Preparation method of multifunctional electromagnetic shielding film

Abstract

The invention relates to the technical field of electromagnetic shielding film preparation, in particular to a multifunctional electromagnetic shielding film preparation method which comprises the following steps: S1, dissolving Zn-Mn Fe2O4 nanoparticles in a dopamine solution, and magnetically stirring at room temperature; then, adding a glucose aqueous solution into the solution in four times; transferring into a high-pressure kettle, carrying out heat preservation for two times, adding stronger ammonia water, and carrying out ultrasonic treatment, so as to finally obtain CB-coated Zn-Mn Fe2O4 powder; s2, adding the bacterial nano cellulose and MXene powder into deionized water, and magnetically stirring; then, CB-coated Zn-Mn Fe2O4 powder is added while stirring is conducted, stirring continues to be conducted, and then ultrasonic treatment is conducted; and finally, performing vacuum-assisted suction filtration in an environment of applying a rotating external magnetic field, and performing hot-pressing drying on the film in a vacuum drying oven to obtain the electromagnetic shielding film. The electromagnetic shielding film prepared by the method is high in shielding effectiveness, good in material tensile property and excellent in composite material performance.

Description

Technical Field

[0001] The present invention relates to the technical field of electromagnetic shielding film preparation, and particularly to a preparation method of a multifunctional electromagnetic shielding film. Background Art

[0002] With the popularization of 5G / 6G communication technologies and the iterative upgrading of military equipment, the widespread application of high-frequency and high-power electronic devices has made the electromagnetic interference (EMI) problem increasingly severe. Electromagnetic interference not only causes signal distortion and data transmission errors in electronic devices (according to IEEE statistics, 30% of the global 5G base station failures in 2023 were caused by EMI), long-term exposure to high-frequency electromagnetic fields can induce a decline in immunity and an increased risk of cancer, and it is vulnerable to high-frequency electromagnetic wave interference damage in modern warfare. Therefore, the development of electromagnetic shielding materials with high electromagnetic shielding performance (SE) is of great significance for the upgrading of 5G / 6G electronic devices, the integrated development of advanced electronic systems, human health, and the protection of troops and equipment in modern warfare.

[0003] Traditional metal materials such as copper, aluminum, and their alloys, although having high conductivity and excellent electromagnetic shielding efficiency, their defects such as high density, easy corrosion, and poor processing flexibility severely limit their applications in lightweight and wearable electronic devices; at the same time, the skin effect causes their shielding efficiency to decrease by more than 40% in the 5G millimeter-wave band, and relying solely on the conductive loss mechanism, it is impossible to achieve broadband coverage through magnetic loss or polarization loss. Graphene-based materials, although having the advantages of light weight and flexibility, their intrinsic diamagnetism results in a shielding efficiency of less than 30 dB in the high-frequency band, and the physical mixing interface polarization effect with polymers is weak. The emerging MXene materials, although having ultra-high conductivity, their single-component film shielding mechanism is single, with low magnetic permeability and weak polarization loss, resulting in the SE value in the high-frequency band dropping sharply below 25 dB, and their mechanical properties are weak and environmental stability is poor. In the prior art, whether it is metal, graphene, or MXene-based materials, it is difficult to balance lightweight, broadband high-efficiency shielding, mechanical toughness, environmental stability, and other multifunctions.

[0004] Therefore, in this field, there is an urgent need to develop an MXene-based electromagnetic shielding material that can achieve multi-mechanism synergistic loss and multifunctional integration while having high electromagnetic shielding performance. Summary of the Invention

[0005] In order to solve the problems pointed out in the above background art, the present invention provides a preparation method of a multifunctional electromagnetic shielding film.

[0006] A preparation method of a multifunctional electromagnetic shielding film includes the following steps:

[0007] S1. Dissolve Zn-Mn Fe2O4 nanoparticles in dopamine solution, stir magnetically at room temperature to form a polydopamine coating on the surface of Zn-Mn Fe2O4 nanoparticles; subsequently, add an aqueous glucose solution containing a surfactant to the above solution in 4 portions, then stir magnetically and disperse ultrasonically; then transfer to an autoclave for two heat-insulation treatments, add concentrated ammonia water, perform ultrasonic treatment, and finally centrifuge, wash and freeze-dry to obtain CB@Zn-Mn Fe2O4 powder with a core-shell structure;

[0008] S2. Add bacterial nanocellulose (BCNF) and MXene powder to deionized water and stir magnetically; subsequently, add CB@Zn-MnFe2O4 powder while stirring, continue stirring and then perform ultrasonic treatment; finally, perform vacuum-assisted filtration under a rotating external magnetic field, and then thermally press and dry the film in a vacuum drying oven to obtain an electromagnetic shielding film (MXene / CB@Zn-MnFe2O4).

[0009] Further, in step S1, the pH of the dopamine solution is 9, the buffer solution is Tris-HCl, and the time for magnetic stirring of Zn-Mn Fe2O4 nanoparticles in the dopamine solution is 12 h.

[0010] Further, in step S1, the glucose concentrations in the aqueous glucose solutions containing a surfactant added in 4 portions are 0.4 M, 0.6 M, 0.8 M, and 1.0 M in sequence, the interval between each addition is 2 h, continuous stirring is maintained when adding the aqueous glucose solution containing a surfactant, and the surfactant added is one of polyvinylpyrrolidone or cetyltrimethylammonium bromide; after adding all the aqueous glucose solutions containing a surfactant, continue magnetic stirring for 2 h, and then disperse ultrasonically for 1 h.

[0011] Further, in step S1, after adding the aqueous glucose solution containing a surfactant, stir magnetically and disperse ultrasonically for 1 h.

[0012] Further, in step S1, the two heat-insulation treatments in the autoclave are to first heat-insulate at 180 °C for 4 h, and then heat-insulate at 220 °C for 8 h; ultrasonic treatment is performed for 2 h after adding ammonia water, the washing is alternately performed with absolute ethanol and deionized water, the freeze-drying time is 48 h, and the freeze-drying temperature is -60 °C.

[0013] Further, in step S2, the mass ratio between CB@Zn-MnFe2O4 powder and MXene powder is 1:(1 - 3), and the mass ratio between bacterial nanocellulose and MXene powder is 1:1.

[0014] Furthermore, in step S2, the bacterial nanocellulose and MXene powder are magnetically stirred in deionized water for 30 minutes; and the stirring is continued for 2 hours after the CB@Zn-Mn Fe2O4 powder is added.

[0015] Furthermore, in step S2, the rotating external magnetic field applied is 0.5 T, the rotation speed is 100 rpm, and the pore size of the filter membrane for vacuum-assisted filtration is 0.22 μm; the film is hot-pressed and dried in a vacuum drying oven at 40° C. for 48 hours.

[0016] The advantages and beneficial effects of the present invention are:

[0017] 1. The present invention introduces -OH and -NH2 active sites to the surface of Zn-MnFe2O4 through a polydopamine coating, and guides the directional deposition of CB through hydrogen bonding, π-π conjugation of catechol groups, etc. Gradient addition of glucose solution avoids local supersaturation leading to the agglomeration of CB formed by subsequent carbonization, and ensures the slow deposition of CB and the precise control of its shell thickness, wherein the surfactant stabilizes the system through the steric hindrance effect. The temperature and time are controlled in a heat preservation kettle in two stages, and the excessive growth of CB is suppressed in the low temperature stage to form more deposition sites and accelerate the growth of CB in the high temperature stage. Finally, the surface of CB is amino treated to introduce -NH to enhance the binding ability with MXene sheets. In the present invention, dopamine plays a role similar to a bridge, so that the CB formed after glucose carbonization covers Zn-Mn Fe2O4 evenly, which is convenient for it to cooperate with MXene to build a network and improve the overall performance of the material.

[0018] 2. The high-conductivity CB coated Zn-MnFe2O4 established a conductive shell and a magnetic core, and the high-intrinsic-conductivity MXene cooperated with it to build a continuous conductive network, which dominated the low-frequency electromagnetic wave reflection and dielectric loss; the doping of Zn-Mn Fe2O4 magnetic nanomaterials provided a magnetic center and thus brought about a high magnetic permeability, and the vertical gradient self-assembly guided by the magnetic field further improved the magnetic permeability, and enhanced the magnetic loss capacity through hysteresis loss, eddy current loss and natural resonance; Zn-MnFe2O4, CB and MXene were combined with each other through hydrogen bonds and covalent bonds, which enhanced the interface dipole response, formed a heterogeneous interface, triggered the interface multipolarization loss, enhanced dielectric relaxation, and enhanced electromagnetic wave absorption; MXene sheets and CB@Zn-MnFe2O4 magnetic conductive nanospheres distributed between them constructed a complex three-dimensional "maze" structure, which extended the electromagnetic wave propagation path within a limited scale and achieved multiple reflection losses; the vertical gradient self-assembly arrangement further reduced surface reflection and increased absorption efficiency. The synergy of magnetic-electric-polarization multi-mechanisms makes the ratio of the material's complex dielectric constant and complex magnetic permeability approach 1, reducing surface reflection, thereby optimizing impedance matching, reducing the reflection ratio and increasing the absorption ratio.

[0019] 3. In addition to synergistically improving the electromagnetic shielding performance through multiple loss mechanisms, the present invention also realizes the integration of multiple functions such as high mechanical properties, photothermal conversion, environmental stability, and environmental adsorption. Enhancement of mechanical properties; the catechol groups of the polydopamine coating are combined with carbon black through π-π conjugation, enhancing the interfacial bonding ability;

[0020] After the CB@Zn-MnFe2O4 nanoparticles are aminated, the -NH formed reacts with the -OH of MXene to form hydrogen bonds, and the π-π stacking enhances the binding force. The magnetic nanoparticles serve as physical cross-linking points to inhibit interlayer slippage; the intercalation of BCNF between MXene layers constructs a three-dimensional network structure similar to "reinforced concrete" to organize interlayer stacking and enhance rigidity; through vacuum-assisted filtration, the self-assembly of CB@Zn-MnFe2O4 particles within the MXene sheets is realized. Their uniform dispersion and multi-layer structure design enable stress transfer and thus hinder the crack initiation and propagation paths, significantly improving the mechanical properties such as the tensile strength, elongation at break, and elastic modulus of the film. The high flexibility (mechanical properties) enables the film to adapt to dynamic bending and avoid brittle fracture, realizing the function of "flexible electromagnetic shielding" and being used in wearable devices. The high tensile strength ensures that the material maintains structural integrity under complex working conditions such as high-speed air flow impact, guaranteeing the stable shielding efficiency.

[0021] 4. Integration of electrothermal activation self-healing - magnetic response recovery self-cleaning - environmental stability multifunction: The film has good electrothermal conversion performance. Joule heat is generated during the conductive loss process, and the thermal activation enhances the mobility of the CB chain segments. Microcracks are repaired through hydrogen bond recombination to extend the service life; the surface functional group hydroxyl of MXene and the CB amino group can efficiently adsorb heavy metal ions such as 2+ Pb 2+ and Cd, and then rapid recovery is achieved through the magnetic response of zinc manganese ferrite therein, possessing environmental adsorption ability and achieving the effect of self-cleaning under harsh environments; the CB tightly coats the Zn-MnFe2O4 nanoparticles, inhibiting the oxidation of MXene, resisting corrosion in acid, alkali, and salt spray environments, and enhancing environmental stability.

[0022] 5. Simplified process, reduced cost, scalable production, and environmentally friendly: Dispersing MXene, doping CB@Zn-MnFe2O4, and integrating vacuum filtration into film formation reduce traditional process steps and energy consumption; at the same time, the whole process is a solution method, and the reaction kettle can be scaled up to more than 50 L for large-scale mass production in engineering; the technology for recycling zinc manganese ferrite from waste batteries is relatively mature, and the cost is much lower than that of other metal-based materials. The costs of drugs such as glucose and dopamine are also extremely low, and glucose is a renewable carbon source, avoiding the use of toxic carbon sources such as aniline in the existing technology. The cost of large-scale preparation of MXene has also been significantly reduced. Description of the Drawings

[0023] Figure 1Microscopic image of CB@Zn-MnFe2O4 prepared in Example 1 of the present invention;

[0024] Figure 2 Transmission electron microscope image of the electromagnetic shielding film prepared in Example 1 of the present invention;

[0025] Figure 3 Schematic process diagram of the preparation method of the present invention;

[0026] Figure 4 Schematic diagram of the MXene / CB@Zn-MnFe2O4 film structure and its electromagnetic shielding mechanism. Detailed implementation manners

[0027] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0028] Please refer to Figures 1 to 4 , the present invention provides:

[0029] Example 1

[0030] A preparation method of a multifunctional electromagnetic shielding film, the preparation method comprising the following steps:

[0031] S1. Dissolve 10 g of Zn-Mn Fe2O4 nanoparticles in 200 ml of dopamine solution with a pH of 9 and using Tris-HCl as a buffer. The concentration of dopamine is 2 mg / ml. Magnetically stir at 3500 rpm for 12 h at room temperature to form a polydopamine coating on the surface of Zn-Mn Fe2O4. Subsequently, add an aqueous glucose solution containing cetyltrimethylammonium bromide (CTAB) to the above solution. The concentration of cetyltrimethylammonium bromide is 2.4 mg / ml. The aqueous glucose solution is added in 4 portions. The glucose concentrations of the added solutions are 0.4 M, 0.6 M, 0.8 M, and 1.0 M in sequence. The volume of the glucose solution added in the first two times is 50 ml each, and the volume of the glucose solution added in the last two times is 75 ml each. The interval between each addition of the glucose solution is 2 h. When adding glucose, continue to magnetically stir at 3500 rpm. After adding all the glucose solutions, continue to magnetically stir at 4000 rpm for 2 h and then ultrasonically disperse for 1 h. The ultrasonic frequency is 40 kHz. Then transfer it to an autoclave, keep it at 180 °C for 4 h and then at 220 °C for 8 h. Glucose dehydrates and carbonizes to form a carbon black shell layer. Then add 100 ml of concentrated ammonia water with a mass fraction of 28%, ultrasonically treat for 2 h, and the ultrasonic frequency is 40 kHz. Finally, alternately centrifuge and wash with absolute ethanol and deionized water and freeze-dry at -60 °C for 48 h to obtain CB@Zn-Mn Fe2O4 powder with a core-shell structure;

[0032] S2. Add 15 g of BCNF and 15 g of MXene to 150 ml of deionized water, magnetically stir at 3500 rpm for 30 min. Subsequently, add 15 g of the CB@Zn-Mn Fe2O4 powder obtained in step S1 while stirring, continue to stir at 3000 rpm for 2 h and then ultrasonically treat for 2 h. The ultrasonic frequency is 40 kHz. Finally, under the environment of applying a 0.5 T rotating external magnetic field, perform vacuum-assisted filtration for 4 h (apply a vertically downward magnetic field and then rotate around the z-axis). The pore size of the filter membrane for vacuum-assisted filtration is 0.22 μm. Then thermally press and dry the film in a vacuum drying oven for 48 h, and use a 5 kg counterweight for thermal pressing to obtain the MXene / CB@Zn-Mn Fe2O4 film.

[0033] Example 2

[0034] S1. Dissolve 10 g of Zn-Mn Fe2O4 nanoparticles in 200 ml of dopamine solution with a pH of 9 and using Tris-HCl as a buffer. The concentration of dopamine is 2 mg / ml. Magnetically stir at 3500 rpm for 12 h at room temperature to form a polydopamine coating on the surface of Zn-Mn Fe2O4. Subsequently, add an aqueous glucose solution containing cetyltrimethylammonium bromide (CTAB) to the above solution. The concentration of cetyltrimethylammonium bromide is 2.4 mg / ml. The aqueous glucose solution is added in 4 portions. The glucose concentrations of the added solutions are 0.4 M, 0.6 M, 0.8 M, and 1.0 M in sequence. The volume of the glucose solution added in the first two times is 50 ml each, and the volume of the glucose solution added in the last two times is 75 ml each. The interval between each addition of the glucose solution is 2 h. Keep magnetically stirring at 3500 rpm when adding glucose. After adding all the glucose solutions, continue to magnetically stir at 4000 rpm for 2 h and then ultrasonically disperse for 1 h. The ultrasonic frequency is 40 kHz. Then transfer it to an autoclave, keep it at 180 °C for 4 h and then at 220 °C for 8 h. Glucose dehydrates and carbonizes to form a carbon black shell layer. Then add 100 ml of concentrated ammonia water with a mass fraction of 28%, ultrasonically treat for 2 h, and the ultrasonic frequency is 40 kHz. Finally, alternately centrifuge and wash with absolute ethanol and deionized water and freeze-dry at -60 °C for 48 h to obtain CB@Zn-Mn Fe2O4 powder with a core-shell structure;

[0035] S2. Add 15 g of BCNF and 15 g of MXene to 150 ml of deionized water, magnetically stir at 3500 rpm for 30 min. Subsequently, while stirring, add 10 g of the CB@Zn-Mn Fe2O4 powder obtained in step S1, continue to stir at 3000 rpm for 2 h and then ultrasonically treat for 2 h. The ultrasonic frequency is 40 kHz. Finally, under the environment of applying a 0.5 T rotating external magnetic field, vacuum-assisted filtration is carried out for 4 h (apply a vertically downward magnetic field and then rotate around the z-axis). The pore size of the filter membrane for vacuum-assisted filtration is 0.22 μm. Then heat-press and dry the film in a vacuum drying oven for 48 h, and use a 5 kg counterweight for heat pressing to obtain the MXene / CB@Zn-Mn Fe2O4 film.

[0036] Example 3

[0037] A preparation method of a multifunctional electromagnetic shielding film, and the preparation method includes the following steps:

[0038] S1. Dissolve 10 g of Zn-Mn Fe2O4 nanoparticles in 200 ml of dopamine solution with a pH of 9 and using Tris-HCl as a buffer. The concentration of dopamine is 2 mg / ml. Stir magnetically at 3500 rpm for 12 h at room temperature to form a polydopamine coating on the surface of Zn-Mn Fe2O4. Subsequently, add an aqueous glucose solution containing polyvinylpyrrolidone (PVP) to the above solution. The concentration of cetyltrimethylammonium bromide is 2.4 mg / ml. The aqueous glucose solution is added in 4 portions, and the glucose concentrations of the added solutions are 0.4 M, 0.6 M, 0.8 M, and 1.0 M in sequence. The first two portions of the glucose solution are both 50 ml, and the last two portions are both 75 ml. The interval between each addition of the glucose solution is 2 h. When adding glucose, continue to stir magnetically at 3500 rpm. After adding all the glucose solutions, continue to stir magnetically at 4000 rpm for 2 h and then ultrasonically disperse for 1 h. The ultrasonic frequency is 40 kHz. Then transfer it to an autoclave, keep it at 180 °C for 4 h and then at 220 °C for 8 h. Glucose is dehydrated and carbonized to form a carbon black shell layer. Then add 100 ml of concentrated ammonia water with a mass fraction of 28%, ultrasonically treat for 2 h, and the ultrasonic frequency is 40 kHz. Finally, alternately centrifuge and wash with absolute ethanol and deionized water and freeze-dry at -60 °C for 48 h to obtain CB@Zn-MnFe2O4 powder with a core-shell structure;

[0039] S2. Add 15 g of BCNF and 15 g of MXene to 150 ml of deionized water, stir magnetically at 3500 rpm for 30 min. Subsequently, while stirring, add 15 g of the CB@Zn-Mn Fe2O4 powder obtained in step S1, continue to stir at 3000 rpm for 2 h and then ultrasonically treat for 2 h. The ultrasonic frequency is 40 kHz. Finally, under the environment of applying a 0.5 T rotating external magnetic field, perform vacuum-assisted filtration for 4 h (apply a vertical downward magnetic field and then rotate around the z-axis). The pore size of the filter membrane for vacuum-assisted filtration is 0.22 μm. Then thermally press and dry the film in a vacuum drying oven for 48 h, and use a 5 kg counterweight for thermal pressing to obtain a MXene / CB@Zn-Mn Fe2O4 film.

[0040] In the above examples, the Zn-Mn Fe2O4 nanoparticles are prepared by a solvothermal method, with a particle size of 300 nm and a specific surface area of 100 m 2 / g.

[0041] MXene is obtained by etching the MAX phase with LiF and HCl and ultrasonic exfoliation. The MAX phase is Ti3C2T x , T x can be a hydroxyl group.

[0042] Comparative Example 1

[0043] The difference between Comparative Example 1 and Example 1 is that the glucose solution containing surfactant was added in 4 portions in step S1 and changed to be added at one time, where the concentration of glucose was 0.74 M and the added amount was 250 ml.

[0044] Comparative Example 2

[0045] The difference between Comparative Example 2 and Example 1 is that the glucose solution containing surfactant was added in 4 portions in step S1 and changed to be added with a carbon black solution containing surfactant, where the concentration of carbon black was 0.38 M, the concentration of surfactant was the same as that in Example 1, and the added amount was 250 ml.

[0046] Comparative Example 3

[0047] The difference between Comparative Example 3 and Example 1 is that the addition of dopamine was cancelled, and the remaining steps were exactly the same as those in Example 1.

[0048] Comparative Example 4

[0049] The difference between Comparative Example 4 and Example 1 is that the addition of glucose solution was completely cancelled and changed to be added with a deionized aqueous solution containing surfactant, where the concentration of surfactant was the same as that in Example 1, and the added amount was 250 ml.

[0050] A total of 6 groups of electromagnetic shielding films were prepared through the above Examples 1 - 3 and Comparative Examples 1 - 3. The tensile strength, conductivity, and shielding effectiveness of these 6 groups of electromagnetic shielding films were measured, and the measurement results are shown in Table 1 below:

[0051] Table 1: Performance test table of electromagnetic shielding films prepared in Examples 1 - 3 and Comparative Examples 1 - 3

[0052]

[0053]

[0054] It can be seen from the data in Table 1 above that in the present invention, adding the glucose solution in multiple portions can effectively prevent the aggregation of CB, improve the tensile strength and shielding effectiveness of the prepared material; in addition, compared with the method of directly adding carbon black, the performance of the material is further improved; furthermore, the bridging effect of dopamine on carbon black is reflected in the improvement of the tensile strength and shielding effectiveness of the material.

[0055] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A preparation method of a multifunctional electromagnetic shielding film, characterized in that It includes the following steps: S1. Dissolve Zn-Mn Fe2O4 nanoparticles in dopamine solution and stir magnetically at room temperature. Subsequently, add an aqueous glucose solution containing a surfactant to the above solution in 4 portions, and then stir magnetically and ultrasonically disperse. Then transfer it to an autoclave for two heat-insulations, add concentrated ammonia water, perform ultrasonic treatment, and finally centrifuge, wash and freeze-dry to obtain CB@Zn-Mn Fe2O4 powder with a core-shell structure; S2. Add bacterial nanocellulose and MXene powder to deionized water and stir magnetically. Subsequently, add CB@Zn-Mn Fe2O4 powder while stirring, continue stirring and then perform ultrasonic treatment. Finally, perform vacuum-assisted filtration under a rotating external magnetic field, and then hot-press and dry the film in a vacuum drying oven to obtain an electromagnetic shielding film.

2. The preparation method of the multifunctional electromagnetic shielding film according to claim 1, characterized in that, In step S1, the pH of the dopamine solution is 9, the buffer solution is Tris-HCl, and the time for magnetic stirring of Zn-Mn Fe2O4 nanoparticles in the dopamine solution is 12 h.

3. The preparation method of the multifunctional electromagnetic shielding film according to claim 1, characterized in that, In the aqueous glucose solution containing a surfactant added in 4 portions in step S1, the glucose concentrations are 0.4 M, 0.6 M, 0.8 M, and 1.0 M in sequence, the interval between each addition is 2 h, continuous stirring is maintained when adding the aqueous glucose solution containing a surfactant, and the surfactant added is one of polyvinylpyrrolidone or cetyltrimethylammonium bromide; After adding all the aqueous glucose solution containing a surfactant, continue magnetic stirring for 2 h, and then ultrasonically disperse for 1 h.

4. The preparation method of the multifunctional electromagnetic shielding film according to claim 1, characterized in that, In step S1, after adding the aqueous glucose solution containing a surfactant, stir magnetically and ultrasonically disperse for 1 h.

5. The preparation method of the multifunctional electromagnetic shielding film according to claim 1, characterized in that, In step S1, the two heat-insulations in the autoclave are: first, heat-insulate at 180 °C for 4 h, and then heat-insulate at 220 °C for 8 h; after adding ammonia water, perform ultrasonic treatment for 2 h, the washing is alternately performed with absolute ethanol and deionized water, and the time for freeze-drying is 48 h, and the temperature for freeze-drying is -60 °C.

6. The preparation method of the multifunctional electromagnetic shielding film according to claim 1, characterized in that, In step S2, the mass ratio between CB@Zn-Mn Fe2O4 powder and MXene powder is 1:(1 - 3), and the mass ratio between bacterial nanocellulose and MXene powder is 1:

1.

7. The preparation method of the multifunctional electromagnetic shielding film according to claim 1, characterized in that, In step S2, bacterial nanocellulose and MXene powder are magnetically stirred in deionized water for 30 min; after adding CB@Zn-MnFe2O4 powder, continue stirring for 2 h.

8. The preparation method of the multifunctional electromagnetic shielding film according to claim 1, wherein, In step S2, the rotating external magnetic field applied is 0.5 T, the rotation speed is 100 rpm, and the pore size of the filter membrane for vacuum-assisted filtration is 0.22 μm; The film is hot-press dried in a vacuum drying oven at 40 °C for 48 h.

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