Preparation method and application of electromagnetic shielding material

Abstract

The invention discloses a preparation method and application of an electromagnetic shielding material. The preparation method mainly comprises the following steps: S1, preparing a hollow silver nanotube through an improved solvothermal method; s2, silver nanotube gel with an ice crystal interlayer is prepared through a directional freeze drying method; s3, after the silver nanotube gel is treated, MXene nanosheets are doped into the treated silver nanotube gel, and a silver nanotube / MXene layered stacked structure is obtained; and S4, further processing the layered superposed structure in the step S3 to obtain the final electromagnetic shielding material. The silver nanotube is prepared in one step for the first time by adopting a compound growth regulator and a surfactant. A silver nanotube / MXene layered superposition structure with a special structure is obtained through bidirectional ice crystal growth, the material shows a good electromagnetic shielding effect under the bidirectional enhancement of the hollow structure of the silver nanotube and the layered superposition structure, and the shielding effectiveness (SE) of the material can reach 72 dB or above through tests.

Description

Technical Field

[0001] This invention relates to the field of novel material preparation technology, and in particular to a method for preparing and applying an electromagnetic shielding material. Background Technology

[0002] With the rapid advancement of communication technology, various electronic and electrical devices have emerged in large numbers, leading to the widespread application of electromagnetic waves in commercial, civilian, and military fields, permeating every aspect of our lives. However, as the electromagnetic environment becomes increasingly complex, electromagnetic pollution caused by electromagnetic waves has been recognized by the World Health Organization (WHO) as the fourth leading cause of pollution after air pollution, water pollution, and noise pollution.

[0003] Electromagnetic pollution manifests itself in three main ways: electromagnetic interference (EMI), harm to human health, and electromagnetic information leakage. Specifically, electromagnetic interference disrupts or hinders the normal operation of nearby electronic equipment, especially precision electronic devices. Harm to human health primarily manifests as damage or disruption of normal bodily functions, leading to various diseases, such as through thermal or cumulative effects. Electromagnetic information leakage arises because electromagnetic waves carry a large amount of information; once leaked, it poses a significant hidden danger. Therefore, controlling electromagnetic pollution at a reasonable level is a pressing practical problem that needs to be addressed.

[0004] Currently, common electromagnetic shielding materials mainly include metallic materials, polymer materials, and materials based on Ti3C2T. x MXene is a representative two-dimensional multilayer material. Among these, metallic materials suffer from drawbacks such as easy oxidation and corrosion, magnetic leakage at joints, difficulty in achieving lightweight designs, and poor stretchability; polymer materials, while not easily oxidized and capable of lightweight production, suffer from uneven distribution and agglomeration. However, since the Gogotsi group first prepared Ti3C2T with metallic conductivity... x since [1] Ti3C2T x Its superior electromagnetic shielding performance has been reported in an increasing number of publications. [2-5] However, single-layer or multi-layer MXenes materials are prone to oxidation and are unstable, and their mechanical properties are poor when they are made into thin films.

[0005] Therefore, it is of great significance to develop an electromagnetic shielding material with excellent electromagnetic shielding performance and wide applicability.

[0006] To improve the overall performance of electromagnetic shielding materials, researchers, based on the Schelkunoff formula, enhanced the material's reflective and absorptive shielding effectiveness by increasing its electrical conductivity and internal multiple losses.

[0007] To improve the electrical conductivity of materials, Gustav Nyström et al. prepared a composite aerogel of cellulose nanofibers / silver nanowires (AgNWs) using an ice-templating method. This aerogel exhibited a good pore structure and excellent shielding performance, with a shielding efficiency exceeding 70 dB in the X-band. [6] Zhonglei Ma et al. prepared a multifunctional wearable silver nanowire-decorated leather (AgNW / leather) nanocomposite material using a simple vacuum-assisted filtration process. Under vacuum-assisted filtration, the AgNWs entered the porous structure of the leather's flesh surface, forming physical entanglement and hydrogen bonding interactions with collagen fiber bundles, thus constructing a highly efficient 3D conductive network. The material achieved a shielding efficiency of 55 dB. [7] Yuezhan Feng et al. fabricated a transparent conductive electrode with electromagnetic shielding properties using polydimethylsiloxane (PDMS) / silver nanowires (AgNW). This electrode features a grid-like conductive network fabricated through a pre-stretching method. The grid-like AgNW network endows the PDMS / AgNW film with excellent photoelectric properties, achieving 32.2 dB of electromagnetic shielding performance in the X-band while maintaining high transmittance. Therefore, this material can be applied to the electromagnetic shielding protection of wearable devices. [8] .

[0008] To improve the internal multiple losses of materials, Fengfeng Jia et al. developed an asymmetric hybrid film using para-aramid nanofibers (PANFs), carboxylated multi-walled carbon nanotubes (c-MWCNTs), and silver nanowires (AgNWs) via vacuum-assisted filtration and freeze-drying. The robust and high aspect ratio of PANFs provided the matrix foundation for the formation of large-scale hybrid films, offering feasible support for the conductive building blocks c-MWCNTs and AgNWs. Due to its unique asymmetric porous structure, the prepared c-MWCNT / AgNWs / PANFs hybrid film (8 wt% c-MWCNTs and 4 wt% AgNWs) maintained highly efficient EMI shielding performance, achieving a shielding effectiveness (SE) of 40.59 dB. Furthermore, the shielding effectiveness and absorption coefficient could be adjusted by the c-MWCNT content, AgNW content, and the c-MWCNT to AgNW ratio. With increasing conductivity, the c-MWCNT / AgNWs / PANFs hybrid film exhibits an adjustable shielding effectiveness between 9.40 and 40.59 dB. [9] .

[0009] Therefore, while there is a certain research foundation for improving electromagnetic shielding effectiveness by controlling the conductivity and porous structure of materials, most studies only target electromagnetic shielding in the X-band. Developing a simple method to prepare electromagnetic shielding materials with excellent shielding performance and wide applicability remains a challenge.

[0010] See the relevant existing technology literature as follows: [1]Michael N ,Murat K ,Volker P , et al.Two-dimensional nanocrystals produced by exfoliation of Ti3AlC2. [J]. Advancedmaterials, 2011, 23 (37):4248-53. [2]Shahzad F ,Alhabeb M ,Hatter BC , et al.Electromagneticinterference shielding with 2D transition metal carbides (MXenes) [J].Science, 2016, 353 (6304) [3]Aamir I ,Pradeep S ,Min CK . ElectromagneticInterferenceShielding: 2D MXenes for Electromagnetic Shielding: A Review[J].AdvancedFunctional Materials, 2020, 30 (47) [4]Yun T ,Kim H ,Iqbal A , et al. ElectromagneticInterferenceShielding: Electromagnetic Shielding of Monolayer MXene Assemblies [J].Advanced Materials, 2020, 32 (9) [5]Meikang H, Danzhen Z, ECS, et al. Electrochemically modulated interaction of MXenes with microwaves. [J]. Nature nanotechnology, 2023, 18(4) [6]Zhihui Z ,Tingting W ,Daxin H , et al.Ultralight, Flexible, andBiomimetic Nanocellulose / Silver Nanowire Aerogels for ElectromagneticInterference Shielding. [J]. ACS nano, 2020, 14 (3) [7]Zhihui Z ,Tingting W ,Daxin H , et al.Ultralight, Flexible, andBiomimetic Nanocellulose / Silver Nanowire Aerogels for ElectromagneticInterference Shielding. [J]. ACS nano, 2020, 14 (3) [8]Zhonglei M, Xiaolian [9]Yuezhan F ,Jianzhou S ,Gaojie H , et al. TransparentandStretchable Electromagnetic Interference Shielding Film with Fence-likeAligned Silver Nanowire Conductive Network. [J]. Small methods, 2023, 7 (7) Summary of the Invention

[0011] The purpose of this invention is to prepare a lightweight, flexible material capable of absorbing electromagnetic waves across a broad spectrum using a simple method. This material is not only easy to prepare and has the advantage of large-scale production, but also has excellent electromagnetic shielding performance due to its special structural design.

[0012] To enable those skilled in the art to clearly understand the specific content of the present invention, the specific content of the present invention is now described in detail below.

[0013] A method for preparing an electromagnetic shielding material mainly includes the following steps: S1: Hollow silver nanotubes were prepared by an improved solvothermal method; S2: A silver nanotube gel with ice crystal interlayers was prepared by directional freeze-drying. S3: After processing the above silver nanotube gel, MXene nanosheets are incorporated to obtain a silver nanotube / MXene layered stacked structure; S4: Further process the layered superimposed structure in step S3 above to obtain the final electromagnetic shielding material.

[0014] Preferably, the improved solvothermal method described in step S1 of this invention differs from the prior art, which requires the preparation of a template agent followed by secondary processing to obtain silver nanotubes. Instead, hollow silver nanotubes can be obtained directly through a single solvothermal step. The method for preparing hollow silver nanotubes mainly includes the following steps: First, a suitable silver source, growth regulator, surfactant, and solvent are selected and mixed; then, the mixed reactants are transferred to a reactor vessel for reaction; finally, the reaction product is processed through centrifugation, washing, and other steps to obtain the desired hollow silver nanotubes.

[0015] Preferably, in step S2, directional freezing refers to bidirectional freezing, which controls the growth direction of ice crystals to obtain a silver nanotube gel with a sandwich structure. Bidirectional freezing, unlike unidirectional freezing, can provide a temperature gradient in two dimensions, causing the ice crystals to transform from columnar growth to planar growth.

[0016] Preferably, the silver nanotube gel in step S3 is treated by either freeze-drying or supercritical drying to remove ice crystals.

[0017] Preferably, the incorporation of MXene nanosheets in step S3 refers to mixing the aforementioned silver nanotube gel with MXene nanosheets. Under the action of force, the MXene nanosheets will continuously enter the interlayer pores of the silver nanotube gel, thereby obtaining a layered superimposed structure of silver nanotubes / MXene.

[0018] Preferably, the further processing of the layered superimposed structure in step S3 in step S4 refers to further coating the layered superimposed structure with polyaniline. On the one hand, this can improve the mechanical strength of the material, and on the other hand, it can also improve the electromagnetic shielding performance of the material. Finally, under the synergistic effect of the above steps, through optimized structural design, the electromagnetic shielding performance of the material can be improved, and lightweight, high-strength and flexible properties can also be achieved.

[0019] Preferably, the silver source in step S1 is silver nitrate; the growth regulator is a mixture of sodium chloride and copper chloride in a mass ratio of 1:1-2; the surfactant is polyvinylpyrrolidone, specifically a mixture of K30 and K80 in a mass ratio of 1:0.5; and the reaction solvent is ethylene glycol.

[0020] The selection of the aforementioned composite growth regulator and surfactant differs from existing technologies. Existing technologies, through the selection of a single reactant, such as a single growth regulator and surfactant, generally produce silver nanowires rather than silver nanotubes. This is a major feature that distinguishes this invention from existing technologies and is also an innovation of this invention.

[0021] Preferably, the concentration of MXene nanosheets in step S3 is 0.1-0.5 mg / ml. The MXene nanosheets are incorporated into the interlayer pores of the silver nanotube gel by vacuum drying, thereby obtaining a silver nanotube / MXene layered stacked structure.

[0022] Preferably, in step S4, for the coating of the silver nanotube / MXene layered stacked structure, the layered stacked structure can be mechanically compacted first, and then coated in situ.

[0023] Compared with the prior art, the present invention achieves the following beneficial technical effects: 1) Silver nanotubes were prepared in one step for the first time by using a composite growth regulator and surfactant.

[0024] 2) Through bidirectional ice crystal growth, a layered superimposed structure of silver nanotubes / MXene with a special structure was obtained. With the bidirectional enhancement of the hollow structure of silver nanotubes and the layered superimposed structure, the material exhibited a good electromagnetic shielding effect. After testing, its shielding effectiveness (SE) can reach more than 72 dB.

[0025] 3) By coating the surface of the material with polyaniline, not only is the electromagnetic shielding performance of the material further improved, but the mechanical properties of the material can also be improved, thereby meeting the high strength and flexibility requirements of the application. Attached Figure Description

[0026] Figure 1Transmission electron microscope images of silver nanotubes prepared in Example 1 of this invention, including low-magnification and high-magnification images; Figure 2 Mechanical property test diagram of the polyaniline-coated silver nanotube / MXene layered stacked structure prepared in Example 1 of this invention; Detailed Implementation

[0027] To clearly and thoroughly explain the technical solution of the present invention, enabling those skilled in the art to fully understand and implement it, the technical solution of the present invention is described below through specific embodiments. It should be noted that the following specific embodiments are merely illustrative and do not constitute a limitation of the present invention. Furthermore, appropriate modifications made by those skilled in the art without departing from the concept of the present invention are all within the protection scope of the present invention.

[0028] Example 1 Measure 40 mL of ethylene glycol and add 0.58 g of silver nitrate. Stir thoroughly under light until completely dissolved. Add a mixture of K30 and K80 in a mass ratio of 1:0.5 to the aforementioned ethylene glycol solution until completely dissolved. Then, add 2.4 mL of a mixture of sodium chloride and copper chloride in a mass ratio of 1:1 to the aforementioned ethylene glycol solution. After mixing evenly, transfer the reaction mother liquor to a three-necked flask. In a heating pack, heat to 100 °C at a heating rate of 5 °C / min and hold for 30 min. Then, heat to 210 °C at a heating rate of 2 °C / min and hold for 10 min. Quickly cool to room temperature. Finally, after centrifugation and washing, the desired hollow silver nanotubes can be obtained.

[0029] The hollow silver nanotubes prepared above were used to obtain a silver nanotube gel with ice crystal interlayers through a bidirectional freezing method. Then, the ice crystals were directly sublimated to obtain a silver nanotube aerogel by freeze drying. This aerogel was then mixed with MXene nanosheets at a concentration of 0.1 mg / ml and dried in a vacuum drying oven to obtain a silver nanotube / MXene layered stacked structure. The above layered stacked structure was then subjected to a conventional in-situ polymerization process of polyaniline to obtain the final electromagnetic shielding material.

[0030] Example 2 Measure 40 mL of ethylene glycol and add 0.58 g of silver nitrate. Stir thoroughly under light until completely dissolved. Add a mixture of K30 and K80 in a mass ratio of 1:0.5 to the aforementioned ethylene glycol solution until completely dissolved. Then, add 2.4 mL of a mixture of sodium chloride and copper chloride in a mass ratio of 1:1 to the aforementioned ethylene glycol solution. After mixing evenly, transfer the reaction mother liquor to a three-necked flask. In a heating pack, heat to 100 °C at a heating rate of 5 °C / min and hold for 30 min. Then, heat to 210 °C at a heating rate of 2 °C / min and hold for 10 min. Quickly cool to room temperature. Finally, after centrifugation and washing, the desired hollow silver nanotubes can be obtained.

[0031] The hollow silver nanotubes prepared above were used to obtain a silver nanotube gel with ice crystal interlayers through a bidirectional freezing method. Then, the ice crystals were directly sublimated by freeze drying to obtain a silver nanotube aerogel. This aerogel was then mixed with MXene nanosheets at a concentration of 0.3 mg / ml and dried in a vacuum drying oven to obtain a silver nanotube / MXene layered stacked structure. The above layered stacked structure was then subjected to a conventional in-situ polymerization process of polyaniline to obtain the final electromagnetic shielding material.

[0032] Example 3 Measure 40 mL of ethylene glycol and add 0.58 g of silver nitrate. Stir thoroughly under light until completely dissolved. Add a mixture of K30 and K80 in a mass ratio of 1:0.5 to the aforementioned ethylene glycol solution until completely dissolved. Then, add 2.4 mL of a mixture of sodium chloride and copper chloride in a mass ratio of 1:2 to the aforementioned ethylene glycol solution. After mixing evenly, transfer the reaction mother liquor to a three-necked flask. In a heating pack, heat to 100 °C at a heating rate of 5 °C / min and hold for 30 min. Then, heat to 210 °C at a heating rate of 2 °C / min and hold for 10 min. Quickly cool to room temperature. Finally, after centrifugation and washing, the desired hollow silver nanotubes can be obtained.

[0033] The hollow silver nanotubes prepared above were used to obtain a silver nanotube gel with ice crystal interlayers by a bidirectional freezing method. Then, the ice crystals were directly sublimated by freeze drying to obtain a silver nanotube aerogel. This aerogel was then mixed with MXene nanosheets at a concentration of 0.5 mg / ml and dried in a vacuum drying oven to obtain a silver nanotube / MXene layered stacked structure. The above layered stacked structure was then subjected to a conventional in-situ polymerization process of polyaniline to obtain the final electromagnetic shielding material.

[0034] Example 4 Measure 40 mL of ethylene glycol and add 0.58 g of silver nitrate. Stir thoroughly under light until completely dissolved. Add a mixture of K30 and K80 in a mass ratio of 1:0.5 to the aforementioned ethylene glycol solution until completely dissolved. Then, add 2.4 mL of a mixture of sodium chloride and copper chloride in a mass ratio of 1:1 to the aforementioned ethylene glycol solution. After mixing evenly, transfer the reaction mother liquor to a three-necked flask. In a heating pack, heat to 100 °C at a heating rate of 5 °C / min and hold for 30 min. Then, heat to 210 °C at a heating rate of 2 °C / min and hold for 10 min. Quickly cool to room temperature. Finally, after centrifugation and washing, the desired hollow silver nanotubes can be obtained.

[0035] The hollow silver nanotubes prepared above were used to obtain a silver nanotube gel with ice crystal interlayers through a bidirectional freezing method. Then, the ice crystals were directly sublimated to obtain a silver nanotube aerogel by freeze-drying. This aerogel was then mixed with MXene nanosheets at a concentration of 0.1 mg / ml and dried in a vacuum drying oven to obtain a silver nanotube / MXene layered stacked structure. After drying, the obtained layered stacked structure was mechanically compacted by mechanical lamination. Finally, the layered stacked structure was subjected to a conventional in-situ polymerization process of polyaniline to obtain the final electromagnetic shielding material.

[0036] Comparative Example 1 Other experimental conditions were the same as in Example 1, except that PVP was used as a single surfactant and sodium chloride was used as a growth regulator, which could only produce silver nanowires.

[0037] Comparative Example 2 Other experimental conditions were the same as in Example 1, except that gradient heating was not used. Instead, the temperature was directly increased to 210°C at a heating rate of 5°C / min and then held at that temperature. This method also failed to produce silver nanotubes.

Claims

1. A method for preparing an electromagnetic shielding material, characterized in that, The main steps include: S1: Hollow silver nanotubes were prepared by an improved solvothermal method; S2: A silver nanotube gel with ice crystal interlayers was prepared by directional freeze-drying. S3: After processing the above silver nanotube gel, MXene nanosheets are incorporated to obtain a silver nanotube / MXene layered stacked structure; S4: Further process the layered superimposed structure in step S3 above to obtain the final electromagnetic shielding material.

2. The method for preparing an electromagnetic shielding material according to claim 1, characterized in that, The preparation of hollow silver nanotubes by the improved solvothermal method mainly includes the following steps: First, a suitable silver source, growth regulator, surfactant and solvent are selected and mixed; then, the mixed reactants are transferred to a reactor vessel for reaction; finally, the reaction product is processed by centrifugation, washing and other processes to obtain the desired hollow silver nanotubes.

3. The method for preparing an electromagnetic shielding material according to claim 1, characterized in that, In step S2, directional freezing refers to bidirectional freezing.

4. The method for preparing an electromagnetic shielding material according to claim 2, characterized in that, In step S1, the silver source is silver nitrate; the growth regulator is a mixture of sodium chloride and copper chloride in a mass ratio of 1:1-2; the surfactant is polyvinylpyrrolidone, specifically a mixture of K30 and K80 in a mass ratio of 1:0.5; and the reaction solvent is ethylene glycol.

5. The method for preparing an electromagnetic shielding material according to claim 1, characterized in that, The concentration of MXene nanosheets in step S3 is 0.1-0.5 mg / ml.

6. The method for preparing an electromagnetic shielding material according to claim 1, characterized in that, The further processing of the layered superimposed structure in step S3 in step S4 refers to further coating the layered superimposed structure with polyaniline.

7. The method for preparing an electromagnetic shielding material according to claim 6, characterized in that, In step S4, for the coating of the silver nanotube / MXene layered stacked structure, preferably, the layered stacked structure can be mechanically compacted first, and then in-situ coated.

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