Layered structure composite aerogel and preparation method and application thereof

Abstract

The application provides a layered structure composite aerogel and a preparation method and application thereof, and belongs to the technical field of electromagnetic shielding materials. The layered structure composite aerogel provided by the application comprises an absorption layer and a reflection layer arranged in a stack; the absorption layer is polybenzoxazole aerogel doped with MXene / Ni composite conductive filler; and the reflection layer is polybenzoxazole aerogel doped with MXene nanosheets. In the application, the absorption layer has good impedance matching and electromagnetic wave absorption capacity, and the reflection layer has high conductivity, so that the layered structure composite aerogel obtained can effectively reduce the reflection coefficient thereof under the premise of ensuring high electromagnetic shielding performance, and realize electromagnetic shielding with low reflection characteristics.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electromagnetic shielding materials, and particularly relates to a layered structure composite aerogel and a preparation method and application thereof. BACKGROUND

[0002] Two-dimensional layered transition metal carbide, nitride or carbonitride (MXene) has outstanding electrical conductivity, excellent corrosion resistance and chemical activity, among which Ti3C2T x is the most widely used, and has become the focus of attention in the field of polymer-based electromagnetic shielding composite materials, and the related research and development are extremely rapid. However, the high electrical conductivity (σ) of Ti3C2T x determines the mechanism of electromagnetic shielding as electrical conductivity loss, which often leads to unbalanced electromagnetic parameters of the material, and the impedance matching with air cannot be achieved, and the electromagnetic waves are easily reflected on the surface of the material, causing secondary pollution of electromagnetic waves.

[0003] Studies have shown that the introduction of both conductive fillers (MXene) and magnetic fillers in polymer-based electromagnetic shielding composite materials can endow the composite material with the ability to cause electrical loss and magnetic loss of electromagnetic waves, which is helpful to adjust the impedance matching and reduce the secondary pollution of electromagnetic waves to the environment. The commonly used magnetic fillers are mainly magnetic metal particles, such as iron, cobalt, nickel and their oxides and alloys, etc. Since nickel has high Snoek limit in the GHz range, distinguishable magnetic permeability, high magnetic saturation strength, high temperature resistance and strong corrosion resistance, it is usually used in combination with conductive fillers to achieve better shielding effect through electromagnetic synergy while adjusting the impedance matching. The introduction of magnetic metal particles is beneficial to adjusting the impedance matching of the material, and to a certain extent, reduces the reflection coefficient of the electromagnetic shielding composite material, but the electromagnetic shielding performance still relies on the strong impedance mismatch caused by the high electrical conductivity of the material, and it is difficult to achieve high electromagnetic shielding effectiveness and low reflectivity at the same time. SUMMARY

[0004] The purpose of the present application is to provide a layered structure composite aerogel and a preparation method and application thereof. The layered structure composite aerogel provided by the present application can effectively reduce the reflection coefficient while ensuring high electromagnetic shielding performance, and realize electromagnetic shielding with low reflection characteristics.

[0005] In order to achieve the above-mentioned purpose of the application, the present application provides the following technical solutions:

[0006] The present application provides a layered structure composite aerogel, which comprises an absorption layer and a reflection layer arranged in a stack; the absorption layer is a poly-p-phenylene benzobisoxazole aerogel doped with MXene / Ni composite conductive filler; and the reflection layer is a poly-p-phenylene benzobisoxazole aerogel doped with MXene nanosheet.

[0007] Preferably, the volume fraction of the MXene / Ni composite conductive filler in the absorption layer is 1-3%; and the mass fraction of the MXene nanosheet in the reflection layer is 40-80%.

[0008] Preferably, the MXene / Ni composite conductive filler comprises MXene nanosheets and Ni nanoparticles loaded on the surface of the MXene nanosheets.

[0009] Preferably, the preparation method of the MXene / Ni composite conductive filler comprises the following steps:

[0010] Mixing a Ni source, MXene nanosheets, hydrazine hydrate and ethylene glycol, and performing a hydrothermal reduction reaction under alkaline conditions to obtain the MXene / Ni composite conductive filler.

[0011] Preferably, the Ni source comprises NiCl2·6H2O and / or Ni(acac)2; the MXene nanosheet comprises Ti3C2T2 nanosheet and / or Ti4N3 nanosheet; the mass ratio of the Ni source and MXene nanosheet is 0.5-4:0.1; the temperature of the hydrothermal reduction reaction is 70-100℃, and the time is 0.5-2h.

[0012] Preferably, the raw material for preparing the poly-p-phenylene benzobisoxazole aerogel in the absorption layer and the reflection layer comprises poly-p-phenylene benzobisoxazole nanofibers.

[0013] The preparation method of the poly-p-phenylene benzobisoxazole nanofiber comprises the following steps: mixing poly-p-phenylene benzobisoxazole fibers with an acid solution, and performing acid treatment to obtain the poly-p-phenylene benzobisoxazole nanofiber.

[0014] The present application provides a preparation method of the layered structure composite aerogel as described in the above technical solution, which comprises the following steps:

[0015] Mixing the poly-p-phenylene benzobisoxazole nanofiber with water to obtain a poly-p-phenylene benzobisoxazole nanofiber water dispersion;

[0016] Mixing part of the poly-p-phenylene benzobisoxazole nanofiber water dispersion with MXene nanosheets, and performing a first freezing under liquid nitrogen to prepare a reflection layer.

[0017] Mixing the remaining poly-p-phenylene benzobisoxazole nanofiber dispersion with MXene / Ni composite conductive filler, and performing a second freezing under liquid nitrogen to prepare an absorption layer on the surface of the reflection layer to obtain an aerogel precursor.

[0018] Performing freeze-drying on the aerogel precursor to obtain the layered structure composite aerogel.

[0019] Preferably, the concentration of the poly-p-phenylene benzobisoxazole nanofiber aqueous dispersion is 2.5-10 mg·mL -1 .

[0020] Preferably, the temperature of the freeze-drying is-70 DEG C, and the pressure is not more than 2 Pa.

[0021] The application provides application of the layered structure composite aerogel in an electromagnetic shielding material.

[0022] The application provides a layered structure composite aerogel, which comprises an absorption layer and a reflection layer arranged in a stack; the absorption layer is poly-p-phenylene benzobisoxazole aerogel doped with MXene / Ni composite conductive filler; and the reflection layer is poly-p-phenylene benzobisoxazole aerogel doped with MXene nanosheet. In the application, the absorption layer has good impedance matching and electromagnetic wave absorption capacity, and the reflection layer has high conductivity, so that the obtained layered structure composite aerogel has excellent electromagnetic shielding performance. The layered structure composite aerogel has a unique layered structure, so that electromagnetic waves undergo the process of 'absorption-reflection-reabsorption' in the composite aerogel. Moreover, in the application, the layered structure composite aerogel prepared by the freeze-drying method has a porous structure, can adjust the impedance matching capacity of the layered structure composite aerogel, and is convenient for multiple reflection, scattering and absorption of electromagnetic waves in the interior of the layered structure composite aerogel, so that the electromagnetic shielding performance of the layered structure composite aerogel is improved and the reflection coefficient is reduced. The examples show that the electromagnetic shielding efficiency of the layered structure composite aerogel prepared in the application is increased from 0.021 dB of pure PNF aerogel to 38.8-71.2 dB, and the reflection coefficient in the whole X wave band is less than 0.5, so that the high electromagnetic shielding performance mainly based on absorption is realized.

[0023] Further, the present application uses poly-p-phenylene benzobisoxazole nanofiber (PNF) as a matrix to prepare a layered structure composite aerogel. Specifically, the present application uses deprotonation technology to prepare PNF with excellent mechanical properties, heat resistance, flame retardancy and chemical stability, introduces hydrogen bonding force between poly-p-phenylene benzobisoxazole (PBO) molecular chains to solve the problem of difficult forming of PNF aerogel; then through the method of "electrostatic adsorption-solvothermal reduction", the magnetic Ni nanoparticles in the form of sea urchin are successfully grown in situ on the surface of MXene, a heterostructure MXene / Ni composite conductive filler is prepared, which well adjusts the impedance mismatch problem of MXene; finally, based on the layered module design, the layered structure composite aerogel (MNP-MP aerogel) is prepared by layer-by-layer freeze-drying, wherein the absorption layer of the layered structure composite aerogel is poly-p-phenylene benzobisoxazole aerogel doped with MXene / Ni composite conductive filler (referred to as MNP aerogel), and the reflection layer is poly-p-phenylene benzobisoxazole aerogel doped with MXene nanosheet (referred to as MP aerogel), realizing the characteristics of high electromagnetic shielding and low reflection coefficient of the composite aerogel. Based on the layered module design, the electromagnetic module is reasonably assembled to realize the high unification of electromagnetic wave absorption and shielding.

[0024] Further, in the prior art, PNF aerogel is prepared by solvent replacement, which is a complicated operation and time-consuming, and can damage the network structure inside the PNF aerogel; while in the present application, PNF is prepared by deprotonation technology, compared with the prior art, acid treatment can precipitate PNF dissolved in acid, and then the precipitated PNF is reconfigured into PNF aqueous solution with various concentrations, which is convenient for subsequent freeze-drying, and in the deprotonation process, the oxazole ring of PBO molecular chain is opened to form -NH2 and -COOH, which is beneficial to its dispersion in aqueous solution and improves the molecular interaction between PNF, forming a strong three-dimensional skeleton structure, which is beneficial to the subsequent forming of the obtained aerogel.

[0025] Further, in the present application, the layer-by-layer freeze-drying process can well combine the absorption layer and the reflection layer together without obvious gap, and a tightly combined layered structure composite aerogel is prepared.

[0026] Further, the present application successfully grows the sea urchin-like Ni nanoparticles in situ on the surface of MXene nanosheet through the method of "electrostatic adsorption-solvothermal reduction"; wherein the Ni nanoparticles are uniformly coated on the surface of the MXene nanosheet, forming a relatively perfect "point-plane" heterostructure. BRIEF DESCRIPTION OF DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed in the embodiments will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained from these drawings without creative labor.

[0028] Figure 1 SEM image of MXene / Ni composite conductive filler;

[0029] Figure 2 SEM image and EDS image of MXene / Ni composite conductive filler;

[0030] Figure 3 SEM image and EDS image of the layered structure composite aerogel, the absorption layer and the reflection layer obtained in Example 1. DETAILED DESCRIPTION

[0031] The present application provides a layered structure composite aerogel, comprising an absorption layer and a reflection layer arranged in a stack; the absorption layer is a poly (p-phenylene benzobisoxazole) aerogel doped with MXene / Ni composite conductive filler; and the reflection layer is a poly (p-phenylene benzobisoxazole) aerogel doped with MXene nanosheet.

[0032] In the present application, unless otherwise specified, the raw materials used are commercially available or prepared by methods well known to those skilled in the art.

[0033] The mass fraction of MXene nanosheet in the reflection layer is preferably 40-80%, and can be 40%, 60% or 80% in particular.

[0034] In the present application, the MXene nanosheet preferably comprises Ti3C2T2 nanosheet and / or Ti4N3 nanosheet, and more preferably is Ti3C2T2 nanosheet. In the present application, the preparation method of the MXene nanosheet preferably comprises the following steps: mixing hydrochloric acid, water and lithium fluoride, adding Ti3AlC2 powder to the obtained mixture under ice water bath condition, performing etching reaction to obtain etching material; sequentially performing first centrifugation and water washing on the etching material, and repeating the first centrifugation and water washing until the pH value of the first supernatant obtained after the first centrifugation approaches neutral, and collecting the precipitate obtained by centrifugation at this time; mixing the precipitate with water, performing ultrasonic treatment under argon atmosphere, performing second centrifugation on the obtained water dispersion, collecting the second supernatant, and drying the second supernatant to obtain MXene nanosheet. In the present application, the concentration of the hydrochloric acid is preferably 10 mol / L; and the mass ratio of the hydrochloric acid, water, lithium fluoride and Ti3AlC2 powder is preferably 54:6:4.8:3. The etching reaction in the present application is preferably performed under sealed condition; the temperature of the etching reaction is preferably 35℃, and the time is preferably 24h. In the present application, the rotation speed of the first centrifugation is preferably 3500rpm; the time of the ultrasonic treatment is preferably 15min; the rotation speed of the second centrifugation is preferably 3500rpm, and the time of the second centrifugation is preferably 1h; and the drying is preferably vacuum freeze-drying. In the present application, the MXene nanosheet is preferably single-layer or few-layer MXene nanosheet; the number of layers of the MXene nanosheet is preferably 1-10 layers, and more preferably is 1-6 layers; the thickness of the single-layer MXene nanosheet is preferably 2nm, and the thickness of the few-layer MXene nanosheet is preferably not more than 10nm.

[0035] The volume fraction of the MXene / Ni composite conductive filler in the absorption layer in the present application is preferably 1-3%, and more preferably is 2.96%.

[0036] In the present application, the MXene / Ni composite conductive filler preferably comprises MXene nanosheet and Ni nanoparticles loaded on the surface of the MXene. In the present application, the Ni nanoparticles are loaded on the surface of the MXene by electrostatic adsorption.

[0037] The preparation method of the MXene / Ni composite conductive filler in the present application preferably comprises the following steps: mixing Ni source, MXene nanosheet, hydrazine hydrate and ethylene glycol, and performing hydrothermal reduction reaction under alkaline condition to obtain the MXene / Ni composite conductive filler.

[0038] In the present application, the Ni source preferably comprises NiCl2·6H2O and / or Ni(acac)2, more preferably NiCl2·6H2O; the MXene nanosheet preferably comprises Ti3C2T2 nanosheet and / or Ti4N3 nanosheet, more preferably Ti3C2T2 nanosheet; and the mass ratio of the Ni source to the MXene nanosheet is preferably 0.5-4:0.1, more preferably 2.4:0.1.

[0039] In the present application, the Ni source is dissolved in ethylene glycol (EG), and the MXene nanosheet is added and ultrasonically dispersed, and the obtained mixed dispersion liquid is mixed with a sodium hydroxide solution and hydrazine hydrate to perform a hydrothermal reduction reaction. In the present application, the sodium hydroxide solution is preferably a sodium hydroxide ethylene glycol solution, and the concentration of the sodium hydroxide ethylene glycol solution is preferably 1 mol / L. The mass ratio of the Ni source, ethylene glycol, sodium hydroxide solution, and hydrazine hydrate in the present application is preferably 0.9-3.5:76-295:12-47:9-35, more preferably 2.4:205:33:25. The temperature of the hydrothermal reduction reaction in the present application is preferably 70-100℃, more preferably 90℃; and the time is preferably 0.5-2h, more preferably 1h. After the hydrothermal reduction reaction, the present application preferably collects magnetic materials using a magnet, and the magnetic materials are sequentially washed and dried to obtain the MXene / Ni composite conductive filler. In the present application, the washing preferably comprises sequential water washing and alcohol washing, and the reagent used for the alcohol washing is preferably anhydrous ethanol; and the drying is preferably vacuum drying.

[0040] In the present application, the raw material for preparing the poly-p-phenylene benzobisoxazole aerogel in the absorption layer and the reflection layer comprises poly-p-phenylene benzobisoxazole nanofibers. In the absorption layer of the present application, the mass fraction of the poly-p-phenylene benzobisoxazole nanofibers is preferably 5-20%, more preferably 10%. In the reflection layer of the present application, the mass fraction of the poly-p-phenylene benzobisoxazole nanofibers is preferably 20-60%, more preferably 20%.

[0041] The preparation method of the poly-p-phenylene benzobisoxazole nanofiber preferably comprises the following steps: mixing poly-p-phenylene benzobisoxazole fibers with an acid solution, performing acid treatment, and obtaining the poly-p-phenylene benzobisoxazole nanofiber. In the present application, the acid solution preferably comprises methane sulfonic acid (MSA) and trifluoroacetic acid (TFA), and the mass ratio of the methane sulfonic acid and the trifluoroacetic acid is preferably 0.5-1:0.5-1, more preferably 1:1; the mass ratio of the poly-p-phenylene benzobisoxazole fibers and the acid solution is preferably 0.1-1:100, more preferably 0.1:100. In the present application, the acid treatment time is preferably 24-72 h, more preferably 48 h; and the acid treatment is preferably performed under stirring. In the present application, the diameter of the poly-p-phenylene benzobisoxazole nanofiber is preferably 100 nm. In the present application, the micron-sized PBO fibers are changed into PBO nanofibers (i.e., PNF) with a diameter of about 100 nm through acid treatment.

[0042] The present application also provides a preparation method of the layered structure composite aerogel described in the above technical solution, comprising the following steps: mixing poly-p-phenylene benzobisoxazole nanofibers with water to obtain a poly-p-phenylene benzobisoxazole nanofiber water dispersion; mixing part of the poly-p-phenylene benzobisoxazole nanofiber water dispersion with MXene nanosheets, performing first freezing under liquid nitrogen to prepare a reflection layer; mixing the remaining poly-p-phenylene benzobisoxazole nanofiber dispersion with MXene / Ni composite conductive filler, performing second freezing under liquid nitrogen to prepare an absorption layer on the surface of the reflection layer, and obtaining an aerogel precursor; and freeze-drying the aerogel precursor to obtain the layered structure composite aerogel.

[0043] In the present application, the mass ratio of the poly-p-phenylene benzobisoxazole nanofiber, the MXene nanosheet, the MXene / Ni composite conductive filler, and the water is preferably 7.6:5-20:28:1013, and can be 7.6:5:28:1013, 7.6:7.5:28:1013, or 7.6:20:28:1013.

[0044] In the present application, the concentration of the poly-p-phenylene benzobisoxazole nanofiber water dispersion is preferably 2.5-10 mg·mL -1 , more preferably 7.5 mg·mL -1 .

[0045] The present application mixes part of the poly-p-phenylene benzobisoxazole nanofiber aqueous dispersion with MXene nanosheets to obtain a MXene-PNF aqueous dispersion (MP aqueous dispersion); pours the MXene-PNF aqueous dispersion into a mold, places the mold on a copper block, and immerses the copper block in liquid nitrogen to perform first freezing to obtain a reflection layer; mixes the remaining poly-p-phenylene benzobisoxazole nanofiber dispersion with MXene / Ni composite conductive filler to obtain a MXene / Ni composite conductive filler-PNF aqueous dispersion (MNP aqueous dispersion); pours the MXene / Ni composite conductive filler-PNF aqueous dispersion into the mold on the copper block still immersed in liquid nitrogen to perform second freezing to prepare an absorption layer on the surface of the reflection layer to obtain an aerogel precursor; and performs freeze drying on the aerogel precursor to obtain the layered structure composite aerogel. In the present application, the time of the first freezing is preferably 10-40 s, and more preferably 20 s; and the time of the second freezing is preferably 2 min. In the present application, the freeze drying is preferably performed in a freeze dryer; and the temperature of the freeze drying is preferably -70℃, and the pressure is preferably not more than 2 Pa.

[0046] The present application also provides the application of the layered structure composite aerogel in the above technical solution or the layered structure composite aerogel obtained by the preparation method in the above technical solution in electromagnetic shielding materials.

[0047] The technical solutions in the present application will be clearly and completely described below in combination with the embodiments in the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0048] 1 part by weight in the embodiment is “20 g”;

[0049] The particle size of the Ti3AlC2 powder used in the embodiment is 38 μm.

[0050] Embodiment 1

[0051] (1) 54 parts by weight of HCl (10 mol / L) and 6 parts by weight of deionized water were weighed into a reaction kettle, 4.8 parts by weight of LiF was added, and ultrasonic treatment was performed for 8 min to obtain a mixed solution; 3 parts by weight of Ti3AlC2 powder was added to the mixed solution under the condition of ice water bath and magnetic stirring, and after uniform mixing, it was sealed and stirred at 35℃ for 24 h under the condition of magnetic stirring. After stirring, centrifugation was performed at a speed of 3500 rpm, and the material obtained by centrifugation was washed with water, and the centrifugation and water washing were repeated until the pH value of the supernatant obtained by centrifugation was close to neutral, and the mud-shaped precipitate obtained at this time was collected. The mud-shaped precipitate was dispersed in deionized water and ultrasonically treated for 15 min under an argon atmosphere, and the obtained water dispersion was centrifuged at a speed of 3500 rpm for 1 h, and after centrifugation, the supernatant was collected, and the supernatant was vacuum freeze-dried to obtain single-layer or few-layer MXene nanosheets (the number of layers is 1-10 layers, the thickness of single-layer MXene nanosheets is 2 nm, and the thickness of few-layer MXene nanosheets is not more than 10 nm).

[0052] (2) 2.4 parts by weight of NiCl2·6H2O was dissolved in 205 parts by weight of EG, then 0.1 parts by weight of MXene nanosheets obtained in step (1) was added and ultrasonically dispersed to obtain a mixed dispersion. The mixed dispersion was added to a reaction kettle, 33 parts by weight of an EG solution (1 mol / L) of NaOH and 25 parts by weight of N2H4·H2O were added and uniformly mixed, and then the mixture was reacted in an oven at 90℃ for 1 h. After the reaction was completed, the magnetic material was collected by a magnet, and the magnetic material was sequentially washed with deionized water and anhydrous ethanol, and then vacuum dried to obtain a MXene / Ni composite conductive filler with a heterostructure.

[0053] (3) 0.1 parts by weight of PBO fiber was dispersed in 50 parts by weight of a mixed acid solution of methane sulfonic acid (MSA) and trifluoroacetic acid (TFA), and stirred for 48 h to obtain a PBO mixed acid dispersion. The PBO mixed acid dispersion was dropped into 600 parts by weight of deionized water at a speed of 15000 rpm to precipitate PNF from the mixed acid solution to obtain a PNF-containing liquid. The PNF-containing liquid was vacuum filtered, and repeatedly washed with deionized water until neutral, and finally the PNF was uniformly dispersed in deionized water by a high-speed homogenizer to obtain a PNF water dispersion (the concentration was 7.5 mg·mL -1 ).

[0054] (4) 138.6 parts by weight of PNF aqueous dispersion (containing 2.6 parts by weight of PNF) and 28 parts by weight of MXene / Ni composite conductive filler were mixed by a high-speed homogenizer to obtain MNP aqueous dispersion; 672 parts by weight of PNF aqueous dispersion (containing 5 parts by weight of PNF) and 3.3 parts by weight of MXene nanosheets were mixed by an ultra-high-speed homogenizer to obtain MP aqueous dispersion. The MP aqueous dispersion was poured into a rectangular mold (25 mm in length and 13 mm in width; with a copper plate at the bottom and polytetrafluoroethylene on all sides). The rectangular mold was placed on a copper block, which was immersed in liquid nitrogen and frozen for 20 seconds to obtain a poly(p-phenylene benzobisoxazole) aerogel doped with MXene nanosheets, i.e., a reflective layer (the mass fraction of MXene nanosheets in the reflective layer was 40%). The MNP aqueous dispersion was poured into the rectangular mold containing the reflective layer and frozen under liquid nitrogen for 2 minutes to prepare a poly(p-phenylene benzobisoxazole) aerogel doped with MXene / Ni composite conductive filler on the surface of the reflective layer, i.e., an absorption layer was prepared on the surface of the reflective layer, i.e., an aerogel precursor. The aerogel precursor was placed in a freeze dryer and freeze-dried at a temperature of -70°C and a pressure of <2 Pa for 48 hours to obtain a layered composite aerogel, designated MNP-MP-40 aerogel.

[0055] The SEM image of the MXene / Ni composite conductive filler is as follows: Figure 1 As shown. Figure 1 The researchers successfully in situ grew sea urchin-shaped nickel nanoparticles on the surface of MXene nanosheets via an electrostatic adsorption-solvothermal reduction method. The nickel nanoparticles, approximately 200 nm in size, were uniformly coated on the surface of the MXene nanosheets, with only slight aggregation and stacking. Their micromorphology was optimal, forming a relatively complete "point-surface" heterostructure.

[0056] The SEM and EDS images of the MXene / Ni composite conductive filler are as follows: Figure 2 As shown, (a) is the SEM image of MXene / Ni composite conductive filler, (a') and (a") are EDS images of MXene / Ni composite conductive filler. Figure 2 It can be seen that this further proves that the "electrostatic adsorption-solvothermal reduction" method can effectively anchor Ni nanoparticles on the surface of MXene nanosheets.

[0057] Example 2

[0058] (1) MXene nanosheets, MXene / Ni composite conductive fillers and PNF aqueous dispersion (concentration of 7.5 mg mL) were prepared according to the conditions of Example 1. -1 ).

[0059] (2) The composition of the MP water dispersion was adjusted to 672 parts by weight of the PNF water dispersion (containing 5 parts by weight of PNF) and 7.5 parts by weight of MXene nanosheets, and the remaining conditions were the same as in Example 1 (i.e., the mass fraction of MXene nanosheets in the reflection layer was 60%), to prepare a layered structure composite aerogel, denoted as MNP-MP-60 aerogel.

[0060] Example 3

[0061] (1) The MXene nanosheets, MXene / Ni composite conductive filler and PNF water dispersion (concentration of 7.5 mg·mL -1 ) were prepared according to the conditions of Example 1.

[0062] (2) The composition of the MP water dispersion was adjusted to 672 parts by weight of the PNF water dispersion (containing 5 parts by weight of PNF) and 20 parts by weight of MXene nanosheets, and the remaining conditions were the same as in Example 1 (i.e., the mass fraction of MXene nanosheets in the reflection layer was 80%), to prepare a layered structure composite aerogel, denoted as MNP-MP-80 aerogel.

[0063] The SEM and EDS images of the layered structure composite aerogel, the absorption layer and the reflection layer obtained in Example 3 are shown in Figure 3 , wherein (a) and (a') are SEM images of the layered structure composite aerogel, (a") is an EDS image of the layered structure composite aerogel, (b), (b') and (b") are SEM images of the absorption layer, and (c), (c') and (c") are SEM images of the reflection layer. It can be seen from Figure 3 that the assembled MNP-MP aerogel has a clear layered structure and there is no obvious gap between the two layers, and the two layers can be well assembled together; and compared with the lower layer of MP aerogel, the internal pore structure of the upper layer of MNP aerogel is more irregular and the pore size is larger.

[0064] Test Example 1

[0065] According to the ASTM D5568-08 standard (Standard Test Method for Measurement of the Relative Complex Permittivity and Permeability of Solid Materials Under Microwave Frequencies), the layered structure composite aerogels obtained in Examples 1-3 were tested using a MS4644A type vector network analyzer of Japan Anritsu Co., Ltd. The sample size of the layered structure composite aerogel was 22.4 mm x 11.2 mm x 7.6 mm, and the test frequency range was 8.2-12.4 GHz. The total shielding effectiveness (SET), the absorption effectiveness (SEA) and the reflection effectiveness (SER) were obtained by calculating and analyzing the S parameters (S11, S22, S21 and S21) measured by the vector network analyzer.

[0066] The test results show that the electromagnetic shielding performance of the layered structure composite aerogel MNP-MP-40 obtained in Example 1 is 38.8 dB, and the reflection coefficient is 0.18.

[0067] The electromagnetic shielding performance of the layered structure composite aerogel MNP-MP-60 obtained in Example 2 is 57.5 dB, and the reflection coefficient is 0.09.

[0068] The electromagnetic shielding performance of the layered structure composite aerogel MNP-MP-80 obtained in Example 3 is 71.2 dB, and the reflection coefficient is 0.10.

[0069] Although the above examples make a detailed description of the present application, it is only a part of the embodiments of the present application, but not all the embodiments, and other embodiments can be obtained according to the present embodiments without creativity, which all belong to the protection scope of the present application.

Claims

1. A layered composite aerogel comprising an absorption layer and a reflection layer stacked together; the absorption layer is a poly(p-phenylene benzobisoxazole) aerogel doped with a MXene / Ni composite conductive filler; and the reflection layer is a poly(p-phenylene benzobisoxazole) aerogel doped with MXene nanosheets.

2. The layered composite aerogel according to claim 1, characterized in that The volume fraction of the MXene / Ni composite conductive filler in the absorption layer is 1 to 3%; the mass fraction of the MXene nanosheets in the reflection layer is 40 to 80%.

3. The layered composite aerogel according to claim 1 or 2, characterized in that: The MXene / Ni composite conductive filler includes MXene nanosheets and Ni nanoparticles supported on the surface of the MXene nanosheets.

4. The layered composite aerogel according to claim 3, characterized in that The preparation method of the MXene / Ni composite conductive filler comprises the following steps: A Ni source, MXene nanosheets, hydrazine hydrate and ethylene glycol are mixed and subjected to a hydrothermal reduction reaction under alkaline conditions to obtain the MXene / Ni composite conductive filler.

5. The layered composite aerogel according to claim 4, characterized in that: The Ni source includes NiCl2·6H2O and / or Ni(acac)2; the MXene nanosheets include Ti3C2T2 nanosheets and / or Ti4N3 nanosheets; the mass ratio of the Ni source to the MXene nanosheets is 0.5-4:0.1; the temperature of the hydrothermal reduction reaction is 70-100°C, and the time is 0.5-2h.

6. The layered composite aerogel according to claim 1 or 2, characterized in that: The raw materials for preparing the poly(p-phenylene benzobisoxazole) aerogel in the absorption layer and the reflection layer include poly(p-phenylene benzobisoxazole) nanofibers; The preparation method of the poly(p-phenylene benzobisoxazole) nanofiber comprises the following steps: mixing the poly(p-phenylene benzobisoxazole) fiber with an acid solution and performing acid treatment to obtain the poly(p-phenylene benzobisoxazole) nanofiber.

7. A method for preparing the layered composite aerogel according to any one of claims 1 to 6, comprising the following steps: mixing poly(p-phenylene benzobisoxazole) nanofibers with water to obtain a poly(p-phenylene benzobisoxazole) nanofiber aqueous dispersion; Mixing a portion of the poly(p-phenylene benzobisoxazole) nanofiber aqueous dispersion with MXene nanosheets, and performing a first freezing under liquid nitrogen conditions to prepare a reflective layer; mixing the remaining poly(p-phenylene benzobisoxazole) nanofiber dispersion with the MXene / Ni composite conductive filler, and performing a second freezing under liquid nitrogen conditions to prepare an absorption layer on the surface of the reflective layer to obtain an aerogel precursor; The aerogel precursor is freeze-dried to obtain the layered composite aerogel.

8. The preparation method according to claim 7, characterized in that The concentration of the poly(p-phenylene benzobisoxazole) nanofiber aqueous dispersion is 2.5 to 10 mg·mL -1 .

9. The preparation method according to claim 7, characterized in that The freeze-drying temperature is -70°C and the pressure does not exceed 2Pa.

10. Use of the layered composite aerogel according to any one of claims 1 to 6 or the layered composite aerogel prepared by the method according to any one of claims 7 to 9 in electromagnetic shielding materials.

Images