min and annealed for 2 h to convert the iron-cobalt double metal hydroxide into cobalt ferrite, obtaining a cobalt ferrite supported on nitrogen and sulfur co-doped porous carbon composite.

[0056] The performance of the cobalt ferrite supported on nitrogen and sulfur co-doped porous carbon composite provided in the above examples and comparative examples was tested, and the results are as follows.

[0057] As Figures 1 - 2 shown, high-resolution transmission electron microscopy and field emission scanning electron microscopy were used to characterize the microscopic morphology of the in-situ growth of bimetallic nanoparticles on the surface of honeycomb porous carbon after high-temperature pyrolysis. As Figure 1 shown in the SEM images, when Fe 3+ :Co 2+ = 1:1, a small amount of nanoparticles adhered to the surface of the porous carbon matrix, indicating that the bimetallic nanoparticles at a 1:1 ratio failed to achieve uniform growth in the carbon matrix. Energy dispersive spectrometer (EDS) was used to detect the element distribution in the composite material. As Figure 1 shown in the figures (d)-(k) in Figure 2 Six elements, C, N, O, S, Fe, and Co, could be detected in Figure 2As shown in Figures (c) to (e), three crystal planes with lattice spacings (0.253 nm, 0.201 nm, and 0.332 nm) were observed for the nanoparticle clusters loaded in the porous carbon matrix, corresponding to the (311) crystal plane of CoFe2O4, the (110) crystal plane of Fe 0.5 Co 0.5 and the (002) crystal plane of C. In addition, in the selected area electron diffraction pattern (SAED) of the sample, multiple bright and distinct diffraction rings could be clearly observed. Measured from the inside out, they corresponded to the (002) crystal plane of C, the (311) crystal plane of CoFe2O4, and the (110) crystal plane of Fe 0.5 Co 0.5 respectively. From the continuity and brightness of the diffraction rings, it could be preliminarily judged that the composite particles inside the sample all existed in the form of polycrystals and had good crystallinity. The measurement results of SAED corresponded to those of HRTEM, proving the existence of the crystal structures of Fe 0.5 Co 0.5 , CoFe2O4, and C in the sample.

[0058] Figure 3 Figure (a) to (c) of [ID] shows the SEM image of the sample. When Fe 3+ :Co 2+ = 3:1, large-area agglomeration of the bimetallic nanoparticles occurred, and obvious coverage of the bimetallic nanoparticle agglomerates appeared on the porous carbon matrix. In addition, the nanoparticle agglomerates showed regional attachment, making the components of the composite material non-uniform. Through EDS mapping detection, six elements, namely C, N, O, S, Fe, and Co, could be detected in [ID]. Among them, the signals of Fe and Co elements were more obvious than those of the cobalt ferrite-loaded nitrogen and sulfur-doped porous carbon composite material in Example 1, as shown in Figure 3 Figures (d) to (k) of [ID].

[0059] Figure 4 Figures (a) to (c) of [ID] show the TEM image. It can be observed that obvious and morphologically non-uniform nanoclusters formed by nanoparticle agglomeration adhered to the carbon material. Compared with the sample of the cobalt ferrite-loaded nitrogen and sulfur-doped porous carbon composite material in Example 1, there were more nanoparticle clusters, as shown in Figure 4 Figures (d) to (e) of [ID]. Through the HRTEM image, two crystal planes with lattice spacings (0.250 nm and 0.330 nm) were observed for the irregular nanoparticle clusters loaded in the porous carbon matrix, corresponding to the (331) crystal plane of CoFe2O4 and the (002) crystal plane of C respectively. In Figure 4In the SAED pattern of the sample in Figure (f), several bright and clear diffraction rings can be clearly observed in the inner circle. After measurement, they correspond to the (002) crystal plane of C and the (311) crystal plane of CoFe2O4 from the inside to the outside. Compared with the diffraction rings of the cobalt ferrite supported nitrogen and sulfur doped porous carbon composite material sample in Example 1, they are relatively darker, indicating that the overall crystal condition of the material is poorer. The large-area agglomeration of nanoparticles in the sample microstructure may lead to the formation of a continuous conductive network in the composite material, restricting the dissipation effect of the porous structure on electromagnetic waves, resulting in the generation of a higher dielectric constant and thus weakening the impedance matching performance of the material.

[0060] As Figure 5 shown in the SEM image of the sample, when Fe 3+ :Co 2+ = 1:3, magnetic nanoparticles with uniform particle sizes successfully grow on the surface of the porous carbon matrix, and their average particle size is about 80 nm to 100 nm. It can be clearly observed in the figure that the nanoparticles are evenly distributed in the macropore structure, ensuring the retention of the hierarchical pore structure. Through EDS mapping detection, the uniform distribution of six elements C, N, O, S, Fe, and Co can be detected in it, as shown in Figures (d) to (k) in Figure 5 . From Figure 6 Figures (a) and (b), it can be clearly observed that spherical bimetallic nanoparticles with obvious shapes are evenly attached to the surface of the matrix, which can generate a large number of heterojunctions, facilitating the formation of heterointerfacial polarization and further optimizing the electromagnetic wave loss.

[0061] Through HRTEM images, as shown in Figures (c) to (e) in Figure 6 , three crystal planes with crystal plane spacings (0.252 nm, 0.201 nm, and 0.330 nm) are observed for the nanoparticles loaded in the porous carbon matrix, corresponding to the (311) crystal plane of CoFe2O4, the (110) crystal plane of FeCo, and the (002) crystal plane of C respectively. In addition, in the SAED pattern of the sample, multiple bright diffraction rings can be clearly observed. After measurement, they correspond to the (002) crystal plane of C, the (311) crystal plane of CoFe2O4, and the (110) crystal plane of FeCo from the inside to the outside, proving that the sample exists in a polycrystalline form inside and has the crystal structures of CoFe2O4, metallic FeCo, and graphite carbon.

[0062] XRD was used to characterize the crystal structures and chemical compositions of the series of cobalt ferrite supported nitrogen and sulfur doped porous carbon composite material samples in Examples 1 to 3, as shown in Figure 7As shown in Figure (a), for the series of cobalt ferrite supported nitrogen and sulfur doped porous carbon composite materials in Examples 1 to 3, the weak broad peak located at about 2θ = 26.3° belongs to the (110) lattice plane of carbon (C#41-1487). Since the porous carbon matrix is basically a disordered graphite carbon lattice structure, the corresponding diffraction peak intensity is significantly lower. From the XRD pattern of the cobalt ferrite supported nitrogen and sulfur doped porous carbon composite material sample in Example 1, it can also be observed that seven obvious diffraction peaks appear at 2θ = 18.27°, 30.06°, 35.41°, 43.03°, 53.39°, 56.91° and 62.49°, respectively corresponding to the (Co 0.2 Fe 0.8 )Co 0.8 Fe 1.2 O4 (JCPDS#97-003-9131) of the (111), (220), (311), (400), (422), (511) and (440) crystal planes. Among them, the diffraction peak with the strongest signal appears at 2θ = 35.41° corresponding to the (Co 0.2 Fe 0.8 )Co 0.8 Fe 1.2 O4 of the (311) crystal plane, which is consistent with the result of measuring its lattice fringes in HRTEM. From the XRD pattern of the cobalt ferrite supported nitrogen and sulfur doped porous carbon composite material sample in Example 3, it can be observed that eight obvious diffraction peaks appear at 2θ = 18.33°, 30.15°, 35.52°, 37.15°, 43.17°, 53.56°, 57.1° and 62.7°, respectively corresponding to the (Co 0.15 Fe 0.85 )(Co 0.85 Fe 1.15 )O4 (JCPDS#97-016-0059) of the (111), (220), (311), (222), (400), (422), (511) and (440) crystal planes. Among them, the diffraction peak with the strongest signal appears at 2θ = 35.52° corresponding to the (Co 0.2 Fe 0.8 )Co 0.8 Fe 1.2 O4 of the (311) crystal plane, which is consistent with the measurement result of HRTEM. At the same time, from the XRD pattern of the cobalt ferrite supported nitrogen and sulfur doped porous carbon composite material sample in Example 3, it is observed that eight obvious diffraction peaks appear at 2θ = 18.278°, 30.066°, 35.413°, 37.043°, 43.038°, 53.391°, 56.914° and 62.496°, respectively corresponding to Fe(Co 1.02 Fe 0.98) (111), (220), (311), (222), (400), (422), (511) and (440) crystal planes of O4 (JCPDS#97 - 018 - 8640), where the diffraction peak with the strongest signal appears at 2θ = 35.413°, corresponding to the (311) crystal plane of Fe(Co 1.02 Fe 0.98 )O4, which is consistent with the measurement results of HRTEM. The slight differences in the diffraction peak positions among the three samples are mainly due to the different proportions of Fe 3+ and Co 2+ ions, which will lead to different spatial distributions and coordination environments of metal ions in the product.

[0063] The graphitization degree of carbon materials is crucial for dielectric loss. Therefore, Raman spectroscopy was used to study the graphitization degree of the series of samples of cobalt ferrite - loaded nitrogen - sulfur - doped porous carbon composites in Examples 1 to 3. Figure 7 Figure (b) shows two diffraction peaks at approximately 1341 cm -1 and 1593 cm -1 , corresponding to the D band and G band of the three samples respectively. The intensity ratios (I D / I G ) of the cobalt ferrite - loaded nitrogen - sulfur - doped porous carbon composite samples in Examples 1 to 3 are 2.018, 2.094 and 2.401 respectively. The results show that when the proportion of Fe 3+ and Co 2+ changes and the nanoparticles are unevenly dispersed, the local high particle concentration will form stress concentration areas in the carbon matrix, destroying the crystal order of the carbon material and resulting in a decrease in the graphitization degree. While the cobalt ferrite - loaded nitrogen - sulfur - doped porous carbon composite in Example 2 with a uniform distribution has the highest I D / I G , indicating a higher graphitization degree. At the same time, metal nanoparticles catalyze the rearrangement of carbon atoms at high temperatures, promoting the transformation of the disordered carbon structure into an ordered graphite structure, and the graphitization degree is significantly improved compared to the carbon matrix N / S - HPC. In addition, we also characterized the SSA and pore size distribution characteristics of the series of samples of cobalt ferrite - loaded nitrogen - sulfur - doped porous carbon composites in Examples 1 to 3 by BET. In Figure 7 Figure (c), all samples show typical type - IV isotherms, indicating the presence of mesoporous structures. The SSAs of the cobalt ferrite - loaded nitrogen - sulfur - doped porous carbon composites in Examples 1 to 3 are 185.2456 m 2 / g, 203.3695 m 2 / g and 126.857 m 2 / g respectively, and the total pore volumes are 0.3378 cm 3 / g, 0.2555 cm 3 / g and 0.1991 cm 3 / g. The pore size and average pore size of the cobalt ferrite supported nitrogen and sulfur doped porous carbon composite material of Example 1 are both larger than those of other samples. The total pore volume and average pore size of the cobalt ferrite supported nitrogen and sulfur doped porous carbon composite material of Example 3 are the smallest, as shown in Figure 7 Figure (d) of

[0064] The elemental composition and chemical state of the cobalt ferrite supported nitrogen and sulfur doped porous carbon composite materials of Examples 1 to 3 were determined by XPS. In Figure 8 the XPS survey spectrum of Figure (a), six characteristic peaks of C1s, N1s, O 1s, S 2p, Fe 2p and Co2p were detected, indicating that six elements of C, N, O, S, Fe and Co exist in all three materials. In the C1s spectra of the cobalt ferrite supported nitrogen and sulfur doped porous carbon composite materials of Examples 1 to 3, as shown in Figure 8 Figure (b), there are four characteristic peaks at ~284.8 eV, 286.1 eV, 287.09 eV and 288.9 eV, which can correspond to C-C / C═C, C-O, C-N and C═O / COOH bonds respectively. As shown in Figure 8 Figure (c), the N1s spectra of the cobalt ferrite supported nitrogen and sulfur doped porous carbon composite materials of Examples 1 to 3 detected characteristic peaks at 401.2 eV, 400.1 eV and 398.5 eV, corresponding to the characteristic peaks of graphitic N, pyrrolic N and pyridinic N respectively. It can be observed that the N1s characteristic peak of the cobalt ferrite supported nitrogen and sulfur doped porous carbon composite material of Example 2 shifts towards the higher binding energy direction. This may be because the introduction of magnetic particles causes the electrons at the interface to transfer from the N atom to the surface of the magnetic particles, resulting in a decrease in the electron density of N, a weakening of the electron environment around the N atom, an increase in the binding energy, and the N 1s peak shifting towards the higher binding energy direction. The introduction of magnetic nanoparticles affects the electron distribution around N, resulting in a slight shift in its binding energy. In the S2p spectra of the cobalt ferrite supported nitrogen and sulfur doped porous carbon composite materials of Examples 1 to 3, as shown in Figure 8 Figure (d), there are four characteristic peaks located at 163.2, 165.3, 168.4 and 169.7 eV respectively, corresponding to S2p of S-C, S═C and Co-S bonds 3 / 2 and S2p 1 / 2 , indicating that the S element exists in the composite material in the forms of C-S, C═S and Co-S. Figure 8 The Co 2p spectrum in Figure (e) of 3 / 2 shows two main peaks located at about 781.1 eV and 796.5 eV, which are attributed to Co 2p 1 / 2 and Co 2p 3+ , respectively, and there are two located at 786.8 eV and 804.5 eV, which are attributed to Co 3+ and Co2+ satellite peaks. In the Fe 2p spectrum, as shown in Figure 8 (f) of Figure 8 , the two main peaks at 711.1 eV and 724.6 eV are Fe 2p 3 / 2 and Fe 2p 1 / 2 respectively, and the satellite peak is located at 718.4 eV, indicating that the cobalt ferrite supported nitrogen and sulfur doped porous carbon composite samples of Examples 1 to 3 all contain multivalent iron ions (Fe 2+ and Fe 3 + ). From the above results, it can be concluded that the successful introduction of Fe and Co in the FC / NSC composite enriches the loss mechanism of the material, improves the magnetic loss ability of the matrix, and the constructed heterogeneous interface will provide a large number of interfacial polarizations for the material, enhancing the polarization loss.

[0065] To characterize the magnetism of the samples, the hysteresis loops of the cobalt ferrite supported nitrogen and sulfur doped porous carbon composites of Examples 1 to 3 were measured by the PPMS method. The introduction of Fe and Co magnetic particles endows the cobalt ferrite supported nitrogen and sulfur doped porous carbon composites of Examples 1 to 3 with obvious magnetism, which is beneficial to improving the magnetic loss and enriching the loss mechanism, and improving the electromagnetic wave impedance matching characteristics of the material. The initial magnetic permeability (μ i ) of the material determines its magnetic properties, and usually the saturation magnetization intensity (M s ) and coercivity (H c ) of the material are used to evaluate the magnitude of μ i of the material. The larger the M s or the smaller the H c of the material, the larger the μ i of the material. As shown in Figure 9 , the cobalt ferrite supported nitrogen and sulfur doped porous carbon composite samples of Examples 1 to 3 all have typical soft magnetic hysteresis loop characteristics. The saturation magnetization intensities of the cobalt ferrite supported nitrogen and sulfur doped porous carbon composites of Examples 1 to 3 are 22.028 emu / g, 34.645 emu / g and 16.856 emu / g respectively, and the coercivities are 86.11 Oe, 121.29 Oe and 59.15 Oe respectively. The differences in M s of the three groups of samples are mainly related to the ratio and distribution of Fe 3+ and Co 2+ . When Fe 3+ :Co 2+ = 1:3, the contribution of magnetic particles is more significant. Therefore, the M sis higher. The cobalt ferrite supported nitrogen and sulfur doped porous carbon composite materials of Example 1 and the cobalt ferrite supported nitrogen and sulfur doped porous carbon composite material samples of Example 3 may have reduced overall magnetism due to particle aggregation and uneven distribution. The H of the cobalt ferrite supported nitrogen and sulfur doped porous carbon composite material of Example 2 c is the highest, which may produce a more stable magnetic domain structure. At the same time, the cobalt ferrite supported nitrogen and sulfur doped porous carbon composite material of Example 2 has the largest remanent magnetization (M r ), indicating that the internal magnetic particles have stronger magnetic coupling effects, which will be beneficial to improving the magnetic hysteresis loss of the material and enhancing the magnetoelectric synergistic effect.

[0066] As Figure 10 shown, the electromagnetic parameter changes of the composite materials with three different ratios (the cobalt ferrite supported nitrogen and sulfur doped porous carbon composite material of Example 1, the cobalt ferrite supported nitrogen and sulfur doped porous carbon composite material of Example 2, the cobalt ferrite supported nitrogen and sulfur doped porous carbon composite material of Example 3) in the frequency range of 2 GHz to 18 GHz intuitively display the dielectric and magnetic properties of the three different samples. As Figure 10 shown in Figure (a), the electric field energy storage capacity of the material can be characterized by ε'. The ε' value of the cobalt ferrite supported nitrogen and sulfur doped porous carbon composite material of Example 2 is the highest, significantly higher than the other two ratios, reaching up to 7.26 near 2 GHz. It gradually decreases with the increase of frequency and flattens out in the high frequency band (>12 GHz), which is related to the dielectric relaxation process inside the material, indicating its strong dielectric properties. The best ability to store electric field energy is attributed to the charge transport of the porous conductive network and the heterointerface polarization. The ε' value of the cobalt ferrite supported nitrogen and sulfur doped porous carbon composite material of Example 1 is relatively low, fluctuating between 3.5 and 4.5 as a whole, and showing a slow downward trend with the increase of frequency. The ε' value of the cobalt ferrite supported nitrogen and sulfur doped porous carbon composite material of Example 3 is the lowest, fluctuating between 3.0 and 4.0 as a whole, with a relatively stable trend, indicating that the energy storage capacities of these two are relatively weak. This is due to the non-uniform distribution and microstructure of the magnetic particles in the carbon-based material, resulting in a low charge storage capacity of the material. As Figure 10As shown in Figure (b) of , the cobalt ferrite supported nitrogen and sulfur doped porous carbon composite of Example 2 has an ε″ value significantly higher than that of other samples, especially prominent in the low frequency band (2 GHz - 6 GHz), and then gradually decreases towards the high frequency region, indicating its best dielectric loss performance. While the ε″ of the cobalt ferrite supported nitrogen and sulfur doped porous carbon composite of Example 1 and the cobalt ferrite supported nitrogen and sulfur doped porous carbon composite of Example 3 is relatively low (0.5 - 1.5), and the ability to dissipate electromagnetic waves is limited. The tangent of the dielectric loss angle is a quantitative index to measure dielectric loss. The loss factor of the cobalt ferrite supported nitrogen and sulfur doped porous carbon composite of Example 2 is significantly higher, especially exceeding 1.0 in the frequency range of 2 GHz - 5 GHz, indicating its strong dielectric energy dissipation characteristics. The loss factors of the cobalt ferrite supported nitrogen and sulfur doped porous carbon composite of Example 1 and the cobalt ferrite supported nitrogen and sulfur doped porous carbon composite of Example 3 basically maintain around 0.2 - 0.3, indicating their weak ability to attenuate electromagnetic waves, as Figure 10 shown in Figure (c) of . As Figure 10 shown in Figure (d) of , the variation range of the μ′ values of the three samples is small, indicating that their magnetic field energy storage capabilities are all weak. The cobalt ferrite supported nitrogen and sulfur doped porous carbon composite of Example 3 has large fluctuations at 4 GHz - 10 GHz, which may be due to the local magnetic resonance effect. The μ″ values of the three samples are also small, as Figure 10 shown in Figure (e) of , fluctuating around 0.01 - 0.06 as a whole, while the magnetic losses of the cobalt ferrite supported nitrogen and sulfur doped porous carbon composite of Example 3 and the cobalt ferrite supported nitrogen and sulfur doped porous carbon composite of Example 2 are more obvious. The cobalt ferrite supported nitrogen and sulfur doped porous carbon composite of Example 3 has local peaks in the low frequency band (4 GHz - 10 GHz), and the cobalt ferrite supported nitrogen and sulfur doped porous carbon composite of Example 2 shows an obvious increase at 10 GHz - 18 GHz, indicating that the material has a better magnetic response in the medium and high frequency ranges, but the magnetic losses of the three groups of samples are all weak. The tangent of the magnetic loss angle is used to quantify the magnitude of magnetic loss. The cobalt ferrite supported nitrogen and sulfur doped porous carbon composite of Example 3 and the cobalt ferrite supported nitrogen and sulfur doped porous carbon composite of Example 1 are more obvious in the low frequency region, especially having peaks around 4 GHz - 8 GHz. The cobalt ferrite supported nitrogen and sulfur doped porous carbon composite of Example 3 shows higher magnetic loss performance in the low frequency region. The cobalt ferrite supported nitrogen and sulfur doped porous carbon composite of Example 2 has a lower magnetic loss in the low frequency region and its magnetic loss performance is significantly improved when approaching the medium and high frequency region (10 GHz - 18 GHz), as Figure 10Figure (f). In summary, the cobalt ferrite supported nitrogen and sulfur doped porous carbon composite of Example 2 has the best dielectric loss and mainly realizes electromagnetic wave absorption through dielectric loss. The cobalt ferrite supported nitrogen and sulfur doped porous carbon composite of Example 3 shows certain advantages in magnetic loss. The overall dielectric and magnetic properties of the cobalt ferrite supported nitrogen and sulfur doped porous carbon composite sample of Example 1 are weak.

[0067] To explore the influence rules of absorber filling amount and magnetic particle concentration on the wave absorption performance, first set Fe 3+ :Co 2+ = 1:1. The wave absorption performance of the cobalt ferrite supported nitrogen and sulfur doped porous carbon composite of Example 1 under different filling ratios is as shown in Figure 11 and Figure 12 . There is no obvious wave absorption performance at a filling amount of 5wt%. When the filling amount is increased to 10wt%, the minimum reflection loss only reaches -11.85 dB at a matching thickness of 4.50 mm, and the maximum effective absorption bandwidth is 2.72 GHz (9.04 GHz - 11.76 GHz) at 4.31 mm. As the filling amount is further increased, the minimum reflection loss reaches -40.84 dB (9.36 GHz) at a matching thickness of 3.89 mm, and the maximum effective absorption bandwidth is 6.08 GHz (11.92 GHz - 18 GHz) at 2.81 mm. As the filling amount gradually increases, the wave absorption performance of the cobalt ferrite supported nitrogen and sulfur doped porous carbon composite of Example 1 gradually improves. When the filling amount reaches 15wt%, it has good wave absorption performance.

[0068] When Fe 3+ :Co 2+ is set to 1:3, the wave absorption performance of the cobalt ferrite supported nitrogen and sulfur doped porous carbon composite of Example 2 is as shown in Figure 13 and Figure 14As shown in the figure. At a lower filling amount (5 wt%), the cobalt ferrite supported nitrogen and sulfur doped porous carbon composite of Example 2 has a minimum reflection loss of -55.33 dB (10.48 GHz) at a matching thickness of 3.98 mm, and a maximum effective absorption bandwidth of 7.60 GHz (10.4 GHz - 18 GHz) at 3.25 mm. In the thickness range of 1 mm - 5 mm, the maximum effective absorption bandwidth reaches 11.92 GHz (6.08 GHz - 18 GHz). When the filling amount is increased to 10 wt%, the minimum reflection loss reaches -55.95 dB (15.28 GHz) at a matching thickness of 2.71 mm, the effective absorption bandwidth reaches 7.92 GHz (10.08 GHz - 18 GHz) at 3.07 mm, covering the Ku band and 48% of the X band, and the maximum effective absorption bandwidth reaches 12.08 GHz (5.92 GHz - 18 GHz). When the filling amount is increased to 15 wt%, the cobalt ferrite supported nitrogen and sulfur doped porous carbon composite of Example 2 has an effective absorption bandwidth of 7.68 GHz (10.32 GHz - 18 GHz) at 2.92 mm, and a minimum reflection loss of -42.72 dB at 2.26 mm and 18 GHz frequency. The maximum effective absorption bandwidth within the tested thickness range also reaches 12.08 GHz (5.92 GHz - 18 GHz). This shows that the cobalt ferrite supported nitrogen and sulfur doped porous carbon composite of Example 2 can achieve excellent microwave absorption performance at different filling amounts, and can reach the best loss performance at a low filling amount of 10 wt%, realizing an ultra-wide frequency absorption bandwidth covering the entire Ku band and partially covering the X band.

[0069] When Fe 3+ :Co 2+ is set to 3:1, the microwave absorption performance of the cobalt ferrite supported nitrogen and sulfur doped porous carbon composite of Example 3 is as shown in Figure 15 and Figure 16 the figure. At 5 wt%, there is no obvious microwave absorption performance. As the filling amount increases (10 wt%), the minimum reflection loss only reaches -10.68 dB, and the absorption bandwidth is less than 1 GHz. A small increase in the filling amount does not bring an improvement in the loss performance. When the filling amount reaches 15 wt%, the minimum reflection loss increases to -28.28 dB (4.03 mm, 9.36 GHz), and the effective absorption bandwidth expands to 5.2 GHz (12.8 GHz - 18 GHz), nearly covering the entire Ku band. The increase in the filling amount does not bring a significant improvement in the microwave absorption performance of the cobalt ferrite supported nitrogen and sulfur doped porous carbon composite of Example 3, and only relatively good microwave absorption performance is achieved at 15 wt%.

[0070] In summary, by introducing layered double hydroxide (FeCo) magnetic nanoparticles into the nitrogen and sulfur-doped porous carbon matrix, the present invention realizes the synergistic effect of magnetic loss and dielectric loss, significantly improves the broadband absorption performance of the material, and effectively solves the technical problems of the existing materials that it is impossible to balance light weight and strong magnetic loss and the lack of impedance matching.

[0071] Obviously, those skilled in the art can make various modifications and deformations to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and deformations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention also intends to include these modifications and deformations.

Claims

1. Preparation method of cobalt ferrite supported nitrogen and sulfur doped porous carbon composite material, characterized in that, It includes the following steps: Using nitrogen and sulfur co-doped porous carbon as the substrate, under the action of 2-methylimidazole, a hydrothermal reaction occurs between soluble iron salt and soluble cobalt salt to in-situ grow iron-cobalt double metal hydroxide nanosheets on the surface of the nitrogen and sulfur co-doped porous carbon, obtaining a composite precursor. Under a protective atmosphere, the composite precursor is heated to 700 °C to 900 °C for annealing, converting the iron-cobalt double metal hydroxide into cobalt ferrite, and obtaining a cobalt ferrite-loaded nitrogen and sulfur co-doped porous carbon composite material.

2. The preparation method according to claim 1, characterized in that, Based on the mass of the cobalt ferrite-loaded nitrogen and sulfur co-doped porous carbon composite material, the loading amount of cobalt ferrite is 4.5% to 6.5%.

3. The preparation method according to claim 1, characterized in that, The molar ratio of the soluble iron salt to the soluble cobalt salt is 1 to 3:1 to 3.

4. The preparation method according to claim 1, characterized in that, The mass ratio of the nitrogen and sulfur co-doped porous carbon to 2-methylimidazole is 1:4 to 5.

5. The preparation method according to claim 1, characterized in that, The temperature of the hydrothermal reaction is 100 °C to 120 °C.

6. The preparation method according to claim 1, wherein The annealing time is 1.5 h to 3 h.

7. The preparation method according to claim 1, characterized in that, The preparation method of the nitrogen and sulfur co-doped porous carbon includes the following steps: Under a protective atmosphere, sodium citrate dihydrate and thioacetamide are heated to 550 °C to 650 °C for annealing, and then cooled to room temperature to obtain a primary product. The primary product is etched in a hydrochloric acid solution and freeze-dried to obtain nitrogen and sulfur co-doped porous carbon.

8. A cobalt ferrite-loaded nitrogen and sulfur co-doped porous carbon composite material prepared by the preparation method according to any one of claims 1 to 7.

9. An application of the cobalt ferrite-loaded nitrogen and sulfur co-doped porous carbon composite material according to claim 8 in the preparation of an electromagnetic wave absorption material.

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