Electromagnetic shielding aerogel with double-layer structure and preparation method thereof

Abstract

The application discloses electromagnetic shielding aerogel with a double-layer structure and a preparation method thereof, and the electromagnetic shielding aerogel is composed of cellulose nanofibers, hollow cobalt-nickel carbon nanocages and few-layer MXene, and the electromagnetic shielding aerogel has a double-layer structure. The electromagnetic shielding aerogel has excellent terahertz shielding efficiency with low reflection characteristics, and has great application potential in the fields of lightweight multifunctional electromagnetic shielding composites, special electromagnetic protection facilities, electromagnetic stealth materials and anti-severe environment electronic equipment.

Description

Technical Field

[0001] This invention belongs to the field of materials, specifically relating to an electromagnetic shielding aerogel with a double-layer structure and its preparation method. The electromagnetic shielding aerogel prepared by this method not only has excellent low-reflection characteristics and gigahertz electromagnetic shielding efficiency, but also has excellent heterogeneous photothermal conversion performance. It has great application potential in the fields of lightweight multifunctional electromagnetic shielding composite materials, special electromagnetic protection facilities, electromagnetic stealth materials, and electronic equipment resistant to harsh environments. Background Technology

[0002] Electromagnetic shielding materials are a class of materials that can absorb or reflect electromagnetic waves. They can be used not only to prevent abnormal operation of electronic devices due to electromagnetic interference, but also to prevent diseases caused by the thermal effects of electromagnetic radiation on the human body. In recent years, an increasing number of researchers have designed and prepared various electromagnetic shielding materials for shielding electromagnetic waves. For example, Zhang et al. proposed using electron beam evaporation to load vertical copper-nickel onto graphene nanowalls, successfully preparing a thin film composite with electromagnetic shielding effects (JZZhang, HLShen, ZHWang, TRWu, Carbon. 2024, 225, 119144); Guo et al. modified the matrix film with Cu and Ni, and prepared a novel electromagnetic shielding material using chemical plating and casting methods (BZGuo, JYLiang, JFChen, Y.Zhao, RSC). Adv., 2022, 12, 29688-29696); Wang et al. proposed using electrodeposition to prepare composite films with electromagnetic shielding effects by combining Bi2Te3 and carbon cloth (X. Wang, TF Shi, CL Wan, PA Zong, ZG Liu, W. Huang, Carbon, 2023, 213, 118298); These electromagnetic shielding materials have good electromagnetic shielding capabilities, but their application range is limited by their high density and susceptibility to corrosion. Shahzad et al. prepared a novel two-dimensional material MXene with high conductivity electromagnetic shielding film obtained by acid etching, achieving excellent electromagnetic shielding performance under the premise of corrosion resistance and low density (F. Shahzad, Bi2Te3 M. Alhabeb, CB Hatter, B. Anasori, SM Hong, CMKoo, Y. Gogotsi, Science, 2016, 353, 1137-1140).

[0003] However, the electromagnetic shielding materials mentioned above rely primarily on reflection for electromagnetic loss, making it difficult to achieve electromagnetic stealth. Furthermore, the electromagnetic waves reflected back into free space can easily cause secondary electromagnetic pollution, resulting in poor environmental performance. With the increasing demand for electromagnetic shielding materials in today's society, they are difficult to apply to lightweight, multifunctional electromagnetic shielding composite materials with specific low-reflection requirements, special electromagnetic protection facilities, and electronic equipment resistant to harsh environments. Therefore, it is still necessary to develop an electromagnetic shielding material with multifunctional low-reflection characteristics to further enhance its application value. Summary of the Invention

[0004] To address the problems of traditional methods, according to one aspect of the present invention, one objective of the present invention is to provide an electromagnetic shielding aerogel with a double-layer structure. The electromagnetic shielding aerogel not only has excellent shielding capabilities with low reflection characteristics, but also has certain photothermal conversion capabilities, low density, and the possibility of large-scale production. It has great application potential in the fields of lightweight multifunctional electromagnetic shielding composite materials, special electromagnetic protection facilities, electromagnetic stealth materials, and electronic equipment resistant to harsh environments.

[0005] An electromagnetic shielding aerogel with a double-layer structure is composed of cellulose nanofibers, hollow cobalt-nickel-carbon nanocages, and few-layer MXene. The electromagnetic shielding aerogel has a double-layer structure, with the first layer composed of cellulose nanofibers and hollow cobalt-nickel-carbon nanocages, and the second layer composed of cellulose nanofibers and few-layer MXene.

[0006] Preferably, in the electromagnetic shielding aerogel according to the present invention, the weight contents of the hollow cobalt-nickel-carbon nanocage in the first layer and the few-layer MXene in the second layer are the same or different, and preferably the contents of the two are the same.

[0007] Preferably, the cellulose nanofiber content in the first and second layers of the electromagnetic shielding aerogel according to the present invention is the same.

[0008] Preferably, in the electromagnetic shielding aerogel with a double-layer structure according to the present invention, the weight ratio of the few-layer MXene and the hollow cobalt-nickel-carbon nanocage in the electromagnetic shielding aerogel is 0.1:1 to 10:1, more preferably 0.3:1 to 3:1, and even more preferably 1:1.

[0009] Preferably, in the electromagnetic shielding aerogel according to the present invention, the weight ratio of the few-layer MXene powder to the cellulose nanofibers is 0.1:1 to 1:1; more preferably 0.25:1 to 0.75:1, and even more preferably 0.5:1.

[0010] Preferably, in the electromagnetic shielding aerogel according to the present invention, the weight ratio of the hollow cobalt-nickel-carbon nanocage to the cellulose nanofiber is 0.1:1 to 1:1; more preferably 0.25:1 to 0.75:1, and even more preferably 0.5:1.

[0011] According to another aspect of the present invention, an object of the present invention is to provide a method for preparing an electromagnetic shielding aerogel having a double-layer structure, comprising the following steps:

[0012] 1) Preparation of hollow cobalt-nickel carbon nanocages

[0013] Under stirring conditions, 6 parts by weight of zinc nitrate hexahydrate and 6 parts by weight of 2-methylimidazole were added to 100 parts by weight of methanol. The mixture was stirred at room temperature for 24 hours, and after centrifugation and washing at 8000 r / min × 5 min, the zinc-based zeolite imidazole ester skeleton was obtained. Under stirring conditions, 0.5 parts by weight of the above-synthesized zinc-based zeolite imidazole ester skeleton was added to 100 parts by weight of anhydrous methanol containing 3 parts by weight of cobalt nitrate hexahydrate and 3 parts by weight of nickel nitrate hexahydrate. The mixture was stirred at room temperature for 1 hour. A cobalt-nickel ion-modified zinc-based zeolite imidazole ester framework was obtained; then, it was added to 100 parts by weight of methanol containing 6 parts by weight of 2-methylimidazole, and centrifuged and washed at 8000 r / min for 5 min to obtain the cobalt-nickel zinc-based zeolite imidazole ester framework; the synthesized cobalt-nickel zinc-based zeolite imidazole ester framework was dried under vacuum at 80 degrees Celsius, placed in a tube furnace under nitrogen atmosphere protection, and heated to 800 degrees Celsius at a heating rate of 2 degrees Celsius per minute for carbonization for 2 hours to obtain hollow cobalt-nickel carbon nanocages;

[0014] 2) Preparation of few-layer MXene solution

[0015] One part by weight of LiF was dissolved in 20 parts by weight of 9M hydrochloric acid, and then one part by weight of Ti3AlC2 powder was added and stirred for 48 hours. The resulting suspension was centrifuged at 3500 r / min for 5 minutes and washed with deionized water until the pH of the supernatant was ≥5. The supernatant was then discarded. The resulting precipitate was dispersed in 25 parts by weight of deionized water, sonicated in an ice bath for 1 hour, and then collected at 3500 r / min for 60 minutes to obtain a few-layer MXene solution. The few-layer MXene solution was frozen in a -4°C freezer and then freeze-dried in a vacuum freeze dryer at -48°C and a vacuum degree of 20 Pa to obtain few-layer MXene powder.

[0016] 3) Preparation of a double-layer electromagnetic shielding aerogel

[0017] Under ultrasonic and stirring conditions, the few-layer MXene powder obtained in step 2) above is dispersed in a 1% (w / w) aqueous solution of cellulose nanofibers at a weight ratio of 0.1:1 to 1:1, preferably 0.25:1 to 0.75:1, and more preferably 0.5:1 to cellulose nanofibers. The dispersion is then placed in a container and frozen at -4°C. The hollow cobalt-nickel carbon nanocages obtained in step 1) above are dispersed in a 1% (w / w) aqueous solution of cellulose nanofibers at a weight ratio of 0.1:1 to 1:1, preferably 0.25:1 to 0.75:1, and more preferably 0.5:1 to cellulose nanofibers. The dispersion is then poured onto the frozen few-layer MXene / cellulose nanofibers at a volume ratio of 1:1. The dispersion is then frozen again at -4°C and freeze-dried in a vacuum freeze dryer at -48°C and a vacuum of 20 Pa to obtain a bilayer electromagnetic shielding aerogel.

[0018] According to another aspect of the invention, another object of the invention is to provide the use of the electromagnetic shielding aerogel with the double-layer structure in electromagnetic stealth devices and electronic equipment resistant to harsh environments.

[0019] Beneficial effects

[0020] 1. The preparation method of the electromagnetic shielding aerogel according to the present invention is simple and has a wide range of applications;

[0021] 2. The electromagnetic shielding aerogel prepared according to the present invention has the characteristics of low density and good stability;

[0022] 3. The electromagnetic shielding aerogel prepared according to the present invention has excellent low-reflection characteristics and gigahertz electromagnetic shielding performance.

[0023] 4. The electromagnetic shielding aerogel prepared according to the present invention shows good performance in actual simulated electromagnetic shielding tests, and has the potential for size adjustment and large-scale production.

[0024] 5. The key feature of this invention is that the electromagnetic shielding aerogel has a double-layer structure. This double-layer structure brings about the aforementioned excellent electromagnetic stealth effect. The double-layer structure allows incident electromagnetic waves to undergo multiple scattering and reflections between the absorption layer and the reflection layer. The absorption layer extends the propagation path of electromagnetic waves and reduces reflection. The reflection layer blocks electromagnetic waves and enhances the electromagnetic wave shielding capability. Attached Figure Description

[0025] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0026] Figure 1 This is a flowchart illustrating the preparation process of the electromagnetic shielding aerogel according to the present invention.

[0027] Figure 2 X-ray diffraction patterns of the first and second layers of the electromagnetic shielding aerogel prepared according to Example 1, cellulose nanofibers, few-layer MXene, and hollow cobalt-nickel-carbon nanocages.

[0028] Figure 3 Transmission electron microscopy (TEM) images of hollow cobalt-nickel-carbon nanocages, few-layer MXene, and cellulose nanofibers prepared according to Example 1.

[0029] Figure 4 Raman spectra of few-layer MXene, cobalt-nickel-zinc-based zeolite imidazole ester framework and hollow cobalt-nickel-carbon nanocage prepared according to Example 1.

[0030] Figure 5 The images show the gas adsorption-desorption curves, specific surface areas, and corresponding pore size distributions of the cobalt-nickel-zinc-based zeolite imidazole ester framework and hollow cobalt-nickel-carbon nanocages prepared according to Example 1.

[0031] Figure 6 The energy dispersive X-ray spectroscopy (EDS) spectrum of the hollow cobalt-nickel carbon nanocage prepared according to Example 1 is shown in the transmission electron microscope.

[0032] Figure 7 The image shows a scanning electron microscope (SEM) image of the electromagnetic shielding aerogel prepared according to Example 1.

[0033] Figure 8 Optical photographs of the electromagnetic shielding aerogels prepared according to Example 1 and Comparative Examples 1-2.

[0034] Figure 9 This is for testing the electromagnetic shielding performance of the electromagnetic shielding aerogels prepared according to Examples 1-7 and Comparative Examples 1-3.

[0035] Figure 10 The electromagnetic stealth correlation coefficients of the electromagnetic shielding aerogels prepared according to Examples 1-7 and Comparative Examples 1-3 were tested.

[0036] Figure 11 This is for testing the electromagnetic shielding performance of the electromagnetic shielding aerogels prepared according to Example 1 and Comparative Example 3.

[0037] Figure 12 This is an application test simulating the actual electromagnetic shielding performance of the electromagnetic shielding aerogel according to Example 1.

[0038] Figure 13 This is a lightweight feature image of the electromagnetic shielding aerogel prepared according to Example 1. Detailed Implementation

[0039] The present invention will now be described in detail. Before proceeding with the description, it should be understood that the terminology used in this specification and the appended claims should not be construed as limited to its general or dictionary meaning, but rather should be interpreted according to the meaning and concept corresponding to the technical aspects of the invention, based on the principle that the inventors are allowed to appropriately define the terms for the best interpretation. Therefore, the description presented herein is merely a preferred example for illustrative purposes and is not intended to limit the scope of the invention. It should be understood that other equivalents or modifications can be obtained from it without departing from the spirit and scope of the invention.

[0040] In this document, the terms “comprising,” “including,” “having,” “containing,” or any other similar terms are open-ended conjunctions intended to cover non-exclusive inclusions. For example, a composition or article containing a plurality of elements is not limited to those listed herein, but may also include other elements not explicitly listed but typically inherent to the composition or article. Furthermore, unless explicitly stated to the contrary, the term “or” is inclusive, not exclusive. For example, the condition “A or B” is satisfied in any of the following cases: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); A and B are both true (or exist). Moreover, in this document, the terms “comprising,” “including,” “having,” and “containing” should be interpreted as specifically disclosed and simultaneously cover closed or semi-closed conjunctions such as “composed of” and “substantially composed of.”

[0041] In this document, all features or conditions defined in the form of numerical ranges or percentage ranges are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible secondary ranges and individual values ​​within those ranges, particularly integer values. For example, a range description of "1 to 8" should be considered as specifically disclosing all secondary ranges such as 1 to 7, 2 to 8, 2 to 6, 3 to 6, 4 to 8, 3 to 8, etc., particularly secondary ranges defined by all integer values, and should be considered as specifically disclosing individual values ​​within those ranges such as 1, 2, 3, 4, 5, 6, 7, 8, etc. Unless otherwise specified, the foregoing interpretation applies to all content throughout this invention, regardless of its scope.

[0042] If a quantity or other numerical value or parameter is expressed as a range, a preferred range, or a series of upper and lower limits, it should be understood that this document has specifically disclosed all ranges consisting of any upper or preferred value of that range and the lower or preferred value of that range, regardless of whether such ranges are separately disclosed. Furthermore, when a range of numerical values ​​is mentioned herein, unless otherwise stated, the range shall include its endpoints and all integers and fractions within the range.

[0043] The electromagnetic shielding aerogel with a double-layer structure prepared according to the method of the present invention not only has excellent gigahertz electromagnetic shielding performance with low reflection characteristics, but also has unique bi-sided heterogeneous photothermal conversion performance. Figure 1 This is a flowchart illustrating the preparation process of electromagnetic shielding aerogel according to the present invention.

[0044] In the preparation method according to the present invention, the weight ratio of few-layer MXene to hollow cobalt-nickel carbon nanocages is 0.1:1 to 10:1, more preferably 0.3:1 to 3:1, and even more preferably 1:1. When the weight ratio of few-layer MXene to hollow cobalt-nickel carbon nanocages is greater than 3:1, the electromagnetic stealth capability of the electromagnetic shielding aerogel decreases. When the weight ratio of few-layer MXene to hollow cobalt-nickel carbon nanocages is less than 0.3:1, the electromagnetic shielding capability of the electromagnetic shielding aerogel decreases.

[0045] In the preparation method according to the present invention, the weight ratio of the few-layer MXene powder to the cellulose nanofibers is 0.1:1 to 1:1; preferably 0.25:1 to 0.75:1, and more preferably 0.5:1. When the weight ratio of few-layer MXene to cellulose nanofibers is greater than 0.75:1, the electromagnetic shielding aerogel has insufficient magnetism. When the weight ratio of few-layer MXene to cellulose nanofibers is less than 0.25:1, the electromagnetic shielding aerogel has insufficient conductivity.

[0046] In the preparation method according to the present invention, the weight ratio of the hollow cobalt-nickel carbon nanocage to the cellulose nanofiber is 0.1:1 to 1:1; preferably 0.25:1 to 0.75:1, and more preferably 0.5:1. When the weight ratio of the hollow cobalt-nickel carbon nanocage to the cellulose nanofiber is greater than 0.75:1, the conductivity of the electromagnetic shielding aerogel is insufficient. When the weight ratio of few-layer MXene to the hollow cobalt-nickel carbon nanocage is less than 0.25:1, the magnetism of the electromagnetic shielding aerogel is insufficient.

[0047] The cellulose nanofibers used in the preparation method according to the present invention are not particularly limited and can be commercially available products, such as the cellulose nanofiber product TOCNF-PL-2 purchased from Tianjin Wood Elf Technology Co., Ltd.

[0048] According to the preparation method of the present invention, the double-layer electromagnetic shielding aerogel has a double-layer structure. When the electromagnetic shielding aerogel does not have a double-layer structure, the electromagnetic components and non-conductive components in the electromagnetic shielding aerogel permeate each other severely, resulting in a decrease in electromagnetic shielding ability.

[0049] Specifically, according to the electromagnetic shielding aerogel with a double-layer structure, steps 1) preparing hollow cobalt-nickel-carbon nanocages and step 2) preparing few-layer MXene solution are conventional preparation methods and are not limited to the methods specified in the invention content section of this disclosure.

[0050] Electromagnetic shielding performance is typically determined by factors such as magnetic and electrical losses, electric and magnetic dipoles, and multiple interfaces. Magnetic and electrical losses are crucial aspects, significantly influencing shielding effectiveness through the absorption and dissipation of electromagnetic energy. The presence and characteristics of electric and magnetic dipoles also play an indispensable role in electromagnetic shielding; their distribution and state significantly impact shielding performance. Furthermore, multiple interfaces are a significant factor. The unique characteristics of interfaces formed between different media alter the propagation path and reflection of the electromagnetic field, further impacting overall electromagnetic shielding performance. Few-layer MXene and hollow cobalt-nickel-carbon nanocages exhibit strong electrical and magnetic losses. The bilayer design with asymmetric charge distribution leads to the polarization of electric / magnetic dipoles, forming interacting dipoles and generating multiple interfaces.

[0051] The electromagnetic shielding aerogel prepared according to the method of the present invention exhibits excellent electromagnetic shielding performance with low reflection characteristics. With a reflection coefficient of 0.28, its electromagnetic shielding capability in the gigahertz range can reach 35.1 dB. With a reflection coefficient of 0.25, its electromagnetic shielding capability in the gigahertz range can reach 21.2 dB.

[0052] The following embodiments are merely examples illustrating implementations of the present invention and do not constitute any limitation on the present invention. Those skilled in the art will understand that modifications made without departing from the spirit and concept of the present invention fall within the protection scope of the present invention. Unless otherwise specified, the reagents and instruments used in the following embodiments are commercially available products.

[0053] Example 1

[0054] 1) Preparation of hollow cobalt-nickel carbon nanocages

[0055] Under stirring conditions, 6 g of zinc nitrate hexahydrate and 6 g of 2-methylimidazole were added to 100 g of methanol. The mixture was stirred at room temperature for 24 hours, and after centrifugation and washing at 8000 r / min for 5 min, a zinc-based zeolite imidazolium ester skeleton was obtained. Under stirring conditions, 0.5 g of the synthesized zinc-based zeolite imidazolium ester skeleton was added to 100 g of anhydrous methanol containing 3 g of cobalt nitrate hexahydrate and 3 g of nickel nitrate hexahydrate. The mixture was stirred at room temperature for 1 hour to obtain a cobalt-nickel ion modified zinc-based zeolite imidazolium ester skeleton. Then, a mixture containing 6 g of zinc nitrate hexahydrate and 2-methylimidazole was added to the methanol. 100g of 2-methylimidazole was centrifuged and washed at 8000r / min for 5min to obtain a cobalt-nickel-zinc zeolite imidazole ester framework. The synthesized cobalt-nickel-zinc zeolite imidazole ester framework was dried under vacuum at 80°C and placed in a tube furnace under nitrogen atmosphere protection. The temperature was increased to 800°C at a heating rate of 2°C per minute for 2 hours to obtain hollow cobalt-nickel carbon nanocages.

[0056] 2) Preparation of few-layer MXene solution

[0057] 1 g LiF was dissolved in 20 g hydrochloric acid (9 M), and then 1 g Ti3AlC2 powder was added and stirred for 48 h. The resulting suspension was centrifuged at 3500 r / min for 5 min, washed with deionized water until the pH of the supernatant was ≥ 5, and the supernatant was discarded. The resulting precipitate was dispersed in 25 g deionized water, sonicated in an ice bath for 1 h, and then collected at 3500 r / min for 60 min to obtain a few-layer MXene solution. The few-layer MXene solution was frozen in a -4 °C freezer and then freeze-dried in a vacuum freeze dryer at -48 °C and a vacuum degree of 20 Pa to obtain few-layer MXene powder.

[0058] 3) Preparation of a double-layer electromagnetic shielding aerogel

[0059] Under ultrasonic and stirring conditions, the few-layer MXene powder obtained in step 2) above is dispersed in a 1% (w / w) aqueous solution of cellulose nanofibers at a weight ratio of 1:2. Then, 300 mL of this solution is placed in a container and frozen at -4°C. The hollow cobalt-nickel carbon nanocages obtained in step 1) above are dispersed in a 1% (w / w) aqueous solution of cellulose nanofibers at a weight ratio of 1:2. Then, 300 mL of this solution is poured onto the frozen few-layer MXene / cellulose nanofibers, with a volume ratio of 1:1. The solution is then frozen again at -4°C and freeze-dried in a vacuum freeze dryer at -48°C and a vacuum degree of 20 Pa to obtain a bilayer electromagnetic shielding aerogel, wherein the weight ratio of few-layer MXene to hollow cobalt-nickel carbon nanocages is 1:1.

[0060] like Figure 2As shown, the electromagnetic shielding aerogel prepared in Example 1 was analyzed using X-ray diffraction patterns. It can be seen that the diffraction peaks of each component in the first and second layers of the electromagnetic shielding aerogel are obvious, proving the successful preparation of the composite material and the successful construction of the double-layer structure.

[0061] like Figure 3 As shown, the hollow cobalt-nickel carbon nanocages, few-layer MXene, and cellulose nanofibers prepared in Example 1 were characterized by transmission electron microscopy, further demonstrating the successful synthesis of the raw materials.

[0062] like Figure 4 As shown, Raman spectroscopy was performed on the few-layer MXene, cobalt-nickel-zinc-based zeolite imidazole ester framework, and hollow cobalt-nickel-carbon nanocages prepared in Example 1. It can be seen that after carbonization, the cobalt-nickel-zinc-based zeolite imidazole ester framework was transformed into hollow cobalt-nickel-carbon nanocages with a high degree of graphitization.

[0063] like Figure 5 As shown, the cobalt-nickel-zinc-based zeolite imidazole ester framework and hollow cobalt-nickel-carbon nanocage prepared in Example 1 were analyzed using a fully automated specific surface area and porosity analyzer, which proved the successful construction of the hollow structure of the material.

[0064] like Figure 6 As shown, energy dispersive spectroscopy (EDS) was used to analyze the hollow cobalt-nickel carbon nanocages prepared in Example 1, which further confirmed the elemental distribution within its structure.

[0065] like Figure 7 As shown, the electromagnetic shielding aerogel prepared in Example 1 was tested by scanning electron microscopy, which proved its porous structure and the different properties of its bilayer structure.

[0066] Figure 13 As shown in Example 1, the electromagnetic shielding aerogel can be easily supported by dandelion fluff without bending, indicating that the electromagnetic shielding aerogel has a lightweight characteristic with a density of 31.2 mg / cm³. 3 .

[0067] Example 2

[0068] Except for the weight ratio of few-layer MXene to hollow cobalt-nickel-carbon nanocages in the bilayer electromagnetic shielding aerogel being adjusted to 1:3, the electromagnetic shielding aerogel (BZMN-5-1:3) was prepared according to the same preparation steps as in Example 1. Specifically, under ultrasonic and stirring conditions, few-layer MXene powder was dispersed in a 1% (w / w) aqueous solution of cellulose nanofibers at a weight ratio of 1:4, and then placed in a container and frozen at -4°C. Hollow cobalt-nickel-carbon nanocages were dispersed in a 1% (w / w) aqueous solution of cellulose nanofibers at a weight ratio of 3:4, and then poured on top of the frozen few-layer MXene / cellulose nanofibers, with a volume ratio of 1:1 between the two solutions. The mixture was then frozen again at -4°C, and then freeze-dried in a vacuum freeze dryer at -48°C and a vacuum degree of 20 Pa to obtain the bilayer electromagnetic shielding aerogel.

[0069] Example 3

[0070] Except for the content ratio of few-layer MXene to hollow cobalt-nickel carbon nanocages in the bilayer electromagnetic shielding aerogel being controlled at 3:1, the electromagnetic shielding aerogel (BZMN-5-3:1) was prepared according to the same preparation steps as in Example 1. Specifically, under ultrasonic and stirring conditions, few-layer MXene powder was dispersed in a 1% (w / w) aqueous solution of cellulose nanofibers at a weight ratio of 3:4 to 3:4, and then placed in a container and frozen at -4°C. Hollow cobalt-nickel carbon nanocages were dispersed in a 1% (w / w) aqueous solution of cellulose nanofibers at a weight ratio of 1:4 to 1%, and then poured on top of the frozen few-layer MXene / cellulose nanofibers. The volume ratio of the two solutions was 1:1. The mixture was then frozen again at -4°C, and then freeze-dried in a vacuum freeze dryer at -48°C and a vacuum degree of 20 Pa to obtain the bilayer electromagnetic shielding aerogel.

[0071] Example 4

[0072] Except for the ratio of few-layer MXene to cellulose nanofibers in the bilayer electromagnetic shielding aerogel being controlled at 0.1:1, and the ratio of hollow cobalt-nickel carbon nanocages to cellulose nanofibers being controlled at 0.1:1, the electromagnetic shielding aerogel (BZMN-1-1:1) was prepared according to the same preparation steps as in Example 1. Specifically, under ultrasonic and stirring conditions, few-layer MXene powder was dispersed into a 1% (w / w) aqueous solution of cellulose nanofibers at a weight ratio of 0.1:1 to 0.1:1, and then placed in a container and frozen at -4°C. Hollow cobalt-nickel carbon nanocages were dispersed into a 1% (w / w) aqueous solution of cellulose nanofibers at a weight ratio of 0.1:1 to 0.1:1, and then poured onto the frozen few-layer MXene / cellulose nanofibers, with a volume ratio of 1:1 between the two solutions. The mixture was then frozen at -4°C and freeze-dried in a vacuum freeze dryer at -48°C and a vacuum degree of 20 Pa to obtain the bilayer electromagnetic shielding aerogel.

[0073] Example 5

[0074] Except for the ratio of few-layer MXene to cellulose nanofibers in the bilayer electromagnetic shielding aerogel being controlled at 0.2:1, and the ratio of hollow cobalt-nickel carbon nanocages to cellulose nanofibers being controlled at 0.2:1, the electromagnetic shielding aerogel (BZMN-2-1:1) was prepared according to the same preparation steps as in Example 1. Specifically, under ultrasonic and stirring conditions, few-layer MXene powder was dispersed into a 1% (w / w) aqueous solution of cellulose nanofibers at a weight ratio of 0.2:1 to 0.2:1, and then placed in a container and frozen at -4°C. Hollow cobalt-nickel carbon nanocages were dispersed into a 1% (w / w) aqueous solution of cellulose nanofibers at a weight ratio of 0.2:1 to 0.2:1, and then poured onto the frozen few-layer MXene / cellulose nanofibers, with a volume ratio of 1:1 between the two solutions. The mixture was then frozen at -4°C and freeze-dried in a vacuum freeze dryer at -48°C and a vacuum degree of 20 Pa to obtain the bilayer electromagnetic shielding aerogel.

[0075] Example 6

[0076] Except for the ratio of few-layer MXene to cellulose nanofibers in the bilayer electromagnetic shielding aerogel being controlled at 0.3:1, and the ratio of hollow cobalt-nickel carbon nanocages to cellulose nanofibers being controlled at 0.3:1, the electromagnetic shielding aerogel (BZMN-3-1:1) was prepared according to the same preparation steps as in Example 1. Specifically, under ultrasonic and stirring conditions, few-layer MXene powder was dispersed into a 1% (w / w) aqueous solution of cellulose nanofibers at a weight ratio of 0.3:1 to 0.3:1, and then placed in a container and frozen at -4°C. Hollow cobalt-nickel carbon nanocages were dispersed into a 1% (w / w) aqueous solution of cellulose nanofibers at a weight ratio of 0.3:1 to 0.3:1, and then poured onto the frozen few-layer MXene / cellulose nanofibers, with a volume ratio of 1:1 between the two solutions. The mixture was then frozen at -4°C and freeze-dried in a vacuum freeze dryer at -48°C and a vacuum degree of 20 Pa to obtain the bilayer electromagnetic shielding aerogel.

[0077] Example 7

[0078] Except for the ratio of few-layer MXene to cellulose nanofibers in the bilayer electromagnetic shielding aerogel being controlled at 0.4:1, and the ratio of hollow cobalt-nickel carbon nanocages to cellulose nanofibers being controlled at 0.4:1, the electromagnetic shielding aerogel (BZMN-4-1:1) was prepared according to the same preparation steps as in Example 1. Specifically, under ultrasonic and stirring conditions, few-layer MXene powder was dispersed into a 1% (w / w) aqueous solution of cellulose nanofibers at a weight ratio of 0.4:1 to 0.4:1, and then placed in a container and frozen at -4°C. Hollow cobalt-nickel carbon nanocages were dispersed into a 1% (w / w) aqueous solution of cellulose nanofibers at a weight ratio of 0.4:1 to 0.4:1, and then poured onto the frozen few-layer MXene / cellulose nanofibers, with a volume ratio of 1:1 between the two solutions. The mixture was then frozen at -4°C and freeze-dried in a vacuum freeze dryer at -48°C and a vacuum degree of 20 Pa to obtain the bilayer electromagnetic shielding aerogel.

[0079] Comparative Example 1

[0080] Except for the ratio of few-layer MXene to cellulose nanofibers in the bilayer electromagnetic shielding aerogel being controlled at 1:1, and the ratio of hollow cobalt-nickel-carbon nanocages to cellulose nanofibers being controlled at 0:1 (i.e., without hollow cobalt-nickel-carbon nanocages), the electromagnetic shielding aerogel (BZMN-5-1:0) was prepared according to the same preparation steps as in Example 1. Specifically, under ultrasonic and stirring conditions, few-layer MXene powder was dispersed in a 1% (by weight) aqueous solution of cellulose nanofibers at a weight ratio of 1:1, and then placed in a container and frozen at -4°C. Then, an equal volume of the 1% (by weight) aqueous solution of cellulose nanofibers was added, and the mixture was frozen again at -4°C. Finally, it was freeze-dried in a vacuum freeze dryer at -48°C and a vacuum degree of 20 Pa to obtain the bilayer electromagnetic shielding aerogel.

[0081] Comparative Example 1

[0082] Except for the ratio of few-layer MXene to cellulose nanofibers in the bilayer electromagnetic shielding aerogel being controlled at 0:1 (i.e., MXene is absent), and the ratio of hollow cobalt-nickel-carbon nanocages to cellulose nanofibers being controlled at 1:1, the electromagnetic shielding aerogel (BZMN-5-0:1) was prepared according to the same preparation steps as in Example 1. Specifically, a 1% (w / w) aqueous solution of cellulose nanofibers was placed in a container and frozen at -4°C. Under ultrasonic and stirring conditions, hollow cobalt-nickel-carbon nanocages were dispersed into the 1% (w / w) aqueous solution of cellulose nanofibers at a weight ratio of 1:1 to cellulose nanofibers. Then, the same volume was poured onto the frozen cellulose nanofiber cryosol, and the mixture was frozen at -4°C. Finally, it was freeze-dried in a vacuum freeze dryer at -48°C and a vacuum degree of 20 Pa to obtain the bilayer electromagnetic shielding aerogel.

[0083] Comparative Example 3

[0084] The amounts of few-layer MXene, hollow cobalt-nickel carbon nanocages, and cellulose nanofiber aqueous solution were the same as in Example 1, but the MXene and hollow cobalt-nickel carbon nanocage cellulose nanofiber aqueous solution were directly mixed in without stratification. The remaining preparation steps were the same as in Example 1 to obtain the electromagnetic shielding aerogel (RZMN-5-1:1). Specifically, under ultrasonic and stirring conditions, few-layer MXene powder, hollow cobalt-nickel carbon nanocages, and 1% by weight of cellulose nanofiber solution were mixed and dispersed evenly at a weight ratio of 1:1:2. The mixture was then placed in a container and frozen at -4°C, and then freeze-dried in a vacuum freeze dryer at -48°C and a vacuum degree of 20 Pa to obtain an electromagnetic shielding aerogel with a randomly mixed structure.

[0085] Table 1. Solid content of samples from the examples and comparative examples

[0086]

[0087] like Figure 8 As shown, from left to right, the first and second layers of the electromagnetic shielding aerogel prepared in Example 1 and Comparative Examples 1-2 are clearly distinguished in color, proving the successful construction of their electromagnetic shielding aerogel double-layer structure.

[0088] Experiment Example 1: Gigahertz Electromagnetic Shielding Experiment

[0089] The electromagnetic shielding aerogels prepared in Examples 1-7 and Comparative Examples 1-3 were cut to the appropriate size for the waveguide cavity of the vector network analyzer, and then fixed in the waveguide cavity of the vector network analyzer. Under electromagnetic wave radiation at frequencies of 8.2-12.4 GHz, the S-parameters before and after electromagnetic wave transmission were measured, and the electromagnetic shielding efficiency was calculated from the S-parameters.

[0090] Figure 9 Electromagnetic shielding performance tests were conducted on the electromagnetic shielding aerogels prepared in Examples 1-7 and Comparative Examples 1-3. The test results showed that the electromagnetic shielding efficiency of the aerogel in Example 1 was greater than 20dB, and it could shield more than 99% of electromagnetic wave radiation, proving that it has good electromagnetic shielding performance.

[0091] Figure 10 Electromagnetic stealth performance tests were conducted on the electromagnetic shielding aerogels prepared in Examples 1-7 and Comparative Examples 1-3. The test results showed that the aerogel of Example 1 had an absorption coefficient as high as 0.75, which could hide more than 75% of electromagnetic wave radiation, proving that it had good electromagnetic stealth performance.

[0092] Figure 11 The test results show that the electromagnetic shielding aerogels prepared in Example 1 and Comparative Example 3 have electromagnetic shielding energy efficiency. The test results show that the double-layer structure can give the electromagnetic shielding aerogels better shielding performance, and Example 1 has the best electromagnetic shielding performance with low reflection characteristics.

[0093] Experimental Example 2: Simulation of Actual Electromagnetic Shielding

[0094] The electromagnetic shielding aerogel prepared in Example 1 was placed between a running electronic device and an electromagnetic radiation detector, and the electromagnetic shielding capability of the electromagnetic shielding aerogel was tested by observing the changes in the values ​​of the electromagnetic radiation detector.

[0095] Figure 12The figures show the actual electromagnetic shielding simulation test results and corresponding numerical changes of the electromagnetic shielding aerogel prepared in Example 1. When the electromagnetic shielding aerogel is not placed, the electromagnetic radiation detector reading increases and the alarm light illuminates. When the electromagnetic shielding aerogel is placed, the electromagnetic radiation detector reading decreases and the alarm light goes out. The figures demonstrate that the electromagnetic shielding aerogel prepared in Example 1 has good shielding performance against electromagnetic waves, and the radiation intensity after shielding is within the safety threshold specified by the International Commission on Non-Ionizing Radiation Protection.

[0096] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. An electromagnetic shielding aerogel with a double-layer structure, comprising cellulose nanofibers, hollow cobalt-nickel-carbon nanocages, and few-layer MXene, wherein the electromagnetic shielding aerogel has a double-layer structure, the first layer being composed of cellulose nanofibers and hollow cobalt-nickel-carbon nanocages, and the second layer being composed of cellulose nanofibers and few-layer MXene.

2. The electromagnetic shielding aerogel with a double-layer structure according to claim 1, characterized in that, The first and second layers of the electromagnetic shielding aerogel have the same content of cellulose nanofibers.

3. The electromagnetic shielding aerogel with a double-layer structure according to claim 1, characterized in that, In the electromagnetic shielding aerogel, the weight ratio of the few-layer MXene to the hollow cobalt-nickel-carbon nanocage is 0.1:1 to 10:

1.

4. The electromagnetic shielding aerogel with a double-layer structure according to claim 1, characterized in that, In the electromagnetic shielding aerogel, the weight ratio of the few-layer MXene to the hollow cobalt-nickel-carbon nanocage is 0.3:1 to 3:

1.

5. The electromagnetic shielding aerogel with a double-layer structure according to claim 1, characterized in that, In the electromagnetic shielding aerogel, the weight ratio of the few-layer MXene to the hollow cobalt-nickel-carbon nanocage is 1:

1.

6. The electromagnetic shielding aerogel with a double-layer structure according to claim 1, characterized in that, The weight ratio of the few-layer MXene to the cellulose nanofibers is 0.1:1 to 1:

1.

7. The electromagnetic shielding aerogel with a double-layer structure according to claim 1, characterized in that, The weight ratio of the few-layer MXene to the cellulose nanofibers is from 0.25:1 to 0.75:

1.

8. The electromagnetic shielding aerogel with a double-layer structure according to claim 1, characterized in that, The weight ratio of the few-layer MXene to the cellulose nanofibers is 0.5:

1.

9. The electromagnetic shielding aerogel with a double-layer structure according to claim 1, characterized in that, The weight ratio of the hollow cobalt-nickel carbon nanocage to the cellulose nanofiber is 0.1:1 to 1:

1.

10. The electromagnetic shielding aerogel with a double-layer structure according to claim 1, characterized in that, The weight ratio of the hollow cobalt-nickel carbon nanocage to the cellulose nanofiber is 0.25:1 to 0.75:

1.

11. The electromagnetic shielding aerogel with a double-layer structure according to claim 1, characterized in that, The weight ratio of the hollow cobalt-nickel carbon nanocage to the cellulose nanofiber is 0.5:

1.

12. A method for preparing an electromagnetic shielding aerogel with a double-layer structure according to any one of claims 1 to 11, comprising the following steps: 1) Preparation of hollow cobalt-nickel carbon nanocages Under stirring conditions, 6 parts by weight of zinc nitrate hexahydrate and 6 parts by weight of 2-methylimidazole were added to 100 parts by weight of methanol. The mixture was stirred at room temperature for 24 hours, and after centrifugation at 8000 r / min × 5 min, the zinc-based zeolite imidazole ester skeleton was obtained. Under stirring conditions, 0.5 parts by weight of the synthesized zinc-based zeolite imidazole ester skeleton was added to 100 parts by weight of anhydrous methanol containing 3 parts by weight of cobalt nitrate hexahydrate and 3 parts by weight of nickel nitrate hexahydrate. The mixture was stirred at room temperature for 1 hour to obtain… A cobalt-nickel ion-modified zinc-based zeolite imidazole ester framework was obtained; then it was added to 100 parts by weight of methanol containing 6 parts by weight of 2-methylimidazole, and centrifuged and washed at 8000 r / min for 5 min to obtain the cobalt-nickel zinc-based zeolite imidazole ester framework; the synthesized cobalt-nickel zinc-based zeolite imidazole ester framework was dried under vacuum at 80 degrees Celsius, placed in a tube furnace under nitrogen atmosphere protection, and heated to 800 degrees Celsius at a heating rate of 2 degrees Celsius per minute for carbonization for 2 hours to obtain hollow cobalt-nickel carbon nanocages; 2) Preparation of few-layer MXene powder One part by weight of LiF was dissolved in 20 parts by weight of hydrochloric acid in 9M solution, and then one part by weight of Ti3AlC2 powder was added and stirred for 48 hours. The resulting suspension was centrifuged at 3500 r / min for 5 minutes and washed with deionized water until the pH of the supernatant was ≥5. The supernatant was then discarded. The precipitate was added to 25 parts by weight of deionized water, sonicated in an ice bath for 1 hour, and then centrifuged at 3500 r / min for 60 minutes. The supernatant was collected to obtain a few-layer MXene solution. The few-layer MXene solution was frozen in a -4°C freezer and then freeze-dried in a vacuum freeze dryer at -48°C and a vacuum of 20 Pa to obtain few-layer MXene powder. 3) Preparation of a double-layer electromagnetic shielding aerogel Under ultrasonic and stirring conditions, the few-layer MXene powder obtained in step 2) above was dispersed into a 1% (w / w) aqueous solution of cellulose nanofibers at a weight ratio of 0.1:1 to 1:1 with cellulose nanofibers. The solution was then placed in a container and frozen at -4°C. The hollow cobalt-nickel carbon nanocages obtained in step 1) above were dispersed into a 1% (w / w) aqueous solution of cellulose nanofibers at a weight ratio of 0.1:1 to 1:1 with cellulose nanofibers. The solution was then poured onto the frozen few-layer MXene / cellulose nanofibers, with a volume ratio of 1:1 between the two solutions. The solution was then frozen again at -4°C and then freeze-dried in a vacuum freeze dryer at -48°C and a vacuum degree of 20 Pa to obtain a bilayer electromagnetic shielding aerogel.

13. The preparation method according to claim 12, characterized in that, In step 3), the weight ratio of the few-layer MXene powder obtained in step 2) to the cellulose nanofibers is 0.25:1 to 0.75:1; and the weight ratio of the hollow cobalt-nickel carbon nanocages obtained in step 1) to the cellulose nanofibers is 0.25:1 to 0.75:

1.

14. The preparation method according to claim 12, characterized in that, In step 3), the weight ratio of the few-layer MXene powder obtained in step 2) to the cellulose nanofibers is 0.5:1; and the weight ratio of the hollow cobalt-nickel carbon nanocages obtained in step 1) to the cellulose nanofibers is 0.5:

1.

15. Use of the electromagnetic shielding aerogel with a double-layer structure according to any one of claims 1 to 11 in electromagnetic stealth devices.

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