Co3O4atC / Ni / Ti3C2Tx nanofiber composite wave-absorbing material and preparation method thereof

Abstract

The invention provides a Co3O4 (at) C / Ni / Ti3C2Tx nanofiber composite wave-absorbing material and a preparation method of the Co3O4 (at) C / Ni / Ti3C2Tx nanofiber composite wave-absorbing material. The preparation method comprises the following steps: preparing a Co3O4 (at) C / Ni core-shell structure material, preparing a fibrous Ti < 3 > C < 2 > T < x > MXene material, and compounding Co3O4 (at) C / Ni and Ti < 3 > C < 2 > T < x > MXene to prepare the Co3O4 (at) C / Ni / Ti < 3 > C < 2 > T < x > nanofiber composite wave-absorbing material. The Co3O4 (at) C / Ni core-shell structure prepared by a dopamine coating method can provide abundant heterogeneous interfaces and multiple reflectivity. Co3O4 (at) C / Ni and Ti3C2Tx MXene are compounded by using an electrostatic self-assembly technology, and the core-shell-fiber composite structure not only prolongs the loss path of electromagnetic waves, but also increases a conductive loss mode and shows excellent wave absorbing performance by integrating dielectric loss, magnetic loss, a multiple reflection mechanism and structural advantages.

Description

Technical Field

[0001] The present invention belongs to the field of functional materials, and specifically relates to a Co3O4@C / Ni / Ti3C2T x Nanofiber composite absorbing material and preparation method thereof. Background Art

[0002] With the rapid development of communication technology, electromagnetic wave absorbing (EMA) materials have received increasing attention in the military field and daily life. EMA materials can absorb and consume incident electromagnetic waves within a typical frequency range. Electromagnetic waves will be reflected multiple times internally and converted into heat or other forms of energy. In this process, the inherent characteristics of electromagnetic dielectric loss or magnetic loss play a key role in balancing impedance matching and promoting electromagnetic wave attenuation. The dielectric loss effect is caused by conduction loss, dielectric relaxation loss and resonance loss; while magnetic loss is mainly caused by magnetic resonance. In addition, the structure of composite materials, such as core-shell structure, microsphere structure and sandwich structure, are conducive to the absorption and loss of electromagnetic waves. Therefore, the synthesis strategy for constructing EMA materials should focus on these aspects. MXene is a typical two-dimensional inorganic conductive polymer material. Its layered structure offers numerous advantages, including large surface area, excellent mechanical flexibility, high ionic conductivity, and tunable surface and edge atomic defects, making it a promising material for electromagnetic shielding. Based on the performance requirements of the composite material, dielectric loss can be used as the theoretical basis for constructing absorbers, and the structural unit materials can be optimized to achieve the desired overall performance. Generally, strong attenuation loss and good impedance matching are necessary for excellent electromagnetic wave absorption. However, excessively high MXene conductivity can lead to an impedance mismatch between the MXene surface and free space, thereby enhancing the reflection of incident electromagnetic waves. Generally speaking, combining high-dielectric-constant materials with medium-loss components is considered an effective design approach to achieve appropriate impedance matching and improve electromagnetic wave absorption. Magnetic materials can not only compensate for the insufficient magnetic loss of MXene but also adjust its impedance mismatch. Furthermore, the heterogeneous structure of the composite material can introduce additional interfaces and defects to improve the loss of incident electromagnetic waves. Summary of the Invention

[0003] Technical problem to be solved: The excessively high conductivity of MXene will lead to impedance mismatch between the MXene surface and free space, thereby enhancing the reflection of incident electromagnetic waves. In order to improve its performance, the present invention combines Co3O4@C / Ni / Ti3C2T x By compounding it with it, a nanofiber composite absorbing material is prepared, and the structure of the composite material is optimized to make up for the insufficient magnetic loss of MXene, reduce its impedance mismatch, and enhance the absorbing performance of the material.

[0004] Technical solution: a Co3O4@C / Ni / Ti3C2T x The preparation method of the nanofiber composite wave absorbing material comprises the following steps: Step 1. Preparation of Co3O4@C / Ni core-shell structure material: Co3O4 powder is uniformly dispersed in an ethanol aqueous solution, ultrasonically treated, and then an appropriate amount of ammonia solution is added to adjust the pH value of the reaction system. After stirring, dopamine hydrochloride and a nickel salt precursor are added in sequence. After stirring and reacting, the mixture is separated, washed, and heat-treated to obtain a Co3O4@C / Ni core-shell structure material; Step 2. Preparation of fibrous Ti3C2T x MXene material: Lithium salt is dissolved in concentrated hydrochloric acid solution, MAX phase precursor powder is added and mixed thoroughly, and then etching reaction is carried out. After the reaction is completed, the product is filtered, washed, and centrifuged. The product is redispersed in deionized water and ultrasonically treated to peel off the few-layer Ti3C2T x MXene nanosheets are mixed with alkaline solution and oscillated at constant temperature to obtain fibrous Ti3C2T x MXene dispersion; Step 3. Preparation of Co3O4@C / Ni / Ti3C2T x Nanofiber composite absorber: Co3O4@C / Ni core-shell structure material and surfactant are dispersed in deionized water, ultrasonically treated and mechanically stirred to form a uniform dispersion system, and fibrous Ti3C2T x MXene dispersion was mechanically stirred for composite reaction, the product was collected by centrifugation, washed and freeze-dried to obtain Co3O4@C / Ni / Ti3C2T x Nanofiber composite absorbing materials. Furthermore, the concentration of the ethanol aqueous solution in step 1 is 60-65% (v / v), the pH value of the reaction system is adjusted to 10-11, the nickel salt precursor is nickel chloride hexahydrate or nickel nitrate hexahydrate, and the mass ratio of Co3O4, dopamine hydrochloride and nickel salt precursor is (2-4):(1-2):1. Furthermore, the stirring reaction time in step 1 is 8-10 hours, and the heat treatment conditions are drying at 50-60°C for 10-12 hours, heating to 500°C at a rate of 3-6°C / min, and keeping warm for 8 hours. Furthermore, the concentration of concentrated hydrochloric acid in step 2 is 9-12 mol / L, the mass ratio of lithium salt, MAX phase precursor powder and concentrated hydrochloric acid is (1-3): (1-3): (20-50), and the alkaline solution is 5-6 mol L -1 NaOH solution, Ti3C2T x The mass ratio of MXene nanosheets to alkaline solution is 1:(13-15). Furthermore, in step 2, the etching reaction temperature is 35° C., the centrifugal speed is 3000-4000 rpm, the constant temperature oscillation temperature is 40-50° C., and the time is 35-40 h. Furthermore, in step 3, the mass ratio of the Co3O4@C / Ni core-shell structure material, the surfactant and the deionized water is (3-5): (5-7): (6-10), and the Co3O4@C / Ni core-shell structure material and the fibrous Ti3C2T x The mass ratio of MXene is 1:(1-3). Furthermore, in step 3, the ultrasonic treatment time is 20-40 min, the mechanical stirring rate is 500-700 rpm, the mechanical stirring time is 4-6 h, the centrifugal speed is 9000-10000 rpm, the centrifugal time is 8-10 min, and the freeze-drying time is 12-16 h. The Co3O4@C / Ni / Ti3C2T prepared by the above preparation method x Nanofiber composite absorbing materials. The Co3O4@C / Ni / Ti3C2T prepared by the above preparation method x Application of nanofiber composite absorbing materials in electromagnetic protection materials. Beneficial effects: 1. The present invention anchors Co3O4@C / Ni core-shell nanoparticles on fibrous Ti3C2T by polydopamine coating method. x A composite electrode material with significant advantages is constructed on the MXene carrier. The key advantage of this design lies in the multi-level synergistic optimization: in the core-shell structure, the inner carbon shell (C) acts as a flexible buffer layer, effectively inhibiting the volume expansion of Co3O4 during the charge and discharge process, preventing particle pulverization and improving cycle stability, while improving conductivity and reducing side reactions; the outer nickel shell (Ni) further provides high conductivity and mechanical strength, optimizes charge transfer and interfacial reaction kinetics, and the double-layer structure of inner carbon and outer nickel synergistically improves the overall performance of the active material; the fibrous Ti3C2T x The MXene carrier provides an interwoven, vine-like, highly conductive three-dimensional network skeleton, which not only provides a high specific surface area loading platform for a large number of core-shell nanoparticles, maximizing the active material loading, but more importantly, enables the attached nanoparticles to directly utilize the excellent conductive pathways of MXene to achieve efficient electron transport, overcoming the contact resistance problem in traditional electrodes; at the same time, the inherent flexibility of the fiber network enhances the structural stability of the overall electrode; this composite structure constructed by core-shell protection, strong interface coupling and a three-dimensional conductive skeleton ultimately synergistically achieves the comprehensive electrochemical performance of high capacity, excellent rate performance and long cycle life. 2. The present invention adopts the polydopamine coating method, whose core advantages lie in its mild and universal operability and strong interfacial adhesion ability. Its abundant catechol and amino functional groups serve as strong binding sites, and through various interactions, a stable low-resistance chemical bonding interface is constructed between the particles and the MXene carrier, ensuring uniform and firm attachment of the particles and significantly promoting interfacial electron transport. 3. The present invention adjusts the Co3O4@C / Ni and Ti3C2T x The mass ratio of nanofibers and the use of electric / magnetic loss, rich heterogeneous interfaces and inherent defects on the surface of MXene fibers can significantly enhance the material's absorption performance. x MXene was used and its structure was optimized to improve the electromagnetic wave absorption performance and broaden the absorption band. 4. The present invention successfully achieved the x The structure of MXene is integrated, and each component maintains good crystallinity. The synthesis method is simple and novel, and the performance is excellent, which lays a solid structural foundation for subsequent performance research. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 Co3O4@C / Ni / Ti3C2T x Schematic diagram of the preparation of nanofiber composite absorber; Figure 2 The Co3O4@C / Ni core-shell structure material and fibrous Ti3C2T x MXene materials, Co3O4@C / Ni / Ti3C2T x XRD patterns of nanofiber composites; Figure 3 Co3O4@C / Ni / Ti3C2T prepared in Example 1 x Measurement scan of nanofiber composite absorbing material; Figure 4 TEM images of Example 1, a and b are TEM images of Co3O4@C / Ni core-shell structure materials, c and d are dimensional Ti3C2T x TEM images of MXene materials, e and f are Co3O4@C / Ni / Ti3C2T x TEM image of nanofiber composites; Figure 5 Co3O4@C / Ni / Ti3C2T prepared in Examples 1-3 xAnalysis diagram of the absorbing parameters of the nanofiber composite absorbing material, Figure a is the analysis diagram of the complex dielectric constant ε′, Figure b is the analysis diagram of the complex dielectric constant ε″, Figure c is the analysis diagram of the complex magnetic permeability μ′, Figure d is the analysis diagram of the complex magnetic permeability μ″, Figure e is the analysis diagram of the dielectric loss tangent (tanεE), and Figure f is the analysis diagram of the loss tangent (tanμE); Figure 6 Co3O4@C / Ni / Ti3C2T prepared in Examples 1-3 and Comparative Examples 1-8 x Reflection loss diagram of nanofiber composite absorbing material, wherein Figure 1 is the reflection loss diagram of Example 1, Figure 2 is the reflection loss diagram of Example 2, Figure 3 is the reflection loss diagram of Example 3, Figure 4 is the reflection loss diagram of Comparative Example 1, Figure 5 is the reflection loss diagram of Comparative Example 2, Figure 6 is the reflection loss diagram of Comparative Example 3, Figure 7 is the reflection loss diagram of Comparative Example 4, Figure 8 is the reflection loss diagram of Comparative Example 5, Figure 9 is the reflection loss diagram of Comparative Example 6, Figure 10 is the reflection loss diagram of Comparative Example 7, and Figure 11 is the reflection loss diagram of Comparative Example 8. DETAILED DESCRIPTION The present invention will be further described below with reference to the accompanying drawings and embodiments. The following embodiments are intended to explain the present invention, but the present invention is not limited to the following embodiments: Example 1 A Co3O4@C / Ni / Ti3C2T x The nanofiber composite absorbing material comprises the following steps: Step 1. Preparation of Co3O4@C / Ni core-shell structure material: Disperse 0.6g Co3O4 in a mixture of 100mL of ethanol and 60mL of deionized water, and then ultrasonicate for 30min. Then add 5mL of ammonia solution. After stirring for 10min, add 0.3g of dopamine hydrochloride and 0.3g of nickel chloride hexahydrate to the above solution. Mechanical stirring is carried out at room temperature for 10h. Then, the sample is separated using an external magnetic field, and then washed with deionized water and anhydrous ethanol 6 times respectively, and dried at 60℃ for 10h. Then, the sample is carbonized for 5h at a heating rate of 5℃ / min and a nitrogen atmosphere of 100mL / min to obtain Co3O4@C / Ni core-shell structure material. Step 2. Preparation of fibrous Ti3C2T x MXene materials: 1.0 g of LiF was dissolved in 20 mL of HCl (9 M), and then 1.0 g of MAX phase was added. After dispersion, the mixture was transferred to a polytetrafluoroethylene container and heated to 35 ° C for 24 h under magnetic stirring. The precipitate obtained by centrifugation was washed to neutrality, then dispersed in water and ultrasonicated for 30 min. The upper limit of the centrifugal speed was controlled at 4000 rpm and the lower limit was controlled at 3000 rpm. The suspension obtained by ultrasonication was Ti3C2Tx MXene nanosheet dispersion. 0.5g of exfoliated few-layer Ti3C2T x MXene nanosheets were added to 60 mL of NaOH solution (6 mol L -1 ) and shaken at 40 °C for 36 h to obtain fibrous Ti3C2T x MXene dispersion. Step 3. Preparation of fibrous Co3O4@C / Ni / Ti3C2T x MXene composite absorber: 30 mg Co3O4@C / Ni nanoparticles, 50 mg CTAB, and 60 mL deionized water were added to a 150 mL three-necked flask and then ultrasonicated for 30 min. Mechanical stirring was then performed for 2 h. 15 mL Ti3C2T x The layered solution (2 mg / mL) was stirred mechanically for 4 h and washed with deionized water three times (9000 rpm, 10 min). The Co3O4@C / Ni / Ti3C2T x Nanofiber dispersion. Co3O4@C / Ni / Ti3C2T was synthesized by vacuum freeze drying for 12 h. x Nanofiber composite materials. Example 2 A Co3O4@C / Ni / Ti3C2T x The nanofiber composite absorbing material comprises the following steps: Step 1. Preparation of Co3O4@C / Ni core-shell structure material: Disperse 0.6g Co3O4 in a mixture of 100mL of ethanol and 60mL of deionized water, and then ultrasonicate for 30min. Then add 5mL of ammonia solution. After stirring for 10min, add 0.3g of dopamine hydrochloride and 0.3g of nickel chloride hexahydrate to the above solution. Mechanical stirring is carried out at room temperature for 10h. Then, the sample is separated using an external magnetic field, and then washed with deionized water and anhydrous ethanol 6 times respectively, and dried at 60℃ for 10h. Then, the sample is carbonized for 5h at a heating rate of 5℃ / min and a nitrogen atmosphere of 100mL / min to obtain Co3O4@C / Ni core-shell structure material. Step 2. Preparation of fibrous Ti3C2T x MXene materials: 1.0 g of LiF was dissolved in 20 mL of HCl (9 M), and then 1.0 g of MAX phase was added. After dispersion, the mixture was transferred to a polytetrafluoroethylene container and heated to 35 ° C for 24 h under magnetic stirring. The precipitate obtained by centrifugation was washed to neutrality, then dispersed in water and ultrasonicated for 30 min. The upper limit of the centrifugal speed was controlled at 4000 rpm and the lower limit was controlled at 3000 rpm. The suspension obtained by ultrasonication was Ti3C2Tx MXene nanosheet dispersion. 0.5g of exfoliated few-layer Ti3C2T x MXene nanosheets were added to 60 mL of NaOH solution (6 mol L -1 ) and shaken at 40 °C for 36 h to obtain fibrous Ti3C2T x MXene dispersion. Step 3. Preparation of fibrous Co3O4@C / Ni / Ti3C2T x MXene composite absorber: 30 mg Co3O4@C / Ni nanoparticles, 50 mg CTAB, and 60 mL deionized water were added to a 150 mL three-necked flask and then ultrasonicated for 30 min. Mechanical stirring was then performed for 2 h. 30 mL Ti3C2T x The layered solution (2 mg / mL) was stirred mechanically for 4 h and washed with deionized water three times (9000 rpm, 10 min). The Co3O4@C / Ni / Ti3C2T x Nanofiber dispersion. Co3O4@C / Ni / Ti3C2T was synthesized by vacuum freeze drying for 12 h. x Nanofiber composite materials. Example 3 A Co3O4@C / Ni / Ti3C2T x The nanofiber composite absorbing material comprises the following steps: Step 1. Preparation of Co3O4@C / Ni core-shell structure material: Disperse 0.6g Co3O4 in a mixture of 100mL of ethanol and 60mL of deionized water, and then ultrasonicate for 30min. Then add 5mL of ammonia solution. After stirring for 10min, add 0.3g of dopamine hydrochloride and 0.3g of nickel chloride hexahydrate to the above solution. Mechanical stirring is carried out at room temperature for 10h. Then, the sample is separated using an external magnetic field, and then washed with deionized water and anhydrous ethanol 6 times respectively, and dried at 60℃ for 10h. Then, the sample is carbonized for 5h at a heating rate of 5℃ / min and a nitrogen atmosphere of 100mL / min to obtain Co3O4@C / Ni core-shell structure material. Step 2. Preparation of fibrous Ti3C2T x MXene materials: 1.0 g of LiF was dissolved in 20 mL of HCl (9 M), and then 1.0 g of MAX phase was added. After dispersion, the mixture was transferred to a polytetrafluoroethylene container and heated to 35 ° C for 24 h under magnetic stirring. The precipitate obtained by centrifugation was washed to neutrality, then dispersed in water and ultrasonicated for 30 min. The upper limit of the centrifugal speed was controlled at 4000 rpm and the lower limit was controlled at 3000 rpm. The suspension obtained by ultrasonication was Ti3C2Tx MXene nanosheet dispersion. 0.5g of exfoliated few-layer Ti3C2T x MXene nanosheets were added to 60 mL of NaOH solution (6 mol L -1 ) and shaken at 40 °C for 36 h to obtain fibrous Ti3C2T x MXene dispersion. Step 3. Preparation of fibrous Co3O4@C / Ni / Ti3C2T x MXene composite absorber: 30 mg Co3O4@C / Ni nanoparticles, 50 mg CTAB, and 60 mL deionized water were added to a 150 mL three-necked flask and then ultrasonicated for 30 min. Mechanical stirring was then performed for 2 h. 45 mL Ti3C2T x The layered solution (2 mg / mL) was stirred mechanically for 4 h and washed with deionized water three times (9000 rpm, 10 min). The Co3O4@C / Ni / Ti3C2T x Nanofiber dispersion. Co3O4@C / Ni / Ti3C2T was synthesized by vacuum freeze drying for 12 h. x Nanofiber composite materials. Comparative Example 1 The difference between this comparative example and Example 1 is that Co3O4 is not treated with C / Ni coating, and is not prepared into core-shell structure nanoparticles, but fibrous Co3O4 / Ti3C2T x MXene composite absorbing materials, specifically as follows: Step 1. Preparation of fibrous Ti3C2T x MXene materials: 1.0 g of LiF was dissolved in 20 mL of HCl (9 M), and then 1.0 g of MAX phase was added. After dispersion, the mixture was transferred to a polytetrafluoroethylene container and heated to 35 ° C for 24 h under magnetic stirring. The precipitate obtained by centrifugation was washed to neutrality, then dispersed in water and ultrasonicated for 30 min. The upper limit of the centrifugal speed was controlled at 4000 rpm and the lower limit was controlled at 3000 rpm. The suspension obtained by ultrasonication was Ti3C2T x MXene nanosheet dispersion. 0.5g of exfoliated few-layer Ti3C2T x MXene nanosheets were added to 60 mL of NaOH solution (6 mol L -1 ) and shaken at 40 °C for 36 h to obtain fibrous Ti3C2T x MXene dispersion. Step 2. Preparation of fibrous Co3O4 / Ti3C2T xMXene composite absorber: 30 mg Co3O4, 50 mg CTAB and 60 mL deionized water were added to a 150 mL three-necked flask and then ultrasonicated for 30 min. Then mechanical stirring was performed for 2 h. Then, 15 mL Ti3C2T x The layered solution (2 mg / mL) was stirred mechanically for 4 h and washed three times with deionized water (9000 rpm, 10 min). The Co3O4 / Ti3C2T x Nanofiber dispersion. Co3O4 / Ti3C2T was synthesized by vacuum freeze drying for 12 h. x Nanofiber composite materials. Comparative Example 2 The difference between this comparative example and Example 1 is that Co3O4 is not compounded with Ni, and fibrous Co3O4@C / Ti3C2T is prepared. x MXene composite absorbing materials, specifically as follows: Step 1. Preparation of Co3O4@C core-shell structure material: Disperse 0.6g of Co3O4 in a mixture of 100mL of ethanol and 60mL of deionized water, and then ultrasonicate for 30min. Then add 5mL of ammonia solution. After stirring for 10min, add 0.3g of dopamine hydrochloride to the above solution. Mechanical stirring is carried out at room temperature for 10h. Then, the sample is separated using an external magnetic field, and then washed with deionized water and anhydrous ethanol 6 times respectively, and dried at 60℃ for 10h. Then, the sample is carbonized for 5h at a heating rate of 5℃ / min and a nitrogen atmosphere of 100mL / min to obtain Co3O4@C core-shell structure material. Step 2. Preparation of fibrous Ti3C2T x MXene materials: 1.0 g of LiF was dissolved in 20 mL of HCl (9 M), and then 1.0 g of MAX phase was added. After dispersion, the mixture was transferred to a polytetrafluoroethylene container and heated to 35 ° C for 24 h under magnetic stirring. The precipitate obtained by centrifugation was washed to neutrality, then dispersed in water and ultrasonicated for 30 min. The upper limit of the centrifugal speed was controlled at 4000 rpm and the lower limit was controlled at 3000 rpm. The suspension obtained by ultrasonication was Ti3C2T x MXene nanosheet dispersion. 0.5g of exfoliated few-layer Ti3C2T x MXene nanosheets were added to 60 mL of NaOH solution (6 mol L -1 ) and shaken at 40 °C for 36 h to obtain fibrous Ti3C2T x MXene dispersion. Step 3. Preparation of fibrous Co3O4@C / Ti3C2T xMXene composite absorber: 30 mg Co3O4@C nanoparticles, 50 mg CTAB, and 60 mL deionized water were added to a 150 mL three-necked flask and then ultrasonicated for 30 min. Mechanical stirring was then performed for 2 h. Then, 15 mL Ti3C2T x The fiber solution (2 mg / mL) was stirred mechanically for 4 h and washed three times with deionized water (9000 rpm, 10 min). The Co3O4@CTi3C2T x Nanofiber dispersion. Co3O4@C / Ni / Ti3C2T was synthesized by vacuum freeze drying for 12 h. x Nanofiber composite materials. Comparative Example 3 The difference between this comparative example and Example 1 is that the fibrous Ti3C2T x MXene is not compatible with Co3O4@C core-shell structure materials, as follows: Preparation of fibrous Ti3C2T x MXene materials: 1.0 g LiF was dissolved in 20 mL HCl (9 M), and then 1.0 g MAX phase was added. After dispersion, the mixture was transferred to a polytetrafluoroethylene container and heated to 35 ° C for 24 h under magnetic field stirring. The precipitate obtained by centrifugation was washed to neutrality, then dispersed in water and ultrasonicated for 30 min. The upper limit of the centrifugal speed was controlled at 4000 rpm and the lower limit was controlled at 3000 rpm. The suspension obtained by ultrasonication was Ti3C2T x MXene nanosheet dispersion. 0.5g of exfoliated few-layer Ti3C2T x MXene nanosheets were added to 60 mL of NaOH solution (6 mol L -1 ) and shaken at 40 °C for 36 h to obtain fibrous Ti3C2T x MXene dispersion. Comparative Example 4 The difference between this comparative example and Example 1 is that Ti3C2T x MXene materials are not prepared into fiber form, as follows: Step 1. Preparation of Co3O4@C / Ni core-shell structure material: Disperse 0.6g Co3O4 in a mixture of 100mL of ethanol and 60mL of deionized water, and then ultrasonicate for 30min. Then add 5mL of ammonia solution. After stirring for 10min, add 0.3g of dopamine hydrochloride and 0.3g of nickel chloride hexahydrate to the above solution. Mechanical stirring is carried out at room temperature for 10h. Then, the sample is separated using an external magnetic field, and then washed with deionized water and anhydrous ethanol 6 times respectively, and dried at 60℃ for 10h. Then, the sample is carbonized for 5h at a heating rate of 5℃ / min and a nitrogen atmosphere of 100mL / min to obtain Co3O4@C / Ni core-shell structure material. Step 2. Preparation of layered Ti3C2T x MXene materials: 1.0 g of LiF was dissolved in 20 mL of HCl (9 M), and then 1.0 g of MAX phase was added. After dispersion, the mixture was transferred to a polytetrafluoroethylene container and heated to 35 ° C for 24 h under magnetic stirring. The precipitate obtained by centrifugation was washed to neutrality, then dispersed in water and ultrasonicated for 30 min. The upper limit of the centrifugal speed was controlled at 4000 rpm and the lower limit was controlled at 3000 rpm. The suspension obtained by ultrasonication was Ti3C2T x MXene nanosheet dispersion. Step 3. Preparation of Co3O4@C / Ni / Ti3C2T x MXene composite absorber: 30 mg Co3O4@C / Ni nanoparticles, 50 mg CTAB, and 60 mL deionized water were added to a 150 mL three-necked flask and then ultrasonicated for 30 min. Mechanical stirring was then performed for 2 h. Then, 15 mL Ti3C2T x The layered solution (2 mg / mL) was stirred mechanically for 4 h and washed with deionized water three times (9000 rpm, 10 min). The Co3O4@C / Ni / Ti3C2T x Nanofiber dispersion. Co3O4@C / Ni / Ti3C2T was synthesized by vacuum freeze drying for 12 h. x Nanocomposite materials. Comparative Example 5 The difference between this comparative example and Example 1 is that Co3O4@C / Ni / Ti3C2T x Ni in the nanofiber composite material is replaced by Al as follows: Step 1. Preparation of Co3O4@C / Al core-shell structure material: Disperse 0.6g of Co3O4 in a mixture of 100mL of ethanol and 60mL of deionized water, and then ultrasonicate for 30min. Then add 5mL of ammonia solution. After stirring for 10min, add 0.3g of dopamine hydrochloride and 0.3g of aluminum chloride hexahydrate to the above solution. Mechanical stirring is carried out at room temperature for 10h. Then, the sample is separated using an external magnetic field, and then washed with deionized water and anhydrous ethanol 6 times respectively, and dried at 60℃ for 10h. Then, the sample is carbonized for 5h at a heating rate of 5℃ / min and a nitrogen atmosphere of 100mL / min to obtain Co3O4@C / Al core-shell structure material. Step 2. Preparation of fibrous Ti3C2T x MXene materials: 1.0 g of LiF was dissolved in 20 mL of HCl (9 M), and then 1.0 g of MAX phase was added. After dispersion, the mixture was transferred to a polytetrafluoroethylene container and heated to 35 ° C for 24 h under magnetic stirring. The precipitate obtained by centrifugation was washed to neutrality, then dispersed in water and ultrasonicated for 30 min. The upper limit of the centrifugal speed was controlled at 4000 rpm and the lower limit was controlled at 3000 rpm. The suspension obtained by ultrasonication was Ti3C2T x MXene nanosheet dispersion. 0.5g of exfoliated few-layer Ti3C2T x MXene nanosheets were added to 60 mL of NaOH solution (6 mol L -1 ) and shaken at 40 °C for 36 h to obtain fibrous Ti3C2T x MXene dispersion. Step 3. Preparation of fibrous Co3O4@C / XX / Ti3C2T x MXene composite absorber: 30 mg Co3O4@C / Al nanoparticles, 50 mg CTAB, and 60 mL deionized water were added to a 150 mL three-necked flask and then ultrasonicated for 30 min. Mechanical stirring was then performed for 2 h. Then, 15 mL Ti3C2T x The layered solution (2 mg / mL) was stirred mechanically for 4 h and washed with deionized water three times (9000 rpm, 10 min) to collect Co3O4@C / Al / Ti3C2T x Nanofiber dispersion. Co3O4@C / Al / Ti3C2T was synthesized by vacuum freeze drying for 12 h. x Nanofiber composite materials. Comparative Example 6 The difference between this comparative example and Example 1 is that Co3O4@C / Ni / Ti3C2T xThe Co3O4 in the nanofiber composite material is replaced by Fe2O3 as follows: Step 1. Preparation of Fe2O3@C / Ni core-shell structure material: Disperse 0.6g of Fe2O3 in a mixture of 100mL of ethanol and 60mL of deionized water, and then ultrasonicate for 30min. Then add 5mL of ammonia solution. After stirring for 10min, add 0.3g of dopamine hydrochloride and 0.3g of nickel chloride hexahydrate to the above solution. Mechanical stirring is carried out at room temperature for 10h. Then, the sample is separated using an external magnetic field, and then washed with deionized water and anhydrous ethanol 6 times respectively, and dried at 60℃ for 10h. Then, the sample is carbonized for 5h at a heating rate of 5℃ / min and a nitrogen atmosphere of 100mL / min to obtain Fe2O3@C / Ni core-shell structure material. Step 2. Preparation of fibrous Ti3C2T x MXene materials: 1.0 g of LiF was dissolved in 20 mL of HCl (9 M), and then 1.0 g of MAX phase was added. After dispersion, the mixture was transferred to a polytetrafluoroethylene container and heated to 35 ° C for 24 h under magnetic stirring. The precipitate obtained by centrifugation was washed to neutrality, then dispersed in water and ultrasonicated for 30 min. The upper limit of the centrifugal speed was controlled at 4000 rpm and the lower limit was controlled at 3000 rpm. The suspension obtained by ultrasonication was Ti3C2T x MXene nanosheet dispersion. 0.5g of exfoliated few-layer Ti3C2T x MXene nanosheets were added to 60 mL of NaOH solution (6 mol L -1 ) and shaken at 40 °C for 36 h to obtain fibrous Ti3C2T x MXene dispersion. Step 3. Preparation of fibrous Fe2O3@C / Ni / Ti3C2T x MXene composite absorber: 30 mg of Fe2O3@C / Ni nanoparticles, 50 mg of CTAB, and 60 mL of deionized water were added to a 150 mL three-necked flask and then ultrasonicated for 30 min. Mechanical stirring was then performed for 2 h. Then, 15 mL of Ti3C2T x The layered solution (2 mg / mL) was stirred mechanically for 4 h and washed with deionized water three times (9000 rpm, 10 min). The Fe2O3@C / Ni / Ti3C2T x Nanofiber dispersion. Fe2O3@C / Ni / Ti3C2T was synthesized by vacuum freeze drying for 12 h. x Nanofiber composite materials. Comparative Example 7 The difference between this comparative example and Example 1 is that the Co3O4@C / Ni core-shell structure material and the fibrous Ti3C2T x The mass ratio of MXene is 1:4, as follows: Step 1. Preparation of Co3O4@C / Ni core-shell structure material: Disperse 0.6g Co3O4 in a mixture of 100mL of ethanol and 60mL of deionized water, and then ultrasonicate for 30min. Then add 5mL of ammonia solution. After stirring for 10min, add 0.3g of dopamine hydrochloride and 0.3g of nickel chloride hexahydrate to the above solution. Mechanical stirring is carried out at room temperature for 10h. Then, the sample is separated using an external magnetic field, and then washed with deionized water and anhydrous ethanol 6 times respectively, and dried at 60℃ for 10h. Then, the sample is carbonized for 5h at a heating rate of 5℃ / min and a nitrogen atmosphere of 100mL / min to obtain Co3O4@C / Ni core-shell structure material. Step 2. Preparation of fibrous Ti3C2T x MXene materials: 1.0 g of LiF was dissolved in 20 mL of HCl (9 M), and then 1.0 g of MAX phase was added. After dispersion, the mixture was transferred to a polytetrafluoroethylene container and heated to 35 ° C for 24 h under magnetic stirring. The precipitate obtained by centrifugation was washed to neutrality, then dispersed in water and ultrasonicated for 30 min. The upper limit of the centrifugal speed was controlled at 4000 rpm and the lower limit was controlled at 3000 rpm. The suspension obtained by ultrasonication was Ti3C2T x MXene nanosheet dispersion. 0.5g of exfoliated few-layer Ti3C2T x MXene nanosheets were added to 60 mL of NaOH solution (6 mol L -1 ) and shaken at 40 °C for 36 h to obtain fibrous Ti3C2T x MXene dispersion. Step 3. Preparation of fibrous Co3O4@C / Ni / Ti3C2T x MXene composite absorber: 30 mg Co3O4@C / Ni nanoparticles, 50 mg CTAB and 60 mL deionized water were added to a 150 mL three-necked flask and then ultrasonicated for 30 min. Mechanical stirring was then performed for 2 h. Then, 60 mL Ti3C2T x The fibrous solution (2 mg / mL) was stirred mechanically for 4 h and washed three times with deionized water (9000 rpm, 10 min). The Co3O4@C / Ni / Ti3C2T x Nanofiber dispersion. Co3O4@C / Ni / Ti3C2T was synthesized by vacuum freeze drying for 12 h. x Nanofiber composite materials. Comparative Example 8 The difference between this comparative example and Example 1 is that the Co3O4@C / Ni core-shell structure material and the fibrous Ti3C2T x The mass ratio of MXene is 2:1, as follows: Step 1. Preparation of Co3O4@C / Ni core-shell structure material: Disperse 0.6g Co3O4 in a mixture of 100mL of ethanol and 60mL of deionized water, and then ultrasonicate for 30min. Then add 5mL of ammonia solution. After stirring for 10min, add 0.3g of dopamine hydrochloride and 0.3g of nickel chloride hexahydrate to the above solution. Mechanical stirring is carried out at room temperature for 10h. Then, the sample is separated using an external magnetic field, and then washed with deionized water and anhydrous ethanol 6 times respectively, and dried at 60℃ for 10h. Then, the sample is carbonized for 5h at a heating rate of 5℃ / min and a nitrogen atmosphere of 100mL / min to obtain Co3O4@C / Ni core-shell structure material. Step 2. Preparation of fibrous Ti3C2T x MXene materials: 1.0 g of LiF was dissolved in 20 mL of HCl (9 M), and then 1.0 g of MAX phase was added. After dispersion, the mixture was transferred to a polytetrafluoroethylene container and heated to 35 ° C for 24 h under magnetic stirring. The precipitate obtained by centrifugation was washed to neutrality, then dispersed in water and ultrasonicated for 30 min. The upper limit of the centrifugal speed was controlled at 4000 rpm and the lower limit was controlled at 3000 rpm. The suspension obtained by ultrasonication was Ti3C2T x MXene nanosheet dispersion. 0.5g of exfoliated few-layer Ti3C2T x MXene nanosheets were added to 60 mL of NaOH solution (6 mol L -1 ) and shaken at 40 °C for 36 h to obtain fibrous Ti3C2T x MXene dispersion. Step 3. Preparation of fibrous Co3O4@C / Ni / Ti3C2T x MXene composite absorber: 30 mg Co3O4@C / Ni nanoparticles, 50 mg CTAB, and 60 mL deionized water were added to a 150 mL three-necked flask and then ultrasonicated for 30 min. Mechanical stirring was then performed for 2 h. 7.5 mL Ti3C2T x The fibrous solution (2 mg / mL) was stirred mechanically for 4 h and washed three times with deionized water (9000 rpm, 10 min). The Co3O4@C / Ni / Ti3C2T x Nanofiber dispersion. Co3O4@C / Ni / Ti3C2T was synthesized by vacuum freeze drying for 12 h. xNanofiber composite materials. Performance measurement: 1. The Co3O4@C / Ni prepared in step 1 of Example 1 and the fibrous Ti3C2T prepared in step 2 were tested and analyzed by Lab X XRD-6000 X-ray diffractometer. x MXene and fibrous Co3O4@C / Ni / Ti3C2T prepared in step 3 of Example 1 x Phase components of MXene composite absorbers. The results are as follows Figure 2 As shown, Co3O4@C / Ni nanoparticles show typical spinel structure diffraction peaks, all characteristic peak positions correspond perfectly to the standard card, and no impurity peaks are observed, indicating that the sample has high crystallinity and phase purity. x The XRD pattern of the composite material not only retains the characteristic diffraction peaks of Co3O4@C / Ni but also exhibits the unique crystal plane diffraction signals of MXene. Notably, the shift in the characteristic MXene peaks indicates a shift in the lattice spacing within the composite, providing direct structural evidence for the formation of a fibrous structure. This composite structure significantly enhances its absorption performance, primarily due to the synergistic effects of three factors: 1. Expanded MXene interlayer spacing: The increased interplanar spacing of the fibrous MXene support enhances the interfacial polarization effect, allowing trapped charges to migrate and relax under the influence of the electromagnetic field, dissipating energy. 2. Core-shell structure and heterogeneous interfaces: The formation of the Co3O4@C / Ni core-shell particles introduces numerous lattice distortions, defects, and heterogeneous interfaces, which act as strong dipole polarization centers, dissipating electromagnetic waves through polarization relaxation. 3. Strongly coupled conductive network: Dopamine hydrochloride achieves a stable, low-resistance connection between the core-shell particles and the MXene fibers, constructing an efficient three-dimensional conductive network. This greatly promotes conductive losses (eddy current effect), while the unique hierarchical structure extends the electromagnetic wave path through multiple reflections / scattering, allowing the above loss mechanism to absorb energy more fully. 2. The prepared fibrous Co3O4@C / Ni / Ti3C2T was analyzed by theta 300xt X-ray photoelectron spectroscopy x Elements of MXene composite absorbers were characterized. The results of Example 3 are as follows Figure 3As shown in the complete X-ray photoelectron spectroscopy (XPS) analysis, we clearly detected the characteristic signal peaks of C1s, O1s, Ti 2p, Ni 2p and Co 2p. This result provides direct and key experimental evidence for the multi-level structure design of composite materials from the level of elemental composition and chemical state. The core principle is that XPS accurately analyzes the type, chemical state and relative content of elements by measuring the kinetic energy of photoelectrons emitted after the surface of the material is excited by X-rays. Specific to this system: C1s signal comes not only from the carbon shell in the core-shell structure Co3O4@C / Ni (such as sp 2 / sp 3 The presence of hybrid carbon) also significantly comes from the carbon skeleton and functional groups (such as CC / C=C, CO, C=O) in the polydopamine (PDA) coating that connects the particles to the carrier. Its peak position and peak shape can further reveal the chemical environment of the carbon (such as the rich oxygen-containing functional group characteristics in PDA); the O1s signal has multiple sources, including Co3O4 lattice oxygen, rich oxygen-containing end groups on the surface of the MXene carrier, adsorbed oxygen or defective oxygen in the PDA layer and carbon shell, and its fine peak separation can reflect the distribution of oxygen species and the interfacial bonding state (such as the possible existence of Ti-O-Co / Ni or CO-Ti bonds); the Ti 2p doublet clearly indicates the presence of fibrous Ti3C2Tx MXene carrier, and its binding energy position and peak spacing can support the layered structural characteristics of MXene and its surface chemistry (such as Ti-C, Ti-O / Ti-OH bonds); the Ni 2p signal directly confirms the successful coating of the nickel shell (Ni) on the outer layer of the core-shell structure, and its binding energy and satellite peak characteristics can be used to distinguish metallic nickel (Ni 0 ) and possible oxidation states of nickel (Ni 2+ ); The Co 2p signal is attributed to the core active component Co3O4, and its characteristic spin-orbit splitting peaks (Co 2p3 / 2 and Co 2p1 / 2) and strong satellite peaks are typical Co 3+ / Co 2+ The coexistence of these elements and their detailed spectral characteristics not only verify the successful integration of all pre-defined components (Co3O4 core, C / Ni shell, PDA interface layer, and Ti3C2Tx support) in the target composite material, but also, through analysis of the chemical shifts and relative intensities of each element, as well as the possible emergence of new interface-related peaks (such as Ti-OC), reveal in-depth information about the electronic interactions between components (such as charge transfer between Co3O4 and the Ni shell), the chemical bonding state of the heterogeneous interface (such as strong adhesion mediated by PDA), and the surface chemical environment. This provides a crucial microstructural basis for understanding its superior microwave absorption properties (such as optimized impedance matching, enhanced interfacial polarization, and conductive loss). 3. The Co3O4@C / Ni prepared in step 1 of Example 1 and the fibrous Ti3C2T prepared in step 2 of Example 1 were observed by HT7800 Hitachi transmission electron microscope. x MXene and fibrous Co3O4@C / Ni / Ti3C2T prepared in step 3 of Example 1 x The morphology of MXene composite absorber materials was characterized. The results are as follows Figure 4 As shown, Figure 4 Figures 4(a) and 4(b) reveal the unique structure of the Co₃O₄@C / Ni composite. Prepared via a multi-coating technique, this composite exhibits uniform spherical shapes with diameters ranging from 200-300 nm, forming a typical "core-shell" structure with excellent monodispersity. The carbon layer tightly coats the surface of the Co₃O₄ core, effectively preventing aggregation caused by the Co₃O₄'s magnetic properties. Furthermore, nickel nanoparticles with diameters of approximately 20-30 nm are uniformly attached to the outer surface of the carbon layer. Figure 4 (c) to (f) further show the Ti3C2T formed after alkaline oscillation x The fibrous structure of MXene materials and their good combination with Co3O4@C / Ni particles. XPS and XRD analysis accurately confirmed the elemental composition and valence state of the composite material, while TEM images verified the structure with Co3O4 as the core, C layer wrapped, and Ni nanoparticles attached, and showed that the fibrous Ti3C2T x MXene successfully supported Co3O4@C / Ni particles, thus confirming the successful preparation of fibrous composites. xThe formation mechanism of MXene's transition from a layered to a fibrous structure is essentially a dimensional transformation of two-dimensional materials, regulated by surface chemistry. Its core lies in achieving a controlled transition from layered to fibrous structures through precise control of the material's surface chemical state. This process begins with the selective etching of the MAX phase. In an acidic environment, a highly oxidizing fluorine-containing etchant preferentially attacks the metal-carbon bonds of the metal atomic layer in the MAX phase, stripping the metal atoms from the crystal structure through a coordination dissolution mechanism, while simultaneously forming abundant terminal groups on the nascent Ti3C2 surface. These terminal groups not only determine the surface charge distribution of MXene nanosheets but also serve as active sites for subsequent self-assembly. Their type and number directly influence the colloidal stability and interfacial interaction energy of the material. When the system is transferred to an alkaline environment, the terminal hydroxyl groups undergo deprotonation under strong alkaline conditions, leading to the formation of localized negatively charged regions at the edges of the nanosheets. Under kinetic control, a specific attraction between the charged edges and the neutral basal planes drives the nanosheets to align through an "edge-to-face" contact mode. Van der Waals forces act as the primary driving force for the axially dense stacking of the nanosheets, while the residual hydrogen bond network provides lateral stabilization, preventing excessive aggregation. Notably, the solution ionic strength plays a key role in this stage, balancing the repulsive and attractive forces between the nanosheets by regulating the thickness of the double layer, ensuring the formation of fibers with a high aspect ratio rather than disordered aggregates. Finally, freeze-drying achieves structural fixation, further optimizing the fiber structure through a templating effect. Furthermore, the intermolecular forces of the terminal groups form a cross-linked network during dehydration, conferring excellent mechanical integrity to the fibers. 4. The fibrous Co3O4@C / Ni / Ti3C2T prepared in Example 1, Example 2 and Example 3 were analyzed by Agilent N5222a vector network analyzer. x The absorbing parameters of MXene composite absorbing materials are analyzed. The results are as follows Figure 5 As shown, Figure 5 The frequency-dependent changes in the electromagnetic properties of Examples 1-3 are described in detail, including the complex dielectric constant (ε′ and ε″), complex magnetic permeability (μ′ and μ″), dielectric loss tangent (tanεE), and magnetic loss tangent (tanμE). The dynamic changes in these parameters not only reveal the diversity of the electromagnetic properties of the materials, but also provide inspiration for revealing the mysteries of their physical mechanisms. As for the real part of the complex dielectric constant (ε′), Figure 5 The ε′ value of Example 2 in (a) is significantly higher than that of Example 1 and Example 3, while its imaginary part (ε″) is almost the same among the three. According to the free electron theory, this phenomenon is mainly attributed to the difference in conductivity. With the thickening of the carbon layer and the introduction of Ni nanoparticles, the carrier concentration and free electron mobility on the surface of the composite material are significantly improved, thereby enhancing the conductivity and dielectric response of the material. Figure 5 The changes in complex magnetic permeability in (c) and (d) show that the μ′ value of Example 3 is the most prominent, indicating an enhanced magnetization ability. This may be due to the small size effect of Ni nanoparticles and their aggregation state, which optimizes the formation and arrangement of magnetic domains, thereby enhancing the magnetic properties of the material. Although the μ″ value of Example 3 is slightly higher, which means that the magnetic loss is also larger, this does not mean that it has the best absorption performance, because excessive magnetic loss may cause reflection of electromagnetic waves. Figure 5 In (e), the tanεE value of Example 2 is higher, which directly reflects the enhancement of its dielectric loss capability. This is attributed to the sufficient addition of carbon shell and Ni source, which together promote the accumulation and polarization of surface charge of the material, thereby increasing the dielectric loss. On the other hand, in Figure 5 In (f), Example 2 has a higher tanμE value than the other two groups, indicating that its magnetic loss and dielectric loss are relatively balanced. This coordinated loss mechanism generally indicates that the material has stronger electromagnetic wave absorption capacity and exhibits better electromagnetic wave absorption properties. 5. The fibrous Co3O4@C / Ni / Ti3C2T prepared in Examples 1-3 was analyzed by Agilent N5222a vector network analyzer. x Reflection loss analysis was performed on MXene and the composite absorbing materials of Comparative Examples 1-8. Figure 6 Figures 1-3 describe the microwave absorption characteristics of the three samples of Examples 1-3. Specifically, the minimum reflection loss (RL) value of the sample of Example 1 with a thickness of 4.0 mm is -34.6 dB, and its maximum effective bandwidth is 6.7 GHz; the sample of Example 2 with a thickness of 5.0 mm performs better in microwave absorption, with an RL value as low as -44.9 dB and an extended bandwidth of 6.7 GHz; the minimum RL value of the sample of Example 3 with a thickness of 4.0 mm is -41.1 dB, and the effective bandwidth is 5.1 GHz. In order to explore the intrinsic reasons for the excellent performance of the example samples, we used a network analyzer to conduct a detailed study of the 2-18 GHz frequency band. The study shows that dielectric loss is mainly composed of three major mechanisms: interface polarization, dipole polarization, and Debye relaxation phenomenon. Interface polarization mainly originates from the heterogeneous interfaces formed between different components. These interfaces act as polarization centers and effectively enhance the overall polarization effect. On the other hand, dipole polarization is generated when electric dipoles are excited under the action of a high-frequency electric field, and its intensity is closely related to the number of crystal defects in the material. Considering the fibrous Co3O4@C / Ni / Ti3C2T x Due to the complex preparation process and component composition, the material contains a large number of defects in the lattice, which can provide more positions for dipole polarization to improve the efficient absorption of microwaves. Figure 6 Figure 4 is comparative example 1, where Co3O4 / Ti3C2T x(Without core-shell structure), the minimum reflection loss (RL) value of the comparative example 1 sample with a thickness of 5.0 mm is -22.8 dB, and its maximum effective bandwidth is 4.7 GHz. Its reflection loss performance is significantly weaker than that of Example 1. The core problem is that the simplification of the structure leads to the lack of multiple loss mechanisms. Co3O4 is directly loaded on the surface of the MXene fiber, without the dielectric buffering effect of the carbon layer (C) or the magnetic loss supplement of the nickel layer (Ni). This leads to two defects: insufficient polarization loss: there is a lack of carbon layer transition between Co3O4 and MXene, the number of heterogeneous interfaces is sharply reduced, and the interface polarization effect is weakened; the impedance mismatch is aggravated: the high conductivity of MXene is in direct contact with the dielectric properties of Co3O4, the electromagnetic wave is enhanced in surface reflection, and it is difficult to enter the interior of the material and be dissipated. Figure 6 Figure 5 is comparative example 2, where Co3O4@C / Ti3C2T x The lowest reflection loss (RL) value for a 5.0mm-thick sample (without the Ni layer) was -26.5dB, with a maximum effective bandwidth of 4.1GHz. While the introduction of a carbon layer improves interfacial polarization, shortcomings remain in the magnetic loss domain. The absence of the nickel shell (Ni) results in a decrease in the overall magnetic permeability (μ") of the material, weakening its magnetic resonance loss capability. While the carbon layer improves dielectric loss, it lacks the magnetic response modulation of Ni, resulting in suboptimal impedance matching (particularly high reflection loss at low frequencies). Figure 6 Figure 6 is comparative example 3, pure Ti3C2T x MXene fiber, as a single-component material, has a minimum reflection loss (RL) value of -13.7dB for a sample with a thickness of 5.5mm. Its maximum effective bandwidth is 2.9GHz, and its RL performance is the worst, exposing the intrinsic defects of MXene: high conductivity causes strong reflection: the impedance of the MXene surface and the free space is seriously mismatched, and most electromagnetic waves are reflected; the loss mechanism is single: it only relies on limited dielectric loss (conduction loss + dipole polarization), without magnetic loss compensation, and lacks the heterogeneous interface enhanced polarization effect. Figure 6 Figure 7 shows comparative example 4, layered MXene (non-fibrous structure). The minimum reflection loss (RL) value of the sample with a thickness of 5.0 mm is -31.6 dB, and its maximum effective bandwidth is 4.1 GHz. When ordinary layered MXene is used instead of fibrous MXene, the performance is significantly deteriorated, highlighting the core advantages of the fiber structure: shortened loss path: the two-dimensional stacking structure of layered MXene limits the multiple reflections of electromagnetic waves, while the three-dimensional network of fibrous MXene can extend the wave propagation path; directional transmission failure: the "waveguide effect" of the fiber can cause the electromagnetic wave to be transmitted and dissipated along the axial direction, and the layered structure does not have this feature. Figure 6Figure 8 shows comparative example 5. The minimum reflection loss (RL) value of comparative example 5 with a thickness of 5.5 mm is -18.3 dB, and its maximum effective bandwidth is 4.7 GHz. The main reason why the absorption performance is reduced by replacing nickel with other materials is the loss of magnetic loss capacity and the failure of magnetic-dielectric synergistic regulation. As a typical magnetic metal, the core contribution of nickel is to provide a significant imaginary part of magnetic permeability (μ”) and magnetic resonance loss mechanism, which is the key to achieving broadband and efficient absorption. After removing nickel, even if a high dielectric loss material (such as a carbon layer) is introduced, the system loses the crucial magnetic loss path, resulting in a significant weakening of the total loss capacity. More importantly, the absorption performance is highly dependent on the matching of material impedance with free space, which requires a certain synergistic balance between the complex dielectric constant (ε) and the complex magnetic permeability (μ). Figure 6 Figure 9 is comparative example 6. The minimum reflection loss (RL) value of the sample is -19.3dB, and its maximum effective bandwidth is 4.1GHz. The presence of nickel can effectively adjust the overall magnetic response and compensate for the mismatch that may be caused by the high dielectric constant. Once replaced with non-magnetic or weakly magnetic materials (such as pure carbon, ceramics or certain polymers), the magnetic permeability (μ' and μ") of the material in the low frequency band is significantly reduced, while the dielectric constant (ε' and ε") is relatively high, causing the impedance to deviate seriously from the ideal value (Z≈1). This magneto-electric imbalance causes a large amount of incident electromagnetic waves to be reflected on the surface rather than dissipated inside the material, especially in the low-frequency region with longer wavelengths, the reflection loss (RL) rises sharply, and the overall absorption performance deteriorates. In short, the lack of nickel's magnetic loss and its ability to optimize impedance are the essential reasons for the performance degradation. Figure 6 Figure 10 shows comparative example 7, with a Co3O4@C / Ni to MXene mass ratio of 1:4 (MXene excess). The minimum reflection loss (RL) value of the sample with a thickness of 5.0 mm is -33.5 dB, and its maximum effective bandwidth is 3.2 GHz. When the proportion of MXene is too high, the conductive network overload causes negative effects: severe impedance mismatch: excessive MXene causes a surge in the overall conductivity of the material, making it difficult for electromagnetic waves to penetrate the interior of the material; dilution of magnetic components: the magnetic loss contribution of Co3O4@C / Ni is diluted, weakening the low-frequency wave absorption capability. Figure 6 Figure 11 is comparative example 8, with a Co3O4@C / Ni and MXene mass ratio of 2:1 (insufficient MXene). The minimum reflection loss (RL) value of the sample with a thickness of 4.5 mm is -34.3 dB, and its maximum effective bandwidth is 5.2 GHz. When the proportion of MXene is too low, the three-dimensional conductive skeleton is imperfect: the charge transfer efficiency decreases: the density of the MXene fiber network is insufficient, the electron transfer between the core-shell particles is hindered, and the conductive loss is reduced; the interface polarization is weakened: the number of heterogeneous interfaces provided by the MXene carrier is reduced, and the polarization relaxation loss is limited. The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Any person skilled in the art can, without departing from the spirit and technical solution of the present invention, use the methods and technical contents disclosed above to make many possible changes and modifications to the technical solution of the present invention, or modify it into an equivalent embodiment with equivalent changes. Therefore, any simple modification, equivalent replacement, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A Co3O4@C / Ni / Ti3C2T x The method for preparing a nanofiber composite absorbing material is characterized in that: The following steps are involved: Step 1. Preparation of Co3O4@C / Ni core-shell structure material: Co3O4 powder is uniformly dispersed in an ethanol aqueous solution, ultrasonically treated, and then an appropriate amount of ammonia solution is added to adjust the pH value of the reaction system. After stirring, dopamine hydrochloride and a nickel salt precursor are added in sequence. After stirring and reacting, the mixture is separated, washed, and heat-treated to obtain a Co3O4@C / Ni core-shell structure material; Step 2. Preparation of fibrous Ti3C2T x MXene material: Lithium salt is dissolved in concentrated hydrochloric acid solution, MAX phase precursor powder is added and mixed thoroughly, and then etching reaction is carried out. After the reaction is completed, the product is filtered, washed, and centrifuged. The product is redispersed in deionized water and ultrasonically treated to peel off the few-layer Ti3C2T x MXene nanosheets are mixed with alkaline solution and oscillated at constant temperature to obtain fibrous Ti3C2T x MXene dispersion; Step 3. Preparation of Co3O4@C / Ni / Ti3C2T x Nanofiber composite absorber: Co3O4@C / Ni core-shell structure material and surfactant are dispersed in deionized water, ultrasonically treated and mechanically stirred to form a uniform dispersion system, and fibrous Ti3C2T x MXene dispersion was mechanically stirred for composite reaction, the product was collected by centrifugation, washed and freeze-dried to obtain Co3O4@C / Ni / Ti3C2T x Nanofiber composite absorbing materials.

2. A Co3O4@C / Ni / Ti3C2T according to claim 1 x The method for preparing a nanofiber composite absorbing material is characterized by: In step 1, the concentration of the ethanol aqueous solution is 60-65% (v / v), the pH value of the reaction system is adjusted to 10-11, the nickel salt precursor is nickel chloride hexahydrate or nickel nitrate hexahydrate, and the mass ratio of Co3O4, dopamine hydrochloride and nickel salt precursor is (2-4):(1-2):

1.

3. A Co3O4@C / Ni / Ti3C2T according to claim 1 x The method for preparing a nanofiber composite absorbing material is characterized by: The stirring reaction time in step 1 is 8-10 hours, and the heat treatment conditions are drying at 50-60° C. for 10-12 hours, heating to 500° C. at a rate of 3-6° C. / min, and keeping warm for 8 hours.

4. A Co3O4@C / Ni / Ti3C2T according to claim 1 x The method for preparing a nanofiber composite absorbing material is characterized by: The concentration of concentrated hydrochloric acid in step 2 is 9-12 mol / L, the mass ratio of lithium salt, MAX phase precursor powder and concentrated hydrochloric acid is (1-3): (1-3): (20-50), and the alkaline solution is 5-6 mol L -1 NaOH solution, Ti3C2T x The mass ratio of MXene nanosheets to alkaline solution is 1:(13-15).

5. A Co3O4@C / Ni / Ti3C2T according to claim 1 x The method for preparing a nanofiber composite absorbing material is characterized by: In step 2, the etching reaction temperature is 35° C., the centrifugal speed is 3000-4000 rpm, the constant temperature oscillation temperature is 40-50° C., and the time is 35-40 h.

6. A Co3O4@C / Ni / Ti3C2T according to claim 1 x The method for preparing a nanofiber composite absorbing material is characterized by: In the step 3, the mass ratio of the Co3O4@C / Ni core-shell structure material, the surfactant and the deionized water is (3-5): (5-7): (6-10), and the Co3O4@C / Ni core-shell structure material and the fibrous Ti3C2T x The mass ratio of MXene is 1:(1-3).

7. The Co3O4@C / Ni / Ti3C2T according to claim 1 x The method for preparing a nanofiber composite absorbing material is characterized by: In step 3, the ultrasonic treatment time is 20-40 min, the mechanical stirring rate is 500-700 rpm, the mechanical stirring time is 4-6 h, the centrifugal speed is 9000-10000 rpm, the centrifugal time is 8-10 min, and the freeze-drying time is 12-16 h.

8. Co3O4@C / Ni / Ti3C2T prepared by the preparation method according to any one of claims 1 to 7 x Nanofiber composite absorbing materials.

9. Co3O4@C / Ni / Ti3C2T prepared by the preparation method according to any one of claims 1 to 7 x Application of nanofiber composite absorbing materials in electromagnetic protection materials.

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