MXene / CoFe2O4-coated CNT multifunctional composite film and preparation method thereof

Abstract

The invention discloses an MXene / CoFe2O4-coated CNT multifunctional composite film and a preparation method thereof, and relates to the technical field of electromagnetic functional materials and flexible electric heating materials. The thin film adopts a three-layer sandwich structure of an MXene conducting layer, a CoFe2O4 and CNT composite middle layer and an MXene surface packaging layer. The preparation method of the thin film comprises the following steps: (1) preparing an MXene suspension; (2) preparation of CoFe2O4 (at) CNT powder; (3) preparing a CoFe2O4 (at) CNT aqueous dispersion; and (4) assembling a multi-layer composite membrane. The composite film has excellent electromagnetic interference shielding effectiveness and rapid and controllable Joule heating performance, meanwhile, the shielding efficiency in the X-waveband frequency range can reach 44.41 dB at most, and rapid temperature rise from room temperature to 216 DEG C and high-stability electric heating response can be achieved under the low voltage of 1-5V. The multifunctional thin film has the advantages of being light, thin, flexible, simple and convenient in process, capable of being produced on a large scale and the like, and has wide application prospects in application of manufacturing of flexible electronic devices, electromagnetic protection and intelligent heating.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electromagnetic protection and flexible electrocaloric materials, and particularly relates to a MXene / CoFe2O4@CNT multifunctional composite film and a preparation method thereof. BACKGROUND

[0002] With the rapid development of information technology, communication electronics and intelligent equipment, the problem of electromagnetic wave radiation pollution is increasingly prominent. Excessive electromagnetic radiation not only interferes with the normal operation of precision instruments, but also causes potential harm to human health and the ecological environment. At the same time, energy crisis and environmental pollution have become major challenges faced by the world, and the development of green, efficient and renewable energy utilization and energy management technology has become the focus of international research. Under this background, multifunctional materials with electromagnetic interference shielding and electrocaloric conversion functions have attracted widespread attention. Electromagnetic shielding technology can effectively attenuate electromagnetic wave energy through reflection, absorption and multiple scattering mechanisms, thereby protecting electronic devices from external interference; and Joule heating technology can efficiently convert electrical energy into heat energy, providing core support for flexible defrosting, wearable heaters, intelligent temperature control systems and the like. If electromagnetic shielding and electrocaloric regulation can be realized in the same material system, it will greatly promote the integration and lightweight development of flexible electronic devices and intelligent protection systems.

[0003] However, the existing material system still has many bottlenecks. On the one hand, although traditional metal shielding materials (such as copper, aluminum, stainless steel, etc.) have high electrical conductivity, they are heavy, flexible, and easily oxidized and corroded, which are not suitable for use in wearable or miniaturized devices; on the other hand, although polymer-based composite materials are lightweight and flexible, due to uneven dispersion of conductive fillers and poor interface bonding, their electromagnetic shielding efficiency and thermal stability are generally low, and it is difficult to balance high electrical conductivity and high durability.

[0004] In recent years, new nanomaterials such as MXene, carbon nanotubes (CNTs) and magnetic cobalt ferrite (CoFe2O4) have become ideal candidates for constructing multifunctional composite systems due to their excellent electrical, magnetic and structural properties. MXene, as a kind of two-dimensional transition metal carbide / nitride, has high carrier mobility and rich surface functional groups, which can provide good conductive paths and interface bonding platforms; carbon nanotubes have excellent electrical conductivity, mechanical flexibility and low density, and can form a three-dimensional interconnected conductive network; and cobalt ferrite nanoparticles have significant magnetic loss characteristics, which can achieve magnetic absorption through natural resonance and eddy current effect. However, single material systems often have performance bias: MXene and CNTs have excellent electrical conductivity, but are mainly reflective and have insufficient absorption; CoFe2O4 has magnetic loss characteristics, but has low electrical conductivity and cannot achieve efficient electromagnetic attenuation when used alone. In addition, the interface compatibility and dispersion of different materials are poor, the interlayer bonding is weak, and the thermal cycle stability is insufficient, which seriously restricts the comprehensive performance of the composite system.

[0005] Therefore, how to realize the synergistic coupling of dielectric materials (MXene, CNTs) and magnetic materials (CoFe2O4) through interface engineering and structural design, construct a stable “dielectric-magnetic-dielectric” multilayer structure system, and simultaneously realize efficient electromagnetic absorption, excellent electrical conductivity and rapid Joule heating function, has become a key scientific and technical problem to be solved in the field. SUMMARY

[0006] In order to overcome the problems of complex material structure, poor interface bonding, difficult to balance electrical conductivity and magnetic loss performance and the like in the prior art, the present application provides a MXene / CoFe2O4@CNT multifunctional composite film and a preparation method thereof. The film realizes the synergistic enhancement of multi-mechanism absorption of electromagnetic waves and rapid Joule heating through a unique “dielectric-magnetic-dielectric” layered structure design, while ensuring lightweight and flexibility, the material is endowed with excellent electromagnetic protection and electrothermal conversion performance.

[0007] In order to achieve the above purpose, the present application provides the following technical scheme: According to a first aspect of the present application, a MXene / CoFe2O4@CNT multifunctional composite film is provided, which comprises a MXene conductive layer, a CoFe2O4@CNT composite intermediate layer and a MXene surface encapsulation layer which are stacked in sequence.

[0008] Further, in the CoFe2O4@CNT composite intermediate layer, cobalt ferrite nanoparticles are uniformly anchored on the surface of carboxylated carbon nanotubes to form a dielectric-magnetic synergistic structure.

[0009] Further, the MXene is Ti3C2T x , and the Tx is -OH, -O, or -F functional group.

[0010] Further, the total thickness of the composite film is 10-30 µm, and the mass per unit area is less than 0.2 g / cm².

[0011] Further, the electromagnetic shielding effectiveness of the composite film is greater than 40 dB in the frequency range of 8.2-12.4 GHz.

[0012] Further, the surface temperature of the composite film under a direct current voltage of 1-5 V can be raised from room temperature to above 200℃ within 60 s.

[0013] According to a second aspect of the present application, a preparation method of MXene / CoFe2O4@CNT multifunctional composite film is provided, comprising the following steps (1) Preparation of MXene suspension: MXene suspension is prepared by etching Ti3AlC2 with LiF / HCl; (2) Preparation of CoFe2O4@CNT powder: Carboxylated carbon nanotubes, iron nitrate nonahydrate, and cobalt acetate tetrahydrate are added in a mixed solvent containing ethylene glycol and urea, and then hydrothermal reaction is carried out at 180℃ for 12 h, followed by washing and drying to obtain CoFe2O4@CNT powder; (3) Preparation of CoFe2O4@CNT dispersion: CoFe2O4@CNT powder is compounded with sodium dodecylbenzenesulfonate at a mass ratio of 1:10, and then deionized water is added and ultrasonic dispersion is carried out to obtain stable CoFe2O4@CNT water dispersion; (4) Assembly of multi-layer composite film: vacuum filtration method is used to sequentially deposit each layer of MXene / CoFe2O4@CNT multifunctional composite film, and the following operations are carried out: a. The MXene suspension obtained in step (1) is vacuum filtered and deposited to form a MXene conductive layer; b. The CoFe2O4@CNT water dispersion obtained in step (3) is vacuum filtered and deposited on the MXene conductive layer to form a CoFe2O4@CNT composite intermediate layer; c. The MXene suspension obtained in step (1) is vacuum filtered and deposited on the CoFe2O4@CNT composite intermediate layer to form a MXene surface encapsulation layer, and after drying, the MXene / CoFe2O4@CNT multifunctional composite film is peeled off.

[0014] Further, in step (1), the concentration of the MXene suspension is 1 mg / mL, the etching temperature is 40℃, and the time is 24 h.

[0015] Further, the molar ratio of the cobalt acetate tetrahydrate to the iron nitrate nonahydrate in step (2) is 1:2, the molar ratio of the urea to the iron nitrate nonahydrate is 6:1, and the pH value of the solution is controlled at 9-10.

[0016] Further, the deposition volume of each layer of the vacuum filtration is as follows: 3 mL for each of the MXene conductive layer and the MXene surface encapsulation layer, 6-14 mL for the CoFe2O4@CNT composite intermediate layer, and 1 mg / mL for each of the concentration of the MXene layer and the concentration of the CoFe2O4@CNT layer.

[0017] The application provides a preparation method of a MXene / CoFe2O4@CNT multifunctional composite film. 1. Structural innovation and performance synergy: The MXene-CoFe2O4@CNT-MXene "dielectric-magnetic-dielectric" layered structure has high conductivity, high magnetic loss, and multi-interface polarization effect, which significantly improves the electromagnetic wave attenuation efficiency.

[0018] 2. Excellent electrothermal performance: The continuous conductive network and the magnetic dielectric synergistic structure enable the film to achieve rapid and stable Joule heating response at low voltage, with high heating rate and uniform heat distribution.

[0019] 3. High stability and flexibility: The outer MXene surface encapsulation layer effectively improves the structural integrity, and the film still maintains stable electrical properties under repeated bending or thermal cycling conditions.

[0020] 4. Simple process and easy to scale: All steps can be completed under normal pressure and temperature conditions without the need for vacuum deposition equipment, which is suitable for roll-to-roll flexible electronic production and has potential for large-scale application. BRIEF DESCRIPTION OF DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the application or the technical solutions in the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only exemplary, and for those skilled in the art, other drawings can be obtained without creative labor on the basis of the provided drawings.

[0022] The structures, proportions, sizes, etc. shown in the specification are only used to cooperate with the content disclosed in the specification, to be understood and read by those skilled in the art, and do not define the limiting conditions for the implementation of the application, so they do not have technical significance. Any modification of the structure, change of the proportion relationship or adjustment of the size, without affecting the effect and purpose that can be achieved by the application, should still fall within the scope of the technical content disclosed by the application.

[0023] Figure 1 A schematic diagram of the preparation process of the MXene / CoFe2O4@CNT multifunctional composite film provided by the present application is shown in the figure; Figure 2 A TEM image of the CoFe2O4@CNT powder provided by the present application is shown in the figure; Figure 3 An energy spectrum (EDS) element area distribution map of C, O, Fe and Co elements of the CoFe2O4@CNT powder provided by the present application is shown in the figure; Figure 4 An SEM image of the cross-sectional morphology of the MXene / CoFe2O4@CNT multifunctional composite film provided by the present application is shown in the figure; Figure 5 An electromagnetic shielding efficiency diagram of the MXene / CoFe2O4@CNT multifunctional composite film and the M / CNT 14 composite film under 8.2-12.4 GHz provided by the present application is shown in the figure; Figure 6 A time-temperature curve diagram of the MXene / CoFe2O4@CNT multifunctional composite film provided by the present application under 4V voltage is shown in the figure; Figure 7 A time-temperature curve diagram of the MXene / CoFe2O4@CNT multifunctional composite film provided by the present application under different voltages is shown in the figure; Figure 8 A cyclic electric heating test curve diagram of the MXene / CoFe2O4@CNT multifunctional composite film provided by the present application under 4V voltage is shown in the figure; Figure 9 An electromagnetic shielding efficiency diagram of the MXene / CoFe2O4@CNT multifunctional composite film provided by the present application under 8.2-12.4 GHz in untreated, acid and alkali environments is shown in the figure. DETAILED DESCRIPTION

[0024] The embodiments of the present application are described below by specific examples, and those skilled in the art can easily understand other advantages and effects of the present application from the content disclosed in the specification. Obviously, the described examples are part of the examples of the present application, but not all. Based on the examples in the present application, all other examples obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0025] According to a first aspect of the present application, a MXene / CoFe2O4@CNT multifunctional composite film is provided, which includes a MXene conductive layer, a CoFe2O4@CNT composite intermediate layer and a MXene surface packaging layer which are stacked in sequence.

[0026] In the CoFe2O4@CNT composite intermediate layer, the cobalt ferrite nanoparticles are uniformly anchored on the surface of the carboxylated carbon nanotubes, forming a dielectric-magnetic synergistic structure.

[0027] In the formula, MXene is Ti3C2T x , T x is an -OH, -O, or -F functional group.

[0028] In the formula, the total thickness of the composite film is 10-30 µm, and the mass per unit area is less than 0.2 g / cm².

[0029] In the formula, the electromagnetic shielding effectiveness of the composite film in the frequency range of 8.2-12.4 GHz is greater than 40 dB.

[0030] In the formula, the surface temperature of the composite film under a direct current voltage of 1-5 V can be raised from room temperature to above 200°C within 60 s.

[0031] According to a second aspect of the present application, a preparation method of a MXene / CoFe2O4@CNT multifunctional composite film is provided, comprising the following steps (1) Preparation of MXene suspension: MXene suspension is prepared by etching Ti3AlC2 with LiF / HCl; (2) Preparation of CoFe2O4@CNT powder: carboxylated carbon nanotubes, iron nitrate nonahydrate, and cobalt acetate tetrahydrate are added to a mixed solvent containing ethylene glycol and urea, and then hydrothermal reaction is carried out at 180°C for 12 h, followed by washing and drying to obtain CoFe2O4@CNT powder; (3) Preparation of CoFe2O4@CNT aqueous dispersion: CoFe2O4@CNT powder is compounded with sodium dodecylbenzenesulfonate at a mass ratio of 1:10, and then deionized water is added and ultrasonic dispersion is carried out to obtain a stable CoFe2O4@CNT aqueous dispersion; (4) Assembly of multi-layer composite film: vacuum filtration method is used to sequentially deposit each layer of the MXene / CoFe2O4@CNT multifunctional composite film, and the following operations are carried out: a. The MXene suspension obtained in step (1) is vacuum filtered and deposited to form a MXene conductive layer; b. The CoFe2O4@CNT aqueous dispersion obtained in step (3) is vacuum filtered and deposited on the MXene conductive layer to form a CoFe2O4@CNT composite intermediate layer; c. The MXene suspension obtained in step (1) is vacuum filtered and deposited on the CoFe2O4@CNT composite intermediate layer to form a MXene surface encapsulation layer, and after drying, the MXene / CoFe2O4@CNT multifunctional composite film is peeled off.

[0032] The concentration of the MXene suspension in step (1) is 1 mg / mL, the etching temperature is 40°C, and the time is 24 h.

[0033] The molar ratio of cobalt acetate tetrahydrate to iron nitrate nonahydrate in step (2) is 1:2, the molar ratio of urea to iron nitrate nonahydrate is 6:1, and the pH value of the solution is controlled at 9-10.

[0034] The deposition volume of each layer in vacuum filtration is as follows: 3 mL for the MXene conductive layer and the MXene surface packaging layer, and 6-14 mL for the CoFe2O4@CNT composite intermediate layer, wherein the concentration of the MXene layer and the concentration of the CoFe2O4@CNT layer are both 1 mg / mL.

[0035] The application will be described in detail below with specific examples.

[0036] Example 1 The present embodiment provides a preparation method of a MXene / CoFe2O4@CNT multifunctional composite film, comprising the following steps: The specific implementation steps are as shown in Figure 1 S1, preparation of each functional layer material: (1) Preparation of MXene suspension: 1 g of Ti3AlC2 powder (Jilin 11 Technology Co., Ltd.) is weighed and placed in a polytetrafluoroethylene beaker. An etching solution is prepared: 2 g of lithium fluoride (LiF) is dissolved in 20 mL of hydrochloric acid (36 wt%) to generate in-situ HF under room temperature stirring for 20 min. Then the Ti3AlC2 powder is slowly added to the reaction solution, and the reaction is carried out at 40°C in a constant temperature water bath for 24 h. After the reaction is completed, the obtained suspension is washed by centrifugation at 6000 rpm for multiple times until the pH of the supernatant approaches 7. The obtained precipitate is mechanically shaken to form a single-layer or few-layer MXene suspension with a concentration of 1-6 mg / mL, which is ready for use.

[0037] (2) Preparation of CoFe2O4@CNT powder: 50 mg of carboxylated multi-walled carbon nanotubes (purity > 95 wt.%) is weighed and added to a mixed solvent (10 mL of deionized water + 20 mL of ethylene glycol), and ultrasonic dispersion is carried out for 30 min to obtain a uniform suspension. Then Fe(NO3)3·9H2O (1 mmol), Co(CH3COO)2·4H2O (0.5 mmol), and urea (6 mmol) are added, and the mixture is stirred magnetically for 1 h, then transferred to a 50 mL polytetrafluoroethylene-lined stainless steel reaction kettle, and hydrothermal reaction is carried out at 180°C for 12 h. After the reaction is completed, the mixture is naturally cooled to room temperature, washed by centrifugation (3000 rpm, deionized water 3 times, ethanol 2 times), and dried to obtain black CoFe2O4@CNT powder. ​

[0038] (3) Preparation of CoFe2O4@CNT aqueous dispersion: 50 mg of CoFe2O4@CNT powder and sodium dodecylbenzenesulfonate (SDBS) were added to a certain volume of deionized water at a mass ratio of 1:10, and a probe ultrasonic dispersion was performed to obtain a CoFe2O4@CNT aqueous dispersion with a concentration of 1 mg / mL.

[0039] S2, Preparation of composite film: (1) Adjustment of MXene suspension concentration The MXene suspension was ultrasonically dispersed with deionized water to adjust the concentration to 1 mg / mL. The obtained suspension had good dispersibility and stability, and no obvious sedimentation was observed after standing for 24 h.

[0040] (2) Vacuum filtration layer-by-layer assembly A polytetrafluoroethylene (PTFE) filter membrane with a pore size of 0.45 μm was used as the substrate. The vacuum degree was controlled at -0.08 MPa. First, 3 mL of MXene suspension was filtered to form a conductive layer, which had a two-dimensional sheet layer dense packing structure, ensuring a smooth surface and good conductive path. Then, different volumes of CoFe2O4@CNT aqueous dispersion were filtered to form a composite intermediate layer, which had a three-dimensional interwoven network structure, with carbon nanotubes constructing a conductive skeleton and cobalt ferrite nanoparticles uniformly distributed on the tube wall, realizing a magnetic-dielectric synergistic effect. Finally, 3 mL of MXene suspension was filtered again to form a surface encapsulation layer to improve the structural integrity. After filtration, the sample was naturally dried for 2 h, and then placed in a vacuum drying oven at 60°C for 12 h to obtain a composite film after peeling. The obtained film was overall smooth and dense, with a silver-gray to dark gray color, a smooth surface and a metallic luster.

[0041] To obtain different layer thicknesses and composite intermediate layer proportions, the volume of CoFe2O4@CNT aqueous dispersion was adjusted to 6 mL, 8 mL, 10 mL, 12 mL and 14 mL in five groups, while the deposition volume of MXene layer was kept constant (3 mL). The five groups of samples were denoted as M / CFO@CNT x / M (x is the volume of the intermediate layer), which were used for subsequent performance comparison.

[0042] In this example, CoFe2O4@CNT aqueous dispersion with a volume of 14 mL was used for subsequent performance determination, i.e., M / CFO@CNT 14 / M.

[0043] The multifunctional composite film M / CFO@CNT x / M prepared by the above-mentioned optimized process has a tight combination between the functional layers, showing excellent electrical conductivity and environmental stability, providing a reliable guarantee for subsequent applications. The preparation process parameters are clear and have good repeatability, and are suitable for large-scale production.

[0044] Example 2 The present embodiment provides a preparation method of MXene / CNT multifunctional composite film, comprising the following steps: The specific implementation steps are as shown in Figure 1 The specific implementation steps are as shown in S1, preparation of each functional layer material: Preparation of MXene suspension: 1 g of Ti3AlC2 powder (Jilin 11 Technology Co., Ltd.) was placed in a polytetrafluoroethylene beaker. An etching solution was prepared: 2 g of lithium fluoride (LiF) was dissolved in 20 mL of hydrochloric acid (36 wt%), and stirred at room temperature for 20 min to generate in-situ HF. Then the Ti3AlC2 powder was slowly added to the reaction solution, and reacted at 40°C in a constant temperature water bath for 24 h. After the reaction was completed, the obtained suspension was centrifuged at 6000 rpm and washed several times until the supernatant pH was close to 7. The obtained precipitate was mechanically shaken to form a single-layer or few-layer MXene suspension, with a concentration of 1-6 mg / mL, ready for use.

[0045] Preparation of CNT aqueous dispersion: 50 mg of CNT powder and sodium dodecylbenzenesulfonate (SDBS) were added to a certain volume of deionized water at a mass ratio of 1:10, and a CNT aqueous dispersion with a concentration of 1 mg / mL was obtained by probe ultrasonic dispersion.

[0046] S2, preparation of composite film: (1) Redispersion and concentration adjustment of MXene suspension The MXene suspension was ultrasonically dispersed for 30 min, and the MXene suspension concentration was adjusted to 1 mg / mL with deionized water. The obtained suspension should have good dispersibility and stability, and no obvious sedimentation was observed after standing for 24 h.

[0047] (2) Vacuum filtration layer-by-layer assembly A polytetrafluoroethylene (PTFE) filter membrane with a pore size of 0.45 μm was used as the substrate. The vacuum degree was controlled at -0.08 MPa. First, 3 mL of MXene suspension was filtered to form a bottom conductive layer, which had a two-dimensional sheet layer dense accumulation structure, ensuring a smooth surface and good conductive path; then 14 mL of CNT aqueous dispersion was filtered to form a composite intermediate layer, which had a three-dimensional interwoven network structure, and the carbon nanotubes constructed a conductive skeleton; and then 3 mL of MXene suspension was filtered to form a surface encapsulation layer, which was used to improve the structural integrity. After filtration, the sample was naturally dried for 2 h, and then placed in a vacuum drying oven at 60°C for 12 h. After peeling off, a composite film was obtained, and the obtained composite film was denoted as M / CNT 14 / M. For comparison with Example 1.

[0048] The difference between Example 1 and Example 2 is whether CoFe2O4 is added in the composite intermediate layer.

[0049] Example 3 The characterization test of the CoFe2O4@CNT powder in this example is as follows: The transmission electron microscope (TEM, model: JEOL JEM-2100F, acceleration voltage 200kV) is used in the present application to analyze the size distribution of CoFe2O4 nanoparticles and the binding state on the surface of carbon nanotubes. As shown in Figure 2 The TEM image shows that the particle size of CoFe2O4 nanoparticles is mainly distributed between 10-15nm. The carbon nanotube surface is uniformly coated, and the tight interface between the particles and the tube wall indicates that the two form stable interface bonding.

[0050] As shown in Figure 3 The energy spectrum (EDS) element area distribution map of the CoFe2O4@CNT powder is used to determine the uniformity of the distribution of Fe, Co, C, and O elements. The EDS element area scanning result shows that the four elements of Fe, Co, C, and O are uniformly distributed on the carbon nanotube, which proves the successful preparation of the CoFe2O4@CNT powder.

[0051] Example 4 The test of the MXene / CoFe2O4@CNT multifunctional composite film in this example is as follows: The field emission scanning electron microscope (SEM, model: Zeiss Gemini 500, resolution 1.0nm, working voltage 5kV) is used in the present application to observe the cross-sectional morphology of the MXene / CoFe2O4@CNT multifunctional composite film. As shown in Figure 4 The SEM image of the cross-sectional morphology of the MXene / CoFe2O4@CNT multifunctional composite film provided by the present application is shown. From the cross-sectional view, it can be seen that the composite film has a clear "sandwich" layered structure: the MXene conductive layer, the CoFe2O4@CNT intermediate layer, and the MXene surface packaging layer are combined tightly, the interface transition is smooth, and there is no delamination or falling off. The multilayer structure provides rich paths for the multiple scattering and absorption of electromagnetic waves. Further verification of the structural uniformity of the composite system.

[0052] Example 5 The test of the MXene / CoFe2O4@CNT multifunctional composite film in this example is as follows: In order to study the electromagnetic shielding behavior and mechanism of the MXene / CoFe2O4@CNT multifunctional composite film prepared in the present application, the electromagnetic parameters and shielding effectiveness of the sample are systematically tested and analyzed.

[0053] The results are as follows:Figure 5 As shown in the figure, the MXene / CoFe2O4@CNT multi-layer composite film prepared in the application exhibits excellent electromagnetic shielding performance in the X-band (8.2-12.4 GHz) range. Taking the M / CFO@CNT 14 sample as an example, the average total shielding effectiveness (SET) is significantly higher than that of the composite film without adding the composite intermediate layer (M / CNT 14 , which can reach 42.93 dB, reaches a peak at 8.2 GHz, the absorption effectiveness (SEA) is 25.96 dB, and the reflection effectiveness (SER) is 16.96 dB. It shows that the addition of the CoFe2O4@CNT composite layer can effectively improve the electromagnetic shielding capacity of the composite film, and also shows that the electromagnetic energy loss of the film is mainly dominated by the absorption mechanism, rather than simple reflection. When the electromagnetic wave is incident on the surface of MXene, due to the impedance mismatch between air and MXene layer, part of the electromagnetic wave is first reflected; the electromagnetic wave penetrating into the layer is scattered and absorbed multiple times in the multi-layer structure. The MXene layer provides a continuous conductive path, and the conductive electrons produce current loss (Ohmic loss) under the alternating electromagnetic field; the cobalt ferrite nanoparticles in the CoFe2O4@CNT composite layer realize magnetic energy dissipation through natural resonance and eddy current loss; the three-dimensional conductive network constructed by CNTs promotes charge polarization and the formation of interface electric dipoles, further improving dielectric loss. The multiple reflections between layers and the micro-gap structure between MXene layers also cause the propagation path of electromagnetic waves inside the film to be lengthened, so that the energy is absorbed multiple times. In addition, the magnetic CFO nanoparticles and CNTs and MXene exhibit a synergistic effect, forming a dielectric-magnetic-dielectric synergistic absorption mechanism, which significantly improves the total shielding effectiveness.

[0054] Example 6 The test of the MXene / CoFe2O4@CNT multifunctional composite film in this embodiment is as follows: To comprehensively evaluate the electro-thermal stability and service life of the prepared film under continuous power-on conditions, the application designs a long-term durability test. The test method is as follows: the film sample is fixed on a heat-insulating base, and a thermocouple is fixed on the surface center point of the base using a high-temperature resistant adhesive tape to monitor the temperature change. Then, a constant direct current voltage of 4V is applied to the sample to simulate the harsh continuous working conditions. During the entire test process, the data acquisition system automatically records the time (s), real-time temperature (℃) and applied voltage (V), and the temperature data acquisition interval is set to 5s to ensure that the temperature dynamics of the film can be accurately captured.

[0055] The time-temperature curve of the MXene / CoFe2O4@CNT multifunctional composite film under a voltage of 4V is as Figure 6 shown, which is used to characterize the long-term running stability of the film. Figure 6The highest temperature (Tmax) reached by the film after heating at 4 V for about 7200 s MAX , further demonstrating its excellent stability in joule heating applications. This stable joule heating performance is attributed to its unique "sandwich" structure: the MXene encapsulation layer of the dense surface layer effectively ensures the integrity of the conductive path of the film; at the same time, the CNT network in the middle not only enhances the mechanical strength of the overall conductive network, but also helps to uniformly disperse the current and heat, avoiding the generation of local hot spots. The synergistic effect of the two ensures the functional integrity and reliability of the film under long-term, high-power working conditions, laying a solid foundation for its practical application in flexible electronic devices.

[0056] Example 7 The MXene / CoFe2O4@CNT multifunctional composite film in this example was tested as follows: To comprehensively evaluate the application of the prepared film in the field of electrocaloric materials, the electrocaloric performance of the film was systematically evaluated. A direct current was applied to the film at different voltages (1-5 V), and the change of the surface temperature of the film with time was recorded, and the results are shown in Figure 7 The MXene / CoFe2O4@CNT multifunctional composite film showed a rapid and significant electrocaloric response: the temperature increased nonlinearly with the increase of voltage, and could rapidly rise from room temperature (27℃) to 216.7℃ within 60s; after the voltage was removed, the film could also cool to the ambient temperature within 100s, showing a rapid thermal response and recovery ability.

[0057] The results show that the M / CFO@CNT 14 film has excellent comprehensive performance in the field of electrocaloric materials: the rapid heating process is due to the efficient, low-resistance three-dimensional conductive network formed by MXene and carbon nanotubes (CFO@CNT), which ensures smooth transmission of current and efficient joule heat conversion. The moderate nonlinear temperature rise curve reflects the homogenization effect of the introduction of CFO@CNT on the current distribution, effectively avoiding local overheating. At the same time, the excellent cooling rate proves that the film itself has a relatively low heat capacity, and it has a high efficient heat exchange capacity with air, which is crucial for its application in scenarios that require rapid thermal cycling (such as intermittent electronic devices).

[0058] Example 8 The MXene / CoFe2O4@CNT multifunctional composite film in this example was tested as follows: To verify the M / CFO@CNT 14The reliability of the MXene / CoFe2O4@CNT multifunctional composite film under repeated on-off electrical working conditions was tested by strict electro-thermal cycle stability test. The test method was as follows: the film sample was connected to a direct current power supply, and the cycle program was set to be continuously powered for 2 min at 4 V working voltage, and then completely powered off for 1 min, which was defined as a complete "on-off" cycle, and repeated for 10 cycles. During the whole test process, the temperature change of the film surface was monitored and recorded in real time by a thermocouple.

[0059] The test results are shown in Figure 8 After 10 complete "on-off" cycles, the M / CFO@CNT 14 / M film showed extremely stable electro-thermal response characteristics. Specifically, the repeatability of its time-temperature curve was extremely high, and the temperature trajectory change rate between different cycle periods was less than 2%; at the same time, the fluctuation range of the peak temperature reached in each cycle period was strictly controlled within ±2℃.

[0060] The test results fully confirmed that the M / CFO@CNT 14 / M film had excellent fatigue resistance. This excellent cycle stability was mainly due to its stable composite structure: the internal CFO@CNT heterojunction conductive network provided a stable current path and heat generation mechanism, and the external dense MXene encapsulation layer effectively improved the conductive path and heat conduction path. Ensured the durability and reliability of the film performance under long-term, intermittent working conditions.

[0061] Example 9 The test of the MXene / CoFe2O4@CNT multifunctional composite film in this embodiment was as follows: To verify the reliability of the M / CFO@CNT 14 / M composite film prepared by the present application under harsh environments, we evaluated its stability. The test was carried out in a normal temperature environment, with 0.1 M H2SO4 solution and 1 M NaOH solution as the working environment to simulate acid and alkali corrosion. The M / CFO@CNT 14 / M composite film without acid / alkali solution treatment was used as a control.

[0062] The results are shown in Figure 9As shown, the composite film retains 72.1% of the initial electromagnetic shielding effectiveness after immersion in 0.1M H2SO4. In 1M NaOH solution, the film retains 68.7% of its initial electromagnetic shielding effectiveness. This chemical stability is attributed to the influence of the sandwich structure. Although the dense MXene outer layer will be corroded and oxidized, the combination of the intermediate CFO@CNT layer enables the composite film to maintain a solid conductive network, ensuring that it still exhibits excellent electromagnetic shielding performance. In addition, the highly entangled 3D carbon nanotube (CNT) network and the interface interaction between the components enable the composite film to maintain structural integrity under harsh conditions.

[0063] In summary, the MXene / CoFe2O4@CNT multifunctional composite film prepared by the present application successfully realizes the synergistic enhancement of electromagnetic shielding and electro-thermal conversion functions through the "dielectric-magnetic-dielectric" layered structure design, and has the advantages of uniform microstructure, high shielding effectiveness, fast electro-thermal response, strong environmental stability and the like. The present application provides reliable material support for the integrated application of flexible electronic devices, electromagnetic protection and intelligent heating systems.

[0064] Although the present application has been described in detail above with general description and specific embodiments, some modifications or improvements can be made on the basis of the present application, which is obvious to those skilled in the art. Therefore, these modifications or improvements made on the basis of not deviating from the spirit of the present application, all belong to the scope of protection required by the present application.

Claims

1. A multifunctional composite film of MXene / CoFe2O4@CNT, characterized in that, The film comprises an MXene conductive layer, a CoFe2O4@CNT composite intermediate layer, and an MXene surface encapsulation layer, which are stacked sequentially.

2. The MXene / CoFe2O4@CNT multifunctional composite film as described in claim 1, characterized in that, In the CoFe2O4@CNT composite intermediate layer, cobalt ferrite nanoparticles are uniformly anchored on the surface of carboxylated carbon nanotubes, forming a dielectric-magnetic synergistic structure.

3. The MXene / CoFe2O4@CNT multifunctional composite film as described in claim 1, characterized in that, The MXene is Ti3C2T x The T x It has –OH, –O or –F functional groups.

4. The MXene / CoFe2O4@CNT multifunctional composite film as described in claim 1, characterized in that, The total thickness of the composite film is 10–30 µm, and the mass per unit area is less than 0.2 g / cm².

5. The MXene / CoFe2O4@CNT multifunctional composite film as described in claim 1, characterized in that, The composite film has an electromagnetic shielding effectiveness greater than 40 dB in the frequency range of 8.2–12.4 GHz.

6. The MXene / CoFe2O4@CNT multifunctional composite film as described in claim 1, characterized in that, The surface temperature of the composite film can rise from room temperature to over 200°C within 60 seconds under a DC voltage of 1–5V.

7. The method for preparing the MXene / CoFe2O4@CNT multifunctional composite thin film according to any one of claims 1-6, characterized in that, Includes the following steps: (1) Preparation of MXene suspension: MXene suspension was obtained by etching Ti3AlC2 with LiF / HCl; (2) Preparation of CoFe2O4@CNT powder: Carboxylated carbon nanotubes, ferric nitrate nonahydrate and cobalt acetate tetrahydrate were added to a mixed solvent containing ethylene glycol and urea. The mixture was hydrothermally reacted at 180°C for 12 h. After washing and drying, CoFe2O4@CNT powder was obtained. (3) Preparation of CoFe2O4@CNT dispersion: CoFe2O4@CNT powder and sodium dodecylbenzenesulfonate were mixed at a mass ratio of 1:10 and deionized water was added. The mixture was then ultrasonically dispersed to obtain a stable CoFe2O4@CNT aqueous dispersion. (4) Assembly of multilayer composite membrane: The MXene / CoFe2O4@CNT multifunctional composite membrane was deposited sequentially using vacuum filtration, and the following operations were performed: a. Vacuum filter and deposit the MXene suspension obtained in step (1) to form an MXene conductive layer; b. Vacuum filter the CoFe2O4@CNT aqueous dispersion obtained in step (3) and deposit it on the MXene conductive layer to form a CoFe2O4@CNT composite intermediate layer; c. Vacuum filter the MXene suspension obtained in step (1) onto the CoFe2O4@CNT composite intermediate layer to form an MXene surface encapsulation layer. After drying, peel it off to form an MXene / CoFe2O4@CNT multifunctional composite film.

8. The method for preparing the MXene / CoFe2O4@CNT multifunctional composite film as described in claim 7, characterized in that, In step (1), the concentration of the MXene suspension is 1 mg / mL, the etching temperature is 40℃, and the etching time is 24 h.

9. The method for preparing the MXene / CoFe2O4@CNT multifunctional composite film as described in claim 7, characterized in that, In step (2), the molar ratio of cobalt acetate tetrahydrate to ferric nitrate nonahydrate is 1:2, the molar ratio of urea to ferric nitrate nonahydrate is 6:1, and the pH of the solution is controlled at 9–10.

10. The method for preparing the MXene / CoFe2O4@CNT multifunctional composite film as described in claim 7, characterized in that, The deposition volumes of each layer in the vacuum filtration are as follows: 3 mL for both the MXene conductive layer and the MXene surface encapsulation layer, and 6–14 mL for the CoFe2O4@CNT composite intermediate layer. The concentrations of the MXene layer solution and the CoFe2O4@CNT layer solution are both 1 mg / mL.

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