Carbon-coated multistage transition metal sulfide wave-absorbing material as well as preparation method and application thereof

Abstract

The invention discloses a carbon-coated multistage transition metal sulfide wave-absorbing material as well as a preparation method and application thereof, and belongs to the technical field of electromagnetic wave absorbing materials. The preparation method of the carbon-coated multi-stage transition metal sulfide wave-absorbing material comprises the following steps: reacting a transition metal source with a nitrogen-containing sulfur source in a solvent to form a transition metal sulfide with a multi-stage nano structure; the transition metal sulfide and the carbon source precursor are subjected to electrostatic self-assembly in water, the carbon source precursor is adsorbed on the transition metal sulfide, and then carbonization treatment is performed in a protective atmosphere to obtain the carbon-coated multistage transition metal sulfide wave-absorbing material. A nitrogen-doped carbon shell is constructed on the surface of the transition metal sulfide through an in-situ polymerization carbonization method, and the prepared carbon-coated multistage transition metal sulfide wave-absorbing material has excellent wave-absorbing performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of wave-absorbing materials, and more particularly to a carbon-coated multi-level transition metal sulfide wave-absorbing material, a preparation method and an application thereof. BACKGROUND

[0002] With the rapid development of 5G / 6G communication, Internet of Things and military stealth technology, the problem of electromagnetic pollution is becoming increasingly serious due to the proliferation of electronic devices, and it is urgent to develop new electromagnetic wave absorbing materials that are thin, light, wide and strong. Metal sulfides (such as CoS and CuS) have become a research hotspot to replace traditional ferrite and carbon-based wave-absorbing materials due to their high dielectric loss, good chemical stability and adjustable structure. However, single sulfides have inherent defects: CoS has insufficient intrinsic conductivity and a low dielectric constant (εr ε' ≈6–8), making it difficult to achieve strong loss; CuS has high conductivity but poor impedance matching, which can easily cause electromagnetic wave reflection; the structural limitation of multi-level sulfides (such as hollow microspheres and flower-like structures) is that although they can enhance scattering, the narrow effective bandwidth of less than 4 GHz and high filler load of more than 60% restrict their practical application.

[0003] Recent studies have shown that carbon layer coating is an effective strategy to optimize the wave-absorbing performance of sulfides. The carbon layer can introduce multiple loss mechanisms such as interfacial polarization and conductivity loss and adjust the impedance matching. For example, MoS2@ hollow carbon core-shell structure widens the EAB to 6 GHz through hetero-interface polarization; or magnetic carbon nanotubes are coated by a carbon layer, which adjusts the dielectric / magnetic loss synergy to improve the effective absorption bandwidth by more than 40%. However, existing carbon coating technologies, such as MOF derivation and CVD, require complex templates and are difficult to universally adapt to different semiconductor types of sulfides (such as CoS and CuS, which have opposite dielectric requirements), resulting in poor wave-absorbing performance of the materials. SUMMARY

[0004] To solve the above problems, the present application provides a carbon-coated multi-level transition metal sulfide wave-absorbing material, a preparation method and an application thereof. The present application constructs a nitrogen-doped carbon shell on the surface of the transition metal sulfide through in-situ polymerization and carbonization, and the prepared carbon-coated multi-level transition metal sulfide wave-absorbing material has excellent wave-absorbing performance, and simultaneously solves the contradiction between low loss of CoS and high reflection of CuS, achieving a wide-frequency absorption of EAB≥5 GHz under a filler amount of 50%, thereby providing a solution for high-frequency electromagnetic compatibility.

[0005] The first object of the present application is to provide a preparation method of a carbon-coated multi-level transition metal sulfide wave-absorbing material, comprising the following steps: The transition metal source and the nitrogen-containing sulfur source react in a solvent. During the reaction, the sulfur ions in the nitrogen-containing sulfur source combine with the transition metal ions in the transition metal source to form a transition metal sulfide with a multi-level nanostructure. Transition metal sulfides and carbon source precursors undergo an electrostatic self-assembly reaction in water, adsorbing the carbon source precursors onto the transition metal sulfides. Then, under a protective atmosphere, carbonization treatment is carried out to form a carbon layer on the surface of the transition metal sulfides, resulting in a carbon-coated multi-level transition metal sulfide microwave absorbing material.

[0006] The multi-level structure described in this invention refers to the ordered or semi-ordered organizational morphology of materials at different scales, that is, the further assembly, stacking or aggregation of basic units at the nanoscale (such as nanoparticles, nanofibers, and nanosheets) to form secondary and tertiary structures at the micrometer or even larger scales.

[0007] In a preferred embodiment of the present invention, the molar ratio of the transition metal source to the sulfur source is 4:1.3 to 10.

[0008] When the sulfur source accounts for an excessive proportion, non-stoichiometric products or polysulfides are easily generated, leading to lattice distortion and increased defects; special morphologies (such as hollow structures) may be formed, but uniformity is difficult to control; excessive sulfur can coat the grains, affecting crystallinity and purity. The electrical conductivity of the composite material may be abnormal; excessive sulfurization may destroy the carbon layer structure of the PDA, affecting its dielectric regulation function; introducing too many defects may lead to a decrease in material stability.

[0009] When the proportion of sulfur source is too small, sulfur vacancies appear in the product. The metal elements may not be completely sulfided, and the sulfur vacancies become carrier scattering centers, reducing the mobility. In addition, the reaction is incomplete, and unreacted metal oxides or other intermediate phases are present in the product.

[0010] In a preferred embodiment of the present invention, the transition metal source is a cobalt source or a copper source.

[0011] When the transition metal source is cobalt, in the preparation of transition metal sulfides with multi-level nanostructures, the cobalt source and the sulfur source are dissolved in a solvent and subjected to a hydrothermal reaction. During the reaction, thiourea (CH4N2S) slowly decomposes and releases sulfur. 2- Ions. These S 2- With Co in solution 2+ The two particles combine to form CoS crystal nuclei. The initially formed CoS crystal nuclei preferentially grow along specific crystal planes under hydrothermal conditions, forming CoS with a specific morphology. Then, hexadecyltrimethylammonium bromide is dissolved with the CoS in water. The hexadecyltrimethylammonium bromide forms positively charged micelles / microemulsions in water, which can adsorb the negatively charged CoS particles onto their surfaces, inducing the particles to aggregate at the micelle interface and forming a multi-level (core-shell / multi-shell) structure.

[0012] When copper is used as the transition metal source, in the preparation of transition metal sulfides with multi-level nanostructures, the copper and sulfur sources are dissolved in a solvent and subjected to a hydrothermal reaction. During the hydrothermal process, the copper and sulfur sources react to form CuS crystal nuclei. The concentration of the sulfur source (i.e., the copper-sulfur molar ratio) has a decisive influence on the morphology of the final product. Studies have found that different reactant ratios (copper:sulfur) result in CuS powders with different morphologies, such as nanoflowers (spheres) and prisms. For example, when the ratio is 1:1, a flower-like structure composed of nanosheets is easily formed; while when the sulfur source ratio is significantly increased (e.g., 1:4 or 1:5), the morphology of CuS is significantly different. 2- When the concentration is high enough, it will coat the nascent CuS crystal nucleus, significantly affecting its anisotropic growth and tending to induce the crystal to grow in a specific direction, forming prismatic or other morphologies.

[0013] In a preferred embodiment of the present invention, the molar ratio of the carbon source precursor to the transition metal sulfide is 1:3 to 5.

[0014] In a preferred embodiment of the present invention, the carbonization temperature is 700℃~900℃ and the carbonization time is 0.5h~1.5h during the carbonization process. A carbonization temperature higher than 900℃ or a carbonization time exceeding 1.5h may lead to excessive graphitization of the carbon layer, significantly increasing electrical conductivity; a large amount of nitrogen is lost, and defects are reduced; high temperatures may cause sulfide decomposition or structural changes, and the interface between the carbon layer and the sulfide core may also change. This results in an excessively high imaginary part of the overall dielectric constant of the composite material, easily leading to impedance mismatch, and electromagnetic waves being reflected extensively on the material surface, making it difficult to penetrate the interior; although electrical conductivity may be enhanced, polarization loss (especially dipole polarization) is weakened due to nitrogen loss and the reduction of defects.

[0015] Carbonization temperatures below 700℃ or carbonization times less than 0.5h may result in insufficient graphitization of the carbon layer, leading to an amorphous carbon structure and low electrical conductivity. Incomplete carbonization of the carbon source, while retaining a significant amount of nitrogen, may also result in poor conductivity of the carbon layer. Furthermore, the interfacial bonding between the carbon layer and the sulfide core may be insufficient. Ultimately, this leads to insufficient electrical conductivity loss in the composite material, and the polarization loss capacity may also be limited due to the disordered carbon layer and weak carrier migration ability. Consequently, the overall attenuation capability is weak, making it difficult to effectively dissipate electromagnetic waves.

[0016] In a preferred embodiment of the present invention, the sulfur source is thiourea or a combination of thiourea and thioacetamide.

[0017] The main function of thioacetamide is as a sulfur source, which releases sulfur ions (S ions) slowly and controllably in the reaction system. 2- ), and transition metal ions (Co) 2+ or Cu 2+The combination of these ions generates metal sulfides (CoS or CuS) with a multi-level structure. This slow release of sulfur ions makes the nucleation and growth process of metal sulfides (CoS or CuS) relatively mild and controllable, avoiding particle agglomeration and unevenness caused by instantaneous large-scale precipitation. This makes it easier to generate multi-level nanostructures with regular morphology and good dispersibility.

[0018] The primary function of thiourea is to release sulfur ions and regulate morphology. Unlike thioacetamide, it releases sulfur ions at a slower rate, controlled by temperature and pH, and the release process can last from tens of minutes to several hours. This provides a continuous sulfur source for subsequent crystal growth, inhibits excessive nucleus aggregation, and results in more uniform particle size and more controllable morphology. The synergy of the fast and slow sulfur sources allows the system to obtain sufficient nuclei (high yield) while controlling nucleus growth through the slow-released thiourea, avoiding coarse particles or agglomeration. Secondly, thiourea contains amino groups, which leave nitrogen doping (N-doped carbon layer) during high-temperature carbonization, improving the conductivity and electromagnetic wave absorption performance of the final CoS@C. The core contribution of nitrogen lies in its ability to significantly enhance polarization relaxation (especially dipole polarization) and finely control the conductivity of the composite material, thereby synergistically optimizing impedance matching and loss mechanisms. This allows a single strategy to be effectively adapted to different types of semiconductor sulfides, from high-dielectric (e.g., CoS) to low-dielectric (e.g., CuS). Without nitrogen, while a pure carbon layer can still provide some conductivity and interface effects, it falls short in terms of significantly enhancing polarization loss capability and finely controlling electrical properties. The effectiveness and universality of solving the dielectric compatibility problem between CoS and CuS may also be compromised. Therefore, nitrogen doping is a crucial and significantly advantageous design approach.

[0019] The addition of thioacetamide induces a rod-like structure in nanomaterials, while thiourea causes the structure to lean towards 3D spherical nanosheets. For flower-shaped CoS, this invention considers altering its flower-like morphology by adding a multi-level structure.

[0020] For materials like CoS, which inherently possess high dielectric constants and strong conductivity losses, the main challenge lies in preventing significant electromagnetic wave reflection due to severe impedance mismatch. Non-spherical anisotropic structures exhibit differentiated dielectric properties across their different crystal orientations. When these structures are oriented or randomly arranged within a matrix, they can macroscopically disrupt the material's dielectric symmetry, effectively modulating the equivalent dielectric constant of the composite material to better match the impedance of free space. This means that electromagnetic waves can more easily penetrate the material's interior rather than be reflected.

[0021] Furthermore, one-dimensional or two-dimensional structures inherently possess more surface atoms and edges, providing a richer array of interfacial polarization (also known as the Maxwell-Wagner-Seller effect) sites compared to isotropic spherical structures. When electromagnetic waves interact with these heterogeneous interfaces, charge accumulates, resulting in significant polarization relaxation losses. Moreover, the numerous heterogeneous interfaces within hierarchical structures assembled from nanosheets or nanorods further enhance this effect. CuS, on the other hand, is designed from the outset to synthesize disc-like hierarchical structures. For CuS, with its relatively low intrinsic dielectric constant, the core task is to actively and efficiently attenuate electromagnetic waves that have already penetrated the material. Disc-like hierarchical structures demonstrate unique value in this regard. Disc-like structures are typically formed by bending or assembling two-dimensional nanosheets, possessing extremely high specific surface areas. This provides numerous interaction interfaces for electromagnetic waves, increasing their chances of contact with the material. Simultaneously, the complex pores and layered spaces within the disc-like structure force electromagnetic waves to undergo multiple reflections and scatterings, significantly extending the propagation path and thus more fully converting electromagnetic energy into heat or other forms of dissipation. This disc-shaped, multi-level structure assembled from nanounits introduces numerous defects and interfaces, which are excellent polarization centers (such as dipole polarization). Under the influence of an alternating electromagnetic field, these polarization centers relax, generating strong dielectric losses. In the design of this invention, the interlayer gaps within the disc can also form an effective resonant cavity, further absorbing electromagnetic waves in specific frequency bands and forming a dense and effective absorber. Compared to loose, flower-shaped structures, disc-shaped structures may be easier to stack more tightly during the fabrication of absorbing coatings, facilitating the introduction of more absorbing active units (CuS) per unit volume and promoting synergistic effects among them, thereby macroscopically improving the overall attenuation capability of the material.

[0022] If only one sulfur source is added, thiourea can be selected. Thiourea alone can simultaneously increase sulfur ion concentration and induce the formation of 3D spherical hierarchical structures. However, thioacetamide cannot be used alone as a sulfur source in the system of this invention. This is because the relatively rapid release characteristic of thioacetamide provides sufficient sulfur ions quickly in the early stages of the reaction, ensuring that the system can form high-density crystal nuclei. This is the basis for achieving high yield and solves the problem of insufficient nucleation when using thiourea alone. Subsequently, the slow and continuous release of sulfur ions from thiourea becomes dominant. It provides a stable and controllable growth environment for the already formed crystal nuclei, allowing them to orderly self-assemble into disc-like and other hierarchical structures.

[0023] In a preferred embodiment of the present invention, the carbon source precursor is an organic molecule, a polymer, or a carbohydrate compound.

[0024] In a preferred embodiment of the present invention, when preparing carbon-coated multi-level transition metal sulfide microwave absorbing materials, different carbon source precursors can be selected according to the material system, performance requirements, process conditions, and cost control. For example, organic molecules can be citric acid, vitamin C, or dopamine; polymers can be conductive polymers, such as polypyrrole or polyaniline; and sugar compounds can be glucose or sucrose, etc.

[0025] The carbon source precursor used in this invention is polydopamine. Dopamine undergoes self-oxidative polymerization under weakly acidic conditions to generate a thin polydopamine film. The film is tightly bonded to the surface of transition metal sulfides through π-π, hydrogen bonds and metal coordination, playing the role of a self-assembled coating. At the same time, it provides a nitrogen-doped carbon source for subsequent carbonization. This is a self-assembly behavior, thereby forming a carbon-coated multi-level transition metal sulfide microwave absorbing material.

[0026] The second objective of this invention is to provide a carbon-coated multi-level transition metal sulfide microwave absorbing material prepared by the above-described method. The core structural advantage of this invention lies in abandoning the commonly used flower-shaped structure and employing targeted and precise morphology design to address the distinct dielectric properties of CoS (high dielectric) and CuS (low dielectric). For high dielectric CoS, which is prone to impedance mismatch, a non-flower-shaped anisotropic structure is selected, utilizing its structural asymmetry to optimize impedance matching and facilitate effective electromagnetic wave entry. For low dielectric CuS, which has insufficient intrinsic loss capability, a disc-shaped multi-level structure is chosen, maximizing multiple reflections and polarization losses through its large specific surface area and complex internal space, thus strongly attenuating electromagnetic waves. This differentiated structural design based on the intrinsic properties of the material is key to achieving high-performance microwave absorbing materials.

[0027] A third objective of this invention is to provide the application of the above-mentioned carbon-coated multi-level transition metal sulfide absorbing material in the preparation of electromagnetic wave absorbing materials.

[0028] Compared with the prior art, the present invention has the following beneficial effects: This invention uses transition metal and sulfur sources as raw materials to prepare transition metal sulfides with a multi-level structure. The advantage of this multi-level structure in microwave absorption performance stems from its ability to synergistically optimize two core parameters: impedance matching and attenuation capability. First, the multi-level structure itself and the numerous heterogeneous interfaces it introduces can effectively adjust the equivalent electromagnetic parameters of the composite material, making it more compatible with free space and thus absorbing electromagnetic waves. Second, its complex three-dimensional spatial structure can greatly extend the electromagnetic wave propagation path, providing more opportunities for various loss mechanisms (such as interface polarization and conductivity loss) to interact through multiple reflections and scattering, thereby dissipating electromagnetic waves. Finally, this structure achieves efficient synergy between impedance matching and multiple loss mechanisms, thus potentially yielding stronger absorption intensity (lower reflection loss) and a wider effective absorption bandwidth.

[0029] Then, transition metal sulfides are composited with carbon layers (C) to form carbon-coated multi-level transition metal sulfide absorbing materials. The introduction of carbon layers significantly improves the electromagnetic wave absorption performance of the material. Carbon materials possess excellent conductivity and absorption characteristics, enabling them to effectively absorb and dissipate electromagnetic wave energy, thereby enhancing the material's absorption capability. Studies have shown that carbon-based composite materials exhibit excellent performance in the field of electromagnetic wave absorption; for example, carbon fiber and carbonyl iron powder composites demonstrate good absorption performance in the 2-18 GHz frequency range. Therefore, the introduction of carbon layers not only broadens the absorption bandwidth of the material but also enhances its absorption capability in the high-frequency band.

[0030] Furthermore, the introduction of a carbon layer helps improve the structural stability of the material. The carbon layer can protect the structural stability of sulfide materials under high temperatures or complex environments, preventing structural damage or performance degradation during preparation or use. Simultaneously, the carbon layer may promote the formation of a multi-level structure in the material, thereby enhancing its multiple reflection and scattering effects in electromagnetic wave absorption, further improving its wave absorption performance.

[0031] The introduction of a carbon layer causes the decomposition of some organic matter during pyrolysis, thus forming channels. This may promote the formation of a porous structure in the material, thereby enhancing its multiple reflection and scattering effects on electromagnetic waves. The porous structure can effectively increase the propagation path of electromagnetic waves within the material, thereby improving absorption efficiency. Studies have shown that porous materials have significant advantages in the field of electromagnetic wave absorption; for example, porous electromagnetic wave absorbing materials exhibit excellent absorption performance within a specific frequency range.

[0032] In summary, this invention significantly improves the electromagnetic wave absorption performance of cobalt sulfide and copper sulfide materials by introducing a carbon layer, and has good application prospects. Attached Figure Description

[0033] Figure 1 The images show scanning electron microscope (SEM) images of CoS and CuS in disc form, where (a) is CoS prepared in Comparative Example 1 and (b) is CuS prepared in Comparative Example 2.

[0034] Figure 2 High-magnification transmission electron microscopy (TEM) images of CoS and disc-shaped CuS are shown. (a) CoS prepared in Comparative Example 1 at a scale bar of 100 nm; (b) CuS prepared in Comparative Example 2 at a scale bar of 100 nm; (c) CoS prepared in Comparative Example 1 at a scale bar of 50 nm; and (d) CuS prepared in Comparative Example 2 at a scale bar of 50 nm.

[0035] Figure 3 The images are scanning electron microscope (SEM) images of CoS@C and CuS@C, where (a) is CoS@C prepared in Example 1 and (b) is CuS@C prepared in Example 2.

[0036] Figure 4 The images are high-magnification transmission electron microscope (TEM) images of CoS@C and CuS@C. (a) is a TEM image of CoS@C prepared in Example 1 at a scale bar of 500 nm, (b) is a TEM image of CuS@C prepared in Example 2 at a scale bar of 500 nm, (c) is a TEM image of CoS@C prepared in Example 1 at a scale bar of 100 nm, (d) is a TEM image of CuS@C prepared in Example 2 at a scale bar of 50 nm, (e) is a TEM image of CuS@C prepared in Example 2 at a scale bar of 10 nm, and (f) is a TEM image of CuS@C prepared in Example 2 at a scale bar of 2 nm. The inset in (f) is a calculation diagram of the lattice fringe spacing of the CuS portion in CuS@C prepared in Example 2.

[0037] Figure 5 X-ray diffraction patterns of CoS prepared in Comparative Example 1 and CoS@C prepared in Example 1.

[0038] Figure 6 X-ray diffraction patterns of CuS prepared in Comparative Example 2 and CuS@C prepared in Example 2.

[0039] Figure 7 The dielectric constant diagrams are for CoS@C prepared in Example 1 and CoS prepared in Comparative Example 1.

[0040] Figure 8 The dielectric constant diagrams are for CuS@C prepared in Example 2 and CuS prepared in Comparative Example 2.

[0041] Figure 9 The reflection loss diagram is for CoS prepared in Comparative Example 1.

[0042] Figure 10 The reflection loss diagram is for CuS prepared in Comparative Example 2.

[0043] Figure 11 The image shows the reflection loss of CoS@C prepared in Example 1.

[0044] Figure 12 The image shows the reflection loss of CuS@C prepared in Example 2.

[0045] Figure 13 The angular distribution characteristics of electromagnetic wave scattering performance of CoS prepared in Comparative Example 1 and CoS@C prepared in Example 1 under a single-station radar scattering cross section are shown.

[0046] Figure 14 The image shows the angular distribution characteristics of electromagnetic wave scattering performance of CuS prepared in Comparative Example 2 and CuS@C prepared in Example 2 under a single-station radar scattering cross section. Detailed Implementation

[0047] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0048] For semiconductors requiring different carbon layer properties (such as CoS which may require thinner carbon layers with lower graphitization to suppress excessively high conductivity; while CuS may require continuous, uniform carbon layers to maximize interface effects), the same set of process parameters cannot simultaneously meet these requirements using MOF derivation or CVD methods.

[0049] Impact on high dielectric constant semiconductors (such as CoS): The introduction of a carbon layer further significantly increases the overall conductivity and imaginary part of the dielectric constant of the composite material. This easily leads to impedance mismatch, making it difficult for electromagnetic waves to penetrate the material's interior, instead resulting in significant reflection at the surface, violating the core requirement of "high-efficiency absorption and low reflection" for microwave absorbing materials. Simultaneously, excessively high conductivity may also disrupt the inherent polarization loss mechanism of the semiconductor itself, leading to a singular loss mechanism.

[0050] Impact on low dielectric constant semiconductors (such as CuS): The introduction of carbon layers can moderately improve the conductivity of composite materials, but its more important role may be the formation of numerous heterogeneous interfaces with the semiconductor core. These interfaces, under the influence of alternating electromagnetic fields, induce significant interfacial polarization (Maxwell-Wagner-Seller effect), thereby enhancing polarization relaxation loss—a beneficial synergy. However, if the thickness, graphitization degree, or distribution of the carbon layer is uneven, not only will it be impossible to effectively construct an ideal interfacial structure, but the introduction of excessive free carbon may also lead to leakage current, thus reducing the polarization effect and limiting the improvement in dielectric loss performance.

[0051] This invention employs a carbon source (such as polydopamine) coating followed by carbonization strategy. Its core advantage lies in the precise control of carbon layer thickness, effectively solving the problem of poor universality in traditional carbon coating technologies. This strategy can be tailored to the intrinsic characteristics of different types of semiconductor sulfides, such as CoS (high dielectric) and CuS (low dielectric): for CoS, which is prone to impedance mismatch, a thin carbon layer is constructed to introduce interfacial polarization while suppressing excessive conductivity growth; for CuS, which requires enhanced loss capability, a slightly thicker carbon layer can synergistically enhance conductivity loss and interfacial polarization. This precise control capability optimizes the impedance matching and synergistic effect of multiple loss mechanisms in the composite material, significantly improving electromagnetic wave absorption performance. Furthermore, the excellent adhesion of the PDA precursor and the mild processing conditions further ensure the universality of this method and its ability to maintain its microstructure.

[0052] This invention constructs a continuous carbon shell on the surface of sulfides through in-situ carbonization of a carbon source (such as polydopamine), forming a composite microwave absorption system with a core-shell heterogeneous structure and multi-level channels. The polydopamine carbonization forms a uniformly coated conductive carbon layer, which, together with the sulfide core, constitutes a multi-level heterogeneous interface of "core + shell + pores," significantly enhancing interface polarization and electromagnetic wave multiple scattering, effectively extending the propagation path and improving loss efficiency. Pure sulfide materials have poor impedance matching and are prone to electromagnetic wave reflection; while pure carbon materials have a single dielectric loss and limited absorption intensity. Therefore, this invention, through composite design and multi-level structural control, simultaneously optimizes impedance matching and attenuation capabilities, thereby improving microwave absorption performance.

[0053] This invention proposes a novel microwave absorbing material, which is a carbon-shell-coated CoS / CuS core-shell structure absorbing material containing both sulfides and carbon. It may contain unavoidable impurities. The sulfides are CoS or cake-shaped CuS, and the carbon source is polydopamine.

[0054] The sulfide acts as the core in the core-shell structure of the material, while the carbonized polydopamine acts as the shell, forming a specific spatial configuration. A detailed description follows.

[0055] Example 1 (1) Dissolve 3 mmol of cobalt nitrate hexahydrate, 4 mmol of thioacetamide, and 1.31 mmol of thiourea in 60 mL of deionized water and stir magnetically for 30 min. Transfer to a 100 mL stainless steel autoclave and react at 160 °C for 8 h, then cool to room temperature. Wash three times each with anhydrous ethanol and deionized water, and dry in a forced-air drying oven at 60 °C for 12 h to obtain the product CoS.

[0056] (2) Dissolve 0.02 g cetyltrimethylammonium bromide (CTAB) and 0.25 g CoS in 30.0 mL of deionized water, and then transfer the solution to 150.0 mL of a deionized aqueous solution containing 1.44 g of 2-MIM to obtain a mixture.

[0057] Dopamine hydrochloride was added to the mixture at a molar ratio of 1:3 to dopamine hydrochloride and CoS. The mixture was stirred at 800 rpm for 40 min, aged at room temperature for 12 h, and excess free PDA was removed from the turbid solution by differential centrifugation. The residue was then washed 2-3 times with deionized water and anhydrous ethanol to obtain a precipitate. Methanol was added to the precipitate, ensuring it was completely submerged, and the mixture was allowed to stand for 24 h for solvent exchange. After filtration and drying, a powder was obtained. The powder was placed in a tube furnace under N2 atmosphere and carbonized at 800 °C for 1 h to obtain CoS@C.

[0058] Example 2 (1) 2 mmol CuCl2·2H2O and 5 mmol thiourea were dissolved in 15 mL of N,N-dimethylamide to form two homogeneous solutions. The two solutions were mixed and stirred to form a dark red solution. The mixed solution was transferred to a Teflon autoclave and reacted at 170 °C for 2 h, and then naturally cooled to room temperature. The mixture was collected and washed several times with deionized water and anhydrous ethanol, and dried at 60 °C for 12 h. Finally, the collected precursor was calcined in air at 400 °C for 3 h to obtain a black cake-shaped CuS powder.

[0059] (2) Dopamine hydrochloride and cake CuS were mixed in a 1:3 molar ratio. 0.264 g of cake CuS and 0.173 g of dopamine hydrochloride were dispersed in 50 mL of deionized water and stirred at 800 r / min for 40 min. After aging for 12 h, excess and free dopamine hydrochloride were removed using a differential centrifuge. The residue was washed several times with deionized water to obtain a precipitate. The precipitate was placed in methanol for 24 h for solvent exchange, filtered and dried, and then carbonized at 800 °C for 1 h under a N2 atmosphere to obtain CuS@C.

[0060] Example 3 (1) Dissolve 3 mmol of cobalt nitrate hexahydrate, 4 mmol of thioacetamide, and 1.31 mmol of thiourea in 60 mL of deionized water and stir magnetically for 30 min. Transfer to a 100 mL stainless steel autoclave and react at 160 °C for 8 h, then cool to room temperature. Wash three times each with anhydrous ethanol and deionized water, and dry in a forced-air drying oven at 60 °C for 12 h to obtain the product CoS.

[0061] (2) Dissolve 0.02 g cetyltrimethylammonium bromide (CTAB) and 0.25 g CoS in 30.0 mL of deionized water, and then transfer the solution to 150.0 mL of a deionized aqueous solution containing 1.44 g of 2-MIM to obtain a mixture.

[0062] Dopamine hydrochloride was added to the mixture at a molar ratio of 1:4 to dopamine hydrochloride and CoS. The mixture was stirred at 800 rpm for 40 min and aged for 12 h. Excess free PDA was removed from the turbid solution by differential centrifugation. The residue was then washed 2-3 times with deionized water and anhydrous ethanol to obtain a precipitate. The precipitate was placed in methanol for 24 h for solvent exchange. After filtration and drying, a powder was obtained. The powder was placed in a tube furnace under N2 atmosphere and carbonized at 800 °C for 1 h to obtain CoS@C-1.

[0063] Example 4 (1) 2 mmol CuCl2·2H2O and 5 mmol thiourea were dissolved in 15 mL of N,N-dimethylamide to form two homogeneous solutions. The two solutions were mixed and stirred to form a dark red solution. The mixed solution was transferred to a Teflon autoclave and reacted at 170 °C for 2 h, and then naturally cooled to room temperature. The mixture was collected and washed several times with deionized water and anhydrous ethanol, and dried at 60 °C for 12 h. Finally, the collected precursor was calcined in air at 400 °C for 3 h to obtain a black cake-shaped CuS powder.

[0064] (2) Dopamine hydrochloride and cake-shaped CuS were mixed at a molar ratio of 1:4. 0.264 g of cake-shaped CuS and 0.130 g of dopamine hydrochloride were dispersed in 50 mL of deionized water and stirred at 800 r / min for 40 min. After aging for 12 h, excess and free dopamine hydrochloride were removed using a differential centrifuge. The residue was washed several times with deionized water to obtain a precipitate. The precipitate was placed in methanol for 24 h for solvent exchange, filtered and dried, and then carbonized at 800 °C for 1 h under a N2 atmosphere to obtain CuS@C-1.

[0065] Example 5 (1) Dissolve 3 mmol of cobalt nitrate hexahydrate, 4 mmol of thioacetamide, and 1.31 mmol of thiourea in 60 mL of deionized water and stir magnetically for 30 minutes. Transfer to a 100 mL stainless steel autoclave and react at 160 °C for 8 h, then cool to room temperature. Wash three times each with anhydrous ethanol and deionized water, and dry in a forced-air drying oven at 60 °C for 12 h to obtain CoS.

[0066] (2) Dissolve 0.02 g cetyltrimethylammonium bromide (CTAB) and 0.25 g CoS in 30.0 mL of deionized water, and then transfer the solution to 150.0 mL of a deionized aqueous solution containing 1.44 g of 2-MIM to obtain a mixture.

[0067] Dopamine hydrochloride was added to the mixture at a molar ratio of CoS to dopamine hydrochloride of 1:5. The mixture was stirred at 800 rpm for 40 min and aged for 12 h. Excess free PDA was removed from the turbid solution by differential centrifugation. The residue was then washed 2-3 times with deionized water and anhydrous ethanol to obtain a precipitate. The precipitate was placed in methanol for 24 h for solvent exchange. After filtration and drying, the powder was placed in a tube furnace under N2 atmosphere and carbonized at 800 °C for 1 h to obtain CoS@C-2.

[0068] Example 6 (1) 2 mmol CuCl2·2H2O and 5 mmol thiourea were dissolved in 15 mL of N,N-dimethylamide to form two homogeneous solutions. The two solutions were mixed and stirred to form a dark red solution. The mixed solution was transferred to a Teflon autoclave and reacted at 170 °C for 2 h, and then naturally cooled to room temperature. The mixture was collected and washed several times with deionized water and anhydrous ethanol, and dried at 60 °C for 12 h. Finally, the collected precursor was calcined in air at 400 °C for 3 h to obtain a black cake-shaped CuS powder.

[0069] (2) Dopamine hydrochloride and cake-shaped CuS were mixed at a molar ratio of 1:5. 0.264 g of cake-shaped CuS and 0.104 g of dopamine hydrochloride were dispersed in deionized water and stirred at 800 r / min for 40 min. After aging for 12 h, excess and free dopamine hydrochloride were removed using a differential centrifuge. The residue was washed several times with deionized water to obtain a precipitate. The precipitate was placed in methanol for 24 h for solvent exchange, filtered and dried, and then carbonized at 800 °C for 1 h under a N2 atmosphere to obtain CuS@C-2.

[0070] Example 7 (1) Dissolve 3 mmol of cobalt nitrate hexahydrate and 5 mmol of thiourea in 60 mL of deionized water and stir magnetically for 30 min. Transfer to a 100 mL stainless steel autoclave and react at 160 °C for 8 h, then cool to room temperature. Wash three times each with anhydrous ethanol and deionized water, and dry in a forced-air drying oven at 60 °C for 12 h to obtain the product CoS.

[0071] (2) Dissolve 0.02 g cetyltrimethylammonium bromide (CTAB) and 0.25 g CoS in 30.0 mL of deionized water, and then transfer the solution to 150.0 mL of a deionized aqueous solution containing 1.44 g of 2-MIM to obtain a mixture.

[0072] 0.173 g of dopamine hydrochloride was added to the mixture according to a molar ratio of CoS to dopamine hydrochloride of 1:3. The mixture was stirred at 800 rpm for 40 min, aged at room temperature for 12 h, and excess free PDA was removed from the turbid solution by differential centrifugation. The residue was then washed 2-3 times with deionized water and anhydrous ethanol to obtain a precipitate. Methanol was added to the precipitate, ensuring it was completely submerged, and the mixture was allowed to stand for 24 h for solvent exchange. After filtration and drying, a powder was obtained. The powder was placed in a tube furnace under N2 atmosphere and carbonized at 700 °C for 1.5 h to obtain CoS@C.

[0073] Example 8 (1) Dissolve 3 mmol of cobalt nitrate hexahydrate and 10 mmol of thiourea in 60 mL of deionized water and stir magnetically for 30 min. Transfer to a 100 mL stainless steel autoclave and react at 160 °C for 8 h, then cool to room temperature. Wash three times each with anhydrous ethanol and deionized water, and dry in a forced-air drying oven at 60 °C for 12 h to obtain the product CoS.

[0074] (2) Dissolve 0.02 g cetyltrimethylammonium bromide (CTAB) and 0.25 g CoS in 30.0 mL of deionized water, and then transfer the solution to 150.0 mL of a deionized aqueous solution containing 1.44 g of 2-MIM to obtain a mixture.

[0075] According to the molar ratio of CoS to dopamine hydrochloride of 1:3, 0.173 g of dopamine hydrochloride was added to the mixture. The mixture was stirred at 800 rpm for 40 min, aged at room temperature for 12 h, and excess free PDA was removed from the turbid solution by differential centrifugation. The residue was then washed 2-3 times with deionized water and anhydrous ethanol to obtain a precipitate. Methanol was added to the precipitate, covering it completely, and the mixture was allowed to stand for 24 h for solvent exchange. After filtration and drying, a powder was obtained. The powder was placed in a tube furnace under N2 atmosphere and carbonized at 900 °C for 0.5 h to obtain CoS@C.

[0076] Comparative Example 1 3 mmol of cobalt nitrate hexahydrate, 4 mmol of thioacetamide, and 1.31 mmol of thiourea were dissolved in 60 mL of deionized water and magnetically stirred for 30 min. The mixture was transferred to a 100 mL stainless steel autoclave and reacted at 160 °C for 8 h, then cooled to room temperature. The mixture was then washed three times each with anhydrous ethanol and deionized water, and dried in a forced-air drying oven at 60 °C for 12 h to obtain the product CoS.

[0077] Comparative Example 2 2 mmol CuCl₂·2H₂O and 5 mmol thiourea were dissolved separately in 15 mL of N,N-dimethylamide to form two homogeneous solutions. These two solutions were mixed and stirred to form a dark red solution. The mixture was transferred to a Teflon autoclave and reacted at 170 °C for 2 h, then allowed to cool naturally to room temperature. The mixture was collected and washed several times with deionized water and anhydrous ethanol, then dried at 60 °C for 12 h. Finally, the collected precursor was calcined in air at 400 °C for 3 h to obtain a black cake-like CuS powder.

[0078] Comparative SEM image 1 as shown Figure 1 As shown in (a), the CoS sample exhibits flower-like microspheres composed of a large number of interconnected nanosheets tightly packed together. These nanosheets constitute a three-dimensional hierarchical structure with significant porosity and rough surface morphology, indicating that it has a high specific surface area, which is beneficial for subsequent functionalization modification.

[0079] In comparison, Figure 1 The disc-shaped CuS sample in Comparative Example 2 (b) exhibits a clear spherical structure with an open disc arrangement. This structure consists of vertically aligned nanosheets radiating outward from the center, forming a multi-level hierarchical structure with significant interlayer gaps and a central cavity. This configuration displays an expanded surface area and abundant exposed edges.

[0080] Both samples were successfully synthesized using the aforementioned hydrothermal method, exhibiting complex multilevel morphologies. Their structural differences stemmed from the use of different metal precursors and solvent systems in the synthesis process. These precisely controllable nanostructures provide an ideal substrate for subsequent polydopamine-derived carbon layers, demonstrating their promising potential for enhancing electromagnetic wave absorption performance through optimized interfacial polarization and multiple scattering mechanisms.

[0081] Figure 2 The microstructures of CoS and cake-shaped CuS before carbon shell coating were characterized using transmission electron microscopy (TEM). Figure 2 As shown in (a), the CoS prepared in Comparative Example 1 exhibits an irregular blocky stacked structure, which is formed by the interlacing of nanosheets to form abundant mesoporous and macroporous channels with a scale of hundreds of nanometers. This multi-level pore structure originates from the directional self-assembly of thioacetamide and cobalt ions during hydrothermal process. Figure 2 In (b), the disc-shaped CuS exhibits micron-sized spherical and blocky aggregates, with its surface composed of open flower-like topologies formed by vertically grown nanosheets. This morphological feature is closely related to the anisotropic crystal growth mechanism regulated by organic amide solvent. Figure 2 (c) and Figure 2 (d) further reveals the local fine structures of the two materials prepared in Comparative Example 1 and Comparative Example 2 at the 50 nm scale, showing clear lattice fringes and interface connections, providing ample interfacial bonding sites for the subsequent uniform coating of polydopamine-derived carbon layers. These hierarchical structures, by increasing the specific surface area and constructing multiple scattering interfaces, lay a solid structural foundation for improving the electromagnetic wave absorption performance of the final CoS@C and CuS@C core-shell materials.

[0082] The products of Examples 1 and 2 are as follows Figure 3 The surface morphology of the CoS@C and CuS@C composite materials coated with carbon shells was compared and displayed using scanning electron microscopy (SEM). Figure 3 As shown in (a), the CoS@C material prepared in Example 1 presents an irregular blocky aggregate with a continuous carbon layer covering the surface to form a core-shell structure. The original nanosheet stacking pores are filled with carbon, and carbon layer wrinkles can be seen in the edge region. The scale distribution is in the range of 200 nm to 500 nm. Figure 3In (b) of Example 2, the CuS@C prepared retains the flower-like microsphere topology, but the surface roughness of the nanosheets is significantly reduced, indicating that the carbon layer uniformly covers the surface of the CuS nanosheets. Fracture marks in the carbon layer are visible in some areas, exposing the underlying sulfide crystal structure. Both samples retain the multi-level structural characteristics of the precursor, with a carbon coating thickness of approximately 20 nm to 50 nm. The dense structure of the precursor in CoS@C results in a more complete carbon layer coating, while the open structure of CuS@C causes the carbon layer to exhibit a locally discontinuous distribution. This carbon shell coating not only stabilizes the multi-level structure but also introduces dielectric loss units into the composite material, enhancing its microwave absorption performance by controlling the matching of electromagnetic parameters.

[0083] Figure 4 The microstructure and crystal features of the carbon-shell-coated CoS@C and CuS@C nanocomposites in Examples 1 and 2 were characterized using a transmission electron microscope (TEM) system.

[0084] Figure 4 Image (a) shows that the CoS@C prepared in Example 1 is an irregular aggregate with a dark core of CoS and a light gray carbon layer surrounding it, forming a continuous core-shell structure with a scale of about 200 nm to 500 nm. Figure 4 Image (b) shows that the CuS@C prepared in Example 2 presents a relatively regular spherical core-shell unit with a core CuS size of about 300 nm and an outer carbon shell thickness of about 20 nm to 30 nm. The contrast between light and dark is clear, showing that the carbon layer is uniformly coated. Figure 4 (c) and (d) are high-magnification images of CoS@C prepared in Example 1 and CuS@C prepared in Example 2, respectively, further revealing the core-shell interface region. It can be seen that the carbon layer and sulfide form a tight contact without obvious gaps or peeling. Figure 4 In (e), the interface between CuS and the carbon layer in CuS@C prepared in Example 2 is clearly shown under high resolution transmission electron microscopy (marked by white dashed lines). The CuS region is dark black, the carbon layer is gray, and the interface is continuous and intact. Figure 4 In (f), the high-resolution TEM image of the CuS core shows a lattice fringe spacing of 0.306 nm, corresponding to the (100) crystal plane of hexagonal CuS (marked by a white circle), indicating that CuS is a nanocrystalline structure.

[0085] The results show that both materials were successfully coated with carbon layers, with good core-shell interface bonding and preserved crystal structure. This structure is beneficial for enhancing dielectric polarization and interface scattering, thereby improving electromagnetic wave absorption performance.

[0086] Figure 5The XRD patterns of CoS prepared in Comparative Example 1 and the carbon-coated product CoS@C prepared in Example 1 were compared. The CoS sample showed obvious diffraction peaks at 2θ = 30.1°, 35.2°, 46.8°, and 54.7°, corresponding to the (311), (400), (511), and (440) crystal planes of the standard card (JCPDS No. 86-2273, Co9S8), respectively. Simultaneously, some peak positions corresponded to Co... 1-x The S-phase (JCPDS No. 42-08926) match indicates that the sample has a multiphase mixed structure. After carbon coating, the diffraction peak positions of CoS@C did not shift significantly, but the diffraction intensity generally decreased, and the full width at half maximum (FWHM) increased slightly. This indicates that the introduction of the carbon layer did not change the crystal structure of CoS, but may have caused lattice micro-strain or partial amorphization.

[0087] Figure 6 The XRD patterns of CuS prepared in Comparative Example 2 and CuS@C prepared in Example 2 are compared with the simulated patterns. Uncoated CuS exhibits characteristic diffraction patterns of typical hexagonal CuS (covellite, JCPDS No. 06-0464) at 2θ = 27.7°, 29.3°, 31.8°, and 47.9°, corresponding to the (100), (101), (102), and (110) crystal planes, respectively. The diffraction peaks of carbon-coated CuS@C are still clearly visible, but their intensity is reduced, and no impurity peaks appear, indicating that the carbon coating did not destroy the crystal integrity of CuS. The broadening phenomenon may be related to the amorphous properties of the carbon layer and interfacial stress. The simulated and experimental patterns are in high agreement, further verifying the accuracy of phase identification.

[0088] The carbon coating process did not significantly change the crystal phase composition of CoS and CuS, but it caused a decrease in diffraction intensity and a broadening of peak shape. This is attributed to the amorphous covering effect of the carbon layer and the lattice defects that may be introduced during the coating process. This structural feature is beneficial to enhance interfacial polarization loss and improve the performance of the composite material in electromagnetic wave absorption.

[0089] The method for determining the dielectric constant of CoS@C in Example 1 was as follows: CoS@C powder and paraffin were mixed at a mass ratio of 5:5 to prepare coaxial samples with outer and inner diameters of 7 mm and 3 mm respectively, and a thickness of 2.0 mm to 3.5 mm. The complex permittivity and complex permeability of the samples from 2 GHz to 18 GHz were measured using a vector network analyzer. The measurement results are as follows: Figure 7 As shown.

[0090] From the real part curve of the dielectric constant, the CoS@C prepared in Example 1 showed a higher ε' value than pure CoS across all frequency bands, and exhibited a wide-band relaxation peak in the low-frequency region (such as around 4 GHz), indicating that the introduction of the carbon layer significantly enhanced the polarization capability of the material. As the frequency increased, the ε' value of both types of materials showed a decreasing trend, exhibiting typical dispersion characteristics.

[0091] Regarding the imaginary part, the ε'' value of CoS@C prepared in Example 1 is generally higher than that of CoS prepared in Comparative Example 1, especially showing a significant peak in the range of 8 GHz to 12 GHz, indicating that the carbon shell effectively improves the dielectric loss capability. The ε'' curve of CoS@C exhibits multiple relaxation characteristics, with shoulder peaks or inflections at multiple frequency points, which may be related to the multiple relaxation processes caused by interfacial polarization and the carbon-sulfide heterostructure.

[0092] The enhanced dielectric properties of CoS@C composites are mainly due to the following mechanisms: (1) The carbon layer acts as a conductive network, which improves the overall conductivity and leads to increased conductive loss; (2) The heterogeneous interface formed between the CoS core and the carbon shell introduces a large number of interfacial polarization sites; (3) The carbon coating may optimize the impedance matching characteristics, making it easier for electromagnetic waves to enter the interior of the material and be dissipated.

[0093] The results show that carbon shell coating effectively modulates the dielectric properties of CoS materials, and provides an important way to improve electromagnetic wave absorption performance by enhancing polarization and loss mechanisms.

[0094] The method for determining the dielectric constant of CuS@C in Example 2 was as follows: CoS@C powder and paraffin were mixed in a 5:5 ratio to prepare coaxial samples with outer and inner diameters of 7 mm and 3 mm respectively, and a thickness of 2.0 mm to 3.5 mm. The complex dielectric constant and complex permeability of the samples from 2 GHz to 18 GHz were measured using a vector network analyzer. The measurement results are shown below. Figure 8 As shown.

[0095] Overall, the ε' and ε'' values ​​of both CuS@C in Example 2 and CuS in Comparative Example 2 show a decreasing trend with increasing frequency, exhibiting significant dispersion behavior. The real and imaginary parts of the dielectric constant of CuS@C are lower than those of the uncoated CuS sample in all frequency bands, indicating that the introduction of the carbon layer reduces the overall dielectric response of the material.

[0096] In the real part curves, the ε' value of CuS@C exhibits a significant relaxation peak in the 2 GHz–6 GHz range, followed by a gradual flattening in the high-frequency region, while the CuS sample shows a more gradual decreasing trend. The imaginary part curves show a broadband loss peak in the 8 GHz–12 GHz range for CuS@C, which may be related to interfacial polarization relaxation introduced by the carbon layer. Notably, the CuS sample shows an abnormally high ε'' value in the 14 GHz–16 GHz range, which may be related to the material's inherent lattice vibrations or electronic transitions.

[0097] This difference in dielectric behavior is mainly attributed to the multiple effects of carbon coating: (1) the carbon layer, as a semiconductor coating, may restrict charge migration and reduce the overall conductivity; (2) the Maxwell-Wagner polarization effect induced by the carbon-CuS interface has a significant impact in specific frequency bands; (3) the introduction of the carbon layer may optimize the impedance matching characteristics of the material, making it easier for electromagnetic waves to penetrate the material. These findings indicate that by controlling the carbon coating conditions, the dielectric properties of composite materials can be effectively controlled, providing a new approach for optimizing the electromagnetic wave absorption performance in specific frequency bands.

[0098] Figure 9 and Figure 10 The electromagnetic wave reflection loss (RL) performance of two composite materials, CoS-50% (Comparative Example 1) and CuS-50% (Comparative Example 2), as a function of thickness, was systematically compared in the frequency band from 2 GHz to 18 GHz.

[0099] In terms of absorption intensity, the CoS-50% sample achieved the best absorption performance at a thickness of 3.8 mm, with the lowest reflection loss (RL). min The value is -30.81 dB. Figure 9 The CuS-50% material exhibits stronger absorption performance even at a relatively small thickness of 1.8 mm. min Up to -38.06dB ( Figure 10 This indicates that CuS-based materials have a superior loss mechanism under thin-layer conditions.

[0100] From the perspective of effective absorption bandwidth (EAB, RL≤-10dB), CoS-50% has an EAB of 1.19GHz with a thickness of 4.3mm. In contrast, CuS-50% can achieve a wideband absorption of 3.00GHz with a thickness of only 1.8mm, and its EAB coverage is significantly better than that of CoS-50% material.

[0101] Both materials exhibit typical multi-peak characteristics in their reflection loss curves, indicating the existence of multiple polarization relaxation processes. The RL peak of CoS-50% shifts to lower frequencies with increasing thickness, consistent with the 1 / 4 wavelength matching model. CuS-50% achieves broadband strong absorption even at relatively thin thicknesses (1.8 mm to 2.8 mm), indicating that it has superior impedance matching characteristics and dielectric loss capability.

[0102] Figure 11 and Figure 12 The curves showing the reflection loss (RL) performance as a function of thickness for the two composite materials, CoS@C-50% prepared in Example 1 and CuS@C-50% prepared in Example 2, in the frequency range of 2 GHz to 18 GHz are presented respectively.

[0103] In terms of absorption performance, CoS@C-50% material achieves the best absorption performance at a thickness of 2.7 mm, with the lowest reflection loss (RL). min The value is -43.42 dB. Figure 11 The material exhibits the maximum effective absorption bandwidth (EAB, RL≤-10dB) at a thickness of 2.2mm, reaching 5.01 GHz. The sample demonstrates good absorption performance across a thickness range of 1.7mm to 4.7mm, with RL values ​​generally below -20 dB.

[0104] In comparison, CuS@C-50% material exhibits the best overall performance at a thickness of 2.9 mm, with its RL... min Achieving -44.12dB, while simultaneously obtaining an EAB of 4.70GHz at this thickness. Figure 12 Although its maximum EAB is slightly lower than that of CoS@C-50% material, it exhibits more stable absorption performance within the same thickness range (1.9mm to 4.9mm), and all curves maintain a low RL value over a wide frequency range.

[0105] Both the CoS@C-50% material prepared in Example 1 and the CuS@C-50% material prepared in Example 2 exhibit significant thickness-dependent reflection loss curves. As the thickness increases, the absorption peak shifts to the lower frequency region, consistent with the typical characteristics of the quarter-wavelength interference model. The CoS@C-50% material achieves broadband absorption even with a thin layer (2.2 mm), while the CuS@C-50% material achieves both strong absorption and broadband characteristics at a medium thickness (2.9 mm).

[0106] Figure 13 The angular distribution characteristics of electromagnetic wave scattering performance of CoS prepared in Comparative Example 1 and the carbon-coated derivative CoS@C (50% mass loading) prepared in Example 1 under a single-station radar cross section (RCS) are shown. Figure 14The electromagnetic wave scattering performance angular distribution characteristics of CuS prepared in Comparative Example 2 and the carbon-coated derivative CuS@C (50% loading mass fraction) prepared in Example 2 under a single-station radar cross section (RCS) are shown.

[0107] The test frequencies were 7.52 GHz (CoS), 11.76 GHz (CoS@C), 6.24 GHz (CuS), and 12.16 GHz (CuS@C), with an ideal electrical conductor (PEC) as the reference.

[0108] In terms of scattering intensity, both carbon-coated materials exhibited significantly lower RCS values ​​than their corresponding uncoated samples and PEC across the entire angular range (-90° to 90°). CoS@C-50% achieved the lowest RCS value near 0°, approximately -25 dB·m. 2 Compared to PEC (approximately 25 dB·m), 2 The RCS is reduced by more than 50 dB, demonstrating excellent scattering reduction capabilities. CuS@C-50% also exhibits significant RCS attenuation near normal incidence, with values ​​below -20 dB·m. 2 .

[0109] In terms of angular adaptability, the carbon-coated sample maintains a stable low RCS characteristic within a small incident angle range (±30°), and the curve fluctuation is smoother than that of the uncoated sample, indicating that the carbon layer effectively improves the wide-angle impedance matching characteristics of the material. Although the uncoated samples (CoS-50% and CuS-50%) show some scattering reduction at certain angles, their overall RCS is still significantly higher than that of the carbon-coated sample, and obvious scattering peaks appear at larger incident angles.

[0110] The performance improvement brought about by carbon coating is mainly attributed to the fact that the carbon layer, acting as an impedance matching layer, optimizes the wave impedance matching between the material and free space, reducing electromagnetic wave reflection; the dielectric polarization and conductivity loss induced by the carbon-sulfide interface synergistically enhance electromagnetic wave energy conversion; and the introduction of the carbon layer may further dissipate incident electromagnetic energy through a multiple scattering mechanism. Carbon shell coating can significantly improve the radar wave scattering reduction capability of CoS and CuS composite materials and broaden the effective operating angle range, providing experimental evidence for their application in the field of electromagnetic stealth.

[0111] It should be noted that, Figure 5 and Figure 6 In this context, 2θ is denoted as 2 Theta, and intensity is denoted as Intensity. Figure 7 and Figure 8 In this context, frequency is denoted as Frequency, and the real and imaginary parts of the dielectric constant are denoted as Real and Imaginary Part. Figures 9 to 12In this context, frequency is denoted as Frequency, and reflection loss is denoted as Reflection Loss. Figures 13 to 14 In this context, the angle of incidence is denoted as Theta, and the radar cross section is denoted as RCS. Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make further changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of this invention.

[0112] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for preparing a carbon-coated multi-level transition metal sulfide microwave absorbing material, characterized in that, Includes the following steps: The transition metal source and the nitrogen-containing sulfur source react in a solvent. During the reaction, the sulfur ions in the nitrogen-containing sulfur source combine with the transition metal ions in the transition metal source to form a transition metal sulfide with a multi-level nanostructure. Transition metal sulfides and carbon source precursors undergo an electrostatic self-assembly reaction in water, adsorbing the carbon source precursors onto the transition metal sulfides. Then, under a protective atmosphere, carbonization treatment is carried out to form a carbon layer on the surface of the transition metal sulfides, resulting in a carbon-coated multi-level transition metal sulfide microwave absorbing material.

2. The method for preparing a carbon-coated multi-level transition metal sulfide microwave absorbing material according to claim 1, characterized in that, The molar ratio of transition metal source to sulfur source is 3:5 to 10.

3. The method for preparing a carbon-coated multi-level transition metal sulfide microwave absorbing material according to claim 1, characterized in that, The transition metal source is either cobalt or copper.

4. The method for preparing a carbon-coated multi-level transition metal sulfide microwave absorbing material according to claim 1, characterized in that, The molar ratio of carbon source precursor to transition metal sulfide is 1:3 to 5.

5. The method for preparing a carbon-coated multi-level transition metal sulfide microwave absorbing material according to claim 1, characterized in that, During the carbonization process, the carbonization temperature is 700℃~900℃ and the carbonization time is 0.5 h~1.5 h.

6. The method for preparing a carbon-coated multi-level transition metal sulfide microwave absorbing material according to claim 1, characterized in that, The sulfur source is thiourea or a combination of thiourea and thioacetamide.

7. The method for preparing a carbon-coated multi-level transition metal sulfide microwave absorbing material according to claim 1, characterized in that, The carbon source precursor can be any one of organic molecules, conductive polymers, and carbohydrate compounds.

8. The method for preparing a carbon-coated multi-level transition metal sulfide microwave absorbing material according to claim 7, characterized in that, The organic molecules are citric acid, vitamin C, or dopamine; the conductive polymers are polypyrrole or polyaniline; and the carbohydrate compounds are glucose or sucrose.

9. A carbon-coated multi-level transition metal sulfide microwave absorbing material prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the carbon-coated multi-level transition metal sulfide absorbing material as described in claim 9 in the preparation of electromagnetic wave absorbing materials.

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